Zhongxue Chen

Surface-oriented and nanoflake-stacked LiNi0.5Mn1.5O4 spinel for high-rate and long-cycle-life lithium ion batteries

Spinel LiNi0.5Mn1.5O4 has attracted extensive interest as an appealing cathode material of next generation lithium-ion batteries to meet the cost/performance requirements for electric vehicle applications and renewable electric energy storage. In this paper, we report, for the first time, a nanoflake-stacked LiNi0.5Mn1.5O4 spinel with oriented growth of the (001) planes synthesized via an in situ template route. The resultant LiNi0.5Mn1.5O4 cathode delivers an initial discharge capacity of 133.5 mA h g−1 at 1 C with capacity retention of 86% after 500 cycles. X-ray diffraction and transmission electron microscopy results suggest that the growth of (111) facets on the surfaces of the nanoflake-stacked LiNi0.5Mn1.5O4 spinel is significantly restricted, which helps to inhibit the dissolution of manganese from the lattice and ensure an excellent cycling stability. Moreover, the very thin nanoflakes and large interspaces between the nanoflakes are favorable for Li ion transportation, leading to a fast kinetics of the LiNi0.5Mn1.5O4 spinel. As a result, the material demonstrates a reversible capacity of 96 mA h g−1 even at 50 C rate, showing a feasible application for high-power lithium ion batteries. In particular, this study provides a synthetic strategy to fabricate insertion materials with a surface-oriented morphology and nanoflake-stacked structure for energy storage, fast-ion conductors and other applications.

A 3D nanostructure of graphene interconnected with hollow carbon spheres for high performance lithium–sulfur batteries

To better suppress the capacity decay over cycling and improve the electrical insulation of the sulfur cathode for lithium–sulfur (Li–S) batteries, we designed a novel three-dimensional nanostructure of graphene interconnected with hollow carbon spheres (3D rGO–HCS) as the sulfur host. The 3D rGO–HCS nanostructure was first prepared via a hydrothermal self-assembly method followed by carbonization and etching of the SiO2 core, then sulfur was impregnated into the nanostructure by an in situ solution deposition method to obtain the S@rGO–HCS cathode. The as-prepared cathode material delivers a high discharge capacity of ∼770 mA h g−1 at 4 C rate. More importantly, it has a high capacity retention of 93.9% after 100 cycles and demonstrates a low capacity-decay rate of 0.052% per cycle after 400 cycles at 0.5 C rate. The superior comprehensive electrochemical performance of the S@rGO–HCS cathode is ascribed to the synergic effects from the 3D graphene-network design, including fast electron and ion transportation, efficient confinement of polysulfide dissolution and shuttling and successful maintenance of structural integrity.

Facile synthesis and stable lithium storage performances of Sn- sandwiched nanoparticles as a high capacity anode material for rechargeable Li batteries

A simple synthetic route was developed to obtain Sn-sandwiched composite nanoparticles by mechanical ball-milling ductile Sn particles with rigid SiC nanocores to form a SiC@Sn core-shell nanocomposite and then carbon-coating the SiC@Sn nanoparticles with graphite to produce the SiC@Sn@C nanoparticles. Such a novel nanostructure can effectively buffer the mechanical stress and prevent the aggregation of the Sn nanolayer and therefore improve the electrochemical utilization and cycling stability of electroactive Sn during Li-storage reaction. The Sn-sandwiched nanoparticles as-prepared exhibited a considerable high Li-storage capacity of ∼600 mA h g−1 and an excellent cycling stability with ∼90% capacity retention at 100 cycles, showing a prospect for practical lithium battery applications. In particular, the reported synthetic method is very simple, low-cost and pollution-free, enabling it to be readily adopted for large-scale production and also to be extended for other attractive lithium storage metals and alloys.

Enhanced Li Storage Performance of LiNi0.5Mn1.5O4–Coated 0.4Li2MnO3·0.6LiNi1/3Co1/3Mn1/3O2 Cathode Materials for Li-Ion Batteries

In this study, Li-rich cathode, 0.4Li2MnO3·0.6LiNi1/3Co1/3Mn1/3O2 was synthesized by a resorcinol formaldehyde assisted sol-gel method for the first time. Then, the surface of the as-prepared Li-rich cathode was modified with different amounts of LiNi0.5Mn1.5O4 (5, 10, and 20 wt %) through a simple dip-dry approach. The structural and electrochemical characterizations revealed that the spinel LiNi0.5Mn1.5O4 coating not only can prevent electrolytes from eroding the Li-rich core but also can facilitate fast lithium ion transportation. As a result, the 20 wt % coated sample delivered an initial discharge capacity of 298.6 mAh g(-1) with a Coulombic efficiency of 84.8%, compared to 281.1 mAh g(-1) and 70.2%, respectively, for the bare sample. Particularly, the coated sample demonstrates a Li storage capacity of 170.7 mAh g(-1) and capacity retention of 94.4% after 100 cycles at a high rate of 5 C (1250 mA g(-1)), showing a prospect for practical lithium battery applications. More significantly, the synthetic method proposed in this work is facile and low-cost and possibly could be adopted for large-scale production of surface-modified cathode materials.

Recent Progress in Iron-Based Electrode Materials for Grid-Scale Sodium-Ion Batteries

Grid-scale energy storage batteries with electrode materials made from low-cost, earth-abundant elements are needed to meet the requirements of sustainable energy systems. Sodium-ion batteries (SIBs) with iron-based electrodes offer an attractive combination of low cost, plentiful structural diversity and high stability, making them ideal candidates for grid-scale energy storage systems. Although various iron-based cathode and anode materials have been synthesized and evaluated for sodium storage, further improvements are still required in terms of energy/power density and long cyclic stability for commercialization. In this Review, progress in iron-based electrode materials for SIBs, including oxides, polyanions, ferrocyanides, and sulfides, is briefly summarized. In addition, the reaction mechanisms, electrochemical performance enhancements, structure-composition-performance relationships, merits and drawbacks of iron-based electrode materials for SIBs are discussed. Such iron-based electrode materials will be competitive and attractive electrodes for next-generation energy storage devices.

Graphene oxide wrapped hierarchical porous carbon–sulfur composite cathode with enhanced cycling and rate performance for lithium sulfur batteries

A graphene oxide sheet wrapped hierarchical porous carbon–sulfur (HPC–S@GO) composite was designed by a two-step method to improve the lithium sulfur battery performance. With this nanostructure design, the hierarchical porous carbon supplies an electronic transport pathway and provides a large pore volume to load the sulfur while the encapsulated graphene oxide sheet is effective in trapping sulfur and polysulfides during cycling. The obtained HPC–S@GO composite delivers prolonged cycling stability and an enhanced rate performance: the capacity fading is 0.12% per cycle over 400 cycles at 1 C (1672 mA g−1) rate, and the capacities at 0.2, 0.5, 1, 2 and 5 C rate are 1333.3, 896.9, 763.0, 669.5 and 505.6 mA h g−1, respectively.

A facile one-step hydrothermal synthesis of α-Fe2O3 nanoplates imbedded in graphene networks with high-rate lithium storage and long cycle life

In this study, we demonstrate a facile one-step hydrothermal strategy to build a nanostructure of α-Fe2O3 nanoplates imbedded in graphene networks, using water and glycerol as hydrothermal solvents. The graphene oxide was chemically reduced with Fe2+ and glycerol, and the obtained α-Fe2O3 nanoplates with a thickness of 20–30 nm and a side length of 100–300 nm are well wrapped by and in tight contact with the flexible conductive graphene networks. When used as the anode material for lithium ion batteries, the rGO/α-Fe2O3 nanoplate composite demonstrates high discharge capacities of ∼896 mA h g−1 up to 200 cycles at 5 C and ∼429 mA h g−1 up to 1000 cycles even at a 10 C rate. The excellent lithium storage performance could be attributed to the synergistic effects of the unique structures, which can provide fast electron transport and shorten the diffusion path of the Li ions as well as accommodate the volume change of the composite in the cycling.

Hydrothermal preparation of nitrogen, boron co-doped curved graphene nanoribbons with high dopant amounts for high-performance lithium sulfur battery cathodes

In this work, we for the first time synthesized nitrogen, boron co-doped curved graphene nanoribbons (NBCGNs) by a facile hydrothermal process using oxidized curved graphene nanoribbons (O-CGNs), urea and boric acid as the carbon precursor and heteroatom sources. The influence of N and B co-doping on the morphology, structure, composition and related electrochemical performance of the NBCGNs was systematically investigated, and the results show that urea and boric acid coexisting in the hydrothermal system not only act as the N and B doping sources but also act as the catalysts to boost the synergistical doping of N and B. It is the synergistical effect of N and B co-doping that endows the NBCGNs with enlarged specific surface area as well as pore volume, improved conductivity, promoted sulfur dispersibility and strengthened adsorbability for polysulfides caused by the notably increased doped N and B contents and higher percentage of the N–B structure when compared with the counterparts. As a result, the as-prepared NBCGN/S cathode presented synergistically enhanced cyclability and rate capability. Therefore, our results not only provide a superior carbon host for Li–S batteries but also offer a common approach to the preparation of heteroatom doped carbon nanomaterials with an optimized structure and composition.

High Rate, Long Lifespan LiV3 O8 Nanorods as a Cathode Material for Lithium-Ion Batteries

LiV3 O8 nanorods with controlled size are successfully synthesized using a nonionic triblock surfactant Pluronic-F127 as the structure directing agent. X-ray diffraction, scanning electron microscopy, and transmission electron microscopy techniques are used to characterize the samples. It is observed that the nanorods with a length of 4-8 µm and diameter of 0.5-1.0 µm distribute uniformly. The resultant LiV3 O8 nanorods show much better performance as cathode materials in lithium-ion batteries than normal LiV3 O8 nanoparticles, which is associated with the their unique micro-nano-like structure that can not only facilitate fast lithium ion transport, but also withstand erosion from electrolytes. The high discharge capacity (292.0 mAh g-1 at 100 mA g-1 ), high rate capability (138.4 mAh g-1 at 6.4 A g-1 ), and long lifespan (capacity retention of 80.5% after 500 cycles) suggest the potential use of LiV3 O8 nanorods as alternative cathode materials for high-power and long-life lithium ion batteries. In particular, the synthetic strategy may open new routes toward the facile fabrication of nanostructured vanadium-based compounds for energy storage applications.

Understanding Voltage Decay in Lithium-Rich Manganese-Based Layered Cathode Materials by Limiting Cutoff Voltage

The effect of the cutoff voltages on the working voltage decay and cyclability of the lithium-rich manganese-based layered cathode (LRMO) was investigated by electrochemical measurements, electrochemical impedance spectroscopy, ex situ X-ray diffraction, transmission electron microscopy, and energy dispersive spectroscopy line scan technologies. It was found that both lower (2.0 V) and upper (4.8 V) cutoff voltages cause severe voltage decay with cycling due to formation of the spinel phase and migration of the transition metals inside the particles. Appropriate cutoff voltage between 2.8 and 4.4 V can effectively inhibit structural variation as the electrode demonstrates 92% capacity retention and indiscernible working voltage decay over 430 cycles. The results also show that phase transformation not only on high charge voltage but also on low discharge voltage should be addressed to obtain highly stable LRMO materials.