Chemistry: electrical current producing apparatus – product – and – Current producing cell – elements – subcombinations and... – Electrode
Patent
1994-02-25
1995-11-07
Kalafut, Stephen
Chemistry: electrical current producing apparatus, product, and
Current producing cell, elements, subcombinations and...
Electrode
205 59, H01M 404, H01M 448
Patent
active
054647088
DESCRIPTION:
BRIEF SUMMARY
This invention relates to a method of making a reversible electrochemical cell incorporating a material based on titanium dioxide, and to use of this material in an electrochemical cell.
Titanium dioxide occurs in two forms: anatase and rutile. It has hitherto been found that lithium can be inserted into these two forms to very different extents. The chemical lithiation of anatase titania with n-butyl lithium results in a maximum stoichiometry of Li.sub.0.7 TiO.sub.2 (see M. S. Whittingham et al., J. Electrochem. Soc., 124, 1388 (1977)), whereas it has been reported that only small amounts of lithium, no more than 2 atomic percent, can be chemically inserted into the rutile form (see D. W. Murphy et al., Solid State Ionics, 9 & 10, 413 (1983)). The lithiated anatase material Li.sub.x TiO.sub.2 has been cycled in an electrochemical cell over the range of x from 0.15 to 0.45 using a lithium perchlorate/propylene carbonate electrolyte, with an average cell voltage of about 1.7 V (see F. Bonino et al., J. Power Sources, 6, 261 (1981)), whereas rutile titania in such a cell was found to have poor capacity and to have a significantly lower discharge voltage.
According to the present invention there is provided a method of making a rechargeable electrochemical cell with a cathode containing as the active material a material of stoichiometric formula Li.sub.x TiO.sub.2, wherein x is above 0.5 but is no higher than 1.0, and the method comprises the successive steps of: (i) assembling an electrochemical cell having an anode comprising metallic lithium as active material; a non-aqueous lithium ion conducting electrolyte; and a cathode containing titanium dioxide in its rutile form as active cathode material; and (ii) discharging the cell at an elevated temperature between 100.degree. C. and 150.degree. C. such that the cathode material is transformed into material of formula Li.sub.x TiO.sub.2.
Preferably the elevated temperature is about 120.degree. C. Preferably the electrolyte comprises a complex of poly(ethylene oxide) and a lithium salt such as LiCF.sub.3 SO.sub.3 or LiClO.sub.4, this providing a solid-state electrolyte.
In a second aspect, the invention provides a reversible electrochemical cell incorporating, as an active electrode material, a material of stoichiometric formula Li.sub.x TiO.sub.2, where x is above 0.5 but is no higher than 1.0, the material having an X-ray diffraction pattern using copper K-alpha radiation as shown in FIG. 4(d).
The invention will now be further described with reference to the accompanying drawings, in which:
FIG. 1 shows discharge graphs for electrochemical cells incorporating anatase titanium dioxide;
FIG. 2 shows discharge graphs for electrochemical cells incorporating rutile titanium dioxide;
FIG. 3 shows graphically the variation in capacity with discharge cycle for the cells of FIG. 1 and of FIG. 2; and
FIG. 4 shows graphically X-ray diffraction patterns at successive stages during the first discharge of a cell incorporating rutile titanium dioxide .
Experiments have been carried out using the two different forms of titanium dioxide, anatase and rutile. Composite cathodes containing titanium dioxide sample, ketjen carbon black, poly(ethylene oxide)(PEO) (MW 4000000) and LiClO.sub.4 were prepared by doctor blade casting from the appropriate solvent slurry onto a nickel current collector. The resulting cathodes had the composition 45 vol. % titanium dioxide, 5 vol. % carbon and 50 vol. % PEO-LiClO.sub.4 ([EO units]/[Li]=12) with a capacity of about 1 mA h cm.sup.-2 based on a value of 335 mA h g.sup.-1, (corresponding to the insertion of one lithium into TiO.sub.2). Sheets of the electrolyte PEO-LiClO.sub.4 ([EO units]/[Li]=12) were cast from acetonitrile solution onto silicone release paper. Solid state cells containing a lithium foil anode with an active area of 40 cm.sup.2 were constructed in a dry room (T=20.degree. C., dewpoint temperature -30.degree. C.) and assembled using a combination of heat and pressure, each cell consisting of a nickel foil current collector, a
REFERENCES:
patent: 4009052 (1977-02-01), Whittingham
patent: 4357215 (1982-11-01), Goodenough et al.
patent: 5023153 (1991-06-01), Weppner
patent: 5147739 (1992-09-01), Beard
patent: 5284721 (1994-02-01), Beard
J. E. Bauerle, "Study of Solid Electrolyte Polarization by a Complex Admittance Method", J. Phys. Chem Solids, vol. 30, pp. 2657-2670 1969.
Kanamura et al. "Diffusion of Lithium in the TiO.sub.2 cathode of a Lithium Battery" J. Power Sources, vol. 20, 1987 pp. 127-134.
Ohzuku et al. "Electrochemistry of Anatase titanium dioxide in lithium nonaqueous cells", J. Power Sources, vol. 14 1985 pp. 153-166.
"Lithium Insertion in Different TiO.sub.2 Modifications," B. Zachau-Christiansen et al, Solid State Ionics, 28-30 (1988), pp. 1176-1182.
"A Simple One-Electron MO Model for the Intercalation of Lithium in TiO.sub.2 and MnO.sub.2," M. Voinov, Procs. Electrochem. Soc. 1981, vol. 81, Part 4.
"Cathodic Reactions of Various Metallic Oxides in Nonaqueous Electrolytes Containing Lithium Ions," S. Yoshizawa et al, 32nd ISE Metting, Dubrovnik (1981), pp. 864-867. month not available.
"Nonaqueous Lithium/Titanium Dioxide Cell," T. Ohzuku et al, Electrochimica ACTA. (1979), vol. 24, pp. 219-222.
Macklin William J.
Neat Robin J.
Chaney Carol
Hinds William R.
Kalafut Stephen
United Kingdom Atomic Energy Authority
LandOfFree
Titanium dioxide-based material does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Titanium dioxide-based material, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Titanium dioxide-based material will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-196309