How well do lithium iron phosphate batteries perform at low temperatures?
The use of lithium-ion batteries is limited in low-temperature environments. Besides the severe degradation of discharge capacity, lithium-ion batteries cannot be charged at low temperatures. During low-temperature charging, the intercalation of lithium ions and the lithium plating reaction on the battery's graphite electrodes occur simultaneously and compete with each other. At low temperatures, the diffusion of lithium ions in graphite is inhibited, and the conductivity of the electrolyte decreases, leading to a reduced intercalation rate. Meanwhile, the lithium plating reaction becomes more likely to occur on the graphite surface.
Studies have shown that a 3500mAh battery, if operated in an environment of -10℃, will experience a rapid decrease in capacity to 500mAh after less than 100 charge-discharge cycles, essentially rendering it unusable. In other words, in an environment of -10℃, if an electric vehicle is charged and discharged once a day, the battery will need to be replaced after three months.
Reasons affecting the low-temperature performance of lithium iron phosphate batteries
1. Positive electrode structure
The three-dimensional structure of the cathode material restricts the diffusion rate of lithium iron phosphate batteries, with the effect being particularly pronounced at low temperatures. Different cathode materials have different three-dimensional structures. Currently, the main cathode materials used in electric vehicle power lithium batteries are lithium iron phosphate, nickel-cobalt-manganese ternary materials, and lithium manganese oxide. At -20℃, the discharge capacity of lithium iron phosphate batteries can only reach 67.38% of their room-temperature capacity, while nickel-cobalt-manganese ternary batteries can reach 70.1%.
2. High melting point solvents
Because the electrolyte mixture contains high-melting-point solvents, the viscosity of lithium-ion battery electrolytes increases at low temperatures. When the temperature is too low, the electrolyte will solidify, resulting in a decrease in the lithium-ion transport rate in the electrolyte.
3. Lithium-ion diffusion rate
The diffusion rate of lithium ions in graphite anodes decreases at low temperatures. The increased charge migration impedance of lithium-ion batteries at low temperatures, leading to a reduced diffusion rate of lithium ions in graphite anodes, is a significant factor affecting the low-temperature performance of lithium iron phosphate batteries.
4. SEI membrane
At low temperatures, the SEI film on the negative electrode of lithium iron phosphate batteries thickens, and the increased impedance of the SEI film leads to a decrease in the conduction rate of lithium ions in the SEI film. Ultimately, the lithium-ion battery forms polarization during charging and discharging at low temperatures, reducing the charging and discharging efficiency.
5. Production Environment
As a high-tech product with numerous chemical raw materials and complex processes, lithium iron phosphate batteries have very high requirements for their production environment, including temperature, humidity, and dust. If these requirements are not properly controlled, the battery quality will fluctuate.
In summary, multiple factors currently influence the low-temperature performance of lithium iron phosphate batteries, such as the structure of the cathode, the migration rate of lithium ions in different parts of the battery, the thickness and chemical composition of the SEI film, and the selection of lithium salts and solvents in the electrolyte. Low-temperature performance limits the application of lithium-ion batteries in electric vehicles, specialized fields, and extreme environments; therefore, developing lithium-ion batteries with excellent low-temperature performance is an urgent market demand.
