Cathodes In Lithium Cells Research Articles

Synthesis, structural and electrochemical properties of V4O9 cathode for lithium batteries.

Single-phase three-dimensional vanadium oxide (V4O9) was synthesized by reduction of V2O5 using a gas stream of ammonia/argon (NH3/Ar). The as-synthesized oxide, prepared by this simple gas reduction method was subsequently electrochemically transformed into a disordered rock salt type-"Li3.7V4O9" phase while cycling over the voltage window 3.5 to 1.8V versus Li. The Li-deficient phase delivers an initial reversible capacity of ∼260mAhg-1 at an average voltage of 2.5V vs. Li+/Li0. Further cycling to 50 cycles yields a steady 225mAhg-1. Ex situ X-ray diffraction studies confirmed that (de) intercalation phenomena follows a solid-solution electrochemical reaction mechanism. As demonstrated, the reversibility and capacity utilization of this V4O9 is found to be superior to battery grade, micron-sized V2O5 cathodes in lithium cells.

New Ether-functionalized Morpholinium- and Piperidinium-based Ionic Liquids as Electrolyte Components in Lithium and Lithium-Ion Batteries.

Here, two ionic liquids, N-ethoxyethyl-N-methylmorpholinium bis(trifluoromethanesulfonyl)imide (M1,2O2 TFSI) and N-ethoxyethyl-N-methylpiperidinium bis(trifluoromethanesulfonyl)imide (P1,2O2 TFSI) were synthesized and compared. Fundamental relevant properties, such as thermal and electrochemical stability, density, and ionic conductivity were analyzed to evaluate the effects caused by the presence of the ether bond in the side chain and/or in the organic cation ring. Upon lithium salt addition, two electrolytes suitable for lithium batteries applications were found. Higher conducting properties of the piperidinium-based electrolyte resulted in enhanced cycling performances when tested with LiFePO4 (LFP) cathode in lithium cells. When mixing the P1,2O2 TFSI/LiTFSI electrolyte with a tailored alkyl carbonate mixture, the cycling performance of both Li and Li-ion cells greatly improved, with prolonged cyclability delivering very stable capacity values, as high as the theoretical one in the case of Li/LFP cell configurations.

Highly conductive cathode materials for Li-ion batteries prepared by thermal nanocrystallization of selected oxide glasses

Glassy analogs of two important cathode materials for Li-ion cells: V2O5 and phosphoolivine LiFePO4 were heat-treated in order to prepare nanocrystallized materials with high electronic conductivity of up to 7×10−2Scm−1 and ca 7×10−3Scm−1 at 25°C, respectively. There is a clear correlation between the crystallization phenomena and the increase in the electrical conductivity for both groups of glasses. Electrochemical tests of heat-treated glasses of the V2O5–P2O5 system, used as cathodes in lithium cells confirm their good gravimetric capacity and reversibility. Heat-treatment of glasses of the Li2O–FeO–V2O5–P2O5 system also leads to a high increase in the conductivity and to formation of nanocrystalline grains in the glassy matrix, evidenced by HR-TEM images. The temperature dependence of the conductivity of these materials follows the Arrhenius formula. The presented results indicate that the overall increase in conductivity in nanocrystallized materials is due to good charge transport properties of their interfacial regions.

Electrochemical properties of Cu2S with ether-based electrolyte in Li-ion batteries

Investigation of Cu2S as cathode in lithium cells with ether-based electrolytes shows a discharge voltage plateau at 1.7 and 2.25V in the first cycle which slowly evolve, respectively, to 1.74 and 1.94V in the following cycles. This transition process has been analyzed by ex situ X-ray diffraction, scanning electron microscopy (SEM), and electrochemical impedance spectroscopy (EIS). The discharged products are identified as Li2S and elemental copper, and the charged product is Cu1.96S, all of which are crystalline during cycling. SEM reveals a pulverization process of particles during the phase transition and the EIS shows a significant reduction in charge transfer resistance after charges. The Cu2S electrodes exhibit a relatively stable discharge capacity of around 250mAhg−1 at rates of C/10, C/5, and C/2 after a capacity decline in the first cycle. Coulombic efficiency starts to decrease in early cycles as the rate increases. The poor cyclability and low Coulombic efficiency at high rates like 1C rate indicate the transition process is limited at high rates due to the large particle size.

Preparation of lithium ion conducting solid electrolyte of NASICON-type Li1+xAlxTi2−x(PO4)3 (x = 0.3) obtained by using the mechanochemical method and its application as surface modification materials of LiCoO2 cathode for lithium cell

Amorphous a-LATP (x = 0.3) fine powder with the composition of Li1+xAlxTi2−x(PO4)3 in Li2O–Al2O3–TiO2–P2O5 system was prepared directly from a mixture of Li2O, γ-Al2O3, TiO2, and P2O5 as starting materials, by using a mechanical milling (MM) technique at room temperature. A NASICON-type Li1+xAlxTi2−x(PO4)3 (x = 0.3) (c-LATP (x = 0.3)) solid solution was obtained by the heat treatment of mechanochemically prepared amorphous a-LATP (x = 0.3) material. The sintered c-LATP (x = 0.3) pellet showed high lithium ion conductivity of the order of 10−4 S cm−1 at room temperature and activation energy of about 35 kJ mol−1. The high-conducting lithium ion c-LATP (x = 0.3) solid electrolyte fine powders were investigated as surface modification materials of LiCoO2 cathode in lithium cells using nonaqueous electrolyte solutions. The c-LATP (x = 0.3)-modified LiCoO2 electrodes exhibited high capacity (ca. 180 mAh g−1) and good cycle performance with a high charge cut-off potential of 4.5 V (vs. Li/Li+) in lithium cell. The increase in the electrode/electrolyte interfacial resistance for the LiCoO2 electrode modified with c-LATP (x = 0.3) fine powder was inhibited.

Charge–discharge properties of LiCoO2 electrodes modified by olivine-type compounds of LiMgPO4 for lithium secondary batteries

Fine particles of Olivine-type LiMgPO4 were prepared directly from a mixture of Li2O, MgO, and P2O5 as starting materials using a mechanical milling technique at room temperature. LiMgPO4 fine particles were investigated as surface modification materials of LiCoO2 cathodes in lithium cells. Electrolytes of these cells were 1 mol dm−3 LiPF6-ethylene carbonate (EC)/ethyl methyl carbonate (EMC) (3:7 volume ratio). LiMgPO4-modified LiCoO2 cathodes exhibited better charge–discharge performance for high charge cut-off potential of 4.5 V (vs. Li/Li+) in lithium cells than that of LiCoO2 cathode. Olivine-type LiMgPO4 may inhibit oxidative decomposition of the electrolytes on LiCoO2 particle surface without a crystal structure change of LiCoO2 for high charge cut-off potentials.

LiFePO 4 and graphite electrodes with ionic liquids based on bis(fluorosulfonyl)imide (FSI) − for Li-ion batteries

Ambient-temperature ionic liquids (IL) based on bis(fluorosulfonyl)imide (FSI) as anion and 1-ethyl-3-methyleimidazolium (EMI) or N-methyl- N-propylpyrrolidinium (Py13) as cations have been investigated with natural graphite anode and LiFePO 4 cathode in lithium cells. The electrochemical performance was compared to the conventional solvent EC/DEC with 1 M LiPF 6 or 1 M LiFSI. The ionic liquid showed lower first coulombic efficiency (CE) at 80% compared to EC–DEC at 93%. The impedance spectroscopy measurements showed higher resistance of the diffusion part and it increases in the following order: EC–DEC–LiFSI < EC–DEC–LiPF 6 < Py13(FSI)–LiFSIE = MI(FSI)–LiFSI. On the cathode side, the lower reversible capacity at 143 mAh g −1 was obtained with Py13(FSI)–LiFSI; however, a comparable reversible capacity was found in EC–DEC and EMI(FSI)–LiFSI. The high viscosity of the ionic liquids suggests that different conditions such as vacuum and 60 °C are needed to improve impregnation of IL in the electrodes. With these conditions, the reversible capacity improved to 160 mAh g −1 at C/24. The high-rate capability of LiFePO 4 was evaluated in polymer–IL and compared to the pure IL cells. The reversible capacity at C/10 decreased from 155 to only 126 mAh g −1 when the polymer was present.

Nanosized LiM YMn 2− YO 4 (M = Cr, Co and Ni) spinels synthesized by a sucrose-aided combustion method : Structural characterization and electrochemical properties

Spinels of composition LiM Y Mn 2− Y O 4, M = Cr 3+, Co 3+, or Ni 2+, Y = 0.1 and 1 for the Cr and Co dopants, Y = 0.05 and 0.5 for the Ni sample, have been synthesized by a sucrose-aided combustion method. The samples as prepared require of an additional thermal treatment at 700 °C, 1 h to get stoichiometric single-phase spinels. The samples consist of aggregated particles of small size (45–50 nm) as deduced from transmission electron microscopy and X-ray powder diffraction. The electrochemical behaviour of the six spinels as cathodes in lithium cells has been analysed at 5 and 4 V under high current, 1 C rate. At 5 V the discharge capacity of LiNi 0.5Mn 1.5O 4 is higher than the one shown by LiCrMnO 4 and LiCoMnO 4, and it shows an elevated cyclability, i.e. capacity retention of 85.3% after 100 cycles. At 4 V the discharge capacity is similar for LiNi 0.05Mn 1.95O 4, LiCr 0.1Mn 1.9O 4 and LiCo 0.1Mn 1.9O 4, and all the three spinels show similar and very high cyclability, i.e. capacity retention >90% after 100 cycles. The spinels preserve their starting capacity up to currents as high as 2 C rate. The nanometric size of the samples explains the high rate capability of the synthesized spinels.

Crystallinity Control of a Nanostructured LiNi0.5Mn1.5O4 Spinel via Polymer‐Assisted Synthesis: A Method for Improving Its Rate Capability and Performance in 5 V Lithium Batteries

AbstractLi–Ni–Mn spinels of nominal composition LiNi0.5Mn1.5O4, which are functional materials for electrodes in high‐voltage lithium batteries, are prepared by thermal decomposition of mixed nanocrystalline oxalates obtained by grinding hydrated salts and oxalic acid in the presence of polyethyleneglycol 400. Their structure, microstructure, and texture are established from combined X‐ray photoelectron spectroscopy (XPS), X‐ray diffraction, transmission electron microscopy (TEM), IR spectroscopy, and N2 absorption measurements. The polymer tailors the shape of particles, which adopt a nanorodlike morphology at low temperatures (400 °C). In fact, the nanorods consist of highly distorted oriented nanocrystals connected by a polymer‐based film as inferred from IR and XPS spectra. The electrochemical properties of spinels in this peculiar form are quite poor, mainly as a result of the high microstrain content of their nanocrystals. Raising the temperature up to 800 °C partially destroys the nanorods, which become highly crystalline nanoparticles approximately 80 nm in size. At this temperature, the polymer facilitates crystal growth; this leads to highly crystalline polyhedral nanoparticles as revealed from TEM images and microstrain data. Following functionalization as a cathode in lithium cells, this material exhibits a very good rate capability, coulombic efficiency, and capacity retention even upon cycling at voltages as high as 5 V. Moreover, it withstands fast‐charge–slow‐discharge processes, which is an important cycle‐life‐related property for commercial batteries.

Electrochemical performance of the (Ni, Cr) doped spinel material as cathode in lithium cells

The (Ni:Cr) doped lithiated manganese oxide electrode is prepared by wet chemical route using citric acid as the precursor material. The various physical and chemical properties of the prepared electrode material were studied by DSC, XRD, FTIR, Raman and SEM measurements. The electrical conducting property of the electrode was studied by the d.c. conductivity measurements. The electrochemical property was also evaluated by using test cells with the (Ni:Cr) doped spinel electrode. The cycle life was found to be increased upon increasing dopant concentration.

Ion-exchange properties of P2-Na xMnO 2: evidence of the retention of the layer structure based on chemical reactivity data and electrochemical measurements of lithium cells

The ion-exchange properties of two P2-type layered Na x MnO 2 bronzes ( x=0.6, 0.75) with a differential microstructure were studied in LiCF 3SO 3 solutions in acetonitrile under ambient conditions. Na + ions are readily exchanged with Li +, but the reaction causes a significant loss of crystallinity that results in some amorphization. The feasibility of the process increases with increasing structural disorder in the parent compound; conversion, however, is incomplete. The ability of the exchanged material to intercalate water in the air is consistent with the formation of an Li–Mn–O compound that retains the layered framework. Also, the electrochemical data obtained for this material as cathode in lithium cells are consistent with retention of the layer structure and exclude a potential spinel transition due to the ion-exchange reaction. However, the cycling properties of cells made from these layered compounds are quite modest, probably because of the strong structural disorder induced by the lithium reaction.

Synthesis, characterization and comparative study of the electrochemical properties of doped lithium manganese spinels as cathodes for high voltage lithium batteries

Three series of spinels of nominal composition LiMxMn2 − xO4 (M = Fe, Co, Ni; x ≈ 0.3) were prepared by using a carbonate-based precursor method followed by calcining in the air at 400, 600 and 900°C. The spinels were characterized by chemical analysis, X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS), and tested as cathodes in lithium cells over the range 3.5 to 5.2 V vs Li/Li+. XPS data revealed that Co and Fe adopt a tervalent oxidation state whereas Ni is in a divalent state. No sign of Mn2+ was detected. Above 400°C, all the spinels contain a small fraction of a transition element in their 8a tetrahedral sites, together with lithium ions. The three series have the ability to extract lithium above 4.5V, which is accompanied by the oxidation of the dopant transition metal. The reversibility of this reaction increases with higher calcining temperatures as a result of better crystallinity and the smoother particle surfaces. However, the iron spinels depart from this trend; thus, the cell obtained from the sample heated at 600°C possesses good cycling properties and maintains a capacity of ca. 100 A h kg−1 upon cycling. By contrast, the Fe-containing spinel obtained at 900°C loses its whole capacity after the first few cycles. Partial extrusion of iron as Fe2O3 and non-uniformity in particle size and shape may account for its poor electrochemical behavior. The Co- and Ni-containing spinels obtained at 900°C lack these features; their cells exhibit excellent capacity retention upon extended cycling and are capable of delivering 100 and 120 A h kg−1, respectively, at an average voltage of 4.5 V. They can supply a higher energy density than the common spinel LiMn2O4.

Thermal, electrochemical and structural properties of stabilized LiNiyCo1-y-zMzO2 lithium-ion cathode material prepared by a chemical route

Layered compounds, such as LiNiO2 and LiCoO2 , have been extensively studied as active cathodic materials in lithium-ion batteries. Mixed oxides having general formula LiNiyCo1−yO2 represent a good compromise between the limited cyclability of LiNiO2 and the high cost of LiCoO2. However, recent studies have demonstrated that LiNiyCo1−yO2 compounds are thermally unstable in their charged state, undergoing exothermic reactions that might cause thermal runaway and safety concern. The stability of the compounds may be greatly controlled by doping with a suitable metal, M = Al, Mg. In this work we further investigate the role of the doping metal on the thermal, electrochemical and structural characteristics of the LiNiyCo1−y−zMzO2 electrode materials. These materials were prepared using a soft chemistry route, to achieve the proper control of the chemical homogeneity and of the microstructural properties of the final samples. The thermal behavior of the doped LiNiyCo1−y−zMzO2, where M = Al, was studied using differential scanning calorimetry. The structural properties upon cycling were investigated by a recently, in-house developed, in situ energy dispersive X-ray diffraction (EDXD) technique. The reversibility and rate capabilities of the cathodes in lithium cells were characterized using electrochemical equipment.

Stable form of LiMnO2 as cathode in lithium cell

The invention disclosed relates to a new method of forming spinel-related λ-Li 2-x Mn 2 O 4 , wherein 0≦x≦2, solely by electrochemical means with air-stable orthorhombic LiMnO 2 as the starting material. This spinel-related material is hydroscopic, metastable and is typically made by chemical means, followed by electrochemical conversion of spinel-type LiMn 2 O 4 . Also disclosed are new secondary lithium ion electrochemical cells employing as initial active cathode material a compound of formula LiMnO 2 , having a specific orthorhombic crystal structure.

Electrochemical properties of defective Li 1− xMn 2− δO 4 spinels prepared by a sol–gel method used as cathodes in lithium cells

Lithium-deficient spinels of formula Li 1− x Mn 2− δ O 4 ( x=0.26–0.28) (0≤ δ≤0.04) were synthetized by using a sol–gel method involving dissolution of Mn(acac) 3 (acac=acetylacetonate) and Li 2CO 3 in propionic acid. Gel pyrolysis produced pure spinel phases of highly uniform particle shape. Various samples were prepared over the temperature range 400–800°C and tested as cathodic materials in 4 and 3 V lithium cells. Differences in composition, lattice microstrain and crystallite and particle size, account for the influence of the firing temperature on the electrochemical behaviour of these materials. The best performance in 4 V cells was exhibited by a sample calcined at 600°C. This spinel delivers a capacity of 105 A h kg −1, which corresponds to the extraction of over 90% of its lithium content. The cell maintained excellent cyclability at moderate discharge rates. By contrast, the spinels (particularly the low temperature samples) proved unsuitable as cathodes in 3 V cells.

5506078 Method of forming a stable form of limno2 as cathode in lithium cell

5506078 Method of forming a stable form of limno2 as cathode in lithium cell

Carbon filaments and carbon black as a conductive additive to the manganese dioxide cathode of a lithium electrolytic cell

Carbon filaments, when surface treated and used in stead of carbon black as the conductive additive to MnO 2 cathodes in lithium cells, produced a more gently sloping discharge curve (desirable for applications requiring end-of-life indication). These filament composite cathode plates also occupied less volume (higher packing density) and were handleable without the use of a binder, thus resulting in higher volumetric energy density than the carbon black counterpart. The Li/MnO 2 discharge capacity increased with the cathode's electrolyte absorptivity and rate of electrolyte absorption, as opposed to the cathode's electrical conductivity, whether carbon filaments or carbon black was used. The cathode's electrolyte absorption characteristics and packing density and the carbon's electron transfer rate were enhanced by surface treatment of the carbon. For carbon filaments, solvent cleansing, followed by either surfactant treatment or chopping plus drying, was effective; solvent cleansing also decreased the volume resistivity of both the carbon compact and the MnO 2/filament compact. For carbon black, surfactant treatment was effective and resulted in increases in test cell discharge capacity, open- and closed-circuit voltages (OCV and CCV), and cathode packing density. The volume electrical resistivity of the filament compact was lower than that of the carbon black compact, but the volume resistivity of the composite cathode was higher using carbon filaments instead of carbon black; the latter is due to the spreadability of carbon black between the MnO 2 particles.

Lithium-cobalt-nickel-oxide cathode materials prepared at 400°C for rechargeable lithium batteries

A series of compounds LiCo 1− x Ni x O 2 (0⩽ x⩽1) has been synthesised at 400°C. For x⩽0.2, the products are es sentially single phase and have a cubic-close-packed oxygen-ion lattice. When used as cathodes in lithium cells these compounds discharge most of their capacity at a significantly lower voltage (3.8–3.3 V) than a standard LiCoO 2 electrode synthesised at 900°C (4.4–3.8 V). The capacities obtained from nickel-doped electrodes are significantly higher than those obtained from LiCoO 2 electrodes prepared at 400°C.

ChemInform Abstract: Characteristics of Brannerite‐Type CuV2‐xMoxO6 (0 ≤ x ≤ 1) Cathodes for Lithium Cells.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Analytical characterization by X-ray photoelectron spectroscopy of quaternary chalcogenides for cathodes in lithium cells

Cdln2S2Se2 cathodes, discharged in a lithium cell at significant points of the discharge curve, have been analysed by X-ray photoelectron spectroscopy (XPS) and information on the surface chemical composition has been used to obtain a deeper knowledge of the cell discharge mechanism.XPS characterization indicated that, with an initial discharge greater than 0.3 F, the cathode surface chemistry was heavily modified, owing mainly to a topotactic reaction of electrolyte anions at the interface and, to a lesser extent, to the intercalation (and reduction) of electrolyte anions into the layered structure of the chalcogenide.On the basis of thermodynamic considerations the formation of species identified by XPS on the discharged cathodes has been tentatively explained and the results seem to reinforce the general model obtained by a previous electrochemical and X-ray diffraction investigation.