The analysis of major trends on Lithium battery anode materials -electrolyte
The electrolyte is an ionic conductor that conducts electricity between the positive and negative electrodes of the battery, and is prepared by a certain ratio of raw materials such as electrolyte lithium salt, high-purity organic solvent and necessary additives.It plays a vital role in battery energy density, power density, wide temperature applications, cycle life, and safety performance.
Due to the increasing application of lithium batteries, the requirements for electrolytes of various lithium batteries are inevitably different.
1. High specific energy electrolyte
Pursuing high specific energy is the biggest research direction of lithium ion batteries.Especially when mobile devices occupy more and more people's lives, battery life has become the most critical performance of batteries.In the future, the development of high energy density batteries will inevitably be high voltage positive electrodes and silicon negative electrodes.The negative electrode silicon has a large gram capacity and is attracting attention, but it cannot be applied due to its own swelling effect.In recent years, the research direction has been transformed into a silicon carbon negative electrode, which has a relatively high gram capacity and a small volume change, and different film forming additives have different circulation effects in the silicon carbon negative electrode.
2. High power electrolyte
At present, commercial lithium-ion batteries are difficult to achieve high-rate continuous discharge.The main reason is that the battery ear is extremely hot, and the internal resistance causes the overall temperature of the battery to be too high, which is prone to thermal runaway.Therefore, it is required that the electrolyte can suppress the temperature rise of the battery too fast while maintaining high conductivity.For power batteries, achieving fast charging is also an important direction for the development of electrolytes.The high-power battery not only imposes high solid-phase diffusion on the electrode material, but also requires nanometer to make the ion migration path short, control the thickness of the pole piece and compaction.
Also put forward higher requirements for the electrolyte:
（1） high dissociation electrolyte salt;
（2） solvent compound - lower viscosity;
（3）interface control - lower membrane impedance.
3. Wide temperature electrolyte
When the battery is at a high temperature, the decomposition of the electrolyte itself and the side reaction of the material and the electrolyte member are prone to increase;
At low temperatures, there may be an increase in electrolyte salt precipitation and a decrease in the impedance of the negative SEI film.The so-called wide temperature electrolyte is to make the battery have a wider working environment.
4. Safety electrolyte
The safety of the battery is mainly reflected in the burning and even the explosion.First of all, the battery is flammable. Therefore, when the battery is overcharged, overdischarged, or short-circuited, when it receives acupuncture and squeezing from the outside, when the outside temperature is too high, it may cause a safety accident.Therefore, flame retardancy is a major direction in the study of safe electrolytes.The flame retardant function is obtained by adding a flame retardant additive to a conventional electrolyte, generally using a phosphorus-based or halogen-based flame retardant.Flame retardant additives are required to be reasonably priced and do not impair electrolyte performance.In addition, the use of room temperature ionic liquids as electrolytes has also entered the research stage, and the use of flammable organic solvents in batteries will be completely eliminated.And the ionic liquid has the characteristics of extremely low vapor pressure, good thermal stability/chemical stability, and non-flammability, which will greatly improve the safety of the lithium ion battery.
5. Long circulating electrolyte
Due to the current technical difficulties in the recovery of lithium batteries, especially the recovery of power batteries, improving battery life is one way to alleviate this situation.
There are two main research ideas for long-circulating electrolytes.First, the stability of the electrolyte, including thermal stability, chemical stability, voltage stability;
Second, the stability with other materials requires stable film formation with the electrode, no oxidation with the separator, and no corrosion with the current collector.