Mechanofusing garnet solid electrolyte on the surface of Ni-rich layered oxide cathode towards high-rate capability of cylindrical Li-ion battery cells

Abstract

The interface between solid electrolytes and cathode materials determines charge storage mechanism of Li-ion batteries; however, it has not yet been fully investigated and understood. Herein, a diluted amount at 1 wt% of heterogenous lithium garnet Li7La3Zr2O12 (LLZO) solid electrolyte particles was chemically bonded to the Ni-rich LiNi0.8Mn0.1Co0.1O2 (NMC811) cathode by a scalable mechanofusion process. The interface chemistry was intensively investigated by an ex situ extended X-ray absorption fine structure (EXAFS). In situ X-ray diffraction was also used to investigate the charge storage mechanism of LLZO-NMC811. It was found that the LLZO-LaNiO3-NMC811 strong bond at the interface can enhance the microstructural stability leading to high-rate capability up to 7.5C. For the charge storage mechanism, the lithium intercalation/deintercalation in NMC-LLZO undergoes a slower phase transition since the LLZO-LaNiO3 interface can modulate Li concentration gradient and kinetics where the surface of NMC will not be fully emptied (during charge) or filled (during discharge). This will benefit the rate capability of LLZO-modified NMC material in which the Li concentration at the surface will not quickly reach a threshold value before the cut-off voltage. The practical applications of LLZO-NMC811 were eventually demonstrated in 2.1 Ah 18650-format cells with high-capacity retention and high-rate capability.