Secondary battery

Abstract

The embodiment of the invention provides a secondary battery. The secondary battery comprises a positive plate, a negative plate, a diaphragm and electrolyte, the negative plate comprises a negative active material; the electrolyte comprises an electrolyte solvent and a film-forming additive; the secondary battery satisfies 0.02 < = (Voi / D50) * Voh * m < = 21; wherein Voi represents the OI value of the negative electrode active material; d50 represents the particle size value when the cumulative distribution of the negative electrode active material reaches 50%; voh represents the single-side width of the negative plate exceeding the positive plate; m represents the proportion of the film-forming additive in the electrolyte. The secondary battery is used for achieving a high-temperature-resistant effect.

Description

Technical Field

[0001] This application relates to the field of battery technology, and more particularly to a secondary battery. Background Technology

[0002] Secondary batteries, also known as rechargeable batteries or storage batteries, are batteries that can be recharged after being discharged to activate the active materials and continue to be used.

[0003] However, at high temperatures, the solid electrolyte membrane inside a secondary battery will decompose and recombine, which will affect the battery's performance at high temperatures.

[0004] Therefore, there is an urgent need for a high-temperature resistant secondary battery. Summary of the Invention

[0005] This application provides a secondary battery to achieve high temperature resistance.

[0006] In a first aspect, embodiments of this application provide a secondary battery, which includes a positive electrode, a negative electrode, a separator, and an electrolyte; the negative electrode includes a negative electrode active material; and the electrolyte includes an electrolyte solvent and a film-forming additive.

[0007] The secondary battery satisfies: 0.02≤(Voi / D50)×Voh×m≤21;

[0008] Among them, Voi represents the OI value of the negative electrode active material; D50 represents the particle size when the cumulative distribution of the negative electrode active material reaches 50%; Voh represents the width of the negative electrode sheet extending beyond the positive electrode sheet on one side; and m represents the proportion of film-forming additives in the electrolyte.

[0009] In one possible implementation, the proportion m of the film-forming additive in the electrolyte is 0.2-7.

[0010] In one possible implementation, the width Voh of the negative electrode extending beyond the positive electrode on one side is 0.5mm-3mm.

[0011] In one possible implementation, the OI value Voi of the negative electrode active material is I(004) / I(110);

[0012] Wherein, I(004) characterizes the diffraction peak intensity of the 004 crystal plane in the X-ray diffraction pattern of the negative electrode active material; I(110) characterizes the diffraction peak intensity of the 110 crystal plane in the X-ray diffraction pattern of the negative electrode active material.

[0013] In one possible implementation, the OI value (Voi) of the negative electrode active material is 3-7.

[0014] In one possible implementation, the particle size D50 when the cumulative distribution of the negative electrode active material reaches 50% is 7μm-15μm.

[0015] In one possible implementation, the negative electrode sheet further includes a conductive agent, a binder, and a thickener.

[0016] In one possible implementation, the positive electrode sheet includes a positive electrode active material, a conductive agent, and a binder.

[0017] In one possible implementation, the diaphragm includes a substrate layer and a surface treatment layer.

[0018] In one possible implementation, the electrolyte further includes a lithium salt.

[0019] The secondary battery provided in this application embodiment, by limiting the secondary battery to satisfy 0.2≤(Voi / D50)×Voh×m≤21, reasonably controls the relationship between the OI value (Voi) of the negative electrode active material, the particle size (D50) of the negative electrode active material, the width of the negative electrode sheet exceeding the positive electrode sheet on one side (Voh), and the proportion of film-forming additives in the electrolyte (m), effectively improving the high-temperature resistance of the secondary battery, reducing the occurrence of safety problems such as internal short circuits, expansion, and leakage under high temperature, enhancing the stability and reliability of the battery in high-temperature environments, and extending the high-temperature cycle life and storage performance of the battery. Attached Figure Description

[0020] The accompanying drawings, which are incorporated in and form part of this specification, illustrate embodiments consistent with this application and, together with the description, serve to explain the principles of this application.

[0021] Figure 1 A schematic diagram of a single-cell structure of a secondary battery provided in an embodiment of this application;

[0022] Figure 2 This is a schematic diagram showing the coverage of a positive electrode and a negative electrode as provided in an embodiment of this application.

[0023] Explanation of reference numerals in the attached diagram: 1-Negative electrode current collector, 2-Negative electrode membrane, 3-Positive electrode current collector, 4-Positive electrode membrane, 5-Separator, 7-Negative electrode plate, 6-Positive electrode plate.

[0024] The accompanying drawings have illustrated specific embodiments of this application, which will be described in more detail below. These drawings and descriptions are not intended to limit the scope of the concept in any way, but rather to illustrate the concept of this application to those skilled in the art through reference to specific embodiments. Detailed Implementation

[0025] Exemplary embodiments will now be described in detail, examples of which are illustrated in the accompanying drawings. When the following description relates to the drawings, unless otherwise indicated, the same numbers in different drawings denote the same or similar elements. The embodiments described in the following exemplary embodiments do not represent all embodiments consistent with this application. Rather, they are merely examples of apparatuses and methods consistent with some aspects of this application as detailed in the appended claims.

[0026] A secondary battery, also known as a rechargeable battery or accumulator, is a battery that can be reused by restoring the activity of active materials that have been deactivated after discharge through charging. However, under high-temperature conditions, the solid electrolyte interphase (SEI) membrane inside a secondary battery is prone to irreversible decomposition and recombination reactions, leading to decreased battery interface stability and increased impedance, which in turn significantly affects its cycle life, rate performance, and safety characteristics.

[0027] Therefore, developing secondary batteries with excellent high-temperature resistance has become a key technical problem that urgently needs to be solved.

[0028] Figure 1 This is a schematic diagram of a single-cell structure of a secondary battery provided in an embodiment of this application. Figure 1 As shown, the secondary battery includes a negative current collector 1, a negative electrode membrane 2, a positive current collector 3, a positive electrode membrane 4, and a separator 5.

[0029] For example, the negative electrode active material of the negative electrode membrane can be graphite, which is combined with conductive agents, thickeners, binders, etc. to form a slurry and coated on the surface of the negative electrode current collector.

[0030] Figure 2 This is a schematic diagram illustrating the coverage of a positive electrode and a negative electrode according to an embodiment of this application. Figure 2 As shown. Figure 2 The dark gray portion refers to the positive electrode plate 6. Figure 2 The section of the electrode with the diagonal line in the middle refers to the negative electrode 7; the area where the negative electrode 7 extends beyond the positive electrode 6 is the overhang area; the width of the negative electrode 7 extending beyond the positive electrode 6 on one side is called Voh.

[0031] The overhang region is the extension of the negative electrode 7 beyond the edge of the positive electrode 6 in the battery stacking or winding structure. This region is the part of the negative electrode active material that is not covered by the positive electrode active material. It usually does not participate in electrochemical reactions, but plays a role in safety protection and process assistance.

[0032] The single-sided width (Voh) is the distance by which the negative electrode 7 extends beyond the positive electrode 6 on one side; that is, the vertical distance from the edge of the positive electrode to the corresponding edge of the negative electrode. The unit is usually millimeters (mm) or micrometers (μm), depending on the battery size and precision requirements.

[0033] This application provides a secondary battery, which includes a positive electrode, a negative electrode, a separator, and an electrolyte. The negative electrode includes a negative electrode active material. The electrolyte includes an electrolyte solvent and a film-forming additive. The secondary battery satisfies the following condition: 0.02 ≤ (Voi / D50) × Voh × m ≤ 21. Wherein, Voi represents the OI value of the negative electrode active material; D50 represents the particle size value when the cumulative distribution of the negative electrode active material reaches 50%; Voh represents the width of the negative electrode extending beyond the positive electrode on one side; and m represents the proportion of the film-forming additive in the electrolyte.

[0034] For example, a secondary battery includes a positive electrode, a negative electrode, a separator, and an electrolyte. The negative electrode includes a negative electrode active material. The electrolyte includes an electrolyte solvent and film-forming additives.

[0035] Optionally, the negative electrode sheet further includes a negative electrode current collector and a negative electrode film disposed on at least one surface of the negative electrode current collector and comprising a negative electrode active material.

[0036] For example, the negative electrode film is disposed on at least one surface of the negative electrode current collector and includes a negative electrode active material and related auxiliary materials. The negative electrode active material is a key substance participating in the electrochemical reaction of the battery. During charging, it undergoes an oxidation reaction to store energy; during discharging, it undergoes a reduction reaction to release energy. The separator is a physical barrier in the secondary battery structure, effectively isolating the positive and negative electrode materials to prevent direct contact that could lead to internal short circuits. At the same time, the microporous structure inside the separator allows lithium ions in the electrolyte to pass freely, forming a charge-discharge circuit and ensuring normal battery operation. The electrolyte solvent is the main component of the electrolyte, providing a liquid environment for the electrolyte. It can dissolve electrolyte salts and other additives, ensuring that ions can move freely between the positive and negative electrodes, thereby realizing charge transfer inside the battery. It is an important medium for the battery to achieve its charge-discharge function. During the first charge-discharge of the battery, the film-forming additives undergo a chemical reaction on the surface of the negative electrode to form a stable SEI film. This film is selective, allowing lithium ions to pass freely while preventing solvent molecules and other impurities in the electrolyte from directly contacting the negative electrode, reducing the occurrence of side reactions, and improving the cycle stability and safety of the battery. Furthermore, the proportion of film-forming additives affects the quality and performance of the SEI film, which in turn affects the overall performance of the battery.

[0037] For example, the secondary battery satisfies: 0.02≤(Voi / D50)×Voh×m≤21;

[0038] Among them, Voi represents the OI value of the negative electrode active material; D50 represents the particle size when the cumulative distribution of the negative electrode active material reaches 50%; Voh represents the width of the negative electrode sheet extending beyond the positive electrode sheet on one side; and m represents the proportion of film-forming additives in the electrolyte.

[0039] For example, the OI value, or Orientation Index, measures the degree of orientation of the crystals in a negative electrode active material. Crystal orientation refers to the spatial arrangement of grains within a crystal; different orientations affect the physical and chemical properties of the material. In secondary batteries, the OI value of the negative electrode active material affects the lithium-ion transport rate within the material. A higher OI value indicates a more consistent crystal orientation, which may facilitate lithium-ion transport in some directions but could also hinder transport in others. Conversely, a lower OI value indicates a more random crystal orientation, resulting in a more uniform lithium-ion transport path. Therefore, a suitable OI value is crucial for optimizing battery charge-discharge performance and improving cycle life.

[0040] For example, D50, also known as median diameter or median particle size, represents the particle size at which the cumulative particle size distribution percentage reaches 50% in the particle size distribution curve of the negative electrode active material. Simply put, it's the particle diameter at which half of the negative electrode active material's particles are sorted by size. The size of D50 affects the specific surface area, packing density, and lithium-ion insertion and extraction kinetics of the negative electrode active material. A smaller D50 means finer particles and a larger specific surface area, providing more reactive sites, which is beneficial for rapid lithium-ion insertion and extraction, thus improving the battery's charge and discharge rate; however, it also increases the degree of side reactions on the particle surface, increasing capacity loss during cycling and storage. A larger D50, on the other hand, means larger particles, a smaller specific surface area, a relatively longer lithium-ion transport path, and potentially a slower charge and discharge rate, but a higher packing density, which is beneficial for improving the battery's energy density.

[0041] For example, Voh refers to the width of the negative electrode sheet that exceeds that of the positive electrode sheet on one side. During battery charging and discharging, lithium ions repeatedly insert and extract between the positive and negative electrodes. If the size of the negative electrode sheet is not properly matched to the positive electrode sheet, lithium may deposit at the edge of the negative electrode, forming lithium dendrites. The growth of lithium dendrites may puncture the separator, causing an internal short circuit and leading to safety issues. A suitable Voh value ensures that there is sufficient negative electrode material to receive lithium ions extracted from the positive electrode during battery charging and discharging, preventing excessive lithium deposition at the edge of the negative electrode, thereby improving battery safety and cycle stability.

[0042] For example, film-forming additives are an important component of the electrolyte. During the first charge and discharge of the battery, they undergo a chemical reaction on the surface of the negative electrode to form an SEI film. m represents the mass percentage of the film-forming additive in the electrolyte. The quality and performance of the SEI film directly affect the battery's cycle life, charge / discharge efficiency, and safety. A suitable m value can form a stable, dense, and highly conductive SEI film that allows lithium ions to pass freely while preventing solvent molecules and other impurities in the electrolyte from directly contacting the negative electrode, reducing side reactions and thus improving the battery's cycle stability and safety. If the m value is too small, the formed SEI film may be incomplete or unstable, failing to effectively protect the negative electrode; if the m value is too large, the SEI film may be too thick, increasing the resistance to lithium ion transport and reducing the battery's charge / discharge efficiency.

[0043] The secondary battery provided in this application embodiment, by limiting the secondary battery to satisfy 0.02≤(Voi / D50)×Voh×m≤21, reasonably controls the relationship between the OI value (Voi) of the negative electrode active material, the particle size (D50) of the negative electrode active material, the width of the negative electrode sheet exceeding the positive electrode sheet on one side (Voh), and the proportion of film-forming additives in the electrolyte (m), effectively improving the high-temperature resistance of the secondary battery, reducing the occurrence of safety problems such as internal short circuits, expansion, and leakage under high temperature, enhancing the stability and reliability of the battery in high-temperature environments, and extending the high-temperature cycle life and storage performance of the battery.

[0044] In one possible implementation, the proportion m of the film-forming additive in the electrolyte is 0.2-7.

[0045] For example, the proportion m of the film-forming additive in the electrolyte is 0.2-7; for instance, the proportion m of the film-forming additive in the electrolyte can be 0.2, 1, 3, 5, 7 or any combination thereof.

[0046] When m is in the range of 0.2-7, the film-forming additive can undergo appropriate chemical reactions on the electrode surface to form a stable and dense SEI film. This film can effectively prevent further direct contact between the electrolyte and the electrode active materials, reduce the decomposition reaction of the electrolyte under conditions such as high temperature, thereby reducing the battery's self-discharge rate and improving the battery's storage performance.

[0047] In one possible implementation, the width Voh of the negative electrode extending beyond the positive electrode on one side is 0.5mm-3mm.

[0048] For example, the width Voh of the negative electrode extending beyond the positive electrode on one side is 0.5mm-3mm; for instance, the width Voh of the negative electrode extending beyond the positive electrode on one side can be 0.5mm, 0.8mm, 1mm, 1.5mm, 2mm, 2.5mm, 3mm or any combination thereof.

[0049] During battery charging and discharging, electrode materials expand and contract. If the Voh (Volume Overhang) is too small, the negative electrode may not completely cover the positive electrode during battery stacking or winding, leading to lithium ion deposition at the electrode edges and the formation of lithium dendrites, which can cause internal short circuits in severe cases. Controlling the Voh between 0.5mm and 3mm allows sufficient space for electrode expansion, ensuring that the negative electrode always completely covers the positive electrode under various operating conditions, effectively preventing short circuits and improving battery safety. At high temperatures, the expansion of electrode materials intensifies. If the Voh is too small, the electrode alignment accuracy of the stacking or winding equipment during battery production is limited, making it impossible to guarantee that the negative electrode completely covers the positive electrode. This could lead to positive electrode leakage, lithium deposition, and the formation of lithium dendrites, posing a battery safety hazard. A suitable Voh provides equipment fluctuation margin for the area where the negative electrode covers the positive electrode, while also effectively reducing the energy density reduction caused by excessive negative electrode material and the loss of active lithium in the negative electrode overhang area, improving capacity retention during storage and cycling.

[0050] In one possible implementation, the OI value Voi of the negative electrode active material is I(004) / I(110); where I(004) characterizes the diffraction peak intensity of the 004 crystal plane in the X-ray diffraction pattern of the negative electrode active material; and I(110) characterizes the diffraction peak intensity of the 110 crystal plane in the X-ray diffraction pattern of the negative electrode active material.

[0051] For example, the OI value Voi = I(004) / I(110) is the relative ratio of the diffraction peak intensities of the 004 and 110 crystal planes, which comprehensively reflects the orientation and structural characteristics of these two crystal planes in the negative electrode active material. When I(004) is relatively larger than I(110), it indicates that the orientation of the 004 crystal plane is more obvious than that of the 110 crystal plane, that is, more 004 crystal planes tend to be aligned parallel to a certain direction, and the OI value is larger in this case; conversely, when I(110) is relatively larger, the OI value is smaller, indicating that the orientation of the 110 crystal plane is relatively more prominent or the orientation of the 004 crystal plane is more random.

[0052] The OI value is closely related to the performance of secondary batteries. A suitable OI value can optimize the transport path of lithium ions in the negative electrode material, improve the lithium ion insertion and extraction rates, and thus improve the charge-discharge performance and cycle stability of the battery. For example, in some cases, a higher OI value may be beneficial to improve the rate performance of the battery, but an excessively high OI value may also lead to an increase in the internal resistance of the battery, affecting the overall performance of the battery. Therefore, by controlling the magnitudes of I(004) and I(110), and thus adjusting the OI value, important references can be provided for the design and optimization of secondary batteries.

[0053] During battery charge-discharge cycles, the negative electrode active material undergoes repeated expansion and contraction, which can lead to structural damage and performance degradation. A suitable Voi value can help the negative electrode material maintain a more stable structure during cycling. When the 004 and 110 crystal planes are aligned, the stress generated during expansion and contraction can be distributed more evenly, reducing localized stress concentration and thus lowering the probability of material cracking and pulverization, thereby extending the battery's cycle life.

[0054] In one possible implementation, the OI value (Voi) of the negative electrode active material is 3-7.

[0055] For example, the OI value Voi of the negative electrode active material is 3-7; for instance, the OI value Voi of the negative electrode active material can be 3, 4, 5, 6, 7 or any combination thereof.

[0056] The OI value reflects the degree of orientation of a specific crystal facet in the negative electrode active material. When Voi is between 3 and 7, the crystal orientation of the negative electrode active material is conducive to the insertion and extraction of lithium ions. The 004 and 110 crystal faces, under these values, form a more reasonable channel structure, allowing lithium ions to diffuse more smoothly within the negative electrode material and reducing resistance during transport. This enables lithium ions to quickly insert into the negative electrode during charging and rapidly extract during discharging, thereby improving the battery's charge and discharge efficiency, shortening charging time, and increasing the battery's usable capacity.

[0057] In one possible implementation, the particle size D50 when the cumulative distribution of the negative electrode active material reaches 50% is 7μm-15μm.

[0058] For example, the particle size D50 when the cumulative distribution of the negative electrode active material reaches 50% can be 7 μm, 8 μm, 9 μm, 10 μm, 11 μm, 12 μm, 13 μm, 14 μm, 15 μm or any combination thereof.

[0059] A suitable D50 particle size range helps to construct a good lithium-ion transport channel. Within this range, the particle size of the negative electrode active material is moderate, neither too small, leading to overly tight contact between particles and increasing the tortuosity of lithium-ion transport, nor too large, causing excessively long diffusion paths for lithium ions within the particles. A particle size of 7μm-15μm allows lithium ions to be inserted and extracted relatively smoothly in the negative electrode material, thereby improving the battery's charge and discharge efficiency, shortening charging time, and increasing the battery's usable capacity.

[0060] In one possible implementation, the negative electrode sheet further includes a conductive agent, a binder, and a thickener.

[0061] Optionally, the negative electrode sheet includes a negative electrode active material, a conductive agent, a binder, and a thickener.

[0062] For example, the negative electrode active material includes graphite material; wherein, the graphite material includes one or more of natural graphite and artificial graphite.

[0063] For example, natural graphite is mined from graphite mines and is mainly divided into flake graphite and amorphous graphite. Its crystal structure has typical layered characteristics, with carbon atoms arranged in a hexagonal pattern to form graphene sheets, which are bonded together by relatively weak van der Waals forces. Natural graphite has good electronic conductivity, providing a fast electron transport channel for the insertion and extraction of lithium ions, which is beneficial to improving the charging and discharging efficiency of batteries.

[0064] For example, artificial graphite is typically prepared from raw materials such as petroleum coke and pitch coke through a series of complex processes including crushing, screening, batching, kneading, molding, calcination, and graphitization. By controlling the preparation process conditions, the crystal structure and physicochemical properties of artificial graphite can be adjusted. Compared with natural graphite, artificial graphite has a more regular crystal structure, better isotropy, and more uniform lithium ion insertion and extraction within the graphite, which can effectively mitigate volume changes during battery charging and discharging and improve battery cycle stability.

[0065] For example, the conductive agent may include, but is not limited to, at least one of conductive carbon black (Super P), carbon nanotubes (CNTs), carbon fibers, flake graphite, graphene, metallic materials, or conductive polymers. The conductive carbon black may include, but is not limited to, at least one of acetylene black or Ketjen black. The aforementioned carbon nanotubes may include, but are not limited to, single-walled carbon nanotubes and / or multi-walled carbon nanotubes. The aforementioned carbon fibers may include, but are not limited to, vapor-grown carbon fibers (VGCF) and / or carbon nanofibers.

[0066] For example, the adhesive may include, but is not limited to, at least one of polyacrylic acid, sodium polyacrylate, potassium polyacrylate, lithium polyacrylate, polyimide, polyvinyl alcohol, carboxymethyl cellulose, sodium carboxymethyl cellulose, lithium carboxymethyl cellulose, polyimide, polyamide-imide, styrene-butadiene rubber, or polyvinylidene fluoride.

[0067] For example, the thickener may include at least one of carboxymethyl cellulose or sodium carboxymethyl cellulose.

[0068] In one possible implementation, the positive electrode sheet includes a positive electrode active material, a conductive agent, and a binder.

[0069] For example, the positive electrode active material may include, but is not limited to, at least one of lithium nickel cobalt manganese oxide (e.g., NCM811, NCM622, NCM523, NCM111), lithium nickel cobalt aluminum oxide, lithium iron phosphate, lithium-rich manganese-based materials, lithium cobalt oxide (LiCoO2), lithium manganese oxide, lithium manganese iron phosphate, or lithium titanate.

[0070] For example, the conductive agent can be the same type as the conductive agent in the negative electrode sheet described above.

[0071] For example, the adhesive can be the same type as the adhesive in the negative electrode sheet described above.

[0072] In one possible implementation, the diaphragm includes a substrate layer and a surface treatment layer.

[0073] For example, the membrane substrate layer can be a nonwoven membrane or composite membrane with a porous structure, and the material of the substrate layer can include at least one of polyethylene, polypropylene, polyethylene terephthalate or polyimide.

[0074] For example, at least one surface of the substrate layer is provided with a surface treatment layer, which may be a polymer layer or an inorganic layer, or a layer formed by mixing polymers and inorganic substances.

[0075] In one possible implementation, the electrolyte also includes a lithium salt.

[0076] Optionally, the electrolyte includes an electrolyte solvent, a film-forming additive, and a lithium salt.

[0077] For example, the electrolyte solvent includes, but is not limited to, at least one of carbonate compounds, carboxylic acid ester compounds, ether compounds, or other organic solvents. The aforementioned carbonate compounds may include, but are not limited to, at least one of chain carbonate compounds, cyclic carbonate compounds, or fluorocarbonate compounds.

[0078] Alternatively, the carbonate solvent may be: ethylene carbonate (EC), ethyl methyl carbonate (EMC), or diethyl carbonate (DEC).

[0079] During the first charge and discharge cycle of a battery, ethylene carbonate (EC) undergoes a decomposition reaction on the electrode surface, forming a stable electrolyte interphase (SEI) film. This film possesses electronic insulation and ion conductivity properties, preventing further direct reactions between the electrolyte and the electrodes, reducing electrolyte consumption, and improving battery cycle life. EMC's viscosity falls between that of ethylene carbonate and some other high-viscosity solvents. It neither increases lithium-ion migration resistance like high-viscosity solvents nor causes excessive electrolyte volatility like low-viscosity solvents. This moderate viscosity helps improve the ionic conductivity of the electrolyte, resulting in better charge and discharge performance. DEC's low viscosity effectively reduces the overall viscosity of the electrolyte, increasing the migration rate of lithium ions within the electrolyte, thereby improving the battery's rate performance and enabling rapid charge and discharge in a short time.

[0080] Optionally, the mass ratio of EC, EMC, and DEC in the electrolyte solvent is 3:5:2.

[0081] For example, the mass ratio of EC, EMC and DEC in the electrolyte solvent is 3:5:2.

[0082] For example, the lithium salt can be an inorganic lithium salt, an organic lithium salt, or a mixture of organic and inorganic lithium salts.

[0083] Optionally, inorganic lithium salts include, but are not limited to, lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, and lithium hexafluoroarsenate; organic lithium salts include, but are not limited to, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium di(oxalate)borate, and lithium di(fluorooxalate)borate.

[0084] The secondary battery of this application embodiment achieves improved high-temperature resistance through multi-dimensional precise design. The battery includes a positive electrode, a negative electrode containing negative electrode active material, and an electrolyte containing film-forming additives, satisfying the parameters 0.02 ≤ (Voi / D50) × Voh × m ≤ 21. Specifically, Voi is 3-7, optimizing the lithium-ion transport channel; D50 is 7μm-15μm, facilitating lithium-ion transport and electrode stability; Voh is 0.5mm-3mm, preventing lithium dendrite formation; and m is 0.2-7, forming a stable SEI film. The combined effect of these parameters ensures that (Voi / D50) × Voh × m is within a reasonable range. This achieves improved overall battery performance, including increased charge / discharge efficiency, enabling fast charging and longer discharge; enhanced rate performance to meet the demands of high-power devices; extended cycle life, reducing replacement costs; and improved safety, avoiding thermal runaway, short circuits, and other problems, ensuring stable operation.

[0085] The present invention will be further described below through specific embodiments.

[0086] Example 1

[0087] Methods for preparing secondary batteries:

[0088] The negative electrode active material is graphite with an OI value (Voi) of 3.3 and a particle size (D50) of 11.5 μm. Graphite, conductive carbon black, sodium carboxymethyl cellulose or lithium carboxymethyl cellulose, and styrene-butadiene rubber are mixed in a mass ratio of 96.5:1.0:0.7:1.8, with deionized water added as a solvent. The mixture is stirred until homogeneous to prepare a negative electrode slurry with a solid content of 52%. The negative electrode slurry is uniformly coated onto the surface of a 6 μm thick copper foil current collector and dried at 105 °C to complete the single-sided coating of the negative electrode sheet. The above steps are then repeated on the other side of the current collector, and after drying, a double-sided coated negative electrode sheet is obtained. After cold pressing, die-cutting, and slitting, negative electrode sheets with dimensions of 835.9 mm × 65 mm are obtained for later use, with a Voh value of 1.5 mm. The areal density of the negative electrode material is 89.2 g / m³. 2 The compaction density of the negative electrode material layer is 1.55 g / cm³. 3 .

[0089] The positive electrode active material is prepared by uniformly dispersing lithium iron phosphate, conductive carbon black, and polyvinylidene fluoride (PVDF) binder in a mass ratio of 96.5:1.5:2 with N-methylpyrrolidone solvent to obtain a positive electrode slurry with a solid content of 65%. The positive electrode slurry is uniformly coated onto the surface of a 12 μm thick aluminum foil current collector and dried at 105°C to obtain a single-sided coated positive electrode sheet. The above steps are then repeated on the other side of the current collector, and after drying, a double-sided coated positive electrode sheet is obtained. After cold pressing, die-cutting, and slitting, positive electrode sheets with dimensions of 734.9 mm × 62 mm are obtained for later use. The areal density of the positive electrode material is 220 g / m³. 2 The compaction density of the positive electrode material layer is 2.45 g / cm³. 3 .

[0090] The diaphragm material is a 12μm thick polyethylene film.

[0091] The electrolyte is prepared by mixing organic solvents EC, EMC, and DEC in a mass ratio of EC:EMC:DEC = 30:50:20 in a dry argon atmosphere to obtain a base solvent. Then, film-forming additive vinyl sulfate and lithium salt lithium hexafluorophosphate are added to the base solvent, dissolved, and mixed evenly to obtain the electrolyte. The electrolyte contains 12% lithium salt and 5.5% film-forming additive, with the remainder being the base solvent.

[0092] The prepared separator, negative electrode, and positive electrode are stacked sequentially, and pre-wound to ensure that the separator is positioned between the negative and positive electrodes. Then, after winding, hot pressing, tab welding, casing, encapsulation, vacuum drying, electrolyte injection, high-temperature settling, formation, and capacity testing, a secondary battery is obtained.

[0093] Example 2

[0094] The preparation method of the secondary battery in Example 2 is basically the same as that in Example 1, except that Voi is 6, the particle size D50 is 13.8 μm, Voh is 1.5 mm, and m is 5.5%.

[0095] Example 3

[0096] The preparation method of the secondary battery in Example 3 is basically the same as that in Example 1, except that Voi is 6.8, the particle size D50 is 14.7 μm, Voh is 1.5 mm, and m is 7.0%.

[0097] Example 4

[0098] The preparation method of the secondary battery in Example 4 is basically the same as that in Example 1, except that Voi is 5, the particle size D50 is 13.5 μm, Voh is 3 mm, and m is 5.5%.

[0099] Example 5

[0100] The preparation method of the secondary battery in Example 5 is basically the same as that in Example 1, except that Voi is 6.2, the particle size D50 is 9.8 μm, Voh is 1.5 mm, and m is 5.5%.

[0101] Example 6

[0102] The preparation method of the secondary battery in Example 6 is basically the same as that in Example 1, except that Voi is 4.2, the particle size D50 is 12.0 μm, Voh is 2.5 mm, and m is 0.3%.

[0103] Example 7

[0104] The preparation method of the secondary battery in Example 7 is basically the same as that in Example 1, except that Voi is 6.2, particle size D50 is 9.8 μm, Voh is 2.5 mm, and m is 5.5%.

[0105] Example 8

[0106] The preparation method of the secondary battery in Example 8 is basically the same as that in Example 1, except that Voi is 6.2, the particle size D50 is 7.3 μm, Voh is 2.5 mm, and m is 7.0%.

[0107] Comparative Example 1

[0108] The preparation method of the secondary battery in Comparative Example 1 is basically the same as that in Example 1, except that Voi is 8.3, the particle size D50 is 12.5 μm, Voh is 1.5 mm, and m is 5.5%.

[0109] Comparative Example 2

[0110] The preparation method of the secondary battery in Comparative Example 2 is basically the same as that in Example 1, except that Voi is 5.7, the particle size D50 is 15.4 μm, Voh is 1.5 mm, and m is 5.5%.

[0111] Comparative Example 3

[0112] The preparation method of the secondary battery in Comparative Example 3 is basically the same as that in Example 1, except that Voi is 6, the particle size D50 is 13.2 μm, Voh is 4.0 mm, and m is 5.5%.

[0113] Comparative Example 4

[0114] The preparation method of the secondary battery in Comparative Example 4 is basically the same as that in Example 1, except that Voi is 6, the particle size D50 is 14.2 μm, Voh is 0.5 mm, and m is 0.2%.

[0115] Comparative Example 5

[0116] The preparation method of the secondary battery in Comparative Example 5 is basically the same as that in Example 1, except that Voi is 5.1, the particle size D50 is 7.1 μm, Voh is 1.5 mm, and m is 0.2%.

[0117] Comparative Example 6

[0118] The preparation method of the secondary battery in Comparative Example 6 is basically the same as that in Example 1, except that Voi is 5.1, the particle size D50 is 7.1 μm, Voh is 4.0 mm, and m is 8.0%.

[0119] The performance of the hybrid supercapacitors in each embodiment and comparative example was tested through the following process, and the results are shown in Table 1.

[0120] Example 1: The above-mentioned secondary battery was packaged, pre-charged, and capacity-balanced. The capacity was measured (the upper limit of the formation voltage was 3.65V, and the formation temperature was 45℃; after formation, the battery was left to stand at room temperature for 24 hours, and then charged and discharged twice at room temperature at a rate of 0.5C (battery capacity balancing), and finally the capacity of about 30% was measured). Under the condition of 25℃, the battery was charged at a constant current and constant voltage of 0.5C to 3.65V, then constant voltage to 0.05C, left to stand for 0.5 hours, and then discharged at a constant current of 0.5C to 2.2V. The above charging and discharging process was repeated twice, and the capacity of the second discharge was recorded as the initial capacity C0. The battery was then stored at 60°C with a full charge (i.e., charged to 3.65V at 0.5C constant current and constant voltage) for 30 days. After that, the secondary battery was discharged to 2.2V at 0.5C, and then charged to 3.65V at 0.5C constant current and constant voltage (constant voltage to 0.05C). After standing for 0.5 hours, it was discharged to 2.2V at 0.5C to obtain the 30-day storage recovery capacity C30. The 30-day recovery capacity retention rate = C30 / initial capacity × 100%, and this value is listed in Table 1.

[0121] Example 2: The above-mentioned secondary battery was packaged, pre-charged, and capacity-balanced. The capacity was measured (the upper limit of the formation voltage was 3.65V, and the formation temperature was 45℃; after formation, the battery was left to stand at room temperature for 24 hours, and then charged and discharged twice at room temperature at a rate of 0.5C (battery capacity balancing), and finally the capacity of about 30% was measured). Under the condition of 25℃, the battery was charged at a constant current and constant voltage of 0.5C to 3.65V, then constant voltage to 0.05C, left to stand for 0.5 hours, and then discharged at a constant current of 0.5C to 2.2V. The above charging and discharging process was repeated twice, and the capacity of the second discharge was recorded as the initial capacity C0. The battery was then stored at 60°C with a full charge (i.e., charged to 3.65V at 0.5C constant current and constant voltage) for 90 days. After that, the secondary battery was discharged to 2.2V at 0.5C, and then charged to 3.65V at 0.5C constant current and constant voltage (constant voltage to 0.05C). After standing for 0.5 hours, it was discharged to 2.2V at 0.5C to obtain the 90-day storage recovery capacity C90. The 90-day recovery capacity retention rate = C90 / initial capacity × 100%, and this value is listed in Table 1.

[0122] Table 1

[0123]

[0124] The following conclusions can be drawn from Table 1:

[0125] 1) Effect of film-forming additive mass percentage (m) on battery capacity recovery retention rate

[0126] As can be seen from the data in Examples 1-8 and Comparative Examples 4-6, the value of m has a significant impact on the battery's capacity retention. A suitable value of m (e.g., m = 5.5% in Example 1, resulting in a 30-day capacity retention rate of 98.82% and a 90-day capacity retention rate of 97.33%) helps to form a stable solid electrolyte interphase (SEI) film on the electrode surface, reducing side reactions between the electrolyte and the electrode and improving the battery's high-temperature storage performance. If the value of m is too small (e.g., m = 0.2% in Comparative Example 4, resulting in a 30-day capacity retention rate of 93.45% and a 90-day capacity retention rate of 90.65%), the SEI film may not be complete or stable enough, failing to effectively suppress side reactions and leading to rapid capacity decay. If the value of m is too large (e.g., m = 8.0% in Comparative Example 6, resulting in a 30-day capacity retention rate of 94.88% and a 90-day capacity retention rate of 93.26%), although a thicker SEI film can be formed, it may increase the battery's internal resistance, affecting ion transport, which is also detrimental to battery performance and leads to a decrease in capacity retention.

[0127] 2) The effect of the width (Voh) of the negative electrode extending beyond the positive electrode on the battery's capacity recovery retention rate.

[0128] Comparing Examples 1, 4, 6, 7, and 8 with Comparative Examples 3, 4, and 6, it can be seen that the value of Voh has a certain impact on battery performance. When Voh is within a certain range (e.g., in Example 1, Voh is 1.5 mm, the 30-day recovery capacity retention rate is 98.82%, and the 90-day recovery capacity retention rate is 97.33%; in Example 4, when Voh is increased to 3.0 mm, the 30-day recovery capacity retention rate drops to 97.77%, and the 90-day recovery capacity retention rate drops to 96.62%), an excessively large Voh may lead to changes in the internal structure of the battery, affecting ion transport and electrochemical reactions, thus reducing the capacity retention rate. On the other hand, an excessively small Voh (e.g., in Comparative Example 4, Voh is 0.5 mm, the 30-day recovery capacity retention rate is 93.45%, and the 90-day recovery capacity retention rate is 90.65%) may also be detrimental to the stability of battery performance, possibly because an excessively thin negative electrode sheet cannot effectively support the active material and maintain the stability of the battery structure.

[0129] 3) The influence of OI value (Voi) and particle size (D50) of the negative electrode active material on the battery's capacity recovery retention rate.

[0130] Data from Examples 1-8 and Comparative Examples 1-2 show that the combination of Voi and D50 significantly affects the 30-day and 90-day capacity retention rates of the battery. For example, in Example 1, with a Voi of 3.3 and a D50 of 11.5 μm, the 30-day capacity retention rate was 98.82%, and the 90-day capacity retention rate was 97.33%. However, in Comparative Example 1, with a Voi of 8.3 and a D50 of 12.5 μm, the 30-day capacity retention rate decreased to 95.32%, and the 90-day capacity retention rate decreased to 91.89%. This indicates that a relatively low Voi value combined with a suitable D50 value helps improve the battery's capacity retention rate, possibly because a suitable Voi and D50 can give the negative electrode active material better structural stability and electrochemical performance, reducing capacity decay during high-temperature storage.

[0131] 4) The influence of the range of values ​​of (Voi / D)×Voh×m on the battery recovery capacity retention rate

[0132] Observing the relationship between the (Voi / D)×Voh×m value and the battery capacity retention rate of each embodiment and comparative example, it was found that when the (Voi / D)×Voh×m value is in the range of 0.05-14.86, the battery performance varies to some extent. However, overall, when the (Voi / D)×Voh×m value is between 2.37-7.21 (as in Examples 1-5), the 30-day and 90-day capacity recovery retention rates of the battery are relatively high and stable; when the (Voi / D)×Voh×m value is too low (as in Examples 6 and Comparative Examples 4 and 5, the values ​​are 0.05, 0.04, and 0.22, respectively) or too high (as in Comparative Examples 3 and 6, the values ​​are 10.03 and 22.99, respectively), the battery capacity retention rate decreases. This indicates that the (Voi / D)×Voh×m value needs to be within a relatively suitable range to ensure good high-temperature storage performance of the battery. This suitable range is approximately between 2.37 and 7.21. Within this range, the synergistic effect of the parameters enables the battery to achieve a good balance between structural stability and electrochemical performance. Finally, it should be noted that other embodiments of the invention will be readily apparent to those skilled in the art upon consideration of the specification and practice of the invention disclosed herein. This invention is intended to cover any variations, uses, or adaptations of the invention that follow the general principles of the invention and include common knowledge or customary techniques in the art not disclosed herein. It is not limited to the precise structures described above and shown in the accompanying drawings, and various modifications and changes can be made without departing from its scope. The scope of the invention is limited only by the appended claims.

Claims

1. A secondary battery, characterized in that, The secondary battery includes a positive electrode, a negative electrode, a separator, and an electrolyte; the negative electrode includes a negative electrode active material; the electrolyte includes an electrolyte solvent and a film-forming additive. The secondary battery satisfies: 0.02≤(Voi / D50)×Voh×m≤21; Among them, Voi represents the OI value of the negative electrode active material; D50 represents the particle size when the cumulative distribution of the negative electrode active material reaches 50%; Voh represents the width of the negative electrode sheet extending beyond the positive electrode sheet on one side; and m represents the proportion of film-forming additives in the electrolyte.

2. The battery according to claim 1, characterized in that, The proportion m of the film-forming additive in the electrolyte is 0.2-7.

3. The battery according to claim 1, characterized in that, The width Voh of the negative electrode extending beyond the positive electrode on one side is 0.5mm-3mm.

4. The battery according to claim 1, characterized in that, The OI value Voi of the negative electrode active material is I(004) / I(110); Wherein, I(004) characterizes the diffraction peak intensity of the 004 crystal plane in the X-ray diffraction pattern of the negative electrode active material; I(110) characterizes the diffraction peak intensity of the 110 crystal plane in the X-ray diffraction pattern of the negative electrode active material.

5. The battery according to claim 4, characterized in that, The OI value (Voi) of the negative electrode active material is 3-7.

6. The battery according to claim 1, characterized in that, The particle size D50 when the cumulative distribution of the negative electrode active material reaches 50% is 7μm-15μm.

7. The battery according to any one of claims 1-6, characterized in that, The negative electrode also includes a conductive agent, a binder, and a thickener.

8. The battery according to any one of claims 1-6, characterized in that, The positive electrode sheet includes a positive electrode active material, a conductive agent, and a binder.

9. The battery according to any one of claims 1-6, characterized in that, The diaphragm includes a substrate layer and a surface treatment layer.

10. The battery according to any one of claims 1-6, characterized in that, The electrolyte also includes lithium salt.

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