The influence of electrolyte on the performance of lithium battery

　　Electrolyte is a very important part of lithium-ion batteries. It can affect many aspects of the performance of lithium batteries, mainly affecting the following aspects:

　　1. Impact on battery capacity

　　The electrolyte affects the reversible capacity of the electrode material to a large extent, because the charging and discharging process of the battery is always the process of interacting with the electrolyte.

　　During the working process of lithium-ion batteries, there are a large number of side reactions. These factors affect the reversible capacity to varying degrees. Therefore, different types of raw materials, even different models of different manufacturers, are required to configure electrolytes with different formulations.

　　2. Impact on battery internal resistance and rate charge and discharge performance

　　The sum of ohmic internal resistance, interface resistance, and polarization internal resistance is the total impedance of lithium-ion batteries. It is an important indicator to measure the performance of chemical power sources and directly affects the battery's working voltage, working current, output energy and power.

　　The ohmic resistance is mainly derived from the conductivity of the electrolyte. The higher the internal resistance of the battery. Under normal circumstances, the interface resistance is significantly higher than the ohmic resistance.

　　Rate charge-discharge performance is an important indicator to measure the capacity retention capacity of lithium-ion batteries under fast charge-discharge conditions. The rate charge and discharge performance of the battery depends on the internal resistance, which is closely related to the composition and properties of the electrolyte.

　　3. Impact on battery operating temperature range

　　Among all environmental factors, temperature has the most obvious impact on battery performance. Under low temperature conditions, the rate of electrode reaction decreases, and the performance of the battery decreases significantly. When the temperature is increased, the electrode reaction intensifies, but the undesirable side reactions are also intensified at the same time, which affects the performance of the battery. Therefore, the best temperature for battery operation should be the temperature that is most conducive to electrode reaction without obvious side reactions. The operating temperature range of lithium-ion batteries is usually -10-45°C; the minimum operating temperature is generally not lower than -20°C. The maximum operating temperature generally does not exceed 60°C.

　　The main way to broaden the operating temperature range of lithium batteries is to improve the conductivity of the electrolyte under low temperature conditions and the stability under high temperature conditions.

　　4. Impact on battery storage and cycle life

　　The aging of lithium-ion batteries during long-term storage is the key to battery storage performance. A commercial lithium-ion battery, even if it is never used, has a storage life of only about 3 years. There are many reasons for battery aging. The electrolyte affects or even determines the storage life of the battery to a large extent.

　　5. Impact on battery safety

　　Lithium-ion batteries will deposit metal lithium on the surface of the negative electrode under overcharge conditions, and a series of unsafe side reactions will occur inside the battery, which brings significant safety issues.

　　The source of the safety problems of lithium-ion batteries is still the volatility and high flammability of the electrolyte itself. To fundamentally eliminate the safety hazards of batteries, it is necessary to eliminate the flammability of organic solvents, and develop safer or use electrolyte systems that do not burn at all. This is a critical technical difficulty particularly for large-scale, high-power-density lithium-ion batteries.

　　6. Impact on battery self-discharge performance

　　The appearance of impurities in the electrolyte is an important cause of battery self-discharge. This is because the oxidation potential of impurities is generally lower than the positive electrode potential of lithium-ion batteries, which will continue to consume the active materials of the positive and negative materials and cause self-discharge. Therefore, lithium-ion batteries have high requirements on the composition and purity of the electrolyte.

　　7. Impact on battery overcharge and over-discharge behavior

　　Under some practical application conditions, when multiple lithium-ion batteries are used in series to obtain a higher voltage, there is often an obvious capacity mismatch. The battery pack will always have individual batteries overcharged during charging and individual batteries during discharge. The over-discharge of the battery will affect the life span and also bring obvious safety hazards.

　　Electrolyte is an important way to prevent the battery from overcharging and discharging. Most research is to establish an internal overcharge and discharge protection mechanism inside the organic liquid electrolyte.

　　Lithium-ion battery (LIB) has become the main energy storage solution in modern social life. Among them, lithium iron phosphate batteries are a perfect substitute for lead-acid batteries, and are the first choice for grid-connected peak shaving, off-grid energy storage, photovoltaic energy storage, UPS, data center and other industries.