应变对层状锰系锂离子电池正极材料输出电压的影响

利用第一性原理方法系统研究了不同应 变模式对LiMnO₂和Li₂MnO₃输出电压的影响, 建立了输出电压与弹性常数及应变之间的关系. 发现所有应变对输出电压都是降低的, 且应变效应是各向异性的. 大部分的单轴应变5%时对输出电压的降低都小于0.1 V. 由于层状的电极材料层间的键合作用较弱, 且受脱锂后形成的锂空位影响较大, 当从锂层脱出锂时, 垂直于层方向的应变对输出电压影响较大; 而对Li₂MnO₃系统从过渡金属层中脱锂时, 平行于层的应变对输出电压影响更大. Li₂MnO₃骨架支撑的层状固溶体系中, 应变使高电压充电阶段的电压维持在截断电压之下, 并打开过渡金属层中锂的迁移通道, 产生较为持久的充电而可能获得较大的充电容量.

Strain effect on the intercalation potential of the layered Mn-contained lithium ion batteries cathode materials: a first principles method

The strain effects on the intercalation potentials of LiMnO₂ and Li₂MnO₃ are investigated by the first principles method, and the relationship between the intercalation potential and the strain is given in the form of elastic response. All the modes of strain reduce the intercalation potential and the effect is anisotropic. Most of the single modes reduce the potential by less than 0.1 V when the strains are 5%. The bonding between the host layers is rather sensitive to the strain perpendicular to the host layer when the lithium vacancy left by lithium extraction is in the lithium layer, thus that strain brings more reduction to the intercalation potential; whereas for the Li₂MnO₃ system when lithium is extracted form the transition metal layer, the strain along the host layer brings more reduction to the potential. For the Li₂MnO₃-stabilized LiMO₂ (M=Mn, Ni, Co) solid solution system, the strain can keep the voltage of the high potential charging stage lower than the cut-off voltage, and open up the migrating pathway of lithium in the transition metal layer, therefore the charging can last a long time and larger charging capacity is achieved.