Chemical conversion of parasitic residual lithium compounds into beneficial artificial interface for cycle life improvement of LiNi0.8Mn0.1Co0.1O2 cathodes

Abstract

LiNi0.8Mn0.1Co0.1O2 (NMC811) is the suitable cathode material for 300 Wh kg−1 lithium-ion battery packs due to their high specific capacity and operating potential of ∼3.7 V. The major bottleneck in the commercialization of NMC811 arises from the formation of residual lithium compounds (RLCs) on the surface during synthesis, its accumulation during storage, and the bulk/interfacial degradation when cycled using conventional electrolytes. Removing RLCs and ceasing their reformation complicate the material production line. Herein, we propose a single-step solution of converting parasitic RLCs into beneficial artificial interfaces by reacting RLCs with LiPF6 and Lithium Bis(oxalate)borate salts in tandem. It results in a bilayer arrangement of multiple components having LiF and Li3PO4 in the inner layer and LixBOyFz in the outer layer. The interface-modified material retains 90 % of initial capacity over 200 cycles, whereas the pristine NMC811 loses ∼50% capacity. The surface modification improves coulombic efficiency, reduces voltage polarization, lowers the growth of resistances with the progression of cycling, regulates the composition of cathode-electrolyte interphase, restricts cationic disorder, and provides interfacial stability during long-term cycling. In short, the applied methodology not only mitigates the issue of detrimental RLCs but also boosts the electrochemical performances of Ni-rich cathodes significantly.