Negative electrode sheet, secondary battery, and power consumption device

Abstract

This application provides a negative electrode sheet, a secondary battery, and a power consumption device. The negative electrode sheet includes a current collector and a negative electrode film layer, the negative electrode film layer includes a first film layer provided on one or both sides of the current collector and a second film layer provided on the side of the first film layer away from the current collector, the negative electrode active material of the first film layer and the negative electrode active material of the second film layer each independently contain a silicon-based negative electrode material, and the silicon-based negative electrode material of the second film layer contains a porous silicon negative electrode material, the content of the silicon-based negative electrode material of the first film layer is smaller than the content of the silicon-based negative electrode material of the second film layer. This improves the charging capacity and cycle characteristics of the secondary battery.

Description

Technical Field

[0001] Cross - reference to related applications This application claims the priority of a Chinese patent application with application number 202310798399.1 and title "Negative electrode sheet, secondary battery and power consumption device", filed on June 30, 2023, and the entire content of the application is incorporated herein by reference.

[0002] This application relates to the field of battery technology, particularly to negative electrode sheets, secondary batteries and power consumption devices.

Background Art

[0003] Lithium - ion batteries have advantages such as high energy density, high output density and long cycle life, so they are widely applied in electronic devices such as notebook computers, mobile phones, digital cameras, etc. In recent years, with the rapid development of new energy and clean energy vehicles, the requirements for the performance and safety of new - type power batteries and energy storage batteries have become even higher, and the need for the battery to withstand various harsh operating conditions has also been increasing day by day.

[0004] Currently, in order to improve the performance of lithium - ion batteries, many studies focus on the development and improvement of electrode materials and electrolytes. For example, silicon materials have a very high theoretical specific capacity (>4000 mAh / g), much higher than that of graphite reaching the limiting capacity, equivalent to about 10 times that of graphite, and the voltage with respect to lithium is not high either. Therefore, it becomes the most promising candidate for high - energy - density batteries. By using a silicon negative electrode instead of some conventional graphite negative electrodes, the specific capacity of the negative electrode active material can be improved. However, since silicon significantly undergoes volume expansion during the lithium insertion / desorption process, the silicon material is likely to rapidly powderize and fall off from the electrode sheet during the cycle process, losing contact with the current collector and thus being unable to fully exert the activity of the silicon material.

Summary of the Invention

Problems to be Solved by the Invention

[0005] The present application provides a negative electrode sheet, a secondary battery, and an electric power consumption device that improve the charging ability and cycle characteristics of the secondary battery.

Means for Solving the Problems

[0006] According to the first aspect of the present application, a negative electrode sheet is provided, which includes a current collector and a negative electrode film layer. The negative electrode film layer includes a first film layer provided on one or both sides of the current collector, and a second film layer provided on the side of the first film layer away from the current collector. The negative electrode active material in the first film layer and the negative electrode active material in the second film layer each independently contain a silicon-based negative electrode material, and the silicon-based negative electrode material in the second film layer contains a porous silicon negative electrode material. The content of the silicon-based negative electrode material in the first film layer is smaller than the content of the silicon-based negative electrode material in the second film layer.

[0007] In the negative electrode sheet of the present application, the lower first film layer contains a silicon-based negative electrode material, thereby improving the energy density of the negative electrode sheet. At the same time, since the content of the silicon-based negative electrode material in the first film layer located in the lower layer is relatively small, the problem of peeling of the silicon-based negative electrode material from the current collector due to powdering of the silicon-based negative electrode material in the cycling process can be effectively alleviated. The second film layer located on the surface layer has a porous silicon negative electrode material, thus effectively avoiding the problem of reduction in the specific capacity of the battery due to a pore-forming agent such as porous carbon. And the porous silicon negative electrode material can increase the pores on the surface layer, improving the defect that lithium ions cannot be inserted into the negative electrode of the polar sheet due to the destruction of the pores on the surface layer in the roller rolling process. In addition, the content of the silicon-based negative electrode material in the second film layer located in the upper layer is more than that in the first film layer located in the lower layer. Especially, since the upper layer has a porous silicon negative electrode material, lithium is preferentially inserted into the upper layer, the lithium insertion path is shorter, and the reaction kinetics is better. Thereby, the charging ability of the negative electrode sheet is improved, and the cycle characteristics of the battery are improved by suppressing lithium precipitation.

[0008] In any embodiment of the first aspect, the surface density M1 of the first film layer is 4.5 mg / cm². 2 ~20 mg / cm³ 2 The range is such that the surface density M2 of the second film layer is 4.5 mg / cm². 2 ~20 mg / cm³ 2 It is within the range.

[0009] In any embodiment of the first aspect, the weight ratio of the first film layer to the second film layer is 95:5 to 30:70, and more selectively 90:10 to 40:60. This improves the synergistic effect of the two film layers.

[0010] In any embodiment of the first aspect, the porosity of the first film layer is in the range of 20% to 50%, the porosity of the second film layer is in the range of 20% to 70%, and the porosity of the negative electrode film layer is in the range of 20% to 70%, thereby not only improving the lithium ion insertion capacity but also increasing the specific capacity of the negative electrode sheet.

[0011] In any embodiment of the first aspect, the thickness of the second film layer is 10 μm to 20 μm, and this thickness sufficiently solves the problem of pore collapse on the surface of the negative electrode sheet due to roller rolling.

[0012] In any embodiment of the first aspect, the mass content of the silicon-based anode material in the first film layer is 0.5% to 50%, and / or the mass content of the porous silicon anode material in the second film layer is 0.5% to 70%, and selectively, the mass content of the porous silicon anode material in the anode film layer is 1% to 60%. This maximizes the specific capacity of the anode sheet through the silicon-based anode material in the two film layers.

[0013] In any embodiment of the first aspect, the second film layer comprises a porous silicon anode material, a graphite anode material, a binder, a dispersant, and a conductive agent, wherein the conductive agent comprises one or more conductive carbon and carbon nanotubes, and selectively, the mass percentage of the porous silicon anode material in the second film layer is 0.5% to 70%, selectively, the mass percentage of the graphite anode material in the second film layer is 25% to 90%, selectively, the mass percentage of the binder in the second film layer is 1% to 8%, selectively, the mass percentage of the dispersant in the second film layer is 0.5% to 2%, selectively, the mass percentage of the conductive carbon in the second film layer is 0.5% to 5%, and selectively, the mass percentage of the carbon nanotubes in the second film layer is 0.05% to 2%. The combination of the porous silicon anode material and the graphite anode material improves the volume stability of the second film layer during the cycling process through the structural stability of the graphite anode material, and improves the specific capacity and lithium-ion conductivity of the second film layer through the porous silicon anode material.

[0014] In any embodiment of the first aspect, the first film layer comprises a silicon-based anode material, a graphite anode material, a binder, a dispersant, and a conductive agent, wherein the conductive agent comprises one or more conductive carbon and carbon nanotubes, and selectively, the mass percentage of the silicon-based anode material in the first film layer is 0.5% to 50%, selectively, the mass percentage of the graphite anode material in the first film layer is 45% to 97.5%, selectively, the mass percentage of the binder in the first film layer is 1% to 3%, selectively, the mass percentage of the dispersant in the first film layer is 0.3% to 1.5%, selectively, the mass percentage of the conductive carbon in the first film layer is 0% to 3%, and selectively, the mass percentage of the carbon nanotubes in the first film layer is 0% to 0.5%. By combining the silicon-based anode material and the graphite anode material, the adhesion stability between the first film layer and the current collector can be improved, and the specific capacity of the first film layer can be improved to some extent.

[0015] In any embodiment of the first aspect, the silicon-based anode material of the first film layer includes any one or more of a silicon material, a silicon oxide material, and a porous silicon anode material, and the content of the porous silicon anode material in the first film layer is smaller than the content of the porous silicon anode material in the second film layer. Thereby, the uniformity of the pores in the entire anode film layer is improved.

[0016] In any embodiment of the first aspect, the Dv 50 of the porous silicon anode material is between 3 μm and 20 μm, selectively 4 μm to 15 μm, and / or the BET specific surface area of the porous silicon anode material is 1 m 2 / g to 30 m 2 / g, selectively between 6 m 2 / g and 20 m 2 / g. Thereby, the volumetric energy density of the anode sheet is further improved.

[0017] In any embodiment of the first aspect, the porous silicon anode material includes a core and a coating layer, the core is porous silicon, the porous silicon includes elemental silicon and a silicon compound, the silicon compound includes silicon oxide, and the coating layer covers the surface of the core. The porous silicon anode material using a core-shell structure improves the energy density of the anode sheet, alleviates the volume expansion of the silicon-based anode material, and improves the cycle stability of a high-energy density battery.

[0018] In any embodiment of the first aspect, the coating layer includes any one or more of a metal compound of silicon, dilithium metasilicate, amorphous carbon, and carbon nanotubes. By coating one or more of the above materials, the mechanical structural stability or conductivity of the porous silicon anode material can be improved.

[0019] In any embodiment of the first aspect, the coating layer comprises a first coating layer, a second coating layer, and a third coating layer, wherein the first coating layer covers the surface of the core and contains dilithium metasilicate; the second coating layer covers the surface of the first coating layer and contains a silicon metal compound, selectively comprising Ti, Mg, and / or Al as the metal element in the silicon metal compound; the third coating layer covers the surface of the second coating layer and contains amorphous carbon, selectively comprising hard carbon and / or soft carbon. The first coating layer contains dilithium metasilicate and can generate lithium salts and an inert phase (lithium oxide) during the lithium insertion process. The generation of lithium salts reduces lithium ion consumption in the positive electrode active material during the initial lithium insertion, thereby improving the initial Coulombic efficiency of the battery. The generation of the inert phase effectively mitigates volume expansion and can improve the battery's cycle characteristics. The second coating layer, provided between the first and third coating layers, contains a silicon metal compound and possesses excellent mechanical strength, mitigating the volume expansion of the internal silicon material and improving cycle characteristics. The third coating layer mitigates the volume expansion of the first coating layer, improving cycle characteristics, and also enhances the protective effect on the first coating layer. For example, it prevents the first coating layer from coming into direct contact with water and prevents the dissolution and gas generation of dilithium metasilicate in the first coating layer.

[0020] In any embodiment of the first aspect, the silicon compound further comprises a silicon metal compound, the silicon metal compound coating the surface of the elemental silicon, and the metal element of the silicon metal compound selectively comprises Ti, Mg and / or Al. By coating the surface of the elemental silicon with a silicon metal compound, the volume expansion of the elemental silicon can be mitigated and the cycle properties can be improved.

[0021] In any embodiment of the first aspect, the coating layer includes a first coating layer and a third coating layer. The first coating layer covers the surface of the core and contains dilithium metasilicate. The third coating layer covers the surface of the first coating layer and contains amorphous carbon. Selectively, the amorphous carbon material includes hard carbon and / or soft carbon. The first coating layer contains dilithium metasilicate and can generate lithium salts and an inert phase (lithium oxide) during the lithium insertion process. The generation of lithium salts reduces lithium ion consumption in the positive electrode active material during the initial lithium insertion, thereby improving the initial Coulombic efficiency of the battery. The generation of the inert phase effectively mitigates volume expansion and can improve the battery's cycle characteristics. The third coating layer mitigates volume expansion of the first coating layer, improves cycle characteristics, and can also improve the protective effect on the first coating layer, for example, by preventing the first coating layer from coming into direct contact with water and preventing the dissolution and gas generation of dilithium metasilicate in the first coating layer.

[0022] In any embodiment of the first aspect, the third coating layer further comprises carbon nanotubes, which can improve the conductivity of the porous silicon anode material and provide sufficient constraint on the porous silicon anode material via the carbon nanotubes, thereby mitigating volume expansion during the charge-discharge process and controlling the polarization inside the cell of the anode sheet to improve the cycle characteristics of the cell.

[0023] In any embodiment of the first aspect, the masses of the porous silicon negative electrode material in the first film layer and the second film layer are m1 and m2 respectively, the mass percentages of the carbon nanotubes belonging to the porous silicon negative electrode material in the first film layer and the second film layer are C1 and C2 respectively, and the masses of the carbon nanotubes remaining in the first film layer and the second film layer after removing the carbon nanotubes in the porous silicon negative electrode material are S1 and S2 respectively. The first film layer and the second film layer are the first film layer per unit area and the second film layer per unit area respectively, and satisfy the relationships of (m2×C2 + S2) / M2 = (m1×C1 + S1) / M1, m2≥m1, S1≥S2, and S2 = m1×m2×(C2 - C1) / (m2 - m1). Due to the limitation of the above relational expression, by making full use of the carbon nanotubes, the binding force to the silicon-based negative electrode material can be further improved, the repulsion of the negative electrode sheet can be effectively suppressed, and the polarization of the negative electrode sheet can be minimized.

[0024] In any embodiment of the first aspect, the Dv50 of the above silicon single crystal is in the range of 0 < Dv50 ≤ 10 nm, and optionally, the Dv50 of the silicon single crystal is in the range of 2 nm < Dv50 ≤ 8 nm. Adopting nanosized silicon single crystal is advantageous for mixing with silicon oxide, advantageous for improving the energy density of the battery, and advantageous for reducing the coating difficulty on the core structure and improving the cycle stability of the battery.

[0025] In any embodiment of the first aspect, the chemical formula of the above silicon oxide is SiOx, where 0 < x ≤ 2, and the Dv50 of the silicon oxide is in the range of 2 μm ≤ Dv50 ≤ 13 μm. It is advantageous for mixing with silicon single crystal and for improving the energy density of the battery.

[0026] In any embodiment of the first aspect, the dilithium metasilicate comprises one or more of Li2SiO3, Li2Si2O5, Li4SiO4, Li2Si3O7, Li8SiO6, Li6Si2O7, Li4Si2O7, Li2Si4O7, and LiSiO3, wherein selectively, the dilithium metasilicate comprises at least Li2SiO3, more selectively, the mass of Li2SiO3 is at least 50% of the mass of the first coating layer, and more selectively, the mass of Li2SiO3 is at least 70% of the mass of the first coating layer. This effectively reduces lithium ion consumption in the positive electrode active material during initial lithium insertion in the first coating layer, and the battery has high initial Coulomb efficiency.

[0027] In any embodiment of the first aspect, the thickness of the first coating layer is 10% to 80% of the particle radius of the porous silicon anode material, selectively the thickness of the second coating layer is 1 nm to 50 nm, selectively the thickness of the third coating layer is 1 nm to 1000 nm, and selectively 5 nm to 300 nm. Within the above thickness range, the particles improve the battery energy density while effectively suppressing the volume expansion of the anode material, thereby improving the cycle stability of the high-energy-density battery.

[0028] According to a second aspect of the present application, a secondary battery is provided comprising a positive electrode sheet, a negative electrode sheet, a separator, and an electrolyte, wherein the negative electrode sheet is any one of the above-mentioned negative electrode sheets. The secondary battery of the present application has excellent charging capacity, high energy density, and excellent cycle characteristics.

[0029] According to a third aspect of the present application, a power consumption device is provided that includes a secondary battery selected from the secondary batteries of the present application. The power consumption device of the present application has better safety. [Brief explanation of the drawing]

[0030] To more clearly explain the technical solutions in the embodiments of this application, the necessary drawings for the embodiments are briefly described below. It should be understood that the drawings shown below represent only a few embodiments of this application, and those skilled in the art can obtain further drawings based on these drawings without requiring any creative effort.

[0031] [Figure 1] This is a schematic diagram of the structure of a negative electrode sheet according to one embodiment of the present invention. [Figure 2] This is a schematic diagram of the structure of a porous silicon anode material according to one embodiment of the present invention. [Figure 3] This is a schematic diagram of the structure of a porous silicon anode material according to another embodiment of the present application. [Figure 4] This is a schematic diagram of the structure of a porous silicon anode material according to yet another embodiment of the present application. [Figure 5] This is a schematic diagram of a secondary battery according to one embodiment of the present invention. [Figure 6] Figure 5 is an exploded view of a secondary battery according to one embodiment of the present invention. [Figure 7] This is a schematic diagram of a battery module according to one embodiment of the present invention. [Figure 8] This is a schematic diagram of a battery pack according to one embodiment of the present invention. [Figure 9] Figure 8 is an exploded view of a battery pack according to one embodiment of the present invention. [Figure 10] This is a schematic diagram of a power consumption device that uses a secondary battery as a power source according to one embodiment of the present invention.

[0032] In drawings, the drawings are not drawn according to actual proportions. (Explanation of symbols)

[0033] 01 Current collector, 02 First film layer, 03 Second film layer 10 Porous silicon anode material, 11 Core, 12 First coating layer, 13 Second coating layer, 14 Third coating layer, 111 Elemental silicon, 112 Silicon oxide, 113 Metallic silicon compounds 1 Battery pack, 2 Upper casing, 3 Lower casing, 4 Battery module, 5 Secondary battery, 51 Housing, 52 Electrode assembly, 53 Cap assembly. [Modes for carrying out the invention]

[0034] Embodiments of the present application will be described in more detail below with reference to the drawings and examples. The detailed description of the following embodiments and drawings are used to illustrate the principles of the present application, but are not intended to limit the scope of the present application, and the present application is not limited to the embodiments described.

[0035] The embodiments specifically disclosing the negative electrode sheet, secondary battery, and power consumption device of the present application will be described in detail below, with reference to the drawings as appropriate. However, unnecessary detailed explanations may be omitted. For example, detailed explanations of well-known matters and redundant explanations of structures that are actually the same may be omitted. This is to avoid making the following explanation unnecessarily long and to make it easily understandable to those skilled in the art. The drawings and the following explanation are provided to enable those skilled in the art to fully understand the present application and are not intended to limit the topics described in the claims.

[0036] The “range” disclosed herein is defined in the form of a lower and upper limit, and a given range is defined by selecting one lower limit and one upper limit, the selected lower and upper limits defining the boundaries of a particular range. Ranges defined in this manner may or may not include the values ​​at both ends and can be combined in any way, that is, any lower limit can be combined with any upper limit to form a range. For example, if the ranges 60-120 and 80-110 are listed for a particular parameter, it is understood that the ranges 60-110 and 80-120 are also expected. Similarly, if the minimum range values ​​1 and 2 are listed, and the maximum range values ​​3, 4 and 5 are listed, the ranges 1-3, 1-4, 1-5, 2-3, 2-4 and 2-5 are all intended. In this application, unless otherwise specified, the numerical range “a-b” means an abbreviated expression for any combination of real numbers between a and b, where both a and b are real numbers. For example, the numerical range "0 to 5" means that all real numbers between "0 to 5" are listed in this specification, and "0 to 5" is merely an abbreviated expression for combinations of these numbers. Also, when a parameter is described as an integer ≥ 2, it is equivalent to disclosing that the parameter is, for example, an integer such as 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0037] Unless otherwise specified, all embodiments and optional embodiments of this application can be combined to form new technical inventions.

[0038] Unless otherwise specified, all technical features and optional technical features of this application can be combined to form new technical concepts.

[0039] Unless otherwise specified, all steps of the present invention may be performed sequentially or randomly, preferably sequentially. For example, if the method includes steps (a) and (b), it means that the method may include steps (a) and (b) performed sequentially, or steps (b) and (a) performed sequentially. For example, if the method may further include step (c), it means that step (c) may be added to the method in any order, for example, the method may include steps (a), (b), and (c), or steps (a), (c), and (b), or steps (c), (a), and (b), etc.

[0040] As used herein, “includes” and “inclusive” refer to both open and closed forms unless otherwise specified. For example, “includes” and “inclusive” may include or include other components not listed, or may include or include only the listed components.

[0041] In this application, unless otherwise specified, the term “or” is inclusive. For example, the phrase “A or B” means “A, B, or both A and B.” More specifically, the condition “A or B” is satisfied by either A being true (or existing) and B being false (or not existing), A being false (or not existing) and B being true (or existing), or both A and B being true (or existing).

[0042] [Secondary battery] Secondary batteries, also known as rechargeable batteries or storage batteries, are batteries that can be used continuously by recharging after they have been discharged, thereby activating the active material.

[0043] Generally, a secondary battery includes a positive electrode sheet, a negative electrode sheet, a separator, and an electrolyte. During the charging and discharging process of the battery, active ions (e.g., lithium ions) reciprocate between the positive and negative electrode sheets, being inserted and removed. The separator is placed between the positive and negative electrode sheets and primarily serves to prevent short circuits between the positive and negative electrodes while also allowing active ions to pass through. The electrolyte primarily serves to conduct active ions between the positive and negative electrode sheets.

[0044] [Negative electrode sheet] In the process of research into improving the performance of lithium-ion batteries, numerous studies have gradually revealed that the design of a rational electrode structure is crucial for the conduction paths of ions and electrons throughout the electrode. By optimizing the electrode structure, it is possible to improve the conductivity of the electrode and the permeability of the electrolyte, thereby increasing the conduction rate of electrons and ions within the electrode, and further improving battery performance such as energy density and multiplier. However, obtaining a thick electrode that simultaneously possesses both good electron / ion conductivity and a high load capacity for the active material remains a major challenge.

[0045] For example, even with thick electrode sheets coated in multiple layers, there is still a problem where the surface pores of the polar sheet, which are about 10-20 μm deep, are crushed during the roller rolling process. As a result, lithium ions in the electrolyte cannot effectively diffuse into the interior of the polar sheet, significantly reducing the charging capacity. To solve this problem, a technique has been proposed to improve the porosity of the surface layer by adding a pore-forming agent, such as porous carbon, to the film layer which is the surface layer of the negative electrode sheet. However, when porous carbon is used, the energy density of the polar sheet is lost, which in turn reduces the specific capacity of the battery. To solve the above problems, one typical embodiment of the present invention provides a negative electrode sheet, as shown in Figure 1, which includes a current collector 01 and a negative electrode film layer, the negative electrode film layer includes a first film layer 02 and a second film layer 03, the first film layer 02 is provided on one or both sides of the current collector 01, the second film layer 03 is provided on the side of the first film layer 02 away from the current collector 01, the negative electrode active material in the first film layer 02 and the negative electrode active material in the second film layer 03 each independently include a silicon-based negative electrode material, and the silicon-based negative electrode material in the second film layer 03 includes a porous silicon negative electrode material 10, and the content of the silicon-based negative electrode material in the first film layer 02 is smaller than the content of the silicon-based negative electrode material in the second film layer 03.

[0046] In the negative electrode sheet of this application, the lower first film layer 02 contains a silicon-based negative electrode material, thereby improving the energy density of the negative electrode sheet. At the same time, because the content of the silicon-based negative electrode material in the lower first film layer 02 is relatively low, the problem of peeling of the silicon-based negative electrode material from the current collector 01 due to powdering of the silicon-based negative electrode material during the cycle process can be effectively mitigated. The surface second film layer 03 has a porous silicon negative electrode material 10, and therefore effectively avoids the problem of a decrease in the specific capacity of the battery due to porosity-forming agents such as porous carbon. Furthermore, the porous silicon negative electrode material 10 can increase the pores on the surface, improving the defect in which lithium ions cannot be inserted into the negative electrode of the polar sheet due to the destruction of surface pores during the roller rolling process. In addition, the content of the silicon-based negative electrode material in the upper second film layer 03 is higher than that in the lower first film layer 02, and especially because the upper layer has a porous silicon negative electrode material 10, lithium is preferentially inserted into the upper layer, the lithium insertion path is shorter, and the reaction kinetics are better. This improves the charging capacity of the negative electrode sheet and suppresses lithium deposition, thereby improving the battery's cycle characteristics.

[0047] The first film layer 02 may be provided in direct contact with the current collector 01, or a primer layer may be provided between the first film layer 02 and the current collector 01. The second film layer 03 only needs to be located on the surface of the negative electrode sheet, and the second film layer 03 may be provided in direct contact with the first film layer 02, or other negative electrode film layers may be provided between them.

[0048] The following method can be used to measure the content of the silicon-based anode material described above. In the first step, anode sheet samples are prepared in advance by mixing silicon-based anode material and graphite material with multiple different mass ratios (when measuring anode sheets that contain other anode materials, the anode sheet samples may be prepared based on the type of material of the anode sheet being measured). In the second step, each sample is taken, placed in a scanning electron microscope, and the energy spectrum is measured to obtain the relative mass percentage of silicon element in each anode sheet sample. In the third step, the relative mass percentage of silicon element in each anode sheet sample is used as the x-coordinate, and the mass percentage of silicon-based anode material in each anode sheet sample is used as the y-coordinate. A standard curve is drawn and fitted to obtain a quantitative relationship. In the fourth step, the negative electrode sheet to be measured is cut with a CP (ion beam) to confirm the thickness of the two vertical film layers. Then, using the powder scraping method, the powder of the upper second film layer is scraped off first, followed by the powder of the lower first film layer. The relative mass percentage of silicon element in each is measured, and the mass percentage of silicon-based negative electrode material in the first and second film layers of the measured object is calculated based on the quantitative relationship formula described above.

[0049] In some embodiments, the surface density M1 of the first film layer 02 is 4.5 mg / cm². 2 ~20 mg / cm³ 2 The range is such that the surface density M2 of the second film layer 03 is 0.2 mg / cm². 2 ~20 mg / cm³ 2 The above weight range ensures the effective thickness of the two film layers. In some embodiments, the surface density M1 of the first film layer 02 is 4.5 mg / cm². 2 , 5 mg / cm³ 2 , 7 mg / cm³ 2 , 10 mg / cm³ 2 , 15 mg / cm³ 2 or 20 mg / cm³ 2 It may be 5 mg / cm³, preferably 5 mg / cm³. 2 ~7 mg / cm³ 2In some embodiments, the surface density M2 of the second film layer 03 is 0.2 mg / cm³. 2 , 0.3 mg / cm³ 2 , 0.4 mg / cm³ 2 , 1 mg / cm³ 2 , 2 mg / cm³ 2 , 3 mg / cm³ 2 , 5 mg / cm³ 2 , 10 mg / cm³ 2 , 17 mg / cm³ 2 or 20 mg / cm³ 2 It may be, preferably 0.3 mg / cm³ 2 ~17 mg / cm³ 2 That is the case.

[0050] The second film layer 03 of the present application primarily improves the surface porosity with the porous silicon anode material 10 contained therein. In some embodiments, the weight ratio of the first film layer 02 to the second film layer 03 is 95:5 to 30:70, and more selectively 90:10 to 40:60, for example, 90:10, 80:20, 70:30, 60:40, 50:50, or 40:60. In the above embodiments, especially when the first film layer 02 is used as the main component of the anode film layer, it plays the main role of the anode sheet, compensating for the deficiencies of the first film layer 02 via the second film layer 03, and improving the synergistic effect of the two film layers.

[0051] In some embodiments, the porosity of the first film layer 02 is in the range of 20% to 50%, the porosity of the second film layer 03 is in the range of 20% to 70%, and the porosity of the negative electrode film layer is in the range of 20% to 70%, for example, 20%, 30%, 40%, 50%, 60%, or 70%, and the negative electrode film layer having the above porosity not only improves the lithium ion insertion capacity through the pores but also improves the specific capacity of the negative electrode sheet through the negative electrode active material.

[0052] In some embodiments, the thickness of the second film layer 03 is 10 μm to 20 μm, for example, 10 μm, 12 μm, 15 μm, 18 μm, or 20 μm, and this thickness sufficiently solves the problem of pore collapse on the surface of the negative electrode sheet due to roller rolling.

[0053] The following steps can be used to measure the weight of the two film layers described above. After confirming the thickness of the two film layers in the vertical direction using the CP cross-section, the powder scraping method was used to first scrape off the powder from the upper second film layer, then scrape off the powder from the lower first film layer, and weigh them. Then the powder from the lower first film layer was scraped off and weighed, thereby obtaining the weights and proportions of the first and second film layers, respectively.

[0054] The following steps can be used to describe the porosity measurement method described above. After photographing the cross-section of the CP and scanning it with imaging software to calculate the porosity of the cross-section and the first film layer 02 and the second film layer 03, multiple CP cross-sections were scanned and photographed, and the porosity of the first film layer 02 and the second film layer 03 of the polar sheet was calculated using the software.

[0055] In order to maximize the energy density of the negative electrode sheet, in some embodiments, the mass content of the silicon-based negative electrode material in the first film layer 02 is 0.5% to 50%, selectively 1% to 45%, 1% to 15%, 2% to 10%, or 5% to 10%, for example, 1%, 2%, 5%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, or 50%, and / or the mass content of the porous silicon negative electrode material 10 in the second film layer 03 is 0.5% to 70%, selectively 5% to 65% The mass content of porous silicon anode material 10 in the anode film layer is selectively 1% to 60%, selectively 5% to 55%, 5% to 25%, 5% to 20%, or 10% to 20%, for example, 1% to 5%, 10% to 15%, 20% to 60%, 15% to 55%, 40% to 45%, 50% to 55%, 60% to 65%, or 70%. This maximizes the specific capacity of the anode sheet through the silicon-based anode material in the two film layers.

[0056] In some embodiments, in addition to silicon-based anode materials, the anode active material can also be anode active materials known in the art for batteries. For example, the anode active material may include at least one of the following materials: artificial graphite, natural graphite, soft carbon, hard carbon, tin-based materials, lithium titanate, etc. The tin-based material can be selected from at least one of elemental tin, tin oxide compounds, and tin alloys. However, this application is not limited to these materials, and other conventional materials usable as anode active materials for batteries may be used. These anode active materials may be used individually or in combination of two or more types.

[0057] The first and second film layers of the present application include, in addition to the anode active material, a binder, a dispersant, and a conductive agent, which are included in general-purpose anode film layers. In some embodiments, the second film layer includes a porous silicon anode material, a graphite anode material, a binder, a dispersant, and a conductive agent, wherein the conductive agent includes one or more of conductive carbon and carbon nanotubes, and selectively, the mass percentage of the porous silicon anode material in the second film layer is 0.5% to 70%, selectively, the mass percentage of the graphite anode material in the second film layer is 25% to 90%, selectively, the mass percentage of the binder in the second film layer is 1% to 8%, selectively, the mass percentage of the dispersant in the second film layer is 0.5% to 2%, selectively, the mass percentage of the conductive carbon in the second film layer is 0.5% to 5%, and selectively, the mass percentage of the carbon nanotubes in the second film layer is 0.05% to 2%. By combining porous silicon anode material and graphite anode material, the volume stability during the cycling process of the second film layer is improved through the structural stability of the graphite anode material, and the specific capacity and lithium-ion conductivity of the second film layer are improved through the porous silicon anode material.

[0058] In some embodiments, the binder, as an example, comprises at least one of styrene-butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethacrylic acid (PMAA), and carboxymethyl chitosan (CMCS).

[0059] In some embodiments, the conductive agent exemplary includes at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0060] In some embodiments, the dispersant, for example, comprises at least one of sodium carboxymethylcellulose (CMC), polyvinylpyrrolidone (PVP), and polyacrylamide (PAM).

[0061] In some embodiments, the first film layer comprises a silicon-based anode material, a graphite anode material, a binder, a dispersant, and a conductive agent, wherein the conductive agent comprises one or more conductive carbon and carbon nanotubes, and selectively, the mass percentage of the silicon-based anode material in the first film layer is 0.5% to 50%, selectively, the mass percentage of the graphite anode material in the first film layer is 45% to 97.5%, selectively, the mass percentage of the binder in the first film layer is 1% to 3%, selectively, the mass percentage of the dispersant in the first film layer is 0.3% to 1.5%, selectively, the mass percentage of the conductive carbon in the first film layer is 0% to 3%, and selectively, the mass percentage of the carbon nanotubes in the first film layer is 0% to 0.5%. Since the content of graphite anode material in the first film layer is relatively higher than that in the second film layer, the structural stability of the first film layer and the adhesion stability of the current collector are improved, and the specific capacity of the first film layer is improved to some extent by adding silicon-based anode material.

[0062] Furthermore, the conductive performance of carbon nanotubes is better in the conductive agents of the first and second film layers, and the linear structure of carbon nanotubes plays a role in constraining the silicon-based anode material to some extent, effectively mitigating the volume expansion of the silicon-based anode material, suppressing powdering, and thereby improving the battery's cycle characteristics.

[0063] In some optional embodiments, the silicon-based anode material of the first film layer comprises any one or more of the group consisting of silicon material, silicon oxide material, and porous silicon anode material, or the silicon-based anode material of the first film layer is a porous silicon anode material. The content of the porous silicon anode material in the first film layer should be less than the content of the porous silicon anode material in the second film layer. This improves the uniformity of pores throughout the anode film layer.

[0064] In some embodiments, the Dv of the porous silicon anode material 50 The specific surface area (BET) of the porous silicon anode material is between 3 μm and 20 μm, for example, 3 μm, 4 μm, 5 μm, 7 μm, 10 μm, 12 μm, 15 μm, or 20 μm, and selectively between 4 μm and 15 μm, and / or the specific surface area (BET) of the porous silicon anode material is 1 m². 2 / g~30m 2 It is located between / g and selectively 6m 2 / g~20m 2 It is between / g. This improves the cycle characteristics and charging capacity of the negative electrode sheet.

[0065] The above Dv50 was measured using a laser particle size analyzer (e.g., Malvern Master Size 3000), referring to the recommended standard GB / T19077.1-2016. Here, Dv50 is the particle size corresponding to the point when the cumulative volume distribution of the material being measured reaches 50%.

[0066] BET specific surface area is a value obtained by measuring the specific surface area of ​​a material using the low-temperature nitrogen adsorption-desorption method.

[0067] Material porosity: The porosity of silicon-based anode materials can be measured using a true density porosity analyzer (e.g., AccuPyc II 1340).

[0068] The porous silicon anode material of this application can use any porous silicon anode material that is common in the art. For example, a simple porous silicon material or a porous silicon material with a coating can be used. In some embodiments, as shown in any of Figures 2 to 4, the porous silicon anode material includes a core 11 and a coating layer, the core 11 being porous silicon, the porous silicon comprising elemental silicon 111 and a silicon compound, the silicon compound comprising silicon oxide 112, and the coating layer covering the surface of the core. Porous silicon anode materials using a core-shell structure improve the charging capacity of the anode sheet while simultaneously mitigating the volume expansion of the silicon-based anode material and improving the cycle stability of high-energy-density batteries. Those skilled in the art can obtain the composition of the porous silicon in the core portion of the porous silicon material by removing the material as an external coating layer via nuclear magnetic resonance (NMR) technology (e.g., the BRUKER AVANCE III HD 500MHz apparatus).

[0069] Elemental silicon has a high theoretical lithium insertion capacity (approximately 4200 mAh / g) and a low lithium insertion potential, giving it great potential for applications in the battery field. However, elemental silicon exhibits a significant volume expansion effect, which reduces the cycle stability of batteries. Silicon oxide refers to a binary compound composed of silicon and oxygen. Compared to elemental silicon, silicon oxide exhibits a smaller volume expansion effect, mitigating the volume expansion effect and improving the cycle stability of batteries.

[0070] In some embodiments, the coating layer comprises any one or more of the following: silicon metal compounds, dilithium metasilicate, amorphous carbon, and carbon nanotubes. By coating with one or more of the above materials, the mechanical structural stability or conductivity of the porous silicon anode material can be improved. There may be multiple coating methods for each of the above materials, and where feasible, it may be a single-layer coating, or each material may be coated in a multi-layer configuration.

[0071] "Dilithium metasilicate" refers to a series of compounds produced by the reaction of metallic lithium with silicic acid. "Amorphous carbon" refers to, for example, allotropic isomers of carbon, indicating carbon in a transition state, and usually refers collectively to carbon elements other than graphite and diamond.

[0072] As shown in Figure 2, in some embodiments, the coating layer includes a first coating layer 12 and a third coating layer 14. The first coating layer 12 covers the surface of the core 11 and contains dilithium metasilicate. The third coating layer 14 covers the surface of the first coating layer 12 and contains amorphous carbon. Selectively, the amorphous carbon material includes hard carbon and / or soft carbon. The first coating layer contains dilithium metasilicate and can generate lithium salts and an inert phase (lithium oxide) during the lithium insertion process. The generation of lithium salts reduces lithium ion consumption in the positive electrode active material during the initial lithium insertion, thereby improving the initial Coulomb efficiency and charging capacity of the battery. The generation of the inert phase effectively mitigates volume expansion and can improve the battery's cycle characteristics. The third coating layer mitigates volume expansion of the first coating layer, improves cycle characteristics, and can also improve the protective effect on the first coating layer, for example, by preventing the first coating layer from coming into direct contact with water and preventing the dissolution and gas generation of dilithium metasilicate in the first coating layer.

[0073] The porous silicon anode material shown in Figure 2 can be manufactured by the following method.

[0074] 1. By synthesizing silicon crystal particles and silicon dioxide using vapor deposition to obtain silicon suboxide, and adjusting the temperature during vapor deposition to 600°C to 1200°C, the D of silicon suboxide is obtained. VThe temperature was controlled, and the resulting silicon dioxide particles were dispersed in water. Then, polyvinylpyrrolidone in a molar ratio of 5-15:1 to silicon dioxide was added, and the mixture was boiled under reflux for 2-5 hours. After cooling to room temperature, an inorganic base solution (e.g., sodium hydroxide solution) with a concentration of 0.01 mmol / L-0.1 mmol / L was added, and etching was carried out for several hours with stirring. The resulting suspension was centrifuged, washed 2-3 times, dried at 100°C-110°C for 1-3 hours, and then calcined in a muffle furnace at 500°C-600°C for 3-5 hours to obtain porous silicon dioxide, which formed the core structure. The porous silicon dioxide was polished to obtain its D V Adjust 50, and adjust the polishing time between 0.5h and 24h, D V By changing 50 and further filtering, D V The value 50 can be fine-tuned.

[0075] 2. Amorphous carbon: An amorphous carbon source such as asphalt was mixed with the core structure described above, and then subjected to high-temperature treatment for 1 to 10 hours (for example, the amorphous carbon source was mixed with the core structure in a mass ratio of 0.01:1 to 0.1:1). The temperature was controlled to 700°C to 1500°C to obtain a coating layer containing amorphous carbon.

[0076] 3. The material obtained in step 2 is mixed with a lithium source (for example, lithium powder, lithium hydride, lithium oxide, lithium carbonate, or organolithium) (for example, the material obtained in step 2 is mixed with the lithium source in a mass ratio of 1:0.09 to 1:0.2), and subjected to high-temperature treatment at 300°C to 1000°C for 1 to 5 hours. This allows lithium ions to penetrate the amorphous carbon coating layer and form a first coating layer containing dilithium metasilicate that covers the core structure inside the amorphous carbon.

[0077] 4. Finally, the material obtained in step 3 was mixed with a carbon nanotube solution, with a mass ratio of 1:0.02 to 1:0.1 between the material obtained in step 3 and the carbon nanotubes. This mixture was then subjected to high-temperature treatment at 100°C to 400°C to induce a bonding reaction, causing the carbon nanotubes to coat the surface of the material and form a third coating layer of amorphous carbon material and carbon nanotubes.

[0078] As shown in Figure 3, in some embodiments, the coating layer comprises a first coating layer 12, a second coating layer 13, and a third coating layer 14, wherein the first coating layer 12 covers the surface of the core 11 and contains dilithium metasilicate; the second coating layer 13 covers the surface of the first coating layer 12 and contains a silicon metal compound, selectively containing Ti, Mg, and / or Al as the metal elements in the silicon metal compound; the third coating layer 14 covers the surface of the second coating layer 13 and contains amorphous carbon, selectively containing hard carbon and / or soft carbon as the amorphous carbon material. Furthermore, the second coating layer provided between the first and third coating layers contains a silicon metal compound and has excellent mechanical strength, can mitigate the volume expansion of the internal silicon material, and can improve cycle characteristics.

[0079] The porous silicon anode material shown in Figure 3 can be manufactured by the following method.

[0080] 1. Silicon crystal particles and silicon dioxide were synthesized by vapor deposition to obtain silicon suboxide. The obtained silicon suboxide particles were dispersed in water, and then polyvinylpyrrolidone in a molar ratio of 5-15:1 to silicon dioxide was added. The mixture was boiled under reflux for 2-5 hours and cooled to room temperature. Next, an inorganic base solution (e.g., sodium hydroxide solution) with a concentration of 0.01 mmol / L to 0.1 mmol / L was added, and etching was carried out with stirring for several hours. The resulting suspension was centrifuged, washed 2-3 times, dried at 100°C-110°C for 1-3 hours, and then calcined in a muffle furnace at 500°C-600°C for 3-5 hours to obtain porous silicon suboxide, which formed the core structure.

[0081] 2. Amorphous carbon: After mixing an amorphous carbon source such as asphalt with the above core structure, a high-temperature treatment was performed for 1 to 10 hours, controlling the temperature to 700°C to 1500°C to obtain a coating layer containing amorphous carbon.

[0082] 3. The material obtained in step 2 above is mixed with a lithium source (e.g., lithium powder, lithium hydride, lithium oxide, lithium carbonate, or organolithium) and subjected to high-temperature treatment at 300°C to 1000°C for 1 to 5 hours. This allows lithium ions to penetrate the amorphous carbon coating layer and form a first coating layer containing dilithium metasilicate that covers the core structure inside the amorphous carbon.

[0083] 4. Production of silicon metal compound coating layer: The metal coating raw material and the material obtained in step 3 are mixed in a mass ratio of 0.001:1 to 0.02:1. The resulting material is subjected to high-temperature treatment at 600°C to 1000°C for 0.5 to 2 hours. After treatment, the material is stirred in a ball mill for 10 to 60 minutes. The metal ions penetrate the amorphous carbon coating layer, and a second coating layer containing the silicon metal compound can be formed inside the amorphous carbon and on the surface of the dilithium metasilicate.

[0084] 5. Finally, the material obtained in step 4 was mixed with a carbon nanotube solution, and this was subjected to high-temperature treatment at 100°C to 400°C to induce a bonding reaction, thereby coating the surface of the material with carbon nanotubes and forming a third coating layer in which amorphous carbon material and carbon nanotubes were mixed.

[0085] The above-mentioned metal coating raw materials include, but are not limited to, metal salts and metal oxides.

[0086] As shown in Figure 4, in some embodiments, based on the structure shown in Figure 2, the silicon compound further comprises a silicon metal compound 113, which coats the surface of elemental silicon. "Silicon metal compound" refers to a compound produced from a transition metal and silicon. Selectively, the metal elements of the silicon metal compound include Ti, Mg, and / or Al. Coating the surface of elemental silicon with a silicon metal compound can mitigate the volume expansion of elemental silicon, improving its cycle characteristics and charging capacity.

[0087] The porous silicon anode material shown in Figure 4 can be manufactured by the following method.

[0088] 1. Silicon crystal particles and silicon dioxide were synthesized by vapor deposition to obtain silicon suboxide. The obtained silicon suboxide particles were dispersed in water, and then polyvinylpyrrolidone in a molar ratio of 5-15:1 to silicon dioxide was added. The mixture was boiled under reflux for 2-5 hours and cooled to room temperature. Next, an inorganic base solution (e.g., sodium hydroxide solution) with a concentration of 0.01 mmol / L to 0.1 mmol / L was added, and etching was carried out with stirring for several hours. The resulting suspension was centrifuged, washed 2-3 times, dried at 100°C-110°C for 1-3 hours, and then calcined in a muffle furnace at 500°C-600°C for 3-5 hours to obtain porous silicon suboxide.

[0089] 2. Manufacturing of the silicon metal compound coating layer: The metal coating raw material was mixed with the porous silicon oxide, and the resulting material was subjected to high-temperature treatment at 800°C to 1300°C for 1 to 6 hours. The high-temperature treated material was then polished, and this coating (coating) reacted directly with the silicon crystal particles through a phase-selective reaction, forming a silicon metal compound coating layer on the surface of the silicon element, thus creating a core structure.

[0090] 3. Amorphous carbon: After mixing an amorphous carbon source such as asphalt with the above core structure, a high-temperature treatment was performed for 1 to 10 hours, controlling the temperature to 700°C to 1500°C to obtain a coating layer containing amorphous carbon.

[0091] 4. The material obtained in step 3 above is mixed with a lithium source (e.g., lithium powder, lithium hydride, lithium oxide, lithium carbonate, or organolithium) and subjected to high-temperature treatment at 300°C to 1000°C for 1 to 5 hours. This allows lithium ions to penetrate the amorphous carbon coating layer and form a first coating layer containing dilithium metasilicate that covers the core structure inside the amorphous carbon.

[0092] 5. Finally, the material obtained in step 4 was mixed with a carbon nanotube solution, and this was subjected to high-temperature treatment at 100°C to 400°C to induce a bonding reaction, thereby coating the surface of the material with carbon nanotubes and forming a third coating layer in which amorphous carbon material and carbon nanotubes were mixed.

[0093] The hard carbon mentioned above refers to carbon that is difficult to graphitize, and is a product of the thermal decomposition of high-molecular-weight polymers. Typical hard carbons include resin carbon, thermally decomposed organic polymers, and carbon black. Soft carbon generally refers to black carbon, which is a highly aromatic compound carbonized by thermal decomposition of fossil fuels and biomass under oxygen-deficient conditions. In the embodiments described above, amorphous carbon may be hard carbon only, soft carbon only, or a mixture of hard carbon and soft carbon. Amorphous carbon has a large interlayer distance and a fast lithium insertion rate, thus contributing to an improvement in the overall performance of the battery.

[0094] In some embodiments, the third coating layer further comprises carbon nanotubes. The carbon nanotubes can improve the conductivity of the porous silicon anode material and provide sufficient constraint on the porous silicon anode material via the carbon nanotubes, mitigating volume expansion during the charge-discharge process and controlling the polarization inside the cells of the anode sheet to improve the cycle characteristics of the cells. Definitions: In the first film layer 02 and the second film layer 03, the masses of the porous silicon anode material 10 are m1 and m2, respectively; the mass percentages of carbon nanotubes belonging to the porous silicon anode material 10 in the first film layer 02 and the second film layer 03 are C1 and C2, respectively; the masses of carbon nanotubes remaining in the first film layer 02 and the second film layer 03 after the removal of carbon nanotubes from the porous silicon anode material 10 are S1 and S2, respectively; and the first film layer 02 and the second film layer 03 are the first film layer 02 and the second film layer 03 per unit area, respectively. In order to ensure sufficient restraint of the porous silicon anode material 10 and effectively suppress the rebound of the anode sheet, in some embodiments, the design is such that a combination of carbon nanotubes in the third coating layer, carbon nanotubes in the first film layer 02, and carbon nanotubes in the second film layer 03 satisfies the relationships (m2×C2+S2) / M2=(m1×C1+S1) / M1, m2≧m1, S1≧S2, and S2=m1×m2×(C2-C1) / (m2-m1), further improving the restraint force on the silicon anode material, effectively suppressing the rebound of the anode sheet, and minimizing the polarization of the anode sheet.

[0095] The masses of the porous silicon anode material in the first and second film layers are m1 and m2, respectively, and their measurement is performed by referring to the measurement method for the silicon-based anode material content described above.

[0096] Measurement of the mass percentages C1 and C2 of carbon nanotubes on the surface of the porous silicon negative electrode material: Using SEM, the number and length of carbon nanotubes present on the surfaces of multiple silicon particles were measured. The chain length and number of monomers of the carbon nanotubes were modeled, and the mass per corresponding single carbon nanotube was calculated. An average value was obtained from the masses of multiple carbon nanotubes and regarded as the mass of the carbon nanotubes on the surface of the porous silicon negative electrode material. Subsequently, the mass percentages C1 and C2 of the carbon nanotubes in the porous silicon negative electrode material were calculated based on the volume and true density of the porous silicon negative electrode material.

[0097] The masses of the carbon nanotubes remaining in the first film layer and the second film layer are S1 and S2, respectively. After confirming the thicknesses of the two film layers in the vertical direction by the CP (ion beam) cross-section, using the powder scraping method, first scrape the powder of the second film layer, which is the upper layer, and then scrape the powder of the first film layer, which is the lower layer. Each of the obtained powders was equally divided into n equal parts and uniformly dispersed and arranged on the SEM material holder. The number of carbon nanotubes in each sample was measured by SEM, and based on the above calculation method, the masses of the carbon nanotubes in the first film layer and the second film layer were calculated.

[0098] In some embodiments, the Dv50 of the elemental silicon is in the range of 0 < Dv50 ≤ 10 nm, and optionally, the Dv50 of the elemental silicon is in the range of 2 nm < Dv50 ≤ 8 nm. Adopting nano-sized elemental silicon is advantageous for mixing with silicon oxide, further advantageous for improving the charging capacity of the battery, and also advantageous for reducing the difficulty of coating the core structure and improving the cycle stability of the battery.

[0099] The chemical formula of "silicon oxide" is SiOx, where 0 < x ≤ 2. For example, it can be silicon monoxide (SiO) or silicon dioxide (SiO2). In some embodiments, the Dv50 of the silicon oxide used is in the range of 2 μm ≤ Dv50 ≤ 13 μm. This is advantageous for mixing with elemental silicon and can improve the energy density of the battery.

[0100] In some embodiments, the above-mentioned dilithium metasilicate contains one or more of Li2SiO3, Li2Si2O5, Li4SiO4, Li2Si3O7, Li8SiO6, Li6Si2O7, Li4Si2O7, Li2Si4O7, and LiSiO3. Optionally, the dilithium metasilicate contains at least Li2SiO3, thereby effectively reducing the lithium ion consumption in the cathode active material during the first lithium insertion in the first coating layer, and the battery has a high first Coulomb efficiency. Further, optionally, the mass of Li2SiO3 is at least 50% of the mass of the first coating layer, for example, 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, or 90%. More optionally, the mass of Li2SiO3 is at least 70% of the mass of the first coating layer, ensuring that the first coating layer has high lithium conductivity and improving the charging capacity of the entire material.

[0101] Standard samples with different contents of Li2SiO3 were prepared according to the types of dilithium metasilicate in the first coating layer. By measuring with TOF-SIMES, measured contents with different Li2SiO3 contents were obtained, and a standard curve showing the measured content and the actual content was plotted. The first coating layer was measured by TOF-SIMES to obtain the measured content of Li2SiO3, and by comparing this value with the standard curve, the accurate content of Li2SiO3 was obtained.

[0102] In any embodiment of the first aspect, the thickness of the first coating layer is 10% to 80% of the particle radius of the porous silicon anode material, selectively the thickness of the second coating layer is 1 nm to 50 nm, selectively the thickness of the third coating layer is 1 nm to 1000 nm, and selectively 5 nm to 300 nm. Within the above thickness range, the particles improve the battery energy density while effectively suppressing the volume expansion of the anode material, thereby improving the cycle stability and charging capacity of high-energy-density batteries. Each of the above thicknesses is measured from the outside to the inside of the particle by TOF-SIMS, and the thickness of each coating layer is determined based on the material detected at different depths. When manufacturing the porous silicon anode material, the thickness of each coating layer can be controlled by adjusting the amount of raw material used corresponding to each coating layer.

[0103] In some embodiments, the negative electrode current collector can be a metal foil or a composite current collector. For example, copper foil can be used as the metal foil. The composite current collector may include a polymer substrate layer and a metal layer formed on at least one surface of the polymer substrate layer. The composite current collector can be formed by forming a metal material (such as copper, copper alloys, nickel, nickel alloys, titanium, titanium alloys, silver, and silver alloys) on a polymer material substrate (for example, a substrate such as polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), or polyethylene (PE)).

[0104] In some embodiments, a negative electrode sheet can be manufactured by the following method: Components for manufacturing the negative electrode sheet, such as a negative electrode active material, a conductive agent, a binder, and any other components, are dispersed in a solvent (e.g., deionized water) to form a negative electrode paste, the negative electrode paste is coated onto a negative electrode current collector, and the negative electrode sheet can be obtained through steps such as drying and cold pressing.

[0105] [Positive electrode sheet] The positive electrode sheet generally includes a positive electrode current collector and a positive electrode film layer placed on at least one surface of the positive electrode current collector, the positive electrode film layer containing a positive electrode active material.

[0106] Exemplary, the positive electrode current collector has two opposing surfaces in its own thickness direction, and the positive electrode film layer is provided on one or both of the two opposing surfaces of the positive electrode current collector.

[0107] In some embodiments, the positive electrode current collector can be a metal foil or a composite current collector. As the metal foil, for example, aluminum foil can be used. The composite current collector may include a polymer substrate layer and a metal layer formed on at least one surface of the polymer substrate layer. The composite current collector can be formed by forming a metal material (such as aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy) on a polymer material substrate (for example, a substrate such as polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), or polyethylene (PE)).

[0108] In some embodiments, the positive electrode active material can be any known positive electrode active material for batteries. Exemplarily, the positive electrode active material may include at least one of olivine-structured lithium-containing phosphates, lithium transition metal oxides, and their respective modified compounds. However, the present application is not limited to these materials, and other conventional materials usable as positive electrode active materials for batteries may be used. These positive electrode active materials may be used individually or in combination of two or more. Examples of lithium transition metal oxides include lithium cobalt oxide (LiCoO2, etc.), lithium nickel oxide (LiNiO2, etc.), lithium manganese oxide (LiMnO2, LiMn2O4, etc.), lithium nickel cobalt oxide, lithium manganese cobalt oxide, lithium nickel manganese oxide, and lithium nickel cobalt manganese oxide (LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2(NCM 333(Also known as), LiNi 0.5 Co 0.2 Mn 0.3 O2(NCM 523 (Also known as) LiNi 0.5 Co 0.25 Mn 0.25 O2(NCM 211 (Also known as), LiNi 0.6 Co 0.2 Mn 0.2 O2(NCM 622 (Also known as), LiNi 0.8 Co 0.1 Mn 0.1 O2(NCM 811 (Also known as) Lithium nickel cobalt aluminum oxide (LiNi 0.85 Co 0.15 Al 0.05 The olivine structure lithium-containing phosphate may include, but is not limited to, at least one of O2 (and other modified compounds thereof) and its modified compounds. The olivine structure lithium-containing phosphate may include, but is not limited to, at least one of lithium iron phosphate (e.g., LiFePO4 (also called LFP)), a composite material of lithium iron phosphate and carbon, lithium manganese phosphate (e.g., LiMnPO4), a composite material of lithium manganese phosphate and carbon, lithium iron manganese phosphate, and a composite material of lithium iron manganese phosphate and carbon.

[0109] In some embodiments, the positive electrode film layer may selectively further contain a binder. As an example, the binder may include at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorine-containing acrylate resins.

[0110] In some embodiments, the positive electrode film layer may further selectively contain a conductive agent. Exemplarily, the conductive agent may include at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0111] In some embodiments, a positive electrode sheet can be manufactured by the following method: Components for manufacturing the positive electrode sheet, such as a positive electrode active material, a conductive agent, a binder, and any other components, are dispersed in a solvent (e.g., N-methylpyrrolidone) to form a positive electrode paste, the positive electrode paste is applied to a positive electrode current collector, and the positive electrode sheet can be obtained through processes such as drying and cold pressing.

[0112] [Electrolyte] The electrolyte plays a role in conducting ions between the positive electrode sheet and the negative electrode sheet. This application does not particularly limit the type of electrolyte, and it can be selected as needed. For example, the electrolyte may be a liquid, a gel, or a solid.

[0113] In some embodiments, the electrolyte is a liquid and comprises an electrolyte salt and a solvent.

[0114] In some embodiments, the electrolyte salt can be selected from at least one of lithium hexafluoride phosphate, lithium tetrafluoroborate, lithium perchlorate, lithium hexafluoride arsenate, lithium bisfluorosulfonylimide, lithium bistrifluoromethanesulfonylimide, lithium trifluoromethanesulfonate, lithium difluorophosphate, lithium difluorooxalate borate, lithium bisoxalate borate, lithium difluorobisoxalate phosphate, and lithium tetrafluorooxalate phosphate.

[0115] In some embodiments, the solvent can be selected from at least one of ethylene carbonate, propylene carbonate, methyl ethyl carbonate, diethyl carbonate, dimethyl carbonate, dipropyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, butylene carbonate, fluoroethylene carbonate, methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate, 1,4-butyrolactone, sulfolane, dimethyl sulfone, methyl ethyl sulfone, and diethyl sulfone.

[0116] In some embodiments, the electrolyte selectively further comprises additives. For example, the additives may include a negative electrode film-forming additive, a positive electrode film-forming additive, and further, additives that can improve specific characteristics of the battery, such as additives that improve the overcharge characteristics of the battery, or additives that improve the high-temperature or low-temperature characteristics of the battery.

[0117] [Separator] In some embodiments, the secondary battery further includes a separator. The present application does not particularly limit the type of separator, and any known porous structure separator having good chemical and mechanical stability can be selected.

[0118] In some embodiments, the material of the separator can be selected from at least one of glass fiber, nonwoven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator may be a single-layer film or a multilayer composite film, and is not particularly limited. If the separator is a multilayer composite film, the materials of each layer may be the same or different, and are not particularly limited.

[0119] In some embodiments, the positive electrode sheet, negative electrode sheet, and separator can be manufactured into an electrode assembly via a winding process or a lamination process.

[0120] In some embodiments, the secondary battery may include an outer casing. This casing is used to enclose the electrode assembly and electrolyte.

[0121] In some embodiments, the casing material of the secondary battery may be a hard case such as a rigid plastic case, an aluminum case, or a steel case. The casing material of the secondary battery may also be a soft pack such as a pouch-type soft pack. The material of the soft pack may be plastic, and examples of plastics include polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0122] This invention does not particularly limit the shape of the secondary battery, and it may be cylindrical, prismatic, or any other shape. For example, Figure 5 shows a prismatic secondary battery 5 as an example.

[0123] In some embodiments, referring to Figure 6, the exterior material may include a housing 51 and a cover plate 53. The housing 51 may include a bottom plate and side plates connected to the bottom plate, forming a housing cavity enclosed by the bottom plate and side plates. The housing 51 has an opening that communicates with the housing cavity, and the cover plate 53 can cover the opening to seal the housing cavity. The positive electrode sheet, negative electrode sheet, and separator can form an electrode assembly 52 via a winding or lamination process. The electrode assembly 52 is sealed within the housing cavity. The electrolyte is impregnated into the electrode assembly 52. ​​The number of electrode assemblies 52 included in the secondary battery 5 may be one or more, and those skilled in the art can select according to specific practical requirements.

[0124] In some embodiments, the secondary batteries can be assembled into a battery module, and the number of secondary batteries included in the battery module may be one or more, the specific number of which can be selected by those skilled in the art depending on the application and capacity of the battery module.

[0125] Figure 7 shows an example of a battery module 4. Referring to Figure 7, in the battery module 4, multiple secondary batteries 5 can be installed in sequence along the length of the battery module 4. Of course, they can be arranged in any other manner. Furthermore, these multiple secondary batteries 5 can be fixed in place with fasteners.

[0126] Selectively, the battery module 4 may further comprise an outer case having a housing space for accommodating multiple secondary batteries 5.

[0127] In some embodiments, the battery modules can be further assembled into a battery pack, and the number of battery modules in the battery pack may be one or more, the specific number of which can be selected by those skilled in the art depending on the application and capacity of the battery pack.

[0128] Figures 8 and 9 show an example of a battery pack 1. Referring to Figures 8 and 9, the battery pack 1 may include a battery case and a plurality of battery modules 4 installed inside the battery case. The battery case includes an upper housing 2 and a lower housing 3, the upper housing 2 can be placed over the lower housing 3 and form a sealed space for housing the plurality of battery modules 4. The plurality of battery modules 4 can be arranged inside the battery case in any way.

[0129] Furthermore, the present application provides a power consumption device comprising at least one of a secondary battery, a battery module, or a battery pack relating to the present application. The secondary battery, battery module, or battery pack may be used as a power source for the power consumption device, or as an energy storage element for the power consumption device. The power consumption device may include, but is not limited to, mobile devices (e.g., mobile phones, laptops, etc.), electric vehicles (e.g., pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), trains, ships and satellites, energy storage systems, etc.

[0130] As the power consumption device, a secondary battery, battery module, or battery pack can be selected according to the usage requirements.

[0131] Figure 10 shows an example of a power consumption device. This power consumption device is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle, etc. To meet the high power output and high energy density requirements for the secondary battery of this power consumption device, a battery pack or battery module can be used.

[0132] [Examples] The following describes examples of the present application. The examples described below are illustrative and are for interpretive purposes only, and should not be considered as limitations thereon. Unless otherwise specified in the examples, the examples should be carried out in accordance with the techniques or conditions described in the literature in the art or in accordance with the product specifications. Unless otherwise specified, the reagents or equipment used are all commercially available, common products.

[0133] [Table 1]

[0134] 1. Porous silicon anode material Manufacturing process for porous silicon anode material 1 1. Silicon crystal particles and silicon dioxide were synthesized by vapor deposition to obtain silicon suboxide. The deposition temperature was controlled to 800°C. The obtained silicon suboxide particles were dispersed in water. Then, polyvinylpyrrolidone in a molar ratio of 10:1 to silicon dioxide was added, and the mixture was boiled under reflux for 3 hours. After cooling to room temperature, a 0.05 mmol / L sodium hydroxide solution was added, and etching was carried out for 4 hours with stirring. The resulting suspension was centrifuged, washed 2-3 times, dried at 105°C for 2 hours, and then calcined in a muffle furnace at 550°C for 4 hours to obtain porous silicon suboxide. The obtained porous silicon suboxide was polished and sieved to obtain its D V Adjust the size of 50.

[0135] 2. Manufacturing of a silicon metal compound coating layer: TiO2, a metal coating raw material, was mixed with the silicon oxide in a mass ratio of 0.003:1. The resulting material was subjected to high-temperature treatment at 1000°C for 4 hours. The high-temperature treated material was then polished. This coating reacted directly with silicon crystal particles through a phase-selective reaction, forming a silicon TiSi coating layer on the surface of the silicon element, creating a core structure.

[0136] 3. Amorphous carbon: Asphalt was mixed with the above core structure in a mass ratio of 0.05:1, and then subjected to a high-temperature treatment for 6 hours, with the temperature controlled to 1100°C, to obtain a coating layer containing amorphous carbon.

[0137] 4. The material obtained in step 3 above is mixed with lithium carbonate in a mass ratio of 1:0.2 and subjected to high-temperature treatment at 800°C for 3 hours. This allows the lithium ions to penetrate the amorphous carbon coating layer and form a first coating layer containing dilithium metasilicate that covers the core structure inside the amorphous carbon.

[0138] 5. Finally, the material obtained in step 4 was mixed with a carbon nanotube solution, with a mass ratio of 1:0.08 between the material obtained in step 4 and the carbon nanotubes. This mixture was then subjected to high-temperature treatment at 250°C to induce a bonding reaction, coating the surface of the material with carbon nanotubes and forming a third coating layer of amorphous carbon material and carbon nanotubes.

[0139] Based on the manufacturing process of porous silicon anode material 1 described above, porous silicon anode materials 2 to 5 were obtained by adjusting the polishing time and sieving particle size.

[0140] Based on the manufacturing process of porous silicon anode material 1 described above, porous silicon anode materials 6 to 10 were obtained by adjusting the temperature during gas-phase deposition.

[0141] Based on the manufacturing process of the porous silicon anode material 1 described above, porous silicon anode materials 11 to 14 with different first coating layer thicknesses were obtained by adjusting the mass content of the porous silicon material and lithium carbonate.

[0142] Based on the manufacturing process of the porous silicon anode material 1 described above, a porous silicon anode material 15 was obtained by halving the amount of TiO2 used as a metal coating raw material.

[0143] Manufacturing process for porous silicon anode material 16 The only difference from the manufacturing process of porous silicon anode material 1 is the use of MgCl2 instead of TiO2.

[0144] Manufacturing process for porous silicon anode material 17 1. Silicon crystal particles and silicon dioxide were synthesized by vapor deposition to obtain silicon suboxide. The deposition temperature was controlled to 800°C. The obtained silicon suboxide particles were dispersed in water. Then, polyvinylpyrrolidone in a molar ratio of 10:1 to silicon dioxide was added, boiled under reflux for 3 hours, and cooled to room temperature. Next, a sodium hydroxide solution was added, and etching was carried out for several hours while stirring. The resulting suspension was centrifuged, washed 2-3 times, dried at 105°C for 2 hours, and then calcined in a muffle furnace at 550°C for 4 hours to obtain porous silicon suboxide, which formed the core structure. The obtained porous silicon suboxide was polished and sieved to obtain its D V Adjust the size of 50.

[0145] 2. Amorphous carbon: Asphalt was mixed with the above core structure in a mass ratio of 0.05:1, and then subjected to a high-temperature treatment for 6 hours, with the temperature controlled to 1000°C, to obtain a coating layer containing amorphous carbon.

[0146] 3. The material obtained in step 2 above is mixed with lithium carbonate in a mass ratio of 1:1.2 and subjected to high-temperature treatment at 800°C for 3 hours. This allows lithium ions to penetrate the amorphous carbon coating layer and form a first coating layer containing dilithium metasilicate that covers the core structure inside the amorphous carbon.

[0147] 4. Production of silicon metal compound coating layer: Mix the metal coating raw material and the material obtained in step 3 in a mass ratio of 0.015:1, treat the resulting material at a high temperature of 1000°C for 1 hour, and stir the treated material in a ball mill for 30 minutes. The metal ions can penetrate the amorphous carbon coating layer, forming a second coating layer containing the silicon metal compound inside the amorphous carbon and on the surface of the dilithium metasilicate.

[0148] 5. Finally, the material obtained in step 4 was mixed with a carbon nanotube solution, with a mass ratio of 1:0.08 between the material obtained in step 4 and the carbon nanotubes. This mixture was then subjected to high-temperature treatment at 250°C to induce a bonding reaction, coating the surface of the material with carbon nanotubes and forming a third coating layer of amorphous carbon material and carbon nanotubes.

[0149] Based on the manufacturing process of the porous silicon anode material 17 described above, porous silicon anode materials 18 to 21 were obtained by adjusting the amount of metal coating raw material used.

[0150] Based on the manufacturing process of the porous silicon anode material 17 described above, porous silicon anode materials 22 and 23 were obtained by adjusting the amount of asphalt used.

[0151] Based on the manufacturing process of the porous silicon anode material 17 described above, a porous silicon anode material 24 was obtained by adjusting the amount of carbon nanotubes used.

[0152] Manufacturing process for porous silicon anode material 25 The only difference from the manufacturing process of porous silicon anode material 17 is the use of MgCl2 instead of TiO2.

[0153] Manufacturing process for porous silicon anode material 26 1. Silicon crystal particles and silicon dioxide were synthesized by vapor deposition to obtain silicon suboxide. The deposition temperature was controlled to 800°C. The obtained silicon suboxide particles were dispersed in water, and then polyvinylpyrrolidone in a molar ratio of 10:1 to silicon dioxide was added. The mixture was boiled under reflux for 3 hours and cooled to room temperature. Next, a 0.05 mmol / L sodium hydroxide solution was added, and etching was carried out for several hours while stirring. The resulting suspension was centrifuged, washed 2-3 times, dried at 105°C for 2 hours, and then calcined in a muffle furnace at 550°C for 4 hours to obtain porous silicon suboxide, which formed the core structure.

[0154] 2. Amorphous carbon: Asphalt was mixed with the above core structure in a mass ratio of 1.2:1, and then subjected to a high-temperature treatment for 6 hours, with the temperature controlled to 1100°C, to obtain a coating layer containing amorphous carbon.

[0155] 3. The material obtained in step 2 above is mixed with lithium carbonate in a mass ratio of 1:1.2 and subjected to high-temperature treatment at 800°C for 3 hours. This allows lithium ions to penetrate the amorphous carbon coating layer and form a first coating layer containing dilithium metasilicate that covers the core structure inside the amorphous carbon.

[0156] 4. Finally, the material obtained in step 3 was mixed with a carbon nanotube solution, with a mass ratio of 1:0.08 between the material obtained in step 3 and the carbon nanotubes. This mixture was then subjected to high-temperature treatment at 250°C to induce a bonding reaction, coating the surface of the material with carbon nanotubes and forming a third coating layer of amorphous carbon material and carbon nanotubes.

[0157] Manufacturing process for silicon anode material 27 1. Silicon crystal particles and silicon dioxide were synthesized by vapor deposition to obtain silicon suboxide, which formed the core structure.

[0158] 2. Amorphous carbon: Asphalt was mixed with the above core structure in a mass ratio of 1.2:1, and then subjected to a high-temperature treatment for 6 hours, with the temperature controlled to 1100°C, to obtain a coating layer containing amorphous carbon.

[0159] 3. The material obtained in step 2 above is mixed with lithium carbonate in a mass ratio of 1:1.2 and subjected to high-temperature treatment at 800°C for 3 hours. This allows lithium ions to penetrate the amorphous carbon coating layer and form a first coating layer containing dilithium metasilicate that covers the core structure inside the amorphous carbon.

[0160] 4. Finally, the material obtained in step 3 was mixed with a carbon nanotube solution, with a mass ratio of 1:0.08 between the material obtained in step 3 and the carbon nanotubes. This mixture was then subjected to high-temperature treatment at 250°C to induce a bonding reaction, coating the surface of the material with carbon nanotubes and forming a third coating layer of amorphous carbon material and carbon nanotubes.

[0161] Measurement of manufactured porous silicon anode material: Dv50: Measured using a laser particle size analyzer (such as Malvern Master Size 3000), referring to the recommended standard GB / T 19077.1-2016. Here, Dv50 is the corresponding particle size when the cumulative volume distribution of the material being measured reaches 50%. When forming a core structure, the Dv50 of elemental silicon was measured using the method described above, and after all coating layers were applied, the Dv50 of the porous silicon anode material was measured using the method described above.

[0162] BET specific surface area: This is the value obtained by measuring the specific surface area of ​​a porous silicon anode material using the low-temperature nitrogen adsorption-desorption method.

[0163] Measurement of Li2SiO3 mass content: The corresponding Li2SiO3 content was obtained by measuring with TOF-SIMES, and the standard curve was measured using a standard sample. By comparing the results with the standard curve, the accurate Li2SiO3 content was obtained.

[0164] Measurement of each coating layer thickness: The thickness of each coating layer was determined based on the material detected at different depths, measured from the outside to the inside of the particle using TOF-SIMS.

[0165] Measurement of carbon nanotube content: Using a scanning electron microscope (SEM), the number and length of carbon nanotubes present on the surface of multiple silicon particles were measured. The chain length and monomer count of the carbon nanotubes were modeled, and the corresponding mass per single carbon nanotube was calculated. The average value was obtained from the masses of multiple carbon nanotubes and considered to be the mass of carbon nanotubes on the surface of the porous silicon anode material. Subsequently, based on the deposition and true density of the porous silicon anode material, the mass percentages C1 and C2 of carbon nanotubes in the porous silicon anode material in the two film layers of the anode sheet described below were calculated.

[0166] The test results are recorded in Tables 1 and 2.

[0167] [Table 2A] [Table 2B]

[0168] [Table 3]

[0169] 2. Manufacturing of negative electrode sheets Negative electrode sheet 1: The application weight is 10 mg / cm². 2The coating weight ratio of the first coating layer to the second coating layer is 70:30. In the first coating layer, the mass content of porous silicon anode material 1, graphite, binder, dispersant, conductive agent SP, and conductive agent CNT is 10%, 85.73%, 2%, 1.2%, 1%, and 0.07%, respectively. In the second coating layer, the mass content of porous silicon anode material 1, graphite, binder, dispersant, conductive agent SP, and conductive agent CNT is 30%, 65.19%, 2.4%, 1.2%, 1%, and 0.21%, respectively.

[0170] According to the weight ratios described above, each raw material for the first coating layer was thoroughly stirred and mixed in an appropriate amount of aqueous solvent to form a uniform negative electrode paste, thereby obtaining the first negative electrode paste. The second negative electrode paste was obtained by the same method. The first negative electrode paste was applied to the surface of the copper foil, which is the negative electrode current collector, and the second negative electrode paste was applied to the surface of the first negative electrode paste. After drying and cold pressing, a negative electrode sheet 1 was obtained. The surface density M1 of the first film layer and the surface density M2 of the second film layer formed on each negative electrode sheet are recorded in Table 2.

[0171] The only difference between negative electrode sheets 2 to 27 and negative electrode sheet 1 is that, in order, the porous silicon negative electrode material 2 to 27 is used instead of the porous silicon negative electrode material 1 in negative electrode sheet 1.

[0172] All negative electrode sheets 27 to 36 use porous silicon negative electrode material 1. However, the amount used, surface density, thickness, and film layer mass percentage of the first and second film layers are shown in Table 3. The amount of graphite used was adjusted according to the amount of porous silicon negative electrode material 1, graphite, binder, dispersant, and conductive agent SP used in the first film layer so that the total mass ratio of porous silicon negative electrode material 1, graphite, binder, dispersant, conductive agent SP, and conductive agent CNT was 100%. The amount of graphite used in the second film layer was adjusted so that the total mass ratio of porous silicon negative electrode material 1, graphite, binder, dispersant, conductive agent SP, and conductive agent CNT was 100%.

[0173] In the negative electrode sheet 37, a silicon negative electrode material 27 was used instead of the porous silicon negative electrode material 1 in the negative electrode sheet 1.

[0174] Measurement of the negative electrode sheet: Measurement of porosity of the negative electrode film layer: A cross-section of the CP was photographed, scanned with imaging software, and the porosity of the corresponding cross-section was calculated. Then, multiple CP cross-sections were scanned and photographed, and the porosity of the negative electrode film layer was calculated using the software.

[0175] Thickness: The thickness was measured by photographing the cross-section of the CP (polycarbonate).

[0176] Let A be the weight ratio of the first film layer to the second film layer.

[0177] Based on the amount of raw materials used and the data in Tables 1 and 2, 1 cm 2 For each of the first and second film layers, the masses m1 and m2 of the porous silicon anode material in the first and second film layers are calculated, the mass percentages C1 and C2 of the carbon nanotubes belonging to the porous silicon anode material in the first and second film layers are calculated, the carbon nanotubes in the porous silicon anode material are removed, and the masses of the carbon nanotubes remaining in the first and second film layers are S1 and S2, respectively.

[0178] [Table 4A] [Table 4B] [Table 4C]

[0179] Note: The silicon-based anode material in the anode sheet 37 is the same as the silicon-based anode material 27.

[0180] 3. Secondary battery Example 1 Negative electrode sheet: The above-mentioned negative electrode sheet 1 was used as the negative electrode sheet for the secondary battery of Example 1.

[0181] Positive electrode sheet: The application weight is 25.5 mg / cm². 2 The positive electrode sheet is coated in a single layer, and the mass content of the ternary material NCM811, PVDF, conductive agent SP, and conductive agent CNT is 96.5%, 1.5%, 1.5%, and 0.5%, respectively.

[0182] According to the weight ratios described above, each raw material was thoroughly stirred and mixed in an appropriate amount of solvent NMP to form a uniform positive electrode paste. Next, the positive electrode paste was applied to the surface of aluminum foil, which served as the positive electrode current collector, and a positive electrode sheet was obtained after drying and cold pressing.

[0183] Electrolyte: The electrolyte contains a solvent, a lithium salt, and additives. The types and proportions of the solvent are EC:DMC:DEC = 0.3:0.5:0.2, the lithium salt content is 1.0 mol / L, and the film-forming additive contains 8% FEC.

[0184] Separator: Use a PE separator.

[0185] The negative electrode sheets of the secondary batteries in Examples 2 to 37 are negative electrode sheets 2 to 37 in order, while the positive electrode sheet, electrolyte, and separator are all the same as in Example 1.

[0186] The negative electrode sheet of the secondary battery in Comparative Example 1 is negative electrode sheet 38, and the positive electrode sheet, electrolyte, and separator are all the same as in Example 1.

[0187] Measurement of specific capacity: A coin-type half-cell was fabricated by combining a negative electrode sheet with a lithium sheet, and a charge-discharge test was performed at 25°C at a rate of 0.04C. The voltage range was 0.05V to 2V, and after measuring the discharge capacity, the specific capacity of the negative electrode active material was calculated using the formula: specific capacity = test capacity / mass of active material.

[0188] Cycle characteristics test: At 25°C, the secondary batteries manufactured in each example and comparative example were charged at a 1C rate with a constant current until the cutoff voltage reached 4.25V, then charged at a constant voltage until the current was ≤0.05C, left to stand for 5 minutes, and then discharged at a 1C rate with a constant current until the cutoff voltage reached 2.8V, left to stand for 5 minutes. This constituted one charge-discharge cycle. The batteries were subjected to charge-discharge cycle testing according to this method until their capacity was reduced to 80%. The number of cycles at this time represents the battery's cycle life at 25°C.

[0189] Charging capacity test: At 25°C, the batteries of each example and comparative example were subjected to their initial charge and discharge at 1C (i.e., a current value that allows for complete discharge of the theoretical capacity in 1 hour). Specifically, the batteries were charged with a constant current at a rate of 1C up to a voltage of 4.25V, then charged with a constant voltage down to a current of ≤0.05C, then left to stand for 5 minutes, and discharged with a constant current at a rate of 0.33C up to a voltage of 2.8V. The measured discharge capacity at this time was recorded as C0.

[0190] Next, the batteries were charged sequentially with constant currents of 1.0C0, 1.3C0, 1.5C0, 1.8C0, 2.0C0, 2.3C0, 2.5C0, and 3.0C0 until all batteries reached a charge cutoff voltage of 4.25V or a negative electrode cutoff potential of 0V (whichever came first was used as the reference). After each charge cycle, all batteries needed to be discharged with a constant current of 1C0 until they reached a discharge cutoff voltage of 2.8V. The negative electrode potential was recorded when the State of Charge (SOC) reached 10%, 20%, 30%, ..., 80% at different charge rates. From this data, charge rate negative electrode potential curves were plotted at different SOCs, and the charge rate at which the negative electrode potential reached 0V at each SOC state was calculated by linear fitting. The charge rate is the charge window in the State of Charge (SOC) state, defined as C10%SOC, C20%SOC, C30%SOC, C40%SOC, C50%SOC, C60%SOC, C70%SOC, and C80%SOC, respectively. The charging time T (in min) required for the battery to charge from 10%SOC to 80%SOC was calculated according to the formula (60 / C20%SOC + 60 / C30%SOC + 60 / C40%SOC + 60 / C50%SOC + 60 / C60%SOC + 60 / C70%SOC + 60 / C80%SOC) × 10%. A shorter time indicates better rapid charging performance of the battery.

[0191] The test results are recorded in Table 4.

[0192] [Table 5A] [Table 5B]

[0193] From a comparison of Examples 1 to 5, the porous silicon anode material D V 50 changes directly affect the battery's cycle characteristics and charging capacity, particularly the D of porous silicon anode material. V It was found that the battery's charging capacity decreases as the value of 50 increases.

[0194] From a comparison of Examples 6-10, the D of elemental silicon V A change of 50 affects the battery's charging capacity and cycle characteristics, and the D content of elemental silicon. V It was found that as the value of 50 increases, both the battery's cycle characteristics and charging capacity decrease.

[0195] A comparison of Examples 11-14 revealed that changes in the thickness of the first coating layer containing dilithium metasilicate affect the battery's charging capacity and cycle characteristics. It was found that increasing the thickness of the first coating layer improves the battery's cycle characteristics but decreases its charging capacity.

[0196] A comparison of Examples 17-20 revealed that changes in the thickness of the silicon metal compound, which is the second coating layer, affect the battery's charging capacity and cycle characteristics. As the thickness of the second coating layer increases, the battery's cycle characteristics initially improve before declining, and the charging capacity gradually decreases. This is because the second coating layer improves the ability to suppress the expansion of the silicon material and thus improves cycle characteristics, but its poor conductivity worsens the dynamic characteristics as the coating thickness increases.

[0197] A comparison of Examples 1, 17, and 27 revealed that different coating methods significantly affect the battery's cycle characteristics and charging capacity.

[0198] From a comparison with Examples 1, 28-37, and Comparative Example 1, it was found that increasing the content of porous silicon anode material in the second film layer improves the battery's charging capacity. Furthermore, the particularly excellent specific capacity in Example 28 is due to the high content of porous silicon anode material in the first film layer, and the deterioration in cycle characteristics is also due to the high content of porous silicon anode material in the first film layer.

[0199] While the present application has been described with reference to preferred embodiments, various improvements and substitutions of components with equivalents can be made without departing from the scope of the application. In particular, each technical feature mentioned in each embodiment can be combined in any manner, provided that there is no structural inconsistency. The present application is not limited to the specific embodiments disclosed herein and includes all technical solutions included in the claims. [Explanation of Symbols]

[0200] 01 Current collector 02 First film layer 03 Second film layer 10 Porous silicon anode material 11 cores 12. First coating layer 13. Second coating layer 14. Third coating layer 111 Elemental Silicon 112 Silicon oxides 113 Silicon Metal Compounds 1 Battery pack 2 Upper cabinet 3 Lower cabinet 4 Battery Modules 5 Secondary battery 51 Housing 52 Electrode Assembly 53 Cap Assembly

Claims

1. It includes a current collector (01) and a negative electrode film layer, The negative electrode film layer is A first film layer (02) is provided on one or both sides of the current collector (01), The first film layer (02) includes a second film layer (03) provided on one side of the first film layer (02) away from the current collector (01), A negative electrode sheet in which the negative electrode active material in the first film layer (02) and the negative electrode active material in the second film layer (03) each independently contain a silicon-based negative electrode material, and the silicon-based negative electrode material in the second film layer (03) contains a porous silicon negative electrode material (10), and the content of the silicon-based negative electrode material in the first film layer (02) is less than the content of the silicon-based negative electrode material in the second film layer (03).

2. The surface density M1 of the first film layer (02) is 4.5 mg / cm². ２ ~20 mg / cm³ ２ The range is such that the surface density M2 of the second film layer (03) is 4.5 mg / cm². ２ ~20 mg / cm³ ２ The negative electrode sheet according to claim 1, wherein the weight ratio of the first film layer (02) to the second film layer (03) is in the range of 95:5 to 30:70, more selectively 90:10 to 40:60, the porosity of the first film layer (02) is in the range of 20% to 50%, the porosity of the second film layer (03) is in the range of 20% to 70%, the porosity of the negative electrode film layer is in the range of 20% to 70%, and the thickness of the second film layer (03) is selectively 10 μm to 20 μm.

3. The anode sheet according to claim 1 or 2, wherein the mass content of the silicon-based anode material in the first film layer (02) is 0.5% to 50%, and / or the mass content of the porous silicon anode material (10) in the second film layer (03) is 0.5% to 70%, and selectively, the mass content of the porous silicon anode material (10) in the anode film layer is 1% to 60%.

4. The anode sheet according to any one of claims 1 to 3, wherein the second film layer (03) comprises the porous silicon anode material (10), graphite anode material, binder, dispersant, and conductive agent, the conductive agent comprises one or more conductive carbon and carbon nanotubes, and selectively, the mass percentage of the porous silicon anode material (10) in the second film layer (03) is 0.5% to 70%, selectively, the mass percentage of the graphite anode material in the second film layer (03) is 25% to 90%, selectively, the mass percentage of the binder in the second film layer (03) is 1% to 8%, selectively, the mass percentage of the dispersant in the second film layer (03) is 0.5% to 2%, selectively, the mass percentage of the conductive carbon in the second film layer (03) is 0.5% to 5%, and selectively, the mass percentage of the carbon nanotubes in the second film layer (03) is 0.05% to 2%.

5. The first film layer (02) comprises the silicon-based anode material, graphite anode material, binder, dispersant, and conductive agent, wherein the conductive agent comprises one or more conductive carbon and carbon nanotubes, and selectively, the mass percentage of the silicon-based anode material in the first film layer (02) is 0.5% to 50%, selectively, the mass percentage of the graphite anode material in the first film layer (02) is 45% to 97.5%, selectively, the mass percentage of the binder in the first film layer (02) is 1% to 3%, and selectively, the mass percentage of the dispersant in the first film layer (02) is 0.3% to 1%. The negative electrode sheet according to any one of claims 1 to 4, wherein the mass percentage of conductive carbon in the first film layer (02) is 5%, and selectively, the mass percentage of carbon nanotubes in the first film layer (02) is 0 to 3%, and selectively, the mass percentage of carbon nanotubes in the first film layer (02) is 0 to 0.5%, and selectively, the silicon-based negative electrode material comprises any one or more of the group consisting of silicon material, silicon oxide material and porous silicon negative electrode material (10), and the content of the porous silicon negative electrode material (10) in the first film layer (02) is less than the content of the porous silicon negative electrode material (10) in the second film layer (03).

6. The Dv of the porous silicon negative electrode material (10) ５０ is between 3 μm and 20 μm, selectively between 4 μm and 15 μm, and / or the BET specific surface area of the porous silicon negative electrode material (10) is 1 m ２ / g to 30 m ２ / g, selectively between 6 m ２ / g and 20 m ２ / g. The negative electrode sheet according to any one of claims 1 to 5

7. The porous silicon anode material (10) is A porous silicon comprising elemental silicon and a silicon compound, wherein the silicon compound comprises a core (11) containing silicon oxide, A negative electrode sheet according to any one of claims 1 to 6, comprising a coating layer covering the surface of the core (11).

8. The negative electrode sheet according to claim 7, wherein the coating layer comprises one or more of a silicon metal compound, dilithium metasilicate, amorphous carbon, and carbon nanotubes.

9. The aforementioned coating layer is The surface of the core (11) is covered with a first coating layer (12) containing dilithium metasilicate, A second coating layer (13) covers the surface of the first coating layer (12) and contains a silicon metal compound, wherein the metal element of the silicon metal compound selectively contains Ti, Mg and / or Al. The negative electrode sheet according to claim 8, comprising a third coating layer (14) that covers the surface of the second coating layer (13) and contains amorphous carbon, wherein the amorphous carbon material selectively contains hard carbon and / or soft carbon.

10. The aforementioned coating layer is The surface of the core (11) is covered with a first coating layer (12) containing dilithium metasilicate, The negative electrode sheet according to claim 8, comprising a third coating layer (14) that covers the surface of the first coating layer (12) and contains amorphous carbon, wherein the amorphous carbon material selectively contains hard carbon and / or soft carbon.

11. The negative electrode sheet according to any one of claims 7, 8, or 10, wherein the silicon compound further comprises a silicon metal compound, the silicon metal compound coats the surface of the silicon element, and the metal element of the silicon metal compound selectively comprises Ti, Mg, and / or Al.

12. The negative electrode sheet according to any one of claims 9 to 11, wherein the third coating layer further comprises the carbon nanotubes.

13. In the first film layer (02) and the second film layer (03), the masses of the porous silicon anode material (10) are m1 and m2, respectively, and in the first film layer (02) and the second film layer (03), the mass percentages of carbon nanotubes belonging to the porous silicon anode material (10) are C1 and C2, respectively, and after removing the carbon nanotubes from the porous silicon anode material (10), the first film layer (02) and the The negative electrode sheet according to claim 12, wherein the masses of carbon nanotubes remaining in the two film layers (03) are S1 and S2, respectively, the first film layer (02) and the second film layer (03) are the first film layer (02) and the second film layer (03) per unit area, respectively, and satisfy the following relationships: (m2 × C2 + S2) / M2 = (m1 × C1 + S1) / M1, m2 ≥ m1, S1 ≥ S2, and S2 = m1 × m2 × (C2 - C1) / (m2 - m1).

14. The negative electrode sheet according to any one of claims 7 to 13, wherein the Dv50 of the elemental silicon is in the range of 0 < Dv50 ≤ 10 nm, and selectively, the Dv50 of the elemental silicon is in the range of 2 nm < Dv50 ≤ 8 nm.

15. The negative electrode sheet according to any one of claims 7 to 14, wherein the chemical formula of the silicon oxide is SiOx, where 0 < x ≤ 2, and the Dv50 of the silicon oxide is in the range of 2 μm ≤ Dv50 ≤ 13 μm.

16. The aforementioned dilithium metasilicate is Li ２ SiO ３ Li ２ Si ２ O ５ Li ４ SiO ４ Li ２ Si ３ O ７ Li ８ SiO ６ Li ６ Si ２ O ７ Li ４ Si ２ O ７ Li ２ Si ４ O ７ and LiSiO ３ The dilithium metasilicate comprises one or more of the following, and selectively, the dilithium metasilicate is at least Li ２ SiO ３ Including, and further selectively the Li ２ SiO ３ The mass of is at least 50% of the mass of the first coating layer, and further selectively the Li ２ SiO ３ The negative electrode sheet according to claim 9 or 10, wherein the mass of the first coating layer is at least 70% of the mass of the first coating layer.

17. The anode sheet according to any one of claims 9 to 16, wherein the thickness of the first coating layer is 10% to 80% of the particle radius of the porous silicon anode material (10), selectively the thickness of the second coating layer is 1 nm to 50 nm, selectively the thickness of the third coating layer is 1 nm to 1000 nm, and selectively 5 nm to 300 nm.

18. A secondary battery comprising a positive electrode sheet, a negative electrode sheet, a separator, and an electrolyte, wherein the negative electrode sheet is the negative electrode sheet described in any one of claims 1 to 17.

19. A power consumption device comprising a secondary battery selected from the secondary batteries described in claim 18.

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