Lithium-ion batteries have been around for nearly 30 years and while they have been wildly successful in the consumer electronics and automotive sectors, it is not surprising that new technologies are waiting in the wings to address its limitations.

Already, several lithium-ion manufacturers are now producing batteries with cathodes that have a greater nickel content to meet the demand for greater energy density, which translates to longer driving ranges for electric vehicles (EVs).

But there’s another technology looking to be the next big thing in the sector.

Solid state batteries have been proposed as a solution to the intrinsic limitations of current lithium-ion batteries that use liquid electrolytes in terms of safety, performance, form factor and costs.

Notable developers include Volkswagen-backed QuantumScape, which is looking to commercialise the technology.

So just what are the differences between the two technologies?


Why solid electrolytes trump their liquid counterparts

Most current lithium-ion technologies employ liquid electrolyte that contains lithium salts within an organic solvent.

However, the solid electrolyte interface, which is caused as a result of the de-composition of the electrolyte at the negative electrode, limits the effective conductance.

Furthermore, liquid electrolyte needs expensive membranes to separate the cathode and anode, as well as an impermeable casing to avoid leakage.

These factors constrain the size and shape of these batteries and are further compounded by the fact that liquid electrolytes have safety and health issues as they use flammable and corrosive liquids.

In contrast, IDTechEx noted in a research report that solid state electrolytes used lithium metal and high-voltage cathode materials.

While early generation solid state batteries offer no obvious advantage over liquid-based batteries, which can reach an energy density of over 700 watt hours per litre (Wh/L) at cell level that allows for a maximum driving range of about 500km for EVs, they do provide other benefits.

Firstly, as both the electrodes and the electrolyte are solid state, the solid electrolyte also behaves as the separator, allowing volume and weight reduction due to the elimination of components such as the separator and casing.

This also allows for more compact arrangement of cells in the battery pack.

Perhaps more importantly, the removal of flammable liquid electrolytes can be an avenue for safer, long-lasting batteries as they are more resistant to changes in temperature and physical damages occurred during usage.

Solid state batteries could also have longer lives as they can handle more charge/discharge cycles before degradation.

Coupled with the use of high voltage cathode materials and high-energy-density lithium metal anode, solid state batteries could have energy densities beyond 1,000Wh/L.


Like DVDs vs streaming, competing solid state battery technologies

However, the advent of solid state batteries has to cross a significant hurdle.

IDTechEx noted there were multiple technology approaches available in the industry.

Solid-state electrolytes can be roughly segmented into three categories: organic types, inorganic types, and composite. The inorganic types are further broken into polymer, oxide and sulphide systems.

Each type has its own set of advantages and disadvantages. Polymer systems are easy to process but suffer from high operating temperatures and worse stability, while sulphide systems suffer from the difficulty of manufacturing and toxic by-products generated during manufacturing.

Nonetheless, solid state batteries might not be very far away.

Volkswagen said it would offer solid state batteries on a limited basis by the middle of this decade while Toyota has indicated that they could arrive as early as 2025.