How does a lithium ion battery work? And how does the mnemonic OIL RIG help us understand the processes?
A battery consists of an anode (negative terminal) and a cathode (positive terminal). A polymer separator prevents direct contact, and a liquid electrolyte allows movement of ions between the layers. The anode and cathode are connected via an external circuit.
Operation is via redox reactions – transfer of electrons, causing oxidation and reduction of species.
A handy mnemonic to understand this: OIL RIG.
➡ 𝗢xidation 𝗜s 𝗟oss of electrons
➡ 𝗥eduction 𝗜s 𝗚ain of electrons.
What does this look like when the cell operates?
Using an example with Lithium Iron Phosphate (LFP) Cathode and Graphite Anode, what happens to Lithium ions (Li+) and electrons (e−):
𝗖𝗵𝗮𝗿𝗴𝗶𝗻𝗴
Voltage is applied, giving energy for reaction
Reaction: LiFePO4 + 6 C -> FePO4 + LiC6
➡ 𝗖𝗮𝘁𝗵𝗼𝗱𝗲 is 𝗿𝗲𝗱𝘂𝗰𝗲𝗱. Loses Li+ ions and e−
➡ Li ions migrate through electrolyte to anode
➡ Electrons flow round the circuit to anode
➡ 𝗔𝗻𝗼𝗱𝗲 is 𝗼𝘅𝗶𝗱𝗶𝘀𝗲𝗱, incorporates Li+ and e−
𝗗𝗶𝘀𝗰𝗵𝗮𝗿𝗴𝗶𝗻𝗴
The battery is connected to a circuit, and energy released
Reaction: FePO4 + LiC6 -> LiFePO4 + 6 C
➡ 𝗔𝗻𝗼𝗱𝗲 is 𝗿𝗲𝗱𝘂𝗰𝗲𝗱. Loses Li+ ions and e−
➡ Li ions migrate through electrolyte to cathode
➡ Electrons flow round the circuit to cathode
➡ 𝗖𝗮𝘁𝗵𝗼𝗱𝗲 is 𝗼𝘅𝗶𝗱𝗶𝘀𝗲𝗱, incorporates Li+ and e−
This process is reversible, and hence can be done for many charge/discharge cycles. Over time there is gradual degradation which reduces the cell performance.
Next time your battery is running low think of OIL RIG and how you need to plug in to reduce your cathode species!
CPI
CPI support companies through the ‘valley of death’ of technology scale up by providing access to expertise and open access facilities for development. CPI specialise in automation of battery R&D from powders to cells, accelerating development and decreasing time to market.
See also: Anode, Cathode, Separator, Standard Electrode Potentials