Pseudo zero-strain insertion materials for Li-ion batteries: cross-sectional observations of LiNi1/2Co1/2O2, LiNi1/3Co1/3Mn1/3O2, and LiNi0.8Co0.15Al0.05O2

Constructing robust interfaces between a positive (or negative) electrode and a solid electrolyte is essential for realizing more practical all-solid-state lithium-ion batteries (ALIBs). For the negative electrode, a zero-strain insertion material exists, Li[Li1/3Ti5/3]O-4, which indicates a virtually 0% change in lattice volume (Delta V). In contrast, for the positive electrode, no zero-strain insertion material is currently available. In this paper, we observed cross-sections of charged Li (x) Ni1/2Co1/2O2 (NC11), Li (x) Ni1/3Co1/3Mn1/3O2 (NCM111), and Li (x) Ni0.8Co0.15Al0.05O2 (NCA) samples to clarify whether these positive electrode materials are applicable for ALIBs. Hardly any fractures were observed between primary particles in the NC11 and NCM111 samples, while fractures were observed in the NCA sample. This difference was due to the pseudo zero-strain character of the NC11 and NCM111 samples, which have Delta V values of approximately 0%, although their lattice parameters vary with x. Therefore, the ability of NC11 and NCM111 to maintain ionic and electronic contacts with a solid electrolyte makes them ideal positive electrode materials for ALIBs.