High rate lithium cobalt oxide positive electrode material and manufacturing method thereof

Abstract

A high-rate lithium cobaltate cathode material, which contains a multi-channel network formed by fast ionic conductor Li.sub.M.sub.O.sub., mainly consists of lithium cobaltate. The lithium cobaltate is melted together with the fast ionic conductor Li.sub.M.sub.O.sub. in the form of primary particles to form secondary particles. Besides, the lithium cobaltate is embedded in the multi-channel network formed by fast ionic conductor Li.sub.M.sub.O.sub.. The element M in Li.sub.M.sub.O.sub. is one or more of Ti, Zr, Y, V, Nb, Mo, Sn, In, La, W and 14, 15, 212. The lithium cobaltate cathode material is mainly obtained by uniformly mixing cobaltous oxide impregnated with a hydroxide of M and lithium source, then by the sintering reaction in an air atmosphere furnace at a high temperature. The product of the present invention can greatly promote the lithium ion conductivity of the lithium cobaltate cathode material during the charging and discharging process of the lithium-ion battery, and improve the rate performance of the material.

Claims

1. A high-rate lithium cobaltate cathode material for a liquid state lithium ion battery, the high-rate lithium cobaltate cathode material comprising lithium cobaltate with or without a doping element M and a fast ionic conductor Li.sub.M.sub.O.sub., wherein: an element M in Li.sub.M.sub.O.sub. is one or more of Ti, Zr, Y, V, Nb, Mo, Sn, In, La, or W, 14, 15, and 212, the lithium cobaltate with or without the doping element M is represented by Li.sub.1+yCo.sub.1xM.sub.xO.sub.2, the doping element M is one or more of Mg, Al, Si, Sc, Ni, Mn, Ga, or Ge, 0x0.1, and 0.01y0.01, the high-rate lithium cobaltate cathode material is represented by a chemical formula of Li.sub.1+yCo.sub.1xM.sub.xO.sub.2zLi.sub.M.sub.O.sub., and 0.005z0.01, the high-rate lithium cobaltate cathode material comprises a multi-channel network formed by the fast ionic conductor Li.sub.M.sub.O.sub., the lithium cobaltate with or without the doping element M, as primary particles, is melted integrally with the fast ionic conductor Li.sub.M.sub.O.sub. so as to form secondary particles, and the lithium cobaltate with or without the doping element M is embedded in the multi-channel network formed by the fast ionic conductor Li.sub.M.sub.O.sub..

2. A method for preparing a high-rate lithium cobaltate cathode material comprising lithium cobaltate with or without a doping element M and a fast ionic conductor Li.sub.M.sub.O.sub., wherein: an element M in Li.sub.M.sub.O.sub. is one or more of Ti, Zr, Y, V, Nb, Mo, Sn, In, La, or W, 14, 15, and 212, the lithium cobaltate with or without the doping element M is represented by Li.sub.1+yCo.sub.1xM.sub.xO.sub.2, the doping element M is one or more of Mg, Al, Si, Sc, Ni, Mn, Ga, or Ge, 0x0.1, and 0.01y0.01, the high-rate lithium cobaltate cathode material comprises a multi-channel network formed by the fast ionic conductor Li.sub.M.sub.O.sub., the lithium cobaltate with or without the doping element M, as primary particles, is melted integrally with the fast ionic conductor Li.sub.M.sub.O.sub. so as to form secondary particles, the lithium cobaltate with or without the doping element M is embedded in the multi-channel network formed by the fast ionic conductor Li.sub.M.sub.O.sub., and the method comprises: mixing cobaltous oxide impregnated with a hydroxide of the element M and a lithium source to obtain a homogenous mixture; and sintering the homogenous mixture in an air atmosphere furnace at a high temperature, or mixing cobaltous oxide impregnated with a hydroxide of the element M, a lithium source and an additive containing the doping element M to obtain a homogenous mixture; and sintering the homogenous mixture in an air atmosphere furnace at a high temperature.

3. The method according to claim 2, wherein the method further comprises the following steps to obtain the cobaltous oxide impregnated with the hydroxide of the element M: dissolving an organic compound containing the element M in anhydrous ethanol under stirring to obtain a solution; adding a porous cobalt oxide into the solution; dispersing the porous cobalt oxide into the solution with a disperser for 0.5-1 h; adding an aqueous ethanol solution with a volume ratio of ethanol to water of 5 to 20 and stirring for 2 to 5 h; filtering under vacuum to obtain a first filter cake; and drying the first filter cake to obtain the cobaltous oxide impregnated with the hydroxide of the element M.

4. The method according to claim 3, wherein: the method further comprises pre-sintering a precursor to obtain the porous cobalt oxide, the porous cobalt oxide has a porosity of 0.5% to 5%, the porous cobalt oxide has an average pore size ranging from 100 nm to 500 nm, the precursor is CoCO.sub.3.H.sub.2O or CoC.sub.2O.sub.4.H.sub.2O, and 0 9, and the organic compound containing the element M is one or more of an alkoxide of the element M, an alkyl compound of the element M, a carbonyl compound of the element M, or a carboxyl compound of the element M.

5. The method according to claim 4, wherein the method further comprises the following steps to obtain the porous cobalt oxide: injecting a part of a precipitant solution with a pH of 6-14 into a reaction kettle; simultaneously adding a cobalt salt solution, a complexing agent solution and a remaining part of the precipitant solution into the reaction kettle by parallel flows, under stirring and protection of an inert gas, such that a reaction mixture is formed and a reaction starts, wherein the reaction is performed at a pH of 6-14 and at a temperature of 0 C. to 85 C.; aging the reaction mixture after the cobalt salt solution is completely added into the reaction kettle; filtering the reaction mixture to obtain a second filter cake; drying the second filter cake to obtain the precursor; subjecting the precursor to the pre-sintering in an air atmosphere furnace; and sieving the pre-sintered precursor to obtain the porous cobalt oxide.

6. The method according to claim 5, wherein: the cobalt salt solution is a solution formed by dissolving at least one of CoCl.sub.2.bH.sub.2O, CoSO.sub.4.bH.sub.2O, or Co(NO.sub.3).sub.2.bH.sub.2O in water, and 0b6, a concentration of Co.sup.2+ in the cobalt salt solution is 70-200 g/L, the complexing agent solution is an ammonia water or an aminocarboxylate solution, and the precipitant solution is a carbonate solution, an oxalic acid, or an oxalate solution.

7. The method according to claim 5 wherein: an aging time for aging the reaction mixture after the cobalt salt solution is completely added into the reaction kettle is 4 to 8 hours, and the subjecting the precursor to the pre-sintering in an air atmosphere furnace comprises firstly sintering at 300 C. to 500 C. for 2 to 5 hours, and then sintering at 700 C. to 800 C. for 2 to 5 hours.

8. The method according to claim 2, wherein: the lithium source is one or more of lithium carbonate, lithium hydroxide, or lithium oxide, and the additive containing the doping element M is at least one of oxide, hydroxide, carboxylate, carbonate, or basic carbonate of the doping element M.

9. The method according to claim 2, wherein the sintering is performed at 850 C. to 1000 C. for 6 to 20 hours.

Description

BRIEF INTRODUCTION OF THE DRAWINGS

(1) In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the embodiments or the prior art description will be briefly described below. It is obvious that the drawings in the following description are some embodiments of the present invention. And those skilled in the art can obtain other drawings based on these drawings without any creative work.

(2) FIG. 1 is the diagram of the lithium ion transport path in the charging process of the lithium cobaltate particles in the present invention, and the discharge process is reversed.

(3) FIG. 2 is the SEM photograph of the porous cobalt oxide before impregnation in embodiment 1 of the present invention.

(4) FIG. 3 is the SEM photograph of the porous cobalt oxide after impregnation in embodiment 1 of the present invention.

(5) FIG. 4 is the SEM photograph of a lithium cobaltate cathode material LCO-1 in embodiment 1 of the present invention.

DETAILED DESCRIPTION

(6) In order to facilitate the understanding of the present invention, the present invention will be described more fully and detailed hereinafter in combination with drawings and preferred embodiments. But, the scope of protection of the present invention is not limited to the specific embodiments below.

(7) Unless otherwise specified, all technical terms used hereinafter have the same meaning as commonly understood by those of the ordinary skills in the art. The terminology used herein is for describing specific embodiments, and is not intended to limit the scope of the present invention.

(8) Unless otherwise specified, all kinds of raw materials, reagents, instruments, equipment, etc. used in the present invention can be purchased commercially or prepared by existing methods.

Embodiment 1

(9) A high-rate lithium cobaltate cathode material mainly consists of lithium cobaltate. The lithium cobaltate cathode material contains a multi-channel network formed by fast ionic conductor Li.sub.2TiO.sub.3, and the lithium cobaltate is melted together with the fast ionic conductor Li.sub.2TiO.sub.3 in the form of primary particles to form secondary particles. The lithium cobaltate is embedded in the multi-channel network formed by the above fast ionic conductor Li.sub.2TiO.sub.3. The chemical formula of the lithium cobaltate cathode material of the present embodiment can be represented by Li.sub.0.99CoO.sub.20.005Li.sub.2TiO.sub.3 and it has a layered structure.

(10) The method for preparing the high-rate lithium cobaltate cathode material of the present embodiment includes the following steps:

(11) (1) A CoCl.sub.2 solution was prepared, the concentration of Co.sup.2+ in the solution was controlled at 110 g/L. The concentrated ammonium hydroxide and distilled water was used to form a complexing agent ammonium hydroxide solution at a volume ratio of 1:10. 1.2 mol/L sodium bicarbonate solution was used for the precipitant solution.

(12) (2) A volume of of the precipitant solution was injected into a 25 L reaction kettle, the pH of the solution was controlled at 6.0 to 8.0. Under the strong agitation and inert gas protection, the CoCl.sub.2 solution above-mentioned, ammonium hydroxide solution and sodium bicarbonate solution were simultaneously injected into the reaction kettle by a parallel flow method to carry out the reaction, and the pH was controlled to be 6.0-8.0 during the stirring reaction, the reaction kettle temperature was controlled at 70 C. to 80 C. After the CoCl.sub.2 solution was completely injected, a filter cake was obtained by aging for 4-8 hours, and then filtration

(13) (3) The filter cake obtained in the above step (2) in an oven at 120 C. for 3 h was dried to obtain cobaltous carbonate (particle size of 5.5 m).

(14) (4) The cobaltous carbonate obtained in the above step (3) was pre-sintered at 400 C. for 3 h, and then sintered at 750 C. for 3 h to obtain porous cobalt oxide (particle size of 5.0 m), numbered PC-1 (see FIG. 2), with the average pore diameter of 100 nm and the porosity of 0.5%.

(15) (5) 42 g of butyl titanate solution was dissolved in 500 g of anhydrous ethanol, and stirred for 0.5 h, 3000 g of porous cobalt oxide PC-1 obtained in the step (4) under vigorous stirring of a disperser was added, stirred for 0.5 h. Then ethanol solution was added, the volume ratio of ethanol to water was 6, and stirred for another 3 h. The filter cake was suction filtered, and dried in an oven to obtain cobalt oxide impregnated with Ti(OH).sub.4, numbered as PC-2 (see FIG. 3).

(16) (6) 920 g of lithium carbonate and 2000 g of cobalt oxide PC-2 obtained in the above step (5) were dry-mixed uniformly to obtain a mixture.

(17) (7) The mixture obtained in the above step (6) in an air atmosphere furnace was sintered at 950 C. for 10 h. After cooling, the universal pulverizer was pulverized for 20 s, and the particle size was controlled at 5.5 to 6.0 m to obtain the high-rate lithium cobaltate cathode material (numbered LCO-1, see FIG. 4).

Embodiment 2

(18) A high-rate lithium cobaltate cathode material mainly consists of lithium cobaltate. The lithium cobaltate cathode material contains a multi-channel network formed by fast ionic conductor Li.sub.2TiO.sub.3, and the lithium cobaltate is melted together with the fast ionic conductor Li.sub.2TiO.sub.3 in the form of primary particles to form secondary particles. The lithium cobaltate is embedded in the multi-channel network formed by the aforementioned fast ionic conductor Li.sub.2TiO.sub.3. The chemical formula of the lithium cobaltate cathode material of the present embodiment can be represented by Li.sub.1.00Co.sub.0.99Mg.sub.0.005Al.sub.0.005O.sub.20.005Li.sub.2TiO.sub.3 and it has a layered structure.

(19) The method for preparing the high-rate lithium cobaltate cathode material of the present embodiment includes the following steps:

(20) (1)-(5): steps (1)-(5) of the present embodiment are the same as those of the embodiment 1.

(21) (6) 936 g of lithium carbonate, 2000 g of cobalt oxide PC-2 obtained in the above embodiment 1, 5 g of magnesium oxide and 6.5 g of aluminium oxide were dry-mixed uniformly to obtain a mixture.

(22) (7) The mixture obtained in the above step (6) was sintered in an air atmosphere furnace at 000 C. for 10 h. After cooling, the universal pulverizer was pulverized for 20 s, and the particle size was controlled at 5.5 to 6.0 m to obtain the high-rate lithium cobaltate cathode material (numbered LCO-2).

Control Embodiment 1

(23) A lithium cobaltate cathode material with a chemical formula of Li.sub.0.99CoO.sub.20.005Li.sub.2TiO.sub.3 has a layered structure, wherein the existing form of Li.sub.2TiO.sub.3 is mainly enriched on the surface of the particles. The preparation method of the lithium cobaltate cathode material of the present control embodiment specifically includes the following steps:

(24) (1) 920 g of lithium carbonate, 2000 g of PC-1 (synthesized in embodiment 1) and 10 g, of titanium dioxide were dry-mixed uniformly to obtain a mixture.

(25) (2) The mixture obtained in the above step (1) was sintered in an air atmosphere furnace at 950 C. for 10 h. After cooling, the universal pulverizer was pulverized for 20 s, and the particle size was controlled at 5.5 to 6.0 m to obtain the lithium cobaltate cathode material (numbered LCO-0).

Embodiment 3

(26) A high-rate lithium cobaltate cathode material mainly consists of lithium cobaltate. The lithium cobaltate cathode material contains a multi-channel network formed by fast ionic conductor LiNbO.sub.3, and the lithium cobaltate is melted together with the fast ionic conductor LiNbO.sub.3 in the form of primary particles to form secondary particles. The lithium cobaltate is embedded in the multi-channel network formed by the aforementioned fast ionic conductor LiNbO.sub.3. The chemical formula of the lithium cobaltate cathode material of the present embodiment can be represented by Li.sub.1.01CoO.sub.20.001LiNbO.sub.3 and it has a layered structure.

(27) The method for preparing the high-rate lithium cobaltate cathode material of the present embodiment includes the following steps:

(28) (1) A CoSO.sub.4 solution was prepared, the concentration of Co.sup.2+ in the solution was controlled at 150 g/L. The concentrated ammonium hydroxide and distilled water was used to form a complexing agent solution at a volume ratio of 1:10. 1.5 mol/L ammonium oxalate solution was used for the precipitant solution.

(29) (2) A volume of of the precipitant solution was injected into a 25 L reaction kettle. Under the strong agitation and inert gas protection, the CoSO.sub.4 solution above-mentioned, ammonium hydroxide solution and ammonium oxalate solution were simultaneously injected into the reaction kettle by a parallel flow method to carry out the reaction, and the pH was controlled to be 6.0-7.0 during the stirring reaction, the reaction kettle temperature was controlled at 25 C. After the CoSO.sub.4 solution was completely injected, a filter cake was obtained by aging: for 4-8 h, and then filtration.

(30) (3) The filter cake obtained in the above step (2) was dried in an oven at 120 C. for 3 h to obtain cobalt oxalate (particle size of 7.5 m).

(31) (4) The cobalt oxalate obtained in the above step (3) was pre-sintered at 300 C. for 2 h, and then sinter at 700 C. for 5 h to obtain porous cobalt oxide (particle size of 6.5 m), numbered PC-3, with the average pore diameter of 500 nm and the porosity of 5%.

(32) (5) 120 g of niobium ethoxide solution was dissolved in 2000 g of anhydrous ethanol, stirred for 0.5 h. 3000 g of porous cobalt oxide PC-3 obtained in the step (4) under vigorous stirring of a disperser was added, stirred for 1.0 h. Then ethanol solution was added, the volume ratio of ethanol to water was 20, and stirred for another 5 h. The cobalt oxide impregnated with Nb(OH).sub.5, numbered as PC-4 was obtained by suction filtration, and drying the filter cake in an oven to obtain.

(33) (6) 938 g of lithium carbonate and 2000 g of cobalt oxide PC-4 which was obtained in the above step (5) were dry-mixed uniformly to obtain a mixture.

(34) (7) The mixture obtained in the above step (6) was sintered in an air atmosphere furnace at 900 C. for 10 h. After cooling, the universal pulverizer was pulverized for 20 s, and the particle size was controlled at 6.5 to 7.0 m to obtain the high-rate lithium cobaltate cathode material, numbered as LCO-3.

Embodiment 4

(35) A high-rate lithium cobaltate cathode material mainly consists of lithium cobaltate. The lithium cobaltate cathode material contains a multi-channel network formed by fast ionic conductor Li.sub.2WO.sub.4, and the lithium cobaltate is melted together with the fast ionic conductor Li.sub.2WO.sub.4 in the form of primary particles to form secondary particles. The lithium cobaltate is embedded in the multi-channel network formed by the aforementioned fast ionic conductor Li.sub.2WO.sub.4. The chemical formula of the lithium cobaltate cathode material of the present embodiment can be represented by Li.sub.1.00CoO.sub.20.008Li.sub.2WO.sub.4 and it has a layered structure.

(36) The method for preparing the high-rate lithium cobaltate cathode material of the present embodiment includes the following steps:

(37) (1) A Co(NO.sub.3).sub.2 solution was prepared, the concentration of Co.sup.2+ in the solution was controlled at 100 g/L. The concentrated ammonium hydroxide and distilled water was used to form a complexing agent solution at a volume ratio of 1:10. 1.5 mol/L ammonium oxalate solution was used for the precipitant solution.

(38) (2) A volume of of the precipitant solution was injected into a 25 L reaction kettle. Under the strong agitation and inert gas protection, the Co(NO.sub.3).sub.2 solution above-mentioned, ammonium hydroxide solution and ammonium oxalate solution were simultaneously injected into the reaction kettle by a parallel flow method to carry out the reaction, and the pH was controlled to be 6.0-7.0 during the stirring reaction, the reaction kettle temperature was controlled at 25 C. After the Co(NO.sub.3).sub.2 solution was completely injected, a filter cake was obtained by aging for 4-8 h, and then filtration.

(39) (3) The filter cake obtained in the above step (2) was dried in an oven at 120 C. for 3 h to obtain cobalt oxalate (particle size of 7.0 m).

(40) (4) The cobalt oxalate obtained in the above step (3) was pre-sintered at 500 C. for 3 h, and then was sintered at 800 C. for 5 h to obtain porous cobalt oxide (particle size of 6.5 m), numbered PC-5, with the average pore diameter of 200 nm and the porosity of 1%. p (5) 135 g of tungsten ethanol solution was dissolved in 2500 g of anhydrous ethanol, stirred for 0.5 h. 3000 g of porous cobalt oxide PC-5 obtained in the step (4) under vigorous stirring of a disperser was added, stirred for 1.5 h. Then ethanol solution was added, the volume ratio of ethanol to water is 15, and stirred for another 4 h. The cobalt oxide impregnated with W(OH).sub.6, numbered as PC-6 was obtained by suction filtration, and drying the filter cake in an oven.

(41) (6) 928 g of lithium carbonate and 2000 g of cobalt oxide PC-6 which was obtained in the above step (5) were dry-mixed an to obtain a mixture.

(42) (7) The mixture obtained in the above step (6) was sintered in an air atmosphere furnace at 1000 C. for 10 h. After cooling, the universal pulverizer was pulverized for 20 s, and the particle size was controlled at 6.5 to 7.0 m to obtain the high-rate lithium cobaltate cathode material, numbered as LCO-4.

(43) The electrochemical properties of the five products obtained in the above Embodiment 1, 2, 3, 4 and control embodiment 1 were tested. The test methods are described below.

(44) Assembly of 063048 type square battery: the active admixture, PVDF and conductive carbon black was mixed in a mass ratio of 95.4:2.5:2.1, then NMP was added and the mixture was stirred to prepare a slurry. The slurry was applied onto an aluminum foil, and dried at 120 C. to obtain a cathode sheet. Then anode sheet, separator, electrolyte, etc were assembled into a 063048 type battery. The charge and discharge performance test of the battery is carried out at room temperature, and the battery is charged by constant current and then constant voltage. When the charge cut-off voltage is 4.2V or 4.35V, using constant current discharge, when the cut-off voltage is 3.0V and the charging current density is 0.5 C, the discharge current density is 0.2 C/1 C/10 C/20 C/50 C.

(45) Table 1. shows the rate performance of the LCO-0/1/2/3/4 tested at different voltages.

(46) TABLE-US-00001 TABLE 1 the rate performance of the LCO-0/1/2/3/4 tested at different voltages. 3.0~4.2 V 3.0~4.35 V Number Test items 0.2 C 1 C 10 C 20 C 50 C 0.2 C 1 C 10 C 20 C 50 C Embodiment 1 Rate 100 99.9 98.5 96.7 88.6 100 95.6 90.1 83.6 72.2 LCO-1 retention (%) plateau 3.805 3.774 3.716 3.585 3.471 3.842 3.795 3.742 3.648 3.498 (V) Embodiment 2 Rate 100 99.7 97.3 94.3 87.2 100 97.6 92.3 87.2 85.7 LCO-2 retention (%) plateau 3.795 3.764 3.700 3.564 3.442 3.821 3.776 3.724 3.619 3.497 (V) control Rate 100 99.6 95.5 84.7 75.1 100 94.1 85.5 64.7 45.1 embodiment retention LCO-0 (%) plateau 3.791 3.752 3.685 3.544 3.427 3.804 3.751 3.642 3.511 3.409 (V) Embodiment 3 Rate 100 99.9 98.5 97.7 91.2 100 94.5 86.5 64.0 55.1 LCO-3 retention (%) plateau 3.875 3.868 3.756 3.685 3.651 3.884 3.761 3.655 3.511 3.509 (V) Embodiment 4 Rate 100 99.9 98.5 97.0 89.6 100 94.9 87.2 64.7 65.1 LCO-4 retention (%) plateau 3.860 3.853 3.716 3.625 3.571 3.870 3.765 3.664 3.521 3.519 (V)

(47) FIG. 1 shows schematic diagram of lithium ion transport during charging of the lithium cobaltate particles of the present invention. The solid line represents the lithium ion transport path in the cathode material particles prepared in the embodiments of the present invention, and the dotted line represents that of the control embodiment. In the process of impregnating porous cobalt oxide with butyl titanate, tetra-n-butyl titanate is hydrolyzed to form Ti(OH).sub.4 which is filled into the gap and micropores inside the porous cobalt oxide particles to form a continuous film on the surface of the impregnated particles. During the sintering process of synthesizing lithium cobaltate, the ionic radius of Ti.sup.4+ is much larger than that of Co.sup.3+. It is not easy to be dissolved into the lithium cobalt oxide crystal structure, but reacts with lithium ions to fibrin a multi-channel network structure Li.sub.2TiO.sub.3 phase. Lithium cobaltate primary particles are embedded in a multi-channel network of fast ionic conductor and with which melted together to form secondary particles.

(48) As seen from Table 1 above, the capacity retention rate and plateau at 50 C rate of LCO-1/2/3/4 prepared by cobalt oxide impregnated with butyl titanate in the 4.2 V test are both significantly higher than in the control embodiment LCO-0. This indicates that the existence of the LCO-1/2/3/4 multi-channel network structure of fast tome conductor greatly increases the lithium ion transmission rate and effectively increases the discharge capacity and plateau of the material. When LCO-2 is tested at 4.35V, the capacity retention rate and plateau at 50 C rate are significantly higher than those of LCO-1, LCO-3 and LCO-4 in the embodiments. This is caused by that for the 4.35V high-voltage material, Mg and Al doping can effectively improve the structural stability of the material, and thus the rate performance at high voltage is excellent.