CN115275109A - Long-cycle lithium iron phosphate thick electrode, preparation method thereof and lithium ion battery - Google Patents
Long-cycle lithium iron phosphate thick electrode, preparation method thereof and lithium ion battery Download PDFInfo
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- CN115275109A CN115275109A CN202211014823.0A CN202211014823A CN115275109A CN 115275109 A CN115275109 A CN 115275109A CN 202211014823 A CN202211014823 A CN 202211014823A CN 115275109 A CN115275109 A CN 115275109A
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- GELKBWJHTRAYNV-UHFFFAOYSA-K lithium iron phosphate Chemical compound [Li+].[Fe+2].[O-]P([O-])([O-])=O GELKBWJHTRAYNV-UHFFFAOYSA-K 0.000 title claims abstract description 161
- HBBGRARXTFLTSG-UHFFFAOYSA-N Lithium ion Chemical compound [Li+] HBBGRARXTFLTSG-UHFFFAOYSA-N 0.000 title claims abstract description 21
- 229910001416 lithium ion Inorganic materials 0.000 title claims abstract description 21
- 238000002360 preparation method Methods 0.000 title claims abstract description 18
- 229910052744 lithium Inorganic materials 0.000 claims abstract description 179
- WHXSMMKQMYFTQS-UHFFFAOYSA-N Lithium Chemical compound [Li] WHXSMMKQMYFTQS-UHFFFAOYSA-N 0.000 claims abstract description 176
- 238000000576 coating method Methods 0.000 claims abstract description 148
- 239000011248 coating agent Substances 0.000 claims abstract description 147
- 239000013589 supplement Substances 0.000 claims abstract description 143
- 239000002245 particle Substances 0.000 claims abstract description 117
- 238000000034 method Methods 0.000 claims abstract description 24
- 239000010410 layer Substances 0.000 claims description 108
- 239000011247 coating layer Substances 0.000 claims description 77
- 239000011230 binding agent Substances 0.000 claims description 61
- 239000002002 slurry Substances 0.000 claims description 57
- 239000006258 conductive agent Substances 0.000 claims description 48
- 239000003795 chemical substances by application Substances 0.000 claims description 44
- 239000002033 PVDF binder Substances 0.000 claims description 24
- 229920002981 polyvinylidene fluoride Polymers 0.000 claims description 23
- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical group [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 claims description 16
- 238000007756 gravure coating Methods 0.000 claims description 8
- 229920000049 Carbon (fiber) Polymers 0.000 claims description 5
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- 239000002041 carbon nanotube Substances 0.000 claims description 5
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- 229910021389 graphene Inorganic materials 0.000 claims description 5
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- 238000007765 extrusion coating Methods 0.000 claims description 3
- 239000007788 liquid Substances 0.000 claims 6
- 239000008187 granular material Substances 0.000 claims 4
- 230000015572 biosynthetic process Effects 0.000 abstract description 11
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- 239000007791 liquid phase Substances 0.000 abstract description 8
- 230000002349 favourable effect Effects 0.000 abstract description 5
- 238000007599 discharging Methods 0.000 abstract description 4
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- 230000009286 beneficial effect Effects 0.000 description 7
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- SECXISVLQFMRJM-UHFFFAOYSA-N N-Methylpyrrolidone Chemical compound CN1CCCC1=O SECXISVLQFMRJM-UHFFFAOYSA-N 0.000 description 4
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- 229910000398 iron phosphate Inorganic materials 0.000 description 1
- WBJZTOZJJYAKHQ-UHFFFAOYSA-K iron(3+) phosphate Chemical compound [Fe+3].[O-]P([O-])([O-])=O WBJZTOZJJYAKHQ-UHFFFAOYSA-K 0.000 description 1
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- 239000007774 positive electrode material Substances 0.000 description 1
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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
- H01M4/136—Electrodes based on inorganic compounds other than oxides or hydroxides, e.g. sulfides, selenides, tellurides, halogenides or LiCoFy
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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
- 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
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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
- H01M4/139—Processes of manufacture
- H01M4/1397—Processes of manufacture of electrodes based on inorganic compounds other than oxides or hydroxides, e.g. sulfides, selenides, tellurides, halogenides or LiCoFy
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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
- H01M4/36—Selection of substances as active materials, active masses, active liquids
- H01M4/58—Selection of substances as active materials, active masses, active liquids of inorganic compounds other than oxides or hydroxides, e.g. sulfides, selenides, tellurides, halogenides or LiCoFy; of polyanionic structures, e.g. phosphates, silicates or borates
- H01M4/5825—Oxygenated metallic salts or polyanionic structures, e.g. borates, phosphates, silicates, olivines
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- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
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- H01M4/62—Selection of inactive substances as ingredients for active masses, e.g. binders, fillers
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Abstract
The invention provides a long-cycle lithium iron phosphate thick electrode, a preparation method thereof and a lithium ion battery. The first coating and the second coating respectively contain small-particle lithium iron phosphate and large-particle lithium iron phosphate, and the double-layer coating structure with the large and small particles can effectively improve the liquid phase transmission efficiency and the dynamic performance of the lithium iron phosphate thick electrode; meanwhile, the lithium supplement layer can effectively make up the irreversible capacity loss in the thick electrode and improve the cycle performance of the electrode, the lithium supplement layer is arranged on the outermost layer, is also favorable for discharging produced gas in the formation process, and has synergistic effect with the first coating and the second coating, and meanwhile, the rate capability and the cycle performance of the lithium iron phosphate thick electrode are improved.
Description
Technical Field
The invention belongs to the technical field of batteries, and relates to a long-cycle lithium iron phosphate thick electrode, a preparation method thereof and a lithium ion battery.
Background
With the increase of the thickness of the electrode, the proportion of the active material is obviously increased, so that the energy density of the single battery can be obviously improved, and therefore, the development of the thick electrode has important significance for improving the energy density of the battery. However, as the thickness of the electrode increases, the transmission of liquid-phase lithium ions of the pole piece is hindered, which leads to the increase of the internal resistance of the battery, the reduction of the utilization rate of the active material and the remarkable attenuation of the cycle performance and the rate performance.
The main methods and strategies for improving the rate performance of the thick electrode are to develop high-rate anode and cathode materials, regulate and control the porous structure of the thick electrode, develop novel electrolyte and the like. The design and regulation of the porous structure of the thick electrode are the most effective and widely applied technical methods for improving the rate performance, for example, the thick electrode is subjected to pore forming, and the construction of through pores formed after pore forming can obviously improve the infiltration rate of the electrolyte of the thick electrode and improve the rate performance of the electrolyte; for example, patent CN114400301a, it improves the wetting effect of the electrolyte in the thick electrode by preparing the thick electrode and constructing the pore array in the electrode. However, the irreversible capacity loss during cycling of the thick electrode is severe as compared to the conventional electrode, and the above-described method is not effective in reducing the capacity loss during cycling, and therefore, in order to improve the cycling performance of the thick electrode, the electrode sheet may be subjected to a pre-lithiation treatment.
The prelithiation technology is divided into anode prelithiation and cathode prelithiation. The method for preparing the lithium-containing anode plate comprises the following steps of (1) compounding metal lithium on at least one side surface of an anode plate to obtain a pre-lithium anode plate, wherein lithium tapes, lithium powder, lithium foils and the like are usually adopted as lithium supplement agents for the anode pre-lithiation, for example, in patent CN 112786971A; however, lithium metal such as lithium powder and lithium ribbon is extremely sensitive to the temperature and humidity in the environment, and has a great safety risk. The pre-lithiation of the positive electrode usually adopts Li 2 NiO 2 、Li 5 FeO 4 、Li 2 A lithium supplement agent such as O, which can release lithium to compensate for active lithium consumed by SEI when first charged, thereby improving battery cycle performance; such as patent CN114203990A, which converts Li 2 NiO 2 、Li 5 FeO 4 The lithium ion battery with the lithium supplementing effect is prepared by adding the lithium supplementing agent and the positive active material into a solvent together to prepare positive slurry, and then coating the positive slurry on the surface of a current collector.
In conclusion, the preparation of the lithium iron phosphate thick electrode with excellent rate capability and cycle performance has great significance for the research and development of lithium ion batteries.
Disclosure of Invention
Aiming at the problems in the prior art, the invention aims to provide a long-cycle lithium iron phosphate thick electrode, a preparation method thereof and a lithium ion battery. According to the lithium iron phosphate thick electrode, the first coating, the second coating and the lithium supplement layer are sequentially arranged on the surface of the current collector, the first coating and the second coating respectively contain small-particle lithium iron phosphate and large-particle lithium iron phosphate, and the structure of double-layer coating of the large particles and the small particles can effectively improve the liquid phase transmission efficiency and the dynamic performance of the lithium iron phosphate thick electrode; meanwhile, the lithium supplement layer can effectively make up the irreversible capacity loss in the thick electrode and improve the cycle performance of the electrode, the lithium supplement layer is arranged on the outermost layer, is also favorable for discharging produced gas in the formation process, and has synergistic effect with the first coating and the second coating, and meanwhile, the rate capability and the cycle performance of the lithium iron phosphate thick electrode are improved.
In the invention, the long circulation refers to that the capacity retention rate of the battery is still not lower than 80.6% after the battery is circulated for 5000 circles under the multiplying power of 0.5C/0.5C; "Thick electrode" means that the thickness of the electrode is not less than 100 μm.
In order to achieve the purpose, the invention adopts the following technical scheme:
in a first aspect, the invention provides a thick lithium iron phosphate electrode, which comprises a current collector and a first coating layer arranged on at least one side surface of the current collector, wherein the first coating layer is further sequentially provided with a second coating layer and a lithium supplement layer on one side surface far away from the current collector, the first coating layer comprises small-particle lithium iron phosphate, and the second coating layer comprises large-particle lithium iron phosphate.
Preferably, the median particle size of the small-particle lithium iron phosphate in the first coating is 0.1-1 μm.
Preferably, the median particle size of the large-particle lithium iron phosphate in the second coating layer is 1-10 μm, and the median particle size of the large-particle lithium iron phosphate is larger than that of the small-particle lithium iron phosphate.
Preferably, the lithium supplement layer comprises a lithium supplement agent and a binder.
Preferably, the mass ratio of the lithium supplement agent to the binder in the lithium supplement layer is (30-50) to (20-60).
Preferably, the lithium supplement layer further includes a conductive agent.
Preferably, the mass ratio of the lithium supplement agent to the conductive agent to the binder in the lithium supplement layer is (30-50) to (10-30) to (20-60).
Preferably, the lithium supplement agent comprises Li 2 NiO 2 、Li 5 FeO 4 And Li 2 Any one of O or a combination of at least two of O.
Preferably, the total thickness of the first coating layer and the second coating layer is 100 to 1000 μm.
Preferably, the thickness ratio of the first coating layer to the second coating layer is 1:4 to 2:1.
Preferably, the thickness of the lithium supplement layer is 3 to 10 μm.
Preferably, the first coating layer and the second coating layer independently comprise a conductive agent and a binder.
Preferably, the mass ratio of the small-particle lithium iron phosphate to the binder to the conductive agent in the first coating is (90-95): (1-2): (3-5).
Preferably, the mass ratio of the large-particle lithium iron phosphate to the binder to the conductive agent in the second coating is (92-96): (1-2): 1-2).
Preferably, the conductive agent in the first coating layer, the conductive agent in the second coating layer, and the conductive agent in the lithium supplement layer independently include any one of carbon black, acetylene black, ketjen black, carbon nanotubes, carbon fibers, and graphene, or a combination of at least two thereof.
Preferably, the binder in the first coating, the binder in the second coating, and the binder in the lithium supplement layer independently comprise polyvinylidene fluoride.
Preferably, the compacted density of the lithium iron phosphate thick electrode is 2.4-2.7 g/cm 3 。
In a second aspect, the invention provides a method for preparing a thick lithium iron phosphate electrode according to the first aspect, wherein the method comprises the following steps:
respectively adopting small-particle lithium iron phosphate and large-particle lithium iron phosphate to prepare a first slurry and a second slurry, preparing a lithium supplementing slurry, coating the first slurry, the second slurry and the lithium supplementing slurry on the surface of a current collector, and forming a first coating, a second coating and a lithium supplementing layer which are sequentially stacked on the surface of at least one side of the current collector to obtain a lithium iron phosphate thick electrode.
Preferably, the first slurry, the second slurry and the lithium supplement slurry are applied to the surface of the current collector in the following manner:
and coating the first slurry and the second slurry on at least one side surface of the current collector in a double-layer coating mode, baking to obtain a first coating and a second coating, and coating the lithium supplementing slurry on the surface of the second coating to obtain a lithium supplementing layer.
Preferably, the lithium supplement slurry is coated on the surface of the current collector by a slit extrusion coating, a gravure coating or a micro-gravure coating.
In a third aspect, the invention provides a lithium ion battery, and the positive electrode of the lithium ion battery adopts the thick lithium iron phosphate electrode according to the first aspect.
Compared with the prior art, the invention has the following beneficial effects:
the lithium iron phosphate thick electrode comprises a current collector, and a first coating, a second coating and a lithium supplementing layer which are sequentially arranged on the surface of the current collector, wherein the first coating and the second coating respectively contain small-particle lithium iron phosphate and large-particle lithium iron phosphate, and the structure of double-layer coating of the small and large particles can effectively improve the liquid phase transmission efficiency and the dynamic performance of the lithium iron phosphate thick electrode, so that the multiplying power performance of the lithium iron phosphate thick electrode is greatly improved. Meanwhile, the lithium iron phosphate thick electrode also comprises a lithium supplement layer arranged on the surface of one side, away from the current collector, of the second coating, and the lithium supplement layer can effectively make up for irreversible capacity loss of the thick electrode and remarkably improve the cycle performance of the thick electrode; the lithium supplement layer is arranged on the surface of the thick electrode, and gas generated in the formation process is easy to discharge, so that the gas is efficiently discharged in the formation stage, and the stability of the battery in the subsequent cycle process is prevented from being influenced. The specific first coating, the second coating and the lithium supplement layer cooperate with each other, so that the rate capability and the cycle performance of the lithium iron phosphate thick electrode can be improved simultaneously.
Drawings
Fig. 1 is a schematic structural diagram of a thick lithium iron phosphate electrode according to an embodiment of the present invention.
Fig. 2 is a schematic structural diagram of an apparatus for preparing a thick lithium iron phosphate electrode according to an embodiment of the present invention.
Fig. 3 is a graph comparing the performance of lithium iron phosphate thick electrodes of examples 1 to 5 of the present invention and comparative examples 1 to 5 at different rates.
Fig. 4 is a graph comparing the performance of the lithium iron phosphate thick electrodes of examples 1 to 5 of the present invention and comparative examples 1 to 5 at different cycle numbers.
Wherein, 1-current collector; 2-a first coating; 3-a second coating; 4-lithium supplement layer; 5, an unwinding device; 6-double layer simultaneous coating die; 7-a drying device; 8-lithium supplement coating device; 9-a rolling device; 10-a winding device.
Detailed Description
The technical solution of the present invention is further explained by the following embodiments. It should be understood by those skilled in the art that the examples are only for the understanding of the present invention and should not be construed as the specific limitations of the present invention.
The development of a thick electrode is an important method and strategy for improving the energy density of a lithium battery, the internal resistance of the battery is obviously increased along with the increase of the thickness of the electrode, the rate capability of the battery is rapidly deteriorated, the irreversible reaction in the circulating process is aggravated, and the service life of the battery is obviously reduced. In order to simultaneously optimize the rate capability and the cycle performance of the thick electrode, the invention provides the long-cycle lithium iron phosphate thick electrode, the preparation method thereof and the lithium ion battery, and the long-cycle lithium iron phosphate thick electrode has important value in the development and application aspects of the lithium ion battery thick electrode.
The invention provides a lithium iron phosphate thick electrode, which is shown in a schematic structural diagram in fig. 1, and comprises a current collector 1 and a first coating layer 2 arranged on at least one side surface of the current collector 1, wherein the first coating layer 2 is further provided with a second coating layer 3 and a lithium supplement layer 4 in sequence on one side surface far away from the current collector 1, the first coating layer 2 comprises small-particle lithium iron phosphate, and the second coating layer 3 comprises large-particle lithium iron phosphate.
The lithium iron phosphate thick electrode comprises a current collector 1, and a first coating 2, a second coating 3 and a lithium supplement layer 4 which are sequentially arranged on the surface of the current collector 1, wherein the first coating 2 and the second coating 3 respectively contain small-particle lithium iron phosphate and large-particle lithium iron phosphate, the particle size of the lithium iron phosphate in the first coating 2 close to the surface of the current collector 1 is smaller, and the particle size of the lithium iron phosphate in the second coating 3 far away from the surface of the current collector 1 is larger. On the other hand, the lithium iron phosphate thick electrode also comprises a lithium supplement layer 4 arranged on the surface of one side, away from the current collector 1, of the second coating 3, and the lithium supplement layer 4 can effectively make up the irreversible capacity loss of the thick electrode and remarkably improve the cycle performance of the thick electrode; meanwhile, the lithium supplement layer 4 is arranged on the surface of the thick electrode, and gas generated in the formation process is easy to discharge, so that the gas is efficiently discharged in the formation stage, and the stability of the battery in the subsequent cycle process is prevented from being influenced. The specific first coating 2, the second coating 3 and the lithium supplement layer 4 in the invention have synergistic effect, and the rate capability and the cycle performance of the lithium iron phosphate thick electrode can be improved simultaneously.
In some embodiments, the small-particle lithium iron phosphate in the first coating layer 2 has a median particle size of 0.1 to 1 μm, and may be, for example, 0.1 μm, 0.2 μm, 0.3 μm, 0.4 μm, 0.5 μm, 0.6 μm, 0.7 μm, 0.8 μm, 0.9 μm, 1 μm, or the like.
In some embodiments, the median particle size of the large-particle lithium iron phosphate in the second coating layer 3 is 1 to 10 μm, and may be, for example, 1 μm, 2 μm, 3 μm, 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, or 10 μm, and the like, and the median particle size of the large-particle lithium iron phosphate is larger than the median particle size of the small-particle lithium iron phosphate.
In the present invention, the median particle diameter is a value known in the art, also referred to as median particle diameter or average particle diameter D50, and is used to indicate the average particle size of the active material, and the physical meaning is that particles smaller than this diameter account for 50% of the total volume of the particles, and particles larger than this diameter also account for 50% of the total volume of the particles. The median particle size can be conveniently determined using a laser particle size analyzer.
According to the invention, the median particle diameters of large-particle lithium iron phosphate and small-particle lithium iron phosphate are further optimized, when the particle diameter of large particles is larger, the solid-phase transmission path of lithium ions in the second coating 3 is obviously increased, the solid-phase diffusion rate of the lithium ions is obviously deteriorated, the dynamic performance is rapidly attenuated, and in addition, the compaction density of the thick electrode is lower. When the particle size of the small particles is smaller, the pores among the first coating 2 are smaller, the liquid phase transmission resistance of the electrolyte is large, the liquid phase ohmic resistance is remarkably increased, and meanwhile, the large specific surface area of the small particles causes the thick electrode to have low compacted density and poor cycle performance, so that the thick electrode with excellent rate performance and good cycle stability is difficult to obtain.
In some embodiments, the lithium supplement layer 4 includes a lithium supplement agent and a binder.
In some embodiments, the mass ratio of the lithium supplement agent to the binder in the lithium supplement layer 4 is (30-50): (20-60), wherein the selection range of the lithium supplement agent (30-50) can be, for example, 30, 32, 34, 36, 38, 40, 42, 44, 46, 48 or 50, etc., and the selection range of the binder (20-60) can be, for example, 20, 25, 30, 35, 40, 45, 50, 55 or 60, etc.
In the invention, when the lithium supplement layer 4 contains the lithium supplement agent and a large amount of the binder, on one hand, the large amount of the binder can be coated on the surface of the lithium supplement agent, so that the contact of the lithium supplement agent and air in the preparation process of the lithium iron phosphate thick electrode is effectively avoided, the side reaction on the surface of the lithium supplement agent or the surface of a pole piece can be effectively inhibited, the stability is improved, and longer circulation is realized; on the other hand, because the lithium supplement layer 4 contains the binder with higher content, when the lithium supplement agent is reduced or disappeared after the lithium supplement agent exerts the lithium supplement effect in the formation stage, the lithium supplement layer 4 can be changed into a polymer film-shaped binder layer to be coated on the surface of the lithium iron phosphate thick electrode, and the binder layer contains pores caused by gas production of the lithium supplement agent, so that the diaphragm wrinkling is effectively inhibited, the wettability of the diaphragm is improved, and the rate capability and the cycle performance of the thick electrode are further improved. Therefore, the lithium supplement layer 4 contains the lithium supplement agent and the binder in a mass ratio of (30-50) to (20-60), so that the stability of the pre-lithiation can be improved, and the battery interface effect can be optimized.
In some embodiments, the lithium supplement layer 4 further comprises a conductive agent.
In some embodiments, the mass ratio of the lithium supplement agent, the conductive agent and the binder in the lithium supplement layer 4 is (30-50): (10-30): (20-60), wherein the selection range of the lithium supplement agent (30-50) can be, for example, 30, 32, 34, 36, 38, 40, 42, 44, 46, 48 or 50, etc., the selection range of the conductive agent (10-30) can be, for example, 10, 12, 14, 16, 18, 20, 22, 24, 26, 28 or 30, etc., and the selection range of the binder (20-60) can be, for example, 20, 25, 30, 35, 40, 45, 50, 55 or 60, etc.
According to the invention, the surface of the lithium supplement agent can be coated by the conductive agent and the binder with higher contents, and the conductive agent, the binder and the lithium supplement agent with higher contents can inhibit the occurrence of side reactions on the surface of the lithium iron phosphate thick electrode according to proper content proportion, so that the pre-lithium stability of the lithium supplement layer 4 is improved; meanwhile, the high-content conductive agent remarkably improves the de-intercalation reaction rate of the lithium supplement agent, and is cooperated with the specific first coating 2 and the specific second coating 3, so that the coulomb efficiency of the pole piece after lithium supplement is remarkably improved.
In some embodiments, the lithium supplement agent comprises Li 2 NiO 2 、Li 5 FeO 4 And Li 2 Any one of O or a combination of at least two of O.
In some embodiments, the total thickness of the first coating layer 2 and the second coating layer 3 is 100 to 1000 μm, for example, 100 μm, 200 μm, 300 μm, 400 μm, 500 μm, 600 μm, 700 μm, 800 μm, 900 μm, or 1000 μm, and the like, and in this thickness range, it is beneficial to improve the energy density and the cycle performance of the battery cell, and if the thickness is too high, the polarization of the battery is large, and the cycle life is significantly reduced.
In some embodiments, the thickness ratio of the first 2 and second 3 coatings is 1:4 to 2:1, for example 1:4, 1:3, 1:2, 1:1, 1.5 or 2:1, and the like.
According to the invention, the thickness ratio of the first coating 2 to the second coating 3 is controlled within the range of 1:4-2:1, so that the pore structure of the thick electrode can be effectively regulated and controlled, the transmission of electrolyte in the thickness direction of the electrode is promoted, and the dynamic performance and the cycling stability of the thick electrode are improved.
In some embodiments, the thickness of the lithium supplement layer 4 is 3 to 10 μm, for example, 3 μm, 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, or 10 μm, and the thickness is selected to be favorable for exerting the pre-lithium effect, better combine with the first coating layer 2 and the second coating layer 3, improve the cycle performance of the lithium iron phosphate thick electrode, and also be favorable for improving the effects of inhibiting membrane wrinkling and improving membrane wettability after the lithium iron phosphate thick electrode is changed into the binder layer in the formation stage, and further improve the rate capability and cycle performance of the lithium iron phosphate thick electrode.
In some embodiments, the first coating layer 2 and the second coating layer 3 independently include a conductive agent and a binder.
In the present invention, "independently" means that the two choices do not interfere with each other, for example, the first coating layer 2 and the second coating layer 3 further include a conductive agent and a binder independently, the first coating layer 2 may include the conductive agent, the second coating layer 3 may include the binder, or both the first coating layer 2 and the second coating layer 3 may include the conductive agent and the binder, the two choices do not interfere with each other, and when both the first coating layer 2 and the second coating layer 3 include the conductive agent and/or the binder, the kind of the conductive agent and/or the binder in the first coating layer 2 may be the same as or different from that in the second coating layer 3.
In some embodiments, the mass ratio of the small-particle lithium iron phosphate to the binder and the conductive agent in the first coating layer 2 is (90-95) to (1-2) to (3-5), wherein the small-particle lithium iron phosphate may be selected from a range (90-95) of, for example, 90, 91, 92, 93, 94, or 95, the binder may be selected from a range (1-2) of, for example, 1, 1.1, 1.2, 1.5, 1.8, or 2, and the conductive agent may be selected from a range (3-5) of, for example, 3, 3.2, 3.5, 3.8, 4, 4.2, 4.5, or 5.
In some embodiments, the mass ratio of the large-particle lithium iron phosphate, the binder, and the conductive agent in the second coating layer 3 is (92 to 96): (1-2) wherein the large-particle lithium iron phosphate can be selected from the range of 90-96 (90-96) such as 90, 91, 92, 93, 94, 95 or 96, the binder can be selected from the range of 1-2 (1-2) such as 1, 1.1, 1.2, 1.5, 1.8 or 2, and the conductive agent can be selected from the range of 1-2 (1-2) such as 1, 1.1, 1.2, 1.5, 1.8 or 2.
In some embodiments, the conductive agent in the first coating layer 2, the conductive agent in the second coating layer 3, and the conductive agent in the lithium supplement layer 4 independently include any one or a combination of at least two of carbon black, acetylene black, ketjen black, carbon nanotubes, carbon fibers, and graphene, and may be, for example, a combination of carbon black and acetylene black, a combination of carbon fibers and graphene, a combination of ketjen black and carbon nanotubes, or a combination of carbon black, acetylene black, ketjen black, carbon nanotubes, carbon fibers and graphene.
In some embodiments, the binder in the first coating 2, the binder in the second coating 3, and the binder in the lithium supplement layer 4 independently comprise polyvinylidene fluoride (PVDF).
In some embodiments, the compacted density of the lithium iron phosphate thick electrode is 2.4-2.7 g/cm 3 For example, it may be 2.45g/cm 3 、2.5g/cm 3 、2.55g/cm 3 、2.6g/cm 3 、2.65g/cm 3 Or 2.7g/cm 3 And the like.
It should be noted that, the pole piece in the battery generally needs to be dried and rolled after being prepared, and the compacted density of the lithium iron phosphate thick electrode in the invention refers to the compacted density of the pole piece after being dried and rolled.
The specific embodiment of the invention also provides a preparation method of the lithium iron phosphate thick electrode, and the preparation method comprises the following steps:
respectively adopting small-particle lithium iron phosphate and large-particle lithium iron phosphate to prepare first slurry and second slurry, preparing and supplementing lithium slurry, coating the first slurry, the second slurry and the lithium supplementing slurry on the surface of a current collector 1, and forming a first coating 2, a second coating 3 and a lithium supplementing layer 4 which are sequentially stacked on the surface of at least one side of the current collector 1 to obtain a lithium iron phosphate thick electrode.
In some embodiments, applying the first slurry, the second slurry, and the lithium replenishment slurry to the surface of the current collector 1 is performed as follows:
and coating the first slurry and the second slurry on at least one side surface of the current collector 1 in a double-layer coating mode, baking to obtain a first coating 2 and a second coating 3, and coating the lithium supplementing slurry on the surface of the second coating 3 to obtain a lithium supplementing layer 4.
In some embodiments, the dual layer coating is performed using a dual layer simultaneous coating die 6.
In some embodiments, the lithium supplement slurry is applied to the surface of the current collector 1 by a method including slot extrusion coating, gravure coating, or micro-gravure coating.
In some embodiments, the lithium supplement slurry is prepared in a sealing device, so that the lithium supplement slurry can effectively avoid contact with air in the preparation process, and the binder and the conductive agent are coated on the surface of the lithium supplement agent after discharging, so that the occurrence of surface side reaction is further inhibited, and the stability is improved.
The specific embodiment of the invention also provides a device for preparing a lithium iron phosphate thick electrode, the structural schematic diagram of which is shown in fig. 2, and the device comprises an unreeling device 5, a double-layer simultaneous coating die head 6, a lithium supplement coating device 8, a rolling device 9 and a reeling device 10 which are sequentially arranged.
In some embodiments, a drying device 7 is further disposed between the double-layer simultaneous coating die 6 and the lithium supplement coating device 8, and between the lithium supplement coating device 8 and the rolling device 9.
According to the invention, an unreeling device 5 unreels a current collector 1, a first slurry and a second slurry are simultaneously coated on the surface of the current collector 1 through a double-layer simultaneous coating die head 6, a drying device 7 dries the current collector, a lithium supplement coating device 8 is utilized to coat the lithium supplement slurry on the surface of a second coating 3 formed by the second slurry, the drying device 7 dries the current collector again, a lithium supplement layer 4 is formed on the surface of the second coating 3, and the lithium supplement layer is rolled by a rolling device 9 to obtain a lithium iron phosphate thick electrode.
In some embodiments, the lithium supplement coating device 8 is a micro-gravure coating device, the micro-gravure coating device is thin and is a seal coating device, which is suitable for the coating of the lithium supplement slurry, and is beneficial to air isolation, thereby further enhancing the stability of the lithium supplement slurry.
The invention also provides a lithium ion battery, and the anode of the lithium ion battery adopts the lithium iron phosphate thick electrode.
The lithium ion battery has higher rate performance and excellent cycle performance, and also has higher capacity retention rate after 5000 cycles.
Example 1
The embodiment provides a thick electrode of lithium iron phosphate, and its schematic structure is shown in fig. 1, the thick electrode of lithium iron phosphate includes that mass ratio is 94 in the first coating 2 including collecting body 1 and setting gradually first coating 2, second coating 3 and the lithium supplement layer 4 on collecting body 1 side surface, first coating 2: 2:4, small-particle lithium iron phosphate, a binder PVDF and conductive agent carbon black, wherein the median particle size of the small-particle lithium iron phosphate is 0.5 mu m; the second coating 3 comprises a coating with a mass ratio of 96:2:2, large-particle lithium iron phosphate, a binder PVDF and a conductive agent carbon black, wherein the median particle size of the large-particle lithium iron phosphate is 3 μm; the lithium supplement layer 4 comprises a lithium supplement agent Li with a mass ratio of 45 5 FeO 4 Carbon black and PVDF;
the thickness of the first coating layer 2 is 100 mu m, the thickness of the second coating layer 3 is 200 mu m, the thickness of the lithium supplement layer 4 is 5 mu m, and the compaction density of the lithium iron phosphate thick electrode is 2.3g/cm 3 。
The embodiment also provides a preparation method of the lithium iron phosphate thick electrode, which comprises the following steps:
(1) Stirring and dispersing small-particle lithium iron phosphate, PVDF (polyvinylidene fluoride), carbon black and a solvent N-methylpyrrolidone (NMP) to obtain a first slurry; stirring and dispersing large-particle lithium iron phosphate, PVDF, carbon black and NMP to obtain a second slurry; mixing Li 5 FeO 4 Stirring and dispersing carbon black, PVDF and NMP to obtain lithium supplement slurry;
(2) Coating the first slurry and the second slurry on the surface of one side of a current collector 1 by adopting a double-layer simultaneous coating die head 6, respectively forming a first coating 2 with the thickness of 100 mu m and a second coating 3 with the thickness of 200 mu m on the surface of the current collector 1, coating the lithium supplementing slurry on the surface of the second coating 3 after baking to obtain a lithium supplementing layer 4 with the thickness of 5 mu m, and rolling after drying to obtain a compact density of 2.3g/g/cm 3 The lithium iron phosphate thick electrode of (1).
Example 2
The embodiment provides a thick electrode of lithium iron phosphate, and its schematic structure is shown in fig. 1, the thick electrode of lithium iron phosphate includes that mass ratio is 94 in the first coating 2 including collecting body 1 and setting gradually first coating 2, second coating 3 and the lithium supplement layer 4 on collecting body 1 side surface, first coating 2: 2:4, small-particle lithium iron phosphate, a binder PVDF and conductive agent carbon black, wherein the median particle size of the small-particle lithium iron phosphate is 0.5 mu m; the second coating 3 comprises a coating with a mass ratio of 96:2:2, large-particle lithium iron phosphate, a binder PVDF and a conductive agent carbon black, wherein the median particle size of the large-particle lithium iron phosphate is 5 microns; the lithium supplement layer 4 comprises a lithium supplement agent Li with a mass ratio of 45 2 NiO 2 Carbon black and PVDF;
the thickness of the first coating layer 2 is 100 mu m, the thickness of the second coating layer 3 is 200 mu m, the thickness of the lithium supplement layer 4 is 5 mu m, and the compaction density of the lithium iron phosphate thick electrode is 2.3g/cm 3 。
The preparation method of the lithium iron phosphate thick electrode in the embodiment is the same as that of the embodiment 1.
Example 3
This embodiment provides a thick electrode of lithium iron phosphate, its schematic structure diagram is shown in fig. 1, the thick electrode of lithium iron phosphate includes the mass flow body 1 and sets gradually first coating 2, the second coating 3 and mends lithium layer 4 on the mass flow body 1 side surface, package in the first coating 2The mass ratio of the components is 94:2:4, small-particle lithium iron phosphate, a binder PVDF and conductive agent carbon black, wherein the median particle size of the small-particle lithium iron phosphate is 0.5 mu m; the second coating 3 comprises a coating with a mass ratio of 96:2:2, large-particle lithium iron phosphate, a binder PVDF and a conductive agent carbon black, wherein the median particle size of the large-particle lithium iron phosphate is 3 mu m; the lithium supplement layer 4 comprises a lithium supplement agent Li with a mass ratio of 50 2 NiO 2 Carbon black and PVDF;
the thickness of the first coating layer 2 is 150 mu m, the thickness of the second coating layer 3 is 150 mu m, the thickness of the lithium supplement layer 4 is 5 mu m, and the compaction density of the lithium iron phosphate thick electrode is 2.3g/cm 3 。
The preparation method of the lithium iron phosphate thick electrode in the embodiment is the same as that in the embodiment 1.
Example 4
The embodiment provides a thick electrode of lithium iron phosphate, and its schematic structure is shown in fig. 1, the thick electrode of lithium iron phosphate includes that mass ratio is 94 in the first coating 2 including collecting body 1 and setting gradually first coating 2, second coating 3 and the lithium supplement layer 4 on collecting body 1 side surface, first coating 2: 2:4, small-particle lithium iron phosphate, a binder PVDF and a conductive agent carbon black, the median particle size of the small-particle lithium iron phosphate is 0.3 mu m; the second coating 3 comprises a coating with a mass ratio of 96:2:2, large-particle lithium iron phosphate, a binder PVDF and a conductive agent carbon black, wherein the median particle size of the large-particle lithium iron phosphate is 5 microns; the lithium supplement layer 4 comprises a lithium supplement agent Li with a mass ratio of 50 2 NiO 2 Carbon black and PVDF;
the thickness of the first coating layer 2 is 150 mu m, the thickness of the second coating layer 3 is 150 mu m, the thickness of the lithium supplement layer 4 is 10 mu m, and the compaction density of the lithium iron phosphate thick electrode is 2.3g/cm 3 。
The preparation method of the lithium iron phosphate thick electrode in the embodiment is the same as that in the embodiment 1.
Example 5
The embodiment provides a thick electrode of lithium iron phosphate, and its schematic structure is shown in fig. 1, the thick electrode of lithium iron phosphate includes that mass ratio is 94 in the first coating 2 including collecting body 1 and setting gradually first coating 2, second coating 3 and the lithium supplement layer 4 on collecting body 1 side surface, first coating 2: 2:4 small particle of phosphorusLithium iron phosphate, a binder PVDF and a conductive agent carbon black, wherein the median particle size of small-particle lithium iron phosphate is 0.3 mu m; the second coating 3 comprises a coating with a mass ratio of 96:2:2, large-particle lithium iron phosphate, a binder PVDF and a conductive agent carbon black, wherein the median particle size of the large-particle lithium iron phosphate is 5 microns; the lithium supplement layer 4 comprises a lithium supplement agent Li with a mass ratio of 50 2 NiO 2 Carbon black and PVDF;
the thickness of the first coating layer 2 is 150 mu m, the thickness of the second coating layer 3 is 150 mu m, the thickness of the lithium supplement layer 4 is 10 mu m, and the compaction density of the lithium iron phosphate thick electrode is 2.5g/cm 3 。
The preparation method of the lithium iron phosphate thick electrode in the embodiment is the same as that of the embodiment 1.
Example 6
Removing Li in the lithium supplement layer 4 5 FeO 4 The mass ratio of carbon black to PVDF was changed to 63.
Example 7
Removing Li in the lithium-supplementing layer 4 5 FeO 4 The mass ratio of carbon black to PVDF was changed to 30.
Example 8
The procedure of example 1 was repeated except that the median diameter of the small-sized lithium iron phosphate particles was 1.5. Mu.m.
Example 9
The procedure of example 1 was repeated except that the median diameter of the large-particle lithium iron phosphate particles was 11 μm.
Comparative example 1
The thickness of the second coating layer 3 was changed to 305 μm, except that the first coating layer 2 and the lithium supplement layer 4 were not provided, that is, the surface of the current collector 1 was coated with only the second slurry having the same composition as that of example 1 but different in thickness, and the remaining portions were identical to example 1.
Comparative example 2
The thickness of the second coating layer 3 was changed to 305 μm, except that the first coating layer 2 and the lithium supplement layer 4 were not provided, that is, the surface of the current collector 1 was coated with only the second slurry having the same composition as that of example 2 but different in thickness, and the remaining portions were identical to example 2.
Comparative example 3
The thickness of the second coating 3 was changed to 305 μm, that is, only the second slurry having the same composition as that of example 3 but a different thickness was coated on the surface of the current collector 1, except that the first coating 2 and the lithium supplement layer 4 were not provided, and the remaining process was the same as example 3.
Comparative example 4
The thickness of the second coating 3 was replaced with 310 μm, that is, the surface of the current collector 1 was coated with only the second slurry having the same composition as in example 4 but a different thickness, except that the first coating 2 and the lithium supplement layer 4 were not provided, and the remaining examples were the same as example 4.
Comparative example 5
The thickness of the second coating layer 3 was replaced with 310 μm, except that the first coating layer 2 and the lithium supplement layer 4 were not provided, that is, the surface of the current collector 1 was coated with only the second slurry having the same composition as in example 5 but different in thickness, and the rest was identical to example 5.
Comparative example 6
The thickness of the first coating layer 2 was changed to 305 μm, that is, the surface of the current collector 1 was coated with only the first slurry having the same composition as that of example 1 but having a different thickness, except that the second coating layer 3 was not provided, and the remaining steps were identical to those of example 1.
Comparative example 7
The same procedure as in example 1 was repeated except that the lithium supplement layer 4 was not provided.
Comparative example 8
The same procedure as in example 1 was repeated, except that the lithium supplement layer 4 was not provided, and the lithium supplement agent in the lithium supplement slurry was added to the second slurry so that the lithium supplement agent was included in the second coating layer 3.
The mass of the lithium supplement agent in the second coating layer 3 of this comparative example was equal to the mass of the lithium supplement agent in the lithium supplement layer 4 of example 1.
1. Assembly of lithium ion batteries
The lithium iron phosphate thick electrodes prepared in the embodiment and the comparative example are subjected to die cutting and slitting to prepare the positive electrode, graphite is used as the negative electrode, and 1M LiPF is adopted 6 (EC: DMC: EMC =5 = 2) as an electrolyte, and a lamination and injection process was performed to obtain a lithium ion battery.
2. Performance testing
(1) Rate capability: at 25 ℃, the capacity retention rates of the batteries prepared by the lithium iron phosphate thick electrodes under different multiplying factors are tested, the voltage interval is 2.5-3.65V, the multiplying factors are 0.5C, 1C, 2C and 3C respectively, the capacity retention rates are calculated by dividing the discharge capacities under different multiplying factors by the discharge capacity under 0.33C to obtain the capacity retention rates under the corresponding multiplying factors, and the test results are shown in table 1 and fig. 3.
(2) Cycle performance: at 25 ℃, the capacity retention rate of the battery prepared by the lithium iron phosphate thick electrode under different cycle turns is tested, the voltage interval is 2.5-3.65V, the multiplying power is 0.5C/0.5C, the cycle turns are 1000 turns, 2000 turns, 3000 turns and 5000 turns respectively, the capacity retention rate is calculated by dividing the discharge capacity of the first turn by the discharge capacity of the 1000 turns, 2000 turns, 3000 turns and 5000 turns respectively to obtain the capacity retention rate under the corresponding cycle turns, and the test results are shown in table 2 and fig. 4.
TABLE 1
TABLE 2
To sum up, the embodiments 1 to 9 show that the lithium iron phosphate thick electrode of the present invention sequentially has the first coating layer 2, the second coating layer 3 and the lithium supplement layer 4 on the surface of the current collector 1, the first coating layer 2 and the second coating layer 3 respectively contain small-particle lithium iron phosphate and large-particle lithium iron phosphate, and the structure of the large-particle and small-particle double-layer coating can effectively improve the liquid phase transmission efficiency and the dynamic performance of the lithium iron phosphate thick electrode; meanwhile, the lithium supplement layer 4 can effectively make up the irreversible capacity loss in the thick electrode and improve the cycle performance of the electrode, the lithium supplement layer 4 is arranged on the outermost layer, is also favorable for discharging produced gas in the formation process, and is cooperated with the first coating 2 and the second coating 3, so that the rate capability and the cycle performance of the lithium iron phosphate thick electrode are improved.
Fig. 1 and fig. 2 are a rate performance comparison graph and a cycle performance comparison graph of examples 1 to 5 and comparative examples 1 to 5, respectively, and it can be seen from fig. 1 and fig. 2 that the lithium iron phosphate thick electrode prepared by using the specific three-layer structure of the present invention can maintain a high thickness and a high compaction density, and simultaneously ensure the rate performance and the cycle performance, the lithium iron phosphate thick electrode in examples 1 to 5 has a high capacity retention rate under different rates, and is not less than 85% even under a high rate of 3C, and has a long cycle performance, and the capacity retention rate is still about 90% after 5000 cycles of circulation; in comparative examples 1 to 5, the electrode does not contain a double-layer coating structure of large and small particles, and does not contain the lithium supplement layer 4, and after the electrode is prepared into a thick electrode with the same thickness and compacted density, the rate performance is remarkably reduced, and the capacity retention rate after 5000 cycles is reduced by nearly 10%, which is remarkably inferior to that of examples 1 to 5.
As can be seen from comparison between example 1 and comparative example 6 in tables 1-2, when the lithium iron phosphate thick electrode does not include the second coating 3, although the total thickness of the coating is not changed, the entire pole piece does not include a structure coated with two layers of large and small particles, which is not beneficial to improving the liquid phase transmission efficiency and the kinetic performance of the thick electrode, and is not beneficial to exerting the synergistic effect with the lithium supplement layer 4, so the rate performance and the cycle performance of comparative example 6 are significantly inferior to those of example 1.
As can be seen from the comparison between the example 1 and the comparative examples 7 to 8 in the tables 1 to 2, the rate capability and the cycle performance of the lithium iron phosphate thick electrode cannot be effectively improved without arranging the lithium supplement layer 4 or adding a lithium supplement agent into the second coating 3; in comparative example 7, the lithium supplement layer 4 is not arranged, so that irreversible capacity loss of the thick electrode cannot be compensated, and the cycle performance is extremely poor; although the lithium supplement agent with the same content is added in the comparative example 8, the lithium supplement agent in the comparative example 8 is positioned in the second coating 3, the occurrence of surface side reaction cannot be inhibited through the coating effect of the adhesive and the conductive agent, the generated gas is not easy to discharge during formation, an adhesive layer cannot be formed on the surface of a pole piece to inhibit the membrane from wrinkling and improve the membrane wettability, and the interface performance of the battery is remarkably reduced; thus, comparative examples 7-8 are significantly inferior to example 1 in both rate capability and long cycle performance.
As can be seen from the comparison between the embodiment 1 and the embodiments 6 to 7 in tables 1 to 2, the lithium supplement agent, the conductive agent and the binder in the lithium supplement layer 4 of the present invention can inhibit the occurrence of side reactions on the surface of the lithium iron phosphate thick electrode and improve the pre-lithium stability of the lithium supplement layer 4 according to a suitable content ratio; in the embodiment 6, the content of the binder is low, which is not beneficial to forming a coating film on the surface of the lithium supplement agent and reducing the contact with air, and is not beneficial to generating a binder layer in the formation stage of the lithium supplement layer 4, thereby affecting the stability of the thick pole piece; the excessive content of the binder in example 7 affects the rate of the deintercalation reaction of the lithium supplement agent after the binder film is coated, and causes a large surface resistance, so the rate capability and the cycle performance of example 1 are better than those of examples 6 to 7.
As can be seen from the comparison between the example 1 and the examples 8 to 9 in tables 1 to 2, the size of the small-particle lithium iron phosphate in the first coating layer 2 and the size of the large-particle lithium iron phosphate in the second coating layer 3 affect the electrochemical performance of the thick pole piece; in example 8, the small-particle lithium iron phosphate has a large median particle size, which results in a low solid phase diffusion rate at the bottom layer and an increased polarization; in example 9, the large median particle size of the large-particle lithium iron phosphate results in an increase in surface diffusion path and an increase in internal resistance of the electrode; therefore, the rate capability of the lithium iron phosphate thick electrode in example 1 is best.
The above description is only for the specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto, and it should be understood by those skilled in the art that any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope of the present invention are within the protection scope and the disclosure of the present invention.
Claims (10)
1. The utility model provides a thick electrode of lithium iron phosphate, its characterized in that, the thick electrode of lithium iron phosphate includes the mass flow body and sets up the first coating on the at least side surface of mass flow body, first coating still has set gradually the second coating and mends the lithium layer in a side surface of keeping away from the mass flow body, including the small granule lithium iron phosphate in the first coating, including the large granule lithium iron phosphate in the second coating.
2. The thick lithium iron phosphate electrode of claim 1, wherein the median particle size of the small-particle lithium iron phosphate in the first coating layer is 0.1-1 μm;
preferably, the median particle size of the large-particle lithium iron phosphate in the second coating layer is 1-10 μm, and the median particle size of the large-particle lithium iron phosphate is larger than that of the small-particle lithium iron phosphate.
3. The thick lithium iron phosphate electrode according to claim 1 or 2, wherein the lithium supplement layer comprises a lithium supplement agent and a binder;
preferably, the mass ratio of the lithium supplement agent to the binder in the lithium supplement layer is (30-50) to (20-60);
preferably, the lithium supplement layer further comprises a conductive agent;
preferably, the mass ratio of the lithium supplement agent, the conductive agent and the binder in the lithium supplement layer is (30-50): (10-30): (20-60);
preferably, the lithium supplement agent comprises Li 2 NiO 2 、Li 5 FeO 4 And Li 2 Any one of O or a combination of at least two of O.
4. The thick lithium iron phosphate electrode according to any one of claims 1 to 3, wherein the total thickness of the first coating layer and the second coating layer is 100 to 1000 μm;
preferably, the thickness ratio of the first coating layer to the second coating layer is 1:4 to 2:1;
preferably, the thickness of the lithium supplement layer is 3 to 10 μm.
5. The lithium iron phosphate thick electrode according to any one of claims 1 to 4, wherein the first coating layer and the second coating layer independently comprise a conductive agent and a binder;
preferably, the mass ratio of the small-particle lithium iron phosphate to the binder to the conductive agent in the first coating is (90-95) to (1-2) to (3-5);
preferably, the mass ratio of the large-particle lithium iron phosphate to the binder to the conductive agent in the second coating is (92-96) to (1-2);
preferably, the conductive agent in the first coating layer, the conductive agent in the second coating layer and the conductive agent in the lithium supplement layer independently comprise any one of carbon black, acetylene black, ketjen black, carbon nanotubes, carbon fibers and graphene or a combination of at least two of the same;
preferably, the binder in the first coating, the binder in the second coating, and the binder in the lithium supplement layer independently comprise polyvinylidene fluoride.
6. The thick lithium iron phosphate electrode according to any one of claims 1 to 5, wherein the compacted density of the thick lithium iron phosphate electrode is 2.4 to 2.7g/cm 3 。
7. The method for preparing the lithium iron phosphate thick electrode according to any one of claims 1 to 6, wherein the method comprises the following steps:
adopt small granule lithium iron phosphate and large granule lithium iron phosphate to prepare first thick liquids and second thick liquids respectively to prepare and mend lithium thick liquids, will first thick liquids, second thick liquids and the coating of mend lithium thick liquids are to the surface of mass flow body, form first coating, second coating and the benefit lithium layer that stacks gradually on at least one side surface of mass flow body, obtain the thick electrode of lithium iron phosphate.
8. The preparation method according to claim 7, wherein the application of the first slurry, the second slurry and the lithium supplement slurry to the surface of the current collector is performed as follows:
and coating the first slurry and the second slurry on at least one side surface of the current collector in a double-layer coating mode, baking to obtain a first coating and a second coating, and coating the lithium supplement slurry on the surface of the second coating to obtain a lithium supplement layer.
9. The preparation method according to claim 7 or 8, wherein the manner of coating the lithium supplement slurry on the surface of the current collector comprises slot extrusion coating, gravure coating or micro-gravure coating.
10. A lithium ion battery, characterized in that, the lithium iron phosphate thick electrode according to any one of claims 1-6 is adopted as the positive electrode of the lithium ion battery.
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| CN116435459B (en) * | 2023-06-08 | 2023-11-24 | 合肥国轩高科动力能源有限公司 | Positive plate and preparation method thereof, lithium ion battery and preparation method thereof |
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