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Funding Information: This work has been funded by the Academy of Finland Project (Grant No. 348403), the Start-up Funding offered by Ningbo University of Technology to J.Y., and the Start-up Package of T10108 Professorship offered by Aalto University to Y.L. Q.Q. and P.Y. acknowledge financial support from the China Scholarship Council (Grant Nos. 201906150134 and 202006120046). Publisher Copyright: © 2022 The Authors. Published by American Chemical Society. Nonaqueous redox flow batteries (NARFBs) hold potential application as an electricity energy storage for intermittent renewable energy and can operate with high voltage and energy density. However, their further development is impeded by lack of a proper membrane. Herein, a flexible freestanding anionic metal-organic framework (MOF)-based membrane is prepared through a solution casting method, with an anionic MOF (UiO-66-SO3Li) and polyvinylidene fluoride. The prepared membrane shows an impressive ionic selectivity (37.6) of Li+ to N-(ferrocenylmethyl)-N,N-dimethyl-N-ethylammonium (Fc1N112+) ions and high ionic conductivity. Benefiting from the unique micropore structure of MOF and the anionic transport channels of Li+ across the membrane, the resultant Li-based hybrid NARFB delivers a high-capacity retention (99.95% per cycle) over 500 cycles with a well-assembled stable interphase after long time lithium plating/stripping, which decreases the voltage efficiency during the cycling. Calculations reveal that the membrane easily desolvates Li+ in the unique micropore structure of MOF before Li deposition occurs, which suppresses parasitic reaction and accelerates Li uniform deposition. This work provides a viable method to design bifunctional NARFB membranes which achieve ion sieving and ion exchange functions.

Funding Information: This work was supported by the National Natural Science Foundation of China (Grant no. 21636007 ), the Start-up Foundation offered by Ningbo University of Technology to J.S. Yuan, and the Start-up Package of T10108 Professorship offered by Aalto University to Y.D. Li. Publisher Copyright: © 2022 Elsevier Ltd Redox flow battery (RFB) has been widely considered to be one of the most promising grid-scale energy-storage technology. The membrane, namely separator, serves as preventing the crossover of the positive and negative active species, while facilitating the transport of the supporting electrolyte ions, is crucial to achieve a high performance and a long-term stability for an RFB. Advances in RFBs require high-performance and low-cost membranes with high ion-selective transport for the application of large-scale energy storage. Two-dimensional (2D) materials have emerged as promising functional materials owing to their atomic-scale thickness and unique physical/chemical properties, which have great potential in the application of RFB membrane. Focusing on the recent state-of-the-art of 2D materials, in this mini review, various 2D materials applied in the membrane for RFB are briefly introduced. A perspective on the near-future developments of 2D materials in RFB membranes is presented.

Continuous fast pyrolysis is developed for in situ synthesis of ultra‐small metal oxide nanoparticles embedded into three‐dimensional macroporous carbon matrix as demonstrated by the TiO2/carbon nanohybrid. The TiO2 nanoparticles with the average size of 4.6 nm ± 0.6 nm are uniformly distributed in the in situ generated macroporous carbon matrix. When evaluated as an anode in a lithium‐ion battery, the macroporous TiO2/C nanohybrid exhibits a reversible capacity of 483 mAh g–1 after 500 cycles at a current density of 67 mA g–1, which is 3.6 times higher than that of the TiO2/C calcined in a conventional batchwise way. Besides, the capacity retains 93 mAh g–1 at a high current density of 670 mA g–1. It reveals that the continuous fast pyrolysis is an efficient method to fabricate carbon composition based metal oxides as lithium‐ion battery anode materials.

Micro‐sized porous silicon‐based anode materials gain much interest due to good cycling stability, high rate performance, reasonable tap density and low processing cost. Self‐templating process is developed to construct micro‐sized macro‐/mesoporous silicon through magnesiothermic reduction of Stöber silica. The size of the silica particles plays a vital role in the structure control of the porous silicon. In this work, silica particles with a diameter of 130 nm are used as templates to guide the synthesis of micro‐sized macro‐/mesoporous silicon. The magnesiothermic reduction temperature is varied in a systematic way to reveal the self‐templating mechanism comprehensively. It is found that the silica particles with small diameter of 130 nm still exercise the self‐templating effect during the magnesiothermic reduction process in the temperature range of 700 to 900°C. Based on the experimental results, the structure‐property correlation of the porous silicon anode is unveiled. Improved electrochemical performance is demonstrated by the porous silicon compared to the commercial nano‐sized silicon.

Ultrafine SnO2/Sn nanoparticles encapsulated into the adjustable mesoporous carbon matrix has been successfully fabricated by a facile route. The mesoporous carbon effectively improve the conductivity of the SnO2/Sn, prevent the aggregation, accommodate the strain of volume change and provide high interface area with the electrolyte, thus resulting in excellent cycling performance. A reversible capacity of 1105 mAh g–1 still retained after 290 cycles at 200 mA g–1, and the capacity still can keep at 107 mAh g–1 at high current density of 10 A g–1. The porous structures by the in situ SiOx template provide an appropriate specific surface area, which contributes to a relatively high capacitive contribution.

Highlights The PEDOT:PSS flexible electrodes with a unique CF3SO3H treatment exhibited high electrical characteristics and stability.An energy level tuning effect was induced to create a suitable work function.Flexible organic solar cells yielded a record-high efficiency of 16.61%, a high flexibility, and a good thermal stability. Electronic supplementary material The online version of this article (10.1007/s40820-020-00566-3) contains supplementary material, which is available to authorized users., Nonfullerene organic solar cells (OSCs) have achieved breakthrough with pushing the efficiency exceeding 17%. While this shed light on OSC commercialization, high-performance flexible OSCs should be pursued through solution manufacturing. Herein, we report a solution-processed flexible OSC based on a transparent conducting PEDOT:PSS anode doped with trifluoromethanesulfonic acid (CF3SO3H). Through a low-concentration and low-temperature CF3SO3H doping, the conducting polymer anodes exhibited a main sheet resistance of 35 Ω sq−1 (minimum value: 32 Ω sq−1), a raised work function (≈ 5.0 eV), a superior wettability, and a high electrical stability. The high work function minimized the energy level mismatch among the anodes, hole-transporting layers and electron-donors of the active layers, thereby leading to an enhanced carrier extraction. The solution-processed flexible OSCs yielded a record-high efficiency of 16.41% (maximum value: 16.61%). Besides, the flexible OSCs afforded the 1000 cyclic bending tests at the radius of 1.5 mm and the long-time thermal treatments at 85 °C, demonstrating a high flexibility and a good thermal stability. Electronic supplementary material The online version of this article (10.1007/s40820-020-00566-3) contains supplementary material, which is available to authorized users.

TiO2/SiOx/carbon nanohybrid consisting of super-small sized TiO2 and SiOx nanoparticles is in situ formed within the in situ formed carbon matrix using difunctional methacrylate monomers as solvent and carbon source. The relative composition of TiO2 and SiOx is systematically tuned by varying the feeding mass ratio of the precursors (TEOS/TTIP) and HF etching treatment after the carbonization process. The super-small sized TiO2 and SiOx nanoparticles are well intermixed with each other and homogeneously dispersed throughout the carbon matrix, where a good control over crystallinity, morphology, and microstructure of the nanohybrids is achieved. Synergistic effects are demonstrated from both TiO2 and SiOx regarding the increased reversible capacity from the SiOx phase and maintenance of good cyclic stability by the TiO2 component when being used in lithium-ion batteries. A good balance is achieved in terms of reversible capacity, capacity retention, and rate performance in the TiO2/SiO2/C nanohybrid prepared with the TEOS/TTIP mass ratio of 1.0. The reversible capacities are improved by around two times compared to the SiOx free sample with a good capacity retention of 78 %, which exhibits good rate capability at the current densities up to 3350 mA g−1 as well.

Blending different cathode materials to construct composites can be in compatibility with their individual advantages to exhibit better electrochemical performances. In this study, we blend Li-rich and classical layered cathode materials to realize the suppression of voltage decay. The electrochemical results indicate that the composite electrodes show better capacity retention exceeding 90% after 100 cycles. More importantly, the cumulative voltage decay of the composite materials with different ratio are 280 mV and 140 mV for 100 cycles’ duration, which are much lower than that of the single component with 390 mV in Li-rich layered cathode, respectively. Based on the ex situ X-ray diffraction, the blended composites show the structural origin of synergy effect, which are like a pair of parallel resistors to reciprocally buffer the crystal structure change during the charge and discharge process between Li-rich and classical layered cathode materials. Blending of layered cathode oxide materials with the synergy effect provide a possible approach to achieve more excellent electrochemical performances in lithium-ion batteries.

Li-rich layered oxides are highlighted as promising candidates for the next-generation cathode materials in Li-ion batteries, but suffer from poor cycling stability and voltage fading during the cycling process. Currently, less efforts are devoted to addressing these issues through exploring novel binders. In this work, we explore an aqueous binder of xanthan gum with double helix superstructure containing abundant charged functional groups. This unique structure is beneficial to the occurrence of significant mechanical interlocking effect and formation of chemical bond with particles’ surface, which can effectively suppress electrode exfoliation, particle pulverization and structural degradation during cycling. As a consequence, the electrode with xanthan gum still delivers the discharge capacity of 275.6 mAh g−1 with the retention of 98.4% after 200 cycles at 0.1C rate. Accordingly, the mid-point discharge voltage remains 87% (about 2.3 mV/per cycle drop). The current study provides a useful insight into how to design and develop superior binders based on charged double-helix superstructure for potential low-cost and environmentally friendly aqueous processing of high energy density Li-ion batteries.

SiOx due to their high theoretical specific capacity and moderate volume expansion, have been considered as alternative anode materials for next-generation Li-ion batteries. However, the electronic isolate effect originated from the huge volume variation during the repeated cycling processes results in poor cycling performance and low reversible capacity, as well as inferior rate performance. Here, we report a facile and catalyst-free synthetic route to prepare carbon coated Si nanowires connected SiOx anode materials which is supposed to address these problems. Micrometer-sized Si nanowires in-situ grow on the surface of micro-SiO at optimized temperature without catalyst assistance, following a CVD process for carbon coating. The carbon coated Si nanowires not only act as electrochemical active materials, but also efficiently accommodate the electronic isolate effect of micro-SiO particles, thus remarkably improving the electrochemical performance. As a result, the carbon coated Si nanowires connected SiOx anode exhibits high reversible capacity of ∼750 and 617.5 mAh g−1 at 0.5C and 1C (1C = 1500 mA g−1), respectively. Meanwhile, an ultrahigh capacity retention of >92% after 300 cycles is achieved at a high area mass loading of 1.8 mg cm−2.

Silicon (Si) is regarded as one of the most promising lithium-ion battery anodes to replace commercial graphite due to its exceptional theoretical capacity, appropriate voltage profile, environmental friendliness and natural abundance. It is crucial to develop effective strategies to improve the cyclic performance of the Si anodes. A new concept to synthesize Si/carbon composite with three dimensional (3D) hierarchical macro-/mesoporous structure is reported. Stober silica (SiO2) particles are used as templating agent and precursor for Si simultaneously. Unlike conventional work reported previously, here the silica particles are composited with carbon matrix before magnesiothermic reduction. Difunctional methacrylate monomers are used as solvent and carbon source coupled with a fast, environmental friendly and energy saving photo polymerization to prepare the SiO2/C composite. Based on a self-templating mechanism during the magnesiothermic reduction process, 3D hierarchical macro-/mesoporous Si is formed in situ within the carbon matrix. Compared to the Si/carbon composite composed of micro-sized Si and bare macro-/mesoporous Si, the cyclic performance is significantly improved with a reasonable mass loading density. Good rate performance is exhibited comparable to the bare porous Si. The hierarchical macro-/mesoporous structure within the carbon matrix helps to retain the porous Si structure, which effectively improves the electrochemical performance.

Gel polymer electrolytes (GPEs) have attracted ever-increasing attention in Li-ion batteries, due to their great thermal stability and excellent electrochemical performance. Here, a flexible poly(vinylidene fluoride

Antimony (Sb) has been regarded as one of the most promising anode materials for both lithium-ion batteries (LIBs) and sodium-ion batteries (SIBs) and attracted much attention in recent years. Alleviating the volumetric effect of Sb during charge and discharge processes is the key point to promote Sb-based anodes to practical applications. Carbon dioxide (CO

Intercalation transition metal oxides (ITMO) have attracted great attention as lithium-ion battery negative electrodes due to high operation safety, high capacity and rapid ion intercalation. However, the intrinsic low electron conductivity plagues the lifetime and cell performance of the ITMO negative electrode. Here we design a new carbon-emcoating architecture through single CO2activation treatment as demonstrated by the Nb2O5/C nanohybrid. Triple structure engineering of the carbon-emcoating Nb2O5/C nanohybrid is achieved in terms of porosity, composition, and crystallographic phase. The carbon-embedding Nb2O5/C nanohybrids show superior cycling and rate performance compared with the conventional carbon coating, with reversible capacity of 387 mA h g−1at 0.2 C and 92% of capacity retained after 500 cycles at 1 C. Differential electrochemical mass spectrometry (DEMS) indicates that the carbon emcoated Nb2O5nanohybrids present less gas evolution than commercial lithium titanate oxide during cycling. The unique carbon-emcoating technique can be universally applied to other ITMO negative electrodes to achieve high electrochemical performance.

Silicon is regarded as one of the most promising next generation lithium-ion battery anodes due to its exceptional theoretical capacity, appropriate voltage profile, and vast abundance. Nevertheless, huge volume expansion and drastic stress generated upon lithiation cause poor cyclic stability. It has been one of the central issues to improve cyclic performance of silicon-based lithium-ion battery anodes. Constructing hierarchical macro-/mesoporous silicon with a tunable pore size and wall thickness is developed to tackle this issue. Rational structure design, controllable synthesis, and theoretical mechanical simulation are combined together to reveal fundamental mechanisms responsible for an improved cyclic performance. A self-templating strategy is applied using Stöber silica particles as a templating agent and precursor coupled with a magnesiothermic reduction process. Systematic variation of the magnesiothermic reduction time allows good control over the structures of the porous silicon. Finite element mechanical simulations on the porous silicon show that an increased pore size and a reduced wall thickness generate less mechanical stress in average along with an extended lithiation state. Besides the mechanical stress, the evolution of strain and displacement of the porous silicon is also elaborated with the finite element simulation.

Metallic lithium, with super high theoretical specific capacity, enjoys great potential as an anode for rechargeable batteries. However, safety issues caused by lithium dendrite growth as well as limited cycling life restrict its practical application. Herein we validate that the application of a new dual-salt electrolyte composed of Lithium difluorophosphate (LiPO2F2) and lithium bis(fluorosulfony)imide (LiFSI) in the same proportion enables the improved long-term cycling performance along with high coulombic efficiency for lithium metal batteries. With 1 M LiPO2F2 and 1 M LiFSI in 1,2-dimethoxyethane as the electrolyte, a Li/Cu cell can be cycled at 1 mA for more than 300 cycles with a deposited capacity of 1.0 mAh. It also displays that a homogeneous and dendrite free solid electrolyte interphase layer is generated on the Cu electrode, which can be ascribed to the favorable stability of LiPO2F2 and high ionic conductivity of LiFSI. These results deliver perceptions for the advancement of high-performance lithium metal anode.

One of the crucial challenge for developing high safety and high voltage lithium ion batteries is to find a reliable electrolyte system. In this work, we report a kind of hybrid electrolytes, which are used for high-voltage lithium ion batteries and are expected to be able to effectively enhance the battery safety. The hybrid electrolytes are obtained by incorporating silane-Al2O3 (Al2O3-ST) into liquid electrolyte, which combines the merits of both solid electrolyte and liquid electrolyte. The Al2O3-ST nanoparticles help to increase lithium-ion transference number and to enhance battery safety, while liquid electrolyte contributes to high ionic conductivity. The cycling stability and rate capacity of LiNi0.5Mn1.5O4/Li batteries are improved by using the hybrid electrolytes. Nail-penetration tests indicate that LiNi0.6Mn0.2Co0.2O2/graphite battery with hybrid electrolyte owns obviously enhanced safety than that using traditional liquid electrolyte. This work provides new insight on electrolyte design for high-safety high-voltage lithium ion batteries.

A facile scalable synthesis of hierarchical Sb/C micro-/nanohybrid has been addressed in this work, which possesses the advantages of both micrometer and nanometer scale structures as lithium-ion battery anode. Difunctional methacrylate monomers are used as solvent and carbon source as well. Liquid precursor of antimony(III) n-butoxide is dissolved in the resin monomer solution, and further incorporated into the cross-linking polymer network via photo polymerization. Through calcination in argon/hydrogen atmosphere, antimony nanoparticles are in situ formed by carbothermal reduction, and homogeneously embedded in the in situ formed micrometer sized carbon matrix. The morphology, structure, crystallinity, spatial dispersion, composition, and electrochemical performance of the Sb/C micro-/nanohybrid are systematically investigated. The cyclic and rate performance of the Sb/C micro-/nanohybrid anode have been effectively improved compared to the pure carbon anode. A reversible capacity of 362 mAh g−1 is achieved with a reasonable mass loading density after 300 cycles at 66 mA g−1, corresponding to capacity retention of 79%. With reducing mass loading density, the reversible capacity reaches 793 mAh g−1 after 100 cycles. Moreover, the electrochemical performance of Sb/C micro-/nanohybrid as sodium-ion battery anode is also investigated in this study. Sb/C hierarchical micro-/nanohybrid lithium-ion battery anode with good cyclic stability is synthesized in a scalable way using difunctional methacrylate monomers as solvent and carbon source, where a reversible capacity of 362 mAh g−1 is achieved after 300 cycles with a reasonable mass loading density, corresponding to capacity retention of 79%

Silicon (Si) has been regarded as one of the most promising anodes for next-generation lithium-ion batteries (LIBs) due to its exceptional capacity, appropriate voltage profile, and reliable operation safety. However, poor cyclic stability and moderate rate performance have been critical drawbacks to hamper the practical application of Si-based anodes. It has been one of the central issues to develop new strategies to improve the cyclic and rate performance of the Si-based lithium-ion battery anodes. In this work, super-small metal nanoparticles (2.9 nm in diameter) are in situ synthesized and homogeneously embedded in the in situ formed nitrogen-doped carbon matrix, as demonstrated by the Si/Ag/C nanohybrid, where epoxy resin monomers are used as solvent and carbon source. With tiny amount of silver (2.59% by mass), the Si/Ag/C nanohybrid exhibits superior rate performance compared to the bare Si/C sample. Systematic structure characterization and electrochemical performance tests of the Si/Ag/C nanohybrids have been performed. The mechanism for the enhanced rate performance is investigated and elaborated. The temperature-dependent I-V behavior of the Si/Ag/C nanohybrids with tuned silver contents is measured. Based on the model, it is found that the super-small silver nanoparticles mainly increase charge carrier mobility instead of the charge carrier density in the Si/Ag/C nanohybrids. The evaluation of the total electron transportation length provided by the silver nanoparticles within the electrode also suggests significantly enhanced charge carrier mobility. The existence of tremendous amounts of super-small silver nanoparticles with excellent mechanical properties also contributes to the slightly improved cyclic stability compared to that of simple Si/C anodes.

In this work, we extracted 95% of the electrochemically available Li from LiNi0.8Co0.15Al0.05O2 (NCA) by galvanostatically charging the NCA/MCMB full cell to 4.7 V. Joint powder X-ray and neutron diffraction (XRD & ND) studies were undertaken for NCA at highly charged states at the first cycle, and discharged states at different cycles. The results indicate that the bulk structure of NCA maintains the O3 structure up to the extraction of 0.90 Li per formula unit. In addition, we found that the transition metal layer becomes more disordered along the c-axis than along the a- and b-axes upon charging. This anisotropic disorder starts to develop no later than 4.3 V on charge and continues to grow until the end of charge. As Li is re-inserted during discharge, the structure that resembles the pristine NCA is recovered. The irreversible loss of Li and the migration of Ni to the Li layer have been quantified by the joint XRD and ND refinement and the results were further verified by solid state 7Li NMR and magnetic measurements. Our work clearly demonstrates that the NCA bulk retains a robust, single phase O3 structure throughout the wide delithiation range (up to 0.9 Li per formula unit of NCA) and is suitable for higher energy density usage with proper modifications.

A new recovery method for fast and efficient selective leaching of lithium from lithium iron phosphate cathode powder is proposed. Lithium is expelled out of the Oliver crystal structure of lithium iron phosphate due to oxidation of Fe 2 + into Fe 3 + by ammonium persulfate. 99% of lithium is therefore leached at 40 °C with only 1.1 times the amount of ammonium persulfate without the help of acid treatment. The use of ammonium persulfate also avoids the necessity to remove other metal ions in the later purification process. Various characterization methods including SEM, XPS, XRD are used to explore the experimental leaching mechanism. Theoretical investigations are performed which reveals the E-pH diagram of Fe–P–Li–H2O thermodynamic equilibrium. It confirms the possibility and suggests appropriate pH range allowing direct conversion from lithium iron phosphate to iron phosphate with great energy saving and reduced use of acid and base. Based on the experimental and theoretical results, a green and efficient closed-loop recycling route for lithium iron phosphate is proposed.

Despite the promising high energy density, Li-rich layered oxides still suffer from capacity fade and voltage decay during prolonged cycling. Doping could be effective in addressing such problems, but current studies pay less attention on rhombohedral phases. To this end, Al incorporated Li 1.14 (Ni 0.136 Co 0.10 Al 0.03 Mn 0.544 )O 2 oxides are investigated. Rietveld refined X-ray diffraction and transmission electron microscope results, along with electrochemical analyses, prove the substitution of Al for Co as well as its influence mainly on rhombohedral components. With slight capacity decreases, Al doped cathodes attain superior cycling performances, presenting a capacity retention up to 94.7% as compared to 81.7% for the pristine ones after 100 cycles. Most importantly, the fatal voltage decay, is alleviated as well through the obstructed formation of spinel-like phases, which are confirmed by the ex-situ XRD and further estimated by Raman spectra. Additionally, interfaces of Al doped electrodes are also somewhat enhanced as indicated by the electrochemical impedance study. These results suggest a notable stabilization effects on host framework in Li-rich layered oxides through manipulations on rhombohedral phases.

© 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim The oxidative decomposition mechanism of fluoroethylene carbonate (FEC) used in high-voltage batteries is investigated by using density functional theory (DFT). Radical cation FEC•+ is formed from FEC by transferring one electron to electrode and the most likely decomposition products are CO2 and 2-fluoroacetaldehyde radical cation. Other possible products are CO, formaldehyde and formyl fluoride radical cations. These radical cations are surrounded by much FEC solvent and their radical center may attack the carbonyl carbon of FEC to form aldehyde and oligomers of alkyl carbonates, which is similar with the oxidative decomposition of EC. Then, our experimental result reveals that FEC-based electrolyte has rather high anodic stability. It can form a robust SEI film on the positive electrode surface, which can inhibit unwanted electrolyte solvent and LiPF6 salts decomposition, alleviate Mn/Ni dissolution and therefore, improve the coulombic efficiency and the cycling stability of high voltage LiNi0.5Mn1.5O4 positive electrodes. This work displays that FEC-based electrolyte systems have considerable potential replacement of the EC-based electrolyte for the applications in 5 V Li-ion batteries.

Lithium-rich layered oxides (LrLOs) deliver extremely high specific capacities and are considered to be promising candidates for electric vehicle and smart grid applications. However, the application of LrLOs needs further understanding of the structural complexity and dynamic evolution of monoclinic and rhombohedral phases, in order to overcome the issues including voltage decay, poor rate capability, initial irreversible capacity loss and etc. The development of aberration correction for the transmission electron microscope and concurrent progress in electron spectroscopy, have fueled rapid progress in the understanding of the mechanism of such issues. New techniques based on the transmission electron microscope are first surveyed, and the applications of these techniques for the study of the structure, migration of transition metal, and the activation of oxygen of LrLOs are then explored in detail, with a particular focus on the mechanism of voltage decay. Keywords: Lithium-ion battery, Transmission electron microscope, Lithium-rich layered oxide, Cathode material

Three dimensional (3D) porous silicon/reduced graphene oxide (Si/rGO) composites with typical networks have suffered damage during electrode preparation, which evidently affects the cycle and rate capabilities of Si/rGO anodes. Here, a controllable evaporation dry method is proposed to fabricate structure-preserved 3D porous Si/rGO anode materials by tuning the pore size distribution of the networks. As a result, after evaporation drying for 3.5 h, the optimal sample of 3D porous Si/rGO anode (denoted as Si–G-3.5) with a pore size of ∼500 nm could preserve its 3D network during the electrode preparation process. While the structures of Si/rGO composites with different drying times (denoted as Si–G-0, Si–G-2.5 and Si–G-4) failed to be preserved. Consequently, The Si–G-3.5 anode exhibits a high reversible specific capacity of 1563 mA h g−1 at 50 mA g−1, 90% capacity retention after 100 cycles and superior rate capability (955 mA h g−1 at 2 A g−1).

Substantial effort has been devoted to both scientific and technological developments of wearable, flexible, semitransparent, and sensing electronics (e.g., organic/perovskite photovoltaics, organic thin‐film transistors, and medical sensors) in the past decade. The key to realizing those functionalities is essentially the fabrication of conductive electrodes with desirable mechanical properties. Conductive polymers (CPs) of poly(3,4‐ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) have emerged to be the most promising flexible electrode materials over rigid metallic oxides and play a critical role in these unprecedented devices as transparent electrodes, hole transport layers, interconnectors, electroactive layers, or motion‐sensing conductors. Here, the current status of research on PEDOT:PSS is summarized including various approaches to boosting the electrical conductivity and mechanical compliance and stability, directly linked to the underlying mechanism of the performance enhancements. Along with the basic principles, the most cutting edge‐progresses in devices with PEDOT:PSS are highlighted. Meanwhile, the advantages and plausible problems of the CPs and as‐fabricated devices are pointed out. Finally, new perspectives are given for CP modifications and device fabrications. This work stresses the importance of developing CP films and reveals their critical role in the evolution of these next‐generation devices featuring wearable, deformable, printable, ultrathin, and see‐through characteristics.

Niobium dioxide (NbO2) features a high theoretical capacity and an outstanding electron conductivity, which makes it a promising alternative to the commercial graphite negative electrode. However, studies on NbO2 based lithium-ion battery negative electrodes have been rarely reported. In the present work, NbO2 4 nanoparticles homogeneously embedded in carbon matrix are synthesized using a dental resin monomer (bisphenol A glycidyl dimethacrylate, Bis-GMA) as solvent and carbon source and niobium ethoxide (NbETO) as the precursor. Thermal polymerization and calcination under Ar/H2 atmosphere at 900 °C are applied, to synthesize the NbO2/carbon nanohybrid in a facile scalable way. It is revealed that a low Bis-GMA/NbETO mass ratio (from 1:1 to 1:2) enables the conversion of Nb (V) to Nb (IV) due to increased porosity induced by alcoholysis reaction between the NbETO and Bis-GMA. The fundamental mechanisms responsible for the formation of NbO2 are elaborated, which involve the reduction of Nb (V) by in situ generated carbon monoxide. The as-prepared NbO2/carbon nanohybrid delivers a reversible capacity of 225 mA h g-1 after 500 cycles at 1 C rate with the Coulombic efficiency of more than 99.4 % in the cycles. Various experimental and theoretical approaches including solid state NMR, ex situ XRD, differential electrochemical mass spectrometry, and density functional theory (DFT) are utilized to understand the fundamental lithiation/delithiation mechanisms of the NbO2/carbon nanohybrid. The results suggest that the NbO2/carbon nanohybrid bearing high capacity, long cycle life and low gas-evolution is promising for lithium storage applications.

Migration of transition metal (TM) ions to tetrahedral sites plays a crucial role on structural transformation and electrochemical behaviors for Li-rich layered oxides. Here, incorporating small B3+ in the tetrahedral interstice is employed to block the migration channel of TM ions and stabilize the crystal structure. Benefiting from their good structural stability, Li-rich layered materials with B-doped Li1.198Ni0.129Co0.129Mn0.535B0.01O2 and Li1.196Ni0.127Co0.127Mn0.529B0.02O2, exhibit excellent cycling performance and voltage stability. After 51 cycles at 0.2 C, 1 mol.% boron incorporated sample can deliver 211 mAh g−1 with capacity retention of 89.9%, which is much higher than that of the undoped sample of 177 mAh g−1 with the retention of 79.2%. Moreover, the declined voltage per cycle decreases from 3.6885 mV to 2.7530 mV after 2 mol.% boron doping. XRD patterns after extended cycling verified the suppression of the structural transformation by the incorporation of boron.

Li-rich layered oxides with micro-sized primary particles usually exhibit higher pellet density and better cycling performance. However, it is often at the expense of high reversible capacity. Here, we reported a simple strategy through a new chemical lithiation with micro-sized spinel-precursors and Na 2 S 2 O 8 surface treatment to obtain micro-sized particles in the Li-rich Li 1.172 Ni 0.135 Co 0.135 Mn 0.539 O 2 oxide without compromising its discharge capacity (260 mAh/g at 0.1C). Benefited from its larger particles and lower specific surface area, the obtained micron Li-rich layered material manifests its higher pellet density (3.18 g/cm 3 ) and better cycling performance in comparison with the nano-sized Li-rich layered material. After 100 cycles at 0.1 C, it can still deliver a capacity of 192 mAh/g with retention of 74%, much higher than 167 mAh/g with retention of 67% of the nano-sized sample. Moreover, the micron Li-rich layered material also exhibits good rate performance with a capacity of 174 mAh/g at 2C benefited from the 3D Li + insertion/extraction channel of its surface spinel content. These results may provide a new insight on improving pellet density of high-performance Li-rich layered cathode materials.

A new strategy to synthesize hierarchical, porous titania/carbon (TiO2/C) hybrid microspheres via solvothermal reaction in N,N'-dimethyl formamide (DMF) has been developed. In situ formed polystyrene (PS) colloids have been used as templating agent and carbon source, through which TiO2/PS microspheres with a diameter of ca. 1 μm are built by packed TiO2 nanoparticles of tens of nanometers. The TiO2/PS microspheres are converted to TiO2/C microspheres with different amounts of carbon under controlled calcination condition. The mechanism investigation unveils that the introduction of concentrated HCl creates surface tension between PS and DMF, leading to the formation of PS colloids in solution. The solvothermal treatment further promotes the formation of PS colloids and integration of the titania nanoparticles within the PS colloids. The morphology, crystallinity, nature and content of carbon, UV-Vis absorption, carbon doping, pore size distribution, pore volume, and BET surface area of the TiO2 microspheres with different amounts of carbon have been measured. The applications of the TiO2/C hybrid microspheres as photo catalyst for water splitting and lithium-ion battery anode have been demonstrated. Superior photo catalytic activity for hydrogen conversion under both full spectrum and visible light illumination compared to commercial P25 has been observed for the TiO2/C microspheres with 2 wt% of carbon. Besides, the TiO2/C microspheres with 8 wt% of carbon as lithium-ion battery anode showed a much higher capacity than the bare TiO2 microsphere anode. The origin for the enhanced performance as photo catalyst and lithium-ion battery anode is discussed.

It is a great challenge to combine good cycling performance with high rate capability for LiMn 1–x M x PO 4 cathode materials owing to the Mn dissolution upon cycling and its low electronic/ionic conductivity. Here, we report a novel concentration-gradient structure of LiMn 0.8 Fe 0.2 PO 4 material constructed by solvothermal treatment. This material shows a linear increase of Mn concentration from the edge to the particle centre, but the inverse trend for Fe concentration, which leads to the formation of Mn-rich phase in bulk and Fe-rich phase at surface. The Fe-rich phase effectively suppresses the corrosion from the electrolyte that minimizes the Mn dissolution and also improves the electronic/ionic conductivity of the surface that decreases the cathode/electrolyte interface resistance. Consequently, this concentration-gradient material achieves superior capacity retention with 98% after 50 cycles at 1 °C even at elevated temperature, and also exhibits an excellent rate capability with the reversible capacity of 130 mA h g −1 at 5 °C rate. These results suggest that the concentration-gradient LiMn 0.8 Fe 0.2 PO 4 is an ideal type of cathode material for high performance Lithium ion batteries.

Copper sulfide (CuS) nanorods with the size of sub-10 nm are synthesized via a facile sol gel method without post thermal treatment. The as-prepared CuS nanorods are characterized by X-ray diffraction, transmission electron microscope, and energy dispersive X-ray spectroscopy as hexagonal covellite CuS. The as-prepared CuS nanorods utilized as anode material exhibit a high reversible capacity and excellent cycling stability up to 250 cycles, as well as high Coulombic efficiency. The unique structure of the CuS nanorods should be responsible for their excellent electrochemical performance. (C) 2015 Elsevier B.V. All rights reserved.

Template-free synthesis of TiO2 architectures with controlled morphology evolution has been developed through solvothermal reaction in 1,4-dioxane. By simply varying the molar ratio of the concentrated HCl over Titanium isopropoxide (TTIP) from 0 to 5.0, series of morphologies including nanoparticle-built microspheres, nanoparticle-built microspheres decorated with nanorods, nanorod cauliflowers, and nanorod dendrites have been obtained. The influence of several key factors on the morphology control of TiO2 has been systematically investigated. These parameters include the mass (molar) ratio of HCl/TTIP, solvothermal reaction temperature and time, acid species (concentrated nitric acid), and solvent type (tetrahydrofuran and 1,3-dioxane). The mechanism for the formation of the TiO2 architectures with controlled morphology evolution has been discussed. The application of the TiO2 architectures as water splitting photocatalyst and lithium–ion battery anode has been demonstrated. And the corresponding structure–property correlation has been discussed.

Silicon, as a next generation anode material, suffers from low electronic conductivity and large volume changes during the lithiation/delithiation process, resulting in very large capacity fading upon cycling. Herein, we design a novel sandwich-structured Si/C electrode formed between two conductive carbon layers. In this configuration, the bottom carbon layer functions as a buffer layer to increase the adhesion to the Cu foil and to avoid peeling-off of the active materials, whereas the top carbon layer on the electrolyte side serves as a barrier layer to prevent the electrode surface from cracking and delaminating. As expected, the sandwich-structured Si/C electrode delivers a high reversible capacity of 1230 mA h g−1 at current density of 150 mA g−1 and exhibits excellent cycling stability without obvious capacity decay after 70 cycles. This simple and effective design would be a promising approach to obtain high performance and cost-effective Si anodes on a large-scale, especially for industrial manufacturing of high energy density Li-ion batteries.