The potassium (K) metal anode, following the "Holy Grail" Li metal anode, is one of the most promising anode materials for next-generation batteries. In comparison with Li, K exhibits even more pronounced energy storage properties. However, it suffers from similar challenges as most alkali metal anodes, such as safety and cyclability issues. Borrowing strategies from Li/Na metal anodes, the three-dimensional (3D)-structured current collector has proven to be a universal and effective strategy. This study examines the recent research progress of 3D-structured electrodes for K metal anodes, focusing on the most commonly used host materials, including carbon-, metal-, and MXene-related electrode materials. Finally, existing challenges, various perspectives on the rational design of K metal anodes, and the future development of K batteries are presented.

Despite the significant advances achieved in recent years, the development of efficient electrolyte additives to mitigate the performance degradation during long-term cycling of high-energy density lithium||nickel-rich (Li||Ni-rich) batteries remains a significant challenge. To achieve a rational design of electrolytes and avoid unnecessary waste of resources due to trial and error, it is crucial to have a comprehensive understanding of the underlying mechanism of key electrolyte components, including salts, solvents, and additives. Herein, we present the utilization of lithium difluoro(oxalate) borate (B) (LiDFOB), a B-containing lithium salt, as a functional additive for Li||LiNi_0.85Co_0.1Mn_0.05O₂ (NCM85) batteries, and comprehensively investigate its mechanism of action towards enhancing the stability of both anode and cathode interfaces. The preferential reduction and oxidation decomposition of DFOB^- leads to the formation of a robust and highly electronically insulating boron-rich interfacial film on the surface of both the Li anode and NCM85 cathode. This film effectively suppresses the consumption of active lithium and the severe decomposition of the electrolyte. Furthermore, the presence of B elements in the cathode-electrolyte interfacial film, such as BF₃, BF₂OH, and BF₂OBF₂ compounds, can coordinate with the lattice oxygen of the cathode, forming strong coordination bonds. This can significantly alleviate lattice oxygen loss and mitigate detrimental structural degradation of the Ni-rich cathode. Consequently, the Li||NCM85 battery cycled in LiDFOB-containing electrolyte displays superior capacity retention of 74% after 300 cycles, even at a high charge cut-off voltage of 4.6 V. The comprehensive analysis of the working mechanisms of LiDFOB offers valuable insights for the rational design of electrolytes featuring multifunctional lithium salts or additives for high energy density lithium metal batteries.

Potassium-ion batteries (PIBs) are a promising candidate for low-cost and large-scale energy storage due to their abundant potassium resources. However, the potassiation-depotassiation of K⁺ presents a significant challenge due to its large ionic radius, which results in the pulverization of active materials and poor cyclability. Thus, researchers are exploring anode materials with a high specific capacity, long cyclability, and excellent rate capability. In this context, alloy-type anode materials are exceptional candidates due to their high theoretical capacity and low working potential. Nonetheless, the large volume expansion of active materials limits their practical application. This review discusses various strategies for overcoming these challenges, including nanostructure design, heterostructure design, alloy engineering, and compositing. The review provides a comprehensive overview of the current state of research on alloy-based anodes for PIBs and offers insights into promising directions for future work toward commercializing PIBs.

The oxygen evolution reaction (OER) and oxygen reduction reaction (ORR) are crucial half-reactions of green electrochemical energy storage and conversion technologies, such as electrochemical water-splitting devices and regenerative fuel cells. Researchers always committed to synthesizing earth-abundant-element-based nanomaterials as high-efficiency electrocatalysts for realizing their industrial applications. In this review, we briefly elaborate on the underlying mechanisms of OER and ORR during the electrochemical process. Then, we systematically sum up the recent research progress in representative metal-free carbon (C)-based electrocatalysts; metal-nitrogen-C electrocatalysts; and nonprecious-metal OER/ORR electrocatalysts, including transition-metal oxides, phosphides, nitrides/oxynitrides, chalcogenides, and carbides. Among these, some representative bifunctional electrocatalysts for the OER/ORR are mentioned. In particular, we discuss the effects of physicochemical properties-morphology, phases, crystallinity, composition, defects, heteroatom doping, and strain engineering-on the comprehensive performance of the abovementioned electrocatalysts, with the aim of establishing the nanostructure-function relationships of the electrocatalysts. In addition, the development directions of OER and ORR electrocatalysts are determined and highlighted. The generic approach in this review expands the frontiers of and provides inspiration for developing high-efficiency OER/ORR electrocatalysts.

The fast development of modern battery research highly relies on advanced characterisation methods to unveil the fundamental mechanisms of their electrochemical processes. The continued development of in situ characterisation techniques allows the study of dynamic changes during battery cycling rather than just the initial and the final phase. Among these, in situ transmission electron microscopy (TEM) is able to provide direct observation of the structural and morphological evolution in batteries at the nanoscale. Using a compact liquid cell configuration, which allows a fluid to be safely imaged in the high vacuum of the TEM, permits the study of a wide range of candidate liquid electrolytes. In this review, the experimental setup is outlined and the important points for reliable operation are summarised, which are critical to the safety and reproducibility of experiments. Furthermore, the application of in situ liquid cell TEM in understanding various aspects, including dendrite growth, the solid electrolyte interface (SEI) formation, and the electrode structural evolution in different battery systems, is systematically presented. Finally, challenges in the current application and perspectives of the future development of the in situ liquid cell TEM technique are briefly addressed.

Understanding the interactions between single metallic atom/clusters (SMACs) has been taken to an unprecedented level, due to the delicate conditions required to produce exotic phenomena in electrode materials, such as thermocatalysis, electrocatalysis, and energy storage devices. Recently, state-of-the-art synthesis methods, such as one-step pyrolysis and multistep pyrolysis, have been developed for SMACs. Herein the interactions between SMACs such as synergetic, charge redistribution effects, and mutual assistance effects, are studied. SMACs have the advantage of maximum utilization of atoms and scattered active sites compared to single metal atoms, and they also have flexible and tunable atom clusters. SMACs have been widely developed and have shown excellent catalytic performance in electrocatalysis. Herein, the self-interaction between SMACs and their catalytic mechanisms are systematically described. The challenges in current synthesis strategies, catalytic mechanisms, and industrial applications of SMACs are analyzed, and a possible synthesis method for SMACs is proposed.

Solid-state lithium (Li)-sulfur (S) batteries are promising secondary batteries because of their high energy density and high safety, but their practical application is severely hindered by poor Li-ions (Li⁺) transport in batteries due to low ionic conduction of the electrolyte and unstable electrode/electrolyte interface. Here, we address the issue by using a polyurethane (PU)-based electrolyte. The polar urethane/urea groups of PU reduce the hopping energy barrier of Li⁺, which results in high ionic conductivity of 1.8 × 10^-4 S cm^-1 (25 °C), high ion transference number of 0.54, and low activation energy of 0.39 eV. In addition, the polar urethane/urea groups endow the electrolyte with high adhesion, which allows the electrode/electrolyte interfaces to self-heal timely after being damaged during cycling. Benefiting from these merits, a symmetric Li||Li cell using the polyolefin-PU-bis(trifluoromethane)sulfonimide lithium salt electrolyte can cycle for approximately 800 h with a stable overpotential (approximately 40 mV), and a solid-state Li-S battery using the electrolyte delivers a specific capacity of approximately 610 mAh g^-1 after testing for 125 cycles at a S loading of about 4 mg cm^-2. Self-healing of the electrode/electrolyte interfaces during cycling was observed in situ by a laser confocal microscope. This study demonstrates the importance of polar groups in electrolytes in maintaining a fast and stable Li⁺ transport, which can be applied to other solid-state batteries.

High lithium (Li)-ion conductive solid electrolytes with mechanical stability are quite important in the development of long-term safe and high-performance solid-state Li-sulfur batteries (LSBs). Accordingly, we prepared a pore-filling solid electrolyte (PFSE) by introducing poly(ethylene glycol) double-grafted (poly(arylene ether sulfone) (PAES-g-2PEG), ionic liquid (IL), and ethylene carbonate (EC) into a porous polypropylene/polyethylene/polypropylene (PP/PE/PP) substrate. While the PP/PE/PP substrate provides the membrane with the mechanical strength, the PAES-g-2PEG filler provides high Li-ion conductivity due to the facile ion conduction pathway formation via percolation in the presence of IL and EC. This synergistic effect allowed the prepared PFSE membranes to exhibit both high mechanical strength of 200 MPa, thermal stability above 150 °C, and high ion conductivity of 0.604 mS cm^-1 with a Li-transfer number of 0.41. Moreover, PFSE membranes also achieved a large electrochemical potential window of 4.60 V and high cyclic stability after 500 h of Li-stripping/plating. The LSB cell based on a PFSE membrane showed excellent electrochemical performance with preserving 95% of initial capacity after 200 cycles at a 0.2 C-rate.

Herein, a single-ion polymer electrolyte is reported for high-voltage and low-temperature lithium-metal batteries that enables suppressing the growth of dendrites, even at high current densities of 2 mA cm^-2. The nanostructured electrolyte was introduced into the cell by mechanically processing the polymer powder via an easily scalable process. Important for the potential application in commercial battery cells is the finding that it does not induce aluminum corrosion at high voltages and leads to low interfacial resistance with lithium metal. These beneficial characteristics, in combination with its high single-ion conductivity and its high anodic stability, allow for the stable cycling of state-of-the-art lithium-ion cathodes, such as NMC₁₁₁ and NMC₆₂₂, in combination with a lithium metal anode at 20 °C and even 0 °C for several hundred cycles.