Improving the Performance of Graphite/ LiNi0.5Mn1.5O4 Cells at High Voltage and Elevated Temperature with Added Lithium Bis(oxalato) Borate (LiBOB)

Abstract

The performance of the graphite/ LiNi0.5Mn1.5O4 cells cycled to 4.8 V (vs Li/Li+) with 1.0 M LiPF6 in EC/EMC (3/7, v/v) with and without added LiBOB (1.5 and 2.5% (wt)) at 25 and 55°C has been investigated. The initial discharge capacity of the cells with added LiBOB is slightly lower than the cells without added LiBOB. However, after 30 cycles at 55°C, the cells with standard electrolyte suffer poor capacity retention (20%). The cells with 1.5% or 2.5% LiBOB have good cycling stability at 55°C with 63 and 69% capacity retention, respectively, after 30 cycles. The cells containing added LiBOB also have better coulombic efficiency and lower impedance after cycling at 55°C. Ex-situ surface analysis of both the anode and the cathode extracted from graphite/LiNi0.5Mn1.5O4 cells was conducted via a combination of XPS, SEM, TEM with EDX, and ICP-MS. The improved cycling performance with added LiBOB can be attributed to the inhibition of electrolyte decomposition at the electrode surfaces and inhibition of Mn and Ni dissolution from the cathode and deposition on the anode upon cycling at high voltage and elevated temperature.