p L290~304 ' This invention relates to secondary lithium batteries. More particularly, the present invention relates to secondary lithium batteries which utilize a layered lithiurn molybdenum o~ide as the cathode material. During the past decade, the demand for high energy storage devices has generated considerable interest in the study of secondary rechargeable batteries and has led to the discovery of promising battery systerns includiny ambient temperature lithium cells. Unfortunately, the praetical utilization of such systems has never been realized, such being attributed to limitations imposed by electrode characteristics, namely the absence of suitable catnode materials as well as the ;~ ; likelihood of dencdritic regrowth of lithium on anode surfaces which results in short circuitiny of the cell ~ after several cycles. f~ In recent years, workers in the art surmounted the cathode limitation by discovery of a new class of solid state electrode materials, commonly termed transition metal dichalcogenides such as TiS2 and VS2 l~ These materials evidence an open Iayered structure and I currently accommodate lithium reversibly, -that is, the lithium may enter the structure and be readily removed thereErom. This mechanisrn, which is reEerred to as an 25 intercalation reaction, is not limited to the layered structure referred to but also is applicable to three dimensional structures having large open channels as found in V6O13 and in the Chevrel phases. Des~ite the availability of these materials, commercial application 30 has not been attained because of the limited cycling 1iEe oE thc? lithium anode~. More recently, these prior art limitations were I overcome by the cllerrlical and electrochemical insertion of lithium into Mo6Se~6 In my U.S. Patent 4,604,33~, issued ,1 ,, '. ; , ~ : : ~L29(~804 Oll August 5, 19~6, a method for the pre,oaration of Lix~o6Se6 anodes by electrochemical fabrication of a cell comprising lithium metal as the anode and Mo6se~ as the cathode was described. The Lix~o6Se6 so prepared was found suitable as the anode of a secondary lithium cell. Although such anodes are of interest for commercial use, it has been determined ~that the overall cell capacity is often lowered, so prompting the continued search for cathode materials with high discharge/charge voltages ~hich comp-nsate for the smaller celi capacity. In accordance with the present invention, this end has been successEully attained by the use of LixMo2O4 cathodes wherein x ranges from 0.3 to 2. Studies have revealed that the intercalation/deintercalation process in LixMo2O4 occurs at an average potential of 3.1 volts and that Li/LixMo2O4 t-~lectrochemical cells maintain their cell capacity over several cycles while sustaining high current drains. Furthermore, structural studies of the described cathodes have shown that Lixr~lo2o4 is a multiphase intercalation system over the range of composition wherein ~ x has a value from 0.3 to 2 with the presence of single ¦ phase domains which undergo hydration reactions leading to ~ new compounds of the formula Lix(H2o)y ~24 wherein x j ranges from 0.3 to 2 and y ranges from 0.75 to 0.95. ~ 25 The invention wiI1 b-- more fully understood by I reference to the following detailed description taken in conjunction with the accompanyiny drawing wherein: Fig. 1 is an exploded view of a non-aqueous secondary lithium cell in accordance with th-.- invention; Figs. 2(a) - 2(c) are yraphical representations on coordinates of lithium atoms (x) in LixMo?O~ against voltaga showing the cycling characteristics of Li/LixMo2O4 electrochemical cells over a wide range of potential an-3 over several cycles; and . Fig. 3(a) - 3(d) are graphical representations l on coordinates of lithhlm atoms (x) irl LixMo2O4 against r voltage showing the ability of the Li/LixMo2O4 cells to , I . .: ' '. , - 1 29g~ 4 sustain high charge and discharge current densities at cycling currents ranying rom 200,uA/cm2 to 2mAjcm With reference now more particularly to Fig. 1, there is shown an exploded view of a typical lithium battery of the inventi~on. Shown is cathode 11 in powder form, disposed upon stainless steel disc I2, anode 13 and filter paper 14 which has been soaked in a suitable electrolyte such as lithium perchlorate. The structure also includes polypropylene fittincJs 15 and 16, steel disc 17, fitting 1~, sprirlg 19, plunger 20, stainless steel rod 21 and cap screws 22 and 230 The fittings, when compressed, provide an air tiyht ambient Eor the battery. In order to prevent electrochemical contact between plunger 20 and the various Eittinys in the battery, it is advantageous to coat the plunger with a suitable ; protective film. In the Eabrication of a lithium battery in I accordance with the invention, the Initial step involves ; the preparation of the LixMo2O4 cathode. This end is effected by the low temperature ion exchange of lithium for sodium in NaxMo2o4 in accordance with tne -Eollowing equation: (I) Na2l~oO~ + MOO;2 + Mo -> 1.5Nal 33Mo~O~ -33M24 + LiI(ln excess) -> Ll ~o o The Nal 33Mo2O4 obtained in accordance with Equation (I) is prepared by ~nown techniques in vacuo at temperatures of the order oE 700C~ The LixMo204 phase is obtained by thoroug~ly mixing powdered Nal 33Mo~O4 with LiI salt which has been previously degassecl in vacuum. The mixed powder is then pressed into a pellet and plac~d ¦ in an evacuated chamber and maintained at a temperature of I ~ approximately 300C for several days. Temperatures appreciably in excess o-f 300C result in the Eormation oE a MO2 impurity phase. Following, the pellet is yround and ; ': . ~ .' . :: :, :.: :~ _ ~ Z90~304 -- 4 the prior processing procedure is repeated. Then, the reaction procluct is washed to remove residual salts. X- ray diffraction patterns reveal the presence of a single phase product. From chemical analysis the following 5 formula Lil 33Mo~04 was ascribed to the lithiated phase. The Lil 33Mo204 may then be used as cathode 11 f in the preparation of a structure oE the type shown in Fig. l wherein lithium is used as the anode 13. Specifically, electrochemical swa~elock test cells are lO prepared in a helium atmosphere using a Lil 33Mo204 cathode prepared as describecl with a lithium metal disc as the anode, the electrodes beiny separated by porous glass paper soaked in 0.95m LiC104 in propylene carbonate as the electrolyte. The cells so obtained were then evaluated by 15 equivalent charging and discharging a-t a constant current rate while monitoring potential as a function of time. Two identical Li/LixMo204 electrochemical cells, designated (1) and (2), respectively, prepared as described above were cycled over a wide range of potential 20 (0.5 to 4.5 volts). Cycling data was obtained by first ~` charging and discharging cell 1 and cell 2 respectively from their open circuit voltage potential of 2.5 volts. With reference now to Fig. 2(a), it may be noted that 1 lithium atom may be removed from Lil 33Mo204 25 (oxidation) as the potential is elevated from 2.5 to 4.5 volts [cell (1)], while 0.7 lithium atoms may be added~to Lil 33Mo204 (reduction) as the potential is lowered from 2.5 to 0.5 volts [cell (2)l. This data clearly indicates that LixMo20~ can exist over a wide range of compositions (0.35 < x < 2). jl The behavior oE cell (1) over a complete cycle `~ is shown in ~iy. 2(b). The discharge curve confirms that 1.7 lithium atoms can enter the host structure down to a potential of 0.5 volt but, more remarkably is the ability ` 35 to reintercalate the 1.7 lithium atoms by recharging the cell from 0.5 to 4.5 volts. It is this reversibility characteristic that suggests the use of LixMo20~ as a " ,, ~ -. ~ '`: ,~, , , : , , . ' ," " , .... , 29()804 . -- 5 :` cathode Eor room temperature secondary batteries. rrhe practical use of this material first requires charging in order to obtain the lowest possible value of x, that is, the maximum energy density. sased upon an electrochemical stoichiometry of 0.35 < x < 2 and an average cell voltage oE 3 volts, -the theoretical energy density of the Li/LixMo2o4 cells is about 530 wh/kg of cathode material compared to 480 wh/kg for Tis2 cathodes or twice as large as that oE the secondary lead-acid batteries presently ~, lO beiny marketed commercially. ¦ The re~versibility of the lithium intercalation ! process into LixMo2O4 was studied further by cycling cell (1) at a current density of 150 ~A/cm2 over seven cycles. ,~ ~ Fig. 2(c) reveals that at this current rate the cell is readily reversible and ~retains its full capacity through ~ I the seventh cycle. In evaluating secondary batteries, it~is also .~ ~ important to,determine the ability of the battery to sustain high charge and discharge current'densities. The 20~ behavior of a Li/LixMo2O4 cell with respect to cycling~ currents ranging from ~00 ,uA/cm2 to 2mA/cm2 is shown in Fig. 3. , :, ! : : The cells tested were prepared by spreading powdered Lix~o2O4 onto a stainless steel disk of known , ~ 25 area. It is noted that over the range of 200 ~A/cm t:o 2mAjcm2 the lithium intercalation process was revarsible~. he overvoltage (difference between charge and discharge potentials) increased with a concurrent decrease in cell capacity as the current increased to 2m~/cm2 at which level the cell retains 60~ of its full capacity. ~lowever, I this los~ in capacity is less than that measured on j identical cel]s including TiS2 cathode materials. The following exemplary embodiment whlch is set forth solely for purposes of exposition describes the characteristics of the Li/Lix~o2O4 cells. ., :;~ .:: -. ` , lZ90804 ~ 6 -- Example Fiv~ g~ams of ~al 33Mo2O4 was obtained by reaction of 99% purity Na2Mo2O~ 99~ purity ~2 and 99~9% purity molybdenum powder at 700C in an evacuated electron beam welded copper tube. The Nal 33Mo2O~, in powdered form was mixed with LiI salt degassed at 340C under a vacuum of lO- torr. The mixed powder was then pressed ; with a pellet and placed in an evacuated silicon tube. ~ The temperature was then increased to 300C and maintained i lO there at for three days. The tube was then opened, the pellet ground and again treated in the foregoing manner for an additional three days. Following, the product was wasned with distilled acetonitrile to remove residual salts of lithium and sodium iodide. Atomic absorption analysis of the marked product (for lithium and sodium content) indicated complete ion exchange reaction since the amount of sodium left was less than 0.l% while the amount of lithium was equal to 3.6~ by weight, so resulting in a compound of the formula Lil 33Mo2O~ The x-ray diEfraction pattern oE the lithiated phase indicated a single phase product. All Bragy peaks were indexed on the basis of a monoclinic cell with lattice parameters being identical to those reported in the literature for single crystals of the h-Lil 5Mo2O~ phase. In light of the fact that single phases in the NaxMo2O4 system undergo hydration, the lithiated phases obtained herein were added to water at 50C ~hile stirring over a period oE 48 hours. The solutions were then filtercd and the solids dried with acetone and x-rayed. Thermogravimetric analysis revealed the presence oE Li] 33(~2)0 95MO2O4 and hi2(~2)~.75 2 4 ! While the inv2ntion has been described in detail in the foregoiny specification, the aEoresaid is by way af illustration only and is not restrictive in character. It will be appreciated by those skilled in the art that the processing para;neters ~nay be varied without departure from the spirit and ~scope of the invention. Modifications :` : . ' , ~.2908(1~ - 7 - which will reaclily s~pport themselves to those skilled in the art are all consldered within the scope of the inv*ntiorl, reierence beinq ~ade to the ~p,endel ~lalm-. ' : : ', ~ ' , ,~ : ., . I ;' ~ ' , ~ ., .. - .