The problems that arise when using high-nickel materials in conjunction with electrolytes are complex to solve and have high technical barriers. Without sufficient R&D capabilities, it is difficult for companies to produce electrolyte products that are compatible with high-nickel materials.
1. High specific energy electrolyte
The pursuit of high specific energy is currently the biggest research direction for lithium-ion batteries, especially as mobile devices occupy an increasingly larger proportion of people's lives, battery life has become the most critical performance characteristic of batteries.
As shown in the figure, the future development of high-energy-density batteries will inevitably involve high-voltage positive electrodes and silicon negative electrodes. Silicon negative electrodes have attracted attention due to their large specific capacity, but their swelling effect limits their application. In recent years, research has shifted to silicon-carbon negative electrodes, which have relatively high specific capacity and small volume change. Different film-forming additives result in varying cycle performance on silicon-carbon negative electrodes.
2. High-power electrolyte
Currently, commercially available lithium-ion batteries struggle to achieve high-rate continuous discharge, primarily due to severe overheating of the battery tabs and excessively high overall battery temperature caused by internal resistance, making them prone to thermal runaway. Therefore, electrolytes need to maintain high conductivity while suppressing rapid battery temperature rise. For power batteries, achieving fast charging is also a crucial direction for electrolyte development.
High-power batteries not only place demands on electrode materials such as high solid-phase diffusion, nano-sizing to shorten ion migration paths, and control of electrode thickness and compaction, but also place higher demands on electrolytes: 1. High-dissociation electrolyte salts; 2. Solvent composites - lower viscosity; 3. Interface control - lower membrane impedance.
3. Wide-temperature range electrolyte
At high temperatures, batteries are prone to electrolyte decomposition and increased side reactions between materials and electrolyte components; while at low temperatures, electrolyte salt precipitation and a significant increase in the impedance of the negative electrode SEI film may occur. A wide-temperature electrolyte is designed to provide the battery with a broader operating environment. The following diagram compares the boiling points and solidification of various solvents.
4. Safety Electrolyte
Battery safety primarily hinges on combustion and even explosion. Batteries themselves are flammable; therefore, overcharging, over-discharging, short-circuiting, external irritation such as punctures or pressure, and excessively high temperatures can all trigger safety incidents. Consequently, flame retardancy is a major research direction for safe electrolytes.
Flame retardancy is achieved by adding flame retardant additives to conventional electrolytes, typically phosphorus-based or halogen-based. These additives must be reasonably priced and not impair electrolyte performance. Furthermore, the use of room-temperature ionic liquids as electrolytes is under research, which would completely eliminate the use of flammable organic solvents in batteries. Ionic liquids also possess characteristics such as extremely low vapor pressure, good thermal/chemical stability, and non-flammability, significantly improving the safety of lithium-ion batteries.
5. Long-circulation electrolyte
Since the recycling of lithium batteries, especially power batteries, still faces significant technical challenges, improving battery life is one way to alleviate this situation.
The research approach for long-cycle electrolytes mainly focuses on two aspects: first, the stability of the electrolyte, including thermal stability, chemical stability, and voltage stability; and second, its stability with other materials, requiring stable film formation with the electrodes, no oxidation with the diaphragm, and no corrosion with the current collector.
