CN117219729A - Lithium iron phosphate positive plate and preparation method and application thereof - Google Patents
Lithium iron phosphate positive plate and preparation method and application thereof Download PDFInfo
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- CN117219729A CN117219729A CN202311188745.0A CN202311188745A CN117219729A CN 117219729 A CN117219729 A CN 117219729A CN 202311188745 A CN202311188745 A CN 202311188745A CN 117219729 A CN117219729 A CN 117219729A
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- iron phosphate
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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 91
- 238000002360 preparation method Methods 0.000 title abstract description 19
- 239000011247 coating layer Substances 0.000 claims abstract description 151
- 239000010410 layer Substances 0.000 claims abstract description 81
- 239000006258 conductive agent Substances 0.000 claims abstract description 50
- 239000011248 coating agent Substances 0.000 claims abstract description 45
- 238000000576 coating method Methods 0.000 claims abstract description 45
- 239000002245 particle Substances 0.000 claims abstract description 25
- 229910001416 lithium ion Inorganic materials 0.000 claims abstract description 24
- HBBGRARXTFLTSG-UHFFFAOYSA-N Lithium ion Chemical compound [Li+] HBBGRARXTFLTSG-UHFFFAOYSA-N 0.000 claims abstract description 18
- 239000011230 binding agent Substances 0.000 claims abstract description 8
- 239000006255 coating slurry Substances 0.000 claims description 59
- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 claims description 43
- 238000000034 method Methods 0.000 claims description 23
- 239000002041 carbon nanotube Substances 0.000 claims description 21
- 229910021393 carbon nanotube Inorganic materials 0.000 claims description 21
- 229910002804 graphite Inorganic materials 0.000 claims description 20
- 239000010439 graphite Substances 0.000 claims description 20
- 239000000203 mixture Substances 0.000 claims description 12
- VNWKTOKETHGBQD-UHFFFAOYSA-N methane Chemical group C VNWKTOKETHGBQD-UHFFFAOYSA-N 0.000 claims description 11
- SECXISVLQFMRJM-UHFFFAOYSA-N N-Methylpyrrolidone Chemical group CN1CCCC1=O SECXISVLQFMRJM-UHFFFAOYSA-N 0.000 claims description 8
- 230000007423 decrease Effects 0.000 claims description 7
- 239000003792 electrolyte Substances 0.000 claims description 5
- 239000002904 solvent Substances 0.000 claims description 4
- 230000005540 biological transmission Effects 0.000 abstract description 9
- 239000011148 porous material Substances 0.000 abstract description 9
- NCZYUKGXRHBAHE-UHFFFAOYSA-K [Li+].P(=O)([O-])([O-])[O-].[Fe+2].[Li+] Chemical compound [Li+].P(=O)([O-])([O-])[O-].[Fe+2].[Li+] NCZYUKGXRHBAHE-UHFFFAOYSA-K 0.000 abstract description 6
- 238000005096 rolling process Methods 0.000 description 41
- 239000002002 slurry Substances 0.000 description 32
- 239000011149 active material Substances 0.000 description 22
- 239000002033 PVDF binder Substances 0.000 description 21
- 229920002981 polyvinylidene fluoride Polymers 0.000 description 21
- 238000001035 drying Methods 0.000 description 17
- 229910010707 LiFePO 4 Inorganic materials 0.000 description 14
- 230000000052 comparative effect Effects 0.000 description 10
- 229910010710 LiFePO Inorganic materials 0.000 description 7
- XAGFODPZIPBFFR-UHFFFAOYSA-N aluminium Chemical compound [Al] XAGFODPZIPBFFR-UHFFFAOYSA-N 0.000 description 7
- 229910052782 aluminium Inorganic materials 0.000 description 7
- 230000009286 beneficial effect Effects 0.000 description 7
- 239000011888 foil Substances 0.000 description 7
- 238000005056 compaction Methods 0.000 description 6
- 238000000265 homogenisation Methods 0.000 description 6
- 239000000463 material Substances 0.000 description 6
- 150000002500 ions Chemical class 0.000 description 5
- 230000001105 regulatory effect Effects 0.000 description 4
- OIFBSDVPJOWBCH-UHFFFAOYSA-N Diethyl carbonate Chemical compound CCOC(=O)OCC OIFBSDVPJOWBCH-UHFFFAOYSA-N 0.000 description 2
- KMTRUDSVKNLOMY-UHFFFAOYSA-N Ethylene carbonate Chemical group O=C1OCCO1 KMTRUDSVKNLOMY-UHFFFAOYSA-N 0.000 description 2
- 239000013543 active substance Substances 0.000 description 2
- 229910052799 carbon Inorganic materials 0.000 description 2
- 239000002131 composite material Substances 0.000 description 2
- 239000006185 dispersion Substances 0.000 description 2
- JBTWLSYIZRCDFO-UHFFFAOYSA-N ethyl methyl carbonate Chemical compound CCOC(=O)OC JBTWLSYIZRCDFO-UHFFFAOYSA-N 0.000 description 2
- 238000002474 experimental method Methods 0.000 description 2
- 238000012986 modification Methods 0.000 description 2
- 230000004048 modification Effects 0.000 description 2
- 238000007709 nanocrystallization Methods 0.000 description 2
- 239000007774 positive electrode material Substances 0.000 description 2
- WHXSMMKQMYFTQS-UHFFFAOYSA-N Lithium Chemical compound [Li] WHXSMMKQMYFTQS-UHFFFAOYSA-N 0.000 description 1
- RTAQQCXQSZGOHL-UHFFFAOYSA-N Titanium Chemical compound [Ti] RTAQQCXQSZGOHL-UHFFFAOYSA-N 0.000 description 1
- 229910021383 artificial graphite Inorganic materials 0.000 description 1
- 230000003247 decreasing effect Effects 0.000 description 1
- 230000007547 defect Effects 0.000 description 1
- IEJIGPNLZYLLBP-UHFFFAOYSA-N dimethyl carbonate Chemical compound COC(=O)OC IEJIGPNLZYLLBP-UHFFFAOYSA-N 0.000 description 1
- 238000009826 distribution Methods 0.000 description 1
- 230000000694 effects Effects 0.000 description 1
- 229910021385 hard carbon Inorganic materials 0.000 description 1
- 229910052744 lithium Inorganic materials 0.000 description 1
- -1 lithium hexafluorophosphate Chemical compound 0.000 description 1
- 229910003002 lithium salt Inorganic materials 0.000 description 1
- 159000000002 lithium salts Chemical group 0.000 description 1
- 239000002931 mesocarbon microbead Substances 0.000 description 1
- 238000005457 optimization Methods 0.000 description 1
- 239000003960 organic solvent Substances 0.000 description 1
- 230000010287 polarization Effects 0.000 description 1
- 238000011160 research Methods 0.000 description 1
- 239000002153 silicon-carbon composite material Substances 0.000 description 1
- 229910021384 soft carbon Inorganic materials 0.000 description 1
- 238000012360 testing method Methods 0.000 description 1
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- Battery Electrode And Active Subsutance (AREA)
Abstract
The invention belongs to the technical field of lithium iron phosphate lithium ion batteries, relates to a positive plate of a lithium iron phosphate lithium ion battery, and in particular relates to a lithium iron phosphate positive plate, and a preparation method and application thereof. The active coating comprises a current collector, wherein at least two active coating layers are arranged on the surface of the current collector; the particle size of the lithium iron phosphate is gradually reduced from the inner layer to the outer layer, and the conductivity of the conductive agent is gradually increased from the inner layer to the outer layer; the active coating layer comprises the following components in percentage by mass: 0.5-2.5% of conductive agent, 1.5-2.5% of binder and the balance of lithium iron phosphate; the particle size of the lithium iron phosphate is 0.6-1.8 mu m. According to the invention, on the premise of ensuring that the addition amount of the lithium iron phosphate is not reduced, the internal pore diameter structure of the pole piece is optimized, and the internal lithium ion transmission impedance and the direct current internal resistance of the battery are reduced, so that the rate capability and the cycle performance of the lithium iron phosphate lithium ion battery are improved.
Description
Technical Field
The invention belongs to the technical field of lithium iron phosphate lithium ion batteries, relates to a positive plate of a lithium iron phosphate lithium ion battery, and in particular relates to a lithium iron phosphate positive plate, and a preparation method and application thereof.
Background
The disclosure of this background section is only intended to increase the understanding of the general background of the invention and is not necessarily to be construed as an admission or any form of suggestion that this information forms the prior art already known to those of ordinary skill in the art.
The lithium iron phosphate is an olivine-structured positive electrode material, the electron and ion transmission rate is low, the pore diameter distribution state of the pole piece is difficult to control during coating, and the poor pore diameter state after rolling can further aggravate polarization in the battery cycle process, so that the cycle performance of the lithium ion battery prepared by using the lithium iron phosphate as the positive electrode material is affected.
According to research and understanding of the inventor, the main methods for improving the multiplying power performance and the cycle performance of the lithium iron phosphate lithium ion battery at present are carbon coating, material nanocrystallization, conductive agent addition and the like, wherein the methods of carbon coating and material nanocrystallization need to improve the lithium iron phosphate per se, and the cost is high; and the addition of the conductive agent may result in a decrease in the addition amount of lithium iron phosphate, thereby decreasing the battery energy density.
Disclosure of Invention
In order to solve the defects in the prior art, the invention aims to provide the lithium iron phosphate positive plate and the preparation method and application thereof, and the lithium iron phosphate positive plate can optimize the internal pore structure of a pole piece and reduce the internal lithium ion transmission impedance and the internal DC resistance of a battery on the premise of ensuring that the addition amount of lithium iron phosphate is not reduced, so that the multiplying power performance and the cycle performance of the lithium iron phosphate battery are improved.
In order to achieve the above purpose, the technical scheme of the invention is as follows:
in one aspect, a lithium iron phosphate positive electrode sheet comprises a current collector, wherein at least two active coating layers are arranged on the surface of the current collector; taking an active coating layer close to the surface of a current collector as an inner layer, taking an active coating layer far away from the surface of the current collector as an outer layer, gradually reducing the particle size of lithium iron phosphate from the inner layer to the outer layer, and gradually increasing the conductivity of the conductive agent from the inner layer to the outer layer;
the active coating layer comprises the following components in percentage by mass: 0.5-2.5% of conductive agent, 1.5-2.5% of binder and the balance of lithium iron phosphate; the particle size of the lithium iron phosphate is 0.6-1.8 mu m.
In order to improve the transmission efficiency of ions and electrons in the positive plate, a plurality of active coating layers are arranged, and particle sizes of active substances lithium iron phosphate in different active coating layers and the conductivity of a conductive agent are adjusted, wherein the particle sizes of the lithium iron phosphate are gradually reduced from an inner layer to an outer layer, so that the internal pore structure is sequentially increased from the outer layer to the inner layer, and the transmission efficiency of the ions in the positive plate to a current collector is improved; the invention is beneficial to the electronic transmission of the current collector to the inner active coating layer due to higher conductivity of the current collector, and the conductivity of the conductive agent is gradually increased from the inner layer to the outer layer, so that the efficiency of the inner layer in transmitting electrons to the outer layer is improved.
In addition, experiments of the invention also find that the lithium iron phosphate positive plate has the effect of improving the low-temperature performance of the lithium ion battery prepared by the lithium iron phosphate positive plate.
On the other hand, according to the preparation method of the lithium iron phosphate positive plate, different active coating slurries are prepared according to the proportion, the type and the particle size requirements of the lithium iron phosphate, the conductive agent and the binder in different active coating layers, and the different active coating slurries are coated on the surface of a current collector so that at least two active coating layers are formed on the surface of the current collector, wherein the particle size of the lithium iron phosphate is gradually reduced from an inner layer to an outer layer, and the conductivity of the conductive agent is gradually increased from the inner layer to the outer layer.
In a third aspect, an application of the lithium iron phosphate positive plate in a lithium ion battery is provided.
The beneficial effects of the invention are as follows:
1. according to the invention, the anode plate is provided with the multi-layer active coating, so that the particle size of the lithium iron phosphate is gradually reduced from the inner layer to the outer layer, the pore diameter structure in the electrode plate is optimized, the lithium ion transmission resistance in the battery is reduced, and the low-temperature performance is improved.
2. According to the invention, the anode plate is provided with the multi-layer active coating, so that the conductivity of the conductive agent gradually increases from the inner layer to the outer layer, the direct current internal resistance of the battery is obviously reduced, and the cycle stability of the battery is improved.
3. According to the invention, the multi-layer active coating layers are arranged, the particle sizes of lithium iron phosphate and the conductivity of the conductive agent in the multi-layer active coating layers are regulated, the structure and the materials are regulated, the reduction of the content of the lithium iron phosphate is avoided, the reduction of the energy density of the battery is prevented, the capacity of the positive electrode of the battery can be effectively improved, and the preparation method is simple.
4. Experiments show that the lithium iron phosphate positive plate provided by the invention can effectively improve the discharge efficiency of the battery.
Drawings
The accompanying drawings, which are included to provide a further understanding of the invention and are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and together with the description serve to explain the invention.
Fig. 1 is a schematic cross-sectional structure of a lithium iron phosphate positive plate according to embodiment 1 of the present invention, wherein 1, a positive current collector, 2, a first coating layer, 3, a second coating layer, 4, and an outer coating layer;
FIG. 2 is a graph showing the ordinary temperature cycle trend in the examples of the present invention and the comparative examples.
Detailed Description
It should be noted that the following detailed description is exemplary and is intended to provide further explanation of the invention. Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs.
It is noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of exemplary embodiments according to the present invention. As used herein, the singular is also intended to include the plural unless the context clearly indicates otherwise, and furthermore, it is to be understood that the terms "comprises" and/or "comprising" when used in this specification are taken to specify the presence of stated features, steps, operations, devices, components, and/or combinations thereof.
In view of the difficulty in simultaneously considering the energy density of the battery and the multiplying power performance and the cycle performance of the battery of the existing lithium iron phosphate positive plate, the invention provides a lithium iron phosphate positive plate, and a preparation method and application thereof.
In an exemplary embodiment of the present invention, a lithium iron phosphate positive electrode sheet is provided, including a current collector, the surface of which is provided with at least two active coating layers; taking an active coating layer close to the surface of a current collector as an inner layer, taking an active coating layer far away from the surface of the current collector as an outer layer, gradually reducing the particle size of lithium iron phosphate from the inner layer to the outer layer, and gradually increasing the conductivity of the conductive agent from the inner layer to the outer layer;
the active coating layer comprises the following components in percentage by mass: 0.5-2.5% of conductive agent, 1.5-2.5% of binder and the balance of lithium iron phosphate; the particle size of the lithium iron phosphate is 0.6-1.8 mu m.
In some embodiments, the density of the active coating layer decreases gradually from the inner layer to the outer layer. The method is more beneficial to optimizing the internal pore diameter structure of the pole piece, further improves the internal ion transmission rate of the lithium ion battery and reduces the internal impedance of the battery.
The thickness of each active coating layer may be the same or different, and in some embodiments, the thickness of the active coating layer decreases gradually from the inner layer to the outer layer. The outermost layer has higher conductivity requirement, and higher requirements on the type and/or the proportion of the conductive agent, so that the cost is greatly increased, and the preparation cost can be reduced by adopting the mode. Meanwhile, as the particle size of the inner-layer lithium iron phosphate is larger, the pores are larger, so that the thickness of the inner layer is higher, the addition amount of the inner-layer lithium iron phosphate is more beneficial to ensuring, and the energy density of the battery is ensured.
The conductivity of the conductive agent may be controlled by the kind of the conductive agent (e.g., the conductivity of the conductive carbon black, the conductive graphite, and the carbon nanotubes is sequentially increased) or the addition amount of the conductive agent (the addition amount is high, the electron conductivity is good), and in some embodiments, the conductive agent of the innermost layer is the conductive carbon black, and the conductive agent of the outermost layer is a mixture of the conductive graphite and the carbon nanotubes.
In some embodiments, the quality of the lithium iron phosphate gradually decreases from the inner layer to the outer layer.
In some embodiments, three active coating layers are provided on the surface of the current collector. The inner layer conductive agent is conductive carbon black, the middle layer conductive agent is a mixture of conductive graphite and carbon nano tubes, and the outer layer conductive agent is a mixture of conductive graphite and carbon nano tubes; wherein the content of the inner layer conductive agent is the same as that of the outer layer conductive agent, the content of the middle layer conductive agent is lower than that of the inner layer conductive agent, and the content of the middle layer carbon nano tube is lower than that of the outer layer carbon nano tube. The particle size of the lithium iron phosphate is D50 particle size. Specifically, the D50 particle size of the three active coating layers is sequentially from large to small: d50 is more than 1.4 mu m and less than or equal to 1.8 mu m, D50 is more than 1.0 mu m and less than or equal to 1.4 mu m, D50 is more than 0.6 mu m and less than or equal to 1.0 mu m. The D50 particle size refers to the particle size of 50% of particles.
According to the preparation method of the lithium iron phosphate positive plate, different active coating slurries are prepared according to the proportion, the types and the particle sizes of the lithium iron phosphate, the conductive agent and the binder in different active coating layers, and the different active coating slurries are coated on the surface of a current collector so that at least two active coating layers are formed on the surface of the current collector, wherein the particle sizes of the lithium iron phosphate are gradually reduced from an inner layer to an outer layer, and the conductivity of the conductive agent is gradually increased from the inner layer to the outer layer.
In some embodiments, the solvent of the reactive coating slurry is N-methylpyrrolidone. The organic solvent can better disperse the lithium iron phosphate, the conductive agent and the binder uniformly, and is more beneficial to playing the performance of each material.
In some embodiments, the viscosity of the reactive coating slurry is 5000 to 8000 Pa.s. Under this condition, the composite material can be better compounded with a current collector.
In some embodiments, different reactive coating slurries are applied sequentially, each of which is followed by baking and rolling. The multi-time rolling is beneficial to adjusting the density of different active coating layers, wherein the inner layer is subjected to the most rolling times, the density is higher than that of the outer layer, and the optimization of the pore diameter structure inside the pole piece is facilitated, so that the internal ion transmission rate of the lithium ion battery is improved, and the internal impedance of the battery is reduced. Meanwhile, the composite strength between the inner layer and the current collector is improved, and falling off is avoided.
Taking three layers of active coating layers as an example, the preparation process is as follows:
(1) Coating the surface of a current collector with the first active coating slurry, drying, and rolling to prepare a primary rolling positive plate;
(2) Coating the second active coating slurry on the surface of the primary rolling positive plate, and rolling to prepare a secondary rolling positive plate after drying;
(3) And coating the third active coating slurry on the surface of the secondary rolling positive plate, drying, and rolling to prepare the lithium iron phosphate positive plate.
Wherein the coating density in the step (1) is 15.0-23.0 mg/cm 2 The method comprises the steps of carrying out a first treatment on the surface of the The compaction density of the one-time rolled pole piece is 2.3+/-0.1 g/cm 3 。
The coating density in the step (2) is 11.4+/-0.2 mg/cm 2 The method comprises the steps of carrying out a first treatment on the surface of the The compaction density of the one-time rolled pole piece is 2.35+/-0.1 g/cm 3 。
The coating density in the step (3) is 3.5-11.5 mg/cm 2 The method comprises the steps of carrying out a first treatment on the surface of the The compaction density of the one-time rolled pole piece is 2.4+/-0.1 g/cm 3 。
The coating density refers to the density of the layered material after the solvent is removed after the reactive coating slurry is coated.
The third embodiment of the invention provides an application of the lithium iron phosphate positive plate in a lithium ion battery.
Specifically, the lithium ion battery comprises a positive electrode, a negative electrode, electrolyte and a diaphragm, wherein the positive electrode is the lithium iron phosphate positive plate.
The active materials of the negative electrode are graphite, mesocarbon microbeads, soft carbon, hard carbon, lithium titanate, silicon-carbon composite materials and the like.
The solvent of the electrolyte is Ethylene Carbonate (EC), diethyl carbonate (DEC), dimethyl carbonate (DMC), methyl ethyl carbonate (EMC) or the like.
The solute of the electrolyte is lithium salt, such as lithium hexafluorophosphate and the like.
In order to enable those skilled in the art to more clearly understand the technical scheme of the present invention, the technical scheme of the present invention will be described in detail below with reference to specific examples and comparative examples.
In the following examples and comparative examples, all equipment and materials are commercially available or are commonly used in the industry; methods employed, unless otherwise indicated, are conventional in the art.
Example 1
The lithium iron phosphate positive plate comprises a positive current collector 1, wherein the surface of the positive current collector is coated with a first coating layer 2, the surface of the first coating layer is coated with a second coating layer 3, and the surface of the second coating layer is coated with an outermost coating layer 4. The positive current collector 1 is aluminum foil. The first coating layer 2 is prepared from the following components in percentage by mass: 97.5% LiFePO of the HexPart family (trade Mark, 1.4 μm < D50 < 1.8 μm) 4 Active material, 1.0% conductive carbon black, 1.5% polyvinylidene fluoride; the second coating layer 3 is prepared from the following components in percentage by mass: yusheng (trade mark, 1.0 μm < D50 < 1.4 μm) 97.1% LiFePO 4 Active material, 0.7% conductive agent (0.5% conductive graphite +0.2% carbon nanotubes), 2.2% polyvinylidene fluoride. The outermost coating layer 4 is made of the following components in percentage by mass: desquare nano (trade trademark, 0.6 μm < D50 < 1.0 μm) 96.8% LiFePO 4 Active material, 1.0% conductive agent (0.5% conductive graphite +0.5% carbon nanotubes), 2.2% polyvinylidene fluoride. A portion of N-methylpyrrolidone was added during homogenization to adjust the viscosity.
The preparation method comprises the following steps:
(1) And adding the slurry required by the first coating layer 2 into a stirrer according to the formula proportion, and homogenizing, dispersing and adjusting the slurry to the viscosity of 600 Pa.s to obtain the first coating slurry for later use.
(2) And adding the slurry required by the second coating layer 3 into a stirrer according to the formula proportion, and homogenizing, dispersing and adjusting the slurry to the viscosity of 600 Pa.s to obtain the second coating slurry for later use.
(3) Adding the slurry required by the outermost coating layer 4 into a stirrer according to the formula proportion, and homogenizing, dispersing and adjusting the slurry to the viscosity of 600 Pa.s to obtain the outermost coating slurry for later use.
(4) Coating the first coating slurry obtained in the step (1) on the surface of the positive electrode current collector 1, wherein the coating surface density is 19.0mg/cm 2 The method comprises the steps of carrying out a first treatment on the surface of the Drying and rolling the mixture in a coating oven to form a first coating layer of the positive electrode, and compacting the first coating layer to be 2.3g/cm 3 And (5) standby application.
(5) Coating the second coating slurry obtained in the step (2) on the first coating layer obtained in the step (4), wherein the density of the second coating layer is 11.4mg/cm 2 Drying and rolling the mixture in a coating oven to form a positive electrode second coating layer, wherein the compacted density of the pole piece is 2.35g/cm 3 For standby application;
(6) Applying the outermost coating slurry obtained in the step (3) onto the second coating layer obtained in the step (5), the density of the outermost coating layer being 7.6mg/cm 2 The method comprises the steps of carrying out a first treatment on the surface of the The compacted density of the pole piece is 2.35g/cm 3 The thickness of the pole piece after rolling is 174-176 mu m. And drying and rolling the lithium iron phosphate anode sheet through a coating oven to obtain the lithium iron phosphate anode sheet.
Comparative example 1
The preparation method of the lithium iron phosphate positive plate comprises the following steps:
a lithium iron phosphate positive plate comprises a positive current collector and an active substance coating layer. The first coating layer slurry is prepared from the following components in percentage by mass: anda (trade mark, 1.4 μm < D50 < 1.8 μm) 96.5% LiFePO 4 Active material, 2.0% conductive carbon black, 1.5% polyvinylidene fluoride; the second coating layer slurry is prepared from the following components in percentage by mass: de Fang (trade Mark, 1.0 μm < D50 < 1.4 μm) 96.1% LiFePO 4 Active material, 1.7% conductive agent (1.0% conductive graphite +0.7% carbon nanotubes), 2.2% polyvinylidene fluoride. The outermost coating layer slurry is prepared from the following components in percentage by mass: 95.8% LiFePO of German (trade Mark, 0.6 μm < D50 < 1.0 μm) 4 Active material, 2.0% conductive agent (1.0% conductive graphite +1.0% carbon nanotubes), 2.2% polyvinylidene fluoride. A portion of N-methylpyrrolidone was added during homogenization to adjust the viscosity.
The preparation method comprises the following steps:
(1) Adding the slurry required by the first coating layer into a stirrer according to the formula proportion, homogenizing, dispersing and adjusting the viscosity to 600 mpa.s to obtain the first coating slurry for later use.
(2) And adding the slurry required by the second coating layer into a stirrer according to the formula proportion, and homogenizing, dispersing and adjusting the slurry to the viscosity of 600 Pa.s to obtain the second coating slurry for later use.
(3) Adding the slurry required by the outermost coating layer into a stirrer according to the formula proportion, homogenizing and dispersing to adjust the viscosity to 600 mpa.s to obtain the outermost coating slurry for later use.
(4) And (3) coating the first, second and third coating slurries obtained in the steps (1), (2) and (3) according to the weight parts of 5:3:2, adding the mixture into a stirrer, and regulating the dispersion of the homogenate to the viscosity of 6000 Pa.s to obtain mixed coating slurry for later use.
(5) Coating the first mixed coating slurry obtained in the step (4) on an aluminum foil current collector in the step, wherein the coating surface density is 38mg/cm 2 Drying and rolling the pole piece by a coating oven, wherein the compacted density of the pole piece is 2.35g/cm < 3 >, and the pole piece is ready for use; the thickness of the pole piece after rolling is 174-176 mu m. And drying and rolling to obtain the lithium iron phosphate positive plate.
Comparative example 2
The lithium iron phosphate positive plate comprises a positive current collector 1, wherein a first coating layer 2 is coated on the surface of the positive current collector, a second coating layer 3 is coated on the surface of the first coating layer, and an outermost coating layer 4 is coated on the surface of the second coating layer. The positive current collector 1 is aluminum foil. The first coating layer 2 is prepared from the following components in percentage by mass: 97.5% LiFePO of the HexPart family (trade Mark, 1.4 μm < D50 < 1.8 μm) 4 Active material, 1.0% conductive carbon black, 1.5% polyvinylidene fluoride; the second coating layer 3 is prepared from the following components in percentage by mass: yusheng (trade mark, 1.0 μm < D50 < 1.4 μm) 97.1% LiFePO 4 Active material, 0.7% conductive agent (0.5% conductive graphite +0.2% carbon nanotubes), 2.2% polyvinylidene fluoride. The outermost coating layer 4 is made of the following components in percentage by mass: defant nano (trade trademark, 0.6 μm < D50 < 1.0 μm) 96.8% LiFePO 4 Active material, 1.0% conductive agent (0.5% conductive graphite +0.5% carbon nanotubes), 2.2% polyvinylidene fluoride. Part of N-methyl is added during homogenizationPyrrolidone was used for viscosity adjustment.
The preparation method comprises the following steps:
(1) And adding the slurry required by the first coating layer 2 into a stirrer according to the formula proportion, and homogenizing, dispersing and adjusting the slurry to the viscosity of 600 Pa.s to obtain the first coating slurry for later use.
(2) And adding the slurry required by the second coating layer 3 into a stirrer according to the formula proportion, and homogenizing, dispersing and adjusting the slurry to the viscosity of 600 Pa.s to obtain the second coating slurry for later use.
(3) And adding the slurry required by the third coating layer 4 into a stirrer according to the formula proportion, and homogenizing, dispersing and adjusting the slurry to the viscosity of 600 Pa.s to obtain the outermost coating slurry for later use.
(4) And (3) coating the first, second and third coating slurries obtained in the steps (1), (2) and (3) according to the weight parts of 5:3:2, adding the mixture into a stirrer, and regulating the dispersion of the homogenate to the viscosity of 6000 Pa.s to obtain mixed coating slurry for later use.
(5) Coating the mixed coating slurry obtained in the step (4) on the surface of the positive electrode current collector 1, wherein the coating surface density is 19.0mg/cm 2 The method comprises the steps of carrying out a first treatment on the surface of the Forming a first coating layer of the positive electrode by baking and rolling, wherein the rolling compaction is 2.3g/cm 3 For standby application;
(6) Applying the mixed coating slurry obtained in the step (4) to the first coating layer obtained in the step (5), wherein the density of the second coating layer is 11.4mg/cm 2 Forming a positive electrode second coating layer by baking and rolling, wherein the compacted density of the pole piece is 2.35g/cm 3 For standby application;
(7) Applying the mixed coating slurry obtained in the step (4) to the second coating layer obtained in the step (6), wherein the density of the outermost coating layer is 7.6mg/cm 2 The method comprises the steps of carrying out a first treatment on the surface of the The compacted density of the pole piece is 2.35g/cm 3 The thickness of the pole piece after rolling was 175 μm. And drying and rolling to obtain the lithium iron phosphate positive plate.
The lithium iron phosphate positive plate prepared in the above examples and comparative examples is made into a lithium ion battery (the negative electrode of the lithium ion battery is an artificial graphite system, and the electrolyte and the diaphragm are all common systems in industry). And testing the capacity, efficiency, alternating current impedance and direct current internal resistance of the prepared lithium ion battery respectively.
The first discharge capacity and the efficiency of the lithium ion battery prepared from the lithium iron phosphate positive electrode sheets prepared in examples and comparative examples at a normal temperature of 25℃and 0.33C charge and discharge are shown in Table 1.
Table 1 first charge-discharge properties of examples and comparative examples
As can be seen from table 1, the first discharge capacity and the first charge-discharge efficiency of the lithium iron phosphate positive plate prepared by the examples are 5297mAh and 91.3% respectively, while the first discharge capacity and the first charge-discharge efficiency of the lithium iron phosphate positive plate prepared by the comparative examples 1 and 2 are 5165mAh and 90.8%, 5180mAh and 90.7% respectively, which are lower than those of the lithium iron phosphate positive plate prepared by the examples, and the arrangement of the multilayer coating layer is described to be beneficial to improving the capacity and efficiency of the lithium ion battery.
Comparison of 1C charge-discharge cycle trend at normal temperature of 25 ℃ as shown in figure 2, the cycle decay trend of the examples is better than that of the comparative examples, indicating that the lithium iron phosphate positive plate prepared by the examples can improve cycle performance.
Example 2
The lithium iron phosphate positive plate comprises a positive current collector, wherein a first coating layer is coated on the surface of the positive current collector, a second coating layer is coated on the surface of the first coating layer, and an outermost coating layer is coated on the surface of the second coating layer. The positive current collector is aluminum foil. The first coating layer 2 is prepared from the following components in percentage by mass: 97.5% LiFePO of the HexPart family (trade Mark, 1.4 μm < D50 < 1.8 μm) 4 Active material, 1.0% conductive carbon black, 1.5% polyvinylidene fluoride; the second coating layer 3 is prepared from the following components in percentage by mass: yusheng (trade mark, 1.0 μm < D50 < 1.4 μm) 97.1% LiFePO 4 Active material, 0.7% conductive agent (0.5% conductive graphite +0.2% carbon nanotubes), 2.2% polyvinylidene fluoride. The outermost coating layer 4 is made of the following components in percentage by mass: desquare nano (trade trademark, 0.6 μm < D50 < 1.0 μm) 96.8% LiFePO 4 Active material, 1.0% conductive agent (0.5% conductive graphite+0)5% carbon nanotubes), 2.2% polyvinylidene fluoride. A portion of N-methylpyrrolidone was added during homogenization to adjust the viscosity.
The preparation method comprises the following steps:
(1) Adding the slurry required by the first coating layer into a stirrer according to the formula proportion, homogenizing, dispersing and adjusting the viscosity to 600 mpa.s to obtain the first coating slurry for later use.
(2) And adding the slurry required by the second coating layer into a stirrer according to the formula proportion, homogenizing, dispersing and adjusting the viscosity to 5000 Pa.s to obtain the second coating slurry for later use.
(3) Adding the slurry required by the outermost coating layer into a stirrer according to the formula proportion, homogenizing and dispersing to adjust the viscosity to 600 mpa.s to obtain the outermost coating slurry for later use.
(4) Coating the first coating slurry obtained in the step (1) on the surface of the positive electrode current collector 1, wherein the coating surface density is 15.2mg/cm 2 The method comprises the steps of carrying out a first treatment on the surface of the Forming a first coating layer of the positive electrode by baking and rolling, wherein the rolling compaction is 2.3g/cm 3 And (5) standby application.
(5) Coating the second coating slurry obtained in the step (2) on the first coating layer obtained in the step (4), wherein the density of the second coating layer is 11.4mg/cm 2 Forming a positive electrode second coating layer by baking and rolling, wherein the compacted density of the pole piece is 2.35g/cm 3 For standby application;
(6) Applying the outermost coating slurry obtained in the step (3) onto the second coating layer obtained in the step (5), the density of the outermost coating layer being 11.4mg/cm 2 The method comprises the steps of carrying out a first treatment on the surface of the The compacted density of the pole piece is 2.35g/cm 3 The thickness of the pole piece after rolling was 175 μm. And drying and rolling to obtain the lithium iron phosphate positive plate.
Example 3
The lithium iron phosphate positive plate comprises a positive current collector, wherein a first coating layer is coated on the surface of the positive current collector, a second coating layer is coated on the surface of the first coating layer, and an outermost coating layer is coated on the surface of the second coating layer. The positive current collector is aluminum foil. The first coating layer 2 is prepared from the following components in percentage by mass: 97.5% LiFePO of the HexPart family (trade Mark, 1.4 μm < D50 < 1.8 μm) 4 Active material, 1.0% conductive carbon black, 1.5% polyvinylidene fluoride; the saidThe second coating layer 3 is prepared from the following components in percentage by mass: yusheng (trade mark, 1.0 μm < D50 < 1.4 μm) 97.1% LiFePO 4 Active material, 0.7% conductive agent (0.5% conductive graphite +0.2% carbon nanotubes), 2.2% polyvinylidene fluoride. The outermost coating layer 4 is made of the following components in percentage by mass: desquare nano (trade trademark, 0.6 μm < D50 < 1.0 μm) 96.8% LiFePO 4 Active material, 1.0% conductive agent (0.5% conductive graphite +0.5% carbon nanotubes), 2.2% polyvinylidene fluoride. A portion of N-methylpyrrolidone was added during homogenization to adjust the viscosity.
The preparation method comprises the following steps:
(1) Adding the slurry required by the first coating layer into a stirrer according to the formula proportion, homogenizing, dispersing and adjusting the viscosity to 600 mpa.s to obtain the first coating slurry for later use.
(2) And adding the slurry required by the second coating layer into a stirrer according to the formula proportion, and homogenizing, dispersing and adjusting the slurry to the viscosity of 600 Pa.s to obtain the second coating slurry for later use.
(3) Adding the slurry required by the outermost coating layer into a stirrer according to the formula proportion, homogenizing and dispersing to adjust the viscosity to 600 mpa.s to obtain the outermost coating slurry for later use.
(4) Coating the first coating slurry obtained in the step (1) on the surface of the positive electrode current collector 1, wherein the coating surface density is 22.8mg/cm 2 The method comprises the steps of carrying out a first treatment on the surface of the Forming a first coating layer of the positive electrode by baking and rolling, wherein the rolling compaction is 2.3g/cm 3 And (5) standby application.
(5) Coating the second coating slurry obtained in the step (2) on the first coating layer obtained in the step (4), wherein the density of the second coating layer is 11.4mg/cm 2 Forming a positive electrode second coating layer by baking and rolling, wherein the compacted density of the pole piece is 2.35g/cm 3 For standby application;
(6) Applying the outermost coating slurry obtained in the step (3) onto the second coating layer obtained in the step (5), the density of the outermost coating layer being 3.8mg/cm 2 The method comprises the steps of carrying out a first treatment on the surface of the The compacted density of the pole piece is 2.35g/cm 3 The thickness of the pole piece after rolling was 175 μm. And drying and rolling to obtain the lithium iron phosphate positive plate.
Example 4
Lithium iron phosphate positive electrodeThe sheet comprises an anode current collector, wherein the surface of the anode current collector is coated with a first coating layer, the surface of the first coating layer is coated with a second coating layer, and the surface of the second coating layer is coated with an outermost coating layer. The positive current collector is aluminum foil. The first coating layer is prepared from the following components in percentage by mass: 97.5% LiFePO of the HexPart family (trade Mark, 1.4 μm < D50 < 1.8 μm) 4 Active material, 1.0% conductive carbon black, 1.5% polyvinylidene fluoride; the second coating layer is prepared from the following components in percentage by mass: yusheng (trade mark, 1.0 μm < D50 < 1.4 μm) 97.1% LiFePO 4 Active material, 0.7% conductive agent (0.5% conductive graphite +0.2% carbon nanotubes), 2.2% polyvinylidene fluoride. The outermost coating layer 4 is made of the following components in percentage by mass: desquare nano (trade trademark, 0.6 μm < D50 < 1.0 μm) 96.8% LiFePO 4 Active material, 1.0% conductive agent (0.5% conductive graphite +0.5% carbon nanotubes), 2.2% polyvinylidene fluoride. A portion of N-methylpyrrolidone was added during homogenization to adjust the viscosity.
The preparation method comprises the following steps:
(1) And adding the slurry required by the first coating layer into a stirrer according to the formula proportion, homogenizing, dispersing and adjusting the viscosity to 5000 Pa.s to obtain the first coating slurry for later use.
(2) And adding the slurry required by the second coating layer into a stirrer according to the formula proportion, homogenizing, dispersing and adjusting the viscosity to 5000 Pa.s to obtain the second coating slurry for later use.
(3) Adding the slurry required by the outermost coating layer into a stirrer according to the formula proportion, homogenizing, dispersing and adjusting the viscosity to 5000 Pa.s to obtain the outermost coating slurry for later use.
(4) Coating the first coating slurry obtained in the step (1) on the surface of the positive electrode current collector 1, wherein the coating surface density is 19.0mg/cm 2 The method comprises the steps of carrying out a first treatment on the surface of the Drying and rolling the mixture in a coating oven to form a first coating layer of the positive electrode, and compacting the first coating layer to be 2.3g/cm 3 And (5) standby application.
(5) Coating the second coating slurry obtained in the step (2) on the first coating layer obtained in the step (4), wherein the density of the second coating layer is 11.4mg/cm 2 Drying and rolling the mixture in a coating oven to form a positive electrode second coating layer, wherein the compacted density of the pole piece is 2.35g/cm 3 For standby application;
(6) Applying the outermost coating slurry obtained in the step (3) onto the second coating layer obtained in the step (5), the density of the outermost coating layer being 7.6mg/cm 2 The method comprises the steps of carrying out a first treatment on the surface of the The compacted density of the pole piece is 2.35g/cm 3 The thickness of the pole piece after rolling is 174-176 mu m. And drying and rolling the lithium iron phosphate anode sheet through a coating oven to obtain the lithium iron phosphate anode sheet.
Example 5
The lithium iron phosphate positive plate comprises a positive current collector, wherein a first coating layer is coated on the surface of the positive current collector, a second coating layer is coated on the surface of the first coating layer, and an outermost coating layer is coated on the surface of the second coating layer. The positive current collector is aluminum foil. The first coating layer is prepared from the following components in percentage by mass: 97.5% LiFePO of the HexPart family (trade Mark, 1.4 μm < D50 < 1.8 μm) 4 Active material, 1.0% conductive carbon black, 1.5% polyvinylidene fluoride; the second coating layer is prepared from the following components in percentage by mass: yusheng (trade mark, 1.0 μm < D50 < 1.4 μm) 97.1% LiFePO 4 Active material, 0.7% conductive agent (0.5% conductive graphite +0.2% carbon nanotubes), 2.2% polyvinylidene fluoride. The outermost coating layer 4 is made of the following components in percentage by mass: desquare nano (trade trademark, 0.6 μm < D50 < 1.0 μm) 96.8% LiFePO 4 Active material, 1.0% conductive agent (0.5% conductive graphite +0.5% carbon nanotubes), 2.2% polyvinylidene fluoride. A portion of N-methylpyrrolidone was added during homogenization to adjust the viscosity.
The preparation method comprises the following steps:
(1) And adding the slurry required by the first coating layer into a stirrer according to the formula proportion, homogenizing, dispersing and adjusting the viscosity to be 800 Pa.s to obtain the first coating slurry for later use.
(2) And adding the slurry required by the second coating layer into a stirrer according to the formula proportion, homogenizing, dispersing and adjusting the viscosity to be 800 Pa.s to obtain the second coating slurry for later use.
(3) Adding the slurry required by the outermost coating layer into a stirrer according to the formula proportion, homogenizing, dispersing and adjusting the viscosity to be 800 Pa.s to obtain the outermost coating slurry for later use.
(4) The first step (1) is carried outThe coating slurry is coated on the surface of the positive electrode current collector 1, and the coating surface density is 19.0mg/cm 2 The method comprises the steps of carrying out a first treatment on the surface of the Drying and rolling the mixture in a coating oven to form a first coating layer of the positive electrode, and compacting the first coating layer to be 2.3g/cm 3 And (5) standby application.
(5) Coating the second coating slurry obtained in the step (2) on the first coating layer obtained in the step (4), wherein the density of the second coating layer is 11.4mg/cm 2 Drying and rolling the mixture in a coating oven to form a positive electrode second coating layer, wherein the compacted density of the pole piece is 2.35g/cm 3 For standby application;
(6) Applying the outermost coating slurry obtained in the step (3) onto the second coating layer obtained in the step (5), the density of the outermost coating layer being 7.6mg/cm 2 The method comprises the steps of carrying out a first treatment on the surface of the The compacted density of the pole piece is 2.35g/cm 3 The thickness of the pole piece after rolling is 174-176 mu m. And drying and rolling the lithium iron phosphate anode sheet through a coating oven to obtain the lithium iron phosphate anode sheet.
The above description is only of the preferred embodiments of the present invention and is not intended to limit the present invention, but various modifications and variations can be made to the present invention by those skilled in the art. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention should be included in the protection scope of the present invention.
Claims (10)
1. The lithium iron phosphate positive plate is characterized by comprising a current collector, wherein at least two active coating layers are arranged on the surface of the current collector; taking an active coating layer close to the surface of a current collector as an inner layer, taking an active coating layer far away from the surface of the current collector as an outer layer, gradually reducing the particle size of lithium iron phosphate from the inner layer to the outer layer, and gradually increasing the conductivity of the conductive agent from the inner layer to the outer layer;
the active coating layer comprises the following components in percentage by mass: 0.5-2.5% of conductive agent, 1.5-2.5% of binder and the balance of lithium iron phosphate; the particle size of the lithium iron phosphate is 0.6-1.8 mu m.
2. The lithium iron phosphate positive electrode sheet according to claim 1, wherein the density of the active coating layer gradually decreases from the inner layer to the outer layer.
3. The lithium iron phosphate positive electrode sheet according to claim 1, wherein the thickness of the active coating layer gradually decreases from the inner layer to the outer layer.
4. The lithium iron phosphate positive electrode sheet according to claim 1, wherein the innermost conductive agent is conductive carbon black, and the outermost conductive agent is a mixture of conductive graphite and carbon nanotubes;
or, the quality of lithium iron phosphate gradually decreases from the inner layer to the outer layer.
5. The lithium iron phosphate positive electrode sheet according to claim 1, wherein three active coating layers are provided on the surface of the current collector.
6. A method for preparing the lithium iron phosphate positive plate according to any one of claims 1 to 5, characterized in that different active coating slurries are prepared according to the proportion, types and particle sizes of lithium iron phosphate, conductive agents and binders in different active coating layers, and the different active coating slurries are coated on the surface of a current collector so that at least two active coating layers are formed on the surface of the current collector, wherein the particle sizes of the lithium iron phosphate are gradually reduced from an inner layer to an outer layer, and the conductivity of the conductive agents is gradually increased from the inner layer to the outer layer.
7. The method for preparing a lithium iron phosphate positive electrode sheet according to claim 6, wherein the solvent of the active coating slurry is N-methylpyrrolidone;
alternatively, the viscosity of the reactive coating paste is 5000 to 8000 Pa.s.
8. The method for preparing a lithium iron phosphate positive electrode sheet according to claim 6, wherein different active coating slurries are sequentially coated, and each coating is dried and rolled.
9. Use of the lithium iron phosphate positive electrode sheet according to any one of claims 1 to 5 in a lithium ion battery.
10. The use of the lithium iron phosphate positive electrode sheet according to claim 9 in a lithium ion battery, wherein the lithium ion battery comprises a positive electrode, a negative electrode, an electrolyte and a separator, and the positive electrode is the lithium iron phosphate positive electrode sheet.
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