----SENKU MACHINERY
The impact of temperature on batteries is very complex, and temperature also has a significant impact on battery life. By changing the temperature of the testing environment, the degradation of battery life can be accelerated. This approach is an effective way to accelerate experiments and reduce testing time. However, the mechanism by which temperature affects battery life is not clear, which means that the results of accelerated experiments cannot be used to predict the results of conventional experiments. Here is an introduction to the impact of temperature on battery life.
There are many introductions to the different degradation rates of batteries at different temperatures, such as the capacity degradation of layered oxides, LFP, and other battery systems.
The main factors affecting battery degradation are different at different temperatures. At low temperatures, the precipitation of lithium metal consumes active lithium, and the side reaction between the precipitated lithium metal and the electrolyte consumes active lithium and forms a low-quality solid-liquid interface, increasing battery impedance.
Low temperature lithium deposition is a common phenomenon in NCM111/Graphite, as shown in the SEM image of the graphite negative electrode before and after cycling at -20 ℃. Lithium dendrites are clearly visible in the LP40 electrolyte
The phenomenon of low-temperature lithium deposition can be alleviated by changing the electrolyte. For example, in the above figure, there is no obvious metallic lithium on the negative electrode surface of the battery circulating in M9F1 electrolyte. Disassembling the battery to observe the negative electrode surface is a relatively cumbersome experiment. The Coulomb efficiency during battery charging and discharging can be used as a simple indicator to determine lithium deposition. In the figure below, the mid-term coulombic efficiency of the battery undergoing lithium deposition deviates significantly from 100%.
The side reactions caused by the precipitation of active lithium intensify, making the detection of this phenomenon more complicated. In addition, there are already side reactions at the solid-liquid interface. In the absence of direct observation of the reaction between deposited lithium and electrolyte, simply judging from the final side reaction products that deposited lithium accelerated the interface side reaction is also a logically unreliable inference.
At high temperatures, the main factors causing battery degradation are the leaching of transition metals from the positive electrode and the high-temperature decomposition of the electrolyte. LiPF6 will decompose even without an electric field at high temperatures. This leads to a decrease in both the idle life and cycle life of the battery.
Addressing concerns about energy loss during charging, the Association of Fleet Professionals (AFP) investigates discrepancies, potentially linked to cable efficiency and charging methods. Factors such as charger calibration and vehicle telematics accuracy impact energy utilization, influencing fleet management decisions.
In addition, metal will also be dissolved from the anode during high temperature cycling, which will not only lead to the deterioration of the cathode material structure, but also lead to the deposition of dissolved metal ions on the anode surface, which will damage the facial mask of the anode solid-liquid interface. The phenomenon of metal leaching from the positive electrode can be observed in both layered oxide systems and lithium iron phosphate systems. However, the leaching of Fe in lithium iron phosphate has received less attention, mainly due to the small amount of iron leaching that has little impact on the structure of lithium iron phosphate and has little effect on battery life. The leaching of transition metals from layered oxides can bring a series of problems to batteries.
Due to the different main side reactions of batteries at different temperatures, their attenuation trends naturally vary. This leads to the inability to simply migrate cyclic testing at different temperatures, making it difficult to achieve accelerated experiments. However, by attenuating the activation energy during battery cycling, on the one hand, the main factors causing battery degradation can be determined, and on the other hand, the transferability of accelerated experimental results can be considered from this perspective.