PYROMETALLURGICAL PROCESS FOR RECYCLING OF NIMH BATTERIES

Abstract

The present disclosure concerns a method of producing a nickel-containing hydrogen storage alloy for use in a nickel metal hydride battery, the method comprising the steps: i. Providing a mixed active material comprising used positive electrode active material and used negative electrode active material; ii. Reducing the mixed active material, thereby obtaining a reduced active material; iii. Adding one or more metals to the reduced active material; iv. Remelting the mixture obtained in step iii; thereby obtaining a nickel-containing hydrogen storage alloy. The present disclosure also concerns nickel-containing hydrogen storage alloys obtained by the disclosed method.

Claims

1. A method of producing a nickel-containing hydrogen storage alloy for use in a nickel metal hydride battery, the method comprising: i. providing a mixed active material including used positive electrode active material and used negative electrode active material; ii. reducing the mixed active material, thereby obtaining a reduced active material; iii. adding one or more metals to the reduced active material to obtain a mixture; iv. melting the mixture; and v. cooling the melt, thereby obtaining a nickel-containing hydrogen storage alloy.

2. The method according to claim 1, wherein the used positive electrode active material includes nickel oxyhydroxide and the used negative electrode active material includes an AB.sub.5 alloy, wherein A is mischmetal, La, Ce or Ti, and B is Ni, Co, Mn or Al.

3. The method according to claim 1, wherein the nickel-containing hydrogen storage alloy is AB.sub.5, wherein A is mischmetal, La, Ce or Ti, and B is Ni, Co, Mn or Al.

4. The method according to claim 1, wherein the one or more metals in step iii are chosen from mischmetal, La, Al, virgin AB.sub.5 alloy, or mixtures thereof.

5. The method according to claim 4, wherein the mischmetal or La are added in quantities sufficient to recreate the elemental ratio of an AB.sub.5 alloy.

6. The method according to claim 1, wherein the reduction in step ii is performed under a hydrogen atmosphere of about 700 mBar.

7. The method according to claim 1, wherein the reduction in step ii is performed at a temperature of about 200 C. to about 500 C.

8. The method according to claim 1, wherein a product of step ii and/or step iii is stored under inert atmosphere prior to further use.

9. The method according to claim 1, comprising a step of removing electrode support materials and washing the used positive and the used negative electrode active materials prior to step i.

10. The method according to claim 1, wherein slag is removed from the melt in step iv.

11. The method according to claim 1, wherein melting in step iv is performed at 900-1100 C.

12. The method according to claim 1, wherein in step v, the melt is cooled over at least 10 hours.

13. A nickel-containing hydrogen storage alloy for use in nickel metal-hydride batteries, obtained by the method of claim 1.

14. The nickel-containing hydrogen storage alloy according to claim 13, wherein the nickel-containing hydrogen storage alloy is an AB.sub.5 alloy; and wherein A is mischmetal, La, Ce or Ti, and B is Ni, Co, Mn or Al.

15. A nickel-containing hydrogen storage alloy comprising nickel obtained from used positive electrode active material.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0038] For a fuller understanding of the present invention and further objects and advantages of it, the detailed description set out below should be read together with the accompanying drawings, in which the same reference notations denote similar items in the various diagrams, and in which:

[0039] FIG. 1 is a flow diagram illustrating the proposed recycling process for NiMH electrodes.

[0040] FIG. 2a is a x-ray diffractogram of an initial negative electrode material.

[0041] FIG. 2b is a x-ray diffractogram of an initial mixed electrode material.

[0042] FIG. 2c is a x-ray diffractogram of a reduced negative electrode material.

[0043] FIG. 2d is a x-ray diffractogram of a reduced mixed electrode material.

[0044] FIG. 3a is an XRD pattern for mixed crushed sample after reduction.

[0045] FIG. 3b is an XRD pattern for mixed non-crushed sample after reduction.

[0046] FIG. 4a is an XRD pattern for negative material after reduction 1 and arc melting.

[0047] FIG. 4b is an XRD pattern for mixed material after reduction 1 and arc melting.

[0048] FIG. 5a shows a series of XRD patterns obtained by reduction in-situ for mixed material.

[0049] FIG. 5b shows the end scan XRD pattern obtained from reduction in-situ for mixed material.

[0050] FIG. 6a shows a series of XRD patterns for the reduction of Ni(OH)2 at different temperatures showing the reduction from the orange and pink patterns (bottom) to the blue pattern (top, at 200 C.).

[0051] FIG. 6b shows the XRD pattern for Nickel showing an increase in the intensity from 200 C. and taken from the same XRD pattern scan as FIG. 6a.

[0052] FIG. 7a shows the XRD pattern for the pure mixed material before reduction.

[0053] FIG. 7b shows the XRD pattern for pure mixed material after reduction at 250 C. and 700 mbar pressure under argon environment.

[0054] FIG. 8 shows the XRD pattern for reference LaNi5 produced using the arc melting process.

[0055] FIG. 9a shows the XRD pattern for the material after reduction showing the La.sub.2Ni.sub.3 phase in red and Ni also present.

[0056] FIG. 9b shows the XRD pattern for the material in FIG. 9(a) after heat treatment.

[0057] FIG. 10a shows the SEM image of the Heat Treatment sample showing traces of LaNi5 in the centered structure.

[0058] FIG. 10b shows the SEM image of the Heat Treatment sample showing the main La2O3 structure.

[0059] FIG. 11a shows the XRD pattern for the refined arc melting stage showing only LaNi.sub.5 and slight traces of Nickel.

[0060] FIG. 11b shows the XRD pattern for the slag material produced from the arc melting stage mainly showing La.sub.2O.sub.3 with traces of LaNi5.

[0061] FIG. 12a shows the XRD pattern end scan for Negative material in-situ reduction showing at 250 C. where the La(OH)3 peak is.

[0062] FIG. 12b shows the XRD pattern for negative material showing a zoomed version of FIG. 12a where the decrease in intensity of La(OH)3 is between 250 and 275 C.

[0063] FIG. 13 shows the XRD pattern resulting from the reduction of mixed material at 300 C. with vacuum heating at 600 C. method and after arc melting.

[0064] FIG. 14 shows the XRD pattern for the mixed material after reduction at 300 C. and vacuum at 600 C.

[0065] FIG. 15a shows the XRD pattern for the new reduction of the mixed material before reduction.

[0066] FIG. 15b shows the XRD pattern for the new reduction of the mixed material after reduction.

[0067] FIG. 16a shows the XRD of the initial mixed material, wherein the reduction stages and arc melting are done under storage of Argon environment.

[0068] FIG. 16b shows the mixed material after reduction, wherein the reduction stages and arc melting are done under storage of Argon environment.

DETAILED DESCRIPTION

[0069] Pyro-Metallurgy for NiMH Batteries

[0070] In order to look at pyro-metallurgy methods to recycle NiMH batteries, one has to look into the thermodynamic behavior of these elemental components and suitable metal/slag recovery systems, environmental processing, energy balance and feasibility of the intended pyro-metallurgical process.

Thermodynamic Properties:

[0071] Previous reports has suggested that for NiMH batteries [20] the temperature range should be between 1400 C. and 1700 C. depending on the refractory material and composition of rare earth slag and metallic ratios. Retention time and reaction conditions will also be crucial in the process. One of the main techniques used to obtain thermodynamic properties of metal hydride systems [24] is using the equilibrium pressure for hydrogen as a function of temperature and percentage of hydrogen content in the hydride. The system works in such a way that as hydrogen is dissolved in the metal alloy, the equilibrium hydrogen pressure is increased until the solubility is reached [24].

[0072] With the addition of more hydrogen, the hydrogen saturated metal (metal phase) is converted to the metal hydride until it reaches above the composition (at the n value) and this leads to an increase in pressure in the system [24]. The increase in temperature affects the system in such a way that homogenous range of the metal hydride phase widens and the solubility of hydrogen in the metal increases [24]. The thermodynamic activities of the solid can therefore be written by the van't Hoff equation:

R ln P.sub.H2=(H/T)S5

[0073] The absorption and desorption of the metal hydride is also important for the percentage hydrogen content in the system. More specifically for the LaNi5 metal hydride the isotherm for its degradation after a number of cycles is what can used to determine what factors can be improved upon in the system (see ref [26]). Based on the phase of the material that is initially present in the system, one has to look at the phase diagram for LaNi5 to understand at what temperatures and compositions the desired phase can be reached. This is important as it can relate to the exact steps taken in the pyro-metallurgy process in order to reach the correct composition of the material, see ref [28].

Energy Balance:

[0074] For example when looking at the HTMR (High Temperature Metal Recovery) process, the energy balance can be done on the system to partially determine the environmental impact and energy consumption [9]. The HTMR process is based on the traditional technique used to recycle rechargeable batteries using the pyro-metallurgical process. The process usually consists of a mechanical shredding stage (could also be milling or size reducing step), a reduction step, smelting and casting. The process will also consist of wet scrubber and filtration stages in between which are also important for environmental reasons [9] and a basic energy balance will be included to see if the process is feasible. The energy of the system will be based on the first law of thermodynamics:

Useful Energy.sub.output=Energy.sub.inputEnergy.sub.loss(6) [9]

[0075] Due to the smelting and reduction stages contributing most energy, the input and output energy can be done mainly around these. The factors influencing the energy of the system will be, the type of furnace and operating conditions, time of cycle, chemical reaction, slag system (if necessary) and utilities.

Proposed Process Flow for Recycling

[0076] FIG. 1 is a process flow diagram illustrating the proposed recycling process for NiMH electrodes, and wherein the reference signs indicate: [0077] 1 Positive Spent Feed [0078] 2 Negative spent feed [0079] 3 Lab/Quality control [0080] 4 Homogenous mixing/blending [0081] 5 Washing/Drying Stage [0082] 6 Stage reduction [0083] 7 Dust recovery system [0084] 7 Mixing/Blending Stage [0085] 9 Lanthanum feed [0086] 10 Hydrogen supply [0087] 11 High Temperature Furnace Smelting [0088] 12 Electrochemistry Process and Performance Testing [0089] 13 Feed to Final Product/Main raw material feed

[0090] Table 1 below refers to the phase numbers in FIG. 1 and describes what each phase number represents in the proposed process.

TABLE-US-00001 TABLE 1 Phase Number Description Parameters No 1 Feed positive and negative Homogeneous mixing, Correct spent material, Blending ratio, weigh feeder and Mixing No 2 Washing and Drying Stage Washing with water depends on initial weight & filter drying No 3 Stage Reduction In-situ Reduction with Hydrogen Gas, temperature 30-600 C., 1 BAR H.sub.2, XRD No 4 Dust Recovery System Important to account for any loses and re-feed material back into the process. Also for safety reasons No 5 Lanthanum Re-feed, Metal Depends on the quality or the re-feed processed material and fed by weight and quality No 6 Blending/Mixing Stage Important for homogeneous mixing of material to obtain correct specifications of final material, weigh feeder No 7 High Temperature Furnace Parameters depends on type of Smelting machine/furnace used, temperature 1300-2000 C., Argon 400 mbar pressure. Might also contain a re-feed system depending on slag and impurities No 8 Electrochemistry Process Depends on High Temperature parameters, Compositions of AB.sub.5, Performance of material and Nilar specifications

Experimental Methods

[0091] The samples collected from Nilar were electrodes from 1 module containing the positive and negative electrodes (mixed) together in water (for safety purposes). Also provided was a single negative electrode from 1 module also in water. The scrim was also included in the mixed sample. The material (both samples, mixed and negative) was removed from the scrim and washed with around 500 ml of water and dried using a standard filter and filter paper.

Initial Sample Preparation:

[0092] The first sample taken was from the negative electrode. A small amount of sample was taken to be analyzed in the XRD. Around 7 g of sample was initially washed to be used for analysis.

[0093] The second sample taken was from the mixed electrodes. The same procedure was followed for it.

[0094] The samples was then analyzed using XRD.

X-Ray Diffraction

[0095] X ray diffraction is a technique used to identify the phase of a crystalline material and can provide information on the unit cell dimensions [25]. It uses monochromatic X rays generated by a cathode ray tube and is directed to a crystalline sample with constructive interference when the conditions for Bragg's Law is satisfied. The incident ray is related to the diffracted angle and the lattice spacing in the sample and the sample is scanned through a range of 2theta for all possible diffracted directions [25]. The diffracted rays are then detected (by a detector) and processed and counted. A pattern is then created based on the given lattice spacing of the crystalline sample and generated in the program to be analyzed further.

Parameters:

[0096] Initially a quick scan (around 10 min) of the sample was done to identify what can be expected in the sample. The XRD pattern is then compared with the expected elements in the sample with a data based program. Thereafter a job is created to do a longer sample scan running for about 3 hours and angle range from 10 to 90 and angle step of 0.008 per 192 s (pre-programmed settings).

Sample Preparation:

[0097] An important part of obtaining good results is to do proper sample preparation (powder samples). A small amount of sample is taken and placed into grinding crucible. A few drops of ethanol is added and the sample is grinded by hand until it is very fine and slightly wet. The sample is then placed gently on a silica based sample screen with a shiny center (of course the sample holder should be cleaned properly before use with ethanol and dried). The sample is then spread very evenly on the center and excess is removed gently. The sample is then dried under light to remove excess ethanol and thereafter the sample is ready for analysis.

Vacuum Furnace (MPF)

[0098] The furnace used is the vacuum furnace. The aim was to reduce the Nickel Hydroxide in the positive and negative electrode material (the mixed material) to nickel metal and any Lanthanum hydroxide in the initial sample to lanthanum metal (if possible) by heating at 600 C. under a hydrogen gas atmosphere for 4 hours. The pressure is set to 600 mbar inside the chamber and the system is flushed with a unique flushing technique. When the system is at atmospheric pressure (1000 mbar), the glass tube (sample holder) can be removed safely. The sample is placed in a suitable crucible (5-10 g) making sure the crucible is cleaned before. The glass tube is then secured tightly onto the chamber and screws tighten and a safety wire net placed on the glass. The vacuum pump can be started and the valve opened very slowly to drop the pressure until 0 mbar and thereafter the valve is opened fully to create complete vacuum. The argon valve can then be opened slowly to flush the system with argon gas (+400 mbar). The valves is then closed and the vacuum valve is then opened to remove the gas from the system. This can be done twice to completely flush the system. Thereafter the system can be flushed with hydrogen gas (400 mbar) and pumped out with vacuum. Thereafter the hydrogen can be filled in the chamber until 600 mbar in this case. All the valves is then closed and the furnace is heated up to 600 C. Once the temperature is 600 C. and the system is safe, the sample is placed in the exact center of the furnace and left for the duration of 4 hours. Thereafter the sample (once cooled) can be analyzed by the XRD to find traces of Nickel hydroxide after the reduction step.

Arc Furnace

[0099] The arc furnace is a very specialized high beam melting furnace used to liquefy and solidify metals under high temperatures to either change the structure of the metals or to see what effects it has on hard materials. The furnace using argon gas to purge the chamber, this is usually done about three times to make sure the chamber environment is clean. The inside of the chamber, the copper and metal sample chamber is also cleaned properly before use. The arc furnace uses a vacuum pump to pump out the gases and to maintain a desired pressure in the system. The arc furnace also has high power generator which generators the main power source for the beam. Once the chamber is clean and all safety checks are done, the getter sample is placed in the sample chamber. The getter consists of a pure titanium melted pellet previously prepared for the arc furnace test. The titanium getter is important for the system as it acts as an oxygen consumer (oxygen getter) to remove all the oxygen from the chamber before the sample can be melted. This is important as you want an oxygen free zone when melting the sample. The titanium is good for this purpose because it reacts very rapidly with oxygen and this can be tested by the colour of the titanium metal after is has been melted. The blue and yellow colour usually shows signs of oxygen and if all oxygen has been removed the titanium metal will remain silvery in colour. This test is done before testing the desire sample so as to make sure all the oxygen is removed from the chamber. Once this the sample can be melting using the same procedure as for melting the titanium getter. It is however very important that the sample be made into a pellet using the hydraulic press as the arc furnace does not take powdered samples. The pressed pellet sample is melted about five times on each side to get a complete and uniform representative sample. Only once this is done is the sample completely melted and can then be analyzed or treated further.

In-Situ XRD Flowing Hydrogen Gas Reduction

[0100] For the in-situ set up, the material is prepared the same as it would be for an X-ray diffraction experiment with the difference being in the placement and sample holder of the set-up. The sample must be place on a small plastic stand and placed vertically in the small furnace surrounding the sample and tightened into place. The X-ray detector and X-ray beam is therefore on opposite sides of the furnace with a glass screen to view the sample through. The necessary gas tubes (in this case hydrogen) is connected on the incoming end to make contact with the sample in the holder and the gas pressure and flow is setup corrected before starting the step up program.

[0101] The experiment usually runs for a few hours depending on the temperature range and step changes made. The program will therefore capture all the XRD patterns and necessary data during the run to be analyzed at the end.

Heat Treatment

[0102] For the heat treatment experiment the aim was to change phases of the Lanthanum Nickel compound formed during the reduction stages. The ratio according to the phase diagram, was slightly shifted to the left (the lanthanum ratio was slightly higher than nickel in the AB5) and therefore to change the phase required that the temperature was increased to 1000 C. and cooled slowly under a controlled environment (step cooling). This meant that the phase diagram needed to be consulted for the LaNi5 and the experiment designed according to it.

[0103] The sample was first prepared by cleaning the silicon tube used in the experiment and the sample was placed inside (+1 g) of sample. The neck of the tube was burnt using a blow torch and then vacuum sealed using a specialized vacuum pump and piping system to completely remove all the air in the tube. This process takes around 30 min to completely obtain vacuum. The tube is then sealed using the blow torch again to obtain a smaller tube and this is then weighed and placed into the pit furnace. The furnace is then programmed accordingly. The program used for the heat treatment program was a 12 hour ramp up time to 1000 C., maintaining the temperature at 1000 C. for 5 days, followed by a 24 hours ramp down time to ambient temperature.

Summary of the Reduction Experiments:

[0104] The methods used was mainly X-Ray Diffraction to initially analyze the contents of the material and to analyze the material during and after main process conditions were changed. The XRD machine used was the Bruker D8 Advance diffractometers for Powder Diffraction (XRPD) and also the D8 twin twin for Powder Diffraction. The pyro-metallurgical process equipment included MPF Furnace, Arc Furnace and Pit Furnace. Other laboratory equipment included glovebox, fume-hood, pellet press etc. The following is the summary of the experimental methods for the reduction process:

TABLE-US-00002 TABLE 2 The reduction experiments done for all the material Sample/Method Temperature name ( C.) Pressure(mbar) Other conditions Initial Reduction 600 600 4 hrs 1 (no special requirements) Reduction 2 250 800 overnight (particle size) Reduction in-situ 30-300-30 1 bar Flowing H2 gasstep change 30-300-30 Reduction 3 250-500 800 Vacuum at 500 Reduction without 250 700 No vacuum for 4 hrs vacuum special handling

Results and Discussion

[0105] The results for the first part of the project is presented by the XRD patterns of the initial material, the mixed material and the negative material from the electrodes. This is to establish what chemical elements are present and to give an idea of what the compositions might be.

Initial Measurements

[0106] The initial measurements were to analyze the material and establish a process path which can be followed initially to understand more about the material.

[0107] FIGS. 2a-2d show X-ray diffractograms (XRD) for (a) Initial negative electrode material (b) Initial mixed material (c) reduced negative material (d) reduced mixed material.

[0108] It's clear from these results that after reduction of the initial mixed material for the reduced mixed (FIG. 2d) there is only nickel present whereas for the reduced negative (FIG. 2c) there is nickel, AB.sub.5 and traces of Ni(OH).sub.2. This proves that the reduction conditions initially were not ideal for the material and hence the conditions were adjusted.

Reduction for Crushed and Non-Crushed Material (Reduction 2)

[0109] FIG. 3(a) shows an XRD pattern for mixed crushed sample after reduction, and FIG. 3 (b) shows a mixed non-crushed sample after reduction.

[0110] The comparison of the two samples show that non-crushed sample after reduction with Hydrogen and same conditions does not have much difference although non-crushed sample is favoured because the traces of LaNi.sub.5 is slightly more.

Initial Arc Melting Process

[0111] FIG. 4(a) shows an XRD for negative material after reduction 1 and arc melting, whereas FIG. 4(b) shows an XRD for mixed material after reduction 1 and arc melting.

[0112] The mixed material shows traces of nickel only and therefore means that the process needs to be improved. This however also indicates that the Lanthanum from the AB.sub.5 has been consumed and therefore the reduction process is not effect. Also the negative material contains more LaNi.sub.5 which is expected initially but also maintains it throughout the process. This could also therefore mean that depending on the initial ratio of the mixed material (negative and positive) will have an effect on the amount of LaNi.sub.5 present at the end of the process.

Reduction In-Situ with Hydrogen Gas Flow

[0113] Conditions: 1 bar Hydrogen gas pressure, Step change for temperature 30 C.300 C.30 C. in increments of 50 C. Each scan contained short and long scans (Short scan 30 min, Long scan 3 hr).

[0114] FIG. 5(a) shows a series of XRD patterns from reduction in-situ for mixed material. FIG. 5(b) shows the end scan XRD pattern for reduction in-situ for mixed material.

[0115] FIG. 6(a) shows the XRD pattern for the reduction of Ni(OH).sub.2 at different temperatures showing the reduction from the orange and pink patterns (bottom) to the blue pattern (top, at 200 C.). FIG. 6(b) shows the XRD pattern for Nickel showing an increase in the intensity from 200 C. and taken from the same XRD pattern scan as FIG. 6(a).

[0116] This therefore proves that the in-situ reduction experiment under flowing hydrogen can reduce the Ni(OH).sub.2 and at the same time increases the intensity of the Nickel. Also the LaNi.sub.5 intensity is slightly higher when compared to the reduction with the MPF. This therefore stands to reason that the in-situ reduction experiment is better suited for this type of system and is due to the reaction kinetics:

Ni(OH).sub.2(s)+H.sub.2(g).fwdarw.Ni.sub.(s)+2H.sub.2O.sub.(g)(7)

[0117] Therefore based on the forward reaction being favoured it means that the water vapor will be formed and be removed from the system at the same time. Therefore looking at the reaction rate constant for the above reaction

[Ni][H.sub.2O]/[Ni(OH).sub.2][H.sub.2]=K

[0118] And with the solids in the equation being equal to 1 it means the reaction will therefore depend on the partial pressure of the gases (water vapor and hydrogen gas)

[0119] [1][pH.sub.2O]/[1][pH.sub.2] and the water vapor pressure will tend to 1 too because it is being removed from the system, so therefore the equation will always be >>0.

[0120] Based on the success of the reduction stage in-situ, it stands to reason that adding the additional Lanthanum according to the correct ratio of LaNi.sub.5 (AB.sub.5) and allowing the nickel to react with this lanthanum we can produce the desired LaNi.sub.5 again and therefore achieve the recycled rate of the spent mixed material. However achieving this also means refining the reduction stage to a more suitable process and therefore hence the different techniques for improvements was investigated.

Reduction at 250 C. and 700 Mbar Pressure Under Argon Environment

[0121] FIG. 7(a) shows the XRD pattern for the pure mixed material before reduction. FIG. 7(b) shows the XRD pattern for pure mixed material after reduction. Both samples were initially stored under argon environment to avoid formation of La.sub.2O.sub.3.

[0122] These results shows that the Nickel intensities are decreased and could therefore mean that the Lanthanum added to the system has to some extent reacted with the Nickel because of the small traces of LaNi.sub.5, although it is not at a desired state yet. It was then decided that a reference sample of pure LaNi.sub.5 can be produced and used as a comparison for the desired material. FIG. 8 shows the XRD pattern for this reference LaNi5 produced using the arc melting process. Also the patterns show less La.sub.2O.sub.3 which therefore means that it is important for the material to be stored in an oxygen free environment.

Heat Treatment

[0123] Based on one of the reduction experiments where the conditions were changed to 300 C. at 800 mbar H.sub.2 with the MPF, the results showed a La.sub.2Ni.sub.3 phase which was unusual for these conditions and the heat treatment experiment was introduced to change the phase of the material to the LaNi.sub.5 based on the LaNi.sub.5 phase diagram.

[0124] FIG. 9(a) shows the XRD pattern for the material after reduction showing the La.sub.2Ni.sub.3 phase in red and Ni also present. FIG. 9(b) shows the XRD pattern for the material in FIG. 9(a) after heat treatment.

[0125] These results shows that the phases have changed from La.sub.2Ni.sub.3 to LaNi.sub.5 based on the programmed pit furnace experiment but however shows high intensities of La.sub.2O.sub.3 (red patterns in FIG. 9b) which is not desired. From the figure it is clear that the LaNi.sub.5 phase can be achieved using this method, although it is still also clear that there is La.sub.2O.sub.3 still present in the process (strong peaks of oxides) and this needs to be further investigated. The scan also shows no or very few amounts of nickel metal which suggests that the nickel has reacted with the lanthanum and the AB.sub.5 has been formed successfully.

Scanning Electron Microscope (SEM) Images

[0126] The SEM images were taken from the samples used in the reduction number 3 and heat treatment experiments to see what the La.sub.2O.sub.3 structure and traces of the LaNi.sub.5 formed during these processes might look like. FIG. 10a shows the SEM image of the Heat Treatment sample showing traces of LaNi5 in the centered structure. FIG. 10b shows the SEM image of the Heat Treatment sample showing the main La2O3 structure. From FIG. 10a it is seen as a lump of nickel with traces of LaNi.sub.5 inside the structure and in FIG. 10b it is only the La.sub.2O.sub.3 structure that is observed.

Refined Arc Melting Process

[0127] Based on all the previous results it is clear that the LaNi.sub.5 can be formed but with a more refined arc melting stage and using the refined reduction method also under argon stored environment. The results of the refined arc melting stage will then be compared to the reference LaNi.sub.5 which was produced also by a more refined method.

[0128] FIG. 11a shows the XRD pattern for the refined arc melting stage showing only LaNi.sub.5 and slight traces of Nickel. FIG. 11b shows the XRD pattern for the slag material produced from the arc melting stage mainly showing La2O3 with traces of LaNi5.

[0129] Based on the figure shown, it is clear that the refined arc melting method has proven to show an increase in the LaNi.sub.5 phase. This therefore means that the refining of the process can therefore produce a higher quality material. However the slag produced from the material was also analyzed and based on the calculation results showed a 25.24% loss due to slag.

[0130] The slag is formed after the first melt on most occasions during the arc melting process and usually moves to the outer layer. This could therefore mean that it could be easier to separate at a later stage of the process.

Steps and Observations

[0131] Try and use average amount of sample (around 2-3 g) [0132] After each melt remove slag and re-melt [0133] Keep the amount of melts to a minimum [0134] Try and keep the exposure to air of the sample as short as possible [0135] Study the sample and look closely at where slag is formed and where metallic is formed [0136] Add initial 10% extra La to addition La [0137] Place La and pellet in close contact with each other [0138] Weight all sample and slag after each melt [0139] Add the extra-extra La after the second melt when most of the slag is removed [0140] Analyze all the material

Conclusion and Outlook

[0141] To conclude it was initially not easy to establish a process path where it was obvious or not that the mixed material can produce a LaNi5 compound and hence the trial and error experiments especially regarding the reduction phase. However with the process conditions changes made, it become more obvious which conditions would be better suited for the material until a reduction process of 250 C. with no vacuum pumping and pressure of 700 mbar under Hydrogen atmosphere for 4 hrs. This process can also be further investigated but for these purposes it seems to be successful. Also the arc melting process took some work and different techniques to prepare sample specifically with no or limited exposure to air. Hence the steps and observations which was noted based on this material and process equipment used. The overall result is that the material can be recycled to produce a good quality LaNi5 compound and this can be incorporated into the process operations as an optimized version of the proposed process flow for the Nickel Metal Hydride material.

REFERENCE

[0142] [1] Academic Database 2000-2014, Nickel-metal hydride battery, website: www.en.academic.ru/dic.nsf/enwiki/11817092 (visited 5 Feb. 2016) [0143] [2] Ovshinsky et al. Chemically and compositionally modified solid solution disordered multiphase Nickel hydroxide positive electrode for alkaline rechargeable electrochemical cells, Ovonic Battery Company Inc., Troy, Mich., (1994) United States Patent [0144] [3] Robert C. Stempal et al, Ovonic Battery Co. Nickel-metal hydride: Ready to serve, November (1998), 29-34 [0145] [4] Nilar Doc No: 73-F006-R01. Nilar, Product information, Nilar 12V Energy Module, website: www.nilar.com (visited 28 Jan. 2016) [0146] [5] Nilar Doc No: 73-F001-R02. Nilar Technical Manual, Nilar Energy Battery, website: www.nilar.com (visited 28 Jan. 2016) [0147] [6] Energizer, Nickel Metal Hydride (NiMH) Handbook and Application manual, version: NiMH02.01, Energizer Battery Manufacturing Inc. 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Appendix A: Calculations for Lanthanum Addition to the System

[0171] Using the A/B ratio as 7.8 (from the initial material sent from Nilar)

TABLE-US-00003 TABLE 3 The atomic weight percentages for the initial mixed material and for the desired phase of AB5 (LaNi.sub.7.8) (LaNi.sub.5) ratio 7.8 ratio 5 Ni 76.683 Ni 67.875 La 23.316 La 32.128 total 100 total 100

[0172] Therefore the aim would be to move from the 7.8 ration phase of nickel and lanthanum to the 5 ratio phase by adding additional lanthanum during the process.

[0173] The calculations for the sample weight and lanthanum addition are as follows:

[0174] First to establish the correct amount of sample weight for the arc melting: 2 g

Lanthanum based on 2 g sample: 223.31676/100=0.46633 g

Nickel: 276.68324/100=1.53366 g

[0175] Therefore calculate the total sample amount:

1.5366100/67.87=2.259702 g total

Therefore new La: 2.25970232.128/100=0.725997 g

Exact amount=0.7259970.46633=0.259667 g add 10% gives 0.28562 g (round off to 0.32)

[0176] Calculate the Percentage of Slag Obtained from the System

Exact sample weight for arc melting=2.0678 (pellet) and 0.3148 g (La)=2.3826 g

TABLE-US-00004 TABLE 4 The amount of melts during the arc melting process and the related weights of sample and slag Melt Total sample weight Total slag weight number after melt (g) after melt (g) 1st 2.2856 0.2826 2.sup.nd 1.9265 0.4712 3rd 2.1235 2.1235 2.0966 = 0.0269

[0177] At this stage the extra La was added to account for the losses due to the formation of La.sub.2O.sub.3

[0178] Total new sample after the 2 melts: 1.4392 g (assume all Nickel)

Total sample=1.4392100/67.87=2.1205 g

La=2.120532.128/100=0.68127 g

Therefore the 3.sup.rd melt sample=1.4392 g (sample of all Ni)+0.6843 (extra La)=2.1235 g

After.sub.3R melt weight=2.0966 g (loss=2.1235-2.0966=0.0269 g)

Therefore percentage losses=total slag/total sample100:

Total amount of sample: 2.3826 (initial sample)+0.6843 (extra La added)=3.0669 g

Total slag=0.2826+0.4712+0.0269=0.7807 g

% loss=0.7807/3.0669100=25.45% (However this can still be recycled and refined further!)

Calculation for % Lanthanum Added

[0179]
Initial La for pellet (0.3148 g)+extra La (0.6843 g)=0.9991 g

Total sample=3.0669 g

% La=0.9991 g/3.0669100=32.57%

Appendix B: Extended Results from Other Contributing Experiments Performed

Negative In-Situ Reduction:

[0180] Based on the In-situ reduction results the negative material was also reduced under the same conditions as the positive but because it already contains LaNi.sub.5 it is considered to be easier to reduce and therefore the challenge for the negative material is reducing the La(OH).sub.3 which is slightly more challenging than the Ni(OH).sub.2. FIG. 12a shows the XRD pattern end scan for Negative material in-situ reduction showing at 250 C. where the La(OH)3 peak is. The pattern still shows the nickel and LaNi5. FIG. 12b shows the XRD pattern for negative material showing a zoomed version of FIG. 12a where the decrease in intensity of La(OH)3 is between 250 and 275 C. These results show that to some extent in the negative material the La(OH).sub.3 is reduced but less when compared to Ni(OH).sub.2.

Mixed Material Reduction at 300 C. and 800 Mbar Pressure Hydrogen Pressure

[0181] A few different methods were tried to achieve similar results with the in-situ experiment but was not entirely successful. The following was the reduction tried at 300 C. and 800 mbar pressure Hydrogen atmosphere with a vacuum heating step at 600 C. included after treating the material overnight and adding the additional Lanthanum and arc melted at the end. FIG. 13 shows the XRD pattern resulting from the reduction at 300 C. with vacuum heating at 600 C. method and after arc melting.

[0182] Based on this, it showed that the phase of La.sub.2Ni.sub.3 was present (the pink peaks) and therefore looking at the phase diagram for LaNi.sub.5 it was decided that the material can be heat treated to reach the LaNi.sub.5 phase (See the heat treatment results section). The material after reduction for the same process however showed a strange phase of material which hasn't been seen before with this type of material. The phase was a lanthanum nickel oxide (possibly LaNiO.sub.3) as seen from FIG. 14. FIG. 14 shows the XRD pattern for the mixed material after reduction at 300 C. and vacuum at 600 C. The nickel (blue) is present together with the Lanthanum Nickel Oxide phase (red).

The Reduction Stages Changed to 250 C. and Difference Between Vacuum and No Vacuum

[0183] Based on the in-situ reduction experiment, it was seen that the optimal temperature for reduction was around 250 C. and therefore it would make more sense to reduce the material at this temperature and not increase beyond this as to save energy and to continue using the MFP vacuum furnace as it is seen to be a cheaper option (in industry) than the flowing Hydrogen. The in-situ experiment however showed that it is possible to reduce the Ni(OH).sub.2 material as desired and obtain nickel metal which can be used for further treatment. The experiments that followed however showed that it is also possible to achieve the desired reduction conditions using the vacuum MFP furnace but meant that the parameters of the reaction needed to be adjusted accordingly as the material is sensitive.

[0184] FIG. 15a shows the XRD pattern for the new reduction of the mixed material before reduction, whereas FIG. 15b shows the XRD pattern for the new reduction of the mixed material after reduction.

[0185] Once the desired reduction stage was achieved with the MFP furnace, the limiting factor to achieve desired recycling rates of the AB.sub.5 was at the arc melting stage where the material seems to not react completely (that is the lanthanum and nickel). For this a reference sample was done with pure nickel and lanthanum in the arc furnace to see if the desired ratios can be achieved and therefore the aim would therefore be to achieve the same or similar XRD pattern as the reference sample. It was also observed that there was a fair amount of La.sub.2O.sub.3 material which is undesired and still needed to be treated and therefore the conclusion was drawn that the lanthanum in the system reacts (to a certain degree) with the oxygen in air. This was proved with material that was standing and exposed to air over some period of time and analyzed again using XRD. The test was to determine whether the lanthanum was reacting with oxygen and therefore looking at figures in the initial section, it shows true to this point. It was then decided to store all materials in a glove-box argon environment after each stage to reduce this chance of the lanthanum reacting and therefore causing loses.

The Reduction Stages and Arc Melting Done Under Storage of Argon Environment

[0186] Based on success of the methods used and formation of AB.sub.5 it was decided that the process can be refined further to achieve an even higher degree of recycled material but refining the reduction stage and arc melting stages. It is therefore seen that the AB.sub.5 can be obtained so therefore the aim would be to refine the process. The shortcoming of the method is that exposure to oxygen causes the material to form lanthanum oxide and therefore reduces the LaNi.sub.5 as the lanthanum oxygen reaction is favoured. The approach is therefore to use the cheapest and easiest methods and if possible reduce the process stages but still produce the desired material. The following XRD patterns are based on a more pure form of the material (by not exposing it to oxygen) and still doing the reduction and arc melting stages but with a more refined approach. [0187] FIG. 16a shows the XRD of the initial mixed material. FIG. 16b shows the mixed material after reduction. [0188] The difference between the initial sample before reduction and after reduction is the intensity of the nickel peaks have increased and the LaNi.sub.5 is less. Also traces of Nickel oxide is present after reduction which is strange in this case and could also benefit from further investigations.

[0189] Looking at the metallic sample after the arc melting, it was observed that the material is mainly nickel and that the lanthanum did not react as expected. The outer layer which is considered to be the slag contains mainly La.sub.2O.sub.3 and nickel and traces of LaNi.sub.5. This however means that some of the lanthanum has however reacted but is less and most of it has formed the oxide. However the experiment was repeated and this time the results showed that the intensities were less in all the compounds present (LaNi.sub.5, La.sub.2O.sub.3 and nickel) but the most important observation was the fact that the material was softer compared to the first metallic sample after arc melting. The changes to the repeat sample was not that much different but the handling of the sample was done more carefully and the lanthanum was added as pieces at the arc melting stage. Also the amount of melts was reduced to maximum of three and after the second melt the sample was removed and analyzed and found to be softer. This could therefore mean that reducing the melts and preparing the lanthanum after (not during the pellet producing stage) could have a slight difference in producing the LaNi.sub.5. Also a slight excess of initial lanthanum was added to the repeat sample which was not the case in the first test (in the first test the calculated exact amount of lanthanum was added) see Appendix A for calculations of lanthanum. This could mean that an excess of lanthanum could compensate for the formation of oxide and favor the formation of LaNi.sub.5. The slag of this material also shows traces of LaNi.sub.5 although much less but has high intensities of nickel which means that there is still room for improvements. Another observation made as that when less initial sample was used the effect was better as the lanthanum had come into closer contact with the nickel and seemed to react better when comparing the XRD patterns of the samples with less material than the samples with initially more weight. This could also relate to the dynamics of the arc furnace where less material seems to perform better than more.