Secondary battery and preparation method thereof, energy storage battery pack and electrical equipment

Abstract

The present application relates to the field of energy storage, and provides a secondary battery and a preparation method thereof, an energy storage battery pack and an electrical device, wherein the preparation method comprises: forming a first active layer having a first hole and a second active layer having a second hole; the preparation step of forming the second active layer comprises: obtaining a camphor precursor based on second camphor particles and a pre-carbonized solution, and coating the surface of the camphor precursor with a carbonized material; heat-treating the camphor precursor to obtain carbon-coated camphor particles; uniformly stirring the carbon-coated camphor particles, a second negative electrode material, a second conductive agent and a second adhesive with a second dispersed solution to obtain a second coating slurry; covering the second coating slurry on a current collector having the first active layer, wherein the second coating slurry will flow into part of the first holes, and after drying, a second active layer having carbon-coated second holes is formed; and winding or stacking the positive electrode sheet, the negative electrode sheet and the separator to obtain a secondary battery.

Description

Technical Field

[0001] The present application relates to the field of energy storage, and in particular to a secondary battery and a preparation method thereof, an energy storage battery pack, and electrical equipment. Background Art

[0002] With the rapid development of the energy storage market, energy storage battery cells are being updated and iterated at an accelerated pace. Currently, battery cell products are moving towards large capacity and high energy density. In addition to developing positive and negative electrode materials with higher specific capacity, battery cell design often aims to increase the energy density of the battery cell by increasing the electrode coating surface density and increasing the compaction density. However, this will significantly increase the electrochemical impedance of the electrode, especially for the negative electrode. This increase in the electrochemical impedance of the electrode increases the risk of lithium plating during charging, leading to cell capacity degradation.

[0003] However, the current methods or preparation processes for improving electrochemical impedance and increasing battery cell energy density are relatively complicated, and will affect the porosity of the negative electrode and reduce the tortuosity of the electrode, thus causing new problems. Summary of the Invention

[0004] The embodiments of the present application provide a secondary battery and a preparation method thereof, an energy storage battery pack, and an electrical device, which are at least beneficial for improving the porosity and electrochemical performance of the negative electrode sheet and enhancing the rate performance of the electrode sheet.

[0005] According to some embodiments of the present application, on the one hand, an embodiment of the present application provides a method for preparing a secondary battery, comprising: forming a negative electrode sheet, the negative electrode sheet comprising: the negative electrode sheet comprising: a negative electrode current collector, a first active layer and a second active layer stacked in sequence, the first active layer having a first hole, the second active layer having a second hole, the second porosity of the second active layer being greater than the first porosity of the first active layer; the preparation steps for forming the second active layer comprising: preparing carbon-coated camphor particles; preparing a second coating slurry, the second coating slurry comprising the carbon-coated Camphor particles; covering the negative electrode current collector having the first active layer with the second coating slurry, wherein the second coating slurry flows into at least a portion of the first pores and is dried to form the second active layer; wherein, during the drying process, the camphor particles in the carbon-coated camphor particles are sublimated to form the second pores; providing a positive electrode sheet and a separator, stacking the negative electrode sheet, the separator and the positive electrode sheet in sequence, obtaining a bare cell by winding or laminating, placing the bare cell into a battery shell, injecting an electrolyte into the battery shell and then encapsulating it to obtain a secondary battery.

[0006] In some embodiments, the second coating slurry further includes: a second negative electrode material, a second conductive agent, a second adhesive and a second dispersed solution; the mass ratio of the carbon-coated camphor particles, the second negative electrode material, the second conductive agent, the second adhesive and the second dispersed solution is (0.4~0.6): (96~97.2): (0.4~0.6): (2.0~2.8): (160~200).

[0007] In some embodiments, the second adhesive includes styrene-butadiene rubber, carboxymethyl cellulose and polyacrylic acid, and the mass ratio of styrene-butadiene rubber, carboxymethyl cellulose and polyacrylic acid is (0.8-1.2): (0.6-0.8): (0.6-0.8).

[0008] In some embodiments, in the process step of obtaining the second coating slurry, the carboxymethyl cellulose, the polyacrylic acid and the styrene-butadiene rubber are added in sequence, and the stirring speed is controlled to increase first and then decrease.

[0009] In some embodiments, the preparation steps of the carbon-coated camphor particles include: dispersing the second camphor particles in a pre-carbonized solution, the pre-carbonized solution containing a carbonized material, drying to obtain a camphor precursor, and coating the surface of the camphor precursor with the carbonized material; heat-treating the camphor precursor to convert the camphor precursor into the carbon-coated camphor particles; the pre-carbonized solution includes a sucrose aqueous solution, and the mass fraction of the sucrose aqueous solution in the pre-carbonized solution is 3 to 7 parts; the mass fraction of the second camphor particles in the sucrose aqueous solution is 55wt% to 70wt%.

[0010] In some embodiments, the heat treatment process steps include: placing the camphor precursor in a heat treatment device, introducing an inert gas, heating to 160°C~200°C, and carbonizing for 5min~15min, and obtaining the carbon-coated camphor particles after cooling; the thickness of the carbon shell in the carbon-coated camphor particles is 15nm~20nm.

[0011] In some embodiments, the preparation step of forming the first active layer includes: stirring the first camphor particles, the first negative electrode material, the first conductive agent and the first adhesive with the first dispersion solution to obtain a first coating slurry; covering the first coating slurry on the negative electrode current collector with a coating density of 100 g / m 2 ~110g / m 2 , and drying to obtain the first active layer, wherein the first camphor particles sublime after drying, and the positions occupied by the first camphor particles are converted into the first holes.

[0012] In some embodiments, after forming the first active layer, the process further includes: providing a carbon source gas and a carrier gas, and forming a carbon nanotube layer on the surface of the first active layer by a plasma vapor deposition process at a temperature of 700°C to 900°C; the thickness of the carbon nanotube layer is 200μm to 500μm.

[0013] In some embodiments, the second particle size of the second camphor particles is smaller than the first particle size of the first camphor particles; the first particle size is 15 μm to 20 μm; and the second particle size is 5 μm to 10 μm.

[0014] In some embodiments, the mass ratio of the first camphor particles, the first negative electrode material, the first conductive agent, the first adhesive, and the first dispersed solution is (0.2~0.4): (96~97.2): (0.8~1.2): (2.0~2.8): (160~200).

[0015] In some embodiments, the first conductive agent includes carbon nanotubes and conductive carbon black, and the mass ratio of the carbon nanotubes to the conductive carbon black is (0.4-0.6): (0.4-0.6).

[0016] According to some embodiments of the present application, on the other hand, embodiments of the present application provide a secondary battery prepared by the above-mentioned method for preparing a secondary battery, comprising: a battery shell having a cavity therein, and an electrolyte therein; a bare cell, the bare cell being located in the cavity and immersed in the electrolyte; the bare cell comprising a stacked positive electrode sheet, a separator and a negative electrode sheet, wherein the negative electrode sheet comprises: a negative electrode collector, a first active layer and a second active layer, the first active layer being located on the surface of the current collector, the second active layer being located on the surface of the first active layer, the first active layer having a first pore therein, the second active layer having a second pore wrapped by a carbon shell therein, the second porosity of the second active layer being greater than the first porosity of the first active layer; the electrolyte is also located in the first pore and the second pore.

[0017] In some embodiments, the negative electrode sheet further includes: a carbon nanotube layer, wherein the carbon nanotube layer is located between the first active layer and the second active layer.

[0018] According to some embodiments of the present application, another aspect of the embodiments of the present application provides an energy storage battery pack, including: a secondary battery prepared by the method for preparing a secondary battery as described in any one of the above embodiments or a secondary battery as described in the above embodiments.

[0019] According to some embodiments of the present application, on the other hand, embodiments of the present application provide an electrical device, including: a secondary battery prepared by the method for preparing a secondary battery as described in any of the above embodiments, a secondary battery as described in the above embodiments, or an energy storage battery pack as described in the above embodiments.

[0020] The technical solution provided by the embodiments of the present application has at least the following advantages:

[0021] The preparation method of the secondary battery provided in the embodiment of the present application is provided with a first active layer and a second active layer on the negative electrode current collector of the negative electrode sheet, and the second porosity of the second active layer is greater than the first porosity of the first active layer, so that the electrolyte can be immersed in the first active layer via the second hole of the second active layer, thereby reducing the difficulty of electrolyte infiltration and improving electronic conductivity. Secondly, the second camphor particles coated with a carbon shell are used as the carrier of the second hole. After the second camphor particles are sublimated, the carbon shell can support the void structure, effectively solving the problem of the collapse of the coating structure due to hollowing, while improving the electronic conductivity of the second active layer. Secondly, there is a first hole in the first active layer. When the second active layer is formed, the slurry can partially flow into the first hole to play a pinning effect, thereby improving the bonding force between the first active layer and the second active layer. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] One or more embodiments are exemplified by the figures in the corresponding drawings. These exemplified descriptions do not constitute a limitation on the embodiments. Unless otherwise stated, the figures in the drawings do not constitute a scale limitation. In order to more clearly illustrate the embodiments of the present application or the technical solutions in the traditional technology, the drawings required for use in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0023] Figure 1 A flow chart of a method for preparing a secondary battery provided in one embodiment of the present application;

[0024] Figure 2 A schematic structural diagram of a negative electrode sheet in a secondary battery provided in one embodiment of the present application. DETAILED DESCRIPTION

[0025] As can be seen from the background art, the porosity, electrochemical performance and rate performance of current negative electrode sheets need to be further improved.

[0026] Analysis found that one of the reasons for the porosity, electrochemical performance and rate performance of the negative electrode is that, in order to overcome the problem of increased impedance caused by high surface density and high compaction, the positive and negative electrode formula ratio is usually adjusted, such as increasing the proportion of conductive particles to increase the electronic conductivity of the electrode; and to improve ionic conductivity, a reasonable particle size ratio is usually used to increase the electrode porosity and reduce the electrode tortuosity. However, these measures have limited effect on solving the problem of rising electrode impedance. The use of a reasonable active material particle size ratio cannot significantly improve the ionic conductivity of the electrode, and the porosity distribution of the electrode is still unreasonable. Simply increasing the ratio of conductive particles can reduce the electronic resistance of the electrode within a certain range, but ionic impedance is the shortcoming of the electrode, and the effect of improving the electrochemical impedance of the entire electrode is negligible. Therefore, only by simultaneously improving the electronic conductivity and ionic conductivity of the negative electrode can the electrochemical performance of the electrode be effectively improved and the rate performance of the electrode be improved. In addition, pore-forming agents are also used to increase porosity. Although these methods can increase the ionic conductivity of the electrode, they can also easily cause the electrode structure to collapse.

[0027] The embodiments of the present application provide a secondary battery and a preparation method thereof, an energy storage battery pack, and an electrical device. Pores are formed by sublimating camphor particles, and the camphor particles are wrapped with carbon to ensure the stability of the pores and prevent the collapse of the pores. The conductivity is improved based on the first active layer, the second active layer, and the carbon shell, thereby improving the electrochemical performance and rate performance of the negative electrode sheet.

[0028] In the description of the embodiments of this application, the technical terms "first" and "second" are used only to distinguish different objects and should not be understood to indicate or imply relative importance or implicitly specify the quantity, specific order, or primary and secondary relationship of the indicated technical features. In the description of the embodiments of this application, the meaning of "plurality" is more than two, unless otherwise clearly and specifically defined.

[0029] References herein to "embodiments" mean that a particular feature, structure, or characteristic described in connection with the embodiments may be included in at least one embodiment of the present application. The appearance of this phrase in various places in the specification does not necessarily refer to the same embodiment, nor does it constitute an independent or alternative embodiment that is mutually exclusive of other embodiments. It is understood, both explicitly and implicitly, by those skilled in the art that the embodiments described herein may be combined with other embodiments.

[0030] In the description of the embodiments of this application, the term "and / or" is simply a description of the association relationship between associated objects, indicating that three relationships can exist. For example, A and / or B can represent the following three situations: A exists, A and B exist at the same time, and B exists. In addition, the character " / " in this document generally indicates that the associated objects are in an "or" relationship.

[0031] In the description of the embodiments of the present application, the term "multiple" refers to more than two (including two). Similarly, "multiple groups" refers to more than two groups (including two groups), and "multiple pieces" refers to more than two pieces (including two pieces).

[0032] In the description of the embodiments of the present application, the technical terms "center", "longitudinal", "lateral", "length", "width", "thickness", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", "clockwise", "counterclockwise", "axial", "radial", "circumferential", etc., indicating the orientation or position relationship, are based on the orientation or position relationship shown in the accompanying drawings, and are only for the convenience of describing the embodiments of the present application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation on the embodiments of the present application.

[0033] In the description of the embodiments of the present application, unless otherwise expressly specified or limited, technical terms such as "installed," "connected," "connected," and "fixed" should be understood in a broad sense. For example, they can refer to fixed connections, detachable connections, or integration; mechanical connections or electrical connections; direct connections or indirect connections through an intermediate medium; internal connections between two components or interactions between two components. Those skilled in the art can understand the specific meanings of the above terms in the embodiments of the present application based on specific circumstances.

[0034] In the accompanying drawings corresponding to the embodiments of the present application, the thickness and area of ​​the layers are exaggerated for better understanding and ease of description. When describing a component (such as a layer, film, region, or substrate) as being on another component or on the surface of another component, the component may be "directly" located on the surface of the other component, or a third component may be present between the two components. Conversely, when describing a component as being on the surface of another component or as being formed or provided on the surface of a component, it means that there is no third component between the two components. In addition, when describing a component as being "substantially" formed on another component, it means that the component is not formed on the entire surface (or front surface) of the other component, nor is it formed on a portion of the edge of the entire surface.

[0035] In the description of the embodiments of this application, when a component "includes" another component, unless otherwise specified, other components are not excluded, and other components may be further included. In addition, when a component such as a layer, film, region, or plate is referred to as being "on / located on" another component, it can be "directly on" the other component (i.e., located on the surface of the other component with no other components between them) or another component can be present between them. In addition, when a component such as a layer, film, region, or plate is "directly on" another component, or when a component such as a layer, film, region, or plate is located on the surface of another component, it means that no other components are located between them.

[0036] The terms used herein in the description of the various embodiments are intended only to describe the specific embodiments and are not intended to be limiting. As used in the description of the various embodiments and the appended claims, "part" is intended to include the plural form unless the context clearly indicates otherwise. A component includes a layer, film, region, or plate.

[0037] The following detailed description of the various embodiments of the present application is provided in conjunction with the accompanying drawings. However, those skilled in the art will appreciate that many technical details are provided in the various embodiments of the present application to facilitate a better understanding of the present application. However, even without these technical details and the various variations and modifications based on the following embodiments, the technical solutions claimed in the present application can still be implemented.

[0038] Figure 1 A flow chart of a method for preparing a secondary battery provided in one embodiment of the present application; Figure 2 A schematic structural diagram of a negative electrode sheet in a secondary battery provided in one embodiment of the present application.

[0039] According to some embodiments of the present application, the present application provides a method for preparing a secondary battery, referring to Figure 1 The preparation method includes: forming a negative electrode sheet, the negative electrode sheet includes: a negative electrode current collector, a first active layer and a second active layer stacked in sequence, the first active layer has a first hole, the second active layer has a second hole, and the second porosity of the second active layer is greater than the first porosity of the first active layer; the preparation step of forming the second active layer includes: preparing carbon-coated camphor particles; preparing a second coating slurry, the second coating slurry includes carbon-coated camphor particles; covering the second coating slurry on the negative electrode current collector having the first active layer, wherein the second coating slurry flows into at least a portion of the first holes, and drying is performed to form the second active layer; wherein during the drying process, the camphor particles in the carbon-coated camphor particles are sublimated to form second holes; providing a positive electrode sheet and a separator, stacking the negative electrode sheet, the separator and the positive electrode sheet in sequence, obtaining a bare cell by winding or laminating, placing the bare cell into a battery shell, injecting an electrolyte into the battery shell and then encapsulating it to obtain a secondary battery.

[0040] A negative electrode sheet is formed, the negative electrode sheet comprising: a negative electrode current collector, a first active layer and a second active layer, the first active layer being located on a surface of the negative electrode current collector, the second active layer being located on a surface of the first active layer away from the first active layer, the first active layer having first pores, the second active layer having second pores, and the second porosity of the second active layer being greater than the first porosity of the first active layer; the preparation steps for forming the second active layer comprising: dispersing second camphor particles in a pre-carbonized solution, the pre-carbonized solution containing a carbonized material, drying to obtain a camphor precursor, the surface of the camphor precursor being coated with the carbonized material; subjecting the camphor precursor to a pre-carbonized solution; and The method comprises the steps of: performing a heat treatment to convert a camphor precursor into carbon-coated camphor particles; uniformly stirring the carbon-coated camphor particles, a second negative electrode material, a second conductive agent, and a second adhesive with a second dispersion solution to obtain a second coating slurry; covering the second coating slurry on the negative electrode current collector having the first active layer, wherein the second coating slurry flows into at least a portion of the first pores, and forming a second active layer after drying; wherein the camphor particles in the carbon-coated camphor particles are sublimated after the drying treatment, the carbon shells of the carbon-coated camphor particles are retained, and the positions occupied by the camphor particles in the carbon-coated camphor particles are converted into second pores having a carbon coating.

[0041] The preparation method of the secondary battery provided in the embodiment of the present application is provided with a first active layer and a second active layer on the negative electrode current collector of the negative electrode sheet, and the second porosity of the second active layer is greater than the first porosity of the first active layer, so that the electrolyte can be immersed in the first active layer via the second hole of the second active layer, thereby reducing the difficulty of electrolyte infiltration and improving electronic conductivity. Secondly, the second camphor particles coated with a carbon shell are used as the carrier of the second hole. After the second camphor particles are sublimated, the carbon shell can support the void structure, effectively solving the problem of the collapse of the coating structure due to hollowing, while improving the electronic conductivity of the second active layer. Secondly, there is a first hole in the first active layer. When the second active layer is formed, the slurry can partially flow into the first hole to play a pinning effect, thereby improving the bonding force between the first active layer and the second active layer.

[0042] The preparation method provided above will be described in detail below.

[0043] According to the appearance classification, the prepared secondary batteries can be divided into square cells, round cells or soft-pack cells. According to the capacity classification, the secondary batteries can be divided into 50Ah, 100Ah, 150Ah, 200Ah, 280Ah, 306Ah, 314Ah, 500+Ah, 800+Ah and 1000+Ah and other models. According to the chemical composition and working principle classification of the bare cells of the secondary battery, the secondary battery can be a lithium-ion battery, a lead-acid battery, a sodium-ion battery or a nickel-metal hydride battery. The embodiment of the present application takes the preparation method of a lithium-ion battery as an example. Those skilled in the art can replace the lithium ions in the positive electrode sheet, the negative electrode sheet and the electrolyte with corresponding metal ions according to actual needs. For example, in sodium-ion batteries, the lithium transition metal oxide of the subsequent positive electrode active material is replaced by any of the corresponding layered metal oxides (such as NaFeO2), polyanion compounds (NaFePO4) and Prussian blue compound systems (such as NaMnFe(CN)6-zH2O), and the electrolyte is replaced by any of the organic liquid electrolyte, solid composite electrolyte or solid electrolyte.

[0044] refer to Figure 2 The negative electrode current collector 100 can be copper foil. Copper foil has low electrical conductivity but high electron transport capacity. Copper foil also has weak lithium insertion capacity and captures fewer lithium ions, thereby effectively reducing lithium ion loss. In other embodiments, the negative electrode current collector can also be a foam copper current collector, a copper mesh current collector, or a three-dimensional nano-copper array current collector.

[0045] In some embodiments, the negative electrode current collector 100 can be a composite current collector, including a polymer material layer and a metal coating, the metal coating is located on the upper and lower sides of the polymer material layer, the polymer material layer is PET (polyethylene terephthalate), PP (polypropylene), PI (polyimide), etc., and the metal coating is a copper layer.

[0046] In some embodiments, the negative electrode current collector 100 may also be a carbon-based current collector, i.e., a conductive carbon layer is formed on a copper foil. The conductive carbon layer can serve as a protective layer, effectively protecting the current collector from corrosion and thereby increasing the lifespan of the current collector. Furthermore, the conductive carbon layer itself has a low resistivity, thus preventing excessive electrical losses. The conductive carbon layer can be made of flake graphite, spherical graphite, carbon nanotubes, graphene, and the like.

[0047] It should be noted that the carbon-based current collector can be formed by coating both the upper and lower surfaces of the copper foil with a conductive carbon layer, or by coating a portion of the copper foil with a conductive carbon layer. The portion of the copper foil coated with a conductive carbon layer can include the copper foil corresponding to the first active layer (and a portion of the tab area not covered by the first active layer) having a conductive carbon layer; or the tab area having a conductive carbon layer; or the first active layer and a portion of the tab area having a conductive carbon layer, etc.

[0048] In some embodiments, the active material particles in the first active layer 110 and the second active layer 130 are carriers of oxidation reactions in the battery cell, such as the negative electrode material in the first active layer and the negative electrode material in the second active layer.

[0049] In some embodiments, the negative electrode active material can be divided into two categories: carbon materials and non-carbon materials: carbon-based materials include graphite materials (natural graphite, artificial graphite and mesophase carbon spheres) and other carbon-based materials (hard carbon, soft carbon and graphene); non-carbon-based materials can be further divided into titanium-based materials, silicon-based materials, tin-based materials, nitrides and metallic lithium, etc.

[0050] In some embodiments, a first active layer 110 and a second active layer 130 are provided on the negative electrode current collector 100. By providing two layers of active material layers, firstly, the first active layer 110 is closer to the negative electrode current collector 100, so that the stability and conductivity of the lower surface of the negative electrode current collector 100 connected to the active coating are better, thereby improving the electrochemical performance and cycle performance of the negative electrode; secondly, the second active layer 130 is far away from the negative electrode current collector 100 and is in contact with the diaphragm. The surface of the corresponding negative electrode side is prone to lithium deposition, so the second active layer 130 in contact with the diaphragm can focus on stability and conductivity, which is conducive to the smooth insertion and extraction of lithium ions inside the positive and negative electrode materials.

[0051] Thus, the second active layer 130 is provided with second pores 131, and the first active layer 110 is provided with first pores 111. The second porosity of the second active layer 130 is greater than the first porosity of the first active layer 110. The second pores 131 can increase the porosity of the negative electrode sheet, thereby facilitating the storage of electrolyte and effectively improving the negative electrode sheet's liquid retention capacity. During the charge and discharge process, the transmission distance of lithium ions is reduced, and gaps are formed between the active material particles in the negative electrode sheet, providing a buffer for the cyclic expansion of the active material particles, further improving the negative electrode sheet's charging capacity.

[0052] In some embodiments, the preparation step of forming the first active layer 110 includes: uniformly stirring first camphor particles, a first negative electrode material, a first conductive agent, and a first adhesive with a first dispersion solution to obtain a first coating slurry.

[0053] In some embodiments, the first camphor particle is named 1,7,7-trimethylbicyclo[2.2.1]heptan-2-one, and its chemical formula is C 10 H 16 The average particle size of the first camphor particles is 15 μm to 20 μm. The particle size is the diameter of the particles, and the average particle size refers to the diameter of most particles or the average length of irregular particles.

[0054] In some embodiments, in the first coating slurry, the mass ratio of the first camphor particles, the first negative electrode material, the first conductive agent, the first binder, and the first dispersion solution is (0.2-0.4): (96-97.2): (0.8-1.2): (2.0-2.8): (160-200). Increasing the mass ratio of the first conductive agent to 0.8-1.2, compared to a conventional conductive agent mass ratio of 0.4-0.6 (e.g., the mass ratio of the second conductive agent), can increase the proportion of conductive particles in the negative electrode active material, thereby improving the electronic conductivity of the first active layer 110 and, in turn, enhancing the electrochemical performance and cycling performance of the negative electrode sheet.

[0055] In some embodiments, the first negative electrode material may include graphite. The graphite may be secondary particles. This secondary particle size is smaller, allowing for better ion diffusion. The secondary particles can provide lower impedance and thus higher conductivity. Secondary particles refer to the size of aggregated particles, while primary particles, as used herein, refer to the size of individual fine grains.

[0056] In some embodiments, the first conductive agent includes carbon nanotubes (CNTs) and conductive carbon black (SPs), and the mass ratio of the carbon nanotubes to the conductive carbon black is (0.4-0.6): (0.4-0.6).

[0057] In some embodiments, the first adhesive comprises styrene-butadiene rubber (SBR), carboxymethyl cellulose (CMC), and polyacrylic acid (PAA), with the mass ratio of styrene-butadiene rubber, carboxymethyl cellulose, and polyacrylic acid being (0.8-1.2): (0.6-0.8): (0.6-0.8). The styrene-butadiene rubber aqueous solution is used as the adhesive to reduce the phenomenon of electrode demolding and decarburization during the coating, cutting, slitting, and winding processes of electrode production, thereby optimizing the processing performance of the electrode, and the resulting electrode has good flexibility; carboxymethyl cellulose mainly plays a dispersing and thickening role, thereby reducing the amount of adhesive used; polyacrylic acid is a water-soluble high molecular polymer formed by the polymerization of acrylic acid monomers. The large number of carboxylic acid groups on polyacrylic acid can form a strong interaction with the active substance, thereby having good bonding properties and improving the cycling stability of the battery cell during the battery cell cycle.

[0058] In some embodiments, the first dispersion solution may be deionized water.

[0059] In summary, the process for forming the first coating slurry provided in the embodiments of the present application can be as follows: the mass ratio of each substance is as follows: graphite (first negative electrode material): 96 to 97.2 parts, PAA (first binder): 0.6 to 0.8 parts, SBR (first binder): 0.8 to 1.2 parts, CMC (first binder): 0.6 to 0.8 parts, SP (first conductive agent): 0.4 to 0.6 parts, CNT (first conductive agent): 0.4 to 0.6 parts, first camphor particles: 0.2 to 0.4 parts, deionized water: 160 to 200 parts. The above amounts of graphite powder, SP, CMC, and first camphor particles are added to a mixing tank and dry mixed for 30 minutes. The stirring speed is 15 rpm and the dispersion speed is 500 rpm. Then, add a small portion (e.g., 80 parts by weight) of deionized water and knead and stir for 60 minutes at a stirring speed of 20 rpm and a dispersion speed of 300 rpm. Then, add the remaining deionized water (e.g., 105 parts by weight) and disperse at high speed at a stirring speed of 22 rpm and a dispersion speed of 1000 rpm. Then, add CNT and PAA and disperse for 30 minutes at a stirring speed of 22 rpm and a dispersion speed of 600 rpm. Finally, add SBR and continue stirring for 30 minutes at a stirring speed of 22 rpm and a dispersion speed of 500 rpm to obtain the first coating slurry.

[0060] Continue to refer Figure 1 The preparation steps for forming the first active layer 110 include: covering the negative electrode current collector 100 with a first coating slurry with a coating density of 100 g / m 2 ~110g / m 2 After drying, the first active layer 110 is obtained, the first camphor particles are sublimated, and the positions occupied by the first camphor particles are transformed into first holes 111.

[0061] In some embodiments, after the first coating slurry is covered on the negative electrode current collector, it is baked at 80°C for 12 hours. During the baking process, the first camphor particles will sublime and then separate from the coating, leaving holes at the original position, namely the first holes 111, which are convenient for the subsequent second coating slurry to flow in and form the second active layer 130. In this way, the second active layer 130 is not only located on the surface of the first active layer 110, but also located inside the first active layer 110, thereby being able to play a pinning effect and effectively improve the bonding strength between the first active layer 110 and the second active layer 130.

[0062] In other embodiments, an electrolytic graphite pore-forming process can be used, wherein the above-mentioned raw materials, except for the first camphor particles, are mixed, coated, and dried to form a first active layer. The first active layer is then placed in an electrolytic cell, and the negative electrode current collector is connected to a power source. When current passes through the electrolytic cell, ions in the electrolyte are electrolyzed, resulting in a chemical reaction that etches the graphite surface, forming pores, i.e., first pores.

[0063] In some embodiments, reference Figure 2 After forming the first active layer 110, the process also includes providing a carbon source gas and a carrier gas to form a carbon nanotube layer 120 on the surface of the first active layer 110 using a plasma vapor deposition process at a temperature of 700°C to 900°C. The carbon nanotube layer 120 effectively reduces the impedance caused by the coating interface and improves the lateral electronic conductivity of the coating.

[0064] In some embodiments, the thickness of the carbon nanotube layer 120 is 200 μm to 500 μm. The thickness of the carbon nanotube layer 120 can be 200 μm, 230 μm, 250 μm, 282 μm, 303 μm, 348 μm, 369 μm, 391 μm, 403 μm, 431 μm, 466 μm, 482 μm, or 500 μm. The thickness of the carbon nanotube layer 120 allows the subsequently formed second coating slurry to flow into the first holes 111 through the holes in the carbon nanotube layer 120, and the electrolyte to flow into the first active layer 110 through these holes. The thickness of the carbon nanotube layer 120 can also improve electrical conductivity, thereby reducing the impedance between the first active layer 110 and the second active layer 130.

[0065] In some embodiments, the carbon source gas may be methane or ethanol, and the carrier may be an inert gas such as argon.

[0066] Continue to refer Figure 1 The steps of forming the second active layer 130 can be divided into: forming a camphor precursor, coating the surface of the camphor precursor with a carbonized material; forming carbon-coated camphor particles; forming a second coating slurry; and forming the second active layer 130.

[0067] The process steps for forming a camphor precursor include: dissolving camphor particles in ethanol to form a saturated solution, obtaining micron-sized second camphor particles by spray drying, dispersing the second camphor particles in a pre-carbonized solution, stirring to evaporate the solvent so that the carbonized material evenly wraps the second camphor particles, and drying to obtain a camphor precursor, wherein the surface of the camphor precursor is coated with the carbonized material.

[0068] In some embodiments, the pre-carbonized solution includes a sucrose aqueous solution, the mass fraction of the sucrose aqueous solution is 3 parts to 7 parts; the mass fraction of camphor particles in the sucrose aqueous solution is 55wt% to 70wt%.

[0069] The second camphor particles can be made of the same material as the first camphor particles, except that the average particle size of the first camphor particles is smaller than that of the second camphor particles. The average particle size of the first camphor particles is 15 μm to 20 μm, while the average particle size of the second camphor particles is 5 μm to 10 μm.

[0070] The average particle size of the second camphor particles may specifically be 5 μm, 6 μm, 7 μm, 8 μm, 9 μm or 10 μm.

[0071] In some embodiments, the heat treatment process includes placing a camphor precursor in a heat treatment device, introducing an inert gas, heating to 160°C to 200°C, and carbonizing for 5 minutes to 15 minutes, and cooling to obtain carbon-coated camphor particles. The carbonization process controls the carbonization temperature and time to prevent excessive sublimation of the second camphor particles, and cools to obtain carbon-coated camphor particles. The carbon shell retained in the carbon-coated camphor particles can effectively support the structure, prevent the electrode structure from collapsing, and at the same time improve the electronic conductivity of the second active layer 130.

[0072] In some embodiments, the thickness of the carbon shell 132 in the carbon-coated camphor particles is 15 nm to 20 nm. For example, the thickness of the carbon shell 132 may be 15 nm, 16 nm, 17 nm, 18 nm, 19 nm, or 20 nm.

[0073] In some embodiments, the mass ratio of the carbon-coated camphor particles, the second negative electrode material, the second conductive agent, the second adhesive, and the second dispersion solution is (0.4-0.6): (96-97.2): (0.4-0.6): (2.0-2.8): (160-200).

[0074] In some embodiments, the second adhesive includes styrene-butadiene rubber, carboxymethyl cellulose, and polyacrylic acid, and the mass ratio of styrene-butadiene rubber, carboxymethyl cellulose, and polyacrylic acid is (0.8-1.2): (0.6-0.8): (0.6-0.8).

[0075] It should be noted that the second conductive agent in the second coating slurry is SP. The second negative electrode material is primary graphite particles. The other components, the second binder and the second dispersion are the same as the first binder and the first dispersion in the first coating slurry.

[0076] In some embodiments, in the process of obtaining the second coating slurry, carboxymethyl cellulose, polyacrylic acid, and styrene-butadiene rubber are added in sequence, while the stirring speed is controlled to increase first and then decrease.

[0077] Specifically, the weight ratio of each substance is: graphite (primary graphite): 96-97.2 parts, PAA: 0.6-0.8 parts, SBR: 0.8-1.2 parts, CMC: 0.6-0.8 parts, SP: 0.4-0.6 parts, carbon-coated camphor granules: 0.4-0.6 parts, deionized water: 160-200 parts. The above amounts of graphite powder, SP, CMC, and carbon-coated camphor granules were added to a mixing tank and dry-mixed for 30 minutes at a stirring speed of 15 rpm and a dispersion speed of 500 rpm. A small amount (80 parts by weight) of deionized water was then added and kneaded and stirred for 60 minutes at a stirring speed of 20 rpm and a dispersion speed of 300 rpm. Then add the remaining deionized water (105 parts by mass) and disperse at high speed, with a stirring revolution speed of 22 rpm and a dispersion speed of 1000 rpm. Then add PAA and disperse for 30 minutes, with a stirring revolution speed of 22 rpm and a dispersion speed of 600 rpm. Finally, add SBR and continue stirring for 30 minutes, with a stirring revolution speed of 22 rpm and a dispersion speed of 500 rpm to obtain a second coating slurry.

[0078] The process steps for forming the second active layer 130 include: coating the second coating slurry on the first active layer 110 after the surface treatment, with a coating surface density of 100g / m 2 ~110g / m 2 During the coating process, the coating slurry will flow into part of the first holes 111. The double-layer negative electrode sheet obtained by the above coating is rolled and the compaction density is 1.5g / cm 3 ~1.6g / cm 3 The rolled electrode is baked at 60°C for 24 hours. During the baking process, the camphor particles in the carbon-coated camphor particles will sublime and separate from the coating, thereby effectively improving the porosity of the second active layer 130 and its ionic conductivity. At the same time, the retained carbon coating can improve the electronic conductivity of the layer. Combined with the excellent electronic conductivity of the first active layer 110 and the carbon nanotube layer 120 coating, it also makes up for the problem of large ionic impedance of the thick negative electrode close to the current collector and large electronic impedance away from the current collector. The negative electrode shows excellent rate performance.

[0079] It should be noted that the coating area density of the first coating slurry and the second coating slurry can be determined in a ratio according to actual conditions. The second coating slurry partially fills the first holes 111, but does not completely fill the first holes 111, so that some of the first holes 111 can still be filled with electrolyte, while the first holes filled with the second coating slurry constitute part of the second active layer.

[0080] In summary, for the first active layer 110, the first active layer 110 close to the negative electrode current collector is made of secondary particle type graphite, and the proportion of conductive particles is increased, and the carbon nanotube layer 120 is introduced to increase the conductivity and other measures to ensure the improvement of the electronic conductivity of this layer to the greatest extent. In this way, the electronic conductivity of the second active layer 130 away from the negative electrode current collector is ensured. At the same time, in order to ensure compliance with the connection in the coating and take into account the improvement of the ionic conductivity of the first active layer 110, camphor particles are used to form pores in the first active layer 110, and a layer of carbon nanotube layer 120 is deposited on the surface of the first active layer 110 by vapor deposition, which effectively reduces the impedance caused by the coating interface and improves the lateral electronic conductivity of the coating.

[0081] For the second active layer 130, a template method is used to increase its porosity and thus its ionic conductivity. The template method involves adding solid particles that are easily sublimated by heat, such as 1,7,7-trimethylbicycloheptan-2-one (camphor) with a carbon coating on its surface, to its coating slurry. During the subsequent electrode baking, these particles will sublime, thereby effectively increasing the porosity of this layer of coating. At the same time, the second active layer 130 is a surface coating. The application of the surface coating template method can maximize the volatilization of the template particles by heat without affecting the subsequent electrical performance of the electrode. The increase in the porosity of the second active layer 130 can maximize the ionic conductivity of the first active layer 110. At the same time, when the camphor sublimates and evaporates, the retained carbon shell can effectively support the structure, preventing the electrode structure from collapsing, while also improving the electronic conductivity of the second active layer 130. The above design of the first active layer 110 and the second active layer 130 effectively ensures the high rate performance of the coating.

[0082] After forming the negative electrode sheet, the method further includes: die-cutting a portion of the negative electrode current collector according to preset parameters so that the end of the negative electrode current collector forms a negative electrode tab; and cutting the negative electrode current collector to form multiple identical negative electrode sheets.

[0083] The positive electrode sheet includes a positive electrode current collector and a positive electrode active material layer, wherein the positive electrode current collector can be aluminum foil.

[0084] The separator can be located between the positive electrode and the negative electrode to prevent short circuit problems caused by physical contact between the positive electrode and the negative electrode, while allowing ions to be conducted through the electrolyte and hindering the transmission of electrons, so that the ions and electrons form a circuit during the charging and discharging process of the battery.

[0085] The separator may be any one of a microporous membrane, a modified microporous membrane, a non-woven fabric separator, and a composite separator. The separator may be coated with polyvinylidene fluoride (PVDF) material to impart excellent adhesion and flexibility to the separator.

[0086] refer to Figure 1, the positive electrode sheet, negative electrode sheet and separator are wound or stacked.

[0087] In some embodiments, the winding process involves passing the separator, positive electrode sheet, and negative electrode sheet through a winding machine to form a single core. The order is to wrap the positive electrode sheet with the negative electrode sheet, and then separate the positive and negative electrodes with the separator. The stacking process involves stacking the separator, positive electrode sheet, and negative electrode sheet in sequence, and then rolling and cutting them into a single battery cell.

[0088] The preparation method also includes: welding the tabs to the adapter, connecting the other end of the adapter to the terminal post; and engaging the top cover with the battery case. The adapter is located in the cavity, and the terminal post passes through the top cover.

[0089] Among them, the adapter plate includes at least a first adapter plate and a second adapter plate, the pole includes a positive pole pole and a negative pole pole, the first adapter plate is electrically connected to the positive pole tab and the positive pole pole of the positive pole plate respectively, and the second adapter plate is electrically connected to the negative pole tab and the negative pole pole of the negative pole plate respectively.

[0090] The preparation method of the secondary battery provided in the embodiment of the present application is provided with a first active layer 110 and a second active layer 130 on the negative electrode current collector of the negative electrode sheet, and the second porosity of the second active layer 130 is greater than the first porosity of the first active layer 110, so that the electrolyte can be immersed in the first active layer 110 through the second hole 131 of the second active layer, thereby reducing the difficulty of electrolyte infiltration and improving electronic conductivity. Secondly, the second camphor particles coated with carbon shells are used as carriers of the second holes 131. After the second camphor particles are sublimated, the carbon shell 132 can support the void structure, effectively solving the problem of coating structure collapse due to hollowing, while improving the electronic conductivity of the second active layer 130. Secondly, the first active layer 110 has a first hole 111. When the second active layer 130 is formed, the slurry can partially flow into the first hole 111 to play a pinning effect, thereby improving the bonding force between the first active layer 110 and the second active layer 130.

[0091] Accordingly, according to some embodiments of the present application, the embodiments of the present application further provide a secondary battery, which can be prepared using the preparation method provided in the above embodiments. The technical features that are the same as or corresponding to the above embodiments will not be described in detail here.

[0092] According to some embodiments of the present application, on the other hand, embodiments of the present application provide a secondary battery, including: a battery shell, the battery shell having a cavity, the cavity having an electrolyte; a bare battery cell, the bare battery cell being located in the cavity and immersed in the electrolyte; the bare battery cell including a positive electrode sheet, a separator and a negative electrode sheet arranged in a stacked manner, wherein the negative electrode sheet includes: a negative electrode collector 100, a first active layer 110 and a second active layer 130, the first active layer 110 being located on the surface of the current collector, the second active layer 130 being located on the surface of the first active layer 110, the first active layer 110 having a first hole 111, the second active layer 130 having a second hole 131 covered with a carbon shell 132, the second porosity of the second active layer 130 being greater than the first porosity of the first active layer 110; the electrolyte is also located in the first hole 111 and the second hole 131.

[0093] In some embodiments, the negative electrode sheet further includes a carbon nanotube layer 120 , and the carbon nanotube layer 120 is located between the first active layer 110 and the second active layer 130 .

[0094] According to some embodiments of the present application, another aspect of the embodiments of the present application provides an energy storage battery pack, including: a secondary battery prepared by the method for preparing a secondary battery as in any of the above embodiments or a secondary battery as in the above embodiments.

[0095] According to some embodiments of the present application, on the other hand, embodiments of the present application provide an electrical device, including: a secondary battery prepared by the method for preparing a secondary battery as in any of the above embodiments, a secondary battery as in the above embodiments, or an energy storage battery pack as in the above embodiments.

[0096] The beneficial effects of the embodiments of the present application will be further illustrated below in combination with examples and comparative examples.

[0097] Example 1:

[0098] (1) Preparation of the first coating slurry: The mass fractions of each substance are as follows: graphite (raw material is secondary particles): 96.4 parts, PAA: 0.6 parts, SBR: 1.2 parts, CMC: 0.6 parts, SP: 0.4 parts, CNT: 0.4 parts, first camphor particles: 0.4 parts, deionized water: 185 parts. The above amounts of graphite powder, SP, CMC and first camphor particles are added to a mixing tank and dry mixed for 30 minutes at a stirring speed of 15 rpm and a dispersion speed of 500 rpm. Thereafter, 80 parts of deionized water are added and kneaded and stirred for 60 minutes at a stirring speed of 20 rpm and a dispersion speed of 300 rpm. Then add the remaining deionized water (105 parts) and disperse at high speed, with a stirring revolution speed of 22 rpm and a dispersion speed of 1000 rpm. Then add CNT and PAA and disperse for 30 minutes, with a stirring revolution speed of 22 rpm and a dispersion speed of 600 rpm. Finally, add SBR and continue stirring for 30 minutes, with a stirring revolution speed of 22 rpm and a dispersion speed of 500 rpm to obtain the first coating slurry.

[0099] (2) Preparation of the first active layer and the carbon nanotube layer:

[0100] The first coating slurry is applied on the copper foil with a coating surface density of 105 g / m 2 The coated electrode is baked at 80°C for 12 hours. During the baking process, the first camphor particles sublime and detach from the coating, leaving the first holes in their original position and forming the first active layer. This facilitates the flow of the subsequent coating slurry, which can achieve a pinning effect. A carbon nanotube layer is grown on the surface of the baked electrode. A carbon source gas (methane or ethanol) and a carrier gas (argon) are introduced into the reactor in a certain ratio. At high temperature (700°C) and high pressure, the carbon source gas decomposes. The decomposed carbon source gas is gradually cooled and bombarded with the first active layer. After a period of gas bombardment, a carbon nanotube layer is formed on its surface. The thickness of the carbon nanotube layer is 300μm.

[0101] (3) Preparation of carbon-coated camphor particles:

[0102] A certain amount of camphor was dissolved in ethanol to form a saturated solution, and micron-sized second camphor particles were obtained by spray drying. The second camphor particles were dispersed in a sucrose aqueous solution (7 parts by mass (the mass proportion of the second camphor particles in the solution was 55wt%)), and the solvent was evaporated by stirring to allow the sugar to evenly coat the second camphor particles. The sugar was then dried to obtain sugar-camphor composite particles, i.e., camphor precursors. The coated camphor precursor was placed in a tube furnace and rapidly heated to 180°C by inert gas and maintained for 15 minutes to carbonize the precursor. The carbonized camphor particles were then cooled to obtain carbon-coated camphor particles with a carbon shell thickness of 20 nm.

[0103] (4) Preparation of the second coating slurry:

[0104] The weight percentages of each substance are as follows: graphite (primary particles): 97 parts, PAA: 0.6 parts, SBR: 0.8 parts, CMC: 0.6 parts, SP: 0.4 parts, carbon-coated camphor granules: 0.6 parts, and deionized water: 185 parts. The graphite powder, SP, CMC, and carbon-coated camphor granules were placed in a mixing tank and dry-mixed for 30 minutes at a stirring speed of 15 rpm and a dispersion speed of 500 rpm. Then, 80 parts of deionized water were added and kneaded and stirred for 60 minutes at a stirring speed of 20 rpm and a dispersion speed of 300 rpm. Then add the remaining deionized water (105 parts) and disperse at high speed, with a stirring revolution speed of 22 rpm and a dispersion speed of 1000 rpm. Then add PAA and disperse for 30 minutes, with a stirring revolution speed of 22 rpm and a dispersion speed of 600 rpm. Finally, add SBR and continue stirring for 30 minutes, with a stirring revolution speed of 22 rpm and a dispersion speed of 500 rpm to obtain a second coating slurry.

[0105] (5) Preparation of the second active layer:

[0106] The second coating slurry was coated on the first active layer after the surface treatment, and the coating surface density was 105 g / m 2 During the coating process, the second coating slurry will flow into part of the first pores. The double-layer negative electrode sheet obtained by the above coating is rolled and the compaction density is 1.5g / cm 3 ~1.6g / cm 3 The rolled electrode is baked at 60°C for 24 hours. During the baking process, the camphor in the carbon-coated camphor sublimates and separates from the coating, thereby forming a second hole and a second active layer.

[0107] Example 2:

[0108] The difference from Example 1 is that the mass fraction of the first camphor particles in the first active layer is 0.2 parts.

[0109] Example 3:

[0110] The difference from Example 1 is that the mass fraction of the carbon-coated camphor particles in the second active layer is 0.4 parts.

[0111] Example 4:

[0112] The difference from Example 1 is that the temperature of the preparation process of the carbon nanotube layer is changed, that is, under a high temperature of 900° C. and a high pressure, the thickness of the carbon nanotube layer is 500 μm.

[0113] Example 5:

[0114] The difference from Example 1 is that the preparation process of the carbon-coated camphor particles is changed, the mass fraction of sucrose water is controlled to 3 parts, the temperature in the tube furnace is 200° C., and the carbon shell thickness of the obtained carbon-coated camphor particles is 15 nm.

[0115] Comparative Example 1:

[0116] The weight percentages of each material are as follows: graphite (raw material: secondary particles): 96.8 parts, PAA: 0.6 parts, SBR: 1.2 parts, CMC: 0.6 parts, SP: 0.4 parts, CNT: 0.4 parts, and deionized water: 185 parts. The aforementioned amounts of graphite powder, SP, and CMC were added to a mixing tank and dry-mixed for 30 minutes at a stirring speed of 15 rpm and a dispersion speed of 500 rpm. 80 parts of deionized water were then added and kneaded and stirred for 60 minutes at a stirring speed of 20 rpm and a dispersion speed of 300 rpm. The remaining deionized water (105 parts) was then added and dispersed at high speed at a stirring speed of 22 rpm and a dispersion speed of 1000 rpm. CNT and PAA were then added and dispersed for 30 minutes at a stirring speed of 22 rpm and a dispersion speed of 600 rpm. Finally, SBR was added and stirred for another 30 minutes at a stirring speed of 22 rpm and a dispersion speed of 500 rpm to obtain the first coating slurry.

[0117] The first coating slurry is applied on the copper foil with a coating surface density of 210 g / m 2 The coated electrode is then rolled to a compaction density of 1.5 g / cm 3 between.

[0118] Comparative Example 2:

[0119] The difference from Example 1 is that the preparation of the carbon nanotube layer in step (2) is not included.

[0120] Comparative Example 3:

[0121] The difference from Example 1 is that the preparation of carbon-coated camphor particles in step (3) is not included. The mass fractions of the substances in the preparation of the second coating slurry (4) are as follows: graphite (raw material is primary particles): 97 parts, PAA: 0.6 parts, SBR: 0.8 parts, CMC: 0.6 parts, SP: 0.4 parts, second camphor particles: 0.6 parts, and deionized water: 185 parts. The second camphor particles are still the second camphor particles provided in step (3), but the outer shell is not coated with a carbon shell.

[0122] The above embodiments and comparative examples were sequentially subjected to electrode sheet wettability tests and electrode sheet conductivity tests. The negative electrode sheets provided in the above embodiments and comparative examples were prepared into secondary batteries and subjected to electrochemical performance tests. The test results were summarized and recorded in Table 1.

[0123] Electrode plate wettability test: The electrode's wettability is reflected in its ability to absorb electrolyte and the amount absorbed per unit time. The usual wettability test involves comparing the absorption rate of the same amount of electrolyte by different electrode plates of the same weight, with the one that absorbs the most quickly having greater absorption capacity. Alternatively, the absorption and storage capacity of different electrode plates of the same weight, when immersed in electrolyte, is compared, with the heavier plate having greater absorption capacity. The negative electrode plates prepared in the examples and comparative examples were weighed and tested for electrolyte absorption rate and absorption capacity, respectively.

[0124] Electrode Sheet Conductivity Test: The conductivity test primarily measures the membrane resistance of the battery's electrode sheets. The test method measures the membrane resistance per unit area under unit pressure. The membrane resistance of the negative electrode sheets prepared in the Examples and Comparative Examples was tested.

[0125] Electrochemical performance test: The test temperature is 25±2°C. Charge at a constant power of 0.5C to 3.65±0.01V. Wait for 10 minutes, then discharge at a rate of 0.5P (discharge rate) to a cutoff voltage of 2.5V. Record the capacity and use it as the initial capacity for the rate test. Then charge at a constant current of 1C to 3.65±0.01V. Wait for 10 minutes, then discharge at a rate of 1P to a cutoff voltage of 2.5V. Record the capacity and use it as the rate capacity of 1P. The C-rate (abbreviated as C) is a value relative to the rated capacity of the battery. For example, if a battery has a rated capacity of 200Ah, then a 1C charge or discharge rate is equivalent to a 200A charge or discharge rate. Based on this definition, 0.5C means the battery can be fully charged in 2 hours, while 1C means it can be fully charged in 1 hour. Similarly, 0.5P means the battery can be fully discharged in 2 hours, while 1P means it can be fully discharged in 1 hour.

[0126] Table 1

[0127]

[0128] As can be seen from Table 1, compared with Comparative Example 1, Examples 1 to 5 include: adding first camphor particles to the preparation process of the first active layer; forming the carbon nanotube layer after forming the first active layer; and adding second camphor particles to the preparation process of the second active layer; and the outer layer of the second camphor particles is further coated with a carbon shell. This can increase the rate at which the negative electrode sheet absorbs the electrolyte and reduce the resistance of the negative electrode sheet, thereby obtaining better rate performance.

[0129] The experimental data of Example 1 and Comparative Example 2 show that the carbon nanotube layer can reduce the resistance of the negative electrode sheet, but at the same time it will affect the absorption of the electrolyte. Therefore, combined with the data of Example 4, it can be seen that the thickness of the carbon nanotube layer is controlled to ensure that the resistance of the negative electrode sheet can be reduced while having good absorption of the electrolyte.

[0130] The experimental data of Example 1 and Comparative Example 3 show that first camphor particles, i.e., first pores, are formed in the first active layer, but second pores are not formed in the second active layer, resulting in a low electrolyte absorption rate and a high resistance.

[0131] Those skilled in the art will appreciate that the above-described embodiments are specific examples for implementing the present application, and that in actual applications, various changes in form and detail may be made thereto without departing from the spirit and scope of the present application. Any person skilled in the art may make various changes and modifications without departing from the spirit and scope of the present application. Therefore, the scope of protection of the present application shall be based on the scope defined in the claims.

Claims

1. A method for preparing a secondary battery, characterized in that: include: A negative electrode sheet is formed, the negative electrode sheet comprising: a negative electrode current collector, a first active layer, and a second active layer stacked in sequence, the first active layer having first pores therein, the second active layer having second pores therein, and the second porosity of the second active layer being greater than the first porosity of the first active layer; the preparation step of forming the second active layer comprises: preparing carbon-coated camphor particles; preparing a second coating slurry, the second coating slurry comprising the carbon-coated camphor particles; Covering the negative electrode current collector having the first active layer with the second coating slurry, wherein the second coating slurry flows into at least a portion of the first pores, and drying is performed to form the second active layer; wherein during the drying process, the camphor particles in the carbon-coated camphor particles sublime to form the second pores; A positive electrode sheet and a separator are provided, and the negative electrode sheet, separator and positive electrode sheet are stacked in sequence to obtain a bare cell by winding or laminating. The bare cell is placed in a battery shell, and an electrolyte is injected into the battery shell and then packaged to obtain a secondary battery.

2. The method for preparing a secondary battery according to claim 1, wherein: The second coating slurry also includes: a second negative electrode material, a second conductive agent, a second adhesive and a second dispersed solution; the mass ratio of the carbon-coated camphor particles, the second negative electrode material, the second conductive agent, the second adhesive and the second dispersed solution is (0.4~0.6): (96~97.2): (0.4~0.6): (2.0~2.8): (160~200).

3. The method for preparing a secondary battery according to claim 2, wherein: The second adhesive includes styrene-butadiene rubber, carboxymethyl cellulose and polyacrylic acid, and the mass ratio of styrene-butadiene rubber, carboxymethyl cellulose and polyacrylic acid is (0.8-1.2): (0.6-0.8): (0.6-0.8).

4. The method for preparing a secondary battery according to claim 3, wherein: In the process step of obtaining the second coating slurry, the carboxymethyl cellulose, the polyacrylic acid and the styrene-butadiene rubber are added in sequence, and the stirring speed is controlled to show a trend of first increasing and then decreasing.

5. The method for preparing a secondary battery according to claim 1, wherein: The preparation steps of the carbon-coated camphor particles include: dispersing second camphor particles in a pre-carbonized solution, wherein the pre-carbonized solution contains a carbonized material, drying to obtain a camphor precursor, and coating the surface of the camphor precursor with the carbonized material; heat-treating the camphor precursor to convert the camphor precursor into the carbon-coated camphor particles; the pre-carbonized solution includes a sucrose aqueous solution, and the sucrose aqueous solution accounts for 3 to 7 parts by weight of the pre-carbonized solution; and the mass proportion of the second camphor particles in the sucrose aqueous solution is 55 wt% to 70 wt%.

6. The method for preparing a secondary battery according to claim 5, wherein: The heat treatment process comprises the following steps: placing the camphor precursor in a heat treatment device, introducing an inert gas, heating the precursor to 160° C. to 200° C., carbonizing the precursor for 5 to 15 minutes, and cooling the precursor to obtain the carbon-coated camphor particles; the thickness of the carbon shell in the carbon-coated camphor particles is 15 nm to 20 nm.

7. The method for preparing a secondary battery according to claim 5, wherein: The preparation steps for forming the first active layer include: Evenly stirring the first camphor particles, the first negative electrode material, the first conductive agent, and the first adhesive with the first dispersion solution to obtain a first coating slurry; The first coating slurry is covered on the negative electrode current collector, and the coating density is 100g / m 2 ~110g / m 2 , and drying to obtain the first active layer, wherein the first camphor particles sublime after drying, and the positions occupied by the first camphor particles are converted into the first holes.

8. The method for preparing a secondary battery according to claim 7, wherein: After forming the first active layer, the method further includes: providing a carbon source gas and a carrier gas, and forming a carbon nanotube layer on the surface of the first active layer by a plasma vapor deposition process at a temperature of 700°C to 900°C; the thickness of the carbon nanotube layer is 200μm to 500μm.

9. The method for preparing a secondary battery according to claim 7, wherein: The second particle size of the second camphor particles is smaller than the first particle size of the first camphor particles; the first particle size is 15 μm to 20 μm; and the second particle size is 5 μm to 10 μm.

10. The method for preparing a secondary battery according to claim 7, wherein: The mass ratio of the first camphor particles, the first negative electrode material, the first conductive agent, the first adhesive and the first dispersion solution is (0.2~0.4): (96~97.2): (0.8~1.2): (2.0~2.8): (160~200).

11. The method for preparing a secondary battery according to claim 10, wherein: The first conductive agent includes carbon nanotubes and conductive carbon black, and the mass ratio of the carbon nanotubes to the conductive carbon black is (0.4-0.6): (0.4-0.6).

12. A secondary battery prepared by the method for preparing a secondary battery according to any one of claims 1 to 11, characterized in that: include: A battery case, wherein the battery case has a cavity therein, and the cavity contains an electrolyte; a bare battery cell, the bare battery cell being located in the cavity and immersed in the electrolyte; The bare battery cell includes a stacked positive electrode sheet, a separator and a negative electrode sheet, wherein the negative electrode sheet includes: a negative electrode current collector, a first active layer and a second active layer, the first active layer is located on the surface of the current collector, the second active layer is located on the surface of the first active layer, the first active layer has first pores, the second active layer has second pores wrapped in a carbon shell, and the second porosity of the second active layer is greater than the first porosity of the first active layer; the electrolyte is also located in the first pores and the second pores.

13. The secondary battery according to claim 12, characterized in that The negative electrode sheet further includes a carbon nanotube layer, and the carbon nanotube layer is located between the first active layer and the second active layer.

14. An energy storage battery pack, characterized in that: include: A secondary battery prepared by the method for preparing a secondary battery according to any one of claims 1 to 11, or a secondary battery according to claim 12 or 13.

15. An electrical device, characterized in that: include: A secondary battery prepared by the method for preparing a secondary battery according to any one of claims 1 to 11, a secondary battery according to claim 12 or 13, or an energy storage battery pack according to claim 14.

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