The Effect of Electrolyte on Battery Performance

The Effect of Electrolyte on Battery Performance

The influence of electrolyte on macro electrochemical performance of lithium ion battery includes the following aspects:

1. Impact on battery capacity

Although the electrode material of lithium ion battery specific capacity is a prerequisite for, but also largely affect the electrode materials of electrolyte irreversible capacity, this is because the electrode material of lithium embedded, process and cycle is the process of interaction with the electrolyte, the interaction interface state of the electrode materials and internal structure change has important influence.

In the working process of lithium ion battery, in addition to the REDOX reactions occurring at the positive and negative poles when lithium ions are embedded and removed, there are also a large number of side reactions, such as the oxidation and reduction decomposition of electrolytes on the positive and negative poles, the surface passivation of active substances on the electrode, and the high interface impedance between electrode and electrolyte. All these factors affect the capacity of electrode materials to varying degrees. Therefore, some electrolyte systems can make electrode materials show excellent capacity of embedding and delithium, while some electrolyte systems have great damage to electrode materials.

2. Influence on battery internal resistance and rate charge-discharge performance

Internal resistance refers to the resistance of the current through the battery, including ohmic internal resistance and the polarization resistance of the electrode in the electrochemical process, for lithium ion batteries, should also include the interface resistance between the electrode and electrolyte. Therefore, the sum of ohm internal resistance, electrode/electrolyte interface resistance and polarization internal resistance is the total internal resistance of lithium ion battery, which is an important index to measure the performance of chemical power supply, and directly affects the battery working voltage, working current, output energy and power.

The ohmic resistance of the battery is mainly due to the conductivity of the electrolyte, but also includes the resistance of the electrode material and the diaphragm. The conductive mechanism of the electrolyte part is ionic conduction, and the resistance of the conductive process is usually much greater than that of the electronic part. The interface resistance between electrode and electrolyte plays an important role in lithium ion battery. The greater the resistance of lithium ion crossing the interface, the higher the internal resistance of the battery. In general, the interfacial resistance is significantly higher than the ohmic resistance.

Lithium ion batteries, lithium ion layer and delaminating are embedded in the electrode and electrolyte phase interface, the ease of the reaction, electrochemical polarization degree, not only related to the nature of electrode material, and interface in the electrolyte and electrode materials, lithium ion electrolyte in the existing state and lithium ion is related to such factors as the interaction between the electrolyte. In this sense, the properties of electrolyte system also affect the polarization resistance of batteries to a certain extent.
Rate charging-discharge performance is an important index to measure the capacity retention ability of lithium ion batteries under rapid charging-discharge conditions. The rate charge-discharge performance of the battery depends on the mobility of lithium ion in the electrode material, the conductivity of electrolyte and the mobility of lithium ion at the electrode/electrolyte phase interface, the latter two are closely related to the composition and properties of electrolyte.

3. Influence on the operating temperature range of the battery

Due to the high temperature dependence of electrode reaction at the interface between electrode and electrolyte, temperature has the most obvious influence on battery performance among all environmental factors. Under low temperature conditions, the electrode reaction rate decreases, and even the reaction stops, the performance of the battery is significantly reduced, and even cannot be used normally. When the temperature is raised, the electrode reaction is intensified, but the side reaction of electrode/electrolyte interface is also intensified, which often has great damage to the battery, and the performance of the battery is affected. Therefore, the best working temperature of the battery should be the temperature that is most conducive to electrode reaction without obvious side reaction. The operating temperature range of liquid lithium ion battery is usually -10-45℃. The lowest operating temperature is generally not less than -20 ° C, the highest operating temperature is generally not more than 60 ° C.

For lithium-ion batteries with liquid electrolyte, the main way to expand the working temperature range is to expand the liquid path of electrolyte, improve the conductivity and stability of electrolyte at low temperature and high temperature. For solid electrolytes, to expand the operating temperature range, it is necessary to improve the conductivity of the electrolyte at room temperature or even low temperature and reduce the interfacial impedance between the electrolyte and the electrode material.

4. Influence on battery storage and cycle life

The aging of lithium ion batteries in the long-term storage process is the key to affect the storage performance of batteries. Even if a commercial lithium ion battery is never used, its storage life is only about 3 years. Battery aging reason is various, including electrode set fluid corrosion and electrode active material from a collection of fluid loss and loss of electrochemical activity is the main reason, and the nature of electrolyte and fluid corrosion and the stability of the electrode material in which are closely related, therefore, to a great extent, influence and even determine the battery electrolyte storage life.