Light-Weight Free-Standing Carbon Nanotube-Silicon Films for Anodes of Lithium Ion Batteries

Abstract

These authors contributed equally to this work. Because of their high energy and power density, lithium ion batteries that were mainly used for portable electronics are now extending to large applications such as power tools and vehicle electrification. Extensive research has been carried out to find new electrode materials and new electrode structure designs to improve energy densities for both anode and cathode. Silicon as an anode material has attracted extensive research because it has the highest known capacity, more than 10 times the value of the current commercial graphite anode. However, the intrinsic volume expansion and contraction of Si during Li cycling cause rapid capacity fading and limit its wide application. Various approaches have been carried out to overcome this issue, including the use of nanosized active materials, 1Ϫ6 active/inactive composite materials, 7Ϫ9 and siliconϪcarbon composites.9Ϫ14 These studies have resulted in improvements of the electrochemical performance of Si-based anodes, but only to a limited extent. Recently we found silicon nanowires directly grown on a current collector can greatly improve the performance of the Si anode due to the excellent electrical connection between Si nanowires and the current collector and the nature of one-dimensionality to effectively release the strain. 15,16 Cho and coworkers also demonstrated great anode performance using carbon-coated, very small (Յ10 nm) silicon nanoparticles (SiNPs) or silicon nanotubes. 17,18 However, in these nanosilicon electrodes, the heavy current collector is larger in weight than Si active material. In a commercial lithium ion cell, the anode material is usually coated on a copper foil current collector to form an anode electrode in thin sheet form. The metal current collector on the anode side is usually a 10 m thick copper sheet with an areal density ϳ10 mg/cm 2 . This copper sheet is a relatively heavy component in a lithium ion cell, which is comparable in weight to the anode active material and accounts for ϳ10% of the total weight of the cell. 19Random networks of carbon nanotube (CNT) have been explored as transparent electrodes in various devices including solar cells, organic light emitting diodes, and smart windows, where CNT networks show optical transmittances of ϳ80% and sheet resistances of 100Ϫ1000 Ohm/sq. 20Ϫ25 Recently, we reported the replacement of the conventional metal current collector with lightweight, CNT-enabled conductive paper, which can significantly reduce the weight of Li-ion batteries.19,26 Inks of CNT

Chemomechanical modeling of lithiation-induced failure in high-volume-change electrode materials for lithium ion batteries

“…The large surface-to-volume ratio of nanoscale materials, such as nanowires, nanoparticles, nanotubes, and nanothick thin films, facilitate stress relaxation and enhance flaw tolerance, and is thus tougher than their bulk counterparts. 4 The shortened ion and electron diffusion paths and increased surface area of the electrodes for fast chemical reactions 4,96,97 of nanosized structures also enhance the rate performance. Material compositing, wherein one material component (e.g., Si) is used to store Li, and the other (e.g., carbon) to enhance the overall conductivity and mechanical stability, 61,[98][99][100][101] has also been adopted to improve the electrochemical performance of the electrode materials.…”

MoS2/Graphene Composite Paper for Sodium-Ion Battery Electrodes

“…1,34 Although layered graphite has been ruled out for sodium-based systems (as Na ions do not tend to form staged intercalation compounds with graphite), [38][39][40] a graphene based free-standing paper based electrode can provide a porous and flexible support structure for a TMDC to undergo a reversible conversion type reaction with Na-ions. It can also act an efficient electronic current collector, thereby eliminating the need for metallic substrate (generally a 10 µm thick foil at 10 mg.cm -2 ), 41,42 electrically conducting additives and polymeric binders that amount to a total of approx. 10 % of the cell weight 42 in traditional negative electrodes.…”

“…It can also act an efficient electronic current collector, thereby eliminating the need for metallic substrate (generally a 10 µm thick foil at 10 mg.cm -2 ), 41,42 electrically conducting additives and polymeric binders that amount to a total of approx. 10 % of the cell weight 42 in traditional negative electrodes. [43][44][45][46][47][48] Herein, we provide the first report of (a) synthesis of composite papers from acid functionalized MoS 2 and reduced graphene oxide flakes, (b) improved capacity and high efficiency reversible Na storage in the self-standing flexible MoS 2 /graphene electrodes at room temperatures, and (c) mechanical characterization that highlight the high strain to failure in these composite papers.…”

Revealing lithium–silicide phase transformations in nano-structured silicon-based lithium ion batteries via in situ NMR spectroscopy

“…However, this high capacity is associated with large volume changes (of up to 300%) 1,2 , resulting in fracture, capacity loss [3][4][5][6][7] and cell design issues. Recently, various nano/micro-sized Si powders 3,[8][9][10][11][12] , nano-Si composites 8,[13][14][15][16] and Si nanowire (SiNW)-based LIBs have been reported 9,[17][18][19] , which can help accommodate the volume expansion. An alternative practical strategy involves the use of Si/graphite composite structures that couple the good capacity and cyclability of graphite with a small fraction of the Si capacity (of an all-Si electrode) to provide modest but still significant increases in capacity.…”