Positive electrode sheet, battery, and electric device

Abstract

The present application provides a positive electrode sheet, a battery, and an electric device. The positive electrode sheet comprises a positive electrode current collector and a plurality of positive electrode active material layers stacked on the surface of at least one side of the positive electrode current collector; the positive electrode active material layers comprise a positive electrode material; the positive electrode material comprise a first positive electrode active material and a second positive electrode active material; the particle size D150 of the first positive electrode active material and the particle size D250 of the second positive electrode active material satisfies D150<85 nm and 85 nm<D250<400 nm; in a direction from the positive electrode current collector to the positive electrode active material layers, among the plurality of positive electrode active material layers, the mass content of the first positive electrode active material in the positive electrode material gradually decreases, and the mass content of the second positive electrode active material in the positive electrode material gradually increases. The positive electrode sheet has excellent compaction density and energy density, helping to reduce the internal resistance of the battery and improve the power performance of the battery.

Description

Positive electrode sheet, battery and electric device

[0001] The present application claims priority to the Chinese patent application No. 202410851886.4, filed on June 27, 2024, entitled “Positive electrode sheet, battery and electric device”, the whole content of which is incorporated herein by reference. TECHNICAL FIELD

[0002] The present application relates to the technical field of batteries, in particular to a positive electrode sheet, a battery and an electric device. BACKGROUND

[0003] Compared with traditional batteries, lithium ion batteries have the advantages of high voltage, long service life, environmental friendliness, etc., and are widely used in electronic devices, automobiles, aerospace, etc. Among them, the positive electrode directly affects the performance of the lithium ion battery. The active materials currently used in the positive electrode have the advantages of high capacity, high safety, good cycle performance, etc. However, the ion conductivity and electronic conductivity of some active materials are relatively low, and the compaction density and energy density of the positive electrode are poor, which will increase the internal resistance of the battery and affect the power performance of the battery, which is not conducive to the use of lithium ion batteries. SUMMARY

[0004] In view of this, the present application provides a positive electrode sheet, a battery and an electric device.

[0005] In a first aspect, the present application provides a positive electrode sheet, comprising a positive current collector and a plurality of layers of positive active material layers stacked on at least one side surface of the positive current collector, the positive active material layer comprising a positive material, the positive material comprising a first positive active material and a second positive active material, the particle size D150 of the first positive active material and the particle size D250 of the second positive active material satisfying: D150 < 85 nm, 85 nm ≤ D250 ≤ 400 nm, and in the direction from the positive current collector to the positive active material layer, in the plurality of layers of positive active material layers, the mass content of the first positive active material in the positive material gradually decreases, and the mass content of the second positive active material in the positive material gradually increases.

[0006] Optionally, the particle size distribution curve of the positive material in each positive active material layer has a first peak and a second peak; the particle size corresponding to the peak value of the first peak is D1, with unit of nm, and the particle size corresponding to the peak value of the second peak is D2, with unit of nm, wherein 0.1 < D1 / D2 < 0.4; and / or, taking the sum of the peak area percentage of the first peak and the peak area percentage of the second peak as 100%, the peak area percentage of the first peak is S1%, and the peak area percentage of the second peak is S2%, wherein 0.25 < S1 / S2 < 10.

[0007] Optionally, in the multi-layered positive active material layer, the mass content of the first positive active material in the positive material gradually decreases from 85-95% to 20-40% in the direction from the positive current collector to the positive active material layer.

[0008] Optionally, in the multi-layered positive active material layer, the mass content of the second positive active material in the positive material gradually increases from 5-15% to 60-80% in the direction from the positive current collector to the positive active material layer.

[0009] Optionally, the particle size D150 of the first positive active material and the particle size D250 of the second positive active material satisfy: 10nm≤D150<85nm, 85nm≤D250≤300nm.

[0010] Optionally, the particle size D150 of the first positive active material and the particle size D250 of the second positive active material satisfy: 20nm≤D150≤80nm, 85nm≤D250≤200nm.

[0011] Optionally, the areal density of the positive electrode sheet is 200g / m2-700g / m2.

[0012] Optionally, the absolute value of the difference in areal density of the multi-layered positive active material layer is 0g / m2-10g / m2.

[0013] Optionally, the thickness of the positive active material layer is 80μm-280μm.

[0014] Optionally, the absolute value of the difference in thickness of the multi-layered positive active material layer is 0μm-10μm.

[0015] Optionally, the material of the positive material includes at least one of lithium manganese iron phosphate and lithium iron phosphate.

[0016] Optionally, the number of layers of the positive active material layer in the positive electrode sheet is 2-5.

[0017] Optionally, when the positive electrode sheet comprises two layers of the positive electrode active material layer, the two layers of the positive electrode active material layer comprise a first layer of the positive electrode active material layer arranged on one side of the positive electrode current collector and a second layer of the positive electrode active material layer arranged on the surface of the first layer of the positive electrode active material layer away from the positive electrode current collector; in the first layer of the positive electrode active material layer, the mass content of the first positive electrode active material in the positive electrode material is 85%-95%, and the mass content of the second positive electrode active material in the positive electrode material is 5%-15%; in the second layer of the positive electrode active material layer, the mass content of the first positive electrode active material in the positive electrode material is 20%-40%, and the mass content of the second positive electrode active material in the positive electrode material is 60%-80%.

[0018] Optionally, when the positive electrode sheet comprises three layers of the positive electrode active material layer, the three layers of the positive electrode active material layer comprise a first layer of the positive electrode active material layer arranged on one side of the positive electrode current collector, a second layer of the positive electrode active material layer arranged on the surface of the first layer of the positive electrode active material layer away from the positive electrode current collector, and a third layer of the positive electrode active material layer arranged on the surface of the second layer of the positive electrode active material layer away from the positive electrode current collector; in the first layer of the positive electrode active material layer, the mass content of the first positive electrode active material in the positive electrode material is 85%-95%, and the mass content of the second positive electrode active material in the positive electrode material is 5%-15%; in the second layer of the positive electrode active material layer, the mass content of the first positive electrode active material in the positive electrode material is 50%-80%, and the mass content of the second positive electrode active material in the positive electrode material is 20%-50%; in the third layer of the positive electrode active material layer, the mass content of the first positive electrode active material in the positive electrode material is 20%-40%, and the mass content of the second positive electrode active material in the positive electrode material is 60%-80%.

[0019] In a second aspect, the present application provides a battery comprising the negative electrode sheet and the positive electrode sheet of the first aspect.

[0020] In a third aspect, the present application provides a power consumption device comprising the battery of the second aspect.

[0021] In the positive electrode sheet provided by the present application, the proportion of the small-particle-size first positive electrode active material close to the current collector is large, the compaction density of the positive electrode active material layer is high, the electronic conductivity is good, the proportion of the large-particle-size second positive electrode active material away from the current collector is large, the porosity of the positive electrode active material layer is high, and the ionic conductivity is good, so that the compaction density, energy density and power performance of the positive electrode sheet as a whole are excellent, which helps to reduce the internal resistance of the battery, improve the energy density and power performance of the battery, so that the battery has excellent electrochemical performance and is conducive to its use in power consumption devices. BRIEF DESCRIPTION OF DRAWINGS

[0022] In order to more clearly illustrate the technical solutions of the embodiments of the present application or the prior art, the accompanying drawings needed to be used in the embodiments or prior art description will be briefly introduced. The specific embodiments described herein are only used to explain the present application, and are not used to limit the present application.

[0023] FIG. 1 is a cross-sectional schematic view of a positive electrode tab provided by an embodiment of the present application.

[0024] FIG. 2 is a particle size distribution curve of the positive electrode material in the third positive electrode active material layer of the positive electrode tab prepared in Example 3. DETAILED DESCRIPTION

[0025] The technical solutions in the embodiments of the present application will be described clearly and completely below with reference to the accompanying drawings in the embodiments of the present application. Obviously, the described embodiments are only some of the embodiments of the present application, but not all the embodiments of the present application. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative work fall within the scope of protection of the present application.

[0026] Please refer to FIG. 1, which is a cross-sectional schematic view of a positive electrode tab provided by an embodiment of the present application. The positive electrode tab 100 includes a positive electrode current collector 10 and a plurality of positive electrode active material layers 20 stacked on at least one side surface of the positive electrode current collector 10. The positive electrode active material layer 20 includes a positive electrode material, and the positive electrode material includes a first positive electrode active material and a second positive electrode active material. The particle size D150 of the first positive electrode active material and the particle size D250 of the second positive electrode active material satisfy: D150 < 85 nm, 85 nm ≤ D250 ≤ 400 nm. In the direction from the positive electrode current collector 10 to the positive electrode active material layer 20 (as shown by the arrow in FIG. 1), in the plurality of positive electrode active material layers 20, the mass content of the first positive electrode active material in the positive electrode material gradually decreases, and the mass content of the second positive electrode active material in the positive electrode material gradually increases.

[0027] The particle size D150 of the first positive electrode active material in the present application refers to the particle size corresponding to the volume distribution percentage of the first positive electrode active material reaching 50%; the particle size D250 of the second positive electrode active material refers to the particle size corresponding to the volume distribution percentage of the second positive electrode active material reaching 50%. In the positive electrode sheet provided by the present application, each positive electrode active material layer contains first positive electrode active material and second positive electrode active material with different particle sizes, the particle size of the first positive electrode active material is smaller than that of the second positive electrode active material, so that the first positive electrode active material mainly plays a role in packing and filling and improving the compaction density, the second positive electrode active material mainly plays a role in improving the porosity, and the first positive electrode active material and the second positive electrode active material synergistically improve the performance of each positive electrode active material layer; at the same time, the proportion of small-particle-size first positive electrode active material near the current collector side in the positive electrode sheet is higher, so that the compaction density of the positive electrode active material layer is high, improving its electronic conductivity, and the proportion of large-particle-size second positive electrode active material away from the current collector side is higher, so that the porosity of the positive electrode active material layer is high, improving its ionic conductivity, and the setting of the mass content change of the first positive electrode active material and the second positive electrode active material in the multi-layer positive electrode active material makes the compaction density, energy density and power performance of the positive electrode sheet excellent, which is conducive to its use in the battery, reduces the internal resistance of the battery and improves the power performance of the battery.

[0028] In an embodiment of the present application, the particle size distribution curve of the positive electrode material in each positive electrode active material layer has a first peak and a second peak, the peak value of the first peak corresponds to a particle size D1, unit: nm, the peak value of the second peak corresponds to a particle size D2, unit: nm, wherein 0.1 < D1 / D2 < 0.4; and / or, taking the sum of the peak area ratio of the first peak and the peak area ratio of the second peak as 100%, the peak area ratio of the first peak is S1%, and the peak area ratio of the second peak is S2%, wherein 0.25 < S1 / S2 < 10. In the present application, the peak area ratio of the first peak and the second peak represents the mass ratio of the first positive electrode active material and the second positive electrode active material. In this way, the combination of the small particle size first positive electrode active material and the large particle size second positive electrode active material can achieve better filling and stacking, which is beneficial to improve the compaction density of the positive electrode sheet, and thus helps to improve the energy density of the battery. The particle size distribution curve of the positive electrode material has an abscissa of particle size, unit: nm, and an ordinate of volume ratio, unit: %. It can be understood that, since the ratio of D1 / D2 is less than 1, i.e. the particle size corresponding to the first peak is small, and the particle size corresponding to the second peak is large, in the particle size distribution curve, the first peak is closer to the ordinate than the second peak; since along the direction from the positive electrode current collector to the positive electrode active material layer, the mass content of the first positive electrode active material in the positive electrode material of the multi-layer positive electrode active material layer gradually decreases, and the mass content of the second positive electrode active material gradually increases, therefore, along the direction from the positive electrode current collector to the positive electrode active material layer, the ratio of S1 / S2 in the particle size distribution curve of the positive electrode material of the multi-layer positive electrode active material layer gradually decreases. Specifically, the ratio of D1 / D2 can be but is not limited to 0.12, 0.15, 0.17, 0.18, 0.2, 0.22, 0.25, 0.27, 0.3, 0.35, 0.37 or 0.39, etc.; the ratio of S1 / S2 can be but is not limited to 0.3, 0.5, 1, 1.5, 2, 2.5, 3, 3.5, 4, 4.5, 5, 5.5, 6, 6.5, 7, 7.5, 8, 8.5, 9 or 9.5, etc. In an embodiment of the present application, 0.5 < S1 / S2 < 9, which is beneficial to further improve the performance of the positive electrode sheet.

[0029] The number of layers of the positive electrode active material layer in the positive electrode tab of the present application can be two layers, or more than two layers, such as three layers, four layers, five layers, six layers, seven layers, etc., which can be set according to actual needs. The number of layers of the positive electrode active material layer in the positive electrode tab in the present application refers to the number of layers on one side of the positive electrode current collector, and the positive electrode active material layer is arranged on one side or both sides of the positive electrode current collector; when the positive electrode current collector has positive electrode active material on both sides, the number of layers of the positive electrode active material layer arranged on both sides of the positive electrode current collector can be the same or different, which can be set according to actual needs. In an embodiment of the present application, the number of layers of the positive electrode active material layer in the positive electrode tab is 2-5. That is, the positive electrode tab can have two layers of positive electrode active material layer to five layers of positive electrode active material layer, which can further improve the ionic conductivity and liquid retention level of the positive electrode active material layer away from the current collector, and help to further improve the performance of the positive electrode tab.

[0030] In an embodiment of the present application, the material of the positive electrode material includes at least one of lithium manganese iron phosphate and lithium iron phosphate. The ionic conductivity and electronic conductivity of lithium manganese iron phosphate and lithium iron phosphate are low, and the positive electrode tab designed by the present application can effectively avoid excessive influence of the low ionic conductivity and electronic conductivity of lithium manganese iron phosphate and lithium iron phosphate, so that the positive electrode tab has good ionic conductivity and electronic conductivity, thereby improving the performance of the positive electrode tab. In an embodiment of the present application, the material of the positive electrode tab is lithium manganese iron phosphate. The conductivity of lithium manganese iron phosphate is lower than that of lithium iron phosphate, and the positive electrode tab designed by the present application can obviously avoid the influence of the low conductivity of lithium manganese iron phosphate, effectively exert the performance advantage of lithium manganese iron phosphate, and further improve the performance of the positive electrode tab. In an embodiment of the present application, the material of the positive electrode tab is lithium iron phosphate.

[0031] In an embodiment of the present application, the material of the first positive electrode active material includes at least one of lithium manganese iron phosphate and lithium iron phosphate, and the material of the second positive electrode active material includes at least one of lithium manganese iron phosphate and lithium iron phosphate. In an embodiment of the present application, the material of the first positive electrode active material is the same as the material of the second positive electrode active material. In an embodiment, the material of the first positive electrode active material and the material of the second positive electrode active material are both lithium manganese iron phosphate.

[0032] In an embodiment of the present application, the chemical formula of lithium manganese iron phosphate is LiMnxFe1-xPO4, wherein 0.55≤x≤0.85. The manganese element content in the lithium manganese iron phosphate is appropriate, the energy density thereof can be better than that of lithium iron phosphate, and the conductivity and capacity are better than those of lithium manganese phosphate, which better improves the use performance of the positive electrode tab. Specifically, x can be but is not limited to 0.55, 0.6, 0.62, 0.65, 0.7, 0.73, 0.75, 0.8 or 0.85, etc.

[0033] In the multi-layer positive electrode active material layer in the direction from the positive electrode current collector to the positive electrode active material layer, the mass content of the first positive electrode active material (D150 < 85 nm) in the positive electrode material gradually decreases, and the mass content of the second positive electrode active material (85 nm≤D250≤400 nm) in the positive electrode material gradually increases. For example, the surface of the positive electrode current collector is provided with a first layer of positive electrode active material, the surface of the first layer of positive electrode active material is provided with a second layer of positive electrode active material, the surface of the second layer of positive electrode active material is provided with a third layer of positive electrode active material, and so on. The mass content of the first positive electrode active material in the first layer of positive electrode active material is a1%, the mass content of the second positive electrode active material is b1%, the mass content of the first positive electrode active material in the second layer of positive electrode active material is a2%, the mass content of the second positive electrode active material is b2%, the mass content of the first positive electrode active material in the third layer of positive electrode active material is a3%, the mass content of the second positive electrode active material is b3%, and so on. Among them, a1, a2, a3, …, aN-1, aN gradually decrease, and b1, b2, b3, …, bN-1, bN gradually increase. Therefore, compared with the positive electrode active material layer far from the current collector, the positive electrode active material layer close to the current collector has more small-particle-size first positive electrode active material, which helps to improve the compaction density of the positive electrode active material layer close to the current collector, thereby improving its electronic conductivity; compared with the positive electrode active material layer close to the current collector, the positive electrode active material layer far from the current collector has more large-particle-size second positive electrode active material, which helps to improve the porosity of the positive electrode active material layer far from the current collector, which is conducive to the transmission of ions, thereby improving its ionic conductivity; such arrangement improves the ionic conductivity and electronic conductivity of the entire positive electrode sheet, which helps to improve the performance of the positive electrode sheet.

[0034] In an embodiment of the present application, in the multilayer positive active material layer, the mass content of the first positive active material in the positive material gradually decreases from 85-95% to 20-40% in the direction from the positive current collector to the positive active material layer. That is, compared with the positive active material layer far from the positive current collector, the mass content of the first positive active material in the positive active material layer close to the positive current collector is high, which can better fill the accumulation, further improve the compaction density and electronic conductivity, and help to improve the energy density of the positive electrode sheet and the battery; compared with the positive active material layer close to the positive current collector, the mass content of the first positive active material in the positive active material layer far from the positive current collector is low, and the porosity is high, which is beneficial to the transmission of active ions and improves the ionic conductivity, further improving the performance of the positive electrode sheet. It can be understood that the gradual decrease of the mass content of the first positive active material in the positive material of the multilayer positive active material layer in the direction from the positive current collector to the positive active material layer can be linear decrease, or non-linear decrease, such as gradient decrease, parabolic decrease, etc. Specifically, in the multilayer positive active material layer, the mass content of the first positive active material in the positive material can be but not limited to gradually decreasing from 85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%, 93%, 94% or 95% to 20%, 21%, 22%, 23%, 24%, 25%, 26%, 27%, 28%, 29%, 30%, 31%, 32%, 33%, 34%, 35%, 36%, 37%, 38%, 39% or 40% and the like in the direction from the positive current collector to the positive active material layer.

[0035] In an embodiment of the present application, in the multilayer positive active material layer, the mass content of the second positive active material in the positive material gradually increases from 5-15% to 60-80% in the direction from the positive current collector to the positive active material layer. That is, compared with the positive active material layer far from the positive current collector side, the mass content of the second positive active material in the positive active material layer close to the positive current collector side is low, which is beneficial to the filling and accumulation of the small particle size first positive active material, further improves the compaction density and electronic conductivity, and helps to improve the energy density of the positive electrode sheet and the battery; compared with the positive active material layer close to the positive current collector side, the mass content of the second positive active material in the positive active material layer far from the positive current collector side is high, and the porosity is high, which is beneficial to the transmission of active ions and improves the ionic conductivity, further improves the performance of the positive electrode sheet. It can be understood that the gradual increase of the mass content of the second positive active material in the positive material of the multilayer positive active material layer in the direction from the positive current collector to the positive active material layer can be linear increase or nonlinear increase, such as gradient increase, parabolic increase, etc. Specifically, in the multilayer positive active material layer, the mass content of the second positive active material in the positive material can gradually increase from 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14% or 15% to 60%, 61%, 62%, 63%, 64%, 65%, 66%, 67%, 68%, 69%, 70%, 71%, 72%, 73%, 74%, 75%, 76%, 77%, 78%, 79% or 80%, etc.

[0036] In an embodiment of the present application, when the positive electrode sheet includes two layers of positive active material layers, the two layers of positive active material layers include a first layer of positive active material layer arranged on the side of the positive current collector and a second layer of positive active material layer arranged on the surface of the first layer of positive active material layer away from the positive current collector; in the first layer of positive active material layer, the mass content of the first positive active material in the positive material is 85-95%, and the mass content of the second positive active material in the positive material is 5-15%; in the second layer of positive active material layer, the mass content of the first positive active material in the positive material is 20-40%, and the mass content of the second positive active material in the positive material is 60-80%, which is beneficial to obtain a positive electrode sheet with excellent compaction density, energy density and power performance.

[0037] In an embodiment of the present application, when the positive electrode plate comprises three layers of positive electrode active material layers, the three layers of positive electrode active material layers comprise a first layer of positive electrode active material layer arranged on one side of the positive electrode current collector, a second layer of positive electrode active material layer arranged on the surface of the first layer of positive electrode active material layer away from the positive electrode current collector, and a third layer of positive electrode active material layer arranged on the surface of the second layer of positive electrode active material layer away from the positive electrode current collector; in the first layer of positive electrode active material layer, the mass content of the first positive electrode active material in the positive electrode material is 85%-95%, and the mass content of the second positive electrode active material in the positive electrode material is 5%-15%; in the second layer of positive electrode active material layer, the mass content of the first positive electrode active material in the positive electrode material is 50%-80%, and the mass content of the second positive electrode active material in the positive electrode material is 20%-50%; in the third layer of positive electrode active material layer, the mass content of the first positive electrode active material in the positive electrode material is 20%-40%, and the mass content of the second positive electrode active material in the positive electrode material is 60%-80%. In this way, it is beneficial to obtain a positive electrode plate with excellent compaction density, energy density and power performance.

[0038] In an embodiment of the present application, along the direction from the positive electrode current collector to the positive electrode active material layer, the mass ratio of the first positive electrode active material to the second positive electrode active material in the positive electrode material of the multilayer positive electrode active material layer gradually decreases from 5.7-18 to 0.25-0.67. In this way, the compaction density and energy density of the positive electrode plate are ensured, and at the same time, the power performance of the positive electrode plate is improved. It can be understood that along the direction from the positive electrode current collector to the positive electrode active material layer, the gradual decrease of the mass ratio of the first positive electrode active material to the second positive electrode active material in the positive electrode material of the multilayer positive electrode active material layer can be linear decrease, or non-linear decrease, such as gradient decrease, parabolic decrease, etc. Specifically, along the direction from the positive electrode current collector to the positive electrode active material layer, the mass ratio of the first positive electrode active material to the second positive electrode active material in the positive electrode material of the multilayer positive electrode active material layer can be but not limited to gradually decreasing from 5.7, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17 or 18 to 0.25, 0.3, 0.33, 0.35, 0.37, 0.4, 0.41, 0.45, 0.48, 0.5, 0.52, 0.55, 0.57, 0.6, 0.62, 0.63, 0.65 or 0.67, etc.

[0039] The particle size D150 of the first positive electrode active material in the present application is less than 85 nm, and the particle size D150 of the second positive electrode active material is 85 nm-400 nm, so that the first positive electrode active material plays a role of stacking and filling to improve the compaction density, and the second positive electrode active material plays a role of improving the porosity, and the two synergistically improve the compaction density, energy density and power performance of the positive electrode sheet. The particle size of the first positive electrode active material and the second positive electrode active material in the present application refers to the primary particle size. In an embodiment of the present application, 10 nm≤D150<85 nm. That is, the particle size D50 of the positive electrode material is 10 nm-400 nm, which is beneficial to the molding of the positive electrode active material layer and the improvement of the performance of the positive electrode sheet. In an embodiment of the present application, 10 nm≤D150<85 nm, 85 nm≤D250≤300 nm. That is, the particle size D50 of the positive electrode material is 10 nm-300 nm, which is beneficial to the improvement of the performance of the positive electrode sheet. In an embodiment of the present application, 20 nm≤D150≤80 nm, 85 nm≤D250≤200 nm. That is, the particle size D50 of the positive electrode material is 20 nm-200 nm, which is beneficial to the molding of the positive electrode active material layer and the further improvement of the compaction density, energy density and power performance of the positive electrode sheet.

[0040] In an embodiment of the present application, the ratio of the particle size D250 of the second positive electrode active material to the particle size D150 of the first positive electrode active material is greater than or equal to 4, which is beneficial to the matching of the first positive electrode active material and the second positive electrode active material in the positive electrode active material layer, the molding of the positive electrode active material layer and the further improvement of the performance of the positive electrode sheet.

[0041] In an embodiment of the present application, along the direction from the positive electrode current collector to the positive electrode active material layer, the compaction density of the multilayer positive electrode active material layer gradually decreases from 2.5 g / cm3-2.53 g / cm3 to 2.47 g / cm3-2.49 g / cm3. In this way, the positive electrode active material layer close to the current collector side has a higher compaction density, which is beneficial to the improvement of the electronic conductivity of the positive electrode sheet.

[0042] In an embodiment of the present application, the thickness of the positive electrode active material layer is 80 μm-280 μm. Specifically, the thickness of the positive electrode active material layer can be, but is not limited to, 80 μm, 100 μm, 110 μm, 120 μm, 150 μm, 160 μm, 175 μm, 180 μm, 200 μm, 210 μm, 225 μm, 230 μm, 250 μm or 270 μm, etc.

[0043] In an embodiment of the present application, the absolute value of the thickness difference of the multi-layer positive electrode active material layer is 0 μm-10 μm. Specifically, the absolute value of the thickness difference of the multi-layer positive electrode active material layer can be, but is not limited to, 0 μm, 1 μm, 2 μm, 3 μm, 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm or 10 μm, etc.

[0044] In an embodiment of the present application, the area density of the positive electrode tab is 200 g / m2-700 g / m2, so that the energy density and kinetic performance of the positive electrode tab are appropriate, which can improve the capacity of the positive electrode tab and the battery, and is beneficial to the use of the battery in the electrical equipment.

[0045] In an embodiment of the present application, the absolute value of the area density difference of the multi-layer positive electrode active material layer is 0 g / m2-10 g / m2, which further improves the energy density and kinetic performance of the positive electrode tab. In the present application, the number of layers and the thickness of the positive electrode active material layer can be designed according to the area density of the positive electrode tab.

[0046] In an embodiment of the present application, the mass content of the positive electrode active material in the positive electrode active material layer is greater than or equal to 80%, which is beneficial to improving the electrochemical performance of the positive electrode. Specifically, the mass content of the positive electrode active material in the positive electrode active material layer can be greater than or equal to 82%, 85%, 88%, 90%, 93%, 95%, 97% or 98%, etc.

[0047] In an embodiment of the present application, the positive electrode active material layer further comprises at least one of a positive electrode binder and a positive electrode conductive agent. Specifically, the positive electrode binder can include, but is not limited to, at least one of polyvinylidene fluoride, polytetrafluoroethylene, sodium carboxymethyl cellulose, butyl latex and nitrile rubber; the positive electrode conductive agent can include, but is not limited to, at least one of conductive carbon black, carbon nanotube, graphene, carbon fiber, carbon black and graphite. In an embodiment of the present application, the mass content of the positive electrode conductive agent in the positive electrode active material layer is less than or equal to 5%. Specifically, the mass content of the positive electrode conductive agent in the positive electrode active material layer can be, but is not limited to, 0.1%, 0.5%, 1%, 2%, 3%, 4% or 5%, etc. In an embodiment, the mass content of the positive electrode conductive agent in the positive electrode active material layer can be 0.1%-5%. In an embodiment of the present application, the mass content of the positive electrode binder in the positive electrode active material layer is less than or equal to 10%. Specifically, the mass content of the positive electrode binder in the positive electrode active material layer can be, but is not limited to, 0.1%, 0.5%, 2%, 4%, 5%, 7%, 8% or 9%, etc. In an embodiment, the mass content of the positive electrode binder in the positive electrode active material layer is 0.1%-10%.

[0048] In an embodiment of the present application, the positive current collector is selected from a metal foil or an alloy foil. The metal foil includes copper, titanium, aluminum, platinum, iridium, ruthenium, nickel, tungsten, tantalum, gold or silver foil, and the alloy foil includes stainless steel or an alloy containing at least one of copper, titanium, aluminum, platinum, iridium, ruthenium, nickel, tungsten, tantalum, gold and silver. Specifically, the positive current collector can be an aluminum foil.

[0049] The present application provides a method for preparing a positive electrode tab, including: forming a multi-layer positive active material layer on the surface of the positive current collector to obtain the positive electrode tab. The preparation method is simple and convenient to operate, and can prepare the positive electrode tab in any of the embodiments.

[0050] In an embodiment of the present application, the positive electrode slurry can be coated on the surface of the positive current collector, and the positive active material layer is formed after drying. In an embodiment of the present application, the positive electrode slurry can be coated on the surface of the positive current collector, and the positive active material layer is formed after drying. Then, the positive electrode slurry containing different mass contents of the first positive active material and the second positive active material is coated again and dried again. The above operation is repeated to prepare a multi-layer positive active material layer, and the positive electrode tab is formed after rolling and cutting. In an embodiment, the positive electrode slurry includes a solvent and a positive material. Further, the positive electrode slurry further includes a positive binder and a positive conductive agent. Still further, the positive electrode slurry further includes a dispersing agent. Specifically, the positive material is uniformly mixed with the binder, the conductive agent, the dispersing agent and the like to form the positive electrode slurry. The solvent can be but is not limited to N-methyl pyrrolidone, and the preparation of the positive electrode slurry can adopt a wet method or a semi-dry method.

[0051] The present application provides a battery including a negative electrode tab and the positive electrode tab in any of the embodiments. The battery has excellent energy density and power performance, which is beneficial to the use of the battery. Specifically, the battery can be but is not limited to a lithium ion battery and the like.

[0052] In an embodiment of the present application, the negative electrode tab includes a negative current collector and a negative active material layer disposed on the surface of the negative current collector. In an embodiment of the present application, the negative current collector is selected from a metal foil or an alloy foil. The metal foil includes copper, aluminum, nickel, iron or cobalt foil, and the alloy foil includes an alloy of at least one of copper, aluminum, nickel, iron and cobalt or stainless steel. In an embodiment, the material of the negative current collector includes at least one of copper, aluminum, nickel, iron and cobalt or stainless steel. Specifically, the negative current collector can be a copper foil. In an embodiment of the present application, the negative active material layer includes a negative active material. The negative active material can include carbon material, silicon material, etc. In an embodiment of the present application, the negative active material layer can further include at least one of a negative conductive agent and a negative binder. Specifically, the negative conductive agent can include, but is not limited to, at least one of conductive carbon black, carbon nanotube, carbon fiber, carbon black and graphite; and the negative binder can include, but is not limited to, at least one of polytetrafluoroethylene, polyvinylidene fluoride, sodium carboxymethyl cellulose, butyl rubber latex, nitrile rubber. In an embodiment, the mass content of the negative conductive agent in the negative active material layer is less than or equal to 5%. Specifically, the mass content of the negative conductive agent in the negative active material layer can be, but is not limited to, 0.1%, 0.5%, 1%, 2%, 3%, 4% or 5%, etc. In a specific embodiment, the mass content of the negative conductive agent in the negative active material layer can be 0.1%-5%. In an embodiment, the mass content of the negative binder in the negative active material layer is less than or equal to 10%. Specifically, the mass content of the negative binder in the negative active material layer can be, but is not limited to, 0.1%, 0.5%, 2%, 4%, 5%, 7%, 8% or 9%, etc. In a specific embodiment, the mass content of the negative binder in the negative active material layer is 0.1%-10%. In an embodiment of the present application, at least one of the negative binder and the negative conductive agent can be mixed with the negative active material in a solvent to form a negative slurry, the negative slurry is coated on the surface of the negative current collector, and the negative electrode tab is obtained after drying.

[0053] In an embodiment of the present application, the battery further comprises an electrolyte and a separator. In an embodiment of the present application, at least part of the positive electrode plate is immersed in the electrolyte, and at least part of the negative electrode plate is immersed in the electrolyte, so as to ensure normal operation of the battery. The materials of the electrolyte and the separator in the present application can be selected as needed. In an embodiment of the present application, the electrolyte comprises a solute and an organic solvent. The solute can be selected according to the type of the battery, for example, the solute of the electrolyte in a lithium ion battery can be lithium salt. Specifically, the lithium salt can include, but is not limited to, at least one of lithium hexafluorophosphate, lithium hexafluoroarsenate, lithium perchlorate, lithium hexafluoroborate and lithium bis-trifluoromethanesulfonimide; the organic solvent can include, but is not limited to, at least one of ethylene carbonate (EC), methyl ethyl carbonate (EMC), dimethyl carbonate (DMC), diethyl carbonate (DEC), vinylene carbonate (VC) and fluoroethylene carbonate (FEC). In an embodiment, the positive electrode plate, the negative electrode plate and the separator can be assembled and placed in the shell, and after the electrolyte is filled, the battery is packaged. In another embodiment of the present application, the battery can be a solid-state battery.

[0054] The present application provides a power consuming device comprising the battery of any of the above embodiments. The battery in the power consuming device provided by the present application has excellent electrochemical performance, thereby improving the use performance and service life of the power consuming device. Specifically, the power consuming device can refer to a vehicle, an electronic device, an energy storage system, etc., and the above-mentioned battery can be arranged in the power consuming device in the form of a single battery, a battery module, a battery pack, etc.

[0055] The effects of the technical solutions of the present application are further described below through specific examples.

[0056] Embodiment 1

[0057] A positive electrode plate comprises a positive electrode current collector, a first layer of positive electrode active material layer stacked on the surface of the positive electrode current collector, and a second layer of positive electrode active material layer stacked on the surface of the first layer of positive electrode active material layer, wherein the positive electrode active material layer comprises a positive electrode material (lithium manganese iron phosphate), a binder (polyvinylidene fluoride, PVDF) and a conductive agent (carbon nanotube, CNT), and the mass ratio of the positive electrode material (lithium manganese iron phosphate) : the binder (PVDF) : the conductive agent (CNT) is 96:2.5:1.5.

[0058] The particle size distribution curve of the positive electrode material of each layer of positive electrode active material layer has a first peak and a second peak, and the peak value corresponding to the particle size D1 of the first peak is 40 nm, and the peak value corresponding to the particle size D2 of the second peak is 160 nm; taking the sum of the peak area ratio of the first peak and the peak area ratio of the second peak as 100%, the peak area ratio S1% of the first peak is 90%, and the peak area ratio S2% of the second peak is 10%, the ratio of S1 / S2 in the first layer of positive electrode active material layer is 9 (the mass content of the first positive electrode active material in the positive electrode material is 90%, and the D150 of the first positive electrode active material is 44 nm; the mass content of the second positive electrode active material in the positive electrode material is 10%, and the D250 of the second positive electrode active material is 190 nm); the ratio of S1 / S2 in the second layer of positive electrode active material layer is 4:6 (the mass content of the first positive electrode active material in the positive electrode material is 40%, and the D150 of the first positive electrode active material is 44 nm; the mass content of the second positive electrode active material in the positive electrode material is 60%, and the D250 of the second positive electrode active material is 190 nm).

[0059] The surface density of the first layer of positive electrode active material layer and the second layer of positive electrode active material layer is equal, and the single surface density of the positive electrode sheet is 200 g / m2.

[0060] Example 2

[0061] The same as example 1, except that the positive electrode sheet further comprises a third layer of positive electrode active material layer, the third layer of positive electrode active material layer is arranged on the side surface of the second layer of positive electrode active material layer away from the positive electrode current collector, the ratio of S1 / S2 in the particle size distribution curve of the positive electrode material of the first layer of positive electrode active material layer is 9, the ratio of S1 / S2 in the particle size distribution curve of the positive electrode material of the second layer of positive electrode active material layer is 7:3 (the mass content of the first positive electrode active material in the positive electrode material is 70%, and the D150 of the first positive electrode active material is 44 nm; the mass content of the second positive electrode active material in the positive electrode material is 30%, and the D250 of the second positive electrode active material is 190 nm), and the ratio of S1 / S2 in the particle size distribution curve of the positive electrode material of the third layer of positive electrode active material layer is 4:6.

[0062] Example 3

[0063] The positive electrode sheet is substantially the same as that of Example 2, except that the positive electrode sheet further includes a fourth positive electrode active material layer, the fourth positive electrode active material layer is disposed on the side surface of the third positive electrode active material layer facing away from the positive electrode current collector, the ratio of S1 / S2 in the particle size distribution curve of the positive electrode material of the first positive electrode active material layer is 9, the ratio of S1 / S2 in the particle size distribution curve of the positive electrode material of the second positive electrode active material layer is 4 (the mass content of the first positive electrode active material in the positive electrode material is 80%, and the D150 of the first positive electrode active material is 44 nm; the mass content of the second positive electrode active material in the positive electrode material is 20%, and the D250 of the second positive electrode active material is 190 nm), the particle size distribution curve of the positive electrode material of the third positive electrode active material layer is as shown in FIG. 2, the ratio of S1 / S2 in the particle size distribution curve of the positive electrode material of the third positive electrode active material layer is 1.5 (the mass content of the first positive electrode active material in the positive electrode material is 60%, and the D150 of the first positive electrode active material is 44 nm; the mass content of the second positive electrode active material in the positive electrode material is 40%, and the D250 of the second positive electrode active material is 190 nm), and the ratio of S1 / S2 in the particle size distribution curve of the positive electrode material of the fourth positive electrode active material layer is 4:6.

[0064] Example 4

[0065] The positive electrode sheet is substantially the same as that of Example 3, except that the positive electrode sheet further includes a fifth positive electrode active material layer, the fifth positive electrode active material layer is disposed on the side surface of the fourth positive electrode active material layer facing away from the positive electrode current collector, the ratio of S1 / S2 in the particle size distribution curve of the positive electrode material of the first positive electrode active material layer is 9, the ratio of S1 / S2 in the particle size distribution curve of the positive electrode material of the second positive electrode active material layer is 4, the ratio of S1 / S2 in the particle size distribution curve of the positive electrode material of the third positive electrode active material layer is 1.5, the ratio of S1 / S2 in the particle size distribution curve of the positive electrode material of the fourth positive electrode active material layer is 5:5 (the mass content of the first positive electrode active material in the positive electrode material is 50%, and the D150 of the first positive electrode active material is 44 nm; the mass content of the second positive electrode active material in the positive electrode material is 50%, and the D250 of the second positive electrode active material is 190 nm), and the ratio of S1 / S2 in the particle size distribution curve of the positive electrode material of the fifth positive electrode active material layer is 4:6.

[0066] Example 5

[0067] The positive electrode sheet is substantially the same as that of Example 1, except that the peak particle sizes corresponding to the first peak and the second peak in the positive electrode sheet are different, the peak particle size D1 corresponding to the first peak is 30 nm, and the peak particle size D2 corresponding to the second peak is 110 nm.

[0068] Comparative Example 1

[0069] A positive electrode sheet, comprising a positive electrode current collector and a positive electrode active material layer arranged in layers on the surface of the positive electrode current collector, the positive electrode active material layer comprising a positive electrode material (lithium manganese iron phosphate), a binder (PVDF) and a conductive agent (CNT), wherein the mass ratio of the positive electrode material (lithium manganese iron phosphate) : binder (PVDF) : conductive agent (CNT) is 95 : 2.5 : 1.5, the positive electrode material comprising 85% by mass of lithium manganese iron phosphate having a peak particle size D1 of 40 nm in a first peak and 15% by mass of lithium manganese iron phosphate having a peak particle size D2 of 160 nm in a second peak, and the single-sided density of the positive electrode sheet is 200 g / m2.

[0070] Comparative Example 2

[0071] The same as Example 1, except that the ratio of the two layers of active material in the positive electrode sheet is exchanged, i.e. the ratio of S1 / S2 in the first layer of positive electrode active material layer is 4:6; the ratio of S1 / S2 in the second layer of positive electrode active material layer is 9.

[0072] Performance detection

[0073] The limit compaction density of the positive electrode sheet provided in the above examples and comparative examples is detected, and the specific method is as follows: the electrode sheet is rolled using a rolling machine, and the rolling pressure is gradually increased until the active material peels off or cracks, the electrode sheet cracks or the belt breaks, the maximum pressure condition under which a complete electrode sheet can be obtained is taken, and the thickness and area density of the obtained electrode sheet are tested to calculate the compaction density of the electrode sheet. The results are shown in Table 1.

[0074] The positive electrode sheet provided in the above examples and comparative examples is assembled with a negative electrode sheet (specifically obtained by coating a negative electrode slurry on a copper foil current collector and drying, the mass ratio of graphite, carbon black conductive agent and binder carboxymethyl cellulose in the negative electrode is 97:1:2), a separator (polypropylene separator) and an electrolyte (specifically a mixture of lithium hexafluorophosphate: ethylene carbonate: diethyl carbonate: vinylene carbonate in a mass ratio of 12.93:43.54:43.54:4) in the same way to form a full cell, and the discharge specific capacity, room temperature charge peak power, room temperature discharge peak power and room temperature discharge direct current internal resistance (DCIR) of the formed full cell are tested.

[0075] Among them, the discharge specific capacity test conditions are: constant current and constant voltage charging at room temperature 1 / 3C to 4.3V, cutoff current 0.02C, discharging at room temperature to 2.0V, three times of cycle, taking the last discharge specific capacity;

[0076] The normal-temperature charge peak power test method is as follows: the battery is adjusted to 80%, and after 1C charging for 30 s, the SOC is adjusted back to 80%, and after the open circuit voltage is stable, the current is increased to 2C for continuous testing, and then the current is gradually increased until the charging time is less than 30 s when the upper limit voltage (4.3 V) is charged, the maximum current when the charging time reaches 30 s is taken, and the charge peak power is calculated;

[0077] The normal-temperature discharge peak power test method is as follows: the battery is adjusted to 80%, and after 1C discharging for 30 s, the SOC is adjusted back to 80%, and after the open circuit voltage is stable, the current is increased to 2C for continuous testing, and then the current is gradually increased until the discharge time is less than 30 s when the lower limit voltage (2.0 V) is discharged, the maximum current when the discharge time reaches 30 s is taken, and the discharge peak power is calculated;

[0078] The normal-temperature discharge DCIR test method is as follows: the battery is adjusted to 80%, and after 1 h of standing, the voltage is V0; after 1.5C discharging for 30 s, the voltage is recorded as V1; the discharge DCIR is the absolute value of (V1-V0) / 1.5, and the unit is mΩ·Ah; the results are shown in Table 1.

[0079] Table 1 Performance test results

[0080] Compared with the comparative examples, the discharge specific capacity, charge and discharge peak power of the positive electrode plate prepared in examples 1-5 are obviously improved, and the discharge DCIR is reduced, and the more intensive the gradient of the particle arrangement is, the more obvious the improvement effect is. As can be seen from example 4, when the number of layers of the positive electrode active material layer is more, the limit compaction density of the positive electrode plate slightly decreases, but the reduction ratio is less than 1%, which has little effect on the energy density, and the compaction density in actual application will not reach the limit compaction density, so the slight reduction of the limit compaction density in example 4 will not cause obvious loss of energy density, and the high energy density can still be maintained, the battery internal resistance is reduced, and the battery power performance is improved. In summary, the compaction density, energy density and power performance of the positive electrode plate provided in the application are excellent, which helps to reduce the internal resistance of the battery, improve the energy density and power performance of the battery, so that the battery has excellent electrochemical performance, and is beneficial to the use of the battery.

[0081] The above describes the preferred embodiments of the application, but cannot be construed as limiting the scope of the application. It should be noted that for ordinary skilled persons in the art, without departing from the principles of the application, a number of improvements and refinements can be made, which are also considered within the protection scope of the application.

Claims

1. A positive electrode sheet, characterized by, The positive electrode active material layer includes a positive electrode material, and the positive electrode material includes a first positive electrode active material and a second positive electrode active material, wherein the particle size D150 of the first positive electrode active material and the particle size D250 of the second positive electrode active material satisfy D150 < 85 nm and 85 nm ≤ D250 ≤ 400 nm. In the direction from the positive electrode current collector to the positive electrode active material layer, in the multilayer positive electrode active material layer, the mass content of the first positive electrode active material in the positive electrode material gradually decreases, and the mass content of the second positive electrode active material in the positive electrode material gradually increases. The particle size distribution curve of the positive electrode material in each layer of the positive electrode active material layer has a first peak and a second peak.

2. The cathode sheet of claim 1, wherein, The peak value of the first peak corresponds to a particle size D1, and the peak value of the second peak corresponds to a particle size D2, wherein 0.1 < D1 / D2 < 0.

4. The peak area ratio of the first peak to the sum of the peak area ratios of the first peak and the second peak is S1%, and the peak area ratio of the second peak to the sum of the peak area ratios of the first peak and the second peak is S2%, wherein 0.25 < S1 / S2 < 10. In the direction from the positive electrode current collector to the positive electrode active material layer, in the multilayer positive electrode active material layer, the mass content of the first positive electrode active material in the positive electrode material gradually decreases from 85%-95% to 20%-40%, and the mass content of the second positive electrode active material in the positive electrode material gradually increases from 5%-15% to 60%-80%.

3. The cathode sheet of claim 1, wherein The particle size D150 of the first positive electrode active material and the particle size D250 of the second positive electrode active material satisfy 10 nm ≤ D150 < 85 nm and 85 nm ≤ D250 ≤ 300 nm.

4. The cathode sheet of claim 1, wherein The particle size D150 of the first positive electrode active material and the particle size D250 of the second positive electrode active material satisfy 20 nm ≤ D150 ≤ 80 nm and 85 nm ≤ D250 ≤ 200 nm.

5. The positive electrode sheet according to claim 1 or 4, wherein The areal density of the positive electrode sheet is 200 g / m2-700 g / m2.

6. The cathode sheet of claim 1, wherein The absolute value of the difference in areal density of the multilayer positive electrode active material layer is 0 g / m2-10 g / m2. The thickness of the positive electrode active material layer is 80 μm-280 μm.

7. The cathode sheet of claim 1, wherein The absolute value of the difference in thickness of the multilayer positive electrode active material layer is 0 μm-10 μm. The material of the positive electrode material includes at least one of manganese iron lithium phosphate and lithium iron phosphate.

8. The cathode sheet of claim 1, wherein, The number of layers of the positive electrode active material layer in the positive electrode sheet is 2-5.

9. The cathode sheet of claim 1, wherein, ​ 10. The cathode electrode of claim 9, wherein the cathode electrode is characterized by, When the positive electrode sheet comprises two layers of the positive electrode active material layer, the two layers of the positive electrode active material layer comprise a first layer of the positive electrode active material layer disposed on one side of the positive electrode current collector and a second layer of the positive electrode active material layer disposed on the surface of the first layer of the positive electrode active material layer away from the positive electrode current collector; in the first layer of the positive electrode active material layer, the mass content of the first positive electrode active material in the positive electrode material is 85%-95%, and the mass content of the second positive electrode active material in the positive electrode material is 5%-15%; in the second layer of the positive electrode active material layer, the mass content of the first positive electrode active material in the positive electrode material is 20%-40%, and the mass content of the second positive electrode active material in the positive electrode material is 60%-80%.

11. The cathode sheet of claim 9, wherein, When the positive electrode sheet comprises three layers of the positive electrode active material layer, the three layers of the positive electrode active material layer comprise a first layer of the positive electrode active material layer disposed on one side of the positive electrode current collector, a second layer of the positive electrode active material layer disposed on the surface of the first layer of the positive electrode active material layer away from the positive electrode current collector, and a third layer of the positive electrode active material layer disposed on the surface of the second layer of the positive electrode active material layer away from the positive electrode current collector; in the first layer of the positive electrode active material layer, the mass content of the first positive electrode active material in the positive electrode material is 85%-95%, and the mass content of the second positive electrode active material in the positive electrode material is 5%-15%; in the second layer of the positive electrode active material layer, the mass content of the first positive electrode active material in the positive electrode material is 50%-80%, and the mass content of the second positive electrode active material in the positive electrode material is 20%-50%; in the third layer of the positive electrode active material layer, the mass content of the first positive electrode active material in the positive electrode material is 20%-40%, and the mass content of the second positive electrode active material in the positive electrode material is 60%-80%.

12. A battery, characterized by The battery comprises a negative electrode sheet and the positive electrode sheet according to any one of claims 1-11.

13. An electrical device, characterized by The battery according to claim 12.

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