Preparation Of Modified Silicon/graphite Composite Anode Materials And Their Lithium Storage Properties

The low theoretical capacity of conventional graphite anode limits its widespread application in various fields.Preparation of high-performance Si/graphite composites with nano-Si(3600 mAh/g)modified micron-sized graphite,which could address the issues of huge volume variation during repeated charge/discharge cycles and low electric conductivity of Si,and low capacity of graphite,has attracted enormous attention from both industry and academia.So far,various synthetic routes have been developed for preparing Si/graphite composite,including solid-phase ball-milling,liquid-phase mixing and chemical vapor deposition.To promote the practical application of Si/graphite anode material,further new type of preparation process is absolutely necessary.In this dissertation,the facile,efficient and controllable techniques are introduced to prepare micro-nano structured Si/graphite composite associated with uniform and stable structure.The main research contents of this dissertation are divided into two parts:1.We report a wet grinding process combined with chemical vapor deposition method for scalable fabrication the Si/graphite/Cu-Carbon nanotubes(CNTs)composite.The main process includes ball-milling of commercial micro-sized Si,Cu and graphite,and followed by catalytic growth of carbon nanotubes via Cu.The Si,Cu and graphite components are uniformly distributed in the composite.Meanwhile,in-situ synthesized carbon nanotubes is able to cross-link all components tightly and construct a three-dimensional robust and conductive network.When the Si/graphite/Cu-CNTs composite evaluated as anode for lithium-ion batteries,it maintains a high reversible capacity of 646.5 mAh/g after the 100th cycle at 0.2 A/g with a capacity retention of 87.6%and 538 mAh/g after 200 cycles at 0.5 A/g,which is much better than electrochemical performance of Si/graphite/Cu and Si/graphite composites.The improved electrochemical performance of the Si/graphite/Cu-CNTs composite is mainly due to the combined action of graphite,Cu and CNTs,which can synergistically improve the electrical conductivity and the structural integrity during electrochemical cycle.2.The micro-nanostructured graphite/Si/reduced graphene oxides composite(SGG)is prepared by a controllable and scalable self-assembly method.The self-assembly process is realized by the hydrogen bond interaction between acylamino-modified graphite and graphene oxides(GO)containing abundant functional groups(carboxyl or hydroxyl).During this process,Si nanoparticles areembedded between graphite and GO sheets uniformly.This novel structural design is able to overcome the incompatibility between Si nanoparticles and micro-sized graphite.As a result,the as-prepared SGG anode delivers a reversible specific capacity of 572 mAh/g at 0.2 C(1 C = 600 mA/g),502.2 mAh/g at 0.8 C after 600 cycles with a capacity retention of 92%,and the reversible capacity is maintained at 390 mAh/g even at 10 C.The excellent electrochemical performance can be ascribed to stable structure and three-dimensional conductive network constructed by graphite and graphene sheets,which can relieve the huge volume expansion of Si and enhance the conductivity.