A negative electrode sheet, a secondary battery, and an electric device

Abstract

This application provides a negative electrode sheet, a secondary battery, and an electrical device. The negative electrode sheet includes a current collector and a negative electrode film. The negative electrode film includes: a first film layer disposed on one or both sides of the current collector; and a second film layer disposed on the side of the first film layer away from the current collector. The negative electrode active materials in the first and second film layers each independently include silicon-based negative electrode materials, and the silicon-based negative electrode material in the second film layer includes porous silicon negative electrode materials. The content of silicon-based negative electrode material in the first film layer is less than the content of silicon-based negative electrode material in the second film layer. This improves the charging capacity and cycle performance of the secondary battery.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of batteries, in particular to a negative electrode sheet, a secondary battery and an electric device. BACKGROUND

[0002] Lithium ion batteries have the advantages of high energy density, high power density and long cycle life, and are widely used in portable electronic devices such as notebook computers, mobile phones, digital cameras and other electronic products. In recent years, with the rapid development of new energy and clean energy vehicles, higher requirements have been put forward for the performance and safety of new power batteries and energy storage batteries, and the demand for batteries that can withstand various extreme working conditions is also increasing.

[0003] At present, in order to improve the performance of lithium ion batteries, many researches are focused on the development and improvement of electrode materials and electrolytes. For example, silicon material has a high theoretical specific capacity (> 4000 mAh / g), which is much higher (about 10 times) than graphite which has reached the limit capacity, and the voltage to lithium is not high, which is expected to become the first choice of high energy density batteries. Although using silicon negative electrode to replace part of the traditional graphite negative electrode can improve the gram capacity of the negative active material, however, silicon will produce severe volume expansion during lithium intercalation / deintercalation, which will cause the silicon material to be easily pulverized and fall off from the electrode sheet during the cycle process, thereby losing the contact between the current collector and the active material, and failing to fully play the activity of the silicon material. SUMMARY

[0004] The present application provides a negative electrode sheet, a secondary battery and an electric device to improve the charging capacity and cycle performance of the secondary battery.

[0005] In a first aspect of the present application, a negative electrode sheet is provided, comprising a current collector and a negative film layer, the negative film layer comprising: a first film layer arranged on one side or both sides of the current collector; a second film layer arranged on the side of the first film layer away from the current collector; the negative active material in the first film layer and the negative active material in the second film layer each independently comprises a silicon-based negative material, and the silicon-based negative material in the second film layer comprises a porous silicon negative material, the content of the silicon-based negative material in the first film layer is less than the content of the silicon-based negative material in the second film layer.

[0006] The negative pole piece of the present application contains silicon-based negative pole material in the lower first film layer, thereby improving the energy density of the negative pole piece, and the relatively small amount of silicon-based negative pole material in the lower first film layer effectively alleviates the problem of peeling from the current collector caused by the pulverization of the silicon-based negative pole material during the cycle process. The second film layer on the surface contains porous silicon negative pole material, thereby effectively avoiding the problem of reduced battery capacity caused by the use of pore-forming agents such as porous carbon; and the porous silicon negative pole material can increase the surface porosity, improve the defect that lithium ions cannot be embedded into the negative pole of the pole piece due to the damage to the surface porosity caused by rolling; and the content of silicon-based negative pole material in the upper second film layer is greater than that in the lower first film layer, especially the upper layer contains porous silicon negative pole material, so the upper layer preferentially embeds lithium, the lithium embedding path is shorter, the kinetics is better, thereby improving the charging capacity of the negative pole piece and effectively alleviating lithium precipitation, thereby improving the cycle performance of the battery.

[0007] In any embodiment of the first aspect, the surface density M1 of the first film layer is in the range of 4.5 mg / cm 2 ~20 mg / cm 2 , the surface density M2 of the second film layer is in the range of 4.5 mg / cm 2 ~20 mg / cm 2 .

[0008] In any embodiment of the first aspect, the weight ratio of the first film layer and the second film layer is 95:5~30:70, and further optionally 90:10~40:60. The synergistic effect of the two film layers is improved.

[0009] In any embodiment of the first aspect, the porosity of the first film layer is in the range of 20%~50%, the porosity of the second film layer is in the range of 20%~70%, and the porosity of the negative pole film layer is in the range of 20%~70%, which can improve the lithium ion embedding capacity and increase the gram capacity of the negative pole piece.

[0010] In any embodiment of the first aspect, the thickness of the second film layer is 10 μm ~20 μm, which sufficiently solves the problem of negative pole piece surface porosity being crushed caused by rolling.

[0011] In any embodiment of the first aspect, the mass content of silicon-based negative pole material in the first film layer is 0.5%~50%, and / or the mass content of porous silicon negative pole material in the second film layer is 0.5%~70%, and optionally, the mass content of porous silicon negative pole material in the negative pole film layer is 1%~60%. The silicon-based negative pole material in the two film layers is used to improve the gram capacity of the negative pole piece as much as possible.

[0012] 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 of conductive carbon and carbon nanotubes; optionally, the porous silicon anode material comprises 0.5% to 70% by mass in the second film layer; optionally, the graphite anode material comprises 25% to 90% by mass in the second film layer; optionally, the binder comprises 1% to 8% by mass in the second film layer; optionally, the dispersant comprises 0.5% to 2% by mass in the second film layer; optionally, the conductive carbon comprises 0.5% to 5% by mass in the second film layer; optionally, the carbon nanotubes comprise 0.05% to 2% by mass in the second film layer. By employing a combination of porous silicon anode material and graphite anode material, the structural stability of the graphite anode material is utilized to improve the volume stability of the second film layer during cycling, while the porous silicon anode material is used to improve the specific capacity and lithium-ion transport capability of the second film layer.

[0013] 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 of conductive carbon and carbon nanotubes; optionally, the silicon-based anode material comprises 0.5% to 50% by mass in the first film layer; optionally, the graphite anode material comprises 45% to 97.5% by mass in the first film layer; optionally, the binder comprises 1% to 3% by mass in the first film layer; optionally, the dispersant comprises 0.3% to 1.5% by mass in the first film layer; optionally, the conductive carbon comprises 0% to 3% by mass in the first film layer; optionally, the carbon nanotubes comprise 0% to 0.5% by mass in the first film layer. The combination of silicon-based and graphite anode materials improves the adhesion stability between the first film layer and the current collector, and can also increase the specific capacity of the first film layer to a certain extent.

[0014] In any embodiment of the first aspect, the silicon-based anode material of the first film layer includes any one or more of the group consisting of silicon material, silicon-oxygen material, and porous silicon anode material, and the content of porous silicon anode material in the first film layer is less than the content of porous silicon anode material in the second film layer, thereby improving the uniformity of the overall pore size of the anode film layer.

[0015] In any embodiment of the first aspect, the Dv of the aforementioned porous silicon anode material 50 The diameter is between 3μm and 20μm, and can be selected between 4μm and 15μm; and / or the BET specific surface area of ​​the porous silicon anode material is 1m². 2 / g~30m 2 Between / g; optionally in 6m 2 / g~20m 2between 3000 mAh / g and 4000 mAh / g. In order to further improve the volume energy density of the negative electrode sheet.

[0016] In any embodiment of the first aspect, the porous silicon negative electrode material comprises: a core, the core being porous silicon, the porous silicon comprising silicon element and a compound of silicon, the compound of silicon comprising an oxide of silicon; a cladding layer, the cladding layer being cladded on the surface of the core. The porous silicon negative electrode material with a core-shell structure can improve the energy density of the negative electrode sheet, relieve the volume expansion of the silicon-based negative electrode material, and improve the cycle stability of the high-energy-density battery.

[0017] In any embodiment of the first aspect, the cladding layer comprises any one or more of a metal compound of silicon, lithium silicate, amorphous carbon, and carbon nanotube. Cladding the one or more materials can improve the mechanical structural stability or electrical conductivity of the porous silicon negative electrode material.

[0018] In any embodiment of the first aspect, the cladding layer comprises: a first cladding layer, the first cladding layer being cladded on the surface of the core, the first cladding layer comprising lithium silicate; a second cladding layer, the second cladding layer being cladded on the surface of the first cladding layer, the second cladding layer comprising a metal compound of silicon, and optionally the metal element of the metal compound of silicon comprises Ti, Mg, and / or Al; and a third cladding layer, the third cladding layer being cladded on the surface of the second cladding layer, the third cladding layer comprising amorphous carbon, and optionally the material of the amorphous carbon comprises hard carbon and / or soft carbon. The first cladding layer comprising lithium silicate can generate lithium salt and inert phase (lithium oxide) during lithium intercalation, the generation of lithium salt can reduce the consumption of lithium ions in the positive electrode active material during the first lithium intercalation, so that the battery has a higher first coulomb efficiency, and the generation of inert phase can effectively relieve the volume expansion and improve the cycle performance of the battery. The second cladding layer arranged between the first cladding layer and the third cladding layer comprises a metal compound of silicon, which has strong mechanical strength and can buffer the volume expansion of the internal silicon material to improve the cycle performance. The third cladding layer can buffer the volume expansion of the first cladding layer on the one hand to improve the cycle performance, and on the other hand can improve the protection of the first cladding layer to avoid direct contact of the first cladding layer with water and prevent the dissolution of lithium silicate in the first cladding layer and gas production.

[0019] In any embodiment of the first aspect, the compound of silicon further comprises a metal compound of silicon, the metal compound of silicon being cladded on the surface of the silicon element, and optionally the metal element of the metal compound of silicon comprises Ti, Mg, and / or Al. Cladding the metal compound of silicon on the surface of the silicon element can buffer the volume expansion of the silicon element to improve the cycle performance.

[0020] In any embodiment of the first aspect, the coating layer comprises: a first coating layer coated on the surface of the core, the first coating layer comprising lithium silicate; and a third coating layer coated on the surface of the first coating layer, the third coating layer comprising amorphous carbon, which may comprise hard carbon and / or soft carbon. The first coating layer comprises lithium silicate, which can generate lithium salt and inert phase (lithium oxide) during lithium intercalation, the generation of lithium salt can reduce the consumption of lithium ions in the positive active material during the first lithium intercalation, so that the battery has a higher first coulomb efficiency, and the generation of inert phase can effectively alleviate the volume expansion and improve the cycle performance of the battery; the third coating layer can buffer the volume expansion of the first coating layer and improve the cycle performance, and can also improve the protection of the first coating layer, avoid direct contact between the first coating layer and water, and prevent the dissolution and gas production of lithium silicate in the first coating layer.

[0021] In any embodiment of the first aspect, the third coating layer further comprises carbon nanotubes, which can improve the conductivity of the porous silicon negative electrode material, and can also realize sufficient binding of the porous silicon negative electrode material, alleviate the volume expansion during charging and discharging, control the polarization in the negative electrode cell, and improve the cycle performance of the cell.

[0022] In any embodiment of the first aspect, the mass of the porous silicon negative electrode material in the first film layer and the second film layer is m1 and m2 respectively; the mass percentage of the carbon nanotubes in the porous silicon negative electrode material in the first film layer and the second film layer is C1 and C2 respectively; the mass of the remaining carbon nanotubes in the first film layer and the second film layer excluding the carbon nanotubes in the porous silicon negative electrode material is 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 following relationship: (m2xC2+S2) / M2=(m1xC1+S1) / M1, m2≥m1, S1≥S2, S2=m1xm2x(C2-C1) / (m2-m1). The above relationship can limit the use of carbon nanotubes, further improve the binding capacity of the silicon-based negative electrode, effectively inhibit the rebound of the negative electrode sheet, and minimize the polarization of the negative electrode sheet.

[0023] In any embodiment of the first aspect, the Dv50 of the silicon element is in the range of 0<Dv50≤10 nm; optionally, the Dv50 of the silicon element is in the range of 2 nm<Dv50≤8 nm. The use of nanoscale silicon element is conducive to the mixing of silicon oxide, which is conducive to improving the energy density of the battery and reducing the coating difficulty of the core structure and improving the cycle stability of the battery.

[0024] In any embodiment of the first aspect, the chemical formula of the silicon oxide is SiOx, where 0 < x ≤ 2; the Dv50 range of the silicon oxide is: 2 μm ≤ Dv50 ≤ 13 μm. This is beneficial for mixing with elemental silicon and improving the energy density of the battery.

[0025] In any embodiment of the first aspect, the lithium silicate comprises one or more of Li₂SiO₃, Li₂Si₂O₅, Li₄SiO₄, Li₂Si₃O₇, Li₈SiO₆, Li₆Si₂O₇, Li₄Si₂O₇, Li₂Si₄O₇, and LiSiO₃; optionally, the lithium silicate comprises at least Li₂SiO₃, further optionally the mass of Li₂SiO₃ is at least 50% of the mass of the first coating layer, and even more optionally the mass of Li₂SiO₃ is at least 70% of the mass of the first coating layer. This allows the first coating layer to effectively reduce the consumption of lithium ions in the positive electrode active material during the initial lithium intercalation process, resulting in a higher initial coulombic efficiency of the battery.

[0026] 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; optionally, the thickness of the second coating layer is 1 nm to 50 nm; optionally, the thickness of the third coating layer is 1 nm to 1000 nm, or optionally 5 nm to 300 nm. Within the above thickness range, the particles effectively reduce the volume expansion of the anode material while increasing the battery energy density, thereby improving the cycle stability of the high-energy-density battery.

[0027] A second aspect of this application provides a secondary battery, comprising a positive electrode, a negative electrode, a separator, and an electrolyte, wherein the negative electrode is any of the aforementioned types. The secondary battery of this application exhibits good charging capability, high energy density, and good cycle performance.

[0028] A third aspect of this application provides an electrical device including a secondary battery selected from the secondary batteries described above. The electrical device of this application offers improved safety. Attached Figure Description

[0029] To more clearly illustrate the technical solutions of the embodiments of this application, the drawings used in the embodiments of this application will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on the drawings without creative effort.

[0030] Figure 1 This is a schematic diagram of the structure of a negative electrode sheet provided in one embodiment of this application.

[0031] Figure 2This is a schematic diagram of the structure of a porous silicon anode material provided in one embodiment of this application.

[0032] Figure 3 This is a schematic diagram of the structure of a porous silicon anode material provided in another embodiment of this application.

[0033] Figure 4 This is a schematic diagram of the structure of a porous silicon anode material provided in another embodiment of this application.

[0034] Figure 5 This is a schematic diagram of a secondary battery according to one embodiment of this application.

[0035] Figure 6 yes Figure 5 An exploded view of a secondary battery according to one embodiment of this application is shown.

[0036] Figure 7 This is a schematic diagram of a battery module according to one embodiment of this application.

[0037] Figure 8 This is a schematic diagram of a battery pack according to one embodiment of this application.

[0038] Figure 9 yes Figure 8 An exploded view of a battery pack according to one embodiment of this application is shown.

[0039] Figure 10 This is a schematic diagram of an electrical device that uses a secondary battery as a power source according to one embodiment of this application.

[0040] The accompanying drawings are not drawn to scale.

[0041] Explanation of reference numerals in the attached figures:

[0042] 01 Current collector; 02 First membrane layer; 03 Second membrane layer;

[0043] Porous silicon anode material; 10; 11 Core; 12 First coating layer; 13 Second coating layer; 14 Third coating layer; 111 Elemental silicon; 112 Oxide of silicon; 113 Metallic compound of silicon;

[0044] 1 Battery pack; 2 Upper housing; 3 Lower housing; 4 Battery module; 5 Secondary battery; 51 Housing; 52 Electrode assembly; 53 Top cover assembly. Detailed Implementation

[0045] The embodiments of this application will be described in further detail below with reference to the accompanying drawings and examples. The detailed description of the following embodiments and the accompanying drawings are used to illustrate the principles of this application by way of example, but should not be used to limit the scope of this application, that is, this application is not limited to the described embodiments.

[0046] The following detailed description, with appropriate reference to the accompanying drawings, specifically discloses embodiments of the negative electrode, secondary battery, and power-consuming device of this application. However, unnecessary detailed descriptions may be omitted. For example, detailed descriptions of well-known matters and repetitive descriptions of practically identical structures may be omitted. This is to avoid unnecessarily lengthy descriptions and to facilitate understanding by those skilled in the art. Furthermore, the accompanying drawings and the following description are provided for the purpose of enabling those skilled in the art to fully understand this application and are not intended to limit the subject matter of the claims.

[0047] The "range" disclosed in this application is defined by a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, which define the boundaries of a particular range. Ranges defined in this way can include or exclude endpoints and can be arbitrarily combined; that is, any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60~120 and 80~110 are listed for a specific parameter, it is also expected that ranges of 60~110 and 80~120 are also included. Furthermore, if minimum range values ​​of 1 and 2 are listed, and if maximum range values ​​of 3, 4, and 5 are listed, then the following ranges are all expected: 1~3, 1~4, 1~5, 2~3, 2~4, and 2~5. In this application, unless otherwise stated, the numerical range "a~b" represents a shortened representation of any combination of real numbers between a and b, where a and b are real numbers. For example, the numerical range "0~5" indicates that all real numbers between "0~5" have been listed in this article; "0~5" is simply a shortened representation of these numerical combinations. Furthermore, when a parameter is stated 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.

[0048] Unless otherwise specified, all embodiments and optional embodiments of this application can be combined to form new technical solutions.

[0049] Unless otherwise specified, all technical features and optional technical features of this application may be combined to form new technical solutions.

[0050] Unless otherwise specified, all steps in this application may be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), indicating that the method may include steps (a) and (b) performed sequentially, or it may include steps (b) and (a) performed sequentially. For example, the mention that the method may also include step (c) indicates that step (c) may be added to the method in any order. For example, the method may include steps (a), (b), and (c), or it may include steps (a), (c), and (b), or it may include steps (c), (a), and (b), etc.

[0051] Unless otherwise specified, the terms "comprising" and "including" as used in this application can be open-ended or closed-ended. For example, "comprising" and "including" can mean that other components not listed may also be included, or that only the listed components may be included.

[0052] Unless otherwise specified, the term "or" is inclusive in this application. For example, the phrase "A or B" means "A, B, or both A and B". More specifically, the condition "A or B" is satisfied by any of the following conditions: A is true (or exists) and B is false (or does not exist); A is false (or does not exist) and B is true (or exists); or both A and B are true (or exist).

[0053] [Rechargeable Battery]

[0054] Secondary batteries, also known as rechargeable batteries or storage batteries, are batteries that can be recharged after being discharged to activate the active materials and continue to be used.

[0055] Typically, a secondary battery consists of a positive electrode, a negative electrode, a separator, and an electrolyte. During charging and discharging, active ions (such as lithium ions) repeatedly insert and extract between the positive and negative electrodes. The separator, positioned between the positive and negative electrodes, primarily prevents short circuits while allowing active ions to pass through. The electrolyte, also positioned between the positive and negative electrodes, mainly serves to conduct active ions.

[0056] [Negative electrode plate]

[0057] In the research process of improving the performance of lithium-ion batteries, many studies have gradually discovered that a reasonable electrode structure design is crucial for the ion and electron transport pathways within the entire electrode. By optimizing the electrode structure, the conductivity and electrolyte wetting properties of the electrode can be improved, thereby increasing the transport rate of electrons and ions throughout the electrode and ultimately enhancing the battery's energy density and rate capability. However, obtaining a thick electrode that possesses both excellent electron / ion transport characteristics and a high loading of active materials remains a significant challenge.

[0058] For example, even with multi-layered coated thick electrode sheets, the surface pores at a depth of about 10-20 μm are still blocked during the rolling process, preventing lithium ions in the electrolyte from effectively diffusing into the electrode interior and significantly reducing charging capacity. To address this issue, some technologies increase surface porosity by adding pore-forming agents to the surface film of the negative electrode sheet, such as using porous carbon. However, the use of porous carbon leads to a loss of energy density in the electrode sheet, thereby reducing the specific capacity of the battery. To solve the above problems, a typical embodiment of this application provides a negative electrode sheet, such as...Figure 1 As shown, the negative electrode includes a current collector 01 and a negative electrode film. The negative electrode film includes a first film layer 02 and a second film layer 03. The first film layer 02 is disposed on one or both sides of the current collector 01. The second film layer 03 is disposed 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 silicon-based negative electrode material, and the silicon-based negative electrode material in the second film layer 03 includes porous silicon negative electrode material 10. The content of silicon-based negative electrode material in the first film layer 02 is less than the content of silicon-based negative electrode material in the second film layer 03.

[0059] In the negative electrode of this application, the lower first film layer 02 contains silicon-based negative electrode material, thereby increasing the energy density of the negative electrode. Simultaneously, the relatively low content of silicon-based negative electrode material in the lower first film layer 02 effectively alleviates the problem of silicon-based negative electrode material pulverizing and peeling off from the current collector 01 during cycling. The surface second film layer 03 contains porous silicon negative electrode material 10, thus effectively avoiding the problem of reduced battery specific capacity caused by the use of pore-forming agents such as porous carbon. Furthermore, the porous silicon negative electrode material 10 increases surface porosity, improving the defect where lithium ions cannot be intercalated into the negative electrode due to damage to surface pores caused by rolling. Moreover, the content of silicon-based negative electrode material in the upper second film layer 03 is greater than that in the lower first film layer 02, especially with the presence of porous silicon negative electrode material 10 in the upper layer. Therefore, lithium intercalation is preferentially performed in the upper layer, resulting in a shorter lithium intercalation path and better kinetics, thereby improving the charging capability of the negative electrode and effectively alleviating lithium plating, thus improving the battery's cycle performance.

[0060] The first film layer 02 can be directly disposed on the current collector 01 or a base layer can be disposed between the first film layer 02 and the current collector 01; the second film layer 03 can be directly disposed on the first film layer 02 or other negative electrode film layers can be disposed between the two, as long as the second film layer 03 is located on the surface of the negative electrode sheet.

[0061] The content determination of the aforementioned silicon-based anode material can be performed using the following method: First, prepare multiple anode sample samples with different mass ratios, obtained by mixing silicon-based anode material and graphite material (if other anode materials are being measured in the anode sample, the type of material in the anode sample being measured can be used as a reference for preparing the anode sample); Second, take samples from each sample and perform energy dispersive spectroscopy (EDS) analysis using a scanning electron microscope to obtain the relative mass percentage of silicon in each anode sample; Third, determine the relative mass percentage of silicon in each anode sample... Using the content as the abscissa and the mass percentage of silicon-based anode material in each anode sample as the ordinate, a standard curve is plotted and fitted to obtain a quantitative relationship. In the fourth step, for the anode sheet to be tested, the thickness of the upper and lower film layers is confirmed by CP (ion beam) sectioning. Then, using the powder scraping method, the powder of the upper second film layer is scraped out first, and the powder of the lower first film layer is scraped out. The relative mass percentage of silicon element in each layer is measured, and the mass percentage of silicon-based anode material in the first and second film layers to be tested is calculated according to the quantitative relationship.

[0062] In some embodiments, the areal density M1 of the first film layer 02 is in the range of 4.5 mg / cm³. 2 ~20mg / cm 2 The areal density M2 of the second film layer 03 mentioned above is in the range of 0.2 mg / cm³. 2 ~20mg / cm 2 The aforementioned weight range ensures the effective thickness of the two film layers. In some embodiments, the areal density M1 of the first film layer O2 can be 4.5 mg / cm³. 2 5mg / cm 22 7mg / cm 2 10mg / cm 2 15mg / cm 2 and 20mg / cm 2 Preferably 5 mg / cm 2 ~7mg / cm 2 In some embodiments, the areal density M2 of the second film layer 03 can be 0.2 mg / cm³. 2 0.3 mg / cm 2 0.4 mg / cm 2 1mg / cm 2 2mg / cm 2 3mg / cm 2 5mg / cm 2 10mg / cm 2 17mg / cm 2 and 20mg / cm 2 Preferably 0.3 mg / cm 2 ~17mg / cm2 .

[0063] The main function of the second film layer 03 in this application is to increase the surface porosity by utilizing the porous silicon anode material 10 therein. In some embodiments, the weight ratio of the first film layer 02 and the second film layer 03 is 95:5 to 30:70, and can be further selected as 90:10 to 40:60, such as 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 body of the anode film layer, the main function of the anode electrode is brought into play, and the second film layer 03 is used to compensate for the defects of the first film layer 02, thereby improving the synergistic effect of the two film layers.

[0064] 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%. The negative electrode film layer with the above porosity can both improve the lithium-ion intercalation capability by utilizing the porosity and increase the specific capacity of the negative electrode sheet by utilizing the negative electrode active material.

[0065] In some embodiments, the thickness of the second film layer 03 is 10μm to 20μm, such as 10μm, 12μm, 15μm, 18μm or 20μm. This thickness effectively solves the problem caused by the pores on the surface of the negative electrode sheet being crushed due to rolling.

[0066] The method for determining the weight of the two film layers can be referred to as follows: confirm the thickness of the upper and lower film layers through the CP cross section, and then use the powder scraping method to first scrape off the powder of the upper second film layer and weigh it; then scrape off the powder of the lower first film layer and weigh it, so that the weight and ratio of the first film layer and the second film layer can be obtained respectively.

[0067] The above-mentioned method for determining porosity can be referred to as follows: take a CP cross-section photo, scan it with imaging software, calculate the porosity of the corresponding cross-section and the first film layer 02 and the second film layer 03, and then take multiple CP cross-section scan photos and calculate the porosity of the first film layer 02 and the second film layer 03 in the electrode sheet by software.

[0068] To maximize the energy density of the negative electrode, in some embodiments, the mass content of the silicon-based negative electrode material in the first film layer 02 is 0.5% to 50%, optionally 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%, optionally 5% to 65%, 10% to 60%, or 1% to 70%. The content of porous silicon anode material 10 in the anode film layer is 5%~55% or 20%~50%, for example, 5%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, or 70% by mass. Alternatively, the content of porous silicon anode material 10 in the anode film layer is 1%~60%, which can be selected as 5%~55%, 5%~25%, 5%~20%, or 10%~20%, for example, 1%, 5%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, or 60%. This is to maximize the specific capacity of the anode electrode by utilizing the silicon-based anode material in both film layers.

[0069] In some embodiments, in addition to silicon-based anode materials, the anode active material may also employ anode active materials known in the art for use in batteries. As an 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, and lithium titanate, etc. Tin-based materials may be selected from at least one of elemental tin, tin oxides, and tin alloys. However, this application is not limited to these materials, and other conventional materials that can be used as battery anode active materials may also be used. These anode active materials may be used alone or in combination of two or more.

[0070] In addition to the negative electrode active material, the first and second films of this application also contain binders, dispersants, and conductive agents commonly found in negative electrode films. In some embodiments, the second film includes a porous silicon negative electrode material, a graphite negative electrode material, a binder, a dispersant, and a conductive agent, wherein the conductive agent comprises one or more of conductive carbon and carbon nanotubes. Optionally, the porous silicon negative electrode material has a mass percentage content of 0.5% to 70% in the second film; optionally, the graphite negative electrode material has a mass percentage content of 25% to 90% in the second film; optionally, the binder has a mass percentage content of 1% to 8% in the second film; optionally, the dispersant has a mass percentage content of 0.5% to 2% in the second film; optionally, the conductive carbon has a mass percentage content of 0.5% to 5% in the second film; optionally, the carbon nanotubes have a mass percentage content of 0.05% to 2% in the second film. A combination of porous silicon anode material and graphite anode material is used. The structural stability of the graphite anode material is used to improve the volume stability of the second film layer during cycling, while the porous silicon anode material is used to improve the specific capacity and lithium-ion transport capability of the second film layer.

[0071] In some embodiments, as an example, the adhesive includes 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).

[0072] In some embodiments, as an example, the conductive agent includes at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0073] In some embodiments, as an example, the dispersant includes at least one of sodium carboxymethyl cellulose (CMC), polyvinylpyrrolidone (PVP), and polyacrylamide (PAM).

[0074] In some embodiments, the first film layer includes 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 of conductive carbon and carbon nanotubes; optionally, the silicon-based anode material has a mass percentage content of 0.5% to 50% in the first film layer; optionally, the graphite anode material has a mass percentage content of 45% to 97.5% in the first film layer; optionally, the binder has a mass percentage content of 1% to 3% in the first film layer; optionally, the dispersant has a mass percentage content of 0.3% to 1.5% in the first film layer; optionally, the conductive carbon has a mass percentage content of 0% to 3% in the first film layer; optionally, the carbon nanotubes have a mass percentage content of 0% to 0.5% in the first film layer. The content of graphite anode material in the first film layer is higher than that in the second film layer, thus improving the structural stability of the first film layer and the adhesion stability of the current collector; moreover, the addition of silicon-based anode material can improve the specific capacity of the first film layer to a certain extent.

[0075] In addition, the carbon nanotubes in the conductive agent of the first and second films have better conductivity, and the linear structure of the carbon nanotubes plays a certain role in binding the silicon-based anode material, effectively alleviating the volume expansion of the silicon-based anode material, reducing its pulverization, and thus improving the cycle performance of the battery.

[0076] In some embodiments, the silicon-based anode material of the first film layer includes any one or more of the group consisting of silicon material, silicon-oxygen material, and porous silicon anode material, or the silicon-based anode material of the first film layer is a porous silicon anode material, provided that the content of porous silicon anode material in the first film layer is less than the content of porous silicon anode material in the second film layer. This improves the uniformity of the overall pore size of the anode film layer.

[0077] In some embodiments, the Dv of the above-mentioned porous silicon anode material 50 The surface area is between 3μm and 20μm, for example, 3μm, 4μm, 5μm, 7μm, 10μm, 12μm, 15μm or 20μm, with a selectable range of 4μm to 15μm; and / or the BET specific surface area of ​​the porous silicon anode material is between 1 and 30m². 2 Between / g; optionally in 6 m 2 / g~20m 2 Between / g. This is to further improve the cycle performance and charging capability of the negative electrode.

[0078] The Dv50 value mentioned above can be determined using a laser particle size analyzer (such as a MalvernMaster Size 3000) in accordance with standard GB / T 19077.1-2016. Dv50 refers to the particle size corresponding to a cumulative volume distribution percentage of 50% for the measured material.

[0079] The BET specific surface area is the specific surface area of ​​the material determined using the low-temperature nitrogen adsorption-desorption method.

[0080] Material porosity: The porosity of silicon-based anode materials can be measured using a true density porosity tester (such as AccuPyc II 1340).

[0081] The porous silicon anode material of this application can be a commonly used porous silicon anode material in the art, such as a simple porous silicon material or a coated porous silicon material. In some embodiments, such as... Figures 2 to 4 As shown, the aforementioned porous silicon anode material includes a core 11 and a coating layer. The core 11 is porous silicon, comprising elemental silicon 111 and silicon compounds, including silicon oxide 112. The coating layer is applied to the surface of the core. This core-shell structure of the porous silicon anode material improves the charging capability of the anode sheet while mitigating volume expansion in silicon-based anode materials, thus improving the cycle stability of high-energy-density batteries. Those skilled in the art can obtain the composition of the porous silicon core in the porous silicon material by excluding the material in the outer coating layer using nuclear magnetic resonance (NMR) technology (such as a BRUKERAVANCE Ⅲ HD 500MHz device).

[0082] Elemental silicon possesses a high theoretical lithium intercalation capacity (approximately 4200 mAh / g) and a low lithium intercalation potential, making it a promising candidate for battery applications. However, its significant volume expansion effect leads to poor cycle stability. Silicon oxides, on the other hand, are binary compounds composed of silicon and oxygen. Their volume expansion effect is smaller than that of elemental silicon, thus mitigating the volume expansion effect and improving battery cycle stability.

[0083] In some embodiments, the coating layer includes one or more of silicon metal compounds, lithium silicate, amorphous carbon, and carbon nanotubes. By coating with one or more of these materials, the mechanical structural stability or conductivity of the porous silicon anode material can be improved. The coating methods for these materials can be varied; where feasible, it can be a single-layer coating or multiple layers of coating for each material.

[0084] "Lithium silicate" refers to a series of compounds formed by the reaction of metallic lithium with silicic acid; "amorphous carbon" refers to a transitional state of carbon, such as allotropes of carbon, and usually refers to carbon elements other than graphite and diamond.

[0085] like Figure 2As shown, in some embodiments, the coating layer includes a first coating layer 12 and a third coating layer 14. The first coating layer 12 is coated on the surface of the core 11 and includes lithium silicate. The third coating layer 14 is coated on the surface of the first coating layer 12 and includes amorphous carbon. Optionally, the amorphous carbon material includes hard carbon and / or soft carbon. The first coating layer includes lithium silicate, which can generate lithium salt and an inert phase (lithium oxide) during the lithium intercalation process. The generation of lithium salt can reduce the consumption of lithium ions in the positive electrode active material during the first lithium intercalation process, so that the battery has a higher first coulombic efficiency and charging capacity. The generation of the inert phase can effectively alleviate volume expansion and improve the cycle performance of the battery. The third coating layer can buffer the volume expansion of the first coating layer and improve the cycle performance. On the other hand, it can improve the protection of the first coating layer, prevent the first coating layer from directly contacting water, and prevent the dissolution and gas generation of lithium silicate in the first coating layer.

[0086] Figure 2 The porous silicon anode material shown can be prepared using the following methods:

[0087] 1. Silicon suboxide is synthesized from silicon grains and silicon dioxide through vapor deposition. The density of silicon suboxide is adjusted by regulating the vapor deposition temperature between 600℃ and 1200℃. V 50. Disperse silica particles in water, then add polyvinylpyrrolidone (molar ratio of silica to polyvinylpyrrolidone is 5~15:1), heat to boiling and reflux for 2h~5h, cool to room temperature, then add an inorganic alkaline solution (concentration of 0.01mmol / L~0.1mmol / L, such as sodium hydroxide solution), stir and etch for several hours. Centrifuge the resulting suspension, wash with water 2-3 times, dry at 100℃~110℃ for 1h~3h, and then calcine in a muffle furnace at 500℃~600℃ for 3h~5h to obtain porous silica. As the core structure, the D of the porous silica is adjusted by grinding. V 50 distribution, for example, adjusting the grinding time between 0.5h and 24h to make D V 50 changes, and can be further analyzed by screening D. V 50 will be further adjusted;

[0088] 2. Amorphous carbon: Amorphous carbon sources such as asphalt are mixed with the above-mentioned core structure and then subjected to high-temperature treatment for 1h to 10h (for example, the amorphous carbon source and the core structure are mixed at a mass ratio of 0.01:1 to 0.1:1), with the temperature controlled at 700℃ to 1500℃, to obtain a coating layer containing amorphous carbon.

[0089] 3. Mix the material obtained in step 2 with a lithium source (for example, mix the material obtained in step 2 with a lithium source at a mass ratio of 1:0.09 to 1:0.2), such as lithium powder, lithium hydride, lithium oxide, lithium carbonate or organic lithium, and treat it at a high temperature of 300℃ to 1000℃ for 1h to 5h. Lithium ions will pass through the amorphous carbon coating layer and form a first coating layer containing lithium silicate on the core structure inside the amorphous carbon.

[0090] 4. Finally, the material obtained in step 3 is mixed with the carbon nanotube solution, wherein the mass ratio of the material obtained in step 3 to the carbon nanotube is 1:0.02~1:0.1. The mixture undergoes a bonding reaction at a high temperature of 100℃~400℃, coating the carbon nanotube onto the surface of the material to form a third coating layer consisting of amorphous carbon material and carbon nanotube.

[0091] like Figure 3 As shown, in some embodiments, the aforementioned coating layer includes a first coating layer 12, a second coating layer 13, and a third coating layer 14. The first coating layer 12 coats the surface of the core 11 and comprises lithium silicate. The second coating layer 13 coats the surface of the first coating layer 12 and comprises a silicon metal compound, optionally including Ti, Mg, and / or Al as the metal element. The third coating layer 14 coats the surface of the second coating layer 13 and comprises amorphous carbon, optionally including hard carbon and / or soft carbon. Further, a second coating layer disposed between the first and third coating layers comprises a silicon metal compound, which has strong mechanical strength and can buffer the volume expansion of the internal silicon material, improving cycle performance.

[0092] Figure 3 The porous silicon anode material shown can be prepared using the following methods:

[0093] 1. Silicon suboxide is synthesized from silicon grains and silicon dioxide by vapor deposition. The silicon suboxide particles are dispersed in water, and then polyvinylpyrrolidone (molar ratio of silicon dioxide to silicon dioxide is 5~15:1) is added. The mixture is heated to boiling and refluxed for 2h~5h. After cooling to room temperature, an inorganic alkaline solution (concentration of 0.01mmol / L~0.1mmol / L, such as sodium hydroxide solution) is added. The mixture is then stirred and etched for several hours. The resulting suspension is centrifuged, washed with water 2-3 times, dried at 100℃~110℃ for 1h~3h, and then calcined in a muffle furnace at 500℃~600℃ for 3h~5h to obtain porous silicon suboxide as the core structure.

[0094] 2. Amorphous carbon: Amorphous carbon sources such as pitch are mixed with the above-mentioned core structure and then subjected to high-temperature treatment for 1 to 10 hours, with the temperature controlled at 700℃ to 1500℃, to obtain a coating layer containing amorphous carbon.

[0095] 3. Mix the material obtained in step 2 above with a lithium source, such as lithium powder, lithium hydride, lithium oxide, lithium carbonate or organic lithium, and treat it at a high temperature of 300℃~1000℃ for 1h~5h. Lithium ions will pass through the amorphous carbon coating layer and form a first coating layer containing lithium silicate on the core structure inside the amorphous carbon.

[0096] 4. Preparation of silicon metal compound coating layer: The metal coating raw material and the material obtained in step 3 are mixed at a mass ratio of 0.001:1 to 0.02:1. The mixed material is subjected to high temperature treatment at 600℃ to 1000℃ for 0.5h to 2h. The treated material is ball-milled and stirred for 10min to 60min. Metal ions will penetrate the amorphous carbon coating layer and form a second coating layer of silicon-containing metal compound inside the amorphous carbon and on the surface of lithium silicate.

[0097] 5. Finally, the material obtained in step 4 is mixed with the carbon nanotube solution and subjected to a bonding reaction at a high temperature of 100℃~400℃ to coat the carbon nanotubes onto the material surface, forming a third coating layer that is a mixture of amorphous carbon material and carbon nanotubes.

[0098] The aforementioned metal coating materials include, but are not limited to, metal salts and metal oxides.

[0099] like Figure 4 As shown, in some embodiments, in Figure 2 Based on the structure shown, the aforementioned silicon compound also includes a silicon metal compound 113, which coats the surface of elemental silicon. "Silicon metal compound" refers to a compound formed by a transition metal and silicon; optionally, the metal element in the silicon metal compound includes Ti, Mg, and / or Al. Coating the surface of elemental silicon with a silicon metal compound can buffer the volume expansion of elemental silicon, improving cycle performance and charging capability.

[0100] Figure 4 The porous silicon anode material shown can be prepared using the following methods:

[0101] 1. Silicon suboxide is synthesized by vapor deposition from silicon grains and silicon dioxide. The silicon suboxide particles are dispersed in water, and then polyvinylpyrrolidone (molar ratio of 5~15:1 with silicon dioxide) is added. The mixture is heated to boiling and refluxed for 2h~5h. After cooling to room temperature, an inorganic alkaline solution (concentration of 0.01mmol / L~0.1mmol / L, such as sodium hydroxide solution) is added. The mixture is then stirred and etched for several hours. The resulting suspension is centrifuged, washed with water 2-3 times, dried at 100℃~110℃ for 1h~3h, and then calcined in a muffle furnace at 500℃~600℃ for 3h~5h to obtain porous silicon suboxide.

[0102] 2. Preparation of silicon metal compound coating layer: The metal coating raw material is mixed with the porous silicon suboxide, and the mixed material is subjected to high temperature treatment at 800℃~1300℃ for 1h~6h, and the high temperature treated material is ground. The coating reacts directly with the silicon grains through phase selection reaction to obtain a silicon metal compound coating layer formed on the surface of elemental silicon as the core structure.

[0103] 3. Amorphous carbon: Amorphous carbon sources such as pitch are mixed with the above-mentioned core structure and then subjected to high-temperature treatment for 1 to 10 hours, with the temperature controlled at 700℃ to 1500℃, to obtain a coating layer containing amorphous carbon.

[0104] 4. Mix the material obtained in step 3 above with a lithium source, such as lithium powder, lithium hydride, lithium oxide, lithium carbonate or organic lithium, and treat it at a high temperature of 300℃~1000℃ for 1h~5h. Lithium ions will pass through the amorphous carbon coating layer and form a first coating layer containing lithium silicate on the core structure inside the amorphous carbon.

[0105] 5. Finally, the material obtained in step 4 is mixed with the carbon nanotube solution and subjected to a bonding reaction at a high temperature of 100℃~400℃ to coat the carbon nanotubes onto the material surface, forming a third coating layer that is a mixture of amorphous carbon material and carbon nanotubes.

[0106] The aforementioned hard carbon refers to carbon that is difficult to graphitize and is a thermal decomposition product of polymers. Common hard carbons include resin carbon, organic polymer pyrolysis carbon, and carbon black. Soft carbon generally refers to black carbon, a highly aromatic substance produced by the pyrolysis and carbonization of fossil fuels and biomass under oxygen-deficient conditions. In the embodiments described above in this application, amorphous carbon may be only hard carbon, only soft carbon, or a mixture of hard and soft carbon. Due to the large interlayer spacing and fast lithium insertion rate of amorphous carbon, it is beneficial to the overall performance of the battery.

[0107] In some embodiments, the third coating layer further includes carbon nanotubes. Carbon nanotubes can improve the conductivity of the porous silicon anode material, and by utilizing carbon nanotubes to fully confine the porous silicon anode material, they alleviate volume expansion during charging and discharging, control the polarization inside the anode cell, and improve the cycle performance of the cell. Definitions: The masses of the porous silicon anode material 10 in the first film layer 02 and the second film layer 03 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; excluding the carbon nanotubes in the porous silicon anode material 10, the remaining masses of carbon nanotubes in the first film layer 02 and the second film layer 03 are S1 and S2, respectively; the first film layer 02 and the second film layer 03 are respectively the first film layer 02 per unit area and the second film layer 03 per unit area. To ensure sufficient confinement of the porous silicon anode material 10 and effectively suppress the rebound of the anode sheet, in some embodiments, the carbon nanotubes in the third coating layer, the carbon nanotubes in the first film layer 02, and the carbon nanotubes in the second film layer 03 are designed to satisfy the following relationship: (m2×C2+S2) / M2=(m1×C1+S1) / M1, m2≥m1, S1≥S2, S2=m1×m2×(C2-C1) / (m2-m1), which further improves the confinement ability of the silicon-based anode, effectively suppresses the rebound of the anode sheet, and minimizes the polarization of the anode sheet.

[0108] The determination of the masses m1 and m2 of the porous silicon anode material in the first and second films mentioned above is based on the aforementioned method for determining the content of silicon-based anode materials.

[0109] The determination of the mass percentage C1 and C2 of carbon nanotubes on the surface of the aforementioned porous silicon anode material is as follows: SEM can be used to count the number and length of carbon nanotubes on the surface of multiple silicon particles. The mass of a single carbon nanotube is obtained by simulating the chain length and number of molecules of the carbon nanotubes. The average value of the calculated number of carbon nanotubes is then used as the mass of the carbon nanotubes on the surface of the porous silicon anode material. Finally, the mass percentage C1 and C2 of the carbon nanotubes in the porous silicon anode material are calculated using the volume and true density of the porous silicon anode material.

[0110] The remaining carbon nanotubes in the first and second films are S1 and S2, respectively. The thickness of the upper and lower films is determined by CP (ion beam) cross-section. Then, the powder of the upper second film is scraped out first, and the powder of the lower first film is scraped out. Each is then divided into n equal parts to ensure uniform distribution on the SEM sample stage. The number of carbon nanotubes is then counted by SEM test, and the mass of carbon nanotubes in the first and second films is calculated using the calculation method described above.

[0111] In some embodiments, the Dv50 range of the aforementioned elemental silicon is: 0 < Dv50 ≤ 10 nm; optionally, the Dv50 range of the elemental silicon is: 2 nm < Dv50 ≤ 8 nm. Using nanoscale elemental silicon facilitates the mixing of silicon oxides with it, thereby improving the battery's charging capability; it also helps reduce the difficulty of encapsulating the core structure, improving the battery's cycle stability.

[0112] The chemical formula for "silicon oxide" is SiOx, where 0 < x ≤ 2, such as silicon monoxide (SiO) and silicon dioxide (SiO2). In some embodiments, the Dv50 range of the silicon oxide used is: 2 μm ≤ Dv50 ≤ 13 μm. This is beneficial for mixing with elemental silicon and improving the energy density of the battery.

[0113] In some embodiments, the lithium silicate comprises one or more of Li₂SiO₃, Li₂Si₂O₅, Li₄SiO₄, Li₂Si₃O₇, Li₈SiO₆, Li₆Si₂O₇, Li₄Si₂O₇, Li₂Si₄O₇, and LiSiO₃. Optionally, the lithium silicate comprises at least Li₂SiO₃, which effectively reduces the consumption of lithium ions in the positive electrode active material during the first lithium intercalation process, resulting in a higher initial coulombic efficiency of the battery. Further optionally, the mass of Li₂SiO₃ is at least 50% of the mass of the first coating layer, such as 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, or 90%. More preferably, the mass of Li₂SiO₃ is at least 70% of the mass of the first coating layer, ensuring high lithium conductivity of the first coating layer and improving the overall charging capability of the material.

[0114] Standard samples with different Li2SiO3 contents were prepared according to the type of lithium silicate in the first coating layer. The test content of different Li2SiO3 contents was obtained by TOF-SIMES testing, and a standard curve was established between the test content and the actual content. The test content of Li2SiO3 in the first coating layer was obtained by TOF-SIMES testing, and the accurate Li2SiO3 content was obtained by comparing it with the standard curve.

[0115] 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. Optionally, the thickness of the second coating layer is 1 nm to 50 nm; optionally, the thickness of the third coating layer is 1 nm to 1000 nm, or optionally 5 nm to 300 nm. Within the above thickness range, the particles effectively reduce the volume expansion of the anode material while increasing the battery energy density, thus improving the cycle stability and charging capability of the high-energy-density battery. The thickness is measured from the outside to the inside of the particle using TOF-SIMES, and the thickness of each coating layer is determined by the material at different depths. When preparing the porous silicon anode material, the amount of raw material corresponding to each coating layer is adjusted to counteract the adjustment of its thickness.

[0116] In some embodiments, the negative electrode current collector may be a metal foil or a composite current collector. For example, copper foil may be used as the metal foil. The composite current collector may include a polymer material substrate and a metal layer formed on at least one surface of the polymer material substrate. The composite current collector may be formed by forming a metal material (copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer material substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0117] In some embodiments, the negative electrode sheet can be prepared by dispersing the above-mentioned components for preparing the negative electrode sheet, such as negative electrode active material, conductive agent, binder and any other components, in a solvent (e.g., deionized water) to form a negative electrode slurry; coating the negative electrode slurry onto a negative electrode current collector, and then obtaining the negative electrode sheet after drying, cold pressing and other processes.

[0118] [Positive electrode plate]

[0119] A positive electrode typically includes a positive current collector and a positive electrode film layer disposed on at least one surface of the positive current collector, the positive electrode film layer including a positive active material.

[0120] As an example, the positive current collector has two surfaces opposite each other in its own thickness direction, and the positive electrode film layer is disposed on either or both of the two opposite surfaces of the positive current collector.

[0121] In some embodiments, the positive current collector may be a metal foil or a composite current collector. For example, aluminum foil may be used as the metal foil. The composite current collector may include a polymer substrate and a metal layer formed on at least one surface of the polymer substrate. The composite current collector may be formed by forming a metal material (aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0122] In some embodiments, the positive electrode active material may be a known battery positive electrode active material. As an example, the positive electrode active material may include at least one of the following materials: lithium phosphates with an olivine structure, lithium transition metal oxides, and their respective modified compounds. However, this application is not limited to these materials, and other conventional materials that can be used as battery positive electrode active materials may also be used. These positive electrode active materials may be used alone or in combination of two or more. Examples of lithium transition metal oxides include, but are not limited to, lithium cobalt oxides (such as LiCoO2), lithium nickel oxides (such as LiNiO2), lithium manganese oxides (such as LiMnO2, LiMn2O4), lithium nickel cobalt oxides, lithium manganese cobalt oxides, lithium nickel manganese oxides, and lithium nickel cobalt manganese oxides (such as LiNi). 1 / 3 Co 1 / 3 Mn 1 / 3 O2 (also known as NCM) 333 LiNi 0.5 Co 0.2 Mn 0.3 O2 (also known as NCM) 523 LiNi 0.5 Co 0.25 Mn 0.25 O2 (also known as NCM) 211 LiNi 0.6 Co 0.2 Mn 0.2 O2 (also known as NCM) 622 LiNi 0.8 Co 0.1 Mn 0.1 O2 (also known as NCM) 811 ), lithium nickel cobalt aluminum oxide (such as LiNi) 0.85 Co 0.15 Al 0.05At least one of O2 and its modified compounds. Examples of lithium phosphates with an olivine structure include, but are not limited to, lithium iron phosphate (such as LiFePO4 (also referred to as LFP)), lithium iron phosphate and carbon composites, lithium manganese phosphate (such as LiMnPO4), lithium manganese phosphate and carbon composites, lithium manganese iron phosphate, and lithium manganese iron phosphate and carbon composites.

[0123] In some embodiments, the positive electrode film layer may optionally include a binder. As an example, the binder may include at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), PVDF-tetrafluoroethylene-propylene terpolymer, PVDF-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorinated acrylate resin.

[0124] In some embodiments, the positive electrode film may optionally include a conductive agent. As an example, the conductive agent may include at least one selected from superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0125] In some embodiments, the positive electrode sheet can be prepared by dispersing the above-mentioned components for preparing the positive electrode sheet, such as positive active material, conductive agent, binder and any other components, in a solvent (e.g., N-methylpyrrolidone) to form a positive electrode slurry; coating the positive electrode slurry onto the positive electrode current collector, and then obtaining the positive electrode sheet after drying, cold pressing and other processes.

[0126] [Electrolytes]

[0127] The electrolyte acts as a conductor of ions between the positive and negative electrodes. This application does not impose specific restrictions on the type of electrolyte; it can be selected according to requirements. For example, the electrolyte can be liquid, gel, or entirely solid.

[0128] In some embodiments, the electrolyte is liquid and includes an electrolyte salt and a solvent.

[0129] In some embodiments, the electrolyte salt may be selected from at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium hexafluoroarsenate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium trifluoromethanesulfonate, lithium difluorophosphate, lithium difluorooxalate borate, lithium dioxalate borate, lithium difluorodioxalate phosphate, and lithium tetrafluorooxalate phosphate.

[0130] In some embodiments, the solvent may 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, butyl 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.

[0131] In some embodiments, the electrolyte may optionally include additives. As examples, additives may include negative electrode film-forming additives, positive electrode film-forming additives, and may also include additives that can improve certain battery performance, such as additives that improve battery overcharge performance, additives that improve battery high-temperature or low-temperature performance, etc.

[0132] [Isolation membrane]

[0133] In some embodiments, the secondary battery also includes a separator. This application does not impose any particular limitation on the type of separator; any known porous separator with good chemical and mechanical stability can be selected.

[0134] 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 can be a single-layer film or a multi-layer composite film, without particular limitation. When the separator is a multi-layer composite film, the materials of each layer can be the same or different, without particular limitation.

[0135] In some implementations, the positive electrode, negative electrode, and separator can be fabricated into an electrode assembly using a winding or stacking process.

[0136] In some embodiments, the secondary battery may include an outer packaging. This outer packaging may be used to encapsulate the electrode assembly and electrolyte described above.

[0137] In some embodiments, the outer packaging of the secondary battery can be a hard shell, such as a hard plastic shell, an aluminum shell, or a steel shell. The outer packaging of the secondary battery can also be a soft pack, such as a pouch. The material of the soft pack can be plastic; examples of plastics include polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0138] This application does not impose any particular limitation on the shape of the secondary battery; it can be cylindrical, square, or any other arbitrary shape. For example, Figure 5 This is an example of a square-structured secondary battery 5.

[0139] In some implementations, refer to Figure 6The outer packaging may include a housing 51 and a cover 53. The housing 51 may include a base plate and side plates connected to the base plate, the base plate and side plates forming a receiving cavity. The housing 51 has an opening communicating with the receiving cavity, and the cover 53 can be placed over the opening to close the receiving cavity. A positive electrode, a negative electrode, and a separator can be formed into an electrode assembly 52 using a winding or stacking process. The electrode assembly 52 is encapsulated within the receiving cavity. Electrolyte is immersed in the electrode assembly 52. ​​The secondary battery 5 may contain one or more electrode assemblies 52, which can be selected by those skilled in the art according to specific practical needs.

[0140] In some implementations, the secondary batteries can be assembled into a battery module, and the number of secondary batteries contained in the battery module can be one or more, the specific number of which can be selected by those skilled in the art according to the application and capacity of the battery module.

[0141] Figure 7 This is battery module 4, used as an example. (See reference...) Figure 7 In battery module 4, multiple secondary batteries 5 can be arranged sequentially along the length of battery module 4. Of course, they can also be arranged in any other manner. Furthermore, these multiple secondary batteries 5 can be fixed in place using fasteners.

[0142] Optionally, the battery module 4 may also include a housing with a receiving space in which a plurality of secondary batteries 5 are received.

[0143] In some embodiments, the battery modules described above can also be assembled into a battery pack, and the number of battery modules contained in the battery pack can be one or more, the specific number of which can be selected by those skilled in the art according to the application and capacity of the battery pack.

[0144] Figure 8 and Figure 9 This is battery pack 1 as an example. (See reference...) Figure 8 and Figure 9 The battery pack 1 may include a battery box and multiple battery modules 4 disposed within the battery box. The battery box includes an upper body 2 and a lower body 3, with the upper body 2 covering the lower body 3 to form a closed space for accommodating the battery modules 4. The multiple battery modules 4 can be arranged in any manner within the battery box.

[0145] In addition, this application also provides an electrical device, which includes at least one of the secondary battery, battery module, or battery pack provided in this application. The secondary battery, battery module, or battery pack can be used as a power source for the electrical device, or as an energy storage unit for the electrical device. The electrical 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.), electric trains, ships and satellites, energy storage systems, etc.

[0146] As the electrical device, a secondary battery, battery module, or battery pack can be selected according to its usage requirements.

[0147] Figure 10 This is an example of an electrical device. The device could be a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle. To meet the high power and high energy density requirements of the secondary battery for this device, a battery pack or battery module can be used.

[0148] [Example]

[0149] The following describes embodiments of this application. The embodiments described below are exemplary and are only used to explain this application, and should not be construed as limiting this application. Where specific techniques or conditions are not specified in the embodiments, they are performed according to the techniques or conditions described in the literature in this field or according to the product instructions. Reagents or instruments used, unless otherwise specified, are all conventional products that can be obtained commercially.

[0150]

[0151] I. Porous Silicon Anode Materials

[0152] Preparation process of porous silicon anode material 1

[0153] 1. Silicon suboxide was synthesized from silicon grains and silicon dioxide via vapor deposition. The deposition temperature was controlled at 800℃. Silicon suboxide particles were dispersed in water, and then polyvinylpyrrolidone (molar ratio to silicon dioxide 10:1) was added. The mixture was heated to boiling and refluxed for 3 hours. After cooling to room temperature, a 0.05 mmol / L sodium hydroxide solution was added, and the mixture was stirred and etched for 4 hours. The resulting suspension was centrifuged, washed 2-3 times with water, dried at 105℃ for 2 hours, and then calcined in a muffle furnace at 550℃ for 4 hours to obtain porous silicon suboxide. The obtained porous silicon suboxide was then ground, sieved, and its density (D) was adjusted. V Size 50;

[0154] 2. Preparation of silicon metal compound coating layer: The metal coating raw material TiO2 and silicon suboxide are mixed at a mass ratio of 0.003:1. The mixed material is subjected to high temperature treatment at 1000℃ for 4 hours and then ground. The coating reacts directly with the silicon grains through phase selection reaction to obtain a silicon TiSi coating layer formed on the surface of elemental silicon as the core structure.

[0155] 3. Amorphous carbon: The asphalt and the above core structure are mixed at a mass ratio of 0.05:1 and then subjected to high temperature treatment for 6 hours, with the temperature controlled at 1100℃, to obtain a coating layer containing amorphous carbon.

[0156] 4. The material obtained in step 3 above is mixed with lithium carbonate at a mass ratio of 1:0.2 and subjected to high temperature treatment at 800°C for 3 hours. Lithium ions pass through the amorphous carbon coating layer and form a first coating layer containing lithium silicate on the core structure inside the amorphous carbon.

[0157] 5. Finally, the material obtained in step 4 is mixed with the carbon nanotube solution, wherein the mass ratio of the material obtained in step 4 to the carbon nanotube is 1:0.08. The mixture undergoes a bonding reaction at a high temperature of 250°C, coating the carbon nanotube onto the surface of the material to form a third coating layer consisting of amorphous carbon material and carbon nanotube.

[0158] Based on the above-described preparation process of porous silicon anode material 1, porous silicon anode materials 2 to 5 are obtained by adjusting the grinding time and sieving particle size.

[0159] Based on the above-mentioned preparation process of porous silicon anode material 1, porous silicon anode materials 6 to 10 are obtained by adjusting the temperature of vapor deposition.

[0160] Based on the above-mentioned preparation process of porous silicon anode material 1, the mass content of porous silicon material and lithium carbonate is adjusted to obtain porous silicon anode materials 11 to 14 with different thicknesses of the first coating layer.

[0161] Based on the above-mentioned preparation process of porous silicon anode material 1, the amount of metal-coated raw material TiO2 is halved to obtain porous silicon anode material 15.

[0162] Preparation process of porous silicon anode material 16

[0163] The only difference between the preparation process of porous silicon anode material 1 and that of MgCl2 is used instead of TiO2.

[0164] Preparation process of porous silicon anode material 17

[0165] 1. Silicon suboxide is synthesized from silicon grains and silicon dioxide via vapor deposition. The deposition temperature is controlled at 800℃. Silicon suboxide particles are dispersed in water, and then polyvinylpyrrolidone (molar ratio to silicon dioxide is 10:1) is added. The mixture is heated to boiling and refluxed for 3 hours. After cooling to room temperature, sodium hydroxide solution is added, and the mixture is stirred and etched for several hours. The resulting suspension is centrifuged, washed 2-3 times with water, dried at 105℃ for 2 hours, and then calcined in a muffle furnace at 550℃ for 4 hours to obtain porous silicon suboxide. Using this as the core structure, the obtained porous silicon suboxide is ground, sieved, and its density (D) is adjusted. V Size 50;

[0166] 2. Amorphous carbon: The asphalt and the above core structure are mixed at a mass ratio of 0.05:1 and then subjected to high temperature treatment for 6 hours, with the temperature controlled at 1000℃, to obtain a coating layer containing amorphous carbon.

[0167] 3. Mix the material obtained in step 2 with lithium carbonate at a mass ratio of 1:1.2 and treat it at 800°C for 3 hours. Lithium ions will pass through the amorphous carbon coating layer and form a first coating layer containing lithium silicate on the core structure inside the amorphous carbon.

[0168] 4. Preparation of silicon metal compound coating layer: The metal coating raw material and the material obtained in step 3 are mixed at a mass ratio of 0.015:1. The mixed material is subjected to high temperature treatment at 1000℃ for 1 hour. The treated material is ball-milled and stirred for 30 minutes. Metal ions will pass through the amorphous carbon coating layer and form a second coating layer containing silicon metal compound inside the amorphous carbon and on the surface of lithium silicate.

[0169] 5. Finally, the material obtained in step 4 is mixed with the carbon nanotube solution, wherein the mass ratio of the material obtained in step 4 to the carbon nanotubes is 1:0.08. A bonding reaction occurs during high-temperature treatment at 250℃, coating the carbon nanotubes onto the material surface to form a third coating layer consisting of amorphous carbon material and carbon nanotubes.

[0170] Based on the above-mentioned preparation process of porous silicon anode material 17, porous silicon anode materials 18 to 21 are obtained by adjusting the amount of metal coating raw materials.

[0171] Based on the above-mentioned preparation process of porous silicon anode material 17, porous silicon anode materials 22 and 23 were obtained by adjusting the amount of asphalt.

[0172] Based on the above-mentioned preparation process of porous silicon anode material 17, porous silicon anode material 24 is obtained by adjusting the amount of carbon nanotubes.

[0173] Preparation process of porous silicon anode material 25

[0174] The only difference between the preparation process of porous silicon anode material 17 and that of MgCl2 is used instead of TiO2.

[0175] Preparation process of porous silicon anode material 26

[0176] 1. Silicon suboxide is synthesized from silicon grains and silicon dioxide by vapor deposition. The deposition temperature is controlled at 800℃. The silicon suboxide particles are dispersed in water, and then polyvinylpyrrolidone (molar ratio with silicon dioxide is 10:1) is added. The mixture is heated to boiling and refluxed for 3 hours. After cooling to room temperature, a sodium hydroxide solution with a concentration of 0.05 mmol / L is added, and the mixture is stirred and etched for several hours. The resulting suspension is centrifuged, washed with water 2-3 times, dried at 105℃ for 2 hours, and then calcined in a muffle furnace at 550℃ for 4 hours to obtain porous silicon suboxide as the core structure.

[0177] 2. Amorphous carbon: The asphalt and the above core structure are mixed at a mass ratio of 1.2:1 and then subjected to high temperature treatment for 6 hours, with the temperature controlled at 1100℃, to obtain a coating layer containing amorphous carbon.

[0178] 3. Mix the material obtained in step 2 with lithium carbonate at a mass ratio of 1:1.2 and treat it at 800°C for 3 hours. Lithium ions will pass through the amorphous carbon coating layer and form a first coating layer containing lithium silicate on the core structure inside the amorphous carbon.

[0179] 4. Finally, the material obtained in step 3 is mixed with the carbon nanotube solution, wherein the mass ratio of the material obtained in step 3 to the carbon nanotubes is 1:0.08. A bonding reaction occurs during high-temperature treatment at 250℃, coating the carbon nanotubes onto the material surface to form a third coating layer consisting of amorphous carbon material and carbon nanotubes.

[0180] Preparation process of silicon anode material 27

[0181] 1. Silicon suboxide is synthesized from silicon grains and silicon dioxide through vapor deposition, serving as the core structure;

[0182] 2. Amorphous carbon: The asphalt and the above core structure are mixed at a mass ratio of 1.2:1 and then subjected to high temperature treatment for 6 hours, with the temperature controlled at 1100℃, to obtain a coating layer containing amorphous carbon.

[0183] 3. Mix the material obtained in step 2 with lithium carbonate at a mass ratio of 1:1.2 and treat it at 800°C for 3 hours. Lithium ions will pass through the amorphous carbon coating layer and form a first coating layer containing lithium silicate on the core structure inside the amorphous carbon.

[0184] 4. Finally, the material obtained in step 3 is mixed with the carbon nanotube solution, wherein the mass ratio of the material obtained in step 3 to the carbon nanotube is 1:0.08. The mixture undergoes a bonding reaction at a high temperature of 250°C, coating the carbon nanotube onto the surface of the material to form a third coating layer consisting of a mixture of amorphous carbon material and carbon nanotube.

[0185] Testing of the prepared porous silicon anode material:

[0186] Dv50: Determined using a laser particle size analyzer (such as Malvern MasterSize 3000) in accordance with standard GB / T 19077.1-2016. Dv50 represents the particle size corresponding to a cumulative volume distribution percentage of 50% in the measured material. When forming the core structure, the Dv50 of elemental silicon is determined using the above method. After all coating layers are applied, the Dv50 of the porous silicon anode material is determined using the above method.

[0187] BET specific surface area: The specific surface area of ​​porous silicon anode materials was determined using a low-temperature nitrogen adsorption-desorption method.

[0188] Li2SiO3 content determination: The content of Li2SiO3 was obtained by TOF-SIMES test, and the standard curve was obtained by testing the standard sample. The accurate content of Li2SiO3 was obtained by comparing with the standard curve.

[0189] Coating thickness measurement: The thickness of each coating layer was determined by measuring the material at different depths from the outside to the inside of the particle using TOF-SIMES.

[0190] Determination of carbon nanotube content: SEM can be used to count the number and length of carbon nanotubes on the surface of multiple silicon particles. By simulating the chain length and number of molecules of the carbon nanotubes, the mass of a single carbon nanotube can be obtained. The average value obtained by calculating the number of multiple carbon nanotubes is taken as the mass of carbon nanotubes on the surface of the porous silicon anode material. Then, using the volume and true density of the porous silicon anode material, the mass percentages C1 and C2 of carbon nanotubes in the two film layers of the anode sheet are calculated.

[0191] The test results are recorded in Tables 1 and 2.

[0192]

[0193]

[0194] Negative electrode plate 1:

[0195] Coating weight 10mg / cm 2The coating weight ratio of the first coating layer to the second coating layer is 70:30. In the first coating layer, the mass contents of porous silicon anode material 1, graphite, binder, dispersant, conductive agent SP, and conductive agent CNT are 10%, 85.73%, 2%, 1.2%, 1%, and 0.07%, respectively. In the second coating layer, the mass contents of porous silicon anode material 1, graphite, binder, dispersant, conductive agent SP, and conductive agent CNT are 30%, 65.19%, 2.4%, 1.2%, 1%, and 0.21%, respectively.

[0196] The raw materials of the first coating layer are thoroughly mixed in an appropriate amount of solvent water according to the above weight ratio to form a uniform negative electrode slurry, thus obtaining the first negative electrode slurry; the second negative electrode slurry can be obtained by the same method; the first negative electrode slurry is coated on the surface of the copper foil of the negative electrode current collector, and the second negative electrode slurry is coated on the surface of the first negative electrode slurry; after drying and cold pressing, the negative electrode sheet 1 is obtained, and the surface density M1 of the first film layer and the surface density M2 of the second film layer formed in each negative electrode sheet are recorded in Table 2.

[0197] The difference between negative electrode plates 2 to 27 and negative electrode plate 1 is that the porous silicon negative electrode material 1 in negative electrode plate 1 is replaced by the corresponding porous silicon negative electrode material 2 to 27 in sequence.

[0198] Porous silicon anode material 1 is used in negative electrode sheets 27 to 36. However, the amount, areal density, thickness and mass percentage of the material in the first and second film layers are shown in Table 3. Due to the change in the amount of graphite, the amount of graphite is adjusted so that the total mass fraction of porous silicon anode material 1, graphite, binder, dispersant and conductive agent SP in the first film layer meets 100%. The amount of graphite is also adjusted so that the total mass fraction of porous silicon anode material 1, graphite, binder, dispersant, conductive agent SP and conductive agent CNT in the second film layer meets 100%.

[0199] The negative electrode 37 uses silicon negative electrode material 27 to replace the porous silicon negative electrode material 1 in the negative electrode 1.

[0200] Testing of the negative electrode:

[0201] Determination of the porosity of the negative electrode film: The cross-section of the CP is photographed and scanned using imaging software. The porosity of the corresponding cross-section is calculated. Then, the porosity of the negative electrode film is obtained by scanning and photographing multiple CP cross-sections and calculating using software.

[0202] Thickness: Thickness was measured by photographing the CP cross-section.

[0203] The weight ratio of the first film layer to the second film layer is denoted as A.

[0204] Calculate the amount of raw materials used and the data in Tables 1 and 2 for each 1cm. 2In the first and second films, the masses of the porous silicon anode material in the first and second films are m1 and m2, respectively; the mass percentages of carbon nanotubes belonging to the porous silicon anode material in the first and second films are C1 and C2, respectively. Excluding the carbon nanotubes in the porous silicon anode material, the masses of the remaining carbon nanotubes in the first and second films are S1 and S2, respectively.

[0205]

[0206] III. Secondary batteries

[0207] Example 1

[0208] Negative electrode plate:

[0209] The above-mentioned negative electrode 1 is used as the negative electrode of the secondary battery in Example 1.

[0210] Positive electrode sheet:

[0211] Coating weight: 25.5 mg / cm³ 2 The cathode is a single-layer coated cathode, with the mass contents of ternary material NCM811, PVDF, conductive agent SP, and conductive agent CNT being 96.5%, 1.5%, 1.5%, and 0.5%, respectively.

[0212] The raw materials are thoroughly mixed in an appropriate amount of NMP solvent according to the above weight ratio to form a uniform positive electrode slurry; the positive electrode slurry is coated on the surface of the positive electrode current collector aluminum foil; after drying and cold pressing, the positive electrode sheet is obtained.

[0213] Electrolyte: The electrolyte includes solvent, lithium salt and additives. The solvent types and contents are as follows: EC:DMC:DEC=0.3:0.5:0.2, the lithium salt content is 1.0 mol / L, and the film-forming additives include 8% FEC.

[0214] Diaphragm: PE diaphragm is used;

[0215] The negative electrode plates of the secondary batteries in Examples 2 to 37 are negative electrode plates 2 to 37 respectively, and the positive electrode plates, electrolytes and separators are the same as in Example 1.

[0216] The negative electrode of the secondary battery in Comparative Example 1 is negative electrode 38, and the positive electrode, electrolyte and separator are the same as in Example 1.

[0217] Gram capacity test:

[0218] The negative electrode and lithium sheet were made into a button half-cell for testing. The cell was charged and discharged at 25°C at a rate of 0.04C, with a voltage range of 0.05V-2V. The capacity was tested and the specific capacity of the negative electrode was calculated. Specific capacity = test capacity / mass of active material.

[0219] Cyclic performance test:

[0220] At 25°C, the secondary batteries prepared in each embodiment and comparative example were charged at a constant current rate of 1 C to the charging cutoff voltage of 4.25V, then charged at a constant voltage until the current ≤0.05C, allowed to stand for 5 minutes, and then discharged at a constant current rate of 1 C to the discharge cutoff voltage of 2.8V, allowed to stand for 5 minutes. This constitutes one charge-discharge cycle. The batteries were subjected to cyclic charge-discharge tests according to this method until the battery capacity decreased to 80%. The number of cycles at this point is the cycle life of the battery at 25°C.

[0221] Charging capability test:

[0222] At 25°C, the batteries of the above embodiments and comparative examples were charged and discharged for the first time at a current of 1C (i.e., the current value at which the theoretical capacity is completely discharged within 1 hour). Specifically, the batteries were charged at a constant current rate of 1C to a voltage of 4.25V, then charged at a constant voltage rate to a current ≤0.05C, left to stand for 5 minutes, and then discharged at a constant current rate of 0.33C to a voltage of 2.8V. The actual capacity was recorded as C0.

[0223] Then, the battery is sequentially charged at constant current rates of 1.0C0, 1.3C0, 1.5C0, 1.8C0, 2.0C0, 2.3C0, 2.5C0, and 3.0C0 until the full battery charging cutoff voltage of 4.25V or the negative terminal cutoff potential (whichever comes first). After each charge, it is discharged at 1C0 until the full battery discharge cutoff voltage of 2.8V. The charging rate is recorded at different rates until 10%, 20%, 30%, ..., 80% SOC (State of Charge). The negative electrode potential corresponding to the state of charge (SOC) is plotted, and the charging rate-negative electrode potential curves are drawn for different SOC states. After linear fitting, the charging rate corresponding to the negative electrode potential of 0V under different SOC states is obtained. This charging rate is the charging window under that SOC state, denoted as C10%SOC, C20%SOC, C30%SOC, C40%SOC, C50%SOC, C60%SOC, C70%SOC, and C80%SOC. The charging time T for the battery to charge from 10%SOC to 80%SOC is 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%, in minutes. The shorter the charging time, the better the battery's fast charging performance.

[0224] The test results are recorded in Table 4.

[0225]

[0226]

[0227] A comparison of Examples 1 to 5 shows that the D of porous silicon anode materials... V A 50% change will directly affect the battery's cycle performance and charging capability, especially with the increase in the D of porous silicon anode materials. V As the value increases by 50, the battery's charging capacity decreases.

[0228] As can be seen from the comparison of Examples 6 to 10, the D of elemental silicon V A 50% change will affect the battery's charging capacity and cycle performance, with the D of elemental silicon... V With an increase of 50, both the battery's cycle performance and charging capacity decrease.

[0229] As can be seen from the comparison of Examples 11 to 14, the change in the thickness of the first coating layer containing lithium silicate will affect the charging capacity and cycle performance of the battery. As the thickness of the first coating layer increases, the cycle performance of the battery improves, but the charging capacity also improves.

[0230] As can be seen from the comparison of Examples 17 to 20, the change in the thickness of the metal compound of the second coating layer silicon will affect the charging capacity and cycle performance of the battery. As the thickness of the second coating layer increases, the cycle performance of the battery first increases and then decreases, while the charging capacity gradually decreases. This is because the second coating layer increases the anti-expansion ability of the silicon material and improves the cycle performance. However, the conductivity of the second coating layer is poor, and the increase in coating thickness will deteriorate the kinetics.

[0231] The comparison of Examples 1, 17, and 27 shows that different coating methods have a significant impact on the cycle performance and charging capability of the battery.

[0232] The comparison between Examples 1, 28 to 37 and Comparative Example 1 shows that the increased content of porous silicon anode material in the second film layer helps to improve the charging capability of the battery; and the specific capacity of Example 28 is more outstanding because the content of porous silicon anode in the first film layer is relatively large, and its cycle performance decline is also due to the high content of porous silicon anode in the first film layer.

[0233] Although this application has been described with reference to preferred embodiments, various modifications can be made thereto and components can be replaced with equivalents without departing from the scope of this application. In particular, the technical features mentioned in the various embodiments can be combined in any manner, provided there is no structural conflict. This application is not limited to the specific embodiments disclosed herein, but includes all technical solutions falling within the scope of the claims.

Claims

1. A negative electrode sheet, comprising a current collector (01) and a negative electrode film layer, said negative electrode film layer comprising: The first membrane layer (02) is disposed on one or both sides of the current collector (01); The second membrane layer (03) is disposed on the side of the first membrane 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). 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). The porous silicon anode material (10) comprises: The core (11) is porous silicon, which includes elemental silicon and silicon compounds, including silicon oxides. The coating layer covers the surface of the core (11) and includes any one or more of the following: a metal compound of silicon, lithium silicate, amorphous carbon, and carbon nanotubes.

2. The negative electrode sheet according to claim 1, wherein, The areal density M1 of the first film layer (02) is in the range of 4.5 mg / cm³. 2 ~20mg / cm 2 The areal density M2 of the second film layer (03) ranges from 4.5 mg / cm². 2 ~20mg / cm 2 .

3. The negative electrode sheet according to claim 2, wherein, The weight ratio of the first film layer (02) to the second film layer (03) is 95:5 to 30:

70.

4. The negative electrode sheet according to claim 3, wherein, The weight ratio of the first film layer (02) to the second film layer (03) is 90:10 to 40:

60.

5. The negative electrode sheet according to claim 2, wherein, The porosity of the first membrane layer (02) is in the range of 20% to 50%, the porosity of the second membrane layer (03) is in the range of 20% to 70%, and the porosity of the negative electrode membrane layer is in the range of 20% to 70%.

6. The negative electrode sheet according to claim 2, wherein, The thickness of the second film layer (03) is 10 μm ~ 20 μm.

7. The negative electrode sheet according to any one of claims 1 to 6, wherein, The mass content of silicon-based anode material in the first film layer (02) is 0.5% to 50%; and / or the mass content of porous silicon anode material (10) in the second film layer (03) is 0.5% to 70%.

8. The negative electrode sheet according to claim 7, wherein, The mass content of the porous silicon anode material (10) in the anode film layer is 1% to 60%.

9. The negative electrode sheet according to any one of claims 1 to 6, wherein, The second film layer (03) includes the porous silicon anode material (10), the graphite anode material, the binder, the dispersant and the conductive agent, wherein the conductive agent contains conductive carbon.

10. The negative electrode sheet according to any one of claims 1 to 6, wherein, The second film layer (03) includes the porous silicon anode material (10), the graphite anode material, the binder, the dispersant and the conductive agent, wherein the conductive agent comprises carbon nanotubes.

11. The negative electrode sheet according to claim 9, wherein, The porous silicon anode material (10) has a mass percentage content of 0.5% to 70% in the second film layer (03).

12. The negative electrode sheet according to claim 9, wherein, The graphite anode material has a mass percentage content of 25% to 90% in the second film layer (03).

13. The negative electrode sheet according to claim 9, wherein, The adhesive has a mass percentage content of 1% to 8% in the second film layer (03).

14. The negative electrode sheet according to claim 9, wherein, The dispersant has a mass percentage content of 0.5% to 2% in the second film layer (03).

15. The negative electrode sheet according to claim 9, wherein, The conductive carbon in the second film layer (03) has a mass percentage content of 0.5% to 5%.

16. The negative electrode sheet according to claim 10, wherein, The carbon nanotubes in the second film layer (03) have a mass percentage content of 0.05% to 2%.

17. The negative electrode sheet according to any one of claims 1 to 6, wherein, The first film layer (02) includes the silicon-based anode material, the graphite anode material, the binder, the dispersant and the conductive agent, wherein the conductive agent contains conductive carbon.

18. The negative electrode sheet according to any one of claims 1 to 6, wherein, The first film layer (02) includes the silicon-based anode material, the graphite anode material, the binder, the dispersant and the conductive agent, wherein the conductive agent contains carbon nanotubes.

19. The negative electrode sheet according to claim 17, wherein, The mass percentage of the silicon-based anode material in the first film layer (02) is 0.5% to 50%.

20. The negative electrode sheet according to claim 17, wherein, The graphite anode material has a mass percentage content of 45% to 97.5% in the first film layer (02).

21. The negative electrode sheet according to claim 17, wherein, The adhesive has a mass percentage content of 1% to 3% in the first film layer (02).

22. The negative electrode sheet according to claim 17, wherein, The mass percentage of the dispersant in the first film layer (02) is 0.3% to 1.5%.

23. The negative electrode sheet according to claim 17, wherein, The conductive carbon has a mass percentage content of 0-3% in the first film layer (02).

24. The negative electrode sheet according to claim 18, wherein, The carbon nanotubes in the first film layer (02) have a mass percentage content of 0~0.5%.

25. The negative electrode sheet according to claim 17, wherein, The silicon-based anode material includes any one or more of the group consisting of silicon material, silicon-oxygen material and porous silicon anode material (10), wherein the content of the porous silicon anode material (10) in the first film layer (02) is less than the content of the porous silicon anode material (10) in the second film layer (03).

26. The negative electrode sheet according to any one of claims 1 to 6, wherein, The Dv of the porous silicon anode material (10) 50 The surface area is between 3 μm and 20 μm; and / or the BET specific surface area of ​​the porous silicon anode material (10) is 1 m². 2 / g~30m 2 Between / g.

27. The negative electrode sheet according to claim 26, wherein, The Dv of the porous silicon anode material (10) 50 Between 4μm and 15μm.

28. The negative electrode sheet according to claim 26, wherein, The porous silicon anode material (10) has a BET specific surface area of ​​6 m². 2 / g~20m 2 Between / g.

29. The negative electrode sheet according to claim 1, wherein, The coating layer includes: A first coating layer (12) is applied to the surface of the core (11), and the first coating layer (12) comprises lithium silicate. A second coating layer (13) is applied to the surface of the first coating layer (12), and the second coating layer (13) comprises a metal compound of silicon. A third coating layer (14) is applied to the surface of the second coating layer (13), and the third coating layer (14) comprises amorphous carbon.

30. The negative electrode sheet according to claim 29, wherein, The metallic elements in the silicon metal compound include Ti, Mg and / or Al.

31. The negative electrode sheet according to claim 29, wherein, The amorphous carbon material includes hard carbon and / or soft carbon.

32. The negative electrode sheet according to claim 1, wherein, The coating layer includes: A first coating layer (12) is applied to the surface of the core (11), and the first coating layer includes the lithium silicate. A third coating layer (14) is applied to the surface of the first coating layer (12), and the third coating layer (14) includes the amorphous carbon.

33. The negative electrode sheet according to claim 32, wherein, The amorphous carbon material includes hard carbon and / or soft carbon.

34. The negative electrode sheet according to claim 1, wherein, The silicon compounds also include silicon metal compounds, which coat the surface of the elemental silicon.

35. The negative electrode sheet according to claim 32 or 33, wherein, The silicon compounds also include silicon metal compounds, which coat the surface of the elemental silicon.

36. The negative electrode sheet according to claim 34, wherein, The metallic elements in the silicon metal compound include Ti, Mg and / or Al.

37. The negative electrode sheet according to claim 35, wherein, The metallic elements in the silicon metal compound include Ti, Mg and / or Al.

38. The negative electrode sheet according to any one of claims 30 to 33, wherein, The third coating layer also includes the carbon nanotubes.

39. The negative electrode sheet according to claim 35, wherein, The third coating layer also includes the carbon nanotubes.

40. The negative electrode sheet according to claim 38, wherein, The masses of the porous silicon anode material (10) in the first film layer (02) and the second film layer (03) 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; excluding the carbon nanotubes in the porous silicon anode material (10), the masses of the remaining carbon nanotubes in the first film layer (02) and the second film layer (03) are S1 and S2, respectively; the first film layer (02) and the second film layer (03) are the first film layer (02) per unit area and the second film layer (03) per unit area, respectively, and satisfy the following relationship: (m2×C2+S2) / M2=(m1×C1+S1) / M1, m2≥m1, S1≥S2, S2=m1×m2×(C2-C1) / (m2-m1).

41. The negative electrode sheet according to claim 39, wherein, The masses of the porous silicon anode material (10) in the first film layer (02) and the second film layer (03) 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; excluding the carbon nanotubes in the porous silicon anode material (10), the masses of the remaining carbon nanotubes in the first film layer (02) and the second film layer (03) are S1 and S2, respectively; the first film layer (02) and the second film layer (03) are the first film layer (02) per unit area and the second film layer (03) per unit area, respectively, and satisfy the following relationship: (m2×C2+S2) / M2=(m1×C1+S1) / M1, m2≥m1, S1≥S2, S2=m1×m2×(C2-C1) / (m2-m1).

42. The negative electrode sheet according to any one of claims 1, 29 to 33, wherein, The Dv50 range of the silicon is: 0 < Dv50 ≤ 10 nm.

43. The negative electrode sheet according to claim 41, wherein, The range of Dv50 for the silicon element is: 2nm < Dv50 ≤ 8nm.

44. The negative electrode sheet according to any one of claims 1, 29 to 33, wherein, The chemical formula of the silicon oxide is SiOx, where 0 < x ≤ 2; the Dv50 range of the silicon oxide is: 2 μm ≤ Dv50 ≤ 13 μm.

45. The negative electrode sheet according to any one of claims 29 to 33, wherein, The lithium silicate includes one or more of Li2SiO3, Li2Si2O5, Li4SiO4, Li2Si3O7, Li8SiO6, Li6Si2O7, Li4Si2O7, Li2Si4O7 and LiSiO3.

46. ​​The negative electrode sheet according to claim 45, wherein, The lithium silicate includes at least Li2SiO3.

47. The negative electrode sheet according to claim 46, wherein, The mass of the Li2SiO3 is at least 50% of the mass of the first coating layer.

48. The negative electrode sheet according to claim 47, wherein, The mass of the Li2SiO3 is at least 70% of the mass of the first coating layer.

49. The negative electrode sheet according to any one of claims 29 to 33, wherein, The thickness of the first coating layer is 10% to 80% of the particle radius of the porous silicon anode material (10).

50. The negative electrode sheet according to any one of claims 29 to 31, wherein, The thickness of the second coating layer is 1 nm to 50 nm.

51. The negative electrode sheet according to any one of claims 29 to 33, wherein, The thickness of the third coating layer is 1 nm to 1000 nm.

52. The negative electrode sheet according to claim 51, wherein, The thickness of the third coating layer is 5 nm to 300 nm.

53. A secondary battery, comprising a positive electrode, a negative electrode, a separator, and an electrolyte, wherein, The negative electrode sheet is any one of claims 1 to 52.

54. An electrical device comprising a secondary battery, wherein, The secondary battery is the secondary battery as described in claim 53.

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