固相燃烧法制备去顶角八面体LiZn0.08Al0.01Mn1.91O4正极材料及其电化学性能

通过固相燃烧法快速合成了包含{111}、{100}和{110}晶面的单晶去顶角八面体形貌LiZn_0.08Al_0.01Mn_1.91O₄正极材料。结果表明，Zn-Al共掺促进了尖晶石型LiMn₂O₄材料的晶体发育和晶面择优生长，形成了单晶去顶角八面体形貌晶粒，有效抑制了Jahn-Teller效应，减缓了Mn溶解，增强了其晶体结构稳定性，显著提升了合成材料的电化学性能。LiZn_0.08Al_0.01Mn_1.91O₄在5C和10C下的首次放电比容量分别为92.6和76.5 mAh·g^-1，经过2 000次循环后的容量保持率分别为70.4%和74.8%。即使在15C高倍率下，仍有64.2 mAh·g^-1的首次放电比容量，循环800次后容量保持率达到82.2%。与LiZn_0.08Mn_1.92O₄相比，LiZn_0.08Al_0.01Mn_1.91O₄正极材料具有较大的Li+扩散系数(1.02×10^-11 cm²·s^-1)和较小的表观活化能(25.60 kJ·mol^-1)，表明Zn-Al共掺和单晶形貌调控策略能够降低Li+在脱/嵌过程的能垒和增大Li+在电极材料中的扩散速率。

Synthesis and electrochemical properties of truncated octahedral LiZn0.08Al0.01Mn1.91O4 cathode material by solid-state combustion method

A single-crystal truncated octahedral morphology LiZn_0.08Al_0.01Mn_1.91O₄ cathode material with {111}, {110}, and {100} crystal surfaces was synthesized by a solid-state combustion method. The results show that Zn-Al co-doped promotes the crystal development and the selective growth of crystal surfaces of spinel LiMn₂O₄ materials, while forming single-crystal truncated octahedral grain. The Zn-Al co-doped sample effectively inhibits the Jahn-Teller effect and reduces Mn dissolution, thus enhancing the crystal structure stability and significantly improving the electrochemical performance. The initial discharge specific capacity of LiZn_0.08Al_0.01Mn_1.91O₄ were 92.6 and 76.5 mAh·g^-1 at 5C and 10C, the corresponding capacity retention remained 70.4% and 74.8% after 2 000 cycles, respectively. Even at a high current density of 15C, the initial discharge capacity was still 64.2 mAh·g^-1, and the capacity retention can reach 82.2% after 800th cycles. Compared with LiZn_0.08Mn_1.92O₄, the LiZn_0.08Al_0.01Mn_1.91O₄ cathode material had a larger Li⁺ diffusion coefficient (1.02×10^-11 cm²·s^-1) and smaller apparent activation energy (25.60 kJ mol^-1). The results show that the Zn-Al co-doped and monocrystalline morphology control strategy can reduce the energy barrier of Li⁺ during the de-intercalation process and increase the diffusion rate in electrode materials.