Lithiation of ramsdellite–pyrolusite MnO2; NMR,XRD, TEM and electrochemical investigation of the discharge mechanism

Electrolytic manganese dioxide (EMD) is made in aqueous sulfuric acid and neutralized or ion exchanged with aqueous lithium hydroxide before use in Li batteries. Solid state Li NMR studies show that Li is present on surface and vacancy sites and migrates into Mn (III) related sites after heat treatment to remove water. During heat treatment the MnO₂ rearranges from ramsdellite/pyrolusite intergrowth EMD to a defect pyrolusite heat-treated manganese dioxide (HEMD). EMD exhaustively treated with lithium hydroxide solution has 40–50% of the protons in EMD exchanged for Li ions to produce a structurally unchanged γ-MnO₂. Li magic angle spinning (MAS) NMR reveals that this lithiated material contains lithium in cation vacancy and Mn (III) related sites in the MnO₂ lattice in addition to ionic Li on the surface. During heat treatment, the vacancy lithium content prevents the ramsdellite to pyrolusite rearrangement in HEMD formation. Instead, an ordered ramsdellite/pyrolusite intergrowth of lithiated manganese dioxide (LiMD) is formed with an approximate composition of 50% ramsdellite and 50% pyrolusite. Li MAS NMR of LiMD shows Li resonances near 280 and 560 ppm, consistent with Li transition from surface and cation vacancy sites into the ramsdellite lattice.LiMD discharged against lithium shows two processes, one near 3.1 V, the other about 2.8 V. Li MAS NMR studies show the initial reduction results a lithium resonance near 560 ppm associated with Li near a mixed valence Mn (III/IV) environment followed by appearance of a resonance near 100 ppm consistent with a Li environment near Mn (III). TEM studies of the reduced material show initial expansion of the ramsdellite lattice accompanied by a loss in crystallinity in the 3.1 V discharge process followed by disappearance of the pyrolusite content via conversion to ramsdellite in the second discharge process.     

Preparation of manganese oxide with high density by decomposition of MnCO3 and its application to synthesis of LiMn2O4

Manganese oxide with high tap density was prepared by decomposition of spherical manganese carbonate, and then LiMn₂O₄ cathode materials were synthesized by solid-state reaction between the manganese oxide and lithium carbonate. Structure and properties of the samples were determined by X-ray diffraction, Brunauer–Emmer–Teller surface area analysis, scanning electron microscope and electrochemical measurements. With increase of the decomposition temperature from 350 °C to 900 °C, the tap density of the manganese oxide rises from 0.91 g cm⁻³ to 2.06 g cm⁻³. Compared with the LiMn₂O₄ cathode made from chemical manganese dioxide or electrolytic manganese dioxide, the LiMn₂O₄ made from manganese oxide of this work has a larger tap density (2.53 g cm⁻³), and better electrochemical performances with an initial discharge capacity of 117 mAh g⁻¹, a capacity retention of 93.5% at the 15th cycle and an irreversible capacity loss of 2.24% after storage at room temperature for 28 days.     

Electrochemical synthesis of birnessite-type layered manganese oxides for rechargeable lithium batteries

Layered manganese dioxide (MnO₂) films intercalated with Li⁺, Na⁺ or Mg²⁺ ions were synthesized by a one-step electrochemical method. The electrodeposition was potentiostatically performed by applying an anodic potential of 1.0 V vs. Ag/AgCl in an aqueous MnSO₄ solution containing a perchlorate salt of the cation. The electrodeposited oxide films have a birnessite-type layered structure with alkali cations and water molecules between manganese oxide layers. The galvanostatic charge–discharge experiments performed in 1 M LiPF₆-DME/PC solution indicated that the Mg²⁺-intercalated MnO₂ electrode exhibits an initial discharge capacity as large as 140 mAh g⁻¹ and it shows a better capacity retention during cycling as compared with the Li⁺- or Na⁺-intercalated MnO₂ electrode.     

Cerium and zinc: Dual-doped LiMn2O4 spinels as cathode material for use in lithium rechargeable batteries

Pristine spinel lithium manganese oxide (LiMn₂O₄) and zinc- and cerium-doped lithium manganese oxide [LiZn_xCe_yMn_2−x−yO₄ (x = 0.01–0.10; y = 0.10–0.01)] are synthesized for the first time via the sol–gel route using p-amino benzoic acid as a chelating agent to obtain micron-sized particles and enhanced electrochemical performance. The sol–gel route offers shorter heating time, better homogeneity and control over stoichiometry. The resulting spinel product is characterized through various methods such as thermogravimetic and differential thermal analysis (TG/DTA), Fourier-transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive X-ray analysis (EDAX) and electrochemical galvanostatic cycling studies. Charge–discharge studies of LiMn₂O₄ samples heated at 850 °C exhibit a discharge capacity of 122 mAh g⁻¹ and a corresponding 99% coulombic efficiency in the 1st cycle. The discharge capacity and cycling performance of LiZn_0.01Ce_0.01Mn_1.98O₄ is found to be superior (124 mAh g⁻¹), with a low capacity fade (0.1 mAh g⁻¹ cycle⁻¹) over the investigated 10 cycles.     

Nickel oxyhydroxide/manganese dioxide composite as a candidate electrode material for alkaline secondary cells

Nickel hydroxide and manganese dioxide are used in alkaline cells as positive electrode materials. Positive electrodes comprising a nickel oxyhydroxide/manganese dioxide composite, with modification by Bi₂O₃, deliver a combined reversible discharge capacity of 2.25e per metal atom (650 mAh g⁻¹ metal content), which is higher than that realized from electrodes of either component taken singly. The composite discharges with two potential plateaux, the first appearing at 325 mV corresponds to the discharge of the nickel component, whereas the second at −600 mV is due to the manganese component. Composites of NiO(OH)/MnO₂ can be used as a new electrode material with higher discharge capacity than conventional electrodes.     

TiO2(B) as a promising high potential negative electrode for large-size lithium-ion batteries

Needle-like TiO₂(B) powder was obtained from K₂Ti₄O₉ precursor by ion exchange to protons, followed by dehydration. The charge and discharge characteristics of the TiO₂(B) powder were investigated as a high potential negative electrode in lithium-ion batteries. It had a high discharge capacity of 200–250 mAh g⁻¹ at around 1.6 V vs. Li/Li⁺, which was comparable with that of TiO₂(B) nanowires and nanotubes prepared via a hydrothermal reaction in alkaline solution. It showed very good cycleability, and gave a discharge capacity of 170 mAh g⁻¹ even in the 650th cycle. It also had a high rate capability, and gave a discharge capacity of 106 mAh g⁻¹ even at 10 °C.     

Fabrication and electrochemical characterization of a vertical array of MnO2 nanowires grown on silicon substrates as a cathode material for lithium rechargeable batteries

A complementary metal-oxide-semiconductor (CMOS) compatible process for fabricating on-chip microbatteries based on nanostructures has been developed by growing manganese dioxide nanowires on silicon dioxide (SiO₂)/silicon (Si) substrate as a cathode material for lithium rechargeable batteries. High aspect-ratio anodized aluminum oxide (AAO) template integrated on SiO₂/Si substrates can be exploited for fabrication of a vertical array of nanowires having high surface area. The electrolytic manganese dioxide (EMD) nanowires are galvanostatically synthesized by direct current (dc) electrodeposition. The microstructure of these nanowire arrays is investigated by scanning electron microscopy and X-ray diffraction. Their electrochemical tests show that the discharge capacity of about 150 mAh g⁻¹ is maintained during a few cycles at the high discharge/charge rate of 300 mA g⁻¹.     

Electrochemical properties of manganese oxide coated onto carbon nanotubes for energy-storage applications

Birnessite-type manganese dioxide (MnO₂) is coated uniformly on carbon nanotubes (CNTs) by employing a spontaneous direct redox reaction between the CNTs and permanganate ions (MnO₄⁻). The initial specific capacitance of the MnO₂/CNT nanocomposite in an organic electrolyte at a large current density of 1 A g⁻¹ is 250 F g⁻¹. This is equivalent to 139 mAh g⁻¹ based on the total weight of the electrode material that includes the electroactive material, conducting agent and binder. The specific capacitance of the MnO₂ in the MnO₂/CNT nanocomposite is as high as 580 F g⁻¹ (320 mAh g⁻¹), indicating excellent electrochemical utilization of the MnO₂. The addition of CNTs as a conducting agent improves the high-rate capability of the MnO₂/CNT nanocomposite considerably. The in situ X-ray absorption near-edge structure (XANES) shows improvement in the structural and electrochemical reversibility of the MnO₂/CNT nanocomposite after heat-treatment.     

Synthesis and electrochemical properties of Li1−xFe0.8Ni0.2O2–LixMnO2 (Mn/(Fe + Ni + Mn) = 0.8) material

A new type of Li_1−xFe_0.8Ni_0.2O₂–Li_xMnO₂ (Mn/(Fe + Ni + Mn) = 0.8) material was synthesized at 350 °C in air atmosphere using a solid-state reaction. The material had an XRD pattern that closely resembled that of the original Li_1−xFeO₂–Li_xMnO₂ (Mn/(Fe + Mn) = 0.8) with much reduced impurity peaks. The Li/Li_1−xFe_0.8Ni_0.2O₂–Li_xMnO₂ cell showed a high initial discharge capacity above 192 mAh g⁻¹, which was higher than that of the parent Li/Li_1−xFeO₂–Li_xMnO₂ (186 mAh g⁻¹). We expected that the increase of initial discharge capacity and the change of shape of discharge curve for the Li/Li_1−xFe_0.8Ni_0.2O₂–Li_xMnO₂ cell is the result from the redox reaction from Ni²⁺ to Ni³⁺ during charge/discharge process. This cell exhibited not only a typical voltage plateau in the 2.8 V region, but also an excellent cycle retention rate (96%) up to 45 cycles.     

Cost-effective and ecologically safe electrolyte for lithium batteries

The electrochemical characteristic of solutions of lithium benzolsulfonate in dimethylsulfoxide is considered. DTA/TGA is employed to analyze the thermal stability of salt. The conductivity of solutions was determined. So, for example, conductivity lithium benzolsulfonate in dimethylsulfoxide is 3.8 mSm/cm. The area electrochemical stability of solutions is in an interval 4.5–4.6 V. Electrochemical properties of lithium manganese oxide spinel in tested solutions were investigated. The charge–discharge capacity of lithium manganese oxide spinel is 65 mAh g⁻¹ (in interval of potentials from 3.2 to 4.4 V Li/Li⁺) and 190 mAh g⁻¹ (in interval of potentials from 1.8 to 4.0 V Li/Li⁺) for vanadium oxide (V).     

Surface-modified maghemite as the cathode material for lithium batteries

The inorganic–organic hybrid maghemite (γ-Fe₂O₃)/polypyrrole (PPy) was synthesized and evaluated as cathode-active material for room temperature lithium batteries. The nanometer-sized core–shell structure of the hybrid consisting of the maghemite core with surface modified by PPy was evidenced from the morphological examination. The cathode fabricated with the as-prepared hybrid material delivered an initial discharge capacity of 233 mAh g⁻¹ and a reversible capacity of ∼62 mAh g⁻¹ after 50 charge–discharge cycles. A much higher performance with an initial discharge capacity of 378 mAh g⁻¹ and a reversible capacity of ∼100 mAh g⁻¹ was achieved with the cathode based on the segregated active material, which was obtained by subjecting the as-prepared hybrid material to an additional ball-milling process. The study demonstrates the promising lithium insertion characteristics of the nanometer-sized core–shell maghemite/PPy particles prepared under optimized conditions for application in secondary batteries.     

Boron doped lithium trivanadate as a cathode material for an enhanced rechargeable lithium ion batteries

Boron was doped into lithium trivanadate through an aqueous reaction process followed by heating at 100 °C. The B-LiV₃O₈ materials as a cathode in lithium batteries exhibits a specific discharge capacity of 269.4 mAh g⁻¹ at first cycle and remains 232.5 mAh g⁻¹ at cycle 100, at a current density of 150 mAh g⁻¹ in the voltage range of 1.8–4.0 V. The B-LiV₃O₈ materials show excellent stability, with the retention of 86.30% after 100 cycles. These result values are higher than those previous reports indicating B-LiV₃O₈ prepared by our synthesis method is a promising candidate as cathode material for rechargeable lithium batteries. The enhanced discharge capacities and their stabilities indicate that boron atoms promote lithium transferring and intercalating/deintercalating during the electrochemical processes and improve the electrochemical performance of LiV₃O₈ cathode.     

Supercapacitive behaviors and their temperature dependence of sol–gel synthesized nanostructured manganese dioxide in lithium hydroxide electrolyte

In the present work, a nanostructured manganese dioxide material was synthesized by a sol–gel method starting with manganese acetate (MnAc₂·4H₂O) and citric acid (C₆H₈O₇·H₂O) raw materials, and characterized by X-ray diffraction, infrared spectroscopic and transmission electron microscope techniques. The electrochemical properties and the influence of temperature on supercapacitive behaviors of the nano-MnO₂ electrode in 1 M LiOH electrolyte were investigated using electrochemical methods. Experimental results show that the MnO₂ electrode can exhibit an excellent pseudocapacitive behavior in 1 M LiOH electrolyte, and a high specific capacitance of 317 F g⁻¹ can be obtained at a charge/discharge current rate of 100 mA g⁻¹ and at the temperature of 25 °C. We found that temperature has a crucial influence on the discharge specific capacitance of the electrode. The specific capacitance at 25 °C is higher than that at 15 or 35 °C.     

Fabrication of MnO2-pillared layered manganese oxide through an exfoliation/reassembling and oxidation process

MnO₂-pillared layered manganese oxide has been first fabricated by a delamination/reassembling process followed by oxidation reaction and then by heat treatment. The structural evolution of MnO₂-pillared layered manganese oxide has been characterized by XRD, SEM, DSC-GTA, IR and N₂ adsorption-desorption. MnO₂-pillared layered manganese oxide shows a relative high thermal stability and mesoporous characteristic. The layered structure with a basal spacing of 0.66 nm could be maintained up to 400 °C. The electrochemical properties of the synthesized MnO₂-pillared layered manganese oxide have been studied using cyclic voltammetry in a mild aqueous electrolyte. Sample MnO₂–BirMO (300 °C) shows good capacitive behavior and cycling stability, and the specific capacitance value is 206 F g⁻¹.     

Electrochemical performance of VOMoO4 as negative electrode material for Li ion batteries

Polycrystalline samples of VOMoO₄ are prepared by a solid-state reaction method and their electrochemical properties are examined in the voltage window 0.005–3 V versus lithium. The reaction mechanism of a VOMoO₄ electrode for Li insertion/extraction is followed by ex situ X-ray diffraction analysis. During initial discharge, a large capacity (1280 mAh g⁻¹) is observed and corresponds to the reaction of ∼10.3 Li. The ex situ XRD patterns indicate the formation of the crystalline phase Li₄MoO₅ during the initial stages of discharge, which transforms irreversibly to amorphous phases on further discharge to 0.005 V. On cycling, the reversible capacity is due to the extraction/insertion of lithium from the amorphous phases. A discharge capacity of 320 mAh g⁻¹ is obtained after 80 cycles when cycling is performed at a current density of 120 mA g⁻¹.     

Sol–gel synthesis of Mg1.03Mn0.97SiO4 and its electrochemical intercalation behavior

Magnesium manganese silicate (Mg_1.03Mn_0.97SiO₄) was prepared by a sol–gel method and evaluated as an intercalation electrode material for rechargeable magnesium batteries. The crystalline Mg_1.03Mn_0.97SiO₄ phase was obtained after heating at 900 °C and its electrochemical performance was characterized at room temperature. The pure magnesium manganese silicate exhibits a relatively low reversible specific capacity in the electrolyte comprising 0.25 mol L⁻¹ Mg(AlCl₂EtBu)₂/THF owing to its poor electronic conductivity. Using a ball mill in the presence of acetylene black, and in situ carbon coating, the resulting composites present an improved discharge voltage plateau (1.6 V vs. Mg/Mg²⁺) and increased discharge specific capacity (92.9 mAh g⁻¹ at a C/50 rate). The Mg lower price and its feasibility for rechargeable batteries make magnesium manganese silicate an attractive candidate for rechargeable magnesium based batteries.     

Lithium iron phosphate with high-rate capability synthesized through hydrothermal reaction in glucose solution

Carbon-coated lithium iron phosphate (LiFePO₄/C) was hydrothermally synthesized from commercial LiOH, FeSO₄ and H₃PO₄ as raw materials and glucose as carbon precursor in aqueous solution at 180 °C for 6 h followed by being fired at 750 °C for 6 h. The samples were characterized by X-ray powder diffraction (XRD), scanning electron microscopy (SEM) and constant current charge–discharge cycling test. The results show that the synthesized powders are in situ coated with carbon precursor produced from glucose. At ambient temperature (25 ± 2 °C), the specific discharge capacities are 154 mAh g⁻¹ at 0.2 C and 136 mAh g⁻¹ at 5 C rate, and the cycling capacity retention rate reaches 98% over 90 cycles. The excellent electrochemical performance can be correlated with the in situ formation of carbon precursor/carbon, thus leading to the even distribution of carbon and the enhancement of conductibility of individual grains.     

Electrochemical properties of Cu6Sn5 alloy powders directly prepared by spray pyrolysis

Spherical shape Cu–Sn alloy powders with fine size for lithium secondary battery were directly prepared by spray pyrolysis. The mean size and geometric standard deviation of the Cu–Sn alloy powders prepared at a temperature of 1100 °C were 0.8 μm and 1.2, respectively. The powders prepared at a temperature of 1100 °C with low flow rate of carrier gas as 5 l min⁻¹ had main XRD peaks of Cu₆Sn₅ alloy and copper-rich Cu₃Sn alloy phases. Cu and Sn components were well dispersed inside the submicron-sized alloy powders. The discharge capacities of the Cu₆Sn₅ alloy powders prepared at a flow rate of 5 l min⁻¹ dropped from 485 to 313 mAh g⁻¹ by the 20th cycle at a current density of 0.1 C. On the other hand, the discharge capacities of the Cu–Sn alloy powder prepared at a flow rate of 20 l min⁻¹ dropped from 498 to 169 mAh g⁻¹ by the 20th cycle at a current density of 0.1 C.     

Cathode performance of olivine-type LiFePO4 synthesized by chemical lithiation

Chemical lithiation with LiI in acetonitrile was performed for amorphous FePO₄ synthesized from an equimolar aqueous suspension of iron powder and an aqueous solution of P₂O₅. An orthorhombic LiFePO₄ olivine structure was obtained by annealing a chemically lithiated sample at 550 °C for 5 h in Ar atmosphere. The average particle size remained at approximately 250 nm even after annealing. The lithium content in the sample was quantitatively confirmed by Li atomic absorption analysis and ⁵⁷Fe Mössbauer spectroscopy. While an amorphous FePO₄/carbon composite cathode has a monotonously decreasing charge–discharge profile with a reversible capacity of more than 140 mAh g⁻¹, the crystallized LiFePO₄/carbon composite shows a 3.4 V plateau corresponding to a two-phase reaction. This means that the lithium in the chemically lithiated sample is electrochemically active. Both amorphous FePO₄ and the chemically lithiated and annealed crystalline LiFePO₄ cathode materials showed good cyclability (more than 140 mAh g⁻¹ at the 40th cycle) and good discharge rate capability (more than 100 mAh g⁻¹ at 5.0 mA cm⁻²). In addition, the fast-charge performance was found to be comparable to that with LiCoO₂.     

Performance improvement of LiMn2O4 as cathode material for lithium ion battery with bismuth modification

Spinel lithium manganese oxides (LiMn₂O₄) modified with and without bismuth by sol–gel method were investigated by theoretical calculation and experimental techniques, including galvanostatic charge/discharge test (GC), cyclic voltammetry (CV), chronopotentiometry (CP), electrochemical impedance spectroscopy (EIS), inductively coupled plasma (ICP), powder X-ray diffraction (XRD), BET measurement, and infrared spectroscopy (IR). It is found that the performance of LiMn₂O₄ can be improved by the bismuth modification. The modified and the unmodified samples have almost the same initial discharge capacity, 118 and 120 mAh g⁻¹, respectively. However, the modified sample has better cyclic stability than the unmodified sample. After 100 cycles, the capacity remains 100 and 89 mAh g⁻¹ for the modified and the unmodified samples, respectively. Moreover, the results from EIS show that the modified sample has a quicker kinetic process for Li ion intercalation/de-intercalation than the unmodified one; the charge-transfer resistance of the former is less than one-sixth of that of the latter. After immersion in electrolyte (DMC:EC:EMC = 1:1:1, 1 mol L⁻¹ LiPF₆) for 10 h at room temperature, the modified sample has less change in open circuit potential, crystal volume, and vibration absorption of Mn–O bond, and has less dissolution of manganese into solution than the unmodified sample.