Disordered Rock-Salt Oxide Cathode for Next-Generation Energy Storage

Abstract

Disordered rock-salt (DRX) oxides break the conventional requirement of long-range cation ordering for lithium-ion battery cathodes. Their lithium-excess, cation-disordered framework enables three-dimensional Li⁺ percolation, broad compositional flexibility, and synergistic cation–anion redox chemistry, offering a viable route toward high-capacity, Co/Ni-free cathodes. Despite reversible capacities exceeding 250–300 mAh·g⁻¹, practical implementation is hindered by poor electronic conductivity, voltage hysteresis, oxygen loss, transition-metal migration, and synthesis challenges. This perspective summarizes progress from two aspects: synthesis methodology and performance optimization. Conventional solid-state, mechanochemical, and sol-gel routes are discussed, followed by emerging strategies including molten-salt, microwave, Joule heating, and thermal shock synthesis. We then highlight performance enhancement strategies such as compositional design, anion engineering, short-range order regulation, particle-size and single-crystal control, surface coating, and conductive network construction. Finally, we discuss remaining challenges and future directions for developing scalable, low-cost, high-energy DRX cathodes, particularly toward Co/Ni-free and ultimately d⁰-free chemistries.

Graphical abstract

Keywords

Disordered rock-salt oxides / Short-range order engineering / Cathode materials / Lithium-ion batteries / Electrochemical performance

Highlight

	● Synthesis methodology and performance optimization are integrated as two parallel pillars for DRX cathode design.
	● Trade-offs in composition, short-range order, and microstructure engineering are critically assessed.
	● Interfacial degradation and limited full-cell validation are identified as key practical bottlenecks.
	● A holistic roadmap is outlined toward scalable, Co/Ni-free, and d 0-free DRX cathodes.

1 Introduction

Lithium-ion batteries (LIBs) stand as the backbone of electrochemical energy storage, powering electric vehicles (EVs), portable electronics, and grid-scale renewable energy integration to propel the global transition to clean energy [1-3]. For decades, high-performance cathode design has been rooted in long-range ordered crystal structures, including layered oxides, spinel oxides, and olivine phosphates, which have enabled the commercial success of LIBs [4–6]. The Goodenough group made pioneering contributions to this field by establishing three major cathode families, each with distinct long-range ordered frameworks. Layered LiCoO₂ (Mizushima et al. [4]) features a two-dimensional Li⁺ diffusion pathway within the ordered R \overline{3}m structure, setting the foundation for modern intercalation cathodes. Spinel LiMn₂O₄ (Thackeray et al. [5]) adopts a three-dimensional channel topology in the Fd \overline{3}m framework, enabling faster ion transport albeit at a lower practical capacity. Olivine LiFePO₄ (Padhi et al. [6]) relies on the ordered Pnma structure with one-dimensional Li⁺ tunnels, offering exceptional thermal stability and cycle life yet suffering from intrinsically low electronic conductivity. Despite the distinct structural merits of each family, these ordered materials face insurmountable bottlenecks as next-generation LIBs demand higher energy density, longer cycle life, lower cost, and more secure supply chains [7]. Layered oxides undergo irreversible phase transitions and lattice collapse during deep delithiation, while most rely on scarce cobalt and high-content nickel that create supply chain vulnerabilities [8]. Spinel oxides lack sufficient capacity for long-range EV requirements, and olivine phosphates are limited by low conductivity and operating voltage [9–10]. Structural rigidity further restricts compositional flexibility, making it difficult to achieve Co/Ni-free formulations that balance high capacity and stability [11–12].

Disordered rock-salt (DRX) oxides have emerged as a transformative solution to these challenges, redefining the design paradigm for LIB cathodes and representing the most promising subclass of disordered cathode materials [13–14]. Distinct from long-range ordered rock-salt and other conventional ordered cathode structures, DRX oxides are characterized by the absence of long-range cation periodicity in the cubic rock-salt lattice while retaining local short-range order (SRO) [15–16]. Their lithium-excess stoichiometry further unlocks a set of unique electrochemical properties. This intrinsic structural disorder enables the formation of three-dimensional isotropic Li⁺ percolation pathways. It thus eliminates the sluggish two-dimensional diffusion, anisotropic lattice strain, and structural collapse issues that plague layered oxides during deep delithiation [15,17]. Moreover, DRX oxides exhibit unparalleled compositional flexibility. They allow the full elimination of Co and Ni in favor of earth-abundant transition metals such as Mn, Fe, Ti and Nb. This benefit directly addresses the critical supply chain vulnerabilities of conventional cathodes [14,18–19]. Most notably, Mn-based DRX systems leverage synergistic cation-anion dual redox activity. They deliver reversible specific capacities exceeding 250 mAh·g⁻¹ [20–21]. The value far surpasses those of conventional Mn-based ordered cathodes [22-24] and are comparable to those of high-nickel layered oxides [25-27]. These advantages align perfectly with the dual demands of high performance and sustainability. They simultaneously overcome the technical limitations and resource constraints of traditional ordered cathode materials.

The practical application of DRX oxides is hindered by two intertwined challenges: synthesis control and high-voltage instability. Conventional methods such as high-temperature sintering offer limited tunability of SRO, while energy-intensive ball milling is difficult to scale. Meanwhile, high-voltage operation triggers irreversible oxygen loss, transition metal migration, and voltage hysteresis. In this perspective, we argue that overcoming these obstacles requires treating synthesis and performance optimization as interconnected design problems. Our analysis identifies electronic conductivity, SRO controllability, and full-cell validation as the most urgent bottlenecks, and we critically assess emerging strategies, including high-entropy stabilization, low-entropy SRO suppression, and d⁰-free chemistries, from both fundamental and practical standpoints. We first review the evolution of synthesis routes from conventional solid-state, mechanochemical, and sol-gel methods to emerging techniques such as molten-salt, microwave, Joule heating, and thermal shock synthesis. We then discuss strategies for enhancing electrochemical performance, including compositional design, SRO engineering, microstructure control, and conductive network construction. We conclude by outlining remaining challenges and future directions toward practical, Co/Ni-free, and ultimately d⁰-free DRX cathodes.

2 Fundamental Understanding and Challenges of DRX Oxides

Driven by the demand for high-energy-density and resource-efficient cathode materials that overcome the limitations of conventional ordered oxides, DRX oxides have emerged as a highly promising candidate for next-generation LIBs (Fig. 1). Since cation disorder was once considered detrimental to Li⁺ transport, the evolution of DRX research offers a notable example of how a paradigm shift in understanding can open up new material design opportunities.

In 1991, Delmas and colleagues [28] first identified disordered Li₃V₂O₅ as a new cathode phase prepared by electrochemical lithiation of Li_xV₂O₅ with 0 < x < 1. This material delivered a high energy density of 800 Wh·kg⁻¹. Nevertheless, this seminal work did not trigger widespread follow-up research on disordered cathodes. A pivotal revival came in 2014, when Ceder’s group [13] proposed the percolation network theory during studies on Li_1.211Mo_0.467Cr_0.3O₂. This theory unveiled that zero-transition metal (0-TM) fast Li⁺ diffusion channels form in cation-disordered lithium-rich oxides when Li/TM ≥ 1.09, with Li⁺ migrating via a classic o-t-o (octahedral-tetrahedral-octahedral) pathway. Lee et al. [13] further corroborated that 0-TM channels become the dominant Li⁺ transport paths and form a continuous percolation network only above the 1.09 Li threshold; a higher Li content expands this network, delivering ultrahigh reversible capacity for DRX cathodes. Furthermore, Urban et al. [15,29] provided profound insights into the electronic structure of DRX oxides, highlighting the critical role of incorporating at least one redox-inactive d⁰ cation. Such d⁰ species can accommodate octahedral structural evolutions during charge-discharge cycling with minimal energetic penalty. Among the most extensively investigated DRX cathodes are V-based, Mn-based, and Fe-based systems, while the commonly employed redox-inactive metal centers are d⁰ cations such as Ti⁴⁺, V⁵⁺, Nb⁵⁺, and Mo⁶⁺.

Featuring a breakthrough in addressing the intrinsic capacity bottleneck of traditional ordered cathodes and enabling a wide elemental selection of earth-abundant redox-active metals, DRX materials provide a distinctive structural platform to balance superior electrochemical performance and sustainable material development. The publication trends of the past decade collected from Google Scholar using the keyword “disordered rock-salt” are shown in Fig. 2A, revealing a steadily growing research interest in this emerging class of electrode materials. Meanwhile, we have summarized the relevant keywords for DRX materials in Fig. 2B.

2.1 Crystal structure and Li⁺ transport mechanisms

Structurally, DRX oxides generally adopt the stoichiometry of Li_1+xM_1-xO₂, where M represents redox-active transition metal, crystallizing in the cubic Fm \overline{3}m space group with a fully disordered cation sublattice (Fig. 2C). The cation disorder does not preclude fast Li⁺ transport. As established by Ceder's percolation theory, a sufficient Li excess creates a connected network of 0-TM channels that enables three-dimensional Li⁺ migration via an o-t-o pathway.

However, disorder does not mean complete randomness. Although DRX materials are widely assumed to exhibit fully random distributions of metal and anionic species in theory, local SRO has been widely observed. Such short-range correlations are driven by energetic preferences, in which certain cations tend to approach or avoid each other. Kan et al. [30] employed density functional theory (DFT) calculations and revealed that SRO in disordered structures modulates the Li⁺ diffusion network, facilitates faster Li⁺ migration, and introduces anisotropic or plane-dependent Li⁺ diffusivity even in three-dimensional rock-salt lattices. This indicates a critical relationship between SRO and Li⁺ percolation. Ji et al. [16] also uncovered that cation SRO ubiquitously exists in long-range disordered DRX materials and fully controls the local Li⁺ diffusion environment, thereby determining the formation and connectivity of Li⁺ percolation networks. This implies that the spatial distribution of cations at the short-range scale directly governs whether the 0-TM channels form a percolating network or remain isolated.

The combination of long-range disorder and SRO translates into a set of attractive electrochemical properties. Benefiting from the percolating 0-TM network, DRX cathodes typically deliver reversible specific capacities in the range of 250–350 mAh·g⁻¹, with some compositions approaching 300–350 mAh·g⁻¹ and energy densities exceeding 1000 Wh·kg⁻¹. The operating voltage window is generally between 1.5 and 4.8 V vs. Li⁺/Li, with average discharge voltages around 2.8–3.5 V depending on the transition metal composition. These metrics place DRX cathodes on par with or even above conventional high-nickel layered oxides, while offering the distinct advantage of being free from Co and Ni. Such performance characteristics make DRX a compelling candidate for next-generation energy storage systems.

2.2 Key challenges for practical application

The practical development of DRX cathodes, however, faces several interconnected challenges that must be systematically addressed.

First, poor electronic conductivity. The intrinsic electronic conductivity of Mn-based DRX is typically 10⁻¹⁰–10⁻⁸ S·cm⁻¹, which is three to four orders of magnitude lower than that of layered oxides. To compensate, most laboratory studies incorporate 20–30 wt.% carbon additives, which dramatically reduces electrode level energy density and volumetric capacity. Practical cathodes require areal capacities above 4 mAh·cm⁻² to ensure sufficient cell-level energy density [31–32].

Second, voltage hysteresis and low Coulombic efficiency. DRX cathodes relying on oxygen redox typically display a large voltage hysteresis (> 0.5 V) between charge and discharge, along with a first cycle Coulombic efficiency of only 65%–80% [33–34]. These inefficiencies stem from the slow kinetics of O–O bond formation and breaking, as well as irreversible oxygen loss associated with transition metal migration at high potentials.

Third, limited long-term cycling stability. The cumulative effects of oxygen release, transition metal dissolution (particularly Mn in Mn-based DRX), surface densification, and electrolyte decomposition lead to rapid capacity fade and voltage decay during prolonged cycling. The structural evolution of the DRX framework under repeated deep delithiation and relithiation remains incompletely understood, and the formation of resistive surface layers further impedes Li⁺ transport over extended cycles.

Fourth, stringent synthesis requirements. Achieving the desired cation disorder, controlled SRO, and uniform elemental distribution demands precise synthesis conditions. Conventional high-temperature sintering offers limited tunability of SRO and Li distribution, while high-energy ball milling is energy-intensive and unsuitable for scalable production. Rapid synthesis methods such as Joule heating and microwave processing show promise but still require industrial optimization.

Fifth, compositional constraints and supply chain concerns. While DRX materials eliminate Co and Ni, most high-performance compositions still rely on d⁰ cations (Ti⁴⁺, Nb⁵⁺, Mo⁶⁺, Zr⁴⁺) to stabilize the disordered lattice. These elements, though less critical than Co and Ni, are still subject to price volatility and geopolitical constraints. Moreover, d⁰ cations contribute “dead weight” that dilutes specific capacity and energy density, and their electronic configurations do not facilitate electron hopping, further degrading electronic conductivity.

These five challenges are not independent; they are deeply intertwined. Poor electronic conductivity exacerbates rate capability limitations; oxygen loss triggers voltage hysteresis and transition metal migration; surface degradation shortens cycle life; and synthesis constraints limit compositional exploration. Therefore, addressing DRX performance requires a holistic approach that integrates solutions across multiple fronts. In the following sections, we examine how advances in synthesis methods and targeted performance enhancement have been developed to tackle these challenges, and we assess the remaining gaps toward practical application.

3 Synthesis Methods Evolution: Moving Beyond Conventional Approaches

DRX oxides represent a promising class of high-capacity cathode materials with exceptional compositional tunability. Since cation disorder is inherently governed by chemical interactions in metal oxides, rational control over structural disorder is essential for material design. Synthesis therefore plays a decisive role in tailoring the disorder level, Li⁺ transport network, and electrochemical performance of DRX cathodes. There are mainly several methods such as solid-state reaction method, mechanochemical method and sol-gel method. The DRX materials prepared by different methods are summarized in Table 1.

3.1 Solid-state method

Solid-state synthesis is the most direct and widely used method for DRX preparation. The typical process involves thoroughly mixing metal precursors (e.g., carbonates, oxides, or fluorides) by ball milling, followed by calcination at high temperatures (typically 900–1100  °C) under an inert atmosphere (Fig. 3A). This method is simple, scalable, and compatible with a wide range of transition metal compositions, making it the most common route for DRX synthesis reported in the literature.

Solid-state synthesis has demonstrated remarkable versatility in accessing diverse DRX compositions and structures. Liu et al. [35] successfully applied conventional solid-state sintering to Mn-rich DRX systems, demonstrating that the method can accommodate high Mn content while maintaining phase purity. Mei et al. [36] further showed that solid-state reaction can construct a disordered rock-salt/disordered spinel heterostructure via a tetrahedral Li-stuffing strategy, indicating that conventional calcination is capable of producing complex phase assemblies beyond single-phase DRX. Moreover, high-entropy DRX compositions [49], which rely on high configurational entropy to suppress SRO and stabilize the disordered lattice, have been reliably synthesized using solid-state protocols. Jiao et al. [50] extended solid-state methods to fluorinated DRX systems, demonstrating that conventional calcination can effectively incorporate fluorine into the DRX lattice, leading to expanded Li percolation networks and suppressed oxygen loss. These examples collectively illustrate that solid-state synthesis offers a robust platform for exploring a wide compositional space.

However, conventional solid-state synthesis faces several intrinsic processing challenges that limit its ability to produce high-performance DRX materials. First, the slow kinetics of solid-state diffusion necessitates prolonged high-temperature treatment (typically > 12 h) and results in limited control over particle size and morphology, often requiring post-synthesis pulverization that introduces surface defects and compromises crystallinity. Second, poor solid–solid contact between precursor particles leads to inhomogeneous reactions, resulting in phase impurities and uneven elemental distribution. Third, when fluorine is required in the composition, high-temperature calcination causes severe fluorine loss due to LiF volatilization above its melting point (848 °C), and intermediate phases such as Li₂(Mn,Ti)O₃ may form, hindering effective fluorination. Fourth, the limited heating rate and thermal profile flexibility of conventional furnaces make it difficult to precisely control SRO and lithium distribution, which are critical for Li⁺ transport kinetics.

Several efforts have been made to address these processing limitations. To mitigate fluorine loss, alternative precursor designs have been explored. Szymanski et al. [51] systematically investigated fluorination pathways and identified that at low temperatures, MnF₂ reacts with the Li source to form LiF as an intermediate, trapping F in strong Li–F bonds, while at high temperatures, LiF volatilizes above 848 °C, inhibiting effective fluorination. Building on this understanding, Avvaru et al. [37] developed a low-temperature solid-state strategy using unconventional precursors (Li₆MnO₄ and MnF₂), achieving high fluorination levels (y up to 0.34) while avoiding the formation of fluorine blocking intermediate phases, and reducing the calcination temperature from above 900 °C to 800 °C.

Beyond fluorine chemistry, alternative precursor routes have also been explored to improve the efficiency of solid-state synthesis. Chambers et al. [52] developed a two-step combustion synthesis approach using glycine nitrate precursors to produce a lithiated transition metal oxide intermediate, which is subsequently reacted with LiF at 800–1000  °C for only 1 h to form DRX. This method significantly reduces the total processing time compared to conventional solid-state synthesis, which typically requires over 12 h of calcination.

In addition to precursor design, improving precursor homogeneity is also critical for achieving phase-pure DRX. Simple modifications to the mixing protocol, such as using ethanol as a wet milling medium instead of dry mixing, have been shown to significantly enhance precursor uniformity and reduce impurity phases. Despite these advances, the fundamental constraints of solid-state synthesis, particularly the trade-off between high temperature requirements for cation diffusion and the need for controlled SRO, remain difficult to overcome, motivating the development of alternative synthesis approaches discussed in the following sections.

3.2 Mechanochemical method

Compared with solid-state methods, mechanochemical synthesis uses mechanical force from high-energy ball milling to drive reactions, enabling low-temperature preparation of DRX materials (Fig. 3B). This method employs high-energy ball milling to impose mechanical stress on stoichiometric lithium and metal precursors, triggering room-temperature solid-state reactions and random cationic occupation to directly yield DRX powder. The high energy input during milling promotes extensive cation disordering that cannot be achieved via thermal treatment, making it ideal for synthesizing metastable DRX cathodes, such as those with high fluorine content.

Reitano et al. [38] first demonstrated the synthesis of d⁰-element-free Ni–Mn binary DRX oxides via mechanochemistry, using a ball milling speed of 600 r/min for 20 h at room temperature to directly obtain the DRX phase without any high-temperature calcination. Moreover, mechanochemical synthesis allows the introduction of cation vacancies directly during ball milling by adjusting the Li content in the precursor mixture, as demonstrated in Mn–Nb DRX systems [39]. In that work, the precursors were ball milled at 450 r/min for 45 h, and the as-milled products exhibited controlled vacancy concentrations and modified SRO without additional heat treatment. Mechanochemistry also supports the construction of heterogeneous nanocomposite DRX with spinel/DRX nanodomains, as reported by Lee et al. [40], where high-energy ball milling of Li, Mn, Ti, and F precursors at 800 r/min for 5 h promotes local phase separation at the nanoscale, forming a nanocomposite structure that helps suppress oxygen loss and Jahn-Teller distortion. Most importantly, one-pot mechanosynthesis permits the incorporation of polyanion groups into DRX lattices [41]. By ball milling Li₂O, Mn₂O₃, MnO₂, and Li₃PO₄ precursors at 800 r/min for 5 h, polyanion groups were directly incorporated into the rock-salt lattice, producing Co/Ni-free cathodes with ultrahigh capacity and improved high-voltage stability, delivering energy densities above 1100 Wh·kg⁻¹ with > 70% retention over 100 cycles.

Mechanochemical synthesis yields only nanoscale particles (50–200 nm), which boosts specific energy density, typically exceeding 700 Wh·kg⁻¹. However, this renders it unsuitable for applications requiring large-sized DRX materials while exacerbating metastable surface side reactions. Most mechanochemically derived DRX cathodes are highly air- and moisture-sensitive, readily forming surface lithium impurities that consume cyclable lithium and impair full-cell performance. Together, the high-energy input required for synthesis and the intrinsic sensitivity of resulting materials severely limit the scalable application of this route.

3.3 Sol-gel method

Sol-gel synthesis enables excellent molecular-level mixing, offering better compositional homogeneity and structural stability than solid-state and mechanochemical methods (Fig. 3C). The sol-gel method synthesizes homogeneous DRX powder via solution-phase hydrolysis and condensation of metal precursors, followed by low-temperature calcination to achieve uniform cation disorder and fine particle morphology.

Liu et al. [42] synthesized a series of cation-disordered rock-salt cathode materials, Li_1+z/3Ni_1/2-z/2Ti_1/2+z/6O₂ (z = 0, 0.1, 0.2, 0.3, 0.4, 0.5), via the sol-gel route using an oil bath at 80 °C for 24 h and calcination at 600 °C under oxygen flow, among which Li_1.1Ni_0.35Ti_0.55O₂ delivered a reversible specific capacity of 116.5 mAh·g⁻¹ at 20 mA·g⁻¹. Furthermore, Kodalle et al. [43] systematically investigated the effects of two solvents, dimethylformamide (DMF) and 2-methoxyethanol (2-ME), on the crystallization of Li_1.2Mn_0.4Ti_0.4O₂ (LMTO-DRX) during sol-gel synthesis. Using acetic acid as a chelating agent and calcining at 1000 °C under argon atmosphere, they verified that DMF with strong coordination ability facilitates the formation of pure DRX. The liquid-phase environment inherent to sol-gel synthesis enables the in situ fabrication of coated DRX materials. For instance, Zhou et al. [44] first employed the sol-gel method to prepare Mn²⁺-based DRX cathodes, using sucrose as a carbon source and calcining at 1000 °C under argon protection. This process achieved a thin carbon coating simultaneously during DRX formation. For sol-gel synthesis to become a sustainable and competitive manufacturing route for next-generation DRX cathode materials, future efforts must focus on developing low-cost, environmentally benign solvents and continuous, scalable solution-processing strategies.

3.4 Advanced methods

Although numerous synthetic routes have been developed for DRX materials, they all suffer from inherent drawbacks. Structural design of DRX, especially the regulation of SRO and Li⁺ percolation networks, is difficult to achieve independently using the three conventional methods mentioned above. Therefore, developing optimized synthetic pathways that enable precise structural control and performance improvement of DRX has become a major research focus in recent years.

The molten salt method can provide a molten environment similar to a liquid phase, enabling the obtainment of DRX materials with controllable size distribution (Fig. 3D). Ahmed et al. [45] utilized CsBr as the molten salt medium to rapidly nucleate DRX phases at 800 °C for 5 h, followed by low-temperature annealing at 600 °C. This strategy enabled the direct synthesis of highly crystalline, monodisperse primary particles with an average size of approximately 118 nm. The obtained Li_1.2Mn_0.4Ti_0.4O₂ delivered an initial discharge capacity of ~220 mAh·g⁻¹ at 20 mA·g⁻¹ within 1.5–4.8 V and had 85% capacity retention after 100 cycles. By integrating molten salt synthesis with conventional solid-state reaction, this work achieves high crystallinity while preserving fine particle dimensions.

Both the microwave method (Fig. 3E) and the rapid sintering method (Fig. 3F) can complete the synthesis of DRX materials within a few minutes. Wu et al. [46] found that the conventional solid-state method must rely on d⁰ structural stabilizers such as Ti⁴⁺/Nb⁵⁺/Zr⁴⁺, otherwise pure-phase DRX cannot be synthesized. The research team proposed microwave heating at 600 W for 5 min followed by immediate water quenching to lock the metastable phase, obtaining micron-sized single-crystal particles (0.5–3 μm) of Li_1.1Mn_0.9O_1.9F_0.1. It was found that SRO still exists in the local structure, with a capacity retention rate of up to 92.3% after 100 cycles and an energy density as high as ~605 Wh·kg⁻¹. Park et al. [47] rapidly synthesized Li_1.2Mn_0.4Ti_0.4O₂ via Joule heating at a heating rate of 5.90 °C·s⁻¹, with a total synthesis duration of 2100 s and a power consumption of 400–500 W, greatly reducing the synthesis cost. The initial discharge capacity was ~230.6 mAh·g⁻¹, and the capacity retention reached 87.0% after 100 cycles. Compared with other methods, Joule heating can achieve both controllable SRO and uniform element distribution. Pure-phase DRX can be obtained by rapid heating and cooling directly under an Ar atmosphere. Luan et al. [48] demonstrated that high-temperature shock synthesis enables ultrafast production of DRX materials (Mn/Co/Cr/Ti/Nb/V systems) at a heating rate of ~3200 °C·s⁻¹ within 1 s, yielding highly crystalline nanoparticles of 10–20 nm. This approach suppresses Li volatilization and impurity formation relative to conventional methods. The synthesized Li_1.2Co_0.4Nb_0.4O₂ delivers a discharge capacity of 234.8 mAh·g⁻¹ at 20 mA·g⁻¹ between 1.5–4.6 V and a capacity retention of 68.6% after 50 cycles. Notably, this method can also directly regenerate degraded DRX cathodes. Although the DRX obtained by this method exhibits ordinary cyclic stability, this ultrafast, universal and scalable method provides insights for the future realization of efficient and low-cost synthesis of DRX.

4 Strategies to Improve Electrochemical Performance

The intrinsically poor electronic conductivity of DRX oxides (~10⁻⁷–10⁻⁹ S·cm⁻¹ for DRX vs. ~10⁻³ S·cm⁻¹ for LiCoO₂) [53], which arises from the disordered cation sublattice and the absence of extended transition metal-oxygen-transition metal networks [53–54], limits their rate capability and cycle life. Below, we discuss four complementary strategies to overcome these challenges, each targeting specific performance metrics while collectively addressing the electronic conductivity deficit.

4.1 Compositional design

A large number of studies [13,15,55] have shown that maintaining Li/TM ≥ 1.09 is essential to ensure the formation of a 0-TM percolation network, which serves as the foundation for DRX to achieve high capacity. This has also been verified by numerous studies, and DRX materials with favorable performance such as Li_1.3Nb_0.3Mn_0.4O₂ [56–57], Li_0.89Fe_0.44Ti_0.45O₂ [58] and Li_1.2Mn_0.4Ti_0.4O₂ [47,59] have been synthesized. On the other hand, to stabilize the crystal lattice, it is necessary to introduce d⁰ elements (Ti⁴⁺, Nb⁵⁺, Mo⁶⁺) [60-64], but d⁰ elements generally do not participate in electronic conduction and instead further reduce electronic conductivity. It should be noted that while d⁰ cations are indispensable for stabilizing the DRX lattice, their redox-inactive nature does not contribute to electronic conduction. Therefore, we propose that an optimal compositional design should balance the fraction of d⁰ stabilizers with redox-active transition metals that possess higher electronic mobility (such as Mn^3+/4+, Fe³⁺), thereby constructing localized electronic pathways within the disordered lattice without sacrificing the Li⁺ percolation network [65].

Park et al. [66] recently demonstrated that elevating the overall Mn valence state by partially substituting Ti⁴⁺ with Mn⁴⁺ (Li_1.2Mn_0.6Ti_0.2O_1.9F_0.1) effectively suppresses the over-reduction of Mn³⁺ to Mn²⁺ and subsequent Mn dissolution (Fig. 4A). As a result, this Mn-enriched DRX cathode delivers a capacity retention of 67.7% after 200 cycles, substantially outperforming the baseline composition (Li_1.2Mn_0.5Ti_0.3O_1.9F_0.1), which retains only 45.4% of its initial capacity, while both compositions achieve comparable reversible capacities of ~250 mAh·g⁻¹. Fong et al. [67] demonstrated reversible Fe²⁺/Fe³⁺ redox in an Fe²⁺-based DRX cathode (Li_1.2Fe²⁺_0.6Nb_0.2O_1.4F_0.6), achieving a high capacity of ~290 mAh·g⁻¹ and an energy density of ~700 Wh·kg⁻¹ by minimizing reliance on oxygen redox and reducing voltage hysteresis. Furthermore, the combination of Fe^3+/4+ and Mn^3+/4+ redox couples can stabilize the lattice reaction pathway in DRX cathodes [68]. Lee et al. [69] demonstrated that combining Fe^3+/4+ redox with Mn^3+/4+ redox in Fe-based DRX oxyfluorides (Li₂Fe_0.5M_0.5O₂F; M = Fe, Ti, Mn) stabilizes the oxygen-dependent Fe^3+/4+ redox by suppressing ligand-to-metal charge transfer upon charging, thereby reducing oxygen oxidation and increasing Coulombic efficiency (Fig. 4B). The resulting composition achieved a high capacity of 309 mAh·g⁻¹ and an energy density of 998 Wh·kg⁻¹.

Beyond binary or ternary composition tuning, the high-entropy strategy incorporates multiple transition metal species at near equimolar ratios, offering a further avenue to suppress detrimental SRO and stabilize the DRX lattice. Lun et al. [70] first applied the high-entropy concept to DRX cathodes, showing that increasing the number of transition metal species progressively suppresses SRO and boosts performance; a six-TM HE-DRX delivers 307 mAh·g⁻¹ and retains > 170 mAh·g⁻¹ at 2000 mA·g⁻¹. Zhou et al. [49] developed Li_1.25Ni_0.1Co_0.1Fe_0.1Cr_0.1Ti_0.2Nb_0.15O_1.8F_0.2 and revealed that the high-entropy effect promotes Li⁺ diffusion and stabilizes lattice oxygen through synergistic charge compensation among multiple transition metals, thereby suppressing oxygen loss and structural degradation (Fig. 4C). Their HE-DRX delivers an initial capacity of 277.6 mAh·g⁻¹ with 83.5% retention after 200 cycles.

While both high-entropy and low-entropy strategies have demonstrated effectiveness in enhancing capacity and rate capability, each approach carries inherent limitations that warrant careful consideration from a compositional design perspective. High-entropy systems introduce significant synthesis complexity arising from the need to homogenize multiple precursors, which increases both cost and the risk of phase impurities. The synergistic mechanisms among the constituent elements remain poorly understood, and the optimal composition space is vast, making rational design challenging without extensive computational screening. Low-entropy strategies, on the other hand, offer a more compositionally confined approach but impose stringent processing windows; the intended cation ordering effects are highly sensitive to synthesis conditions such as precursor homogeneity, calcination temperature, and cooling rate. Moreover, the applicable composition range is narrow, and long-term cycling stability of low-entropy DRX compositions has yet to be systematically demonstrated. A rational choice between these two compositional design routes should therefore consider not only electrochemical performance but also synthesis feasibility, cost, and the specific application requirements.

In addition to cation regulation, anion site engineering also provides abundant design freedom for improving the electrochemical performance of DRX. Among them, fluorination (i.e., partial substitution of O²⁻ with F⁻) has been widely proven to be an effective strategy for suppressing irreversible oxygen oxidation reactions, stabilizing the crystal lattice, and broadening the Li⁺ percolation network. Wu et al. [71] developed a fluorination-induced integrated structure design for a micron-sized DRX cathode Li_1.2Ni_1/3Ti_1/3W_2/15O_1.85F_0.15 (Fig. 4D). This strategy combines in situ F substitution to regulate anionic redox activity, an ultrathin LiF coating to mitigate parasitic reactions, and a single-crystal structure to suppress densification-degradation, synergistically achieving a reversible capacity of 290.3 mAh·g⁻¹ at 0.05 C, 78.5% capacity retention after 50 cycles, and a rate capability of 102.8 mAh·g⁻¹ at 2 C. Jiao et al. [50] unraveled the multiscale mechanism of fluorination in Li_1.2Ti_0.35Ni_0.35Nb_0.1O_1.8F_0.2, revealing that fluorination induces local Li-rich environments around F sites, increasing the number of fast 0-TM channels by 2.4% and, more importantly, raising the proportion of percolating 0-TM channels from 2.9% to 8.7%, thereby unlocking more accessible Li⁺ pathways and improving capacity release. Anion regulation is mainly aimed at addressing the issue of oxygen being prone to loss in DRX materials. Beyond fluorination, Huang et al. [72] introduced oxygen vacancies into Mn-based DRX by substituting labile oxygen with vacancies (Fig. 4E). They found that oxygen vacancies favor high Li coordination and reduce unhybridized oxygen states, thereby suppressing oxygen oxidation. This strategy lowers the average Mn valence to activate the Mn²⁺/Mn⁴⁺ redox couple, unlocking over 300 mAh·g⁻¹ and substantially improving capacity and voltage retention. Dasari and Chen [73] further demonstrated that oxygen vacancies promote rapid activation of the DRX-to-δ transformation, achieving nearly 100% capacity retention over 100 cycles. In brief, balancing Li excess, d⁰ stabilizers, redox metals, and anion engineering is essential. The key challenge is moving beyond trial and error toward predictive design that captures synergistic and trade-off effects.

4.2 SRO engineering

Since Ceder’s group first revealed in 2019 [16] that SRO fully governs Li⁺ transport in DRX cathodes, engineering SRO has largely become a central strategy for optimizing Li⁺ diffusion kinetics. Ceder’s group [74] further demonstrated that introducing a partial spinel-like cation order directly engineers SRO in DRX, which eliminates phase transitions and creates a highly connected 0-TM percolation network. This SRO control enables specific energies exceeding 1100 Wh·kg⁻¹ and high-rate performance of more than 100 mAh·g⁻¹ at above 20 A·g⁻¹. Zhang et al. [75] demonstrated that short-range spinel-like ordering formed within the DRX matrix (Fig. 5A) after a proton exchange assisted post treatment significantly enhances intrinsic Li⁺ mobility. This SRO engineering strategy enables micrometer sized particles to deliver more than 280 mAh·g⁻¹ at a slow rate and retain over 150 mAh·g⁻¹ at a high-rate of 2000 mA·g⁻¹.

Notably, SRO is not universally beneficial. Monte Carlo simulations have shown that the presence of SRO in DRX cathodes generally leads to reduced Li percolation compared to a random arrangement of transition metal species. This is because certain SRO configurations can decrease the number of 0-TM environments, which are the preferred sites for fast Li⁺ migration, thereby limiting the connectivity of the percolation network and compromising rate capability. In light of this, Ceder’s group [70] later introduced the high-entropy (HE) concept into DRX cathodes. By comparing DRX cathodes containing two, four or six transition metal species, they demonstrated that SRO systematically decreases whereas energy density and rate capability systematically increase as more TM species are mixed together. Electron diffraction in Fig. 5B revealed that diffuse scattering from SRO progressively weakens from the binary to the six-component system, confirming that high-entropy mixing suppresses SRO. To directly suppress such unfavorable SRO, Ahn et al. [76] proposed a low-entropy strategy that directly suppresses harmful SRO by tuning electrostatic interactions and cationic size effects. They incorporated Ti⁴⁺ into a Li–Nb–Mn DRX to weaken high valence driven interactions and increase ionic size mismatch with Li⁺, thereby promoting Li/TM mixing and energetically disfavoring SRO formation. The optimized composition Li_1.2Nb_0.15Mn_0.55Ti_0.1O₂ delivers a high capacity of ~327 mAh·g⁻¹ and an energy density of ~1026 Wh·kg⁻¹, substantially outperforming the SRO prone baseline (~274 mAh·g⁻¹, ~837 Wh·kg⁻¹). Electron microscopy revealed Li-rich configurations in Ti-free composition, which were rarely seen after Ti incorporation, confirming that limiting TM diversity and Mn dominance suppresses local SRO (Fig. 5C). In addition to compositional tuning, synthesis conditions offer another route to control SRO. Park et al. [47] demonstrated that rapid Joule heating synthesis enables precise control over SRO in Mn-based DRX cathodes. Compared to conventional furnace synthesis, a Joule heated Li_1.2Mn_0.4Ti_0.4O₂ sample achieved reduced SRO (evidenced by weaker diffuse scattering in electron diffraction patterns in Fig. 5D) while maintaining a near phase-pure DRX structure and uniform elemental distribution, leading to improved rate capability (161 mAh·g⁻¹ vs. 137 mAh·g⁻¹ at 1 A·g⁻¹).

Thus, the distinction between beneficial and detrimental SRO lies in whether the local cation arrangement promotes or disrupts the connectivity of 0-TM percolation networks. While spinel-like partial ordering can enhance Li⁺ transport, many SRO configurations reduce 0-TM site connectivity and impair rate capability. A major challenge remains to predict and deliberately design SRO motifs that favor fast ion conduction, moving beyond empirical suppression strategies [77].

4.3 Microstructure control

The low electronic conductivity of DRX limits its rate capability. Microstructure engineering addresses this issue through multiple mechanisms: reducing particle size, eliminating grain boundaries via single crystals, applying protective surface coatings, and constructing conductive networks.

Ahmed et al. [45] synthesized sub-200 nm single-crystalline DRX particles with high crystallinity (Fig. 6A). The small particle size shortens Li⁺ and electron diffusion distances, while the single-crystal nature eliminates grain boundary resistance. As a result, this well-dispersed microstructure delivers 85% capacity retention over 100 cycles with minimal voltage decay of only 4.8 mV per cycle, in contrast to conventionally pulverized material (38.6% retention, 7.5 mV decay per cycle). However, reducing particle size is not universally beneficial. Zhang et al. [78] revealed that sub-micron particles exhibit higher anionic redox activity but suffer from inferior cycling stability compared to micron-sized particles, highlighting a trade-off between capacity utilization and long-term durability. They also found that engineering particle size effectively modulated the balance between cationic and anionic redox contributions.

In addition to particle size control, single crystallization offers an effective strategy to enhance Li⁺ transport kinetics in DRX cathodes. The core advantage of single crystals lies in the elimination of grain boundary resistance that is prevalent in conventional polycrystalline materials. Moreover, single crystals remove the interference from kinetic factors such as particle size distribution, crystal facets, grain boundaries, and mechanical strain, thereby providing an ideal platform to unravel the intrinsic Li⁺ transport mechanisms of DRX materials. Kan et al. [30] synthesized micrometer sized Li_1.3Nb_0.3Mn_0.4O₂ single crystals as a model system to eliminate these extrinsic interferences (Fig. 6B). This approach allowed them to unambiguously reveal that local SRO modulates the Li diffusion network and can even introduce anisotropic Li⁺ diffusivity within the rock-salt lattice.

Besides, applying protective surface coatings offers an additional lever to stabilize the cathode electrolyte interface and suppress parasitic reactions without altering bulk composition. Cambaz et al. [79] explored surface modification of Li_1.2Ni_1/3Ti_1/3Mo_2/15O₂ with a LiNbO₃ layer (Fig. 6C). The coating altered the voltage profile, resulting in a higher average discharge voltage and enhanced cycling stability with lower impedance compared to the unmodified material. The improvement was attributed to mitigated surface densification through Nb doping and surface modification. Huang et al. [80] applied an Al₂O₃ coating onto Li_1.2Ti_0.4Mn_0.4O₂ via atomic layer deposition (ALD). The coated cathode exhibited significantly enhanced cycling stability, retaining 90.9% of its initial capacity after 15 cycles compared to 79.7% for the pristine material, attributed to the Al₂O₃ layer alleviating oxygen release and inhibiting undesirable side reactions. Zhang et al. [81] demonstrated that direct fluorination of a DRX cathode (Li_1.15Ni_0.375Ti_0.375Mo_0.1O₂) leads to the formation of a LiF surface layer rather than bulk fluorine substitution (Fig. 6D). This LiF coating improves specific energy and capacity retention, demonstrating the feasibility of direct fluorination as a surface engineering strategy for high-voltage DRX cathodes. Extending to high-entropy DRX, Zhou et al. [82] applied an Al₂O₃ ALD coating (Fig. 6E) and observed similar interfacial stabilization effects. The uniform Al₂O₃ coating improves initial Coulombic efficiency from 68.6% to 85.4% and capacity retention after 50 cycles from 46.6% to 60.5% by suppressing electrolyte decomposition on the cathode surface. However, the coating cannot prevent bulk phase degradation during prolonged cycling, highlighting the need for integrated bulk and surface stabilization strategies.

The most direct way to compensate for the intrinsically poor electronic conductivity of DRX is to construct an efficient electronic percolation network at the electrode level. Patil et al. [31] systematically compared carbon additives in Li_1.2Mn_0.5Ti_0.3O_1.9F_0.1 cathodes and found that electrodes containing 10 wt.% graphite (Gr) significantly outperform those with conventional disordered carbon (Fig. 6F). The graphite-based cathodes achieve a reversible capacity of ~260 mAh·g⁻¹ with 85% capacity retention after 50 cycles and a rate capability of ~135 mAh·g⁻¹ at 1000 mA·g⁻¹, benefiting from a uniform graphitic coating that protects the particle surface and a robust conductive network. Xu et al. [59] deposited amorphous carbon on Li_1.2Mn_0.4Ti_0.4O₂ particles to increase electrical conductivity by five orders of magnitude, then ball milled the material with multiwall carbon nanotubes (CNT) to create an efficient electrical percolation network (Fig. 6G). The CNT based electrode, with 78.7 wt.% active material loading, delivers an electrode level gravimetric discharge capacity of 121 mAh·g⁻¹ after 50 cycles, largely outperforming the Super P C65 based electrode (44 mAh·g⁻¹). Besides, Zhou et al. [44] synthesized carbon coated Li_1.2Mn_0.2Ti_0.6O₂ via a one-step sol-gel method using sucrose as the carbon source, delivering an initial discharge capacity of 119.6 mAh·g⁻¹ with 76.1% retention after 20 cycles.

Despite the effectiveness of these morphology and microstructure engineering strategies, each comes with inherent trade-off. The field must move beyond isolated optimizations toward integrated designs that balance particle size, crystallinity, surface stability, and electronic percolation to unlock the full potential of DRX cathodes.

4.4 Interfacial stability and full-cell performance

The preceding sections have discussed various strategies to enhance the intrinsic electrochemical performance of DRX cathodes in half-cell configurations. However, transitioning these materials into practical batteries requires addressing challenges that are often masked in half-cells. A critical bottleneck is the cathode-electrolyte interface (CEI), where oxygen redox activity triggers lattice oxygen release, surface reconstruction, and sustained parasitic reactions that consume active lithium and degrade the electrolyte. These interfacial degradation mechanisms are the primary reason why full-cell performance lags far behind half-cell demonstrations. The following two subsections address these interconnected challenges from the perspective of fundamental interface chemistry and practical cell-level validation.

4.4.1 Interfacial degradation

Brinkmann et al. [83] demonstrated that carbonate-based electrolytes are fundamentally incompatible with DRX surfaces. In Li_1.25Fe_0.5Nb_0.25O₂, carbonate electrolytes produced only 34% capacity retention after 100 cycles, whereas an ionic liquid achieved 72% retention. The difference arises from CEI chemistry: carbonates form a thick, continuously growing layer that increases impedance, while ionic liquids form a thin, stable CEI with minimal growth.

Zhou et al. [84] systematically tracked CEI evolution in Li_1.2Mn_0.4Ti_0.4O₂ (LMTO) and identified a LiF-dominated CEI that grows continuously with cycling, directly correlating with oxygen loss, Mn over-reduction, and TM dissolution. Liu et al. [85] revealed that fluoroethylene carbonate (FEC), an additive effective for layered oxides, can be detrimental for fluorinated DRX, with dehydrofluorination generating hydrogen fluoride (HF) that attacks the cathode surface and forms an insulating fluorinated layer.

Crafton et al. [86] identified two voltage-driven degradation modes: high-voltage charging (> 4.6 V) drives oxidative electrolyte decomposition, while discharging below 2.0 V drives reductive degradation. Theibault et al. [87] demonstrated that Mn dissolution is primarily driven by high-voltage structural rearrangements (> 4.2 V), rather than acid-induced disproportionation alone. Dissolved TM species migrate to the anode, disrupt the solid electrolyte interphase (SEI), and create a feedback loop that amplifies degradation.

Collectively, these studies reveal that interfacial degradation in DRX cathodes is not a single process but a cascade of interconnected events: oxygen release triggers surface reconstruction, which accelerates electrolyte decomposition and CEI growth, which in turn promotes TM dissolution and crossover. The conventional carbonate-based electrolytes and additives optimized for layered oxide cathodes are largely incompatible with DRX surfaces, making interfacial stability a primary, rather than secondary, determinant of cycling performance. These degradation pathways, masked in half-cells by excess electrolyte and infinite Li supply, become immediately consequential in full-cell configurations.

4.4.2 Full-cell performance

The degradation cascade described above becomes immediately consequential in full cells, where finite electrolyte and limited Li inventory leave little margin to compensate for CEI growth, TM crossover, and Li loss.

Huang et al. [88] systematically investigated Gr||DRX full cells using a Mn-rich DRX cathode and identified cyclable Li inventory loss as the primary failure mode. Two interconnected mechanisms were found to be responsible: first, the DRX material is inherently sensitive to ambient exposure, forming surface Li impurities (Li₂CO₃, LiOH) that contribute to anomalously low first-cycle Coulombic efficiency; second, structural instability during cycling triggers Mn dissolution, and the dissolved Mn²⁺ migrates to the graphite anode, where it reacts with Li_xC_y compounds and catalyzes electrolyte decomposition, further consuming active Li. To mitigate these issues, they employed an electrochemical activation process to stabilize the DRX structure and suppress Mn dissolution, combined with chemical pre-lithiation of the graphite anode and a LiTFSI-containing electrolyte additive. This integrated strategy achieved 91% capacity retention over 150 cycles in Gr||DRX full cells, demonstrating that the half-cell-to-full-cell gap can be meaningfully narrowed through targeted engineering.

These findings underscore a critical reality: the commercial viability of DRX cathodes hinges not on bulk composition or intrinsic capacity alone, but on interfacial stability and its consequences for full-cell operation. Half-cell metrics (> 300 mAh·g⁻¹, > 1000 Wh·kg⁻¹) are necessary but insufficient. Full cells impose additional constraints, including finite Li inventory, lean electrolyte, and long-term cycling, that remain largely unaddressed. The 150-cycle benchmark achieved by Huang et al., while encouraging, falls far short of the 500–1000 cycles required for EV applications. Furthermore, the 20–30 wt.% carbon content needed to offset DRX’s poor electronic conductivity severely undermines electrode-level energy density, a limitation that interfacial engineering alone cannot overcome.

Looking forward, the practical deployment of DRX cathodes will require a paradigm shift from isolated half-cell optimization to integrated full-cell co-design. This entails coupling bulk composition design with electrolyte systems that are intrinsically compatible with DRX surface chemistry, voltage-window management to avoid both oxidative and reductive degradation, electrode-level conductive network engineering that minimizes carbon content while maintaining electronic percolation, and scaled synthesis routes that produce phase-pure DRX with controlled particle morphology and surface chemistry. Only through such a holistic approach can the promise of DRX cathodes, including high capacity, Co/Ni-free chemistry, and sustainable energy storage, be translated from laboratory demonstrations to commercially viable battery technologies.

4.5 Theoretical insights guiding DRX design

The percolation theory proposed by Lee et al. in 2014 [13] is the most prominent example. By calculating the connectivity of 0-TM channels as a function of Li content, it predicted a critical Li/TM ≥ 1.09 threshold for macroscopic Li⁺ transport. This prediction has since become the foundational design rule for all DRX compositions and has been validated in numerous subsequent studies.

DFT calculations have been employed to address several key questions that experiments alone could not easily resolve. For instance, Kitchaev et al. [89] used DFT to establish design principles for high TM capacity in DRX, revealing that the TM redox capacity is limited by the availability of electrons near the Fermi level and that fluorination can effectively lower the TM valence state to increase cationic capacity. Urban et al. [29] systematically investigated the electronic structure origin of cation disorder in transition metal oxides, showing that the tendency toward disorder is governed by the competition between cation cation and cation anion interactions, providing a rational basis for selecting d⁰ stabilizers.

Monte Carlo simulations have been essential for understanding the relationship between SRO and Li⁺ percolation. Ouyang et al. [90] demonstrated that SRO can either enhance or impede Li⁺ transport depending on the specific cation arrangements, and that fluorination modifies SRO through strong Li–F interactions. These simulations revealed that the effect of fluorination on Li⁺ transport is not monotonic. Low fluorination levels can be either beneficial or detrimental depending on the intrinsic SRO of the unfluorinated oxide, while high fluorination levels are consistently beneficial, a counterintuitive prediction that was later confirmed experimentally.

More recently, high-throughput DFT calculations combined with cluster expansion have enabled rapid screening of stable compositions in the vast DRX chemical space. Wang et al. [91] systematically investigated the elemental stability of 18,810 high-entropy DRX compositions through comprehensive data driven phase diagram analysis. Their work established elemental stability rules for high-entropy DRX cathodes, demonstrating that pronounced cation disorder arises from large off lattice distortions and the absence of high valence cations. They also identified an inverse correlation between disordering tendency and phase stability, indicating a fundamental trade-off that must be considered when designing high-entropy compositions. In a parallel study, the same group demonstrated that DFT based high-throughput screening can efficiently predict which HE-DRX compositions are thermodynamically stable and likely to form a single phase disordered rock-salt structure, guiding experimental synthesis without exhaustive trial and error. Their predictions were validated by successful synthesis of previously unreported HE-DRX compositions containing Cu as redox active centers and Sb/Sn as charge compensators.

Machine learning approaches are now emerging as complementary tools for predicting SRO motifs and diffusion pathways. Ullberg et al. [92] combined DFT with crystal graph neural networks to perform high-throughput screening of DRX compositions, identifying structural factors that contribute to SRO formation and predicting thermodynamically stable disordered phases. Liao et al. [93] developed a descriptor-based SRO modeling method that significantly reduces computational cost while preserving accuracy, revealing how configurational entropy suppresses SRO in high-entropy DRX to enhance diffusion dynamics. Sun et al. [94] further demonstrated a physically informed graph neural network that predicts DRX discharge performance using only composition inputs, enabling rapid screening across vast chemical spaces without requiring explicit structural characterization.

These computational tools are particularly valuable for navigating the vast composition space of high-entropy DRX, where the number of possible element combinations makes exhaustive experimental exploration impractical. For example, Wang et al. [95] performed high-throughput DFT calculations on 18,810 high-entropy DRX compositions, identifying an inverse correlation between disordering tendency and phase stability. This finding directly addresses a key practical concern: while high-entropy compositions are designed to suppress SRO, achieving a fully disordered state often requires pushing the material toward metastable regimes, where phase purity becomes difficult to maintain. The synthesis challenge, as noted in the previous section, is that high-entropy systems demand careful balancing of multiple precursors to avoid impurity phases, while low-entropy strategies impose narrow processing windows. Computational screening can mitigate these difficulties by rapidly down selecting compositions that are both thermodynamically accessible and likely to exhibit the desired disorder. Nevertheless, the application of machine learning to DRX systems remains in its early stages, and the development of models that can reliably predict long term cycling stability still poses an open challenge.

4.6 Toward Co/Ni-free, high-energy DRX: a holistic perspective

The ultimate goal of DRX cathode development is to deliver high energy density using only earth-abundant, low-cost transition metals, free not only from Co and Ni but also from redox-inactive d⁰ cations (Ti⁴⁺, Nb⁵⁺, Mo⁶⁺, Zr⁴⁺). Achieving such d⁰-free compositions, containing none of these redox inactive species, would eliminate the “dead weight” that dilutes specific capacity and energy density, and reduce reliance on less abundant d⁰ elements such as Nb and Mo. To date, several Co/Ni-free DRX compositions have been demonstrated, including Li_1.2Mn_0.2Ti_0.6O₂, [62] Li_1.2Mn_0.6Ti_0.2O_1.9F_0.1 [66] and Li_1.2Fe_0.6Nb_0.2O_1.4F_0.6 [67]. Traditional DRX design has relied heavily on high-valent d⁰ species to stabilize the DRX lattice against irreversible phase transformations during cycling. While these d⁰ cations are effective structural stabilizers, they come with intrinsic drawbacks: they do not participate in charge compensation, contributing only “dead weight” that dilutes specific capacity and energy density. Moreover, their electronic configurations, with d orbitals either fully occupied or completely empty, do not facilitate electron hopping, further degrading the already low electronic conductivity of DRX materials. From a supply-chain perspective, although d⁰ metals are less critical than Co and Ni, elements such as Nb and Mo are still subject to price volatility and geopolitical constraints, limiting long-term sustainability.

Encouragingly, recent advances have demonstrated that d⁰ cations are not an absolute necessity. Wu et al. [46] reported a d⁰-free DRX cathode realized through non-equilibrium solid-state synthesis that controls atomic disorder. The removal of d⁰ species enables a micrometer-sized manganese-based DRX cathode to achieve a high capacity of 220 mAh·g⁻¹ and an energy density of approximately 770 Wh·kg⁻¹ while extending cycle life by more than three times compared to conventional d⁰-stabilized DRX. Reitano et al. [38] presented a new class of DRX materials obtained via mechanochemistry without any d⁰ stabilizing element, with the target composition Li_1.2Ni_0.2Mn_0.60O₂. The best composition delivers a specific capacity approaching 191 mAh·g⁻¹ and an energy density of approximately 668 Wh·kg⁻¹, though significant voltage hysteresis and polarization remain challenges to be addressed. These studies collectively demonstrate that d⁰-free DRX cathodes can achieve competitive energy densities compared to conventional d⁰-containing counterparts. Future efforts should focus on developing scalable synthesis routes, such as low-temperature non-equilibrium processing and mechanochemistry, combined with defect engineering to activate high-capacity redox couples without compromising structural stability.

5 Conclusions and Outlook

In summary, DRX oxides break the conventional requirement of long-range cation ordering, enabling three-dimensional Li⁺ percolation, broad compositional flexibility, and synergistic cation–anion redox chemistry for high-capacity, Co/Ni-free cathodes. However, several critical gaps prevent these excellent material properties from being realized in practical batteries. The challenges of poor electronic conductivity, voltage hysteresis and low Coulombic efficiency, limited full-cell validation, synthesis scalability and cost, and the trade-off between particle size and stability remain largely unresolved. Each of these challenges directly corresponds to the fundamental limitations identified earlier: the absence of extended electronic networks in the disordered structure, the irreversibility of oxygen redox reactions, the gap between half-cell and full-cell performance metrics, the energy intensity of current synthesis routes, and the conflicting requirements for particle size optimization.

Despite the remarkable progress in performance enhancement discussed above, the translation of laboratory scale DRX cathodes into commercially viable products still faces substantial hurdles. In half cell configurations with low mass loadings (< 3 mg·cm⁻²) and excess lithium metal anodes, the best Co/Ni-free DRX cathodes have achieved specific capacities exceeding 300 mAh·g⁻¹ (e.g., 307 mAh·g⁻¹ by Lun et al. [70]) and energy densities above 1000 Wh·kg⁻¹ (e.g., ~1050 Wh·kg⁻¹ by Lee et al. [96] and ~1026 Wh·kg⁻¹ for Ahn et al. [76]). These material level metrics are comparable to or even better than those of conventional Ni-rich layered cathodes, underscoring the promise of DRX chemistry.

However, the transition from half-cell to full-cell requires confronting the cathode-electrolyte interface. Oxygen redox activity triggers lattice oxygen release, TM migration, and sustained electrolyte decomposition, forming a resistive CEI that continuously consumes active lithium. In full cells with finite Li inventory and lean electrolyte, these degradation pathways rapidly deplete the limited lithium reservoir, causing premature failure that is not observed in Li-metal half-cells. Recent full-cell studies have achieved 91% capacity retention over 150 cycles through electrochemical activation and pre-lithiation, yet this remains far below the 500–1000 cycle EV benchmark. We therefore emphasize that future research must prioritize systematic full-cell evaluations under realistic conditions and integrate interfacial stabilization with bulk design to achieve practical viability.

To bridge the gap between laboratory breakthroughs and practical deployment, future research should prioritize: (i) developing intrinsic electronic conductivity enhancement strategies, such as partial reduction of transition metals or in situ formation of conductive spinel-like phases; (ii) designing low-hysteresis DRX compositions via high-entropy mixing, fluorination, or redox-active metal substitution; (iii) conducting systematic full-cell evaluations under realistic conditions (graphite anode, lean electrolyte, high areal loading, 25–45  °C operation); (iv) establishing scalable, low-cost synthesis protocols that yield phase-pure DRX with controlled particle morphology and surface chemistry; and (v) developing predictive models for SRO design that move beyond empirical suppression strategies to deliberately engineer beneficial local ordering. Only by simultaneously addressing bulk electronic conductivity, interfacial stability, and full-cell engineering can DRX cathodes transition from promising laboratory materials to commercially viable, sustainable battery components.

The development of DRX has already reshaped cathode design for LIBs, enabling Co/Ni-free compositions with capacities exceeding 300 mAh·g⁻¹ and energy densities above 1000 Wh·kg⁻¹. Encouragingly, recent demonstrations of d⁰-free DRX cathodes prove that high-valent stabilizers are not absolute necessities, opening a new frontier for truly sustainable materials. With continued progress in addressing the remaining challenges, DRX cathodes hold the potential to fundamentally decouple battery performance from critical metal supply chains, contributing to a more sustainable energy future.

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