The limited resources and uneven distribution of lithium stimulate strong motivation to develop new rechargeable batteries that use alternative charge carriers. Potassium-ion batteries (PIBs) are at the top of the list of alternatives because of the abundant raw materials and relatively high energy density, fast ion transport kinetics in the electrolyte, and low cost. However, several challenges still hinder the development of PIBs, such as low reversible capacity, poor rate performance, and inferior cycling stability. Research on the cathode is currently focused on developing materials with high energy density and cycling stability, mainly including layered transition metal oxides, polyanion compounds, organic compounds, etc. Anodes based on intercalation reactions, conversion reactions, and alloying with potassium are currently under development, and promising results have been published. This review comprehensively summarizes the research effort to date on the electrode material optimization (e.g., crystals, morphology, reaction mechanisms, and interface control), the synthesis methods, and the full cell fabrication for PIBs to enhance the electrochemical potassium storage and provide a platform for further development in this battery system.

The KMg₄(PO₄)₃:Eu²⁺ phosphor was prepared by the conventional high temperature solid-state reaction. The crystal structure, luminescence and reflectance spectra, thermal stability, quantum efficiency and the application for N-UV LED were studied respectively. The phase formation and crystal structure of KMg₄(PO₄)₃:Eu²⁺ were confirmed from the powder X-ray diffraction and the Rietveld refinement. The concentration quenching of Eu²⁺ in the KMg₄(PO₄)₃ host was determined to be 1mol% and the quenching mechanism was certified to be the dipole–dipole interaction. The energy transfer critical distance of as-prepared phosphor was calculated to be about 35.84Å. Furthermore, the phosphor exhibited good thermal stability and the corresponding activation energy ΔE was reckoned to be 0.24eV. Upon excitation at 365nm, the internal quantum efficiency of the optimized KMg₄(PO₄)₃:Eu²⁺ was estimated to be 50.44%. The white N-UV LEDs was fabricated via KMg₄(PO₄)₃:Eu²⁺, green-emitting (Ba,Sr)₂SiO₄:Eu²⁺ and red-emitting CaAlSiN₃:Eu²⁺ phosphors with a near-UV chip. The excellent color rendering index (Ra = 96) at a correlated color temperature (5227.08K) with CIE coordinates of x = 0.34, y = 0.35 of the WLED device indicates that KMg₄(PO₄)₃:Eu²⁺ is a promising blue-emitting phosphor for white N-UV light emitting diodes (LEDs).

A novel polyimide derivative is prepared by a condensation polymerization of pyromellitic dianhydride and 2,6-diaminoanthraquinone and a flexible electrode film –SWNT is further fabricated by filtration with single-walled carbon nanotube dispersions. connects different carbonyl groups of dianhydride and quinone together, therefore combining the advantages of different units together. Electrochemical tests show that –SWNT can transfer three electrons reversibly and theoretical calculations also prove that. –SWNT shows a high capacity of 190 mA h g⁻¹ and superior rate performance, maintaining 120 mA h g⁻¹ at 20C. –SWNT is a promising flexible electrode because of its good performance and flexibility.