The main reasons for battery degradation at low temperatures are: First, low temperatures result in lower internal resistance and a larger thermal diffusion area, leading to increased internal resistance. Second, the battery's internal and external charge transfer capabilities are poor, and localized irreversible polarization occurs when the battery deforms. Third, electrolyte molecules move slowly at low temperatures and cannot diffuse effectively as the temperature rises. Therefore, battery degradation is severe at low temperatures, resulting in significant performance degradation.
1. Current Status of Low-Temperature Battery Technology
Lithium-ion power batteries prepared at low temperatures require high-performance technologies and materials. The severe performance degradation of lithium-ion power batteries at low temperatures is due to increased internal resistance, which hinders electrolyte diffusion and shortens cell cycle life. Therefore, research on low-temperature power battery technology has made some progress in recent years. Traditional high-temperature lithium-ion batteries exhibit poor high-temperature performance and remain unstable at low temperatures; low-temperature cells are large, have low capacity, and poor low-temperature cycle performance; polarization is significantly stronger at low temperatures than at high temperatures; increased electrolyte viscosity at low temperatures leads to fewer charge-discharge cycles; cell safety and battery life decrease at low temperatures; and overall performance deteriorates. Furthermore, the short cycle life and safety hazards of low-temperature cells pose new requirements for power battery safety. Therefore, developing stable, safe, reliable, and long-life power battery materials for low-temperature environments is a key focus of low-temperature lithium-ion battery research. Currently, the main low-temperature lithium-ion battery materials available domestically and internationally include:
Lithium metal anode materials: Due to the advantages of lithium metal, such as high chemical stability, high conductivity, and good low-temperature charge-discharge performance, it is widely used in electric vehicles;
Carbon anode materials are widely used in electric vehicles due to their advantages such as good heat resistance, low-temperature cycling performance, low conductivity, and low-temperature cycle life at low temperatures.
Organic electrolytes exhibit better performance at low temperatures;
Polymer electrolytes: Polymer molecules have relatively short chains and high affinity;
Inorganic materials: Inorganic polymers exhibit good performance parameters (conductivity) and good compatibility with electrolyte activity;
Fewer metal oxides;
Inorganic substances: inorganic polymers, etc.
2. The impact of low temperature environment on lithium batteries
The cycle life of lithium batteries primarily depends on the discharge process, and low temperature is a significant factor affecting the lifespan of lithium products. Typically, at low temperatures, phase transitions occur on the battery surface, causing surface structural damage and resulting in a reduction in capacity and cell capacity. At high temperatures, gas is generated within the cell, accelerating heat diffusion; at low temperatures, this gas cannot escape quickly, accelerating the phase transition in the battery liquid. The lower the temperature, the more gas is generated, and the slower the phase transition in the battery liquid. Therefore, the internal material changes of the battery are more drastic and complex at low temperatures, making it easier for gases and solids to be generated within the battery materials. Simultaneously, excessively low temperatures can lead to a series of destructive reactions, such as irreversible chemical bond breakage at the interface between the negative electrode material and the electrolyte; it also reduces the degree of electrolyte self-assembly, shortens cycle life, and decreases the ability of lithium-ion charge transfer to the electrolyte. During charging and discharging, a series of chain reactions occur, including polarization during lithium-ion charge transfer, battery capacity decay, and internal stress release, affecting the cycle life and energy density of lithium-ion batteries. At low temperatures, the lower the temperature, the more intense and complex the various destructive reactions such as oxidation-reduction reactions on the battery surface, thermal diffusion, and phase changes inside the cell become. In some cases, the complete destruction of the battery can trigger a series of chain reactions, such as electrolyte self-assembly, slower reaction speed, more severe battery capacity decay, and poorer lithium-ion charge migration ability at high temperatures.
3. Prospects for the Research Progress of Low Temperature in Lithium-ion Battery Technology
In low-temperature environments, battery safety, cycle life, and cell temperature stability are all affected, and the impact of low temperatures on lithium battery life cannot be ignored. Currently, the development of low-temperature power battery technologies, employing various methods such as separators, electrolytes, and positive and negative electrode materials, has made some progress. In the future, the development of low-temperature lithium battery technology should focus on improvements in the following aspects:
A lithium battery material system with high energy density, long lifespan, low degradation, small size, and low cost at low temperatures has been developed.
Continuously improve the battery's internal resistance control capability through structural design and material preparation technology;
When developing high-capacity, low-cost lithium battery systems, attention should be paid to the influence of key factors such as electrolyte additives, lithium-ion interfaces with positive and negative electrodes, and internal active materials.
Improving battery cycle performance (charge-discharge specific energy), battery thermal stability at low temperatures, lithium battery safety at low temperatures, and other battery technology development directions;
Develop a power battery system solution with high safety performance, high cost, and low cost under low temperature conditions;
Develop and promote the application of low-temperature battery-related products;
Develop high-performance, low-temperature resistant battery materials and device technologies.
Of course, in addition to the research directions mentioned above, there are many other research directions that can further improve battery performance under low temperature conditions, increase the energy density of low temperature batteries, reduce battery degradation under low temperature conditions, and extend battery life. However, the more important issue is how to achieve high performance, high safety, low cost, long driving range, long life, and low cost commercial use of batteries under low temperature conditions. This is a key issue that needs to be addressed and resolved in current research.
