Wide operating temperature range electrolytes for lithium-ion capacitors achieving high performance

Abstract

The present invention provides for two types of wide operating temperature range electrolyte formulations that contain methyl butyrate (MB) and additives have been investigated and compared in Lithium-ion capacitors (LICs), which were consisted of hard carbon (HC)/stabilized lithium metal powder (SLMP) anodes and activated carbon (AC) cathodes. The electrolyte L1 that was 1M LiPFin ethylene carbonate (EC)+ethyl methyl carbonate (EMC)+MB (20:20:60 v/v %)+0.1M lithium bis(oxalato)borate (LiBOB) and electrolyte L2 that was 1M LiPFin EC+EMC+MB (20:20:60 v/v %)+0.1M lithium difluoro(oxalato)borate (LiDFOB) enabled the LICs to discharge at the temperature as low as −40° C., which the conventional electrolyte LP30 that was 1 M LiPFin EC+dimethyl carbonate (DMC) (50:50 w/w %) could not achieve. At the low temperature of −40° C., L2 held more than 64% of the discharge capacity at 30° C., while the L1 only had the discharge capacity retention of 30%. In addition, L2 proved to achieve better cycling performance compared to L1. After 10,000 cycles, the capacity retention of L1 and L2 were about 86.6% and 84.7%, which demonstrated the stable cycling performance for electrolyte L1 and L2. In summary, L2 was the most suitable electrolyte for the LICs energy storage devices which would be applied in the temperature as low as −40° C.