Sol-gel synthesis of nanometer silicon/silicon suboxide/carbon anode material

A stacked Si/SiO_(x)/C composite anode material with carbon-coated structure was prepared by sol-gel method combined with carbothermal reduction using organic silicon.The results of X-ray diffractometry, scanning electron microscopy, and elemental analysis show that the Si/SiO_(x)/C material is a secondary particle with a porous micronanostructure, and the presence of nanometer silicon does not affect the carbothermal reduction and carbon coating.Electrochemical test results indicate that the specific capacity and first coulombic efficiency of SiO_(x)/C composite with nanometer silicon can be increased to 1 946.05 mAh/g and 76.49%,respectively.The reversible specific capacity of Si/SiO_(x)/C material blended with graphite is 749.69 mAh/g after 100 cycles at a current density of 0.1 C,and the capacity retention rate is up to 89.03%.Therefore, the composite has excellent electrochemical cycle stability.

Mg-doped,carbon-coated,and prelithiated SiO_(x) as anode materials with improved initial Coulombic efficiency for lithium-ion batteries

Silicon suboxide(SiO_(x),x≈1)is promising in serving as an anode material for lithium-ion batteries with high capacity,but it has a low initial Coulombic efficiency(ICE)due to the irreversible formation of lithium silicates during the first cycle.In this work,we modify SiO_(x) by solid-phase Mg doping reaction using low-cost Mg powder as a reducing agent.We show that Mg reduces SiO_(2) in SiO_(x) to Si and forms MgSiO_(3) or Mg_(2)SiO_(4).The MgSiO_(3) or Mg_(2)SiO_(4) are mainly distributed on the surface of SiO_(x),which suppresses the irreversible lithium-ion loss and enhances the ICE of SiO_(x).However,the formation of MgSiO_(3) or Mg_(2)SiO_(4) also sacrifices the capacity of SiO_(x).Therefore,by controlling the reaction process between Mg and SiO_(x),we can tune the phase composition,proportion,and morphology of the Mg-doped SiO_(x) and manipulate the performance.We obtain samples with a capacity of 1226 mAh g^(–1) and an ICE of 84.12%,which show significant improvement over carbon-coated SiO_(x) without Mg doping.By the synergistical modification of both Mg doping and prelithiation,the capacity of SiO_(x) is further increased to 1477 mAh g^(–1) with a minimal compromise in the ICE(83.77%).

A review on the critical challenges and progress of SiO_(x)-based anodes for lithium-ion batteries

With the advantages of abundant resources,high specific capacity,and relatively stable cycling performance,silicon suboxides(SiO_(x) ,x<2)have been recently suggested as promising anodes for next-generation lithium-ion batteries(LIBs).SiO_(x) exhibits superior storage capability because of the presence of silicon and smaller volume change upon charge/discharge than Si owing to the buffering effect of the initial lithiation products of inert lithium oxide and lithium silicates,enabling a stable cycle life of electrodes.However,significant improvements such as overcoming issues related to volume changes in cycling and initial irreversible capacity loss and enhancing the ionic and electronic charge transport in poorly conducting SiO_(x) electrodes,are still needed to achieve the satisfactory performance required for commercial applications.This review summarizes recent progress on the cycling performance and initial coulombic efficiency of SiO_(x) .Advances in the design of particle morphology and composite composition,prelithiation and prereduction methods,and usage of electrolyte additives and optimized electrode binders are discussed.Perspectives on the promising research directions that might lead to further improvement of the electrochemical properties of SiO_(x) -based anodes are noted.This paper can serve as a basis for the research and development of high-energy-density LIBs.

Sandwich-like structure C/SiO_(x)@graphene anode material with high electrochemical performance for lithium ion batteries

Silicon suboxide(SiO_(x),0<x<2)is recognized as one of the next-generation anode materials for high-energy-density lithium ion batteries(LIBs)due to its high theoretical specific capacity and abundant resource.However,the severe mechanical instability arising from large volume variation upon charge/discharge cycles frustrates its electrochemical performance.Here we propose a well-designed sandwich-like structure with sandwiched SiO_(x) nanoparticles between graphene sheets and amorphous carbon-coating layer so as to improve the structural stability of SiO_(x) anode materials during cycling.Graphene sheets and carbon layer together construct a three-dimensional conductive network around SiO_(x) particles,which not only improves the electrode reactions kinetics,but also homogenizes local current density and thus volume variation on SiO_(x) surface.Moreover,Si-O-C bonds between SiO_(x) and graphene endow the strong particle adhesion on graphene sheets,which prevents SiO_(x) peeling from graphene sheets.Owing to the synergetic effects of the structural advantages,the C/SiO_(x)@graphene material exhib-its an excellent cyclic performance such as 890 mAh/g at 0.1 C rate and 73.7%capacity retention after 100 cycles.In addition,it also delivers superior rate capability with a capacity recovery of 886 mAh/g(93.7%recovery rate)after 35 cycles of ascending steps at current range of 0.1-5 C and finally back to 0.1 C.This study provides a novel strategy to improve the structural stability of high-capacity anode materials for lithium/sodium ion batteries.

Rational structure design to realize high-performance SiOx@C anode material for lithium ion batteries

Silicon suboxide(SiOx)is considered to be one of the most promising materials for next-generation anode due to its high energy density.For its preparation,the wet-chemistry method is a cost-effective and readily scalable route,while the so-derived SiOx usually shows lower capacity compared with that prepared by high temperature-vacuum evaporation route.Herein,we present an elaborate particle structure design to realize the wet-chemistry preparation of a high-performance SiOx/C nanocomposite.Dandelion-like highly porous SiOx particle coated with conformal carbon layer is designed and prepared.The highly-porous SiOx skeleton provides plenty specific surface for intimate contact with carbon layer to allow a deep reduction of SiOx to a low O/Si ratio at relatively low temperature(700℃),enabling a high specific capacity.The abundant mesoscale voids effectively accommodate the volume variation of SiOx skeleton,ensuring the high structural stability of SiOx@C during lithiation/delithiation process.Meanwhile,the three-dimensional(3D)conformal carbon layer provides a fast electron/ion transportation,allowing an enhanced electrodereaction kinetics.Owing to the optimized O/Si ratio and well-engineered structure,the prepared SiOx@C electrode delivers an ultra-high capacity(1,115.8 mAh·g^-1 at 0.1 A·g^-1 after 200 cycles)and ultra-long lifespan(635 mAh·g^-1 at 2 A·g^-l after 1,000 cycles).To the best of our knowledge,the achieved combination of ultra-high specific capacity and ultra-long cycling life is unprecedented.

Efficient fluidization intensification process to fabricate in-situ dispersed(SiO+G)/CNTs composites for high-performance lithium-ion battery anode applications

An efficient fluidization process intensification method was proposed to prepare carbon nanotube(CNT)-enhanced high-performance SiO anodes for lithium-ion batteries.The introduction of graphite particles decreased bonding among SiO particles,inhibiting agglomerate growth and enhancing fluidization.The(SiO+G)/CNTs composites were synthesized by fluidized bed chemical vapor deposition with the CNTs grown in-situ,which ensured uniform dispersion and superior anchoring of the CNTs.The in-situ-grown CNTs and stacked graphite ensured excellent structural stability and conductivity.The synthesized(SiO+G)/CNTs delivered a stable reversible capacity of 466 mAh g^(−1) after 125 cycles and a capacity of∼200 mAh g^(−1) at 2 A g^(−1).The charging results indicated that the 3D network structure comprising CNTs and graphite not only effectively buffered the electrode expansion but also greatly improved mechanical flexibility.