Ji Qian

Free-Standing Hierarchically Sandwich-Type Tungsten Disulfide Nanotubes/Graphene Anode for Lithium-Ion Batteries

Transition metal dichalcogenides (TMD), analogue of graphene, could form various dimensionalities. Similar to carbon, one-dimensional (1D) nanotube of TMD materials has wide application in hydrogen storage, Li-ion batteries, and supercapacitors due to their unique structure and properties. Here we demonstrate the feasibility of tungsten disulfide nanotubes (WS2-NTs)/graphene (GS) sandwich-type architecture as anode for lithium-ion batteries for the first time. The graphene-based hierarchical architecture plays vital roles in achieving fast electron/ion transfer, thus leading to good electrochemical performance. When evaluated as anode, WS2-NTs/GS hybrid could maintain a capacity of 318.6 mA/g over 500 cycles at a current density of 1A/g. Besides, the hybrid anode does not require any additional polymetric binder, conductive additives, or a separate metal current-collector. The relatively high density of this hybrid is beneficial for high capacity per unit volume. Those characteristics make it a potential anode material for light and high-performance lithium-ion batteries.

An effective approach to protect lithium anode and improve cycle performance for Li-S batteries.

Lithium oxalyldifluoroborate (LiODFB) has been investigated as an organic electrolyte additive to improve the cycling performance of Li-S batteries. Cell test results demonstrate that an appropriate amount of LiODFB added into the electrolyte leads to a high Coulombic efficiency. Analyses by energy dispersive X-ray spectroscopy, X-ray photoelectron spectroscopy, and the density functional theory showed that LiODFB promotes the formation of a LiF-rich passivation layer on the lithium metal surface, which not only blocks the polysulfide shuttle, but also stabilizes the lithium surface.

Freestanding three-dimensional core-shell nanoarrays for lithium-ion battery anodes.

Structural degradation and low conductivity of transition-metal oxides lead to severe capacity fading in lithium-ion batteries. Recent efforts to solve this issue have mainly focused on using nanocomposites or hybrids by integrating nanosized metal oxides with conducting additives. Here we design specific hierarchical structures and demonstrate their use in flexible, large-area anode assemblies. Fabrication of these anodes is achieved via oxidative growth of copper oxide nanowires onto copper substrates followed by radio-frequency sputtering of carbon-nitride films, forming freestanding three-dimensional arrays with core–shell nano-architecture. Cable-like copper oxide/carbon-nitride core–shell nanostructures accommodate the volume change during lithiation−delithiation processes, the three-dimensional arrays provide abundant electroactive zones and electron/ion transport paths, and the monolithic sandwich-type configuration without additional binders or conductive agents improves energy/power densities of the whole electrode.

Facile Synthesis of Boron-Doped rGO as Cathode Material for High Energy Li–O2 Batteries

To improve the electrochemical performance of the high energy Li-O2 batteries, it is important to design and construct a suitable and effective oxygen-breathing cathode. Herein, a three-dimensional (3D) porous boron-doped reduction graphite oxide (B-rGO) material with a hierarchical structure has been prepared by a facile freeze-drying method. In this design, boric acid as the boron source helps to form the 3D porous structure, owing to its cross-linking and pore-forming function. This architecture facilitates the rapid oxygen diffusion and electrolyte penetration in the electrode. Meanwhile, the boron-oxygen functional groups linking to the carbon surface or edge serve as additional reaction sites to activate the ORR process. It is vital that boron atoms have been doped into the carbon lattices to greatly activate the electrons in the carbon π system, which is beneficial for fast charge under large current densities. Density functional theory calculation demonstrates that B-rGO exhibits much stronger interactions with Li5O6 clusters, so that B-rGO more effectively activates Li-O bonds to decompose Li2O2 during charge than rGO does. With B-rGO as a catalytic substrate, the Li-O2 battery achieves a high discharge capacity and excellent rate capability. Moreover, catalysts could be added into the B-rGO substrate to further lower the overpotential and enhance the cycling performance in future.

An Effectively Activated Hierarchical Nano‐/Microspherical Li1.2Ni0.2Mn0.6O2 Cathode for Long‐Life and High‐Rate Lithium‐Ion Batteries

Rechargeable lithium-ion batteries with high energy and high power density are required in the application of electric vehicles and portable electronics. Herein, we introduce a type of spherical Li-rich cathode material, Li1.2Ni0.2Mn0.6O2, assembled from uniform nanocubes by a facile polyvinylpyrrolidone (PVP)-assisted hydrothermal method. The material with a hierarchical nano-/microstructure exhibits stable high-rate performance. Furthermore, the precipitant (i.e., urea) and the structure-directing agent (i.e., PVP) effectively activated the Li2 MnO3 components in the microscale material to achieve a high specific capacity of 298.5 mAh g(-1) in the first cycle. This Li-rich cathode material still delivered 243 mAh g(-1) at 0.1 C after 200 cycles and the capacity retentions at 0.5, 1, 2, and 5 C were 94.4, 78.7, 76.3, and 67.8% after 150 cycles, respectively. The results make this Li-rich nano-/microstructure a promising cathode material for long-life and high-performance lithium-ion batteries.

Light-weight functional layer on a separator as a polysulfide immobilizer to enhance cycling stability for lithium–sulfur batteries

A light-weight boron-functionalized reduced graphene oxide (B-rGO) layer (only 0.2–0.3 mg cm−2) coated on a separator is demonstrated to improve the cycling stability and rate performance of lithium–sulfur batteries. Such an enhanced performance is ascribed to: (i) the boron species in B-rGO can enhance the binding with polysulfides, which helps suppress the shuttle reactions, thus alleviating overcharge and self-discharge; (ii) a certain amount of the boron doped into the graphene matrix can improve the electrical conductivity of the coating layer, thus enhancing the utilization of sulfur and improving the rate performance of the cells. With the B-rGO coated separator, the severe self-discharge of Li–S batteries can be alleviated. More importantly, for the high sulfur loading cathodes (above 4.5 mg cm−2), an improved high areal capacity of 4.71 mA h cm−2 can be achieved using the B-rGO coated separator. The above results demonstrate the potential of the B-rGO coated separator for practical lithium–sulfur batteries, and such a strategy can be extended to other energy storage systems.

Boron-doped microporous nano carbon as cathode material for high-performance Li-S batteries

In this study, a boron-doped microporous carbon (BMC)/sulfur nanocomposite is synthesized and applied as a novel cathode material for advanced Li-S batteries. The cell with this cathode exhibits an ultrahigh cycling stability and rate capability. After activation, a capacity of 749.5 mAh/g was obtained on the 54th cycle at a discharge current of 3.2 A/g. After 500 cycles, capacity of 561.8 mAh/g remained (74.96% retention), with only a very small average capacity decay of 0.056%. The excellent reversibility and stability of the novel sulfur cathode can be attributed to the ability of the boron-doped microporous carbon host to both physically confine polysulfides and chemically bind these species on the host surface. Theoretical calculations confirm that boron-doped carbon is capable of significantly stronger interactions with the polysulfide species than undoped carbon, most likely as a result of the lower electronegativity of boron. We believe that this doping strategy can be extended to other metal-air batteries and fuel cells, and that it has promising potential for many different applications.

A polypyrrole-supported carbon paper acting as a polysulfide trap for lithium–sulfur batteries

Lithium–sulfur (Li–S) batteries with high theoretical capacities and low cost are a strong candidate for future energy storage, but their development is hindered by many shortcomings, such as high-rate capacity decay due to the “shuttle effect”. Herein, we increase the capacity retention and cycle life of the Li–S battery through the addition of an interlayer made of polypyrrole (PPy)-treated carbon paper (CP) in a Li–S battery. We first quantitatively investigate the effect of the thickness of the carbon paper and then optimize a novel interlayer prepared by using PPy adhered to the carbon paper. The results show that 300 μm CP is the best choice among the three thicknesses. The CP-300 samples deliver a reversible capacity of 490 mAh g−1 after 200 cycles with a 0.5 C rate and show the best rate performance. Because of the porous structure and conductivity of the as-prepared PPy interlayer, the battery incorporating the PPy interlayer exhibits more excellent cycle performance and better rate performance than the CP batteries. Surprisingly, the PPy-coated CP-200 battery displays a reversible capacity of 555 mAh g−1 after 200 cycles with a 0.5 C rate. This feasible way to modify a carbon paper interlayer may have promising prospects in the Li–S battery field.

Strongly Coupled Carbon Nanosheets/Molybdenum Carbide Nanocluster Hollow Nanospheres for High‐Performance Aprotic Li–O2 Battery

A highly efficient oxygen electrode is indispensable for achieving high-performance aprotic lithium-O2 batteries. Herein, it is demonstrated that strongly coupled carbon nanosheets/molybdenum carbide (α-MoC1-x ) nanocluster hierarchical hybrid hollow spheres (denoted as MoC1-x /HSC) can work well as cathode for boosting the performance of lithium-O2 batteries. The important feature of MoC1-x /HSC is that the α-MoC1-x nanoclusters, uniformly incorporated into carbon nanosheets, can not only effectively prevent the nanoclusters from agglomeration, but also help enhance the interaction between the nanoclusters and the conductive substrate during the charge and discharge process. As a consequence, the MoC1-x /HSC shows significantly improved electrocatalytic performance in an aprotic Li-O2 battery with greatly reduced charge and discharge overpotentials and long cycle stability. The ex situ scanning electron microscopy, X-ray diffraction, and X-ray photoelectron spectroscopy studies reveal that the mechanism for the high-performance Li-O2 battery using MoC1-x /HSC as cathode is that the incorporated molybdenum carbide nanoclusters can make oxygen reduction on their surfaces easy, and finally form amorphous film-like Li-deficient Li2 O2 with the ability to decompose at a low potential. To the best of knowledge, the MoC1-x /HSC of this paper is among the best cathode materials for lithium-O2 batteries reported to date.

Zirconia-supported solid-state electrolytes for high-safety lithium secondary batteries in a wide temperature range

High safety is a long-sought-after goal in the energy storage field. We fabricate a high-safety solid-state electrolyte by in situ immobilizing ionic liquids within a nanoporous zirconia-supported matrix. This ionogel electrolyte provides a combination of the solid-like physical support and liquid-like ionic transport performance, which substantially improves the thermal stability and safety without sacrificing ionic conductivity. Both Raman spectra and density functional theory computations indicate that the zirconia skeleton interacts with the Li salts, promoting the dissociation and transport of Li+. The solid-state cell assembled with this electrolyte possesses excellent cycling performance, with a discharge capacity of 135.9 mA h g−1 after 200 cycles at 30 °C and works well in a wide operating temperature range from −10 to 90 °C. Moreover, the good compatibility and stable interface toward Li–metal anodes in a symmetrical cell demonstrates the usefulness of the electrolyte in Li–metal batteries. These results indicate that this ionogel electrolyte has great promise for application in the energy storage field because of its dramatically improved safety characteristic.