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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 Li 2 WO 4 -coated and gradient W-doped 0.98LiNi 0.5 Mn 0.5 O 2 ·0.02Li 2 WO 4 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 Li 2 WO 4 surface, the 0.98LiNi 0.5 Mn 0.5 O 2 ·0.02Li 2 WO 4 cathode demonstrates superior electrochemical performance to W-doped LiNi 0.49 Mn 0.49 W 0.02 O 2 and WO 3 coated 0.98LiNi 0.5 Mn 0.5 O 2 ·0.02WO 3 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 0.5 Mn 0.5 O 2 ·0.02Li 2 WO 4 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 0.5 Mn 0.5 O 2 , the enhanced performance of 0.98LiNi 0.5 Mn 0.5 O 2 ·0.02Li 2 WO 4 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., Competing Interests: There are no conflicts to declare., (This journal is © The Royal Society of Chemistry.)

Li-rich and Mn-based layered oxides are the most promising candidates for next-generation high energy density cathode materials. However, inherent problems including poor rate performance, continuous capacity degradation, and voltage fading hinder their commercial utilization. Herein, a lattice- and interfacial-modified Li 1.2 Mn 0.54 Co 0.13 Ni 0.13 O 2 with a pristine-layered bulk structure, Na- and S-doped transition phase, and epitaxially grown Na 2 Mn (SO 4 ) 2 ( C 2/ c symmetry) layer were constructed by Na 2 S treatment. The monoclinic Na 2 Mn(SO 4 ) 2 not only acts as an interface protective layer, alleviating the harmful electrode-electrolyte reactions, but also promotes formation of oxygen vacancy in the layered structure, enhancing reversibility of oxygen redox. The Na and S surface lattice doping leads to enhanced Li + diffusion and alleviates the chance of oxygen release. With the positive effects provided by the stable interfacial layer and lattice modification, the modified cathodes with moderate Na 2 S treatment shows alleviated capacity and voltage decay and enhanced electrochemical kinetics. Especially, the washed cathode with 3 wt % Na 2 S treatment delivers a discharge specific capacity of 305 at 0.1 C and 219 mA h g -1 at 1 C, as well as 93.15% capacity retention and 88.20% voltage retention after 200 cycles at 1 C.