Cells with higher voltages are discharged to bring them in line with the rest of the pack. The BMS achieves this by monitoring the voltages of all individual cells within a battery. The primary function of the BMS is to bring all the cells in a battery to the same state of charge and to maintain them in that condition throughout the life of the battery. This provides the optimum combination of packing density, thermal management and protection required for industrial and automotive applications.īattery Management Systems – Battery Management Systems (BMS) are an essential component for the safe operation of multi-cell lithium-ion batteries. This would not be possible with a Lithium Cobalt Oxide (LCO) cell, as it has an operating voltage of 3.7V.Ĭell structure – The cell structure for larger capacity cells uses a prismatic design with robust metal walls. Four of these cells can be connected in series to make a 12Volt automotive battery, which is directly compatible with most vehicle electrical systems. For example, Lithium Iron Phosphate (LFP) cells combine a carbon negative electrode with an iron phosphate positive electrode to make a cell with an operating voltage of 3.2V. Some examples of the chemicals that can be paired together to make cells are shown below: As each pair of materials will make a cell with different electrical properties, it is important to select the right cell for a particular application and not to mix or replace cells with different chemistries. This is a very active area of research and development, which is promoting the use of lithium-ion batteries in an increasing number of applications. Many different types of chemical can be used to make the electrode materials which carry the lithium-ions. During re-charge the process goes into reverse and lithium-ions move back through the electrolyte. To balance the charge transfer within the cell, positively charged lithium-ions move through an internal electrolyte circuit between the positive and negative electrodes. During discharge, electrical charge moves through an external wire circuit between the electrodes of the battery. Lithium-ion op eration employs the same principles as any other rechargeable battery. At end of life the cells should be recycled but they contain no controlled toxic materials such as cadmium, mercury and lead. This means that it is possible to use lithium-ion cells in closed cabinets, completely isolated from their surroundings. There are no gas emissions from charging cells and heat loss, due to charging inefficiency, is very low. The interaction between lithium-ion cells and the environment is very mild. This gives them greater operating flexibility than lead acid cells. In applications where charging power or time may be limited, such as solar PV systems or stop-start cars, it is not harmful to operate lithium-ion cells continuously at partial state of charge. As well as the high-energy density of the cells, they are able to discharge at a higher power and can then be re-charged much more quickly. However, there are many other ways in which they are superior to traditional battery chemistries. The high-energy density and large number of discharge cycles provided by lithium-ion cells are the most important factors, which make them indispensable in mobile phones and electric vehicles alike. Starting with cameras and mobile phones, the technology has become the power source of choice for everything from cordless power tools to large scale energy storage and automotive applications. The introduction of lithium-ion cells was driven by the need for a lightweight rechargeable cell to power the rapidly growing market for portable electronic equipment in the 1990’s.
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