Secondary battery cell, lithium ion battery and electric device

Abstract

The invention provides a secondary battery monomer, a lithium ion battery and a power utilization device. The secondary battery monomer comprises a shell, an electrode assembly, an electrode terminal and a fixed part, the positive pole piece comprises a positive active material, and the positive active material comprises lithium-containing transition metal phosphate and lithium-containing transition metal oxide; based on the total mass of the positive electrode active material, the mass content m1 of the lithium-containing phosphoric acid is greater than or equal to 40wt% and less than or equal to 70wt%; 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 penetrates through the first through hole, and the step part protrudes out of the peripheral 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 is provided with a first end face deviating from the first wall, and the height H1 between the first end face and the outer wall of the first wall is larger than or equal to 1.5 mm and smaller than or equal to 3 mm.

Description

Technical Field

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

[0002] In recent years, secondary batteries, mainly lithium-ion batteries, have been widely used in energy storage power systems such as hydropower, thermal, wind and solar power stations, as well as power tools, electric bicycles, electric motorcycles, electric vehicles, military equipment, aerospace and other fields, and have thus achieved great development.

[0003] Improving the energy density of secondary battery cells is the research focus of lithium-ion batteries. At present, the energy density of lithium-ion batteries is mainly limited by the positive electrode active materials, and the purpose of improving energy density is usually achieved by combining different positive electrode active materials. However, while improving the energy density, the mixed positive electrode active materials may affect other properties of the secondary battery cells, such as cycle performance, safety performance, etc. Therefore, how to balance the energy density and safety performance of secondary battery cells has become a technical problem that needs to be solved urgently. Summary of the invention

[0004] The present application is made in view of the above 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 have 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 housing, an electrode assembly, an electrode terminal and a fixing member; the electrode assembly is accommodated in the housing, the electrode assembly comprises a positive electrode plate, the positive electrode plate comprises a positive electrode active material, the positive electrode active material comprises a lithium-containing transition metal phosphate and a lithium-containing transition metal oxide, and the mass content m1 of the lithium-containing phosphoric acid satisfies the following: 40wt%≤m1≤70wt% based on the total mass of the positive electrode active material; the housing comprises a first wall, the first wall comprises a first through hole; the electrode terminal comprises a main body and A step portion, at least part of the main body is penetrated by the first through hole, the step portion protrudes from the outer peripheral surface of the main body, 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 for the main body to pass through; in the thickness direction of the first wall, at least part 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 an embodiment of the present application, the positive electrode active material includes both a lithium-containing transition metal phosphate and a lithium-containing transition metal oxide, and the height of the electrode terminal of the secondary battery cell protruding from the outer shell is controlled within the range of 1.5mm-3mm by abutting the electrode terminal with the fixing member. As a result, the secondary battery cell can take into account both safety performance and energy density.

[0007] In a possible implementation manner, in the thickness direction of the first wall, the fixing member has a second end surface facing the first wall, and the first end surface exceeds the second end surface.

[0008] In the embodiment of the present application, the first end face of the electrode terminal exceeds the second end face, that is, in the thickness direction of the first wall, the end face farthest from the first wall is the first end face. Therefore, by setting the fixing member, the height of the electrode terminal exceeding the first wall can be controlled within the range of 1.5mm-3mm.

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

[0010] In the embodiment of the present 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, it is possible to improve the safety performance and energy density of the secondary battery cell while ensuring that the connection stability between the first end face and the second end face is as good as possible.

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

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

[0013] In a 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 the present application, the selection of lithium-containing transition metal oxides doped with heteroatoms helps to improve the stability of the lithium-containing transition metal oxides at high temperatures, and further improves the safety performance of the secondary battery cells.

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

[0016] In a 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 / cm 3 ≤ρ1≤2.9g / cm 3 (2) The single-sided coating weight CW1 of the positive electrode film layer satisfies: 190g / m 2 ≤CW1≤230g / m 2 ; (3) The thickness h1 of the positive electrode current collector satisfies: 10μm≤h1≤13μm.

[0017] In the embodiments of the present application, by controlling the compaction density of the positive electrode plate and the coating weight of the positive electrode film layer within a suitable range, it helps to improve the lithium ion dynamics, thereby reducing the polarization of the secondary battery cell during the cycle process, and helping to improve the safety performance of the secondary battery cell; by controlling the thickness of the positive electrode collector within a suitable range, it helps to reduce the thickness of the positive electrode plate, and helps to improve the energy density of the secondary battery cell.

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

[0019] In a 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 a possible implementation, the negative electrode plate includes a negative electrode current collector and a negative electrode film layer disposed on at least one surface of the negative electrode current collector, and the negative electrode film layer includes a negative electrode active material.

[0021] In a 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 / cm 3 ≤ρ2≤1.55g / cm 3 (5) The single-sided coating weight CW2 of the negative electrode film layer satisfies: 90g / 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 the present application, by controlling the compaction density of the negative electrode pole piece and the coating weight of the negative electrode film layer within a suitable range, it helps to improve the lithium ion dynamics, thereby reducing the polarization of the secondary battery cell during the cycle process, 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 helps to reduce the thickness of the negative electrode pole piece, and helps to improve the energy density of the secondary battery cell.

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

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

[0025] In the embodiments of the present application, by controlling the average volume particle size of graphite within a suitable range, it helps to improve lithium ion kinetics, helps to reduce the polarization of secondary battery cells during the cycle process, and improves the safety performance of secondary battery cells.

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

[0027] In the embodiment of the present 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 helpful to increase the contact area between the step portion and the fixing member, thereby helping to improve the connection strength between the step portion and the fixing member.

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

[0029] In the embodiments of the present application, by adopting a laminated 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 improved.

[0030] In one possible implementation, the electrode assembly includes a main body and a pole tab, wherein the pole tab is connected to one end of the main body facing the first wall; the secondary battery cell includes a current collecting component, wherein the current collecting component is arranged between the first wall and the main body, and the current collecting component includes a first connecting portion and a second connecting portion connected to each other, wherein the first connecting portion is connected to the electrode terminal, and the second connecting portion is connected to the pole tab; wherein, along the thickness direction of the current collecting component, 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 the present application, by setting the thickness of the first connecting portion of the current collecting member to be greater than the thickness of the second connecting portion, the thickness of the area where the current collecting member is connected to the electrode terminal is greater than the thickness of the area where the current collecting member is connected to the pole tab. Since the thickness requirement of the area where the current collecting member is connected to the pole tab is less than the thickness requirement of the area where the current collecting member is connected to the electrode terminal, the thickness of the current collecting member can be effectively optimized while the current collecting member can be connected to the electrode terminal and the pole tab, so as to reduce the overall weight of the current collecting member and save the space occupied by the current collecting member, 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 a possible implementation, 0.5 mm ≤ S1 ≤ 1.2 mm; and / or 0.3 mm ≤ S2 ≤ 1 mm.

[0033] In the embodiment of the present application, by controlling the thickness of the first connection part and the thickness of the second connection part within a suitable range, the connection strength between the first connection part and the electrode terminal and between the second connection part and the tab can be met while improving the energy density of the secondary battery cell.

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

[0035] In the embodiments of the present application, selecting an electrolyte with higher ion conductivity helps to improve the lithium ion dynamics during the cycle of the secondary battery cell, helps to reduce the polarization of the secondary battery cell during the cycle, and improves the safety performance of the secondary battery cell.

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

[0037] In the embodiments of the present application, by selecting a linear carboxylate as a solvent and controlling its mass content in the electrolyte within a suitable range, it helps to reduce the viscosity of the electrolyte, thereby helping to improve the lithium ion kinetics.

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

[0039] In the embodiments of the present application, by selecting LiPF6 and LiFSI as lithium salts, it helps to improve the lithium ion conductivity and high temperature resistance of the electrolyte, thereby helping to improve the lithium ion dynamics during the cycle of the secondary battery cells, reduce the polarization of the secondary battery cells during the cycle, and improve the safety performance of the secondary battery cells.

[0040] In a second aspect, a secondary battery is provided, wherein the secondary battery comprises the secondary battery cell according to any implementation of the first aspect.

[0041] In a third aspect, an electrical device is provided, wherein the electrical device comprises a secondary battery cell in any implementation manner of the first aspect, and / or a secondary battery in the second aspect. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the drawings required for use in the embodiments of the present application will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on the drawings without paying creative work.

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

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

[0045] Figure 3 A partial exploded view of a secondary battery cell.

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

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

[0048] Figure 6 A schematic diagram of an electrode terminal.

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

[0050] Figure 8 A cross-sectional schematic diagram of another laminated electrode assembly.

[0051] Fig. 9 A cross-sectional schematic diagram of a wound electrode assembly.

[0052] Fig.10 It is a partial schematic diagram of a secondary battery cell.

[0053] Fig.11 A schematic diagram of a battery. Figure numbers: 10-electrode assembly, 11-positive electrode sheet, 12-negative electrode sheet, 13-separating film, 20-secondary battery cell, 21-housing, 22-electrode terminal, 23-riveting block, 24-current collecting member, 26-insulating member, 27-sealing member, 28-fixing member, 30-lithium-ion battery, 101-main body of electrode assembly, 102-ear, 211-first wall, 212-housing, 213-end cover, 221-main 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 box body portion, 302-second box body portion, 2111-first through hole, 2121-opening, 2211-first end face, 2212-first groove, 2221-third end face. DETAILED DESCRIPTION

[0054] Hereinafter, the embodiments of the secondary battery cell, lithium-ion battery and electrical device of the present application are specifically disclosed in detail with appropriate reference to the accompanying drawings. However, there may be cases where unnecessary detailed descriptions are omitted. For example, there are cases where detailed descriptions of well-known matters and repeated descriptions of actually the same structures are omitted. This is to avoid the following description from becoming unnecessarily lengthy and to facilitate the understanding of those skilled in the art. In addition, the drawings and the following descriptions are provided for those skilled in the art to fully understand the present application and are not intended to limit the subject matter described in the claims.

[0055] "Scope" disclosed in the present application is limited in the form of lower limit and upper limit, and a given range is limited by selecting a lower limit and an upper limit, and the selected lower limit and upper limit define the boundary of a special range. The scope limited in this way can be including end values ​​or not including end values, and can be arbitrarily combined, that is, any lower limit can form a scope with any upper limit combination. For example, if the scope of 60-120 and 80-110 is listed for a specific parameter, it is understood that the scope of 60-110 and 80-120 is also expected. In addition, if the minimum range values ​​1 and 2 are listed, and if the maximum range values ​​3,4 and 5 are listed, the following scope can be all expected: 1-3, 1-4, 1-5, 2-3, 2-4 and 2-5. In the present application, unless otherwise specified, the numerical range "ab" represents the abbreviation of any real number combination between a and b, wherein a and b are real numbers. For example, the numerical range "0-5" means that all real numbers between "0-5" are listed in this document, and "0-5" is just an abbreviation of these numerical combinations. In addition, when a parameter is expressed as an integer ≥ 2, it is equivalent to disclosing that the parameter is, for example, an integer of 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0056] In the description of this application, it should be noted that, unless otherwise specified, "multiple" means more than two; the terms "upper", "lower", "left", "right", "inner", "outer", etc., indicating directions 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 direction, be constructed and operated in a specific direction, and therefore cannot be understood as limiting this application. In addition, the terms "first", "second", "third", etc. are only used for descriptive purposes and cannot be understood as indicating or implying relative importance.

[0057] If not otherwise specified, in this application, the phrase "A and / or B" means "A, B, or both A and B". More specifically, any of the following conditions satisfies the condition "A and / or B": 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).

[0058] If there is no special explanation, all steps of the present application can be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), which means that the method may include steps (a) and (b) performed sequentially, or may include steps (b) and (a) performed sequentially. For example, the method may further include step (c), which means that step (c) may be added to the method in any order. For example, the method may include steps (a), (b) and (c), or may include steps (a), (c) and (b), or may include steps (c), (a) and (b), etc.

[0059] Unless otherwise specified, all embodiments and optional embodiments of the present application can be combined with each other to form a new technical solution.

[0060] Unless otherwise specified, the following terms have the following meanings. Any undefined terms have their generally accepted meanings in the art.

[0061] If mentioned, "lithium-containing transition metal phosphate" refers to a type of salt including lithium, transition metal, and phosphate ions, such as lithium iron phosphate, lithium iron manganese phosphate, and the like.

[0062] As mentioned, "lithium-containing transition metal oxides" refers to a class of oxides including lithium elements and transition metal elements. Structurally, it includes ternary materials with layered structures, LiCoO2, LiNiO2, etc., and also includes LiMn2O4 with spinel structure, etc. Ternary materials refer to lithium transition metal oxides including three different transition metal elements. It should be understood that trace amounts of other transition metal elements can also be doped in ternary materials, and it is generally believed that ternary materials doped with other transition metal elements are still ternary materials.

[0063] If mentioned, "linear carbonate" refers to a class of substances with a chain structure and containing carbonate groups (-OCO-O-), such as dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), etc.

[0064] Next, embodiments of the present application are introduced.

[0065] In recent years, lithium-ion batteries have been widely used in power tools, electronic products, electric vehicles, aerospace and other fields due to their high energy density and long service life, and have achieved great development. Usually, the secondary battery cell of a lithium-ion battery includes a positive electrode plate, a negative electrode plate, an electrolyte and a separator. During the charge and discharge process of the secondary battery cell, the active ions are embedded and released back and forth between the positive electrode plate and the negative electrode plate. Among them, the electrolyte plays a role in conducting active ions between the positive electrode plate and the negative electrode plate. The separator is arranged between the positive electrode plate and the negative electrode plate, which allows the active ions to pass through while preventing the positive and negative electrodes from short-circuiting, so that the electrochemical reaction in the secondary battery cell proceeds normally.

[0066] Improving the energy density of secondary battery cells has always been a research focus in the battery field. Positive electrode active materials are one of the direct factors that directly affect the energy density of secondary battery cells. Lithium-containing transition metal phosphates with good thermal stability and lithium-containing transition metal oxides with high gram capacity are both commonly used positive electrode active materials, but the low gram capacity of lithium-containing transition metal phosphates is not conducive to improving the energy density of secondary battery cells. Lithium-containing transition metal oxides are beneficial to improving the energy density of secondary battery cells, but their safety performance is poor. At present, there are some schemes for mixing the two, hoping to obtain secondary battery cells that take into account both safety performance and high capacity, but the mixing of the two is actually a trade-off between safety performance and energy density, and cannot solve the problem of reduced energy density caused by mixing the two.

[0067] In view of this, the embodiments of the present application provide a secondary battery cell, a lithium-ion battery, and an electrical device. The secondary battery cell can have both high energy density and good safety performance.

[0068] Next, the secondary battery cell provided by the present application is introduced.

[0069] [Secondary battery cell]

[0070] First, a secondary battery cell is provided, the secondary battery cell comprises a housing, an electrode assembly, an electrode terminal and a fixing member. The electrode assembly is contained in the housing, the electrode assembly comprises a positive electrode plate, the positive electrode plate comprises a positive electrode active material, the positive electrode active material comprises a lithium-containing transition metal phosphate and a lithium-containing transition metal oxide, and the mass content m1 of the lithium-containing phosphoric acid satisfies, based on the total mass of the positive electrode active material: 40wt%≤m1≤70wt%; optionally, 45wt%≤m1≤70wt%. The shell includes a first wall, and the first wall includes a first through hole; the electrode terminal includes a main body and a step portion, at least part of the main body is passed through the first through hole, the step portion protrudes from the outer peripheral surface of the main body, 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 for the main body to pass through; in the thickness direction of the first wall, at least part of the fixing member is located between the first wall and the step portion and abuts against the step 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.

[0071] Specifically, m1 can be 40wt%, 42wt%, 44wt%, 45wt%, 46wt%, 48wt%, 50wt%, 52wt%, 54wt%, 56wt%, 58wt%, 60wt%, 62wt%, 64wt%, 66wt%, 68wt%, 70wt%, or its value is within the range obtained by combining any two of the above 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, 3mm, or its value is within the range obtained by combining any two of the above values. The higher the mass content of the lithium-containing transition metal phosphate in the positive electrode active material, the better the thermal stability of the secondary battery cell, and the 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 space occupied by the portion of the electrode terminal of the secondary battery cell protruding from the shell and the overall space ratio 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 the lithium-containing transition metal phosphate within 40wt%-70wt% and controlling H1 within the range of 1.5mm-3mm, the secondary battery cell can take into account both safety performance and energy density.

[0072] The above embodiments are described in more detail below with reference to the accompanying drawings. Figure 1-2 This is a schematic structural diagram of a secondary battery cell of the present application. Figure 1As shown, the secondary battery cell 20 includes a housing 21 and an electrode assembly 10 . The electrode assembly 10 is accommodated in the housing 21 . The housing 21 includes a first wall 211 . The electrode terminal 22 is disposed on the first wall 211 .

[0073] More specifically, the housing 21 may include a shell 212 and an end cap 213. The shell 212 is formed with a receiving cavity inside, and the receiving cavity has an opening 2121, that is, the shell 212 is a hollow structure with one end open, and the end cap 213 covers the opening 2121 of the shell 212 and forms a sealed connection to form 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 may be one of the multiple walls of the shell 212. Exemplarily, in Figure 1 and Figure 2 In the figure, the first wall 211 is the end cover 213 of the shell 21. Of course, in other embodiments, the first wall 211 can also be the bottom wall of the shell 212 arranged opposite to the end cover 213 in the thickness direction X of the end cover 213 or the side wall adjacent to the end cover 213 and abutting against each other.

[0074] The shell 212 can be in various shapes, such as a cylinder, a cuboid, etc. The shape of the shell 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, the shell 212 can be a cylindrical structure; if the electrode assembly 10 is a cuboid structure, the shell 212 can be a cuboid structure. Of course, the end cap 213 can also be a variety of structures, such as a plate-like structure or a hollow structure with one end open. For example, in Figure 1 and Figure 2 In the embodiment, the shell 212 is a rectangular parallelepiped structure. It should be understood that the shell 21 is not limited to the aforementioned structure, and the shell 21 may also be other structures. For example, the shell 21 includes a shell 212 and two end caps 213. The shell 212 is a hollow structure with openings 2121 on opposite sides. One end cap 213 is correspondingly covered at one opening 2121 of the shell 212 to form a sealed connection, so as to form a sealed space for accommodating the electrode assembly 10 and the electrolyte.

[0075] The electrode assembly 10 contained in the housing 21 may be one or more. Figure 2 In the embodiment, the outer shell 21 of the secondary battery cell 20 is provided with two electrode assemblies 10, and the two electrode assemblies 10 are stacked along the thickness direction thereof, 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 accommodated in the outer shell 21 may be one, three, four, five, six, seven or eight, etc.

[0076] The electrode terminal 22 is a component used to output or input electric energy to the secondary battery cell 20. For example, the electrode terminal 22 can be made of a variety of materials, such as copper, iron, aluminum, steel, aluminum alloy, etc. The end of the electrode terminal 22 facing the electrode assembly 10 is connected to the current collecting member 24, and the end of the electrode terminal 22 away from the electrode assembly 10 is used to connect to the current collecting member to achieve the input or output of electric energy of the secondary battery cell 20. Figure 1-2 In the embodiment, the secondary battery cell 20 includes two electrode terminals 22, and correspondingly, each electrode assembly 10 has two tabs 102, and the polarities of the two tabs 102 are opposite. 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.

[0077] Figure 3 It is an exploded view of a partial structure of a secondary battery cell 20 of the present application. Figure 4 This is a cross-sectional view of a partial structure of a secondary battery cell 20 of the present application. Figure 5 for Figure 4 Schematic diagram of a local area. Figure 6 Schematic diagram of the structure of an electrode terminal 22.

[0078] refer to Figure 3-5 The first wall 211 includes a first through hole 2111, and the electrode terminal 22 includes a main body 221 and a step portion 222. The step portion 222 protrudes from the outer peripheral surface of the main body 221, and the step portion 222 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, and the fixing member 28 includes a second through hole 281 for the main body 221 to pass through. 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 step portion 222 and abuts against the step portion 222. The main body 221 has a first end surface 2211 facing the outside of the secondary battery cell 20, as shown in FIG. Figure 5 As shown, the height between the first end surface 2211 and the outer wall of the first wall 211 is H1.

[0079] Generally speaking, Figure 6As shown, the electrode terminal 22 of the secondary battery cell 20 is riveted to the wall portion of the housing 21, for example, to the first wall 211, by a rivet block 23 that wraps the electrode terminal 22. In the thickness direction of the first wall 211, the surface of the wall portion of the rivet block 23 away from the first wall 211 will exceed the outer end surface of the electrode terminal 22 or be flush with the outer end surface of the electrode terminal 22. This design is to give the electrode terminal 22 additional protection and support to reduce the risk of loosening of the electrode terminal 22. At the same time, the electric energy of the secondary battery cell 20 can be transmitted to the inside of the secondary battery cell 20 through the rivet block 23. An insulating member can be provided between the rivet block 23 and the first wall 213 to isolate the first wall 213 and the rivet block 23. Due to the process requirements of riveting, the electrode terminal 22 needs to have a sufficient contact area with the rivet block 23 to ensure the stability of the structure, so the height of the electrode terminal 22 and the rivet block 23 under this design is usually high.

[0080] The positive electrode active material includes both lithium-containing transition metal oxides and lithium-containing transition metal phosphates. By combining lithium-containing transition metal phosphates with good thermal stability with lithium-containing transition metal oxides with high gram capacity, the safety performance of the secondary battery cell 20 can be effectively improved, but with a loss in energy density.

[0081] In this embodiment, while controlling the content of lithium-containing transition metal phosphate to be between 40wt% and 70wt%, the electrode terminal 22 is fixed and supported by the fixing member 28 abutting against the electrode terminal 22, which not only can omit the riveting block 23 structure, but also can control the height of the electrode terminal 22 protruding from the first wall 211 to be within the range of 1.5mm-3mm, reducing the space occupied by the portion of the electrode terminal 22 protruding from the housing 21 of the secondary battery cell 20 and the proportion of the total space of the secondary battery cell 20, and compensating for the energy density loss caused by mixing lithium-containing transition metal oxides and lithium-containing transition metal phosphates. As a result, the safety performance of the secondary battery cell 20 is improved while the energy density of the secondary battery cell 20 is increased.

[0082] In one embodiment, the fixing member 28 has a second end surface 282 facing away from the first wall 211 , and the first end surface 2211 exceeds the second end surface 282 .

[0083] In such Figure 3-5 In the example shown, the first wall 211 is the end cover 213. The end cover 213 is provided with a first through hole 2111, which penetrates both sides of the end cover 213 along the thickness direction of the end cover 213. The electrode terminal 22 is inserted into the first through hole 2111 to install the electrode terminal 22 on the end cover 213, and the first through holes 2111 are extended from both ends of the electrode terminal 22. The electrode terminal 22 is installed on the end cover 213 in an insulated manner, that is, no electrical connection is formed between the electrode terminal 22 and the end cover 213.

[0084] Specifically, the first end face 2211 exceeds 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 surface farthest from the outer surface of the first wall 211 is the first end face 2211 of the electrode terminal 22.

[0085] The outer peripheral surface of the main body 221 may refer to the outer peripheral surface of a cylinder, or may refer to the peripheral surface of a prism connecting the top surface and the bottom surface of the prism. Taking the main body 221 as a quadrangular prism as an example, the main body 221 includes a top surface, a bottom surface and four side surfaces, the four side surfaces are sequentially connected and arranged around the top surface, and the four side surfaces are respectively connected to the top surface and the bottom surface at both ends in the direction from the top surface to the bottom surface. The above four side surfaces refer to the outer peripheral surface of the main body 221. In some embodiments, the first end surface 2211 is provided with a first groove 2212, and the side surface of the first groove 2212 may also be referred to as the outer peripheral surface of the main body 221. In this embodiment, the main body 221 is shaped like a "convex" character. In some embodiments, the step portion 222 has a third end surface 2221 facing away from the first wall 221.

[0086] The outer contour of the fixing member 28 may include, but is not limited to, circular, elliptical, polygonal, semicircular, etc. The fixing member 28 is made of metal material, for example, aluminum, copper, iron, steel, alloy or composite metal. The step portion 222 may be continuously distributed along the circumference of the main body 221, that is, in a ring shape. It may also be arranged in segments along the circumference of the main body 221, that is, divided into multiple parts, at least one part of which abuts against the fixing member 28. The first through hole 2111 and the second through hole 281 may be light holes or segmented step holes. In the embodiment where the first through hole 2111 and the second through hole 281 are step holes, the cross section of the step hole may include at least one straight line segment and / or at least one oblique line segment and / or at least one arc segment.

[0087] In this embodiment, by making the first end face 2211 of the electrode terminal 22 exceed the second end face 282 of the fixing member 28, in the thickness direction of the first wall 211, the surface of the secondary battery cell 20 that exceeds the maximum height of the outer surface of the first wall 211 is the first end face 2211, eliminating the use of riveting blocks, and making the height of the secondary battery cell 20 exceeding the first wall 211, that is, the height of the electrode terminal 22 protruding from the first wall, further reducing the proportion of the structure outside the shell 21 of the secondary battery cell 20 to the total space of the secondary battery cell 20, thereby improving the energy density of the secondary battery cell 20. Figure 3-5 In the example of , 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.

[0088] Please continue to see Figure 5 In one embodiment, in the thickness direction of the first wall 211 , a height H2 between the first end surface 2211 and the second end surface 282 satisfies: 0.5 mm ≤ H2 ≤ 1.5 mm.

[0089] Specifically, H2 can be 0.5mm, 0.6mm, 0.7mm, 0.8mm, 0.9mm, 1mm, 1.1mm, 1.2mm, 1.3mm, 1.4mm, 1.5mm, or a value thereof within the range obtained by combining any two of the above 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 as much as possible.

[0090] In one embodiment, in the radial direction of the main body 221 , a dimension W1 of the step portion 222 protruding from the outer circumferential surface of the main body 221 satisfies: 0.1 mm≤W1≤5 mm.

[0091] 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 its value is within the range obtained by combining any two of the above values. By controlling the size of the step portion 222 protruding from the outer peripheral surface of the main body 221 within a suitable range, it is beneficial to increase the contact area between the step portion 222 and the fixing member 28, and then it is beneficial to improve the connection strength between the step portion 222 and the fixing member 28.

[0092] Figure 7 and Figure 8 It is a cross-sectional schematic diagram of a laminated electrode assembly. Fig. 9 FIG. 1 is a cross-sectional schematic diagram of a wound electrode assembly. For ease of explanation, the pole ears included in each pole piece are not shown here. Figure 7-9 As shown, the electrode assembly 10 specifically includes a positive electrode sheet 11 and a negative electrode sheet 12 and a separator 13 disposed between the positive electrode sheet 11 and the negative electrode sheet 12 .

[0093] In one embodiment, Figure 7 As shown in the figure, the electrode assembly 10 is a laminated electrode assembly. The electrode assembly 10 includes a plurality of positive electrode sheets 11 and a plurality of negative electrode sheets 12; the plurality of positive electrode sheets 11 and the plurality of negative electrode sheets 12 are alternately stacked in the direction indicated by the arrows in the figure. In another embodiment, as shown in the figure Figure 8 As shown, the electrode assembly 10 includes a plurality of positive electrode sheets 11 and negative electrode sheets 12, the negative electrode sheets 12 may include at least one bending section and a plurality of stacking sections, each bending section is used to connect two stacking sections, and the plurality of positive electrode sheets 11 and the plurality of stacking sections of the negative electrode sheets 12 are alternately stacked in the direction indicated by the arrow in the figure to form another stacked electrode assembly 10. Alternatively, the electrode assembly 10 includes a plurality of negative electrode sheets 12 and positive electrode sheets 11, the positive electrode sheets 11 may include at least one bending section and a plurality of stacking sections, each bending section is used to connect two stacking sections, and the plurality of negative electrode sheets 12 and the plurality of stacking sections of the positive electrode sheets 11 are alternately stacked in the direction indicated by the arrow in the figure to form another stacked electrode assembly 10.

[0094] In one embodiment, Fig. 9 As shown, the electrode assembly 10 may also be a wound electrode assembly. The positive electrode sheet 11 , the separator 13 and the negative electrode sheet 12 of the electrode assembly 10 are wound to form the electrode assembly 10 .

[0095] According to the present application, the electrode assembly 10 is preferably a laminated electrode assembly. Compared with a wound electrode assembly, a laminated electrode assembly has a higher space utilization rate inside the housing 21 of the secondary battery cell 20. When the housing 21 is the same, the laminated electrode assembly can accommodate more active materials in the housing, thereby further improving the energy density of the secondary battery cell 20.

[0096] Fig.10 It is a partial schematic diagram of a secondary battery cell 20 in the electrode terminal 22 area of ​​the present application.

[0097] refer to Figure 1-2 , 4, 10, in one embodiment, the electrode assembly 10 includes a main body 101 and a tab 102, and the tab 102 is connected to one end of the main body 101 facing the first wall 211. The secondary battery cell 20 includes a current collecting member 24, which is disposed between the first wall 211 and the main body 101, and 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.

[0098] Specifically, the main body 101 of the electrode assembly 10 is the main area where the electrochemical reaction of the electrode assembly 10 occurs in the secondary battery cell 20. The main body 101 is a layout formed by winding or stacking the area of ​​the positive electrode plate 11 coated with the positive electrode active material, the separator, and the area of ​​the negative electrode plate 12 coated with the negative electrode active material. The tab 102 is used to output or input the positive or negative electrode of the electrode assembly 10. The tab 102 is used to connect to the electrode terminal 22 to achieve electrical connection between the electrode assembly 10 and the electrode terminal 22. It should be noted that the tab 102 of the electrode assembly 10 is a component formed by stacking and connecting the areas on the positive electrode plate 11 that are not coated with the positive electrode active material or a component formed by stacking and connecting the areas on the negative electrode plate 12 that are not coated with the negative electrode active material. If the tab 102 is used for the positive electrode of the output electrode assembly 10, the tab 102 is a component formed by the regions on the positive electrode sheet 11 that are not coated with the positive electrode active material being stacked and connected to each other; if the tab 102 is used for the negative electrode of the output electrode assembly 10, the tab 102 is a component formed by the regions on the negative electrode sheet 12 that are not coated with the negative electrode active material being stacked and connected to each other. Exemplarily, the tab 102 is connected to one end of the body 101 facing the end cover 213 in the thickness direction X of the end cover 213.

[0099] The current collecting component 24 serves to connect the electrode terminal 22 and the tab 102 to achieve electrical connection between the electrode assembly 10 and the electrode terminal 22. Exemplarily, the material of the current collecting component 24 can be various, such as copper, iron, aluminum, steel, aluminum alloy, etc. The connection structure between the current collecting component 24 and the electrode terminal 22 can be various, such as welding, abutment or bonding, etc. Similarly, the connection structure between the current collecting component 24 and the tab 102 can also be various, such as welding or abutment, etc. There are two electrode terminals 22 and two current collecting components 24, and the two current collecting components 24 are arranged at intervals along the first direction Z. Each electrode terminal 22 is connected to the electrode assembly 10 through a current collecting component 24 to output the positive and negative electrodes of the secondary battery cell 20. As shown Fig.10 As shown, the current collecting member 24 may further include a bending portion 243 , and the first connection portion 241 and the second connection portion 242 are connected via the bending portion 243 .

[0100] In the present embodiment, by setting the thickness S1 of the first connection portion 241 of the current collecting member 24 to be greater than the thickness S2 of the second connection portion 242, the thickness of the area where the current collecting member 24 is connected to the electrode terminal 22 is greater than the thickness of the area where the current collecting member 24 is connected to the pole tab 102. Since the thickness requirement of the area where the current collecting member 24 is connected to the pole tab 102 is less than the thickness requirement of the area where the current collecting member 24 is connected to the electrode terminal 22, the thickness of the current collecting member 24 can be effectively optimized while the current collecting member 24 can be connected to the electrode terminal 22 and the pole tab 102, so as to reduce the overall weight of the current collecting member 24, save the space occupied by the current collecting member 24, and thus optimize the weight and internal space utilization of the secondary battery cell 20. In addition, 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 area of ​​the current collecting member 24 used to connect to the pole ear 102 can be further reduced, so that the thickness of the current collecting member 24 can be further optimized to reduce the overall weight of the current collecting member 24 and save the space occupied by the current collecting member 24, which is beneficial to further reduce the weight of the secondary battery cell 20 and improve the internal space utilization of the secondary battery cell 20, thereby improving the energy density of the secondary battery cell 20.

[0101] In one embodiment, the thickness S1 of the first connection portion 241 satisfies: 0.5 mm ≤ S1 ≤ 1.2 mm; and / or the thickness S2 of the second connection portion 242 satisfies: 0.3 mm ≤ S2 ≤ 1 mm.

[0102] 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, 1.2mm, or a value within the range obtained by combining any two of the above 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, 1mm, or a value within the range obtained by combining any two of the above values.

[0103] In this embodiment, by setting the thickness of the first connection part 241 and the thickness of the second connection part 242 within a suitable range, on the one hand, the structural strength of the first connection part 241 and the second connection part 242 can be improved, so that the first connection part 241 and the second connection part 242 have sufficient thickness to be connected to the electrode terminal 22 and the pole tab 102, which is conducive to improving the connection stability and reliability between the first connection part 241 and the second connection part 242 and the electrode terminal 22 and the pole tab 102, and reducing the phenomenon of insufficient overcurrent between the current collecting component 24 and the electrode terminal 22, and between the current collecting component 24 and the pole tab 102. On the other hand, the connection difficulty between the first connection part 241 and the electrode terminal 22, and between the second connection part 242 and the pole tab 102 can be reduced, and the space occupied by the current collecting component 24 in the housing 21 can be reduced, which is conducive to improving the energy density of the secondary battery cell 20.

[0104] In some other implementations, the current collecting member 24 may be omitted and the electrode tab 102 may be directly connected to the electrode terminal 22 .

[0105] In one embodiment, the average particle size D1 of the particles containing the lithium transition metal oxide satisfies: 2 μm≤D1≤5 μm.

[0106] 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 its value is within the range obtained by combining any two of the above values.

[0107] According to the present application, the smaller the average particle size of the lithium-containing transition metal oxide, the better its structural stability, which is more conducive to the safety performance of the secondary battery cell 20. At the same time, if the average particle size of the lithium-containing transition metal oxide particles is too small, the side reactions between the particles and the electrolyte may increase, which is not conducive to the safety performance of the secondary battery cell 20. Therefore, this embodiment can further improve the safety performance of the secondary battery cell 20 by controlling the average particle size of the lithium-containing transition metal oxide particles within a suitable range.

[0108] In one embodiment, the lithium-containing transition metal oxide comprises: 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.

[0109] Specifically, some M elements may be doped into the lithium-containing transition metal oxide. The doping of the M elements helps to improve the structural stability of the lithium-containing transition metal oxide, thereby helping to improve the safety performance of the secondary battery cell 20 .

[0110] In one embodiment, based on the total mass of the positive electrode active material, the mass content m2 of the lithium-containing transition metal oxide satisfies: 30 wt %≤m2≤60 wt %.

[0111] Specifically, m2 can be 30wt%, 32wt%, 34wt%, 36wt%, 38wt%, 40wt%, 42wt%, 44wt%, 46wt%, 48wt%, 50wt%, 52wt%, 54wt%, 56wt%, 58wt%, 60wt%, or any value within the range obtained by combining any two of the above values. m1+m2=100wt%.

[0112] In one embodiment, the average particle size D2 of the particles containing the lithium transition metal phosphate satisfies: 0.5 μm≤D2≤1.5 μm.

[0113] Specifically, D2 may be 0.5 μm, 0.6 μm, 0.7 μm, 0.8 μm, 0.9 μm, 1 μm, 1.1 μm, 1.2 μm, 1.3 μm, 1.4 μm, 1.5 μm, or a value within the range obtained by combining any two of the above values.

[0114] According to the present application, when the average particle size of the lithium-containing transition metal oxide particles is in the range of 0.5μm-1.5μm, by combining them with 2μm-5μm lithium-containing transition metal phosphate, the safety performance of the secondary battery cell 20 can be improved while the compaction density of the positive electrode plate can be increased, thereby further improving the energy density of the secondary battery cell 20.

[0115] In one embodiment, the lithium-containing transition metal phosphate comprises: 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.

[0116] In one embodiment, the positive electrode sheet 11 satisfies at least one of the following conditions: (1) the compaction density ρ1 of the positive electrode sheet 11 satisfies: 2.5 g / cm 3 ≤ρ1≤2.9g / cm 3 ; (2) The single-sided coating weight CW1 of the positive electrode film meets the following requirements: 190 g / m 2 ≤CW1≤230g / m 2 ; (3) The thickness h1 of the positive electrode current collector satisfies: 10μm≤h1≤13μm.

[0117] 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 , or its value is within the range obtained by combining any two of the above values. 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, 13μm, or its value is within the range obtained by combining any two of the above values.

[0118] According to the present application, the coating weight of the film layer on the pole piece and the compaction density of the pole piece have a certain influence on the lithium ion dynamics during the cycle of the secondary battery cell 20. The greater the coating weight of the film layer and the greater the compaction density of the pole piece, the worse the lithium ion dynamics. Insufficient lithium ion dynamics may cause polarization of the secondary battery cell 20, and then lithium precipitation occurs, affecting the safety performance of the secondary battery cell 20. However, if the coating weight of the film layer is too small and the compaction density of the pole piece is too small, it is not conducive to the energy density of the secondary battery cell 20. The aforementioned pole piece can be a positive pole piece or a negative pole piece. The aforementioned film layer can be a positive electrode film layer or a negative electrode film layer.

[0119] According to the present application, the thinner the thickness of the current collector is, the more conducive it is to reducing the thickness of the pole piece, thereby improving the energy density of the secondary battery cell 20. Too thin a current collector is not conducive to the mechanical strength of the pole piece, and may break during the processing or use of the secondary battery cell 20. The aforementioned current collector can be a positive electrode current collector or a negative electrode current collector.

[0120] Therefore, this embodiment can make the secondary battery cell 20 have both high energy density and good safety performance by controlling the coating weight of the positive electrode film layer, the compacted surface density of the positive electrode sheet 11, and the thickness of the positive electrode collector within a suitable range.

[0121] In one embodiment, the negative electrode sheet 12 includes a negative electrode current collector and a negative electrode film layer disposed on at least one surface of the negative electrode current collector, and the negative electrode film layer includes a negative electrode active material.

[0122] In one embodiment, the negative electrode sheet 12 satisfies at least one of the following conditions: (4) The compaction density ρ2 of the negative electrode sheet 12 satisfies: 1.3 g / cm 3 ≤ρ2≤1.55g / cm 3 ; (5) The single-sided coating weight CW2 of the negative electrode film layer meets the following requirements: 90 g / m 2 ≤CW2≤110g / m 2 ; (6) The thickness h2 of the negative electrode collector satisfies: 4μm≤h2≤6μm.

[0123] Specifically, ρ2 can be 1.3 g / cm 3 , 1.32g / cm 3 , 1.34g / cm 3 , 1.35g / cm 3 , 1.36g / cm 3 , 1.38g / cm 3 , 1.4g / cm 3 , 1.42g / cm 3 , 1.44g / cm 3 , 1.46g / cm 3, 1.48g / 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 , or its value is within the range obtained by combining any two of the above values. h2 can be 4μm, 4.2μm, 4.4μm, 4.6μm, 4.8μm, 5μm, 5.2μm, 5.4μm, 5.6μm, 5.8μm, 6μm, or its value is within the range obtained by combining any two of the above values.

[0124] Similar to the positive electrode sheet 11 , in this embodiment, by controlling the coating weight of the negative electrode film layer, the compacted surface density of the negative electrode sheet 12 , and the thickness of the negative electrode collector within a suitable range, the secondary battery cell 20 can have both high energy density and good safety performance.

[0125] In one embodiment, the negative electrode active material includes graphite.

[0126] In one embodiment, the average volume particle size Dv50 of the graphite satisfies: 10 μm≤Dv50≤14 μm.

[0127] 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 its value is within the range obtained by combining any two of the above values. The average volume particle size of graphite affects the capacity and lithium ion dynamics of the secondary battery cell 20. The smaller the average volume 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 dynamics of the secondary battery cell 20. If the average volume particle size of graphite is too small, the contact area between particles may be insufficient, the internal resistance of the battery cell may be increased, and the cycle performance of the secondary battery cell 20 may be affected. Therefore, this embodiment can help improve the capacity and cycle performance of the secondary battery cell 20 by controlling the average volume particle size of graphite within a suitable range.

[0128] In one embodiment, the secondary battery cell 20 includes an electrolyte, and the ion conductivity σ of the electrolyte satisfies: 7 mS / cm≤σ≤10 mS / cm.

[0129] Specifically, σ can be 7mS / cm, 7.5mS / cm, 8mS / cm, 8.5mS / cm, 9mS / cm, 9.5mS / cm, 10mS / cm, or a value thereof within the range obtained by combining any two of the above values. In this embodiment, selecting an electrolyte with higher ion conductivity helps to improve the lithium ion dynamics during the cycle of the secondary battery cell 20, helps to reduce the probability of polarization of the secondary battery cell 20, and improves the safety performance of the secondary battery cell 20.

[0130] In one embodiment, the electrolyte includes: a solvent, the solvent includes a linear carbonate; based on the total mass of the electrolyte, the mass content m2 of the linear carbonate satisfies 40wt%≤m3≤70wt%.

[0131] Specifically, m3 can be 40wt%, 45wt%, 50wt%, 55wt%, 60wt%, 65wt%, 70wt%, or a value thereof within the range obtained by combining any two of the above values. In this embodiment, by selecting a linear carboxylate as a solvent and controlling its mass content in the electrolyte within a suitable range, it helps to reduce the viscosity of the electrolyte, thereby helping to improve lithium ion dynamics.

[0132] In one embodiment, the electrolyte includes: a lithium salt, the lithium salt includes LiPF6 and LiFSI; based on the total mass of the electrolyte, the mass content m4 of the lithium salt satisfies 13wt%≤m4≤18wt%.

[0133] Specifically, m4 can be 13wt%, 14wt%, 15wt%, 16wt%, 17wt%, 18wt%, or a value thereof within the range obtained by combining any two of the above values.

[0134] In this embodiment, by selecting LiPF6 and LiFSI as lithium salts and controlling the mass content of the lithium salts within an appropriate range, the electrolyte can have a higher ionic conductivity and an appropriate viscosity, which helps to improve the lithium ion conductivity of the electrolyte, thereby helping to improve the lithium ion dynamics during the cycle of the secondary battery cell 20 and improve the safety performance of the secondary battery cell 20.

[0135] In one embodiment, based on the total amount of the lithium salt, the molar content n of LiPF6 satisfies: 50%≤n≤70%.

[0136] Specifically, it can be 50%, 55%, 60%, 65%, 70%, or any value within the range obtained by combining any two of the above values. Too high a concentration of LiFSI may corrode the aluminum foil. In this embodiment, by controlling the molar content of LiPF6 in the lithium salt within a relatively high range, the corrosion of the aluminum foil can be reduced and the safety performance of the secondary battery cell 20 can be improved.

[0137] Next, taking a lithium-ion battery as a specific example, the positive electrode sheet 11, the negative electrode sheet 12, the separator 13 and the electrolyte in the secondary battery cell 20 are described in detail. It should be understood that the lithium-ion battery is only used as 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, lithium-sulfur batteries, etc.

[0138] [Negative electrode]

[0139] The negative electrode sheet 12 generally includes a negative electrode current collector and a negative electrode film layer disposed on at least one surface of the negative electrode current collector. The negative electrode film layer includes a negative electrode active material.

[0140] As an example, the negative electrode current collector has two surfaces opposite to each other in its thickness direction, and the negative electrode film layer is disposed on any one or both of the two opposite surfaces of the negative electrode current collector.

[0141] In one embodiment, the negative electrode current collector may be a metal foil or a composite current collector. For example, as the metal foil, a copper foil may be used. The composite current collector may include a polymer material base layer and a metal layer formed on at least one surface of the polymer material substrate. The composite current collector may be formed by forming a metal material (copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer material substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0142] In one embodiment, the negative electrode active material may adopt the negative electrode active material for batteries known in the art. 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, lithium titanate, etc. The silicon-based material may be selected from at least one of elemental silicon, silicon oxide compounds, silicon-carbon composites, silicon-nitrogen composites, and silicon alloys. The tin-based material may be selected from at least one of elemental tin, tin oxide compounds, and tin alloys. However, the present application is not limited to these materials, and other traditional 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.

[0143] In one embodiment, the negative electrode film layer further includes a binder. The binder can 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).

[0144] In one embodiment, the negative electrode film layer further includes a conductive agent, which can be selected from at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene and carbon nanofibers.

[0145] In one embodiment, the negative electrode film layer further includes other additives, such as a thickener (eg sodium carboxymethyl cellulose (CMC-Na)).

[0146] In one embodiment, the negative electrode sheet 12 can be prepared in the following manner: the components for preparing the negative electrode sheet are formed into a negative electrode slurry. For example, the negative electrode active material, the conductive agent, the binder and any other components are dispersed in a solvent (such as N-methylpyrrolidone) to form a negative electrode slurry. Then, the negative electrode slurry is coated on the negative electrode current collector, and after drying, cold pressing and other processes, the negative electrode sheet 12 can be obtained.

[0147] [Positive electrode]

[0148] The positive electrode sheet 11 includes a positive electrode current collector and a positive electrode film layer disposed on at least one surface of the positive electrode current collector, wherein the positive electrode film layer includes a positive electrode active material.

[0149] As an example, the positive electrode current collector has two surfaces opposite to each other in its thickness direction, and the positive electrode film layer is disposed on any one or both of the two opposite surfaces of the positive electrode current collector.

[0150] In one embodiment, the positive electrode current collector may be a metal foil or a composite current collector. For example, aluminum foil may be used as the metal foil. The composite current collector may include a polymer material base and a metal layer formed on at least one surface of the polymer material base. The composite current collector may be formed by forming a metal material (aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer material substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0151] In another embodiment, examples of lithium-containing transition metal oxides may include, but are not limited to, lithium cobalt oxide (e.g., LiCoO2), lithium nickel oxide (e.g., LiNiO2), lithium manganese oxide (e.g., LiMnO2, LiMn2O4), lithium nickel cobalt oxide, lithium manganese cobalt oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide (e.g., LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2 (also referred to as NCM333), LiNi 0.5 Co 0.2 Mn 0.3 O2 (also referred to as NCM523), LiNi 0.5 Co 0.25 Mn 0.25 O2 (also referred to as NCM211), LiNi 0.6 Co 0.2 Mn 0.2 O2 (also referred to as NCM622), LiNi 0.8 Co 0.1 Mn 0.1 O2 (also referred to as NCM811), lithium nickel cobalt aluminum oxide (such as LiNi 0.85 Co 0.15 Al 0.05O2) and at least one of its modified compounds. Examples of lithium-containing transition metal phosphates with an olivine structure may include, but are not limited to, lithium iron phosphate (such as LiFePO4 (also referred to as LFP)), a composite material of lithium iron phosphate and carbon, lithium manganese phosphate (such as LiMnPO4), a composite material of lithium manganese phosphate and carbon, lithium iron manganese phosphate, and at least one of a composite material of lithium iron manganese phosphate and carbon. The battery is accompanied by the deintercalation and consumption of Li during the charging and discharging process, and the molar content of Li in the positive electrode active material is different when the battery is discharged to different states. In the enumeration of positive electrode active materials in this application, the molar content of Li is the initial state of the material, that is, the state before feeding. The positive electrode active material is used in the battery system, and the molar content of Li will change after charge and discharge cycles. In the enumeration of positive electrode active materials in this application, the molar content of O is only an ideal state value. The release of lattice oxygen will cause the molar content of O to change, and the actual molar content of O will fluctuate.

[0152] 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.

[0153] 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), vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorine-containing acrylate resin.

[0154] 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 of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, graphene and carbon nanofibers.

[0155] In one embodiment, the positive electrode sheet 11 can be prepared in the following manner: the components for preparing the positive electrode sheet are respectively formed into positive electrode slurries. For example, the positive electrode active material, the conductive agent, the binder and any other components are dispersed in a solvent (such as N-methylpyrrolidone) to form a positive electrode slurry. Then, the positive electrode slurry is coated on the positive electrode current collector, and after drying, cold pressing and other processes, the positive electrode sheet 11 can be obtained.

[0156] [Electrolyte]

[0157] The electrolyte plays a role in conducting ions between the positive electrode plate 11 and the negative electrode plate 12. The present application has no specific restrictions on the type of electrolyte, which can be selected according to needs. For example, the electrolyte can be liquid, gel or all-solid.

[0158] In some embodiments, the electrolyte is an electrolyte solution. The electrolyte solution includes an electrolyte salt and a solvent. Some solutions of the electrolyte solution have been mentioned above.

[0159] In addition to the aforementioned scheme, in some embodiments, the electrolyte salt can 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 difluorooxalatoborate, lithium dioxalatoborate, lithium difluorodioxalatophosphate and lithium tetrafluorooxalatophosphate.

[0160] In some embodiments, the solvent may also be selected from at least one of ethylene carbonate, propylene carbonate, ethyl methyl carbonate, diethyl carbonate, dimethyl carbonate, dipropyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, butylene carbonate, fluoroethylene carbonate, methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate, 1,4-butyrolactone, cyclopentane sulfone, dimethyl sulfone, methyl ethyl sulfone and diethyl sulfone.

[0161] In some embodiments, the electrolyte may further include additives, such as negative electrode film-forming additives, positive electrode film-forming additives, and additives that can improve certain battery properties, such as additives that improve battery overcharge performance, additives that improve battery high or low temperature performance, etc.

[0162] [Isolation film]

[0163] The present application has no particular limitation on the type of the isolation membrane 13 . For example, any known isolation membrane with a porous structure having good chemical stability and mechanical stability may be selected.

[0164] In some embodiments, the isolation film 13 includes a porous substrate, and the material of the porous substrate can be selected from at least one of glass fiber, non-woven fabric, polyethylene, polypropylene and polyvinylidene fluoride. The porous substrate can 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 can be the same or different, without particular limitation.

[0165] In some embodiments, the isolation film 13 further includes a porous coating layer, which can play a role of heat resistance and / or adhesion.

[0166] In some embodiments, the porous coating layer includes heat-resistant particles. The heat-resistant particles may include at least one of inorganic particles and organic particles.

[0167] In some embodiments, the inorganic particles may include one or more of inorganic particles having a dielectric constant of 5 or more, inorganic particles having ion conductivity but not storing ions, or inorganic particles capable of electrochemical reactions.

[0168] In some embodiments, the inorganic particles having a dielectric constant of 5 or more may include boehmite, aluminum oxide, barium sulfate, magnesium oxide, magnesium hydroxide, silicon oxide, 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, hectorite, Pb(Zr,Ti)O3 (abbreviated as PZT), Pb1-mLamZr1-nTinO3 (abbreviated as PLZT, 0<m<1, 0<n<1), Pb(Mg3Nb 2 / 3 )O3-PbTiO3 (abbreviated as PMN-PT), and one or more of their respective modified inorganic particles. Optionally, the modification of each inorganic particle can be chemical modification and / or physical modification.

[0169] In some embodiments, inorganic particles having ion conductivity but not storing ions may include Li3PO4, lithium titanium phosphate, Li x1 Ti y1 (PO4)3, Lithium Aluminum Titanate Phosphate Li x2 Al y2 Ti z1 (PO4)3, (LiAlTiP) x3 O y3 Type glass, lanthanum titanate lithium Li x4 La y4 TiO3, Lithium Germanium Phosphate Thiophosphate x5 Ge y5 P z2 S w 、Lithium Nitride Li x6 N y6 、SiS2 glass Li x7 Si y7 S z3 and P2S5 glass Li x8 P y8 S z4One or more of 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 isolation membrane.

[0170] In some embodiments, the inorganic particles capable of undergoing an electrochemical reaction 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.

[0171] In some embodiments, the organic particles may include at least one of a thermoplastic resin polymer, a thermosetting resin polymer, or a cross-linked polymer.

[0172] In some embodiments, the thermoplastic resin polymer may include one or more of polycarbonate organic particles, polymethyl methacrylate organic particles, polyoxymethylene organic particles, polyamide organic particles, styrene-acrylonitrile copolymer, polyphenylene sulfide organic particles, polyetheretherketone organic particles, polyimide organic particles, polysulfone organic particles, polyethersulfone organic particles, polyphenylene sulfone organic particles, polybenzimidazole organic particles, polyamideimide organic particles, and polyethyleneimine organic particles.

[0173] In some embodiments, the thermosetting resin polymer may include one or more of 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.

[0174] In some embodiments, the cross-linked polymer may include one or more of cross-linked styrene-based organic particles and silicon-containing organic cross-linked resin particles.

[0175] In some embodiments, the porous coating layer includes binder particles. The binder particles may include homopolymers or copolymers of acrylate monomer units, homopolymers or copolymers of acrylic acid monomer units, homopolymers or copolymers of styrene monomer units, polyurethane compounds, rubber compounds, homopolymers or copolymers of fluorinated olefin monomer units, homopolymers or copolymers of olefin monomer units, homopolymers or copolymers of unsaturated nitrile monomer units, homopolymers or copolymers of alkylene oxide monomer units, and one or more of the modified compounds of the above homopolymers or copolymers.

[0176] In some embodiments, the binder particles may include copolymers of acrylic acid ester monomer units and styrene monomer units, copolymers of acrylic acid monomer units and styrene monomer units, copolymers of acrylic acid monomer units and acrylic acid ester monomer units and styrene monomer units, copolymers of styrene monomer units and unsaturated nitrile monomer units, copolymers of styrene monomer units and olefin monomer units and unsaturated nitrile monomer units, polytetrafluoroethylene, polychlorotrifluoroethylene, polyvinyl fluoride, polyvinylidene fluoride, polyethylene, polypropylene, polyacrylonitrile, polyethylene oxide, copolymers of different fluorine-containing olefin monomer units, copolymers of fluorine-containing olefin monomer units and vinyl monomer units, copolymers of fluorine-containing olefin monomer units and acrylic acid monomer units, copolymers of fluorine-containing olefin monomer units and acrylic acid ester monomer units, and one or more of the modified compounds of the above homopolymers or copolymers.

[0177] In some embodiments, the binder particles may include butyl acrylate-styrene copolymer, butyl methacrylate-isooctyl methacrylate copolymer, isooctyl methacrylate-styrene copolymer, methacrylate-methacrylic acid-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, 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 one or more of the modified compounds of the above copolymers.

[0178] In some embodiments, the coating may further include a dispersant, for example, may include but is not limited to one or more of dispersants such as alkylphenol polyoxyethylene ether, polyacrylic acid dispersants, and cellulose dispersants. As an example, the dispersant may include but is not limited to one or more of sodium carboxymethyl cellulose, sodium polyacrylate, and ammonium polyacrylate.

[0179] [Lithium-ion battery]

[0180] The present application embodiment provides a lithium-ion battery, including the secondary battery cell 20 in the above embodiment. The lithium-ion battery can be a single physical module including 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, in parallel, or in mixed connection through a busbar component.

[0181] In some embodiments, the lithium-ion battery may be a battery pack. The lithium-ion battery includes a housing and secondary battery cells 20 . The secondary battery cells 20 or battery modules are accommodated in the housing.

[0182] In some embodiments, the box body can be used as a part of the chassis structure of the vehicle. For example, part of the box body can become at least a part of the floor of the vehicle, or part of the box body can become at least a part of the cross beam and longitudinal beam of the vehicle.

[0183] In some embodiments, the lithium-ion battery can be located in an energy storage device, which includes an energy storage container, an energy storage cabinet, and the like.

[0184] Fig.11 Schematic diagram of a lithium-ion battery according to an embodiment of the present application. Fig.11 As shown, the lithium-ion battery 30 may include a plurality of secondary battery cells 20 to meet different power requirements.

[0185] The lithium-ion battery 30 may also include a casing, the interior of which is a hollow structure, and a plurality of secondary battery cells 20 are accommodated in the casing. For example, a plurality of secondary battery cells 20 are connected in parallel, in series, or in a mixed combination and placed in the casing. The casing may include a first casing portion 301 and a second casing portion 302, which cover each other to form the casing. The shapes of the first casing portion 301 and the second casing portion 302 may be determined according to the shapes of the components accommodated therein, for example, they may be determined according to the shape of the combination of the plurality of secondary battery cells 20 accommodated therein, and at least one of the first casing portion 301 and the second casing portion 302 may have an opening. For example, as Fig.11 As shown, only one of the first box body 301 and the second box body 302 may be a hollow rectangular parallelepiped with an opening, and the other may be a plate-shaped to cover the opening. Taking the second box body 302 as a hollow rectangular parallelepiped with an opening, and the first box body 301 as a plate-shaped example, the first box body 301 covers the opening of the second box body 302 to form a box with a closed chamber, which can be used to accommodate multiple secondary battery cells 20.

[0186] For example, unlike Fig.11As shown, the first box body 301 and the second box body 302 can both be hollow cuboids and each have an open face, the opening of the first box body 301 and the opening of the second box body 302 are arranged opposite to each other, and the first box body 301 and the second box body 302 are buckled together to form a box with a closed chamber, which can be used to accommodate multiple secondary battery cells 20. Multiple secondary battery cells 20 are connected in parallel, in series, or in mixed combination and placed in the box formed by the first box body 301 and the second box body 302 buckled together.

[0187] In some embodiments, the lithium-ion battery 30 may also include other components. For example, the lithium-ion battery 30 may also include a busbar component, which may be used to achieve electrical connection between multiple secondary battery cells 20, such as parallel connection, series connection, or mixed connection. Specifically, the busbar component may achieve electrical connection between the secondary battery cells 20 by connecting the electrode terminals of the secondary battery cells 20; or, the busbar component may also achieve electrical connection between the secondary battery cells 20 by connecting other components of the secondary battery cells 20. The busbar component may be fixed to the corresponding component of the secondary battery cell 20 by welding, for example, it may be fixed to the electrode terminal, the sealing structure, or the housing by welding, etc., and the embodiments of the present application are not limited thereto.

[0188] The secondary battery cells 20 can directly form a lithium-ion battery 30 , or can first form a battery module, and then multiple battery modules form a lithium-ion battery 30 .

[0189] [Electrical devices]

[0190] An embodiment of the present application provides an electrical device, comprising the lithium-ion battery described in the above embodiment.

[0191] The electrical device may be a vehicle, a mobile phone, a portable device, a laptop computer, a ship, a spacecraft, an electric toy, an electric tool, and the like. The vehicle may be a fuel vehicle, a gas vehicle, or a new energy vehicle, and the new energy vehicle may be a pure electric vehicle, a hybrid vehicle, or an extended-range vehicle, and the like; the spacecraft may include an airplane, a rocket, a space shuttle, and a spacecraft, and the like; the electric toy may include a fixed or mobile electric toy, such as a game console, an electric car toy, an electric ship toy, and an electric airplane toy, and the like; the electric tool may include a metal cutting electric tool, a grinding electric tool, an assembly electric tool, and an electric tool for railways, such as an electric drill, an electric grinder, an electric wrench, an electric screwdriver, an electric hammer, an impact drill, a concrete vibrator, and an electric planer, and the like. The embodiments of the present application do not impose any special restrictions on the above-mentioned electrical devices.

[0192] The present application provides an electrical device, which is a vehicle.

[0193] The vehicle can be a fuel vehicle, a gas vehicle or a new energy vehicle. The new energy vehicle can be a pure electric vehicle, a hybrid vehicle or an extended-range vehicle, etc. A motor, a controller and a lithium-ion battery 30 can be arranged inside the vehicle, and the controller is used to control the lithium-ion battery 30 to power the motor. For example, a lithium-ion battery 30 can be arranged at the bottom, front or rear of the vehicle. The lithium-ion battery 30 can be used to power the vehicle. For example, the lithium-ion battery 30 can be used as an operating power source for the vehicle, for the circuit system of the vehicle, for example, for the working power requirements during the start-up, navigation and operation of the vehicle. In another embodiment of the present application, the lithium-ion battery 30 can not only be used as an operating power source for the vehicle, but also as a driving power source for the vehicle, replacing or partially replacing fuel or natural gas to provide driving power for the vehicle.

[0194] Hereinafter, the embodiments of the present application will be described. The embodiments described below are exemplary and are only used to explain the present application, and should not be construed as limiting the present application. If no specific techniques or conditions are indicated in the embodiments, the techniques or conditions described in the literature in this area or the product specifications are used. If the manufacturer is not indicated in the reagents or instruments used, they are all conventional products that can be obtained commercially.

[0195] [Examples and Comparative Examples]

[0196] Example 1

[0197] (1) Preparation of negative electrode sheet

[0198] The negative electrode active material graphite, sodium carboxymethyl cellulose, styrene butadiene rubber and acetylene black are mixed in a mass ratio of 96:1:1:2, deionized water is added, and the mixture is stirred evenly in a mixer. Then the slurry is coated on a 6-micron thick copper foil, and after double-sided coating, it is dried in an oven at 120°C, cold pressed, and cut to obtain the negative electrode sheet. The single-sided coating weight of the negative electrode film layer CW2 = 99g / m 2 Among them, the Dv50 of graphite is 12μm.

[0199] (2) Preparation of positive electrode sheet

[0200] The positive electrode active material contains lithium transition metal phosphate LiMn 0.6 Fe 0.4 O4 and Li-containing layered metal oxides LiNi 0.65 Co 0.15 Mn 0.20O2, binder polyvinylidene fluoride PVDF, conductive agent acetylene black, carbon nanotubes are mixed in a mass ratio of 96.5:2:1:0.5 (wherein the mass ratio of lithium-containing transition metal phosphate and lithium-containing layered metal oxide is 1:1), NMP is added, and the mixture is stirred evenly in a mixer, and then the slurry is coated on a 12-micron thick aluminum foil, and after double-sided coating, it is dried in an oven, cold pressed, and cut to obtain a positive electrode sheet. The mass content of lithium-containing transition metal phosphate in the positive electrode active material is m1=50wt%, and the mass content of lithium-containing transition metal oxide is m2=50wt%; m1+m2=100wt%; the average particle size of the particles containing lithium transition metal oxide is D1=4μm, and the average particle size of the particles containing lithium transition metal phosphate is D2=0.8μm; the single-sided coating weight of the positive electrode film layer is CW1=215g / m 2 .

[0201] (3) Preparation of secondary battery monomers

[0202] The positive electrode sheet, the separator, and the negative electrode sheet are stacked in order to form a laminated electrode assembly, which is placed in a shell, injected with electrolyte, and then packaged to obtain a secondary battery cell. The electrolyte is an electrolyte with ethylene carbonate (EC) and diethyl carbonate (DEC) as solvents (volume ratio 1:2) and a lithium salt (LiPF6 and LiFSI, molar ratio 2:1) concentration of 1M. Figure 3-Figure 5 , the structural shell of the secondary battery cell includes a shell and an end cover, the end cover is the first wall of the secondary battery cell, the end cover is provided with a first through hole, the electrode terminal includes a main body and a step portion, the main body of the electrode terminal passes through the first through hole, a fixing is provided between the end cover and the step portion of the electrode terminal, and the fixing abuts against the step portion to fix the electrode terminal. Along the thickness direction of the end cover, the first end face of the main body away from the end cover is the farthest surface beyond the end cover. Thus, the distance between the first end face and the outer wall of the first wall (end cover) is H1=1.5mm, and the distance between the first end face and the second end face is H2=0.5mm. In the radial direction of the main body, the dimension W1=3mm of the step portion protruding from the outer peripheral surface of the main body. The shell part of the shell has a size of 50mm×194mm×110mm.

[0203] Example 2-3

[0204] Compared with the embodiment 1, the difference lies in that 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 beyond the second end face are different from those in the embodiment.

[0205] Embodiment 4-5

[0206] Compared with Example 1, the difference lies in that the mass content m1 of the lithium-containing transition metal phosphate and the mass content m2 of the lithium-containing transition metal oxide are different from those in Example 1.

[0207] Embodiment 6-7

[0208] Compared with Example 1, the difference lies in that the average particle size D1 of the particles containing the lithium transition metal oxide and the average particle size D2 of the particles containing the lithium transition metal oxide are different from those in Example 1.

[0209] Embodiment 8-9

[0210] Compared with Example 1, the difference is that the coating weight CW1 of the positive electrode film layer and the coating weight CW2 of the negative electrode film layer are different from those in Example 1.

[0211] Comparative Example 1

[0212] Compared with Example 1, the difference is that in Comparative Example 1, the height H1 between the first end surface and the outer wall of the first wall is too large.

[0213] Comparative Example 2

[0214] Compared with Example 1, the difference lies in the structure of the secondary battery cell. The shell of the secondary battery cell includes a shell and an end cap. The end cap is the first wall of the secondary battery cell. The end cap is provided with a first through hole, and the main body of the electrode terminal passes through the first through hole. The electrode terminal is protruding from the outside of the end cap and is provided with a rivet block. 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 away from the end cap is the farthest surface beyond the end cap. Therefore, the height H1 between the surface of the rivet block away from the end cap and the outer wall of the first wall (end cap) is 4 mm.

[0215] Comparative Example 3

[0216] Compared with Example 1, the difference is that in Comparative Example 3, the distance H1 between the first end surface and the outer wall of the first wall is too large and the mass content of the lithium-containing transition metal phosphate in the positive electrode active material is too small.

[0217] The product parameters and performance parameters of Examples 1-9 and Comparative Examples 1-3.

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

[0219] In Table 1, "H1" represents the height between the first end face and the outer wall of the first wall; "H2" represents the height between the first end face and the second end face; "m1" represents the mass content of lithium-containing transition metal phosphate in the positive electrode active material; "m2" represents the mass content of lithium-containing transition metal oxide in the positive electrode active material; "D1" represents the average particle size of the particles containing lithium transition metal oxide; "D2" represents the average particle size of the particles containing lithium transition metal phosphate; "CW1" represents the single-sided coating weight of the positive electrode film layer; "CW2" represents the single-sided coating weight of the negative electrode film layer; "T" represents the temperature at which thermal runaway occurs in the hot box test of the secondary battery cell 20; "VED" represents the volume energy density of the secondary battery cell 20.

[0220] According to the comparative analysis of the embodiment and the comparative example, compared with comparative examples 1-3, the embodiments all show a volume energy density that is better than comparative examples 1-3, and a thermal runaway temperature that is basically equivalent to or higher than that of embodiments 1-3. This shows that the embodiment has a thermal runaway temperature that is basically better than that of comparative examples 1-3 and also has a volume energy density that is higher than that of comparative examples 1-3. This proves that through the solution of the embodiment of the present application, the secondary battery cell 20 can have both high energy density and good safety performance.

[0221] According to the comparative analysis of Examples 1-5, it can be seen that, under the premise that the mass content of the lithium-containing transition metal phosphate is within the appropriate range, the greater the height H1 of the electrode terminal 22 protruding from the first wall 211, the smaller the volume energy density of the secondary battery cell 20. By increasing the proportion of the lithium-containing transition metal phosphate in the positive electrode active material, the thermal runaway temperature of the secondary battery cell 20 increases, the safety performance is improved, and the volume energy density decreases. According to the comparative analysis of Comparative Examples 1-2, it can be seen that adjusting the size of the electrode terminal 22 alone or adjusting the proportion of the positive electrode active material alone cannot achieve both safety performance and high energy density. This shows that by controlling the height of the electrode terminal 22 of the secondary battery cell 20 protruding from the first wall 211 within the range of 1.5mm-3mm, and controlling the mass content of the lithium-containing transition metal phosphate in the positive electrode active material within the range of 40wt%-70wt%, the secondary battery cell 20 can simultaneously take into account high energy density and good safety performance. In addition, the height of the electrode terminal 22 protruding from the first wall 211 is also limited by the mechanical parts processing technology, so there is a lower limit to the value of H1. If H1 is less than 1.5 mm, it is difficult to achieve in actual processing and mass production is difficult.

[0222] According to the comparative analysis of Examples 1, 6-7, 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. The possible reason is that the smaller the Dv50, the better the structural stability of the lithium-containing transition metal oxide, and the more stable the chemical reaction can be during the charge and discharge process of the secondary battery cell 20, and the probability of thermal runaway caused by the violent chemical reaction and large amount of heat release is lower. Therefore, regulating 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.

[0223] According to the comparative analysis of Examples 1, 8-9, when the material ratio and structural design of the secondary battery cell 20 are the same, the volume energy density of the secondary battery cell 20 can be further improved by increasing the coating weight of the electrode.

[0224] The following is a brief introduction to the test methods of the physical and chemical parameters and performance parameters involved in the embodiments of the present application. It should be understood that the following test methods are only examples, and other test methods known in the art may also be used for testing.

[0225] 1. Test method for mass content

[0226] The specific type of lithium-containing transition metal oxide is confirmed by the mass ratio of Ni, Co and Mn in CP-EDS, and the specific type of lithium-containing transition metal phosphate is confirmed by the mass ratio of Mn and Fe. Then, the mass content of lithium-containing transition metal oxide is calculated by the mass content of Ni and Co in the mixed ICP, and the mass content of lithium-containing transition metal phosphate is calculated by the mass content of Fe.

[0227] 2. Test method for element molar ratio

[0228] Test equipment: Inductively coupled plasma emission spectrometer (ICP).

[0229] Test method: Digestion: 1+1 aqua regia, digestion method: plate / acid digestion / microwave digestion (high temperature and high pressure ~ 200°C). Test the element mass fractions of nickel, cobalt, manganese and doping elements, calculate the molar amount based on the molar mass of each element, and finally normalize and calculate the molar ratio of nickel, cobalt and manganese.

[0230] 3. Test method for average particle size of particles

[0231] The particle morphology and size of the sample to be tested are obtained by SEM, and elemental analysis is performed based on the SEM mapping results. The lithium-containing transition metal phosphate particles and the lithium-containing transition metal oxide particles are distinguished by the differences in element types and contents (such as P element). The average particle size of the particles of the corresponding material can be calculated based on the number of each type of particles in the SEM image and the long diameter of each particle. Repeat the above process to obtain the average particle size of 20 samples to be tested, calculate the average value of the average particle size, and count it as the average particle size of the particles of the material.

[0232] 4.Dv50 test method

[0233] Testing equipment: particle size testing instrument.

[0234] Pretreatment: Take a clean beaker, add an appropriate amount of the sample to be tested, add a surfactant dropwise and then add a dispersant, and perform ultrasound at 120W / 5min to ensure that the sample is completely dispersed in the dispersant.

[0235] Test: After the sample is poured into the injection tower, it circulates with the solution to the test optical system. When the particles are irradiated by the laser beam, the particle size distribution characteristics (shading degree: 8-12%) can be obtained by receiving and measuring the energy distribution of the scattered light.

[0236] Calculation: Calculate the particle size at the 50% position on the volume particle size distribution curve from small to large, which is Dv50.

[0237] 5. Test method for pole piece compaction density

[0238] Take a unit area of ​​the electrode to be tested, weigh the mass m1 of the material on the unit area of ​​the electrode except the current collector, measure the electrode thickness T1 and the current collector thickness T0, and the compaction density = m1 / (T1-T0).

[0239] 6. Test method for film coating weight

[0240] Take a unit area of ​​the electrode to be tested and weigh the mass of the material other than the current collector on the unit area of ​​the electrode, that is, the coating weight.

[0241] 7. Test method for volume energy density of secondary battery cells

[0242] On the charging and discharging equipment, charge and discharge for 3 cycles at a current density of 0.33C in the range of 2.5-4.25V, and take the discharge energy Q of the 3rd cycle; measure the volume V of the secondary battery cell 20: take a CT scan image of the secondary battery cell 20, and based on the CT scan image, the length T, height h, width L, diameter d, height H and other data of the secondary battery cell 20 can be measured. The volume of the secondary battery cell 20 can be calculated by the formula V = T × h × L + 2 × π × (d / 2) 2×H, the energy density of the secondary battery cell 20 is Q / V (unit: Wh / L). If the shape of the electrode terminal is irregular, the volume of the electrode terminal can be calculated by fitting the irregular shape into a regular shape on a computer and then using the volume calculation formula of a regular shape.

[0243] 8. Safety performance test methods

[0244] The safety performance of the secondary battery cell 20 is characterized by a hot box test. The specific test process is: a fully charged secondary battery cell 20 is placed in an oven, and the temperature is raised from 30°C to 200°C at a temperature rise rate of 2°C / min, and the temperature is kept at 5°C for 30 minutes, and the temperature at which the secondary battery cell 20 catches fire, i.e., its failure temperature, is observed.

[0245] Although the present application has been described with reference to preferred embodiments, various modifications may be made thereto and parts thereof may be replaced with equivalents without departing from the scope of the present application. In particular, the various technical features mentioned in the various embodiments may be combined in any manner as long as there are no structural conflicts. The present 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 comprises: Housing, electrode assembly, electrode terminals and fixings; The electrode assembly is contained in the housing, the electrode assembly comprises a positive electrode sheet, the positive electrode sheet comprises a positive electrode active material, the positive electrode active material comprises a lithium-containing transition metal phosphate and a lithium-containing transition metal oxide, and based on the total mass of the positive electrode active material, the mass content m1 of the lithium-containing transition metal phosphate satisfies: 40wt%≤m1≤70wt%; The housing comprises a first wall, the first wall comprises a first through hole; the electrode terminal comprises a main body and a step portion, at least a portion of the main body is passed through the first through hole, the step portion protrudes from the outer peripheral surface of the main body, and the step portion is located on a side of the first wall facing the outside of the secondary battery cell; the fixing member comprises a second through hole for the main body to pass through; 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 main body has a first end surface facing away from the first wall, and in the thickness direction of the first wall, a height H1 between the first end surface and an 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 fixing member has a second end surface facing away from the first wall, and the first end surface exceeds the second end surface.

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

4. The secondary battery cell according to any one of claims 1 to 3, 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 any one of claims 1 to 4, characterized in that: The lithium-containing transition metal oxide comprises: 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 any one of claims 1 to 5, characterized in that: Based on the total mass of the positive electrode active material, the mass content m2 of the lithium-containing transition metal oxide satisfies: 30wt%≤m2≤60wt%.

7. The secondary battery cell according to any one of claims 1 to 6, characterized in that: The average particle size D2 of the particles containing the lithium transition metal phosphate satisfies: 0.5 μm≤D2≤1.5 μm.

8. The secondary battery cell according to any one of claims 1 to 7, characterized in that: The lithium-containing transition metal phosphate comprises: Li 1+a Mn b A 1-b P 1-c R c O4; Among them, -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 any one of claims 1 to 8, characterized in that: The positive electrode plate includes a positive electrode current collector and a positive electrode film layer disposed on at least one surface of the positive electrode current collector, and the positive electrode plate satisfies at least one of the following conditions: (1) The compaction density ρ1 of the positive electrode sheet satisfies: 2.5 g / cm 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 electrode current collector satisfies: 10 μm ≤ h1 ≤ 13 μm.

10. The secondary battery cell according to any one of claims 1 to 9, characterized in that: The secondary battery cell comprises a negative electrode plate, wherein the negative electrode plate comprises a negative electrode current collector and a negative electrode film layer disposed on at least one surface of the negative electrode current collector, wherein the negative electrode film layer comprises a negative electrode active material.

11. The secondary battery cell according to claim 10, characterized in that: The negative electrode sheet meets at least one of the following conditions: (4) The compaction density ρ2 of the negative electrode sheet satisfies: 1.3 g / cm 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: 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 volume particle size Dv50 of the graphite satisfies: 10 μm≤Dv50≤14 μm.

14. The secondary battery cell according to any one of claims 1 to 13, characterized in that: In the radial direction of the main body, a dimension W1 of the step portion protruding from the outer peripheral surface of the main body satisfies: 0.1 mm ≤ W1 ≤ 5 mm.

15. The secondary battery cell according to any one of claims 1 to 14, characterized in that: The electrode assembly is a laminated electrode assembly.

16. The secondary battery cell according to any one of claims 1 to 15, characterized in that: The electrode assembly comprises a main body and a tab, wherein the tab is connected to one end of the main body facing the first wall; The secondary battery cell includes a current collecting member, the current collecting member is disposed between the first wall and the main body, the current collecting member includes a first connecting portion and a second connecting portion connected to each other, the first connecting portion is connected to the electrode terminal, and the second connecting portion is connected to the electrode tab; Wherein, along the thickness direction of the current collecting member, the thickness S1 of the first connecting portion and the thickness S2 of the second connecting portion satisfy: S1-S2≥0.1 mm.

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

18. The secondary battery cell according to any one of claims 1 to 17, characterized in that: The secondary battery cell includes an electrolyte, and the ion conductivity σ of the electrolyte satisfies: 7mS / cm≤σ≤10mS / cm.

19. The secondary battery cell according to claim 18, characterized in that: The electrolyte comprises: a solvent, the solvent comprising a linear carbonate; 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 salt, the lithium salt comprising 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 comprises the secondary battery cell according to any one of claims 1 to 20.

22. An electrical device, characterized in that: The electrical device comprises the secondary battery cell according to any one of claims 1 to 20, and / or the lithium-ion battery according to claim 21.

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