Lithium ion batteries
The first choice for mobile device energy storage.
|Nominal voltage||3.7 V nominal|
|End-of-charge voltage||4.2 V|
|Energy density||100 – 160 Wh/kg|
|Charging rate (C-rate)||Typically 0.5 – 3 C|
|Discharge rate (C-rate)||0.2 C – 10 C|
|No. of cycles||300 – 1500|
|Temperature range||-20°C ~ +60°C|
|Self-discharge||~ 3% / per month|
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Sony launched the first lithium cobalt dioxide rechargeable battery for a video camera in 1991. Initially used only in these portable devices with high energy requirements, lithium ion batteries can be found in an infinite number of applications today. In addition to mobile phones, laptops, tablets or cameras these kind of batteries can be found in vacuum cleaners, tools, vehicles, storage applications, and large energy storage devices for storing energy from solar cells. Because of their high efficiency, they are being used in more and more new applications that previously could not be operated by battery. Lithium ions (Li+) (which is what gave these batteries their name) can freely move through the electrolyte between the two electrodes of the battery. Lithium ion cells are characterized by a high energy density. The useful life is several years. However, this is highly dependent on its use and storage conditions. Lithium ion cells are especially negatively affected by overcharging. Therefore, lithium ion batteries are provided with a protection circuit that protects the battery from overcharging. Only compatible chargers should be used. Lithium is a chemical element and the lightest metal. It has two advantages for use in batteries. It possesses the largest negative voltage potential and is also the lightest element in solid form. The underlying idea of storing electrical energy by means of chemical processes is more than 200 years old. Galvanic cells are utilized both for single as well as for multiple use for this purpose, either individually or interconnected. Such an element, also called a battery cell, contains two electrodes of conductive material and usually a liquid electrolyte.
A lithium ion cell is made up of a graphite electrode (negative) and a lithium metal oxide electrode (positive). The lithium metal oxide can be manganese, nickel or cobalt. Its composition influences the properties of lithium ion batteries and is different depending on the manufacturer and grade. The nominal voltage of lithium ion cells depends on the electrode material and is 3.6 or 3.7 volts. The charge voltage is usually 4.2 volts.
The electrodes are separated by a separator to prevent short-circuiting between the electrodes. The separator is permeable for lithium ions. The cathode acts as a sponge. It can thus absorb a large number of ions.
A wide range of cylindrical and prismatic cells exists today. Different active materials are used mainly on the cathode side.
The function is basically the same. The characteristics, such as cell voltage, temperature sensitivity, the maximum allowable charge or discharge current vary greatly depending on how it is constructed and are substantially influenced by the electrode material and electrolyte used. For this reason the specification of the subtype (such as “lithium iron phosphate battery”) is more informative than just the general term “lithium ion rechargeable battery”.
The capacity of a lithium ion battery is reduced over time even without use, mainly because of the reaction of lithium with the electrolyte. The rate of decomposition increases with cell voltage and temperature. A deep discharge below 2.0V can damage the battery permanently. It is therefore advisable to store such batteries at room temperature and with a charge of 60%, a compromise between accelerated aging and self-discharge.
When it is cold, the chemical processes take place at a slower pace (including the decomposition of the battery during aging) and the viscosity of the electrolytes used in lithium cells increases greatly, so the internal resistance in lithium ion batteries increases in cold conditions too, thus decreasing the usable power. Moreover, the electrolytes may freeze at temperatures of around -25 ° C. Some manufacturers specify a working range of 0-40 ° C. 18-25 ° C is optimal. Below 10 ° C its capacity may decrease so much because of the increased internal resistance that it will not be enough to run a camcorder or a digital camera.