Positive electrode, battery and electrical equipment

Abstract

The present application provides a positive electrode sheet, a battery, and an electric device. The positive electrode sheet includes a positive electrode current collector and a multilayer positive electrode active material layer stacked on at least one side of the positive electrode current collector. The positive electrode active material layer includes a positive electrode material. The positive electrode material includes a first positive electrode active material and a second positive electrode active material. The particle size D of the first positive electrode active material is 1 50. Particle size D of the second positive electrode active material 2 50 Satisfaction D 1 50<85nm,85nm≤D 2 50≤400nm. In the direction from the positive current collector to the positive active material layer, the mass content of the first positive active material gradually decreases, while the mass content of the second positive active material gradually increases. The positive electrode sheet has excellent compaction density and energy density, which helps reduce the battery's internal resistance and improve battery power performance.

Description

Technical Field

[0001] This application relates to the technical field of batteries, specifically to a positive electrode sheet, a battery, and an electrical device. Background Art

[0002] Compared with traditional batteries, lithium-ion batteries have the advantages of high voltage, long life, environmental friendliness, etc., and are widely used in fields such as electronic devices, automobiles, aerospace, etc. Among them, the positive electrode directly affects the performance of lithium-ion batteries. At present, the active materials used in the positive electrode all have the advantages of high capacity, high safety, good cycle performance, etc. However, the ionic 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, affect the power performance of the battery, and is not conducive to the use of lithium-ion batteries. Summary of the Invention

[0003] In view of this, this application provides a positive electrode sheet, a battery, and an electrical device.

[0004] In a first aspect, this application provides a positive electrode sheet, including a positive electrode current collector and a plurality of positive electrode active material layers stacked on at least one surface of the positive electrode current collector. 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. The particle size D 1 , 2 , , 2 ,

[0006] , ,

[0005] 50 of the second positive electrode active material satisfies: D 2 50 satisfies: D 1 50 < 85 nm, 85 nm ≤ D 2 50 ≤ 400 nm. Along the direction from the positive electrode current collector to the positive electrode active material layer, in 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. [[ID=​​​​

[0007] Optionally, along the direction from the positive electrode current collector to the positive electrode active material layer, in the multiple layers of the positive electrode active material layer, the mass content of the second positive electrode active material in the positive electrode material gradually increases from 5%-15% to 60%-80%.

[0008] Optionally, the particle size D of the first positive electrode active material 1 50. Particle size D of the second positive electrode active material 2 50 satisfies: 10nm≤D 1 50<85nm,85nm≤D 2 50≤300nm.

[0009] Optionally, the particle size D of the first positive electrode active material 1 50. Particle size D of the second positive electrode active material 2 50 satisfies: 20nm≤D 1 50≤80nm, 85nm≤D 2 50≤200nm.

[0010] Optionally, the surface density of the positive electrode sheet is 200g / m 2 -700g / m 2 .

[0011] Optionally, the absolute value of the difference in surface density of the multiple layers of the positive electrode active material is 0 g / m 2 -10g / m 2 .

[0012] Optionally, the thickness of the positive electrode active material layer is 80 μm-280 μm.

[0013] Optionally, the absolute value of the thickness difference between the multiple layers of the positive electrode active material layer is 0 μm-10 μm.

[0014] Optionally, the material of the positive electrode material includes at least one of lithium manganese iron phosphate and lithium iron phosphate.

[0015] Optionally, the number of positive electrode active material layers in the positive electrode plate is 2-5.

[0016] Optionally, when the positive electrode plate includes two layers of positive electrode active material layers, the two layers of positive electrode active material layers include a first layer of positive electrode active material layer arranged on one side of the positive electrode current collector and 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; 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 20%-40%, and the mass content of the second positive electrode active material in the positive electrode material is 60%-80%.

[0017] Optionally, when the positive electrode sheet includes three layers of positive electrode active material layers, the three layers of positive electrode active material layers include 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 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 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%.

[0018] In a second aspect, the present application provides a battery comprising a negative electrode plate and the positive electrode plate described in the first aspect.

[0019] In a third aspect, the present application provides an electrical device comprising the battery described in the second aspect.

[0020] In the positive electrode plate provided by the present application, the small-particle first positive electrode active material on the side close to the current collector accounts for a large proportion, the positive electrode active material layer has a high compaction density and good electronic conductivity, and the large-particle second positive electrode active material on the side away from the current collector accounts for a large proportion, the positive electrode active material layer has a high porosity and good ion conductivity, so that the overall compaction density, energy density and power performance of the positive electrode plate are excellent, which helps to reduce the internal resistance of the battery, improve the energy density and power performance of the battery, and make the battery have excellent electrochemical properties, which is conducive to its use in electrical equipment. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for the embodiments or the description of the prior art. The specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0022] Figure 1 A schematic cross-sectional view of a positive electrode sheet provided in one embodiment of the present application.

[0023] Figure 2 This is the particle size distribution curve of the positive electrode material of the third positive electrode active material layer in the positive electrode sheet prepared in Example 3. DETAILED DESCRIPTION

[0024] The following will be combined with the drawings in the embodiments of this application to clearly and completely describe the technical solutions in the embodiments of this application. Obviously, the embodiments described are only part of the embodiments of this application, not all of the embodiments. Based on the embodiments in this application, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of this application.

[0025] See also Figure 1 , is a cross-sectional schematic diagram of a positive electrode sheet provided in one embodiment of the present application, wherein the positive electrode sheet 100 includes a positive electrode current collector 10 and a multi-layer positive electrode active material layer 20 stacked on at least one side of the positive electrode current collector 10, the positive electrode active material layer 20 includes a positive electrode material, the positive electrode material includes a first positive electrode active material and a second positive electrode active material, and the particle size D of the first positive active material 1 50. Particle size D of the second positive electrode active material 2 50 satisfied: D 1 50<85nm,85nm≤D 2 50≤400nm, along the direction from the positive electrode current collector 10 to the positive electrode active material layer 20 (such as Figure 1 In the multi-layer positive electrode active material layer 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.

[0026] The particle size D of the first positive electrode active material in this application 1 50 refers to the particle size corresponding to when the volume distribution percentage of the first positive electrode active material reaches 50%; the particle size D of the second positive electrode active material 250 refers to the particle size corresponding to when the volume distribution percentage of the second positive electrode active material reaches 50%. In the positive electrode sheet provided in the present application, each positive electrode active material layer contains a first positive electrode active material and a 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 the role of stacking filling and improving the compaction density, and the second positive electrode active material mainly plays the role of improving the porosity. The first positive electrode active material and the second positive electrode active material work synergistically to improve the performance of each positive electrode active material layer; at the same time, the small-particle size first positive electrode active material on the side close to the current collector in the positive electrode sheet accounts for a larger proportion, so that the compaction density of the positive electrode active material layer is high, and its electronic conductivity is improved. The large-particle size second positive electrode active material on the side away from the current collector accounts for a larger proportion, so that the porosity of the positive electrode active material layer is high, and its ionic conductivity is improved. In addition, the setting of changing the mass content of the first positive electrode active material and the second positive electrode active material in the multi-layer positive electrode active material makes the positive electrode sheet have excellent compaction density, energy density and power performance, which is beneficial to its use in the battery, reduces the internal resistance of the battery, and improves the power performance of the battery.

[0027] In an embodiment of the present application, the particle size distribution curve of the cathode material in each layer of the cathode 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 the unit of nm, and the particle size corresponding to the peak value of the second peak is D2, with the unit of nm, where 0.1 < D1 / D2 < 0.4; and / or, taking the sum of the peak area ratios of the first peak and 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%, where 0.25 < S1 / S2 < 10. In the present application, the peak area ratios of the first peak and the second peak represent the mass ratios of the first cathode active material and the second cathode active material. Thus, the combination of the first cathode active material with a small particle size and the second cathode active material with a large particle size can achieve better filling and packing, which is beneficial to improving the compaction density of the cathode electrode sheet, and further contributes to the energy density of the battery. At the same time, the first cathode active material with a small particle size can play the role of a ball bearing to improve the fluidity and stability of the cathode slurry. In the particle size distribution curve of the cathode material, the abscissa is the particle size with the unit of nm, and the ordinate is the volume ratio with the unit of %. It can be understood that since the ratio of D1 / D2 is less than 1, that is, the particle size corresponding to the first peak is small and the particle size corresponding to the second peak is large, the first peak is closer to the ordinate in the particle size distribution curve compared to the second peak; since along the direction from the cathode current collector to the cathode active material layer, in the cathode material of the multi-layer cathode active material layer, the mass content of the first cathode active material gradually decreases and the mass content of the second cathode active material gradually increases, therefore, along the direction from the cathode current collector to the cathode active material layer, in the particle size distribution curve of the cathode material of the multi-layer cathode active material layer, the ratio of S1 / S2 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 improving the performance of the cathode electrode sheet.

[0028] The number of layers of the positive electrode active material layer in the positive electrode sheet 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 sheet 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 positive electrode active materials are arranged on both sides of the positive electrode current collector, the number of layers of the positive electrode active material layers 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 one embodiment of the present application, the number of layers of the positive electrode active material layer in the positive electrode sheet is 2-5. That is to say, the positive electrode sheet can have two to five layers of positive electrode active material layers, which can further improve the ionic conductivity and liquid retention level of the positive electrode active material layer away from the current collector side, and help to further improve the performance of the positive electrode sheet.

[0029] In one embodiment of the present application, the material of the positive electrode material includes at least one of lithium iron manganese phosphate and lithium iron phosphate. The ionic conductivity and electronic conductivity of lithium iron manganese phosphate and lithium iron phosphate are low. The positive electrode plate designed by the present application can effectively avoid the excessive influence of the low ionic conductivity and electronic conductivity of lithium iron manganese phosphate and lithium iron phosphate, so that the positive electrode plate has good ionic conductivity and electronic conductivity, thereby improving the performance of the positive electrode plate. In one embodiment of the present application, the material of the positive electrode plate is lithium iron manganese phosphate. The conductivity of lithium iron manganese phosphate is lower than that of lithium iron phosphate. The positive electrode plate designed by the present application can significantly avoid the influence of the low conductivity of lithium iron manganese phosphate, effectively exert the performance advantages of lithium iron manganese phosphate, and further improve the performance of the positive electrode plate. In one embodiment of the present application, the material of the positive electrode plate is lithium iron phosphate.

[0030] In one embodiment of the present application, the material of the first positive electrode active material includes at least one of lithium iron manganese phosphate and lithium iron phosphate, and the material of the second positive electrode active material includes at least one of lithium iron manganese phosphate and lithium iron phosphate. In one embodiment of the present application, the material of the first positive electrode active material and the material of the second positive electrode active material are the same. In one embodiment, the material of the first positive electrode active material and the material of the second positive electrode active material are both lithium iron manganese phosphate.

[0031] In one embodiment of the present application, the chemical formula of lithium manganese iron phosphate is LiMn x Fe 1-x PO4, where 0.55≤x≤0.85. This lithium manganese iron phosphate has an appropriate manganese content, and its energy density can be superior to lithium iron phosphate, as well as its conductivity and capacity, thereby further improving the performance of the positive electrode. 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.

[0032] In the present application, in the direction from the positive electrode current collector to the positive electrode active material layer, the first positive electrode active material (D 1 50<85nm) in the positive electrode material gradually decreases in mass content, and the second positive electrode active material (85nm≤D 2 50≤400nm) the mass content in the positive electrode material gradually increases. Exemplarily, a first positive electrode active material layer is provided on the surface of the positive electrode current collector, a second positive electrode active material layer is provided on the surface of the first positive electrode active material layer facing away from the positive electrode current collector, ..., an N-1th positive electrode active material layer is provided on the surface facing away from the positive electrode current collector, N is a positive integer greater than or equal to 2, the mass content of the first positive electrode active material in the first positive electrode active material layer 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 positive electrode active material layer is a2%, the mass content of the second positive electrode active material is b2%, ..., the mass content of the first positive active material in the N-1th positive electrode active material layer is a N-1 %,The mass content of the second positive electrode active material is b N-1 %,The mass content of the first positive electrode active material in the Nth positive electrode active material layer is a N %,The mass content of the second positive electrode active material is b N %, where a1, a2, ..., a N-1 、a N Gradually decrease, b1, b2, ..., b N-1 、b N Gradually increases. Therefore, compared with the positive electrode active material layer far from the current collector, the positive electrode active material layer near the current collector contains more of the first positive electrode active material with a small particle size, which helps to increase the compaction density of the positive electrode active material layer near the current collector, thereby improving its electronic conductivity. Compared with the positive electrode active material layer near the current collector, the positive electrode active material layer far from the current collector contains more of the second positive electrode active material with a large particle size, which helps to increase the porosity of the positive electrode active material layer far from the current collector, which is beneficial to ion transmission and thus improves its ionic conductivity. This 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.

[0033] In one embodiment of the present application, 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 gradually decreases from 85%-95% to 20%-40% in the multiple layers of positive electrode active material. In other words, compared with the positive electrode active material layer on the side away from the positive electrode current collector, the mass content of the first positive electrode active material in the positive electrode active material layer on the side close to the positive electrode current collector is higher, which can play a better filling and stacking role, 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 electrode active material layer on the side close to the positive electrode current collector, the mass content of the first positive electrode active material in the positive electrode active material layer on the side away from the positive electrode current collector is lower and the porosity is higher, which is conducive to the transmission of active ions, improves ionic conductivity, and further improves the performance of the positive electrode sheet. It is understood that, 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 can be gradually reduced linearly or nonlinearly, such as a gradient reduction, a parabolic reduction, etc. Specifically, 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 can be, but is not limited to, gradually reduced 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%, etc.

[0034] In one embodiment of the present application, along the direction from the positive electrode current collector to the positive electrode active material layer, the mass content of the second positive electrode active material in the positive electrode material gradually increases from 5%-15% to 60%-80% in the multiple layers of positive electrode active material. In other words, compared with the positive electrode active material layer on the side away from the positive electrode current collector, the mass content of the second positive electrode active material in the positive electrode active material layer on the side close to the positive electrode current collector is low, which is conducive to the filling and stacking of the small-particle first positive electrode active material, further improving the compaction density and electronic conductivity, and helping to improve the energy density of the positive electrode sheet and the battery; compared with the positive electrode active material layer on the side close to the positive electrode current collector, the mass content of the second positive electrode active material in the positive electrode active material layer on the side away from the positive electrode current collector is high, and the porosity is high, which is conducive to the transmission of active ions, improves ionic conductivity, and further improves the performance of the positive electrode sheet. It will be appreciated that the gradual increase in the mass content of the second positive electrode active material in the positive electrode material of the multiple positive electrode active material layers along the direction from the positive electrode current collector to the positive electrode active material layer may be a linear increase or a nonlinear increase, such as a gradient increase, a parabolic increase, etc. Specifically, along the direction from the positive electrode current collector to the positive electrode active material layer, the mass content of the second positive electrode active material in the positive electrode material of the multiple positive electrode active material layers may be, but is not limited to, gradually increasing 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.

[0035] In one embodiment of the present application, when the positive electrode plate includes two layers of positive electrode active material layers, the two layers of positive electrode active material layers include a first layer of positive electrode active material layer arranged on one side of the positive electrode current collector and a second layer of positive electrode active material layer arranged on the surface of the first layer of positive electrode active material 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 20%-40%, and the mass content of the second positive electrode active material in the positive electrode material is 60%-80%, which is conducive to obtaining a positive electrode plate with excellent compaction density, energy density and power performance.

[0036] In one embodiment of the present application, when the positive electrode sheet includes three layers of positive electrode active material layers, the three layers of positive electrode active material layers include a first positive electrode active material layer arranged on one side of the positive electrode current collector, a second positive electrode active material layer arranged on the surface of the first positive electrode active material layer facing away from the positive electrode current collector, and a third positive electrode active material layer arranged on the surface of the second positive electrode active material layer facing away from the positive electrode current collector; in the first 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 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 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%. This is conducive to obtaining positive electrode sheets with excellent compaction density, energy density and power performance.

[0037] In one 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 multi-layer positive electrode active material layer gradually decreases from 5.7-18 to 0.25-0.67. This not only ensures the compaction density and energy density of the positive electrode sheet, but also helps to improve the power performance of the positive electrode sheet. It can be understood that along the direction from the positive electrode current collector to the positive electrode active material layer, the gradual decrease in the mass ratio of the first positive electrode active material to the second positive electrode active material in the positive electrode material of the multi-layer positive electrode active material layer can be a linear decrease or a nonlinear decrease, such as a gradient decrease, a parabolic decrease, etc. Specifically, along the direction from the positive electrode current collector to the positive electrode active material layer, in the positive electrode material of the multi-layer positive electrode active material layer, the mass ratio of the first positive electrode active material to the second positive electrode active material can be, but is not limited to, gradually decreased 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.

[0038] The particle size D of the first positive electrode active material in this application 1 50 is less than 85nm, the particle size D of the second positive electrode active material 150 is 85nm-400nm, so that the first positive electrode active material plays a role of stacking filling and improving the compaction density, and the second positive electrode active material plays a role of improving the porosity. The two work together to 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 this application refers to the primary particle size. In one embodiment of this application, 10nm≤D 1 50<85nm. That is to say, the particle size D50 of the positive electrode material is 10nm-400nm, which is beneficial to the formation of the positive electrode active material layer and also beneficial to improving the performance of the positive electrode sheet. 1 50<85nm,85nm≤D 2 50≤300nm. That is, the particle size D50 of the positive electrode material is 10nm-300nm, which is beneficial to improving the performance of the positive electrode sheet. 1 50≤80nm, 85nm≤D 2 50≤200nm. In other words, the particle size D50 of the positive electrode material is 20nm-200nm, which is not only conducive to the formation of the positive electrode active material layer, but also conducive to further improving the compaction density, energy density and power performance of the positive electrode sheet.

[0039] In one embodiment of the present application, the particle size D of the second positive electrode active material is 2 50 and the particle size D of the first positive electrode active material 1 The ratio of 50 is greater than or equal to 4, which is beneficial to the combination of the first positive electrode active material and the second positive electrode active material in the positive electrode active material layer, is beneficial to the formation of the positive electrode active material layer and further improves the performance of the positive electrode sheet.

[0040] In one embodiment of the present application, the compaction density of the multi-layer positive electrode active material layer is from 2.5 g / cm 3 -2.53g / cm 3 Gradually decreased to 2.47g / cm 3 -2.49g / cm 3 This makes the positive electrode active material layer close to the current collector have a higher compaction density, which is beneficial to improving the electronic conductivity of the positive electrode sheet.

[0041] In one 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 may 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.

[0042] In one embodiment of the present application, the absolute value of the thickness difference of the multiple positive electrode active material layers is 0 μm-10 μm. Specifically, the absolute value of the thickness difference of the multiple positive electrode active material layers 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.

[0043] In one embodiment of the present application, the surface density of the positive electrode sheet is 200g / m 2 -700g / m 2 , which makes the energy density and kinetic performance of the positive electrode plate suitable, can improve the capacity of the positive electrode plate and the battery, and is beneficial to the use of the battery in electrical equipment.

[0044] In one embodiment of the present application, the absolute value of the difference in the surface density of the multi-layer positive electrode active material layer is 0 g / m 2 -10g / m 2 , further improving the energy density and kinetic performance of the positive electrode sheet. In this application, the number and thickness of the positive electrode active material layer can be designed according to the surface density of the positive electrode sheet.

[0045] In one 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 is greater than or equal to 82%, 85%, 88%, 90%, 93%, 95%, 97%, or 98%, etc.

[0046] In one embodiment of the present application, the positive electrode active material layer further includes at least one of a positive electrode binder and a positive electrode conductor. Specifically, the positive electrode binder may include, but is not limited to, at least one of polyvinylidene fluoride, polytetrafluoroethylene, sodium carboxymethyl cellulose, styrene-butadiene latex, and nitrile rubber; the positive electrode conductor may include, but is not limited to, at least one of conductive carbon black, carbon nanotubes, graphene, carbon fiber, carbon black, and graphite. In one embodiment of the present application, the mass content of the positive electrode conductor in the positive electrode active material layer is less than or equal to 5%. Specifically, the mass content of the positive electrode conductor in the positive electrode active material layer may be, but is not limited to, 0.1%, 0.5%, 1%, 2%, 3%, 4%, or 5%. In one embodiment, the mass content of the positive electrode conductor in the positive electrode active material layer may be 0.1%-5%. In one 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 may be, but is not limited to, 0.1%, 0.5%, 2%, 4%, 5%, 7%, 8% or 9%. In one embodiment, the mass content of the positive electrode binder in the positive electrode active material layer is 0.1%-10%.

[0047] In one embodiment of the present application, the positive electrode current collector is selected from a metal foil or alloy foil. Metal foils include copper, titanium, aluminum, platinum, iridium, ruthenium, nickel, tungsten, tantalum, gold, or silver foils, while alloy foils include stainless steel or alloys containing at least one of copper, titanium, aluminum, platinum, iridium, ruthenium, nickel, tungsten, tantalum, gold, and silver. Specifically, the positive electrode current collector may be aluminum foil.

[0048] This application provides a method for preparing a positive electrode sheet, comprising: forming multiple layers of positive electrode active material on the surface of a positive electrode current collector to obtain a positive electrode sheet. This preparation method is simple and easy to operate, and can produce the positive electrode sheet in any of the above embodiments.

[0049] In one embodiment of the present application, a positive electrode slurry can be coated on the surface of a positive electrode current collector, and after drying, a positive electrode active material layer is formed. In one embodiment of the present application, a positive electrode slurry can be coated on the surface of a positive electrode current collector, and after drying, a positive electrode slurry containing a first positive electrode active material and a second positive electrode active material of different mass contents is coated again and dried again. The above operation is repeated to obtain a multi-layer positive electrode active material layer, which is then rolled and cut to form a positive electrode sheet. In one embodiment, the positive electrode slurry includes a solvent and a positive electrode material. Furthermore, the positive electrode slurry also includes a positive electrode binder and a positive electrode conductor. Furthermore, the positive electrode slurry also includes a dispersant. Specifically, the positive electrode material, the binder, the conductor, the dispersant, etc. are uniformly mixed with the solvent to form a positive electrode slurry. The solvent may be, but is not limited to, N-methylpyrrolidone, and the positive electrode slurry may be prepared by a wet method or a semi-dry method.

[0050] The present application provides a battery comprising a negative electrode plate and a positive electrode plate according to any of the above-described embodiments. The battery has excellent energy density and power performance, which facilitates battery use. Specifically, the battery may be, but is not limited to, a lithium-ion battery.

[0051] In one embodiment of the present application, the negative electrode sheet includes a negative electrode current collector and a negative electrode active material layer disposed on the surface of the negative electrode current collector. In one embodiment of the present application, the negative electrode current collector is selected from a metal foil or an alloy foil. Metal foils include copper, aluminum, nickel, iron, or cobalt foils, while alloy foils include alloys of at least one of copper, aluminum, nickel, iron, and cobalt, or stainless steel. In one embodiment, the negative electrode current collector is made of at least one of copper, aluminum, nickel, iron, and cobalt, or stainless steel. Specifically, the negative electrode current collector may be copper foil. In one embodiment of the present application, the negative electrode active material layer includes a negative electrode active material. The negative electrode active material may include carbon materials, silicon materials, and the like. In one embodiment of the present application, the negative electrode active material layer may further include at least one of a negative electrode conductive agent and a negative electrode binder. Specifically, the negative electrode conductive agent may include, but is not limited to, at least one of conductive carbon black, carbon nanotubes, carbon fibers, carbon black, and graphite; the negative electrode binder may include, but is not limited to, at least one of polytetrafluoroethylene, polyvinylidene fluoride, sodium carboxymethyl cellulose, styrene-butadiene latex, and nitrile rubber. In one embodiment, the mass content of the negative electrode conductive agent in the negative electrode active material layer is less than or equal to 5%. Specifically, the mass content of the negative electrode conductive agent in the negative electrode active material layer may be, but is not limited to, 0.1%, 0.5%, 1%, 2%, 3%, 4%, or 5%. In a specific embodiment, the mass content of the negative electrode conductive agent in the negative electrode active material layer may be 0.1%-5%. In one embodiment, the mass content of the negative electrode binder in the negative electrode active material layer is less than or equal to 10%. Specifically, the mass content of the negative electrode binder in the negative electrode active material layer may be, but is not limited to, 0.1%, 0.5%, 2%, 4%, 5%, 7%, 8%, or 9%. In a specific embodiment, the mass content of the negative electrode binder in the negative electrode active material layer is 0.1%-10%. In one embodiment of the present application, at least one of a negative electrode binder and a negative electrode conductor can be mixed with a negative electrode active material in a solvent to form a negative electrode slurry, which is then coated on the surface of a negative electrode current collector and dried to obtain a negative electrode sheet.

[0052] In one embodiment of the present application, the battery further comprises an electrolyte and a separator. In one embodiment of the present application, at least a portion of the positive electrode sheet is immersed in the electrolyte, and at least a portion of the negative electrode sheet is immersed in the electrolyte, thereby ensuring normal operation of the battery. The materials of the electrolyte and separator in the present application can be selected as needed. In one embodiment of the present application, the electrolyte comprises a solute and an organic solvent. The solute can be selected based on the type of battery. For example, the solute in the electrolyte of a lithium-ion battery can be a 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(trifluoromethanesulfonyl)imide; the organic solvent can include, but is not limited to, at least one of ethylene carbonate (EC), ethyl methyl carbonate (EMC), dimethyl carbonate (DMC), diethyl carbonate (DEC), vinylene carbonate (VC), and fluoroethylene carbonate (FEC). In one embodiment, the positive electrode sheet, negative electrode sheet, and separator can be assembled and placed in a housing, filled with electrolyte, and then packaged to form a battery. In another embodiment of the present application, the battery may be a solid-state battery.

[0053] The present application provides an electrical device comprising a battery according to any of the above embodiments. The battery in the electrical device provided herein has excellent electrochemical properties, thereby improving the performance and service life of the electrical device. Specifically, the electrical device may be a vehicle, electronic device, energy storage system, etc., and the battery may be provided in the electrical device in the form of a single cell, a battery module, a battery pack, etc.

[0054] The effects of the technical solution of this application are further illustrated below through specific examples.

[0055] Example 1

[0056] A positive electrode plate includes a positive electrode current collector, a first positive electrode active material layer stacked on the surface of the positive electrode current collector, and a second positive electrode active material layer stacked on the surface of the first positive electrode active material layer, wherein the positive electrode active material layer includes a positive electrode material (lithium manganese iron phosphate), a binder (polyvinylidene fluoride, PVDF) and a conductive agent (carbon nanotube, CNT), wherein 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.

[0057] The particle size distribution curve of the positive electrode material of each positive electrode active material layer has a first peak and a second peak, and the particle size D1 corresponding to the peak value of the first peak is 40 nm, and the particle size D2 corresponding to the peak value of the second peak is 160 nm; taking the sum of the peak area proportion of the first peak and the peak area proportion of the second peak as 100%, the peak area proportion S1% of the first peak is 90%, the peak area proportion S2% of the second peak is 10%, and the ratio S1 / S2 in the first positive electrode active material layer is 9 (the mass content of the first positive electrode active material is 90%, and the D1 of the first positive electrode active material is 10%). 1 50 = 44nm; the mass content of the second positive electrode active material in the positive electrode material is 10%, and the D 2 50=190nm); the ratio of S1 / S2 in the second positive electrode active material layer is 4:6 (the first positive electrode active material accounts for 40% of the mass content of the positive electrode material, and the D of the first positive electrode active material is 40% of the mass content of the positive electrode material. 1 50 = 44nm; the mass content of the second positive electrode active material in the positive electrode material is 60%, and the D of the second positive electrode active material 2 50=190nm).

[0058] The surface density of the first positive electrode active material layer and the second positive electrode active material layer is equal, and the single surface density of the positive electrode sheet is 200g / m 2 .

[0059] Example 2

[0060] The same as Example 1, except that the positive electrode sheet further includes a third positive electrode active material layer, which is arranged on the surface of the second positive electrode active material layer away from the positive electrode current collector. The particle size distribution curve of the positive electrode material of the first positive electrode active material layer has an S1 / S2 ratio of 9, and the particle size distribution curve of the positive electrode material of the second positive electrode active material layer has an S1 / S2 ratio of 7:3 (the first positive electrode active material accounts for 70% of the mass content of the positive electrode material, and the D of the first positive active material is 20%. 1 50 = 44nm; the mass content of the second positive electrode active material in the positive electrode material is 30%, and the D of the second positive electrode active material 2 50=190nm), and the ratio S1 / S2 in the particle size distribution curve of the positive electrode material of the third positive electrode active material layer is 4:6.

[0061] Example 3

[0062] The same as Example 2, except that the positive electrode sheet further includes a fourth positive electrode active material layer, which is arranged on the surface of the third positive electrode active material layer away from the positive electrode current collector, and the S1 / S2 ratio in the particle size distribution curve of the positive electrode material of the first positive electrode active material layer is 9, and the S1 / S2 ratio in the particle size distribution curve of the positive electrode material of the second positive electrode active material layer is 4 (the first positive electrode active material accounts for 80% of the mass content of the positive electrode material, and the D of the first positive active material is 1.34). 1 50 = 44nm; the mass content of the second positive electrode active material in the positive electrode material is 20%, and the D 2 50=190nm), the particle size distribution curve of the positive electrode material of the third positive electrode active material layer is as follows Figure 2 As shown, the particle size distribution curve of the positive electrode material of the third positive electrode active material layer has a ratio of S1 / S2 of 1.5 (the first positive electrode active material accounts for 60% of the mass content of the positive electrode material, and the D 1 50 = 44nm; the mass content of the second positive electrode active material in the positive electrode material is 40%, and the D of the second positive electrode active material 2 50=190nm), and the ratio S1 / S2 in the particle size distribution curve of the positive electrode material of the fourth positive electrode active material layer is 4:6.

[0063] Example 4

[0064] The same as 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 arranged on the surface of the fourth positive electrode active material layer away from the positive electrode current collector, the S1 / S2 ratio in the particle size distribution curve of the positive electrode material of the first positive electrode active material layer is 9, the S1 / S2 ratio in the particle size distribution curve of the positive electrode material of the second positive electrode active material layer is 4, the S1 / S2 ratio in the particle size distribution curve of the positive electrode material of the third positive electrode active material layer is 1.5, and the S1 / S2 ratio in the particle size distribution curve of the positive electrode material of the fourth positive electrode active material layer is 5:5 (the first positive electrode active material accounts for 50% of the mass content of the positive electrode material, and the D of the first positive active material is 20%. 1 50 = 44nm; the mass content of the second positive electrode active material in the positive electrode material is 50%, and the D of the second positive electrode active material 2 50=190nm), and the ratio S1 / S2 in the particle size distribution curve of the positive electrode material of the fifth positive electrode active material layer is 4:6.

[0065] Example 5

[0066] It is roughly the same as 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 particle size D1 corresponding to the peak value of the first peak is 30 nm, and the particle size D2 corresponding to the peak value of the second peak is 110 nm.

[0067] Comparative Example 1

[0068] A positive electrode sheet includes a positive electrode current collector and a positive electrode active material layer stacked on the surface of the positive electrode current collector, wherein the positive electrode active material layer includes 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): the binder (PVDF): the conductive agent (CNT) is 95:2.5:1.5, the positive electrode material includes lithium manganese iron phosphate with a mass content of 85% and a first peak peak particle size D1 of 40nm and lithium manganese iron phosphate with a mass content of 15% and a second peak peak particle size D2 of 160nm, and the single surface density of the positive electrode sheet is 200g / m 2 .

[0069] Comparative Example 2

[0070] It is roughly the same as Example 1, except that the ratios of the two layers of active materials in the positive electrode sheet are exchanged, that is, the ratio of S1 / S2 in the first positive electrode active material layer is 4:6; the ratio of S1 / S2 in the second positive electrode active material layer is 9.

[0071] Performance testing

[0072] The ultimate compaction density of the positive electrode sheets provided in the above-described embodiments and comparative examples was tested. Specifically, the sheet was rolled using a roller press, with the pressure gradually increased until active material peeling or cracking, sheet cracking, or band breakage occurred. The maximum pressure condition that resulted in a complete sheet was then used to test the thickness and areal density of the resulting sheet, and the sheet compaction density was calculated. The results are shown in Table 1.

[0073] The above embodiments and comparative examples provide positive and negative electrode sheets (specifically, the negative electrode slurry is coated on a copper foil current collector and dried, and 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, lithium hexafluorophosphate: ethylene carbonate: diethyl carbonate: vinylene carbonate are mixed in a mass ratio of 12.93:43.54:43.54:4) and are assembled in the same manner to form a full battery. The discharge specific capacity, room temperature charging peak power, room temperature discharge peak power, and room temperature discharge DC internal resistance (DCIR) of the formed full battery are tested.

[0074] The discharge capacity test conditions are as follows: charge at room temperature at 1 / 3C constant current and constant voltage to 4.3V, with a cut-off current of 0.02C, and discharge at room temperature to 2.0V. Cycle three times and take the last discharge capacity.

[0075] Normal temperature charging peak power test method: Adjust the battery charge to 80%, charge at 1C for 30 seconds, then adjust the SOC back to 80%. After the open circuit voltage stabilizes, increase the current to 2C and continue testing. Then gradually increase the current until the charging time is less than 30 seconds when the upper limit voltage (4.3V) is reached. The maximum current after charging for 30 seconds is used to calculate the charging peak power.

[0076] Normal temperature discharge peak power test method: Charge the battery to 80%, discharge at 1C for 30 seconds, then adjust the SOC back to 80%. After the open circuit voltage stabilizes, increase the current to 2C and continue testing. Then gradually increase the current until the discharge time is less than 30 seconds when the lower limit voltage (2.0V) is reached. The maximum current when the discharge time reaches 30 seconds is used to calculate the discharge peak power.

[0077] The DC internal resistance (DCIR) test method for room-temperature discharge is as follows: the battery is charged to 80% and the voltage after standing for 1 hour is recorded as V0. The voltage after discharging at 1.5C for 30 seconds is recorded as V1. The DC internal resistance is the absolute value of (V1-V0) / 1.5, expressed in mΩ·Ah. The results are shown in Table 1.

[0078] Table 1 Performance test results

[0079]

[0080] Compared with the comparative example, the discharge specific capacity, charge and discharge peak power of the positive electrode sheets prepared in Examples 1-5 are significantly improved, and the discharge DC internal resistance is reduced, and the denser the gradient of the particle combination, the more obvious the improvement effect. It can be seen from Example 4 that when the number of positive electrode active material layers is large, the ultimate compaction density of the positive electrode sheet decreases slightly, but the reduction ratio is only less than 1%, which has little effect on the energy density, and in actual applications, the compaction density will not reach the ultimate compaction density. Therefore, the small reduction in the ultimate compaction density in Example 4 will not bring about a significant loss of energy density, and it can still maintain a high energy density, thereby reducing the internal resistance of the battery and improving the power performance of the battery. In summary, the positive electrode sheet provided in this application has excellent compaction density, energy density and power performance, which helps to reduce the internal resistance of the battery, improve the energy density and power performance of the battery, and make the battery have excellent electrochemical properties, which is beneficial to the use of the battery.

[0081] The above is a preferred embodiment of the present application, but it should not be construed as limiting the scope of the present application. It should be noted that those skilled in the art can make various improvements and modifications without departing from the principles of the present application, and such improvements and modifications are also considered to be within the scope of protection of the present application.

Claims

1. A positive electrode plate, characterized in that: The device comprises a positive electrode current collector and a plurality of positive electrode active material layers stacked on at least one side of the positive electrode current collector. The positive electrode active material layer includes a positive electrode material, the positive electrode material includes a first positive electrode active material and a second positive electrode active material, and the particle size D of the first positive electrode active material is 1 50. Particle size D of the second positive electrode active material 2 50 satisfied: D 1 50<85nm,85nm≤D 2 50≤400nm, Along the direction from the positive electrode current collector to the positive electrode active material layer, in the multiple 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.

2. The positive electrode sheet according to claim 1, wherein: 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 particle size corresponding to the peak value of the first peak is D1, in nm, and the particle size corresponding to the peak value of the second peak is D2, in nm, where 0.1 <D1 / D2<0.4, And / or, taking the sum of the peak area proportion of the first peak and the peak area proportion of the second peak as 100%, the peak area proportion of the first peak is S1%, the peak area proportion of the second peak is S2%, wherein 0.25 <S1 / S2<10。 3. The positive electrode sheet according to claim 1, wherein: Along the direction from the positive electrode current collector to the positive electrode active material layer, in the multiple layers of the 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%.

4. The positive electrode sheet according to claim 1, wherein: The particle size D of the first positive electrode active material 1 50. Particle size D of the second positive electrode active material 2 50 satisfies: 10nm≤D 1 50<85nm,85nm≤D 2 50≤300nm.

5. The positive electrode sheet according to claim 1 or 4, characterized in that: The particle size D of the first positive electrode active material 1 50. Particle size D of the second positive electrode active material 2 50 satisfies: 20nm≤D 1 50≤80nm, 85nm≤D 2 50≤200nm.

6. The positive electrode sheet according to claim 1, wherein: The surface density of the positive electrode sheet is 200g / m 2 -700g / m 2 ; The absolute value of the surface density difference of the multiple positive electrode active material layers is 0 g / m 2 -10g / m 2 .

7. The positive electrode sheet according to claim 1, wherein: The thickness of the positive electrode active material layer is 80 μm-280 μm; The absolute value of the thickness difference of the plurality of positive electrode active material layers is 0 μm-10 μm.

8. The positive electrode sheet according to claim 1, wherein: The material of the positive electrode material includes at least one of lithium manganese iron phosphate and lithium iron phosphate.

9. The positive electrode sheet according to claim 1, wherein: The number of positive electrode active material layers in the positive electrode sheet is 2-5.

10. The positive electrode sheet according to claim 9, wherein: When the positive electrode plate includes two layers of positive electrode active material layers, the two layers of positive electrode active material layers include a first layer of positive electrode active material layer arranged on one side of the positive electrode current collector and a second layer of positive electrode active material layer arranged on the surface of the first layer of positive electrode active material 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 20%-40%, and the mass content of the second positive electrode active material in the positive electrode material is 60%-80%.

11. The positive electrode sheet according to claim 9, wherein: When the positive electrode sheet includes three layers of positive electrode active material layers, the three layers of positive electrode active material layers include a first positive electrode active material layer arranged on one side of the positive electrode current collector, a second positive electrode active material layer arranged on the surface of the first positive electrode active material layer facing away from the positive electrode current collector, and a third positive electrode active material layer arranged on the surface of the second positive electrode active material layer facing away from the positive electrode current collector; in the first 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 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 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 in that: It comprises a negative electrode sheet and a positive electrode sheet as described in any one of claims 1 to 11.

13. An electrical device, characterized in that: Including the battery according to claim 12.

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