High temperature and low temperature performance of lithium ion batteries
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2020/12/19 11:03:24
1. High temperature performance
Lithium battery has good high temperature performance, which means that the battery core is in a high temperature environment, the anode and cathode materials, the diaphragm and electrolyte of the battery can maintain good stability, can work normally at high temperature, the life will not accelerate the decay, high temperature is not likely to cause thermal accident out of control.The temperature of the lithium battery shows the thermal state of the battery, in which the essence is the heat generation and heat transfer of the lithium battery.Studying the thermal characteristics of lithium batteries and their heat generation and heat transfer characteristics in different states can help us realize the main ways of exothermic chemical reactions taking place in lithium batteries.
Unsafe behaviors of lithium batteries, including battery overcharge and discharge, rapid charge and discharge, short circuit, mechanical abuse conditions and high temperature thermal shock, are easy to trigger dangerous side reactions inside the battery and generate heat, which directly destroy the passivation film on the surface of negative and positive electrodes.
When the cell temperature rises to 130℃, the SEI film on the cathode surface decomposes, resulting in violent reoxidation and reduction reactions when the anode of highly active lithium carbon is exposed to the electrolyte, and the heat generated makes the battery enter a high-risk state.When the local temperature inside the battery rises above 200℃, oxygen evolution occurs when the anode is decomposed by the passivation film on the surface of the positive electrode, and it continues to react violently with the electrolyte, generating a large amount of heat and forming high internal pressure.When the battery temperature reaches above 240℃, it is accompanied by intense exothermic reaction between lithium carbon cathode and binder.
The temperature of lithium battery has great influence on the safety of lithium battery.The use of the environment itself is also a certain temperature, and lithium batteries in the use of the temperature will also produce.What's more, the temperature will have a great influence on the chemical reaction inside the lithium battery. Too high temperature will even damage the service life of the lithium battery. In serious cases, it will cause safety problems of the lithium battery.
2.Good low temperature performance
Lithium battery has good performance at low temperature, which means that at low temperature, the lithium ions and electrode materials inside the battery maintain relatively high activity, high residual capacity, reduced discharge capacity and high charging rate.
With the decrease of temperature, the residual capacity of lithium battery decays into an accelerating situation.The lower the temperature, the faster the capacity decay.Forced charging at low temperature is very harmful, and it is very easy to cause out-of-control thermal accidents.At low temperature, the activity of lithium ion and electrode active material decreased, and the rate of lithium ion embedded in anode material decreased seriously.When the external power supply is charged with more than the battery's allowed power, a large number of lithium ions accumulate around the negative electrode, and the lithium ions, which have no time to embed in the electrode, get electrons and deposit directly on the electrode surface, forming lithium crystal.The dendrite grows, penetrates the diaphragm directly, and impinges towards the positive pole.Causes the anode and cathode short circuit, then causes the thermal control to occur.
In addition to the severe loss of discharge capacity, lithium-ion batteries cannot be charged at low temperatures.During low temperature charging, the lithium ion embedding and lithium plating reactions on the graphite electrode of the battery exist simultaneously and compete with each other.At low temperature, the diffusion of lithium ions in graphite is inhibited, and the conductivity of electrolyte decreases, which leads to a decrease in the embedding rate. On the graphite surface, lithium plating reaction is more likely to occur.The main reasons for the decline of the life of lithium ion battery at low temperature are the increase of internal impedance and the capacity attenuation caused by the precipitation of lithium ion.
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