Unraveling the stable cathode electrolyte interface in all solid-state thin-film battery operating at 5V

TL;DR

This study demonstrates a stable all-solid-state thin-film Li-ion battery with a high-voltage LNMO cathode and LiPON electrolyte, achieving over 600 cycles with high efficiency, and provides insights into interface stability and engineering.

Contribution

The paper presents a novel all-solid-state thin-film battery with a LNMO cathode and LiPON electrolyte, showing long cycle life and interface stability at 5V.

Findings

Stable performance over 600 cycles with >99% Coulombic efficiency.

Neutron depth profiling shows slight overlithiation at the interface.

Cryogenic electron microscopy confirms stable contact and composition after cycling.

Abstract

Spinel-type LiNi0.5Mn1.5O4 (LNMO) is one of the most promising 5 V-class cathode materials for Li-ion batteries that can achieve high energy density and low production costs. However, in liquid electrolyte cells, the high voltage causes continuous cell degradation through the oxidative decomposition of carbonate-based liquid electrolytes. In contrast, some solid-state electrolytes have a wide electrochemical stability range and can withstand the required oxidative potential. In this work, a thin-film battery consisting of a LNMO cathode with a solid lithium phosphorus oxynitride (LiPON) electrolyte is tested and their interface before and after cycling is characterized. With Li metal as the anode, this system can deliver stable performance for 600 cycles with an average Coulombic efficiency > 99%. Neutron depth profiling indicates a slight overlithiated layer at the interface prior to cycling; a result that is consistent with the excess charge capacity measured during the first cycle. Cryogenic electron microscopy further reveals intimate contact between LNMO and LiPON without noticeable structure and chemical composition evolution after extended cycling, demonstrating the superior stability of LiPON against a high voltage cathode. Consequently, we propose design guidelines for interface engineering that could accelerate the commercialization of a high voltage cell with solid or liquid electrolytes.