After the invention of potassium-ion battery with the prototype device, researchers have increasingly been focusing on enhancing the
specific capacity and
cycling performance with the application of new materials to
electrodes (anode and cathode) and
electrolyte. A general picture of the material used for potassium-ion battery can be found as follows:
Cathodes Besides the original Prussian blue cathode and its analogs, researches on cathode part of potassium ion battery focus on engineering. Kristonite is a 4V cathode material — in the class of potassium
prussian white (KPW) materials. Another
nanostructure and
solid ionics appeared. A series of potassium transition metal oxide such as , have been demonstrated as cathode material with a layered structure. Polyanionic compounds with inductive defects could provide the highest working voltage among other types of cathode for potassium-ion batteries. During the electrochemical cycling process, its crystal structure will be distorted to created more induced defects upon the insertion of potassium ion. Recham
et al first demonstrated that fluorosulfates have a reversible intercalation mechanism with K, Na and Li, since then, other polyanionic compound such as , have been studied, while still limited to the complex synthesis process. Worth noting is an orthodox approach of using organic compound as cathode for potassium-ion battery, such as PTCDA, a red pigment which can bond with 11 potassium ion within single molecule. Classic alloying anodes such as Si, Sb and Sn that can form alloy with lithium ion during cycling process are also applicable for potassium-ion battery. Among them Sb is the most promising candidate due to its low cost and the theoretical capacity up to 660 mAh g−1. Other organic compounds are also being developed to achieve strong mechanical strength as well as maintaining decent performance.
Anodes Same as the case of lithium-ion battery,
graphite could also accommodate the intercalation of potassium within electrochemical process. Whereas with different kinetics, graphite anodes suffer from low capacity retention during cycling within potassium-ion batteries. Thus, the approach of structure engineering of graphite anode is needed to achieve stable performance. Other types of carbonaceous materials besides graphite have been employed as anode material for potassium-ion battery, such as expanded graphite, carbon nanotubes, carbon nanofibers and also nitrogen or phosphorus-doped carbon materials. Conversion anodes which can form compound with potassium ion with boosted storage capacity and reversibility have also been studied to fit for potassium-ion battery. To buffer the volume change of conversion anode, a carbon material matrix is always applied such as , , and so on.
Electrolytes Due to the chemical activity higher than lithium, electrolytes for potassium ion battery requires more delicate engineering to address safety concerns. Commercial ethylene carbonate (EC) and diethyl carbonate (DEC) or other traditional ether/ester liquid electrolyte showed poor cycling performance and fast capacity degradation due to the Lewis acidity of potassium, also the highly flammable feature of it has prevented further application. Ionic liquid electrolyte offers new way to expand electrochemical window of potassium ion battery with much negative redox voltage and it's especially stable with graphite anode. Recently, solid polymer electrolyte for all-solid-state potassium-ion battery have attracted much attention due to its flexibility and enhanced safety, Feng
et al proposed a poly (propylene carbonate)-KFSI solid polymer electrolyte with the frame work of cellulose non-woven membrane, with boosted ionic conductivity of 1.36\times10−5 S cm−1. Research on electrolyte for potassium-ion battery is focusing on achieving fast ion diffusion kinetics, stable SEI formation as well as enhanced safety. == Advantages ==