Every modern electric car has a Li-Ion battery. But how does it work? Let's try to explain the basics.
Li-ion battery consists of four components: anode, cathode, electrolyte and separator. Anode is usually made of graphite. This modification of carbon is advantageous because it forms with lithium so-called intercalation compounds.
Such a compound can be thought of as a shelf on which books are placed, where lithium atoms are books. The distance between the shelves (layers of carbon in graphite) does not change or changes slightly during storage. Thus, graphite can easily absorb lithium and also release it again without volume change.
Cathode usually consists of a mixed oxide, i.e. an oxygen compound containing, in addition to lithium, other metals such as nickel, manganese or cobalt (for example, LixMnyOz or LiyCoyOz).
The liquid electrolyte (solid-state batteries with solid electrolytes are not yet modern) primarily allows lithium ions to migrate, and the separator primarily prevents electrical contact between the anode and cathode, which can lead to a short circuit. However, lithium ions can freely pass through the separator.
In a charged battery, between the carbon layers of graphite, there are lithium atoms - this is the mentioned intercalation compound. When the battery is discharged (that is, when the electric car is running), lithium emits an electron, which flows to the cathode along an electrical line. In the figure below, the electron is shown in yellow:
Along the way, the electron in the motor is used to power the electric vehicle. A positively charged lithium ion (Li+) that migrates through the electrolyte to the cathode (shown in red above).
Then Li+ and electron (e-) get to the cathode. However, the electron does not combine with a lithium ion, but with one of the other metal ions, for example, with a manganese cation, the charge of which decreases as a result. In a lithium manganate cathode, for example, manganese (Mn4+) with a fourfold positive charge is converted into a manganese ion (Mn3+) with a threefold positive charge.
When charging, the process is reversed: the charger pumps electrons from the cathode to the anode. These electrons are taken from the mixed oxide. In our lithium manganate cathode, the manganese again emits an electron:
Mn4+ is formed again from Mn3+ at cathode, and electron migrates to anode. At the same time, the lithium cation moves through the electrolyte to the other pole and combines with an electron, forming uncharged lithium. This returns to its original state.