Battery cell and electrochemical device and electronic equipment comprising same

Abstract

The invention discloses a battery cell, an electrochemical device comprising the same and electronic equipment, and relates to the technical field of electrochemical energy storage. The invention provides a battery cell which comprises a positive thick electrode plate, and the positive thick electrode plate comprises a current collector, a first electrode layer arranged on at least one surface of the current collector and a second electrode layer arranged on the first electrode layer; according to the invention, the relation between the surface density and the tap density is established, so that the distribution of the active substances in the thickness direction of the two layers is coordinated with the microstructure, the total amount of the active substances of the whole thick electrode is ensured, and the transmission bottleneck caused by a single high-density layer is avoided.

Description

Technical Field

[0001] This application relates to the field of electrochemical energy storage technology, and in particular to a battery cell and an electrochemical device and electronic device including the same. Background Technology

[0002] Driven by both technological advancements and environmental policies, the new energy industry has experienced rapid development, with market demands for battery energy density increasing daily. As a core factor influencing battery energy density, cathode materials, based on specific lithium insertion / extraction mechanisms, have seen their specific capacity approach its theoretical limit, leaving increasingly limited room for further breakthroughs in energy density at the raw material level. Against this backdrop, optimizing battery electrode structures to improve energy density has become a crucial research direction and technological requirement for the industry.

[0003] To meet the demand for increased energy density, increasing electrode thickness has become a feasible structural improvement solution. This solution allows for the loading of more active materials within a limited space, directly improving battery energy density and potentially reducing production costs. However, thick electrode structures have significant technical drawbacks: firstly, the electron-lithium ion transport path lengthens with increasing electrode thickness, leading to decreased charge transport efficiency; secondly, the electrolyte's wetting effect on the electrode deteriorates, directly affecting the low-temperature discharge performance, rate charge-discharge performance, and cycle life of lithium batteries; and thirdly, during processing, thick electrodes are prone to breakage and delamination during the baking stage, affecting product consistency and yield.

[0004] To address the aforementioned problems caused by thick electrodes, existing technologies employ dry electrode methods for improvement. However, this method has significant limitations: firstly, it is highly dependent on production equipment, requiring large-scale modifications to mixing, coating, and rolling equipment, resulting in high initial equipment investment costs and high energy consumption during production; secondly, products prepared using this method suffer from poor contact between the material and the current collector, which can lead to active material detachment in severe cases, affecting battery structural stability and safety, and making it difficult to meet the reliability requirements of practical applications. Therefore, this application is submitted. Summary of the Invention

[0005] Based on this, the purpose of this application is to overcome the shortcomings of the prior art and provide a battery cell and an electrochemical device and electronic device including the same.

[0006] To achieve the above objectives, this application proposes a battery cell, including a positive electrode sheet, wherein the positive electrode sheet includes a current collector, a first electrode layer disposed on at least one side of the current collector, and a second electrode layer disposed on the first electrode layer; The areal density of the first electrode layer is C1, and the first electrode layer includes a first positive electrode active material, a first conductive agent and a first binder. The tap density of the first positive electrode active material is D1. The areal density of the second electrode layer is C2, and the second electrode layer includes a second positive electrode active material, a second conductive agent and a second binder. The tap density of the second positive electrode active material is D2. Wherein, C1>C2, D1>D2, and 0.30≤D2 / (D1+D2)≤0.5; the areal density and tap density satisfy the following relationship: C2≈C1×D2 / (D1+D2).

[0007] In some embodiments, the battery cell satisfies at least one of the following conditions: (1) 130 mg / cm 2 ≤C1≤265mg / cm 2 ; (2) 15 mg / cm 2 ≤C2≤160mg / cm 2 ; (3) 0.8 g / cm 3 ≤D1≤2.3g / cm 3 ; (4) 0.8 g / cm 3 ≤D2≤2.3g / cm 3 .

[0008] In some embodiments, the first positive electrode active material and the second positive electrode active material are each independently selected from at least one of nickel-cobalt-manganese ternary materials, nickel-cobalt-aluminum ternary materials, lithium cobalt oxide materials, lithium iron phosphate materials, lithium manganese oxide materials, lithium manganese iron phosphate materials, and nickel-manganese spinel materials.

[0009] In some embodiments, the specific surface area of ​​the first conductive agent is S1, the specific surface area of ​​the second conductive agent is S2, and the 10% ≤ (S2-S1) / S1 ≤ 100%.

[0010] In some embodiments, the battery cell satisfies at least one of the following conditions: (5) 10 m² / g≤S1≤100 m² / g; (6) 30 m² / g≤S2≤200 m² / g.

[0011] In some embodiments, the first conductive agent and the second conductive agent are each independently selected from at least one of conductive carbon black, superconducting carbon black, conductive graphite, graphene, carbon nanotubes, and vapor-grown carbon fibers.

[0012] In some embodiments, the width of the first electrode layer is W1 and the width of the second electrode layer is W2, satisfying W1 > W2.

[0013] In some embodiments, the battery cell satisfies at least one of the following conditions: (7) 100mm≤W1≤600mm; (8)0.2 mm≤W1-W2≤6 mm.

[0014] Another aspect of this application provides an electrochemical device including the aforementioned battery cell.

[0015] This application also proposes an electronic device comprising the aforementioned electrochemical device.

[0016] Compared to existing technologies, the beneficial effects of this application are as follows: By establishing the relationship between the areal densities of the first and second electrode layers, and the relationship between the tap density of the first positive electrode active material and the tap density of the second positive electrode active material, this application has the following advantages: The first electrode layer is close to the current collector and adopts a high tap density D1 (dense structure) and a high areal density C1, which can enhance the interfacial contact with the current collector, reduce the electron conduction resistance, and provide a stable electron transport channel for the thick electrode. At the same time, the high areal density allows for the loading of more active material to ensure the energy density. The second electrode layer is located on the outer layer and adopts a low tap density D2 (loose structure) and a low areal density C2, which can increase porosity, shorten the diffusion path of lithium ions on the electrode surface, improve the electrolyte wetting effect, and alleviate the problem of ion transport lag in thick electrodes. The two-layer structure forms a synergistic effect of "dense inner layer for electron transport and loose outer layer for ion transport," balancing energy density and transport efficiency.

[0017] This application establishes a relationship between the tap density of the first positive electrode active material and the tap density of the second positive electrode active material to balance the mechanical strength and electrochemical performance of the electrode. If D2 / (D1+D2) < 0.3, the porosity of the second electrode layer is too low, which cannot effectively improve electrolyte wetting and ion diffusion, and the rate capability and low-temperature performance defects of thick electrodes still exist. If D2 / (D1+D2) > 0.5, the second electrode layer is too porous, which will lead to a decrease in the overall mechanical strength of the electrode and make it prone to delamination or breakage during processing such as baking and rolling. This range ensures that the outer layer has sufficient porosity to optimize transport, while the dense structure of the inner layer provides support, thus balancing the energy density, reliability and electrochemical performance of thick electrodes.

[0018] This application achieves a match between the loading of active material in the two layers and their density by establishing the relationship between the areal density and tap density, with C2≈C1×D2 / (D1+D2). Since D1>D2, the first electrode layer contains more active material per unit volume, and the high areal density C1 fully utilizes the space utilization of its dense structure. The second electrode layer, with its smaller and less porous D2, avoids pore blockage due to overfilling, ensuring electrolyte permeation channels. This matching coordinates the distribution of active material in the thickness direction with the microstructure of the two layers, ensuring both the total amount of active material in the overall thick electrode and avoiding the transport bottleneck caused by a single high-density layer. Detailed Implementation

[0019] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions in the embodiments of this application will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application. The embodiments of this application may omit unnecessary detailed descriptions. For example, detailed descriptions of well-known matters and repeated descriptions of actually identical structures may be omitted. This is to avoid making the following description unnecessarily lengthy and to facilitate understanding by those skilled in the art.

[0020] In this application, the technical features described in an open-ended manner include both closed technical solutions consisting of the listed features and open technical solutions that include the listed features.

[0021] As used herein, the terms “approximately,” “generally,” “substantially,” and “about” are used to describe and indicate small variations. When used in conjunction with an event or situation, the terms may refer to examples in which the event or situation occurred precisely and examples in which the event or situation occurred very approximately. For example, when used in conjunction with numerical values, the terms may refer to a range of variation less than or equal to ±10% of the numerical value, such as less than or equal to ±5%, less than or equal to ±4%, less than or equal to ±3%, less than or equal to ±2%, less than or equal to ±1%, less than or equal to ±0.5%, less than or equal to ±0.1%, or less than or equal to ±0.05%. For example, if the difference between two values ​​is less than or equal to ±10% of the average of the values ​​(e.g., less than or equal to ±5%, less than or equal to ±4%, less than or equal to ±3%, less than or equal to ±2%, less than or equal to ±1%, less than or equal to ±0.5%, less than or equal to ±0.1%, or less than or equal to ±0.05%), then the two values ​​can be considered "substantially" the same.

[0022] Additionally, quantities, ratios, and other numerical values ​​are sometimes presented in range format in this document. It should be understood that such range format is for convenience and brevity and should be interpreted flexibly to include not only the numerical values ​​explicitly specified as range limits, but also all individual numerical values ​​or subranges covered within the range, as if each numerical value and subrange were explicitly specified.

[0023] In the detailed description and claims, a list of items connected by the terms "one of," "among," "a kind of," or other similar terms may mean any of the listed items. For example, if items A and B are listed, then the phrase "one of A and B" means only A or only B. In another example, if items A, B, and C are listed, then the phrase "one of A, B, and C" means only A; only B; or only C. Item A may contain a single element or multiple elements. Item B may contain a single element or multiple elements. Item C may contain a single element or multiple elements.

[0024] In the detailed description and claims, the list of items connected by the term "at least one of" can mean any combination of the listed items. For example, if items A and B are listed, then the phrase "at least one of A and B" means only A; only B; or A and B. In another example, if items A, B, and C are listed, then the phrase "at least one of A, B, and C" means only A; or only B; only C; A and B (excluding C); A and C (excluding B); B and C (excluding A); or all of A, B, and C.

[0025] Throughout this specification, references to "implementation," "partial implementation," "one implementation," "another implementation," "specific method," or "partial method" mean that at least one implementation or embodiment in this application includes the specific features, structures, materials, or characteristics described in that implementation or embodiment.

[0026] In this application, numerical ranges are involved. Unless otherwise specified, the numerical ranges mentioned above are considered continuous and include the minimum and maximum values ​​of the range, as well as every value between the minimum and maximum values. Any lower limit can be combined with any upper limit to form a range not explicitly stated; and any lower limit can be combined with other lower limits to form a range not explicitly stated, just as any upper limit can be combined with any other upper limit to form a range not explicitly stated. Furthermore, each individually disclosed point or single value can itself serve as a lower or upper limit and be combined with any other point or single value or with other lower or upper limits to form a range not explicitly stated.

[0027] Although illustrative embodiments have been demonstrated and described, those skilled in the art should understand that the above embodiments should not be construed as limiting the invention, and that changes, substitutions and modifications can be made to the embodiments without departing from the spirit, principles and scope of the invention.

[0028] This application proposes a battery cell, including a positive electrode sheet, the positive electrode sheet including a current collector, a first electrode layer disposed on at least one side of the current collector, and a second electrode layer disposed on the first electrode layer; The areal density of the first electrode layer is C1, and the first electrode layer includes a first positive electrode active material, a first conductive agent and a first binder. The tap density of the first positive electrode active material is D1. The areal density of the second electrode layer is C2, and the second electrode layer includes a second positive electrode active material, a second conductive agent and a second binder. The tap density of the second positive electrode active material is D2. Wherein, C1>C2, D1>D2, and 0.30≤D2 / (D1+D2)≤0.5; the areal density and tap density satisfy the following relationship: C2≈C1×D2 / (D1+D2).

[0029] This application establishes the relationship between the areal densities of the first and second electrode layers, and the relationship between the tap density of the first and second positive electrode active materials. This has the following advantages: The first electrode layer, located close to the current collector, employs a high tap density D1 (dense structure) and a high areal density C1, which enhances the interfacial contact with the current collector, reduces electron conduction resistance, and provides a stable electron transport channel for the thick electrode. Simultaneously, the high areal density allows for the loading of more active material, ensuring a basic energy density. The second electrode layer, located on the outer layer, employs a low tap density D2 (loose structure) and a low areal density C2, which increases porosity, shortens the diffusion path of lithium ions on the electrode surface, improves electrolyte wetting, and alleviates the problem of ion transport lag in thick electrodes. The two-layer structure forms a synergistic effect of "dense inner layer for electron transport and loose outer layer for ion transport," balancing energy density and transport efficiency, and exhibiting a high cycle capacity retention rate.

[0030] This application establishes a relationship between the tap density of the first positive electrode active material and the tap density of the second positive electrode active material to balance the mechanical strength and electrochemical performance of the electrode. If D2 / (D1+D2) < 0.3, the porosity of the second electrode layer is too low, which cannot effectively improve electrolyte wetting and ion diffusion, and the rate capability and low-temperature performance defects of thick electrodes still exist. If D2 / (D1+D2) > 0.5, the second electrode layer is too porous, which will lead to a decrease in the overall mechanical strength of the electrode and make it prone to delamination or breakage during processing such as baking and rolling. This range ensures that the outer layer has sufficient porosity to optimize transport, while the dense structure of the inner layer provides support, thus balancing the energy density, reliability and electrochemical performance of thick electrodes.

[0031] This application achieves a match between the loading of active material in the two layers and their density by establishing the relationship between the areal density and tap density, with C2≈C1×D2 / (D1+D2). Since D1>D2, the first electrode layer contains more active material per unit volume, and the high areal density C1 fully utilizes the space utilization of its dense structure. The second electrode layer, with its smaller and less porous D2, avoids pore blockage due to overfilling, ensuring electrolyte permeation channels. This matching coordinates the distribution of active material in the thickness direction with the microstructure of the two layers, ensuring both the total amount of active material in the overall thick electrode and avoiding the transport bottleneck caused by a single high-density layer.

[0032] In some implementations, D2 / (D1+D2) can be 0.3, 0.35, 0.4, 0.45, 0.48 or 0.5, or fall within the range of any two of the above values.

[0033] In some implementations, 130 mg / cm 2 ≤C1≤265mg / cm 2 For example, the areal density C1 of the first electrode layer can be 130 mg / cm³. 2 150mg / cm 2 180mg / cm 2 200mg / cm 2 230mg / cm 2 250mg / cm 2 Or 265mg / cm 2 Or it falls within the range of any two of the above values.

[0034] In some implementations, 15 mg / cm 2 ≤C2≤160mg / cm 2 For example, the areal density C2 of the second electrode layer can be 15 mg / cm³. 2 30mg / cm 2 50mg / cm2 80mg / cm 2 100mg / cm 2 120mg / cm 2 150mg / cm 2 Or 160mg / cm 2 Or it falls within the range of any two of the above values.

[0035] In some implementations, 180 mg / cm 2 ≤C1+C2≤400mg / cm 2 In some implementations, 200 mg / cm 2 ≤C1+C2≤300mg / cm 2 For example, C1+C2 can be 180 mg / cm³. 2 200mg / cm 2 520mg / cm 2 280mg / cm 2 300mg / cm 2 320mg / cm 2 350mg / cm 2 Or 400mg / cm 2 Or it falls within the range of any two of the above values.

[0036] In some implementations, 0.8 g / cm 3 ≤D1≤2.3g / cm 3 For example, the tap density D1 of the first positive electrode active material can be 0.8 g / cm³. 3 0.85g / cm 3 0.9g / cm 3 0.95g / cm 3 1.0g / cm 3 1.2g / cm 3 1.4g / cm 3 1.6g / cm 3 Or 2.3g / cm 3 Or it falls within the range of any two of the above values.

[0037] In some implementations, 0.8 g / cm 3 ≤D2≤2.3g / cm 3 For example, the tap density D2 of the second positive electrode active material can be 0.8 g / cm³. 3 0.85g / cm 3 0.9g / cm 3 0.95g / cm 31.0g / cm 3 1.2g / cm 3 1.4g / cm 3 1.6g / cm 3 Or 2.3g / cm 3 Or it falls within the range of any two of the above values.

[0038] This application balances electrode mechanical strength, energy density, and electrochemical transport efficiency by limiting the tap density of the first and second positive electrode active materials. If the tap density is below 0.8 g / cm³, the electrode microstructure is too porous, which not only leads to insufficient active material loading, making it difficult to meet the energy density requirements of thick electrodes, but also reduces the electrode mechanical strength, making it prone to delamination and breakage during processing such as baking and rolling. If the tap density is above 2.3 g / cm³, the electrode structure is excessively dense, which significantly reduces porosity, hinders electrolyte wetting and lithium-ion diffusion, exacerbates the ion transport bottleneck of thick electrodes, and leads to deterioration in rate performance and low-temperature performance. This numerical range ensures that both electrode layers have sufficient structural stability and active material loading capacity, while reserving reasonable porosity space for ion transport, thus adapting to the overall performance requirements of layered thick electrodes.

[0039] This application, by limiting the areal density of the first and second electrode layers, can ensure the total amount of active material to achieve energy density, while avoiding pore blockage in the second electrode layer, and can effectively alleviate the transmission lag problem of thick electrodes.

[0040] In some embodiments, the first positive electrode active material and the second positive electrode active material are each independently selected from at least one of nickel-cobalt-manganese ternary materials (NCM), nickel-cobalt-aluminum ternary materials, lithium cobalt oxide materials (LCO), lithium iron phosphate materials (LFP), lithium manganese oxide materials, lithium manganese iron phosphate materials (LMFP), and nickel-manganese spinel materials.

[0041] In some embodiments, the specific surface area of ​​the first conductive agent is S1, the specific surface area of ​​the second conductive agent is S2, and the 10% ≤ (S2-S1) / S1 ≤ 100%.

[0042] In some implementations, 40% ≤ (S2-S1) / S1 ≤ 90%.

[0043] This application, by defining the relationship between the specific surface areas of the first and second conductive agents, can better adapt to the structural characteristics of the layered electrode and optimize the electron conduction network. The first electrode layer is close to the current collector, and a smaller S1 prevents excessive dispersion of the conductive agent from crowding out the pores, while ensuring interfacial contact stability with the current collector, thus constructing a highly efficient electron transport substrate. The second electrode layer has a porous structure, with S2 greater than S1 and satisfying 10% ≤ (S2-S1) / S1 ≤ 100%. This allows for the formation of denser conductive pathways through a larger specific surface area, compensating for insufficient electron conduction caused by the porous surface active material. (S2-S1) / S1 ≥ 10% ensures a substantial improvement in S2 compared to S1, avoiding insignificant improvement in the conductive network; (S2-S1) / S1 ≤ 100% prevents excessively large S2 from causing conductive agent aggregation, avoiding blockage of electrode pores, ensuring unobstructed electrolyte wetting and lithium-ion diffusion channels, ultimately achieving synergistic optimization of electron conduction and ion transport.

[0044] In some embodiments, 10 m² / g ≤ S1 ≤ 100 m² / g; for example, the specific surface area S1 of the first conductive agent can be 10 m² / g, 20 m² / g, 40 m² / g, 50 m² / g, 70 m² / g, 80 m² / g or 100 m² / g, or within the range of any two of the above values.

[0045] In some embodiments, 30 m² / g ≤ S2 ≤ 200 m² / g; for example, the specific surface area S2 of the second conductive agent can be 30 m² / g, 40 m² / g, 50 m² / g, 70 m² / g, 80 m² / g, 100 m² / g, 120 m² / g, 140 m² / g, 160 m² / g, 180 m² / g or 200 m² / g, or within the range of any two of the above values.

[0046] This application limits the specific surface area of ​​the first and second electrode layers. The specific surface area range of the first electrode layer is such that the conductive network will not be discontinuous due to an excessively small specific surface area, nor will it be excessively porous due to an excessively large specific surface area, thus ensuring unobstructed lithium-ion transport channels. The specific surface area of ​​the second electrode layer ensures that the conductive network density is substantially improved compared to the first electrode layer, enabling the formation of dense conductive pathways in a porous structure.

[0047] In some embodiments, the first conductive agent and the second conductive agent are each independently selected from at least one of conductive carbon black, superconducting carbon black, conductive graphite, graphene, carbon nanotubes, and vapor-grown carbon fibers.

[0048] In some embodiments, the width of the first electrode layer is W1 and the width of the second electrode layer is W2, satisfying W1 > W2.

[0049] This application, by defining the width relationship between the first and second electrode layers, can adapt to the structural functions, processing, and electrochemical performance requirements of layered electrodes. The first electrode layer, close to the current collector, has a wider width (W1) that increases the contact area with the current collector, enhancing the stability of electron conduction. Simultaneously, it provides more sufficient structural support for the thick electrode, improving overall mechanical strength and adapting to the high areal density and high tap density characteristics of the inner layer. The second electrode layer has a porous structure; a narrower width (W2) reduces edge stress in the porous surface area, preventing cracking and delamination during processing such as baking and rolling due to the weaker mechanical strength of the outer layer. It also shortens the diffusion distance of the electrolyte on the surface, ensuring uniform wetting and optimizing lithium-ion transport efficiency. This width difference makes the two electrode layers functionally complementary: W1 ensures energy density and structural stability, while W2 mitigates the performance and processing defects of the porous outer layer, achieving a balance in the overall performance of the thick electrode.

[0050] In some implementations, 100mm ≤ W1 ≤ 600mm; for example, the width W1 of the first electrode layer can be 100mm, 150mm, 200mm, 250mm, 300mm, 350mm, 400mm, 500mm or 600mm, or within the range of any two of the above values.

[0051] In some implementations, 0.2mm ≤ W1-W2 ≤ 6mm; for example, W1-W2 can be 0.2mm, 0.5mm, 1mm, 2mm, 3mm, 4mm, 5mm or 6mm, or fall within the range of any two of the above values.

[0052] By limiting the widths of the first and second electrode layers, this application ensures that the first electrode layer has sufficient active material loading area to match the energy density requirements of high areal density C1; at the same time, it ensures that the second electrode layer has sufficient effective ion transport area, avoiding a sharp drop in the utilization rate of surface active material due to excessive narrowness.

[0053] In some embodiments, the first adhesive and the second adhesive are each independently selected from at least one of polyvinylidene fluoride (PVDF), poly(vinylidene fluoride)-hexafluoropropylene (PVDF-HFP), polytetrafluoroethylene (PTFE), vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, fluorinated acrylate resin, polyacrylic acid, polyacrylonitrile, polyimide, polyurethane, polyvinyl butyral, polyvinylpyrrolidone (PVP), acrylic acid-acrylonitrile-acrylamide copolymer, and acrylic acid-acrylonitrile-acrylate copolymer. The first adhesive and the second adhesive of this application are not limited to the above materials, but also include other materials that can be used as battery positive electrode adhesives.

[0054] In some embodiments, the current collector of the positive electrode thick sheet is a metal foil or a composite current collector. In some embodiments, the metal foil is aluminum foil. The composite current collector may include a metal foil substrate and a positive conductive layer disposed on at least one side of the metal foil substrate.

[0055] In some embodiments, the positive electrode conductive layer may include at least one of carbon, carbon black, graphite, expanded graphite, graphene, graphene nanosheets, carbon fiber, carbon nanofiber, graphitized carbon sheet, carbon tube, carbon nanotube, activated carbon, and mesoporous carbon.

[0056] In some embodiments, the first electrode layer further includes a flexible agent; the flexible agent is at least one selected from polyacrylate rubber, phosphate esters, polyether polyesters, alkane chains, aromatic rings, and amides.

[0057] In some embodiments, the second electrode layer further includes a wetting agent; the wetting agent is at least one of organosilicon, phosphate ester, and silanol nonionic surfactant.

[0058] The primary purpose of the first electrode layer in this application is to resist pressure. However, the addition of conductive agents can make the first electrode layer brittle. By adding a flexible agent, the toughness of the system is improved, thereby increasing the pressure resistance of the first electrode layer. When no flexible agent is present, the particle structure is easily damaged, the electron transport channels are blocked, and the final cycle capacity retention and discharge retention rate are affected. The primary purpose of the second electrode layer in this application is wetting. Conductive agents such as carbon black and graphene can increase wettability. At the same time, the addition of a wetting agent can further improve the wettability of the second electrode layer.

[0059] In some embodiments, the battery cell includes a positive electrode sheet, a negative electrode sheet, a separator, and an electrolyte.

[0060] In some embodiments, the negative electrode sheet includes a negative electrode current collector, and at least one side of the negative electrode current collector is provided with a negative electrode active material layer, the negative electrode active material layer including a negative electrode active material, a negative electrode binder, and a negative electrode conductive agent. This application does not limit the negative electrode active material; any known negative electrode active material can be used.

[0061] In some embodiments, the negative current collector is a metal foil or a composite current collector. In some embodiments, the metal foil is a copper foil. The composite current collector may include a metal foil substrate and a negative conductive layer disposed on at least one side of the metal foil substrate.

[0062] In some embodiments, the negative electrode conductive layer may include at least one of carbon, carbon black, graphite, expanded graphite, graphene, graphene nanosheets, carbon fiber, carbon nanofiber, graphitized carbon sheet, carbon tube, carbon nanotube, activated carbon, and mesoporous carbon.

[0063] In some embodiments, the negative electrode active material may include natural graphite particles, synthetic graphite particles, hard carbon, soft carbon, mesophase carbon microspheres (MCMB), Sn, SnO2, SnO, Li4Ti5O 12 The negative electrode active material is selected from at least one of LTO, Si material, silicon-carbon (Si-C) composite material, silicon-nitrogen (Si-N) composite material, and silicon-oxygen (Si-O) composite material. The negative electrode active material of this application is not limited to the above-mentioned materials, but also includes other materials that can be used as negative electrode active materials for batteries.

[0064] In some embodiments, the silicon-based material accounts for more than 5% of the weight of the negative electrode active material.

[0065] In some embodiments, the negative electrode binder may include at least one of the following: polyacrylic acid, polymethacrylic acid, polyacrylate, polymethacrylate, polyacrylamide, styrene-butadiene rubber, acrylic styrene-butadiene rubber, acrylic acid-acrylonitrile-acrylamide copolymer, acrylic acid-acrylonitrile-acrylate copolymer, acrylonitrile-butadiene rubber, nitrile rubber, acrylonitrile-styrene-butadiene copolymer, acryloyl rubber, butyl rubber, fluororubber, polytetrafluoroethylene, polyvinyl alcohol, polyvinyl acetate, polyepoxychloropropane, polyphosphazene, polyacrylonitrile, polystyrene, latex, acrylic resin, phenolic resin, epoxy resin, carboxymethyl cellulose, hydroxypropyl cellulose, cellulose acetate, cellulose acetate butyrate, cellulose acetate propionate, cyanoethyl cellulose, carboxymethyl chitosan, polyester, polyamide, polyether, polyimide, polycarboxylic acid ester, polycarboxylic acid, polyurethane, alginate, fluorinated polymer, chlorinated polymer, polyvinylidene fluoride, and poly(vinylidene fluoride)-hexafluoropropylene. The negative electrode binder of this application is not limited to the above-mentioned materials, but also includes other materials that can be used as battery negative electrode binders.

[0066] In some embodiments, the negative electrode conductive agent may include at least one of carbon, carbon black, graphite, expanded graphite, graphene, graphene nanosheets, superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon fibers, carbon nanofibers, graphitized carbon sheets, carbon nanotubes, activated carbon, and mesoporous carbon. The negative electrode conductive agent of this application is not limited to the above materials, but also includes other materials that can be used as battery negative electrode conductive agents.

[0067] In some embodiments, the separator separates the negative and positive electrodes and provides a pathway for lithium-ion migration. The use of the separator is not particularly limited, as long as it is a separator commonly used in lithium-ion secondary batteries. In particular, separators with low resistance to electrolyte ion movement and excellent electrolyte permeability are preferred. Specifically, porous polymer membranes can be used, such as those formed from polyolefin-based polymers (e.g., ethylene homopolymers, propylene homopolymers, ethylene / butene copolymers, ethylene / hexene copolymers, ethylene / methacrylate copolymers, etc.). Porous polymer membranes or laminated structures with two or more layers can be used. Alternatively, nonwoven fabrics formed from conventional porous nonwoven fabrics (e.g., glass fibers with high melting points, polyethylene terephthalate fibers, etc.) can be used. Furthermore, coated membranes containing ceramic components or polymer materials can be used to ensure heat resistance or mechanical strength, and can optionally be used as single-layer or multi-layer structures.

[0068] Generally, a diaphragm includes a substrate and a coating applied to the surface of the substrate.

[0069] In some embodiments, the substrate is, but is not limited to, at least one of polyolefins, polyesters, polyacetals, polyamides, polyethylene terephthalate, polycarbonate, polyimide, polyetheretherketone, polyethersulfone, polyphenylene ether, polyphenylene sulfide, polyacrylonitrile, polyvinylidene fluoride, polyoxymethylene, polyoxymethylene, polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene, polytetrafluoroethylene, polysulfone, and polymethyl methacrylate. Some non-limiting examples of polyolefins include at least one of polyethylene (PE), ultra-high molecular weight polyethylene (UHMWPE), high-density polyethylene (HDPE), polypropylene (PP), polyethylene-polypropylene copolymer (PE-PP), and polyethylene-polypropylene-polyethylene copolymer.

[0070] In some embodiments, the electrolyte may include a non-aqueous solvent and a lithium salt.

[0071] In some embodiments, the lithium salt may include at least one of LiPF6, LiBF4, LiAsF6, LiClO4, LiB(C6H5)4, LiCH3SO3, LiCF3SO3, LiN(SO2CF3)2, LiC(SO2CF3)3, LiSiF6, LiBOB, and lithium difluoroborate.

[0072] In some embodiments, the non-aqueous solvent may be at least one of carbonate compounds, carboxylic acid ester compounds, and ether compounds.

[0073] In some embodiments, the carbonate compound may include at least one of chain carbonate compounds, cyclic carbonate compounds, and fluorocarbonate compounds.

[0074] In some embodiments, the chain carbonate compound may include diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), methyl ethyl carbonate (MEC), and combinations thereof.

[0075] In some embodiments, the cyclic carbonate compound may include ethylene carbonate (EC), propylene carbonate (PC), butyl carbonate (BC), vinyl ethylene carbonate (VEC), and combinations thereof.

[0076] In some embodiments, the fluorocarbonate compound may include at least one of fluoroethylene carbonate (FEC), 1,2-difluoroethylene carbonate, 1,1-difluoroethylene carbonate, 1,1,2-trifluoroethylene carbonate, 1,1,2,2-tetrafluoroethylene carbonate, 1-fluoro-2-methylethylene carbonate, 1-fluoro-1-methylethylene carbonate, 1,2-difluoro-1-methylethylene carbonate, 1,1,2-trifluoro-2-methylethylene carbonate, and trifluoromethylethylene carbonate.

[0077] In some embodiments, the carboxylic acid ester compound may include at least one of methyl acetate, ethyl acetate, n-propyl acetate, tert-butyl acetate, methyl propionate, ethyl propionate, propyl propionate, γ-butyrolactone, decanoic acid lactone, valerate lactone, mevalonate lactone, caprolactone, and methyl formate.

[0078] In some embodiments, the ether compound may include dibutyl ether, tetraethylene glycol dimethyl ether, diethylene glycol dimethyl ether, 1,2-dimethoxyethane, 1,2-diethoxyethane, ethoxymethoxyethane, 2-methyltetrahydrofuran, tetrahydrofuran, and combinations thereof.

[0079] In some embodiments, the non-aqueous solvent may also include at least one of dimethyl sulfoxide, 1,2-dioxolane, sulfolane, methyl sulfolane, 1,3-dimethyl-2-imidazolium ketone, N-methyl-2-pyrrolidone, formamide, dimethylformamide, acetonitrile, trimethyl phosphate, triethyl phosphate, trioctyl phosphate, and phosphate esters.

[0080] This application, in another aspect, proposes an electrochemical device including the aforementioned battery cell. This application provides an electrochemical device, including any apparatus in which an electrochemical reaction occurs to interconvert chemical energy and electrical energy, with specific, non-limiting examples including all types of primary batteries, secondary batteries, fuel cells, solar cells, or capacitors. In particular, the electrochemical device is a lithium secondary battery, including lithium metal secondary batteries, lithium-ion secondary batteries, lithium polymer secondary batteries, or lithium-ion polymer secondary batteries.

[0081] This application also proposes an electronic device comprising the aforementioned electrochemical device. The electronic device in this application is not particularly limited and can be any electronic device known in the prior art. The use of the electrochemical device of this invention is not particularly limited and can be used in any electronic device known in the prior art. According to some embodiments of the invention, the electronic device includes, but is not limited to, mobile phones, smartphones, laptops, tablets, wearable devices, smartwatches, smart bracelets, smart glasses, power banks, televisions, game consoles, game controllers, digital cameras, smart speakers, headphones, keyboards, mice, monitors, drones, audio equipment, home appliances, toys, power tools, automobiles, motorcycles, electric bicycles, bicycles, robots, robot dogs, industrial robots, android robots, etc.

[0082] Compared to existing technologies, the beneficial effects of this invention are as follows: By establishing the relationship between the areal densities of the first and second electrode layers, and the relationship between the tap density of the first positive electrode active material and the tap density of the second positive electrode active material, this application has the following advantages: The first electrode layer is close to the current collector and adopts a high tap density D1 (dense structure) and a high areal density C1, which can enhance the interfacial contact with the current collector, reduce the electron conduction resistance, and provide a stable electron transport channel for the thick electrode. At the same time, the high areal density allows for the loading of more active material to ensure the energy density. The second electrode layer is located on the outer layer and adopts a low tap density D2 (loose structure) and a low areal density C2, which can increase porosity, shorten the diffusion path of lithium ions on the electrode surface, improve the electrolyte wetting effect, and alleviate the problem of ion transport lag in thick electrodes. The two-layer structure forms a synergistic effect of "dense inner layer for electron transport and loose outer layer for ion transport," balancing energy density and transport efficiency.

[0083] This application establishes a relationship between the tap density of the first positive electrode active material and the tap density of the second positive electrode active material to balance the mechanical strength and electrochemical performance of the electrode. If D2 / (D1+D2) < 0.3, the porosity of the second electrode layer is too low, which cannot effectively improve electrolyte wetting and ion diffusion, and the rate capability and low-temperature performance defects of thick electrodes still exist. If D2 / (D1+D2) > 0.5, the second electrode layer is too porous, which will lead to a decrease in the overall mechanical strength of the electrode and make it prone to delamination or breakage during processing such as baking and rolling. This range ensures that the outer layer has sufficient porosity to optimize transport, while the dense structure of the inner layer provides support, thus balancing the energy density, reliability and electrochemical performance of thick electrodes.

[0084] This application achieves a match between the loading of active material in the two layers and their density by establishing the relationship between the areal density and tap density, with C2≈C1×D2 / (D1+D2). D1>D2, meaning the first electrode layer contains more active material per unit volume, and the high areal density C1 fully utilizes the space of its dense structure. The second electrode layer has a lower areal density D2, and the lower areal density C2 avoids pore blockage due to overfilling, ensuring electrolyte permeation channels. This matching coordinates the distribution of active material in the thickness direction with the microstructure of the two layers, ensuring the total amount of active material in the overall thick electrode while avoiding the transport bottleneck caused by a single high-density layer.

[0085] Test method: Electrode parameter testing: Electrode separation experimental steps ① Sample preparation: Take a complete electrode sheet (about 1 cm²), clean the surface impurities with anhydrous ethanol to ensure there are no contaminants; place the electrode sheet in a desiccator to ensure the surface is completely dry.

[0086] ② Freezing treatment: Place the electrode sheet in liquid nitrogen (-196℃) and freeze for 10 minutes to make the binder brittle. Quickly cut the electrode sheet with tweezers or a cutting knife to separate the first electrode layer (bottom layer) from the second electrode layer.

[0087] ③ Verify the separation effect; observe the interfaces of each layer using SEM to confirm that there are no residues or structural damage.

[0088] (1) Surface density: 1) Cut out small pieces of the same area (1cm²) from each of the separated layers, weigh them, and the weight ratio is the surface density ratio; 2) Measure the thickness in two dimensions, and combine the measured tap density in step (2) with the surface density. (2) Tap density of positive electrode active material: After the first step of treatment, the electrode is soaked in the organic solvent NMP to dissolve the binder, and the active material powder is separated and dried for later use; then the FT-100A tap density meter is used to test it. The powder is loaded into a graduated cylinder and the volume is stabilized by vertical vibration. The formula is used to calculate: Tap density = powder mass / volume after tapping. (3) Specific surface area of ​​conductive agent: After the first step of treatment, the electrode is immersed in the organic solvent NMP to dissolve the binder, and the conductive agent powder is separated and dried for later use; the sample tube is dried and weighed, the conductive agent powder is added, the test parameters are set, the gas flow rate and the test time are set, and the analysis is started to evaluate the specific surface area. It is necessary to ensure that the dispersion medium is free of bubbles and the test data is stable; if the powder is too fine, it needs to be pressed into tablets to avoid test errors; (4) Width of electrode layer: After step ①, it is measured using a two-dimensional instrument; (5) Low-temperature discharge performance test: The test was conducted in accordance with the national standard GB31241-2014; (6) Cycle capacity retention test: Five lithium-ion secondary batteries prepared in the examples and comparative examples were taken and repeatedly charged and discharged through the following steps, and the cycle capacity retention of the lithium-ion batteries was calculated. Under the condition of 25±℃, the first charge and discharge were performed. Constant current and constant voltage charging was performed at a charging current of 0.1C until the upper limit voltage was 3.65V; then constant current discharge was performed at a discharge current of 0.1C until the final voltage was 2.5V, and the discharge capacity of the first cycle was recorded; then 500 charge and discharge cycles were performed, and the discharge capacity of the 500th cycle was recorded.

[0089] Cycle capacity retention = (Discharge capacity of the 500th cycle / Discharge capacity of the first cycle) × 100%.

[0090] Repeat the above steps, set the experimental temperature to 45℃, and calculate the high-temperature cycling capacity retention rate.

[0091] (7) Processing performance: Appearance, visual inspection, check for broken pieces, coating cracks, etc.; The inventors conducted extensive research experiments during the research process, including designing and fabricating different positive electrode sheets, negative electrode sheets, and lithium-ion batteries, and testing battery performance. Some experimental examples and test results are listed below to illustrate this application: Example 1 This embodiment provides a secondary battery, the preparation method of which includes the following steps: (1) Preparation of positive electrode sheet (a) Lithium iron phosphate, conductive agent (conductive carbon black), binder (PVDF), and flexible agent (polyacrylate rubber) are added to 1-methyl-2-pyrrolidone (NMP) solvent in a mass ratio of 95.1:2.2:2.5:0.2 and stirred thoroughly to form a positive electrode slurry with a solid content of 58%. The positive electrode slurry is then coated on both sides of aluminum foil and baked and rolled to obtain the first electrode layer. (b) Lithium iron phosphate, conductive agent (conductive carbon black), binder (PVDF), and wetting agent (alkyl phosphate) are added to 1-methyl-2-pyrrolidone (NMP) solvent in a mass ratio of 95.1:2.2:2.5:0.2 and stirred thoroughly to form a positive electrode slurry with a solid content of 58%. The positive electrode slurry is then coated on both sides of the first electrode layer, baked, rolled, and cut to obtain the positive electrode sheet. (2) Preparation of negative electrode sheet The negative electrode active material, dispersant (sodium carboxymethyl cellulose CMC), binder (styrene-butadiene rubber SBR), and conductive agent (CNT) are mixed in a weight ratio of negative electrode active material: dispersant: binder: conductive agent = 97.2:1.3:1.3:0.2, and then mixed with deionized water to prepare a negative electrode active material slurry with a solid content of 30%. The negative electrode active material is a mixture of silicon carbon material and graphite, wherein the weight percentage of silicon carbon material in the negative electrode active material is 10%, that is, the mass ratio of silicon carbon material to graphite is 1:9.

[0092] The negative electrode active material slurry is coated on both sides of the current collector copper foil, and after baking, rolling, and cutting, the negative electrode sheet is obtained. (3) The diaphragm is made of 8μm PE membrane; (4) Preparation of electrolyte In a dry argon-atmospheric glove box, ethylene carbonate (EC), propylene carbonate (PC), dimethyl carbonate (DMC), and diethyl carbonate (DEC) were mixed in a weight ratio of 4:4:1:1 to obtain an organic solvent. Lithium salt LiPF6 was then added to the organic solvent, dissolved, and mixed thoroughly to obtain the electrolyte. The mass concentration of LiPF6 in the electrolyte was 8%.

[0093] (5) Secondary battery assembly The prepared positive electrode, separator, and negative electrode are stacked in sequence, with the separator positioned between the positive and negative electrode sheets, and then wound to obtain an electrode assembly. The electrode assembly is placed in an aluminum-plastic film packaging bag, dried, and then injected with electrolyte. After vacuum sealing, settling, formation, degassing, and edge trimming, a lithium-ion battery is obtained.

[0094] Examples 2-6 The process for preparing the secondary battery is the same as in Example 1, except for the parameter adjustments shown in Table 1. The tap density is an inherent property of the positive electrode active material, obtained custom-made by the manufacturer, specifically Hunan Yuneng New Energy Battery Materials Co., Ltd.; the areal density is adjusted using an extrusion coating machine.

[0095] Examples 7-9 The process for preparing the secondary battery is the same as in Example 1, except that the parameters are adjusted as shown in Table 1.

[0096] The areal density is adjusted by an extrusion coating machine.

[0097] Examples 10-13 The process for preparing the secondary battery is the same as in Example 1, except for the parameter adjustments shown in Table 1. The specific surface area of ​​the conductive agent is an inherent property of the conductive agent itself, obtained through customization by the manufacturer, specifically Qingdao Gefit.

[0098] Examples 14-17 The process for preparing the secondary battery is the same as in Example 1, except that the parameters are adjusted as shown in Table 1. The width of the electrode layer is adjusted using an extrusion coating machine.

[0099] Example 18 The process for preparing the secondary battery is the same as in Example 1, except that the first electrode layer does not contain a flexible agent. The remaining components, weight parts, and preparation methods are exactly the same. Lithium iron phosphate, conductive agent (conductive carbon black), and binder (PVDF) are added to 1-methyl-2-pyrrolidone (NMP) solvent in a mass ratio of 95.3:2.2:2.5 and stirred thoroughly to form a positive electrode slurry with a solid content of 58%. The positive electrode slurry is then coated on both sides of an aluminum foil, and after baking and rolling, the first electrode layer is obtained. Comparative Examples 1-2 The process for preparing the secondary battery is the same as in Example 1, except for the parameter adjustments shown in Table 1. The tap density is an inherent property of the positive electrode active material, obtained custom-made by the manufacturer, specifically Hunan Yuneng New Energy Battery Materials Co., Ltd.; the areal density is adjusted using an extrusion coating machine.

[0100] Comparative Example 3 The process for preparing the secondary battery is the same as in Example 1, except that the parameters are adjusted as shown in Table 1. The areal density is adjusted using an extrusion coating machine.

[0101] The relevant parameters of the secondary batteries described in the embodiments and comparative examples of this application are shown in Table 1, and the relationship conditions are shown in Table 2. The performance of the secondary batteries obtained in the above embodiments and comparative examples was tested, and the specific test results are shown in Table 3.

[0102] The parameters in Table 1 are explained below. The first electrode layer has an areal density of C1 mg / cm³. 2 The tap density of the first positive electrode active material is D1 g / cm³. 3 The specific surface area of ​​the first conductive agent is S1m² / g, and the width of the first electrode layer is W1mm. The areal density of the second electrode layer is C2 mg / cm³. 2 C2≈C1×D2 / (D1+D2), and the tap density of the second positive electrode active material is D2g / cm³. 3 The specific surface area of ​​the second conductive agent is S2 m² / g, and the width of the second electrode layer is W2 mm.

[0103] Table 1 Table 2 Table 3 From the above embodiments and comparative examples, it can be seen that this application solves the problems in the processing and use of thick electrodes by sequentially setting a first electrode layer and a second electrode layer on the positive electrode current collector, establishing the relationship between the areal density of the first electrode layer and the second electrode layer, and the relationship between the tap density of the first positive electrode active material and the tap density of the second positive electrode active material, thus ensuring the processing, low temperature and cycle performance of thick electrodes.

[0104] In Examples 1 and 6, the electrode layers prepared using positive electrode active materials with low tap density were prone to breakage during processing due to rolling. Example 9 had a high coating density, making it prone to coating cracking during processing. Example 18, lacking a flexible agent, was also prone to breakage and coating cracking during processing. Comparative Example 1 could not be rolled, Comparative Example 2 had an excessively high tap density in the second electrode layer, making processing difficult and resulting in severe coating cracking. Comparative Example 3 showed a broken electrode sheet in the second electrode layer, exhibiting cracks.

[0105] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of this application and are not intended to limit the scope of protection of this application. Although this application has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of this application without departing from the substance and scope of the technical solutions of this application.

Claims

1. A battery cell, comprising a positive electrode sheet, characterized in that, The positive electrode sheet includes a current collector, a first electrode layer disposed on at least one side of the current collector, and a second electrode layer disposed on the first electrode layer; The areal density of the first electrode layer is C1, and the first electrode layer includes a first positive electrode active material, a first conductive agent and a first binder. The tap density of the first positive electrode active material is D1. The areal density of the second electrode layer is C2, and the second electrode layer includes a second positive electrode active material, a second conductive agent and a second binder. The tap density of the second positive electrode active material is D2. Wherein, C1>C2, D1>D2, and 0.30≤D2 / (D1+D2)≤0.5; the areal density and tap density satisfy the following relationship: C2≈C1×D2 / (D1+D2).

2. The battery cell as described in claim 1, characterized in that, At least one of the following conditions must be met: (1)130mg / cm 2 ≤C1≤265mg / cm 2 ; (2)15 mg / cm 2 ≤C2≤160mg / cm 2 ; (3)0.8g / cm 3 ≤D1≤2.3g / cm 3 ; (4)0.8g / cm 3 ≤D2≤2.3g / cm 3 。 3. The battery cell as described in claim 1, characterized in that, The first positive electrode active material and the second positive electrode active material are each independently selected from at least one of nickel-cobalt-manganese ternary materials, nickel-cobalt-aluminum ternary materials, lithium cobalt oxide materials, lithium iron phosphate materials, lithium manganese oxide materials, lithium manganese iron phosphate materials, and nickel-manganese spinel materials.

4. The battery cell as described in claim 1, characterized in that, The specific surface area of ​​the first conductive agent is S1, the specific surface area of ​​the second conductive agent is S2, and 10% ≤ (S2-S1) / S1 ≤ 100%.

5. The battery cell as described in claim 4, characterized in that, At least one of the following conditions must be met: (5) 10 m² / g≤S1≤100 m² / g; (6) 30 m² / g≤S2≤200 m² / g.

6. The battery cell as described in claim 3, characterized in that, The first conductive agent and the second conductive agent are each independently selected from at least one of conductive carbon black, superconducting carbon black, conductive graphite, graphene, carbon nanotubes, and vapor-grown carbon fibers.

7. The battery cell as described in claim 1, characterized in that, The width of the first electrode layer is W1, and the width of the second electrode layer is W2, satisfying W1 > W2.

8. The battery cell as described in claim 7, characterized in that, At least one of the following conditions must be met: (7) 100mm≤W1≤600mm; (8)0.2 mm≤W1-W2≤6 mm.

9. An electrochemical device, characterized in that, Including the battery cell as described in any one of claims 1-8.

10. An electronic device, characterized in that, Includes the electrochemical device as described in claim 9.

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