(Oxalato)borate: The key ingredient for polyethylene oxide based composite electrolyte to achieve ultra-stable performance of high voltage solid-state LiNi0.8Co0.1Mn0.1O2/lithium metal battery

Searching novel polyethylene oxide (PEO) based composite electrolyte that can be compatible with high voltage cathodes (> 4 V) at room temperature is a long-standing challenge, but essential to achieve high-energy-density for solid-state lithium (Li) metal batteries. Herein, we develop an advanced dual-salts reinforced PEO/garnet solid-state composite electrolyte (SCE) with high ionic conductivity of 9 x 10(-4) S cm(-1) and an electrochemical stability window up to similar to 4.7 V, where the lithium bis(oxalate)borate (LiBOB) is used as additive with LiClO4. The dual-salts reinforced SCE can achieve excellent room temperature cycling performance of LiNi0.8Co0.1Mn0.1O2 (NCM811)/Li metal batteries. The multiplied polymer-ion interactions and formation of Li-B-O/C-O species originated from the (oxalato)borate group of LiBOB effectively promotes the electrochemical stability of the PEO based composite electrolyte and its wetting properties with electrodes. Unwanted non-conductive decomposition products, such as Li2O and Li2CO3, and NCM particles cracking during cycling are successfully suppressed. The NCM811 solid-state cells using the optimized dual-salts composite electrolyte delivers high specific capacity of 190 mA h g(-1) and exhibit stable cycling performance for more than 200 cycles at 25 degrees C.

Automated summary

The dual-salts reinforced PEO/garnet solid-state composite electrolyte developed in this study exhibits high ionic conductivity and excellent electrochemical stability, making it suitable for room temperature cycling of high voltage cathodes with Li metal batteries. The optimized electrolyte can effectively improve the specific capacity of NCM811 solid-state cells and achieve stable cycling performance for over 200 cycles at 25 degrees Celsius.