With the rapid development of electric vehicles worldwide, the market size of electric vehicles has reached $1 trillion in 2020 and will continue to grow at a rate of more than 20% per year in the future. Therefore, electric vehicles as a major mode of transportation, the performance requirements for power batteries will be increasingly high, and the impact of battery decay on power battery performance in low-temperature environments should not be ignored. The main reasons for battery decay in low-temperature environments are: First, the low temperature affects the small internal resistance of the battery, the thermal diffusion area is large, and the internal resistance of the battery increases. Second, the battery inside and outside the charge transfer capacity is poor, the battery deformation will occur when the local irreversible polarization. Third, the low temperature of the electrolyte molecular movement is slow and difficult to diffuse in time when the temperature rises. Therefore, low temperature battery decay is serious, resulting in serious battery performance degradation.
1、The status of low temperature battery technology
The technical and material performance requirements of lithium-ion power batteries prepared at low temperatures are high. The serious performance degradation of lithium-ion power battery in low temperature environment is due to the increase of internal resistance, which leads to the difficulty of electrolyte diffusion and shortened cell cycle life. Therefore, the research on low temperature power battery technology has made some progress in recent years. Traditional high-temperature lithium-ion batteries have poor high-temperature performance, and their performance is still unstable under low-temperature conditions; large volume of low-temperature cells, low capacity, and poor low-temperature cycle performance; polarization is significantly stronger at low temperature than at high temperature; increased viscosity of electrolyte at low temperature leads to a reduction in the number of charge/discharge cycles; reduced safety of cells and reduced battery life at low temperature; and reduced performance in use at low temperature. In addition, the short cycle life of the battery at low temperature and the safety risks of low-temperature cells have put forward new requirements for the safety of power batteries. Therefore, the development of stable, safe, reliable and long-life power battery materials for low-temperature environments is the focus of research on low-temperature lithium-ion batteries. At present, there are several low-temperature lithium-ion battery materials: (1) lithium metal anode materials: lithium metal is widely used in electric vehicles because of its high chemical stability, high electrical conductivity and low-temperature charge and discharge performance; (2) carbon anode materials are widely used in electric vehicles because of their good heat resistance, low-temperature cycle performance, low electrical conductivity and low-temperature cycle life at low temperatures; (3) carbon anode materials are widely used in electric vehicles because of their good heat resistance, low-temperature cycle performance, low electrical conductivity and low-temperature cycle life. in; (3) organic electrolytes have good performance at low temperature; (4) polymer electrolytes: polymer molecular chains are relatively short and have high affinity; (5) inorganic materials: inorganic polymers have good performance parameters (conductivity) and good compatibility between electrolyte activity; (6) metal oxides are less; (7) inorganic materials: inorganic polymers, etc.
2、The effect of low temperature environment on lithium battery
The cycle life of lithium batteries depends mainly on the discharge process, while low temperature is a factor that has a greater impact on the life of lithium products. Usually, under low temperature environment, the surface of the battery will undergo phase change causing surface structure damage, accompanied by capacity and cell capacity reduction. Under high temperature conditions, gas is generated in the cell, which will accelerate thermal diffusion; under low temperature, gas cannot be discharged in time, accelerating the phase change of battery liquid; the lower the temperature, the more gas is generated and the slower the phase change of battery liquid. Therefore, the internal material change of the battery is more drastic and complex under low temperature, and it is easier to generate gases and solids inside the battery material; at the same time, the low temperature will lead to a series of destructive reactions such as irreversible chemical bond breakage at the interface between the cathode material and electrolyte; it will also lead to the reduction of electrolyte self-assembly and cycle life; the lithium ion charge transfer capability to the electrolyte will be reduced; the charging and discharging process will cause a series of chain reactions such as polarization phenomenon during lithium ion charge transfer, battery capacity decay and internal stress release, which affects the cycle life and energy density of lithium ion batteries and other functions. The lower the temperature at low temperature, the more intense and complex the various destructive reactions such as redox reaction on the battery surface, thermal diffusion, phase change inside the cell and even complete destruction will in turn trigger a series of chain reactions such as electrolyte self-assembly, the slower the reaction speed, the more serious the battery capacity decay, and the poorer the lithium ion charge migration ability at high temperature.
3、 Low temperature on the progress of lithium battery technology research prospects
In the low temperature environment, the safety, cycle life and cell temperature stability of the battery will be affected, and the impact of low temperature on the life of lithium batteries cannot be ignored. At present, the low temperature power battery technology research and development using diaphragm, electrolyte, positive and negative electrode materials and other methods have made some progress. In the future, the development of low-temperature lithium battery technology should be improved from the following aspects: (1) the development of lithium battery material system with high energy density, long life, low attenuation, small size and low cost at low temperature; (2) continuous improvement of battery internal resistance control through structural design and material preparation technology; (3) in the development of high-capacity, low-cost lithium battery system, attention should be paid to electrolyte additives, lithium ion and anode and cathode interface and internal active material and other key factors influence; (4) improve the battery cycle performance (charge and discharge specific energy), the thermal stability of the battery in low temperature environment, the safety of lithium batteries in low temperature environment and other battery technology development direction; (5) develop high safety performance, high cost and low cost power battery system solutions in low temperature conditions; (6) develop low temperature battery-related products and promote their application; ( 7) develop high-performance low-temperature resistant battery materials and device technology.
Of course, in addition to the above research directions, there are also many research directions to further improve battery performance under low temperature conditions, improve the energy density of low temperature batteries, reduce battery degradation in low temperature environments, extend battery life and other research progress; but the more important issue is how to achieve high performance, high safety, low cost, high range, long life and low cost commercialization of batteries under low temperature conditions is the current The research needs to focus on breaking through and solving the problem.
Post time: Nov-22-2022