Although alloying transition metal chalcogenides (TMCs) with other chalcogenides can effectively improve their conductivity and electrochemical properties, the optimal alloy content is still uncertain. 
Here,Chen Jian of Southeast University, Zhou Min of University of Science and Technology of China, et alThe effect of dopant concentration on chemical bonding in TMC was studied, and the stepwise conversion reaction mechanism of potassium ion storage was revealed. Theoretical studies have shown that CO085se（co0.85se1 xsx) to reduce the average length of the co-co bond due to the change in electronegativity. When used as the anode of a potassium-ion battery (PIB), the sample with optimized SE S ratio showed excellent rate performance (229 at 10 A g 1).2 ma hg−1）。When Prussian blue (Pb) is used as the cathode, pouch cells show great application potential. In addition, the stepwise K+ storage mechanism caused by the coexistence of S and Se was revealed by in-situ X-ray diffraction and ex-situ transmission electron microscopy techniques. 
Figure 1Preparation process and structural characterization
In conclusion, this work successfully fabricated a flexible free-standing CO0 with a 3D mesh yolk shell structure by chalcogenide design85se1−xsx/cnf。The results showed that S-doping could reduce CO0The average length of the co-co bond in 85SE1 XSX. In addition, the yolk shell structure (i.e., CO0. wrapped in a 3D mesh carbon nanofiber frame85SE1 XSX nanoparticle egg yolk) can effectively alleviate the volume expansion during long-term ion storage. In addition, the K2S and K2Se phases, formed during the stepwise reaction, help to reduce volume expansion and increase ion transport. The CSS CNF-2 electrode exhibited excellent rate performance (229 at 10 Ag 1).2 mA Hg 1) and cycling stability (327 after 1000 cycles at 1 A G1).7 mA Hg 1), which is superior to other reported TMCS anode materials, and the prepared CSS CNF-2 PB pouch battery shows excellent electrochemical performance and practical application potential. Therefore, this alloying design can provide an effective strategy for the construction of high-performance flexible TMCS electrode materials. 
Figure 2Battery performance
modulating co–co bonds **erage length in co0.85se1−xsx to enhance conversion reaction for potassium storage,journal of energy chemistry2023 doi: 10.1016/j.jechem.2023.12.013