高溫熔融鹽電解質之第一原理分子動力學模擬及熱電池性能之有限單元分析

First Principles Molecular Dynamics Simulation of High Temperature Molten-salt Electrolytes and FEM Analysis on Thermal Battery Performance

鄭宜佳(Yi-Chia Cheng)

指導教授 ： 洪哲文

國立清華大學/工學院/動力機械工程學系/碩士(2016年)

摘要

本研究主要以多尺度模擬方法，藉由第一原理分子動力學(FPMD)所計算之材料性質，結合有限元素法(FEM)計算於高溫作用下熔融鹽電解質熱電池之熱/質傳巨觀性能，評估熱電池在不同操作溫度下對電池性能之影響；後續參考國外文獻所提供之實驗結果，以驗證本研究模型之正確性與可行性，進而建立一套具多尺度且完整的模擬工具，期能達到開發新式熔融鹽電解質熱電池之性能預測與最佳化目的。
熱電池又稱為熱激發電池，屬熔融鹽電池的一種，主要特徵為使用之電解質由共晶混合鹽所組成，當外部點火器啟動給予熱源時，透過各單電池的上下熱片傳遞大量的熱，迅速使電解質呈熔融態，並使熱電池開始作電化學反應。本研究首先從熔鹽電解質之二元(binary)材料出發，建構微觀尺度模型，利用量子力學計算原子分布/組成、勢能模型及離子擴散性等，並輔以分子動力學計算離子傳導率、熱傳導率、比熱與熔點等性質；接著運用有限元素分析法建構巨觀尺度模型及代入微觀尺度模型所計算之性質，求解溫度分布及濃度場，並導入電化學理論，進而探討熱電池放電性能最佳化分析與評估熱效應造成之影響。
有別於傳統LiCl-KCl二元(binary)電解質，本研究尚提出具備成本低、安全性佳且不易造成環境破壞等優點之LiCl-LiBr-based三元(ternary)、四元(quaternary)新型電解質材料，並從模擬結果中顯示它們可大幅提升電池性能。其中，三元(ternary)材料擁有較大之比功率，約為傳統二元(binary)材料之1.5倍；此外，四元(quaternary)材料不但可有效降低操作溫度(低熔點)，減少電池失效機率，亦可延長電池作用時間(壽命)。本研究成果，除可有效降低熱電池研發成本，大幅縮減研發時程，可作為未來研發設計新型熱電池之重要參考依據，從而提升台灣國防科技國機國造之競爭力。

關鍵字

熱電池 ； 熔融鹽電解質 ； 第一原理分子動力學 ； 有限單元法 ； 電化學 ； 放電性能

並列摘要

This research aims to develop some novel ternary and quaternary molten electrolytes to enhance the overall performance of high-temperature molten salt batteries. The methodology in this study is based on the multi-scale simulation technique, combining first principle molecular dynamics (FPMD) to obtain material properties with the finite element method (FEM) to predict heat/mass transfer and electrochemical performance in macro-scale performance of molten-salt thermal batteries at different operating temperatures. The simulation result will be compared with reference and experimental result from foreign literature, in order to verify the correctness and feasibility of this research.
Our objective is to optimize the novel electrolytes with the greatest ionic conductivity and lowest melting point, also to develop the multi-cell system with the optimized I-V performance without thermal run-away and short-circuit. The finite element method is used to solve the temperature distribution and concentration field on the LiCl-KCl electrolyte thermal battery at operating temperatures. Besides, the electrochemical theory is needed to analysis the thermal effects of the internal electrolyte, ionic transport phenomena, and the discharge performance. In addition, the internal heat source is carried out to detailed studies, in order to predict the failure of batteries which is caused by two main reasons: thermal runaway and short-circuit.
Finally, this study also predicts macroscopic performances of LiCl-LiBr-based ternary and quaternary systems. All these simulation techniques provide a low cost alternative to experiments and are able to optimize the battery design at the realistic operating conditions.

並列關鍵字

thermal battery ； molten-salt electrolyte ； first principle molecular dynamics ； finite element method ； electrochemistry ； discharge performance

參考文獻

[30] 李皓宇(指導教授 洪哲文)，“熔融電解質熱電池之熱質傳性質與性能分析”， 清華大學動力機械工程學系碩士論文，07/2015.

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