鋰離子電池在能源革命能否成功中扮演者重大角色，除了對電池的性能與技術進行改良外，實際應用上可能遭遇的問題也是一個研究要點。電池一旦製作出來，發生老化反應是不可避免的。在電動車或儲能系統等需要大量電池經串、並聯組成模組或電池包的系統上，少數電池如果產生較高的老化程度就會影響整個模組或電池包的特性表現。如果能早期發現即時根據電化學原理分析老化原因，就能透過電池管理系統做適當處理，因此發展診斷電池老化的方法是有其重要性的。目前，為了解決里程焦慮等問題，快速充電已成為普遍的需求。一般認為快速充電會降低能源效率與加速電池之容量與功率的衰減，若能充分了解快充對電池的老化影響，便能朝這方面去設計電池的充電協議，進而使電池的壽命得以延長。
本研究以定電流分別為0.5C、0.75C、1.0C、1.5C與2.0C的定電流-定電壓充電模式與定電流分別為1.5C、1.0C、0.75C及0.5C的多重定電流-定電壓等六種充電法及固定0.5C定電流放電對日系M廠家的18650三元材料動力電池 (NMC//graphite) 進行800圈充放電循環測試。於開始及其後每完成100圈循環，進行一個0.04C定電流充放電循環與電化學阻抗分析，於100、300與500圈後每完成100圈進行參考性能測試。從0.04C循環可以得到電池的最大可用電容量，電化學阻抗分析與參考性能測試則能了解電池內部的阻抗變化。再由0.04C得到的充電曲線結合電容量增量分析法 (ICA) 與簡單結構模擬法可以估算電池內部的可循環鋰損失 (LLI)、正極活性材料損失 (LAMC) 及負極活性材料損失 (LAMA)。最後在跑完800圈循環後，將電池拆解進行分析，以SEM與TEM分析型態變化；XRD分析結構變化；鈕扣電池分析其成分的衰退，也用作和簡單結構模擬法的結果做對比，了解電池衰退的真正原因。
在最大可用電容量測試的部分，起初與預期相符合，使用大電流充電的電池其電容量保持率較低，而MCC充電協議並無發生減緩電池老化的情形，在300圈時電容量保持率呈現：0.5C > 0.75C > 1.0C > 1.5C > MCC > 2.0C。但在循環後期時發現使用低電流充電的電池，反而會得到較低的電容量保持率，如在循環800圈後電容量保持率呈現：1.5C > 2.0C > 0.75C > 1.0C > MCC > 0.5C。原因為發現在循環後期時，使用低電流充電的電池，在持壓段的時間會明顯增加，於高電壓下的時間提高，進而導致電池衰退速率上升。相關結果說明了在一開始使用低C-rate充電對電池較好，而在後期應設法縮減電池在高電壓下的充電時間，以減緩電池老化。ICA與程式模擬的結果顯示改變電流對電池造成的老化，主要都是以在負極端和可循環鋰的損失為主，如0.5C在跑完800圈後，模擬結果顯示LAMA為27.6%、LLI為22.8%，LAMC僅為2.9%。最後電池拆解分析的結果也顯示了負極的容量衰退遠大於正極，並且由於電池為卷繞型，與預期相符，越往中心的部分會有較大的衰退情形發生，原因為受到循環產生的膨脹收縮擠壓影響較大，而越往表面的部分則較為完整，也顯示了卷繞型電池會有不均勻老化的現象發生。電池拆解分析中求得的LAMA、LAMC與LLI也和程式模擬顯示的結果相符合，顯示本研究中成功建立了用於分析NMC532//graphite電池的診斷方法。

Lithium-ion batteries play an important role in the success of the energy revolution. In addition to improving the performance and technology of batteries, the problems encountered in practical applications are also a research point. Once the battery is manufactured, the aging reaction is inevitable. In systems such as electric vehicles or energy storage systems that require a large number of batteries to be connected in series or in parallel to form modules or battery packs, if a few batteries have a high degree of aging, the performance of the entire module or battery pack will be affected. Therefore, it is vital to develop a method for diagnosing battery aging. If the cause of aging can be found early and analyzed according to the electrochemical principle, the battery management system can promptly and adequately respond to it. Fast charging has become a common demand to solve problems such as range anxiety. It is generally believed that fast charging will reduce energy efficiency and accelerate the degradation of battery capacity and power. If we can fully understand the effect of fast charging on battery aging, we can design a battery charging protocol, thereby extending battery life.
In this study, 18650 power cells with NMC chemistry were obtained from
Japanese M company for charging with various constant rates of 0.5C, 0.75C, 1.0C, 1.5C, 2.0C in CC-CV modes and charging at 1.5C, 1.0C, 0.75C, 0.5C rate sequentially in multiple current-constant voltage charging mode with all discharged at 0.5C rate separately for 800 cycles. At the beginning and every 100 cycles after that, a 0.04C constant current charge-discharge cycle and electrochemical impedance analysis were performed, and after 100, 300, and 500 cycles, a reference performance test was performed every 100 cycles completed. The maximum available capacity of the battery can be obtained from the 0.04C cycle, and the electrochemical impedance analysis and reference performance test can understand the impedance change inside the battery. Then, the charging curve obtained from 0.04C is combined with the incremental capacity analysis (ICA) method and the simplified mechanistic simulation method to estimate the loss of inventory lithium (LLI), loss of active material in the anode (LAMA) and loss of active material in the cathode (LAMC). Finally, the battery was disassembled for post-mortem studies after running 800 cycles. The morphological changes were analyzed by SEM and TEM; the structural changes were analyzed by XRD; the coin cell was analyzed for compositional degradation, and it was also used to compare with the simplified mechanistic simulation method results.
In the section of the maximum available capacity test, batteries charged at high currents had lower capacity retention as initially expected. At the same time, the MCC charging protocol did not mitigate battery aging. The capacity retention shows 0.5C > 0.75C > 1.0C > 1.5C > MCC > 2.0C at 300 cycles. However, it is interesting to note that cells charged at lower currents had lower capacity retention in the period of late cycles. The capacity retention has a decreasing order like 1.5C > 2.0C > 0.75C > 1.0C > MCC > 0.5C at 800 cycles. We found that the time under the constant current section of the battery charged with the low current would increase significantly, and the increased time under high voltage would increase the battery degradation rate. The phenomenon deteriorated during the late period of cycling. The relevant results show that it is better to charge the battery with a lower C-rate at the beginning and try to reduce the charging time under high voltage in the late cycling period to mitigate the battery’s aging. The results of ICA and program simulation show that the battery’s aging is mainly on the negative electrode and inventory lithium. The program simulation shows 27.6% LAMA, 22.8% LLI, and 2.9% LAMC for 0.5C-aged battery at 800 cycles. The results from post-mortem studies also show that the capacity degradation of the negative electrode is much more significant than that of the positive electrode. And since the battery has a wound-electrode construction, as expected, the further to the center part will have a more considerable degradation because it is greatly affected by the expansion and contraction caused by cycling. In contrast, the part further to the surface remains intact, showing the wound-type battery will have uneven aging phenomenon. The LAMA, LAMC, and LLI obtained in the post-mortem analysis are also consistent with the results displayed by the program simulation, indicating that a diagnostic method for analyzing NMC532//graphite batteries has been successfully established in this study.

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