The cathode surface of sulfide-based all-solid-state batteries (SBs) is commonly coated with amorphous-LiNbO3 in order to stabilize charge-discharge reactions. However, high-voltage charging diminishes the advantages, which is caused by problems with the amorphous-LiNbO3 coating layer. This study has investigated the degradation of amorphous-LiNbO3 coating layer directly during the high-voltage charging of SBs. O2 generation via Li extraction from the amorphous-LiNbO3 coating layer is observed using electrochemical gas analysis and electrochemical X-ray photoelectron spectroscopy. This O2 leads to the formation of an oxidative solid electrolyte (SE) around the coating layer and degrades the battery performance. On the other hand, elemental substitution (i.e., amorphous-LiNbxP1- xO3) reduces O2 release, leading to stable high-voltage charge-discharge reactions of SBs. The results have emphasized that the suppression of O2 generation is a key factor in improving the energy density of SBs.

Replacing flammable organic liquid electrolytes with nonflammable solid electrolytes (SEs) in lithium batteries is crucial for enhancing safety across various applications, including portable electronics, electric vehicles, and scalable energy storage. Since typical cathode materials do not possess superionic conductivity, Li-ion conduction in the cathode predominantly relies on incorporating a significant number of SEs as additives to form a composite cathode, which substantially compromises the energy density of solid-state lithium batteries. Here, a halide SE, Li3VCl6 is demonstrated, which not only exhibits a decent Li+ conductivity, but more importantly, delivers a highly reversible capacity of approximately 80 mAh g-1 with an average voltage of 3 V versus Li+/Li. The ionic conductivity of Li3VCl6 experiences marginal fluctuations upon electrochemical lithiation/delithiation, as its prototypical solid-solution reaction results solely in a reduction of lithium vacancy. When combined with the traditional LiFePO4 cathode, the active Li3VCl6 catholyte enables an impressive capacity of 217.1 mAh g-1 LFP and about 50% increase in energy density compared with inactive catholytes. Harnessing the integrated mass of the catholyte-which can serve as an active material-presents an opportunity to boost the extra capacity, rendering it feasible in applications.

Protection of lithium (Li) metal electrode is a core challenge for all-solid-state Li metal batteries (ASSLMBs). Carbon materials with variant structures have shown great effect of Li protection in liquid electrolytes, however, can accelerate the solid-state electrolyte (SE) decomposition owing to the high electronic conductivity, seriously limiting their application in ASSLMBs. Here, a novel strategy is proposed to tailor the carbon materials for efficient Li protection in ASSLMBs, by in situ forming a rational niobium-based Li-rich disordered rock salt (DRS) shell on the carbon materials, providing a favorable percolating Li+ diffusion network for speeding the carbon lithiation, and enabling simultaneously improved lithiophilicity and reduced electronic conductivity of the carbon structure at deep lithiation state. Using the proposed strategy, different carbon materials, such as graphitic carbon paper and carbon nanotubes, are tailored with great ability to speed the interfacial kinetics, homogenize the Li plating/stripping processes, and suppress the SE decompositions, enabling much improved performances of ASSLMBs under various conditions approaching the practical application. This strategy is expected to create a novel roadmap of Li protection for developing reliable high-energy-density ASSLMBs.

All-solid-state batteries (ASSBs) based on inorganic solid electrolytes fascinate a large body of researchers in terms of overcoming the inferior energy density and safety issues of existing lithium-ion batteries. To date, the cathode designs in the ASSBs achieve remarkable achievements, adding the urgency of scaling up the battery system toward inorganic solid-state pouch cell configuration for the application market. Herein, the recent developments of cathode materials and the design considerations for their application in the pouch cell format are reviewed to straighten out the roadmap of ASSBs. Specifically, the intercalation compounds and the conversion materials with conversion chemistries are highlighted and discussed as two potentially valuable material types. This review focuses on the basic electrochemical mechanisms, mechanical contact issues, and sheet-type structure in inorganic solid-state pouch cells with corresponding perspectives, thus guiding the future research direction. Finally, the benchmarks for manufacturing inorganic solid-state pouch cells to meet practical high energy density targets are provided in this review for the development of commercially viable products.