Abstract:This paper discusses in detail the multi-faceted effects of lithium evolution on battery capacity, including active lithium ion loss, lithium dendrite growth, battery performance degradation, safety risks and battery aging. This paper analyzes the various factors that lead to lithium evolution, and focuses on effective strategies to prevent lithium evolution through electrolyte composition adjustment, such as the use of high-concentration electrolytes, functional additives or alternative salts/solvents, optimization of electrolyte formulations, and the use of novel borate-pyran electrolytes, etc., in order to provide a reference for improving the performance and safety of lithium batteries.
I. Introduction
Lithium batteries may be separated during charging and discharging, which seriously affects the capacity, cycle life and safety of the battery. Therefore, it is of great practical significance to study the phenomenon of lithium battery evolution and its prevention and control strategies in depth.
2. The impact of lithium battery evolution on battery capacity
(1) Loss of active lithium ions
During charging, if the lithium ions fail to be embedded in the anode material normally, but instead precipitate on the surface of the anode to form metallic lithium, this will lead to a permanent loss of active lithium ions, thus reducing the usable capacity and performance of the battery.
(2) Growth of lithium dendrites
The growth of lithium dendrites is the main way for lithium evolution to lead to the loss of active lithium ions. Lithium dendrites can continue to grow, piercing the battery separator and causing a short circuit inside the battery, which not only further exacerbates the loss of active lithium ions, but also may cause safety accidents.
(3) Battery performance declines
Lithium separation will increase the internal resistance of the battery, reduce the charging efficiency, reduce the discharge capacity, and affect the rate performance and cycle life of the battery, which greatly shortens the service life of the battery.
(4) Security risks
Excessive lithium separation may lead to an increase in the internal temperature of the battery, causing thermal runaway, and even catastrophic consequences such as combustion and explosion, which poses a serious threat to the safety of users' lives and property.
(5) Aging of batteries
In the case of defects inside the battery, such as the unstable structure of the anode material, the decomposition of the electrolyte, etc., electrode lithium separation is more likely to occur. As the battery life increases, lithium evolution accelerates, becoming one of the main reasons for the decline in battery capacity.
3. Factors affecting lithium battery lithium evolution
(1) Charging rate
Too high a charging rate causes lithium ions to be deposited on the surface of the anode faster than their intercalation rate, triggering lithium precipitation.
(2) Temperature
In the low temperature environment, the diffusion rate of lithium ions slows down, the internal resistance of the battery increases, and lithium precipitation is easy to occur during the charging process.
(3) Aging of batteries
During the long-term use of the battery, the structure and properties of the cathode and anode materials will change, and the composition of the electrolyte will also be lost, which may increase the risk of lithium evolution.
(4) Pole piece design
The unreasonable design of parameters such as specific surface area and porosity of anode materials will affect the insertion and expulsion of lithium ions, resulting in the occurrence of lithium precipitation.
4. Adjust the composition of the electrolyte to prevent lithium battery from detoxifying
(1) High-concentration electrolyte
The use of a higher concentration electrolyte (e.g., ≥4 mol/L) results in a higher ionic density and lower solvent molecular activity than a traditional low-concentration electrolyte. This contributes to the formation of a more stable solid electrolyte interface (SEI) film with good lithium ion conductivity, which makes the deposition and ejection of lithium ions more uniform during charging and discharging, thereby inducing compact lithium metal plating and reducing the occurrence of lithium precipitation.
(ii) Functional additives or alternative salts/solvents
Specific functional additives, such as vinylene carbonate (VC), fluoroethylene carbonate (FEC), etc., can improve the composition and structure of SEI films, enhance their stability and ionic conductivity, and thus reduce lithium loss. In addition, the use of alternative salts/solvents, such as novel ionic liquids or high flash point solvents, can also improve the electrochemical stability and safety of the electrolyte, reducing the potential for lithium evolution.
(3) Optimization of electrolyte formulation
Through in-depth research and optimization of electrolyte formulation, the physicochemical properties of electrolyte can be improved by selecting appropriate solutes, solvents and their ratios. For example, the use of chlorinated ethylene carbonate instead of traditional dimethyl carbonate as a solvent can enhance the oxidation resistance and stability of the electrolyte, reduce the side reactions of lithium ions, and thus reduce the risk of lithium evolution.
(iv) Borate-pyrano electrolyte
Borate-pyran electrolyte is a new type of electrolyte system, and its special structure and chemical properties can significantly improve the cycling stability of batteries. It can reduce the expansion rate of lithium anode, effectively inhibit the growth of lithium dendrites, thereby effectively preventing the occurrence of lithium precipitation, and provide a strong guarantee for the long life and high-performance operation of lithium batteries.
V. Conclusions
The phenomenon of lithium battery separation is one of the key issues affecting the performance and safety of batteries. Through in-depth analysis of the multi-faceted impact of lithium on battery capacity and the factors leading to lithium precipitation, targeted measures can be taken to prevent and control it. Among the various control strategies, the adjustment of electrolyte composition is an effective means. The performance of batteries can be improved, lithium evolution can be reduced, battery life can be extended and battery safety can be improved through the use of highly concentrated electrolytes, functional additives or alternative salts/solvents, optimized electrolyte formulations, and the use of innovative borate-pyran electrolytes. In order to achieve a comprehensive optimization of lithium battery performance, it is also necessary to comprehensively consider the positive and negative electrode materials, battery structure design, manufacturing process and other factors of the battery, and continue to carry out in-depth research and innovation.
Article source: lithium battery technology knowledge platform
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