An electrolyte is a compound that can conduct electricity when dissolved in an aqueous solution or in a molten state, and can dissociate into freely moving ions when dissolved in water or heated. The electrolyte is an important part of the lithium-ion battery, which plays the role of transporting ions and conducting current between the positive and negative electrodes.
Electrolyte, as a key material of lithium-ion batteries, affects or even determines the specific energy, life, safety performance, and charge-discharge performance of the battery. As a practical electrolyte for lithium-ion batteries, the following conditions should be met:
1. Lithium ion conductivity: The electrolyte does not have electronic conductivity, but it must have good ion conductivity. In the general temperature range, the conductivity of the electrolyte is between 1×10-3~2×10-3S/cm. As an electrolyte, it must have excellent ionic conductivity and electronic insulation, allowing it to function as an ion transport medium while reducing its own self-discharge.
2. Ion migration number: The internal charge transport of lithium batteries depends on the migration of ions. A high ion migration number can reduce the concentration polarization during the electrode reaction, so that the battery can produce high energy density and power density. The ideal lithium ion migration number should be as close to 1 as possible.
3. Stability: When the electrolyte is in direct contact with the electrode, side reactions should be avoided as much as possible, which requires the electrolyte to have certain chemical and thermal stability.
4. Mechanical strength: Lithium-ion battery electrolytes need to have high enough mechanical strength to meet the mass production and packaging process of batteries. Li et al. used trimethyl phosphate (TMP) as an additive to the high-voltage electrolyte, and tested Li1.2Mn0.54Ni0.13Co0.13O2 as the positive electrode of the battery. The results showed that adding 1% TMP to the electrolyte can significantly Improve the rate performance and cycle performance of the battery.
5. Excellent mechanical properties: Due to the direct contact with the positive and negative electrodes, the polymer lithium battery electrolyte should have strong toughness, be able to withstand stress changes during battery assembly, storage and use, and not be brittle. At the same time, when used as a separator, it must also have considerable mechanical strength to suppress the generation and piercing of lithium dendrites and prevent the short circuit of the positive and negative electrodes.