高容量金属镓薄膜和粉体作为锂离子电池负极材料的自修复行为研究

Self-healing Behavior of High Capacity Metal Gallium Thin Film and Powder as Anode Material for Li-ion Battery

锂离子电池合金类负极材料比如Si,Sn,因其理论容量远高于目前商业化石墨负极材料受到了广泛的关注.然而,受限于这类材料的循环稳定性,距离其产业化仍然有一定的距离,主要是由于其在电化学充放电过程中锂离子的嵌入和脱出产生巨大的应力而导致出现的不可修复的裂纹.利用金属镓低熔点的物理特性,在其熔点之上研究其脱嵌锂过程中的自修复能力.对制备出金属镓薄膜电极研究发现,25次充放电后,因为固体电解质(SEI)的持续生成,有效自修复区域降低为34μm,自修复区域随着循环次数的增加逐渐降低.同时通过简单的液相分散方法制备出金属镓粉末电极,金属镓粉末大小为3.43μm,尺寸小于有效自修复区域,电化学分析显示该金属镓粉末电极前25次循环能够实现高的可逆容量和稳定的循环性能,25次循环后的金属镓粉末电极的SEM分析显示裂纹平均尺寸大小为1μm,说明金属镓在液体电解液体系中的自修复能力有限.金属镓有望用于非液态电解质体系中的裂纹修复,比如对全固态电池中金属锂粉化的修复.

Alloy anode materials, such as Si, Sn, have attracted much attention due to their much higher theoretical capacities than that of the commercially used graphite electrodes. However, their commercial applications are limited because of the short cycle life due to the large volume changes and non-healable fracture during electrochemical cycling. In this work, we prepared metal Ga thin film electrodes on stainless steel substrate（diameter 1.4 cm, mass load 1.5~2 mg/cm2） to study the self-healing behavior of Ga anodes. After 25 cycles, the cells were disassembled in Ar-filled glove box and the metal Ga thin film electrodes were washed by dimethyl carbonate（DMC） to remove residual Li PF6 and then dried in the vacuum chamber for more than 2 hours before SEM analysis. Based on SEM observation and crack size statistical distribution, we found that the characteristic size of the self-healing area reduced to 34 μm after 25 cycles and gradually reduced with the increasing cycles using low-melting point metal Ga film electrodes at a temperature above the melting point of Ga. Energy dispersive spectrometer（EDS） analysis showed that there was a large amount of F, O and C at the surface of metal Ga thin film electrodes, which are considered as main components of the solid electrolyte interface（SEI） layer. The formation of the SEI layer degrades the self-healing capability of Ga metal thin films because the layer may attach on the crack surfaces after full delithiation, hindering self-healing of the Ga films. Metal Ga powder electrodes（mass load 4.3 mg/cm2） were prepared by simple liquid dispersion method. The size of the Ga metal powder was 3.43 μm, which is smaller than that of effective self-healing area. Electrochemical performance showed improved durability of the metal Ga powder electrodes compared to the metal Ga thin film electrodes. After 25 cycles, the average crack size of the metal Ga powder electrodes was 1 μm based on SEM images. This shows that the self-healing ability of metal Ga in liquid electrolyte is limited. Metal Ga is expected to be used as crack healing agent in non-liquid electrolyte systems, such as the solid-state batteries.