Figure 6 Morphological changes on the surface of the negative electrode
The Impact of High Temperatures on Battery Life
High operating temperatures: On one hand, they cause the long-term reduction of the electrolyte by the anode at low potentials, resulting in the loss of active lithium ions and a decline in electrochemical performance; on the other hand, high temperatures increase side reactions at the anode, leading to the deposition of inorganic reaction products on the anode surface that hinder the insertion and extraction of lithium ions, accelerating battery aging. At high temperatures, these side reactions increase, such as the decomposition, rupture, or dissolution of the SEI film on the negative electrode surface, causing continuous consumption of lithium ions during cycling and rapid capacity decline.
Ahmad A. Pesaran’s research indicates that when the battery operating temperature exceeds 40°C, the battery’s cycle life halves for every 10°C increase. In the battery packs of new energy vehicles, the tight arrangement of individual cells causes heat accumulation, resulting in temperature differences within the pack, leading to different rates of degradation among individual cells, disrupting the uniformity of the pack, and reducing overall performance.
The temperature of the battery is positively correlated with the charge and discharge current. When charging and discharging with a small current, the highest temperature point of the battery pack is in the middle, where heat exchange with the outside is less likely to occur. When charging and discharging with a large current or when the ear structure design is unreasonable, the highest temperature is at the ear.
Therefore, designing a battery cooling system reasonably according to the characteristics and operating environment of power batteries can not only improve the range performance of the vehicle but also enhance the overall safety and reliability.
The Impact of Temperature Differences on Battery Performance
Battery temperature differences can be categorized into two types: internal temperature differences within a battery, which manifest as temperature uniformity; and temperature differences between individual battery cells, which manifest as temperature consistency.
Causes of internal temperature differences: Generally, during low-temperature heating conditions or high-temperature cooling conditions in water-cooling systems, when a battery module is heated or cooled on one side only, a significant internal temperature difference may occur due to the high thermal resistance of the individual battery cells. This temperature difference is related to the internal structure and material composition of the battery and is difficult to avoid from the perspective of thermal management system design.
Causes of temperature differences between cells: The temperature difference between individual battery cells is mainly determined by the arrangement of the battery module and the structure of the battery thermal management system. This temperature difference can be reduced by optimizing the thermal management design.
Impact of internal temperature differences on individual cells
Excessive internal temperature differences in a battery can cause uneven internal impedance, uneven current distribution, and uneven heat generation, which in turn affect the battery’s performance and accelerate the rate of battery capacity degradation. However, the differences between individual cells are usually small, and thus have a minor impact on consistency.
Impact of temperature differences between cells on the battery
Excessive temperature differences between battery cells can lead to inconsistent performance and capacity degradation rates among the cells within a battery assembly. Since the cells within a battery pack are connected in series, any decline in performance or capacity degradation of a single cell will affect the overall performance of the assembly. Therefore, controlling the consistency of battery temperature is crucial.
Additionally, temperature differences between cells can have a continuous cumulative effect. Cells with higher temperatures age faster, generate more heat, and are more prone to high temperatures.
Conclusion
The operating temperature range of lithium batteries varies depending on the type of lithium battery. Both excessively high and low temperatures can affect the performance of lithium batteries, and in severe cases, may even shorten the battery’s lifespan. To effectively charge, the environmental temperature range for lithium batteries should be between 20-30°C.
In summary, the factors affecting the battery’s performance at high and low temperatures can be summarized as: conductivity of the electrolyte, interfacial impedance, SEI film, etc. These factors collectively affect the battery’s performance. Generally speaking, improving the conductivity or electrical conductivity of the battery components (including choosing more conductive active materials, optimizing electrolyte composition, improving the anode SEI film composition, and suppressing the dissolution of surface materials from the cathode) can help reduce the overall impedance of the battery, which is beneficial for enhancing performance at high and low temperatures. Lithium-ion batteries’ adaptability to temperature is similar to that of the human body; both excessively high and low temperatures are detrimental to their optimal function. Choosing the right materials, optimizing structural design, and customizing appropriate usage conditions are necessary to fully realize their performance.
Source: ATC New Energy Three-Electrics WeChat Public Account
https://mp.weixin.qq.com/s/QNMwYXcf_CiZw2zkjSM16A