鋰電池衰退模型之建構與最大放電量分析

Modeling of Capacity Fading and Investigation of Maximum Capacity for Lithium-Ion Batteries

劉師程(Shih-Cheng Liu)

指導教授 ： 吳文方

國立臺灣大學/工學院/工業工程學研究所/碩士(2014年)

https://doi.org/10.6342/NTU.2014.10811

摘要

電池的失效將導致產品性能的衰退、運作能力的喪失、甚至對於人身安全的危害，因此，增進電池健康並降低電池衰退速率是專家學者近年來努力尋求改善的方向。鋰電池衰退的機制及過程相當複雜，就使用條件與外在環境影響而言，影響電池壽命的主要因素為環境溫度、充放電速率、放電深度等。本研究採用NASA Ames Prognostics Center of Excellence (PCoE)針對型號18650商用鋰電池加速試驗之結果數據，首先以擬合與回歸方法建構鋰電池容量之衰退模型，得到兩種可用於鋰電池循環壽命估計的經驗模型：容量衰退率為乘冪趨勢模型與容量衰退率為指數趨勢模型。此兩種模型可大幅減少爾後繁複的實驗過程，用以評估鋰電池在不同環境因素影響下的循環壽命。本研究以此兩模型為基礎，並以電池管理者的角度，針對鋰電池循環壽命、放電深度、放電速率等特性一一討論，嘗試建構一個電池電量最佳化的求解問題，藉以探討使用者使用行為與電池壽命間的關係，同時評估鋰電池失效前所能釋放的最大電量及其壽命。本研究發現在高放電速率情況下，電容量衰退率較符合指數趨勢。本研究也發現在常溫定電流放電、放電速率為1C、電池失效分別定義為70%、60%與50% SOH (State of Health)情況下，當電池端電壓分別放電至3.02 V、2.98 V與2.96 V時停止放電，可得電池生命週期中最大放電量分別為253,997 mAh、284,183 mAh與304,447 mAh，同時也可得到各情況下所對應之失效循環數目。本研究結果可供使用者與電池廠商參考，讓鋰電池在其生命週期中發揮最大效益。

關鍵字

鋰電池衰退模型 ； 循環壽命 ； 放電深度 ； 最佳化

並列摘要

Since the failure of a battery could lead to loss of operation, reduced capability, downtime, and even catastrophic failure, to improve its health and reduce its degradation are important issues to researchers and experts. The mechanism of battery degradation is complicated and related to conditions of usage as well as other external characteristics. Factors affecting the battery life include the ambient temperature, charge and discharge rate, depth of discharge, etc. This research is based on accelerated life test data collected from NASA Ames Prognostics Center of Excellence (PCoE) for its custom-built type 18650 lithium-ion battery. Two capacity fading models are proposed from curve fitting and regression analysis of the data. These two models are then used for estimating cycle-life of the battery in consideration of environmental factors. Based on these two models, this research also investigates relations between battery life and its usage conditions from battery-management point of view. The purpose is to obtain the maximum total capacity of the battery in its life cycle through a battery management optimization problem in which both the depth of discharge and discharge rate are considered. Through the analysis, it is found that an exponential trend fits better than the power trend in capacity fading for higher rates of discharge. It is also found that, when the discharge is in room temperature, the rate of discharge is 1C, and failures of battery are defined as 70%、60% and 50% of the SOH, the maximum total capacities in the life cycle of battery are 253,997, 284,183 and 304,447 mAh, respectively. Moreover, it is suggested to terminate the discharge when the voltage decreases to 3.02 V, 2.98 V and 2.96 V for each of the above conditions. Their corresponding cycle-lives can be found as well. It is believed that the above results can provide battery users as well as manufacturers to achieve the optimal usage of the battery in its life cycle.

並列關鍵字

battery degradation models ； cycle life ； depth of discharge ； optimization

參考文獻

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