铁源前驱体对钠离子电池材料Na_(2)FeP_(2)O_(7)/C的影响

Effect of iron source precursor on sodium-ion battery material Na_(2)FeP_(2)O_(7)/C

采用溶胶-凝胶工艺制备以蔗糖为前驱体的碳包覆NaFeP_(2)O_(7)正极材料,并通过优化铁源提升材料的电化学性能。通过调节蔗糖比例控制包覆碳的含量来改善材料的导电性。铁源为FeSO4·7H_(2)O时,前驱体蔗糖的含量不宜过高;而铁源为Fe(NO_(3))_(3)·9H_(2)O时,则需要较高含量的蔗糖前驱体。铁源为FeSO4·7H_(2)O、Fe(NO_(3))_(3)·9H_(2)O制备的电极材料的循环稳定性较好,以1.0 C在1.5~4.2 V循环300次后,分别能保留73 mAh/g与74 mAh/g的放电比容量,容量保持率为91.6%与95.1%。碳包覆后的材料在20.0 C下的放电比容量超过48 mAh/g,倍率性能良好。通过结构和电化学性能测试,发现以蔗糖作为碳前驱体高温烧结的碳包覆结构改善了电极的电子导电性,并提高了Na+扩散系数,从而提高了电化学性能。

Carbon-coated Na_(2)FeP_(2)O_(7)cathode materials with sucrose as precursors are prepared by sol-gel process,the electrochemical performance of which is improved by optimizing the iron source.The conductivity of the material is improved by adjusting the proportion of sucrose to control the amount of coated carbon.The sucrose content of the precursor shouldn’t be too high when the iron source is FeSO4·7H_(2)O,while a higher sucrose precursor content is required when the iron source is Fe(NO_(3))_(3)·9H_(2)O.The electrode materials prepared by FeSO4·7H_(2)O,Fe(NO_(3))_(3)·9H_(2)O iron sources show good cycle stability,the specific discharge capacity of 73 mAh/g and 74 mAh/g can be retained after 300 cycles at 1.0 C in 1.5-4.2 V,respectively,with the capacity retention rate of 91.6%and 95.1%,respectively.The carbon-coated material exhibits a specific discharge capacity of more than 48 mAh/g at 20.0 C,demonstrating good rate capability.Through the test of structure and electrochemical performance,it is found that the carbon-coated structure made of sucrose as carbon precursor at high temperature improves the electronic conductivity as well as increases the diffusion coefficient of Na+,thus improving the electrochemical performance.