The reasons for the decline in battery performance in winter are mainly attributed to the following aspects
1. **Decrease in electrolyte conductivity**:
At low temperatures, the viscosity of the electrolyte increases, resulting in a decrease in the migration rate of lithium ions and a decrease in the ionic conductivity of the electrolyte. This directly affects the charge and discharge efficiency of the battery, increases the internal resistance of the battery, and thus affects the battery performance.
2. **Increase in electrode/electrolyte interface impedance**:
Under low temperature conditions, the interface stability between the electrolyte and the electrode deteriorates, resulting in an increase in interface impedance. This increase in interface impedance will lead to a decrease in the charge and discharge efficiency of the battery, and the battery capacity and cycle life will be affected accordingly.
3. **Decrease in lithium ion migration rate**:
Under low temperature conditions, the migration rate of lithium ions in the active material body decreases, resulting in a slower kinetic process during battery charge and discharge.
In order to improve battery performance under low temperature conditions, the following measures can be taken:
1. **Optimize electrolyte formulation**:
The low temperature performance of the electrolyte can be improved by using low-viscosity co-solvents or additives to improve its ionic conductivity and interface compatibility at low temperatures. For example, using low melting point solvents/co-solvents to broaden the liquid range and improve low temperature ion conductivity.
2. **Build a stable SEI membrane**:
Build a stable SEI membrane through electrolyte additives and adjusting salt concentration, inhibit the side reactions of the electrolyte, and reduce the continuous consumption of the electrolyte.
3. **Change the solvation structure of the electrolyte**:
Changing the solvation structure of the electrolyte by selecting appropriate solvents/co-solvents, reducing the desolvation energy barrier and accelerating the charge transfer process on the electrode surface.
4. **Thermal management system**:
Design a reasonable battery thermal management system (BTMS) to improve the low temperature performance of lithium-ion batteries and adapt them to harsh low temperature environments. For example, the operating environment temperature of the energy storage system can be maintained by adopting thermal insulation materials in the cabin, configuring air conditioners or liquid cooling units, and reasonably designing air ducts or liquid cooling pipelines.
5. **Electrode material modification**:
The performance of lithium ions at low temperatures can be significantly improved by modifying the positive and negative electrode materials, such as increasing the lithium ion migration rate or electronic conductivity by bulk or surface ion doping, and increasing electronic conductivity by modifying carbon nanomaterials to form a multi-dimensional conductive structure. The above measures can effectively improve the performance of batteries in low temperature environments, making them adaptable to a wider range of application scenarios.
