【作者】 陈玉红；

【导师】 唐致远；

【作者基本信息】 天津大学 ， 应用化学， 2007， 博士

【摘要】 本文围绕锂离子电池爆炸机理及安全性改进这一主题展开了热稳定性好的正极材料Li_xNi_1/3Co_1/3Mn_1/3O₂的合成与改性、防过充剂和阻燃剂的研究。首次对Li_xNi_1/3Co_1/3Mn_1/3O₂的电极反应动力学进行了系统的研究;首次通过阴阳离子Cl^-、Br^-、Zn²⁺、Zr⁴⁺、Ge⁴⁺掺杂和Mg₂（PO₄）₃包覆对Li_xNi_1/3Co_1/3Mn_1/3O₂的动力性和热稳定性进行改性研究;首次把TCEP阻燃剂和环己苯防过充添加剂协同用在自主设计的F型锂离子动力电池中。本工作主要围绕以下几方面工作进行:在对锂离子电池内部产热根源分析的基础上,探讨了锂离子电池在高温、过充以及短路状态下的爆炸机理。发现嵌锂碳与溶剂、电解液热分解和正极热分解反应是诱发电池高温加热时爆炸的主要原因;过充时,过量的锂离子沉积在负极表面,嵌锂碳与溶剂的反应促使电池的爆炸;电池短路瞬间电流产生的热量可能达到正极热分解的温度,正极热分解导致电池的热失控。锂离子电池的安全性可以通过下面的研究得到改进。共沉淀法合成了热稳性较好的Li_xNi_1/3Co_1/3Mn_1/3O₂三元复合正极材料并测试了其安全性。结果表明:共沉淀形成过程中控制pH在11±0.2,Li/ （Mn + Co +Ni）=1.05～1.10,900℃烧结12～20h合成的材料具有较好的结构稳定性和电化学性能;Li_xNi_1/3Co_1/3Mn_1/3O₂起始分解温度在211℃,269℃达到最大放热峰,放热量为252J/g,安全性优于LiCoO₂。首次系统的分析了Li_xNi_1/3Co_1/3Mn_1/3O₂电极过程反应动力学,结果表明电池的结构,电极的嵌锂状态,测试温度对该电极的反应过程都有很大的影响,锂离子扩散步骤是Li_xNi_1/3Co_1/3Mn_1/3O₂电极反应动力学的控制步骤。通过离子掺杂和表面修饰对Li_xNi_1/3Co_1/3Mn_1/3O₂材料改性,以期提高其动力性与安全性。首次合成了Cl^-、Br^-离子掺杂的Li_xNi_1/3Co_1/3Mn_1/3O_1.95M_0.1材料,测试结果表明5%的卤素阴离子（Cl^-、Br^-）替代O^2-可以提高材料的放电比容量、大倍率循环稳定性和热稳定性,其中Cl^-的作用效果更好。探讨了过渡金属离子(Zn²⁺、Fe³⁺、Ti⁴⁺、Zr⁴⁺)掺杂对材料结构性能的影响,掺杂后材料的放电容量的顺序为:Ti⁴⁺-doped >no doped >Zr⁴⁺-doped =Fe³⁺ -doped >Zn²⁺-doped;倍率放电能力依次为:Ti⁴⁺-doped> Zr⁴⁺-doped >Zn²⁺-doped no doped >Fe³⁺-doped;脱锂材料的热稳定性顺序依次为:Ti⁴⁺-doped>Zr⁴⁺-doped>Zn²⁺-doped>Fe³⁺-doped= no doped。主族金属离子掺杂表明5%的Ge⁴⁺、Sn⁴⁺掺杂可以提高材料的倍率循环稳定性和热稳定性,Ge⁴⁺掺杂作用效果优于Sn⁴⁺掺杂。Mg₂（PO₄）₃包覆可以提高Li_1.05Ni_1/3Mn_1/3Co_1/3O₂的大电流放电能力以及热稳定性。系统的研究了联苯和环己苯对锂离子电池的过充保护作用机理。随环己苯浓度的增大,对电池的过充保护能力增强,对电池的综合电性能影响加大,5～7%是比较合适的添加比例。联苯或环己苯配合防爆安全阀能很好的防止电池的过充。5%联苯或7%环己苯与2%含氮化合物三乙胺复合使用可以提高电池过充能力,防止电池膨胀,但导致电池容量的衰减,内阻的增大。5%联苯与1%的成膜添加剂VC复合使用可提高电池的过充能力,防止电池的膨胀。自主设计了高安全高动力性的F型LiMn₂O₄/C锂离子动力电池。双极耳四极片并联的F型电池容量为5Ah,4C倍率充放电循环50次后的容量保持率在92.73%以上。首次提出了防过充剂与阻燃剂的协同保护作用机制,防过充剂（环己苯6%）和阻燃剂（TCEP6%）联用不但可以提高锂离子电池的防过充能力,而且可以提高电池高温环境下的热稳定性,且对电池综合电性能影响较小。6%TCEP和6%CHB与铜箔防爆安全阀联合使用可以大大提高电池的安全性,电池在1C-10V过充、150℃的恒温箱中加热30min均未爆炸。更多还原

【Abstract】 The explosion mechanism and the safety improvement of lithium ion batteries were studied in this paper. Based on this subject, Li_xNi_1/3Co_1/3Mn_1/3O₂ cathode materials with better thermal stability were synthesized and amended by cation and anion replacing or surface coating, the overcharge protection addictives and the flame-retardant addictives were also investigated. The reaction kinetics of Li_xNi_1/3Mn_1/3Co_1/3O₂ cathode was firstly discussed in detail. The M-doped（M=Cl, Br, Zn, Zr, Ge） and Mg₂（PO₄）₃-coated Li_xNi_1/3Co_1/3Mn_1/3O₂ cathode materials were firstly synthesized and studied. The flame-retardant addictives TCEP cooperating with overcharge protection addictives cycleohexyl benzene was firstly adding to the F-type LiMn₂O₄/C dynamic lithium-ion battery.The main heat sources of lithium batteries were tested and the explosion mechanism was analyzed under oven test, overcharge test and short-circuit. The results showed that the explosion of lithium ion battery in oven test was induced by the heat and the air in turn coming from the LixC6/Solvet reacton, electrolyte decomposition and cathode decomposition. The heat and the air coming from the excessiveLixC6/Solvet reacton casued the batteries thermal runawy under the batteries being overcharged .The heat coming from the current may let the batteries reach high temperature in a moment.Li_xNi_1/3Mn_1/3Co_1/3O₂ cathode materials were synthesized via co-precipitation method and the safety was tested.As a result, the material had the better layer structure and good electrochemical performance synthesized under the flowing condition, controlling the pH=11±0.2 at co-precipitation process, sintering 12-20h at 900℃, Li/M ratio in 1.05-1.10. DSC showed that Li_xNi_1/3Mn_1/3Co_1/3O₂ began decomposing at 211℃and reached maximum temperature at 269℃. The safety of of Li1.05Co1/3Ni1/3Mn1/3O2/C 18650 batteries was better than LiCoO₂ /C 18650 batteries under oven test, overcharged test and short circuit. The reaction kinetics of Li_xNi_1/3Mn_1/3Co_1/3O₂ cathode was firstly studied by Eis and the results illuminated that the lithium ion diffused step was the control step of the whole electrochemical reaction kinetics of Li_xNi_1/3Mn_1/3Co_1/3O₂ cathode.The cation and anion doped and surface modified of Li_xNi_1/3Co_1/3Mn_1/3O₂ were studied and the M-doped（M=Cl, Br, Zn, Zr, Ge） and Mg₂（PO₄）₃-coated Li_xNi_1/3Co_1/3Mn_1/3O₂ cathode materials were firstly synthesized and discussed. The results showed that 5%Cl^- or Br^- replacing O^2- of Li_xNi_1/3Co_1/3Mn_1/3O₂ materials especially for Cl^--doped can improve the discharge capacity, high current discharge ability and thermal stability. The discharge capacity order after transition metal Zn²⁺、Fe³⁺、Ti⁴⁺、Zr⁴⁺) doped was Ti⁴⁺-doped >no doped >Zr⁴⁺-doped =Fe³⁺ -doped >Zn²⁺-doped , the rate discharge ability order was Ti⁴⁺-doped> Zr⁴⁺-doped >Zn²⁺-doped no doped >Fe³⁺-doped and the thermal stability order was Ti⁴⁺-doped>Zr⁴⁺-doped>Zn²⁺-doped>Fe³⁺-doped= no doped. Ge⁴⁺or Sn⁴⁺-doped especially Ge⁴⁺-doped enhanced the dynamic performance and thermal stability. Mg3（PO4）2-coating improved high rate discharge capacity and thermal stability.The overcharge protection ability of polymeric additives cyclohexyl benzene （CHB） and biphenyl was studied.The more content cyclohexyl benzene of lithium ion battery made the better overcharge protection ability and the worse cycling performance of batteries, so the best ratio of CHB was 5-7%. 5-7% CHB or biphenyl can resist the batteries with safe-walve explosion ,while can not resist the batteries thermal runaway without safe-valve. Cyclohexyl benzene（ 7%） or biphenyl（ 5%） using jointly with triethyl amine（2% ）can improve the battery overcharge protection ability and prevent the batteries from expanding. But the triethyl amine adding reduced the discharge capacity and increasing the internal resistance.5% biphenyl and 1%VC using jointly not only amended the batteries overcharge protection ability, but also had slightly effect on the electrochemical performance of lithium ion batteries.With batteries structure and manufacturing process mending, the F-type LiMn₂O₄/C dynamic lithium-ion batteries with high safety and high power were firstly manufactured. The results showed that the capacity of the battery with two cathode and two anode paralleling alternately was 5Ah and the capacity holding rate was 92.73% after 50 cycles at 4C rate charge-discharge current density . CHB and TCEP using jointly can improve the battery safety under oven test and overcharge test ,which was firstly brought forword.The electrolyte containing 6%TCEP and 6%CHB and cooper safety-lab on the batteries covers using together could greatly improved the batteries safety and the batteries can not explode or ignite when overcharged at 1C-10V or heated at 150℃oven test.更多还原