Novel architecture of composite electrode for optimization of lithium battery performance

We show that the polymeric binder of the composite electrode may have an important role on the lithium trivanadate Li_1.2V₃O₈ electrode performance. We describe a new tailored polymeric binder combination with controlled polymer–filler (carbon black) interactions that allows the preparation of new and more efficient electrode architecture. Using this polymeric binder, composite electrodes based on Li_1.2V₃O₈ display a room temperature cycling capacity of 280 mAh g⁻¹ (C/5 rate, 3.3–2 V) instead of 150 mAh g⁻¹ using a standard-type (poly(vinylidene fluoride)–hexafluoropropylene (PVdF–HFP) binder) composite electrode. We have coupled scanning electron microscopy (SEM) observations, galvanostatic cycling and electrochemical impedance spectroscopy in order to define and understand the impact of the microstructure of the composite electrode on its electrochemical performance. Derived from these studies, the main key factors that provide efficient charge carrier collection within the composite electrode complex medium are discussed.     

Characterization and preparation of NiO-V2O5 composite film cathodes

NiO-V₂O₅ composite films have been fabricated by 355 nm pulsed laser reactive deposition using mixed metallic Ni and V targets with different molar ratios. The optimal deposition conditions of NiO-V₂O₅ composite films are found to be the substrate temperature of 300 °C and 100 mTorr O₂ ambient. X-ray diffraction (XRD) and scanning electron microscopy (SEM) analyses showed that the crystallinity of the NiO-V₂O₅ composite films gradually decreased with increasing the amount of nickel oxide and transformed to amorphous phase as the molar ratio of NiO/V₂O₅ (x) approaches 0.5. The amorphous (NiO)_0.5V₂O₅ composite film electrode exhibited a specific capacity of 340 mAh/g at a discharge rate of 2 C upon cycling with no obvious fading up to 500 cycles. XRD and X-ray photo-electron spectroscopy (XPS) measurements of NiO-V₂O₅ composite film electrodes revealed that there exists two electrochemical processes upon cycling. During the first discharge, the Li ions insertion process is accompanied by the reduction of NiO into metallic Ni. Then, the reversible processes involving Li ions insertion/extraction in V₂O₅ matrix and oxidation/reduction of Ni and Li₂O take place upon the subsequent cycling.     

Electrochemical lithium insertion into a poly(3,4-ethylenedioxythiophene)PEDOT/V2O5 nanocomposite

A nanocomposite comprised of conductive poly(3,4-ethylene dioxythiophene)PEDOT chains interleaved between the layers of crystalline V₂O₅ powder has been synthesized by direct in situ oxidation. The interlayer spacing of V₂O₅ expands from 4.32 to 13.84 Å and this interlayer separation is consistent with the existence of a monolayer of PEDOT in the V₂O₅ framework. The nanocomposite is coupled with a large-area Li foil counter electrode and a Li wire reference electrode in 1 M LiClO₄ in a mixture of ethylene and dimethylcorbonate (50/50 by volume), the discharge capacity is ≥300 m Ah g⁻¹ which is larger than that of pristine V₂O₅. The significant difference in capacity is explained on the basis of lithium ions insertion/de-insertion between the layers of V₂O₅.     

Novel organic–inorganic poly (3,4-ethylenedioxythiophene) based nanohybrid materials for rechargeable lithium batteries and supercapacitors

Synthesis and characterization of poly (3,4-ethylenedioxythiophene) (PEDOT) interleaved between the layers of crystalline oxides of V and Mo is discussed with special emphasis on their application potential as electrodes for rechargeable Li batteries and supercapacitors. The expansion of the interlayer spacing of crystalline oxides (for example, V₂O₅ causes expansion from 0.43 to 1.41 nm) is consistent with a random layer stacking structure. These hybrid nanocomposites when coupled with a large-area Li foil electrode in 1 M LiClO₄ in a mixture of ethylene and dimethylcarbonate (1:1, v/v), give enhanced discharge capacity compared to pristine oxides. For example a discharge capacity of ∼350 mAh g⁻¹, in the potential range 4.2–2.1 V (versus Li⁺/Li) is obtained for PEDOT–V₂O₅ hybrid which is significantly large compared to that for simple Li-intercalated V₂O_5. The improvement of electrochemical performance compared with that of pristine oxides is attributed to higher electric conductivity, enhanced bi-dimensionality and increased structural disorder. Although these conducting polymer-oxide hybrids delivered more than 300 mAh g⁻¹ in the potential range 1.3–4.3 V, their cycle life needs further improvements to realize their commercial potential. Similarly, the double layer capacitance of MoO₃ increases from ∼40 mF g⁻¹ to ∼300 F g⁻¹ after PEDOT incorporation in the interlayer gap of MoO₃ under similar experimental conditions and the nanocomposite displays intriguing effects with respect to electrochemical Li⁺ insertion. The PEDOT–MoO₃ nanocomposite appears to be a promising electrode material for non-aqueous type supercapacitors.     

Preparation and electrochemical properties of Zn-doped LiNi0.8Co0.2O2

Zn-doped LiZn_yNi_0.8−yCo_0.2O₂ (0.0000≤y≤0.0100) compositions were synthesized by a conventional solid-state method. The products were characterized by XRD, galvanostatic cycling, cyclic voltammetry, electrochemical impedance spectroscopy and thermal analysis. For the LiZn_0.0025Ni_0.7975Co_0.2O₂ system cycled between 3.0 and 4.2 V, the discharge capacities in the 1st and 100th cycles were 170 and 138 mAh/g with charge retention of 81%. The corresponding values for the undoped material were 158 and 97 mAh/g, with charge retention of 61.4%. The improved electrochemical properties of the doped system were attributed to the structural stability derived from incorporating the size-invariant Zn²⁺ ions. The Zn-doped system also showed improved capacity and cyclability when the cycling was performed in a voltage wider window (2.5–4.4 V) and at a higher temperature (55 °C). The structural and electrochemical properties of the doped and undoped materials were correlated.     

Sodium insertion into vanadium pentoxide in methanesulfonyl chloride–aluminum chloride ionic liquid

Methanesulfonyl chloride (MSC) forms a room temperature ionic liquid with AlCl₃. The electrochemical properties of vanadium pentoxide (V₂O₅) films prepared by the sol–gel route were studied in this electrolyte. As a potential cathode, sodium is reversibly intercalated into the V₂O₅ film up to a stoichiometry of 1.6 mole Na/mole V₂O₅ (−1 V versus Al(III)/Al<1.5 V) after the first discharge. The diffusion coefficient (D_Na⁺) in the V₂O₅ film was determined to be between 5E−14 and 9E−12 cm²/s using the potentiostatic intermittent-titration technique.     

Enhanced electrochemical stability of all-polymer redox supercapacitors with modified polypyrrole electrodes

Redox supercapacitors are attracting increasing attention as high power electrochemical sources and can either be coupled with batteries to provide peak power or replace batteries for memory back-up. In the present work, all-polymer solid-state supercapacitors with LiClO₄ and LiCF₃SO₃ doped polypyrrole electrodes and P(VDF-HFP)-PMMA based polymer gel electrolyte are fabricated. The polypyrrole electrodes are irradiated with 160 MeV Ni¹²⁺ ions at 5 × 10¹⁰, 5 × 10¹¹ and 5 × 10¹² ions cm⁻². A comparative study is made between unirradiated and irradiated supercapacitors with polypyrrole-based electrodes. An average capacitance of about 200 F gm⁻¹ is obtained. On successive charging and discharging, the capacitance decreases for supercapacitors with unirradiated electrodes but remains stable when irradiated electrodes are used. In addition, the capacitance is slightly decreased compared with that for unirradiated electrodes. Charge–discharge studies show a decrease in total charge–discharge time for supercapacitors with irradiated electrodes. The capacitance values calculated from cyclic voltammograms are higher than those determined from charge–discharge plots due to the added contribution of a leakage current. The coulombic efficiency of all the supercapacitors is about 90%.     

Triple hybrid materials: A novel concept within the field of organic–inorganic hybrids

We explored a new approach within the field of hybrid materials, namely, an integration of an electroactive inorganic molecule into a conducting polymer that in turn is intercalated into an extended inorganic oxide. In particular we present the specific material formed by hexacyanoferrate-doped polypyrrole or polyaniline inserted in turn into layered V₂O₅. This novel kind of hybrid with three components interacting at a molecular level is what we have called, triple hybrid materials (THM). The synthetic approach was based on our earlier work on PAni/V₂O₅, PAni/HCF and PPy/HCF systems. The materials obtained were characterized by FTIR, XRD, TGA, elemental analyses, and ICP. The electrochemical properties of THMs as insertion cathodes in rechargeable Li cells were also explored. The initial specific charge was high for PPy/HCF/V₂O₅ system (160 Ah kg⁻¹), giving a greater value than for their corresponding simple hybrids: PPy/HCF (69 Ah kg⁻¹) and PPy/V₂O₅ (120 Ah kg⁻¹). Repeated charge–discharge cycles showed a poor cyclability, which could be related to the voltage limit values during recharge, overoxidation of the polymer, or to the detrimental effect of structural water from THMs. Nevertheless, the present work showed a novel route towards a more complex and versatile electroactive hybrid design.     

Synthesis and electrochemical characteristics of LiCrxNi0.5−xMn1.5O4 spinel as 5 V cathode materials for lithium secondary batteries

A series of electrochemical spinel compounds, LiCr_xNi_0.5−xMn_1.5O₄ (x=0, 0.1, 0.3), are synthesized by a sol–gel method and their electrochemical properties are characterized in the voltage range of 3.5–5.2 V. Electrochemical data for LiCr_xNi_0.5−xMn_1.5O₄ electrodes show two reversible plateaus at 4.9 and 4.7 V. The 4.9 V plateau is related to the oxidation of chromium while the 4.7 V plateau is ascribed to the oxidation of nickel. The LiCr_0.1Ni_0.4Mn_1.5O₄ electrode delivers a high initial capacity of 152 mAh g⁻¹ with excellent cycleability. The excellent capacity retention of the LiCr_0.1Ni_0.4Mn_1.5O₄ electrode is largely attributed to structural stabilization which results from co-doping (chromium and nickel) and increased theoretical capacity due to substitution of chromium.     

Li+ ion diffusion in LiMn2O4 thin film prepared by PVP sol–gel method

LiMn₂O₄ thin film (1 μm thick) was prepared on a gold substrate by the PVP sol–gel method. The electrochemical properties of the thin-film electrode were studied in an electrolyte 1 mol dm⁻³ LiClO₄/(ethylene carbonate + diethyl carbonate). The prepared LiMn₂O₄ showed a good charge–discharge performance, and the capacity fade was ca. 20% during 200 cycles. The Li⁺ ion diffusion in the LiMn₂O₄ thin film was investigated by means of potentiostatic intermittent titration technique and electrochemical impedance spectroscopy. The chemical diffusion coefficients were estimated to be 10⁻⁸ to 10⁻¹⁰ cm² s⁻¹.     

Electrochemical characteristics and impedance spectroscopy studies of nano-cobalt silicate hydroxide for supercapacitor

Cobalt silicate hydroxide (Co₃[Si₂O₅]₂[OH]₂) was prepared by chemical method for use in electrochemical capacitors. X-ray diffraction (XRD) and transmission electron microscopy (TEM) tests indicate that the material was pure hexagonal phase with uniform nanometer size distribution. Cyclic voltammeter (CV) and galvanostatic charge/discharge measurements show that the cobalt silicate hydroxide-based electrode has stable electrochemical capacitor properties between potential range of 0.1–0.55 V with a maximum specific capacitance of 237 F g⁻¹ in alkaline solution and 95% of capacity efficiency was reached after 150 cycles. Electrochemical impedance spectra (EIS) investigation illustrates that the capacitance of the test electrode was mainly consisted of pseudo-capacitance, which was caused by underpotential deposition of H₃O⁺ at the electrode surface.     

Synthesis and characterization of spherical morphology [Ni0.4Co0.2Mn0.4]3O4 materials for lithium secondary batteries

Spherical morphology [Ni_0.4Co_0.2Mn_0.4]₃O₄ materials have been synthesized by ultrasonic spray pyrolysis. The Li[Ni_0.4Co_0.2Mn_0.4]O₂ powders were prepared at various pyrolysis temperatures between 500 and 900 °C. The Li[Ni_0.4Co_0.2Mn_0.4]O₂ material prepared at a pyrolysis temperature of 600 °C samples are exhibited excellent electrochemical cycling performance and delivered the highest discharge capacity at over 180 mAh g⁻¹ between 2.8 and 4.4 V. The structural, electrochemical, morphological property and thermal stability of the powders were characterized by X-ray diffraction (XRD), galvanostatic charge/discharge testing, scanning electron microscopy (SEM), and differential scanning calorimeter (DSC), respectively.     

Preparation and characterization of high-density spherical Li4Ti5O12 anode material for lithium secondary batteries

Li₄Ti₅O₁₂ is a very promising anode material for lithium secondary batteries. A novel technique has been developed to prepare Li₄Ti₅O₁₂. The spherical precursor is prepared via an “inner gel” method by TiCl₄ as the raw material. Spherical Li₄Ti₅O₁₂ powders are synthesized by sintering the mixture of spherical precursor and Li₂CO₃. The investigation of XRD, SEM and the determination of the electrochemical properties show that the Li₄Ti₅O₁₂ powders prepared by this method are spherical, and have high tap-density and excellent electrochemical performance. It is tested that the tap-density of the product is as high as 1.64 g cm⁻³, which is remarkably higher than the non spherical Li₄Ti₅O₁₂. Between 1.0 and 3.0 V versus Li, a reversible capacity is as high as 161 mAh g⁻¹ at a current density of 0.08 mA cm⁻².     

Nanocrystalline tin oxides and nickel oxide film anodes for Li-ion batteries

Tin oxides and nickel oxide thin film anodes have been fabricated for the first time by vacuum thermal evaporation of metallic tin or nickel, and subsequent thermal oxidation in air or oxygen ambient. X-ray diffraction (XRD) and scanning electron microscopy (SEM) measurements showed that the prepared films are of nanocrystalline structure with the average particle size <100 nm. The electrochemical properties of these film electrodes were examined by galvanostatic cycling measurements and cyclic voltammetry. The composition and electrochemical properties of SnO_x (1<x<2) films strongly depend on the oxidation temperature. The reversible capacities of SnO and SnO₂ films electrodes reached 825 and 760 mAh g⁻¹, respectively, at the current density of 10 μA cm⁻² between 0.10 and 1.30 V. The SnO_x film fabricated at an oxidation temperature of 600 °C exhibited better electrochemical performance than SnO or SnO₂ film electrode. Nanocrystalline NiO thin film prepared at a temperature of 600 °C can deliver a reversible capacity of 680 mAh g⁻¹ at 10 μA cm⁻² in the voltage range 0.01–3.0 V and good cyclability up to 100 cycles.     

Large scale hydrothermal synthesis and electrochemistry of ammonium vanadium bronze nanobelts

Single crystalline ammonium vanadium oxide bronze NH₄V₄O₁₀ nanobelts were synthesized by the hydrothermal treatment of H₂C₂O₄·2H₂O and NH₄VO₃ at 140 °C for 48 h. The NH₄V₄O₁₀ nanobelts were characterized using a combination of techniques including X-ray diffraction, transmission electron microscopy, selected area electronic diffraction, scanning electron microscopy and X-ray photoelectron spectroscopy techniques. The as-obtained nanobelts are several microns long, typically 30–40 nm wide, and 10–20 nm thick. The electrochemical properties of the nanobelts were tested in cells with metallic lithium as the negative electrode, the first discharge capacity of 171.8 mAh g⁻¹ was achieved.     

Potassium manganese–vanadium oxide cathodes prepared by hydrothermal synthesis

Hydrothermal reactions between potassium permanganate and vanadyl sulfate have been used to synthesize new forms of vanadium oxides. Depending on the reactant ratios and pH values of the reaction mixtures, two different layered materials have been identified. The first one formed at a pH value of 1.6 has an interlayer distance of 10.90 Å and a composition of K_0.16Mn_0.04V₂O_4.94·0.14H₂O, while the second one formed at pH values higher than 3.0 has an interlayer distance of 9.45 Å and a composition of K_0.44V₂O_4.96. Structural analysis indicates that they have a δ-type structure with potassium ions residing in between double sheets of vanadium oxide. The structure and composition of these materials have a profound effect on their charge and discharge properties when used as cathodes in lithium batteries. The sample prepared at a pH value of 2.3 shows best overall performance considering both reversible capacity and cyclability, which is explained with the coexistence of two layered phases in the material. This material has a capacity of over 200 mA h/g between 3.6 and 2.2 V and retains a capacity of 190 mA h/g after 30 cycles. Increase of manganese to vanadium ratio during synthesis leads to a gradual loss of the layered structure and decreased lithium insertion capacity.     

LiMn2O4 cathode materials synthesized by the cellulose–citric acid method for lithium ion batteries

A new technique was employed to synthesize spinel LiMn₂O₄ cathode materials by adding cellulose and citric acid to an aqueous solution of lithium and manganese salts. Various synthesis conditions such as the calcination temperature and the citric acid-to-metal ion molar ratio (R) were investigated to determine the ideal conditions for preparing LiMn₂O₄ with the best electrochemical characteristics. The optimal synthesis conditions were found to be R = 1/3 and a calcination temperature of 800 °C. The initial discharge capacity of the material synthesized using the optimal conditions was 134 mAh g⁻¹, and the discharge capacity after 40 cycles was 125 mAh g⁻¹, at a current density of 0.15 mA cm⁻² between 3.0 and 4.35 V. Details of how the initial synthesis conditions affected the capacity and cycling performance of LiMn₂O₄ are discussed.     

Factors affecting the electrochemical performance of organic/V2O5 hybrid cathode materials

Polyaniline–V₂O₅ hybrid materials have been prepared by an oxidative intercalation reaction and the factors that affect their electrochemical discharge–charge performance have been investigated. The first discharge capacity of a sample produced from a nominal molar ratio of aniline: V₂O₅=3 (V₂O₅–(AN)3.0) is higher than that of a sample prepared from the lower ratio of aniline: V₂O₅=0.5 (V₂O₅–(AN)0.5). The V₂O₅–(AN)0.5 sample also shows better reversibility. Samples have been post-treated at different temperatures in air or oxygen. Post-treatment improves the electrochemical performance of V₂O₅–(AN)0.5 but degrades both the capacity and reversibility of V₂O₅–(AN)3.0. A V₂O₅–(AN)0.5 sample post-treated at 70 °C in air exhibits the best discharge–charge characteristics.     

Preparation and electrochemical studies of Fe-doped Li3V2(PO4)3 cathode materials for lithium-ion batteries

The Fe-doped Li₃V₂(PO₄)₃ cathode materials for Li-ion batteries were synthesized by a conventional solid-state reaction, and the Fe-doping effects on the Li electrochemical extraction/insertion performance of Li₃V₂(PO₄)₃ were investigated by galvanostatic charge/discharge and cyclic voltammetry measurements. The optimal Fe-doping content x is 0.02–0.04 in Li₃Fe_xV_2−x(PO₄)₃ system. The Fe-doped Li₃V₂(PO₄)₃ samples showed a better cyclic ability between 3.0 and 4.9 V, for example, the discharge capacity of Li₃Fe_0.02V_1.98(PO₄)₃ was 177 mAh g⁻¹ in the 1st cycle and 126 mAh g⁻¹ in the 80th cycle. The retention rate of discharge capacity is about 71%, much higher than 58% of the undoped system. The improved electrochemical performances of the Li₃V₂(PO₄)₃ could be attributed to the increased electrical conductivity and structural stability deriving from the incorporation of the Fe³⁺ ions.     

Manganese oxide film electrodes prepared by electrostatic spray deposition for electrochemical capacitors from the KMnO4 solution

Manganese oxide film electrodes for electrochemical capacitors were deposited on the polished Pt foils by electrostatic spray deposition (ESD) from KMnO₄ precursor solution. The electrochemical properties of electrodes were systematically studied using cyclic voltammetry (CV), constant current charge–discharge tests, and electrochemical impedance spectroscopy (EIS). The specific capacitance (SC) of thick deposited film was 149 F g⁻¹ at the very high scan rate of 500 mV s⁻¹, in comparison with 209 F g⁻¹ at the low scan rate of 5 mV s⁻¹. The electrode shows good cyclic performance. The initial SC value was 163 F g⁻¹ and 103% of the initial SC can be retained after 10,000 cycles at the scan rate of 50 mV s⁻¹.