LiBOB as Electrolyte Salt or Additive for Lithium-Ion Batteries Based on LiNi0.8Co0.15Al0.05O2/Graphite

The potential use of lithium bis(oxalato)borate (LiBOB) as electrolyte salt or additive for lithium-ion batteries has been investigated. The electrochemical performances of LiNi0.8Co0.15Al0.05O2 (NCA) and graphite in different electrolyte formulations were studied by galvanostatic techniques and cyclic voltammetry. Differential scanning calorimetry (DSC)/thermal gravimetry (TG), coupled with mass spectrometry, was employed in studying the thermal behavior of charged electrodes in the presence of an electrolyte. The addition of 2 wt % LiBOB to the state-of-the-art LiPF6 electrolytes suffices to form a stable solid electrolyte interface film, thus protecting the graphite from partial exfoliation. The LiBOB graphite cells exhibited a much lower irreversible capacity in the first cycle in comparison with the pure LiPF6 electrolyte. NCA has a better cycling stability in LiBOB when compared to the LiPF6 electrolytes. Also, the discharge capacities obtained at different C-rates between C/5 and 5C were superior to those obtained in LiPF6 if charging at a C/5 rate. NCA/graphite complete cells in LiBOB cycled with coulombic efficiencies comparable to the state-of-the-art LiPF6 electrolytes. The DSC/TG measurements showed that LiBOB significantly improves the thermal stability of the graphite in the PC-containing electrolytes. LiBOB shifts the oxygen release from the NCA layered structure to much higher temperatures in comparison with the LiPF6 electrolyte. (C) 2010 The Electrochemical Society. [DOI: 10.1149/1.3374666] All rights reserved.