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] The present application belongs to the technical field of batteries, and specifically relates to a negative electrode sheet, a method for manufacturing the same, a secondary battery, and an electric power consumption device.

Background Art

[0002] Secondary batteries are widely used in many fields such as energy storage power systems such as hydraulic power plants, thermal power plants, wind power plants, and solar power plants, and electric tools, electric bicycles, electric motorcycles, electric vehicles, military equipment, aerospace, etc. With the application and popularization of secondary batteries, their safety performance has attracted increasing attention. If the safety problems of secondary batteries are not guaranteed, the secondary batteries cannot be used. Therefore, how to improve the safety performance of secondary batteries is an issue to be solved currently.

Summary of the Invention

[0003] An object of the present application is to provide a negative electrode sheet, a method for manufacturing the same, a secondary battery, and an electric power consumption device that can effectively reduce the expansion force of the secondary battery and improve the safety performance of the secondary battery.

[0004] A first aspect of the present application provides a negative electrode sheet including 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 includes a negative electrode active material and an additive, the additive includes a shell wall and a cavity located inside the shell wall, the thickness of the shell wall is d, the volume of the cavity is V h , the volume of the additive is V w Let it be, and the additive satisfies 20 nm ≤ d ≤ 300 nm and 40% ≤ V h / V w ≤ 90%.

[0005] The additive satisfies 20 nm ≤ d ≤ 300 nm and 40% ≤ V h / V wWhen simultaneously satisfying ≤ 90%, the large cavity structure of the additive can generate large elastic deformation, and further, the adverse effects caused by the expansion of the negative electrode can be effectively reduced. On the other hand, the structural stability of the additive is high. Therefore, when large elastic deformation occurs in the additive, problems such as crushing and pulverization do not occur. Therefore, when the amount of the additive used is small and it 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.

[0006] In any embodiment of the present application, 25 nm ≤ d ≤ 200 nm, preferably 40 nm ≤ d ≤ 120 nm. Thereby, it is advantageous for improving the balance of the structural stability of the additive and the strain capacity of the additive, and thereby reducing the adverse effects caused by the expansion of the negative electrode better. When the amount of the additive used is small and it 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.

[0007] In any embodiment of the present application, 60% ≤ V h / V w ≤ 90%, preferably 70% ≤ V h / V w ≤ 89%. Thereby, it is advantageous for the additive to have relatively large elastic deformation and for the particles of the negative electrode active material to expand to provide a buffer space, and thereby reducing the adverse effects caused by the expansion of the negative electrode better. When the amount of the additive used is small and it 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.

[0008] In any embodiment of the present application, the thickness d of the shell wall of the additive, the volume V h of the cavity of the additive and the volume V wIt is obtained by testing in the following manner. A circular sample with a diameter of 0.5 cm is cut out from the negative electrode sheet, and a TEM image of the cross-section is acquired using a transmission electron microscope. The thickness of the shell wall of the additive and the volume particle size of the additive within this region are statistically analyzed. 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 a percentage of 50% in the cumulative distribution curve is defined as the thickness d of the shell wall of the additive, and the volume particle size corresponding to a percentage of 50% in the cumulative distribution curve is defined as the volume particle size Dv50 of the additive. Based on the calculation formula of an ideal sphere, with the obtained volume particle size Dv50 as the diameter, the volume V w of the additive is calculated, and V w =(4 / 3)×π×(Dv50 / 2) 3 whereas the volume V h of the cavity of the additive is V h =(4 / 3)×π×(Dv50 / 2 - d) 3 is as such.

[0009] In any embodiment of the present application, the additive includes one or more 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. Thereby, the swelling force of the secondary battery can be effectively reduced and the safety performance can be improved. On the other hand, the cycle performance and rate performance of the secondary battery can be well guaranteed.

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

[0012] In any embodiment of the present application, the additive includes hollow carbon spheres, preferably including one or more selected from amorphous hollow carbon spheres, graphitized hollow carbon spheres, and hollow graphene spheres. Thereby, the adverse effects caused by the expansion of the negative electrode can be reduced better. 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.

[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%. The present application can effectively reduce the expansion force of the secondary battery and improve the safety performance of the secondary battery when the amount of the additive used is small and does not affect the energy density.

[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 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. Taking the total width of the negative electrode active material layer as 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 and the weight percentage content of the additive in the second portion is w 2 and 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. 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, not only can the expansion force of the secondary battery be effectively reduced and the safety performance of the secondary battery be improved, but also when achieving the same expansion force improvement effect, the amount of the additive used can be further reduced, and the energy density of the secondary battery can be improved.

[0015] In any embodiment of the present application, 0 < w 1 / w 3 ≦ 0.7, and preferably, 0 < w 1 / w 3 ≦ 0.5.

[0016] In any embodiment of the present application, 0 < w 2 / w 3 ≦ 0.7, and preferably, 0 < w 2 / w 3 ≦ 0.5.

[0017] By further adjusting the relationship 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 to be within the above range, when reducing the usage amount of the additive, 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, 0 wt% ≦ w 1 ≦ 2 wt%, and preferably, 0 wt% < w 1 ≦ 1 wt%.

[0019] In any embodiment of the present application, 0 wt% ≦ w 2 ≦ 2 wt%, and preferably, 0 wt% < w 2 ≦ 1 wt%.

[0020] In any embodiment of the present application, 0.01 wt% ≦ w 3 ≦ 5 wt%, and preferably, 0.01 wt% ≦ w 3 ≦ 2 wt%.

[0021] In any embodiment of the present application, w 1 = w 2 is.

[0022] In any embodiment of the present application, the weight percentage content of the negative electrode active material with respect to the total weight of the negative electrode active material layer is 95 wt% to 99 wt%. 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 includes a negative electrode adhesive and / or a negative electrode dispersant.

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

[0025] In any embodiment of the present application, the weight percentage content of the negative electrode dispersant with respect to the total weight of the negative electrode 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 includes a negative electrode conductive agent. Preferably, the weight percentage content of the negative electrode conductive agent with respect to the total weight of the negative electrode active material layer is 0 wt% to 1.5 wt%.

[0027] The second aspect of the present application provides a method for manufacturing a negative electrode sheet, including 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, and cold pressing to obtain a negative electrode sheet. 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 includes 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 . Taking the additive, 20 nm ≤ d ≤ 300 nm, 40% ≤ V h / V w ≤ 90% is satisfied.

[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. Taking the total width of the coating region of the negative electrode current collector as 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. 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. Then, the first slurry, the second slurry, and the third slurry are respectively applied to the first region, the second region, and the third region of the negative electrode current collector, and after drying, a first portion, a second portion, and a third portion of the negative electrode active material layer are respectively formed. The weight percentage content of the additive in the first portion is w 1 and the weight percentage content of the additive in the second portion is w 2 and 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.

[0029] In any embodiment of the present application, the first slurry, the second slurry, and the third slurry employ a single simultaneous coating process or a plurality of step coating processes.

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

[0031] In any embodiment of the present application, the secondary battery satisfies 100 ≦ K ≦ 30000, preferably satisfies 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%, 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 and preferably 2.5×10 8 nm 3 ≤ V h ≤ 1×10 10 nm 3 is satisfied.

[0036] In any embodiment of the present application, 1×10 2 mm 2 ≤ S ≤ 1×10 8 mm 2 and preferably 1×10 3 mm 2 ≤ S ≤ 1×10 6 mm 2 is satisfied.

[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 recovery rate of the first portion of the negative electrode active material layer is ε 1 as described, the initial thickness of the first portion of the negative electrode active material layer is H 1 as described, the unit is μm, the thickness recovery rate of the second portion of the negative electrode active material layer is ε 2 as described, the initial thickness of the second portion of the negative electrode active material layer is H 2 as described, the unit is μm, and the secondary battery satisfies 0 < K 1 / K ≦ 1, 0 < K 2 / K ≦ 1.

Number

[0039] In any embodiment of the present application, 0 < K 1 / K ≦ 0.95.

[0040] In any embodiment of the present application, 0 < K 2 / K ≦ 0.95.

[0041] In any embodiment of the present application, 100 ≦ K 1 ≦ 30000, preferably 120 ≦ K 1 ≦ 8000.

[0042] In any embodiment of the present application, 100 ≦ K 2 ≦ 30000, preferably 120 ≦ K 2 ≦ 8000.

[0043] In any embodiment of the present application, 15% ≦ ε 1 ≦ 35%, preferably 25% ≦ ε 1 ≦ 31%.

[0044] In any embodiment of the present application, 15% ≤ ε 2 ≤ 35%, preferably, 25% ≤ ε 2 ≤ 31%.

[0045] In any embodiment of the present application, 10 μm ≤ H 1 ≤ 250 μm, preferably, 40 μm ≤ H 1 ≤ 120 μm.

[0046] In any embodiment of the present application, 10 μm ≤ H 2 ≤ 250 μm, preferably, 40 μm ≤ H 2 ≤ 120 μm.

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

[0048] When the amount of the additive used is small and does not affect the energy density, the present application can effectively reduce the swelling force of the secondary battery and improve the safety performance of the secondary battery. Since the power consumption device of the present application includes the secondary battery according to the present application, it has at least the same advantages as the secondary battery.

Brief Description of the Drawings

[0049] To clarify the technical solutions of the embodiments of the present application, the following briefly introduces the drawings required for the embodiments of the present application. It is clear that the drawings described below are only some embodiments of the present application. A person skilled in the art can obtain other drawings based on these drawings without creative labor.

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Explanation of Reference Numerals

[0050] 1 Battery pack 2 Upper housing 3 Lower housing 4 Battery module 5 Secondary battery 51 Housing 52 Electrode assembly 53 Cover plate 10 Negative electrode sheet 101 Negative electrode current collector 1011 First region 1012 Second region 1013 Third region 102 Negative electrode active material layer 1021 First part 1022 Second part 1023 Third part 201 Sensor 301 Steel plate 302 Steel plate 303 Steel plate

Embodiments for Carrying Out the Invention

[0051] Hereinafter, embodiments of the negative electrode sheet, its manufacturing method, secondary battery, and power consumption device of the present application will be specifically described in detail with appropriate reference to the drawings. However, detailed descriptions that are not necessary may be omitted. For example, detailed descriptions of known matters or duplicate descriptions of substantially the same configurations may be omitted. This is to avoid making the following description unnecessarily redundant and to facilitate the understanding of those skilled in the art. Note that the accompanying drawings and the following description are provided for those skilled in the art to fully understand the present application and are not intended to limit the subject matter described in the claims.

[0052] In the present application, the "range" disclosed is defined in the form of a lower limit and an upper limit. A predetermined range is defined by selecting one lower limit and one upper limit, and the selected lower limit and upper limit limit the boundary of a special range. The range thus limited may be a range including the end values or not including the end values, and may be arbitrarily combined, that is, any lower limit may be combined with any upper limit to form a range. For example, when ranges of 60 to 120 and 80 to 110 are given for a specific parameter, it is understood that ranges of 60 to 110 and 80 to 120 are also expected. Also, when the minimum range values 1 and 2 and the maximum range values 3, 4, and 5 are given, ranges of 1 to 3, 1 to 4, 1 to 5, 2 to 3, 2 to 4, and 2 to 5 may all be expected. In the present application, unless otherwise explained, the numerical range "a to b" is represented by an abbreviation of any combination of real numbers between a and b, and both a and b are real numbers. For example, the numerical range "0 to 5" indicates that all real numbers between "0 to 5" are listed in this specification, and "0 to 5" is an abbreviated notation of these numerical combinations. Also, the notation that a certain parameter is an integer of 2 or more (≧2) corresponds 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 selectable embodiments of the present application may be combined with each other to form a new technical solution. Also, such a technical solution is considered to be included in the disclosure content of the present application.

[0054] Unless otherwise specified, all technical features of the present application and selectable technical features may be combined with each other to form a new technical solution. Also, such a technical solution is considered to be included in the disclosure content of the present application.

[0055] Unless otherwise specified, all steps of the present application may be performed in order or randomly, but it is preferred to be performed in order. For example, the method includes steps (a) and (b), and the method may include steps (a) and (b) performed in sequence, or may include steps (b) and (a) performed in sequence. For example, the method may further include step (c), and step (c) may be added to the method in any order. For example, the method may include steps (a), (b), and (c), may include steps (a), (c), and (b), or may include steps (c), (a), and (b), etc.

[0056] Unless otherwise specified, the terms "comprise" and "include" described in the present application are meant to be open-ended, and may also be closed-ended. For example, the above "comprise" and the above "include" can represent further "comprising" or "including" other components not listed, or "comprising" or "including" only the listed components.

[0057] Unless otherwise specified, in the present application, the term "or" is inclusive. For example, the phrase "A or B" represents "A, B, or both A and B". More specifically, any of the following conditions is satisfied: 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, in the present application, the terms "first", "second", "third", etc. are for distinguishing different objects and do not describe a specific order or a primary-secondary relationship.

[0059] In the present application, the terms "plurality" and "plural types" mean two or more.

[0060] Unless otherwise specified, the terms used in the present application have well-known meanings commonly understood by those skilled in the art.

[0061] Unless otherwise specified, the numerical values of each parameter referred to in the present application can be measured by various test methods commonly used in the art. For example, they can be measured according to the test method according to the present application.

[0062] In the development of secondary battery technology, improving the electrochemical performance of secondary batteries is an issue that cannot be ignored, and safety performance is also important. During long-term cycling and storage processes, secondary batteries are prone to swelling phenomena caused by changes in the lattice structure of active materials. As the number of cycles and storage period increase, the cycle times and storage cycles of secondary batteries gradually increase. If the swelling force of the secondary battery is too high, the electrolyte infiltrated into the electrode sheet will be extruded, making the electrolyte prone to running out. In this case, the internal active ion transmission path of the secondary battery is blocked, the polarization of the secondary battery increases significantly, the rate performance decays rapidly, the capacity retention rate decreases significantly, and the service life is significantly shortened. In addition, if the swelling force of the 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 swelling force of secondary batteries and improve the safety performance of secondary batteries.

[0064] During the long-term cycling and storage processes of a secondary battery, the change in the thickness of the negative electrode is more obvious than that of the positive electrode, and according to current studies, the increase in the thickness of the negative electrode is considered to be the main cause of the increase in the expansion force of the secondary battery. The prior art attempts to manufacture a negative electrode sheet by adding and mixing hollow carbon spheres and a negative electrode active material during the manufacturing process of the secondary battery, and by reducing the adverse effects caused by the change in the thickness of the negative electrode by the hollow carbon spheres, the cycle performance of the secondary battery is improved and the irreversible capacity loss is reduced. However, the inventors of the present application have discovered during the research process that in the prior art, in order to effectively reduce the expansion force of the secondary battery, the usage amount of the hollow carbon spheres is generally high, which significantly reduces the energy density of the secondary battery.

[0065] Therefore, during the process of intensively studying the expansion problem of the secondary battery, the inventors of the present application added an additive having a cavity structure to the negative electrode sheet, and by adjusting the ratio of the thickness of the shell wall of the additive to the cavity volume, it was discovered that 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 can be improved.

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

[0067] 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 includes 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, the volume of the cavity be V h , the volume of the additive be V w , and the additive satisfies 20nm ≦ d ≦ 300nm, 40% ≦ V h / V w ≦ 90%.

[0068] The additive used in the negative electrode sheet of the present application has a hollow structure, and the cavity structure can provide a buffer space, buffer the expansion of the negative electrode, and reduce the expansion force of the secondary battery. The inventor of the present application discovered the following during the intensive study of the expansion problem of the secondary battery. When the thickness d of the shell wall of the additive is too small and / or the volume ratio V h / V w of the cavity of the additive is too large, the shell wall structure of the additive is fragile, and problems such as crushing and pulverization are likely to occur. Furthermore, since the buffering effect on the expansion of the negative electrode is poor, it is impossible to effectively reduce the expansion force of the secondary battery and improve the safety performance of the secondary battery. When the thickness d of the shell wall of the additive is too large and / or the volume ratio V h / V w of the cavity of the additive is too small, the stability of the shell wall structure of the additive is high, but in this case, the additive is difficult to elastically deform. Furthermore, the buffering effect on the expansion of the negative electrode is also poor, and thus it is also impossible to effectively reduce the expansion force of the secondary battery and improve the safety performance of the secondary battery. When the additive satisfies 20 nm ≤ d ≤ 300 nm and 40% ≤ V h / V w ≤ 90%, the large cavity structure of the additive can generate large elastic deformation, and furthermore, it can effectively reduce the adverse effects caused by the expansion of the negative electrode. On the other hand, since the structural stability of the additive is high, when large elastic deformation occurs in the additive, problems such as 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 amount of the additive used is small and does not affect the energy density.

[0069] In the present application, the thickness d of the shell wall of the additive, the volume V h of the cavity of the additive, and the volume V wcan be obtained by testing through the following method. Cut out a circular sample with a diameter of 0.5 cm from the negative electrode sheet, obtain a TEM image of the cross-section by a Transmission Electron Microscope (TEM), statistically analyze the thickness of the shell wall of the additive and the volume particle size of the additive within the region, respectively obtain the cumulative distribution curves of the thickness of the shell wall of the additive and the volume particle size of the additive, take the thickness corresponding to the percentage of 50% in the cumulative distribution curve as the thickness d of the shell wall of the additive, take the volume particle size corresponding to the percentage of 50% in the cumulative distribution curve as the volume particle size Dv50 of the additive, and based on the calculation formula of an ideal sphere, use the obtained volume particle size Dv50 as the diameter to calculate the volume V w of the additive, where V w =(4 / 3)×π×(Dv50 / 2) 3 and the volume V h of the cavity of the additive is V h =(4 / 3)×π×(Dv50 / 2 - d) 3 .

[0070] In the present application, the thickness d of the shell wall satisfies 20 nm ≤ d ≤ 300 nm. For example, d may be in the range consisting of any numerical value such as 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 more.

[0071] In some embodiments, preferably, 25 nm ≤ d ≤ 200 nm, 25 nm ≤ d ≤ 180 nm, 25 nm ≤ d ≤ 150 nm, 30 nm ≤ d ≤ 150 nm, 40 nm ≤ d ≤ 120 nm, 40 nm ≤ d ≤ 100 nm. Thereby, it is advantageous for improving the structural stability of the additive and balancing the strain capacity of the additive. Thereby, when the adverse effect caused by the expansion of the negative electrode is better reduced, the amount of the additive used is small and the energy density is not affected, the expansion force of the secondary battery can be effectively reduced, and the safety performance of the secondary battery can be improved.

[0072] In the present application, the volume ratio Vh / V w is such that 40% ≦ V h / V w ≦ 90%, for example, V h / V w / V may be in the range consisting of any value such as 48%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90% or more.

[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 w ≦ 89%. This is advantageous for the additive to have a relatively large elastic deformation and provide a buffer space against the expansion of the negative electrode active material particles. Thereby, the adverse effects caused by the expansion of the negative electrode are better reduced, and when the amount of the additive used is small and does not affect the energy density, the expansion force of the secondary battery is effectively reduced, and the safety performance of the secondary battery is improved.

[0074] In some embodiments, 25 nm ≦ d ≦ 200 nm and 60% ≦ V h / V w ≦ 90%. Preferably, 40 nm ≦ d ≦ 120 nm and 70% ≦ V h / V w ≦ 89%. This is advantageous for better achieving both a larger elastic deformation and high structural stability of the additive. Thereby, the adverse effects caused by the expansion of the negative electrode are better reduced. When the amount of the additive used is small and does not affect the energy density, the expansion force of the secondary battery is effectively reduced, and the safety performance of the secondary battery is improved.

[0075] In some embodiments, the additive includes one or more selected from hollow spheres and hollow polyhedra. In the present application, the term "hollow sphere" has a spherical or near-spherical structure and does not control all spheres to ideal spheres. The "hollow polyhedron" may include regular polyhedra such as cubes, or irregular polyhedra.

[0076] In some embodiments, the additive includes hollow spheres. Thereby, the adverse effects caused by the expansion of the negative electrode can be better reduced. 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.

[0077] In some embodiments, by way of example, the additive includes hollow carbon spheres, preferably including one or more of amorphous hollow carbon spheres, graphitized hollow carbon spheres, and hollow graphene spheres. Thereby, the adverse effects caused by the expansion of the negative electrode can be better reduced. 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.

[0078] In further studies, the inventors found 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 caused by the expansion of the negative electrode is weak, and thus 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 gaps between the negative electrode active material particles, which makes it easier to have a high compression density and a low porosity of the negative electrode sheet. On the other hand, when the compression density of the negative electrode sheet is high, the thickness repulsion during the use of the secondary battery of the negative electrode sheet becomes more prominent, which makes the expansion force of the secondary battery significantly increase easily, being disadvantageous for the improvement of the safety performance of the secondary battery. When the compression density of the negative electrode sheet is high, due to the poor wettability and liquid retention property of the negative electrode sheet with respect to the electrolyte, when the expansion force of the secondary battery increases, the electrolyte in the negative electrode sheet is more easily extruded, and further problems such as electrolyte drainage, lithium precipitation on the negative electrode, and a sharp decrease in the capacity during the cycle of the secondary battery are likely to occur. When the compression density of the negative electrode sheet is high, the ion conduction characteristics of the negative electrode sheet become poor, which is further disadvantageous for the cycle performance and rate performance of the secondary battery. At the same time, the inventors further studied that when the usage amount of the additive is the same, the larger the particle size of the additive, the more likely its distribution in the negative electrode active material layer becomes uneven, and further, the effect of reducing the adverse effects caused by the expansion of the negative electrode becomes weak, the effect of reducing the expansion force on the secondary battery becomes poor, and it is also inferior in the improvement effect on the safety performance of the secondary battery. So, it is necessary that the particle size of the additive should not be too large. In some embodiments, 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. Thereby, while effectively reducing the expansion force of the secondary battery and improving the safety performance of the secondary battery, it can be ensured 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 satisfies 1 ≦ (Dv90 - Dv10) / Dv50 ≦ 5, and more preferably satisfies 2 ≦ (Dv90 - Dv10) / Dv50 ≦ 5.

[0080] In the present application, the volume particle sizes Dv10, Dv50, and Dv90 of the material have the meanings well-known in the art, indicating the particle sizes corresponding to the cases where the cumulative volume distribution percentage of the material reaches 10%, 50%, and 90% respectively, and can be measured by known equipment and methods in the art. For example, it can be measured using a laser particle size analyzer with reference to GB / T 19077-2016. As the measuring equipment, a Mastersizer 3000 type laser particle size analyzer manufactured by Malvern Panalytical Ltd. of the UK can be used.

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

[0082] Currently, in the negative electrode sheet of the prior art, although the hollow microballoons have a uniform equal amount distribution, which can reduce the swelling force of the secondary battery, at the same time, the occupancy rate of the negative electrode active material is reduced, and the energy density of the secondary battery is reduced. The inventor of the present application further discovered that the swelling force of the secondary battery is not uniformly distributed during the intensive study of the swelling problem of the secondary battery. Then, by intensively studying the distribution characteristics of the swelling force of the secondary battery, the inventor realized that when the amount of the additive used 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.

[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. Taking the total width of the negative electrode active material layer 102 as W, the width of the first portion 1021 is 1 / 5W, the width of the second portion 1022 is 1 / 5W, the width of the third portion 1023 is 3 / 5W, and the weight percentage content of the additive in the first portion 1021 is w 1 and the weight percentage content of the additive in the second portion 1022 is w 2 and the weight percentage content of the additive in the third portion 1023 is w 3 and 0 ≦ w 1 / w 3 <1, 0 ≦ w 2 / w 3 <1.

[0084] The inventor has intensively studied the distribution process of the swelling force of the secondary battery and discovered the following. In the long-term cycle and storage process of the secondary battery, it was discovered that the degree to which the large surface of the electrode assembly is pressed is the highest. Therefore, 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, not only can the swelling force of the secondary battery be effectively reduced and the safety performance of the secondary battery be improved, but also when the same improvement effect of the swelling force is achieved, the usage amount of the additive can be further reduced and the energy density of the secondary battery can be improved.

[0085] In some embodiments, 0 < w 1 / w 3 ≦ 0.8, 0 < w 1 / w 3 ≦ 0.7, 0 < w 1 / w 3 ≦ 0.6, 0 < w 1 / w 3 ≦ 0.5, 0 < w1 / w 3 is ≤ 0.4.

[0086] In some embodiments, 0 < w 2 / w 3 ≤ 0.8, 0 < w 2 / w 3 ≤ 0.7, 0 < w 2 / w 3 ≤ 0.6, 0 < w 2 / w 3 ≤ 0.5, 0 < w 2 / w 3 is ≤ 0.4.

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

[0088] In some embodiments, 0 wt% ≤ w 1 ≤ 2 wt%, preferably, 0 wt% < w 1 ≤ 1.8 wt%, 0 wt% < w 1 ≤ 1.6 wt%, 0 wt% < w 1 ≤ 1.4 wt%, 0 wt% < w 1 ≤ 1.2 wt%, 0 wt% < w 1 ≤ 1 wt%, 0 wt% < w 1 ≤ 0.8 wt%, 0 wt% < w 1 ≤ 0.6 wt%, 0 wt% < w 1 is ≤ 0.4 wt%.

[0089] In some embodiments, 0 wt% ≤ w 2 ≤ 2 wt%, preferably, 0 wt% < w 2 ≤ 1.8 wt%, 0 wt% < w 2 ≤ 1.6 wt%, 0 wt% < w 2 ≤ 1.4 wt%, 0 wt% < w 2 ≤ 1.2 wt%, 0 wt% < w 2 ≤ 1 wt%, 0 wt% < w 2 ≤ 0.8 wt%, 0 wt% < w2 ≤0.6 wt%, 0 wt% < w 2 is ≤0.4 wt%.

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

[0091] In some embodiments, w 1 = w 2 is.

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

[0093] In some embodiments, the negative electrode active material can employ a negative electrode active material used in known secondary batteries in this field. As an example, the negative electrode active material includes, but is not limited to, one or more of 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 elemental silicon, silicon oxide, silicon-carbon composite, silicon-nitrogen composite, and silicon alloy material. The tin-based material may include one or more of elemental tin, tin oxide, and tin alloy material. The present application is not limited to these materials, and conventionally known materials used as other secondary battery negative electrode active materials may also be used.

[0094] In some embodiments, the volume median 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 includes a negative electrode binder and / or a negative electrode dispersant. The negative electrode binder is used to improve the adhesion between the 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 the negative electrode binder in the present application is not particularly limited, and known materials in the art can be adopted. As an example, the binder may include one or a combination of a plurality of types selected from styrene-butadiene rubber (SBR), water-soluble unsaturated resin SR-1B, aqueous acrylic resin (for example, polyacrylic acid 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 binder relative to the total weight of the negative electrode active material layer may be greater than 0 and not more than 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 the negative electrode dispersant in the present application is not particularly limited, and known materials in the art can be adopted. As an example, the negative electrode dispersant may include sodium carboxymethyl cellulose (CMC). In some embodiments, 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 not more than 1.5 wt%, preferably 0.5 wt% to 1.5 wt%.

[0097] In some embodiments, the negative electrode active material layer further includes a negative electrode conductive agent. The type of the negative electrode conductive agent in the present application is not particularly limited, and known materials in this field can be adopted. As an example, the negative electrode conductive agent may include one or more of superconducting carbon, conductive graphite, acetylene black, carbon black, ketjen 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%. When the weight percentage content of the negative electrode conductive agent is 0 wt%, it indicates that no negative electrode conductive agent is added.

[0098] In some embodiments, preferably, the negative electrode active material layer may further include other auxiliaries such as, for example, PTC thermistor materials.

[0099] In some embodiments, the negative electrode current collector may adopt a metal foil sheet or a composite current collector. As an example of the metal foil sheet, a copper foil can be used. The composite current collector may include a polymer material base layer and a metal material layer formed on at least one surface of the polymer material base layer. As an example, the metal material may include one or more of copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy. As an example, the polymer material base layer 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 other 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 (for example, composed 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. 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 application provides a method for manufacturing a negative electrode sheet.

[0103] The method for manufacturing the negative electrode sheet includes 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. 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 includes 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 let the volume of the additive be V w , and the additive satisfies 20 nm ≤ d ≤ 300 nm and 40% ≤ V h / V w ≤ 90%.

[0104] In some embodiments, as shown in FIG. 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. Let the total width of the coating region of the negative electrode current collector 101 be W, the width of the first region 1011 be 1 / 5W, the width of the second region 1012 be 1 / 5W, and the width of the third region 1013 be 3 / 5W. 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. Then, the first slurry, the second slurry, and the third slurry are respectively applied to the first region 1011, the second region 1012, and the third region 1013 of the negative electrode current collector, and after drying, a first portion 1021, a second portion 1022, and a third portion 1023 of the negative electrode active material layer are respectively formed. Here, the weight percentage content of the additive in the first portion 1021 is w 1 , the weight percentage content of the additive in the second portion 1022 is w 2 , and the weight percentage content of the additive in the third portion 1023 is w3 and 0 ≦ w 1 / w 3 <1, 0 ≦ w 2 / w 3 <1. In the present application, the total width of the coating area 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 includes a negative electrode adhesive and / or a negative electrode dispersant.

[0106] In some embodiments, the negative electrode slurry may include a negative electrode conductive agent. Of course, the negative electrode slurry may not include a negative electrode conductive agent.

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

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

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

[0110] In the process of coating the negative electrode slurry, the first slurry, the second slurry, and the third slurry may adopt a one-time simultaneous coating process or a multi-step coating process.

[0111] The manufacturing method provided by the second aspect of the embodiment of the present application can manufacture the negative electrode sheet according to any of the examples of the first aspect of the embodiment of the present application. In the process of manufacturing the negative electrode sheet, parameters such as the specific types and usage amounts of some of the raw materials used can refer to the negative electrode sheet of the first aspect of the embodiment of the present application, and the description is omitted here.

[0112] In addition, in FIG. 1, the first region 1011, the second region 1012, and the third region 1013 of the negative electrode current collector 101 are distinguished by lines, and the first portion 1021, the second portion 1022, and the third portion 1023 of the negative electrode active material layer 102 are distinguished. However, actually, there is no interface, and the entire negative electrode current collector 101 may be continuous, or the entire negative electrode active material layer 102 may be continuous.

[0113] In some embodiments, along the width direction of the negative electrode current collector 101, the negative electrode current collector 101 may further include an uncoated region (not shown) where the negative electrode active material layer 102 is not provided, that is, the total width of the negative electrode current collector 101 is larger 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] The third aspect of the embodiment of the present application provides a secondary battery. The secondary battery usually includes a positive electrode sheet, a negative electrode sheet, and an electrolyte. The present application has no particular limitation on 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 of the examples of the first aspect of the embodiment of the present application, or the negative electrode sheet manufactured by the manufacturing method described in any one of the second aspects of the embodiment of the present application.

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

Number

[0118] λ is the porosity of the negative electrode sheet, ε is the thickness repulsion rate of the third part 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 C 0 is the initial capacity of the secondary battery, with the unit of mAh, d is the thickness of the shell wall of the additive, with the unit of nm, and V h is the volume of the cavity of the additive, with the unit of nm 3 and S is the area of the single-layer negative electrode sheet, with the unit of mm 2 and H is the initial thickness of the third part of the negative electrode active material layer, with the unit of μm.

[0119] As a result of intensive studies, the inventors have found that if the parameter K of the secondary battery is in the range of 100 to 30000, the expansion force of the secondary battery is small, the safety performance is high, and the energy density of the secondary battery is high.

[0120] In some embodiments, preferably, 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, 500 ≤ K ≤ 8000 are also acceptable.

[0121] In the present application, the porosity of the negative electrode sheet is the meaning known in the art and can be measured by a method known in the art. An exemplary test method is to take a negative electrode sheet coated on one side and cold-pressed (if it is a negative electrode sheet coated on both sides, the negative electrode active material layer on one of the sides can be wiped off first), punch it into a small wafer sample having a certain area to obtain the apparent volume V of the negative electrode sheet 1 and calculate it, and refer to GB / T24586-2009 to use an inert gas (for example, helium gas or nitrogen gas) as a medium, and use the gas replacement method to use a true density tester to measure the true volume V of the negative electrode sheet 2Measure. Porosity of the negative electrode sheet = (V 1 - V 2 ) / V 1 × 100%. As a result of testing a plurality of (for example, 30 sheets) negative electrode sheet samples with good appearance and no edge chipping, the accuracy of the test results can be improved by taking the average value. As the test apparatus, a Micromeritics AccuPyc II 1340 type true density tester can be used.

[0122] ε is the thickness rebound rate of the third part of the negative electrode active material layer when the capacity of the secondary battery has decayed to 80% of the initial capacity of the secondary battery, and ε = (H’ - H) / H. H’ is the thickness obtained by testing the third part of the negative electrode active material layer when the capacity of the secondary battery has decayed to 80% of the initial capacity of the secondary battery. H is the initial thickness of the third part of the negative electrode active material layer, and in the present application, when the number of cycles of the secondary battery is 50 or less, it is the thickness obtained by testing the third part of the negative electrode active material layer.

[0123] In the present application, the initial capacity C 0 of the secondary battery means the capacity of the secondary battery with 50 or fewer cycles.

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

[0125] In some embodiments, 20% ≤ λ ≤ 50%, and for example, λ may be in the range consisting of any numerical value such as 21%, 23%, 25%, 27%, 29%, 31%, 33%, 35%, 37%, 39%, 41%, 43%, 45%, 50% or more. Preferably, 23% ≤ λ ≤ 35%.

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

[0127] In some embodiments, 20 nm ≦ d ≦ 300 nm, for example, d may be in the range consisting of any numerical value such as 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 more. Preferably, 25 nm ≦ d ≦ 200 nm, 25 nm ≦ d ≦ 180 nm, 25 nm ≦ d ≦ 150 nm, 30 nm ≦ d ≦ 150 nm, 40 nm ≦ d ≦ 120 nm, 40 nm ≦ d ≦ 100 nm.

[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 nm 3 、2.5×10 8 nm 3 ≦ V h ≦ 1×10 10 nm 3 is satisfied.

[0129] In some embodiments, 1×10 2 mm 2 ≦ S ≦ 1×10 8 mm 2 、Preferably, 1×10 3 mm 2 ≦ S ≦ 1×10 6 mm 2 、1×10 4 mm 2 ≦ S ≦ 1×106 mm 2 is

[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 rate of the first portion of the negative electrode active material layer is ε 1 is defined as, and the initial thickness of the first portion of the negative electrode active material layer is H 1 is defined as, the unit is μm, the thickness rebound rate of the second portion of the negative electrode active material layer is ε 2 is defined as, and the initial thickness of the second portion of the negative electrode active material layer is H 2 is defined as, the unit is μm, and the secondary battery satisfies 0 < K 1 / K ≦ 1, 0 < K 2 / K ≦ 1.

Number

[0132] The inventor has found the following through intensive research. For the above parameters K 1 , K 2 and K, when 0 < K 1 / K ≦ 1, 0 < K 2 / K ≦ 1 is satisfied, the secondary battery has a small swelling force, high safety performance, and high secondary energy density.

[0133] In some embodiments, 0 < K 1 / K ≦ 0.95, 0 < K 1 / K ≦ 0.94, 0 < K 1 / K ≦ 0.92, 0 < K 1 / K ≦ 0.90, 0 < K 1 / K ≦ 0.88, 0 < K 1 / K ≦ 0.86. This is advantageous for further improving the energy density of the secondary battery.

[0134] In some embodiments, 0 < K 2 / K ≤ 0.95, 0 < K 2 / K ≤ 0.94, 0 < K 2 / K ≤ 0.92, 0 < K 2 / K ≤ 0.90, 0 < K 2 / K ≤ 0.88, 0 < K 2 / K ≤ 0.86. This is advantageous for further improving the energy density of the secondary battery.

[0135] In some embodiments, 100 ≤ K 1 ≤ 30000, preferably, 100 ≤ K 1 ≤ 20000, 120 ≤ K 1 ≤ 16000, 120 ≤ K 1 ≤ 12000, 120 ≤ K 1 ≤ 10000, 120 ≤ K 1 ≤ 9000, 120 ≤ K 1 ≤ 8000, 200 ≤ K 1 ≤ 8000, 300 ≤ K 1 ≤ 8000, 400 ≤ K 1 ≤ 8000, 500 ≤ K 1 ≤ 8000. As a result of intensive studies, the inventor has found that when the parameter K of the secondary battery 1 is within the above range, the secondary battery has a small expansion force and high safety performance, and further has a more improved energy density.

[0136] In some embodiments, 100 ≤ K 2 ≤ 30000, preferably, 100 ≤ K 2 ≤ 20000, 120 ≤ K 2 ≤ 16000, 120 ≤ K 2 ≤ 12000, 120 ≤ K 2 ≤ 10000, 120 ≤ K 2 ≤ 9000, 120 ≤ K 2 ≤ 8000, 200 ≤ K 2 ≤ 8000, 300 ≤ K 2 ≤ 8000, 400 ≤ K 2 ≤ 8000, 500 ≤ K 2 ≤ 8000. As a result of intensive studies, the inventor has found that when the parameter K of the secondary battery2 When it is within the above range, it has been found that the secondary battery has a smaller expansion force and higher safety performance, and further has an improved energy density.

[0137] In some embodiments, 15% ≤ ε 1 ≤ 35%, preferably 25% ≤ ε 1 ≤ 31%.

[0138] In some embodiments, 15% ≤ ε 2 ≤ 35%, preferably 25% ≤ ε 2 ≤ 31%.

[0139] In some embodiments, 10 μm ≤ H 1 ≤ 250 μm, preferably 40 μm ≤ H 1 ≤ 120 μm, 40 μm ≤ H 1 ≤ 100 μm, 40 μm ≤ H 1 ≤ 80 μm.

[0140] In some embodiments, 10 μm ≤ H 2 ≤ 250 μm, preferably 40 μm ≤ H 2 ≤ 120 μm, 40 μm ≤ H 2 ≤ 100 μm, 40 μm ≤ H 2 ≤ 80 μm.

[0141] ε 1 is the thickness rebound rate of the first part 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 1 = (H 1 ’ - H 1 ) / H 1 . H 1 ’ is the thickness obtained by testing the first part 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. H 1 is the initial thickness of the first part of the negative electrode active material layer, and in the present application, when the number of cycles of the secondary battery is 50 or less, it is the thickness obtained by testing the first part of the negative electrode active material layer.

[0142] ε 2 is the thickness rebound rate of the second part 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 2 =(H 2 ’ - H 2 ) / H 2 . H 2 ’ is the thickness obtained by testing the second part 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. H 2 is the initial thickness of the second part of the negative electrode active material layer. In the present application, when the number of cycles of the secondary battery is 50 or less, it is the thickness obtained by testing the second part of the negative electrode active material layer.

[0143] In some embodiments, H, H 1 and H 2 may be the same. That is, when the number of cycles of the secondary battery is 50 or less, the thicknesses of the first part, the second part, and the third part of the negative electrode active material are the same.

[0144] In the present application, the thickness parameters of the negative electrode active material layer (for example, H, H’, H 1 , H 1 ’, H 2 , H 2 ’) 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 according to the present application (for example, thickness, porosity, structure and content of additives, etc.) all mean the parameters of the negative electrode active material layer on one side of the negative electrode current collector. When the negative electrode active material layer is provided on both sides of the negative electrode current collector, one of the negative electrode active material layer parameters is considered to satisfy the present application, that is, within the protection scope of the present 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 a positive electrode active material. For example, the positive electrode current collector has both surfaces facing each other 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 as the positive electrode active material, a positive electrode active material for a secondary battery known in the art can be employed.

[0149] When the secondary battery of the present application is a lithium-ion battery, the positive electrode active material may include one or more of lithium transition metal oxides, lithium-containing phosphates having an olivine structure, and their respective modified compounds. Examples of the lithium transition metal oxide include 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 any one or more of their modified compounds. Examples of the lithium-containing phosphate having an olivine structure include 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 any one or more of their modified compounds. The present application is not limited to these materials, and conventionally known materials used as other secondary battery positive electrode active materials 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 in the lithium-ion secondary battery has a general formula of Li a Ni b Co c M d O e A fIt may contain one or more of the lithium transition metal oxides and their modified compounds thereof. 0.8 ≦ a ≦ 1.2, 0.5 ≦ b < 1, 0 < c < 1, 0 < d < 1, 1 ≦ e ≦ 2, 0 ≦ f ≦ 1, M contains one or more of Mn, Al, Zr, Zn, Cu, Cr, Mg, Fe, V, Ti and B, and A contains one or more of N, F, S and Cl.

[0151] As an example, the positive electrode active material used in the lithium ion secondary battery is LiCoO 2 , LiNiO 2 , LiMnO 2 , LiMn 2 O 4 , LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O 2 (NCM333), LiNi 0.5 Co 0.2 Mn 0.3 O 2 (NCM523), LiNi 0.6 Co 0.2 Mn 0.2 O 2 (NCM622), LiNi 0.8 Co 0.1 Mn 0.1 O 2 (NCM811), LiNi 0.85 Co 0.15 Al 0.05 O 2 , LiFePO 4 and LiMnPO 4 It may contain one or more of them.

[0152] When the secondary battery of the present application is a sodium ion battery, the positive electrode active material may contain one or more of a sodium-containing transition metal oxide, a polyanion material (for example, phosphate, fluorophosphate, pyrophosphate, sulfate, etc.), and a Prussian blue-based material, but is not limited thereto.

[0153] As an example, the positive electrode active material used in the sodium ion battery is NaFeO 2 , NaCoO2 , NaCrO 2 , NaMnO 2 , NaNiO 2 , NaNi 1 / 2 Ti 1 / 2 O 2 , NaNi 1 / 2 Mn 1 / 2 O 2 , Na 2 / 3 Fe 1 / 3 Mn 2 / 3 O 2 , NaNi 1 / 3 Co 1 / 3 Mn 1 / 3 O 2 , NaFePO 4 , NaMnPO 4 , NaCoPO 4 , Prussian blue-based materials and one or more of the materials of the general formula X p M’ q (PO 4 ) r O x Y 3-x may be included. In the general formula X p M’ q (PO 4 ) r O x Y 3-x , 0 < p ≤ 4, 0 < q ≤ 2, 1 ≤ r ≤ 3, 0 ≤ x ≤ 2, X includes one or more selected from H + , Li + , Na + , K + and NH 4 + , M’ is a transition metal cation, preferably includes one or more of V, Ti, Mn, Fe, Co, Ni, Cu and Zn, and Y is a halogen anion, preferably may include one or more of F, Cl and Br.

[0154] In the present application, the modified compound of each of the above positive electrode active materials may be subjected to doping modification and / or surface coating modification on the positive electrode active material.

[0155] In some embodiments, the positive electrode active material layer may further include a positive electrode conductive agent. The type of the positive electrode conductive agent in the present application is not particularly limited. As an example, the positive electrode conductive agent may include one or more of 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 the present application, the type of the positive electrode adhesive is not particularly limited. As an example, the positive electrode adhesive may include one or more of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorine-containing acrylate resin.

[0157] In some embodiments, a metal foil sheet or a composite current collector may be used for the positive electrode current collector. As an example of the metal foil sheet, an aluminum foil can be employed. The composite current collector may include a polymer material base layer and a metal material layer formed on at least one surface of the polymer material base layer. As an example, the metal material may include one or more of aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy. As an example, the polymer material base layer may include one or more of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), and polyethylene (PE).

[0158] The positive electrode active material layer is usually formed by applying a positive electrode slurry to a positive electrode current collector, followed by drying and cold pressing. The positive electrode slurry is generally formed by dispersing a positive electrode active material, an optional conductive agent, an optional adhesive, and any other components in a solvent and stirring them uniformly. The solvent may be, 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 the present application, the type of the electrolyte is not particularly limited and can be selected according to needs. The electrolyte may include, for example, one or more types selected from solid electrolytes and liquid electrolytes (i.e., electrolytic solutions).

[0161] In some embodiments, the electrolyte employs an electrolytic solution, and the electrolytic solution contains an electrolyte salt and a solvent.

[0162] When the secondary battery of the present application is a lithium-ion battery, as an example, the electrolyte salt is lithium hexafluorophosphate (LiPF 6 ), lithium tetrafluoroborate (LiBF 4 ), lithium perchlorate (LiClO 4 ), lithium hexafluoroarsenate (LiAsF 6 ), lithium difluorobis(fluorosulfonyl)imide (LiFSI), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium trifluoromethanesulfonate (LiTFS), lithium difluoroborate (LiDFOB), lithium diborate (LiBOB), lithium difluorophosphate (LiPO 2 F 2 ), lithium difluorodiphosphate (LiDFOP), and lithium tetrafluorophosphate (LiTFOP), and may contain one or more of them.

[0163] When the secondary battery of the present application is a sodium ion battery, the electrolyte salt is sodium hexafluorophosphate (NaPF 6 ), sodium tetrafluoroborate (NaBF 4 ), sodium perchlorate (NaClO 4 ), sodium hexafluoroarsenate (NaAsF 6 ), sodium bis(fluorosulfonyl)imide (NaFSI), sodium bis(trifluoromethanesulfonyl)imide (NaTFSI), sodium trifluoromethanesulfonate (NaTFS), sodium difluorooxalate borate (NaDFOB), sodium lithium bis(oxalate) borate (NaBOB), sodium difluorophosphate (NaPO 2 F 2 ), sodium difluorobis(oxalate) phosphate (NaDFOP), and sodium tetrafluorosilicate phosphate (NaTFOP), and may contain one or more of them.

[0164] The type of the solvent is not particularly limited and can be selected according to needs. In some examples, as an example, the solvent is 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), and may contain one or more of them.

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

[0166] [Separator]

[0167] In a secondary battery using an electrolyte or a secondary battery using a solid electrolyte, a separator is also included. The separator is provided between the positive electrode sheet and the negative electrode sheet, mainly serves to prevent short circuit between the positive electrode and the negative electrode, and at the same time, can allow active ions to pass through. In the present application, the type of the separator is not particularly limited, and any known porous structure separator having good chemical stability and mechanical stability can be selected. The separator may be a single-layer film or a multi-layer composite film. When the separator is a multi-layer 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 non-woven fabric, a film or a composite film having a porous structure, and the material of the base film includes one or more of polyethylene, polypropylene, polyvinylidene fluoride, polyethylene terephthalate and polyimide.

[0169] The 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, an inorganic layer, or a layer containing a mixed polymer and an inorganic substance.

[0170] The inorganic layer contains inorganic particles and an adhesive, and the inorganic particles include, but are not limited to, one or more of 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 contains a polymer, and the material of the polymer may include, but is not limited to, one or more of polyamide, polyacrylonitrile, acrylate polymer, polyacrylic acid, polyacrylate, polyvinylpyrrolidone, polyvinyl ether, and polyvinylidene fluoride.

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

[0173] In some embodiments, the secondary battery may include an exterior. The exterior is used for sealing the above-described electrode assembly and electrolyte.

[0174] In some embodiments, the exterior may be a hard case such as a hard plastic case, an aluminum case, or a steel case. The exterior may also be a soft package such as a bag 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 the present application is not particularly limited, and it may be cylindrical, rectangular, or any other arbitrary shape. FIG. 2 shows a secondary battery 5 having a rectangular structure as an example.

[0176] In some embodiments, as shown in FIG. 3, the exterior can 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 the side plates enclose to form a storage chamber. The housing 51 has an opening communicating with the storage chamber, and the cover plate 53 closes the opening so as to close the storage chamber. The positive electrode sheet, the negative electrode sheet, and the separator can form an electrode assembly 52 by a winding process or a lamination process. The electrode assembly 52 is packaged in the storage cavity. The electrolyte infiltrates 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 needs.

[0177] The manufacturing method of the secondary battery of the present application 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. As an example, a positive electrode sheet, a separator, and a negative electrode sheet are wound or laminated to form an electrode assembly, the electrode assembly is placed in an exterior, and after drying, an electrolyte is injected, and through processes such as vacuum encapsulation, standing, formation, and shaping, a secondary battery can be obtained.

[0178] In some embodiments of the present application, the secondary battery of the present application may be assembled into a battery module, and the number of secondary batteries included in the battery module may be plural, and the specific number may be adjusted according to the application and capacity of the battery module.

[0179] FIG. 4 is a schematic diagram of a battery module 4 as an example. As shown in FIG. 4, in the battery module 4, a plurality of secondary batteries 5 may be arranged in sequence along the longitudinal direction of the battery module 4. Of course, they may be arranged in any other manner. Further, the plurality of secondary batteries 5 may be fixed by fasteners.

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

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

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

[0183] Power consumption device

[0184] The present application further provides a power consumption device including at least one of a secondary battery, a battery module, or a battery pack of the present application. The secondary battery, battery module, or battery pack may be used as a power source of the power consumption device or as an energy storage means of the power consumption device. The power consumption device may be a mobile device (e.g., a mobile phone, a notebook computer, etc.), an electric vehicle (e.g., a pure electric vehicle, a hybrid electric vehicle, a plug-in hybrid electric vehicle, an electric bicycle, an electric scooter, an electric golf cart, an electric truck, etc.), a train, a ship, and a satellite, an energy storage system, etc., but is not limited thereto.

[0185] The power consumption device can select a secondary battery, a battery module, or a battery pack according to needs.

[0186] FIG. 7 is a schematic diagram of a power consumption device as an example. This power consumption device is a pure electric vehicle, a hybrid electric vehicle, a plug-in hybrid electric vehicle, etc. In order to meet the needs for high output and high energy density of this power consumption device, a battery pack or a battery module can be adopted.

[0187] As another example, the power consumption device may be a mobile phone, a tablet computer, a notebook computer, or the like. Generally, this power consumption device is required to be thin, and a secondary battery can be adopted as a power source.

[0188] Example

[0189] The following examples will more specifically illustrate the content of this application. However, these examples are merely illustrative explanations, and it is obvious to those skilled in the art that various modifications and changes can be made within the scope of the disclosure of this application. All values of quantities, percentages, and ratios described in the following examples are based on mass standards unless otherwise specified. Also, all reagents used in the examples may be commercially available or synthesized according to conventional methods, and can be used as they are without further treatment. Moreover, all devices used in the examples are commercially available.

[0190] Example 1-1

[0191] Manufacture of positive electrode sheet

[0192] LiFePO which is 97 wt% of the cathode active material 4 , 1 wt% of carbon black (Super P) which is a conductive agent, and 2 wt% of polyvinylidene fluoride (PVDF) which is an adhesive are sufficiently stirred and mixed in an appropriate amount of solvent NMP to form a uniform cathode slurry. The cathode slurry is uniformly coated on the surface of the cathode current collector aluminum foil, dried, and cold-pressed to obtain a cathode sheet.

[0193] Manufacture of negative electrode sheet

[0194] Graphite, which is the anode active material at 96.99 wt%, styrene-butadiene rubber (SBR), which is the binder at 1.8 wt%, and sodium carboxymethyl cellulose (CMC), which is the dispersant at 1.2 wt%, are sufficiently stirred and mixed with an appropriate amount of solvent deionized water, and then 0.01 wt% of amorphous hollow carbon spheres are added and stirred to form a uniform anode slurry. The anode slurry is uniformly coated on the surface of the anode current collector copper foil, dried, and cold pressed to obtain an anode sheet.

[0195] Preparation of electrolyte

[0196] Ethylene carbonate (EC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) were mixed at a volume ratio of 1:1:1 to obtain an organic solvent, and then sufficiently dried LiPF 6 was dissolved in the above organic solvent to prepare an electrolyte solution with a concentration of 1 mol / L.

[0197] Manufacture of separator

[0198] As the separator, a porous polyethylene film is used.

[0199] Manufacture of secondary battery

[0200] The positive electrode sheet, separator, and negative electrode sheet are stacked and wound in sequence to obtain an electrode assembly. The electrode assembly is placed in an outer package, dried, and then the electrolyte solution is injected, followed by vacuum encapsulation, standing, formation, shaping, and capacity processes to obtain a secondary battery.

[0201] Examples 1-2 to 1-9

[0202] The manufacturing method of the secondary battery is similar to that of Example 1-1, and the difference is that the manufacturing parameters of the negative electrode sheet are different. The specific parameters are shown in Table 1, and in the manufacturing of the negative electrode sheet, the addition amounts of the binder and dispersant do not change.

[0203] Comparative Example 1-1

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

[0205] Graphite, which is a negative electrode active material at 97.1 wt%, styrene-butadiene rubber (SBR), which is an adhesive at 1.8 wt%, sodium carboxymethyl cellulose (CMC), which is a dispersant at 0.7 wt%, and carbon black (Super P), which is a conductive agent at 0.4 wt% were sufficiently stirred and mixed with an appropriate amount of solvent deionized water, and then a negative electrode slurry was formed. The negative electrode slurry was applied to the surface of a negative electrode current collector copper foil, 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 manufacturing method of the secondary battery is similar to that of Example 1-1, and the difference is that the manufacturing parameters of the negative electrode sheet are different. The specific parameters are shown in Table 2, and in the manufacturing of the negative electrode sheet, the addition amounts of the adhesive and the dispersant do not change.

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

[0209] The manufacturing method of the secondary battery is similar to that of Example 1-1, and the difference is that the manufacturing parameters of the negative electrode sheet are different. The specific parameters are shown in Table 3, and in the manufacturing of the negative electrode sheet, the addition amounts of the adhesive and the dispersant do not change.

[0210] Examples 4-1 to 4-4

[0211] The manufacturing method of the secondary battery is similar to that of Example 1-1, and the difference is that the manufacturing parameters of the negative electrode sheet are different. The specific parameters are shown in Table 4, and in the manufacturing of the negative electrode sheet, the addition amounts of the adhesive and the dispersant do not change.

[0212] Example 5-1

[0213] The manufacturing method of the secondary battery is similar to that of Example 1-1, and the difference is that the manufacturing process of the negative electrode sheet is different.

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

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

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

[0217] As shown in FIG. 1, the first slurry, the second slurry, and the third slurry are applied simultaneously to the first region, the second region, and the third region of the negative electrode current collector copper foil, respectively, dried, and cold-pressed to obtain a negative electrode sheet. After the first slurry is dried, the first part of the negative electrode active material layer is formed. After the second slurry is dried, the second part of the negative electrode active material layer is formed. After the third slurry is dried, the third part of the negative electrode active material layer is formed.

[0218] Examples 5-2 to 5-6

[0219] The manufacturing method of the secondary battery is similar to that of Example 5-1, and the difference is that the manufacturing parameters of the negative electrode sheet are different. The specific parameters are shown in Table 5, and in the manufacturing of the negative electrode sheet, the addition amounts of the adhesive and the dispersant do not change.

[0220] Test section

[0221] (1) The thickness d of the shell wall of the additive, the volume V of the cavity of the additive h , the volume V of the additive w test

[0222] A circular sample with a diameter of 0.5 cm is cut out from the negative electrode sheet manufactured above, and a TEM image of the cross section is obtained by a transmission electron microscope (abbreviated as TEM). The thickness of the shell wall of the additive and the volume particle size of the additive in the region are statistically analyzed, 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 the percentage of 50% in the cumulative distribution curve is defined as the thickness d of the shell wall of the additive, and the volume particle size corresponding to the percentage of 50% in the cumulative distribution curve is defined as the volume particle size Dv50 of the additive. From the calculation formula of the ideal sphere, taking the volume particle size Dv50 obtained above as the diameter, the volume V w of the additive is calculated, and V w = (4 / 3) × π × (Dv50 / 2) 3 and the volume V h of the cavity of the additive = (4 / 3) × π × (Dv50 / 2 - d) 3 is obtained by calculation. As the test equipment, a Mastersizer 3000 type laser particle size analyzer manufactured by Malvern Instruments Ltd. in the UK can be used.

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

[0224] The negative electrode active material layer on one side of the negative electrode current collector is wiped off, and then the negative electrode sheet is punched into small wafer samples with a certain area. The apparent volume V 1Calculate it. Refer to GB / T 24586-2009, use an inert gas (for example, helium gas or nitrogen gas) as a medium, and use the gas replacement method to measure the true volume V of the negative electrode sheet using a true density tester. 2 Measure it. The porosity of the negative electrode sheet = (V 1 - V 2 ) / V 1 × 100%. As a result of testing a plurality of (for example, 30 sheets) negative electrode sheet samples with good appearance and no edge chipping, by taking the average value, the accuracy of the test results can be improved. The test apparatus can use a Micromeritics AccuPyc II 1340 type true density tester.

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

[0226] The area of the single-layer negative electrode sheet = the core circumference × 0.5 × the width of the negative electrode sheet.

[0227] (4) Initial capacity C of the secondary battery 0 Test

[0228] At 25°C, charge the secondary battery at a constant current of 1C to 3.65V, let it stand for 30 minutes, then discharge it at a constant current of 1C to 2.5V. This is regarded as one charge-discharge cycle process. Record the discharge capacity at this time, that is, the initial capacity C of the secondary battery. 0 Record it.

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

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

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

[0232] ε is the thickness recovery rate of the third part 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] ε 1 is the thickness recovery rate of the first part 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 1 =(H 1 ’ - H 1 ) / H 1 is.

[0234] ε 2 is the thickness recovery rate of the second part 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 2 =(H 2 ’ - H 2 ) / H 2 is.

[0235] H’, H 1 ’ and H 2 ’ are the thicknesses obtained by testing the third part, the first part, and the second part 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, respectively, and are obtained by testing according to the following method. At 25°C, the secondary battery is charged at a constant current of 1C to 3.65V, left standing for 30 minutes, and then discharged at a constant current of 1C to 2.5V. This is one cycle of charge and discharge process. At this time, the discharge capacity, that is, the initial capacity of the secondary battery, is recorded. The secondary battery is subjected to a cycle charge and discharge test according to the above method, and the discharge capacity after one cycle is recorded until the discharge capacity of the secondary battery decays to 80% of the initial capacity. The negative electrode sheet is disassembled from the secondary battery, the negative electrode sheet is immersed in an organic solvent (for example, dimethyl carbonate) for a predetermined time (for example, 72h or more), then the negative electrode sheet is taken out and dried at a constant temperature and time (for example, in a vacuum oven at 80°C, dried for 6h or more), and then the thicknesses of the third part, the first part, and the second part of the negative electrode active material layer can be measured respectively.

[0236] H, H 1 and H2 are the initial thicknesses of the third portion, the first portion, and the second portion of the negative electrode active material layer, respectively. In each of the examples and comparative examples of the present application, H, H 1 and H 2 In both cases, the thickness of the negative electrode active material layer after cold pressing, that is, 70 μm, is used.

[0237] (7) Secondary battery expansion force test

[0238] At 25°C, the secondary battery is charged to 3.65V at a constant current of 1C, left to stand for 30 minutes, and then discharged to 2.5V at a constant current of 1C, which is one cycle of charge and discharge process, and the discharge capacity at this time, i.e., the initial capacity of the secondary battery, is recorded. The secondary battery is subjected to cycle charge and 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 the steel plate 301 and the steel plate 302, and the force sensor 201 is placed between the steel plate 302 and the steel plate 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] The test results in Tables 1 to 6 are summarized as follows: 20 nm ≦ d ≦ 300 nm, 40% ≦ V h / V w It has been found that adding an additive satisfying ≦90% to the negative electrode sheet can effectively reduce the expansion force of the 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. Preferably, the amount of additive used is 0.01wt%-3wt%, more preferably 0.1wt%-2wt%, and as the amount of additive used continues to increase, the effect of further reducing the expansion force of the secondary battery becomes worse and is disadvantageous to the energy density of the secondary battery.

[0240] Considering the test results in Tables 1 to 6, it can be seen that when the secondary battery satisfies 100≦K≦30000, and preferably satisfies 120≦K≦8000, the secondary battery can have a smaller expansion force.

[0241] When comprehensively considering the test results of Examples 2-1 to 2-4, Comparative Examples 2-1 to 2-2, Examples 3-1 to 3-5, and Comparative Examples 3-1 to 3-2, when the thickness d of the shell wall of the additive is less than 20 nm, the volume occupancy ratio V h / V w is greater than 90%, when the thickness d of the shell wall of the additive is greater than 300 nm, and the volume occupancy ratio V h / V w is less than 40%, it was found that the swelling force of the secondary battery cannot be effectively reduced.

[0242] When comprehensively considering the test results of Examples 2-1 to 2-4 and Examples 3-1 to 3-5, when the usage amount of the additive is the same, the volume occupancy ratio V h / V w is further such that 60% ≤ V h / V w ≤ 90% is satisfied, and preferably 70% ≤ V h / V w ≤ 89% is satisfied, it was found that the secondary battery can have a smaller swelling force.

[0243] When comprehensively considering the test results of Example 2-1 and Examples 4-1 to 4-4, when the volume ratio V h / V w of the cavity of the additive is close to the thickness of the shell wall, and under the condition that the usage amount of the additive is the same, when the volume particle diameter 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 swelling force of the secondary battery, and at the same time it is also advantageous for improving the cycle performance of the secondary battery.

[0244] When comprehensively considering the test results of Examples 1-3, 5-5, 1-4, 5-4, 1-6, 5-1, 1-9, and 5-2, 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 part and a low content of the additive in the first and second parts, when the swelling force of the secondary battery is comparable, the actual usage amount of the additive in the negative electrode sheet can be further reduced, thereby further improving the energy density of the secondary battery.

[0245] When comprehensively considering the test results of Examples 5-2 and 5-3, in addition to Example 5-2, continuously increasing the usage amount of the additive in the third part of the negative electrode active material layer, since the improvement effect of the swelling force of the secondary battery does not increase more significantly, this application can further guide the usage amount of the additive in the negative electrode sheet and further improve the energy density of the secondary battery.

[0246] It should be noted that this application is not limited to the above embodiments. The above embodiments are illustrative, and those having a configuration that is substantially the same as the technical idea within the technical scope of this application and showing the same operational effects are all included in the technical scope of this application. Also, within the scope not departing from the gist of this application, various modifications that can be conceived by those skilled in the art to the embodiments, and other forms constructed by combining some components in the embodiments are also included in the scope of this application.

[0247]

Table 1

[0248]

Table 2

[0249]

Table 3

[0250]

Table 4

[0251]

Table 5

[0252]

Table 6

Claims

1. 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 containing a negative electrode active material and an additive, the additive including a shell wall and a cavity located inside the shell wall, with the thickness of the shell wall being d and the volume of the cavity being V ｈ and the volume of the additive being V ｗ wherein, taking the additive, 20 nm ≤ d ≤ 300 nm and 40% ≤ V ｈ / V ｗ ≤ 90% is satisfied Negative electrode sheet.

2. 25 nm ≤ d ≤ 200 nm, preferably 40 nm ≤ d ≤ 120 nm, and / or 60% ≤ V ｈ / V ｗ ≤ 90%, preferably 70% ≤ V ｈ / V ｗ ≤ 89%. The negative electrode sheet according to Claim 1.

3. 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 ｗ are obtained by testing as follows, A circular sample with a diameter of 0.5 cm is cut out from the negative electrode sheet, and a TEM image of the cross-section 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 statistically analyzed, and the 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 the percentage of 50% in the cumulative distribution curve is defined as the thickness d of the shell wall of the additive, and the volume particle size corresponding to the percentage of 50% in the cumulative distribution curve is defined as the volume particle size Dv50 of the additive. Based on the calculation formula of an ideal sphere, with the obtained volume particle size Dv50 as the diameter, the volume V of the additive ｗ is calculated, and V ｗ = (4 / 3) × π × (Dv50 / 2) ３ wherein the volume V of the cavity of the additive ｈ = (4 / 3) × π × (Dv50 / 2 - d) ３ is as follows. The negative electrode sheet according to Claim 1 or 2.

4. The additive includes one or more selected from hollow spheres and hollow polyhedrons, preferably includes hollow spheres, and / or The volume particle size Dv50 of the additive is 0.85 μm to 5 μm, preferably 1 μm to 2.5 μm, and / or The volume particle size of the additive satisfies 0.5 ≤ (Dv90 - Dv10) / Dv50 ≤ 8, preferably 2 ≤ (Dv90 - Dv10) / Dv50 ≤ 5. The negative electrode sheet according to any one of Claims 1 to 3.

5. The additive includes hollow carbon spheres, preferably includes one or more selected from amorphous hollow carbon spheres, graphitized hollow carbon spheres, and hollow graphene spheres. The negative electrode sheet according to any one of Claims 1 to 4.

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%, preferably 0.1 wt% to 2 wt%. The negative electrode sheet according to any one of Claims 1 to 5.

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. Taking the total width of the negative electrode active material layer as 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 and the weight percentage content of the additive in the second portion is w ２ and 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 is satisfied The negative electrode sheet according to any one of Claims 1 to 6.

8. 0 < w １ / w ３ ≦ 0.7, and preferably, 0 < w １ / w ３ ≦ 0.5, and / or 0 < w ２ / w ３ ≤ 0.7, and preferably, 0 < w ２ / w ３ ≤ 0.5 The negative electrode sheet according to Claim 7.

9. 0 wt% ≤ w １ ≤ 2 wt%, preferably, 0 wt% < w １ ≤ 1 wt%, and / or 0 wt% ≤ w ２ ≤ 2 wt%, preferably, 0 wt% < w ２ ≤ 1 wt%, and / or 0.01 wt% ≤ w ３ ≤ 5 wt%, and preferably, 0.01 wt% ≤ w ３ ≤ 2 wt%. The negative electrode sheet according to Claim 7 or 8.

10. w １ = w ２ is The negative electrode sheet according to any one of Claims 7 to 9.

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 any one of Claims 1 to 10.

12. The negative electrode active material layer further includes a negative electrode adhesive and / or a negative electrode dispersant. Preferably, the weight percentage content of the negative electrode adhesive relative to the total weight of the negative electrode active material layer is 1 wt% to 2.5 wt%. Preferably, the weight percentage content of the negative electrode dispersant relative to the total weight of the negative electrode active material layer is 0.5 wt% to 1.5 wt%. The negative electrode sheet according to any one of Claims 1 to 11.

13. The negative electrode active material layer further includes 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%. The negative electrode sheet according to any one of Claims 1 to 12.

14. 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, and cold pressing to obtain a negative electrode sheet, wherein 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 includes a negative electrode active material and an additive, the additive includes a shell wall and a cavity located inside the shell wall, the thickness of the shell wall is d, the volume of the cavity is V ｈ and the volume of the additive is V ｗ wherein 20 nm ≤ d ≤ 300 nm and 40% ≤ V ｈ / V ｗ ≤ 90% is satisfied 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 region 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. 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. Then, the first slurry, the second slurry, and the third slurry are respectively applied to the first region, the second region, and the third region of the negative electrode current collector, and after drying, a first portion, a second portion, and a third portion of the negative electrode active material layer are respectively formed. The weight percentage content of the additive in the first portion is w １ and the weight percentage content of the additive in the second portion is w ２ and 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, and Preferably, the first slurry, the second slurry, and the third slurry employ a single simultaneous coating process or a plurality of step coating processes. The manufacturing method according to claim 14.

16. A negative electrode sheet according to any one of claims 1 to 13, or a negative electrode sheet manufactured by the manufacturing method according to any one of claims 14 to 15, A secondary battery.

17. The secondary battery satisfies 100 ≤ K ≤ 30000, preferably satisfies 120 ≤ K ≤ 8000, 【Number 1】 λ is the porosity of the negative electrode sheet, 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, C ０ is the initial capacity of the secondary battery, with the unit of mAh, d is the thickness of the shell wall of the additive, and the unit is nm, V ｈ is the volume of the cavity of the additive, with the unit of 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 the unit is μm, The secondary battery according to claim 16.

18. The secondary battery satisfies at least one of the following: (1) 20% ≤ λ ≤ 50%, preferably 23% ≤ λ ≤ 35%, (2) 20% ≤ ε ≤ 40%, preferably 25% ≤ ε ≤ 35%, (3) 20 nm ≤ d ≤ 300 nm, preferably 40 nm ≤ d ≤ 120 nm, (4) 1 × 10 ７ nm ３ ≤ V ｈ ≤ 1 × 10 １２ nm ３ and preferably 2.5 × 10 ８ nm ３ ≤ V ｈ ≤ 1 × 10 １０ nm ３ and (5) 1 × 10 ２ mm ２ ≤ S ≤ 1 × 10 ８ mm ２ and preferably, 1 × 10 ３ mm ２ ≤ S ≤ 1 × 10 ６ mm ２ and (6) 10 μm ≤ H ≤ 250 μm, preferably 40 μm ≤ H ≤ 120 μm, The secondary battery according to claim 17.

19. When the capacity of the secondary battery has decayed to 80% of the initial capacity of the secondary battery, the thickness recovery rate of the first portion of the negative electrode active material layer is ε １ which is expressed as, and the initial thickness of the first portion of the negative electrode active material layer is H １ which is expressed as, the unit is μm, the thickness recovery rate of the second portion of the negative electrode active material layer is ε ２ which is expressed as, and the initial thickness of the second portion of the negative electrode active material layer is H ２ which is expressed as, the unit is μm, and the secondary battery satisfies 0 < K １ / K ≤ 1, 0 < K ２ / K ≤ 1 【Number 2】 The secondary battery according to claim 17 or 18.

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, preferably 120 ≤ K １ ≤ 8000, and / or 100 ≤ K ２ ≤ 30000, preferably 120 ≤ K ２ ≤ 8000 The secondary battery according to claim 19 or 20.

22. 15% ≤ ε １ ≤ 35%, preferably, 25% ≤ ε １ ≤ 31%, and / or 15% ≤ ε ２ ≤ 35%, preferably, 25% ≤ ε ２ ≤ 31%, and / or 10 μm ≤ H １ ≤ 250 μm, preferably 40 μm ≤ H １ ≤ 120 μm, and / or 10 μm ≤ H ２ ≤ 250 μm, and preferably, 40 μm ≤ H ２ ≤ 120 μm The secondary battery according to any one of claims 19 to 21.

23. An electric power consumption device including the secondary battery according to any one of claims 16 to 22.

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