To develop highly efficient thermoelectric materials, the generation of homogeneous heterostructures in a matrix is considered to mitigate the interdependency of the thermoelectric compartments. In this study, Cu₂Te nanoparticles were introduced onto Bi₂Te_2.7Se_0.3 n-type materials and their thermoelectric properties were investigated in terms of the amount of Cu₂Te nanoparticles. A homogeneous dispersion of Cu₂Te nanoparticles was obtained up to 0.4 wt.% Cu₂Te, whereas the Cu₂Te nanoparticles tended to agglomerate with each other at greater than 0.6 wt.% Cu₂Te. The highest power factor was obtained under the optimal dispersion conditions (0.4 wt.% Cu₂Te incorporation), which was considered to originate from the potential barrier on the interface between Cu₂Te and Bi₂Te_2.7Se_0.3. The Cu₂Te incorporation also reduced the lattice thermal conductivity, and the dimensionless figure of merit ZT was increased to 0.75 at 374 K for 0.4 wt.% Cu₂Te incorporation compared with that of 0.65 at 425 K for pristine Bi₂Te_2.7Se_0.3. This approach could also be an effective means of controlling the temperature dependence of ZT, which could be modulated against target applications.

Lithium–sulfur batteries are promising candidates for next‐generation energy storage due to their high energy density and low cost. However, their commercialization is hindered by poor cycling performance caused by the polysulfide shuttle effect. While strategies such as physical barriers or chemical adsorption have been proposed, they inevitably introduce inactive components, reducing energy density. These limitations underscore the need for a more fundamental approach that avoids the use of inactive materials. In this study, a cosolvent‐based electrolyte design as a fundamental strategy is presented to suppress the shuttle effect without relying on inactive additives. A high donor number solvent is used as the base, and four cosolvents with distinct physicochemical properties are individually introduced. By varying the cosolvent, the lithium polysulfides solubility is systematically tuned, directly influencing electrochemical kinetics. Notably, the combination of two low‐miscibility solvents induced local phase separation, which hindered the diffusion of lithium polysulfides and effectively mitigated the shuttle effect. As a result, significantly improved cycling stability is achieved. These findings provide a new direction for Li–S battery electrolyte development, emphasizing the importance of solvent miscibility in governing polysulfide transport.

Iron fluoride, a conversion‐type cathode material with high energy density and low‐cost iron, holds promise for Li‐ion batteries but faces challenges in synthesis, conductivity, and cycling stability. This study addresses these issues by synthesizing micron‐sized iron‐fluoride using a simple solid‐state synthesis. Despite a large particle size, a high capacity of 571 mAh g⁻¹ is achieved, which is attributed to the unique surface and internal pores within the iron‐fluoride particles, which provided a large surface area. This is the first study to demonstrate the feasibility of using large iron fluoride particles to enhance the energy density of the electrode and achieve an iron fluoride full cell with high capacity. Also, the cause of the capacity fading is investigated. Electrode delamination from the current collector, which is the main cause of capacity fading in early cycles, is resolved using a carbon‐coated aluminum (C/Al) current collector. Moreover, iron (Fe) dissolution and the deposition of dissolved Fe on the Li metal also contributed significantly to the degradation. Localized high‐concentration electrolytes (LHCEs) suppress iron dissolution and Li dendrite growth, resulting in long‐cycle stability for 300 cycles. This study provides insights into the further development of conversion‐type metal fluorides across various compositions.