AbstractTo overcome the sluggish kinetics in sodium-ion batteries, sodium titanate/carbon (Na2Ti3O7/C) composite nanofibers as anode materials have successfully been synthesized via a simple electrospinning method. After calcination at 800 °C for 3 h, the obtained Na2Ti3O7 nanoparticles are randomly dispersed in the matrix of in situ pyrolized carbon nanofiber. The Na2Ti3O7/C hybrid nanofiber obtained with 2.5 wt% of poly (vinylpyrrolidone) additive in the precursor solution has the smallest diameter of ~120 nm and the finest particle size of ~40 nm, exhibiting the best rate performance of 101 mAh•g−1 at 4 C and excellent capacity retention of 82% at 1 C after 100 cycles. Furthermore, this composite nanofiber also demonstrates good cycling performance under low current density of 0.1 C, which is attributed to the formation of stable solid electrolyte interface (SEI) film induced by small volume expansion/contraction of the fine Na2Ti3O7 nanoparticles during the charge/discharge process.

•Two new hosts were reported for sky-blue TADF OLEDs.•The peak CE of 34.8 cd A−1, PE of 33.1 lm W−1 and EQE of 16.0% were realized.•The satisfactory CIE coordinate of (0.18, 0.34) was obtained at 100 cd m−2.Two new host materials, CzDPPy and tCzDPPy, were designed and synthesized through the Ullmann-coupling reaction between carbazole/3,6-di-tert-butyl-carbazole and 2,6-bis(2-bromophenyl)pyridine. Their single-crystal structure, thermal, electrochemical, opt-electronic and bipolar carrier-transporting properties were fully investigated. Due to the steric hindrance of carbazole at the ortho positions of diphenylpyridine, both CzDPPy and tCzDPPy adapted highly twisted molecular conformation, which could effectively minimize their π conjugation and endow them the high triplet energies of 2.67 and 2.64 eV, respectively. Organic light-emitting devices (OLEDs) were fabricated by using CzDPPy and tCzDPPy as the host materials and 1,2-bis(carbazol-9-yl)-4,5-dicyanobenzene (2CzPN) as the sky-blue TADF emitter. The peak current efficiency of 34.8 cd A−1, power efficiency of 33.1 lm W−1 and external quantum efficiency of 16.0% were realized for the CzDPPy-based TADF OLED, along with the satisfactory CIE coordinate of (0.18, 0.34) at 100 cd m−2.The new host materials based on the ortho-linked carbazole/diphenylpyridine hybrids could realize max. CE of 34.8 cd A−1, PE of 33.1 lm W−1 and EQE of 16.0% in the sky-blue TADF OLEDs.Download high-res image (263KB)Download full-size image

•LiCoO2 powders are modified with glassy B2O3 through H3BO3 decomposition.•High-voltage (4.5 V) cycling stability and rate capability are greatly improved.•Lithium boron oxide (LBO) as major SEI part is formed on the surface after cycling.•B2O3-modification mitigates high-voltage induced interfacial side reactions.•The as-formed 3D glassy LBO enhances the kinetics of the electrode.In this work, commercial LiCoO2 is modified with a glassy B2O3 by solution mixing with H3BO3 followed by post-calcination in order to enhance its high-voltage electrochemical performance. The glassy B2O3 coating/additive is believed to serve as an effective physiochemical buffer and protection between LiCoO2 and liquid electrolyte, which can suppress the high-voltage induced electrolyte decomposition and active material dissolution. During the early cycling and due to the electrochemical force, the as-coated B2O3 glasses which have 3D open frameworks tend to accommodate some mobile Li+ and form a more chemically-resistant and ion-conductive lithium boron oxide (LBO) interphase as a major component of the solid electrolyte interphase (SEI), which consequently enables much easier Li+ diffusion/transfer at the solid-liquid interfaces upon further cycling. Due to the synergetic effects of B2O3 coating/modification, the high-voltage capacity and energy density of the B2O3-modified LiCoO2 cathode are promisingly improved by 35% and 30% after 100 cycles at 1 C within 3.0–4.5 V vs. Li/Li+. Meanwhile, the high-rate performance of the B2O3-modified electrode is even more greatly improved, showing a capacity of 105 mAh g−1 at 10 C while the bare electrode has dropped to no more than 30 mAh g−1 under this rate condition.

•Glassy Li3PO4 thin film is homogeneously deposited onto lithium metal foils.•Li3PO4 thin film has an electronic conductivity of 1.4 × 10−10 S/cm.•Li3PO4 thin film has an ionic conductivity of 2.8 × 10−8 S/cm.•Li3PO4 coated lithium metal anodes have long cycle life performance.Lithium metal with high theoretical capacity (3860 mAh/g) and low operational voltage (−3.04 V vs. standard hydrogen electrode) reflects to be one of the most high energy density anodes for energy storage devices. While, its high chemical activity to continuously react with electrolytes causing low coulombic efficiency and formation of lithium dendrites leading safety concern limits practical applications. To conquer these challenges, amorphous Li3PO4 thin films with thickness of 0–200 nm are directly coated on the surface of Li metal foil via magnetron sputtering. The as-prepared Li3PO4 has almost insulated property with electronic conductivity of 1.4 × 10−10 S/cm and ionic conductivity of 2.8 × 10−8 S/cm. The conformal coating layer Li3PO4 can successfully suppress the lithium dendrites growth and improve its life span. The remarkable improvements of the Li3PO4-coated Li electrodes are mainly attributed to high chemical stability as well as amorphous nature of Li3PO4, which leads layer-by-layer growth Li film rather than islands form dendrites.Download high-res image (258KB)Download full-size image

•Crystalline and amorphous ZnC8H4O4 are obtained.•Both crystalline and amorphous ZnC8H4O4 have σe of 10−7 S m−1.•Lithium ion diffusion is the rate-determine process.•Amorphous has a high capacity and durable performance.•Amorphous ZnC8H4O4 has a high apparent lithium ion diffusion coefficient.Organic materials offer the advantages of cost-effective, environmental benignity, and molecular structural diversity as applications of electrode materials for lithium ion batteries. In fact, their lithium storage behaviors in terms of dynamics and kinetics intrinsically lie in ion migration in solids. Thus the solid forms including crystalline and amorphous states are crucial for the properties. In this study, a conventional carbonyl type organic material, namely zinc terephthalate (ZnC8H4O4), is obtained in both well-crystalline and amorphous forms and applied as anodes for lithium ion batteries. ZnC8H4O4 with amorphous structure shows higher lithium storage capacity and better capacity retention compared with that of crystalline one. It is ascribed that the amorphous phase provides a higher lithium ion diffusion coefficient than the crystalline one under the conditions of similar electronic conductivity.Both of well-crystalline and amorphous zinc terephthalates ZnC8H4O4 are synthesized and amorphous structure demonstrates a higher capacity and better cycling performance.Download high-res image (329KB)Download full-size image

A novel polymer (PTPBQ) with alternating terephthalate (TP) and benzoquinone (BQ) moieties is synthesized for the first time as an organic cathode for Li-ion batteries. Both TP and BQ moieties probably could remain electrochemically active and thus may make PTPBQ realize a maximum 4-electron redox behaviour and a theoretical specific capacity of up to ∼390 mAh g−1. In its practical application, Li-ion half cells based on PTPBQ can realize discharge capacities of ∼110 mAh g−1 on average for 400 cycles (40 mA g−1, 0.1C), and ∼180 mAh g−1 on average for 200 cycles (80 mA g−1, 0.2C) when the carbon additive is augmented to 40 wt%.

With the increasing demand for high energy density in portable-device Li-ion batteries (LIBs), efforts are devoted to increase and stabilize the capacity of LiCoO2 at high operation voltages. Herein, we report a low-cost and eco-friendly wet-chemical method to coat Al2O3 on LiCoO2, using only aluminium sulphate and water as source materials. A nanoscale oxide layer is coated on the surface of LiCoO2 particles through hydrogen-bonding assisted adsorption of the hydrolysed Al(OH)3 nanoparticles. The as-proposed Al2O3-coating provides excellent physico-chemical protection and kinetically-favourable interfaces for the LiCoO2 electrode, resulting in remarkable improvements of the electrode's cycling stability and rate capability when tested at high cutoff voltages up to 4.7 V (vs. Li/Li+). The synergetic effects of the oxide coating, e.g. alleviated electrolyte decomposition and reduced generation of irreversible solid electrolyte interphase (SEI) constituents (LiF/Li2CO3 and organics), are attributed to the improvements. At the cutoff voltage of 4.5 V, the modified LiCoO2 electrode in this work exhibits excellent cycling stability (147 mA h g−1, 82.6% retention after 500 cycles at 1C) and competitive rate capability (130 mA h g−1 at 10C), which are some of the best results reported so far. The outstanding high-voltage electrode performance and the simple and scalable coating approach show great promise of LiCoO2 cathodes in future high-energy and high-power LIBs.

Iodic acid (HIO3) was exploited as the effective source to build an artificial solid-electrolyte interphase (SEI) on the surface of Li anode. On one hand, HIO3 is a weak solid-state acid and can be easily handled to remove most ion-insulating residues like Li2CO3 and/or LiOH from the pristine Li surface; on the other hand, both the products of LiI and LiIO3 resulted from the chemical reactions between Li metal and HIO3 are reported to be the ion-conductive components. As a result, the lower voltage polarization and impedance, longer cycling lifetime and higher Coulombic efficiency have been successfully achieved in the HIO3-treated Li–Li and Li–Cu cells. By further using the HIO3-treated Li anode into practical Li–S batteries, the impressive results also have been obtained, with average discharge capacities of 719 mAh g–1 for 200 cycles (0.2 C) and 506 mAh g–1 for 500 cycles (0.5 C), which were better than the Li–S batteries using the pristine Li anode (552 and 401 mAh g–1, respectively) under the same conditions.Keywords: iodic acid; lithium anode; lithium battery; Li−S battery; solid-electrolyte interphase;

•Cobalt terephthalate as the organic anode was studied in K-ion cell•Nearly 100% Coulombic efficiencies could be maintained•The average capacities of 146 mAh g−1 for 200 cycles were realizedThe electrochemical behavior of cobalt terephthalate (CoTP) as the organic anode was initially carried out in K-ion battery, with the main intention to test whether the abnormal capacity enhancement of CoTP previously occurring in Li-ion battery could continuously happen in the different K-ion battery system. However, as confirmed by the cyclic voltammetry and X-ray photoelectron spectroscopy (XPS), the Co element of CoTP was irreversibly reduced from Co2+ cation to Co0 atom in the 1st discharge process, thus converting CoTP into K2TP in the following electrochemical cycles. Despite of that, the satisfactory specific and rate capacities could be realized for CoTP after a small amount of conductive Super P was added, with the average capacities of 146 mAh g−1 for 200 cycles under the current density of 60 mA g−1, which were comparable or even superior to some inorganic anodes recently reported for K-ion battery.Download high-res image (180KB)Download full-size image

The systematic investigation of RNO3 salts (R = Li, Na, K, and Cs) as electrolyte additives was carried out for lithium-battery systems. For the first time, the abundant and extremely available KNO3 was proved to be an excellent alternative of LiNO3 for suppression of the lithium dendrites. The reason was ascribed to the possible synergetic effect of K+ and NO3– ions: The positively charged K+ ion could surround the lithium dendrites by electrostatic attraction and then delay their further growth, while simultaneously the oxidative NO3– ion could be reduced and subsequently profitable to the reinforcement of the solid-electrolyte interphase (SEI). By adding KNO3 into the practical Li–S battery, the discharging capacity was enhanced to average 687 mAh g–1 from the case without KNO3 (528 mAh g–1) during 100 cycles, which was comparable to the one with the well-known LiNO3 additive (637 mAh g–1) under the same conditions.

•Electron-insulating/ion-conducting Li3PO4 (LPO) is used to coat LiCoO2 electrodes.•Amorphous LPO layer is coated by a facial magnetron sputtering approach.•High-voltage (4.5 V) and high-temperature (50 °C) cell performances are studied.•LPO-coated LiCoO2 electrodes exhibit improved cycling and rate performances.•High-temperature performance improvements are more dominant after LPO coating.Surface coating has long been an important strategy to improve the electrochemical performances of electrode materials for Li-ion batteries. In this work, an amorphous Li3PO4 (LPO) layer, which is a poor electronic conductor but good ionic conductor, is coated directly on LiCoO2 composite electrodes by magnetron sputtering. The battery performances of the electrodes are studied at both room temperature (RT) and 50 °C. The LPO sputter-coating allows significant improvement of the electrode's cycling stability at both temperatures. With an optimum coating thickness of ∼60 nm, the electrode's capacity after 100 cycles at 1 C can reach 146 mAh g−1 (79.3% retention) and 140 mAh g−1 (78.2% retention) at RT and 50 °C, which are improved by 30% and 200%, respectively, compared to those of the bare LCO electrode. More impressively, the rate capability is also greatly enhanced by LPO-coating, and the observed high-temperature rate capability is even superior to the room-temperature one. The remarkable improvement of the LPO-coated electrodes is mainly attributed to the high chemical stability and temperature-enhanced electrochemical activity of the LPO coating layer, which synergistically serves as a physiochemical protection layer and an efficient pathway for Li+ transport.

Carboxylate-based metal organic frameworks are popular lithium storage electrode materials by using carbonyl groups as redox centers. In this study, alkaline earth metal terephthalates MC8H4O4 (M=Ca, Sr, Ba) are prepared and applied as anodes for lithium ion batteries. The structure differences in terms of crystallography and molecular structures and electrochemical differences resulting from alkaline earth metal ionic radii are explored. It is found that electrostatic interactions between the alkaline metal cations and the terephthalate anions are important to the crystal structure, although these three organic matters consist of alternating layers of terephthalate anions and polyhedrally coordinated metal cations, but do not form iso-structure. Moreover, terephthalate salt with smaller cationic radius is featured with ionic bond behavior, lower discharge potential vs. Li/Li+ and higher discharge capacity with good capacity retention behavior.

•Metal/organic nanocomposite is in-situ formed in Ag2TP.•Ag2TP exhibits 149 mAh g−1 for 500 cycles at 1C in Li-ion cell.•Ag2TP Exhibits 133 mAh g−1 for 100 cycles at 1C in Na-ion cell.Silver terephthalate (Ag2TP) with the theoretical specific capacity of 141 mAh g−1 was intentionally employed as the organic anode in Li-ion and Na-ion batteries respectively, aiming to in-situ generate the conductive metallic particles from the easily-reducible Ag+ cations. Meanwhile, the conveniently-synthesized Ag2TP solids inherently exhibited nanosized objects without any post treatment. Based on these advantages, the Ag2TP anode in Li-ion battery could exhibit discharge capacity of average 149 mAh g−1 at 1C for 500 cycles, maintaining as high as 113 mAh g−1 at the 500th cycle; while the Ag2TP anode in Na-ion battery still displayed similar value of average 133 mAh g−1 at 1C for 100 cycles. These results could represent the new advancement among the organic electrodes of terephthalate salts.

•dilithium 2,5-dihydroxyterephthalate (Li2DHTP) was synthesized via a simple wet chemistry methodology.•Li2DHTP delivers remarkable cycling and rate performance for Li-ion batteries.•The electrochemical processes of 2,5-dihydroxyterephthalic acid (DHTPA) and its Li-salt Li2DHTP were firstly proposed.A functional organic small molecule anode material (dilithium 2,5-dihydroxyterephthalate, Li2DHTP) is synthesized via a simple wet chemistry methodology adopting 2,5-dihydroxyterephthalic acid (DHTPA) as the precursor. It delivers a high specific capacity of 165 mAh/g over 100 cycles with the coulombic efficiency of 98% and shows remarkable rate performance. The organic acid DHTPA also demonstrates electrochemical activity toward Li+ storage and releases but with poor cyclic performance. XRD and FT-IR studies suggest that the de −/lithiation process of chemically replaced Li2DHTP is highly reversible. On the contrary, the de −/lithiation process of electrochemically replaced Li2DHTP intermediate product, where the corresponding DHTPA acid experiences an ion exchange process in the first discharge process, shows quite poor reversibility in the following cycles. The results illustrate that either chemical replacement or electrochemical replacement of DHTPA can generate Li2DHTP electrochemical active material. This methodology might be applied to synthesize advanced organic small molecules conjugated carbonyl materials for energy storage.

Ag particles were selectively added into the organic anode material of calcium terephthalate (CaTP) to improve its electronic conductivity, because Ag metal was the most conductive one and easily accessible from the decomposition of unstable AgNO3 at certain temperatures tolerated by organics. The reduced size of CaTP particles observed after adding Ag particles could increase the specific surface area and shorten the Li+ ion diffusion pathway. Consequently, the resulting CaTP/Ag anode exhibited an enhanced and reversible 92 mA h g−1 capacity under a 240 mA g−1 current density, which was four times higher than that of pristine CaTP under the same conditions. In addition, the cycling performance at 120 mA g−1 current density was also improved in the cycle range of 21st to 130th, with a ∼113 mA h g−1 discharge capacity value, which was also higher than that of pristine CaTP (∼26 mA h g−1).

Cu3P is a potential anode material for lithium-ion batteries with its comparable gravimetric capacity, but several times higher volumetric capacity (4732 mA h cm−3) than graphite. However, the cycling stability of Cu3P is poor at low discharge potentials and high current densities. In this work, Fe addition is employed as a simple strategy to modulate the composition and phase constitution of Cu3P nanopowders synthesized by wet mechanical alloying, and thereby to tune the electrochemical performance of the anode. The addition of Fe results in a composite constitute containing Cu3P as the major phase and some other minor phases including Cu, α-Fe and FeP, which are combinationally determined by X-ray diffraction, energy dispersive X-ray spectroscopy and Mössbauer spectroscopy. Electrochemical tests reveal that both the cycling stability and the rate capability of the electrodes are improved by Fe addition. The Cu3P electrode with 10% Fe addition shows the best cell performance, with the capacity being remarkably improved by over 100%, from 82 mA h g−1 to 178 mA h g−1 after 50 cycles at 0.75C between 2.0 V and 0.5 V vs. Li/Li+. The improvement of the electrochemical performance is engendered by a synergetic effect of the microstructure change of the powders and the presence of Fe-related minor phases, leading to increased electronic conductivity as well as enhanced electrochemical reversibility of the electrode.

Surface coating of composite electrode has recently received increasing attention and has been demonstrated to be effective in enhancing the electrochemical performance of lithium ion battery (LIB) materials. In this work, an electronic-insulating but ionic-conductive lithium carbonate (Li2CO3) is rationally selected as the unique coating material for commercial LiCoO2 (LCO) cathode. Li2CO3 is a well-known constitute in conventional solid electrolyte interface (SEI) layer, which can electrochemically protect the electrode. The carbonate coating layer is deposited on LCO composite electrodes via a facial magnetron sputtering approach. The sputtered Li2CO3 layer serves as an artificial SEI layer between the active material and electrolyte and can impede the formation of the primary SEI layer, which will permanently consume Li+ and reduce the reversible capacity of the electrode. After a 10 min Li2CO3 coating, the capacity retention of the composite electrode is improved from 64.4% to 87.8% when cycled at room temperature in the potential range of 3.0–4.5 V vs Li/Li+ for 60 cycles. The obtained discharge capacity is extended to 161 mAh g–1, which is 36% higher than the uncoated one (118 mAh g–1). When further increasing the charging potential up to 4.7 V, or elevating the operation temperature to 55 °C, the Li2CO3-coated LCO electrodes still display remarkably improved cycling stability.

The selection and optimization of coating material/approach for electrode materials have been under intensive pursuit to address the high-voltage induced degradation of lithium ion batteries. Herein, we demonstrate an efficient way to enhance the high-voltage electrochemical performance of LiCoO2 cathode by postcoating of its composite electrode with Li4Ti5O12 (LTO) via magnetron sputtering. With a nanoscale (∼25 nm) LTO coating, the reversible capacity of LiCoO2 after 60 cycles is significantly increased by 40% (to 170 mAh g–1) at room temperature and by 118% (to 139 mAh g–1) at 55 °C. Meanwhile, the electrode’s rate capability is also greatly improved, which should be associated with the high Li+ diffusivity of the LTO surface layer, while the bulk electronic conductivity of the electrode is unaffected. At 12 C, the capacity of the coated electrode reaches 113 mAh g–1, being 70% larger than that of the uncoated one. The surface interaction between LTO and LiCoO2 is supposed to reduce the space-charge layer at the LiCoO2–electrolyte interface, which makes the Li+ diffusion much easier as evidenced by the largely enhanced diffusion coefficient of the coated electrode (an order of magnitude improvement). In addition, the LTO coating layer, which is electrochemically and structurally stable in the applied potential range, plays the role of a passivation layer or an artificial and friendly solid electrolyte interface (SEI) layer on the electrode surface. Such protection is able to impede propagation of the in situ formed irreversible SEI and thus guarantee a high initial columbic efficiency and superior cycling stability at high voltage.Keywords: ionic conductor; Li4Ti5O12; LiCoO2; lithium ion battery; magnetron sputtering; surface coating;

•Metal organic frameworks CaC8H4O4·3H2O and CaC8H4O4 are applied as anodes for lithium ion batteries.•Appearance of hydration water leads different crystallography structures and electrochemical performance.•Anhydrous CaC8H4O4 has a spacious ordered layer structure, a higher Ca-O chemical bonding interaction and a higher transparent lithium ion diffusion coefficient, delivering a higher capacity, better cycling performance and rate performance than CaC8H4O4·3H2O.Metal organic frameworks have attracted considerable interest as electrode materials for lithium ion batteries. In this paper, the metal organic frameworks hydrated calcium terephthalate (CaC8H4O4·3H2O) and anhydrous calcium terephthalate (CaC8H4O4) as anodes for lithium ion batteries are comparatively studied. Crystallography and local chemical bond analysis are combined to interpret the structure-property of calcium terephthalates. Results show that the anhydrous CaC8H4O4 has a spacious ordered layer structure and a higher Ca-O chemical bonding interaction, delivering a higher capacity, better cycling performance and rate performance than CaC8H4O4·3H2O.Effects of hydration water in calcium terephthalates anodes on the structure, operational voltage and electrochemical performance are systematically studied.

Currently, many organic materials are being considered as electrode materials and display good electrochemical behavior. However, the most critical issues related to the wide use of organic electrodes are their low thermal stability and poor cycling performance due to their high solubility in electrolytes. Focusing on one of the most conventional carboxylate organic materials, namely lithium terephthalate Li2C8H4O4, we tackle these typical disadvantages via modifying its molecular structure by cation substitution. CaC8H4O4 and Al2(C8H4O4)3 are prepared via a facile cation exchange reaction. Of these, CaC8H4O4 presents the best cycling performance with thermal stability up to 570 °C and capacity of 399 mA·h·g−1, without any capacity decay in the voltage window of 0.005–3.0 V. The molecular, crystal structure, and morphology of CaC8H4O4 are retained during cycling. This cation-substitution strategy brings new perspectives in the synthesis of new materials as well as broadening the applications of organic materials in Li/Na-ion batteries.

We have reported a conjugated carbonyl organic calcium terephthalate (CaTPA)-based organic/inorganic composite as anode material for lithium-ion batteries. The bulk CaTPA presents a low electronic conductivity leading to a large electrochemical polarization during charge/discharge process. Graphite is chosen as a conductive additive to improve its electrochemical performance via ball milling. The effect of graphite amount on the electrochemical properties of CaTPA is investigated. The composite with the weight ratio of 100:10 (CaTPA/graphite) (named CaTPAG10) shows the smallest electrochemical polarization, largest Li+ diffusion coefficient, and best rate capability, delivering discharge capacity of 233 mAhg−1 at current rate of 0.1 C and discharge voltage plateau at ~0.8 V. CaTPAG10 further exhibits good cycling performance, from 169 mAhg−1 down to 161 mAhg−1 after 50 cycles, giving a capacity retention of 95 % at 2 C compared with that of 89 % for the pristine CaTPA. To explore commercial application of CaTPA, a full cell with LiCoO2 and CaTPAG10 as a cathode and an anode material, respectively, is tested. The full cell reveals an operational voltage at 2.8 V and reversible capacity of about 138 mAhg−1 at 1 C.

A novel three-dimensional nanostructured, namely nanoporous and irregular nanopillar, composite Cu-Sn anode material for lithium-ion batteries was synthesized by directly oxidizing copper foil slightly in air and deoxidizing under H2/Ar atmosphere. Following that, Sn layer was deposited on as-prepared Cu substrate by the direct current sputtering technique. The morphology, constituent, and electrochemical performance of the obtained samples were characterized by field emission scanning electron microscope, X-ray diffraction, energy-dispersive X-ray spectrometer, and galvanostatic cycling test. The as-prepared Cu-Sn electrode (deposition time 10 min) exhibits a stable coulombic efficiency around 95 % over 50 cycles. The 50th specific capacity is 590 mA h/g at the current of 0.3 C, and at the high rate of 12 C, it exhibits 376 mA h/g which shows a high specific capacity and remarkable rate performance as an anode for lithium-ion batteries. The special 3D nanostructure, herein, can not only effectively offer enough space to accommodate large volume change but also act as structural reinforcement during electrochemical reaction. The simple fabrication approach of this novel nanostructure can be further extended to other anode materials with remarkable electrochemical property.

Lithium terephthalate (Li2C8H4O4) and its carboxylate-based derivatives have been proposed as advanced organic anodes for low cost lithium/sodium ion batteries. One of the key barriers for practical application is poor rate capability due to the intrinsic low electronic conductivity of most organic materials at room temperature. To overcome this issue, porous microspheres consisting of Li2C8H4O4 nanoparticles were synthesized by a common spray drying method for the first time. Furthermore, a straight-forward surface coating technique was developed using urea powder as nitrogen and carbon sources simultaneously. Consequently, a N-doped carbon layer was uniformly coated onto nanostructured Li2C8H4O4 electroactive material at 400 °C by chemical vapor deposition. The composite electrode displays excellent electrochemical performance under high current rate even at room temperature.

Surface modification of LiCoO2 is an effective method to improve its energy density and elongate its cycle life in an extended operation voltage window. In this study, ZnO was directly coated on as-prepared LiCoO2 composite electrodes via radio frequency (RF) magnetron sputtering. ZnO is not only coated on the electrode as thin film but also diffuses through the whole electrode due to the intrinsic porosity of the composite electrode and the high diffusivity of the deposited species. It was found that ZnO coating can significantly improve the cycling performance and the rate capability of the LiCoO2 electrodes in the voltage range of 3.0–4.5 V. The sample with an optimum coating thickness of 17 nm exhibits an initial discharge capacity of 191 mAh g–1 at 0.2 C, and the capacity retention is 81% after 200 cycles. It also delivers superior rate performance with a reversible capacity of 106 mAh g–1 at 10 C. The enhanced cycling performance and rate capability are attributed to the stabilized phase structure and improved lithium ion diffusion coefficient induced by ZnO coating as evidenced by X-ray diffraction, cyclic voltammetry, respectively.Keywords: lithium cobalt oxide; lithium ion diffusion coefficient; RF magnetron sputtering; structure stability; zinc oxide coating

•Submicron-sized Li4Ti5O12/Li2TiO3 was synthesized by solid state process.•Li4Ti5O12/Li2TiO3 composite exhibited excellent rate performance.•Li4Ti5O12/Li2TiO3 composite demonstrated outstanding cycle stability.•The ionic conductivity of Li4Ti5O12/Li2TiO3 was higher than that of Li4Ti5O12.Submicron-sized Li4Ti5O12/Li2TiO3 composites with Li-rich grain boundaries are successfully synthesized by a simple, environmentally benign, mass production preferred solid state process. The crystal phase and morphology are characterized by XRD and SEM. The electrochemical performance is collected by galvanostatic discharge–charge tests, cyclic voltammograms (CV) and electrochemical impedance spectra (EIS) tests. The initial discharge capacity of Li4Ti5O12/Li2TiO3 composite is 155 mAh g−1 at 0.5 C. While the current rate is as high as 10 C, the specific capacity is 113 mAh g−1, and the capacity retention is 98.2% even after 500 cycles. As a reference, the ionic conductivity and the electrochemical performance of Li2TiO3 and Li4Ti5O12/TiO2 composite are also characterized. The extraordinary high rate performance and cycling stability are explained by high ionic conductivity and rich grain boundaries of Li4Ti5O12/Li2TiO3 composite.

•Li4Ti5O12/TiO2/Carbon/Carbon nanotubes composite is prepared via reversed-phase microemulsion-assisted solid state reaction method.•Excess amount of carbon can prevent the growth of Li4Ti5O12 and lead the appearance of impure phase of TiO2.•Li4Ti5O12/TiO2/Carbon/Carbon nanotubes composite delivers superior rate performance and cycle performanceSpinel Li4Ti5O12 (LTO) is a promising anode material of lithium ion batteries for electric vehicles and hybrid electric vehicles due to its long cycle life, well-known stable structure, and high safety. Whereas, the electronic conductivity of spinel LTO is intrinsically low. To circumvent this drawback, composites of Li4Ti5O12/TiO2/Carbon/Carbon nanotubes (LTO/TiO2/C/CNTs) are prepared by a novel wet-chemical method (reversed-phase microemulsion method), including high electronic conductive CNTs and excess TiO2. The presence of carbon can suppress the growth of LTO particles and lead the appearance of TiO2 during synthesis process. The average particle size of LTO is about 30 nm. The LTO/TiO2/C/CNTs composites deliver exceptional electrochemical performance in the voltage window 1.0 -2.5 V. It presents a discharge capacity of 224 mAh.g−1 at 0.15 C and 95 mAh.g−1 at a high current rate of 24 C (4.2 A.g−1). It is found that the TiO2 not only has electrochemical activity but also results in interfacial effect to hugely increase its rate performance.

•We had first synthesized the microspherical Na2Ti3O7 by spray-drying method as anode for sodium-ion batteries system.•We used the sol-gel method to prepare the precursors slurry for spray drying to get the smaller primary particles.•This sample exhibits outstanding rate performance.We report here the spherical Na2Ti3O7 synthesized by spray drying of the sol-gel prepared precursor suspension and followed by a solid-state calcination as advanced anode material for sodium-ion battery. Field-emission scanning electron microscopy analyses show the spherical powders consisting of well-crystallized Na2Ti3O7 primary particles surrounded three-dimensional porous structure. Electrochemical performance was investigated by charge/discharge measurement exhibiting the charge capacity of 93.1 mAh g− 1 even at current rate of 5C after 50th cycle. The electrochemical performance at high current rate is better than that of by a solid-state reaction method. Na2Ti3O7 synthesized by combing spraying-dry and sol-gel method is one of the promising candidates as the anode material of sodium-ion battery.

•Mo thin films were deposited by RF magnetron sputtering at elevated temperature.•Both high power and low pressure resulted in low resistivity but bad adhesion.•A bi-layer Mo was obtained by sequential deposition at different pressures.•The bi-layer Mo showed superior adhesion and a low resistivity of 11.1 μΩ cm.Molybdenum (Mo) thin films are widely used as back contact layers for thin film solar cells. In this work, Mo layers were deposited by radio-frequency (RF) magnetron sputtering at elevated substrate temperature, and their electrical and adhesion properties were investigated with regard to sputtering power and sputtering gas pressure. The crystal structure and morphology of the films were studied using X-ray diffractometry, scanning electron microscopy and atomic force microscopy. It was found that lower pressure and higher power of RF sputtering resulted in lower resistivity of Mo films due to increased kinetic energy of sputtered particles, which improved the crystallinity and compactness of the films. However, bad adhesion was observed for those films with desirable resistivity, exhibiting compressive stress. Through continuous deposition under higher and then lower sputtering gas pressures, a bi-layer Mo film was obtained with desired microstructure and surface morphology, possessing of a low resistivity of 11.1 μΩ cm and excellent adhesion property.

Graphites are widely used for their high electrical conductivity and good thermal and chemical stability. In this work, graphitic carbon-coated lithium titanium (Li4Ti5O12/GC) was successfully synthesized by a simple one-step solid-state reaction process with the assistance of sucrose without elevating sintering temperature. The lattice fringe of 0.208 nm clearly seen from the high-resolution transmission electron microscopy (HRTEM) images was assigned to graphite (010). The average grain size of the as-prepared Li4Ti5O12/GC was about 100–200 nm, 1 order smaller than that of pure Li4Ti5O12 prepared similarly. The rate performance and cycle ability were significantly improved by the hybrid conducting network formed by graphitic carbon on the grains and amorphous carbon between them. The specific capacity retention rate was 66.7 % when discharged at a rate of 12C compared with the capacity obtained at 0.5C. After 300 cycles, the capacity retention was more than 90 % at a high rate of 15C.

•Individual N and C sources are applied to coat N-doped carbon layer on Li4Ti5O12.•This straightforward methodology is easy to optimize N/C ratio and carbon layer thickness.•The N-doped C-coated Li4Ti5O12 presents uniform or serrated surface structure.•Surface modified samples display outstand electrochemical properties at high current rate.We have reported a straightforward strategy to fabricate Li4Ti5O12 composites coated with N-doped carbon layer by using NH3 as N source and sugar as C source, which is a benefit for optimizing carbon layer thickness and tuning atomic ratio of N/C. The composite was synthesized by a conventional solid state reaction with ball milled mixture of TiO2, Li2CO3, and sugar as the precursor, then followed by a high temperature annealing in the atmosphere of Ar and NH3. The choice of titanium source has an impact on the Li4Ti5O12 surface morphology as well as electrochemical properties. N-doped TiO2 can lead to the generation of uniform N-doped C-coating layer, resulting in improved electrochemical performances at high current rate. The N-doped C-coating Li4Ti5O12 obtained by using Anatase TiO2 produces a serrated thin carbon layer, showing the best electrochemical behaviors with the discharge capacity of 100 mAh g−1 at high rate of 24 C and 92.2% of initial capacity after 800 cycles at 12 C, which should be one of the promising anode materials for hybrid electric vehicles.

A one-step route was developed to fabricate Cu(In,Ga)Se2 (CIGS) absorber layers by direct magnetron sputtering from a single quaternary target with the composition of CuIn0.75Ga0.25Se2. The effects of the substrate temperature, the working pressure and the sputtering power on the morphology and phase structure of the CIGS layers were studied using scanning electron microscopy, X-ray diffraction and Raman spectroscopy. The microstructure properties of the layers, including the crystallinity, grain size, compactness and the surface evenness, were found to be strongly dependent on the deposition parameters. CIGS absorbers with compact microstructure and large grains of micrometer size were obtained at 400 °C and 160 W, showing a very strong (220)/(204) orientation preference when sputtered at a higher working pressure. Raman spectra indicated no precipitation of the Cu–Se binary phases, but revealed a slight difference in the Ga/(Ga + In) ratio of different layers. The overall composition of the as-sputtered CIGS film was confirmed to be in agreement with the target composition through energy dispersive X-ray spectroscopy study. In comparison with the conventional co-evaporation or post-selenization synthesis for CIGS, the one-step sputtering route is more simplified and economical, which shows great potential to reduce the production cost of CIGS-based solar cells.Highlights► One-step sputtering simplifies the fabrication of Cu(In,Ga)Se2 (CIGS) absorbers. ► Microstructure of CIGS films is tunable by merely adjusting sputtering parameters. ► High sputtering temperature, pressure, and RF power favor high quality CIGS film. ► Columnar CIGS film has expected stoichiometry and strong (220)/(204) orientation.

•Para-aromatic dicarboxylates could be the organic anodes in K-ion battery.•Satisfactory rate and cyclic capability were achieved in K-ion battery.•Specific capacity of average ~190 mAh g−1 was obtained for 100 cycles.Two small organic molecules, namely potassium terephthalate (K2TP) and potassium 2,5-pyridinedicarboxylate (K2PC), were newly exploited as the highly efficient organic anodes in K-ion batteries. Both K2TP and K2PC exhibited the clear and reversible discharge and charge platforms in K-ion half cells, which were resulted from the redox behavior of organic para-aromatic dicarboxylates. The satisfactory and reversible specific capacities were realized in the K2TP- and K2PC-based K-ion cells, with average values of 181 and 190 mAh g−1 for 100 cycles, respectively. The currently-obtained achievement of organic anodes could make a forward step for the further development of rocking-chair K-ion batteries.Potassium salts of para-aromatic dicarboxylates were initially exploited as the highly advanced organic anodes in K-ion batteries. And the usage of organic anodes could effectively avoid the risk of producing highly-reactive K metal.

•A new family of aromatic dicyanides was developed as the organic electrodes.•1,4-Dicyanobenzene (DCB) and 9.10-dicyanoanthracene (DCA) were studied.•DCA exhibits more stable reduced states and superior electronic conductivity.•DCA achieves reversible and step-by-step, two-electron process.A new redox-active family of aromatic dicyanides was developed as organic electrodes in rechargeable batteries. The detailed electronic properties of two primary representatives of 1,4-dicyanobenzene (DCB) and 9,10-dicyanoanthracene (DCA) were studied. It is discovered that, as compared with DCB, the large aromatic π conjugation in DCA leads to better electron conductivity and more stable reduced states of DCA− and DCA2 −. The Li-ion batteries with DCA electrode are shown to have highly reversible operations.Figure optionsDownload full-size imageDownload high-quality image (163 K)Download as PowerPoint slide

•Large band-gap TiO2 is directly sputter-coated on LiCoO2 composite electrodes.•High-voltage (4.5 V) and high-temperature (50 °C) cell performances are studied.•Remarkable improvement of cycling and rate performances are observed after coating.•TiO2-coating leads to mitigated interfacial side reactions and reduced impedance.•Possible reactions between TiO2 and electrolyte further protect the electrode.Surface coating is a key strategy in lithium-ion battery technologies to achieve a high and stable battery performance. Increasing the operation voltage is a direct way to increase the energy density of the battery. In this work, TiO2 is directly sputtered on as-fabricated LiCoO2 composite electrodes, enabling a controllable oxide coating on the topmost of the electrode. With an optimum coating, the discharge capacity is able to reach 160 mAh g−1 (86.5% retention) after 100 cycles within 3.0–4.5 V at 1 C, which is increased by 40% compared to that of the bare electrode. The high-voltage rate capability of LiCoO2 is also remarkably enhanced after TiO2-coating as reflected by the much larger capacity at 10 C (109 vs. 74 mAh g−1). The artificially introduced oxide coating is believed to make the LiCoO2 electrode more resistant to interfacial side reactions at high voltage and thus minimizes the irreversible loss of the active material upon long cycling. The TiO2 coating layer is also possible to partially react with the decomposition product of electrolyte (e.g. HF) and form a more stable and conductive interphase containing TiFx, which is responsible for the improvement of the rate capability.

Lithium terephthalate (Li2C8H4O4) and its carboxylate-based derivatives have been proposed as advanced organic anodes for low cost lithium/sodium ion batteries. One of the key barriers for practical application is poor rate capability due to the intrinsic low electronic conductivity of most organic materials at room temperature. To overcome this issue, porous microspheres consisting of Li2C8H4O4 nanoparticles were synthesized by a common spray drying method for the first time. Furthermore, a straight-forward surface coating technique was developed using urea powder as nitrogen and carbon sources simultaneously. Consequently, a N-doped carbon layer was uniformly coated onto nanostructured Li2C8H4O4 electroactive material at 400 °C by chemical vapor deposition. The composite electrode displays excellent electrochemical performance under high current rate even at room temperature.