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.

Thermal transport properties of solid solution ${\left({\mathrm{La}}_x{\mathrm{Gd}}_{1-x}\right)}_2{\mathrm{Zr}}_2{\mathrm{O}}_7$ have been investigated for thermal barrier coatings (TBCs) application. The introduction of point defects was intended to provide extra phonon scattering, and much lower thermal conductivity for the solid solution has been obtained compared with ${\mathrm{La}}_2{\mathrm{Zr}}_2{\mathrm{O}}_7$ and ${\mathrm{Gd}}_2{\mathrm{Zr}}_2{\mathrm{O}}_7$. The phonon mean free paths of the solid solution were estimated and discussed with respect to the point defect scattering effect. Young’s modulus and heat capacity of the solid solution, which determine the mean velocity and the carried energy of the phonons, respectively, were measured and both showed suppression compared with the end materials, possibly due to the lattice relaxation aroused by point defects. A theoretical model, which contains no adjustable parameters, was present to accurately describe the thermal conductivities of the solid solution by taking account of the mass and strain field fluctuations induced by the point defects.

Radial mesoporous silica (RMS) sphere was tailor-made for further applications in producing shape-stabilized composite phase change materials (ss-CPCMs) through a facile self-assembly process using CTAB as the main template and TEOS as SiO₂precursor. Novel ss-CPCMs composed of polyethylene glycol (PEG) and RMS were prepared through vacuum impregnating method. Various techniques were employed to characterize the structural and thermal properties of the ss-CPCMs. The DSC results indicated that the PEG/RMS ss-CPCM was a promising candidate for building thermal energy storage applications due to its large latent heat, suitable phase change temperature, good thermal reliability, as well as the excellent chemical compatibility and thermal stability. Importantly, the possible formation mechanisms of both RMS sphere and PEG/RMS composite have also been proposed. The results also indicated that the properties of the PEG/RMS ss-CPCMs are influenced by the adsorption limitation of the PEG molecule from RMS sphere with mesoporous structure and the effect of RMS, as the impurities, on the perfect crystallization of PEG.

A shape-stabilized composite phase change material (ss-CPCM) comprising polyethylene glycol (PEG) and porous carbon was prepared by absorbing PEG into porous carbon, assisted by ultrasound. In the composite, PEG served as a phase change material for thermal energy storage, and the porous carbon, which was prepared from fresh potato via freeze drying followed by heat treatment, was used as an absorbent that also acted as the supporting material. Various analytical techniques were used to investigate the chemical composition, microstructure, and thermal properties of the prepared PEG/porous carbon ss-CPCMs. Scanning electron microscopy, X-ray diffraction and Fourier transform infrared spectroscopic results indicated that PEG was well absorbed and encapsulated in the porous structure of the carbon and that there was no chemical reaction between them during the phase change process. The shape and exudation stability test results indicated that the PEG/porous carbon ss-CPCMs have excellent shape stability, compared to pristine PEG. The contact angle test suggested that the melting PEG has good level of wettability on the carbon so that melting PEG could be well protected from exudation in the porous carbon by surface tension effects, even if the temperature is higher than the melting point of PEG. Differential scanning calorimetric results showed that the PEG/porous carbon ss-CPCMs have considerable phase change enthalpies and thermal storage capabilities. In addition to this, the latent heats of ss-CPCMs increased with increasing contents of PEG in the composites, and the highest value was achieved when the amount of PEG was 50%. Moreover, the thermogravimetric analysis results showed that the composites had excellent thermal stabilities. Based on the above analyses, the prepared ss-CPCM with 50% PEG content proved to be a promising candidate for thermal energy storage applications.