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Nowadays most of the electronic devices that we use in our day-to-day life uses Li-ion batteries. Lithium is the key metal in this type of battery technology with other commonly used metals like Cobalt, Aluminum, Manganese, and Nickel. The functionality of an element in a battery is determined by the Electrochemical Potential. In simple words, Electrochemical Potential is the tendency of a metal element to lose electrons. Due to high electrochemical potential, Lithium metal is very unstable and has a tendency to lose electrons which makes it an excellent choice for cathode material in the battery. The top producers of lithium all over the world are South America, Australia, and China. As our energy consumption is increasing, the demand for lithium will only continue to grow. Since Lithium batteries are powering more and more of our life, why don’t we explore, how exactly the battery works?
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It was not until 1991, that the rechargeable Li-ion batteries became commercially available. Before that, the desirable battery technologies were nickel-cadmium batteries and Lead-acid batteries. In the period between the 1970s – 1990s, most of the contributions to Li-ion batteries were made. Among them, John B. Goodenough, Akira Yoshino, M. Stanley Whittingham were the key contributors, who were awarded later with Nobel Prize in Chemistry in 2019.
Components of Li-ion Battery
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The Li-ion battery cell consists of some major parts which are responsible for generating/storing electricity,
- Electrodes
- Electrolyte
- Separator
The electrodes consist of the positive side or cathode and the negative side or anode. The positive electrode or cathode uses metal oxides [lithium cobalt oxides (LiCoO2)] and the negative electrode or anode uses graphite as material. The only use of graphite as anode material in Li-ion cells is that it has a structural configuration that allows the storage of li-ion in the anode. Apart from that, the graphite material has no role in the chemical reaction in a Li-ion battery cell.
Another important component of the Li-ion battery cell is an electrolyte which can be solid (for Solid State Battery) or liquid. The commonly available Li-ion battery cell uses a liquid mixture of lithium salt with an organic solvent as an electrolyte material. During the charging and discharging process, the electrolyte solution also acts as a medium that allows Li-ion to pass through from anode to cathode and vice versa. And another component used in the battery is the separator. It is a semi-permeable layer that prevents contact between the cathode and anode. And there are two current collectors at the end of the battery cell that helps in the easy flow of electrons in the external circuit. Copper and Aluminum are the common material for the current collectors.
Working Process
During the charging process
When we connect the battery cell with the power source. The lithium atom leaves the molecular structure of metal oxide and ionizes into Li+ ions and electrons as shown in the charging process of the charge cycle below. These released electrons are forced to travel through an external circuit and reach the graphite layer as they are blocked by the electrolyte to penetrate through it. Whereas the Li+ ion will flow towards the anode following the electrons defusing through the electrolyte. After arriving at the anode, the graphite material will trap these ions and electrons. Once all the Li+ ions reach the graphite anode, the cell will be fully charged. And it will store those ions and electrons until we connect the cell with an external circuit for various uses.
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| Charging and Discharging cycle of Li-ion battery. |
During the discharging process
When we connect the battery cell with an external circuit. It will initiate a chemical reaction between the anode and the electrolyte. And the lithium atom in the graphite layers oxidizes releasing electrons and Li+ ions at the anode. The released Li+ ions move towards the cathode diffusing through the electrolyte and the semi-permeable membrane, whereas the electron will be blocked by the electrolyte to pass through it, so the electrons travel through the external circuit to the cathode resulting in the generation of electricity. Once all the Li+ ions reach the cathode section, the cell will be fully discharged. After arriving at the cathode, both the ions will recombine and form a molecular structure of metal oxides. It will remain stable until we plug in that battery cell with the power source.
During the process of charging and discharging, if the internal temperature of the cell rises. This could dry the liquid electrolyte between the cathode and anode resulting in a fire or an explosion due to the direct contact between them. So to prevent that failure the function of the separator comes into practice. A separator is a semi-permeable insulating layer that allows the Li+ ions to flow through it but it insulates the cathode and anode.