Electrode assemblies, secondary batteries, battery modules, battery packs, and power consumption devices

Abstract

The present application provides an electrode assembly, a secondary battery, a battery module, a battery pack, and a power consumption device. The electrode assembly includes a negative electrode sheet, a positive electrode sheet, and a separator located between the negative electrode sheet and the positive electrode sheet, the negative electrode sheet includes a negative electrode current collector and a first negative electrode film layer and a second negative electrode film layer provided on at least one surface of the negative electrode current collector, the first negative electrode film layer is located between the negative electrode current collector and the second negative electrode film layer, and includes a first negative electrode active material including graphite, the second negative electrode film layer includes a second negative electrode active material including hard carbon, the separator includes a base film and a functional coating layer located at least on the side of the base film facing the negative electrode sheet, the functional coating layer includes a ferroelectric material. According to the electrode assembly of the present application, the secondary battery has a high energy density, and can simultaneously have a high charge rate and a long cycle life.

Description

Technical Field

[0001] This application belongs to the technical field of batteries, and specifically relates to electrode assemblies, secondary batteries, battery modules, battery packs, and power consumption devices.

Background Art

[0002] In recent years, secondary batteries have been widely used in many fields such as energy storage power systems like hydroelectric, thermal, wind, and solar power plants, as well as electric tools, electric bicycles, electric motorcycles, electric vehicles, military equipment, and aerospace. With the application and popularization of secondary batteries, the requirements for the energy density, cycle performance, and charging performance at high rates of secondary batteries have been increasing. However, as an important component of secondary batteries, the performance of the negative electrode active material affects the performance of secondary batteries to a certain extent. Graphite is one of the most commonly used negative electrode active materials in secondary batteries and has the advantages of low polarization and high cycle stability, but its theoretical gram capacity (capacity per gram) is only 372 mAh / g. Currently, the performance of commercial graphite has been developed almost to the maximum, and the improvement space for its reversible gram capacity and energy density is very limited. At the same time, the interlayer spacing of graphite is small, and its charging performance at high rates has also been developed almost to the maximum. Hard carbon, as a new negative electrode active material, can realize the rapid absorption and release of active ions during the charge and discharge process of secondary batteries, so it has very broad development prospects. However, the compression density and first Coulomb efficiency of commercial hard carbon are low, which limits the improvement of the energy density of secondary batteries.

Summary of the Invention

[0003] This application provides an electrode assembly, a secondary battery, a battery module, a battery pack, and a power consumption device, aiming to simultaneously have a high charging rate and a long cycle life on the premise that the secondary battery has a high energy density.

[0004] A first aspect of this application provides an electrode assembly comprising a negative electrode sheet, a positive electrode sheet, and a separator located between the negative electrode sheet and the positive electrode sheet, wherein the negative electrode sheet comprises a negative electrode current collector and a first negative electrode film layer and a second negative electrode film layer provided on at least one surface of the negative electrode current collector, the first negative electrode film layer located between the negative electrode current collector and the second negative electrode film layer and comprising a first negative electrode active material comprising graphite, the second negative electrode film layer comprising a second negative electrode active material comprising hard carbon, and the separator comprises a base film and a functional coating layer located at least on the side of the base film facing the negative electrode sheet, the functional coating layer comprising a ferroelectric material.

[0005] In the electrode assembly of this application, a two-layer combination design is achieved by sequentially providing a first negative electrode film layer containing graphite and a second negative electrode film layer containing hard carbon on the surface of the negative electrode current collector. This design compensates for the respective defects of graphite and hard carbon and brings out their respective advantages. The large interlayer spacing of the hard carbon allows for a higher charge rate, and the interposition of graphite between the hard carbon and the negative electrode current collector compensates for the initial Coulomb efficiency of the hard carbon. Furthermore, the potential at which active ions are absorbed into the microporous structure of the hard carbon is approximately 0V, which is close to the potential at which active ions are deposited from the graphite surface. Therefore, the microporous structure of the hard carbon cannot fully utilize its function as a storage site for active ions. However, the inventors of this application have surprisingly found that the above problem can be solved by providing a functional coating layer containing a ferroelectric material on at least the side of the separator closest to the second negative electrode film layer. Ferroelectric materials allow for control over the deposition method of active ions, thereby realizing the large capacity advantage of the microporous structure of hard carbon. Furthermore, by suppressing the continuous reduction deposition of active ions on the graphite surface, the cycle life of the secondary battery can be improved. Consequently, a secondary battery using the electrode assembly of this application can have a long cycle life, be charged at high rates, have a high output voltage, and have a high energy density.

[0006] In any embodiment of this application, the thickness of the functional coating layer is H1 μm, the thickness of the second negative electrode film layer is H2 μm, the thickness of the first negative electrode film layer is H3 μm, and the electrode assembly has an H1 / (H2+H3) ratio of 0.01 to 0.15, and selectively between 0.01 and 0.08. This improves the overall performance of the secondary battery and enables high-rate charging with high energy density.

[0007] In any embodiment of this application, the thickness of the functional coating layer is H1 μm, where H1 is 2 to 10, and selectively 4 to 6. This improves the overall performance of the secondary battery and enables high-rate charging along with high energy density.

[0008] In any embodiment of this application, the thickness of the second negative electrode film layer is H2 μm, the thickness of the first negative electrode film layer is H3 μm, and the negative electrode sheet has an H2 / H3 ratio of 0.10 to 5, and selectively between 0.5 and 4. This allows the second negative electrode film layer and the first negative electrode film layer to exhibit a better synergistic effect.

[0009] In any embodiment of this application, the volume-average particle size Dv50 of the ferroelectric material is d1 μm, where d1 is 1 or less and selectively between 0.05 and 0.8. This improves the overall performance of the secondary battery, enabling high-rate charging with high energy density, while simultaneously reducing production costs.

[0010] In any embodiment of this application, the volume-average particle size Dv50 of the second negative electrode active material is d2 μm, the volume-average particle size Dv50 of the first negative electrode active material is d3 μm, and d2 / d3 is 0.1 to 1, and selectively 0.2 to 0.8. In this case, it is advantageous for the second negative electrode film layer to fully exhibit the effect of improving the high-rate charging capacity of the secondary battery, and for the first negative electrode film layer to fully exhibit the effect of improving the initial Coulomb efficiency and cycle life of the secondary battery. As a result, the overall performance of the secondary battery is improved, and high-rate charging can be achieved along with high energy density.

[0011] In any embodiment of this application, the mass percentage of the ferroelectric material in the functional coating layer is calculated based on the total mass of the functional coating layer, and W1 is between 70% and 95%, and selectively between 80% and 95%. This improves the overall performance of the secondary battery and enables high-rate charging along with high energy density.

[0012] In any embodiment of this application, the functional coating layer further comprises an adhesive. Optionally, the adhesive comprises one or more combinations of styrene-butadiene rubber, polyacrylic acid, sodium polyacrylate, polyacrylamide, polyvinyl alcohol, sodium alginate, polymethacrylic acid, carboxymethyl chitosan, fluorine-containing acrylate resins, polytetrafluoroethylene, homopolymers of vinylidene fluoride, and copolymers thereof.

[0013] In any embodiment of this application, the separator further includes an adhesive layer provided on the surface of the functional coating layer. Optionally, the adhesive layer includes one or more combinations of homopolymers and copolymers of vinylidene fluoride. This improves the winding effect of the electrode assembly and extends the cycle life of the secondary battery.

[0014] In any embodiment of this application, the dielectric constant of the ferroelectric material is 50 or greater, and selectively between 50 and 100,000.

[0015] In any embodiment of this application, the ferroelectric material includes one or more combinations selected from inorganic ferroelectric materials and organic ferroelectric materials. Optionally, the inorganic ferroelectric material includes one or more combinations selected from perovskite oxides, tungsten bronze compounds, bismuth oxide layered compounds, lithium niobate, lithium tantalate, lead metaniobate, and lead barium lithium niobate. The organic ferroelectric material may include one or more combinations selected from vinylidene fluoride homopolymers or copolymers, 2,5-dibromo-3,6-dihydroxy-p-benzoquinone, phenazine-chloranilic acid, and crokonium.

[0016] In any embodiment of this application, the mass percentage of hard carbon in the second negative electrode film layer is calculated based on the total mass of the second negative electrode film layer, and W2 is 68% or more, and selectively 90% to 98%. This is advantageous for the secondary battery to have a higher charge rate.

[0017] In any embodiment of this application, W3 is calculated based on the total mass of the first negative electrode film layer, and the mass percentage of graphite in the first negative electrode film layer is 78% or more, and selectively 90% to 98%. This is advantageous for the secondary battery to have a higher initial Coulomb efficiency and a longer cycle life.

[0018] In any embodiment of this application, the volume-average particle size Dv50 of the second negative electrode active material is d2μm, where d2 is 3 to 11, and selectively 3 to 7. This is advantageous for improving the capacity and energy density of the secondary battery.

[0019] In any embodiment of this application, the particle size distribution index (Dv90-Dv10) / Dv50 of the second negative electrode active material is α1, where α1 is between 0.6 and 5, and selectively between 1 and 4. This is advantageous for improving the high-rate charging capacity and charge / discharge efficiency of the secondary battery.

[0020] In any embodiment of this application, the specific surface area of ​​the second negative electrode active material is 3 m². 2 / g~7m 2 / g, and selectably 4m 2 / g~6m 2 The value is / g. This is advantageous for improving the high-rate charging capacity of secondary batteries.

[0021] In any embodiment of this application, the compressed density of the powder of the second negative electrode active material at 20,000 N is 0.9 g / cm³. 3 ~1.3g / cm 3 Therefore, it is selectable to 1 g / cm³ 3 ~1.2g / cm 3This is advantageous for improving the energy density of the secondary battery.

[0022] In any embodiment of the present application, the second negative electrode active material includes primary particles, secondary particles, or a combination thereof. Optionally, the quantitative ratio of the primary particles in the second negative electrode active material is 90% to 100%. This is advantageous for improving the charging ability of the secondary battery at a high rate.

[0023] In any embodiment of the present application, the volume average particle diameter Dv50 of the first negative electrode active material is d3 μm, where d3 is from 9 to 18, and optionally from 11 to 15. This is advantageous for the secondary battery to have high initial Coulomb efficiency, high energy density, and long cycle life.

[0024] In any embodiment of the present application, the particle size distribution index (Dv90 - Dv10) / Dv50 of the first negative electrode active material is α2, where α2 is from 0.2 to 5, and optionally from 0.3 to 4. This is advantageous for improving the cycle performance of the secondary battery.

[0025] In any embodiment of the present application, the specific surface area of the first negative electrode active material is 0.6 m 2 / g to 1.5 m 2 / g, and optionally 0.8 m 2 / g to 1.4 m 2 / g. This is advantageous for improving the cycle performance of the secondary battery.

[0026] In any embodiment of the present application, the compression density of the powder of the first negative electrode active material at 20000 N is 1.4 g / cm 3 to 1.85 g / cm 3 and optionally 1.6 g / cm 3 to 1.75 g / cm 3 This is advantageous for improving the energy density of the secondary battery.

[0027] In any embodiment of this application, the degree of graphitization of the first negative electrode active material is 91% to 95%, and selectively 92% to 94%. This is advantageous for improving the cycle performance of the secondary battery.

[0028] In any embodiment of this application, the first negative electrode active material comprises artificial graphite, natural graphite, or a combination thereof, and optionally the artificial graphite surface has a carbon coating layer. This is advantageous for improving the cycle performance and high-rate charging capacity of the secondary battery.

[0029] In any embodiment of this application, the first negative electrode active material comprises primary particles, secondary particles, or a combination thereof, and selectively, the proportion of secondary particles in the first negative electrode active material is 90% to 100%. This is advantageous for improving the cycle performance, storage performance, and high-rate charging capacity of the secondary battery.

[0030] A second aspect of this application provides a secondary battery including the electrode assembly of the first aspect of this application.

[0031] A third aspect of this application provides a battery module including a secondary battery according to the second aspect of this application.

[0032] A fourth aspect of this application provides a battery pack including one of the secondary battery of the second aspect of this application and one of the battery module of the third aspect of this application.

[0033] A fifth aspect of this application provides a power consumption device comprising at least one of the secondary battery of the second aspect of this application, the battery module of the third aspect, and the battery pack of the fourth aspect.

[0034] A secondary battery using the electrode assembly of this application has a long cycle life, can be charged at a high rate, has a high output voltage, and has a high energy density. The battery module, battery pack, and power consumption device of this application include the secondary battery of this application and therefore have at least the same advantages as the secondary battery described above. [Brief explanation of the drawing]

[0035] To more clearly explain the technical concept of the embodiments of this application, the drawings necessary for the embodiments of this application are briefly described below. It is clear that the drawings described below are only a few embodiments of this application. Those skilled in the art can obtain further drawings based on these drawings, even without creative work.

[0036] [Figure 1] This is a schematic diagram of one embodiment of the electrode assembly of the present application.

[0037] [Figure 2] This is a schematic diagram of another embodiment of the electrode assembly of the present application.

[0038] [Figure 3] This is a schematic diagram of one embodiment of the secondary battery of the present application.

[0039] [Figure 4] Figure 3 is an exploded schematic diagram of an embodiment of a secondary battery.

[0040] [Figure 5] This is a schematic diagram of one embodiment of the battery module of this application.

[0041] [Figure 6] This is a schematic diagram of one embodiment of the battery pack of this application.

[0042] [Figure 7] Figure 6 is an exploded schematic diagram of an embodiment of the battery pack shown.

[0043] [Figure 8] This is a schematic diagram of one embodiment of a power consumption device that includes a secondary battery as a power source according to the present application.

[0044] In drawings, the drawings are not always drawn to actual size. Explanation of the symbols 1 Battery pack, 2 Upper case, 3 Lower case, 4 Battery module, 5 Secondary battery, 51 Housing, 52 Electrode assembly, 53 Cover plate, 6 Electrode assembly, 10 Negative electrode sheet, 100 Negative electrode current collector, 101 First negative electrode film layer, 102 Second negative electrode film layer, 20 Positive electrode sheet, 200 Positive electrode current collector, 201 Positive electrode film layer, 30 Separator, 300 Base film, 301 Functional coating layer, 302 Adhesive layer. [Modes for carrying out the invention]

[0045] The following describes in detail embodiments of the electrode assembly, secondary battery, battery module, battery pack, and power consumption device specifically disclosed in this application, with appropriate reference to the drawings. However, unnecessary details may be omitted. For example, detailed explanations of known matters or redundant explanations of substantially identical configurations may be omitted. This is to avoid the following description becoming unnecessarily verbose and to facilitate understanding by those skilled in the art. The accompanying drawings and the following description are provided to enable those skilled in the art to fully understand this application and are not intended to limit the subject matter described in the claims.

[0046] The “range” disclosed in this application is defined in the form of a lower limit and an upper limit, and a given range is defined by selecting one lower limit and one upper limit, the selected lower limit and upper limit limit the boundary of a particular range. The range thus limited may include or exclude the endpoints, and may be any combination; that is, any lower limit may be combined with any upper limit to form a range. For example, if the ranges 60-120 and 80-110 are given for a particular parameter, it is understood that the ranges 60-110 and 80-120 are also expected. Also, if the minimum range values ​​1 and 2 and the maximum range values ​​3, 4 and 5 are given, the ranges 1-3, 1-4, 1-5, 2-3, 2-4 and 2-5 may all be expected. In this application, unless otherwise stated, the numerical range “a-b” is an abbreviation indicating any combination of real numbers between a and b, where a and b are both real numbers. For example, the numerical range "0 to 5" in this specification refers to all real numbers between "0 to 5," and "0 to 5" is an abbreviation for combinations of these numbers. Also, when a parameter is described as an integer greater than or equal to 2 (≧2), it is equivalent to disclosing that the parameter is, for example, an integer such as 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0047] Unless otherwise specified, all embodiments and optional embodiments of this application may be combined to form new technical concepts. Such technical concepts are considered to be included in the disclosures of this application.

[0048] Unless otherwise specified, all embodiments and optional embodiments of this application may be combined to form new technical concepts. Such technical concepts are considered to be included in the disclosures of this application.

[0049] Unless otherwise specified, all steps of this application may be performed sequentially or randomly, but it is preferable that they be performed sequentially. For example, if it is stated that the above method includes steps (a) and (b), it means that the above method may include steps (a) and (b) performed sequentially, or it may include steps (b) and (a) performed sequentially. For example, if it is stated that the above method may further include step (c), it means that step (c) may be added to the above method in any order. For example, the above method may include steps (a), (b) and (c), or steps (a), (c) and (b), or steps (c), (a) and (b), etc.

[0050] Unless otherwise specified, the terms “equipped with” and “included” in this application mean open or closed. For example, the terms “equipped with” and “included” above may mean “equipped with” or “included” other components not listed, or “equipped with” or “included” only the listed components.

[0051] Unless otherwise specified, the term "or" is inclusive in this application. For example, the phrase "A or B" means "A, B, or both A and B." More specifically, any of the following conditions are met: A is true (or exists) and B is false (or does not exist), A is false (or does not exist) and B is true (or exists), or both A and B are true (or exist).

[0052] In this application, the terms "multiple" and "multiple types" mean two or more types.

[0053] In this application, the terms "primary particle" and "secondary particle" have meanings well known in the art. Primary particles refer to particles that have not formed an aggregated state, while secondary particles refer to particles that have formed an aggregated state in which two or more primary particles have aggregated. Primary and secondary particles can be easily distinguished by taking SEM images using a scanning electron microscope.

[0054] Hard carbon is a type of carbon that is resistant to graphitization, even at temperatures above 2500°C. Hard carbon is typically obtained by thermal decomposition of precursors such as high-molecular-weight polymers. During the thermal decomposition process, the cross-linking structure of carbon atoms in the precursor inhibits the growth of the carbon layer in the planar direction, resulting in hard carbon structures containing many crystallites of disordered pseudo-graphite structures (abbreviated as graphite crystallites). Hard carbon has a complex structure and contains not only graphite crystallites but also defect structures (e.g., surface defects, lattice defects, etc.) and microporous structures (e.g., open-pore structures, closed-pore structures, etc.). Therefore, active ions are absorbed and released from various angles of the hard carbon, giving secondary batteries excellent high-rate charging capabilities. In particular, hard carbon has unique advantages in the field of power batteries. Compared to graphite, the interplanar spacing of the crystal planes of hard carbon (002) is larger, resulting in higher structural stability of hard carbon during the charge and discharge process, and no significant volume expansion or contraction effects.

[0055] Hard carbon has many defective structures, which catalyze the decomposition of the electrolyte and form a thick solid electrolyte interface (SEI) film, increasing the irreversible loss of active ions. Furthermore, hard carbon has a porous surface structure, which readily adsorbs moisture and oxygen gas from the air, forming various CH functional groups on the surface. These functional groups react with active ions, further increasing the irreversible depletion of active ions. Therefore, compared to graphite, hard carbon has a lower initial Coulombic efficiency and poor cycle performance; for example, the initial Coulombic efficiency is usually less than 80%, and it cannot fully realize the advantages of its high capacity.

[0056] The inventors of this application, through diligent research, propose an electrode assembly that can improve the capacity of hard carbon, and, assuming it provides a high energy density for secondary batteries, further improves its high-rate charging capability and cycle life. Electrode assembly

[0057] Specifically, the electrode assembly of this application includes a negative electrode sheet, a positive electrode sheet, and a separator located between the negative electrode sheet and the positive electrode sheet, wherein the negative electrode sheet includes a negative electrode current collector and a first negative electrode film layer and a second negative electrode film layer provided on at least one surface of the negative electrode current collector, the first negative electrode film layer located between the negative electrode current collector and the second negative electrode film layer and containing a first negative electrode active material containing graphite, the second negative electrode film layer containing a second negative electrode active material containing hard carbon, and the separator includes a base film and a functional coating layer located at least on the side of the base film facing the negative electrode sheet, the functional coating layer containing a ferroelectric material. In some embodiments, the positive electrode sheet, the separator, and the negative electrode sheet can be manufactured by a winding process and / or a lamination process.

[0058] Graphite has the advantages of high initial Coulombic efficiency and high cycle stability, but poor continuous charging performance at high rates. Hard carbon has the advantage of high absorption and release rates of active ions, resulting in excellent charging capacity at high rates, but its low initial Coulombic efficiency and rapid capacity decay result in poor real-world battery capacity. The inventors of this application have found, through their actual research process, that by designing a two-layer combination of graphite and hard carbon sequentially on the surface of the negative electrode current collector, the respective shortcomings of graphite and hard carbon can be compensated for. By placing graphite close to the negative electrode current collector, the initial Coulombic efficiency of hard carbon is compensated for, and by placing hard carbon away from the negative electrode current collector, more active ions are absorbed into the negative electrode more quickly, thus avoiding the poor performance of graphite when continuously charging at high rates.

[0059] However, in the course of further research, the inventors of this application found that when graphite and hard carbon are sequentially placed on the surface of the negative electrode current collector to create a two-layer combination, the effect of improving the charging capacity and energy density of the secondary battery at high rates is undesirable. As a result of diligent investigation, the inventors found that during the charging of the secondary battery, particularly in the final stages of charging, the formation of "dendrites" is a possible factor that affects the improvement of the charging capacity and energy density of the secondary battery at high rates.

[0060] During the charging process of a secondary battery, if there is insufficient space for the negative electrode's active ions to be absorbed, the resistance to absorption of active ions into the negative electrode is too high, and active ions are rapidly released from the positive electrode but not absorbed into the negative electrode in equal amounts, abnormal conditions occur. In such cases, the active ions that are not absorbed into the negative electrode can only obtain electrons from the negative electrode surface and precipitate as elemental metal, thus forming "dendrites." Therefore, the higher the charging rate of the secondary battery, the more serious the "dendrite" problem becomes. The formation of dendrites not only degrades the performance of the secondary battery, but in severe cases, such as shortening the cycle life, they can form sharp topography and puncture the separator, potentially causing a short circuit inside the battery, which can lead to combustion, explosion, and other consequences, increasing the safety risk of the secondary battery. Furthermore, if the continuously accumulating dendrites detach from the negative electrode surface, the electrical contact with the negative electrode current collector is released, preventing them from continuing to participate in the charge-discharge reaction and contributing to the capacity, thus reducing the energy density of the secondary battery.

[0061] After a two-layer combination is formed by sequentially placing graphite and hard carbon on the surface of the negative electrode current collector, in the initial stages of secondary battery charging, active ions are first adsorbed at the surface defects and lattice defects of the hard carbon. This process corresponds to the "high potential slope region" in the hard carbon's charge-discharge curve, at which point the negative electrode potential is generally -2V to -0.1V. As charging continues, active ions are intercalated between the layers of graphite crystallites in the hard carbon, resulting in behavior similar to graphite intercalation. This process corresponds to the "low potential plateau region" in the hard carbon's charge-discharge curve, at which point the negative electrode potential is generally -0.1V to 0V. Furthermore, because hard carbon has an abundant microporous structure, when the negative electrode potential drops to around 0V during secondary charging, active ions are further stored in the microporous structure of the hard carbon, providing extra active ion storage sites and improving the hard carbon's capacity and initial Coulombic efficiency. Furthermore, the longer the discharge plateau in the low-potential plateau region, the higher the reversible capacity of the corresponding hard carbon, and the better the capacity is realized. However, the potential in the low-potential plateau region of hard carbon is close to the potential for dendrite formation on the surface of graphite, and both are around 0V. Therefore, in order to prevent dendrite formation, the capacity realized in the low-potential plateau region of hard carbon is limited, and the function of the microporous structure of hard carbon as a storage site for active ions cannot be fully realized. At the same time, in order to prevent dendrite formation, the cutoff voltage of the negative electrode is generally set high, which lowers the output voltage of the secondary battery as a whole, and further reduces the energy density of the secondary battery. Consequently, the effect of combining graphite and hard carbon in a two-layer combination on the surface of the negative electrode current collector on improving the high-rate charging capacity, energy density, and / or cycle life of the secondary battery is finite.

[0062] The electrode assembly of this application is designed with a two-layer combination, in which a first negative electrode film layer containing graphite and a second negative electrode film layer containing hard carbon are sequentially provided on the surface of the negative electrode current collector, and a functional coating layer containing a ferroelectric material is further provided on the side of the separator closer to the second negative electrode film layer. The ferroelectric material has a spontaneous polarization phenomenon, and when electrons accumulate on the surface of a dendrite, the ferroelectric material spontaneously polarizes under the influence of an electric field, causing the center of the positive charge of the ferroelectric material to move to the electron accumulation region and surround the electron accumulation region. At the same time, the center of the positive charge of the ferroelectric material becomes positively charged, which repels the polarity of the positively charged active ions on the surface of the dendrite, balancing the electron density and reducing the richness of active ions. This suppresses the dendrite from continuing to grow in a direction perpendicular to the electrode sheet.

[0063] Therefore, in the electrode assembly of this application, a two-layer combination design is achieved by sequentially providing a first negative electrode film layer containing graphite and a second negative electrode film layer containing hard carbon on the surface of the negative electrode current collector, thereby compensating for the respective defects of graphite and hard carbon and realizing the advantages of each. Because the interlayer spacing of the hard carbon is large, a higher charging rate can be provided, and because graphite is interposed between the hard carbon and the negative electrode current collector, the initial Coulomb efficiency of the hard carbon can be compensated for. Furthermore, the potential at which active ions are absorbed into the microporous structure of the hard carbon is approximately 0V, which is close to the potential at which active ions are deposited on the surface of graphite, so the function of the microporous structure of the hard carbon as a storage site for active ions cannot be fully exercised. However, the inventors of this application have surprisingly found that the above problem can be solved by providing a functional coating layer containing a ferroelectric material on at least the side of the separator closer to the second negative electrode film layer. Ferroelectric materials allow for control over the deposition method of active ions, thereby realizing the large capacity advantages of the microporous structure of hard carbon and suppressing the continuous reduction deposition of active ions on the graphite surface, thereby improving the cycle life of secondary batteries.

[0064] Specifically, in the initial stages of charging the secondary battery, active ions are rapidly adsorbed to the surface defects and lattice defects of the hard carbon, resulting in the negative electrode sheet having high kinetic performance. In the later stages of charging the secondary battery, the overvoltage can be precisely controlled under the action of the functional coating layer, allowing a large amount of active ions to be stored in the microporous structure of the hard carbon, increasing the length of the low-potential plateau region, and increasing the reversible capacity of the secondary battery, thereby improving the charging capacity and energy density of the secondary battery at high rates. Furthermore, the overvoltage generates a reverse electric field in the functional coating layer, reducing the richness of active ions and suppressing the continued growth of dendrites perpendicular to the electrode sheet, thereby improving the safety and cycle performance of the secondary battery.

[0065] Furthermore, in the electrode assembly of this application, the functional coating layer is provided on the surface of the separator, which is advantageous for the secondary battery to have better overall performance without increasing the number of extra production steps, without damaging the negative electrode sheet, and without affecting the processing performance of the negative electrode sheet. The functional coating layer is provided on the surface of the separator, and further improves the heat resistance of the separator and reduces the thermal shrinkage rate of the separator, thereby contributing to the improvement of the safety performance of the secondary battery, in particular the thermal safety performance.

[0066] Therefore, a secondary battery using the electrode assembly of this application has a long cycle life, can be charged at a high rate, has a high output voltage, and further has a high energy density. [Separator]

[0067] The separator of this application includes a base film and a functional coating layer located at least on the side of the base film facing the negative electrode sheet. The base film has two opposing surfaces in its thickness direction, and the functional coating layer may be provided on both surfaces of the base film, or only on the surface of the base film facing the negative electrode sheet, or selectively on both surfaces of the base film.

[0068] The type of base film described in this application is not particularly limited, and any well-known porous structure film having good chemical and mechanical stability can be selected. In some embodiments, the material of the base film may include one or more combinations selected from glass fiber, nonwoven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The base film may be a single-layer film or a multilayer composite film. If the base film is a multilayer composite film, the materials of each layer may be the same or different.

[0069] In some embodiments, the thickness of the base film may be 7 μm to 12 μm, but this application is not limited thereto.

[0070] The above functional coating layer contains a ferroelectric material. In some embodiments, the dielectric constant of the ferroelectric material is selectively 50 or higher. A higher dielectric constant of the ferroelectric material provides a greater effect in suppressing the continued growth of dendrites perpendicular to the electrode sheet. However, this effect does not continuously increase, and simultaneously, a higher dielectric constant increases the demands on the manufacturing process of the ferroelectric material, thereby increasing production costs. In some embodiments, the dielectric constant of the ferroelectric material may be selectively 50 to 100,000, for example, 50 to 50,000, 50 to 25,000, 50 to 10,000, 50 to 5,000, 50 to 4,000, 50 to 3,000, 50 to 2,000, 100 to 100,000, 100 to 50,000, and 100 to 2,500. 0, 100-10000, 100-5000, 100-4000, 100-3000, 100-2000, 200-100000, 200-50000, 200-25000, 200-10000, 200-5000, 200-4000, 200-3000, 200-2000, or 200-1000 may also be used.

[0071] In this application, the dielectric constant of a ferroelectric material refers to the dielectric constant at room temperature (25±5℃), and has a meaning well known in the art, and can be tested with equipment and methods known in the art. For example, after manufacturing a ferroelectric material into a circular sample, the capacitance C can be tested using an LCR meter, and the dielectric constant ε can be calculated using the formula. ε = (C × d) / (ε0 × A) C is the capacitance in farads (F), d is the thickness of the sample in cm, and A is the area of ​​the sample in cm. 2 Therefore, ε0 is the permittivity of vacuum and ε0 = 8.854 × 10⁻⁴ -14 The value is F / cm. In this application, the test conditions may be 1KHz, 1.0V, and 25±5℃. The test standard may conform to GB / T 11297.11-2015. For sample preparation, refer to Chinese patent application CN114217139A.

[0072] In some embodiments, the ferroelectric material may include one or more types selected from inorganic ferroelectric materials and organic ferroelectric materials. Selectively, the ferroelectric material may include one or more types selected from inorganic ferroelectric materials.

[0073] In some embodiments, the inorganic ferroelectric material may optionally include one or more combinations selected from perovskite structure oxides, tungsten bronze type compounds, bismuth oxide type layered structure compounds, lithium niobate (LiNbO3), lithium tantalate (LiTaO3), lead metaniobate, and lead barium lithium niobate. Furthermore, the inorganic ferroelectric material may optionally be selected from perovskite structure oxides.

[0074] Selectively, the molecular formula of the above perovskite structure oxide is Ba 1-x A x Ti 1-y B yIt is O3. A may contain one or a combination of multiple types selected from Pb, Sr, Ca, K, Na, and Cd, B may contain one or a combination of multiple types selected from Sn, Hf, Zr, Ce, Nb, and Th, and 0 ≦ x ≦ 1, 0 ≦ y ≦ 1. For example, the perovskite structure oxide may be BaTiO3, Ba 1-x1 Sr x1 TiO3 (0 ≦ x1 ≦ 1), SrTiO3, PbTiO3, PbZr y1 Ti 1-y1 O3 (0 ≦ y1 ≦ 1), BaZr y2 Ti 1-y2 O3 (0 < y2 < 1), KNbO3, NaNbO3, and may contain one or a combination of multiple types selected therefrom.

[0075] Optionally, the molecular formula of the tungsten bronze type compound is M z WO3. M may contain one or a combination of multiple types selected from Na, K, Rb, and Cs, and 0 < z < 1. For example, the tungsten bronze type compound may contain one or a combination of multiple types selected from Na z1 WO3 (0 < z1 < 1), K z2 WO3 (0 < z2 < 1).

[0076] Optionally, the molecular formula of the bismuth oxide type layered structure compound is (Bi2O2)(C n-1 D<​​​​​​​​In some embodiments, the organic ferroelectric material may include one or more combinations selected from a homopolymer or copolymer of vinylidene fluoride, 2,5-dibromo-3,6-dihydroxy-p-benzoquinone, phenazine-chloranilic acid, and crokonium.

[0078] In some embodiments, the volume-average particle size Dv50 of the ferroelectric material is d1 μm, and d1 is 1 or less, for example, 0.8 or less, 0.7 or less, 0.6 or less, 0.5 or less, 0.4 or less, 0.3 or less, or 0.2 or less. Selectively, d1 may be 0.01~1, 0.02~1, 0.03~1, 0.04~1, 0.05~1, 0.06~1, 0.07~1, 0.08~1, 0.01~0.8, 0.02~0.8, 0.03~0.8, 0.04~0.8, 0.05~0.8, 0.06~0.8, 0.07~0.8, 0.08~0.8, 0.09~0.8, or 0.1~0.8.

[0079] When the Dv50 of the ferroelectric material is within an appropriate range, the overall performance of the secondary battery is improved, enabling high energy density and high-rate charging, while also reducing production costs. Furthermore, if the Dv50 of the ferroelectric material is large, the resulting interference from the reverse electric field is significant, which may prevent it from balancing the electron density and suppressing the continued growth of dendrites perpendicular to the electrode sheet. This increases the safety risk of the secondary battery when increasing the output voltage to improve energy density, and if the output voltage is reduced to lower the safety risk, the microporous structure of hard carbon cannot fully utilize its function as a storage site for active ions. Additionally, if the Dv50 of the ferroelectric material is small, the manufacturing process becomes more complex, and production costs increase. These issues can be effectively avoided.

[0080] In some embodiments, the thickness of the functional coating layer is H1 μm, the thickness of the second negative electrode film layer is H2 μm, the thickness of the first negative electrode film layer is H3 μm, and the electrode assembly has an H1 / (H2+H3) ratio of 0.01 to 0.15, and selectively between 0.01 and 0.08.

[0081] Through diligent research, the inventors discovered that when the thickness of the functional coating layer H1 μm, the thickness of the second negative electrode film layer H2 μm, and the thickness of the first negative electrode film layer H3 μm satisfy the condition that H1 / (H2+H3) is between 0.01 and 0.15, the overall performance of the secondary battery is improved, enabling high-rate charging with high energy density. Furthermore, if the thickness of the functional coating layer is low and the total thickness of the first and second negative electrode film layers is high, the strength of the reverse electric field provided by the functional coating layer may be insufficient, and it may not perform the function of balancing electron density and suppressing the continued growth of dendrites perpendicular to the electrode sheet. As a result, when increasing the output voltage of the secondary battery to improve energy density, the safety risk of the secondary battery increases. If the output voltage of the secondary battery is reduced to lower the safety risk of the secondary battery, the function of using the microporous structure of hard carbon as a storage site for active ions cannot be fully exercised. Also, if the thickness of the functional coating layer is high and the total thickness of the first and second negative electrode film layers is low, the functional coating layer does not have electrochemical activity and cannot contribute to capacity, so it occupies a lot of volume space and mass, which can effectively avoid affecting the energy density of the secondary battery.

[0082] In some embodiments, the thickness of the functional coating layer is H1 μm, where H1 is between 2 and 10, and selectively between 4 and 6. When the thickness of the functional coating layer is within an appropriate range, the overall performance of the secondary battery is improved, enabling high energy density and high-rate charging. Furthermore, if the functional coating layer is thin, the resulting reverse electric field strength may be insufficient, potentially failing to balance the electron density and suppress the continued growth of dendrites perpendicular to the electrode sheet. This increases the safety risk of the secondary battery when increasing the output voltage to improve energy density. Conversely, if the output voltage is reduced to lower the safety risk, the microporous structure of hard carbon cannot fully utilize its function as a storage site for active ions. Additionally, if the functional coating layer is thick, it lacks electrochemical activity and cannot contribute to capacity, occupying a large volume space and mass, effectively avoiding an impact on the energy density of the secondary battery.

[0083] In some embodiments, the mass percentage of the ferroelectric material in the functional coating layer is calculated based on the total mass of the functional coating layer, and W1 is between 70% and 95%, and selectively between 80% and 95%.

[0084] Through diligent research, the inventors discovered that when the ferroelectric material content is within an appropriate range, the overall performance of the secondary battery is better, enabling high energy density and high-rate charging. Furthermore, when the ferroelectric material content is low, the resulting reverse electric field strength is insufficient, which may prevent the electron density balancing effect and the suppression of dendrite growth perpendicular to the electrode sheet. This increases the safety risk of the secondary battery when increasing the output voltage to improve energy density, and when the output voltage is reduced to lower the safety risk, the microporous structure of hard carbon cannot fully utilize its function as an active ion storage site. Additionally, when the ferroelectric material content is high, the amount of other components in the functional coating layer (e.g., adhesive content) decreases, which effectively avoids poor bonding of the functional coating layer to the base film and makes it prone to detachment from the base film.

[0085] In some embodiments, the functional coating layer may further contain an adhesive to adhere the ferroelectric materials together and to adhere the functional coating layer to the second negative electrode film layer of the negative electrode sheet, thereby improving the winding effect of the electrode assembly and extending the cycle life of the secondary battery. In some embodiments, the adhesive may optionally include one or more combinations of styrene-butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethacrylic acid (PMA), carboxymethyl chitosan (CMCS), fluorine-containing acrylate resins, polytetrafluoroethylene (PTFE), homopolymers of vinylidene fluoride, and copolymers thereof. For example, the vinylidene fluoride copolymer described above may include one or more types selected from vinylidene fluoride-hexafluoropropylene copolymer, vinylidene fluoride-trifluoroethylene copolymer, vinylidene fluoride-chlorotrifluoroethylene copolymer, vinylidene fluoride-tetrafluoroethylene copolymer, vinylidene fluoride-tetrafluoroethylene-propylene ternary copolymer, and vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene ternary copolymer.

[0086] In some embodiments, the functional coating layer may further contain other auxiliary agents. For example, these other auxiliary agents may include dispersants, such as sodium carboxymethylcellulose (CMC).

[0087] In some embodiments, the separator may further include an adhesive layer provided on the surface of the functional coating layer, thereby further improving the winding effect of the electrode assembly and extending the cycle life of the secondary battery. Optionally, the adhesive layer includes one or more combinations of homopolymers and copolymers of vinylidene fluoride. This allows the adhesive layer to have a constant dielectric constant in addition to its adhesive properties. This allows for better suppression of dendrite growth in a direction perpendicular to the electrode sheet. For example, the vinylidene fluoride copolymer may include one or more types selected from vinylidene fluoride-hexafluoropropylene copolymer, vinylidene fluoride-trifluoroethylene copolymer, vinylidene fluoride-chlorotrifluoroethylene copolymer, vinylidene fluoride-tetrafluoroethylene copolymer, vinylidene fluoride-tetrafluoroethylene-propylene ternary copolymer, and vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene ternary copolymer. Selectively, the thickness of the adhesive layer is 1 μm or less.

[0088] The method for manufacturing the separator of this application is well known. In some embodiments, a separator can be manufactured by dispersing a ferroelectric material, an adhesive, and any other components in a solvent to form a slurry, applying the slurry to at least one surface of a base film, and drying it, thereby obtaining the separator. The solvent may be, but is not limited to, N-methylpyrrolidone (NMP) or deionized water. In some embodiments, the method for manufacturing the separator may further include a step of applying a slurry to the surface of a functional coating layer to form an adhesive layer.

[0089] In this application, the parameters of the functional coating layer refer to the parameter range of the functional coating layer on one side of the base film. When the functional coating layer is provided on both sides of the base film, if the parameters of the functional coating layer on either one of the surfaces satisfy the requirements of this application, it is considered to be within the scope of protection of this application.

[0090] The thickness of the functional coating layer of the separator is well known in this art and can be measured using instruments and methods well known in this art. For example, scanning electron microscopy (e.g., ZEISS Sigma 300) testing can more accurately determine the boundary area between the functional coating layer and the base film. Test standards can be found in JY / T010-1996. To ensure the accuracy of the test results, multiple (e.g., five or more) different areas can be randomly selected from the sample and scanned, and the thicknesses of the functional coating layer and base film in the scale test area can be read at a certain magnification (e.g., 500x or more). For accuracy, multiple test areas may be taken and the average value taken. [Negative electrode sheet]

[0091] In some embodiments, the thickness of the second negative electrode film layer is H2 μm, the thickness of the first negative electrode film layer is H3 μm, and the negative electrode sheet satisfies the requirement that H2 / H3 is 0.10 to 5, and selectively 0.5 to 4.

[0092] Through diligent research, the inventors discovered that when the ratio of the thickness of the second negative electrode film layer (H2μm) to the thickness of the first negative electrode film layer (H3μm) is within an appropriate range, the second and first negative electrode film layers can exhibit a better synergistic effect. The second negative electrode film layer primarily bears the pressure for high-rate charging, ensuring that the secondary battery has a high charging rate, while the first negative electrode film layer primarily provides a long cycle life and simultaneously ensures high initial Coulomb efficiency. This results in better overall performance of the secondary battery, enabling high-rate charging with high energy density. Furthermore, when the second negative electrode film layer is thin and the first negative electrode film layer is thick, the high-rate charging pressure borne by the hard carbon in the second negative electrode film layer during the charging process is relatively small. In this case, the graphite in the first negative electrode film layer still plays a dominant role, and the effect of improving the charging rate of the secondary battery is not clear. Also, when the second negative electrode film layer is thick and the first negative electrode film layer is thin, the hard carbon surface contains a large amount of inert functional groups, which increases the irreversible depletion of active ions, affecting the initial Coulomb efficiency of the secondary battery and potentially reducing the cycle life of the secondary battery.

[0093] In some embodiments, the thickness of the second negative electrode film layer is H2 μm, and H2 is 10 to 120, selectively 35 to 110, and more selectively 40 to 100. When the thickness of the second negative electrode film layer is within an appropriate range, it is advantageous for the secondary battery to have a high charge rate.

[0094] In some embodiments, the thickness of the first negative electrode film layer is H3 μm, where H3 is 20 to 100, selectively 25 to 70, and more selectively 28 to 60. When the thickness of the first negative electrode film layer is within an appropriate range, it is advantageous for the secondary battery to have high initial Coulomb efficiency and a long cycle life.

[0095] The second negative electrode film layer contains a second negative electrode active material, and the second negative electrode active material contains hard carbon. Optionally, the mass percentage of the hard carbon in the second negative electrode active material is 70% to 100%, and more optionally 80% to 98%, calculated based on the total mass of the second negative electrode active material. This allows the second negative electrode film layer to contain a large amount of hard carbon, which is advantageous for the secondary battery to have a higher charge rate. In some embodiments, the second negative electrode active material may contain only hard carbon, and in some other embodiments, the second negative electrode active material may further contain other negative electrode active materials in addition to hard carbon, such as graphite, soft carbon, mesocarbon microbeads, silicon-based materials, tin-based materials, and optionally, the mass percentage of the other negative electrode active material in the second negative electrode active material is 30% or less, and more optionally 20% or less, calculated based on the total mass of the second negative electrode active material.

[0096] In some embodiments, the mass percentage of hard carbon in the second negative electrode film layer is W2, where W2 is 68% or more, selectively between 90% and 98%, and is calculated based on the total mass of the second negative electrode film layer. Having a hard carbon content within an appropriate range is advantageous for the secondary battery to have a higher charge rate.

[0097] In some embodiments, the second negative electrode film layer may further contain a conductive agent, which plays a role in collecting a microcurrent between the second negative electrode active material (e.g., hard carbon), reducing the contact resistance of the electrodes, accelerating the electron transfer rate, and simultaneously reducing polarization, thereby improving the charge-discharge efficiency of the secondary battery. For example, the conductive agent may include one or more types selected from superconducting carbon, conductive graphite, acetylene black, carbon black, kecheng black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers. In some embodiments, the mass percentage of the conductive agent is 5% or less, and is calculated based on the total mass of the second negative electrode film layer.

[0098] In some embodiments, the second negative electrode film layer may further contain an adhesive to adhere the second negative electrode active material (e.g., hard carbon) to itself and to adhere the second negative electrode film layer to the first negative electrode film layer. For example, the adhesive may include one or more types selected from styrene-butadiene rubber (SBR), water-soluble unsaturated resin SR-1B, aqueous acrylic resin (e.g., polyacrylate PAA, polymethacrylate PSMA, sodium polyacrylate PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), and carboxymethyl chitosan (CMCS). In some embodiments, the mass percentage of the binder is 5% or less, calculated based on the total mass of the second negative electrode film layer.

[0099] In some embodiments, the second negative electrode film layer may further contain other additives. For example, the other additives may include thickeners such as sodium carboxymethylcellulose (CMC) or PTC thermistor material. In some embodiments, the mass percentage of the other additives is 2% or less, calculated based on the total mass of the second negative electrode film layer.

[0100] The first negative electrode film layer contains a first negative electrode active material containing graphite. Optionally, the mass percentage of graphite in the first negative electrode active material is 80% to 100%, and more optionally, 90% to 98%, calculated based on the total mass of the first negative electrode active material. This is advantageous because the first negative electrode film layer contains a large amount of graphite, resulting in a secondary battery with higher initial Coulomb efficiency and a longer cycle life. In some embodiments, the first negative electrode active material may contain only graphite, and in some other embodiments, the first negative electrode active material may further contain other negative electrode active materials other than graphite, such as hard carbon, soft carbon, mesocarbon microbeads, silicon-based materials, and tin-based materials. Optionally, the mass percentage of the other negative electrode active material in the first negative electrode active material is 20% or less, and more optionally, 10% or less, calculated based on the total mass of the first negative electrode active material.

[0101] In some embodiments, the mass percentage of graphite in the first negative electrode film layer is W3, calculated based on the total mass of the first negative electrode film layer, and W3 is 78% or more, and selectively 90% to 98%. When the graphite content is within an appropriate range, it is advantageous for the secondary battery to have a higher initial Coulomb efficiency and a longer cycle life.

[0102] In some embodiments, the first negative electrode film layer may further contain a conductive agent, which plays a role in collecting a small current between the first negative electrode active material (e.g., graphite), reducing the contact resistance of the electrodes, accelerating the electron transfer rate, and simultaneously reducing polarization, thereby improving the charge-discharge efficiency of the secondary battery. For example, the conductive agent may include one or more types selected from superconducting carbon, conductive graphite, acetylene black, carbon black, kecheng black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers. In some embodiments, the mass percentage of the conductive agent is 5% or less, and is calculated based on the total mass of the first negative electrode film layer.

[0103] In some embodiments, the first negative electrode film layer may further contain an adhesive to adhere the first negative electrode active material (e.g., graphite) to each other, the first negative electrode film layer to the second negative electrode film layer, and the first negative electrode film layer to the negative electrode current collector. For example, the adhesive may include one or more types selected from styrene-butadiene rubber (SBR), water-soluble unsaturated resin SR-1B, aqueous acrylic resin (e.g., polyacrylate PAA, polymethacrylate PSMA, sodium polyacrylate PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), and carboxymethyl chitosan (CMCS). In some embodiments, the mass percentage of the binder is 5% or less and is calculated based on the total mass of the first negative electrode film layer.

[0104] In some embodiments, the first negative electrode film layer may further contain other additives. For example, the other additives may include thickeners such as sodium carboxymethylcellulose (CMC) or PTC thermistor material. In some embodiments, the mass percentage of the other additives is 2% or less, calculated based on the total mass of the first negative electrode film layer.

[0105] In some embodiments, the volume-average particle size Dv50 of the second negative electrode active material is d2 μm, the volume-average particle size Dv50 of the first negative electrode active material is d3 μm, and d2 / d3 is 0.1 to 1, and selectively 0.2 to 0.8.

[0106] In the negative electrode sheet of this application, the first negative electrode film layer employs a first negative electrode active material with a larger particle size, which increases the compressive density of the first negative electrode film layer, and is advantageous for the secondary battery to have a high initial Coulomb efficiency, high energy density, and long cycle life. In the negative electrode sheet of this application, the second negative electrode film layer employs a second negative electrode active material with a smaller particle size, which increases its specific surface area, increases the contact area with the electrolyte, shortens the liquid-phase diffusion pathway and solid-phase diffusion pathway of active ions, and at the same time, better maintains the integrity of the tunnel structure of the second negative electrode film layer, which is advantageous for the secondary battery to have a higher charge rate. Furthermore, the second negative electrode active material has a smaller particle size and higher pressure resistance, which allows the microporous structure of the second negative electrode active material, particularly hard carbon, to be better maintained. This allows the microporous structure of hard carbon to fully utilize its function as an active ion storage site, thereby improving the capacity and energy density of the secondary battery. At the same time, the low compressive density of the second negative electrode film layer allows the electrolyte to quickly permeate the first negative electrode film layer, reducing the polarization of the negative electrode and improving the charge-discharge efficiency of the secondary battery.

[0107] Through further research, the inventors discovered that when the ratio d2 / d3 of the particle size of the second negative electrode active material to the particle size of the first negative electrode active material is within an appropriate range, it is advantageous to fully utilize the effects of the second negative electrode film layer in improving the high-rate charging capacity of the secondary battery and the first negative electrode film layer in improving the initial Coulomb efficiency and cycle life of the secondary battery. As a result, the overall performance of the secondary battery is improved, enabling high-rate charging along with high energy density.

[0108] In some embodiments, the volume-average particle size Dv50 of the second negative electrode active material is d2 μm, where d2 is between 3 and 11, and selectively between 3 and 7. When the particle size of the second negative electrode active material is within an appropriate range, its microporous structure is better maintained, thereby fully utilizing the function of the microporous structure of hard carbon as an active ion storage site to improve the capacity and energy density of the secondary battery. At the same time, when the particle size of the second negative electrode active material is within an appropriate range, the second negative electrode film layer can have a smooth tunnel structure, which allows the electrolyte to pass smoothly through the tunnel structure of the second negative electrode film layer and quickly permeate into the first negative electrode film layer, thereby reducing the polarization of the negative electrode and improving the charge-discharge efficiency of the secondary battery.

[0109] In some embodiments, the particle size distribution index (Dv90-Dv10) / Dv50 of the second negative electrode active material is α1, where α1 is between 0.6 and 5, and selectively between 1 and 4. When the particle size distribution index of the second negative electrode active material is within an appropriate range, it is advantageous to improve the processing performance of the second negative electrode film layer and to have high particle distribution consistency and a smooth tunnel structure throughout the second negative electrode film layer. This is advantageous because different regions of the second negative electrode film layer all have high active ion transmission performance, further improving the high-rate charging capacity of the secondary battery. At the same time, it is advantageous for the electrolyte to quickly permeate the first negative electrode film layer, reducing the polarization of the negative electrode and improving the charge-discharge efficiency of the secondary battery.

[0110] In some embodiments, the specific surface area of ​​the second negative electrode active material is 3 m². 2 / g~7m 2 / g, and selectably 4m 2 / g~6m 2The value is / g. When the specific surface area of ​​the second negative electrode active material is within an appropriate range, the resistance of charge exchange can be reduced, and the second negative electrode film layer provides a smoother tunnel structure, resulting in higher active ion transmission performance and further improving the high-rate charging capacity of the secondary battery. When the specific surface area of ​​the second negative electrode active material is within an appropriate range, the film formation efficiency of the SEI film is improved, the formation of an excessively thick SEI film is avoided, and the irreversible depletion of active ions is reduced, thereby further improving the capacity and cycle performance of the secondary battery.

[0111] In some examples, the compressed density of the powder of the second negative electrode active material at 20,000 N was 0.9 g / cm³. 3 ~1.3g / cm 3 Therefore, it is selectable to 1 g / cm³ 3 ~1.2g / cm 3 Therefore, if the compressed density of the powder of the second negative electrode active material is within an appropriate range, it is advantageous for improving the energy density of the secondary battery.

[0112] In some embodiments, the second negative electrode active material comprises primary particles, secondary particles, or a combination thereof, and selectively, the proportion of primary particles in the second negative electrode active material is 90% to 100%. When the second negative electrode active material contains an appropriate proportion of primary particles, it is advantageous for the second negative electrode film layer to have a short active ion transport path, thereby further improving the high-rate charging capacity of the secondary battery. Furthermore, it is possible to reduce the polarization of the negative electrode and side reactions of the electrolyte, thereby further improving the cycle performance and storage performance of the secondary battery.

[0113] In some embodiments, the volume-average particle size Dv50 of the first negative electrode active material is d3 μm, and d3 is between 9 and 18, and selectively between 11 and 15. When the particle size of the first negative electrode active material is within an appropriate range, it is advantageous for the first negative electrode film layer to have a high compressive density, thereby the secondary battery having a high initial Coulomb efficiency, high energy density, and long cycle life.

[0114] In some embodiments, the particle size distribution index (Dv90-Dv10) / Dv50 of the first negative electrode active material is α2, where α2 is between 0.2 and 5, and selectively between 0.3 and 4. When the particle size distribution index of the first negative electrode active material is within an appropriate range, it is advantageous to improve the processing performance of the first negative electrode film layer and to have high particle distribution consistency and a smooth tunnel structure throughout the first negative electrode film layer. This is advantageous because different regions of the first negative electrode film layer all have high active ion transport performance, thus further improving the cycle performance of the secondary battery.

[0115] In some embodiments, the specific surface area of ​​the first negative electrode active material is 0.6 m². 2 / g~1.5m 2 It is / g, and selectively 0.8m 2 / g~1.4m 2 The value is / g. When the specific surface area of ​​the first negative electrode active material is within an appropriate range, the resistance of charge exchange can be reduced, and the first negative electrode film layer has a smoother tunnel structure, which results in higher active ion transmission performance, thus further improving the cycle performance of the secondary battery.

[0116] In some examples, the compressed density of the first negative electrode active material powder at 20,000 N was 1.4 g / cm³. 3 ~1.85g / cm 3 Therefore, it is selectable to 1.6 g / cm³ 3 ~1.75g / cm 3 Therefore, if the compressed density of the powder of the first negative electrode active material is within an appropriate range, it is advantageous for improving the energy density of the secondary battery.

[0117] In some embodiments, the degree of graphitization of the first negative electrode active material is 91% to 95%, and selectively 92% to 94%. Having the degree of graphitization of the first negative electrode active material within an appropriate range is advantageous for improving the cycle performance of the secondary battery.

[0118] In some embodiments, the first negative electrode active material includes artificial graphite, natural graphite, or a combination thereof. Optionally, the mass percentage of artificial graphite in the first negative electrode active material is 50% or more, optionally 60% to 100%, and is calculated based on the total mass of the first negative electrode active material. Optionally, by further providing a carbon coating layer on the surface of the artificial graphite, the resistance to charge transfer can be further reduced, improving the cycle performance and high-rate charging capability of the secondary battery, and optionally, the carbon coating layer contains amorphous carbon.

[0119] In some embodiments, the first negative electrode active material comprises primary particles, secondary particles, or a combination thereof, and selectively, the proportion of secondary particles in the first negative electrode active material is 90% to 100%. When the first negative electrode active material contains an appropriate proportion of secondary particles, its isotropy is improved, which is advantageous for the first negative electrode film layer to have many active ion transport channels, thereby further improving the high-rate charging capacity of the secondary battery. At the same time, the first negative electrode film layer has a high compressive density, which is advantageous for improving the energy density of the secondary battery. Furthermore, by reducing side reactions between the polarization of the negative electrode and the electrolyte, the cycle performance and storage performance of the secondary battery can be further improved.

[0120] In some embodiments, the compressed density of the negative electrode sheet was 1.4 g / cm³. 3 ~1.85g / cm 3 Therefore, it is selectable to 1.6 g / cm³ 3 ~1.75g / cm 3 Therefore, when the compressed density of the negative electrode sheet is within an appropriate range, it is advantageous for improving the high-rate charging capacity, cycle performance, and energy density of secondary batteries.

[0121] In some embodiments, the negative electrode current collector can be a metal foil film sheet or a composite current collector. Examples of metal foils include copper foil and copper alloy foil. The composite current collector may include a polymer material substrate and a metal material layer formed on at least one surface of the polymer material substrate. For example, the metal material may include one or more types selected from copper, copper alloys, nickel, nickel alloys, titanium, titanium alloys, silver, and silver alloys. The polymer material substrate may include one or more types selected from polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), and polyethylene (PE).

[0122] The method for manufacturing the negative electrode sheet of this application is well known. In some embodiments, a negative electrode sheet can be manufactured by dispersing a first negative electrode active material, a conductive agent, an adhesive, and any other components in a solvent (e.g., deionized water) to form a first slurry, dispersing a second negative electrode active material, a conductive agent, an adhesive, and any other components in a solvent (e.g., deionized water) to form a second slurry, applying the first slurry to a negative electrode current collector and drying it to form a first negative electrode film layer, applying the second slurry to the first negative electrode film layer, and obtaining a negative electrode sheet after processes such as drying and cold pressing.

[0123] The negative electrode current collector has two opposing surfaces in its thickness direction, and the first negative electrode film layer and the second negative electrode film layer may be provided on either one or both of the two opposing surfaces of the negative electrode current collector. Optionally, the functional coating layer may be provided only on the surface of the base film facing the second negative electrode film layer of the negative electrode sheet, thereby reducing the mass of the inert component and improving the energy density of the secondary battery.

[0124] In this application, the first negative electrode film layer and the second negative electrode film layer both refer to the parameter range of the coating layer on one side of the negative electrode current collector. When the first negative electrode film layer and the second negative electrode film layer are provided on two surfaces of the negative electrode current collector, if the parameters of the coating layer on either surface satisfy the requirements of this application, it is considered to be within the scope of protection of this application.

[0125] In the negative electrode sheet of this application, the Dv90, Dv50, and Dv10 of the material have meanings well known in the art and can be measured with instruments and methods well known in the art. For example, referring to the particle size distribution laser diffraction method of GB / T 19077-2016, it can be easily tested using, for example, a laser particle size analyzer of the Mastersizer 2000E laser particle size analyzer from Malvern, UK. Dv90 is the particle size corresponding when the cumulative volume distribution percentage of the material reaches 90%, Dv50 is the particle size corresponding when the cumulative volume distribution percentage of the material reaches 50%, and Dv10 is the particle size corresponding when the cumulative volume distribution percentage of the material reaches 10%.

[0126] In the negative electrode sheet of this application, the specific surface area of ​​the material has a meaning well known in the art and can be measured with instruments and methods well known in the art. For example, it can be tested using the nitrogen adsorption specific surface area analysis test method, referring to GB / T 19587-2017, and calculated by the BET (Brunauer Emmett Teller) method. The nitrogen adsorption specific surface area analysis test can be performed using the Tri-Star 3020 specific surface area pore size analyzer from Micromeritics, Inc., USA.

[0127] In the negative electrode sheet of this application, the degree of graphitization of the material is a well-known concept in the art and can be measured using instruments and methods well known in the art. For example, the test was performed using an X-ray diffractometer (Bruker D8 Discover), and the test was performed with reference to JIS K 0131-1996 and JB / T 4220-2011. 002 After obtaining the formula g=(0.344-d 002The degree of graphitization of the material can be calculated based on ) / (0.344-0.3354)×100%. In the above formula, d 002 This represents the interlayer spacing of the (002) crystal plane in the crystal structure of a material, expressed in nanometers (nm).

[0128] In the negative electrode sheet of this application, the compressive density of the material powder is a well-known concept in the art and can be measured using instruments and methods well known in the art. For example, it can be tested using an electronic pressure tester (e.g., UTM7305) with reference to GB / T24533-2009. One exemplary test method involves weighing 1 g of material and measuring the base area of ​​1.327 cm². 2 The process includes placing the material in a mold, pressurizing it to 2000 kg (equivalent to 20000 N), holding the pressure for 30 seconds, then releasing the pressure and holding it for 10 seconds, after which recording and calculating the compression density of the powder under a 20000 N applied force.

[0129] In the negative electrode sheet of this application, the ratio of primary and secondary particles can be measured using instruments and methods well known in the art, for example, by using a scanning electron microscope. To ensure the accuracy of the test results, multiple (e.g., five or more) different areas can be randomly selected from the test sample and scanned. At a certain magnification (e.g., 1000x or more), the ratio of the number of primary and secondary particles in each area to the total number of particles can be calculated, i.e., the respective ratios of primary and secondary particles in that area. To ensure the accuracy of the test results, multiple test samples (e.g., ten or more) can be taken, the above test can be repeated, and the average value of each test sample can be taken to obtain the final test result. The test standard can be found in JY / T010-1996.

[0130] In the negative electrode sheet of this application, the thicknesses of the first negative electrode film layer and the second negative electrode film layer are as known in the art and can be measured with instruments and methods known in the art. For example, by performing a test with a scanning electron microscope (e.g., ZEISS Sigma 300), the boundary region between the second negative electrode film layer and the first negative electrode film layer can be determined more accurately. One exemplary test method involves cutting the negative electrode sheet into a sample of a certain size (e.g., 2 cm × 2 cm), fixing the negative electrode sheet to the sample stage with paraffin, fixing the sample stage in the sample holder, turning on the power of an argon ion cross-sectional polishing apparatus (e.g., IB-19500CP) and applying a vacuum (e.g., 10°C). -4 The process includes setting the argon gas flow rate (e.g., 0.15 MPa), voltage (e.g., 8 KV), and polishing time (e.g., 2 hours), adjusting the sample stage to swing mode, and starting the polishing. The test standard can be found in JY / T010-1996. To ensure the accuracy of the test results, multiple (e.g., five or more) different areas are randomly selected from the sample and scanned, and the thickness of the first and second negative electrode film layers in the scale test area can be read at a certain magnification (e.g., 500x or more). For accuracy of the test, multiple test areas may be taken and the average value taken.

[0131] In the negative electrode sheet of this application, the compressed density of the negative electrode sheet is a well-known concept in the art and can be measured using equipment and methods known in the art. The compressed density of the negative electrode sheet = surface density of the negative electrode sheet / thickness of the coating layer on one side of the negative electrode current collector. The surface density of the negative electrode sheet is a well-known concept in the art and can be measured using equipment and methods known in the art. One exemplary test method involves punching out a negative electrode sheet coated on one side and cold-pressed (if the negative electrode sheet is coated on both sides, the coating layer on one side can be wiped off first) into a small wafer with an area of ​​S1, weighing it and writing it as M1, then wiping off the coating layer of the weighed negative electrode sheet, weighing the negative electrode current collector and writing it as M0, and writing the surface density of the negative electrode sheet = (M1-M0) / S1.

[0132] Furthermore, the various parameters for the first and second negative electrode active materials may be tested by sampling before coating, or by sampling from the negative electrode sheet, battery assembly, or secondary battery after cold pressing. When the test sample is sampled from the negative electrode sheet, battery assembly, or secondary battery after cold pressing, for example, (1) a step of arbitrarily selecting the cold-pressed coating layer on one side of the negative electrode current collector and sampling the second negative electrode active material (for example, by scraping off the powder using a blade), and ensuring that the depth of scraping does not exceed the boundary region between the second negative electrode film layer and the first negative electrode film layer, and (2) sampling the first negative electrode active material (which may be sampled by scraping off the powder using a blade), and in the cold pressing process, the second negative electrode film Since a mutually fused layer may exist in the boundary region between the layer and the first negative electrode film layer, for the accuracy of the test, when sampling the first negative electrode active material, the mutually fused layer is first scraped off, and then the sample is scraped off from the first negative electrode active material; and (3) the collected first negative electrode active material and second negative electrode active material are each placed in deionized water, then subjected to suction filtration and drying, and the dried powder is sintered at a constant temperature and time (e.g., 400°C, 2h) to remove the adhesive and conductive agent, thereby obtaining a test sample. [Positive electrode sheet]

[0133] In some embodiments, the positive electrode sheet includes a positive electrode current collector and a positive electrode film layer provided on at least one surface of the positive electrode current collector. For example, the positive electrode current collector has two opposing surfaces in its thickness direction, and the positive electrode film layer is provided on one or both of the two opposing surfaces of the positive electrode current collector.

[0134] The above positive electrode film layer includes a positive electrode active material, and the positive electrode active material may be a positive electrode active material for secondary batteries that is well known in the art. For example, the positive electrode active material may include one or more types selected from lithium transition metal oxides, lithium-containing phosphates, and their respective modified compounds. Examples of lithium transition metal oxides include lithium cobalt oxide (e.g., LiCoO2), lithium nickel oxide (e.g., LiNiO2), lithium manganese oxide (e.g., LiMnO2, LiMn2O4), lithium nickel cobalt oxide, lithium manganese cobalt oxide, lithium nickel manganese oxide, and lithium nickel cobalt manganese oxide (e.g., LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2, LiLiLi 0.5 Co 0.2 Mn 0.3 O2, LiLiLi 0.5 Co 0.25 Mn 0.25 O2, LiLiLi 0.6 Co 0.2 Mn 0.2 O2, LiLiLi 0.8 Co 0.1 Mn 0.1 O2), lithium nickel cobalt aluminum oxide (e.g., LiNi 0.85 Co 0.15 Al 0.05 The material may include one or more combinations selected from O2) and its respective modified compounds. Examples of lithium-containing phosphates may include lithium iron phosphate, composite materials of lithium iron phosphate and carbon, lithium manganese phosphate, composite materials of lithium manganese phosphate and carbon, lithium iron manganese phosphate, composite materials of lithium iron manganese phosphate and carbon, and one or more combinations selected from these modified compounds.

[0135] In some embodiments, in order to further increase the energy density of the secondary battery, the positive electrode active material may include one or more combinations of lithium transition metal oxides and their modified compounds shown in Formula 1.

[0136] Li a Ni b Co c M d O e A f Formula 1

[0137] In Formula 1, 0.8 ≤ a ≤ 1.2, 0.5 ≤ b < 1, 0 < c < 1, 0 < d < 1, 1 ≤ e ≤ 2, 0 ≤ f ≤ 1, M may include one or more combinations selected from Mn, Al, Zr, Zn, Cu, Cr, Mg, Fe, V, Ti, and B, and A may include one or more combinations selected from N, F, S, and Cl.

[0138] In the present application, the modified compound of each of the above positive electrode active materials is obtained by doping modification or / and surface coating modification of the above positive electrode active material.

[0139] In some embodiments, the above positive electrode film layer may further include a conductive agent. The conductive agent serves to collect microcurrents between the positive electrode active materials, reduce the contact resistance of the electrode, accelerate the electron transfer rate, reduce polarization, and improve the charge-discharge efficiency of the secondary battery. For example, the above conductive agent may include one or more combinations selected from superconducting carbon, conductive graphite, acetylene black, carbon black, ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers. In some embodiments, based on the total mass of the above positive electrode film layer, the mass percentage of the above conductive agent is 5% or less.

[0140] In some embodiments, the positive electrode film layer may further contain an adhesive to adhere the positive electrode active materials together and to adhere the positive electrode film layer to the positive electrode current collector. For example, the adhesive may include one or more types selected from polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), a ternary copolymer of vinylidene fluoride-tetrafluoroethylene-propylene, a ternary copolymer of vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene, a copolymer of tetrafluoroethylene-hexafluoropropylene, and a fluorine-containing acrylate resin. In some embodiments, the mass percentage of the adhesive is 5% or less, calculated based on the total mass of the positive electrode film layer.

[0141] In some embodiments, the positive electrode current collector can be a metal foil film sheet or a composite current collector. Examples of metal foil film sheets include aluminum foil or aluminum alloy foil. The composite current collector may include a polymer material substrate and a metal material layer formed on at least one surface of the polymer material substrate. For example, the metal material may include one or more types selected from aluminum, aluminum alloys, nickel, nickel alloys, titanium, titanium alloys, silver, and silver alloys. The polymer material substrate may include one or more types selected from polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), and polyethylene (PE).

[0142] The positive electrode film layer described above is generally formed by applying a positive electrode slurry to a positive electrode current collector, drying it, and cold pressing it. The positive electrode slurry is generally formed by dispersing a positive electrode active material, a conductive agent, an adhesive, and any other components in a solvent and stirring it uniformly. The solvent may be, but is not limited to, N-methylpyrrolidone (NMP).

[0143] The electrode assembly 6 of this application will be described below with reference to the drawings.

[0144] Figure 1 is a schematic diagram of one embodiment of the electrode assembly 6 of this application. As shown in Figure 1, the electrode assembly 6 includes a negative electrode sheet 10, a positive electrode sheet 20, and a separator 30 located between the negative electrode sheet 10 and the positive electrode sheet 20. The negative electrode sheet 10 includes a negative electrode current collector 100 and a first negative electrode film layer 101 and a second negative electrode film layer 102 located on both sides of the negative electrode current collector 100, with the first negative electrode film layer 101 located between the negative electrode current collector 100 and the second negative electrode film layer 102. The separator 30 includes a base film 300 and functional coating layers 301 located on both sides of the base film 300. The positive electrode sheet 20 includes a positive electrode current collector 200 and positive electrode film layers 201 located on both sides of the positive electrode current collector 200.

[0145] Figure 2 is a schematic diagram of one embodiment of the electrode assembly 6 of this application. As shown in Figure 2, the electrode assembly 6 includes a negative electrode sheet 10, a positive electrode sheet 20, and a separator 30 located between the negative electrode sheet 10 and the positive electrode sheet 20. The negative electrode sheet 10 includes a negative electrode current collector 100 and a first negative electrode film layer 101 and a second negative electrode film layer 102 located on both sides of the negative electrode current collector 100, with the first negative electrode film layer 101 located between the negative electrode current collector 100 and the second negative electrode film layer 102. The separator 30 includes a base film 300 and a functional coating layer 301 and an adhesive layer 302 located on both sides of the base film 300. The positive electrode sheet 20 includes a positive electrode current collector 200 and a positive electrode film layer 201 located on both sides of the positive electrode current collector 200.

[0146] As shown in Figures 1 and 2, the first negative electrode film layer 101 and the second negative electrode film layer 102 are provided on two surfaces of the negative electrode current collector 100. Of course, in some embodiments, the first negative electrode film layer 101 and the second negative electrode film layer 102 may be provided on only one surface of the negative electrode current collector 100. The positive electrode film layer 201 is provided on two surfaces of the positive electrode current collector 200. Of course, in some embodiments, the positive electrode film layer 201 may be provided on only one surface of the positive electrode current collector 200. The functional coating layer 301 is provided on both sides of the base film 300. Of course, in some embodiments, the functional coating layer 301 may be provided on only one surface of the base film 300 that faces the second negative electrode film layer 102 of the negative electrode sheet 10. secondary battery

[0147] Embodiments of this application further provide a secondary battery. A secondary battery, also called a rechargeable battery or storage battery, is a battery that can be used continuously by activating the active material through charging after discharge. The secondary battery of this application includes the electrode assembly and electrolyte of this application. The secondary battery of this application may be a lithium-containing secondary battery, and in particular may be a lithium-ion secondary battery.

[0148] The electrolyte comprises a lithium salt and a solvent. For example, the lithium salt may include one or a combination of several selected from lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium perchlorate (LiClO4), lithium hexafluoroarsenate (LiAsF6), lithium bisfluorosulfonylimide (LiFSI), lithium bistrifluoromethanesulfonylimide (LiTFSI), lithium trifluoromethanesulfonate (LiTFS), lithium difluorooxalate borate (LiDFOB), lithium disoxalate borate (LiBOB), lithium difluorophosphate (LiPO2F2), lithium difluorodisoxalate phosphate (LiDFOP), and lithium tetrafluorooxalate phosphate (LiTFOP). For example, the above organic solvent may include one or more types selected from ethylene carbonate (EC), propylene carbonate (PC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), butylene carbonate (BC), methyl formate (MF), methyl acetate (MA), ethyl acetate (EA), propyl acetate (PA), methyl propionate (MP), ethyl propionate (EP), propyl propionate (PP), methyl butyrate (MB), ethyl butyrate (EB), 1,4-butyrolactone (GBL), sulfolane (SF), dimethyl sulfone (MSM), methyl ethyl sulfone (EMS), and diethyl sulfone (ESE).

[0149] In some embodiments, the electrolyte may further contain additives, such as a negative electrode film-forming additive and a positive electrode film-forming additive, and may further contain additives that can improve some aspects of the battery's performance, such as an additive that improves the battery's overcharge performance and an additive that improves the battery's high-temperature or low-temperature performance.

[0150] In some embodiments, the secondary battery may include an outer casing. This casing can be used to seal the electrode assembly and electrolyte of this application.

[0151] In some embodiments, the casing of the secondary battery may be a hard package, such as a rigid plastic case, an aluminum case, or a steel case. The casing of the secondary battery may also be a soft package, such as a bug soft package. The material of the soft package may be plastic, such as one or more of the following: polypropylene (PP), polybutylene terephthalate (PBT), or polybutylene succinate (PBS).

[0152] The shape of the secondary battery in this application is not particularly limited and may be cylindrical, rectangular, or any other shape. Figure 3 shows a rectangular secondary battery 5 as an example.

[0153] In some embodiments, as shown in Figure 4, the exterior may include a housing 51 and a cover plate 53. The housing 51 includes a bottom plate and side plates connected to the bottom plate, and the bottom plate and side plates enclose each other to form a housing chamber. The housing 51 has an opening that communicates with the housing chamber, and the cover plate 53 is provided to cover the opening so as to seal the housing chamber. The positive electrode sheet, negative electrode sheet and separator can be formed into an electrode assembly 52 by a winding process and / or a lamination process. The electrode assembly 52 is packaged into the housing chamber. The electrolyte is impregnated into the electrode assembly 52. ​​The number of electrode assemblies 52 included in the secondary battery 5 may be one or more, and may be adjusted as required.

[0154] The method for manufacturing a secondary battery described in this application is well known. In some embodiments, a secondary battery can be formed by assembling a positive electrode sheet, a separator, a negative electrode sheet, and an electrolyte. For example, an electrode assembly can be formed by winding or laminating a positive electrode sheet, a separator, and a negative electrode sheet, the electrode assembly can be placed inside an outer casing, dried, and then an electrolyte can be injected. A secondary battery can then be obtained by going through processes such as vacuum sealing, standing, chemical formation, and shaping.

[0155] In some embodiments of this application, the secondary battery of this application may be assembled into a battery module, and the number of secondary batteries included in the battery module may be multiple, and the specific number may be adjusted according to the application and capacity of the battery module.

[0156] Figure 5 is a schematic diagram of an example battery module 4. As shown in Figure 5, in the battery module 4, the multiple secondary batteries 5 may be arranged sequentially along the longitudinal direction of the battery module 4. Of course, they may be arranged in any other manner. Furthermore, these multiple secondary batteries 5 may be fixed together with fasteners.

[0157] Optionally, the battery module 4 further includes an external case having a housing space, and a plurality of secondary batteries 5 are housed in said housing space.

[0158] In some embodiments, the battery modules may be assembled into a battery pack. The number of battery modules included in the battery pack may be adjusted according to the application and capacity of the battery pack.

[0159] Figures 6 and 7 are schematic diagrams of an example battery pack 1. As shown in Figures 6 and 7, the battery pack 1 may include a battery case and a plurality of battery modules 4 provided in the battery case. The battery case includes an upper case 2 and a lower case 3, with the upper case 2 covering the lower case 3 to form a sealed space for housing the battery modules 4. The plurality of battery modules 4 may be arranged in the battery case in any manner. power consumption equipment

[0160] Embodiments of this application provide a power consumption device comprising at least one of the secondary battery, battery module, or battery pack of this application. The secondary battery, battery module, or battery pack may be used as a power source for the power consumption device or as an energy storage means for the power consumption device. The power consumption device may be, but is not limited to, mobile devices (e.g., mobile phones, laptops, etc.), electric vehicles (e.g., pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), trains, ships, satellites, energy storage systems, etc.

[0161] The above-mentioned power consumption device can be configured to use a secondary battery, battery module, or battery pack depending on the demand.

[0162] Figure 8 is a schematic diagram of an example of a power consumption device. This power consumption device includes pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, etc. To meet the high power and high energy density requirements of this power consumption device, a battery pack or battery module can be used.

[0163] Other examples of power-consuming devices may include mobile phones, tablet computers, and laptop computers. These power-consuming devices generally require a thin profile and can utilize rechargeable batteries as their power source. Examples

[0164] The following examples illustrate the contents of this application in more detail; however, these examples are merely illustrative, and it will be apparent to those skilled in the art that various modifications and changes can be made within the scope of the disclosures of this application. Unless otherwise specified, all parts, percentages, and ratios mentioned in the following examples are based on mass. Furthermore, all reagents used in the examples may be commercially available or synthesized according to conventional methods, and may be used as is without requiring further processing. Furthermore, all apparatus used in the examples are commercially available. Example 1-1

[0165] Process (1): Manufacturing of negative electrode sheets

[0166] S10 Manufacturing of artificial graphite

[0167] After pre-treating the raw coke raw material powder of non-acupuncture petroleum coke, impurities are removed, and then it is mixed with coal pitch and granulated to obtain secondary particles with a Dv50 of 10 μm. The granules are then placed in an Acheson graphitization furnace and graphitized at 3000°C for 24 hours to obtain graphite particles. The obtained graphite particles are mixed with petroleum pitch and then carbonized at 1000°C for 15 hours to obtain artificial graphite. The artificial graphite has a Dv50 of 12 μm, a Dv90 of 20 μm, a Dv10 of 6.5 μm, a degree of graphitization of 92%, and a specific surface area of ​​0.86 m². 2 The density is / g, and the compressed density of the powder is 1.6 g / cm³. 3 Therefore, topography is a secondary particle system.

[0168] Manufacturing of S20 hard carbon

[0169] A precursor is obtained by heat-treating a phenolic resin at 500°C for 30 minutes. The obtained precursor is then pulverized, heat-treated at 1200°C for 20 hours under a nitrogen gas atmosphere, and pulverized again to obtain hard carbon. The hard carbon has a Dv50 of 5 μm, a Dv90 of 10 μm, and a Dv10 of 2.5 μm, with a specific surface area of ​​5 m². 2 The values ​​are / g, and the topography is primary particles.

[0170] S30 Preparation of the First Slurry

[0171] The above-prepared artificial graphite, conductive carbon black as a conductive agent, styrene-butadiene rubber (SBR) as an adhesive, and sodium carboxymethyl cellulose (CMC) as a thickener are mixed at a mass ratio of 96.8:0.8:1.2:1.2, and then added to deionized water. The mixture is stirred by a vacuum stirrer until the system becomes uniform, and a first slurry with a solid content of 66% is obtained.

[0172] S40 Preparation of the Second Slurry

[0173] The above-prepared hard carbon, conductive carbon black as a conductive agent, styrene-butadiene rubber (SBR) as an adhesive, and sodium carboxymethyl cellulose (CMC) as a thickener are mixed at a mass ratio of 95:1.5:3.1:0.4, and then added to deionized water. The mixture is stirred under the action of a vacuum stirrer until the system becomes uniform, and a second slurry with a solid content of 66% is obtained.

[0174] S50 Coating of the Slurry

[0175] The first slurry is coated on one surface of a copper foil, which is a negative electrode current collector with a thickness of 8 μm, and dried to form a first negative electrode film layer. The second slurry is coated on the first negative electrode film layer and dried to form a second negative electrode film layer. Then, the above process is repeated on the other surface of the copper foil, which is the negative electrode current collector. After further passing through processes such as cold pressing, a negative electrode sheet is obtained. The thickness of the first negative electrode film layer on one side of the negative electrode current collector is 59 μm, and the thickness of the second negative electrode film layer is 82 μm. The compression density of the negative electrode sheet is 1.55 g / cm 3 is

[0176] Process (2): Manufacturing of the positive electrode sheet

[0177] LiNi as the positive electrode active material 0.8 Co 0.1 Mn 0.1O2 (NCM811), conductive carbon black (a conductive agent), and polyvinylidene fluoride (PVDF) (an adhesive) are mixed in a mass ratio of 98:1:1. This mixture is then added to the solvent NMP, and the mixture is stirred using a vacuum stirrer until the system is homogeneous to obtain a positive electrode slurry with a solid content of 75%. The positive electrode slurry is then uniformly applied to two surfaces of 13 μm thick aluminum foil, dried at 90°C, and then cold-pressed to obtain a positive electrode sheet with a positive electrode film layer thickness of 114 μm on one side of the positive electrode current collector.

[0178] Step (3): Preparation of electrolyte

[0179] In an environment with a water content of less than 10 ppm, ethylene carbonate (EC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) are mixed in a volume ratio of 1:1:1 to obtain an organic solvent. Then, thoroughly dried LiPF6 is dissolved in the above organic solvent to prepare an electrolyte solution with a concentration of 1 mol / L.

[0180] Process (4): Manufacturing of separators

[0181] Barium titanate (dielectric constant of 3000 or more) with a Dv50 of 100 nm, styrene-butadiene rubber (SBR) as an adhesive, and sodium carboxymethylcellulose (CMC) as a dispersant are mixed in a mass ratio of 85:10:5. This mixture is then added to deionized water and stirred with a vacuum stirrer until the system is uniform to obtain a slurry with a solid content of 40%. The slurry is then applied to two surfaces of a porous polyethylene film (thickness 10 μm), dried, and a functional coating layer with a thickness of 2 μm on each side is formed.

[0182] Process (5): Manufacturing of secondary batteries

[0183] A positive electrode sheet, a separator, and a negative electrode sheet are sequentially laminated so that the side of the separator that covers the functional coating layer faces the second functional layer of the negative electrode sheet. Then, they are wound to obtain an electrode assembly. The electrode assembly is placed in an outer casing, dried, and then an electrolyte is injected. After going through processes such as vacuum sealing, standing, chemical formation, and shaping, a secondary battery is obtained. Examples 1-2 to 1-7

[0184] The secondary battery was manufactured in a similar manner to Example 1-1, except for differences in the slurry coating thickness in the separator manufacturing process and the thickness of the functional coating layer obtained therefrom. For specific parameters, please refer to Table 1. Comparative Example 1-1

[0185] The secondary battery is manufactured in a similar manner to Example 1-1, except that the separator uses a porous polyethylene film. Comparative Example 1-2

[0186] The secondary battery is manufactured in a similar manner to Example 1-1, except that the separator uses a porous polyethylene film and the order of slurry application in the manufacturing of the negative electrode sheet is different.

[0187] First, a second slurry is applied to one surface of a copper foil negative electrode current collector with a thickness of 8 μm, and dried to form a first negative electrode film layer. Then, the first slurry is applied to the first negative electrode film layer and dried to form a second negative electrode film layer. After that, the above process is repeated on the other surface of the copper foil negative electrode current collector, and after processes such as cold pressing, a negative electrode sheet is obtained. The thickness of the first negative electrode film layer on one side of the negative electrode current collector is 82 μm, and the thickness of the second negative electrode film layer is 59 μm. Comparative Examples 1-3

[0188] The secondary battery is manufactured in a manner similar to Example 1-1, except that the separator uses a porous polyethylene film and the second slurry is not applied during the manufacturing of the negative electrode sheet.

[0189] A first slurry is applied to two surfaces of a copper foil negative electrode current collector with a thickness of 8 μm. After drying, cold pressing, and other processes, a negative electrode sheet is obtained. The thickness of the negative electrode film layer on one side of the negative electrode current collector is 141 μm. Comparative Example 1-4

[0190] The secondary battery is manufactured in a similar manner to Example 1-1, except that a porous polyethylene film is used for the separator and the first slurry is not applied during the manufacturing of the negative electrode sheet.

[0191] A second slurry is applied to two surfaces of a copper foil negative electrode current collector with a thickness of 8 μm. After drying, cold pressing, and other processes, a negative electrode sheet is obtained. The thickness of the negative electrode film layer on one side of the negative electrode current collector is 141 μm. Comparative Examples 1-5

[0192] The secondary battery is manufactured in a similar manner to Example 1-1, except that the separator uses a porous polyethylene film and the manufacturing process for the negative electrode sheet is different.

[0193] S10 to S20 are the same as in Example 1-1.

[0194] S30 Preparation of slurry

[0195] The artificial graphite produced above, hard carbon, conductive carbon black as a conductive agent, styrene-butadiene rubber (SBR) as an adhesive, and sodium carboxymethylcellulose (CMC) as a thickener are mixed in a mass ratio of 40:55:1.5:3.1:0.4. This mixture is then added to deionized water and stirred using a vacuum stirrer until the system is homogeneous, yielding a slurry with a solid content of 66%.

[0196] S40 Slurry application

[0197] A slurry is applied to two surfaces of a copper foil negative electrode current collector with a thickness of 8 μm. After drying, cold pressing, and other processes, a negative electrode sheet is obtained. The thickness of the negative electrode film layer on one side of the negative electrode current collector is 141 μm. Comparative Examples 1-6

[0198] The secondary battery is manufactured in a similar manner to Example 1-1, except that the separator uses a porous polyethylene film and the manufacturing process for the negative electrode sheet is different.

[0199] S10 to S30 are the same as in Example 1.

[0200] S40 Preparation of the second slurry

[0201] The hard carbon produced above, barium titanate (Dv50 of 100 nm, dielectric constant of 3000 or more), conductive carbon black as a conductive agent, styrene-butadiene rubber (SBR) as an adhesive, and sodium carboxymethylcellulose (CMC) as a thickener are mixed in a mass ratio of 93:1:1.5:3.1:0.4. This mixture is then added to deionized water and stirred using a vacuum stirrer until the system is homogeneous to obtain a second slurry with a solid content of 66%.

[0202] S50 Slurry Application

[0203] The first slurry is applied to one surface of a copper foil negative electrode current collector with a thickness of 8 μm and dried to form a first negative electrode film layer. The second slurry is then applied to the first negative electrode film layer and dried to form a second negative electrode film layer. The above process is then repeated on the other surface of the copper foil negative electrode current collector, and after further processes such as cold pressing, a negative electrode sheet is obtained. The thickness of the first negative electrode film layer on one side of the negative electrode current collector is 59 μm, and the thickness of the second negative electrode film layer is 82 μm. Test section

[0204] (1) Testing the maximum charge rate

[0205] At 25°C, the rechargeable battery manufactured above is fully discharged at a rate of 0.33C, fully charged at a rate of 0.33C, left to stand for 5 minutes, and then fully discharged at a rate of 0.33C. The discharge capacity obtained at this time is the actual capacity of the rechargeable battery at a rate of 1C and is denoted as C0. The rechargeable battery is fully charged at a rate of xC0 (a gradient of the charging rate, e.g., 1C0, 1.1C0, 1.2C0, 1.3C0, 1.4C0, etc.), left to stand for 5 minutes, and then fully discharged at 1C. After 10 such cycles, the rechargeable battery is fully charged again at 1C. The rechargeable battery is disassembled and the lithium deposition status on the negative electrode sheet surface is observed. If lithium has not deposited on the negative electrode sheet surface, the charging rate is increased until lithium deposits on the negative electrode sheet surface, and the measurement is repeated. The maximum charging rate at which lithium does not deposit on the negative electrode sheet surface is recorded. The higher the maximum charging rate of the rechargeable battery, the better the charging capacity at high rates.

[0206] (2) Energy density test

[0207] At 25°C, the secondary battery manufactured above is fully charged at a rate of 0.33C and fully discharged at a rate of 0.33C. After completing three such cycles, the discharge energy of the secondary battery is recorded. Energy density of the secondary battery = discharge energy of the secondary battery / mass of the secondary battery. In each example and comparative example of this application, the energy density of the secondary battery of the other examples and comparative examples is shown, with the energy density of the secondary battery manufactured in Comparative Example 1-1 being set to 100%.

[0208] (3) Cycle life testing

[0209] At 25°C, the rechargeable battery manufactured as described above is fully discharged at a 1C rate, fully charged at a 1C rate, allowed to stand for 5 minutes, and then fully discharged at a 1C rate. The discharge capacity C0 obtained at this time is taken as the initial capacity of the rechargeable battery. The rechargeable battery is then fully charged at a 3C rate and fully discharged at a 1C rate. A cycle charge-discharge test is performed in this manner, and the discharge capacity is recorded after each cycle until the discharge capacity of the rechargeable battery decreases to 80% of the initial capacity. The cycle life of the rechargeable battery is represented by the number of cycles at this time. It is expected that the cycle life will be longer as the number of cycles of the rechargeable battery increases. [Table 1]

[0210] Summarizing the test results of Examples 1-1 to 1-7 and Comparative Examples 1-1 to 1-6, it was found that secondary batteries using the electrode assembly of this application have both a high charge rate and a long cycle life. In Comparative Example 1-1, since no functional coating layer is provided on the surface of the separator, the manufactured secondary battery cannot have both a high charge rate and a long cycle life. In Comparative Example 1-2, since no functional coating layer is provided on the surface of the separator, and a hard carbon layer and a graphite layer are sequentially provided on the surface of the negative electrode current collector, it is difficult for the secondary battery to achieve both a high charge rate and a long cycle life. In Comparative Example 1-3, since no functional coating layer is provided on the surface of the separator, and a graphite layer is provided only on the surface of the negative electrode current collector, the secondary battery has a long cycle life, but it is difficult to obtain a high charge rate. In Comparative Example 1-4, since no functional coating layer is provided on the surface of the separator, and a hard carbon layer is provided only on the surface of the negative electrode current collector, the secondary battery can have a high charge rate, but it is difficult to have a long cycle life. In Comparative Examples 1-5, a functional coating layer is not provided on the surface of the separator, and a mixed layer of graphite and hard carbon is provided on the surface of the negative electrode current collector. Therefore, it is difficult for the secondary battery to achieve both a high charge rate and a long cycle life. Compared to Comparative Example 1-1, the hard carbon layer of Comparative Example 1-6 also contains barium titanate, but barium titanate has a low effect in suppressing the continued growth of lithium dendrites in a direction perpendicular to the electrode sheet, and is therefore unlikely to significantly improve the charge rate and cycle life of the secondary battery.

[0211] Summarizing the test results of Examples 1-1 to 1-7, it was found that increasing the thickness of the functional coating layer on the separator increased both the maximum charge rate and cycle life of the secondary battery. This is likely because the increased reverse electric field strength due to the functional coating layer enhances the effect of suppressing the continued growth of lithium dendrites perpendicular to the electrode sheet, thereby improving the high-rate charging capacity and cycle performance of the secondary battery.

[0212] Summarizing the test results of Examples 1-1 to 1-7, it was found that when H1 / (H2+H3) is less than 0.01, the functional coating layer of the separator is set to be small relative to the total thickness of the first and second negative electrode film layers, and the effect of suppressing the continued growth of lithium dendrites perpendicular to the electrode sheet is not clear. Consequently, the effect of improving the maximum charge rate of the secondary battery is not clear.

[0213] Summarizing the test results of Examples 1-6 and 1-7, it was found that when H1 is greater than 10, the effect of suppressing the growth of the separator's functional coating layer perpendicular to the lithium dendrite electrode sheet does not increase sustainably. At the same time, the functional coating layer does not have electrochemical activity and cannot contribute to capacity, so when its thickness is greater than 10 μm, the energy density of the secondary battery clearly decreases.

[0214] Next, the inventors studied the effect of the mass percentage of ferroelectric material in the functional coating layer of the separator on the performance of the secondary battery. The secondary batteries of Examples 2-1 to 2-6 are manufactured in a similar manner to Example 1-2, except that the mass percentage of ferroelectric material in the functional coating layer of the separator differs. [Table 2]

[0215] Summarizing the test results of Examples 1-2 and 2-1 to 2-6, it was found that when the thickness of the functional coating layer of the separator was fixed at 4 μm, both the maximum charge rate and cycle life of the secondary battery increased as the mass percentage of the ferroelectric material in the functional coating layer increased. In this case, the increase in the reverse electric field strength due to the functional coating layer increases the effect of suppressing the continued growth of lithium dendrites in a direction perpendicular to the electrode sheet, which is a possible factor that improves the high-rate charging capacity and cycle performance of the secondary battery.

[0216] Summarizing the test results of Comparative Example 1-1 and Example 2-1, it was found that when the mass percentage of the ferroelectric material in the functional coating layer of the separator is small, the resulting functional coating layer does not clearly have the effect of suppressing the continued growth of lithium dendrites in a direction perpendicular to the electrode sheet. Consequently, it was further found that the effect of improving the maximum charge rate of the secondary battery is not clear.

[0217] Summarizing the test results of Examples 2-5 and 2-6, it was found that when the mass percentage of the ferroelectric material in the functional coating layer of the separator is greater than 95%, the cycle performance of the secondary battery is clearly worsened. In this case, a possible cause is that the adhesive content in the functional coating layer of the separator is too low, which may cause the functional coating layer to detach from the surface of the base film during the long-term cycle charge-discharge process of the secondary battery.

[0218] Next, the inventors studied the influence of the volume-average particle size Dv50 of the ferroelectric material in the functional coating layer of the separator on the secondary battery performance. The secondary batteries of Examples 3-1 to 3-6 are manufactured in a similar manner to Example 1-2, except that the volume-average particle size Dv50 of the ferroelectric material in the functional coating layer of the separator differs. [Table 3]

[0219] Summarizing the test results of Examples 1-2 and 3-1 to 3-6, it was found that when the thickness of the separator's functional coating layer is fixed at 4 μm and the mass percentage of the ferroelectric material is fixed at 85%, both the maximum charge rate and cycle life of the secondary battery decrease as the volume-average particle size Dv50 of the ferroelectric material increases. This is a possible factor because as the volume-average particle size Dv50 of the ferroelectric material increases, the interference of the reverse electric field it generates increases, which worsens the effect of suppressing the continued growth of lithium dendrites in the direction perpendicular to the electrode sheet. Therefore, both the maximum charge rate and cycle life of the secondary battery decrease.

[0220] Next, the inventors studied the effect of the thickness of the first negative electrode film layer and the thickness of the second negative electrode film layer on the performance of the secondary battery. The secondary batteries of Examples 4-1 to 4-7 are manufactured in a similar manner to those of Example 1-2, except that the thickness of the first negative electrode film layer and the thickness of the second negative electrode film layer are different. [Table 4]

[0221] In summary, the test results from Examples 4-1 to 4-7 show that increasing the thickness of the second negative electrode film layer increases the maximum charge rate of the secondary battery.

[0222] Summarizing the test results of Examples 4-1 to 4-7, it was found that when the thickness of the second negative electrode film layer H2μm and the thickness of the first negative electrode film layer H3μm satisfy the condition that H2 / H3 is between 0.25 and 4, the secondary battery can simultaneously have a high maximum charge rate and a long cycle life. When H2 / H3 is less than 0.25, the second negative electrode film layer is thin, and the effect of improving the maximum charge rate of the secondary battery is not significant. When H2 / H3 is greater than 4, the second negative electrode film layer is thick, and the cycle performance of the hard carbon itself is poor, resulting in poor cycle performance of the secondary battery. Summarizing the test results of Example 4-7 and Comparative Example 1-4, it was found that when H2 / H3 is greater than 4, the improvement in the cycle life of the secondary battery is not significant.

[0223] This application is not limited to the embodiments described above. The embodiments described above are illustrative, and any configuration that is substantially identical to the technical idea and produces similar effects within the technical scope of this application is included. Furthermore, other forms that can be conceived by a person skilled in the art, which involve various modifications to the embodiments and are constructed by combining some of the components of the embodiments, are also included in the scope of this application, without departing from the spirit of this application.

Claims

1. An electrode assembly comprising a negative electrode sheet, a positive electrode sheet, and a separator positioned between the negative electrode sheet and the positive electrode sheet, The negative electrode sheet comprises a negative electrode current collector and a first negative electrode film layer and a second negative electrode film layer provided on at least one surface of the negative electrode current collector, wherein the first negative electrode film layer is located between the negative electrode current collector and the second negative electrode film layer and comprises a first negative electrode active material containing graphite, and the second negative electrode film layer comprises a second negative electrode active material containing hard carbon. The separator comprises a base film and a functional coating layer located at least on the side of the base film facing the second negative electrode film layer, wherein the functional coating layer comprises an inorganic ferroelectric material. Electrode assembly.

2. The thickness of the functional coating layer is H １ The thickness of the second negative electrode film layer is H ２ The thickness of the first negative electrode film layer is H ３ The electrode assembly is H １ / ( H ２ +H ３ ) satisfies the condition that is between 0.01 and 0.

15. The electrode assembly according to claim 1.

3. The thickness of the functional coating layer is H １ It is μm and H １ The range is 2 to 10. The electrode assembly according to claim 1.

4. The thickness of the second negative electrode film layer is H ２ μm, and the thickness of the first negative electrode film layer is H ３ μm, and the negative electrode sheet satisfies that H ２ / H ３ is 0.10 to 5 The electrode assembly according to claim 1.

5. The volume-average particle size Dv50 of the ferroelectric material is d １ It is μm and d １ It is less than or equal to 1. The electrode assembly according to claim 1.

6. The volume-average particle size Dv50 of the second negative electrode active material is d ２ The volume-average particle size Dv50 of the first negative electrode active material is μm, and d ３ It is μm and d ２ / d ３ It is between 0.1 and 1. The electrode assembly according to claim 1.

7. The mass percentage of the ferroelectric material in the functional coating layer is W1, which is calculated based on the total mass of the functional coating layer, and W1 is between 70% and 95%. The electrode assembly according to claim 1.

8. The functional coating layer further comprises an adhesive. The electrode assembly according to claim 1.

9. The separator further includes an adhesive layer provided on the surface of the functional coating layer. The electrode assembly according to claim 1.

10. The dielectric constant of the ferroelectric material is 50 or more. The electrode assembly according to claim 1.

11. The mass percentage of hard carbon in the second negative electrode film layer is W2, and calculated based on the total mass of the second negative electrode film layer, W2 is 68% or more, and / or The mass percentage of graphite in the first negative electrode film layer is W3, and calculated based on the total mass of the first negative electrode film layer, W3 is 78% or more. The electrode assembly according to claim 1.

12. The second negative electrode active material is (1) The volume average particle size Dv50 of the second negative electrode active material is d ２ It is μm and d ２ The condition that is 3 to 11 is met. The electrode assembly according to claim 1.

13. The first negative electrode active material is (1) The volume average particle size Dv50 of the first negative electrode active material is d ３ It is μm and d ３ The condition that is between 9 and 18 is met. The electrode assembly according to claim 1.

14. The electrode assembly comprises the one described in claim 1. Secondary battery.

15. A secondary battery as described in claim 14, Battery module.

16. A secondary battery as described in claim 14, Battery pack.

17. The invention comprises at least one of the secondary battery described in claim 14, the battery module described in claim 15, and the battery pack described in claim 16. Power consumption equipment.

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