Construction Of High-capacity Silicon-based Anode Materials For Lithium-ion Batteries

Lithium-ion batteries（LIBs）have advantages of high energy density and recyclable use,widely applied in today’s life.Commercial anode material（graphite）shows low specific capacity and some safety issues.Silicon（Si）-based materials have drawn a lot of attention from researchers in recent years due to their abundant reserves,low cost,high specific capacity,and appropriate lithiation potential.In order to obtain excellent-cyclability and high-capacity LIBs anode materials by eco-friendly approach,we systematically investigated Si-based anode materials including optimization of synthesis methods,regulation of morphology and structure and characterization of electrochemical performances.The lithium storage performances of Si-based anode materials have also been optimized and improved.The research achievements have been obtained as follows:（1）Aiming at conductivity and volume expansion issues of Si nanopaticles,we first construct a Si Ox（0<x<2）layer on the surface of Si nanoparticles with a pre-oxidation strategy,followed by conformal coatings of N-doped amorphous carbon through a facile,self-catalyzed polymerization reaction and calcination process.It is found that the Si Ox layer could facilitate the conformal resin coating through strong interactions with the phenolic resin.The fabricated core@double shell structure and micro-nano structure integrate the merits of micromaterials and nanomaterials,resulting in boosted lithium storage performances of Si@Si Ox@C with improved electrical conductivity and electrode structure integrity.When served as the anode material for LIBs,the as-prepared Si@Si Ox@C possesses high reversible capacity(1168 m Ah g^–1 at 200 m A g^–1),excellent rate capability and ideal long-term durability.In addition,the full cells of Si@Si Ox@C//Li Fe PO4 have also been assembled,further verifying the preferable application potential of Si@Si Ox@C in LIBs.This contribution highlights the significant role of interactions between active materials and carbon precursors on fabricating high-performance carbon-coated electrode materials.（2）Aiming at a series of undesirable environmental issues and safety issues caused by traditional wet chemical method and chemical vapor deposition（CVD）method,we herein develop a novel eco-friendly,solvent-free,flammable gas-free and scalable approach to envelope Si Ox submicron particles in N-doped carbon（denoted as Si Ox@NC）.The N-doped carbon encapsulation not only improves the electrical conductivity but also buffers the volume variation of Si Ox,endowing the anode material excellent rate capability,cycling performance and electrode structure integrity.The full cells of Si Ox@NC//Li Fe PO4 have also been assembled and demonstrate excellent electrochemical performances.Furthermore,Si nanoparticle@N-doped carbon and Sn O2 nanoparticle@N-doped carbon composites are also prepared by the solvent-free strategy.Their morphology,structure and electrochemical performances are characterized,respectively.It is found that the developed solvent-free carbon coating strategy can be generally applied to other high-capacity anode materials（such as Si and Sn O2）,which verifies the universality of this solvent-free carbon coating method.（3）The cycling performance of the Si-based anode materials with alloying reaction is not superior when compared with intercalation reaction-based anode materials（such as TiO2）.However,the further development of TiO2 in LIBs is severely hindered by its low specific capacity.Aiming at ordinary cycling performance of Si-based anode materials and low-capacity issues of TiO2,we synthesized Si-doped anatase TiO2/carbon（Si-TiO2/C）microspheres through a spray-drying assisted approach and calcination by adopting a water-soluble titanium（IV）bis（ammonium lactato）dihydroxide as titanium source and tetraethoxysilane as silicon source.Synchrotron radiation X-ray diffraction patterns and corresponding Rietveld refinements demonstrate that the Si is substitutional doped into anatase TiO2 and the doped-Si/Ti atomic ratio is 7.8%.X-ray absorption structure spectra further testify the Si doping in anatase TiO2.In addition,we find that the Si doping can provide additional active sites for Li⁺storage in TiO2,which is evidenced by electron energy loss spectroscopy and X-ray absorption near-edge spectroscopy.When served as the anode material for LIBs,the obtained Si-TiO2/C affords a high reversible capacity(546 m Ah g^–1),excellent rate capability and cyclability.