Chun-Peng Yang

Accommodating lithium into 3D current collectors with a submicron skeleton towards long-life lithium metal anodes

Lithium metal is one of the most attractive anode materials for electrochemical energy storage. However, the growth of Li dendrites during electrochemical deposition, which leads to a low Coulombic efficiency and safety concerns, has long hindered the application of rechargeable Li-metal batteries. Here we show that a 3D current collector with a submicron skeleton and high electroactive surface area can significantly improve the electrochemical deposition behaviour of Li. Li anode is accommodated in the 3D structure without uncontrollable Li dendrites. With the growth of Li dendrites being effectively suppressed, the Li anode in the 3D current collector can run for 600 h without short circuit and exhibits low voltage hysteresis. The exceptional electrochemical performance of the Li-metal anode in the 3D current collector highlights the importance of rational design of current collectors and reveals a new avenue for developing Li anodes with a long lifespan.

An Artificial Solid Electrolyte Interphase Layer for Stable Lithium Metal Anodes

A Li3PO4 solid electrolyte interphase (SEI) layer is demonstrated to be stable in the organic electrolyte, even during the Li deposition/dissolution process. Thus, the Li-conducting Li3PO4 SEI layer with a high Youngs modulus can effectively reduce side reactions between Li metal and the electrolyte and can restrain Li dendrite growth in lithium-metal batteries during cycling.

An Advanced Selenium–Carbon Cathode for Rechargeable Lithium–Selenium Batteries†

The rapidly developing market for mobile electronics and hybrid electric vehicles (HEVs) has prompted the urgent need for batteries with high energy density, long cycle life, high efficiency, and low cost. Recently, rechargeable lithium-sulfur (Li–S) batteries have attracted considerable attention because of their high theoretical gravimetric (volumetric) energy density of 2570 Wh kg 1 (2200 Whl ), and low cost. However, the use of S as cathode material for Li–S batteries suffers from two major issues. One is the insulating nature of S, which results in low active-material utilization and limited rate capability. The other is the formation of electrolytesoluble polysulfides; these polysulfide intermediates, which are generated in the discharge/charge process, dissolve in the electrolyte and migrate to the Li anode, a process known as the shuttle effect. Consequently, the S cathode suffers a significant loss of S during cycling, resulting in a rapid capacity decrease. Many strategies have been used to address these problems, such as the impregnation of S into various conductive porous matrixes, surface coating of S, and the use of suitable electrolytes and additives. Although remarkable improvements have been achieved, the application of Li–S batteries is still hindered by the intrinsic drawbacks of S. Therefore, it is of great importance to explore and develop new high-energy cathode materials with improved electronic conductivity and cycling stability, to cover the shortfalls of S and provide alternative choices for practical applications. From this perspective, selenium, an element belonging to the same group in the periodic table as sulfur, is a prospective candidate for cathode materials. Although Se has a lower theoretical gravimetric capacity (675 mAhg ) than S (1675 mAh g ), its higher density (ca. 2.5 times that of S) offsets the deficiency and provides a high theoretical volumetric capacity density (3253 mAh cm ), comparable to that of S (3467 mAh cm ). It has been reported that Li–Se batteries deliver a high output voltage, so Li–Se batteries are also expected to have a high volumetric energy density. It is known that for applications in portable devices and HEVs, volumetric energy density is more important than gravimetric energy density because of the limited battery packing space. Moreover, the electronic conductivity of Se (1 10 3 Sm ) is considerably higher than that of S (5 10 28 Sm ), which suggests that Se could have higher utilization rate, better electrochemical activity, and faster electrochemical reaction with Li. Therefore, the advantages of Se promise an attractive alternative cathode material for building high-energy batteries for specific applications, including consumer electronics and transportation. However, at present, research on Li–Se batteries is still at a very early stage. Recently, Abouimrane et al. conducted pioneering work on the use of Se as a cathode material. The results show that, even bulk Se has an active material utilization of ca. 45% upon cycling, which is not commonly observed in Li–S batteries with a bulk S cathode. This suggests that Se cathode has a much better activity and a weaker shuttle effect than S. Nevertheless, bulk Se cannot completely deliver the theoretical capacity. Moreover, given the weak interaction between bulk Se and the conductive substrate, the polyselenide species generated during the Li uptake/release process cannot be effectively restrained on the cathode side. Thus, the shuttle effect of Se is not eliminated, which deteriorates the cycling performance of the Se cathode. To address these issues, encapsulation of Se molecules into a conductive porous carbon matrix may greatly improve the electrochemical performance of Se. However, this assumption has not yet been demonstrated, and the mechanism of the electrochemical reaction between Se molecules and Li remains unclear to date. Herein, we report a Se composite cathode material, in which Se is confined as cyclic Se8 molecules in the mesopores of an ordered mesoporous carbon (CMK-3) matrix. When assembled into Li–Se batteries with the water-soluble binder sodium alginate (SA), the Se/CMK-3 composite exhibits novel electrochemical behavior with a single plateau in the discharge/charge process. Data from ex situ Raman and X-ray diffraction (XRD) analysis suggest that this behavior is due to the conversion of cyclic Se8 molecules into chain-like Sen molecules in the carbon channels. Given the high electrochemical activity of the chain-like Sen molecules and the strong interaction between them and the carbon mesopores, this Se cathode shows a high capacity that approaches the theoretical value of Se, and exhibits favorable capacity retention upon cycling. The Se/CMK-3 composite was synthesized through a facile melt-diffusion process from a ball-milled mixture of [*] C.-P. Yang, S. Xin, Dr. Y.-X. Yin, H. Ye, J. Zhang, Prof. Y.-G. Guo CAS Key Laboratory of Molecular Nanostructure and Nanotechnology, and Beijing National Laboratory for Molecular Sciences, Institute of Chemistry, Chinese Academy of Sciences (CAS) Beijing 100190 (P. R. China) E-mail: ygguo@iccas.ac.cn

Sulfur Encapsulated in Graphitic Carbon Nanocages for High-Rate and Long-Cycle Lithium–Sulfur Batteries

Hybrid sp2 carbon with a graphene backbone and graphitic carbon nanocages (G-GCNs) is demonstrated as an ideal host for sulfur in Li-S batteries, because it serves as highly efficient electrochemical nanoreactors as well as polysulfides reservoirs. The as-obtained S/(G-GCNs) with high S content exhibits superior high-rate capability (765 mA h g-1 at 5 C) and long-cycle life over 1000 cycles.

Insight into the effect of boron doping on sulfur/carbon cathode in lithium-sulfur batteries.

To exploit the high energy density of lithium-sulfur batteries, porous carbon materials have been widely used as the host materials of the S cathode. Current studies about carbon hosts are more frequently focused on the design of carbon structures rather than modification of its properties. In this study, we use boron-doped porous carbon materials as the host material of the S cathode to get an insightful investigation of the effect of B dopant on the S/C cathode. Powder electronic conductivity shows that the B-doped carbon materials exhibit higher conductivity than the pure analogous porous carbon. Moreover, by X-ray photoelectron spectroscopy, we prove that doping with B leads to a positively polarized surface of carbon substrates and allows chemisorption of S and its polysulfides. Thus, the B-doped carbons can ensure a more stable S/C cathode with satisfactory conductivity, which is demonstrated by the electrochemical performance evaluation. The S/B-doped carbon cathode was found to deliver much higher initial capacity (1300 mA h g(-1) at 0.25 C), improved cyclic stability, and rate capability when compared with the cathode based on pure porous carbon. Electrochemical impedance spectra also indicate the low resistance of the S/B-doped C cathode and the chemisorption of polysulfide anions because of the presence of B. These features of B doping can play the positive role in the electrochemical performance of S cathodes and help to build better Li-S batteries.

Subzero‐Temperature Cathode for a Sodium‐Ion Battery

A subzero-temperature cathode material is obtained by nucleating cubic prussian blue crystals at inhomogeneities in carbon nanotubes. Due to fast ionic/electronic transport kinetics even at -25 °C, the cathode shows an outstanding low-temperature performance in terms of specific energy, high-rate capability, and cycle life, providing a practical sodium-ion battery powering an electric vehicle in frigid regions.

Electrochemical (De)Lithiation of 1D Sulfur Chains in Li–S Batteries: A Model System Study

In contrast to the extensive studies of the electrochemical behavior of conventional cyclic S8 molecules in Li-S batteries, there has been hardly any investigation of the electrochemistry of S chains. Here we use S chains encapsulated in single- and double-walled carbon nanotubes as a model system and report the electrochemical behavior of 1D S chains in Li-S batteries. An electrochemical test shows that S chains have high electrochemical activity during lithiation and extinctive electrochemistry compared with conventional S8. The confined steric effect provides Li(+) solid-phase diffusion access to insert/egress reactions with S chains. During lithiation, the long S chains spontaneously become short chains, which show higher discharge plateaus and better kinetics. The unique electrochemistry of S chains supplements the existing knowledge of the S cathode mechanism and provides avenues for rational design of S cathode materials in Li-S batteries.

Elemental Selenium for Electrochemical Energy Storage.

To meet the increasing demand for electrochemical energy storage with high energy density, elemental Se is proposed as a new attractive candidate with high volumetric capacity density similar to that of S. Se is chemically and electrochemically analogous to S to a large extent but is saliently featured owing to its semiconductivity, compatibility with carbonate-based electrolytes, and activity with a Na anode. Despite only short-term studies, many advanced Se-based electrode materials have been developed for rechargeable Li batteries, Na batteries, and Li ion batteries. In this Perspective, we review the advances in Se-based energy storage materials and the challenges of Li-Se battery in both carbonate-based and ether-based electrolytes. We also discuss the rational design strategies for future Se-based energy storage systems based on the strengths and weaknesses of Se.

Graphitized Carbon Fibers as Multifunctional 3D Current Collectors for High Areal Capacity Li Anodes

The Li metal anode has long been considered as one of the most ideal anodes due to its high energy density. However, safety concerns, low efficiency, and huge volume change are severe hurdles to the practical application of Li metal anodes, especially in the case of high areal capacity. Here it is shown that that graphitized carbon fibers (GCF) electrode can serve as a multifunctional 3D current collector to enhance the Li storage capacity. The GCF electrode can store a huge amount of Li via intercalation and electrodeposition reactions. The as-obtained anode can deliver an areal capacity as high as 8 mA h cm-2 and exhibits no obvious dendritic formation. In addition, the enlarged surface area and porous framework of the GCF electrode result in lower local current density and mitigate high volume change during cycling. Thus, the Li composite anode displays low voltage hysteresis, high plating/stripping efficiency, and long lifespan. The multifunctional 3D current collector promisingly provides a new strategy for promoting the cycling lifespan of high areal capacity Li anodes.

Hierarchically micro/mesoporous activated graphene with a large surface area for high sulfur loading in Li-S batteries

A hierarchically micro/mesoporous a-MEGO with a high surface area (up to 3000 m2 g−1) and large pore volume (up to 2.14 cm3 g−1) was utilized as a superior carbon host material for high sulfur loading towards advanced Li–S batteries.