Positive electrode sheet, secondary battery, and electric device

Abstract

This application provides a positive electrode sheet, a secondary battery, and an electrical device. The positive electrode sheet can be a positive electrode sheet for winding a battery cell, including a waist region near the waist and an end region away from the waist. The waist region has a first positive electrode film, and the end region has a second positive electrode film. The positive electrode sheet can also be a positive electrode sheet for stacking battery cells, including a central region near the center and an edge region away from the center; the central region has a first positive electrode film, and the edge region has a second positive electrode film.

Description

Technical Field

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

[0002] In recent years, with the increasingly wide application of secondary batteries, they have been widely used in energy storage power systems such as hydropower, thermal power, wind power, and solar power plants, as well as in power tools, electric bicycles, electric motorcycles, electric cars, military equipment, aerospace, and many other fields. Due to the significant development of secondary batteries, higher requirements have been placed on their energy density and cycle performance.

[0003] The relevant technology compensates for the irreversible sodium loss in lithium / sodium-ion batteries during the first charge-discharge cycle by replenishing lithium / sodium. Summary of the Invention

[0004] The inventors discovered that for wound cells, the temperature at the waist of the cell is higher than that at the ends during battery operation; for stacked cells, the temperature at the center of the cell is higher than that at the edges during battery operation. Compared to the lower-temperature regions, the higher-temperature regions exhibit higher electrochemical activity. These regions with high electrochemical activity have higher lithium-ion loss rates and a higher degree of irreversible damage to the cathode material.

[0005] In view of the above-mentioned issues, this application provides a novel positive electrode, a secondary battery, and an electrical device, which are described below.

[0006] The first aspect of this application provides a positive electrode sheet for winding a battery cell, including a waist region near the waist and an end region away from the waist;

[0007] The waist region is provided with a first positive electrode film, and the end region is provided with a second positive electrode film;

[0008] The porosity of the first positive electrode film is greater than that of the second positive electrode film.

[0009] The positive electrode based on the above scheme is used in secondary batteries, which exhibit one or more improved performance characteristics, such as improved cycle life.

[0010] A second aspect of this application provides a positive electrode sheet for a stacked battery cell, comprising a central region near the center and an edge region away from the center;

[0011] The central region is provided with a first positive electrode film, and the edge region is provided with a second positive electrode film;

[0012] The porosity of the first positive electrode film is greater than that of the second positive electrode film.

[0013] The positive electrode based on the above scheme is used in secondary batteries, which exhibit one or more improved performance characteristics, such as improved cycle life.

[0014] In some implementations, the ratio of the porosity of the first positive electrode film to the porosity of the second positive electrode film is 1.003 to 3:1.

[0015] In some embodiments, a first alkali metal ion providing material and / or a second alkali metal ion providing material are distributed within the first positive electrode film. The first alkali metal ion providing material has irreversible capacity, and the second alkali metal ion providing material has reversible capacity. The first alkali metal ion providing material within the first positive electrode film provides P1 ppm of alkali metal ions, and the second alkali metal ion providing material provides Q1 ppm of alkali metal ions.

[0016] The second positive electrode film contains a first alkali metal ion providing material and / or a second alkali metal ion providing material, wherein the first alkali metal ion providing material provides irreversible capacity and the second alkali metal ion providing material provides reversible capacity; the first alkali metal ion providing material in the second positive electrode film provides P2 ppm alkali metal ions and the second alkali metal ion providing material Q2 ppm alkali metal ions;

[0017] The first positive electrode film and the second positive electrode film conform to the following relationship:

[0018] (P 1+ Q1)>(P2+Q2)

[0019] Where P1>0, P2≥0, Q1>0, Q2>0.

[0020] In some implementations, the first positive electrode film and the second positive electrode film conform to the following relationship: (P1 / Q1)>(P2 / Q2).

[0021] In some implementations, the positive electrode has one or more of the following characteristics:

[0022] (1) The value of (P1 / Q1) is 0.1% to 70%;

[0023] (2) The value of (P2 / Q2) ranges from 0 to 70%;

[0024] (3) The value of (P1 / Q1) - (P2 / Q2) is 0.1% to 60%.

[0025] In some implementations, the positive electrode has one or more of the following characteristics:

[0026] (1)P1+Q1=40000~180000ppm;

[0027] (2)P2+Q2=40000~180000ppm;

[0028] (3)(P1+Q1):(P2+Q2)=(1.001~2):1.

[0029] In some implementations, the positive electrode has one or more of the following characteristics:

[0030] (1) The waist region is a strip-shaped region distributed along the length of the positive electrode sheet;

[0031] (2) The end region is a strip-shaped region distributed along the length direction of the positive electrode sheet;

[0032] (3) The width of the waist region is 0.05D to 0.95D, where D is the total width of the active material region on the positive electrode plate;

[0033] (4) The width of the end region is 0.05D to 0.95D, where D is the total width of the active material region on the positive electrode plate;

[0034] (5) The total area of ​​the waist region accounts for 5% to 95% of the total area of ​​the active material region on the positive electrode sheet, and can be selected as 50% to 95%;

[0035] (6) The total area of ​​the end region accounts for 5% to 95% of the total area of ​​the active material region on the positive electrode sheet, and can be selected as 5% to 50%.

[0036] In some implementations, the positive electrode has one or more of the following characteristics:

[0037] (1) The central area is a circular, elliptical, polygonal, or similar shape centered on the center of the positive electrode plate;

[0038] (2) The edge region is a ring-shaped region distributed along the edge of the positive electrode sheet;

[0039] (3) The total area of ​​the central region accounts for 5% to 95% of the total area of ​​the active material region on the positive electrode sheet, and can be selected as 50% to 95%;

[0040] (4) The total area of ​​the edge region accounts for 5% to 95% of the total area of ​​the active material region on the positive electrode sheet, and can be selected as 5% to 50%.

[0041] In some embodiments, the first alkali metal ion material includes one or more of the following: alkali metal nitrides, alkali metal oxides, alkali metal oxide / transition metal complexes, alkali metal peroxides, over-alkali metallized alkali metal oxides, or alkali metal carbon oxides.

[0042] In some implementations, the positive electrode has one or more features:

[0043] (1) The alkali metal nitride is A3N;

[0044] (2) The alkali metal oxide is A2O

[0045] (3) The alkali metal oxide / transition metal complex is A2O / M;

[0046] (4) The alkali metal peroxide is A2O2;

[0047] (5) Over-alkali metallized alkali metal oxides A2NiO2, A5FeO4

[0048] (6) The alkali metal oxocarbides are selected from A2C2O4, A2C4O4, A2C3O5, and A2C4O6;

[0049] Wherein, A is an alkali metal element;

[0050] M is a transition metal element.

[0051] In some embodiments, the second alkali metal ion material comprises one or more of the following:

[0052] (1) Alkali metal ion secondary battery active material with layered structure;

[0053] (2) Alkali metal ion secondary battery active materials with olivine structure;

[0054] (3) Alkali metal ion secondary battery active materials with spinel structure;

[0055] (4) Prussian blue alkali metal ion secondary battery active materials.

[0056] In some embodiments, the alkali metal is selected from lithium, sodium, or a combination thereof.

[0057] In some embodiments, the positive electrode includes a waist region and two end regions, the waist region being located between the two end regions, the waist region containing a first positive electrode film, and the two end regions each containing a second positive electrode film.

[0058] In a second aspect, this application provides a secondary battery comprising the positive electrode sheet described in any of the preceding claims.

[0059] In a third aspect, this application provides an electrical device including the aforementioned secondary battery.

[0060] Beneficial effects

[0061] One or more embodiments of this application have one or more of the following beneficial effects:

[0062] (1) The positive electrode is used in secondary batteries, and the batteries exhibit improved cycle life.

[0063] (2) The porosity of the waist region of the positive electrode is relatively high, which shows a slower growth of expansion force. Attached Figure Description

[0064] Figure 1 This is a schematic diagram of the positive electrode sheet according to one embodiment of this application.

[0065] Figure 2 This is a schematic diagram of a wound battery cell according to one embodiment of this application.

[0066] Figure 3 This is a schematic diagram of the positive electrode sheet according to another embodiment of this application.

[0067] Figure 4 This is a schematic diagram of a stacked battery cell according to one embodiment of this application.

[0068] Figure 5 This is a schematic diagram of a secondary battery according to one embodiment of this application.

[0069] Figure 6 yes Figure 5 An exploded view of a secondary battery according to one embodiment of this application is shown.

[0070] Figure 7 This is a schematic diagram of a battery module according to one embodiment of this application.

[0071] Figure 8 This is a schematic diagram of a battery pack according to one embodiment of this application.

[0072] Figure 9 yes Figure 8 An exploded view of a battery pack according to one embodiment of this application is shown.

[0073] Figure 10 This is a schematic diagram of an electrical device that uses a secondary battery as a power source according to one embodiment of this application.

[0074] Explanation of reference numerals in the attached figures:

[0075] 1 Battery pack; 2 Upper housing; 3 Lower housing; 4 Battery module; 5 Secondary battery; 51 Housing; 52 Electrode assembly; 53 Top cover assembly; 100 Winded cell; 200 Stacked cell; 11 Positive electrode; 12 Negative electrode; 13 Separator; 500 Waist section; 501 First end; 502 Second end; 101 Waist section area; 201 First end area; 202 Second end area; 600 Center; 601 Center area; 602 Edge area. Detailed Implementation

[0076] The following detailed description, with appropriate reference to the accompanying drawings, discloses embodiments of the negative electrode active material and its manufacturing method, positive electrode sheet, negative electrode sheet, secondary battery, battery module, battery pack, and device of this application. However, unnecessary detailed descriptions may be omitted. For example, detailed descriptions of well-known matters and repetitive descriptions of practically identical structures may be omitted. This is to avoid unnecessarily lengthy descriptions and to facilitate understanding by those skilled in the art. Furthermore, the accompanying drawings and the following description are provided to enable those skilled in the art to fully understand this application and are not intended to limit the subject matter of the claims.

[0077] 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.

[0078] Unless otherwise specified, all embodiments and optional embodiments of this application can be combined to form new technical solutions.

[0079] Unless otherwise specified, all technical features and optional technical features of this application may be combined to form new technical solutions.

[0080] 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.

[0081] Unless otherwise specified, the terms "comprising" and "including" as used in this application can be open-ended or closed-ended. For example, "comprising" and "including" can mean that other components not listed may also be included, or that only the listed components may be included.

[0082] Unless otherwise specified, the term "or" is inclusive in this application. For example, the phrase "A or B" means "A, B, or both A and B". More specifically, the condition "A or B" is satisfied by any of the following conditions: A is true (or exists) and B is false (or does not exist); A is false (or does not exist) and B is true (or exists); or both A and B are true (or exist).

[0083] [Rechargeable Battery]

[0084] Secondary batteries, also known as rechargeable batteries or storage batteries, are batteries that can be recharged after being discharged to activate the active materials and continue to be used.

[0085] Typically, a secondary battery consists of a positive electrode, a negative electrode, a separator, and an electrolyte. During charging and discharging, active ions (such as lithium ions) repeatedly insert and extract between the positive and negative electrodes. The separator, positioned between the positive and negative electrodes, primarily prevents short circuits while allowing active ions to pass through. The electrolyte, also positioned between the positive and negative electrodes, mainly serves to conduct active ions.

[0086] [Negative electrode plate]

[0087] The negative electrode sheet 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 electrode active material, which is the negative electrode active material of any one of the claims in this application.

[0088] As an example, the negative electrode current collector has two surfaces opposite each other in its own thickness direction, and the negative electrode film is disposed on either or both of the two opposite surfaces of the negative electrode current collector.

[0089] In some embodiments, the negative electrode current collector may be a metal foil or a composite current collector. For example, copper foil may be used as the metal foil. The composite current collector may include a polymer material substrate and a metal layer formed on at least one surface of the polymer material substrate. The composite current collector may be formed by forming a metal material (copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer material substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0090] In some embodiments, the negative electrode membrane may optionally include a binder. As an example, the binder may be selected from at least one of styrene-butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethacrylic acid (PMAA), and carboxymethyl chitosan (CMCS).

[0091] In some embodiments, the negative electrode film may optionally include a conductive agent. As an example, 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.

[0092] In some embodiments, the negative electrode membrane may optionally include other additives, such as thickeners (e.g., sodium carboxymethyl cellulose (CMC-Na)).

[0093] In some embodiments, the negative electrode sheet can be prepared by dispersing the components used to prepare the negative electrode sheet, such as the negative electrode active material, conductive agent, binder and any other components, in a solvent (e.g., deionized water) to form a negative electrode slurry; coating the negative electrode slurry onto the negative electrode current collector, and then obtaining the negative electrode sheet after drying, cold pressing and other processes.

[0094] [Positive electrode plate]

[0095] The first aspect of this application provides a positive electrode sheet for winding a battery cell, including a waist region near the waist and an end region away from the waist;

[0096] The waist region is provided with a first positive electrode film, and the end region is provided with a second positive electrode film;

[0097] The porosity of the first positive electrode film is greater than that of the second positive electrode film.

[0098] The positive electrode based on the above scheme is used in secondary batteries, which exhibit one or more improved performance characteristics, such as improved cycle life.

[0099] Without being limited by theory, the theoretical basis for the above-mentioned positive electrode sheet to improve battery cycle life is as follows:

[0100] During battery cell operation, the expansion rate of the waist region is greater than that of the end region. This results in the waist region experiencing greater compression from the battery casing compared to the end region, leading to poorer electrolyte reflux in the waist region. Furthermore, prolonged compression degrades the porosity of the negative electrode. The reduced porosity of the compacted negative electrode sheet results in insufficient electrolyte wetting, impaired lithium intercalation kinetics, and a higher likelihood of central lithium plating failure in the later stages of cycling. Therefore, by controlling the porosity of the waist region of the positive electrode sheet to ensure it is greater than that of the end region, space can be reserved in advance to withstand compression, thereby mitigating the adverse effects of compression on the waist region.

[0101] In some implementations, the term "waist" refers to the midpoint of the positive electrode plate used for winding the battery cell along the winding axis. The waist position is equidistant from both ends of the winding axis along the winding axis. The waist region may be symmetrical about the waist.

[0102] In some implementations, "closer to the waist" means that the waist region is closer to the waist than the end region. The waist region may be adjacent to the waist or encompass the waist.

[0103] In some implementations, "away from the waist" means that the end area is further away from the waist compared to the waist area.

[0104] In some embodiments, the area of ​​the waist region can be 10-90% of the area of ​​the positive electrode sheet, for example, 20-80%, 30-70%, 40-60%, or 50%. In some embodiments, the area of ​​the end region can be 10-90% of the area of ​​the positive electrode sheet, for example, 20-80%, 30-70%, 40-60%, or 50%.

[0105] In some embodiments, the end region includes a first end region and a second end region. The area of ​​the first end region can be 5% to 45% of the area of ​​the positive electrode sheet, for example, 10% to 40%, 20% to 30%, or 25%. The area of ​​the second end region can be 5% to 45% of the area of ​​the positive electrode sheet, for example, 10% to 40%, 20% to 30%, or 25%.

[0106] A second aspect of this application provides a positive electrode sheet for a stacked battery cell, comprising a central region near the center and an edge region away from the center;

[0107] The central region is provided with a first positive electrode film, and the edge region is provided with a second positive electrode film;

[0108] The porosity of the first positive electrode film is greater than that of the second positive electrode film.

[0109] The positive electrode based on the above scheme is used in secondary batteries, which exhibit one or more improved performance characteristics, such as improved cycle life.

[0110] Without being limited by theory, the theoretical basis for the above-mentioned positive electrode sheet to improve battery cycle life is as follows:

[0111] During battery cell operation, the central region expands more than the edge regions, resulting in greater compression of the central region by the battery casing. This leads to poorer electrolyte reflux in the central region, and prolonged compression also degrades the porosity of the negative electrode. The reduced porosity of the compacted negative electrode leads to insufficient electrolyte wetting, impaired lithium intercalation kinetics, and a higher likelihood of central lithium plating failure in the later stages of cycling. Therefore, by controlling the porosity of the central region of the positive electrode, ensuring that the porosity of the waist region is greater than that of the first and second edge regions, space can be reserved in advance to withstand compression, thereby mitigating the adverse effects of central region compression.

[0112] In some embodiments, a porous positive electrode membrane is obtained by adding a decomposable material (such as alkali metal carbon oxides) to the positive electrode membrane, and then decomposing the decomposable material under specific conditions (e.g., liquefaction or gasification). After decomposition, pores are formed on the positive electrode membrane at the locations where the decomposable material was originally disposed. Optionally, the decomposition of the decomposable material releases gases (such as CO2) during the process, which helps to increase the size and number of pores. By providing different contents / compositions of the decomposable material in the first and second positive electrode membranes, different pore sizes can be formed in the first and second positive electrode membranes, thereby obtaining a positive electrode membrane with a porosity greater than that of the second positive electrode membrane.

[0113] In some embodiments, the alkali metal carbon oxide is selected from A₂C₂O₄, A₂C₄O₄, A₂C₃O₅, and A₂C₄O₆. Element A is selected from Li, Na, K, or combinations thereof.

[0114] Figure 3 A schematic diagram of the positive electrode sheet of this embodiment is shown. The positive electrode sheet 11 is quadrilateral in shape. Along the surface direction of the positive electrode sheet 11, it includes a central region 601 near the center 600 and an edge region 602 away from the center 600, with the edge region 602 located outside the central region 601. The central region 601 is quadrilateral in shape. The edge region 602 surrounds the periphery of the central region 601.

[0115] Figure 4A schematic diagram of the stacked battery cell of this embodiment is shown. The stacked battery cell 200 has a laminated structure. Specifically, the stacked battery cell 200 includes a plurality of positive electrode plates 11 and a plurality of negative electrode plates 12, which are alternately stacked, and a separator 13 is located between the positive electrode plates 11 and the negative electrode plates 12. In the laminated structure, both the positive electrode plates 11 and the negative electrode plates 12 are sheet-like, and the stacking direction of the positive electrode plates 11 and the negative electrode plates 12 is parallel to the thickness direction of the positive electrode plates 11 and the thickness direction of the negative electrode plates 12.

[0116] In some implementations, the term "center" refers to the geometric center of the positive electrode sheet used for stacked cells. The center region may have the same shape and geometric center as the positive electrode sheet. The area of ​​the center region may be 10–90% of the area of ​​the positive electrode sheet, for example, 20–80%, 30–70%, 40–60%, or 50%. The area of ​​the edge region may also be 10–90% of the area of ​​the positive electrode sheet, for example, 20–80%, 30–70%, 40–60%, or 50%.

[0117] In some implementations, "closer to the center" means that the central area is closer to the center than the peripheral areas. The central area may be adjacent to the center or encompass the center.

[0118] In some implementation schemes, "far from the center" means that the periphery is farther from the center than the central area.

[0119] In some embodiments, the term "first provision of alkali metal ion material" has a first effect of less than 20% (e.g., less than 15%, less than 10%, less than 5%, less than 1%), and they have irreversible capacity.

[0120] In some implementations, the term "secondary alkali metal ion material" has a first-efficiency of 80% or more (e.g., 85% or more, 90% or more, 95% or more, 99% or more) and they have reversible capacity.

[0121] In some embodiments, the first positive electrode film and the second positive electrode film each independently contain a first alkali metal ion-providing material and / or a second alkali metal ion-providing material distributed within the first positive electrode film. The first alkali metal ion-providing material in the first positive electrode film and the second positive electrode film can be the same or different materials. The second alkali metal ion-providing material in the first positive electrode film and the second positive electrode film can be the same or different materials.

[0122] In some implementations, the term "initial efficiency" refers to "initial coulombic efficiency" (ICE). The testing method for the initial coulombic efficiency of the first alkali metal ion donor material and the second alkali metal ion donor material can refer to methods or standards generally accepted in the art. For example, if the test material is assembled into a battery (e.g., a half-cell) as the positive electrode active material, and the initial delithiation capacity C1 and initial lithium insertion capacity C2 of the test material are measured, then the initial coulombic efficiency = C2 / C1 × 100%.

[0123] In some implementations, the porosity of the first positive electrode film is greater than that of the second positive electrode film. Positive electrode sheets based on the above schemes are used in secondary batteries, which exhibit one or more improved performance characteristics, such as improved cycle life.

[0124] In some embodiments, the porosity ratio of the first positive electrode film to the second positive electrode film is 1.003 to 3:1. Positive electrode sheets based on the above schemes are used in secondary batteries, which exhibit one or more improved performance characteristics, such as improved cycle life.

[0125] In some implementations, the porosity ratio of the first positive electrode film to the second positive electrode film is 1.003–1.01:1, 1.01–1.1:1, 1.1–1.2:1, 1.2–1.3:1, 1.3–1.4:1, 1.4–1.5:1, 1.5–1.6:1, 1.6–1.7:1, 1.7–1.8:1, 1.8–1.9:1, 1.9–2:1, 2–2.1:1, 2.1–2.2:1, 2.2–2.3:1, 2.3–2.4:1, 2.4–2.5:1, 2.5–2.6:1, 2.6–2.7:1, 2.7–2.8:1, 2.8–2.9:1, or 2.9–3:1.

[0126] In some embodiments, a first alkali metal ion providing material and / or a second alkali metal ion providing material are distributed within the first positive electrode film. The first alkali metal ion providing material has irreversible capacity, and the second alkali metal ion providing material has reversible capacity. The first alkali metal ion providing material within the first positive electrode film provides P1 ppm of alkali metal ions, and the second alkali metal ion providing material provides Q1 ppm of alkali metal ions.

[0127] The second positive electrode film contains a first alkali metal ion providing material and / or a second alkali metal ion providing material, wherein the first alkali metal ion providing material provides irreversible capacity and the second alkali metal ion providing material provides reversible capacity; the first alkali metal ion providing material in the second positive electrode film provides P2 ppm alkali metal ions and the second alkali metal ion providing material Q2 ppm alkali metal ions;

[0128] The first positive electrode film and the second positive electrode film conform to the following relationship:

[0129] (P 1+ Q1)>(P2+Q2)

[0130] Where P1>0, P2≥0, Q1>0, Q2>0.

[0131] The reasons for the improved battery cycle life, which are not limited by theory, are analyzed as follows:

[0132] The positive electrode sheet based on the above scheme is used in secondary batteries, which exhibit improved cycle life. Without being limited by theory, the reasons for the improved battery cycle life are analyzed as follows:

[0133] In the first positive electrode film (P) 1+ The value of Q1 is relatively large because the first positive electrode film is located in the waist region (or central region) where the temperature is high and the electrochemical activity is high. 1+ Q1) It can compensate for the capacity loss caused by insufficient reversible alkali metal ions due to the excessively rapid consumption rate of alkali metal ions in the waist area (or center area), thereby improving the overall cycle life of the cell.

[0134] The value of (P2+Q2) in the second positive electrode film is relatively small because the second positive electrode film is located in the end region (or edge region) with lower temperature and lower electrochemical activity. 2+ Q2) helps reduce overall costs while avoiding the risk of short circuits caused by metal dendrites on the anode due to excessive alkali metals.

[0135] In some implementations, the first positive electrode film and the second positive electrode film meet the following relationship: (P1 / Q1)>(P2 / Q2).

[0136] The first and / or second alkali metal ion materials play different roles in the battery operation process. The alkali metal ions provided by the first alkali metal ion material are used to compensate for the consumption of alkali metal ions during the battery's life cycle, such as the consumption during the initial film formation reaction and the consumption during the repair film formation reaction during cycling / storage. The alkali metal ions provided by the second alkali metal ion material are used for reversible insertion / extraction / electrochemical reactions in the positive and negative electrode materials. Since the inherent film formation consumption is compensated by the first alkali metal ion material, more reversible alkali metal ions are available to provide electrochemical energy.

[0137] The larger (P1 / Q1) value in the first positive electrode film is due to the fact that the first positive electrode film is located in the waist region where the temperature is high and the electrochemical activity is high. The larger (P1 / Q1) can compensate for the capacity loss caused by the insufficient number of reversible alkali metal ions due to the excessively fast consumption rate of alkali metal ions in the waist region, thereby improving the overall cycle life of the cell.

[0138] The smaller (P2 / Q2) value in the second positive electrode film is beneficial because the second positive electrode film is located in the end region with lower temperature and lower electrochemical activity. The smaller (P2 / Q2) helps to reduce the overall cost and avoids the risk of short circuit caused by metal dendrites in the anode due to excessive alkali metal content.

[0139] In some implementations, the positive electrode has one or more of the following characteristics:

[0140] (1) The value of (P1 / Q1) is 0.1% to 70%;

[0141] (2) The value of (P2 / Q2) ranges from 0 to 70%;

[0142] (3) The value of (P1 / Q1)-(P2 / Q2) is 0.1% to 70%.

[0143] In some implementations, the value of (P1 / Q1) is 0.1%-1%, 1%-5%, 5%-10%, 10%-15%, 15%-20%, 20%-25%, 25%-30%, 30%-35%, 35%-40%, 40%-45%, 45%-50%, 50%-55%, 55%-60%, 60%-65%, or 65%-70%.

[0144] In some implementations, the value of (P2 / Q2) is 0%-0.1%, 0.1%-1%, 1%-5%, 5%-10%, 10%-15%, 15%-20%, 20%-25%, 25%-30%, 30%-35%, 35%-40%, 40%-45%, 45%-50%, 50%-55%, 55%-60%, 60%-65%, or 65%-70%.

[0145] In some implementations, the value of (P1 / Q1)-(P2 / Q2) is 0.1%-1%, 1%-5%, 5%-10%, 10%-15%, 15%-20%, 20%-25%, 25%-30%, 30%-35%, 35%-40%, 40%-45%, 45%-50%, 50%-55%, 55-60%, 60%-65%, or 65%-70%.

[0146] In some implementations, the positive electrode has one or more of the following characteristics:

[0147] (1) The value of (P1 / Q1) is 10% to 30%;

[0148] (2) The value of (P2 / Q2) is 0 to 10%;

[0149] (3) The value of (P1 / Q1)-(P2 / Q2) is 10% to 36%.

[0150] In some implementations, the positive electrode has one or more of the following characteristics:

[0151] (1)P1+Q1=40000~180000ppm;

[0152] (2)P2+Q2=40000~180000ppm;

[0153] (3)(P1+Q1):(P2+Q2)=(1.001~2):1.

[0154] In some implementations, the value of P1+Q1 is 40000-41000ppm, 41000-45000ppm, 40000-50000ppm, 50000-60000ppm, 60000-70000ppm, 70000-80000ppm, 80000-90000ppm, 90000-100000ppm, or 100000-110000ppm. m, 110000-120000ppm, 120000-130000ppm, 130000-140000ppm, 140000-150000ppm, 150000 -160000ppm, 160000-170000ppm, 170000-180000ppm, 175000-18000ppm or 179000-18000ppm.

[0155] In some implementations, the value of P2+Q2 is 40000-41000ppm, 41000-45000ppm, 40000-50000ppm, 50000-60000ppm, 60000-70000ppm, 70000-80000ppm, 80000-90000ppm, 90000-100000ppm, or 100000-110000ppm. m, 110000-120000ppm, 120000-130000ppm, 130000-140000ppm, 140000-150000ppm, 150000 -160000ppm, 160000-170000ppm, 170000-180000ppm, 175000-18000ppm or 179000-18000ppm.

[0156] In some implementations, the value of (P1+Q1):(P2+Q2) is (1.001-1.01):1, (1.01-1.02):1, (1.02-1.03):1, (1.03-1.04):1, (1.04-1.05):1, (1.01-1.1):1, (1.1-1.2):1, (1.2-1.3):1, (1.3-1.4):1, (1.4-1.5):1, (1.5-1.6):1, (1.6-1.7):1, (1.7-1.8):1, (1.8-1.9):1, or (1.9-2):1.

[0157] In some implementations, the positive electrode has one or more of the following characteristics:

[0158] (1) The waist region is a strip-shaped region distributed along the length of the positive electrode sheet;

[0159] (2) The end region is a strip-shaped region distributed along the length direction of the positive electrode sheet;

[0160] (3) The width of the waist region is 0.05D to 0.95D, where D is the total width of the active material region on the positive electrode plate;

[0161] (4) The width of the end region is 0.05D to 0.95D, where D is the total width of the active material region on the positive electrode plate;

[0162] (5) The total area of ​​the waist region accounts for 5% to 95% of the total area of ​​the active material region on the positive electrode sheet, and can be selected as 50% to 95%;

[0163] (6) The total area of ​​the end region accounts for 5% to 95% of the total area of ​​the active material region on the positive electrode sheet, and can be selected as 5% to 50%.

[0164] In some implementations, the term "active material region" refers to the area on the positive electrode where active material is disposed (e.g., coated). The positive electrode may also include a tab region, which is the area where no active material is disposed.

[0165] In some implementations, the width of the waist area is 0.05D-0.15D, 0.15D-0.25D, 0.25D-0.35D, 0.35D-0.45D, 0.45D-0.55D, 0.55D-0.65D, 0.65D-0.75D, 0.75D-0.85D, or 0.85D-0.95D.

[0166] In some implementations, the width of the end region is 0.05D-0.15D, 0.15D-0.25D, 0.25D-0.35D, 0.35D-0.45D, 0.45D-0.55D, 0.55D-0.65D, 0.65D-0.75D, 0.75D-0.85D, or 0.85D-0.95D.

[0167] In some implementations, the total area of ​​the waist region accounts for 5%-15%, 15%-25%, 25%-35%, 35%-45%, 45%-55%, 55%-65%, 65%-75%, 75%-85%, or 85%-95% of the total area of ​​the active material region on the positive electrode sheet.

[0168] In some implementations, the total area of ​​the end region accounts for 5%-15%, 15%-25%, 25%-35%, 35%-45%, 45%-55%, 55%-65%, 65%-75%, 75%-85%, or 85%-95% of the total area of ​​the active material region on the positive electrode sheet.

[0169] In some implementations, the positive electrode has one or more of the following characteristics:

[0170] (1) The central area is a circular, elliptical, polygonal, or similar shape centered on the center of the positive electrode plate;

[0171] (2) The edge region is a ring-shaped region distributed along the edge of the positive electrode sheet;

[0172] (3) The total area of ​​the central region accounts for 5% to 95% of the total area of ​​the active material region on the positive electrode sheet, and can be selected as 50% to 95%;

[0173] (4) The total area of ​​the edge region accounts for 5% to 95% of the total area of ​​the active material region on the positive electrode sheet, and can be selected as 5% to 50%.

[0174] In some implementations, the total area of ​​the central region accounts for 5%-15%, 15%-25%, 25%-35%, 35%-45%, 45%-55%, 55%-65%, 65%-75%, 75%-85%, or 85%-95% of the total area of ​​the active material region on the positive electrode sheet.

[0175] In some implementations, the total area of ​​the edge region accounts for 5%-15%, 15%-25%, 25%-35%, 35%-45%, 45%-55%, 55%-65%, 65%-75%, 75%-85%, or 85%-95% of the total area of ​​the active material region on the positive electrode sheet.

[0176] In some implementations, part or all of the waist region (e.g., 50-100% area, e.g., 70-100% area, e.g., 90-100% area) is covered by a first positive electrode film.

[0177] In some embodiments, part or all of the end region (e.g., 50-100% area, e.g., 70-100% area, e.g., 90-100% area) is covered by a second positive electrode film.

[0178] In some implementations, part or all of the central region (e.g., 50-100% area, e.g., 70-100% area, e.g., 90-100% area) is covered by a first positive electrode film.

[0179] In some implementations, part or all of the edge region (e.g., 50-100% area, e.g., 70-100% area, e.g., 90-100% area) is covered by a second positive electrode film.

[0180] In some embodiments, the first positive electrode film and the second positive electrode film have substantially the same areal density, and the ratio of their areal densities is, for example, 0.8 to 1.2:1, 0.9 to 1.1:1, or 1:1.

[0181] In some embodiments, the first alkali metal ion material includes one or more of the following: alkali metal nitrides, alkali metal oxides, alkali metal oxide / transition metal complexes, alkali metal peroxides, over-alkali metallized alkali metal oxides, or alkali metal carbon oxides.

[0182] In some implementations, the positive electrode has one or more of the following characteristics:

[0183] (1) The alkali metal nitride is A3N;

[0184] (2) The alkali metal oxide is A2O

[0185] (3) The alkali metal oxide / transition metal complex is A2O / M;

[0186] (4) The alkali metal peroxide is A2O2;

[0187] (5) Over-alkali metallized alkali metal oxides A2NiO2, A5FeO4

[0188] (6) The alkali metal oxocarbides are selected from A2C2O4, A2C4O4, A2C3O5, and A2C4O6;

[0189] Wherein, A is an alkali metal element;

[0190] M is a transition metal element.

[0191] In some embodiments, the second alkali metal ion material comprises one or more of the following:

[0192] (1) Alkali metal ion secondary battery active material with layered structure;

[0193] (2) Alkali metal ion secondary battery active materials with olivine structure;

[0194] (3) Alkali metal ion secondary battery active materials with spinel structure;

[0195] (4) Prussian blue alkali metal ion secondary battery active materials.

[0196] In some embodiments, the alkali metal is selected from lithium, sodium, or a combination thereof.

[0197] In some embodiments, the positive electrode includes a waist region and two end regions, the waist region being located between the two end regions, the waist region containing a first positive electrode film, and the two end regions each containing a second positive electrode film.

[0198] In some implementations, the positive electrode of this application is obtained by setting a positive electrode film of different composition in different regions of the positive electrode sheet.

[0199] In some embodiments, the positive electrode includes a first positive electrode film and a second positive electrode film, the first positive electrode film and the second positive electrode film are located in different regions of the positive electrode and are not stacked on top of each other, the first positive electrode film and the second positive electrode film each independently contain a first alkali metal ion providing material and / or a second alkali metal ion providing material, and the first positive electrode film and the second positive electrode film have different compositions.

[0200] In some embodiments, the positive electrode typically 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 including a positive active material (also referred to as "alkali metal ion providing material").

[0201] As an example, the positive current collector has two surfaces opposite each other in its own thickness direction, and the positive electrode film is disposed on either or both of the two opposite surfaces of the positive current collector.

[0202] 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.).

[0203] In some embodiments, the positive electrode active material may be a known battery positive electrode active material. As an example, the positive electrode active material may include at least one of the following materials: lithium phosphates with an olivine structure, lithium transition metal oxides, and their respective modified compounds. However, this application is not limited to these materials, and other conventional materials that can be used as battery positive electrode active materials may also be used. These positive electrode active materials may be used alone or in combination of two or more. Examples of lithium transition metal oxides 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 / 5 n 1 / 3 O2 (also known as NCM) 333 LiNi 0.5 Co 0.2 Mn 0.3 O2 (also known as NCM) 523 LiNi 0.5 Co 0.25 Mn 0.25 O2 (also known as NCM) 211 LiNi 0.6 Co 0.2 Mn 0.2 O2 (also known as NCM) 622 LiNi 0.8 Co 0.1 Mn 0.1 O2 (also known as NCM) 811 ), 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 with an olivine structure include, but are not limited to, lithium iron phosphate (such as LiFePO4 (also referred to as LFP)), lithium iron phosphate and carbon composites, lithium manganese phosphate (such as LiMnPO4), lithium manganese phosphate and carbon composites, lithium manganese iron phosphate, and lithium manganese iron phosphate and carbon composites.

[0204] In some embodiments, the positive electrode membrane may optionally include a binder. As an example, the binder may include at least one selected from polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), PVDF-tetrafluoroethylene-propylene terpolymer, PVDF-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorinated acrylate resin.

[0205] In some embodiments, the positive electrode film may optionally include a conductive agent. As an example, the conductive agent may include at least one selected from superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0206] In some embodiments, the positive electrode sheet can be prepared by dispersing the above-mentioned components for preparing the positive electrode sheet, such as positive active material, conductive agent, binder and any other components, in a solvent (e.g., N-methylpyrrolidone) to form a positive electrode slurry; coating the positive electrode slurry onto the positive electrode current collector, and then obtaining the positive electrode sheet after drying, cold pressing and other processes.

[0207] [Electrolytes]

[0208] The electrolyte acts as a conductor of ions between the positive and negative electrodes. This application does not impose specific restrictions on the type of electrolyte; it can be selected according to requirements. For example, the electrolyte can be liquid, gel, or entirely solid.

[0209] In some embodiments, the electrolyte is liquid and includes an electrolyte salt and a solvent.

[0210] In some embodiments, the electrolyte salt may be selected from at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium hexafluoroarsenate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium trifluoromethanesulfonate, lithium difluorophosphate, lithium difluorooxalate borate, lithium dioxalate borate, lithium difluorodioxalate phosphate, and lithium tetrafluorooxalate phosphate.

[0211] In some embodiments, the solvent may be selected from at least one of ethylene carbonate, propylene carbonate, methyl ethyl carbonate, diethyl carbonate, dimethyl carbonate, dipropyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, butyl carbonate, fluoroethylene carbonate, methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate, 1,4-butyrolactone, sulfolane, dimethyl sulfone, methyl ethyl sulfone, and diethyl sulfone.

[0212] In some embodiments, the electrolyte may optionally include additives. As examples, 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.

[0213] [Isolation membrane]

[0214] In some embodiments, the secondary battery also includes a separator. This application does not impose any particular limitation on the type of separator; any known porous separator with good chemical and mechanical stability can be selected.

[0215] In some embodiments, the material of the separator can be selected from at least one of glass fiber, nonwoven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator can be a single-layer film or a multi-layer composite film, without particular limitation. When the separator is a multi-layer composite film, the materials of each layer can be the same or different, without particular limitation.

[0216] In some implementations, the positive electrode, negative electrode, and separator can be fabricated into an electrode assembly using a winding or stacking process.

[0217] In some embodiments, the secondary battery may include an outer packaging. This outer packaging may be used to encapsulate the electrode assembly and electrolyte described above.

[0218] In some embodiments, the outer packaging of the secondary battery can be a hard shell, such as a hard plastic shell, an aluminum shell, or a steel shell. The outer packaging of the secondary battery can also be a soft pack, such as a pouch. The material of the soft pack can be plastic; examples of plastics include polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0219] This application does not impose any particular limitation on the shape of the secondary battery; it can be cylindrical, square, or any other arbitrary shape. For example, Figure 5 This is an example of a square-structured secondary battery 5.

[0220] In some implementations, refer to Figure 6The outer packaging may include a housing 51 and a cover 53. The housing 51 may include a base plate and side plates connected to the base plate, the base plate and side plates forming a receiving cavity. The housing 51 has an opening communicating with the receiving cavity, and the cover 53 can be placed over the opening to close the receiving cavity. A positive electrode, a negative electrode, and a separator can be formed into an electrode assembly 52 using a winding or stacking process. The electrode assembly 52 is encapsulated within the receiving cavity. Electrolyte is immersed in the electrode assembly 52. ​​The secondary battery 5 may contain one or more electrode assemblies 52, which can be selected by those skilled in the art according to specific practical needs.

[0221] In some implementations, the secondary batteries can be assembled into a battery module, and the number of secondary batteries contained in the battery module can be one or more, the specific number of which can be selected by those skilled in the art according to the application and capacity of the battery module.

[0222] Figure 7 This is battery module 4, used as an example. (See reference...) Figure 7 In battery module 4, multiple secondary batteries 5 can be arranged sequentially along the length of battery module 4. Of course, they can also be arranged in any other manner. Furthermore, these multiple secondary batteries 5 can be fixed in place using fasteners.

[0223] Optionally, the battery module 4 may also include a housing with a receiving space in which a plurality of secondary batteries 5 are received.

[0224] In some embodiments, the battery modules described above can also be assembled into a battery pack, and the number of battery modules contained in the battery pack can be one or more, the specific number of which can be selected by those skilled in the art according to the application and capacity of the battery pack.

[0225] Figure 8 and Figure 9 This is battery pack 1 as an example. (See reference...) Figure 8 and Figure 9 The battery pack 1 may include a battery box and multiple battery modules 4 disposed within the battery box. The battery box includes an upper body 2 and a lower body 3, with the upper body 2 covering the lower body 3 to form a closed space for accommodating the battery modules 4. The multiple battery modules 4 can be arranged in any manner within the battery box.

[0226] In addition, this application also provides an electrical device, which includes at least one of the secondary battery, battery module, or battery pack provided in this application. The secondary battery, battery module, or battery pack can be used as a power source for the electrical device, or as an energy storage unit for the electrical device. The electrical device may include, but is not limited to, mobile devices (e.g., mobile phones, laptops, etc.), electric vehicles (e.g., pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships and satellites, energy storage systems, etc.

[0227] As the electrical device, a secondary battery, battery module, or battery pack can be selected according to its usage requirements.

[0228] Figure 10 This is an example of an electrical device. The device could be a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle. To meet the high power and high energy density requirements of the secondary battery for this device, a battery pack or battery module can be used.

[0229] 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.

[0230] The first alkali metal ion materials provided in the above embodiments and comparative examples have an initial efficiency of less than 20% and they have irreversible capacity.

[0231] The second alkali metal ion materials provided in the above embodiments and comparative examples have an initial efficiency of over 80% and they have reversible capacity.

[0232] Example 1

[0233] Lithium-ion battery manufacturing:

[0234] 1.1 Preparation of the positive electrode

[0235] First positive electrode active slurry: The first alkali metal ion material (Li2C4O4 in this embodiment), the second alkali metal ion material (NCM523 in this embodiment), the conductive agent acetylene black, and the binder polyvinylidene fluoride (PVDF) are mixed evenly in a mass ratio of 0.1%:95.9%:2%:2%, and then added to the solvent NMP to prepare the first positive electrode active slurry.

[0236] Second positive electrode active slurry: The first alkali metal ion material (Li2C4O4 in this embodiment), the second alkali metal ion material (NCM523 in this embodiment), the conductive agent acetylene black (SP), and the binder polyvinylidene fluoride (PVDF) are mixed evenly in a mass ratio of 0%:96%:2%:2%, and then added to the solvent NMP to prepare the second positive electrode active slurry.

[0237] A positive electrode current collector (aluminum foil) for winding a battery cell is provided. The positive electrode current collector is strip-shaped and has a width direction and a length direction. During subsequent battery cell fabrication, the width direction of the positive electrode current collector is used as the winding axis, and the length direction is wound around the winding axis to form a wound battery cell. Along the surface direction of the positive electrode current collector, the positive electrode current collector includes a first end region, a waist region, and a second end region extending along the length direction of the positive electrode sheet. The waist region is located between the first end region and the second end region. The widths of the first end region, the waist region, and the second end region are 0.25D, 0.5D, and 0.25D, respectively, where D is the total width of the active material region (the area coated with active slurry) on the positive electrode current collector, and D = 80 mm.

[0238] On one side of the positive current collector, a first positive active slurry is coated in the waist region, and a second positive active slurry is coated in the first and second end regions. The mixture is then dried at 85°C and cold-pressed. The same operation is performed on the other side of the positive current collector.

[0239] Finally, the material is die-cut and slited to obtain the positive electrode sheet for winding the battery cell.

[0240] Figure 1 A schematic diagram of the positive electrode sheet for winding a battery cell according to Embodiment 1 is shown. Along the width direction of the positive electrode sheet 11, the positive electrode sheet 11 includes a first end portion 501, a waist portion 500, and a second end portion 502. In the surface direction of the positive electrode sheet 11, it includes a first end region 201, a waist region 101, and a second end region 202 extending along the length direction of the positive electrode sheet 11, with the waist region 101 located between the first end region 201 and the second end region 202. The waist region 101 is closer to the waist portion 500 than the first end region 201, and the first end region 201 is farther from the waist portion 500 than the waist region 101, but closer to the first end portion 501. The waist region 101 is closer to the waist portion 500 than the second end region 202, and the second end region 202 is farther from the waist portion 500 than the waist region 201, but closer to the second end portion 502. The waist region 101 is provided with a first positive electrode film, and the first end region 201 and the second end region 201 are respectively provided with a second positive electrode film.

[0241] The widths of the first end region 201, the waist region 101, and the second end region 202 are 0.25D, 0.5D, and 0.25D, respectively, where D is the total width of the active material region on the positive electrode plate 11.

[0242] The waist region 101 of the aforementioned positive electrode sheet is provided with a first positive electrode film. A first alkali metal ion providing material and a second alkali metal ion providing material are distributed within the first positive electrode film (this region has first activity, hereinafter also referred to as the first positive electrode film). The first alkali metal ion providing material has irreversible capacity, and the second alkali metal ion providing material has reversible capacity. The first alkali metal ion providing material within the first positive electrode film provides P1 ppm of alkali metal ions, and the second alkali metal ion providing material Q1 ppm of alkali metal ions.

[0243] The first end region 201 and the second end region 202 of the above-mentioned positive electrode sheet are respectively provided with a second positive electrode film. The second positive electrode film is distributed with a second alkali metal ion providing material (this region has a second activity, hereinafter also referred to as the second positive electrode film). The first alkali metal ion providing material provides irreversible capacity, and the second alkali metal ion providing material provides reversible capacity. The first alkali metal ion providing material in the second positive electrode film provides P2 ppm alkali metal ions, and the second alkali metal ion providing material provides Q2 ppm alkali metal ions.

[0244] The compositions of the first and second positive electrode films are shown in Table 1. The sum of P1 and Q1 (P1+Q1) and the ratio (P1 / Q1), the sum of P2 and Q2 (P2+Q2) and the ratio (P2 / Q2), and the value of (P1+Q1) / (P2+Q2) are shown in Table 1.

[0245] 1.2 Preparation of negative electrode

[0246] The negative electrode active material graphite, conductive agent acetylene black, thickener sodium carboxymethyl cellulose (CMC), and binder styrene-butadiene rubber (SBR) are added to the solvent water at a mass ratio of 96:2:1:1 and mixed evenly to form a negative electrode slurry. The negative electrode slurry is evenly coated on the negative electrode current collector copper foil, dried at 85°C, and then cold-pressed to form a lithium-ion battery negative electrode sheet.

[0247] 1.3 Preparation of the separating membrane

[0248] A porous separator membrane was prepared by using a polyethylene microporous film as the substrate. Inorganic alumina powder, polyvinylpyrrolidone, and acetone solvent were mixed uniformly in a weight ratio of 3:1.5:5.5 to form a slurry, which was then coated onto one side of the substrate and dried to obtain the separator membrane. The coated side of the separator membrane subsequently faced the positive electrode side.

[0249] 1.4 Preparation of Electrolyte

[0250] Lithium hexafluorophosphate was dissolved in a mixed solvent of ethylene carbonate, dimethyl carbonate and ethyl methyl carbonate (the amount of lithium hexafluorophosphate added was 1 mol / L, and the volume ratio of ethylene carbonate, dimethyl carbonate and ethyl methyl carbonate was 1:2:1) to obtain a lithium-ion battery electrolyte.

[0251] 1.5 Assembly of Lithium-ion Batteries

[0252] The above-mentioned positive electrode, negative electrode and separator are wound together to obtain a wound battery cell.

[0253] Winded cells, such as Figure 2 As shown, the wound battery cell 100 includes a positive electrode 11, a negative electrode 12, and a separator 13 separating the positive electrode 11 and the negative electrode 12. The wound battery cell 100 has a wound structure. The positive electrode 11, the negative electrode 12, and the separator 13 are all strip-shaped. The positive electrode 11, the separator 13, and the negative electrode 12 are sequentially stacked and wound two or more times to form the wound battery cell 100. The wound battery cell 100 is flat.

[0254] The wound battery cells are packaged into a battery case and subjected to processes such as liquid injection, formation, and venting to obtain the battery used in the example. The battery is designed with a rated capacity of 200Ah and a cell case size of 60mm*200mm*100mm.

[0255] Examples 2-10

[0256] The difference between Examples 2-10 and Example 1 is that the weight percentages of the first alkali metal ion-providing material (Li2C4O4) and the second alkali metal ion-providing material (NCM523) in the first positive electrode film are different from those in Example 1. See Table 1 for details.

[0257] Comparative Example 1

[0258] The difference between Comparative Example 1 and Example 1 lies in the composition of the first positive electrode film. Specifically, the content of the first alkali metal ion-providing material (Li2C4O4) in the first positive electrode film of Comparative Example 1 is 0.0 wt%. See Table 1 for details.

[0259] Examples 11A-11B, Comparative Examples 2A-2B

[0260] The difference between Examples 11A-11B, Comparative Examples 2A-2B and Example 6 lies in the composition of the first and second positive electrode films. Specifically, the type of alkali metal ion material provided in the second example is different from that in Example 6. See Table 2 for details.

[0261] Examples 12-19

[0262] The difference between Examples 12-29 and Example 6 lies in the composition of the first and second positive electrode films. Specifically, the type of alkali metal ion material provided in the first example is different from that in Example 6. See Table 3 for details.

[0263] Examples 20-21

[0264] The difference between Examples 20 and 21 and Example 6 lies in the composition of the second positive electrode film. Specifically, the weight percentages of the first alkali metal ion-providing material (Li2C4O4) and the second alkali metal ion-providing material (NCM523) in the first positive electrode film differ from those in Example 6. See Table 4 for details.

[0265] Comparative Examples 3A to 3C

[0266] The difference between Comparative Example 3A and Example 2 lies in the composition of the first positive electrode film. Specifically, it uses lithium-rich material Li2MnO3·0.15(LiNi) 0.33 Co 0.33 Mn 0.33 O2) replaces the first alkali metal ion material (Li2C4O4), see Table 5 for details.

[0267] The difference between Comparative Example 3B and Example 5 lies in the composition of the first positive electrode film. Specifically, it uses lithium-rich material Li2MnO3·0.15(LiNi) 0.33 Co 0.33 Mn 0.33 O2) replaces the first alkali metal ion material (Li2C4O4), see Table 5 for details.

[0268] The difference between Comparative Example 3C and Example 6 lies in the composition of the first positive electrode film. Specifically, it uses lithium-rich material Li2MnO3·0.15(LiNi) 0.33 Co 0.33 Mn 0.33 O2) replaces the first alkali metal ion material (Li2C4O4), see Table 5 for details.

[0269] The first-stage efficiency of the aforementioned lithium-rich material is over 90%. The lithium-rich material in the first cathode film provides P*1ppm alkali metal ions, and the lithium-rich material in the second cathode film provides P*2ppm alkali metal ions.

[0270] Analysis and testing

[0271] 1. Detection of porosity of positive electrode sheet

[0272] The tests were conducted in accordance with GB / T 24586-2009, using a true density meter (equipment model: AccuPycⅡ1340) to test the positive electrode sheets of the examples and comparative examples;

[0273] 1. Testing principle: Using the inert gas (helium) replacement method with small molecule diameter, combined with Archimedes' principle and Bohr's law (PV=nRT), the true volume of the material under test is accurately measured, thereby obtaining the porosity of the sample.

[0274] 2. Calculation formulas: Apparent volume V2 = S * H ​​* A; Porosity α = (V2 - V1) / V2 * 100%

[0275] Where: S – sample area, cm² 2 H – Sample thickness, cm; A – Number of samples, EA; V1 – True volume of the sample, cm³ 3 V2 – Apparent volume of the sample, cm³ 3 α—Porosity of the sample, %.

[0276] The porosity of the waist and end regions of the positive electrode sheets in the examples and comparative examples is shown in Tables 1-5.

[0277] 2. Battery life test

[0278] Charge / discharge process (rated capacity 200Ah; in this invention, the potential range used for cycle life testing is adjusted according to system characteristics, such as LiNi). 0.5 Co 0.2 Mn 0.3 The system voltage V0–V1 ranges from 2.8 to 4.3 V, and the LiFePO4 system voltage ranges from 2.5 to 3.65 V. 0.4 Mn 0.6 The voltage range of the PO4 system is 2.5–4.3V.

[0279] The test temperature is 25℃, and the loop program is as follows:

[0280] 1) Let stand for 10 minutes;

[0281] 2) Discharge at 0.33C until the cutoff voltage V0;

[0282] 3) Let stand for 10 minutes;

[0283] 4) Charge at a constant current of 0.33C to the target voltage V1, then continue charging at a constant voltage, with the cutoff condition being I≤0.05C;

[0284] 5) Let stand for 10 minutes;

[0285] 6) Discharge at 0.33C to the cutoff voltage V0; (Record the second discharge capacity as C0)

[0286] 7) Let stand for 10 minutes;

[0287] 8) Repeat steps 4) to 7) and record the discharge capacity C during the cycle test. m ;

[0288] 9) When C m Stop the test when / C0≤80% and record the number of cycles.

[0289] The battery cycle life of the examples and comparative examples are shown in Tables 1-5.

[0290] 3. Material distribution information of the positive electrode sheet

[0291] An exemplary detection method is provided below to detect the distribution of a first alkali metal ion-providing material and a second alkali metal ion-providing material on a positive electrode sheet.

[0292] (1) Provide the positive electrode sheet to be tested;

[0293] (2) Divide the positive electrode sheet to be tested into a grid to obtain multiple test units, and record the position information of each test unit. For example, for a 100mm×1000mm positive electrode sheet, if the grid size is set to 5mm×5mm, it can be divided into 4000 test units;

[0294] (3) Detect the physicochemical parameters of each test unit.

[0295] Physicochemical parameters include, but are not limited to:

[0296] (a) Elemental composition

[0297] Elemental composition can be determined using methods commonly used in the field. For example, referring to EPA 6010D-2014, an iCAP7400 inductively coupled plasma atomic emission spectrometer is used for elemental content testing, with aqua regia as the solvent.

[0298] Element content (mass fraction w / w%) = element mass / (sample weight - current collector mass) * 100%.

[0299] Based on the alkali metal element concentration of each test unit, the total content of alkali metal ions provided by the first alkali metal ion providing material and the second alkali metal ion providing material in the first positive electrode film in the waist region and the end region (P1+Q1)ppm can be determined; and the total content of alkali metal ions provided by the first alkali metal ion providing material and the second alkali metal ion providing material in the second positive electrode film (P2+Q2)ppm can be determined.

[0300]

[0301]

[0302]

[0303]

[0304] Experimental data results analysis and principle explanation

[0305] 1. Factors affecting porosity

[0306] In the above embodiments, the positive electrode sheet includes a first positive electrode film located at the waist and a second positive electrode film located at the ends, with the porosity of the waist being greater than that of the first and second end regions, respectively. Experimental results show that the battery of the embodiments exhibits improved cycle life.

[0307] In Comparative Example 1, the waist region, the first end region, and the second end region have equal porosity. Experimental results show that the battery does not exhibit improved cycle life.

[0308] Without being limited by theory, the theoretical basis for the above-mentioned positive electrode sheet to improve battery cycle life is as follows:

[0309] During cell operation, the expansion rate of the waist region is greater than that of the end region. This results in the waist region experiencing greater compression from the battery casing compared to the end region, leading to poorer electrolyte reflux in the waist region. Furthermore, prolonged compression degrades the porosity of the negative electrode. The reduced porosity of the compacted negative electrode sheet results in insufficient electrolyte wetting, impaired lithium intercalation kinetics, and a higher likelihood of central lithium plating failure in the later stages of cycling. Therefore, by controlling the porosity of the waist region of the positive electrode sheet to ensure it is greater than that of the first and second end regions, space can be reserved in advance to withstand compression, thereby mitigating the adverse effects of compression on the waist region.

[0310] 2. Factors affecting lithium concentration gradient

[0311] In the above embodiments, the positive electrode sheet includes a first positive electrode film located at the waist and a second positive electrode film located at the end. The first positive electrode film and the second positive electrode film satisfy the following relationship:

[0312] (P 1+ Q1)>(P2+Q2)

[0313] Experimental results show that the battery in the example exhibits improved cycle life.

[0314] Examples 1-10 show that, when conforming to (P) 1+ When Q1)>(P2+Q2), (P 1+ The value of (P2+Q2) for Q1 ranged from 1.001 to 1.998, and the batteries all exhibited improved cycle life. In Comparative Example 1, the battery met the (P) value. 1+ Q1)=(P2+Q2), the battery did not show improved cycle life.

[0315] Examples 11A-11B show that the battery uses various positive electrode active materials, while meeting the requirements of (P) 1+ When Q1)>(P2+Q2), all cells exhibit improved cycle life. In Comparative Examples 2A to 2B, the cells meet the condition (P... 1+ Q1)=(P2+Q2), the battery did not show improved cycle life.

[0316] Examples 12-19 show that the battery uses various first-generation alkali metal ion-providing materials, in accordance with (P) 1+ When Q1)>(P2+Q2), improved cycle life is observed in all cases.

[0317] Examples 20-21 show that the battery conforms to (P) 1+ The relationship between Q1)>(P2+Q2), P1 / Q1=20%, and P2 / Q2=2%~6% both indicate improved cycle life.

[0318] In Comparative Examples 3A to 3C, a lithium-rich material was used to replace the first alkali metal ion providing material. Unlike the first alkali metal ion providing material, the lithium-rich material has an initial efficiency of over 90% and reversible capacity. The batteries in Comparative Examples 5 to 7 also did not show a significant improvement in cycle life.

[0319] The positive electrode sheet based on the above embodiment is used in a secondary battery, which exhibits improved cycle life. Without being limited by theory, the reasons for the improved battery cycle life are analyzed as follows:

[0320] In the first positive electrode film (P) 1+ The value of Q1 is relatively large because the first positive electrode film is located in the waist region where the temperature is high and the electrochemical activity is high. 1+ Q1) It can compensate for the capacity loss caused by insufficient reversible alkali metal ions due to the excessively rapid consumption rate of alkali metal ions in the waist area, thereby improving the overall cycle life of the cell.

[0321] The value of (P2+Q2) in the second positive electrode film is relatively small because the second positive electrode film is located in the end region with lower temperature and lower electrochemical activity. 2+ Q2) helps reduce overall costs while avoiding the risk of short circuits caused by metal dendrites on the anode due to excessive alkali metals.

[0322] 3. Factors related to lithium supplementation

[0323] In the above embodiments, the first positive electrode film and the second positive electrode film conform to the following relationship: (P1 / Q1)>(P2 / Q2), which shows improved cycle life.

[0324] The reasons for the improved battery cycle life, which are not limited by theory, are analyzed as follows:

[0325] The first and / or second alkali metal ion materials play different roles in the battery operation process. The alkali metal ions provided by the first alkali metal ion material are used to compensate for the consumption of alkali metal ions during the battery's life cycle, such as consumption during the initial film formation reaction and consumption during the repair film formation reaction during cycling / storage. The alkali metal ions provided by the second alkali metal ion material are used for reversible intercalation / deintercalation / electrochemical reactions in the positive and negative electrode materials. Since the inherent film formation consumption is compensated by the first alkali metal ion material, there are more reversible alkali metal ions available to provide electrochemical energy. The first positive electrode film has a larger (P1 / Q1) value. Because the first positive electrode film is located in the waist region with higher temperature and higher electrochemical activity, the larger (P1 / Q1) can compensate for the capacity loss caused by insufficient reversible alkali metal ions due to the excessively rapid consumption rate of alkali metal ions in the waist region, thereby improving the overall cycle life of the cell.

[0326] The smaller (P2 / Q2) value in the second positive electrode film is beneficial because the second positive electrode film is located in the end region with lower temperature and lower electrochemical activity. The smaller (P2 / Q2) helps to reduce the overall cost and avoids the risk of short circuit caused by metal dendrites in the anode due to excessive alkali metal content.

[0327] It should be noted that this application is not limited to the above-described embodiments. The above embodiments are merely examples, and any embodiments with the same structure and effect as the technical concept within the scope of this application are included in the technical scope of this application. Furthermore, various modifications that can be conceived by those skilled in the art to the embodiments, and other ways of constructing by combining some of the constituent elements of the embodiments, without departing from the spirit of this application, are also included in the scope of this application.

Claims

1. A positive electrode sheet for winding a battery cell, comprising a waist region near the waist and an end region away from the waist along the width direction; The waist region is provided with a first positive electrode film, and the end region is provided with a second positive electrode film; wherein The porosity of the first positive electrode film is greater than that of the second positive electrode film; The first positive electrode film contains a first alkali metal ion providing material and / or a second alkali metal ion providing material. The first alkali metal ion providing material has irreversible capacity, and the second alkali metal ion providing material has reversible capacity. The first alkali metal ion providing material in the first positive electrode film provides P1 ppm of alkali metal ions, and the second alkali metal ion providing material Q1 ppm of alkali metal ions. The second positive electrode film contains a first alkali metal ion providing material and / or a second alkali metal ion providing material, wherein the first alkali metal ion providing material provides irreversible capacity and the second alkali metal ion providing material provides reversible capacity; the first alkali metal ion providing material in the second positive electrode film provides P2 ppm alkali metal ions and the second alkali metal ion providing material Q2 ppm alkali metal ions; The first positive electrode film and the second positive electrode film conform to the following relationship: (P 1+ Q1)>(P2+Q2) Where P1>0, P2≥0, Q1>0, Q2>0; P1+Q1 = 40000~180000ppm; (P1+Q1):(P2+Q2) = (1.001~2):1; The first alkali metal ion material includes one or more of the following: alkali metal nitrides, alkali metal oxides, alkali metal oxide / transition metal complexes, alkali metal peroxides, over-alkali metallized alkali metal oxides, or alkali metal carbon oxides.

2. A positive electrode sheet for a laminated battery cell, comprising a central region near the center and an edge region away from the center; The central region is provided with a first positive electrode film, and the edge region is provided with a second positive electrode film; in, The porosity of the first positive electrode film is greater than that of the second positive electrode film; The first positive electrode film contains a first alkali metal ion providing material and / or a second alkali metal ion providing material. The first alkali metal ion providing material has irreversible capacity, and the second alkali metal ion providing material has reversible capacity. The first alkali metal ion providing material in the first positive electrode film provides P1 ppm of alkali metal ions, and the second alkali metal ion providing material Q1 ppm of alkali metal ions. The second positive electrode film contains a first alkali metal ion providing material and / or a second alkali metal ion providing material, wherein the first alkali metal ion providing material provides irreversible capacity and the second alkali metal ion providing material provides reversible capacity; the first alkali metal ion providing material in the second positive electrode film provides P2 ppm alkali metal ions and the second alkali metal ion providing material Q2 ppm alkali metal ions; The first positive electrode film and the second positive electrode film conform to the following relationship: (P 1+ Q1)>(P2+Q2) Where P1>0, P2≥0, Q1>0, Q2>0; P1+Q1 = 40000~180000ppm; (P1+Q1):(P2+Q2) = (1.001~2):1; The first alkali metal ion material includes one or more of the following: alkali metal nitrides, alkali metal oxides, alkali metal oxide / transition metal complexes, alkali metal peroxides, over-alkali metallized alkali metal oxides, or alkali metal carbon oxides.

3. The positive electrode sheet according to any one of claims 1-2, wherein the ratio of the porosity of the first positive electrode film to the porosity of the second positive electrode film is 1.003~3:

1.

4. The positive electrode sheet according to claim 3, wherein the first positive electrode film and the second positive electrode film meet the following relationship: (P1 / Q1)>(P2 / Q2).

5. The positive electrode sheet according to claim 3, having one or more of the following characteristics: (1) The value of (P1 / Q1) ranges from 0.1% to 70%; (2) The value of (P2 / Q2) ranges from 0 to 70%; (3) The value of (P1 / Q1)-(P2 / Q2) is 0.1%-60%.

6. The positive electrode sheet according to claim 3, wherein it satisfies: (1) P2+Q2 = 40000~180000ppm.

7. The positive electrode sheet according to claim 1, having one or more of the following characteristics: (1) The waist region is a strip-shaped region distributed along the length of the positive electrode sheet; (2) The end region is a strip-shaped region distributed along the length of the positive electrode sheet; (3) The width of the waist region is 0.05D ~ 0.95D, where D is the total width of the active material region on the positive electrode sheet; (4) The width of the end region is 0.05D ~ 0.95D, where D is the total width of the active material region on the positive electrode sheet; (5) The total area of ​​the waist region accounts for 5% to 95% of the total area of ​​the active material region on the positive electrode sheet; (6) The total area of ​​the end region accounts for 5% to 95% of the total area of ​​the active material region on the positive electrode plate.

8. The positive electrode sheet according to claim 7, wherein it satisfies: The total area of ​​the waist region accounts for 50% to 95% of the total area of ​​the active material region on the positive electrode sheet.

9. The positive electrode sheet according to claim 7, wherein it satisfies: The total area of ​​the end region accounts for 5% to 50% of the total area of ​​the active material region on the positive electrode plate.

10. The positive electrode sheet according to claim 2, having one or more of the following characteristics: (1) The central area is a circular, elliptical, or polygonal shape centered on the center of the positive electrode plate; (2) The edge region is a ring-shaped region distributed along the edge of the positive electrode sheet; (3) The total area of ​​the central region accounts for 5% to 95% of the total area of ​​the active material region on the positive electrode sheet; (4) The total area of ​​the edge region accounts for 5% to 95% of the total area of ​​the active material region on the positive electrode sheet.

11. The positive electrode sheet according to claim 10, wherein it satisfies: The total area of ​​the central region accounts for 50% to 95% of the total area of ​​the active material region on the positive electrode sheet.

12. The positive electrode sheet according to claim 10, wherein it satisfies: The total area of ​​the edge region accounts for 5% to 50% of the total area of ​​the active material region on the positive electrode sheet.

13. The positive electrode sheet according to claim 1, having one or more of the following characteristics: (1) The alkali metal nitride is A3N; (2) The alkali metal oxide is A2O (3) The alkali metal oxide / transition metal complex is A2O / M; (4) The alkali metal peroxide is A2O2; (5) Over-alkali metallized alkali metal oxides A2NiO2, A5FeO4, (6) Alkali metal oxocarbides are selected from A2C2O4, A2C4O4, A2C3O5, and A2C4O6; in, A is an alkali metal element; M is a transition metal element.

14. The positive electrode sheet according to claim 1, wherein the second alkali metal ion-providing material comprises one or more of the following: (1) Alkali metal ion secondary battery active materials with layered structure; (2) Alkali metal ion secondary battery active materials with olivine structure; (3) Alkali metal ion secondary battery active materials with spinel structure; (4) Prussian blue alkali metal ion secondary battery active materials.

15. The positive electrode according to claim 1, wherein the alkali metal is selected from lithium, sodium, or a combination thereof.

16. The positive electrode sheet according to claim 1, wherein the positive electrode sheet comprises a waist region and two end regions, the waist region being located between the two end regions, the waist region containing a first positive electrode film, and the two end regions each containing a second positive electrode film.

17. A secondary battery comprising a positive electrode sheet according to any one of claims 1-16.

18. An electrical device comprising a secondary battery selected from the options of claim 17.

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