纳米CoSe修饰氮掺杂多孔碳的可控制备及其锂硫电池多硫化物的催化转化效应

锂硫电池中较差的循环稳定性和倍率性能是实现锂硫电池商业化的技术障碍，其主要原因之一是多硫化物在硫电极内的电化学转化动力学较为缓慢。为此，我们以ZIF-9为前驱体，采用先碳化，再酸化刻蚀，最后硒化的方法合成了含少量催化剂的CoSe修饰氮掺杂多孔碳(CoSe/NC)电极材料，以期提高硫电极内多硫化物的电化学转化动力学性能，并通过流动液相三电极体系对该材料进行电化学动力学表征。结果显示，相较于对比材料，CoSe/NC能够加快多硫化物的氧化还原反应速率，在 0.2mA·cm^-2电流密度下，多硫化物氧化还原反应在CoSe/NC电极上有最小的反应过电位；同时，在0.1 V过电位下，各氧化还原反应也有最大的响应电流。因此，将 CoSe/NC作为硫宿主材料组装电池展现了优异的电化学性能：在 1C(1C=1 675 mA·g^-1)下初始放电比容量为1 068 mAh·g^-1，经过500次循环后，可逆容量仍保持在693 mAh·g^-1。另外，在3C的高电流密度下，放电比容量可高达819 mAh·g^-1。

Controllable synthesis of N-doped porous carbon decorated with nano CoSe and catalytic effect on polysulfides conversion for Li-S battery

The poor cycle stability and rate performance are the technical obstacles to realizing the commercializa-tion of Li-S battery, one of the main reasons is the slow electrochemical conversion kinetics of sulfur active species in the sulfur electrode. In this work, for improving the electrochemical conversion of polysulfides in sulfur elec-trodes, ZIF-9 derived N-doped porous carbon decorated with CoSe (CoSe/NC) was chosen and obtained through car-bonization, acid pickling, and selenylation processes. The electrochemical kinetics of polysulfide conversion on CoSe/NC was studied using a flowing electrolyte three-electrode system. As a result, CoSe/NC composite took an effect on enhancing the reaction rates of polysulfide conversion. CoSe/NC composite gave more help to decrease the reaction overpotential under a current density of 0.2 mA·cm^-2. Meanwhile, the high response currents would be ob-tained with the help of CoSe/NC composite under an overpotential of 0.1 V. Moreover, the redox reaction for Li₂S₂ on CoSe/NC composite had the largest increase in amplitude in exchange current density. Therefore, the batteries as-sembled with CoSe/NC composite as sulfur host displayed fantastic electrochemical performances. The initial dis-charge specific capacity was 1 068 mAh·g^-1 at 1C (1C=1 675 mA·g^-1) and the retentive capacity was as high as 693 mAh·g^-1 after 500 cycles. In addition, the discharge specific capacity can be up to 819 mAh·g^-1 even at a high current density of 3C.