膨胀石墨/硫-氟化气相沉积碳纤维双层正极

Expanded graphite/sulfur-fluorinated vapor-deposited carbon fiber bilayer cathode

对于高性能储能设备的迫切需求,使得理论能量密度达到2600 W·h/kg的锂硫电池(LSBs)变得极具吸引力。然而,低的容量可逆性和硫自身绝缘性的天然缺陷制约了其商业化进程。为了有效改善硫的导电性能,同时抑制多硫化物的穿梭效应,达到提高LSBs电化学性能的目的。本文采用逐层涂覆法在膨胀石墨(EG)/硫(S)复合正极极片表面涂覆氟化气相沉积碳纤维(FVGCF),通过首次放电至2.5 V实现FVGCF嵌锂,在EG/S正极极片表面形成LiF和FVGCF复合层。电化学性能测试和形貌表征结果表明:采用FVGCF新型正极材料具有最佳的循环寿命,EGS-FVGCF在1 C电流密度下的初始放电比容量为691.8 mA·h/g,100次循环之后剩余比容量为549.5 mA·h/g。相对于EGS涂覆的单层结构,在EGS上面涂覆FVGCF的双层电池性能具备极大应用优势,放电过程中生成的LiF能够抑制多硫化物从正极到负极的穿梭。同时,放充电后的电极形貌表征发现FVGCF层的加入减少了极片表面的裂纹,表明FVGCF层在一定程度上缓冲了硫正极的体积膨胀。这种简单易操作的复合结构为开发高性能LSBs提供了一定参考。

The urgent need for high-performance energy storage devices makes lithium-sulfur batteries(LSBs)with theoretical energy densities up to 2600 W·h/kg very attractive.However,the low capacity reversibility and the natural defect of sulfur's self-insulating property restrict its commercialization.In order to effectively improve the electrical conductivity of sulfur while suppressing the shuttle effect of polysulfides,the purpose of improving the electrochemical performance of LSBs is achieved.In this paper,a layer-by-layer coating method was used to coat the surface of the expanded graphite(EG)/sulfur(S)composite cathode with fluorinated vapor-deposited carbon fiber(FVGCF).A composite layer of LiF and FVGCF is formed on the surface of the pole piece.The electrochemical performance test and morphological characterization results show that the new cathode material using FVGCF has the best cycle life.The initial discharge specific capacity of EGS-FVGCF at 1 C current density is 691.8 mA h/g,and the remaining specific capacity after 100 cycles is 549.5 mA h/g.Compared with the EGS-coated single-layer structure,the double-layer battery coated with FVGCF on EGS has great application advantages,and the LiF generated during the discharge process can inhibit the shuttle of polysulfides from the positive electrode to the negative electrode.At the same time,the electrode morphology characterization after discharge and charge found that the addition of the FVGCF layer reduced the cracks on the surface of the pole piece,indicating that the FVGCF layer buffered the volume expansion of the sulfur cathode to a certain extent.This simple and easy-to-operate composite structure provides a certain reference for the development of high-performance LSBs.