Silicon/carbon (Si/C) composites are promising anodes for high-energy-density lithium-ion batteries (LIBs), because they solve the typical problems of a huge volume expansion and poor conductivity of pure Si anodes. Methods for their production are summarized, including ball milling, spray drying, electrostatic spinning, and chemical vapor deposition (CVD), and methods for improving their structure in order to improve electrical conductivity, mitigate expansion, and improve electrochemical performance are outlined, including carbon precursor coating, Si-precursor-based wet chemistry, and Si surface modification.
Lithium/fluorinated carbon(Li/CFx)batteries are among the most promising high-energy-density primary bat-teries.However,substantial heat generation during discharge remains a safety concern,particularly for high-mass-loaded pouch cells.Fluorinated porous carbon(FPC)samples with different degrees of fluorination were obtained by changing the fluorination temperature,and their effects on heat genera-tion in Ah-level Li/FPC pouch cells were examined.The flu-orination temperature not only influences the F/C ratio,but also the C-F bonding configuration,and physicochemical properties of the FPC.Pouch cells using the more highly fluorinated cathodes generated the most heat during discharge.The heat generated also has a clear stage dependence,with the largest difference appearing in the 0-20%depth of discharge range.Post-discharge structural characterization and kinetic analysis showed that the highly fluorinated FPC cathodes have more LiF accumulation concentrated in certain regions,together with a higher charge-transfer resistance,stronger polarization,lower Li+diffusivity,and a higher nucleation overpotential.These factors collectively intensify the early-stage heat generation in the cells.This study shows that the fluorinated cathode structure,LiF evolution,and discharge kinetics jointly govern heat genera-tion in Li/FPC pouch cells,possibly providing a way to improve their thermal safety.
Silicon-carbon (Si/C) composites are promising high-capacity anode materials for next-generation lithium-ion batteries, but their commercialization is hindered by their severe volume expansion during cycling. We report a chemical vapor deposition method using the pyrolysis of silane, in which ultrafine nano-Si enters a porous carbon framework to produce kilogram-scale Si/C composites. The carbon framework with abundant micropores (similar to 1.9 nm), confines the amorphous silicon and accommodates the volume changes of nano-Si during both lithiation and de-lithiation. The resulting Si/C composites have a 56.76% Si content and have a specific capacity of 2179 mAh g(-1), a high initial Coulombic efficiency (ICE) of 93.5%, and a low specific surface area (1.32 m2 g(-1)). In addition to the nanoconfinement effect, the median particle size (D-50, 7.3-13.0 mu m) of the carbon framework was shown to control the mechanical strength, coating uniformity and Li+ transport. A D50 of 8.2 mu m endows the Si/C composites with outstanding comprehensive properties. They have an excellent rate performance with a 97.0% retention at 3 C relative to 0.1 C, show only minor variations in ICE difference at 60 degrees C/-20 degrees C compared with room temperature, and have a low expansion of 35.8% from the delithiated to the lithiated state. The composite was then mixed with graphite to prepare the anode, which was then paired with an NCM523 cathode to assemble pouch cells. The pouch cell retained 87.46% of its initial capacity after 1000 cycles at 1 C. Because of the low expansion of the electrode, the material avoids structural degradation during cycling and thus has an excellent long-term stability.
The design of het- N/S co-doped porous carbon/Fe3O4 hybrid nanostructures has emerged as an Fe3O4porosity efficient approach for improving theHeteroatom electrochemical performance of su-porous percapacitors. A green and cost-ef- incorporation fective method is reported for theEnhanced C N S O Fe3O4charge storage fabrication of a hierarchical porousperformance carbon composite from bacterial cel- Excellent electrochemical performance lulose (BC), lignosulfonic acid (LS), 99.1% both an anchoring agent and a soft molecular template, directing the oxidative polymerization and uni- A sustainable porous carbon electrode for nanofibers in the presence of FeCl3 as the oxidizing agent. Subsequent carbonization under a nitrogen atmosphere results in the formation of an N/S co-doped carbon framework decorated with Fe3O4 nanoparticles, which is denoted C-BCLP. For comparison, a control composite consisting of BC and PPy without LS was carbonized to produce C-BCP. X-ray diffraction patterns confirms the synthesis of Fe3O4 nanoparticles and the preservation of the fibrous carbon structure. Electron microscopy shows that C-BCLP has a highly porous and conductive network with a homogeneous distribution of C, O, N, S and Fe elements. Because of the combined effects of hierarchical porosity, heteroatom doping, and Fe3O4 incorporation, the C-BCLP electrode has high specific capacitances of 338.3 F g-1 at 1 A g-1 and 191.6 F g-1 at 10 A g-1. In addition, it has excellent cycling stability, retaining 99.1% of its initial capacitance after 10 000 charge-discharge cycles, outperforming the C-BCP electrode. The work suggests a promising way to develop next-generation high-performance supercapacitors.
To solve the problems of limited capacity, low initial coulombic efficiency, and poor long-term cycling stability in hard carbon anodes for sodium-ion batteries, a stabilization strategy is reported that uses both microporous confinement and chemical bonding to control the sulfur species. Hard carbon is derived from bituminous coal, taking advantage of its naturally condensed aromatic framework. Using a two-step thermal process, a microporous carbon framework was constructed, followed by gasphase sulfidation to introduce sulfur species. The sulfur is confined in the micropores while forming stable covalent C-S bonds with the carbon matrix, which stabilizes the sulfur by both physical and chemical means and thus suppresses sulfur migration, which prevents interfacial side reactions and introduces additional redox-active sites. As a result, the sample delivers a high reversible capacity of 450 mAh/g after 800 cycles at a current density of 1 A/g, with excellent rate capability and cycling stability. Analysis of the storage mechanism shows that the stabilized sulfur species can reversibly participate in the sodium-ion storage and improve interfacial kinetics.
