Electrolyte is an ion conductor used for conduction between the positive and negative electrodes of the battery. It is composed of electrolyte lithium salt, high-purity organic solvent and necessary additives and other raw materials in a certain proportion. Application, cycle life, safety performance and other aspects play a vital role.
Lithium-ion batteries are composed of casing, positive electrode, negative electrode, electrolyte and diaphragm, among which electrode materials are undoubtedly the focus of everyone's attention and research. But at the same time, the electrolyte is also an aspect that cannot be ignored. After all, the electrolyte, which accounts for 15% of the battery cost, does play a vital role in the energy density, power density, wide temperature application, cycle life, and safety performance of the battery. character of.
Electrolyte is an ion conductor used for conduction between the positive and negative electrodes of the battery. It is made up of raw materials such as electrolyte lithium salt, high-purity organic solvent and necessary additives in a certain proportion. As the application fields of lithium-ion batteries are becoming more and more extensive, the requirements of various lithium-ion batteries for their electrolytes are bound to be different.
The pursuit of high specific energy is currently the biggest research direction of lithium-ion batteries, especially when mobile devices account for an increasing proportion of people's lives, battery life has become the most critical performance of batteries.View more details:eve lifepo4
Negative silicon has a huge gram capacity and has attracted people's attention, but due to its own swelling use, it cannot be applied. In recent years, the research direction has changed to silicon carbon negative electrode, which has relatively high gram capacity and small volume change. Different film-forming additives have different cycling effects on silicon-carbon anodes
- High power electrolyte
At present, it is difficult for commercialized lithium-ion batteries to achieve high-rate continuous discharge. The main reason is that the battery tabs are severely heated, and the internal resistance causes the overall temperature of the battery to be too high, which is prone to thermal runaway. Therefore, it is necessary for the electrolyte to suppress the battery from heating up too quickly while maintaining high conductivity. As for power lithium batteries, realizing fast charging is also an important direction for the development of electrolytes.
High-power batteries not only put forward requirements for high solid-phase diffusion of electrode materials, short ion migration paths through nanometerization, control of electrode sheet thickness and compaction, but also higher requirements for electrolytes: 1. High dissociation electrolytes Salt; 2. Solvent compounding - lower viscosity; 3. Interface control - lower membrane impedance.
- Wide temperature electrolyte
When the battery is at high temperature, it is easy to decompose the electrolyte itself and the side reaction between the material and the electrolyte is intensified; while at low temperature, there may be electrolyte salt precipitation and the impedance of the negative electrode SEI film will increase exponentially. The so-called wide temperature electrolyte is to make the battery have a wider working environment. The figure below shows the comparison chart of boiling point and solidification of various solvents.
- Safe electrolyte
The safety of the battery is mainly reflected in the combustion or even explosion. First of all, the battery itself is flammable, so when the battery is overcharged, overdischarged, short-circuited, when it receives external acupuncture or extrusion, and when the external temperature is too high, may cause safety accidents. Therefore, flame retardancy is an important direction in the research of safe electrolytes.
The flame retardant function is obtained by adding flame retardant additives to the conventional electrolyte. Phosphorous or halogen flame retardants are generally used. The flame retardant additives are required to be reasonably priced and not to damage the performance of the electrolyte. In addition, the use of room temperature ionic liquids as electrolytes has also entered the research stage, which will completely eliminate the use of flammable organic solvents in batteries. Moreover, ionic liquids have the characteristics of extremely low vapor pressure, good thermal/chemical stability, and non-flammability, which will greatly improve the safety of lithium-ion batteries.
- Long cycle electrolyte
Due to the current recovery of lithium-ion batteries, especially the recovery of power lithium batteries, there are still relatively large technical difficulties, so improving the battery life is a way to alleviate this situation.
There are two important research ideas for long-cycle electrolytes. One is the stability of the electrolyte, including thermal stability, chemical stability, and voltage stability; the other is the stability with other materials, which requires stable film formation with electrodes. No oxidation with diaphragm, no corrosion with current collector.
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