From：CTECHI GROUP Limited Release time：2019-01-07
Overview：From the current mainstream technology of lithium-ion batteries, there are mainly several types of lithium cobalt oxide, lithium manganate, lithium iron phosphate and polymer. Their different materials and structural characteristics will affect the preparation technology and use of lithium-ion batteries, resulting in different safety.
From the current mainstream technology of lithium-ion batteries, there are mainly several types of lithium cobalt oxide, lithium manganate, lithium iron phosphate and polymer. Their different materials and structural characteristics will affect the preparation technology and use of lithium-ion batteries, resulting in different safety.
1. Lithium cobalt oxide batteries: The most important feature in preparation is that after full charge, a large number of lithium ions remain in the cathode. That is to say, more lithium ions attached to the cathode can not be accommodated on the cathode, but in the overcharge state, excess lithium ions on the cathode will still swim towards the cathode, because it can not be fully accommodated, lithium metal will be formed on the cathode, because this metal lithium is a dendrite crystal, so it is called dendrite. Once dendrite is formed, it will provide an opportunity to pierce the diaphragm. Diaphragm puncture will result in internal short circuit. Because the main component of the electrolyte is carbonate, lightning and boiling point are lower, so it will burn or even explode at higher temperature. It is easy to control the formation of lithium dendrites in small capacity lithium batteries. Therefore, lithium cobalt oxide batteries are currently limited to small capacity batteries such as portable electronic devices, but can not be used for power batteries.
2. Polymer lithium batteries: In practice, the theoretical specific energy has been greatly improved. Compared with lithium cobalt oxide batteries, polymer batteries can play a better role in high capacity. But from the material point of view, polymer batteries also use lithium cobalt oxide and organic electrolyte, so the safety problem has not been fundamentally solved. From the point of view of use, if the battery is short-circuited, it will produce excessive current. The electrolyte of polymer lithium batteries is colloidal, which is not easy to leak, thus eliminating the possibility of leaking, but it will cause more intense combustion. Therefore, spontaneous combustion is the biggest hidden danger of polymer lithium batteries.
3. Lithium manganate battery: The material of lithium manganate battery has some advantages. It can ensure that the lithium ion of the positive electrode can be completely embedded in the carbon hole of the negative electrode under full charge, instead of remaining in the positive electrode like lithium cobalt oxide, which fundamentally avoids the generation of dendrites. This is a theoretical understanding. In fact, if lithium manganate batteries are subjected to strong external forces, or if materials are cut off during preparation, lithium ions may form rapidly during the charging and discharging cycle. Dendrites are formed when lithium ions are not fully received by the negative electrode. Avoiding this consequence should be guaranteed by testing the battery when it leaves the factory. In a word, the lithium manganate batteries which are qualified will not cause safety accidents. Because the stable structure of lithium manganate makes its oxidation performance far lower than that of lithium cobalt, even if the external short circuit, it can basically avoid the combustion and explosion caused by the precipitation of lithium metal.
4. Lithium iron phosphate battery: This is an ideal power battery, which can be used in electric tools and power cars. The theoretical capacity of lithium iron phosphate is 170 mAh/g, and the actual capacity of materials is 160 mAh/g.
In terms of safety, lithium iron phosphate has high thermal stability and low oxidation ability of electrolyte, so it has high safety. However, its defect is low conductivity, which requires modification technology to improve. As a result, the volume of lithium iron phosphate is too large and the amount of electrolyte is too large. Moreover, lithium iron phosphate technology is still under study because of its large capacity and poor battery consistency.
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