Negative electrode sheet, method for manufacturing the same, secondary battery, and power consumption device

Abstract

The present application provides a negative electrode sheet, a method for manufacturing the same, a secondary battery, and an electric power consumption device. The negative electrode sheet includes a negative electrode current collector and a negative electrode active material layer provided on the negative electrode current collector. The negative electrode active material layer contains a negative electrode active material and an additive. The additive includes a shell wall and a cavity located inside the shell wall. Let the thickness of the shell wall be d and the volume of the cavity be V h , and the volume of the additive be V w . The additive satisfies 20 nm ≤ d ≤ 300 nm and 40% ≤ Vh / Vw ≤ 90%. The present application can effectively reduce the swelling force of the secondary battery and improve the safety performance of the secondary battery.

Description

[Technical Field]

[0001] This application relates to the field of battery technology, and more specifically to negative electrode sheets, methods for manufacturing the same, secondary batteries, and power consumption devices. [Background technology]

[0002] Rechargeable batteries are widely used in many fields, including energy storage and power systems such as hydroelectric, thermal, wind, and solar power plants, as well as power tools, electric bicycles, electric motorcycles, electric vehicles, military equipment, and aerospace. With the increasing application and proliferation of rechargeable batteries, their safety performance is receiving increasing attention. If the safety of a rechargeable battery cannot be guaranteed, it cannot be used. Therefore, improving the safety performance of rechargeable batteries is a challenge that needs to be addressed today. [Overview of the Initiative]

[0003] The present invention aims to provide a negative electrode sheet, a method for manufacturing the same, a secondary battery, and a power consumption device that can effectively reduce the expansion force of a secondary battery and improve the safety performance of the secondary battery.

[0004] A first aspect of the present application provides a negative electrode sheet comprising a negative electrode current collector and a negative electrode active material layer provided on the negative electrode current collector, wherein the negative electrode active material layer comprises a negative electrode active material and an additive, the additive comprising a shell wall and a cavity located inside the shell wall, the thickness of the shell wall being d and the volume of the cavity being V h , the volume of the additive is V w The additive is defined as having a wavelength of 20 nm ≤ d ≤ 300 nm and a density of 40% ≤ V. h / V w It satisfies ≤90%.

[0005] The additive has a range of 20nm ≤ d ≤ 300nm and 40% ≤ V. h / V wWhen ≦90% is satisfied at the same time, the large cavity structure of the additive can generate large elastic deformation, and further can effectively reduce the adverse effects caused by the expansion of the negative electrode. On the other hand, the additive has high structural stability. Therefore, when large elastic deformation occurs in the additive, the problems of crushing and pulverization do not occur. Therefore, the present application can effectively reduce the expansion force of the secondary battery and improve the safety performance of the secondary battery when the usage amount of the additive is small and does not affect the energy density.

[0006] In any embodiment of the present application, 25 nm≦d≦200 nm, preferably 40 nm≦d≦120 nm. This is advantageous for improving the balance between the structural stability of the additive and the strain capacity of the additive, thereby better reducing the adverse effects caused by the expansion of the negative electrode. When the usage amount of the additive is small and does not affect the energy density, the expansion force of the secondary battery can be effectively reduced, and the safety performance of the secondary battery is improved.

[0007] In any embodiment of the present application, 60%≦V h / V w ≦90%, preferably 70%≦V h / V w ≦89%. This advantageously allows the additive to have relatively large elastic deformation and provides buffer space when particles of the negative electrode active material expand, thereby better reducing the adverse effects caused by the expansion of the negative electrode. When the usage amount of the additive is small and does not affect the energy density, the expansion force of the secondary battery can be effectively reduced, and the safety performance of the secondary battery is improved.

[0008] In any embodiment of the present application, the thickness d of the shell wall of the additive, the volume V of the cavity of the additive h and the volume V of the additive wThe following method is used to obtain the additive: A circular sample with a diameter of 0.5 cm is cut from the negative electrode sheet, a TEM image of the cross-section is obtained using a transmission electron microscope, the thickness of the shell wall of the additive and the volume particle size of the additive within the region are statistically calculated, and cumulative distribution curves of the thickness of the shell wall of the additive and the volume particle size of the additive are obtained, respectively, the thickness corresponding to when the percentage in the cumulative distribution curve is 50% is defined as the thickness of the shell wall of the additive d, and the volume particle size corresponding to when the percentage in the cumulative distribution curve is 50% is defined as the volume particle size of the additive Dv50, and based on the formula for calculating an ideal sphere, the volume V of the additive is defined with the obtained volume particle size Dv50 as the diameter. w Calculate V w =(4 / 3)×π×(Dv50 / 2) 3 The volume V of the cavity of the additive h V h =(4 / 3)×π×(Dv50 / 2-d) 3 That is the case.

[0009] In any embodiment of the present application, the additive comprises one or more types selected from hollow spheres and hollow polyhedra, and may include hollow spheres.

[0010] In any embodiment of the present application, the volume particle size Dv50 of the additive is 0.85 μm to 5 μm, preferably 1 μm to 2.5 μm. This effectively reduces the expansion force of the secondary battery and improves safety performance. On the other hand, it is possible to ensure good cycle performance and rate performance of the secondary battery.

[0011] In any embodiment of the present application, the volume particle size of the additive satisfies 0.5 ≤ (Dv90 - Dv10) / Dv50 ≤ 8, and preferably 2 ≤ (Dv90 - Dv10) / Dv50 ≤ 5.

[0012] In any embodiment of the present application, the additive comprises hollow carbon spheres, and preferably comprises one or more selected from the group consisting of amorphous hollow carbon spheres, graphitized hollow carbon spheres and hollow graphene spheres. This can better reduce the adverse effects caused by the expansion of the negative electrode. When the amount of the additive used is small and does not affect the energy density, the expansion force of the secondary battery can be effectively reduced, and the safety performance of the secondary battery is improved.

[0013] In any embodiment of the present application, the weight percentage content of the additive relative to the total weight of the negative electrode active material layer is 0.01 wt% to 3 wt%, preferably 0.1 wt% to 2 wt%. In the present application, when the amount of the additive used is small and does not affect the energy density, the expansion force of the secondary battery can be effectively reduced, and the safety performance of the secondary battery can be improved.

[0014] In any embodiment of the present application, along the width direction of the negative electrode active material layer, the negative electrode active material layer comprises a first portion and a second portion located on edge sides, and a third portion located between the first portion and the second portion. Let the total width of the negative electrode active material layer be W, the width of the first portion is 1 / 5 W, the width of the second portion is 1 / 5 W, and the width of the third portion is 3 / 5 W. The weight percentage content of the additive in the first portion is w1, the weight percentage content of the additive in the second portion is w2, the weight percentage content of the additive in the third portion is w3, and 0≤w1 / w3<1, 0≤w2 / w3<1. By further adjusting the distribution of the additive in the width direction of the negative electrode active material layer, adopting a high content of the additive in the third portion and a low content of the additive in the first portion and the second portion can not only effectively reduce the expansion force of the secondary battery and improve the safety performance of the secondary battery, but also further reduce the usage amount of the additive and improve the energy density of the secondary battery when the same expansion force improvement effect is achieved.

[0015] In any embodiment of the present application, 0<w1 / w3≤0.7, preferably 0<w1 / w3≤0.5.

[0016] In any embodiment of the present application, 0<w2 / w3≤0.7, preferably 0<w2 / w3≤0.5.

[0017] By further adjusting that the relationship of the ratio between the usage amount of the additive in the first part and / or the second part and the usage amount of the additive in the third part falls within the above range, when the usage amount of the additive is further reduced, the swelling force of the secondary battery can be effectively reduced, and the safety performance of the secondary battery can be improved.

[0018] In any embodiment of the present application, 0wt%≤w1≤2wt%, preferably 0wt%<w1≤1wt%.

[0019] In any embodiment of the present application, 0wt%≤w2≤2wt%, preferably 0wt%<w2≤1wt%.

[0020] In any embodiment of the present application, 0.01wt%≤w3≤5wt%, preferably 0.01wt%≤w3≤2wt%.

[0021] In any embodiment of the present application, w1=w2.

[0022] In any embodiment of the present application, based on the total weight of the negative electrode active material layer, the weight percentage content of the negative electrode active material is 95wt% to 99wt%. This is advantageous for improving the energy density of the secondary battery.

[0023] In any embodiment of the present application, the negative electrode active material layer further comprises a negative electrode adhesive and / or a negative electrode dispersant.

[0024] In any embodiment of the present application, based on the total weight of the negative electrode active material layer, the weight percentage content of the negative electrode adhesive is 1wt% to 2.5wt%.

[0025] In any embodiment of the present application, the weight percentage content of the anode dispersant relative to the total weight of the anode active material layer is 0.5 wt% to 1.5 wt%.

[0026] In any embodiment of the present application, the negative electrode active material layer further comprises a negative electrode conductive agent, preferably the weight percentage content of the negative electrode conductive agent relative to the total weight of the negative electrode active material layer is 0 wt% to 1.5 wt%.

[0027] A second aspect of the present application provides a method for manufacturing a negative electrode sheet, comprising: providing a negative electrode slurry containing a negative electrode active material and an additive; and applying the negative electrode slurry to a negative electrode current collector, drying, and cold pressing to obtain a negative electrode sheet, wherein the negative electrode sheet comprises a negative electrode current collector and a negative electrode active material layer provided on the negative electrode current collector, the negative electrode active material layer comprises a negative electrode active material and an additive, the additive comprises a shell wall and a cavity located inside the shell wall, the thickness of the shell wall being d and the volume of the cavity being V h , the volume of the additive is V w The additive has a range of 20nm ≤ d ≤ 300nm and 40% ≤ V. h / V w It satisfies ≤90%.

[0028] In any embodiment of the present application, along the width direction of the negative electrode current collector, the negative electrode current collector includes a first region and a second region located on the edge side, and a third region located between the first region and the second region, the total width of the coating area of ​​the negative electrode current collector is W, the width of the first region is 1 / 5W, the width of the second region is 1 / 5W, and the width of the third region is 3 / 5W, and in the method for manufacturing the negative electrode sheet, the negative electrode slurry is prepared to include a first slurry, a second slurry and a third slurry, and then The first slurry, the second slurry, and the third slurry are applied to the first, second, and third regions of the negative electrode current collector, respectively, and after drying, the first, second, and third portions of the negative electrode active material layer are formed, wherein the weight percentage content of the additive in the first portion is w1, the weight percentage content of the additive in the second portion is w2, the weight percentage content of the additive in the third portion is w3, and 0 ≤ w1 / w3 < 1 and 0 ≤ w2 / w3 < 1.

[0029] In any embodiment of the present application, the first slurry, the second slurry, and the third slurry are provided in a single simultaneous application process or in a multi-step application process.

[0030] A third aspect of the present application provides a secondary battery comprising a negative electrode sheet described in the first aspect of the present application, or a negative electrode sheet manufactured by the manufacturing method described in the second aspect of the present application.

[0031] In any embodiment of the present application, the secondary battery satisfies 100 ≤ K ≤ 30000, preferably 120 ≤ K ≤ 8000.

number

[0032] In any embodiment of the present application, 20% ≤ λ ≤ 50%, preferably 23% ≤ λ ≤ 35%.

[0033] In any embodiment of the present application, 20% ≤ ε ≤ 40%, and preferably 25% ≤ ε ≤ 35%.

[0034] In any embodiment of the present application, 20 nm ≤ d ≤ 300 nm, preferably 40 nm ≤ d ≤ 120 nm.

[0035] In any embodiment of the present application, 1 × 10 7 nm 3 ≤V h ≤ 1 × 10 12 nm 3 Preferably, 2.5 × 10 8 nm 3 ≤V h ≤ 1 × 10 10 nm 3 That is the case.

[0036] In any embodiment of the present application, 1 × 10 2 mm 2 ≤S ≤ 1 × 10 8 mm 2 Preferably, 1 × 10 3 mm 2 ≤S ≤ 1 × 10 6 mm 2 That is the case.

[0037] In any embodiment of the present application, 10 μm ≤ H ≤ 250 μm, preferably 40 μm ≤ H ≤ 120 μm.

[0038] In any embodiment of the present application, when the capacity of the secondary battery decays to 80% of the initial capacity of the secondary battery, the thickness rebound rate of the first portion of the negative electrode active material layer is denoted as ε1, the initial thickness of the first portion of the negative electrode active material layer is denoted as H1, the unit is μm, the thickness rebound rate of the second portion of the negative electrode active material layer is denoted as ε2, the initial thickness of the second portion of the negative electrode active material layer is denoted as H2, the unit is μm, and the secondary battery satisfies 0 < K1 / K ≤ 1 and 0 < K2 / K ≤ 1.

Formula

[0039] In any embodiment of the present application, 0 < K1 / K ≤ 0.95.

[0040] In any embodiment of the present application, 0 < K2 / K ≤ 0.95.

[0041] In any embodiment of the present application, 100 ≤ K1 ≤ 30000, preferably 120 ≤ K1 ≤ 8000.

[0042] In any embodiment of the present application, 100 ≤ K2 ≤ 30000, preferably 120 ≤ K2 ≤ 8000.

[0043] In any embodiment of the present application, 15% ≤ ε1 ≤ 35%, preferably 25% ≤ ε1 ≤ 31%.

[0044] In any embodiment of the present application, 15% ≤ ε2 ≤ 35%, preferably 25% ≤ ε2 ≤ 31%.

[0045] In any embodiment of the present application, 10 μm ≤ H1 ≤ 250 μm, preferably 40 μm ≤ H1 ≤ 120 μm.

[0046] In any embodiment of the present application, 10 μm ≤ H2 ≤ 250 μm, preferably 40 μm ≤ H2 ≤ 120 μm.

[0047] A fourth aspect of the present application provides a power consumption device including a secondary battery according to the third aspect of the present application.

[0048] This invention can effectively reduce the expansion force of a secondary battery and improve its safety performance when the amount of additives used is small and does not affect the energy density. Since the power consumption device of this invention includes the secondary battery according to this invention, it has at least the same advantages as the aforementioned secondary battery. [Brief explanation of the drawing]

[0049] To further clarify the technical concept of the embodiments of this application, the following is a brief introduction of the drawings necessary for the embodiments of this application. It is clear that the drawings described below represent only a few embodiments of this application. Those skilled in the art can obtain further drawings based on these drawings, even without creative work. [Figure 1] This is a schematic diagram of one embodiment of the negative electrode sheet of the present invention. [Figure 2] This is a schematic diagram of one embodiment of the secondary battery of the present invention. [Figure 3] This is an exploded schematic diagram of one embodiment of the secondary battery of the present invention. [Figure 4] This is a schematic diagram of one embodiment of the battery module of the present invention. [Figure 5] This is a schematic diagram of one embodiment of the battery pack of the present invention. [Figure 6] Figure 5 is a schematic exploded view of an embodiment of the battery pack shown. [Figure 7] This is a schematic diagram of one embodiment of a power consumption device that includes a secondary battery of the present invention as a power source. [Figure 8] This is a schematic diagram of a secondary battery expansion force test. Note that the diagram does not necessarily represent the actual proportions. [Explanation of Symbols]

[0050] 1 Battery pack 2 Upper enclosure 3 Lower enclosure 4 Battery Modules 5 Secondary battery 51 Housing 52 Electrode Assembly 53 Cover Plate 10 Negative electrode sheets 101 Negative electrode current collector 1011 First Domain 1012 Second Domain 1013 Third Domain 102 Negative electrode active material layer 1021 Part 1 1022 Part 2 1023 Part 3 201 Sensor 301 Steel plate 302 steel plate 303 Steel plate [Modes for carrying out the invention]

[0051] The following details specifically disclose embodiments of the negative electrode sheet, its manufacturing method, secondary battery, and power consumption device of 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 explanation becoming unnecessarily verbose and to facilitate understanding by those skilled in the art. The accompanying drawings and the following explanation 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.

[0052] 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 limiting the boundary of a special range. The range thus limited may include or exclude 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 minimum range values ​​1 and 2 and 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 for 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" indicates that in this specification, all real numbers between "0 and 5" are listed, and "0 to 5" is an abbreviated notation for combinations of these numbers. Also, the notation that a parameter is an integer greater than or equal to 2 (≧2) 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.

[0053] Unless otherwise specified, all embodiments and optional embodiments of this Application may be combined to form new technical solutions. Such technical solutions are considered to be included in the disclosures of this Application.

[0054] Unless otherwise specified, all technical features and optional technical features 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.

[0055] Unless otherwise specified, all steps of this invention may be performed sequentially or randomly, but it is preferable that they be performed sequentially. For example, the method may include steps (a) and (b), which may include steps (a) and (b) performed sequentially, or steps (b) and (a) performed sequentially. For example, the method may further include step (c), which may be added to the method in any order, for example, the method may include steps (a), (b) and (c), which may include steps (a), (c) and (b), which may include steps (c), (a) and (b), etc.

[0056] Unless otherwise specified, the terms "equip" and "include" in this application mean open-ended or closed-ended. For example, the terms "equip" and "include" above may mean further "equip" or "include" other components not listed, or "equip" or "include" only the listed components.

[0057] Unless otherwise specified, the term "or" in this application is inclusive. 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).

[0058] Unless otherwise specified, the terms "first," "second," "third," etc., used in this application are for distinguishing different subjects and do not describe a specific order or hierarchical relationship.

[0059] In this application, the terms "multiple" and "multiple types" mean two or more types.

[0060] Unless otherwise specified, terms used in this application have the common meanings that are ordinarily understood by those skilled in the art.

[0061] Unless otherwise specified, the numerical values ​​of each parameter referred to herein can be measured by various test methods commonly used in the art, for example, according to the test methods of this application.

[0062] In the development of secondary battery technology, while improving the electrochemical performance of secondary batteries is important, safety performance is also a critical issue that cannot be ignored. During long-term cycles and storage processes, secondary batteries are prone to swelling due to changes in the lattice structure of the active material, and as the number of cycles and storage periods increase, the number of cycles and storage cycles of secondary batteries gradually increases. If the swelling force of a secondary battery is too high, the electrolyte that has permeated the electrode sheet is pushed out, causing the electrolyte to easily deplete. In this case, the active ion transmission path inside the secondary battery is interrupted, the polarization of the secondary battery increases significantly, the rate performance deteriorates rapidly, the capacity retention rate decreases significantly, and the service life is drastically shortened. Furthermore, if the swelling force of a secondary battery is too high, the structure of the secondary battery pack is easily damaged, posing a safety risk.

[0063] Therefore, it is necessary to effectively reduce the expansion force of secondary batteries and improve their safety performance.

[0064] During the long-term cycle and storage process of secondary batteries, changes in the thickness of the negative electrode are more pronounced than those of the positive electrode, and current studies suggest that an increase in the thickness of the negative electrode is the main cause of the increase in the expansion force of the secondary battery. Conventional technology attempts to manufacture a negative electrode sheet by adding and mixing hollow carbon spheres and negative electrode active material during the manufacturing process of secondary batteries, thereby improving the cycle performance of the secondary battery and reducing irreversible capacity loss by reducing the adverse effects of changes in the thickness of the negative electrode with the use of hollow carbon spheres. However, the inventors of this application discovered during their research that conventional technology generally uses a high amount of hollow carbon spheres to effectively reduce the expansion force of the secondary battery, which significantly reduces the energy density of the secondary battery.

[0065] Therefore, in the process of diligently investigating the problem of secondary battery expansion, the inventors of the present invention discovered that by adding an additive having a cavity structure to the negative electrode sheet and adjusting the ratio of the thickness of the additive's shell wall to the cavity volume, it is possible to effectively reduce the expansion force of the secondary battery and improve its safety performance, provided that the amount of additive used is small and does not affect the energy density.

[0066] Specifically, a first aspect of the embodiments of the present application provides a negative electrode sheet.

[0067] The negative electrode sheet comprises a negative electrode current collector and a negative electrode active material layer provided on the negative electrode current collector, the negative electrode active material layer comprises a negative electrode active material and an additive, the additive comprises a shell wall and a cavity located inside the shell wall, the thickness of the shell wall being d and the volume of the cavity being V h , the volume of the additive is V w The additive has a range of 20nm ≤ d ≤ 300nm and 40% ≤ V. h / V w It satisfies ≤90%.

[0068] The additive used in the negative electrode sheet of this application has a hollow structure, and the cavity structure can provide a buffer space, causing the buffered negative electrode to expand and reducing the expansion force of the secondary battery. In the process of diligently investigating the expansion problem of secondary batteries, the inventors of this application discovered the following: the thickness d of the shell wall of the additive is too small, and / or the volume ratio V of the cavity of the additive h / V w If the volume ratio V of the additive cavity is too large, the shell structure of the additive becomes fragile, making it prone to crumbling and pulverization. Furthermore, the buffering effect against the expansion of the negative electrode is poor, making it impossible to effectively reduce the expansion force of the secondary battery and improve the safety performance of the secondary battery. h / V wIf the value is too small, the stability of the additive's shell wall structure is high, but in this case, the additive is less elastically deformable. Furthermore, the buffering effect against the expansion of the negative electrode is also poor, which prevents the effective reduction of the expansion force of the secondary battery and the improvement of the safety performance of the secondary battery. The additive has a value of 20nm ≤ d ≤ 300nm and 40% ≤ V h / V w When the condition ≤90% is met, the large cavity structure of the additive can generate significant elastic deformation, and furthermore, the adverse effects of negative electrode expansion can be effectively reduced. On the other hand, because the structural stability of the additive is high, when significant elastic deformation occurs, the additive does not suffer from crushing or pulverization problems. Therefore, this invention can effectively reduce the expansion force of a secondary battery and improve the safety performance of the secondary battery when the amount of additive used is small and does not affect the energy density.

[0069] In this application, the thickness d of the shell wall of the additive and the volume V of the cavity of the additive are h and the volume V of the additive w This can be obtained by testing in the following way: A circular sample with a diameter of 0.5 cm is cut from the negative electrode sheet, a TEM image of the cross-section is obtained using a transmission electron microscope (TEM), the thickness of the shell wall of the additive and the volume particle size of the additive within the region are statistically calculated, and cumulative distribution curves of the thickness of the shell wall of the additive and the volume particle size of the additive are obtained, respectively, the thickness corresponding to when the percentage in the cumulative distribution curve is 50% is defined as the thickness of the shell wall of the additive d, and the volume particle size corresponding to when the percentage in the cumulative distribution curve is 50% is defined as the volume particle size of the additive Dv50, and based on the calculation formula for an ideal sphere, the volume V of the additive is defined with the obtained volume particle size Dv50 as the diameter. w Calculate, however, V w =(4 / 3)×π×(Dv50 / 2) 3 The volume V of the cavity of the additive h V h =(4 / 3)×π×(Dv50 / 2-d) 3 That is the case.

[0070] In this application, the thickness d of the shell wall satisfies 20 nm ≤ d ≤ 300 nm, and for example, d may be in the range of 25 nm, 30 nm, 40 nm, 50 nm, 60 nm, 70 nm, 80 nm, 90 nm, 100 nm, 120 nm, 140 nm, 160 nm, 180 nm, 200 nm, 300 nm, or any of the above values.

[0071] In some embodiments, the preferred values ​​are 25nm≦d≦200nm, 25nm≦d≦180nm, 25nm≦d≦150nm, 30nm≦d≦150nm, 40nm≦d≦120nm, and 40nm≦d≦100nm. This is advantageous for improving the structural stability of the additive and balancing the strain capacity of the additive. This better reduces the adverse effects of negative electrode expansion, effectively lowers the expansion force of the secondary battery when the amount of additive used is small and does not affect the energy density, and improves the safety performance of the secondary battery.

[0072] In this application, the volume ratio V of the cavity of the additive h / V w 40% ≤ V h / V w Satisfying ≤90%, for example, V h / V w This may be a range consisting of any number greater than or equal to 48%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, or any other number.

[0073] In some embodiments, preferably 50% ≤ V h / V w ≤90%, 55%≤V h / V w ≤90%, 60%≤V h / V w ≤90%, 65%≤V h / V w ≤90%, 70% ≤V h / V w ≤90%, 70% ≤V h / V wThe value is ≤89%. This is advantageous because the additive has relatively large elastic deformation, providing a buffer space against the expansion of the negative electrode active material particles. This better reduces the adverse effects of negative electrode expansion, effectively lowers the expansion force of the secondary battery when the amount of additive used is small and does not affect the energy density, and improves the safety performance of the secondary battery.

[0074] In some examples, 25nm ≤ d ≤ 200nm and 60% ≤ V h / V w The percentage is ≤90%. Preferably, 40nm ≤ d ≤ 120nm and 70% ≤ V h / V w The value is ≤89%. This is advantageous in achieving a better balance between greater elastic deformation and higher structural stability of the additive. This better reduces the adverse effects of negative electrode expansion. When the amount of additive used is small and does not affect the energy density, it effectively reduces the expansion force of the secondary battery and improves the safety performance of the secondary battery.

[0075] In some embodiments, the additive comprises one or more types selected from hollow spheres and hollow polyhedra. In this application, the term “hollow sphere” means having a sphere or a structure close to a sphere, and does not control all spheres to be ideal spheres. “Hollow polyhedra” may include regular polyhedra such as cuboids, or irregular polyhedra.

[0076] In some embodiments, the additive includes hollow spheres. This can better reduce the adverse effects of negative electrode expansion. When the amount of additive used is small and does not affect the energy density, it effectively reduces the expansion force of the secondary battery and improves the safety performance of the secondary battery.

[0077] In some embodiments, the additive includes, as an example, hollow carbon spheres, preferably one or more of amorphous hollow carbon spheres, graphitized hollow carbon spheres, and hollow graphene spheres. This can better reduce the adverse effects of negative electrode expansion, and when the amount of additive used is small and does not affect the energy density, it effectively reduces the expansion force of the secondary battery and improves the safety performance of the secondary battery.

[0078] In further investigation, the inventors discovered that the particle size of the additive affects the improvement effect on the safety performance of the secondary battery. When the particle size of the additive is small, the effect of reducing the adverse effects of negative electrode expansion is weak, and as a result, the effect of reducing the expansion force on the secondary battery is weak. Also, when the particle size of the additive is small, it is easier to fill the voids between the negative electrode active material particles, which makes it easier to have a high compressive density and a low porosity of the negative electrode sheet. On the other hand, when the compressive density of the negative electrode sheet is high, the thickness rebound of the negative electrode sheet during the use of the secondary battery becomes more pronounced, which tends to significantly increase the expansion force of the secondary battery, and is detrimental to improving the safety performance of the secondary battery. When the compressive density of the negative electrode sheet is high, the wettability and liquid retention of the negative electrode sheet to the electrolyte are poor, so when the expansion force of the secondary battery increases, the electrolyte is more easily pushed out of the negative electrode sheet, and problems such as electrolyte depletion, lithium deposition on the negative electrode, and a rapid decrease in capacity during the secondary battery cycle tend to occur. When the compression density of the negative electrode sheet is high, the ion conductivity characteristics of the negative electrode sheet deteriorate, which is detrimental to the cycle performance and rate performance of the secondary battery. At the same time, the inventors further investigated that, when the amount of additive used is the same, the larger the particle size of the additive, the more likely it is that its distribution in the negative electrode active material layer will be non-uniform, further reducing the adverse effects of negative electrode expansion, worsening the effect of reducing the expansion force on the secondary battery, and also worsening the effect of improving the safety performance of the secondary battery. Therefore, the particle size of the additive should not be too large. In some examples, the volume particle size Dv50 of the additive may be 0.85 μm to 5 μm, preferably 0.85 μm to 4 μm, 0.9 μm to 3 μm, 1 μm to 2.5 μm, or 1 μm to 2 μm. This effectively reduces the expansion force of the secondary battery and improves the safety performance of the secondary battery, while ensuring that the secondary battery has good cycle performance and rate performance.

[0079] In some embodiments, the volume particle size of the additive satisfies 0.5 ≤ (Dv90 - Dv10) / Dv50 ≤ 8, preferably 1 ≤ (Dv90 - Dv10) / Dv50 ≤ 5, and further 2 ≤ (Dv90 - Dv10) / Dv50 ≤ 5.

[0080] In this application, the volume particle sizes Dv10, Dv50, and Dv90 of the material have meanings well known in the art, and represent the particle sizes corresponding to when the cumulative volume distribution percentage of the material reaches 10%, 50%, and 90%, respectively, and can be measured with instruments and methods known in the art. For example, they can be measured using a laser particle size analyzer, referring to GB / T 19077-2016. The measuring instrument can be a Mastersizer 3000 laser particle size analyzer from Malvern GmbH, UK.

[0081] In some embodiments, the weight percentage content of the additive is calculated based on the total weight of the negative electrode active material layer, and is 0.01 wt% to 3 wt%, preferably 0.1 wt% to 2.5 wt%, 0.1 wt% to 2 wt%, 0.1 wt% to 1.5 wt%, or 0.1 wt% to 1 wt%. In this application, when the amount of additive used is small and does not affect the energy density, the expansion force of the secondary battery can be effectively reduced and the safety performance of the secondary battery can be improved.

[0082] Currently, in conventional negative electrode sheets, the uniform and equidistant distribution of hollow microballoons reduces the expansion force of the secondary battery, but simultaneously reduces the occupancy rate of the negative electrode active material, thereby lowering the energy density of the secondary battery. In the process of diligently investigating the expansion problem of secondary batteries, the inventors of this application further discovered that the expansion force of the secondary battery is not uniformly distributed. Then, by diligently investigating the distribution characteristics of the expansion force of the secondary battery, the inventors have achieved an effective reduction in the expansion force of the secondary battery and improved the safety performance of the secondary battery when the amount of additive used is further reduced.

[0083] Figure 1 is a schematic diagram of one embodiment of the negative electrode sheet 10 of the present application. As shown in Figure 1, the negative electrode sheet 10 includes a negative electrode current collector 101 and a negative electrode active material layer 102 provided on the negative electrode current collector 101. Along the width direction of the negative electrode active material layer 102, the negative electrode active material layer 102 includes a first portion 1021 and a second portion 1022 located on the edge side, and a third portion 1023 located between the first portion 1021 and the second portion 1022. The total width of the negative electrode active material layer 102 is W, and the first portion 10 The width of portion 21 is 1 / 5W, the width of the second portion 1022 is 1 / 5W, the width of the third portion 1023 is 3 / 5W, the weight percentage content of the additive in the first portion 1021 is w1, the weight percentage content of the additive in the second portion 1022 is w2, the weight percentage content of the additive in the third portion 1023 is w3, and 0 ≤ w1 / w3 < 1, 0 ≤ w2 / w3 < 1.

[0084] The inventors have diligently studied the distribution process of expansion force in secondary batteries and have discovered the following: During long-term cycles and storage processes of secondary batteries, it has been found that the largest surface area of ​​the electrode assembly is subjected to the greatest pressure. Therefore, by further adjusting the distribution of additives in the width direction of the negative electrode active material layer, by employing a high-content additive in the third section and a low-content additive in the first and second sections, the expansion force of the secondary battery can be effectively reduced, improving its safety performance. Furthermore, if the same improvement in expansion force is achieved, the amount of additive used can be further reduced, thereby improving the energy density of the secondary battery.

[0085] In some embodiments, 0 <w1 / w3≦0.8、0<w1 / w3≦0.7、0<w1 / w3≦0.6、0<w1 / w3≦0.5、0<w1 / w3≦0.4である。

[0086] In some embodiments, 0 <w2 / w3≦0.8、0<w2 / w3≦0.7、0<w2 / w3≦0.6、0<w2 / w3≦0.5、0<w2 / w3≦0.4である。

[0087] By further adjusting the relationship between the ratio of the amount of additive used in the first and / or second part and the amount of additive used in the third part to be within the above range, the expansion force of the secondary battery can be effectively reduced and the safety performance of the secondary battery can be improved when the amount of additive used is further reduced.

[0088] In some examples, 0wt% ≤ w1 ≤ 2wt%, preferably 0wt%. <w1≦1.8wt%、0wt%<w1≦1.6wt%、0wt%<w1≦1.4wt%、0wt%<w1≦1.2wt%、0wt%<w1≦1wt%、0wt%<w1≦0.8wt%、0wt%<w1≦0.6wt%、0wt%<w1≦0.4wt%である。

[0089] In some examples, 0wt% ≤ w2 ≤ 2wt%, and preferably 0wt%. <w2≦1.8wt%、0wt%<w2≦1.6wt%、0wt%<w2≦1.4wt%、0wt%<w2≦1.2wt%、0wt%<w2≦1wt%、0wt%<w2≦0.8wt%、0wt%<w2≦0.6wt%、0wt%<w2≦0.4wt%である。

[0090] In some embodiments, 0.01wt% ≤ w3 ≤ 5wt%, preferably 0.01wt% ≤ w3 ≤ 4.5wt%, 0.01wt% ≤ w3 ≤ 4wt%, 0.01wt% ≤ w3 ≤ 3.5wt%, 0.01wt% ≤ w3 ≤ 3wt%, 0.01wt% ≤ w3 ≤ 2.5wt%, 0.01wt% ≤ w3 ≤ 2wt%, 0.01wt% ≤ w3 ≤ 1.5wt%, and 0.01wt% ≤ w3 ≤ 1wt%.

[0091] In some embodiments, w1 = w2.

[0092] In this application, the negative electrode current collector has two opposing surfaces in its thickness direction, and the negative electrode active material layer may be provided on either one or both of the two opposing surfaces of the negative electrode current collector.

[0093] In some embodiments, the negative electrode active material may be a negative electrode active material used in secondary batteries known in the art. For example, the negative electrode active material may include, but is not limited to, one or more of the following: natural graphite, artificial graphite, soft carbon, hard carbon, silicon-based materials, tin-based materials, and lithium titanate. The silicon-based material may include one or more of the following: elemental silicon, silicon oxide, silicon-carbon composites, silicon-nitrogen composites, and silicon alloy materials. The tin-based material may include one or more of the following: elemental tin, tin oxide, and tin alloy materials. This application is not limited to these materials, and other conventionally known materials used as negative electrode active materials for secondary batteries may be used.

[0094] In some embodiments, the volume particle size Dv50 of the negative electrode active material is 8 μm to 22 μm, preferably 12 μm to 18 μm.

[0095] In some embodiments, the weight percentage content of the negative electrode active material relative to the total weight of the negative electrode active material layer may be 95 wt% to 99 wt%. This is advantageous for improving the energy density of the secondary battery.

[0096] In some embodiments, the negative electrode active material layer further comprises a negative electrode adhesive and / or a negative electrode dispersant. The negative electrode adhesive is used to improve adhesion between negative electrode active material particles and between the negative electrode active material and the negative electrode current collector so that the negative electrode sheet forms a good electronic network. The type of negative electrode adhesive in this application is not particularly limited, and materials known in the art may be used. As an example, the adhesive may include one or more combinations selected from styrene-butadiene rubber (SBR), water-soluble unsaturated resin SR-1B, aqueous acrylic resin (e.g., polyacrylate PAA, polymethyl methacrylate PMMA, sodium polyacrylate PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), and carboxymethyl chitosan (CMCS). In some embodiments, the weight percentage content of the negative electrode adhesive relative to the total weight of the negative electrode active material layer may be greater than 0 and 2.5 wt%, preferably 1 wt% to 2.5 wt%. The negative electrode dispersant is used to improve the stability and dispersibility of the negative electrode slurry. The type of negative electrode dispersant in this application is not particularly limited, and materials known in the art can be used. As an example, the negative electrode dispersant may contain sodium carboxymethylcellulose (CMC). In some examples, the weight percentage content of the negative electrode dispersant relative to the total weight of the negative electrode active material layer may be greater than 0 and 1.5 wt% or less, preferably 0.5 wt% to 1.5 wt%.

[0097] In some embodiments, the negative electrode active material layer further comprises a negative electrode conductive agent. The type of negative electrode conductive agent in this application is not particularly limited, and materials known in the art may be used. For example, the negative electrode conductive agent may include one or more of the following: superconducting carbon, conductive graphite, acetylene black, carbon black, Kecheng black, carbon dots, graphene, and carbon nanofibers. In some embodiments, the weight percentage content of the negative electrode conductive agent relative to the total weight of the negative electrode active material layer may be 0 wt% to 1.5 wt%. A weight percentage content of 0 wt% indicates that no negative electrode conductive agent is added.

[0098] In some embodiments, the negative electrode active material layer may preferably contain other additives, such as PTC thermistor material.

[0099] In some embodiments, the negative electrode current collector can be a metal foil sheet or a composite current collector. Copper foil can be used as an example of the metal foil sheet. 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 of copper, copper alloys, nickel, nickel alloys, titanium, titanium alloys, silver, and silver alloys. For example, the polymer material substrate may include one or more of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), and polyethylene (PE).

[0100] The negative electrode sheet does not exclude any additional functional layers other than the negative electrode active material layer. For example, in some embodiments, the negative electrode sheet according to the present application may further include a conductive primer layer (e.g., consisting of a conductive agent and an adhesive) sandwiched between the negative electrode current collector and the negative electrode active material layer and provided on the surface of the negative electrode current collector, and in some embodiments, the negative electrode sheet according to the present application may further include a protective layer coated on the surface of the negative electrode active material layer.

[0101] Manufacturing method

[0102] A second aspect of the embodiments of the present invention provides a method for manufacturing a negative electrode sheet.

[0103] The method for manufacturing the negative electrode sheet comprises providing a negative electrode slurry containing a negative electrode active material and an additive, applying the negative electrode slurry to a negative electrode current collector, drying it, and cold pressing it to obtain a negative electrode sheet, wherein the negative electrode sheet comprises a negative electrode current collector and a negative electrode active material layer provided on the negative electrode current collector, the negative electrode active material layer comprises a negative electrode active material and an additive, the additive comprises a shell wall and a cavity located inside the shell wall, the thickness of the shell wall being d and the volume of the cavity being V h , the volume of the additive is V w The additive has a wavelength of 20 nm ≤ d ≤ 300 nm and 40% ≤ V. h / V w It satisfies ≤90%.

[0104] In some embodiments, as shown in Figure 1, along the width direction of the negative electrode current collector 101, the negative electrode current collector 101 includes a first region 1011 and a second region 1012 located on the edge side, and a third region 1013 located between the first region 1011 and the second region 1012, where the total width of the coated area of ​​the negative electrode current collector 101 is W, the width of the first region 1011 is 1 / 5W, the width of the second region 1012 is 1 / 5W, and the width of the third region 1013 is 3 / 5W, and in the method for manufacturing the negative electrode sheet, the negative electrode slurry is prepared to include a first slurry, a second slurry, and a third slurry, and then, The first slurry, the second slurry, and the third slurry are applied to the first region 1011, the second region 1012, and the third region 1013 of the negative electrode current collector, respectively, and after drying, the first portion 1021, the second portion 1022, and the third portion 1023 of the negative electrode active material layer are formed, where the weight percentage content of the additive in the first portion 1021 is w1, the weight percentage content of the additive in the second portion 1022 is w2, and the weight percentage content of the additive in the third portion 1023 is w3, and 0 ≤ w1 / w3 < 1 and 0 ≤ w2 / w3 < 1. In this application, the total width of the applied region of the negative electrode current collector is the same as the total width of the negative electrode active material layer.

[0105] In some embodiments, the negative electrode slurry comprises a negative electrode adhesive and / or a negative electrode dispersant.

[0106] In some embodiments, the negative electrode slurry may contain a negative electrode conductive agent. Of course, the negative electrode slurry does not have to contain a negative electrode conductive agent.

[0107] In some embodiments, the solvent used to prepare the negative electrode slurry may be N-methylpyrrolidone (NMP) or deionized water, but the present invention is not limited thereto.

[0108] The parameters of the negative electrode slurry in this application, such as concentration, coating weight, and coating thickness, are not particularly limited and can be selected according to the needs.

[0109] In the process of preparing the negative electrode slurry, the form and timing of additive addition are not particularly limited. For example, the additive may be added as a solid powder, as a suspension, by stirring the negative electrode slurry, or during the dry blending stage.

[0110] In the coating process of the negative electrode slurry, the first slurry, the second slurry, and the third slurry may be coated in a single simultaneous coating process, or in multiple step coating processes.

[0111] The manufacturing method provided by a second embodiment of the present invention can be used to manufacture a negative electrode sheet according to any embodiment of the first embodiment of the present invention. In the manufacturing process of the negative electrode sheet, specific types and quantities of some raw materials used can be referenced from the negative electrode sheet of the first embodiment of the present invention, and are therefore omitted from this explanation.

[0112] In Figure 1, lines distinguish the first region 1011, the second region 1012, and the third region 1013 of the negative electrode current collector 101, and the first portion 1021, the second portion 1022, and the third portion 1023 of the negative electrode active material layer 102. However, in reality, no interfaces exist, and the entire negative electrode current collector 101 may be continuous, as may the entire negative electrode active material layer 102.

[0113] In some embodiments, the negative electrode current collector 101 may further include uncoated regions (not shown) along the width direction of the negative electrode current collector 101 where the negative electrode active material layer 102 is not provided, i.e., the total width of the negative electrode current collector 101 is greater than the total width of the coated region of the negative electrode current collector 101 (or the total width of the negative electrode active material layer).

[0114] secondary battery

[0115] A third aspect of an embodiment of the present application provides a secondary battery. A secondary battery generally comprises a positive electrode sheet, a negative electrode sheet and an electrolyte. The present application does not particularly limit the type of the secondary battery, for example, the secondary battery may be a lithium ion battery, a sodium ion battery, or the like.

[0116] The negative electrode sheet used in the secondary battery of the present application includes the negative electrode sheet described in any one of the embodiments of the first aspect of the embodiments of the present application, or the negative electrode sheet manufactured by the manufacturing method described in any one of the second aspect of the embodiments of the present application.

[0117] In some embodiments, the secondary battery satisfies 100≦K≦30000. [Formula]

[0118] λ is the porosity of the negative electrode sheet, ε is the thickness resilience of the third portion of the negative electrode active material layer when the capacity of the secondary battery decays to 80% of the initial capacity of the secondary battery, C0 is the initial capacity of the secondary battery in mAh, d is the thickness of the shell wall of the additive in nm, V h is the volume of the cavity of the additive in nm 3 , S is the area of the single-layer negative electrode sheet in mm 2 , and H is the initial thickness of the third portion of the negative electrode active material layer in μm.

[0119] As a result of intensive studies, the inventor found that when the above parameter K of the secondary battery is between 100 and 30000, the secondary battery has low expansion force, high safety performance, and high energy density.

[0120] In some embodiments, it is preferable to use the following values: 100≦K≦20000, 120≦K≦16000, 120≦K≦12000, 120≦K≦10000, 120≦K≦9000, 120≦K≦8000, 200≦K≦8000, 300≦K≦8000, 400≦K≦8000, and 500≦K≦8000.

[0121] In this application, the porosity of the negative electrode sheet is as known in the art and can be measured by methods known in the art. An exemplary test method involves taking a negative electrode sheet coated on one side and cold-pressed (if the negative electrode sheet is coated on both sides, the negative electrode active material layer on one side can be wiped off first), punching it into a small wafer sample of a certain area, and calculating the apparent volume V1 of the negative electrode sheet; and measuring the true volume V2 of the negative electrode sheet using a true density tester by gas displacement using an inert gas (e.g., helium or nitrogen gas) as a medium, referring to GB / T24586-2009. The porosity of the negative electrode sheet = (V1 - V2) / V1 × 100%. The accuracy of the test results can be improved by taking the average value of the results obtained by testing multiple negative electrode sheet samples (e.g., 30 sheets) that have a good appearance and no powder falloff at the edges. A Micromeritics AccuPyc II 1340 true density tester can be used as the test apparatus.

[0122] ε is the thickness resilience of the third portion of the negative electrode active material layer when the capacity of the secondary battery has decreased to 80% of the initial capacity of the secondary battery, and ε = (H'-H) / H. H' is the test thickness of the third portion of the negative electrode active material layer when the capacity of the secondary battery has decreased to 80% of the initial capacity of the secondary battery. H is the initial thickness of the third portion of the negative electrode active material layer, and in this application, when the number of cycles of the secondary battery is 50 or less, it is the thickness obtained by testing the third portion of the negative electrode active material layer.

[0123] In this application, the initial capacity C0 of a secondary battery refers to the capacity of a secondary battery with a cycle count of 50 revolutions or less.

[0124] In the present application, S is the area of a single-layer negative electrode sheet. When the electrode assembly has a stacked structure, S = the width of the negative electrode sheet × the length of the negative electrode sheet; when the electrode assembly has a wound structure, S = half of the circumferential length of the winding core × the width of the negative electrode sheet.

[0125] In some embodiments, 20%≦λ≦50%, for example, λ may be 21%, 23%, 25%, 27%, 29%, 31%, 33%, 35%, 37%, 39%, 41%, 43%, 45%, 50%, or a range consisting of any of the above numerical values. Preferably, 23%≦λ≦35%.

[0126] In some embodiments, 20%≦ε≦40%, for example, ε may be 21%, 23%, 25%, 27%, 29%, 31%, 33%, 35%, 37%, 40%, or a range consisting of any of the above numerical values. Preferably, 25%≦ε≦35%.

[0127] In some embodiments, 20nm≦d≦300nm, for example, d may be 25nm, 30nm, 40nm, 50nm, 60nm, 70nm, 80nm, 90nm, 100nm, 120nm, 140nm, 160nm, 180nm, 200nm, 300nm, or a range consisting of any of the above numerical values. Preferably, 25nm≦d≦200nm, 25nm≦d≦180nm, 25nm≦d≦150nm, 30nm≦d≦150nm, 40nm≦d≦120nm, 40nm≦d≦100nm.

[0128] In some embodiments, 1×10 7 nm 3 ≦V h ≦1×10 12 nm 3 , preferably 5×10 7 nm 3 ≦V h ≦2×10 10 nm 3 , 1×10 8 nm 3 ≦V h ≦1×10 10 nm3 , 2.5×10 8 nm 3 ≦V h ≦1×10 10 nm 3 .

[0129] In some embodiments, 1×10 2 mm 2 ≦S≦1×10 8 mm 2 , preferably 1×103mm 2 ≦S≦1×10 6 mm 2 , 1×10 4 mm 2 ≦S≦1×10 6 mm 2 .

[0130] In some embodiments, 10 μm ≦ H ≦ 250 μm, preferably 40 μm ≦ H ≦ 120 μm, 40 μm ≦ H ≦ 100 μm, 40 μm ≦ H ≦ 80 μm.

[0131] In some embodiments, when the capacity of the secondary battery decays to 80% of the initial capacity of the secondary battery, the thickness rebound resilience of the first portion of the negative electrode active material layer is denoted as ε1, the initial thickness of the first portion of the negative electrode active material layer is denoted as H1, with a unit of μm; the thickness rebound resilience of the second portion of the negative electrode active material layer is denoted as ε2, the initial thickness of the second portion of the negative electrode active material layer is denoted as H2, with a unit of μm, and the secondary battery satisfies 0<K1 / K≦1 and 0<K2 / K≦1. [Formula]

[0132] The inventor has found through intensive research that when the above parameters K1, K2 and K of the secondary battery satisfy 0<K1 / K≦1 and 0<K2 / K≦1, the secondary battery has low expansion force, high safety performance, and high energy density.

[0133] In some embodiments, 0<K1 / K≤0.95, 0<K1 / K≤0.94, 0<K1 / K≤0.92, 0<K1 / K≤0.90, 0<K1 / K≤0.88, 0<K1 / K≤0.86. This is advantageous for further improving the energy density of the secondary battery.

[0134] In some embodiments, 0<K2 / K≤0.95, 0<K2 / K≤0.94, 0<K2 / K≤0.92, 0<K2 / K≤0.90, 0<K2 / K≤0.88, 0<K2 / K≤0.86. This is advantageous for further improving the energy density of the secondary battery.

[0135] In some embodiments, 100≤K1≤30000, preferably 100≤K1≤20000, 120≤K1≤16000, 120≤K1≤12000, 120≤K1≤10000, 120≤K1≤9000, 120≤K1≤8000, 200≤K1≤8000, 300≤K1≤8000, 400≤K1≤8000, 500≤K1≤8000. As a result of intensive studies, the inventor found that when the above parameter K1 of the secondary battery is within the above range, the secondary battery can further improve the energy density while having low expansion force and high safety performance.

[0136] In some embodiments, 100≤K2≤30000, preferably 100≤K2≤20000, 120≤K2≤16000, 120≤K2≤12000, 120≤K2≤10000, 120≤K2≤9000, 120≤K2≤8000, 200≤K2≤8000, 300≤K2≤8000, 400≤K2≤8000, 500≤K2≤8000. As a result of intensive studies, the inventor found that when the above parameter K2 of the secondary battery is within the above range, the secondary battery can further improve the energy density while having low expansion force and high safety performance.

[0137] In some embodiments, 15%≤ε1≤35%, preferably 25%≤ε1≤31%.

[0138] In some embodiments, 15% ≤ ε2 ≤ 35%, and preferably 25% ≤ ε2 ≤ 31%.

[0139] In some examples, 10 μm ≤ H1 ≤ 250 μm, preferably 40 μm ≤ H1 ≤ 120 μm, 40 μm ≤ H1 ≤ 100 μm, and 40 μm ≤ H1 ≤ 80 μm.

[0140] In some examples, 10 μm ≤ H2 ≤ 250 μm, preferably 40 μm ≤ H2 ≤ 120 μm, 40 μm ≤ H2 ≤ 100 μm, and 40 μm ≤ H2 ≤ 80 μm.

[0141] ε1 is the thickness resilience of the first portion of the negative electrode active material layer when the capacity of the secondary battery has decreased to 80% of the initial capacity of the secondary battery, and ε1 = (H1' - H1) / H1. H1' is the thickness obtained by testing the first portion of the negative electrode active material layer when the capacity of the secondary battery has decreased to 80% of the initial capacity of the secondary battery. H1 is the initial thickness of the first portion of the negative electrode active material layer, and in this application, when the number of cycles of the secondary battery is 50 or less, it is the thickness obtained by testing the first portion of the negative electrode active material layer.

[0142] ε2 is the thickness resilience of the second portion of the negative electrode active material layer when the capacity of the secondary battery has decreased to 80% of the initial capacity of the secondary battery, and ε2 = (H2' - H2) / H2. H2' is the thickness obtained by testing the second portion of the negative electrode active material layer when the capacity of the secondary battery has decreased to 80% of the initial capacity of the secondary battery. H2 is the initial thickness of the second portion of the negative electrode active material layer, and in this application, it is the thickness obtained by testing the second portion of the negative electrode active material layer when the number of cycles of the secondary battery is 50 or less.

[0143] In some embodiments, H, H1, and H2 may be the same. That is, when the number of cycles of the secondary battery is 50 or less, the thickness of the first, second, and third parts of the negative electrode active material is the same.

[0144] In this application, the thickness parameters of the negative electrode active material layer (e.g., H, H', H1, H1', ​​H2, H2') all refer to the thickness of the negative electrode active material layer located on one side of the negative electrode current collector.

[0145] Note that the parameters of each negative electrode active material layer related to this application (e.g., thickness, porosity, structure and content of additives, etc.) all refer to the parameters of the negative electrode active material layer on one side of the negative electrode current collector. If negative electrode active material layers are provided on both sides of the negative electrode current collector, the parameters of either one of the negative electrode active material layers are considered to satisfy the requirements of this application, i.e., to be within the scope of protection of this application.

[0146] [Positive electrode sheet]

[0147] In some embodiments, the positive electrode sheet includes a positive electrode current collector and a positive electrode active material layer provided on at least one surface of the positive electrode current collector and containing positive electrode active material. For example, the positive electrode current collector has two opposing surfaces in the thickness direction, and the positive electrode active material layer is provided on both surfaces of the positive electrode current collector.

[0148] The positive electrode active material layer contains a positive electrode active material, and the positive electrode active material can be a known positive electrode active material for secondary batteries in this field.

[0149] When the secondary battery of the present application is a lithium ion battery, the positive electrode active material may comprise one or more selected from the group consisting of lithium transition metal oxides, lithium-containing phosphates having an olivine structure, and respective modified compounds thereof. Examples of the lithium transition metal oxide include, but are not limited to, one or more selected from the group consisting of lithium cobalt oxide, lithium nickel oxide, lithium manganese oxide, lithium nickel cobalt oxide, lithium manganese cobalt oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, and modified compounds thereof. The lithium-containing phosphate having an olivine structure may comprise one or more selected from the group consisting of lithium iron phosphate, a composite material of lithium iron phosphate and carbon, lithium manganese phosphate, a composite material of lithium manganese phosphate and carbon, lithium manganese iron phosphate, a composite material of lithium manganese iron phosphate and carbon, and modified compounds thereof. The present application is not limited to these materials, and conventionally known materials used as other positive electrode active materials for secondary batteries may also be used.

[0150] In some embodiments, in order to further increase the energy density of the secondary battery, the positive electrode active material used for a lithium ion secondary battery has a general formula of Li a Ni b Co c M d O e A f which may comprise one or more selected from the group consisting of the lithium transition metal oxide represented by and modified compounds thereof, wherein 0.8≦a≦1.2, 0.5≦b<1, 0<c<1, 0<d<1, 1≦e≦2, 0≦f≦1, M comprises one or more selected from the group consisting of Mn, Al, Zr, Zn, Cu, Cr, Mg, Fe, V, Ti and B, and A comprises one or more selected from the group consisting of N, F, S and Cl.

[0151] As an example, the positive electrode active material used for a lithium ion secondary battery includes LiCoO2, LiNiO2, LiMnO2, LiMn2O4, LiNi 1 / 3 Co 1 / 3 Mn 1 / 3O2(NCM333), LiNi 0.5 Co 0.2 Mn 0.3 O2 (NCM523), LiNi 0.6 Co 0.2 Mn 0.2 O2 (NCM622), LiNi 0.8 Co 0.1 Mn 0.1 O2 (NCM811), LiNi 0.85 Co 0.15 Al 0.05 It may contain one or more of the following: O2, LiFePO4, and LiMnPO4.

[0152] When the secondary battery of the present invention is a sodium-ion battery, the positive electrode active material may include, but is not limited to, one or more of the following: sodium-containing transition metal oxides, polyanionic materials (e.g., phosphates, fluorophosphates, pyrophosphates, sulfates, etc.), and Prussian blue-based materials.

[0153] As an example, the positive electrode active materials used in sodium-ion batteries include NaFeO2, NaCoO2, NaCrO2, NaMnO2, NaNiO2, and NaNi 1 / 2 Ti 1 / 2 O2, NaNi 1 / 2 Mn 1 / 2 O2, Na 2 / 3 Fe 1 / 3 Mn 2 / 3 O2, NaNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2, NaFePO4, NaMnPO4, NaCoPO4, Prussian blue-based materials, and general formula X p M' q (PO4) r O x Y 3-x It may contain one or more of the materials of General Formula X. p M' q (PO4) r O x Y 3-x In 0 <p≦4、0<q≦2、1≦r≦3、0≦x≦2であり、Xは、H + Li + kaNa+ , K + and NH4 + It comprises one or more types selected from, where M' is a transition metal cation, preferably one or more types from V, Ti, Mn, Fe, Co, Ni, Cu, and Zn, and Y is a halogen anion, preferably one or more types from F, Cl, and Br.

[0154] In this application, the modified compound of each of the positive electrode active materials may be doped and / or surface coated with the positive electrode active material.

[0155] In some embodiments, the positive electrode active material layer may further contain a positive electrode conductive agent. The type of positive electrode conductive agent in this application is not particularly limited, and as an example, the positive electrode conductive agent may include one or more of the following: superconducting carbon, conductive graphite, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0156] In some embodiments, the positive electrode active material layer may further include a positive electrode adhesive. In this application, the type of positive electrode adhesive is not particularly limited, and as an example, the positive electrode adhesive may include one or more of the following: polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorine-containing acrylate resins.

[0157] In some embodiments, the positive electrode current collector can be a metal foil sheet or a composite current collector. An example of the metal foil sheet is aluminum 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 from aluminum, aluminum alloys, nickel, nickel alloys, titanium, titanium alloys, silver, and silver alloys. For example, the polymer material substrate may include one or more types from polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), and polyethylene (PE).

[0158] The positive electrode active material layer is typically 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 selectable conductive agent, a selectable adhesive, and any other components in a solvent and stirring them uniformly. The solvent may, but is not limited to, N-methylpyrrolidone (NMP).

[0159] [Electrolyte]

[0160] The electrolyte plays a role in conducting active ions between the positive electrode sheet and the negative electrode sheet. In this application, the type of electrolyte is not particularly limited and can be selected according to the needs. The electrolyte may include, for example, one or more types selected from solid electrolytes and liquid electrolytes (i.e., electrolyte solutions).

[0161] In some embodiments, the electrolyte is an electrolyte solution, which comprises an electrolyte salt and a solvent.

[0162] If the secondary battery of this application is a lithium-ion battery, the electrolyte salt may include, as an example, one or more of the following: lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium perchlorate (LiClO4), lithium hexafluoroarsenate (LiAsF6), lithium difluorosulfonylimide (LiFSI), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium trifluoromethanesulfonate (LiTFS), lithium difluorooxalate borate (LiDFOB), lithium disoxalate borate (LiBOB), lithium difluorophosphate (LiPO2F2), lithium difluorodisoxalate phosphate (LiDFOP), and lithium tetrafluorooxalate phosphate (LiTFOP).

[0163] If the secondary battery of this application is a sodium-ion battery, the electrolyte salt may contain one or more of the following: sodium hexafluoride phosphate (NaPF6), sodium tetraborate tetrafluoride (NaBF4), sodium perchlorate (NaClO4), sodium hexafluoride arsenate (NaAsF6), sodium bisfluorosulfonyliimide (NaFSI), sodium bistrifluoromethanesulfonyliimide (NaTFSI), sodium trifluoromethanesulfonate (NaTFS), difluorooxalate borate (NaDFOB), lithium bisoxalate borate (NaBOB), sodium difluorophosphate (NaPO2F2), difluorobisoxalate phosphate (NaDFOP), and sodium tetrafluorooxalate phosphate (NaTFOP).

[0164] The type of solvent is not particularly limited and can be selected according to the needs. In some embodiments, for example, the solvent may include one or more of the following: 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), fluoroethylene carbonate (FEC), 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).

[0165] In some embodiments, the electrolyte may further contain additives. For example, the additives may include negative electrode film-forming additives, positive electrode film-forming additives, and additives that can improve some aspects of the battery's performance, such as additives that improve the battery's overcharge performance, additives that improve the battery's high-temperature performance, and additives that improve the battery's low-temperature power performance.

[0166] [Separator]

[0167] In secondary batteries using an electrolyte or a solid electrolyte, a separator is also included. The separator is provided between the positive electrode sheet and the negative electrode sheet and mainly serves to prevent short circuits between the positive and negative electrodes, while simultaneously allowing active ions to pass through. In this application, the type of separator is not particularly limited, and any known porous structure separator having good chemical and mechanical stability can be selected. The separator may be a single-layer film or a multilayer composite film. If the separator is a multilayer composite film, the materials of each layer may be the same or different.

[0168] In some embodiments, the separator may include a base film and an optional protective coating layer. The base film may include a nonwoven fabric, film, or composite film having a porous structure, and the material of the base film may include one or more of polyethylene, polypropylene, polyvinylidene fluoride, polyethylene terephthalate, and polyimide.

[0169] A protective coating layer may not be provided on the surface of the base film. In some embodiments, a protective coating layer is provided on at least one surface of the base film, and the protective coating layer may be a polymer layer or an inorganic layer, or a layer containing a mixed polymer and an inorganic substance.

[0170] The inorganic layer comprises inorganic particles and an adhesive, the inorganic particles comprising, but not limited to, one or more of the following: aluminum oxide, silicon oxide, magnesium oxide, titanium oxide, hafnium dioxide, tin oxide, cerium dioxide, nickel oxide, zinc oxide, calcium oxide, zirconium oxide, yttrium oxide, silicon carbide, boehmite, aluminum hydroxide, magnesium hydroxide, calcium hydroxide, and barium sulfate.

[0171] The polymer layer comprises a polymer, and the polymer material may include, but is not limited to, one or more of the following: polyamide, polyacrylonitrile, acrylate polymer, polyacrylic acid, polyacrylate salt, polyvinylpyrrolidone, polyvinyl ether, and polyvinylidene fluoride.

[0172] In some embodiments, the positive electrode sheet, the separator, and the negative electrode sheet can be manufactured into an electrode assembly by a winding process or a lamination process.

[0173] In some embodiments, the secondary battery may include an outer casing. The casing is used to seal the electrode assembly and electrolyte described above.

[0174] In some embodiments, the outer packaging may be a hard case such as a rigid plastic case, an aluminum case, or a steel case. The outer packaging may also be a soft package, such as a bug soft package. The material of the soft package may be one or more of polypropylene (PP), polybutylene terephthalate (PBT), and polybutylene succinate (PBS).

[0175] The shape of the secondary battery of this application is not particularly limited and may be cylindrical, rectangular, or any other shape. Figure 2 shows a rectangular secondary battery 5 as an example.

[0176] In some embodiments, as shown in Figure 3, 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 closes the opening so as to close the housing chamber. The positive electrode sheet, negative electrode sheet and separator can be formed into an electrode assembly 52 by a winding or laminating process. The electrode assembly 52 is packaged into the housing cavity. The electrolyte is infused 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 according to the needs.

[0177] The method for manufacturing the secondary battery of the present invention is 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 the positive electrode sheet, separator, and negative electrode sheet, the electrode assembly can be placed in an outer casing, dried, and then the electrolyte can be injected. A secondary battery can then be obtained by going through processes such as vacuum sealing, standing, chemical formation, and shaping.

[0178] In some embodiments of the present invention, the secondary battery 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.

[0179] Figure 4 is a schematic diagram of a battery module 4 as an example. As shown in Figure 4, 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.

[0180] Preferably, the battery module 4 further includes a housing having a housing space, and a plurality of secondary batteries 5 are housed in the housing space.

[0181] In some embodiments, the battery modules may be assembled as a battery pack, and the number of battery modules included in the battery pack may be adjusted according to the application and capacity of the battery pack.

[0182] Figures 5 and 6 are schematic diagrams of an example battery pack 1. As shown in Figures 5 and 6, 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 housing 2 and a lower housing 3, the upper housing 2 covering the lower housing 3 and forming a closed space for housing the battery modules 4. The plurality of battery modules 4 may be arranged in the battery case in any manner.

[0183] power consumption equipment

[0184] The present invention further provides a power consumption device comprising at least one of the secondary battery, battery module, or battery pack of the present invention. 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, and satellites, energy storage systems, etc.

[0185] The aforementioned power consumption device can be configured to use a secondary battery, battery module, or battery pack, depending on the needs.

[0186] Figure 7 is a schematic diagram of an example of a power consumption device. This power consumption device includes pure electric vehicles, hybrid electric vehicles, and plug-in hybrid electric vehicles. To meet the high power and high energy density needs of this power consumption device, battery packs or battery modules can be employed.

[0187] As another example, the power-consuming device may be a mobile phone, tablet computer, or laptop computer. These power-consuming devices generally require a thin design, and rechargeable batteries can be used as the power source.

[0188] Examples

[0189] 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. All quantities, percentages, and ratios described in the following examples are based on mass unless otherwise specified. 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.

[0190] Example 1-1

[0191] Manufacturing of positive electrode sheets

[0192] 97 wt% LiFePO4, a positive electrode active material; 1 wt% carbon black (Super P), a conductive agent; and 2 wt% polyvinylidene fluoride (PVDF), an adhesive, are thoroughly stirred and mixed in an appropriate amount of solvent NMP to form a uniform positive electrode slurry. This slurry is then uniformly applied to the surface of the aluminum foil positive electrode current collector, dried, and cold-pressed to obtain a positive electrode sheet.

[0193] Manufacturing of negative electrode sheets

[0194] After thoroughly mixing 96.99 wt% graphite, which is the negative electrode active material, 1.8 wt% styrene-butadiene rubber (SBR), which is the adhesive, and 1.2 wt% sodium carboxymethylcellulose (CMC), which is the dispersant, with an appropriate amount of solvent-deionized water, 0.01 wt% amorphous hollow carbon spheres are added and stirred to form a uniform negative electrode slurry. The negative electrode slurry is then uniformly applied to the surface of the copper foil of the negative electrode current collector, dried, and cold-pressed to obtain a negative electrode sheet.

[0195] Preparation of electrolyte

[0196] 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.

[0197] Manufacturing of separators

[0198] A porous polyethylene film is used as the separator.

[0199] Manufacturing of rechargeable batteries

[0200] A positive electrode sheet, a separator, and a negative electrode sheet are stacked in order and wound together to obtain an electrode assembly. The electrode assembly is then placed in an outer casing, dried, and then injected with electrolyte. After going through processes such as vacuum sealing, standing, chemical conversion, shaping, and capacity testing, a secondary battery is obtained.

[0201] Examples 1-2 to 1-9

[0202] The method for manufacturing the secondary battery is similar to that of Example 1-1, the only difference being the manufacturing parameters of the negative electrode sheet. The specific parameters are shown in Table 1, and the amounts of adhesive and dispersant added in the manufacturing of the negative electrode sheet remain unchanged.

[0203] Comparative Example 1-1

[0204] The method for manufacturing the secondary battery is similar to that of Example 1-1, but the difference lies in the different manufacturing parameters of the negative electrode sheet.

[0205] After thoroughly stirring and mixing 97.1 wt% graphite, which is the negative electrode active material, 1.8 wt% styrene-butadiene rubber (SBR), which is the adhesive, 0.7 wt% sodium carboxymethylcellulose (CMC), which is the dispersant, and 0.4 wt% carbon black (Super P), which is the conductive agent, with an appropriate amount of solvent-deionized water, a negative electrode slurry is formed. The negative electrode slurry is then applied to the surface of the copper foil of the negative electrode current collector, dried, and cold-pressed to obtain a negative electrode sheet.

[0206] Examples 1-2 to 1-4 and Comparative Examples 2-1 to 2-2

[0207] The method for manufacturing a secondary battery is similar to that of Example 1-1, with the difference lying in the different manufacturing parameters of the negative electrode sheet. The specific parameters are shown in Table 2, and in the manufacturing process of the negative electrode sheet, the addition amounts of the adhesive and the dispersant remain unchanged.

[0208] Examples 3-1 to 3-5 and Comparative Examples 3-1 to 3-2

[0209] The method for manufacturing a secondary battery is similar to that of Example 1-1, with the difference lying in the different manufacturing parameters of the negative electrode sheet. The specific parameters are shown in Table 3, and in the manufacturing process of the negative electrode sheet, the addition amounts of the adhesive and the dispersant remain unchanged.

[0210] Examples 4-1 to 4-4

[0211] The method for manufacturing a secondary battery is similar to that of Example 1-1, with the difference lying in the different manufacturing parameters of the negative electrode sheet. The specific parameters are shown in Table 4, and in the manufacturing process of the negative electrode sheet, the addition amounts of the adhesive and the dispersant remain unchanged.

[0212] Example 5-1

[0213] The method for manufacturing a secondary battery is similar to that of Example 1-1, with the difference lying in the different manufacturing processes of the negative electrode sheet.

[0214] Preparation of the first slurry: 96 wt% of graphite as the negative electrode active material, 1.8 wt% of styrene-butadiene rubber (SBR) as the adhesive, and 1.2 wt% of sodium carboxymethyl cellulose (CMC) as the dispersant are sufficiently stirred and mixed with an appropriate amount of deionized water as the solvent, then 1 wt% of amorphous hollow carbon spheres (same as in Example 1) is added to form the first slurry.

[0215] Preparation of the second slurry: 96 wt% graphite, which is the negative electrode active material, 1.8 wt% styrene-butadiene rubber (SBR), which is the adhesive, and 1.2 wt% sodium carboxymethylcellulose (CMC), which is the dispersant, are thoroughly mixed with an appropriate amount of solvent-deionized water, and then 1 wt% amorphous hollow carbon spheres (same as in Example 1) are added to form the second slurry.

[0216] Preparation of the third slurry: 95.4 wt% graphite, which is the negative electrode active material, 1.8 wt% styrene-butadiene rubber (SBR), which is the adhesive, and 1.2 wt% sodium carboxymethylcellulose (CMC), which is the dispersant, are thoroughly mixed with an appropriate amount of solvent-deionized water, and then 1.6 wt% amorphous hollow carbon spheres (same as in Example 1) are added to form the third slurry.

[0217] As shown in Figure 1, the first slurry, the second slurry, and the third slurry are applied simultaneously to the first, second, and third regions of the negative electrode current collector copper foil, respectively. After drying and cold pressing, a negative electrode sheet is obtained. The first portion of the negative electrode active material layer is formed after the first slurry dries, the second portion of the negative electrode active material layer is formed after the second slurry dries, and the third portion of the negative electrode active material layer is formed after the third slurry dries.

[0218] Examples 5-2 to 5-6

[0219] The method for manufacturing the secondary battery is similar to that of Example 5-1, the only difference being the manufacturing parameters of the negative electrode sheet. The specific parameters are shown in Table 5, and the amounts of adhesive and dispersant added in the manufacturing of the negative electrode sheet remain unchanged.

[0220] Test section

[0221] (1) Thickness d of the shell wall of the additive, volume V of the cavity of the additive. h , volume V of additive w Test

[0222] A circular sample with a diameter of 0.5 cm is cut from the negative electrode sheet manufactured as described above, and a TEM image of the cross-section is obtained using a Transmission Electron Microscope (TEM). The thickness of the additive shell wall and the volume particle size of the additive within this region are statistically calculated, and cumulative distribution curves for the thickness of the additive shell wall and the volume particle size of the additive are obtained, respectively. The thickness corresponding to when the percentage in the cumulative distribution curve is 50% is defined as the thickness of the additive shell wall d, and the volume particle size corresponding to when the percentage in the cumulative distribution curve is 50% is defined as the volume particle size of the additive Dv50. Using the formula for an ideal sphere, the volume V of the additive is calculated using the volume particle size Dv50 obtained above as the diameter. w Calculate V w =(4 / 3)×π×(Dv50 / 2) 3 The volume V of the additive cavity. h =(4 / 3)×π×(Dv50 / 2-d) 3 This is obtained by calculation. The test equipment can be a Mastersizer 3000 laser particle size analyzer from Malvern GmbH, UK.

[0223] (2) Porosity test of the negative electrode sheet

[0224] The negative electrode active material layer is wiped off one side of the negative electrode current collector, and then the negative electrode sheet is punched out into a small wafer sample of a certain area to calculate the apparent volume V1 of the negative electrode sheet. Referring to GB / T24586-2009, the true volume V2 of the negative electrode sheet is measured using a true density tester by gas displacement using an inert gas (e.g., helium or nitrogen gas) as the medium. The porosity of the negative electrode sheet = (V1 - V2) / V1 × 100%. The accuracy of the test results can be improved by taking the average value of the results obtained from testing multiple negative electrode sheet samples (e.g., 30 sheets) that have a good appearance and no powder falloff at the edges. A Micromeritics AccuPyc II 1340 true density tester can be used as the testing apparatus.

[0225] (3) Area test of single-layer negative electrode sheet

[0226] Area of single-layer negative electrode sheet = perimeter of winding core × 0.5 × width of negative electrode sheet.

[0227] (4) Test of initial capacity C0 of secondary battery

[0228] At 25°C, charge the secondary battery to 3.65V at a constant current of 1C, leave it standing for 30 minutes, then discharge it to 2.5V at a constant current of 1C. This is regarded as one cycle of charge-discharge process, and the discharge capacity at this time, that is, the initial capacity C0 of the secondary battery, is recorded.

[0229] (5) Cycle performance test of secondary battery

[0230] At 25°C, charge the secondary battery to 3.65V at a constant current of 1C, leave it standing for 30 minutes, then discharge it to 2.5V at a constant current of 1C. This is one cycle of charge-discharge process. Record the discharge capacity at this time, that is, the initial capacity of the secondary battery, then conduct cyclic charge-discharge test on the secondary battery according to the above method. Until the discharge capacity of the secondary battery decays to 80% of the initial capacity of the secondary battery, record the discharge capacity after each cycle and record the number of cycles.

[0231] (6) Thickness rebound rate test of negative electrode active material layer

[0232] ε is the thickness rebound rate of the third portion of the negative electrode active material layer when the capacity of the secondary battery decays to 80% of the initial capacity of the secondary battery, and ε=(H'-H) / H.

[0233] ε1 is the thickness rebound rate of the first portion of the negative electrode active material layer when the capacity of the secondary battery decays to 80% of the initial capacity of the secondary battery, and ε1=(H1'-H1) / H1.

[0234] ε2 is the thickness rebound rate of the second portion of the negative electrode active material layer when the capacity of the secondary battery decays to 80% of the initial capacity of the secondary battery, and ε2=(H2'-H2) / H2.

[0235] H', H1', ​​and H2' are the thicknesses obtained by testing the third, first, and second portions of the negative electrode active material layer, respectively, when the capacity of the secondary battery has decreased to 80% of its initial capacity, and are obtained by the following method: At 25°C, the secondary battery is charged to 3.65V with a constant current of 1C, left to stand for 30 minutes, and then discharged to 2.5V with a constant current of 1C. This is one charge-discharge cycle, and the discharge capacity at this time, i.e., the initial capacity of the secondary battery, is recorded. The secondary battery is subjected to a cycle charge-discharge test according to the above method, and the discharge capacity after one cycle is recorded until the discharge capacity of the secondary battery decreases to 80% of its initial capacity. The negative electrode sheet can be disassembled from a secondary battery, immersed in an organic solvent (e.g., dimethyl carbonate) for a predetermined time (e.g., 72 hours or more), then removed and dried at a constant temperature and time (e.g., in a vacuum oven at 80°C for 6 hours or more). After this, the thicknesses of the third, first, and second portions of the negative electrode active material layer can be measured, respectively.

[0236] H, H1, and H2 are the initial thicknesses of the third, first, and second portions of the negative electrode active material layer, respectively. In each example and comparative example of this application, H, H1, and H2 are all the thicknesses of the negative electrode active material layer after cold pressing, i.e., 70 μm.

[0237] (7) Expansion force test of secondary batteries

[0238] At 25°C, the secondary battery is charged to 3.65V with a constant current of 1C, left to stand for 30 minutes, and then discharged to 2.5V with a constant current of 1C. This constitutes one charge-discharge cycle, and the discharge capacity at this time, i.e., the initial capacity of the secondary battery, is recorded. The secondary battery is subjected to a cycle charge-discharge test according to the above method, and the discharge capacity after each cycle is recorded until the discharge capacity of the secondary battery decays to 80% of the initial capacity of the secondary battery. During the cycle process, as shown in Figure 8, the secondary battery 5 is placed between steel plates 301 and 302, and the force sensor 201 is placed between steel plates 302 and 303, and the expansion force is monitored when the discharge capacity of the secondary battery decays to 80% of the initial capacity of the secondary battery. The results are shown in Tables 1 to 6.

[0239] Based on the test results in Tables 1 to 6, we can conclude that 20nm ≤ d ≤ 300nm and 40% ≤ V h / V w It has been found that adding an additive satisfying ≤90% to the negative electrode sheet effectively reduces the expansion force of the secondary battery and improves its safety performance, provided that the amount of additive used is small and does not affect the energy density. Preferably, the amount of additive used is 0.01 wt% to 3 wt%, more preferably 0.1 wt% to 2 wt%, as the amount of additive used continues to increase, worsening the effect of further reducing the expansion force on the secondary battery and becoming unfavorable to the energy density of the secondary battery.

[0240] In summary, the test results from Tables 1 to 6 show that when a secondary battery satisfies 100 ≤ K ≤ 30000, and preferably 120 ≤ K ≤ 8000, it can have a smaller expansion force.

[0241] In summary, the test results of Examples 2-1 to 2-4 and Comparative Examples 2-1 to 2-2, and Examples 3-1 to 3-5 and Comparative Examples 3-1 to 3-2 show that the thickness d of the additive's shell wall is less than 20 nm, and the volume occupancy V of the additive's cavity is... h / V w The percentage is greater than 90%, the thickness d of the additive shell wall is greater than 300 nm, and the volume occupancy V of the additive cavity is greater than 90%. h / V w It was found that when the ratio is less than 40%, the expansion force of the secondary battery cannot be effectively reduced.

[0242] In summary, the test results from Examples 2-1 to 2-4 and Examples 3-1 to 3-5 show that when the amount of additive used is the same, the volume occupancy rate of the additive cavity V h / V w Furthermore, 60% ≤ V h / V w Satisfying ≤90%, preferably 70% ≤ V h / V w It was found that secondary batteries can have a smaller expansion force if the condition ≤ 89% is met.

[0243] Based on the test results of Examples 2-1 and 4-1 to 4-4, the volume ratio V of the additive cavity is h / V w Under conditions where the volume particle size is close to the thickness of the shell wall and the amount of additive used is the same, it was found that when the volume particle size of the additive is greater than 0.8 μm, preferably 0.85 μm to 5 μm, and more preferably 1 μm to 2.5 μm, it is advantageous for reducing the expansion force of the secondary battery and simultaneously advantageous for improving the cycle performance of the secondary battery.

[0244] In summary, the test results of Examples 1-3 and 5-5, Examples 1-4 and 5-4, Examples 1-6 and 5-1, Examples 1-9 and 5-2 show that by further adjusting the distribution of the additive in the width direction of the negative electrode active material layer, and by employing a high-content additive in the third portion and a low-content additive in the first and second portions, the actual amount of additive used in the negative electrode sheet can be further reduced when the expansion force of the secondary battery is appropriate, thereby further improving the energy density of the secondary battery.

[0245] In summary, the test results of Examples 5-2 and 5-3 show that, in addition to Example 5-2, increasing the amount of additive used in the third portion of the negative electrode active material layer does not further increase the improvement effect on the expansion force of the secondary battery. Therefore, the present invention can further guide the amount of additive used in the negative electrode sheet, thereby further improving the energy density of the secondary battery.

[0246] 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.

[0247] [Table 1]

[0248] Table 2

[0249] Table 3

[0250] Table 4

[0251] Table 5

[0252] Table 6

Claims

1. The device comprises a negative electrode current collector and a negative electrode active material layer provided on the negative electrode current collector, wherein the negative electrode active material layer comprises a negative electrode active material and an additive, the additive comprises a shell wall and a cavity located inside the shell wall, the additive comprises hollow carbon spheres, the thickness of the shell wall is d and the volume of the cavity is V h The volume of the additive is V w The additive is defined as having a wavelength of 20 nm ≤ d ≤ 300 nm and a density of 40% ≤ V. h / V w Satisfying ≤90%, Negative electrode sheet.

2. 25 nm ≤ d ≤ 200 nm, and / or, 60% ≤ V h / V w ≤90% The negative electrode sheet according to claim 1.

3. The thickness d of the shell wall of the additive, and the volume V of the cavity of the additive. h , and the aforementioned attachment Volume V of the additive w This can be obtained by testing as follows: A circular sample with a diameter of 0.5 cm is cut out from the negative electrode sheet, a cross-sectional TEM image is obtained by a transmission electron microscope, the thickness of the shell wall of the additive and the volume particle size of the additive in the region are counted, cumulative distribution curves of the thickness of the shell wall of the additive and the volume particle size of the additive are obtained respectively, the thickness corresponding to 50% in the cumulative distribution curve is taken as the thickness d of the shell wall of the additive, the volume particle size corresponding to 50% in the cumulative distribution curve is taken as the volume particle size Dv50 of the additive, and based on the calculation formula for an ideal sphere, taking the obtained volume particle size Dv50 as the diameter, the volume V of the additive w is calculated, where V w = (4 / 3) × π × (Dv50 / 2) 3 , and the volume V of the cavity of the additive h = (4 / 3) × π × (Dv50 / 2 - d) 3 . The negative electrode sheet according to claim 1.

4. The volume particle size Dv50 of the additive is 0.85 μm to 5 μm, and / or The volume particle size of the additive satisfies 0.5 ≤ (Dv90 - Dv10) / Dv50 ≤ 8. The negative electrode sheet according to claim 1.

5. The aforementioned additive includes one or more types selected from amorphous hollow carbon spheres, graphitized hollow carbon spheres, and hollow graphene spheres. The negative electrode sheet according to claim 1.

6. The weight percentage content of the additive relative to the total weight of the negative electrode active material layer is 0.01 wt% to 3 wt%. The negative electrode sheet according to claim 1.

7. Along the width direction of the negative electrode active material layer, the negative electrode active material layer includes a first portion and a second portion located on the edge side, and a third portion located between the first portion and the second portion, wherein the total width of the negative electrode active material layer is W, the width of the first portion is 1 / 5W, the width of the second portion is 1 / 5W, the width of the third portion is 3 / 5W, and the weight percentage content of the additive in the first portion is w 1 The additive in the second portion The weight percentage content is w 2 The weight percentage content of the additive in the third portion is as follows: The quantity is lol 3 And 0 ≤ w 1 / w 3 <1, 0 ≤ w 2 / w 3 < 1 The negative electrode sheet according to claim 1.

8. 0<w 1 / w 3 ≤ 0.7 and / or, 0<w 2 / w 3 ≤ 0.7 The negative electrode sheet according to claim 7.

9. 0 wt% ≤ w 1 ≤ 2 wt%, and / or, 0 wt% ≤ w 2 ≤ 2 wt%, and / or, 0.01 wt% ≤ w 3 ≤ 5 wt%, The negative electrode sheet according to claim 7.

10. lol 1 =w 2 That is, The negative electrode sheet according to claim 7.

11. The weight percentage content of the negative electrode active material relative to the total weight of the negative electrode active material layer is 95 wt% to 99 wt%. The negative electrode sheet according to claim 1.

12. The negative electrode active material layer further comprises a negative electrode adhesive and / or a negative electrode dispersant. The negative electrode sheet according to claim 1.

13. The negative electrode active material layer further comprises a negative electrode conductive agent. The negative electrode sheet according to claim 1.

14. The present invention provides a negative electrode slurry containing a negative electrode active material and an additive, and provides a negative electrode sheet by applying the negative electrode slurry to a negative electrode current collector, drying and cold pressing the slurry, wherein the negative electrode sheet comprises a negative electrode current collector and a negative electrode active material layer provided on the negative electrode current collector, the negative electrode active material layer comprises a negative electrode active material and an additive, the additive comprises a shell wall and a cavity located inside the shell wall, the additive comprises hollow carbon spheres, the thickness of the shell wall is d, and the volume of the cavity is V h The volume of the additive is V w The additive has a wavelength of 20 nm ≤ d ≤ 300 nm and a density of 40% ≤ V. h / V w Satisfying ≤90%, A method for manufacturing a negative electrode sheet.

15. Along the width direction of the negative electrode current collector, the negative electrode current collector includes a first region and a second region located on the edge side, and a third region located between the first region and the second region, the total width of the coating area of ​​the negative electrode current collector is W, the width of the first region is 1 / 5W, the width of the second region is 1 / 5W, and the width of the third region is 3 / 5W, and in the method for manufacturing the negative electrode sheet, the negative electrode slurry is made into a first slurry, a second slurry and a third A slurry is prepared, and then the first slurry, the second slurry, and the third slurry are applied to the first, second, and third regions of the negative electrode current collector, respectively, and dried to form the first, second, and third portions of the negative electrode active material layer, and the weight percentage content of the additive in the first portion is w 1 The weight percentage content of the additive in the second part is w 2 The weight percentage content of the additive in the third portion is w 3 And 0 ≤ w 1 / w 3 <1 , 0≦w 2 / w 3 < 1 The manufacturing method according to claim 14.

16. Including the negative electrode sheet described in claim 1, Secondary battery.

17. Along the width direction of the negative electrode active material layer, the negative electrode active material layer includes a first portion and a second portion located on the edge side, and a third portion located between the first portion and the second portion, wherein the total width of the negative electrode active material layer is W, the width of the first portion is 1 / 5W, the width of the second portion is 1 / 5W, and the width of the third portion is 3 / 5W. The aforementioned secondary battery satisfies 100 ≤ K ≤ 30000, [Math 1] λ is the porosity of the negative electrode sheet, ε is the thickness repulsion coefficient of the third portion of the negative electrode active material layer when the capacity of the secondary battery has decreased to 80% of the initial capacity of the secondary battery. C 0 This is the initial capacity of the secondary battery, and its unit is mAh. d is the thickness of the shell wall of the additive, and its unit is nm. V h is the volume of the cavity of the additive, and its unit is nm. 3 And, S is the area of ​​the single-layer negative electrode sheet, and the unit is mm. 2 And, H is the initial thickness of the third portion of the negative electrode active material layer, and its unit is μm. The secondary battery according to claim 16.

18. The aforementioned secondary battery satisfies at least one of the following conditions: (1) 20% ≤ λ ≤ 50%, (2) 20% ≤ ε ≤ 40%, (3) 20 nm ≤ d ≤ 300 nm, (4) 1 x 10 7 nm 3 ≤ V h ≤ 1 × 10 12 nm 3 And, (5) 1 x 10 2 mm 2 ≤ S ≤ 1 × 10 8 mm 2 And, (6) 10 μm ≤ H ≤ 250 μm The secondary battery according to claim 17.

19. When the capacity of the secondary battery has decreased to 80% of its initial capacity, the thickness rebound coefficient of the first portion of the negative electrode active material layer is ε 1 It is expressed as, and the first of the negative electrode active material layers The initial thickness of this part is H 1 It is expressed as, and the unit is μm, and the second of the negative electrode active material layer The rebound rate of the thickness of the part is ε 2 The initial thickness of the second portion of the negative electrode active material layer is expressed as follows: H 2 It is expressed as such, the unit is μm, and the secondary battery is 0 < K 1 / K ≤ 1, 0 < K 2 / K ≤ 1 satisfy, [Math 2] The secondary battery according to claim 17.

20. 0<K 1 / K ≤ 0.95 and / or, 0<K 2 / K ≤ 0.95 The secondary battery according to claim 19.

21. 100 ≤ K 1 ≤ 30000 and / or, 100 ≤ K 2 ≤ 30000 The secondary battery according to claim 19.

22. 15% ≤ ε 1 ≤35%, and / or, 15% ≤ ε 2 ≤35%, and / or, 10 μm ≤ H 1 ≤250 μm and / or, 10 μm ≤ H 2 The size is ≤250 μm. The secondary battery according to claim 19.

23. A power consumption device including the secondary battery described in claim 16.

Images