Measuring the buried interphase between solid electrolytes and lithium metal using neutrons

Abstract

Interfaces are the key to next-generation high-energy batteries including solid-state Li metal batteries. In solid-state batteries, the buried nature of solid-solid electrolyte-electrode interfaces makes studying them difficult. Neutrons have significant potential to non-destructively probe these buried solid-solid interfaces. This work presents a comparative study using both neutron depth profiling (NDP) and neutron reflectometry (NR) to study a model lithium metal-lithium phosphorus oxynitride (LiPON) solid electrolyte system. In the NDP data, no distinct interphase is observed at the interface. NR shows a difference between electrodeposited, and vapor deposited LiPON-Li interfaces but finds both are gradient interphases that are less than 30 nm thick. Additional simulations of the LiPON-Li 2 O-Li system demonstrate that NDP has an excellent resolution in the 20 nm -1 µm regime while NR has an ideal resolution from 0.1 -200 nm with different sample requirements. Together NDP and NR can provide a complementary understanding of interfaces between Li metal and solid electrolytes across relevant length scales.