Aluminum dry-coated and heat treated cathode material precursors

Abstract

Aluminum dry-coated and heat treated cathode material precursors. A particulate precursor compound for manufacturing an aluminum coatedlithium transition metal (M)-oxide powder usable as an active positive electrode material in lithium-ion batteries includes a transition metal (M)-oxide core and a non-amorphous aluminum oxide coating layercovering the core. By providing a heat treatment process for mixed metal precursors that may be combined with an aluminum dry-coating process, novel aluminum containing precursors that may be used to form high quality nickel based cathode materials are obtained. The aluminum dry-coated and heat treated precursors include particles have, compared to prior art precursors, relatively low impurity levels of carbonate and/or sulfide, and can be produced at lower cost.

Claims

1. A particulate precursor compound for manufacturing an aluminum coated lithium transition metal (M)-oxide powder usable as an active positive electrode material in lithium-ion batteries, each particle of said precursor compound comprising: a transition metal (M)-oxide core; and a non-amorphous aluminum oxide Al.sub.2 O.sub.3 coating layer covering said core, wherein said particulate precursor has an aluminum doping level equal to or greater than 5 mol%, said doping level being equal to: Al/(Al +M), with Al +M =1, wherein said particulate precursor compound has a general formula (M-oxide).sub.a.(Al.sub.2O.sub.3).sub.b, wherein a+(2*b)=1, and wherein said transition metal (M) is Ni.sub.xMn.sub.yCo.sub.z, wherein 0.3 x 0.9, 0 y 0.45, and 0 <z 0.4, x+y+z=1; and wherein said transition metal (M) includes further only unavoidable impurities.

2. The particulate precursor compound of claim 1, wherein b 0.4.

3. The particulate precursor compound of claim 1, wherein y=0.

4. The particulate precursor compound of claim 1, wherein said coating layer contains non-amorphous alumina nanoparticles.

5. The particulate precursor compound of claim 1, wherein a carbon content of said precursor compound is reduced by a heat treatment of said precursor compound at temperatures above about 400 C. reaching relatively low values at and above about 600 C. and wherein a sulfate content of said precursor compound is reduced by a heat treatment of said precursor at temperatures at and above aboutn 700 C.

6. The particulate precursor compound of claim 5, wherein said sulfate content is lower than about 0.3 wt %.

7. The particulate precursor compound of claim 1, wherein said precursor compound is free of crystal water.

8. The particulate precursor compound of claim 1, wherein the coating layer has a thickness that does not change with particle size such that relatively smaller particles have a higher aluminum concentration than relatively larger particles of the same particulate precursor compound.

9. A process of preparing the particulate precursor compound of claim 1, comprising: providing for a first quantity of alumina powder having a volume VI; providing for a first quantity of transition metal (M)-oxide, (M)-hydroxide or (M)-oxyhydroxide powder as said particulate precursor, having a volume V2; mixing said first quantity of alumina powder with said first quantity of transition metal (M)-oxide, (M)-hydroxide or (M)-oxyhydroxide in a first dry-coating procedure, wherein V1+V2=V and wherein the first quantity of alumina powder and the first quantity of transition metal (M)-hydroxide or (M)-oxyhydroxide are mixed until said volume V decreases to a volume V3 that has about the same value as VI, thereby covering a transition metal (M)-oxide, (M)-hydroxide or (M)-oxyhydroxide core with a non-amorphous aluminum oxide AI203 coating layer; and heat treating said core covered by said coating layer at a temperature in a range of about 400-800 C.

10. The process of claim 9, wherein said heat treating is performed at a temperature in a range of about 400-600 C.

11. The process of claim 9, further comprising heat treating said core covered by said coating layer at said temperature for duration of 5 hours or 10 hours.

12. The process of claim 9, further comprising reducing carbon content and sulfate content of said precursor compound.

13. The process of claim 9, further comprising obtaining an aluminum dry-coated precursor compound, wherein said core is a transition metal oxide and wherein said core is completely covered by said non-amorphous coating layer.

14. The process of claim 9, further comprising mixing said particulate precursor compound with a lithium precursor compound and sintering the mixture.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The present invention will now be described, by way of example, with reference to the accompanying drawings, in which:

(2) FIG. 1 is a SEM (scanning electron microscope) micrograph of a MOOH precursor core before a first aluminum coating procedure, in accordance with one embodiment of the present invention.

(3) FIG. 2 is a SEM micrograph of the MOOH precursor after a second aluminum coating procedure (10 mol % aluminum), in accordance with one embodiment of the present invention.

(4) FIG. 3 is a X-ray diffraction pattern of a M(OH).sub.2 precursor after a first and a third aluminum coating procedure (5 mol % and 15 mol % aluminum, respectively), in accordance with one embodiment of the present invention.

(5) FIG. 4 is a FESEM (field emission scanning electron microscope) micrograph of a polished cross-section of the MOOH precursor after the second aluminum coating procedure (10 mol % aluminum), in accordance with one embodiment of the present invention.

(6) FIG. 5 is a diagram illustrating the metal stoichiometry obtained by ICP-MS (inductively coupled plasma mass spectrometry) from different size fractions of the MOOH precursor after the second aluminum coating procedure (10 mol % aluminum), in accordance with one embodiment of the present invention.

(7) FIG. 6 is a diagram illustrating the metal stoichiometry obtained by ICP-MS from different size fractions of a M(OH).sub.2 precursor after a first aluminum coating procedure (5 mol % aluminum), in accordance with one embodiment of the present invention.

(8) FIG. 7 is a diagram showing the evolution of diffraction pattern of alumina coated Ni(OH).sub.2 based precursor as a function of heat treatment temperature, in accordance with another embodiment of the present invention; and

(9) FIG. 8 is a diagram illustrating X-ray diffraction pattern of a Ni.sub.0.5Mn.sub.0.3Co.sub.0.2O.sub.2 precursor heat treated at 700 C.

(10) The exemplification set out herein illustrates preferred embodiments of the invention, in one form, and such exemplification is not to be construed as limiting the scope of the invention in any manner.

DETAILED DESCRIPTION OF THE INVENTION

(11) In one embodiment of the present invention an aluminum dry-coating process is provided as a first step, that enables achievement of higher doping levels (than in the prior art) of aluminum in particulate transition metal oxide MO.sub.2, hydroxide M(OH).sub.2 or oxyhydroxide MOOH precursor compounds. The transition metal (M)-oxide, (M)-hydroxide or (M)oxyhydroxide may be obtained by coprecipitation of the sulfates of the elements constituting said transition metal M in the presence of an alkali hydroxide. For example, a nickel/manganese/cobalt precursor compound with the composition MOOH (M=Ni.sub.xMn.sub.yCo.sub.z with 0.3x0.9; 0y0.45 and 0<z0.4 and x+y+z=1) or a nickel/cobalt precursor compound with the composition M(OH).sub.2 may be dry-coated with aluminum oxide (alumina) by filling a mixer, such as a 2L Haensel type mixer, with a certain volume consisting of the particulate precursor and alumina (Al.sub.2O.sub.3) powder (see also Example 1 and Example 2). The mixer is then rotated at a constant speed, for example 1000 rpm, for a time period of, for example, 30 min. During this mixing time, the alumina particles slowly fade out of sight coating the MOOH powder particles and the volume in the mixer decreases. The mixing time may be chosen such that no traces visible to the naked eye of the alumina remain in the end. At that time also the volume does not decrease anymore during mixing. Nano-sized fumed alumina may be used in the process.

(12) The quantity of the particulate precursor and the alumina may be chosen, for example, such that a doping level of 5 mol % alumina is achieved during one coating procedure. Thus, 5 mol % of alumina may be added per 1 mol mixed transition metal precursor. While this ratio of quantities was found to be working well other ratios may also be used. To achieve higher doping levels of aluminum, the described coating procedure may be repeated several times. A doping level of aluminum of 10 mol % may, therefore, be achieved by performing a first coating procedure with 5 mol % of alumina followed by a second coating procedure with 5 mol % of alumina. Consequently, a doping level of alumina of 15 mol % may be achieved by performing three consecutive coating procedures utilizing 5 mol % of alumina each time.

(13) While the volume of the alumina exceeds the volume of the mixed metal oxyde, hydroxide or oxyhydroxide precursor by far, the coated precursor has about the same volume as the original mixed metal hydroxide or oxyhydroxide precursor. The MO.sub.2, MOOH or M(OH).sub.2 powder does not change the color much during the coating procedures. Consequently, the alumina may cover the particles of the precursor with a thin, transparent, relatively dense film.

(14) The final quality of the cathode material prepared from mixed metal precursors depends on the impurity level. Besides obvious impurities like Fe, Cr, Na, . . . also anionic impurities are important. In the case of LNC or LNCA (lithium nickel based cathodes) a carbonate impurity in the final product is highly unwanted. To avoid carbonate the cooking (cooking refers to the reaction to form lithium metal oxide from the metal precursor with a lithium salt) has to be done in expensive, carbon dioxide free gas. We detected that the mixed metal precursors can contain carbonate impurity. During cooking, the carbonate impurity of the precursor tends to form relatively stable and highly undesired lithium carbonate. Therefore, especially in the case of lithium nickel oxide based cathode materials like LNC and NCA it is important to avoid the carbonate impurity in the precursor.

(15) Otherwise, carbonate is a natural impurity in mixed metal precursors. It originates from Na impurity or from reactions with carbon dioxide in the air during the precipitation. It is very difficult to eliminate these natural carbonate impurities in the precursor. The current invention discloses that a heat treatment of the mixed metal precursor at an intermediary temperature allows to efficiently eliminate the carbonate impurity by forming carbonate free metal oxide precursor.

(16) Similar sulfate impurities are natural to the mixed metal hydroxide. They remain from the metal sulfates used during the precipitation reaction. During cooking the sulfate preferably reacts with lithium and forms a highly stable lithium sulfate impurity. The current invention discloses that a heat treatment of the mixed metal precursor at an elevated temperature allows eliminating the sulfate impurity by forming a sulfur free metal oxide precursor.

(17) The heat treatment typically occurs in air. Typical temperatures are 400-900 C., more precisely 500-700 C. to remove carbonate impurities and 700-900 C. to remove sulfur impurities. The exact optimum temperature typically is within this range (typically 400-800 C.) but can be outside. The choice of optimum temperature is the result of an optimization. As an example, the temperature needs to be high enough to effectively remove a large fraction of the carbonate or sulfur impurity. Otherwise in the general case the temperature needs to be low enough to avoid that the reactivity of the final oxide (to prepare single phase lithiated cathode LiMO.sub.2) is low. This can be the case if at the elevated temperature a phase separation into several oxides (fx. spinel+rocksalt phase mixture) happens and progresses too much. Air is the natural gas to do the heat treatment. However, it might be preferred to do the heat treatment in special controlled atmosphere. As an example, using inert gas like nitrogen can prevent the oxidation of M(OH).sub.2 In this case the phase separation to spinelrocksalt phase mixtures is suppressed. Instead of this a single phase mixed rocksalt MO can be achieved which has a better reactivity to form the final single phase LiMO.sub.2 .

(18) Typical treatment times are 2-12 hours. The optimum time is the result of an optimization and can be longer or shorter. Special methods like fluidized bed heating can allow for short reaction times, long reaction times can for example be preferred if a lowering of the heat treatment temperature is desired in order to prevent excessive phase separation.

(19) After the heat treatment, a final precursor compound is obtained which may have a general formula (M-oxide).sub.a.(Al.sub.2O.sub.3).sub.b, with a+(2*b)=1. In one embodiment b0.4. The embodiments of the aluminum dry-coating process are further described in the following examples:

EXAMPLE 1

(20) 1 kg of a NiMnCo based powder with composition MOOH, M=Ni.sub.0.46Mn.sub.0.39Co.sub.0.15 is filled into a mixer (for example a 2L Haensel type Mixer) and 25.5 g of fumed alumina (Al.sub.2O.sub.3) powder is added. During mixing for 30 min at 1000 rpm the fumed alumina slowly fades out of sight and a coated MOOH powder, looking very much like the initial powder (black color, small volume) results. With this ratio of quantities precursor/fumed alumina a doping level of aluminum of 5 mol % is achieved.

(21) Then another 25.5 g of fumed alumina is added, and the mixing is continued for 30 min at 1000 rpm, resulting again in a black powder with small volume. No traces, visible to the naked eye, of the fumed alumina remains after the two coating procedures. Obviously, the all or nearly all of the fumed alumina is utilized to cover the precursor particles with a thin, transparent, relatively dense film. By adding this second coating procedure, a doping level of aluminum of 10 mol % is achieved.

(22) Cross-sections of the 10 mol % Aluminum coated MOOH powder for analysis by FESEM are prepared by immersing the dry-coated precursor powder into a polymer followed by polishing.

EXAMPLE 2

(23) In this example, performed according to the general outline of Example 1, a NiCo core compound with composition M(OH).sub.2 (M=Ni.sub.0.8Co.sub.0.15) is coated with fumed alumina powder. Two sets of coated samples are prepared. The first set of the coated samples has a doping level of aluminum of 5 mol % (5 mol % Al+0.95 mol % M) after performing only one coating procedure. The second set of samples had a doping level of aluminum of 15 mol % after performing three consecutive coating procedures, adding each time 5 mol % of the fumed alumina per 1 mol of the transition metal. X-ray diffraction patterns reveal that the aluminum coating layer is not amorphous. Thus, the crystal structure of the fumed alumina is maintained during the coating procedures and the core of the M(OH).sub.2 precursor particles is surrounded by a coating layer or shell containing crystalline alumina nanoparticles.

(24) Referring to FIGS. 1 and 2, SEM (scanning electron microscope) micrographs of a MOOH precursor before a first aluminum coating procedure and after a second aluminum coating procedure (10 mol % aluminum), respectively, are illustrated according to one embodiment of the present invention and in accordance with the description in Example 1. As can be seen the aluminum coating layers covering the precursor powder particles has high density, is continuous and is smooth. Its thickness varies between 0.1 and 1.5 m. Referring now to FIG. 3, an exemplary X-ray diffraction pattern of a M(OH).sub.2 precursor after a first and a third aluminum coating procedure (5 mol % (bottom) and 15 mol % (top) aluminum, respectively) is illustrated according to one embodiment of the present invention and in accordance with the description in Example 2. The pattern of alumina is added for reference as bottom line. As can be seen, the surface coating is not amorphous. This becomes apparent for the sample coated with 5 mol % aluminum and is clearly noticeable for the sample coated with 15 mol % aluminum (notice the two arrows pointing at peaks corresponding to the alumina pattern). Thus, the crystal structure of the fumed alumina is maintained during the first and also the second coating procedure and the core of each mixed transition metal precursor particle is covered by a non-amorphous coating layer containing crystalline alumina nanoparticles and, therefore, has a crystalline structure.

(25) In FIG. 4, a FESEM (field emission scanning electron microscope) micrograph of a polished cross-section of the MOOH precursor after the second aluminum coating procedure (10 mol % aluminum) is shown illustrated according to one embodiment of the present invention and in accordance with the description in Example 1. The micrograph of FIG. 4 is representative for typical results obtained using the dry-coating process of the present invention. As a guide for the eye, two lines were added that assist in illustrating that the coating layer is complete covering the entire outer surface of each of the precursor particles. As can be seen, the coating layer is relatively dense, thus, having a relatively low porosity.

(26) The coating layer may in average not depend on the size of the precursor particles. If the thickness of the coating layer does not change with particle size (as indicated in FIG. 4) than a composition dependency may be expected since larger particles typically have a lower aluminum stoichiometry. Such a composition dependency, where smaller particles have higher aluminum content than larger particles, is in the case of aluminum doped precursors desirable since especially the smaller precursor particles pose a safety concern due to their relatively low thermal stability and since aluminum increases the thermal stability of the precursor in organic electrolytes. To confirm this, the powder was separated into different size fractions by a fractionation experiment and examined by laser diffraction. In such fractionation experiment, a slow laminar flow of the aluminum covered precursor powder immersed in water was used to separate different size fractions. As can be seen in FIG. 5, a size dependent composition of the aluminum coated precursor was confirmed by ICP-MS (inductively coupled plasma mass spectrometry) analysis from different size fractions of the MOOH precursor after the second aluminum coating procedure (10 mol % aluminum) in accordance with the description in Example 1 and the data displayed in Table 1. Smaller particles have a much higher aluminum concentration than larger particles. The aluminum concentration in the particles decreases from about 12 mol % to about 6 mol % as the size (D50 of the PSD) of the coated precursor particles increases from about 5 m to about 16 m (see also Table 1).

(27) TABLE-US-00001 TABLE 1 Composition (IPC) of the different sized fractions as function of D50 (median) particle size size (m) mol % Sample D10 D50 D90 Ni Mn Co Al Non-fractionated 5.03 9.30 16.51 42.3 35.7 13.7 8.3 Fraction 1 3.38 5.39 8.90 39.9 35.2 12.8 12.2 Fraction 3 5.40 7.52 10.51 42.1 36.5 13.7 7.7 Fraction 5 7.90 10.89 15.00 43.1 36.5 13.0 7.4 Fraction 7 11.16 15.58 21.73 44.3 35.8 13.8 6.0

(28) Referring now to FIG. 6, a diagram illustrating the metal stoichiometry obtained by ICP-MS from different size fractions of a M(OH).sub.2 precursor after a first aluminum coating procedure (5 mol % aluminum) is illustrated in accordance with the description in Example 2. The data were obtained by ICP analysis of size fractionized samples similar as described with FIG. 5. As can be seen, the aluminum content decreases with increasing size of the coated precursor particles.

(29) Furthermore, for the preparation of cathode materials from aluminum precursors it may be essential that the aluminum is present in the form of a coating layer, for example, as achieved by the aluminum dry-coating process in accordance with one embodiment of the present invention. As a counter example, if more than a few weight % of alumia is used, and the alumina is not present as a coating layer but present as separate particles in a mixture, then not all alumina is in contact with the active material and after sintering a powder, being a mixture of insufficiently coated active material and remaining alumina is achieved. Thus, a simple solid state reaction, such as heating a blend of an aluminum precursor, a transition metal precursor and a lithium salt may not lead to a well doped final lithiated product without applying excessive sintering, because Al.sub.2O.sub.3 (corundum), which is a highly inert phase, forms at relatively low temperatures. The corundum is relatively slow to react with the lithium transition metal oxide and, thus, only if excessive high temperatures or excessive long sintering is applied, may a well doped cathode material be achieved. However, such lithiated materials are typically oversintered, which is indicated by relatively large crystallite size that typically causes poor performance. The larger the alumina content, the more pronounced is this problem. Therefore applying a higher doping level of aluminum requires a good coating. Experiments have shown that if the Al.sub.2O.sub.3 is in good contact with the precursor particle in form of a coating layer, which can be obtained, for example, with the above described aluminum dry-coating process in accordance with one embodiment of the present invention, an aluminum coated lithium transitional metal with relatively high Al doping level and high crystallinity may be obtained at relatively low temperatures.

EXAMPLE 3

(30) In another example the present invention provides a heat treatment for alumina coated transition metal oxide MO.sub.2, hydroxide M(OH).sub.2 or oxyhydroxide MOOH precursors that allows to reduce undesirable impurities. One application of aluminum dry-coated precursors is the preparation of high nickel cathode materials, such as LiNi.sub.0.8Co.sub.0.15Al.sub.0.05O.sub.2. A major problem in the preparation of such cathodes is a contamination by carbonate since some carbonate is usually present in the mixed metal precursors. Another problem is the sulfate impurity, often originating from the precursor production process. Furthermore, it was observed that the sulfates and carbonates are much more stable in the lithiated product (cathode material) (LiMO.sub.2) than in the un-lithiated precursor such as MOOH. The reason is the increased thermodynamic stability of Li.sub.2SO.sub.4 and Li.sub.2CO.sub.3 compared with MSO.sub.4 and MCO.sub.3. Thus, a heat treatment of the mixed metal precursor may be effective to remove the volatile SO.sub.4 and CO.sub.3 impurities. Precursor core compounds with composition Ni.sub.0.85Co.sub.0.15(OH).sub.2 are dry-coated with fumed alumina (Al.sub.2O.sub.3) similar as described in Example 2. The composition of the dry-coated precursors is Ni.sub.0.85Co.sub.0.15(OH).sub.2*0.05AlO.sub.1.5. The aluminum dry-coated precursors are heated in air to 400, 600, 800 or 900 C., whereby the core is transformed into a coated oxide. As heat treatment duration, 5 h and 10 h are chosen. After the heat treatment, the sulfate content of the heat treated precursors is measured by ICP and the carbon content is measured by carbon sulfur analysis, using 2 different devices. The results are summarized in Table 2.

(31) TABLE-US-00002 TABLE 2 Characteristics of aluminum dry-coated and heat treated Ni.sub.0.85Co.sub.0.15(OH).sub.2 precursors SO.sub.4 (wt %) C (ppm) Treatment T pretreated pretreated of metal BET metal metal Weight precursor m.sup.2/g precursor precursor loss Color/Structure As received 5.97 0.42 1189 0% Green/Ni(OH).sub.2 400 C., 10 h 68.1 0.52 697 19.07% Black/NiO 600 C., 10 h 12.56 0.52 185 20.18% Green/NiO 800 C., 10 h 4.85 0.16 189 20.78% Green/NiO 900 C., 10 h 3.75 0.27 162 20.92% Green/NiO

(32) Obviously, pre-treating a Ni(OH).sub.2 based (or coated) precursor at T>400 C. causes a reduction in carbonate impurity, reaching relatively low values at T1600 C., with carbon contents below 200 ppm. The sulfate content decreases dramatically at temperatures above 700-800 C. The weight loss is consistent with the decomposition of Ni(OH).sub.2 to form NiO. X-ray analysis shows that all samples prepared at 400 C. are basically single phase NiO, neglecting relatively small peaks due to aluminum containing phases.

(33) Therefore, the core of the precursor particles is a transition metal oxide when the precursor is heat treated at or above 400 C. At intermediary temperature (400 C.) the core is still covered by the remains of the non-amorphous coating layer containing crystalline alumina nano particles. At higher temperature some of the Al diffuses into the core, but the coating remains. Above 800 C. all of the Al will have diffused into the core.

(34) Referring now to FIG. 7, a diagram showing the evolution of diffraction pattern (Intensity in counts per second are given against the scattering angle) of alumina coated Ni(OH).sub.2 based precursors as a function of heat treatment temperature is illustrated according to one embodiment of the present invention and in accordance with the description in Example 2. The bottom diffraction pattern is without Al coating, the next with Al coating but no temperature treatment, then the 4 patterns above are for increasing treatment temperatures from 400 C. to 900 C. At all temperatures a single phase can be observed. Relatively small additional peaks can be observed for the 600 C. sample (3.sup.rd pattern from the top on FIG. 7) and may be attributed to traces of an aluminum containing phase, which was not visible yet at 400 C. It will be visible in a high resolution Xray (for example if the scan time is increased). One possible explanation for this appearance at 600 C. is that the crystallinity of the aluminum containing phase increases with rising temperatures and the peaks become visible. At still higher temperatures, at around 800 C., the second phase has disappeared, possibly due to the creation of a NiCoAl solid state solution. The X-ray diffraction pattern of the major phase may be indexed as single phase Ni(OH).sub.2 (not heat treated) or as single phase NiO (heat treated). Obviously, cobalt, as well as aluminum at higher temperatures, forms a solid state solution.

(35) Furthermore, changes in the morphology of the aluminum dry-coated precursors with composition Ni.sub.0.85Co.sub.0.15(OH).sub.2 occur during the heat treatment, as can be seen in Table 2. At relatively high temperatures, the morphology is spangle-like. The BET surface area has a pronounced maximum at about 400 C. This may be caused by the creation of a mesoporous microstructure. Also, the color changes from green to black to green.

(36) In the following, it will be shown that high quality nickel based cathode materials may be obtained from aluminum dry-coated and heat treated precursor compounds. High quality is related to the requirements by battery manufacturer. It does not only mean good electrochemical performance. Electrochemical performance is only one of many performance parameters. Additionally the manufacturer might request a low carbonate or sulfur content. Typically, even a slight deterioration of electrochemical performance might be accepted if the impurity level can be reduced. Just like described above, precursor core compounds with composition Ni.sub.0.85Co.sub.0.15(OH).sub.2 are dry-coated with fumed alumina (Al.sub.2O.sub.3) similar as described in Example 2. The composition of the dry-coated precursors is Ni.sub.0.85Co.sub.0.15(OH).sub.2*0.05AlO.sub.1.5. The aluminum dry-coated precursors are heat treated in air at 400, 600, 800 or 900 C. As heat treatment duration, 5 h and 10 h are chosen. To obtain the final lithiated product, the cathode material, the aluminum dry-coated and heat treated precursors are mixed with milled LiOH*H.sub.2O and fired at 750 C. for 10 h in a flow of oxygen. The sintering process may be in the temperature range of 700 C. to 1200 C. and may also be done in a flow of air. Following the sinter process, the electrochemical properties of the lithiated materials are determined according to the following procedure:

(37) Preparation of Coin Cells:

(38) First, slurry of active cathode material, super P (carbon conductive additive) and PVDF (binder) in NMP was prepared. The ratio of active:carbon:PVDF was 90:5:5. The slurry was coated by a doctor blade coater on a sheet of aluminum foil. After drying in air at 120 C. electrodes were roll pressed followed by punching of electrode disks. Coin cells with Li metal anode were assembled in a glove box after further drying of the electrodes in vacuum at 90 C.

(39) Coin Cells were Tested in the Following Manner:

(40) 1) The voltage profile is obtained at C/10 rate between 4.3 and 3.0V. (1C rate corresponds to 160 mA/g current) 2) Discharge rate performance (C/5 C2, 1C, 2C, 3C) is measured during cycles 2-6. Charge rate is C/4 3) Cycle 7 and 8 measures the discharge capacity between 4.5 and 3.0V at C/10 and C/1, respectively. 4) From cycle 9 to cycle 30 the cell is cycled between 4.5 and 3.0V. Charge rate is C/4 and discharge rate is C/2. 5) Cycle 31 and cycle 32 re-measure the remaining reversible capacity at C/10 and 1C rate, respectively between 4.5 and 3.0V.

(41) Rate performance is calculated by comparing the ratio of discharge capacity during cycle 2-6 with the discharge capacity at cycle 1. Fading rate is obtained by comparing the remaining reversible capacity at cycle 31 and 6 as well as 32 and 7. The fading rate is expressed as capacity loss per 100 cycles.

(42) The results for the electrochemical testing are shown in Table 3 and the results for a Rietveld analysis of X-ray data are summarized in Table 4.

(43) TABLE-US-00003 TABLE 3 Electrochemical testing for coin cells made with heat-treated Ni.sub.0.85Co.sub.0.15(OH).sub.2 precursors (column: Pre T C. = Precursor Treatment C. and time) against a reference Pre BET QD Qirr rate rate rate f(1 C) f(0.1 C) T C. m2/g mAh/g % 1 C 2 C 3 C 100cy 100cy None 0.398 197.88 9.78 90.89 88.09 86.63 20.3 16.8 400, 0.355 198.52 9.34 91.10 88.41 86.83 14.9 12.1 10 h 600, 0.351 197.24 9.68 91.23 88.69 87.04 16.3 13.1 10 h 800, 0.380 192.04 12.26 92.26 89.78 88.30 21.6 18.3 10 h 900, 0.447 190.57 12.50 92.16 89.68 88.13 25.9 21.2 10 h

(44) As can be seen, the best results, illustrated by a decreased carbon impurity, a high capacity, a good cycling stability or improved rate, may be achieved if the heat treatment is performed at a medium temperature range of about 400-600 C. Thus it is possible to reduce the carbonate impurity of the precursor without sacrificing electrochemical performance of the final product. If the temperature is higher, a reduced cycling stability and lower capacity but also a reduced level of sulfur impurity is obtained. One reason for the poorer performance at higher heat treatment temperatures may be the lower crystallinity. Rietveld refinement of X-ray data (Table 4) shows that at T>600 C. the strain increases significantly while the crystallite size decreases.

(45) TABLE-US-00004 TABLE 4 Rietveld analysis of cathode material made with heat-treated Ni.sub.0.85Co.sub.0.15(OH).sub.2 precursors Ni on size vol c:a Pre T C. a hex A c hex A Li (%) nm strain A3 Corr none 2.86410 14.1772 0.88 138 0.107 33.5719 10.41 400, 10 h 2.86410 14.1800 0.84 138 0.128 33.5786 10.61 600, 10 h 2.86400 14.1792 1.10 132 0.148 33.5743 10.59 800, 10 h 2.86430 14.1830 1.43 119 0.21 33.5903 10.75 900, 10 h 2.86470 14.1808 1.52 117 0.206 33.5945 10.45

EXAMPLE 4

(46) While the successful application of heat treated precursor compounds for nickel based cathode materials has been demonstrated above, this might not always be the case. If the heat treated precursor decomposes into crystalline coexisting phases, then the reactions to form a crystalline final LiMO.sub.2 cathode material are very slow and the final lithiated cathode material has a poor performance. For example, if the heat treatment temperature for a Ni.sub.0.5Mn.sub.0.3Co.sub.0.2O.sub.2 precursor exceeds 400 C., the decomposition into two major phasesa NiO and a M.sub.3O.sub.4 spinel phasecan be observed, and if the temperature exceeds 600 C. the crystalline phase mixture does not allow to achieve high performance product.

(47) Table 5 shows results of coin cell testing in accordance with one embodiment of the present invention. In the case of a higher treatment temperature, the preheated precursor is a phase mixture of crystalline NiO and M.sub.3O.sub.4 spinel, as is illustrated in FIG. 8. Nevertheless, in the case of treatment temperatures <600 C. an excellent electrochemical performance can be achieved from heat treated precursors. Probably at higher temperatures, the phase separation has progressed to a degree that does not allow to achieve good performance. Obviously the crystallite size (domain size) is small enough at 500 C. to allow for the formation of a high crystalline cathode, whereas the larger domain size at 700 C. prevented a final cathode of high crystallinity. FIG. 8 shows a Rietveld refinement of the precursor heat treated at 700 C. The X-ray diffraction pattern is well fitted by a mixture of NiO and M.sub.3O.sub.4 spinel. The thin solid line (just under the diffraction pattern) shows the pattern for NiO (17 wt % according to the refinement). Consequently, the reaction to the final LiMO.sub.2 is difficult and the final LiMO.sub.2 shows poor crystallinity, high strain, and poor electrochemical performance. As can be clearly seen in Table 5, the reversible capacity as well as the rate performance deteriorates at higher treatment temperatures dramatically.

(48) TABLE-US-00005 TABLE 5 Coin cell testing of LiMO.sub.2 (M = Ni.sub.0.5Mn.sub.0.3Co.sub.0.2) prepared from a heat treated oxide precursor. Precursor Rate (per 0.1 C) Phase DC Q 1 C 2 C 3 C Pre T C. composition mAh/g Qirr % (%) (%) (%) 300, 10 h Single phase 169.66 11.68 92.74 89.40 87.02 500, 10 h NiO + M3O4 169.57 11.95 92.62 89.23 86.87 700, 10 h NiO + M3O4 161.26 13.45 92.18 88.50 85.42 800, 10 h NiO + M3O4 145.34 19.31 90.91 86.12 82.46 900, 10 h NiO + M3O4 141.23 17.98 89.74 84.94 81.18

(49) We have shown that a precursor treatment at elevated temperature, typically 500-600 C. is sufficient high to effectively remove the carbonate impurity. During the heat treatment the metal precursor might phase decompose as observed in table 5. At too high temperature the phase decomposition progresses (forming larger separate crystallites) and causes a problem. In this case poor performance cathodes are achieved. At lower temperature, however, the phase decomposition progresses less, occurs at smaller scale, and the small crystallites are sufficient reactive so that the obtained cathode has high crystallinity and shows a good performance. We believe that it always is possible to efficiently remove the carbonate impurity by choosing heat treatment conditions which are strong enough to form the oxide, and release the carbonate but at the same time sufficient weak enough to avoid the full phase deparation into large crystallites.

(50) Comparing the impurity content of the dry-coated and heat treated Ni.sub.0.85Co.sub.0.15(OH).sub.2 precursors shown in Table 2 and the electrochemical performance of the final lithiated cathode material summarized in Tables 3, 4, and 5 indicates that generally a treatment temperature that is high enough to significantly reduce the sulfur and carbon content is too high to achieve a good electrochemical performance of the final lithiated cathode material. Consequently, only if the Ni content is relatively small, or the precursor compound is free of manganese, may a heat treatment temperature be found that is high enough to significantly reduce sulfur and carbon impurities (>700 C.) and not too high to achieve a good electrochemical performance of the final lithiated cathode material. However, a heat treatment will in almost all cases allow to reduce the carbon impurity without scarifying final cathode electrochemical performance.

(51) Furthermore, the aluminum dry-coated particulate mixed transition metal oxide MO.sub.2, metal hydroxide M(OH).sub.2 or oxyhydroxide MOOH precursors in accordance with an advantageous embodiment of the present invention are contrary to known prior art precursors basically free of crystal water. By way of example, hydroxide precursors can be explained as an oxide with one mol crystal water
(M(OH).sub.2=MO+H.sub.2O).

(52) Thus, hydroxides M(OH).sub.2 evolve lots of water and need oxygen.
M(OH).sub.2+Li.sub.2CO.sub.3+O.sub.2.fwdarw.LiMO.sub.2+CO.sub.2+H.sub.2O.

(53) Managing the required large flows of gas (oxygen to the sample, CO.sub.2 and H.sub.2O away from the sample) is a problem at large scale. An ideal reaction would be to use 3-valent metal oxide:
M.sub.2O.sub.3+Li.sub.2CO.sub.3.fwdarw.LiMO.sub.2+CO.sub.2.

(54) This reaction needs no gas (instead of mol O.sub.2) and it also evolves much less gas ( mol instead of 1.5 mol). In this way gas flow management can be dramatically simplified. Thus, the aluminum dry-coated and heat treated precursors in accordance with the present invention have the advantage that they require much less gas flow during large scale production, that means that the throughput in a furnace can be increased which dramatically lowers the production cost.

EXAMPLE 5

(55) Finally, the heat treatment of precursors in accordance with above described embodiment of the present invention may in principle not be limited to high nickel based precursors, but may also be applied to precursors that have different compositions, for example, nickel-manganese-cobalt (NMC) mixed hydroxide precursors. In the case of NMC precursors, the carbon impurity is of less interest because it is easily decomposed during preparation of the final lithated product. Therefore, for these materials, the focus may lie on the sulfur impurity in the precursor as well as in the final lithiated product.

(56) For example, mixed metal hydroxide precursors with the composition MOOH with M=Ni.sub.0.5 Mn.sub.0.3Co.sub.0.2 are heat treated in air at 300, 500, 700, 800 or 900 C. for 10 hours. The precursors are not aluminum dry-coated. Lithiated products are prepared using a Li:M=1.027 stoichiometric ratio (Li precursor: Li.sub.2CO.sub.3) and are sintered for 10 h at 940 C. in air. Table 6 shows the sulfur content after heat treatment of the precursor and of the final lithiated product as a function of the heat treatment temperature. As can be seen, heat treating the precursor lowers the sulfur content significantly. It can further be observed that most of the sulfur present in the precursor after heat treatment is maintained during the sinter process preparing the final lithiated product. It may be concluded that sulfur remains as an impurity in a normal solid state solution and that a precursor heat treatment is essential to obtain a final lithiated product with relatively low sulfur content. In the present example final electrochemical performance deteriorate, however battery producer might accept a certain deterioration if low impurities are required. And, of course, for different compositions or modified process conditions the deterioration might be much less.

(57) Compared to carbonate, removal of a sulfate impurity generally requires a higher temperature. At higher temperature, in case the mixed oxide is not thermodynamically stable, a phase separation will progress much further and create large phase separated crystallites. Therefore a removal of sulfur is not always possible because the large phase separated crystallites are relatively inert so the cooking (reaction of the mixed oxide with a lithium source) will result in a poor performance cathode. Therefore, practically the removal of sulfur might be limited to compositions which form a single phase oxide. When cooking the single phase oxide with a lithium source allows obtaining high quality cathodes. For example, sulfur can be removed from Co(OH).sub.2 because single phase cobalt oxide forms. So the condition for an effective removal of sulfur is that the mixed oxide exists. Without going to details, a large variety of single phase mixed monoxides MO can be prepared. Alternatively, a large variety of mixed spinel phases exist. Finally, special compositions like for example NiMnO3 are of interest.

(58) TABLE-US-00006 TABLE 6 Sulfur content as a function of heat treatment temperature of a Ni.sub.0.5Mn.sub.0.3Co.sub.0.2 precursor. Treatment T of metal SO.sub.4 (wt %) SO.sub.4 (wt %) precursor in metal precursor in lithiated product As received 0.379 300 C., 10 h 0.397 0.374 500 C., 10 h 0.446 0.399 700 C., 10 h 0.427 0.351 800 C., 10 h 0.231 0.182 900 C., 10 h 0.107 0.078

(59) Conclusion

(60) It can be concluded that the present invention provides particulate mixed transition metal hydroxide M(OH).sub.2 or oxyhydroxide MOOH precursors that have been coated with aluminum during a dry-coating process. The obtained aluminum dry-coated precursors are, for example, suitable for preparation of cathode materials for rechargeable lithium and lithium-ion batteries. By providing an aluminum dry-coating process, higher doping levels of aluminum compared to the known prior art may be achieved. The crystal structure of the fumed alumina may be maintained during the coating procedures and the core of each mixed transition metal precursor particle may be surrounded by a coating layer containing crystalline alumina nano particles. Thus, the morphology of the aluminum dry-coated precursors in accordance with the present invention is improved compared to known prior art precursors.

(61) By providing a heat treatment process for mixed metal precursors that may be combined with the aluminum dry-coating process, novel aluminum containing precursors that may be used to form high quality nickel based cathode materials are obtained. The aluminum dry-coated and heat treated precursors include particles having a transition metal oxide core covered by a non-amorphous aluminum oxide coating layer and have, compared to prior art precursors, relatively low impurity levels of carbonate and/or sulfate, and can be produced at lower cost.

(62) The invention can alternatively be described by the following clauses: 1. A particulate precursor compound for manufacturing an aluminum coated lithium transition metal (M)-oxide powder usable as an active positive electrode material in lithium-ion batteries, each particle of said precursor compound comprising: a transition metal (M)-oxide core; and a non-amorphous aluminum oxide Al.sub.2O.sub.3 coating layer covering said core. 2. The precursor compound of clause 1, characterized in that said precursor compound has a general formula (M-oxide).sub.a.(Al.sub.2O.sub.3).sub.b, wherein a+(2*b)=1, and in that said transition metal (M) is Ni.sub.xMn.sub.yCo.sub.z, wherein 0.3x1.9, 0y0.45, and 0<z1.4, x+y+z=1; and wherein said transition metal (M) includes further only unavoidable impurities. 3. The precursor compound of clause 2, wherein b0.4. 4. The precursor compound of clause 2, wherein y=0. 5. The precursor compound of clause 1, wherein said coating layer contains crystalline alumina nanoparticles. 6. The precursor compound of clause 1, wherein a carbon content of said precursor compound is reduced by a heat treatment of said precursor compound at temperatures above about 400 C. reaching relatively low values at and above about 600 C. and wherein a sulfate content of said precursor compound is reduced by a heat treatment of said precursor at temperatures at and above about 700 C. 7. The precursor compound of clause 6, wherein said sulfate content is lower than about 0.3 wt %. 8. The precursor compound of clause 1, characterized in that said precursor compound is basically free of crystal water. 9. The precursor compound of clause 1, wherein said aluminum concentration in said coating layer decreases as the size of said core increases. 10. A process of preparing a particulate precursor compound for manufacturing an aluminum coated lithium transition metal (M)-oxide powder usable as an active positive electrode material in lithium-ion batteries, comprising the steps of: providing for a first quantity of alumina powder having a volume V1; providing for a first quantity of transition metal (M)-oxide, (M)-hydroxide or (M)-oxyhydroxide powder as said particulate precursor, having a volume V2; mixing said first quantity of alumina powder with said first quantity of transition metal (M)-oxide, (M)-hydroxide or (M)-oxyhydroxide in a first dry-coating procedure, wherein V1+V2=V; continue mixing until said volume V decreases to V3 that has about the same value as V1, thereby covering a transition metal (M)-oxide, (M)-hydroxide or (M)-oxyhydroxide core with an non-amorphous aluminum oxide Al.sub.2O.sub.3 coating layer; and heat treating said core covered by said coating layer at a temperature in a range of about 400-800 C. 11. The process of clause 10, wherein said heat treating step is performed at a temperature in a range of about 400-600 C. 12. The process of clause 10, further including the step of heat treating said core covered by said coating layer at said temperature for duration of 5 hour or 10 hours. 13. The process of clause 10, further including the step of reducing carbon content and sulfate content of said precursor compound. 14. The process of clause 10, further including the step of obtaining an aluminum dry-coated precursor compound, wherein said core is a transition metal oxide and wherein said core is completely covered by said non-amorphous coating layer. 15. The process of clause 10, further comprising the step of mixing said particulate precursor with a lithium precursor compound and sintering the mixture.