Li-excess cation-disordered rocksalt (DRX) oxides have shown potential as high-energy-density Li-ion cathodes. They typically exploit O redox to achieve high capacity, which can trigger oxygen loss at the surface, thereby affecting the cathode performance. Here, we elucidate the impact that the surface structural evolution has on their electrochemical properties by comparing two prototypical DRX cathodes, Li_1.2Ni_0.333Ti_0.333Mo_0.133O₂ (LNTMO) and Li_1.2Mn_0.6Nb_0.2O₂ (LMNO). Both cathodes achieve high capacity, but oxygen loss leads to significant polarization for LNTMO, whereas LMNO is far less affected. We show that while metal densification at the particle surface occurs for both materials, the resulting surface structure is strikingly different. A spinel phase forms at the surface of LMNO, which effectively alleviates oxygen loss and allows fast Li transport, whereas a densified DRX forms at the LNTMO surface, which impedes Li transport and cannot mitigate oxygen loss. These findings demonstrate the importance of the surface structure of DRX cathode.

锂过量的阳离子无序岩盐（DRX）氧化物已显示出作为高能量密度锂离子阴极的潜力。他们通常利用O氧化还原来获得高容量，这会触发表面的氧气损失，从而影响阴极性能。在这里，我们通过比较两个原型DRX阴极，即Li _1.2 Ni _0.333 Ti _0.333 Mo _0.133 O ₂（LNTMO）和Li _1.2 Mn _0.6 Nb _0.2 O _2来阐明表面结构演变对其电化学性能的影响。（LMNO）。两个阴极均达到高容量，但氧损失导致LNTMO发生明显极化，而LMNO受的影响则小得多。我们表明，虽然两种材料都在颗粒表面发生金属致密化，但所得的表面结构却截然不同。尖晶石相形成在LMNO的表面，有效地减轻了氧的损失并允许快速的Li传输，而致密的DRX在LNTMO的表面形成，这阻碍了Li的传输并且不能减轻氧的损失。这些发现证明了DRX阴极的表面结构的重要性。