COMPOSITION FOR PREPARATION OF ELECTRODE MATERIAL

Abstract

A nickel-based hydroxide powder is provided which has an average crystallite size, as determined by Scherrer fitting of the (00I) reflections of an XRD powder diffraction pattern of the nickel-based hydroxide powder, of at most 10 nm, together with a process for producing nickel-based hydroxide powders. The nickel-based hydroxide powders find utility as precursors for the formation of lithium transition metal oxide active electrode materials.

Claims

1-25 (canceled)

26. A nickel-based hydroxide powder expressed by the general formula [Ni.sub.xCo.sub.yA.sub.z][O.sub.p(OH).sub.q].sub.a, wherein: A is one or more of V, Ti, B, Zr, Cu, Sn, Cr, Fe, Ga, Si, Mn, Mg, Sr, and Ca; x satisfying 0.75≤x≤0.99 y satisfying 0≤y≤0.2 z satisfying 0<z≤0.1 wherein p is in the range 0≤p<1; q is in the range 0<q≤2; x+y+z=1; and a is selected such that the overall charge balance is 0; and wherein the nickel-based hydroxide powder has an average crystallite size, as determined by Scherrer fitting of the (00l) reflections of an XRD powder diffraction pattern of the nickel-based hydroxide powder, of at most 10 nm.

27. The nickel-based hydroxide powder according to claim 26 wherein A is one or more of V, Ti, B, Zr, Cu, Sn, Cr, Fe, Ga, Si, Mg, Sr, and Ca.

28. The nickel-based hydroxide powder according to claim 26 wherein the nickel-based hydroxide powder has an average crystallite size, as determined by Scherrer fitting of the (00l) reflections of an XRD powder diffraction pattern of the nickel-based hydroxide powder, of at least 2 nm.

29. The nickel-based hydroxide powder according to claim 26 wherein the nickel-based hydroxide powder has an average crystallite size, as determined by Scherrer fitting of the (00l) reflections of an XRD powder diffraction pattern of the nickel-based hydroxide powder, of at most 9 nm, or of at most 8 nm.

30. The nickel-based hydroxide powder according to claim 26 wherein x satisfies 0.8≤x≤0.99.

31. The nickel-based hydroxide powder according to according to claim 26 wherein y greater than zero.

32. The nickel-based hydroxide powder according to claim 26 wherein p is 0, and q is 2.

33. The nickel-based hydroxide powder according to claim 26 wherein A includes Mg.

34. The nickel-based hydroxide powder according to claim 26 wherein A is Mg.

35. The nickel-based hydroxide powder according to claim 26 wherein the sulphur content is less than 10000 ppm.

36. An active electrode material produced by a method comprising the step of dry-mixing a nickel-based hydroxide powder according to claim 26 with a lithium salt, followed by calcining in an oxidising atmosphere.

37. An active electrode material according to claim 36 wherein the lithium salt is lithium hydroxide.

38. An active electrode material according to claim 36 wherein the active electrode material is a lithium transition metal oxide.

39. An electrode comprising an active electrode material according to claim 36, a conductive additive, and a binder.

40. An electrochemical cell comprising an electrode according to claim 39.

41. The use of a nickel-based hydroxide powder satisfying requirements (1) and (2) as a precursor in the preparation of a lithium transition metal oxide active electrode material: (1) the nickel-based hydroxide powder is expressed by the general formula [Ni.sub.xCo.sub.yA.sub.z][O.sub.p(OH).sub.q].sub.a, wherein: A is one or more of V, Ti, B, Zr, Cu, Sn, Cr, Fe, Ga, Si, Mn, Mg, Sr, and Ca; x satisfying 0.75≤x≤0.99 y satisfying 0≤y≤0.2 z satisfying 0<z≤0.1 wherein p is in the range 0≤p<1; q is in the range 0<q≤2; x+y+z=1; and a is selected such that the overall charge balance is 0; and (2) the nickel-based hydroxide powder has an average crystallite size, as determined by Scherrer fitting of the (00l) reflections of an XRD powder diffraction pattern of the nickel-based hydroxide powder, of at most 10 nm.

42. The use according to claim 41 wherein the nickel-based hydroxide powder is expressed by the general formula [Ni.sub.xCo.sub.yA.sub.z][O.sub.p(OH).sub.q].sub.a, wherein: A is one or more of V, Ti, B, Zr, Cu, Sn, Cr, Fe, Ga, Si, Mn, Mg, Sr, and Ca; x satisfying 0.75≤x≤0.99 y satisfying 0≤y≤0.2 z satisfying 0<z≤0.1 wherein p is in the range 0≤p<1; q is in the range 0<q≤2; x+y+z=1; and a is selected such that the overall charge balance is 0; and wherein the nickel-based hydroxide powder has an average crystallite size, as determined by Scherrer fitting of the (00l) reflections of an XRD powder diffraction pattern of the nickel-based hydroxide powder, of at most 10 nm.

43. A method of making a nickel-based hydroxide powder expressed by the general formula [Ni.sub.xCo.sub.yA.sub.z][O.sub.p(OH).sub.q].sub.a, wherein: A is one or more of V, Ti, B, Zr, Cu, Sn, Cr, Fe, Ga, Si, Mn, Mg, Sr, and Ca; x satisfying 0.75≤x≤0.99 y satisfying 0≤y≤0.2 z satisfying 0≤<z≤0.1 wherein p is in the range 0≤p<1; q is in the range 0<q≤2; x+y+z=1; and a is selected such that the overall charge balance is 0; the method including the steps of: supplying, to a reaction vessel, a metal salt solution, a base solution, and an ammonia solution to thereby form an aqueous mixture within the reaction vessel, the metal:ammonia molar ratio of the metal salt solution and the ammonia solution supplied to the reaction vessel being in a range from 1:1 to 1:2.25; mixing the aqueous mixture in the reaction vessel at a reaction temperature of 30-80° C.; adjusting the flow rate or addition amount of the base solution to control the pH of the aqueous mixture to be in the range of 9 to 13, to cause precipitation of the nickel-based hydroxide from the aqueous mixture; filtering the aqueous mixture to extract the precipitated nickel-based hydroxide; and drying to obtain the nickel-based hydroxide powder.

44. A method according to claim 43 wherein the nickel-based hydroxide powder has an average crystallite size, as determined by Scherrer fitting of the (00l) reflections of an XRD powder diffraction pattern of the nickel-based hydroxide powder, of at most 10 nm.

45. A method according to claim 43 wherein the nickel-based hydroxide powder is expressed by the general formula [Ni.sub.xCo.sub.yA.sub.z][O.sub.p(OH).sub.q].sub.a, wherein: A is one or more of V, Ti, B, Zr, Cu, Sn, Cr, Fe, Ga, Si, Mn, Mg, Sr, and Ca; x satisfying 0.75≤x≤0.99 y satisfying 0≤y≤0.2 z satisfying 0<z≤0.1 wherein p is in the range 0≤p<1; q is in the range 0<q≤2; x+y+z=1; and a is selected such that the overall charge balance is 0; and wherein the nickel-based hydroxide powder has an average crystallite size, as determined by Scherrer fitting of the (00l) reflections of an XRD powder diffraction pattern of the nickel-based hydroxide powder, of at most 10 nm.

46. A method according to claim 43 wherein the metal salt solution is a metal sulphate solution or a metal nitrate solution.

47. A method according to claim 46 wherein the metal salt solution is a mixed metal sulphate solution comprising two or more different metal sulphates.

48. A method according to claim 43 wherein the total metal:ammonia ratio is in a range from 1:1.75 to 1:2.

49. A method according to claim 43 wherein the pH of the aqueous mixture is controlled to be in the range of 10.6 to 11.2.

50. A method according to claim 43 wherein the reaction time is between 6 and 30 hours.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0081] Aspects and embodiments of the present invention will now be discussed with reference to the accompanying figures. Further aspects and embodiments will be apparent to those skilled in the art. All documents mentioned in this text are incorporated herein by reference.

[0082] FIG. 1 is a scatter plot showing crystallite size against first cycle efficiency % (FCE%) for a number of samples of nickel-based hydroxide powder. As shown in FIG. 1, by providing a nickel-based hydroxide powder (precursor material) with an average crystallite size, as determined by Scherrer fitting of the (00l) reflections of an XRD powder diffraction pattern of the nickel-based hydroxide powder, of at most 10 nm, it may be possible to provide electrode materials made from said precursor material having improved first cycle efficiency (FCE) in comparison to similar electrode materials produced from precursor materials having an average crystallite size or larger than 10 nm.

[0083] As discussed above, one or more crystallites form primary particles. These primary particles typically agglomerate into substantially spherical secondary particles, as seen in FIG. 2, which is an SEM image showing the general morphology of a precursor material formed by the process as described herein. Secondary particles having a diameter in the range of approximately 2-10 μm can be seen.

[0084] As discussed above, the precursor materials described herein can be used to form active electrode materials e.g. lithium transition metal oxide materials, by lithiation and oxidation. The electrochemical performance (primarily first cycle efficiency FCE%) of electrodes formed from such materials has been assessed in a manner described in further detail below.

[0085] Each of the samples discussed below is a precursor of the composition Ni.sub.0.91Co.sub.0.08Mg.sub.0.01(OH).sub.2. However, each sample is prepared using different precipitation conditions. The crystallite size data reported is of the precursor material. This is then lithiated and oxidised to form an active electrode material having a composition Li.sub.1.03Ni.sub.0.91Co.sub.0.08Mg.sub.0.01O.sub.2, from which an electrode is formed and electrochemically characterised.

CONDITIONS FOR PRECURSOR PRECIPITATION

Precursor Precipitation Operation

[0086] Detailed example sample A: A mixed metal sulphate solution (1.33 M) comprising nickel sulphate hexahydrate, cobalt sulfate heptahydrate and magnesium sulphate at a metal molar ratio of 0.91:0.08:0.01, base solution (2M NaOH) and ammonia solution (2M) were heated to 45° C. then co-fed to a baffled reactor fitted with an agitator set at 450 rpm. The reactor begins with a 1 L heel of water with 50 mL ammonia and a few drops of NaOH to start with a pH of 11 at 45° C. The solutions were pumped to the vessel, using peristaltic pumps over a period of 5 hours with the reaction temperature maintained at 45° C. The pH for the precipitation in this example was 11. The vessel was an open vessel (no lid). The mixed metal flow rate was kept constant at about 3 mL/min, the ammonia solution was fed in at a fixed rate in a 1:1 molar ratio with the metals solution and the pH of the solution adjusted by varying the flow rate of the base solution. The slurry was then vacuum filtered. The obtained solid was washed with hot (about 40° C.) deionised water to remove sodium and sulphate ions. The washed filter cake was then tray dried at 120° C. overnight.

[0087] Samples B, C, D and E were obtained as for sample A with the modification that the reaction time was within the range of 5 to 31 hours. [0088] Sample B [0089] Reaction time: 19 h [0090] Sample C (repeat of B) [0091] Reaction time: 19 h [0092] Sample D [0093] Reaction time: 26 h [0094] Sample E [0095] Reaction time: 31 h

[0096] Samples F and G were obtained as for sample A with the modification that the flow rate of the base solution was fixed at 1 mL/min, the temperature was fixed at 60° C. and the reaction time was varied within the range of 18 to 24 hours. [0097] Sample F [0098] Reaction time: 18 h [0099] Sample G [0100] Reaction time: 24 h

[0101] Samples H, I, J, K, L were obtained as for sample A with the modification that the flow rate of the base solution was fixed at 1 mL/min, the reaction time was fixed at 24 hours and the ammonia-to-metal molar ratio was varied within the range of 1:1 to 8:1. [0102] Sample H [0103] Ammonia-to-metal molar ratio: 2:1 ratio [0104] Sample I [0105] Ammonia-to-metal molar ratio: 4:1 ratio [0106] Sample J [0107] Ammonia-to-metal molar ratio: 6:1 ratio [0108] Sample K (repeat of J with Rushton turbine impeller added to agitation) [0109] Ammonia-to-metal molar ratio: 6:1 ratio [0110] Sample L [0111] Ammonia-to-metal molar ratio: 8:1 ratio

[0112] Sample M and N were obtained as for sample A with the modification that the flow rate of the base solution was fixed at 1 mL/min, the ammonia-to-metal molar ratio was fixed at 2.4:1 and the temperature was varied within the range of 45 to 60° C., and wherein the reaction was carried out in a closed vessel, thereby reducing evaporation of e.g. ammonia. [0113] Sample M [0114] Temperature: 45° C. [0115] Sample N [0116] Temperature: 60° C.

[0117] Sample O was obtained as for sample A with the modification that the flow rate of the base solution was fixed at 1 mL/min, the NaOH concentration was changed to 8.33 M, the ammonia-to-metal ratio was changed to 2:1, the reaction time was 24 hours, the pH was used was 10.6, temperature was 60° C. and stirring speed was 800 rpm.

[0118] Sample P was obtained as for sample A with the modification that the flow rate of the base solution was fixed at 1 mL/min, the NaOH concentration was changed to 8.33 M, the ammonia-to-metal ratio was changed to 2.4:1, the reaction time was 24 hours, the pH was used was 10.6, temperature was 60° C. and stirring speed was 800 rpm.

[0119] Sample Q was obtained as for sample A with the modification that the flow rate of the base solution was fixed at 1 mL/min, the NaOH concentration was changed to 8.33 M, the ammonia-to-metal ratio was changed to 2:1, the reaction time was 8 hours, the pH was used was 10.6, temperature was 60° C. and stirring speed was 800 rpm.

[0120] Sample R was obtained as for sample A with the modification that the flow rate of the base solution was fixed at 1.34 mL/min, the NaOH concentration was changed to 8.33 M, the ammonia-to-metal ratio was changed to 1.5:1, the reaction time was 24 hours, the pH was used was 10.6, temperature was 50° C. and stirring speed was 800 rpm.

[0121] Sample S was obtained as for sample A with the modification that the flow rate of the base solution was fixed at 0.93 mL/min, mixed metal sulphate solution concentrated was changed to 1.9 M, the NaOH concentration was changed to 8.33 M, the ammonia-to-metal ratio was changed to 3:1, the reaction time was 24 hours, the pH was used was 10.6, temperature was 50° C. and stirring speed was 650 rpm.

[0122] Sample T was obtained as for sample A with the modification that the flow rate of the base solution was fixed at 1 mL/min, the NaOH concentration was changed to 8.33 M, the ammonia-to-metal ratio was changed to 2:1, the reaction time was 24 hours.

[0123] Sample U was obtained as for sample A with the modification that the flow rate of the base solution was fixed at 1 mL/min, the NaOH concentration was changed to 8.33 M, the ammonia-to-metal ratio was changed to 1.75:1, the reaction time was 24 hours, the pH was used was 10.6, temperature was 60° C. and stirring speed was 800 rpm. The reaction was performed in a sealed vessel with a positive pressure of N.sub.2.

[0124] Sample V was obtained as for sample A with the modification that the flow rate of the base solution was fixed at 1 mL/min, the NaOH concentration was changed to 8.33 M, the ammonia-to-metal ratio was changed to 2:1, the reaction time was 24 hours, the pH was used was 10.6, temperature was 60° C. and stirring speed was 800 rpm. The reaction was performed in a sealed vessel with a positive pressure of N.sub.2.

[0125] Conditions for lithiation & oxidation of precursor

[0126] A blend of 25 grams total of precursor and dry LiOH with a molar ratio (Li:M) of 1.03 was mixed thoroughly and added onto an alumina crucible. The mixture was calcined in an oven under 2.4 L/min of CO.sub.2 free air. The two-stage ramp 5° C./min up to 450° C., hold for 2 hours followed by 2° C./min up to 700° C., hold for 6 hours, were carried out.

[0127] Experimental protocol for XRD crystallite size measurement

[0128] Powder X-ray diffraction (PXRD) data were collected in reflection geometry using a Bruker AXS D8 diffractometer using Cu Ka radiation (λ=1.5406+1.54439 Å) over the 10<2θ<100° range in 0.02° steps. Phase identification was conducted using Bruker AXS Diffrac Eva V4.2 (2014) with reference to the PDF-4+ database, to ensure that all of the observed scattering could be assigned to nickel hydroxide like phases, and to identify (00l) reflections.

[0129] Peak fitting was performed using Topas.sup.[1] over the 12<2θ<24° range using a Split Pearson VII convoluted with instrumental parameters. The instrumental parameters were determined using a fundamental parameters approach.sup.[2] using reference data collected from NIST660 LaB.sub.6. Crystallite sizes have been calculated using the volume weighted column height LVol-IB method..sup.[3]

[0130] Experimental protocol for electrochemical characterisation

[0131] The electrodes were prepared by blending 94%wt of active material, 3%wt of carbon grade Super C-65 (purchased from Imerys; also known as Timical Super C65) as conductive additive and 3%wt of polyvinylidene fluoride (PVDF) as binder in N-methyl-2-pyrrolidine (NMP) as solvent. The slurry was added onto a reservoir and a 125 μm doctor blade coating (Erichsen) was applied. The electrode was dried at 120° C. for 1 hour before being pressed to achieve a density of 3.0 g/cm.sup.3. Typically, the loading of active material is 9 mg/cm.sup.2. The pressed electrode was cut into 14 mm disks and further dried at 120° C. under vacuum for 12 hours.

[0132] Electrochemical testing was performed with a CR2025-type coin cell, which was assembled in an argon filled glove box (MBraun). Lithium foil was used as an anode. A porous polypropylene membrane (Celgrad 2400) was used as a separator. 1M LiPF.sub.6 in 1:1:1 mixture of ethylene carbonate (EC), dimethyl carbonate (DMC) and ethyl methyl carbonate (EMC) with 1% of vinyl carbonate (VC) was used as electrolyte.

[0133] The cells were tested on a MACCOR 4000 series and were charged and discharged at 0.1C (1C=200 mAh/g) between 3.0 and 4.3 V at 23° C. First cycle efficiency (FCE) is defined as the percentage ratio between the first charge and discharge capacities.

TABLE-US-00001 TABLE 1 precursor average crystallite size against measured FCE % for electrodes made using said precursor sample. Sample # CS_001 (nm) FCE (%) A 7.1 93 B 6.5 91 C 6.7 90 D 6.2 91 E 5.2 91 F 5.0 93 G 5.5 93 H 8.1 92 I 7.1 91 J 13.3 89 K 12.3 91 L 11.7 88 M 10.9 86 N 10.8 87 O 7.8 92 P 9.2 92 Q 8.7 92 R 7.9 91 S 17.2 89 T 10.7 83 U 13.0 90 V 21.0 90
***

[0134] The features disclosed in the foregoing description, or in the following claims, or in the accompanying drawings, expressed in their specific forms or in terms of a means for performing the disclosed function, or a method or process for obtaining the disclosed results, as appropriate, may, separately, or in any combination of such features, be utilised for realising the invention in diverse forms thereof.

[0135] While the invention has been described in conjunction with the exemplary embodiments described above, many equivalent modifications and variations will be apparent to those skilled in the art when given this disclosure. Accordingly, the exemplary embodiments of the invention set forth above are considered to be illustrative and not limiting. Various changes to the described embodiments may be made without departing from the spirit and scope of the invention.

[0136] For the avoidance of any doubt, any theoretical explanations provided herein are provided for the purposes of improving the understanding of a reader. The inventors do not wish to be bound by any of these theoretical explanations.

[0137] Any section headings used herein are for organizational purposes only and are not to be construed as limiting the subject matter described.

[0138] Throughout this specification, including the claims which follow, unless the context requires otherwise, the word “comprise” and “include”, and variations such as “comprises”, “comprising”, and “including” will be understood to imply the inclusion of a stated integer or step or group of integers or steps but not the exclusion of any other integer or step or group of integers or steps.

[0139] It must be noted that, as used in the specification and the appended claims, the singular forms “a,” “an,” and “the” include plural referents unless the context clearly dictates otherwise. Ranges may be expressed herein as from “about” one particular value, and/or to “about” another particular value. When such a range is expressed, another embodiment includes from the one particular value and/or to the other particular value. Similarly, when values are expressed as approximations, by the use of the antecedent “about,” it will be understood that the particular value forms another embodiment. The term “about” in relation to a numerical value is optional and means for example +/− 10%.

REFERENCES

[0140] A number of publications are cited above in order to more fully describe and disclose the invention and the state of the art to which the invention pertains. Citations for these references are provided below. The entirety of each of these references is incorporated herein. [0141] 1. Topas v5.0: General Profile and Structure Analysis Software for Powder Diffraction Data, Bruker AXS, Karlsruhe, Germany, (2003-2015). [0142] 2. R.W. Cheary and A. Coelho, J. Appl. Cryst. (1992), 25, 109-121 [0143] 3. F. Bertaut and P. Blum (1949) C.R. Acad. Sci. Paris 229, 666