Secondary battery cell, lithium-ion battery, and electric device

Abstract

The application provides a secondary battery monomer, a lithium ion battery and an electric device. The secondary battery monomer comprises a shell, an electrode assembly, an electrode terminal and a fixing piece. A positive pole sheet comprises a positive pole active material, and the positive pole active material comprises a lithium-containing transition metal phosphate and a lithium-containing transition metal oxide. The mass content m1 of the lithium-containing phosphate satisfies 40wt%≤m1≤70wt% based on the total mass of the positive pole active material. The shell comprises a first wall, and the first wall comprises a first through hole. The electrode terminal comprises a main body part and a step part. At least part of the main body part is arranged in the first through hole, and the step part protrudes from the outer circumferential surface of the main body part. The fixing piece comprises a second through hole for the main body part to pass through. At least part of the fixing piece is located between the first wall and the step part and abuts against the step part. The main body part has a first end surface away from the first wall, and the height H1 between the first end surface and the outer wall of the first wall satisfies 1.5mm≤H1≤3mm.

Description

Technical Field

[0001] This application relates to the field of batteries, and more specifically, to a secondary battery cell, a lithium-ion battery, and an electrical device. Background Technology

[0002] In recent years, secondary batteries, mainly lithium-ion 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, thus achieving great development.

[0003] Improving the energy density of rechargeable battery cells is a key research focus for lithium-ion batteries. Currently, the energy density of lithium-ion batteries is mainly limited by the positive electrode active material, and this is usually achieved by combining different positive electrode active materials. However, while increasing energy density, the use of mixed positive electrode active materials may affect other performance characteristics of the rechargeable battery cell, such as cycle performance and safety performance. Therefore, how to balance the energy density and safety performance of rechargeable battery cells has become an urgent technical problem to be solved. Summary of the Invention

[0004] This application is made in view of the above-mentioned technical problems, and its purpose is to provide a secondary battery cell, a lithium-ion battery and an electrical device, wherein the secondary battery cell can achieve both high energy density and good safety performance.

[0005] In a first aspect, a secondary battery cell is provided, the secondary battery cell comprising: a casing, an electrode assembly, electrode terminals, and a fixing member; the electrode assembly is housed within the casing, the electrode assembly comprising a positive electrode sheet, the positive electrode sheet comprising a positive electrode active material, the positive electrode active material comprising a lithium transition metal phosphate and a lithium transition metal oxide, wherein, based on the total mass of the positive electrode active material, the mass content m1 of the lithium phosphate satisfies: 40wt% ≤ m1 ≤ 70wt%; the casing comprises a first wall, the first wall comprising a first through hole; the electrode terminals comprise a main body and a... The step portion, at least a portion of the main body portion, passes through the first through hole, the step portion protrudes from the outer peripheral surface of the main body portion, and the step portion is located on the side of the first wall facing the outside of the secondary battery cell; the fixing member includes a second through hole through which the main body portion passes; in the thickness direction of the first wall, at least a portion of the fixing member is located between the first wall and the step portion and abuts against the step portion; the electrode terminal has a first end face facing away from the first wall, and the height H1 between the first end face and the outer wall of the first wall satisfies: 1.5mm≤H1≤3mm.

[0006] In the embodiments of this application, the positive electrode active material includes both lithium transition metal phosphate and lithium transition metal oxide. By abutting the electrode terminals with the fixing member, the height of the electrode terminals protruding from the outer shell of the secondary battery cell is controlled within the range of 1.5mm-3mm. Thus, the secondary battery cell can balance safety performance and energy density.

[0007] In one possible implementation, the fastener has a second end face facing the first wall in the thickness direction of the first wall, the first end face extending beyond the second end face.

[0008] In the embodiments of this application, the first end face of the electrode terminal extends beyond the second end face; that is, the end face furthest from the first wall in the thickness direction of the first wall is the first end face. Therefore, by providing a fixing member, the height of the electrode terminal extending beyond the first wall can be controlled within the range of 1.5mm-3mm.

[0009] In one possible implementation, the height H2 between the first end face and the second end face in the thickness direction of the first wall satisfies: 0.5mm ≤ H2 ≤ 1.5mm.

[0010] In the embodiments of this application, by controlling the height between the first end face and the second end face within a suitable range in the thickness direction of the first wall, the safety performance and energy density of the secondary battery cell can be improved while ensuring good connection stability between the first end face and the second end face.

[0011] In one possible implementation, the average particle size D1 of the lithium transition metal oxide particles satisfies: 2μm≤D1≤5μm.

[0012] In the embodiments of this application, by controlling the average particle size of the lithium transition metal oxide particles within a suitable range, it is helpful to improve the compaction density of the positive electrode sheet, thereby improving the energy density of the secondary battery cell.

[0013] In one possible implementation, the lithium-containing transition metal oxide includes: Li 1+d [Ni x Co y Mn z M e ]O 2-f Wherein, M includes at least one of Zr, Al, Ti, Sb, Nb, Te, Mg, B, Ca, V, Ta or Sr, 0.2≥d≥-0.2, 0.95≥x≥0.5, 0.2≥y≥0.05, 0.3>z>0, 0.3>e≥0, 0.5≥f≥0.

[0014] In the embodiments of this application, by selecting lithium-containing transition metal oxides doped with heteroatoms, it is helpful to improve the stability of lithium-containing transition metal oxides at high temperatures, and further improve the safety performance of secondary battery cells.

[0015] In one possible implementation, the mass content m2 of the lithium-containing transition metal oxide, based on the total mass of the positive electrode active material, satisfies: 30wt% ≤ m2 ≤ 60wt%.

[0016] In one possible implementation, the positive electrode sheet satisfies at least one of the following conditions: (1) the compaction density ρ1 of the positive electrode sheet satisfies: 2.5 g / cm³ 3 ≤ρ1≤2.9g / cm 3 (2) The single-sided coating weight CW1 of the positive electrode film layer satisfies: 190 g / m 2 ≤CW1≤230g / m 2 (3) The thickness h1 of the positive current collector satisfies: 10μm≤h1≤13μm.

[0017] In the embodiments of this application, by controlling the compaction density of the positive electrode sheet and the coating weight of the positive electrode film within a suitable range, it is helpful to improve lithium-ion dynamics, thereby reducing the polarization of the secondary battery cell during cycling and helping to improve the safety performance of the secondary battery cell; by controlling the thickness of the positive electrode current collector within a suitable range, it is helpful to reduce the thickness of the positive electrode sheet and help to improve the energy density of the secondary battery cell.

[0018] In one possible implementation, the average particle size D2 of the lithium transition metal phosphate particles satisfies: 0.5 μm ≤ D2 ≤ 1.5 μm.

[0019] In one possible implementation, the lithium-containing transition metal phosphate includes: Li 1+a Mn b A 1-b P 1-c R c O4; wherein -0.2≤a<1, 0.3≤b≤0.9, 0≤c≤0.1, A includes at least one of Zn, Al, Na, K, Mg, Mo, W, Ti, V, Zr, Fe, Ni, Co, Ga, Sn, Sb, Nb and Ge, and R includes at least one of B, Si, N, S, F, Cl and Br.

[0020] In one possible implementation, 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 a negative electrode active material.

[0021] In one possible implementation, the negative electrode sheet satisfies at least one of the following conditions: (4) the compaction density ρ2 of the negative electrode sheet satisfies: 1.3 g / cm³ 3 ≤ρ2≤1.55g / cm 3 (5) The single-sided coating weight CW2 of the negative electrode film layer satisfies: 90 g / m 2 ≤CW2≤110g / m 2 (6) The thickness h2 of the negative electrode current collector satisfies: 4μm≤h2≤6μm.

[0022] In the embodiments of this application, by controlling the compaction density of the negative electrode sheet and the coating weight of the negative electrode film within a suitable range, it is helpful to improve lithium-ion dynamics, thereby reducing the polarization of the secondary battery cell during cycling and helping to improve the safety performance of the secondary battery cell; by controlling the thickness of the negative electrode current collector within a suitable range, it is helpful to reduce the thickness of the negative electrode sheet and help to improve the energy density of the secondary battery cell.

[0023] In one possible implementation, the negative electrode active material includes graphite.

[0024] In one possible implementation, the average volumetric particle size Dv502 of the graphite satisfies: 10μm≤Dv502≤14μm.

[0025] In the embodiments of this application, by controlling the average volume particle size of graphite within a suitable range, it is helpful to improve lithium-ion dynamics, reduce the polarization of secondary battery cells during cycling, and improve the safety performance of secondary battery cells.

[0026] In one possible implementation, the step portion protrudes from the outer peripheral surface of the main body portion by a dimension W1 that satisfies: 0.1mm ≤ W1 ≤ 5mm in the radial direction of the main body portion.

[0027] In the embodiments of this application, by controlling the size of the step portion protruding from the outer peripheral surface of the main body within a suitable range, it is beneficial to increase the contact area between the step portion and the fastener, thereby improving the connection strength between the step portion and the fastener.

[0028] In one possible implementation, the electrode assembly is a stacked electrode assembly.

[0029] In the embodiments of this application, by employing a stacked electrode assembly, the space utilization rate inside the secondary battery cell can be improved, and the energy density of the secondary battery cell can be further increased.

[0030] In one possible implementation, the electrode assembly includes a body and a tab, the tab being connected to the end of the body facing the first wall; the secondary battery cell includes a current collector, the current collector being disposed between the first wall and the body, the current collector including a first connecting portion and a second connecting portion connected to each other, the first connecting portion being connected to the electrode terminal, and the second connecting portion being connected to the tab; wherein, along the thickness direction of the current collector, the thickness S1 of the first connecting portion and the thickness S2 of the second connecting portion satisfy: S1-S2≥0.1mm.

[0031] In the embodiments of this application, by setting the thickness of the first connecting portion of the current collector to be greater than the thickness of the second connecting portion, the thickness of the area where the current collector is connected to the electrode terminal is greater than the thickness of the area where the current collector is connected to the tab. Since the thickness requirement of the area where the current collector is connected to the tab is less than the thickness requirement of the area where the current collector is connected to the electrode terminal, the thickness of the current collector can be effectively optimized while enabling the current collector to connect to the electrode terminal and the tab. This reduces the overall weight of the current collector and saves the space occupied by the current collector, thereby optimizing the weight and internal space utilization of the secondary battery cell and further improving the energy density of the secondary battery cell.

[0032] In one possible implementation, 0.5mm ≤ S1 ≤ 1.2mm; and / or 0.3mm ≤ S2 ≤ 1mm.

[0033] In the embodiments of this application, by controlling the thickness of the first connecting part and the thickness of the second connecting part within a suitable range, it is possible to improve the energy density of the secondary battery cell while satisfying the connection strength between the first connecting part and the electrode terminal, and between the second connecting part and the tab.

[0034] In one possible implementation, the secondary battery cell includes an electrolyte, the ionic conductivity σ of which satisfies: 7mS / cm≤σ≤10mS / cm.

[0035] In the embodiments of this application, selecting an electrolyte with high ionic conductivity helps to improve lithium-ion kinetics during the cycling process of a secondary battery cell, helps to reduce polarization of the secondary battery cell during cycling, and improves the safety performance of the secondary battery cell.

[0036] In one possible implementation, the electrolyte comprises: a solvent comprising linear carbonate; wherein the mass content of the linear carbonate, m3, based on the total mass of the electrolyte, satisfies 40wt% ≤ m3 ≤ 70wt%.

[0037] In the embodiments of this application, by selecting linear carboxylic acid esters as solvents and controlling their mass content in the electrolyte within a suitable range, it is helpful to reduce the viscosity of the electrolyte, thereby helping to improve lithium-ion kinetics.

[0038] In one possible implementation, the electrolyte comprises a lithium salt, which includes LiPF6 and LiFSI; the mass content m4 of the lithium salt, based on the total mass of the electrolyte, satisfies 13wt% ≤ m4 ≤ 18wt%.

[0039] In the embodiments of this application, by selecting LiPF6 and LiFSI as lithium salts, it is helpful to improve the lithium-ion conductivity and high-temperature resistance of the electrolyte, thereby helping to improve the lithium-ion kinetics during the cycling process of the secondary battery cell, reduce the polarization of the secondary battery cell during the cycling process, and improve the safety performance of the secondary battery cell.

[0040] In a second aspect, a secondary battery is provided, the secondary battery comprising a secondary battery cell in any of the implementable embodiments of the first aspect.

[0041] Thirdly, an electrical device is provided, the electrical device comprising a secondary battery cell in any of the implementable embodiments of the first aspect, and / or a secondary battery in the second aspect. Attached Figure Description

[0042] To more clearly illustrate the technical solutions of the embodiments of this application, the drawings used in the embodiments of this application will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on the drawings without creative effort.

[0043] Figure 1 This is a schematic structural diagram of a secondary battery cell.

[0044] Figure 2 for Figure 1 The exploded view of a single secondary battery cell is shown.

[0045] Figure 3 This is a partial exploded view of a single secondary battery cell.

[0046] Figure 4 This is a partial cross-sectional view of a secondary battery cell.

[0047] Figure 5 for Figure 4 A schematic diagram of a local area.

[0048] Figure 6 This is a schematic diagram of an electrode terminal.

[0049] Figure 7 This is a cross-sectional schematic diagram of a stacked electrode assembly.

[0050] Figure 8 This is a cross-sectional schematic diagram of another type of stacked electrode assembly.

[0051] Figure 9 This is a cross-sectional schematic diagram of a wound electrode assembly.

[0052] Figure 10 This is a partial schematic diagram of a secondary battery cell.

[0053] Figure 11 This is a schematic diagram of a type of battery.

[0054] Reference numerals: 10-Electrode assembly, 11-Positive electrode, 12-Negative electrode, 13-Separator, 20-Secondary battery cell, 21-Shell, 22-Electrode terminal, 23-Riveting block, 24-Current collector, 26-Insulator, 27-Sealer, 28-Fixing component, 30-Lithium-ion battery, 101-Body of electrode assembly, 102-Electrode tab, 211-First wall, 212-Shell, 213-End cap, 221-Body of electrode terminal, 222-Step portion, 241-First connecting portion, 242-Second connecting portion, 243-Bending portion, 281-Second through hole, 282-Second end face, 301-First housing portion, 302-Second housing portion, 2111-First through hole, 2121-Opening, 2211-First end face, 2212-First groove, 2221-Third end face. Detailed Implementation

[0055] The following detailed description, with appropriate reference to the accompanying drawings, specifically discloses embodiments of the secondary battery cell, lithium-ion battery, and power application 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 to enable those skilled in the art to fully understand this application and are not intended to limit the subject matter of the claims.

[0056] 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.

[0057] In the description of this application, it should be noted that, unless otherwise stated, "a plurality of" means two or more; the terms "upper," "lower," "left," "right," "inner," "outer," etc., indicating orientation or positional relationships are only for the convenience of describing this application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation on this application. Furthermore, the terms "first," "second," "third," etc., are used for descriptive purposes only and should not be construed as indicating or implying relative importance.

[0058] Unless otherwise specified, in this application, the phrase "A and / or B" means "A, B, or both A and B". More specifically, the condition "A and / 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).

[0059] 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.

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

[0061] Unless otherwise specified, the following terms have the following meanings. Any undefined terms have their technically accepted meanings.

[0062] If mentioned, "lithium-containing transition metal phosphates" refers to a class of salts that include lithium, transition metal elements, and phosphate ions. For example, this can include materials such as lithium iron phosphate and lithium manganese iron phosphate.

[0063] As mentioned, "lithium-containing transition metal oxides" refers to a class of oxides that include lithium and transition metal elements. Structurally, this includes ternary materials with layered structures, such as LiCoO2 and LiNiO2, as well as LiMn2O4 with a spinel structure. Ternary materials refer to lithium transition metal oxides containing three different transition metal elements. It should be understood that ternary materials can also be doped with trace amounts of other transition metal elements; generally, ternary materials doped with other transition metal elements are still considered ternary materials.

[0064] If mentioned, "linear carbonates" refer to a class of substances with a chain structure containing carbonate groups (-OCO-O-). Examples include dimethyl carbonate (DMC), diethyl carbonate (DEC), and ethyl methyl carbonate (EMC).

[0065] The embodiments of this application will be described next.

[0066] In recent years, lithium-ion batteries have seen significant development due to their high energy density and long lifespan, finding widespread application in power tools, electronic products, electric vehicles, aerospace, and other fields. Typically, a lithium-ion battery cell consists of a positive electrode, a negative electrode, an electrolyte, and a separator. During the charging and discharging process, active ions repeatedly insert and extract between the positive and negative electrodes. The electrolyte acts as a conductor of these active ions between the electrodes. The separator, positioned between the positive and negative electrodes, prevents short circuits while allowing active ions to pass through, ensuring the normal electrochemical reactions within the battery cell.

[0067] Improving the energy density of rechargeable battery cells has always been a key research focus in the battery field. The cathode active material is one of the direct factors affecting the energy density of rechargeable battery cells. Lithium-containing transition metal phosphates with good thermal stability and lithium-containing transition metal oxides with high specific capacity are commonly used cathode active materials. However, the low specific capacity of lithium-containing transition metal phosphates is detrimental to improving the energy density of rechargeable battery cells, while lithium-containing transition metal oxides are beneficial for increasing the energy density, but their safety performance is relatively poor. Currently, some solutions combining the two have been developed in the hope of obtaining rechargeable battery cells that balance safety and high capacity. However, this combination is essentially a trade-off between safety and energy density and does not solve the problem of reduced energy density caused by combining the two materials.

[0068] In view of this, embodiments of this application provide a secondary battery cell, a lithium-ion battery, and an electrical device, wherein the secondary battery cell can balance high energy density and good safety performance.

[0069] Next, the secondary battery cell provided in this application will be introduced.

[0070] [Secondary battery cell]

[0071] Firstly, a secondary battery cell is provided, comprising a casing, an electrode assembly, electrode terminals, and a fixing component. The electrode assembly is housed within the casing and includes a positive electrode sheet. The positive electrode sheet includes a positive electrode active material, which comprises a lithium-containing transition metal phosphate and a lithium-containing transition metal oxide. Based on the total mass of the positive electrode active material, the mass content m1 of the lithium phosphate satisfies: 40wt% ≤ m1 ≤ 70wt%; optionally, 45wt% ≤ m1 ≤ 70wt%. The outer casing includes a first wall, which includes a first through hole; the electrode terminal includes a main body and a stepped portion, at least a portion of the main body is disposed through the first through hole, the stepped portion protrudes from the outer peripheral surface of the main body, and the stepped portion is located on the side of the first wall facing the outside of the secondary battery cell; the fixing member includes a second through hole through which the main body passes; in the thickness direction of the first wall, at least a portion of the fixing member is located between the first wall and the stepped portion and abuts against the stepped portion; the main body has a first end face facing away from the first wall, and in the thickness direction of the first wall, the distance H1 between the first end face and the outer wall of the first wall satisfies: 1.5mm≤H1≤3mm.

[0072] Specifically, m1 can be 40wt%, 42wt%, 44wt%, 45wt%, 46wt%, 48wt%, 50wt%, 52wt%, 54wt%, 56wt%, 58wt%, 60wt%, 62wt%, 64wt%, 66wt%, 68wt%, or 70wt%, or a value within the range obtained by any combination of the above two values. H1 can be 1.5mm, 1.6mm, 1.7mm, 1.8mm, 1.9mm, 2.0mm, 2.1mm, 2.2mm, 2.3mm, 2.4mm, 2.5mm, 2.6mm, 2.7mm, 2.8mm, 2.9mm, or 3mm, or a value within the range obtained by any combination of the above two values. A higher mass content of lithium transition metal phosphate in the positive electrode active material results in better thermal stability of the secondary battery cell, which is more conducive to improving the safety performance of the secondary battery cell, but it affects the energy density of the secondary battery cell. The smaller the distance H1 between the first end face and the outer wall of the first wall, the smaller the proportion of space occupied by the portion of the electrode terminal protruding from the outer shell of the secondary battery cell to the overall space of the secondary battery cell, which is more conducive to improving the energy density of the secondary battery cell. Therefore, by controlling the content of lithium transition metal phosphate to 40wt%-70wt% and controlling H1 to the range of 1.5mm-3mm, the secondary battery cell can achieve both safety performance and energy density.

[0073] The above embodiments will now be described in more detail with reference to the accompanying drawings. Figure 1-2 This is a schematic structural diagram of a secondary battery cell according to this application. Figure 1As shown, the secondary battery cell 20 includes a housing 21 and an electrode assembly 10. The electrode assembly 10 is housed within the housing 21. The housing 21 includes a first wall 211, and electrode terminals 22 are disposed on the first wall 211.

[0074] More specifically, the housing 21 may include a housing 212 and an end cap 213. The housing 212 has an internal cavity with an opening 2121, meaning the housing 212 is a hollow structure open at one end. The end cap 213 covers the opening 2121 of the housing 212, forming a sealed connection to create a sealed space for accommodating the electrode assembly 10 and the electrolyte. Optionally, the first wall 211 for mounting the electrode terminal 22 may be the end cap 213 or one of the multiple walls of the housing 212. For example, in... Figure 1 and Figure 2 In this embodiment, the first wall 211 is the end cap 213 of the outer shell 21. Of course, in other embodiments, the first wall 211 may also be the bottom wall of the shell 212 that is opposite to the end cap 213 in the thickness direction X of the end cap 213, or the side wall that is adjacent to and abuts against the end cap 213.

[0075] The housing 212 can have various shapes, such as a cylinder or a cuboid. The shape of the housing 212 can be determined according to the specific shape of the electrode assembly 10. For example, if the electrode assembly 10 is a cylindrical structure, then the housing 212 can be a cylindrical structure; if the electrode assembly 10 is a cuboid structure, then the housing 212 can be a cuboid structure. Of course, the end cap 213 can also have various structures, such as a plate-like structure or a hollow structure open at one end. For example, in… Figure 1 and Figure 2 In this case, the housing 212 has a cuboid structure. It should be understood that the housing 21 is not limited to the aforementioned structure. The housing 21 can also have other structures. For example, the housing 21 includes the housing 212 and two end caps 213. The housing 212 is a hollow structure with openings 2121 on both sides opposite to each other. One end cap 213 is fitted onto one opening 2121 of the housing 212 to form a sealed connection, thereby forming a sealed space for accommodating the electrode assembly 10 and the electrolyte.

[0076] The electrode assembly 10 housed within the housing 21 can be one or more. For example, in... Figure 2 In this embodiment, the outer casing 21 of the secondary battery cell 20 is provided with two electrode assemblies 10. The two electrode assemblies 10 are stacked along their thickness direction. That is, the two electrode assemblies 10 are stacked along the thickness direction of the secondary battery cell 20. Of course, in other embodiments, the electrode assemblies 10 housed in the outer casing 21 can be one, three, four, five, six, seven or eight, etc.

[0077] Electrode terminal 22 is a component used to input or output electrical energy to the secondary battery cell 20. For example, the electrode terminal 22 can be made of various materials, such as copper, iron, aluminum, steel, or aluminum alloy. The end of electrode terminal 22 facing the electrode assembly 10 is connected to the current collector 24, and the end of electrode terminal 22 away from the electrode assembly 10 is connected to the current collector to realize the input or output of electrical energy to the secondary battery cell 20. Figure 1-2 In this design, the secondary battery cell 20 includes two electrode terminals 22, and correspondingly, each electrode assembly 10 has two tabs 102 with opposite polarities. The two electrode terminals 22 are electrically connected to the two tabs 102 of the electrode assembly 10, respectively, to realize the input or output of the positive and negative electrodes of the secondary battery cell 20.

[0078] Figure 3 This is an exploded view of a partial structure of a secondary battery cell 20 according to this application. Figure 4 This is a cross-sectional view of a partial structure of a secondary battery cell 20 according to this application. Figure 5 for Figure 4 A schematic diagram of a local area. Figure 6 This is a schematic structural diagram of an electrode terminal 22.

[0079] refer to Figure 3-5 The first wall 211 includes a first through hole 2111. The electrode terminal 22 includes a main body 221 and a stepped portion 222. The stepped portion 222 protrudes from the outer peripheral surface of the main body 221 and is located on the side of the first wall 211 facing the outside of the secondary battery cell 20. The secondary battery cell 20 includes a fixing member 28, which includes a second through hole 281 through which the main body 221 passes. In the thickness direction of the first wall 211, at least a portion of the fixing member 28 is located between the first wall 211 and the stepped portion 222 and abuts against the stepped portion 222. The main body 221 has a first end face 2211 facing the outside of the secondary battery cell 20, as shown below. Figure 5 As shown, the height between the first end face 2211 and the outer wall of the first wall 211 is H1.

[0080] Generally speaking, such as Figure 6As shown, the electrode terminals 22 of the secondary battery cell 20 are riveted to the wall of the housing 21 by a riveting block 23 that encloses the electrode terminals 22, for example, riveted to the first wall 211. In the thickness direction of the first wall 211, the surface of the riveting block 23 away from the first wall 211 extends beyond or is flush with the outer end face of the electrode terminals 22. This design is to provide additional protection and support for the electrode terminals 22, reducing the risk of loosening. Simultaneously, the electrical energy of the secondary battery cell 20 can be transferred to the interior of the secondary battery cell 20 through the riveting block 23. An insulating element can be provided between the riveting block 23 and the first wall 211 to isolate them. Due to the riveting process requirements, the electrode terminals 22 need to have sufficient contact area with the riveting block 23 to ensure structural stability; therefore, the height of the electrode terminals 22 and the riveting block 23 in this design is typically relatively high.

[0081] The positive electrode active material includes both lithium-containing transition metal oxides and lithium-containing transition metal phosphates. By combining lithium-containing transition metal oxides with high specific capacity with lithium-containing transition metal phosphates with good thermal stability, the safety performance of the secondary battery cell 20 can be effectively improved, but this is accompanied by a loss of energy density.

[0082] In this embodiment, while controlling the content of lithium transition metal phosphate to be between 40wt% and 70wt%, the electrode terminal 22 is fixed and supported by the fastener 28 abutting against it. This not only eliminates the need for the riveting block 23 structure, but also controls the height of the electrode terminal 22 protruding from the first wall 211 to within the range of 1.5mm-3mm. This reduces the proportion of space occupied by the portion of the electrode terminal 22 protruding from the outer shell 21 of the secondary battery cell 20 to the total space of the secondary battery cell 20, compensating for the energy density loss caused by the mixing of lithium transition metal oxides and lithium transition metal phosphates. Therefore, the safety performance of the secondary battery cell 20 is improved while its energy density is increased.

[0083] In one embodiment, the fastener 28 has a second end face 282 facing away from the first wall 211, and the first end face 2211 extends beyond the second end face 282.

[0084] In such Figure 3-5 In the example shown, the first wall 211 is the end cap 213. The end cap 213 has a first through hole 2111 that extends through both sides of the end cap 213 along its thickness direction. Electrode terminals 22 pass through the first through hole 2111 to mount the electrode terminals 22 onto the end cap 213. Both ends of the electrode terminals 22 extend out of the first through hole 2111. The electrode terminals 22 are insulated from the end cap 213; that is, no electrical connection is formed between the electrode terminals 22 and the end cap 213.

[0085] Specifically, the first end face 2211 extends beyond the second end face 282, which means that, outside the secondary battery cell 20, in the thickness direction of the first wall 211, the second end face 282 is located between the first end face 2211 and the outer surface of the first wall 211. In other words, the face farthest from the outer surface of the first wall 211 is the first end face 2211 of the electrode terminal 22.

[0086] The outer peripheral surface of the main body portion 221 may refer to the outer peripheral surface of a cylinder or the peripheral surface of a prism connecting the top and bottom surfaces of the prism. Taking the main body portion 221 as a quadrangular prism as an example, the main body portion 221 includes a top surface, a bottom surface, and four side surfaces. The four side surfaces are sequentially connected and surround the top surface. The two ends of the four side surfaces in the direction from the top surface to the bottom surface are respectively connected to the top surface and the bottom surface. The above four side surfaces refer to the outer peripheral surface of the main body portion 221. In some embodiments, a first groove 2212 is provided on the first end face 2211, and the side surface of the first groove 2212 can also be referred to as the outer peripheral surface of the main body portion 221. In this embodiment, the main body portion 221 is in a shape similar to a "convex" character. In some embodiments, the step portion 222 has a third end face 2221 facing away from the first wall 211.

[0087] The outer contour of the fixing member 28 may include, but is not limited to, a circle, an ellipse, a polygon, a semi - circle, etc. The fixing member 28 is made of a metal material, for example, made of aluminum, copper, iron, steel, alloy or composite metal. The step portion 222 may be continuously distributed along the circumferential direction of the main body portion 221, that is, in a ring shape. It may also be provided in segments along the circumferential direction of the main body portion 221, that is, divided into multiple parts, and at least one of the parts abuts against the fixing member 28. The first through - hole 2111 and the second through - hole 281 may be a through - hole or a stepped through-hole. In the embodiment where the first through - hole 2111 and the second through - hole 281 are stepped through - holes, the cross - section of the stepped through - hole may include at least one straight line segment and / or at least one oblique line segment and / or at least one arc segment.

[0088] In this embodiment, by making the first end face 2211 of the electrode terminal 22 extend beyond the second end face 282 of the fixing member 28, in the thickness direction of the first wall 211, the surface with the maximum height by which the secondary battery cell 20 extends beyond the outer surface of the first wall 211 is the first end face 2211. While eliminating the use of a riveting block, the height by which the secondary battery cell 20 extends beyond the first wall 211, that is, the height by which the electrode terminal 22 protrudes from the first wall, is further reduced, and the proportion of the structure outside the outer shell 21 of the secondary battery cell 20 in the total space of the secondary battery cell 20 is further reduced, thereby improving the energy density of the secondary battery cell 20. In an example such as Figure 3-5 the secondary battery cell 20 may further include an insulating member 26 to insulate and isolate the end cap 213 and the electrode terminal 22. The secondary battery cell 20 may further include a sealing member 27 to seal the gap between the electrode terminal 22 and the hole wall surface of the first through - hole 2111.

[0089] Please continue reading Figure 5 In one embodiment, in the thickness direction of the first wall 211, the height H2 between the first end face 2211 and the second end face 282 satisfies: 0.5mm≤H2≤1.5mm.

[0090] Specifically, H2 can be 0.5mm, 0.6mm, 0.7mm, 0.8mm, 0.9mm, 1mm, 1.1mm, 1.2mm, 1.3mm, 1.4mm, or 1.5mm, or a value within the range obtained by any combination of the above two values. By controlling H2 within a suitable range, the safety performance and energy density of the secondary battery cell 20 can be improved, while ensuring good connection stability between the electrode terminal 22 and the fixing member 28.

[0091] In one embodiment, the step portion 222 protrudes from the outer peripheral surface of the main body portion 221 by a dimension W1 that satisfies: 0.1mm≤W1≤5mm.

[0092] Specifically, W1 can be 0.1mm, 0.2mm, 0.4mm, 0.6mm, 0.8mm, 1mm, 1.2mm, 1.4mm, 1.6mm, 1.8mm, 2mm, 2.2mm, 2.4mm, 2.6mm, 2.8mm, 3mm, 3.2mm, 3.4mm, 3.6mm, 3.8mm, 4mm, 4.2mm, 4.4mm, 4.6mm, 4.8mm, 5mm, or a value within the range obtained by any combination of the above two values. By controlling the size of the step portion 222 protruding from the outer peripheral surface of the main body portion 221 within a suitable range, it is beneficial to increase the contact area between the step portion 222 and the fastener 28, thereby improving the connection strength between the step portion 222 and the fastener 28.

[0093] Figure 7 and Figure 8 This is a cross-sectional schematic diagram of a stacked electrode assembly. Figure 9 This is a cross-sectional schematic diagram of a wound electrode assembly. For ease of explanation, the tabs included in each electrode are not shown here. Figure 7-9 As shown, the electrode assembly 10 specifically includes a positive electrode 11 and a negative electrode 12, as well as a separator 13 disposed between the positive electrode 11 and the negative electrode 12.

[0094] In one embodiment, such as Figure 7 As shown, the electrode assembly 10 is a stacked electrode assembly. The electrode assembly 10 includes multiple positive electrode plates 11 and multiple negative electrode plates 12; the multiple positive electrode plates 11 and multiple negative electrode plates 12 are alternately stacked along the direction indicated by the arrows in the figure. In another embodiment, as... Figure 8 As shown, the electrode assembly 10 includes multiple positive electrode plates 11 and negative electrode plates 12. Each negative electrode plate 12 may include at least one bent section and multiple stacked sections. Each bent section connects two stacked sections. The multiple positive electrode plates 11 and the multiple stacked sections of the negative electrode plates 12 are alternately stacked in the direction indicated by the arrows in the figure to form another type of stacked electrode assembly 10. Alternatively, the electrode assembly 10 includes multiple negative electrode plates 12 and positive electrode plates 11. Each positive electrode plate 11 may include at least one bent section and multiple stacked sections. Each bent section connects two stacked sections. The multiple negative electrode plates 12 and the multiple stacked sections of the positive electrode plates 11 are alternately stacked in the direction indicated by the arrows in the figure to form another type of stacked electrode assembly 10.

[0095] In one embodiment, such as Figure 9 As shown, the electrode assembly 10 can also be a wound electrode assembly. The positive electrode 11, the separator 13, and the negative electrode 12 of the electrode assembly 10 are wound to form the electrode assembly 10.

[0096] According to this application, the electrode assembly 10 is preferably a stacked electrode assembly. Compared with the wound electrode assembly, the stacked electrode assembly has a higher space utilization rate inside the casing 21 of the secondary battery cell 20. With the same casing 21, the stacked electrode assembly can accommodate more active material inside the casing, thereby further improving the energy density of the secondary battery cell 20.

[0097] Figure 10 This is a partial schematic diagram of a secondary battery cell 20 in the region of electrode terminal 22 according to this application.

[0098] refer to Figure 1-2 4.10. In one embodiment, the electrode assembly 10 includes a body 101 and a tab 102, the tab 102 being connected to the end of the body 101 facing the first wall 211. The secondary battery cell 20 includes a current collector 24, which is disposed between the first wall 211 and the body 101. The current collector 24 includes a first connecting portion 241 and a second connecting portion 242 connected to each other. The first connecting portion 241 is connected to the electrode terminal 22, and the second connecting portion 242 is connected to the tab 102. Along the thickness direction of the first wall 211, the thickness S1 of the first connecting portion 241 and the thickness S2 of the second connecting portion 242 satisfy: S1-S2≥0.1mm.

[0099] Specifically, the main body 101 of the electrode assembly 10 is the primary region where the electrochemical reaction occurs within the secondary battery cell 20. The main body 101 is formed by the region of the positive electrode 11 coated with positive active material, the separator, and the region of the negative electrode 12 coated with negative active material, which are wound or stacked together. The tabs 102 are used to output or input the positive or negative electrode of the electrode assembly 10, and are used to connect to the electrode terminals 22 to achieve electrical connection between the electrode assembly 10 and the electrode terminals 22. It should be noted that the tabs 102 of the electrode assembly 10 are either formed by stacking and connecting regions of the positive electrode 11 that are not coated with positive active material, or by stacking and connecting regions of the negative electrode 12 that are not coated with negative active material. If the tab 102 is used as the positive electrode of the output electrode assembly 10, then the tab 102 is a component formed by stacking and connecting the areas of the positive electrode sheet 11 that are not coated with positive active material; if the tab 102 is used as the negative electrode of the output electrode assembly 10, then the tab 102 is a component formed by stacking and connecting the areas of the negative electrode sheet 12 that are not coated with negative active material. For example, the tab 102 is connected to one end of the body 101 facing the end cap 213 in the thickness direction X.

[0100] The current collector 24 serves to connect the electrode terminal 22 and the tab 102, thereby achieving an electrical connection between the electrode assembly 10 and the electrode terminal 22. For example, the current collector 24 can be made of various materials, such as copper, iron, aluminum, steel, or aluminum alloy. The connection structure between the current collector 24 and the electrode terminal 22 can be various, such as welding, abutment, or bonding. Similarly, the connection structure between the current collector 24 and the tab 102 can also be various, such as welding or abutment. There are two electrode terminals 22 and two current collectors 24, arranged at intervals along the first direction Z. Each electrode terminal 22 is connected to the electrode assembly 10 through one current collector 24 to output the positive and negative terminals of the secondary battery cell 20. Figure 10 As shown, the current collection member 24 may also include a bending portion 243, and the first connecting portion 241 and the second connecting portion 242 are connected by the bending portion 243.

[0101] In this embodiment, by setting the thickness S1 of the first connecting portion 241 of the current collector 24 to be greater than the thickness S2 of the second connecting portion 242, the thickness of the area where the current collector 24 is connected to the electrode terminal 22 is greater than the thickness of the area where the current collector 24 is connected to the tab 102. Since the thickness requirement of the area where the current collector 24 is connected to the tab 102 is less than the thickness requirement of the area where the current collector 24 is connected to the electrode terminal 22, the thickness of the current collector 24 can be effectively optimized while enabling the current collector 24 to connect the electrode terminal 22 and the tab 102, thereby reducing the overall weight of the current collector 24, saving the space occupied by the current collector 24, and thus optimizing the weight and internal space utilization of the secondary battery cell 20. Furthermore, by setting the thickness S1 of the first connecting portion 241 to be greater than or equal to 0.1 mm than the thickness S2 of the second connecting portion 242, the thickness of the current collector 24 in the area connected to the tab 102 can be further reduced. This allows for further optimization of the thickness of the current collector 24, thereby reducing the overall weight of the current collector 24 and saving the space occupied by the current collector 24. This is beneficial for further reducing the weight of the secondary battery cell 20 and improving the internal space utilization of the secondary battery cell 20, thereby increasing the energy density of the secondary battery cell 20.

[0102] In one embodiment, the thickness S1 of the first connecting portion 241 satisfies: 0.5mm≤S1≤1.2mm; and / or the thickness S2 of the second connecting portion 242 satisfies: 0.3mm≤S2≤1mm.

[0103] Specifically, S1 can be 0.5mm, 0.55mm, 0.6mm, 0.65mm, 0.7mm, 0.75mm, 0.8mm, 0.9mm, 1mm, 1.1mm, 1.15mm, or 1.2mm, or a value within the range obtained by any combination of the above two values. S2 can be 0.3mm, 0.35mm, 0.4mm, 0.45mm, 0.5mm, 0.55mm, 0.6mm, 0.7mm, 0.8mm, 0.9mm, 0.95mm, or 1mm, or a value within the range obtained by any combination of the above two values.

[0104] In this embodiment, by setting the thickness of the first connecting portion 241 and the thickness of the second connecting portion 242 within a suitable range, the structural strength of the first connecting portion 241 and the second connecting portion 242 can be improved. This ensures that the first connecting portion 241 and the second connecting portion 242 have sufficient thickness to connect with the electrode terminal 22 and the tab 102, which is beneficial to improving the connection stability and reliability between the first connecting portion 241 and the second connecting portion 242 and the electrode terminal 22 and the tab 102, and reducing the phenomenon of insufficient overcurrent between the current collector 24 and the electrode terminal 22, and between the current collector 24 and the tab 102. On the other hand, it can reduce the connection difficulty between the first connecting portion 241 and the electrode terminal 22, and between the second connecting portion 242 and the tab 102, and can reduce the space occupied by the current collector 24 in the housing 21, which is beneficial to improving the energy density of the secondary battery cell 20.

[0105] In some other implementations, the current collector 24 can be omitted, and the tab 102 can be directly connected to the electrode terminal 22.

[0106] In one embodiment, the average particle size D1 of the lithium transition metal oxide particles satisfies: 2μm≤D1≤5μm.

[0107] Specifically, D1 can be 2μm, 2.2μm, 2.4μm, 2.6μm, 2.8μm, 3μm, 3.2μm, 3.4μm, 3.6μm, 3.8μm, 4μm, 4.2μm, 4.4μm, 4.6μm, 4.8μm, 5μm, or a value within the range obtained by any combination of the above two values.

[0108] According to this application, the smaller the average particle size of lithium transition metal oxide particles, the better their structural stability, which is more beneficial to the safety performance of the secondary battery cell 20. However, if the average particle size of the lithium transition metal oxide particles is too small, side reactions with the electrolyte may increase, which is detrimental to the safety performance of the secondary battery cell 20. Therefore, this embodiment, by controlling the average particle size of the lithium transition metal oxide particles within a suitable range, can further improve the safety performance of the secondary battery cell 20.

[0109] In one embodiment, the lithium-containing transition metal oxide includes: Li 1+d [Ni x Co y Mn z M e ]O 2-fWherein, M includes at least one of Zr, Al, Ti, Sb, Nb, Te, Mg, B, Ca, V, Ta or Sr, 0.2≥d≥-0.2, 0.95≥x≥0.5, 0.2≥y≥0.05, 0.3>z>0, 0.3>e≥0, 0.5≥f≥0.

[0110] Specifically, lithium-containing transition metal oxides can be doped with some M element. Doping with M element helps to improve the structural stability of lithium-containing transition metal oxides, thereby helping to improve the safety performance of secondary battery cell 20.

[0111] In one embodiment, the mass content m2 of lithium transition metal oxide, based on the total mass of the positive electrode active material, satisfies: 30wt% ≤ m2 ≤ 60wt%.

[0112] Specifically, m2 can be 30wt%, 32wt%, 34wt%, 36wt%, 38wt%, 40wt%, 42wt%, 44wt%, 46wt%, 48wt%, 50wt%, 52wt%, 54wt%, 56wt%, 58wt%, 60wt%, or a value within the range obtained by combining any two of the above values. m1 + m2 = 100wt%.

[0113] In one embodiment, the average particle size D2 of the lithium transition metal phosphate particles satisfies: 0.5 μm ≤ D2 ≤ 1.5 μm.

[0114] Specifically, D2 can be 0.5μm, 0.6μm, 0.7μm, 0.8μm, 0.9μm, 1μm, 1.1μm, 1.2μm, 1.3μm, 1.4μm, 1.5μm, or a value within the range obtained by any combination of the above two values.

[0115] According to this application, when the average particle size of lithium transition metal oxide particles is in the range of 0.5μm-1.5μm, by combining lithium transition metal phosphate with a particle size of 2μm-5μm, the safety performance of the secondary battery cell 20 can be improved while the compaction density of the positive electrode sheet can be increased, thereby further improving the energy density of the secondary battery cell 20.

[0116] In one embodiment, the lithium-containing transition metal phosphate includes: Li 1+a Mn b A 1-b P 1-c R cO4; wherein -0.2≤a<1, 0.3≤b≤0.9, 0≤c≤0.1, A includes at least one of Zn, Al, Na, K, Mg, Mo, W, Ti, V, Zr, Fe, Ni, Co, Ga, Sn, Sb, Nb and Ge, and R includes at least one of B, Si, N, S, F, Cl and Br.

[0117] In one embodiment, the positive electrode 11 satisfies at least one of the following conditions: (1) the compaction density ρ1 of the positive electrode 11 satisfies: 2.5 g / cm³ 3 ≤ρ1≤2.9g / cm 3 (2) The single-sided coating weight CW1 of the positive electrode film layer satisfies: 190 g / m 2 ≤CW1≤230g / m 2 (3) The thickness h1 of the positive current collector satisfies: 10μm≤h1≤13μm.

[0118] Specifically, ρ1 can be 2.5 g / m 2 2.6g / cm 3 2.7g / cm 3 2.8g / cm 3 2.9g / cm 3 Or, its value is within the range obtained by combining any two of the above values. CW1 can be 190g / m 2 195g / m 2 200g / m 2 205g / m 2 210g / m 2 215g / m 2 220g / m 2 225g / m 2 230g / m 2 h1 can be 10μm, 10.2μm, 10.4μm, 10.6μm, 10.8μm, 11μm, 11.2μm, 11.4μm, 11.6μm, 11.8μm, 12μm, 12.2μm, 12.4μm, 12.6μm, 12.8μm, or 13μm, or its value can be within the range obtained by any two combinations of the above values.

[0119] According to this application, the coating weight of the film layer on the electrode and the compaction density of the electrode have a certain impact on the lithium-ion kinetics during the cycling process of the secondary battery cell 20. The greater the coating weight of the film layer and the greater the compaction density of the electrode, the worse the lithium-ion kinetics. Insufficient lithium-ion kinetics may lead to polarization in the secondary battery cell 20, resulting in lithium plating and affecting the safety performance of the secondary battery cell 20. However, if the coating weight of the film layer is too small or the compaction density of the electrode is too small, it is also detrimental to the energy density of the secondary battery cell 20. The aforementioned electrode can be a positive electrode or a negative electrode. The aforementioned film layer can be a positive electrode film or a negative electrode film.

[0120] According to this application, a thinner current collector is more conducive to reducing the thickness of the electrode, thereby increasing the energy density of the secondary battery cell 20. However, an excessively thin current collector is detrimental to the mechanical strength of the electrode and may break during the processing or use of the secondary battery cell 20. The aforementioned current collector can be either a positive electrode current collector or a negative electrode current collector.

[0121] Therefore, by controlling the coating weight of the positive electrode film, the compaction density of the positive electrode sheet 11, and the thickness of the positive electrode current collector within a suitable range, this embodiment enables the secondary battery cell 20 to achieve both high energy density and good safety performance.

[0122] In one embodiment, the negative electrode 12 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 a negative electrode active material.

[0123] In one embodiment, the negative electrode 12 satisfies at least one of the following conditions: (4) the compaction density ρ2 of the negative electrode 12 satisfies: 1.3 g / cm³ 3 ≤ρ2≤1.55g / cm 3 (5) The single-sided coating weight CW2 of the negative electrode film layer satisfies: 90 g / m 2 ≤CW2≤110g / m 2 (6) The thickness h2 of the negative electrode current collector satisfies: 4μm≤h2≤6μm.

[0124] Specifically, ρ2 can be 1.3 g / cm³. 3 1.32g / cm 3 1.34 g / cm 3 1.35g / cm 3 1.36 g / cm 3 1.38g / cm 3 1.4g / cm 3 1.42g / cm 3 1.44 g / cm 3 1.46 g / cm 31.48g / cm 3 1.5g / cm 3 Or, its value is within the range obtained by combining any two of the above values. CW2 can be 90g / m 2 92g / m 2 94g / m 2 96g / m 2 98g / m 2 100g / m 2 102g / m 2 104g / m 2 106g / m 2 108g / m 2 110g / m 2 h2 can be 4μm, 4.2μm, 4.4μm, 4.6μm, 4.8μm, 5μm, 5.2μm, 5.4μm, 5.6μm, 5.8μm, or 6μm, or its value can be within the range obtained by any combination of the two values ​​mentioned above.

[0125] Similar to the positive electrode 11, in this embodiment, by controlling the coating weight of the negative electrode film, the compaction density of the negative electrode 12, and the thickness of the negative electrode current collector within a suitable range, the secondary battery cell 20 can achieve both high energy density and good safety performance.

[0126] In one embodiment, the negative electrode active material comprises graphite.

[0127] In one embodiment, the average volumetric particle size Dv50 of graphite satisfies: 10μm≤Dv50≤14μm.

[0128] Specifically, Dv50 can be 10μm, 10.2μm, 10.4μm, 10.6μm, 10.8μm, 11μm, 11.2μm, 11.4μm, 11.6μm, 11.8μm, 12μm, 12.2μm, 12.4μm, 12.6μm, 12.8μm, 13μm, 13.2μm, 13.4μm, 13.6μm, 13.8μm, 14μm, or a value within the range obtained by any combination of the above two values. The average volumetric particle size of graphite affects the capacity and lithium-ion kinetics of the secondary battery cell 20. The smaller the average volumetric particle size of graphite, the larger the specific surface area, which can provide more active sites in the electrochemical reaction, thereby facilitating the extraction and insertion of lithium ions and improving the capacity and lithium-ion kinetics of the secondary battery cell 20. If the average volumetric particle size of graphite is too small, it may result in insufficient contact area between particles, increasing the internal resistance of the battery cell and thus affecting the cycle performance of the secondary battery cell 20. Therefore, this embodiment helps to improve the capacity and cycle performance of the secondary battery cell 20 by controlling the average volumetric particle size of graphite within a suitable range.

[0129] In one embodiment, the secondary battery cell 20 includes an electrolyte, and the ionic conductivity σ of the electrolyte satisfies: 7mS / cm≤σ≤10mS / cm.

[0130] Specifically, σ can be 7 mS / cm, 7.5 mS / cm, 8 mS / cm, 8.5 mS / cm, 9 mS / cm, 9.5 mS / cm, 10 mS / cm, or a value within the range obtained by any combination of the above two values. In this embodiment, selecting an electrolyte with high ionic conductivity helps improve lithium-ion kinetics during the cycling process of the secondary battery cell 20, helps reduce the probability of polarization in the secondary battery cell 20, and improves the safety performance of the secondary battery cell 20.

[0131] In one embodiment, the electrolyte comprises: a solvent, the solvent comprising linear carbonate; and the total mass of the electrolyte, wherein the mass content m2 of the linear carbonate satisfies 40wt% ≤ m3 ≤ 70wt%.

[0132] Specifically, m3 can be 40wt%, 45wt%, 50wt%, 55wt%, 60wt%, 65wt%, 70wt%, or a value within the range obtained by any combination of the above two values. In this embodiment, by selecting a linear carboxylic acid ester as the solvent and controlling its mass content in the electrolyte within a suitable range, it is helpful to reduce the viscosity of the electrolyte, thereby helping to improve lithium-ion kinetics.

[0133] In one embodiment, the electrolyte comprises a lithium salt, including LiPF6 and LiFSI; the mass content of the lithium salt, m4, based on the total mass of the electrolyte, satisfies 13wt% ≤ m4 ≤ 18wt%.

[0134] Specifically, m4 can be 13wt%, 14wt%, 15wt%, 16wt%, 17wt%, 18wt%, or a value within the range obtained by any combination of the above two values.

[0135] In this embodiment, by selecting LiPF6 and LiFSI as lithium salts and controlling the mass content of lithium salts within a suitable range, the electrolyte can have a high ionic conductivity and a suitable viscosity, which helps to improve the lithium-ion conductivity of the electrolyte, thereby helping to improve the lithium-ion kinetics during the cycle of the secondary battery cell 20 and improving the safety performance of the secondary battery cell 20.

[0136] In one embodiment, the molar content n of LiPF6, based on the total amount of the lithium salt, satisfies: 50% ≤ n ≤ 70%.

[0137] Specifically, the concentration can be 50%, 55%, 60%, 65%, 70%, or any value within the range obtained by combining any two of the above values. Excessive LiFSI concentration may corrode the aluminum foil. In this embodiment, by controlling the molar content of LiPF6 in the lithium salt to a higher range, corrosion of the aluminum foil can be reduced, improving the safety performance of the secondary battery cell 20.

[0138] Next, taking a lithium-ion battery as a specific example, the positive electrode 11, negative electrode 12, separator 13, and electrolyte in the secondary battery cell 20 will be described in detail. It should be understood that the lithium-ion battery is only an example, and the solution provided in this application can also be applied to other types of secondary batteries, such as sodium-ion batteries, magnesium-ion batteries, and lithium-sulfur batteries.

[0139] [Negative electrode plate]

[0140] The negative electrode 12 typically 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 includes a negative electrode active material.

[0141] As an example, the negative electrode current collector has two surfaces opposite each other in its own thickness direction, and the negative electrode film layer is disposed on either or both of the two opposite surfaces of the negative electrode current collector.

[0142] In one embodiment, 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 polymeric material substrate and a metal layer formed on at least one surface of the polymeric 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 polymeric material substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0143] In one embodiment, the negative electrode active material may be a negative electrode active material known in the art for use in batteries. As an example, the negative electrode active material may include at least one of the following materials: artificial graphite, natural graphite, soft carbon, hard carbon, silicon-based materials, tin-based materials, and lithium titanate, etc. Silicon-based materials may be selected from at least one of elemental silicon, silicon oxide compounds, silicon-carbon composites, silicon-nitrogen composites, and silicon alloys. Tin-based materials may be selected from at least one of elemental tin, tin oxide compounds, and tin alloys. However, this application is not limited to these materials, and other conventional materials that can be used as negative electrode active materials for batteries may also be used. These negative electrode active materials may be used alone or in combination of two or more.

[0144] In one embodiment, the negative electrode film layer further includes an adhesive. The adhesive 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).

[0145] In one embodiment, the negative electrode film layer further includes 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.

[0146] In one embodiment, the negative electrode film layer also includes other additives, such as thickeners (e.g., sodium carboxymethyl cellulose (CMC-Na)).

[0147] In one embodiment, the negative electrode 12 can be prepared by forming a negative electrode slurry using the components described above. For example, the negative electrode active material, conductive agent, binder, and any other components are dispersed in a solvent (e.g., N-methylpyrrolidone) to form a negative electrode slurry. The negative electrode slurry is then coated onto a negative electrode current collector, and after drying, cold pressing, and other processes, the negative electrode 12 is obtained.

[0148] [Positive electrode plate]

[0149] The positive electrode 11 includes a positive current collector and a positive electrode film layer disposed on at least one surface of the positive current collector, the positive electrode film layer including a positive electrode active material.

[0150] 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.

[0151] In one embodiment, 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.).

[0152] In another embodiment, 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 / 3 Co 1 / 3 Mn 1 / 3 O2 (also known as NCM333), LiNi 0.5 Co 0.2 Mn 0.3 O2 (also known as NCM523), LiNi 0.5 Co 0.25 Mn 0.25 O2 (also known as NCM211), LiNi 0.6 Co 0.2 Mn 0.2 O2 (also known as NCM622), LiNi 0.8 Co 0.1 Mn 0.1 O2 (also known as NCM811), lithium nickel cobalt aluminum oxide (such as LiNi) 0.85 Co 0.15 Al 0.05At least one of O2 and its modified compounds. Examples of lithium-containing transition metal phosphates with an olivine structure include, but are not limited to, lithium iron phosphate (such as LiFePO4 (also referred to as LFP)), lithium iron phosphate and carbon composites, lithium manganese phosphate (such as LiMnPO4), lithium manganese phosphate and carbon composites, lithium manganese iron phosphate, and lithium manganese iron phosphate and carbon composites. During the charging and discharging process, Li undergoes insertion / extraction and consumption, resulting in different molar contents of Li in the positive electrode active material when the battery is discharged to different states. In the examples of positive electrode active materials in this application, the molar content of Li is the initial state of the material, i.e., the state before feeding. After charge-discharge cycles, the molar content of Li changes when the positive electrode active material is applied to the battery system. In the examples of positive electrode active materials in this application, the molar content of O is only an ideal value; lattice oxygen release causes changes in the molar content of O, and the actual molar content of O will fluctuate.

[0153] In one embodiment, the positive electrode active material includes: LiNi 0.90 Co 0.06 Mn 0.04 O2, LiNi 0.7 Co 0.1 Mn 0.2 O2, LiNi 0.7 Co 0.2 Mn 0.1 O2 or LiNi 0.8 Co 0.1 Mn 0.1 At least one of O2.

[0154] In one embodiment, the positive electrode film layer further includes 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.

[0155] In one embodiment, the positive electrode film layer further includes a conductive agent. As an example, the conductive agent may also include at least one selected from superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, graphene, and carbon nanofibers.

[0156] In one embodiment, the positive electrode 11 can be prepared by forming a positive electrode slurry from the components described above. For example, the positive electrode active material, conductive agent, binder, and any other components are dispersed in a solvent (e.g., N-methylpyrrolidone) to form a positive electrode slurry. The positive electrode slurry is then coated onto a positive electrode current collector, and after drying, cold pressing, and other processes, the positive electrode 11 is obtained.

[0157] Electrolyte

[0158] The electrolyte acts as a conductor of ions between the positive electrode 11 and the negative electrode 12. This application does not impose specific limitations on the type of electrolyte; it can be selected according to requirements. For example, the electrolyte can be liquid, gel-like, or entirely solid.

[0159] In some embodiments, the electrolyte is an electrolyte solution. The electrolyte solution comprises an electrolyte salt and a solvent. Some electrolyte solutions have already been mentioned above.

[0160] In addition to the aforementioned schemes, in some embodiments, the electrolyte salt may also 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.

[0161] In some embodiments, the solvent may also 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.

[0162] 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.

[0163] [Isolation membrane]

[0164] This application does not impose any particular restrictions on the type of separator 13. For example, any well-known porous separator with good chemical and mechanical stability can be selected.

[0165] In some embodiments, the separator 13 includes a porous substrate, the material of which may be selected from at least one of glass fiber, nonwoven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The porous substrate may be a single-layer film or a multi-layer composite film, without particular limitation. When the porous substrate is a multi-layer composite film, the materials of each layer may be the same or different, without particular limitation.

[0166] In some embodiments, the separator 13 further includes a porous coating. The porous coating can serve as a heat-resistant and / or adhesive layer.

[0167] In some embodiments, the porous coating includes heat-resistant particles. The heat-resistant particles may include at least one of inorganic particles and organic particles.

[0168] In some embodiments, inorganic particles may include one or more of the following: inorganic particles having a dielectric constant of 5 or greater, inorganic particles having ion conductivity but not storing ions, or inorganic particles capable of undergoing electrochemical reactions.

[0169] In some embodiments, inorganic particles having a dielectric constant of 5 or higher may include boehmite, alumina, barium sulfate, magnesium oxide, magnesium hydroxide, silicon oxides, tin dioxide, titanium oxide, calcium oxide, zinc oxide, zirconium oxide, yttrium oxide, nickel oxide, hafnium dioxide, cerium oxide, zirconium titanate, barium titanate, magnesium fluoride, aluminum hydroxide, barium oxide, silicon carbide, boron carbide, aluminum nitride, silicon nitride, boron nitride, calcium fluoride, barium fluoride, magnesium aluminum silicate, lithium magnesium silicate, sodium magnesium silicate, bentonite, hydropyrite, Pb(Zr,Ti)O3 (abbreviated as PZT), Pb1-mLamZr1-nTinO3 (abbreviated as PLZT, 0 < m < 1, 0 < n < 1), Pb(Mg3Nb) 2 / 3 The inorganic particles can be selected from one or more of PbTiO3 (PMN-PT) and their respective modified inorganic particles. Optionally, the modification of each inorganic particle can be chemical modification and / or physical modification.

[0170] In some embodiments, inorganic particles that are ion-conductive but do not store ions may include Li3PO4, lithium titanium phosphate (Li3PO4), etc. x1 Ti y1 (PO4)3, Lithium aluminum titanium phosphate (Li) x2 Al y2 Ti z1 (PO4)3、(LiAlTiP) x3 O y3 Type glass, lithium lanthanum titanate (Li) x4 La y4 TiO3, lithium germanium thiophosphate (Li) x5 Ge y5 P z2 S w Lithium nitride (Li) x6 N y6 SiS2 type glass Li x7 Si y7 S z3 and P2S5 type glass Li x8 P y8 S z4One or more of the following are given: 0 < x1 < 2, 0 < y1 < 3, 0 < x2 < 2, 0 < y2 < 1, 0 < z1 < 3, 0 < x3 < 4, 0 < y3 < 13, 0 < x4 < 2, 0 < y4 < 3, 0 < x5 < 4, 0 < y5 < 1, 0 < z2 < 1, 0 < w < 5, 0 < x6 < 4, 0 < y6 < 2, 0 < x7 < 3, 0 < y7 < 2, 0 < z3 < 4, 0 < x8 < 3, 0 < y8 < 3, 0 < z4 < 7. This can improve the ion conductivity of the separator.

[0171] In some embodiments, the inorganic particles capable of undergoing electrochemical reactions may include one or more of lithium-containing transition metal oxides, lithium-containing phosphates, carbon-based materials, silicon-based materials, tin-based materials, and lithium-titanium compounds.

[0172] In some embodiments, the organic particles may include at least one of a thermoplastic resin polymer, a thermosetting resin polymer, or a crosslinked polymer.

[0173] In some embodiments, the thermoplastic resin polymer may include one or more of the following: polycarbonate organic particles, polymethyl methacrylate organic particles, polyoxymethylene organic particles, polyamide organic particles, styrene-acrylonitrile copolymer, polyphenylene sulfide organic particles, polyether ether ketone organic particles, polyimide organic particles, polysulfone organic particles, polyether sulfone organic particles, polyphenylene sulfone organic particles, polybenzimidazole organic particles, polyamide-imide organic particles, and polyethyleneimine organic particles.

[0174] In some embodiments, the thermosetting resin polymer may include one or more of the following: phenolic resin organic particles, polymer particles containing triazine ring structural units, epoxy resin organic particles, unsaturated polyester resin organic particles, urea-formaldehyde resin organic particles, and furan resin organic particles.

[0175] In some embodiments, the crosslinking polymer may include one or more of crosslinked styrene organic particles and silicon-containing organic crosslinked resin particles.

[0176] In some embodiments, the porous coating includes binder particles. The binder particles may include homopolymers or copolymers of acrylate monomer units, homopolymers or copolymers of acrylic monomer units, homopolymers or copolymers of styrene monomer units, polyurethane compounds, rubber compounds, homopolymers or copolymers of fluorinated alkenyl monomer units, homopolymers or copolymers of olefinic monomer units, homopolymers or copolymers of unsaturated nitrile monomer units, homopolymers or copolymers of epoxide monomer units, and one or more of the modified compounds of the above homopolymers or copolymers.

[0177] In some embodiments, the adhesive particles may include copolymers of acrylate monomer units and styrene monomer units, copolymers of acrylate monomer units and styrene monomer units, copolymers of acrylate monomer units, acrylate monomer units, and styrene monomer units, copolymers of styrene monomer units and unsaturated nitrile monomer units, copolymers of styrene monomer units, olefin monomer units, and unsaturated nitrile monomer units, polytetrafluoroethylene, polychlorotrifluoroethylene, polyvinylidene fluoride, polyvinylidene fluoride, polyethylene, polypropylene, polyacrylonitrile, polyethylene oxide, copolymers of different fluorinated alkenyl monomer units, copolymers of fluorinated alkenyl monomer units and vinyl monomer units, copolymers of fluorinated alkenyl monomer units and acrylate monomer units, copolymers of fluorinated alkenyl monomer units and acrylate monomer units, and one or more of the modified compounds of the above homopolymers or copolymers.

[0178] In some embodiments, the adhesive particles may include one or more of the following: butyl acrylate-styrene copolymer, butyl methacrylate-isooctyl methacrylate copolymer, isooctyl methacrylate-styrene copolymer, methacrylate-methacrylate-styrene copolymer, methyl acrylate-isooctyl methacrylate-styrene copolymer, butyl acrylate-isooctyl methacrylate-styrene copolymer, butyl acrylate-isooctyl methacrylate-styrene copolymer, butyl methacrylate-isooctyl methacrylate-styrene copolymer, butyl methacrylate-isooctyl methacrylate-styrene copolymer, styrene-acrylonitrile copolymer, styrene-butadiene-acrylonitrile copolymer, methyl acrylate-styrene-acrylonitrile copolymer, isooctyl methacrylate-styrene-acrylonitrile copolymer, styrene-vinyl acetate copolymer, styrene-vinyl acetate-pyrrolidone copolymer, vinylidene fluoride-trifluoroethylene copolymer, vinylidene fluoride-hexafluoropropylene copolymer, vinylidene fluoride-trifluoroethylene-hexafluoropropylene copolymer, vinylidene fluoride-hexafluoropropylene-acrylic acid copolymer, vinylidene fluoride-hexafluoropropylene-acrylate copolymer, and a modified compound of the above copolymers.

[0179] In some embodiments, the coating may further include a dispersant, such as one or more of alkylphenol polyoxyethylene ethers, polyacrylic acid dispersants, and cellulose dispersants, including but not limited to. For example, the dispersant may include one or more of sodium carboxymethyl cellulose, sodium polyacrylate, and ammonium polyacrylate.

[0180] [Lithium-ion battery]

[0181] This application provides a lithium-ion battery, including the secondary battery cell 20 described in the above embodiments. A lithium-ion battery can be a single physical module comprising one or more secondary battery cells 20 to provide higher voltage and capacity. When there are multiple secondary battery cells 20, the multiple secondary battery cells 20 are connected in series, parallel, or in a mixed configuration via a busbar.

[0182] In some embodiments, the lithium-ion battery can be a battery pack, which includes a housing and secondary battery cells 20, wherein the secondary battery cells 20 or battery modules are housed in the housing.

[0183] In some embodiments, the housing may be part of the vehicle's chassis structure. For example, a portion of the housing may be at least a part of the vehicle's floor, or a portion of the housing may be at least a part of the vehicle's crossbeams and longitudinal beams.

[0184] In some embodiments, the lithium-ion battery may be located in an energy storage device. The energy storage device includes energy storage containers, energy storage cabinets, etc.

[0185] Figure 11 This is a schematic diagram of a lithium-ion battery according to an embodiment of this application. Figure 11 As shown, the lithium-ion battery 30 may include multiple secondary battery cells 20 to meet different power usage requirements.

[0186] The lithium-ion battery 30 may further include a housing with a hollow interior, housing multiple secondary battery cells 20. For example, multiple secondary battery cells 20 may be connected in parallel, series, or a combination thereof and then placed inside the housing. The housing may include a first housing portion 301 and a second housing portion 302, which are closed to each other to form the housing. The shapes of the first housing portion 301 and the second housing portion 302 may be determined based on the shape of the internally housed components, for example, based on the shape of the combination of the multiple secondary battery cells 20 housed inside. At least one of the first housing portion 301 and the second housing portion 302 may have an opening. For example, as... Figure 11 As shown, only one of the first housing portion 301 and the second housing portion 302 can be a hollow cuboid with an opening, while the other is plate-shaped to cover the opening. Taking the second housing portion 302 as a hollow cuboid with one opening, and the first housing portion 301 as a plate-shaped example, then the first housing portion 301 covers the opening of the second housing portion 302 to form a housing with a closed chamber, which can be used to accommodate multiple secondary battery cells 20.

[0187] For example, unlike Figure 11As shown, the first housing portion 301 and the second housing portion 302 can both be hollow cuboids with one open side. The openings of the first housing portion 301 and the second housing portion 302 are opposite to each other, and the first housing portion 301 and the second housing portion 302 are interlocked to form a housing with a closed chamber. This chamber can accommodate multiple secondary battery cells 20. The multiple secondary battery cells 20 are connected in parallel, series, or mixed and placed inside the housing formed by the interlocking of the first housing portion 301 and the second housing portion 302.

[0188] In some embodiments, the lithium-ion battery 30 may further include other components. For example, the lithium-ion battery 30 may further include a busbar component, which can be used to realize electrical connections between multiple secondary battery cells 20, such as in parallel, series, or mixed connections. Specifically, the busbar component can realize electrical connections between secondary battery cells 20 by connecting to the electrode terminals of the secondary battery cells 20; or, the busbar component can also realize electrical connections between secondary battery cells 20 by connecting to other components of the secondary battery cells 20. The busbar component can be fixed to corresponding components of the secondary battery cells 20 by welding, for example, by welding to electrode terminals, sealing structures, or housings, etc., and the embodiments of this application are not limited thereto.

[0189] The secondary battery cells 20 can be directly assembled into lithium-ion batteries 30, or they can be first assembled into battery modules, and then multiple battery modules can be assembled into lithium-ion batteries 30.

[0190] [Electrical appliances]

[0191] This application provides an electrical device including the lithium-ion battery described in the above embodiments.

[0192] Electrical devices can include vehicles, mobile phones, portable devices, laptops, ships, spacecraft, electric toys, and power tools, etc. Vehicles can be gasoline-powered cars, natural gas-powered cars, or new energy vehicles; new energy vehicles can be pure electric vehicles, hybrid electric vehicles, or range-extended electric vehicles, etc. Spacecraft include airplanes, rockets, space shuttles, and spacecraft, etc. Electric toys include stationary or mobile electric toys, such as game consoles, electric car toys, electric ship toys, and electric airplane toys, etc. Power tools include metal cutting power tools, grinding power tools, assembly power tools, and railway power tools, such as electric drills, electric grinders, electric wrenches, electric screwdrivers, electric hammers, impact drills, concrete vibrators, and electric planers, etc. This application does not impose any special limitations on the above-mentioned electrical devices.

[0193] This application provides an electrical device, which is a vehicle.

[0194] The vehicle can be a gasoline-powered vehicle, a natural gas-powered vehicle, or a new energy vehicle. New energy vehicles can be pure electric vehicles, hybrid electric vehicles, or range-extended electric vehicles, etc. The vehicle's interior can house a motor, a controller, and a lithium-ion battery 30. The controller is used to control the lithium-ion battery 30 to power the motor. For example, the lithium-ion battery 30 can be located at the bottom, front, or rear of the vehicle. The lithium-ion battery 30 can be used to power the vehicle; for example, it can serve as the vehicle's operating power source for the vehicle's electrical system, such as for the power requirements of starting, navigation, and operation. In another embodiment of this application, the lithium-ion battery 30 can not only serve as the vehicle's operating power source but also as the vehicle's driving power source, replacing or partially replacing gasoline or natural gas to provide driving power for the vehicle.

[0195] 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.

[0196] [Examples and Comparative Examples]

[0197] Example 1

[0198] (1) Preparation of negative electrode sheet

[0199] The negative electrode active materials graphite, sodium carboxymethyl cellulose, styrene-butadiene rubber, and acetylene black were mixed in a mass ratio of 96:1:1:2. Deionized water was added, and the mixture was stirred evenly in a mixer. The slurry was then coated onto a 6-micron thick copper foil, with double-sided coating. After drying in a 120℃ oven, it was cold-pressed and slit to obtain the negative electrode sheet. The single-sided coating weight of the negative electrode film was CW2 = 99 g / m². 2 The Dv50 of graphite is 12 μm.

[0200] (2) Preparation of positive electrode sheet

[0201] The positive electrode active material contains lithium transition metal phosphate LiMn 0.6 Fe 0.4 O4 and lithium-containing layered metal oxides LiNi 0.65 Co 0.15 Mn 0.20O2, polyvinylidene fluoride (PVDF) binder, acetylene black conductive agent, and carbon nanotubes are mixed in a mass ratio of 96.5:2:1:0.5 (where the mass ratio of lithium transition metal phosphate and lithium layered metal oxide is 1:1). NMP is added, and the mixture is stirred evenly in a mixer. The slurry is then coated onto a 12-micron thick aluminum foil, coated on both sides, dried in an oven, cold-pressed, and slit to obtain the positive electrode sheet. The mass content of lithium transition metal phosphate in the positive electrode active material is m1 = 50 wt%, and the mass content of lithium transition metal oxide is m2 = 50 wt%; m1 + m2 = 100 wt%. The average particle size of the lithium transition metal oxide particles is D1 = 4 μm, and the average particle size of the lithium transition metal phosphate particles is D2 = 0.8 μm. The single-sided coating weight of the positive electrode film is CW1 = 215 g / m². 2 .

[0202] (3) Preparation of secondary battery cells

[0203] The positive electrode, separator, and negative electrode are stacked sequentially to form a stacked electrode assembly. This assembly is then placed in a housing, electrolyte is injected, and the battery is sealed to obtain a single secondary battery cell. The electrolyte is a 1M solution using ethylene carbonate (EC) and diethyl carbonate (DEC) as solvents (volume ratio 1:2) and lithium salts (LiPF6 and LiFSI, molar ratio 2:1). See also... Figures 3-5 The secondary battery cell's structure includes a shell and an end cap. The end cap is the first wall of the secondary battery cell and has a first through hole. The electrode terminal includes a main body and a stepped portion. The main body of the electrode terminal passes through the first through hole. A fixing member is provided between the end cap and the stepped portion of the electrode terminal, and the fixing member abuts against the stepped portion to fix the electrode terminal. Along the thickness direction of the end cap, the first end face of the main body facing away from the end cap is the surface that extends furthest beyond the end cap. Thus, the distance H1 between the first end face and the outer wall of the first wall (end cap) is 1.5 mm, and the distance H2 between the first end face and the second end face is 0.5 mm. In the radial direction of the main body, the stepped portion protrudes beyond the outer circumference of the main body by an amount W1 = 3 mm. The dimensions of the shell portion of the outer shell are 50 mm × 194 mm × 110 mm.

[0204] Example 2-3

[0205] Compared with Embodiment 1, the difference lies in the height H1 of the first end face from the outer wall of the first wall and the height H2 of the first end face exceeding the second end face.

[0206] Examples 4-5

[0207] Compared with Example 1, the difference lies in the different mass contents of lithium transition metal phosphate (m1) and lithium transition metal oxide (m2) compared with Example 1.

[0208] Examples 6-7

[0209] Compared with Example 1, the difference lies in the fact that the average particle size D1 and the average particle size D2 of the lithium transition metal oxide particles are different from those in Example 1.

[0210] Examples 8-9

[0211] Compared with Example 1, the difference lies in the coating weight CW1 of the positive electrode film and the coating weight CW2 of the negative electrode film.

[0212] Comparative Example 1

[0213] Compared with Example 1, the difference is that the height H1 of the first end face from the outer wall of the first wall in Comparative Example 1 is too large.

[0214] Comparative Example 2

[0215] Compared to Embodiment 1, the difference lies in the structure of this secondary battery cell. The outer casing of the secondary battery cell includes a housing and an end cap. The end cap is the first wall of the secondary battery cell, and a first through hole is provided on the end cap. The main body of the electrode terminal passes through the first through hole. A rivet block is provided on the outside of the end cap for the electrode terminal, and the top terminal is riveted to the rivet block to fix the electrode terminal. Along the thickness direction of the end cap, the surface of the rivet block facing away from the end cap is the surface that extends furthest beyond the end cap. Therefore, the height H1 between the surface of the rivet block facing away from the end cap and the outer wall of the first wall (end cap) is 4 mm.

[0216] Comparative Example 3

[0217] Compared with Example 1, the difference is that in Comparative Example 3, the distance H1 between the first end face and the outer wall of the first wall is too large and the mass content of lithium transition metal phosphate in the positive electrode active material is too small.

[0218] Product parameters and performance parameters of Examples 1-9 and Comparative Examples 1-3.

[0219] Table 1: Product parameters and performance parameters of Examples 1-9 and Comparative Examples 1-3

[0220] In Table 1, "H1" represents the height between the outer wall of the first end face and the first wall; "H2" represents the height between the first end face and the second end face; "m1" represents the mass content of lithium transition metal phosphate in the positive electrode active material; "m2" represents the mass content of lithium transition metal oxide in the positive electrode active material; "D1" represents the average particle size of lithium transition metal oxide particles; "D2" represents the average particle size of lithium transition metal phosphate particles; "CW1" represents the weight of the positive electrode film coating on one side; "CW2" represents the weight of the negative electrode film coating on one side; "T" represents the temperature at which the secondary battery cell 20 experiences thermal runaway during the hot box test; and "VED" represents the volumetric energy density of the secondary battery cell 20.

[0221] A comparative analysis of the embodiments and comparative examples shows that, compared to comparative examples 1-3, the embodiments all exhibit superior volumetric energy density and thermal runaway temperature that is essentially equivalent to or higher than that of comparative examples 1-3. This indicates that the embodiments possess both a thermal runaway temperature that is substantially superior to that of comparative examples 1-3 and a higher volumetric energy density. Therefore, it is demonstrated that the solution implemented in this application allows the secondary battery cell 20 to possess both high energy density and good safety performance.

[0222] Comparative analysis of Examples 1-5 shows that, under the premise that the mass content of lithium transition metal phosphate is within a suitable range, the greater the height H1 of the electrode terminal 22 protruding from the first wall 211, the lower the volumetric energy density of the secondary battery cell 20. Increasing the proportion of lithium transition metal phosphate in the positive electrode active material increases the thermal runaway temperature of the secondary battery cell 20, improving safety performance, but decreasing the volumetric energy density. Comparative analysis of Examples 1-2 shows that adjusting the size of the electrode terminal 22 alone or adjusting the ratio of the positive electrode active material alone cannot achieve a balance between safety performance and high energy density. This indicates that by controlling the height of the electrode terminal 22 protruding from the first wall 211 of the secondary battery cell 20 within the range of 1.5mm-3mm, and controlling the mass content of lithium transition metal phosphate in the positive electrode active material within the range of 40wt%-70wt%, the secondary battery cell 20 can simultaneously achieve both high energy density and good safety performance. Furthermore, the height of the electrode terminal 22 protruding from the first wall 211 is also limited by the machining process of the mechanical parts, therefore, the value of H1 has a lower limit. If H1 is less than 1.5mm, it is difficult to achieve in actual processing and mass production is challenging.

[0223] Comparative analysis of Examples 1 and 6-7 shows that the smaller the Dv50 of the lithium-containing transition metal oxide, the higher the thermal runaway temperature of the secondary battery cell 20, and the better the safety performance. This is likely because a smaller Dv50 indicates better structural stability of the lithium-containing transition metal oxide, enabling more stable chemical reactions during the charging and discharging process of the secondary battery cell 20, thus reducing the probability of thermal runaway due to vigorous chemical reactions and excessive heat release. Therefore, controlling the Dv50 of the lithium-containing transition metal oxide helps to further improve the safety performance of the high-energy-density secondary battery cell 20.

[0224] According to the comparative analysis of Examples 1 and 8-9, when the material ratio and structural design of the secondary battery cell 20 are the same, the volumetric energy density of the secondary battery cell 20 can be further improved by increasing the coating weight of the electrode.

[0225] The following is a brief description of the testing methods for the physicochemical and performance parameters involved in the embodiments of this application. It should be understood that the following testing methods are only examples, and other testing methods known in the art can also be used for testing.

[0226] 1. Test methods for mass content

[0227] The specific types of lithium-containing transition metal oxides are determined by the mass ratio of Ni, Co, and Mn in CP-EDS, and the specific types of lithium-containing transition metal phosphates are determined by the mass ratio of Mn and Fe. Then, the mass content of lithium-containing transition metal oxides is calculated by the mass content of Ni and Co in the ICP mixture, and the mass content of lithium-containing transition metal phosphates is calculated by the mass content of Fe.

[0228] 2. Test methods for element molar percentage

[0229] Test equipment: Inductively Coupled Plasma Emission Spectrometer (ICP).

[0230] Test method: Digestion: 1+1 aqua regia, digestion method: plate digestion / acid-removing digestion / microwave digestion (high temperature and high pressure ~200℃). The elemental mass fractions of nickel, cobalt, manganese, and doping elements were measured, and the molar amounts were calculated based on the molar mass of each element. Finally, the molar ratio of nickel, cobalt, and manganese was calculated by normalization.

[0231] 3. Test method for average particle size

[0232] The particle morphology and size of the test samples were obtained using SEM. Elemental analysis was performed based on the SEM mapping results. Differences in element type and content (e.g., phosphorus) were used to distinguish between lithium transition metal phosphate particles and lithium transition metal oxide particles. The average particle size of the corresponding material was calculated based on the number of each type of particle in the SEM images and the major and minor axes of each particle. This process was repeated to obtain the average particle size of 20 test samples. The average of these average particle sizes was then calculated and recorded as the average particle size of the material.

[0233] 4. Dv50 Testing Method

[0234] Testing equipment: Particle size analyzer.

[0235] Pretreatment: Take a clean beaker, add an appropriate amount of the sample to be tested, add a surfactant and then add a dispersant, and sonicate at 120W / 5min to ensure that the sample is completely dispersed in the dispersant.

[0236] Test: After the sample is poured into the injection tower, it circulates with the solution to the test optical path system. Under the irradiation of the laser beam, the particle size distribution characteristics can be obtained by receiving and measuring the energy distribution of the scattered light (shading degree: 8-12%).

[0237] Calculation: Calculate the particle size at the 50% position of the volume distribution curve from smallest to largest, which is Dv50.

[0238] 5. Test method for electrode compaction density

[0239] Take a unit area of ​​the electrode to be tested, weigh the mass m1 of the material on the unit area electrode excluding the current collector, measure the electrode thickness T1 and the current collector thickness T0, and the compaction density = m1 / (T1-T0).

[0240] 6. Test method for film coating weight

[0241] Take a unit area of ​​the electrode to be tested and weigh the mass of the material on the unit area electrode, excluding the current collector, i.e., the coating weight.

[0242] 7. Test method for volumetric energy density of secondary battery cells

[0243] The secondary battery cell 20 is charged and discharged for 3 cycles at a current density of 0.33C within a voltage range of 2.5-4.25V on a charging and discharging device. The discharge energy Q of the third cycle is recorded. The volume V of the secondary battery cell 20 is measured by taking a CT scan image of the cell. Based on the CT scan image, the length T, height h, width L, diameter d of the electrode terminals, and height H of the secondary battery cell 20 can be measured. The volume of the secondary battery cell 20 can be calculated using the formula V = T × h × L + 2 × π × (d / 2). 2×H, the energy density of a single 20-cell secondary battery is Q / V (unit: Wh / L). If the electrode terminal is irregularly shaped, its volume can be calculated by fitting the irregular shape into a regular shape on a computer and then using the volume calculation formula for a regular shape.

[0244] 8. Safety performance testing methods

[0245] The safety performance of the secondary battery cell 20 was characterized by a hot box test. The specific test procedure was as follows: the fully charged secondary battery cell 20 was placed in an oven and heated from 30°C to 200°C at a temperature increase rate of 2°C / min, and held at 5°C for 30 minutes. The temperature at which the secondary battery cell 20 caught fire was observed, which is its failure temperature.

[0246] Although this application has been described with reference to preferred embodiments, various modifications can be made thereto and components can be replaced with equivalents without departing from the scope of this application. In particular, the technical features mentioned in the various embodiments can be combined in any manner, provided there is no structural conflict. This application is not limited to the specific embodiments disclosed herein, but includes all technical solutions falling within the scope of the claims.

Claims

1. A secondary battery cell, characterized in that, The secondary battery cell includes: Housing, electrode assembly, electrode terminals, and fixtures; The electrode assembly is housed within the housing. The electrode assembly includes a positive electrode sheet, which includes a positive electrode active material. The positive electrode active material includes a lithium transition metal phosphate and a lithium transition metal oxide. Based on the total mass of the positive electrode active material, the mass content m1 of the lithium transition metal phosphate satisfies: 40wt%≤m1≤70wt%. The outer casing includes a first wall, the first wall including a first through hole; the electrode terminal includes a main body portion and a stepped portion, at least a portion of the main body portion passing through the first through hole, the stepped portion protruding from the outer peripheral surface of the main body portion, the stepped portion being located on the side of the first wall facing the outside of the secondary battery cell; the fixing member includes a second through hole through which the main body portion passes; in the thickness direction of the first wall, at least a portion of the fixing member is located between the first wall and the stepped portion and abuts against the stepped portion; The main body has a first end face facing away from the first wall, and in the thickness direction of the first wall, the height H1 between the first end face and the outer wall of the first wall satisfies: 1.5 mm ≤ H1 ≤ 3 mm.

2. The secondary battery cell according to claim 1, characterized in that, In the thickness direction of the first wall, the fastener has a second end face facing away from the first wall, and the first end face extends beyond the second end face.

3. The secondary battery cell according to claim 2, characterized in that, In the thickness direction of the first wall, the height H2 between the first end face and the second end face satisfies: 0.5 mm ≤ H2 ≤ 1.5 mm.

4. The secondary battery cell according to claim 1, characterized in that, The average particle size D1 of the lithium-containing transition metal oxide particles satisfies: 2 μm ≤ D1 ≤ 5 μm.

5. The secondary battery cell according to claim 1, characterized in that, The lithium-containing transition metal oxide includes: Li 1+d [Ni x Co y Mn z M e O 2-f ; Wherein, M includes at least one of Zr, Al, Ti, Sb, Nb, Te, Mg, B, Ca, V, Ta or Sr, 0.2≥d≥-0.2, 0.95≥x≥0.5, 0.2≥y≥0.05, 0.3>z>0, 0.3>e≥0, 0.5≥f≥0.

6. The secondary battery cell according to claim 1, characterized in that, Based on the total mass of the positive electrode active material, the mass content m2 of the lithium transition metal oxide satisfies: 30wt%≤m2≤60wt%.

7. The secondary battery cell according to claim 1, characterized in that, The average particle size D2 of the lithium transition metal phosphate particles satisfies: 0.5 μm ≤ D2 ≤ 1.5 μm.

8. The secondary battery cell according to claim 1, characterized in that, The lithium-containing transition metal phosphate includes: Li 1+a Mn b A 1-b P 1-c R c O4; Wherein, -0.2≤a<1, 0.3≤b≤0.9, 0≤c≤0.1, A includes at least one of Zn, Al, Na, K, Mg, Mo, W, Ti, V, Zr, Fe, Ni, Co, Ga, Sn, Sb, Nb and Ge, and R includes at least one of B, Si, N, S, F, Cl and Br.

9. The secondary battery cell according to claim 1, characterized in that, 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, and the positive electrode satisfies at least one of the following conditions: (1) The compaction density ρ1 of the positive electrode sheet satisfies: 2.5 g / cm³ 3 ≤ρ1≤2.9 g / cm 3 ; (2) The single-sided coating weight CW1 of the positive electrode film layer satisfies: 190 g / m 2 ≤CW1≤230 g / m 2 ; (3) The thickness h1 of the positive current collector satisfies: 10 μm≤h1≤13 μm.

10. The secondary battery cell according to any one of claims 1-9, characterized in that, The secondary battery cell includes a negative electrode sheet, which 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 a negative electrode active material.

11. The secondary battery cell according to claim 10, characterized in that, The negative electrode sheet satisfies at least one of the following conditions: (4) The compaction density ρ2 of the negative electrode sheet satisfies: 1.3 g / cm³ 3 ≤ρ2≤1.55 g / cm 3 ; (5) The single-sided coating weight CW2 of the negative electrode film layer satisfies: 90 g / m 2 ≤CW2≤110 g / m 2 ; (6) The thickness h2 of the negative electrode current collector satisfies: 4 μm ≤ h2 ≤ 6 μm.

12. The secondary battery cell according to claim 10, characterized in that, The negative electrode active material includes graphite.

13. The secondary battery cell according to claim 12, characterized in that, The average volumetric particle size Dv50 of the graphite satisfies: 10 μm ≤ Dv50 ≤ 14 μm.

14. The secondary battery cell according to any one of claims 1-9, characterized in that, In the radial direction of the main body, the step portion protrudes beyond the outer circumference of the main body by a dimension W1 that satisfies: 0.1 mm ≤ W1 ≤ 5 mm.

15. The secondary battery cell according to any one of claims 1-9, characterized in that, The electrode assembly is a stacked electrode assembly.

16. The secondary battery cell according to any one of claims 1-9, characterized in that, The electrode assembly includes a body and an electrode tab, wherein the electrode tab is connected to the end of the body facing the first wall; The secondary battery cell includes a current collector, which is disposed between the first wall and the main body. The current collector includes a first connecting part and a second connecting part that are connected to each other. The first connecting part is connected to the electrode terminal, and the second connecting part is connected to the tab. Wherein, along the thickness direction of the current collecting member, the thickness S1 of the first connecting part and the thickness S2 of the second connecting part satisfy: S1-S2≥0.1mm.

17. The secondary battery cell according to claim 16, characterized in that, 0.5 mm ≤ S1 ≤ 1.2 mm; and / or 0.3 mm ≤ S2 ≤ 1 mm.

18. The secondary battery cell according to claim 1, characterized in that, The secondary battery cell includes an electrolyte, and the ionic conductivity σ of the electrolyte satisfies: 7 mS / cm ≤ σ ≤ 10 mS / cm.

19. The secondary battery cell according to claim 18, characterized in that, The electrolyte comprises: Solvents, including linear carbonates; Based on the total mass of the electrolyte, the mass content m3 of the linear carbonate satisfies 40wt%≤m3≤70wt%.

20. The secondary battery cell according to claim 18 or 19, characterized in that, The electrolyte comprises: Lithium salts, including LiPF6 and LiFSI; Based on the total mass of the electrolyte, the mass content m4 of the lithium salt satisfies 13wt%≤m4≤18wt%.

21. A lithium-ion battery, characterized in that, The lithium-ion battery includes any one of the secondary battery cells according to claims 1-20.

22. An electrical appliance, characterized in that, The electrical device includes a secondary battery cell as described in any one of claims 1-20, and / or a lithium-ion battery as described in claim 21.

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