| As one of the most promising anodes for Li-ion storage,silicon（Si）anode has the merits of ultrahigh specific capacity,low working potential,and high safety.However,due to its low intrinsic electronic conductivity,unstable interfaces,and considerable volume change during lithiation/delithiation process,Si anode suffers from poor rate performance,low coulombic efficiency,and fast capacity decay on cycling.Thus,the commercial application of the Si anode is seriously hindered.To overcome these limitations,various strategies have been devised.Unfortunately,most of them focus on the structural design and the composition control of the Si-based anodes,ignoring the study of interfacial stability.Moreover,although many previous works have greatly improved the electrochemical performance of the Si-based anodes,their complex,high-cost,and non-green synthesis still impede their practical applications.In this paper,low-cost and environmentally friendly biomass materials are used to modify Si anodes.Several facile,green,and versatile strategies are proposed to synthesize silicon/carbon（Si/C）anodes for practical Li-ion batteries（LIBs）and Li-ion capacitors（LICs）.In this paper,Si/C anodes are prepared from four perspectives,including preparation method optimization,carbon precursor selection,silicon size control,and material dimensional design.Due to the tailored and rational design,the prepared Si/C anodes exhibit high gravimetric capacity,high areal capacity,and high volumetric capacity.The effects of nanostructures,morphologies,and compositions of the Si/C anodes on their interfacial stability and electrochemical performance are analyzed in detail.The energy storage mechanisms and the design principles of the highperformance Si/C anode materials are also summarized.Finally,the LIBs and LICs with high energy density,high power density,and long cycle life are successfully assembled.The specific innovative works and results are as follows:（1）We demonstrate a green and facile method for the preparation of Si/C anodes via conductive network construction and dual-interfacial engineering.Gelatin and Si nanoparticles（NPs）are used as precursors.The good water solubility,film-forming property,and cohesive property enable gelatin to be well-mixed with Si NPs in deionized water.Si/C anode can be easily obtained via conventional slurry coating and low-temperature pyrolysis（referred to as Si@GC）.Notably,no additional binder and conductive agent are required and no organic solvent is used during the electrode preparation.The effects of the morphology,nanostructure,and chemical composition of the Si-based materials on the electrochemical performance are investigated by regulating the pyrolysis temperature and the precursor ratio.Beneficial from the "conductive skeleton"construction and dual-interfacial bonding strategy,the Si@GC anode exhibits high reversible capacity(3160 mAh g-1),high initial columbic efficiency（ICE,85.3%）,and maintained a high capacity of 1613 mAh g-1 even at 5 A g-1.Si@GC anode also delivers a high areal capacity(2.81 mAh cm-2)and a high volumetric capacity(2718 mAh cm-3),showing great prospects for practical application.Furthermore,a high capacity of 1447 mAh g-1 can be maintained even after 250 cycles at 1 A g-1.For the capacitive cathode material,we prepare a kind of Ndoped hierarchically porous carbon using cattle bone as precursor（referred to as NHPC）.Due to the synergistic effect of hydroxyapatite self-activation and KOH chemical-activation,the NHPC possesses high specific surface area with highly interconnected porosity,numerous defects,and good electrical conductivity.The assembled Si@GC//NHPC LIC exhibits high power density(22.3 kW kg-1),high energy density(213 Wh kg-1),and good cycling performance.This work provides a new idea for low-cost and scalable preparation of high-performance energy storage devices,which also opens a new way for the efficient utilization of biomass waste.（2）Based on the previous work,we give an insight into the heteroatom effects of carbon modifiers on anode performance and explore their modification mechanisms from a new point of view.Three polymers（chitosan,alginate,and polyvinylidene fluoride）with different functional groups are used as the carbon precursors to prepare Si/C anodes.Experimental measurements and theoretical calculations show that the presence of N/O-doped carbon enhances the mechanical strength of the Si/C anodes via dual-interfacial bonding.In addition,the presence of N atom can also facilitate charge transfer and ion diffusion.Benefitting from the continuous carbon network and synergy effects of the N,O heteroatoms,chitosan-derived carbon encapsulated Si（referred to as Si@CTSC）anode shows high reversible capacity,good rate capability,and outstanding cycling stability in half cells.The assembled flexible Si@CTSC//LCO pouch cell shows high working voltage（3.75 V）and high energy density(540 Wh kg-1).This work not only provides a new principle for the design of Si/C anodes with high practical performance,but also verifies the universality of this method.（3）We demonstrate an industrially feasible strategy for large-scale production of Si-based anodes by pyrolysis of economical gelatin and ballmilled micron-sized Si particles（BMSi）without using additional binders and conductive agents.The resulting Si/C material（BMSi@GC）exhibits extremely high Si content（93.9%）,high tap density(0.86 cm3 g-1),and good mechanical flexibility.In-situ measurements and time-of-flight secondary ion mass spectrometry dynamic analysis are carried out to track the structural and morphology evolution as well as the solid electrolyte interphase（SEI）film formation of Si-based anodes during lithiation/delithiation process.By virtue of its unique structure and composition,the BMSi@GC anode delivers high ICE（88.2%）,high reversible capacities(2738 mAh g-1,2157 mAh cm-3,and 2.74 mAh cm-2),as well as superior rate capability in half cells.The assembled BMSi@GC//LiCo02 full cell exhibits high working voltage（3.86 V）,high energy density(537 Wh kg-1)as well as long cycle life.This work provides both theoretical and experimental basis for low-cost and large-scale production of high-performance Si/C anodes.（4）We propose a low cost and environmentally friendly strategy to synthesize Si/C anodes.Owing to the confined encapsulation effect of both Ice and KCl templates,0-dimensional Si/2-dimensional carbon（0D-Si/2D-C）materials can be prepared in a controllable way.This unique structure of the 0D-Si/2D-C materials can accelerate charge transfer and facilitate Li-ion transport.In-situ carbon coating layer on the Si surface can effectively inhibit the continuous decomposition of electrolyte,which help to form a stable SEI layer.Face-to-face contact between Si particles and carbon materials can effectively improve the stability of the electrode.Moreover,it can form uniform Li-ion and electron flows on the Si surface during lithiation/delithiation process,which can effectively avoid stress concentration and improve the stability of the electrode.As a result,the prepared Si@GCNS anode shows high specific capacity(2976 mAh g-1),good rate performance,and stable cycling performance(with a capacity retention of 87.6%at 1 A g-1 after 250 cycles).The assembled Si@GCNS//LiCoO2 full cell shows high energy density(460 Wh kg-1)and long cycle life.This work opens up a new way for the construction of Si/C anodes with stable electrode interfaces and fast electron conduction. |
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