A cathode is a terminal through which electric current flows out of a polarized electrical gadget, wherein the direction of electric current is opposite to the direction of the flow of the electron. In this manner, electrons flow around the cathode terminal while current flows far from it.
Remember that the polarity of cathode is not always negative and depends on the type of device under use and can even differ according to the device’s working mode. For example: a gadget which consumes energy has a negatively charged cathode and a gadget that generates power, the cathode is positive. Following the same concept, the discharging battery holds cathode, which is a positive electrode, the terminal at which the electrochemical reduction takes place. Electrochemical reduction is a chemical reaction that causes the transfer of electrons between molecules. Due to this reduction that causes flow of current, cations (positively charged ions) from the electrolytic solution and electrons from the circuit move toward the cathode.
Let us discuss this concept via Li-ion batteries. Li-ion batteries incorporate a double intercalation system, i.e. both anode and cathode have structures that permit extraction and reversible insertion of lithium cations. On a basic level, there are various materials that experience reversible intercalation and can serve as perfect materials for battery cathode. Some of the examples of cathode material being utilized in present day Li-ion batteries include -: LiCoO2, LiNi1/3Co1/3Mn1/3O2 (NMC), LiNi0.8Co0.15Al0.05O2 (NCA), LiFePO4 (LFP) and LiMn2O4 and variants (LMO) with each having their own set of merits attached to them. The choice of cathode material significantly influences the cost and performance of a Li-ion battery.
Three criteria for material selection include:
a) Simplicity and ease of handling
b) Material must be air stable at room temperature.
c) Material must pass the environmental and toxicity concerns.
Related articles:
Battery anode
Metals used in a battery
