鋰電池中小變形對鍍鋰的影響

Abstract

鋰離子的研究至目前為止，均顯示電池在循環過程中會因為電池的的狀態導致同樣的電池有不同的老化行為，甚至引發電池內短路。而在實際的產品中也發現鋰離子電池因為工業製造上有些許的小變形缺陷，進而導致了鋰金屬沉積，但是目前的研究對於其中的機制還並不了解，也沒有物理上的模型可以描述這種行為。電池的機械性質已經有非常多的團隊使用不同的力學模型進行研究，也有非常多關於電池材料的應力應變關係文獻已經發表。但是目前仍然缺少對於工業製程上的缺陷影響電池循環壽命以及性能的文獻，也沒有文獻建立此種描述小缺陷導致的電池老化、損壞行為的物理模型。因此我們蒐集了電池內部各種材料的應力應變關係，再以孔隙率與體積應變關係的連結將力學模型與電化學模型結合，結果顯示鋰離子電池隔離膜機械性質弱於其他電池內部的材料。而最後力學與電化學模型的模擬的結果也能發現電池內部受到的微小變形受產生的局部過度充電的行為以及受到壓縮的負極與隔離膜交界處產生了鋰金屬沉積，而且此種鋰金屬沉積的現象也可以透過降低充電電流來降低小變形缺陷所造成的影響。我們也調整了電池的幾何形狀，發現增加隔離膜厚度也能增強鋰離子電池忍受變形的能力。因此在鋰離子電池的製造、組裝上我們的模型提供了一個方法，能描述電池機械性質與電性之間的關係，也能配合電池材料的機械性質參數、化學參數、導電度參數等等設計出適合其工作環境的電池。此外，我們也利用孔隙率的變化模擬了氣體生成的情況，發現氣體生成會使電解液的濃度梯度增大，出現了劇烈的電解液濃度變化。過高的電解液濃度與過低的電解液濃度則有可能會造成電解液分解，加速鋰離子電池的衰亡。

Lithium ion research has so far found that the same battery has different aging behaviors due to the state of the battery during the cycle of the battery, and even causes a short circuit inside the battery. In actual products, lithium-ion batteries may also be found to have some small deformation defects in industrial manufacturing, which leads to lithium metal deposition. However, the current research does not understand the mechanism, and there is no physical model to describe this behavior. The mechanical properties of batteries have been studied by many teams using different mechanical models, and there are many literatures on the stress-strain relationship of battery materials that have been published. However, there is still a lack of literature on the effects of defects in industrial processes on battery cycle life and performance, and there is no literature to establish such a physical model for describing battery aging and damage behavior caused by small defects. Therefore, we collected the stress-strain relationship of various materials inside the battery, and then combined the mechanical model with the electrochemical model by the relationship between porosity and volumetric strain. The results show that the mechanical properties of the lithium ion battery separator are weaker than those of other materials. Finally, the simulation results of the mechanical and electrochemical models can also find the local overcharge behavior caused by the small deformation inside the battery and the deposition of lithium metal at the junction of the compressed negative electrode and the separator. The phenomenon can also reduce the impact of small deformation defects by reducing the charging current. We also adjusted the geometry of the battery and found that increasing the thickness of the separator also enhances the ability of the lithium-ion battery to withstand deformation. Therefore, in the manufacture and assembly of lithium battery, our model provides a method to describe the relationship between the mechanical properties of the battery and the electrical properties. It can also be designed with the mechanical properties, chemical parameters, conductivity parameters, etc. of the battery materials. Then design a battery suitable for its working environment.In addition, we also used the change in porosity to simulate the gas generation. It was found that the gas generation increased the concentration gradient of the electrolyte and caused a drastic change in electrolyte concentration. Excessive electrolyte concentration and too low electrolyte concentration may cause decomposition of the electrolyte and accelerate the decline of the lithium ion battery.