Lithium-ion battery

The lithium ion battery is a rechargeable battery that is used in many portable electronic devices. The anode is made of graphite while the cathode is a lithium metal oxide, e.g. lithium cobalt oxide or lithium manganese oxide. The electrolyte consists of lithium salt complexes (e.g. LiBF4) in a mixture of organic carbonates (e.g. ethylene carbonate).


Discharging process

Lithium is oxidised at the anode as follows:

LiC_6\rightleftharpoons Li^++C_6+e^-

Electrons move to the copper collector and flow out to power an electronic device like a laptop, while lithium ions migrate across the electrolyte to the cathode. On their return, the electrons move from the aluminium collector to the cathode where they participate in the following reduction reaction:

CoO_2+Li^++e^-\rightleftharpoons LiCoO_2

When fully discharged, most of the lithium ions are stored at the cathode in the form of lithium cobalt oxide.


Charging process

During charging, an external alternating current power source connected to the circuit is converted to a direct current with a voltage that is higher than that produced by the lithium ion battery, i.e. an over-voltage. Electrons are therefore forced to flow to the anode where the reverse reaction takes place:

Li^++C_6+e^-\rightleftharpoons LiC_6

As lithium ions are reduced at the graphite electrode which is now the cathode, lithium cobalt oxide at the other electrode undergoes oxidation:

LiCoO_2\rightleftharpoons CoO_2+Li^++e^-

with the free electrons flowing via the aluminium collector out to the circuit and lithium ions migrating back across the electrolyte to the graphite electrode. When fully charged, most of the lithium ions are stored in the form of LiC6.


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