There is a rapidly increasing interest in energy sources optimized to provide electrical energy at high power levels for short times. Applications include very short pulses for digital electronic devices, the somewhat longer power pulse demands of some implantable medical devices, and the much larger transient power needs in connection with vehicle traction.

Several mechanisms can be used to provide short term energy, with fundamentally different characteristics and applicability to different types of transient output requirements.

Four different electrochemical methods can be used to evaluate the critical materials parameters in insertion reaction materials that might be applicable to such applications, and spreadsheet techniques can be used to model the transient transport behavior of such electrodes under various conditions. LaPlace transform methods can then be used to convert information about the physical mechanisms and parameters of individual components into the dynamic response of an electrochemical system.

Transition metal oxides have been evaluated extensively in the past as cathode materials for lithium cells. The major emphasis of recent research has been to develop lithium-ion or rockingchair cells that are assembled in the discharged state with a lithiated transition metal oxide cathode and a carbon anode. Although these cells are significantly safer to use than lithium cells with metallic lithium anodes, the possibility of depositing lithium at the surface of the carbon particles at the top of charge or at high rates of charge cannot be discounted. This paper discusses some recent developments in fabricating rocking-chair cells with transition metal oxide host structures as both anode and cathode, the anode providing a relatively low voltage vs. lithium and the cathode a relatively highvoltage vs. lithium. These cells avoid the reduction and oxidation of lithium during charge and discharge and, therefore, reduce the safety hazards of lithium cells. Improved safety is gained, however, at the expense of cell voltage and specific energy.

A process recently developed at Arthur D. Little, Inc. has enabled the direct and rapid production of LiMOx intercalation cathode materials having specific and controlled geometric and topographic attributes. Results of a comparative study of the electrochemical and spectroscopic characteristics of LiMn204 from several commercial sources and LiMn204 prepared using our process are reported. Improved electrochemical performance observed for the LiMn204 cathode material produced using ADL's process are tentatively related to the small and uniform grain size and to the possible additional influence of electronic defects associated with surface states.

Spinel phases Li-Mn-C with Li/Mn ratios between 0.35 and 0.8 were synthesized. The relationships between composition, manganese valence, vacancy fraction and electrochemical capacity are described using a new composition-valence phase diagram. Electrochemical performances in lithium batteries are compared. The best materials showed constant capacit> 140 Ah/kg in the range 3.5/2 V in liquid electrolyte batteries up to 20 cycles, without the usual capacity drop observed in stoichiometric LiMn204.

The 2D lithiated manganese oxide with Rancieite-type structure (lithium phyllomanganate), synthesized via a soft chemistry route (T≤60ºC) is hydrated at room temperature and can be dehydrated progressively by a thermal treatment. This compound and a series of samples obtained after annealing at different temperatures were characterized and studied for their electrochemical lithium intercalation properties. They are poorly crystallized, with however the advantage of a manganese oxidation state very close to 4, a mustto get high specific capacity. Their chemical characterization was achieved after gathering results obtained from complementary techniques such as AAS, redox titration, TGA and XPS measurements. Special care was taken for the chemical characterization of electrode compositions effectively used in the electrochemical cells.

Electrochemical lithium intercalation was systematically studied for the series of samples, when starting in charge or in discharge after assembly of the Li battery. The electrochemical behavior is discussed in relation with the manganese average oxidation state and the interlayer water content. Materials of the series showing the larger specific capacities were further examined on the application point of view, for their reversibility, cyclability and high rate capability upon Li intercalation.

This work shows that the anhydrous material which is obtained at 300ºC, with the composition Li0.42MnIII0.20MnIV0.8002.11, is a promising rechargeable layered manganese dioxide material.

Lithium-deficient cathode materials Li1-xCoO2 where x = 0.1, 0.4 and 0.6 were prepared electrochemically from the stoichiometric parent compound (x = 0.0).The materials were observed to be air-stable, and x-ray diffraction characterization yielded good agreement with the in situ studies of Dahn and co-workers, regarding changes in lattice parameters. In addition to both static and magic angle spinning (MAS) 7Li NMR, measurements, the samples were investigated by EPR and cobalt K-edge NEXAFS. The removal of Li is accompanied by compensating electrons from the Co d-orbitals, asevidenced by both shifts in the NEXAFS peak and the observation of EPR signals due to spins localized on the Co ions. These spins, in turn, result in dramatic 7Li chemical shifts (89 ppm for x = 0.6) and line broadening. Whereas MAS analysis of Li0.9CoO2 indicates two magnetically inequivalent Li sites, the spectra becometoo broad to resolve different sites for higher values of x. Finally NMR linewidth and spinlattice relaxation measurements as a function of temperature suggest a modest increase in Li+ ion mobility for Li-deficient samples as compared to the parent compound.

Lithium can be intercalated into a variety of materials using aqueous electrochemical methods, provided that certain criteria are met. The materials must be stable in concentrated Li+ aqueous solution and Li intercalation must take priority over hydrogen intercalation. We use X-ray and neutron diffraction, as well as electrochemical methods to investigate if lithium or hydrogen is intercalated into certain hosts. For example, spinel Li2Mn2O4 can be made from spinel LiMn204 by intercalating one Li per mole in an electrochemical cell with 1 M LiOH electrolyte. If the electrochemical reduction is carried out further, beyond one electron per mole, Mn(OH)2 is then formed, as we prove using neutron diffraction. By carefully selecting electrode materials and electrolyte composition it is possible to make rechargeable lithium-ion cells with aqueous electrolytes. For example, LiMn204/γ-Li0.36MnO2 can be selected as an electrode couple, and5 M LiNO3 in water as an electrolyte to make lithium-ion cells with aqueous electrolytes.

Ageing of the manganese substituted nickel hydroxides in 5M-KOH electrolytic medium leadsto a structure interstratification which is related to spontaneous oxidation of trivalentmanganese ions to the tetravalent state, As far as the electrochemical behavior is concerned, the trend to interstratification has a positive influence on the stability of the capacity upon cycling. In addition, the chargeability is improved by the presence of manganese.

even manganese dioxide (MD) forms including natural ramsdellite, β-MnO2 and samples with structures intermediate between these two types, have been analyzed interms of chemical and structural disorder. XRD and IR spectra show that natural ramsdellite contains groutellite, MnO1.5(OH)0.5. The OH absorption band in the 3400cm-1 region is sharp for groutellite, less intense on CMD spectrum, andsuperimposed to a broad and diffuse absorption ranging from 3600 to 2000cm-1 in most γ-MnO2's. The OH groups are associated with Mn+3 defects, while the broad and diffuse absorption band can be assigned to protons in empty MnO6 octahedra, and so related to instable manganese oxydation state between Mn3+ and Mn4+.

A potentiostatic study in IM and 7M KOH shows that the stoichiometric oxides, ramsdelliteand β-MnO2, are not reduced, while CMD and EMD are reversibly reduced by H+/-einsertion. In 7M KOH, a reversible reduction occurs for both CMDs and EMDs until -0.2 V, while a heterogeneous mechanism destroys the structure at lower potential (70% capacity loss after 3 redox cycles). Only ramsdellite and β-MnO2 can be cycled reversibly below -0.37 V, but the drained capacity is very low for β-MnO2.

The presence of Mn3+ and Mn4+ vacancies associated to structural disorderin synthetic MDs increases their reduction potential and completely modifies the chemicalproperties. This mixed valence state seems to be at the origin of the reduction properties by proton insertion in protonic electrolytes.

This paper presents an investigation of electrochemical proton intercalation in two chemically prepared MDs containing low amounts of structural defects and in a natural MD containing 89%of highly crystalline ramsdellite. XRD examination of equilibrated partly reduced synthetic samples confirms the formation of groutite as a final reduction product and, before mid-reduction, suggests the formation of a solid solution between ramsdellite and groutellite H0.5MnO2. In contrast, electrochemical spectroscopy hint at a two-phase process with an equilibrium potential at –60 m V vs Hg/HgO. The implication of the structural defects on these observations are discussed.

Several examples of dissolution-recrystallization processes at the nickel hydroxide electrode are reviewed. Some of them are very well known and have been studied for a few yearsin the case of Ni/Cd cells. The cycling of the ∝-type nickel hydroxide leads to the ∝→β transformation through dissolution of the a phase in the electrolyte (KOH) and recrystallization of the β phase from the solution. Further cycling of the resulting βex ∝phase causes an ageing effect which occursvia the solution (Oswald ripening). More recently, a strong ripening phenomenon has been observed by studying the behavior of nickel hydroxides cycling in Ni/H2 cells. By simulating the ageing of charged and discharged materials under hydrogen pressure inKOH media, it has been shown that in the absence of voltage, hydrogen cannot be responsible for the strong ripening effect. Synergetic effects between hydrogen and voltage have to be considered.

We have studied the electrochemical characteristics of Li/MoO3-based batteries in relation with the morphology of the cathode-active material. The oxides and oxide-hydrates of molybdenum have been prepared with various degrees of heat treatement. The samples were characterized by X-ray diffraction, Raman spectroscopy, and conductivity measurements. The effect of the heat treatment on structural, optical and electrochemical properties are presented in this work. Thermodynamics and kinetics of lithium insertion were studied in MoO3 cathodes. Diffusion coefficients and enhancement factors were calculated as functions of the degree of lithium intercalation in the domain of the galvanic cell reversibility.

In this work, we investigate the influence of surface roughness on the kinetics of Li+ during the insertion process in the well-known electrochromic material WO3. Thin films 500 Å thick have been grown by rf-sputtering and annealed in therange of 25-350ºC. Grazing angle X-ray reflectometry shows that the film roughnessincreases considerably with thermal treatment. These measurements are correlated with chemical diffusion investigations obtained by electrochemical titration in Li/WO3 cells.

The formation of lithium inserted W18O49 phases has been studied byelectrochemical methods. When lithium is inserted, several single phases LixW18O49 are observed in the range 0 ≤ x ≤ 40 between 3 and 1 V. Nevertheless the reaction is reversible only for x ≤ 22. Chemical reactions of W18O49 with different quantities of n-butyllithium have been carried out to isolate and characterize some of these phases. For Li17W18O49, this is ˜1:1 Li/W ratio, electron diffraction experiments clearly indicate that lithium produces a periodicity change, doubling the a, b and c cell parameters. On the other hand, when sodium is inserted in W18O49 two single phase regions NaxW18O49 are observed within the range 0 ≤ x ≤ 1.2 between 3 and 0.5 V.

Completely inorganic thin film lithium ion battery cells have been prepared by vapor deposition processes (vacuum evaporation and sputtering). The negative and positive electrodes were films of disordered carbon and lithium cobalt oxide, respectively. The results of battery charging/discharging and other measurements (e.g., in-situ lithium chemical diffusion constant measurements for the carbon films) indicate that disordered carbon films have a relatively high reversible charge capacity, (> 160 mC/μmand possibly higher than 360 mC/cm2-μm, or > 296 and possibly 667 mAh/g, respectively, assuming the measured film density of 1.5g/cm3), and a lithium chemical diffusion constant at room temperature ≈10-9 cm2/s. These results suggest that disordered carbon films should be good substitutes for metallic lithium in thin film rechargeable batteries.

A thin film deposition technique is described whereby the oxidation condition of as-deposited iridium oxide thin films can be manipulated by varying deposition conditions. Iridium oxide thin films were deposited by reactive rf magnetron sputtering in a H2/O2/Ar gas blend. Optical emission spectroscopy, an in-situ process monitor, was employed to observe redox interactions in the deposition plasma. The plasma spectra exhibited characteristics normally observed in hydrogen flame spectroscopy. A competitive redox balance was found to exist between atomic O and atomic H emissions. Plasma redox conditions defined by the H-O emissions could be accessed by a variety of gas flow conditions. Electrochemical aspects of the IrOx films were examined by cyclic voltammetry. Electrochromic capabilities were demonstrated through optical transmittance.

For 15 years, the chemistry of the intercalation of donors species into graphite has beenlargely developed and a great number of new phases were discovered : over 100 if one takes into account the various stages and stacking, which involves different properties of the compounds for a given intercalate. Four new systems and synthesis methods were developed : intercalation of metallic alloys containing an alkali metal, ionic species (alkali metal hydrides, hydroxides and, even chlorides), alkali metals with oxygen (by addition to the metal of a small quantity of its peroxide M2O2), intercalation under high pressure of the alkali metal. Those new syntheses, still in progress, lead to compounds in which the first stages exhibit a fairly high intercalate/carbon ratio : from LiC2 to MC4 (M = Na, K, Rb or Cs) instead of LiC6 or MC8 obtained by classical methods.

The increase of this ratio confers them interesting properties and possibilities of application, especially in the field of new materials for primary or secondary batteries.

Several types of carbonaceous materials are evaluated as negative electrodes for lithium storage in polymer electrolyte based cells operated at 100ºC. The corresponding faradaic efficiencies of the spherical cycle and the achieved reversible first capacity and rate capacity will be given. A meso carbon yielded a higher capacity than the theoretical 372 mAh/g. This is tentatively explained by the necessary enhancement of the carbon/polymer interfacial properties through the formation of C-Li-O bonding at the carbon surface and by the possible formation of multilayers of lithium on the external a,b planes of disordered carbons. The formation of the passivating layer on the carbon surface will be described.

A lithium-ion type battery using coke and LiNiO2 as the negative and positive leads and POE-LiCIO4 was operated at 100ºC and cycled galvanostatically. Good reversible capacity was attained with the LiNiO2 electrode.

Vanadium pentoxide gels V205.nH20 are formed via the condensation of vanadic acid in aqueous solutions. They exhibit both ionic and electronic conductivity and could therefore be used as cathode materials in lithium batteries or electrochromic display devices. The polymerization process leads to ribbon-like vanadium pentoxide particles. In a given range of concentration, sols and gels exhibit a homogeneous lyotropic nematic phase in which the ribbons align in the same direction. Ordered fluid phases are thus obtained leading to oriented films when deposited onto flat substrates. Moreover, mixed oxides MxV205 (M = Na+, K+,Ba2+, Al3+, Fe3+,Fe3+,...) exhibiting some preferred orientation are obtained via ion exchange.These compounds exhibit improved lectrochemical properties (specific capacity, cycling properties) compared to usual mixed oxides prepared via solid state reactions.

This paper emphasizes the interest of sol-gel synthesis in obtaining high performance cathodic materials. New vanadium oxides, vanadium bronzes (MxV2O5) and manganese oxides (MnO2) are prepared via the sol-gel process using inorganic precursors in aqueous medium. Their electrochemical behaviour (working potential, specific capacity, kinetics of Li transport, rechargeability, cycle life) is investigated and discussed in relation with their specific structural, chemical and physical features. In particular, the results are compared to that achieved for the corresponding classical compounds prepared via a synthesis route involving solid state reactions or precipitationreactions.