Sn薄膜沉积时间对首周锂离子容量损失的影响

Effect of deposition time on capacity losses of the 1st cycle for Sn thin films as anodes of Li-ion batteries

通过控制直流磁控溅射时间在15～3 600 s之间制备出系列不同厚度的Sn薄膜负极,研究了沉积时间变化对首周不可逆容量损失的影响。当Sn薄膜沉积时间为15 s时,首周放电容量远远大于理论容量,其中首周充放电不可逆容量损失占首周放电容量的56%以上,1.5 V至锡锂合金化反应电位0.67 V之间出现的SEI膜是造成该不可逆容量的主要原因。随着薄膜沉积时间增加,首周容量损失呈现非单调变化趋势。当沉积时间低于600 s时,首周容量损失与SEI膜容量变化趋势基本一致;当沉积时间长于600 s时,首周容量损失单调递增,而SEI膜容量单调下降,说明SEI膜的形成不再是首周容量损失的主要原因。应用X射线衍射仪和扫描电子显微镜对不同沉积时间Sn薄膜进行结晶形态和表面形貌分析,探讨了薄膜表面形貌、结晶形态与SEI膜容量及首周不可逆容量损失之间的关系。

A series of Sn thin films were prepared by direct current magnetron sputtering with the deposition time ranging from 15 s to 3 600 s. When the deposition time was 15 s, the irreversible capacity of 1st discharge/charge cycle was more than 56% of the discharge capacity, which was mainly attributed to a slope plateau representing the formation of solid-state electrolyte interface （SEI） layer between 1.5 V and 0. 67 V. The changed trend of irreversible capacity was consistent with that of SEI capacity when deposition time was less than 600 s. When the deposition time was over 600 s, the total irreversible capacity increased quickly with the deposition time. As a contrast, SEI capacity exhibited a different tendency when the deposition time was more than 120 s, where the SEI capacity decreased monotonously with the increase of the deposition time. By virtue of XRD and SEM analytical techniques, it was found that the morphology and crystallinity of the film played important roles in the SEI capacity and irreversi- ble capacity losses of the 1st cycle.