Chemistry of inorganic compounds – Oxygen or compound thereof – Metal containing
Patent
1997-11-07
2000-03-28
Straub, Gary P.
Chemistry of inorganic compounds
Oxygen or compound thereof
Metal containing
423593, C01B 1314, C01G 1314
Patent
active
060428058
DESCRIPTION:
BRIEF SUMMARY
The present invention is concerned with a method for synthesising an essentially V.sub.2 O.sub.5 -free vanadium oxide having a mean vanadium oxidation state of at least +4 but lower than +5 from NH.sub.4 VO.sub.3, said vanadium oxide preferably consisting essentially of V.sub.6 O.sub.13, VO.sub.2 or any mixture thereof.
Vanadium oxides having a mean vanadium oxidation state between +5 and +4 have attracted much attention as potential active cathode materials in secondary lithium batteries. These materials are generally prepared from NH.sub.4 VO.sub.3 (ammonium metavanadate).
Single phase V.sub.2 O.sub.5 is readily synthesised by heating NH.sub.4 VO.sub.3 in air (see e.g. K. C. Khulbe and R. S. Mann, Can. Jour. Chem, Vol. 53 (1975), p. 2917). The lower oxides, especially V.sub.6 O.sub.13 (mean oxidation state +41/3) and VO.sub.2 (mean oxidation state +4), are more difficult to obtain as single-phase materials (see e.g. U. von Sacken and J. R. Dahn, J. Power Sources, Vol. 26 (1989), p. 461).
In J. Thermal Anal., Vol. 16 (1979) 659 Trau discusses the problem of obtaining phase-pure V.sub.6 O.sub.13 under thermal decomposition of NH.sub.4 VO.sub.3 without using added reduction reactants. The use of SO.sub.2 as a reducing agent for V.sub.2 O.sub.5 to form V.sub.6 O.sub.13 is technically very complicated; it is difficult to stop the reduction and obtain a homogeneous single-phase V.sub.6 O.sub.13 powder. Trau instead suggests thermal decomposition in a stream of pure nitrogen gas with slow heating to 500-550.degree. C., and a post-treatment with boiling NaOH.sub.(aq) to remove V.sub.2 O.sub.5 as proposed by Yankelvich et al. in Ukr. Khim. Zh., Vol. 42 (1976) 659.
Brown et al. reports in J. Thermal Anal, Vol. 6 (1974) 529 the formation of lower oxides using an NH.sub.3 atmosphere when decomposing NH.sub.4 VO.sub.3.
U.S. Pat. No. 4,486,400 describes a process for preparing stoichiometric V.sub.6 O.sub.13 by thermal decomposing ammonium metavanadate in a nitrogen atmosphere to produce nonstoichiometric V.sub.6 O.sub.13, followed by heating the obtained nonstoichiometric V.sub.6 O.sub.13 in an CO/CO.sub.2 -atmosphere having a composition giving an oxygen partial pressure equal to the oxygen partial pressure over stoichiometric V.sub.6 O.sub.13 to form stoichiometric V.sub.6 O.sub.13.
U.S. Pat. No. 4,035,476 describes the preparation of agglomerated vanadium oxides of the formula V.sub.2 O.sub.x, wherein x is between 3.8 and 4.6, by thermal decomposition of ammonium polyvanadate ((NH.sub.4).sub.2.O.3V.sub.2 O.sub.5.nH.sub.2 O) at a temperature of 600 to 900.degree. C. and permitting the solid decomposition products and reducing agents to react.
JP 62-197317 describes the production of V.sub.6 O.sub.13 or V.sub.2 O.sub.4 by introducing NH.sub.4 VO.sub.3, optionally mixed with .ltoreq.15% V.sub.2 O.sub.5, into a reaction vessel, heating to a temperature of 380 to 750.degree. C. at a rate of 0.5 to 30 K/min, keeping this temperature for 30 min to 3 hours and keeping the pressure at about 3 atm or below by means of a pressure-control valve.
Impurities in the cathode material generally have a negative influence on the overall battery performance, especially the battery capacity declines faster in the presence of impurities. In particular it is has been shown that even small amounts of other VO.sub.x phases, especially V.sub.2 O.sub.5, has a negative influence on the lithium intercalating properties of V.sub.6 O.sub.13 and VO.sub.2.
Thus, although several methods for the manufacturing of lower vanadium oxides are known there still exists a need for an improved synthesis method for the preparation of lower vanadium oxides of high purity, i.e. essentially free of V.sub.2 O.sub.5.
Accordingly, it is an object of the invention to provide a method for synthesising an essentially V.sub.2 O.sub.5 -free vanadium oxide having a mean vanadium oxidation state of at least +4 but lower than +5 from NH.sub.4 VO.sub.3, said vanadium oxide preferably consisting essentially of V.sub.6 O.sub.13, VO.sub.2 or any mixture thereof.
It has been
REFERENCES:
patent: 4035476 (1977-07-01), Ilmaier
patent: 4486400 (1984-12-01), Riley
patent: 4965150 (1990-10-01), Dahn et al.
patent: 5443809 (1995-08-01), Olsen
patent: 5545496 (1996-08-01), Chang et al.
K. C. Khulbe et al., "Thermal Decomposition of Ammonium Metavandate", Can. J. Chem., 53(1975)2917-2921.
U. Von Sacken et al., "TGA/MS Studies of the Termal Decomposition of NH.sub.4 VO.sub.3 ", J. Power Sources, 26(1989)461-465.
J. Trau, "Preparation of the Vanadium Oxide V.sub.6 O.sub.3 ", J. Thermal Analysis, 16(1979)201-204.
M. E. Brown et al., "The Terminal Decomposition of Ammonium Metavanadate II", J. Thermal Analysis, 6(1974)529-514.
Yankelvich et al., Ukr. Khim. Zlh, 42(1976)659-660.
Danionics A/S
Nguyen Cam N.
Straub Gary P.
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