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.
Keywords: LiNiCoAlO; cation mixing; gradient cathode; phase transition; solid-state battery.