RESUMEN
The porous structure of composite nanofibers plays a key role in improving their electrochemical performance. However, the dynamic evolution of pore structures and their action during ion intercalation/extraction processes for negative electrodes are not clear. Herein, porous carbon composite nanofibers (Fe@Fe2O3/PCNFs) were prepared as negative electrode materials for potassium-ion batteries. Electrochemical test findings revealed that the composites had good electrochemical characteristics, and the porous structure endowed composite electrodes with pseudo-capacitive behaviors. After 1500 discharge/charge cycles at a current density of 1000 mA g-1, the specific capacity of the potassium-ion batteries was 144.8 mAh g-1. We innovatively used synchrotron small-angle X-ray scattering (SAXS) technique to systematically investigate the kinetic process of potassium formation in composites and showed that the kinetic process of potassium reaction in composites can be divided into four stages, and the pores with smaller average diameter distribution are more sensitive to changes in the reaction process. This work paves a new way to study the deposition kinetics of potassium in porous materials, which facilitates the design of porous structures and realizes the development of alkali metal ion-anode materials with high energies.
RESUMEN
The growth of lithium dendrites and the shuttle of polysulfides in lithium metal batteries (LMBs) have hindered their development. In LMBs, the cathode and anode are separated by a separator, although this does not solve the battery's issues. The use of biomass materials is widespread for modifying the separator due to their porous structure and abundant functional groups. LMBs perform more electrochemically when lithium ions are deposited uniformly and polysulfide shuttling is reduced using biomass separators. In this review, we analyze the growth of lithium dendrite and the shuttle of polysulfide in LMBs, summarize the types of biomass separator materials and the mechanisms of action (providing mechanical barriers, promoting uniform deposition of metal ions, capturing polysulfides, shielding polysulfide). The prospect of developing new separator materials from the perspective of regulating ion transport and physical sieving efficiency as well as the application of advanced technologies such as synchrotron radiation to characterize the mechanism of action of biomass separators is also proposed.
RESUMEN
Fe2O3 is considered a potential electrode material owing to its high theoretical capacity, low cost, and non-toxic characteristics. However, the significant volume expansion and structural degradation during charging and discharging hinder its application in potassium ion batteries. The electrochemical properties of the electrode material are primarily influenced by the diffusion efficiency of ions and the mechanics of the object. From the construction of a one dimensional structure, a three-dimensional flower-like Fe2O3 with a high specific surface and low-dimensional spherical Fe2O3 were prepared. Considering the convenience and visualization of the research, micron-scale Fe2O3 was prepared, although the larger particle size will lose part of the capacity. Notably, compared with the spherical structure, the specific capacity of the flower structure was increased by about 100%. The von Mises stress distribution on the two structures was simulated by the finite element method, revealing the mechanism of electrode failure induced by volume expansion and confirming the vital role of the multidimensional system in relieving stress concentration and improving electrochemical performance. Furthermore, synchrotron radiation soft X-ray absorption spectrum and X-ray micro-tomography revealed the phase transformation process and reaction mechanism of Fe2O3 in potassium ion batteries. The dimensional structure construction strategy reported here can provide theoretical support for modifying transition metal oxides.