锂离子电池硅基负极循环过程中的膨胀应力

Studies on the swelling force during cycling of Si-based anodes in lithium ion batteries

研究硅基负极在充放电及循环过程中的膨胀对开发下一代高比能锂离子动力电池具有重要意义。本工作采用商业化的SiO_(x)/Graphite为负极匹配高比能镍钴锰酸锂[Li(Ni_(0.8)Mn_(0.1)Co_(0.1))O_(2),NCM811]正极,组装了60 Ah大软包电池,并对其进行循环膨胀应力、应力增长机理与膨胀应力的改善等方面的研究。结果表明SiO_(x)材料的构成为3~5 nm Si颗粒分散在无定形的SiO_(2)内部,首次充放电比容量为1840.9/1380 mAh/g,库仑效率为75%。大软包电池单次充放电膨胀应力的变化为7320 N,约为石墨负极的4倍。工作温度越高容量衰减越快,衰减到70%SOH时,25、45和60℃对应的循环次数分别为980、850和500次,对应的最大膨胀应力分别为25107、25490、23667 N。此外,机理分析发现电池循环膨胀应力的增长和容量衰减之间为线性相关,CP(cross section polisher)-SEM分析发现膨胀应力的增加主要来自于SiO_(x)颗粒表面的破裂及副反应导致的SEI(solid electrolyte interphase)增厚。通过测定缓冲垫压缩曲线的方法筛选了合适的聚氨酯类缓冲垫,验证对循环无影响,但可以显著改善膨胀应力的增加,膨胀应力降低50%,这些结果将为更好地应用高比容量的硅基负极材料奠定基础。

Studying the swelling force of Si-based anodes for the next generation of high energy lithium-ion batteries is crucial.In this study,we assembled 60-Ah large pouch batteries with commercialized SiO_(x)/Graphite and NCM811 cathode,tested their cycle life and swelling force increase,and studied the relevant mechanisms and strategies for reducing the swelling force.The structure of SiO_(x) was a 3~5 nm Si core distributed in amorphous SiO_(2),and the specific capacity of SiO_(x) in the first cycle was 1380 m Ah/g and the first columbic efficiency was ca.75%.The swelling force increase during the first cycle was 7320 N,which was 4times higher than that of graphite-based batteries.The cycling tests under different ambient temperatures showed high temperature-dependent tendency.At 25℃,45℃,and 60℃,the cycle numbers were 980,850,and 500,corresponding to 70%SOH,with the maximum swelling force being 25107,25490,and 23667 N,respectively.The root cause for the swelling force increase was the solid electrolyte interface growth and thickening with repeated electrochemical cycles.The compression curve was applied to sorting appropriate cushion that can accommodate the swelling force.The results showed that polyurethane cushion had the best compression properties,reducing the swelling force by 50%.This study provides a foundation for using SiO_(x) in large-scale lithium-ion batteries.