Week 1 Understanding Different Battery Chemistry

Week 1 Understanding Different Battery Chemistry

Lithium Batteries

Since the late 1980s rechargeable lithium cells have come onto the market. They offer greatly increased energy density in comparison with other rechargeable batteries, though at greatly increased cost. It is a well-established feature of the most expensive laptop computers and mobile phones that lithium rechargeable batteries are specified, rather than the lower cost NiCad or NiHM cells that we have been considering earlier.

The lithium polymer battery uses lithium metal for the negative electrode and a transition metal intercalation oxide for the positive. In the resulting chemical reaction, the lithium combines with the metal oxide to form a lithium metal oxide and release energy. When the battery is recharged the chemical reaction is reversed. The lithium is thus both a reactant and the mobile ion that moves through the electrolyte.

The overall chemical reaction is:

xLi + MyOz ←→ LixMyOz

The solid lithium negative electrode has been a cause of problems with this type of cell; there are safety difficulties and sometimes a decrease in performance due to passivation. Thus, they have been largely superseded by the lithium ion battery. 2.6.3 The lithium ion battery the lithium ion battery was introduced in the early 1990s and it uses a lithiated transition metal intercalation oxide for the positive electrode and lithiated carbon for the negative electrode. The electrolyte is either a liquid organic solution or a solid polymer. Electrical energy is obtained from the combination of the lithium carbon and the lithium metal oxide to form carbon and lithium metal oxide.

The overall chemical reaction for the battery is:

C6Lix + MyOz ←→ 6C + LixMyOz

An important point about lithium ion batteries is that accurate control of voltage is needed when charging lithium cells. If it is slightly too high it can damage the battery, and if too low the battery will be insufficiently charged. Suitable commercial chargers are being developed along with the battery.

Type	Anode	Cathode	Redox reactions
Lithium Titanate Batteries (LTO)	Li4Ti5O12 --> Ti5O12 + 4Li+ + 4e-	4Mn2O4 + 4Li+ + 4e- -->4LiMn2O4	Li4Ti5O12 + 4Mn2O4 --> 4LiMn2O4 + Ti5O12
Lithium manganese oxide batteries (LMO)	LiC6 -->xLi+ + xe- + C6	Li1-xMn2O4 + xLi+ + xe--->LiMnO2	LiC6 + Mn204 -->C6 + LiMnO2
Lithium nickel cobalt aluminum oxide (NCA)	LiC6 -->xLi+ + xe- +C6	Li1-xMO2 + xLi+ + xe- --> LiMO2	Li1-xMO2+ LiC6 -->Li1-xMO2 + C6
Lithium Nickel Manganese Cobalt Oxide (NMC)	LiC6 -->xLi+ + xe- + C6	Li1-xMO2+ xLi+ + xe- -->LiMO2	Li1-xMO2 + LiC6 --> Li1-xMO2 + C6
lithium iron phosphate (LFP)	LiC6 -->xLi+ + xe- + C6	FePO4 + Li++ e- -->LiFePO4	LiFePO4 + 6C -->LiC6 + FePO4