Multilayered Si/RGO anode nanostructures, featuring alternating Si nanoparticle (NP) and RGO layers, good mechanical stability, and high electrical conductivity, allow Si NPs to easily expand between RGO layers, thereby leading to high reversible capacity up to 2300 mAh g(-1) at 0.05 C (120 mA g(-1) ) and 87% capacity retention (up to 630 mAh g(-1) ) at 10 C after 152 cycles.

No abstract

Lithium titanate (LTO), Li 4 Ti 5 O 12 is a promising material for energy storage due to its high-rate capabilities and safety. However, gas generation, which can be observed under high-temperature operation, present a challenge to the large-scale application of lithium ion batteries made from LTO anodes. Here we analyzed sources of gas generation in an LTO system through isotopic tagging of primary suspected sources of H 2 . Specifically, we added small amounts of heavy water (D 2 O) to the electrolyte, D 2 O to the LTO electrode, or deuterated dimethyl carbonate (DMC) to the electrolyte. Upon cycling, the isotopic tagging method enables the separation of deuterated from non-deuterated gas products using combined gas chromatography and mass spectroscopy (GC/MS) analysis. The results demonstrate that cell performance and generation of H 2 are both strongly related to moisture content within the cells. Cells with deuterated DMC in the electrolyte show negligible breakdown as determined by the lack of H-D/D 2 gas production when compared to samples that contain D 2 O added into the electrode or electrolyte. These results indicate that the primary source of gas generation in LTO-based cells is residual moisture in the electrodes and electrolyte, reinforcing the importance of low-moisture processing conditions for LTO-based lithium ion batteries. The rechargeable lithium ion battery is one of the most important energy storage technologies today as the power source in hybrid electric vehicles (HEVs), plug-in hybrid electric vehicles (PHEVs) and full electric vehicles (EVs) as well as for large-scale storage of renewable energy.1 Current lithium ion batteries typically utilize a graphite anode because of the low potential vs Li, good cycle life and good rate capability. However, safety is a major issue that hinders the wide scale usage of lithium ion batteries in automobiles. At elevated temperatures using graphite anodes, for example, the solid electrolyte interphase (SEI) between the non-aqueous electrolyte and the graphite surface becomes less stable and may even decompose at temperatures as low as 60• C. 2,3 Lithium ion batteries containing lithium titanate (LTO) anodes, Li 4 Ti 5 O 12 , are promising energy storage systems for their higher rate capabilities, safety, and long cycle-life, owing to their zero volumetric growth during lithiation 4,5 and higher anode voltage compared to graphite. Gas generation is a common phenomenon leading to the degradation of battery performance in Li-ion batteries. In LTO specifically, the gas generation and associated swelling, which are accelerated under high-temperature operation, present a challenge to the widespread application of lithium ion batteries made from LTO anodes. 6,7 Much research has focused on gas evolution in LTO anode based cells. It is well known that much of the gas generation can be attributed to chemical decomposition and redox decomposition of the electrolyte solvents on the anode or cathode. A well-defined mechanism for gas generation from LTO based cell...

Tin is a promising anode candidate for nextgeneration lithium-ion batteries with a high energy density, but suffers from the huge volume change (ca. 260 %) upon lithiation. To address this issue, here we report a new hierarchical tin/carbon composite in which some of the nanosized Sn particles are anchored on the tips of carbon nanotubes (CNTs) that are rooted on the exterior surfaces of micro-sized hollow carbon cubes while other Sn nanoparticles are encapsulated in hollow carbon cubes. Such a hierarchical structure possesses a robust framework with rich voids, which allows Sn to alleviate its mechanical strain without forming cracks and pulverization upon lithiation/de-lithiation. As a result, the Sn/C composite exhibits an excellent cyclic performance, namely, retaining a capacity of 537 mAh g À1 for around 1000 cycles without obvious decay at a high current density of 3000 mA g À1 .Existing commercial graphite anodes are capable of delivering a capacity of approximately 330 mAh g À1 , thereby approaching its theoretical capacity (372 mAh g À1 ). New anodes are required to meet the demands of next-generation lithium-ion batteries (LIBs) for high energy and power densities and a long cycle life. Sn, despite its high costs, is of significant interest and has been investigated extensively because of its high capacity (993.4 mAh g À1 ; from Sn to Li 4.4 Sn), abundance, and environmentally-friendliness; however, a huge volume change of the Sn anode (ca. 260 %) upon lithiation leads to very poor cyclic performance, inhibiting its practical applications.To address this issue, besides employing Sn-based nanocrystals [1,2] and thin films, [3][4][5] forming SnM (M = Co, [6] Cu, [7]

Silicon, an anode material with the highest capacity for lithium-ion batteries, needs to improve its cyclic performance prior to practical applications. Here, we report on a novel design of Si/metal composite anode in which Si nanoparticles are welded onto surfaces of metal particles by forming intermetallic interphases through a rapid heat treatment. Unlike pure Si materials that gradually lose electrical contact with conductors and binders upon repeated charging and discharging cycles, Si in the new Si/metal composite can maintain the electrical contact with the current collector through the intermetallic interphases, which are inactive and do not lose physical contact with the conductors and binders, resulting in significantly improved cyclic performance. Within 100 cycles, only 23.8% of the capacity of the pure Si anode is left while our Si/Ni anode obtained at 900 °C maintains 73.7% of its capacity. Therefore, the concept of employing intermetallic interphases between Si nanoparticles and metal particles provides a new avenue to improve the cyclic performance of Si-based anodes.

An intermetallic NiSi x coating layer was introduced on the Si surface by sputtering Ni onto Si, followed by heat-treatment. The resulting chemically bonded NiSi x layer, unlike physically coated layers that typically can crack and detach from Si surfaces upon repeated cycling, remains connected with the bulk Si as a skin-like protective surface.Si, as an anode for lithium-ion batteries, possesses the highest theoretical capacity of 3579 mA h g À1 at room temperature. 1 Cyclic performance is one of the critical issues to be addressed for Si anodes prior to their practical application. The large volume changes of Si anodes upon charging and discharging lead to the pulverization of Si particles and unstable solid-state electrochemical interphase (SEI) layers.To help construct better SEI layers, besides using electrolyte additives, forming a coating on Si surfaces is a good approach. Metal oxides (TiO 2 , 2-5 Al 2 O 3 , 6-8 Co 3 O 4 , 9,10 and RuO 2 , 11 etc.) were used to coat Si particles or thin lms. For example, Lotfabad et al. 2 used an atomic layer deposition (ALD) to coat TiO 2 on silicon nanowires; the obtained materials show better cyclic performance compared with the pristine Si nanowires. Metals (such as Al, 12 Ag, 13 Cu, 14-17 and Ni 17 ) have also been coated on Si surfaces to improve the cyclic performance of Si anodes. For example, Murugesan et al. 15 synthesized Cu-coated Si particles by depositing copper on the a-Si:H particles using a polyol reduction method. Since the SEI layer on carbon is much more stable and carbon possesses a higher electrical conductivity, coating carbon on Si surfaces has been investigated intensively. 18-21 For example, Wang et al. 18 synthesized Si nanowires coated with carbon by thermal decomposition of ethylene. Coating conductive polymers is another choice. 22-24 However, because of the large volume expansion of Si upon lithiation,

Practical applications of high‐capacity silicon anodes face significant challenges due to the huge volume change during the lithiation/delithiation process and the relatively low intrinsic electrical conductivity. J. Chen and co‐workers report on page 758 a multilayered Si/reduced graphene oxide anode that offers superior reversible specific capacity, rate capability, and cycling performance.

lithium ion insertion into or extraction from TiO 2 , and thus has been extensively investigated in recent years using various templates such as Fe 2 O 3 , [ 5c , 6 ] C, [ 7 ] SiO 2 , [ 8 ] polystyrene, [ 9 ] and cetyl trimethylammonium bromide (CTAB). [ 10 ] In addition, hollow TiO 2 has been prepared by etching Ti powder in the presence of H 2 O 2 and HF (40 wt%). [ 11 ] Here, we report a new template (namely, CaCO 3 ) for fabricating hollow TiO 2 . Compared with previous methods for the synthesis of hollow TiO 2 , [ 5c , 6a , 6b , 7-11 ] our use of CaCO 3 as a template offers advantages of being surfactant-free, HF-free, and low-cost. The as-obtained hollow TiO 2 is capable of delivering 255.9 mAh g −1 with excellent cycling performance (retaining 83% of its reversible capacity after 1500 cycles).The experimental details are shown in the Supporting Information. Figure 1 a illustrates the synthesis of porous TiO 2 by using CaCO 3 (typically 40-100 nm, Figure S1, Supporting Information) as a template and titanium tetraisopropoxide (TTIP) as the titanium source. During the hydrolysis of TTIP, the water content was controlled to increase gradually by dropwise adding three water/ethanol solutions with volumetric ratios of 1:9 (10 mL), 1:4 (5 mL), and 1:1 (2 mL), so that the TTIP was allowed to gradually hydrolyze to Ti(OH) 4 , coating the surface of the CaCO 3 . The CaCO 3 @Ti(OH) 4 must be heat-treated before removal of the CaCO 3 templates, because otherwise it is diffi cult to obtain hollow TiO 2 . Actually, most of the white precipitates, after acid leaching, were observed to start fl oating on the water surface during the subsequent washing step, which made it impossible to separate the precipitates from the solution by centrifugation. The choice of the heating temperature was based on the thermogravimetric/differential thermal analysis (TG/DTA) results. As shown in Figure S2 of the Supporting Information, CaCO 3 @Ti(OH) 4 lost 4 wt% of its mass between 120 and 200 °C, with an exothermic shoulder peak. Our results indicate that 180 °C is a high enough temperature to convert Ti(OH) 4 to TiO 2 · x H 2 O; thus, we selected this temperature to prevent the formation of CaTiO 3 at higher temperatures. Although CaTiO 3 is an interesting capacitor material, [ 12 ] it is inactive for lithium ion insertion; we preferred to avoid the formation of CaTiO 3 in this study.We selected a dilute HCl solution to leach the CaCO 3 template, similar to our process for synthesizing hollow Si through chemical vapor deposition, [ 13 ] which is more environmentally friendly than the use of HF acid to etch the SiO 2 template [ 8 ] or Ti powder [ 11 ] during the preparation of hollow TiO 2 . After acid leaching CaCO 3 , the amorphous hollow TiO 2 · x H 2 O was annealed at 500 °C to convert it to hollow crystalline TiO 2 . Figures 1 b-i show scanning electron microscopy (SEM) images of the as-prepared hollow TiO 2 with various wall thicknesses; TiO 2 is widely applied in lithium-ion batteries (LIBs), dye-sensitized solar cells, photoc...