中國儲能網訊：隨著科技發(fā)展，人類對能源的需求與日俱增，而目前商業(yè)化的鋰離子電池(理論容量372mAh/g)已不能滿足該需求，高容量密度電池的開發(fā)已成為研究熱點。
鋰金屬具有高理論比容量(3860mAh/g)，在儲能領域有很大應用潛力。然而鋰枝晶的生長，不僅降低了電池性能，而且容易發(fā)生短路，造成安全隱患。這些問題嚴重阻礙了鋰金屬電池的發(fā)展和實際應用。
為解決上述問題，科學家們提出了各種方案，如制備三維嵌鋰基體、鋰金屬表面包覆、隔膜改性等。但這些方式增加了電池整體重量，且制備過程繁瑣，不利于商業(yè)化生產。
最近，Qian等通過對比不同電解液環(huán)境對鋰枝晶生長的影響，提出高濃度LiFSI醚類電解液環(huán)境下，即使沒有嵌鋰基體，仍可有效抑制鋰枝晶在銅集流體上的生長，同時，電池庫倫效率也有顯著提高。
Figure 1. Schematicillustrations of battery configurations. a) State-of-the-art Li-ion battery,i.e., Cu|C6||LiFePO4|Al. b) Anode-free battery,i.e.,Cu||LiFePO4|Al.
實驗以Cu-LiFePO4電池為研究體系，分別選用1 M LiPF6-EC/DMC(1/2 v/v)酯類電解液和4 MLiFSI-DME醚類電解液進行對比。實驗結果表明隨著循環(huán)次數增加，酯類電解液環(huán)境下電池電阻增加明顯，而4 MLiFSI-DME醚類電解液環(huán)境下，電阻增幅較小。
而且在4 MLiFSI-DME環(huán)境下，多次循環(huán)后平均庫倫效率大于99%。即使在2 mA cm-2電流密度下，庫倫效率仍接近100%。
另外，該研究發(fā)現(xiàn)通過調節(jié)測試條件，也可提高庫倫效率。當鋰以0.2 mA cm-2沉積，2mA cm-2脫出時，平均庫倫效率可達99.6%，高于一直以0.2 mA cm-2/2mAcm-2進行循環(huán)的庫倫效率。
Figure 2. Nyquistplot of anode-free Cu||LiFePO4 cells with either 1 M LiPF6-EC/DMC(dashed line) or 4 M LiFSI-DME (solid line) after differentcycles whencharged/discharged at 0.2 mA cm?2. All data were collectedatdischarged state of the cells.
Figure 3. Electrochemical performance of anode-freeCu||LiFePO4 cells with either 1 M LiPF6-EC/DMC or 4 M LiFSI-DME.a) Charge/discharge voltageprofiles for the first three cycles with the twoelectrolytes. b) Capacity retention and CE of the cells with the twoelectrolytes as a function of cycle numberwhen charged/discharged at 0.2 mA cm?2(open symbols: charge capacity, filled symbols:discharge capacity). c) Capacityretention of the cells with 4 M LiFSI-DME charged/discharged at differentcurrent densities.
Figure 4. Cycling performance of Cu||Li and Cu||LiFePO4cells with 4 M LiFSI-DME cycled at different current densities. a) Li||LiFePO4cell cycled withlow-rate (C/5) charging and high-rate (2 C) discharging. b) CEof Cu||Li cells. A capacity of 0.5 mAh cm?2 was used to plate the Limetal, which wassubsequently stripped by cycling to 1.0 V versus Li/Li+.c) Charge/discharge voltage profiles for the first 30 cycles of the anode-freecells (Cu||LiFePO4)with 4 MLiFSI-DME cycled at different currentdensities. d) Discharge capacity and CE of anode-free Cu||LiFePO4cells charged at 0.2 mA cm?2 anddischarged at either 0.2 or 2.0 mAcm?2 (open symbols: charge capacity, filled symbols: dischargecapacity).
綜上，該工作提出了一種可有效抑制鋰枝晶生長的電解質，并通過表征解釋其原因，對鋰金屬電池的研究和大規(guī)模生產具有指導意義。
相關研究成果發(fā)表在著名刊物Advanced Functionalmaterials上(DOI：10.1002/adfm.201602353.) JiangfengQian, Brian D. Adams, Jianming Zheng,Ji-Guang Zhanget al. Anode-Free RechargeableLithium Metal Batteries.Adv. Funct. Mater. 2016.)。
