【作者】 宋宁；

【导师】 张乃庆；

【作者基本信息】 哈尔滨工业大学 ， 化学工程与技术， 2019， 硕士

【摘要】 目前商业化的锂离子电池使用了有机电解液,存在着易燃易爆等危险。随着锂离子电池在大规模储能系统中的应用,电池的安全问题应得到更高的重视。使用固态电解质取代传统的有机电解液可大幅提升电池的安全性。固态电解质可分为无机材料和有机聚合物材料两种。无机电解质中Li₇La₃Zr₂O₁₂（LLZO）具有离子电导率高、对锂稳定性好、电化学窗口宽、机械性能优异等优点。但无机电解质存在较大脆性,且与电极间为固固相接触存在较大的界面阻抗,在短期内难以得到大规模应用。聚合物电解质与电极接触阻抗小,但室温下离子电导率过低限制了使用。此外还存在着对Li稳定性差、Li迁移数低等问题。本文通过将无机电解质材料LLZO与聚合物电解质PEO复合,结合两者的优点,制备出综合性能优异的复合电解质。并装配全固态电池进行电化学性能研究。主要研究内容包括:（1）采用固相反应法制备Al掺杂立方相LLZO电解质片,探究了Li含量、Al₂O₃添加量、烧结温度、保温时间对LLZO成相的影响。通过在原料中添加20%过量Li源,1mass%Al₂O₃在1100℃下保温15h制备出了Al-LLZO立方相电解质片。离子电导率为4.84×10^-4S/cm,致密度为90.8%,锂传导活化能为0.31eV。（2）在前文的基础上,通过Al、Ta共掺杂进一步改性,提高电解质的性能。制备组成为Li_6.35La₃Zr_1.8Ta_0.2Al_0.15O₁₂的LLZO电解质,离子电导率提高到7.31×10^-4S/cm,致密度为94.9%,锂传导活化能降低至0.29eV。装配Li|Li对称电池,通过共掺杂将极限电流密度提升至0.1mA/cm²。装配LiFePO₄|LLZO|Li全电池,在0.5C电流下循环50圈后全电池放电比容量由152.3mAh/g降低至99.1mAh/g,容量保持率为65.1%。在1C的电流下循环50圈后,放电比容量由149.9mAh/g降低至92.8mAh/g,容量保持率为61.2%。（3）制备了PEO/LiTFSI聚合物电解质,在EO:Li的摩尔比为16:1时得到综合性能最为优异的聚合物电解质,室温下离子电导率为1.16×10^-5S/cm。将LLZO与PEO复合,制备复合电解质,当LLZO添加量为30mass%时性能最佳。通过添加LLZO活性填料,将室温下离子电导率提升至3.08×10^-5S/cm。此外,复合电解质将对Li稳定电压由4.3V提升至4.8V,提高了Li界面的稳定性。装配LiFePO₄|SPE|Li全固态电池在50℃下进行充放电循环测试,在0.5C的电流下循环100圈后,放电比容量由151.8mAh/g降至137.6mAh/g,容量保持率为90.6%。在1C的电流下循环50圈后,容量由142.9mAh/g降至126.9mAh/g,容量保持率为88.8%。更多还原

【Abstract】 At present,commercial lithium-ion batteries use organic electrolytes,which are flammable and explosive.With the application of lithium-ion batteries in large-scale energy storage systems,the safety of lithium-ion batteries should be given higher attention.Using solid electrolyte instead of traditional organic electrolyte can greatly improve the safety of lithium ion batteries.Solid electrolyte can be divided into inorganic material and organic polymer material.Among the inorganic electrolytes,Li₇La₃Zr₂O₁₂（LLZO）has the advantages of high ionic conductivity,good stability to lithium,wide electrochemical window and excellent mechanical properties at room temperature.However,inorganic electrolytes are brittle and have large interface impedance with electrodes,which makes it difficult to be widely used in a short time.The polymer electrolyte has a small contact resistance with the electrode,but the ion conductivity is too low at room temperature which limits its use.In this paper,the inorganic electrolyte LLZO and the polymer electrolyte PEO were combined to prepare the composite electrolyte with excellent comprehensive performance.And then assemble the all-solid-state batteries to study the electrochemical performance.The main work includes:（1）Al-doped cubic LLZO electrolyte was prepared by solid-state reaction.The effects of Li content,Al₂O₃ addition amount,sintering temperature and time on the phase formation of LLZO were investigated.Al-LLZO cubic phase electrolyte was prepared by adding 20%excess Li source and 1 mass%Al₂O₃ for 15 hours at 1100 C.Al-LLZO cubic phase electrolyte was prepared by adding 20%excess Li source and 1 mass%Al₂O₃ to the raw material and calcining at 1100 C for 15h.At room temperature,the ionic conductivity is 4.84×10^-4S/cm,the density is 90.8%,and the activation energy of lithium conduction is 0.31eV.（2）On the basis of the previous work,the properties of electrolyte were further improved by co-doping Al and Ta.The LLZO electrolyte consisting of Li Li_6.35La₃Zr_1.8Ta_0.2Al_0.15O₁₂2 was prepared.The ionic conductivity was increased to7.31×10^-4S/cm at room temperature,the density was 94.9%,and the lithium conduction activation energy was reduced to 0.29eV.Li|Li symmetrical battery was assembled,and the limiting current density was increased to 0.1mA/cm² by co-doping.LiFePO₄|LLZO|Li all-solid-state battery was assembled.After 50 cycles at 0.5C current,the specific discharge capacity of the battery was reduced from 152.3mAh/g to 99.1mAh/g,and the capacity retention rate was 65.1%.After 50 cycles at 1C current,the discharge specific capacity decreased from 149.9mAh/g to 92.8mAh/g,and the capacity retention rate was61.2%.（3）PEO/LiTFSI polymer electrolyte was prepared,and the polymer electrolyte with the best comprehensive performance was obtained when the molar ratio of EO:Li is 16:1.And the ionic conductivity is 1.16×10^-5S/cm at room temperature.Then LLZO and PEO were compounded to prepare composite electrolyte.The performance was best when the amount of LLZO added was 30 mass%.By adding LLZO filler,the ionic conductivity was increased to 3.08×10^-5S/cm at room temperature.In addition,the composite electrolyte can increase the stability voltage from 4.3V to 4.8V,which improves the stability of Li interface.The charge-discharge cycle of LiFePO4|SPE|Li solid-state battery was tested at 50℃.After 100 cycles at 0.5C,the specific discharge capacity decreased from 151.8mAh/g to 137.6mAh/g,and the capacity retention rate was 90.6%.After 50cycles at 1C current,the capacity decreased from 142.9mAh/g to 126.9mAh/g and the capacity retention rate was 88.8%.更多还原