基于水凝胶衍生的硅/碳纳米管/石墨烯纳米复合材料及储锂性能

Hydrogel-Derived Three-Dimensional Porous Si-CNT@G Nanocomposite with High-Performance Lithium Storage

通过氧化石墨烯(GO)和壳聚糖(Cs)之间的氢键以及静电作用形成GO水凝胶,从而将纳米硅颗粒和碳纳米管(CNT)原位包封于其中,再经冷冻干燥及随后的热处理制得三维硅/碳纳米管/石墨烯(Si-CNT@G)纳米复合材料。采用X射线衍射(XRD)、扫描电子显微镜(SEM)和透射电子显微镜(TEM)、热重分析(TGA)等技术对制得样品的物相、结构和微观形貌等进行了表征。结果表明,所得复合材料在CNT纵横交织的石墨烯网络中,均匀地分布着纳米硅颗粒。当作为锂离子电池的负极材料时,在两种碳介质的协同作用下,有效缓冲硅材料在充放电过程中脱/嵌锂引起的体积变化,缩短了锂离子和电子传输的距离,Si-CNT@G复合材料表现出较好的循环稳定性以及倍率性能。在500 m A·g^-1的充放电电流密度下,经过200圈循环后,其放电比容量仍高达673.7 m Ah·g^-1,容量保持率高达97%;即使将充放电电流密度升至2000 m A·g^-1时,该复合材料仍保持有566.9 m Ah·g^-1的高可逆放电比容量。独特的制备方法和优越的储锂性能,使得Si-CNT@G纳米复合材料成为理想的高性能锂离子电池负极材料的候选.

Silicon is a promising anode material for lithium-ion batteries(LIBs)because of its natural abundance,high theoretical capacity,and relatively low working potential for lithium storage.However,two main obstacles exist that hinder its commercial application.One is the large volume variation during prolonged cycling,which causes irreversible cracking and disconnection of the active mass from the current collector and subsequently rapid decay of capacity of the electrode.The other is its poor intrinsic electronic conductivity,which seriously restricts its rate performance.To date,strategies to improve its cycling stability and rate capability include rational designs of different Si nanostructures and the incorporation of conductive agents.In this study,we present a novel and effective method to fabricate a Si/C composite.Through hydrogen bonding and the electrostatic interaction between graphene oxides(GO)and acidized chitosans(Cs),a hybrid hydrogel was fabricated in which silicon nanoparticles and carbon nanotubes were encapsulated in situ.Following freeze-drying and subsequent calcination,a three-dimensional porous silicon/carbon nanotube/graphene(Si-CNT@G)nanocomposite was obtained.The phase,structure,and morphology of the sample were characterized by means of X-ray diffraction(XRD),scanning electron microscopy(SEM),transmission electron microscopy(TEM)and thermogravimetric analysis(TGA).The results show that the silicon nanoparticles were uniformly distributed in the graphene network,which was interwoven with carbon nanotubes.The resultant Si-CNT@G nanocomposite featured a porous three-dimensional conductive carbonaceous support,providing short pathways for electrons,conductive transport highways for lithium ions,a sufficient interface for contact of the electrolyte and electrode,and an effective buffer matrix to alleviate structural change during discharge/charge cycling.Benefiting from these particular features,the as-prepared SiCNT@G nanocomposite exhibited superior lithium storage performance with high specific capacity and excellent long-term cycling stability when evaluated as an anode material for LIBs.For example,a high discharge capacity of 673.7 m Ah·g^-1 can be retained after 200 discharge/charge cycles at a current density of 500 m A·g^-1 in the potential range of 0.01-1.20 V,with a decent capacity retention of 97%.Even when at a current density of 2000 m A·g^-1,a high discharge capacity of 566.9 m Ah·g^-1 can still be retained.In contrast,the discharge capacity of pure silicon nanoparticles,when tested under the same conditions,was practically nil.These results suggest that the Si-CNT@G nanocomposite is a promising anode material for high-performance LIBs.