Analysis of 5 major trends in the development of lithium-ion battery electrolyte technology
The electrolyte is an ionic 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 solvents and necessary additives in a certain proportion. , Wide temperature applications, cycle life, safety performance and other aspects play a vital role.
Lithium-ion batteries are composed of a shell, a positive electrode, a negative electrode, an electrolyte and a separator. The electrode material is undoubtedly the focus of 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.
The electrolyte is an ionic 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 in a certain proportion. Dubbed. As the application fields of lithium-ion batteries become more and more extensive, all kinds of lithium-ion batteries have different requirements for their electrolyte.
The pursuit of high specific energy is currently the biggest research direction of lithium-ion batteries, especially when mobile devices occupy more and more proportions in people’s lives, battery life becomes The most critical performance of the battery.
The silicon anode has a huge gram capacity and has attracted people’s attention. However, due to its own swelling purpose, it cannot be applied. In recent years, the research direction has changed to silicon carbon anode, which has Relatively high gram capacity and small volume change, different film-forming additives have different cycling effects on silicon carbon anode
2, high-power electrolyte
At present, it is difficult for commercial lithium electronic batteries to achieve high-rate continuous discharge. The important reason is that the battery tabs generate serious heat, and the internal resistance causes the overall temperature of the battery to be too high, which is prone to heat. out of control. Therefore, the electrolyte should be able to prevent the battery from heating up too quickly while maintaining high conductivity. Regarding power lithium batteries, fast charging is also an important direction for electrolyte development.
High-power batteries not only impose requirements on electrode materials such as high solid phase diffusion, nanometerization to make ion migration paths short, control of electrode thickness and compaction, etc., but also requirements for electrolyte Higher requirements are put forward: 1. High degree of dissociation electrolyte salt; 2. Solvent recombination-lower viscosity; 3. Interface control-lower membrane impedance.
3. Wide temperature electrolyte
Batteries are prone to self-decomposition of electrolyte and materials and electrolyte at high temperature The side reactions of the parts are intensified; and at low temperatures, there may be electrolyte salt precipitation and the negative electrode SEI film impedance will increase exponentially. The so-called wide temperature electrolyte is to make the battery have a wider working environment. The following figure shows the boiling point comparison chart and solidification comparison chart of various solvents.
4. Safety electrolyte
The safety of the battery is important in combustion and even explosion. First of all, the battery itself has Flammability, so when the battery is overcharged, over-discharged, short-circuited, when it receives external needle sticks, squeezing, and when the external temperature is too high, it 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 into the conventional electrolyte. Generally, phosphorus or halogen-based flame retardants are used, and the price of flame-retardant additives is required to be reasonable and not harmful Electrolyte performance. 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. In addition, 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.
5. Long-cycle electrolyte
Due to the current recycling of lithium-ion batteries, especially the recycling of power lithium batteries There are still greater technical difficulties, so increasing the life of the battery is a way to alleviate this situation.
There are two important points in the research thinking of 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 requires stable film formation with the electrode, no oxidation with the diaphragm, and no corrosion with the current collector.