Here we report our findings in synthesis and characterization of porous Co3O4 nanofibers coated with a surface-modification layer, reduced graphene oxide. The unique porous Co3O4@rGO architecture enables efficient stress relaxation and fast Li+ ions and electron transport during discharge/charge cycling. When tested in a half cell, the Co3O4@rGO electrodes display high Coulombic efficiency, enhanced cyclic stability, and high rate capability (∼900 mAh/g at 1A/g, and ∼600 mAh/g at 5 A/g). The high capacity is contributed by a stable capacity yielded from reversible conversion reactions above 0.8 V vs. Li/Li+, and a increasing capacity induced by the electrolyte decomposition and interfacial storage between 0.8 0.01 V during discahrge. A full cell constructed from a Co3O4@rGO anode and a LiMn2O4 cathode delivers good capacity retention with operation voltage of ∼2.0 V. These performances are better than those of other full cells using alloy or metal oxide anodes. Our work is a preliminary attempt for practicality of high capacity metal oxide anodes in Li-ion batteries used for the electronic devices.Download high-res image (217KB)Download full-size image

In order to further enhance the reversible capacity and cyclability for lithium storage of Sn-based alloy anode materials, a spherical-shaped Sn–Fe3O4@C ternary-phase composite consisting of nanosized tin (Sn), magnetite (Fe3O4), and graphite (C) was prepared via a two-step process using high-efficiency discharge plasma-assisted milling (P-milling). Ultrafine Sn nanoparticles were embedded and tightly contacted with nanosized Fe3O4, with graphite nanosheets coating the outside to form a multiscale spherical structure. The Sn–Fe3O4@C nanocomposite anodes demonstrate a stable and high capacity of 793 mA h g−1 after 240 cycles between 0.01 and 3.0 V vs. Li/Li+ at 200 mA g−1. Furthermore, a reversible capacity of ∼750 mA h g−1 was obtained after 500 cycles, even when the current density increased to 2000 mA g−1. The high capacity, good cycle performance, and superior high-rate capability characteristics were attributed to the unique nanostructure of the Sn–Fe3O4@C composites. The good dispersion of co-existing Sn and Fe3O4 nanoballs in a spherical carbon matrix resulted in an electrode with high structural stability and fast kinetics for Li ion and electron transfer, which contributed to high reversibility of alloying reactions in Sn and conversion reactions of Fe3O4. Furthermore, the spherical shape of the materials and simple preparation as compared to those of commercial anodes make the Sn–Fe3O4@C composites good candidates for practical applications.

•Two-step ball milling was used to produce an amorphous-Si/WC@Graphene(SW@G) composite.•Concrete-like core-shell structure with high stability was designed.•Multiscale WC particle strengthen the inside structure.•Graphene coating outside much enhanced the cycling stability and conductivity.•The SW@G anode exhibited long cycle life and superior volumetric capacity.Improving the electron conductivity and lithiated structure stability for Si anodes can result in high stable capacity in cells. A Silicon/Wolfram Carbide@Graphene (SW@G) composite anode is designed and produced by a simple two-step ball milling the mixture of coarse-grained Si with good conductive wolfram carbide (WC) and graphite. The SW@G composite consists of multiple-scale WC particles, which are uniformly distributed in amorphous Si matrices, and wrapped by graphene nanosheets (GNs) on the outside. Owing to the unique concrete-like core-shell structure, the wrapping of GNs on the Si improves the conductivity and structural stability of the composite. The inner WC particles which tightly connect the Si and graphene act as the cornerstone to resist large volumetric expansion of Si during charge/discharge, and in particular serve as the high-speed channels of electrons as well as provide more interface paths for Li+ to accelerate their transfer inside the Si. 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. The synthetic method developed in this work paves the way for large-scale manufacturing of high performance Li storage anodes using commercially available materials and technologies.

To improve the coulombic efficiency (CE) and cycle life of SnO2 anode in lithium ion batteries, SnO2–Cu–graphite composites with dual scale embedding structure are synthesized by ball milling. The SnO2–Cu composite, in which SnO2 nanoparticles with grain size less than 10 nm are uniformly dispersed in inactive nanocrystalline Cu matrix, is firstly obtained by milling the mixture of SnO2 and Cu nanopowders (molar ratio 1:2), and then further milling with graphite (C) to obtain SnO2–Cu–C composite with microsized graphite sheets as matrix of SnO2–Cu composite. The 50 h-milled SnO2–Cu composite exhibits higher initial CE (76.0 ± 1.5%) and subsequent CE than 50 h-milled SnO2. Furthermore, the SnO2–Cu–C composite anode is capable of retaining a maximum charge capacity of 450.8 mA h g−1 at 100 mA g−1 after 80 cycles with a capacity retention ratio of 74.4%, displaying superior cyclic stability to as-milled SnO2, SnO2–Cu and SnO2–C composites. The improved CE and cycleability are attributed to the unique dual scale embedding structure that offers good conductivity of electron and lithium ion as well as the nanostructure stability of active materials. This unique composite structure might be extended to other high-capacity anode materials, to achieve high performance lithium ion batteries.

•A new ternary composite containing SnO2, in-situ formed CuO and graphite nano-sheets was prepared by bead milling.•Wrapping of graphite nano-sheets benefits the reversible formation of SnO2 and CuO in the repeatedly charging process.•SnO2-CuO-graphite nanocomposite anode delivers higher stable capacity than the SnO2-Cu-graphite hybrid.•Wet-phase bead milling is feasible to prepare multi-phase nanocomposite as high performance anode for Li-ion battery.A ternary nanocomposite of SnO2, CuO and graphite is prepared by bead milling in alcohol, during which the graphite is greatly thinned to form graphite nano-sheets that wrapping the SnO2and in-situ formed CuO nanoparticles. This unique microstructure of SnO2-CuO-graphite nanocomposite benefits the reversible formation of SnO2 and CuO in the repeatedly charging process, and thus significantly improves the cyclic stability and rate capability. The reversible capacity of this ternary nanocomposite remains 561.2 mAh g−1 at 0.1 A g−1 after 150 cycles, much higher than that of the SnO2-graphite, and CuO-graphite hybrids.

•Lithiation-induced stress distribution in core/shell Sn-C anodes was simulated.•Sn-Li2O-C composite of a double-coating structure sustains less deformation.•Sn whiskers grow in cycled Sn-C electrodes due to lithiation-induced strain effect.•Double core/shell structure anodes with different Sn distributions are designed.To explore the capacity fading mechanism during long-term cycling of the milled Sn-C lithium storage anodes, the structural stability of the cycled Sn-C electrodes has been investigated using internal strain distribution as indicator by simulation with different two-dimensional core/shell nanostructure models solved by Lagrangian description, combining with experimental results. It is revealed that the Sn-C composite of a double-coating structure with the smaller Sn coated by a stiff layer Li2O and embedding in graphite sustains less deformation, and has higher structural stability than the single-coating one. Due to the lithiation-induced stress and strain effect, Sn particles aggregate and the Sn whiskers grow in the cycled Sn-C electrodes that observed by SEM and TEM, which is closely related to the Sn transportation. This strain induced structural damage causes the capacity fading of Sn anodes. Based on the simulation of strain distribution induced by lithiation, the nanostructure has been designed for Sn-C electrodes of smaller Sn particles embedded in matrix with large elastic modulus and proper thickness to obtain optimized combination of capacity and cycleability. It would provide a guideline for designing material and microstructure of anodes for lithium ion batteries.

In order to further enhance the reversible capacity and cyclability for lithium storage of Sn-based alloy anode materials, a spherical-shaped Sn–Fe3O4@C ternary-phase composite consisting of nanosized tin (Sn), magnetite (Fe3O4), and graphite (C) was prepared via a two-step process using high-efficiency discharge plasma-assisted milling (P-milling). Ultrafine Sn nanoparticles were embedded and tightly contacted with nanosized Fe3O4, with graphite nanosheets coating the outside to form a multiscale spherical structure. The Sn–Fe3O4@C nanocomposite anodes demonstrate a stable and high capacity of 793 mA h g−1 after 240 cycles between 0.01 and 3.0 V vs. Li/Li+ at 200 mA g−1. Furthermore, a reversible capacity of ∼750 mA h g−1 was obtained after 500 cycles, even when the current density increased to 2000 mA g−1. The high capacity, good cycle performance, and superior high-rate capability characteristics were attributed to the unique nanostructure of the Sn–Fe3O4@C composites. The good dispersion of co-existing Sn and Fe3O4 nanoballs in a spherical carbon matrix resulted in an electrode with high structural stability and fast kinetics for Li ion and electron transfer, which contributed to high reversibility of alloying reactions in Sn and conversion reactions of Fe3O4. Furthermore, the spherical shape of the materials and simple preparation as compared to those of commercial anodes make the Sn–Fe3O4@C composites good candidates for practical applications.