Engineering manganese-rich phospho-olivine cathode materials with exposed crystal {010} facets for practical Li-ion batteries

Manganese-rich LiMn1-yFeyPO4 (e.g., LiMn0.7Fe0.3PO4) is emerging as the most promising olivine cathode ma-terial after LiFePO4, which has a current market demand of >500000 tons per year. However, its commercial application is challenging because of its poor kinetic properties. Although nanocrystallization is a transformative paradigm for improving the kinetics, it results in the concomitant problem of increasing the specific surface area of the material, which leads to more interfacial side reactions. Here, we develop a polyol solvothermal method to boost the particle size (decrease the specific surface area) whilst simultaneously regulating the crystal orientation (improving the kinetics) of LiMn0.7Fe0.3PO4. Importantly, the synthesis can be used at the ton scale, with the off -take potential reaching 1000 tons per year. Cobalt doping and carbon coating are combined to further increase the kinetic properties. Electrochemical measurements demonstrate that the diffusion of the Li+ kinetics is increased by 58.6 % and 46.1 % for the Fe2+/3+ and Mn2+/3+ redox couple during charging and 92.0 % and 21.2 % during discharging, respectively. A capacity of 150 mAh g- 1 at a 5C rate is then delivered. In full batteries (14000 mAh), the capacity retention reaches 89.6 % over 1000 cycles at a 1C rate.

Automated summary

A polyol solvothermal method is developed to synthesize LiMn0.7Fe0.3PO4, which can simultaneously increase particle size (decrease specific surface area) and regulate crystal orientation (improve kinetics) to enhance lithium ion diffusion kinetics. Cobalt doping and carbon coating further improve the kinetic properties. Electrochemical measurements show increased Li+ diffusion kinetics for the Fe2+/3+ and Mn2+/3+ redox couple during charging and discharging, respectively. The material exhibits a capacity of 150 mAh g-1 at a 5C rate, and in full batteries, it retains 89.6% capacity over 1000 cycles at a 1C rate.