Method of preparation of a compound on the base of a derivative of vanadiumoxide for cathodes of thermal cells.

p0001The present invention relates to a process for preparing a compound based on vanadium oxide derivative for thermal battery cathode.

p0002Vanadium oxide including vanadium pentoxide, can be directly used as active cathode material in a thermal cell, firstly due to the absence of electronic conductivity, and, secondly, because of its reactivity in molten chloride media.

p0003Mixing with an electronically conductive type graphite or carbon black may seem an obvious solution for the skilled in the art to improve the conductivity of cathodes. However, when V₂O₅ mixture and carbon black, and that attempts to use this composition in a thermal battery cathode are obtained mixtures which are unstable and poorly conductive. Stack, the result always results in successive levels of discharge potential. In addition, mixtures containing a quantity of graphite or carbon black sufficient to improve the conductivity are still very difficult to pelletize.

p0004Other methods have been proposed for preparing vanadium oxide derivatives may serve as cathode materials for thermal batteries.

p0005US-A-4,315,905 patent proposes in particular to manufacture an electron-conductive product for use as a cathode material or cathode coating, by heating the vanadium pentoxide reducing or neutral gas atmosphere (hydrogenated nitrogen or helium). Thus, a mixture containing a V₆O₁₃ both sides share a derivative unidentified V₂O₅, but no example of the use of this compound is given.

p0006European Patent BE-A-145 261 of November 6, 1984 describes the use of a cathode material selected from one or more of the following compounds: V₆O_{13 + x} (0 ≦ x ≦ 0.5), VO_{2 ± z} (0 ≦ z ≦ 0.05) Liy V₂O₅ (0.88 ≦ y ≦ 1), and V₃O₇ LiV₃O₈. However, the above-described compounds are not satisfactory for use as cathode material for thermal batteries. In particular, they do not exhibit a stable discharge voltage, as the examples of discharge given in the patent. The discharge curves show, regardless of the compound employed, a large slope and multiple bearings. In addition, the preparation process requires several successive operations before the final cathode mixture can be obtained containing the electronic conductor and an amount of electrolyte suitable; its preparation time which is of the order of 8 hours to several days is prohibitive.

p0007The present invention aims to implement an easy method of preparing a compound based on a vanadium oxide derivative which can be used as a cathode material in a thermal cell and exhibiting good stability of the discharge voltage.

p0008The present invention relates to a process for preparing a compound based on a likely vanadium oxide derivative to be used as cathode material in a thermal cell, characterized in that - It sends a powder mixture with the vanadium pentoxide V₂O₅, a carbonaceous material in a proportion by weight of V₂O₅ between 3% and 20%, and a mixture of alkaline halides in a proportion by weight of V₂O₅ between 15 % and 50%, - One carries out a heat treatment at a temperature above the melting temperature of said mixture of halides, said temperature being between 365 ° and 650 ° C, for a duration between 15 minutes and 2 hours.

p0009Preferably - Said carbonaceous material is carbon black, such as carbon black, acetylene or benzene. - The said mixture of alkaline halides is a mixture of lithium halides and potassium selected from the eutectic LiCl-KCl, the LiCl-KCl mixtures containing between 50% and 80% LiCl mole fraction, ternary mixtures of LiCl -LiBr LiF-LiCl-LiBr-KBr. - The proportion by weight of said carbonaceous material is between 5% and 10%. - The proportion by weight of said mixture of alkaline halides is between 30% and 45%. - Said processing temperature is between 410 ° C and 550 ° C and the duration of said heat treatment is between 1/2 hour and 1 hour.

p0010The compound thus obtained is ground after cooling to `to obtain a particle size less than 100 microns. It is then formed into pellet for use as cathode.

p0011The present invention also relates to a thermal battery comprising the above cathode and further a lithium anode or lithium alloy selected from lithium-aluminum compounds, lithium-silicon and lithium-boron, and an electrolyte composed of a gelling agent and said mixture of alkaline halides.

p0012Said gelling agent may be chosen from SiO₂, MgO, Al₂O₃.

p0013Unexpectedly, it appears that during melting vanadium pentoxide and the mixture of alkali halides, the presence of carbon black has a very specific role on the nature of the resulting mixture. This could be explained by the existence of superficial carbon-oxygen bonds formed during the high temperature treatment and then facilitating electronic transfers.

p0014The mixture of V₂O₅ with the carbon and the mixture of alkaline halides allows for the thermal treatment period a controlled and reproducible decomposition. It is possible that the carbon also functions as a catalyst for this decomposition.

p0015The method according to the invention allows the production of a complex compound, whose properties are well suited for use as thermal battery cathode: - This complex is stable in the useful temperature range for use in thermal battery. - It presents, in constant current discharge, a single stable discharge bearing relative to a lithium electrode; this level can be at +2.5 volts. - It is well suited for the manufacture of thin wafers.

p0016Other features and advantages of the present invention will become apparent from the following description of embodiments illustrative but not limiting.

p0017In the accompanying drawing:<ul><li>- Figure 1 shows discharge curves for a cathode of the prior art and a cathode obtained by the process according to the invention,</li><li>- Figure 2 shows a discharge curve for a cathode 5 variant obtainable by the method according to the invention,</li><li>- Figure 3 shows discharge curves of a thermal battery pack according to the invention and a prior art battery pack.</li></ul>

p0018In a first example of implementation, are intimately mixed for one hour 100 grams of powder of V₂O₅ with 50 grams of LiCl-KCl eutectic and 10 grams of acetylene black. This mixture is then placed in an oven and heated under an inert atmosphere, such as argon, at 550 ° C for 30 minutes. The composition A obtained is cooled with dry and ground to a particle size less than 100 microns.

p0019then directs A cathode of thickness 0.4 mm by tabletting. It sends a monocouple having a cathode, an electrolyte containing the eutectic LiCl-KCl added a gelling agent as SiO₂, and an anolyte based on a lithium alloy and aluminum LiAl.

p0020Is illustrated in Figure 1 in a graph the ordinate the voltage V (in volts) and the abscissa the time t in seconds, the discharge A of the previous monocouple with a current density of 100 mA / cm² and 450 ° C . a voltage plateau was observed at 2.15 volts.

p0021discharging B was shown under conditions quite similar, of a prior art cathode made by the method described in the European patent application BE-A-145 261, wherein one starts from a mixture including VO₂ and γ -LiV₂O₅. a plurality of discharge levels is observed and the advantage of the composition according to the invention thus appears very clearly.

p0022other compositions were made starting from the same initial products and in the same proportions as in the first example cited above, and by modifying the heat treatment. Table I gives for each treatment the initial tension of monocouple Vo (in volts), the voltage level V (in volts), the capacitance C of monocouple (in mAh) with a stop voltage to 2.0 volts, and Rt% yield.

p0023The optimum conditions are between 410 ° C and 550 ° C with a duration of between 30 minutes and 1 hour. <tables id="tabl0001" num="0001"><table frame="all"><title>TABLE I</title><tgroup cols="6" colsep="1" rowsep="0"><colspec colnum="1" colname="col1" colwidth="26.25mm" /><colspec colnum="2" colname="col2" colwidth="26.25mm" /><colspec colnum="3" colname="col3" colwidth="26.25mm" /><colspec colnum="4" colname="col4" colwidth="26.25mm" /><colspec colnum="5" colname="col5" colwidth="26.25mm" /><colspec colnum="6" colname="col6" colwidth="26.25mm" /><thead valign="top"><row><entry namest="col1" nameend="col2" align="center">Treatment</entry><entry namest="col3" nameend="col3" rowsep="0" align="center">Vo (V)</entry><entry namest="col4" nameend="col4" rowsep="0" align="center">V level (V)</entry><entry namest="col5" nameend="col6" align="center">Stop at 2.0 V / LiAl</entry></row><row><entry namest="col1" nameend="col1" align="center">Temperature</entry><entry namest="col2" nameend="col2" align="center">duration</entry><entry namest="col3" nameend="col3" /><entry namest="col4" nameend="col4" /><entry namest="col5" nameend="col5" align="center">C (mAh)</entry><entry namest="col6" nameend="col6" align="center">Rt (%) *</entry></row></thead><tbody valign="top"><row><entry namest="col1" nameend="col1" align="right">365 ° C</entry><entry namest="col2" nameend="col2" align="right">1h</entry><entry namest="col3" nameend="col3" align="right">2.85</entry><entry namest="col4" nameend="col4" align="right">2.50</entry><entry namest="col5" nameend="col5" align="right">9.2</entry><entry namest="col6" nameend="col6" align="right">44</entry></row><row><entry namest="col1" nameend="col1" /><entry namest="col2" nameend="col2" /><entry namest="col3" nameend="col3" /><entry namest="col4" nameend="col4" align="right">2.25</entry><entry namest="col5" nameend="col5" /><entry namest="col6" nameend="col6" /></row><row><entry namest="col1" nameend="col1" /><entry namest="col2" nameend="col2" /><entry namest="col3" nameend="col3" /><entry namest="col4" nameend="col4" align="right">2.15</entry><entry namest="col5" nameend="col5" /><entry namest="col6" nameend="col6" /></row><row><entry namest="col1" nameend="col1" align="right">365 ° C</entry><entry namest="col2" nameend="col2" align="right">2 h</entry><entry namest="col3" nameend="col3" align="right">material</entry><entry namest="col4" nameend="col4" align="right">no</entry><entry namest="col5" nameend="col5" align="right">pastillable</entry><entry namest="col6" nameend="col6" /></row><row><entry namest="col1" nameend="col1" align="right">550 ° C</entry><entry namest="col2" nameend="col2" align="right">15 min</entry><entry namest="col3" nameend="col3" align="right">2.32</entry><entry namest="col4" nameend="col4" align="right">2.11</entry><entry namest="col5" nameend="col5" align="right">14.0</entry><entry namest="col6" nameend="col6" align="right">67</entry></row><row><entry namest="col1" nameend="col1" align="right">550 ° C</entry><entry namest="col2" nameend="col2" align="right">30 min</entry><entry namest="col3" nameend="col3" align="right">2.30</entry><entry namest="col4" nameend="col4" align="right">2.11</entry><entry namest="col5" nameend="col5" align="right">13.8</entry><entry namest="col6" nameend="col6" align="right">72</entry></row><row><entry namest="col1" nameend="col1" align="right">550 ° C</entry><entry namest="col2" nameend="col2" align="right">1h</entry><entry namest="col3" nameend="col3" align="right">2.22</entry><entry namest="col4" nameend="col4" align="right">2.15</entry><entry namest="col5" nameend="col5" align="right">19.6</entry><entry namest="col6" nameend="col6" align="right">74</entry></row><row><entry namest="col1" nameend="col1" align="right">550 ° C</entry><entry namest="col2" nameend="col2" align="right">2 h</entry><entry namest="col3" nameend="col3" align="right">2.25</entry><entry namest="col4" nameend="col4" align="right">2.12</entry><entry namest="col5" nameend="col5" align="right">12.6</entry><entry namest="col6" nameend="col6" align="right">60</entry></row><row><entry namest="col1" nameend="col1" align="right">650 ° C</entry><entry namest="col2" nameend="col2" align="right">30 min</entry><entry namest="col3" nameend="col3" align="right">2.32</entry><entry namest="col4" nameend="col4" align="right">2.09</entry><entry namest="col5" nameend="col5" align="right">7.0</entry><entry namest="col6" nameend="col6" align="right">35</entry></row><row><entry namest="col1" nameend="col1" align="right">650 ° C</entry><entry namest="col2" nameend="col2" align="right">1h</entry><entry namest="col3" nameend="col3" align="right">2.38</entry><entry namest="col4" nameend="col4" align="right">2.09</entry><entry namest="col5" nameend="col5" align="right">9.2</entry><entry namest="col6" nameend="col6" align="right">44</entry></row></tbody></tgroup><tgroup cols="6" colsep="0" rowsep="0"><colspec colnum="1" colname="col1" colwidth="26.25mm" /><colspec colnum="2" colname="col2" colwidth="26.25mm" /><colspec colnum="3" colname="col3" colwidth="26.25mm" /><colspec colnum="4" colname="col4" colwidth="26.25mm" /><colspec colnum="5" colname="col5" colwidth="26.25mm" /><colspec colnum="6" colname="col6" colwidth="26.25mm" /><tbody valign="top"><row><entry namest="col1" nameend="col6" align="justify">* Calculated on Rt 1 F</entry></row></tbody></tgroup></table></tables>

p0024In Example 2, was mixed as previously 500 grams of V₂O₅ with 250 grams of electrolyte and 25 grams of acetylene black. This mixture was heated to 410 ° C under inert atmosphere for 1 hour. The composition obtained was ground and formed into pellet to form a cathode C.

p0025A stack composed of said cathode, a pellet of LiCl-KCl electrolyte with gelling Al₂O₃, and an anode of a thin film of lithium-boron alloy is discharged at 450 ° C at constant current density of 100 mA / cm². The corresponding curve C is given in Figure 2. There is a voltage level of 2.5 volts.

p0026then sends a cell stack obtained by the same method as that described above. The cathode material is that of Example 1. The electrolyte pellets contain 85% of eutectic LiCl-KCl and 15% SiO₂. The pellets anolyte contains 90% LiAl alloy and 10% of eutectic LiCl-KCl.

p0027An exemplary structure of such a battery is described in "Proceedings of the 32nd International Power Sources Symposium, Electrochemical Society Inc., 1986, pages 686 and following" by Douglass J. Briscoe, Daniel GLEN, SAFT America Inc.

p0028A battery of the invention was discharged at room temperature at a current density of 220 mA / cm², with periodic current pulses 2 seconds at 600 mA / cm² (see curve F of Figure 3). With such discharge conditions, the voltage after 45 seconds of discharge is 27 V (25 V for the pulses at high speed). Under the same discharge conditions, a battery using the conventional cathode material FeS₂ and identical on all the other points will have a discharge voltage of 22.2 V at a discharge current density of 200 mA / cm², and 20.2 V under 600 mA / cm² (see curve E in Figure 3).

p0029Of course, the invention is not limited to the embodiments given above.