【作者】 李鑫；

【导师】 马建民；

【作者基本信息】 湖南大学 ， 物理学， 2021， 硕士

【摘要】 锂金属是最具有吸引力的电化学储能阳极材料之一。然而,在电化学沉积过程中锂枝晶的生长导致库仑效率低和安全性问题,长期以来阻碍了可充电锂金属电池的应用。因此,通过在电解液中加入添加剂来抑制锂枝晶的生长,稳定锂金属负极是一种行之有效的策略。本论文主要围绕电解液添加剂对锂金属负极的保护作用展开研究,并通过一系列表征手段对其中存在的机理进行了探究。利用Li Ni_xMn_yCo_zO₂（NCM）材料作为阴极,对含添加剂的电解液的实用性进行了验证。主要包括以下内容:（1）三氟甲烷磺酸1,1,1,3,3,3-六氟异丙酯（HFPTf）作为碳酸酯类电解液添加剂,通过形成稳定的固体电解液界面层（SEI）,使锂负极得以稳定。该SEI富含能够降低Li⁺扩散能垒的Li F和分布在上层的高导电Li₂SO_x（x=0,3,4）。这种特殊结构的SEI可以快速传导Li⁺,避免了锂枝晶的出现。HFPTf添加剂还能改变Li⁺溶剂化的一级鞘层结构,使Li⁺更容易脱溶剂化。最终研究结果显示,当测试条件为0.5 m A cm^-2(沉积容量是0.25 m Ah cm^-2)时,含1 wt%HFPTf电解液的Li‖Li电池实现了超过1000 h的稳定循环。此外,在阴极表面形成了薄而均匀的阴极电解液界面层（CEI）,抑制了NCM811中的金属离子溶出。结果使得Li‖NCM811全电池在100 m A g^-1下循环150次后获得70%的容量保持。（2）七氟丁酰咪唑（HFBMZ）作为碳酸酯类电解液添加剂,实现了稳定锂金属负极的作用。首先,HFBMZ作为添加剂能够清除电解液中微量的水和HF,能够起到减少SEI表面的副产物和抑制NCM622的金属离子溶出的作用。其次,HFBMZ作为添加剂能够使得电解液-隔膜界面具有很好的润湿性,有利于增加Li⁺的流量。HFBMZ在锂金属表面被还原生成稳定的SEI和均匀的CEI,来稳定电池的循环。实验结果证明,在含有1 wt%HFBMZ的电解液中,在0.5 m A cm^-2的测试条件下,Li‖Li电池实现了约1200 h的稳定循环(负载容量:0.25 m Ah cm^-2)。Li‖NCM622全电池在100 m A g^-1下循环150次后获得92%的容量保持。更多还原

【Abstract】 Lithium is one of the most attractive anode materials for electrochemical energy storage.However,the growth of lithium dendrite in the electrochemical deposition process leads to low coulomb efficiency and safety problems,which has hindered the application of rechargeable lithium metal batteries for a long time.Therefore,adding additives to the electrolyte to inhibit the growth of lithium dendrite and stabilize lithium metal anode is an effective strategy.In this paper,the protective effect of electrolyte additives on lithium metal anode was studied,and the mechanism was explained by a series of characterization methods.In addition,Li Ni_xMn_yCo_zO₂（NCM）was used as cathode to verify the practicability of the electrolyte containing additives.It mainly includes the following contents:（1）1,1,1,3,3,3-Hexafluoroisopropyl Trifluoromethanesulfonate（HFPTf）was developed as an electrolyte additive.By formin g a stable solid electrolyte interface layer（SEI）,the growth of lithium dendrite was greatly inhibited and the Li metal anode was protected.The SEI has Li F bottom layer which can reduce Li⁺diffusion barrier and Li₂SO_x（x=0,3,4）which is highly conductive distributed in the upper layer.The special structure of SEI can conduct Li⁺rapidly and avoid the growth of Li dendrite.HFPTf additive can also change the structure of the first-order sheath of Li⁺solvation,making Li⁺easier to desolvent.The results show that the Li‖Li symmetrical cell with 1 wt%HFPTf-contained electrolyte achieves cycle stability of more than 1000 h at 0.5 m A cm^-2 current density and 0.25 m Ah cm^-2 deposition capacity.In addition,a thin and uniform cathode electrolyte interface layer（CEI）was formed,which inhibits the dissolution of metal ions from the cathode material.The capacity retention rate of Li‖NCM811 cell is 70%after 150 cycles with current density of 100 m A g^-1.（2）1-（Heptafluorobutyryl）imidazole（HFBMZ）was developed as an electrolyte additive to stabilize the anode of lithium metal batteries.First,HFBMZ can remove the trace H₂O and HF in electrolyte,and can reduce by-products on SEI surface and inhibit the dissolution of metal ions of NCM622.Secondly,HFBMZ can make the electrolyte diaphragm interface have good wettability,which is conducive to increase the flow rate of Li⁺and inhibit the growth of dendrites.In addition,HFBMZ is reduced to stable SEI and even CEI on the surface of lithium metal,which improves the cycle performance and the rate performance of the cells.The experimental results show that the Li‖Li symmetrical cells has achieved stable cycle for more than 1200 h under the condition of current density of 0.5 m A cm^-2 and capacity of 0.25 m Ah cm^-2in electrolyte containing 1 wt%HFBMZ.The capacity retention rate of Li‖NCM622cell is 92%after 150 cycles with current density of 100 m A g^-1.更多还原