热电池正极材料表面重构柔性中空碳泡层抑制界面钝化层形成机制研究

Thermal batteries use molten salts as electrolytes, which are widely used in guided missiles, space exploration and underground mining due to their high energy density and long shelf life. The transition-metal disulfides (FeS2 and CoS2) have become commercial cathode materials of thermal battery. However, the high resistance and low thermal stability of FeS2, high cost and low voltage of CoS2 limit the discharge performances of thermal battery. NiS2 with low-cost have been considered to be attractive alternatives because the thermal stability and discharge performance of NiS2 is intermediate between that of FeS2 and CoS2..However, the interfacial passivation layer is easy to be formed by the aggregation of discharge products between NiS2 cathode and electrolyte, which not only results in high discharge voltage attenuation, but also causes security problems. In this project, the high voltage attenuation of NiS2 cathode materials will be studied in thermal battery. The micro/nano- NiS2/C composite cathode materials will be synthesized by the metal salt-assisted polymer-blow process, the nano-sized flexible hollow carbon bubble layer of composite cathode materials surface will be constructed by the activation of KOH and micro-corrosion of HCl. On the one hand, the volume shrinkage and interfacial separation of electrode would be reduced by rebuilding the micro-structure of cathode materials surface. On the other hand, confinement effect of flexible hollow carbon bubble layer would suppress the migration of discharge products and improve the interfacial stability. Grasping the method of rebuilding the structure of flexible hollow carbon bubble layer base on synthesizing kinetic factors. The micro/nano- NiS2/C composite cathode materials with high thermal stability ( 620 ℃) and high tap density (1.7 g cm-3) are synthesized by the above method. Clearing the relationship of between flexible hollow carbon bubble layer structure, interfacial stability and performances by in-situ (contact angle meter) and ex-situ characterization methods. Revealing the mechanism of optimizing the interfacial structure and performances by interfacial evolution. Expounding the mechanism of that the formation of inert passivation layer is suppressed by flexible hollow carbon bubble layer. Realizing the sustainable discharge of micro/nano- NiS2/C composite cathode materials with high voltage in thermal battery. .Based on the above researches, the project would not only provide examples for the preparation of cathode materials with high specific energy and high temperature molten salt electrochemistry theory, but also expand the application of in-situ method and flexible hollow carbon bubble layer in other batteries.

热电池是以常温不导电，高温高导电的熔融盐为电解质，采用热激活的一次性电池，因其具有比能量高、储存时间长且耐高自旋强震动等特点，被广泛应用于导弹、深海探测及采矿等领域。过渡金属硫化物（FeS2和CoS2）是已商业化的热电池正极材料，然而FeS2正极的低热稳定性和高电阻，CoS2正极的低电压和高成本始终限制着热电池性能的提升。NiS2的放电性能及成本均处于FeS2和CoS2之间，被认为是下一代高性能热电池的理想正极材料。.申请者前期研究发现，热电池NiS2正极-电解质界面易形成一层以放电产物Ni单质和Li2S为主要成分的钝化层，不仅会导致热电池高电压衰减，还引发安全问题。因此，本项目以缓解热电池NiS2正极高电压衰减为目的，拟采用金属盐辅助聚合物吹塑法预先制备微纳NiS2/C复合正极材料，并经KOH活化和HCl微刻蚀在其表面重构纳米级柔性中空碳泡层。一方面通过重构微纳NiS2/C材料表面微结构来缓解正极体积收缩，防止界面分离，降低界面电阻；另一方面借助柔性中空碳泡层的限域效应抑制放电产物迁移，提高界面稳定性。掌握合成动力学因素调控柔性中空碳泡层结构的方法，制备热稳定性高于620 ℃且振实密度高于1.7 g cm-2的高性能微纳NiS2/C复合正极材料，研究不同使役条件下，不同尺寸的柔性中空碳泡层缓解高电压衰减的效果，基于改造后接触角测试仪原位表征热电池放电过程中的界面变化，并结合非原位表征方法研究微观材料界面钝化层抑制机理，明晰柔性中空碳泡层结构-界面稳定性-性能间的构效关系，揭示界面演变优化材料结构及性能的机理，阐明柔性中空碳泡层抑制界面钝化层形成机制，以实现热电池微纳NiS2/C正极高电压的可持续放电。.该项目不仅可为制备热电池高性能复合正极材料和完善高温熔盐电化学理论提供范例，还可拓展接触角测试仪原位表征手段及柔性中空碳泡层结构在其他电池领域的应用。

热电池是一类重要的特种化学电源，以NiS2为代表的过渡金属硫化物正极材料虽具有较高的比容量，然而其高电压的快速衰减限制了热电池性能的提高。本项目旨在以NiS2为研究对象，通过KOH活化和HCl微刻蚀在微纳NiS2/C表面重构一层厚度可控的纳米级柔性中空碳泡层，抑制电压衰减。主要研究内容和结果如下：.1）建立中空碳泡层结构提高热电池用微纳NiS2/C正极性能的理论模型。一方面，柔性中空碳泡层能够缓解电极的体积变化，提高界面物理稳定性; 另一方面，通过柔性中空碳泡层的结构限域效应抑制放电产物的迁移，提高界面化学稳定性，进而降低界面电阻，缓解热电池NiS2正极材料的高电压衰减，提高其比能量。.2）构建高性能热电池用NiS2薄膜电极。针对项目中碳添加导致压片电极脱粉、断裂等缺陷，以碳纤维为基底，原位构建厚度可调的NiS2薄膜电极，并研究了其在低电流密度下，超高比容量的放电机制，为热电池用CFx电极材料的应用提供了理论支撑。.3）明晰热电池NiS2正极材料结构与性能的构效关系。受限于熔盐缺陷，多级微纳NiS2电极粉末并不适合热电池体系，纳米NiS2和微纳NiS2粉末由于能够与熔盐充分混合，表现出较高的放电性能。此外，高温烧结可调控NiS2与熔盐之间的界面接触，可提高离子传导能力和增加界面电荷转移通道，为进一步提高热电池性能具有重要意义。.4）高性能热电池用V2O5正极材料的研究。针对MgO粘接剂降低电极电子传输能力, 创新性采用多级结构的限域效应构建了热电池用无粘接剂型V2O5/熔盐电极，提高电极电子传输能力，从而增大比能量。针对热电池V2O5正极活性材料、熔盐和电子导电剂之间存在界面孔隙，阻碍了界面电荷的快速转换。我们设计了一种快速高温焊接策略，重构了界面电荷传输通道，提高了界面电荷传输动力学。该研究为通过在电极中构建高效电荷传输动力学增强热电池放电性能提供了理论依据。