【作者】 史新妍；

【导师】 张晓；

【作者基本信息】 青岛科技大学 ， 化学， 2023， 硕士

【摘要】 目前,锂价格上涨导致使用锂离子电池（LIBs）的成本增加,因此,寻找新型的替代品迫在眉睫。钠离子电池（SIBs）由于低成本且工作机制与LIBs相似,成为LIBs有潜力的替代品。但是Na⁺的半径比Li⁺大,这意味着一些在LIBs中性能优异的材料无法直接用于SIBs。因此,开发性能优异和稳定的电极材料仍然是电化学领域研究热点。近年来,过渡金属硒化物（TMSs）因其固有的金属特性、独特的二维构型、层状结构和高理论容量等优点成为有潜力的SIBs负极材料。金属掺杂和设计具有异质界面的TMSs被研究者认为是可以有效提高Na⁺存储反应动力学的策略,因为这两种策略可以引起晶格结构膨胀或收缩,减少离子扩散阻碍。本文主要围绕过渡金属硒化物的制备与改性为中心展开储钠性能研究,主要的工作内容和结果如下:（1）采用聚多巴胺（PDA）功能化的Co-MOF作为前驱体,经过高温磷化和硒化来设计氮掺杂碳包覆的Co（PO₃）₂/Co Se₂异质结构。异质结构可以通过促进电荷转移和提高表面电容的贡献率来获得高性能的钠离子电池。异质界面可以提供大量的暴露活性位点,加快Na⁺传输速度;多相协同作用加速Na⁺扩散,促进电荷转移动力学,并增强稳定性。碳包覆使材料在反复循环过程中仍能保证结构完整性。在上述策略的启发下设计的电极,展现出优异的电化学性能,在0.1 A g^-1时表现出333.4 m Ah g^-1的高储钠性能,经过100次循环后容量稳定在310.6 m Ah g^-1,容量保持率约为93.2%;在2 A g^-1进行1000次循环后仍能表现出192.7 m Ah g^-1的可逆容量。（2）采用聚多巴胺（PDA）功能化的Co Mo-MOF作为前驱体,通过高温硒化制备氮掺杂碳包覆的Co掺杂MoSe₂材料。通过优化Co和Mo金属比例得到稳定的材料（Co-MoSe₂（1-5）@PNC）。氮掺杂碳的包覆可以提高容量,同时有效缓解活性物质在循环过程中的体积膨胀,提高稳定性;片状纳米片组成的花状结构增大了材料比表面积;Co的掺杂增加了表面活性位点,加快了Na⁺在表面的嵌入和脱出速率。这些结构的优势,使合成的Co-MoSe₂（1-5）@PNC材料展现出高比容量和循环稳定性(在0.1 A g^-1循环100次后容量稳定在320.1 m Ah g^-1,容量保持率约为88%),以及高倍率性能(5 A g^-1的高电流密度下为210.5 m Ah g^-1)。（3）通过简单的室温陈化法合成普鲁士蓝类似物（Ni Co-PBA）,将其与碳材料高温硒化得到碳改性的Co Se₂和Ni Se₂复合材料（Ni-Co-Se@C）。用碳材料对过渡金属硒化物进行改性,可以增强材料的反应动力学与导电性。Co Se₂和Ni Se₂形成了有利的多相协同体系,可以增强电极的电化学性能。所设计的材料与有较好的电化学性能,在0.1 A g^-1下循环50次容量保持在177.1 m Ah g^-1,循环稳定性较好。更多还原

【Abstract】 Currently,the rising cost of lithium has led to an increase in the cost of using lithium-ion batteries（LIBs）,making it urgent to search for new alternatives.Given the economic volatility of LIBs,sodium ion batteries（SIBs）are potential alternatives to LIBs due to their cost and similar working mechanism to LIBs.However,the larger radius of Na⁺than Li⁺,which means that some materials that perform well in LIBs cannot be used directly in SIBs.Therefore,the development of electrode materials with excellent performance and stability remains a hot topic of research in electrochemistry.Transition metal selenides（TMSs）are being explored as anode materials for SIBs due to their metallic properties,two-dimensional conformation,layered structure,and high theoretical capacity.Metal doping and heterostructure interfaces could improve the kinetics of Na⁺storage reactions in TMSs by inducing lattice expansion or contraction and reducing ion diffusion barriers.In this paper,we focused on the preparation and modification of transition metal selenides for sodium storage applications.The main research work and results are as follows:（1）The N-doped carbon-coated Co（PO₃）₂/Co Se₂ heterostructure was designed via high-temperature selenization by using polydopamine（PDA）-functionalized Co-MOF as a precursor.Heterostructure can achieve high-performance sodium-ion batteries by promoting charge transfer and increasing the contribution of surface capacitance.Heterojunction interfaces can provide a large number of exposed active sites,accelerate Na⁺transport speed.Multiphase synergistic effects accelerates Na⁺diffusion,promotes charge transfer kinetics,and enhances stability.Carbon coating ensures structural integrity of materials during repeated cycling.The electrode designed based on the aforementioned strategy exhibits excellent electrochemical performance.When used as anode of SIBs,Co（PO₃）₂/Co Se₂ could show a high sodium storage capacity of 333.4m Ah g^-1 at 0.1 A g^-1 and maintain a stable capacity of 310.6 m Ah g^-1 after 100 cycles with a capacity retention of about 93.2%.Even after 1000 cycles at 2 A g^-1,it could maintain a reversible capacity of 192.7 m Ah g^-1.（2）N-doped carbon-coated Co-doped MoSe₂ materials were prepared via high-temperature selenization using polydopamine（PDA）functionalized Co Mo-MOF as a precursor.Stable composite materials（Co-MoSe₂（1-5）@PNC）were obtained by optimizing the Co and Mo metal ratios.The N-doped carbon coating can increase the capacity and effectively alleviate volume expansion of active materials during cycling process,improving electrode stability.The flower-shaped structure composed of sheet-like nanosheets increases the specific surface area.Co-doping increases the surface active sites and accelerates Na⁺insertion and extraction rates on the surface.The advantages of these structures enable the synthesized Co-MoSe₂（1-5）@PNC composite material to exhibit high specific capacity,cycling stability and high rate performance.The capacity remains stable at 320.1 m Ah g^-1 after 100 cycles at 0.1 A g^-1,with a capacity retention rate of about 88%,and the specific capacity is 210.5 m Ah g^-1 at a high current density of 5 A g^-1.（3）A Prussian blue analogue（Ni Co-PBA）synthesised by a simple room temperature ageing method was used as a precursor,which was selenised at high temperature with carbon material to obtain carbon modified Co Se₂ and Ni Se₂composites（Ni-Co-Se@C）.The modification of transition metal selenides with carbon materials enhances the reaction kinetics and electrical conductivity of the materials.The Co Se₂ and Ni Se₂ phases in the material form a favourable multiphase synergistic system that enhances the electrochemical performance of the electrodes.The designed material shows better electrochemical performance than the control material,with a capacity retention of 177.1 m Ah g^-1 after 50 cycles at 0.1 A g^-1and good cycle stability.更多还原