隨著世代演進以及科技進步，磷酸鋰鐵電池已被廣泛應用於大型儲能系統及電動汽車中。然而隨著全球電動車產業之快速發展，伴隨而來的是大量廢棄磷酸鋰鐵電池。由於磷酸鋰鐵電池中含有電解質及金屬，若廢電池未經適當處理，其所產生的有毒化學物質極可能對生物及環境造成危害。此外，近年來市場對於鋰資源及磷礦之需求持續成長，其可能造成鋰及磷相關礦物於未來面臨資源枯竭問題。為減少廢磷酸鋰鐵電池對環境造成之污染以及解決鋰磷資源枯竭問題，如何有效回收廢磷酸鋰鐵電池中之鋰及磷資源為一重要課題。
本研究目的主要為利用次臨界水萃取回收廢磷酸鋰鐵電池中之鋰及磷，並探討實驗參數如酸種類、酸濃度、固液比、反應溫度、反應時間及雙氧水添加量對萃取效率之影響。實驗結果顯示，萃取效率隨著酸濃度增加以及固液比減少而增加；反應溫度、反應時間及雙氧水添加量增加會造成磷酸鐵固體沈澱產生，進而降低鐵及磷之萃取效率。當使用濃度為0.5 N之鹽酸，固液比為10 g/L，反應溫度為100 °C，反應時間為5分鐘時，自廢磷酸鋰鐵電池中萃取鋰及磷可達到最佳效率，其效率分別為93.56%及94.71%。此外，由PHREEQC模擬結果可得知，將磷由浸出液選擇性沈澱為磷酸銨鎂(MgNH4PO4．6H2O)於熱力學上不可行，其原因為浸出液中含有其他高濃度金屬離子如鐵及錳，阻礙磷酸銨鎂沈澱生成。

Lithium iron phosphate (LFP) batteries have been widely applied in large-scale energy storage systems and electric vehicles (EVs). A significant amount of spent LFP batteries was generated worldwide recently due to the rapid development of EVs. Spent LFP batteries may cause environmental problems because of their harmful electrolyte and metals content. Furthermore, the growing demand for lithium (Li) and phosphorus (P) would lead to the depletion of these two resources in the coming years. Hence, it is crucial to develop an appropriate way for recycling Li and P from spent LFP batteries.
This study focused on the recovery of Li and P from spent LFP batteries utilizing subcritical water extraction (SWE). The effects of acid type (HCl and ascorbic acid), acid concentration (0.1-1.5 N), solid to liquid ratio (S/L) (10-40 g/L), reaction temperature (100-150 °C), reaction time (5-30 min), and H2O2 addition (0-2 vol%) were investigated.
From the experimental results, the leaching efficiency increased with increasing acid concentration and decreasing S/L. The reaction temperature, reaction time, and H2O2 addition would lead to the formation of FePO4 compounds, decreasing the leaching efficiency of Fe and P. The leaching efficiency of Li and P reached 93.56% and 94.71%, respectively, under the following conditions: 0.5 N of HCl, S/L of 10 g/L, reaction temperature of 100 °C, and reaction time of 5 min. Simulation results showed that selective precipitation of P as struvite (MgNH4PO4．6H2O) from the leaching solution was not feasible due to the high concentration of metal ions in the leaching solution.

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