Liquan Chen

Room-temperature stationary sodium-ion batteries for large-scale electric energy storage

Room-temperature stationary sodium-ion batteries have attracted great attention particularly in large-scale electric energy storage applications for renewable energy and smart grid because of the huge abundant sodium resources and low cost. In this article, a variety of electrode materials including cathodes and anodes as well as electrolytes for room-temperature stationary sodium-ion batteries are briefly reviewed. We compare the difference in storage behavior between Na and Li in their analogous electrodes and summarize the sodium storage mechanisms in the available electrode materials. This review also includes some new results from our group and our thoughts on developing new materials. Some perspectives and directions on designing better materials for practical applications are pointed out based on knowledge from the literature and our experience. Through this extensive literature review, the search for suitable electrode and electrolyte materials for stationary sodium-ion batteries is still challenging. However, after intensive research efforts, we believe that low-cost, long-life and room-temperature sodium-ion batteries would be promising for applications in large-scale energy storage system in the near future.

A new class of Solvent-in-Salt electrolyte for high-energy rechargeable metallic lithium batteries

Liquid electrolyte plays a key role in commercial lithium-ion batteries to allow conduction of lithium-ion between cathode and anode. Traditionally, taking into account the ionic conductivity, viscosity and dissolubility of lithium salt, the salt concentration in liquid electrolytes is typically less than 1.2u2009molu2009l(-1). Here we show a new class of Solvent-in-Salt electrolyte with ultrahigh salt concentration and high lithium-ion transference number (0.73), in which salt holds a dominant position in the lithium-ion transport system. It remarkably enhances cyclic and safety performance of next-generation high-energy rechargeable lithium batteries via an effective suppression of lithium dendrite growth and shape change in the metallic lithium anode. Moreover, when used in lithium-sulphur battery, the advantage of this electrolyte is further demonstrated that lithium polysulphide dissolution is inhibited, thus overcoming one of todays most challenging technological hurdles, the polysulphide shuttle phenomenon. Consequently, a coulombic efficiency nearing 100% and long cycling stability are achieved.

Direct atomic-scale confirmation of three-phase storage mechanism in Li4Ti5O12 anodes for room-temperature sodium-ion batteries

Room-temperature sodium-ion batteries attract increasing attention for large-scale energy storage applications in renewable energy and smart grid. However, the development of suitable anode materials remains a challenging issue. Here we demonstrate that the spinel Li4Ti5O12, well-known as a zero-strain anode for lithium-ion batteries, can also store sodium, displaying an average storage voltage of 0.91u2009V. With an appropriate binder, the Li4Ti5O12 electrode delivers a reversible capacity of 155u2009mAhu2009g(-1) and presents the best cyclability among all reported oxide-based anode materials. Density functional theory calculations predict a three-phase separation mechanism, 2Li4Ti5O12+6Na(+)+6e(-)↔Li7Ti5O12+Na6LiTi5O12, which has been confirmed through in situ synchrotron X-ray diffraction and advanced scanning transmission electron microscope imaging techniques. The three-phase separation reaction has never been seen in any insertion electrode materials for lithium- or sodium-ion batteries. Furthermore, interfacial structure is clearly resolved at an atomic scale in electrochemically sodiated Li4Ti5O12 for the first time via the advanced electron microscopy.

Nanostructured ceria-based materials: synthesis, properties, and applications

The controllable synthesis of nanostructured CeO2-based materials is an imperative issue for environment- and energy-related applications. In this review, we present the recent technological and theoretical advances related to the CeO2-based nanomaterials, with a focus on the synthesis from one dimensional to mesoporous ceria as well as the properties from defect chemistry to nano-size effects. Seven extensively studied aspects regarding the applications of nanostructured ceria-based materials are selectively surveyed as well. New experimental approaches have been demonstrated with an atomic scale resolution characterization. Density functional theory (DFT) calculations can provide insight into the rational design of highly reactive catalysts and understanding of the interactions between the noble metal and ceria support. Achieving desired morphologies with designed crystal facets and oxygen vacancy clusters in ceria via controlled synthesis process is quite important for highly active catalysts. Finally, remarks on the challenges and perspectives on this exciting field are proposed.

Lithium storage in nitrogen-rich mesoporous carbon materials

Nitrogen-rich mesoporous carbon materials were obtained by pyrolyzing gelatin between 700 and 900 °C with a nano-CaCO3 template. The mesoporous structure and the high nitrogen content endowed these materials with reversible capacities up to ca. 1200 mA h g−1. The high specific surface area and the nitrogen doping are responsible for the capacity loss in the initial cycle. FTIR and XPS studies indicate that the nitrogen in the material exists in the form of pyridinic, pyrrolic/pyridonic and graphitic nitrogen. The Raman spectroscopic analysis indicates that the structure of the mesoporous carbon becomes more disordered during discharge and is restored during recharge, a behavior similar to that in nitrogen-free hard carbon materials. The reversible structural variation of these carbon materials ensures their high cyclic reversibility.

A zero-strain layered metal oxide as the negative electrode for long-life sodium-ion batteries

Room-temperature sodium-ion batteries have shown great promise in large-scale energy storage applications for renewable energy and smart grid because of the abundant sodium resources and low cost. Although many interesting positive electrode materials with acceptable performance have been proposed, suitable negative electrode materials have not been identified and their development is quite challenging. Here we introduce a layered material, P2-Na0.66[Li0.22Ti0.78]O2, as the negative electrode, which exhibits only ~0.77% volume change during sodium insertion/extraction. The zero-strain characteristics ensure a potentially long cycle life. The electrode material also exhibits an average storage voltage of 0.75u2009V, a practical usable capacity of ca. 100u2009mAhu2009g(-1), and an apparent Na(+) diffusion coefficient of 1 × 10(-10)u2009cm(-2)u2009s(-1) as well as the best cyclability for a negative electrode material in a half-cell reported to date. This contribution demonstrates that P2-Na0.66[Li0.22Ti0.78]O2 is a promising negative electrode material for the development of rechargeable long-life sodium-ion batteries.

Lithium Storage in Li4Ti5O12 Spinel: The Full Static Picture from Electron Microscopy

The full static picture of Li storage in Li(4)Ti(5)O(12) is derived using the latest spherical aberration-corrected scanning transmission electron microscopy and first-principles calculations. The accommodation of the additional Li(+) is directly visualized and the distribution of electrons introduced by lithium insertion deduced. Moreover, Li(4)Ti(5)O(12) is found to transform into Li(7)Ti(5)O(12) on lithiation by developing a dislocation-free coherent hetero-interface.

Single Lithium‐Ion Conducting Polymer Electrolytes Based on a Super‐Delocalized Polyanion

A novel single lithium-ion (Li-ion) conducting polymer electrolyte is presented that is composed of the lithium salt of a polyanion, poly[(4-styrenesulfonyl)(trifluoromethyl(S-trifluoromethylsulfonylimino)sulfonyl)imide] (PSsTFSI(-)), and high-molecular-weight poly(ethylene oxide) (PEO). The neat LiPSsTFSI ionomer displays a low glass-transition temperature (44.3u2009°C; that is, strongly plasticizing effect). The complex of LiPSsTFSI/PEO exhibits a high Li-ion transference number (tLi (+) =0.91) and is thermally stable up to 300u2009°C. Meanwhile, it exhibits a Li-ion conductivity as high as 1.35×10(-4) u2005Su2009cm(-1) at 90u2009°C, which is comparable to that for the classic ambipolar LiTFSI/PEO SPEs at the same temperature. These outstanding properties of the LiPSsTFSI/PEO blended polymer electrolyte would make it promising as solid polymer electrolytes for Li batteries.

A superior low-cost amorphous carbon anode made from pitch and lignin for sodium-ion batteries

Sodium-ion batteries (SIBs) are a promising candidate for grid electricity storage due to their potential low cost. The development of anode materials is a crucial step to promote the commercialization of SIBs, and amorphous carbon materials are likely to be the most promising alternatives among all proposed anode materials. However, the cost of the reported carbon materials is still very high due to the expensive precursors and their low carbon yield. Here, we report an amorphous carbon (AC) material made from low cost pitch. The amorphous carbon material with an amazing high carbon yield of 57% was achieved by utilizing the emulsification interaction between pitch and lignin to suppress the graphitization of pitch during the carbonization. The effects of heat-treatment temperatures and the pitch/lignin mass ratios on the morphology, microstructure and the electrochemical performance of AC were systematically investigated. By optimizing experimental conditions, we achieved one representative AC with a suitable morphology and microstructure, which exhibits promising performances with a high reversible capacity of 254 mA h g−1, a high initial coulombic efficiency of 82% and excellent cycling stability. This is the first demonstration that the pitch can be successfully applied in fabricating amorphous carbon anode materials for SIBs with superior low cost and high performance.

Synthesis and Electrochemical Performance of Graphene‐like WS2

Graphene-like and platelike WS2 were obtained by solid-state reactions. High-resolution (HR) TEM, BET, and Raman scattering studies show that the graphene-like WS2 is a few-layer-structured material. It exhibits better electrochemical performances than the platelike WS2. Structural characterization indicates that metallic W and Li2S are the end products of discharge (0.01 V versus Li(+)/Li), whereas metallic W and S are the recharge (3.00 V) products. In addition, X-ray absorption near-edge structure (XANES) characterization shows that the d electrons of W deviate towards the Li (or S) atom during the discharge/charge process, thus forming a weak bond between W and Li2S (or S).