| 摘要: | 近十年來，筆記型電腦、智慧型手機、車用電子裝置等設備迅速發展與普及，可攜式直流電源與電池亦隨之快速發展與創新。由於鋰離子電池具有高能量密度、較高功率及長壽命，且可充放電次數可數百次以上，因此，自SONY公司於1991年發表第一個商業用鋰離子電池後，各種鋰離子電池大量開發與運用，但在鋰離子電池大量運用期間，鋰離子電池卻開始出現因過熱、火災等意外事故導致人員受傷，電池的安全運輸、儲存與使用開始受重視。尤其在鋰離子電池充放電或環境溫度高於200℃時，電解液會與正極材料產生反應並釋出氧氣，導致電池發生洩漏、過熱、起火或爆炸等事故。去鋰化正極材料代表鋰離子電池於完全充電後，鋰離子由正極脫出並嵌入負極形成的過渡金屬氧化物。反之，鋰化正極材料代表在完全放電後，鋰離子由負極脫出並嵌入正極形成的鋰化正極材料。為了解正極材料與電解液的放熱行為，本研究運用微差掃描熱卡計（Differential Scanning Calorimeter, DSC）針對四種去鋰化(Co3O4、Mn2O4、FePO4、NiO2)與三種鋰化正極材料(LiCoO2、LiMn2O4、LiFePO4)分別混合五種電解液最常使用的有機碳酸酯類(DEC、DMC、EC、EMC、PC)，利用最簡化實驗環境(即，不包含鋰鹽、黏著劑與庫倫靜電位能場)，以模擬完全充電後與完全放電後之正極材料與電解液間熱分解危害情況，藉由測定所得之熱危害分析數據（放熱起始溫度與放熱量等數據）評估各別正極材料與電解液間之相對不穩定性。研究結果發現，鋰化正極材料的熱穩定性排序為：LiFePO4 > LiCoO2 > LiMn2O4；去鋰化正極材料的熱穩定性排序為: FePO4 > Co3O4 > Mn2O4 > NiO2。此外，由去鋰化與鋰化正極材料分別混合五種電解液之絕熱測試比較得知: 鈷酸鋰正極材料在模擬完全充電後較模擬完全放電後安全；錳酸鋰正極材料在充、放電後，對其放熱起始溫度影響不大；磷酸鋰鐵正極材料不論在充電或放電後，其放熱量皆低於200Jg-1(<250 Jg-1)，顯示熱穩定性良好，由本質較安全的理念適合用以開發大型動力或車用電池。
In the recent decade, equipments such as laptops, smart phones, and electronic products for vehicles have been developing rapidly and have had booming and innovating portable power sources and batteries. As the lithium-ion battery has high energy density, high power, and a long life, it can be charged and discharged to supply DC power more than several hundred times. Ever since SONY released the first commercial lithium-ion battery in 1991, a large variety of lithium-ion batteries has been massively developed and used. But during the extensive applications of lithium-ion batteries, they began to cause accidents. These incidents were due to various abuses such as overheating and fires, which led to injuries. The safety conditions of transportation, storage, and the use of the battery are now needed to be assessed seriously. When the lithium-ion battery is operated above 200 ℃under normal or abusive conditions, electrolyte and cathode material in charged and discharged states will especially react with each other and release oxygen that causes the battery to leak, catch fire, or explode.When a lithium-ion battery is charged, lithium ions migrate from their cathode and insert into their anode. In this study, de-lithiated cathode materials were used to simulate a lithium-ion battery in a fully charged state at which all lithium ions migrated from the cathode to the anode made of transition metal oxide and graphite, respectively. In contrast, lithiated cathode materials were used to simulate a lithium-ion battery in a fully discharged state at which all lithium ions were de-inserted from anode back to the cathode.In this study, four de-lithiated cathode materials (Co3O4, Mn2O4, FePO4, NiO2) and three lithiated cathode material (LiCoO2 , LiMn2O4, LiFePO4) were mixed, respectively, with five kinds of electrolyte that are the most commonly used organic carbonates (DEC, DMC, EC, EMC, PC) to compare their thermal instabilities which were then determined by DSC in the simplified chemical environment (i.e., without a lithium salt, adhesives and Coulomb electrostatic potential field). Data of exothermic onset temperature, peak temperature, and heat of reaction were investigated to clarify the relative instabilities of these cathode materials with individual carbonate.Results show that intrinsic stabilities of these lithiated cathode materials were ranked as followed: LiFePO4 > LiCoO2 > LiMn2O4 and Intrinsic instabilities of these de-lithiated cathode materials were ranked as followed: FePO4 > Co3O4 > Mn2O4 > NiO2. In addition, the results from the adiabatic tests show that lithium cobalt oxide cathode material is safer at a simulated fully charged state than that of a simulated discharged state. Lithium manganese oxide cathode material shows little or no effect on its exothermic onset temperature in either a simulated fully charged or a fully discharged state. Lithium iron phosphate cathode material shows the heat released is below 200Jg-1 (< 250 Jg-1) in both simulated fully charged and fully discharged state and depicts a good thermal stability suitable for safer development of large power and vehicle battery. |
