Solid-state batteries differ from conventional batteries in particular by the solid electrolyte. The task of the electrolyte is to conduct ions between the anode and cathode. Depending on the cell chemistry the ion to be conducted is different, for example in lithium-ion batteries the lithium cation or in sodium-ion batteries the sodium cation. Frequently, charge transport in solid electrolytes is based on different jump processes in the solid state lattice . The characteristics of these processes vary depending on the electrolyte used and also depend on the formation of various defects, such as Schottky defects, Frenkel defects or occupied interstitial spaces
To use solid electrolytes in solid state batteries, they should have the highest possible ionic conductivity and a very low electronic conductivity. To enable solid state batteries to exceed the energy densities of conventional accumulators, metallic anodes must be used. In the case of a lithium-ion battery, metallic lithium would therefore have to be used instead of the graphite previously used. Metallic lithium tends to form dendrites when the battery is cyclized. Dendrites can grow from the lithium anode to the cathode, causing an electrical short circuit. This is also the reason why the use of metallic lithium in conventional batteries was not possible until now. Further requirements for solid electrolytes are therefore a good stability against lithium as well as against the formation of dendrites The reasons for the formation of dendrites in lithium-ion solid state batteries have not yet been fully clarified and are being intensively researched
Solid state batteries basically have the following two characteristics: low power density and high energy density. The first limitation occurs because of the difficulty of transmitting high currents across solid-state interfaces. On the other hand, these accumulators have certain advantages that outweigh this disadvantage: they are easy to miniaturize (they can be manufactured, for example, in the form of a thin layer) and there is no risk that the electrolyte could damage the accumulator through leaks. They usually have a very long life and shelf life and usually do not show any abrupt changes in their performance even with temperature fluctuations (which can cause freezing or boiling of the electrolyte in liquid electrolytes). Another advantage of solid state batteries (in contrast to lithium-ion batteries) is that they are not flammable.