Positive electrode sheet, method for manufacturing the same, battery including the same, and electric device

Abstract

The application provides a positive electrode sheet, a preparation method thereof, a battery containing the same, and a power utilization device. The positive electrode sheet comprises a positive electrode active material; the positive electrode active material comprises: an inner core comprising a lithium transition metal oxide containing nickel, wherein the proportion of the number of moles of Ni elements is greater than or equal to 0.7 based on the total number of moles of transition metal elements in the lithium transition metal oxide containing nickel; and a coating layer coated on at least part of the surface of the inner core, the coating layer comprising nickel salt particles.

Description

Technical Field

[0001] This application relates to the field of battery technology, and in particular to a positive electrode sheet and its preparation method, a battery containing the same, and an electrical device. Background Technology

[0002] Secondary batteries rely on the repeated insertion and extraction of active ions between the positive and negative electrodes for charging and discharging. Lithium-ion batteries, in particular, possess outstanding characteristics such as high energy density, long cycle life, and the absence of pollution and memory effect. Therefore, as a clean energy source, secondary batteries have gradually expanded from electronic products to large-scale devices such as electric vehicles, in line with sustainable development strategies for the environment and energy.

[0003] With the development of electronic products, electric vehicles and other devices, people have put forward higher requirements for the energy density and fast charging performance of secondary batteries. Summary of the Invention

[0004] To achieve the above objectives, this application provides a positive electrode sheet that can improve the energy density, cycle performance, and fast charging performance of a battery containing the positive electrode sheet; this application also provides a method for preparing the positive electrode sheet, a battery containing the positive electrode sheet, and an electrical device.

[0005] An embodiment of the first aspect of this application provides a positive electrode sheet, which includes a positive electrode active material. The positive electrode active material includes: a core comprising a nickel-containing lithium transition metal oxide, wherein the molar percentage of Ni element is greater than or equal to 0.7 based on the total molar number of transition metal elements in the nickel-containing lithium transition metal oxide; and a coating layer covering at least a portion of the surface of the core, the coating layer comprising nickel salt particles.

[0006] Not intended to be limited to any theory or interpretation, the positive electrode sheet of this application embodiment includes the aforementioned positive electrode active material, enabling the high-nickel positive electrode material system battery to possess both high energy density, good cycle performance, and good fast-charging performance. Specifically, the core of the positive electrode active material includes the aforementioned nickel-containing lithium transition metal oxide, i.e., a high-nickel positive electrode material, thereby enabling the positive electrode active material to have a high theoretical specific capacity, thus allowing the battery to have a high energy density. The coating layer of the positive electrode active material includes nickel salt particles. On the one hand, the nickel salt particles have a low nickel content, thus not only possessing high structural stability but also being less prone to violent reactions with the fast-charging high-conductivity electrolyte, thereby delaying the contact between the high-nickel positive electrode material and the electrolyte; on the other hand, compared to the low-nickel ternary material layer in related technologies, the coating layer containing nickel salt particles can withstand greater stress, thereby suppressing the cracking of the positive electrode active material particles during cycling and reducing the risk of pulverization and deactivation of the high-nickel positive electrode material. Therefore, the positive electrode sheet of this application embodiment can also effectively improve the cycle performance of the battery. In addition, nickel salt particles have good ion transport capabilities, which can enable the positive electrode active material to maintain good ion transport performance, thereby allowing the battery to have good fast charging performance.

[0007] In addition, compared with the low-nickel ternary cathode materials in related technologies, the nickel salt particles in the embodiments of this application have low preparation cost and mature preparation process, which can reduce the cost of secondary batteries and increase the production capacity of secondary batteries.

[0008] Therefore, the positive electrode sheet of this application embodiment is applied to a secondary battery, which enables the battery to have high energy density, high production capacity, good cycle performance and good fast charging performance.

[0009] In any embodiment of this application, based on the total mass of the core, the mass percentage of Ni in the core is w1%; based on the total mass of the coating layer, the mass percentage of Ni in the coating layer is w2%; and the positive electrode active material satisfies: w2 < w1. This helps to delay the contact between the core and the fast-charging highly conductive electrolyte, thereby improving the structural stability of the positive electrode active material during fast charging, and consequently improving the battery's cycle performance and fast-charging performance.

[0010] In any embodiment of this application, the coating layer includes a plurality of nickel salt particle layers stacked in a direction away from the core.

[0011] Optionally, in the multiple nickel salt particle layers, the mass percentage of Ni in the nickel salt particle layer farther from the core is less than the mass percentage of Ni in the nickel salt particle layer closer to the core.

[0012] When the coating layer includes multiple nickel salt particle layers, these layers can release the stress accumulated in the core during cycling. In particular, when the mass percentage of Ni in the multiple nickel salt particle layers decreases sequentially away from the core, each layer can slowly release stress layer by layer. This significantly reduces the risk of cracking in the positive electrode active material particles, thereby delaying the contact between the core and the fast-charging, highly conductive electrolyte, and reducing the risk of pulverization and deactivation of the high-nickel positive electrode material.

[0013] In any embodiment of this application, the thickness of the coating layer is 100nm-5μm, and can be selected as 200nm-900nm.

[0014] In any embodiment of this application, the volumetric particle size Dv50 of the kernel is 1.2μm-15μm, and can be selected as 10μm-15μm.

[0015] When the thickness of the coating layer and / or the volume distribution particle size Dv50 of the core meet the given range, it can not only effectively delay the contact between the core and the fast-charging high-conductivity electrolyte, but also enable the positive electrode active material to have a high theoretical specific capacity.

[0016] In any embodiment of this application, the volume distribution particle size Dv50 of the nickel salt particles is 50nm-500nm, and can be selected as 50nm-200nm.

[0017] When the volume distribution particle size Dv50 of nickel salt particles meets the given range, it helps to form a dense coating layer, thereby delaying the contact between the core and the fast-charging high-conductivity electrolyte, which in turn helps to improve the cycle performance of the battery. On the other hand, it helps to reduce the porosity between the positive electrode active material particles in the positive electrode sheet, thereby increasing the compaction density of the positive electrode film, which in turn helps to improve the energy density of the battery.

[0018] In any embodiment of this application, the nickel-containing lithium transition metal oxide includes LiNi. x Co y Mn z O2, where 0.7 ≤ x < 1.0, 0 < y < 0.3, 0 < z < 0.3. This allows secondary batteries to possess both high energy density and good cycle performance.

[0019] In any embodiment of this application, the nickel salt particles comprise nickel oxyacid salts.

[0020] Optionally, the nickel salt particles include at least one of nickel acetate, nickel silicate, or nickel carbonate.

[0021] The aforementioned types of nickel salt particles have low nickel content and good ion transport capabilities, which can improve the battery's cycle performance and fast charging performance.

[0022] In any embodiment of this application, the positive electrode sheet includes a positive current collector and a positive electrode film layer located on at least one side of the positive current collector, with the positive active material distributed in the positive electrode film layer. The compaction density of the positive electrode film layer is greater than or equal to 3.6 g / cm³. 3 3.6g / cm³ is an option. 3 -4.6g / cm 3 This allows the positive electrode active material particles in the positive electrode film to be in close contact, increasing the content of positive electrode active material per unit volume, thereby allowing the secondary battery to have a higher energy density.

[0023] An embodiment of the second aspect of this application provides a method for preparing a positive electrode sheet, comprising: providing an initial positive electrode sheet, the initial positive electrode sheet comprising initial positive electrode particles, the initial positive electrode particles comprising a nickel-containing lithium transition metal oxide, wherein, based on the total molar number of transition metal elements in the nickel-containing lithium transition metal oxide, the molar percentage of Ni element is greater than or equal to 0.7; immersing the initial positive electrode sheet in a nickel salt solution and drying it to form a coating layer comprising nickel salt particles on at least a portion of the surface of the initial positive electrode particles, thereby obtaining the positive electrode sheet. The positive electrode sheet comprises a positive electrode active material, the positive electrode active material comprising: a core comprising a nickel-containing lithium transition metal oxide, wherein, based on the total molar number of transition metal elements in the nickel-containing lithium transition metal oxide, the molar percentage of Ni element is greater than or equal to 0.7; and a coating layer covering at least a portion of the surface of the core, the coating layer comprising nickel salt particles.

[0024] According to the method of this application embodiment, the prepared positive electrode sheet includes the above-mentioned positive electrode active material, enabling the high-nickel positive electrode material system battery to possess both high energy density, good cycle performance, and good fast-charging performance. Specifically, the core of the positive electrode active material includes the above-mentioned nickel-containing lithium transition metal oxide, i.e., a high-nickel positive electrode material, thereby enabling the positive electrode active material to have a high theoretical specific capacity, thus allowing the battery to have a high energy density. The coating layer of the positive electrode active material includes nickel salt particles. On the one hand, the nickel salt particles have a low nickel content, thus not only having high structural stability, but also being less prone to violent reactions with the fast-charging high-conductivity electrolyte, thereby delaying the contact between the high-nickel positive electrode material and the electrolyte; on the other hand, compared with the low-nickel ternary material layer in related technologies, the coating layer containing nickel salt particles can withstand greater stress, thereby suppressing the cracking phenomenon of the positive electrode active material particles during cycling and reducing the risk of pulverization and deactivation of the high-nickel positive electrode material. Therefore, the positive electrode sheet of this application embodiment can also effectively improve the cycle performance of the battery. In addition, nickel salt particles have good ion transport capabilities, which can enable the positive electrode active material to maintain good ion transport performance, thereby allowing the battery to have good fast charging performance.

[0025] Furthermore, the method according to the embodiments of this application forms a coating layer including nickel salt particles on at least a portion of the surface of the initial positive electrode particles through impregnation. This method is not only simple to operate and has low production costs, but it can also improve the compaction density of the positive electrode film. Therefore, it can also improve the production capacity and energy density of the secondary battery.

[0026] Therefore, the positive electrode sheet prepared according to the method of this application embodiment can be applied to a secondary battery to effectively improve the battery's energy density, power production, cycle performance and fast charging performance.

[0027] In any embodiment of this application, immersing the initial positive electrode sheet in a nickel salt solution and drying it includes: sequentially immersing the initial positive electrode sheet in multiple nickel salt solutions and drying it to form a plurality of nickel salt particle layers stacked on at least a portion of the surface of the initial positive electrode particles.

[0028] Optionally, in various nickel salt solutions, the mass percentage of Ni element decreases sequentially based on the total mass of the solid components in the nickel salt solution.

[0029] The above-described embodiments can form multiple nickel salt particle layers stacked on at least a portion of the surface of the initial positive electrode particles. Therefore, during charge-discharge cycles, the multiple nickel salt particle layers can release the stress accumulated in the core. In particular, as the mass percentage of Ni in the multiple nickel salt particle layers decreases sequentially away from the core, the multiple nickel salt particle layers can also release stress slowly layer by layer. This significantly reduces the risk of cracking of the positive electrode active material particles, thereby delaying the contact between the core and the fast-charging highly conductive electrolyte, and reducing the risk of pulverization and deactivation of the high-nickel positive electrode material.

[0030] In any embodiment of this application, the molar concentration of Ni element in the nickel salt solution is 0.05 mol / L to 0.6 mol / L. This facilitates the formation of nickel salt particles of suitable size and a nickel salt particle layer of suitable thickness on the surface of the initial positive electrode particles.

[0031] In any embodiment of this application, the mass percentage of Ni element is 5%-60% based on the total mass of the solid components in the nickel salt solution. When the mass percentage of Ni element meets the given range, the coating layer can have a suitable Ni element content, thereby enabling the coating layer to maintain good structural stability during the charge-discharge cycle of the battery.

[0032] In any embodiment of this application, the solid component in the nickel salt solution includes the nickel salt and optional additives.

[0033] Optionally, optional additives include binders and / or conductive agents;

[0034] Alternatively, the adhesive may include a water-based adhesive; the conductive agent may include a conductive carbon material.

[0035] This helps to form a coating layer with appropriate thickness and Ni content.

[0036] In any embodiment of this application, the initial positive electrode sheet includes a positive current collector and an initial positive electrode film layer located on at least one side of the positive current collector, and the compaction density of the initial positive electrode film layer is 3.1 g / cm³. 3 -4.1g / cm 3 This allows the prepared positive electrode sheet to have a high compaction density, thus enabling the secondary battery to have a high energy density.

[0037] An embodiment of the third aspect of this application provides a battery including a positive electrode sheet of the first aspect, or a positive electrode sheet prepared according to the method of the second aspect. This battery can at least possess high energy density, good cycle performance, and good fast-charging performance.

[0038] In any embodiment of this application, the battery cell further includes an electrolyte, the electrolyte having an ionic conductivity of 10 mS / cm or higher at 25°C, preferably between 10 mS / cm and 18 mS / cm. This allows the battery to have good fast-charging performance.

[0039] An embodiment of the fourth aspect of this application provides an electrical device, including the battery of the third aspect.

[0040] The electrical device in this application includes a battery from the third aspect, and therefore has at least the same advantages as a battery. Attached Figure Description

[0041] Figure 1 This is a schematic diagram of the structure of the positive electrode active material in one embodiment of this application.

[0042] Figure 2 This is a schematic diagram illustrating an embodiment of the battery cell of this application.

[0043] Figure 3 yes Figure 2 An exploded view of an embodiment of the battery cell of this application is shown.

[0044] Figure 4 This is a schematic diagram of one embodiment of the battery module of this application.

[0045] Figure 5 This is a schematic diagram of one embodiment of the battery pack of this application.

[0046] Figure 6 yes Figure 5 The diagram shown is an exploded view of an embodiment of the battery pack of this application.

[0047] Figure 7 This is a schematic diagram of one embodiment of the power supply device of this application, which may include a battery pack or battery module as a power source according to the embodiments of this application.

[0048] 10 Positive electrode active material; 11 Core; 12 Coating layer; 12a Nickel salt particle layer; 1 Battery pack; 2 Upper casing; 3 Lower casing; 4 Battery module; 5 Battery cell; 51 Housing; 52 Electrode assembly; 53 Cover plate. Detailed Implementation

[0049] The following detailed description, with appropriate reference to the accompanying drawings, discloses the positive electrode sheet of this application, its preparation method, and embodiments of batteries and power devices comprising the same. However, unnecessary detailed descriptions may be omitted. For example, detailed descriptions of well-known matters and repetitive descriptions of practically identical structures may be omitted. This is to avoid unnecessarily lengthy descriptions and to facilitate understanding by those skilled in the art. Furthermore, the accompanying drawings and the following description are provided for the purpose of enabling those skilled in the art to fully understand this application and are not intended to limit the subject matter of the claims.

[0050] The "range" disclosed in this application is defined by a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, which define the boundaries of a particular range. Ranges defined in this way can include or exclude endpoints and can be arbitrarily combined; that is, any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60-120 and 80-110 are listed for a specific parameter, it is expected that ranges of 60-110 and 80-120 are also included. Furthermore, if minimum range values ​​of 1 and 2 are listed, and if maximum range values ​​of 3, 4, and 5 are listed, then the following ranges are all expected: 1-3, 1-4, 1-5, 2-3, 2-4, and 2-5. In this application, unless otherwise stated, the numerical range "ab" represents a shortened representation of any combination of real numbers between a and b, where a and b are real numbers. For example, the numerical range "0-5" indicates that all real numbers between "0-5" have been listed in this article; "0-5" is simply a shortened representation of these numerical combinations. Furthermore, when a parameter is stated as an integer ≥2, it is equivalent to disclosing that the parameter is, for example, an integer such as 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0051] Unless otherwise specified, all embodiments and optional embodiments of this application can be combined to form new technical solutions.

[0052] Unless otherwise specified, all technical features and optional technical features of this application may be combined to form new technical solutions.

[0053] Unless otherwise specified, all steps in this 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 it may include steps (b) and (a) performed sequentially. For example, the mention that the method may also include step (c) indicates that step (c) may be added to the method in any order. For example, the method may include steps (a), (b), and (c), or it may include steps (a), (c), and (b), or it may include steps (c), (a), and (b), etc.

[0054] Unless otherwise stated, the values ​​of the parameters mentioned in this application can be determined using various testing methods commonly used in the art, for example, according to the testing methods given in the embodiments of this application. Unless otherwise stated, the test temperature for each parameter is 25°C.

[0055] Unless otherwise stated, all ratio parameters involved in this application are compared under the condition that the units are the same. For example, the thickness ratio of A to B is 1.2:1, in which case the thickness units of A and B are the same.

[0056] With the development of electronic products, electric vehicles and other devices, people have put forward higher requirements for the energy density and fast charging performance of secondary batteries.

[0057] High-nickel cathode materials, such as lithium transition metal oxides with a Ni molar ratio of 0.7 or higher in the transition metal elements, have become a research hotspot in high-energy-density battery systems in recent years due to their advantages such as high reversible capacity and low cost. However, secondary batteries using high-nickel cathode materials experience severe cation mixing during cycling. This cation mixing leads to an irreversible phase transition in the high-nickel cathode material, thereby exacerbating changes in its crystal structure, increasing internal stress within the particles, inducing microcracks, and increasing the risk of particle cracking, pulverization, and deactivation, ultimately deteriorating the battery's cycle performance.

[0058] Furthermore, when faced with the demand for fast charging performance, secondary batteries typically use electrolytes with high conductivity (i.e., fast-charging high-conductivity electrolytes). However, high-nickel cathode materials are prone to violent reactions with fast-charging high-conductivity electrolytes. This exacerbates the irreversible capacity loss of the high-nickel cathode material, further deteriorating the battery's cycle performance.

[0059] In view of this, embodiments of this application provide a positive electrode sheet, which enables the battery containing the positive electrode sheet to have high energy density, good cycle performance and good fast charging performance; this application also provides a method for preparing the positive electrode sheet, a battery containing the positive electrode sheet and an electrical device.

[0060] Positive electrode sheet

[0061] An embodiment of the first aspect of this application provides a positive electrode sheet comprising a positive electrode active material. The positive electrode active material includes a core and a coating layer, the coating layer covering at least a portion of the surface of the core. The core comprises a nickel-containing lithium transition metal oxide, wherein the molar percentage of Ni element is greater than or equal to 0.7 based on the total molar number of transition metal elements in the nickel-containing lithium transition metal oxide; the coating layer comprises nickel salt particles.

[0062] In-depth research has shown that delaying the contact between high-nickel cathode materials and fast-charging high-conductivity electrolytes, while maintaining good ion transport capabilities in the high-nickel cathode material, is one of the effective means to improve the cycle performance and fast-charging performance of batteries based on high-nickel cathode materials. Related technologies involve repeatedly coating low-nickel ternary cathode material layers onto the surface of high-nickel ternary cathode material particles to obtain a composite cathode material with a high-nickel ternary cathode material inner layer and a low-nickel ternary cathode material outer layer. However, on the one hand, producing this composite cathode material is time-consuming, labor-intensive, and costly; on the other hand, during the charge-discharge cycle of the battery, the stress generated by the high-nickel ternary cathode material easily causes the low-nickel ternary cathode material layer to crack, resulting in very limited improvement in the battery's cycle performance and fast-charging performance.

[0063] Not intended to be limited to any theory or interpretation, the positive electrode sheet of this application embodiment includes the aforementioned positive electrode active material, enabling the high-nickel positive electrode material system battery to possess both high energy density, good cycle performance, and good fast-charging performance. Specifically, the core of the positive electrode active material includes the aforementioned nickel-containing lithium transition metal oxide, i.e., a high-nickel positive electrode material, thereby enabling the positive electrode active material to have a high theoretical specific capacity, thus allowing the battery to have a high energy density. The coating layer of the positive electrode active material includes nickel salt particles. On the one hand, the nickel salt particles have a low nickel content, thus not only possessing high structural stability but also being less prone to violent reactions with the fast-charging high-conductivity electrolyte, thereby delaying the contact between the high-nickel positive electrode material and the electrolyte; on the other hand, compared to the low-nickel ternary material layer in related technologies, the coating layer containing nickel salt particles can withstand greater stress, thereby suppressing the cracking of the positive electrode active material particles during cycling and reducing the risk of pulverization and deactivation of the high-nickel positive electrode material. Therefore, the positive electrode sheet of this application embodiment can also effectively improve the cycle performance of the battery. In addition, nickel salt particles have good ion transport capabilities, which can enable the positive electrode active material to maintain good ion transport performance, thereby allowing the battery to have good fast charging performance.

[0064] In addition, compared with the low-nickel ternary cathode materials in related technologies, the nickel salt particles in the embodiments of this application have low preparation cost and mature preparation process, which can reduce the cost of secondary batteries and increase the production capacity of secondary batteries.

[0065] Therefore, the positive electrode sheet of this application embodiment is applied to a secondary battery, which enables the battery to have high energy density, high production capacity, good cycle performance and good fast charging performance.

[0066] In the embodiments of this application, the nickel-containing lithium transition metal oxide may be one or more of the nickel-containing lithium transition metal oxides and their modified compounds known in the art for use in secondary batteries. Examples of nickel-containing lithium transition metal oxides may include, but are not limited to, one or more of lithium nickel oxide, lithium nickel cobalt oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, and their modified compounds, with a nickel content of 0.7 or more. The phrase "nickel content of 0.7 or more" can mean that, based on the total molar amount of transition metal elements in the nickel-containing lithium transition metal oxide, the molar amount of Ni is greater than or equal to 0.7. For example, for lithium nickel cobalt manganese oxide, "nickel content of 0.7 or more" can mean that the molar amount of Ni / (molar amount of Ni + molar amount of Co + molar amount of Mn) ≥ 0.7.

[0067] The structure of the positive electrode active material included in the positive electrode sheet provided in this application embodiment can be characterized using equipment and methods known in the art. For example, the positive electrode active material particles can be subjected to argon ion cross-section polishing, the polished cross-section of the positive electrode active material particles can be observed by scanning electron microscopy (SEM), and the cross-sectional EDS elemental distribution map of the positive electrode active material particles can be determined by EDS energy dispersive spectroscopy. Based on the Ni element distribution in the EDS elemental distribution map, the structure of the positive electrode active material can be determined.

[0068] In some implementations, based on the total mass of the core, the mass percentage of Ni in the core is w1%; based on the total mass of the coating layer, the mass percentage of Ni in the coating layer is w2%; the positive electrode active material can satisfy: w2 < w1.

[0069] Not intended to be limited by any theory or explanation, when the coating layer has a low Ni content, it can maintain good structural stability during the battery's charge-discharge cycles. This helps to delay the contact between the core and the fast-charging highly conductive electrolyte, thereby improving the structural stability of the positive electrode active material during fast charging, and ultimately enhancing the battery's cycle performance and fast-charging performance.

[0070] w1 and w2 have meanings known in the art and can be determined using equipment and methods known in the art. For example, w1 and w2 can be determined based on the EDS elemental surface distribution map of the positive electrode active material. The EDS elemental surface distribution map of the positive electrode active material can be obtained by the method described above, and will not be elaborated here.

[0071] In some embodiments, the coating layer may include multiple layers of nickel salt particles stacked in a direction away from the core. Figure 1 This is a schematic diagram of the structure of the positive electrode active material according to one embodiment of this application. Figure 1 As shown, the positive electrode active material 10 may include a core 11 and a coating layer 12. The coating layer 12 may coat at least a portion of the surface of the core 11. The coating layer 12 may include a plurality of nickel salt particle layers 12a stacked in a direction away from the core.

[0072] In this embodiment, the mass percentage of Ni element in multiple nickel salt particle layers is not specifically limited.

[0073] In some implementations, the mass percentage of Ni in the innermost nickel salt particle layer is greater than that in the outermost nickel salt particle layer in the direction away from the core.

[0074] Optionally, in some embodiments, the mass percentage of Ni in the nickel salt particle layers farther from the core is less than the mass percentage of Ni in the nickel salt particle layers closer to the core. For example, the coating layer comprises multiple nickel salt particle layers stacked along a direction farther from the core, and any two nickel salt particle layers can satisfy: w a <w b w a % represents the mass percentage of Ni element in the nickel salt particle layer relatively far from the core, w b % indicates the mass percentage of Ni element in the nickel salt particle layer relatively close to the core.

[0075] Not intended to be limited to any theory or explanation, when the coating layer includes the aforementioned multiple nickel salt particle layers, these layers can release the stress accumulated in the core during cycling. In particular, when the mass percentage of Ni in the nickel salt particle layers farther from the core is less than that in the nickel salt particle layers closer to the core, the multiple nickel salt particle layers can also release stress slowly layer by layer. This significantly reduces the risk of cracking of the positive electrode active material particles, thereby delaying the contact between the core and the fast-charging highly conductive electrolyte, and reducing the risk of pulverization and deactivation of the high-nickel positive electrode material. Therefore, the positive electrode sheet of this embodiment, when applied to a secondary battery, can significantly improve the battery's cycle performance and fast-charging performance.

[0076] In some embodiments, the thickness of the coating layer can be 100nm-5μm, for example, it can be 100nm, 110nm, 120nm, 140nm, 160nm, 180nm, 200nm, 500nm, 1μm, 2μm, 4μm, 5μm, or any range of two of the above values.

[0077] Optionally, in some embodiments, the thickness of the coating layer can be 200nm-900nm, for example, it can be 200nm, 300nm, 400nm, 500nm, 600nm, 700nm, 800nm, 900nm, or any range of two of the above values.

[0078] In some implementations, the volumetric distribution particle size Dv50 of the kernel can be 1.2μm-15μm, for example, it can be 1.2μm, 2μm, 4μm, 6μm, 8μm, 10μm, 15μm, or any range of two of the above values.

[0079] Optionally, in some implementations, the volumetric distribution particle size Dv50 of the kernel can also be 10μm-15μm, for example, it can be 10μm, 11μm, 12μm, 13μm, 14μm, 15μm, or any range of two of the above values.

[0080] Not intended to be limited by any theory or explanation, when the thickness of the coating layer and / or the volumetric particle size Dv50 of the core meet the given range, not only can the contact between the core and the fast-charging highly conductive electrolyte be effectively delayed, but the positive electrode active material can also have a high theoretical specific capacity. Therefore, the positive electrode sheet of this application, when applied to a secondary battery, not only enables the battery to have good cycle performance and good fast-charging performance, but also allows the battery to have a high energy density.

[0081] The thickness of the coating layer and the volume distribution particle size Dv50 of the core material mentioned above have meanings known in the art and can be determined using equipment and methods known in the art. As an example, they can be obtained by the following method: A region is randomly selected in the positive electrode sheet, a cross-section parallel to the thickness direction of the positive electrode sheet is made, argon ion cross-section polishing is performed, and an electron microscope (SEM) image is taken at a magnification of 3000x or higher (e.g., 3000x or 5000x); the SEM image is processed, and the contrast is adjusted appropriately until the outline of the positive electrode active material particles is clearly visible; the thickness of the coating layer and the core particle size in each positive electrode active material particle in the cross-section are statistically analyzed using software, and the thickness of the coating layer and the volume distribution particle size Dv50 of the core are calculated. As another example, a sample can be taken from the positive electrode sheet to obtain positive electrode active material powder, which is then directly subjected to argon ion cross-section polishing and an SEM image is taken. The thickness of the coating layer and the volume distribution particle size Dv50 of the core are determined using the SEM image.

[0082] In some embodiments, the volume distribution particle size Dv50 of the nickel salt particles can be 50nm-500nm, for example, it can be 50nm, 100nm, 150nm, 200nm, 250nm, 300nm, 350nm, 400nm, 450nm, 500nm, or any range of two of the above values.

[0083] Optionally, in some embodiments, the volume distribution particle size Dv50 of the nickel salt particles can also be 50nm-200nm, for example, it can be 50nm, 60nm, 70nm, 80nm, 90nm, 100nm, 110nm, 120nm, 130nm, 140nm, 150nm, 160nm, 170nm, 180nm, 190nm, 200nm, or any range of two of the above values.

[0084] It is not intended to be limited to any theory or explanation. When the volume distribution particle size Dv50 of nickel salt particles meets the given range, it helps to form a dense coating layer, thereby delaying the contact between the core and the fast-charging high-conductivity electrolyte, which in turn helps to improve the cycle performance of the battery. On the other hand, it helps to reduce the porosity between the positive electrode active material particles in the positive electrode sheet, thereby increasing the compaction density of the positive electrode film, which in turn helps to improve the energy density of the battery.

[0085] The volumetric particle size distribution (Dv50) of nickel salt particles has a meaning well-known in the art and can be determined using equipment and methods known in the art. As an example, it can be obtained by the following method: A region is randomly selected in the positive electrode sheet, a cross-section parallel to the thickness direction of the positive electrode sheet is made, and the cross-section is polished with argon ions. An electron microscope (SEM) image is then taken at a magnification of 5000x or higher (e.g., 5000x-20000x). The SEM image is processed, and the contrast is adjusted appropriately until the outline of the nickel salt particles in the coating layer is clearly visible. The particle size of the nickel salt particles in the cross-section is statistically analyzed using software, and the volumetric particle size distribution (Dv50) of the nickel salt particles is determined based on the statistical results.

[0086] In some embodiments, the nickel-containing lithium transition metal oxide may include LiNi. x Co y Mn z O2, where 0.7≤x<1.0, 0<y<0.3, 0<z<0.3.

[0087] Not intended to be limited by any theory or interpretation, the positive electrode in the embodiments of this application has a specific structure in which the positive active material has good structural stability even with a high Ni content. When the nickel-containing lithium transition metal oxide contained in the core includes the above-mentioned high-nickel ternary positive electrode material, the secondary battery can have both high energy density and good cycle performance.

[0088] It should be noted that the elemental ratios in the nickel-containing lithium transition metal oxides mentioned in this application refer to the elemental ratios in the core before the positive electrode active material is formed into a battery and assembled. Those skilled in the art will understand that some elements are consumed during the formation and cycling processes in the positive electrode, battery, or electrical device. Even if the measured elemental ratios in the core are outside the aforementioned range, they should still fall within the scope of this application. For example, due to the consumption of lithium ions during the formation and cycling processes, the measured lithium content in the core may be less than 1. Simultaneously, if lithium replenishment is performed on the positive and negative electrode sheets, the measured lithium content in the core may be greater than 1 after the formation and cycling processes. Furthermore, due to the potential loss of oxygen elements in the core during cycling, the measured oxygen content in the core may be less than 2.

[0089] In some embodiments, nickel salt particles may include nickel oxoacid salts.

[0090] Optionally, in some embodiments, the nickel salt particles may include at least one of nickel acetate, nickel silicate, or nickel carbonate.

[0091] Not intended to be limited to any particular theory or explanation, the aforementioned types of nickel salt particles have a low nickel content, which not only results in high structural stability but also makes them less prone to violent reactions with fast-charging, highly conductive electrolytes. This delays the contact between the high-nickel cathode material and the electrolyte, improving the battery's cycle performance. Furthermore, these nickel salt particles also possess excellent ion transport capabilities, allowing the cathode active material to maintain good ion transport performance, thus enabling the battery to have good fast-charging performance.

[0092] In some embodiments, the positive electrode includes a positive current collector and a positive electrode film layer located on at least one side of the positive current collector, wherein the positive active material is distributed in the positive electrode film layer. The compaction density of the positive electrode film layer may be greater than or equal to 3.6 g / cm³. 3 3.6g / cm³ is an option. 3 -4.6g / cm 3 .

[0093] In the positive electrode sheet of this application embodiment, the positive electrode active material has a specific structure, which allows the positive electrode film layer to have a high compaction density. This ensures that the positive electrode active material particles in the positive electrode film layer are in close contact, increasing the content of positive electrode active material per unit volume, thereby allowing the secondary battery to have a high energy density.

[0094] The compaction density of the positive electrode film has a meaning known in the art and can be tested using equipment and methods known in the art. The compaction density of the positive electrode film = areal density of the positive electrode film / thickness of a single-sided positive electrode film. The areal density of the positive electrode film has a meaning known in the art and can be tested using equipment and methods known in the art. For example, take a positive electrode sheet that has been coated on one side and cold-pressed (if it is a double-sided coated positive electrode sheet, the positive electrode film on one side can be wiped off first), cut it into small discs, and weigh them; then wipe off the positive electrode film of the weighed positive electrode sheet and weigh the current collector. The areal density of the positive electrode film = (weight of the small disc - weight of the current collector) / area of ​​the small disc.

[0095] In this embodiment, the positive electrode may include a positive current collector and a positive electrode film layer disposed on at least one side of the positive current collector and comprising a positive active material. For example, the positive current collector has two surfaces opposite each other in its thickness direction, and the positive electrode film layer is disposed on either or both of the two opposite surfaces of the positive current collector.

[0096] In some embodiments, the positive electrode film may optionally include a positive electrode conductive agent. This application does not impose any particular limitation on the type of positive electrode conductive agent. As an example, the positive electrode conductive agent includes at least one of superconducting carbon, conductive graphite, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0097] In some embodiments, the positive electrode film layer may optionally include a positive electrode binder. This application does not impose any particular limitation on the type of positive electrode binder. As an example, the positive electrode binder may include at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorinated acrylate resins.

[0098] In some embodiments, the positive current collector may be a metal foil or a composite current collector. An example of a metal foil is aluminum foil. The composite current collector may include a polymer substrate and a metal layer formed on at least one surface of the polymer substrate. An example of a metal material may be at least one selected from aluminum, aluminum alloys, nickel, nickel alloys, titanium, titanium alloys, silver, and silver alloys. An example of a polymer substrate may be at least one selected from polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), and polyethylene (PE).

[0099] Preparation method

[0100] Secondly, embodiments of this application provide a method for preparing a positive electrode sheet, comprising the following steps S10 to S20.

[0101] S10 provides an initial positive electrode sheet, which includes initial positive electrode particles. The initial positive electrode particles include a nickel-containing lithium transition metal oxide, wherein, based on the total number of moles of transition metal elements in the nickel-containing lithium transition metal oxide, the molar percentage of Ni element is greater than or equal to 0.7.

[0102] In step S10, the initial positive electrode sheet can be prepared by methods known in the art, and is not limited thereto. As an example, a positive electrode slurry can be coated onto a positive electrode current collector, dried, and cold-pressed to form a positive electrode film layer on the surface of the current collector, thereby obtaining the initial positive electrode sheet. The positive electrode slurry can be formed by dispersing the aforementioned nickel-containing lithium transition metal oxide, optional conductive agent, optional binder, and any other components in a solvent and stirring until homogeneous. The solvent can be N-methylpyrrolidone (NMP), but is not limited thereto.

[0103] S20, the initial positive electrode sheet is immersed in a nickel salt solution and dried to form a coating layer including nickel salt particles on at least a portion of the surface of the initial positive electrode particles, thereby obtaining a positive electrode sheet.

[0104] In step S20, the nickel salt particles may include the nickel salt particles described in the first aspect. The embodiments of the nickel salt particles have been described in detail above and will not be repeated here. A nickel salt solution can be obtained by dissolving the nickel salt particles in a solvent. The solvent only needs to be able to dissolve the nickel salt particles. When the nickel salt particles are a specific substance, those skilled in the art can select an appropriate solvent according to actual needs, and no limitation is made here. In some embodiments, the nickel salt particles used to prepare the nickel salt solution have a volume distribution particle size (Dv50) of 50 nm to 500 nm.

[0105] Step S20 involves forming a coating layer on the surface of the initial positive electrode particles through impregnation. Nickel salt particles can fill the gaps between the initial positive electrode particles, forming a dense protective film on the surface of the initial positive electrode particles. This effectively delays the contact between the initial positive electrode particles and the fast-charging, highly conductive electrolyte. Furthermore, filling the gaps between the initial positive electrode particles with nickel salt particles can increase the compaction density of the initial positive electrode film, thereby improving the energy density of the positive electrode sheet.

[0106] The positive electrode sheet prepared according to steps S10 and S20 includes a positive electrode active material, which includes a core and a coating layer, the coating layer covering at least a portion of the surface of the core. The core includes a nickel-containing lithium transition metal oxide, wherein, based on the total molar number of transition metal elements in the nickel-containing lithium transition metal oxide, the molar percentage of Ni element is greater than or equal to 0.7; the coating layer includes nickel salt particles.

[0107] According to the method of this application embodiment, the prepared positive electrode sheet includes the above-mentioned positive electrode active material, enabling the high-nickel positive electrode material system battery to possess both high energy density, good cycle performance, and good fast-charging performance. Specifically, the core of the positive electrode active material includes the above-mentioned nickel-containing lithium transition metal oxide, i.e., a high-nickel positive electrode material, thereby enabling the positive electrode active material to have a high theoretical specific capacity, thus allowing the battery to have a high energy density. The coating layer of the positive electrode active material includes nickel salt particles. On the one hand, the nickel salt particles have a low nickel content, thus not only having high structural stability, but also being less prone to violent reactions with the fast-charging high-conductivity electrolyte, thereby delaying the contact between the high-nickel positive electrode material and the electrolyte; on the other hand, compared with the low-nickel ternary material layer in related technologies, the coating layer containing nickel salt particles can withstand greater stress, thereby suppressing the cracking phenomenon of the positive electrode active material particles during cycling and reducing the risk of pulverization and deactivation of the high-nickel positive electrode material. Therefore, the positive electrode sheet of this application embodiment can also effectively improve the cycle performance of the battery. In addition, nickel salt particles have good ion transport capabilities, which can enable the positive electrode active material to maintain good ion transport performance, thereby allowing the battery to have good fast charging performance.

[0108] Furthermore, the method according to the embodiments of this application forms a coating layer including nickel salt particles on at least a portion of the surface of the initial positive electrode particles through impregnation. This method is not only simple to operate and has low production costs, but it can also improve the compaction density of the positive electrode film. Therefore, it can also improve the production capacity and energy density of the secondary battery.

[0109] Therefore, the positive electrode sheet prepared according to the method of this application embodiment can be applied to a secondary battery to effectively improve the battery's energy density, power production, cycle performance and fast charging performance.

[0110] In some embodiments, immersing the initial positive electrode sheet in a nickel salt solution and drying it may specifically include: immersing the initial positive electrode sheet in a variety of nickel salt solutions in sequence and drying it to form a plurality of nickel salt particle layers stacked on at least a portion of the surface of the initial positive electrode particles.

[0111] Optionally, in multiple nickel salt solutions, the mass percentage of Ni element decreases sequentially based on the total mass of the solid components in the nickel salt solution. This allows the mass percentage of Ni element in the multiple nickel salt particle layers of the cathode active material's coating layer to decrease sequentially away from the core.

[0112] In this embodiment, the impregnation time is not specifically limited and can be adjusted by those skilled in the art according to actual needs. For example, the impregnation time can be 2 hours to 48 hours. The drying time and temperature are not specifically limited and can be adjusted by those skilled in the art according to actual needs. For example, the drying time can be 2 hours to 48 hours, and the drying temperature can be 80°C to 120°C.

[0113] In the above embodiments, by sequentially immersing the initial positive electrode sheet in various nickel salt solutions and drying it, multiple nickel salt particle layers can be formed on at least a portion of the surface of the initial positive electrode particles. Thus, during charge-discharge cycles, the multiple nickel salt particle layers can release the stress accumulated in the core. In particular, as the mass percentage of Ni in the multiple nickel salt particle layers decreases sequentially away from the core, the multiple nickel salt particle layers can also slowly release stress layer by layer. This significantly reduces the risk of cracking of the positive electrode active material particles, thereby delaying the contact between the core and the fast-charging high-conductivity electrolyte, and reducing the risk of pulverization and deactivation of the high-nickel positive electrode material. Therefore, the positive electrode sheet prepared in the embodiments of this application, when applied to a secondary battery, can significantly improve the battery's cycle performance and fast-charging performance.

[0114] In some embodiments, the molar concentration of Ni in the nickel salt solution can be 0.05 mol / L to 0.6 mol / L, for example, it can be 0.05 mol / L, 0.1 mol / L, 0.2 mol / L, 0.3 mol / L, 0.4 mol / L, 0.5 mol / L, 0.6 mol / L, or any range of two of the above values.

[0115] It is not intended to be limited to any theory or explanation, but when the molar concentration of Ni in the nickel salt solution is within the above-mentioned suitable range, it helps to form nickel salt particles of suitable size and nickel salt particle layer of suitable thickness on the surface of the initial positive electrode particles.

[0116] In some embodiments, the mass percentage of Ni element can be 5%-60% based on the total mass of the solid components in the nickel salt solution, for example, it can be 5%, 10%, 20%, 30%, 40%, 50%, 60%, or any combination of two of the above values.

[0117] When the mass percentage of Ni meets the given range, the coating layer can have an appropriate Ni content, thus maintaining good structural stability during battery charge-discharge cycles. This helps delay the contact between the core and the fast-charging highly conductive electrolyte, thereby improving the structural stability of the positive electrode active material during fast charging, and ultimately enhancing the battery's cycle performance and fast-charging performance.

[0118] In some embodiments, the solid component in the nickel salt solution may include the nickel salt and optional additives.

[0119] Optionally, optional additives include binders and / or conductive agents.

[0120] Alternatively, the adhesive may include a water-based adhesive. A water-based adhesive generally refers to an adhesive that can use water as a dispersant or solvent. Examples of water-based adhesives may include one or more water-based adhesives known in the art, such as at least one of water-based polyvinylidene fluoride (PVDF) and its derivatives, polyacrylic acid and its derivatives, acrylonitrile copolymers, sodium alginate and its derivatives, and polyacrylates and their derivatives, without limitation herein. In some embodiments, the water-based adhesive may include water-based PVDF.

[0121] The conductive agent may include conductive carbon materials. For example, it may include at least one of superconducting carbon, conductive graphite, acetylene black, carbon black, and Ketjen black. In some embodiments, the aqueous binder may include Ketjen black.

[0122] This helps to form a coating layer with appropriate thickness and Ni content.

[0123] In some embodiments, the initial positive electrode includes a positive current collector and an initial positive electrode film layer located on at least one side of the positive current collector, wherein the compaction density of the initial positive electrode film layer can be 3.1 g / cm³. 3 -4.1g / cm 3 This allows the prepared positive electrode sheet to have a high compaction density, thus enabling the secondary battery to have a high energy density.

[0124] Battery

[0125] The battery mentioned in the embodiments of this application may be a single physical module comprising one or more battery cells to provide higher voltage and capacity. When there are multiple battery cells, the multiple battery cells are connected in series, parallel, or mixed via a busbar.

[0126] Typically, a battery cell includes an electrode assembly and an electrolyte. The electrode assembly includes a positive electrode, a negative electrode, and a separator. During the charging and discharging process of the battery cell, active ions (such as lithium ions) repeatedly insert and extract between the positive and negative electrodes. The separator, located between the positive and negative electrodes, prevents short circuits while allowing active ions to pass through. The electrolyte, situated between the positive and negative electrodes, conducts the active ions.

[0127] [Positive electrode plate]

[0128] In the battery cell of this application embodiment, the positive electrode sheet of the electrode assembly may include the positive electrode sheet of the first aspect or the positive electrode sheet prepared according to the method of the second aspect. The embodiments of the positive electrode sheet have been described and illustrated in detail above, and will not be repeated here. It is understood that the battery cell of this application embodiment can achieve the beneficial effects of any of the above-described embodiments of the positive electrode sheet of this application embodiment.

[0129] [Negative electrode plate]

[0130] The negative electrode sheet may include a negative current collector and a negative electrode film layer disposed on at least one side of the negative current collector and comprising a negative electrode active material. For example, the negative current collector has two surfaces opposite 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 current collector.

[0131] The negative electrode active material may be any negative electrode active material known in the art for use in secondary batteries. As an example, the negative electrode active material may include, but is not limited to, at least one of natural graphite, artificial graphite, soft carbon, hard carbon, silicon-based materials, tin-based materials, and lithium titanate. Silicon-based materials may include at least one of elemental silicon, silicon oxide, silicon-carbon composites, silicon-nitrogen composites, and silicon alloys. Tin-based materials may include at least one of elemental tin, tin oxide, and tin alloys.

[0132] In some embodiments, the negative electrode film layer may optionally include a negative electrode conductive agent. This application does not impose any particular limitation on the type of negative electrode conductive agent. As an example, the negative electrode conductive agent may include at least one of superconducting carbon, conductive graphite, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0133] In some embodiments, the negative electrode film layer may optionally include a negative electrode binder. This application does not impose any particular limitation on the type of negative electrode binder. As an example, the negative electrode binder may include at least one of styrene-butadiene rubber (SBR), water-soluble unsaturated resin SR-1B, waterborne acrylic resins (e.g., polyacrylic acid PAA, polymethacrylic acid PMAA, sodium polyacrylate PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), and carboxymethyl chitosan (CMCS).

[0134] In some embodiments, the negative electrode film may optionally include other additives. As an example, other additives may include thickeners, such as sodium carboxymethyl cellulose (CMC-Na), PTC thermistor materials, etc.

[0135] In some embodiments, the negative electrode current collector may be a metal foil or a composite current collector. As an example of a metal foil, copper foil may be used. The composite current collector may include a polymeric material substrate and a metal material layer formed on at least one surface of the polymeric material substrate. As an example, the metal material may include at least one of copper, copper alloys, nickel, nickel alloys, titanium, titanium alloys, silver, and silver alloys. As an example, the polymeric material substrate may include at least one of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), and polyethylene (PE).

[0136] The negative electrode film is typically formed by coating a negative electrode slurry onto a negative electrode current collector, followed by drying and cold pressing. The negative electrode slurry is usually formed by dispersing the negative electrode active material, optional conductive agent, optional binder, and other optional additives in a solvent and stirring until homogeneous. The solvent can be N-methylpyrrolidone (NMP) or deionized water, but is not limited to these.

[0137] The negative electrode sheet does not exclude other additional functional layers besides the negative electrode film layer. For example, in some embodiments, the negative electrode sheet also includes a conductive undercoat layer (e.g., composed of a conductive agent and an adhesive) sandwiched between the negative electrode current collector and the negative electrode film layer and disposed on the surface of the negative electrode current collector. In some embodiments, the negative electrode sheet of this application also includes a protective layer covering the surface of the negative electrode film layer.

[0138] [Isolation membrane]

[0139] A separator is disposed between the positive and negative electrode plates to provide isolation. This application does not impose any particular limitation on the type of separator; any known porous separator with good chemical and mechanical stability can be selected.

[0140] In some embodiments, the material of the separator can be selected from one or more of glass fiber, nonwoven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator can be a single-layer film or a multi-layer composite film. When the separator is a multi-layer composite film, the materials of each layer can be the same or different, without particular limitation.

[0141] [Electrolytes]

[0142] The electrolyte acts as a conductor of ions between the positive and negative electrodes. This application does not specifically limit the type of electrolyte; it can be selected according to requirements. For example, the electrolyte can be liquid or gel-like.

[0143] In some embodiments, the electrolyte is an electrolyte solution. The electrolyte solution includes an electrolyte salt and a solvent.

[0144] In some embodiments, the electrolyte salt may be selected from at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium hexafluoroarsenate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium trifluoromethanesulfonate, lithium difluorophosphate, lithium difluorooxalate borate, lithium dioxalate borate, lithium difluorodioxalate phosphate, and lithium tetrafluorooxalate phosphate.

[0145] In some embodiments, the solvent may be selected from at least one of ethylene carbonate, propylene carbonate, methyl ethyl carbonate, diethyl carbonate, dimethyl carbonate, dipropyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, butyl carbonate, fluoroethylene carbonate, methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate, 1,4-butyrolactone, sulfolane, dimethyl sulfone, methyl ethyl sulfone, and diethyl sulfone.

[0146] In some embodiments, the electrolyte may optionally include additives. For example, additives may include negative electrode film-forming additives, positive electrode film-forming additives, and may also include additives that can improve certain battery performance, such as additives that improve battery overcharge performance, additives that improve battery high-temperature or low-temperature performance, etc.

[0147] In some embodiments, the electrolyte has an ionic conductivity of 10 mS / cm or higher at 25°C, preferably between 10 mS / cm and 18 mS / cm. This allows the battery to have good fast-charging performance.

[0148] The ionic conductivity of an electrolyte has a meaning known in the art and can be determined using equipment and methods known in the art. For example, it can be determined using a conductivity meter, referring to HG / T 4066-4067-2008.

[0149] In some embodiments, the positive electrode, the separator, and the negative electrode can be fabricated into an electrode assembly using a winding process or a stacking process.

[0150] In some embodiments, the battery cell also includes a housing for containing the electrode assembly and electrolyte. The housing of the battery cell can be a rigid housing, such as a hard plastic housing, an aluminum housing, a steel housing, etc. The housing of the battery cell can also be a pouch, such as a pouch-type pouch. The pouch material can be plastic; examples of plastics include polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0151] This application does not impose any particular limitation on the shape of the battery cell; it can be cylindrical, square, or any other arbitrary shape. For example, Figure 2 The example shown is a square-structured battery cell 5.

[0152] In some implementations, refer to Figure 3 The outer casing may include a housing 51 and a cover plate 53. The housing 51 may include a base plate and side plates connected to the base plate, the base plate and side plates forming a receiving cavity. The housing 51 has an opening communicating with the receiving cavity, and the cover plate 53 can cover the opening to close the receiving cavity. A positive electrode sheet, a negative electrode sheet, and a separator can be formed into an electrode assembly 52 by a winding process or a stacking process. The electrode assembly 52 is encapsulated within the receiving cavity. Electrolyte is immersed in the electrode assembly 52. ​​The number of electrode assemblies 52 contained in a single battery cell 5 can be one or more, which can be selected by those skilled in the art according to specific practical needs.

[0153] The method for preparing the battery cell in this application is well known. In some embodiments, the electrode assembly can be placed in a housing, dried, and then injected with electrolyte. After vacuum sealing, settling, formation, and shaping, the battery cell is obtained.

[0154] In some embodiments, the battery mentioned in this application refers to a single physical module comprising one or more battery cells to provide higher voltage and capacity. For example, the battery mentioned in this application may be a battery module or a battery pack. A battery generally includes a housing for encapsulating one or more battery cells. The housing prevents liquids or other foreign matter from affecting the charging or discharging of the battery cells.

[0155] In some implementations, there can be multiple battery cells in the battery, which can be connected in series, parallel, or a combination thereof. A combination thereof means that multiple battery cells are connected in both series and parallel. Multiple battery cells can be directly connected in series, parallel, or a combination thereof, and then the whole assembly of multiple battery cells is housed in a housing. Alternatively, multiple battery cells can first be connected in series, parallel, or a combination thereof to form a battery module, and then multiple battery modules can be connected in series, parallel, or a combination thereof to form a whole assembly, which is then housed in a housing.

[0156] Figure 4 This is a schematic diagram of battery module 4 as an example. Figure 4 As shown, there are multiple battery cells 5, which are connected in series, parallel, or a combination thereof to form a battery module 4. The multiple battery cells 5 in the battery module 4 can be electrically connected through a busbar to achieve the series, parallel, or combination connection. In the battery module 4, the multiple battery cells 5 can be arranged sequentially along the length of the battery module 4. Of course, they can also be arranged in any other arbitrary manner. Furthermore, the multiple battery cells 5 can be fixed in place using fasteners.

[0157] In some embodiments, the battery modules described above can also be assembled into a battery pack, and the number of battery modules contained in the battery pack can be adjusted according to the application and capacity of the battery pack.

[0158] Figure 5 and Figure 6 This is a schematic diagram of battery pack 1 as an example. Figure 5 and Figure 6 As shown, the battery pack 1 may include a housing and multiple battery modules 4 disposed within the housing. The multiple battery modules 4 in the battery pack 1 can be electrically connected via a busbar component to achieve series, parallel, or mixed connection. The housing includes an upper housing 2 and a lower housing 3. The upper housing 2 covers the lower housing 3, forming a closed space for accommodating the battery modules 4. The multiple battery modules 4 can be arranged in any manner within the battery housing.

[0159] Electrical appliances

[0160] This application also provides an electrical device, which includes a battery cell provided in this application embodiment. The battery cell is used to provide electrical energy. The battery cell can be used as a power source for the electrical device or as an energy storage unit for the electrical device. The electrical device may include, but is 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 and satellites, energy storage systems, etc.

[0161] As the electrical device, a single battery cell, a battery module containing multiple battery cells, or a battery pack can be selected according to its usage requirements.

[0162] Figure 7This is an example of an electrical device. The device could be a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle. To meet the device's requirements for high power and high energy density, a battery pack or battery module can be used.

[0163] Another example of an electrical device could be a mobile phone, tablet, or laptop. These devices typically require a slim and lightweight design and can use a single battery cell as their power source.

[0164] Example

[0165] The following describes embodiments of this application. The embodiments described below are exemplary and are only used to explain this application, and should not be construed as limiting this application. Where specific techniques or conditions are not specified in the embodiments, they are performed according to the techniques or conditions described in the literature in this field or according to the product instructions. Reagents or instruments used, unless otherwise specified, are all conventional products that can be obtained commercially.

[0166] Example 1

[0167] Preparation of positive electrode sheet

[0168] Nickel acetate, a nickel salt with a volume distribution particle size (Dv50) of 200 nm, was mixed with an aqueous binder (PVDF) and a conductive agent (Ketjen black) to prepare nickel salt solutions with molar concentrations of Ni of 0.6 mol / L, 0.45 mol / L, 0.35 mol / L, 0.25 mol / L, 0.15 mol / L, and 0.05 mol / L. For all nickel salt solutions with different Ni molar concentrations, the molar concentrations of the aqueous binder and the conductive agent were both 0.05 mol / L.

[0169] The initial positive electrode particles LiNi 0.9 Co 0.05 Mn 0.05 (NCM9055), conductive agent acetylene black, and binder polyvinylidene fluoride (PVDF) are mixed uniformly in an appropriate amount of solvent N-methylpyrrolidone (NMP) at a mass ratio of 96.5:1.5:2 to obtain a positive electrode slurry. The positive electrode slurry is coated onto a positive electrode current collector aluminum foil, and the initial positive electrode sheet is obtained through processes such as drying, cold pressing, slitting, and cutting. The compaction density of the positive electrode film layer of the initial positive electrode sheet is 3.5 g / cm³. 3 .

[0170] The initial positive electrode sheet was immersed in a nickel salt solution with a Ni molar concentration of 0.6 mol / L for 6 hours, followed by drying in an oven at 120°C for 2 hours; this was the first immersion. The initial positive electrode sheet was then repeatedly immersed in nickel salt solutions of 0.45 mol / L, 0.35 mol / L, 0.25 mol / L, 0.15 mol / L, and 0.05 mol / L, respectively, to complete the second to sixth immersions, yielding the positive electrode sheet. The molar concentration of Ni in the nickel salt solution used for the i-th immersion is denoted as c. i mol / L, i is 1, 2, 3, 4, 5 or 6.

[0171] Preparation of negative electrode sheet

[0172] Artificial graphite, silicon suboxide, acetylene black (conductive agent), styrene-butadiene rubber (SBR) (binder), and sodium carboxymethyl cellulose (CMC) (batch) are mixed evenly in an appropriate amount of deionized water at a mass ratio of 90:5:2:2:1 to obtain a negative electrode slurry. The negative electrode slurry is coated onto a copper foil (negative electrode current collector), and the negative electrode sheet is obtained through drying, cold pressing, slitting, and cutting processes.

[0173] Preparation of the separating membrane

[0174] Polyethylene film is used as the separation membrane.

[0175] Preparation of electrolyte

[0176] Lithium salt (a mixture of LiPF6 and LiFSI in a mass ratio of 2:8) was dissolved in a solvent prepared by mixing ethylene carbonate (EC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) in a volume ratio of 1:1:1 to obtain an electrolyte with a lithium salt concentration of 1 mol / L.

[0177] Preparation of secondary batteries

[0178] The positive electrode, separator, and negative electrode are stacked and wound in sequence to obtain an electrode assembly. The electrode assembly is placed in an outer packaging, dried, and then injected with electrolyte. After vacuum sealing, settling, formation, and shaping, a secondary battery is obtained.

[0179] Examples 2-11, 13-14

[0180] Based on the preparation process of the positive electrode sheet in Example 1, according to Table 1, the preparation parameters such as the type of initial positive electrode particles, the type of nickel salt, the volume distribution particle size Dv50 of the nickel salt particles, and the number of impregnations were adjusted to prepare the positive electrode sheets of Examples 2-11 and 13-14.

[0181] The preparation of the negative electrode, separator, electrolyte, and secondary battery in Examples 2-11 and 13-14 is the same as in Example 1.

[0182] Example 12

[0183] Based on the preparation process of the positive electrode sheet in Example 1, an initial positive electrode sheet was prepared.

[0184] The initial positive electrode sheet was immersed in a nickel acetate solution with a Ni molar concentration of 0.6 mol / L for 6 hours, followed by drying in an oven at 120°C for 2 hours; this was the first immersion. Subsequently, the initial positive electrode sheet was immersed in a mixed solution of nickel acetate and nickel silicate with a Ni molar concentration of 0.3 mol / L (molar ratio of nickel acetate to nickel silicate 1:1) for 6 hours, followed by drying in an oven at 120°C for 2 hours. Finally, the initial positive electrode sheet was immersed in a mixed solution of nickel acetate, nickel silicate, and nickel sulfate with a Ni molar concentration of 0.15 mol / L (molar ratio of nickel acetate, nickel silicate, and nickel sulfate 1:1:1) for 6 hours, followed by drying in an oven at 120°C for 2 hours to obtain the positive electrode sheet.

[0185] The preparation of the negative electrode, separator, electrolyte, and secondary battery in Example 12 is the same as in Example 1.

[0186] Comparative Examples 1-3

[0187] Based on the preparation process of the initial positive electrode sheet in Example 1, positive electrode sheets of Comparative Examples 1-3 were prepared. The initial positive electrode particle of Comparative Example 1 was LiNi. 0.9 Co 0.05 Mn 0.05 (NCM9055); The initial cathode particles of Comparative Example 2 were LiNi 0.8 Co 0.1 Mn 0.1 (NCM811); The initial cathode particles of Comparative Example 3 were LiNi 0.7 Co 0.2 Mn 0.1 (NCM721).

[0188] The preparation of the negative electrode, separator, electrolyte, and secondary battery in Comparative Examples 1-3 was the same as in Example 1.

[0189] Test section

[0190] Cyclic performance test

[0191] At 25℃, after allowing the secondary battery to rest for 5 minutes, it is charged at a constant current rate of 0.33C (where 1C represents the current value corresponding to the theoretical capacity of the battery being completely discharged within 1 hour) to 4.25V. Then, it is charged at a constant voltage of 4.25V to the cutoff current of 0.05C, allowed to rest for 5 minutes, and then discharged at a constant current rate of 0.5C to 2.8V, allowed to rest for 5 minutes. This constitutes one charge-discharge cycle. The above steps are repeated for the same secondary battery, and the discharge capacity D0 of the first cycle and the discharge capacity D of the 1000th cycle are recorded. 1000 The cycle capacity retention rate P of a secondary battery 1000 =D 1000 / D0×100%.

[0192] The test results are detailed in Table 2.

[0193] Table 1

[0194] Serial Number Initial positive electrode particles Nickel salts <![CDATA[c1]]> <![CDATA[c2]]> <![CDATA[c3]]> <![CDATA[c4]]> <![CDATA[c5]]> <![CDATA[c6]]> Nickel salt Dv50 Example 1 NCM9055 Nickel acetate 0.6 0.45 0.35 0.25 0.15 0.05 200nm Example 2 NCM9055 Nickel silicate 0.6 0.45 0.35 0.25 0.15 0.05 200nm Example 3 NCM9055 Nickel carbonate 0.6 0.45 0.35 0.25 0.15 0.05 200nm Example 4 NCM9055 Nickel acetate 0.6 0.45 0.35 0.25 0.15 / 200nm Example 5 NCM9055 Nickel acetate 0.6 0.45 0.35 0.25 / / 200nm Example 6 NCM9055 Nickel acetate 0.6 0.45 0.35 / / / 200nm Example 7 NCM9055 Nickel acetate 0.6 0.45 / / / / 200nm Example 8 NCM9055 Nickel acetate 0.6 / / / / / 200nm Example 9 NCM9055 Nickel acetate 0.6 0.45 0.35 0.25 0.15 0.05 50nm Example 10 NCM9055 Nickel acetate 0.6 0.45 0.35 0.25 0.15 0.05 100nm Example 11 NCM9055 Nickel acetate 0.6 0.45 0.35 0.25 0.15 0.05 500nm Example 12 NCM9055 Mixed nickel salts 0.6 0.3 0.15 / / / 200nm Example 13 NCM811 Nickel acetate 0.6 0.45 0.35 0.25 0.15 0.05 200nm Example 14 NCM721 Nickel acetate 0.6 0.45 0.35 0.25 0.15 0.05 200nm Comparative Example 1 NCM9055 / / / / / / / / Comparative Example 2 NCM811 / / / / / / / / Comparative Example 3 NCM721 / / / / / / / /

[0195] Table 2

[0196] Table 2-1

[0197] Serial Number Coating thickness <![CDATA[Pole piece compaction g / cm 3 > Cyclic performance Example 1 900nm 4.10 90.56％ Example 2 900nm 4.10 89.87％ Example 3 900nm 4.10 90.46％ Example 4 800nm 4.05 90.42％ Example 5 700nm 3.95 89.45％ Example 6 500nm 3.80 88.79％ Example 7 300nm 3.60 88.12％ Example 8 200nm 3.55 87.76％ Example 9 900nm 4.10 92.23％ Example 10 900nm 4.10 91.86％ Example 11 900nm 4.10 90.35％ Example 12 400nm 3.70 91.77％ Comparative Example 1 / 3.50 87.55％

[0198] Table 2-2

[0199] Serial Number Coating thickness <![CDATA[Electrode compaction g / cm 3 > Cyclic performance Example 13 900nm 4.10 91.54％ Example 14 900nm 4.10 93.25％ Comparative Example 2 / 3.50 89.65％ Comparative Example 3 / 3.50 91.56％

[0200] Based on the test results in Tables 1 and 2, it can be seen that the positive electrode sheet of this application embodiment includes a specific positive electrode active material. This positive electrode active material has a specific structure and composition, and can exhibit high stability during the charge-discharge cycle of the battery. Therefore, the positive electrode sheet of this application embodiment, when applied to a secondary battery, can effectively improve the battery's cycle performance.

[0201] In contrast, the positive electrode of Comparative Example 1, containing the conventional ternary positive electrode material NCM9055, exhibits significantly lower cycle performance in its secondary battery compared to Examples 1-12. The positive electrode of Comparative Example 2, containing the conventional ternary positive electrode material NCM811, also shows significantly lower cycle performance in its secondary battery compared to Example 13. Furthermore, the positive electrode of Comparative Example 3, containing the conventional ternary positive electrode material NCM721, demonstrates significantly lower cycle performance in its secondary battery compared to Example 14.

[0202] For the compounds given but not listed in the examples, since their chemical properties and electrochemical reaction properties are similar to those of the compounds listed in the examples, they are all applicable to the technical solutions of the present invention, and therefore will not be listed here.

[0203] It should be noted that this application is not limited to the above-described embodiments. The above embodiments are merely examples, and any embodiments with the same structure and effect as the technical concept within the scope of this application are included in the technical scope of this application. Furthermore, various modifications that can be conceived by those skilled in the art to the embodiments, and other ways of constructing by combining some of the constituent elements of the embodiments, without departing from the spirit of this application, are also included in the scope of this application.

Claims

1. A positive electrode sheet, comprising a positive electrode active material; The positive electrode active material includes: The core comprises a nickel-containing lithium transition metal oxide, wherein, based on the total molar number of transition metal elements in the nickel-containing lithium transition metal oxide, the molar percentage of Ni is greater than or equal to 0.7; and A coating layer, covering at least a portion of the surface of the core, the coating layer comprising nickel salt particles; the inner layer of the coating layer having a greater mass percentage of Ni than the outer layer of Ni along a direction away from the core.

2. The positive electrode sheet according to claim 1, wherein, Based on the total mass of the core, the mass percentage of Ni in the core is w1%; based on the total mass of the cladding layer, the mass percentage of Ni in the cladding layer is w2%. The positive electrode active material satisfies: w2 < w1.

3. The positive electrode sheet according to claim 1 or 2, wherein, The coating layer comprises multiple layers of nickel salt particles stacked in a direction away from the core.

4. The positive electrode sheet according to claim 3, wherein, In the plurality of nickel salt particle layers, the mass percentage of Ni in the nickel salt particle layers farther from the core is less than the mass percentage of Ni in the nickel salt particle layers closer to the core.

5. The positive electrode sheet according to any one of claims 1-4, wherein, The thickness of the coating layer is 100 nm-5 μm; and / or The volumetric particle size distribution (Dv50) of the kernel is 1.2 μm-15 μm.

6. The positive electrode sheet according to claim 5, wherein, The thickness of the coating layer is 200nm-900nm; and / or The volumetric particle size distribution (Dv50) of the kernel is 10 μm-15 μm.

7. The positive electrode sheet according to any one of claims 1-6, wherein, The volume distribution particle size Dv50 of the nickel salt particles is 50nm-500nm.

8. The positive electrode sheet according to claim 7, wherein, The volume distribution particle size Dv50 of the nickel salt particles is 50nm-200nm.

9. The positive electrode sheet according to any one of claims 1-8, wherein, The nickel-containing lithium transition metal oxide includes LiNi x Co y Mn z O2, where 0.7≤x<1.0, 0<y<0.3, 0<z<0.

3.

10. The positive electrode sheet according to any one of claims 1-9, wherein, The nickel salt particles comprise nickel oxyacid salts.

11. The positive electrode sheet according to claim 10, wherein, The nickel salt particles include at least one of nickel acetate, nickel silicate, or nickel carbonate.

12. The positive electrode sheet according to any one of claims 1-11, wherein, The positive electrode includes a positive current collector and a positive electrode film layer located on at least one side of the positive current collector, wherein the positive active material is distributed in the positive electrode film layer; The compaction density of the positive electrode film is greater than or equal to 3.6 g / cm³. 3 .

13. The positive electrode sheet according to claim 12, wherein, The compaction density of the positive electrode film is 3.6 g / cm³. 3 -4.6g / cm 3 .

14. A method for preparing a positive electrode sheet, comprising: An initial positive electrode sheet is provided, the initial positive electrode sheet comprising initial positive electrode particles, the initial positive electrode particles comprising a nickel-containing lithium transition metal oxide, wherein, based on the total molar number of transition metal elements in the nickel-containing lithium transition metal oxide, the molar percentage of Ni element is greater than or equal to 0.

7. The initial positive electrode sheet is immersed in a nickel salt solution and dried to form a coating layer including nickel salt particles on at least a portion of the surface of the initial positive electrode particles, thereby obtaining the positive electrode sheet. The positive electrode sheet includes a positive electrode active material, which includes: The core comprises a nickel-containing lithium transition metal oxide, wherein, based on the total molar number of transition metal elements in the nickel-containing lithium transition metal oxide, the molar percentage of Ni is greater than or equal to 0.7; and A coating layer, covering at least a portion of the surface of the core, the coating layer comprising nickel salt particles; the inner layer of the coating layer having a greater mass percentage of Ni than the outer layer of Ni along a direction away from the core.

15. The method according to claim 14, wherein, The step of immersing the initial positive electrode sheet in a nickel salt solution and then drying it includes: The initial positive electrode sheet is sequentially immersed in a variety of nickel salt solutions and dried to form a plurality of nickel salt particle layers stacked on at least a portion of the surface of the initial positive electrode particles.

16. The method according to claim 15, wherein, In the various nickel salt solutions, the mass percentage of Ni element decreases sequentially based on the total mass of the solid components in the nickel salt solution.

17. The method according to any one of claims 14-16, wherein, In the nickel salt solution, the molar concentration of Ni is 0.05 mol / L to 0.6 mol / L; and / or Based on the total mass of the solid components in the nickel salt solution, the mass percentage of Ni is 5%-60%.

18. The method according to any one of claims 14-17, wherein, The solid component of the nickel salt solution includes the nickel salt and optional additives.

19. The method according to claim 18, wherein, The optional additives include binders and / or conductive agents.

20. The method according to claim 19, wherein, The adhesive includes a water-based adhesive; the conductive agent includes a conductive carbon material.

21. The method according to any one of claims 14-20, wherein, The initial positive electrode includes a positive current collector and an initial positive electrode film layer located on at least one side of the positive current collector, wherein the compaction density of the initial positive electrode film layer is 3.1 g / cm³. 3 -4.1g / cm 3 .

22. A battery comprising a positive electrode sheet according to any one of claims 1-13, or a positive electrode sheet prepared by the method according to any one of claims 14-21.

23. The battery according to claim 22, wherein, The battery also includes an electrolyte, which has an ionic conductivity of 10 mS / cm or higher at 25°C.

24. The battery according to claim 23, wherein, The electrolyte has an ionic conductivity of 10 mS / cm-18 mS / cm at 25°C.

25. An electrical device comprising a battery according to any one of claims 22-24.

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