CN117954607A - Positive electrode material and preparation method thereof - Google Patents
Positive electrode material and preparation method thereof Download PDFInfo
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- CN117954607A CN117954607A CN202410157849.3A CN202410157849A CN117954607A CN 117954607 A CN117954607 A CN 117954607A CN 202410157849 A CN202410157849 A CN 202410157849A CN 117954607 A CN117954607 A CN 117954607A
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- 239000007774 positive electrode material Substances 0.000 title claims abstract description 70
- 238000002360 preparation method Methods 0.000 title abstract description 29
- WHXSMMKQMYFTQS-UHFFFAOYSA-N Lithium Chemical compound [Li] WHXSMMKQMYFTQS-UHFFFAOYSA-N 0.000 claims abstract description 62
- 229910052744 lithium Inorganic materials 0.000 claims abstract description 62
- 229910052720 vanadium Inorganic materials 0.000 claims abstract description 61
- LEONUFNNVUYDNQ-UHFFFAOYSA-N vanadium atom Chemical group [V] LEONUFNNVUYDNQ-UHFFFAOYSA-N 0.000 claims abstract description 61
- WSMQKESQZFQMFW-UHFFFAOYSA-N 5-methyl-pyrazole-3-carboxylic acid Chemical group CC1=CC(C(O)=O)=NN1 WSMQKESQZFQMFW-UHFFFAOYSA-N 0.000 claims abstract description 49
- 238000000034 method Methods 0.000 claims abstract description 34
- 239000011248 coating agent Substances 0.000 claims abstract description 25
- 238000000576 coating method Methods 0.000 claims abstract description 25
- 239000011247 coating layer Substances 0.000 claims abstract description 20
- 229910000625 lithium cobalt oxide Inorganic materials 0.000 claims abstract description 9
- BFZPBUKRYWOWDV-UHFFFAOYSA-N lithium;oxido(oxo)cobalt Chemical compound [Li+].[O-][Co]=O BFZPBUKRYWOWDV-UHFFFAOYSA-N 0.000 claims abstract description 9
- 239000002243 precursor Substances 0.000 claims description 42
- 238000005245 sintering Methods 0.000 claims description 19
- 239000007787 solid Substances 0.000 claims description 18
- 238000003756 stirring Methods 0.000 claims description 16
- 239000000203 mixture Substances 0.000 claims description 15
- 239000007788 liquid Substances 0.000 claims description 14
- 239000010405 anode material Substances 0.000 claims description 13
- 239000012298 atmosphere Substances 0.000 claims description 12
- 238000002156 mixing Methods 0.000 claims description 12
- 239000002253 acid Substances 0.000 claims description 10
- 229910017052 cobalt Inorganic materials 0.000 claims description 10
- 239000010941 cobalt Substances 0.000 claims description 10
- GUTLYIVDDKVIGB-UHFFFAOYSA-N cobalt atom Chemical compound [Co] GUTLYIVDDKVIGB-UHFFFAOYSA-N 0.000 claims description 10
- 229910052760 oxygen Inorganic materials 0.000 claims description 10
- 239000001301 oxygen Substances 0.000 claims description 10
- QVGXLLKOCUKJST-UHFFFAOYSA-N atomic oxygen Chemical compound [O] QVGXLLKOCUKJST-UHFFFAOYSA-N 0.000 claims description 9
- 238000001704 evaporation Methods 0.000 claims description 8
- 230000008020 evaporation Effects 0.000 claims description 8
- 238000010438 heat treatment Methods 0.000 claims description 8
- 238000001035 drying Methods 0.000 claims description 6
- VHUUQVKOLVNVRT-UHFFFAOYSA-N Ammonium hydroxide Chemical group [NH4+].[OH-] VHUUQVKOLVNVRT-UHFFFAOYSA-N 0.000 claims description 5
- 235000011114 ammonium hydroxide Nutrition 0.000 claims description 5
- 230000001105 regulatory effect Effects 0.000 claims description 5
- 239000002904 solvent Substances 0.000 claims description 5
- 239000003795 chemical substances by application Substances 0.000 claims description 4
- 238000004519 manufacturing process Methods 0.000 claims description 4
- 230000000630 rising effect Effects 0.000 claims description 3
- 230000008569 process Effects 0.000 abstract description 26
- HBBGRARXTFLTSG-UHFFFAOYSA-N Lithium ion Chemical compound [Li+] HBBGRARXTFLTSG-UHFFFAOYSA-N 0.000 abstract description 19
- 229910001416 lithium ion Inorganic materials 0.000 abstract description 19
- 239000011244 liquid electrolyte Substances 0.000 abstract description 9
- 230000007797 corrosion Effects 0.000 abstract description 7
- 238000005260 corrosion Methods 0.000 abstract description 7
- 239000002245 particle Substances 0.000 abstract description 5
- 230000002829 reductive effect Effects 0.000 abstract description 5
- 239000011229 interlayer Substances 0.000 abstract description 4
- 230000015572 biosynthetic process Effects 0.000 abstract description 3
- 230000008602 contraction Effects 0.000 abstract description 3
- 239000007772 electrode material Substances 0.000 abstract description 3
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- 238000012546 transfer Methods 0.000 abstract description 3
- 238000012360 testing method Methods 0.000 description 17
- UNTBPXHCXVWYOI-UHFFFAOYSA-O azanium;oxido(dioxo)vanadium Chemical group [NH4+].[O-][V](=O)=O UNTBPXHCXVWYOI-UHFFFAOYSA-O 0.000 description 12
- UBEWDCMIDFGDOO-UHFFFAOYSA-N cobalt(2+);cobalt(3+);oxygen(2-) Chemical compound [O-2].[O-2].[O-2].[O-2].[Co+2].[Co+3].[Co+3] UBEWDCMIDFGDOO-UHFFFAOYSA-N 0.000 description 12
- GPKIXZRJUHCCKX-UHFFFAOYSA-N 2-[(5-methyl-2-propan-2-ylphenoxy)methyl]oxirane Chemical group CC(C)C1=CC=C(C)C=C1OCC1OC1 GPKIXZRJUHCCKX-UHFFFAOYSA-N 0.000 description 10
- 239000003792 electrolyte Substances 0.000 description 8
- CURLTUGMZLYLDI-UHFFFAOYSA-N Carbon dioxide Chemical compound O=C=O CURLTUGMZLYLDI-UHFFFAOYSA-N 0.000 description 6
- KRKNYBCHXYNGOX-UHFFFAOYSA-N citric acid Chemical group OC(=O)CC(O)(C(O)=O)CC(O)=O KRKNYBCHXYNGOX-UHFFFAOYSA-N 0.000 description 6
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- XGZVUEUWXADBQD-UHFFFAOYSA-L lithium carbonate Chemical group [Li+].[Li+].[O-]C([O-])=O XGZVUEUWXADBQD-UHFFFAOYSA-L 0.000 description 5
- 238000005253 cladding Methods 0.000 description 4
- 238000009831 deintercalation Methods 0.000 description 4
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- 229910052808 lithium carbonate Inorganic materials 0.000 description 4
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- LFQSCWFLJHTTHZ-UHFFFAOYSA-N Ethanol Chemical group CCO LFQSCWFLJHTTHZ-UHFFFAOYSA-N 0.000 description 3
- 229960004543 anhydrous citric acid Drugs 0.000 description 3
- 238000004364 calculation method Methods 0.000 description 3
- 239000001569 carbon dioxide Substances 0.000 description 3
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- PQVSTLUFSYVLTO-UHFFFAOYSA-N ethyl n-ethoxycarbonylcarbamate Chemical group CCOC(=O)NC(=O)OCC PQVSTLUFSYVLTO-UHFFFAOYSA-N 0.000 description 3
- 230000006872 improvement Effects 0.000 description 3
- GLXDVVHUTZTUQK-UHFFFAOYSA-M lithium hydroxide monohydrate Substances [Li+].O.[OH-] GLXDVVHUTZTUQK-UHFFFAOYSA-M 0.000 description 3
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Abstract
The invention discloses a positive electrode material and a preparation method thereof, and relates to the technical field of lithium ion batteries. The positive electrode material comprises a positive electrode unit and a coating layer, wherein the coating layer is coated on the surface of the positive electrode unit; wherein the positive electrode unit is vanadium doped lithium cobalt oxide, and the coating layer is lithium tantalate. The positive electrode material is modified by doping vanadium in a lithium cobaltate phase, and by utilizing the characteristics of stable V-O chemical bond, high vanadium electron conductivity and the like, the cycle and multiplying power performance of the positive electrode material can be improved, the interlayer spacing of the positive electrode material can be enlarged, the migration of lithium ions is facilitated, in addition, the positive electrode material adopts lithium tantalate to carry out surface coating on the vanadium-doped lithium cobaltate, the corrosion of liquid electrolyte to the electrode material can be prevented in the process of promoting surface charge transfer, the surface stress caused by the expansion and contraction of the positive electrode material in the process of inserting and extracting lithium ions is reduced, and the formation of microcracks in particles is reduced, so that the structural stability of the positive electrode material in the cycle process is improved.
Description
Technical Field
The invention relates to the technical field of lithium ion batteries, in particular to a positive electrode material and a preparation method thereof.
Background
Lithium ion batteries have become very promising energy storage devices in power tools, electric vehicles, and energy storage systems due to their excellent energy and power density, long cycle life, low self-discharge rate, and excellent safety.
However, in the charge and discharge process of the lithium ion battery, solvation and desolvation of lithium ions are continuously carried out, the anode material continuously reacts with the liquid electrolyte to carry out ion and electron exchange, meanwhile, the anode material is also corroded by the liquid electrolyte, so that transition metal is dissolved out, structural collapse of the anode material is finally initiated, and adverse effects such as circulating water and gas production can occur.
To address the safety issues and cell life issues associated with liquid electrolytes, many researchers have desired to use solid electrolytes in place of traditional liquid electrolytes. However, the mobility of solid electrolytes is poor, the lithium ion transport capacity is limited, and the application of solid electrolytes in the field of lithium batteries is greatly limited. Therefore, development of a modified cathode material that is resistant to corrosion by liquid electrolytes and has a long cycle life has become a primary goal for many researchers.
Disclosure of Invention
Aiming at the defects of the prior art, the invention provides a positive electrode material and a preparation method thereof.
The invention discloses a positive electrode material, which comprises a positive electrode unit and a coating layer, wherein the coating layer is coated on the surface of the positive electrode unit; wherein the positive electrode unit is vanadium doped lithium cobalt oxide, and the coating layer is lithium tantalate.
According to one embodiment of the invention, in the vanadium-doped lithium cobaltate, the doping amount of vanadium is 1-10 wt% of the mass of the cobalt source, and the coating amount of the lithium tantalate is 0.3-2.1 wt% of the mass of the positive electrode unit.
The preparation method of the positive electrode material disclosed by the invention comprises the following steps:
S1, mixing a first lithium source and a cobalt source to obtain a precursor;
s2, mixing a second lithium source with an acid source, and regulating the pH value to obtain a precursor solution;
S3, adding a vanadium source and a precursor into the precursor solution, heating and stirring, and sintering a solid obtained by evaporation to obtain vanadium-doped lithium cobalt oxide;
S4, dispersing the vanadium-doped lithium cobaltate in a solvent, adding lithium tantalate to obtain a solid-liquid mixture, heating and stirring the solid-liquid mixture, and drying and sintering the solid obtained by evaporation to obtain the anode material.
According to an embodiment of the present invention, in step S1, the mass ratio of the first lithium source to the cobalt source is (0.5 to 1.5): (1.5-3).
According to an embodiment of the present invention, in step S2, the mass ratio of the second lithium source to the acid source is (0.5 to 2): (1-2).
According to an embodiment of the present invention, in step S2, the pH value is adjusted by the adjusting agent after the second lithium source is mixed with the acid source, wherein the adjusting agent is ammonia water, and the pH value is adjusted to 10.8±0.1.
According to an embodiment of the present invention, in step S3, the mass ratio of the vanadium source to the precursor solution is (0.5-2): (1-3).
According to one embodiment of the invention, in step S3, a vanadium source and a precursor are sequentially added into the precursor solution, stirring is carried out at 70-100 ℃, and the solid obtained by evaporation is sintered for 10-14 hours at 750-800 ℃ in an oxygen atmosphere, wherein the temperature rising rate of sintering is 5 ℃/min.
According to an embodiment of the present invention, in step S4, the mass ratio of vanadium doped lithium cobaltate to lithium tantalate is (40-400): 1.
According to one embodiment of the present invention, in step S4, the solid-liquid mixture is stirred at 70 to 100 ℃ for 4 to 6 hours, the evaporated solid is dried at 80 to 120 ℃ for 10 to 14 hours, and then sintered at 700 to 800 ℃ under air atmosphere for 10 to 12 hours, thereby obtaining the positive electrode material.
Compared with the prior art, the positive electrode material and the preparation method thereof have the following advantages:
the positive electrode material disclosed by the invention is subjected to bulk phase doping modification and surface phase cladding on the basis of the traditional lithium cobaltate, so that the problems of short cycle life and the like caused by dissolution of transition metal, gas production by oxidation of electrolyte, and poor bulk phase stability of the positive electrode material in the cycle process of the traditional lithium cobaltate are solved.
Firstly, the vanadium is doped in the lithium cobaltate phase for modification, and by utilizing the characteristics of stable V-O chemical bond, high vanadium electron conductivity and the like, the cycle and rate capability of the positive electrode material can be improved, the interlayer spacing of the positive electrode material can be enlarged, the migration of lithium ions is facilitated, in addition, the crystal lattice of the positive electrode material can be enlarged, the crystal lattice oxygen can be kept stable, the increase rate of electrode or electrolyte interface polarization in the cycle process is inhibited, and the cycle performance and rate capability of the positive electrode material are further improved.
In addition, the invention adopts lithium tantalate to carry out surface phase cladding on vanadium doped lithium cobaltate, and utilizes the characteristics of high dielectric constant, good mechanical property and the like of the lithium tantalate, thereby being capable of preventing the corrosion of liquid electrolyte to electrode materials in the process of promoting surface charge transfer, reducing the surface stress caused by the expansion and contraction of the positive electrode materials in the process of lithium ion intercalation and deintercalation, reducing the formation of microcracks in particles, and further improving the structural stability of the positive electrode materials in the circulating process.
Drawings
The accompanying drawings, which are included to provide a further understanding of the application and are incorporated in and constitute a part of this specification, illustrate embodiments of the application and together with the description serve to explain the application and do not constitute a limitation on the application. In the drawings:
FIG. 1 is an SEM image of sample eight;
FIG. 2 is an SEM image of fifteen samples;
FIG. 3 is an SEM image of sample eighteen;
FIG. 4 is an SEM image of nineteen samples;
Fig. 5 is an XRD pattern of samples eight, fifteen, eighteen and nineteen.
Detailed Description
Various embodiments of the invention are disclosed in the following drawings, in which details of the practice are set forth in the following description for the purpose of clarity. However, it should be understood that these practical details are not to be taken as limiting the invention. That is, in some embodiments of the invention, these practical details are unnecessary. Moreover, for the sake of simplicity of illustration, some well-known and conventional structures and components are shown in the drawings in a simplified schematic manner.
In addition, the descriptions of the "first," "second," and the like, herein are for descriptive purposes only and are not intended to be specifically construed as order or sequence, nor are they intended to limit the invention solely for distinguishing between components or operations described in the same technical term, but are not to be construed as indicating or implying any relative importance or order of such features. Thus, a feature defining "a first" or "a second" may explicitly or implicitly include at least one such feature. In addition, the technical solutions of the embodiments may be combined with each other, but it is necessary to base that the technical solutions can be realized by those skilled in the art, and when the technical solutions are contradictory or cannot be realized, the combination of the technical solutions should be considered to be absent and not within the scope of protection claimed in the present invention.
The invention provides a positive electrode material which is used for manufacturing a positive electrode plate of a lithium ion battery. The positive electrode material comprises a positive electrode unit and a coating layer, wherein the surface of the positive electrode unit is coated by the coating layer. Wherein the positive electrode unit is vanadium doped lithium cobalt oxide, and the coating layer is lithium tantalate (LiTaO 3).
Specifically, the doping amount of vanadium is 1-10wt% of the mass of the cobalt source, and the coating amount of lithium tantalate is 0.3-2.1wt% of the mass of the positive electrode unit. Wherein, the calculation formula of the doping amount of vanadium is as follows: the calculation formula of the coating amount of lithium tantalate is as follows: /(I)
According to the invention, bulk phase doping modification and surface phase cladding are carried out on the basis of the traditional lithium cobaltate, meanwhile, the surface phase and bulk phase stability of the lithium cobaltate are improved, the problems of shortened cycle life and the like caused by dissolution of transition metal, oxidation of electrolyte to produce gas, poor bulk phase stability of a positive electrode material and the like in the cycle process of the traditional lithium cobaltate are solved, the corrosion of the electrolyte to the lithium cobaltate and the irreversible phase transformation process of the lithium cobaltate in the lithium ion intercalation and deintercalation process are inhibited, the cycle stability of the lithium cobaltate under a high-voltage system is improved, and the long cycle target under high voltage is realized.
Firstly, the vanadium is doped in the lithium cobaltate phase for modification, and the cycle and the multiplying power performance of the anode material can be effectively improved by utilizing the characteristics of V-O chemical bond stability, high vanadium electron conductivity and the like. Vanadium is used as high-valence metal (+ 5), and proper vanadium doping can enlarge interlayer spacing of the anode material, so that migration of lithium ions is facilitated. ; in addition, vanadium generally coexists in +5 and +4 valence states, and the conductivity of the material can be improved by rapid electron transfer between V 5+ and V 4+. Therefore, the vanadium doping can increase the crystal lattice of the positive electrode material, so that the lattice oxygen is kept stable, the increase rate of electrode or electrolyte interface polarization in the cycling process is restrained, and the cycling performance and the rate capability of the positive electrode material are further improved.
In addition, the invention adopts lithium tantalate to carry out surface phase cladding on vanadium doped lithium cobaltate, and utilizes the characteristics of high dielectric constant, good mechanical property and the like of the lithium tantalate, thereby being capable of preventing the corrosion of liquid electrolyte to electrode materials in the process of promoting surface charge transfer, reducing the surface stress caused by the expansion and contraction of the positive electrode materials in the process of lithium ion intercalation and deintercalation, reducing the formation of microcracks in particles, and further improving the structural stability of the positive electrode materials in the circulating process.
The invention also provides a preparation method of the positive electrode material, which is used for preparing the positive electrode material. The preparation method of the positive electrode material comprises the following steps:
S1, mixing a first lithium source and a cobalt source to obtain a precursor;
s2, mixing a second lithium source with an acid source, and regulating the pH value to obtain a precursor solution;
S3, adding a vanadium source and a precursor into the precursor solution, heating and stirring, and sintering a solid obtained by evaporation to obtain vanadium-doped lithium cobalt oxide;
S4, dispersing the vanadium-doped lithium cobaltate in a solvent, adding lithium tantalate to obtain a solid-liquid mixture, heating and stirring the solid-liquid mixture, and drying and sintering the solid obtained by evaporation to obtain the anode material.
In the step S1, the mass ratio of the first lithium source to the cobalt source is (0.5-1.5): (1.5-3). Wherein the first lithium source is lithium carbonate (Li 2CO3) and the cobalt source is tricobalt tetraoxide (Co 3O4).
In the step S2, the mass ratio of the second lithium source to the acid source is (0.5-2): (1-2). The second lithium source is mixed with the acid source and then the pH value is adjusted to 10.8+/-0.1 by the regulator. Wherein the second lithium source is lithium hydroxide monohydrate (LiOH. H 2 O), the acid source is anhydrous citric acid, and the regulator is ammonia water (NH 3·H2 O).
In the step S3, the mass ratio of the vanadium source to the precursor solution is (0.5-2): (1-3). Sequentially adding a vanadium source and a precursor into the precursor solution, stirring at 70-100 ℃, and sintering the evaporated solid for 10-14 h at 750-800 ℃ and in an oxygen atmosphere, wherein the sintering temperature rising rate is 5 ℃/min. Wherein the vanadium source is ammonium metavanadate (NH 4VO3).
In the step S4, the mass ratio of the vanadium doped lithium cobaltate to the lithium tantalate is (40-400): 1. adding vanadium doped lithium cobaltate into a solvent, stirring for 20min at 80 ℃ to accelerate dissolution, and adding lithium tantalate to obtain a solid-liquid mixture. Stirring the solid-liquid mixture at 70-100 ℃ for 4-6 hours, drying the evaporated solid at 80-120 ℃ for 10-14 hours, and sintering the solid at 700-800 ℃ for 10-12 hours in air atmosphere to obtain the anode material. Wherein the solvent is absolute ethyl alcohol (C 2H5 OH).
In order to better illustrate the effect of the positive electrode material of the present invention on a lithium ion battery, a detailed description of nineteen samples of positive electrode material is provided below.
Sample one
The positive electrode material provided by the first sample comprises a positive electrode unit, wherein the positive electrode unit is vanadium doped lithium cobalt oxide, and the doping amount of vanadium is 1 weight percent of the mass of cobaltosic oxide.
The preparation method of the positive electrode material comprises the following steps:
S1, fully mixing 375g of lithium carbonate with 763g of cobaltosic oxide to obtain a precursor;
S2, the mass ratio is 1:1, mixing lithium hydroxide monohydrate with anhydrous citric acid, and regulating the pH value to 10.8+/-0.1 by using ammonia water to obtain a precursor solution;
S3, adding 7.63g of ammonium metavanadate and all precursors into 15.26g of precursor solution in sequence, stirring at 80 ℃, and sintering the evaporated solid for 12 hours at 770 ℃ in an oxygen atmosphere to obtain the anode material.
Sample two
Compared with the sample one, the doping amount of vanadium in the positive electrode material provided by the sample two is 2 weight percent of the mass of tricobalt tetraoxide. Correspondingly, the ammonium metavanadate was used in an amount of 15.26g and the precursor solution was used in an amount of 30.52g during the preparation.
Sample three
In the positive electrode material provided by the sample three, the doping amount of vanadium is 3wt% of the mass of tricobalt tetraoxide relative to the sample one. Correspondingly, the ammonium metavanadate was used in an amount of 22.89g and the precursor solution was used in an amount of 45.78g during the preparation.
Sample four
In the positive electrode material provided in sample four, the doping amount of vanadium was 4wt% of the mass of tricobalt tetraoxide relative to sample one. Correspondingly, the ammonium metavanadate was used in an amount of 30.52g and the precursor solution was used in an amount of 61.04g during the preparation.
Sample five
In the positive electrode material provided in sample five, the doping amount of vanadium was 5wt% of the mass of tricobalt tetraoxide relative to sample one. Correspondingly, the ammonium metavanadate was used in an amount of 38.15g and the precursor solution was used in an amount of 76.30g during the preparation.
Sample six
In the positive electrode material provided in sample six, the doping amount of vanadium was 6wt% of the mass of tricobalt tetraoxide relative to sample one. Correspondingly, the ammonium metavanadate was used in an amount of 45.78g and the precursor solution was used in an amount of 91.56g during the preparation.
Sample seven
In the positive electrode material provided in sample seven, the doping amount of vanadium was 7wt% of the mass of tricobalt tetraoxide relative to sample one. Correspondingly, the ammonium metavanadate was used in an amount of 53.41g and the precursor solution was used in an amount of 106.82g during the preparation.
Sample eight
In the positive electrode material provided in sample eight, the doping amount of vanadium was 8wt% of the mass of tricobalt tetraoxide relative to sample one. Correspondingly, the ammonium metavanadate was used in an amount of 61.04g and the precursor solution was used in an amount of 122.08g during the preparation.
Sample nine
Compared with the sample one, the doping amount of vanadium in the positive electrode material provided by the sample nine is 9 weight percent of the mass of the tricobalt tetraoxide. Correspondingly, the ammonium metavanadate is used in an amount of 68.67g and the precursor solution is used in an amount of 137.34g in the preparation process.
Sample ten
Compared with the sample I, the doping amount of vanadium in the positive electrode material provided by the sample ten is 10 weight percent of the mass of the tricobalt tetraoxide. Correspondingly, the ammonium metavanadate is used in an amount of 76.30g and the precursor solution is used in an amount of 152.60g in the preparation process.
Sample eleven
The positive electrode material provided by the sample eleven comprises a positive electrode unit and a coating layer, wherein the surface of the positive electrode unit is coated by the coating layer. Wherein the positive electrode unit is lithium cobaltate, the coating layer is lithium tantalate, and the coating amount of the lithium tantalate is 0.3 weight percent of the mass of the positive electrode unit.
The preparation method of the positive electrode material comprises the following steps:
S1, fully mixing 375g of lithium carbonate with 763g of cobaltosic oxide to obtain a precursor;
S2, annealing the precursor for 30min at 500 ℃, and sintering for 10h at 1000 ℃ to obtain lithium cobaltate; wherein the annealing heating rate is 3 ℃/min, and the sintering heating rate is 2 ℃/min;
S3, dispersing 400g of lithium cobaltate in 450mL of absolute ethyl alcohol, stirring at 80 ℃ for 20min to accelerate dissolution, then adding 1.2g of lithium tantalate to obtain a solid-liquid mixture, stirring the solid-liquid mixture at 80 ℃ for 5h, drying the evaporated solid at 100 ℃ for 12h, and sintering at 750 ℃ and air atmosphere for 10h to obtain the positive electrode material.
Twelve samples
In the positive electrode material provided in sample twelve, the coating amount of lithium tantalate was 0.6wt% of the mass of the positive electrode unit, relative to sample eleven. Correspondingly, the amount of lithium tantalate used in the preparation process was 2.4g.
Sample thirteen
In the positive electrode material provided in sample thirteenth, the coating amount of lithium tantalate was 0.9wt% of the mass of the positive electrode unit with respect to sample eleven. Correspondingly, the amount of lithium tantalate used in the preparation process was 3.6g.
Sample fourteen
Compared with sample eleven, in the positive electrode material provided by sample fourteen, the coating amount of lithium tantalate is 1.2wt% of the mass of the positive electrode unit. Correspondingly, the amount of lithium tantalate used in the preparation process was 4.8g.
Fifteen samples
In the cathode material provided in sample fifteen, the coating amount of lithium tantalate was 1.5wt% of the mass of the cathode unit with respect to sample eleven. Correspondingly, the amount of lithium tantalate used in the preparation process was 6.0g.
Sixteen samples
In the cathode material provided in sample sixteen, the coating amount of lithium tantalate was 1.8wt% of the mass of the cathode unit with respect to sample eleven. Correspondingly, the amount of lithium tantalate used in the preparation process was 7.2g.
Seventeen samples
In the positive electrode material provided in sample seventeen, the coating amount of lithium tantalate was 2.1wt% of the mass of the positive electrode unit with respect to sample eleven. Correspondingly, the amount of lithium tantalate used in the preparation process was 8.4g.
Sample eighteen
The anode material provided by the sample eighteen comprises an anode unit and a coating layer, wherein the surface of the anode unit is coated by the coating layer. Wherein the positive electrode unit is vanadium doped lithium cobalt oxide, and the coating layer is lithium tantalate. The doping amount of vanadium is 7wt% of the mass of cobaltosic oxide, and the coating amount of lithium tantalate is 1.5wt% of the mass of the positive electrode unit.
The preparation method of the positive electrode material comprises the following steps:
S1, fully mixing 375g of lithium carbonate with 763g of cobaltosic oxide to obtain a precursor;
S2, the mass ratio is 1:1, mixing lithium hydroxide monohydrate with anhydrous citric acid, and regulating the pH value to 10.8+/-0.1 by using ammonia water to obtain a precursor solution;
S3, adding 53.41g of ammonium metavanadate and all precursors into 106.82g of precursor solution in sequence, stirring at 80 ℃, and sintering the evaporated solid for 12 hours at 770 ℃ in an oxygen atmosphere to obtain vanadium-doped lithium cobaltate;
S4, dispersing 400g of vanadium-doped lithium cobaltate in 450mL of absolute ethyl alcohol, stirring at 80 ℃ for 20min to accelerate dissolution, then adding 6.0g of lithium tantalate to obtain a solid-liquid mixture, stirring the solid-liquid mixture at 80 ℃ for 5h, drying the evaporated solid at 100 ℃ for 12h, and sintering at 750 ℃ and air atmosphere for 10h to obtain the anode material.
Sample nineteen
The positive electrode material provided by the nineteenth sample comprises a positive electrode unit, and the positive electrode unit is lithium cobaltate.
The preparation method of the positive electrode material comprises the following steps:
S1, fully mixing 375g of lithium carbonate with 763g of cobaltosic oxide to obtain a precursor;
s2, sintering the precursor for 12 hours at 770 ℃ in an oxygen atmosphere, and then sintering for 10 hours at 750 ℃ in an air atmosphere to obtain the anode material.
EDS analysis was performed on the positive electrode materials of samples one to nineteen, and the analysis results are shown in table 1:
TABLE 1 EDS analysis results for samples one through nineteen
In addition, sample eight, sample fifteen, sample eighteen and sample nineteen were selected for SEM and XRD tests, i.e., the morphology and microstructure of the positive electrode material were comprehensively analyzed by scanning electron microscopy (SEM, verios, fei) and X-ray diffraction techniques, and the results are shown in fig. 1 to 5.
In addition, positive electrode materials of the first to nineteenth samples are respectively manufactured into lithium ion batteries by adopting the same preparation method, and the prepared lithium ion batteries are respectively subjected to a gram capacity test, a high-temperature cycle performance test, an impedance test, a CO 2 release test and a multiplying power discharge performance test, and the tests are briefly described as follows:
Gram capacity test: at 25 ℃, constant-current charge and discharge (0.1C) is adopted to study the charge and discharge performance of the material, and the voltage range is 3.0V-4.55V; and calculating the first charge and discharge efficiency according to the charge and discharge gram capacity.
High temperature cycle performance test: at 45 ℃, charging the button cell to 4.60V according to a constant current and a constant voltage of 0.1C, cutting off the current to 0.05C, discharging to 3.0V according to a constant current of 0.1C, and calculating the capacity retention rate at 50 weeks after 80 times of charging and discharging according to the circulation, wherein the calculation formula is as follows:
the cycle capacity retention rate (%) = (cycle discharge capacity at 50 th cycle/first cycle discharge capacity) ×100% at 50 th cycle.
And (3) testing the rate discharge performance: at 25 ℃, the button cell is charged to 4.60V according to a constant current and a constant voltage of 0.1C, the cut-off current is 0.05C, then the button cell is discharged to 3.0V according to a constant current of 0.1C, and the discharge capacity at the moment is recorded to be the initial capacity. And then charging the button cell to 4.60V according to a constant current and constant voltage of 0.1C, wherein the cut-off current is 0.05C, then discharging to 3.0V according to a constant current of 2.0C, and recording the discharge capacity at the moment, namely the discharge capacity. The percentage of the rate discharge capacity at this time= (discharge capacity/initial capacity) ×100% was calculated. Impedance testing: EIS data are collected at room temperature by using IVIUMSTAT impedance analyzer, the amplitude is 5mA, the frequency range is 10 < -2 > -105 Hz, and Zview software is used for fitting to obtain impedance data.
CO 2 release test: two polyether-ether-ketone (PEEK) adhesive capillaries are used as gas inlets and outlets. The output tube was connected to Thermo Scientific Mass Spectrometer (MS). In the circulation process, high-purity Ar gas is used as carrier gas, and the flow is 3mL/min. In the constant current charging process, the current is 60mA/g, and an MS spectrum is acquired every 30 seconds.
The test results of the gram capacity test, the high temperature cycle performance test, the impedance test, and the CO 2 release test are shown in table 2.
Table 2 results of each of samples one through nineteen
From the test results of table 1, the doping of vanadium and the coating of lithium tantalate in the positive electrode materials of samples one to nineteen were confirmed. The difference between the eighth and nineteenth samples is the presence or absence of doping with vanadium, and it can be seen from fig. 1 and 4 that doping with vanadium does not significantly change the bulk structure of lithium cobaltate. The difference between the fifteen and nineteen samples is that there is a coating of lithium tantalate, and it can be seen from fig. 2 and 4 that the coating of lithium tantalate can significantly improve the surface stability of lithium cobaltate. The samples eight and eighteen are different in the presence of the coating of lithium tantalate, and the samples fifteen and eighteen are different in the presence of the doping of vanadium, and as can be seen from the combination of fig. 1 to 3, the doping of vanadium and the coating of lithium tantalate have a synergistic effect, so that the bulk stability and the surface stability of lithium cobaltate are obviously improved.
The positive electrode materials of samples one to ten were compared, except for the doping amount of vanadium. As shown by combining the test results in table 2, when the doping amount of vanadium is 1-7wt%, the cycle capacity retention rate can be improved well, and the DCR growth rate in the cycle charge-discharge process is suppressed, because the high valence vanadium element can expand the interlayer spacing, promote the lithium ion diffusion rate, promote the stability of the bulk phase of lithium cobaltate in the cycle process, and is particularly expressed in that the number of particle cracks in the cycle process is reduced. However, the doping amount of the vanadium is excessive, namely, the doping amount of the vanadium is more than 7wt%, the improvement amplitude of the cycle stability is gradually reduced, and the vanadium is taken as an inactive element and does not have electrochemical activity, and occupies main element sites, so that the excessive vanadium doping causes excessive capacity loss of lithium cobaltate, and the energy density requirement cannot be met.
The positive electrode materials of the eleven to seventeen comparative samples were different in the coating amount of lithium tantalate. According to the test results in Table 2, the lithium tantalate coating is added on the surface of the lithium cobaltate, and when the coating amount is 0.3-1.5 wt%, the surface stability of the lithium cobaltate is obviously improved, the corrosion of the electrolyte to the surface of the lithium cobaltate is inhibited, meanwhile, the oxidation of cathode oxygen anions into oxygen in the cyclic charge and discharge process and the reaction with the electrolyte to generate carbon dioxide are inhibited, and the release amount of the carbon dioxide is obviously reduced, so that the lithium tantalate coating has obvious inhibition effect on the generation of carbon dioxide and the growth of DCR in the cyclic process, and the cyclic capacity retention rate is further improved. However, the increase of the coating amount of lithium tantalate as a coating layer is visually represented by the increase of the thickness of the coating layer, and when the coating thickness is too thick, the initial impedance of lithium cobaltate is increased, thereby preventing the smooth progress of the lithium ion intercalation and deintercalation process and causing adverse effects such as low-temperature performance reduction.
The difference between the sample seven and the sample eighteen is that the lithium tantalate is coated or not, the difference between the sample fifteen and the sample eighteen is that the vanadium doping or not, and the test result in combination with the table 2 shows that the doping of the vanadium and the coating of the lithium tantalate have a synergistic effect on the improvement of the performance of the lithium cobaltate, inhibit the collapse of the structure and the cracking of particles of the lithium cobaltate in the circulating process, and form a protective barrier between the lithium cobaltate and the electrolyte at the same time, thereby avoiding the corrosion of the surface of the lithium cobaltate caused by the direct contact of the liquid electrolyte and the lithium cobaltate, improving the stability of the traditional lithium battery in the circulating process, and finally realizing the purpose of prolonging the service life of the battery core under a high-voltage system.
The foregoing description is only illustrative of the invention and is not to be construed as limiting the invention. Various modifications and variations of the present invention will be apparent to those skilled in the art. Any modification, equivalent replacement, improvement, or the like, which is within the spirit and principles of the present invention, should be included in the scope of the claims of the present invention.
Claims (10)
1. The positive electrode material is characterized by comprising a positive electrode unit and a coating layer, wherein the coating layer is coated on the surface of the positive electrode unit; the positive electrode unit is vanadium doped lithium cobalt oxide, and the coating layer is lithium tantalate.
2. The positive electrode material according to claim 1, wherein the doping amount of vanadium in the vanadium-doped lithium cobaltate is 1 to 10wt% of the mass of the cobalt source, and the coating amount of the lithium tantalate is 0.3 to 2.1wt% of the mass of the positive electrode unit.
3. A method for producing the positive electrode material according to claim 1 or 2, comprising the steps of:
S1, mixing a first lithium source and a cobalt source to obtain a precursor;
s2, mixing a second lithium source with an acid source, and regulating the pH value to obtain a precursor solution;
S3, adding a vanadium source and a precursor into the precursor solution, heating and stirring, and sintering a solid obtained by evaporation to obtain vanadium-doped lithium cobalt oxide;
S4, dispersing the vanadium-doped lithium cobaltate in a solvent, adding lithium tantalate to obtain a solid-liquid mixture, heating and stirring the solid-liquid mixture, and drying and sintering the solid obtained by evaporation to obtain the anode material.
4. The method according to claim 3, wherein in the step S1, the mass ratio of the first lithium source to the cobalt source is (0.5 to 1.5): (1.5-3).
5. The method of producing a positive electrode material according to claim 3, wherein in the step S2, the mass ratio of the second lithium source to the acid source is (0.5 to 2): (1-2).
6. The method according to claim 3, wherein in the step S2, the second lithium source is mixed with the acid source and then the pH is adjusted by an adjusting agent, wherein the adjusting agent is ammonia water, and the pH is adjusted to 10.8±0.1.
7. The method according to claim 3, wherein in the step S3, the mass ratio of the vanadium source to the precursor solution is (0.5-2): (1-3).
8. The method for preparing a positive electrode material according to claim 3, wherein in the step S3, a vanadium source and a precursor are sequentially added into the precursor solution, the mixture is stirred at 70-100 ℃, and the solid obtained by evaporation is sintered for 10-14 hours at 750-800 ℃ under an oxygen atmosphere, wherein the sintering temperature rising rate is 5 ℃/min.
9. The method according to claim 3, wherein in the step S4, the mass ratio of the vanadium doped lithium cobaltate to the lithium tantalate is (40-400): 1.
10. The method of producing a positive electrode material according to claim 3, wherein in the step S4, the solid-liquid mixture is stirred at 70 to 100 ℃ for 4 to 6 hours, the evaporated solid is dried at 80 to 120 ℃ for 10 to 14 hours, and the dried solid is sintered at 700 to 800 ℃ under an air atmosphere for 10 to 12 hours to obtain the positive electrode material.
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