Positive plate, preparation method thereof and battery
By layering lithium-rich materials, lithium manganese iron phosphate, and ternary materials in the positive electrode, and optimizing particle size, thickness, and porosity, the problems of low energy density and poor cycle performance of lithium manganese iron phosphate batteries are solved, achieving efficient lithium replenishment and structural stability, and improving the overall performance of the battery.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- EVE ENERGY CO LTD
- Filing Date
- 2026-04-10
- Publication Date
- 2026-05-12
AI Technical Summary
Lithium manganese iron phosphate batteries have low energy density and poor cycle performance. Furthermore, during the preparation of the cathode slurry, lithium-rich materials are prone to react with environmental moisture, resulting in poor slurry stability and processability, which affects the lithium replenishment effect.
The structure employs a layered structure consisting of a lithium-rich material layer, a first positive electrode active layer, and a second positive electrode active layer. The lithium-rich material layer is located close to the current collector. The first positive electrode active layer contains lithium manganese iron phosphate, and the second positive electrode active layer contains ternary materials. By controlling the particle size, thickness, and porosity of each layer, the ratio of binder and conductive agent is optimized, side reactions are reduced, and lithium-ion release efficiency and charge transport path are improved.
It improves lithium replenishment, enhances the electrochemical performance, structural stability, and cycle life of the cathode, reduces the risk of side reactions, and improves the voltage stability and high-current charge/discharge capability of the battery.
Smart Images
Figure CN122025547A_ABST
Abstract
Description
Technical Field
[0001] This application relates to the field of battery technology, specifically to a positive electrode sheet and its preparation method, and a battery. Background Technology
[0002] Lithium manganese iron phosphate (LiMn) l-x Fe x PO4 (0 < x < 1), as a phosphate cathode material, possesses both the good thermal stability and high specific capacity of lithium iron phosphate (LiFePO4) and the high voltage window and high specific energy of lithium manganese phosphate (LiFePO4). In addition, it has the advantages of low cost and good safety. In the future development, it is very likely to replace lithium iron phosphate cathode material and be applied to power batteries and energy storage batteries.
[0003] However, lithium manganese iron phosphate (LFP) batteries have low energy density and poor cycle performance, which limits their application. To improve the cycle life of LFP batteries, additional high-capacity lithium replenishment materials are usually added to the positive electrode. In related technologies, when replenishing lithium to the positive electrode, a small amount of high-capacity material is usually added during the preparation of the positive electrode slurry. Because LFP has a specific surface area as high as 20m²... 2 When the lithium content is above a certain level (g), the slurry readily absorbs moisture from the environment during the preparation of the cathode slurry. This causes the lithium-rich material to undergo side reactions and cross-link with the binder in the slurry, significantly reducing the stability and processability of the slurry. Consequently, the lithium replenishment effect is poor, and the performance of the cathode is affected. Summary of the Invention
[0004] The embodiments of this application provide a positive electrode sheet and its preparation method, a battery and its formation method, which can reduce side reactions between lithium-rich materials and other materials, improve lithium replenishment effect, and improve the electrochemical performance, structural stability and cycle life of the positive electrode sheet.
[0005] In a first aspect, embodiments of this application provide a positive electrode sheet, comprising: current collector; A lithium-rich material layer is disposed on at least one side of the current collector, and the lithium-rich material layer includes a lithium-rich material; The first positive electrode active layer is disposed on the side of the lithium-rich material layer away from the current collector, and the first positive electrode active layer includes lithium manganese iron phosphate. The second positive electrode active layer is disposed on the side of the first positive electrode active layer away from the lithium-rich material layer, and the second positive electrode active layer includes a ternary material.
[0006] In the positive electrode sheet provided in this application embodiment, the lithium-rich material layer is set separately, which reduces the probability of side reactions between the lithium-rich material and other materials, improves the stability and processability of the lithium-rich material layer, and ensures the lithium replenishment effect. The lithium-rich material layer is positioned close to the current collector, allowing it to directly contact the current collector. During the formation and charging process, the lithium-rich material can quickly gain electrons, promoting a decomposition reaction and releasing lithium ions efficiently, resulting in a good lithium replenishment effect. The first positive electrode active layer includes lithium manganese iron phosphate, and the second positive electrode active layer includes ternary materials. Lithium ions released from the lithium-rich material layer can sequentially pass through the first and second positive electrode active layers into the electrolyte, playing a lithium replenishment role. The first positive electrode active layer has a moderate diffusion coefficient, which can reduce the excessive absorption of lithium ions by the second positive electrode active layer. Furthermore, the second positive electrode active layer has high conductivity, which can shorten the charge transport path and improve the high-current charging and discharging capability. Since the operating voltage of lithium manganese iron phosphate (LFP) is lower than that of ternary materials, the second positive electrode active layer containing ternary materials, located on the outside, can preferentially deintercalate and intercalate lithium, reducing the risk of overcharging LFP at high voltages and improving voltage stability. LFP has an olivine structure, resulting in minimal volume change during charging and discharging, which can buffer the stress deformation of the ternary materials in the second positive electrode active layer during charging and discharging, reducing the risk of cracking in the positive electrode sheet. The outer location of the second positive electrode active layer also reduces side reactions from the dissolution of transition metals in the first positive electrode active layer, improving cycle life. In other words, the positive electrode sheet provided in this application can reduce side reactions between lithium-rich materials and other materials, improve lithium replenishment, and enhance the electrochemical performance, structural stability, and cycle life of the positive electrode sheet.
[0007] In some embodiments, the chemical formula of the lithium-rich material is Li x M y O z Wherein, M is selected from at least one of Al, Ni and Co, 1 < x ≤ 2.0, 1.5 ≤ z ≤ 2.0; And / or, the ternary material includes at least one of lithium nickel cobalt manganese oxide and lithium nickel cobalt aluminum oxide.
[0008] The chemical formulas of lithium-rich materials, as described above, exhibit high energy density and good structural stability, ensuring effective lithium replenishment while reducing side reactions between lithium-rich materials and other materials. Lithium nickel cobalt manganese oxide and lithium nickel cobalt aluminum oxide possess high energy density, good structural stability, and high operating voltage, thus improving the performance of the cathode.
[0009] In some embodiments, the thickness of the lithium-rich material layer is 10 μm-16 μm.
[0010] By setting the thickness of the lithium-rich material layer within the aforementioned range, the amount of lithium released can be guaranteed, and the risk of lithium dendrite growth can be reduced. Furthermore, within this thickness range, the volume expansion rate of the lithium-rich material layer can be controlled within a reasonable range, ensuring the stability of the cathode sheet.
[0011] In some embodiments, in the lithium-rich material layer, the particle size D50 of the lithium-rich material is 5μm-15μm, and the particle size distribution range is 1μm-20μm; And / or, in the first positive electrode active layer, the particle size D50 of lithium manganese iron phosphate is 0.5μm-1.2μm, and the particle size distribution range is 0.1μm-25μm; And / or, in the second positive electrode active layer, the particle size D50 of the ternary material is 5μm-12μm, and the particle size distribution range is 5μm-12μm.
[0012] In the lithium-rich material layer, the particle size D50 and distribution range of the lithium-rich material are within the aforementioned range, which can reduce the agglomeration of the lithium-rich material, reduce side reactions between the lithium-rich material and other materials, and have a good delithiation effect, ensuring the lithium replenishment effect. In the first positive electrode active layer, the particle size D50 and distribution range of lithium manganese iron phosphate within the aforementioned range can achieve a high compaction density, improve energy density, and have a low specific surface area, which can reduce side reactions with other materials. In the second positive electrode active layer, the particle size D50 and distribution range of the ternary material are within the aforementioned range, which can balance high power performance and energy density, and the volume change of the ternary material is more uniform during cycling, ensuring the cycling stability of the second positive electrode active layer.
[0013] In some embodiments, the porosity of the first positive electrode active layer is 20%-30%; And / or, the porosity of the second positive electrode active layer is 25%-35%.
[0014] With the porosity of the first positive electrode active layer within the aforementioned range, it can achieve high compaction density while retaining sufficient pores for electrolyte permeation and can accommodate stress generated during cycling, reducing crack propagation between particles. With the porosity of the second positive electrode active layer within the aforementioned range, it can balance high power performance and structural stability, allowing the gas generated by the ternary material during overcharging or high temperature to be released quickly, reducing the probability of side reactions and improving the stability of the second positive electrode active layer.
[0015] In some embodiments, the current collector includes a composite aluminum foil layer, which includes a polymer layer and a first aluminum foil layer and a second aluminum foil layer disposed on opposite sides of the polymer layer.
[0016] The melting point of the polymer layer is typically between 120℃ and 260℃. When the internal temperature of the battery rises abnormally, the polymer layer melts to form an insulating barrier, which can cut off the electron conduction path and reduce the risk of thermal runaway propagation. The polymer layer has a low elastic modulus, which can absorb the stress generated by the expansion or contraction of the positive electrode during battery charging and discharging.
[0017] In some embodiments, the current collector further includes a carbon coating layer disposed between the composite aluminum foil layer and the lithium-rich material layer.
[0018] By setting a carbon coating layer between the composite aluminum foil layer and the lithium-rich material layer, the contact resistance between the lithium-rich material layer and the composite aluminum foil layer can be reduced, ensuring that the lithium-rich material layer can quickly release lithium ions during the battery formation and charging process, thus achieving a good lithium replenishment effect.
[0019] In some embodiments, the thickness of the carbon coating layer is 0.5 μm-1 μm.
[0020] By keeping the thickness of the carbon coating layer within the above range, good conductivity can be ensured, and the overall thickness and cost of the positive electrode sheet can be controlled.
[0021] In some embodiments, the total amount of lithium manganese iron phosphate and ternary materials is in the mass ratio of lithium-rich materials to (93-97.8):(0.2-5); And / or, the mass ratio of lithium manganese iron phosphate to ternary materials is 98:2 to 50:50.
[0022] That is, the mass ratio of positive electrode active material to lithium-rich material in the positive electrode sheet is (93-97.8):(0.2-5.0). This provides a sufficient lithium source, ensuring lithium replenishment, improving the battery's initial efficiency, extending its cycle life, and reducing the safety risks and cost increases caused by excessive lithium-rich material addition. It also reduces the volume expansion caused by excessive lithium-ion deposition on the negative electrode surface, ensuring the battery's structural stability. A higher proportion of lithium manganese iron phosphate (LFP) leverages the high stability of its olivine structure to reduce the risk of thermal runaway, ensuring safety performance. Furthermore, the ternary material ensures energy density and guarantees the synergistic effect between the first and second positive electrode active layers in the positive electrode sheet.
[0023] In some embodiments, the lithium-rich material layer further includes a first binder, the first positive electrode active layer further includes a first conductive agent and a second binder, and the second positive electrode active layer further includes a second conductive agent and a third binder. In the positive electrode sheet, the total mass of lithium manganese iron phosphate and ternary materials is A, the mass of lithium-rich materials is B, the total mass of the first binder, the second binder and the third binder is C, and the total mass of the first conductive agent and the second conductive agent is D, satisfying: A:B:C:D=(93-97.8):(0.2-5):(1.2-2.5):(0.5-2):(0-0.5).
[0024] By ensuring that the proportions of each component in the positive electrode meet the above conditions, the loading of active material in the positive electrode can be guaranteed, as well as the energy density and capacity of the positive electrode. Furthermore, by using a suitable binder ratio, the bonding performance between each layer can be guaranteed, ensuring the structural stability of the positive electrode and good conductivity, thus giving the positive electrode excellent overall performance.
[0025] In some embodiments, the first conductive agent includes conductive carbon black and carbon nanotubes; And / or, the second conductive agent includes conductive carbon black and carbon nanotubes.
[0026] By using a first conductive agent and a second conductive agent, including conductive carbon black and carbon nanotubes, a three-dimensional conductive network can be constructed by taking advantage of the small particle size of conductive carbon black and the high aspect ratio of carbon nanotubes, thereby enhancing the mechanical properties of the first positive electrode active layer and extending cycle life.
[0027] Secondly, embodiments of this application provide a method for preparing a positive electrode sheet, comprising: Provide current collectors; A lithium-rich slurry comprising a lithium-rich material and a first binder is provided, and the lithium-rich slurry is coated on at least one side of a current collector to form a lithium-rich material layer; A first positive electrode slurry comprising lithium manganese iron phosphate, a second binder and a first conductive agent is provided. The first positive electrode slurry is coated on the side of the lithium-rich material layer facing away from the current collector to form a first positive electrode active layer. A second positive electrode slurry comprising a ternary material, a third binder, and a second conductive agent is provided. The second positive electrode slurry is coated onto the side surface of the first positive electrode active layer opposite to the lithium-rich material layer to form a second positive electrode active layer, thereby obtaining a positive electrode sheet.
[0028] That is, a lithium-rich material layer, a first positive electrode active layer, and a second positive electrode active layer are sequentially formed on the surface of the current collector by coating to obtain a positive electrode sheet. The method for preparing the positive electrode sheet provided in this application embodiment has all the beneficial effects of the positive electrode sheet as described above, and will not be repeated here.
[0029] In some embodiments, the solid content of the lithium replenishment slurry is 65%-75%; And / or, the solid content of the first cathode slurry is 65%-75%; And / or, the solid content of the second cathode slurry is 65%-75%.
[0030] By keeping the solid content of the lithium replenishment slurry, the first cathode slurry, and the second cathode slurry within the above-mentioned range, the stability of the slurry can be improved, sedimentation and agglomeration can be reduced, coating efficiency can be increased, and the uniformity of the coating can be guaranteed.
[0031] Thirdly, embodiments of this application provide a battery comprising a positive electrode sheet as described above, and / or a positive electrode sheet prepared by the method described above.
[0032] The battery provided in this application embodiment has all the beneficial effects of the positive electrode as described above, which will not be repeated here.
[0033] In some embodiments, after the battery undergoes formation, the lithium-rich material in the positive electrode has the chemical formula Li. a M b O c Wherein, M is selected from at least one of Al, Ni and Co, 0.5≤a≤2.0, 1.5≤c≤2.0, and 2.0≤c / a≤4.0.
[0034] That is, after the battery undergoes formation, some lithium ions in the lithium-rich material are released, which has a lithium replenishment effect, resulting in a decrease in the ratio of lithium to oxygen in the lithium-rich material. Attached Figure Description
[0035] Figure 1 This is a schematic diagram of the cross-sectional structure of the positive electrode sheet provided in the embodiments of this application.
[0036] Explanation of reference numerals in the attached figures: 10. Current collector; 11. Composite aluminum foil layer; 111. Polymer layer; 112. First aluminum foil layer; 113. Second aluminum foil layer; 12. Carbon coating layer; 20. Lithium-rich material layer; 30. First positive electrode active layer; 40. Second positive electrode active layer. Detailed Implementation
[0037] The technical solutions in the embodiments of this application will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. Based on the embodiments in this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application. Furthermore, it should be understood that the specific implementation methods described herein are only for illustration and explanation of this application and are not intended to limit this application.
[0038] Firstly, such as Figure 1As shown, an embodiment of this application provides a positive electrode sheet, including a current collector 10, a lithium-rich material layer 20, a first positive electrode active layer 30, and a second positive electrode active layer 40. The lithium-rich material layer 20 is disposed on at least one side of the current collector 10, and the lithium-rich material layer 20 includes a lithium-rich material. The first positive electrode active layer 30 is disposed on the side of the lithium-rich material layer 20 opposite to the current collector 10, and the first positive electrode active layer 30 includes lithium manganese iron phosphate. The second positive electrode active layer 40 is disposed on the side of the first positive electrode active layer 30 opposite to the lithium-rich material layer 20, and the second positive electrode active layer 40 includes a ternary material.
[0039] In the positive electrode provided in this application embodiment, the lithium-rich material layer 20 is set separately, which reduces the probability of side reactions between the lithium-rich material and other materials, improves the stability and processability of the lithium-rich material layer 20, and ensures the lithium replenishment effect. The lithium-rich material layer 20 is positioned close to the current collector 10, allowing the lithium-rich material to directly contact the current collector 10. During the formation and charging process, the lithium-rich material can quickly gain electrons, promoting a decomposition reaction and releasing lithium ions with high efficiency and good lithium replenishment effect. The first positive electrode active layer 30 includes lithium manganese iron phosphate, and the second positive electrode active layer 40 includes ternary materials. The lithium ions released from the lithium-rich material layer 20 can sequentially pass through the first positive electrode active layer 30 and the second positive electrode active layer 40 into the electrolyte, playing a lithium replenishment role. The diffusion coefficient of the first positive electrode active layer 30 is moderate, which can reduce the excessive absorption of lithium ions by the second positive electrode active layer 40. Furthermore, the second positive electrode active layer 40 has high conductivity, which can shorten the charge transport path and improve the high-current charging and discharging capability. Since the operating voltage of lithium manganese iron phosphate (LFP) is lower than that of ternary materials, the second positive electrode active layer 40, containing ternary materials, is located on the outside and can preferentially deintercalate and intercalate lithium, reducing the risk of overcharging LFP at high voltages and improving voltage stability. LFP has an olivine structure, resulting in minimal volume change during charging and discharging, which can buffer the stress deformation of the ternary materials in the second positive electrode active layer 40 during charging and discharging, reducing the risk of cracking of the positive electrode sheet. The outer location of the second positive electrode active layer 40 also reduces the side reactions of transition metal dissolution in the first positive electrode active layer 30, improving cycle life. In other words, the positive electrode sheet provided in this application embodiment can reduce side reactions between lithium-rich materials and other materials, improve lithium replenishment effect, and enhance the electrochemical performance, structural stability, and cycle life of the positive electrode sheet.
[0040] Furthermore, the arrangement of "lithium-rich material layer 20 - first positive electrode active layer 30 - second positive electrode active layer 40" allows some of the lithium ions released from the lithium-rich material layer 20 to be stored in the first positive electrode active layer 30 containing lithium manganese iron phosphate, and then slowly released during subsequent cycles to continuously replenish lithium losses. The layered structure of the first positive electrode active layer 30 and the second positive electrode active layer 40 enables the outer second positive electrode active layer 40 to withstand reactions under high voltage, reducing the structural degradation of lithium manganese iron phosphate in the first positive electrode active layer 30 under high voltage, and improving the battery's overall capacity retention rate through synergistic effects.
[0041] In some embodiments, the chemical formula of the lithium-rich material is Li x M y O z Where M is selected from at least one of Al, Ni and Co, 1 < x ≤ 2.0, and 1.5 ≤ z ≤ 2.0.
[0042] The chemical formula of the lithium-rich material is as described above. It has a high energy density and good structural stability, which can ensure the lithium replenishment effect and reduce the side reactions between the lithium-rich material and other materials.
[0043] In some embodiments, the ternary material includes at least one of lithium nickel cobalt manganese oxide and lithium nickel cobalt aluminum oxide.
[0044] Lithium nickel cobalt manganese oxide and lithium nickel cobalt aluminum oxide have high energy density, good structural stability, and high operating voltage, which can improve the performance of the positive electrode.
[0045] In some embodiments, the thickness of the lithium-rich material layer 20 is 10 μm-16 μm.
[0046] By setting the thickness of the lithium-rich material layer 20 within the aforementioned range, the amount of lithium released can be guaranteed, and the risk of lithium dendrite growth can be reduced. Furthermore, within this thickness range, the volume expansion rate of the lithium-rich material layer 20 can be controlled within a reasonable range, ensuring the stability of the positive electrode sheet.
[0047] For example, the thickness of the lithium-rich material layer 20 can be 10 μm, 11 μm, 12 μm, 13 μm, 14 μm, 15 μm or 16 μm.
[0048] In some embodiments, in the lithium-rich material layer 20, the particle size D50 of the lithium-rich material is 5μm-12μm, and the particle size distribution range is 5μm-12μm.
[0049] In the lithium-rich material layer 20, the particle size D50 and distribution range of the lithium-rich material are within the above range, which can reduce the agglomeration of the lithium-rich material, reduce the side reactions between the lithium-rich material and other materials, have a good delithiation effect, and ensure the lithium replenishment effect.
[0050] For example, the particle size D50 of the lithium-rich material can be 10 μm, 11 μm, 12 μm, 13 μm, 14 μm or 15 μm.
[0051] In some embodiments, in the first positive electrode active layer 30, the particle size D50 of lithium manganese iron phosphate is 0.5μm-1.2μm, and the particle size distribution range is 0.1μm-25μm.
[0052] In the first positive electrode active layer 30, the particle size D50 and distribution range of lithium manganese iron phosphate within the above range can achieve a high compaction density, improve energy density, and have a low specific surface area, which can reduce side reactions with other materials.
[0053] For example, the particle size D50 of lithium manganese iron phosphate can be 0.5 μm, 0.6 μm, 0.7 μm, 0.8 μm, 0.9 μm, 1 μm, 1.1 μm or 1.2 μm.
[0054] In some embodiments, in the second positive electrode active layer 40, the particle size D50 of the ternary material is 10μm-15μm, and the particle size distribution range is 1μm-20μm.
[0055] In the second positive electrode active layer 40, the particle size D50 and distribution range of the ternary material are within the above range, which can balance high power performance and energy density. During cycling, the volume change of the ternary material is more uniform, ensuring the cycling stability of the second positive electrode active layer 40.
[0056] For example, the particle size D50 of the ternary material can be 5μm, 6μm, 7μm, 8μm, 9μm, 10μm, 11μm or 12μm.
[0057] In some embodiments, the porosity of the first positive electrode active layer 30 is 20%-30%.
[0058] The porosity of the first positive electrode active layer 30 is within the above range, which can achieve high compaction density while retaining sufficient porosity for electrolyte permeation, and can accommodate the stress generated during cycling, reducing the propagation of cracks between particles.
[0059] For example, the porosity of the first positive electrode active layer 30 can be 20%, 21%, 22%, 23%, 24%, 25%, 26%, 27%, 28%, 29% or 30%.
[0060] In some embodiments, the porosity of the second positive electrode active layer 40 is 25%-35%.
[0061] The porosity of the second positive electrode active layer 40 is within the above range, which can balance high power performance and structural stability, allowing the gas generated by the ternary material during overcharging or high temperature to be released quickly, reducing the probability of side reactions and improving the stability of the second positive electrode active layer 40.
[0062] In some embodiments, the porosity of the second positive electrode active layer 40 can be 25%, 26%, 27%, 28%, 29%, 30%, 31%, 32%, 33%, 34%, or 35%.
[0063] In some embodiments, the current collector 10 includes a composite aluminum foil layer 11, which includes a polymer layer 111 and a first aluminum foil layer 112 and a second aluminum foil layer 113 disposed on opposite sides of the polymer layer 111.
[0064] The melting point of polymer layer 111 is typically between 120℃ and 260℃. When the internal temperature of the battery rises abnormally, polymer layer 111 melts to form an insulating barrier, which can cut off the electron conduction path and reduce the risk of thermal runaway propagation. Polymer layer 111 has a low elastic modulus, which can absorb the stress generated by the expansion or contraction of the positive electrode during battery charging and discharging.
[0065] In some embodiments, the current collector 10 further includes a carbon coating layer 12 disposed between the composite aluminum foil layer 11 and the lithium-rich material layer 20.
[0066] By setting a carbon coating layer 12 between the composite aluminum foil layer 11 and the lithium-rich material layer 20, the contact resistance between the lithium-rich material layer 20 and the composite aluminum foil layer 11 can be reduced, ensuring that the lithium-rich material layer 20 can quickly release lithium ions during the battery formation and charging process, thus achieving a good lithium replenishment effect.
[0067] In some embodiments, the thickness of the carbon coating layer 12 is 0.5 μm-1 μm.
[0068] By keeping the thickness of the carbon coating layer 12 within the above-mentioned range, good conductivity can be ensured, and the overall thickness and cost of the positive electrode sheet can be controlled.
[0069] For example, the thickness of the carbon coating layer 12 can be 0.5 μm, 0.6 μm, 0.7 μm, 0.8 μm, 0.9 μm or 1 μm.
[0070] In some embodiments, the total amount of lithium manganese iron phosphate and ternary materials is in the mass ratio of (93-97.8):(0.2-5) of lithium-rich materials.
[0071] That is, the mass ratio of positive electrode active material to lithium-rich material in the positive electrode sheet is (93-97.8):(0.2-5.0), which can provide sufficient lithium source, ensure lithium replenishment effect, improve the first efficiency of the battery, extend the cycle life of the battery, and reduce the increase in safety risks and cost caused by excessive addition of lithium-rich material, reduce the volume expansion caused by excessive deposition of lithium ions on the negative electrode surface, and ensure the structural stability of the battery.
[0072] For example, the mass ratio of lithium manganese iron phosphate and ternary materials to lithium-rich materials can be 93:0.2, 93:0.5, 93:1, 93:2, 93:3, 93:4, 93:5, 94:0.2, 94:0.5, 94:1, 94:2, 94:3, 94:4, 94:5, 95:0.2, 95:0.5, 95:1, 95:2, 95:3, 95 :4, 95:5, 96:0.2, 96:0.5, 96:1, 96:2, 96:3, 96:4, 96:5, 97:0.2, 97:0.5, 97:1, 97:2, 97:3, 97:4, 97:5, 97.8:0.2, 97.8:0.5, 97.8:1, 97.8:2, 97.8:3, 97.8:4 or 97.8:5.
[0073] In some embodiments, the mass ratio of lithium manganese iron phosphate to ternary materials is 98:2 to 50:50.
[0074] By using a higher proportion of lithium manganese iron phosphate, the high stability of the lithium manganese iron phosphate olivine structure can be utilized to reduce the risk of thermal runaway and ensure safety performance. Furthermore, the energy density can be guaranteed by using ternary materials, ensuring the synergistic effect between the first positive electrode active layer 30 and the second positive electrode active layer 40 in the positive electrode sheet.
[0075] In some embodiments, the lithium-rich material layer 20 further includes a first binder, the first positive electrode active layer 30 further includes a first conductive agent and a second binder, and the second positive electrode active layer 40 further includes a second conductive agent and a third binder. In the positive electrode sheet, the total mass of lithium manganese iron phosphate and ternary materials is A, the mass of lithium-rich materials is B, the total mass of the first binder, the second binder and the third binder is C, and the total mass of the first conductive agent and the second conductive agent is D, satisfying: A:B:C:D=(93-97.8):(0.2-5):(1.2-2.5):(0.5-2):(0-0.5).
[0076] By ensuring that the proportions of each component in the positive electrode meet the above conditions, the loading of active material in the positive electrode can be guaranteed, as well as the energy density and capacity of the positive electrode. Furthermore, by using a suitable binder ratio, the bonding performance between each layer can be guaranteed, ensuring the structural stability of the positive electrode and good conductivity, thus giving the positive electrode excellent overall performance.
[0077] In some embodiments, the first conductive agent includes conductive carbon black and carbon nanotubes.
[0078] By using a first conductive agent comprising conductive carbon black and carbon nanotubes, the advantages of small particle size of conductive carbon black and high aspect ratio of carbon nanotubes can be utilized to construct a three-dimensional conductive network, enhance the mechanical properties of the first positive electrode active layer 30, and extend cycle life.
[0079] In some embodiments, the second conductive agent includes conductive carbon black and carbon nanotubes.
[0080] By using a second conductive agent, including conductive carbon black and carbon nanotubes, a three-dimensional conductive network can be constructed by taking advantage of the small particle size of conductive carbon black and the high aspect ratio of carbon nanotubes, thereby enhancing the mechanical properties of the first positive electrode active layer 30 and extending cycle life.
[0081] Secondly, embodiments of this application provide a method for preparing a positive electrode sheet, comprising: Provide current collector 10; A lithium-rich slurry comprising a lithium-rich material and a first binder is provided, and the lithium-rich slurry is coated on at least one side of the current collector 10 to form a lithium-rich material layer 20. A first positive electrode slurry comprising lithium manganese iron phosphate, a second binder and a first conductive agent is provided. The first positive electrode slurry is coated on the side surface of the lithium-rich material layer 20 away from the current collector 10 to form a first positive electrode active layer 30. A second positive electrode slurry comprising a ternary material, a third binder, and a second conductive agent is provided. The second positive electrode slurry is coated onto the surface of the first positive electrode active layer 30 that is opposite to the lithium-rich material layer 20 to form a second positive electrode active layer 40, thereby obtaining a positive electrode sheet.
[0082] That is, a lithium-rich material layer 20, a first positive electrode active layer 30, and a second positive electrode active layer 40 are sequentially formed on the surface of the current collector 10 by coating, thereby obtaining a positive electrode sheet. The method for preparing the positive electrode sheet provided in this application embodiment has all the beneficial effects of the positive electrode sheet as described above, and will not be repeated here.
[0083] The first, second, and third adhesives can be conventional adhesives in the art, and may be the same or different, which will not be elaborated here. Similarly, the first and second conductive agents can also be conventional conductive agents in the art, and may be the same or different, which will not be elaborated here.
[0084] In some embodiments, the solid content of the lithium replenishment slurry is 65%-75%; And / or, the solid content of the first cathode slurry is 65%-75%; And / or, the solid content of the second cathode slurry is 65%-75%.
[0085] By keeping the solid content of the lithium replenishment slurry, the first cathode slurry, and the second cathode slurry within the above-mentioned range, the stability of the slurry can be improved, sedimentation and agglomeration can be reduced, coating efficiency can be increased, and the uniformity of the coating can be guaranteed.
[0086] Thirdly, embodiments of this application provide a battery comprising a positive electrode sheet as described above, and / or a positive electrode sheet prepared by the method described above.
[0087] The battery provided in this application embodiment has all the beneficial effects of the positive electrode as described above, which will not be repeated here.
[0088] In some embodiments, after the battery undergoes formation, the lithium-rich material in the positive electrode has the chemical formula Li. a M b O c Wherein, M is selected from at least one of Al, Ni and Co, 0.5≤a≤2.0, 1.5≤c≤2.0, and 2.0≤c / a≤4.0.
[0089] That is, after the battery undergoes formation, some lithium ions in the lithium-rich material are released, which has a lithium replenishment effect, resulting in a decrease in the ratio of lithium to oxygen in the lithium-rich material.
[0090] In some embodiments, the battery formation method includes: Charge the battery to the first cutoff voltage V1 at a current of 0.1C-0.5C; Let the battery stand for 1-4 hours; Discharge the battery with a current of 0.1C-1C to the second cutoff voltage V2; Where V1 > V2.
[0091] Charging to the first cutoff voltage under a current of 0.1C-0.5C helps to build a dense SEI film, activate lithium manganese iron phosphate and ternary materials in the positive electrode, improve the specific capacity of the ternary materials, reduce the risk of structural collapse of lithium manganese iron phosphate, and allow lithium ions to fully diffuse after standing for 1-4 hours, eliminating local concentration polarization, achieving a more uniform lithium replenishment effect, and alleviating the volume expansion stress caused during charging. During discharge under a current of 0.1C-1C, it can repair local defects in the SEI film and optimize the consistency between the negative electrode interface and the battery.
[0092] For example, the charging current can be 0.1C, 0.2C, 0.3C, 0.4C or 0.5C, the resting time can be 1h, 1.5h, 2h, 2.5h, 3h, 3.5h or 4h, and the discharging current can be 0.1C, 0.2C, 0.3C, 0.4C, 0.5C, 0.6C, 0.7C, 0.8C, 0.9C or 1C.
[0093] The embodiments of this application are further illustrated below with reference to specific examples. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of this application. Experimental methods in the following embodiments that do not specify specific conditions are generally performed according to the conditions recommended by the manufacturer.
[0094] Unless otherwise specified, the preparation methods of the negative electrode, electrolyte, separator, and battery, as well as the battery formation method, in the following examples and comparative examples are as follows: Preparation method of negative electrode sheet: The negative electrode active material, conductive agent and binder are dispersed in a solvent in a mass ratio of (96~97):(1~2):(1.5-2) to obtain a negative electrode slurry; the negative electrode slurry is coated on the negative electrode current collector 10, and after drying and cold pressing, a negative electrode sheet is obtained. Electrolyte preparation method: Lithium salt, solvent, and additives are mixed in a mass ratio of to obtain the electrolyte; Diaphragm: 9μm thick; Battery assembly method: The vacuum-dried positive and negative electrode plates, along with the separator, are cut, die-cut, and slit, then assembled into a square aluminum casing; finally, electrolyte is injected under high temperature and negative pressure to form the battery. Battery formation method: Charge the battery at a current of 0.3C to the first cutoff voltage of 4.2V; Let the battery stand for 2.5 hours; Discharge the battery at a current of 0.5C to the second cutoff voltage of 2.5V.
[0095] Example 1 (1) Provide a current collector 10; wherein the current collector 10 includes a composite aluminum foil layer 11 and a carbon coating layer 12 coated on one side of the composite aluminum foil layer 11, the composite aluminum foil layer 11 includes a polymer layer 111 and aluminum foil layers located on opposite sides of the polymer layer 111, and the thickness of the carbon coating layer 12 is 0.7 μm; (2) A lithium-rich material and a first binder are mixed to prepare a lithium-replenishing slurry with a solid content of 70%. The lithium-replenishing slurry is coated on the surface of the carbon coating layer 12 to form a lithium-rich material layer 20. The lithium-rich material has the chemical formula Li2Co1O2, the particle size D50 of the lithium-rich material is 12μm, the particle size distribution range is 1μm-20μm, the first binder is polyvinylidene fluoride (PVDF), and the thickness of the lithium-rich material layer 20 is 13.5μm. (3) A first positive electrode slurry with a solid content of 70% is prepared by mixing lithium manganese iron phosphate, a second binder and a first conductive agent. The first positive electrode slurry is coated on the surface of the lithium-rich material layer 20 to form a first positive electrode active layer 30. The particle size D50 of lithium manganese iron phosphate is 0.8 μm and the particle size distribution range is 0.1 μm-25 μm. The second binder is polyvinylidene fluoride (PVDF). The first conductive agent is SP / CNT (the mass ratio of conductive carbon black SP and carbon nanotube CNT is 1:1). The porosity of the first positive electrode active layer 30 is 25%. (3) A second positive electrode slurry with a solid content of 70% is prepared by mixing lithium nickel cobalt manganese oxide, a third binder, and a second conductive agent. The second positive electrode slurry is coated on the surface of the first positive electrode active layer 30 to form a second positive electrode active layer 40, thereby obtaining a positive electrode sheet. The lithium nickel cobalt manganese oxide has a particle size D50 of 8 μm and a particle size distribution range of 5 μm-12 μm. The third binder is polyvinylidene fluoride (PVDF), the second conductive agent is (conductive carbon black SP and carbon nanotubes CNT in a mass ratio of 1:1), and the porosity of the second positive electrode active layer 40 is 30%. (4) Assemble the positive electrode, negative electrode, separator, and electrolyte into a battery according to the method described above, and form the battery according to the method described above; In the positive electrode sheet, by mass ratio, (lithium manganese iron phosphate + lithium nickel cobalt manganese oxide): lithium-rich material: (first binder + second binder + third binder): (first conductive agent + second conductive agent) = 95:2.5:1.2:1.3.
[0096] Example 2 (1) Provide a current collector 10; wherein the current collector 10 includes a composite aluminum foil layer 11 and a carbon coating layer 12 coated on one side of the composite aluminum foil layer 11, the composite aluminum foil layer 11 includes a polymer layer 111 and aluminum foil layers located on opposite sides of the polymer layer 111, and the thickness of the carbon coating layer 12 is 0.5 μm; (2) A lithium-rich material and a first binder are mixed to prepare a lithium replenishing slurry with a solid content of 70%. The lithium replenishing slurry is coated on the surface of the carbon coating layer 12 to form a lithium-rich material layer 20. The lithium-rich material has the chemical formula Li2Co1O2, the particle size D50 of the lithium-rich material is 10μm, the particle size distribution range is 1μm-20μm, the first binder is polyvinylidene fluoride (PVDF), and the thickness of the lithium-rich material layer 20 is 1μm. (3) A first positive electrode slurry with a solid content of 70% is prepared by mixing lithium manganese iron phosphate, a second binder and a first conductive agent. The first positive electrode slurry is coated on the surface of the lithium-rich material layer 20 to form a first positive electrode active layer 30. The particle size D50 of the lithium manganese iron phosphate is 1.2 μm and the particle size distribution range is 0.1 μm-25 μm. The second binder is polyvinylidene fluoride (PVDF). The first conductive agent is SP / CNT (the mass ratio of conductive carbon black SP and carbon nanotube CNT is 1:1). The porosity of the first positive electrode active layer 30 is 20%. (3) A second positive electrode slurry with a solid content of 70% is prepared by mixing lithium nickel cobalt manganese oxide, a third binder, and a second conductive agent. The second positive electrode slurry is coated on the surface of the first positive electrode active layer 30 to form a second positive electrode active layer 40, thereby obtaining a positive electrode sheet. The lithium nickel cobalt manganese oxide has a particle size D50 of 5 μm and a particle size distribution range of 5 μm-12 μm. The third binder is polyvinylidene fluoride (PVDF), the second conductive agent is SP / CNT (the mass ratio of conductive carbon black SP and carbon nanotubes CNT is 1:1), and the porosity of the second positive electrode active layer 40 is 35%. (4) Assemble the positive electrode, negative electrode, separator, and electrolyte into a battery according to the method described above, and form the battery according to the method described above; In the positive electrode sheet, by mass ratio, (lithium manganese iron phosphate + lithium nickel cobalt manganese oxide): lithium-rich material: (first binder + second binder + third binder): (first conductive agent + second conductive agent) = 93:5:1:1.
[0097] Example 3 (1) Provide a current collector 10; wherein the current collector 10 includes a composite aluminum foil layer 11 and a carbon coating layer 12 coated on one side of the composite aluminum foil layer 11, the composite aluminum foil layer 11 includes a polymer layer 111 and aluminum foil layers located on opposite sides of the polymer layer 111, and the thickness of the carbon coating layer 12 is 1 μm. (2) A lithium-rich material and a first binder are mixed to prepare a lithium replenishing slurry with a solid content of 70%. The lithium replenishing slurry is coated on the surface of the carbon coating layer 12 to form a lithium-rich material layer 20. The lithium-rich material has the chemical formula Li2Co1O2, the particle size D50 of the lithium-rich material is 15μm, the particle size distribution range is 1μm-20μm, the first binder is polyvinylidene fluoride (PVDF), and the thickness of the lithium-rich material layer 20 is 10μm. (3) A first positive electrode slurry with a solid content of 70% is prepared by mixing lithium manganese iron phosphate, a second binder and a first conductive agent. The first positive electrode slurry is coated on the surface of the lithium-rich material layer 20 to form a first positive electrode active layer 30. The particle size D50 of the lithium manganese iron phosphate is 0.5 μm and the particle size distribution range is 0.1 μm-25 μm. The second binder is polyvinylidene fluoride (PVDF). The first conductive agent is SP / CNT (the mass ratio of conductive carbon black SP and carbon nanotube CNT is 1:1). The porosity of the first positive electrode active layer 30 is 30%. (3) A second positive electrode slurry with a solid content of 70% is prepared by mixing lithium nickel cobalt manganese oxide, a third binder, and a second conductive agent. The second positive electrode slurry is coated on the surface of the first positive electrode active layer 30 to form a second positive electrode active layer 40, thereby obtaining a positive electrode sheet. The particle size D50 of lithium nickel cobalt manganese oxide is 12 μm, and the particle size distribution range is 5 μm-12 μm. The third binder is polyvinylidene fluoride (PVDF), the second conductive agent is SP / CNT (the mass ratio of conductive carbon black SP and carbon nanotube CNT is 1:1), and the porosity of the second positive electrode active layer 40 is 25%. (4) Assemble the positive electrode, negative electrode, separator, and electrolyte into a battery according to the method described above, and form the battery according to the method described above; In the positive electrode sheet, by mass ratio, (lithium manganese iron phosphate + lithium nickel cobalt manganese oxide): lithium-rich material: (first binder + second binder + third binder): (first conductive agent + second conductive agent) = 97.8:0.2:1:1.
[0098] Example 4 (1) Provide a current collector 10; wherein the current collector 10 includes a composite aluminum foil layer 11 and a carbon coating layer 12 coated on one side of the composite aluminum foil layer 11, the composite aluminum foil layer 11 includes a polymer layer 111 and aluminum foil layers located on opposite sides of the polymer layer 111, and the thickness of the carbon coating layer 12 is 0.7 μm; (2) A lithium-rich material and a first binder are mixed to prepare a lithium replenishing slurry with a solid content of 65%. The lithium replenishing slurry is coated on the surface of the carbon coating layer 12 to form a lithium-rich material layer 20. The lithium-rich material has the chemical formula Li2Co1O2, the particle size D50 of the lithium-rich material is 12μm, the particle size distribution range is 1μm-20μm, the first binder is polyvinylidene fluoride (PVDF), and the thickness of the lithium-rich material layer 20 is 13.5μm. (3) A first positive electrode slurry with a solid content of 75% is prepared by mixing lithium manganese iron phosphate, a second binder and a first conductive agent. The first positive electrode slurry is coated on the surface of the lithium-rich material layer 20 to form a first positive electrode active layer 30. The particle size D50 of the lithium manganese iron phosphate is 0.8 μm and the particle size distribution range is 0.1 μm-25 μm. The second binder is polyvinylidene fluoride (PVDF). The first conductive agent is SP / CNT (the mass ratio of conductive carbon black SP and carbon nanotube CNT is 1:1). The porosity of the first positive electrode active layer 30 is 25%. (3) A second positive electrode slurry with a solid content of 65% is prepared by mixing lithium nickel cobalt manganese oxide, a third binder, and a second conductive agent. The second positive electrode slurry is coated on the surface of the first positive electrode active layer 30 to form a second positive electrode active layer 40, thereby obtaining a positive electrode sheet. The lithium nickel cobalt manganese oxide has a particle size D50 of 8 μm and a particle size distribution range of 5 μm-12 μm. The third binder is polyvinylidene fluoride (PVDF), the second conductive agent is SP / CNT (the mass ratio of conductive carbon black SP and carbon nanotubes CNT is 1:1), and the porosity of the second positive electrode active layer 40 is 30%. (4) Assemble the positive electrode, negative electrode, separator, and electrolyte into a battery according to the method described above, and form the battery according to the method described above; In the positive electrode sheet, by mass ratio, (lithium manganese iron phosphate + lithium nickel cobalt manganese oxide): lithium-rich material: (first binder + second binder + third binder): (first conductive agent + second conductive agent) = 95:2.5:1.2:1.3.
[0099] Example 5 (1) Provide a current collector 10; wherein the current collector 10 includes a composite aluminum foil layer 11 and a carbon coating layer 12 coated on one side of the composite aluminum foil layer 11, the composite aluminum foil layer 11 includes a polymer layer 111 and aluminum foil layers located on opposite sides of the polymer layer 111, and the thickness of the carbon coating layer 12 is 0.5 μm; (2) A lithium-rich material and a first binder are mixed to prepare a lithium-replenishing slurry with a solid content of 70%. The lithium-replenishing slurry is coated on the surface of the carbon coating layer 12 to form a lithium-rich material layer 20. The lithium-rich material has the chemical formula Li2Co1O2, the particle size D50 of the lithium-rich material is 10μm, the particle size distribution range is 1μm-20μm, the first binder is polyvinylidene fluoride (PVDF), and the thickness of the lithium-rich material layer 20 is 13.5μm. (3) A first positive electrode slurry with a solid content of 70% is prepared by mixing lithium manganese iron phosphate, a second binder and a first conductive agent. The first positive electrode slurry is coated on the surface of the lithium-rich material layer 20 to form a first positive electrode active layer 30. The particle size D50 of the lithium manganese iron phosphate is 0.5 μm and the particle size distribution range is 0.1 μm-25 μm. The second binder is polyvinylidene fluoride (PVDF). The first conductive agent is SP / CNT (the mass ratio of conductive carbon black SP and carbon nanotube CNT is 1:1). The porosity of the first positive electrode active layer 30 is 20%. (4) A second positive electrode slurry with a solid content of 70% is prepared by mixing lithium nickel cobalt manganese oxide, a third binder, and a second conductive agent. The second positive electrode slurry is coated on the surface of the first positive electrode active layer 30 to form a second positive electrode active layer 40, thereby obtaining a positive electrode sheet. The particle size D50 of lithium nickel cobalt manganese oxide is 5 μm, and the particle size distribution range is 5 μm-12 μm. The third binder is polyvinylidene fluoride (PVDF), the second conductive agent is SP / CNT (the mass ratio of conductive carbon black SP and carbon nanotube CNT is 1:1), and the porosity of the second positive electrode active layer 40 is 25%. (5) Assemble the positive electrode, negative electrode, separator, and electrolyte into a battery according to the method described above, and form the battery according to the method described above; In the positive electrode sheet, by mass ratio, (lithium manganese iron phosphate + lithium nickel cobalt manganese oxide): lithium-rich material: (first binder + second binder + third binder): (first conductive agent + second conductive agent) = 95:2.5:1.2:1.3.
[0100] Comparative Example 1 (1) Provide a current collector 10; wherein the current collector 10 includes a composite aluminum foil layer 11 and a carbon coating layer 12 coated on one side of the composite aluminum foil layer 11, the composite aluminum foil layer 11 includes a polymer layer 111 and aluminum foil layers located on opposite sides of the polymer layer 111, and the thickness of the carbon coating layer 12 is 0.7 μm; (2) A first positive electrode slurry with a solid content of 70% is prepared by mixing lithium manganese iron phosphate, a first binder and a first conductive agent. The first positive electrode slurry is coated on the surface of the carbon coating layer 12 to form a first positive electrode active layer 30. The particle size D50 of lithium manganese iron phosphate is 0.8 μm and the particle size distribution range is 0.1 μm-25 μm. The first binder is polyvinylidene fluoride (PVDF). The first conductive agent is SP / CNT (the mass ratio of conductive carbon black SP and carbon nanotube CNT is 1:1). The porosity of the first positive electrode active layer 30 is 25%. (3) A second positive electrode slurry with a solid content of 70% is prepared by mixing lithium nickel cobalt manganese oxide, a second binder, and a second conductive agent. The second positive electrode slurry is coated on the surface of the first positive electrode active layer 30 to form a second positive electrode active layer 40, thereby obtaining a positive electrode sheet. The lithium nickel cobalt manganese oxide has a particle size D50 of 8 μm and a particle size distribution range of 5 μm-12 μm. The second binder is polyvinylidene fluoride (PVDF), the second conductive agent is SP / CNT (the mass ratio of conductive carbon black SP and carbon nanotube CNT is 1:1), and the porosity of the second positive electrode active layer 40 is 30%. (4) Assemble the positive electrode, negative electrode, separator, and electrolyte into a battery according to the method described above, and form the battery according to the method described above; In the positive electrode sheet, by mass ratio, (lithium manganese iron phosphate + lithium nickel cobalt manganese oxide) : (first binder + second binder) : (first conductive agent + second conductive agent) = 97.5 : 1.2 : 1.3.
[0101] Comparative Example 2 (1) Provide a current collector 10; wherein the current collector 10 includes a composite aluminum foil layer 11 and a carbon coating layer 12 coated on one side of the composite aluminum foil layer 11, the composite aluminum foil layer 11 includes a polymer layer 111 and aluminum foil layers located on opposite sides of the polymer layer 111, and the thickness of the carbon coating layer 12 is 0.7 μm; (2) A lithium-rich material and a first binder are mixed to prepare a lithium-replenishing slurry with a solid content of 70%. The lithium-replenishing slurry is coated on the surface of the carbon coating layer 12 to form a lithium-rich material layer 20. The lithium-rich material has the chemical formula Li2Co1O2, the particle size D50 of the lithium-rich material is 12μm, the particle size distribution range is 1μm-20μm, the first binder is polyvinylidene fluoride (PVDF), and the thickness of the lithium-rich material layer 20 is 13.5μm. (3) A positive electrode slurry with a solid content of 70% is prepared by mixing lithium manganese iron phosphate, a second binder and a conductive agent in a mass ratio of . The positive electrode slurry is coated on the surface of the lithium-rich material layer 20 to form a positive electrode active layer, thus obtaining a positive electrode sheet; wherein, the particle size D50 of lithium manganese iron phosphate is 0.8μm and the particle size distribution range is 0.1μm-25μm, the second binder is polyvinylidene fluoride (PVDF), the first conductive agent is SP / CNT (the mass ratio of conductive carbon black SP and carbon nanotube CNT is 1:1), and the porosity of the positive electrode active layer is 25%; (4) Assemble the positive electrode, negative electrode, separator, and electrolyte into a battery according to the method described above, and form the battery according to the method described above; In the positive electrode sheet, the mass ratio of lithium manganese iron phosphate : (first binder + second binder) : first conductive agent is 95:2.5:1.2:1.3.
[0102] Comparative Example 3 (1) Provide a current collector 10; wherein the current collector 10 includes a composite aluminum foil layer 11 and a carbon coating layer 12 coated on one side of the composite aluminum foil layer 11, the composite aluminum foil layer 11 includes a polymer layer 111 and aluminum foil layers located on opposite sides of the polymer layer 111, and the thickness of the carbon coating layer 12 is 0.7 μm; (2) A lithium-rich material and a first binder are mixed to prepare a lithium-replenishing slurry with a solid content of 70%. The lithium-replenishing slurry is coated on the surface of the carbon coating layer 12 to form a lithium-rich material layer 20. The lithium-rich material has the chemical formula Li2Co1O2, the particle size D50 of the lithium-rich material is 12μm, the particle size distribution range is 1μm-20μm, the first binder is polyvinylidene fluoride (PVDF), and the thickness of the lithium-rich material layer 20 is 13.5μm. (3) A first positive electrode slurry with a solid content of 70% is prepared by mixing lithium nickel cobalt manganese oxide, a second binder and a first conductive agent in a mass ratio of 1. The first positive electrode slurry is coated on the surface of the carbon coating layer 12 to form a first positive electrode active layer 30, thereby obtaining a positive electrode sheet. The particle size D50 of lithium nickel cobalt manganese oxide is 8 μm, and the particle size distribution range is 5 μm-12 μm. The second binder is polyvinylidene fluoride (PVDF), the first conductive agent is SP / CNT (the mass ratio of conductive carbon black SP and carbon nanotube CNT is 1:1), and the porosity of the first positive electrode active layer 30 is 30%. (3) A second positive electrode slurry with a solid content of 70% is prepared by mixing lithium manganese iron phosphate, a third binder, and a second conductive agent in a mass ratio of . The second positive electrode slurry is coated on the surface of the lithium-rich material layer 20 to form a second positive electrode active layer 40. The particle size D50 of the lithium manganese iron phosphate is 0.8 μm, and the particle size distribution range is 0.1 μm-25 μm. The third binder is polyvinylidene fluoride (PVDF), the second conductive agent is SP / CNT (the mass ratio of conductive carbon black SP and carbon nanotube CNT is 1:1), and the porosity of the second positive electrode active layer 40 is 25%. (4) Assemble the positive electrode, negative electrode, separator, and electrolyte into a battery according to the method described above, and form the battery according to the method described above; In the positive electrode sheet, by mass ratio, (lithium manganese iron phosphate + lithium nickel cobalt manganese oxide): (first binder + second binder + third binder): (first conductive agent + second conductive agent) = 95:2.5:1.2:1.3.
[0103] The batteries in Examples 1-5 and Comparative Examples 1-3 were subjected to morphological observation, full-charge interface color observation, specific capacity testing, and cycle performance testing. The electrode morphology was directly observed with the naked eye to determine surface smoothness. The full-charge interface color observation method involved charging the battery at 0.33C to a cutoff voltage of 4.2V at 25°C, then disassembling the battery to observe the surface morphology of the negative electrode. The specific capacity testing method involved performing a 0.33C charge-discharge cycle within a voltage range of 2.5V-4.2V at 25°C, and measuring the specific capacity during this process. The cycle life testing method involved performing a 0.1C charge-discharge cycle within a voltage range of 2.5V-4.2V at 25°C, and recording the number of cycles when the capacity reached 80% of the initial capacity; this number represents the cycle life. The test results are shown in Table 1. Table 1
[0104] As shown in Table 1, compared with Comparative Example 1, when the positive electrode does not contain the lithium-rich material layer 20, the capacity and cycle performance of the battery composed of it are significantly reduced. Compared with Comparative Example 2, when the positive electrode does not contain the ternary material layer, the capacity and cycle performance of the battery composed of it are also significantly reduced. Compared with Comparative Example 3, when the positions of the ternary material layer and the lithium manganese iron phosphate material layer are interchanged, it will result in obvious pits on the interface of the coated positive electrode. At the same time, after the battery composed of the positive electrode is fully charged, local purple spot defects appear on the interface, the capacity and cycle performance are significantly reduced, and there are also serious problems such as local lithium plating. Compared with Examples 1-5, the thickness and mass ratio of the lithium-rich material layer 20 vary within a certain range, and the interface of the positive electrode composed of the material layer is good. As the mass ratio of the lithium-rich material layer 20 increases, the specific capacity and cycle performance of the battery composed of the positive electrode also show an increasing trend.
[0105] In summary, the embodiments of this application, by reasonably setting the lithium-rich material layer 20 and the first positive electrode active layer 30 containing lithium manganese iron phosphate and the second positive electrode active layer 40 containing ternary materials, can ensure the surface morphology of the positive electrode sheet, significantly improve the specific capacity and cycle performance of the battery, reduce the generation of local lithium plating defects, significantly improve the overall performance of the battery, and produce unexpected technical effects.
[0106] The embodiments of this application have been described in detail above. Specific examples have been used to illustrate the principles and implementation methods of this application. The description of the above embodiments is only for the purpose of helping to understand the method and core ideas of this application. At the same time, for those skilled in the art, there will be changes in the specific implementation methods and application scope based on the ideas of this application. Therefore, the content of this specification should not be construed as a limitation of this application.
Claims
1. A positive electrode plate, characterized in that, include: current collector; A lithium-rich material layer is disposed on at least one side of the current collector, and the lithium-rich material layer includes a lithium-rich material; A first positive electrode active layer is disposed on the side of the lithium-rich material layer away from the current collector, and the first positive electrode active layer includes lithium manganese iron phosphate. The second positive electrode active layer is disposed on the side of the first positive electrode active layer away from the lithium-rich material layer, and the second positive electrode active layer includes a ternary material.
2. The positive electrode sheet according to claim 1, characterized in that, The chemical formula of the lithium-rich material is Li x M y O z Wherein, M is selected from at least one of Al, Ni and Co, 1 < x ≤ 2.0, 1.5 ≤ z ≤ 2.0; And / or, the ternary material includes at least one of lithium nickel cobalt manganese oxide and lithium nickel cobalt aluminum oxide.
3. The positive electrode sheet according to claim 1, characterized in that, The thickness of the lithium-rich material layer is 10μm-16μm.
4. The positive electrode sheet according to claim 1, characterized in that, In the lithium-rich material layer, the particle size D50 of the lithium-rich material is 10μm-15μm, and the particle size distribution range is 1μm-20μm; And / or, in the first positive electrode active layer, the particle size D50 of the lithium manganese iron phosphate is 0.5μm-1.2μm, and the particle size distribution range is 0.1μm-25μm; And / or, in the second positive electrode active layer, the particle size D50 of the ternary material is 5μm-12μm, and the particle size distribution range is 5μm-12μm.
5. The positive electrode sheet according to claim 1, characterized in that, The porosity of the first positive electrode active layer is 20%-30%; And / or, the porosity of the second positive electrode active layer is 25%-35%.
6. The positive electrode sheet according to claim 1, characterized in that, The current collector includes a composite aluminum foil layer, which includes a polymer layer and a first aluminum foil layer and a second aluminum foil layer disposed on opposite sides of the polymer layer.
7. The positive electrode sheet according to claim 6, characterized in that, The current collector also includes a carbon coating layer, which is disposed between the composite aluminum foil layer and the lithium-rich material layer.
8. The positive electrode sheet according to claim 7, characterized in that, The thickness of the carbon coating layer is 0.5μm-1μm.
9. The positive electrode sheet according to any one of claims 1-8, characterized in that, The total amount of lithium manganese iron phosphate and the ternary material is in the mass ratio of the lithium-rich material to (93-97.8):(0.2-5); And / or, the mass ratio of the lithium manganese iron phosphate to the ternary material is 98:2 to 50:
50.
10. The positive electrode sheet according to any one of claims 1-8, characterized in that, The lithium-rich material layer further includes a first binder, the first positive electrode active layer further includes a first conductive agent and a second binder, and the second positive electrode active layer further includes a second conductive agent and a third binder; In the positive electrode sheet, the total mass of the lithium manganese iron phosphate and the ternary material is A, the mass of the lithium-rich material is B, the total mass of the first binder, the second binder and the third binder is C, and the total mass of the first conductive agent and the second conductive agent is D, satisfying: A:B:C:D=(93-97.8):(0.2-5):(1.2-2.5):(0.5-2):(0-0.5).
11. The positive electrode sheet according to claim 10, characterized in that, The first conductive agent includes conductive carbon black and carbon nanotubes; And / or, the second conductive agent includes conductive carbon black and carbon nanotubes.
12. A method for preparing a positive electrode sheet, characterized in that, include: Provide current collectors; A lithium-rich slurry comprising a lithium-rich material and a first binder is provided, and the lithium-rich slurry is coated on at least one side of the current collector to form a lithium-rich material layer; A first positive electrode slurry comprising lithium manganese iron phosphate, a second binder, and a first conductive agent is provided. The first positive electrode slurry is coated onto the side surface of the lithium-rich material layer facing away from the current collector to form a first positive electrode active layer. A second positive electrode slurry comprising a ternary material, a third binder, and a second conductive agent is provided. The second positive electrode slurry is coated onto the surface of the first positive electrode active layer that is opposite to the lithium-rich material layer to form a second positive electrode active layer, thereby obtaining the positive electrode sheet.
13. The method for preparing the positive electrode sheet according to claim 12, characterized in that, The solid content of the lithium replenishing slurry is 65%-75%; And / or, the solid content of the first positive electrode slurry is 65%-75%; And / or, the solid content of the second positive electrode slurry is 65%-75%.
14. A battery, characterized in that, This includes the positive electrode sheet as described in any one of claims 1-11, and / or the positive electrode sheet prepared by the method described in any one of claims 12-13.
15. The battery according to claim 14, characterized in that, After the battery undergoes formation, the lithium-rich material in the positive electrode has the chemical formula Li. a M b O c Wherein, M is selected from at least one of Al, Ni and Co, 0.5≤a≤2.0, 1.5≤c≤2.0, and 2.0≤c / a≤4.0.