基于转化型复合材料结构调控及其储钠机制研究

【作者】 李慧；

【导师】 李昭莹； 马春荣；

【作者基本信息】 青岛大学 ， 动力工程（专业学位）， 2025， 硕士

【摘要】 随着全球能源需求的持续增长以及储能应用场景的日益多样化,钠离子电池凭借资源丰富、成本低廉和本征安全性高等优势,正逐步成为锂离子电池的有力替代技术。电极材料作为电池的核心组成,对电化学性能具有决定性影响。目前,钠离子电池的正极材料研究已取得较大进展,然而兼具高倍率性能与长循环寿命的负极材料仍面临诸多挑战。商业化硬碳在倍率性能与循环稳定性之间难以兼顾,而转化型过渡金属硫/硒化物由于具备层状结构和较高理论容量,成为研究热点。但其在充放电过程中易发生严重的体积膨胀和缓慢的动力学过程,导致结构粉化、多硫化物穿梭效应以及初始库伦效率低下等关键问题,限制了其实际应用。针对上述瓶颈,本研究以过渡金属化合物为模型体系,围绕多硫化物穿梭、电子/离子传导性差及体积效应等核心问题,提出表/界面异质结构协同调控策略,通过优化材料的本征结构与界面反应动力学,系统探究其储钠机制。具体研究内容包括:（1）针对二硫化钼在钠离子存储中的结构稳定性差与动力学缓慢问题,提出表/界面协同催化机制。通过在二硫化钼为片层结构中引入单原子Co（Co-MoS₂/SC）,诱导MoS₂产生2H→1T相变,削弱Mo-S键强度并重构Mo 4d轨道电子分布,从而显著降低Na⁺扩散势垒。与此同时晶格内形成的Co-S-C活性位点可催化Na PF₆/DME电解液中P-F和C-O键断裂,快速构建超薄且导电性优异的SEI层,抑制多硫化物溶解及界面副反应。单原子Co位点的自催化特性进一步增强转化反应的可逆性。该Co-MoS₂/SC复合负极在20 A g^-1下比容量达288 mAh g^-1,在10 A g^-1下循环2000次后容量保持率为96.2%,实现了结构稳定性与界面反应动力学的协同优化。该机制经密度泛函理论计算与实验验证得以确认。（2）针对多硫化物穿梭效应,构建了TiO₂纳米颗粒修饰的MoS₂/碳纳米管复合电极（CNT-MoS₂/TiO₂-C）。研究发现,TiO₂与MoS₂之间具有较高的界面结合能,可有效锚定Na₂S等中间产物,抑制多硫化物溶解及团聚导致的容量衰减。同时,异质界面诱导的储钠机制由传统相变向固溶体-赝电容协同模式转变,显著提升Na⁺扩散速率。原位表征与第一性原理计算揭示,TiO₂/MoS₂界面可重构电子局域化分布,降低Na⁺吸附能并缩短扩散路径,显著提高界面反应动力学。该材料在0.2 A g^-1下展现出540 mAh g^-1的高可逆容量,在5 A g^-1下循环3000次后容量保持率达89%,在10 A g^-1倍率条件下容量保持率超过90%。（3）通过电化学驱动原位构建了具有原子级别接触面的FeSe/Fe S异质结构嵌入硫掺杂的碳中（FeSe/Fe S-SC）。原位XRD与非原位TEM表征证实,异质界面通过诱导Na₂S/Na₂Se复合相的稳定生成,缓解多硒化物溶解并缩短Na⁺扩散路径。²³Na固体核磁分析表明,S/Se双阴离子界面提供了额外的钠存储活性位点,显著提升复合材料的比容量,与此同时,界面内建电场则加快了电荷转移速率。使得该材料在1 A g^-1下展现出498 mAh g^-1的高可逆容量,在15 A g^-1仍保持421 mAh g^-1,并在3A g-1下循环3000次后容量保持率达82.4%。更多还原

【Abstract】 With the continuous growth of global energy demands and increasing diversification of energy storage applications,sodium-ion batteries（SIBs）are emerging as a promising alternative to lithium-ion batteries due to their resource abundance,cost-effectiveness,and intrinsic safety.As the core component determining electrochemical performance,electrode materials play a pivotal role.While significant progress has been achieved in cathode materials for SIBs,the development of anode materials combining high-rate capability with long-term cyclability remains challenging.Commercial hard carbon struggles to balance rate performance and cycling stability,whereas conversion-type transition metal sulfides/selenides have attracted extensive attention owing to their layered structures and high theoretical capacities.However,their practical applications are hindered by severe volume expansion,sluggish kinetics during cycling,structural pulverization,polysulfide shuttling effects,and low initial Coulombic efficiency.To address these limitations,this study focuses on transition metal compounds as model systems and proposes a heterostructure engineering strategy for synergistic regulation of surface/interface properties,aiming to optimize intrinsic structures and interfacial reaction kinetics while systematically investigating sodium storage mechanisms.The research comprises three main aspects:（1）To address the poor structural stability and sluggish kinetics of MoS₂ in sodium storage,a surface/interface synergistic catalytic mechanism was proposed.By introducing single-atom Co into MoS₂ nanosheets（Co-MoS₂/SC）,the 2H→1T phase transition of MoS₂was induced,which weakened Mo-S bond strength and reconstructed the electron distribution of Mo 4d orbitals,thereby significantly reducing Na⁺diffusion barriers.Simultaneously,the Co-S-C active sites formed in the lattice catalyzed the cleavage of P-F and C-O bonds in Na PF₆/DME electrolyte,enabling rapid formation of an ultra-thin and highly conductive SEI layer to suppress polysulfide dissolution and interfacial side reactions.The self-catalytic properties of single-atom Co sites further enhanced the reversibility of conversion reactions.The Co-MoS₂/SC composite anode delivered a specific capacity of 288 mAh g^-1 at 20 A g^-1 and maintained 96.2%capacity retention after2000 cycles at 10 A g^-1,achieving synergistic optimization of structural stability and interfacial kinetics.This mechanism was confirmed by density functional theory（DFT）calculations and experimental validation.（2）For suppressing polysulfide shuttling,a TiO₂ nanoparticle-decorated MoS₂/carbon nanotube composite electrode（CNT-MoS₂/TiO₂-C）was constructed.The strong interfacial binding energy between TiO₂ and MoS₂ effectively anchored Na₂S intermediates,mitigating capacity fading caused by polysulfide dissolution and aggregation.Moreover,the heterointerface induced a transition from conventional phase-transformation to solid-solution-pseudocapacitance synergistic sodium storage mechanisms,significantly enhancing Na⁺diffusion rates.In situ characterization and first-principles calculations revealed that the TiO₂/MoS₂ interface reconstructed electron localization distributions,reduced Na+ adsorption energy,and shortened diffusion pathways,thereby boosting interfacial reaction kinetics.This material exhibited a high reversible capacity of 540 mAh g^-1 at 0.2 A g^-1 with 89%capacity retention after 3000 cycles at 5 A g^-1,maintaining over90%capacity retention even at 10 A g^-1.（3）An electrochemically driven in situ construction strategy was developed to fabricate FeSe/Fe S heterostructures with atomic-level contact interfaces embedded in sulfur-doped carbon（FeSe/Fe S-SC）.In situ XRD and ex situ TEM analyses confirmed that heterointerfaces stabilized Na₂S/Na₂Se composite phases through interfacial induction,alleviating polyselenide dissolution and shortening Na⁺diffusion paths.²³Na solid-state NMR analysis demonstrated that S/Se dual-anion interfaces provided additional sodium storage active sites,significantly improving specific capacity,while built-in electric fields accelerated charge transfer rates.Consequently,the composite delivered a high reversible capacity of 498 mAh g^-1 at 1 A g^-1,retained 421 mAh g^-1 at 15 A g^-1,and achieved 82.4%capacity retention after 3000 cycles at 3 A g^-1.更多还原