Secondary battery and electric device

Abstract

The invention provides a secondary battery and an electric device. The secondary battery comprises a positive pole piece, the positive pole piece comprises a positive pole film layer, the positive pole film layer comprises a positive pole active material containing transition metal elements, based on the total mole number of the transition metal elements in the positive pole active material, the mole content of a nickel element is not lower than 85%, and the mole content of a nickel element is not lower than 10%. The energy per unit area of the positive electrode film layer on one side of the positive electrode plate is 15-35 mWh / cm < 2 >, and can be 20-35 mWh / cm < 2 > optionally; the negative electrode plate comprises a negative electrode film layer, the negative electrode film layer comprises a negative electrode active material of a carbon-silicon composite material, and the carbon-silicon composite material comprises carbon matrix particles with a carbon skeleton and silicon nanoparticles attached to the carbon skeleton. According to the secondary battery, through the matching design of the positive electrode active material and the negative electrode active material, the energy density of the secondary battery is improved.

Description

[0001] This application is a divisional application based on the invention with application number 202480001336.1, application date June 7, 2024, applicant CATL, and invention title "Secondary Battery and Power Consumption Device". Cross-reference to related applications

[0002] This application claims priority to patent application No. PCT / CN2023 / 087384, filed on April 10, 2023, entitled "Secondary Battery and Electrical Device", the entire contents of which are incorporated herein by reference. Technical Field

[0003] This application relates to the field of lithium battery technology, and in particular to a high-energy-density secondary battery and its power supply device. Background Technology

[0004] In recent years, as secondary batteries have been widely used in energy storage power systems such as hydropower, thermal power, wind power and solar power plants, as well as in many fields such as power tools, electric bicycles, electric motorcycles, electric cars, military equipment, and aerospace, the market's performance requirements for secondary batteries have become increasingly higher.

[0005] Lithium-ion batteries are currently widely used high-quality, high-energy-density small secondary batteries, but with the rapid development of their application fields, there is an urgent need to further improve their energy density. Summary of the Invention

[0006] This application is made in view of the above-mentioned issues, and its purpose is to provide a secondary battery having a high energy density.

[0007] A first aspect of this application provides a secondary battery, comprising: a positive electrode sheet, the positive electrode sheet including a positive electrode film layer, the positive electrode film layer including a positive electrode active material of a transition metal element, wherein the molar content of nickel element is not less than 85% based on the total molar number of transition metal elements in the positive electrode active material, and the unit area energy of the positive electrode film layer on one side of the positive electrode sheet is 15-35 mWh / cm². 2 Available in 20-35 mWh / cm³ 2 ; A negative electrode sheet, the negative electrode sheet comprising a negative electrode film layer, the negative electrode film layer comprising a negative electrode active material of a carbon-silicon composite material, the carbon-silicon composite material comprising carbon matrix particles having a carbon skeleton and silicon nanoparticles attached to the carbon skeleton.

[0008] This application overcomes the limitations of theoretical capacity of positive and negative electrode materials in the prior art by combining high-nickel-content positive electrode active materials with carbon-silicon composite materials, and realizes the preparation of high-energy-density secondary batteries.

[0009] In any embodiment, the weight z of the secondary battery casing and the weight JR of the bare cell of the secondary battery satisfy the following relationship: 0.01≤z / JR≤0.42; optionally, 0.01≤z / JR≤0.1 or 0.02≤z / JR≤0.07.

[0010] Through the above structural design, the mass of the secondary battery is further reduced, and the energy density of the battery is significantly improved.

[0011] In any embodiment, the carbon matrix particles include a three-dimensional network cross-linked porous structure, and at least a portion of the silicon nanoparticles are disposed in the three-dimensional network cross-linked porous structure.

[0012] While silicon nanoparticles have a large theoretical specific capacity, their large expansion rate and poor structural stability during charge and discharge degrade the cycle performance of the battery. The carbon-based particles of this application possess a stable three-dimensional cross-linked porous framework structure, which provides ample space for the silicon nanoparticles. This prevents the silicon nanoparticles from agglomerating and mitigates the adverse effects of their volume expansion on the negative electrode, thereby effectively improving the cycle performance of the secondary battery.

[0013] A high nickel content can increase the specific capacity of the positive electrode, thereby improving the energy density of the secondary battery. However, excessively high nickel content can lead to increased lithium-nickel mixing, causing transition metals to easily dissolve and deposit on the negative electrode, affecting the battery's cycle performance. The three-dimensional cross-linked carbon framework of the carbon-silicon material in this application can cooperate with the positive electrode active material, reducing the deposition of transition metals on silicon nanoparticles and mitigating the negative impact of transition metal deposition on the silicon-based material's performance, thus further improving the cycle performance of the secondary battery.

[0014] In any embodiment, in the outer peripheral region of the silicon-carbon composite material, the mass percentage A1 of carbon in the silicon-carbon composite material relative to the total mass of the silicon-carbon composite material and the mass percentage B1 of silicon in the silicon-carbon composite material relative to the total mass of the silicon-carbon composite material satisfy 0.8 ≤ B1 / A1 ≤ 2.5, optionally, 1 ≤ B1 / A1 ≤ 1.5, wherein the outer peripheral region of the silicon-carbon composite material is a region extending from the outer surface of the silicon-carbon composite material to the interior of the silicon-carbon composite material at a distance within r / 2, where r represents the minor axis of the silicon-carbon composite material.

[0015] During the cycling process of a secondary battery, silicon nanoparticles may undergo volume expansion. When the peripheral region of the carbon-silicon composite material satisfies 0.8≤B1 / A1≤2.5, silicon nanoparticles can be attached to the carbon framework relatively uniformly. The carbon matrix particles can significantly limit the volume expansion of silicon nanoparticles. At the same time, the pores formed during the deposition of silicon nanoparticles also provide a buffer space for the expansion of silicon itself, thereby improving the structural stability of the negative electrode active material and thus improving the cycle performance of the secondary battery.

[0016] In any embodiment, in the central region of the carbon-silicon composite material, the mass percentage A2 of carbon in the carbon-silicon composite material relative to the total mass of the carbon-silicon composite material and the mass percentage B2 of silicon in the carbon-silicon composite material relative to the total mass of the carbon-silicon composite material satisfy 1.05≤A2 / B2≤50, optionally, 1.05≤A2 / B2≤3, wherein the central region of the carbon-silicon composite material is a region within r / 2 of the geometric center of the carbon-silicon composite material.

[0017] The central region of the carbon-silicon composite material of this application satisfies 1.05≤A2 / B2≤50, which can further improve the uniformity of silicon nanoparticles adhering to the carbon skeleton, thereby further improving the structural stability of the negative electrode active material and improving its cycle performance.

[0018] In any embodiment, the mass percentage A of carbon relative to the total mass of the carbon-silicon composite material tends to decrease along the direction from the geometric center of the carbon-silicon composite material to the outer surface of the carbon-silicon composite material, and the mass percentage B of silicon relative to the total mass of the carbon-silicon composite material tends to increase along the direction from the geometric center of the carbon-silicon composite material to the outer surface of the carbon-silicon composite material.

[0019] From the outer periphery to the center, the carbon content in the carbon-silicon composite material of this application shows an increasing trend, which can better support the three-dimensional network cross-linked pore structure and improve the structural stability of the carbon skeleton. From the center to the outer periphery, the silicon content in the carbon-silicon composite material of this application shows an increasing trend, which can significantly improve the capacity of the negative electrode active material. The distribution of carbon and silicon elements in the carbon-silicon composite material of this application effectively improves the cycle stability of the battery.

[0020] In any embodiment, the silicon nanoparticles in the carbon-silicon composite material have a mass percentage content of greater than or equal to 40%; optionally, it is 40%-60%.

[0021] Traditional carbon-silicon composite materials suffer from difficulties in effectively increasing silicon loading due to the tendency of nanoparticles to aggregate, thus hindering capacity improvement and ultimately limiting battery energy density optimization. This application addresses this issue by attaching silicon nanoparticles to carbon matrix particles with a carbon framework. This significantly increases the silicon content in the carbon-silicon composite material, enhancing its theoretical capacity. Furthermore, it reduces the amount of silicon required in the negative electrode film, thereby minimizing negative electrode expansion and achieving simultaneous optimization of secondary battery energy density and cycle performance.

[0022] In any embodiment, the negative electrode active material further includes a carbon-based active material.

[0023] In any embodiment, the carbon-based active material includes one or more of graphite, hard carbon, soft carbon, and porous carbon.

[0024] Adding carbon-based active materials to the negative electrode active material can improve the rate performance and cycle performance of secondary batteries.

[0025] In any embodiment, based on the total mass of the negative electrode active material, the mass percentage α of the carbon-silicon composite material is 10%-100%, and optionally, the mass percentage of the carbon-silicon composite material is 30%-40%.

[0026] When the content of the carbon-silicon composite material in this application is 10%-100%, the secondary battery has a high energy density. When the mass percentage of the carbon-silicon composite material is 30%-40%, the battery improves both energy density and cycle performance and rate performance.

[0027] In any embodiment, the negative electrode film layer includes a conductive agent, the conductive agent including carbon nanotubes with an aspect ratio > 2500, and / or, Based on the total mass of the negative electrode film, the mass percentage of the carbon nanotubes is 0.1% to 0.5%, and can be selected as 0.3% to 0.5%.

[0028] Because the carbon-silicon composite material in this application has a high content, the volume expansion of silicon nanoparticles can cause the negative electrode film to rebound to some extent. After repeated charging and discharging, the particles in the negative electrode active material will lose electrical contact. Using carbon nanotubes with the aforementioned aspect ratio can suppress the rebound of the negative electrode film and enhance the conductivity of the negative electrode sheet. Moreover, in order to improve the mass energy density of the battery, the battery adopts a thick coating design. The addition of carbon nanotubes improves the electron transport of the thick electrode sheet through long-range conductivity, further optimizing the rate performance of the battery.

[0029] In any implementation, the negative electrode sheet satisfies: The areal density of the negative electrode film layer on one side of the negative electrode sheet is 4 mg / cm³.2 -15mg / cm 2 8mg / cm 2 -14mg / cm 2 , and / or The compaction density of the negative electrode film layer on one side of the negative electrode sheet is 1.6 g / cm³. 3 -1.8g / cm 3 .

[0030] The battery employs a thick coating design to ensure sufficient loading of active materials, further improving the battery's mass energy density. Furthermore, while the electrodes possess high areal density, the electrode sheets also have suitable compaction density, enabling the battery to maintain both high mass energy density and good rate performance.

[0031] In any embodiment, the positive electrode active material includes Li a Ni x Co y M 1-x-y O 2-b M includes at least one of Mn, Al, B, Zr, Sr, Y, Sb, W, Ti, Mg and Nb. Optionally, M includes at least one of Mn, Al, B, Zr, Sr, W, Mg and Nb; 0.2≤a≤1.2; -0.2≤b≤0.2; 0.85≤x≤1, 0≤y≤0.15. Optionally, 0.92≤x≤0.98, 0<y≤0.08.

[0032] Increasing the content of transition metal nickel in the positive electrode active material can improve the mass energy density of the secondary battery.

[0033] In any implementation, the positive electrode sheet satisfies: The areal density of the positive electrode film layer on one side of the positive electrode sheet is 18 mg / cm³. 2 -45mg / cm 2 25mg / cm 2 -45mg / cm 2 ; and / or, The compaction density of the positive electrode film layer on one side of the positive electrode sheet is 3.3 g / cm³. 3 -3.6g / cm 3 3.4g / cm³ is an optional value. 3 -3.6g / cm 3 .

[0034] Within the aforementioned ranges, the areal density and compaction density of the positive electrode film can ensure a high gravimetric energy density in the secondary battery while further improving its rate performance and cycle performance. Specifically, when the areal density and compaction density of the positive electrode film are low, the positive electrode film contains less positive active material per unit area, resulting in a decrease in the gravimetric energy density of the secondary battery. Conversely, when the areal density and compaction density of the positive electrode film are too high, the positive electrode film contains more positive active material per unit area, leading to excessive dissolution and deposition of transition metals at the negative electrode, thus affecting the cycle performance of the secondary battery.

[0035] In any embodiment, the gravimetric energy density of the secondary battery is 280Wh / kg-500Wh / kg, optionally 360Wh / kg-500Wh / kg or 400Wh / kg-500Wh / kg; and / or, C0 is the capacity of the secondary battery, in Ah, and C0 is 35Ah-200Ah, optionally 45Ah-190Ah.

[0036] A second aspect of this application provides an electrical device comprising the secondary battery described in the first aspect. Attached Figure Description

[0037] Figure 1 This is a schematic diagram of a secondary battery cell according to one embodiment of this application; Figure 2 yes Figure 1 An exploded view of a secondary battery cell according to an embodiment of this application is shown. Figure 3 This is a schematic diagram of a battery module according to one embodiment of this application; Figure 4 This is a schematic diagram of a battery pack according to one embodiment of this application; Figure 5 yes Figure 4 An exploded view of a battery pack according to one embodiment of this application is shown; 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.

[0038] Explanation of reference numerals in the attached figures: 1 Battery pack; 2 Upper housing; 3 Lower housing; 4 Battery module; 5 Secondary battery cell; 51 Housing; 52 Electrode assembly; 53 Cover plate. Detailed Implementation

[0039] The following detailed description, with appropriate reference to the accompanying drawings, specifically discloses embodiments of the battery and power-consuming device of this application. However, unnecessary detailed descriptions may be omitted. For example, detailed descriptions of well-known matters and repetitive descriptions of practically identical structures may be omitted. This is to avoid unnecessarily lengthy descriptions and to facilitate understanding by those skilled in the art. Furthermore, the accompanying drawings and the following description are provided for the purpose of enabling those skilled in the art to fully understand this application and are not intended to limit the subject matter of the claims.

[0040] 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.

[0041] Unless otherwise specified, all embodiments and optional embodiments of this application can be combined to form new technical solutions.

[0042] Unless otherwise specified, all technical features and optional technical features of this application may be combined to form new technical solutions.

[0043] 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.

[0044] Unless otherwise specified, the terms "comprising" and "including" as used in this application can be open-ended or closed-ended. For example, "comprising" and "including" can mean that other components not listed may also be included, or that only the listed components may be included.

[0045] Unless otherwise specified, the term "or" is inclusive in this application. For example, the phrase "A or B" means "A, B, or both A and B". More specifically, the condition "A or B" is satisfied by any of the following conditions: A is true (or exists) and B is false (or does not exist); A is false (or does not exist) and B is true (or exists); or both A and B are true (or exist).

[0046] High-energy lithium-ion batteries have garnered widespread market attention due to their crucial role in strategically important sectors such as advanced information processing terminals and electric vehicles. Although the energy density of commercially available lithium-ion batteries has reached 150-200 Wh / kg, the theoretical capacity limitations of the positive and negative electrode materials make it difficult to further increase the energy density to meet market demands.

[0047] [Rechargeable Battery] Based on this, this application proposes a secondary battery to further improve the gravimetric energy density of the secondary battery.

[0048] In some embodiments, the secondary battery includes a positive electrode and a negative electrode. The positive electrode includes a positive electrode film layer containing a positive electrode active material with transition metal elements. Based on the total molar number of transition metal elements in the positive electrode active material, the molar content of nickel is not less than 85%. The energy per unit area of ​​the positive electrode film layer on one side of the positive electrode is 15-35 mWh / cm². 2 Available in 20-35 mWh / cm³ 2 ; The negative electrode sheet includes a negative electrode film layer, which contains a negative electrode active material of carbon-silicon composite material. The carbon-silicon composite material includes carbon matrix particles with a carbon skeleton and silicon nanoparticles attached to the carbon skeleton.

[0049] In some embodiments, the carbon framework is a solid structure, and silicon nanoparticles are attached to at least a portion of the surface of the carbon framework.

[0050] In some embodiments, the carbon skeleton is a porous skeleton structure, and silicon nanoparticles are attached to at least a portion of the surface of the carbon skeleton and into the pores of the carbon skeleton, wherein the silicon nanoparticles can fill all or part of the pores of the carbon skeleton.

[0051] In some embodiments, the carbon framework is a porous framework structure, where the pores refer to recessed structures that are recessed relative to the outer surface of the negative electrode active material and into the interior of the negative electrode active material, or through-pores that penetrate the negative electrode active material. The composition of the pore structure includes pore size, pore length, and pore size distribution. The pore size of the porous carbon framework of the carbon matrix particles includes micropores, mesopores, and macropores. Micropores are pores with a diameter of less than about 2 nanometers. Mesopores are pores with a diameter of about 2 to about 5 nanometers. Macropores are pores with a diameter greater than 50 nanometers.

[0052] The characteristics of the positive and negative electrode sheets can be observed and tested under a scanning electron microscope and / or energy dispersive spectroscopy after disassembling the battery. As an example, the carbon skeleton of the carbon-silicon composite material can be tested using equipment and methods known in the art. For example, it can be tested using a scanning electron microscope (ZEISS Sigma 300). As an example, the following steps can be taken: after disassembling the battery, take the negative electrode sheet, cut the negative electrode sheet into a sample of a certain size (e.g., 6mm × 6mm), clamp the sample with two conductive and thermally conductive sheets (e.g., copper foil), and fix the sample to the copper foil with adhesive (e.g., double-sided tape). Press it with a flat iron block of a certain mass (e.g., 400g) for a certain time (e.g., 1h), trim the edges with scissors, and stick it to a sample stage with conductive adhesive. The sample stage is then mounted and secured on the sample holder. The argon ion cross-section polisher (e.g., IB-19500CP) is powered on and a vacuum is created (e.g., 10Pa-4Pa). The argon flow rate (e.g., 0.15MPa), voltage (e.g., 8KV), and polishing time (e.g., 2 hours) are set. The sample stage is adjusted to rocking mode to begin polishing. After polishing, the ion-polished cross-sectional morphology image of the sample is obtained using a scanning electron microscope (e.g., ZEISS Sigma 300). The acquired scanning electron microscope images are analyzed using energy dispersive spectroscopy (EDS) to obtain the distribution statistics of carbon and silicon elements. Similarly, scanning and elemental analysis of the positive electrode sheet allows for compositional analysis.

[0053] In some implementations, the silicon nanoparticles have a nanometer-scale particle size, which makes it easier for them to adhere uniformly to the carbon framework when deposited in a porous structure.

[0054] In some embodiments, carbon matrix particles and silicon nanoparticles are combined to form a carbon-silicon composite material. The carbon-silicon composite material may consist of particles with irregular geometric shapes. In this case, the particle diameter can be characterized using a triaxial diameter characterization method. The specific characterization method is as follows: the major diameter l and minor diameter r are measured on the planar projection of the carbon-silicon composite material, and the thickness h of the carbon-silicon composite material is measured in the direction perpendicular to the projection plane. Alternatively, the carbon-silicon composite material can be understood as being placed in a cuboid tangent to it, with the long side of the cuboid being l, the short side being r, and the thickness being h, in order to reflect the actual size of the carbon-silicon composite material.

[0055] In some implementations, the energy per unit area of ​​the positive electrode film layer on one side of the positive electrode can be 15 mWh / cm². 2 16mWh / cm 2 17mWh / cm 2 18mWh / cm 2 19mWh / cm 2 20mWh / cm 2 21mWh / cm 2 22mWh / cm 2 23mWh / cm 2 25mWh / cm 2 27mWh / cm 2 29mWh / cm 2 31mWh / cm 2 33mWh / cm 2 35mWh / cm 2 Or the value within the range formed by any two of the above points.

[0056] The energy per unit area of ​​the positive electrode film on one side of the positive electrode sheet can be measured using methods and equipment commonly used in the art. As an example, the energy per unit area of ​​the positive electrode film on one side of the positive electrode sheet can be measured using the following steps: The battery cell is placed at a certain temperature (e.g., 25°C) for a certain period of time (e.g., 2 hours), ensuring the battery cell temperature is at room temperature (e.g., 25°C). The battery cell is charged at a certain rate (e.g., 0.33C) at a certain temperature (e.g., 25°C) to the charging cutoff voltage, and then charged at a constant voltage at this charging cutoff voltage until the current reaches 0.05C, at which point charging is stopped (C represents the rated capacity of the battery cell). The battery cell is placed at a certain temperature (e.g., 25°C) for a certain period of time (e.g., 1 hour), and then discharged at a certain temperature (e.g., 25°C) at a certain rate (0.33C) to the discharge cutoff voltage, recording the total discharge energy as E0. The battery is disassembled, the positive electrode sheet is removed, and the length and width of the film on the positive electrode sheet are measured using a ruler to obtain the area value S0 of the positive electrode film. When the positive electrode is coated on both sides, the energy per unit area of ​​the positive electrode film is E0 / (2×S0); when the positive electrode film is coated on one side, the energy per unit area of ​​the positive electrode is E0 / S0.

[0057] In the above test method, the charging cutoff voltage is 4.25V, the discharging cutoff voltage is 2.0V, and the charging rate and discharging rate are both 0.33C.

[0058] This application, by combining a high-nickel-content positive electrode active material with a carbon-silicon composite material, breaks through the theoretical capacity limitations of existing positive and negative electrode materials, and realizes the preparation of high-energy-density secondary batteries.

[0059] The weight of the bare cell and the casing of a secondary battery can be tested using equipment and methods known in the art. For example, it can be tested using an electronic balance. As an example, the following steps can be taken: First, separate the battery casing from the bare cell; second, to remove the electrolyte free inside the bare cell, soak the bare cell in dimethyl carbonate (DMC) solvent for 4 hours, then transfer it to a 60°C forced-air drying oven for 4 hours to obtain a dried bare cell; third, place the battery casing and the bare cell separately on an electronic balance and weigh them to obtain the weight of the secondary battery casing and the bare cell.

[0060] The mass percentage of the carbon-silicon composite material can be tested using equipment and methods known in the art. For example, it can be obtained by measuring the mass of the negative electrode active material in the negative electrode film, the silicon content, and the silicon content in the carbon-silicon composite material, and then converting these values.

[0061] As an example, you can follow these steps: (1) Take two batteries with identical designs. Disassemble the first battery and remove the negative electrode sheet. Soak the negative electrode sheet in dimethyl carbonate (DMC) solvent for 4 hours. Then, calcine it in a box-type resistance furnace at 400°C for 2 hours to remove the binder, and obtain the negative electrode active material. Weigh the material and record it as M0. Digest the negative electrode active material sample with aqua regia and hydrofluoric acid. Perform ICP testing on the completely digested solution to obtain the mass percentage of silicon in the negative electrode active material, which is recorded as X0. The mass of silicon in the negative electrode active material, M1, can be obtained by multiplying M0 and X0. (2) Disassemble another battery and remove the negative electrode sheet. Soak the negative electrode sheet in dimethyl carbonate (DMC) solvent for 4 hours, and then calcine it in a box-type resistance furnace at 400°C for 2 hours to remove the binder and other auxiliary materials in the electrode sheet, thereby obtaining the negative electrode active material. Separate the carbon-silicon composite material by graded screening or other screening methods known in the art, and then completely digest the separated carbon-silicon composite material with aqua regia and hydrofluoric acid. Perform ICP test on the digested solution to obtain the mass content ratio of silicon element in the carbon-silicon composite material (X1). (3) Based on the above calculation results, we can obtain that the mass of the carbon silicon composite material in the secondary battery cell is M2=M1 / X1, and the mass percentage of the carbon silicon composite material is M2 / M0×100%. [Negative Electrode Active Materials] In some embodiments, the matrix particles include a three-dimensional network cross-linked porous structure, and at least a portion of the silicon nanoparticles are disposed in the three-dimensional network cross-linked porous structure.

[0062] In this application, "three-dimensional network cross-linked pore structure" refers to a structure in which two or more pores are interconnected or interwoven and share the same pore volume in a pore structure formed by carbon matrix particles.

[0063] While silicon nanoparticles have a large theoretical specific capacity, their large expansion rate and poor structural stability during charge and discharge degrade the cycle performance of the battery. The carbon-based particles of this application possess a stable three-dimensional cross-linked porous framework structure, which provides ample space for the silicon nanoparticles. This prevents the silicon nanoparticles from agglomerating and mitigates the adverse effects of their volume expansion on the negative electrode, thereby effectively improving the cycle performance of the secondary battery.

[0064] A high nickel content can increase the specific capacity of the positive electrode, thereby improving the mass energy density of the secondary battery. However, excessively high nickel content can increase lithium-nickel mixing, leading to the easy dissolution and deposition of transition metals on the negative electrode, affecting the battery's cycle performance. The three-dimensional cross-linked carbon framework of the carbon-silicon material in this application can cooperate with the positive electrode active material, reducing the deposition of transition metals on silicon nanoparticles and mitigating the negative impact of transition metal deposition on the silicon-based material's performance, thus further improving the cycle performance of the secondary battery.

[0065] In some embodiments, in the outer peripheral region of the silicon-carbon composite material, the mass percentage A1 of carbon in the silicon-carbon composite material relative to the total mass of the silicon-carbon composite material and the mass percentage B1 of silicon in the silicon-carbon composite material relative to the total mass of the silicon-carbon composite material satisfy 0.8 ≤ B1 / A1 ≤ 2.5, optionally, 1 ≤ B1 / A1 ≤ 1.5, wherein the outer peripheral region of the silicon-carbon composite material is a region extending from the outer surface of the silicon-carbon composite material to the interior of the silicon-carbon composite material at a distance within r / 2, where r represents the minor axis of the silicon-carbon composite material.

[0066] The silicon-carbon composite material of this application includes an outer peripheral region, which can be understood as a region extending from the outer surface of the silicon-carbon composite material to the interior of the silicon-carbon composite material at a distance of r / 2 or less.

[0067] In some implementations, B1 / A1 can be 0.8, 0.9, 1, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.8, 1.9, 2.0, 2.1, 2.2, 2.3, 2.4, 2.5 or a range of any two of the above values.

[0068] During the cycling process of a secondary battery, silicon nanoparticles may undergo volume expansion. When the peripheral region of the carbon-silicon composite material satisfies 0.8≤B1 / A1≤2.5, silicon nanoparticles can be attached to the carbon framework relatively uniformly. The carbon matrix particles can significantly limit the volume expansion of silicon nanoparticles. At the same time, the pores formed during the deposition of silicon nanoparticles also provide a buffer space for the expansion of silicon itself, thereby improving the structural stability of the negative electrode active material and thus improving the cycle performance of the secondary battery.

[0069] In some embodiments, in the central region of the carbon-silicon composite material, the mass percentage A2 of carbon in the carbon-silicon composite material relative to the total mass of the carbon-silicon composite material and the mass percentage B2 of silicon in the carbon-silicon composite material relative to the total mass of the carbon-silicon composite material satisfy 1.05≤A2 / B2≤50, optionally, 1.05≤A2 / B2≤3, wherein the central region of the carbon-silicon composite material is a region within r / 2 of the geometric center of the carbon-silicon composite material.

[0070] The silicon-carbon composite material of this application includes a central region, which can be understood as a region within r / 2 of the geometric center of the silicon-carbon composite.

[0071] In some implementations, A2 / B2 can be 1.05, 1.1, 1.15, 1.20, 1.25, 1.30, 1.40, 1.50, 1.60, 1.70, 1.80, 1.90, 2.0, 2.2, 2.5, 2.8, 3.0, 5, 10, 15, 20, 25, 30, 35, 40, 45, 50, or a range of any two of the above values.

[0072] The mass percentage of silicon and carbon elements relative to the total mass of the carbon-silicon composite material can be measured using methods and equipment known in the art. For example, the mass percentage of silicon can be measured by emission spectroscopy. As an example, the procedure can be as follows: After disassembling the battery, remove the negative electrode, remove the binder, take the carbon-silicon composite material as a sample, digest the sample with a strong acidic solution (e.g., aqua regia and HF hydrofluoric acid), and perform ICP testing on the solution after 15 minutes of digestion and the solution after complete digestion. The silicon content in the solution after 15 minutes of digestion is the silicon content in the "outer region of the carbon-silicon composite material," and the difference between the silicon content in the completely digested and 15-minute digested solutions is the silicon content in the "central region of the carbon-silicon composite." For example, the mass percentage of carbon can be analyzed by infrared absorption carbon-sulfur content analysis according to the GB / T20123-2006 test standard. As an example, the following steps can be followed: After disassembling the battery, take out the negative electrode sheet, remove the binder, take the carbon-silicon composite material as a sample, and test the carbon content at 20 minutes as the carbon content of the "outer peripheral region of the carbon-silicon composite material". The difference between the carbon content at 20 minutes and the end of the test is the carbon content of the "central region of the carbon-silicon composite material".

[0073] The central region of the carbon-silicon composite material of this application satisfies 1.05≤A2 / B2≤50, which can further improve the uniformity of silicon nanoparticles adhering to the carbon skeleton, thereby further improving the structural stability of the negative electrode active material. It can improve the energy density of the secondary battery while taking into account long cycle performance.

[0074] In some embodiments, the mass percentage A of carbon relative to the total mass of the carbon-silicon composite material tends to decrease along the direction from the geometric center of the carbon-silicon composite material towards the outer surface of the carbon-silicon composite material, while the mass percentage B of silicon relative to the total mass of the carbon-silicon composite material tends to increase along the direction from the geometric center of the carbon-silicon composite material towards the outer surface of the carbon-silicon composite material.

[0075] In some implementations, since silicon carbide composites may be irregularly shaped, the geometric center of the silicon carbide composite may be equivalent to the geometric center of the cuboid tangent to it.

[0076] From the outer periphery to the center, the carbon content in the carbon-silicon composite material of this application shows an increasing trend, which can better support the three-dimensional network cross-linked pore structure and improve the structural stability of the carbon skeleton. From the center to the outer periphery, the silicon content in the carbon-silicon composite material of this application shows an increasing trend, which can significantly improve the capacity of the negative electrode active material. The distribution of carbon and silicon elements in the carbon-silicon composite material of this application effectively improves the cycle stability of the battery.

[0077] In some embodiments, the mass percentage of silicon nanoparticles in the silicon-carbon composite material is greater than or equal to 40%; optionally, it is 40%-60%.

[0078] In some embodiments, the mass percentage of nanoparticles in the silicon-carbon composite material can be 40%, 45%, 50%, 60%, 75%, 80%, or a value within a range consisting of any two of the above.

[0079] Traditional carbon-silicon composite materials suffer from difficulties in effectively increasing silicon loading due to the tendency of nanoparticles to aggregate, thus hindering capacity improvement and ultimately limiting the optimization of battery energy density. This application addresses this issue by attaching silicon nanoparticles to carbon matrix particles with a carbon framework. This significantly increases the silicon content in the carbon-silicon composite material, enhancing its theoretical capacity. Furthermore, it reduces the amount of silicon required in the negative electrode film, thereby minimizing negative electrode expansion and achieving simultaneous optimization of secondary battery energy density and cycle performance.

[0080] In some embodiments, the negative electrode active material also includes a carbon-based active material.

[0081] In some embodiments, the carbon-based active material includes one or more of graphite, hard carbon, soft carbon, and porous carbon.

[0082] In some embodiments, the carbon-based active material is selected from graphite or hard carbon.

[0083] Adding carbon-based active materials to the negative electrode active material can improve the rate performance and cycle performance of secondary batteries.

[0084] In some embodiments, the mass percentage α of the carbon-silicon composite material is 10%-100% based on the total mass of the negative electrode active material. Optionally, the mass percentage of the carbon-silicon composite material is 30%-40%.

[0085] In some embodiments, based on the total mass of the negative electrode active material, the mass percentage α of the carbon-silicon composite material can be 10%, 20%, 25%, 30%, 35%, 40%, 50%, 60%, 70%, 80%, 90%, 100%, or a value within a range consisting of any two of the above points.

[0086] When the content of the carbon-silicon composite material in this application is 10%-100%, the secondary battery has a high energy density. When the mass percentage of the carbon-silicon composite material is 30%-40%, the battery improves both energy density and cycle performance and rate performance.

[0087] In some embodiments, the negative electrode film layer includes a conductive agent, which includes carbon nanotubes with an aspect ratio > 2500, and / or... Based on the total mass of the negative electrode film, the mass percentage of carbon nanotubes is 0.1%~0.5%, and can be selected as 0.3%-0.5%.

[0088] In some embodiments, the mass percentage of carbon nanotubes can be 0.1%, 0.15%, 0.2%, 0.25%, 0.3%, 0.35%, 0.4%, 0.45%, 0.5%, or any value within the range formed by any two of the above points.

[0089] In some embodiments, the conductive agent may also include at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, graphene, and carbon nanofibers.

[0090] Because the carbon-silicon composite material in this application has a high content, the volume expansion of silicon nanoparticles can cause the negative electrode film to rebound to some extent. After repeated charging and discharging, the particles in the negative electrode active material will lose electrical contact. Using carbon nanotubes with the aforementioned aspect ratio can suppress the rebound of the negative electrode film and enhance the conductivity of the negative electrode sheet. Moreover, in order to improve the mass energy density of the battery, the battery adopts a thick coating design. The addition of carbon nanotubes improves the electron transport of the thick electrode sheet through long-range conductivity, further optimizing the kinetic performance of the battery.

[0091] In some embodiments, the negative electrode sheet satisfies the following condition: the areal density of the negative electrode film layer on one side of the negative electrode sheet is 4 mg / cm³. 2 -15mg / cm 2 8mg / cm 2 -14mg / cm 2 , and / or The compaction density of the negative electrode film layer on one side of the negative electrode sheet is 1.6 g / cm³. 3 -1.8g / cm 3 .

[0092] In some embodiments, the areal density of the negative electrode film layer on one side of the negative electrode sheet can be 4 mg / cm³. 2 5mg / cm 2 6mg / cm 2 7mg / cm 2 8mg / cm 2 9mg / cm 2 10mg / cm 2 11mg / cm 2 12mg / cm 2 13mg / cm 2 14mg / cm 2 15mg / cm 2 Or the value within the range formed by any two of the above points.

[0093] In some embodiments, the compaction density of the negative electrode film layer on one side of the negative electrode sheet can be 1.6 g / cm³. 3 1.65g / cm 3 1.7g / cm 3 1.75g / cm 3 1.8g / cm 3 Or the value within the range formed by any two of the above points.

[0094] The battery employs a thick coating design to ensure sufficient loading of active materials, further improving the battery's mass energy density and the energy per unit area of ​​the positive electrode film. Furthermore, while the electrodes possess high areal density, the electrode sheets also exhibit suitable compaction density, ensuring both the mass energy density of the secondary battery and its kinetic performance.

[0095] [Negative electrode plate] The negative electrode sheet includes a negative current collector and a negative electrode film layer disposed on at least one surface of the negative current collector, the negative electrode film layer including the negative electrode active material of this application.

[0096] 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.).

[0097] In some embodiments, the negative electrode film 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).

[0098] In some embodiments, the negative electrode film may optionally include other additives, such as thickeners (e.g., sodium carboxymethyl cellulose (CMC-Na)).

[0099] In some embodiments, the negative electrode sheet can be prepared by dispersing the above-mentioned components for preparing the negative electrode sheet, such as negative electrode active material, conductive agent, binder and any other components, in a solvent (e.g., deionized water) to form a negative electrode slurry; coating the negative electrode slurry onto a negative electrode current collector, and then obtaining the negative electrode sheet after drying, cold pressing and other processes.

[0100] [Positive electrode active material] In some embodiments, the positive electrode active material includes Li a Ni x Co y M 1-x-y O 2-b M includes at least one of Mn, Al, B, Zr, Sr, Y, Sb, W, Ti, Mg and Nb. Optionally, M includes at least one of Mn, Al, B, Zr, Sr, W, Mg and Nb. 0.2≤a≤1.2; -0.2≤b≤0.2; 0.85≤x≤1, 0≤y≤0.15. Optionally, 0.92≤x≤0.98, 0<y≤0.08.

[0101] In some implementations, 'a' can be a value of 0.2, 0.4, 0.6, 0.8, 1.0, 1.2, or any two of the above points within a range.

[0102] In some implementations, b can be a value within the range of -0.2, -0.1, 0, 0.1, 0.2, or any two of the above points.

[0103] In some implementations, x can be a value of 0.85, 0.87, 0.89, 0.91, 0.93, 0.95, 0.97 or any two of the above points, and y can be 0, 0.03, 0.05, 0.07, 0.09, 0.11, 0.13 or any two of the above points.

[0104] Increasing the content of transition metal nickel in the positive electrode active material can improve the mass energy density of the secondary battery.

[0105] In some embodiments, M includes Mn. In some embodiments, M includes Al. In some embodiments, M includes B. In some embodiments, M includes Zr. In some embodiments, M includes Sr. In some embodiments, M includes W. In some embodiments, M includes Mg. In some embodiments, M includes Nb.

[0106] Compared with commonly used binary cathode active materials, ternary cathode active materials exhibit superior electrochemical performance. Specifically, doping the aforementioned M element into the cathode active material can optimize the particle size and particle size distribution, thereby improving the electron and lithium-ion transport performance and ultimately increasing the mass energy density of the secondary battery.

[0107] In some implementations, the positive electrode sheet satisfies: The areal density of the positive electrode film layer on one side of the positive electrode is 19 mg / cm³. 2 -45mg / cm 2 25mg / cm 2 -45mg / cm 2 ; and / or, The compaction density of the positive electrode film layer on one side of the positive electrode sheet is 3.3 g / cm³. 3 -3.6g / cm 3 3.4g / cm³ is an optional value. 3 -3.6g / cm 3 .

[0108] In some embodiments, the areal density of the positive electrode film layer on one side of the positive electrode sheet can be 19 mg / cm³. 2 20mg / cm 2 22mg / cm 2 24mg / cm 2 26mg / cm 2 28mg / cm 2 30mg / cm 2 32mg / cm 2 34mg / cm 2 36mg / cm 2 38mg / cm 2 40mg / cm 2 42mg / cm 2 44mg / cm 2 Or the value within the range formed by any two of the above points.

[0109] In some embodiments, the compaction density of the positive electrode film layer on one side of the positive electrode sheet can be 3.45 g / cm³. 3 3.5g / cm 33.55g / cm 3 Or the value within the range formed by any two of the above points.

[0110] The areal density and compaction density of the positive electrode film layer on one side of the positive electrode or the negative electrode film layer on one side of the negative electrode can be measured using methods and equipment commonly used in the art. As an example, the compaction density of the film layer on one side of the electrode can be measured as follows: when the electrode is coated on one side, the compaction density of the film layer on one side of the electrode = m / (V1-V2); when the electrode is coated on both sides, the compaction density of the film layer on one side of the electrode = m / [2×(V1-V2)], where m represents the weight of the film layer, V1 represents the volume of the electrode, 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. The product of the surface area of ​​the electrode and the thickness of the electrode is the volume of the electrode, V1; the product of the surface area of ​​the electrode and the thickness of the current collector is V2. The thickness of the current collector and the thickness of the electrode are obtained by measuring the thickness of the empty foil in the tab area using a micrometer. As an example, the areal density of the film layer on one side of the electrode can be determined as follows: When the electrode is coated on one side, the areal density of the film layer on one side of the electrode = m / S; when the electrode is coated on both sides, the areal density of the film layer on one side of the electrode = m / (2×S), where m represents the weight of the film layer and S represents the area of ​​the film layer. m can be obtained by subtracting the weight of the current collector from the weight of the electrode. The length and width of the film layer can be measured with a ruler.

[0111] Within the aforementioned ranges, the areal density and compaction density of the positive electrode film can ensure that the secondary battery has a high gravimetric energy density and a high energy per unit area of ​​the positive electrode film, while further improving the power performance and cycle performance of the secondary battery. Specifically, when the areal density and compaction density of the positive electrode film are low, the positive electrode film contains less positive active material per unit area, resulting in a decrease in the gravimetric energy density of the secondary battery; when the areal density and compaction density of the positive electrode film are too high, the positive electrode film contains more positive active material per unit area, resulting in excessive dissolution and deposition of transition metals at the negative electrode, thus affecting the cycle performance of the secondary battery.

[0112] [Positive electrode plate] The positive electrode includes a positive current collector and a positive electrode film layer disposed on at least one surface of the positive current collector, the positive electrode film layer including the positive electrode active material of this application.

[0113] As an example, the positive current collector has two surfaces opposite each other in its own thickness direction, and the positive electrode film layer is disposed on either or both of the two opposite surfaces of the positive current collector.

[0114] In some embodiments of this application, 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 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 (aluminum, aluminum 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.).

[0115] In some embodiments of this application, the positive electrode film layer may optionally include a binder. As an example, the binder may include at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), PVDF-tetrafluoroethylene-propylene terpolymer, PVDF-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorinated acrylate resin.

[0116] In some embodiments of this disclosure, the positive electrode film may optionally include a conductive agent. As an example, the conductive agent may include at least one selected from superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0117] In some embodiments of this disclosure, 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 a positive current collector, and then obtaining the positive electrode sheet after drying, cold pressing and other processes.

[0118] [Electrolytes] 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.

[0119] In some embodiments, the electrolyte is an electrolyte solution. The electrolyte solution includes an electrolyte salt and a solvent.

[0120] 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.

[0121] 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.

[0122] 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.

[0123] [Isolation membrane] In some embodiments, the secondary battery also includes a separator. This application does not impose any particular limitation on the type of separator; any known porous separator with good chemical and mechanical stability can be selected.

[0124] 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.

[0125] [Preparation Method] In some implementations, the positive electrode, negative electrode, and separator can be fabricated into an electrode assembly using a winding or stacking process.

[0126] In some embodiments, the gravimetric energy density of the secondary battery is 280Wh / kg-500Wh / kg, optionally 360Wh / kg-500Wh / kg or 400Wh / kg-500Wh / kg; and / or, The capacity C0 of the secondary battery is 35Ah-200Ah, with a selectable range of 45Ah-190Ah.

[0127] In some embodiments, the mass energy density of the secondary battery can be 280 Wh / kg, 300 Wh / kg, 320 Wh / kg, 350 Wh / kg, 360 Wh / kg, 370 Wh / kg, 380 Wh / kg, 390 Wh / kg, 400 Wh / kg, 410 Wh / kg, 420 Wh / kg, 430 Wh / kg, 450 Wh / kg, 500 Wh / kg, 360 Wh / kg, 360 Wh / kg, or a value within the range formed by any two of the above.

[0128] In some embodiments, the capacity C0 of the secondary battery is 35Ah, 40Ah, 43Ah, 45Ah, 48Ah, 50Ah, 60Ah, 80Ah, 100Ah, 130Ah, 160Ah, 200Ah, or a value within the range formed by any two of the above.

[0129] In this application, the mass energy density of the secondary battery can be measured using methods and equipment commonly used in the art. As an example, the mass energy density of the secondary battery can be measured using the following steps: The battery cell is placed at a certain temperature (e.g., 25°C) for a certain period of time (e.g., 2 hours), ensuring the battery cell temperature is at room temperature (e.g., 25°C). At a certain temperature (e.g., 25°C), the battery cell is charged at a certain rate (e.g., 0.33C) to the charging cutoff voltage, and then charged at this charging cutoff voltage under constant voltage until the current reaches 0.05C, at which point charging is stopped (C represents the rated capacity of the battery cell). The battery cell is placed at a certain temperature (e.g., 25°C) for a certain period of time (e.g., 1 hour), and then discharged at a certain temperature (e.g., 25°C) at a certain rate (0.33C) to the discharge cutoff voltage, recording the total discharge energy of the battery cell as E0. The battery cell is placed on an electronic balance until its weight stabilizes, and the battery cell weight value M0 is read. Battery mass energy density = Battery cell discharge energy E0 / Battery cell weight M0.

[0130] 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.

[0131] 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 This is an example of a square-structured secondary battery 5.

[0132] In some of these embodiments, reference is made to Figure 2 The outer packaging may include a housing 51 and a cover 53. The housing 51 may include a base plate and side plates connected to the base plate, the base plate and side plates forming a receiving cavity. The housing 51 has an opening communicating with the receiving cavity, and the cover 53 can be placed over the opening to close the receiving cavity. The positive electrode, negative electrode, and separator may 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 secondary battery 5 may contain one or more electrode assemblies 52, which can be selected by those skilled in the art according to specific practical needs.

[0133] In some embodiments, the weight z of the secondary battery casing and the weight JR of the bare cells of the secondary battery satisfy the following relationship: 0.01≤z / JR≤0.42; optionally, 0.01≤z / JR≤0.1 or 0.02≤z / JR≤0.07.

[0134] In some implementations, z / JR can be 0.015, 0.025, 0.03, 0.04, 0.05, 0.06, 0.07, 0.08, 0.09, 0.1, 0.2, 0.3, 0.4, or a value within a range consisting of any two of the above points.

[0135] In some implementations, the secondary battery is a pouch cell with a z / JR ratio of 0.01-0.1 or 0.03-0.07.

[0136] In some implementations, the secondary battery is a hard-shell cell with a z / JR ratio of 0.1-0.42 or 0.1-0.3.

[0137] Through the above structural design, the secondary battery can be guaranteed to have a significantly higher mass energy density, while the outer wall has sufficient structural strength, thus achieving high safety performance.

[0138] [Battery Module] 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.

[0139] 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.

[0140] Optionally, the battery module 4 may also include a housing with a receiving space in which multiple battery cells 5 are received.

[0141] [Battery Pack] 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.

[0142] Figure 4 and Figure 5 This is battery pack 1 as an example. (See reference...) Figure 4 and Figure 5The 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.

[0143] [Electrical appliances] A second aspect of this application provides an electrical device comprising the secondary battery of the first aspect.

[0144] Electrical devices may include, but are 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.

[0145] As an electrical device, a secondary battery, battery module, or battery pack can be selected according to its usage requirements.

[0146] 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 device's requirements for high power and high-quality energy density in its secondary batteries, a battery pack or battery module can be used.

[0147] Another example device could be a mobile phone, tablet, or laptop. These devices typically require a slim and lightweight design and can use a rechargeable battery as their power source.

[0148] Example 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.

[0149] Example 1 I. Preparation Method 1. Preparation of positive electrode sheet Preparation of the positive electrode active material: Lithium hydroxide and dried high-nickel ternary precursor were weighed according to the stoichiometric ratio of the chemical formula. The mixture was then thoroughly mixed in a high-speed mixer and sintered in a kiln at 760℃ for 20 h in an oxygen atmosphere. After cooling, the matrix material was obtained. This material was washed with water at a mass ratio of 1:5 for 30 min, centrifuged, filtered, and then subjected to vibration drying at a vibration frequency of 30 Hz for 5 h to obtain the positive electrode active material.

[0150] A positive electrode slurry is prepared by uniformly mixing positive electrode active material, conductive agent carbon black, and binder polyvinylidene fluoride (PVDF) in an N-methylpyrrolidone (NMP) solution at a mass ratio of 97%:1%:2%. The slurry is then uniformly coated onto a positive electrode current collector, coated onto an aluminum foil surface using an extrusion coating machine, and dried. Finally, the coated electrode is cold-pressed using a cold press to obtain the final positive electrode sheet.

[0151] 2. Preparation of negative electrode sheet Preparation of carbon-silicon composite materials: Silicon nanoparticles are formed by chemical vapor deposition (CVD) of silicon precursor onto a porous carbon framework, resulting in a carbon-silicon composite. The size of the silicon nanoparticles and their deposition depth within the porous carbon material are controlled by adjusting deposition conditions such as gas flow rate and reaction chamber pressure.

[0152] Artificial graphite and silicon-carbon composite materials, conductive carbon black, carbon nanotubes, styrene-butadiene rubber (SBR) binder, and sodium carboxymethyl cellulose (CMC) thickener are thoroughly mixed in a certain proportion with an appropriate amount of deionized water to form a uniform negative electrode slurry. The negative electrode slurry is coated onto a negative electrode current collector and dried to obtain a negative electrode film. The aspect ratio of the carbon nanotubes is 3000, and the mass percentage of carbon nanotubes is 0.4% based on the total mass of the negative electrode film.

[0153] 3. Separating membrane Polyethylene film (PE diaphragm) is used as the separation membrane.

[0154] 4. Electrolyte Ethylene carbonate, methyl ethyl carbonate, and diethyl carbonate were mixed in a volume ratio of 1:1:1 to obtain an organic solvent. The fully dried lithium salt LiPF6 was dissolved in the mixed organic solvent to prepare an electrolyte with a concentration of 1 mol / L.

[0155] 5. Battery manufacturing The above-mentioned positive electrode sheet, separator, and negative electrode sheet are wound in sequence to obtain a bare cell; the bare cell is placed in a soft-pack packaging shell, dried, and then injected with electrolyte. After vacuum sealing, settling, formation, and shaping processes, a lithium-ion battery is obtained.

[0156] Examples 2-4 The preparation method is similar to that of Example 1. The difference is that the design parameters of the shell were adjusted in Examples 2-3, and the design parameters of the shell were adjusted in Example 4 using a hard shell packaging shell. The specific parameters are detailed in Table 1.

[0157] Example 5-20 The preparation method is similar to that in Example 1, except that the relevant parameters in the preparation steps of the negative electrode active material or the positive electrode active material are adjusted. For details of the parameters, please refer to Table 1.

[0158] Comparative Examples 1-4 The preparation method is similar to that of Example 1, except that the type of negative electrode active material added or the relevant parameters in the preparation steps of positive electrode active material or negative electrode active material are adjusted. Comparative Example 1 uses a hard-shell packaging shell, as detailed in Table 1.

[0159] II. Performance Testing 1. Battery performance test 1.1 Mass Energy Density 1) The method for measuring the discharge energy of a single battery cell is as follows: The battery cells were left to stand at 25°C for 2 hours to ensure the temperature remained at 25°C. At 25°C, the battery cells were charged at 0.33C to the charging cutoff voltage, and then continued to be charged at this cutoff voltage under constant voltage until the current reached 0.05C, at which point charging was stopped (where C represents the rated capacity of the battery cell). The battery cells were then left to stand at 25°C for 1 hour, and then discharged at 0.33C to the discharge cutoff voltage at 25°C. The total discharge energy of the battery cell was recorded as E0. The charging cutoff voltage was 4.25V, and the discharge cutoff voltage was 2.0V.

[0160] 2) The method for measuring the weight of a single battery cell is as follows: Place the battery cell on the electronic balance until the weight stabilizes, and read the weight value M0 of the battery cell.

[0161] 3) The formula for calculating the battery's mass energy density is as follows: Battery mass energy density = Discharge energy of a single battery cell E0 / Weight of a single battery cell M0 1.2 Cyclic Performance The voltage calibration method is as follows: The battery cells were left to stand at 25°C for 2 hours to ensure the temperature remained at 25°C. At 25°C, the battery cells were charged to 4.25V at a rate of 0.33C0, then charged at a constant voltage of 4.25V until a current of 0.05C0 was reached, followed by a 1-hour rest. At 25°C, the cells were discharged to 0.95C0 at a rate of 0.33C0, and the voltage V1 was recorded at this point. After resting for 5 minutes, the cells were discharged to 2.0V at 25°C at a rate of 0.33C0. After resting for 5 minutes, the battery cells were charged to 0.97C0 at 25°C, and after resting for 5 minutes, the voltage V2 was recorded at this point.

[0162] The loop test process is as follows: The battery cells were left to stand at 25°C for 2 hours to ensure the temperature remained at 25°C. The battery cells were then charged to voltage V2 at 0.33C0 at 25°C and left to stand for 0.5 hours. The battery cells were then discharged to V1 at 0.33C0 at 25°C and left to stand for 0.5 hours. A full charge-discharge cycle test was then performed until the secondary battery capacity decreased to 80% of its initial capacity. The test was then stopped, and the number of cycles was recorded.

[0163] 1.3 Ratio Performance At 25℃, the battery was fully charged at x C and then fully discharged at 1C 10 times. Then, the battery was fully charged at x C again. The negative electrode was then removed, and the lithium deposition on its surface was observed. If no lithium deposition was observed, the charging rate x C was increased in increments of 0.1C until lithium deposition occurred on the negative electrode surface. The test was then stopped. The maximum charging rate of the battery was the charging rate minus 0.1C. The full charge cutoff voltage was 4.25V, and the full discharge cutoff voltage was 2.0V.

[0164] 1.4 Capacity Testing The battery cells were left to stand at 25°C for 2 hours to ensure the temperature remained at 25°C. At 25°C, the battery cells were charged at 0.33C to the charging cutoff voltage, and then continued to be charged at this cutoff voltage under constant voltage until the current reached 0.05C, at which point charging was stopped (where C represents the rated capacity of the battery cell). The battery cells were then left to stand at 25°C for 1 hour, and then discharged at 0.33C to the discharge cutoff voltage at 25°C. The total discharge capacity C0 of the battery cells was recorded. The charging cutoff voltage was 4.25V, and the discharge cutoff voltage was 2.0V.

[0165] 1.5. Weight of battery casing and bare cell First, separate the battery casing and the bare cell. Second, to remove the electrolyte inside the bare cell, soak the bare cell in dimethyl carbonate (DMC) solvent for 4 hours, and then transfer it to a 60°C forced-air drying oven to dry for 4 hours to obtain a dried bare cell. Third, place the battery casing and the bare cell on an electronic balance and weigh them to obtain the weight of the secondary battery casing (z) and the weight of the bare cell (JR).

[0166] 2. Performance testing of positive and negative electrode plates 2.1 Method for measuring the unit surface density of the positive electrode film layer on one side of the positive electrode sheet and the negative electrode film layer on one side of the negative electrode sheet. When the electrode is coated on one side only, the areal density of the film layer on one side of the electrode is m / S. When the electrode is coated on both sides only, the areal density of the film layer on one side of the electrode is m / (2×S), where m represents the weight of the film layer and S represents the area of ​​the film layer. m can be obtained by subtracting the weight of the current collector from the weight of the electrode. The length and width of the film layer can be measured with a ruler.

[0167] 2.2 Method for testing the energy per unit area of ​​the positive electrode film layer on one side of the positive electrode sheet The battery cells were left to stand at 25°C for 2 hours to ensure the temperature remained at 25°C. At 25°C, the cells were charged at 0.33C to the charging cutoff voltage, and then continued to be charged at this cutoff voltage under constant voltage until the current reached 0.05C, at which point charging was stopped (where C represents the rated capacity of the battery cell). The battery cells were then left to stand at 25°C for 1 hour, and then discharged at 0.33C to the discharge cutoff voltage at 25°C. The total discharge capacity C0 and total discharge energy E0 of the battery cells were recorded. The battery was disassembled, and the positive electrode was removed. The length and width of the film on the positive electrode were measured using a ruler to obtain the area value S0 of the positive electrode film. When the positive electrode was double-sided coated, the energy per unit area of ​​the positive electrode film = E0 / (2×S0); when the positive electrode was single-sided coated, the energy per unit area of ​​the positive electrode film = E0 / S0. The charging cutoff voltage was 4.25V, and the discharging cutoff voltage was 2.0V.

[0168] 2.3 Method for measuring silicon content in carbon-silicon composite materials The silicon content was determined using inductively coupled plasma (ICP) emission spectroscopy, as follows: Silicon-carbon composite materials were digested with aqua regia and HF hydrofluoric acid. Since the digestion time is positively correlated with the depth of silicon dissolution in the silicon-carbon particles, gradient ICP tests were performed on solutions with different digestion times. Combined with statistical analysis of the silicon-carbon material using transmission electron microscopy (TEM), it was found that the silicon content in the solution digested for 15 minutes corresponded to the silicon content in the "outer peripheral region of the silicon-carbon composite material," while the difference in silicon content between the completely digested and 15-minute digested solutions corresponded to the silicon content in the "central region of the silicon-carbon composite."

[0169] 2.4 Methods for measuring carbon content in carbon-silicon composite materials The carbon-sulfur content analysis by infrared absorption method was conducted according to the GB / T20123-2006 test standard, as follows: After disassembling the battery, the negative electrode sheet was taken out, the binder was removed, and the carbon-silicon composite material was taken as a sample. The carbon content at 20 minutes was the carbon content of the "outer peripheral region of the carbon-silicon composite material", and the difference between the carbon content at 20 minutes and the end of the test was the carbon content of the "central region of the carbon-silicon composite material".

[0170] 2.5 Method for measuring the minor diameter (r) of carbon-silicon composite materials The minor diameter r was determined according to the triaxial characterization method, specifically as follows: the minor diameter r was determined on the planar projection diagram of the carbon-silicon composite.

[0171] III. Analysis of Test Results for Each Embodiment and Comparative Example Batteries for each embodiment and comparative example were prepared according to the above method, and various performance parameters were measured. The parameters of the secondary batteries are shown in Table 1 below, and the performance test results of the secondary batteries are shown in Table 2 below.

[0172]

[0173]

[0174]

[0175]

[0176] Based on the results in the table above, from Comparative Example 1 and Examples 1-20, Comparative Example 2 and Example 1, and Examples 9-12, it can be seen that when the nickel content in the positive electrode active material is ≥85%, the resulting secondary battery has a higher mass energy density and the positive electrode film layer has a higher energy per unit area. From Comparative Example 1 and Examples 1-20, it can be seen that when the negative electrode active material includes a carbon-silicon composite material with a three-dimensional network cross-linked porous structure, the resulting secondary battery has better cycle performance. From Comparative Example 3 and Example 1, and Comparative Example 4 and Example 5, it can be seen that carbon-silicon composite materials can improve the cycle performance of secondary batteries compared to other composite materials, such as silicon-oxygen materials.

[0177] As demonstrated in Examples 1-4, when using the same type of packaging shell, the gravimetric energy density of the secondary battery increases when the ratio of shell weight to bare cell weight decreases. By controlling the ratio of the secondary battery shell weight to bare cell weight within the range specified in this application, the secondary battery exhibits a high gravimetric energy density.

[0178] As shown in Examples 1 and 5-8, the mass percentage of the carbon-silicon composite material affects the energy density, cycle performance, and rate performance of the secondary battery. When the mass percentage of the carbon-silicon composite material is between 20% and 100%, the secondary battery exhibits a relatively good energy density. Furthermore, when the mass percentage of the carbon-silicon composite material is between 30% and 40%, a balance is achieved between energy density, cycle performance, and rate performance.

[0179] As shown in Examples 1 and 17-20, the ratio of silicon to carbon in the negative electrode active material affects the cycle performance and rate performance of the secondary battery. Specifically, adjusting the ratio to 0.8 ≤ B1 / A1 ≤ 2.5, especially 1 ≤ B1 / A1 ≤ 1.5, and adjusting the ratio to 1.05 ≤ A2 / B2 ≤ 50, especially 1.05 ≤ A2 / B2 ≤ 3, can improve the cycle performance and rate performance of the secondary battery.

[0180] As can be seen from Examples 1 and 13-16, increasing the areal density of the film layer improves the gravimetric energy density of the secondary battery and the energy per unit area of ​​the positive electrode film layer, but it also affects the cycle performance and rate performance of the secondary battery to some extent. Within the areal density range of the positive and negative electrode films in this application, the obtained secondary battery achieves a balance between gravimetric energy density, energy per unit area of ​​the positive electrode film layer, cycle performance, and rate performance.

[0181] In summary, the secondary battery of this application achieves higher mass energy density and improved cycle performance and rate performance through the close cooperation of negative electrode active materials and positive electrode active materials.

[0182] 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 positive electrode includes a positive electrode sheet, which contains a positive electrode film layer. The positive electrode film layer contains a positive electrode active material with transition metal elements. Based on the total molar number of transition metal elements in the positive electrode active material, the molar content of nickel is not less than 85%. The energy per unit area of ​​the positive electrode film layer on one side of the positive electrode sheet is 15-35 mWh / cm². 2 Available in 20-35 mWh / cm³ 2 ; A negative electrode sheet, the negative electrode sheet comprising a negative electrode film layer, the negative electrode film layer comprising a negative electrode active material of a carbon-silicon composite material, the carbon-silicon composite material comprising carbon matrix particles having a carbon skeleton and silicon nanoparticles attached to the carbon skeleton.

2. The secondary battery according to claim 1, characterized in that, The carbon skeleton comprises a solid structure, and the carbon nanoparticles are attached to at least a portion of the surface of the carbon skeleton.

3. The secondary battery according to claim 1, characterized in that, The carbon skeleton includes a porous skeleton structure, and the silicon nanoparticles are attached to at least a portion of the surface of the carbon skeleton and the pores of the carbon skeleton, wherein the silicon nanoparticles can at least partially fill the pores of the carbon skeleton.

4. The secondary battery according to any one of claims 1-3, characterized in that, The weight z of the secondary battery casing and the weight JR of the bare battery cell satisfy the following relationship: 0.01≤z / JR≤0.42; or optionally 0.01≤z / JR≤0.1 or 0.02≤z / JR≤0.

07.

5. The secondary battery according to claim 4, characterized in that, The secondary battery includes pouch cells, and the weight z of the secondary battery casing and the weight JR of the pouch cells satisfy the following relationship: 0.01≤z / JR≤0.1; optionally, 0.03≤z / JR≤0.

07.

6. The secondary battery according to claim 4, characterized in that, The secondary battery includes a hard-shell cell, and the weight z of the secondary battery casing and the weight JR of the hard-shell cell satisfy the following relationship: 0.1≤z / JR≤0.42; optionally, 0.1≤z / JR≤0.

3.

7. The secondary battery according to any one of claims 1-6, characterized in that, The carbon matrix particles include a three-dimensional network cross-linked porous structure, and at least a portion of the silicon nanoparticles are disposed in the three-dimensional network cross-linked porous structure.

8. The secondary battery according to any one of claims 1-7, characterized in that, In the outer peripheral region of the carbon-silicon composite material, the mass percentage A1 of carbon in the carbon-silicon composite material relative to the total mass of the carbon-silicon composite material and the mass percentage B1 of silicon in the carbon-silicon composite material relative to the total mass of the carbon-silicon composite material satisfy 0.8≤B1 / A1≤2.5, optionally, 1≤B1 / A1≤1.5, wherein the outer peripheral region of the carbon-silicon composite material is the region extending from the outer surface of the carbon-silicon composite material to the interior of the carbon-silicon composite material at a distance within r / 2, where r represents the minor axis of the carbon-silicon composite material.

9. The secondary battery according to any one of claims 1-8, characterized in that, In the central region of the carbon-silicon composite material, the mass percentage of carbon relative to the total mass of the carbon-silicon composite material, A2, and the mass percentage of silicon relative to the total mass of the carbon-silicon composite material, B2, satisfy 1.05 ≤ A2 / B2 ≤ 50, optionally, 1.05 ≤ A2 / B2 ≤ 3, wherein the central region of the carbon-silicon composite material is the region within r / 2 of the geometric center of the carbon-silicon composite material, where r represents the minor axis of the carbon-silicon composite material.

10. The secondary battery according to any one of claims 1-9, characterized in that, The mass percentage A of carbon relative to the total mass of the carbon-silicon composite material tends to decrease along the direction from the geometric center of the carbon-silicon composite material towards the outer surface of the carbon-silicon composite material, while the mass percentage B of silicon relative to the total mass of the carbon-silicon composite material tends to increase along the direction from the geometric center of the carbon-silicon composite material towards the outer surface of the carbon-silicon composite material.

11. The secondary battery according to any one of claims 1-10, characterized in that, The silicon nanoparticles in the carbon-silicon composite material have a mass percentage of greater than or equal to 40%; optionally, it is 40%-60%.

12. The secondary battery according to any one of claims 1-11, characterized in that, The negative electrode active material also includes carbon-based active materials.

13. The secondary battery according to claim 12, characterized in that, The carbon-based active material includes one or more of graphite, hard carbon, soft carbon, and porous carbon.

14. The secondary battery according to any one of claims 1-13, characterized in that, Based on the total mass of the negative electrode active material, the mass percentage α of the carbon-silicon composite material is 10%-100%, and optionally, the mass percentage of the carbon-silicon composite material is 30%-40%.

15. The secondary battery according to any one of claims 1-14, characterized in that, The negative electrode film layer includes a conductive agent, which includes carbon nanotubes with an aspect ratio > 2500, and / or... Based on the total mass of the negative electrode film, the mass percentage of the carbon nanotubes is 0.1% to 0.5%, and can be selected as 0.3% to 0.5%.

16. The secondary battery according to claim 15, characterized in that, The conductive agent also includes at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, graphene, and carbon nanofibers.

17. The secondary battery according to any one of claims 1-16, characterized in that, The negative electrode sheet satisfies: The areal density of the negative electrode film layer on one side of the negative electrode sheet is 4 mg / cm³. 2 -15mg / cm 2 8mg / cm 2 -14mg / cm 2 , and / or The compaction density of the negative electrode film layer on one side of the negative electrode sheet is 1.6 g / cm³. 3 -1.8g / cm 3 .

18. The secondary battery according to any one of claims 1-17, characterized in that, The positive electrode active material includes Li a Ni x Co y M 1-x-y O 2-b M includes at least one of Mn, Al, B, Zr, Sr, Y, Sb, W, Ti, Mg and Nb. Optionally, M includes at least one of Mn, Al, B, Zr, Sr, W, Mg and Nb; 0.2≤a≤1.2, -0.2≤b≤0.2; 0.85≤x≤1, 0≤y≤0.

15. Optionally, 0.92≤x≤0.98, 0<y≤0.

08.

19. The secondary battery according to any one of claims 1-18, characterized in that, The positive electrode plate satisfies: The areal density of the positive electrode film layer on one side of the positive electrode sheet is 18 mg / cm³. 2 -45mg / cm 2 25mg / cm 2 -45mg / cm 2 ; and / or, The compaction density of the positive electrode film layer on one side of the positive electrode sheet is 3.3 g / cm³. 3 -3.6g / cm 3 3.4g / cm³ is an optional value. 3 -3.6g / cm 3 .

20. The secondary battery according to any one of claims 1-19, characterized in that, The secondary battery has a mass energy density of 280Wh / kg-500Wh / kg, optionally 360Wh / kg-500Wh / kg or 400Wh / kg-500Wh / kg; and / or, The capacity C0 of the secondary battery is 35Ah-200Ah, and can be selected as 45Ah-190Ah.

21. An electrical appliance, characterized in that, The secondary battery includes any one of claims 1-20.

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