Compatibility between Li1.5Al0.5Ge1.5(PO4)3-based solid electrolyte and LiNi1/3Co1/3Mn1/3O2 cathode

Abstract

All-solid-state batteries (ASSBs) have a higher energy density and improved safety compared to traditional lithium-ion batteries. The problem of high interface resistance between the solid electrolyte and electrode materials needs to be addressed for the ASSBs production. Solid electrolytes of the Li_1.5Al_0.5Ge_1.5(PO₄)₃ (LAGP) family with the NASICON-type structure possess a high lithium-ion conductivity and stability in air. In this work, Si-modified LAGP glass-ceramics (LAGSP) with a total Li⁺ conductivity of 3·10⁻⁴ S cm⁻¹ at 25 °C and a compact microstructure is considered. LiNi_1/3Co_1/3Mn_1/3O₂ (NCM) is a promising cathode material which offers a high specific capacity and better cycle performance. Chemical interaction between the above-mentioned components at high temperature for the solid-solid interface creation was studied. The thermal behavior of the mechanical mixture of solid electrolyte and cathode material was studied by DSC method at temperatures of up to 900 °C. The phase composition of their mechanical mixture after heat treatment at different temperatures (500, 730 and 800 °C) was investigated by XRD. It was shown that the structure of the initial phases did not change after heat treatment at 500 °C. However, Li₃PO₄, Li₄P₂O₇, NiAl₂O₄ and GeO₂ phases begin to appear after annealing at 730 °C, while Co₂MnO₄, LiCoPO₄, SiO₂, GeO₂, Li₃PO₄ and Li₉Al₃(P₂O₇)₃(PO₄)₂ formation was observed at 800 °C. Heating at 800 °C leads to a complete degradation of the solid electrolyte. Therefore, it was proposed to create a LAGSP | NCM interface using a liquid electrolyte. LiPF₆-based liquid electrolyte was used as a buffer layer between solid electrolyte and cathode for enhancing the interfacial contact. Symmetrical NCM | solid electrolyte | NCM and NCM |LiPF₆ | solid electrolyte | LiPF₆ | NCM cells are assembled and their resistance at room temperature is measured. It was established that modified cells had the lowest resistance at room temperature (1.2 kΩ·cm²) compared to unmodified cells (162 kΩ·cm²).