The Effect of Single versus Polycrystalline Cathode Particles on All‐Solid‐State Battery Performance

Abstract Lithium‐thiophosphate‐based all‐solid‐state batteries (ASSBs) are increasingly attracting attention for high‐density electrochemical energy storage. In this work, the cycling performance of single and polycrystalline forms of LiNi x Co y Mn z O 2 (NCM, with ≥83% Ni content) cathode active materials in ASSB cells with an Li 4 Ti 5 O 12 composite anode is explored, and the advantages and disadvantages of both morphologies are discussed. The virtual lack of grain boundaries in the quasi‐single‐crystalline material is found to contribute to improved stability by eliminating the tendency of Ni‐rich NCM particles to crack during cycling, due to volume differences between the lithiated and delithiated phases. Although the higher crack resistance mitigates effects of chemical oxidation of the lithium thiophosphate solid electrolyte, the cells suffer from electrochemical side reactions occurring at the cathode interfaces. However, coating the single‐crystal particles with a protective LiNbO 3 overlayer helps to stabilize the interface between cathode active material and solid electrolyte, leading to a capacity retention of 93% after 200 cycles (with q dis ≈ 160 mAh g NCM −1 or 1.7 mAh cm −2 at C/5 rate and 45 °C). Overall, this work highlights the importance of addressing electro‐chemo‐mechanical phenomena in ASSB electrodes.