Upcycling NCM cathodes by tailoring superexchange interaction for ultrastable energy storage properties

Abstract

Driven by ∼100% recovery rate, direct regeneration has been regarded as a promising recycling strategy. However, during solid-state regeneration process, limited by robust Ni–O–Ni superexchange interactions of inactive rock-salt phases, they still suffer from inferior lithium replenishment and physicochemical heterogeneity, always along with poor energy storage properties and batch consistency. Herein, supported by theoretical calculations, a “four-in-one” W-assisted recycling strategy is proposed to induce successful regeneration of spent NCM. Benefiting from weakened Ni–O–Ni superexchange with regulated Ni states, the targeted phase transition into layered structures is established with robust Ni²⁺–O²⁻–Mn⁴⁺ superexchange interactions and suppressed oxygen loss. Meanwhile, after W-introduction, the total magnetic moments are reduced about 12.65 μB, meanwhile the exchange energy increases to −0.7795 eV, and internal strains are obviously alleviated. The as-optimized samples exhibit 92.6% and 81.8% capacity retentions at 1.0 C and 10.0 C at 4.6 V after 100 cycles. As revealed by kinetic analysis and in/ex-situ measurements, accelerated lithium diffusion and reduced internal strains are further demonstrated, along with weakened side reactions. In summary, this work is expected to achieve high homogeneity and cycling durability at high voltages, and provides an effective strategy for upcycling degraded NCM into high-performance NCM.