Negative electrode sheet, lithium-ion battery, battery assembly, and electric device
Patent Information
- Application Number
- PCT/CN2026/083420
- Authority / Receiving Office
- WO · WO
- Patent Type
- Applications
- Current Assignee / Owner
- Priority Date
- 2025-03-17
- Filing Date
- 2026-03-13
- Publication Date
- 2026-09-24
Smart Images
Figure CN2026083420_24092026_PF_FP_ABST
Abstract
Description
Negative electrode, lithium-ion battery, battery module and electrical device
[0001] Priority information
[0002] This disclosure requests priority and benefits from patent application No. 2025103175171, filed with the China National Intellectual Property Administration on March 17, 2025, the entire contents of which are incorporated herein by reference. Technical Field
[0003] This disclosure relates to the field of battery technology, specifically to negative electrode sheets, lithium-ion batteries, battery modules, and electrical devices. Background Technology
[0004] With increasingly stringent usage requirements, power batteries need to simultaneously possess good fast-charging performance and long cycle life. However, fast-charging performance and cycle life of power batteries are mutually influential and restrictive; often, a long cycle life may be accompanied by poor fast-charging performance, while good fast-charging performance may degrade cycle life. Therefore, developing batteries that balance fast-charging performance and cycle life is one of the challenges facing lithium-ion batteries.
[0005] Public content
[0006] This disclosure aims to at least partially address one of the technical problems in the related art. To this end, this disclosure proposes a lithium-ion battery that balances fast charging performance and cycle life.
[0007] A first aspect of this disclosure provides a negative electrode sheet. According to an embodiment of this disclosure, the negative electrode sheet includes: a negative electrode current collector and a negative electrode active material layer disposed on at least one side of the negative electrode current collector. The negative electrode active material layer includes a negative electrode active material, and includes a first negative electrode active material layer and a second negative electrode active material layer. The first negative electrode active material layer is located between the negative electrode current collector and the second negative electrode active material layer, and the first negative electrode active material layer includes a first negative electrode active material, while the second negative electrode active material layer includes a second negative electrode active material.
[0008] The composite factor of the negative electrode active material layer The value range is 0.9 to 1.5;
[0009] Wherein, a1 is the I of the first negative electrode active material. D1 / I G1 Value, a2 is the I of the second negative electrode active material D2 / I G2 Values, b1 is the porosity of the first negative electrode active material layer, and b2 is the porosity of the second negative electrode active material layer; I D1This indicates that the Raman spectrum of the first negative electrode active material is at 1350±60 cm⁻¹. -1 The integral area of peak D at point I G1 This indicates that the Raman spectrum of the first negative electrode active material is at 1580±60 cm⁻¹. -1 The integral area of peak G at point I; D2 This indicates that the Raman spectrum of the second negative electrode active material is at 1350±60 cm⁻¹. -1 The integral area of peak D at point I G2 This indicates that the Raman spectrum of the second negative electrode active material is at 1580±60 cm⁻¹. -1 The integral area of peak G at that location.
[0010] In this negative electrode, the composite factor Q satisfies the above conditions. The negative electrode active material can work synergistically with the negative electrode structure design. When applied to lithium-ion batteries, it can fully utilize the fast-charging capability of lithium-ion batteries, significantly improve lithium-ion liquid phase diffusion, eliminate the risk of lithium plating during electrode operation, effectively improve the fast-charging performance of lithium-ion batteries, and also provide better cycle life for lithium-ion batteries.
[0011] According to the embodiments of this disclosure, the composite factor Q has a value range of 1.1 to 1.4.
[0012] According to embodiments of the present disclosure, the negative electrode sheet satisfies at least one of the following conditions: a1 is 0.5~1.6; a2 is 1.0~1.8; b1 is 25%~38%; b2 is 35%~48%.
[0013] According to embodiments of the present disclosure, the negative electrode sheet satisfies at least one of the following conditions: a1 is 0.8 to 1.3; a2 is 1.0 to 1.45; b1 is 30% to 35%; b2 is 38% to 42%.
[0014] According to an embodiment of this disclosure, a2 / a1 is 0.6 to 1.5. According to an embodiment of this disclosure, a2 / a1 is 0.8 to 1.3.
[0015] According to an embodiment of this disclosure, a1 < a2.
[0016] According to an embodiment of this disclosure, b2 / b1 > 1.0. According to an embodiment of this disclosure, b2 / b1 ≥ 1.12.
[0017] According to embodiments of this disclosure, the negative electrode active material I D / I G The value of a ranges from 0.05 to 2.5.
[0018] According to embodiments of this disclosure, the negative electrode active material I D / I G The value of a is 0.5 to 1.9.
[0019] According to embodiments of this disclosure, the porosity b of the negative electrode active material layer is 30% to 48%.
[0020] According to embodiments of this disclosure, the porosity b of the negative electrode active material layer is 32% to 42%.
[0021] According to embodiments of this disclosure, the Dv50 particle size of the negative electrode active material is 5 μm to 18 μm.
[0022] According to embodiments of this disclosure, the Dv50 particle size of the negative electrode active material is 7 μm to 16 μm.
[0023] According to embodiments of this disclosure, the negative electrode active material includes at least one of graphite, hard carbon, and silicon carbon, wherein the mass percentage of graphite in the negative electrode active material is greater than 80%.
[0024] A second aspect of this disclosure provides a lithium-ion battery. According to an embodiment of this disclosure, the lithium-ion battery includes a positive electrode, a negative electrode (as described above), a separator, and an electrolyte, wherein the separator is located between the positive and negative electrode. This lithium-ion battery exhibits superior fast-charging performance and a long cycle life.
[0025] According to an embodiment of the present disclosure, the positive electrode sheet includes a positive current collector and a positive active material layer disposed on at least one side of the positive current collector. The positive active material layer includes at least one of a layered positive active material, an olivine-type phosphate active material, and a spinel-structured positive active material.
[0026] According to embodiments of this disclosure, the positive electrode active material layer includes at least one of lithium iron phosphate, lithium manganese phosphate, and lithium manganese iron phosphate.
[0027] According to embodiments of this disclosure, the positive electrode active material layer includes a lithium replenishing agent, which includes at least one of lithium-rich lithium iron ore and lithium-rich lithium nickel ore.
[0028] According to embodiments of this disclosure, the electrolyte comprises a solvent, a lithium salt, and an additive, and the electrolyte satisfies at least one of the following conditions: the solvent comprises at least one selected from ethylene carbonate, diethyl carbonate, methyl ethyl carbonate, methyl formate, methyl acetate, ethyl acetate, butyl acetate, methyl propionate, ethyl propionate, methyl butyrate, ethyl butyrate, and propyl butyrate; the lithium salt comprises at least one selected from lithium hexafluorophosphate, lithium bis(fluorosulfonyl)imide, lithium dioxalate borate, lithium difluorooxalate borate, lithium difluorophosphate, and lithium difluorodioxalate phosphate; the additive comprises at least one selected from carbonates (e.g., vinylene carbonate VC, fluorovinyl carbonate FEC), sulfates (e.g., vinyl sulfate DTD), and sulfonates (e.g., 1,3-propanesulfonyl lactone PS, methyl methylene disulfonate MMDS); the additive accounts for 0% to 6% of the total mass of the electrolyte.
[0029] A third aspect of this disclosure provides a battery assembly. According to embodiments of this disclosure, the battery and assembly include the lithium-ion battery described above. This battery assembly simultaneously exhibits superior fast-charging performance and a longer cycle life.
[0030] In a fourth aspect, this disclosure provides an electrical device. According to embodiments of this disclosure, the electrical device includes the lithium-ion battery or the battery pack described above. This electrical device has excellent fast-charging capability and a long service life. Attached Figure Description
[0031] Figure 1 is a schematic diagram of the image porosity recognition process of this disclosure. Embodiments of the present invention
[0032] Embodiments of the present invention are described in detail below, examples of which are illustrated in the accompanying drawings. The embodiments described below with reference to the accompanying drawings are exemplary and intended to explain the present invention, and should not be construed as limiting the present invention.
[0033] This disclosure is based on the inventors' discoveries and understanding of the following facts and problems:
[0034] The inventors of this disclosure explored various factors affecting the fast-charging performance and lifespan of lithium-ion batteries, discovering that increasing the areal loading of the electrode can improve the energy density of lithium-ion batteries, but the severe deterioration of lithium-ion liquid-phase transport leads to a sharp decline in fast-charging performance. Specifically, due to the low intrinsic conductivity of the electrolyte, the excessively long characteristic length of the high areal loading electrode, the low porosity of the electrode structure, and the high tortuosity, lithium ions have difficulty diffusing deep into the electrode due to the excessive distance. During high-rate charging, a huge concentration gradient is rapidly established in the electrode thickness direction, resulting in an excessively high lithium-ion concentration on the electrode surface. These lithium ions preferentially embed into the surface negative electrode active material, leading to a high lithium intercalation amount and low potential. When the SOC (state of charge) of the surface negative electrode active material is too high, the overpotential for lithium intercalation on the surface of the surface negative electrode active material is higher than the overpotential for lithium plating, causing lithium plating on the surface of the negative electrode active material. Severe lithium plating can lead to irreversible safety problems. Optimizing the properties of the negative electrode active material can improve fast-charging performance, but it consumes more active lithium, resulting in a deterioration in the lifespan of the lithium-ion battery. Furthermore, if the properties of the negative electrode active material and the electrode structure design are mismatched, on the one hand, the fast charging capability of the system cannot be fully utilized, and on the other hand, the high-temperature lifespan of the lithium-ion battery may be severely degraded.
[0035] By comprehensively considering various factors, in order to achieve high fast-charging performance and long lifespan of lithium-ion batteries, the inventors designed a new electrochemical system based on electrochemical theory, the properties of negative electrode active materials, and electrode characteristics. They optimized the electrode pore structure and kinetic distribution based on the physicochemical properties of negative electrode active materials, balancing the requirements of lithium-ion batteries for lifespan and fast-charging performance, thus enabling lithium-ion batteries to have excellent fast-charging capabilities and excellent lifespan.
[0036] In view of this, the present disclosure provides a negative electrode, a lithium-ion battery, a battery module, and an electrical device, which significantly improves the diffusion of lithium ions in the liquid phase, eliminates the risk of lithium plating during electrode operation, thereby improving the fast charging capability of the lithium-ion battery and ensuring the service life of the lithium-ion battery.
[0037] A first aspect of this disclosure provides a negative electrode sheet. According to an embodiment of this disclosure, the negative electrode sheet includes: a negative electrode current collector and a negative electrode active material layer disposed on at least one side of the negative electrode current collector. The negative electrode active material layer includes a negative electrode active material, and includes a first negative electrode active material layer and a second negative electrode active material layer. The first negative electrode active material layer is located between the negative electrode current collector and the second negative electrode active material layer, and the first negative electrode active material layer includes a first negative electrode active material, while the second negative electrode active material layer includes a second negative electrode active material.
[0038] The composite factor Q of the negative electrode active material layer = The value range is 0.9 to 1.5;
[0039] Wherein, a1 is the I of the first negative electrode active material. D1 / I G1 Value, a2 is the I of the second negative electrode active material D2 / I G2 Values, b1 is the porosity of the first negative electrode active material layer, and b2 is the porosity of the second negative electrode active material layer; I D1 This indicates that the Raman spectrum of the first negative electrode active material is at 1350±60 cm⁻¹. -1 The integral area of peak D at point I G1 This indicates that the Raman spectrum of the first negative electrode active material is at 1580±60 cm⁻¹. -1 The integral area of peak G at point I; D2 This indicates that the Raman spectrum of the second negative electrode active material is at 1350±60 cm⁻¹. -1 The integral area of peak D at point I G2 This indicates that the Raman spectrum of the second negative electrode active material is at 1580±60 cm⁻¹. -1 The integral area of peak G at that location.
[0040] In this negative electrode, the composite factor Q satisfies the above conditions, and the properties of the negative electrode active material can work synergistically with the negative electrode structure design. When applied to lithium-ion batteries, it can fully exert the fast charging capability of the system, significantly improve the lithium-ion liquid phase diffusion, eliminate the risk of lithium plating during electrode operation, effectively improve the fast charging performance of lithium-ion batteries, and also have better cycle life.
[0041] Specifically, the I of the negative electrode active material D / I G The value I is used to characterize the degree of graphitization and defect density of the negative electrode active material. D / I G The lower the value, the higher the degree of graphitization of the negative electrode active material, meaning that the graphite structure of the negative electrode active material is more complete and has fewer defects; conversely, the lower the degree of graphitization of the negative electrode active material, meaning that there are more defects and disordered structures in the negative electrode active material.
[0042] I D / I GThe value can be obtained through Raman spectroscopy. For lithium-ion batteries that have been tested and rated for capacity, the lithium-ion battery can be discharged to a zero-electric state and disassembled under an inert atmosphere to obtain the negative electrode sheet. After washing the negative electrode sheet with a volatile solvent such as dimethyl carbonate (DMC) and drying it, the second negative electrode active material layer is separated by adhesive tape. Then, the remaining powder on the negative electrode sheet is scraped off and marked as the first particle; the powder particles on the surface of the adhesive tape are scraped off and marked as the second particle. The scraped first and second particles are respectively immersed in N-methylpyrrolidone (NMP) and ultrasonically treated to dissolve the binder such as SBR (styrene-butadiene rubber), and then the first and second negative electrode active materials are obtained. The I value of the first negative electrode active material is calculated by integrating the area ratio of the D peak and the G peak of the first and second negative electrode active materials obtained by Raman spectroscopy. D1 / I G1 Value and I of the second negative electrode active material D2 / I G2 value.
[0043] It is worth adding that the I of the negative electrode active material tested before preparation D / I G I, the negative electrode active material obtained after disassembling the battery D / I G There may be some discrepancies, but it can be understood that both are within the margin of error and are basically consistent.
[0044] It is understandable that the type of negative electrode active material and its physicochemical parameters can affect the I of the negative electrode active material. D / I G Value. Taking graphite as the negative electrode active material as an example, amorphous residual carbon and coke raw materials can affect the I value of the negative electrode active material. D / I G The I value of graphite can be controlled by changing the graphite granulation process, the type, quantity, and process of the carbon material coating layer, and the selection of coke raw materials. D / I G Values. As an example, different I values can be obtained by adjusting the coating amount of amorphous carbon in the negative electrode active material, using different proportions of negative electrode active materials with different coating amounts of amorphous carbon (e.g., 0%, 0.3%, 0.7%, 1.5%, 2%, 3%, 3.5%, etc.), the particle size and particle size distribution of the negative electrode active material, using different proportions of negative electrode active materials with different particle sizes and particle size distributions, and different sequences of preparation steps (e.g., graphitization before granulation, granulation before graphitization, etc.). D / I G value.
[0045] Specifically, porosity refers to the ratio of pore volume to total volume in a material, and is commonly used to describe the number and size of pores within the material. For batteries that have already undergone capacity testing, the battery can be discharged to a zero-electrical state and disassembled under an inert atmosphere to obtain the negative electrode sheet. The negative electrode sheet is then washed with a volatile solvent such as dimethyl carbonate (DMC) and dried. The porosity of the first and second negative electrode active material layers can be obtained by testing the negative electrode sheet using Nano-CT (Nano-Computed Tomography), followed by three-dimensional reconstruction to analyze the electrode structure and obtain the porosity, etc.
[0046] It is understandable that the morphology, particle size, and rolling pressure during the preparation of the negative electrode active material can affect the porosity of the negative electrode active material layer. The porosity of the negative electrode active material layer can be adjusted by adjusting the above parameters. As an example, the morphology and particle size of the negative electrode active material can be adjusted by regulating whether the negative electrode active material has amorphous carbon coating, the amount of amorphous carbon coating (e.g., amorphous carbon coating of 0, 0.3%, 0.7%, 1.5%, 2%, 3%, 3.5%, etc.), using different coated negative electrode active materials in different proportions, using negative electrode active materials with different particle sizes and particle size distributions in different proportions, controlling the preparation process of the negative electrode active material (graphitization before granulation, granulation before graphitization, etc.), and using negative electrode active materials prepared in different processes in different proportions.
[0047] In some embodiments, the composite factor Q can range from 1.1 to 1.4. For example, the composite factor Q can specifically be 0.9, 0.95, 1.0, 1.05, 1.1, 1.15, 1.2, 1.25, 1.3, 1.35, 1.4, etc. Within this range, the lithium-ion liquid-phase diffusion capability can be further improved, the risk of lithium plating can be reduced, and a longer cycle life can be maintained.
[0048] According to embodiments of this disclosure, a1 can be 0.5 to 1.6. In some specific embodiments, a1 can be 0.8 to 1.3. In other specific embodiments, a1 can be 0.8 to 1.1. As examples, a1 can specifically be 0.5, 0.6, 0.7, 0.8, 0.9, 1.0, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, etc. Therefore, the physicochemical properties of the first negative electrode active material can optimize the kinetic distribution of the negative electrode active material layer, and can also synergize with the porosity of the negative electrode active material to fully utilize the fast-charging performance of the lithium-ion battery.
[0049] According to embodiments of this disclosure, a2 can be 1.0 to 1.8. According to embodiments of this disclosure, a2 can be 1.0 to 1.45. As examples, a2 can specifically be 0.8, 0.85, 0.9, 0.95, 1.0, 1.05, 1.1, 1.15, 1.2, 1.25, 1.3, 1.35, 1.4, 1.45, 1.5, 1.55, 1.6, 1.65, 1.7, 1.75, 1.8, etc. Therefore, the physicochemical properties of the second negative electrode active material can optimize the kinetic distribution of the negative electrode active material layer, and can also synergize with the porosity of the negative electrode active material to fully utilize the fast-charging performance of the lithium-ion battery.
[0050] According to embodiments of this disclosure, a2 / a1 can be 0.6 to 1.5. In some specific embodiments, a2 / a1 can be 0.8 to 1.3. As examples, a2 / a1 can specifically be 0.6, 0.65, 0.7, 0.75, 0.8, 0.85, 0.9, 0.95, 1.0, 1.05, 1.1, 1.15, 1.2, 1.25, 1.3, 1.35, 1.4, 1.45, 1.5, etc. Within the above ranges, a2 / a1 allows for better matching of the first and second negative electrode active material layers, improving the overall dynamic distribution of the negative electrode active material layers and fully leveraging the fast-charging performance of the lithium-ion battery, thereby obtaining a lithium-ion battery that balances fast charging and lifespan.
[0051] According to the embodiments of this disclosure, a1 < a2. Therefore, the first negative electrode active material has a higher degree of graphitization, a more complete graphite structure, and fewer defects. The optimized graphite structure can reduce the resistance to lithium-ion transport, making it easier for lithium ions to be transported deep into the negative electrode sheet. This helps to reduce the excessive lithium-ion concentration difference between the surface and interior of the negative electrode active material layer during high-rate charging, thereby improving the fast-charging performance of the lithium-ion battery and reducing the risk of lithium plating.
[0052] According to embodiments of this disclosure, b1 is 25% to 38%. According to embodiments of this disclosure, b1 is 30% to 35%. As examples, b1 can specifically be 25%, 23%, 27%, 28%, 29%, 30%, 31%, 32%, 33%, 34%, 35%, 36%, 37%, 38%, etc. Within the above-mentioned porosity range, the first negative electrode active material layer has better lithium-ion liquid phase diffusion ability, which can easily diffuse into the depth of the electrode, and can better match with the type of negative electrode active material and its physicochemical properties, thereby improving the fast charging capability of lithium-ion batteries and achieving a long lifespan.
[0053] According to embodiments of this disclosure, b2 is 35% to 45%. According to embodiments of this disclosure, b2 is 38% to 42%. As examples, b2 can specifically be 35%, 36%, 37%, 38%, 39%, 40%, 41%, 42%, 43%, 44%, 45%, etc. Within the above-mentioned porosity range, lithium ions can quickly wet the second negative electrode active material layer, reducing the possibility of a large lithium ion concentration difference forming between the surface and interior of the negative electrode active layer. Furthermore, it can better coordinate with the type and physicochemical properties of the negative electrode active material, improving the fast-charging capability of the lithium-ion battery while achieving a long lifespan.
[0054] According to embodiments of this disclosure, b2 / b1 > 1.0. In some specific embodiments, 1.5 ≥ b2 / b1 ≥ 1.12. As an example, b2 / b1 can specifically be 1, 1.01, 1.02, 1.03, 1.04, 1.05, 1.06, 1.07, 1.08, 1.09, 1.1, 1.11, 1.12, 1.13, 1.14, 1.15, 1.16, 1.17, 1.18, 1.19, 1.2, 1.21, 1.22, 1.23, 1.24, 1.25, 1.3, 1.35, 1.4, 1.45, 1.5, etc. With this configuration, lithium ions can quickly wet the second negative electrode active material layer and enter the first negative electrode active material layer. The lithium ion transport resistance is relatively small, which helps to reduce the risk of lithium plating and improve the fast-charging performance of the lithium-ion battery.
[0055] According to embodiments of this disclosure, the negative electrode active material I D / I G The value 'a' is 0.05~2.5. In some embodiments, the I of the negative electrode active material... D / I G The value of a is 0.5 to 1.9. In other embodiments, the I of the negative electrode active material... D / I G The value of a is 0.8~1.5. As an example, the Ia of the negative electrode active material... D / I G The value 'a' can specifically be 0.05, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1.0, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9, 2.0, 2.1, 2.2, 2.3, 2.4, 2.5, etc. The I of the negative electrode active material... D / I G Within the above range, the values can be coordinated with the structure and porosity design of the negative electrode active material layer to fully utilize the fast charging capability of the battery system while maintaining a long cycle life.
[0056] Specifically, the I of the negative electrode active material D / I G The value can be tested using the following method: The lithium-ion battery can be discharged to a zero-charge state, disassembled under an inert atmosphere to obtain the negative electrode sheet, washed with a volatile solvent such as dimethyl carbonate (DMC), and then dried. The entire negative electrode active material layer is scraped off from the negative electrode current collector, and the scraped particles are immersed in N-methylpyrrolidone (NMP), ultrasonically treated to dissolve binders such as SBR (styrene-butadiene rubber), and then the negative electrode active material is obtained. The I value of the negative electrode active material is calculated by integrating the area ratio of the D peak and the G peak obtained through Raman spectroscopy. D / I G Value a.
[0057] According to embodiments of this disclosure, the porosity b of the negative electrode active material layer is 30% to 48%. According to embodiments of this disclosure, the porosity b of the negative electrode active material layer is 32% to 42%. As examples, the porosity b of the negative electrode active material layer can specifically be 30%, 31%, 32%, 33%, 34%, 35%, 36%, 37%, 38%, 39%, 40%, 41%, 42%, 43%, 44%, 45%, 46%, 47%, 48%, etc. Within the above porosity range, a longer cycle life can be achieved, while the lithium-ion liquid phase transport capability is better, which is beneficial for improving the fast-charging performance of lithium-ion batteries and reducing the risk of lithium plating.
[0058] Specifically, the porosity b of the negative electrode active material layer can be measured by mercury intrusion porosimetry. By gradually increasing the pressure and measuring the amount of mercury intrusion, the porosity of the negative electrode active material layer can be calculated.
[0059] According to embodiments of this disclosure, the Dv50 particle size of the negative electrode active material is 5 μm to 18 μm. In some embodiments, the Dv50 particle size of the negative electrode active material is 7 μm to 16 μm. As an example, the Dv50 particle size of the negative electrode active material can specifically be 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm, 11 μm, 12 μm, 13 μm, 14 μm, 15 μm, 16 μm, 17 μm, 18 μm, etc. Specifically, if the Dv50 particle size is too small, the surface area of the negative electrode active material is too large, resulting in excessive loss of active lithium and affecting the porosity of the negative electrode active material layer, thereby affecting battery performance and energy density; if the Dv50 particle size is too large, the lithium-ion diffusion path is too long, degrading fast-charging performance. A Dv50 particle size within the above range is beneficial for obtaining a lithium-ion battery that balances cycle life and fast-charging performance.
[0060] It is understandable that the Dv50 particle size of both the first and second negative electrode active materials can be in the range of 5μm to 18μm, and the Dv50 particle size of the first and second negative electrode active materials can be the same or different.
[0061] In this article, Dv50 particle size has a well-known meaning in the art, referring to the median diameter of a particle size distribution. Specifically, it is a point on the particle size distribution curve such that half of the total volume of the particle population has a particle diameter smaller than Dv50, and the other half has a particle diameter larger than Dv50. Dv50 particle size can be measured using methods known in the art. For example, it can be determined using a laser particle size analyzer (such as the Malvern Mastersizer 3000) according to standard GB / T19077.1-2016.
[0062] For batteries that have already undergone capacity testing, the battery can be discharged to a zero-electrical state and disassembled under an inert atmosphere to obtain the negative electrode sheet. The negative electrode sheet is then washed with a volatile solvent such as dimethyl carbonate (DMC) and dried. The entire negative electrode material layer is scraped off the electrode sheet, and the scraped powder particles are immersed in N-methylpyrrolidone (NMP). Ultrasonic treatment is then used to dissolve binders such as SBR, resulting in the negative electrode active material. This material can then be tested using a laser particle size analyzer (such as a Malvern Mastersizer 3000) according to standard GB / T19077.1-2016.
[0063] According to embodiments of this disclosure, the negative electrode active material includes at least one of graphite, hard carbon, and silicon carbide, wherein the mass percentage of graphite in the negative electrode active material is greater than 80%. Specifically, the mass percentage of graphite in the negative electrode active material can be 81%, 82%, 83%, 84%, 85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, 100%, etc. The above-mentioned negative electrode active material has a high capacity and can be designed in conjunction with the structure and porosity of the negative electrode active material layer to improve the lithium-ion transport capacity, enhance the fast-charging performance of lithium-ion batteries, and reduce the risk of lithium plating.
[0064] It is understood that the statement that the mass percentage of graphite in the negative electrode active material is greater than 80% means that the mass percentage of graphite in the entire negative electrode active material layer is greater than 80%. Specifically, the mass percentage of graphite in the first negative electrode active material can be greater than 80% or less than or equal to 80%; the mass percentage of graphite in the second negative electrode active material can also be greater than 80% or less than or equal to 80%. As an example, the mass percentage of graphite in the first negative electrode active material is greater than 80%, and the mass percentage of graphite in the second negative electrode active material is also greater than 80%.
[0065] According to embodiments of this disclosure, the negative electrode active material layer may further include a negative electrode binder. In some embodiments, the negative electrode binder may include, but is not limited to, at least one of styrene-butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethacrylic acid (PMAA), and carboxymethyl chitosan (CMCS).
[0066] According to embodiments of this disclosure, the negative electrode active material layer may further include a negative electrode conductive agent. In some embodiments, the negative electrode conductive agent may include, but is not limited to, at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.
[0067] According to embodiments of this disclosure, the negative electrode current collector can be a metal current collector or a composite current collector. For example, metal current collectors include, but are not limited to, copper foil current collectors; composite current collectors may include a polymer material substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.) and a metal layer (copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver, silver alloy, etc.) formed on at least one surface of the polymer material substrate.
[0068] A second aspect of this disclosure provides a lithium-ion battery. According to an embodiment of this disclosure, the lithium-ion battery includes a positive electrode, a negative electrode (as described above), a separator, and an electrolyte, wherein the separator is located between the positive and negative electrode. This lithium-ion battery exhibits superior fast-charging performance and a longer cycle life.
[0069] According to the embodiments of this disclosure, there are no particular limitations on the specific type of lithium-ion battery. For example, from the perspective of shape, the lithium-ion battery includes, but is not limited to, prismatic batteries and cylindrical batteries, etc., and this disclosure does not impose any particular limitations. From the perspective of the core structure, the core of the lithium-ion battery can be a wound core (i.e., a core formed by winding positive electrode sheets, negative electrode sheets, and separators stacked together) or a stacked core (i.e., multiple positive electrode sheets, negative electrode sheets, and separators stacked together to form a core). The outer shell can be a hard shell (such as a steel shell, a hard plastic shell, etc.) or a soft shell (such as an aluminum-plastic film shell, a pouch-type soft shell, etc.), etc., and this disclosure does not impose any particular limitations.
[0070] According to embodiments of this disclosure, the positive electrode sheet includes a positive current collector and a positive active material layer disposed on at least one side of the positive current collector. In some embodiments of this disclosure, the positive active material may include at least one of the following: layered positive active materials (e.g., nickel-cobalt-manganese ternary positive electrode materials, nickel-cobalt-aluminum ternary positive electrode materials, lithium nickel oxide / sodium, lithium cobalt oxide / sodium, lithium manganese oxide / sodium, lithium-rich / sodium layered and rock salt phase layered materials), olivine-type phosphate active materials (e.g., lithium iron phosphate, lithium manganese phosphate, lithium manganese iron phosphate, etc.), and spinel-structured positive active materials (e.g., spinel lithium manganese oxide, spinel lithium nickel manganese oxide, lithium-rich spinel lithium manganese oxide, and lithium nickel manganese oxide, etc.). In some embodiments, the positive active material layer includes at least one of lithium iron phosphate, lithium manganese phosphate, and lithium manganese iron phosphate. As an example, the positive active material layer includes lithium iron phosphate. Therefore, the lithium-ion battery has a longer cycle life and better safety performance.
[0071] It is understood that the aforementioned positive electrode active materials should be interpreted broadly, including not only unmodified intrinsic positive electrode active materials, but also modified positive electrode active materials that have undergone doping and / or coating modifications. For example, lithium iron phosphate can include intrinsic lithium iron phosphate, doped lithium iron phosphate, coated lithium iron phosphate, and lithium iron phosphate that has undergone both doping and coating modifications.
[0072] According to embodiments of this disclosure, the positive electrode active material layer includes a lithium replenishing agent, which includes at least one of lithium-rich lithium iron phosphate and lithium-rich lithium nickel phosphate. This replenishes the loss of active lithium and further extends the cycle life of the lithium-ion battery.
[0073] According to embodiments of this disclosure, the positive electrode active material layer further includes a positive electrode binder. In some embodiments, the positive electrode binder may include at least one selected from polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), PVDF-tetrafluoroethylene-propylene terpolymer, PVDF-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorinated acrylate resins. Therefore, the positive electrode active material layer can be better bonded to the positive electrode current collector, with strong adhesion, and problems such as positive electrode active material detachment are less likely to occur.
[0074] According to embodiments of this disclosure, the positive electrode active material layer further includes a positive electrode conductive agent. In some embodiments, the positive electrode conductive agent may include at least one selected from superconducting carbon, conductive graphite, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers. This effectively improves conductivity, reduces internal resistance, and enhances the electrochemical performance of lithium-ion batteries.
[0075] According to embodiments of this disclosure, the positive current collector can be a metal current collector or a composite current collector. For example, metal current collectors include, but are not limited to, aluminum foil current collectors; composite current collectors may include a polymer material base layer (such as a base layer of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.) and a metal layer (copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) formed on at least one surface of the polymer material base film.
[0076] According to embodiments of this disclosure, the electrolyte includes a solvent, a lithium salt, and additives.
[0077] In some embodiments, the solvent includes at least one selected from ethylene carbonate (EC), dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), methyl formate, methyl acetate (MA), ethyl acetate (EA), butyl acetate, methyl propionate, ethyl propionate (EP), methyl butyrate, ethyl butyrate, and propyl butyrate. In some specific embodiments, the solvent includes at least one selected from EC, EMC, DEC, DMC, EA, MA, and EP. As an example, the solvent includes at least one selected from EC, EMC, DMC, EA, and MA. This allows for sufficient dissolution of lithium salts, provides an ion transport medium, and also helps improve the electrochemical and safety performance of lithium-ion batteries.
[0078] In some embodiments, the lithium salt includes at least one of lithium hexafluorophosphate (LiPF6), lithium bis(fluorosulfonyl)imide (LiFSI) (LiN(SO2F)2), lithium dioxolaneborate (LiB(C2O4)2, LiBOB), lithium difluorooxolaneborate (LiBF2C2O4, LiDFOB), lithium difluorophosphate (LiPO2F2), and lithium difluorodioxolaneborate (LiDFOP). Lithium salts can provide lithium ions to lithium-ion batteries, support electrolyte stability and electrochemical reactions, contribute to the formation of a protective SEI film, improve conductivity, and enhance the safety of lithium-ion batteries.
[0079] In some embodiments, the additive includes at least one of carbonates, sulfates, and sulfonates. As an example, the carbonate may include at least one of fluoroethylene carbonate (FEC) and vinylene carbonate (VC); the sulfate may include vinyl sulfate (DTD); and the sulfonate may include at least one of 1,3-propanesulfonyl lactone (PS) and methyl methylene disulfonate (MMDS). This facilitates the formation of a stable SEI film on the negative electrode surface, further improving the cycle stability of the lithium-ion battery.
[0080] In some embodiments, the additive accounts for 0% to 6% of the total mass of the electrolyte. For example, the specific percentage of the additive in the total mass of the electrolyte can be 0%, 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, 5.5%, 6%, etc. Within the above range, the performance of lithium-ion batteries can be improved without causing significant other negative impacts.
[0081] A third aspect of this disclosure provides a battery assembly. According to embodiments of this disclosure, the battery assembly includes the lithium-ion battery described above. This battery assembly simultaneously exhibits good fast-charging performance and a long cycle life.
[0082] According to the embodiments of this disclosure, the specific type of battery assembly is not particularly limited, and includes, but is not limited to, battery modules and battery packs. It is understood that the specific structure of battery modules and battery packs can refer to conventional technology, and this disclosure does not impose any particular limitations.
[0083] In a fourth aspect, this disclosure provides an electrical device. According to embodiments of this disclosure, the electrical device includes the lithium-ion battery or the battery pack described above. This electrical device has excellent fast-charging capability and a long service life.
[0084] According to embodiments of this disclosure, the specific type of electrical device is not particularly limited and can be any device that uses a lithium-ion battery as a power source or energy storage unit. As examples, electrical devices include, but are not limited to, 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.), mobile terminals (e.g., mobile phones, laptops, game consoles, wearable devices, etc.), drones, aerospace equipment, satellites, ships, energy storage systems, etc.
[0085] It is understandable that, in addition to the lithium-ion battery mentioned above, the electrical device also includes other necessary structures and components, all of which can be made with reference to conventional technologies. For example, an electric vehicle may include a body, chassis, tires, navigation system, radar system, steering system, braking system, lubrication system, cooling system, driving system, etc., which will not be described in detail here.
[0086] The embodiments of this disclosure are described in detail below.
[0087] Example 1
[0088] 1. Preparation of negative electrode sheet
[0089] A first negative electrode slurry (corresponding to the first negative electrode active material layer) was prepared in deionized water at a mass ratio of 9:1 for graphite (secondary particulate graphite with carbon coating layer (Dv50 particle size 13.6μm, carbon coating amount 2%) and primary particulate graphite without carbon coating layer (Dv50 particle size 9μm)), conductive agent conductive carbon black, thickener carboxymethyl cellulose CMC, and binder styrene-butadiene rubber SBR. A second negative electrode slurry (corresponding to the second negative electrode active material layer) was prepared in deionized water at a mass ratio of 100:1:1.5:1.35 using primary particulate graphite (Dv50 particle size 13.6 μm, carbon coating 2%) and non-carbon-coated primary particulate graphite (Dv50 particle size 9 μm), conductive agent conductive carbon black, thickener carboxymethyl cellulose (CMC), and binder styrene-butadiene rubber (SBR). The slurry was then coated onto both sides of the copper foil current collector using a double-layer coating die. The negative electrode sheet was obtained through drying, rolling, and sheet forming processes. The a2 / a1 ratio of the negative electrode sheet was controlled to be 0.95, and the b2 / b1 ratio to be 1.05.
[0090] 2. Preparation of the positive electrode sheet
[0091] A positive electrode slurry was prepared by mixing lithium iron phosphate (LiFePO4), lithium supplement (Li5FeO4), conductive agent (conductive carbon black and multi-walled carbon nanotubes in a mass ratio of 2:3), and polyvinylidene fluoride (PVDF) in a mass ratio of 97:0.3:1.0:1.6. The slurry was coated on both sides of the positive electrode current collector fluid-coated carbon aluminum foil. After drying, rolling, and sheet forming, the positive electrode sheet was obtained.
[0092] 3. Battery assembly
[0093] The negative electrode, separator (12 μm polypropylene base film) and positive electrode obtained above are placed in sequence and stacked to obtain a battery cell. The battery cell is placed in the outer packaging foil and injected with electrolyte. After processing such as formation and capacity testing, a soft-pack lithium-ion battery is obtained.
[0094] The electrolyte was prepared in an argon-atmospheric glove box with a water content of <10 ppm. First, ethylene carbonate (EC), ethyl methyl carbonate (EMC), dimethyl carbonate (DMC), and ethyl acetate (EA) were mixed in a mass ratio of 3:3:2:2. Then, 1 mol / L of lithium hexafluorophosphate (LiPF6) and lithium bis(fluorosulfonyl)imide (LiFSI) were added. Next, 1 wt% of fluoroethylene carbonate (FEC), 0.5 wt% of methylene disulfonate (MMDS), and 4 wt% of ethylene carbonate (VC) were added, and the mixture was thoroughly mixed to obtain the electrolyte.
[0095] Example 2
[0096] Similar to Example 1, except that the graphite in the first negative electrode active material is a mixture of secondary particulate graphite with a carbon coating layer (Dv50 particle size 13.6 μm, carbon coating amount 2.5%) and primary particulate graphite without a carbon coating layer (Dv50 particle size 9 μm) in a mass ratio of 9:1, and the graphite in the first negative electrode active material is a mixture of secondary particulate graphite with a carbon coating layer (Dv50 particle size 13.6 μm, carbon coating amount 2.5%) and primary particulate graphite without a carbon coating layer (Dv50 particle size 9 μm) in a mass ratio of 8:2, and the a2 / a1 ratio of the negative electrode sheet is controlled to be 0.97 and the b2 / b1 ratio to be 1.12.
[0097] Example 3
[0098] Similar to Example 1, except that the graphite in the first negative electrode active material is a mixture of secondary particulate graphite with a carbon coating layer (Dv50 particle size 13.6 μm, carbon coating amount 3%) and primary particulate graphite without a carbon coating layer (Dv50 particle size 9 μm) in a mass ratio of 8:2, and the graphite in the first negative electrode active material is a mixture of secondary particulate graphite with a carbon coating layer (Dv50 particle size 13.6 μm, carbon coating amount 2.5%) and primary particulate graphite without a carbon coating layer (Dv50 particle size 9 μm) in a mass ratio of 9:1, and the a2 / a1 ratio of the negative electrode sheet is controlled to be 0.98 and the b2 / b1 ratio to be 1.18.
[0099] Example 4
[0100] Similar to Example 1, except that the ratio of a2 / a1 to the negative electrode is controlled to be 0.98 and the ratio of b2 / b1 to be 1.23.
[0101] Example 5
[0102] Similar to Example 1, except that the ratio of a2 / a1 to the negative electrode is controlled to be 0.81 and the ratio of b2 / b1 to be 1.05.
[0103] Example 6
[0104] Similar to Example 1, except that the ratio of a2 / a1 to the negative electrode is controlled to be 0.81 and the ratio of b2 / b1 to be 1.12.
[0105] Example 7
[0106] Same as Example 1, except that the ratio of a2 / a1 to the negative electrode is controlled to be 1.07 and the ratio of b2 / b1 is controlled to be 1.18.
[0107] Example 8
[0108] Same as Example 1, except that the ratio of a2 / a1 to the negative electrode is controlled to be 1.07 and the ratio of b2 / b1 is controlled to be 1.23.
[0109] Example 9
[0110] Similar to Example 1, except that the ratio of a2 / a1 to the negative electrode is controlled to be 0.88 and the ratio of b2 / b1 to be 1.05.
[0111] Example 10
[0112] Similar to Example 1, except that the ratio of a2 / a1 to the negative electrode is controlled to be 0.89 and the ratio of b2 / b1 to be 1.12.
[0113] Example 11
[0114] Similar to Example 1, except that the ratio of a2 / a1 to the negative electrode is controlled to be 0.91 and the ratio of b2 / b1 to be 1.18.
[0115] Example 12
[0116] Similar to Example 1, except that the ratio of a2 / a1 to the negative electrode is controlled to be 0.89 and the ratio of b2 / b1 to be 1.23.
[0117] Example 13
[0118] Same as Example 1, except that the ratio of a2 / a1 to the negative electrode is controlled to be 1.14 and the ratio of b2 / b1 to be 1.05.
[0119] Example 14
[0120] Same as Example 1, except that the ratio of a2 / a1 to the negative electrode is controlled to be 1.08 and the ratio of b2 / b1 is controlled to be 1.12.
[0121] Example 15
[0122] Same as Example 1, except that the ratio of a2 / a1 to the negative electrode is controlled to be 1.12 and the ratio of b2 / b1 is controlled to be 1.01.
[0123] Example 16
[0124] Same as Example 1, except that the ratio of a2 / a1 to the negative electrode is controlled to be 1.00 and the ratio of b2 / b1 to be 1.10.
[0125] Example 17
[0126] Similar to Example 1, except that the ratio of a2 / a1 to the negative electrode is controlled to be 1.13 and the ratio of b2 / b1 to be 1.35.
[0127] Example 18
[0128] Same as Example 1, except that the ratio of a2 / a1 to the negative electrode is controlled to be 1.08 and the ratio of b2 / b1 is controlled to be 1.30.
[0129] Example 19
[0130] Similar to Example 1, except that the ratio of a2 / a1 to the negative electrode is controlled to be 0.77 and the ratio of b2 / b1 to be 1.08.
[0131] Example 20
[0132] Similar to Example 1, except that the ratio of a2 / a1 to the negative electrode is controlled to be 0.70 and the ratio of b2 / b1 to be 1.05.
[0133] Example 21
[0134] Same as Example 1, except that the ratio of a2 / a1 to the negative electrode is controlled to be 1.07 and the ratio of b2 / b1 to be 1.50.
[0135] Example 22
[0136] Same as Example 1, except that the a2 / a1 ratio of the negative electrode is controlled to be 1.00 and the b2 / b1 ratio is controlled to be 1.40.
[0137] Example 23
[0138] Similar to Example 1, except that the ratio of a2 / a1 to the negative electrode is controlled to be 0.88 and the ratio of b2 / b1 to be 1.15.
[0139] Example 24
[0140] Same as Example 1, except that the a2 / a1 ratio of the negative electrode is controlled to be 1.00 and the b2 / b1 ratio is controlled to be 1.40.
[0141] Example 25
[0142] Similar to Example 1, except that the ratio of a2 / a1 to the negative electrode is controlled to be 1.25 and the ratio of b2 / b1 to be 1.50.
[0143] Example 26
[0144] Similar to Example 1, except that the ratio of a2 / a1 to the negative electrode is controlled to be 0.81 and the ratio of b2 / b1 to be 1.05.
[0145] Example 27
[0146] Similar to Example 1, except that the ratio of a2 / a1 to the negative electrode is controlled to be 1.25 and the ratio of b2 / b1 to be 1.50.
[0147] Example 28
[0148] Similar to Example 27, except that adjusting the compaction of the negative electrode sheet increases the porosity of both the first and second negative electrode active material layers, but the ratios of a2 / a1 and b2 / b1 remain unchanged.
[0149] Comparative Example 1
[0150] Same as Example 1, except that the ratio of a2 / a1 to the negative electrode is controlled to be 0.6 and the ratio of b2 / b1 to be 1.12.
[0151] Comparative Example 2
[0152] Same as Example 1, except that the ratio of a2 / a1 to the negative electrode is controlled to be 1.27 and the ratio of b2 / b1 is controlled to be 1.04.
[0153] Comparative Example 3
[0154] Similar to Example 1, except that the ratio of a2 / a1 to the negative electrode is controlled to be 0.49 and the ratio of b2 / b1 to be 0.88.
[0155] Table 1
[0156]
[0157] Performance testing:
[0158] 1. Particle size distribution of negative electrode active material: Particle size distribution was measured using a laser particle size analyzer, such as the Mastersizer 3000 laser particle size analyzer from Malvern Instruments Ltd., UK, in accordance with GB / T 19077-2016 laser diffraction method, to obtain the Dv50 particle size of the negative electrode active material.
[0159] 2. I of the negative electrode active material D / I G :I D I represents the peak intensity of the D peak in the Raman spectrum of the negative electrode active material. G The peak intensity of the G peak in the Raman spectrum of the negative electrode active material is given. ① The lithium-ion battery is discharged to zero charge and disassembled under an inert atmosphere to obtain the negative electrode sheet. After washing the negative electrode sheet with a volatile solvent such as dimethyl carbonate (DMC) and drying it, the second negative electrode active material layer is separated by adhesive tape. Then, the remaining powder on the negative electrode sheet is scraped off and marked as the first particle; the powder particles on the surface of the adhesive tape are scraped off and marked as the second particle. The scraped first and second particles are respectively immersed in N-methylpyrrolidone (NMP) and ultrasonically treated to dissolve the binder such as SBR (styrene-butadiene rubber), thus obtaining the first and second negative electrode active materials. The I of the first and second negative electrode active materials is calculated by integrating the area ratio of the D peak and the G peak by Raman spectroscopy. D1 / I G1 Value and I of the second negative electrode active material D2 / I G2Value. ② Discharge the lithium-ion battery to zero charge state, disassemble it under an inert atmosphere to obtain the negative electrode sheet, wash the negative electrode sheet with volatile solvents such as dimethyl carbonate (DMC) and then air dry it. Scrape off the entire negative electrode active material layer from the negative electrode current collector, and immerse the scraped particles in N-methylpyrrolidone (NMP), sonicate to dissolve the SBR (styrene-butadiene rubber) and other binders, and then obtain the negative electrode active material. Calculate the I value of the negative electrode active material by integrating the area ratio of the D peak and the G peak obtained by Raman spectroscopy. D / I G Value a.
[0160] 3. Porosity: Measured by mercury porosimetry.
[0161] ① For the entire negative electrode active material layer: For batteries that have already been tested and rated for capacity, the battery can be discharged to a zero-electrical state and disassembled under an inert atmosphere to obtain the negative electrode sheet. The negative electrode sheet is then washed with a volatile solvent such as dimethyl carbonate (DMC) and dried. Measurement is performed using mercury intrusion porosimetry, which is based on the principle that a non-wetting liquid (mercury) enters the pores of a material under pressure. Since mercury is non-wetting to most materials at room temperature, external pressure is required to force it into the pores. According to the Washburn equation, pressure is inversely proportional to pore size; therefore, by gradually increasing the pressure and measuring the amount of mercury intrusion, the distribution of different pore sizes and the total porosity can be calculated.
[0162] ② For the first negative electrode active material: X-ray tomography (Nano-CT) is performed on the electrode sheet, and then the porosity distribution is obtained through three-dimensional reconstruction. The porosity of the first negative electrode active layer is obtained by cutting the image.
[0163] ③ For the second negative electrode active material layer: X-ray tomography (Nano-CT) is performed on the electrode sheet, and then the porosity distribution is obtained through three-dimensional reconstruction. The porosity of the second negative electrode active layer is obtained by cutting the image.
[0164] 5. 7C Lithium Plating Boundary: During the charging process of a lithium-ion battery, when lithium plating occurs on the negative electrode, its electrode thickness increases sharply, causing an inflection point in the thickness growth of the lithium-ion battery. Therefore, an in-situ thickness gauge can be used to measure the thickness change of the lithium-ion battery during charging, and a SOC-thickness curve can be plotted. By reading the SOC at the thickness inflection point, the lithium plating boundary under different test conditions can be obtained. Specifically, the battery is placed in a 25°C oven and charged at a 7C current from 0 SOC to a cutoff voltage of 3.8V. The change in cell thickness at different rates is monitored, and the lithium plating boundary of the cell can be obtained after data processing.
[0165] 6. Cycle Life Test: At 60℃, charge the lithium-ion battery at a constant current of 1C to 3.8V, then continue constant voltage charging until the current reaches 0.05C. At this point, the lithium-ion battery is fully charged, and the charging capacity is recorded as the first charge capacity. After letting the lithium-ion battery rest for 10 minutes, discharge it at a constant current of 1C to 2.0V. This completes one charge-discharge cycle, and the discharge capacity is recorded as the first discharge capacity. Perform cycle charge-discharge tests on the lithium-ion battery using the above method, and record the discharge capacity after each cycle. The capacity retention rate (%) of the lithium-ion battery after 500 cycles at 60℃ = (Discharge capacity after 500 cycles / Discharge capacity of the first cycle) × 100%.
[0166] Table 2: Test Results
[0167]
[0168] The test results in Table 2 show that the composite factor Q of the negative electrode active material layer is... The value of is in the range of 0.9 to 1.5. Lithium-ion batteries have a low risk of lithium plating and a high capacity retention rate. However, the composite factor Q of the comparative ratio does not meet the above range, and lithium-ion batteries cannot take into account both the risk of lithium plating and the capacity retention rate.
[0169] In the description of this invention, it should be understood that the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Thus, a feature defined as "first" or "second" may explicitly or implicitly include at least one of that feature. In the description of this invention, "a plurality of" means at least two, such as two, three, etc., unless otherwise explicitly specified.
[0170] In the description of this specification, the references to terms such as "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., refer to specific features, structures, materials, or characteristics described in connection with that embodiment or example, which are included in at least one embodiment or example of the present invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.
[0171] Although embodiments of the present invention have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those skilled in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of the present invention.
Claims
1. A negative electrode, comprising: A negative electrode current collector and a negative electrode active material layer disposed on at least one side of the negative electrode current collector, the negative electrode active material layer comprising a negative electrode active material. The negative electrode active material layer includes a first negative electrode active material layer and a second negative electrode active material layer. The first negative electrode active material layer is located between the negative electrode current collector and the second negative electrode active material layer. The first negative electrode active material layer includes a first negative electrode active material, and the second negative electrode active layer includes a second negative electrode active material. The composite factor Q of the negative electrode active material layer = The value range is 0.9 to 1.5; Wherein, a1 is the I of the first negative electrode active material. D1 / I G1 Value, a2 is the I of the second negative electrode active material D2 / I G2 Values, b1 is the porosity of the first negative electrode active material layer, and b2 is the porosity of the second negative electrode active material layer; I D1 This indicates that the Raman spectrum of the first negative electrode active material is at 1350±60 cm⁻¹. -1 The integral area of peak D at point I G1 This indicates that the Raman spectrum of the first negative electrode active material is at 1580±60 cm⁻¹. -1 The integral area of peak G at point I; D2 This indicates that the Raman spectrum of the second negative electrode active material is at 1350±60 cm⁻¹. -1 The integral area of peak D at point I G2 This indicates that the Raman spectrum of the second negative electrode active material is at 1580±60 cm⁻¹. -1 The integral area of peak G at that location.
2. The negative electrode sheet according to claim 1, wherein, The value range of the composite factor Q is 1.1 to 1.
4.
3. The negative electrode sheet according to claim 1 or 2, satisfying at least one of the following conditions: a1 is 0.5~1.6; a2 is 1.0~1.8; b1 is 25%~38%; b2 is 35%~48%.
4. The negative electrode sheet according to claim 3, wherein at least one of the following conditions is met: a1 is 0.8~1.3; a2 is 1.0~1.45; b1 is 30%~35%; b2 is 38%~42%.
5. The negative electrode sheet according to any one of claims 1 to 4, wherein, a2 / a1 is 0.6~1.
5.
6. The negative electrode sheet according to claim 5, wherein, a2 / a1 is 0.8~1.
3.
7. The negative electrode sheet according to any one of claims 1 to 6, wherein, a1 < a2.
8. The negative electrode sheet according to any one of claims 1 to 7, wherein, b2 / b1 > 1.
0.
9. The negative electrode sheet according to claim 8, wherein, 1.5≥b2 / b1≥1.
12.
10. The negative electrode sheet according to any one of claims 1 to 9, wherein, The negative electrode active material I D / I G The value of a ranges from 0.05 to 2.
5.
11. The negative electrode according to claim 10, wherein, The negative electrode active material I D / I G The value of a is 0.5 to 1.
9.
12. The negative electrode sheet according to any one of claims 1 to 11, wherein, The porosity b of the negative electrode active material layer is 30%~48%.
13. The negative electrode according to claim 12, wherein, The porosity b of the negative electrode active material layer is 32%~42%.
14. The negative electrode sheet according to any one of claims 1 to 13, wherein, The particle size of the negative electrode active material Dv50 is 5μm~18μm.
15. The negative electrode according to claim 14, wherein, The particle size of the negative electrode active material Dv50 is 7μm~16μm.
16. The negative electrode sheet according to any one of claims 1 to 15, wherein, The negative electrode active material includes at least one of graphite, hard carbon, and silicon carbon, wherein the mass percentage of graphite in the negative electrode active material is greater than 80%.
17. A lithium-ion battery, comprising a positive electrode, a negative electrode according to any one of claims 1 to 16, a separator, and an electrolyte, wherein the separator is located between the positive electrode and the negative electrode.
18. The lithium-ion battery according to claim 17, wherein, The positive electrode sheet includes a positive current collector and a positive active material layer disposed on at least one side of the positive current collector. The positive active material layer includes at least one of a layered positive active material, an olivine-type phosphate active material, and a spinel-structured positive active material.
19. The lithium-ion battery according to claim 18, wherein, The positive electrode active material layer includes at least one of lithium iron phosphate, lithium manganese phosphate, and lithium manganese iron phosphate.
20. The lithium-ion battery according to claim 18 or 19, wherein, The positive electrode active material layer includes a lithium replenishing agent, which includes at least one of lithium-rich lithium iron ore and lithium-rich lithium nickel ore.
21. The lithium-ion battery according to any one of claims 17 to 20, wherein, The electrolyte comprises a solvent, a lithium salt, and additives, and the electrolyte satisfies at least one of the following conditions: The solvent includes at least one of ethylene carbonate, diethyl carbonate, methyl ethyl carbonate, methyl formate, methyl acetate, ethyl acetate, butyl acetate, methyl propionate, ethyl propionate, methyl butyrate, ethyl butyrate, and propyl butyrate. The lithium salt includes at least one of lithium hexafluorophosphate, lithium difluorosulfonylimide, lithium dioxaborate, lithium difluorooxaborate, lithium difluorophosphate, and lithium difluorodioxaborate. The additives include at least one of carbonates, sulfates, and sulfonates; The additive accounts for 0% to 6% of the total mass of the electrolyte.
22. A battery assembly comprising the lithium-ion battery according to any one of claims 17 to 21.
23. An electrical device comprising a lithium-ion battery according to any one of claims 17 to 21 or a battery assembly according to claim 22.