Hong-Bin Yao

Interconnected hollow carbon nanospheres for stable lithium metal anodes

For future applications in portable electronics, electric vehicles and grid storage, batteries with higher energy storage density than existing lithium ion batteries need to be developed. Recent efforts in this direction have focused on high-capacity electrode materials such as lithium metal, silicon and tin as anodes, and sulphur and oxygen as cathodes. Lithium metal would be the optimal choice as an anode material, because it has the highest specific capacity (3,860 mAh g(-1)) and the lowest anode potential of all. However, the lithium anode forms dendritic and mossy metal deposits, leading to serious safety concerns and low Coulombic efficiency during charge/discharge cycles. Although advanced characterization techniques have helped shed light on the lithium growth process, effective strategies to improve lithium metal anode cycling remain elusive. Here, we show that coating the lithium metal anode with a monolayer of interconnected amorphous hollow carbon nanospheres helps isolate the lithium metal depositions and facilitates the formation of a stable solid electrolyte interphase. We show that lithium dendrites do not form up to a practical current density of 1 mA cm(-2). The Coulombic efficiency improves to ∼ 99% for more than 150 cycles. This is significantly better than the bare unmodified samples, which usually show rapid Coulombic efficiency decay in fewer than 100 cycles. Our results indicate that nanoscale interfacial engineering could be a promising strategy to tackle the intrinsic problems of lithium metal anodes.

A Flexible and Highly Pressure-Sensitive Graphene- Polyurethane Sponge Based on Fractured Microstructure Design

A fractured microstructure design: A new type of piezoresistive sensor with ultra-high-pressure sensitivity (0.26 kPa(-1) ) in low pressure range (<2 kPa) and minimum detectable pressure of 9 Pa has been fabricated using a fractured microstructure design in a graphene-nanosheet-wrapped polyurethane (PU) sponge. This low-cost and easily scalable graphene-wrapped PU sponge pressure sensor has potential application in high-spatial-resolution, artificial skin without complex nanostructure design.

The synergetic effect of lithium polysulfide and lithium nitrate to prevent lithium dendrite growth

Lithium metal has shown great promise as an anode material for high-energy storage systems, owing to its high theoretical specific capacity and low negative electrochemical potential. Unfortunately, uncontrolled dendritic and mossy lithium growth, as well as electrolyte decomposition inherent in lithium metal-based batteries, cause safety issues and low Coulombic efficiency. Here we demonstrate that the growth of lithium dendrites can be suppressed by exploiting the reaction between lithium and lithium polysulfide, which has long been considered as a critical flaw in lithium-sulfur batteries. We show that a stable and uniform solid electrolyte interphase layer is formed due to a synergetic effect of both lithium polysulfide and lithium nitrate as additives in ether-based electrolyte, preventing dendrite growth and minimizing electrolyte decomposition. Our findings allow for re-evaluation of the reactions regarding lithium polysulfide, lithium nitrate and lithium metal, and provide insights into solving the problems associated with lithium metal anodes.

Understanding the Role of Different Conductive Polymers in Improving the Nanostructured Sulfur Cathode Performance

Lithium sulfur batteries have brought significant advancement to the current state-of-art battery technologies because of their high theoretical specific energy, but their wide-scale implementation has been impeded by a series of challenges, especially the dissolution of intermediate polysulfides species into the electrolyte. Conductive polymers in combination with nanostructured sulfur have attracted great interest as promising matrices for the confinement of lithium polysulfides. However, the roles of different conductive polymers on the electrochemical performances of sulfur electrode remain elusive and poorly understood due to the vastly different structural configurations of conductive polymer-sulfur composites employed in previous studies. In this work, we systematically investigate the influence of different conductive polymers on the sulfur cathode based on conductive polymer-coated hollow sulfur nanospheres with high uniformity. Three of the most well-known conductive polymers, polyaniline (PANI), polypyrrole (PPY), and poly(3,4-ethylenedioxythiophene) (PEDOT), were coated, respectively, onto monodisperse hollow sulfur nanopsheres through a facile, versatile, and scalable polymerization process. The sulfur cathodes made from these well-defined sulfur nanoparticles act as ideal platforms to study and compare how coating thickness, chemical bonding, and the conductivity of the polymers affected the sulfur cathode performances from both experimental observations and theoretical simulations. We found that the capability of these three polymers in improving long-term cycling stability and high-rate performance of the sulfur cathode decreased in the order of PEDOT > PPY > PANI. High specific capacities and excellent cycle life were demonstrated for sulfur cathodes made from these conductive polymer-coated hollow sulfur nanospheres.

Two-dimensional layered transition metal disulphides for effective encapsulation of high-capacity lithium sulphide cathodes

Fully lithiated lithium sulphide (Li2S) is currently being explored as a promising cathode material for emerging energy storage applications. Like their sulphur counterparts, Li2S cathodes require effective encapsulation to reduce the dissolution of intermediate lithium polysulphide (Li2Sn, n=4-8) species into the electrolyte. Here we report, the encapsulation of Li2S cathodes using two-dimensional layered transition metal disulphides that possess a combination of high conductivity and strong binding with Li2S/Li2Sn species. In particular, using titanium disulphide as an encapsulation material, we demonstrate a high specific capacity of 503 mAh g(-1)(Li2S) under high C-rate conditions (4C) as well as high areal capacity of 3.0 mAh cm(-2) under high mass-loading conditions (5.3 mg(Li2S) cm(-2)). This work opens up the new prospect of using transition metal disulphides instead of conventional carbon-based materials for effective encapsulation of high-capacity electrode materials.

Improved lithium-sulfur batteries with a conductive coating on the separator to prevent the accumulation of inactive S-related species at the cathode-separator interface†

Lithium–sulfur (Li–S) batteries are highly attractive for future generations of portable electronics and electric vehicles due to their high energy density and potentially low cost. In the past decades, various novel electrodes and electrolytes have been tested to improve Li–S battery performance. However, these designs on electrodes and electrolytes have not fully addressed the problem of low cycling stability of Li–S batteries. Here, we show the role of the separator in the capacity decay of the Li–S battery, namely that it can accommodate a large amount of polysulfides inside which then precipitates as a thick layer of inactive S-related species. Using a thin conductive coating on the separator to prevent the formation of the inactive S-related species layer, we show that the specific capacity and cycling stability of the Li–S battery are both improved significantly compared to the battery with a pristine separator. Combining this separator design with a monodisperse sulfur nanoparticle cathode, we show Li–S batteries with a life of over 500 cycles with an initial specific capacity of 1350 mA h g−1 at C/2 and a cycle decay as low as 0.09% per cycle.

Improving lithium–sulphur batteries through spatial control of sulphur species deposition on a hybrid electrode surface

Lithium-sulphur batteries are attractive owing to their high theoretical energy density and reasonable kinetics. Despite the success of trapping soluble polysulphides in a matrix with high surface area, spatial control of solid-state sulphur and lithium sulphide species deposition as a critical aspect has not been demonstrated. Herein, we show a clear visual evidence that these solid species deposit preferentially onto tin-doped indium oxide instead of carbon during electrochemical charge/discharge of soluble polysuphides. To incorporate this concept of spatial control into more practical battery electrodes, we further prepare carbon nanofibers with tin-doped indium oxide nanoparticles decorating the surface as hybrid three-dimensional electrodes to maximize the number of deposition sites. With 12.5 μl of 5 M Li2S8 as the catholyte and a rate of C/5, we can reach the theoretical limit of Li2S8 capacity ~\n1,470 mAh g(-1) (sulphur weight) under the loading of hybrid electrode only at 4.3 mg cm(-2).

Balancing surface adsorption and diffusion of lithium-polysulfides on nonconductive oxides for lithium-sulfur battery design

Lithium–sulfur batteries have attracted attention due to their six-fold specific energy compared with conventional lithium-ion batteries. Dissolution of lithium polysulfides, volume expansion of sulfur and uncontrollable deposition of lithium sulfide are three of the main challenges for this technology. State-of-the-art sulfur cathodes based on metal-oxide nanostructures can suppress the shuttle-effect and enable controlled lithium sulfide deposition. However, a clear mechanistic understanding and corresponding selection criteria for the oxides are still lacking. Herein, various nonconductive metal-oxide nanoparticle-decorated carbon flakes are synthesized via a facile biotemplating method. The cathodes based on magnesium oxide, cerium oxide and lanthanum oxide show enhanced cycling performance. Adsorption experiments and theoretical calculations reveal that polysulfide capture by the oxides is via monolayered chemisorption. Moreover, we show that better surface diffusion leads to higher deposition efficiency of sulfide species on electrodes. Hence, oxide selection is proposed to balance optimization between sulfide-adsorption and diffusion on the oxides.

Ultrathin two-dimensional atomic crystals as stable interfacial layer for improvement of lithium metal anode.

Stable cycling of lithium metal anode is challenging due to the dendritic lithium formation and high chemical reactivity of lithium with electrolyte and nearly all the materials. Here, we demonstrate a promising novel electrode design by growing two-dimensional (2D) atomic crystal layers including hexagonal boron nitride (h-BN) and graphene directly on Cu metal current collectors. Lithium ions were able to penetrate through the point and line defects of the 2D layers during the electrochemical deposition, leading to sandwiched lithium metal between ultrathin 2D layers and Cu. The 2D layers afford an excellent interfacial protection of Li metal due to their remarkable chemical stability as well as mechanical strength and flexibility, resulting from the strong intralayer bonds and ultrathin thickness. Smooth Li metal deposition without dendritic and mossy Li formation was realized. We showed stable cycling over 50 cycles with Coulombic efficiency ∼97% in organic carbonate electrolyte with current density and areal capacity up to the practical value of 2.0 mA/cm(2)and 5.0 mAh/cm(2), respectively, which is a significant improvement over the unprotected electrodes in the same electrolyte.

Artificial Nacre‐like Bionanocomposite Films from the Self‐Assembly of Chitosan–Montmorillonite Hybrid Building Blocks

In the last decade, there has been a trend in chemistry to reduce the human impact on the environment. Special attention has been paid to the replacement of conventional petroleum-based plastics by materials based on biopolymers. However, the mechanical and thermal properties and functionalities of these biopolymers have to be enhanced to be competitive with the petroleum-based plastics from the viewpoint of practical applications. One of the most promising solutions to overcome these drawbacks is the elaboration of bionanocomposite, namely the dispersion of nanosized filler into a biopolymer matrix. Because of their functional properties, bionanocomposites as green nanocomposites based on biopolymers and layered silicates (clays) have received intensive attention in materials science. 4] Chitosan and montmorillonite (MTM), an abundant polysaccharide and a natural clay respectively, have been widely used as the constituents of bionanocomposites. The intercalation of chitosan into MTM and the dispersion of MTM nanosheets in the chitosan matrix have been systematically investigated. Bionanocomposites based on chitosan intercalation into MTM can be used as a sensor applied in the potentiometric determination of several anions. Bionanocomposite films formed through the dispersion of MTM nanosheets in the chitosan matrix have shown enhancement of the mechanical and thermal properties compared with the pure chitosan film. Unfortunately, the enhancement of the tensile strength and thermal stability of the chitosan–MTM bionanocomposite film is still low far from the expectations in industry. Systematic studies are carried out in materials science on natural materials with the objective of duplicating their properties in artificial materials. Natural nanocomposites provide prime design models of lightweight, strong, stiff, and tough materials due to the hierarchical organization of the micro and nanostructures. One attractive biological model for artificial material design is nacre (mother-of-pearl). The microscopic architecture of nacre has been classically illustrated as a “brick-and-mortar” arrangement that plays an important role in the amazing mechanical properties of the nacre. This arrangement is constituted of highly aligned inorganic aragonite platelets surrounded by a protein matrix, which serves as a glue between the platelets. Recently, the microstructure of the nacre has been mimicked by several innovative techniques to fabricate the artificial nacre-like materials with high mechanical performance. For example, layer-by-layer (LBL) deposition combining with cross-linking yielded poly(vinyl alcohol)/MTM nacre-like nanocomposites with a tensile strength of up to 400 MPa; the ice-crystal templates of the microscopic layers were designed to form a brick-and-mortar microstructured Al2O3/poly(methyl methacrylate) composite that is 300 times tougher than its constituents; the assembly of Al2O3 platelets on the air/water interface and sequent spincoating was developed into the fabrication of lamellar Al2O3/ chitosan hybrid films with high flaw tolerance and ductility; the self-assembly of nanoclays with polymers coating by a paper-making method resulted in the nacre-mimetic films; and nacre-like structural MTM–polyimide nanocomposites were fabricated by centrifugation deposition-assisted assembly. Our group has also fabricated nacre-like chitosanlayered double hydroxide hybrid films with a tensile strength of up to 160MPa by sequential dipping coating and the LBL technique. The concept of mimicking nacre and recently developed innovative techniques inspired us to fabricate the highly sustainable artificial nacre-like chitosan–MTM bionanocomposite film with high performance to seek a promising material for the replacement of conventional petroleumbased plastics. Herein, we introduce a novel approach to fabricate artificial nacre-like chitosan–MTM bionanocomposite films by self-assembly of chitosan–MTM hybrid building blocks (Scheme 1). The chitosan molecules are very easily coated onto exfoliated MTM nanosheets to yield the hybrid building blocks by strong electrostatic and hydrogen-bonding interactions. These hybrid building blocks can be dispersed in distilled water and then aligned to a nacre-like lamellar microstructure by vacuum-filtrationor water-evaporationinduced self-assembly because of the role that the orientation of the nanosheets and linking of the chitosan play. The fabrication process is simple, fast, time-saving, and easily scaled up compared with the LBL, ice-crystal-template, and other techniques. [*] H. B. Yao, Z. H. Tan, H. Y. Fang, Prof. Dr. S. H. Yu Division of Nanomaterials and Chemistry Hefei National Laboratory for Physical Sciences at Microscale Department of Chemistry National Synchrotron Radiation Laboratory University of Science and Technology of China Hefei, Anhui 230026 (P.R. China) Fax: (+ 86)551-360-3040 E-mail: shyu@ustc.edu.cn Homepage: http://staff.ustc.edu.cn/~ yulab/