UC Berkeley

The electrolyte, a key component for the successful operation of energy materials, is greatly affected by its solvents. The influence of solvents on the electrochemical performance of a LiFePO4/C composite cathode was investigated at various operating temperatures. The reaction kinetics of the LiFePO4/C composite electrode, including changes of rate capability, redox potential, polarization degree, electrode reaction process, exchange current densities, and activation energies, were evaluated using various techniques. The composition and volume ratio of solvents greatly affect the electrode kinetics. In the mixed solvents of ethylene carbonate (EC), dimethyl carbonate (DMC) and ethyl methyl carbonate (EMC), EMC is beneficial for the room temperature performance, while the substitution of 20 vol % of EMC by ethyl acetate (EA) is good for the low temperature performance. When 30 vol % of DMC is substituted by 10 vol % of EMC and 20 vol % of EA, the exchange current density increases from 0.022 to 0.038 mA cm−2 at −20 °C, while the activation energy of the charge-transfer process decreases from 48.36 to 33.01 kJ mol−1. Possible mechanisms for improving the electrochemical performance using different solvents have been analyzed. These results are significant for the exploration of appropriate electrolytes for the extensive applications of LiFePO4/C composite electrodes.