| Exploring lithium-ion battery（LIB）with high energy density and long cycle life is the urgent needs of developing energy storage technique such as portable electronic products,electric vehicles and energy storage stations.The anode material,as a key part of the LIB,largely determines its capacity and performance.Silicon（Si）is a promising new anode material due to its high theoretical capacity(4200 mAh g-1,Li4.4Si),the moderate reaction potential,and natural abundance.However,the serious volume effect and poor electrical conductivity of Si material leads to problems such as capacity decay and poor rate performance,which hinders its application as a commercial LIB anode material.Therefore,we developed a new generation of Si/C composite anode material and improved its electrochemical performance through the material structural designing.In this paper,three kinds of Si/C composites with a coating structure were prepared by simple process and large-scale production.And also,the structural design of the composites were studied by adjusting the preparation process and raw materials in order to obtain the Si/C composites with high electrochemical performance.The main research contents are as follows:First,Si/G composite anode material with a structure of graphene nanosheet（GNs）coated Si was prepared by the plasma ball-milling（P-milling）using nano-Si powder and common graphite as raw materials.The mechanical stress and plasma impact coupling effect of P-milling can efficiently peel off the graphite to produce GNs and in situ coated nano-Si particles.And also,we studied the effect of milling time on the structure evaluation and electrochemical performance of Si/G composites.The in-situ formed GNs can inhibit the aggregation of nano-Si particles and buffer volume changes,which significantly improved its electrochemical performance.Furthermore,in order to peeling the GNs efficiently and obtaining a more homogeneous structure of GNs-coated Si,we use the expanded graphite（EG）instead of common graphite as GNs source to prepare a Si/EG composite.In this way,the cycling performance of as-obtained Si/EG composite was improved.Besides,the P-milling method is efficient,simple and controllable and can be adopted for large-scale production of Si/C composite anodes.Second,we summarized the scientific experience of Si/G and Si/EG composites.And we found that achieving better combination between Si and GNs buffer matrices as well as maintaining their electrical contact are the keys to enhancing the structural stability.Therefore,Si nanoparticles and EG are treated by combining high energy wet ball-milling in sucrose solution with subsequent pyrolysis treatment to produce this Si@C/G composites.The wet ball-milling can uniformly disperse the Si nanoparticles in the GNs matrix which were obtained by peeling EG.The pyrolysis treatment of sucrose can in-situ coating the Si particles and closely connecting with the GNs to form the secondary particles in the scale of micrometers.This structure can effectively inhibit the aggregation of Si nanoparticles,and enhance the effect of conductive buffer GNs matrix,so that the electrochemical performance of Si@C/G composites are much better than the pristine Si nanoparticles and Si/GNs sample.In addition,after the adjustment of mass ratio of Si,C and GNs components,we found that the Si30@C40/G30 sample had a relatively high discharge capacity and a good cycling stability.Its discharge capacity could remaine 645 mAh g-1 after 300 cycles,and the corresponding capacity decay rate was less than 0.06%per cycle.In order to reduce the cost of raw materials and enhance the practicability of the preparation method,we use micron-scale coarse Si instead of the higher price of Si nanoparticles as raw materials and the two-step high energy ball-milling method.In the first step,the wolfram carbide（WC）hard alloy was added to assist in refining the coarse Si,and the effects of the milling process on the formation of amorphous silicon were systematically investigated.In the second step,graphite was added as the buffer matrix material to obtain the SW@G composites with concrete-like structures.The effects of WC and GNs on the microstructure and electrochemical properties of SW@G were discussed in detail.The inner WC particles which tightly connect the Si and the graphene act as the cornerstone to resist large volumetric expansion of Si during charge/discharge,and in particular are serves as the high-speed channels of electrons as well as provide more interface paths for Li+to accelerate their transfer inside the Si.And the GNs obtained from peeling of graphite can further improve the structural stability and conductivity of SW.These contribute to the excellent electrochemical properties of SW@G composite anode,including high volumetric capacity（three times higher than that of graphite）,superior rate capability,and long-life stable cycleability.At last,the MnO2@CFP electrode prepared by electrodeposition has the characteristic structure of nanosheets and nanocrystals,which can provide a large number of electrode/electrolyte contact interface and short ion diffusion path.In the Zn-MnO2 system,the as-obtained MnO2@CFP electrode has excellent cycle performance（6.5 C stable for10,000 weeks）and extremely fast reaction kinetics.Electrochemical and structural analysis identify that the cathode experience a consequent H+and Zn2+insertion/extraction process with high reversibility and cycling stability.In the study of electrochemical performance of TiS2 in WIS electrolyte,the TiS2 was successfully used as a negative electrode material in aqueous LIB for the first time.The wide electrochemical window and low chemical activity of H2O in the WIS electrolyte not only significantly enhanced the electrochemical reversibility of TiS2 but also effectively suppressed the hydrolysis side reaction in the aqueous electrolyte.Paired with a LiMn2O4 cathode,the LiMn2O4/TiS2 full cell deliever a relatively high discharge voltage of 1.7 V and an energy density of 78 Wh kg-1 as well as a satisfactory rate performance. |
