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What factors limit the charge/discharge rate performance of lithium battery?

- Jan 18, 2019 -

1164113-3p2s-lithium-polymer-battery-for-taxi top light 7.4V 30000mAh

High Rate Battery Heat-resisting Battery

The charge and discharge rate performance of lithium battery is directly related to the migration ability of lithium ions in the anode and cathode, electrolyte and the interface between them. All factors that affect the migration rate of lithium ions (these factors can also be equivalent to the internal resistance of the battery) will affect the charge and discharge rate performance of lithium ion battery. In addition, the heat dissipation rate inside the battery is also an important factor affecting the rate performance. If the heat dissipation rate is slow, the heat accumulated during charging and discharging at a high rate cannot be transferred out, which will seriously affect the safety and service life of lithium battery. Therefore, the study and improvement of charge and discharge rate performance of lithium battery mainly focus on improving the migration speed of lithium ions and the heat dissipation rate inside the battery.

1. Internal resistance of lithium battery

In general, conductive agents will be added inside the positive active material, so as to reduce the contact resistance between the active material and the positive matrix/collector fluid, improve the conductivity of the positive material (ion and electron conductivity), and improve the multiplier performance. Different materials and different shapes of conductive agents will have an impact on the internal resistance of lithium battery, and then affect its multiplier performance.

The positive and negative collector (pole ear) is the carrier of energy transfer between lithium ion battery and the outside world. Therefore, the multiplier performance and cycle life of lithium battery can be improved by changing the material, size, extraction mode and connection process of the collector fluid.

In addition, the absorbance and porosity of the membrane also have a great influence on the permeability of lithium ions, and also affect the multiplier performance of lithium battery to a certain extent (relatively small).

The infiltration degree of lithium battery electrolyte and positive and negative electrode materials will affect the contact resistance at the interface between electrolyte and electrode, thus affecting the multiplier performance of the battery. The total amount of electrolyte, viscosity, impurity content and porosity of positive and negative electrode materials will change the contact impedance between electrolyte and electrode, which is an important research direction to improve the multiplier performance.

2. Ionic conductivity of electrolytes

The ionic conductivity of the electrolyte, like the resistance of water, has a great influence on the swimming speed of lithium ions. At present, the organic electrolyte used in lithium ion battery, whether it is liquid electrolyte or solid electrolyte, its ionic conductivity is not very high. The resistance of electrolyte becomes an important part of the resistance of the whole battery.

In addition to improving the ionic conductivity of electrolytes, the chemical and thermal stability of electrolytes should also be emphasized. When charging and discharging at a high rate, the range of the electrochemical window of the battery is very wide. If the chemical stability of the electrolyte is not good, it is easy to be oxidized and decomposed on the surface of the anode material, affecting the ionic conductivity of the electrolyte.

3. Positive and negative lithium battery diffusion capacity

The rate at which a lithium battery is released and embedded in the positive/negative active material, that is, the rate at which lithium ions escape from the positive/negative active material or find a place in the active material from the surface of the positive/negative electrode, is an important factor affecting the charging and discharging rate.

Factors affecting the charging and discharging performance of lithium battery with high rate:

The poor capacitance is the biggest problem in the charging and discharging process of lithium battery cathode, which is mainly related to the structure of electrode material, particle size, electrode conductivity and the stability of SEI film on the electrode surface.

The size of the material and the size of the cathode material of lithium battery are directly related to the length of the diffusion path of lithium ions in it, which has a great influence on the high magnification performance of the electrode.

Electrode surface resistance, lithium ion in the process of embedding the cathode, the first thing to spread to the solid electrolyte interphase film (SEI film) and cathode material interface, so the electrode surface resistance is equivalent to a threshold in the process of lithium ion diffusion, affecting the embedded lithium ions and out, especially at high rate charge and discharge more obvious.