LiFePO4在不同pH值水溶液中电化学性能表现及其衰减机理

LiFePO₄在含Li⁺水溶液中的电化学性能稳定性与水溶液的pH值密切相关，当溶液的pH值达到11后LiFePO₄在充放电循环过程中的容量衰减十分明显. 通过循环伏安测试、交流阻抗测试、电极充放电性能测试、非原位X射线衍射测试以及化学分析的方式对其容量衰减机理进行了研究. 结果表明LiFePO₄在pH=7的LiNO₃水溶液中具有相对最高的电化学稳定性，但是LiFePO₄材料在水溶液中较之其在有机电解液中依然会有较差的电化学性能表现. 认为LiFePO₄在水介质中的容量衰减现象归因于其在持续充放电过程中的Li、Fe、P溶解，同时电极表面也会附着一层沉淀物. 这些最终导致了材料晶体结构的破坏、电极极化的增大以及电极容量的衰减.

Electrochemical Performance and Capacity Fading Mechanism of LiFePO4 at Different pH Aqueous Electrolyte Solutions

The electrochemical stability of LiFePO₄ in a Li⁺-containing aqueous electrolyte solution is critically dependent on the pH value of the aqueous solution. It shows a considerable decay in capacity of LiFePO₄ upon cycling when the pH value is increased to 11. The mechanism responsible for the capacity fading is extensively investigated by means of cyclic voltammogram, ac impedance, charge/discharge, ex situ X-ray diffraction, and chemical analysis. LiFePO₄ is relatively electrochemically stable in LiNO₃ aqueous solution with pH=7. But the electrochemical performance of LiFePO₄ in aqueous electrolyte is inferior to that in organic electrolyte. It is attributed to the loss of Li and the Fe, P dissolution during prolonged charge-discharge in aqueous medium. A precipitate is formed on the surface of LiFePO₄ electrodes. It results in the change of crystalline structure, a large electrode polarization, and capacity fading.