Constructing a Li-gradient in Li-Mn-O spinel for long-life lithium-ion batteries

Owing to the rapid Li ion extraction/insertion kinetics, Li-Mn-O spinels are promising candidates for high-power lithium-ion batteries that is required in electric vehicles. However, the Li-Mn-O spinel cathodes always suffer from poor cycling stability in practical due to the dissolution of Mn and Jahn-Teller distortion. Herein, we report on a new design of constructing a Li-gradient in Li-Mn-O spinel, which is achieved by surface treatment with lithium naphthalenide solution. The as-obtained Li_1+xMn_2-xO₄ spinels exhibit a Li-gradient with decreasing Li concentration from surface to interior. Importantly, the highly doped surface ensures good cycle stability while the lightly doped bulk maintains a relatively high capacity. This work provides a new design for Li-Mn-O spinels to mitigate their stability problem.