Single-crystal Li-rich layered cathodes with suppressed voltage decay by double-layer interface engineering

Despite lithium-rich layered oxides (LLO) are promising candidates for the next-generation cathode materials, the rapid voltage and capacity decay, caused by structural degradation, are primary challenges towards their real-world applications. Herein, via a facial and large-scale treatment method, a robust double layer (DL) cathode-electrolyte interphase (CEI), with outermost layer of amorphous Li3PO4 (LPO) and medium layer of LixNiyMn3-x-yO4 with disordered spinel structure, is uniformly introduced onto the surface of single-crystal Li1.2Ni0.2Mn0.6O2. The double-layer CEI effectively blocks the phase transition from the layered LLO structure into spinel and then rock salt, and thus relieves the voltage decay in cycling. Meanwhile, the CEI blocks the diffusion of TM-ions into the electrolyte and extra O release in cycling, since there are nearly no voids rich in defected rock-salt structure in their edges in the cycled DL-LLO. We further theoretically disclose that the defected rock-salt phase has indeed a high dissolvability of TM and the large irreversibility of O reactivity, which is an accelerator for the structural degradation in cycling. Accordingly, the problems of voltage decay and capacity fading of the modified DL-LLO are greatly relieved and with a voltage drop of only 0.83 mV per cycle and a capacity retention of 82.5 % over 300 cycles at 1 C. This work provides a guidance for effective surface treatment strategies in developing stable Li-rich layered cathodes with high capacity and cyclability.