Synergistic Effect of Bis(2,2,2-trifluoroethyl) Carbonate and Succinonitrile in Suppressing the Dissolution of Nickel for Performance Improvement of Nickel-Rich Lithium Metal Batteries

Nickel-rich layered transition metal (TM) oxide cathode materials become the prospective candidates for high-energy lithium-ion batteries on account of their significant role in improving specific energy and power density. However, the decomposition of the electrolyte caused by the catalytic reaction of highly active Ni4+ ions together with the deposition of TM ions dissolved into the electrolyte upon the anode surface eventually deteriorates the capacity and cycling stability of nickel-rich lithium metal batteries. Herein, the effectively synergistic effect of a bis(2,2,2-trifluoroethyl) carbonate (BTFC) and succinonitrile (SN) electrolyte in suppressing the TM nickel ion dissolution in a nickel-rich lithium metal battery by building a reliable and protective electrode/electrolyte interface was reported. While SN was used to improve the electrochemical stability of the electrolyte, the oxidation products of BTFC can form a dense and stable passivated layer covering up the surface of the electrode. With the strong coordination ability of F bonding to the high-valence Ni ions, the continued TM nickel ion dissolution in the hybrid electrolyte was prevented. Thus, the NCA||Li cell with the designed electrolyte demonstrates an obvious improvement of capacity retention from 53.3% to 82.1% after 100 cycles compared with a conventional electrolyte. The remarkable rate performance is witnessed with high specific capacity over 120 mAh g–1 at the rate of 1000 mA g–1. The results provide insight into improving the performance of Ni-rich lithium metal batteries by the electrolyte manipulation strategy. The fundamental mechanism understanding of this synergistic effect in this study may facilitate the development of cooperative electrolytes with an advanced nickel-rich cathode for next-generation batteries.