功能互补炭材料及其在锂硫电池中电化学性能

Nitrogen-doped CMK-3@graphene hybrids as a sulfur host material for use in lithium-sulfur batteries

  • 摘要: 由于锂硫电池成本低、理论能量密度高、安全、环保,使其极具潜力成为下一代新能源储能体系。但循环过程中电极材料结构产生破坏及多硫穿梭效应是锂硫电池容量衰减的主要原因。为此,本文提出了采用功能互补的炭材料-氮掺杂石墨烯包覆CMK-3材料(N-(CMK-3@G))来解决该问题。该材料基于功能互补原理,利用CMK-3防止石墨烯堆叠及二维石墨烯包覆在CMK-3外面抑制多硫穿梭,并采用氮掺杂的化学吸附提高锂硫电池正极的电化学性能。以N-(CMK-3@G)/S复合材料作为锂硫电池正极,在电流密度为335 mA·g-1时,300次循环后其可逆放电容量为867.3 mAh·g -1,容量保持率为82%。与N-CMK-3/S和N-G/S正极相比,N-(CMK-3@G)/S复合电极倍率性能及极化特性都得到了较大的改善。从炭材料功能出发,对材料设计,不仅可结合CMK-3及石墨烯的功能特点,形成作用互补,提高锂硫电池的循环性能,且氮掺杂可通过化学作用强化对多硫吸附,抑制多硫离子的穿梭,进一步提高锂硫电池性能。

     

    Abstract: Sulfur as a cathode material has the advantages of low cost, high theoretical energy density and safety. However, the capacity decay and a shuttle effect are major problems that cause poor coulombic efficiency and a short cycling life. An ordered mesoporous carbon, CMK-3 was oxidized by 67% HNO3, added to a graphene oxide suspension, sonicated, freeze-dried and annealed in NH3 to obtain a nitrogen-doped CMK-3@graphene hybrid, which was melt-infiltrated with sulfur to prepare a cathode material for lithium-sulfur batteries. Results indicate that the CMK-3 particles are uniformly dispersed in graphene sheets and their surfaces are coated with graphene. The N-(CMK-3@G)/S has a reversible discharge capacity of 867.3 mAh·g-1 after 300 cycles at a current density of 335 mA·g-1 with a capacity retention of 82%. Compared with N-CMK-3/S and N-G/S cathodes, the rate performance and polarization characteristics are also improved. The graphene coating on CMK-3 traps soluble polysulfides during the charge/discharge process and nitrogen doping facilitates chemical adsorption of polysulfides to inhibit the shuttle effect, which together improve the performance of the battery.

     

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