Ni-Ion-Chelating Strategy for Mitigating the Deterioration of Li-Ion Batteries with Nickel-Rich Cathodes.

Ni-rich cathodes are the most promising candidates for realizing high-energy-density Li-ion batteries. However, the high-valence Ni 4+ ions formed in highly delithiated states are prone to reduction to lower valence states, such as Ni 3+ and Ni 2+ , which may cause lattice oxygen loss, cation mixing, and Ni ion dissolution. Further, LiPF 6 , a key salt in commercialized electrolytes, undergoes hydrolysis to produce acidic compounds, which accelerate Ni-ion dissolution and the interfacial deterioration of the Ni-rich cathode. Dissolved Ni ions migrate and deposit on the surface of the graphite anode, causing continuous electrolyte decomposition and threatening battery safety by forming Li dendrites on the anode. Herein, 1,2-bis(diphenylphosphino)ethane (DPPE) chelates Ni ions dissolved from the Ni-rich cathode using bidentate phosphine moieties and alleviates LiPF 6 hydrolysis via complexation with PF 5 . Further, DPPE reduces the generation of corrosive HF and HPO 2 F 2 substantially compared to the amounts observed using trimethyl phosphite and tris(trimethylsilyl) phosphite, which are HF-scavenging additives. Li-ion cells with Ni-rich cathodes and graphite anodes containing DPPE exhibit remarkable discharge capacity retentions of 83.4%, with high Coulombic efficiencies of >99.99% after 300 cycles at 45 °C. The results of this study will promote the development of electrolyte additives.