Positive electrode sheet, preparation method therefor, battery cell, battery, and electric apparatus

Abstract

A positive electrode sheet, a preparation method therefor, a battery cell, a battery, and an electric apparatus. The positive electrode sheet comprises: a positive electrode current collector; a first positive electrode active material film layer disposed on at least one side of the positive electrode current collector, the first positive electrode active material film layer comprising solid first positive electrode active material particles; and a second positive electrode active material film layer disposed between the first positive electrode active material film layer and the positive electrode current collector, the second positive electrode active material film layer comprising second positive electrode active material particles having a hollow structure. During charging and discharging of a battery, comprising the positive electrode sheet of an embodiment helps to balance the disembedding speed of active ions in the first positive electrode active material film layer and the second positive electrode active material film layer, which is beneficial to the gram capacity of the positive electrode sheet, and improves the cycling stability of the battery. The battery cell, battery, and electric apparatus comprising the positive electrode sheet also have the described advantages.

Description

Positive electrode sheet and preparation method thereof, battery cell, battery and electrical device

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims priority to Chinese patent application No. 202410116827.2 filed on January 29, 2024, entitled “Positive electrode sheet and preparation method thereof, battery cell, battery and electrical device”, the entire contents of which are incorporated herein by reference. Technical Field

[0003] The present application relates to the field of battery technology, and in particular to a positive electrode plate and a preparation method thereof, a battery cell, a battery and an electrical device. Background Art

[0004] In recent years, the application of batteries, particularly lithium-ion batteries, has become increasingly widespread. They are now widely used in energy storage systems such as hydropower, thermal, wind, and solar power plants, as well as in power tools, electric bicycles, electric motorcycles, electric vehicles, military equipment, aerospace, and other fields. This tremendous advancement in batteries has led to higher demands on their energy density, cycle performance, and safety.

[0005] In order to increase the capacity of the battery, the active material film layer of the positive electrode is usually designed to be thicker, but it still cannot meet the requirements of improving the battery capacity and cycle performance, and needs further improvement.

[0006] Summary of the Invention

[0007] The present application provides a positive electrode plate and a preparation method thereof, a battery cell, a battery and an electrical device. The positive electrode plate has a high gram capacity and good cycle stability.

[0008] In a first aspect, an embodiment of the present application provides a positive electrode sheet, comprising:

[0009] positive electrode current collector;

[0010] A first positive electrode active material film layer is provided 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;

[0011] 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 includes second positive electrode active material particles with a hollow structure.

[0012] According to the embodiments of the present application, the positive electrode sheet including the embodiments of the present application improves the discharge gram capacity and stability of the positive electrode sheet during the charge and discharge process of the battery, and improves the charge and discharge time of the positive electrode sheet in the battery. The reason for this may be that: during the mass transfer process of the electrolyte, the active ion concentration gradually decreases from the diaphragm to the positive electrode sheet near the positive electrode current collector, and the solid first positive electrode active material particles in the first positive electrode active material film layer have a relatively long deintercalation distance for the active ions in the first positive electrode active material film layer (the mass transfer distance is relatively long); the second positive electrode active material film layer includes 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 for 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 deintercalation speed of the active ions in the first positive electrode active material film layer and the second positive electrode active material film layer, and balances the difference in the charge and discharge (SOC) speed of the active ions between the first positive electrode active material film layer and the second positive electrode active material film layer, thereby facilitating the performance of the gram capacity of the positive electrode sheet.

[0013] In addition, the second positive electrode active material particles have a hollow structure, which is conducive to the presence of the second positive electrode active material particles in the positive electrode sheet, dispersing the stress of the positive electrode sheet during the cycle, improving the cycle stability of the positive electrode sheet, and helping to further improve the cycle performance of the battery.

[0014] 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.

[0015] When nickel-containing positive electrode active particles are used in batteries, taking lithium batteries as an example, such as Ni 2+ Ionic radius and Li + The radii of the electrodes are similar, and the phenomenon of cation mixing will seriously occur, which will cause the electrochemical performance of the lithium-containing ternary positive electrode active material to decline. Especially in the high nickel system, the cation mixing trend increases and the battery cycle performance deteriorates. According to the embodiment 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 shortens the distance for lithium ion proton transfer. In general, the first positive electrode active material film layer has a high lithium ion concentration, but the lithium ion solid phase mass transfer distance is longer, and the second positive electrode active material film layer has a low lithium ion concentration, but the solid phase mass transfer time is shorter, which balances the difference in the deintercalation and extraction of active lithium ions between the active material particles in the positive electrode sheet, which is beneficial to the gram capacity of the positive electrode sheet, and reduces the ratio of the active material particles in the positive electrode sheet that do not participate in the charge and discharge cycle to the entire active material particles, thereby increasing the gram capacity of the positive electrode sheet and improving the cycle performance of the positive electrode sheet in the battery.

[0016] In some optional embodiments, the average particle size Dv of the first positive electrode active material particles is1 50 is greater than or equal to the average particle size Dv of the second positive electrode active material particles 2 50.

[0017] According to the embodiment of the present application, the average particle size Dv of the first positive electrode active material particles is 1 50 is greater than or equal to the average particle size Dv of the second positive electrode active material particles 2 50, which is beneficial to increase the mass transfer distance of the first positive electrode active material particles in the first positive electrode active material film layer and reduce 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 deintercalation speed of the two layers, thereby improving the gram capacity and cycle performance of the positive electrode sheet.

[0018] In addition, the average particle size Dv of the first positive electrode active material particles is 1 50 is relatively large, which is beneficial to increase the porosity of the first positive electrode active material film layer, thereby facilitating the presence of the first positive electrode active material particles in the positive electrode sheet, dispersing the stress of the first positive electrode active material particles in the positive electrode sheet during the cycle, and improving the cycle stability of the positive electrode sheet, which is beneficial to further improve the cycle performance of the battery.

[0019] In some optional embodiments, the average particle size Dv of the first positive electrode active material particles is 1 50 is 8μm~18μm.

[0020] According to the embodiment of the present application, the average particle size Dv of the first positive electrode active material particles is 1 50 In the above range, it is beneficial to increase 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 deintercalation speed of the two layers, thereby improving the gram capacity and cycle performance of the positive electrode sheet.

[0021] In some optional embodiments, the average particle size Dv of the second positive electrode active material particles is 2 50 is 2μm~10μm.

[0022] According to the embodiment of the present application, the average particle size Dv of the second positive electrode active material particles is 2 50 In the above range, it is beneficial to reduce 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 deintercalation speed of the two layers, thereby improving the gram capacity and cycle performance of the positive electrode sheet.

[0023] In some optional embodiments, the particle size distribution span of the first positive electrode active material particles is 0.3-0.7.

[0024] According to the embodiment of the present application, the particle size distribution span of the first positive electrode active material particles is within the above range, which can increase the compaction density of the material, increase the discharge capacity of the battery, balance the active ion deintercalation speed of the two layers, and thus improve the gram capacity and cycle performance of the positive electrode sheet.

[0025] In some optional embodiments, the particle size distribution span of the second positive electrode active material particles is 0.9-1.3.

[0026] According to the embodiment of the present application, the particle size distribution span of the second positive electrode active material particles within the above range can increase the compaction density of the material, increase the discharge capacity of the battery, balance the active ion deintercalation speed of the two layers, and thus improve the gram capacity and cycle performance of the positive electrode sheet.

[0027] In some optional embodiments, the inner diameter d1 of the hollow structure is 0.6 μm to 5 μm.

[0028] According to the embodiment 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 the charge and discharge process, play a role in stabilizing the structure and improving the cycle performance. On the other hand, the second positive electrode active material particles have more three-dimensional channels, which expand the contact area between the material and the electrolyte, shorten the migration distance of lithium ions, and thus increase 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, and thus have more active sites for lithium ions, which increases the gram capacity of the material, increases the gram capacity of the positive electrode sheet, and increases the energy density of the battery.

[0029] In some optional embodiments, the thickness d2 of the outer wall of the hollow structure is 0.6 μm to 10 μm.

[0030] In the embodiment of the present application, controlling the outer wall thickness d2 of the hollow structure within an appropriate range can improve the structural stability of the second positive electrode active material particles, increase the gram capacity 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.

[0031] Dv of the second positive electrode active material particles 2 50. The inner diameter d1 and outer wall thickness d2 of the hollow structure are important parameters of the second positive electrode active material particles, which affect the structural properties of the material. 250. When the inner diameter d1 and 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 gram capacity of the material and improving the structural stability of the material. When it is applied to lithium batteries for charge and discharge cycles, the lithium-nickel mixing phenomenon is effectively improved, and the migration rate of active ions and electrons is significantly improved, which is beneficial to the balance of the active ion deintercalation rate in the positive electrode of the battery, thereby benefiting the cycle performance of the battery.

[0032] In some optional embodiments, the first positive electrode active material particles and the second positive electrode active material particles have the following general structural formulas: Li a Ni x Co y M 1-x-y O2, wherein M includes one or more of Mn, Al, B, Zr, Sr, Y, Sb, W, Ti, Mg, Nb, and Ba, 0.55≤x≤1.05, 0≤y≤0.45, and 0.8≤a≤1.2.

[0033] According to the embodiment of the present application, the use of the above materials can ensure that the first positive electrode active material film layer and the second active material film layer have a higher gram capacity, thereby increasing the gram capacity of the positive electrode sheet, so that the battery has a high discharge capacity and energy density.

[0034] In some optional embodiments, the specific surface area of ​​the first positive electrode active material particles is 0.1 m 2 / g-0.5m 2 / g.

[0035] In some optional embodiments, the specific surface area of ​​the second positive electrode active material particles is 0.35 m 2 / g-0.8m 2 / g.

[0036] According to the embodiment 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 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 deintercalation speed of the two layers, thereby improving the gram capacity and cycle performance of the positive electrode sheet.

[0037] In some optional embodiments, the tap density of the first positive electrode active material particles is 1.8 g / cm 3 -4g / cm 3 .

[0038] In some optional embodiments, the tap density of the second positive electrode active material particles is 1.3 g / cm 3 -2.6g / cm 3 .

[0039] According to the embodiment of the present application, the first positive electrode active material particles have a suitable tap density and the second positive electrode active material particles have a suitable tap density, 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 deintercalation speeds of the two layers, thereby improving the gram capacity and cycle performance of the positive electrode sheet.

[0040] In some optional embodiments, the second positive electrode active material film layer comprises third positive electrode active material particles, and the average particle size Dv of the second positive electrode active material particles is 2 50 is greater than the average particle size Dv of the third positive electrode active material particles 3 50.

[0041] In this 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, and the third positive electrode active material particles are matched 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 active ion deintercalation in the second positive electrode active material film layer, and balancing the difference in charge and discharge speed (SOC difference) between the first active material film layer and the second active material film layer, which is beneficial to the performance of gram capacity.

[0042] In some optional embodiments, the average particle size Dv of the third positive electrode active material particles is 3 50 is 0.8μm to 5μm.

[0043] According to the embodiment of the present application, the average particle size Dv of the third positive electrode active material particles is 3 50 In the above range, the particle size is relatively small and the anisotropy is smaller. At this time, the volume expansion rate of the third positive electrode active material particles in the battery during charging and discharging is lower, which makes the cycle stability of the third positive electrode active material particles better, further improves the cycle stability of the overall positive electrode sheet, and further improves the cycle performance of the battery.

[0044] In some optional embodiments, the specific surface area of ​​the third positive electrode active material particles is 0.4 m 2 / g-0.9m 2 / g.

[0045] According to the embodiment of the present application, the specific surface area of ​​the third positive electrode active material particles is within the above range, which is conducive 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.

[0046] 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 second positive electrode active material particles within an appropriate range, the battery has high discharge capacity and energy density, excellent rate performance and cycle performance, and comprehensively improves the electrochemical performance of the battery.

[0047] In some optional embodiments, the tap density of the third positive electrode active material particles is 1.8 g / cm 3 -3.4g / cm 3 .

[0048] According to the embodiment of the present application, the tap density of the third positive electrode active material particles is within the above range, which is conducive to controlling the 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.

[0049] In some optional embodiments, the third positive electrode active material particles are one or more of particles with a hollow structure and solid particles.

[0050] In some optional embodiments, the particle size distribution span of the third positive electrode active material particles is 0.8-1.5.

[0051] According to the embodiment of the present application, the particle size distribution span of the third positive electrode active material particles is within the above range, which is beneficial to improving the compaction density of the second active material film layer, balancing the active ion deintercalation speed of the two layers, and improving the stability of the positive electrode sheet, thereby improving the gram capacity and cycle performance of the positive electrode sheet.

[0052] In some optional embodiments, the third positive electrode active material particles include the following structural formula: Li a Ni x Co y M 1-x-y O2, wherein M includes one or more of Mn, Al, B, Zr, Sr, Y, Sb, W, Ti, Mg, Nb, and Ba, 0.55≤x≤1.05, 0≤y≤0.45, and 0.8≤a≤1.2.

[0053] According to the embodiment of the present application, the use of the above-mentioned materials can ensure that the second active material film layer has a higher gram capacity, thereby increasing the gram capacity of the positive electrode sheet, so that the battery has a high discharge capacity and energy density.

[0054] In some optional 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 The above-mentioned positive electrode active materials can better balance the charge and discharge speed of the positive electrode sheet in the battery, balance the average charging efficiency of its surface and the side close to the positive electrode current collector, improve the gram capacity of the positive electrode sheet, and make the battery have high discharge capacity and energy density.

[0055] 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).

[0056] According to the embodiment 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, which is beneficial to balance the deintercalation speed of active ions in the two active material film layers, improve the stability of the positive electrode sheet, and thus improve the gram capacity and cycle performance of the positive electrode sheet.

[0057] In some optional embodiments, the thickness h1 of the first positive electrode active material film layer is 130-200 μm.

[0058] In some optional embodiments, the thickness h2 of the second positive electrode active material film layer is 50-170 μm.

[0059] According to the embodiment 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 deintercalation and insertion speed of active ions in the two active material film layers, improve the stability of the positive electrode sheet, and thus improve the gram capacity and cycle performance of the positive electrode sheet.

[0060] 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.

[0061] In some optional embodiments, the porosity of the first positive electrode active material film layer is 26%-50%.

[0062] In some optional embodiments, the compaction density of the first positive electrode active material layer is 2.9 g / cm 3 -3.3g / cm 3 In some optional embodiments, the second cathode active material layer has a compaction density of 3.2 g / cm 3 -3.7g / cm 3In some optional embodiments, the compaction density of the first positive electrode active material film layer is less than the compaction density of the second positive electrode active material film layer.

[0063] According to the embodiment 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 porosity and compaction density, it is beneficial to improve the electrochemical performance of the positive electrode sheet in the battery and improve the overall performance of the battery.

[0064] In some optional embodiments, the gram capacity of the first cathode active material film layer is 225 mAh / g-240 mAh / g. In some optional embodiments, the gram capacity of the second cathode active material film layer is 220 mAh / g-235 mAh / g.

[0065] According to the embodiments of the present application, by detecting that the ratio of the capacity of the first positive electrode active material film layer and the second positive electrode active material film layer is within the above range after the positive electrode plate is subjected to charge and discharge cycles in the button cell / battery cell, the deintercalation and insertion speeds of the active ions in the first positive electrode active material film layer and the second positive electrode active material film layer are balanced, which is beneficial to the capacity of the positive electrode plate and improves the utilization rate of the positive electrode active material.

[0066] In a second aspect, an embodiment of the present application provides a method for preparing a positive electrode sheet, comprising:

[0067] providing a second slurry containing second positive electrode active material particles, wherein the second positive electrode active material particles have a hollow structure;

[0068] coating a second slurry on the positive electrode current collector to form a second positive electrode active material film layer;

[0069] providing a first slurry containing first positive electrode active material particles, wherein the first positive electrode active material particles are solid particles;

[0070] The first slurry is applied to form a first positive electrode active material film layer on a side of the second positive electrode active material film layer away from the positive electrode current collector, thereby manufacturing a positive electrode sheet.

[0071] According to an embodiment of the present application, a second slurry containing particles of a second positive electrode active material is coated on the positive electrode current collector to form a second positive electrode active material film layer, and a first slurry containing particles of a first positive electrode active material is coated 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, so that during the charge and discharge process of the battery, the positive electrode sheet comprising the embodiment of the present application has a gradually decreasing concentration of active ions from the diaphragm to the positive electrode sheet near the positive electrode current collector during the mass transfer of the electrolyte, so that the first positive electrode active material particles in the first positive electrode active material film layer are solid particles, and the active ions are concentrated in the first positive electrode active material layer. The deintercalation distance of the 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 deintercalation 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 deintercalation speed of the active ions in the first positive electrode active material film layer and the second positive electrode active material film layer, and balances the difference in the charge and discharge (SOC) speed of the active ions between the first positive electrode active material film layer and the second positive electrode active material film layer, which is beneficial to the performance of the gram capacity of the positive electrode sheet.

[0072] According to an embodiment of the present application, the Li / Ni mixing ratio of the first positive electrode active material film layer and the second positive electrode active material film layer is within the above range, which shows that the first positive electrode active material film layer and the second positive electrode active material film layer obtained by adopting the above setting balance the difference in the charge and discharge (SOC) rate of the active ions between the first positive electrode active material film layer and the second positive electrode active material film layer, thereby also improving the positive electrode sheet gram capacity and cycle performance.

[0073] In some optional embodiments, the second slurry includes, by mass percentage, a mixture of 60%-90% of the second positive electrode active material particles and 10%-40% of the third positive electrode active material particles.

[0074] According to an embodiment of the present application, 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 are controlled. On the basis of balancing the active ion deintercalation rate of the first positive electrode active material film layer and the second positive electrode active material film layer, the structural stability of the positive electrode sheet and the charge and discharge rate of the battery are taken into account.

[0075] In a third aspect, embodiments of the present application provide a battery cell comprising the positive electrode sheet of the first aspect or the positive electrode sheet prepared by the method of the second aspect. According to embodiments of the present application, the battery cell comprises the aforementioned positive electrode sheet, and thus the battery has the beneficial effects of the aforementioned positive electrode sheet.

[0076] In a fourth aspect, an embodiment of the present application provides a battery comprising the battery cell of the third aspect. According to the embodiment of the present application, the battery comprises the aforementioned battery cell, and thus the battery has the beneficial effects of the aforementioned battery cell.

[0077] In a fifth aspect, an embodiment of the present application provides an electrical device comprising the battery of the fourth aspect. According to the embodiment of the present application, the electrical device comprises the aforementioned battery, and thus the electrical device has the beneficial effects of the aforementioned battery. BRIEF DESCRIPTION OF THE DRAWINGS

[0078] FIG1 is a microscopic schematic diagram of a hollow structure portion of a second positive electrode active material particle according to one embodiment of the present application.

[0079] FIG2 is a schematic diagram of a battery cell according to an embodiment of the present application.

[0080] FIG. 3 is an exploded view of the battery cell according to the embodiment of the present application shown in FIG. 2 .

[0081] FIG4 is a schematic diagram of a battery module according to an embodiment of the present application.

[0082] FIG5 is a schematic diagram of a battery according to an embodiment of the present application.

[0083] FIG. 6 is an exploded view of the battery shown in FIG. 5 according to an embodiment of the present application.

[0084] FIG. 7 is a schematic diagram of an electrical device using a battery cell as a power source according to an embodiment of the present application.

[0085] Explanation of Reference Numerals: 1. Battery; 2. Upper housing; 3. Lower housing; 4. Battery module; 5. Battery cell; 51. Housing; 52. Electrode assembly; 53. Top cover assembly. The drawings in this application are not necessarily drawn to scale. DETAILED DESCRIPTION

[0086] Below, with appropriate reference to the accompanying drawings, the embodiments of the positive electrode sheet and its preparation method, battery cell, battery and electrical device of the present application are specifically disclosed in detail. However, there may be cases where unnecessary detailed descriptions are omitted. For example, there are cases where detailed descriptions of well-known matters and repeated descriptions of actually the same structure are omitted. This is to avoid the following description from becoming unnecessarily lengthy and to facilitate the understanding of those skilled in the art. In addition, the 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 described in the claims.

[0087] The "ranges" disclosed herein are defined in terms of lower and upper limits, where a given range is defined by selecting a lower limit and an upper limit, and the selected lower and upper limits define the boundaries of the particular range. Ranges defined in this manner can be inclusive or exclusive of the end values ​​and can be combined arbitrarily, i.e., 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, it is understood that ranges of 60 to 110 and 80 to 120 are also contemplated. Furthermore, if minimum range values ​​of 1 and 2 are listed, and if maximum range values ​​of 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 this application, unless otherwise indicated, the numerical range "a to b" is a shorthand representation of any combination of real numbers between a and b, where a and b are both real numbers. For example, a numerical range of "0-5" indicates that all real numbers between "0-5" are listed herein, and "0-5" is simply an abbreviation for these numerical combinations. Furthermore, when a parameter is expressed as an integer ≥ 2, this is equivalent to disclosing that the parameter is, for example, an integer of 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0088] Unless otherwise specified, all embodiments and optional embodiments of the present application can be combined with each other to form a new technical solution.

[0089] Unless otherwise specified, all technical features and optional technical features of this application can be combined with each other to form a new technical solution.

[0090] Unless otherwise specified, all steps of the present application may be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), indicating that the method may include steps (a) and (b) performed sequentially, or may include steps (b) and (a) performed sequentially. For example, the method may further include step (c), indicating that step (c) may be added to the method in any order, for example, the method may include steps (a), (b) and (c), or may include steps (a), (c) and (b), or may include steps (c), (a) and (b), etc.

[0091] Unless otherwise specified, the terms "include" and "comprising" used in this application may be open-ended or closed-ended. For example, "include" and "comprising" may indicate that other components not listed may also be included or that only the listed components are included.

[0092] Unless otherwise specified, the term "or" is inclusive in this application. For example, the phrase "A or B" means "A, B, or both A and B." More specifically, the condition "A or B" is satisfied by any of the following conditions: A is true (or exists) and B is false (or does not exist); A is false (or does not exist) and B is true (or exists); or both A and B are true (or exist).

[0093] Unless otherwise specified, the terms "connected" and "connection" in this application should be understood broadly. For example, they can refer to fixed connection, detachable connection, or integral connection; they can refer to direct connection, indirect connection through an intermediate medium, or internal communication between two components. Those skilled in the art will understand the specific meanings of the above terms in this application based on specific circumstances.

[0094] If not otherwise specified, in this application, the term "attach" refers to connection by adhesion, coating, etc.

[0095] 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 a primary-secondary relationship.

[0096] Unless otherwise specified, in this application, the term "active ions" refers to ions that can be intercalated and extracted between the positive and negative electrodes of a battery cell, including but not limited to lithium ions, sodium ions, etc.

[0097] The term "several" or "multiple" used in this application refers to two or more items (including two items). The term "several" or "multiple items" used in this application refers to two or more items (including two items).

[0098] Nickel-rich ternary materials have become a popular choice for battery cell cathode active materials due to their high theoretical specific capacity, high discharge platform, and low cost. Consequently, the active material film layer of the cathode electrode is typically designed to be thicker to accommodate more cathode active material, thereby increasing the battery's capacity and energy density.

[0099] As the thickness of the active material film layer of the positive electrode sheet reaches a certain level, the capacity and energy density of the battery can only be improved to a limited extent, accompanied by deterioration of the battery cycle performance and reduction of the rate performance.

[0100] After research and analysis, it was found that the deterioration of battery performance may be caused by the uneven deintercalation of active ions on the surface of the active material film layer and the active material film layer close to the positive electrode current collector.

[0101] Further analysis revealed that during the charge and discharge process, lithium-ion batteries also experience interfacial side reactions, which can lead to continuous electrolyte decomposition at the interface between the positive and negative electrodes, as well as phase transitions at the interface of the positive electrode active material. This leads to a loss of active Li and an increase in lithium-ion battery impedance, resulting in a decrease in the performance of the positive electrode sheet in the battery. It is necessary to develop a positive electrode sheet with high specific capacity, excellent cycle performance, and rate performance to meet the application needs of the next generation of electrochemical systems.

[0102] Based on this, the present application provides a positive electrode sheet with high gram capacity and cycle stability, which can be used in batteries to effectively improve the energy density and cycle performance of the battery.

[0103] The specific implementation methods of this application are described in detail below.

[0104] Positive electrode

[0105] In a first aspect, an embodiment of the present application provides a positive electrode sheet, comprising:

[0106] positive electrode current collector;

[0107] A first positive electrode active material film layer is provided 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;

[0108] 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 includes second positive electrode active material particles with a hollow structure.

[0109] The solid first positive electrode active material particles in the first positive electrode active material film layer may be present in a content of 75% to 100%. At the microscopic level, it is not necessary for each first positive electrode active material particle to be 100% completely solid.

[0110] In the embodiments of this application, a solid first positive electrode active material particle refers to a particle composed entirely of matter, with no voids or voids within a range that is difficult to clearly detect. A solid first positive electrode active material particle is relatively homogeneous throughout the particle and lacks distinct, detectable voids, unlike a hollow structure.

[0111] In an embodiment of the present application, the solid first positive electrode active material particles may be polycrystalline particles with a relatively large average particle size. Polycrystalline particles are particles composed of multiple crystal particles. Crystals are structures of ordered arrangements of atoms or molecules, while polycrystalline particles have many small crystal particles, which 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 positive electrode active material is agglomerated. In the present application, primary particles and secondary particles have meanings well known in the art. Among them, primary particles refer to non-agglomerated particles; secondary particles refer to agglomerated particles formed by the aggregation of two or more primary particles. Primary particles and secondary particles can be easily distinguished by taking SEM images using a scanning electron microscope.

[0112] Secondary particles can be tested using any method known in the art. As an example, after imaging using a scanning electron microscope at 500x magnification, 200 to 600 intact, unobstructed secondary particles of the positive electrode active material are randomly selected from the electron micrograph. The average of the longest diameters of the primary particles in the micrograph is recorded as the average particle size.

[0113] In the embodiments of the present application, the term "hollow" refers to a solid structure with a cavity inside surrounded by a distinct shell. In the embodiments of the present application, the term "hollow structure" refers to a structure with a hollow part or a central pore. The hollow structure is usually surrounded by a solid shell or wall and is hollow inside. 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 that are smaller than solid particles, which can be secondary particles. As an example, a micrograph of the second positive electrode active material particles is shown in Figure 1.

[0114] According to the embodiments of the present application, the positive electrode sheet including the embodiments of the present application improves the discharge capacity and stability of the positive electrode sheet during the battery charging and discharging process, and shortens the charging time of the positive electrode sheet in the battery.

[0115] 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. 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), which is beneficial to the balance of the deintercalation speed of the active ions in the first positive electrode active material film layer and the second positive electrode active material film layer, and balances the difference in the charge and discharge (SOC) speed of the active ions between the first positive electrode active material film layer and the second positive electrode active material film layer.

[0116] In addition, the second positive electrode active material particles have a hollow structure, which is conducive to the presence of the second positive electrode active material particles in the positive electrode sheet, dispersing the stress of the positive electrode sheet during the cycle, and improving the cycle stability of the positive electrode sheet, which is conducive to further improving the cycle performance of the battery. Therefore, it can also reduce the breakage of the positive electrode active particles, improve the interface performance, and improve the overpressure cracking and brittleness problems of the positive electrode sheet.

[0117] 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.

[0118] In the related art, when nickel-containing positive electrode active particles are applied to batteries, taking lithium batteries as an example, such as Ni 2+ Ionic radius and Li + The radii of the cathode and cathode materials are similar, and the phenomenon of cation mixing will occur seriously, causing the electrochemical performance of lithium-containing ternary positive electrode active materials to decline. Especially in the high nickel system, the cation mixing trend increases and the battery cycle performance deteriorates.

[0119] According to the embodiment of the present application, the first positive electrode active material film layer comprises solid first positive electrode active material particles, and the second positive electrode active material film layer comprises hollow particles, thereby improving the discharge capacity and stability of the positive electrode plate and improving the cycle performance of the positive electrode plate in the battery. The reason for this may be that the distance for lithium ions to transfer protons is shortened. Generally speaking, the lithium ion concentration of the first positive electrode active material film layer is high, but the lithium ion solid phase mass transfer distance is longer. The lithium ion concentration of the second positive electrode active material film layer is low, but the solid phase mass transfer time is shorter, which balances the differences in the intercalation and deintercalation of active lithium ions between the active material particles in the positive electrode plate, is beneficial to the specific capacity of the positive electrode plate, and improves the utilization rate of the active material particles in the positive electrode plate.

[0120] In some optional embodiments, the average particle size Dv of the first positive electrode active material particles is 1 50 is greater than or equal to the average particle size Dv of the second positive electrode active material particles 2 50.

[0121] According to the embodiment of the present application, the average particle size Dv of the first positive electrode active material particles is 1 50 and the average particle size Dv of the second positive electrode active material particles 2The ratio of 50 is within 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 and 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 deintercalation speed of the two layers, thereby improving the gram capacity and cycle performance of the positive electrode sheet.

[0122] In addition, the average particle size Dv of the first positive electrode active material particles is 1 50 is relatively large, which is beneficial to increase the porosity of the first positive electrode active material film layer, thereby facilitating the presence of the first positive electrode active material particles in the positive electrode sheet, dispersing the stress of the first positive electrode active material particles in the positive electrode sheet during the cycle, and improving the cycle stability of the positive electrode sheet, which is beneficial to further improve the cycle performance of the battery.

[0123] In some optional embodiments, the average particle size Dv of the first positive electrode active material particles is 1 50 is 8μm~18μm, and can be optionally 8μm~12μm.

[0124] Alternatively, the average particle size Dv of the first positive electrode active material particles is 1 50 can be any value among 8μm, 9μm, 10μm, 11μm, 12μm, 13μm, 14μm, 15μm, 16μm, 17μm, 18μm, or a range thereof.

[0125] According to the embodiment of the present application, the average particle size Dv of the first positive electrode active material particles is 1 50 In the above range, it is beneficial to increase 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 deintercalation speed of the two layers, thereby improving the gram capacity and cycle performance of the positive electrode sheet.

[0126] In some optional embodiments, the average particle size Dv of the second positive electrode active material particles is 2 50 is 2μm~10μm, and can be optionally 3μm~8μm.

[0127] Alternatively, the average particle size Dv of the second positive electrode active material particles is 2 50 can be any value among 2μm, 3μm, 4μm, 5μm, 6μm, 7μm, 8μm, 9, 10 or a range thereof.

[0128] According to the embodiment of the present application, the average particle size Dv of the second positive electrode active material particles is 250 In the above range, it is beneficial to reduce 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 deintercalation speed of the two layers, thereby improving the gram capacity and cycle performance of the positive electrode sheet.

[0129] In some optional embodiments, the particle size distribution span of the first positive electrode active material particles is 0.3-0.7.

[0130] Optionally, the particle size distribution span of the first positive electrode active material particles may 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 thereof.

[0131] According to the embodiment of the present application, the particle size distribution span of the first positive electrode active material particles is within the above range, which can increase the compaction density of the material, increase the discharge capacity of the battery, balance the active ion deintercalation speed of the two layers, and thus improve the gram capacity and cycle performance of the positive electrode sheet.

[0132] In some optional embodiments, the particle size distribution span of the second positive electrode active material particles is 0.9-1.3.

[0133] Optionally, the particle size distribution span of the second positive electrode active material particles may be any value selected from 0.9, 0.95, 1.0, 1.05, 1.10, 1.15, 1.20, 1.25, and 1.30, or a range thereof.

[0134] According to the embodiment of the present application, the particle size distribution span of the second positive electrode active material particles within the above range can increase the compaction density of the material, increase the discharge capacity of the battery, balance the active ion deintercalation speed of the two layers, and thus improve the gram capacity and cycle performance of the positive electrode sheet.

[0135] In any embodiment of the present application, the particle size distribution span (SPAN) is calculated as (Dv90-Dv10) / Dv50, which represents the particle size distribution of the positive electrode active material, where D v 50 indicates the particle size at which 50% of the volume is accumulated from the small particle size side in the volume-based particle size distribution of the positive electrode active material; Dv10 indicates the particle size at which 10% of the volume is accumulated from the small particle size side in the volume-based particle size distribution of the positive electrode active material; Dv90 indicates the particle size at which 90% of the volume is accumulated from the small particle size side in the volume-based particle size distribution of the positive electrode active material.

[0136] In this application, the volume average particle size D of the negative electrode active material is v 50, Dv10, Dv90 / particle size distribution span (Dv 90-D v 10) / D v 50 are all well-known in the art and can be measured using instruments and methods known in the art. For example, they can be measured using a laser particle size analyzer (e.g., Master Size 3000) with reference to GB / T 19077-2016 Particle Size Distribution Laser Diffraction Method.

[0137] In some optional embodiments, the inner diameter d1 of the hollow structure is 0.6 μm to 5 μm, and optionally 0.9 μm to 4 μm.

[0138] Alternatively, the inner diameter d1 of the hollow structure may be any value selected from the group consisting of 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, and 5 μm, or a range thereof. In the embodiments of the present 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 particle (positive electrode active material).

[0139] According to the embodiment 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 the charge and discharge process, play a role in stabilizing the structure and improving the cycle performance. On the other hand, the second positive electrode active material particles have more three-dimensional channels, which expand the contact area between the material and the electrolyte, shorten the migration distance of lithium ions, and thus increase 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, and thus have more active sites for lithium ions, which increases the gram capacity of the material, increases the gram capacity of the positive electrode sheet, and increases the energy density of the battery.

[0140] The inner diameter of the hollow structure can be tested by any means known in the art. As an example, a conductive glue is attached to the sample table, a powdered sample of the positive electrode active material is spread on the conductive glue, the unadhered powder is blown away with an ear bulb, gold is sprayed, and the particles of the powdered sample are cross-sectioned using argon plasma. A scanning electron microscope is used to obtain a scanning electron microscope photo of the powdered sample at an acceleration voltage of 10kV and an emission current of 10mA. According to the scanning electron microscope photo, the inner diameter of the hollow structure is measured, at least three samples are measured, and at least 50 sets of data are measured for each sample. The average value of the data is taken as the inner diameter of the hollow structure of the sample.

[0141] In some optional embodiments, the thickness d2 of the outer wall of the hollow structure is 0.6 μm to 10 μm, and optionally 0.9 μm to 7 μm.

[0142] Optionally, the outer wall thickness d2 of the hollow structure can be any value among 0.6μm, 0.7μm, 0.8μm, 0.9μm, 1.0μm, 1.5μm, 2.0μm, 2.5μm, 3μm, 4μm, 5μm, 6μm, 7μm, 8μm, 9μm, 10μm or a range of their combinations.

[0143] In the embodiment of the present application, controlling the outer wall thickness d2 of the hollow structure within an appropriate range can improve the structural stability of the hollow structure, increase the gram capacity 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.

[0144] Herein, the term "outer wall thickness of the hollow structure" refers to the thickness of the outer shell layer of the hollow structure (second positive electrode active material particle).

[0145] The thickness of the outer wall of the hollow structure can be tested by any means known in the art. As an example, a conductive glue is attached to the sample table, a powdered sample of the second positive electrode active material particles is spread on the conductive glue, the unadhered powder is blown away with an ear bulb, gold is sprayed, and the particles of the powdered sample are cross-sectioned using argon plasma. A scanning electron microscope is used to obtain a scanning electron microscope photo of the powdered sample at an accelerating voltage of 10kV and an emission current of 10mA. The outer wall thickness of the hollow structure is measured according to the scanning electron microscope image, at least three samples are measured, at least 50 sets of data are measured for each sample, and the average value of the data is taken as the outer wall thickness of the hollow structure of the sample.

[0146] Dv of the second positive electrode active material particles 2 50. The inner diameter d1 and 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 properties of the material. 2 50. When the inner diameter d1 and outer wall thickness d2 of the hollow structure are within a suitable range, the material has more active sites for lithium ions, which increases the gram capacity of the material, thereby increasing the gram capacity of the material and improving the structural stability of the material. When applied to lithium batteries for charge and discharge cycles, the lithium-nickel mixing phenomenon is effectively improved, and the migration rate of lithium ions and electrons is significantly improved, which is beneficial to the balance of the deintercalation and insertion speed of active ions in the positive electrode of the battery, thereby improving the stability of the battery.

[0147] In some optional embodiments, the specific surface area of ​​the first positive electrode active material particles is 0.1 m 2 / g-0.5m 2 / g, optional 0.2m 2 / g-0.3m 2 / g.

[0148] Alternatively, the specific surface area of ​​the first positive electrode active material particles may be 0.1 m 2 / g,0.15m 2 / g,0.2m 2 / g,0.25m 2 / g,0.3m 2 / g,0.35m 2 / g,0.4m 2 / g,0.45m 2 / g,0.5m 2 / g is any numerical value or a range composed thereof.

[0149] In some optional embodiments, the specific surface area of ​​the second positive electrode active material particles is 0.35 m 2 / g-0.8m 2 / g, optional 0.4m 2 / g-0.6m 2 / g.

[0150] Alternatively, the specific surface area of ​​the second positive electrode active material particles may be 0.4 m 2 / g,0.45m 2 / g,0.5m 2 / g,0.55m 2 / g,0.6m 2 / g,0.65m 2 / g,0.7m 2 / g,0.75m 2 / g,0.8m 2 / g is any numerical value or a range composed thereof.

[0151] The specific surface areas of the first positive electrode active material particles and the second positive electrode active material particles are well known in the art and can be measured using instruments and methods well known in the art. For example, they can be tested using a nitrogen adsorption specific surface area analysis test method and calculated using the BET (Brunauer Emmett Teller) method, wherein the nitrogen adsorption specific surface area analysis test can be performed using a Tri Star II specific surface and pore analyzer from Micromeritics, USA.

[0152] According to the embodiments of the present application, the specific surface area of ​​the first positive electrode active material particles and the specific surface area 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 active ion deintercalation speeds of the two layers, thereby improving the gram capacity and cycle performance of the positive electrode sheet.

[0153] In some optional embodiments, the tap density of the first positive electrode active material particles is 1.8 g / cm 3 -4g / cm 3 , optional 2g / cm 3 -3g / cm 3 .

[0154] Optionally, the tap density of the first positive electrode active material particles may be 1.8 g / cm 3 ,1.85g / cm 3 ,1.9g / cm 3 ,1.95g / cm 3 ,2.0g / cm 3 ,2.05g / cm 3 ,2.1g / cm 3 ,2.15g / cm 3 ,2.2g / cm 3 ,2.25g / cm 3 ,2.3g / cm 3 ,2.35g / cm 3 ,2.4g / cm 3 ,2.45g / cm 3 ,2.5g / cm 3 ,2.55g / cm 3 ,2.6g / cm 3 ,2.65g / cm 3 ,2.7g / cm 3 ,2.75g / cm 3 ,2.8g / cm 3 ,2.85g / cm 3 ,2.9g / cm 3 ,2.95g / cm 3 ,3.0g / cm 3 ,3.05g / cm 3 ,3.1g / cm 3 ,3.15g / cm 3 ,3.2g / cm 3 ,3.25g / cm 3 ,3.3g / cm 3 ,3.35g / cm 3 ,3.4g / cm 3 ,3.45g / cm 3 ,3.5g / cm 3 ,3.55g / cm 3 ,3.6g / cm 3 ,3.65g / cm 3 ,3.7g / cm 3,3.75g / cm 3 ,3.8g / cm 3 ,3.85g / cm 3 ,3.9g / cm 3 ,3.95g / cm 3 ,4g / cm 3 Any numerical value or range thereof.

[0155] In some optional embodiments, the tap density of the second positive electrode active material particles is 1.3 g / cm 3 -2.6g / cm 3 , optional 1.5g / cm 3 -1.8g / cm 3 .

[0156] Optionally, the tap density of the second positive electrode active material particles may be 1.3 g / cm 3 ,1.35g / cm 3 ,1.4g / cm 3 ,1.45g / cm 3 ,1.5g / cm 3 ,1.55g / cm 3 ,1.6g / cm 3 ,1.65g / cm 3 ,1.7g / cm 3 ,1.75g / cm 3 ,1.8g / cm 3 ,1.85g / cm 3 ,1.9g / cm 3 ,1.95g / cm 3 ,2.0g / cm 3 ,2.05g / cm 3 ,2.1g / cm 3 ,2.15g / cm 3 ,2.2g / cm 3 ,2.25g / cm 3 ,2.3g / cm 3 ,2.35g / cm 3 ,2.4g / cm 3 ,2.45g / cm 3 ,2.5g / cm 3 ,2.55g / cm 3 ,2.6g / cm 3 Any numerical value or range thereof.

[0157] 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 active ion deintercalation speeds of the two layers, thereby improving the gram capacity and cycle performance of the positive electrode sheet.

[0158] The tap density of the first positive electrode active material particles and the second positive electrode active material particles can be measured using instruments and methods known in the art, for example, using a tap density tester, such as a FZS4-4B tap density tester.

[0159] In some optional embodiments, the second positive electrode active material film layer comprises third positive electrode active material particles, and the average particle size D of the second positive electrode active material particles is V 2 50 and the average particle size D of the third positive electrode active material particles V 3 The ratio of 50 is (1.5~9):1.

[0160] In the embodiments of the present application, the third positive electrode active material particles may have an average particle size smaller than that of the second positive electrode active material particles. The third positive electrode active material particles may be single crystal particles. Single crystal particles have a completely uniform crystal structure, with atoms, molecules, or ions within the entire particle arranged in an orderly manner in the same direction and without grain boundaries or other types of crystal defects. The third positive electrode active material particles may be primary particles.

[0161] Primary particles usually refer to the most basic particle units in a multi-particle system. Primary particles can be tiny particles or particle clusters. They refer to the particles of the positive electrode active material before they agglomerate.

[0162] The primary particle size of the positive electrode active material can be measured using any method known in the art. As an example, after imaging using a scanning electron microscope at 500x magnification, 200 to 600 intact, unobstructed primary particles of the positive electrode active material are randomly selected from the electron microscopic image. The average of the longest diameters of the primary particles in the microscopic image is recorded as the average particle size.

[0163] In this embodiment 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 350 is within the above range, and the third positive electrode active material particles are matched 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 active ion deintercalation in the second positive electrode active material film layer, and balancing the difference in charge and discharge speed (SOC difference) between the first active material film layer and the second active material film layer, which is beneficial to the performance of gram capacity.

[0164] In some optional embodiments, the average particle size D of the third positive electrode active material particles is V 3 50 is 0.8μm to 5μm, and can be optionally 2μm to 5μm.

[0165] According to the embodiment of the present application, the average particle size D of the third positive electrode active material particles is V 3 50 In the above range, the particle size is relatively small and the anisotropy is smaller. At this time, the volume expansion rate of the third positive electrode active material particles in the battery during charging and discharging is lower, which makes the cycle stability of the third positive electrode active material particles better, further improves the cycle stability of the overall positive electrode sheet, and further improves the cycle performance of the battery.

[0166] In some optional embodiments, the specific surface area of ​​the third positive electrode active material particles is 0.4 m 2 / g-0.9m 2 / g, optional 0.6m 2 / g-0.8m 2 / g.

[0167] According to the embodiment of the present application, the specific surface area of ​​the third positive electrode active material particles is within the above range, which is conducive 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.

[0168] The specific surface area of ​​the first and second positive electrode active material particles can be measured using any method known in the art. For 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 performed using a TriStar II 3020 instrument. The positive electrode active material is dispersed in a dispersant (ethanol), ultrasonicated for 30 minutes, and then dried in a vacuum drying oven. Finally, the specific surface area of ​​the positive electrode active material is measured using a specific surface area meter.

[0169] The larger the specific surface area of ​​the first positive electrode active material particles, the second positive electrode active material particles, and the third positive electrode active material particles, the more active sites in the positive electrode active material, the faster the positive electrode active material exchanges electrons, and the better the battery's kinetic performance. However, too many active sites will increase the side reactions between the positive electrode active material and the electrolyte, worsening the battery's cycle performance, while too few active sites will lead to a decrease in the chemical reaction in the battery system, resulting in poor battery capacity and cycle performance.

[0170] 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 an appropriate range, the battery has high discharge capacity and energy density, excellent rate performance and cycle performance, and comprehensively improves the electrochemical performance of the battery.

[0171] In some optional embodiments, the tap density of the third positive electrode active material particles is 1.8 g / cm 3 -3.4g / cm 3 , optional 2g / cm 3 -2.2g / cm 3 .

[0172] According to the embodiment of the present application, the tap density of the third positive electrode active material particles is within the above range, which is conducive to controlling the 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.

[0173] In some optional embodiments, the third positive electrode active material particles are one or more of particles with a hollow structure and solid particles.

[0174] In some optional embodiments, the particle size distribution span of the third positive electrode active material particles is 0.8-1.5.

[0175] According to the embodiment of the present application, the particle size distribution span of the third positive electrode active material particles is within the above range, which is beneficial to improving the compaction density of the second active material film layer, balancing the active ion deintercalation speed of the two layers, and improving the stability of the positive electrode sheet, thereby improving the gram capacity and cycle performance of the positive electrode sheet.

[0176] 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 a well-known meaning in the art, that is, the particle size corresponding to the cumulative particle size distribution of 50% on a volume basis, which can be detected by known methods. For example, a laser diffraction particle size distribution measuring instrument (Malvern Mastersizer 3000) is used to measure the particle size distribution according to the particle size distribution laser diffraction method GB / T19077-2016 to obtain Dv50. Dv10 represents the particle size of the positive electrode active material in the volume-based particle size distribution, from the small particle size side, reaching the volume cumulative 10%; Dv90 represents the particle size of the positive electrode active material in the volume-based particle size distribution, from the small particle size side, reaching the volume cumulative 90%. As an example, reference can be made to GB / T 19077-2016 / ISO 13320:2009 particle size distribution laser diffraction method, and the measurement can be performed using the Malvern 3000 device.

[0177] 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 a meaning well known in the art. The particle size distribution span (SPAN) is calculated as (Dv90-Dv10) / Dv50, which represents the particle distribution of the positive electrode active material, wherein Dv50 represents the particle size of the positive electrode active material in the volume-based particle size distribution, from the small particle size side to 50% of the volume accumulation; Dv10 represents the particle size of the positive electrode active material in the volume-based particle size distribution, from the small particle size side to 10% of the volume accumulation; and Dv90 represents the particle size of the positive electrode active material in the volume-based particle size distribution, from the small particle size side to 90% of the volume accumulation.

[0178] According to the above definition, the Dv50, Dv10, and Dv90 values ​​of the positive electrode active material are measured according to the method specified in GB / T19077-2016, and the SPAN of the positive electrode active material is further calculated. In any embodiment of this application, the term "positive electrode active material" may include one or more of the first positive electrode active material particles, the second positive electrode active material particles, and the third positive electrode active material particles.

[0179] Maintaining SPAN in a wider range can increase the compaction density of the material and improve the discharge capacity of the battery.

[0180] 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:(5-23.5).

[0181] Optionally, the ratio of the thickness h1 of the first positive electrode active material layer to the thickness h2 of the second positive electrode active material layer can be 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 any range thereof.

[0182] According to an embodiment 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 and insertion speed of the active ions in the two active material film layers, improve the stability of the positive electrode sheet, and thus improve the gram capacity and cycle performance of the positive electrode sheet.

[0183] In some optional embodiments, the thickness h1 of the first positive electrode active material film layer is 130-200 μm.

[0184] Alternatively, the thickness h1 of the first positive electrode active material layer may 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 a range thereof.

[0185] In some optional embodiments, the thickness h2 of the second positive electrode active material film layer is 50-170 μm.

[0186] Optionally, the thickness h2 of the second positive electrode active material film layer can be any value among 50μm, 55μm, 60μm, 65μm, 70μm, 75μm, 80μm, 85μm, 90μm, 95μm, 100μm, 105μm, 110μm, 115μm, 120μm, 125μm, 130μm, 135μm, 140μm, 145μm, 150μm, 155μm, 160μm, 165μm, 170μm or a range of their compositions.

[0187] 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 measured using commonly used detection methods in the art. The positive electrode sheet is cut along the thickness direction and polished to obtain a smooth cross-section. The thickness h1 and the thickness h2 of the first positive electrode active material film layer of the positive electrode sheet are measured using a scanning electron microscope. At least three samples are measured, with at least 50 data points measured for each sample. The average of the data is taken as the thickness h1 and the thickness h2 of the first positive electrode active material film layer of the sample.

[0188] In some optional embodiments, the ratio of the thickness h1 of the first positive electrode active material layer to the sum of the masses of the first positive electrode active material layer and the second positive electrode active material layer is 1.2-2 μm / g.

[0189] 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 1.2μm / g, 1.3μm / g, 1.4μm / g, 1.5μm / g, 1.6μm / g, 1.7μm / g, 1.8μm / g, 1.9μm / g, 2.0μm / g or a range of their compositions.

[0190] According to an embodiment 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 deintercalation and deintercalation speeds 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 of the positive electrode sheet, and thus is beneficial to the cycle performance of the battery.

[0191] The thickness h1 of the first positive electrode active material film layer and the sum of the masses of the first and second positive electrode active material film layers can be measured using methods commonly used in the art. A prepared positive electrode sheet can be taken and weighed to a mass of M. The first and second positive electrode active material film layers in the positive electrode sheet 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 to M1. The sum of the thickness h1 of the first positive electrode active material film layer and the masses of the first and second positive electrode active material film layers = M - M1. At least three positive electrode sheet samples can be measured, with at least 50 data points measured for each sample, and the data averaged.

[0192] 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; 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%.

[0193] Herein, “porosity” refers to the ratio of the pore volume in the first cathode active material layer to the total volume of the first cathode active material layer or the ratio of the pore volume in the second cathode active material layer to the total volume of the second cathode active material layer.

[0194] The porosity of the first and second cathode active material layers can be measured using any method known in the art. For example, the porosity can be measured using the gas displacement method in accordance with GB / T 24586. Porosity = (V1 - V2) / V1 × 100%, where V1 is the apparent volume of the sample and V2 is the actual volume of the sample.

[0195] In some optional embodiments, the compaction density of the first positive electrode active material film layer is less than the compaction density of the second positive electrode active material film layer; optionally, the compaction density of the first positive electrode active material film layer is 2.9 g / cm 3 -3.3g / cm 3 ; Optionally, the second positive electrode active material layer compaction density is 3.2g / cm 3 -3.7g / cm 3 .

[0196] The compacted density of the first and second positive electrode active material film layers can be measured using instruments and methods known in the art, such as an electronic pressure tester, such as the UTM7305. The compacted density of the positive electrode sheet can be calculated using the formula PD = M / (d × A), where M is the mass of a 40 mm diameter disc, which can be obtained by weighing it ten times and averaging it; d is the thickness of the cold-pressed positive electrode sheet, which can be obtained by measuring the thickness of each disc cut to a diameter of 40 mm and averaging it; and A is the area of ​​the 40 mm disc.

[0197] In some optional embodiments, the capacity ratio 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 gram capacity of the first positive electrode active material film layer is 225mAh / g-240mAh / g; optionally, the gram capacity of the second positive electrode active material film layer is 220mAh / g-235mAh / g.

[0198] Optionally, the capacity ratio of the first positive electrode active material film layer to the second positive electrode active material film layer may 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 a range thereof.

[0199] According to the embodiments of the present application, by detecting that the ratio of the capacity of the first positive electrode active material film layer and the second positive electrode active material film layer is within the above range after the positive electrode plate is subjected to charge and discharge cycles in the button cell / battery cell, the deintercalation and insertion speeds of the active ions in the first positive electrode active material film layer and the second positive electrode active material film layer are balanced, which is beneficial to the capacity of the positive electrode plate and improves the utilization rate of the positive electrode active material.

[0200] The gram capacity of the first positive electrode active material film layer and the second positive electrode active material film layer can be tested by any means known in the art. As an example, a fresh positive electrode sheet can be sampled to prepare a button battery, with the lithium sheet as the negative electrode. At 25°C and normal pressure, the button battery is charged at a constant current rate of 0.02C to a voltage of 3.5V, then charged at a constant current rate of 0.1C to a voltage of 4.3V, and then charged at a constant voltage of 4.3V until the current drops to 0.05C. The charge capacity at this time is recorded, which is the first lithium de-capacity; then the battery is discharged at a constant current rate of 0.1C to a voltage of 2.5V, and the discharge capacity at this time is recorded, which is the first lithium insertion capacity. Then, another set of fresh positive electrode sheets is used to prepare a button battery from the positive electrode sheet after peeling off the first positive electrode active material film layer. The lithium sheet is used as the negative electrode for testing, and the charge capacity at this time is recorded, which is the first lithium insertion capacity. As another example, a disassembled battery can be used to obtain a first powder of a first positive electrode active material film layer and a second powder of a second positive electrode active material film layer. The first powder and the second powder are then prepared into fresh positive electrode sheets containing the first and second positive electrode active material film layers for testing.

[0201] In some optional embodiments, the first positive electrode active material particles and the second positive electrode active material particles have the following general structural formulas: Li a Ni x Co y M 1-x-y O2, wherein M includes one or more of Mn, Al, B, Zr, Sr, Y, Sb, W, Ti, Mg, Nb, and Ba, 0.55≤x≤1.05, 0≤y≤0.45, and 0.8≤a≤1.2.

[0202] In some embodiments, Li a Ni x Co y M 1-x-y In O2, a is any value selected from 0.8, 0.9, 1.0, 1.01, 1.02, 1.03, 1.04, and 1.05, or a range consisting of any two of these values.

[0203] In some embodiments, Li a Ni x Co y M1-x-y In O2, x is any value selected from 0.55, 0.6, 0.7, 0.8, 0.9, 0.95, and 0.995, or a range consisting of any two of these values.

[0204] 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 consisting of any two values ​​thereof.

[0205] 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.

[0206] 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.

[0207] 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.

[0208] 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.

[0209] 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.

[0210] According to the embodiment of the present application, the use of the above-mentioned materials can ensure that the second active material film layer has a higher gram capacity, thereby increasing the gram capacity of the positive electrode sheet, so that the battery has a high discharge capacity and energy density.

[0211] In some optional embodiments, the third positive electrode active material particles include the following structural formula: Li a Ni x Co y M 1-x-y O2, wherein M includes one or more of Mn, Al, B, Zr, Sr, Y, Sb, W, Ti, Mg, Nb, and Ba, 0.55≤x≤1.05, 0≤y≤0.45, and 0.8≤a≤1.2.

[0212] According to the embodiment of the present application, the use of the above-mentioned materials can ensure that the second active material film layer has a higher gram capacity, thereby increasing the gram capacity of the positive electrode sheet, so that the battery has a high discharge capacity and energy density.

[0213] In some optional 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 The above-mentioned positive electrode active materials can better balance the charge and discharge speed of the positive electrode sheet in the battery, balance the average charging efficiency of its surface and the side close to the positive electrode current collector, improve the gram capacity of the positive electrode sheet, and make the battery have high discharge capacity and energy density.

[0214] In some embodiments, the positive electrode sheet includes a positive electrode current collector and a positive electrode active material film layer disposed on at least one surface of the positive electrode current collector, wherein the positive electrode active material film layer includes first positive electrode active material particles and second positive electrode active material particles.

[0215] As an example, the positive electrode current collector has two surfaces facing each other in its thickness direction, and the positive electrode active material film layer is disposed on either or both of the two facing surfaces of the positive electrode current collector.

[0216] In some embodiments, the positive electrode current collector may be a metal foil or a composite current collector. For example, aluminum foil may be used as the metal foil. The composite current collector may include a polymer material base and a metal layer formed on at least one surface of the polymer material base. The composite current collector may be formed by forming a metal material (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.).

[0217] 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 that are well known in the art. As an example, the positive electrode active material may include at least one of the following materials: lithium-containing phosphates 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 traditional materials that can be used as positive electrode active materials for batteries may also be used. These positive electrode active materials may be used alone or in combination of two or more. 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 (also referred to as NCM 333 ), LiNi 0.5 Co 0.2 Mn 0.3 O2 (also referred to as NCM 523 ), LiNi 0.5 Co 0.25 Mn 0.25 O2 (also referred to as NCM 211 ), LiNi 0.6 Co 0.2 Mn 0.2 O2 (also referred to as NCM 622 ), LiNi 0.8 Co 0.1 Mn 0.1 O2 (also referred to as NCM 811 ), lithium nickel cobalt aluminum oxide (such as LiNi 0.85 Co 0.15 Al 0.05O2) and its modified compounds. Examples of olivine-structured lithium-containing phosphates may include, but are not limited to, at least one of lithium iron phosphate (such as LiFePO4 (also referred to 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 iron manganese phosphate, and a composite material of lithium iron manganese phosphate and carbon.

[0218] In some embodiments, the positive electrode active material film layer may further optionally include a binder. As an example, the binder may include at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), a vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, a vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, a tetrafluoroethylene-hexafluoropropylene copolymer, and a fluorine-containing acrylate resin.

[0219] In some embodiments, the positive electrode active material film layer may further include a conductive agent. For 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.

[0220] In some embodiments, the positive electrode sheet can be prepared by the following method: the components for preparing the positive electrode sheet, such as the positive electrode active material, the conductive agent, the binder and any other components, are dispersed in a solvent (such as N-methylpyrrolidone) to form a positive electrode slurry; the positive electrode slurry is coated on the positive electrode current collector, and after drying, cold pressing and other processes, the positive electrode sheet can be obtained.

[0221] Method for preparing positive electrode sheet

[0222] In a second aspect, an embodiment of the present application provides a method for preparing a positive electrode sheet, comprising:

[0223] providing a second slurry containing second positive electrode active material particles, wherein the second positive electrode active material particles have a hollow structure;

[0224] coating a second slurry on the positive electrode current collector to form a second positive electrode active material film layer;

[0225] providing a first slurry containing first positive electrode active material particles, wherein the first positive electrode active material particles are solid particles;

[0226] The first slurry is applied to form a first positive electrode active material film layer on a side of the second positive electrode active material film layer away from the positive electrode current collector, thereby manufacturing a positive electrode sheet.

[0227] According to an embodiment of the present application, a second slurry containing particles of a second positive electrode active material is coated on the positive electrode current collector to form a second positive electrode active material film layer, and a first slurry containing particles of a first positive electrode active material is coated 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, so that during the charge and discharge process of the battery, the positive electrode sheet comprising the embodiment of the present application has a gradually decreasing concentration of active ions from the diaphragm to the positive electrode sheet near the positive electrode current collector during the mass transfer of the electrolyte, so that the first positive electrode active material particles in the first positive electrode active material film layer are solid particles, and the active ions are concentrated in the first positive electrode active material layer. The deintercalation distance of the 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 deintercalation 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 deintercalation speed of the active ions in the first positive electrode active material film layer and the second positive electrode active material film layer, and balances the difference in the charge and discharge (SOC) speed of the active ions between the first positive electrode active material film layer and the second positive electrode active material film layer, which is beneficial to the performance of the gram capacity of the positive electrode sheet.

[0228] 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.

[0229] In some optional embodiments, the second slurry includes, by mass percentage, a mixture of 60%-90% of the second positive electrode active material particles and 10%-40% of the third positive electrode active material particles.

[0230] According to an embodiment of the present application, 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 are controlled. On the basis of balancing the active ion deintercalation rate of the first positive electrode active material film layer and the second positive electrode active material film layer, the structural stability of the positive electrode sheet and the charge and discharge rate of the battery are taken into account.

[0231] battery cells

[0232] In a third aspect, embodiments of the present application provide a battery cell comprising the positive electrode sheet of the first aspect or the positive electrode sheet prepared by the method of the second aspect. According to embodiments of the present application, the battery cell comprises the aforementioned positive electrode sheet, and thus the battery has the beneficial effects of the aforementioned positive electrode sheet.

[0233] Typically, a battery consists of a positive electrode, a negative electrode, an electrolyte, and a separator. During the battery's charge and discharge processes, active ions are inserted and removed between the positive and negative electrodes. The electrolyte conducts ions between the positive and negative electrodes. The separator, located between the positive and negative electrodes, primarily prevents short circuits between the positive and negative electrodes while allowing ions to pass through.

[0234] 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, and the positive electrode plate is charged at 0.33C from an initial state to a cut-off voltage of 4.25V, and discharged at 1C to a cut-off voltage of 2.7V in a battery cell, and the charge and discharge cycle is performed until the capacity of the battery cell is 80% of the initial state.

[0235] In the XRD diffraction patterns of the first positive electrode active material particles and the second positive electrode active material particles, the I 003 / I 104 value and the I of the second positive electrode active material particle 003 / I 104 The ratio between the values ​​is (1~1.5):1.

[0236] According to the embodiment of the present application, the first positive electrode active material particles have an I 003 / I 104 The value represents the (003) crystal plane diffraction peak intensity I of the first positive electrode active material particle. 003 and (104) crystal plane diffraction peak intensity I 104 The ratio of the second positive electrode active material particles I 003 / I 104 The (003) crystal plane diffraction peak intensity I of the second positive electrode active material particle is 003 and (104) crystal plane diffraction peak intensity I 104 ratio.

[0237] According to the embodiment of the present application, by controlling the I 003 / I 104 value and the I of the second positive electrode active material particle 003 / I 104 The ratio between the values ​​is in an appropriate range, which is beneficial to controlling the lithium-nickel mixing of the first active material film layer and the second active material film layer, balancing the rates of lithium ion insertion and extraction in the first active material film layer and the second active material film layer, and improving the performance of the battery.

[0238] As an example, the (003) crystal plane diffraction peak intensity I of the first positive electrode active material particle is 003 and (104) crystal plane diffraction peak intensity I 104Or the (003) crystal plane diffraction peak intensity I of the second positive electrode active material particles 003 and (104) crystal plane diffraction peak intensity I 104 The detection method can be: disassemble the positive electrode from the battery, take the positive electrode, the area of ​​​​3*3cm 2 Up to 4*4cm 2 ; Take 5-10g of the powder of the first positive electrode active material film layer and the second positive electrode active material film layer respectively. If the powder of the first positive electrode active material film layer and the second positive electrode active material film layer is a block sample after scraping, grind it and prepare the sample in a glove box. The average particle size of the prepared powder is <30μm and can pass through a 200-mesh sieve; use a sample trough with a depth of 1mm and a diameter of 25mm for sampling, and adopt a flat plate sample preparation method for sample preparation. Then carry out the test: starting angle 15°, ending angle 70°, step length 0.01°, each step length 0.6s. Among them, the fixed core parameters of the XRD detection equipment (such as the XRD detection equipment of Bruker, Germany) are: voltage: 40KV, current: 40mA, anti-scattering slit: 1mm.

[0239] As an example, the general structural 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 independently: Li a Ni x Co y M 1-x-y O2, wherein M includes one or more of Mn, Al, B, Zr, Sr, Y, Sb, W, Ti, Mg, Nb, and Ba, 0.55≤x≤1.05, 0≤y≤0.45, and 0.8≤a≤1.2. The diffraction angle 2θ1 of the crystal plane (003) of the first positive electrode active material particle is 18.55° to 18.85°, the diffraction angle 2θ2 of the crystal plane (003) of the second positive electrode active material particle 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 crystal plane of the first positive electrode active material particle (104) is 44.30° to 44.50°, the diffraction angle 2θ4 of the crystal plane of the second positive electrode active material particle (104) is 45.10° to 45.30°, and the difference Δθ2 between the two is 0.65° to 0.85°; in each XRD diffraction pattern of the first positive electrode active material particle and the second positive electrode active material particle, the diffraction peak intensity I of the (003) crystal plane of the first positive electrode active material particle can be measured respectively. 003 and (104) crystal plane diffraction peak intensity I 104 The ratio of the (003) crystal plane diffraction peak intensity I of the second positive electrode active material particles 003 and (104) crystal plane diffraction peak intensity I 104 ratio.

[0240] [Negative electrode]

[0241] The negative electrode sheet includes a negative electrode current collector and a negative electrode film layer disposed on at least one surface of the negative electrode current collector. The negative electrode film layer includes a negative electrode active material.

[0242] As an example, the negative electrode current collector has two surfaces opposite to each other in its thickness direction, and the negative electrode film layer is disposed on either or both of the two opposite surfaces of the negative electrode current collector.

[0243] In some embodiments, the negative electrode current collector may be a metal foil or a composite current collector. For example, copper foil may be used as the metal foil. The composite current collector may include a polymer base layer and a metal layer formed on at least one surface of the polymer base material. The composite current collector may be formed by forming a metal material (copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy, etc.) on a polymer base material (such as a base material of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0244] In some embodiments, the negative electrode active material may be a negative electrode material for a battery that is well known in the art. As an example, the negative electrode active material may include at least one of the following materials: artificial graphite, natural graphite, soft carbon, hard carbon, silicon-based materials, tin-based materials, lithium titanate, etc. The silicon-based material may be selected from at least one of elemental silicon, silicon oxides, silicon-carbon composites, silicon-nitrogen composites, and silicon alloys. The tin-based material may 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 traditional materials that can be used as negative electrode materials for batteries may also be used. These negative electrode materials may be used alone or in combination of two or more.

[0245] In some embodiments, the negative electrode active material has a gram capacity of 600 mAh / g to 2500 mAh / g.

[0246] In some embodiments, the negative electrode active material includes silicon monoxide.

[0247] In some embodiments, based on the total mass of the negative electrode active material, the mass content of silicon monoxide is 20%-100%, optionally 50%-100%.

[0248] In some embodiments, the negative electrode film layer may further include a binder. The binder may 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).

[0249] In some embodiments, the negative electrode film layer may further include a conductive agent, which may be selected from at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0250] In some embodiments, the negative electrode film layer may optionally include other additives, such as a thickener (eg, sodium carboxymethyl cellulose (CMC-Na)).

[0251] In some embodiments, the negative electrode sheet can be prepared by the following method: the components for preparing the negative electrode film layer, such as the negative electrode material, the conductive agent, the binder and any other components, are dispersed in a solvent (such as deionized water) to form a negative electrode slurry; the negative electrode slurry is coated on the negative electrode collector, and after drying, cold pressing and other processes, the negative electrode sheet can be obtained.

[0252] [Electrolytes]

[0253] The electrolyte conducts ions between the positive and negative electrodes. This application does not specify the type of electrolyte, and the electrolyte can be selected based on the needs. For example, the electrolyte can be liquid, gel, or solid.

[0254] In some embodiments, the electrolyte is an electrolyte solution comprising an electrolyte salt and a solvent.

[0255] 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 difluorooxalatoborate, lithium dioxalatoborate, lithium difluorodioxalatophosphate, and lithium tetrafluorooxalatophosphate.

[0256] In some embodiments, the solvent can be selected from at least one of ethylene carbonate, propylene carbonate, ethyl methyl carbonate, diethyl carbonate, dimethyl carbonate, dipropyl carbonate, methylpropyl carbonate, ethylpropyl 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, cyclopentane, dimethyl sulfone, methyl ethyl sulfone and diethyl sulfone.

[0257] In some embodiments, the electrolyte may further include additives. For example, the additives may include negative electrode film-forming additives, positive electrode film-forming additives, and additives that can improve certain battery properties, such as additives that improve battery overcharge performance, and additives that improve battery high or low temperature performance.

[0258] [Isolation film]

[0259] In some embodiments, the battery cell further includes a separator. The present application has no particular limitation on the type of separator, and any known porous separator with good chemical and mechanical stability can be selected.

[0260] 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.

[0261] In some embodiments, the positive electrode sheet, the negative electrode sheet, and the separator can be formed into an electrode assembly through a winding process or a lamination process.

[0262] In some embodiments, a battery may include a battery cell including the above-described electrode assembly.

[0263] In some embodiments, the battery cell may include an outer packaging that can be used to encapsulate the electrode assembly and the electrolyte.

[0264] In some embodiments, the outer packaging of the battery cell may be a hard shell, such as a hard plastic shell, an aluminum shell, or a steel shell. Alternatively, the outer packaging of the battery cell may be a soft shell, such as a pouch-type soft shell. The soft shell may be made of plastic, such as polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0265] The present application has no particular limitation on the shape of the battery cell, which can be cylindrical, square, or any other shape. For example, FIG2 shows a battery cell 5 with a square structure as an example.

[0266] In some embodiments, referring to Figure 3, the outer packaging may include a shell 51 and a cover plate 53. The shell 51 may include a bottom plate and a side plate connected to the bottom plate, and the bottom plate and the side plate enclose a receiving cavity. The shell 51 has an opening connected to 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 isolation membrane can be formed into an electrode assembly 52 through a winding process or a lamination process. The electrode assembly 52 is encapsulated in the receiving cavity. The electrolyte is infiltrated in the electrode assembly 52. ​​The number of electrode assemblies 52 contained in the battery cell 5 can be one or more, and those skilled in the art can select according to specific actual needs.

[0267] Battery

[0268] In a fourth aspect, an embodiment of the present application provides a battery comprising the battery cell of the third aspect. According to the embodiment of the present application, the battery comprises the aforementioned battery cell, and thus the battery has the beneficial effects of the aforementioned battery cell.

[0269] In some embodiments, the battery may further include a case; the battery cells are housed in the case.

[0270] The battery may include one or more battery cells, and those skilled in the art may select the specific number based on the application and capacity of the battery.

[0271] Furthermore, in the above-described battery, multiple battery cells are assembled to form a battery module. Figure 4 shows an example of a battery module 4. Referring to Figure 4 , within the battery module 4, multiple battery cells 5 can be arranged sequentially along the length of the battery module 4. Of course, any other arrangement is also possible. Furthermore, the multiple battery cells 5 can be secured using fasteners.

[0272] Optionally, the battery module 4 may further include a housing having an accommodation space, and the plurality of battery cells 5 are accommodated in the accommodation space.

[0273] Figures 5 and 6 illustrate an example battery 1. Referring to Figures 5 and 6 , the battery 1 may include a battery box and multiple battery modules 4 disposed within the box. The battery box comprises an upper case 2 and a lower case 3. The upper case 2 can be positioned over the lower case 3 to form an enclosed space for accommodating the battery modules 4. The multiple battery modules 4 can be arranged in any manner within the battery box.

[0274] In some embodiments, the battery may be a battery cell.

[0275] Electrical devices

[0276] In a fifth aspect, an embodiment of the present application provides an electrical device comprising the battery of the fourth aspect. According to the embodiment of the present application, the electrical device comprises the aforementioned battery, and thus the electrical device has the beneficial effects of the aforementioned battery.

[0277] The battery can be used as a power source or as an energy storage unit for the electrical devices. The electrical devices may include, but are not limited to, mobile devices (e.g., mobile phones, laptops, etc.), electric vehicles (e.g., 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.

[0278] As the electrical device, the above-mentioned battery can be selected according to its usage requirements.

[0279] FIG7 shows an example of an electric device, which may be a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle.

[0280] As another example, the device may be a mobile phone, a tablet computer, a notebook computer, etc. Such a device is usually required to be lightweight and thin, and may use a battery consisting of only battery cells as a power source.

[0281] Example

[0282] Below, the embodiment of the present application is described. The embodiment described below is exemplary and is only used to explain the present application, and is not to be construed as limiting the present application. Where specific techniques or conditions are not specified in the embodiments, the techniques or conditions described in the literature in this area or the product specifications are used. Reagents or instruments used that do not specify the manufacturer are conventional products that can be obtained commercially.

[0283] Example 1

[0284]

Preparation of positive electrode sheet

[0285] The second positive electrode active material particles and the third positive electrode active material particles are nickel-cobalt-manganese (NCM) ternary material LiNi 0.96 Co 0.02 Mn 0.01 Ba 0.01 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), the conductive agent carbon black, and the binder polyvinylidene fluoride (PVDF) are mixed in a mass ratio of 97:1:2, and N-methylpyrrolidone is added. The mixture is stirred for 0.5-6 hours to obtain a positive electrode slurry with a solid content of 68%. The slurry is then evenly coated on the positive electrode current collector to obtain a second positive electrode active material film layer, wherein the average particle size of the second positive electrode active material particles is DV 2 50 is 7 μm, the inner diameter d1 is 3 μm, the outer wall thickness d2 is 4 μm, and other parameters and parameters of the third positive electrode active material particles are shown in Table 1.

[0286] The first cathode active material particle nickel cobalt manganese (NCM) ternary material LiNi 0.96 Co 0.02 Mn 0.01 Ba 0.01 O2. First, the positive electrode active material particles, the conductive agent carbon black, and the binder polyvinylidene fluoride (PVDF) are mixed in a mass ratio of 97:1:2, and N-methylpyrrolidone is added. The mixture is stirred for 0.5-6 hours to obtain a positive electrode slurry with a solid content of 68%. The slurry is then evenly coated on the positive electrode current collector with a coating mass of 35 mg / cm 2 , a first positive electrode active material film layer was prepared. The parameters of the first positive electrode active material particles are shown in Table 1.

[0287] After drying, cold pressing and cutting, the positive electrode sheet is obtained.

[0288]

Preparation of lithium batteries

[0289] Positive electrode sheet: the positive electrode sheet prepared as described above.

[0290] Preparation of the negative electrode sheet: The negative electrode active material (i.e., artificial graphite and silicon carbon, wherein 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 hydroxymethyl cellulose (CMC-Na) are added to deionized water in a weight ratio of 94.5:1:0.375:2.8:1.325, and mixed and stirred for 0.5-6 hours to obtain a first active material layer slurry; the slurry is evenly coated on the negative electrode current collector in layers and dried.

[0291] Isolation film: 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 aluminum oxide and a binder polyvinylidene fluoride. The mass content of aluminum oxide in the coating is 80%, and the mass content of the binder polyvinylidene fluoride in the coating is 20%.

[0292] Electrolyte: LiPF6 and LIFSI were 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 a molar concentration of LiPF6 and LIFSI of 1 mol / L respectively.

[0293] Lithium battery assembly: The positive electrode sheet, separator, and negative electrode sheet are wound in sequence to obtain a bare cell; the bare cell is placed in a packaging shell, dried, and then injected with electrolyte. After vacuum packaging, standing, formation, shaping and other processes, a lithium-ion battery is obtained.

[0294] Example 2-1 to Example 2-2

[0295] Similar to Example 1, the difference is that the first positive electrode active material particles, the second positive electrode active material particles, and the third positive electrode active material particles in Example 2-1 are nickel-cobalt-manganese (NCM) ternary materials LiNi 0.97 Co 0.01 Mn 0.01 Ba 0.01 O2. The first positive electrode active material particles, the second positive electrode active material particles, and the third positive electrode active material particles in Example 2-2 are made of nickel-cobalt-manganese (NCM) ternary material LiNi 0.98 Co 0.01 Mn 0.005 Ba 0.005 O2.

[0296] Example 3-1 to Example 3-3

[0297] Similar to Example 1, the difference is that the parameters of the first positive active material particles in Example 3-1 and Example 3-3 are different, as shown in Table 1.

[0298] Example 4-1 to Example 4-9

[0299] Similar to Example 1, the differences are: the particle size, content, and second active material film thickness h2 of the second and third positive electrode active material particles are different. In Example 4-2, the second positive electrode active material particles have an inner diameter d1 of 4 μm and an outer wall thickness d2 of 3 μm, indicating a hollow structure. In Example 4-3, the second positive electrode active material particles have an inner diameter d1 of 2 μm and an outer wall thickness d2 of 5 μm. In Examples 4-4 and 4-5, the content of the second positive electrode active material particles in the second active material film layer varies. In Example 4-6, the thickness h2 of the second positive electrode active material film layer varies. In Examples 4-7 and 4-8, the particle size parameters of the third positive electrode active material particles vary. Example 9 does not include third positive electrode active material particles. Details are shown in Table 1.

[0300] Comparative Example 1

[0301] Similar to Example 1, except that the first, second, and third positive active material particles in Comparative Example 1 were replaced with the first positive active material particles in Example 1, serving as the positive active particles in the positive electrode sheet. The thickness of the active material film layer in Comparative Example 1 was the sum of the thicknesses of the first and second positive active material films in Example 1, which was 300 μm.

[0302] Comparative Example 2

[0303] Similar to Example 1, except that the first, second, and third positive active material particles in Comparative Example 2 were 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 was the sum of the thicknesses of the first and second positive active material films in Example 1, which was 300 μm.

[0304] Comparative Example 3

[0305] Similar to Example 1, except that the first, second, and third positive active material particles in Comparative Example 3 were 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 was the sum of the thicknesses of the first and second positive active material films in Example 1, which was 300 μm.

[0306] Performance Testing

[0307] The batteries obtained in the above examples and comparative examples were subjected to performance tests, respectively. The test results are shown in Table 2.

[0308] 1) Discharge capacity test

[0309] The battery cell prepared above was allowed to rest at 25°C for 2 hours to ensure the cell temperature was 25°C. At 25°C, the battery cell was charged at 0.1C to a charge cutoff voltage of 4.25V. Constant voltage charging was then continued at this charge cutoff voltage until the current reached 0.02C, at which point charging was terminated (where C represents the rated capacity of the battery cell). The battery cell was allowed to rest at 25°C for 0.5 hours. At 25°C, the battery cell was discharged at 0.1C to a discharge cutoff voltage of 2.7V. The total discharge capacity (C0) of the battery cell was recorded.

[0310] 2) Energy density test

[0311] Battery Cell Capacity Test: The prepared battery cell was allowed to stand at 25°C for 2 hours, ensuring the cell temperature was 25°C. At 25°C, the battery cell was charged at 0.1C to the charge cutoff voltage. Constant voltage charging was then continued at the same charge cutoff voltage until the current reached 0.05C, at which point the charge was cutoff (where C represents the rated capacity of the battery cell). The battery cell was allowed to stand at 25°C for 1 hour. At 25°C, the battery cell was discharged at 0.1C to the discharge cutoff voltage. The total discharge capacity (C0) released by the battery cell was recorded, and the total discharge energy (E0) was recorded.

[0312] Battery cell weight measurement: Place the battery cell on an electronic balance until the weight stabilizes, and read the battery cell weight value M0.

[0313] Energy density calculation: Battery cell discharge energy E0 / battery cell weight M0 is the energy density of the battery cell.

[0314] 3) 10~80% SOC charging time test

[0315] Voltage calibration: Place a laminated three-electrode battery cell of the same battery design at 25°C for 30 minutes; at 25°C, charge the battery cell at 0.33C to the charge cut-off voltage, and then continue constant voltage charging at the charge cut-off voltage until the current reaches 0.05C, at which point the charge is cut off (where C represents the rated capacity of the battery cell); place the cell at 25°C for 1 hour; at 25°C, discharge the cell at 0.33C to the discharge cut-off voltage, and record the total discharge capacity C1 of the cell; place the cell at 25°C for 1 hour.

[0316] Charging test: The stacked three-electrode cell was incubated at 25°C for 30 minutes; the discharge voltage was set to 0.33C1 DC; the cell was incubated for 5 minutes; the charge voltage was set to xC1 CC (the three electrodes monitor the anode potential, and the next step is skipped when the anode potential is 0V). This step was repeated nine times, with x values ​​of 5, 4, 4.5, 3, 2, 1, 0.8, 0.5, and 0.33, respectively. The x value corresponding to the anode potential of 0V and the charge capacity Cx were used.

[0317] 4) Battery cycle capacity retention test

[0318] The voltage calibration method of the battery cells prepared in each embodiment and comparative example is as follows:

[0319] Place the battery cell at 25°C for 2 hours, ensuring that the temperature of the battery cell is 25°C; charge the battery cell to 4.25V at 0.33C0 at 25°C, and charge it at a constant voltage of 4.25V to a current of 0.05C0; place it at rest for 1 hour; discharge it at 0.33C0 at 25°C for 0.95C0, and record the voltage V1 at this time; place it at rest for 5 minutes; discharge it at 0.33C0 at 25°C to 2.7V; place it at rest for 5 minutes; charge the battery cell to 0.97C0 at 0.33C0 at 25°C, and record the voltage V2 at this time; place it at rest for 2 hours

[0320] The cycle test process is as follows: let the battery cell stand at 25°C for 2 hours to ensure the battery cell temperature is 25°C; charge the battery cell at 0.33C0 at 25°C to voltage V2; let it stand for 0.5 hours; discharge the battery cell at 0.33C0 at 25°C to voltage V1, recording the capacity at this point as Cn; let it stand for 0.5 hours; and continue the battery cycle charge and discharge test in this manner until the battery capacity decays to 80%. The number of cycles at this point is the battery's cycle life at 25°C.

[0321] The relevant parameters and test results of the battery positive electrode sheets of the embodiment and comparative example are recorded in Table 1-2.

[0322] 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.

[0323] 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).

[0324] 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 plate, comprising: positive electrode current collector; a first positive electrode active material film layer, disposed on at least one side of the positive electrode current collector, wherein 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 provided 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.

2. The positive electrode sheet according to claim 1, wherein: The particle sizes of the first positive electrode active material particles and the second positive electrode 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) Average particle size Dv of the first positive electrode active material particles 1 50 is 8μm~18μm; 3) The average particle size Dv of the second positive electrode active material particles 2 50 is 2μm~10μm; 3) The particle size distribution span of the first positive electrode active material particles is 0.3 to 0.7; 4) The particle size distribution span of the second positive electrode 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 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 formulas: Li a Ni x Co y M 1-x-y O2, wherein M includes one or more of Mn, Al, B, Zr, Sr, Y, Sb, W, Ti, Mg, Nb, and Ba, 0.55≤x≤1.05, 0≤y≤0.45, and 0.8≤a≤1.

2.

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

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

5. The positive electrode sheet according to any one of claims 1 to 4, wherein: The second positive electrode active material film layer comprises third positive electrode active material particles, and the average particle size of the second positive electrode active material particles is Dv 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 electrode active material particles meet one or more of the following conditions: 1) The average particle size Dv of the third positive electrode active material particles 3 50 is 0.8μm~5μm; 2) The specific surface area of the third positive electrode active material particles is 0.4 m 2 / g~0.9m 2 / g; 3) The tap density of the third positive electrode active material particles is 1.8 g / cm 3 ~3.4g / cm 3 ; 4) The third positive electrode active material particles are one or more of particles with a hollow structure and solid particles; 5) The particle size distribution span of the third positive electrode active material particles is 0.8 to 1.5; 6) The third positive electrode active material particles include the following structural formula: Li a Ni x Co y M 1-x-y O2, among which, M package It includes one or more of Mn, Al, B, Zr, Sr, Y, Sb, W, Ti, Mg, Nb, and Ba, 0.55≤x≤1.05, 0≤y≤0.45, and 0.8≤a≤1.

2.

7. The positive electrode sheet according to any one of claims 1 to 6, wherein: 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 Any one or more of O2.

8. The positive electrode sheet according to any one of claims 1 to 7, wherein: The thickness h1 of the first positive electrode active material layer and the thickness h2 of the second positive electrode active material layer meet one or more of the following conditions: 1) 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); 2) The thickness h1 of the first positive electrode active material film layer is 130 to 200 μm; 3) The thickness h2 of the second positive electrode active material film layer is 50 to 170 μm.

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

10. A method for preparing a positive electrode sheet, wherein: include: providing a second slurry containing second positive electrode active material particles, wherein the second positive electrode active material particles have a hollow structure; coating a second slurry on the positive electrode current collector to form a second positive electrode active material film layer; providing a first slurry containing first positive electrode active material particles, wherein the first positive electrode active material particles are solid particles; The first slurry is applied to form a first positive electrode active material film layer on a side of the second positive electrode active material film layer away from the positive electrode current collector, thereby manufacturing a positive electrode sheet.

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

12. A battery cell, wherein: The invention comprises 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, wherein: The battery cell according to claim 12 is included.

14. An electrical device, wherein: Including the battery according to claim 13.

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