椰壳基分级多孔炭锂硫电池正极材料的制备及性能研究

The Li?S battery has a high theoretical energy density of 2567 W h/kg, based on the electrochemical reaction of 16Li + S8 → 8Li2S and the theoretical specific capacities of 1673 for S cathode and 3861 mAh/g for Li anode, respectively, making it a promising choice for the next generation of high-energy rechargeable batteries, except the low cost and environmental friendness of sulfur (S). However, although substantial progress has been achieved, the challenges remain because two most important impediments for the Li-S batteries are still not completely solved：low utilization of active materials resulted from the poor electrical conductivity of sulfur, and the intrinsic polysulfide shuttle due to the solubility of polysulfide during discharge and charge processes. To address these obstacles in the project, based on the electrochemical mechanism of Li-S battery and the investigation of cathode materials presently, we will prepared the porous carbon with different pore size from the coconut shell which is a abundant boimass resource in tropical Hainan island.Then the three dimensional hierarchical porous carbon was prepared using the obtained coconut-based carbon as matrix through polymeric sol-gel method following high temperature treatment. These porous carbon loading sulfur will employed as cathode materials of Li-S batteries, The properties and electrochemical behavior of polysulfide, including the transform, dissolution, diffusion and the electrochemical reaction characteristics and shuttle effects in different carbon pore structure during the electrochemical process will investigated. Accordingly, the effects of the carbon pore structure on the cathode properties for Li-S batteries, including the sulfur carries capacity, discharge voltage, the oxidation/reduction reaction characteristics and cyclability, will determined. Due to the rich biomass resources in Hainan island, this project concerning the preparation of porous carbon with rich pore structure and the simple synthesized process at large scale are very important for both application research for Li-S batteries and Hainan local economical and scientific technology development.

锂硫电池具有比能量高、原料丰富、成本低、环境友好等优点，有望成为新一代高能电池体系，但循环性能差是制约其实用化的主要障碍。项目针对锂硫电池正极材料存在的活性物质利用率低、放电中间产物多硫化物的"穿梭效应"而导致电池循环性能差的难题，基于对现有锂硫电池的电化学反应机理的认识和正极材料的研究现状，利用海南丰富的生物废弃物椰壳为原料，制备不同孔结构的多孔炭,并结合高分子溶胶-凝胶转化法,调节孔结构制备三维分级多孔炭材料，负载硫用于锂硫电池正极，研究多硫化物在多孔炭的不同尺度孔隙中的转换、溶解、扩散、电化学反应特征和多硫化物穿梭效应特点，由此确定多孔炭孔结构参数对硫负载量、充放电容量及平台电压、氧化/还原特性和循环性能的影响和对应关系。项目结合海南热带生物资源丰富的特点，研制孔隙发达的炭材料及简单而便于规模化的制备工艺，不仅对锂硫电池的研究和应用具有重要意义，而且对当地经济和科技发展具有推动作用。

由于电动汽车、移动通信和其他便携式电子设备的快速发展，以及随着人们环保意识的提高，可再生能源已被广泛使用。锂硫电池作为一种新型的二次电池，相对于传统的锂离子电池的正极活性材料，硫单质具有储量丰富，价格低廉等诸多优点，因此，锂硫电池作为一种极有潜力的储能系统，为满足现代电子器件及高级电动汽车的高能量密度的迫切需求，提供了一个很有希望的选择。.椰壳是自然界丰富存在的一种可再生资源，通过对椰壳进行炭化、活化或石墨化等处理可以得到不同的椰壳基炭材料，包括多孔活性炭以及多孔石墨烯。本项目通过对不同工艺的探索，将椰壳基生物炭转化为多孔石墨烯，并且制备出的多孔石墨烯具有高纯度，高电导率(32.14 S/cm)和高比表面积（1506 m2/g）。该项研究探索出了硬炭结构石墨化的新方向，为该领域的推进提供了理论和实际意义。负载硫组装成的锂硫电池比容量高达1200 mA h/g，循环100次后的容量仍然高达900 mA h/g。并且，将其应用到超级电容器中，也达到了良好的电容性能，能量密度为23.07 Wh/kg时功率密度达135 W/kg。同时，该项目还制备出了性能优良的椰壳分级多孔炭，比表面积最高达到3831 m2/g，孔体积达到了2.289 cm3/g，其中含有42.8 %的介孔。在水性电解液中，1 A/g电流密度下表现出260 F/g的高比电容，100 A/g时保持在216 F/g，能量密度最高达到13.35 Wh/kg，同时具有突出的倍率性能和优良的循环稳定性。.此外，通过模板法技术制备的双壳层SnO2@C中空纳米球，将其负载硫之后形成S/SnO2@C复合电极材料，将其组装成锂硫电池，在200 mA/g的电流密度下，首次放电容量为1473.1 mAh/g，在3200 mA/g 的电流密度下，经100次循环后，容量保持率高达95.7 %，容量衰减仅为每循环0.043 %。为了解决SnO2的导电性较差的问题，我们又提出了一种基于碳/TiO2/碳三明治结构的新型空间限域策略，结合碳热还原反应制备TiC纳米颗粒铆钉中空碳球(TiC@C)，这种独特的TiC@C结构在大倍率充放电条件下具有优异的循环稳定性，在1600 mA/g的电流密度下，首次放电容量为732.6 mAh/g，经过1000次循环后，容量保持在443.2 mAh/g，容量衰减仅为每循环0.0395 %。