What is a battery electrolyte? How does it work?

What is a battery electrolyte? How does it work?

Lithium battery electrolyte plays a vital role in the battery, often referred to as the "blood" of lithium batteries, and is one of the key carriers of ion transport within the battery. Lithium battery electrolytes are usually composed of solvents, lithium salts, and additives. These ingredients promote the conduction of lithium ions between the positive and negative electrodes, thereby realizing the charging and discharging process of the battery.

Types of lithium battery electrolytes

Lithium battery electrolytes can be divided into liquid electrolytes, solid electrolytes, and gel electrolytes according to their physical state.

Liquid electrolytes

Liquid electrolytes are one of the earliest electrolytes used in lithium batteries, including organic liquid electrolytes and room temperature ionic liquid electrolytes, and the technology has matured. The electrolyte is mainly composed of lithium salts, organic solvents, and additives. Lithium salts conduct lithium ions, and organic solvents serve as a medium for ion migration within the battery. Additives are used to enhance the stability and conductivity of the electrolyte.

Solid electrolytes

Solid electrolytes include solid polymer electrolytes and inorganic solid electrolytes. They are mainly composed of lithium salts, polymer matrices, and additives. Solid electrolytes provide lithium batteries with higher safety and energy density, but they currently face challenges related to ion conductivity and battery cycle life.

Gel electrolyte

Gel electrolyte is an electrolyte between liquid and solid electrolyte, with unique characteristics such as high ionic conductivity and low leakage risk. Gel electrolyte mainly includes polymer matrix, lithium salt, organic solvent and additives. By adjusting the ratio of polymer matrix to lithium salt, the electrolyte can be gelled, thereby improving battery safety and cycle life.

Impact of lithium battery electrolyte on battery performance

Next, we will discuss the impact of lithium battery electrolyte on various aspects of battery performance, including capacity, operating temperature range, storage and cycle life, and self-discharge.

1. Impact on battery capacity

Although the electrolyte is not a direct factor affecting battery capacity, it plays a vital role in the working process of lithium batteries. The de-lithiation and lithium insertion process of electrode materials is closely related to the electrolyte. This interaction affects the interface state and internal structure of electrode materials, directly affecting the battery capacity, and indirectly affecting the battery capacity.

2. Impact on the operating temperature range of the battery

Temperature directly affects the chemical reaction inside the battery. At low temperatures, the chemical reaction rate decreases, thereby reducing battery performance. On the contrary, at high temperatures, the reaction rate is accelerated, and the side reaction rate is also accelerated, which may damage the battery. In order to mitigate the impact of temperature on battery operation, it is crucial to expand the operating temperature range of the electrolyte, improve its conductivity at low temperatures, and improve its stability at high temperatures.

3. Impact on battery storage and cycle life

Battery aging during long-term storage is a key factor affecting the cycle life of lithium batteries. Factors affecting battery aging include corrosion of electrode current collectors, loss of electrochemical activity of electrode active materials, etc., which are all related to the properties of the electrolyte. Therefore, the electrolyte has a great influence on the storage life of the battery.

4. Impact on battery self-discharge performance

The main factors affecting the self-discharge of lithium batteries include negative electrode self-discharge, electrolyte composition and purity, etc. Negative electrode self-discharge refers to the escape of lithium from the negative electrode or entry into the electrolyte in the form of Li+, and its rate depends on the surface state and catalytic activity of the negative electrode, which are all affected by the electrolyte. Therefore, optimizing the electrolyte composition can effectively reduce the self-discharge rate of the battery.

If the electrolyte contains impurities, it will cause battery self-discharge. The oxidation potential of impurities is usually lower than the positive electrode potential of lithium batteries, so they are easily oxidized on the positive electrode surface. The oxide is then reduced at the negative electrode, which continuously consumes the active material and causes self-discharge. Therefore, strict requirements on the composition and purity of the electrolyte are essential: the electrolyte should be a good ionic conductor and electronic insulator, should not degrade within the working potential range of the electrode, and should be thermally stable, with melting and boiling points much higher than the working temperature. The electrolyte should also be inert to battery components such as diaphragms, electrode substrates, and battery casing materials.

In summary, lithium battery electrolyte, as an important component of lithium batteries, has a vital impact on the performance of lithium batteries. With the continuous development of lithium battery technology and the continuous introduction of new electrolyte materials, the performance of lithium batteries is expected to be significantly improved.