用于高性能锂硫电池隔膜的a-MEGO@g-C_3N_4复合材料（英文）

Nitrogen-rich a-MEGO@g-C_3N_4 coating on separator for advanced Li-S battery

由于具有高能量密度和环境友好性,锂硫电池成为备受关注的下一代电化学储能系统,然而硫和硫化锂的低电导率和多硫化锂的穿梭效应严重影响锂硫电池的实际比容量和循环性能.本研究制备出了具有高氮含量(原子数分数20.08%)和高比表面积(1000m^2·g^(-1))的a-MEGO@g-C_3N_4复合材料,并将其用作隔膜修饰层.在0.1C(1C=1675mA·g^(-1))的充放电速度下,采用修饰隔膜的电池首次放电容量达1244mAh·g^(-1);在0.5C下循环800次,衰减率为0.062%,两项指标明显优于对比电池.实验研究发现,a-MEGO@g-C_3N_4隔膜修饰后电池性能的提高来源于两方面:(1)高比表面积的a-MEGO@g-C_3N_4通过物理吸附固定多硫化物;(2)g-C_3N_4与多硫化锂通过形成C-S键与Li-N键抑制穿梭效应,并对溶解的活性物质实现再利用.本研究为以g-C_3N_4为基础的高氮碳材料在锂硫电池中的应用提供了可能.

Lithium-sulfur batteries are widely seen as a promising next-generation energy storage system owing to their ultrahigh energy density and environmental benignity, yet the low electrical conductivity of sulfur and the shuttle effect of dissolved polysulfides result in poor cycling performance. An a-MEGO@g-C3N4composite coated on polypropylene separator with high nitrogen content （atomic percent 20.08%） and specific surface area （1000 m2· g-l） was developed to inhibit polysulfide shuttling. The prepared lithium-sulfur battery with the a-MEGO@g-C3N4 coated separator delivered a specific capacity of 1244 mAh · g-1 at 0.1C （1C=1675 mA · g-1） and a capacity decay rate of 0.062% per cycle after 800 charge/discharge cycles at 0.5 C, which are both superior to the battery assembled with standard separator. Further experimental studies indicate that the improved electrochemical performance is attributed to the superior surface area and nitrogen content which immobilize the polysulfides and reuse the trapped active material. This work is expected to benefit the future development of g-C3N4 based carbon materials with optimal nitrogen content and surface area for Li-S batteries.