Reinforcing the stability of cobalt-free lithium-rich layered oxides via Li-poor Ni-rich surface transformation

Lithium-rich layered oxides are one of the most promising cathode materials for lithium-ion batteries due to their super-high capacity and low cost. However, extensive surface destruction, which originates from side reactions between the oxidative surface and the reductive electrolyte, leads to fast capacity fading along with the inevitable voltage drop. Here, we report a cobalt-free lithium-rich layered oxide Li1.2Mn0.6Ni0.2O2 (LMNO) with an electrochemically stable Li-poor nickel-rich surface by simple excessive calcination treatment. We show that the Li-poor nickel-rich surface possesses a rock-salt structure, greatly enhancing the interface stability and suppressing surface side reactions and Mn-ion dissolution. As a result, the modified LMNO, with a Li-poor nickel-rich surface of 4.2 nm thickness, can gain an improved resistance against extensive surface destruction, which delivers a stable capacity of 239.5 mA h g(-1) after 100 cycles at 0.1C and a mitigated voltage decay of only 3.885 mV per cycle. This work provides a facile and feasible strategy to enhance the surface properties of LMNO cathode materials without using heteroatom dopants or heterogeneous coatings, which is conducive to the design of high-performance cathode materials.