【作者】 李敏；

【导师】 刘海萍；

【作者基本信息】 哈尔滨工业大学 ， 材料与化工（专业学位）， 2025， 硕士

【摘要】 随着全球新能源产业向高纬度、高海拔等极端环境拓展,锂离子电池的低温性能面临越来越严峻的挑战。然而,传统碳酸酯基锂离子电池在低温中（-20℃以下）,普遍存在放电容量衰减、循环寿命缩短等问题,严重制约低温供能装备发展。虽然优化电解液体系能降低电解液的凝固点、抑制电极/电解液界面副反应、提升高电压正极材料结构稳定性,但现有设计往往以损害电解液的高温稳定性为代价。为此,本研究采用“多元溶剂降凝-双锂盐协同解离-多添加剂调控界面”三位一体策略,协同提升电池的低温性能与高温/高电压稳定性。首先,引入低熔点、低黏度的乙酸丙酯（PA）、高介电常数的碳酸乙烯酯（EC）和抗氧化电位较高的碳酸甲乙酯（EMC）,以双氟磺酰亚胺锂（Li FSI）部分替代Li PF₆,使-50℃电解液的电导率仍>1 m S cm^-1。在添加剂方面,碳酸亚乙烯酯（VC）、氟代碳酸乙烯酯（FEC）、硫酸乙烯酯（DTD）和二氟磷酸锂（Li PO₂F₂）共同作用调控负极界面,使18650电池0.5C的放电容量>室温容量的90%（-40℃）。此外,HTCN（1,3,6己烷三腈）在高电压条件下（4.4 V）参与正极/电解质界面（CEI）的构建,有效地保障了高电压体系下的循环稳定性,使18650电池0.5C循环500次后的容量保持率>90%。其次,调整双锂盐及三元溶剂的组成比例,使电解液兼具低温解离与电极兼容性,进一步降低了电解液的黏度（40.25 m Pa s,-40℃）,凝固点也降至-60℃以下,显著地改善了低温环境下的离子迁移环境。进一步添加双氟代碳酸乙烯酯（DFEC）和碳酸乙烯亚乙酯（VEC）,在负极表面构建由聚合物薄层包裹、富含Li F等无机成分的梯度固体电解质界面（SEI）,凭借优异的离子传导性与机械韧性,使18650电池在-60℃以0.5C放电时,容量达室温的80%以上;-40℃循环100次后,容量保持率仍超80%。同时,HTCN与三甲基硅烷磷酸酯（TMSP）协同作用抑制了电池在60℃环境中的产气。此外,本研究综合运用差示扫描量热法（DSC）、粘度测试、拉曼光谱（Raman）,以及X射线光电子能谱（XPS）、透射电子显微镜（TEM）和扫描电子显微镜（SEM）等表征技术,对电解液及固体电解质界面（SEI）进行多尺度分析。同时,结合量子化学计算所得的电解液各组分分子前线轨道能级数据,探究电解液组成与电池性能间的内在联系,解析各组分在改善电池低温性能、提升高温稳定性过程中的作用机制。最后,本研究结合低温锂离子电池领域的产业政策导向与市场应用现状,分析了本研究电解液的原料成本、工艺成本与应用价值。证实了本研究电解液不仅在电解液配方、添加剂应用和界面调控上具有创新性,而且兼具经济性与可行性,具有重要的工程应用价值与学术意义。更多还原

【Abstract】 As the global new energy industry expands into extreme environments like high latitudes and high altitudes,the low-temperature performance of lithium-ion batteries（LIBs）faces increasingly severe challenges.However,traditional carbonate-based LIBs commonly suffer from significant discharge capacity fading and shortened cycle life at low temperatures（below-20℃）,severely constraining the development of low-temperature power supply equipment.While optimizing the electrolyte system can lower the freezing point,suppress side reactions at the electrode/electrolyte interface,and enhance the structural stability of high-voltage cathode materials,existing designs often compromise the high-temperature stability of the electrolyte.To address this,this study employs a ternary strategy of“Multi-solvent Freezing Point Depression-Dual-Li-salt Synergistic Dissociation-Multi-additive Interface Regulation”to synergistically enhance both the low-temperature performance and high-temperature/high-voltage stability of batteries.Firstly,propyl acetate（PA）with a low melting point and low viscosity,ethylene carbonate（EC）with a high dielectric constant,and ethyl methyl carbonate（EMC）with a relatively high oxidation resistance potential are introduced.Lithium bis（fluorosulfonyl）imide（Li FSI）is used to partially replace Li PF₆,ensuring that the conductivity of the electrolyte at-50℃is still greater than 1 m S cm^-1 For additives,synergistic effects of vinylene carbonate（VC）,fluoroethylene carbonate（FEC）,ethylene sulfate（DTD）,and lithium difluorophosphate（Li PO₂F₂）regulated the anode interface,enabling 18650 batteries to deliver>90%of room-temperature capacity at 0.5C discharge rate（-40℃）.Moreover,HTCN（1,3,6-hexanetricarbonitrile）formed a dense cathode electrolyte interphase（CEI）under high voltage（4.4 V）,effectively ensuring cycling stability in high-voltage systems,achieving>90%capacity retention after 500 cycles at0.5C for 18650 batteries.Secondly,adjusting the composition ratio of dual lithium salts and ternary solvents endowed the electrolyte with both low-temperature dissociation capability and electrode compatibility.This further reduced electrolyte viscosity（40.25 m Pa s at-40℃）and depressed freezing point below-60℃,significantly improving ionic migration environment in low-temperature conditions.Additional introduction of difluoroethylene carbonate（DFEC）and vinylethylene carbonate（VEC）constructed gradient solid electrolyte interphase（SEI）with polymer thin-layer encapsulation and Li F-rich inorganic components on anode surfaces.Benefiting from excellent ionic conductivity and mechanical toughness,18650 batteries achieved>80%of room-temperature capacity at0.5C discharge rate（-60℃）,maintaining>80%capacity retention after 100 cycles（-40℃）.Simultaneously,synergistic effects of HTCN and trimethylsilyl phosphate（TMSP）effectively suppressed gas generation in 60℃environments.Additionally,this study employed comprehensive characterization techniques including Differential Scanning Calorimetry（DSC）,viscosity testing,Raman spectroscopy,X-ray Photoelectron Spectroscopy（XPS）,Transmission Electron Microscopy（TEM）,and Scanning Electron Microscopy（SEM）for multi-scale analysis of the electrolyte and SEI.Combined with quantum chemical calculations providing frontier molecular orbital energy levels of electrolyte components,this elucidated the intrinsic links between electrolyte composition and battery performance,revealing the mechanistic roles of each component in improving low-temperature performance and enhancing high-temperature stability.Finally,considering industrial policy orientations and market applications in low-temperature lithium-ion battery field,this study systematically analyzed raw material costs,process costs,and application value of the proposed electrolyte.Results confirmed that the electrolyte demonstrates innovation in formulation design,additive application,and interface regulation while maintaining economic feasibility and practicality,exhibiting significant engineering application value and academic significance.更多还原