Tris (trimethylsilyl) borate (TMSB) as a cathode surface film forming additive for 5V Li/LiNi0.5Mn1.5O4 Li-ion cells

The cycling performance of 5 V Li/LiNi0.5Mn1.5O4 cells with 1.0 M LiPF6 EC/DMC (1/2, v/v) with and without TMSB (0.2, 0.5, 1.0 and 2.0 wt.%) has been investigated. After 200 cycles, the cells with 1.0 wt.% TMSB have superior cycling performance with 95.3% capacity retention; while the cells with baseline electrolyte only maintain 84.4% capacity retention. The cells with 1.0 wt.% TMSB containing electrolyte have lower impedance after cycling at high voltage. In addition, the TMSB added cells show superior elevated temperature storage performance, the discharge capacity is 122.1 mAh g−1 and 109.9 mAh g−1 for the cells with and without TMSB after storage at 60 °C for a week at fully charged state, respectively. In order to further understand the effects of TMSB on LiNi0.5Mn1.5O4 cathode upon cycling at high voltage, scanning electron microscopy (SEM), thermal-gravimetric analysis (TGA), transmission electron microscopy (TEM) with energy-dispersive X-ray spectroscopy (EDX), X-ray photoelectron spectroscope (XPS), Fourier transform infrared spectroscopy (FTIR), and inductively coupled plasma mass spectrometry (ICP-MS) analysis were conducted after the cycling test. The results indicate that the use of TMSB can form a stable and compact film on the surface of the LiNi0.5Mn1.5O4 electrode, which inhibits the continuous decomposition of the electrolyte and reduces the dissolution of Mn and Ni from the bulk cathode material.