Terms Of Cycles Research Articles

Influence of non-linear diffusion controlled phenomena on the sorption capability of PEO-Salt-SiO2 composite electrolyte: A study on property optimization

The present research, reports the hygrothermal behavior of poly [ethylene oxide] (PEO) based composite film (500 and1000 μm) containing NH4I and KBr (5–20 wt%) as the mobile phase and non-reactive silica (15 wt%) as the filler. These are termed as PK/NSiO2-series for solvent sorbed and (PK/NSiO2)NS for non-swelled film. The novelty of the research lies in the analyses of non-Fickian solvent diffusion trait of films using python programming. The presence of ions and its variable polarizable nature is found to influence the number density of bonded and free solvent content along with the extend of cross linkage. Introduction of silica is found to enhance the ionic conductivity (about one order higher) of the film irrespective of the type of charge carrier owing to the improved dispersion within the matrix. Non-Fickian diffusion is found to influence the ionic conductivity of P2K20SiO2 (10−5Scm−1 to 10−2 Scm−1) minimizing the degradation to 0.2 %ΔC/1000 h (>1 %ΔC/1000 h, tested for 2000 h) compared to P2N20NSiO2. In contrast, ion migration in P2NSiO2 is guided by Rice and Roth model and being more polarizable ions, the mobility is significant which maximizes the conductivity to ∼10−1 Scm−1. Microstructural study shows heterogenous nucleation to be more pronounced upon addition of silica filler wherein the homogeneity, inter fibrillar interaction and grain growth of spherulites is higher. This tends to extend amorphous regions thereby propagating the ion migration path. The influence of sorption process is studied in terms of electrochemical impedance, dielectric analyses and long term cyclability (20,000 h) in terms of loss tangent.

A “two cooking with one fish” strategy for modulating both polyaniline cathode and zinc anode towards enhanced kinetics and cycling stability for aqueous zinc ion batteries

The adverse stability of both polyaniline (PANI) and Zn anode remains a challenge to the long−term cyclability and rate capability of aqueous Zn−PANI batteries. Herein, a “two–cooking with one fish” strategy is presented to modulate both PANI cathode and Zn anode, in which nanoscale graphene sheets in cathode can promote ordered growth of PANI array, being conducive to provide large electrochemical active area and efficient transport pathways and alleviate volume variation during repeated charging/discharging process. Meanwhile, the honeycomb–like structure of graphene sheets as protective layer can accelerate zinc ion transport kinetics and suppress side reactions and zinc dendrite growth. Consequently, the optimized G/Zn symmetric cell delivers a remarkable lifespan over 1000 h at 1 mA cm−2 with 1 mAh cm−2. Furthermore, the assembled PANI/G/CC||G/Zn battery could deliver a specific capacity of 265.8 mAh g−1 at 0.2 A g−1, excellent rate capability (145.5 mAh g−1 at 20 A g−1), a maximum energy density of 246.9 W h kg−1 and power density of 8675.9 W kg−1, and especially capacity retention of 91.1 % after 10000 cycles. Combining with additional merits of low cost, eco–friendliness, and safe operation, our design will shed light on resolving the issues on cyclability and rate capability of aqueous Zn−PANI batteries.

Investigation of Heteroatom Doped Graphene Anode for High-Capacity Alkali Metal-Ion Batteries

The drastic growth of Li-ion batteries (LIBs) in global electronic market and low crustal abundance of Li demands for more abundant alternatives such as sodium and potassium having similar electrochemical properties. Sodium-ion battery (SIB) and potassium-ion battery (PIB) can be used “side-by-side” to LIB which can help battery technology progress efficiently. 1Graphite has been a commercial anode in LIB due to its low cost, high abundance, high electrical conductivity, with a theoretical storage capacity (LiC6) of 372 mAh g-1. In contrast the utilization of graphite in SIBs and PIBs is challenging. This is due to the large radius and unstable graphite-intercalation compounds (NaC64) giving very low theoretical capacity of 30 mAh g-1. In PIBs, graphite exhibits a theoretical capacity of 279 mAh g-1 but suffers from poor stability due to huge volume expansion (60%) in fully potassiated state (KC8). Thus, focus is now shifted on to class of amorphous carbon materials such as hard carbon, soft carbon, graphene etc. with variations in micro-structures, larger interlayer spacing, and defect rich sites promoting enhanced capacity and stability even at high current densities. 2 In my presentation I will be discussing about the synthesis of heteroatom doped graphene with high charge storage and stability for LIB, SIB and PIB compared to graphite. The heteroatom doped graphene exhibits nearly 1000 mAh g-1 (LIB), 380 mAh g-1 (SIB) and 379 mAh g-1 (PIB) at a low current density of 25 mAg-1. Additionally, the elastic nature of ultrathin graphene nanosheets aids in attaining long term cyclability at 1 A g-1 with high-capacity retention of 83% for 300 cycles (LIB), 73% for 400 cycles (SIB) and 91% for 600 cycles (PIB). The enhanced stability in case of PIB, is attributed to optimizing solid electrolyte interphase (SEI) components and improving interfacial reaction kinetics at high current densities. Choice of high concentrated electrolyte (HCE) over conventional KPF6 in EC:DEC determines the nature of SEI and thereby helps in achieving cycling stability. The stability in SEI is characterized via voltage profile and understanding chemical composition by ex-situ X-ray photoelectron spectroscopy. Robust SEI in HCE is due to difference in anion structure studied by Raman spectroscopy.Furthermore, the charge-discharge mechanism, alkali ion diffusion kinetics and structure-activity relationship of electrode materials was investigated using various techniques like cyclic voltammetry profiles at different scan rates and Galvanostatic intermittent titration technique (GITT). Additionally, deeper insights into the fundamental understanding of interfacial and bulk behavior were provided with the help of in-situ Raman spectroscopy and in-situ potentiostatic electrochemical impedance spectroscopy (PEIS) analysis. The investigation of peak area and shift in D (defect) and G (graphitic) band analyzed from in-situ Raman studies helped in understanding the evolution and reversibility of alkali ion storage behavior during charging and discharging. PEIS analysis gave us a thorough understanding of the evolution of stable SEI on charging-discharging and after cycling, which helps us to understand the long-term stability in LIB, SIB and PIB.

Fabrication of an efficient supercapacitor based on defective mesoporous carbon as electrode material utilizing Reactive Blue 15 as novel redox mediator for natural aqueous electrolyte

Herein, the application of Reactive Blue 15 as novel and efficient redox additive for natural aqueous electrolyte was reported in where defective mesoporous carbon (DMC) with the interconnected porous network was applied as electrode material. Excellent electrochemical performance is achieved at 0.05 M of R. B. 15 in 1 M Na2SO4 electrolyte. The obtained data from RAMAN, SEM, TEM, and Nitrogen adsorption/desorption confirmed the DMC structure. The supercapacitive performance of DMC and DMC electrodes with RB redox additive in 1 M Na2SO4 as electrolyte was evaluated by cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), and galvanostatic charge/discharge (GCD) techniques. Compared to DMC, the DMC-RB/Na2SO4 delivered the highest specific capacitance reaching to 207 F/g at the applied current density of 0.5 A/g. Moreover, the DMC-RB/Na2SO4 exhibited long term cyclability, in where 76% of specific capacitance was retained after 3000 GCD measurement at the high current density of 1 A/g. Also, the specific energy of 18.45 Wh/kg was obtained for the symmetric device which shows nearly threefold increase over the DMC electrode with pure Na2SO4 electrolyte.

Navajoite phase V5O12•6H2O nanorods with ultra−long lifespan for aqueous zinc−ion batteries

Aqueous zinc−ion batteries have attracted wide attention because of their low cost and high safety advantages, whereas the cathode materials with stable internal structure and fast transfer channels are urgently needed. Herein, a Navajoite phase V5O12•6 H2O nanorods has been prepared via a facile hydrothermal method, and proved to be a good choice as the cathode of ZIBs because of the excellent structural stability and special Zn2+ ion transfer channel. Electrochemical measurements demonstrate that the as−fabricated V5O12•6 H2O nanorods can disclose a high rate performance (405 mA h g−1 under 0.1 A g−1), a long−term cyclability (81.2% maintained after 20,000 cycles under 10 A g−1) and an excellent energy output (338.04 Wh kg−1 at 227 W kg−1). In addition, various ex−situ characterizations have revealed the electrochemical mechanism in V5O12•6 H2O cathode during reversible Zn2+ ion intercalation/de−intercalation process. The impressive electrochemical performance of V5O12•6 H2O cathode shows its high potential in practical applications.

Improving electrochemical properties of LiNi0.8Mn0.1Co0.1O2 cathode materials for lithium ion batteries by controlling calcination gas atmosphere

Layered lithium nickel manganese cobalt oxides (LiNixMnyCozO2, x + y + z = 1) with high Ni content (x ≥ 0.8), called as high Ni NMC, are one of the most promising cathode materials for lithium-ion batteries of electric vehicle (EV) application. High Ni NMC synthesis includes a calcination step under pure O2 atmosphere to minimize Li/Ni mixing in crystal structure, which highly influences the long term cyclability and C-rate capability of batteries. Herein, we demonstrate that the electrochemical properties of high Ni LiNi0.8Mn0.1Co0.1O2 (NMC811) cathode materials for lithium ion batteries can be further improved by controlling the calcination atmosphere. Interestingly, the results showed that a slightly oxygen deficient calcination atmosphere (mixture of O2/Ar with 96/4 vol% ratio) is effective to provide a stable discharge capacity retention (89%) after 200 cycles, and high C-rate capability (>70% at 20C vs 1C), whereas NMC811 calcined under pure O2 suffers from an excessive oxidation of Ni and Co on the surface and an increase of residual lithium, leading to an increase of surface resistance, as a consequence, a fast capacity fade over cycling and lower C-rate capability. The finding of this study suggests that calcination atmosphere could play a key role in determining the electrochemical properties of high Ni cathode materials, and can also be interesting from the industrial point of view, since producing O2 with a small deficiency (e.g. Ar) needs less efforts in the purification than pure O2.

Electrodeposition of Three-Dimensional Au Nanowire Networks and Their Application As Catalysts for Methanol Electro-Oxidation

In this talk we will first present the synthesis of free-standing, stable gold nanowire network with controlled morphology and geometry by ion-track technology and electrodeposition. Etched ion-track membranes with interconnected nanochannels are produced by sequential GeV heavy ion irradiation of polymer foils from four directions, and subsequent etching and enlargment of the created ion-tracks. Au nanowire networks with three different nanowire diameters are synthesized by potentiostatic electrodeposition in the templates. Nanowire growth rate and homogeneity are tuned by varying the deposition potential. The electrochemical surface area was determined for each sample by CV analysis of surface oxide reduction reaction charge transfer. We will also discuss the catalytic performance of these Au nanowire networks towards methanol electro-oxidation, acting as an electrode in a half-cell setup. High current density and high catalytic activity were recorded. The Au nanowire networks provided up to 200 times higher peak current density than a flat Au electrode, along with excellent long term cyclability, which the current density drops only 5% over 200 CV cycles. SEM studies of the morphology and crystallinity of the nanowires before and after the methanol oxidation reaction will also be presented in the talk.Figure 1. (a) SEM image of Au nanowire network, (b) Cyclic Voltammograms recorded for a of Au nanowire network in 0.1 M KOH with (solid line) and without (dash line) 1 M MeOH. Figure 1

Facilitating sustainable oxygen-redox chemistry for P3-type cathode materials for sodium-ion batteries

Herein, the surface of the P3-Na0.6[Mn0.6Co0.2Mg0.2]O2 cathode material is fortified by introducing an ionic-conducting sodium-phosphate nanolayer (NaPO3, ≈10-nm thickness). This layer facilitates Na+-ion diffusion owing to its sufficiently high ionic conductivity (≈10–6 S cm–1). Moreover, the NaPO3 coating layer prevents the precipitation of surface byproducts generated from reaction with the electrolyte. The NaPO3-coated P3-Na0.6[Mn0.6Co0.2Mg0.2]O2 electrode can thus retain over 80% of the first capacity after 200 cycles not only at 0.1C but also at a high rate (5C), with a capacity retention of 88% after 300 cycles. Reversible transition-metal and oxygen redox are evidenced by X-ray absorption near-edge spectroscopy, X-ray photoelectron spectroscopy, time-of-flight secondary-ion mass spectroscopy, and operando differential electrochemical mass spectroscopy, which reveal mitigated surface-byproduct formation. These findings demonstrate the possibility of the use of oxygen redox for high-energy SIBs, ensuring long term cyclability.

The origin of stability and high Co2+/3+ redox utilization for FePO4-coated LiCo0.90Ti0.05PO4/MWCNT nanocomposites for 5 V class lithium ion batteries.

Highly-dispersed 10 wt% FePO4 (FP)-coated LiCo0.90Ti0.05PO4 (LCTP) was successfully synthesized within a multiwalled carbon nanotube matrix via our original ultracentrifugation process. 10 wt% FP-coated LCTP sample showed a higher discharge capacity of 116 mA h g−1 together with stable cycle performance over 99% of capacity retention at the 100th cycle in high voltage. A combination of TEM, XRD, XPS, and XAFS analyses suggests that (i) Ti4+-substitution increases the utilization of Co redox (capacity increase) in LCP crystals by suppressing the Co3O4 formation and creating the vacancies in Co sites, and (ii) the FP-coating brought about the Fe enrichment of the surface of LCTP which prevents an irreversible crystal structure change and electrolyte decomposition during cycling, resulting in the stable cycle performance.

(Invited) Quantifying Outgassing, Surface Oxygen Depletion and Solid Carbonate Evolution to Understand Interfacial Reactivity in Cathode Active Materials

Complex degradation processes at the cathode-electrolyte interface limit the high voltage application of conventional and emerging cathode materials (e.g., Li or Ni-rich LiMO2, M= Li, Ni, Mn, Co, (NMC) layered oxides and Li-excess disordered rocksalt materials). We will present results in which quantitative gas evolution and acid titrations are used to identify key contributions to these high voltage instabilities in Ni-rich and Li-rich NMC materials, including electrolyte degradation evolution and the impact that residual solid carbonate has on parasitic reactions.1-2 This presentation will emphasize the need to accurately quantify these minor side reactions to fully understand their large influence on battery performance. We show that by using a short aqueous rinse on NMC powders prior to their integration into porous electrodes, adventitious carbonates are removed from the material surface, which also undergoes a structural change. Both of these effects dramatically reduce parasitic gas evolution from the materials and, in certain cases, improve the active material’s long term cyclability without compromising its capacity.3-4

In-situ grown of polyaniline on defective mesoporous carbon as a high performance supercapacitor electrode material

Abstract Herein, the preparation of a nanocomposite based on a defective mesoporous carbon (DMC) and polyaniline (PANI) as an efficient electrode material for the supercapacitor application is reported. DMC, with the interconnected porous network, was synthesized through a facile process using sucrose, commercial nanoparticles of SiO2 and KNO3 as carbon precursor, hard template and defect generating agent respectively. DMC/PANI nanocomposite was produced via an in-situ polymerization of aniline in the presence of DMC. The preparation of PANI in the porous matrix of DMC was proved using different structural analyses including FT-IR, Nitrogen adsorption/desorption, SEM and TEM. The supercapacitive performance of the obtained nanocomposite (DMC/PANI) was evaluated by cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS) and galvanostatic charge/discharge (GCD) techniques applying 1 M H2SO4 as electrolyte. Compared to DMC and pure PANI, the DMC/PANI delivered the highest specific capacitance reaching to 985 F g−1 at the applied current density of 0.5 A g−1. Even at high charge/discharge rate of 10 A g−1, the excellent specific capacitance of 780 F g−1 was achieved. Moreover, DMC/PANI composite exhibited long term cyclability, in where 82% of specific capacitance was retained after 5000 GCD measurement at high current density of 5 A g−1. Further, a symmetric supercapacitor device based on DMC/PANI was successfully assembled and specific energy of 32 Wh kg−1 at specific power of 125 W kg−1 was obtained. The presented results are higher or comparable to the earlier reported works based on carbon/PANI composite.

Porous FeOx/carbon nanocomposites with different iron oxidation degree for building high-performance lithium ion batteries

Transition metal oxides have attracted lots of interest for lithium ion battery (LIB) due to the high theoretical capacity, however, the large specific volume change, low electrical conductivity and slow intrinsic lithiation/delithiation still limit the practical applications. In order to overcome the challenge, a novel type of high temperature annealing treatment for the synthesis of 3D porous FeOx nanocrystals embedded in a partially carbon matrix as an example for high-performance LIB is reported. The FeOx/carbon nanocomposites with coral-like architecture achieved at 700 °C (F700) exhibit good long term cyclability with a reversible capacity 1012 mAh g−1 remain after 500 cycles at 1.0 A g−1 and the high rate capacity with a reversible capacity of 233 mAh g−1 even at extremely high current density of 20 A g−1. These excellent electrochemical performances could be attributed to the 3D porous structure and carbon coating, which could not only provide excellent electronic conductivity and enough elastic buffer space to accommodate volume changes upon lithium insertion/extraction, but also effectively avoid agglomeration of the Fe3O4 nanocrystals and maintain the structural integrity of the electrode during the charge/discharge process.

Nitrogen self-doped carbon sheets anchored hematite nanodots as efficient Li-ion storage anodes through pseudocapacitance mediated redox process

The evolution of ultrathin carbon layers self-doped by nitrogen assists the formation of α-Fe2O3 nanodots embedded in N-rich carbon sheets by a surfactant-less self-assembly approach and they are reported as anode materials for lithium-ion batteries. The resulting Fe2O3 nanodots confine to size of 3–7nm with evenly embedding in a two-dimensional N-rich carbon sheets. As an anode material, the Fe2O3ND/NC electrode delivers a reversible capacity of 917mAhg−1 at 0.1C rate after 100 cycles and a good rate capability and long term cyclability of 476mAhg−1 at 3C rate after 325 cycles. Detailed investigation through the differential capacity (dQ/dV) and galvanostatic charge/discharge techniques reveal and distinguish the dual role of charge storage, i.e., faradaic and pseudocapacitive processes are involved in realizing improved electrochemical performances. The contribution of the pseudocapacitive capacity from the electrochemical processes accounts for 216mAhg−1, which are due to the Li storages in both the tiny size Fe2O3 and the defective sites of N-doped carbon sheets as portrayed through a model schematic. Altogether, the report paves way for accomplishing multiple avenues, such as in-situ nitrogen doping, preparation of nanodots and ultrathin N-doped carbon sheets for applications in energy conversion and storage devices.

Exploration of electrochemical and lithium transport properties of BaNb3.6O10 as an anode material for lithium-ion batteries

The present study adopts a simple solid-state reaction to successfully prepare phase-pure BaNb3.6O10 as an anode material for lithium-ion batteries. The Rietveld refinement confirms the orthorhombic crystal structure of this material with Pma2 space group. BaNb3.6O10 delivers a specific discharge capacity of 152 mAh/g at a current density of 100 mA/g with a promising capacity retention of 93% after 50 cycles. According to the cyclic voltammetry analysis, BaNb3.6O10 possesses a low polarization of 0.13 V. When the current density is increased five-fold to 500 mA/g, the specific capacity of 119 mAh/g is achieved with a remarkable capacity retention of 78% after 300 cycles. Based on the analysis of cyclic voltammetry and galvanostatic intermittent titration, the diffusion coefficient of BaNb3.6O10 is calculated to be around 10−14 cm2/s. The diffusive contribution towards specific capacity at 0.1 mV/s for BaNb3.6O10 is 67%, which is high than other anodes. Ex-situ XRD analysis reveals that BaNb3.6O10 possesses the same orthorhombic structure after 300 cycles resulting in long term cyclability.

Endogenous Nanoparticles Strain Perovskite Host Lattice Providing Oxygen Capacity and Driving Oxygen Exchange and CH4 Conversion to Syngas

AbstractParticles dispersed on the surface of oxide supports have enabled a wealth of applications in electrocatalysis, photocatalysis, and heterogeneous catalysis. Dispersing nanoparticles within the bulk of oxides is, however, synthetically much more challenging and therefore less explored, but could open new dimensions to control material properties analogous to substitutional doping of ions in crystal lattices. Here we demonstrate such a concept allowing extensive, controlled growth of metallic nanoparticles, at nanoscale proximity, within a perovskite oxide lattice as well as on its surface. By employing operando techniques, we show that in the emergent nanostructure, the endogenous nanoparticles and the perovskite lattice become reciprocally strained and seamlessly connected, enabling enhanced oxygen exchange. Additionally, even deeply embedded nanoparticles can reversibly exchange oxygen with a methane stream, driving its redox conversion to syngas with remarkable selectivity and long term cyclability while surface particles are present. These results not only exemplify the means to create extensive, self‐strained nanoarchitectures with enhanced oxygen transport and storage capabilities, but also demonstrate that deeply submerged, redox‐active nanoparticles could be entirely accessible to reaction environments, driving redox transformations and thus offering intriguing new alternatives to design materials underpinning several energy conversion technologies.

Endogenous Nanoparticles Strain Perovskite Host Lattice Providing Oxygen Capacity and Driving Oxygen Exchange and CH4 Conversion to Syngas

Particles dispersed on the surface of oxide supports have enabled a wealth of applications in electrocatalysis, photocatalysis, and heterogeneous catalysis. Dispersing nanoparticles within the bulk of oxides is, however, synthetically much more challenging and therefore less explored, but could open new dimensions to control material properties analogous to substitutional doping of ions in crystal lattices. Here we demonstrate such a concept allowing extensive, controlled growth of metallic nanoparticles, at nanoscale proximity, within a perovskite oxide lattice as well as on its surface. By employing operando techniques, we show that in the emergent nanostructure, the endogenous nanoparticles and the perovskite lattice become reciprocally strained and seamlessly connected, enabling enhanced oxygen exchange. Additionally, even deeply embedded nanoparticles can reversibly exchange oxygen with a methane stream, driving its redox conversion to syngas with remarkable selectivity and long term cyclability while surface particles are present. These results not only exemplify the means to create extensive, self-strained nanoarchitectures with enhanced oxygen transport and storage capabilities, but also demonstrate that deeply submerged, redox-active nanoparticles could be entirely accessible to reaction environments, driving redox transformations and thus offering intriguing new alternatives to design materials underpinning several energy conversion technologies.

Controlled Oxygen Redox for Excellent Power Capability in Layered Sodium-Based Compounds

Inducing anionic redox reaction of transition metal oxides in sodium ion batteries is one of the most reliable way to enhance capacity. Unfortunately, although the delivered capacity obtained from the transition-metal redox and oxygen redox is one of highest among sodium cathodes, the system suffered from not only serious capacity fading but also poor rate capability because of the sluggish kinetics of the oxygen redox. Given the overlapping in the density of states (DOS) between the oxygen 2p and cobalt 3d (Co4+/3+) orbitals in LiCoO2, which is one of the most representative materials showing good cyclability and acceptable rate performances, we applied this phenomenon to P2 Na0.6[Mg0.2Mn0.8 − xCox]O2 (x = 0.0–0.2). The P2 Na0.6[Mg0.2Mn0.8 − xCox]O2 (x = 0.0–0.2) compounds were synthesized using a spray pyrolysis method. NaNO3, Mn(NO3)2·4H2O, Mg(NO3)2·6H2O, Co(NO3)2·6H2O, citric acid, and sucrose were used as starting materials for the spray pyrolysis. Calcination was conducted at 870 °C in air to obtain the P2 Na0.6[Mg0.2Mn0.8 − xCox]O2 (x = 0.0–0.2). The compounds were stored in an Ar-filled glove box to minimize the moisture contact during storage. Powder X-ray diffraction (XRD; PANalytical, Empyrean) using Cu Kα radiation was employed to identify the crystalline phases of the as-prepared P2 Na0.6[Mg0.2Mn0.8 − xCox]O2 (x = 0.0–0.2) powders. The produced powders were examined using scanning electron microscopy (SEM; SU-8010, Hitachi) to analyze morphology of P2 Na0.6[Mg0.2Mn0.8 − xCox]O2 (x = 0.0–0.2) powders. Differential scanning calorimetry (DSC; Pyris 1, Perkin–Elmer) measurements were performed to analyze the thermal stability of desodiated electrodes. R2032 coin-type cells using Na metal as the negative electrode were assembled for electrochemical cell tests. The electrolyte solution was 0.5 M NaPF6 in a mixed solvent of propylene carbonate (PC) and fluoroethylene carbonate (FEC) in a volume ratio of 98:2. The fabricated cells were charged and then discharged between 1.5 and 4.6 V at a rate of 0.1C (26 mA g− 1), and the current was further raised to 5C (1.3 A g− 1) for a long-term cycle test at 25 °C. X-ray absorption near edge structure (XANES) spectroscopy was employed to understand the variation in the oxidation states of the transition metals and oxygen. Transmission electron microscopy (TEM; JEM-F200, JEOL) was used to analyze structural factors of the pristine P2 Na0.6[Mg0.2Mn0.6Co0.2]O2 electrode and the electrode after 1000 cycles. Density functional theory (DFT) calculations were performed using the projector augmented wave method implemented in the Vienna ab initio simulation package (VASP). Among studied compounds P2 Na0.6[Mg0.2Mn0.8 − xCox]O2 (x = 0.0–0.2), P2 Na0.6[Mg0.2Mn0.6Co0.2]O2 electrode delivered high discharge capacity of about 214 mAh g− 1, which is attributed to the reactions of Co4+/3+, O1 − /2 −, and Mn4+/3+, with approximately 87% (186 mAh g− 1) of the capacity retention over 100 cycles at a rate of 0.1 C (26 mA g-1). More importantly, the present P2 Na0.6[Mg0.2Mn0.6Co0.2]O2 was able to deliver discharge capacities of approximately 108 mAh g− 1 at a rate of 5C (1.3 A g− 1), showing capacity retention of over 72% (78 mAh g− 1) after 1000 cycles (Figure 1). This outstanding electrode performance was rationalized by theoretical calculations; namely, the incorporation of Co in the crystal structure was shown to dramatically reduce the band-gap energies. Detailed information will be presented at the conference. Figure 1. Long–term cyclability at 5 C (1.3 A g− 1) for x = 0.2 in P2 Na0.6[Mg0.2Mn0.8 − xCox]O2. Figure 1

Enhanced active sulfur in soft carbon via synergistic doping effect for ultra–stable lithium–ion batteries

The formation of C–S bonds with high activity in a carbon skeleton is considered to be one of the most effective strategies to facilitate highly reversible alkali storage reactions. In this work, by the combination of heteroatomic control and structural design, N, P and S ternary–doped hierarchical porous soft carbon (NPSC) is obtained with a high concentration of C–S bonds, large specific surface area and large graphitic interlayer spacing. As anode materials for lithium–ion batteries (LIBs), NPSC exhibits a reversible capacity of 500 mA h g−1 and 90% capacity retention can be realized at 500 mA g−1 after 500 cycles, showing its high–rate capability and long–term cyclability. In addition, a full cell based on a LiVPO4F cathode and an NPSC anode delivers high discharge capacity and superior cycling stability. This high performance is attributed to the introduction of P, which promotes the utilization of S through the formation of C–S bonds. In addition, the synergistic doping effect increases the interlayer spacing, facilitating rapid interfacial Li+ adsorption and diffusion reactions. This strategy provides an efficient route toward excellent heteroatom–doped carbon for energy storage and conversion applications.

A P2-type Na0.7(Ni0.6Co0.2Mn0.2)O2 cathode with excellent cyclability and rate capability for sodium ion batteries.

A new P2-type Na0.7(Ni0.6Co0.2Mn0.2)O2 was prepared via co-precipitation and its electrochemical properties as a cathode for sodium ion batteries were compared with those of O3-type Na(Ni0.6Co0.2Mn0.2)O2, focusing on phase stability and cycling performance. The P2-type delivered a high capacity of 108 mA h g-1 after 300 cycles at 2C.

Highly stable SnO2–Fe2O3–C hollow spheres for reversible lithium storage with extremely long cycle life

SnO2-Fe2O3-C triple-shell hollow nano-spheres are fabricated by combining the template-based sol-gel coating technique and hydrothermal method, and their electrochemical performance as an anode for lithium ion batteries (LIBs) is investigated, particularly focusing on their structural stability and long term cyclability. To accomplish this, same-sized SnO2 solid spheres, Fe2O3 solid spheres, SnO2-Fe2O3 solid spheres, SnO2-Fe2O3-C solid spheres, SnO2 hollow spheres and SnO2-Fe2O3 hollow spheres are prepared in a similar manner and their cyclic performances are compared. It is found that the as-synthesized 80 nm-sized SnO2-Fe2O3-C hollow sphere electrode exhibits an extraordinary reversible capacity (1100 mA h g-1 after 100 cycles at 200 mA g-1) and excellent long cycle stability (475 mA h g-1 after 1000 cycles at 2000 mA g-1), which are attributed to the Fe-enhanced reversibility of the Li2O reduction reaction, high electrical conductivity, high Li+ ion mobility, and structural stability of the carbon-coated triple-shell hollow spheres.