近年來，隨著科技的進步與能源需求的增加，生產製作較為簡單且具有高能量密度的無陽極鋰金屬電池被視為能解決能源問題的明日之星，但是相較於技術已成熟穩定的商業用鋰離子電池，無陽極鋰金屬電池仍然有許多問題需解決，如充放電過程中生成鋰枝晶穿透隔離膜造成的電池短路、有限鋰源造成的較低的庫倫效率與不佳的電容維持率導致的低循環壽命等，為了解決上述關於鋰枝晶與有限鋰源等問題，如何高效利用電池中有限鋰源與使其沉積出具有較平整表面的方法變得更加重要，本研究設計了一款使用以LiFSI作為主鹽搭配含鈉離子的鹽類，輔以醚類溶劑DME與稀釋劑TTE為基底配製而成的雙金屬局部高濃度電解液來改善上述常見的無陽極鋰金屬電池的缺點。
本研究著重探討以鈉鹽做為局部高濃度電解液的添加劑，透過將電解液中部分鈉離子先行還原至銅薄表面提升其與鋰離子的界面親和力，後以in-situ的方式將其餘鈉離子與鋰離子一同還原至銅箔表面，藉由鈉離子較大的離子半徑以及其與鋰離子不同的離子移動速率等特性，抑制無陽極鋰金屬電池中鋰枝晶大量生長的問題，本研究以1.5M LiFSI in DME/TTE(2:3 v/v)局部高濃度作為原始未改質電解液，加入各濃度NaFSI進行鋰鹽與鈉鹽的比例優化，再以不同種類的鈉鹽(NaF、NaBF4、NaPF6、NaTFSI)進行各種陰離子團對電化學影響之比較，最後對電解液中的游離溶劑含量進行調整，以此開發出一款更適合無陽極鋰金屬電池的電解液。
雖然過程中遇到LiFSI電解液腐蝕正極後鋁箔與鈕扣電池之不鏽鋼元件等問題，但我們藉由將鈕扣電池系統更改為軟包電池成功避免掉大部分腐蝕效應所帶來的影響使實驗得以繼續進行，最後，相較於一般商用電解液1M LiPF6 in EC/DEC(1:1 v/v)與1.5M LiFSI in DME/TTE(1:4 v/v)局部高濃度電解液於在無陽極軟包電池下分別在經過50次與100次充放電循環後僅殘餘5.6 %、62.25%的電容維持率，經優化後的1.45M LiFSI+0.05 M NaTFSI電解液在100次充放電循環後能具有高達73.97%的電容維持率且其沉積的鋰金屬亦具有較緻密且平整的表面。

Recently, with the development of technology and the increasing energy demand, the simple production process and higher energy density anode-free lithium metal batteries have been considered a promising solution to the energy problem. However, compared to stable commercial lithium-ion batteries, anode-free lithium metal batteries still face numerous challenges. Common issues such as lithium dendrite penetrating the separator cause short circuits, lower Coulombic efficiency, and poor capacity retention, leading to shorter cycle life due to limited lithium resources. To address these common problems related to lithium dendrites and limited lithium resources, it becomes crucial to efficiently utilize the limited lithium to make lithium deposition with a more uniform surface. This study designed a bimetallic localized high-concentration electrolyte system. Using LiFSI as the main salt, combined with sodium-containing salts based on the ether solvent DME and the diluent TTE, to improve the drawbacks of conventional anode-free lithium metal batteries.
This work uses sodium salts as additives in the localized high-concentration electrolyte. By earlier deposition of partial sodium ions to enhance the interface affinity between lithium ions and copper surface, and then in-situ deposition of both sodium and lithium ions onto the copper foil surface, the study aims to suppress the excessive growth of lithium dendrites in anode-free lithium metal batteries by the different ionic radius and migration rate of sodium ions. The study initially used 1.5M LiFSI in DME/TTE (2:3 v/v) as the original unmodified electrolyte. Various concentrations of sodium salt were subsequently added to optimize the salt-to-solvent ratio. To assess their electrochemical impact, further comparison was conducted using different sodium salts (NaF, NaBF4, NaPF6, NaTFSI). Finally, adjustments were made to the content of free solvents in the electrolyte to develop an electrolyte more suitable for anode-free lithium metal batteries.
Although we encountered issues such as corrosion of aluminum foils and stainless steel components during the process, the experiment continued by successfully switching the system from a coin cell system to a pouch cell system, which mitigated the detrimental effects of corrosion. Finally, compared to the typical commercial electrolytes of 1M LiPF6 in EC/DEC (1:1 v/v) and 1.5M LiFSI in DME/TTE (1:4 v/v) electrolyte, which showed only 5.6 % and 62.25 % capacity retention, respectively, after 50 and 100 charge-discharge cycles in anode-free pouch cells, the optimized 1.45M LiFSI+0.05M NaTFSI electrolyte achieved high capacity retention of 73.97 % after 100 charge-discharge cycles and show the uniform surface after cycling.

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