A potassium-ion battery or K-ion battery (abbreviated as KIB) is a type of battery and analogue to lithium-ion batteries, using potassium ions for charge transfer instead of lithium ions. It was invented by the Iranian/American chemist Ali Eftekhari (President of the American Nano Society) in 2004.
History The prototype device used a potassium anode and a Prussian blue compound as the cathode material for its high electrochemical stability. The prototype was successfully used for more than 500 cycles. A recent review showed currently that several pragmatic materials have been successfully used as the anode and cathode for the new generations of potassium-ion batteries. For example, the conventional anode material graphite has been shown that it can be used as an anode in a potassium-ion battery. In 2024, Group1, created Kristonite for the cathode.
Materials 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 K0.3MnO2, K0.55CoO2 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 K3V2(PO4)3, KVPO4F 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 MoS2@rGO, Sb2S3-SNG, SnS2-rGO and so on.
Electrolytes Because the chemical activity of potassium is higher, potassium ion batteries place higher demands on the electrolyte, and developing suitable electrolytes has proven challenging. Commercial ethylene carbonate (EC), diethyl carbonate (DEC) and similar traditional ether/ester liquid electrolytes show poor cycling performance and rapid capacity degradation due to the Lewis acidity of potassium. These electrolytes are also highly flammable, presenting safety hazards, and research has turned towards other electrolyte materials. Ionic liquid electrolytes offer the possibility of wide electrochemical window and without flammability and have been studied with the potassium ion battery, achieving improved stability, particularly with a 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 × {\displaystyle \times } 10−5 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.
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