Stabilizing Capacity Retention in NMC811/Graphite Full Cells via TMSPi Electrolyte Additives

Abstract

Developing high-energy-density cathodes with prolonged cycling life is crucial to the continuing success of lithium-ion batteries. In particular, nickel-rich layered LiNi0.8Mn0.1Co0.1O2 (NMC811) cathodes are receiving growing interest due to their high reversible capacities in the range of 160–200 mAh/g and reduced content of critical and expensive cobalt. Nevertheless, nickel-rich NMC materials still encounter several challenges limiting their long-term cyclability, such as irreversible structural rearrangements, transition-metal dissolution, high surface reactivity, and parasitic oxidation of organic electrolyte at the surface of delithiated Li1–zNixMnyCo1–x–yO2 at high voltages. Here, we investigate the use of several electrolyte additives that can alleviate capacity fading through the formation of a protective layer passivating the surface of nickel-rich NMC811. Film-forming cathode additives should decompose prior to the solvents and cover the electrode surface with a protection layer which prevents further oxidative decomposition of the electrolyte and minimizes surface side reactions. We find that the addition of 1 vol. % tris(trimethylsilyl)phosphite (TMSPi) in combination with 1 vol. % vinylene carbonate (VC) to a standard electrolyte consisting of 1 M LiPF6 in ethylene carbonate (EC):dimethyl carbonate (DMC) (1:1 vol.) significantly enhances the capacity retention of NMC811/graphite full cells. Remarkably, a discharge capacity retention of 91% is achieved after 200 cycles at C/3.