锂离子电池石墨基负极材料储锂性能的第一性原理研究

First-principles of lithium storage performance of graphite-based anode materials for lithium ion battery

结合基于密度泛函理论的第一性原理平面波赝势方法,研究了石墨晶胞中嵌入不同数量的锂离子所产生晶体结构的变化、形成能、电子结构以及锂离子的迁移过程,并通过测试磁控溅射法制备的石墨薄膜电极的充放电循环性能证明了仿真结果。研究发现:随着锂离子嵌入数量的增加,石墨晶胞的体积逐渐增加,当嵌入6个锂离子后,石墨晶胞体积膨胀了20.52%,体系的形成能降至-68.612 eV,形成能下降趋势平缓,表明石墨晶胞在嵌锂过程中非常稳定;石墨晶胞的电荷密度主要集中在C—C键,锂离子的嵌入降低了C—C键之间的电荷密度,并未破坏C—C键;锂离子通过空位迁移的方式迁移到石墨层间所需要克服的迁移势垒最低。

The changes of crystal structure,formation energy,electronic structure and lithium-ion migration process caused by intercalating different amounts of lithium ions in graphite cells were studied with the first-principles plane wave pseudopotential method based on density functional theory.The simulation results were verified by testing the charge-discharge cycle performance of graphite film electrodes prepared by magnetron sputtering.The results show that the volume of graphite unit cell increased gradually with the continuous intercalation of lithium ions,when six lithium ions were intercalated,the volume of graphite unit cell expanded by 20.52%,the formation energy of the system decreased to-68.612 eV,the formation energy decreased slowly,which indicates that the graphite unit cells were very stable in the lithium intercalation process;the charge density of graphite unit cells was mainly concentrated in the C-C bond,while the intercalation of lithium ions reduced the charge density between the C-C bonds but did not destroy the C-C bond.The migration barrier needed to overcome for lithium ion to migrate to graphite layers through vacancy migration is the lowest one.