18650 battery 3500mah

Five major trends in the development of 18650 battery 3500mah electrolyte technology

The electrolyte is an ionic conductor that conducts between the positive and negative electrodes of the battery. It is composed of electrolyte lithium salts, high-purity organic solvents and necessary additives in a certain proportion. It plays a vital role in the energy density, power density, wide temperature application, cycle life, safety performance and other aspects of the battery.

Lithium-ion batteries are composed of shells, positive electrodes, negative electrodes, electrolytes and diaphragms. Among them, the 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, safety performance and other aspects of the battery.

The electrolyte is an ionic conductor that conducts between the positive and negative electrodes of the battery. It is composed of electrolyte lithium salts, high-purity organic solvents 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 occupy an increasing proportion in people's lives, battery life has become the most critical performance of batteries.

Negative silicon has a huge gram capacity and has attracted people's attention, but it cannot be applied due to its own swelling purpose. In recent years, the research direction has shifted to silicon-carbon negative electrodes, which have relatively high gram capacity and small volume changes. Different film-forming additives have different cycle effects on silicon-carbon negative electrodes.

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 heats up seriously, and the internal resistance causes the overall temperature of the battery to be too high, which is prone to thermal runaway. Therefore, the electrolyte should be able to suppress the battery from heating up too fast while maintaining high conductivity. As for power lithium batteries, achieving fast charging is also an important direction for the development of electrolytes.

High-power batteries not only require high solid-phase diffusion, nano-sizing to shorten the ion migration path, and control the thickness and compaction of the electrode sheet for electrode materials, but also require higher requirements for electrolytes: 1. High dissociation electrolyte salt; 2. Solvent composite-lower viscosity; 3. Interface control-lower membrane impedance.

3. Wide-temperature electrolyte

When the battery is at high temperature, the electrolyte itself is prone to decomposition and the side reactions between the material and the electrolyte are aggravated; while at low temperature, electrolyte salt precipitation and negative electrode SEI membrane impedance may increase exponentially. The so-called wide-temperature electrolyte is to give the battery a wider working environment. The following figure is a boiling point comparison chart and solidification comparison chart of various solvents.

4. Safety electrolyte

The safety of the battery is mainly reflected in combustion and even explosion. First of all, the battery itself is flammable. Therefore, when the battery is overcharged, over-discharged, short-circuited, punctured or squeezed by the outside world, or when the outside temperature is too high, it may cause safety accidents. Therefore, flame retardancy is an important direction for the research of safe electrolytes.

The flame retardant function is obtained by adding flame retardant additives to conventional electrolytes. Generally, phosphorus or halogen flame retardants are 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 exclude the use of flammable organic solvents in batteries. And ionic liquids have the characteristics of extremely low vapor pressure, good thermal stability/chemical stability, and non-flammability, which will greatly improve the safety of lithium-ion batteries.

5. Long-cycle electrolyte

Since the recycling of lithium-ion batteries, especially the recycling of power lithium batteries, still has great technical difficulties, improving the life of the battery 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 the electrode, no oxidation with the diaphragm, and no corrosion with the current collector.

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