Slightly Li-enriched chemistry enabling super stable LiNi0.5Mn0.5O2 cathodes under extreme conditions

Abstract

High voltage/high temperature operation aggravates the risk of capacity attenuation and thermal runaway of layered oxide cathodes due to crystal degradation and interfacial instability. A combined strategy of bulk regulation and surface chemistry design is crucial to handle these issues. Here, we present a simultaneous Li₂WO₄-coated and gradient W-doped 0.98LiNi_0.5Mn_0.5O₂·0.02Li₂WO₄ cathode through modulating the content of the exotic dopant and stoichiometric lithium salt during lithiation calcination. Benefiting from the slightly Li-enriched chemistry induced by the hetero-epitaxially grown Li₂WO₄ surface, the 0.98LiNi_0.5Mn_0.5O₂·0.02Li₂WO₄ cathode demonstrates superior electrochemical performance to W-doped LiNi_0.49Mn_0.49W_0.02O₂ and WO₃ coated 0.98LiNi_0.5Mn_0.5O₂·0.02WO₃ cathodes without a Li-enriched phase. Specifically, when cycled in the potential range of 2.7–4.5 V at 30 °C, the 0.98LiNi_0.5Mn_0.5O₂·0.02Li₂WO₄ cathode possesses a high discharge capacity of 199.2 and 156.5 mA h g⁻¹ at 0.1 and 5C and a capacity retention of 92.88% after 300 cycles at 1C. Even at a high cut-off voltage of 4.6 V, it still retains a capacity retention of 91.15% after 200 cycles at 1C and 30 °C. Compared with LiNi_0.5Mn_0.5O₂, the enhanced performance of 0.98LiNi_0.5Mn_0.5O₂·0.02Li₂WO₄ can be attributed to its robust bulk and stable interface, inhibited lattice oxygen release, and improved Li⁺ transport kinetics. Our work emphasizes the significance of the slightly Li-enriched chemistry and bulk modulation strategy in stabilizing cathodes and hence unlocks vast possibilities for future cathode design.