PROCESS FOR MAKING A CATHODE ACTIVE MATERIAL FOR A LITHIUM ION BATTERY

Abstract

A process for making a cathode active material for a lithium ion battery is described. The process includes (a) a step of synthesizing a mixed oxide of formula Li.sub.1+xTM.sub.1xO.sub.2 at a temperature ranging from 750 to 1000 C. in an oxidizing atmosphere, where TM is a combination of two or more transition metals of Mn, Co and Ni and, optionally, at least one more metal of Ba, Al, Ti, Zr, W, Fe, Cr, K, Mo, Nb, Mg, Na and V, and x is a number ranging from zero to 0.2, (b) a step of cooling down the material obtained from step (a) to a temperature ranging from 100 to 400 C., (c) a step of adding at least one reactant of BF.sub.3, SO.sub.2 and SO.sub.3 at the temperature of 100 to 400 C., and (d) a step of cooling down to a temperature of 50 C. or below.

Claims

1. A process for making a cathode active material for a lithium ion battery, said process comprising: (a) synthesizing a mixed oxide of formula Li.sub.1+xTM.sub.1xO.sub.2 at a temperature ranging from 750 to 1000 C. in an oxidizing atmosphere, wherein TM is a combination of two or more transition metals selected from the group consisting of Mn, Co and Ni and, optionally, at least one more metal selected from the group consisting of Ba, Al, Zr, W, Fe, Cr, K, Mo, Nb, Mg, Na and V, and x ranges from zero to 0.2, (b) cooling down the mixed oxide obtained from (a) to a temperature ranging from 100 to 400 C., (c) adding at least one reactant selected from the group consisting of BF.sub.3, SO.sub.2, and SO.sub.3 at the temperature of 100 to 400 C., and (d) cooling down to a temperature of 50 C. or below.

2. The process according to claim 1, wherein TM is a combination of metals of formula (I)
Ni.sub.aCo.sub.bMn.sub.cM.sub.d(I) where a ranges from 0.3 to 0.9, b ranges from 0.05 to 0.4, c ranges from 0.05 to 0.6, d ranges from zero to 0.1, M is selected from the group consisting of Ba, Al, Ti, Zr, W, Fe, Cr, K, Mo, Nb, Mg, Na and V, and a+b+c+d=1.

3. The process according to claim 1, wherein said mixed oxide is synthesized from a mixture of at least one lithium salt and a mixed oxide, hydroxide, carbonate or oxyhydroxide of TM.

4. The process according to claim 3, wherein said lithium salt is selected from the group consisting of lithium hydroxide and lithium carbonate.

5. The process according to claim 1, wherein the oxidizing atmosphere in (a) is selected from the group consisting of air, oxygen and oxygen-enriched air.

6. The process according to claim 1, wherein in (c) said reactant is added to a stream of oxygen, oxygen-enriched dry air, dry air, nitrogen, a noble gas or a combination thereof.

7. The process according to claim 1, wherein (c) and (d) are performed in an atmosphere of air, oxygen, nitrogen, a noble gas or a combination thereof.

8. The process according to claim 7, wherein a concentration of the reactant ranges from 0.1 to 3% by volume, with respect to the atmosphere in which (c) is carried out.

9. The process according to claim 1, further comprising: (e) after (c) and before (d), maintaining the temperature in the range of from 100 to 400 C.

10. The process according to claim 9, wherein (a) and at least one of (b) to (e) is performed under a flow of gas.

11. The process according to claim 1, wherein (a) to (d) are performed in a roller hearth kiln, a pusher kiln or a rotary kiln.

12. (canceled)

Description

GENERAL REMARKS

[0070] The following precursors were used:

[0071] A precursor was made by precipitating a mixed NiCoMn carbonate from a solution containing nickel sulfate/cobalt sulfate/manganese sulfate in a molar ratio of 23:12:65 followed by drying under air at 200 C. Precipitating agent was aqueous sodium carbonate solution in aqueous ammonia solution. Average particle diameter (D50): 10.2 m.

[0072] Nl: liters at normal conditions: 20 C./one atmosphere.

I. Manufacture of Cathode Active Materials

I.1: Manufacture of Oxide MO.1

[0073] Step (a.1): The following equipment is used: in a roller hearth kiln, a saggar filled with an intimate mixture of precursor and Li.sub.2CO.sub.3 so the molar ratio of lithium to the sum of transition metals is 1.42:1. Said mixture is heated to 800 C. in a forced stream of air. When a temperature of 800 C. is reached, heating is continued at 800 C. over a period of time of 4 hours. The formation of metal oxide (MO.1) is observed, formula 0.42Li.sub.2MnO.sub.3.0.58Li(Ni.sub.0.4Co.sub.0.2Mn.sub.0.4)O.sub.2. This corresponds to a formula of Li.sub.1.17TM.sub.0.83O.sub.2.

[0074] Step (b.1): in the same roller hearth kiln, the saggar is moved on and allowed to cool down to 120 C. within two hours in dry oxygen (30% by vol) in Ar.

[0075] Step (c.1): The air supply is shut down and replaced by O.sub.2/Ar/SO.sub.3 mixture in a ratio of 30:70:0.5 by volume. Over 30 minutes, metal oxide (MO.1) is exposed to a gas stream of O.sub.2/Ar/SO.sub.3. Since the SO.sub.3 has been made in parallel by a one-stage SO.sub.2-oxidation at a V.sub.2O.sub.5-catalyst the SO.sub.3 contains some SO.sub.2 (maximum 30% by mole).

[0076] After said treatment according to step (c.1), the material so obtained was cooled down to ambient temperature, step (d.1). MO.1 was obtained.

I.2: Manufacture of Oxide MO.2

[0077] Step (a.1) is repeated as above.

[0078] Step (b.2): in the same roller hearth kiln, the saggar is moved on and allowed to cool down to 200 C. within two hours in dry oxygen (30% by vol) in Ar.

[0079] Step (c.2): The air supply is shut down and replaced by O.sub.2/Ar/SO.sub.3 mixture in a ratio of 30:70:0.5 by volume. Over one hour, metal oxide (MO.1) is exposed to a gas stream of O.sub.2/Ar/503. Since the SO.sub.3 has been made in parallel by a one-stage SO.sub.2-oxidation at a V.sub.2O.sub.5-catalyst the SO.sub.3 contains about 5% by vol. of SO.sub.2.

[0080] After said treatment according to step (c.2), the material so obtained is cooled down to ambient temperature, step (d.2). MO.2 is obtained. MO.2 has a sulfur content of 0.9% by weight, determined by combustion analysis (CHNS). Compared to C-MO.3, the difference is 0.6% by weight.

I.3: Manufacture of Comparative Oxide C-MO.3 (No SO.SUB.3 .Treatment)

[0081] Step (a.1): The following equipment is used: in a roller hearth kiln, a saggar filled with an intimate mixture of precursor and Li.sub.2CO.sub.3 so the molar ratio of lithium to the sum of transition metals is 1.42:1. Said mixture is heated to 800 C. in a forced stream of air. The formation of metal oxide (MO.1) is observed, formula 0.42Li.sub.2MnO.sub.3 0.58Li(Ni.sub.0.4Co.sub.0.2Mn.sub.0.4)O.sub.2.

[0082] Then, the material so obtained is cooled down to ambient temperature, step (d.3). C-MO.3 was obtained. The residual sulfur content was 0.3% by weight, determined by CHNS. The sulfate most likely stems from sulfate adsorbed during the precipitation process.

I.4: Manufacture of MO.4:

[0083] Step (a.1) was repeated as above.

[0084] Step (b.4): in the same roller hearth kiln, the saggar was moved on and allowed to cool down to 400 C. within two hours in pure nitrogen.

[0085] Step (c.4-1): The N.sub.2 supply was shut down and replaced by N.sub.2/SO.sub.2 mixture in a ratio of 98:2 by volume. Over 2 hours, metal oxide (MO.1) was exposed to a flow of N.sub.2/SO.sub.2, 6 cm.sup.3/min. No impurities of the SO.sub.3 were detectable.

[0086] After said treatment according to step (c.4-1), the material so obtained was cooled down to ambient temperature, step (d.4). MO.4-1 was obtained. In MO.4-1 the resulting ratio of sulfur to the sum of transition metals, S/(Ni+Mn+Co) was 0.47% by weight, determined Inductively Coupled Plasma (ICP). From the S 2p peak of XPS spectra the amounts of sulfates were estimated as follows: 16% sulfates of transition metals [i.e., MnSO.sub.4, NiSO.sub.4, and CoSO.sub.4,] and 84% of Li.sub.2SO.sub.4.

[0087] Step (c.4-1) was repeated with fresh samples from (b.4), but the treatments with N.sub.2/SO.sub.2 had durations of 60 or 30 minutes, respectively. MO.4-2 and MO.4-3 were obtained.

TABLE-US-00001 TABLE 1 Storage of cathode active materials storage conditions Test product MO.1 Inert atmosphere MO.1* MO.2 Inert atmosphere MO.2* MO.4-1 Inert atmosphere MO.4-1* MO.1 Ambient conditions MO.1** MO.2 Ambient conditions MO.2** MO.4 Ambient conditions MO.4-1** C-MO.3 Inert atmosphere C-MO.3* C-MO.3 Ambient conditions C-MO.3** Inert atmosphere: Ar-filled glovebox (25 C., <0.1 ppm H.sub.2O and CO.sub.2) Ambient conditions: 1 week, 25 C., 100% relative humidity, atmospheric CO.sub.2

I.5: Manufacture of MO.5-1 and MO.5-2

[0088] A precursor was made by precipitating a mixed NiCoMn carbonate from a solution containing nickel sulfate/cobalt sulfate/manganese sulfate in a molar ratio of 85:10:05 followed by drying under air at 120 C. and sieving. Precipitating agent was aqueous sodium hydroxide solution in aqueous ammonia solution. Average particle diameter (D50): 11.0 m.

[0089] Step (a.5): The following equipment is used: in a roller hearth kiln, a saggar was filled with an intimate mixture of the above precursor and LiOH monohydrate so the molar ratio of lithium to the sum of transition metals was 1.03:1. Said mixture was heated to 760 C. in a forced stream of a mixture of N.sub.2:O.sub.2 40:60 in volume %. When a temperature of 760 C. is reached, heating is continued at 760 C. over a period of time of 10 hours. The formation of metal oxide (MO.5) was observed, formula Li.sub.1.02(Ni.sub.0.85Co.sub.0.10Mn.sub.0.05)O.sub.2.02.

[0090] Step (b.5): in the same roller hearth kiln, the saggar was moved on and allowed to cool down to 400 C. within two hours in pure nitrogen.

[0091] Step (c.5-1): The N.sub.2 supply was shut down and replaced by N.sub.2/SO.sub.2 mixture in a ratio of 98:2 by volume. Over 5 minutes, metal oxide (MO.5-1) was exposed to a flow of N.sub.2/SO.sub.2, 6 cm.sup.3/min. No impurities of the SO.sub.2 were detectable.

[0092] Step (c.5-2): The N.sub.2 supply was shut down and replaced by N.sub.2/SO.sub.2 mixture in a ratio of 98:2 by volume. Over 20 minutes, metal oxide (MO.5-2) was exposed to a flow of N.sub.2/SO.sub.2, 6 cm.sup.3/min. No impurities of the SO.sub.2 were detectable.

[0093] After said treatment according to step (c.5-1) or (c.5-2, the materials so obtained were cooled down to ambient temperature, step (d.5). MO.5-1 and (MO.5-2) were obtained.

II. Testing of Cathode Active Materials

[0094] To produce a cathode, the following ingredients are blended under stirring with one another under inert conditions:

[0095] 46.25 g of active material, 1.75 g polyvinylidene difluoride, (PVdF), commercially available as Kynar Flex 2801 from Arkema Group, 2 g carbon black, BET surface area of 62 m.sup.2/g, commercially available as Super C 65L from Timcal.

[0096] While stirring, a sufficient amount of N-methylpyrrolidone (NMP) is added in several steps and the mixture is stirred with a planetary orbital mixer (Thinky) until a stiff, lump-free paste has been obtained.

[0097] Cathodes are prepared as follows: On an 18 m thick aluminum foil, the above paste is applied with a 100 m four-edge-blade. The loading after drying is 1.5 mAh/cm.sup.2. Disc-shaped cathodes with a diameter of 14 mm are punched out of the foil and compressed at 2.5 t for 20 seconds. The cathode discs are then weighed, dried for 14 hours in a vacuum oven at 120 C. and introduced into an argon glove box without exposure to ambient air. Then, cells with the cathodes are assembled.

[0098] Electrochemical testing was conducted in CR2032 coin type cells. The electrolyte used was 80 l of a 1 M solution of LiPF.sub.6 in fluoroethylene carbonate/diethyl carbonate/fluorinated ether K2 (volume ratio 64:12:24).

[0099] Alternatively, electrochemical testing was conducted in coin cells of 2325-type fabricated with Li-metal counter electrodes, two Celgard 2500 polypropylene separators, and electrolyte solution (LP57, BASF) comprising ethylene carbonate-ethyl methyl carbonate (3:7), and 1M LiPF.sub.6.

[0100] Anode: lithium foil, thickness 0.45 mm, separated from the cathode by two glass-fiber separators, thickness 0.025 mm each

TABLE-US-00002 TABLE 2 Cycling conditions of inventive cells and comparative cells Potential range C-rate C-rate Segment [V vs. Li.sup.+/Li] Charge Discharge Cycles 1 Activation 4.8-2.0 C/15 (CC) C/15 (CC) 1 2 Slow cycling 4.7-2.0 C/10 (CC) C/10 (CC) 3 3 DCIR pulse (40% SOC)-2.0.sup. C/10 (CC) C/10 (CC) 1 4 Fast cycling 4.7-2.0 C/2 (CCCV) 3C (CC) 3 5 Standard cycling 4.7-2.0 C/2 (CCCV) 1C (CC) 33

[0101] Segments 2 to 5 are looped. C-rate referenced to 250 mAh/g.sub.HE-NCM; CC (constant current), CCCV (constant current constant voltage with C/10 lower current limit), DCIR (direct current internal resistance) measurement at 40% SOC (state of charge).

TABLE-US-00003 TABLE 3 Specific discharge capacities at ambient temperature. Specific discharge capacity [mAh/g.sub.HE-NMC] at cycle number 40 (1 C) 80 (1 C) 120 (1 C) 160 (1 C) 200 (1 C) 240 (1 C) 44 (0.1 C) 84 (0.1 C) 124 (0.1 C) 164 (0.1 C) 204 (0.1 C) 244 (0.1 C) sample rate 48 (3 C) 88 (3 C) 128 (3 C) 168 (3 C) 208 (3 C) 248 (3 C) C-MO. 3* 1 C 221 1 214 1 210 1 207 2 195 2 201 2 0.1 C 251 0 245 4 249 0 248 0 200 47 245 0 3 C 174 3 167 4 163 4 157 4 149 6 142 6 MO. 1* 1 C 224 1 218 1 215 1 213 1 210 1 207 1 0.1 250 0 249 0 249 0 248 0 247 1 246 0 3 C 185 1 179 1 174 3 169 4 164 4 154 6

[0102] Average and maximum deviation of two cells per sample

TABLE-US-00004 TABLE 3a Specific capacities of first activation at 30 C. 1st C [mA .Math. h/g] 1st D [mA .Math. h/g] 1st C. E. [%] C-MO.3 332.5 1 281.2 3 84.5% MO.4-1 336.1 2 294.8 3 87.7%

TABLE-US-00005 TABLE 3b Specific discharge capacities at 30 C. [mA .Math. h/g] 0.1 C 0.33 C 0.8 C 1 C 2 C 4 C 1 C/0.1 C C-MO. 3 249 2 236 3 221 3 214.7 3 190 5 136 18 86.0% MO. 4-1 263 3 257 2 241 5 .sup.238 2 220 2 178 9 90.5%

TABLE-US-00006 TABLE 4 Specific discharge capacities during cycling at C/3 at 30 C. 1st 10th 50th 80th Q80/Q1 [mA .Math. h/g] [mA .Math. h/g] [mA .Math. h/g] [mA .Math. h/g] [%] C-MO.3 226 3.sup. 221 3.sup. 207 4 188 6 83.2% MO.4-1 253 1.6 249 1.4 236 3 220 7 87.0%

[0103] Average and maximum deviation of three cells per sample

TABLE-US-00007 TABLE 5 CO.sub.2 evolution from 1.03 g cathode active materials mixed with 240 l of 1.5M LiClO.sub.4 in ethylene carbonate at 60 C. CO.sub.2 [mol] CO.sub.2 [mol] CO.sub.2 [mol] after 3 h after 7 h after 12 h C-MO.3* 7 8 9 C-MO.3** 20 26 30 MO.1** 11 13 15

[0104] The CO.sub.2 evolution is measured by On-line Electrochemical Mass Spectrometry (OEMS)

[0105] Alternative cycling conditions of inventive cells and comparative cells for coin cells based upon MO.5:

[0106] The first two cycles were performed at C/10 rate, charging to 4.3V and discharged to 3V with a 30 min constant voltage step at 4.3 V. The C rate is defined as 185 mAh/g. All subsequent cycles were charged at C/2 rate and discharged at different rates namely 0.2 C, 0.5 C, 1 C, 2 C, 3 C, 5 C and 0.2 C rate for two cycles each and continued to cycling at 1 C rate up to 125 Cycles. The specific capacities obtained initially and at various rates and cycling are shown in Tables 5-7.

TABLE-US-00008 TABLE 6 Specific discharge capacities during cycling at 1 C at 25 C. Cycling 1.sup.st 10.sup.th 30.sup.th 50.sup.th 100.sup.th Q50/Q1 Q100/Q1 Sample mAh/g mAh/g mAh/g mAh/g mAh/g % % MO. 5 187.8 185.2 178.7 172.4 157.8 91.8 84.0 MO. 5-1 189.4 188.2 185.1 181.1 170.3 95.6 89.9 MO. 5-2 179.8 179.6 176.9 174.3 165.1 96.9 91.8

[0107] average of 3 cells per sample