Lithium-ion(LiIon)batteries are characterized by their high power density, which at several 1,000 W/kg is higher than that of all other accumulators. In addition, the LiIon battery is thermally stable, has a constant output voltage over the entire discharge period, a long service life and knows no memory effect.
Lithium has a high negative potential of -3.05 V in the electrochemical voltage series, which makes the potential difference with other materials very high. Incombination with copper (0.16 V), this results in a voltage difference of 3.21 V. The nominal voltage of lithium-ion batteries is 3.6 V, the charge end voltage is 4.2 V, the discharge end voltage is about 2.5 V, and the C coefficient for the charge current is 1C.
Important characteristics of lithium cells
In the lithium-ion battery, the anode consists of a copper foil coated with graphite or a graphite compound. In more powerful LiIon batteries such as the lithium titanate battery, the graphite of the anode is replaced by lithium titanate. The cathode of the LiIon battery is made of a lithium compound consisting of the oxides of cobalt, manganese or nickel. Between the electrodes is the electrolyte in which positively charged lithium ions move between the cathode and the anode. The electrolyte is a dissolved lithium salt in which the lithium ions move freely. Between the electrodes is a separator through which only the lithium ions can pass. When current flows through a load, the ions move from the negative cathode to the positive anode. The charge is balanced by electrons flowing across the load. During charging, the current and ion movement are reversed. Depending on whether the electrolyte is liquid or solid, they are referred to as lithium-ion batteries or, as solid-state batteries, lithium-polymer batteries.
The various lithium-ion batteries differ mainly in the anode material, which can be cobalt, manganese, nickel-cobalt, nickel-cobalt-manganese (NKM), iron phosphate or titanate. The different materials result in different energy densities, power densities, rated voltages and charge cycles. For cobalt, energy density values range up to 190 Wh/kg, for manganese up to 120 Wh/kg, and for nickel-cobalt-manganese (NKM) up to 130 Wh/kg. Energy density is up to 400 Wh/kg for high-energy versions such as the lithium-sulfur battery or over 1 kWh/kg for the lithium-air battery, and between 2 kW/kg and 4 kW/kg for high- performance versions. The number of discharge and charge cycles is about 1,500.
The power curve of lithium-ion batteries is strongly temperature-dependent and has its maximum at temperatures between 20 °C and 40 °C. At 0 °C, the power is only 60% of the maximum power, and at 60 °C it is already zero.
Charging and service life
LiIon batteries are charged from the deep discharge threshold using the IU charging method with constant current until the nominal voltage is reached. After that, they continue to be charged at a constant voltage. If the state of charge is below the deep discharge threshold, then the deep discharged battery is prepared by charging it with low current until the minimum voltage is reached. The charge factor for this type of battery is approx. 1.4.
Lithium-ion batteries have a service life of about twenty thousand charge cycles and are used as powerful energy sources in handhelds, palmtops, notebooks and cell phones. Through the use of nanotechnology, Li-ion batteries are undergoing rapid development with improved performance and longer life. Because of their energy density, they are also being used in electric vehicles. The upcoming battery generations will be nano-phosphate batteries and as an alternative to LiIon batteries will come the sodium-ion battery.
Marking of lithium cells
For battery labeling, there is a designation system introduced by Japanese companies that consists of three letters and a five- digit number. The first letter stands for lithium (I), the second for cobalt (C), manganese (M) or iron phosphate (F), and the third for recharchable (R). The following numbers apply to round cells and indicate the diameter and height in millimeters. Accordingly, there are a variety of engineering and size versions with diameters ranging from 10 mm, through 14 mm, 17 mm and 18 mm, and lengths ranging from 33 mm to 65 mm. For example, the example for the cylindrical cell type IMR18650 states that it is a rechargeable lithium manganese dioxide battery with a diameter of 18 mm and a height of 65 mm.