嵌钠深度对钠离子电池硬碳负极存储性能的影响

Effect of Sodiated Degree on Storage Performance of Hard Carbon Anode in Sodium Ion Batteries

采用扣式半电池研究了嵌钠深度(SOC)对钠离子电池硬碳负极存储性能的影响,并用X射线光电子能谱(XPS)研究了存储过程中固体电解质界面(SEI)的老化机制。结果表明,高SOC状态下存储(>70%),硬碳活性钠的损失较高,存储6天活性钠损失高达30 mAh/g(占总容量的10%以上)。低SOC状态下有利于减缓存储的老化进程,相应的活性钠损失仅为0.7 mAh/g。这是因为在高SOC状态下,硬碳负极的电位与电解液还原电位之间存在较大的电位差,存储期间持续消耗电解液和活性钠生成大量有机组分,造成SEI厚度明显增加,从而增大界面阻抗;而低SOC存储期时,SEI的厚度增加并不明显,不稳定的有机成分转变成无机成分的重构过程主导了SEI的老化进程。

In this paper,the effect of sodiated degree(SOC)on the storage performance of the hard carbon anode of sodium ion batteries was investigated using a half cell,and the aging mechanism of the solid electrolyte interface(SEI)during storage was studied by X-ray photoelectron spectroscopy(XPS).The results show that storage at high SOC state(>70%)leads to a high loss of active sodium in hard carbon,with a loss of up to 30 mAh/g(more than 10%of the total capacity)for 6 days of storage.The low SOC state is beneficial to slow down the aging process of storage,and the corresponding active sodium loss is only 0.7 mAh/g.The reason for this is that in the high SOC state,there is a large potential gap between the potential of the hard carbon anode and the electrolyte reduction potential,and the continuous consumption of electrolyte and active sodium during the storage period generates a large amount of organic components,resulting in a significant increase in the thickness of SEI,which increases the interfacial impedance.In contrast,the increase in the thickness of SEI was not significant during the low SOC storage period,and the reconfiguration process of the unstable organic components into inorganic components dominated the aging process of SEI.