【作者】 王庆红；

【导师】 袁华堂；

【作者基本信息】 南开大学 ， 材料物理与化学， 2012， 博士

【摘要】 近期研究表明，Co-非金属复合物（如Co-B、Co-Si、Co-P等）、CoO、Co₃O₄、Co（OH）₂等Co基材料在碱液中具有良好的储能性能。作为碱性二次电池负极材料，Co基材料具有较高的放电容量和较好的循环性能，但是有关非金属部分对Co电极的电化学性能的影响机理鲜有报道，而且Co基材料的电化学性能有待进一步提高。作为超级电容器材料，氧化钴、硫化钴等也受到广泛关注，但对其电化学性能的研究尚不深入。与以上Co基材料类似，Co-S复合物和CoS化合物也体现出良好的电化学性能，且制备简单、易于控制形貌。本文将以Co-S材料作为研究对象，研究其作为碱性二次电池负极材料和超级电容器电极材料的电化学性能。第一部分：Co-S材料作为碱性二次电池负极材料的性能研究运用简单混合法、球磨法和水热法制备了两种Co-S复合物和两种CoS化合物。作为碱性二次电池负极材料，Co-S复合物电极的放电容量高达350mAh g1，且循环性能良好，CoS化合物电极的放电容量很低，仅有40mAh g1左右。两者电化学性能差别的主要原因是所含S起的作用不同：复合物材料中的S能提高Co的分散性能，且在电化学反应过程中能够溶解，使电极内产生空隙，进一步促进了Co与电解液直接的充分接触，提高了Co的利用率，使得Co-S复合物材料表现出较好的电化学性能；而CoS化合物材料中的Co以CoS形式存在，即使经过多周反应，大部分Co仍然不能释放出来，Co的利用率较低，导致其电化学性能较差。运用简单水热法制备了系列Co₉S₈纳米片包覆Co颗粒的Co-S复合材料。研究发现复合材料的比表面积远远大于单质Co，Co-S材料的最高放电容量达到420.2mAh g^-1，循环200周后仍保持在410mAh g^-1，单质Co的最高放电容量只有214.5mAh g^-1，且衰减严重。电化学性能显著提高的主要原因为复合物材料比表面的增大，以及Co₉S₈的包覆降低了Co（OH）₂向HCoO₂^-的转化，从而使Co的利用率提高，循环稳定性提高。运用水热/溶剂热法制备了系列由具有分级结构的Co颗粒组装而成的链状Co，探讨了反应时间、反应温度及溶剂对产物形貌的影响。制备的Co的最高放电容量为560mAh g^-1，循环120周后，放电容量仍保持在480mAh g^-1，经过与单质硫复合改性后，电化学性能得到进一步提高，Co的链状结构及表面特殊的微纳结构都对其性能的提高都起到了重要作用。第二部分：CoS材料作为超级电容器电极材料的性能研究采用简单的溶剂热法，分别以TAA、CS₂和S粉为硫源合成了纯度较高、结晶良好的花状CoS、花状CoS_1.097和空心球状的CoS₂，研究了反应温度、反应时间和溶剂对产物形貌的影响。作为超级电容器材料，在碱性电解液体系中，CoS、CoS_1.097和CoS₂均体现出了较好的氧化还原赝电容的特性。采用两步法制备Co₃S₄纳米空心球，并成功的合成出Co₃S₄/rGO复合物。研究发现，作为超级电容器材料，Co₃S₄/rGO复合物的最高放电比容量为676.1Fg^-1，经过1000周充放电循环之后仍然维持在610.9F g^-1，容量保持率为90%，性能远远优于Co₃S₄纳米空心球。加入石墨烯之后电化学性质显著提高的主要原因是（a） Co₃S₄纳米空心球与石墨烯之间的相互作用提高了纳米空心球之间、石墨烯网络之间的电子传导率，有利于提高材料的放电容量及倍率性能；（b）以rGO为基底制备的Co₃S₄分散性明显提高，避免了Co₃S₄纳米空心球的团聚，提高了材料的比表面积，从而提高了材料电化学性能。更多还原

【Abstract】 Recently, it is demonstrated that Co-based materials, such as Co-nonmetalcomposites （Co-B, Co-Si, Co-P）, CoO, Co₃O₄and Co（OH）₂possess excellent energystorage properties in alkaline solution. As negative electrode materials for alkalinerechargeable batteries, Co-based materials display high discharge capacity and goodcycle stability. However, the function mechanism of nonmetals on theelectrochemical performances of the Co electrode is rarely reported. Furthermore, theelectrochemical properties of Co-based materials are still needed to be improved.Cobalt oxide and cobalt sulfides are also widely investigated as the electrodematerials for supercapacitors, but the research is not enough in-depth. Similar to theabove Co-based materials, Co-S composites and CoS compound display goodelectrochemical behaviors. And it is easy to prepared the Co-S materials and controltheir morphologies. In view of the above question, Co-S materials are studies asnegative materials for alkaline rechargeable batteries and electrode materials forsupercapacitors.Part1Investigation of Co-S materials as negative materials for alkalinerechargeable batteriesKinds of Co-S composite and CoS compound are prepared by simple mixing, ballmilling and hydrothermal method, respectively. As negative electrode materials foralkaline rechargeable batteries, Co-S composite electrodes display high dischargecapacities of350mAh g1and good cycle stabilities. However, the CoS compoundelectrodes display quite low discharge capacity of40mAh g^-1. The differences of theelectrochemical properties are mainly due to the function of S in the electrodes: forCo-S electrodes, sulfur powders may improve the dispersion of Co particles and theyare easy to dissolve in alkaline aqueous during cycling, further enlarge the contactarea between Co and alkaline solution, which are favorable for improving thedischarge capacities. However, for CoS compound electrodes, the utilization of Co isdecreased because CoS is stable in alkaline solution, showing low discharge capacities.A series of novel Co-S composites composed of metallic Co coated with Co₉S₈areprepared via a facile hydrothermal method and investigated as negative electrodes forsecondary alkaline batteries. Compared with pure Co, the BET surface areas of Co-Scomposites are greatly increased. The maximum discharge capacity of the Co-Selectrode reaches420mAh g^-1and remains at410mAh g^-1after200cycles, while thedischarge capacity of pure Co electrode is only214.5mAh g^-1and rapidly decreases.The increase of the BET surface area and the coating structure of the Co-S compositedo favor for improving the usage of Co in the electrode and the cycling stability.Chainlike Co materials assembled by hierarchical nanostructures are synthesizedvia a facile hydrothermal and solvothermal method. Effects of reaction time,temperature and solvents on the morphologies are studied. The highest dischargecapacity of the as-prepared Co is about560mAh g^-1and it still remains480mAh g^-1after120cycles. The electrochemical properties are further improved by mixing withsulphur powder. The chainlike structures and the special morphology surface texturesare favourable for the improvement of electrochemical properties.Part2Investigation of CoS as electrode materials for supercapacitorsFlower-like CoS, CoS_1.097and CoS₂hollow spheres are prepared by a facilesolvothermal method using TAA, CS₂and S powder as sulfur sources, respectively.Effects of reaction time, temperature and solvents on the morphologies are studied.As the electrode materials for supercapacitors, the as-prepared CoS, CoS_1.097andCoS₂display typical pseudocapacitance performance in KOH aqueous solution.Co₃S₄hollow nanospheres and Co₃S₄/rGO hybrid are described by a noveltwo-step method. Electrochemical measurements reveal that the as-preparedCo₃S₄/rGO composite displays highest discharge capacitance of676.1F g^-1and it stillremains610.9F g^-1after1000cycles, with the capacitance retention rate of90%,which is better than the Co₃S₄hollow nanospheres. Several features make theCo₃S₄/rGO composite for high capacity, excellent rate capability and cycling stability.Firstly, the intimate interaction between the graphene substrates and the Co₃S₄directly anchored on them afford facile electron transport between individual hollowsphere and the conducting graphene network, which is the key to both of the high specific capacitance and the rate capability of Co₃S₄/rGO. The interaction also leadsto a good dispersion of the Co₃S₄grown on the rGO sheets to avoid aggregation,which is also helpful for the improvement of electrochemical properties.更多还原