Secondary battery cell and electric device

Abstract

Embodiments of the present application provide a secondary battery cell and an electric device. The secondary battery cell comprises an electrode assembly. The electrode assembly comprises a positive electrode sheet and a negative electrode sheet. The positive electrode sheet comprises a positive electrode active material; and the positive electrode active material comprises a lithium-containing phosphate and a lithium-containing transition metal oxide. The negative electrode sheet comprises a negative electrode active material; and the negative electrode active material comprises graphite. At 25°C, the discharge plateau voltage v of the secondary battery cell at a discharge rate of 1 / 3 C within a voltage range of 2.5-4.25 V satisfies: 3.6 V≤v≤3.67 V. The secondary battery cell provided by the present application can have both high energy density and good cycle performance.

Description

Secondary battery cells and electrical devices Cross-references to related applications

[0001] This patent document claims priority and benefit to Chinese Patent Application No. 202411648210.1, filed on November 18, 2024, entitled "Secondary Battery Cell and Electrical Device". The entire contents of the aforementioned patent application are incorporated herein by reference as a part of the disclosure of this patent document. Technical Field

[0002] This application relates to the field of batteries, and more specifically, to a secondary battery cell and an electrical device. Background Technology

[0003] In recent years, secondary batteries, mainly lithium-ion batteries, have been widely used in energy storage power systems such as hydropower, thermal power, wind power and solar power plants, as well as in many fields such as power tools, electric bicycles, electric motorcycles, electric cars, military equipment, and aerospace, thus achieving great development.

[0004] Improving the energy density of rechargeable battery cells is a key research focus for lithium-ion batteries. However, increasing energy density may negatively impact other performance characteristics of the rechargeable battery cells, such as cycle performance and safety. Therefore, balancing energy density and cycle performance in rechargeable battery cells has become a pressing technical challenge. Summary of the Invention

[0005] This application is made in view of the above-mentioned technical problems, and its purpose is to provide a secondary battery cell and an electrical device, wherein the secondary battery cell can effectively improve cycle performance under the premise of high energy density.

[0006] In a first aspect, a secondary battery cell is provided, the secondary battery cell comprising: an electrode assembly, the electrode assembly comprising a positive electrode and a negative electrode, the positive electrode comprising a positive active material, the positive active material comprising a lithium phosphate and a lithium transition metal oxide, the negative electrode comprising a negative active material, the negative active material comprising graphite; the secondary battery cell, at 25°C, has a discharge plateau voltage v within the voltage range of 2.5V-4.25V at a discharge rate of 1 / 3C, satisfying: 3.6V≤v≤3.67V.

[0007] In the embodiments of this application, the positive electrode active material includes both lithium phosphate and lithium transition metal oxide, the negative electrode active material includes graphite, and the discharge plateau voltage of the secondary battery cell is controlled within a specific range of 3.6V-3.67V. Thus, the secondary battery cell can effectively improve cycle performance under the premise of high energy density.

[0008] In some embodiments, the lithium-containing phosphate includes lithium-containing transition metal phosphates.

[0009] In some embodiments, the lithium-containing phosphate includes those with the molecular formula Li. 1+a Mn b A 1-b P 1-c R c One or more of the compounds of O4 or their modified compounds, -0.2≤a<1, 0.3≤b≤0.9, 0≤c≤0.1, A includes one or more of Zn, Al, Na, K, Mg, Mo, W, Ti, V, Zr, Fe, Ni, Co, Ga, Sn, Sb, Nb and Ge, and R includes one or more of B, Si, N, S, F, Cl and Br.

[0010] In some embodiments, the lithium-containing transition metal oxide comprises Li x Ni y Co z M k Me p O r E s Wherein, M includes one or more elements selected from Mn and Al, Me includes one or more elements selected from Zr, Zn, Cu, Cr, Mg, Fe, V, Ti, Sr, Sb, Y, W or Nb, and E includes one or more elements selected from N, F, S and Cl; 0.8≤x≤1.15, 0<y<1, 0<z<1, 0<k<1, 0≤p≤0.1, 1≤r≤2, 0≤s≤1.

[0011] In the embodiments of this application, by controlling the proportion of each metal element in lithium phosphate and lithium transition metal oxide within a suitable range, the discharge voltage platform of the secondary battery cell can be affected, so that the discharge voltage platform of the secondary battery cell is within the designed range.

[0012] In some embodiments, the volume distribution particle size Dv501 of the positive electrode active material satisfies: 1.5μm≤Dv501≤3μm.

[0013] In some embodiments, the lithium-containing phosphate satisfies at least one of the following conditions (1)-(2): (1) the lithium-containing phosphate includes one or more elements selected from Al, Ti, and V; (2) the lithium-containing phosphate includes a first lithium-containing phosphate and a second lithium-containing phosphate, wherein the volume distribution particle size Dv50 of the first lithium-containing phosphate is... 1-1 Satisfies: 0.05μm≤Dv50 1-1 ≤0.3μm; and / or, the volume distribution particle size Dv50 of the second lithium phosphate. 1-2 Satisfies: 1μm≤Dv501-2 ≤3μm; (3) The volume distribution particle size Dv50 of the lithium phosphate 1-3 Satisfies: 0.8μm≤Dv50 1-3 ≤1.2μm.

[0014] In some embodiments, the lithium-containing transition metal oxide satisfies at least one of the following conditions (1)-(4): (1) the volume distribution particle size Dv50 of the lithium-containing transition metal oxide. 1-4 Satisfies: 3μm≤Dv50 1-4 (2) The volume distribution particle size Dv101 of the lithium-containing transition metal oxide satisfies: 1.5μm≤Dv101≤2.5μm; (3) The volume distribution particle size Dv901 of the lithium-containing transition metal oxide satisfies: 7.5μm≤Dv901≤9.5μm; (4) The particle size distribution of the lithium-containing transition metal oxide satisfies: 0.95≤(Dv901-Dv101)≤5μm; 1-4 ) / Dv50 1-4 ≤1.5.

[0015] Having the particle size of lithium phosphate and / or lithium transition metal oxide within a suitable range helps to regulate the discharge voltage plateau of the secondary battery cell, keeping the discharge voltage plateau of the secondary battery cell within the designed range, thereby further improving the energy density and cycle performance of the battery.

[0016] In some embodiments, the mass content m1 of lithium phosphate, based on the total mass of the positive electrode active material, satisfies: 40% ≤ m1 ≤ 70%.

[0017] When the mass fraction of lithium phosphate in the positive electrode active material is within a suitable range, the discharge voltage platform of the secondary battery cell can be effectively adjusted within the design range, thereby further improving the energy density and cycle performance of the battery. At the same time, the structure of lithium phosphate is relatively stable and it is not easy to release oxygen during battery thermal runaway, thereby further improving the thermal safety performance of the battery.

[0018] In some embodiments, the positive electrode includes a conductive agent, the conductive agent including carbon nanotubes, and the diameter d of the carbon nanotubes satisfies: 7μm≤d≤13μm.

[0019] Using carbon nanotubes with a suitable diameter as a conductive agent can effectively construct a conductive network between the conductive agent and the positive electrode active material, thereby helping to improve the rate performance and cycle performance of secondary battery cells.

[0020] In some embodiments, the positive electrode sheet includes a positive current collector and a positive electrode film layer disposed on at least one surface of the positive current collector, the positive electrode film layer including the positive electrode active material.

[0021] In some embodiments, the coating weight ρ1 on one side of the positive electrode film layer satisfies: 190 g / m 2 ≤ρ1≤230g / m 2 .

[0022] In the embodiments of this application, by controlling the coating weight of the positive electrode film within a suitable range, it is possible to help improve the energy density of the secondary battery cell and also affect the discharge voltage plateau of the secondary battery cell, so that the discharge voltage plateau of the secondary battery cell is within the designed range.

[0023] In some embodiments, the compaction density P1 of the positive electrode film layer satisfies: 2.5 g / cm³ 3 ≤P1≤2.9g / cm 3 Optionally, 2.8 g / cm³ 3 ≤P1≤2.9g / cm 3 .

[0024] In the embodiments of this application, by controlling the compaction density of the positive electrode film within a suitable range, it is helpful to improve lithium-ion dynamics, thereby reducing the polarization of the secondary battery cell during cycling and helping to improve the cycle performance of the secondary battery cell.

[0025] In some embodiments, the thickness h1 of the positive current collector satisfies: 10μm≤h1≤13μm.

[0026] In the embodiments of this application, by controlling the thickness of the positive current collector within a suitable range, it is helpful to reduce the thickness of the positive electrode sheet and improve the energy density of the secondary battery cell.

[0027] In some embodiments, the average volumetric particle size Dv502 of the negative electrode active material satisfies: 10μm≤Dv502≤14μm.

[0028] In the embodiments of this application, controlling the average volume particle size of the negative electrode active material within a suitable range helps to improve lithium-ion dynamics and improve the rate performance and cycle performance of secondary battery cells.

[0029] In some embodiments, the negative electrode sheet includes a negative current collector and a negative electrode film layer disposed on at least one surface of the negative current collector, the negative electrode film layer including the negative electrode active material.

[0030] In some embodiments, the coating weight ρ2 on one side of the negative electrode film layer satisfies: 90 g / m 2 ≤ρ2≤110g / m 2 .

[0031] In the embodiments of this application, controlling the coating weight of the negative electrode film within a suitable range helps to improve the energy density of the secondary battery cell.

[0032] In some embodiments, the compaction density P2 of the negative electrode film layer satisfies: 1.3 g / cm³ 3 ≤P2≤1.55g / cm 3 Optionally, 1.4 g / cm³ 3 ≤P2≤1.5g / cm 3 .

[0033] In the embodiments of this application, by controlling the compaction density of the negative electrode film within a suitable range, it is helpful to improve lithium-ion kinetics, thereby reducing the polarization of the secondary battery cell during cycling and helping to improve the cycle performance of the secondary battery cell.

[0034] In some embodiments, the thickness h2 of the negative electrode current collector satisfies: 4μm≤h2≤6μm.

[0035] In the embodiments of this application, by controlling the thickness of the negative electrode current collector within a suitable range, it is helpful to reduce the thickness of the negative electrode sheet and improve the energy density of the secondary battery cell.

[0036] In some embodiments, the electrode assembly is a stacked electrode assembly.

[0037] In the embodiments of this application, by employing a stacked electrode assembly, the energy density of the secondary battery cell can be further improved.

[0038] In some embodiments, the secondary battery cell includes a housing, and the electrode assembly is housed within the housing; the housing includes a first wall, and electrode terminals are disposed on the first wall; the electrode assembly includes a body and a tab, the tab being connected to the end of the body facing the first wall; the secondary battery cell includes a current collector, the current collector including a first connecting portion and a second connecting portion connected to each other, the first connecting portion being connected to the electrode terminals, and the second connecting portion being connected to the tab; wherein, along the thickness direction of the first wall, the thickness D1 of the first connecting portion satisfies: 0.5mm≤D1≤1.2mm; the thickness D2 of the second connecting portion satisfies: 0.3mm≤D2≤1mm.

[0039] In the embodiments of this application, by controlling the thickness of the second connecting portion to be less than the thickness of the first connecting portion, the thickness of the area where the current collector is connected to the electrode terminal is greater than the thickness of the area where the current collector is connected to the tab. Since the thickness requirement of the area where the current collector is connected to the tab is less than the thickness requirement of the area where the current collector is connected to the electrode terminal, the thickness of the current collector can be effectively optimized while enabling the current collector to connect to the electrode terminal and the tab. This reduces the overall weight of the current collector and saves the space occupied by the current collector, thereby increasing the energy density of the secondary battery cell. Furthermore, the thicknesses of both the first and second connecting portions are controlled within a suitable range, which can improve the energy density of the secondary battery cell while satisfying the connection strength between the first connecting portion and the electrode terminal, and between the second connecting portion and the tab.

[0040] In some embodiments, the first wall includes a first through hole; the electrode terminal includes a main body portion and a stepped portion, at least a portion of the main body portion passing through the first through hole, the stepped portion protruding from the outer peripheral surface of the main body portion and disposed outside the secondary battery cell; the secondary battery cell includes a fixing member, the fixing member including a second through hole through which the main body portion passes; in the thickness direction of the first wall, at least a portion of the fixing member is located between the first wall and the stepped portion and abuts against the stepped portion, the main body portion has a first end face facing the outside of the secondary battery cell, the fixing member has a second end face facing the outside of the secondary battery cell, and the first end face extends beyond the second end face.

[0041] In the embodiments of this application, the surface of the secondary battery cell with the maximum height exceeding the outer surface of the first wall in the thickness direction of the first wall is the first end face. When using electrode terminals of the same specification, the height of the secondary battery cell exceeding the first wall can be reduced accordingly, thereby increasing the proportion of the space inside the secondary battery cell casing to the total space of the battery, and thus improving the energy density of the battery.

[0042] In some embodiments, in the thickness direction of the first wall, the height difference H between the first end face and the second end face satisfies: 0.5mm≤H≤1.5mm.

[0043] In the embodiments of this application, by controlling the height difference between the first end face and the second end face within a suitable range in the thickness direction of the first wall, the energy density of the battery can be improved while ensuring good connection stability between the first end face and the second end face.

[0044] In some embodiments, the step portion protrudes from the outer peripheral surface of the main body portion by a dimension W1 that satisfies the following condition: 0.1mm ≤ W1 ≤ 5mm.

[0045] In the embodiments of this application, by controlling the size of the step portion protruding from the outer peripheral surface of the main body within a suitable range, it is beneficial to increase the contact area between the step portion and the fastener, thereby improving the connection strength between the step portion and the fastener.

[0046] In some embodiments, the secondary battery cell includes an electrolyte, wherein the ionic conductivity σ of the electrolyte satisfies: 7mS / cm≤σ≤10mS / cm.

[0047] In the embodiments of this application, selecting an electrolyte with high ionic conductivity helps to improve lithium-ion kinetics during the cycling process of a secondary battery cell, thereby improving the cycle performance of the secondary battery cell.

[0048] In some embodiments, the electrolyte comprises a solvent, the solvent comprising linear carbonate; and the mass content m2 of the linear carbonate, based on the total mass of the electrolyte, satisfies 40wt% ≤ m2 ≤ 70wt%.

[0049] In the embodiments of this application, by selecting linear carboxylic acid esters as solvents and controlling their mass content in the electrolyte within a suitable range, it is helpful to reduce the viscosity of the electrolyte, thereby helping to improve lithium-ion kinetics.

[0050] In some embodiments, the electrolyte comprises a lithium salt, including LiPF6 and LiFSI; the mass content of the lithium salt m3, based on the total mass of the electrolyte, satisfies 13wt% ≤ m3 ≤ 18wt%.

[0051] In the embodiments of this application, by selecting LiPF6 and LiFSI as lithium salts, it is helpful to improve the lithium-ion conductivity and high-temperature resistance of the electrolyte, thereby helping to improve the lithium-ion kinetics during the cycle of the secondary battery cell and improve the cycle performance of the secondary battery cell.

[0052] In some embodiments, the molar percentage n of LiPF6, based on the total amount of the lithium salt, satisfies: 50% ≤ n ≤ 70%.

[0053] In the embodiments of this application, by controlling the molar content of LiPF6 in the lithium salt to be within a high range, it helps to form a stable SEI film on the surface of the negative electrode, thereby helping to improve the cycle performance of the secondary battery cell 20.

[0054] In some embodiments, the secondary battery cell includes a separator, the separator comprising a porous substrate, the thickness h3 of the porous substrate satisfying: h3≤7μm; optionally, 3μm≤h3≤5μm. Controlling the thickness of the porous substrate within the given range helps to further improve the energy density of the secondary battery cell.

[0055] In a second aspect, a secondary battery is provided, the secondary battery comprising a secondary battery cell in any of the implementable embodiments of the first aspect.

[0056] Thirdly, an electrical device is provided, the electrical device comprising a secondary battery cell in any of the implementable embodiments of the first aspect, and / or a secondary battery in the second aspect. Attached Figure Description

[0057] To more clearly illustrate the technical solutions of the embodiments of this application, the drawings used in the embodiments of this application will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on the drawings without creative effort.

[0058] Figure 1 is a cross-sectional schematic diagram of a stacked electrode assembly.

[0059] Figure 2 is a cross-sectional schematic diagram of another type of stacked electrode assembly.

[0060] Figure 3 is a cross-sectional schematic diagram of a wound electrode assembly.

[0061] Figure 4 is a schematic structural diagram of a secondary battery cell.

[0062] Figure 5 is an exploded view of the secondary battery cell shown in Figure 4.

[0063] Figure 6 is a partial schematic diagram of a secondary battery cell.

[0064] Figure 7 is a partial exploded view of a secondary battery cell.

[0065] Figure 8 is a partial cross-sectional view of a secondary battery cell.

[0066] Figure 9 is a schematic diagram of a local area in Figure 8.

[0067] Figure 10 is a schematic diagram of a secondary battery. Detailed Implementation

[0068] The embodiments of the secondary battery cell and power-consuming device of this application are hereby disclosed in detail with appropriate reference to the accompanying drawings. However, unnecessary detailed descriptions may be omitted. For example, detailed descriptions of well-known matters and repetitive descriptions of actually identical structures may be omitted. This is to avoid making the following description unnecessarily lengthy and to facilitate understanding by those skilled in the art. Furthermore, the accompanying drawings and the following description are provided to enable those skilled in the art to fully understand this application and are not intended to limit the subject matter of the claims.

[0069] The "range" disclosed in this application is defined by a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, which define the boundaries of a particular range. Ranges defined in this way can include or exclude endpoints and can be arbitrarily combined; that is, any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60-120 and 80-110 are listed for a specific parameter, it is expected that ranges of 60-110 and 80-120 are also included. Furthermore, if minimum range values ​​of 1 and 2 are listed, and if maximum range values ​​of 3, 4, and 5 are listed, then the following ranges are all expected: 1-3, 1-4, 1-5, 2-3, 2-4, and 2-5. In this application, unless otherwise stated, the numerical range "ab" represents a shortened representation of any combination of real numbers between a and b, where a and b are real numbers. For example, the numerical range "0-5" indicates that all real numbers between "0-5" have been listed in this article; "0-5" is simply a shortened representation of these numerical combinations. Furthermore, when a parameter is stated as an integer ≥2, it is equivalent to disclosing that the parameter is, for example, an integer such as 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0070] In the description of this application, it should be noted that, unless otherwise stated, "a plurality of" means two or more; the terms "upper," "lower," "left," "right," "inner," "outer," etc., indicating orientation or positional relationships are only for the convenience of describing this application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation on this application. Furthermore, the terms "first," "second," "third," etc., are used for descriptive purposes only and should not be construed as indicating or implying relative importance.

[0071] Unless otherwise specified, in this application, the phrase "A and / or B" means "A, B, or both A and B". More specifically, the condition "A and / or B" is satisfied by any of the following conditions: A is true (or exists) and B is false (or does not exist); A is false (or does not exist) and B is true (or exists); or both A and B are true (or exist).

[0072] Unless otherwise specified, all steps in this application may be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), indicating that the method may include steps (a) and (b) performed sequentially, or it may include steps (b) and (a) performed sequentially. For example, the mention that the method may also include step (c) indicates that step (c) may be added to the method in any order. For example, the method may include steps (a), (b), and (c), or it may include steps (a), (c), and (b), or it may include steps (c), (a), and (b), etc.

[0073] Unless otherwise specified, all embodiments and optional embodiments of this application can be combined to form new technical solutions.

[0074] Unless otherwise specified, the following terms have the following meanings. Any undefined terms have their technically accepted meanings.

[0075] If mentioned, "lithium-containing phosphates" refers to a class of salts that include lithium and phosphate ions.

[0076] When "lithium-containing phosphates" further include transition metals, they can be called "lithium-containing transition metal phosphates".

[0077] "Lithium-containing phosphates" can include, for example, lithium iron phosphate materials and lithium manganese iron phosphate materials.

[0078] As mentioned, "lithium-containing transition metal oxides" refers to a class of oxides that include lithium and transition metal elements. Structurally, this includes ternary materials with layered structures, such as LiCoO2 and LiNiO2, as well as LiMn2O4 with a spinel structure. Ternary materials refer to lithium transition metal oxides containing three different transition metal elements, such as lithium-containing nickel-cobalt-manganese oxides and lithium-containing nickel-cobalt-aluminum oxides. It should be understood that ternary materials can also be doped or coated with trace amounts of other transition metal elements; generally, ternary materials doped or coated with other transition metal elements are still considered ternary materials.

[0079] As mentioned, "discharge rate" refers to the current required for a single secondary battery cell to discharge its rated capacity within a specified time. It is numerically equal to a multiple of the rated capacity and is usually represented by the letter C. Discharge rate = Discharge current / Rated capacity. The discharge rate is a measure of how quickly a secondary battery cell discharges. For example, if a battery's rated capacity is discharged completely in 1 hour, the discharge rate of that secondary battery cell is 1C.

[0080] As mentioned, "discharge plateau voltage" refers to the voltage corresponding to the "plateau region" in the voltage-capacity or voltage-time curve under constant current discharge conditions. In the voltage-capacity or voltage-time curve during the discharge process, the voltage decreases rapidly as the discharge capacity or discharge time increases, then remains almost constant or changes very little, before rapidly decreasing to the cutoff voltage. The portion of the curve where the voltage remains almost constant or changes very little is the "plateau region." The discharge plateau voltage can be the voltage corresponding to the plateau region (where the voltage remains almost constant) or the median of the voltage range corresponding to the plateau region (where the voltage changes). The discharge plateau voltage of a single secondary battery cell can also be approximately calculated using the ratio of the discharge energy to the discharge capacity of the secondary battery cell, i.e., discharge plateau voltage = discharge energy / discharge capacity, where the unit of discharge energy is Wh and the unit of discharge capacity is Ah.

[0081] If mentioned, "linear carbonates" refer to a class of substances with a chain structure containing carbonate groups (-OCO-O-). Examples include dimethyl carbonate (DMC), diethyl carbonate (DEC), and ethyl methyl carbonate (EMC).

[0082] The embodiments of this application will be described next.

[0083] In recent years, rechargeable batteries have seen significant development due to their high energy density and long lifespan, finding widespread application in power tools, electronic products, electric vehicles, aerospace, and other fields. Typically, a rechargeable battery cell includes a positive electrode, a negative electrode, an electrolyte, and a separator. During the charging and discharging process, active ions repeatedly insert and extract between the positive and negative electrodes. The electrolyte acts as a conductor of these active ions between the electrodes. The separator, positioned between the positive and negative electrodes, prevents short circuits while allowing active ions to pass through, ensuring the normal electrochemical reactions within the battery cell.

[0084] Improving the energy density of rechargeable battery cells has always been a key research focus in the battery field. The cathode active material is one of the direct factors affecting the energy density of rechargeable battery cells. Lithium-containing phosphates with good thermal stability and lithium-containing transition metal oxides with high specific capacity are commonly used cathode active materials. However, lithium-containing phosphates have a relatively low specific capacity, which is not conducive to improving the energy density of rechargeable battery cells, while lithium-containing transition metal oxides are beneficial for improving the energy density of rechargeable battery cells, but their safety performance is relatively poor. Currently, some solutions combining both have been developed in the hope of obtaining rechargeable battery cells that balance safety performance and high capacity.

[0085] Furthermore, from a practical application perspective, in addition to the energy density and safety performance of individual rechargeable battery cells, the cycle performance of these cells is also an important performance indicator. When a mixed material containing lithium phosphate and lithium transition metal oxide is selected as the positive electrode active material, the cycle performance of the rechargeable battery cell may not meet the application requirements.

[0086] In view of this, embodiments of this application provide a secondary battery cell, a secondary battery, and an electrical device, wherein the discharge plateau voltage of the secondary battery cell is controlled within a suitable range, enabling the secondary battery cell to achieve both high energy density and good cycle performance.

[0087] Next, the secondary battery cell provided in this application will be introduced.

[0088] [Secondary battery cell]

[0089] Firstly, a secondary battery cell is provided, comprising an electrode assembly including a positive electrode and a negative electrode. The positive electrode includes a positive current collector and a positive electrode film disposed on at least one surface of the positive current collector. The positive electrode film includes a positive active material, comprising lithium phosphate and lithium transition metal oxide. The negative electrode includes a negative current collector and a negative electrode film disposed on at least one surface of the negative current collector. The negative electrode film includes a negative active material, comprising graphite. The secondary battery cell, at 25°C and a discharge rate of 1 / 3C, has a discharge plateau voltage v within the voltage range of 2.5V-4.25V that satisfies the following condition: 3.6V ≤ v ≤ 3.67V.

[0090] The secondary battery cell of this application, with the positive electrode active material including lithium phosphate and lithium transition metal oxide, and by controlling the discharge plateau voltage of the secondary battery cell within a specific voltage range, can effectively improve the cycle performance of the battery while maintaining a high energy density. Specifically, under the same mass or volume, the higher the discharge plateau voltage, the more energy the secondary battery can release. However, if the discharge plateau voltage is too high, it will cause redox reactions in the electrolyte of the secondary battery cell, producing gas and consuming the active lithium ions in the electrolyte, thus affecting the cycle performance of the secondary battery cell. Specifically, when the positive electrode active material includes both lithium phosphate and lithium transition metal oxide, if the discharge plateau voltage is too low (e.g., below 3.6V), the energy density of the battery cell will be low. This may be because the content of lithium transition metal oxide in the positive electrode active material is low or the structure has collapsed, resulting in a very limited contribution to the discharge capacity during the discharge process. If the discharge plateau voltage is too high (e.g., above 3.67V), it may lead to poor battery cycle performance. This could be because the positive electrode active material contains a high proportion of lithium-containing transition metal oxides, resulting in a high discharge plateau voltage for the individual battery cells. An excessively high discharge plateau voltage can cause side reactions and gas production in the electrolyte, affecting the cycle performance of the individual cells. Therefore, when the positive electrode active material includes both lithium-containing phosphates and lithium-containing transition metal oxides, controlling the discharge plateau voltage within a given range can effectively improve the cycle performance of the battery while maintaining a high energy density.

[0091] The discharge plateau voltage of a single secondary battery cell can be adjusted by modifying the active materials and electrode preparation process parameters. These parameters include, for example, the type, ratio, and particle size of the active materials, and the coating weight and compaction density of the electrode.

[0092] It should be understood that, considering the normal error of test conditions, if the discharge platform voltage tested under the above conditions within the range of 25℃±2℃ falls within the range defined in this application, it can be considered equivalent to the test result at 25℃ and thus fall within the scope of this application.

[0093] In some embodiments, the mass fraction m1 of the lithium phosphate in the positive electrode active material satisfies: 40wt% ≤ m1 ≤ 70wt%; optionally, 45wt% ≤ m1 ≤ 70wt%.

[0094] Specifically, m1 can be 40wt%, 42wt%, 44wt%, 45wt%, 46wt%, 48wt%, 50wt%, 52wt%, 54wt%, 56wt%, 58wt%, 60wt%, 62wt%, 64wt%, 66wt%, 68wt%, 70wt%, or a value within the range obtained by any combination of the above two values.

[0095] By controlling the mass content of lithium phosphate within a suitable range, the ratio of lithium phosphate to lithium transition metal oxide in the positive electrode active material can be indirectly adjusted. This helps to regulate the discharge plateau voltage of the secondary battery cell within a specific range, thus enabling the secondary battery cell to achieve both high energy density and good cycle performance. Furthermore, lithium phosphate exhibits good thermal stability. When the positive electrode active material includes both lithium phosphate and lithium transition metal oxide, controlling the lithium phosphate content within the aforementioned range allows for further improvement in the energy density and cycle performance of the secondary battery while maintaining high safety. This is because the thermal stability of lithium transition metal oxide is generally lower than that of lithium phosphate, and it is prone to side reactions with the electrolyte at high temperatures, which may affect the safety and cycle performance of the secondary battery cell.

[0096] In some embodiments, lithium-containing phosphates include lithium-containing transition metal phosphates.

[0097] In some embodiments, lithium phosphates include those with the molecular formula Li 1+a Mn b A 1-b P 1-c R c One or more of the following compounds or modified compounds of O4, wherein -0.2 ≤ a < 1, 0.3 ≤ b ≤ 0.9, 0 ≤ c ≤ 0.1, A includes one or more of Zn, Al, Na, K, Mg, Mo, W, Ti, V, Zr, Fe, Ni, Co, Ga, Sn, Sb, Nb, and Ge, and R includes one or more of B, Si, N, S, F, Cl, and Br; and / or, lithium-containing transition metal oxides include those with the molecular formula Li x Ni y Co z M k Me p O r E s Wherein, M includes one or more elements from Mn and Al, Me includes one or more elements from Zr, Zn, Cu, Cr, Mg, Fe, V, Ti, Sr, Sb, Y, W or Nb, and E includes one or more elements from N, F, S and Cl; 0.8≤x≤1.15, 0<y<1, 0<z<1, 0<k<1, 0≤p≤0.1, 1≤r≤2, 0≤s≤1.

[0098] Specifically, manganese in the positive electrode active material helps to improve the discharge plateau voltage of the secondary battery cell. In this embodiment, by selecting a mixture of manganese-containing lithium phosphate and lithium-containing transition metal oxide, the discharge plateau voltage of the secondary battery cell is improved, thereby further enhancing the energy density of the secondary battery cell. Additionally, the lithium-containing transition metal oxide may contain some me, which helps to improve the stability of the lithium-containing transition metal oxide, thus helping to improve the cycle performance of the secondary battery cell. Furthermore, by controlling the proportion of each metal element in the lithium-containing transition metal oxide within a suitable range, the discharge voltage plateau of the secondary battery cell can also be affected, ensuring that the discharge voltage plateau of the secondary battery cell is within the designed range, thus enabling the secondary battery cell to achieve both high energy density and good cycle performance.

[0099] In other embodiments, examples of lithium transition metal oxides may include, but are not limited to, lithium cobalt oxides (such as LiCoO2), lithium nickel oxides (such as LiNiO2), lithium manganese oxides (such as LiMnO2, LiMn2O4), lithium nickel cobalt oxides, lithium manganese cobalt oxides, lithium nickel manganese oxides, and lithium nickel cobalt manganese oxides (such as LiNi). 1 / 3 Co 1 / 3 Mn 1 / 3 O2 (also known as NCM333), LiNi 0.5 Co 0.2 Mn 0.3 O2 (also known as NCM523), LiNi 0.5 Co 0.25 Mn 0.25 O2 (also known as NCM211), LiNi 0.6 Co 0.2 Mn 0.2 O2 (also known as NCM622), LiNi 0.8 Co 0.1 Mn 0.1 O2 (also known as NCM811), lithium nickel cobalt aluminum oxide (such as LiNi) 0.85 Co 0.15 Al 0.05At least one of O2 and its modified compounds. Examples of lithium phosphates include, but are not limited to, lithium iron phosphate (such as LiFePO4 (also referred to as LFP)), lithium iron phosphate and carbon composites, lithium manganese phosphate (such as LiMnPO4), lithium manganese phosphate and carbon composites, lithium iron manganese phosphate, and lithium iron manganese phosphate and carbon composites. During the charging and discharging process, Li undergoes insertion / extraction and consumption, resulting in different molar contents of Li in the positive electrode active material when the battery is discharged to different states. In the examples of positive electrode active materials in this application, the molar content of Li refers to the initial state of the material, i.e., the state before feeding. After charge-discharge cycles, the molar content of Li changes when the positive electrode active material is applied to the battery system. In the examples of positive electrode active materials in this application, the molar content of O is only an ideal value; lattice oxygen release causes changes in the molar content of O, and the actual molar content of O will fluctuate.

[0100] In positive electrode active materials including Li 1+d [Ni f Co g Mn h M i ]O 2-e In the example, d is 0, and the positive electrode active material includes LiNi. 0.7 Co 0.1 Mn 0.2 O2. As another example, d>0, positive electrode active materials include LiNi. 0.7 Co 0.1 Mn 0.1 Al 0.1 O2.

[0101] In some embodiments, 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.

[0102] In some embodiments, the volume distribution particle size Dv501 of the positive electrode active material satisfies: 1.5μm≤Dv501≤3μm.

[0103] Specifically, Dv501 can be 1.5μm, 1.6μm, 1.7μm, 1.8μm, 1.9μm, 2μm, 2.1μm, 2.2μm, 2.3μm, 2.4μm, 2.5μm, 2.5μm, 2.6μm, 2.7μm, 2.8μm, 2.9μm, 3μm, or a value within the range obtained by any combination of the above two values.

[0104] In some embodiments, the lithium phosphate includes one or more elements selected from Al, Ti, and V. Specifically, the lithium phosphate may also include trace elements such as Al, Ti, and V, which help improve the structural stability of the lithium phosphate, thereby further improving the cycle performance of the secondary battery cell.

[0105] In some embodiments, the lithium-containing phosphate includes a first lithium-containing phosphate and a second lithium-containing phosphate, wherein the volume distribution particle size Dv50 of the first lithium-containing phosphate is... 1-1 Satisfies: 0.05μm≤Dv50 1-1 ≤0.3μm; Volume distribution particle size Dv50 of the second lithium phosphate 1-2 Satisfies: 1μm≤Dv50 1-2 ≤3μm. Specifically, Dv50 1-1 The value can be 0.05μm, 0.08μm, 0.1μm, 0.12μm, 0.14μm, 0.16μm, 0.18μm, 0.2μm, 0.22μm, 0.24μm, 0.26μm, 0.28μm, or 0.3μm, or a value within the range obtained by any combination of two of the above values. Dv50 1-2 The particle size can be 1μm, 1.2μm, 1.4μm, 1.6μm, 1.8μm, 2μm, 2.2μm, 2.4μm, 2.6μm, 2.8μm, 3μm, or a value within the range obtained by any combination of two of the above values. Combining two lithium phosphates with different particle sizes helps to increase the compaction density of the positive electrode, thereby further improving the energy density of the secondary battery.

[0106] In some embodiments, the volume distribution particle size Dv50 of lithium phosphate is... 1-3 Satisfies: 0.8μm≤Dv50 1-3 ≤1.2μm.

[0107] Specifically, Dv50 1-3The particle size can be 0.8μm, 0.9μm, 1μm, 1.1μm, 1.2μm, or any value within the range obtained by combining any two of the above values. The particle size of the lithium phosphate has a certain influence on the discharge plateau voltage of the secondary battery cell. The smaller the volume distribution particle size of the lithium phosphate, the smaller the diffusion path of lithium ions, which is more conducive to the diffusion of lithium ions and the higher the discharge plateau voltage of the secondary battery cell. However, if the volume distribution particle size of the lithium phosphate is too small, the particles are prone to agglomeration, thereby increasing the internal resistance of the battery cell and being detrimental to the cycle stability of the secondary battery cell. Therefore, this embodiment, by controlling the volume distribution particle size of the lithium phosphate within a suitable range, can further improve the energy density and cycle performance of the secondary battery cell.

[0108] In some embodiments, the volume distribution particle size Dv50 of the lithium transition metal oxide is... 1-4 Satisfies: 3μm≤Dv50 1-4 ≤5μm.

[0109] In some embodiments, the volume distribution particle size Dv101 of the lithium transition metal oxide satisfies: 1.5 μm ≤ Dv101 ≤ 2.5 μm.

[0110] In some embodiments, the volume distribution particle size Dv901 of the lithium transition metal oxide satisfies: 7.5 μm ≤ Dv901 ≤ 9.5 μm.

[0111] In some embodiments, the particle size distribution of the lithium-containing transition metal oxide satisfies: 0.95 ≤ (Dv901 - Dv10) 1-4 ) / Dv50 1-4 ≤1.5.

[0112] Specifically, Dv50 1-4 The micrometer value can be 3μm, 3.2μm, 2.4μm, 2.6μm, 2.8μm, 4μm, 4.2μm, 4.4μm, 4.6μm, 4.8μm, or 5μm, or a value within the range obtained by any combination of two of the above values. The micrometer value of Dv101 can be 1.5μm, 1.6μm, 1.7μm, 1.8μm, 1.9μm, 2μm, 2.1μm, 2.2μm, 2.3μm, 2.4μm, or 2.5μm, or a value within the range obtained by any combination of two of the above values. Dv901 can be 7.5μm, 7.6μm, 7.7μm, 7.8μm, 7.9μm, 8μm, 8.1μm, 8.2μm, 8.3μm, 8.4μm, 8.5μm, 8.6μm, 8.7μm, 8.8μm, 8.9μm, or 9μm, or a value within the range obtained by any combination of two of the above values. (Dv901-Dv10) 1-4 ) / Dv50 1-4It can be 0.95, 1, 1.05, 1.1, 1.15, 1.2, 1.25, 1.3, 1.35, 1.4, 1.45, 1.5, or a value within the range obtained by any combination of the above two values.

[0113] The particle size of lithium-containing transition metal oxides has a certain influence on the discharge plateau voltage of a secondary battery cell. The smaller the volume distribution particle size of the lithium-containing transition metal oxides, the higher the discharge plateau voltage of the secondary battery cell. However, if the volume distribution particle size of the lithium-containing transition metal oxides is too small, side reactions between them and the electrolyte may increase, potentially affecting the cycle performance of the secondary battery cell. Therefore, this embodiment, by controlling the volume distribution particle size of the lithium-containing transition metal oxides within a suitable range, can further improve the energy density and cycle performance of the secondary battery cell.

[0114] In some embodiments, the positive electrode includes a conductive agent, which includes carbon nanotubes, wherein the diameter d of the carbon nanotubes satisfies: 7μm≤d≤13μm.

[0115] Specifically, carbon nanotubes include at least one of single-walled carbon nanotubes and multi-walled carbon nanotubes. d can be 7 μm, 8 μm, 9 μm, 10 μm, 11 μm, 12 μm, 13 μm, or a value within the range obtained by any combination of the above two values. Conductive agents have a certain impact on the internal resistance, rate performance, and cycle performance of secondary battery cells. Compared to conductive agents such as conductive carbon black and Ketjen black, carbon nanotubes have a linear contact with the positive electrode active material, which can form a better conductive network between the positive electrode active material, resulting in higher conductivity. This reduces polarization during the cycling process of secondary battery cells and improves the rate performance and cycle performance of the secondary battery cells.

[0116] Generally, smaller carbon nanotube diameters result in better conductivity, but smaller diameters also increase the difficulty of fabrication, hindering production efficiency. Therefore, in this embodiment, selecting carbon nanotubes with a smaller but suitable diameter as the conductive agent helps improve the rate performance, cycle performance, and production efficiency of the secondary battery cells.

[0117] Carbon nanotubes can be at least one of single-walled carbon nanotubes or multi-walled carbon nanotubes.

[0118] In some embodiments, the coating weight ρ1 on one side of the positive electrode film layer satisfies: 190 g / m 2 ≤ρ1≤230g / m 2 .

[0119] Specifically, ρ1 can be 190g / m 2 195g / m 2 200g / m 2205g / 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.

[0120] According to this application, the coating weight of the film layer on the electrode also has a certain impact on the discharge plateau voltage of the secondary battery cell. The smaller the coating weight, the higher the discharge plateau voltage; however, if the coating weight is too small, it is also detrimental to the energy density of the secondary battery cell. Therefore, this embodiment, by controlling the coating weight of the positive electrode film layer within a suitable range, can ensure that the discharge voltage plateau of the secondary battery cell is within the designed range, thereby further improving the energy density and cycle performance of the secondary battery cell.

[0121] In some embodiments, the compaction density P1 of the positive electrode film layer satisfies: 2.5 g / cm³ 3 ≤P1≤2.9g / cm 3 .

[0122] Specifically, P1 can be 2.5 g / m 2 2.6g / cm 3 2.7g / cm 3 2.8g / cm 3 2.9g / cm 3 The density of the positive electrode film is either greater than or within the range obtained by combining any two of the above values. A higher compaction density of the positive electrode film is more beneficial for improving the energy density of the secondary battery cell. However, excessively high compaction density may affect the wetting of the positive electrode film by the electrolyte, thereby affecting lithium-ion kinetics. Therefore, in this embodiment, by controlling the compaction density of the positive electrode film within a suitable range, the energy density of the secondary battery cell can be improved, and the wetting of the positive electrode film by the electrolyte can be facilitated, thereby reducing polarization. ， Improving the kinetics of lithium ions at the positive electrode can improve the cycle performance of secondary battery cells.

[0123] In some embodiments, the thickness h1 of the positive current collector satisfies: 10μm≤h1≤13μm.

[0124] Specifically, h1 can be 10μm, 10.2μm, 10.4μm, 10.6μm, 10.8μm, 11μm, 11.2μm, 11.4μm, 11.6μm, 11.8μm, 12μm, 12.2μm, 12.4μm, 12.6μm, 12.8μm, or 13μm, or a value within the range obtained by any combination of the above two values. A thinner current collector is more conducive to reducing the thickness of the positive electrode, thereby increasing the energy density of the secondary battery cell. However, an excessively thin current collector will affect the mechanical strength of the electrode, potentially causing breakage during the processing or use of the secondary battery cell, leading to a sharp decrease in the capacity of the secondary battery cell and negatively impacting its energy density. This embodiment, by controlling the thickness of the positive electrode current collector within a suitable range, helps to improve the energy density of the secondary battery cell.

[0125] In some embodiments, in addition to graphite as mentioned above, the negative electrode active material may also include negative electrode active materials known in the art for use in batteries. As an example, the negative electrode active material may include at least one of the following materials: soft carbon, hard carbon, silicon-based materials, tin-based materials, and lithium titanate, etc. Silicon-based materials may be selected from at least one of elemental silicon, silicon oxides, silicon-carbon composites, silicon-nitrogen composites, and silicon alloys. Tin-based materials may be selected from at least one of elemental tin, tin oxides, and tin alloys. However, this application is not limited to these materials, and other conventional materials that can be used as negative electrode active materials for batteries may also be used. These negative electrode active materials may be used alone or in combination of two or more.

[0126] In some embodiments, the average volumetric particle size Dv502 of the negative electrode active material satisfies: 10μm≤Dv502≤14μm.

[0127] Specifically, Dv502 can have a particle size of 10 μm, 10.2 μm, 10.4 μm, 10.6 μm, 10.8 μm, 11 μm, 11.2 μm, 11.4 μm, 11.6 μm, 11.8 μm, 12 μm, 12.2 μm, 12.4 μm, 12.6 μm, 12.8 μm, 13 μm, 13.2 μm, 13.4 μm, 13.6 μm, 13.8 μm, or 14 μm, or a value within the range obtained by any combination of the above two values. The average volumetric particle size of the negative electrode active material affects the capacity and cycle performance of the secondary battery cell. The smaller the average volumetric particle size of the negative electrode active material, 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 of the secondary battery cell. If the average particle size of the negative electrode active material is too small, it may lead to insufficient contact area between particles, increasing the internal resistance of the secondary battery cell and thus affecting its cycle performance. Therefore, this embodiment helps to improve the capacity and cycle performance of the secondary battery cell by controlling the average particle size of the negative electrode active material within a suitable range.

[0128] In some embodiments, the coating weight ρ3 on one side of the negative electrode film layer satisfies: 90 g / m 2 ≤ρ3≤110g / m 2 .

[0129] Specifically, ρ3 can be 90 g / 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 The negative electrode coating weight also affects the discharge plateau voltage of the secondary battery cell. A higher single-sided coating weight results in a lower discharge plateau voltage. This embodiment, by controlling the negative electrode coating weight within a suitable range, ensures that the discharge voltage plateau of the secondary battery cell is within the designed range, thereby enabling the secondary battery cell to achieve good cycle performance while maintaining high energy density.

[0130] In some embodiments, the compaction density P2 of the negative electrode film layer satisfies: 1.3 g / cm³ 3 ≤P2≤1.55g / cm 3 Optionally, 1.4 g / cm³3 ≤P2≤1.5g / cm 3 .

[0131] Specifically, ρ4 can be 1.3 g / cm³. 3 1.32g / cm 3 1.34 g / cm 3 1.35g / cm 3 1.36 g / cm 3 1.38g / cm 3 1.4g / cm 3 1.42g / cm 3 1.44 g / cm 3 1.46 g / cm 3 1.48g / cm 3 1.5g / cm 3 The density of the negative electrode film, or its value, falls within the range obtained by combining any two of the above values. A higher compaction density of the negative electrode film is more beneficial for improving the energy density of the secondary battery cell. However, excessively high compaction density may affect the wetting of the negative electrode active material by the electrolyte, thereby affecting lithium-ion kinetics. Therefore, in this embodiment, by controlling the compaction density of the negative electrode film within a suitable range, the energy density of the secondary battery cell can be improved, and the wetting of the negative electrode sheet by the electrolyte can be facilitated, thereby reducing polarization, enhancing the kinetics of lithium ions at the negative electrode sheet, and thus improving the cycle performance of the secondary battery cell.

[0132] In some embodiments, the thickness h2 of the negative electrode current collector satisfies: 4μm≤h2≤6μm.

[0133] Specifically, h2 can be 4μm, 4.2μm, 4.4μm, 4.6μm, 4.8μm, 5μm, 5.2μm, 5.4μm, 5.6μm, 5.8μm, 6μm, or a value within the range obtained by any combination of the above two values. This embodiment, by controlling the thickness of the negative electrode current collector within a suitable range, helps to improve the energy density of the secondary battery cell.

[0134] Figures 1 and 2 are schematic cross-sectional views of a stacked electrode assembly. Figure 3 is a schematic cross-sectional view of a wound electrode assembly. For ease of explanation, the tabs of each electrode are not shown here. As shown in Figures 1-3, the electrode assembly 10 includes a positive electrode 11 and a negative electrode 12, and a separator 13 disposed between the positive electrode 11 and the negative electrode 12.

[0135] In some embodiments, as shown in FIG1, the electrode assembly 10 is a stacked electrode assembly. The electrode assembly 10 includes a plurality of positive electrode plates 11 and a plurality of negative electrode plates 12; the plurality of positive electrode plates 11 and the plurality of negative electrode plates 12 are alternately stacked in the direction indicated by the arrows in the figure. In another embodiment, as shown in FIG2, the electrode assembly 10 includes a plurality of positive electrode plates 11 and a plurality of negative electrode plates 12, the negative electrode plate 12 may include at least one bent section and a plurality of stacked sections, each bent section being used to connect two stacked sections, the plurality of positive electrode plates 11 and the plurality of stacked sections of negative electrode plates 12 are alternately stacked in the direction indicated by the arrows in the figure to form another stacked electrode assembly 10. Alternatively, the electrode assembly 10 includes a plurality of negative electrode plates 12 and a positive electrode plate 11. The positive electrode plate 11 may include at least one bent section and a plurality of stacked sections. Each bent section is used to connect two stacked sections. The plurality of negative electrode plates 12 and the plurality of stacked sections of the positive electrode plate 11 are alternately stacked in the direction shown by the arrow in the figure to form another stacked electrode assembly 10.

[0136] In some embodiments, as shown in FIG3, the electrode assembly 10 can also be a wound electrode assembly. The positive electrode 11, the separator 13, and the negative electrode 12 of the electrode assembly 10 are wound to form the electrode assembly 10.

[0137] According to this application, the electrode assembly 10 is preferably a stacked electrode assembly. Compared with the wound electrode assembly, the stacked electrode assembly has a higher space utilization rate inside the casing of the secondary battery cell 20. With the same casing, the stacked electrode assembly can accommodate more active material inside the casing, thereby further improving the energy density of the secondary battery cell.

[0138] Figures 4 and 5 are schematic structural diagrams of a secondary battery cell 20 according to this application.

[0139] As shown in Figures 4-5, in some embodiments, the secondary battery cell 20 includes a housing 21, the electrode assembly 10 is housed in the housing 21, the housing 21 includes a first wall 211, and the electrode terminal 22 is disposed on the first wall 211.

[0140] More specifically, the outer casing 21 may include a housing 212 and an end cap 213. The housing 212 has an internal cavity with an opening 2121, meaning the housing 212 is a hollow structure open at one end. The end cap 213 covers the opening 2121 of the housing 212 and forms a sealed connection to create a sealed space for accommodating the electrode assembly 10 and the electrolyte. Optionally, the first wall 211 for mounting the electrode terminal 22 may be the end cap 213 or one of the multiple walls of the housing 212. For example, in Figures 4 and 5, the first wall 211 is the end cap 213 of the housing 21. Of course, in other embodiments, the first wall 211 may also be the bottom wall of the housing 212 opposite to the end cap 213 in the thickness direction X, or a side wall adjacent to and abutting against the end cap 213.

[0141] The housing 212 can have various shapes, such as a cylinder or a cuboid. The shape of the housing 212 can be determined according to the specific shape of the electrode assembly 10. For example, if the electrode assembly 10 is a cylindrical structure, the housing 212 can be a cylindrical structure; if the electrode assembly 10 is a cuboid structure, the housing 212 can be a cuboid structure. Of course, the end cap 213 can also have various structures, such as a plate-like structure or a hollow structure with one end open. For example, in Figures 4 and 5, the housing 212 is a cuboid structure. It should be understood that the outer shell 21 is not limited to the aforementioned structures. The outer shell 21 can also have other structures. For example, the outer shell 21 includes a housing 212 and two end caps 213. The housing 212 is a hollow structure with openings 2121 on both sides opposite each other. One end cap 213 is fitted onto one opening 2121 of the housing 212 to form a sealed connection, thereby forming a sealed space for accommodating the electrode assembly 10 and the electrolyte.

[0142] Figure 6 is a partial schematic diagram of a secondary battery cell 20 in the region of electrode terminal 22 according to this application.

[0143] Referring to Figures 4-6, in some embodiments, the electrode assembly 10 includes a body 101 and a tab 102, with the tab 102 connected to the end of the body 101 facing the first wall 211. The secondary battery cell 20 includes a current collector 24 disposed between the first wall 211 and the body 101. The current collector 24 includes a first connecting portion 241 and a second connecting portion 242 connected to each other. The first connecting portion 241 is connected to the electrode terminal 22, and the second connecting portion 242 is connected to the tab 102. Along the thickness direction X of the first wall 211, the thickness D1 of the first connecting portion 241 satisfies: 0.5mm ≤ D1 ≤ 1.2mm; the thickness D2 of the second connecting portion 242 satisfies: 0.3mm ≤ D2 ≤ 1mm.

[0144] Specifically, the main body 101 of the electrode assembly 10 is the primary region where the electrochemical reaction occurs within the secondary battery cell 20. The main body 101 is formed by the region of the positive electrode 11 coated with positive active material, the separator, and the region of the negative electrode 12 coated with negative active material, which are wound or stacked together. The tabs 102 are used to output or input the positive or negative electrode of the electrode assembly 10, and are used to connect to the electrode terminals 22 to achieve electrical connection between the electrode assembly 10 and the electrode terminals 22. It should be noted that the tabs 102 of the electrode assembly 10 are either formed by stacking and connecting regions of the positive electrode 11 that are not coated with positive active material, or by stacking and connecting regions of the negative electrode 12 that are not coated with negative active material. If the tab 102 is used as the positive electrode of the output electrode assembly 10, then the tab 102 is a component formed by stacking and connecting the areas of the positive electrode sheet 11 that are not coated with positive active material; if the tab 102 is used as the negative electrode of the output electrode assembly 10, then the tab 102 is a component formed by stacking and connecting the areas of the negative electrode sheet 12 that are not coated with negative active material. For example, the tab 102 is connected to one end of the body 101 facing the end cap 213 in the thickness direction X.

[0145] The electrode assembly 10 housed within the housing 21 can be one or more. For example, in FIG5, the housing 21 of the secondary battery cell 20 is provided with two electrode assemblies 10, which are stacked along their thickness direction. That is, the two electrode assemblies 10 are stacked along the thickness direction of the secondary battery cell 20. Of course, in other embodiments, the electrode assembly 10 housed within the housing 21 can be one, three, four, five, six, seven, or eight, etc.

[0146] Electrode terminal 22 is a component used to output or input electrical energy to the secondary battery cell 20. For example, the electrode terminal 22 can be made of various materials, such as copper, iron, aluminum, steel, or aluminum alloy. The end of electrode terminal 22 facing electrode assembly 10 is connected to current collector 24, and the end of electrode terminal 22 away from electrode assembly 10 is connected to current collector 24 to realize the input or output of electrical energy to the secondary battery cell 20. A first through hole 2111 is provided on end cover 213, extending through both sides of end cover 213 along its thickness direction X. Electrode terminal 22 passes through the first through hole 2111 to mount it on end cover 213, with both ends of electrode terminal 22 extending out of the first through hole 2111. Electrode terminal 22 is insulated from end cover 213, meaning no electrical connection is formed between electrode terminal 22 and end cover 213. The secondary battery cell 20 may also include an insulating member 26 to insulate and isolate the end cap 213 and the electrode terminal 22. The secondary battery cell 20 may also include a sealing member 27 to seal the gap between the electrode terminal 22 and the wall surface of the first through hole 2111.

[0147] In Figures 4 and 5, the secondary battery cell 20 includes two electrode terminals 22. 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.

[0148] The current collector 24 serves to connect the electrode terminal 22 and the tab 102 to achieve an electrical connection between the electrode assembly 10 and the electrode terminal 22. For example, the current collector 24 can be made of various materials, such as copper, iron, aluminum, steel, or aluminum alloy. The connection structure between the current collector 24 and the electrode terminal 22 can be various, such as welding, abutment, or bonding. Similarly, the connection structure between the current collector 24 and the tab 102 can also be various, such as welding or abutment. There are two electrode terminals 22 and two current collectors 24, arranged at intervals along the first direction Z. Each electrode terminal 22 is connected to the electrode assembly 10 through one current collector 24 to output the positive and negative terminals of the secondary battery cell 20. As shown in Figure 6, the current collector 24 may also include a bending portion 243, through which the first connecting portion 241 and the second connecting portion 242 are connected.

[0149] For example, D1 can be 0.5mm, 0.55mm, 0.6mm, 0.65mm, 0.7mm, 0.75mm, 0.8mm, 0.9mm, 1mm, 1.1mm, 1.15mm, or 1.2mm, or a value within the range obtained by any combination of the above two values. D2 can be 0.3mm, 0.35mm, 0.4mm, 0.45mm, 0.5mm, 0.55mm, 0.6mm, 0.7mm, 0.8mm, 0.9mm, 0.95mm, or 1mm, or a value within the range obtained by any combination of the above two values.

[0150] In this embodiment, the thickness of the area of ​​the current collector 24 used to connect the electrode terminal 22 is greater than the thickness of the area of ​​the current collector 24 used to connect the tab 102. Since the thickness requirement of the area where the current collector 24 connects to the tab 102 is less than the thickness requirement of the area where the current collector 24 connects to the electrode terminal 22, the thickness of the current collector 24 can be effectively optimized while still enabling it to connect the electrode terminal 22 and the tab 102. This reduces the overall weight of the current collector 24 and saves space, thereby optimizing the weight and internal space utilization of the secondary battery cell 20 and improving its energy density.

[0151] Furthermore, by setting the thickness of the first connecting portion 241 and the thickness of the second connecting portion 242 within a suitable range, on the one hand, the structural strength of the first connecting portion 241 and the second connecting portion 242 can be improved, ensuring that the first connecting portion 241 and the second connecting portion 242 have sufficient thickness to connect with the electrode terminal 22 and the tab 102. This is beneficial to improving the connection stability and reliability between the first connecting portion 241 and the second connecting portion 242 and the electrode terminal 22 and the tab 102, and reducing the phenomenon of insufficient overcurrent between the current collector 24 and the electrode terminal 22, and between the current collector 24 and the tab 102. On the other hand, it can reduce the connection difficulty between the first connecting portion 241 and the electrode terminal 22, and between the second connecting portion 242 and the tab 102, and can reduce the space occupied by the current collector 24 in the housing 21, which is beneficial to improving the energy density of the secondary battery cell 20.

[0152] Figure 7 is an exploded view of a partial structure of a secondary battery cell 20 according to this application. Figure 8 is a cross-sectional view of a partial structure of a secondary battery cell 20 according to this application, and Figure 9 is a schematic diagram of a local area in Figure 8.

[0153] As shown in FIGS. 7-9, in some embodiments, the first wall 211 includes a first through hole 2111, the electrode terminal 22 includes a main body portion 221 and a stepped portion 222, the stepped portion 222 protrudes from the outer peripheral surface of the main body portion 221, and the stepped 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 portion 221 to pass through. In the thickness direction of the first wall 211, at least a part of the fixing member 28 is located between the first wall 211 and the stepped portion 222 and abuts against the stepped portion 222. The main body portion 221 has a first end face 2211 facing the outside of the secondary battery cell 20, the fixing member 28 has a second end face 282 facing the outside of the secondary battery cell 20, and the first end face 2211 extends beyond the second end face 282.

[0154] Specifically, the outside of the secondary battery cell 20 refers to the part outside the accommodation space of the housing 21 of the secondary battery cell 20. The first end face 2211 extending beyond the second end face 282 means that, on the outside of the secondary battery cell 20, in the thickness direction of the first wall 211, the second end face 282 is located between the first end face 2211 and the outer surface of the first wall 211. In other words, the face farthest from the outer surface of the first wall 211 is the first end face 2211 of the electrode terminal 22.

[0155] The outer peripheral surface of the main body portion 221 may refer to the outer peripheral surface of a cylinder or the peripheral surface of a prism connecting the top surface and the bottom surface of the prism. Taking the main body portion 221 as a quadrangular prism as an example, the main body portion 221 includes a top surface, a bottom surface and four side surfaces. The four side surfaces are sequentially connected and surround the top surface, and the two ends of the four side surfaces in the direction from the top surface to the bottom surface are respectively connected to the top surface and the bottom surface. The above four side surfaces refer to the outer peripheral surface of the main body portion 221. In some embodiments, a first groove 2212 is provided on the first end face 2211, and the side surface of the first groove 2212 can also be referred to as the outer peripheral surface of the main body portion 221. In this embodiment, the main body portion 221 is in a shape similar to a "convex" shape. In some embodiments, the stepped portion 222 has a third end face 2221 facing away from the first wall 211.

[0156] The outer contour of the fixing member

[0157] In this embodiment, the surface of the secondary battery cell 20 with the maximum height exceeding the outer surface of the first wall 211 in the thickness direction of the first wall 211 is the first end face 2211. When using electrode terminals 22 of the same specification, the height of the secondary battery cell 20 exceeding the first wall 211 can be reduced accordingly, thereby increasing the proportion of the space inside the casing 21 of the secondary battery cell 20 to the total space of the secondary battery cell 20, and thus increasing the energy density of the secondary battery cell 20.

[0158] The electrode terminal 22 also includes a limiting part 223, which protrudes from the outer peripheral surface of the main body 221 and is located inside the first wall 211. The limiting part 223 is used to restrict the electrode terminal 22 from moving to the outside of the housing 21.

[0159] Exemplarily, the insulating member 26 includes a body portion 261 and a first extension portion 262. The body portion 261 is located between the fixing member 28 and the first wall 211, and the body portion 261 is provided with a third through hole 2611 through which the power supply terminal 22 passes. The first extension portion 262 is located on the outer periphery of the fixing member 28 and surrounds the edge of the body portion 261. The sealing member 27 is at least partially located between the first wall 211 and the limiting portion 223.

[0160] In some embodiments, the height difference H between the first end face 2211 and the second end face 282 in the thickness direction of the first wall 211 satisfies: 0.5mm≤H≤1.5mm.

[0161] Specifically, D can be 0.5mm, 0.6mm, 0.7mm, 0.8mm, 0.9mm, 1mm, 1.1mm, 1.2mm, 1.3mm, 1.4mm, or 1.5mm, or a value within the range obtained by any combination of the above two values. By controlling H within a suitable range, the energy density of the secondary battery cell 20 can be improved while ensuring good connection stability between the first end face 2211 and the second end face 282.

[0162] In some embodiments, the step portion 222 protrudes from the outer peripheral surface of the main body portion 221 by a dimension W1 that satisfies: 0.1mm≤W1≤5mm.

[0163] Specifically, W1 can be 0.1mm, 0.2mm, 0.4mm, 0.6mm, 0.8mm, 1mm, 1.2mm, 1.4mm, 1.6mm, 1.8mm, 2mm, 2.2mm, 2.4mm, 2.6mm, 2.8mm, 3mm, 3.2mm, 3.4mm, 3.6mm, 3.8mm, 4mm, 4.2mm, 4.4mm, 4.6mm, 4.8mm, 5mm, or a value within the range obtained by any combination of the above two values. By controlling the size of the step portion 222 protruding from the outer peripheral surface of the main body portion 221 within a suitable range, it is beneficial to increase the contact area between the step portion 222 and the fastener 28, thereby improving the connection strength between the step portion 222 and the fastener 28.

[0164] In some embodiments, the secondary battery cell 20 includes an electrolyte, and the ionic conductivity σ of the electrolyte satisfies: 7mS / cm≤σ≤10mS / cm.

[0165] Specifically, σ can be 7 mS / cm, 7.5 mS / cm, 8 mS / cm, 8.5 mS / cm, 9 mS / cm, 9.5 mS / cm, 10 mS / cm, or a value within the range obtained by any combination of the above two values. A higher ionic conductivity of the electrolyte is more beneficial to the lithium-ion kinetics within the secondary battery cell 20, thus improving the cycle performance of the secondary battery cell 20. Excessively high ionic conductivity of the electrolyte is detrimental to the stability of the electrolyte and may cause an increase in side reactions within the battery cell 20, affecting the cycle stability of the secondary battery cell 20. In this embodiment, by controlling the ionic conductivity of the electrolyte within a suitable range, it helps to improve the lithium-ion kinetics during the cycling process of the secondary battery cell 20, thereby improving the cycle performance of the secondary battery cell 20.

[0166] In some embodiments, the electrolyte comprises: a solvent, the solvent comprising linear carbonate; and the total mass of the electrolyte, wherein the mass content m2 of the linear carbonate satisfies 40wt% ≤ m2 ≤ 70wt%.

[0167] Specifically, m2 can be 40wt%, 45wt%, 50wt%, 55wt%, 60wt%, 65wt%, 70wt%, or a value within the range obtained by any combination of the above two values. In this embodiment, by selecting a linear carboxylic acid ester as the solvent and controlling its mass content in the electrolyte within a suitable range, it is helpful to reduce the viscosity of the electrolyte, thereby helping to improve lithium-ion kinetics.

[0168] In some embodiments, the electrolyte comprises a lithium salt, including LiPF6 and LiFSI; the mass content of the lithium salt m3, based on the total mass of the electrolyte, satisfies 13wt% ≤ m3 ≤ 18wt%.

[0169] Specifically, m3 can be 13wt%, 14wt%, 15wt%, 16wt%, 17wt%, 18wt%, or a value within the range obtained by any combination of the above two values.

[0170] LiFSI possesses high ionic conductivity and good high-temperature stability, which helps improve the high-temperature cycle performance of battery cells. By selecting LiPF6 and LiFSI as lithium salts and controlling their contents within a suitable range, it is helpful to improve the lithium-ion conductivity and high-temperature resistance of the electrolyte, thereby helping to improve the lithium-ion kinetics during the cycling process of secondary battery cell 20 and enhancing its cycle performance.

[0171] In some embodiments, the molar percentage n of LiPF6, based on the total amount of the lithium salt, satisfies: 50% ≤ n ≤ 70%.

[0172] Specifically, it can be 50%, 55%, 60%, 65%, 70%, or a value within the range obtained by any combination of the above two values. LiPF6 has good film-forming stability. By controlling the molar content of LiPF6 within a high range, it helps to form a stable SEI film on the surface of the negative electrode, thus helping to improve the cycle performance of the secondary battery cell 20.

[0173] Next, using a lithium-ion battery as a specific example, a detailed description will be given of the positive electrode, negative electrode, separator, and electrolyte in the secondary battery cell 20. It should be understood that the lithium-ion battery is only an example, and the solution provided in this application can also be applied to other types of secondary batteries, such as sodium-ion batteries, magnesium-ion batteries, and lithium-sulfur batteries.

[0174] [Negative electrode plate]

[0175] The negative electrode 12 typically includes a negative current collector and a negative electrode film layer disposed on at least one surface of the negative current collector. The negative electrode film layer includes a negative electrode active material, which may include graphite.

[0176] In some embodiments, the graphite material may be at least one of artificial graphite and natural graphite.

[0177] As an example, the negative electrode current collector has two surfaces opposite each other in its own thickness direction, and the negative electrode film layer is disposed on either or both of the two opposite surfaces of the negative electrode current collector.

[0178] In some embodiments, the negative electrode current collector may be a metal foil or a composite current collector. For example, copper foil may be used as the metal foil. The composite current collector may include a polymer substrate and a metal layer formed on at least one surface of the polymer substrate. The composite current collector may be formed by forming a metal material (copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0179] In some embodiments, the negative electrode film layer further includes an adhesive. The adhesive may be selected from at least one of styrene-butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethacrylic acid (PMAA), and carboxymethyl chitosan (CMCS).

[0180] In some embodiments, the negative electrode film layer further includes a conductive agent. The conductive agent may be selected from at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0181] In some embodiments, the negative electrode film layer also includes other additives, such as thickeners (e.g., sodium carboxymethyl cellulose (CMC-Na)).

[0182] In some embodiments, the negative electrode 12 can be prepared by forming a negative electrode slurry using the components described above. For example, the negative electrode active material, conductive agent, binder, and any other components are dispersed in a solvent (e.g., N-methylpyrrolidone) to form a negative electrode slurry. The negative electrode slurry is then coated onto a negative electrode current collector, and after drying, cold pressing, and other processes, the negative electrode 12 is obtained.

[0183] [Positive electrode plate]

[0184] The positive electrode 11 includes a positive current collector and a positive electrode film layer disposed on at least one surface of the positive current collector. The positive electrode film layer includes a positive electrode active material, which includes lithium phosphate and lithium transition metal oxide.

[0185] As an example, the positive current collector has two surfaces opposite each other in its own thickness direction, and the positive electrode film layer is disposed on either or both of the two opposite surfaces of the positive current collector.

[0186] In some embodiments, the positive current collector may be a metal foil or a composite current collector. For example, aluminum foil may be used as the metal foil. The composite current collector may include a polymer substrate and a metal layer formed on at least one surface of the polymer substrate. The composite current collector may be formed by forming a metal material (aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0187] In some embodiments, the positive electrode film layer further includes a binder. As an example, the binder may include at least one selected from polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), PVDF-tetrafluoroethylene-propylene terpolymer, PVDF-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorinated acrylate resin.

[0188] In some embodiments, the positive electrode film layer further includes a conductive agent. As an example, the conductive agent may also include at least one selected from superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, graphene, and carbon nanofibers.

[0189] In some embodiments, the positive electrode 11 can be prepared by forming a positive electrode slurry from the components described above. For example, the positive electrode active material, conductive agent, binder, and any other components are dispersed in a solvent (e.g., N-methylpyrrolidone) to form a positive electrode slurry. The positive electrode slurry is then coated onto a positive electrode current collector, and after drying, cold pressing, and other processes, the positive electrode 11 is obtained.

[0190] Electrolyte

[0191] The electrolyte acts as a conductor of ions between the positive electrode 11 and the negative electrode 12. This application does not impose specific limitations on the type of electrolyte; it can be selected according to requirements.

[0192] In addition to the lithium salt types mentioned in the preceding embodiments, in some embodiments, the electrolyte salt may also be selected from at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium hexafluoroarsenate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium trifluoromethanesulfonate, lithium difluorophosphate, lithium difluorooxalate borate, lithium dioxalate borate, lithium difluorodioxalate phosphate, and lithium tetrafluorooxalate phosphate.

[0193] In some embodiments, the solvent may also be selected from at least one of ethylene carbonate, propylene carbonate, methyl ethyl carbonate, diethyl carbonate, dimethyl carbonate, dipropyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, butyl carbonate, fluoroethylene carbonate, methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate, 1,4-butyrolactone, sulfolane, dimethyl sulfone, methyl ethyl sulfone, and diethyl sulfone.

[0194] In some embodiments, the electrolyte may optionally include additives. For example, additives may include negative electrode film-forming additives, positive electrode film-forming additives, and may also include additives that can improve certain battery performance, such as additives that improve battery overcharge performance, additives that improve battery high-temperature or low-temperature performance, etc.

[0195] [Isolation membrane]

[0196] This application does not impose any particular restrictions on the type of separator 13. For example, any well-known porous structure separator 13 with good chemical and mechanical stability can be selected.

[0197] In some embodiments, the separator 13 includes a porous substrate, the material of which may be selected from at least one of glass fiber, nonwoven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The porous substrate may be a single-layer film or a multi-layer composite film, without particular limitation. When the porous substrate is a multi-layer composite film, the materials of each layer may be the same or different, without particular limitation.

[0198] In some embodiments, the thickness h3 of the porous substrate satisfies: h3≤7μm; optionally, 3μm≤h3≤5μm.

[0199] Specifically, h3 can be 1μm, 2μm, 3μm, 4μm, 5μm, 6μm, 7μm, or a value within the range obtained by any combination of the above two values. Controlling the thickness of the porous substrate within the given range helps to further improve the energy density of the secondary battery cell.

[0200] In some embodiments, the separator 13 further includes a porous coating. The porous coating can serve as a heat-resistant and / or adhesive layer.

[0201] In some embodiments, the porous coating includes heat-resistant particles. The heat-resistant particles may include at least one of inorganic particles and organic particles.

[0202] In some embodiments, inorganic particles may include one or more of the following: inorganic particles having a dielectric constant of 5 or greater, inorganic particles having ion conductivity but not storing ions, or inorganic particles capable of undergoing electrochemical reactions.

[0203] In some embodiments, inorganic particles having a dielectric constant of 5 or higher may include boehmite, alumina, barium sulfate, magnesium oxide, magnesium hydroxide, silicon oxides, tin dioxide, titanium oxide, calcium oxide, zinc oxide, zirconium oxide, yttrium oxide, nickel oxide, hafnium dioxide, cerium oxide, zirconium titanate, barium titanate, magnesium fluoride, aluminum hydroxide, barium oxide, silicon carbide, boron carbide, aluminum nitride, silicon nitride, boron nitride, calcium fluoride, barium fluoride, magnesium aluminum silicate, lithium magnesium silicate, sodium magnesium silicate, bentonite, hydropyrite, Pb(Zr,Ti)O3 (abbreviated as PZT), Pb1-mLamZr1-nTinO3 (abbreviated as PLZT, 0 < m < 1, 0 < n < 1), Pb(Mg3Nb) 2 / 3 The inorganic particles can be selected from one or more of PbTiO3 (PMN-PT) and their respective modified inorganic particles. Optionally, the modification of each inorganic particle can be chemical modification and / or physical modification.

[0204] In some embodiments, inorganic particles that are ion-conductive but do not store ions may include Li3PO4, lithium titanium phosphate (Li3PO4), etc. x1 Ti y1 (PO4)3, Lithium aluminum titanium phosphate (Li) x2 Al y2 Ti z1 (PO4)3、(LiAlTiP) x3 O y3 Type glass, lithium lanthanum titanate (Li) x4 La y4 TiO3, lithium germanium thiophosphate Li x5 Ge y5 P z2 S w Lithium nitride (Li) x6 N y6 SiS2 type glass Li x7 Si y7 S z3 and P2S5 type glass Li x8 P y8 S z4 One or more of the following are given: 0 < x1 < 2, 0 < y1 < 3, 0 < x2 < 2, 0 < y2 < 1, 0 < z1 < 3, 0 < x3 < 4, 0 < y3 < 13, 0 < x4 < 2, 0 < y4 < 3, 0 < x5 < 4, 0 < y5 < 1, 0 < z2 < 1, 0 < w < 5, 0 < x6 < 4, 0 < y6 < 2, 0 < x7 < 3, 0 < y7 < 2, 0 < z3 < 4, 0 < x8 < 3, 0 < y8 < 3, 0 < z4 < 7. This can improve the ion conductivity of the separator.

[0205] In some embodiments, the inorganic particles capable of undergoing electrochemical reactions may include one or more of lithium-containing transition metal oxides, lithium-containing phosphates, carbon-based materials, silicon-based materials, tin-based materials, and lithium-titanium compounds.

[0206] In some embodiments, the organic particles may include at least one of a thermoplastic resin polymer, a thermosetting resin polymer, or a crosslinked polymer.

[0207] In some embodiments, the thermoplastic resin polymer may include one or more of the following: polycarbonate organic particles, polymethyl methacrylate organic particles, polyoxymethylene organic particles, polyamide organic particles, styrene-acrylonitrile copolymer, polyphenylene sulfide organic particles, polyether ether ketone organic particles, polyimide organic particles, polysulfone organic particles, polyether sulfone organic particles, polyphenylene sulfone organic particles, polybenzimidazole organic particles, polyamide-imide organic particles, and polyethyleneimine organic particles.

[0208] In some embodiments, the thermosetting resin polymer may include one or more of the following: phenolic resin organic particles, polymer particles containing triazine ring structural units, epoxy resin organic particles, unsaturated polyester resin organic particles, urea-formaldehyde resin organic particles, and furan resin organic particles.

[0209] In some embodiments, the crosslinking polymer may include one or more of crosslinked styrene organic particles and silicon-containing organic crosslinked resin particles.

[0210] In some embodiments, the porous coating includes binder particles. The binder particles may include homopolymers or copolymers of acrylate monomer units, homopolymers or copolymers of acrylic monomer units, homopolymers or copolymers of styrene monomer units, polyurethane compounds, rubber compounds, homopolymers or copolymers of fluorinated alkenyl monomer units, homopolymers or copolymers of olefinic monomer units, homopolymers or copolymers of unsaturated nitrile monomer units, homopolymers or copolymers of epoxide monomer units, and one or more of the modified compounds of the above homopolymers or copolymers.

[0211] In some embodiments, the adhesive particles may include copolymers of acrylate monomer units and styrene monomer units, copolymers of acrylate monomer units and styrene monomer units, copolymers of acrylate monomer units, acrylate monomer units, and styrene monomer units, copolymers of styrene monomer units and unsaturated nitrile monomer units, copolymers of styrene monomer units, olefin monomer units, and unsaturated nitrile monomer units, polytetrafluoroethylene, polychlorotrifluoroethylene, polyvinylidene fluoride, polyvinylidene fluoride, polyethylene, polypropylene, polyacrylonitrile, polyethylene oxide, copolymers of different fluorinated alkenyl monomer units, copolymers of fluorinated alkenyl monomer units and vinyl monomer units, copolymers of fluorinated alkenyl monomer units and acrylate monomer units, copolymers of fluorinated alkenyl monomer units and acrylate monomer units, and one or more of the modified compounds of the above homopolymers or copolymers.

[0212] In some embodiments, the adhesive particles may include one or more of the following: butyl acrylate-styrene copolymer, butyl methacrylate-isooctyl methacrylate copolymer, isooctyl methacrylate-styrene copolymer, methacrylate-methacrylate-styrene copolymer, methyl acrylate-isooctyl methacrylate-styrene copolymer, butyl acrylate-isooctyl methacrylate-styrene copolymer, butyl acrylate-isooctyl methacrylate-styrene copolymer, butyl methacrylate-isooctyl methacrylate-styrene copolymer, butyl methacrylate-isooctyl methacrylate-styrene copolymer, styrene-acrylonitrile copolymer, styrene-butadiene-acrylonitrile copolymer, methyl acrylate-styrene-acrylonitrile copolymer, isooctyl methacrylate-styrene-acrylonitrile copolymer, styrene-vinyl acetate copolymer, styrene-vinyl acetate-pyrrolidone copolymer, vinylidene fluoride-trifluoroethylene copolymer, vinylidene fluoride-hexafluoropropylene copolymer, vinylidene fluoride-trifluoroethylene-hexafluoropropylene copolymer, vinylidene fluoride-hexafluoropropylene-acrylic acid copolymer, vinylidene fluoride-hexafluoropropylene-acrylate copolymer, and a modified compound of the above copolymers.

[0213] In some embodiments, the coating may further include a dispersant, such as one or more of alkylphenol polyoxyethylene ethers, polyacrylic acid dispersants, and cellulose dispersants, including but not limited to. For example, the dispersant may include one or more of sodium carboxymethyl cellulose, sodium polyacrylate, and ammonium polyacrylate.

[0214] [Rechargeable Battery]

[0215] This application provides a secondary battery, including the secondary battery cell 20 described in the above embodiments. The secondary battery can be a single physical module comprising one or more secondary battery cells to provide higher voltage and capacity. When there are multiple secondary battery cells 20, the multiple secondary battery cells 20 are connected in series, parallel, or in a mixed configuration via a busbar.

[0216] In some embodiments, the secondary battery can be a battery pack, which includes a housing and a secondary battery cell 20, wherein the secondary battery cell 20 or battery module is housed in the housing.

[0217] In some embodiments, the housing may be part of the vehicle's chassis structure. For example, a portion of the housing may be at least a part of the vehicle's floor, or a portion of the housing may be at least a part of the vehicle's crossbeams and longitudinal beams.

[0218] In some embodiments, the secondary battery may be located in the energy storage device. The energy storage device includes energy storage containers, energy storage cabinets, etc.

[0219] Figure 10 is a schematic diagram of a battery according to an embodiment of this application. As shown in Figure 10, the battery 30 may include a plurality of secondary battery cells 20 to meet different power usage needs.

[0220] The battery 30 may also include a housing with a hollow interior, housing multiple secondary battery cells 20. For example, multiple secondary battery cells 20 may be connected in parallel, series, or a combination thereof and then placed inside the housing. The housing may include a first housing portion 301 and a second housing portion 302, which are fitted together to form the housing. The shapes of the first housing portion 301 and the second housing portion 302 may be determined by the shape of the components housed within, for example, by the shape of the combination of the multiple secondary battery cells 20 housed within. At least one of the first housing portion 301 and the second housing portion 302 may have an opening. For example, as shown in FIG10, only one of the first housing portion 301 and the second housing portion 302 may be a hollow cuboid with an opening, while the other may be plate-shaped to cover the opening. Taking the second box section 302 as a hollow cuboid with an opening, and the first box section 301 as a plate as an example, the first box section 301 covers the opening of the second box section 302 to form a box with a closed chamber, which can be used to accommodate multiple secondary battery cells 20.

[0221] In addition, this application also provides an electrical device that includes the secondary battery described in the foregoing embodiments.

[0222] For example, unlike that shown in Figure 10, the first housing portion 301 and the second housing portion 302 can both be hollow cuboids with one open side each. The openings of the first housing portion 301 and the second housing portion 302 are opposite to each other, and the first housing portion 301 and the second housing portion 302 are interlocked to form a housing with a closed chamber. This chamber can be used to accommodate multiple secondary battery cells 20. The multiple secondary battery cells 20 are connected in parallel, series, or mixed and placed in the housing formed by the interlocking of the first housing portion 301 and the second housing portion 302.

[0223] In some embodiments, the secondary battery may further include other components. For example, the secondary battery may further include a busbar component, which can be used to realize electrical connections between multiple secondary battery cells 20, such as in parallel, series, or mixed connections. Specifically, the busbar component can realize electrical connections between secondary battery cells 20 by connecting to the electrode terminals of the secondary battery cells 20; or, the busbar component can also realize electrical connections between secondary battery cells 20 by connecting to other components of the secondary battery cells 20. The busbar component can be fixed to corresponding components of the secondary battery cells 20 by welding, for example, by welding to electrode terminals, sealing structures, or housings, etc., and the embodiments of this application are not limited thereto.

[0224] The secondary battery cells 20 can be directly assembled into secondary battery 30, or they can be first assembled into battery modules, and then multiple battery modules can be assembled into secondary battery 30.

[0225] [Electrical appliances]

[0226] This application provides an electrical device, including the battery described in the above embodiments.

[0227] Electrical devices can include vehicles, mobile phones, portable devices, laptops, ships, spacecraft, electric toys, and power tools, etc. Vehicles can be gasoline-powered cars, natural gas-powered cars, or new energy vehicles; new energy vehicles can be pure electric vehicles, hybrid electric vehicles, or range-extended electric vehicles, etc. Spacecraft include airplanes, rockets, space shuttles, and spacecraft, etc. Electric toys include stationary or mobile electric toys, such as game consoles, electric car toys, electric ship toys, and electric airplane toys, etc. Power tools include metal cutting power tools, grinding power tools, assembly power tools, and railway power tools, such as electric drills, electric grinders, electric wrenches, electric screwdrivers, electric hammers, impact drills, concrete vibrators, and electric planers, etc. This application does not impose any special limitations on the above-mentioned electrical devices.

[0228] This application provides an electrical device, which is a vehicle.

[0229] The vehicle can be a gasoline-powered vehicle, a natural gas-powered vehicle, or a new energy vehicle. New energy vehicles can be pure electric vehicles, hybrid electric vehicles, or range-extended electric vehicles, etc. The vehicle's interior can house a motor, a controller, and a secondary battery 30. The controller is used to control the secondary battery 30 to supply power to the motor. For example, the secondary battery 30 can be located at the bottom, front, or rear of the vehicle. The secondary battery 30 can be used for vehicle power supply; for example, it can serve as the vehicle's operating power source for the vehicle's electrical system, such as for the power needs of starting, navigation, and operation. In another embodiment of this application, the secondary battery 30 can not only serve as the vehicle's operating power source but also as the vehicle's drive power source, replacing or partially replacing gasoline or natural gas to provide driving power to the vehicle.

[0230] The following describes embodiments of this application. The embodiments described below are exemplary and are only used to explain this application, and should not be construed as limiting this application. Where specific techniques or conditions are not specified in the embodiments, they are performed according to the techniques or conditions described in the literature in this field or according to the product instructions. Reagents or instruments used, unless otherwise specified, are all conventional products that can be obtained commercially.

[0231] [Examples and Comparative Examples]

[0232] Example 1

[0233] (1) Preparation of positive electrode sheet

[0234] The positive electrode active material (containing lithium phosphate LiMn) 0.6 Fe 0.4 O4 and lithium-containing layered metal oxides LiNi 0.65 Co 0.15 Mn 0.20 O2 (80wt%:20wt%), polyvinylidene fluoride (PVDF) binder, acetylene black conductive agent, and carbon nanotubes were mixed in a mass ratio of 96.5:2:1:0.5. NMP was added, and the mixture was stirred evenly in a mixer. The slurry was then coated onto a 12-micron thick aluminum foil, dried in an oven, cold-pressed, and slit to obtain the positive electrode sheet. The volume distribution particle size (Dv50) of the lithium phosphate was 1.1 μm, the volume distribution particle size (Dv50) of the lithium transition metal oxide was 3.8 μm, and the Dv50 of the positive electrode active material after mixing lithium phosphate and lithium transition metal oxide was 1.68 μm. The coating weight on one side of the positive electrode film was ρ1 = 214 g / m². 2 The compaction density of the positive electrode film is P1 = 2.46 g / cm³. 3 .

[0235] (2) Preparation of negative electrode sheet

[0236] Artificial graphite, sodium carboxymethyl cellulose, styrene-butadiene rubber, and acetylene black (negative electrode active materials) were mixed in a mass ratio of 96:1:1:2. Deionized water was added, and the mixture was stirred evenly in a mixer. The slurry was then coated onto a 6-micron thick copper foil, dried in an oven, cold-pressed, and slit to obtain the negative electrode sheet. The volumetric particle size distribution (Dv50) of the artificial graphite was 12 μm, and the single-sided coating weight of the negative electrode film was ρ1 = 99 g / m². 2 The compaction density of the negative electrode film is P1 = 1.4 g / cm³. 3 .

[0237] (3) Preparation of electrolyte

[0238] In an argon-atmospheric glove box with a water content of <10 ppm, ethylene carbonate (EC) and ethyl methyl carbonate (DEC) were mixed at a volume ratio of 1:2. Then, lithium hexafluorophosphate (LiPF6) and lithium bis(fluorosulfonyl)imide (LiFSI) were uniformly dissolved in the solvent. Additives PS and VC were then added to obtain the electrolyte. The molar concentration of lithium salt in the electrolyte was 1 mol / L, and the molar ratio of LiPF6 to LiFSI was 2:1. Additives PS and VC accounted for 1.5% and 1.0% of the electrolyte by mass, respectively.

[0239] (4) Separating membrane

[0240] Polyethylene is used as the separator.

[0241] (5) Preparation of secondary battery cells

[0242] The positive electrode, separator, and negative electrode are stacked in sequence and wound to obtain an electrode assembly. The electrode assembly is placed in a housing, electrolyte is injected, and then it is encapsulated to obtain a secondary battery cell. The battery cell has a thickness of 63 mm, a width of 280 mm, and a height of 82 mm.

[0243] Examples 2-6, Comparative Example 1

[0244] Compared with Example 1, the difference is that the parameters of the positive electrode active material or the parameters of the positive electrode sheet are different from those in Example 1, as detailed in Table 1.

[0245] Product parameters and performance parameters of Examples 1-6 and Comparative Example 1.

[0246] Table 1: Product parameters and performance parameters of Examples 1-6 and Comparative Example 1

[0247] In Table 1, "m%" represents the mass content of the corresponding substance in the positive electrode active material, "Dv50" represents the volume distribution particle size Dv50 of the corresponding substance, "positive electrode Dv50" represents the volume distribution particle size Dv50 of the positive electrode active material, "coating weight" represents the single-sided coating weight of the positive electrode film on the positive electrode sheet, "compact density" represents the compaction density of the positive electrode film, "energy density" represents the volumetric energy density of the battery cell, and "cycle performance" represents the number of cycles of the battery cell under normal temperature cycling test. The specific process of the cycle test is detailed in the testing section below.

[0248] The comparative analysis of the embodiments and the comparative examples shows that the embodiments, through the adjustment of various parameters, keep the discharge plateau voltage of the battery cell 20 within a limited range, which effectively improves the cycle performance of the battery while maintaining a high energy density. In contrast, the discharge plateau voltage of the comparative examples is not within the limited range, resulting in poorer cycle performance.

[0249] The following is a brief description of the testing methods for the physicochemical and performance parameters involved in the embodiments of this application. It should be understood that the following testing methods are only examples, and other testing methods known in the art can also be used for testing.

[0250] 1. Test method for discharge plateau voltage

[0251] At 25℃, the secondary battery cell is charged at a constant current of 1 / 3C to the cutoff voltage of 4.25V, then charged at a constant voltage until the current is ≤0.05C, and then discharged at a constant current of 1 / 3C to the cutoff voltage of 2.5V. The discharge energy E0, discharge capacity C0, and discharge plateau voltage v=E0 / C0 are recorded.

[0252] 2. Test methods for mass content

[0253] The mass ratio of Ni, Co, and Mn in the test material was determined by CP-EDS, and the specific type of lithium-containing transition metal oxide was identified based on this ratio. The mass ratio of Mn and Fe in the test material was also determined by CP-EDS, and the specific type of lithium-containing phosphate was identified based on this ratio. Then, the mass content of lithium-containing transition metal oxides was calculated from the mass content of Ni in the ICP of the test material, and the mass content of lithium-containing phosphates was calculated from the mass content of Fe.

[0254] 3. Test methods for element molar percentage

[0255] Test equipment: Inductively Coupled Plasma Emission Spectrometer (ICP).

[0256] Test method: Digestion: 1+1 aqua regia, digestion method: plate digestion / acid-removing digestion / microwave digestion (high temperature and high pressure ~200℃). The elemental mass fractions of nickel, cobalt, manganese, and doping elements were measured, and the molar amounts were calculated based on the molar mass of each element. Finally, the molar ratio of nickel, cobalt, and manganese was calculated by normalization.

[0257] 4. Dv50 Testing Method

[0258] Testing equipment: Particle size analyzer.

[0259] Pretreatment: Take a clean beaker, add an appropriate amount of the sample to be tested, add a surfactant and then add a dispersant, and sonicate at 120W / 5min to ensure that the sample is completely dispersed in the dispersant.

[0260] Test: After the sample is poured into the injection tower, it circulates with the solution to the test optical path system. Under the irradiation of the laser beam, the particle size distribution characteristics can be obtained by receiving and measuring the energy distribution of the scattered light (shading degree: 8%-12%).

[0261] Calculation: Calculate the particle size at the 50% position of the volume distribution curve from smallest to largest, which is Dv50.

[0262] 5. Test method for film coating weight

[0263] Cut a fixed area of ​​positive electrode sheet (negative electrode sheet) and weigh it. Weigh and calculate the weight of a positive current collector (negative current collector) of the same area beforehand. Subtract the weight of the positive current collector (negative current collector) from the weight of the positive electrode sheet (negative electrode sheet), and then divide by the fixed area to obtain the coating weight of the positive electrode film (negative electrode film).

[0264] 6. Test method for membrane compaction density

[0265] Take a unit area of ​​the electrode to be tested, weigh the mass m1 of the material on the unit area electrode excluding the current collector, measure the electrode thickness T1 and the current collector thickness T0, and the compaction density = m1 / (T1-T0).

[0266] 7. Test method for volumetric energy density of secondary battery cells

[0267] Perform three charge-discharge cycles on a charging and discharging device at a current density of 0.33C within the range of 2.5-4.25V, and take the discharge energy Q of the third cycle.

[0268] Measuring the volume V of the secondary battery cell 20: A CT scan image of the secondary battery cell 20 is taken. Based on the CT scan image, the length T, height h (excluding the height of the electrode terminals), width L, diameter d of the electrode terminals, and height H of the secondary battery cell 20 can be measured. The volume of the secondary battery cell 20 can be calculated using the formula V = T × h × L + 2 × π × (d / 2). 2 The energy density of the secondary battery cell 20, calculated by ×H, is Q / V (unit: Wh / L). If the electrode terminal is irregularly shaped, its volume can be calculated by fitting the irregular shape into a regular shape on a computer and then using the volume calculation formula for a regular shape.

[0269] 8. Cyclic performance testing methods

[0270] The secondary battery cell 20 under test is charged to 4.25V at a charging current of 0.5C, and after CV reaches 0.02C, it is discharged to 2.5V at a discharging current of 1C. The cycle is continued until the capacity of the secondary battery cell 20 is 80% of the initial capacity. Then the charging and discharging are stopped. The number of cycles of the secondary battery cell 20 at this time is the number of cycles of the secondary battery cell 20 to 80% SOH.

[0271] Although this application has been described with reference to preferred embodiments, various modifications can be made thereto and components can be replaced with equivalents without departing from the scope of this application. In particular, the technical features mentioned in the various embodiments can be combined in any manner, provided there is no structural conflict. This application is not limited to the specific embodiments disclosed herein, but includes all technical solutions falling within the scope of the claims.

Claims

1. A secondary battery cell, characterized in that, The secondary battery cell includes: An electrode assembly, comprising a positive electrode and a negative electrode, wherein the positive electrode comprises a positive active material, the positive active material comprising a lithium phosphate and a lithium transition metal oxide, and the negative electrode comprises a negative active material, the negative active material comprising graphite; The discharge plateau voltage v of the secondary battery cell at 25°C and a discharge rate of 1 / 3C within the voltage range of 2.5V-4.25V satisfies the following condition: 3.6V≤v≤3.67V.

2. The secondary battery cell according to claim 1, characterized in that, The lithium-containing phosphates include lithium-containing transition metal phosphates; Optionally, the lithium-containing phosphate includes those with the molecular formula Li. 1+a Mn b A 1-b P 1-c R c One or more of the following compounds or modified compounds of O4, wherein -0.2 ≤ a < 1, 0.3 ≤ b ≤ 0.9, 0 ≤ c ≤ 0.1, A includes one or more of Zn, Al, Na, K, Mg, Mo, W, Ti, V, Zr, Fe, Ni, Co, Ga, Sn, Sb, Nb, and Ge, and R includes one or more of B, Si, N, S, F, Cl, and Br; and / or, The lithium-containing transition metal oxide includes those with the molecular formula Li. x Ni y Co z M k Me p O r E s Wherein, M includes one or more elements selected from Mn and Al, Me includes one or more elements selected from Zr, Zn, Cu, Cr, Mg, Fe, V, Ti, Sr, Sb, Y, W or Nb, and E includes one or more elements selected from N, F, S and Cl; 0.8≤x≤1.15, 0<y<1, 0<z<1, 0<k<1, 0≤p≤0.1, 1≤r≤2, 0≤s≤1.

3. The secondary battery cell according to claim 1 or 2, characterized in that, The volume distribution particle size Dv501 of the positive electrode active material satisfies: 1.5μm≤Dv501≤3μm.

4. The secondary battery cell according to any one of claims 1-3, characterized in that, The lithium-containing phosphate satisfies at least one of the following conditions (1)-(3): (1) The lithium phosphate includes one or more elements selected from Al, Ti, and V; (2) The lithium-containing phosphate includes a first lithium-containing phosphate and a second lithium-containing phosphate, wherein the volume distribution particle size of the first lithium-containing phosphate is Dv50. 1-1 Satisfies: 0.05μm≤Dv50 1-1 ≤0.3μm; and / or, the volume distribution particle size Dv50 of the second lithium phosphate. 1-2 Satisfies: 1μm≤Dv50 1-2 ≤3μm; (3) The volume distribution particle size Dv50 of the lithium phosphate 1-3 Satisfies: 0.8μm≤Dv50 1-3 ≤1.2μm.

5. The secondary battery cell according to any one of claims 1-4, characterized in that, The volume distribution particle size Dv50 of the lithium-containing transition metal oxide 1-4 Satisfies: 3μm≤Dv50 1-4 ≤5μm; and / or, The volume distribution particle size Dv101 of the lithium-containing transition metal oxide satisfies: 1.5 μm ≤ Dv101 ≤ 2.5 μm; and / or, The volume distribution particle size Dv901 of the lithium-containing transition metal oxide satisfies: 7.5 μm ≤ Dv901 ≤ 9.5 μm; and / or, The particle size distribution of the lithium-containing transition metal oxide satisfies: 0.95 ≤ (Dv901 - Dv10) 1-4 ) / Dv50 1- 4≤1.

5.

6. The secondary battery cell according to any one of claims 1-5, characterized in that, Based on the total mass of the positive electrode active material, the mass content m1 of the lithium phosphate satisfies: 40wt% ≤ m1 ≤ 70wt%.

7. The secondary battery cell according to any one of claims 1-6, characterized in that, The positive electrode sheet includes a conductive agent, which includes carbon nanotubes; The diameter d of the carbon nanotube satisfies: 7μm≤d≤13μm.

8. The secondary battery cell according to any one of claims 1-7, characterized in that, The positive electrode includes a positive current collector and a positive electrode film layer disposed on at least one surface of the positive current collector, the positive electrode film layer including the positive electrode active material.

9. The secondary battery cell according to claim 8, characterized in that, The coating weight ρ1 on one side of the positive electrode film layer satisfies: 190 g / m 2 ≤ρ1≤230g / m 2 .

10. The secondary battery cell according to claim 8 or 9, characterized in that, The compaction density P1 of the positive electrode film layer satisfies: 2.5 g / cm³ 3 ≤P1≤2.9g / cm 3 ; 2.8g / cm³ is optional 3 ≤P1≤2.9g / cm 3 .

11. The secondary battery cell according to any one of claims 8-10, characterized in that, The thickness h1 of the positive current collector satisfies: 10μm≤h1≤13μm.

12. The secondary battery cell according to any one of claims 1-11, characterized in that, The average volumetric particle size Dv502 of the negative electrode active material satisfies: 10μm≤Dv502≤14μm.

13. The secondary battery cell according to any one of claims 1-12, characterized in that, The negative electrode sheet includes a negative current collector and a negative electrode film layer disposed on at least one surface of the negative current collector, the negative electrode film layer including the negative electrode active material.

14. The secondary battery cell according to claim 13, characterized in that, The coating weight ρ2 on one side of the negative electrode film layer satisfies: 90 g / m 2 ≤ρ2≤110g / m 2 .

15. The secondary battery cell according to claim 13 or 14, characterized in that, The compaction density P2 of the negative electrode film layer satisfies: 1.3 g / cm³ 3 ≤P2≤1.55g / cm 3 ; 1.4g / cm³ is optional. 3 ≤P2≤1.5g / cm 3 .

16. The secondary battery cell according to any one of claims 13-15, characterized in that, The thickness h2 of the negative electrode current collector satisfies: 4μm≤h2≤6μm.

17. The secondary battery cell according to any one of claims 1-16, characterized in that, The electrode assembly is a stacked electrode assembly.

18. The secondary battery cell according to any one of claims 1-17, characterized in that, The secondary battery cell includes a casing; the casing includes a first wall, and electrode terminals are disposed on the first wall; the electrode assembly includes a body and a tab, and the tab is connected to the end of the body facing the first wall. The secondary battery cell includes a current collector, which includes a first connecting part and a second connecting part that are connected to each other. The first connecting part is connected to the electrode terminal, and the second connecting part is connected to the tab. Wherein, along the thickness direction of the first wall, the thickness D1 of the first connecting part satisfies: 0.5mm≤D1≤1.2mm; the thickness D2 of the second connecting part satisfies: 0.3mm≤D2≤1mm.

19. The secondary battery cell according to claim 18, characterized in that, The first wall includes a first through hole; The electrode terminal includes a main body and a stepped portion. At least a portion of the main body passes through the first through hole, and the stepped portion protrudes from the outer peripheral surface of the main body and is disposed outside the secondary battery cell. The secondary battery cell includes a fixing member, and the fixing member includes a second through hole through which the main body portion passes; In the thickness direction of the first wall, at least a portion of the fastener 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 the outside of the secondary battery cell, and the fastener has a second end face facing the outside of the secondary battery cell. The first end face extends beyond the second end face.

20. The secondary battery cell according to claim 19, characterized in that, In the thickness direction of the first wall, the height difference H between the first end face and the second end face satisfies: 0.5mm≤H≤1.5mm.

21. The secondary battery cell according to claim 19 or 20, characterized in that, In the radial direction of the main body, the dimension W1 by which the stepped portion protrudes from the outer peripheral surface of the main body satisfies: 0.1mm≤W1≤5mm.

22. The secondary battery cell according to any one of claims 1-21, characterized in that, The secondary battery cell includes an electrolyte, and the ionic conductivity σ of the electrolyte satisfies: 7mS / cm≤σ≤10mS / cm.

23. The secondary battery cell according to claim 22, characterized in that, The electrolyte comprises: Solvents, including linear carbonates; Based on the total mass of the electrolyte, the mass content m2 of the linear carbonate satisfies 40wt% ≤ m2 ≤ 70wt%.

24. The secondary battery cell according to claim 22 or 23, characterized in that, The electrolyte comprises: Lithium salts, including LiPF6 and LiFSI; Optionally, based on the total mass of the electrolyte, the mass content m3 of the lithium salt satisfies 13wt% ≤ m3 ≤ 18wt%.

25. The secondary battery cell according to claim 24, characterized in that, Based on the total amount of the lithium salt, the molar percentage n of LiPF6 satisfies: 50% ≤ n ≤ 70%.

26. The secondary battery cell according to any one of claims 1-25, characterized in that, The secondary battery cell includes a separator, which includes a porous substrate. The thickness h3 of the porous substrate satisfies the following conditions: h3≤7μm; optionally, 3μm≤h3≤5μm.

27. An electrical appliance, characterized in that, The electrical device includes a secondary battery cell as described in any one of claims 1-26.

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