【作者】 王琳；

【导师】 蒋青青；

【作者基本信息】 中南民族大学 ， 物理化学， 2022， 硕士

【摘要】 锂离子电池（LIBs）因高能量密度被广泛应用。然而,锂资源有限且分布不均,锂离子电池替代体系的研究受到广泛关注。钾离子电池（PIBs）和LIBs工作原理相似,且钾资源储量丰富,其氧化还原电位与锂更为接近（K⁺/K:-2.93 V vs.Li⁺/Li:-3.04 V）。钾离子半径大（1.38?）,造成嵌入/脱嵌过程中电极材料体积变化严重,扩散动力学迟缓,循环稳定性差,倍率容量低。开发低成本、可大规模制备且具有优异电化学性能的PIBs电极材料是推动PIBs发展的关键。本文为设计开发高效率的负极材料进行了以下研究工作:（1）N掺杂提高碳基体电导率;（2）中空结构增加材料与电解质的有效接触面积;（3）金属硒/硫化物提高电导率和可逆容量;（4）层状双氢氧化物（LDH）丰富K⁺扩散途径。MoSe₂在加速K⁺嵌入/脱嵌方面很有潜力,但纯MoSe₂电导率低且在长循环过程中有团聚现象。在第二章中采用简单的溶剂热法将MoSe₂纳米片生长在N掺杂多孔碳多面体（NPCP）上,两者的协同作用可以有效防止MoSe₂纳米片的团聚。N掺杂增强碳基体的导电性,扩大碳基的层间距,为K⁺提供潜在的结合活性位点。通过电化学性能发现,NPCP@MoSe₂核-壳复合材料比纯MoSe₂具有更高的初始性能以及更好的循环和倍率性能。在第三章中设计合成了一种具有碳纳米管（CNTs）的硒化钴/空心碳多面体材料。首先制备多面体核壳拓扑结构的ZIF-8@ZIF-67作为前驱体,将前驱体高温煅烧得到表面分布CNTs的空心碳多面体（Co@CNNCP）,最后硒化得到Co-Se@CNNCP。在0.1 A g^-1电流密度下,80次循环后其比容量为410 m A h g^-1;在0.5 A g^-1电流密度下,200次循环后其比容量为253 m A h g^-1,容量保持率为100%。基于循环伏安曲线的反应动力学分析表明,电化学过程主要由赝电容贡献。碳纳米管能够抑制金属硒化物颗粒的团聚,空心碳多面体在重复的K⁺嵌入/脱嵌过程中有助于保持结构的完整性,保证了Co-Se@CNNCP的长循环稳定性。第四章中采用自模板原位转化策略,引入镍离子刻蚀ZIF-67,获得表面均匀分布LDH纳米片的十二面体纳米笼。硫化处理后,Co₉S₈纳米颗粒均匀且紧密地嵌在LDH壳层中（LDH-S）。最后通过简单的水热方法将碳点（CDs）锚定在LDH-S上（CDs@LDH-S）。LDH-S在0.1 A g^-1时的初始放电/充电容量分别为1387 m A h g^-1和582m A h g^-1,经过200次循环后,容量损耗为33%。CDs@LDH-S在0.5 A g^-1的电流密度下,循环1000次后的容量可达200 m A h g^-1。中空多孔结构保证了电解液与电极材料的密切接触,缩短了钾离子扩散长度。均匀分布的高导电超细Co₉S₈颗粒形成一个导电网络,加速电子和离子的有效传输。CDs的存在进一步提高电极导电性,稳定电极结构。通过非原位表征证明了LDH基电极中Co³⁺/Co²⁺和Ni²⁺/Ni³⁺的可逆价态变化和钾离子嵌入/提取时的结构稳定性。借助密度泛函理论（DFT）计算确定了低能量势垒（<0.36 e V）的LDH层之间有利的转移路径。更多还原

【Abstract】 Lithium-ion batteries（LIBs）are widely used due to the high energy density.However,the research on the alternatives of LIBs has received extensive attention because of the limited and uneven distribution of lithium resources.Potassium-ion batteries（PIBs）are similar to LIBs in terms of working principle.Potassium is abundant and its redox potential is very close to that of lithium（K⁺/K:-2.93 V vs.Li⁺/Li:-3.04 V）.Whereas,the large radius of potassium ions（1.38?）results in severe volume changes of electrode materials,sluggish diffusion kinetics,poor cycling stability and low rate capacity during insertion/extraction process.The key factor of the development of PIBs is to exploit low-cost and mass-produced PIBs electrode materials with excellent electrochemical performance.In order to design and develop high-efficiency anode materials,the following research are carried out in this paper:（1）N doping improves the conductivity of carbon matrix;（2）hollow structure increases the effective contact area between the material and the electrolyte;（3）metal selenium/sulfide improves conductivity and reversible capacity;（4）layered double hydroxide（LDH）enriches the K⁺diffusion pathway.MoSe₂ has great potential in accelerating K⁺insertion/extraction,but pure MoSe₂ has low electrical conductivity and agglomerates during long cycling.In Chapter 2,MoSe₂nanosheets are grown on N-doped porous carbon polyhedra（NPCP）by a simple solvothermal method.The synergistic effect of MoSe₂and NPCP can prevent the agglomeration of MoSe₂nanosheets.N doping enhances the conductivity of the carbon matrix,expands the interlayer spacing,and provides potential binding active sites for K⁺.The NPCP@MoSe₂ core-shell nano-architectures display higher initial performance,better cycling stability and superior rate performance than pure MoSe₂.In Chapter 3,a cobalt selenide/hollow carbon polyhedron material with carbon nanotubes（CNTs）is designed and synthesized.Firstly,ZIF-8@ZIF-67 with polyhedral core-shell topology is synthesized as a precursor.Then the precursor is calcined at high temperature to obtain a hollow carbon polyhedron with CNTs on the surface（Co@CNNCP）.Finally,the Co-Se@CNNCP is obtained by selenization.The specific capacity is 410 m A h g^-1over 80 cycles at 0.1 A g^-1.At 0.5 A g^-1,the specific capacity is 253 m A h g^-1 after 200 cycles with a capacity retention of 100%.The kinetic analysis based on cyclic voltammetry proves the electrochemical process is mainly contributed by pseudocapacitance.The cycling stability of Co-Se@CNNCP mainly relies on carbon nanotubes which inhibit the agglomeration of metal selenide nanoparticles and maintain the structural integrity of hollow carbon polyhedra during the processes of K⁺insertion/extraction.In Chapter 4,ZIF-67 is etched by nickel ions via a self-template in situ transformation strategy to obtain dodecahedral nanocages with uniformly distributed LDH nanosheets on the surface.After sulfuration treatment,Co₉S₈ nanoparticles are embedded on the LDH nanocages（LDH-S）tightly.Finally,carbon dots（CDs）are anchored on LDH-S by a simple hydrothermal method（CDs@LDH-S）.The initial discharge/charge capacities of LDH-S at 0.1A g^-1 are 1387 m A h g^-1 and 582 m A h g^-1 respectively,with 33%capacity loss after 200cycles.The CDs@LDH-S exhibites a capacity of 200 m A h g^-1 after 1000 cycles at 0.5 A g^-1.The hollow porous structure not only ensures the close contact between the electrolyte and the electrode material,but also shortens the diffusion length of potassium ions.The uniformly distributed ultrafine Co₉S₈ forms a conductive network that accelerates the efficient transport of electrons and ions.The presence of CDs further improves the electrode conductivity and structural stability.Ex-situ characterizations prove the reversible valence changes of Co³⁺/Co²⁺and Ni²⁺/Ni³⁺in LDH-based electrodes and the structural stability during intercalation/extraction of K⁺.Favorable transfer paths between LDH layers with low energy barriers（<0.36 e V）are identified by density functional theory（DFT）calculations.更多还原