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We obtained a highly delithiated sample of Li0.04NiO2 using acid leaching. The Rietveld analysis of its X-ray diffraction pattern indicated that the sample was a mixture of three phases. Two of them maintained the pristine structure with cubic close-packing layers while the other phase had a cadmium iodide structure with hexagonal close-packing layers. We examined the electrochemical behavior of this sample as a positive electrode material for lithium batteries. The discharge capacity was smaller than that of a Li0.10NiO2 sample obtained by acid leaching, suggesting that the capacity loss is due to the formation of the phase with the cadmium iodide structure.
With an objective to overcome the cyclability problems of manganese oxides, solution-based procedures are pursued to synthesize metastable manganese oxides. Reduction of permanganate with lithium iodide in an acetonitrile medium followed by heating at 250 °C in vacuum gives an amorphous lithium sodium manganese oxyiodide that is intimately mixed with crystalline NaIO3. On the other hand, oxidation of manganese acetate with lithium or hydrogen peroxide in presence of lithium hydroxide followed by firing at T < 500 °C gives the metastable spinel oxides, Li4Mn5O12 and Li2Mn4O9-δ. The amorphous manganese oxide exhibits excellent cyclability with a capacity > 275 mAh/g at 4.3-1.5 V. The presence of NaIO3 and a unique microstructure are found to play a critical role in the electrochemical properties. Although Li4Mn5O12 could be achieved without much oxygen vacancies, Li2Mn4O9-δ has significant amount of oxygen vacancies with δ > 0.35. Both Li4Mn5O12 and Li2Mn4O9-δ exhibit capacities around 150 mAh/g with good cyclability in the 3 V region.
LiNi1−xCoxO2(x=0.2, 0.3, 0.4) was synthesized through a sintering process from two different types of source materials of nickel and cobalt, namely each respective hydroxide and oxide, and composite hydroxide. Influence of the difference on charge-discharge characteristics, crystal structure and distribution of the metal elements was investigated.
The composite hydroxides formulated in Ni1−xCox(OH)2 as the source material brought better homogenized composite lithiated nickel based metal oxides exhibiting the larger specific discharge capacity. Further modification of LiNi0.6Co0.4)2 by manganese through sintering from the composite hydroxide including manganese brought a good charge-discharge cycle performance as well as a high discharge capacity of 160mAh/g level.
A cylindrical test cell of 18mm in diameter and 65mm in height using the LiNi0.6Co0.3Mn0.1O2 exhibited discharge capacity of 1700mAh which is larger than that using LiCoO2, and also exhibited a competitive charge-discharge cycle performance to commercialized lithium ion batteries.
Electrolytic V2O5 materials were prepared by electrochemical oxidation of vanadyl ions in aqueous solution. The electrodeposition reaction includes two steps: an oxidation into soluble species followed by a precipitation. With the use of various electrodeposition conditions and subsequent heat treatment it is possible to obtain e-V2O5 compounds with different VIV and water contents.
e-V2O5 compounds are mixed valence, hydrated vanadic acids and their formula can be written as H0.4V2O5.2−δ.nH2 with 0.04<8<0.22 and 0<n<1.8. These poorly crystallized layered compounds undergo a phase transformation into α-V2O5 starting at 240°C.
The electrochemical intercalation of lithium into these compounds shows two main single phase phenomena at ≈3.2V/Li and ≈2.6V/Li. Their capacity retention is better than that of other V2O5 reference compounds, but the reversible capacity down to 2V is only ≈100Ah/kg at a rate faster than C/5, due to kinetic limitations.
Nb2O5 powder was prepared by heating niobium hydroxide in the temperature range from 600 to 1000°C. The crystal system of Nb2O5 compounds depended on the heating temperatures, i.e., hexagonal, orthorhombic and monoclinic Nb2O5 compounds were obtained at 600, 800 and 1000°C, respectively. Electrochemical lithium intercalation into the three Nb2O compounds was investigated in a cell with an LiClO4-propylene carbonate electrolytic solution for the application as lithium battery cathodes. As a result, they displayed good charge-discharge performance as the cathode of 2 V class-lithium battery, which will play important role in power supply for IC memory backup developed recently. The thermodynamics and kinetics of the lithium intercalation into the Nb2O5 cathode have been investigated. The thermodynamic parameters, such as standard free energies, lithium partial molar entropy, interaction energies between ions, the crystal lattice parameters, and the kinetic parameters, such as chemical and self diffusion constants, have been obtained as a function of x-value in LiNb2O5.
The crystal structures, microstructures and electrochemical properties of Al-doped lithium manganese oxide materials LiAlxMn1−xO2 (0 ≤ x ≤ 0.1) prepared by solid state reactions have been investigated. A1 doping results in increased cation disorder in the orthorhombic polymorph of LiMnO2, and produces layered monoclinic LiMnO2 with an α-NaFeO2 type crystal structure. The formation of monoclinic LiAlxMn1-xO2 confirms earlier observations by Chiang et al. [1,2]. A mechanism is proposed for the orthorhombic-monoclinic transformation, based on Li-Mn inversion in the orthorhombic structure. Al ions substitute in Mn sites in the monoclinic phase and give rise to microstrain in the [2 0 -l] planes. Microstructural analysis by scanning electron microscopy has revealed Al-deficient striations which may represent residual zones of orthorhombic phase. In cycling tests in Li button cells, increasing the amount of Al dopant extends the number of cycles required for the capacity to evolve to its maximum value, but results in increased stability of the capacity at 55 °C. The layered structure of the monoclinic materials is retained on the first cycle, but transforms to a spinel-type structure on extended cycling.
LiCoO2 single crystal particles were obtained by super critical water synthesis (SCWS) under optimized preparation conditions. The particle size of the LiCoO2 was less than 1 μm, which was much smaller than that of LiCoO2 prepared by a standard method. However, some unknown crystalline and amorphous phases coexisted with the well defined LiCoO2 single crystal particles. The discharge and charge characteristics of the LiCoO2 prepared by the SCWS were examined by some electrochemical methods. In the first cycle, an irreversible behavior was observed, and then the gradual decrease of the discharge capacity with discharge and charge cycle was also detected. The stable discharge capacity was estimated to be 80 mA h g−1 after the 100th cycle. This result may be due to the existence of amorphous phases and some structural defects.
LiNi0.8Co0.2O2 and LiNiO2 have been characterized in-situ XRD. LiNi0.8Co0.2O2 does not undergo a monoclinic phase transformation but remains a hexagonal lattice throughout the entire charging cycle. It is hypothesized that Co-doping may help stabilize the hexagonal structure.
Highly crystalline, textured thin films of LiCoxAl1-xO2 (x=0, 0.5) have been grown by pulsed laser deposition. Films of both stoichiometries were dense and uniaxially textured with Li, Co (or Co, A1) layers parallel to the substrate. It was found that crystal quality depended strongly on oxygen partial pressure, substrate temperature, and substrate material. The deposition of LiCo0.5Al0.5O2 is also highly dependent upon laser fluence, requiring at least 12.8 J/cm2 for high quality films. Chemical diffusion measurements were performed over a wide range of lithium contents using the potentiostatic intermittent titration technique. Maximum and minimum effective for LiCoO2 were 4.0 × 10−11 and 1.2 × 10−2 cm2/s, respectively, and for LiCo0.5A10.5O2, 2.2 × 10−12 and 8.0 × 10−17 cm2/s, respectively.
The layered structure LixTiS2 and LixCoO2 are excellent reversible cathodes for lithium batteries. However, layered lithium manganese oxides are metastable relative to the spinel form on cycling in lithium batteries. They may be stabilized in the layer form by insertion of larger ions such as potassium in the interlayer region, which minimizes the diffusion of the manganese ions from the MnO2 blocks. Their low conductivity is an impediment to their use in high rate batteries. Cobalt can be doped into the layered alkali manganese dioxides, MxMn1-yCoyO2 for M = K or Na, during the hydrothermal synthesis from the alkali permanganates. A single phase is obtained up to about 5% mole cobalt. The cobalt doping is found to enhance the conductivity by two orders of magnitude relative to pure KxMnO2.
Most studies focused on fundamental aspects of cathode materials in lithium ion battery employ porous electrodes, which are made of polymer bonded transition metal oxide powders mixed with conductors such as carbon. However, the powder morphology and the presence of carbon and polymeric binders affect the physical, chemical and electrochemical behaviors significantly. Therefore, transition metal oxide based materials in thin film form, which are dense and contain no additives, are emerging as promising alternatives to study fundamental properties in lithium ion batteries. Pulsed laser ablation (PLD) was used to deposit highly textured thin and thick porous films of LiMn2O4. Effect of various parameters such as substrates and deposition conditions were studied on the microstructure of these films. Microstructure studies of these films were carried out using x-ray diffraction and scanning electron microscopy. The electrochemical measurements were carried out in a glove box using cyclic voltammetery, electrochemical cycling and AC Impedance spectroscopy in a half-cell configuration with lithium metal as an anode and reference electrode and LiMn2O4 film as a cathode. Results indicate differences in film morphology greatly effect electrochemical kinetics of Li intercalation and de-intercalation. Thin films show good electrochemical characteristics such as high rate capability, good coulombic efficiency and rechargeability till 400 cycles.
The development of high capacity cathode materials for lithium ion batteries has resulted in three materials dominating the market, lithiated manganese, cobalt and nickel oxides and mixtures thereof. In the search for greater energy storage, we have examined a number of vanadium oxides.
Comparing the ratio of lithium to metal atom in the three compounds listed above allows for the extraction of one lithium atom per two metal atoms. If the cathode is vanadium based, the number of cycleable lithiums increases to a value closer to 0.75–1.00.
Despite the fact that vanadium oxides operate at lower voltages, a net gain in energy is observed from the use of LixVyOz over the currently available materials. Lithiation of LiV3O7.9 for use in a lithium ion cell is the focus of this paper. Chemical lithiation by reducing lithium salt will be described.
The layered oxides, among the wide family of intercalation compounds, have received considerable attention as positive electrode materials in high-energy density lithium and lithium ion batteries. Within this frame LiNiO2 and LiCoO2 oxides and their solid solutions have been extensively studied as they (and the LiMn2O4 spinels) are the only known materials able to intercalate reversibly lithium at high cell voltage (3.5-4 V). Recently, solid solutions such as LiNi1-xCoxO2 have attracted the attention as alternative cathodes to the state of art LiCoO2 in commercial rechargeable Li-ion batteries. Here we have used the Complex Sol-Gel Process (CSGP) to prepare LiNi1-xCoxO2 (x= 0, 0.25, 0.5, 0.75, 1). Starting sols were prepared from Li+-(1-x)Ni2+-xCo2+ acetate aqueous solution in two different routes. According to route-A aqueous ammonia was added to a starting solution containing 0.2M ascorbic acid (ASC) on 1 M total Me. According to route B the starting acetate solutions were first alkalized by ammonia and then the ascorbic acid was added. Regular sols were concentrated to 1/3 of their initial volume and dried slowly up to 170°C. Thermal transformation of the gels to solids was studied by XRD and IR. The electrochemical properties of the compound LiNi0.75Co0.25O2 prepared by the Route-A were evaluated and reported.
Thin films of crystalline and amorphous V2O5 were deposited by pulsed laser deposition (PLD) and the chemical diffusion coefficients, , were measured by the potentiostatic intermittent titration technique (PITT). In crystalline V2O5 films, the maximum and minimum were found to be 1.7 × 10−2 cm2/s and 5.8 × 10−15 cm2/s respectively, with a general trend for to rise in single-phase regions. The changes in correlated well to the known phases in LiV2O5. In amorphous V2O5 films, exhibited a smooth, continuous decrease as the Li concentration increased.
The surface-modification of manganese dioxide has been carried out for the purpose of increasing the discharge capacity of alkaline manganese battery. The characteristics of the obtained material has been investigated by using XAFS (X-ray absorption fine structure), Raman spectroscopy and ESR. It seems that composite oxide of Ti and Mn is formed on the surface of the surface-modified manganese dioxide (SMMD) particles. XRD measurement data on the discharged product demonstrates that SMMD suppresses the byproduct, and discharge characteristics of SMMD is improved compared to the conventional manganese dioxide.
Combined soft and solid state chemistry followed by precise XRD investigations allow us to determine the Li-V-O system as well as the structural modifications induced by Li insertion in silver vanadates. On the base of these studies we propose an interpretation of both Li//V2O5 and Li//Ag2V4O11 batteries electrochemical behavior. In the I<x<3 domain, disproportionation of V4+, occurs leading to the formation of different mixtures between lithium vanadates and vanadium oxides. The different domains are related to the different steps observed in the Li//V2O5 discharge curve. It is also demonstrated that the sprouting phenomenon occurring in the Ag1+xV3O8 vanadate induces the formation of a new phase Ag2V4O11 instead of the oxygen deficient form Ag2V4O11-y. According single crystal XRD structural determination this phase is shown to be isostructural with Li1+xV3O8. Electrochemical Li insertion starts with the reduction of Ag+ leading to the lithiated phase meaning that whatever the starting phase used, the main insertion process occurs in Li1+xV3O8.
A novel family of salts suitable for lithium battery application was synthesized and characterized. These salts have a large delocalized anion whose charge is spread over a single SO2 and a phenyl ring. Remarkable properties were obtained for the lithium N-(3-trifluoromethyl phenyl) trifluoromethanesulfonamide salt or LiTFPTS. The electrochemical stability window is around 4.0 V and its conductivity in solid poly(ethylene oxide) or PEO is close to the one of the lithium perchlorate salt. Calorimetric analysis also showed that LiTFPTS behaves as a plasticizer since it hinders, to a certain extent, the PEO crystallization when it is used in a solid polymer matrix. Above all, its synthesis is quite straightforward and leads to potentially inexpensive salts as the starting amines are made commercially on a large scale.
A new series of polysiloxane-based single-ion conductors was prepared. These contain solvating oligoether sidechains and covalently linked aluminosilicate or alkoxy/siloxy-aluminate anions attached to the polysiloxane backbone. Of these two systems, the polymers containing aluminosilicate [(SiO)4Al]− anions show higher room temperature conductivities (10−6 S/cm) than those with alkoxy/siloxyaluminate [(SiO)2(CH2O)2A1]− anions (10−7 S/cm). The incorporation of longer covalent tethers between the alkoxy/siloxyaluminate anion and the polymer backbone results in enhanced room temperature conductivities at high ion loadings. Differential scanning calorimetry data provide a rationale for the high conductivity.
Nanocomposite electrolytes based on lithium hectorite (LiHect) clay dispersed in highdielectric organic solvents such as ethylene carbonate (EC) and propylene carbonate (PC) are shown to exhibit room-temperature conductivities exceeding 10−4 S/cm. The LiHect-based composites reveal lithium ion transference numbers of ∼0.8, as measured by the steady-state current method. In addition, dynamic rheological techniques show this system to be mechanically stable with elastic modulus G' exceeding 107 dynes/cm 2 and yield stress exceeding 104 dynes/cm2.
Thermal instabilities were identified in SONY-type lithium-ion cells and correlated with interactions of cell constituents and reaction products. Three temperature regions of interaction were identified and associated with the state of charge (degree of Li intercalation) of the cell. Anodes were shown to undergo exothermic reactions as low as 100°C involving the solid electrolyte interface (SEI) layer and the LiPF6 salt in the electrolyte (EC:PC:DEC/LiPF6). These reactions could account for the thermal runaway observed in these cells beginning at 100°C. Exothermic reactions were also observed in the 200°C-300°C region between the intercalated lithium anodes, the LiPF6 salt, and the PVDF. These reactions were followed by a hightemperature reaction region, 300°C-400°C, also involving the PVDF binder and the intercalated lithium anodes. The solvent was not directly involved in these reactions but served as a moderator and transport medium. Cathode exothermic reactions with the PVDF binder were observed above 200°C and increased with the state of charge (decreasing Li content). This offers an explanation for the observed lower thermal runaway temperatures for charged cells.