CN113594411A - Positive plate and battery - Google Patents
Positive plate and battery Download PDFInfo
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- CN113594411A CN113594411A CN202110907373.7A CN202110907373A CN113594411A CN 113594411 A CN113594411 A CN 113594411A CN 202110907373 A CN202110907373 A CN 202110907373A CN 113594411 A CN113594411 A CN 113594411A
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- 239000011149 active material Substances 0.000 claims abstract description 127
- 239000002245 particle Substances 0.000 claims abstract description 56
- 239000000463 material Substances 0.000 claims abstract description 41
- 229910001463 metal phosphate Inorganic materials 0.000 claims abstract description 29
- 239000011230 binding agent Substances 0.000 claims description 13
- 239000006258 conductive agent Substances 0.000 claims description 13
- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 claims description 12
- 239000002033 PVDF binder Substances 0.000 claims description 10
- 229920002981 polyvinylidene fluoride Polymers 0.000 claims description 10
- 229910002804 graphite Inorganic materials 0.000 claims description 6
- 239000010439 graphite Substances 0.000 claims description 6
- 229910001386 lithium phosphate Inorganic materials 0.000 claims description 6
- VNWKTOKETHGBQD-UHFFFAOYSA-N methane Chemical compound C VNWKTOKETHGBQD-UHFFFAOYSA-N 0.000 claims description 6
- TWQULNDIKKJZPH-UHFFFAOYSA-K trilithium;phosphate Chemical compound [Li+].[Li+].[Li+].[O-]P([O-])([O-])=O TWQULNDIKKJZPH-UHFFFAOYSA-K 0.000 claims description 6
- 239000001768 carboxy methyl cellulose Substances 0.000 claims description 5
- DPXJVFZANSGRMM-UHFFFAOYSA-N acetic acid;2,3,4,5,6-pentahydroxyhexanal;sodium Chemical compound [Na].CC(O)=O.OCC(O)C(O)C(O)C(O)C=O DPXJVFZANSGRMM-UHFFFAOYSA-N 0.000 claims description 4
- ILRRQNADMUWWFW-UHFFFAOYSA-K aluminium phosphate Chemical compound O1[Al]2OP1(=O)O2 ILRRQNADMUWWFW-UHFFFAOYSA-K 0.000 claims description 4
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- 125000002573 ethenylidene group Chemical group [*]=C=C([H])[H] 0.000 claims description 2
- 239000010410 layer Substances 0.000 description 85
- 229910052744 lithium Inorganic materials 0.000 description 19
- WHXSMMKQMYFTQS-UHFFFAOYSA-N Lithium Chemical compound [Li] WHXSMMKQMYFTQS-UHFFFAOYSA-N 0.000 description 18
- 239000011248 coating agent Substances 0.000 description 15
- 238000000576 coating method Methods 0.000 description 15
- 238000012360 testing method Methods 0.000 description 10
- HBBGRARXTFLTSG-UHFFFAOYSA-N Lithium ion Chemical compound [Li+] HBBGRARXTFLTSG-UHFFFAOYSA-N 0.000 description 9
- 229910001416 lithium ion Inorganic materials 0.000 description 9
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- 229910001429 cobalt ion Inorganic materials 0.000 description 5
- XLJKHNWPARRRJB-UHFFFAOYSA-N cobalt(2+) Chemical compound [Co+2] XLJKHNWPARRRJB-UHFFFAOYSA-N 0.000 description 5
- 239000003792 electrolyte Substances 0.000 description 5
- SECXISVLQFMRJM-UHFFFAOYSA-N N-Methylpyrrolidone Chemical compound CN1CCCC1=O SECXISVLQFMRJM-UHFFFAOYSA-N 0.000 description 4
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- KRHYYFGTRYWZRS-UHFFFAOYSA-N Fluorane Chemical compound F KRHYYFGTRYWZRS-UHFFFAOYSA-N 0.000 description 2
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- BQCIDUSAKPWEOX-UHFFFAOYSA-N 1,1-Difluoroethene Chemical compound FC(F)=C BQCIDUSAKPWEOX-UHFFFAOYSA-N 0.000 description 1
- KZEVSDGEBAJOTK-UHFFFAOYSA-N 1-(2,4,6,7-tetrahydrotriazolo[4,5-c]pyridin-5-yl)-2-[5-[2-[[3-(trifluoromethoxy)phenyl]methylamino]pyrimidin-5-yl]-1,3,4-oxadiazol-2-yl]ethanone Chemical compound N1N=NC=2CN(CCC=21)C(CC=1OC(=NN=1)C=1C=NC(=NC=1)NCC1=CC(=CC=C1)OC(F)(F)F)=O KZEVSDGEBAJOTK-UHFFFAOYSA-N 0.000 description 1
- VZSRBBMJRBPUNF-UHFFFAOYSA-N 2-(2,3-dihydro-1H-inden-2-ylamino)-N-[3-oxo-3-(2,4,6,7-tetrahydrotriazolo[4,5-c]pyridin-5-yl)propyl]pyrimidine-5-carboxamide Chemical compound C1C(CC2=CC=CC=C12)NC1=NC=C(C=N1)C(=O)NCCC(N1CC2=C(CC1)NN=N2)=O VZSRBBMJRBPUNF-UHFFFAOYSA-N 0.000 description 1
- IHCCLXNEEPMSIO-UHFFFAOYSA-N 2-[4-[2-(2,3-dihydro-1H-inden-2-ylamino)pyrimidin-5-yl]piperidin-1-yl]-1-(2,4,6,7-tetrahydrotriazolo[4,5-c]pyridin-5-yl)ethanone Chemical compound C1C(CC2=CC=CC=C12)NC1=NC=C(C=N1)C1CCN(CC1)CC(=O)N1CC2=C(CC1)NN=N2 IHCCLXNEEPMSIO-UHFFFAOYSA-N 0.000 description 1
- WTFUTSCZYYCBAY-SXBRIOAWSA-N 6-[(E)-C-[[4-[2-(2,3-dihydro-1H-inden-2-ylamino)pyrimidin-5-yl]piperazin-1-yl]methyl]-N-hydroxycarbonimidoyl]-3H-1,3-benzoxazol-2-one Chemical compound C1C(CC2=CC=CC=C12)NC1=NC=C(C=N1)N1CCN(CC1)C/C(=N/O)/C1=CC2=C(NC(O2)=O)C=C1 WTFUTSCZYYCBAY-SXBRIOAWSA-N 0.000 description 1
- DEXFNLNNUZKHNO-UHFFFAOYSA-N 6-[3-[4-[2-(2,3-dihydro-1H-inden-2-ylamino)pyrimidin-5-yl]piperidin-1-yl]-3-oxopropyl]-3H-1,3-benzoxazol-2-one Chemical compound C1C(CC2=CC=CC=C12)NC1=NC=C(C=N1)C1CCN(CC1)C(CCC1=CC2=C(NC(O2)=O)C=C1)=O DEXFNLNNUZKHNO-UHFFFAOYSA-N 0.000 description 1
- 229920002134 Carboxymethyl cellulose Polymers 0.000 description 1
- 229910032387 LiCoO2 Inorganic materials 0.000 description 1
- 229910052782 aluminium Inorganic materials 0.000 description 1
- XAGFODPZIPBFFR-UHFFFAOYSA-N aluminium Chemical compound [Al] XAGFODPZIPBFFR-UHFFFAOYSA-N 0.000 description 1
- 239000006256 anode slurry Substances 0.000 description 1
- 229910021383 artificial graphite Inorganic materials 0.000 description 1
- 230000009286 beneficial effect Effects 0.000 description 1
- 230000005540 biological transmission Effects 0.000 description 1
- 235000010948 carboxy methyl cellulose Nutrition 0.000 description 1
- 239000008112 carboxymethyl-cellulose Substances 0.000 description 1
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- 238000005253 cladding Methods 0.000 description 1
- 229910017052 cobalt Inorganic materials 0.000 description 1
- 239000010941 cobalt Substances 0.000 description 1
- GUTLYIVDDKVIGB-UHFFFAOYSA-N cobalt atom Chemical compound [Co] GUTLYIVDDKVIGB-UHFFFAOYSA-N 0.000 description 1
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- 239000007774 positive electrode material Substances 0.000 description 1
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Images
Classifications
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- 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
- H01M4/13—Electrodes for accumulators with non-aqueous electrolyte, e.g. for lithium-accumulators; Processes of manufacture thereof
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M10/00—Secondary cells; Manufacture thereof
- H01M10/05—Accumulators with non-aqueous electrolyte
- H01M10/052—Li-accumulators
- H01M10/0525—Rocking-chair batteries, i.e. batteries with lithium insertion or intercalation in both electrodes; Lithium-ion batteries
-
- 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
- H01M4/62—Selection of inactive substances as ingredients for active masses, e.g. binders, fillers
- H01M4/628—Inhibitors, e.g. gassing inhibitors, corrosion inhibitors
-
- 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
- H01M2004/021—Physical characteristics, e.g. porosity, surface area
-
- 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
- H01M2004/026—Electrodes composed of, or comprising, active material characterised by the polarity
- H01M2004/028—Positive electrodes
-
- 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
Abstract
The invention provides a positive plate and a battery, wherein the positive plate comprises a current collector, one side or two sides of the current collector are coated with a first active material layer, one side of the first active material layer, which is far away from the current collector, is coated with a second active material layer, and the outer surface of active material particles in the second active material layer is coated with a metal phosphate material. The embodiment of the invention can improve the safety of the battery.
Description
Technical Field
The invention relates to the technical field of batteries, in particular to a positive plate and a battery.
Background
Lithium ion batteries are widely used in portable electronic products, energy storage devices and new energy vehicles due to their advantages of high energy density, long cycle life, no memory effect, environmental friendliness, etc. People's requirement to the electronic equipment performance constantly improves, also proposed higher requirement to lithium ion battery's volume energy density, nevertheless along with the promotion of charging voltage, lithium ion battery's security sharply descends, and research shows that electric core is gradient distribution on the pole piece surface in the cyclic process current density, by pole piece surface to inside, current density reduces gradually, that is to say the pole piece surface is changeed taking place phase transition, granule breakage scheduling problem in the cyclic process, and this security that can lead to the battery reduces. Therefore, the safety of the current lithium ion battery is low.
Disclosure of Invention
The embodiment of the invention provides a positive plate and a battery, which aim to solve the problem of low safety of the battery in the prior art.
In a first aspect, embodiments of the present invention provide a positive electrode sheet, one or both sides of a current collector are coated with a first active material layer, one side of the first active material layer, which is away from the current collector, is coated with a second active material layer, and the outer surfaces of active material particles in the second active material layer are coated with a metal phosphate material.
Optionally, in the second active material layer, the thickness of the metal phosphate material coated outside each active material particle is less than or equal to 40 nm.
Optionally, the mass percentage of the metal phosphate material in the second active material layer is 0.01% to 1%.
Optionally, the metal phosphate material is a lithium phosphate material or an aluminum phosphate material.
Optionally, the thickness ratio of the first active material layer to the second active material layer is 3: 7-7: 3.
Optionally, the active material particles in the second active material layer have a median particle diameter D50 of 9-14 μm.
Optionally, the median particle diameter D50 of the active material particles in the first active material layer is 5-20 μm.
Optionally, the first active material layer and/or the second active material layer further include a conductive agent, and the conductive agent includes at least one of conductive graphite, ultrafine graphite, acetylene black, conductive carbon black SP, superconducting carbon black, carbon nanotubes, and conductive carbon fibers.
Optionally, the first active material layer and/or the second active material layer further comprise a binder, and the binder comprises at least one of polyvinylidene fluoride, polytetrafluoroethylene, sodium carboxymethyl cellulose, styrene-butadiene rubber, polyurethane, polyvinyl alcohol, polyvinylidene fluoride, and a copolymer of vinylidene fluoride and fluorinated olefin.
In a second aspect, embodiments of the present invention further provide a battery, including a separator, a negative electrode sheet, and a positive electrode sheet as in any one of the above embodiments, wherein at least one layer of the separator is present between the positive electrode sheet and the negative electrode sheet.
In the embodiment of the invention, one side or two sides of the current collector of the positive plate are coated with the first active material layer, one side, far away from the current collector, of the first active material layer is coated with the second active material layer, and active material particles in the second active material layer are coated with the metal phosphate material, so that the dissolution of cobalt ions in the electrolyte and the gas release caused by decomposition reaction due to direct contact of the electrolyte and high-concentration tetravalent cobalt ions of the active material particles in the second active material layer can be avoided.
Drawings
In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings required to be used in the description of the embodiments of the present invention will be briefly introduced below, and it is obvious that the drawings in the following description are only some embodiments of the present invention, and it is obvious for those skilled in the art to obtain other drawings based on these drawings without inventive exercise.
Fig. 1 is a schematic structural diagram of a positive electrode sheet provided in an embodiment of the present invention;
fig. 2 is a schematic diagram of the cycle performance of the battery provided by the embodiment of the invention.
Detailed Description
The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are some, not all, embodiments of the present invention. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
Referring to fig. 1, the embodiment of the present invention provides a positive electrode sheet, including a current collector 100, wherein one side or both sides of the current collector 100 are coated with a first active material layer 200, one side of the first active material layer 200 away from the current collector 100 is coated with a second active material layer 300, and the outer surface of active material particles in the second active material layer 300 is coated with a metal phosphate material.
In the embodiment of the present invention, the positive plate may be applied to a cell structure of a lithium battery, in the cell structure of the lithium battery, the positive plate and the negative plate are generally disposed opposite to each other, and a separator is formed between the positive plate and the negative plate. The current collector 100 of the positive electrode tab may be an aluminum foil, one or both sides of the current collector 100 may be coated with a first active material layer 200, and a side of the first active material layer 200 away from the current collector 100 is coated with a second active material layer 300. In other words, the first active material layer 200 is located between the second active material layer 300 and the current collector 100 on the same side as the current collector 100.
It is understood that the active material of the first active material layer 200 may be provided according to actual needs, and may be a lithium cobaltate material or a ternary material containing cobalt. The active material of the second active material layer 300 may be the same as the active material of the first active material layer 200, and further, since the active material on the surface layer of the pole piece is more likely to cause phase change, particle breakage, and the like, the active material particles in the second active material layer 300 may be coated with a metal phosphate material, and the metal phosphate material may be coated on the active material particles in a shell shape, that is, a protective shell made of a layer of metal phosphate may be formed on the active material particles.
Specifically, the active material of the second active material layer 300 described above may be obtained by: polyphosphoric acid (MMA) and conventional lithium cobaltate are weighed according to the molar ratio of Co to P of 98.5 to 0.2, are uniformly stirred and mixed, are placed in a muffle furnace at 950 ℃ for sintering for 12 hours, and then the sintered product is crushed to obtain the modified lithium cobaltate with the core-shell structure.
In the embodiment of the invention, one side or two sides of the current collector 100 of the positive plate are coated with the first active material layer 200, one side of the first active material layer 200, which is far away from the current collector 100, is coated with the second active material layer 300, and active material particles in the second active material layer 300 are coated with the metal phosphate material, so that the dissolution of cobalt ions in the electrolyte and the gas release caused by the decomposition reaction caused by the direct contact of the electrolyte and tetravalent cobalt ions with high concentration of active material particles in the second active material layer 300 can be avoided, and the greater the dissolution amount of the cobalt ions on the surface layer of the active material particles is, the more likely the local structure on the surface layer of the active material particles is to collapse, so that the situation of the local structure on the surface layer of the active material particles in the circulation process can be alleviated by adopting the positive plate of the embodiment of the invention, and the safety of the battery is improved.
Because the chemical property of the metal phosphate is stable, the potential safety hazard caused by the direct reaction of the electrolyte and active material particles can be avoided, meanwhile, the corrosion of hydrofluoric acid generated by the reaction of the electrolyte and a small amount of water in the lithium cobaltate core structure to the positive active material can be avoided, the battery capacity is ensured, and meanwhile, the safety of the battery is further improved. In addition, the metal phosphate material also has good ionic conductivity and Young modulus, has a delay effect on the increase of the surface resistance of the pole piece, and can improve the cycle performance of the battery.
It should be noted that, in some embodiments, the active material particles in the first active material layer 200 may also be coated with the metal phosphate material, so as to further improve the safety of the battery. Of course, since the active material particles on the surface layer of the electrode sheet are more likely to collapse, and the coating of the metal phosphate material on the surface layer of the active material particles may reduce the battery capacity to some extent, in order to ensure the battery capacity, the first active material layer 200 may use conventional lithium cobaltate particles.
Alternatively, in the second active material layer 300, the thickness of the metal phosphate material coated outside each active material particle is less than or equal to 40 nm.
It is understood that the coating thickness of the active material layer is related to the battery capacity, and generally, the thicker the active material layer is, the more active material particles are contained, the larger the battery capacity is, and the larger the coating thickness is, the lower the transmission rate of lithium ions is, and the slower the charging rate is accordingly. Therefore, in the embodiment of the present invention, in order to increase the battery capacity while ensuring the safety of the battery, the thickness of the metal phosphate material coated outside each active material particle in the second active material layer 300 may be less than or equal to 40 nm. Thus, the number of active material particles in the second active material layer 300 can be increased under the condition that the thickness of the second active material layer 300 is constant, thereby increasing the battery capacity.
Similarly to the above-described embodiment, the mass percentage of the metal phosphate material in the second active material layer 300 may be set according to actual needs, and in the embodiment of the present invention, the mass percentage of the metal phosphate material may be preferably 0.01% to 1% in order to improve the battery capacity while ensuring the battery safety.
Optionally, the metal phosphate material is a lithium phosphate material or an aluminum phosphate material.
In the embodiment of the present invention, the active material of the positive electrode is usually a lithium cobaltate material, so as to avoid introducing doping elements, the metal phosphate material may be a lithium phosphate material, lithium cobaltate and polyphosphoric acid (MMA) are uniformly mixed by stirring, the mixture is placed in a muffle furnace at 950 ℃ for sintering for 12 hours, and then the sintered product is crushed to obtain lithium cobaltate particles coated with the lithium phosphate material. Of course, the metal phosphate material may be an aluminum phosphate material.
As can be seen from the above, the use of lithium cobaltate coated with a metal phosphate material as an active material reduces the capacity of the battery to some extent, and the thickness ratio of the first active material layer 200 to the second active material layer 300 can be set according to actual needs in order to balance the battery capacity and the battery safety. In an embodiment of the invention, a thickness ratio of the first active material layer 200 to the second active material layer 300 may be 3:7 to 7: 3. It is understood that, in the case where the overall thickness of the coating layer of the current collector 100 is not changed, the greater the thickness of the first active material layer 200, the greater the battery capacity.
In the case of lithium cobaltate particles, the smaller the particle size, the more active the particles are, and in order to make the delithiation amount of the bottom layer and the surface layer of the positive electrode sheet more uniform, in the embodiment of the present invention, the median particle size D50 of the active material particles in the second active material layer 300 may be 9 to 14 μm, and the median particle size D50 of the active material particles in the first active material layer 200 may be 5 to 20 μm. It is to be understood that the first active material layer 200 and/or the second active material layer 300 may be composed of active materials having the same particle size or may be obtained by size particle grading.
The conductive agent is used for improving the transfer rate of electrons in the electrode and reducing the ohmic resistance of the electrode. The material can be set according to actual needs. Optionally, in an embodiment of the present invention, the first active material layer 200 and/or the second active material layer 300 further include a conductive agent, and the conductive agent includes at least one of conductive graphite, ultrafine graphite, acetylene black, conductive carbon black SP, superconducting carbon black, carbon nanotubes, and conductive carbon fibers.
The binder is used for ensuring uniformity and safety in pulping, plays a role in binding particles, and can be set according to actual needs, and optionally, in the embodiment of the present invention, the first active material layer 200 and/or the second active material layer 300 further include a binder, and the binder includes at least one of polyvinylidene fluoride, polytetrafluoroethylene, sodium carboxymethyl cellulose, styrene-butadiene rubber, polyurethane, polyvinyl alcohol, polyvinylidene fluoride, and a copolymer of vinylidene fluoride-fluorinated olefin.
The embodiment of the invention also provides a battery, which comprises a diaphragm, a negative plate and the positive plate as claimed in any one of claims 1 to 9, wherein at least one layer of the diaphragm is arranged between the positive plate and the negative plate.
Since the battery provided by the embodiment of the present invention adopts all the technical solutions of the above embodiments, at least all the beneficial effects brought by the technical solutions of the above embodiments are achieved, and details are not repeated herein.
In addition, the embodiment of the invention also provides a preparation method of the positive plate and a preparation method of the lithium ion battery containing the positive plate, wherein the preparation method of the positive plate comprises the following steps:
step 101, mixing conventional lithium cobaltate, a conductive agent and a binder according to a certain proportion, adding N-methyl pyrrolidone, stirring and dispersing to prepare anode inner layer slurry.
102, mixing the modified lithium cobaltate, the conductive agent B and the binder according to a certain proportion, then adding N-methyl pyrrolidone, stirring and dispersing to prepare the outer layer slurry of the positive electrode, wherein lithium cobaltate particles of the modified lithium cobaltate are coated by a metal phosphate material.
And 103, coating the slurry of the inner layer and the slurry of the outer layer of the positive electrode on a current collector of the positive electrode together by double-layer coating equipment (double-sided coating), drying, cutting, and tabletting to prepare the composite positive plate.
The preparation method of the battery also comprises the following steps:
and step 104, mixing the negative electrode active material, the conductive agent, the binder and the thickening agent according to a certain proportion, adding deionized water, stirring and dispersing to prepare negative electrode slurry. And then coating the negative electrode slurry on a negative electrode current collector (double-sided coating), drying, slitting and preparing a sheet to obtain the negative electrode sheet.
And 105, preparing the composite positive plate prepared in the step 103, the negative plate prepared in the step 104, a diaphragm and an aluminum-plastic film into a battery, then performing the procedures of liquid injection, aging, formation, pre-circulation and the like, and finally testing the electrochemical performance of the battery.
In order to better understand the invention, specific implementation procedures of the invention will be described in detail in specific implementation modes.
Example 1
Preparing anode inner layer slurry:
mixing lithium cobaltate, a conductive agent and a binder according to a certain proportion, adding N-methyl pyrrolidone, stirring and dispersing to prepare the anode inner layer slurry. In the positive electrode slurry, the solid component contained 97.3 wt% of conventional lithium cobaltate, 1.5 wt% of conductive carbon black, and 1.2 wt% of Polyvinylidene Fluoride (PVDF).
Preparing slurry of the outer layer of the positive electrode:
mixing the modified lithium cobaltate, the conductive agent and the binder according to a certain proportion, adding N-methyl pyrrolidone, stirring and dispersing to prepare the anode slurry. In the positive electrode slurry, the solid components contained 97.8 wt% of lithium cobaltate (LiCoO2), 1.1 wt% of conductive carbon black, and 1.1 wt% of polyvinylidene fluoride (PVDF).
Then through double-deck coating equipment with anodal inside and outside thick liquids once coating on anodal mass flow body (two-sided coating), wherein, thickness is anodal skin: and (3) drying, slitting and preparing the anode piece, wherein the ratio of the anode inner layer to the cathode inner layer is 3: 7.
Preparing a negative plate:
mixing the negative active material, the conductive agent, the binder and the thickening agent according to a certain proportion, adding deionized water, stirring and dispersing to prepare negative slurry. In the negative electrode slurry, solid components comprise 96.9% of artificial graphite, 0.5% of conductive carbon black, 1.3% of sodium carboxymethylcellulose (CMC) and 1.3% of Styrene Butadiene Rubber (SBR), and then the negative electrode slurry is coated on a negative electrode current collector (double-sided coating), and the negative electrode pole piece is prepared by drying, slitting and tabletting.
Preparing a battery:
and (3) preparing the positive plate prepared in the first step and the negative plate prepared in the second step, a diaphragm and an aluminum-plastic film into a battery, then performing the working procedures of liquid injection, aging, formation, sorting and the like, and finally testing the electrochemical performance and the safety performance (mainly needle abuse) of the battery.
Preparation of modified lithium cobaltate:
the preparation method of the lithium cobaltate is consistent with the conventional mode, and the preparation method of the lithium phosphate coating layer comprises the following steps: polyphosphoric acid (MMA) and conventional lithium cobaltate are weighed according to the molar ratio of Co to P of 98.5 to 0.2, are uniformly stirred and mixed, are placed in a muffle furnace at 950 ℃ for sintering for 12 hours, and then the sintered product is crushed to obtain the modified lithium cobaltate with the core-shell structure.
The preparation environment temperature of the electrode material is kept at 20-30 ℃, and the humidity is less than or equal to 40% RH.
The equipment for preparing the electrode material comprises: the device comprises a stirrer, a coating machine, a roller press, a splitting machine, a pelleter, an ultrasonic spot welding machine, a top side sealing machine, an ink-jet printer, a film sticking machine, a liquid injection machine, a formation cabinet, a cold press, a separation cabinet, a vacuum oven and the like.
Example 2 was provided, and example 2 was different from example 1 in that the coating thickness was the positive electrode outer layer: the positive electrode inner layer is 5: 5.
Example 3 was provided, and example 3 differs from example 1 in that the coating thickness was the positive electrode outer layer: the positive electrode inner layer is 7: 3.
Example 4 was set, and example 4 was different from example 1 described above in that the median particle diameter D50 of the active material particles in the first active material layer was 5 μm, and the rest remained the same as example 1.
Example 5 was set, and example 5 was different from example 1 described above in that the median particle diameter D50 of the active material particles in the first active material layer was 18 μm, and the rest remained in accordance with example 1.
Example 6 was set, and example 6 was different from example 1 described above in that the median particle diameter D50 of the active material particles in the second active material layer was 3 μm, and the rest remained the same as example 1.
Example 7 was provided, and example 7 was different from example 1 described above in that the median particle diameter D50 of the active material particles in the second active material layer was 25 μm, and the rest remained in accordance with example 1.
Example 8 was set up, and example 8 was different from example 1 in that the thickness of the metal phosphate material coated on each active material particle in the second active material layer was 50nm, and the rest was the same as example 1.
Meanwhile, a comparative example 1 was set in which the positive electrode outer layer material was not provided, that is, only the conventional lithium cobaltate slurry was coated on the current collector, and the remaining conditions were kept the same.
The following tests were carried out for the above examples 1 to 8 and comparative examples:
and (3) furnace temperature testing: the lithium ion batteries of the above examples 1 to 8 and comparative examples were subjected to a needling test, the test procedure being as follows: firstly, charging the battery to an upper limit voltage (cut off at 0.02C) at 0.2C, and testing the initial state of the battery, including voltage, internal resistance, thickness and the like; then the battery is put into an oven and heated at the initial temperature of 25 plus or minus 3 ℃, the temperature rise rate is 5 plus or minus 2 ℃, the temperature rises to 130 plus or minus 2 ℃, and the test is finished after the temperature is kept for 60 min.
And (3) cycle testing: discharging the battery to the lower limit voltage at 0.7C, charging to the upper limit voltage at 1.5C, discharging to the lower limit voltage at 0.5C in a constant temperature room at 45 ℃, and circulating for 800 weeks to calculate the capacity retention rate of the battery.
The test results are shown in table 1 and fig. 2:
TABLE 1
| Furnace temperature pass rate | High temperature cycle capacity retention ratio/500T | ED/Wh l-1 | |
| Example 1 | 5/5PASS | 88.42％ | 765 |
| Example 2 | 5/5PASS | 89.16％ | 753 |
| Example 3 | 5/5PASS | 89.20％ | 746 |
| Example 4 | 3/5PASS | / | 768 |
| Example 5 | 4/5PASS | / | 766 |
| Example 6 | 2/5PASS | / | 755 |
| Example 7 | 4/5PASS | / | 738 |
| Example 8 | 5/5PASS | / | 735 |
| Comparative example 1 | 1/5PASS | 81.45％ | 770 |
The results in table 1 show that the furnace temperature test of comparative example 1 has a low pass rate, i.e., poor safety, and low high-temperature cycle performance, and cannot meet the performance requirements of the lithium ion battery. The furnace temperature experiment passing rates of the embodiments 1-8 of the invention are higher than those of the comparative example 1, and as can be seen from fig. 2, the high-temperature cycle performance of the embodiments 1-3 is higher, so that the safety and the cycle performance of the lithium ion battery are effectively improved. In examples 4 to 7, the oven temperature performance was significantly lost after the particle size of the active material layer was adjusted. Example 8, while the safety was good after increasing the cladding thickness, the energy density loss was severe. The embodiment 1 can be selected specifically in practical application because the cycle retention rate and the oven temperature passage rate of the embodiment 1 are more excellent.
The above description is only for the specific embodiments of the present invention, but the scope of the present invention is not limited thereto, and any person skilled in the art can easily conceive of the changes or substitutions within the technical scope of the present invention, and the changes or substitutions should be covered within the scope of the present invention. Therefore, the protection scope of the present invention shall be subject to the protection scope of the claims.
Claims (10)
1. The positive plate comprises a current collector and is characterized in that one side or two sides of the current collector are coated with a first active material layer, one side, far away from the current collector, of the first active material layer is coated with a second active material layer, and the outer surface of active material particles in the second active material layer is coated with a metal phosphate material.
2. The positive electrode sheet according to claim 1, wherein the thickness of the metal phosphate material externally coated with each active material particle in the second active material layer is less than or equal to 40 nm.
3. The positive electrode sheet according to claim 1, wherein the mass percentage of the metal phosphate material in the second active material layer is 0.01% to 1%.
4. The positive electrode sheet according to any one of claims 1 to 3, wherein the metal phosphate material is a lithium phosphate material or an aluminum phosphate material.
5. The positive electrode sheet according to claim 1, wherein a thickness ratio of the first active material layer to the second active material layer is 3:7 to 7: 3.
6. The positive electrode sheet according to claim 1, wherein the active material particles in the second active material layer have a median particle diameter D50 of 9 to 14 μm.
7. The positive electrode sheet according to claim 1, wherein the active material particles in the first active material layer have a median particle diameter D50 of 5 to 20 μm.
8. The positive electrode sheet according to claim 1, wherein the first active material layer and/or the second active material layer further comprises a conductive agent, and the conductive agent comprises at least one of conductive graphite, ultrafine graphite, acetylene black, conductive carbon black SP, superconducting carbon black, carbon nanotubes, and conductive carbon fibers.
9. The positive electrode sheet according to claim 1, wherein the first active material layer and/or the second active material layer further comprises a binder, the binder comprising at least one of polyvinylidene fluoride, polytetrafluoroethylene, sodium carboxymethylcellulose, styrene butadiene rubber, polyurethane, polyvinyl alcohol, polyvinylidene fluoride, and a copolymer of vinylidene fluoride-fluorinated olefin.
10. A battery comprising a separator, a negative electrode sheet, and the positive electrode sheet according to any one of claims 1 to 9, wherein at least one layer of the separator is present between the positive electrode sheet and the negative electrode sheet.
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| CN102856530A (en) * | 2011-06-30 | 2013-01-02 | 清华大学 | Lithium ion battery |
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| CN105098193A (en) * | 2015-09-24 | 2015-11-25 | 宁德时代新能源科技有限公司 | Positive plate and lithium ion battery comprising same |
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| CN110660961A (en) * | 2018-06-28 | 2020-01-07 | 宁德时代新能源科技股份有限公司 | Positive plate and lithium ion battery |
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| CN102856530A (en) * | 2011-06-30 | 2013-01-02 | 清华大学 | Lithium ion battery |
| CN103311539A (en) * | 2013-05-17 | 2013-09-18 | 深圳市慧通天下科技股份有限公司 | High-voltage high-energy-density lithium ion battery |
| US20160351973A1 (en) * | 2015-06-01 | 2016-12-01 | Energy Power Systems LLC | Nano-engineered coatings for anode active materials, cathode active materials, and solid-state electrolytes and methods of making batteries containing nano-engineered coatings |
| CN105098193A (en) * | 2015-09-24 | 2015-11-25 | 宁德时代新能源科技有限公司 | Positive plate and lithium ion battery comprising same |
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