Surficial Structure Retention Mechanism for LiNi0.8Co0.15Al0.05O2 in a Full Gradient Cathode.

A LiNi0.8Co0.15Al0.05O2 (NCA) solid battery was assembled by coupling an NCA cathode with a polyvinylidene fluoride (PVDF)/Li6.75La3Z1.75Ta0.25O12 (LLZTO) composite polymer electrolyte and a Li anode. A NiO-like phase transition is regarded as the reason for interface impedance, which leads to drastic capacity fading during cycling. A gradient cathode with excessive addition of Li6.75La3Zr1.75Ta0.25O12 was fabricated at the cathode/electrolyte interface to overcome the increased impedance. Using high-resolution transmission electron microscopy and electron energy loss spectra, the formation of a unique localized cation migration (LCM) region was confirmed on the NCA surface. The formation of an LCM region hindered further distortion and enhanced the capacity retention of the spinel lattice.