CN114212833B - Modified lithium cobalt oxide positive electrode material, preparation method thereof, positive electrode plate and secondary battery - Google Patents
Modified lithium cobalt oxide positive electrode material, preparation method thereof, positive electrode plate and secondary battery Download PDFInfo
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- 239000010416 ion conductor Substances 0.000 claims abstract description 39
- WHXSMMKQMYFTQS-UHFFFAOYSA-N Lithium Chemical compound [Li] WHXSMMKQMYFTQS-UHFFFAOYSA-N 0.000 claims abstract description 35
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- 239000000395 magnesium oxide Substances 0.000 claims description 3
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- TWNQGVIAIRXVLR-UHFFFAOYSA-N oxo(oxoalumanyloxy)alumane Chemical group O=[Al]O[Al]=O TWNQGVIAIRXVLR-UHFFFAOYSA-N 0.000 claims description 3
- 239000010406 cathode material Substances 0.000 claims 2
- 238000005562 fading Methods 0.000 abstract description 4
- 230000001133 acceleration Effects 0.000 abstract description 3
- HBBGRARXTFLTSG-UHFFFAOYSA-N Lithium ion Chemical compound [Li+] HBBGRARXTFLTSG-UHFFFAOYSA-N 0.000 description 23
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- 230000000052 comparative effect Effects 0.000 description 11
- 229910000625 lithium cobalt oxide Inorganic materials 0.000 description 9
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- UBEWDCMIDFGDOO-UHFFFAOYSA-N cobalt(II,III) oxide Inorganic materials [O-2].[O-2].[O-2].[O-2].[Co+2].[Co+3].[Co+3] UBEWDCMIDFGDOO-UHFFFAOYSA-N 0.000 description 4
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- NDLPOXTZKUMGOV-UHFFFAOYSA-N oxo(oxoferriooxy)iron hydrate Chemical compound O.O=[Fe]O[Fe]=O NDLPOXTZKUMGOV-UHFFFAOYSA-N 0.000 description 1
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Classifications
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- C—CHEMISTRY; METALLURGY
- C01—INORGANIC CHEMISTRY
- C01G—COMPOUNDS CONTAINING METALS NOT COVERED BY SUBCLASSES C01D OR C01F
- C01G51/00—Compounds of cobalt
- C01G51/40—Cobaltates
- C01G51/42—Cobaltates containing alkali metals, e.g. LiCoO2
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M4/00—Electrodes
- H01M4/02—Electrodes composed of, or comprising, active material
- H01M4/36—Selection of substances as active materials, active masses, active liquids
- H01M4/48—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides
- H01M4/52—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of nickel, cobalt or iron
- H01M4/525—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of nickel, cobalt or iron of mixed oxides or hydroxides containing iron, cobalt or nickel for inserting or intercalating light metals, e.g. LiNiO2, LiCoO2 or LiCoOxFy
-
- C—CHEMISTRY; METALLURGY
- C01—INORGANIC CHEMISTRY
- C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
- C01P2006/00—Physical properties of inorganic compounds
- C01P2006/40—Electric properties
-
- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
- Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
- Y02E60/10—Energy storage using batteries
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- Chemical & Material Sciences (AREA)
- Inorganic Chemistry (AREA)
- Organic Chemistry (AREA)
- Chemical Kinetics & Catalysis (AREA)
- Electrochemistry (AREA)
- General Chemical & Material Sciences (AREA)
- Battery Electrode And Active Subsutance (AREA)
Abstract
The invention provides a modified lithium cobalt oxide positive electrode material and a preparation method thereof, a positive electrode plate and a secondary battery, and the modified lithium cobalt oxide positive electrode material comprises the following steps: firstly, preparing a first premix containing a large-particle cobalt source and a second premix containing a small-particle cobalt source by using a premix; then sintering the first premix and the second premix respectively to obtain a primary sintered first primary material and a primary sintered second primary material; then crushing the first primary material for primary sintering and the second primary material for primary sintering to obtain the first primary material for primary crushing and the second primary material for primary crushing; then mixing and crushing the first primary material for one time, crushing the second primary material for one time, adding a second aluminum source, metal oxide, a fast ion conductor and a coated fluxing agent for mixing, and stirring to obtain a mixture; and finally, carrying out secondary sintering and crushing on the mixture to obtain the modified lithium cobalt oxide anode material. Compared with the prior art, the positive electrode material obtained by the invention overcomes the problems of capacity fading acceleration and unbalanced performance exertion of the conventional lithium cobaltate material in a 4.5V system.
Description
Technical Field
The invention relates to the field of secondary batteries, in particular to a modified lithium cobalt oxide positive electrode material, a preparation method, a positive electrode plate and a secondary battery.
Background
With the rapid development of intelligent equipment, the coming of the 5G era of a new generation mobile communication network, the requirement of electric equipment on the capacity of a lithium ion battery is continuously improved, and the expectations of people on the improvement of the energy density of the lithium ion battery are higher. Increasing the operating voltage is the most direct and efficient way to increase the energy density of the battery, and therefore, developing high voltage positive electrode materials is an important development direction in the industry.
The high energy density and excellent combination property of lithium cobaltate are always the first choice of the positive electrode material of consumer batteries. LCO of 4.45V and 4.48V is mature in the market and is put into use, and development of lithium cobaltate of 4.5V or higher voltage is gradually carried out. However, various problems are also brought about with the increase of the voltage. The operating voltage reached around 4.5V, which is referred to as the self crystal structure of lithium cobaltate, undergoes an O 3→H1-3→O1 phase change. When the charging voltage reaches 4.55V, the phase change of the crystal structure is irreversible, and lithium ions in the lithium cobaltate cannot be intercalated into the original layered structure, so that the reversible capacity of the lithium battery is reduced. The main embodiments are as follows: 1) The phase transition kinetics becomes worse, resulting in an increase in internal resistance at high potential; 2) The structure is changed greatly, and the structure of O 3 disappears; 3) Cell parameters expand and contract severely; 4) The slipping phase transition is not fully reversible resulting in capacity voltage decay. The macroscopic appearance of the giant cell parameters causes the volume of the material particles to expand and contract, and the change of the particles causes the electrode material to change so as to lead the cell to decay.
Therefore, in order to solve the practical application of the high-voltage lithium cobaltate, the design and regulation of the material end are required to be carried out on the phase change process in the high-voltage region, so that the cycle reversibility of the material end is enhanced, and other performances such as gram capacity and low-temperature exertion are ensured.
Disclosure of Invention
The invention aims to provide a preparation method of a modified lithium cobalt oxide positive electrode material, which is used for designing and regulating a material end in a phase change process in a high-voltage region so as to solve the problems of capacity fading acceleration and unbalanced performance of the existing lithium cobalt oxide high-voltage system.
In order to achieve the above purpose, the present invention adopts the following technical scheme:
the preparation method of the modified lithium cobalt oxide positive electrode material comprises the following steps:
S1, preparing premix: s11) premixing a lithium source, a first cobalt source, a first aluminum source, an additive and a solvent, and vacuum drying after premixing to obtain a first premix; s12) premixing a lithium source, a second cobalt source, a first aluminum source, an additive and a solvent, and vacuum drying after premixing to obtain a second premix; wherein the particle size of the second cobalt source is smaller than the particle size of the first cobalt source;
s2, primary sintering: sintering the first premix to obtain a primary sintered first primary material; sintering the second premix to obtain a primary sintered second primary material;
S3, primary crushing: crushing the primary sintered first primary material for 5-7 hours to obtain a primary crushed first primary material; crushing the primary sintered second primary material for 3-5 hours to obtain a primary crushed second primary material;
S4, mixing: mixing the primary crushing first primary material and the primary crushing second primary material according to the mass ratio of 9:1-6:4, adding a second aluminum source, a metal oxide, a fast ion conductor and a coating fluxing agent, mixing, and stirring to obtain a mixture;
s5, secondary sintering and crushing: raising the temperature of the mixture to 850-950 ℃ at a heating rate of 4-6 ℃/min, and sintering for 8-12 h; and cooling and annealing after sintering, and crushing for 3-5 hours to obtain the modified lithium cobalt oxide anode material.
Preferably, in the step S1, the first cobalt source and the second cobalt source both contain 5000-7000 ppm of aluminum; the additive is Mg (NO 3)2), and the solvent is isopropanol.
Preferably, in step S11, the aluminum content in the first aluminum source is 0.01 to 1% of the sum of the lithium content in the lithium source and the cobalt content in the first cobalt source; in step S12, the aluminum content in the aluminum source is 0.01 to 1% of the sum of the lithium content in the lithium source and the cobalt content in the second cobalt source.
Preferably, in step S11 and step S12, the stoichiometric ratio of Li: co: al element is 1.05:0.993: (0.0004 to 0.01).
Preferably, in step S1, the premixing process of the premix is as follows: mixing for 5-7 h at the rotating speed of 250-350 r/min, and then vacuum drying for 10-14 h at the temperature of 70-90 ℃ to obtain a first premix and a second premix respectively.
Preferably, in step S2, a sintering process of the first premix is as follows: sintering for 2-4 h at a heating rate of 2-4 ℃/min, then maintaining at 500-600 ℃ for 2-4 h, then sintering for 5-8 h at a heating rate of 1-2 ℃/min, then maintaining at 1000-1200 ℃ for 11-13 h, and cooling and annealing after sintering to obtain the primary sintered first primary material.
Preferably, in step S2, the primary sintering process of the second premix is as follows: sintering for 5-7 h at a heating rate of 2-4 ℃/min, then maintaining at 500-600 ℃ for 2-4 h, then sintering for 5-8 h at a heating rate of 1-2 ℃/min, then maintaining at 1000-1200 ℃ for 11-13 h, and cooling and annealing after sintering to obtain the primary sintered second primary material.
Preferably, in step S4, the second aluminum source is aluminum oxide; the metal oxide is any one of titanium dioxide, magnesium oxide and ferric oxide; the fast ion conductor is lanthanum lithium zirconate; the coating fluxing agent is LiF.
Preferably, in the step S4, the content of the second aluminum source is 400-600 ppm; the content of the metal oxide is 600-800 ppm; the content of the fast ion conductor is 20-2000 ppm; the coating fluxing agent is 700-900 ppm.
Preferably, in the step S4, the stirring speed is 1000-1400 rpm/min, and the stirring time is 6h.
The second object of the present invention is to provide a modified lithium cobalt oxide positive electrode material prepared by the method for preparing a modified lithium cobalt oxide positive electrode material according to any one of the above.
The third object of the present invention is to provide a positive electrode sheet comprising the modified lithium cobalt oxide positive electrode material.
The fourth object of the invention is to provide a secondary battery, comprising a positive plate, a negative plate and a diaphragm arranged between the positive plate and the negative plate, wherein the positive plate is the positive plate.
Compared with the prior art, the invention has the beneficial effects that: according to the preparation method provided by the invention, the modified lithium cobalt oxide anode material with good low-temperature performance and excellent high-temperature cycle performance can be obtained by adopting the method of gradient doping of the Al element and coating a layer of fast ion conductor on the surface of the composite material. Compared with the one-time addition of Al element, the gradient doping and cladding design of the Al element has better improvement on the bulk phase structure of the lithium cobaltate, and is beneficial to the improvement of the high-temperature cycle performance; the fast ion conductor is used as a coating layer, so that the ion embedding and extracting rate can be further improved, the polarization is reduced, the low-temperature charge and discharge performance and the cycle performance of the material are obviously improved, and meanwhile, the material has the advantage of gram capacity. Therefore, the modified lithium cobalt oxide anode material overcomes the problems of capacity fading acceleration and unbalanced performance exertion of the conventional lithium cobalt oxide material in a 4.5V system, and further improves the energy density of the whole secondary battery.
Detailed Description
The first aspect of the invention provides a preparation method of a modified lithium cobalt oxide positive electrode material, which comprises the following steps:
s1, preparing premix: s11) premixing a lithium source, a first cobalt source, a first aluminum source, an additive and a solvent, and vacuum drying after premixing to obtain a first premix; s12) premixing a lithium source, a second cobalt source, a first aluminum source, an additive and a solvent, and vacuum drying after premixing to obtain a second premix; the particle size of the second cobalt source is smaller than that of the first cobalt source, namely the first cobalt source is a large-particle cobalt source, and the second cobalt source is a small-particle cobalt source;
s2, primary sintering: sintering the first premix to obtain a primary sintered first primary material; sintering the second premix to obtain a primary sintered second primary material;
S3, primary crushing: crushing the primary sintered first primary material for 5-7 hours to obtain a primary crushed first primary material; crushing the primary sintered second primary material for 3-5 hours to obtain a primary crushed second primary material;
S4, mixing: mixing the primary crushing first primary material and the primary crushing second primary material according to the mass ratio of 9:1-6:4, adding a second aluminum source, a metal oxide, a fast ion conductor and a coating fluxing agent, mixing, and stirring to obtain a mixture;
s5, secondary sintering and crushing: raising the temperature of the mixture to 850-950 ℃ at a heating rate of 4-6 ℃/min, and sintering for 8-12 h; and cooling and annealing after sintering, and crushing for 3-5 hours to obtain the modified lithium cobalt oxide anode material.
In some embodiments, in step S1, the first cobalt source and the second cobalt source both contain 5000-7000 ppm of aluminum; the additive is Mg (NO 3)2), and the solvent is isopropanol.
Specifically, the lithium source can be Li 2CO3, the first cobalt source and the second cobalt source are Co 3O4 containing 5000-7000 ppm of aluminum, the first aluminum source is (Al (NO 3)3)·9H2 O). After premixing, the aluminum source is mainly volatilized isopropanol and moisture in vacuum drying, and the additive of Mg (NO 3)2 is helpful for uniform dispersion of the premix on one hand, and on the other hand, magnesium ions also assist Al elements to ensure the crystal structure of lithium cobaltate.
The preparation is carried out by adopting an aluminum-containing cobalt source, namely, aluminum is added as three gradients, wherein the first aluminum is an aluminum-containing cobalt source, the second aluminum is a first aluminum source added into the premix, and the third aluminum is a second aluminum source added into the compound. The ionic radius of the Al element is similar to Co 3+, so that LiCo 1-xAlxO2 can be formed in a certain range without causing the change of the crystal structure of lithium cobaltate, and on one hand, the open circuit voltage and the ionic diffusion coefficient of the material can be improved; in addition, the Al element has the characteristics of rich resources, low price and no pollution. According to the invention, the stability of the bulk phase structure of the lithium cobaltate material can be effectively improved by doping Al element in a gradient way, so that the cycle performance of the lithium cobaltate material under a high-voltage system is ensured.
Preferably, in step S11, the aluminum content in the first aluminum source is 0.01 to 1% of the sum of the lithium content in the lithium source and the cobalt content in the first cobalt source; in step S12, the aluminum content in the aluminum source is 0.01 to 1% of the sum of the lithium content in the lithium source and the cobalt content in the second cobalt source.
More preferably, in both step S11 and step S12, the stoichiometric ratio of Li: co: al element is 1.05:0.993: (0.0004 to 0.01). Further preferably, the stoichiometric ratio of Li to Co to Al element is 1.05:0.993:0.001. the lithium content is added in 5% excess to compensate for lithium loss during subsequent high temperature sintering.
In some embodiments, in step S1, the premix premixing process is: mixing for 5-7 h at the rotating speed of 250-350 r/min, and then vacuum drying for 10-14 h at the temperature of 70-90 ℃ to obtain a first premix and a second premix respectively. Preferably, the premixing process of the premix comprises the following steps: mixing for 6 hours at the rotating speed of 300r/min, and then vacuum drying for 12 hours at 80 ℃ to volatilize the solvent and the water to obtain a first premix and a second premix respectively.
In some embodiments, in step S2, the primary sintering process of the first premix is: sintering for 2-4 h at a heating rate of 2-4 ℃/min, then maintaining at 500-600 ℃ for 2-4 h, then sintering for 5-8 h at a heating rate of 1-2 ℃/min, then maintaining at 1000-1200 ℃ for 11-13 h, and cooling and annealing after sintering to obtain the primary sintered first primary material. Preferably, the primary sintering process of the first premix comprises the following steps: sintering for 3 hours at a heating rate of 3 ℃/min, then maintaining at 500-600 ℃ for 2 hours, then sintering for 6 hours at a heating rate of 1.5 ℃/min, then maintaining at 1000-1200 ℃ for 11-13 hours, and annealing at a cooling rate of 1.5 ℃/min after sintering to obtain the primary sintered first primary material.
In some embodiments, in step S2, the primary sintering process of the second premix is: sintering for 5-7 h at a heating rate of 2-4 ℃/min, then maintaining at 500-600 ℃ for 2-4 h, then sintering for 5-8 h at a heating rate of 1-2 ℃/min, then maintaining at 1000-1200 ℃ for 11-13 h, and cooling and annealing after sintering to obtain the primary sintered second primary material. Preferably, the primary sintering process of the second premix comprises the following steps: sintering for 6h at a heating rate of 3 ℃/min, then maintaining at 500-600 ℃ for 2h, then sintering for 6h at a heating rate of 1.5 ℃/min, then maintaining at 1000-1200 ℃ for 11-13 h, and annealing at a cooling rate of 1.5 ℃/min after sintering to obtain a primary sintered second primary material.
In some embodiments, in step S4, the mass ratio of the primary crushed first primary material to the primary crushed second primary material is 8:2.
In some embodiments, in step S4, the second aluminum source is aluminum oxide; the second aluminum source does not contain crystal water, and is directly added for carrying out the third Al doping so as to better ensure the bulk phase structure of the lithium cobaltate material.
In some embodiments, in step S4, the metal oxide is any one of titanium dioxide, magnesium oxide, and iron oxide. Preferably, the metal oxide is titanium dioxide.
In some embodiments, in step S4, the fast ion conductor is Lithium Lanthanum Zirconate (LLZO); the LLZO fast ion conductor is used as a coating layer, so that the lithium ion intercalation and deintercalation rate can be further improved, the polarization is reduced, and the low-temperature charge and discharge performance and the cycle performance of the material are remarkably improved. In addition, the lithium cobalt oxide positive electrode material has the advantage of gram capacity exertion, and the full-electric gram capacity exertion of the lithium cobalt oxide positive electrode material without LLZO coating is different by 3-5 mAh/g.
In some embodiments, in step S4, the clad flux is LiF.
In some embodiments, in step S4, the second aluminum source is present in an amount of 400 to 600ppm; the content of the metal oxide is 600-800 ppm; the content of the fast ion conductor is 20-2000 ppm; the coating fluxing agent is 700-900 ppm.
In some embodiments, in step S4, the stirring rate is 1000 to 1400rpm/min and the stirring time is 6 hours.
In some embodiments, in step S5, the secondary sintering and crushing process is: raising the temperature of the mixture to 850-950 ℃ at a heating rate of 5 ℃/min, and sintering for 10h; and (3) annealing at a cooling rate of 3 ℃/min after sintering, cooling to room temperature, and crushing for 3-5 h to obtain the doped and coated modified lithium cobalt oxide anode material.
The second aspect of the invention provides a modified lithium cobalt oxide positive electrode material prepared by the preparation method of the modified lithium cobalt oxide positive electrode material.
The third aspect of the invention provides a positive electrode sheet comprising the modified lithium cobalt oxide positive electrode material.
The fourth aspect of the present invention provides a secondary battery, comprising a positive plate, a negative plate and a separator spaced between the positive plate and the negative plate, wherein the positive plate is the positive plate.
In order to make the technical solution and advantages of the present invention more apparent, the present invention and its advantageous effects will be described in further detail below with reference to the specific embodiments, but the embodiments of the present invention are not limited thereto.
Example 1
The preparation method of the modified lithium cobalt oxide positive electrode material comprises the following steps:
s1, preparing premix:
S11) selecting a large-particle precursor Co 3O4 with the precursor Al content of 6000ppm for sintering experiments, wherein Li 2CO3、Co3O4、(Al(NO3)3)·9H2) is prepared according to the following steps of: 0.993:0.001 mixing, namely adding 1200ppm of Mg (NO 3)2 additive into isopropanol serving as a solvent, premixing in an inclined mixer at the rotating speed of 300r/min for 6 hours, and drying overnight under vacuum at 80 ℃ for 12 hours after premixing to obtain a first premix;
S12) selecting a small particle precursor Co 3O4 with the precursor Al content of 6000ppm for sintering experiments, wherein Li 2CO3、Co3O4、(Al(NO3)3)·9H2) is prepared according to the following steps of: 0.993:0.001 mixing, namely adding 1200ppm of Mg (NO 3)2 additive into isopropanol serving as a solvent, premixing in an inclined mixer at the rotating speed of 300r/min for 6 hours, and drying overnight under vacuum at 80 ℃ for 12 hours after premixing to obtain a second premix;
S2, primary sintering:
s21) transferring the large-particle first premix obtained in the step S11 into a muffle furnace for sintering, wherein the sintering is carried out for 3 hours at a heating rate of 3 ℃/min, then the sintering is carried out for 2 hours at 500-600 ℃, then the sintering is carried out for 6 hours at a heating rate of 1.5 ℃/min, then the sintering is carried out for 11-13 hours at 1050+/-30 ℃, and the annealing is carried out at a cooling rate of 1.5 ℃/min after the sintering, so as to obtain a primary sintered first primary material;
s22) transferring the small-particle second premix obtained in the step S12 into a muffle furnace for sintering, firstly sintering for 6 hours at a heating rate of 3 ℃/min, then sintering for 2 hours at 500-600 ℃, then sintering for 6 hours at a heating rate of 1.5 ℃/min, then sintering for 11-13 hours at 1050+/-30 ℃, and annealing at a cooling rate of 1.5 ℃/min after sintering to obtain a primary sintered second primary material;
S3, primary crushing: crushing the primary sintered first primary material for 5-7 hours to obtain a primary crushed first primary material; crushing the primary sintered second primary material for 3-5 hours to obtain a primary crushed second primary material;
S4, mixing: mixing the primary crushing first primary material and the primary crushing second primary material according to the mass ratio of 8:2, adding 200ppm LLZO (lithium lanthanum zirconate) fast ion conductor, 700ppmTiO 2、500ppmAl2O3 and 800ppmLiF, mixing, and stirring for 6 hours at 1000-1400 rpm/min to obtain a mixture;
S5, secondary sintering and crushing: raising the temperature of the mixture to 900+/-30 ℃ at the heating rate of 5 ℃/min, and sintering for 10 hours; and (3) annealing at a cooling rate of 3 ℃/min after sintering, cooling to room temperature, and crushing for 4 hours to obtain the modified lithium cobalt oxide anode material.
The modified lithium cobalt oxide anode material is applied to an anode plate.
The preparation method of the positive plate comprises the following steps: the modified lithium cobaltate, conductive agent superconducting carbon (Super-P), conductive agent carbon tube (LB 101) and binder polyvinylidene fluoride (PVDF) are mixed according to the mass ratio of 97.6:0.6:0.5:1.3, uniformly mixing to prepare lithium ion battery anode slurry with certain viscosity, coating the slurry on a current collector aluminum foil, drying at 85 ℃ and then cold pressing; then trimming, cutting pieces, splitting, drying at 110 ℃ for 4 hours under vacuum condition after splitting, and welding the tab to prepare the lithium ion battery positive plate.
And applying the positive plate of the lithium ion battery to the lithium ion battery.
The lithium ion battery comprises a positive plate, a negative plate, a diaphragm and electrolyte, wherein the diaphragm and the electrolyte are arranged between the positive plate and the negative plate at intervals.
The preparation method of the negative plate comprises the following steps: the graphite, super-conductive carbon (Super-P), sodium carboxymethyl cellulose (CMC) as a thickener and Styrene Butadiene Rubber (SBR) as a binder are mixed according to the mass ratio of 97.7:1.1:1.2 preparing slurry, coating the slurry on a current collector copper foil, drying at 85 ℃, trimming, cutting pieces, splitting, drying at 110 ℃ for 4 hours under vacuum after splitting, and welding tabs to prepare the lithium ion battery negative plate.
The separator was an 8 μm oil-based separator.
The preparation method of the electrolyte comprises the following steps: lithium hexafluorophosphate (LiPF 6) was dissolved in a mixed solvent composed of Ethylene Carbonate (EC), dimethyl carbonate (DMC) and Ethyl Methyl Carbonate (EMC) (mass ratio of the three was 1; 2:1), to obtain an electrolyte with a concentration of 1 mol/L.
Preparation of a lithium ion battery: winding the positive plate, the diaphragm and the negative plate into a battery cell, wherein the diaphragm is positioned between the positive plate and the negative plate, the positive electrode is led out by spot welding of an aluminum tab, and the negative electrode is led out by spot welding of a nickel tab; and then placing the battery core in an aluminum-plastic packaging bag, injecting the electrolyte, and performing procedures such as packaging, formation, capacity and the like to prepare the lithium ion battery.
Example 2
Unlike example 1, which is the content of the fast ion conductor in the preparation step S4 of the modified lithium cobalt oxide positive electrode material, 400ppm of LLZO (lanthanum lithium zirconate) fast ion conductor was added.
The remainder is the same as embodiment 1 and will not be described here again.
Example 3
Unlike example 1, which is the addition of 600ppm LLZO (lanthanum lithium zirconate) fast ion conductor, the content of fast ion conductor in the preparation step S4 of the modified lithium cobalt oxide positive electrode material.
The remainder is the same as embodiment 1 and will not be described here again.
Example 4
Unlike example 1, which is the addition of 800ppm LLZO (lanthanum lithium zirconate) fast ion conductor, the content of fast ion conductor in the preparation step S4 of the modified lithium cobalt oxide positive electrode material.
The remainder is the same as embodiment 1 and will not be described here again.
Example 5
Unlike example 1, which is the addition of 1000ppm LLZO (lanthanum lithium zirconate) fast ion conductor, the content of fast ion conductor in the preparation step S4 of the modified lithium cobalt oxide positive electrode material.
The remainder is the same as embodiment 1 and will not be described here again.
Example 6
Unlike example 1, which is the content of the fast ion conductor in the preparation step S4 of the modified lithium cobalt oxide positive electrode material, 1200ppm of LLZO (lanthanum lithium zirconate) fast ion conductor was added.
The remainder is the same as embodiment 1 and will not be described here again.
Example 7
Unlike example 1, which is to add 1400ppm of LLZO (lanthanum lithium zirconate) fast ion conductor, the content of fast ion conductor in the preparation step S4 of the modified lithium cobalt oxide positive electrode material.
The remainder is the same as embodiment 1 and will not be described here again.
Example 8
Unlike example 1, which is the addition of 1600ppm of LLZO (lanthanum lithium zirconate) fast ion conductor, the content of fast ion conductor in the preparation step S4 of the modified lithium cobalt oxide positive electrode material.
The remainder is the same as embodiment 1 and will not be described here again.
Example 9
Unlike example 1, which is the addition of 1800ppm LLZO (lanthanum lithium zirconate) fast ion conductor, the content of fast ion conductor in the preparation step S4 of the modified lithium cobalt oxide positive electrode material.
The remainder is the same as embodiment 1 and will not be described here again.
Example 10
Unlike example 1, which is the addition of 2000ppm LLZO (lanthanum lithium zirconate) fast ion conductor, the content of fast ion conductor in the preparation step S4 of the modified lithium cobalt oxide positive electrode material.
The remainder is the same as embodiment 1 and will not be described here again.
Comparative example 1
Unlike example 1, the content of the fast ion conductor in the preparation step S4 of the modified lithium cobalt oxide positive electrode material was different, and the fast ion conductor was not added in this example.
The remainder is the same as embodiment 1 and will not be described here again.
Comparative example 2
Unlike example 1, the second aluminum source was not added in the preparation step S4 of the modified lithium cobalt oxide positive electrode material, and the aluminum source was added at one time when it was a premix.
The remainder is the same as embodiment 1 and will not be described here again.
Comparative example 3
The preparation of a modified lithium cobalt oxide positive electrode material was different from example 1.
S1, selecting a precursor Co 3O4 with a precursor Al content of 6000ppm for a sintering experiment, and carrying out a Li 2CO3、Co3O4、(Al(NO3)3)·9H2) according to the stoichiometric ratio of Li to Co to Al of 1.05:0.993:0.001 mixing, adding 1200ppm Mg (NO 3)2 dispersant) into isopropanol as solvent, premixing in an inclined mixer at 300r/min for 6 hr, and vacuum drying at 80deg.C for 12 hr to obtain premix;
S2, transferring the obtained premix into a muffle furnace for sintering, firstly sintering for 3 hours at a heating rate of 3 ℃/min, then maintaining at 500-600 ℃ for sintering for 2 hours, then sintering for 6 hours at a heating rate of 1.5 ℃/min, then maintaining at 1050+/-30 ℃ for sintering for 11-13 hours, annealing at a cooling rate of 1.5 ℃/min, and crushing to obtain a primary material;
s3, mixing the initial material with 200ppm LLZO (lithium lanthanum zirconate) fast ion conductor, 700ppmTiO 2、500ppmAl2O3 and 800ppmLiF, and stirring for 6 hours at 1000-1400 rpm/min to obtain a mixture;
S4, heating the mixture to 900+/-30 ℃ at a heating rate of 5 ℃/min, and sintering for 10 hours; and (3) annealing at a cooling rate of 3 ℃/min after sintering, cooling to room temperature, and crushing for 4 hours to obtain the modified lithium cobalt oxide anode material.
The remainder is the same as embodiment 1 and will not be described here again.
Comparative example 4
The preparation of a modified lithium cobalt oxide positive electrode material was different from example 1.
S1, selecting a precursor Co 3O4 with a precursor Al content of 6000ppm for a sintering experiment, and carrying out a Li 2CO3、Co3O4、(Al(NO3)3)·9H2) according to the stoichiometric ratio of Li to Co to Al of 1.05:0.993:0.001 mixing, adding 1200ppm Mg (NO 3)2 dispersant) into isopropanol as solvent, premixing in an inclined mixer at 300r/min for 6 hr, and vacuum drying at 80deg.C for 12 hr to obtain premix;
S2, transferring the obtained premix into a muffle furnace for sintering, firstly sintering for 3 hours at a heating rate of 3 ℃/min, then maintaining at 500-600 ℃ for sintering for 2 hours, then sintering for 6 hours at a heating rate of 1.5 ℃/min, then maintaining at 1050+/-30 ℃ for sintering for 11-13 hours, annealing at a cooling rate of 1.5 ℃/min, and crushing to obtain a primary material;
s3, mixing the initial material with 200ppm LLZO (lithium lanthanum zirconate) fast ion conductor and 800ppmLiF, and stirring at 1000-1400 rpm/min for 6h to obtain a mixture;
S4, heating the mixture to 900+/-30 ℃ at a heating rate of 5 ℃/min, and sintering for 10 hours; and (3) annealing at a cooling rate of 3 ℃/min after sintering, cooling to room temperature, and crushing for 4 hours to obtain the modified lithium cobalt oxide anode material.
The positive electrode sheets and lithium ion batteries obtained in examples 1 to 10 and comparative examples 1 to 4 were subjected to performance tests.
1) Gram capacity and first efficiency test of positive electrode material: and taking the prepared positive plate as a positive electrode, weighing and recording the mass of the active material, and taking the lithium plate as a negative electrode to manufacture at least three 2025 button cells. The cell was placed in a thermostatic chamber at 25℃and allowed to stand for 12h. The standing button cell was charged to a voltage of 4.48V at a constant current of 0.2C, then charged to a current of 0.05C at a constant voltage of 4.48V, and then discharged to a voltage of 3.0V at a constant current of 0.2C, which is a charge-discharge cycle. Gram capacity and first efficiency are respectively based on the average value of three batteries.
Gram capacity = discharge capacity/active weight
First efficiency = discharge capacity/charge capacity 100%
2) And (3) testing the cycle performance of the lithium ion battery: and respectively placing the lithium ion batteries in a constant temperature chamber at 25 ℃, and standing for 30 minutes to enable the lithium ion batteries to reach constant temperature. The lithium ion battery which reaches the constant temperature is charged to a voltage of 4.50V at a constant current of 0.5C, then charged to a current of 0.05C at a constant voltage of 4.50V, and then discharged to a voltage of 3.0V at a constant current of 0.5C, which is a charge-discharge cycle. And repeating the charge and discharge, and respectively calculating the capacity retention rate of the lithium ion battery for 300 times.
The test results are shown in Table 1 below.
TABLE 1
| Numbering device | Gram capacity (mAh/g) | First time efficiency (%) | 300 Cycles at 25℃retention/% |
| Example 1 | 186.53 | 94.03％ | 67.9％ |
| Example 2 | 186.65 | 93.89％ | 68.3％ |
| Example 3 | 187.14 | 93.97％ | 71.9％ |
| Example 4 | 187.53 | 94.00％ | 72.4％ |
| Example 5 | 187.72 | 94.14％ | 72.7％ |
| Example 6 | 187.83 | 93.6％ | 70.2％ |
| Example 7 | 188.57 | 93.7％ | 69.4％ |
| Example 8 | 187.98 | 93.9％ | 68.3％ |
| Example 9 | 187.54 | 93.76％ | 67.6％ |
| Example 10 | 186.73 | 93.86％ | 67.5％ |
| Comparative example 1 | 183.23 | 92.66％ | 60.3％ |
| Comparative example 2 | 186.76 | 91.44％ | 53.3％ |
| Comparative example 3 | 185.64 | 88.65％ | 59.47％ |
| Comparative example 4 | 185.47 | 90.48％ | 49.57％ |
As can be seen from the comparison between the embodiment 1 and the comparative examples 2 to 4, the preparation method of doping Al elements by adopting the mixture of the large and small particles can effectively improve the cycle performance of the lithium ion battery, mainly because the Al elements can improve the open-circuit voltage and the ion diffusion coefficient of the material, and the special mode of doping Al by adopting the distribution gradient can effectively improve the bulk phase structural stability of the lithium cobalt oxide in a high-voltage system, thereby effectively improving the cycle performance of the lithium ion battery.
In addition, as can be seen from the comparison of examples 1 to 10 and comparative example 1, the cycle performance of the lithium ion battery is increased along with the increase of the content of the fast ion conductor, mainly because the fast ion conductor can better coat the lithium cobalt oxide modified by the Al element at a large content, so as to ensure the stability of the lithium cobalt oxide and increase the rate of intercalation and deintercalation of lithium ions, and further improve the cycle performance. However, with too high a content of fast ion conductor, the cycle performance of lithium ion batteries tends to decrease, because the output of ions is hindered from affecting the performance of lithium cobalt oxide when the package is too thick.
In conclusion, the modified lithium cobalt oxide positive electrode material obtained by the preparation method provided by the invention overcomes the problems of accelerated capacity fading and unbalanced performance exertion of the conventional lithium cobalt oxide material in a 4.5V system, and effectively improves the first efficiency and the cycle performance of the battery.
Variations and modifications of the above embodiments will occur to those skilled in the art to which the invention pertains from the foregoing disclosure and teachings. Therefore, the present invention is not limited to the above-described embodiments, but is intended to be capable of modification, substitution or variation in light thereof, which will be apparent to those skilled in the art in light of the present teachings. In addition, although specific terms are used in the present specification, these terms are for convenience of description only and do not limit the present invention in any way.
Claims (13)
1. The preparation method of the modified lithium cobalt oxide positive electrode material is characterized by comprising the following steps of:
S1, preparing premix: s11) premixing a lithium source, a first cobalt source, a first aluminum source, an additive and a solvent, and vacuum drying after premixing to obtain a first premix; s12) premixing a lithium source, a second cobalt source, a first aluminum source, an additive and a solvent, and vacuum drying after premixing to obtain a second premix; wherein the particle size of the second cobalt source is smaller than that of the first cobalt source, the first cobalt source and the second cobalt source both contain 5000-7000 ppm of aluminum, and the additives in S11 and S12 are Mg (NO 3 )2;
s2, primary sintering: sintering the first premix to obtain a primary sintered first primary material; sintering the second premix to obtain a primary sintered second primary material;
S3, primary crushing: crushing the primary sintered first primary material for 5-7 hours to obtain a primary crushed first primary material; crushing the primary sintered second primary material for 3-5 hours to obtain a primary crushed second primary material;
S4, mixing: mixing the primary crushing first primary material and the primary crushing second primary material according to the mass ratio of 9:1-6:4, adding a second aluminum source, a metal oxide, a fast ion conductor and a coating fluxing agent, mixing, stirring to obtain a mixture, wherein the fast ion conductor is lanthanum lithium zirconate, the content of the second aluminum source is 400-600ppm, and the second aluminum source is aluminum oxide;
s5, secondary sintering and crushing: raising the temperature of the mixture to 850-950 ℃ at a heating rate of 4-6 ℃/min, and sintering for 8-12 h; and cooling and annealing after sintering, and crushing for 3-5 hours to obtain the modified lithium cobalt oxide anode material.
2. The method for preparing a modified lithium cobalt oxide positive electrode material according to claim 1, wherein in step S1, the solvents are isopropyl alcohol.
3. The method for producing a modified lithium cobalt oxide positive electrode material according to claim 1, wherein in step S11, the aluminum content in the first aluminum source is 0.01 to 1% of the sum of the lithium content in the lithium source and the cobalt content in the first cobalt source; in step S12, the aluminum content in the aluminum source is 0.01 to 1% of the sum of the lithium content in the lithium source and the cobalt content in the second cobalt source.
4. The method for producing a modified lithium cobalt oxide positive electrode material according to claim 3, wherein in step S11 and step S12, the stoichiometric ratio of Li: co: al element is 1.05: 0.993: (0.0004 to 0.01).
5. The method for preparing a modified lithium cobalt oxide positive electrode material according to any one of claims 1 to 4, wherein in step S1, the premix premixing process is as follows: mixing for 5-7 h at the rotating speed of 250-350 r/min, and then vacuum drying for 10-14 h at the temperature of 70-90 ℃ to obtain a first premix and a second premix respectively.
6. The method for preparing a modified lithium cobaltate cathode material according to claim 1, wherein in step S2, the primary sintering process of the first premix is: sintering for 2-4 h at a heating rate of 2-4 ℃/min, then maintaining at 500-600 ℃ for 2-4 h, then sintering for 5-8 h at a heating rate of 1-2 ℃/min, then maintaining at 1000-1200 ℃ for 11-13 h, and cooling and annealing after sintering to obtain the primary sintered first primary material.
7. The method for preparing a modified lithium cobaltate cathode material according to claim 1, wherein in step S2, the primary sintering process of the second premix is: sintering for 5-7 h at a heating rate of 2-4 ℃/min, then maintaining at 500-600 ℃ for 2-4 h, then sintering for 5-8 h at a heating rate of 1-2 ℃/min, then maintaining at 1000-1200 ℃ for 11-13 h, and cooling and annealing after sintering to obtain the primary sintered second primary material.
8. The method for preparing a modified lithium cobalt oxide positive electrode material according to claim 1, wherein in the step S4, the metal oxide is any one of titanium dioxide, magnesium oxide and iron oxide; the coating fluxing agent is LiF.
9. The method for producing a modified lithium cobalt oxide positive electrode material according to claim 8, wherein in step S4, the content of the metal oxide is 600 to 800ppm; the content of the fast ion conductor is 20-2000 ppm; the coating fluxing agent is 700-900 ppm.
10. The method for producing a modified lithium cobaltate positive electrode material according to claim 9, wherein in the step S4, the stirring rate is 1000 to 1400rpm/min and the stirring time is 6 hours.
11. A modified lithium cobalt oxide positive electrode material prepared by the method for preparing a modified lithium cobalt oxide positive electrode material according to any one of claims 1 to 10.
12. A positive electrode sheet comprising the modified lithium cobalt oxide positive electrode material of claim 11.
13. A secondary battery comprising a positive electrode sheet, a negative electrode sheet, and a separator interposed between the positive electrode sheet and the negative electrode sheet, wherein the positive electrode sheet is the positive electrode sheet of claim 12.
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