Lithium-ion batteries are widely used in electric vehicles and other fields, but the limited fast charging capacity has become a key problem restricting their development.
1.Material property influence.
The fast charging capacity of lithium-ion batteries is limited by the characteristics of key materials such as cathode and anode materials and electrolytes. At present, although cathode materials such as nickel-cobalt-lithium manganese oxide (NCM) and lithium iron phosphate (LFP) have good performance in terms of energy density and cycle life, the fast charging performance is relatively poor. In addition, anode materials are prone to lithium precipitation during fast charging, resulting in degraded battery performance and safety issues.
2.Electrochemical reaction limitations.
During the fast charging process of lithium-ion batteries, the electrochemical reaction speed is limited, resulting in an increase in internal resistance, an increase in heat generation, and a decrease in performance. Especially at high temperatures, the electrochemical reaction rate constant decreases, further limiting the fast charging capability. In addition, the rate performance of the battery is closely related to the electrochemical reaction kinetic parameters, and increasing the reaction rate is helpful to improve the fast charging performance.
3.Thermal management issues.
During the fast charging process, it is difficult to dissipate the heat generated by the battery evenly and effectively, resulting in an increase in battery temperature, which in turn affects the performance and safety of the battery. Lithium-ion batteries are prone to adverse reactions such as lithium evolution at high temperatures, which aggravates performance degradation. In order to solve the problem of thermal management, researchers propose a variety of low-temperature heating methods and battery cooling system designs to improve fast charging performance and safety.
4.Battery Management System (BMS) Limitations.
The battery management system controls the charging rate and cut-off voltage of the battery during the fast charging process to ensure the safety of the battery. However, BMS can limit the battery's power rating at low temperatures, resulting in a decrease in charging efficiency. In addition, the monitoring and control of the battery status by the BMS will also affect the fast charging performance.
5.Charging strategy impact.
The charging strategy has an important impact on the fast charging performance of lithium-ion batteries. A suitable charging strategy can reduce the internal resistance of the battery and improve the charging efficiency, thereby improving the fast charging performance. At present, researchers have proposed a variety of charging strategies, such as constant current-constant voltage charging, dual-stage charging, etc., but in practical applications, the optimization effect of charging strategies is limited due to factors such as battery materials and thermal management.
The reasons for the limited fast charging capacity of lithium-ion batteries mainly include material properties, electrochemical reactions, thermal management, battery management systems, and charging strategies.