What Is Battery Electrolyte and How Does It Work?
Lithium battery electrolyte plays a crucial role within the battery, often referred to as the “blood” of lithium battery. It is one of the key carriers for ion transmission inside the battery. Typically, lithium battery electrolyte consists of solvent, lithium salt, and additives. These components facilitate lithium ion conduction between the positive and negative electrodes, enabling the battery’s charging and discharging processes.
Types of Lithium Battery Electrolytes
Lithium battery electrolytes can be categorized into liquid electrolytes, solid electrolytes, and gel electrolytes based on their physical state.
Liquid Electrolyte
Liquid electrolyte is one of the earliest types used in lithium battery and includes organic liquid electrolytes and room temperature ionic liquid electrolytes. It has now reached technical maturity. This electrolyte mainly comprises lithium salts, organic solvents, and additives. The lithium salt conducts lithium ions, while the organic solvent serves as a medium for ion migration within the battery. Additives are included to enhance the electrolyte’s stability and conductivity.
Solid Electrolytes
Solid electrolytes consist of solid polymer electrolytes and inorganic solid electrolytes. These are primarily composed of lithium salts, polymer matrix, and additives. Solid electrolytes offer greater safety and energy density for lithium battery, but currently, they face challenges related to ionic conductivity and battery cycle life.
Gel Electrolyte
Gel electrolyte is a type that sits between liquid and solid electrolytes. It possesses unique characteristics such as higher ionic conductivity and a lower risk of liquid leakage. The gel electrolyte mainly includes a polymer matrix, lithium salt, organic solvent, and additives. By adjusting the ratio of polymer matrix to lithium salt, the electrolyte can achieve gelation, 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 critical role during the operation of the lithium battery. The processes of delithiation and lithiation of the electrode material is closely related to the electrolyte. This interaction affects the interface condition and internal structure of the electrode material, which directly influences battery capacity, thereby indirectly affecting it.
2.Impact on Battery Operating Temperature Range
Temperature directly impacts the chemical reactions inside the battery. At low temperatures, the chemical reaction rate decreases, reducing battery performance. Conversely, at high temperatures, the reaction rate increases, along with the rate of side reactions, which can damage the battery. To mitigate the impact of temperature on battery operation, broadening the electrolyte’s operating temperature range, enhancing its conductivity at low temperatures, and improving its stability at high temperatures are crucial.
3.Impact on Battery Storage and Cycle Life
Battery aging during long-term storage is a key factor affecting the cycle life of lithium battery. Factors influencing battery aging include corrosion of the electrode current collector and the loss of electrochemical activity of the electrode’s active material, which are related to the properties of the electrolyte. Therefore, the electrolyte greatly impacts the storage life of the battery.
4.Impact on Battery Self-Discharge Performance
The main factors affecting the self-discharge of lithium battery include the negative electrode’s self-discharge, electrolyte composition, and purity. Negative self-discharge occurs when lithium escapes from the negative electrode or enters the electrolyte as Li+. Its rate depends on the surface condition and catalytic activity of the negative electrode, which are influenced by the electrolyte. Therefore, optimizing the electrolyte composition can effectively reduce the battery’s self-discharge rate.
If impurities are present in the electrolyte, they can cause the battery to self-discharge. Impurities typically have a lower oxidation potential than the positive electrode potential of lithium battery, making them prone to oxidation on the positive electrode’s surface. The oxides are then reduced on the negative electrode, continually consuming the active materials and causing self-discharge. Therefore, strict requirements on the composition and purity of the electrolyte are essential: the electrolyte should be a good ionic conductor and an electronic insulator, should not degrade within the working potential range of the electrodes, and should be thermally stable with melting and boiling points far beyond the operating temperature.The electrolyte also should be inert towards the battery components such as the separator, electrode substrates, and battery enclosure materials.
In summary, lithium battery electrolyte, as a critical component of lithium battery, significantly impacts their performance. With the continuous development of lithium battery technology and new electrolyte materials, the performance of lithium battery is expected to see significant advancements.