| 摘要: | 鈉元素的豐富儲量與低廉成本，使其在鈉離子電池領域受到日益重視。過去數十年間，業界為推動鈉離子電池的實際應用投入了持續不懈的努力。然而，傳統液態電解質(LE)存在的可燃性和洩漏風險，構成了重大的安全隱憂。以固態電解質取代液態電解質被視為一種極具前景的策略，為有效解決LE的安全相關問題，因此本研究開發出更安全、穩定的固態電解質。
在本研究中，我們成功開發了一種適用於鈉離子電池的陶瓷/高分子複合固態電解質(CSE)薄膜。使用聚偏氟乙烯(Poly(vinylidene)difluoride, PVDF)、醋酸纖維素(Cellulose Acetate, CA)及鈉鹽(NaPF6) 混合形成高分子基體，隨後將水熱法合成的Na1+xAlxTi2-x(PO4)3(NATP)陶瓷粉末分散於基體溶液中，經由溶液澆鑄法製備而成開發具有最佳性能的CSE薄膜。透過優化鈉鹽混摻適量的NaPF6至高分子基體中(PVDF: CA: NaPF6 =4: 1: 2)後其離子電導率達2.1×10-4 S/cm。為了進⼀步改善固態電解質的熱穩定性及電化學性能，我們添加NATP至PVDF/CA/NaPF6高分子固態電解質中，發現當PVDF: CA: NaPF6 : NATP=4: 1: 2: 1時的CSE具有最佳的電化學性能，展現出卓越的熱穩定性/化學穩定性、較低可燃性和更佳的耐用程度。
實驗結果顯示，所開發的CSE薄膜具有良好的電化學穩定性和循環可逆性。其離子電導率高達5.2×10-4 S/cm以及高鈉離子轉移數0.66，在0.1 mA/cm2電流密度進行鈉沉積與剝落行為可維持超過600小時的穩定狀態，表明可以有效避免鈉枝晶形成所造成的電池短路等安全性問題。將所開發的CSE搭配少量電解液(1M NaPF6 in PC/EMC)應用於鎳鐵錳層狀氧化物正極材料的鈉離子半電池能獲得約120 mAh/g @ 0.2 C的放電容量，而全電池體系則可實現112.6 mAh/g @ 0.2 C的放電容量，並在循環200圈後仍有85 %以上電容保持率同時具有穩定的庫倫效率(~100 %)，亦可以應用於軟包電池當中擁有優異的電化學表現。
綜合上述結果，本研究開發的CSE固態電解質薄膜不僅具備寬廣的電化學電位窗口(~5 V) 和卓越的高溫熱穩定性(~250 ℃)，其高離子電導率、高離子轉移數更有助於提升鈉離子電池的放電容量，這一類CSE複合材料在鈉離子電池領域展現出了廣闊的應用前景。
;The abundant reserves and low cost of sodium have garnered increasing attention for sodium-ion batteries (SIBs). Over the past few decades, significant industry efforts have been dedicated to promoting the practical application of SIBs. However, the flammability and leakage risks associated with traditional liquid electrolytes (LEs) present substantial safety concerns. To address these safety issues, this study aims to develop safer and more stable solid-state electrolytes, with the replacement of LEs , which is considered a highly promising strategy.
In this study, we successfully developed a polymer/ceramic composite solid electrolyte (CSE) film for sodium-ion batteries (SIBs) applications. The polymer matrix was formed by blending poly(vinylidene fluoride) (PVDF), cellulose acetate (CA), and sodium salt (NaPF6). Subsequently, Na1+xAlxTi2-x(PO4)3 (NATP) ceramic powder, synthesized via the hydrothermal method, was dispersed into the matrix solution. The CSE films were then fabricated using a solution casting method to achieve optimal performance. By optimizing the sodium salt content, with the mixture ratio of PVDF: CA: NaPF6 = 4: 1: 2, an ionic conductivity of 2.1×10-4 S/cm was achieved. To further enhance the thermal stability and electrochemical performance of the solid-state electrolyte, NATP was incorporated into the PVDF/CA/NaPF6 polymer electrolyte. The optimal electrochemical performance was observed with a composition of PVDF: CA: NaPF6: NATP = 4: 1: 2: 1, exhibiting superior thermal stability, chemical stability, reduced flammability, and enhanced durability.
Experimental results demonstrated that the developed CSE film possesses excellent electrochemical stability and cycling reversibility. The CSE achieved a high ionic conductivity of 5.2×10-4 S/cm and a high sodium ion transference number of 0.66. It maintained stable sodium deposition and stripping behavior for over 600 hours at a current density of 0.1 mA/cm2, effectively preventing short circuits caused by sodium dendrite formation. When paired with a small amount of liquid electrolyte, the CSE applied in a sodium-ion half-cell with nickel-iron-manganese layered oxide cathode material achieved a discharge capacity of approximately 120 mAh/g @ 0.2 C. In a full-cell configuration, a discharge capacity of 112.6 mAh/g @ 0.2 C was realized, with stable Coulombic efficiency (~100%), demonstrating excellent electrochemical performance in pouch cells as well.
In summary, the CSE film developed in this study exhibits a wide electrochemical potential window (~5 V) and outstanding thermal stability at high temperatures (~250 °C). Its high ionic conductivity and transference number significantly contribute to the improved discharge capacity of SIBs. These findings highlight the promising application potential of CSE composite materials in the field of sodium-ion batteries. |
