氮掺杂碳包覆Na_(3)V_(2)(PO_(4))_(2)F_(3)钠离子电池正极材料的制备与性能

Nitrogen-doped carbon-coated Na_(3)V_(2)(PO_(4))_(2)F_(3) cathode materials for sodium-ion batteries: Preparation and electrochemical performance

锂储量的有限性和不断攀升的锂资源价格限制了锂离子电池在大规模能源存储领域的应用发展,亟需发展可替代锂离子电池的低成本储能技术。在诸多新型二次电池储能体系中,钠离子电池由于钠资源丰富及与锂离子电池相似的储能机制受到了广泛关注。在钠离子电池正极材料中,钠超离子导体材料Na_(3)V_(2)(PO_(4))_(2)F_(3)(NVPF)不仅具有高的工作电压和放电容量,还表现出良好的热稳定性和较小的体积效应,因而具有广阔的应用前景。本工作采用低温水热反应和后续煅烧法制备NVPF,通过在水热过程中添加尿素和柠檬酸制备了氮掺杂碳包覆NVPF的复合材料(NVPF@C-N)。氮元素掺杂改善了碳包覆层的孔道结构和电导率,NVPF@C-N复合材料作为钠离子电池正极材料表现出高的可逆容量以及优异的倍率性能,在1 C下的初始放电比容量为121 mAh/g,10 C下的放电比容量为110 mAh/g,甚至在90 C的高电流密度下放电比容量仍具有66 mAh/g。此外,NVPF@C-N正极材料展示了高的循环稳定性,在1 C下循环200次后的充放电平台能够得到充分保持,且放电比容量仍高达111 mAh/g;特别地,NVPF@C-N在10 C下循环1000次后的容量保持率高达87%,在6000次循环后的容量保持率为54%。

The limited lithium reserves and the increasing cost of lithium sources have hampered extensive applications of lithium-ion batteries to large-scale electric energy storage.It is significantly urgent to develop alternative low-cost electric energy storage devices,during which rechargeable sodium-ion batteries(SIBs)have attracted extensive attention due to abundant sodium resources and similar electrochemical properties to lithium-ion batteries.Na_(3)V_(2)(PO_(4))_(2)F_(3)(NVPF)is considered as one of the most promising candidates,owing to the merits of super high ionic conductivity,high theoretical specific capacity,good thermal stability and small volume effect.In this work,through hydrothermal process and post calcination,nitrogen-doped carbon-coated NVPF(NVPF@C-N)composites were obtained by adding urea and citric acid during the hydrothermal process.Particularly,nitrogen doping could substantially enhance the pore structure and electrical conductivity of the carbon layer.When used as the SIB cathode,NVPF@C-N exhibited high reversible capacity and excellent rate capability.Under 1 C and 10 C rates,the NVPF@C-N cathode delivered initial discharge capacity of 121 mAh/g and 110 mAh/g,respectively.Even at the rate of 90 C,66 mAh/g can be obtained.For the cycling stability of NVPF@C-N,the voltage plateau still could be well maintained even after 200 cycles at the rate of 1 C,and the electrode still retained a capacity of 111 mAh/g.Particularly,a retention of 87%was obtained after 1000 cycles at the rate of 10 C,and a retention of 54%was still maintained even after 6000 cycles.