Insights into Boron-Based Polyanion-Tuned High-Nickel Cathodes for High-Energy-Density Lithium-Ion Batteries

Ultrahigh-Ni layered oxide cathodes (Ni content >90%) are at the forefront for potentially enabling higher-energy-density lithium-ion batteries. Unfortunately, they suffer from rapid capacity fade, poor thermal stability, and increased air sensitivity. Introduction of boron-based polyanion into layered cathodes has been found to be effective in stabilizing high-Ni cathodes, but the mechanism behind it is not yet fully understood. To develop a better understanding, we present here an extensive characterization of the ultrahigh-Ni cathode LiNi_0.94Co_0.06O₂ (NC) and B₂O₃–LiNi_0.94Co_0.06O₂ (B–NC). The B–NC delivers a capacity of 223 mA h g^–1 with 80% capacity retention after 400 cycles in full cells with graphite anodes, superior to 61% retention for NC. In-depth interphase investigations reveal that the improved cyclability is attributed to the development of a well-passivated boron/phosphorus-rich cathode-electrolyte interphase in B–NC. Moreover, B–NC demonstrates a considerably enhanced air-exposure and thermal stability. A 30-day air-stored B–NC delivers a discharge capacity of 125 mA h g^–1 at 10C rate, in sharp contrast to 65 mA h g^–1 for the stored NC. This work advances the understanding of the effect boron-based polyanion insertion into layered oxides has on battery performance and offers a viable strategy for developing practically viable ultrahigh-Ni cathodes with high-energy density.