A Solid-state battery (SSB) is an electrical battery that uses a solid electrolyte to conduct ions between the electrodes, instead of the liquid or gel polymer electrolytes found in conventional batteries. Solid-state batteries offer much higher energy density than typical lithium batteries.

From 1831 to 1834, Michael Faraday discovered the solid electrolytes silver sulfide and lead fluoride, which laid the foundation for solid-state ionics.

Although solid-state batteries were discovered in the 19th century, their widespread application has been hindered by the high and complex manufacturing costs. 
With the development of the times, new energy sources have been rapidly advancing, and leveraging China's advantages in the entire industrial chain, the issue of solid-state batteries is gradually being resolved and being widely applied in various industries, especially in the field of Electric Vehicles.

What are the differences between the Lithium-ion battery & Solid-state battery?

>> Firstly, let's check the structure of the Lithium-ion battery:

This technology is now used in the vast majority of electric vehicles in circulation. 

Every lithium-ion cell has two electrodes, i.e., compounds that can accept the intercalation of lithium ions inside their structure. 

    > A cathode, i.e., the positive pole of the battery made of cathodic material (eg, LFP, NMC, LMO, etc) and the current collector

    > An anode, i.e., the negative pole of the battery, made of anodic material (eg, carbon or graphite) and the current collector
A central separator, i.e., a thin layer made from a plastic polymer (polyethylene or polypropylene), which acts as a mechanical separator between the anode and cathode and works as an insulator.

    > An electrolyte: i.e., the medium through which ions move; an organic liquid that contains lithium salt. The electrolyte fills the entire volume inside the cell, soaks the electrodes, and allows the lithium ions to move by acting as a connecting link between the cathode and anode.

In the lithium-ion battery, the separator does not have any other functions apart from insulation and is totally submerged in the liquid electrolyte, which soaks everything inside the cell and becomes a real medium through which lithium ions move between the cathode and anode, where the anode is made from a graphite structure. 

The lithium ions, therefore, move through the electrolyte and intercalate in the crystal structures of the two anode and cathode electrodes (structures which have empty spaces inside, where the lithium ions fit as they are very small particles).

>> Secondly, let's check the Solid-state battery structure:

The internal structure of a solid-state cell is very different, as all its parts are solid. While in traditional lithium batteries, the electrolyte is a liquid, solid-state cells are formed of:

    > A cathode (or positive electrode), which can be made with the same compounds as a lithium-ion battery (eg, LFP/LFMP, NMC, LMO, etc.)
    > A separator, generally ceramic or solid polymer, which also works as the electrolyte
    > An anode made of lithium metal (pure lithium)

The grey central layer serves as both the solid-state separator and the electrolyte, acting independently as the separator between the anode and cathode. It therefore becomes the medium through which the ions move, and also has electric insulating properties, and acts as a mechanical separator between the anode and cathode. 
The fact that there is this solid, resistant support allows the removal of the graphite structure on the anode part and ensures that lithium metal accumulates directly on the anode (there are also semi-solid solutions where the electrolyte is a gel).

>> How does a solid-state battery work?

When the cell is charging, the lithium particles move from the cathode, through the structure of the atoms that form the separator, and then move in between the separator itself and the anode’s electrical contact, thus forming a solid layer of pure lithium.  In this way, the anode will only be formed of lithium particles and will have a smaller volume than a lithium-ion technology anode, which contains the graphite structure.

>> What are the current strengths of solid-state battery technology?

The key factor of safety:

Solid-state batteries do not have a liquid electrolyte, which in lithium-ion batteries is one of the most challenging components in terms of safety, because it is volatile and therefore more flammable. Furthermore, this is replaced by a thicker separator layer formed of a material that is mechanically more resistant to high temperatures (because it has a ceramic composition with various additives); this makes the separation between the anode and cathode more reliable, so much so that it prevents short circuits, even in the event of misuse or deterioration, and therefore the intrinsic safety of the cells increases.

Another advantage in terms of safety is the greater resistance to dendrites, or the sharp, uneven build-up of lithium that forms during movement from the cathode to the anode. In fact, lithium does not move evenly and tends to group together and form points which, like real pins, grow and, in some extreme cases, can pierce the separator. However, thanks to its thickness, solid separators are more resistant to piercing from dendrites and therefore avoid possible short circuits and the gradual deterioration of the cell.

Highest energy density

The greater intrinsic safety helps bring another major improvement: the use of a pure metal anode encourages a huge increase in energy density. This is essentially down to the removal of the graphite anode (which in lithium-ion batteries contains the ions when they migrate). In a solid-state battery, during the transfer, only the ions remain, and a bulky, heavy compound part is removed, which does not actively contribute to energy generation.

According to the latest studies, solid-state batteries have an energy density 2-2.5 times higher than current lithium-ion technology, and this huge advantage would result in a lighter and smaller battery. This is certainly a breakthrough for electric mobility, which would benefit from greater range and a lighter weight.

Ultra-fast charging speed

Recent research indicates that solid-state batteries charge up to 6 times faster than currently available batteries. However, this figure remains uncertain and depends on the development of this new technology. According to information from BYD Group, their second-generation blade battery, still using a liquid electrolyte, already allows a car to be ready in 5 minutes, fully charged in 9 minutes, only adds 3 minutes at -30°C. 
Therefore, we can expect that solid-state batteries will charge even faster.