Recent progress in fluorinated electrolytes for improving the performance of Li–S batteries

Lithium–sulfur(Li–S) batteries represent a "beyond Li-ion" technology with low cost and high theoretical energy density and should fulfill the ever-growing requirements of electric vehicles and stationary energy storage systems. However, the sulfur-based conversion reaction in conventional liquid electrolytes results in issues like the so-called shuttle effect of polysulfides and lithium dendrite growth, which deteriorate the electrochemical performance and safety of Li–S batteries. Optimization of conventional organic solvents(including ether and carbonate) by fluorination to form fluorinated electrolytes is a promising strategy for the practical application of Li–S batteries. The fluorinated electrolytes, owing to the high electronegativity of fluorine, possesses attractive physicochemical properties, including low melting point,high flash point, and low solubility of lithium polysulfide, and can form a compact and stable solid electrolyte interphase(SEI) with the lithium metal anode. Herein, we review recent advancements in the development of fluorinated electrolytes for use in Li–S batteries. The effect of solvent molecular structure on the performance of Li–S batteries and the formation mechanism of SEI on the cathode and anode sides are analyzed and discussed in detail. The remaining challenges and future perspectives of fluorinated electrolytes for Li–S batteries are also presented.     

Nanocarbons and their hybrids as catalysts for non-aqueous lithium–oxygen batteries

Rechargeable lithium-oxygen(Li–O_2) batteries have been considered as the most promising candidates for energy storage and conversion devices because of their ultra high energy density. Until now, the critical scientific challenges facing Li–O_2batteries are the absence of advanced electrode architectures and highly efficient electrocatalysts for both oxygen reduction reaction(ORR) and oxygen evolution reaction(OER), which seriously hinder the commercialization of this technology. In the last few years, a number of strategies have been devoted to exploring new catalysts with novel structures to enhance the battery performance. Among various of oxygen electrode catalysts, carbon-based materials have triggered tremendous attention as suitable cathode catalysts for Li–O_2batteries due to the reasonable structures and the balance of catalytic activity, durability and cost. In this review, we summarize the recent advances and basic understandings related to the carbon-based oxygen electrode catalytic materials, including nanostructured carbon materials(one-dimensional(1D) carbon nanotubes and carbon nanofibers, 2D graphene nanosheets, 3D hierarchical architectures and their doped structures), and metal/metal oxide-nanocarbon hybrid materials(nanocarbon supporting metal/metal oxide and nanocarbon encapsulating metal/metal oxide). Finally, several key points and research directions of the future design for highly efficient catalysts for practical Li–O_2batteries are proposed based on the fundamental understandings and achievements of this battery field.     

Recent advances in chemical adsorption and catalytic conversion materials for Li–S batteries

Owing to their low cost, high energy densities, and superior performance compared with that of Li-ion batteries, Li–S batteries have been recognized as very promising next-generation batteries. However, the commercialization of Li–S batteries has been hindered by the insulation of sulfur, significant volume expansion, shuttling of dissolved lithium polysulfides(Li PSs), and more importantly, sluggish conversion of polysulfide intermediates. To overcome these problems, a state-of-the-art strategy is to use sulfur host materials that feature chemical adsorption and electrocatalytic capabilities for Li PS species. In this review, we comprehensively illustrate the latest progress on the rational design and controllable fabrication of materials with chemical adsorbing and binding capabilities for Li PSs and electrocatalytic activities that allow them to accelerate the conversion of Li PSs for Li–S batteries. Moreover, the current essential challenges encountered when designing these materials are summarized, and possible solutions are proposed. We hope that this review could provide some strategies and theoretical guidance for developing novel chemical anchoring and electrocatalytic materials for high-performance Li–S batteries.     

The recent progress of pitch-based carbon anodes in sodium-ion batteries

Sodium-ion batteries(SIBs)have attracted significant attentions as promising alternatives to lithium-ion batteries for large-scale energy storage applications.Here carbon materials are considered as the most competitive anodes for SIBs based on their low-cost,abundant availability and excellent structural stability.Pitch,with high carbon content and low cost,is an ideal raw precursor to prepare carbon materials for large-scale applications.Nevertheless,the microstructures of pitch-based carbon are highly ordered with smaller interlayer distances,which are unfavorable for Na ion storage.Many efforts have been made to improve the sodium storage performance of pitch-based carbon materials.This review summarizes the recent progress about the application of pitch-based carbons for SIBs anodes in the context of carbon’s morphology and structure regulation strategies,including morphology adjustment,heteroatoms doping,fabricating heterostructures,and the increase of the degree of disorder.Besides,the advantages,present challenges,and possible solutions to current issues in pitch-based carbon anode are discussed,with the highlight of future research directions.This review will provide a deep insight into the development of low-cost and high-performance pitch-based carbon anode for SIBs.     

Failure analysis of pouch-type Li–O2 batteries with superior energy density

Li–O2 batteries have attracted significant interest in the past decade owing to their superior high specific energy density in contrast to conventional lithium ion batteries.An 8.7-Ah Li–O2 pouch cell with768.5 Wh kg^-1 was fabricated and characterized in this investigation and the factors that influenced the electrochemical performance of the Li–O2 pouch cell were studied.In contrast to coin/Swagelok-type Li–O2 cells,it was demonstrated that the high-loading air electrode,pulverization of the Li anode,and the large-scale inhomogeneity of the large pouch cell are the major reasons for the failure of Li–O2 batteries with Ah capacities.In addition,safety tests of large Li–O2 pouch cells were conducted for the first time,including nail penetration,crushing,and thermal stability.It was indicated that a self-limiting mechanism is a key safety feature of these batteries,even when shorted.In this study,Li–O2 batteries were investigated in a new size and capacity-scale,which may provide useful insight into the development of practical pouch-type Li–O2 batteries.     

An integrated approach to improve the performance of lean–electrolyte lithium–sulfur batteries

While the sulfur conversion reaction kinetics in Li–S batteries is nowadays improved by the use of appropriate electrocatalysts,it remains a challenge for the batteries to perform well under the lean electrolyte condition where polysulfide shuttle,electrode passivation and the loss of electrolyte due to side reactions,are aggravated.These challenges are addressed in this study by the tandem use of a polysulfide conversion catalyst and a redox–targeting mediator in a gel sulfur cathode.Specifical...     

Heteroatom dopant strategy triggered high-potential plateau to non-graphitized carbon with highly disordered microstructure for high-performance sodium ion storage

Non-graphitized carbon(NGC) has been extensively utilized as carbonaceous anode in sodium-ion batteries(SIBs). However, more optimization to achieve competitive capacity and stability is still challenging for SIBs. In the study, the dopant strategy is utilized to construct nitrogen/sulfur-doped non-graphitized carbon(N-NGC or S-NGC) shell decorated on three-dimensional graphene foam(GF) as a self-support electrode. The highly disordered microstructures of heteroatom doped carbons are produced by...     

Hierarchical N-doped carbon nanocages/carbon textiles as a flexible O2 electrode for Li–O2 batteries

The conventional Li–O2 battery(LOB)has hardly been considered as a next-generation flexible electronics thus far,since it is bulk,inflexible and limited by the absence of an adjustable cell configuration.Here,we present a flexible Li–O2 cell using N-doped carbon nanocages grown onto the carbon textiles(NCNs/CTs)as a self-standing and binder-free O2 electrode.The highly flexible NCNs/CTs exhibits an excellent mechanic durability,a promising catalytic activity towards the ORR and OER,a considerable cyclability of more than 70 cycles with an overpotential of 0.36 V on the 1 stcycle at a constant current density of 0.2 m A/cm2,a good rate capability,a superior reversibility with formation and decomposition of desired Li2 O2,and a highly electrochemical stability even under stringent bending and twisting conditions.Our work represents a promising progress in the material development and architecture design of O2 electrode for flexible LOBs.     

Bimetallic Ni–Co MOF@PAN modified electrospun separator enhances high-performance lithium-sulfur batteries

Lithium–sulfur(Li–S) batteries with high energy density are considered promising energy storage devices for the next generation. Nevertheless, the shuttle effect and the passive layer between the separator and the electrodes still seriously affect the cycle stability and life. Herein, a bimetallic Ni–Co metal–organic framework(MOF) with adsorption and catalytic synergism for polysulfides was successfully synthesized as an electrospinning separator sandwich for Li–S batteries. Introducing porous ...     

Modified carbon cloth as positive electrode with high electrochemical performance for vanadium redox flow batteries

Carbon cloth modified by hydrothermal treatment in ammonia water is developed as the positive electrode with high electrochemical performance for vanadium redox flow batteries.The SEM shows that the treatment has no obvious influence on the morphology of carbon cloth.XPS measurements indicate that the nitrogenous functional groups can be introduced on the surface of carbon cloth successfully.The electrochemical performance of V（IV）/V（V） redox couple on the prepared electrode is evaluated with cyclic voltammetry and linear sweep voltammetry measurements.The N-doped carbon cloth exhibits outstanding electrochemical activity and reversibility toward V（IV）/V（V） redox couple.The rate constant of V（IV）/V（V） redox reaction on carbon cloth can increase to 2.27 × 10^-4cm/s from 1.47 × 10^-4cm/s after nitrogen doping.The cell using N-doped carbon cloth as positive electrode has larger discharge capacity and higher energy efficiency compared with the cell using pristine carbon cloth.The average energy efficiency of the cell using N-doped carbon cloth for 50 cycles at 30 m A/cm² is 87.8%,4.3% larger than that of the cell using pristine carbon cloth.It indicates that the N-doped carbon cloth has a promise application prospect in vanadium redox flow batteries.     

Recent progress on the recycling technology of Li-ion batteries

Lithium-ion batteries(LIBs)have been widely applied in portable electronic devices and electric vehicles.With the booming of the respective markets,a huge quantity of spent LIBs that typically use either LiFePO₄ or Li N_xCo_yMn_zO₂ cathode materials will be produced in the very near future,imposing significant pressure for the development of suitable disposal/recycling technologies,in terms of both environmental protection and resource reclaiming.In this review,we firstly do a comprehensive summary of the-state-of-art technologies to recycle Li N_xCo_yMn_zO₂ and LiFePO₄-based LIBs,in the aspects of pretreatment,hydrometallurgical recycling,and direct regeneration of the cathode materials.This closed-loop strategy for cycling cathode materials has been regarded as an ideal approach considering its economic benefit and environmental friendliness.Afterward,as for the exhausted anode materials,we focus on the utilization of exhausted anode materials to obtain other functional materials,such as graphene.Finally,the existing challenges in recycling the LiFePO₄ and Li N_xCo_yMn_zO₂ cathodes and graphite anodes for industrial-scale application are discussed in detail;and the possible strategies for these issues are proposed.We expect this review can provide a roadmap towards better technologies for recycling LIBs,shed light on the future development of novel battery recycling technologies to promote the environmental benignity and economic viability of the battery industry and pave way for the large-scale application of LIBs in industrial fields in the near future.     

All-solid-state flexible asymmetric supercapacitors with high energy and power densities based on NiCo_2S_4@MnS and active carbon

Electrode material based on a novel core–shell structure consisting of NiCo_2S_4(NCS) solid fiber core and Mn S(MS) sheet shell(NCS@MS) in situ grown on carbon cloth(CC) has been successfully prepared by a simple sulfurization-assisted hydrothermal method for high performance supercapacitor. The synthesized NiCo_2S_4@Mn S/CC electrode shows high capacitance of 1908.3 F g~(-1) at a current density of 0.5 A g~(-1) which is higher than those of NiCo_2S_4 and Mn S at the same current density. A flexible all-solid-state asymmetric supercapacitor(ASC) is constructed by using NiCo_2S_4@Mn S/CC as positive electrode, active carbon/CC as negative electrode and KOH/poly(vinyl alcohol)(PVA) as electrolyte. The optimized ASC shows a maximum energy density of 23.3 Wh kg~(-1) at 1 A g~(-1), a maximum power density of about7.5 kw kg~(-1) at 10 A g~(-1) and remarkable cycling stability. After 9000 cycles, the ASC still exhibited67.8% retention rate and largely unchanged charge/discharge curves. The excellent electrochemical properties are resulted from the novel core–shell structure of the NiCo_2S_4@Mn S/CC electrode, which possesses both high surface area for Faraday redox reaction and superior kinetics of charge transport. The NiCo_2S_4@Mn S/CC electrode shows a promising potential for energy storage applications in the future.     

Recent advances in electrospun electrode materials for sodium-ion batteries

Sodium-ion batteries(SIBs)have been considered as an ideal choice for the next generation large-scale energy storage applications owing to the rich sodium resources and the analogous working principle to that of lithium-ion batteries(LIBs).Nevertheless,the larger size and heavier mass of Na⁺ion than those of Li⁺ion often lead to sluggish reaction kinetics and inferior cycling life in SIBs compared to the LIB counterparts.The pursuit of promising electrode materials that can accommodate the rapid and stable Na-ion insertion/extraction is the key to promoting the development of SIBs toward a commercial prosperity.One-dimensional(1 D)nanomaterials demonstrate great prospects in boosting the rate and cycling performances because of their large active surface areas,high endurance for deformation stress,short ions diffusion channels,and oriented electrons transfer paths.Electrospinning,as a versatile synthetic technology,features the advantages of controllable preparation,easy operation,and mass production,has been widely applied to fabricate the 1 D nanostructured electrode materials for SIBs.In this review,we comprehensively summarize the recent advances in the sodium-storage cathode and anode materials prepared by electrospinning,discuss the effects of modulating the spinning parameters on the materials’micro/nano-structures,and elucidate the structure-performance correlations of the tailored electrodes.Finally,the future directions to harvest more breakthroughs in electrospun Na-storage materials are pointed out.     

Perspective of alkaline zinc-based flow batteries

Energy storage technologies have been identified as the key in constructing new electric power systems and achieving carbon neutrality, as they can absorb and smooth the renewables-generated electricity. Alkaline zinc-based flow batteries are well suitable for stationary energy storage applications, since they feature the advantages of high safety, high cell voltage and low cost. Currently, many alkaline zinc-based flow batteries have been proposed and developed, e.g., the alkaline zinc–iron flo...     

Li–air batteries:air stability of lithium metal anodes

Aprotic rechargeable lithium–air batteries(LABs) with an ultrahigh theoretical energy density(3,500 Wh kg^-1) are known as the‘holy grail’ of energy storage systems and could replace Li-ion batteries as the next-generation high-capacity batteries if a practical device could be realized. However, only a few researches focus on the battery performance and reactions in the ambient air environment, which is a major obstacle to promote the practical application of LABs. Here, we have summar...     

Preparation and Characterization of Self-Supporting Flexible Nitrogen-Doped Carbon Fabric Electrode北大核心CSCD

With the wide applications of intelligent wearable devices in various fields, developing a new generation of flexible energy storage devices has become a major challenge for the current technology. As a wide application of wearable flexible substrate, cotton fabric has the advantages over low price, non-toxic and environmental friendly, but the poor conductivity becomes a major problem limiting its development. As a nitrogen-containing conducting polymer, polypyrrole is traditionally used as electrode materials, but poor mechanical performance and cycle stability severely limit its application in electrode materials. In this article, a self-supporting flexible nitrogen-doped carbon fabric electrode was prepared by in situ polymerization-high temperature calcination method using cotton as a substrate and polypyrrole as a nitrogen source. The high temperature carbonization transformed the non-conductive cotton fabric into a good conductive carbon fabric while retaining its original three-dimensional structure and the nitrogen was mixed into carbon materials at the same time. The structure was characterized by Fourier infrared spectroscopy, specific surface area test, scanning electron microscopy and X-ray photoelectron spectroscopy. The results demonstrated that the cotton fiber was uniformly coated by polypyrrole that was subsequently carbonized into nanocarbon, the specific surface area of the obtained nitrogen-doped carbon (N-CT) electrode was 495.0 m2·g-1and the nitrogen content was 2.26%. The electrochemical performance test showed that the N-CT electrode had a capacitance of 256.2 F·g-1at a current density of 0.5 A·g-1. The stability test revealed that the capacitance retention was 98.3% and the coulomb effciency was about 98.8% after 5000 charge-discharge cycles. Meanwhile, the N-CT electrode exhibited good flexibility and mechanical properties. © Journal of Electrochemistry 2018.     

Promise and challenge of vanadium-based cathodes for aqueous zinc-ion batteries

Aqueous zinc-ion batteries(ZIBs)have got wide attention with the increasing demands for energy resource recently.It has a number of merits compared with lithium-ion batteries,such as enhanced safety,low cost and environmental friendliness.Vanadium-based materials have been developed to serve as the cathodes of ZIBs for many years.But there are also some challenges to construct high performance ZIBs in the future.Herein,we reviewed the research progress of vanadium-based cathodes and discussed the energy storage mechanisms in ZIBs.In addition,we summarized the major challenges faced by vanadium-based cathodes and the corresponding ways to improve electrochemical performance of ZIBs.Finally,some excellent vanadium-based cathodes are summarized to pave the way for future research in ZIBs.     

TiN nanocrystal anchored on N-doped graphene as effective sulfur hosts for high-performance lithium-sulfur batteries

Lithium-sulfur(Li-S)batteries have become prospective candidates for next-generation energy storage owing to the high energy density and low cost.However,the sluggish kinetics of the electrochemical reaction and shuttle effect result in a rapid capacity decay.Herein,a titanium nitride nanocrystal/Ndoped graphene(TiN@NG)composite is developed to host elemental sulfur.The TiN nanoparticles decorated on graphene sheets attract Li polysulfides(LiPSx)and catalyze the electrochemical reduction and oxidation of LiPSx in the discharge and charge processes,respectively.These two effects effectively restrain the dissolution of the LiPSx and accelerate the electrochemical reactions,thereby,alleviating the shuttle effect.As a result,the cathode composed of TiN@NG/S delivers a remarkable reversible capacity(1390 mA h g^-1 at 0.1 C)and excellent cycling performance(730 mA h g^-1 after 300 cycles).We believe that this work can bring some inspiration for designing high-performance Li-S batteries.     

Cryoactivated proton-involved redox reactions enable stable-cycling fiber cooper metal batteries operating at -50 °C

Fiber-shaped batteries that feature outstanding flexibility, light weight, and wovenability are extremely attractive for powering smart wearable electronic textiles, which further stimulates their demand in extreme environments. However, there are rare reports on ultralow-temperature fiber batteries to date.This is mainly attributed to the poor conductivity of electrodes and freezing of electrolytes that restrain their satisfactory flexible operation in cold environments. Herein, we propose a fi...     

Graphene oxide:An emerging electromaterial for energy storage and conversion

This paper gives a comprehensive review of the recent progress on electrochemical energy storage devices using graphene oxide(GO).GO,a single sheet of graphite oxide,is a functionalised graphene,carrying many oxygen-containing groups.This endows GO with various unique features for versatile applications in batteries,capacitors and fuel cells.Specific applications are considered principally including use in electrodes as the active materials to enhance the performance or as substrates to diversify the structures,in solid-state electrolytes and membranes to improve the ionic conductivity and mechanical properties,and in interlayers to protect the electrodes,membranes or current collectors.Furthermore,the challenges and future prospects are discussed in the paper for encouraging further research and development of GO applications.