Impact of Lithium Bis(oxalate)borate Electrolyte Additive on the Performance of High-Voltage Spinel/Graphite Li-Ion Batteries

The impact of lithium bis(oxalate)borate (LiBOB) electrolyte additive on the performance of full lithium-ion cells pairing the high-voltage spinel cathode with the graphite anode was systematically investigated. Adding 1 wt % LiBOB to the electrolyte significantly improved the cycle life and Coulombic efficiency of the full-cells at 30 and 45 °C. As the LiBOB was preferentially oxidized and reduced compared with LiBOB-free electrolyte during cycling, their relative contributions to the improved capacity retention in full-cells was gauged by pairing fresh and LiBOB-treated electrodes with various combinations. The results indicated that a solid–electrolyte interphase (SEI) film on graphite produced by the reduction of the LiBOB additive is more robust and stable against Mn dissolution problem during cycling at 45 °C compared with the SEI formed by the reduction of the base (LiBOB-free) electrolyte. In addition, a 3 wt % LiBOB-added electrolyte showed reduced Mn dissolution compared with the base electrolyte after storing the fully charged Li1–x Ni0.42Fe0.08Mn1.5O4 (LNFMO) electrodes at 60 °C for one month. It is believed that LiBOB aids in stabilizing the electrolyte by trapping the PF5, i.e., sequestering the radical which tends to oxidize EC and DEC electrolyte solvents. Thus, oxidation is suppressed on the carbon black particles in the positive electrode, as evidenced by scanning electron microscopy (SEM) and Fourier transform infrared spectroscopy (FT-IR) analyses. As a result, HF generation is suppressed, which in turn results in less Mn dissolution from the spinel cathode.