Multi-functional nitrile-based electrolyte additives enable stable lithium metal batteries with high-voltage nickel-rich cathodes†

A rechargeable lithium (Li) metal anode combined with a high-voltage nickel-rich layered cathode has been considered a promising combination for high-energy Li metal batteries (LMBs). However, they usually suffer from insufficient cycling life because of the unstable electrochemical stability of both electrodes. In this work, we report an advanced multi-functional additive, 1,3,6-hexanetricarbonitrile (HTCN), in a conventional carbonate-based electrolyte. This rationally designed electrolyte formation generates an ideal cathode electrolyte interphase (CEI) for LiNi_0.8Co_0.1Mn_0.1O₂ (NCM811) and a solid electrolyte interphase (SEI) for Li metal, successfully realizing stable ion transport kinetics. Then, theoretical calculations, physical characterization and electrochemical tests confirm that HTCN is more easily adsorbed on the NCM811 surface where it is oxidized to construct a stable CEI film involving the detachment of the CN group in a linear chain. Simultaneously, HTCN shows a more negative electron affinity and is easier to reduce, constructing a robust SEI film resulting from the detachment of the CN group in the side chain. Consequently, the assembled 50 μm-thin NCM811//Li (9.0 mg cm⁻² of mass loading) delivers a desired energy density of ∼330 W h kg⁻¹ at the cell level and an excellent cycling stability of 120 cycles with 88% capacity retention at 1C.