锂二次电池金属锂负极的改性研究
发布时间：2018-09-12 12:23
【摘要】：金属锂具有极高的理论比容量(3860 mAh/g)和最负的电极电位(-3.04 V vs.标准氢电极),是最有前景的下一代锂电池负极材料。然而,循环过程中锂枝晶的形成和生长以及金属锂与电解液的反应,导致锂负极安全性和稳定性差的问题,严重限制金属锂负极的应用。针对以上问题,本文分别从电解液和锂负极结构两方面开展改性研究工作,抑制锂枝晶的形成,改善锂二次电池金属锂负极的安全性和稳定性。对电解液的改性方面,在碳酸酯类电解液中使用添加剂硼酸三(2,2,2-三氟乙基)酯(TTFEB)改善电解液的性质和锂负极界面性质。一方面,通过TTFEB中缺电子中心硼原子与锂盐中阴离子的耦合作用,促进锂盐的解离,提高电解液的锂离子迁移数,从而提高锂离子在电解液中的迁移能力,促进锂电极表面浓度的均匀分布,抑制锂枝晶的产生。另一方面,理论计算和电化学测试结果表明TTFEB具有较高的还原分解电位,可以优先于电解液在负极表面分解形成富含LiF的SEI膜,从而提高SEI膜的稳定性,抑制枝晶的产生。加入2%TTFEB后,锂电极的可逆性和稳定性显著提升,Li|Cu电池在0.1 mA/cm2电流密度下的循环效率由90%提高至96%,Li|Li对称电池的循环寿命提高至1000 h以上,界面阻抗更小且更为稳定。对锂电极在循环过程中的形貌研究发现,TTFEB的加入明显抑制锂枝晶的产生,在SEI膜组分的研究中,证实TTFEB可以形成富含LiF的SEI膜,抑制电解液的还原分解。TTFEB在锂二次全电池中应用时,2%TTFEB的加入显著提高了Li|LiFePO4电池的循环稳定性和倍率性能,500次循环后的容量保持率和库伦效率都明显提升,高倍率下的容量保持率明显提高,且TTFEB能抑制全电池中金属锂电极表面锂枝晶的形成以及在循环过程中逐渐粉化。对锂负极结构的改性方面,采用真空热蒸镀的方法,在锂电极掺入少量的In制备富锂Li-In合金负极取代锂电极作为锂二次电池负极材料。通过对工艺条件的探索,可知蒸发源中In含量为20%,电源输出功率为95 W时,富锂Li-In合金的电化学性能最好,其循环稳定性相比于Li电极显著提升。在Li|LiFePO4电池中的循环寿命可由140次提高至超过300次,对称电池界面稳定性和循环稳定性显著提升,锂溶解/沉积可逆性明显提高。通过对电极结构、形貌、表面膜组分的表征和分析,研究富锂Li-In合金改善锂电极循环稳定性的作用机制。研究结果表明,In的加入可以抑制循环过程中锂枝晶的形成和电极剧烈体积变化引起的粉化现象,同时,锂电极与电解液的反应活性降低,SEI膜的稳定性提高,从而减少活性锂的消耗,显著提升锂电极的循环稳定。
[Abstract]:Lithium metal has extremely high theoretical specific capacity (3860 mAh/g) and the most negative electrode potential (-3.04 V vs.). Standard hydrogen electrode) is the most promising cathode material for the next generation of lithium batteries. However, the formation and growth of lithium dendrite and the reaction between lithium metal and electrolyte lead to the problem of poor safety and stability of lithium anode, which seriously limits the application of lithium anode. In order to improve the safety and stability of lithium anode in lithium secondary battery, the modification of electrolyte and lithium anode structure was carried out in order to restrain the formation of lithium dendrite and improve the safety and stability of lithium negative electrode. In the aspect of modification of electrolyte, the additive of triborate trisodiborate (TTFEB) was used in carbonate electrolyte to improve the properties of electrolyte and the interface property of lithium negative electrode. On the one hand, the coupling of electron deficient boron atoms in TTFEB and anions in lithium salts can promote the dissociation of lithium salts and increase the lithium-ion mobility of the electrolyte, thus enhancing the mobility of lithium ions in the electrolyte. Promote the uniform distribution of lithium electrode surface concentration and inhibit the formation of lithium dendrite. On the other hand, the theoretical calculation and electrochemical measurements show that TTFEB has a higher reduction potential and can be preferentially decomposed on the anode surface to form LiF rich SEI film, thus improving the stability of SEI film and inhibiting the dendrite formation. After the addition of 2%TTFEB, the reversibility and stability of the lithium-ion electrode significantly improved the cycle efficiency of Li Cu cell at current density of 0.1 mA/cm2 from 90% to 96%. The cycle life of Li symmetric battery was increased to more than 1000 h, and the interface impedance was smaller and more stable. It was found that the addition of TTFEB significantly inhibited the formation of lithium dendrites. In the study of the composition of SEI films, it was proved that TTFEB can form SEI films rich in LiF. When inhibiting the reduction and decomposition of electrolyte. TTFEB was used in the lithium secondary battery, the addition of TTFEB significantly improved the cycle stability, capacity retention and Coulomb efficiency of the Li LiFePO4 battery after 500 cycles. The capacity retention rate at high rate was significantly increased, and TTFEB could inhibit the formation of lithium dendrite on the surface of the metal lithium electrode and the gradual pulverization during the cycling process. In the aspect of modification of lithium negative electrode structure, lithium Li-In alloy anode electrode was prepared by vacuum thermal evaporation method and a small amount of In was added into lithium electrode to replace lithium electrode as cathode material for lithium secondary battery. Through the exploration of the process conditions, it can be seen that the electrochemical properties of the lithium-rich Li-In alloy are the best when the content of In in the evaporator is 20 and the power output power is 95 W, and the cyclic stability of the lithium-rich Li-In alloy is significantly improved than that of the Li electrode. The cycle life of Li LiFePO4 battery can be increased from 140 times to more than 300 times, the interface stability and cycle stability of symmetric cell are improved significantly, and the reversible lithium-ion dissolution / deposition is improved obviously. The mechanism of improving the cyclic stability of lithium electrode by Li-rich Li-In alloy was studied by the characterization and analysis of electrode structure, morphology and composition of surface film. The results show that the addition of in can inhibit the formation of lithium dendrite and the powder phenomenon caused by the drastic volume change of the electrode. At the same time, the reaction activity of lithium electrode with electrolyte decreases the stability of SEI film. Thus, the consumption of active lithium is reduced, and the cycle stability of lithium electrode is improved significantly.
【学位授予单位】：哈尔滨工业大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TM912
本文编号：2238996
[Abstract]:Lithium metal has extremely high theoretical specific capacity (3860 mAh/g) and the most negative electrode potential (-3.04 V vs.). Standard hydrogen electrode) is the most promising cathode material for the next generation of lithium batteries. However, the formation and growth of lithium dendrite and the reaction between lithium metal and electrolyte lead to the problem of poor safety and stability of lithium anode, which seriously limits the application of lithium anode. In order to improve the safety and stability of lithium anode in lithium secondary battery, the modification of electrolyte and lithium anode structure was carried out in order to restrain the formation of lithium dendrite and improve the safety and stability of lithium negative electrode. In the aspect of modification of electrolyte, the additive of triborate trisodiborate (TTFEB) was used in carbonate electrolyte to improve the properties of electrolyte and the interface property of lithium negative electrode. On the one hand, the coupling of electron deficient boron atoms in TTFEB and anions in lithium salts can promote the dissociation of lithium salts and increase the lithium-ion mobility of the electrolyte, thus enhancing the mobility of lithium ions in the electrolyte. Promote the uniform distribution of lithium electrode surface concentration and inhibit the formation of lithium dendrite. On the other hand, the theoretical calculation and electrochemical measurements show that TTFEB has a higher reduction potential and can be preferentially decomposed on the anode surface to form LiF rich SEI film, thus improving the stability of SEI film and inhibiting the dendrite formation. After the addition of 2%TTFEB, the reversibility and stability of the lithium-ion electrode significantly improved the cycle efficiency of Li Cu cell at current density of 0.1 mA/cm2 from 90% to 96%. The cycle life of Li symmetric battery was increased to more than 1000 h, and the interface impedance was smaller and more stable. It was found that the addition of TTFEB significantly inhibited the formation of lithium dendrites. In the study of the composition of SEI films, it was proved that TTFEB can form SEI films rich in LiF. When inhibiting the reduction and decomposition of electrolyte. TTFEB was used in the lithium secondary battery, the addition of TTFEB significantly improved the cycle stability, capacity retention and Coulomb efficiency of the Li LiFePO4 battery after 500 cycles. The capacity retention rate at high rate was significantly increased, and TTFEB could inhibit the formation of lithium dendrite on the surface of the metal lithium electrode and the gradual pulverization during the cycling process. In the aspect of modification of lithium negative electrode structure, lithium Li-In alloy anode electrode was prepared by vacuum thermal evaporation method and a small amount of In was added into lithium electrode to replace lithium electrode as cathode material for lithium secondary battery. Through the exploration of the process conditions, it can be seen that the electrochemical properties of the lithium-rich Li-In alloy are the best when the content of In in the evaporator is 20 and the power output power is 95 W, and the cyclic stability of the lithium-rich Li-In alloy is significantly improved than that of the Li electrode. The cycle life of Li LiFePO4 battery can be increased from 140 times to more than 300 times, the interface stability and cycle stability of symmetric cell are improved significantly, and the reversible lithium-ion dissolution / deposition is improved obviously. The mechanism of improving the cyclic stability of lithium electrode by Li-rich Li-In alloy was studied by the characterization and analysis of electrode structure, morphology and composition of surface film. The results show that the addition of in can inhibit the formation of lithium dendrite and the powder phenomenon caused by the drastic volume change of the electrode. At the same time, the reaction activity of lithium electrode with electrolyte decreases the stability of SEI film. Thus, the consumption of active lithium is reduced, and the cycle stability of lithium electrode is improved significantly.
【学位授予单位】：哈尔滨工业大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TM912
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