Constructing a simple conductive-elastic layer on graphite surfaces for high-rate and long-life lithium-ion batteries

Abstract

Graphite serves as a pivotal anode material in lithium-ion batteries. However, issues such as the co-embedding of solvent molecules during cycling and rapid capacity degradation at high rates have greatly hampered the practical application and development of graphite materials. Herein, this study proposes a straightforward, cost-effective, and environmentally benign strategy for modifying graphite anodes, with the dual objectives of enhancing high-rate capability and prolonging cycle life. Using water as the primary solvent and polyacrylonitrile as the coating material, a highly conductive, flexible, and strongly bonded polymer cladding layer is designed by combining solid−liquid coating and low-temperature heat treatment technologies. This innovative design not only effectively prevents the co-embedding of solvent molecules and mitigates the volume change of graphite particles during extended cycling, but also successfully constructs a dense and efficient electron transport network on the graphite surface. Leveraging the stability advantages brought by the high electron cloud overlap of C=N bonds (comprising σ bonds and π bonds), the conductivity and structural stability of the material are enhanced. This ultimately results in the successful synthesis of the G@C-PAN core−shell material, which exhibits high-rate performance and exceptional long-cycling stability. The results indicate that the material retains a high specific capacity of 328.12 mAh·g⁻¹ with 96.18% capacity retention after 250 cycles at 0.5C. Furthermore, it exhibits an impressive specific capacity retention of 97.20% after 500 cycles at 2C. This study presents a sustainable, economically viable, and scalable approach for commercializing high-performance graphite-based lithium-ion batteries.

Graphical abstract

Keywords

lithium-ion battery / graphite anode / polyacrylonitrile / cyclization / carbon coating / long-life

1 Introduction

As the global remains concentrated on clean energy and environmental conservation, lithium-ion batteries (LIBs) have emerged as key components across various fields, including electric vehicles, consumer electronics, and energy storage systems, owing to their exceptional energy efficiency and renewable characteristics [1, 2]. As an essential component of LIBs, graphite is widely used because of its advantages such as high specific capacity, low cost, small specific surface area, and charge-discharge voltage platform [3]. Nevertheless, the limitations of graphite materials in terms of cycle stability and charging/discharging rates have emerged as bottlenecks that impede their ability to meet the current market demand. This limitation arises from two primary sources. The first is the inadequate compatibility between graphite and solvent, and the co-embedded solvent molecules lead to the exfoliation and pulverization of the graphite layer [4]. Secondly, the disparity in lithium de-intercalation rates between the interior and exterior of graphite particles exacerbates the occurrence of lithium precipitation during high-rate cycling [5]. Hence, the research on modifying graphite anode materials is significant for breaking through the bottleneck of LIBs and meeting the current market demands and technological advancements.

In recent years, researchers have dedicated considerable effort to addressing graphite’s electrochemical performance shortcomings through many modification strategies [6]. The focus of the research is on refining the microstructure of the graphite surface and augmenting the electrochemical stability. These modification strategies include structural design [7−9], surface coating [10, 11], surface doping [12], and composite materials [13]. Surface coating is the main performance enhancement method in the commercial production of graphite, whereby the graphite surface is coated with a layer of protective material via simple mixing and coating. By effectively minimizing its specific surface area and reducing the irreversible capacity loss during the initial lithiation process, this approach significantly enhances the first-time Coulombic efficiency. Furthermore, the coating layer can inhibit the volume effect of graphite particles during cycling, thereby effectively reducing the chalking and shedding, and enhancing the cycling stability of the battery [14]. Importantly, the coating layer not only introduces additional lithium storage sites but also optimizes the Li⁺ transport path and enhances the Li⁺ diffusion rate, which in turn improves the multiplicity performance of the battery. Ideally, the surface coating should consist of a continuous, intact, and elastic thin layer capable of efficiently conducting electrons and Li⁺, as well as effectively coping with the strain effects of the Li⁺ de-intercalation process [15]. The amorphous carbon layer by carbonized pitch and the metal oxide coating layer can enhance the electrochemical stability of graphite to a certain extent [16]. However, the relatively limited performance of the amorphous carbon layer in isolating solvents and electrons constrains its potential for application under high-rate cycling conditions. Meanwhile, the metal oxide coating, due to its high brittleness, weak bonding force, and the tendency to increase charge transfer impedance to some extent, results in the initial Coulombic efficiency and cycle stability still needing further improvement. Furthermore, the environmental pollution and high energy consumption accompanying the preparation process cannot be ignored. In contrast, the conductive polymer coating layer is an ideal coating material for enhancing graphite performance. It provides graphite with excellent electrical conductivity, outstanding flexibility and elasticity, and improved graphite surface wetting characteristics, all of which significantly enhance the material’s high-rate performance and cycling stability [17, 18].

Polyacrylonitrile (PAN) is an electrically conductive polymer compound with a rich conjugated π-electron system. In a low-temperature reaction environment, polyacrylonitrile is pyrolyzed to cyclized polyacrylonitrile (C-PAN) through a series of reactions including cyclization, cross-linking, and dehydrogenation [19]. The conjugated π-electron system in C-PAN provides excellent electron-conducting properties, while also demonstrating good chemical stability, as well as excellent Li⁺ transport capability under rapid cycling conditions. Research has demonstrated that utilizing C-PAN for the modification of cathode materials is an effective strategy to broaden its application potential and elevate its electrochemical performance [20]. However, previous studies dissolved PAN in an organic solvent and carbonized the precursor at high temperature as a modified material [21]. At the same time, the use of C-PAN to change the anode material research is obviously lacking. This work innovatively proposes a graphite surface modification strategy based on simplicity, environmental friendliness, and energy saving. The precursor of polyacrylonitrile-coated graphite (G@PAN) is to be low-temperature heat-treated, and a dense, flexible, highly electronically, and ionically conductive C-PAN coating layer is successfully constructed on the graphite surface. Utilizing the stability advantages conferred by the more stable C=N bonds inherent in C-PAN, the structure and chemical stability of the graphite anode are enhanced while the interfacial properties with the electrolyte are improved. C-PAN has excellent chemical stability, and its continuous, fully covered, and flexible coating layer can effectively prevent the co-embedding behavior of solvent molecules, as well as inhibit the volume effect of graphite particles during the long cycling process, consequently ensuring the integrity and stability of the graphite structure. Meanwhile, the conjugated π-electron system inside the C-PAN constructs an efficient electron transport network on the graphite surface, effectively accelerating the electron transport rate. G@C-PAN exhibits excellent fast charging/discharging performance and long cycling performance. The G@C-PAN exhibits a specific capacity of 328.12 mAh·g⁻¹ after 250 cycles at 0.5C, with a specific capacity retention rate of 96.18%. Furthermore, it maintains a high specific capacity retention rate of 97.20% even after 500 cycles at a higher rate of 2C. It is expected that this study will provide new ideas and methods for the modification of anode materials for LIBs and promote the further development of LIB technology.

2 Experimental section

2.1 Material

Polyacrylonitrile (PAN, M_w = 150 000) is purchased Shanghai Aladdin Biochemical Technology Co., Ltd. The graphite (G) material is provided by Hunan Rongli New Material Technology Co., Ltd. All drugs and reagents are used directly without further purification.

2.2 Preparation of G@C-PAN material

The graphite anode material coated with cyclized polyacrylonitrile (G@C-PAN) was successfully fabricated through a combination of solid-phase ball milling, liquid-phase coating, and low-temperature heat treatment processes (Fig.1). To start with, 0.15 g PAN and 1.5 g G were added to a ball milling jar with a ball-to-material ratio of 10:1. The milling parameters included a rotational speed of 300 r/min, with alternating the direction of milling every 20 minutes (forward and backward), for a total of 4 h. Placed in a drying cabinet at 70 °C for 2 h was the resulting powder. The ball milling method evenly distributes PAN on the surface of graphite particles through intense mechanical stress, which is crucial for the subsequent liquid-phase coating process. The powder was introduced into a blended solution containing 50 mL of deionized water and 5 mL of ethanol, sealed with a sealing film, and then ultrasonicated for 20 min, followed by continuous stirring at 25 °C for 5 h. Subsequently, it was stirred at 60 °C until the solvent was evaporated and dried under vacuum overnight to prepare polyacrylonitrile-coated graphite material (G@PAN). The liquid-phase coating method stabilizes the PAN coating and disperses the graphite particles, further enhancing the PAN coverage and bonding strength. Lastly, the material was heated to 300 °C in an air atmosphere at a heating rate of 2 °C/min and held for 4 h. Under low-temperature heat treatment conditions, polyacrylonitrile underwent cyclization, resulting in crosslinking and oxidation of linear chains to form a stable ladder-like structure. The cooled powder at room temperature was grinded using a mortar. Subsequently, the cyclic polyacrylonitrile-coated graphite material (G@C-PAN) was obtained. In addition, for comparison, 0.075 g and 0.225 g PAN are coated with 1.5 g graphite material, respectively, and are denoted as G@C-PAN-05 and G@C-PAN-15.

2.3 Electrode preparation

The active materials (G@C-PAN) and conductive carbon black (Super P) were ground together well in an onyx mortar and then dispersed in deionized water containing carboxymethyl cellulose (CMC), which were mixed well with magnetic stirring for 8 h at a mass ratio of 8:1:1 (G@C-PAN : Super P : CMC) to obtain a water-based slurry coating. The paste coating was uniformly applied to the copper foil using a 100 μm spatula, followed by drying in a vacuum drying oven at 100 °C for a duration of 12 h. Subsequently, the coated foil was cut into round pieces with a diameter of 12 mm using a press. The half-cell assembly process is completed within a glove box filled with argon gas (oxygen and water pressure are less than 1 ppm). Using the positive and negative shells of the CR2025 coin cell, the negative pole piece is placed in the center of the positive shell. Then a 12 mm lithium piece is used as the counter electrode to assemble the half-cell button cell, which is sealed with the battery sealing machine.

2.4 Electrochemical measurement and characterization

The diaphragm was Celgard 2400 polypropylene membrane. The electrolyte composition was 1.0 mol·L⁻¹ LiPF₆ EC/DEC/DMC = 1:1:1 Vol%, with an additional 1% vinylene carbonate. The cells underwent charge/discharge tests within a voltage range of 0.005-2 V (vs Li/Li⁺), utilizing a battery testing system (NEWARE, Shenzhen, China). Cyclic voltammetry measurements and electrochemical impedance spectroscopy (EIS, 0.01−10⁵ Hz, with a voltage amplitude of 5 mV) were performed on the cells at a CHI600E electrochemical workstation (Chenhua, Shanghai, China).

Using a scanning electron microscope (SEM; S-4800, Japan, operated at 5 kV and 10 μA) and a transmission electron microscope (TEM; Titan G2 60-300), the surface morphological characteristics of the materials were examined. The elemental distribution in the sample was analyzed using energy-dispersive X-ray spectroscopy (EDS) with an operating voltage of 20 kV and a current of 10 μA. The X-ray diffraction analysis (XRD, Shimadzu 7000 S/L type 40 kV, Cu Kα) and Raman spectrometry (Raman, Thermo Fisher Nicolet iS10, 532 nm, 100−4000 cm⁻¹) characterized the chemical structure of the materials. The full-spectrum and high-resolution scans of the elements C, O, N, F, and Li were completed using X-ray photoelectron spectroscopy (XPS, Al K_α).

3 Results and discussion

3.1 Structural characterization

The surface structure of the graphite anode material, both before and after coating modification, was observed using SEM. A comparison is made between the SEM images of the pristine graphite [Fig.2(a)] and the modified graphite [Fig.2(d)]. Pristine graphite particles display an irregularly spherical morphology, with an average particle size of approximately 10 μm. The surface is not entirely smooth, displaying a multitude of protuberances. At the lateral edges, a layer-stacking structure formed by van der Waals forces is discernible. This structural feature may lead to the co-embedding of solvent molecules, a volume effect, and a discrepancy in the rate of Li⁺ intercalation/deintercalation between the interior and the edges of the graphite particles during the cycling process [22]. Consequently, the pristine graphite anode is unable to maintain long-term cycling stability at high rates. The highly conductive polymer capping layer has the potential to enhance Li+ kinetics in graphite, thereby meeting the demand for stable long-term graphite cycling and rapid ionic migration [23, 24]. Consequently, the obtained precursors are subjected to low-temperature heat treatment to induce the cyclization reaction of PAN, thereby transforming PAN into C-PAN. As illustrated in Fig.2(d), the G@C-PAN displays a comparable particle size to that of pristine graphite. However, the surface structure morphology is more compact, exhibiting no discernible holes on the particle surface. Instead, it is coated with a continuous layer of dense C-PAN. Additionally, observation results show that there is inhomogeneity in the surface coatings of the two materials, G@C-PAN-05 and G@C-PAN-15, with phenomena of local accumulation and partial agglomeration occurring (Supplementary Fig. S1). The microstructure of G and G@C-PAN was further observed by TEM. G has a highly ordered layered accumulation form with a smooth surface and no cladding layer [Figs. 2(b, c)]. In contrast, the surface of G@C-PAN is coated by a continuous, dense, and surface-adherent conjugated amorphous coating [Figs. 2(e, f) and Supplementary Fig. S2(a)]. During the low-temperature heat treatment process, PAN undergoes a transition, transforming from a linear molecular structure into a more stable ladder-like one through cross-linking and cyclization reactions. Therefore, the C-PAN layer possesses excellent elastic and conductive properties. It can effectively facilitate electron transfer and enhance structural stability, thereby contributing to the long-term cycle stability of graphite materials. This is further demonstrated in subsequent electrochemical performance tests.

An analysis of the distribution of the C-PAN layer across the surface of G was performed employing an EDS. In the G@C-PAN anode material, the distribution of N elements was found to be essentially superimposed on that of C and O elements, which was also consistent with the morphology and size of G particles [Fig. 2(g), Supplementary Figs. S2(b, c)]. This indicates that the nitrogen element present in the carbon precursor is effectively retained during the heat treatment process and distributed uniformly on the surface of the graphite particles. The primary reason lies in the high efficiency and straightforwardness of the adopted precursor synthesis method, enabling PAN to uniformly coat the graphite surface and penetrate deeply into the internal pores and crack structures of the particles, resulting in a substantial boost to the overall structural stability.

The crystalline structures of G@C-PAN and G were characterized using XRD [Fig.3(a)]. The results indicated that the diffraction peaks of G@C-PAN were consistent with those observed in graphite (PDF#98-000-02). Furthermore, a strong characteristic diffraction peak was observed near 26.5°, which corresponds to the graphite (002) peak. The intensities of the peaks are directly proportional to the degree of graphitization [25]. In comparison to G, the graphite (002) diffraction peak of G@C-PAN undergoes a slight low-angle shift, and the intensity of the 002 peak is diminished (Supplementary Fig. S3). This phenomenon can be attributed to the fact that the cladding of the C-PAN layer introduces additional interfaces or defects between the graphite crystal layers, which modifies the orientation of the graphite crystals, increases the disorder and layer spacing of the graphite crystals, as well as facilitates Li⁺ transport. This suggests that PAN has been successfully coated on the G surface and that a cyclization/dehydrogenation reaction of PAN has been triggered by low-temperature heat treatment, resulting in the formation of a C-PAN layer on the graphite surface. The layer spacing d₀₀₂ of the graphite crystalline structure is calculated by Bragg’s formula. Subsequently, the interlayer spacing and graphitization degree of G@C-PAN are determined by applying the Mering–Maire formula [Supplementary Eq. (S1)]. The results show that G@C-PAN possesses an interlayer spacing of 0.33654 nm and a graphitization degree of 86.74% (Supplementary Table S1). Furthermore, the orientation index value I₍₀₀₄₎/I₍₁₁₀₎, defined as the ratio of peak intensities of 54.5° (004) and 77.4° (110) crystalline surfaces) of G@C-PAN is 1.000, which is lower than the OI value of graphite (1.065) [26]. The ordering of the material itself is reduced, and the embedded active center of Li⁺ on the surface of G@C-PAN is increased. These effectively promote the de/embedding motion of Li⁺.

The Raman spectra of G@C-PAN and G are depicted in Fig.3(b). The G@C-PAN material exhibits a Raman spectrum featuring two broad bands: the D band centered at 1360 cm⁻¹ and the G band centered at 1580 cm⁻¹. These bands are indicative of sp³-type disordered and sp²-type graphitization carbon, respectively. The defective and disordered structural features of the material are represented by the D peak, while the G peak represents the ordered graphitized structural features. The relative proportion of disordered and ordered structures within the material can be further elucidated by examining the ratio of the D peak intensity to the G peak intensity (I_D/I_G). In comparison to the I_D/I_G value of pristine graphite (0.116), the I_D/I_G ratio of G@C-PAN has increased to 1.045. This result also corroborates the introduction of the C-PAN layer results in the formation of additional defects and electrochemically active sites on the surface of the pristine graphite. This leads to an increase in the proportion of disordered structures, as indicated by the I_D/I_G ratio of the C-PAN layer. This finding follows the results of the X-ray diffraction analyses.

The changes in the functional group before and after PAN cyclization were observed by FT-IR. In Fig.3(c), three distinct peaks at 2246 cm⁻¹, 1455 cm⁻¹, and 1383 cm⁻¹ are observable for PAN, which are attributed to the tensile vibration of C≡N and the bending vibrations of −CH₂ and −CH− respectively. Upon the synthesis of C-PAN, two more peaks emerge at 1592 cm⁻¹ and 1286 cm⁻¹, which can be ascribed to the tensile vibrations of the C=N and C−N bonds, respectively. Simultaneously, the intensity of the characteristic peak for C≡N (2246 cm⁻¹) decreases significantly, with only a small fraction of C≡N remaining. Additionally, the characteristic peak intensity of −CH₂ (1455 cm⁻¹) basically disappeared, while the characteristic peak intensity of −CH− related vibrations increased. These observations are attributed to the cross-linking and cyclization reaction of PAN induced by heat treatment at a low temperature, resulting in the formation of C-PAN. During this process, the cyanide (C≡N) group is transformed into C=N and C−N bonds, and the molecular structure gradually shifts from a linear chain to a more stable, trapezoidal-like structure. At this stage, there is a significant amount of C=N present in C-PAN, accompanied by a minor quantity of C≡N and C−N bonds, suggesting that the degree of cyclization is incomplete. In the C=N bond, there are overlapping regions of two electron clouds, forming a σ bond and a π bond, respectively, which results in a relatively high degree of electron cloud overlap. The moderate bond energy and electron cloud density of the C=N covalent bond render it superior in terms of structural stability and electrical conductivity to both C≡N and C−N. Additionally, the strength of −CH₂ bonds is also reduced during the dehydrogenation reaction. The principle of functional group changes before and after the cyclization of PAN is illustrated in Fig.4.

The XPS spectra before and after PAN coating graphite are shown in Fig.3(d)−(i). All the spectra are corrected with C 1s (284.8 eV). In comparison to the XPS total spectrum of graphite, the total spectrum of G@C-PAN [Fig.3(d)] exhibits a distinct N-element signal at approximately 400.0 eV, which substantiates the presence of the C-PAN layer [27]. The C 1s XPS spectra of G@C-PAN exhibit four characteristic peaks located at 284.8 eV, 285.5 eV, 286.8 eV, and 288.0 eV, corresponding to C=C/C−C, C−N, C−O, and O−C=O, respectively [Fig. 3(e) and Supplementary Fig. S4]. This observation further indicates that the C-PAN containing nitrogen atoms is successfully encapsulated on the graphite surface. Furthermore, as illustrated in Fig.3(c), the N element in PAN predominantly exists in the form of cyano-bonds (C≡N). There is only a prominent peak of C≡N in its N 1s spectrum before the heat treatment process. Following the low-temperature heat treatment, the original single symmetric peak gradually transformed into an asymmetric broad peak with a more complex morphology. This suggests that the PAN underwent a cyclization/dehydrogenation reaction, resulting in a change in the binding state of the N element. As a result, three peaks (N2, N1, N3) with binding energies of 398.2, 399.0 eV, and 400.0 eV in the N 1s, respectively [Fig.3(f) and Fig.4] [28]. The presence of the N1 peak at 399.0 eV, which corresponds to the cyanogen group (N≡C), suggests that structural constraints have hindered a portion of the PAN from fully participating in the cyclization reaction, ultimately leading to incomplete cyclization of the sample. The N2 peak (398.2 eV) and the N3 peak (400.0 eV) signify the formation of pyridine N and substituent graphite groups, respectively. Both have delocalized sp² π bonds, which can effectively improve electronic conductivity. The findings confirm that the cyclization reaction of PAN occurred, leading to the formation of a conjugate structure with off-domain sp² π bonds. The O 1s XPS spectra of G and G@C-PAN exhibit two characteristic peaks located at 531.4 eV and 533.2 eV, corresponding to C=O and C−O, respectively [Fig.3(g)−(i)] [29]. The application of low-temperature heat treatment in an air atmosphere resulted in the induction of cyclization/cross-linking reactions in PAN. The dehydrogenation reaction of the cyclization process forms abundant oxygen vacancies. At the same time, oxygen is compensated in the air to effectively promote the cyclization reaction. A comparative analysis of the samples before and after coating revealed an increase in the C=O content. This is ascribed to the oxidation reactions that occur in air, involving the conjugated polymers and graphite-like structures formed through cyclization reactions (Fig.4) [30].

3.2 Electrochemical performances

Assemble Li⁺||G and Li⁺||G@C-PAN half-cells to evaluate the electrochemical performance of the materials. At a scan rate of 0.1 mV·s⁻¹, the CV curves of the G and G@C-PAN anodes are presented in Supplementary Fig. S5, respectively. During the scanning process, the reduction and oxidation peaks of both G and G@C-PAN exhibit essentially identical positions. This demonstrates that the graphite surface coating of C-PAN does not affect its properties. The initial CV curves for the G@C-PAN and G anodes at a scan rate of 0.1 mV·s⁻¹ are more closely compared in Fig.5(a). The initial redox peak potential difference of the G@C-PAN anode (ΔE = 0.21) is smaller than that of the G anode (ΔE = 0.28). This indicates that the G@C-PAN anode has a lower degree of polarization and higher electrochemical reversibility during the electrochemical process [31, 32]. This is due to its high conductivity characteristic, which not only effectively inhibits capacity fade caused by interfacial side reactions, ensuring structural stability, but also reduces the overpotential of reactions and minimizes polarization phenomena, thereby achieving excellent cycle reversibility.

Fig.5(b) shows the charge−discharge curves of the G and G@C-PAN anode at 0.1C. The G@C-PAN exhibits initial charge/discharge specific capacities of 379.72 and 438.48 mAh·g⁻¹, respectively, with an initial coulombic efficiency (ICE) of 86.60%. Compared with the pristine graphite (the initial charge/discharge specific capacities of 358.70 and 400.56 mAh·g⁻¹, respectively, with the ICE of 89.55%), the ICE of the G@C-PAN are reduced, but both of their charge/discharge specific capacities are increased. The charging specific capacity of the G@C-PAN anode surpasses the theoretical specific capacity of graphite. The conjugated layer of C-PAN provides more migration channels and active sites for Li⁺, accelerating the transport of Li⁺ and enhancing the lithium storage capacity of graphite. However, due to the mismatch of the Li⁺ dissociation mechanism at the N-active site and the increase of the specific surface area, more lithium is consumed during the formation of the SEI film, resulting in a decrease in ICE. In addition, the G@C-PAN-05 anode has initial charge/discharge specific capacities of 365.77 and 439.05 mAh·g⁻¹, and an ICE of 83.31%. The G@C-PAN-15 anode, on the other hand, has initial charge/discharge specific capacities of 393.86 and 475.23 mAh·g⁻¹, respectively, and an ICE of 82.88%. Due to the uneven coating, although the charge-discharge capacity is increased, the ICE is decreased (Supplementary Fig. S6). Fig.5(c) shows the G@C-PAN anode’s charge−discharge curves at 0.1C. Notably, a stable SEI film is formed in the first cycle, and the charge-discharge curves after that almost coincide

After activation at 0.1C, the G@C-PAN anode undergoes a low-rate cycling test at 0.2C (Supplementary Fig. S7). The G@C-PAN anode demonstrated a minor reduction in its specific charging capacity, decreasing from 364.70 mAh·g⁻¹ initially to 362.28 mAh·g⁻¹ after 55 cycles, while maintaining a high capacity retention rate of 99.34%. This indicates that the G@C-PAN anode has high specific capacity and excellent cycling stability at a low rate. Moreover, the cycling performance of G and G@C-PAN anodes at 0.5C is shown in Fig.5(d). The charging specific capacity of G anode is 236.92 mAh·g⁻¹ after 250 cycles. Unlike G, the C-PAN forms a continuous and dense protective layer, accompanied by a conductive network, on the surface of G. The charging specific capacity of G@C-PAN decreases from the initial 341.14 to 328.12 mAh·g⁻¹ with a capacity retention of 96.18% after 250 cycles. Therefore, under low-rate conditions, G@C-PAN exhibits better cycle stability and higher specific capacity.

The rate performance of G and G@C-PAN are illustrated in Fig.5(e). At current rates of 0.2C, 0.5C, 1C, 2C, 3C, and 5C, the specific capacities of the G@C-PAN anode are 365.32, 325.34, 256.27, 159.73, 88.47, and 36.17 mAh·g⁻¹, respectively. Significant enhancement in specific capacity is observed for the G@C-PAN anode with the conductive network of the C-PAN layer. Notably, when the current rate suddenly returns to 0.2C, the G@C-PAN anode swiftly regains its reversible capacity, reaching 365.93 mAh·g⁻¹ and remaining stable for over 60 cycles, demonstrating excellent reversibility and structural stability. However, when the coating amount is relatively small or large, it will cause uneven distribution of Li⁺, resulting in a lack of Li⁺ diffusion channels and changes in local stress, among a series of problems. Under such circumstances, although the G@C-PAN-05 and G@C-PAN-15 anodes show a slight increase in specific capacity at low rates, they exhibit a rapid decay of capacity at high rates. Meanwhile, this situation will also lead to irreversible structural damage, and when the current rate returns to 0.2C, their capacity will also experience an irreversible decrease (Supplementary Fig. S8). As the current multiplicity increased, the G anode showed a relative voltage rush and low potential plateau deficit. In contrast, the C-PAN layer forms a continuous, dense and highly conductive network on the graphite surface. This network enables the G@C-PAN anode to demonstrate low polarisation and low potential plateau retention. The G@C-PAN anode shows excellent and stable rate performance (Supplementary Fig. S9).

The cyclic performance of the G@C-PAN anode at 2C is shown in Fig.5(f). The G@C-PAN anode exhibited excellent cycling stability. The specific capacity declined slightly from an initial 129.01 to 125.40 mAh·g⁻¹ after 500 cycles, with a high capacity retention rate of 97.20%. In contrast, the capacity retention rate of the pristine G anode reached only 58.92%. The sharp capacity drop is due to solvent molecule co-embedding during cycling, causing irreversible graphite layer expansion and stripping. In the synthesis of G@C-PAN modified material, PAN undergoes cyclization/cross-linking reaction, transforming into a conjugated structure with sp² π bonds, which significantly enhances the electronic conductivity. Furthermore, the integrated structural design of G@C-PAN ensures the density and continuity of the cladding layer, successfully preventing interfacial reactions and graphite layer exfoliation [33]. Meanwhile, the cyclized polyacrylonitrile layer on the graphite surface has elasticity with large layer spacing, effectively inhibiting the volume expansion effect of graphite during cycling. Importantly, selecting an appropriate PAN coating amount plays a crucial role in its structural stability and electrochemical stability at high rates (Supplementary Fig. S10). Therefore, the C-PAN layer can promote electron transport and maintain good structural integrity, which further validates the rationality of the structural design of this modified material. In comparison with other reported graphite-coated modified material anodes, the G@C-PAN anode in this work exhibits excellent cycling stability (Supplementary Table S2).

The ion diffusion kinetic properties of G and G@C-PAN anode are further elucidated by employing the constant current intermittent titration technique (GITT). The results show that the G@C-PAN anode exhibits less ohmic polarisation effect and voltage hysteresis during the lithiation process [Fig.6(a, b) and Supplementary Figs. S11(a)−(c)] [34, 35]. In addition, the diffusion coefficient of D_Li⁺ showed a characteristic “W” curve, suggesting a storage mechanism involving phase transitions during surface and interlayer diffusion [Supplementary Eq. (S2)] [36]. The G@C-PAN anode exhibited higher Li⁺ diffusion coefficients (D_Li⁺) than the G anode during the lithiation process. That is, it provides more migration channels for Li⁺ at low potentials and exhibits better ion diffusion kinetics [35, 37]. The electrochemical impedance spectra also support this observation. The Warburg coefficients (σ) and the D_Li⁺ are calculated by the Supplementary Eq. (S3). According to Fig. 6(d), the slope value of the G@C-PAN (116.5) anode corresponding to the σ is about one-third of that of the G (478.5) anode, and the D_Li⁺ values of G@C-PAN and G are 2.04×10⁻¹² and 1.21×10⁻¹³, respectively. The enhancement of D_Li⁺ values indicates that the G@C-PAN possesses more Li⁺ intercalation active center, which effectively promotes the diffusion kinetics of Li⁺ [38]. The interfacial state and impedance characteristics during the cycling process are further explored using impedance method analysis. The Nyquist curves of the G and G@C-PAN anodes following activation cycling are displayed in Fig.6(c). The impedance spectra are simulated by constructing equivalent circuits. Compared to pristine graphite, which has a charge transfer impedance (R_ct) of 107.2 Ω, G@C-PAN has a far reduced R_ct of 18.3 Ω [Supplementary Fig. S11(d)]. This indicates that the C-PAN layer enhances the wettability between the G and the electrolyte, resulting in a significant reduction of the R_ct between them and thereby facilitating the rapid diffusion of Li⁺ [39]. The EIS reaction impedance can be used to calculate the exchange current density through the Supplementary Eq. (S4) [40]. The results [Fig.6(e)] indicate that the j₀ value of the G@C-PAN anode is 1.24, which is higher than that of the G anode (0.21), and the lithiation effect is more pronounced. It implies that the surface of the G@C-PAN anode features numerous active sites, thereby facilitating efficient diffusion of Li⁺. The above results further support the conclusion that the C-PAN cladding can enhance the electrochemical reaction kinetics and improve the electrochemical performance of the anode.

The electrochemical kinetics results demonstrate that the C-PAN layer leads to an enhancement in material conductivity and a lowering of impedance. To delve deeper into the mechanism by which the C-PAN layer influences the stability of the anode-electrolyte interface, the anodes after cycling tests are analyzed by the EIS testing [Fig.7(a) and Supplementary Fig. S11(d)]. After 200 cycles, the R_ct value of G increased from 107.2 Ω to 236.2 Ω. In contrast, the change in the R_ct value of G@ C-PAN is significantly smaller than that of G (from 18.3 Ω to 98.1 Ω). This validates that the C-PAN layer promotes the rapid diffusion of Li⁺ and reduces interfacial resistance by effectively inhibiting interfacial reactions.

In addition, the SEM morphology analysis results [Fig.7(b, c)] provide further support for this observation. The surface of the G particles exhibits evident cracks and numerous black spots after 200 cycles. These defects may lead to the penetration of the electrolyte into the graphite surface layer through the cracks, which induces the co-insertion phenomenon of the solvent molecules, and triggers severe structural exfoliation and fragmentation, resulting in the rapid decay of the anode capacity [41−43]. During the charge and discharge cycles of LIBs, the original graphite anode undergoes volume changes due to the insertion and extraction of lithium ions, leading to damage to its layered structure and the formation of cracks. Additionally, the decomposition of the electrolyte and the instability of the SEI film result in irreversible side reactions, generating insoluble black spots and exacerbating the formation of cracks [26]. In contrast, the G@C-PAN anode exhibits a complete and smooth surface feature after cycling, with no apparent cracks, presenting a denser structural morphology. On the one hand, the meticulously designed C-PAN layer, due to its excellent density and elasticity, provides effective protection for the anode during charging and discharging cycles, preventing solvent co-insertion and inhibiting the volume effect of graphite particles. On the other hand, specific sites within the PAN molecular structure facilitate rapid adsorption and diffusion of lithium ions, and the uniform coating layer ensures uniform insertion of lithium ions into the graphite interior, reducing local stress and irreversible side reactions. This dual effect optimizes lithium ion transport and achieves a smooth surface without black spots on the modified graphite particles [26]. Thus, the long-term cycling stability of the G@C-PAN anode is ensured, further verifying the reasonableness and effectiveness of the design of the cladding layer.

To further investigate in depth the influence of the C-PAN layer on the SEI layer, XPS analysis is conducted to examine the SEI composition of G and G@C-PAN anodes after 200 cycles. In the F 1s [Figs. 7(d) and (g)], two key fluorine-based components are identified: the peak at 684.8 eV corresponds to the formation of LiF, whereas the peak at 686.5 eV is attributed to be associated with the formation of Li_xPO_yF_z. Both are the reduction products of LiPF₆. It’s worth noting that the G@C-PAN anode’s SEI layer has a LiF ratio of 53.06% after cycling, much higher than the G anode’s 8.70%. Meanwhile, The Li 1s also show a higher proportion of LiF in the SEI layer on the G@C-PAN anode compared to the G anode (Supplementary Fig. S12). These results suggest the formation of a LiF-rich SEI layer on the G@C-PAN anode surface, characterized by exceptional interfacial stability and a high lithium ion diffusion rate. It not only prevents further decomposition of the electrolyte and the occurrence of side reactions, mitigating interfacial instability caused by excessive Li⁺ concentration gradients and avoiding local over-concentration or depletion of Li⁺, thus reducing the probability of issues such as dendrite formation and SEI membrane rupture at the interface, but also provides a stable transmission channel for Li⁺, enhancing the cycle stability of the anode. Furthermore, the intensity of CO₃⁻² (290.0 eV) on the surface of the G@C-PAN anode is higher than that of the G anode, as well as the intensity of O−C=O (288.5 eV) and C=O/C−O−C (531.8 eV) is lower than that of the G anode in the C 1s and O 1s [Fig.7(e, f, h, i)]. Since C-PAN retains a strong polar cyano group (−CN), it has a high affinity for carbonates and brings better wettability to modified graphite materials. Subsequently, the C-PAN layer tightly encapsulates the surface of the graphite anode, forming an effective isolation barrier that significantly reduces the area of direct contact between the electrolyte and the graphite anode, thereby mitigating the reduction-induced decomposition of the electrolyte on the graphite surface. Furthermore, the C-PAN layer facilitates the formation of a solid electrolyte interface (SEI) film rich in LiF, which serves as a stable interface to help decrease further decomposition of the electrolyte and shield the graphite anode from electrolyte erosion. Lastly, the active sites within the molecular structure of C-PAN exert a positive influence on the adsorption and diffusion of Li⁺, significantly enhancing the transport kinetics of Li⁺ at the surface of the graphite anode [44]. This proves that the C-PAN layer positively inhibits the reductive decomposition of the electrolyte. The above XPS results indicate that the C-PAN layer can effectively suppress the decomposition of the electrolyte and also promote the formation of a stable SEI layer.

4 Conclusions

The objective of this study is to explore a strategy for the preparation of high-magnification, cycle-stable LIBs that are both environmentally friendly and economically viable. The precursor of polyacrylonitrile-coated graphite will be heat-treated at a low temperature to form a dense, continuous, and flexible C-PAN coating on the surface layer of graphite particles. The C-PAN layer, with its excellent high electrical conductivity, chemical stability, and large spacing between layers. The N-rich element in the C-PAN layer serves to provide additional active sites for Li⁺ adsorption, thus raising the specific capacity. At the same time, the stability of the anode structure is further enhanced. In addition, the stable C=N of high electron cloud overlap enables the C-PAN layer to effectively inhibit the volume effect and breakage of graphite particles, thereby enhancing the electrochemical stability of the material and improving its cyclic performance. Thanks to the multiple functional properties of the cyclized polyacrylonitrile layer, a high-performance G@C-PAN core-shell structured material is successfully prepared. The specific capacity of the G@C-PAN is 328.12 mAh·g⁻¹ after 250 cycles at 0.5C multiplicity, with a capacity retention rate of 96.18%. Furthermore, the material exhibited a high specific capacity retention of 97.20% after 500 cycles at a high multiplicity of 2C, indicating excellent high-magnification performance and long cycling stability. In conclusion, this study proposes a new way for the commercialization of graphite anode materials that is environmentally friendly, cost-effective, and has wide applicability.

References

[1] F. M. N. U. Khan, M. G. Rasul, A. S. M. Sayem, and N. K. Mandal, Design and optimization of lithium-ion battery as an efficient energy storage device for electric vehicles: A comprehensive review, J. Energy Storage 71, 108033 (2023)

[2] T. Y. Xu, H. W. Feng, W. Liu, Y. Wang, and H. H. Zheng, Opportunities and challenges of high-entropy materials in lithium-ion batteries, Rare Met. 43(10), 4884 (2024)

[3] W. Yan, Z. Chen, S. Ma, S. Chen, Y. Lu, M. Wang, L. Chen, Q. Huang, B. Wang, Y. Su, J. Wang, N. Li, and F. Wu, Unraveling the relationship between the mineralogical characteristics and lithium storage performance of natural graphite anode materials, Carbon 227, 119270 (2024)

[4] Y. Yu, J. Xu, K. Duanmu, V. Shutthanandan, S. Wi, Z. Yang, Y. Liu, X. Lyu, K. Qian, M. Agarwal, Z. Zhang, Y. Zhang, T. Li, C. Liu, V. Murugesan, and J. Xie, Stabilizing graphite anode in electrolytes with nanoscale anion networking for high-rate lithium storage, ACS Energy Lett. 9(10), 5002 (2024)

[5] Y. Xiong, Y. Liu, L. Chen, S. Zhang, X. Zhu, T. Shen, D. Ren, X. He, J. Qiu, L. Wang, Q. Hu, and H. Zhang, New insight on graphite anode degradation induced by Li-plating, Energy Environ. Mater. 5(3), 872 (2022)

[6] D. Wu and Z. Zhou, Recent progress of computational investigation on anode materials in Li ion batteries, Front. Phys. (Beijing) 6(2), 197 (2011)

[7] H. Gong, H. Xiao, L. Ye, and X. Ou, High-performance expanded graphite regenerated from spent lithium-ion batteries by integrated oxidation and purification method, Waste Manag. 171, 292 (2023)

[8] J. H. Shim and S. Lee, Characterization of graphite etched with potassium hydroxide and its application in fast-rechargeable lithium ion batteries, J. Power Sources 324, 475 (2016)

[9] G. Wang, A. Mijailovic, J. Yang, J. Xiong, S. E. Beasley, K. Mathew, B. Zhou, W. Lu, B. W. Sheldon, and Q. Wu, Particle size effect of graphite anodes on performance of fast charging Li-ion batteries, J. Mater. Chem. A 11(40), 21793 (2023)

[10] J. Huang, J. Zeng, K. Zhu, R. Zhang, and J. Liu, High-performance aqueous zinc–manganese battery with reversible Mn ²⁺/Mn⁴⁺ double redox achieved by carbon coated MnO_x nanoparticles, Nano-Micro Lett. 12(1), 110 (2020)

[11] S. Luo, F. Liu, W. Tianxu, Y. Liu, C. Zhang, C. Bie, M. Liu, P. K. Chu, K. Huo, and B. Gao, Regeneration of spent graphite via graphite-like turbostratic carbon coating for advanced Li ion battery anode, Energy Storage Mater. 73, 103833 (2024)

[12] Y. Sheng, X. Yue, W. Hao, Y. Dong, Y. Liu, and Z. Liang, Balancing the ion/electron transport of graphite anodes by a La-doped TiNb₂O₇ functional coating for fast-charging Li-ion batteries, Nano Lett. 24(12), 3694 (2024)

[13] S. Huang, L. Z. Cheong, D. Wang, and C. Shen, Nanostructured phosphorus doped silicon/graphite composite as anode for high-performance lithium-ion batteries, ACS Appl. Mater. Interfaces 9(28), 23672 (2017)

[14] S. Huang, Q. Fan, X. Chen, Y. Wu, L. Liu, Z. Yu, and J. Xu, From graphite of used lithium-ion batteries to holey graphite coated by carbon with enhanced lithium storage capability, J. Colloid Interface Sci. 676, 197 (2024)

[15] Q. Sun,G. Hu,Z. Peng,Y. Cao,F. Zhu, Y. Zhang,H. Gao,K. Du, Achieving a bifunctional conformal coating on nickel-rich cathode LiNi_{0. 8}Co_{0. 1}Mn_{0. 1}O₂ with half-cyclized polyacrylonitrile, Electrochim. Acta 386, 138440 (2021)

[16] Y. Gao, J. Zhang, Y. Chen, and C. Wang, Improvement of the electrochemical performance of spent graphite by asphalt coating, Surf. Interfaces 24, 101089 (2021)

[17] Y. Shao, J. Xu, A. Amardeep, Y. Xia, X. Meng, J. Liu, and S. Liao, Lithium-ion conductive coatings for nickel-rich cathodes for lithium-ion batteries, Small Methods 8(12), 2400256 (2024)

[18] Y. Yu, C. Yang, Y. Jiang, J. Zhu, Y. Zhao, S. Liang, K. Wang, Y. Zhou, Y. Liu, J. Zhang, and M. Jiang, Sponge-like porous-conductive polymer coating for ultrastable silicon anodes in lithium-ion batteries, Small 19(47), 2303779 (2023)

[19] J. Ma, Z. Zheng, Y. Tang, H. Nagashima, and T. Miyoshi, Chemical reactions in poly(acrylonitrile-co-itaconic acid) during stabilization as revealed by solid-state NMR spectroscopy and ¹³C isotope labeling, Carbon 215, 118432 (2023)

[20] T. T. B. Tran, E. J. Park, H. I. Kim, H. J. Jang, and J. T. Son, Solvent-free dry cyclized polyacrylonitrile-coated LiNi_0.87Co_0.13O₂ cathode for improving the electrochemical performance of Li-ion batteries, Mater. Chem. Phys. 290, 126590 (2022)

[21] F. Wu, W. Li, L. Chen, J. Wang, W. Bao, Y. Lu, J. Tan, S. Chen, R. Chen, and Y. Su, Simultaneously fabricating homogeneous nanostructured ionic and electronic pathways for layered lithium-rich oxides, J. Power Sources 402, 499 (2018)

[22] S. Weng, S. Wu, Z. Liu, G. Yang, X. Liu, X. Zhang, C. Zhang, Q. Liu, Y. Huang, Y. Li, M. N. Ateş, D. Su, L. Gu, H. Li, L. Chen, R. Xiao, Z. Wang, and X. Wang, Localized-domains staging structure and evolution in lithiated graphite, Carbon Energy 5(1), e224 (2023)

[23] Y. B. Cao, X. Y. Qi, K. H. Hu, Y. Wang, Z. Gan, Y. Li, G. Hu, Z. Peng, and K. Du, Conductive polymers encapsulation to enhance electrochemical performance of Ni-rich cathode materials for Li-ion batteries, ACS Appl. Mater. Interfaces 10(21), 18270 (2018)

[24] T. Wang, W. Wang, D. Zhu, L. Huang, and Y. Chen, Improvement of the overall performances of LiMn₂O₄ via surface-modification by polypyrrole, Mater. Res. Bull. 71, 91 (2015)

[25] Y. Wang, L. Ren, Y. Liu, X. Liu, K. Huang, X. Wei, J. Li, X. Qi, and J. Zhong, Carbon matrix/SiNWs heterogeneous block as improved reversible anodes material for lithium ion batteries, J. Energy Chem. 23(1), 105 (2014)

[26] P. Du, X. Fan, B. Zhang, L. Cao, J. Ren, X. Ou, X. Guo, and Q. Liu, The lithiophobic-to-lithiophilic transition on the graphite towards ultrafast-charging and long-cycling lithium-ion batteries, Energy Storage Mater. 50, 648 (2022)

[27] Y. Huang, J. Xia, G. Hu, Y. Cao, Z. Peng, J. Fan, Y. Tao, T. Li, Z. Zhang, Z. Xue, and K. Du, Conductive cyclized polyacrylonitrile coated LiNi_0.6Co_0.2Mn_0.2O₂ cathode with the enhanced electrochemical performance for Li-ion batteries, Electrochim. Acta 332, 135505 (2020)

[28] X. Hu, H. Jiang, Q. Hou, M. Yu, X. Jiang, G. He, and X. Li, Scalable SPAN membrane cathode with high conductivity and hierarchically porous framework for enhanced ion transfer and cycling stability in Li–S batteries, ACS Mater. Lett. 5(8), 2047 (2023)

[29] D. Wang, H. Dong, H. Zhang, Y. Zhang, Y. Xu, C. Zhao, Y. Sun, and N. Zhou, Enabling a high performance of mesoporous α-Fe₂O₃ anodes by building a conformal coating of cyclized-PAN network, ACS Appl. Mater. Interfaces 8(30), 19524 (2016)

[30] J. Wang, Q. Yuan, Z. Ren, C. Sun, J. Zhang, R. Wang, M. Qian, Q. Shi, R. Shao, D. Mu, Y. Su, J. Xie, F. Wu, and G. Tan, Thermochemical cyclization constructs bridged dual-coating of Ni-rich layered oxide cathodes for high-energy Li-ion batteries, Nano Lett. 22(13), 5221 (2022)

[31] B. Ke, S. Cheng, C. Zhang, W. Li, J. Zhang, R. Deng, J. Lin, Q. Xie, B. Qu, L. Qiao, D. L. Peng, and X. Wang, Low-temperature flexible integration of all-solid-state thin-film lithium batteries enabled by spin-coating electrode architecture, Adv. Energy Mater. 14(12), 2303757 (2024)

[32] W. Qu, Y. Yuan, C. Wen, J. Zhu, X. Liang, S. Chen, Z. Li, G. Cao, and M. Zhang, Ultra-long life and high rate performance zinc-iodine batteries simultaneously enabled by a low-spin electrode, Energy Storage Mater. 75, 103993 (2025)

[33] M. S. Song, G. Chang, D. W. Jung, M. S. Kwon, P. Li, J. H. Ku, J. M. Choi, K. Zhang, G. R. Yi, Y. Cui, and J. H. Park, Strategy for boosting Li-ion current in silicon nanoparticles, ACS Energy Lett. 3(9), 2252 (2018)

[34] W. Qu, J. Zhu, G. Cao, S. Chen, Y. Tan, B. Chen, and M. Zhang, Ni single-atom bual catalytic electrodes for long life and high energy efficiency zinc-iodine batteries, Small 20(26), 2310475 (2024)

[35] L. Wang, Y. Jiang, S. Y. Li, X. H. Chen, F. S. Xi, X. H. Wan, W. H. Ma, and R. Deng, Scalable synthesis of N-doped Si/G@voids@C with porous structures for high-performance anode of lithium-ion batteries, Rare Met. 42(12), 4091 (2023)

[36] W. Qu, Y. Cai, B. Chen, and M. Zhang, Heterointerface engineering-induced oxygen defects for the manganese dissolution inhibition in aqueous zinc ion batteries, Energy Environ. Mater. 7(3), e12645 (2024)

[37] W. Li, L. Deng, J. Cao, B. Ke, X. Wang, S. Ni, S. Cheng, and B. Lu, Current-adaptive Li-ion storage mechanism in high-rate conversion-alloying metal chalcogenides, Adv. Funct. Mater. 34(44), 2407246 (2024)

[38] W. Chen, H. Qu, R. Shi, J. Wang, H. Ji, Z. Zhuang, J. Ma, D. Tang, J. Li, J. Tang, G. Ji, X. Xiao, Y. Zhu, and G. Zhou, Upcycling spent graphite into fast-charging anode materials through interface regulation, ACS Energy Lett. 9(7), 3505 (2024)

[39] B. Ke, C. Zhang, S. Cheng, W. Li, R. Deng, H. Zhang, J. Lin, Q. Xie, B. Qu, D. L. Peng, and X. Wang, Tape-casting electrode architecture permits low-temperature manufacturing of all-solid-state thin-film microbatteries, Interdiscip. Mater. 3(4), 621 (2024)

[40] W. Cai, C. Yan, Y. X. Yao, L. Xu, R. Xu, L. L. Jiang, J. Q. Huang, and Q. Zhang, Rapid lithium diffusion in order@disorder pathways for fast-charging graphite anodes, Small Struct. 1(1), 2000001 (2020)

[41] J. C. Abrego-Martinez, Y. Wang, V. Vanpeene, and L. Roué, From waste graphite fines to revalorized anode material for Li-ion batteries, Carbon 209, 118004 (2023)

[42] Y. Huang, C. Wang, H. Lv, Y. Xie, S. Zhou, Y. Ye, E. Zhou, T. Zhu, H. Xie, W. Jiang, X. Wu, X. Kong, H. Jin, and H. Ji, Bifunctional interphase promotes Li⁺ de‐solvation and transportation enabling fast‐charging graphite anode at low temperature, Adv. Mater. 36(13), 2308675 (2024)

[43] S. Tu, B. Zhang, Y. Zhang, Z. Chen, X. Wang, R. Zhan, Y. Ou, W. Wang, X. Liu, X. Duan, L. Wang, and Y. Sun, Fast-charging capability of graphite-based lithium-ion batteries enabled by Li₃P-based crystalline solid–electrolyte interphase, Nat. Energy 8(12), 1365 (2023)

[44] M. Niu,L. Dong,J. Yue,Y. Li,Y. Dong, S. Cheng,S. Lv,Y. H. Zhu,Z. Lei,J. Y. Liang, S. Xin,C. Yang,Y. G. Guo, A fast-charge graphite anode with a Li-ion-conductive, electron/solvent-repelling interface, Angew. Chem. Int. Ed. 63(21), e202318663 (2024)

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