Doped Electrode Material Research Articles

Enhancing the energy storage performance of titanium dioxide electrode material by green doping of Nd2O3 nanoparticles for electrochemical supercapacitors

Doping of sesquioxide alloy onto TiO2 nanomaterials was carried out in a novel green chemistry method using Corallo carpus epigaeus to fabricate the electrodes for pseudocapacitors. The conducted X-ray diffraction studies demonstrated the tetragonal phase of TiO2 and hexagonal phase of Nd2O3 nanomaterials. Morphological analysis revealed the irregular shape of TiO2 materials, each exceeding 100 nm in size, while Nd2O3 materials exhibited a spherical shape within the range of 10–20 nm. Electrochemical investigations unveiled a quasi-rectangular shape in cyclic voltammetric studies and a triangular shape in galvanostatic reactions, suggesting superior electrochemical performance of the electrodes. The doped electrodes exhibited a higher specific capacitance value (785.71 F/g) compared to pure TiO2 (707.14 F/g) at a current density of 1 A/g. These findings affirm the suitability of doped electrode materials for applications in electrical energy storage.

N, P, S triple-doped honeycomb porous carbon multi-dimensionally enhanced CoP for pseudocapacitance-driven high-power lithium storage

Enhancing the electrical conductivity and relieving the volume expansion is essential to boost the lithium storage performance of CoP. Herein, carbon-coated CoP particles are uniformly embedded into N, P, and S triple-doped honeycomb porous carbon (CoP@NPSC) synthesized via a one-step foaming method. In this structure, N, P, and S doping improved the charge transfer kinetics, ion transport capacity, and pseudocapacitance contribution of the CoP@NPSC electrode, respectively. The synergistic effect of the three elements further endows CoP@NPSC with abundant electrochemical reaction sites, optimized pore structure and high electrical conductivity. In addition, the CoP nanoparticles are stably embedded in the pore channels by forming surface chemical bonds with the honeycomb porous carbon, and the carbon sheets are connected by triangular branched chains, which enhances the structural stability and effectively mitigates the volume expansion of CoP. Based on the excellent structure with triple-doping synergistic effect, the CoP@NPSC anode applied to lithium-ion batteries delivers ultra-high reversible capacity (1237.7 mAh g−1 at 0.5 A g−1) and ultra-long cycle stability at high rates (280.3 and 241.8 mAh g−1 at 5.0 and 10.0 A g−1 after 5000 cycles with no significant capacity decay). This study provides an effective strategy for designing high-performance doped electrode materials.

Highly stable Co-doped MnO2 nanoarrays as enhanced cathode materials for aqueous zinc-ion batteries

ABSTRACT Aqueous zinc-ion batteries (ZIBs) are a promising battery technology because of low costs and high safety. However, dissolution, self-aggregation and irreversible phase changes during charge and discharge of cathode materials may severely restrict the cycle stability of ZIBs. The main objective of this work was to prepare a more stable cathode material. For this purpose, we successfully prepared transition metal Co-doped MnO2 (Co-MnO2) using a simple one-step potentiostatic electrodeposition method. Co-MnO2 showed a high specific capacity of 237 mAh g−1 at 0.1 A g−1. Even at a high current density of 4 A g−1, the capacity retention was 87 mAh g−1. When returning back to 0.1 A g−1, the capacity retention rate exceeded 100%. Compared with long-cycle performance of the undoped MnO2, the electrochemical performance of the ion-doped electrodes with transition metal was significantly improved. The results indicate that transition metal doped electrode material (here Co-MnO2) can significantly improve the electrochemical performance and structural stability of the electrode material and improve the cycling performance. The results are relevant for the developing advanced cathodes for ZIBs.

Two-step synthesis of B and N co-doped porous carbon composites by microwave-assisted hydrothermal and pyrolysis process for supercapacitor application

A series of nitrogen and boron co-doped porous carbon composites (BNCs) were obtained using quick, easy and environmentally microwave-assisted hydrothermal treatment combined with a pyrolysis process subsequent. Biomass waste of fir bark is used as the carbon precursor, while ammonium pentaborate tetrahydrate is used as both boron (B) and nitrogen (N) source. The synthesis process and characteristics of the developed BNCs are investigated, and the results show that the N and B is successfully doped, generating a synergetic effect on the structure, surface characteristics and electrochemical properties. The BNCs achieves specific surface area up to 955 m2 g−1 with mainly microporosity, and possess 10–13 % of B and 15~20 % of N content. The gravimetric capacitance values for the electrodes containing BNC-20 active materials is 188 F g−1 at 0.5 A g−1, 2 times that of non-doped carbon, while maintaining 90% capacitance retention capability after 10,000 charge/discharge cycles. Furthermore, the assembled symmetric cell yielded high performance of volumetric capacitive of 91 F cm−3 at 0.5 A g−1, superior energy density of 9.33 Wh kg−1 at 400 W kg−1 with 91% capacitance retention after 10,000 charge/discharge cycles at 1 A g−1. Our work offers a potential relatively low-cost, effective and environmentally design of heteroatoms doped electrode materials with enhanced supercapacitors performance.

An efficient pseudocapacitor electrode material with co-doping of iron (II) and sulfur in luminescent graphene quantum dots

An efficient electrode material (Fe (II)S-GQDs) has been prepared by co-doping of sulfur and iron atoms with Graphene quantum dots. A top down synthesis method including a facile and one-pot hydrothermal was used to develop high capacity and good stability electrode material by selecting ferrous sulphate powder (FeSO4.7H2O) and graphene oxide (GO) as a precursor material. The results obtained from TEM measurements reveal the size alters from micrometer graphene sheets of GO to nano-meter dots for GQDs and Fe (II)S-GQDs. The electrochemical studies reveal that Fe(II) S doped GQDs can exhibit a reversible redox reaction with excellent specific capacitance of 476.2 F/g as compared to that of GQDs (143F/g). It has been found that there is an improvement in electrical conductivity and electron transfer in addition to the largest charge storage capacity. More remarkably, the doped electrode material shows a small charge transfer resistance (Rct) value (30 Ω) in case of Fe(II)S-GQDs as compared to GQDs (2.5 kΩ) due to fast diffusion of ion and electron between working electrodes and electrolyte.

(Battery Division Postdoctoral Associate Research Award Sponsored by MTI Corporation and the Jiang Family Foundation) Synchrotron Characterization to Inform Design for Cathode Materials in Li/Na Batteries

The ever-increasing demand for renewable energy storage and electrifying transportation calls for developing high energy density electrode materials for rechargeable alkali metal ion batteries. Cathode materials such as layered oxides play a crucial role in determining the energy density and safety of batteries. Major efforts have been invested to push the cathode capacity approaching its theoretical limit while reducing the cost of raw materials (e.g., Co-free cathode pathways). However, the technical challenges are amplified under aggressive operating conditions, particularly at elevated temperatures or high charging voltages. Understanding the fading mechanisms under these aggressive conditions (e.g., chemomechanical breakdown, interfacial degradation, metal dissolution, charge heterogeneity) will inform the material design principles. With advanced synchrotron X-ray, electron, and electrochemical diagnostics, we will present our recent progress in probing the fading mechanisms in Li ion and Na ion batteries. Our study has treated batteries as ecosystems and thoroughly considered the cathode-anode crosstalk. Finally, we will explain how we have made use of the gained knowledge to guide our syntheses of Co-free Li cathodes, water-processable Na cathodes, and hierarchically doped electrode materials.

Superior electrochemical properties of Li[Li0.2Ni0.18Mn0.6Mg0.02]O2 cathode material with hierarchical micro−nanostructure for lithium ion batteries

Li[Li0.2Ni0.18Mn0.6Mg0.02]O2 electrode material with hierarchical micro‒nanostructure is prepared via a porous polypropylene membrane as the hard template. The X‒ray diffraction (XRD) spectrum shows that the doping of Mg2+ does not affect the crystal structure of the sample, and there is no diffraction peaks related to any impurities. The scanning electron microscopy (SEM), transmission electron microscopy (TEM) and energy dispersive spectroscopy (EDS) mapping deliver that the sample composed of nanoparticles has a porous sheet‒like structure, and the elements (i.e., Mn, Ni, Mg and O) are uniformly distributed in the viewed regions. The X‒ray photoelectron spectroscopy (XPS) shows that the valence states of the Mg, Mn and Ni elements in the sample are +2, +4 and + 2, respectively, and a small amount of Mn3+ and Ni3+ is also present for the valence degeneracy effect. Electrochemical properties show that the Mg2+‒doped electrode material compared with pristine sample has lower initial irreversible capacity loss, higher charge/discharge specific capacity, better rate performance and capacity retention. The outstanding electrochemical performance of the Li[Li0.2Ni0.18Mn0.6Mg0.02]O2 could be attributed to the enhanced structure stability, improved the purity for the decrease of valence degeneracy, reduced the charge transfer resistance and improved the diffusion coefficient of lithium ions during prolonged cycling.

Doping supervalent rare earth ion in LiFePO4/C through hydrothermal method

Hydrothermal synthesized LiFePO4/C and LiFe0.95M0.05PO4/C (M=Sm, Eu, Yb) are studied in this paper. The samples are characterized by X-ray diffraction (XRD), scanning electron microscope (SEM), energy dispersive spectroscopy (EDS), thermogravimetric analysis and Brunauer–Emmett–Teller (BET). The electrochemical performance is evaluated via galvanostatic charge–discharge, electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV). The hydrothermal synthesized particles are nano scale level. The results show that the first discharge capacity of the as-prepared LiFePO4/C and LiFe0.95M0.05PO4/C (M=Sm, Eu, Yb) is 109.4mAh/g, 153.6mAh/g, 144.0mAh/g and 160.7mAh/g at 0.2 C, respectively, and reduces to 65.1mAh/g, 147.7mAh/g, 141.3mAh/g and 152.6mAh/g after 20cycles, respectively. The specific surface area of LiFePO4/C and LiFe0.95M0.05PO4/C (M=Sm, Eu, Yb) is 18.3m2/g, 25.2m2/g, 21.5m2/g and 25.4m2/g, respectively. The exchange current density for LiFe0.95M0.05PO4/C (M=Sm, Eu, Yb) composite is 121mA·g−1, 89.8mA·g−1, 138.8mA·g−1, respectively, which is much larger than that for LiFePO4/C, 12.5mA·g−1. The result of cyclic voltammetry indicates that the difference between anode peak potential and cathode peak potential reduces and the reversibility of electrochemical reaction is enhanced at doped electrode materials. The electrochemical performances are apparently improved due to doping supervalent rare earth ion in LiFePO4/C.

Excellent rate performance and high capacity of Mo doped layered cathode material Li[Li0.2Mn0.54Ni0.13Co0.13]O2 derived from an improved coprecipitation approach

A Mo-doped layered cathode materials Li[Li0.2Mn0.54Ni0.13Co0.13]O2 (LMNC) with an excellent rate performance and high capacity have been successfully synthesized by a facile and novel organic co-precipitation process. The effect of trace Mo-doped on the surface morphology and crystal structures have been investigated by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS). The results reveal that the Mo6+-doped electrode material with an optimal content could show a uniform particles size distribution and well-crystallization. Electrochemical measurements, including charge-discharge, cyclic voltammetry (CV) and electrochemical impedance spectra (EIS) have also been employed. It is demonstrated that the Mo-doped LMNC composites exhibit significant improvements on the electrochemical performance including the capacity, rate capability and cycle performance. For example, the initial discharge capacity is 260.8mAhg−1 at 1C for an optimal Mo-doped electrode, and still maintains an initial discharge capacity of 142.3 and 85.5mAhg−1 at 10 and 20C, and capacity retention could still be 83.56% and 96.14% after 100 cycles, respectively, indicating its excellent cycle and rate capability for LMNC materials. It is believed that the remarkably enhanced rate capability and cycling stability of these modified electrodes might be ascribed to trace Mo substitution prepared by this organic co-precipitation process.

Investigation on physiochemical properties of Mn substituted spinel cobalt oxide for supercapacitor applications

Investigation on physiochemical properties and electrochemical performance of doped cobalt spinel oxide was carried by doping manganese ions into the cobalt oxide spinel system at various concentrations (5% - 20%) using co-precipitation method. The influence of Mn incorporation on the structure and physical properties of the cobalt oxide were investigated using XRD, FTIR and HRSEM. It was found that, with Mn addition unit cell volume increases and the crystallite growth of the electrode materials was hindered. Jahn teller distortion associated with Mn3+ ions has made the spinel lattice more compressible, aiding facile insertion/exertion of electrolyte ions. From SEM observations, compact agglomerates found in pure cobalt oxide changes to loosely packed agglomerates on Mn addition. From the XPS studies, manganese concentration in the doped samples were identified to be close to the initial doping percentage (MnxCo3-xO4; x=4.61, 8.25, 14.13 & 18.10%). It also reveals the preferential octahedral occupancy of Mn3+ ions in cobalt oxide spinel lattice. Electrochemical characterization of as synthesized electrode materials was performed with cyclic voltammetry (CV), chronopotentiometry (CP) and electrochemical impedance spectroscopy (EIS). Specific current density of the electrodes increased with increasing Mn content for fixed scan rates. Specific capacitance (SC) values were calculated for the electrode materials from CV and CP. Electrode material doped with 20% Mn exhibits the highest SC of 440 Fg−1. Low equivalent series resistance (ESR) and reduced ion diffusion resistance was observed for Mn doped electrode materials. According to the results, 10% and 20% manganese doped cobalt oxide electrode materials demonstrates superior capacitive behavior than other prepared materials. Mn addition has improved the compound integrity on cycling and also increased the overall electrochemical performance of the electrode materials.

Doping effects on the physicochemical and electrochemical properties of lanthanum manganite

The structural, thermal, electrical, and electrochemical properties of La0.7Ca0.3Mn1-x(Co,Ni)xO3 and La0.6Sr0.4Mn1-x(Co,Ni)xO3 (x = 0, 0.02, 0.05, 0.1) electrode materials were studied. Doping of the cubic perovskites with Co or Ni increases the fraction of Mn4+ ions, up to 49% in La0.7Ca0.1O3 and 57% in La0.6Sr0.4Mn0.95Co0.05O3. The 300-K conductivity of La0.7Ca0.3Mn1-xNixO3 passes through a maximum atx = 0.05, while that of La0.6Sr0.4Mn1-xCoxO3 decreases steadily with increasingx. In the range 300–1100 K, the conductivity of the Ca-containing manganites exhibits semiconducting behavior, whereas that of the Sr-containing materials shows metallic behavior. No phase transformations were detected in this temperature range. In the four systems, the thermal-expansion coefficients are virtually independent ofx. In both undoped and doped electrode materials, the resistance parameterp/d of electrode layers on solid-electrolyte substrates shows semiconducting behavior at temperatures from 300 to 1100 K and oxygen partial pressures from 102 to 105 Pa. With increasing oxygen partial pressure or electrode-layer thickness (d = 15–100 mg/cm2),p/d decreases. The optimal electrode-layer thickness is found to be about 50 mg/cm2. The introduction of Co or Ni into the electrode materials decreases the polarization resistance of the electrode layer in gas/electrode/electrolyte systems. Compositions ensuring the lowest polarization resistance were found.