Secondary battery, composite current collector and preparation method therefor, and electric device

Abstract

Provided in the present application are a secondary battery, a composite current collector and a preparation method therefor, and an electric device. The secondary battery comprises a positive electrode sheet and a negative electrode sheet, wherein the positive electrode sheet and the negative electrode sheet each comprise a current collector, the current collector of at least one of the positive electrode sheet and the negative electrode sheet is a composite current collector, the composite current collector comprises a titanium substrate layer and a conductive layer arranged on at least one side of the titanium substrate layer, the thickness of the titanium substrate layer is 2 μm to 10 μm, and the sheet resistance of the conductive layer is 0.0018 Ω / □ to 0.017 Ω / □.

Description

Secondary batteries, composite current collectors and their preparation methods, and electrical devices

[0001] Related applications

[0002] This application claims priority to Chinese Patent Application No. 2025101264749, filed on January 27, 2025, entitled "Secondary Battery, Composite Current Collector and Preparation Method Thereof, and Electrical Device", the entire contents of which are incorporated herein by reference. Technical Field

[0003] This application relates to the field of battery technology, and in particular to a secondary battery, a composite current collector and its preparation method, and an electrical device. Background Technology

[0004] In recent years, the application range of secondary batteries, such as lithium-ion batteries, has become increasingly wide. They are 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. The significant development of secondary batteries has placed higher demands on the strength, conductivity, and lightweighting of current collectors to meet the high energy density requirements of batteries. However, current current collectors suffer from the problem of not being able to simultaneously achieve optimal tensile strength, lightweighting, and conductivity. Summary of the Invention

[0005] Based on this, this application provides a secondary battery, a composite current collector and its preparation method, and an electrical device, wherein the composite current collector has high tensile strength and conductivity, and is lightweight, thereby improving the energy density of the secondary battery.

[0006] In a first aspect, this application provides a secondary battery, including a positive electrode and a negative electrode, wherein the positive electrode and the negative electrode include a current collector, and the current collector of at least one of the positive electrode and the negative electrode is a composite current collector, wherein the composite current collector includes a titanium substrate layer and a conductive layer disposed on at least one side of the titanium substrate layer, the thickness of the titanium substrate layer is 2μm to 10μm, and the sheet resistance of the conductive layer is 0.0018Ω / □ to 0.017Ω / □.

[0007] In the aforementioned secondary battery, at least one of its positive and negative electrode plates employs a composite current collector. This composite current collector uses a titanium substrate layer of a specific thickness, which not only possesses good tensile strength but also has a low density. Furthermore, a conductive layer with a specific resistance is provided on at least one side of the titanium substrate layer, achieving good strength and conductivity for the composite current collector. Thus, the composite current collector combines the advantages of high tensile strength, conductivity, and lightweight design, reducing or avoiding the problem of metal plating tearing leading to a decrease in the conductivity of the composite current collector, or even causing an internal short circuit in the battery, thereby improving the battery's power performance and safety. In addition, the lightweight composite current collector helps reduce the overall weight of the battery, thereby increasing the energy density of the secondary battery.

[0008] The aforementioned composite current collector is suitable for high energy density battery designs. Using this composite current collector in a secondary battery can improve the battery's energy density while reducing or avoiding metal plating tearing, thereby enhancing the battery's power performance and safety.

[0009] In some embodiments, one or more of the following features are satisfied:

[0010] (1) The thickness of the titanium substrate layer is 3μm to 5μm;

[0011] (2) The sheet resistance of the conductive layer is 0.0025Ω / □~0.01Ω / □.

[0012] By further controlling the thickness of the titanium matrix layer, good tensile strength, lightweight, and electrical conductivity can be achieved simultaneously.

[0013] In some embodiments, the conductive layer is a conductive metal layer;

[0014] Optionally, the conductive layer is a conductive metal plating layer.

[0015] The conductive metal layer not only has good conductivity but also superior strength, thus reducing or avoiding the risk of the metal coating being torn, and improving the conductivity and safety performance of the battery.

[0016] In some embodiments, the conductive layer is made of an alloy of one or more elements selected from silver, copper, gold, aluminum, magnesium, nickel, iron, and tin.

[0017] In some embodiments, the conductive layer is provided on opposite sides of the titanium substrate layer in the composite current collector;

[0018] Optionally, the thickness ratio of the conductive layer on opposite sides of the titanium substrate layer is 1:(0.9 to 1.1).

[0019] In some embodiments, the total thickness of the conductive layer in the composite current collector is 1 μm to 20 μm, and optionally 2 μm to 10 μm.

[0020] In some embodiments, the conductive layer is made of one or an alloy of silver and copper; the total thickness of the conductive layer in the composite current collector is 1.1 μm to 8.4 μm, optionally 1.1 μm to 6 μm, and more preferably 2 μm to 3 μm. This allows for high conductivity with a relatively small thickness, thus enabling the composite current collector to achieve both better conductivity and lightweight design.

[0021] In some embodiments, the conductive layer is made of one or an alloy of gold and aluminum; the total thickness of the conductive layer in the composite current collector is 1.6 μm to 14.1 μm, optionally 3 μm to 7 μm. This allows for high conductivity with a relatively small thickness, thus enabling the composite current collector to achieve both better conductivity and lightweight design.

[0022] In some embodiments, the conductive layer is made of an alloy of one or more elements selected from magnesium, nickel, iron, and tin; the total thickness of the conductive layer in the composite current collector is 3 μm to 20 μm. This allows the composite current collector to achieve high conductivity with a relatively small thickness, thus combining better conductivity with lightweight design.

[0023] In some embodiments, the thickness of the titanium substrate layer in the composite current collector is 20% to 90%, optionally 30% to 70%. Further controlling the thickness ratio of the titanium substrate layer in the composite current collector allows the composite current collector to better balance good tensile strength and conductivity.

[0024] In some embodiments, the titanium matrix layer contains 85% to 100% titanium by mass, and optionally 90% to 99.99%.

[0025] In some embodiments, the titanium substrate layer comprises one or a stack of two of the following: a titanium elemental layer and a titanium alloy layer.

[0026] In some embodiments, one or more of the following features are satisfied:

[0027] (1) The tensile strength of the composite current collector is 500 MPa to 1600 MPa, and can be selected as 800 MPa to 1200 MPa;

[0028] (2) The fracture elongation of the composite current collector is 1.5% to 6%, and can be selected as 2% to 4%;

[0029] (3) The elongation at break of the titanium matrix layer is 1.5% to 4%, and can be selected as 2% to 3%;

[0030] (4) The elongation at break of the conductive layer is 2% to 7%, and can be selected as 3% to 5%;

[0031] (5) The surface density of the composite current collector is 15 g / m³. 2 ~95g / m 2 15g / m 2 ~40g / m 2 ;

[0032] (6) The sheet resistance of the composite current collector is 0.0018Ω / □~0.015Ω / □.

[0033] In some embodiments, the composite current collector further includes a base coating layer disposed on the conductive layer, the base coating layer comprising a conductive agent and a binder;

[0034] Optionally, the thickness of the base coating layer on one side is 0.25μm to 5μm, and can be 0.5μm to 3μm.

[0035] In some embodiments, the negative electrode sheet includes the composite current collector and a negative electrode active layer disposed on at least one side of the composite current collector; satisfying one or more of the following characteristics:

[0036] (1) The negative electrode active layer includes one or more of silicon-based materials and carbon-based materials; optionally, the mass content of silicon element in the negative electrode active layer is 0% to 90%, more preferably 2% to 60%;

[0037] (2) The negative electrode active layer includes a lithium metal layer.

[0038] Silicon-based materials possess high specific capacity, which is beneficial for achieving high energy density in secondary batteries. This composite current collector has high tensile strength and can also restrain the volume expansion of the negative electrode, reducing or suppressing tearing of the outer conductive layer, thereby improving the battery's conductivity, enabling high-power performance, and enhancing the safety performance of secondary batteries.

[0039] As the negative electrode active layer, the lithium metal layer possesses a good theoretical specific capacity, enabling the secondary battery to store and release more energy within the same volume or weight, thus achieving better energy density. Furthermore, due to the low electrode potential of lithium metal, when paired with suitable positive electrode materials, it can generate a higher battery voltage, further improving the battery's energy output and power performance. Additionally, lithium metal has good conductivity, allowing electrons to conduct rapidly across the surface of the lithium metal layer, effectively reducing internal battery resistance, improving charge and discharge efficiency, and enhancing power performance.

[0040] In some embodiments, the positive electrode sheet includes a positive active layer, the positive active layer comprising a positive active material, the positive active material comprising a nickel-containing lithium salt;

[0041] The nickel-lithium salt includes those with the chemical formula Li a Ni x Co y M z Compounds of O2, wherein 0.9≤a≤1.5, 0.6≤x≤1, 0≤y≤0.4, x+y+z=1; M is one or more of Mn, Al, Zr, Sr, B, Ti, Mg and Sn.

[0042] In a second aspect, this application provides a composite current collector, comprising a titanium substrate layer and a conductive layer disposed on at least one side of the titanium substrate layer, wherein the thickness of the titanium substrate layer is 2 μm to 10 μm and the sheet resistance of the conductive layer is 0.0018 Ω / □ to 0.017 Ω / □.

[0043] In some embodiments, the composite current collector is the composite current collector in the secondary battery provided in the first aspect of this application.

[0044] A third aspect of this application provides a method for preparing a composite current collector, comprising the following steps:

[0045] A conductive layer is formed on at least one side of a titanium substrate layer; the thickness of the titanium substrate layer is 2 μm to 10 μm, and the sheet resistance of the conductive layer is 0.0018 Ω / □ to 0.017 Ω / □.

[0046] In a fourth aspect, this application provides an electrical device comprising at least one of the secondary battery provided in the first aspect of this application, the composite current collector provided in the second aspect of this application, and the composite current collector prepared by the preparation method provided in the third aspect of this application.

[0047] Details of one or more embodiments of this application are set forth in the following drawings and description. Other features, objects, and advantages of this application will become apparent from the specification, drawings, and claims. Attached Figure Description

[0048] To better describe and illustrate the embodiments or examples provided in this application, reference may be made to one or more accompanying drawings. Additional details or examples used to describe the drawings should not be considered as limiting the scope of any of the disclosed applications, the currently described embodiments or examples, or the best mode of conduct of these applications as currently understood. Furthermore, the same reference numerals denote the same parts throughout the drawings. In the drawings:

[0049] Figure 1 is a schematic diagram of a composite current collector according to an embodiment of this application.

[0050] Figure 2 is a schematic cross-sectional view of the composite current collector according to an embodiment of this application shown in Figure 1.

[0051] Figure 3 is a schematic diagram of a secondary battery according to an embodiment of this application.

[0052] Figure 4 is an exploded view of the secondary battery according to one embodiment of this application, as shown in Figure 3.

[0053] Figure 5 is a schematic diagram of a battery device according to an embodiment of this application.

[0054] Figure 6 is a schematic diagram of a battery pack according to one embodiment of this application.

[0055] Figure 7 is an exploded view of the battery pack of one embodiment of this application shown in Figure 6.

[0056] Figure 8 is a schematic diagram of an electrical device using a secondary battery as a power source according to an embodiment of this application.

[0057] Explanation of reference numerals in the attached drawings: 1. Battery pack; 2. Upper casing; 3. Lower casing; 4. Battery assembly; 5. Battery cell; 51. Housing; 52. Electrode assembly; 53. Cover plate; 6. Electrical device; 7. Composite current collector; 71. Titanium substrate layer; 72. Conductive layer. Detailed Implementation

[0058] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0059] The "range" disclosed in this application can be defined in the form of 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; any endpoint can be independently included or excluded, and they can be combined arbitrarily, meaning 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 ​​1 and 2 are listed, and maximum range values ​​3, 4, and 5 are also 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 document; "0-5" is simply a shortened representation of these numerical combinations. Furthermore, stating that a parameter is an integer ≥2 is equivalent to disclosing that the parameter is, for example, an integer 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc. For instance, stating that a parameter is an integer selected from "2-10" is equivalent to listing the integers 2, 3, 4, 5, 6, 7, 8, 9, and 10.

[0060] In this application, the terms "multiple" or "various" are used unless otherwise specified, referring to a quantity greater than or equal to 2. For example, "one or more" means one or more types.

[0061] Unless otherwise specified, all embodiments and optional embodiments of this application can be combined to form new technical solutions.

[0062] In this document, the term "embodiment" means that a particular feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment or implementation of this application. The appearance of this phrase in various places throughout the specification does not necessarily refer to the same embodiment, nor is it a separate or alternative embodiment mutually exclusive with other embodiments. It will be explicitly and implicitly understood by those skilled in the art that the embodiments described herein can be combined with other embodiments. The term "implementation" as used herein has a similar understanding.

[0063] Those skilled in the art will understand that the order in which the steps are written in the methods of various embodiments or examples does not imply a strict execution order and does not constitute any limitation on the implementation process. The detailed execution order of each step should be determined by its function and possible internal logic. Unless otherwise specified, all steps of this application may be performed sequentially or randomly, preferably sequentially. For example, if the method includes steps (a) and (b), it means that the method may include steps (a) and (b) performed sequentially, or it may include steps (b) and (a) performed sequentially. For example, if the method may also include step (c), it means that step (c) can 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.

[0064] In this application, unless otherwise specified, A (e.g., B) means that B is a non-limiting example of A, and it is understood that A is not limited to B.

[0065] In this application, "optionally," "optionally," and "optional" mean that something is optional, that is, it means that it is selected from either "with" or "without." If there are multiple "optional" entries in a technical solution, unless otherwise specified and there are no contradictions or mutual constraints, each "optional" entry shall be independent.

[0066] Traditional current collectors directly use highly conductive metals; however, their density is too high, making weight reduction impossible. Some composite current collectors use a plastic substrate with an adhesive layer and a metal plating layer sequentially applied to both surfaces. The metal plating layer is typically copper or aluminum, thus achieving weight reduction and increasing battery energy density. However, the overall strength of this composite current collector is too low. In practical applications, it has been found that battery conductivity is severely affected, even leading to internal short circuits, failing to meet usage requirements.

[0067] Furthermore, in high-energy-density batteries, such as those using silicon or lithium metal as the negative electrode, the significant volume expansion of the negative electrode leads to excessive stretching of the plastic substrate in the composite current collector. This causes tearing of the outer metal plating, severely affecting the conductivity of the composite current collector and even causing internal short circuits. With the increasing demand for high-energy-density batteries, especially in the high-potential field of aerospace batteries, it is also necessary to achieve a balance between high energy density and high power performance.

[0068] Current current current collectors suffer from a trade-off between high tensile strength, lightweight design, and high conductivity. This application provides a secondary battery, a composite current collector, a method for preparing the same, and an electrical device thereof. The composite current collector exhibits high tensile strength and conductivity while being lightweight, thereby improving the energy density of the secondary battery.

[0069] The first aspect of this application provides a secondary battery, including a positive electrode and a negative electrode, wherein the positive electrode and the negative electrode include a current collector, and the current collector of at least one of the positive electrode and the negative electrode is a composite current collector, wherein the composite current collector includes a titanium substrate layer and a conductive layer disposed on at least one side of the titanium substrate layer, the thickness of the titanium substrate layer is 2μm to 10μm, and the sheet resistance of the conductive layer is 0.0018Ω / □ to 0.017Ω / □.

[0070] In this paper, sheet resistance, also known as sheet resistance, refers to the resistance between edges of a square thin-film conductive material, and its unit is ohms per square (Ω / □). Sheet resistance = resistivity (ρ) / thickness (d), and is only related to the resistivity ρ and thickness d of the material. Therefore, this application uses the sheet resistance of the conductive layer as a characteristic parameter relating the material type and thickness of the conductive layer. By controlling the range of the sheet resistance of the conductive layer, the conductivity of the composite current collector can be controlled.

[0071] In the aforementioned secondary battery, at least one of its positive and negative electrode plates employs a composite current collector. This composite current collector uses a titanium substrate layer of a specific thickness, which not only possesses good tensile strength but also has a low density. Furthermore, a conductive layer with a specific resistance is provided on at least one side of the titanium substrate layer, achieving good strength and conductivity for the composite current collector. Thus, the composite current collector combines the advantages of high tensile strength, conductivity, and lightweight design, reducing or avoiding the problem of metal plating tearing leading to a decrease in the conductivity of the composite current collector, or even causing an internal short circuit in the battery, thereby improving the battery's power performance and safety. In addition, the lightweight composite current collector helps reduce the overall weight of the battery, thereby increasing the energy density of the secondary battery.

[0072] The aforementioned composite current collector is suitable for high energy density battery designs. Using this composite current collector in a secondary battery can improve the battery's energy density while reducing or avoiding metal plating tearing, thereby enhancing the battery's power performance and safety.

[0073] The sheet resistance of the conductive layer can be obtained by the ratio of its resistivity to its thickness. The resistivity (ρ) is determined based on the material of the conductive layer, while the thickness (d) is obtained by scanning electron microscopy (SEM) of the cross-section of the composite current collector and measuring the thickness of the conductive layer within it. This method is primarily applicable to cases where the resistivity of the conductive layer material is known, especially when the resistivity of the conductive layer material is known.

[0074] When the resistivity of the conductive layer alloy material is unknown, it can be tested using resistivity testing methods.

[0075] For the composite current collector in this application, its titanium substrate layer is also conductive. Therefore, the titanium substrate layer and the conductive layer are essentially connected in parallel to form the composite current collector. Thus, the sheet resistance of the conductive layer can be obtained from the overall sheet resistance of the composite current collector and the sheet resistance of the titanium substrate layer. The overall sheet resistance of the composite current collector can be tested using a four-probe sheet resistance meter: four equally spaced probes are placed on the surface of the current collector, a small current I is supplied to the two outer probes by a constant current source, and the voltage V between the two middle probes is measured, allowing direct reading of the current collector's sheet resistance. The sheet resistance of the titanium substrate layer is similar and can be obtained by the ratio of the resistivity to the thickness of the titanium substrate layer.

[0076] It should be noted that in Comparative Example 1, since the substrate is a PET layer, which is an insulating layer, the sheet resistance of its conductive layer can be tested by the above method, or it can be directly tested by the sheet resistance of the composite current collector. The sheet resistance obtained is the sheet resistance of the conductive layer.

[0077] To achieve high energy density, secondary batteries include, but are not limited to, battery systems using silicon or lithium metal as the negative electrode. However, these negative electrode materials suffer from volume expansion. This composite current collector has high tensile strength and can also restrain the volume expansion of the negative electrode, reducing or suppressing tearing of the outer conductive layer, thereby improving the battery's conductivity, achieving high power performance, and enhancing the safety performance of secondary batteries.

[0078] As an example, the thickness of the titanium substrate layer can be 2 μm, 2.5 μm, 3 μm, 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 9.5 μm, 10 μm, or within a range defined by any two of the above values ​​as endpoints. In some embodiments, the thickness of the titanium substrate layer is 3 μm to 5 μm. By further controlling the thickness of the titanium substrate layer, good tensile strength, lightweight, and electrical conductivity can be achieved.

[0079] In one embodiment, the titanium substrate layer may be formed by means of rolling or the like.

[0080] As an example, the sheet resistance of the conductive layer can be 0.0018 Ω / □, 0.002 Ω / □, 0.003 Ω / □, 0.004 Ω / □, 0.005 Ω / □, 0.006 Ω / □, 0.007 Ω / □, 0.008 Ω / □, 0.009 Ω / □, 0.010 Ω / □, 0.011 Ω / □, 0.012 Ω / □, 0.013 Ω / □, 0.014 Ω / □, 0.015 Ω / □, 0.016 Ω / □, or 0.017 Ω / □, or any two of the above values ​​as endpoints. In some embodiments, the sheet resistance of the conductive layer is 0.0025 Ω / □ to 0.01 Ω / □.

[0081] In some embodiments, the conductive layer is a conductive metal layer. The conductive metal layer can be a single type of metal, an alloy of multiple metals, or a stack of both. The conductive metal layer not only has good conductivity but also superior strength, thus reducing or avoiding the risk of tearing of the metal plating and improving the battery's conductivity and safety performance.

[0082] In some embodiments, the composite current collector can be prepared by forming a conductive layer on at least one side of a titanium substrate layer. The conductive layer can be formed by methods including magnetron sputtering, vapor deposition, and electrochemical deposition. Optionally, the conductive layer is a conductive metal plating. The conductive metal plating can be formed by one or more of magnetron sputtering, vapor deposition, and electrochemical deposition.

[0083] As an example, a conductive metal coating can be prepared by: firstly, forming a base metal layer on at least one side of a titanium substrate layer by magnetron sputtering; and then forming an electroplated metal layer on the base metal layer by electrochemical deposition. The conductive metal coating thus formed includes a base metal layer disposed on at least one side of the titanium substrate layer and an electroplated metal layer disposed on the base metal layer. The base metal layer is tightly bonded to the titanium substrate layer and provides an adhesion surface for the electroplated metal layer, thereby improving the adhesion of the conductive metal coating.

[0084] In some embodiments, the conductive layer is made of one or more elements selected from silver, copper, gold, aluminum, magnesium, nickel, iron, and tin, or an alloy of these elements. Further, the conductive layer may include a metal layer formed from one of the aforementioned metallic elements, an alloy layer of multiple metals, or a stack of both.

[0085] As a non-limiting example, the titanium substrate layer has two surfaces opposite each other in its own thickness direction, and the conductive layer is disposed on either or both of the two opposite surfaces of the titanium substrate layer.

[0086] In some embodiments, the conductive layers are respectively disposed on opposite sides of the titanium substrate layer in the composite current collector. Referring to Figures 1 and 2, an example composite current collector 7 includes a titanium substrate layer 7 and conductive layers 72 disposed on opposite sides of the titanium substrate layer 7.

[0087] Optionally, the thickness ratio of the conductive layer on opposite sides of the titanium substrate layer is 1:(0.9 to 1.1); as an example, this thickness ratio can be 0.9:1, 1:1, 1.1:1, or within a range formed by any two of the above values ​​as endpoints. Further, the thickness of the conductive layer on opposite sides of the titanium substrate layer is the same.

[0088] In some embodiments, the total thickness of the conductive layer in the composite current collector is 1 μm to 20 μm. For example, the total thickness of the conductive layer can be 1 μm, 1.1 μm, 1.2 μm, 1.5 μm, 1.6 μm, 1.9 μm, 2 μm, 2.5 μm, 3 μm, 4 μm, 4.5 μm, 4.6 μm, 5 μm, 6 μm, 6.5 μm, 7 μm, 7.3 μm, 8 μm, 9 μm, 9.5 μm, 10 μm, 11 μm, 12 μm, 13 μm, 14 μm, 14.1 μm, 14.5 μm, 15 μm, 16 μm, 17 μm, 18 μm, 19 μm, or 20 μm, or within the range defined by any two of the above values ​​as endpoints. Further, the total thickness of the conductive layer in the composite current collector is 2 μm to 10 μm.

[0089] In some embodiments, the conductive layer is made of one or an alloy of silver and copper. Further, the total thickness of the conductive layer in the composite current collector is 1.1 μm to 8.4 μm, optionally 1.1 μm to 6 μm, and more preferably 2 μm to 3 μm. This allows for high conductivity with a relatively small thickness, enabling the composite current collector to achieve both better conductivity and lightweight design.

[0090] Furthermore, the conductive layer is made of copper. Copper not only has good conductivity but is also inexpensive. Furthermore, when the negative electrode uses a composite current collector, the conductive layer may optionally include copper to achieve higher conductivity in the composite current collector. As an example, the conductive layer may include or be a copper layer, with a total thickness of 1.1 μm to 8.4 μm, optionally 1.1 μm to 6 μm, and more preferably 2 μm to 3 μm.

[0091] As an example, the conductive layer may include or be a silver layer, the total thickness of which is 1.1 μm to 7.9 μm, optionally 1.1 μm to 6 μm, and more preferably 2 μm to 3 μm.

[0092] In some embodiments, the conductive layer is made of one or an alloy of gold and aluminum. Further, the total thickness of the conductive layer in the composite current collector is 1.6 μm to 14.1 μm, optionally 1.9 μm to 7 μm, and more preferably 3 μm to 7 μm. This allows for high conductivity with a relatively small thickness, enabling the composite current collector to achieve both better conductivity and lightweight design.

[0093] Furthermore, the conductive layer is made of aluminum. Aluminum not only has good conductivity but is also inexpensive. Furthermore, when the positive electrode uses a composite current collector, the conductive layer may optionally include aluminum to achieve higher conductivity in the composite current collector. As an example, the conductive layer may include or be an aluminum layer with a total thickness of 1.9 μm to 14.1 μm, optionally 2 μm to 10 μm.

[0094] As an example, the conductive layer may include or be a gold layer, with a total thickness of 1.6 μm to 12 μm, optionally 2 μm to 10 μm.

[0095] In some embodiments, the conductive layer is made of an alloy of one or more elements selected from magnesium, nickel, iron, and tin. Further, the total thickness of the conductive layer in the composite current collector is 2 μm to 20 μm, optionally 2 μm to 15 μm, and more preferably 3 μm to 10 μm. This allows the composite current collector to achieve high conductivity with a relatively small thickness, thus combining better conductivity with lightweight design.

[0096] As an example, the conductive layer may include or be a magnesium layer, with a total thickness of 3 μm to 20 μm.

[0097] As an example, the conductive layer may include or be a nickel layer with a total thickness of 4.6 μm to 20 μm.

[0098] As an example, the conductive layer may include or be an iron layer, with a total thickness of 6.5 μm to 20 μm.

[0099] As an example, the conductive layer may include or be a tin layer, with a total thickness of 7.3 μm to 20 μm.

[0100] In some embodiments, the thickness of the titanium substrate layer in the composite current collector is 20% to 90%, optionally 30% to 70%. As an example, the thickness percentage of the titanium substrate layer in the composite current collector can be 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, or 90%, or within a range defined by any two of the above values. Further controlling the thickness percentage of the titanium substrate layer in the composite current collector allows for a better balance between tensile strength and conductivity.

[0101] In some embodiments, the mass content of titanium in the titanium substrate layer is 85% to 100%, optionally 90% to 99.99%. As an example, the mass content of titanium in the titanium substrate layer can be 85%, 88%, 90%, 92%, 95%, 98%, 99%, 99.5%, 99.9%, 99.99%, 100%, or a range defined by any two of the above values ​​as endpoints.

[0102] In some embodiments, the titanium substrate layer comprises one or a stack of two of the following: a titanium elemental layer and a titanium alloy layer.

[0103] As an example, the titanium substrate layer can be made of one or more of TA1, TA2, TA4, TA16, and TC4. Further, the elemental titanium layer can be made of one or more of TA1 and TA2. Further, the titanium alloy layer can be made of one or more of TA4, TA16, and TC4.

[0104] Alternatively, the titanium substrate layer may be made of TA1, which has the advantage of being easy to process into foil.

[0105] In some embodiments, the tensile strength of the composite current collector is 500 MPa to 1600 MPa, and optionally 800 MPa to 1200 MPa.

[0106] In some embodiments, the elongation at break of the composite current collector is 1.5% to 6%, optionally 2% to 4%.

[0107] In some embodiments, the elongation at break of the titanium substrate layer is 1.5% to 4%, optionally 2% to 3%. As an example, the elongation at break of the titanium substrate layer can be 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, or within a range defined by any two of the above values ​​as endpoints. This application prioritizes meeting the tensile strength requirement of the titanium substrate layer. A higher elongation at break of the titanium substrate layer indicates greater resistance to tearing, but in practice, it is difficult to achieve both simultaneously. Therefore, controlling it within this range ensures a good balance between tensile strength and tear resistance.

[0108] In some embodiments, the elongation at break of the conductive layer is 2% to 7%, optionally 3% to 5%. As an example, the elongation at break of the conductive layer can be 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, 5.5%, 6%, 6.5%, 7%, or within a range formed by any two of the above point values ​​as endpoints.

[0109] In some embodiments, the areal density of the composite current collector is 15 g / m³. 2 ~95g / m 2 15g / m 2 ~40g / m 2 As an example, the surface density of a composite current collector can be 15 g / m³. 2 20g / m 2 25g / m 2 30g / m 2 35g / m 2 40g / m 2 45g / m 2 50g / m 2 55g / m 2 60g / m 2 65g / m2 70g / m 2 75g / m 2 80g / m 2 85g / m 2 90g / m 2 95g / m 2 , or the range formed by any two of the above point values ​​as endpoints.

[0110] In some embodiments, the sheet resistance of the composite current collector is 0.0018 Ω / □ to 0.015 Ω / □. As an example, the sheet resistance of the composite current collector can be 0.0018 Ω / □, 0.002 Ω / □, 0.003 Ω / □, 0.004 Ω / □, 0.005 Ω / □, 0.006 Ω / □, 0.007 Ω / □, 0.008 Ω / □, 0.009 Ω / □, 0.010 Ω / □, 0.011 Ω / □, 0.012 Ω / □, 0.013 Ω / □, 0.014 Ω / □, 0.015 Ω / □, or within a range formed by any two of the above values ​​as endpoints.

[0111] In some embodiments, the composite current collector further includes a base coating layer disposed on the conductive layer, the base coating layer comprising a conductive agent and a binder. The base coating layer can improve the overall conductivity of the electrode.

[0112] Optionally, the thickness of the base coating on one side is 0.25 μm to 5 μm, and can be selected as 0.5 μm to 3 μm. As an example, the thickness of the base coating on one side can be 0.25 μm, 0.5 μm, 1 μm, 1.25 μm, 1.5 μm, 2 μm, 2.25 μm, 2.5 μm, 3 μm, 3.25 μm, 3.5 μm, 4 μm, 4.25 μm, 4.5 μm, 5 μm, or within the range formed by any two of the above point values ​​as endpoints.

[0113] Furthermore, the binder in the base layer includes at least one of polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethacrylic acid (PMAA), carboxymethyl chitosan (CMCS), and fluorinated acrylate resin.

[0114] Furthermore, the aforementioned adhesive is a conductive polymer adhesive, including at least one of epoxy resin conductive adhesive, phenolic resin conductive adhesive, polyurethane conductive adhesive, thermoplastic resin conductive adhesive, and polyimide conductive adhesive.

[0115] Further, the binder content in the primer layer is 10% to 60% by mass. Further, the conductive agent content in the primer layer is 30% to 90% by mass. Further, the conductive agent in the primer layer may include one or more of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0116] In some embodiments, the negative electrode includes a negative current collector and a negative active layer disposed on at least one side of the negative current collector.

[0117] As a non-limiting example, the negative electrode current collector has two surfaces opposite each other in its own thickness direction, and the negative electrode active layer is disposed on either or both of the two opposite surfaces of the negative electrode current collector.

[0118] Furthermore, the negative electrode current collector adopts the aforementioned composite current collector. The negative electrode sheet includes the aforementioned composite current collector and a negative electrode active layer disposed on at least one side of the composite current collector.

[0119] The negative electrode active layer includes a negative electrode active material. As a non-limiting example, the negative electrode active material may include one or more of the following materials: silicon-based materials, carbon-based materials, tin-based materials, and lithium titanate, etc. Silicon-based materials may include one or more of elemental silicon, silicon oxide compounds, silicon-carbon composites, silicon-nitrogen composites, and silicon alloys. Carbon-based materials include one or more of artificial graphite, natural graphite, soft carbon, and hard carbon. Tin-based materials may include one or more of elemental tin, tin oxide compounds, and tin alloys.

[0120] Furthermore, the negative electrode active layer includes one or more of silicon-based and carbon-based materials. Even further, the negative electrode active layer includes a silicon-based material. Silicon-based materials have a higher specific capacity, which is beneficial for achieving higher energy density in secondary batteries. This composite current collector has high tensile strength and can also restrain the volume expansion of the negative electrode, reducing or suppressing tearing of the outer conductive layer, thereby improving the battery's conductivity, achieving high power performance, and enhancing the safety performance of the secondary battery.

[0121] Optionally, the mass content of silicon-based material in the negative electrode active layer is 0% to 99%, more preferably 5% to 90%. As an example, the mass content of silicon-based material in the negative electrode active layer is 0%, 1%, 2%, 3%, 4%, 5%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, 95%, 99%, or within a range formed by any two of the above values ​​as endpoints.

[0122] Optionally, the mass content of silicon in the negative electrode active layer is 0% to 90%, more preferably 2% to 60%. As an example, the mass content of silicon in the negative electrode active layer is 0%, 1%, 2%, 3%, 4%, 5%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, or within the range formed by any two of the above values ​​as endpoints.

[0123] In some embodiments, the negative electrode active layer may optionally include a binder. The binder may include one or more 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).

[0124] In some embodiments, the negative electrode active layer may optionally include a conductive agent. The conductive agent may include one or more of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0125] In some embodiments, the negative electrode active layer may also optionally include other additives, such as thickeners (e.g., sodium carboxymethyl cellulose (CMC-Na)).

[0126] 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 (a non-limiting example of a solvent is deionized water) to form a negative electrode slurry; coating the negative electrode slurry onto at least one surface of a negative electrode current collector, and then obtaining the negative electrode sheet after drying, cold pressing, and other processes. The surface of the negative electrode current collector coated with the negative electrode slurry can be a single surface of the negative electrode current collector or both surfaces of the negative electrode current collector. The solid content of the negative electrode slurry can be 40wt% to 60wt%. The viscosity of the negative electrode slurry at room temperature can be adjusted to 2000 to 10000 mPa·s. When coating the negative electrode slurry, the coating unit areal density (dry weight, minus solvent) can be 75 g / m². 2 ~220g / m 2 The compaction density of the negative electrode active layer can be 1.0 g / cm³. 3 ~1.8g / cm 3 .

[0127] In other embodiments, the negative electrode active layer includes a lithium metal layer. As a negative electrode active layer, the lithium metal layer has a good theoretical specific capacity, enabling the secondary battery to store and release more energy within the same volume or weight, i.e., achieving better energy density. Furthermore, because lithium metal has a low electrode potential, when paired with a suitable positive electrode material, it can generate a higher battery voltage, thereby further improving the battery's energy output and power performance. In addition, lithium metal has good conductivity, allowing electrons to conduct rapidly on the surface of the lithium metal layer, effectively reducing the battery's internal resistance, improving charge and discharge efficiency, and enhancing power performance.

[0128] In some embodiments, 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 a positive electrode active material.

[0129] As a non-limiting example, the positive current collector has two surfaces opposite each other in its own thickness direction, and the positive active layer is disposed on either or both of the two opposite surfaces of the positive current collector.

[0130] Furthermore, the positive electrode current collector adopts the improved composite current collector described above in this application.

[0131] In some embodiments, both the positive current collector and the negative current collector adopt the composite current collector described above in this application.

[0132] In other examples, while the positive electrode current collector uses the aforementioned composite current collector, the negative electrode current collector may optionally use other current collectors, including but not limited to metal foil or other composite current collectors.

[0133] In other examples, while the negative electrode current collector uses the aforementioned composite current collector, the positive electrode current collector may optionally use other current collectors, including but not limited to metal foils or other composite current collectors. For example, aluminum foil may be used as the metal foil. Other composite current collectors 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 can be obtained by forming a metal material on the polymer material substrate. Non-limiting examples of the metal material in the positive electrode current collector may include one or more of aluminum, aluminum alloys, nickel, nickel alloys, titanium, titanium alloys, silver, and silver alloys. Non-limiting examples of the polymer material substrate in the positive electrode current collector may include one or more of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), and polyethylene (PE).

[0134] The positive electrode sheet includes a positive active layer, which contains a positive active material. The positive active material may be any known battery positive active material. As a non-limiting example, the positive active material may include one or more of the following: 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 active materials may also be used. These positive active materials may be used alone or in combination of two or more.

[0135] Non-limiting examples of lithium phosphates with an olivine structure may include, but are not limited to, one or more of lithium iron phosphate, lithium iron phosphate and carbon composites, lithium manganese phosphate, lithium manganese phosphate and carbon composites, lithium iron manganese phosphate, and lithium iron manganese phosphate and carbon composites. Examples of lithium transition metal oxides may include, but are not limited to, one or more of lithium cobalt oxide, lithium manganese oxide, lithium manganese cobalt oxide, lithium nickel oxide, and their modified compounds. Non-limiting examples of lithium cobalt oxides may include LiCoO2. Non-limiting examples of lithium manganese oxides may include LiMnO2 and LiMn2O4.

[0136] Lithium nickel oxides or their modified compounds can also be called nickel-containing lithium salts. Positive electrode active materials may include one or more of lithium nickel oxides or their modified compounds. Nickel-containing lithium salts include those with the chemical formula Li. a Ni x Co y M z Compounds of O2, wherein 0.9≤a≤1.5, 0.6≤x≤1, 0≤y≤0.4, x+y+z=1; M is one or more of Mn, Al, Zr, Sr, B, Ti, Mg and Sn.

[0137] As an example, the value of 'a' can be 0.9, 1, 1.1, 1.2, 1.3, 1.4, 1.5, or any two of the above point values ​​as endpoints within the range.

[0138] As an example, the value of x can be 0.6, 0.62, 0.64, 0.65, 0.66, 0.68, 0.7, 0.72, 0.74, 0.75, 0.76, 0.78, 0.8, 0.82, 0.84, 0.85, 0.86, 0.88, 0.9, 0.92, 0.94, 0.95, 0.96, 0.98, 1, or any two of the above values ​​as endpoints. Optionally, 0.8 ≤ x ≤ 1.

[0139] As an example, the value of y can be 0, 0.02, 0.05, 0.08, 0.1, 0.12, 0.15, 0.18, 0.2, 0.22, 0.24, 0.25, 0.28, 0.3, 0.32, 0.34, 0.35, 0.36, 0.38, 0.4, or any two of the above values ​​as endpoints. Optionally, 0 ≤ y ≤ 0.2.

[0140] As examples, nickel-containing lithium salts include, but are not limited to, one or more of lithium nickel oxide, lithium nickel cobalt oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide, and lithium nickel cobalt aluminum oxide. Non-limiting examples of lithium nickel oxides may include LiNiO2. Non-limiting examples of lithium nickel cobalt manganese oxides may include LiNi 0.8 Co 0.1 Mn 0.1 O2 (also known as NCM) 811 Examples of lithium nickel cobalt aluminum oxides include LiNi, etc. 0.8 Co 0.15 Al 0.05 O2.

[0141] In some embodiments, the positive electrode active layer may optionally include a binder. As a non-limiting example, the binder may include one or more of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), PVDF-tetrafluoroethylene-propylene terpolymer, PVDF-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorinated acrylate resins.

[0142] In some embodiments, the positive electrode active layer may optionally include a conductive agent. As a non-limiting example, the conductive agent may include one or more of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0143] In some embodiments, the positive electrode sheet can be prepared by dispersing the components used to prepare the positive electrode sheet, such as the positive active material, conductive agent, binder, and any other components, in a solvent to form a positive electrode slurry; coating the positive electrode slurry onto at least one surface of the positive electrode current collector, and then obtaining the positive electrode sheet through processes such as drying and cold pressing. The solvent can be selected from, but is not limited to, any of the solvents described in the foregoing embodiments, such as N-methylpyrrolidone (NMP). The surface of the positive electrode current collector coated with the positive electrode slurry can be a single surface of the positive electrode current collector or both surfaces of the positive electrode current collector. The solid content of the positive electrode slurry can be 40 wt% to 80 wt%.

[0144] Typically, a secondary battery consists of a positive electrode, a negative electrode, an electrolyte, and a separator. During charging and discharging, active ions move back and forth between the positive and negative electrodes, inserting and releasing. The electrolyte acts as a conductor between the positive and negative electrodes. The separator, positioned between the positive and negative electrodes, primarily prevents short circuits while allowing ions to pass through.

[0145] electrolytes

[0146] Electrolytes function to conduct ions between the positive and negative electrode plates. This application does not impose any particular restrictions on the type of electrolyte; it can be selected according to requirements. For example, the electrolyte can be liquid, gel, or completely solid.

[0147] In some embodiments, the electrolyte is an electrolyte solution. The electrolyte solution includes an electrolyte salt and a solvent.

[0148] In some embodiments, the electrolyte has a conductivity of 7 mS / cm to 15 mS / cm at 25°C, optionally 8 mS / cm to 13 mS / cm. As an example, the electrolyte has conductivity of 7 mS / cm, 8 mS / cm, 9 mS / cm, 10 mS / cm, 11 mS / cm, 12 mS / cm, 13 mS / cm, 14 mS / cm, or 15 mS / cm at 25°C, or within a range defined by any two of the above values ​​as endpoints.

[0149] In some embodiments, the electrolyte salt may include one or more of lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium perchlorate (LiClO4), lithium hexafluoroarsenate (LiAsF6), lithium bis(fluorosulfonyl)imide (LiFSI), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium trifluoromethanesulfonate (LiTFS), lithium difluorophosphate (LiPO2F2), lithium difluorooxalate borate (LiDFOB), lithium dioxalate borate (LiBOB), lithium difluorodioxalate phosphate (LiDFOP), and lithium tetrafluorooxalate phosphate (LiTFOP).

[0150] In some embodiments, the solvent includes at least one of ether solvents, ester solvents, and sulfone solvents.

[0151] As an example, the ether solvent may include at least one of ethylene glycol dimethyl ether (DME), diethylene glycol dimethyl ether (DEGDME), triethylene glycol dimethyl ether (TRGDME), tetraethylene glycol dimethyl ether (TEGDME), and 1,3-dioxolane (DOL);

[0152] As an example, the ester solvent may include at least one of ethylene carbonate (EC), propylene carbonate (PC), butyl carbonate (BC), vinylene carbonate (VC), fluoroethylene carbonate (FEC), methyl ethyl carbonate (EMC), dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), γ-butyrolactone (BL), 1,3-propanesulfonate lactone (1,3-PS), methyl propionate (MP), methyl butyrate (MB), ethyl acetate (EA), ethyl propionate (EP), propyl propionate (PP), and ethyl butyrate (EB).

[0153] 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.

[0154] In some embodiments, the additives in the electrolyte may include, but are not limited to, one or more of fluoroethylene carbonate (FEC), difluoroethylene carbonate (DFEC), trifluoromethyl ethylene carbonate (TFPC), etc.

[0155] Separating membrane

[0156] 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.

[0157] In some embodiments, the material of the separator may include one or more of glass fiber, nonwoven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator may 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 may be the same or different, without particular limitation.

[0158] In some embodiments, the thickness of the isolation membrane is 6 μm to 40 μm, and optionally 12 μm to 20 μm.

[0159] A second aspect of this application provides a composite current collector, comprising a titanium substrate layer and a conductive layer disposed on at least one side of the titanium substrate layer, wherein the thickness of the titanium substrate layer is 2 μm to 10 μm and the sheet resistance of the conductive layer is 0.0018 Ω / □ to 0.017 Ω / □.

[0160] In some embodiments, the composite current collector is the composite current collector in the secondary battery provided in the first aspect of this application, and therefore has the same features and beneficial effects as the composite current collector described above, which will not be repeated here.

[0161] A third aspect of this application provides a method for preparing a composite current collector, comprising the following steps: forming a conductive layer on at least one side of a titanium substrate layer; wherein the thickness of the titanium substrate layer is 2 μm to 10 μm, and the sheet resistance of the conductive layer is 0.0018 Ω / □ to 0.017 Ω / □.

[0162] The detailed steps of the above-mentioned composite current collector preparation method have been described above and will not be repeated here.

[0163] In a fourth aspect, this application provides an electrical device including at least one of the secondary battery provided in the first aspect of this application, the composite current collector provided in the second aspect of this application, and the composite current collector provided in the third aspect of this application.

[0164] The secondary battery and power-consuming device of this application will be described below with appropriate reference to the accompanying drawings.

[0165] As described above, a typical secondary battery includes a positive electrode, a negative electrode, an electrolyte, and a separator. In some embodiments, the positive electrode, negative electrode, and separator are fabricated into an electrode assembly using a winding or stacking process. The electrolyte is disposed between the positive and negative electrode plates. Further, the electrolyte is an electrolyte solution that wets the electrode assembly.

[0166] A secondary battery includes at least one battery cell. A secondary battery may include one or more battery cells.

[0167] In this application, unless otherwise specified, "cell battery" refers to the basic unit capable of converting chemical energy into electrical energy, and generally includes at least a positive electrode, a negative electrode, and an electrolyte. During the charging and discharging process of the battery, active ions move back and forth between the positive and negative electrode plates, inserting and extracting. The electrolyte acts as a conductor for the active ions between the positive and negative electrode plates.

[0168] This application does not impose any particular limitation on the shape of the battery cell; it can be cylindrical, square, or any other arbitrary shape. For example, the secondary battery shown in Figure 3 is a battery cell, which serves as an example of a square-structured battery cell.

[0169] In some embodiments, the battery cell may include an outer packaging. This outer packaging can be used to encapsulate the electrode assembly described above. Furthermore, an electrolyte is also disposed within the outer packaging for wetting the electrode assembly.

[0170] In some embodiments, the outer packaging of the battery cell can be a rigid 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-type soft pack. The material of the soft pack can be plastic, and further, non-limiting examples of plastic can include one or more of polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0171] In some embodiments, referring to FIG4, the outer packaging may include a housing 51 and a cover plate 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 plate 53 can be placed over the opening to close the receiving cavity. The positive electrode sheet, negative electrode sheet, and separator may be formed into an electrode assembly 52 by a winding process or a stacking process. The electrode assembly 52 is encapsulated within the receiving cavity. The electrode assembly 52 is immersed in an electrolyte. The number of electrode assemblies 52 contained in the battery cell 5 may be one or more, which can be selected by those skilled in the art according to actual needs.

[0172] In some embodiments, the secondary battery can be a battery device or a battery pack. A battery device includes at least one battery cell. The number of battery cells in a battery device can be one or more, and those skilled in the art can select an appropriate number based on the application and capacity of the battery device.

[0173] Figure 5 shows a battery device 4 as an example. Referring to Figure 5, in the battery device 4, multiple battery cells 5 can be arranged sequentially along the length of the battery device 4. Of course, they can also be arranged in any other arbitrary manner. Furthermore, the multiple battery cells 5 can be fixed in place by fasteners.

[0174] Optionally, the battery device 4 may also include a housing with a receiving space in which multiple battery cells 5 are received.

[0175] In some embodiments, the battery devices described above can also be assembled into a battery pack, and the number of battery devices contained in the battery pack can be one or more. Those skilled in the art can select an appropriate number according to the application and capacity of the battery pack.

[0176] Figures 6 and 7 illustrate a battery pack 1 as an example. Referring to Figures 6 and 7, the battery pack 1 may include a battery compartment and multiple battery devices 4 disposed within the battery compartment. The battery compartment includes an upper compartment 2 and a lower compartment 3, the upper compartment 2 covering the lower compartment 3 to form a closed space for accommodating the battery devices 4. The multiple battery devices 4 can be arranged in any manner within the battery compartment.

[0177] In addition, one embodiment of this application also provides an electrical device, which includes the secondary battery provided in this application. The secondary battery can be used as the power source of the electrical device or as the energy storage unit of the electrical device. The electrical device may include, but is not limited to, aircraft, aviation equipment, mobile devices, electric vehicles, electric trains, ships and satellites, energy storage systems, etc. Among them, mobile devices may be, for example, mobile phones, laptops, etc.; electric vehicles may be, for example, pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc., but are not limited to.

[0178] As an electrical device, a rechargeable battery can be selected based on its usage requirements.

[0179] Figure 8 shows an example of an electrical device 6. This electrical device is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle, etc. To meet the high power and high energy density requirements of the secondary battery for this electrical device, a battery pack or battery device can be used as the power source.

[0180] Another example device could be a mobile phone, tablet, or laptop. These devices typically require a slim and lightweight design and can use a single battery cell as their power source.

[0181] To make the technical problems, technical solutions, and beneficial effects solved by this application clearer, the application will be further described in detail below with reference to embodiments and accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. The following description of at least one exemplary embodiment is merely illustrative and is in no way intended to limit this application or its applications. Based on the embodiments in this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0182] Where specific techniques or conditions are not specified in the examples, they shall be performed in accordance with the techniques or conditions described in the literature in this field or in accordance with the product instructions. Reagents or instruments whose manufacturers are not specified are all commercially available conventional products.

[0183] Example 1

[0184] 1. Preparation of composite current collectors.

[0185] 1.1 The titanium foil (specifically TA1) is rolled to the corresponding thickness (as shown in Table 1) by rolling to obtain the titanium substrate layer.

[0186] 1.2 A Cu underlay layer of the same thickness was formed on both sides of the titanium substrate layer by magnetron sputtering under the same conditions.

[0187] 1.3 Electroplating is performed on the Cu underlayers on both sides of the titanium substrate layer obtained in step 1.2 until the total thickness of the Cu conductive layers on both sides of the titanium substrate layer reaches the corresponding thickness (the thickness of the Cu conductive layers on both sides is the same), as shown in Table 1.

[0188] 2. Preparation of negative electrode sheet.

[0189] Conductive carbon black, styrene-butadiene rubber, and sodium carboxymethyl cellulose were dissolved in deionized water at a weight ratio of 70:25:5 and mixed evenly to prepare a primer slurry.

[0190] The negative electrode active material silicon carbide, conductive carbon black (Super P), styrene-butadiene rubber (SBR), and sodium carboxymethyl cellulose (CMC Na) were dissolved in deionized water at a weight ratio of 95.5:1:2.2:1.3 and mixed evenly to prepare a negative electrode slurry.

[0191] The primer slurry was uniformly coated onto the composite current collector described above, and dried to form a primer layer with a thickness of 1 μm. Then, the negative electrode slurry was uniformly coated onto the primer layer, and dried to form the negative electrode active layer. The resulting electrode sheet was then cold-pressed and slit to obtain the negative electrode sheet. The compaction density of the negative electrode active layer was 1.2 g / cm³. 3 .

[0192] In this application, the compaction density of the negative electrode active layer or the positive electrode active layer in the electrode sheet is tested by the following method: the battery is disassembled, the electrode sheet is taken out, and it is punched into a piece with an area of ​​S = 1540.25 mm². 2 Take a small circular electrode, measure its weight M and thickness L, and then take another electrode. Remove the film layer from the surface of the electrode to remove the remaining empty current collector foil. Similarly, punch it to a diameter S = 1540.25 mm. 2 The small round piece is weighed, and the mass M0 of the empty aluminum foil is measured. Then the compaction density PD = (M-M0) / S / (L-L0), where L0 is the thickness of the current collector foil.

[0193] 3. Preparation of the positive electrode sheet.

[0194] A nickel-cobalt-manganese ternary material (NCM811), conductive carbon black (SP), carbon nanotubes (CNT), and polyvinylidene fluoride (PVDF) binder were mixed evenly at a weight ratio of 95:2.5:0.5:2 to obtain a positive electrode slurry. The positive electrode slurry was then uniformly coated onto a positive electrode current collector (a 12 μm thick aluminum foil). After drying, a positive electrode active layer was formed. The resulting material was then cold-pressed and slit to obtain the positive electrode sheet. The compaction density of the positive electrode active layer was 3.5 g / cm³. 3 .

[0195] 4. Separation membrane.

[0196] A 12μm thick PP (polypropylene) membrane was selected as the separator.

[0197] 5. Preparation of electrolyte.

[0198] An organic solvent was prepared by mixing ethylene carbonate (EC), dimethyl carbonate (DMC), and ethyl methyl carbonate (EMC) in a mass ratio of 1:1:1. Thoroughly dried LiPF6 was then dissolved in this organic solvent to prepare an electrolyte.

[0199] The concentration of LiPF6 in the total mass of the electrolyte is 1 mol / L.

[0200] The conductivity of the electrolyte is tested as follows: A conductivity meter is used. The measuring electrode is inserted into the electrolyte, the instrument is connected, and a small voltage is applied. The conductivity of the electrolyte can be directly measured. The conductivity of the electrolyte at 25℃ is 8 mS / cm.

[0201] 6. Battery manufacturing.

[0202] The positive electrode, separator, and negative electrode are stacked in sequence and wound using a winding machine to obtain a bare battery cell. The electrode assembly is placed in an outer shell, dried, and then injected with electrolyte. After vacuum sealing, settling, formation, and degassing, a lithium-ion secondary battery is finally obtained. The electrolyte injection coefficient is 1.6 g / Ah.

[0203] Example 2

[0204] It is basically the same as Example 1, except that the preparation steps of the composite current collector are different. In addition, the composite current collector is applied to the positive electrode sheet instead of the negative electrode sheet. In Example 2, the negative electrode sheet uses a copper foil with a thickness of 6μm.

[0205] The specifics are as follows:

[0206] 1.1 The titanium foil (material TA1) is rolled to the corresponding thickness (as shown in Table 1) by rolling to obtain the titanium substrate layer.

[0207] 1.2 An Al underlay layer of the same thickness was formed on both sides of the titanium substrate layer by magnetron sputtering under the same conditions.

[0208] 1.3 Electroplating is performed on the Al underlayers on both sides of the titanium substrate layer obtained in step 1.2 until the total thickness of the Al conductive layers on both sides of the titanium substrate layer reaches the corresponding thickness (the Al conductive layers on both sides are the same), as shown in Table 1.

[0209] Examples 3-7

[0210] It is basically the same as Example 1, except that at least one of the parameters, namely the thickness of the titanium substrate and the total thickness of the conductive layer, is different, as shown in Table 1.

[0211] Examples 8-10

[0212] It is basically the same as Example 2, except that the total thickness of the conductive layer is different, as shown in Table 1.

[0213] Comparative Example 1

[0214] It is basically the same as Example 1, except that the composite current collector is different. Specifically:

[0215] The negative electrode current collector (composite current collector) is a stack of copper metal coating / PET (polyethylene terephthalate) / copper metal coating. The thickness of the copper metal coating on both sides is the same, and the thickness of the PET and the total thickness of the copper metal coating are shown in Table 1.

[0216] Comparative Example 2

[0217] It is basically the same as Example 1, except that the negative electrode current collector is a single copper foil with a thickness as shown in Table 1.

[0218] Comparative Example 3

[0219] It is basically the same as Example 1, except that the negative electrode current collector is a single titanium foil (material TA1) with the thickness shown in Table 1.

[0220] Comparative Example 4

[0221] It is basically the same as Example 10, except that at least one of the parameters, namely the thickness of the titanium substrate and the total thickness of the conductive layer, is different, as shown in Table 1.

[0222] Comparative Examples 5-6

[0223] It is basically the same as Example 1, except that at least one of the parameters, namely the thickness of the titanium substrate and the total thickness of the conductive layer, is different, as shown in Table 1.

[0224] The following are performance tests.

[0225] 1. Surface density of composite current collector.

[0226] The areal density of the composite current collector was tested using the following method: the composite current collector was punched into a piece with an area of ​​S = 1540.25 mm². 2 If a small circular piece is used, and its weight M is measured, then the surface density of the composite current collector is M / S.

[0227] 2. Tensile strength and elongation at break of the composite current collector.

[0228] Using an Instron tensile testing machine (INSTRON 3343), a 100 mm long and 15 mm wide specimen was stretched at a stretching speed of 2 mm / min with a gauge length of 50 mm. The stretching curve was measured, and the tensile strength (tensile force / cross-sectional area) of the current collector was calculated based on the maximum tensile force in the stretching curve. The elongation at break was divided by the length before stretching as the elongation at break. Each specimen was measured in parallel 6 times, and the average value was calculated as the tensile strength and elongation at break of that specimen.

[0229] 3. Shear resistance of the conductive layer.

[0230] The sheet resistance of the conductive layer is calculated as resistivity (ρ) / thickness (d), where resistivity (ρ) is determined based on the material of the conductive layer, and thickness (d) is obtained by scanning electron microscopy (SEM) of the cross-section of the composite current collector and by measuring the thickness of the conductive layer within it. Thus, the sheet resistance of the conductive layer is obtained, with units of Ω / □, denoted as R1, as shown in Table 1. 4. Sheet resistance of the composite current collector.

[0231] The composite current collector was cut into square samples with a length and width preferably not less than 20 mm, while the thickness remained unchanged. The sheet resistance of the composite current collector was measured using the four-probe method, and the unit was Ω / □, denoted as R2, as shown in Table 1.

[0232] The sheet resistance of the current collector is tested using a four-probe sheet resistance tester: four equally spaced probes are placed on the surface of the current collector, and a small current I is supplied to the two outer probes by a constant current source. Then, the voltage V between the two middle probes is measured, and the sheet resistance of the current collector can be read directly.

[0233] 5. Battery performance.

[0234] Test methods for capacity retention and large-area temperature rise of battery cells

[0235] Temperature sensing wires are arranged on the surface of the battery cell to continuously monitor the temperature rise during the test of the D-Rate 2C capacity retention rate.

[0236] At 25℃, charge at a constant current rate of 1 / 3C to 4.25V, then switch to constant voltage charging until the current drops to 0.05C. After resting for 30 minutes, discharge at a constant current rate of 1 / 3C to 2.5V and record the discharge capacity as C1. Then charge at a constant current rate of 1 / 3C to 4.25V again, then switch to constant voltage charging until the current drops to 0.05C. After resting for 30 minutes, record the initial temperature T1. Finally, discharge at a constant current rate of 2C to 2.5V and record the discharge capacity as C2. Record the final temperature T2.

[0237] D-Rate 2C capacity retention rate = C2 / C1*100%, process temperature rise = T2-T1.

[0238] Table 1

[0239] As shown in Table 1, the main problem with Comparative Example 1, which uses a lightweight composite current collector with PET as the base layer, is that its tensile strength is too low. It cannot restrain the high volume expansion of the silicon anode. The copper metal plating is easily torn during repeated charging and discharging, which leads to a decrease in the conductivity of the composite current collector and even causes a short circuit inside the battery.

[0240] Comparative Example 2 uses the most commonly used negative electrode current collector copper foil, which has lower resistance. Compared with the composite current collector in the embodiment, its tensile strength is also lower, and its areal density is higher, which is not conducive to the design and use of high weight energy density batteries.

[0241] Comparative Example 3 uses titanium foil as the negative electrode current collector. Since the density of titanium is about half that of copper, the areal density is halved and the tensile strength is greatly improved. However, due to the poor conductivity of titanium itself, its resistance is also greatly deteriorated. Therefore, the battery using Comparative Example 3 exhibits poor power performance and also worsens the heat generation during battery use.

[0242] Comparative Example 4 used titanium foil as the substrate to form a composite current collector, but due to the low thickness of the titanium foil, its tensile strength was still too low.

[0243] Comparative Examples 5 and 6 used titanium foil as the substrate and a copper metal layer as the conductive layer to form a composite current collector. In Comparative Example 5, the copper metal layer was thinner, resulting in higher resistances R1 and R2. Consequently, the battery using Comparative Example 5 exhibited poor power performance and worsened heat generation during battery use. In Comparative Example 6, the copper metal layer was thicker, resulting in a higher areal density, which is unfavorable for the design and use of high-energy-density batteries. Compared to Comparative Examples 1 to 6, the composite current collectors in each embodiment have higher tensile strength and conductivity, thus exhibiting better capacity retention and lower temperature rise, while also maintaining a lower areal density, enabling weight reduction and thereby improving the energy density of the secondary battery.

[0244] As can be seen from Examples 1, 3-4, when the thickness of the titanium substrate layer gradually increases from 2μm to 10μm, the resistance R2 of the composite current collector decreases, the temperature rise of the battery cell decreases, but the areal density increases accordingly. Further controlling the thickness of the titanium substrate layer to within 3μm to 5μm can balance high conductivity and low areal density.

[0245] As can be seen from Examples 1, 5 to 7, the total thickness of the copper conductive layer gradually increases from 1.1 μm to 8.4 μm, the resistance R2 of the composite current collector decreases, the temperature rise of the battery cell decreases, but the areal density increases accordingly; further controlling the total thickness of the copper conductive layer to 1.1 μm to 6 μm, and optionally selecting 2 μm to 3 μm, can balance high conductivity and low areal density.

[0246] As can be seen from Examples 2, 8 to 10, the total thickness of the aluminum conductive layer gradually increases from 1.6 μm to 14.1 μm, the resistance R2 of the composite current collector decreases, the temperature rise of the battery cell decreases, but the areal density increases accordingly; further controlling the total thickness of the aluminum conductive layer to within 3 μm to 7 μm can balance high conductivity and low areal density.

[0247] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0248] The embodiments described above are merely illustrative of several implementation methods of this application, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the invention patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of this application, and these all fall within the protection scope of this application. Therefore, the protection scope of this patent application should be determined by the appended claims, and the specification and drawings can be used to interpret the scope of the claims.

Claims

A secondary battery includes a positive electrode and a negative electrode, each comprising a current collector. The current collector in at least one of the positive and negative electrodes is a composite current collector, comprising a titanium substrate layer and a conductive layer disposed on at least one side of the titanium substrate layer. The thickness of the titanium substrate layer is 2 μm to 10 μm, and the sheet resistance of the conductive layer is 0.0018 Ω / □ to 0.017 Ω / □. The secondary battery according to claim 1, wherein It meets one or more of the following characteristics: (1) The thickness of the titanium substrate layer is 3μm to 5μm; (2) The sheet resistance of the conductive layer is 0.0025Ω / □~0.01Ω / □. The secondary battery according to any one of claims 1 to 2, wherein The conductive layer is a conductive metal layer; Optionally, the conductive layer is a conductive metal plating layer. The secondary battery according to any one of claims 1 to 3, wherein The conductive layer is made of an alloy of one or more elements selected from silver, copper, gold, aluminum, magnesium, nickel, iron, and tin. The secondary battery according to any one of claims 1 to 4, wherein In the composite current collector, the conductive layer is provided on each of the opposite sides of the titanium substrate layer; Optionally, the thickness ratio of the conductive layer on opposite sides of the titanium substrate layer is 1:(0.9 to 1.1). The secondary battery according to any one of claims 1 to 5, wherein The total thickness of the conductive layer in the composite current collector is 1μm to 20μm, and can be selected as 2μm to 10μm. The secondary battery according to any one of claims 4 to 6, wherein The conductive layer is made of one or an alloy of silver and copper; the total thickness of the conductive layer in the composite current collector is 1.1 μm to 8.4 μm, optionally 1.1 μm to 6 μm, and more preferably 2 μm to 3 μm. The secondary battery according to any one of claims 4 to 6, wherein The conductive layer is made of one or an alloy of gold and aluminum; the total thickness of the conductive layer in the composite current collector is 1.6 μm to 14.1 μm, and can be 3 μm to 7 μm. The secondary battery according to any one of claims 4 to 6, wherein The conductive layer is made of an alloy of one or more elements selected from magnesium, nickel, iron, and tin; the total thickness of the conductive layer in the composite current collector is 3 μm to 20 μm. The secondary battery according to any one of claims 1 to 9, wherein In the composite current collector, the thickness of the titanium substrate layer accounts for 20% to 90%, and can be selected as 30% to 70%. The secondary battery according to any one of claims 1 to 10, wherein The titanium matrix layer contains 85% to 100% titanium by mass, and may be 90% to 99.99%. The secondary battery according to any one of claims 1 to 11, wherein The titanium substrate layer comprises one or a stack of two types of titanium elemental layer and titanium alloy layer. The secondary battery according to any one of claims 1 to 12, wherein It meets one or more of the following characteristics: (1) The tensile strength of the composite current collector is 500 MPa to 1600 MPa, and can be selected as 590 MPa to 1200 MPa; (2) The fracture elongation of the composite current collector is 1.5% to 6%, and can be selected as 2% to 4%; (3) The elongation at break of the titanium matrix layer is 1.5% to 4%, and can be selected as 2% to 3%; (4) The elongation at break of the conductive layer is 2% to 7%, and can be selected as 3% to 5%; (5) the areal density of the composite current collector is 15 g / m 2 ~ 95 g / m 2 , optionally 15 g / m 2 ~ 40 g / m 2 ; (6) The sheet resistance of the composite current collector is 0.0018Ω / □~0.015Ω / □. The secondary battery according to any one of claims 1 to 13, wherein The composite current collector further includes a base coating layer disposed on the conductive layer, the base coating layer comprising a conductive agent and a binder; Optionally, the thickness of the base coating layer on one side is 0.25μm to 5μm, and can be 0.5μm to 3μm. The secondary battery according to any one of claims 1 to 14, wherein The negative electrode sheet includes the composite current collector and a negative electrode active layer disposed on at least one side of the composite current collector; and satisfies one or more of the following characteristics: (1) The negative electrode active layer includes one or more of silicon-based materials and carbon-based materials; optionally, the mass content of silicon element in the negative electrode active layer is 0% to 90%, more preferably 2% to 60%; (2) The negative electrode active layer includes a lithium metal layer. The secondary battery according to any one of claims 1 to 15, wherein The positive electrode sheet includes a positive active layer, the positive active layer contains a positive active material, and the positive active material includes a nickel-containing lithium salt; The nickel-lithium salt includes those with the chemical formula Li a Ni x Co y M z Compounds of O2, wherein 0.9≤a≤1.5, 0.6≤x≤1, 0≤y≤0.4, x+y+z=1; M is one or more of Mn, Al, Zr, Sr, B, Ti, Mg and Sn. A composite current collector includes a titanium substrate layer and a conductive layer disposed on at least one side of the titanium substrate layer. The thickness of the titanium substrate layer is 2 μm to 10 μm, and the sheet resistance of the conductive layer is 0.0018 Ω / □ to 0.017 Ω / □. The composite current collector of claim 17, wherein The composite current collector is the composite current collector as described in any one of claims 2 to 16. A method for preparing a composite current collector includes the following steps: A conductive layer is formed on at least one side of a titanium substrate layer; the thickness of the titanium substrate layer is 2 μm to 10 μm, and the sheet resistance of the conductive layer is 0.0018 Ω / □ to 0.017 Ω / □. An electrical device comprising at least one of the secondary battery according to any one of claims 1 to 16, the composite current collector according to claim 17 or 18, and the composite current collector prepared by the preparation method according to claim 19.

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