Secondary battery, method for manufacturing the same, and electric device

Abstract

The application relates to a secondary battery, a manufacturing method thereof and a power utilization device, and belongs to the technical field of batteries. The secondary battery comprises a negative electrode sheet, the negative electrode sheet comprises a negative electrode active material layer, the negative electrode active material layer comprises first negative electrode active material particles and second negative electrode active material particles, the first negative electrode active material particles have an angular shape, and the second negative electrode active material particles comprise silicon-based material particles and a coating layer located on surfaces of the silicon-based material particles and having a pore structure, the coating layer comprises amorphous carbon. The secondary battery provided by the application can balance high energy density and good cycle performance.

Description

Technical Field

[0001] This application relates to the field of battery technology, and in particular to a secondary battery, its manufacturing method, and an electrical device thereof. Background Technology

[0002] Rechargeable batteries are widely used in various applications such as electric transportation, energy storage systems, and emergency power supplies. With the increasing number of applications, the performance requirements for rechargeable batteries are also becoming more stringent. These requirements include high energy density while maintaining good cycle performance. Therefore, how to improve the energy density of rechargeable batteries while simultaneously ensuring good cycle performance has become a pressing technical problem that needs to be solved. Summary of the Invention

[0003] This application provides a secondary battery, a method for manufacturing the same, and an electrical device thereof, which can achieve both high energy density and good cycle performance.

[0004] In a first aspect, embodiments of this application provide a secondary battery, including a negative electrode sheet, the negative electrode sheet including a negative electrode active material layer, the negative electrode active material layer including a first negative electrode active material particle and a second negative electrode active material particle, the first negative electrode active material particle having an angular shape, the second negative electrode active material particle including silicon-based material particles and a coating layer located on the surface of the silicon-based material particles and having a porous structure, the coating layer including amorphous carbon.

[0005] In the secondary battery provided in this application embodiment, the first negative electrode active material particles have an angular shape, which allows a gap to be formed between them and adjacent first negative electrode active material particles to accommodate second negative electrode active material particles. The second negative electrode active material particles include silicon-based material particles and a coating layer with a porous structure on the surface of the silicon-based material particles. The coating layer includes amorphous carbon, which gives the second negative electrode active material particles strong resistance to pressure and puncture. This allows the second negative electrode active material particles to be embedded between the first negative electrode active material particles after cold pressing and to form a conductive network in contact with the first negative electrode active material particles, thereby increasing the compaction density of the negative electrode active material layer. Moreover, the breakage of the second negative electrode active material particles is reduced during the cold pressing process, thereby enabling the secondary battery to have a high energy density. Furthermore, the porous structure of the coating layer of the silicon-based material particles reduces the volume expansion of the second negative electrode active material particles, and the gaps formed between the first negative electrode active material particles can reserve space to accommodate the volume expansion of the second negative electrode active material particles. This further reduces the decrease in conductivity of the negative electrode due to the volume expansion of the silicon-based material particles, thus enabling the secondary battery to have good cycle performance. Therefore, the secondary battery provided by the embodiments of this application can achieve both high energy density and good cycle performance.

[0006] In some embodiments of this application, the mass percentage of the second negative electrode active material particles is 1% to 10% based on the mass of the negative electrode active material layer.

[0007] In some embodiments of this application, the mass percentage of the second negative electrode active material particles is 3% to 8% based on the mass of the negative electrode active material layer.

[0008] In the above technical solution, the mass ratio of the second negative electrode active material particles is within the above range, which can reduce the occurrence of crushing of the second negative electrode active material particles, and also allow the second negative electrode active material particles to have a suitable volume expansion to match the gap between the first negative electrode active material particles, thereby further helping to improve the energy density and cycle performance of the secondary battery.

[0009] In some embodiments of this application, based on the mass of the negative electrode active material layer, the total mass ratio of the first negative electrode active material particle and the second negative electrode active material particle is 90% to 98%, and the mass ratio of the first negative electrode active material particle and the second negative electrode active material particle is (87 to 96):(1 to 10).

[0010] In some embodiments of this application, the mass ratio of the first negative electrode active material particle to the second negative electrode active material particle is (90-94):(3-7).

[0011] In the above technical solution, based on the mass of the negative electrode active material layer, the total mass ratio of the first negative electrode active material particles and the second negative electrode active material particles is within the above range, which can improve the specific capacity of the negative electrode active material and help form a good conductive network to improve the conductivity of the negative electrode active material layer, thereby enabling the secondary battery to have higher energy density and better cycle performance.

[0012] When the mass ratio of the first negative electrode active material particles to the second negative electrode active material particles is within the above range, the negative electrode active material layer can achieve both appropriate compaction density and good ion transport capability, and can also reduce the occurrence of breakage of the second negative electrode active material particles, thereby further improving the energy density and cycle performance of the secondary battery.

[0013] In some embodiments of this application, the silicon-based material particles include one or more of nano-silicon, silicon oxide, and silicon carbide.

[0014] In some embodiments of this application, the silicon-based material particles include silicon carbide compounds, which include porous carbon and silicon-containing materials located within the porous carbon.

[0015] In some embodiments of this application, the mass percentage of silicon element is 0.04% to 6% based on the mass of the negative electrode active material layer.

[0016] In the above-mentioned technical solution, the mass ratio of silicon element within the above range can not only improve the capacity of the negative electrode active material, but also reduce the volume expansion of the second negative electrode active material particles, thereby improving the energy density and cycle performance of the secondary battery.

[0017] In some embodiments of this application, the silicon-containing material includes one or more of elemental silicon, nano-silicon, and silicon alloys.

[0018] In some embodiments of this application, the coating layer includes a first coating layer and a second coating layer, and the pore structure includes a first pore structure and a second pore structure. The first coating layer is located on the surface of the silicon-based material particles and between the second coating layer. The first pore structure is located in the first coating layer, and the second pore structure is located in the second coating layer. The porosity of the first pore structure is greater than that of the second pore structure. The second coating layer includes amorphous carbon.

[0019] In the above technical solution, the porosity of the first pore structure is relatively larger than that of the second pore structure, allowing the first coating layer to have more pores. This provides space for the volume expansion of silicon-based material particles, reducing the volume expansion of the second negative electrode active material particles and improving the cycle performance of the secondary battery. Furthermore, the relatively smaller porosity of the second pore structure increases the structural strength of the second negative electrode active material particles, thereby helping to increase the compaction density of the negative electrode active material layer and ultimately improving the energy density of the secondary battery.

[0020] In some embodiments of this application, the porosity of the first pore structure is 50% to 80%.

[0021] In some embodiments of this application, the porosity of the second pore structure is 0% to 1%.

[0022] In the above technical solution, the porosity of the first pore structure and the second pore structure are respectively set within the above range, which can further improve the cycle performance and energy density of the secondary battery.

[0023] In some embodiments of this application, the first negative electrode active material particles comprise artificial graphite and / or natural graphite.

[0024] In some embodiments of this application, the compaction density of the single-sided negative electrode active material layer is 1.7 g / cm³. 3 ~1.9g / cm 3 .

[0025] In some embodiments of this application, a positive electrode sheet is also included, which comprises a positive active material layer, and the compaction density of the positive active material layer on one side is 3 g / cm³. 3 ~4g / cm 3 .

[0026] In some embodiments of this application, the positive electrode active material layer includes a positive electrode active material, which includes a lithium-containing positive electrode active material and / or a sodium-containing positive electrode active material.

[0027] In some embodiments of this application, the lithium-containing cathode active material includes lithium phosphate materials and / or lithium ternary cathode active materials.

[0028] Secondly, embodiments of this application provide a method for manufacturing a secondary battery, comprising:

[0029] A first negative electrode active material particle, a second negative electrode active material particle, a binder, and a conductive agent are added to a solvent to form a negative electrode active material layer slurry. The first negative electrode active material particle has an angular shape. The second negative electrode active material particle includes silicon-based material particles and a coating layer with a porous structure located on the surface of the silicon-based material particles. The coating layer includes amorphous carbon.

[0030] The negative electrode active material slurry is coated onto the surface of the negative electrode current collector to form a negative electrode active material slurry layer. After drying and cold pressing, the negative electrode sheet is obtained.

[0031] In some embodiments of this application, the method for preparing the second negative electrode active material particles includes: mixing silicon-based material particles with a slurry containing foaming material and a first carbon source, and subjecting the mixture to calcination treatment, so that a first coating layer with a first pore structure is formed on the surface of the silicon-based material particles;

[0032] Silicon-based material particles with a first coating layer are placed in a second carbon source atmosphere for vapor deposition to form a second coating layer with a second porous structure and containing amorphous carbon on the surface of the first coating layer, thereby obtaining second negative electrode active material particles.

[0033] In some embodiments of this application, the first carbon source includes one or more of dopamine, polyacrylonitrile, epoxy resin, glucose, sucrose, cellulose, lignin, and pitch.

[0034] In some embodiments of this application, the foaming material includes one or more of carbonate foaming agents, alkane foaming agents, fluorocarbon foaming agents, and compressed gas foaming agents.

[0035] In some embodiments of this application, the carbonate foaming agent includes one or more of calcium carbonate, magnesium carbonate, and sodium bicarbonate.

[0036] In some embodiments of this application, the hydrocarbon blowing agent includes one or more of methane, ethane, pentane, n-butane, isobutane, and cyclopentane.

[0037] In some embodiments of this application, the fluorocarbon blowing agent includes one or more of hydrochlorofluorocarbons, hydrofluorocarbons, and hydrofluoroolefins.

[0038] In some embodiments of this application, the compressed gas foaming agent includes one or more of carbon dioxide, air, and inert gases.

[0039] In some embodiments of this application, the calcination temperature is 300°C to 500°C.

[0040] In some embodiments of this application, the carbon source includes one or more of acetylene, methane, ethanol, and ethylene.

[0041] In some embodiments of this application, the flow rate of the carbon source is 500 sccm to 10000 sccm.

[0042] In some embodiments of this application, the temperature of vapor deposition is 300°C to 600°C, and the time of vapor deposition is 0.5h to 2h.

[0043] In some embodiments of this application, cold pressing includes a first cold pressing and a second cold pressing, wherein the pressure of the first cold pressing is 3t to 5t, and the time of the first cold pressing is 25s to 60s.

[0044] In some embodiments of this application, the pressure of the second cold press is 3t to 5t, and the time of the second cold press is 15s to 40s.

[0045] Thirdly, embodiments of this application also provide an electrical device, including a secondary battery as described in the first aspect of this application or a secondary battery manufactured by the manufacturing method described in the second aspect of this application. Attached Figure Description

[0046] To more clearly illustrate the technical solutions of the embodiments of this application, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of this application and should not be regarded as a limitation of the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0047] Figure 1 This is a schematic diagram of a secondary battery according to one embodiment of this application.

[0048] Figure 2 yes Figure 1 An exploded view of a secondary battery according to one embodiment of this application is shown.

[0049] Figure 3 This is a schematic diagram of a battery module according to one embodiment of this application.

[0050] Figure 4 This is a schematic diagram of a battery pack according to one embodiment of this application.

[0051] Figure 5 yes Figure 4 An exploded view of a battery pack according to one embodiment of this application is shown.

[0052] Figure 6 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.

[0053] Figure 7 These are SEM images of the first negative electrode active material particles provided in some embodiments of this application.

[0054] Figure 8 These are SEM images of the second negative electrode active material particles provided in some embodiments of this application.

[0055] Figure 9 These are SEM images of the negative electrode sheet provided in some embodiments of this application after argon ion cutting technology.

[0056] Explanation of reference numerals in the attached figures:

[0057] 1-Battery pack; 2-Upper housing; 3-Lower housing; 4-Battery module; 5-Secondary battery; 51-Housing shell; 52-Electrode assembly; 53-Top cover assembly. Detailed Implementation

[0058] The following detailed description, with appropriate reference to the accompanying drawings, discloses embodiments of the secondary battery, its manufacturing method, and its power-consuming device. However, unnecessary details may be omitted. For example, detailed descriptions of well-known facts 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.

[0059] 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 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 "ab" 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.

[0060] Unless otherwise specified, all embodiments and optional embodiments of this application can be combined to form new technical solutions.

[0061] Unless otherwise specified, all technical features and optional technical features of this application may be combined to form new technical solutions.

[0062] 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.

[0063] With the increasing application scenarios of secondary batteries, higher requirements are being placed on their energy density and cycle performance.

[0064] In the negative electrode of secondary batteries, the theoretical specific capacity of currently used commercial graphite anode active materials is around 372 mAh / g, which is insufficient to meet the requirements for higher energy densities. Compared to the specific capacity of commercial graphite anode active materials, the maximum theoretical specific capacity of pure silicon anode active materials can reach 4200 mAh / g. Therefore, using silicon-based anode active materials can significantly improve the energy density of secondary batteries, meeting the requirements for higher energy densities.

[0065] However, silicon-based anode active materials have low structural strength, which is not conducive to the formation of high-density anode active material layers through cold pressing. Furthermore, silicon-based anode active materials are easily crushed during cold pressing, thus limiting their ability to improve the energy density of secondary batteries. In addition, during secondary battery charging, silicon-based anode active materials embed active ions, causing volume expansion and resulting in problems such as pulverization and shedding of the anode active material layer. This can even damage the SEI film on the surface of the anode sheet, leading to continuous SEI film growth, consuming limited active ions, and ultimately causing a decline in cycle performance.

[0066] Therefore, it is urgent to solve the technical problem of secondary batteries that balance high energy density and good cycle performance.

[0067] In view of this, this application provides a secondary battery and an electrical device that can achieve both high energy density and good cycle performance.

[0068] The term "secondary battery" as used in this article refers to a single secondary battery cell, battery module, or battery pack.

[0069] Typically, a single secondary battery cell includes a positive electrode, a negative electrode, an electrolyte, and a separator. During charging and discharging, active ions move back and forth between the positive and negative electrodes, inserting and releasing. The electrolyte acts as a conductor between the positive and negative electrodes. The separator, positioned between the positive and negative electrodes, primarily prevents short circuits while allowing ions to pass through.

[0070] This application provides a secondary battery including a negative electrode sheet, the negative electrode sheet including a negative electrode active material layer, the negative electrode active material layer including a first negative electrode active material particle and a second negative electrode active material particle, the first negative electrode active material particle having an angular shape, the second negative electrode active material particle including silicon-based material particles and a coating layer located on the surface of the silicon-based material particles and having a porous structure, the coating layer including amorphous carbon.

[0071] In this paper, angular shapes refer to any shape in which the surface protrudes outward to form an angular structure. This shape can be observed by scanning with a scanning electron microscope (SEM); for example, the morphology and structure can be observed after vacuum sputtering gold onto the sample using a JSM-5610LV scanning electron microscope from FEI Corporation, USA.

[0072] A pore structure refers to a structure that has pores (recesses), which can be confirmed, for example, by observation using a scanning electron microscope (SEM).

[0073] Amorphous carbon refers to carbon materials with a very low degree of graphitization, exhibiting an approximately amorphous morphology (or lacking a fixed shape and periodic structural regularity). The carbon atoms in amorphous carbon have no regular arrangement, therefore, amorphous carbon can be characterized by transmission electron microscopy (TEM). By using focused ion beam (FIB) to cut a thin slice approximately 100 nm thick from the middle of the negative electrode active material particles, and then performing TEM on the slice, it was observed that the surface region includes a coating layer. The lattice fringes in the coating layer exhibit long-range disorder and short-range order, and the electron diffraction pattern shows a halo-like appearance, indicating that the coating layer contains amorphous carbon. Amorphous carbon has high hardness, thus enabling the second negative electrode active material to possess good pressure resistance and puncture resistance.

[0074] In the secondary battery provided in this application embodiment, the first negative electrode active material particles have an angular shape, which allows a gap to be formed between them and adjacent first negative electrode active material particles to accommodate second negative electrode active material particles. The second negative electrode active material particles include silicon-based material particles and a coating layer with a porous structure on the surface of the silicon-based material particles. The coating layer includes amorphous carbon, which gives the second negative electrode active material particles strong resistance to pressure and puncture. This allows the second negative electrode active material particles to be embedded between the first negative electrode active material particles after cold pressing and to form a conductive network in contact with the first negative electrode active material particles, thereby increasing the compaction density of the negative electrode active material layer. Moreover, the breakage of the second negative electrode active material particles is reduced during the cold pressing process, thereby enabling the secondary battery to have a high energy density. Furthermore, the porous structure of the coating layer of the silicon-based material particles reduces the volume expansion of the second negative electrode active material particles, and the gaps formed between the first negative electrode active material particles can reserve space to accommodate the volume expansion of the second negative electrode active material particles. This further reduces the decrease in conductivity of the negative electrode due to the volume expansion of the silicon-based material particles, thus enabling the secondary battery to have good cycle performance. Therefore, the secondary battery provided by the embodiments of this application can achieve both high energy density and good cycle performance.

[0075] The embodiments of this application can further improve the energy density and cycle performance of the secondary battery by controlling the mass ratio of the second negative electrode active material particles in the negative electrode active material layer.

[0076] In some embodiments of this application, the mass percentage of the second negative electrode active material particles is 1% to 10% based on the mass of the negative electrode active material layer. Having the mass percentage of the second negative electrode active material particles within this range can reduce the occurrence of crushing of the second negative electrode active material particles and increase the capacity of the secondary battery. It also allows the second negative electrode active material particles to have appropriate volume expansion to accommodate the gaps between the first negative electrode active material particles, thereby further contributing to improving the energy density and cycle performance of the secondary battery.

[0077] In some optional embodiments of this application, the mass percentage of the second negative electrode active material particles is 3% to 8% based on the mass of the negative electrode active material layer.

[0078] For example, based on the mass of the negative electrode active material layer, the mass percentage of the second negative electrode active material particles can be, but is not limited to, 1%, 1.2%, 1.4%, 1.6%, 1.8%, 2%, 2.2%, 2.4%, 2.6%, 2.8%, 3%, 3.2%, 3.4%, 3.6%, 3.8%, 4%, 4.2%, 4.4%, 4.6%, 4.8%, 5%, 5.2%, 5.4%, 5.6%, 5.8%, 6%, 6.2%, 6.4%, 6.6%, 6.8%, 7%, 7.2%, 7.4%, 7.6%, 7.8%, 8%, 8.2%, 8.4%, 8.6%, 8.8%, 9%, 9.2%, 9.4%, 9.6%, 9.8%, 10%, or a range of any two of the above values.

[0079] The embodiments of this application can further improve the energy density and cycle performance of the secondary battery by controlling the total mass ratio of the first negative electrode active material particles and the second negative electrode active material particles in the negative electrode active material layer and the ratio between the two.

[0080] In some embodiments of this application, based on the mass of the negative electrode active material layer, the total mass ratio of the first negative electrode active material particle and the second negative electrode active material particle is 90% to 98%, and the mass ratio of the first negative electrode active material particle and the second negative electrode active material particle is (87 to 96):(1 to 10).

[0081] In the above embodiments, based on the mass of the negative electrode active material layer, the total mass ratio of the first negative electrode active material particles and the second negative electrode active material particles is within the above range, which can improve the specific capacity of the negative electrode active material and help form a good conductive network to improve the conductivity of the negative electrode active material layer, thereby enabling the secondary battery to have higher energy density and better cycle performance.

[0082] When the mass ratio of the first negative electrode active material particles to the second negative electrode active material particles is within the above range, the negative electrode active material layer can have a suitable compaction density and high capacity, while also forming a good conductive network, thereby further improving the energy density and cycle performance of the secondary battery.

[0083] In some embodiments of this application, the mass ratio of the first negative electrode active material particle to the second negative electrode active material particle is (90-94):(3-7). The total mass percentage of the first negative electrode active material particle and the second negative electrode active material particle is 90%-98%, and the mass ratio of the first negative electrode active material particle to the second negative electrode active material particle is (87-96):(1-10).

[0084] For example, based on the total mass of the negative electrode active material layer, the total mass ratio of the first negative electrode active material particles and the second negative electrode active material particles may be, but is not limited to, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, or any combination of the above values.

[0085] Based on the total mass ratio of the first negative electrode active material particles and the second negative electrode active material particles, the mass ratio of the first negative electrode active material particles and the second negative electrode active material particles can be, but is not limited to, 87:10, 88:9, 89:8, 90:7, 91:6, 92:5, 93:4, 94:3, 95:2, 96:1, etc.

[0086] Furthermore, in some embodiments, the mass percentage of the first negative electrode active material particles is 87% to 96%, and the mass percentage of the second negative electrode active material particles is 1% to 10%.

[0087] The embodiments of this application can improve the energy density and cycle performance of the secondary battery by selecting suitable silicon-based material particles to make the second negative electrode active material particles have a high capacity while further reducing their volume expansion.

[0088] In some embodiments of this application, the silicon-based material particles include one or more of nano-silicon, silicon oxide, and silicon carbide. These silicon-based material particles not only have high capacity but also low volume expansion, thereby further improving the energy density and cycle performance of the secondary battery.

[0089] In some embodiments of this application, the silicon-based material particles include silicon-carbon compounds, which comprise porous carbon and silicon-containing materials located within the porous carbon. The porous carbon helps improve the conductivity of the negative electrode active material, while the silicon-containing material located within the porous carbon further reduces the volume expansion of the silicon-based material particles, thereby further improving the cycle performance of the secondary battery.

[0090] In some embodiments of this application, the mass percentage of silicon element is 0.04% to 6% based on the mass of the negative electrode active material layer.

[0091] In this embodiment, the silicon content in the negative electrode active material layer can be measured using methods and equipment known in the art, such as inductively coupled plasma (ICP) emission spectroscopy. As an example, the following steps can be followed: After separating the negative electrode sheet of the battery cell, thoroughly clean it with dimethyl carbonate (DMC), dry it, and collect the negative electrode active material layer using a scraping method. Take 0.4 g of the collected negative electrode active material layer as a sample and place it in a 25 ml beaker. Digest the sample with a strong acidic solution (e.g., 10 mL of 65% nitric acid and 10 mL of 40% hydrofluoric acid). The silicon content in the completely digested solution is the average silicon content based on the total mass of the negative electrode active material layer.

[0092] In the above-mentioned technical solution, the mass ratio of silicon element within the above range can not only improve the capacity of the negative electrode active material, but also reduce the volume expansion of the second negative electrode active material particles, thereby improving the energy density and cycle performance of the secondary battery.

[0093] In some embodiments of this application, the silicon-containing material includes one or more of elemental silicon, nano-silicon, and silicon alloys.

[0094] In some embodiments of this application, the coating layer includes a first coating layer and a second coating layer, and the pore structure includes a first pore structure and a second pore structure. The first coating layer is located on the surface of the silicon-based material particles and between the second coating layer. The first pore structure is located in the first coating layer, and the second pore structure is located in the second coating layer. The porosity of the first pore structure is greater than that of the second pore structure. The second coating layer includes amorphous carbon.

[0095] In this paper, porosity has a meaning known in the art and can be tested using methods known in the art.

[0096] In the above technical solution, the porosity of the first pore structure is relatively larger than that of the second pore structure, allowing the first coating layer to have more pores. This provides space for the volume expansion of silicon-based material particles, reducing the volume expansion of the second negative electrode active material particles and improving the cycle performance of the secondary battery. Furthermore, the relatively smaller porosity of the second pore structure increases the structural strength of the second negative electrode active material particles, thereby helping to increase the compaction density of the negative electrode active material layer and ultimately improving the energy density of the secondary battery.

[0097] In some embodiments of this application, the porosity of the first pore structure is 50% to 80%. The porosity of the second pore structure is 0% to 1%.

[0098] In the above technical solution, the pores of the first coating layer and the second coating layer are respectively set within the above range, which can further improve the cycle performance and energy density of the secondary battery.

[0099] For example, the porosity of the first coating layer may be, but is not limited to, 50%, 51%, 52%, 53%, 54%, 55%, 56%, 57%, 58%, 59%, 60%, 61%, 62%, 63%, 64%, 65%, 66%, 67%, 68%, 69%, 70%, 71%, 72%, 73%, 74%, 75%, 76%, 77%, 78%, 79%, 80%, or a range of any two of the above values.

[0100] In some embodiments of this application, the first negative electrode active material particles comprise artificial graphite and / or natural graphite.

[0101] In some embodiments of this application, the compaction density of the single-sided negative electrode active material layer is 1.7 g / cm³. 3 ~1.9g / cm 3 .

[0102] In this paper, the compaction density of the negative electrode active material layer has a meaning known in the art and can be measured using methods and equipment known in the art. As an example, the compaction density of the negative electrode active material layer can be determined by the following steps: Compaction density of the negative electrode active material layer = m / (V1-V2), where m represents the weight of the negative electrode active material layer, V1 represents the volume of the electrode sheet, and V2 represents the volume of the current collector. m can be obtained by subtracting the weight of the current collector from the weight of the electrode sheet. The product of the surface area and thickness of the electrode sheet is the volume V1 of the electrode sheet, and the product of the surface area and thickness of the current collector is V2. The thickness of the current collector and the thickness of the electrode sheet are obtained by measuring the thickness of the empty foil in the tab area using a micrometer.

[0103] In the above embodiments, the compaction density of the single-sided negative electrode active material layer is within the above range, which can help improve the energy density of the secondary cell while also enabling it to have good ion transport capability to reduce its internal resistance, thereby improving the cycle performance of the secondary battery.

[0104] For example, the compaction density of the side negative electrode active material layer is 1.7 g / cm³. 3 1.72g / cm 3 1.73g / cm 3 1.74 g / cm 3 1.75g / cm 3 1.76 g / cm 3 1.77g / cm 3 1.78g / cm 3 1.79g / cm 3 1.8g / cm 3 1.81 g / cm 3 1.82g / cm 3 1.83g / cm 3 1.84 g / cm 3 1.85g / cm 3 1.86 g / cm 3 1.87 g / cm 3 1.88g / cm 3 1.89 g / cm 3 1.9g / cm 3 Or the range of values ​​formed by any two of the above values.

[0105] In some embodiments of this application, the coating weight of the single-sided negative electrode active material layer is 0.1 g / cm³. 2 ~0.3g / cm 2 .

[0106] In some embodiments of this application, a positive electrode sheet is also included, which comprises a positive active material layer, and the compaction density of the positive active material layer on one side is 3 g / cm³. 3 ~4g / cm 3 .

[0107] In some embodiments of this application, the coating weight of the single-sided positive electrode active material layer is 0.2 g / cm³. 2 ~0.6g / cm 2 .

[0108] Secondly, embodiments of this application provide a method for manufacturing a secondary battery, comprising:

[0109] A first negative electrode active material particle, a second negative electrode active material particle, a binder, and a conductive agent are added to a solvent to form a negative electrode active material layer slurry. The first negative electrode active material particle has an angular shape. The second negative electrode active material particle includes silicon-based material particles and a coating layer with a porous structure located on the surface of the silicon-based material particles. The coating layer includes amorphous carbon.

[0110] The negative electrode active material slurry is coated onto the surface of the negative electrode current collector to form a negative electrode active material slurry layer. After drying and cold pressing, the negative electrode sheet is obtained.

[0111] In some embodiments of this application, the method for preparing the second negative electrode active material particles includes: mixing silicon-based material particles with a slurry containing foaming material and a first carbon source, and subjecting the mixture to calcination treatment, so that a first coating layer with a first pore structure is formed on the surface of the silicon-based material particles;

[0112] Silicon-based material particles with a first coating layer are placed in a second carbon source atmosphere for vapor deposition to form a second coating layer with a second porous structure and containing amorphous carbon on the surface of the first coating layer, thereby obtaining second negative electrode active material particles.

[0113] In some embodiments of this application, the first carbon source includes one or more of dopamine, polyacrylonitrile, epoxy resin, glucose, sucrose, cellulose, lignin, and pitch.

[0114] In some embodiments of this application, the foaming material includes one or more of carbonate-based foaming agents, alkane-based foaming agents, fluorocarbon-based foaming agents, and compressed gas-based foaming agents. These foaming materials can form a coating layer with high porosity, thereby helping to reduce the volume expansion of silicon-based material particles and thus improving the cycle performance of the secondary battery.

[0115] In some embodiments of this application, the carbonate foaming agent includes one or more of calcium carbonate, magnesium carbonate, and sodium bicarbonate.

[0116] In some embodiments of this application, the hydrocarbon blowing agent includes one or more of methane, ethane, pentane, n-butane, isobutane, and cyclopentane.

[0117] In some embodiments of this application, the fluorocarbon blowing agent includes one or more of hydrochlorofluorocarbons, hydrofluorocarbons, and hydrofluoroolefins.

[0118] In some embodiments of this application, the compressed gas foaming agent includes one or more of carbon dioxide, air, and inert gases.

[0119] In some embodiments of this application, the calcination temperature is 300°C to 500°C. A calcination temperature within this range is beneficial for forming a uniform first coating layer.

[0120] In some embodiments of this application, the second carbon source includes one or more of acetylene, methane, ethanol, and ethylene.

[0121] In some embodiments of this application, the flow rate of the second carbon source is 500 sccm to 10000 sccm.

[0122] In some embodiments of this application, the temperature of vapor deposition is 300°C to 600°C, and the time of vapor deposition is 0.5h to 2h.

[0123] In some embodiments of this application, cold pressing includes a first cold pressing and a second cold pressing, wherein the pressure of the first cold pressing is 3t to 5t, and the time of the first cold pressing is 25s to 60s;

[0124] In some embodiments of this application, the pressure of the second cold press is 3t to 5t, and the time of the second cold press is 15s to 40s.

[0125] [Positive electrode plate]

[0126] In embodiments of this application, the positive current collector has two surfaces opposite each other in its own thickness direction, and the positive active material layer is disposed on either or both of the two opposite surfaces of the positive current collector.

[0127] 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.).

[0128] In some embodiments, when the secondary battery is a lithium-ion battery, 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 positive electrode active materials for batteries 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 may 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 / 3Co1 / 3 Mn 1 / 3 O2 (which can also be abbreviated as NCM333), LiNi 0.5 Co 0.2 Mn 0.3 O2 (which can also be abbreviated as NCM523), LiNi 0.5 Co 0.25 Mn 0.25 O2 (which can also be abbreviated as NCM211), LiNi 0.6 Co 0.2 Mn 0.2 O2 (which can also be abbreviated as NCM622), LiNi 0.8 Co 0.1 Mn 0.1 O2 (which can also be abbreviated as NCM811), LiNi 0.9 Co 0.05 Mn 0.05 O2 (which can also be abbreviated as NCM9), lithium nickel cobalt aluminum oxide (such as LiNi 0.8 Co 0.15 Al 0.05 O2) and at least one of its modified compounds, etc. Examples of olivine-structured lithium phosphate may include, but are not limited to, lithium iron phosphate (such as LiFePO4 (which can also be abbreviated as LFP)), a composite material of lithium iron phosphate and carbon, lithium manganese phosphate (such as LiMnPO4), a composite material of lithium manganese phosphate and carbon, lithium manganese iron phosphate, and at least one of a composite material of lithium manganese iron phosphate and carbon.

[0129] In some embodiments, in order to further improve the energy density of the secondary battery, the positive electrode active material for a lithium-ion battery may include a lithium transition metal oxide having the general formula Li a Ni b Co c M d O e A f and one or more of its modified compounds. 0.8 ≤ a ≤ 1.2, 0.5 ≤ b < 1, 0 < c < 1, 0 < d < 1, 1 ≤ e ≤ 2, 0 ≤ f ≤ 1, M is selected from one or more of Mn, Al, Zr, Zn, Cu, Cr, Mg, Fe, V, Ti, and B, and A is selected from one or more of N, F, S, and Cl.

[0130] In some embodiments, by way of example, the positive electrode active material for a lithium-ion battery may include LiCoO2, LiNiO2, LiMnO2, LiMn2O4, LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2 (NCM333), LiNi 0.5 Co0.2 Mn 0.3 O2(NCM523), LiNi 0.6 Co 0.2 Mn 0.2 O2(NCM622), LiNi 0.8 Co 0.1 Mn 0.1 O2(NCM811), LiNi 0.85 Co 0.15 Al 0.05 One or more of O2, LiFePO4 and LiMnPO4.

[0131] In this application, the modified compounds of the above-mentioned positive electrode active materials can be doped and / or surface coated to modify the positive electrode active materials, such as polyanionic compounds.

[0132] As an optional technical approach in this application, the polyanionic compound can be Li 1+x Mn 1-y A y P 1-z R z O4; where x is any value in the range of -0.100 to 0.100, y is any value in the range of 0.001 to 0.500, z is any value in the range of 0.001 to 0.100, A includes one or more elements selected from Zn, Al, Na, K, Mg, Mo, W, Ti, V, Zr, Fe, Ni, Co, Ga, Sn, Sb, Nb and Ge, and R includes one or more elements selected from B, S, Si and N;

[0133] As an optional technical approach in this application, the polyanionic compound can be Li a A e Mn 1-f B f P 1-g C g O 4-n D n Wherein, A includes one or more elements selected from Zn, Al, Na, K, Mg, Nb, Mo, and W; B includes one or more elements selected from Ti, V, Zr, Fe, Ni, Mg, Co, Ga, Sn, Sb, Nb, and Ge; C includes one or more elements selected from B, S, Si, and N; D includes one or more elements selected from S, F, Cl, and Br; a is selected from the range of 0.9 to 1.1, e is selected from the range of 0.001 to 0.1, f is selected from the range of 0.001 to 0.5, g is selected from the range of 0.001 to 0.1, n is selected from the range of 0.001 to 0.1, and the second positive electrode active material is electrically neutral.

[0134] During the charge and discharge process of the battery, the insertion and extraction of Li and its consumption will occur, and the molar content of Li is different when the battery is discharged to different states. In the list of cathode materials in this application, the molar content of Li is the initial state of the material, that is, the state before feeding. When the cathode material is applied to the battery system, after charge and discharge cycles, the molar content of Li will change.

[0135] In the list of cathode materials in this application, the molar content of O is only the theoretical state value, and the release of oxygen from the lattice will cause the molar content of oxygen to change, and the actual molar content of O will fluctuate.

[0136] As an optional technical solution of this application, the polyanionic compound can be Na 4+x R 3-y P 4-m O 15 / C; wherein, 0 < x < 0.5, 0 < y ≤ 0.5, 0 < m ≤ 0.2, and R includes at least one of Mg, Al, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Zr, Cr, Nb, Mo, In, Ga, Sn, Hf, Ta, W, and Pb.

[0137] As an optional technical solution of this application, the polyanionic compound can be Na x-a A a V y-b M b (PO4) 2-2c (DO4) 2c F z-d Q d , wherein the A element represents an alkali metal element that dopes and replaces the Na element, the M element represents a metal element that replaces the V element, the D element represents a doping element that replaces the P element, the Q element represents a doping element that replaces the F element, the D element includes at least one of Si and S, the Q element includes at least one of Cl and O; 3.5 ≤ x ≤ 4.5, 0 ≤ a ≤ 0.15x, 0.8 ≤ y ≤ 1.1, 0 ≤ b ≤ x, 0.8 ≤ z ≤ 1.1, 0 ≤ d ≤ 0.2z. Optionally, the A element includes at least one of K and Li; the M element includes at least one of Fe, Cr, Al, Sc, Ga, In, Ti, Zr, Mn, Zn, Ni, Cu, and Co.

[0138] In some embodiments, when the secondary battery is a sodium-ion battery, the positive electrode active material may include at least one of the following materials: polyanionic compounds, sodium transition metal oxides, Prussian blue compounds, and their respective modified compounds. However, this application is not limited to these materials, and other conventional materials that can be used as positive electrode active materials for batteries may also be used. These positive electrode active materials may be used alone or in combination of two or more.

[0139] Among them, the polyanionic compound can be Li 1+x Mn 1-y A y P 1-z R z O4; where x is any value in the range of -0.100 to 0.100, y is any value in the range of 0.001 to 0.500, z is any value in the range of 0.001 to 0.100, A includes one or more elements selected from Zn, Al, Na, K, Mg, Mo, W, Ti, V, Zr, Fe, Ni, Co, Ga, Sn, Sb, Nb and Ge, and R includes one or more elements selected from B, S, Si and N.

[0140] As an optional technical approach in this application, the polyanionic compound can be Li a A e Mn 1-f B f P 1-g C g O 4-n D n Wherein, A includes one or more elements selected from Zn, Al, Na, K, Mg, Nb, Mo, and W; B includes one or more elements selected from Ti, V, Zr, Fe, Ni, Mg, Co, Ga, Sn, Sb, Nb, and Ge; C includes one or more elements selected from B, S, Si, and N; D includes one or more elements selected from S, F, Cl, and Br; a is selected from the range of 0.9 to 1.1, e is selected from the range of 0.001 to 0.1, f is selected from the range of 0.001 to 0.5, g is selected from the range of 0.001 to 0.1, n is selected from the range of 0.001 to 0.1, and the second positive electrode active material is electrically neutral.

[0141] As an optional technical approach in this application, the polyanionic compound can be Na... 4+x R 3-y P 4-m O 15 / C; wherein, 0 < x < 0.5, 0 < y ≤ 0.5, 0 < m ≤ 0.2, and R includes at least one of Mg, Al, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Zr, Cr, Nb, Mo, In, Ga, Sn, Hf, Ta, W, and Pb.

[0142] As an optional technical solution of the present application, the polyanionic compound may be Na x-a A a V y-b M b (PO4) 2-2c (DO4) 2c F z-d Q d , wherein the A element represents an alkali metal element that dopes and replaces the Na element, the M element represents a metal element that replaces the V element, the D element represents a doping element that replaces the P element, the Q element represents a doping element that replaces the F element, the D element includes at least one of Si and S, the Q element includes at least one of Cl and O; 3.5 ≤ x ≤ 4.5, 0 ≤ a ≤ 0.15x, 0.8 ≤ y ≤ 1.1, 0 ≤ b ≤ 0.3y, 0 ≤ c ≤ 0.15, 0.8 ≤ z ≤ 1.1, 0 ≤ d ≤ 0.2z. Optionally, the A element includes at least one of K and Li; the M element includes at least one of Fe, Cr, Al, Sc, Ga, In, Ti, Zr, Mn, Zn, Ni, Cu, and Co.

[0143] In the sodium transition metal compound, the transition metal may be at least one of Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, Zr, and Ce. The sodium transition metal oxide is, for example, Na x MO2, wherein M is one or more of Mn, Fe, Ni, Co, Cr, Cu, Ti, and V, and 0 < x ≤ 1.

[0144] The Prussian blue compound may be a class of compounds having sodium ions, transition metal ions, and cyanide ions (CN - ). The transition metal may be at least one of Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, Zr, and Ce. The Prussian blue compound is, for example, Na a Me b Me' c (CN)6, wherein Me and Me' are each independently at least one of Mn, Fe, Ni, Co, Cu, and Zn, 0 < a ≤ 2, 0 < b < 1, 0 < c < 1.

[0145] In some embodiments, the positive electrode active material layer may optionally include a binder. As an example, the binder may include at least one selected from polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), PVDF-tetrafluoroethylene-propylene terpolymer, PVDF-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorinated acrylate resin.

[0146] In some embodiments, the positive electrode active material layer 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.

[0147] 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.

[0148] [Negative electrode plate]

[0149] In some embodiments, the negative electrode sheet includes a negative current collector and a layer of negative active material disposed on at least one surface of the negative current collector.

[0150] As an example, the negative electrode current collector has two surfaces opposite each other in its own thickness direction, and the negative electrode active material layer is disposed on either or both of the two opposite surfaces of the negative electrode current collector.

[0151] 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.).

[0152] In some embodiments, the negative electrode active material layer may optionally include a binder. The binder may be selected from 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).

[0153] In some embodiments, the negative electrode active material layer may optionally include a conductive agent. The conductive agent may be selected from at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0154] In some embodiments, the negative electrode active material layer may also optionally include other additives, such as thickeners (e.g., sodium carboxymethyl cellulose (CMC-Na)).

[0155] In some embodiments, the negative electrode sheet can be prepared by dispersing the components used to prepare the negative electrode sheet, such as first negative electrode active material particles, second negative electrode active material particles, 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.

[0156] In other embodiments, the current collector of the negative electrode sheet typically includes a current collector body and a base coating. The base coating can be disposed on at least one side of the current collector body. The base coating basically does not contain negative electrode active material, and may include a small amount of carbon material. However, the carbon material forms a thin coating and cannot function as a negative electrode active material. In this embodiment, the negative electrode sheet can be an electrode sheet without a negative electrode active material layer. For a negative electrode sheet without a negative electrode active material layer, when the current collector of the negative electrode sheet does not contain a base coating, the negative electrode sheet also includes a negative electrode film layer, which can be disposed on the surface of at least one side of the current collector; when the current collector of the negative electrode sheet includes a base coating, the film layer can be disposed on the surface of the base coating away from the current collector.

[0157] In some embodiments, the negative electrode film layer may further include a binder for fixing the additive to the negative electrode sheet. The type of binder is not particularly limited, and those skilled in the art can choose flexibly according to actual needs.

[0158] [Electrolytes]

[0159] 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.

[0160] In some embodiments, the electrolyte is an electrolyte solution. The electrolyte solution includes an electrolyte salt and a solvent.

[0161] 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.

[0162] 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.

[0163] In some embodiments, the electrolyte may optionally include additives. For example, 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.

[0164] [Isolation membrane]

[0165] This application does not impose any particular restrictions on the type of separator membrane; any known porous separator membrane with good chemical and mechanical stability can be selected.

[0166] 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.

[0167] In some implementations, the positive electrode, negative electrode, and separator can be fabricated into an electrode assembly using a winding or stacking process.

[0168] 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.

[0169] 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.

[0170] 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 1 The example shown is a square-structured battery cell 5.

[0171] In some implementations, refer to Figure 2The outer packaging may include a housing 51 and a cover plate 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 plate 53 can be placed over the opening to close the receiving cavity. The positive electrode sheet, negative electrode sheet, and separator can be formed into an electrode assembly 52 by a winding process or a stacking process. The electrode assembly 52 is encapsulated within the receiving cavity. Electrolyte is immersed in the electrode assembly 52. ​​The number of electrode assemblies 52 contained in a single battery cell 5 can be one or more, which can be selected by those skilled in the art according to specific practical needs.

[0172] In some implementations, individual battery cells can be assembled into a battery module. The number of individual battery cells contained in a battery module can be one or more, and the specific number can be selected by those skilled in the art based on the application and capacity of the battery module.

[0173] Figure 3 This is battery module 4, used as an example. (See reference...) Figure 3 In battery module 4, multiple battery cells 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 battery cells 5 can be fixed in place using fasteners.

[0174] Optionally, the battery module 4 may also include a housing with a receiving space in which multiple battery cells 5 are received.

[0175] 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.

[0176] Figure 4 and Figure 5 This is battery pack 1 as an example. (See reference...) Figure 4 and Figure 5 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.

[0177] In addition, this application also provides an electrical device, which includes the secondary battery provided in this application. The secondary battery can be used as the power source of the electrical device or as the energy storage unit of the electrical device. The electrical device may include, but is not limited to, mobile devices (such as mobile phones, laptops, etc.), electric vehicles (such as 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.

[0178] As the electrical device, a single battery cell, a battery module, or a battery pack can be selected according to its usage requirements.

[0179] Figure 6 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 individual battery cells, a battery pack or battery module can be used.

[0180] Another example device could be a mobile phone, tablet, or laptop. These devices typically require a slim and lightweight design and can use a single battery cell as their power source.

[0181] I. Implementation Examples

[0182] 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.

[0183] Example 1

[0184] (1) Preparation of positive electrode sheet

[0185] The positive electrode active material NCM9, the binder polyvinylidene fluoride (PVDF), and the conductive carbon were mixed in an N-methylpyrrolidone (NMP) solvent at a mass ratio of 98:1:1 to prepare a positive electrode slurry. The positive electrode slurry was uniformly coated on the surface of aluminum foil, and then dried, cold-pressed, and slit to obtain the positive electrode sheet.

[0186] (2) Preparation of the second negative electrode active material particles

[0187] Porous silicon-carbon material particles (wherein nano-silicon is deposited within the pores of porous carbon, and the silicon content is 40% by mass, based on the mass of the porous silicon-carbon material particles) are mixed with a slurry containing sodium bicarbonate and glucose, and then calcined to form a first coating layer with a porosity of 70% on the surface of the silicon-based material particles. The silicon-based material particles with the first coating layer are then subjected to vapor deposition in a methane atmosphere with a flow rate of 1000 sccm to form a second coating layer with a porosity of 0.2% on the surface of the first coating layer, thus obtaining the second negative electrode active material particles. Figure 8 The SEM image shown.

[0188] (3) Preparation of negative electrode sheet

[0189] Graphite with angular shapes (such as...) Figure 7 The graphite (as shown), second negative electrode active material particles, conductive agent acetylene black, binder styrene-butadiene rubber (SBR), and thickener sodium methyl cellulose (CMC-Na) are mixed in a deionized water solvent at a mass ratio of 92:5:1:1:1 to prepare a negative electrode slurry. The negative electrode slurry is uniformly coated onto the surface of a copper foil, dried, and cold-pressed to form a negative electrode sheet. The cold pressing includes a first cold pressing and a second cold pressing. The first cold pressing is performed at a pressure of 3t for 40 seconds. After the first cold pressing, the sheet is allowed to stand for 1 hour before the second cold pressing, which is then performed at a pressure of 3t for 30 seconds. Figure 9 The image shown is a SEM image of the negative electrode sheet after argon ion cutting technology.

[0190] (4) Preparation of electrolyte

[0191] In a nitrogen-atmospheric glove box (H2O < 0.1 ppm, O2 < 0.1 ppm), ethylene carbonate (EC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), and lithium hexafluorophosphate (LiPF6) were stirred and mixed evenly to obtain an electrolyte. The volume ratio of EC, EMC, and DEC was 1:1:1, and the volume molar concentration of LiPF6 was 1 mol / L.

[0192] (5) Separating membrane

[0193] The separator includes a porous polyethylene (PE) polymer membrane and a coating disposed on the surface of the porous polyethylene polymer membrane, the coating including boehmite.

[0194] (6) Preparation of battery cells

[0195] The positive electrode, separator, and negative electrode are stacked and wound in sequence to obtain an electrode assembly, with the separator positioned between the positive and negative electrodes. Tabs are welded to the electrode assembly, which is then placed in an aluminum casing and baked at 90°C to remove moisture. The electrolyte is then injected and the casing is sealed to obtain a non-charged battery. The non-charged battery then undergoes a series of processes including settling, cold pressing, formation, shaping, and capacity testing to obtain a single battery cell.

[0196] Examples 2-6

[0197] The differences between Examples 2-6 and Example 1 are shown in Table 1.

[0198] Comparative Example 1

[0199] Compared with Example 1, the first negative electrode active material particles in Comparative Example 1 are spherical artificial graphite.

[0200] II. Testing Section

[0201] (1) Observation of the shape of the first negative electrode active material particles

[0202] The shape of the first negative electrode active material particles was observed using SEM (Self-Electron Microscopy), such as... Figure 7 and Figure 9 As shown.

[0203] (2) Test of silicon content

[0204] After separating the negative electrode sheet of the battery cell, it was thoroughly cleaned with dimethyl carbonate (DMC) and dried. The negative electrode active material layer was then collected by the scraping method. 0.4g of the collected negative electrode active material layer was taken as a sample and placed in a 25ml beaker. 10mL of 65% nitric acid and 10mL of 40% hydrofluoric acid were added to digest the sample. Finally, inductively coupled plasma (ICP-CIP) technology was used to test the Si element and its mass percentage in the negative electrode active material.

[0205] (3) Cyclic performance test

[0206] At 25°C, the secondary battery prepared in the example was charged and discharged on a Newway tester at 1C / 1C with a voltage range of 2.5-4.25V until the capacity of the secondary battery was less than 80% of the initial capacity. The number of cycles of the secondary battery was recorded to characterize the cycle performance of the cell, with the unit being cycles.

[0207] The test results are shown in Table 1.

[0208] III. Analysis of Test Results for Each Embodiment and Comparative Example

[0209] Battery cells for each embodiment and comparative example were prepared according to the above method, and various performance parameters were measured. The results are shown in Table 1 below.

[0210] Table 1

[0211]

[0212]

[0213] A comparison of the test results from Examples 1-6 and Comparative Example 1 shows that the first negative electrode active material particle has an angular shape, and the second negative electrode active material particle is located between two adjacent first negative electrode active material particles. The second negative electrode active material particle includes a silicon-based material particle, a first coating layer on the surface of the silicon-based material particle, and a second coating layer on the surface of the first coating layer. The combination of the first negative electrode active material particle and the second negative electrode active material particle enables the secondary battery to achieve both high energy density and good cycle performance.

[0214] It should be noted that this application is not limited to the above-described embodiments. The above embodiments are merely examples, and any embodiments with the same structure and effect as the technical concept within the scope of this application are included in the technical scope of this application. Furthermore, various modifications that can be conceived by those skilled in the art to the embodiments, and other ways of constructing by combining some of the constituent elements of the embodiments, without departing from the spirit of this application, are also included in the scope of this application.

Claims

1. A secondary battery, characterized in that, The device includes a negative electrode sheet, which includes a negative electrode active material layer. The negative electrode active material layer includes a first negative electrode active material particle and a second negative electrode active material particle. The first negative electrode active material particle has an angular shape. The second negative electrode active material particle includes silicon-based material particles and a coating layer with a porous structure located on the surface of the silicon-based material particles. The coating layer includes amorphous carbon.

2. The secondary battery according to claim 1, characterized in that, Based on the mass of the negative electrode active material layer, the mass percentage of the second negative electrode active material particles is 1% to 10%. Optionally, the mass percentage of the second negative electrode active material particles is 3% to 8%.

3. The secondary battery according to claim 2, characterized in that, Based on the mass of the negative electrode active material layer, the total mass ratio of the first negative electrode active material particles and the second negative electrode active material particles is 90% to 98%, and the mass ratio of the first negative electrode active material particles to the second negative electrode active material particles is (87 to 96):(1 to 10). Optionally, the mass ratio of the first negative electrode active material particles to the second negative electrode active material particles is (90-94):(3-7).

4. The secondary battery according to claim 1, characterized in that, The silicon-based material particles include one or more of nano-silicon, silicon oxides, and silicon carbide compounds. Optionally, the silicon-based material particles include silicon carbide, which includes porous carbon and silicon-containing material located inside the porous carbon; Optionally, based on the mass of the negative electrode active material layer, the mass percentage of silicon is 0.04% to 6%; Optionally, the silicon-containing material includes one or more of elemental silicon, nano-silicon, and silicon alloys.

5. The secondary battery according to claim 1, characterized in that, The coating layer includes a first coating layer and a second coating layer, and the pore structure includes a first pore structure and a second pore structure. The first coating layer is located between the surface of the silicon-based material particles and the second coating layer. The first pore structure is located in the first coating layer, and the second pore structure is located in the second coating layer. The porosity of the first pore structure is greater than that of the second pore structure. The second coating layer includes the amorphous carbon. Optionally, the porosity of the first pore structure is 50% to 80%.

6. The secondary battery according to claim 1, characterized in that, The first negative electrode active material particles include artificial graphite and / or natural graphite.

7. The secondary battery according to claim 1, characterized in that, The compaction density of the negative electrode active material layer on one side is 1.7 g / cm³. 3 ~1.9g / cm 3 ; Optionally, the secondary battery further includes a positive electrode sheet, which comprises a positive active material layer, and the compaction density of the positive active material layer on one side is 3 g / cm³. 3 ~4g / cm 3 .

8. The secondary battery according to claim 7, characterized in that, The positive electrode active material layer includes a positive electrode active material, which includes a lithium-containing positive electrode active material and / or a sodium-containing positive electrode active material. Optionally, the lithium-containing cathode active material includes lithium phosphate materials and / or lithium ternary cathode active materials.

9. A method for manufacturing a secondary battery, characterized in that, include: A first negative electrode active material particle, a second negative electrode active material particle, a binder, and a conductive agent are added to a solvent to form a negative electrode active material layer slurry. The first negative electrode active material particle has an angular shape, and the second negative electrode active material particle includes silicon-based material particles and a coating layer with a porous structure located on the surface of the silicon-based material particles. The coating layer includes amorphous carbon. The negative electrode active material layer slurry is coated onto the surface of the negative electrode current collector to form a negative electrode active material slurry layer. After drying and cold pressing, a negative electrode sheet is obtained.

10. The manufacturing method according to claim 9, characterized in that, The preparation method of the second negative electrode active material particles includes: The silicon-based material particles are mixed with a slurry containing a foaming material and a first carbon source, and then calcined to form a first coating layer with a first pore structure on the surface of the silicon-based material particles. The silicon-based material particles with the first coating layer are placed in a second carbon source atmosphere for vapor deposition to form a second coating layer with a second porous structure and containing amorphous carbon on the surface of the first coating layer, thereby obtaining the second negative electrode active material particles.

11. The manufacturing method according to claim 10, characterized in that, The first carbon source includes one or more of dopamine, polyacrylonitrile, epoxy resin, glucose, sucrose, cellulose, lignin, and pitch; And / or, the foaming material includes one or more of carbonate foaming agents, alkane foaming agents, fluorocarbon foaming agents, and compressed gas foaming agents; Optionally, the carbonate foaming agent includes one or more of calcium carbonate, magnesium carbonate, and sodium bicarbonate; Optionally, the hydrocarbon blowing agent includes one or more of methane, ethane, pentane, n-butane, isobutane, and cyclopentane; Optionally, the fluorocarbon blowing agent includes one or more of hydrochlorofluorocarbons, hydrofluorocarbons, and hydrofluoroolefins; Optionally, the compressed gaseous foaming agent includes one or more of carbon dioxide, air, and inert gases; And / or, the calcination temperature is 300℃~500℃.

12. The manufacturing method according to claim 10, characterized in that, The second carbon source includes one or more of acetylene, methane, ethanol, and ethylene; And / or, the flow rate of the second carbon source is 500 sccm to 10000 sccm.

13. The manufacturing method according to claim 12, characterized in that, The temperature of the vapor deposition is 300℃~600℃, and the time of the vapor deposition is 0.5h~2h; And / or, the cold pressing includes a first cold pressing and a second cold pressing, wherein the pressure of the first cold pressing is 3t to 5t, and the time of the first cold pressing is 25s to 60s; the pressure of the second cold pressing is 3t to 5t, and the time of the second cold pressing is 15s to 40s.

14. An electrical appliance, characterized in that, Includes a secondary battery as described in any one of claims 1 to 8 or a secondary battery manufactured by the manufacturing method described in any one of claims 9 to 13.

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