2009年10月28日 星期三
2009年9月11日 星期五
2009年9月10日 星期四
Why is the LiFePO4 battery so safe?
1. When we overcharge Lithium cobalt battery may result in materials unstable, even after repeated charge-discharge will cause deformation of crystal structure.
The situation is, the cathode of lithium cobalt oxide in lithium atoms will be continued lose electrons by the potential and to form positive Ion. Then it move through the electrolyte by attract with the negative electrode, finally it attached to the anode carbon structure. However, the lithium atom number that leaving off from lithium cobalt oxide shall be controlled in a certain ratio, or lithium cobalt oxide would become unstable, cobalt oxide is generated there and then.
When the lithium-cobalt batteries experience repeated charge-discharge cycles, lithium cobalt oxide layer structure might be deformed, causing the battery power storage volume smaller. Generally speaking, the Cycle Life of lithium cobalt batteries is about 500 times or so.
2. Lithium iron phosphate (LiFePO4) has a strong covalent bond, it is relatively stable when overcharge; olivine structure (as the figure above) could extend battery life.
When we charging Lithium iron phosphate battery, it will release lithium atoms into iron phosphate, as phosphate phosphorus and oxygen has a strong covalent bond structure. Lithium iron phosphate battery will not release oxygen when we overcharge, and therefore there is no explosive Crack to happen. In addition, lithium iron phosphate materials are olivine crystal structure; it is more solid compared to lithium cobalt oxide layer structure. For this reason, the Cycle Life of lithium iron phosphate batteries can reach about 2000 times.
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