Battery Chemistry

The fundamental battery chemistry or more correctly the Electrochemistry. This is the cathode, anode and electrolyte. What are they, who makes them, where next on the roadmap, what is the latest research and what are the pros and cons of each.

The main chemistries are:

Aluminium Air

High energy density and low cost. The aluminium anode and air cathode along with an aqueous electrolyte, generate power through the oxidation of aluminium by oxygen from the air. However, a major issue is the corrosion of the aluminium anode thus reducing capacity and compromising calendar life.

Aluminium Ion

The aluminium metal anode can exchange three electrons during the electrochemical process, hence can deliver a high theoretically high volumetric and gravimetric capacity. However, anode, cathode and electrolyte development is required before this type of cell can exploit the high energy density with a stability over a lifetime of cycles.

Dual-Ion

A battery technology that offers a low cost solution for grid based storage. Cations and anions both participate in the intercalation and deintercalation processes using graphite as both cathode and anode material.

Fluoride-Ion

Seen as a replacement for lithium and possibly the post-lithium technology with “up to 7x the Wh/kg” of current Lithium technology.

Lead Acid

The Lead Acid Battery is a battery with electrodes of lead oxide and metallic lead that are separated by an electrolyte of sulfuric acid. Energy density 40-60 Wh/kg.

Lithium Air

Promised as the beyond lithium ion technology with unrivaled energy density. However, even though a huge amount of scientific effort has gone into understanding the chemistry and reactions it is not mature enough to develop into a workable battery at this stage. If anything the focus has moved to solid state lithium ion batteries.

Lithium Ion

In a rechargeable lithium ion battery lithium ions move from the negative electrode to the positive electrode during discharge, and back when charging. Current production cells have an energy density ~280Wh/kg.

The cathode is a lithium transition metal oxide, eg manganese or cobalt or a combination of transitional metals: LCO, LMO, NCA, NMC, LFP, LMFP. The anode is normally a graphite-based material, which can intercalate or release lithium, this can have a percentage of Silicon to increase the capacity. Alternatively the anode can be Lithium Titanate (LTO).

Lithium Sulfur

Perhaps the most mature of the beyond Li-ion’ battery chemistries with a potential energy density of >600Wh/kg. Also with the potential for substantially reduced costs and improved safety. However, a number of challenges mean that cycle life has been poor. Hence the potential attracts attention and much needed research at the fundamental chemistry stage.

Magnesium-Ion

Function very similar to lithium-ion batteries, comparable energy density to lithium-ion along with potential for improvement as there are double the electrons for every individual magnesium ion. Magnesium is more abundant than lithium. However, there are a lot more possible side reactions with magnesium-ion.

Nickel Cadmium

Rechargeable battery that uses nickel oxide hydroxide and metallic cadmium as electrodes.

Nickel Metal Hydride

The Nickel Metal Hydride battery has a nickel-hydroxide cathode, a metal hydride (a variety of metal alloys are used) anode, and aqueous potassium hydroxide electrolyte. This is a rechargeable battery chemistry that has been superseded by lithium ion, but has seen a lot of use in Toyota hybrids. Energy density 40-110 Wh/kg at cell level.

Potassium Ion

Potential to be a low cost storage based chemistry, but large large change of ~60% of graphite with the insertion of K ions puts high strain on lattice and so limits cycling. Technology development is behind that of Lithium and Sodium Ion based batteries.

Sodium Ion

Analogous to the lithium-ion battery but using sodium ions (Na+) as the charge carriers. The working of the sodium based chemistry and cell construction are almost identical with those of the commercially widespread lithium-ion battery types, but sodium compounds are used instead of lithium compounds.

Solid-State

Any battery technology that uses solid electrodes and solid electrolyte. This offers potential improvements in energy density and safety, but has very significant challenges with cycling, manufacturing and durability of the solid sandwich.

Zinc Air

Perhaps the most promising metal-air battery technology. Typically it has a zinc anode, an oxygen permeable cathode, a separator, and a caustic alkaline electrolyte. Promising low cost, high stability and high energy density.

References

  1. Jianmin Ma et al, “The 2021 battery technology roadmap”, 2021 J. Phys. D: Appl. Phys. 54 183001