PROCESS FOR MAKING A PARTIALLY COATED ELECTRODE ACTIVE MATERIAL

Abstract

Process for making a partially coated electrode active material wherein said process comprises the following steps: (a) Providing an electrode active material according to general formula Li.sub.1+1TM.sub.1−xO.sub.2, wherein TM comprises Ni and, optionally, at least one transition metal selected from Co and Mn, and, optionally, at least one element selected from Al, Mg, Ba and B, transition metals other than Ni, Co, and Mn, and x is in the range of from −0.05 to 0.2, wherein at least 50 mole-% of the transition metal of TM is Ni, (b) treating said electrode active material with an aqueous formulation containing an inorganic aluminum compound dispersed or slurried in water, (c) separating off the water, (d) thermal treatment of the material obtained from step (c).

Claims

1. A process for making a partially coated electrode active material comprising the steps of: (a) providing an electrode active material according to general formula Li.sub.1+xTM.sub.1−xO.sub.2, wherein TM comprises Ni, and, optionally, at least one transition metal chosen from Co and Mn, and, optionally, at least one element chosen from Al, Mg, Ba, and B, and transition metals other than Ni, Co, and Mn, and x ranges from −0.05 to 0.20, wherein at least 50 mole-% of the transition metal of TM is Ni; (b) treating the electrode active material from step (a) with an aqueous formulation comprising a water-insoluble inorganic aluminum compound dispersed or slurried in water, wherein water-insoluble is a solubility of less than 0.1 g aluminum compound/I water at 25° C.; and (c) separating off the water by filtration or a centrifuge; (d) treating thermally the material obtained from step (c).

2. The process according to claim 1, wherein TM is a combination of metals according to general formula (I).
(Ni.sub.aCO.sub.bMn.sub.c).sub.1−dM.sup.1.sub.d  (I) wherein a ranges from 0.6 to 0.99; b ranges from 0.01 to 0.20; c ranges from zero to 0.20; and d ranges from zero to 0.10; M.sup.1 is at least one chosen from Al, Mg, Ti, Mo, Nb, W and Zr; and a+b+c=1.

3. The process according to claim 2, wherein c is zero, M.sup.1 is Al and d is in the ranges from 0.01 to 0.05.

4. The process according to claim 1, wherein the inorganic aluminum compound in step (b) is chosen from aluminum oxide compounds.

5. The process according to claim 4, wherein the aluminum oxide compound in step (b) is aluminum oxides dispersed or aluminum oxides slurried in water.

6. The process according to claim 1, wherein the aqueous formulation in step (b) is a colloidal solution.

7. The process according to claim 1, wherein step (d) comprises calcinating at a maximum temperature ranging from 300° C. to 700° C.

8. The process according to claim 1, wherein step (d) comprising drying at a maximum temperature ranging from 40° C. to 250° C.

9. The process according to claim 1, wherein TM is chosen from Ni.sub.0.6Co.sub.0.2Mn.sub.0.2, Ni.sub.0.7Co.sub.0.2Mn.sub.0.1, Ni.sub.0.8Co.sub.0.1Mn.sub.0.1, Ni.sub.0.88Co.sub.0.055Al.sub.0.055, Ni.sub.0.9Co.sub.0.45Al.sub.0.045, and Ni.sub.0.85Co.sub.0.1Mn.sub.0.05.

10. The process according to claim 1, wherein a molar amount of residual lithium of the electrode active material provided in step (a) exceeds a molar amount of aluminum of inorganic aluminum compound.

Description

[0127] The present invention is further illustrated by the following working examples.

[0128] General remarks: N-methyl-2-pyrrolidone: NMP.

I. Synthesis of a Cathode Active Material

I.1 Synthesis of a Precursor TM-OH.1

[0129] A stirred tank reactor was filled with deionized water and 49 g of ammonium sulfate per kg of water. The solution was tempered to 55° C. and a pH value of 12 was adjusted by adding an aqueous sodium hydroxide solution.

[0130] The co-precipitation reaction was started by simultaneously feeding an aqueous transition metal sulfate solution and aqueous sodium hydroxide solution at a flow rate ratio of 1.8, and a total flow rate resulting in a residence time of 8 hours. The transition metal solution contained Ni, Co and Mn at a molar ratio of 8.5:1.0:0.5 and a total transition metal concentration of 1.65 mol/kg. The aqueous sodium hydroxide solution was a 25 wt. % sodium hydroxide solution and 25 wt. % ammonia solution in a weight ratio of 6. The pH value was kept at 12 by the separate feed of an aqueous sodium hydroxide solution. Beginning with the start-up of all feeds, mother liquor was removed continuously. After 33 hours all feed flows were stopped. The mixed transition metal (TM) oxyhydroxide precursor was obtained by filtration of the resulting suspension, washing with distilled water, drying at 120° C. in air and sieving.

I.2 Conversion of TM-OH.1 into a Cathode Active Materials

I.2.1 Manufacture of a Comparative Cathode Active Material, C-CAM.1, Step (a.1)

[0131] C-CAM.1 (Comparative): The mixed transition metal oxyhydroxide precursor obtained according to 1.1 was mixed with Al.sub.2O.sub.3 (average particle diameter 6 nm) to obtain a concentration of 0.3 mole-% Al relative to Ni+Co+Mn+Al and LiOH monohydrate to obtain a Li/(TM+Al) molar ratio of 1.06. The mixture was heated to 760° C. and kept for 10 hours in a forced flow of a mixture of 60% oxygen and 40% nitrogen (by volume). After cooling to ambient temperature the powder was deagglomerated and sieved through a 32 μm mesh to obtain the electrode active material C-CAM 1.

[0132] D50=9.0 μm determined using the technique of laser diffraction in a Mastersize 3000 instrument from Malvern Instruments. The Al-content was determined by ICP analytics and corresponded to 780 ppm. Residual moisture at 250° C. was determined to be 300 ppm.

II. Treatment of Cathode Active Materials with Aqueous Formulation Containing an Inorganic Aluminum Compound, and Comparison Experiments

[0133] Ultra-dry air: moisture-free and CO.sub.2-free air

II.1 Treatment with an Aqueous Dispersion of AlOOH

[0134] Step (b.1): An amount of 0.37 g of Al(O)(OH) with an average primary particle diameter of 20 nm was stirred with 67 ml of de-ionized water. A colloidal solution of Al(O)(OH) with a pH value of 4.06 was obtained to which 100 g C-CAM.1 were added. The molar ratio of Al.sub.dispersion/(TM+Al) was 0.006. The resultant slurry was stirred at ambient temperature over a period of 5 minutes.

[0135] Step (c.1): Then, the water was removed by filtration through a Buchner funnel.

[0136] Step (d.1): The resultant filter cake was dried in ultra-dry air at 70° C. for 2 hours and then at 120° C. over a period of 10 hours followed by a thermal treatment at 700° C. for one hour in a forced flow of oxygen. Inventive cathode active material CAM.2 was obtained.

II.2 Treatment with an Aqueous Slurry of Al.sub.2O.sub.3

[0137] Step (b.2): An amount of 0.32 g of Al.sub.2O.sub.3 with an average primary particle diameter of 5 μm was stirred with 67 ml of de-ionized water. A slurry with a pH value of 3.58 was obtained to which 100 g C-CAM.1 were added. The molar ratio of Al.sub.dispersion/(TM+Al) was 0.006. The resultant slurry was stirred at ambient temperature over a period of 5 minutes. At the end of step (b.3), the pH value was 12.88.

[0138] Step (c.2): The resultant dispersion was then transferred to a filter press and filtered.

[0139] Step (d.2): The resultant filter cake was dried in ultra-dry air at 70° C. for 2 hours and then at 120° C. over a period of 10 hours followed by a thermal treatment at 700° C. for one hour in an atmosphere of oxygen. Inventive cathode active material CAM.3 was obtained.

[0140] II.3 Treatment with an Aqueous Slurry of Al.sub.2O.sub.3

[0141] Steps (b.2) and (c.2) were repeated as above.

[0142] Step (d.3): The resultant filter cake was dried in ultra-dry air at 70° C. for 2 hours and then at 120° C. over a period of 10 hours followed by a thermal treatment at 600° C. for one hour in an atmosphere of oxygen. Inventive cathode active material CAM.4 was obtained.

II.4 Treatment with an Aqueous Slurry of Al.sub.2O.sub.3

[0143] Steps (b.2) and (c.2) were repeated as above.

[0144] Step (d.4): The resultant filter cake was dried in ultra-dry air at 70° C. for 2 hours and then at 120° C. over a period of 10 hours followed by a thermal treatment at 500° C. for one hour in an atmosphere of oxygen. Inventive cathode active material CAM.5 was obtained.

II.5 Treatment with an Aqueous Slurry of Al.sub.2O.sub.3

[0145] Steps (b.2) and (c.2) were repeated as above.

[0146] Step (d.5): The resultant filter cake was dried in ultra-dry air at 70° C. for 2 hours and then at 120° C. over a period of 10 hours followed by a thermal treatment at 400° C. for one hour in an atmosphere of oxygen. Inventive cathode active material CAM.6 was obtained.

[0147] II.6 Manufacture of Comparative Cathode Active Material C-CAM.7

[0148] Comparative step (b.6): An amount of 100 g of C-CAM.1 was added to 67 ml of distilled water. The resultant slurry was stirred at ambient temperature over a period of 5 minutes.

[0149] Step (c.6): The resultant dispersion was then transferred to a filter press and filtered.

[0150] Step (d.6): The resultant filter cake was dried ultra-dry air at 70° C. for 2 hours and then at 120° C. over a period of 10 hours. Comparative cathode active material C-CAM.7 was obtained.

II.7 Treatment with an Aqueous Dispersion of AlOOH

[0151] Steps (b.1) and (c.1) were repeated as above.

[0152] Step (d.7): The resultant filter cake was dried in vacuo at 40° C. over a period of 10 hours, followed by a thermal treatment at 650° C. for one hour in a forced flow of oxygen. Inventive cathode active material CAM.8 was obtained.

II.8 Treatment with an Aqueous Dispersion of AlOOH in which Aluminum Sulfate was Dissolved

[0153] Step (b.8): An amount of 0.28 g of Al(O)(OH) with an average primary particle diameter of 20 nm was stirred with 67 ml of de-ionized water. An amount of 0.27 g of Al.sub.2(SO.sub.4).sub.3 was added. A colloidal solution of Al(O)(OH) was obtained to which 100 g C-CAM.1 were added. 100 g of CCAM.1 were added so that the molar ratio of Al(from AlOOH) to Al (from aluminum sulfate) was 4:1. The molar ratio of Al.sub.dispersion/(TM+Al) was 0.006. The resultant slurry was stirred at ambient temperature over a period of 3 minutes.

[0154] Step (c.8): Then, the water was removed by filtration through a Büchner funnel.

[0155] Step (d.8): The resultant filter cake was dried in vacuo at 40° C. over a period of 10 hours, followed by a thermal treatment at 700° C. for one hour in a forced flow of oxygen. Inventive cathode active material CAM.9 was obtained.

III. Testing of Cathode Active Material

III.1 Electrode Manufacture, General Procedure

III.1.1 Cathode Manufacture

[0156] Positive electrode: PVDF binder (Solef® 5130) was dissolved in NMP (Merck) to produce a 7.5 wt. % solution. For electrode preparation, binder solution (3 wt. %), graphite (SFG6L, 2 wt. %), and carbon black (Super C65, 1 wt.-%) were suspended in NMP. After mixing using a planetary centrifugal mixer (ARE-250, Thinky Corp.; Japan), either any of inventive CAM.1 to CAM.7 or a comparative cathode active material (94 wt. %) was added and the suspension was mixed again to obtain a lump-free slurry. The solid content of the slurry was adjusted to 65%. The slurry was coated onto Al foil using a KTF-S roll-to-roll coater (Mathis AG). Prior to use, all electrodes were calendared. The thickness of cathode material was 70 μm, corresponding to 15 mg/cm.sup.2. All electrodes were dried at 105° C. for 7 hours before battery assembly.

III.1.2: Pouch Cell Anode Manufacture

[0157] Graphite and carbon black were thoroughly mixed. CMC (carboxymethyl cellulose) aqueous solution and SBR (styrene butadiene rubber) aqueous solution were used as binder. The mixture of graphite and carbon black, weight ration cathode active material:carbon:CMC:SBR like 96:0.5:2:1.5, was mixed with the binder solutions and an adequate amount of water was added to prepare a suitable slurry for electrode preparation. The thus obtained slurry was coated by using a roll coater onto copper foil (thickness=10 μm) and dried under ambient temperature. The sample loading for electrodes on Cu foil was fixed to be 10 mg cm.sup.−2 for single layer pouch cell testing.

III.2: Electrolyte Manufacture

[0158] A base electrolyte composition was prepared containing 12.7 wt % of LiPF.sub.6, 26.2 wt % of ethylene carbonate (EC), and 61.1 wt % of ethyl methyl carbonate (EMC) (EL base 1), based on the total weight of EL base 1. To this base electrolyte formulation 2 wt. % of vinylene carbonate (VC) was added (EL base 2).

III.3 Test Cell Manufacture

III.3.1 Coin-Type Half Cells

[0159] Coin-type half cells (20 mm in diameter and 3.2 mm in thickness) comprising a cathode prepared as described under IV.1.1 and lithium metal as working and counter electrode, respectively, were assembled and sealed in an Ar-filled glove box. In addition, the cathode and anode and a separator were superposed in order of cathode II separator II Li foil to produce a half coin cell. Thereafter, 0.15 mL of the EL base 1 which is described above (IV.2) were introduced into the coin cell.

III.3.2 Pouch Cells

[0160] Single layer Pouch cells (70 mAh) comprising an anode prepared as described above in IV.1.1 and a graphite electrode according to IV.1.2, were assembled and sealed in an Ar-filled glove box. The cathode and the anode and a separator were superposed in order of cathode II separator II anode to produce a several layer-pouch cell. Thereafter, 0.8 mL of the EL base 2 electrolyte were introduced into the Laminate pouch cell.

IV Evaluation of Cell Performance

IV.1 Evaluation of Coin Half-Cell Performance

[0161] Cell performance were evaluated using the produced coin type battery. For the battery performances, initial capacity and reaction resistance of cell were measured.

[0162] The initial performance and cycle were measured as follows:

[0163] Coin half cells according to IV.3.1 were tested in a voltage range between 4.3 V to 2.8 V at room temperature. For the initial cycles, the initial lithiation was conducted in the CC-CV mode, i.e., a constant current (CC) of 0.1 C was applied until reaching 0.01 C. After 10 min resting time, reductive lithiation was carried out at constant current of 0.1 C up to 2.8 V. For the cycling, the current density is 0.1 C. The results are summarized in

[0164] The cell reaction resistance was calculated by the following method.

[0165] The coin cells after the evaluation of the initial performance is recharged to 4.3V, and the resistance is measured by the AC impedance method using potentiostat and frequency response analyzer system (Solartron CellTest System 1470E). From the EIS spectra can be divided into Ohmic resistance and relative resistance. The results are summarized in Table 1. [%] relative resistance is based on the resistance of cell based on C-CAM.8 as 100%.

TABLE-US-00001 TABLE 1 Initial charge and discharge capacity with initial reaction resistance, coin cell 1.sup.st 1.sup.st Charge Discharge Coulombic R Relative R capacity capaity efficiency (impedance) (impedance) CAM [mA .Math. h/g] [mA .Math. h/g] [%] [Ω] [%] CAM.2 234 208 89% 18.5 26 CAM.3 233 212 91% 10.3 15 CAM.4 232 214 92% 9.1 13 CAM.5 232 216 93% 19.1 27 C-CAM.7 232 209 90% 70.9 100

IV.2 Evaluation of Long-Term Electrochemical Performance of Single Layer Pouch Cell

IV.2.1 Long-Term Electrochemical Performance at 45° C.

[0166] Pouch cells according to IV.3.2 were tested in a voltage range between 4.2 V to 2.5 V at room temperature and 45° C.

[0167] In the formation step, said pouch cells were charged to 3.1 V at a constant current of 0.1 C and then charged at a constant voltage of 3.1 V until the current value reached 0.01 C at initial cycles. Afterwards, these cells were degassed. After degassing, cell volume was measured by Archimedes method. After then, the pouch cells charged to 4.2 V at the constant current of 0.1 C and then charged at a constant voltage of 4.2 V until the current value reached 0.01 C. These cells were aged at 45° C. for 1 day and then transferred to 25° C. to check the capacity and rate performance. For 25 degC cycle testing, the cells transferred to 25 degC oven and the current density increased to 1.0 C. for 45 degC cycle testing, the cells transfer to 45 degC oven and the current density also increased to 1.0 C. The results of discharge capacity and cycle stability after 400 cycles are summarized in Table 2.

IV.2.2 Gas Mount at 45° C. Cycling

[0168] Every 200 cycles, cell volume was measured again. The cycling gas amount of the cells is determined as the volume difference before and after cycling of cells. The results are displayed in Table 2.

IV.2.3 DCIR at 25° C. Cycling

[0169] Every 100 cycles, direct current resistance (“DCIR” was measured. For these cells the DCIR was measured at 4.2 V at 25° C. The results are shown in Tables 2 and 3.

TABLE-US-00002 TABLE 2 Long-time performance, pouch cell, 45° C. Gas 400 Relative R Q1 Q400 Q400/Q1 cycl (impedance) CAM [mA .Math. h/g] [mA .Math. h/g] [%] [cm.sup.3] [%] CAM.3 198 177 89% 0.0712  34 C-CAM.1 194 166 86% 0.2097 100 C-CAM.7 196 172 88% n.d. n.d. n.d.: not determined

TABLE-US-00003 TABLE 3 Long-time performance, pouch cell, 25° C. Q1 Q400 Q400/ DCIR DCIR [mA .Math. [mA .Math. Q1 before DCIR growth CAM h/g] h/g] [%] 1.sup.st cycle 400 [%] CAM.3 189 165 88 1.041 1.342 129 C-CAM.1 184 164 89 1.271 2.155 170 C-CAM.7 183 153 84 1.350 2.800 207