EP1337468A1

EP1337468A1 - Vanadium oxide hydrate compositions

Info

Publication number: EP1337468A1
Application number: EP00970624A
Authority: EP
Inventors: Carmine Torardi
Original assignee: EI Du Pont de Nemours and Co
Current assignee: EIDP Inc
Priority date: 2000-10-07
Filing date: 2000-10-07
Publication date: 2003-08-27
Also published as: WO2002030824A9; AU2000279975A1; WO2002030824A1; CN1454184A; KR20030059177A; JP2004511407A

Abstract

Disclosed herein are new vanadium oxide hydrate compositions highly suitable for use as electrode-active materials in primary and secondary lithium and lithium ion batteries, and a process for their preparation.

Description

TITLE VANADIUM OXIDE HYDRATE COMPOSITIONS FIELD OF THE INVENTION This invention pertains to new vanadium oxide hydrate compositions highly suitable for use as electrode-active materials in primary and secondary lithium and lithium ion batteries, and processes for their preparation.

BACKGROUND While long known in the art, vanadium oxide hydrates, generally described by the formula V2θ5^»nH2θ, have generally not exhibited the combination of high lithium ion insertion capacity, low hysteresis in charge/discharge cycles, high power density, and low sensitivity to discharge rate which is required for practical use in rechargeable, or "secondary", lithium batteries.

Le et al., U.S. Patent 5,674,642, has disclosed a fibrous V2θ5^#nH2θ composition with sufficiently high litluum insertion capacity to make it a practical choice for an electrode active material in lithium batteries. Similar fibrils and ribbons formed according to the process of Le et al. disclosed in S. Passerini et al., Electrochimica Acta, Vol. 44, 1999, pp. 2209-2217, and J. Livage, Chem. Mater. Vol. 3, 1991, pp. 578-593.

It is known in the art to combine an electrode active material with a binder resin and carbon black to form an electrode paste or ink for use in battery applications. The carbon black greatly enhances the performance of the electrode material, allowing it to achieve a much higher percentage of its theoretical capacity at high rates of charge and discharge. Le et al., op.cit., discloses such a composition but considerable sacrifice in capacity and reversibility is still encountered at high rates of charge and discharge; the problem grows more aggravated at higher rates.

Further improvement in capacity towards the theoretical limit at high rates of discharge and charge could be realized by forming electrodes with ever higher ratios of carbon black to V₂θ5'nH2θ, at constant binder amount, but there are practical limits to these ratios. Larger amounts of carbon black without concomitant increases in binder results in a loss of mechanical integrity in the electrode layer formed. Increases in binder would then so dilute the amount of electrode active material to badly degrade the energy density of the resultant battery. Further disclosed by Le et al., op.cit. , are compositions of V2θ5*nH2θ with 4-7% by weight of chemically bound carbon solvent residues which provide improvements in the electrochemical potential of a battery but only maintain the capacity and reversibility attributes of the parent composition. Le et al. describe a gelation method for making V2θ₅ ^»nH₂O which is complicated, slow, and expensive. In the textbook, Advanced Inorganic Chemistry (4^th Edition, J. Wiley & Sons, Inc., 1980, p. 711) by Cotton and Wilkinson, is described a method which consists of precipitating a brick-red form of V2O5 by addition of mineral acid to an aqueous vanadate solution. This method is also employed in EP 747123 A2, but the resultant product is described as being of low yield, highly contaminated, and of variable properties. A similar method is also employed by Theobald, Bulletin de la Societe Chimique de France 1975, no. 7-8, pages 1607-1612 with similarly poor results. SUMMARY OF THE INVENTION

The present invention provides for a process for producing MxV2θ5Ay^»nH2θ where M is selected from the group consisting of NH4⁺, Na⁺, K⁺, Rb⁺, Cs⁺, and Li⁺; A is selected from the group consisting of NO3-, SO ^-2, and Cl^~; 0<x<0.7, and 0<y<0.7; and, 0.1<n<2, the process comprising combining a water-soluble vanadate salt with water to form a solution; and, adding to said solution a strong inorganic acid such that the molar ratio of acid protons to vanadium is in the range of 0.70:1 to 6:1. Additionally, the present invention provides for an electrode-active material composition comprising non-fibrous MxV2θ5Ay*nH2θ wherein M is selected from the group consisting of NH₄ ⁺, Na⁺, K⁺, Rb⁺, Cs⁺, and Li⁺; A is selected from the group consisting of NO₃-, SO4"², and Cl^~; 0<x<0.7, and 0<y<0.7; and, 0.1<n<2, the process comprising 0.1<n<2.0, said electrode-active material composition being characterized by an initial discharge capacity of 315 to 400 mAh/per gram of electrode-active material composition.

Still further provided is an electrode composition comprising the electrode-active material composition of the invention.

Finally provided is a electrochemical cell comprising an electrode composition comprising the electrode-active material composition of the invention.

BRIEF DESCRIPTION OF DRAWINGS Figure 1 represents a graphical depiction of the initial discharge capacity determined in Examples 1-16 as a function of H/N ratio.

Figures 2a and 2b depict scanning electron micrographs at magnifications of 10,000 and 30,000 respectively of the non-fibrous product of Example 10.

Figures 3 a and 3b depict scanning electron micrographs at magnifications of 10,000 and 30,000 respectively of the non-fibrous product of Example 16. Figures 4 and 5 depict the initial discharge curve and first re-charge curve showing milliamp-hours per gram of electrode-active material versus voltage as determined in Examples 10 and 16 respectively.

DETAILED DESCRIPTION The present invention is directed to a process for forming a highly purified, non-fibrous form of V2θ5^»nH2θ wherein 0.1<n<2 which is highly suitable for use as an electrode-active material in batteries, particularly lithium and lithium ion primary and secondary batteries, and to the compositions, electrodes, and electrochemical cells formed therewith. It is found in the practice of the process of the invention that the V2θ5^»nH2θ formed thereby normally exhibits a degree of contamination from residual cation of the vanadate salt and residual anion from the strong acid employed in the process of the invention. This residue does not affect the suitability of V2θ5^»nH2θ of the invention for its intended use.

Since the residue is chemically incorporated into the product, the product of the process of the present invention is more properly designated by the formula MxV2θ5AynH2θ wherein M is selected from the group consisting of NH4⁺, Na⁺, K⁺, Rb⁺, Cs⁺, and Li⁺; A is selected from the group consisting of NO3", SO4-², and C1-; 0<x<0.7, and 0<y<0.7; and 0.1<n<2. Preferably, x and y are as close to zero as possible, but in practice they usually are about 0.2. For the purpose of clarity and ease of usage in the present invention, the term 'N2θ5^»nH2θ" will be employed as a shorthand to indicate the product of the process of the present invention to encompass the full range of the values of both x and y, namely 0 to 0.7.

In the process of the invention, a water soluble vanadate salt is dissolved in water preferably accompanied by heating, followed by precipitation at high yield of the desired V2θ5*nH2θ product. The resulting product exhibits a non-fibrous morphology, and is characterized by a surprisingly high initial discharge capacity in a standard lithium battery test cell with very high reversibility.

For the purpose of the present invention the term "initial discharge capacity" refers to the electrical discharge capacity of a standard lithium metal cell in which the V2θ₅*nH2θ compositions of the invention have been incorporated as the electrode-active cathode material. The "initial discharge capacity" determined in a standardized configuration is believed to be a relative indicator of the inherent lithium ion insertion capacity of the V2θ5*nH2θ compositions of the invention. For the purpose of the present invention, initial discharge capacity is determined as follows: the V2θ5^»nH₂O of the invention is combined with carbon black and a binder resin as in the various embodiments hereinbelow described to form an electrode ink or paste. The electrode ink or paste so-formed is combined in a standard lithium metal coin cell configuration described hereinbelow. The coin cell so formed is in the charged state. The cell is then subject to discharging over the range of 4-1.5 volts while voltage (V) and current (I) are measured as a function of time. The measurement of initial discharge capacity begins with a constant current discharge at 0.5 ma. When the voltage reaches 1.5 volts, the discharge mode is changed to constant voltage wherein the voltage is held constant while the current slowly decays to 1/10^th the original value, i.e., 0.05 ma. This constant voltage portion of the discharge, which allows the cell to nearly reach equilibrium, has the effect of reducing the potential drops from the current so that the remaining cell polarization is principally due to the over potential required for lithium insertion into the cathode material. The initial discharge capacity is the integrated charge transfer during both the constant current and constant voltage portion of the discharge. For performing these measurements, it has been found suitable to employ a Maccor series 4000 tester (Maccor, Inc., Tulsa, Oklahoma) using channels with a 10 ma maximum current capability and Version 3.0 (SP1) software.

In the process of the invention, water, preferably deionized water, is combined with a vanadate salt and the mixture so formed is preferably heated, preferably with agitation, to a temperature in the range of 80°C up to and including the boiling point of the mixture to form a solution having a vanadium concentration in the range of 0.01-3 M, preferably 0.1-1 M. Suitable vanadate salts include ammonium, alkali, and alkaline earth vanadates such as NH4VO3, L1NO3, ΝaVO₃, KVO3, RbVO₃, CsVO₃, and MgV₂O₆. Preferred are NH4VO3, L1VO3, KVO3, MgV₂O₆. Most preferred are NH4VO3, L1VO3, and MgV₂O₆. In the alternative, V2O5 can be combined with aqueous ammonium, alkali, or alkaline earth hydroxide in stoichiometric quantities to form in situ the corresponding vanadate solution. Most preferably the solution is heated to its boiling point.

To the preferably heated, most preferably boiling, solution so formed is added a strong mineral acid to provide an acid proton to vanadium ratio

(designated the "H/V ratio" hereinafter) in the range of about 0.70:1 to 6:1. Suitable acids for the practice of the invention include H2SO4, HNO3, HC1, or other strong acid, except phosphorus-containing acids which will undesirably form vanadium phosphate side products. Furthermore, in the case of vanadate salts of NH4 and Rb, and probably Na, K, and Cs, the acid vanadium ratio must be high enough, typically at least 1:1, to avoid or minimize the co-formation of M2N6O16. Acids may be incorporated in concentrated or dilute form, with the dilute form preferred for safety. After acid addition, mixing, preferably with heating at a temperature of at least 80°C, and most preferably at the boiling point, should be continued for at least 1 minute but may continue for several hours. Normally, mixing for 5-60 minutes will suffice. The resulting V2θ5^»nH2θ precipitate may be recovered by any convenient method including settling followed by decanting the supernatant liquid, filtration, centrifugation and so forth. The precipitate is characterized by a non-fibrous morphology and a contamination level of less than about 15%, normally less than about 4%.

The dissolution of the vanadate salt in the water maybe accomplished in most cases at any convenient temperature including room temperature, but it is found in the practice of the invention that the rate of dissolution is quite slow at room temperature, and is greatly increased by heating, particularly to a temperature at or near the boiling point. At temperatures below the boiling point, dissolution is considerably enhanced by agitation. Precipitation of the V2θ₅ ^»nH2θ of the invention by acid addition to the vanadate salt solution may be accomplished at any convenient temperature including room temperature. However, it is found in the practice of the invention that it is highly desirable to effect the reaction at elevated temperature, particular in the range from 80°C to the boiling point of the solution. Effecting the reaction at the boiling point is most preferred. It is found in the practice of the invention that both reduced yield and reduced product quality or performance are likely to result when the temperature of reaction is below 80°C.

Though not strictly necessary, it is highly preferred that the recovered solid, however collected, be re-slurried with fresh water to remove contaminants, followed by once again recovering the solid. The number of washing steps required to achieve the desired level of purity will depend upon the solubility of the impurities, the amount of water employed, the desired level of purity, and the efficiency of the slurrying process. It has been found in the practice of the invention that for many purposes it is sufficient to discontinue washing when the pH of the supernatant liquid reaches about pH=2 or higher.

The recovered solid is then dried by any convenient means including but not limited to radiative warming and oven heating. Following drying, pulverization, and sieving, the V2θ5^,nH2θ so produced is ready for incorporation into an electrode composition. The resulting precipitate is a non-fibrous form of V2θ₅ ^«nH2θ with a high initial discharge capacity. The percentage of the dissolved vanadium precipitated, which largely determines the single pass product yield, is largely determined by the H/N ratio, with the highest yield achieved at H/N ratios of about 1:1 to 2:1. By the term "non-fibrous" is meant not having a microstructure consisting of fibers or ribbons as revealed by scanning electron microscopy at magnifications of about 30,000x. Figures 2a and 2b depict scanning electron micrographs of the specimen of Example 10 herein at magnifications of 10,000 and 30,000 respectively; Figure 3 a and 3b represent similar micrographs for the coated-on- carbon specimen of Example 16 herein.

The non-fibrous N2O5M1H2O made by the process of the invention is characterized by markedly higher initial discharge capacity than V2θ5^»nH2θ made by a vanadium salt acid precipitation process outside the H/N ratio limits of the process of the invention. This is shown in Figure 1 wherein the initial discharge capacity is shown as a function of H/V ratio for the specific embodiments hereinbelow exemplified. Of particular note is the rapid rise and fall-off of initial discharge capacity at the lower and upper limits of the H/N ratio range suitable for the practice of the invention. The optimum H/N ratio is achieved at H/N ratios of about 1.5 : 1 to 2.5 : 1.

Outside the preferred range of H/N ratio, the product begins to deteriorate with reduced yields, increased contamination and reduced initial discharge capacity. Beyond the range of 0.70 H/N 6, these less desirable characteristics are obtained. The N2θ5^»nH2θ of the invention imparts a high degree of reversibility to the standard lithium test cell described herein. As much as 99% percent of useable capacity can be restored by re-charging. That is shown graphically in Figures 4 and 5 which depict, respectively, the discharge associated with Examples 10 and 16 hereinbelow described, each followed by a charge cycle which represented a reversal of the discharge cycle. As can be seen from the figures, low polarization was observed. Examples 10 and 16 represent the same synthesis with the difference being that Example 16 involved a coated-carbon composition and Example 10 did not. The polarization of the coated carbon specimen was less than that of the N2θ5*nH2θ specimen not coated onto carbon, as indicated by the closer proximity of the curves in the low- voltage region. This beneficial effect of the coated-carbon compositions becomes considerably more pronounced with increasing rate of discharge and charge.

Cycle life is defined as the number of cycles of charging and discharging cycles to which the test coin cell can be subject before the discharge capacity decreases to 80% of its initial value. It is believed by the inventor hereof that cycle life achieves an optimum value at an H/N ratio of about 4. That is to say that there appears to be some trade-off between yield and initial discharge capacity on the one hand, and cycle life on the other. It is further found in the practice of the invention that the initial discharge capacity depends upon the cation of the vanadium salt employed in the process of the invention. The highest initial discharge capacity is achieved when the V₂O5'nH₂O is produced from NH4VO3, LiVO₃, or MgV₂O₆. One of skill in the art will understand that the requisites of a given application of the N2θ5^,nH2θ of the invention will entail different trade-offs among the several process variables herein described in order to achieve the product which is best suited to that application.

In one preferred embodiment of the process of the invention, elemental carbon, for example carbon black, is slurried into the vanadium salt solution prior to the addition of the acid. In the practice of the invention, the carbon black may be added to the water before the vanadium salt is dissolved therein, simultaneously with the dissolution of the vanadium salt, or after the dissolution of the vanadium salt. The resulting precipitation product after acid addition in the manner hereinabo ve described is a finely dispersed powder of carbon black coated with V2θ₅ ^»nH2θ which is highly preferred for use in secondary or rechargeable lithium batteries. The coated carbon black product exhibits the high initial discharge capacity characteristic of the V2θ5*nH2θ, with low polarization, high capacity retention at high discharge rates, and high vanadium utility or energy efficiency. The amount of carbon black found suitable for the practice of the invention is of an amount ranging from 1-12%, preferably 4-8%, by weight on the weight of the total weight of the final isolated carbon- V₂O5 '10120 dried powder. 1-12% by weight correspond to a carbon-vanadium mole ratio of about 0.1-1.2 when n~l .2, a preferred value. Any form of finely dispersed elemental carbon is suitable for the practice of the invention. Super P carbon black, commercially available from MMM S.A. Carbon, Brussels, Belgium, is one such suitable elemental carbon which has a surface area of about 62 m²/g. While no particular limitations on surface area have been determined for the carbon black suitable for use in the present invention, it is believed that higher surface areas are preferred over lower surface areas. In one embodiment, the carbon black is first slurried separately in aqueous dispersion, and the resulting slurry is added to the heated vanadate solution.

The process of the invention may be performed in both batch and continuous modes. A continuous process, with a recycle stream of unprecipitated vanadate salt, is particularly desirable when the reaction is run under relatively low-yield conditions.

It is preferred in the process of the invention to reduce the values of x and y to as close to zero as possible, as well as to remove any other residual ionic contamination such as adsorbed protons. This is achieved by thorough washing of the precipitated product in water followed by filtration.

It is well known in the art of electrochemical cell fabrication to form an electrode composition by combining an electrode-active material, such as the V2θ5^#nH2θ of the invention, with carbon black and a binder resin to provide improved electronic conductivity as well as superior physical integrity to the electrode composition. However, it is found in practice that 8% by weight of carbon black represents a typical practical maximum carbon black concentration because amounts in excess of 8% often cause the electrode composition to become undesirably intractable and brittle. The present invention solves the problem of incorporating additional elemental carbon into the composition with minimum deleterious effects on the physical integrity of the electrode composition formed according to the practice hereof. For example, a preferred electrode composition of the invention comprises a V2θ5^»nH2θ-coated carbon black composition incorporating 8% carbon black formed according to the process of the invention as hereinabove described. That composition can be combined according to the teachings of the art with an additional 8% of carbon black and a binder resin to form a tough, formable electrode composition with 16% carbon black and the improved electrochemical performance expected from the higher overall carbon black concentration in the electrode composition.

Suitable binder resins include EPDM rubber, polyvinylidene fluoride and its copolymers for example with hexafiuoropropylene as well as other resins such as are known in the art as suitable for the purpose. Binder resins are normally first dissolved in fugitive solvents before combining with the other ingredients of the electrode. Suitable solvents are well known in the art and include acetone, cyclohexane, and cyclopentanone, among others. Not all binders suitable for the practice of the invention required dissolution in a solvent.

It is found in the practice of the invention that the electrode composition of the invention comprising elemental carbon coated with V₂θ5*nH2θ exhibits considerable benefits over a similar electrode composition comprising

V2θ5^»nH2θ of the invention when the V₂θ5^»nH2θ is not coated onto elemental carbon. These benefits include reduced polarization on charge/discharge cycles, higher initial discharge capacity per gram of vanadium, and much lower reduction in initial discharge capacity with increasing rate of discharge. The process of the invention for producing V2θ5^,nH₂O-coated carbon may also be employed to add or dope in other elements. For example, if prior to precipitation of V2θ5^»nH₂O by acid addition, one adds a transition metal or metal compound, a chemically modified precipitated product is obtained after acid addition, with the general formula, M_xB_zV2θ5A •11H2O, where M is a cation derived from the vanadate salt from which the V2θ₅ ^»nH2θ of the invention has been precipitated and x = 0.0-0.7, A is an anion derived from the acid, y = 0.0-0.7, B is a transition, main group, or rare-earth metal, z = 0.0-1.0, and n = 0.1-2.0. The invention is further described in the following specific embodiments.

It will be understood by those skilled in the art that the invention is capable of numerous modifications, substitutions, and rearrangements without departing from the spirit or essential attributes of the invention.

Most of the specific embodiments hereinbelow involve the formation of a standard electrochemical cell wherein the electrode composition of the embodiment is employed as a cathode against a lithium metal anode. Lithium-ion cells may also be formed according to the process of the invention, and may be preferred in numerous applications.

A lithium-ion battery is assembled in the charged state by either using an anode material which contains already the appropriate cyclable lithium or some fraction thereof. This may be achieved as is known in the art, for example, by contacting lithium metal or some other lithium source with a carbon-based anode material during cell assembly which will allow the necessary cyclable lithium to be accommodated in the carbon structure. Another means for using the claimed materials in lithium-ion cells would involve intentional prelithiation of the vanadium oxide hydrates for example by either chemical means or electrochemical means. This would increase the lithium content in the claimed materials to desirably higher levels for use in lithium-ion batteries with initially discharged anodes. An example of a lithium ion cell is provided in Example 17.

EXAMPLES In the following Examples 1-16, vanadium oxide hydrate was formed, and then combined with other materials, such as are known in the art, to form an electrode which was incorporated into a lithium cell, all these steps being accomplished according to the methods described below. The lithium discharge capacity of the coin cell so formed was determined, and the results plotted against the acid vanadium ratio employed in forming the V2θ5^»nH2θ of the invention, as shown in Figure 1.

EXAMPLE 1 18.2 g L1VO3 were added to about 450 ml deionized H2O while stirring with a Teflon coated magnetic stirring bar in a 1 liter Pyrex beaker. The contents of the beaker were heated to the boiling point to form a solution. With stirring, 7.5 ml of concentrated HNO3 were added to the boiling solution. The resulting solution was continued at the boil while stirring for 5 minutes. The H/V ratio was 0.7.

The beaker was then removed from the heat and stirring continued at room temperature for 3.5 hours. The unwashed gelatinous precipitate was collected on filter paper by suction filtration. The product filtered very slowly and the filtrate was orange in color indicating the presence of a considerable amount of unprecipitated vanadium. The pH of the filtrate, measured with multi-color strip pH paper, was about 3. The filter cake was dried under an IR heat lamp overnight, yielding 7.4 grams of material. A composition of (Li)o.o7N2C^|5(Nθ3)o 07 O.9H2O was derived from chemical and thermogravimetric analyses. On the basis of this composition, a product yield of 42% was calculated. An X-ray powder diffraction pattern showed only the lines of V2θ5*nH₂O.

After grinding to produce a powder, the powder was sieved through a 200 mesh screen to get powder suitable for making a cathode. To make the electrode, 1.5000 g of the powder were combined with 0.1364 g of Super P carbon black commercially available from MMM S.A. Carbon, Brussels, Belgium, and 1.705 g of a 4 wt % solution of EPDM rubber in cyclohexane. 2.5 ml extra cyclohexane were added to improve flow. The mixture was shaken in a capped glass vial for 15 minutes on a mechanical shaker to form a cathode paste.

The cathode paste was spread onto a sheet of Teflon® FEP (E. I. du Pont de Nemours and Company, Wilmington DE) and drawn down to form a film using a doctor blade having a 15 mil gap. The dried film, consisting of 88% by weight powder, 4% by weight binder, and 8% by weight carbon black, was hot-pressed through a calendar roller between Kapton® polyimide sheets (DuPont) at 2000 psi and 110°C to form a consolidated electrode sheet suitable for use as a cathode in a lithium battery. The thickness of the sheet was 115 micrometers. The resultant consolidated electrode sheet was employed as a cathode against a Li metal anode in an electrochemical cell. LiPFg in EC/DMC (ethylene carbonate/dimethyl carbonate) served as the electrolyte solution. A glass fiber separator was used between the electrodes. Disks of cathode, anode, and separator were cut with punches. In a dry nitrogen atmosphere, the cathode and separator pieces were soaked in electrolyte solution, then stacked along with the Li into a coin-cell pan and sealed under pressure using the 2325 Coin Cell Crimper System manufactured by the National Research Council of Canada. The coin cell was tested as described above and the initial discharge capacity was determined to be 315 mAh/g.

EXAMPLE 2 15.6 g of anhydrous V2O5 and 7.2 g of LiOH^^O were combined with 900 ml of deionized water and treated as in Example 1 to form V2θ5^#nH2θ, except that dilute H2SO4, made by combining 3.6 ml of concentrated H2SO4 with 40 ml H2O, was added to the boiling solution, the duration of heating after acid addition was 35 minutes. The H/V ratio was 0.75.

The beaker was then removed from the heat and stirring discontinued. The unwashed gelatinous solid, which did not settle after one hour, was collected on filter paper by suction filtration. The product filtered very slowly and the filtrate was orange in color indicating the presence of a considerable amount of unprecipitated vanadium. The pH of the filtrate, measured with multi-color strip pH paper, was about 3. The filter cake was spread onto a large cover glass and dried at room temperature for four days and under an IR heat lamp for 2 hours, yielding 12.5 grams of dried powder. An impurity phase, believed to be

Li2Sθ4^»H2θ, was seen in x-ray powder diffraction. A nonreactive impurity has the effect of diluting the active material and lowering the overall Li insertion capacity. A product yield of 65% was estimated.

The resulting dried powder of V2θ₅ ^»nH2θ was then processed and combined as described in Example 1 to form an electrode 108 micrometers thick, which was incorporated into a coin cell as in Example 1, and the initial discharge capacity found to be 265 mAh/g.

EXAMPLE 3 18.2 g of L1VO3 were combined with 900 ml of deionized water and treated as in Example 1 to form V2θ5^,nH₂O, except that dilute H2SO4, made by combining 4.8 ml of concentrated H2SO4 with 20 ml H2O, was added to the boiling solution, the duration of heating after acid addition was 15 minutes. The H/V ratio was 1.0.

The beaker was then removed from the heat and stirring discontinued. Solids were allowed to settle until the beaker was cool to the touch. About 400 ml of supernatant liquid were decanted. The decanted supernatant liquid was pale yellow in color indicating the presence of some unprecipitated vanadium. About 400 ml of fresh H₂O were added to the precipitate in the beaker, which was then slurried with the water by stirring for about one minute. The precipitate was allowed to settle for 10 minutes, and about 500 ml of the supernatant liquid was decanted. About 500 ml fresh H2O was added, and slurried for one minute. The precipitate was allowed to settle for about 20 minutes and again the supernatant liquid was decanted.

The solid was collected on filter paper by suction filtration. The pH of the filtrate, measured with multi-color strip pH paper, was about 3. The filter cake was spread onto a large cover glass and dried under an IR heat lamp, yielding 17.2 grams of dried powder. A was derived from chemical and thermogravimetric analyses. On the basis of this composition, a product yield of 97% was calculated. An X-ray powder diffraction pattern showed only the lines of V2θ5^»nH2θ.

The resulting dried powder of V₂O5 nH₂O was then processed and combined as described in Example 1 to form an electrode 115 micrometers thick, which was incorporated into a coin cell as in Example 1, and the initial discharge capacity found to be 355 mAh/g.

EXAMPLE 4 50.0 g of anhydrous V2O5 and 23.1 g of LiOH-^O were combined with 350 ml of deionized water in a 600 ml Pyrex beaker and stirred with a Teflon coated magnetic stirring bar and heated to about 80°C to form a solution. With stirring, 50 ml of concentrated HC1 were added to the hot solution. The H/N ratio was 1.1. After 15 minutes, the heating and stirring were discontinued, and the slurry cooled to room temperature. The solid was collected on filter paper by suction filtration. The filter cake was dried overnight under an IR heat lamp, then reslurried with about 500 ml fresh deionized water, and again collected on filter paper by suction and dried under IR heat. A composition of Liø^N OsCl_Q^'O-S^O was derived from a thermogravimetric analysis assuming the two-step reaction Li₀.₂V₂O₅Cl_{0 2}*0.5H₂O → Li_{0 2}V₂O₅ + 0.5 H₂O + 0.1 Cl₂. An X-ray powder diffraction pattern showed only the lines of V2θ5^»nH2θ

The resulting dried powder of V2θ5^»nH2θ was then processed and combined as described in Example 1, except the amounts of active material, EPDM binder, and carbon black, were 90%, 2%, and 8% by weight, respectively, to form an electrode 90 micrometers thick, which was incorporated into a coin cell as in Example 1. The initial discharge capacity was found to be 378 mAh/g. EXAMPLE 5

20.1 g of NH4VO3 were combined with 450 ml of deionized water and treated as in Example 1 to form V2θ₅ ^»nH2θ, except that 15 ml of concentrated HNO3 were added to the boiling solution, the duration of heating after acid addition was 5 minutes. The H/N ratio was 1.4.

The beaker was then removed from the heat and stirring continued until the beaker was cool to the touch. After collecting the solid on filter paper by suction filtration, the wet solid was slurried in 350 ml of fresh deionized water by stirring with a magnetic stir bar for 1 minute, then collected as before. The solid was again slurried with a fresh 350 ml portion of water and collected as before.

The pH of the filtrate was now about 3. The filter cake was dried in air at 110°C.

15.4 g of product were obtained. A composition of

(ΝH4)o_,ιV2θ5(Νθ3)o_, ^'0.8H2θ was derived from a thermogravimetric analysis.

On the basis of this composition, a product yield of 88% was calculated. An X-ray powder diffraction pattern showed only the lines of V2θ5^#nH2θ.

The resulting dried powder of V2 O5^,nH2O was then processed and combined as described in Example 1 to form an electrode 125 micrometers thick, which was incorporated into a coin cell as in Example 1, and the initial discharge capacity found to be 367 mAh/g. EXAMPLE 6

18.2 g of L1VO3 were combined with 450 ml of deionized water and treated as in Example 1 to form V2θ5»nH2θ, except 15 ml of concentrated HNO3 were carefully added to the boiling solution, the duration of heating after acid addition was 10 minutes. The H/N ratio was 1.4. The beaker was then removed from the heat and allowed to cool to about room temperature. After collecting the solid on filter paper by suction filtration, the wet solid was slurried in 400 ml fresh deionized water by stirring with the magnetic stir bar for 1 minute, then collected as before. The pH of the filtrate, measured with multi-color strip pH paper, was about 1. The filter cake was dried under an IR heat lamp, yielding 15.5 grams of dried product. A composition of (Li)o.o5N2C⁾5(NO3)o.o5TH2O was derived from chemical and thermogravimetric analyses. On the basis of this composition, a product yield of 89% was calculated. An X-ray powder diffraction pattern showed only the lines of V2θ5*nH₂O. The resulting dried powder of V2θ5*nH2θ was then processed and combined as described in Example 1 to form an electrode 110 micrometers thick, which was incorporated into a coin cell as in Example 1, and the initial discharge capacity found to be 340 mAh/g. EXAMPLE 7 20.1 g of NH4VO3 were combined with 900 ml of deionized water and treated as in Example 5 to form V2θ5*nH2θ, except that the duration of heating after acid addition was 20 minutes. The beaker was then removed from the heat and stirring discontinued. The solids settled quickly and were allowed to settle for 5 minutes. About 600 ml of supernatant liquid were decanted. The decanted supernatant liquid was pale yellow in color indicating the presence of some unprecipitated vanadium. About 700 ml of fresh H₂O were added to the precipitate in the beaker, which was then slurried with the water by stirring for about one minute. The precipitate was allowed to settle for.10 minutes, and about 700 ml of the supernatant liquid were decanted. About 700 ml fresh H2O were added, and slurried for one minute. The precipitate was allowed to settle for about 20 minutes and again the supernatant liquid was decanted. The pH of the supernatant liquid was about 2. The product was easily and quickly collected on filter paper by suction filtration. The moist cake was crumbled onto a large cover glass and dried in air at room temperature for 3.5 days to give 15.8 grams of material. The voluminous product was easily powdered in a mortar. A composition of ( H4)₀.ιV₂θ5(Nθ3)o.ι O.7H2O was derived from a thermogravimetric analysis. An X-ray powder diffraction pattern showed only the lines of V2θ5*nH2θ. On the basis of this composition, a product yield of 91% was calculated.

The resulting dried powder of V2θ₅ ^»nH2θ was then processed and combined as described in Example 1 to form an electrode 130 micrometers thick, which was incorporated into a coin cell as in Example 1, and the initial discharge capacity found to be 370 mAh/g.

EXAMPLE 8 8.2 g of NH4VO3 were combined with 150 ml of deionized water and treated as in Example 1 to form N2θ5^»nH2θ, except that 6.6 ml concentrated HΝO3 were added, the duration of heating after acid addition was 2 minutes and the H/N ratio was 1.5.

The beaker was then removed from the heat and stirring continued until the beaker was warm to the touch. The product was easily and quickly collected on filter paper by suction filtration. The unwashed cake was dried overnight under an infrared heat lamp. was derived from a thermogravimetric analysis. An X-ray powder diffraction pattern showed only the lines of V2θ₅*nH2θ. The resulting dried powder of V2θ₅*nH2θ was then processed and combined as described in Example 1, except the amounts of active material, EPDM binder, and carbon black, were 90%, 2%, and 8% by weight, respectively, to form an electrode 120 micrometers thick, which was incorporated into a coin cell as in Example 1, and the initial discharge capacity found to be 383 mAh/g.

EXAMPLE 9 18.3 g MgV2θs were used to make V2θ5^»nH2θ as in Example 3, except a solution of 9.5 ml concentrated H2SO4 in 20 ml deionized water was added, and the H/N ratio was 2.1. The beaker was then removed from the heat and stirring discontinued. The solids settled quickly and were allowed to settle for 5 minutes. About 700 ml of supernatant liquid were decanted. The decanted supernatant liquid was pale yellow in color indicating the presence of some unprecipitated vanadium. About 700 ml of fresh H₂O were added to the precipitate in the beaker, which was then slurried with the water by stirring for about one minute. The precipitate was allowed to settle for 10 minutes, and about 700 ml of the supernatant liquid were decanted. The washing/decanting step was repeated two more times. The pH of the supernatant liquid from the last wash was between 3 and 4. The product was easily and quickly collected on filter paper by suction filtration. The moist cake was crumbled onto a large cover glass and dried in air at room temperature for

2.5 days, then under an infrared heat lamp for 5 hours. 16.3 g were obtained. The product was easily powdered in a mortar. A product yield of 96% was estimated. An X-ray powder diffraction pattern showed only the lines of V2θ5^»nH2θ. The resulting dried powder of V2θ5*nH2θ was then processed and combined as described in Example 1 to form an electrode 123 micrometers thick, which was incorporated into a coin cell as in Example 1, and the initial discharge capacity found to be 365 mAh/g.

EXAMPLE 10 20.1 g of ΝH4VO3 were combined with 900 ml of deionized water and treated as in Example 1 to form V2θ5^,nH2θ, except that a solution of 9.6 ml of concentrated H2SO4 in 25 ml deionized H2O was used, and the duration of heating after acid addition was 20 minutes. The H/V ratio was 2.

The beaker was then removed from the heat and stirring discontinued. The solids settled quickly. Washing was done as described in Example 7. The pH of the final supernatant liquid was about 2. The product was easily and quickly collected on filter paper by suction filtration. The moist cake was easily crumbled onto a large cover glass and dried in a typical manner to give 16.2 g of product. The voluminous material was easily powdered in a mortar. A composition of (NH4)θ.l2N2C>5(Sθ4)o.o6'()-8H2θ was derived from chemical and thermogravimetric analyses. On the basis of this composition, a product yield of 92% was calculated. The product was shown to be non-fibrous by SEM images up to 30,000x. An X-ray powder diffraction pattern showed only the lines of V₂0₅-nH₂0.

The resulting dried powder of V θ5^«nH2θ was then processed and combined as described in Example 1 to form an electrode 130 micrometers thick, which was incorporated into a coin cell as in Example 1, and the initial discharge capacity found to be 370 mAh/g. EXAMPLE 11

Example 10 was repeated except that a solution of 9.6 ml of concentrated H2SO4 in 40 ml deionized H₂O was used, and the duration of heating after acid addition was 60 minutes. The H/V ratio was 2. 15.4 g of product were recovered. A composition of (ΝH4)_0-i2V2θ5(Sθ4)o.o6^'0.6H2θ was derived from a thermogravimetric analysis. On the basis of this composition, a product yield of 89% was calculated. An X-ray powder diffraction pattern showed only the lines ofV₂O₅ ιH2θ.

The resulting dried powder of V2θ₅ ^»nH2θ was then processed and combined as described in Example 1 to form an electrode 125 micrometers thick, which was incorporated into a coin cell as in Example 1, and the initial discharge capacity found to be 374 mAh/g.

EXAMPLE 12 Example 7 was repeated, except that 30 ml of concentrated HNO3 were added, and the H/V ratio was 2.8. After washing and drying as in Example 7, 12.4 g of material were recovered. A composition of

(NH4)o.o9V₂O5(NO3)o.o9^'0.5H₂O was derived from a thermogravimetric analysis. On the basis of this composition, a product yield of 73% was calculated. An X-ray powder diffraction pattern showed only the lines of V O5*nH₂O.

The resulting dried powder of V^S'ILE^O was then processed and combined as described in Example 1 to form an electrode 115 micrometers thick, which was incorporated into a coin cell as in Example 1, and the initial discharge capacity found to be 350 mAh/g.

EXAMPLE 13 Example 10 was repeated except that a solution of 19.2 ml of concentrated H₂SO in 40 ml deionized H₂O was used. The H/V ratio was 4. 13.6 g of product were recovered. A composition of (NH4)o.i2V2θ5(Sθ4)o.o6'lH2θ was derived from a thermogravimetric analysis. On the basis of this composition, a product yield of 76% was calculated. An X-ray powder diffraction pattern showed only the lines of V₂O5'nH₂O.

The resulting dried powder of N2θ₅ ^»nH2θ was then processed and combined as described in Example 1 to form an electrode 115 micrometers thick, which was incorporated into a coin cell as in Example 1, and the initial discharge capacity found to be 325 mAh/g.

EXAMPLE 14 Example 3 was repeated, except that a solution consisting of 19.2 ml concentrated H2SO4 in 50 ml deionized H₂O was added, and the duration of heating after acid addition was 20 minutes. The H/N ratio was 4. After washing and drying, 10.8 g of product were obtained. A product yield of 62% was estimated. An X-ray powder diffraction pattern showed only the lines of V₂O₅mH2θ.

The resulting dried powder of N2θ5^»nH2θ was then processed and combined as described in Example 1 to form an electrode 98 micrometers thick, which was incorporated into a coin cell as in Example 1, and the initial discharge capacity found to be 321 mAh/g.

EXAMPLE 15 Example 10 was repeated except that a solution of 28.8 ml of concentrated H2SO4 in 50 ml deionized H2O was used. The H/N ratio was 6. 9.6 g of product were recovered. A product yield of 55% was estimated. An X-ray powder diffraction pattern showed only the lines of N2θ5^»nH2θ.

The resulting dried powder of V2θ5^,nH₂O was then processed and combined as described in Example 1 to form an electrode 105 micrometers thick, which was incorporated into a coin cell as in Example 1, and the initial discharge capacity found to be 272 mAh/g.

EXAMPLE 16 20.1 g ΝH4VO3 was added to about 900 ml deionized H2O while stirring with a Teflon coated magnetic stirring bar in a 1 liter Pyrex beaker. The contents of the beaker were heated to the boiling point to form a solution. 1.56 g of

Super P carbon black commercially available from MMM S.A. Carbon, Brussels, Belgium was slurried in 100 ml of deionized H2O by shaking and the resulting slurry stirred into the boiling solution. The amount of added carbon black would give ~ 8% by weight of carbon in the product. With stirring, the vanadium-solution/carbon-black mixture was reheated to boiling.

9.6 ml of concentrated H2SO4 was diluted into 30-40 ml deionized H2O, and the diluted acid added to the boiling composition with stirring. The H/N ratio was 2. The resulting mixture was continued at the boil while stirring for 15 minutes.

The beaker was then removed from the heat and stirred for one hour. Solids were allowed to settle for 5 minutes. The warm supernatant liquid was decanted.

The precipitate was re-slurried in a fresh aliquot of H2O for about one minute. The precipitate was again allowed to settle for about 10 minutes, and the supernatant liquid was decanted. A second aliquot of fresh water was added and the washing and solid separation process repeated. The washed, settled precipitate was collected on filter paper by suction filtration. The filter cake was chopped into small pieces and dried in air for about 64 hours, followed by drying under an IR heat lamp for four hours. An X-ray powder diffraction pattern showed only the lines of V2θ5^#nH2θ.

After grinding to produce a powder, the powder was sieved through a 200 mesh screen to get powder suitable for making a cathode. The product was found by SEM to be non-fibrous up to 30,000x magnification.

Two electrodes were made using different binders. One electrode was made as described in Example 1 to form an electrode 120 micrometers thick, which was incorporated into a coin cell as in Example 1, and the initial discharge capacity found to be 350 mAh/g.

For the other electrode, 1.0000 g of the powder was combined with 0.1000 g of MMM Super P carbon, 0.1539 g Kynarflex from Elf Atochem, 0.285 g dibutylpthalate, and 4.6 ml acetone. The mixture was shaken in a capped glass vial for 15 minutes on a mechanical shaker. The cathode paste was spread onto a sheet of Teflon® FEP and drawn down to form a film using a doctor blade having a 10 mil gap. After acetone evaporation, the dibutylpthalate was extracted with dimethyl ether. The dried film, consisting of 79.8% by weight active powder, 12.2% by weight binder, and 8% by weight carbon black, was hot-pressed through calendar rolls between Kapton® sheets at 2000 psi and 110°C to form a consolidated sheet suitable for use as a cathode in a lithium battery. The thickness of the sheet was 86 micrometers.

A disk of the cathode sheet was cut with a punch and incorporated into a coin cell as described in Example 1. The initial discharge capacity was found to be 357 mAh/g. EXAMPLE 17 The electrode of Example 16 was employed as a cathode in a Li-ion electrochemical cell. The anode consisted of lithiated graphite that was formed in the coin cell by reacting at room temperature thin disks of Li metal and graphite. 6.0000 g of graphite powder MCMB25-28 (Osaka Gas Company, Japan) were combined with 0.1936 g of Super P carbon black ( MMM S.A. Carbon, Brussels, Belgium), and 6.452 g of a 4 wt % solution of EPDM rubber in cyclohexane. 2.0 ml extra cyclohexane were added to improve flow. The mixture was shaken in a capped glass vial for 15 minutes on a mechamcal shaker to form a graphite paste.

The graphite paste was spread onto a sheet of Teflon® FEP (DuPont Company, Wilmington, DE) and drawn down to form a film using a doctor blade having a 40 mil gap. After drying, the film, consisting of 93% by weight graphite, 4% by weight binder, and 3% by weight carbon black, was hot-pressed in a calendar between Kapton® polyimide sheets (DuPont) at 2000 psi and 110°C to form a consolidated electrode sheet. The thickness of the sheet was about 295 micrometers.

Disks of cathode, graphite, Li metal, and fiberglass separator were cut with punches, the graphite and Li metal in a glove box with a dry nitrogen atmosphere. hi the glove box, the cathode and separator pieces were soaked in electrolyte solution consisting of LiPFg in EC/DMC (ethylene carbonate/dimethyl carbonate), then stacked along with two graphite disks and one Li disk, the Li disk having a thickness of about 100 micrometers, into a coin-cell pan and sealed under pressure using the 2325 Coin Cell Crimper System manufactured by the National Research Council of Canada.

The coin cells were allowed to stand for 90 hours before testing. The quantities of graphite and Li metal gave a lithium-graphite composition of about LiCio which was believed to ensure that no Li metal would remain in the coin cell prior to testing. The coin cell was tested according to the standard method herein employed except that the voltage range was adjusted from 1.5-4.0 volts to

1.4-3.9 volts because the voltage of the lithium-graphite anode was observed to be about 0.09 volts relative to Li metal. Under the unoptimized coin-cell assembly described above, 92% of the initial discharge capacity obtained in Example 16 was obtained for the Li-ion cell of the present example. EXAMPLE 18

Example 10 was repeated but the heated solution was cooled to room temperature before the acid was added. After 10 minutes, only a small amount of solid formed. More solid was observed after 1 hour, and even more solid formed after stirring overnight. The supernatant liquid was found to contain soluble, unprecipitated vanadium. The supernatantant liquid was decanted, and the solid was slurried with fresh deionized water by stirring for about one minute. The precipitate was allowed to settle for about 10 minutes. The pH of the supernatant liquid wash, measured with multi-color strip pH paper, was 3. The washed, settled precipitate was collected on filter paper by suction filtration. The filter cake was chopped into small pieces and dried in air overnight. 14 g were obtained. Formation of the desired product was confirmed by X-ray powder diffraction. A composition of (NH4)o.i4V2O5(SO4)o.o7'l-lH2O was derived from a thermogravimetric analyses. On the basis of this composition, a product yield of 77% was calculated. An x-ray powder diffraction pattern showed only the lines of V₂O₅ ^»nH₂O. The resulting dried powder of V2θ₅ ^»nH2θ was then processed and combined as described in Example 1 to form an electrode 120 um thick, which was incorporated into a coin cell as in Example 1, and the lithium capacity found to be 330 mAh/g, according to the method hereinabove described.

EXAMPLE 19 20.1 g NH4VO3 were added to about 900 ml deionized H2O while stirring with a Teflon® coated magnetic stirring in a 1 liter Pyrex beaker. The contents of the beaker were heated to the boiling point to form a solution, followed by cooling the solution to room temperature. With stirring, 19.2 ml of concentrated H2SO4, diluted in 50 ml H2O, were added to the solution. The acid proton/vanadium ratio was 4. After 4 hours, only a trace amount of solid had formed.

EXAMPLE 20 Example 10 was repeated except that the solution temperature was reduced to 45°C before the acid was added.

The reaction was held at about 45 °C overnight. The acid proton/vanadium ratio was 2. The supernatant liquid was found to contain some soluble, unprecipitated vanadium. The supernatatant liquid was decanted, and the solid was slurried with fresh deionized water by stirring for about one minute. The precipitate was allowed to settle for about 10 minutes. The pH of the supernatant liquid was, measured with multi-color strip pH paper, was 2-3. The washed, settled precipitate was collected on filter paper by suction filtration. The filter cake was chopped into small pieces and dried in air to give 15.8 g of product. X-ray powder diffraction showed the product to consist mainly of the desired material plus some (NH₄)₂V₆θi₆. An estimate of the yield 0^₂0₅*^0, assuming 10% (NH₄)₂V₆O₁₆ impurity, was 75-80%.

The resulting dried mixed-phase powder was then processed and combined as described in Example 1 to form an electrode 120 um thick, which was incorporated into a coin cell as in Example 1, and the lithium capacity found to be 329 mAh/g, according to the method hereinabove described.

Claims

I claim:

1. A process for producing M V2O5 Ay'ri^O where M is selected from the group consisting of NH4⁺, Na⁺, K⁺, Rb⁺, Cs⁺, and Li⁺; A is selected from the group consisting of NO₃", SO4-², and Cl"; 0<x<0.7, and 0<y<0.7; and, 0.1 <n<2, the process comprising combining a vanadate salt with water to form a solution; and, adding to said solution a strong inorganic acid such that the molar ratio of acid protons to vanadium is in the range of 0.70:1 to 6:1.

2. The process of Claim 1 further comprising the step of heating the solution to a temperature in the range from 80°C to the boiling point of the solution before adding said strong inorganic acid.

3. The process of Claim 1 further comprising the step of dispersing elemental carbon in the solution prior to adding the acid.

4. The process of Claim 1 wherein the molar ratio is in the range of 1 : 1 to 4:1.

5. The process of Claim 1 wherein the concentration of vanadate salt in the solution is in the range from 0.1-1 molar.

6. The process of Claim 3 wherein the concentration of carbon represents 1-12% by weight of the total weight of carbon plus MxV2θ5Ay*nH₂O in the final product.

7. The process of Claim 3 wherein the concentration of carbon represents 4-8% by weight of the total weight of carbon plus MxV2θ₅Ay^»nH2θ in the final product.

8. A composition comprising non-fibrous MxV2θ5Ay^,nH2θ where M is selected from the group consisting of NH₄ ⁺, Na⁺, K⁺, Rb⁺, Cs+, and Li⁺; A is selected from the group consisting of NO3", SO4"², and Cl"; 0<x<0.7, and 0.1<n<2.0, said composition being characterized by an initial discharge capacity of 315 to 400 mAh g.

9. The composition of Claim 8 further comprising 1-12% by weight elemental carbon wherein the MXV2O5 Ay*nH2θ is present as a coating on the carbon.

10. The composition of Claim 9 wherein the composition comprises 4-8% by weight elemental carbon of the total weight of carbon plus MxV2θ5Ay^#nH2θ.

11. An electrode comprising the composition of Claims 8, 9 or 10.

12. An electrochemical cell comprising the electrode of Claim 11.

13. The electrochemical cell of Claim 12 in the form of a lithium or lithium-ion cell.