| 摘要: | 由於鈉資源分布廣泛且成本低廉，鈉離子電池近年來被視為鋰離子電池之潛在替代技術。然而，傳統液態電解質存在可燃性與滲漏風險，限制其在大規模應用中的安全性與穩定性。相較之下，固態電解質具備高熱穩定性、良好機械強度及不易燃等特性，有望解決上述安全疑慮，提升儲能系統整體可靠性。
本研究開發一種應用於鈉離子電池之複合型固態電解質 (CSE)，其高分子基質係以溶液鑄膜法製備，包含聚偏二氟乙烯-六氟丙烯共聚物(Poly(vinylidene fluoride-co-hexafluoropropylene), PVDF-HFP)、聚乙烯吡咯烷酮(Polyvinylpyrrolidone, PVP)與鈉鹽(NaPF₆)，並添加經水熱法合成之磷酸鈦鋁鈉Na₁₊ₓAlₓTi₂₋ₓ(PO₄)₃ (NATP)作為活性填料，以及石墨相碳氮化物(graphitic carbon nitride, g-C₃N₄)奈米顆粒作為惰性填料。
CSE 展現出優異的熱穩定性，初始熱裂解溫度可達約 260 °C，並具備良好的機械性能，包括高抗拉強度與優異延展性，顯示其具備應用於實際裝置之潛力。進一步透過交流阻抗分析測得其室溫下離子電導率為 5.61 × 10⁻⁴ S cm⁻¹，顯示其具備連續且高效的離子傳輸通道。經穩態極化測試，所得鈉離子轉移數高達 0.69，顯示該系統對陽離子具高度選擇性，並可有效降低陰離子累積造成的濃度極化現象。為評估其界面穩定性與抑制鈉枝晶生長之能力，本研究組裝鈉金屬對稱電池並探討離子沉積剝落行為，結果顯示，在電流密度0.05 mA cm⁻² 條件下，該電池可穩定運行超過 1000 小時，且極化電壓變化微小，證實該 CSE 具備穩定的鈉金屬界面相容性，並有效抑制枝晶形成，顯著提升系統之操作壽命與安全性。
綜合上述優異之物理與電化學特性，本研究進一步將此 CSE 實際應用於全電池組裝，並分別評估其於鈕扣型與軟包型封裝形式下之電化學性能。在鈕扣電池中，選用層狀氧化物鎳鐵錳（NIM）作為正極材料，搭配硬碳（HC）負極，於 0.2C 充放電倍率下可達 78.8mAh g⁻¹ 的初始放電容量，並能穩定循環達 500 次以上，電容保持率約為76.7%，展現出優異的循環穩定性。相較之下，於相同電極組成與倍率條件下，軟包電池亦展現優越表現，經 300 次循環後仍可維持 83.2 mAh g⁻¹ 的容量，對應容量保持率達約 90.2%，證明其在實際封裝應用中具備高度穩定性與可行性。
本研究成功開發出具高離子傳導性與界面穩定性的複合型固態電解質，展現其於鈉離子電池中的應用潛力。透過優化高分子基質與雙填料比例，不僅提升電解質之結構穩定性與熱機械性能，亦有效抑制鈉枝晶生成，並在充放電循環中展現優異的穩定性，為未來高安全性儲能系統提供可行解決方案。
;Due to the widespread abundance and low cost of sodium resources, sodium-ion batteries (SIBs) have emerged in recent years as a promising alternative to lithium-ion batteries (LIBs). However, conventional liquid electrolytes pose safety concerns such as flammability and leakage, which limit their stability and applicability in large-scale systems. In contrast, solid-state electrolytes (SSEs), characterized by high thermal stability, robust mechanical strength, and non-flammability, offer a viable solution to enhance the overall safety and reliability of energy storage systems.
In this study, a composite solid-state electrolyte (CSE) for SIBs was developed using a solution casting technique. The polymer matrix consists of poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP), polyvinylpyrrolidone (PVP), and sodium salt (NaPF₆). Additionally, Na₁₊ₓAlₓTi₂₋ₓ(PO₄)₃ (NATP), synthesized via hydrothermal methods, was incorporated as an active filler, while graphitic carbon nitride (g-C₃N₄) nanoparticles served as an inert filler.
The resulting CSE exhibited excellent thermal stability, with an initial thermal decomposition temperature of approximately 260 °C, along with outstanding mechanical properties, including high tensile strength and notable flexibility, indicating its applicability in practical devices. Electrochemical impedance spectroscopy revealed a room-temperature ionic conductivity of 5.61 × 10⁻⁴ S cm⁻¹, suggesting the presence of continuous and efficient ion transport pathways. Moreover, steady-state polarization measurements demonstrated a high sodium-ion transference number of 0.69, indicating strong cation selectivity and effective suppression of concentration polarization due to anion accumulation.
To further assess interfacial stability and dendrite suppression capability, symmetric Na||CSE||Na cells were assembled and subjected to long-term cycling. At a current density of 0.05 mA cm⁻², the cell maintained stable operation for over 1000 hours with minimal voltage fluctuation, confirming the electrolyte’s stable interfacial compatibility with sodium metal and its effectiveness in inhibiting dendritic growth, thereby significantly enhancing operational lifespan and safety.
Based on the promising physicochemical and electrochemical properties, the CSE was further applied to full-cell configurations, and its performance was evaluated in both coin-cell and pouch-cell formats. In the coin-cell setup, layered nickel-iron-manganese oxide (NIM) was used as the cathode and hard carbon (HC) as the anode. Under a 0.2C charge-discharge rate, the initial discharge capacity reached 78.8 mAh g⁻¹, with stable cycling performance maintained over 500 cycles and a capacity retention of approximately 76.7%. Comparatively, pouch cells under identical electrode composition and current density delivered a discharge capacity of 83.2 mAh g⁻¹ after 300 cycles, corresponding to a capacity retention of 90.2%, demonstrating the CSE’s high stability and feasibility in practical packaging applications.
In conclusion, this study successfully developed a CSE with high ionic conductivity and interfacial stability, demonstrating its potential for application in sodium-ion batteries. Through the optimization of polymer matrix composition and dual-filler content, the CSE not only exhibited enhanced structural and thermal-mechanical stability but also effectively suppressed sodium dendrite formation. The system showed excellent long-term cycling stability, offering a promising solution for future high-safety energy storage technologies. |
