Positive pole piece and preparation method thereof, battery monomer, battery and electric device

Abstract

The invention provides a positive pole piece and a preparation method thereof, a battery monomer, a battery and an electric device. The positive pole piece comprises a positive current collector and a negative current collector, the first positive electrode active material film layer is arranged on at least one side of the positive electrode current collector, and the first positive electrode active material film layer comprises solid first positive electrode active material particles; the second positive electrode active material film layer is arranged between the first positive electrode active material film layer and the positive electrode current collector, and the second positive electrode active material film layer comprises second positive electrode active material particles with hollow structures. According to the positive pole piece provided by the embodiment of the invention, in the charging and discharging process of the battery, the de-intercalation speed of active ions in the first positive active material film layer and the second positive active material film layer is favorably balanced, the gram capacity of the positive pole piece is favorably exerted, and the cycling stability of the battery is improved. The battery monomer, the battery and the electric device comprising the positive pole piece also have the advantages.

Description

Technical Field

[0001] The present application relates to the technical field of batteries, and particularly to a positive electrode sheet, a preparation method thereof, a battery cell, a battery and an electrical device. Background Art

[0002] In recent years, with the increasingly wide application range of batteries represented by lithium-ion batteries, batteries are widely used in energy storage power systems such as hydroelectric, thermal, wind and solar power stations, as well as in multiple fields such as power tools, electric bicycles, electric motorcycles, electric vehicles, military equipment, aerospace, etc. Due to the great development of batteries, higher requirements are also put forward for their energy density, cycle performance, safety performance, etc.

[0003] In order to increase the capacity of the battery, the active material film layer of the positive electrode sheet is usually designed to be relatively thick, but still cannot meet the requirements of increasing the battery capacity and cycle performance, and further improvement is needed. Summary of the Invention

[0004] The present application provides a positive electrode sheet, a preparation method thereof, a battery cell, a battery and an electrical device, and the positive electrode sheet has good cycle stability while having a high specific capacity.

[0005] In a first aspect, an embodiment of the present application provides a positive electrode sheet, including:

[0006] A positive electrode current collector;

[0007] A first positive electrode active material film layer disposed on at least one side of the positive electrode current collector, and the first positive electrode active material film layer includes solid first positive electrode active material particles;

[0008] A second positive electrode active material film layer disposed between the first positive electrode active material film layer and the positive electrode current collector, and the second positive electrode active material film layer includes second positive electrode active material particles having a hollow structure.

[0009] According to the embodiments of the present application, during the charge and discharge process of the battery including the positive electrode sheet of the embodiments of the present application, the discharge specific capacity and stability of the positive electrode sheet are improved, and the charge and discharge time of the positive electrode sheet in the battery is increased. The possible reasons for analysis are as follows: during the electrolyte mass transfer process, the concentration of active ions gradually decreases from the separator to the vicinity of the positive current collector of the positive electrode sheet. For the solid first positive active material particles in the first positive active material film layer, the insertion and extraction distance of active ions in the first positive active material film layer is relatively long (the mass transfer distance is relatively long); the second positive active material film layer includes second positive active material particles with a hollow structure. The second positive active material particles with a hollow structure reduce the insertion and extraction distance of active ions in the second positive active material film layer (the mass transfer distance is relatively short), which is beneficial to the balance of the insertion and extraction speeds of active ions in the first positive active material film layer and the second positive active material film layer respectively, and balances the difference in the charge and discharge (SOC) speeds of active ions between the first positive active material film layer and the second positive active material film layer, thus facilitating the exertion of the specific capacity of the positive electrode sheet.

[0010] In addition, the second positive active material particles have a hollow structure, which is beneficial to the existence of the second positive active material particles in the positive electrode sheet, disperses the stress during the cycling process of the positive electrode sheet, improves the cycling stability of the positive electrode sheet, and is beneficial to further improving the cycling performance of the battery.

[0011] In some embodiments, the first positive active material particles and the second positive active material particles are respectively nickel-containing positive active particles.

[0012] When the nickel-containing positive active particles are applied to a battery, taking a lithium battery as an example, such as Ni 2+ ion radius and Li + have similar radii, which will seriously cause the phenomenon of cation mixing, resulting in the decline of the electrochemical performance of the lithium-containing ternary positive active material. Especially in the high-nickel system, the trend of cation mixing increases, and the cycling performance of the battery deteriorates. According to the embodiments of the present application, the first positive active material film layer includes solid first positive active material particles, and the second positive active material film layer includes hollow particles, which shortens the distance for lithium ions to transfer protons. Generally, the lithium ion concentration in the first positive active material film layer is high, but the solid-state mass transfer distance of lithium ions is longer. The lithium ion concentration in the second positive active material film layer is low, but the solid-state mass transfer time is shorter, which balances the difference in the insertion and extraction of active lithium ions between the active material particles in the positive electrode sheet, is beneficial to the exertion of the specific capacity of the positive electrode sheet, reduces the ratio of the active material particles that do not participate in the charge and discharge cycle to the total active material particles in the positive electrode sheet, thereby improving the specific capacity of the positive electrode sheet and the cycling performance of the positive electrode sheet in the battery.

[0013] In some alternative embodiments, the average particle size Dv of the first positive active material particles1 50 is greater than or equal to the average particle size Dv of the second positive electrode active material particles 2 50.

[0014] According to an embodiment of the present application, the average particle size Dv of the first positive electrode active material particles 1 50 is greater than or equal to the average particle size Dv of the second positive electrode active material particles 2 50 is beneficial to increasing the mass transfer distance of the first positive electrode active material particles in the first positive electrode active material film layer, reducing the mass transfer distance of the second positive electrode active material particles in the second positive electrode active material film layer, thereby coping with the phenomenon that the active ion concentration in the first positive electrode active material film layer is relatively high and the active ion concentration in the second positive electrode active material film layer is relatively low, balancing the active ion insertion / extraction rates of the two layers, and thus improving the specific capacity and cycling performance of the positive electrode sheet.

[0015] In addition, the average particle size Dv of the first positive electrode active material particles 1 50 is relatively large, which is beneficial to increasing the porosity of the first positive electrode active material film layer, and thus is beneficial to the first positive electrode active material particles existing in the positive electrode sheet, dispersing the stress of the first positive electrode active material particles in the positive electrode sheet during the cycling process, and improving the cycling stability of the positive electrode sheet, which is beneficial to further improving the cycling performance of the battery.

[0016] In some optional embodiments, the average particle size Dv of the first positive electrode active material particles 1 50 is 8 μm to 18 μm.

[0017] According to an embodiment of the present application, the average particle size Dv of the first positive electrode active material particles 1 50 within the above range is beneficial to increasing the mass transfer distance of the first positive electrode active material particles in the first positive electrode active material film layer, thereby coping with the phenomenon that the active ion concentration in the first positive electrode active material film layer is relatively high and the active ion concentration in the second positive electrode active material film layer is relatively low, balancing the active ion insertion / extraction rates of the two layers, and thus improving the specific capacity and cycling performance of the positive electrode sheet.

[0018] In some optional embodiments, the average particle size Dv of the second positive electrode active material particles 2 50 is 2 μm to 10 μm.

[0019] According to an embodiment of the present application, the average particle size Dv of the second positive electrode active material particles 2 50 within the above range is beneficial to reducing the mass transfer distance of the second positive electrode active material particles in the second positive electrode active material film layer, thereby coping with the phenomenon that the active ion concentration in the first positive electrode active material film layer is relatively high and the active ion concentration in the second positive electrode active material film layer is relatively low, balancing the active ion insertion / extraction rates of the two layers, and thus improving the specific capacity and cycling performance of the positive electrode sheet.

[0020] In some optional embodiments, the particle size distribution span of the first positive electrode active material particles is 0.3 - 0.7.

[0021] According to the embodiments of the present application, when the particle size distribution span of the first positive electrode active material particles is within the above range, the tap density of the material can be increased, the discharge capacity of the battery can be increased, the deintercalation rate of active ions in the two layers can be balanced, thereby increasing the specific capacity per gram of the positive electrode sheet and the cycle performance.

[0022] In some optional embodiments, the particle size distribution span of the second positive electrode active material particles is 0.9 - 1.3.

[0023] According to the embodiments of the present application, when the particle size distribution span of the second positive electrode active material particles is within the above range, the tap density of the material can be increased, the discharge capacity of the battery can be increased, the deintercalation rate of active ions in the two layers can be balanced, thereby increasing the specific capacity per gram of the positive electrode sheet and the cycle performance.

[0024] In some optional embodiments, the inner diameter d1 of the hollow structure is 0.6 μm to 5 μm.

[0025] According to the embodiments of the present application, the second positive electrode active material particles have a hollow structure, which can buffer the volume change of the second positive electrode active material particles during charge and discharge, and play a role in stabilizing the structure and improving the cycle performance. On the other hand, there are many three-dimensional pores in the second positive electrode active material particles, which expands the contact area between the material and the electrolyte, shortens the migration distance of lithium ions, thereby increasing the speed of active ions in the second positive electrode active material film layer, which is beneficial to reducing the internal resistance of the battery, and the battery has excellent rate performance. At the same time, the second positive electrode active material particles have a hollow structure, so they have more active sites for lithium ions, which improves the specific capacity per gram of the material, the specific capacity per gram of the positive electrode sheet, and the energy density of the battery.

[0026] In some optional embodiments, the outer wall thickness d2 of the hollow structure is 0.6 μm to 10 μm.

[0027] In the embodiments of the present application, controlling the outer wall thickness d2 of the hollow structure within a suitable range can improve the structural stability of the second positive electrode active material particles, increase the specific capacity per gram of the material in the positive electrode sheet, improve the energy density, rate performance and cycle performance of the battery, and comprehensively improve the electrochemical performance of the battery.

[0028] Dv of the second positive electrode active material particles 2 50, the inner diameter d1 and the outer wall thickness d2 of the hollow structure are important parameters of the second positive electrode active material particles, which affect the structural performance of the material. Dv of the second positive electrode active material particles 250. When the inner diameter d1 and the outer wall thickness d2 of the hollow structure are within a suitable range, the material has more active sites for active ions, thereby increasing the specific capacity of the material. At the same time, the structural stability of the material can be improved. When it is applied to a lithium battery for charge and discharge cycles, the phenomenon of lithium-nickel mixing is effectively improved, and the migration rates of active ions and electrons are significantly increased, which is beneficial to the balance of the insertion and extraction speeds of active ions in the positive electrode sheet of the battery, and thus beneficial to the cycle performance of the battery.

[0029] In some alternative embodiments, the first positive electrode active material particles and the second positive electrode active material particles have the following structural general formulas respectively: Li a Ni x Co y M 1-x-y O2, where M includes one or more of Mn, Al, B, Zr, Sr, Y, Sb, W, Ti, Mg, Nb, Ba, 0.55 ≤ x ≤ 1.05, 0 ≤ y ≤ 0.45, 0.8 ≤ a ≤ 1.2.

[0030] According to the embodiments of the present application, using the above materials can ensure that the first positive electrode active material film layer and the second active material film layer have a high specific capacity, thereby increasing the specific capacity of the positive electrode sheet and enabling the battery to have a high discharge capacity and energy density.

[0031] In some alternative embodiments, the specific surface area of the first positive electrode active material particles is 0.1 m 2 / g - 0.5 m 2 / g.

[0032] In some alternative embodiments, the specific surface area of the second positive electrode active material particles is 0.35 m 2 / g - 0.8 m 2 / g.

[0033] According to the embodiments of the present application, the first positive electrode active material particles have a suitable specific surface area, and the second positive electrode active material particles respectively have a suitable specific surface area, thereby dealing with the phenomenon that the concentration of active ions in the first positive electrode active material film layer is relatively high and the concentration of active ions in the second positive electrode active material film layer is relatively low, balancing the insertion and extraction speeds of active ions in the two layers, and thus increasing the specific capacity and cycle performance of the positive electrode sheet.

[0034] In some alternative embodiments, the tap density of the first positive electrode active material particles is 1.8 g / cm 3 -4 g / cm 3 .

[0035] In some alternative embodiments, the tap density of the second positive electrode active material particles is 1.3 g / cm 3 -2.6 g / cm 3 .

[0036] According to an embodiment of the present application, the first positive electrode active material particles have an appropriate tap density and the second positive electrode active material particles have an appropriate tap density, thereby coping with the phenomenon that the concentration of active ions in the first positive electrode active material film layer is relatively high and the concentration of active ions in the second positive electrode active material film layer is relatively low, balancing the intercalation and deintercalation rates of active ions in the two layers, and thus improving the specific capacity and cycle performance of the positive electrode sheet.

[0037] In some alternative embodiments, the second positive electrode active material film layer includes third positive electrode active material particles, and the average particle size Dv of the second positive electrode active material particles 2 50 is greater than the average particle size Dv of the third positive electrode active material particles 3 50.

[0038] In an embodiment of the present application, the average particle size Dv of the second positive electrode active material particles is controlled 2 50 and the average particle size Dv of the third positive electrode active material particles 3 50 is within the above range. The combination of the third positive electrode active material particles and the second positive electrode active material particles is beneficial to increasing the mass transfer distance of the second positive electrode active material film layer, increasing the intercalation and deintercalation rate of active ions in the second positive electrode active material film layer, balancing the charge and discharge rate difference (SOC difference) between the first active material film layer and the second active material film layer, and is beneficial to the exertion of the specific capacity.

[0039] In some alternative embodiments, the average particle size Dv of the third positive electrode active material particles 3 50 is 0.8 μm to 5 μm.

[0040] According to an embodiment of the present application, the average particle size Dv of the third positive electrode active material particles 3 50 is within the above range. Its particle size is relatively small and its anisotropy is smaller. At this time, the volume expansion rate of the third positive electrode active material particles during charge and discharge in the battery is relatively low, making the cycle stability of the third positive electrode active material particles better, which can further improve the overall cycle stability of the positive electrode sheet and further improve the cycle performance of the battery.

[0041] In some alternative embodiments, the specific surface area of the third positive electrode active material particles is 0.4 m 2 / g - 0.9 m 2 / g.

[0042] According to an embodiment of the present application, the specific surface area of the third positive electrode active material particles is within the above range, which is beneficial to controlling the specific surface area and compaction density of the second positive electrode active material film layer, improving the cycle stability of the positive electrode sheet, and further improving the cycle performance of the battery.

[0043] In summary, by controlling the specific surface areas of the first positive electrode active material particles, the second positive electrode active material particles, and the third positive electrode active material particles within an appropriate range, the battery has a high discharge capacity and energy density, excellent rate performance and cycling performance, and comprehensively improves the electrochemical performance of the battery.

[0044] In some alternative embodiments, the tap density of the third positive electrode active material particles is 1.8 g / cm 3 - 3.4 g / cm 3 .

[0045] According to the embodiments of the present application, when the tap density of the third positive electrode active material particles is within the above range, it is beneficial to control the compaction density of the second positive electrode active material film layer, improve the cycling stability of the positive electrode sheet, and further improve the cycling performance of the battery.

[0046] In some alternative embodiments, the third positive electrode active material particles are one or more of particles with a hollow structure and solid particles.

[0047] In some alternative embodiments, the particle size distribution span of the third positive electrode active material particles is 0.8 - 1.5.

[0048] According to the embodiments of the present application, when the particle size distribution span of the third positive electrode active material particles is within the above range, it is beneficial to increase the compaction density of the second active material film layer, balance the deintercalation rate of active ions in the two layers, improve the stability of the positive electrode sheet, and thus increase the specific capacity per gram and cycling performance of the positive electrode sheet.

[0049] In some alternative embodiments, the third positive electrode active material particles include the following structural general formula: Li a Ni x Co y M 1-x-y O2, where M includes one or more of Mn, Al, B, Zr, Sr, Y, Sb, W, Ti, Mg, Nb, Ba, 0.55 ≤ x ≤ 1.05, 0 ≤ y ≤ 0.45, 0.8 ≤ a ≤ 1.2.

[0050] According to the embodiments of the present application, using the above materials can ensure that the second active material film layer has a high specific capacity per gram, thereby increasing the specific capacity per gram of the positive electrode sheet and enabling the battery to have a high discharge capacity and energy density.

[0051] In some alternative embodiments, the first positive electrode active material particles, the second positive electrode active material particles, and the third positive electrode active material particles respectively include LiNi 0.96 Co 0.02 Mn 0.01 Ba 0.01 O2, LiNi 0.97 Co0.01 Mn 0.01 Ba 0.01 O2, LiNi 0.98 Co 0.01 Mn 0.005 Ba 0.005 Any one or more of O2. The above positive electrode active material can better balance the charge and discharge speed of the positive electrode plate in the battery, balance the average of the charging efficiency on its surface and on the side close to the positive electrode current collector, improve the gram capacity of the positive electrode plate, and enable the battery to have a high discharge capacity and energy density.

[0052] In some optional embodiments, the ratio of the thickness h1 of the first positive electrode active material film layer to the thickness h2 of the second positive electrode active material film layer is 10:(3.3 - 23.5).

[0053] According to the embodiments of the present application, by controlling the ratio of the thickness h1 of the first positive electrode active material film layer to the thickness h2 of the second positive electrode active material film layer within the above range, it is beneficial to control the thickness of the first positive electrode active material film layer and the overall thickness, beneficial to balance the insertion and extraction speed of active ions in the two active material film layers, improve the stability of the positive electrode plate, and thus improve the gram capacity and cycling performance of the positive electrode plate.

[0054] In some optional embodiments, the thickness h1 of the first positive electrode active material film layer is 130 - 200 μm.

[0055] In some optional embodiments, the thickness h2 of the second positive electrode active material film layer is 50 - 170 μm.

[0056] According to the embodiments of the present application, by controlling the first positive electrode active material film layer to have a suitable thickness h1 and the second positive electrode active material film layer to have a suitable thickness h2, it is beneficial to balance the insertion and extraction speed of active ions in the two active material film layers, improve the stability of the positive electrode plate, and thus improve the gram capacity and cycling performance of the positive electrode plate.

[0057] In some optional embodiments, the porosity of the first positive electrode active material film layer is greater than the porosity of the second positive electrode active material film layer.

[0058] In some optional embodiments, the porosity of the first positive electrode active material film layer is 26% - 50%.

[0059] In some optional embodiments, the tap density of the first positive electrode active material film layer is 2.9 g / cm 3 -3.3 g / cm 3 ; in some optional embodiments, the tap density of the second positive electrode active material film layer is 3.2 g / cm 3 -3.7 g / cm 3。In some alternative embodiments, the tap density of the first positive electrode active material film layer is less than that of the second positive electrode active material film layer.

[0060] According to the embodiments of the present application, by controlling the first positive electrode active material film layer and the second positive electrode active material film layer to have appropriate porosities and tap densities, it is beneficial to improve the electrochemical performance of the positive electrode sheet in the battery and enhance the comprehensive performance of the battery.

[0061] In some alternative embodiments, the specific capacity of the first positive electrode active material film layer is 225 mAh / g - 240 mAh / g. In some alternative embodiments, the specific capacity of the second positive electrode active material film layer is 220 mAh / g - 235 mAh / g.

[0062] According to the embodiments of the present application, after detecting the charge-discharge cycles of the positive electrode sheet in the coin cell / battery cell, the ratio of the capacities of the first positive electrode active material film layer and the second positive electrode active material film layer is within the above range, which balances the intercalation and deintercalation rates of the active ions in the first positive electrode active material film layer and the second positive electrode active material film layer, is beneficial to the capacity utilization of the positive electrode sheet, and improves the utilization rate of the positive electrode active material.

[0063] In a second aspect, the embodiments of the present application provide a method for preparing a positive electrode sheet, including:

[0064] Providing a second slurry containing second positive electrode active material particles, the second positive electrode active material particles having a hollow structure;

[0065] Coating the second slurry on the positive electrode current collector and forming a second positive electrode active material film layer;

[0066] Providing a first slurry containing first positive electrode active material particles, the first positive electrode active material particles being solid particles;

[0067] Coating the first slurry so as to form a first positive electrode active material film layer on the side of the second positive electrode active material film layer away from the positive electrode current collector, thereby obtaining the positive electrode sheet.

[0068] According to an embodiment of the present application, a second slurry containing second positive electrode active material particles is coated on the positive electrode current collector to form a second positive electrode active material film layer, and a first slurry containing first positive electrode active material particles is coated so that a first positive electrode active material film layer is formed on the side of the second positive electrode active material film layer away from the positive electrode current collector. Thus, during the charge and discharge process of the battery with the positive electrode plate according to the embodiment of the present application, due to the fact that the concentration of active ions gradually decreases from the separator to the vicinity of the positive electrode current collector in the positive electrode plate during the electrolyte mass transfer process, the first positive electrode active material particles in the first positive electrode active material film layer are solid particles, and the insertion and extraction distance of the active ions in the first positive electrode active material film layer is relatively long (the mass transfer distance is relatively long); the second positive electrode active material film layer contains second positive electrode active material particles with a hollow structure, and the second positive electrode active material particles with a hollow structure reduce the insertion and extraction distance of the active ions in the second positive electrode active material film layer (the mass transfer distance is relatively short), which is beneficial to the balance of the insertion and extraction speeds of the active ions in the first positive electrode active material film layer and the second positive electrode active material film layer, balances the difference in the charge and discharge (SOC) speeds of the active ions between the first positive electrode active material film layer and the second positive electrode active material film layer, and is beneficial to the utilization of the specific capacity of the positive electrode plate.

[0069] According to an embodiment of the present application, the ratio of Li / Ni mixing in the first positive electrode active material film layer and the second positive electrode active material film layer is within the above range, indicating that the first positive electrode active material film layer and the second positive electrode active material film layer obtained by the above settings balance the difference in the charge and discharge (SOC) speeds of the active ions between the first positive electrode active material film layer and the second positive electrode active material film layer, and thus also improve the specific capacity and cycle performance of the positive electrode plate.

[0070] In some optional embodiments, the second slurry includes, by mass percentage, a mixture of 60%-90% of second positive electrode active material particles and 10%-40% of third positive electrode active material particles.

[0071] According to an embodiment of the present application, by controlling the mass content of the second positive electrode active material particles and the mass content of the third positive electrode active material particles in the second positive electrode active material film layer, on the basis of balancing the insertion and extraction speeds of the active ions in the first positive electrode active material film layer and the second positive electrode active material film layer, the structural stability of the positive electrode plate and the charge and discharge speed of the battery are taken into account.

[0072] In a third aspect, an embodiment of the present application provides a battery cell, including the positive electrode plate of the first aspect or the positive electrode plate prepared by the method of the second aspect. According to an embodiment of the present application, the battery cell includes the above positive electrode plate, so the battery has the beneficial effects of the above positive electrode plate.

[0073] Fourth aspect, an embodiment of the present application provides a battery, including the battery cell of the third aspect. According to the embodiment of the present application, this battery includes the above-mentioned battery cell, so this battery has the beneficial effects of the above-mentioned battery cell.

[0074] Fifth aspect, an embodiment of the present application provides an electrical device, including the battery of the fourth aspect. According to the embodiment of the present application, this electrical device includes the above-mentioned battery, so this electrical device has the beneficial effects of the above-mentioned battery. Description of the Drawings

[0075] Figure 1 is a micrograph of the hollow structure portion of the second positive electrode active material particles of an embodiment of the present application.

[0076] Figure 2 is a schematic diagram of a battery cell of an embodiment of the present application.

[0077] Figure 3 is Figure 2 an exploded view of the battery cell of an embodiment of the present application shown in.

[0078] Figure 4 is a schematic diagram of a battery module of an embodiment of the present application.

[0079] Figure 5 is a schematic diagram of a battery of an embodiment of the present application.

[0080] Figure 6 is Figure 5 an exploded view of the battery of an embodiment of the present application shown in.

[0081] Figure 7 is a schematic diagram of an electrical device using the battery cell of an embodiment of the present application as a power source.

[0082] Description of the Reference Numerals:

[0083] 1. Battery; 2. Upper box body; 3. Lower box body; 4. Battery module; 5. Battery cell; 51. Housing; 52. Electrode assembly; 53. Top cover assembly.

[0084] The drawings of the present application are not necessarily drawn to scale. Detailed Embodiments

[0085] Hereinafter, embodiments of the positive electrode sheet, its preparation method, battery cell, battery, and electrical device of the present application will be specifically described in detail with reference to the accompanying drawings as appropriate. However, there may be cases where unnecessary details are omitted. For example, there are cases where details of well-known matters are omitted and repeated descriptions of actually identical structures are omitted. This is to prevent the following description from becoming unnecessarily lengthy and to facilitate understanding by those skilled in the art. In addition, the accompanying drawings and the following description are provided for those skilled in the art to fully understand the present application and are not intended to limit the subject matter recited in the claims.

[0086] The "ranges" disclosed in the present application are defined in the form of lower and upper limits. A given range is defined by selecting a lower limit and an upper limit, and the selected lower limit and upper limit define the boundary of a particular range. The ranges defined in this way can include or exclude the end values and can be combined arbitrarily, that is, any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60 to 120 and 80 to 110 are listed for a particular parameter, ranges of 60 to 110 and 80 to 120 are also contemplated. In addition, if the minimum range values 1 and 2 are listed, and if the maximum range values 3, 4, and 5 are listed, the following ranges are all contemplated: 1 to 3, 1 to 4, 1 to 5, 2 to 3, 2 to 4, and 2 to 5. In the present application, unless otherwise specified, the numerical range "a to b" represents an abbreviated representation of any real number combination between a and b, where a and b are both real numbers. For example, the numerical range "0 to 5" means that all real numbers between "0 to 5" have been fully listed herein, and "0 to 5" is only an abbreviated representation of these numerical combinations. Additionally, when a certain parameter is expressed as an integer ≥2, it is equivalent to disclosing that the parameter is, for example, the integer 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0087] If there is no special instruction, all embodiments and optional embodiments of the present application can be combined with each other to form a new technical solution.

[0088] If there is no special instruction, all technical features and optional technical features of the present application can be combined with each other to form a new technical solution.

[0089] Unless otherwise specified, all steps of this application can be carried out sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), indicating that the method may include steps (a) and (b) carried out sequentially, or may also include steps (b) and (a) carried out sequentially. For example, when it is mentioned that the method may further include step (c), it means that step (c) can be added to the method in any order. For example, the method may include steps (a), (b), and (c), or may also include steps (a), (c), and (b), or may include steps (c), (a), and (b), etc.

[0090] Unless otherwise specified, the terms "comprising" and "including" mentioned in this application are open-ended and can also be closed-ended. For example, "comprising" and "including" can mean that other components not listed may also be included or comprised, or may only include or comprise the listed components.

[0091] Unless otherwise specified, in this application, the term "or" is inclusive. For example, the phrase "A or B" means "A, B, or both A and B". More specifically, any of the following conditions satisfies the condition "A or B": A is true (or exists) and B is false (or does not exist); A is false (or does not exist) while B is true (or exists); or both A and B are true (or exist).

[0092] Unless otherwise specified, in this application, the terms "connected" and "joined" should be understood in a broad sense. For example, it can be a fixed connection, a detachable connection, or an integral connection; it can be directly connected or indirectly connected through an intermediate medium, and can be the communication inside two components. For those of ordinary skill in the art, the specific meanings of the above terms in this application can be understood according to specific circumstances.

[0093] Unless otherwise specified, in this application, the term "attached" refers to connection by means such as adhesion or coating.

[0094] Unless otherwise specified, in this application, the terms "first", "second", "third", "fourth", etc. are used to distinguish different objects, rather than to describe a specific order or primary-secondary relationship.

[0095] Unless otherwise specified, in this application, the term "active ion" refers to an ion that can intercalate and deintercalate between the positive and negative electrodes of a battery cell, including but not limited to lithium ions, sodium ions, etc.

[0096] The terms "several" or "multiple" that appear in this application refer to two or more (including two). The terms "several items" or "multiple items" that appear in this application refer to two or more items (including two items).

[0097] In related technologies, nickel-rich ternary materials have become one of the popular cathode active materials for battery cells due to their high theoretical specific capacity, high discharge platform, and low cost. Therefore, the active material film layer of the cathode electrode is usually designed to be relatively thick, so as to accommodate more cathode active materials, which is beneficial to improving the capacity and energy density of the battery.

[0098] As the thickness of the active material film layer of the cathode electrode reaches a certain level, the capacity and energy density of the battery can only be improved limitedly, and the accompanying battery cycle performance deteriorates and the rate performance decreases.

[0099] Through research and analysis, it is found that the deterioration of battery performance may be caused by the phenomenon of unbalanced insertion and extraction of active ions on the surface of the active material film layer and the active material film layer close to the cathode current collector.

[0100] Further analysis reveals that during the charge and discharge process, due to the existence of interfacial side reactions in lithium-ion batteries, the electrolyte will continuously decompose at the interfaces of the positive and negative electrodes, and phase transformation will occur at the interface of the cathode active material, resulting in the loss of active Li and the increase of the impedance of the lithium-ion battery, leading to the reduction of the performance of the cathode electrode in the battery. It is necessary to develop a cathode electrode with a high specific capacity, excellent cycle performance and rate performance to meet the application needs of the new generation of electrochemical systems.

[0101] Based on this, the present application provides a cathode electrode with a high specific capacity per gram and cycle stability, which can effectively improve the energy density and cycle performance of the battery when applied to the battery.

[0102] The following will detail the specific embodiments of the present application.

[0103] Positive electrode plate

[0104] In the first aspect, an embodiment of the present application provides a cathode electrode, including:

[0105] A cathode current collector;

[0106] A first cathode active material film layer disposed on at least one side of the cathode current collector, the first cathode active material film layer including solid first cathode active material particles;

[0107] A second cathode active material film layer disposed between the first cathode active material film layer and the cathode current collector, the second cathode active material film layer including second cathode active material particles having a hollow structure.

[0108] The content of the solid first cathode active material particles in the first cathode active material film layer can reach 75% to 100%, and it is not necessary that each first cathode active material particle is 100% completely solid at the microscopic level.

[0109] In the embodiments of the present application, the solid first positive electrode active material particles refer to particles that are completely composed of substances, have no voids, or have voids within a range that is difficult to clearly detect. The entire particles of the solid first positive electrode active material particles are relatively homogeneous, and there are no obvious voids that can be clearly detected like a hollow structure.

[0110] In the embodiments of the present application, the solid first positive electrode active material particles can be polycrystalline particles with a relatively large average particle size. Polycrystalline particles are particles composed of multiple crystal grains. A crystal is a structure of atoms or molecules arranged in an orderly manner, and a polycrystal has many small crystal grains that may be arranged in different directions or angles. Generally speaking, polycrystalline particles are large particles such as secondary particles. Secondary particles can be understood as particles after the aggregation of positive electrode active materials. In the present application, the primary particles and secondary particles have the meanings well-known in the art. Among them, the primary particles refer to non-aggregated particles; the secondary particles refer to aggregated particles formed by the aggregation of two or more primary particles. The primary particles and secondary particles can be easily distinguished by taking SEM images using a scanning electron microscope.

[0111] The secondary particles can be tested by any means well-known in the art. As an example, after imaging with a scanning electron microscope at 500 times magnification, randomly select 200 to 600 secondary particles of the positive electrode active material with complete shapes and no occlusion in its electron micrograph, and record the average value of the longest diameter of the primary particles in the micrograph as the average particle size.

[0112] In the embodiments of the present application, the term "hollow" refers to a solid structure surrounded by an obvious shell layer with a cavity inside. In the embodiments of the present application, the term "hollow structure" refers to a structure with a hollow part or a central pore. A hollow structure is usually surrounded by a solid outer shell or wall, and the inside is hollow. In the embodiments of the present application, the hollow structure can be composed of polycrystalline particles with a relatively large average particle size, or can be polycrystalline particles smaller than the solid particles, and it can be secondary particles. As an example, the micrograph of the second positive electrode active material particles is as Figure 1 shown.

[0113] According to the embodiments of the present application, the positive electrode sheet containing the embodiments of the present application improves the discharge specific capacity and stability of the positive electrode sheet during the charge and discharge process of the battery, and shortens the charging time of the positive electrode sheet in the battery.

[0114] The possible reasons for the analysis are as follows: During the mass transfer process of the electrolyte, the concentration of active ions gradually decreases from the separator to the vicinity of the positive electrode current collector on the positive electrode plate. The first positive electrode active material particles in the first positive electrode active material film layer are solid particles, and the insertion and extraction distance of active ions in the first positive electrode active material film layer is relatively long (the mass transfer distance is relatively long); the second positive electrode active material film layer contains second positive electrode active material particles with a hollow structure. The second positive electrode active material particles with a hollow structure reduce the insertion and extraction distance of active ions in the second positive electrode active material film layer (the mass transfer distance is relatively short), which is beneficial to the balance of the insertion and extraction speeds of active ions in the first positive electrode active material film layer and the second positive electrode active material film layer respectively, and balances the difference in the charge and discharge (SOC) speeds of active ions between the first positive electrode active material film layer and the second positive electrode active material film layer.

[0115] In addition, the second positive electrode active material particles have a hollow structure, which is beneficial to the existence of the second positive electrode active material particles in the positive electrode plate, disperses the stress during the cycling process of the positive electrode plate, improves the cycling stability of the positive electrode plate, is beneficial to further improving the cycling performance of the battery, and thus can reduce the fragmentation of the positive electrode active particles, improve the interfacial performance, and improve the overvoltage cracking and brittleness problems of the positive electrode plate.

[0116] In some embodiments, the first positive electrode active material particles and the second positive electrode active material particles are respectively nickel-containing positive electrode active particles.

[0117] In the related art, when nickel-containing positive electrode active particles are applied to a battery, taking a lithium battery as an example, for example, Ni 2+ The ionic radius is similar to that of Li + As a result, the phenomenon of cation mixing will occur seriously, causing the electrochemical performance of the lithium-containing ternary positive electrode active material to decline. Especially in a high-nickel system, the tendency of cation mixing increases, and the cycling performance of the battery deteriorates.

[0118] According to the embodiments of the present application, the first positive electrode active material film layer contains solid first positive electrode active material particles, and the second positive electrode active material film layer contains hollow particles, which improves the discharge specific capacity and stability of the positive electrode plate and improves the cycling performance of the positive electrode plate in the battery. The possible reasons for the analysis are as follows: The distance for lithium ions to transfer protons is shortened. Generally, the lithium ion concentration in the first positive electrode active material film layer is high, but the solid-state mass transfer distance of lithium ions is longer. The lithium ion concentration in the second positive electrode active material film layer is low, but the solid-state mass transfer time is shorter, which balances the difference in the insertion and extraction of active lithium ions between the active material particles in the positive electrode plate, is beneficial to the exertion of the specific capacity of the positive electrode plate, and improves the utilization rate of the active material particles in the positive electrode plate.

[0119] In some optional embodiments, the average particle size Dv of the first positive electrode active material particles 150 is greater than or equal to the average particle size Dv of the second positive electrode active material particles 2 50.

[0120] According to an embodiment of the present application, the average particle size Dv of the first positive electrode active material particles 1 50 and the average particle size Dv of the second positive electrode active material particles 2 The ratio of 50 is in the above range, which is beneficial to increasing the mass transfer distance of the first positive electrode active material particles in the first positive electrode active material film layer, reducing the mass transfer distance of the second positive electrode active material particles in the second positive electrode active material film layer, thereby dealing with the phenomenon that the active ion concentration in the first positive electrode active material film layer is relatively high and the active ion concentration in the second positive electrode active material film layer is relatively low, balancing the active ion insertion / extraction speed of the two layers, and thus improving the specific capacity and cycle performance of the positive electrode sheet.

[0121] In addition, the average particle size Dv of the first positive electrode active material particles 1 50 is relatively large, which is beneficial to increasing the porosity of the first positive electrode active material film layer, and thus beneficial to the first positive electrode active material particles existing in the positive electrode sheet, dispersing the stress of the first positive electrode active material particles in the positive electrode sheet during the cycling process, and improving the cycle stability of the positive electrode sheet, which is beneficial to further improving the cycle performance of the battery.

[0122] In some optional embodiments, the average particle size Dv of the first positive electrode active material particles 1 50 is 8 μm to 18 μm, and may be optionally 8 μm to 12 μm.

[0123] Optionally, the average particle size Dv of the first positive electrode active material particles 1 50 may be any value among 8 μm, 9 μm, 10 μm, 11 μm, 12 μm, 13 μm, 14 μm, 15 μm, 16 μm, 17 μm, 18 μm or a range composed thereof.

[0124] According to an embodiment of the present application, the average particle size Dv of the first positive electrode active material particles 1 50 is in the above range, which is beneficial to increasing the mass transfer distance of the first positive electrode active material particles in the first positive electrode active material film layer, thereby dealing with the phenomenon that the active ion concentration in the first positive electrode active material film layer is relatively high, balancing the active ion insertion / extraction speed of the two layers, and thus improving the specific capacity and cycle performance of the positive electrode sheet.

[0125] In some optional embodiments, the average particle size Dv of the second positive electrode active material particles 2 50 is 2 μm to 10 μm, and may be optionally 3 μm to 8 μm.

[0126] Optionally, the average particle size Dv of the second positive electrode active material particles 2 50 can be any value among 2μm, 3μm, 4μm, 5μm, 6μm, 7μm, 8μm, 9μm, 10μm or a range composed thereof.

[0127] According to an embodiment of the present application, the average particle size Dv of the second positive electrode active material particles 2 50 within the above range is beneficial to reducing the mass transfer distance of the second positive electrode active material particles in the second positive electrode active material film layer, thereby coping with the phenomenon that the active ion concentration in the first positive electrode active material film layer is relatively high and the active ion concentration in the second positive electrode active material film layer is relatively low, and balancing the active ion insertion / extraction rates of the two layers, so as to improve the specific capacity and cycling performance of the positive electrode plate.

[0128] In some alternative embodiments, the span of the particle size distribution of the first positive electrode active material particles is 0.3 - 0.7.

[0129] Optionally, the span of the particle size distribution of the first positive electrode active material particles can be any value among 0.3, 0.35, 0.4, 0.45, 0.5, 0.55, 0.6, 0.65, 0.7 or a range composed thereof.

[0130] According to an embodiment of the present application, the span of the particle size distribution of the first positive electrode active material particles within the above range can improve the tap density of the material, can improve the discharge capacity of the battery, balance the active ion insertion / extraction rates of the two layers, so as to improve the specific capacity and cycling performance of the positive electrode plate.

[0131] In some alternative embodiments, the span of the particle size distribution of the second positive electrode active material particles is 0.9 - 1.3.

[0132] Optionally, the span of the particle size distribution of the second positive electrode active material particles can be any value among 0.9, 0.95, 1.0, 1.05, 1.10, 1.15, 1.20, 1.25, 1.30 or a range composed thereof.

[0133] According to an embodiment of the present application, the span of the particle size distribution of the second positive electrode active material particles within the above range can improve the tap density of the material, can improve the discharge capacity of the battery, balance the active ion insertion / extraction rates of the two layers, so as to improve the specific capacity and cycling performance of the positive electrode plate.

[0134] In any embodiment of the present application, the calculation method of the span (SPAN) of the particle size distribution is (Dv90 - Dv10) / Dv50, which represents the particle distribution of the positive electrode active material, where D v50 represents the particle size at which the positive electrode active material reaches 50% cumulative volume in the volume-based particle size distribution; Dv10 represents the particle size at which the positive electrode active material reaches 10% cumulative volume in the volume-based particle size distribution; Dv90 represents the particle size at which the positive electrode active material reaches 90% cumulative volume in the volume-based particle size distribution.

[0135] In this application, the volume average particle size D of the negative electrode active material v 50, Dv10, Dv90 / particle size distribution span (D v 90 - D v 10) / D v 50 all have meanings well-known in the art and can be measured using instruments and methods known in the art. For example, it can be measured by referring to GB / T 19077-2016 laser diffraction method for particle size distribution, using a laser particle size analyzer (such as Master Size 3000).

[0136] In some alternative embodiments, the inner diameter d1 of the hollow structure is 0.6 μm to 5 μm, and can be optionally 0.9 μm to 4 μm.

[0137] Optionally, the inner diameter d1 of the hollow structure can be any value among 0.6 μm, 0.7 μm, 0.8 μm, 0.9 μm, 1.0 μm, 1.5 μm, 2 μm, 2.5 μm, 3 μm, 3.5 μm, 4 μm, 4.5 μm, 5 μm or a range composed thereof. In the embodiments of this application, the term "inner diameter of the hollow structure" refers to the longest diameter of the circular or quasi-circular cross-section of the internal cavity of the second positive electrode active material particles (positive electrode active material).

[0138] According to the embodiments of this application, the second positive electrode active material particles have a hollow structure, which can buffer the volume change of the second positive electrode active material particles during charge and discharge, playing a role in stabilizing the structure and improving the cycle performance. On the other hand, there are many three-dimensional pores in the second positive electrode active material particles, which expands the contact area between the material and the electrolyte and shortens the migration distance of lithium ions, thereby increasing the speed of active ions in the second positive electrode active material film layer, being beneficial to reducing the internal resistance of the battery, and the battery has excellent rate performance. At the same time, the second positive electrode active material particles have a hollow structure, thus having more active sites for lithium ions, enhancing the specific capacity of the material, increasing the specific capacity of the positive electrode sheet, and increasing the energy density of the battery.

[0139] The inner diameter of the hollow structure can be measured by any means well-known in the art. As an example, conductive adhesive is pasted on the sample stage, and a powdery sample of the positive electrode active material is laid flat on the conductive adhesive. The unadhered powder is blown away with an ear bulb, gold is sprayed, and argon plasma is used to cut the cross-section of the powdery sample particles. Using a scanning electron microscope under the conditions of an acceleration voltage of 10 kV and an emission current of 10 mA, a scanning electron microscope photograph of the powdery sample is obtained. According to the scanning electron microscope photograph, the inner diameter size of the hollow structure is measured. At least three samples are measured, and at least 50 groups of data are measured for each sample. The average value of the data is taken as the inner diameter size of the hollow structure of the sample.

[0140] In some alternative embodiments, the outer wall thickness d2 of the hollow structure is 0.6 μm to 10 μm, and may be optionally 0.9 μm to 7 μm.

[0141] Optionally, the outer wall thickness d2 of the hollow structure can be any value among 0.6 μm, 0.7 μm, 0.8 μm, 0.9 μm, 1.0 μm, 1.5 μm, 2.0 μm, 2.5 μm, 3 μm, 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm or a range composed of them.

[0142] In the embodiments of the present application, controlling the outer wall thickness d2 of the hollow structure within a suitable range can improve the structural stability of the hollow structure, increase the specific capacity per gram of the material in the positive electrode sheet, improve the energy density, rate performance and cycling performance of the battery, and comprehensively improve the electrochemical performance of the battery.

[0143] In this article, the term "outer wall thickness of the hollow structure" refers to the thickness of the outer shell layer of the hollow structure (the second positive electrode active material particles).

[0144] The outer wall thickness of the hollow structure can be measured by any means well-known in the art. As an example, conductive adhesive is pasted on the sample stage, and a powdery sample of the second positive electrode active material particles is laid flat on the conductive adhesive. The unadhered powder is blown away with an ear bulb, gold is sprayed, and argon plasma is used to cut the cross-section of the powdery sample particles. Using a scanning electron microscope under the conditions of an acceleration voltage of 10 kV and an emission current of 10 mA, a scanning electron microscope photograph of the powdery sample is obtained. According to the scanning electron microscope picture, the outer wall thickness of the hollow structure is measured. At least three samples are measured, and at least 50 groups of data are measured for each sample. The average value of the data is taken as the outer wall thickness of the hollow structure of the sample.

[0145] Dv of the second positive electrode active material particles 2 50. The inner diameter d1 and the outer wall thickness d2 of the hollow structure are important parameters of the hollow structure / second positive electrode active material particles, which affect the structural performance of the material. Dv of the second positive electrode active material particles 250. When the inner diameter d1 and the outer wall thickness d2 of the hollow structure are within a suitable range, the material has more active sites for lithium ions, which can improve the specific capacity of the material per gram, thereby increasing the specific capacity of the material. At the same time, the structural stability of the material can be improved. When it is applied to a lithium battery for charge and discharge cycling, the phenomenon of lithium-nickel mixing is effectively improved, and the migration rates of lithium ions and electrons are significantly increased, which is beneficial to the balance of the insertion and extraction speed of active ions in the positive electrode sheet of the battery, thereby improving the stability of the battery.

[0146] In some alternative embodiments, the specific surface area of the first positive electrode active material particles is 0.1 m 2 / g - 0.5 m 2 / g, and may be optionally 0.2 m 2 / g - 0.3 m 2 / g.

[0147] Optionally, the specific surface area of the first positive electrode active material particles can be 0.1 m 2 / g, 0.15 m 2 / g, 0.2 m 2 / g, 0.25 m 2 / g, 0.3 m 2 / g, 0.35 m 2 / g, 0.4 m 2 / g, 0.45 m 2 / g, 0.5 m 2 / g or any value within the range composed thereof.

[0148] In some alternative embodiments, the specific surface area of the second positive electrode active material particles is 0.35 m 2 / g - 0.8 m 2 / g, and may be optionally 0.4 m 2 / g - 0.6 m 2 / g.

[0149] Optionally, the specific surface area of the second positive electrode active material particles can be 0.4 m 2 / g, 0.45 m 2 / g, 0.5 m 2 / g, 0.55 m 2 / g, 0.6 m 2 / g, 0.65 m 2 / g, 0.7 m 2 / g, 0.75 m 2 / g, 0.8 m 2 / g or any value within the range composed thereof.

[0150] The specific surface areas of the first positive electrode active material particles and the second positive electrode active material particles have the meanings well-known in the art and can be measured by instruments and methods well-known in the art. For example, they can be tested by the nitrogen adsorption specific surface area analysis test method and calculated by the BET (Brunauer Emmett Teller) method. Among them, the nitrogen adsorption specific surface area analysis can be carried out by a Tri Star Ⅱ specific surface area and pore size analyzer of Micromeritics Company in the United States.

[0151] According to the embodiments of the present application, the specific surface areas of the first positive electrode active material particles and the second positive electrode active material particles are respectively within the above ranges, indicating that the first positive electrode active material film layer can accommodate more active ions, and the second positive electrode active material film layer can accommodate relatively fewer active ions, which is beneficial to balancing the insertion and extraction rates of active ions in the two layers, thereby improving the specific capacity per gram and the cycling performance of the positive electrode sheet.

[0152] In some optional embodiments, the tapped density of the first positive electrode active material particles is 1.8 g / cm 3 - 4 g / cm 3 , and can be optionally 2 g / cm 3 - 3 g / cm 3 .

[0153] Optionally, the tapped density of the first positive electrode active material particles can be 1.8 g / cm 3 , 1.85 g / cm 3 , 1.9 g / cm 3 , 1.95 g / cm 3 , 2.0 g / cm 3 , 2.05 g / cm 3 , 2.1 g / cm 3 , 2.15 g / cm 3 , 2.2 g / cm 3 , 2.25 g / cm 3 , 2.3 g / cm 3 , 2.35 g / cm 3 , 2.4 g / cm 3 , 2.45 g / cm 3 , 2.5 g / cm 3 , 2.55 g / cm 3 , 2.6 g / cm 3 , 2.65 g / cm 3 , 2.7 g / cm 3 , 2.75 g / cm 3 , 2.8 g / cm 3 , 2.85 g / cm 3 , 2.9 g / cm3 , 2.95 g / cm 3 , 3.0 g / cm 3 , 3.05 g / cm 3 , 3.1 g / cm 3 , 3.15 g / cm 3 , 3.2 g / cm 3 , 3.25 g / cm 3 , 3.3 g / cm 3 , 3.35 g / cm 3 , 3.4 g / cm 3 , 3.45 g / cm 3 , 3.5 g / cm 3 , 3.55 g / cm 3 , 3.6 g / cm 3 , 3.65 g / cm 3 , 3.7 g / cm 3 , 3.75 g / cm 3 , 3.8 g / cm 3 , 3.85 g / cm 3 , 3.9 g / cm 3 , 3.95 g / cm 3 , 4 g / cm 3 any value within or the range composed of them.

[0154] In some alternative embodiments, the tap density of the second positive electrode active material particles is 1.3 g / cm 3 - 2.6 g / cm 3 , optionally 1.5 g / cm 3 - 1.8 g / cm 3 .

[0155] Optionally, the tap density of the second positive electrode active material particles can be 1.3 g / cm 3 , 1.35 g / cm 3 , 1.4 g / cm 3 , 1.45 g / cm 3 , 1.5 g / cm 3 , 1.55 g / cm 3 , 1.6 g / cm 3 , 1.65 g / cm 3 , 1.7 g / cm 3 , 1.75 g / cm 3 , 1.8 g / cm 3 , 1.85 g / cm 3 , 1.9 g / cm 3 , 1.95 g / cm 3 , 2.0 g / cm3 , 2.05 g / cm 3 , 2.1 g / cm 3 , 2.15 g / cm 3 , 2.2 g / cm 3 , 2.25 g / cm 3 , 2.3 g / cm 3 , 2.35 g / cm 3 , 2.4 g / cm 3 , 2.45 g / cm 3 , 2.5 g / cm 3 , 2.55 g / cm 3 , 2.6 g / cm 3 Any value within or the range composed of them.

[0156] According to the embodiments of the present application, the specific surface area of the first positive electrode active material particles and the tap density of the second positive electrode active material particles are respectively within the above ranges, indicating that the first positive electrode active material film layer can accommodate more active ions, and the second positive electrode active material film layer can accommodate relatively fewer active ions, which is beneficial to balancing the insertion and extraction rates of active ions in the two layers, thereby improving the specific capacity and cycling performance of the positive electrode sheet.

[0157] The tap density of the first positive electrode active material particles and the second positive electrode active material particles can be measured by instruments and methods well-known in the art. For example, it can be conveniently measured with a tap density tester, such as the FZS4-4B type tap density tester.

[0158] In some alternative embodiments, the second positive electrode active material film layer contains third positive electrode active material particles, and the average particle size D V 2 50 of the second positive electrode active material particles and the average particle size D V 3 50 of the third positive electrode active material particles has a ratio of (1.5 - 9):1.

[0159] In the embodiments of the present application, the third positive electrode active material particles can be particles with a relatively smaller average particle size compared to the second positive electrode active material particles. The third positive electrode active material particles can be single crystal particles. A single crystal particle refers to a particle with a completely uniform crystal structure, and the atoms, molecules or ions within the entire particle are arranged in an orderly manner in the same direction, without grain boundaries or other types of crystallization defects. The third positive electrode active material particles can be primary particles.

[0160] A primary particle usually refers to the most basic particle unit in a multi-particle system. A primary particle can be a tiny particle or a cluster of particles. It refers to the particle before the positive electrode active material agglomerates.

[0161] The primary particle size of the positive electrode active material can be measured by any means well-known in the art. As an example, after imaging with a scanning electron microscope at 500 times magnification, 200 to 600 primary particles of the positive electrode active material with complete shapes and no occlusion are randomly selected in its electron micrograph, and the average value of the longest diameter of the primary particles in the micrograph is recorded as the average particle size.

[0162] In the embodiments of the present application, the average particle size D of the second positive electrode active material particles is controlled V 2 50 and the average particle size D of the third positive electrode active material particles V 3 When the ratio of 50 is within the above range, the third positive electrode active material particles are combined with the second positive electrode active material particles, which is beneficial to increasing the mass transfer distance of the second positive electrode active material film layer, increasing the speed of insertion and extraction of active ions in the second positive electrode active material film layer, balancing the difference in charge and discharge speeds (SOC difference) between the first active material film layer and the second active material film layer, and is beneficial to the utilization of the specific capacity.

[0163] In some alternative embodiments, the average particle size D of the third positive electrode active material particles V 3 50 is from 0.8 μm to 5 μm, and can be optionally from 2 μm to 5 μm.

[0164] According to the embodiments of the present application, when the average particle size D of the third positive electrode active material particles V 3 is within the above range, its particle size is relatively small and its anisotropy is smaller. At this time, the volume expansion rate of the third positive electrode active material particles during charge and discharge in the battery is relatively low, making the cycle stability of the third positive electrode active material particles better, which can further improve the overall cycle stability of the positive electrode sheet and further improve the cycle performance of the battery.

[0165] In some alternative embodiments, the specific surface area of the third positive electrode active material particles is 0.4 m 2 / g - 0.9 m 2 / g, and can be optionally 0.6 m 2 / g - 0.8 m 2 / g.

[0166] According to the embodiments of the present application, when the specific surface area of the third positive electrode active material particles is within the above range, it is beneficial to control the specific surface area and the compaction density of the second positive electrode active material film layer, improve the cycle stability of the positive electrode sheet, and further improve the cycle performance of the battery.

[0167] The specific surface areas of the first positive electrode active material particles, the second positive electrode active material particles, and the second positive electrode active material particles can be measured by any means well-known in the art. As an example, reference can be made to GB / T 19587-2017 "Determination of Specific Surface Area of Solid Materials by Gas Adsorption BET Method". The measurement is carried out using the equipment TriStar II 3020. The positive electrode active material is dispersed into a dispersant (ethanol), and after ultrasonic treatment for 30 minutes, the obtained material is dried in a vacuum drying oven, and finally the specific surface area of the positive electrode active material is measured using a specific surface area tester.

[0168] The larger the specific surface areas of the first positive electrode active material particles, the second positive electrode active material particles, and the second positive electrode active material particles, the more active sites there are in the positive electrode active material, the faster the exchange rate between the positive electrode active material and electrons, and the better the kinetic performance of the battery. However, too many active sites will increase the side reactions between the positive electrode active material and the electrolyte, deteriorating the cycle performance of the battery, and too few active sites will lead to a decrease in chemical reactions in the battery system, resulting in poor battery capacity and cycle performance.

[0169] By controlling the specific surface areas of the first positive electrode active material particles, the second positive electrode active material particles, and the second positive electrode active material particles within a suitable range, the battery has a high discharge capacity and energy density, excellent rate performance and cycle performance, comprehensively improving the electrochemical performance of the battery.

[0170] In some alternative embodiments, the tap density of the third positive electrode active material particles is 1.8 g / cm 3 -3.4 g / cm 3 , and can be optionally 2 g / cm 3 -2.2 g / cm 3 .

[0171] According to the embodiments of the present application, when the tap density of the third positive electrode active material particles is within the above range, it is beneficial to control the compaction density of the second positive electrode active material film layer, improve the cycle stability of the positive electrode plate, and further improve the cycle performance of the battery.

[0172] In some alternative embodiments, the third positive electrode active material particles are one or more of particles with a hollow structure and solid particles.

[0173] In some alternative embodiments, the particle size distribution span of the third positive electrode active material particles is 0.8 - 1.5.

[0174] According to the embodiments of the present application, when the particle size distribution span of the third positive electrode active material particles is within the above range, it is beneficial to increase the compaction density of the second active material film layer, balance the active ion deintercalation rate of the two layers, improve the stability of the positive electrode plate, and thus improve the specific capacity and cycle performance of the positive electrode plate.

[0175] The Dv50 of the first positive electrode active material particles, the second positive electrode active material particles, and the third positive electrode active material particles has the meaning well-known in the art, that is, the particle size corresponding to when the cumulative particle size distribution reaches 50% based on volume, and can be detected by known methods. For example, using a laser diffraction particle size distribution analyzer (Malvern Mastersizer 3000), according to the laser diffraction method for particle size distribution GB / T19077-2016, the particle size distribution is measured to obtain Dv50. Dv10 represents the particle size at which the positive electrode active material reaches 10% of the cumulative volume in the particle size distribution based on volume starting from the small particle size side; Dv90 represents the particle size at which the positive electrode active material reaches 90% of the cumulative volume in the particle size distribution based on volume starting from the small particle size side. As an example, reference can be made to the laser diffraction method for particle size distribution GB / T 19077-2016 / ISO 13320:2009, and the measurement is carried out using the equipment Malvern 3000.

[0176] The particle size distribution span (SPAN) of the first positive electrode active material particles, the second positive electrode active material particles, and the third positive electrode active material particles has the meaning well-known in the art. The calculation method of the particle size distribution span (SPAN) is (Dv90 - Dv10) / Dv50, which represents the particle distribution of the positive electrode active material, where Dv50 represents the particle size at which the positive electrode active material reaches 50% of the cumulative volume in the particle size distribution based on volume starting from the small particle size side; Dv10 represents the particle size at which the positive electrode active material reaches 10% of the cumulative volume in the particle size distribution based on volume starting from the small particle size side; Dv90 represents the particle size at which the positive electrode active material reaches 90% of the cumulative volume in the particle size distribution based on volume starting from the small particle size side.

[0177] According to the above definition, referring to the method specified in GB / T19077-2016, the Dv50, Dv10, and Dv90 values of the positive electrode active material are measured, and then the SPAN of the positive electrode active material is calculated. In any embodiment of the present application, the term "positive electrode active material" may include one or several of the first positive electrode active material particles, the second positive electrode active material particles, and the third positive electrode active material particles.

[0178] Maintaining the SPAN within a relatively wide range can increase the tap density of the material and can increase the discharge capacity of the battery.

[0179] In some alternative embodiments, the ratio of the thickness h1 of the first positive electrode active material film layer to the thickness h2 of the second positive electrode active material film layer is 10:(5 - 23.5).

[0180] Optionally, the ratio of the thickness h1 of the first positive electrode active material film layer to the thickness h2 of the second positive electrode active material film layer can be any value among 10:5, 10:5.5, 10:6, 10:6.5, 10:7, 10:7.5, 10:8, 10:8.5, 10:9, 10:9.5, 10:10, 10:10.5, 10:11, 10:11.5, 10:12, 10:12.5, 10:13, 10:13.5, 10:14, 10:14.5, 10:15, 10:15.5, 10:16, 10:16.5, 10:17, 10:17.5, 10:18, 10:18.5, 10:19, 10:19.5, 10:20, 10:20.5, 10:21, 10:21.5, 10:22, 10:22.5, 10:23, 10:23.5 or the range composed of them.

[0181] According to the embodiments of the present application, by controlling the ratio of the thickness h1 of the first positive electrode active material film layer to the thickness h2 of the second positive electrode active material film layer within the above range, it is beneficial to balance the deintercalation rate of active ions in the two active material film layers, improve the stability of the positive electrode sheet, and thus improve the specific capacity and cycle performance of the positive electrode sheet.

[0182] In some optional embodiments, the thickness h1 of the first positive electrode active material film layer is 130 - 200 μm.

[0183] Optionally, the thickness h1 of the first positive electrode active material film layer can be any value among 130 μm, 135 μm, 140 μm, 145 μm, 150 μm, 155 μm, 160 μm, 165 μm, 170 μm, 175 μm, 180 μm, 185 μm, 190 μm, 195 μm, 200 μm or the range composed of them.

[0184] In some optional embodiments, the thickness h2 of the second positive electrode active material film layer is 50 - 170 μm.

[0185] Optionally, the thickness h2 of the second positive electrode active material film layer can be any value among 50 μm, 55 μm, 60 μm, 65 μm, 70 μm, 75 μm, 80 μm, 85 μm, 90 μm, 95 μm, 100 μm, 105 μm, 110 μm, 115 μm, 120 μm, 125 μm, 130 μm, 135 μm, 140 μm, 145 μm, 150 μm, 155 μm, 160 μm, 165 μm, 170 μm or the range composed of them.

[0186] The thickness h1 of the first positive electrode active material film layer and the thickness h2 of the second positive electrode active material film layer can be detected by common detection methods in the art. The positive electrode plate is cut along the thickness direction and polished to obtain a smooth cross-section. The thickness h1 of the first positive electrode active material film layer and the thickness h2 of the second positive electrode active material film layer of the positive electrode plate are measured by a scanning electron microscope. At least three samples are measured, and at least 50 data are measured for each sample. The average value of the data is taken as the thickness h1 of the first positive electrode active material film layer and the thickness h2 of the second positive electrode active material film layer of the sample.

[0187] In some alternative embodiments, the ratio of the thickness h1 of the first positive electrode active material film layer to the sum of the masses of the first positive electrode active material film layer and the second positive electrode active material film layer is 1.2 - 2 μm / g.

[0188] Optionally, the ratio of the thickness h1 of the first positive electrode active material film layer to the sum of the masses of the first positive electrode active material film layer and the second positive electrode active material film layer can be any value among 1.2 μm / g, 1.3 μm / g, 1.4 μm / g, 1.5 μm / g, 1.6 μm / g, 1.7 μm / g, 1.8 μm / g, 1.9 μm / g, 2.0 μm / g or a range composed of them.

[0189] According to the embodiments of the present application, controlling the ratio of the thickness h1 of the first positive electrode active material film layer to the sum of the masses of the first positive electrode active material film layer and the second positive electrode active material film layer within the above range is beneficial to controlling and balancing the intercalation and deintercalation rates of active ions in the first positive electrode active material film layer and the second positive electrode active material film layer, beneficial to the capacity utilization of the positive electrode plate, and thus beneficial to the cycle performance of the battery.

[0190] The ratio of the thickness h1 of the first positive electrode active material film layer to the sum of the masses of the first positive electrode active material film layer and the second positive electrode active material film layer can be detected by common methods in the art. A prepared positive electrode plate can be taken and weighed with its mass being M. The first positive electrode active material film layer and the second positive electrode active material film layer in the positive electrode plate are removed in an organic solvent such as ethanol or acetone to obtain a smooth positive electrode current collector. The organic solvent is removed, and the mass of the positive electrode current collector is weighed as M1. The ratio of the thickness h1 of the first positive electrode active material film layer to the sum of the masses of the first positive electrode active material film layer and the second positive electrode active material film layer = M - M1. At least three positive electrode plate samples can be measured, and at least 50 data are measured for each sample. The average value of the data is taken.

[0191] In some alternative embodiments, the porosity of the first positive electrode active material film layer is greater than the porosity of the second positive electrode active material film layer; optionally, the porosity of the first positive electrode active material film layer is 26% - 50%; optionally, the porosity of the second positive electrode active material film layer is 30% - 40%.

[0192] In this text, "porosity" refers to the ratio of the pore volume in the first positive electrode active material film layer to the total volume of the first positive electrode active material film layer or the ratio of the pore volume in the second positive electrode active material film layer to the total volume of the second positive electrode active material film layer.

[0193] The porosity of the first positive electrode active material film layer and the porosity of the second positive electrode active material film layer can be measured by any means well-known in the art. As an example, according to GB / T24586, the gas displacement method is used for measurement. Porosity = (V1 - V2) / V1×100%, where V1 is the apparent volume of the sample and V2 is the true volume of the sample.

[0194] In some alternative embodiments, the tap density of the first positive electrode active material film layer is less than the tap density of the second positive electrode active material film layer; optionally, the tap density of the first positive electrode active material film layer is 2.9 g / cm 3 - 3.3 g / cm 3 ; optionally, the tap density of the second positive electrode active material film layer is 3.2 g / cm 3 - 3.7 g / cm 3 .

[0195] The tap density of the first positive electrode active material film layer and the second positive electrode active material film layer can be determined by instruments and methods well-known in the art. For example, it can be conveniently determined by an electronic pressure testing machine, such as the UTM7305 type electronic pressure testing machine. The tap density of the positive electrode sheet can be calculated by the formula PD = M / (d×A). In the above formula, M is the mass of a small disc with a diameter of 40 mm, which can be obtained by taking the average value of 10 weighings; d is the thickness of the cold-pressed positive electrode sheet, and the value can be obtained by cutting the positive electrode sheet into small discs with a diameter of 40 mm and measuring the thickness respectively and taking the average value; A is the area of the 40 mm small disc.

[0196] In some alternative embodiments, the ratio of the capacities of the first positive electrode active material film layer and the second positive electrode active material film layer satisfies 1:(0.9 - 1.05); optionally, the specific capacity of the first positive electrode active material film layer is 225 mAh / g - 240 mAh / g; optionally, the specific capacity of the second positive electrode active material film layer is 220 mAh / g - 235 mAh / g.

[0197] Optionally, the ratio of the capacities of the first positive electrode active material film layer and the second positive electrode active material film layer can be any value among 1:0.9, 1:1.0, 1:1.01, 1:1.02, 1:1.03, 1:1.04, 1:1.05 or the range composed of them.

[0198] According to the embodiments of the present application, after detecting the charge and discharge cycles of the positive electrode plate in the button cell / battery cell, the ratio of the capacities of the first positive electrode active material film layer and the second positive electrode active material film layer is within the above range, which balances the deintercalation rate of the active ions in the first positive electrode active material film layer and the second positive electrode active material film layer, is beneficial to the capacity utilization of the positive electrode plate, and improves the utilization rate of the positive electrode active material.

[0199] The gram capacities of the first positive electrode active material film layer and the second positive electrode active material film layer can be tested by any means well-known in the art. As an example, a button cell can be prepared by sampling a fresh positive electrode plate, with a lithium sheet as the negative electrode. Under the conditions of 25°C and normal pressure, the button cell is charged at a constant current of 0.02C until the voltage reaches 3.5V, then charged at a constant current of 0.1C until the voltage reaches 4.3V, and then charged at a constant voltage of 4.3V until the current drops to 0.05C. Record the charging specific capacity at this time, which is the first de-lithiation capacity; then discharge at a constant current of 0.1C until the voltage reaches 2.5V, and record the discharge specific capacity at this time, which is the first lithium intercalation capacity. Then, another set of fresh positive electrode plates is used, and a button cell is prepared from the positive electrode plate after peeling off the first positive electrode active material film layer, with a lithium sheet as the negative electrode for detection, and record the charging specific capacity at this time, which is the first lithium intercalation capacity. As another example, batteries disassembled from the battery can also be used to obtain the first powder of the first positive electrode active material film layer and the second powder of the second positive electrode active material film layer respectively. The first powder and the second powder are prepared into fresh positive electrode plates containing the first positive electrode active material film layer and the second positive electrode active material film layer for detection.

[0200] In some alternative embodiments, the first positive electrode active material particles and the second positive electrode active material particles have the following structural general formula: Li a Ni x Co y M 1-x-y O2, where M includes one or more of Mn, Al, B, Zr, Sr, Y, Sb, W, Ti, Mg, Nb, Ba, 0.55 ≤ x ≤ 1.05, 0 ≤ y ≤ 0.45, 0.8 ≤ a ≤ 1.2.

[0201] In some embodiments, in Li a Ni x Co y M 1-x-y O2, a is any value among 0.8, 0.9, 1.0, 1.01, 1.02, 1.03, 1.04, 1.05 or the range composed of any two of these values.

[0202] In some embodiments, in Li a Ni x Co y M 1-x-yIn O2, x is any value among 0.55, 0.6, 0.7, 0.8, 0.9, 0.95, 0.995 or a range composed of any two of these values.

[0203] In some embodiments, Li a Ni x Co y M 1-x-y In O2, y is any value among 0, 0.1, 0.2, 0.3, 0.4, 0.45 or a range composed of any two of these values.

[0204] In some embodiments, Li a Ni x Co y M 1-x-y In O2, 0.90 ≤ x ≤ 1.0, 0 ≤ y ≤ 0.1, 0.8 ≤ a ≤ 1.2.

[0205] In some embodiments, Li a Ni x Co y M 1-x-y In O2, 0.95 ≤ x ≤ 0.995, 0 ≤ y ≤ 0.05, 0.8 ≤ a ≤ 1.2.

[0206] In some embodiments, Li a Ni x Co y Mn 1-x-y In O2, 0.95 ≤ x ≤ 0.995, 0 ≤ y ≤ 0.05, 0.8 ≤ a ≤ 1.2.

[0207] In some embodiments, Li a Ni x Co y Sb 1-x-y In O2, 0.95 ≤ x ≤ 0.995, 0 ≤ y ≤ 0.05, 0.8 ≤ a ≤ 1.2.

[0208] In some embodiments, Li a Ni x Co y In O2, 0.95 ≤ x ≤ 0.995, 0.005 ≤ y ≤ 0.05, x + y = 1, 0.8 ≤ a ≤ 1.2.

[0209] According to the embodiments of the present application, using the above materials can ensure that the second active material film layer has a high specific capacity, thereby improving the specific capacity of the positive electrode plate and enabling the battery to have a high discharge capacity and energy density.

[0210] In some alternative embodiments, the third positive electrode active material particles include the following structural general formula: Lia Ni x Co y M 1-x-y O₂, where M includes one or more of Mn, Al, B, Zr, Sr, Y, Sb, W, Ti, Mg, Nb, Ba, 0.55 ≤ x ≤ 1.05, 0 ≤ y ≤ 0.45, 0.8 ≤ a ≤ 1.2.

[0211] According to the embodiments of the present application, using the above materials can ensure that the second active material film layer has a high specific capacity, thereby increasing the specific capacity of the positive electrode plate, making the battery have a high discharge capacity and energy density.

[0212] In some alternative embodiments, the first positive electrode active material particles, the second positive electrode active material particles, and the third positive electrode active material particles respectively include LiNi 0.96 Co 0.02 Mn 0.01 Ba 0.01 O₂, LiNi 0.97 Co 0.01 Mn 0.01 Ba 0.01 O₂, LiNi 0.98 Co 0.01 Mn 0.005 Ba 0.005 O₂, any one or several of the above. The above positive electrode active materials can better balance the charge and discharge speed of the positive electrode plate in the battery, balance the average of the charging efficiency on its surface and on the side close to the positive electrode current collector, increase the specific capacity of the positive electrode plate, making the battery have a high discharge capacity and energy density.

[0213] In some embodiments, the positive electrode plate includes a positive electrode current collector and a positive electrode active material film layer provided on at least one surface of the positive electrode current collector, and the positive electrode active material film layer respectively includes the first positive electrode active material particles and the second positive electrode active material particles.

[0214] As an example, the positive electrode current collector has two surfaces opposite to each other in its own thickness direction, and the positive electrode active material film layer is provided on any one or both of the two opposite surfaces of the positive electrode current collector.

[0215] In some embodiments, the positive electrode current collector may be a metal foil or a composite current collector. For example, as the metal foil, aluminum foil may be used. The composite current collector may include a polymer material substrate and a metal layer formed on at least one surface of the polymer material substrate. The composite current collector may be formed by forming a metal material (such as aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy, etc.) on a polymer material substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0216] In some embodiments, the first positive electrode active material particles, the second positive electrode active material particles, and the third positive electrode active material particles may be positive electrode active materials for batteries known in the art. By way of example, the positive electrode active material may include at least one of the following materials: lithium phosphate with an olivine structure, lithium transition metal oxides, and their respective modified compounds. However, the present application is not limited to these materials, and other conventional materials that can be used as battery positive electrode active materials may also be used. These positive electrode active materials may be used alone or in combination of two or more. Among them, examples of lithium transition metal oxides may include, but are not limited to, lithium cobalt oxide (such as LiCoO2), lithium nickel oxide (such as LiNiO2), lithium manganese oxide (such as LiMnO2, LiMn2O4), lithium nickel cobalt oxide, lithium manganese cobalt oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide such as LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2 (which may also be abbreviated as NCM 333 ), LiNi 0.5 Co 0.2 Mn 0.3 O2 (which may also be abbreviated as NCM 523 ), LiNi 0.5 Co 0.25 Mn 0.25 O2 (which may also be abbreviated as NCM 211 ), LiNi 0.6 Co 0.2 Mn 0.2 O2 (which may also be abbreviated as NCM 622 ), LiNi 0.8 Co 0.1 Mn 0.1 O2 (which may also be abbreviated as NCM 811 ), lithium nickel cobalt aluminum oxide (such as LiNi 0.85 Co 0.15 Al 0.05at least one of O2) and its modified compounds, etc. Examples of the lithium-containing phosphate with olivine structure may include, but are not limited to, lithium iron phosphate (such as LiFePO4 (which can also be abbreviated as LFP)), a composite material of lithium iron phosphate and carbon, lithium manganese phosphate (such as LiMnPO4), a composite material of lithium manganese phosphate and carbon, lithium manganese iron phosphate, and a composite material of lithium manganese iron phosphate and carbon.

[0217] In some embodiments, the positive electrode active material film layer may also optionally include a binder. As an example, the binder may include at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorinated acrylate resin.

[0218] In some embodiments, the positive electrode active material film layer may also optionally include a conductive agent. As an example, the conductive agent may include at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0219] In some embodiments, the positive electrode plate can be prepared in the following manner: dispersing the components for preparing the positive electrode plate, such as the positive electrode active material, the conductive agent, the binder, and any other components, in a solvent (such as N-methylpyrrolidone) to form a positive electrode slurry; coating the positive electrode slurry on the positive electrode current collector, and after processes such as drying and cold pressing, the positive electrode plate can be obtained.

[0220] Method for preparing a positive electrode plate

[0221] In a second aspect, an embodiment of the present application provides a method for preparing a positive electrode plate, including:

[0222] Providing a second slurry containing second positive electrode active material particles having a hollow structure;

[0223] Coating the second slurry on the positive electrode current collector and forming a second positive electrode active material film layer;

[0224] Providing a first slurry containing first positive electrode active material particles being solid particles;

[0225] Coating the first slurry so as to form a first positive electrode active material film layer on the side of the second positive electrode active material film layer away from the positive electrode current collector, thereby obtaining the positive electrode plate.

[0226] According to an embodiment of the present application, a second slurry containing second positive electrode active material particles is coated on the positive electrode current collector to form a second positive electrode active material film layer, and a first slurry containing first positive electrode active material particles is coated so that a first positive electrode active material film layer is formed on the side of the second positive electrode active material film layer away from the positive electrode current collector. Thus, during the charge and discharge process of the battery with the positive electrode plate of the embodiment of the present application, due to the fact that the concentration of active ions gradually decreases from the separator to the part of the positive electrode plate close to the positive electrode current collector during the electrolyte mass transfer process, the first positive electrode active material particles in the first positive electrode active material film layer are solid particles, and the insertion and extraction distance of the active ions in the first positive electrode active material film layer is relatively long (the mass transfer distance is relatively long); the second positive electrode active material film layer contains second positive electrode active material particles with a hollow structure. The second positive electrode active material particles with a hollow structure reduce the insertion and extraction distance of the active ions in the second positive electrode active material film layer (the mass transfer distance is relatively short), which is beneficial to the balance of the insertion and extraction speeds of the active ions in the first positive electrode active material film layer and the second positive electrode active material film layer, balances the difference in the charge and discharge (SOC) speeds of the active ions between the first positive electrode active material film layer and the second positive electrode active material film layer, and is beneficial to the utilization of the specific capacity of the positive electrode plate.

[0227] The descriptions of the first positive electrode active material particles, the first positive electrode active material film layer, the second positive electrode active material particles, the second positive electrode active material film layer, and the third positive electrode active material particles in any implementation method of the first aspect are independently applicable to this embodiment.

[0228] In some optional implementation manners, the second slurry includes, by mass percentage, a mixture of 60%-90% of second positive electrode active material particles and 10%-40% of third positive electrode active material particles.

[0229] According to an embodiment of the present application, by controlling the mass contents of the second positive electrode active material particles and the third positive electrode active material particles in the second positive electrode active material film layer, on the basis of balancing the insertion and extraction speeds of the active ions in the first positive electrode active material film layer and the second positive electrode active material film layer, the structural stability of the positive electrode plate and the charge and discharge speed of the battery are taken into account.

[0230] Battery cell

[0231] In a third aspect, an embodiment of the present application provides a battery cell, including the positive electrode plate of the first aspect or the positive electrode plate prepared by the method of the second aspect. According to an embodiment of the present application, the battery cell includes the above-mentioned positive electrode plate, so the battery has the beneficial effects of the above-mentioned positive electrode plate.

[0232] Under normal circumstances, a battery includes a positive electrode plate, a negative electrode plate, an electrolyte, and a separator. During the charging and discharging process of the battery, active ions are embedded and extracted back and forth between the positive electrode plate and the negative electrode plate. The electrolyte plays a role in conducting ions between the positive electrode plate and the negative electrode plate. The separator is disposed between the positive electrode plate and the negative electrode plate, mainly to prevent short circuit between the positive and negative electrodes, and at the same time allows ions to pass through.

[0233] In some embodiments, the first positive electrode active material particles and the second positive electrode active material particles are nickel-containing positive electrode active materials. The positive electrode plate in the battery cell is charged from the initial state at 0.33C to the cut-off voltage of 4.25V, and discharged at 1C to the cut-off voltage of 2.7V for charge and discharge cycles until the capacity of the battery cell is 80% of the initial state.

[0234] In the XRD diffraction pattern of the first positive electrode active material particles and the second positive electrode active material particles, the ratio between the I 003 / I 104 value of the first positive electrode active material particles and the I 003 / I 104 value of the second positive electrode active material particles is (1 to 1.5):1.

[0235] According to the embodiments of the present application, the I 003 / I 104 value of the first positive electrode active material particles represents the ratio of the diffraction peak intensity I 003 of the (003) crystal plane of the first positive electrode active material particles to the diffraction peak intensity I 104 of the (104) crystal plane. The I 003 / I 104 value of the second positive electrode active material particles is the ratio of the diffraction peak intensity I 003 of the (003) crystal plane of the second positive electrode active material particles to the diffraction peak intensity I 104 of the (104) crystal plane.

[0236] According to the embodiments of the present application, by controlling the ratio between the I 003 / I 104 value of the first positive electrode active material particles and the I 003 / I 104 value of the second positive electrode active material particles within a suitable range, it is beneficial to control the lithium-nickel mixing situation of the first active material film layer and the second active material film layer, balance the rate of lithium ion insertion and extraction of the first active material film layer and the second active material film layer, and improve the performance of the battery.

[0237] As an example, the diffraction peak intensity I 003 of the (003) crystal plane of the first positive electrode active material particles and the diffraction peak intensity I 104Or the diffraction peak intensity I of the (003) crystal plane of the second positive electrode active material particles 003 and the diffraction peak intensity I of the (104) crystal plane 104 The detection method can be as follows: Disassemble the positive electrode plate from the battery, take the positive electrode plate with an area of 3*3 cm 2 to 4*4 cm 2 ; respectively take the film layer powders of the first positive electrode active material film layer and the second positive electrode active material film layer with a mass of 5-10 g. If the powders of the first positive electrode active material film layer and the second positive electrode active material film layer are block samples after scraping powder, grind them and make samples in a glove box. The average particle size of the prepared samples is <30 μm and can pass through a 200-mesh sieve; use a sample cell with a depth of 1 mm and a diameter of 25 mm for sampling, and use the flat sample preparation method to make samples. Then perform the test: the starting angle is 15°, the ending angle is 70°, the step size is 0.01°, and the duration of each step is 0.6 s. Among them, the fixed core parameters of the XRD detection equipment (such as the XRD detection equipment of Bruker Corporation in Germany): voltage: 40 KV, current: 40 mA, anti-scattering slit: 1 mm.

[0238] As an example, the structural general formulas of the first positive electrode active material particles, the second positive electrode active material particles, and the third positive electrode active material particles are each independently: Li a Ni x Co y M 1-x-y O2, where M includes one or more of Mn, Al, B, Zr, Sr, Y, Sb, W, Ti, Mg, Nb, Ba, 0.55 ≤ x ≤ 1.05, 0 ≤ y ≤ 0.45, 0.8 ≤ a ≤ 1.2. The diffraction angle 2θ1 of the (003) crystal plane of the first positive electrode active material particles is 18.55° to 18.85°, the diffraction angle 2θ2 of the (003) crystal plane of the second positive electrode active material particles is 18.85° to 19.00°, and the difference Δθ1 between the two is 0.20° to 0.30°; the diffraction angle 2θ3 of the (104) crystal plane of the first positive electrode active material particles is 44.30° to 44.50°, the diffraction angle 2θ4 of the (104) crystal plane of the second positive electrode active material particles is 45.10° to 45.30°, and the difference Δθ2 between the two is 0.65° to 0.85°; in the respective XRD diffraction patterns of the first positive electrode active material particles and the second positive electrode active material particles, the ratio of the diffraction peak intensity I of the (003) crystal plane to the diffraction peak intensity I of the (104) crystal plane of the first positive electrode active material particles and the diffraction peak intensity I of the (003) crystal plane of the second positive electrode active material particles 003 and the ratio of the diffraction peak intensity I of the (104) crystal plane 104 can be measured respectively. 003 and the ratio of the diffraction peak intensity I of the (104) crystal plane 104 of the second positive electrode active material particles.

[0239] Negative electrode plate

[0240] The negative electrode plate includes a negative electrode current collector and a negative electrode film layer provided on at least one surface of the negative electrode current collector. The negative electrode film layer includes a negative electrode active material.

[0241] As an example, the negative electrode current collector has two surfaces opposite to each other in its own thickness direction, and the negative electrode film layer is provided on either or both of the two opposite surfaces of the negative electrode current collector.

[0242] In some embodiments, the negative electrode current collector can be a metal foil or a composite current collector. For example, as the metal foil, copper foil can be used. The composite current collector can include a polymer material base layer and a metal layer formed on at least one surface of the polymer material substrate. The composite current collector can be formed by forming a metal material (such as copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy, etc.) on a polymer material substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0243] In some embodiments, the negative electrode active material can be a negative electrode material for batteries well-known in the art. As an example, the negative electrode active material can include at least one of the following materials: artificial graphite, natural graphite, soft carbon, hard carbon, silicon-based materials, tin-based materials, and lithium titanate, etc. The silicon-based material can be selected from at least one of elemental silicon, silicon oxides, silicon-carbon composites, silicon-nitrogen composites, and silicon alloys. The tin-based material can be selected from at least one of elemental tin, tin oxides, and tin alloys. However, the present application is not limited to these materials, and other conventional materials that can be used as battery negative electrode materials can also be used. These negative electrode materials can be used alone or in combination of two or more.

[0244] In some embodiments, the specific capacity of the negative electrode active material is 600 mAh / g - 2500 mAh / g.

[0245] In some embodiments, the negative electrode active material includes silicon monoxide.

[0246] In some embodiments, based on the total mass of the negative electrode active material, the mass content of silicon monoxide is 20% - 100%, and can be optionally 50% - 100%.

[0247] In some embodiments, the negative electrode film layer may also optionally include a binder. The binder can be selected from at least one of styrene-butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethacrylic acid (PMAA), and carboxymethyl chitosan (CMCS).

[0248] In some embodiments, the negative electrode film layer may further optionally include a conductive agent. The conductive agent may be selected from at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0249] In some embodiments, the negative electrode film layer may further optionally include other additives, such as a thickening agent (e.g., sodium carboxymethyl cellulose (CMC-Na)), etc.

[0250] In some embodiments, the negative electrode plate can be prepared in the following manner: dispersing the above components for preparing the negative electrode film layer, such as the negative electrode material, conductive agent, binder, and any other components, in a solvent (e.g., deionized water) to form a negative electrode slurry; coating the negative electrode slurry on the negative electrode current collector, and after processes such as drying and cold pressing, the negative electrode plate can be obtained.

[0251] [Electrolyte]

[0252] The electrolyte plays a role in conducting ions between the positive electrode plate and the negative electrode plate. There is no specific limitation on the type of the electrolyte in this application, and it can be selected according to requirements. For example, the electrolyte can be liquid, gel-like, or all-solid-state.

[0253] In some embodiments, the electrolyte uses an electrolytic solution. The electrolytic solution includes an electrolyte salt and a solvent.

[0254] In some embodiments, the electrolyte salt may be selected from at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium hexafluoroarsenate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium trifluoromethanesulfonate, lithium difluorophosphate, lithium difluorooxalate borate, lithium bis(oxalato)borate, lithium difluoro bis(oxalato)phosphate, and lithium tetrafluorooxalate phosphate.

[0255] In some embodiments, the solvent may be selected from at least one of ethylene carbonate, propylene carbonate, ethyl methyl carbonate, diethyl carbonate, dimethyl carbonate, dipropyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, butylene carbonate, fluoroethylene carbonate, methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate, 1,4-butyrolactone, sulfolane, dimethyl sulfone, methyl ethyl sulfone, and diethyl sulfone.

[0256] In some embodiments, the electrolytic solution may further optionally include additives. For example, the additives may include negative electrode film-forming additives, positive electrode film-forming additives, and may also include additives that can improve certain battery performances, such as additives for improving the overcharge performance of the battery, additives for improving the high-temperature or low-temperature performance of the battery, etc.

[0257] [Separator]

[0258] In some embodiments, the battery cell further includes a separator. The present application does not particularly limit the type of the separator, and any well-known porous separator with good chemical stability and mechanical stability can be selected.

[0259] In some embodiments, the material of the separator can be selected from at least one of glass fiber, non-woven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator can be a single-layer film or a multi-layer composite film, without particular limitation. When the separator is a multi-layer composite film, the materials of each layer can be the same or different, without particular limitation.

[0260] In some embodiments, the positive electrode sheet, the negative electrode sheet, and the separator can be made into an electrode assembly by a winding process or a stacking process.

[0261] In some embodiments, the battery can include a battery cell, and the battery cell includes the above-mentioned electrode assembly.

[0262] In some embodiments, the battery cell can include an outer package. The outer package can be used to encapsulate the above-mentioned electrode assembly and electrolyte.

[0263] In some embodiments, the outer package of the battery cell can be a hard shell, such as a hard plastic shell, an aluminum shell, a steel shell, etc. The outer package of the battery cell can also be a soft package, such as a pouch soft package. The material of the soft package can be plastic, and examples of the plastic can include polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0264] The present application does not particularly limit the shape of the battery cell, and it can be cylindrical, square, or any other shape. For example, Figure 2 is a battery cell 5 with a square structure as an example.

[0265] In some embodiments, referring to Figure 3 , the outer package can include a housing 51 and a cover plate 53. Wherein, the housing 51 can include a bottom plate and side plates connected to the bottom plate, and the bottom plate and the side plates enclose to form a receiving cavity. The housing 51 has an opening communicating with the receiving cavity, and the cover plate 53 can be covered on the opening to close the receiving cavity. The positive electrode sheet, the negative electrode sheet, and the separator can form an electrode assembly 52 through a winding process or a stacking process. The electrode assembly 52 is encapsulated in the receiving cavity. The electrolyte infiltrates into the electrode assembly 52. The number of the electrode assemblies 52 included in the battery cell 5 can be one or more, and those skilled in the art can select according to specific actual needs.

[0266] Battery

[0267] Fourth aspect, an embodiment of the present application provides a battery, including the battery cell of the third aspect. According to the embodiment of the present application, the battery includes the above-mentioned battery cell, so the battery has the beneficial effects of the above-mentioned battery cell.

[0268] In some embodiments, the battery may further include a box body; the battery cell is accommodated in the box body.

[0269] The number of battery cells included in the above-mentioned battery may be one or more, and those skilled in the art can select the specific number according to the application and capacity of the battery.

[0270] Furthermore, in the above-mentioned battery, a plurality of battery cells exist in the form of being assembled into a battery module. Figure 4 This is the battery module 4 as an example. Refer to Figure 4 , in the battery module 4, a plurality of battery cells 5 may be arranged in sequence along the length direction of the battery module 4. Of course, they can also be arranged in any other way. Further, the plurality of battery cells 5 can be fixed by fasteners.

[0271] Optionally, the battery module 4 may further include a housing with an accommodation space, and a plurality of battery cells 5 are accommodated in the accommodation space.

[0272] Figure 5 and Figure 6 This is the battery 1 as an example. Refer to Figure 5 and Figure 6 , the battery 1 may include a battery box and a plurality of battery modules 4 arranged in the battery box. The battery box includes an upper box body 2 and a lower box body 3. The upper box body 2 can cover the lower box body 3 and form a closed space for accommodating the battery module 4. The plurality of battery modules 4 can be arranged in the battery box in any way.

[0273] In some embodiments, the battery may be a battery cell.

[0274] Electric device

[0275] Fifth aspect, an embodiment of the present application provides an electrical device, including the battery of the fourth aspect. According to the embodiment of the present application, the electrical device includes the above-mentioned battery, so the electrical device has the beneficial effects of the above-mentioned battery.

[0276] The battery can be used as the power source of the electrical device or as the energy storage unit of the electrical device. The electrical device may include mobile devices (such as mobile phones, laptops, etc.), electric vehicles (such as pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships, satellites, energy storage systems, etc., but not limited thereto.

[0277] As the electrical device, the above-mentioned battery can be selected according to its usage requirements.

[0278] Figure 7 is an electrical device as an example. The electrical device is a pure electric vehicle, a hybrid electric vehicle, a plug-in hybrid electric vehicle, etc.

[0279] As another example of the device, it can be a mobile phone, a tablet computer, a laptop computer, etc. This device usually requires being thin and light, and a battery including only battery cells can be used as the power source.

[0280] Embodiment

[0281] Hereinafter, embodiments of the present application will be described. The embodiments described below are exemplary and are only used to explain the present application and should not be construed as a limitation to the present application. For those not specified in the embodiments regarding specific technologies or conditions, they shall be carried out according to the technologies or conditions described in the literature in the field or according to the product specifications. For the reagents or instruments not specified regarding the manufacturer, they are all conventional products that can be obtained through commercial purchase.

[0282] Embodiment 1

[0283]

Preparation of the positive electrode sheet

[0284] The second positive electrode active material particles and the third positive electrode active material particles are respectively nickel cobalt manganese (NCM) ternary materials LiNi 0.96 Co 0.02 Mn 0.01 Ba 0.01 O2. The total mass of the second positive electrode active material particles and the third positive electrode active material particles (the mass ratio is 8:2), conductive agent carbon black, and binder polyvinylidene fluoride (PVDF) are mixed at a mass ratio of 97:1:2, N-methylpyrrolidone is added, and the mixture is stirred for 0.5 - 6 h to obtain a positive electrode slurry, and the solid content of the positive electrode slurry is 68%; then it is uniformly coated on the positive electrode current collector to prepare a second positive electrode active material film layer, wherein, the average particle size DV 2 50 of the second positive electrode active material particles is 7 μm, the inner diameter d1 is 3 μm; the outer wall wall thickness d2 is 4 μm, and the other parameters and the parameters of the third positive electrode active material particles are shown in Table 1.

[0285] The first positive electrode active material particles are nickel cobalt manganese (NCM) ternary materials LiNi 0.96 Co 0.02 Mn 0.01 Ba 0.01O2. The first positive electrode active material particles, conductive agent carbon black, and binder polyvinylidene fluoride (PVDF) are mixed at a mass ratio of 97:1:2, and N-methylpyrrolidone is added. The mixture is stirred for 0.5 - 6 h to obtain a positive electrode slurry with a solid content of 68%; then it is uniformly coated on a positive electrode current collector with a coating mass of 35 mg / cm 2 , and a first positive electrode active material film layer is prepared. The parameters of the first positive electrode active material particles are shown in Table 1.

[0286] After drying, cold pressing, and slitting, a positive electrode plate is obtained.

[0287]

Preparation of Lithium Battery

[0288] Positive electrode plate: The positive electrode plate prepared above.

[0289] Preparation of negative electrode plate: The negative electrode active material (i.e., artificial graphite and silicon carbon, where the mass ratio of artificial graphite to silicon carbon is 7:3, and the mass content of silicon element in silicon carbon is 49%), conductive agent carbon black, carbon nanotubes (CNT), binder styrene-butadiene rubber (SBR), and thickener sodium carboxymethyl cellulose (CMC-Na) are added to deionized water according to a weight ratio of 94.5:1:0.375:2.8:1.325, and the mixture is stirred for 0.5 - 6 h to obtain a first active material layer slurry; the slurry is uniformly coated on a negative electrode current collector in layers and dried.

[0290] Separator: A polypropylene film with a thickness of 7 μm is used as the base film, and a 2-μm coating is applied. The coating includes alumina and binder polyvinylidene fluoride. The mass content of alumina in the coating is 80%, and the mass content of binder polyvinylidene fluoride in the coating is 20%.

[0291] Electrolyte: LiPF6 and LIFSI are dissolved in a mixed solvent of ethylene carbonate, ethyl methyl carbonate, diethyl carbonate, and fluoroethylene carbonate (FEC) in a volume ratio of 1:1:1:1 to prepare an electrolyte with molar concentrations of LiPF6 and LIFSI of 1 mol / L respectively.

[0292] Lithium battery assembly: The above positive electrode plate, separator, and negative electrode plate are wound in sequence to obtain a bare battery cell; the bare battery cell is placed in a packaging shell, dried, and then injected with the electrolyte. After processes such as vacuum packaging, standing, formation, and shaping, a lithium-ion battery is obtained.

[0293] Examples 2-1 to 2-2

[0294] Similar to Example 1, the difference is that in Example 2-1, the types of the first positive electrode active material particles, the second positive electrode active material particles, and the third positive electrode active material particles are nickel cobalt manganese (NCM) ternary material LiNi 0.97 Co0.01 Mn 0.01 Ba 0.01 O₂. In Example 2-2, the types of the first positive electrode active material particles, the second positive electrode active material particles, and the third positive electrode active material particles are the nickel-cobalt-manganese (NCM) ternary material LiNi 0.98 Co 0.01 Mn 0.005 Ba 0.005 O₂.

[0295] Examples 3-1 to 3-3

[0296] Similar to Example 1, the difference is that: the parameters of the first positive active material particles in Examples 3-1 to 3-3 are different, as shown in Table 1 specifically.

[0297] Examples 4-1 to 4-9

[0298] Similar to Example 1, the difference is that: the respective particle sizes, respective contents of the second positive electrode active material particles and the third positive electrode active material particles, and the thickness h2 of the second active material film layer are different. Among them, in Example 4-2, the inner diameter d1 of the second positive electrode active material particles is 4 μm; the outer wall wall thickness d2 is 3 μm, from which the hollow structure can be seen. In Example 4-3, the inner diameter d1 of the second positive electrode active material particles is 2 μm; the outer wall wall thickness d2 is 5 μm. In Examples 4-4 to 4-5, the content of the second positive electrode active material particles in the second active material film layer is different. In Example 4-6, the thickness h2 of the second positive electrode active material film layer is different. In Examples 4-7 to 4-8, the particle size parameters of the third positive electrode active material particles are different; in Example 9, the third positive electrode active material particles are not included. As shown in Table 1 specifically.

[0299] Comparative Example 1

[0300] Similar to Example 1, the difference is that: the first positive active material particles, the second positive electrode particles, and the third positive electrode particles in Comparative Example 1 are respectively replaced with the first positive active material particles of Example 1 as the positive active particles of the positive electrode sheet. The thickness of the active material film layer in Comparative Example 1 is the sum of the thicknesses of the first positive electrode active material film layer and the second positive electrode active material film layer described in Example 1, which is 300 μm.

[0301] Comparative Example 2

[0302] Similar to Example 1, the difference is that: the first positive active material particles, the second positive active particles, and the third positive active particles in Comparative Example 2 are respectively replaced with the second positive active material particles in Example 1 as the positive active particles of the positive electrode sheet. The thickness of the active material film layer in Comparative Example 2 is the sum of the thicknesses of the first positive active material film layer and the second positive active material film layer described in Example 1, which is 300 μm.

[0303] Comparative Example 3

[0304] Similar to Example 1, the difference is that: the first positive active material particles, the second positive active particles, and the third positive active particles in Comparative Example 3 are respectively replaced with the third positive active material particles in Example 1 as the positive active particles of the positive electrode sheet. The thickness of the active material film layer in Comparative Example 3 is the sum of the thicknesses of the first positive active material film layer and the second positive active material film layer described in Example 1, which is 300 μm.

[0305] Performance test

[0306] The batteries obtained from the above examples and comparative examples were respectively subjected to performance tests. The test results are shown in Table 2.

[0307] 1) Test of discharge capacity

[0308] The battery monomers prepared above were left standing at 25 °C for 2 h to ensure that the temperature of the battery monomers was 25 °C. At 25 °C, the battery monomers were charged to the charging cut-off voltage of 4.25 V at 0.1C, and then constant voltage charging was continued at this charging cut-off voltage until the current was 0.02C, and the charging was terminated (where C represents the rated capacity of the battery monomer). The battery monomers were left standing at 25 °C for 0.5 h. At 25 °C, the battery monomers were discharged to the discharge cut-off voltage of 2.7 V at 0.1C, and the total discharge capacity C0 released by the battery monomers was recorded.

[0309] 2) Energy density test

[0310] Capacity test of battery monomers: The battery monomers prepared above were left standing at 25 °C for 2 h to ensure that the temperature of the battery monomers was 25 °C. At 25 °C, the battery monomers were charged to the charging cut-off voltage at 0.1C, and then constant voltage charging was continued at this charging cut-off voltage until the current was 0.05C, and the charging was terminated (where C represents the rated capacity of the battery monomer). The battery monomers were left standing at 25 °C for 1 h. At 25 °C, the battery monomers were discharged to the discharge cut-off voltage at 0.1C, and the total discharge capacity C0 released by the battery monomers was recorded. The total discharge energy was E0.

[0311] Measurement of the weight of battery monomers: The battery monomers were placed on an electronic balance until the weight was stable, and the weight value M0 of the battery monomers was read.

[0312] Energy density calculation: The energy density of a single battery cell is the energy E0 discharged by the single battery cell divided by the weight M0 of the single battery cell.

[0313] 3) 10 - 80% SOC charge time test

[0314] Voltage calibration: Let the laminated three - electrode battery cell with the same design of the battery stand still at 25°C for 30 min; at 25°C, charge the single battery cell at 0.33C until the charge cut - off voltage, and then continue to perform constant - voltage charging at this charge cut - off voltage until the current is 0.05C, and the charging stops (where C represents the rated capacity of the single battery cell); stand still at 25°C for 1 h; at 25°C, discharge the single battery cell at 0.33C to the discharge cut - off voltage, and record the total discharge capacity C1 discharged by the single battery cell; stand still at 25°C for 1 h.

[0315] Charge test: Let the laminated three - electrode battery cell stand still at 25°C for 30 min; discharge at 0.33C1 DC to the discharge cut - off voltage; stand still for 5 min; charge at xC1 CC to the charge cut - off voltage (monitor the anode potential of the three - electrode, and jump to the next step when the anode potential is 0V; repeat the above steps 9 times, and the values of x are 5, 4, 4.5, 3, 2, 1, 0.8, 0.5, 0.33 in turn; take the x value and the charge capacity Cx corresponding to the anode potential of 0V.

[0316] 4) Battery cycle capacity retention test

[0317] The method for voltage calibration of the single battery cells prepared in each example and comparative example is as follows:

[0318] Let the single battery cell stand still at 25°C for 2 h to ensure that the temperature of the single battery cell is 25°C; at 25°C, charge the single battery cell at 0.33C0 to 4.25V, and perform constant - voltage charging at 4.25V until the current is 0.05C0; stand still for 1 h; at 25°C, discharge at 0.33C0 for 0.95C0, and record the voltage V1 at this time; stand still for 5 min; at 25°C, discharge at 0.33C0 to 2.7V; stand still for 5 min; at 25°C, charge the single battery cell at 0.33C0 for 0.97C0, and record the voltage V2 at this time; stand still for 2 h

[0319] The cycle test process is as follows: Let the single battery cell stand still at 25°C for 2 h to ensure that the temperature of the single battery cell is 25°C; at 25°C, charge the single battery cell at 0.33C0 to the voltage V2; stand still for 0.5 h; at 25°C, discharge the single battery cell at 0.33C0 to the voltage V1, and record the capacity as Cn at this time; stand still for 0.5 h; perform cyclic charge - discharge tests on the battery according to this method until the battery capacity decays to 80%. The number of cycles at this time is the cycle life of the battery at 25°C.

[0320] The relevant parameters and test results of the battery positive electrode sheets of the embodiment and comparative example are recorded in Table 1-2.

[0321]

[0322]

[0323]

[0324] As can be seen from the data in Table 1, when the first and second positive electrode active material particles of the embodiment are sequentially present in the first and second active material film layers of the positive electrode sheet, the first and second positive electrode active material particles have different material characteristics. Compared to the comparative examples, the positive electrode sheet containing this embodiment shortens the charging time during the battery charge and discharge process, facilitating the utilization of the specific capacity of the positive electrode sheet, increasing the discharge capacity of the battery, and improving the battery's energy density and cycle capacity retention rate. Therefore, the discharge specific capacity, charging time, and number of cycles at 80% of the battery cell's cycle capacity of Example 1 are superior to those of Comparative Examples 1-3.

[0325] Analysis shows that the reasons may be that: during the mass transfer process of the electrolyte, the concentration of active ions gradually decreases from the diaphragm to the positive electrode sheet near the positive electrode current collector, the first positive electrode active material particles in the first positive electrode active material film layer are solid particles, and the deintercalation distance of the active ions in the first positive electrode active material film layer is relatively long (the mass transfer distance is relatively long); the second positive electrode active material film layer contains second positive electrode active material particles with a hollow structure, and the second positive electrode active material particles with a hollow structure reduce the deintercalation distance of the active ions in the second positive electrode active material film layer (the mass transfer distance is relatively short).

[0326] It should be noted that the present application is not limited to the above-mentioned embodiments. The above-mentioned embodiments are merely examples, and any embodiments having substantially the same structure and effect as the technical concept within the scope of the present application are all included in the technical scope of the present application. In addition, without departing from the scope of the present application, any other embodiments that can be conceived by those skilled in the art and that combine some of the constituent elements in the embodiments are also included in the scope of the present application.

Claims

1. A positive electrode sheet, characterized in that, Comprising: A positive current collector; A first positive active material film layer disposed on at least one side of the positive current collector, the first positive active material film layer comprising solid first positive active material particles; A second positive active material film layer disposed between the first positive active material film layer and the positive current collector, the second positive active material film layer comprising second positive active material particles having a hollow structure.

2. The positive electrode sheet according to claim 1, wherein The particle sizes of the first positive active material particles and the second positive active material particles satisfy one or more of the following conditions: 1) The average particle size D of the first positive electrode active material particles V 1 50 is greater than or equal to the average particle size Dv of the second positive electrode active material particles 2 50; 2) The average particle diameter Dv of the first positive electrode active material particles 1 is 8 μm to 18 μm; 3) The average particle size Dv of the second positive electrode active material particles 2 is 2 μm to 10 μm; 3) The particle size distribution span of the first positive active material particles is 0.3 to 0.7; 4) The particle size distribution span of the second positive active material particles is 0.9 to 1.3; 5) The inner diameter d1 of the hollow structure is 0.6 μm to 5 μm; 6) The outer wall wall thickness d2 of the hollow structure is 0.6 μm to 10 μm; 7) The first positive electrode active material particles and the second positive electrode active material particles respectively include the following structural general formula: Li a Ni x Co y M 1-x-y O2, where M includes one or more of Mn, Al, B, Zr, Sr, Y, Sb, W, Ti, Mg, Nb, Ba, 0.55 ≤ x ≤ 1.05, 0 ≤ y ≤ 0.45, 0.8 ≤ a ≤ 1.

2.

3. The positive electrode sheet according to claim 1, wherein The specific surface areas of the first positive active material particles and the second positive active material particles satisfy one or more of the following conditions: 1) The specific surface area of the first positive electrode active material particles is 0.1 m 2 / g to 0.5 m 2 / g; 2) The specific surface area of the second positive electrode active material particles is 0.35 m 2 / g to 0.8 m 2 / g.

4. The positive electrode sheet according to claim 1, wherein, The first positive active material particles and the second positive active material particles satisfy one or more of the following conditions: 1) The tap density of the first positive electrode active material particles is 1.8 g / cm 3 to 4 g / cm 3 ; 2) The tap density of the second positive electrode active material particles is 1.3 g / cm 3 ~2.6 g / cm 3 .

5. The positive electrode sheet according to any one of claims 1 to 4, characterized in that, The second positive electrode active material film layer contains third positive electrode active material particles, and the average particle size Dv of the second positive electrode active material particles 2 50 is greater than the average particle size Dv of the third positive electrode active material particles 3 50.

6. The positive electrode sheet according to claim 5, wherein The third positive active material particles satisfy one or more of the following conditions: 1) The average particle size Dv of the third positive electrode active material particles 3 is 0.8 μm to 5 μm; 2) The specific surface area of the third positive electrode active material particles is 0.4 m 2 / g to 0.9 m 2 / g; 3) The tap density of the third positive electrode active material particles is 1.8 g / cm 3 ~3.4 g / cm 3 ; 4) The third positive active material particles are one or more of particles having a hollow structure and solid particles; 5) The particle size distribution span of the third positive active material particles is 0.8 to 1.5; 6) The third positive electrode active material particles include the following structural general formula: Li a Ni x Co y M 1-x-y O2, where M includes one or more of Mn, Al, B, Zr, Sr, Y, Sb, W, Ti, Mg, Nb, Ba, 0.55 ≤ x ≤ 1.05, 0 ≤ y ≤ 0.45, 0.8 ≤ a ≤ 1.

2.

7. The positive electrode sheet according to any one of claims 1 to 6, characterized in that, The first positive electrode active material particles, the second positive electrode active material particles, and the third positive electrode active material particles respectively include LiNi 0.96 Co 0.02 Mn 0.01 Ba 0.01 O2, LiNi 0.97 Co 0.01 Mn 0.01 Ba 0.01 O2, LiNi 0.98 Co 0.01 Mn 0.005 Ba 0.005 O2, or any one or more of them.

8. The positive electrode sheet according to any one of claims 1 to 7, characterized in that, The thickness h1 of the first positive active material film layer and the thickness h2 of the second positive active material film layer satisfy one or more of the following conditions: 1) The ratio of the thickness h1 of the first positive active material film layer to the thickness h2 of the second positive active material film layer is 10:(3.3 to 23.5); 2) The thickness h1 of the first positive active material film layer is 130 - 200 μm; 3) The thickness h2 of the second positive active material film layer is 50 - 170 μm.

9. The positive electrode sheet according to any one of claims 1 to 8, characterized in that, The positive electrode plate satisfies one or more of the following conditions: 1) The porosity of the first positive active material film layer is greater than the porosity of the second positive active material film layer; 2) The porosity of the first positive active material film layer is 26% - 50%; 3) The porosity of the second positive active material film layer is 30% - 40%; 4) The tap density of the first positive active material film layer is less than the tap density of the second positive active material film layer; 5) The tap density of the first positive electrode active material film layer is 2.9 g / cm 3 - 3.3 g / cm 3 ; 6) The compaction density of the second positive electrode active material film layer is 3.2 g / cm 3 - 3.7 g / cm 3 ; 7) The specific capacity of the first positive active material film layer is 225 mAh / g - 240 mAh / g; 8) The specific capacity of the second positive active material film layer is 220 mAh / g - 235 mAh / g.

10. A method for preparing a positive electrode sheet, characterized in that, Comprising: Providing a second slurry containing second positive active material particles having a hollow structure; Coating the second slurry on the positive current collector and forming a second positive active material film layer; Providing a first slurry containing first positive active material particles which are solid particles; Coat the first slurry so as to form a first positive electrode active material film layer on the side of the second positive electrode active material film layer away from the positive electrode current collector, thereby obtaining a positive electrode sheet.

11. The method according to claim 10, wherein The second slurry comprises, by mass percentage, a mixture of 60%-90% of second positive electrode active material particles and 10%-40% of third positive electrode active material particles.

12. A battery cell, characterized in that, It includes the positive electrode sheet according to any one of claims 1 to 9 or the positive electrode sheet prepared by the method according to claim 10 or 11.

13. A battery, characterized in that, It includes the battery cell according to claim 12.

14. An electrical device, characterized in that, It includes the battery according to claim 13.

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