A battery

Abstract

The application relates to the technical field of lithium batteries and discloses a battery, which comprises an electrode assembly, the electrode assembly comprises a positive electrode sheet, a diaphragm and a negative electrode sheet which are arranged in a stack, the negative electrode sheet comprises a negative electrode active layer which comprises a silicon-carbon material, the cross-section profile of the silicon-carbon material has a first internal angle B°, and B>180; an electrolyte comprises a linear carboxylate; the diaphragm comprises a base material layer and an organic coating layer which is arranged on one side or both sides of the base material layer, the organic coating layer comprises nitrogen-containing organic particles, the molecular structure of the nitrogen-containing organic particles comprises a nitrogen-containing heterocycle, the average particle size of the nitrogen-containing organic particles is denoted as A; A and B satisfy 1<=A / B<=10; and the charge cut-off voltage of the battery is greater than 4.35 V. The battery can improve overcharge safety and high-temperature performance under high voltage.

Description

Technical Field

[0001] This invention relates to the technical field of lithium batteries, and specifically to a type of battery. Background Technology

[0002] With the increasing demands for battery energy density in consumer electronics, silicon-carbon materials are widely used in anodes due to their high capacity. However, existing silicon-carbon anode technologies mostly employ a hybrid system of spherical and irregularly shaped silicon-carbon. This system is prone to systemic failure due to the combined inherent defects of the two materials, severely restricting its industrial application. Specifically, while traditional irregularly shaped silicon-carbon materials have excellent fast-charging performance and low interfacial impedance, their uneven internal stress distribution makes them prone to breakage at the corners of particles due to stress concentration during the rolling process, severely degrading the structural integrity of the electrode. On the other hand, while spherical silicon-carbon with high sphericity exhibits excellent structural stability, its smooth surface and limited contact points with binders and conductive agents mean that during charge-discharge cycles, some areas are prone to gradually disconnecting from the current collector or conductive network due to poor contact, leading to decreased utilization of active materials and rapid decay of cycle capacity. Furthermore, in practical applications, when the battery charging cutoff voltage is increased to above 4.35V, the interfacial side reactions between the silicon-carbon anode and the electrolyte are significantly aggravated, leading to an increase in the risk of battery gas production, expansion, and thermal runaway, making it difficult for the overcharge safety performance to meet application requirements. Summary of the Invention

[0003] The purpose of this invention is to overcome the above-mentioned problems existing in the prior art and provide a battery. The battery provided by this invention can, on the one hand, improve the system failure problem caused by the traditional use of silicon and carbon mixtures, and on the other hand, effectively passivate the surface activity of silicon floating silicon in silicon and carbon materials, suppress side reactions, and significantly improve the overcharge safety performance and high temperature performance of the battery.

[0004] To achieve the above objectives, the first aspect of the present invention provides a battery including an electrode assembly and an electrolyte, wherein the electrode assembly includes a positive electrode, a separator and a negative electrode stacked together. The negative electrode sheet includes a negative electrode active layer, which includes a silicon-carbon material. The cross-sectional profile of the silicon-carbon material has a first interior angle, denoted as B°, where B > 180°. The electrolyte comprises a linear carboxylic acid ester; The membrane includes a substrate layer and an organic coating on one or both sides of the substrate layer. The organic coating includes nitrogen-containing organic particles. The molecular structure of the nitrogen-containing organic particles includes nitrogen-containing heterocycles. The average particle size of the nitrogen-containing organic particles is denoted as A. A and B satisfy: 1 ​​≤ A / B ≤ 10; The charging cutoff voltage of the battery is greater than 4.35V.

[0005] The present invention, by adopting the above technical solution, has the following beneficial effects: In the battery described in this invention, by adjusting the average particle size A of the nitrogen-containing organic particles in the separator organic coating and the first interior angle B of the negative electrode silicon-carbon material, and ensuring that 1 ≤ A / B ≤ 10, the nitrogen-containing organic particles can be moderately dissolved in the electrolyte containing linear carboxylic acid esters, thereby migrating to the negative electrode surface and constructing a nitrogen-rich protective layer on the surface of the silicon-carbon material with a specific interior angle morphology. This protective layer effectively passivates the highly active floating silicon on the surface of the silicon-carbon particles, suppressing its violent side reactions with the electrolyte under overcharge conditions, and slowing down the repeated rupture and repair of the SEI film, thus significantly reducing the consumption of active lithium and gas production. Furthermore, the nitrogen-containing functional groups in the protective layer can complex transition metal ions dissolved from the overcharged positive electrode, blocking their catalytic damage to the negative electrode SEI film. Therefore, under high-voltage lithium cobalt oxide systems with a charging cutoff voltage greater than 4.35V, the overcharge safety and high-temperature performance of the battery are significantly improved.

[0006] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and should be understood to include values ​​close to those ranges or values. For numerical ranges, endpoint values ​​of various ranges, endpoint values ​​of various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein. In this document, unless otherwise specified, data ranges include endpoints. Attached Figure Description

[0007] Figure 1 The image shown is a SEM image of the silicon-carbon material in an example of the present invention. Detailed Implementation

[0008] The following provides a detailed description of specific embodiments of the present invention. It should be understood that the specific embodiments described herein are for illustrative and explanatory purposes only and are not intended to limit the scope of the invention.

[0009] Unless otherwise defined, all scientific and technical terms used in this invention have the same meaning as commonly understood by one of ordinary skill in the art.

[0010] With the increasing demands for battery energy density in consumer electronics, silicon-carbon materials are widely used in anodes due to their high capacity. However, existing silicon-carbon anode technologies mostly employ a hybrid system of spherical and irregularly shaped silicon-carbon materials. This system is prone to systemic failure due to the combined inherent defects of the two materials, severely restricting its industrial application. Therefore, batteries using high-voltage lithium cobalt oxide cathodes and silicon-carbon anodes exhibit significant overcharge safety issues when the charging cutoff voltage exceeds 4.35V.

[0011] To better balance the advantages of irregular blocky silicon-carbon and spherical silicon-carbon, this invention selects a silicon-carbon material with a first interior angle in its cross-sectional profile, where the angle is greater than 180°. On one hand, compared to irregular blocky silicon-carbon, this silicon-carbon material has fewer sharp edges on its surface, making it more resistant to rolling during electrode rolling. On the other hand, this silicon-carbon material has more non-curved surfaces than pure spherical silicon-carbon, increasing the contact sites with conductive agents and binders, thereby effectively suppressing the formation of electrochemical dead zones and thus balancing the battery's fast-charging performance, structural stability, and cycle life. However, when this type of silicon-carbon material is matched with a high-voltage lithium cobalt oxide cathode system (where the battery's charging cut-off voltage is increased to above 4.35V), overcharge safety issues become prominent. Specifically, compared to blocky and spherical silicon-carbon materials, this type of silicon-carbon has more complex and tortuous internal channels. When preparing this material by chemical vapor deposition, the silane gas diffusion path is long, making it prone to premature decomposition on the particle surface, forming loosely bonded floating silicon particles. When a battery is overcharged, the loosely structured floating silicon on the negative electrode surface undergoes a violent side reaction with the electrolyte, which accelerates the rupture and repair of the SEI film, continuously consumes active lithium, and leads to a surge in battery gas production and an increased risk of thermal runaway, resulting in a decrease in the battery's overcharge pass rate.

[0012] To further address the problem of decreased overcharge pass rate caused by floating silicon during the preparation of silicon-carbon materials in this invention, the present invention proposes the following solution: The first aspect of the present invention provides a battery, including an electrode assembly and an electrolyte, wherein the electrode assembly includes a positive electrode, a separator and a negative electrode stacked together; The negative electrode sheet includes a negative electrode active layer, which includes a silicon-carbon material. The cross-sectional profile of the silicon-carbon material has a first interior angle, denoted as B°, where B > 180°. The electrolyte comprises a linear carboxylic acid ester; The membrane includes a substrate layer and an organic coating on one or both sides of the substrate layer. The organic coating includes nitrogen-containing organic particles. The molecular structure of the nitrogen-containing organic particles includes nitrogen-containing heterocycles. The average particle size of the nitrogen-containing organic particles is denoted as A. A and B satisfy: 1 ​​≤ A / B ≤ 10; The charging cutoff voltage of the battery is greater than 4.35V.

[0013] In this invention, the linear carboxylic acid esters in the electrolyte have a slight solubility for nitrogen-containing organic particles, causing them to be slowly released from the separator and migrate to the surface of the negative electrode. Because the silicon-carbon material used in this invention (with a first interior angle greater than 180° in its cross-sectional profile) has open areas, these areas differ from the stress concentration zones at the sharp edges of irregular blocky silicon-carbon materials, and also from the lack of contact sites in spherical silicon-carbon materials, thus providing ideal adsorption and enrichment sites for free nitrogen-containing organic particles in the electrolyte. During charging and discharging, these nitrogen-containing organic particles enriched on the surface of the silicon-carbon material can react on the floating silicon surface, constructing a dense, nitrogen-rich protective layer in situ. This protective layer effectively passivates the surface activity of the floating silicon, inhibiting the repeated rupture and repair of the solid electrolyte interphase (SEI) film caused by the high activity of the floating silicon during battery cycling (especially under overcharge conditions), reducing the continuous consumption of active lithium and electrolyte, thereby significantly reducing the risk of battery gas generation and thermal runaway, and improving overcharge safety performance.

[0014] Meanwhile, nitrogen atoms in the protective layer can react with transition metal ions (such as Co) dissolved from the high-voltage positive electrode. 3+ This protective layer forms a coordination complex, blocking the catalytic destruction of the SEI film by transition metal ions and further stabilizing the anode interface. Furthermore, this protective layer forms in situ in an open area of ​​the silicon-carbon material, bonding firmly to the surface. It maintains good chemical stability and structural integrity even at high temperatures, continuously suppressing side reactions between the anode and electrolyte, reducing capacity decay and gas generation during high-temperature storage and cycling, thereby significantly improving the battery's high-temperature performance.

[0015] The present invention further specifies that the relationship between A and B satisfies: 1 ≤ A / B ≤ 10. The value of A / B can be 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, or any value within the range formed by the pairwise values ​​mentioned above.

[0016] It should be noted that when calculating using the A / B formula, only the numerical value is substituted, and the unit is not considered.

[0017] When the A / B ratio is within the above range, it can significantly improve the battery's overcharge safety performance and high-temperature storage and cycle performance. When the A / B value is too small (<1), that is, the average particle size A of the nitrogen-containing organic particles is relatively small, while the first inner angle B of the silicon-carbon material is relatively large (the silicon-carbon material is close to spherical, the surface tends to be flat, with fewer grooves and reduced pore tortuosity). At this time, the diffusion path of silane gas during deposition is shorter, the amount of floating silicon generated is less, and the defect scale and reactivity of the negative electrode surface are relatively low. However, because the particle size of the nitrogen-containing organic particles is too small, they are prone to agglomeration in the organic coating slurry, making it difficult to disperse evenly. This leads to uneven distribution of nitrogen-containing organic particles in the separator, affecting the pore structure of the separator and the uniform transport of lithium ions, thus affecting the battery's cycle performance. When the A / B value is too large (>10), that is, the average particle size A of the nitrogen-containing organic particles is relatively large, while the first inner angle B of the silicon-carbon material is relatively small (that is, the silicon-carbon material surface has more grooves and higher pore tortuosity). At this point, the long diffusion path of silane gas during chemical vapor deposition makes it prone to premature decomposition and deposition within the pores, resulting in uneven silicon deposition and the formation of a large amount of loosely structured floating silicon in the trench region. However, due to the relatively large particle size of nitrogen-containing organic particles, their contact sites with the electrolyte are limited, and the number of nitrogen-containing molecules released to the negative electrode surface is also limited. This makes it impossible to timely and adequately cover and passivate the large number of dispersed floating silicon active sites in the early stages of battery cycling, thus failing to form an effective protective layer and resulting in limited improvement in overcharge safety performance.

[0018] In some preferred embodiments, A and B satisfy: 2≤A / B≤7.

[0019] In some embodiments, the average particle size A is 200nm-2000nm. For example, the average particle size A can be 200nm, 300nm, 400nm, 600nm, 800nm, 1000nm, 1200nm, 1400nm, 1600nm, 1800nm, 2000nm, or any value within the range of any two of the above values. More preferably, A is 300nm-1000nm. The average particle size of the nitrogen-containing organic particles directly affects their dispersion state in the organic coating and their contact area with the electrolyte. When the average particle size of the nitrogen-containing organic particles is between 200nm and 2000nm, the nitrogen-containing organic particles have a suitable specific surface area. On the one hand, this allows for the formation of a uniform protective layer structure with appropriate porosity in the organic coating, ensuring smooth lithium-ion channels. On the other hand, it facilitates good contact with the electrolyte, thereby forming a protective layer of suitable thickness on the negative electrode surface, further improving the battery's fast-charging performance and overcharge safety.

[0020] It should be noted that the test method for the average particle size A of nitrogen-containing organic particles is as follows: On the image obtained by SEM observation of the organic coating surface, a square or rectangle with the smallest area tangent to a complete nitrogen-containing organic particle is drawn. That is, a square or rectangle with the edge of a complete nitrogen-containing organic particle tangent to the four sides of the square or rectangle is drawn. The side length of the square or the length of the rectangle is the particle size of the nitrogen-containing organic particle. The average value of the particle size of arbitrarily measured 100 nitrogen-containing organic particles on the organic coating surface is recorded as the average particle size.

[0021] In some embodiments, the first interior angle B is 200-300°. Further controlling the interior angle of the silicon-carbon material within this range avoids the problems of high specific surface area and increased side reactions caused by sharp edges, and also prevents it from becoming spherical, which would easily detach from the conductive network during cycling and accelerate cycle life decay.

[0022] "First interior angle B" refers to the angle formed by drawing two straight lines tangent to the cross-sectional profile of a silicon-carbon composite particle in a scanning electron microscope (SEM) image of the particle, starting from a point on the cross-sectional contour closer to the center of the particle. See [link to SEM image]. Figure 1 .

[0023] The first interior angle B refers to the angle between the two sides that make up the angle on one side inside the particle. If both sides are close to or straight, the angle between the two sides that make up the angle on one side inside the particle is directly measured. If the two sides of the angle contain curves, tangents are drawn along the two sides at the intersection point, and the angle between the two tangents inside the particle is measured.

[0024] In some embodiments, the linear carboxylic acid ester accounts for 10%-70% of the total mass of the electrolyte. For example, it can be 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, or any value within the range of any two of these values. Linear carboxylic acid esters include methyl formate, methyl acetate, methyl butyrate, propyl propionate, ethyl propionate, ethyl butyrate, propyl acetate, ethyl acetate, etc. Although nitrogen-containing organic particles are slightly soluble in the electrolyte, their solubility in linear carboxylic acid esters is slightly higher than that in carbonates. When the mass percentage of linear carboxylic acid esters is 10%-70%, the viscosity of the electrolyte is low, which facilitates the migration of nitrogen-containing organic particles to the negative electrode surface. This allows for the in-situ construction of a protective layer rich in nitrogen functional groups on the surface of silicon-carbon materials with specific internal angle morphology, thereby effectively passivating the highly active floating silicon on the surface of the silicon-carbon particles and suppressing their violent side reactions with the electrolyte under overcharge conditions. If the linear carboxylic acid ester content is too low (e.g., <10%), nitrogen-containing organic particles will have difficulty forming an effective protective layer on the negative electrode surface, leading to an increase in side reactions between the floating silicon and the electrolyte. If the content is too high (e.g., >70%), the poor electrochemical stability of the linear carboxylic acid ester at the negative electrode may trigger additional side reactions, especially at high voltages, which will further deteriorate the cycle life of the battery.

[0025] The content of linear carboxylic acid esters can be determined by methods conventional in the art, such as gas chromatography (GC), gas chromatography-mass spectrometry (GCMS), or liquid chromatography (LC).

[0026] In some embodiments, the nitrogen-containing organic particles comprise one or more of the following: 2-mercaptobenzimidazole, melamine cyanurate, uracil, 4,6-dimethyl-2-phenylpyrimidine, cytosine, 2,4-dimercaptopyrimidine, 2,4-dimercapto-5,6-diaminopyrimidine, 4-amino-2,6-dihydroxypyrimidine, melamine thiocyanate, polypyrrole, and sulfonated polytriazole. These specific types of nitrogen-containing organic particles possess nitrogen-containing heterocycles (such as imidazole rings, triazine rings, pyrimidine rings, pyrrole rings, etc.) in their molecular structure, which have abundant lone pairs of electrons. These heterocycles not only interact with the active sites on the negative electrode surface, constructing a stable interfacial film in situ, but also efficiently complex high-valence transition metal ions (such as Co) dissolved from the positive electrode. 3+ Co 4+ This prevents the SEI film from being catalytically decomposed on the negative electrode surface, thereby further reducing the side reactions between the floating silicon and the electrolyte.

[0027] In some embodiments, the nitrogen content in the organic coating on one side is 7%-49% by mass. For example, the nitrogen content can be 7%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 49%, or any value within the range of any two of these values. This nitrogen content range ensures that the organic coating applied to the separator has a sufficient total amount of nitrogen-containing organic particles to provide continuous protection throughout the battery's lifespan. If the nitrogen content is too low (<7%), the total amount of nitrogen-containing organic particles in the organic coating is insufficient, making it impossible to form a sufficiently dense and continuous nitrogen-containing protective layer on the silicon-carbon material surface. This fails to effectively suppress the damage of the SEI film by highly active floating silicon, and the effect of improving battery overcharge safety is not significant. If the nitrogen content is too high (>49%), the nitrogen-containing organic particles may occupy too much of the share of binder and other auxiliary components, affecting the adhesion between the organic coating and the substrate layer as well as its own mechanical strength. During the battery charging and discharging process, the coating may fall off, damaging the stability of the separator. This makes it impossible to continuously supply a sufficient amount of nitrogen-containing organic particles in the later stages of battery cycling to repair the SEI film damage caused by floating silicon activity on the negative electrode surface.

[0028] Nitrogen can be measured using energy-dispersive X-ray spectroscopy (EDS). Specifically, the organic coating surface is first cleaned and dried with solvent, the system is calibrated using a standard sample containing nitrogen, and then EDS surface scanning analysis is performed on the surface of the organic coating under a scanning electron microscope (SEM) to obtain the nitrogen content.

[0029] In some embodiments, the organic coating further includes a first binder, the weight percentage of which is 1%-10% based on the total weight of the organic coating. For example, it can be 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, or any value within the range of any pair of values ​​mentioned above. The thickness of the organic coating is 0.2 μm-5 μm, for example, it can be 0.2 μm, 0.5 μm, 1.0 μm, 1.5 μm, 2.0 μm, 2.5 μm, 3.0 μm, 3.5 μm, 4.0 μm, 4.5 μm, 5.0 μm, or any value within the range of any pair of values ​​mentioned above. By introducing an appropriate amount of binder and controlling the thickness of the organic coating, the adhesion strength between organic particles and between the coating and the substrate is enhanced, preventing the organic coating from detaching during battery assembly and operation. Furthermore, the thickness of the organic coating is limited to a range that does not significantly increase lithium-ion transport impedance, ensuring the integrity of the organic coating structure while maintaining good rate performance and cycle performance.

[0030] In some embodiments, the average aspect ratio of the nitrogen-containing organic particles is denoted as C, and C and B satisfy: B / C = 70-330. For example, B / C can be any point value in the range of 70, 80, 90, 100, 110, 120, 150, 180, 200, 240, 260, 280, 300, 320, 330, or any of the above two-to-one values, preferably B / C = 80-200.

[0031] Controlling the B / C ratio within the aforementioned range can further address the overcharge gas generation and thermal runaway issues caused by the high activity of floating silicon under high voltage conditions. When the ratio is too large (i.e., B is too large or C is too small), both silicon-carbon and nitrogen-containing organic particles tend to be spherical. During charge-discharge cycles, the silicon-carbon material is prone to disconnection from the current collector / conductive agent in some areas, resulting in dead zones that do not participate in electrochemical reactions and causing cycle capacity decay. Furthermore, if the nitrogen-containing organic particles are too small, they are prone to agglomeration, leading to uneven organic coatings and difficulty in ensuring lithium-ion transport, thereby impairing cycle performance. When the ratio is too small (i.e., B is too small or C is too large), the silicon-carbon material has excessively tortuous pores, generating a large amount of loosely structured floating silicon in the trench areas. At the same time, the organic particles are fibrous, have low strength, and are easily broken, making the membrane structure easily damaged. As a result, an effective protective layer cannot be formed on the surface of the floating silicon, and the improvement in overcharge safety performance is limited.

[0032] In some embodiments, the average aspect ratio of the nitrogen-containing organic particles is denoted as C = 1.05-3, for example, it can be 1.05, 1.3, 1.5, 1.8, 2, 2.2, 2.6, 2.8, 3 or any point value within the range of the above two-to-one values.

[0033] By controlling the aspect ratio of nitrogen-containing organic particles within the above range, the nitrogen-containing organic particles are less likely to break under stress during battery manufacturing and charging / discharging due to excessive flatness or strip shape, thus damaging the integrity of the coating. At the same time, the nitrogen-containing organic particles are also prevented from being too close to spherical, which would lead to poor coating contact and the formation of a non-dense and uneven network. This ensures the uniform transport of lithium ions while maintaining the stability of the separator structure and suppressing lithium dendrite piercing, thereby further improving cycle life and safety.

[0034] In this invention, the average aspect ratio of the nitrogen-containing organic particles can be obtained by the following method: using a scanning electron microscope, the surface of the organic coating is observed at a magnification of 10,000 times, the organic particles in the field of view are identified, and the outline of the organic particles is identified using image software ImageJ. The long side of the smallest rectangle tangent to the nitrogen-containing organic particles is L1, and the short side of the smallest rectangle tangent to the nitrogen-containing organic particles is W1. Then, the aspect ratio of the nitrogen-containing organic particles is A1 = L1 / W1 (wherein, when the smallest rectangle tangent to the nitrogen-containing organic particles is a square, the aspect ratio of the nitrogen-containing organic particles is 1). The aspect ratio of 100 nitrogen-containing organic particles is randomly measured, and the average value is taken as the average aspect ratio. It can be understood that when there are fewer than 100 nitrogen-containing organic particles in the field of view, the surface of the nitrogen-containing organic particles can be observed multiple times, and the average of the aspect ratios of the total 100 nitrogen-containing organic particles can be set as the average aspect ratio.

[0035] In some embodiments, the specific surface area of ​​the nitrogen-containing organic particles is 5-30 g / m². 2 For example, it can be 5g / m³. 2 7g / m 2 10g / m 2 15g / m 2 20g / m 2 25g / m 2 30g / m 2 Or any value within the range formed by the pairwise values ​​mentioned above. Controlling the specific surface area of ​​nitrogen-containing organic particles within the above range is beneficial to increasing their contact area with the electrolyte, thereby facilitating the formation of a complete and uniform protective layer on the negative electrode surface. This effectively passivates the high reactivity of floating silicon, inhibits repeated rupture and repair of the SEI film, and can further reduce the gas production and thermal runaway risk under overcharge conditions.

[0036] The specific surface area of ​​the nitrogen-containing organic particles is measured using conventional methods in the field, such as the nitrogen adsorption-desorption method (BET method). It should be noted that the specific surface area measured is the original surface area of ​​the nitrogen-containing organic particles, not the surface area when the membrane is fabricated. In some embodiments, the average particle size of the silicon-carbon material is 4.5 μm-13.5 μm, for example, it can be any value within the range of 4.5 μm, 5 μm, 5.5 μm, 6 μm, 6.5 μm, 7 μm, 7.5 μm, 8 μm, 8.5 μm, 9 μm, 9.5 μm, 10 μm, 10.5 μm, 11 μm, 11.5 μm, 12 μm, 12.5 μm, 13 μm, 13.5 μm, or any value within the range of any two of the above values. Controlling the average particle size of the silicon-carbon material within the above range is beneficial for achieving a good balance between suppressing negative electrode side reactions and rate performance. Specifically, when the average particle size D is within the aforementioned range, silane gas can diffuse sufficiently and deposit uniformly along the porous carbon framework during chemical vapor deposition. This avoids premature decomposition and pore blockage due to excessively long gas diffusion paths caused by excessively large particle sizes, effectively suppressing the excessive formation of surface-floating silicon and reducing the risk of gas generation and thermal runaway. Simultaneously, this particle size range helps maintain a reasonable specific surface area, preventing a significant increase in specific surface area and exacerbated side reactions due to excessively small particle sizes. This reduces the continuous consumption of active lithium and electrolyte, improving battery cycle stability and high-temperature performance. Furthermore, silicon-carbon materials within this particle size range can form a good conductive network and ion transport channels in the electrode, which is beneficial for maintaining high compaction density and rate performance.

[0037] The average particle size of silicon-carbon materials can be obtained through SEM testing, for example, by referring to the aforementioned method for measuring the average particle size of nitrogen-containing organic particles.

[0038] In some embodiments, the silicon content in the negative electrode active layer is 2-50% by mass, for example, it can be 2%, 5%, 8%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, or any value within the range of any two of the above values. Controlling the silicon content within this range helps to achieve a good balance between battery energy density and cycle stability. Specifically, when the silicon content S is within the above range, the silicon-carbon material can provide a significant capacity contribution to the negative electrode, ensuring the battery has a high energy density and avoiding the problem of insufficient capacity of the negative electrode active material and limited energy density improvement due to excessively low silicon content. Simultaneously, this silicon content range allows the carbon skeleton to effectively constrain the volume expansion stress of silicon during charging and discharging, preventing excessively high silicon content from causing a surge in volume expansion, making it difficult for the carbon skeleton to constrain the silicon, leading to particle pulverization and structural failure, thereby maintaining the structural integrity of the negative electrode active layer and the stability of the conductive network. Furthermore, at this silicon content, silane gas can fully penetrate and deposit inside the porous carbon skeleton during chemical vapor deposition, avoiding premature decomposition and blockage of some silicon at the pores on the carbon skeleton surface due to excessive silicon content, thus reducing side reactions caused by floating silicon detaching from the protection of the carbon skeleton.

[0039] The method for testing the silicon content in the negative electrode active layer is as follows: After discharging the battery to 0% SOC, the negative electrode sheet is disassembled and soaked in DMC solvent for 12 hours, followed by rinsing with DMC solvent to remove the lithium salt adhering to the negative electrode sheet. After drying, the negative electrode sheet is subjected to high-temperature treatment at 400℃ in an inert atmosphere for 2 hours (e.g., in a tube furnace under nitrogen or argon atmosphere). The negative electrode active layer can then be peeled off from the negative electrode current collector, and the negative electrode active layer is collected as a test sample. Using a thermogravimetric analyzer (e.g., a TGA 550 thermogravimetric analyzer), the test sample amount is 5mg-15mg. Under an air or oxygen atmosphere, the temperature is increased from room temperature (25℃) to 900℃ at a rate of 10℃ / min, and held at 900℃ for 40 minutes. This allows the non-silicon components in the negative electrode active layer to volatilize while the silicon is fully oxidized to silicon dioxide. Weigh the residual material. The silicon content in the negative electrode active layer can be obtained by the following formula: Silicon content in the negative electrode active layer = 7 × mass of residual material / (15 × mass of test sample).

[0040] In some embodiments, the positive electrode sheet includes a positive electrode active layer, the positive electrode active layer includes a positive electrode active material, and the positive electrode active material includes lithium cobalt oxide; the lithium cobalt oxide is O3-phase lithium cobalt oxide, and the O3-phase lithium cobalt oxide contains at least one of the elements Al, Mg, Y, La, Ti, and Zr. "O3-phase lithium cobalt oxide" refers to a lithium cobalt oxide crystal structure having an α-NaFeO2 type layered structure, with oxygen atoms arranged in a cubic close-packed configuration and lithium ions occupying the interstices of the oxygen octahedrons.

[0041] In some embodiments, the mass content of Al element in the positive electrode active material is 4500 ppm to 15000 ppm, for example, it can be any point value within the range of 4500 ppm, 5000 ppm, 6000 ppm, 7000 ppm, 8000 ppm, 9000 ppm, 10000 ppm, 11000 ppm, 12000 ppm, 13000 ppm, 14000 ppm, 15000 ppm or any point value within the range of the above two points.

[0042] In some embodiments, the mass content of Mg in the positive electrode active material is 200 ppm to 1600 ppm, for example, it can be any value within the range of 200 ppm, 300 ppm, 400 ppm, 500 ppm, 600 ppm, 700 ppm, 800 ppm, 900 ppm, 1000 ppm, 1100 ppm, 1200 ppm, 1300 ppm, 1400 ppm, 1500 ppm, 1600 ppm or any value within the range of the above two values.

[0043] In some embodiments, the mass content of Y element in the positive electrode active material is 100 ppm to 1000 ppm, for example, it can be any point value in the range of 100 ppm, 200 ppm, 300 ppm, 400 ppm, 500 ppm, 600 ppm, 700 ppm, 800 ppm, 900 ppm, 1000 ppm or any point value in the range of the above two points.

[0044] In some embodiments, the mass content of La element in the positive electrode active material is 100ppm-1000ppm, for example, it can be 100 ppm, 200 ppm, 300 ppm, 400 ppm, 500 ppm, 600 ppm, 700 ppm, 800 ppm, 900 ppm, 1000 ppm or any point value in the range of the above two points.

[0045] In some embodiments, the mass content of Ti element in the positive electrode active material is 100ppm-1600ppm, for example, it can be any point value within the range of 100 ppm, 200 ppm, 300 ppm, 400 ppm, 500 ppm, 600 ppm, 700 ppm, 800 ppm, 900 ppm, 1000 ppm, 1100 ppm, 1200 ppm, 1300 ppm, 1400 ppm, 1500 ppm, 1600 ppm or any point value within the range of the above two points.

[0046] In some embodiments, the mass content of Zr element in the positive electrode active material is 40ppm-500ppm, for example, it can be any value within the range of 40ppm, 60ppm, 80ppm, 100ppm, 200ppm, 300ppm, 400ppm, 500ppm or any value within the range of the above two values.

[0047] Specifically, on the one hand, during overcharging, the aforementioned doping elements (at least one of Al, Mg, Y, La, Ti, and Zr) tend to enter the lithium cobalt oxide lattice, suppressing interlayer slip and irreversible phase transitions under high delithiation states, and maintaining the integrity of the layered structure of lithium cobalt oxide. On the other hand, the doping elements are easily enriched on the particle surface, forming a stable surface element doping protective layer, which can effectively suppress cobalt ion dissolution, slow down the oxidative decomposition of the electrolyte on the positive electrode surface, and reduce the lattice oxygen evolution activity under high voltage, thereby improving the positive electrode stability, cycle stability, and overcharge safety.

[0048] The mass content of Al, Mg, Y, La, Ti, and Zr elements can be tested using the following methods: The battery was disassembled, the positive electrode was removed, the lithium salt attached to the positive electrode was removed, the positive electrode active layer was scraped off and sieved, and the mass content of doped elements in lithium cobalt oxide was measured by inductively coupled plasma (ICP).

[0049] In some embodiments, the positive electrode sheet includes a single-sided region, wherein one side surface of the positive current collector in the single-sided region is provided with a positive active layer, and the other side surface is not provided with a positive active layer.

[0050] In wound batteries, the positive electrode single-sided area refers to the single-sided coating area (more commonly the winding tail) set at both ends of the positive electrode sheet along its length. This single-sided coating area is located at the beginning or end of the winding of the positive electrode sheet, and its length is 0.5% to 5% of the total length of the positive electrode sheet. In stacked batteries, the positive electrode single-sided area refers to the outermost single-sided positive electrode sheet, where the positive active material layer is coated only on the side with the positive current collector, while the opposite side is uncoated. Within this single-sided area, the exposed current collector surface without the positive active layer is used to connect tabs or adapters to form an external electrical connection; while the surface with the positive active layer faces inwards and is positioned opposite the separator and negative electrode sheet.

[0051] In the single-sided region, a protective layer is disposed on the surface of the positive electrode active layer away from the positive electrode current collector. The protective layer comprises inorganic particles, which include one or more of metal nitrides, metal oxides, metal hydroxides, metal carbides, and metal borides. For example, the inorganic particles may be selected from alumina (Al2O3), titanium oxide (TiO2), zirconium oxide (ZrO2), silicon oxide (SiO2), manganese oxide (MnO2), magnesium oxide (MgO), nickel oxide (NiO), aluminum hydroxide (AlOOH), boehmite (γ-AlOOH), magnesium hydroxide (Mg(OH)2), titanium nitride (TiN), boron nitride (BN), aluminum nitride (AlN), magnesium nitride (Mg3N2), silicon nitride (Si3N4), silicon carbide (SiC), boron carbide (B4C), titanium carbide (TiC), tungsten carbide (WC), titanium boride (TiB2), zirconium boride (ZrB2), tungsten boride (WB2), molybdenum boride (MoB2), etc. Preferred inorganic particles include Al2O3, AlOOH, TiO2, ZrO2, SiO2, and MnO. 2、 At least one of MgO, Si3N4, and BN.

[0052] These inorganic particles have high thermal conductivity. When a battery is overcharged, the collapse of the positive electrode material structure releasing oxygen and the oxidative decomposition of the electrolyte release a large amount of heat. Conventional electrode coatings contain low thermal conductivity in the positive electrode active material and binder, causing heat to easily accumulate inside the electrode, forming localized hot spots. This accelerates separator shrinkage and damage to the positive electrode electrolyte interface (CEI) film. This invention introduces a protective layer containing highly thermally conductive inorganic particles on the surface of the positive electrode active layer. This allows for the rapid dissipation of heat accumulated during overcharging to the current collector or the external environment, reducing the temperature inside the electrode, alleviating localized hot spots, and further reducing the risk of battery thermal runaway, thus improving overcharge safety.

[0053] In some embodiments, the inorganic particles in the protective layer constitute 50 wt% to 95 wt% by mass, for example, 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, 95%, or any value within the range of any pair of values ​​mentioned above. Maintaining the inorganic particle mass percentage within this range ensures that the protective layer possesses sufficient hardness, strength, and thermal conductivity, while retaining a small amount of binder to maintain adhesion to the positive electrode active layer.

[0054] In some embodiments, the average particle size of the inorganic particles is 0.1 μm-2 μm, for example, 0.1 μm, 0.2 μm, 0.4 μm, 0.6 μm, 0.8 μm, 1.0 μm, 1.2 μm, 1.4 μm, 1.6 μm, 1.8 μm, 2.0 μm, or any value within the range of any pair of values ​​mentioned above. Controlling the average particle size of the inorganic particles within this range is beneficial for improving thermal safety performance while enabling the battery to possess both excellent ion transport performance and high energy density characteristics. Specifically, when the average particle size is within this range, the inorganic particles can achieve uniform dispersion in the slurry, avoiding severe agglomeration problems caused by excessively small particle sizes. This results in the formation of a complete and uniform protective layer on the surface of the positive electrode active layer, ensuring effective heat dissipation and stable protection of the positive electrode interface. Simultaneously, this particle size range will not excessively block the lithium-ion transport channels between the positive electrode materials, which is beneficial for maintaining low electrode polarization and good rate performance. In addition, the particle size is moderate, which will not occupy too much space of active material or significantly increase the thickness of the positive electrode due to excessive particle size, thus helping to maintain a high energy density.

[0055] In some embodiments, the thickness of the protective layer is 0.5 μm-5 μm. For example, it can be 0.5 μm, 1 μm, 2 μm, 3 μm, 4 μm, 5 μm, or any value within the range of any two of the above values. Within this range, the protective layer thickness provides sufficient protection, heat dissipation, and supplementary CEI formation without causing excessive additional impedance to lithium-ion transport, thus ensuring the battery's rate performance.

[0056] In some embodiments, the protective layer further includes an adhesive and a conductive agent. The adhesive includes one or more of polyvinylidene fluoride, styrene-butadiene rubber latex, sodium carboxymethyl cellulose, polyacrylic acid, polyurethane, polyamide, polyvinyl alcohol, polyethyleneimine, and polyimide; the conductive agent includes one or more of carbon black (Super P, Ketjen black), carbon nanotubes, and graphene.

[0057] In some embodiments, the electrolyte further includes a sulfur-containing additive, the sulfur-containing additive comprising... , , , or At least one of the following. Sulfur-containing additives can synergistically interact with nitrogen-containing organic particles, silicon-carbon anodes, and linear carboxylic acid ester electrolytes in the system, further improving overcharge safety and high-temperature performance. Specifically, during the first charge and discharge process, sulfur-containing additives preferentially reduce and form a stable positive electrode electrolyte (CEI) film on the positive electrode surface, effectively inhibiting the dissolution of transition metal ions and the release of active oxygen in the positive electrode material under high voltage, thereby reducing the catalytic damage of the anode SEI film by transition metal ions from the source; at the same time, sulfur-containing additives can also participate in the formation of a dense and stable SEI film on the anode surface, enhancing its mechanical strength and chemical stability, reducing the repeated rupture and repair of the SEI film caused by high-activity defects such as floating silicon on the silicon-carbon anode surface, and reducing the continuous consumption of active lithium and electrolyte.

[0058] In some embodiments, the sulfur-containing additive accounts for 0.1%-6% of the total mass of the electrolyte, for example, it can be 0.1%, 0.5%, 1%, 2%, 3%, 4%, 5%, 6% or any value within the range of the above two-to-one values.

[0059] If the content of sulfur-containing additives is too low, a continuous and dense interface layer cannot be formed on the positive and negative electrode surfaces. The exposed floating silicon and other interfaces will continue to undergo side reactions with the electrolyte during cycling, leading to continuous consumption of active lithium and increased gas generation and heat release. If the content of sulfur-containing additives is too high, the formed CEI and SEI films will become excessively thick, and the interface impedance will increase significantly, resulting in a decrease in battery rate performance and a reduction in discharge capacity.

[0060] The content of sulfur-containing additives can be obtained by gas chromatography (GC), gas chromatography-mass spectrometry (GCMS), or liquid chromatography (LC).

[0061] In some embodiments, the electrolyte further includes nitrile additives, including at least one selected from benzonitrile, succinic anionyl, fluorobenzonitrile, adiponitrile, 1,3,6-hexanetrionitrile, glycerol trionitrile, 1,4-dicyano-2-butene, and ethylene glycol bis(propionitrile) ether. The cyano group in the nitrile additive molecule contains a lone pair of electrons, which can form a strong coordination bond with cobalt atoms on the surface of the lithium cobalt oxide cathode material, thereby preferentially adsorbing onto the active sites of the cathode and forming a stable adsorption layer or cathode electrolyte interface (CEI) film on the cathode surface. This CEI film can effectively inhibit the structural degradation of lithium cobalt oxide under high voltage, reduce the dissolution of transition metal ions and the oxidative decomposition of the electrolyte at high potentials, thereby reducing the risk of catalytic damage to the negative electrode SEI film from the positive electrode side. Meanwhile, nitrile additives mainly act on the positive electrode interface and will not have a negative impact on the interface structure of the negative electrode. Therefore, they can form a synergistic protection mechanism with the protective layer formed on the negative electrode side by nitrogen-containing organic particles slowly released from the organic coating of the separator, and jointly improve the overcharge safety performance and high temperature performance of the battery under the condition that the charging cut-off voltage is greater than 4.35V.

[0062] In some embodiments, the nitrile additive accounts for 0.5%-8% of the total mass of the electrolyte, for example, it can be 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 5%, 6%, 7%, 8%, or any value within the range of the above pairs. Controlling the content of the nitrile additive within the above range is beneficial for forming a stable protective layer at the positive electrode interface, while avoiding adverse effects on the negative electrode interface and rate performance. If the content of the nitrile additive is too low (e.g., below 0.5%), a continuous and complete adsorption layer cannot be formed on the positive electrode surface, resulting in continuous exposure of the active sites on the lithium cobalt oxide surface. Under high voltage, irreversible phase transitions occur, large amounts of cobalt ions dissolve, and the electrolyte undergoes oxidative decomposition. Furthermore, the dissolved cobalt ions migrate to the negative electrode, accelerating the destruction of the SEI film, leading to a sharp increase in gas production and the risk of thermal runaway during overcharging. If the content of nitrile additives is too high (e.g., above 8%), the reduction of nitrile molecules on the negative electrode surface will be insufficient, which will instead damage the stability of the negative electrode interface, resulting in a loose SEI film and increased impedance. At the same time, the excessive amount of nitrile additives will form an excessively thick adsorption layer on the positive electrode surface, which will increase the resistance to lithium ion desolvation and crossing the CEI film, leading to a decrease in battery rate performance.

[0063] In some embodiments, the substrate layer includes a three-dimensional porous network structure with an average pore size of 25nm-75nm. For example, it can be 25nm, 30nm, 35nm, 40nm, 45nm, 50nm, 55nm, 60nm, 65nm, 70nm, 75nm, or any value within the range of any two of these values. Controlling the pore size of the substrate layer within the 25nm-75nm range is beneficial for good electrolyte wetting, maintaining good rate performance, and further enhancing battery safety in the event of overcharging and thermal runaway, in conjunction with the micropore melting closure mechanism. If the pore size is too small, the migration resistance of lithium ions within the separator channels increases significantly, leading to increased battery internal resistance and decreased rate performance. If the pore size is too large, micropore melting closure at high temperatures may not completely seal all channels, and residual conductive paths may cause thermal runaway protection failure.

[0064] In some embodiments, the substrate layer comprises one or more of the following polymers: polyolefin, polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene copolymer, polyvinyl chloride, polytetrafluoroethylene, polyacrylonitrile, polyimide, polyetherimide, polyethylene terephthalate, polybutylene terephthalate, poly(p-phenylene terephthalamide), poly(m-phenylene isophthalamide), polybenzimidazole, polysulfone, polyketone, and derivatives of the above polymers.

[0065] In some embodiments, an organic coating is provided on both sides of the diaphragm substrate, and an adhesive layer is provided on the surface of the organic coating away from the substrate; In some embodiments, an organic coating is provided on one side surface of the diaphragm substrate, and an adhesive layer is provided on the surface of the organic coating away from the substrate, and an adhesive layer is also provided on the other side surface of the substrate where no organic coating is provided.

[0066] In some embodiments, the adhesive layer includes a first particle and a second particle, the first particle being dispersed and the second particle being agglomerated, the first particle being composed of an acrylate polymer.

[0067] In some embodiments, the acrylate polymers include one or more of the following: polymethyl methacrylate, polyethylhexyl acrylate, polybutyl acrylate, acrylate monomer-acrylonitrile copolymer, styrene-acrylate monomer copolymer, acrylate monomer-acrylonitrile-ethylene copolymer, styrene-acrylate monomer-acrylonitrile copolymer, acrylate monomer-ethylene copolymer, ethylhexyl acrylate-methyl methacrylate copolymer, butyl acrylate-methyl methacrylate copolymer, methyl acrylate-N,N-dimethylacrylamide copolymer, ethyl acrylate-2-(diethylamino)ethyl acrylate copolymer, ethyl acrylate-N,N-diethylacrylamide copolymer, and ethyl acrylate-2-(diethylamino)ethyl acrylate.

[0068] In some embodiments, the second particle comprises one or more of the following: polyvinylidene fluoride, polytetrafluoroethylene, polyvinyl fluoride, polyhexafluoropropylene, fluoroethylene-hexafluoropropylene copolymer, vinylidene fluoride-hexafluoropropylene copolymer, tetrafluoroethylene-hexafluoropropylene copolymer, acrylate monomer-acrylonitrile copolymer, styrene-acrylate monomer copolymer, acrylate monomer-acrylonitrile-ethylene copolymer, acrylate monomer-ethylene copolymer, styrene-acrylate monomer-acrylonitrile copolymer, ethylhexyl acrylate-methyl methacrylate copolymer, butyl acrylate-methyl methacrylate copolymer, methyl acrylate-N,N-dimethylacrylamide copolymer, ethyl acrylate-2-(diethylamino)ethyl acrylate copolymer, ethyl acrylate-N,N-diethylacrylamide copolymer, and ethyl acrylate-2-(diethylamino)ethyl acrylate.

[0069] The present invention also provides a method for preparing the above-mentioned positive electrode sheet, the method comprising the following steps: Positive electrode preparation: O3 phase lithium cobalt oxide positive electrode active material, conductive agent (such as acetylene black, carbon nanotubes), and binder (such as polyvinylidene fluoride) are mixed in a solvent (such as N-methylpyrrolidone, NMP) at a predetermined mass ratio and dispersed and stirred at high speed to obtain a positive electrode slurry. The slurry is uniformly coated onto the surface of an aluminum foil current collector using a coating machine, followed by baking, drying, rolling, and slitting to obtain the positive electrode sheet. If a positive electrode protective layer is required, after coating and drying the positive electrode active layer, a slurry containing inorganic particles (such as boehmite), conductive agent, and binder can be coated on the surface of the positive electrode active layer away from the aluminum foil on one side. After drying again, a positive electrode sheet with a protective layer is obtained.

[0070] This invention also provides a method for synthesizing silicon-carbon materials: spherical porous carbon is prepared through steps such as template method, hydrothermal method, and activation using a carbon source (e.g., phenolic resin microspheres). Then, silane gas (e.g., SiH4) is introduced at a suitable temperature (e.g., 500-600℃) via chemical vapor deposition (CVD) to thermally deposit silicon in the pores and surface of the porous carbon. Subsequently, carbon source gas can be introduced again for carbon coating modification. Finally, a silicon-carbon composite material with the morphology (inner angle B°) and composition (silicon content S) required by this invention is obtained.

[0071] The silicon-carbon material provided by this invention can also be obtained through market purchase.

[0072] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0073] Unless otherwise specified, all materials and reagents used in the following examples are commercially available.

[0074] The present invention will now be described in detail with reference to specific embodiments, which are intended to understand rather than limit the invention.

[0075] The lithium-ion batteries in the following examples and comparative examples were all prepared according to the following methods.

[0076] Example 1a The preparation of a battery includes the following steps: 1) Preparation of positive electrode sheet Lithium cobalt oxide (CCO) as the positive electrode active material, polyvinylidene fluoride (PVDF) as the binder, acetylene black as the conductive agent, and carbon nanotubes were mixed at a mass ratio of 97.2:1.7:0.6:0.5 and added to N-methylpyrrolidone (NMP) solvent. The mixture was stirred under vacuum to form a positive electrode slurry, which was then coated onto the surface of a 9 μm thick aluminum foil current collector. The slurry was dried in a vacuum drying oven at 120°C for 8 hours and then slit by roll forming to obtain the positive electrode sheet. The positive electrode active material is O3-phase lithium cobalt oxide, containing Al (7500 ppm) and Mg (1100 ppm).

[0077] 2) Preparation of negative electrode sheet Silicon-carbon composite material (first inner angle 250°), artificial graphite, lithium carboxymethyl cellulose, waterborne polyurethane adhesive, and carbon nanotubes were mixed in a mass ratio of 19.2:76.8:1.5:2:0.5. Deionized water was added and stirred to form a negative electrode slurry. The slurry was then uniformly coated onto both sides of a copper foil using a coating machine, with the surface density on one side controlled at 4.5 mg / cm². 2 After drying, cold pressing, and slitting, the negative electrode sheet is obtained.

[0078] 3) Diaphragm preparation Melamine cyanurate (nitrogen-containing organic particles with an average particle size A of 1000 nm and a specific surface area BET of 8.5 m²) was used. 2 Polyvinylidene fluoride (PVDF) and polymethyl methacrylate (PMMA) are mixed at a mass ratio of 96:4 and thoroughly stirred in deionized water to obtain a slurry with a solid content of 25%. This slurry is uniformly coated onto one side of the substrate layer using a gravure roller, and dried in a multi-section oven at 60°C to form the first coating (i.e., the organic coating). Polyvinylidene fluoride is dissolved in N,N-dimethylacetamide, thoroughly stirred, and then coated onto the surface of the first coating and the other side of the substrate layer using a gravure roller. After water extraction and drying at 60°C, a second coating is formed on the surface of the first coating, and a third coating is formed on the other side of the substrate layer. The weight percentage of the first binder (PMMA) in the organic coating is approximately 4%, and the thickness of the organic coating is approximately 2 μm. The average particle size A of the nitrogen-containing organic particles is 1000 nm, and the average aspect ratio C is approximately 1.5. The mass content of nitrogen in a single-sided organic coating is approximately 28%. The substrate layer is a three-dimensional porous network structure of polyethylene with an average pore size of approximately 50 nm. In this embodiment, A / B ≈ 1000 / 250 = 4.

[0079] 4) Electrolyte In an argon-protected glove box (H2O < 1 ppm, O2 < 1 ppm), ethylene carbonate (EC), propylene carbonate (PC), diethyl carbonate (DEC), and ethyl propionate were mixed thoroughly in a mass ratio of 10:10:19.4:60.6 to obtain an organic solvent. Then, lithium hexafluorophosphate (14% by weight of the total electrolyte), fluoroethylene carbonate (FEC) (15% by weight of the total electrolyte), and a sulfur-containing additive (3% by weight of the total electrolyte) were added to the organic solvent. The electrolyte is prepared by mixing 2% nitrile additive (butadiene nitrile) with water and free acid, and after passing the tests, the desired electrolyte is obtained.

[0080] 5) Preparation of lithium-ion batteries The positive electrode sheet of step 1), the separator of step 3), and the negative electrode sheet of step 2) are stacked and wound in sequence. The wound core is put into an aluminum-plastic film of matching size and sealed. The electrolyte of step 4) is injected under vacuum conditions and vacuum sealed. The battery is obtained through standing, formation and sorting processes.

[0081] Example 6: Referring to Example 1, the difference is that: butadionitrile is replaced with the same mass of 1,3,6-hexanetrionitrile, and... Change to the same quality .

[0082] The preparation of the remaining embodiments and comparative examples was carried out in accordance with Example 1a, with the differences shown in Tables 1 and 2 below: In Tables 1 and 2, the value of A in Example 1 was changed by adjusting the average particle size of the nitrogen-containing organic particles, and the value of B was changed by purchasing silicon-carbon materials with different first inner angles, thereby controlling the value of A / B. Example 2 group controlled the B / C value by adjusting the first inner angle and the average aspect ratio of the nitrogen-containing organic particles; Example 3: The types of nitrogen-containing organic particles were changed; Example 4: The mass content of nitrogen element was changed; Example 5 group changed the content of linear carboxylic acid esters in the electrolyte.

[0083] The difference between Comparative Example 1 and Example 1a lies in the preparation of the diaphragm. Specifically, the organic coating of the diaphragm does not contain nitrogen-containing organic particles, that is, only a polymethyl methacrylate coating is used. Comparative Examples 2 and 3 changed the value of A by adjusting the average particle size of nitrogen-containing organic particles and changed the value of B by purchasing silicon-carbon materials with different first inner angles, thereby controlling the value of A / B. In Comparative Example 4, the value of B is less than 180.

[0084] Table 1 Table 2 Note: " / " indicates that the component was not added or the performance was not measured.

[0085] The batteries prepared in the examples and comparative examples were tested as follows: 1. Overcharge test: Under ambient temperature conditions of (25±5)℃, the fully discharged battery was charged at a constant current of 3C to 5.0V, then switched to constant voltage charging. Charging was stopped after 7 hours or when the battery surface temperature stabilized (temperature difference ≤2℃ within 45 minutes). The criterion for passing the test was that the battery did not catch fire or explode. Ten samples were tested for each example or comparative example, and the number of batteries N that passed the test was recorded as N / 10.

[0086] 2. High-temperature cycling stability test Under ambient temperature (45±5)℃, the battery was charged at a constant current of 0.5C to 4.53V, then charged at a constant voltage of 0.2C, and left to stand for 10 minutes; it was then discharged at 0.2C to 3V and left to stand for 10 minutes. The battery capacity retention rate was obtained by calculating the ratio of the remaining capacity to the initial capacity after 500 cycles.

[0087] The test results are recorded in Table 3. Table 3 As shown in Table 3, the battery of the present invention achieves a synergistic improvement in battery overcharge safety performance and high-temperature cycle performance by using silicon-carbon material with a first interior angle greater than 180° and limiting 1≤A / B≤10.

[0088] It should be noted that, in this document, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitations, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes that element. Furthermore, it should be noted that the scope of the methods and apparatuses in the embodiments of this application is not limited to performing functions in the order shown or discussed, but may also include performing functions substantially simultaneously or in the reverse order, depending on the functions involved. For example, the described methods may be performed in a different order than described, and various steps may be added, omitted, or combined. Additionally, features described with reference to certain examples may be combined in other examples.

[0089] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A battery, characterized in that, The electrode assembly includes an electrode assembly and an electrolyte, wherein the electrode assembly includes a positive electrode, a separator, and a negative electrode stacked together. The negative electrode sheet includes a negative electrode active layer, which includes a silicon-carbon material. The cross-sectional profile of the silicon-carbon material has a first interior angle, denoted as B°, where B > 180°. The electrolyte comprises a linear carboxylic acid ester; The membrane includes a substrate layer and an organic coating on one or both sides of the substrate layer. The organic coating includes nitrogen-containing organic particles. The molecular structure of the nitrogen-containing organic particles includes nitrogen-containing heterocycles. The average particle size of the nitrogen-containing organic particles is denoted as A. A and B satisfy: 1 ​​≤ A / B ≤ 10; The charging cutoff voltage of the battery is greater than 4.35V.

2. The battery according to claim 1, characterized in that, A and B satisfy: 2≤A / B≤7; Preferably, the average particle size A is 200nm-2000nm, more preferably A is 300nm-1000nm; Preferably, the first interior angle B = 200-300°; Preferably, the linear carboxylic acid ester accounts for 10%-70% of the total mass of the electrolyte.

3. The battery according to claim 1, characterized in that, The nitrogen-containing organic particles include one or more of the following: 2-mercaptobenzimidazole, melamine cyanurate, uracil, 4,6-dimethyl-2-phenylpyrimidine, cytosine, 2,4-dimercaptopyrimidine, 2,4-dimercapto-5,6-diaminopyrimidine, 4-amino-2,6-dihydroxypyrimidine, melamine thiocyanate, polypyrrole, and sulfonated polytriazole. Preferably, the nitrogen content in the organic coating on one side is 7%-49% by mass.

4. The battery according to claim 1, characterized in that, The organic coating also includes a first adhesive, which accounts for 1%-10% of the total weight of the organic coating. Preferably, the thickness of the organic coating is 0.2 μm-5 μm.

5. The battery according to claim 1, characterized in that, The average aspect ratio of the nitrogen-containing organic particles is denoted as C, and C and B satisfy: B / C=70-330, preferably B / C=80-200; Preferably, C = 1.05-3; And / or, the specific surface area of ​​the nitrogen-containing organic particles is 5-30 g / m². 2 .

6. The battery according to claim 1, characterized in that, The average particle size of the silicon-carbon material is 4.5 μm-13.5 μm; And / or, the mass content of silicon in the negative electrode active layer is 2%-50%.

7. The battery according to claim 1, characterized in that, The positive electrode sheet includes a positive electrode active layer, the positive electrode active layer includes a positive electrode active material, and the positive electrode active material includes lithium cobalt oxide; Preferably, the lithium cobalt oxide is O3 phase lithium cobalt oxide, which contains at least one of the elements Al, Mg, Y, La, Ti, and Zr. Preferably, the mass content of Al element in the positive electrode active material is 4500ppm-15000ppm; Preferably, the mass content of Mg in the positive electrode active material is 200ppm-1600ppm; Preferably, the mass content of Y element in the positive electrode active material is 100ppm-1000ppm; Preferably, the mass content of La element in the positive electrode active material is 100ppm-1000ppm; Preferably, the mass content of Ti element in the positive electrode active material is 100ppm-1600ppm; Preferably, the Zr content in the positive electrode active material is 40ppm-500ppm.

8. The battery according to claim 7, characterized in that, The positive electrode sheet includes a single-sided region, wherein a positive active layer is disposed on one side surface of the positive current collector in the single-sided region, and no positive active layer is disposed on the other side surface; in the single-sided region, a protective layer is disposed on the surface of the positive active layer away from the positive current collector, the protective layer comprising inorganic particles, the inorganic particles comprising one or more of metal nitrides, metal oxides, metal hydroxides, metal carbides, and metal borides; Preferably, the inorganic particles in the protective layer account for 50 wt%-95 wt% by mass. And / or, the average particle size of the inorganic particles is 0.1 μm-2 μm; And / or, the thickness of the protective layer is 0.5μm-5μm.

9. The battery according to claim 1, characterized in that, The electrolyte also includes sulfur-containing additives, which include... , , , or At least one of them; Preferably, the sulfur-containing additive accounts for 0.1%-6% of the total mass of the electrolyte; And / or, the electrolyte further includes nitrile additives, the nitrile additives including at least one of benzonitrile, succinic anionyl, fluorobenzonitrile, adiponitrile, 1,3,6-hexanetrionitrile, glycerol trionitrile, 1,4-dicyano-2-butene, and ethylene glycol bis(propionitrile) ether; Preferably, the mass of the nitrile additive accounts for 0.5%-8% of the total mass of the electrolyte.

10. The battery according to claim 1, characterized in that, The substrate layer includes a three-dimensional porous mesh structure, and the average pore size of the three-dimensional porous mesh structure is 25nm-75nm; Preferably, the substrate layer comprises one or more of the following polymers: polyolefin, polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene copolymer, polyvinyl chloride, polytetrafluoroethylene, polyacrylonitrile, polyimide, polyetherimide, polyethylene terephthalate, polybutylene terephthalate, poly(p-phenylene terephthalamide), poly(m-phenylene isophthalamide), polybenzimidazole, polysulfone, polyketone, and derivatives of the above polymers.

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