Mengyan Hou

General synthesis of xLi2MnO3·(1 − x)LiMn1/3Ni1/3Co1/3O2 nanomaterials by a molten-salt method: towards a high capacity and high power cathode for rechargeable lithium batteries

Well-crystallized and high-performance xLi2MnO3·(1 − x)LiMn1/3Ni1/3Co1/3O2 (x = 0.3, 0.5, and 0.7) structurally integrated nanomaterials are prepared by a facile molten-salt strategy. The effects of heat-treatment temperature, time, and the molar ratio of KCl flux to reaction precursor on the particle size as well as the electrochemical properties are explored. Our results demonstrate that a 0.5Li2MnO3·0.5LiMn1/3Ni1/3Co1/3O2 electrode delivers a high reversible capacity of 313 mA h g−1 with significant enhancement in the initial coulombic efficiency (87%) at room temperature, exhibits superior rate capability and shows improved electrochemical properties over a wide temperature range, in particular at low temperature.

Improving the electrochemical performance of layered lithium-rich transition-metal oxides by controlling the structural defects

We report the electrochemical properties of layered lithium-rich Li1.2Mn0.54Ni0.13Co0.13O2 cathode materials with various degrees of stacking faults, which are prepared via a facile molten-salt method using a variety of fluxes including KCl, Li2CO3, and LiNO3. The frequency of the stacking faults is highly dependent on the temperature and molten salt type used during the synthesis. A well-crystallized Li1.18Mn0.54Ni0.13Co0.13O2 nanomaterial with a larger amount of stacking faults synthesized at 800 °C for 10 h in an inactive KCl flux delivers a high reversible capacity of ∼310 mA h g−1 at room temperature, while the samples prepared in the chemically active fluxes with a smaller amount of stacking faults show poor electrochemical performance.

Sandwich-like Cr2O3–graphite intercalation composites as high-stability anode materials for lithium-ion batteries

Novel sandwich-like Cr2O3–graphite intercalation composites (Cr2O3–GICs) were synthesized via an intercalation–transformation method. Cr2O3 nanoparticles (NPs) are intercalated between the adjacent carbon layers of graphite and tightly immobilized. The Cr2O3–GICs show promising performance as anode materials for LIBs with a reversible capacity of about 480 mA h g−1 and a relatively low lithium insertion potential. More importantly, the Cr2O3–GICs demonstrate an extremely promising stable cycling performance with over 100% capacity retention after 1000 cycles. Furthermore, the intercalation–transformation method also provides another fabrication method of graphene-based assembled materials.

Interconnected sandwich structure carbon/Si-SiO2/carbon nanospheres composite as high performance anode material for lithium-ion batteries

Abstract In the present work, an interconnected sandwich carbon/Si-SiO2/carbon nanospheres composite was prepared by template method and carbon thermal vapor deposition (TVD). The carbon conductive layer can not only efficiently improve the electronic conductivity of Si-based anode, but also play a key role in alleviating the negative effect from huge volume expansion over discharge/charge of Si-based anode. The resulting material delivered a reversible capacity of 1094 mAh/g, and exhibited excellent cycling stability. It kept a reversible capacity of 1050 mAh/g over 200 cycles with a capacity retention of 96%.

Carbon-coated Li4Ti5O12 nanoparticles with high electrochemical performance as anode material in sodium-ion batteries

Sodium-ion batteries have been considered as promising alternatives to the current lithium-ion batteries owing to their low cost and abundant raw material. The major challenge of their practical implementation is the lack of favourable anode material. Spinel Li4Ti5O12 has been regarded as a potential anode material for its superior capability of sodium-ion storage and relatively appropriate operating voltage. However, the low intrinsic ionic and electronic conductivity of spinel Li4Ti5O12 still remains as its major drawback. Herein, carbon-coated Li4Ti5O12 nanoparticles have been synthesized through a solid-state reaction and a chemical vapour deposition method and used as an anode material for sodium-ion battery. The composite structure demonstrates excellent stability and an initial discharge specific capacity of 120.1 mA h g−1, which is maintained at 101.5 mA h g−1 after 500 cycles corresponding to 85% of capacity retention at a current density of 0.1 A g−1. In addition, a full cell was fabricated with carbon-coated Na3V2(PO4)3 as a positive electrode, which displayed discharge specific capacities of 138.5 mA h g−1 that was maintained at 114.7 mA h g−1 after 50 cycles at a current density of 0.05 A g−1, and the capacity retention was 82.8%. The results indicated that the Li4Ti5O12 nanoparticle with a carbon layer shows a promising electrochemical performance as anode materials in sodium-ion batteries.

Ultrasmall TiO2-Coated Reduced Graphene Oxide Composite as a High-Rate and Long-Cycle-Life Anode Material for Sodium-Ion Batteries

Because of the low cost and abundant nature of the sodium element, sodium-ion batteries (SIBs) are attracting extensive attention, and a variety of SIB cathode materials have been discovered. However, the lack of high-performance anode materials is a major challenge of SIBs. Herein, we have synthesized ultrasmall TiO2-nanoparticle-coated reduced graphene oxide (TiO2@RGO) composites by using a one-pot hydrolysis method, which are then investigated as anode materials for SIBs. The morphology of TiO2@RGO has been characterized using transmission electron microscopy, indicating that the TiO2 nanospheres uniformly grow on the surface of the RGO nanosheet. As-prepared TiO2@RGO composites exhibited a promising electrochemical performance in terms of cycling stability and rate capability, especially the initial cycle Coulombic efficiency of 60.7%, which is higher than that in previous reports. The kinetics of the electrode reaction has been investigated by cyclic voltammetry. The results indicate that the sodium-ion intercalation/extraction behavior is not controlled by the semiinfinite diffusion process, which gives rise to an outstanding rate performance. In addition, the electrochemical performance of TiO2@RGO composites in full cells, coupled with carbon-coated Na3V2(PO4)3 as the positive material, has been investigated. The discharge specific capacity was up to 117.2 mAh g-1, and it remained at 84.6 mAh g-1 after 500 cycles under a current density of 2 A g-1, which shows excellent cycling stability.

A clean and membrane-free chlor-alkali process with decoupled Cl 2 and H 2 /NaOH production

Existing chlor-alkali processes generally use asbestos, mercury or fluorine-containing ion-exchange membranes to separate the simultaneous chlorine production on the anode and hydrogen production on the cathode, and form sodium hydroxide in the electrolyte. Here, using the Na+ de-intercalation/intercalation of a Na0.44MnO2 electrode as a redox mediator, we decouple the chlor-alkali process into two independent steps: a H2 production step with the NaOH formation in the electrolyte and a Cl2 production step. The first step involves a cathodic H2 evolution reaction (H2O → H2) and an anodic Na+ de-intercalation reaction (Na0.44MnO2 → Na0.44−xMnO2), during which NaOH is produced in the electrolyte solution. The second step depends on a cathodic Na+ intercalation reaction (Na0.44−xMnO2 → Na0.44MnO2) and an anodic Cl2 production (Cl → Cl2). The cycle of the two steps provides a membrane-free process, which is potentially a promising direction for developing clean chlor-alkali technology.The chlor-alkali process is an important industrial process to make commodity chemicals; however, it usually requires the use of dangerous chemicals as membrane material. Here, the authors demonstrate clean, membrane-free chlor-alkali electrolysis, where chlorine evolution and hydrogen/sodium hydroxide production are completely decoupled.

Integrating Desalination and Energy Storage using a Saltwater-based Hybrid Sodium-ion Supercapacitor

Ever-increasing freshwater scarcity and energy crisis problems require efficient seawater desalination and energy storage technologies; however, each target is generally considered separately. Herein, a hybrid sodium-ion supercapacitor, involving a carbon-coated nano-NaTi2 (PO4 )3 -based battery anode and an activated-carbon-based capacitive cathode, is developed to combine desalination and energy storage in one device. On charge, the supercapacitor removes salt in a flowing saltwater electrolyte through Cl- electrochemical adsorption at the cathode and Na+ intercalation at the anode. Discharge delivers useful electric energy and regenerates the electrodes. This supercapacitor can be used not only for energy storage with promising electrochemical performance (i.e., high power, high efficiency, and long cycle life), but also as a desalination device with desalination capacity of 146.8 mg g-1 , much higher than most reported capacitive and battery desalination devices. Finally, we demonstrate renewables to usable electric energy and desalted water through combining commercial photovoltaics and this hybrid supercapacitor.