Lithium-Ion Conductivity Epitaxial Layer Contributing to the Structure and Cycling Stability of LiMn2O4 Cathodes

A critical challenge in the commercialization of spinel lithium manganate materials is the bulk structure damage and capacity degradation due to manganese dissolution during battery operation. Hence, Li3PO4 with good ionic conductivity was homogeneously deposited on the surface of spinel lithium manganate by the sol-gel method, aiming to improve the stability and cycling of the spinel structure by an epitaxial layer. The structural and electrochemical characterizations reveal that the presence of the Li3PO4 epitaxial coating prevents the direct contact of the cathode surface and electrolyte, thus enhancing the stability of the structure and reducing the extent of manganese dissolution. Further studies have shown that the contribution of the Li3PO4 layer promotes the diffusion coefficient of lithium ions, which increases from 7.89 x 10-12 to 4.43 x 10-11 cm2 s-1. Meanwhile, the Li3PO4 coating regulates the concentration of oxygen vacancies on the surface of the spinel, effectively reducing the transfer resistance and increasing the electronic conductivity to 3.50 x 10-5 cm-1. Specifically, the discharge specific capacity of the 1.0 wt % Li3PO4- modified electrode is still 115.4 mAh g-1 after 300 cycles, with the capacity retention increased to 90.8%. Even at a high rate of 10C, it still demonstrates excellent rate capability, with the discharge specific capacity more elevated than that of the unmodified material at about 40 mAh g-1. This strategy can simultaneously solve the interfacial instability and bulk structure degradation, thus improving the electrochemical performance of lithium manganate materials.

Automated summary

A sol-gel method was used to evenly deposit Li3PO4 with good ionic conductivity on the surface of spinel lithium manganate, aiming to improve the stability and cycling of the spinel structure by creating an epitaxial layer. The presence of the Li3PO4 coating prevents direct contact between the cathode surface and electrolyte, enhancing stability and reducing manganese dissolution. The Li3PO4 layer also improves the diffusion coefficient of lithium ions and reduces transfer resistance, resulting in improved electrochemical performance.