Secondary battery, method of manufacturing, and electric device

Abstract

The application relates to a secondary battery, a preparation method and a power utilization device. The secondary battery comprises a negative electrode sheet, the negative electrode sheet comprising a negative electrode current collector and a negative electrode active layer located on at least one side of the negative electrode current collector; the negative electrode current collector comprises an iron-containing alloy layer and a conductive layer located on at least one side of the iron-containing alloy layer; the iron-containing alloy layer is a structural layer comprising a reinforcing element and an Fe element, the reinforcing element comprising at least one of a Ni element and a Cr element; the conductive layer comprises at least one of a Cu element and a metal element M2, the metal element M2 being a conductive metal element different from Cu and Fe; the thickness direction of the negative electrode current collector is defined as the longitudinal direction; in the longitudinal direction, the concentration of the Fe element on the surface of the iron-containing alloy layer is lower than the concentration of the Fe element in the interior of the iron-containing alloy layer. The secondary battery has an improved cycle life.

Description

Technical Field

[0001] This application relates to the field of secondary battery technology, and further to secondary batteries, preparation methods, and electrical devices. Background Technology

[0002] During the charge-discharge cycle of a secondary battery, the reversible insertion and extraction of active ions on the negative electrode causes repeated volume expansion and contraction changes. The negative electrode current collector needs to have sufficient strength to withstand the stress during these volume changes to prevent tearing and thus extend battery life. For some batteries experiencing drastic volume changes during charge and discharge, the strength provided by traditional copper foil is limited, posing a risk of negative electrode current collector breakage and capacity reduction, severely impacting battery cycle life. Summary of the Invention

[0003] According to various embodiments and examples of this application, this application provides a secondary battery, a method for its preparation, and an electrical device. This secondary battery has improved cycle life.

[0004] According to some embodiments of the first aspect, a secondary battery is provided, which includes a negative electrode sheet, the negative electrode sheet including a negative current collector and a negative active layer located on at least one side of the negative current collector;

[0005] The negative electrode current collector includes an iron-containing alloy layer and a conductive layer located on at least one side of the iron-containing alloy layer; the iron-containing alloy layer is a structural layer including a reinforcing element and an Fe element, wherein the reinforcing element includes at least one of Ni and Cr elements; the conductive layer includes at least one of Cu and a metallic element M2, wherein the metallic element M2 is a conductive metallic element different from Cu and Fe; the thickness direction of the negative electrode current collector is denoted as the longitudinal direction; in the longitudinal direction, the concentration of Fe element on the surface of the iron-containing alloy layer is lower than the concentration of Fe element inside the iron-containing alloy layer.

[0006] By introducing an iron-containing alloy layer, including reinforcing elements (at least one of Ni and Cr) and Fe, into the negative electrode current collector of the negative electrode sheet, and further controlling the distribution difference of Fe in the thickness direction (denoted as the longitudinal direction) of the negative electrode current collector, the concentration of Fe on the surface of the iron-containing alloy layer is lower than that inside the iron-containing alloy layer. This iron-containing alloy layer can balance strength and ductility. The high concentration of reinforcing elements on the surface is beneficial to providing higher strength, while the high concentration of Fe inside is beneficial to providing better ductility. This allows the negative electrode current collector to better resist volume changes of the negative electrode sheet, improve the structural stability of the negative electrode sheet, reduce the risk of breakage of the negative electrode current collector and the risk of battery capacity drop, and improve the cycle stability and cycle life of the secondary battery. Furthermore, by reducing the distribution concentration of Fe on the surface of the iron-containing alloy layer, the corrosion resistance of the iron-containing alloy layer can be improved, Fe dissolution can be inhibited, and the damage of potentially dissolved Fe ions to the negative electrode solid electrolyte interface (SEI) film can be reduced. Based on the aforementioned multiple effects, but not limited to the aforementioned theory, the secondary battery can be endowed with improved cycle life.

[0007] In some embodiments, the secondary battery satisfies one or more of the following characteristics:

[0008] (a1) The mass concentration of Fe element in the iron-containing alloy layer is greater than or equal to 30%, optionally 30% to 65%, and further optionally 30% to 50%;

[0009] (a2) The mass concentration of the reinforcing element in the iron-containing alloy layer is greater than or equal to 35%, optionally 35% to 70%, and more preferably 50% to 70%;

[0010] (a3) The mass percentage of Ni and Cr elements in the reinforcing elements is 95% to 100%, and optionally 98% to 100%; further optionally, the iron-containing alloy layer is a nickel-iron binary alloy layer, a chromium-iron binary alloy layer, or a nickel-chromium-iron ternary alloy layer.

[0011] (a4) The conductive layer is a copper layer.

[0012] When the mass concentration of Fe element in the iron-containing alloy layer (which can be denoted as C) Fe When the content of iron is greater than or equal to 30% (or even 30% to 65%), by introducing an iron-containing alloy layer with the aforementioned structural design into the negative electrode current collector, the corrosion resistance of the iron-containing alloy layer and the negative electrode current collector can be significantly improved, the leaching of Fe can be significantly reduced, and the cycle life of the secondary battery can be significantly improved.

[0013] By controlling the mass concentration of reinforcing elements in the iron-containing alloy layer (which can be denoted as C), QWithin the aforementioned range, it is beneficial to improve the strength of the negative electrode current collector while taking into account both its strength and ductility.

[0014] When controlling C Fe and C Q Meanwhile, within the aforementioned range, by introducing an iron-containing alloy layer with the aforementioned structural design into the negative electrode current collector, the strength and ductility of the negative electrode current collector can be well balanced, Fe dissolution can be significantly reduced, and the cycle life of the secondary battery can be significantly improved.

[0015] When controlling the mass ratio of Ni and Cr elements in the reinforcing elements (which can be denoted as F), 12 Within the aforementioned range, the negative electrode current collector can achieve a good balance between strength and ductility.

[0016] When the iron-containing alloy layer is a nickel-iron binary alloy layer, a chromium-iron binary alloy layer, or a nickel-chromium-iron ternary alloy layer, the negative electrode current collector can better balance strength and ductility, thus improving the cycle life of the secondary battery.

[0017] In some embodiments, the iron-containing alloy layer includes a central layer and a first surface layer and a second surface layer located on opposite sides of the iron-containing alloy layer, respectively.

[0018] The mass concentrations of Fe in the first surface layer, the central layer, and the second surface layer are denoted as C. F1 C C and C F2 C F1 <C C And C F2 <C C .

[0019] By controlling C F1 <C C And C F2 <C C It can effectively improve the corrosion resistance of iron-containing alloy layers, reduce Fe leaching, and improve the cycle life of secondary batteries.

[0020] In some embodiments, the negative electrode current collector satisfies one or more of the following characteristics:

[0021] (b1) The thickness ratio of the first surface layer to the central layer and the thickness ratio of the second surface layer to the central layer are each independently less than 1, and can be selected as 0.05 to 0.8, or more preferably 0.05 to 0.5;

[0022] (b2) The ratio of the areal density of Fe in the first surface layer to the areal density in the central layer and the ratio of the areal density of Fe in the second surface layer to the areal density in the central layer are each independently less than 1, optionally 0.01 to 0.5, and more preferably 0.02 to 0.3, per unit area in the transverse direction of the iron alloy layer; wherein, transverse direction is the direction perpendicular to the longitudinal direction.

[0023] By comparing the thickness ratio (R) of either the first surface layer or the second surface layer with respect to the central layer H12 Controlling the temperature within the aforementioned range helps to better suppress Fe dissolution and can better balance the strength and ductility of the negative electrode current collector, which is beneficial to improving the cycle life of the secondary battery.

[0024] Based on the transverse unit area of ​​the iron-containing alloy layer, the ratio of the areal density of Fe element in the first or second surface layer to the areal density in the central layer (R) is used. ρ12 Controlling the temperature within the aforementioned range helps to better suppress Fe dissolution and can better balance the strength and ductility of the negative electrode current collector, which is beneficial to improving the cycle life of the secondary battery.

[0025] By R H and R ρ Controlling one or both of these factors within the aforementioned range is also beneficial for improving the corrosion resistance of the negative electrode current collector, inhibiting rust formation, and improving the long-term storage performance of the secondary battery, but it is not limited to the aforementioned theories.

[0026] In some embodiments, the negative electrode current collector satisfies one or more of the following characteristics:

[0027] (c1) The difference in mass concentration of Fe element between the first surface layer and the second surface layer is 0-30%, optionally 0-20%, and further optionally 0-5%;

[0028] (c2) The thickness difference between the first surface layer and the second surface layer is 0 to 1 μm, and can be selected as 0 to 0.5 μm;

[0029] (c3) The thickness of the first surface layer and the second surface layer are each independently 0.1 μm to 2 μm, and can be selected as 0.1 μm to 1 μm; the thickness of the central layer is 2 μm to 6 μm, and can be selected as 2 μm to 4 μm;

[0030] (c4) The thickness percentage of the first surface layer relative to the iron-containing alloy layer and the thickness percentage of the second surface layer relative to the iron-containing alloy layer are each independently 1% to 35%, and optionally 4% to 25%;

[0031] (c5) The mass concentration of Fe in the first surface layer and the mass concentration of Fe in the second surface layer are each independently less than 40%, and can be greater than or equal to 20% and less than 40%, and can be further selected as 20% to 30%;

[0032] (c6) The mass concentration of Fe element in the central layer is greater than or equal to 30%, optionally 30% to 60%, and more preferably 35% to 60%;

[0033] (c7) The sum of the mass concentrations of Ni and Cr elements in the first surface layer and the sum of the mass concentrations of Ni and Cr elements in the second surface layer are each independently greater than or equal to 70%, and can be selected as 70% to 80%.

[0034] (c8) The sum of the mass concentrations of Ni and Cr elements in the central layer is less than or equal to 70%, and can be selected from 40% to 70%, or from 40% to 65%.

[0035] By the difference in mass concentration of Fe element in the first surface layer and the second surface layer (Δ C12 ) and the thickness difference (Δ) between the first surface layer and the second surface layer H12 Controlling one or both of these factors within the aforementioned range is beneficial for reducing the internal stress of the iron-containing alloy layer, reducing or avoiding curling and / or warping problems of the negative electrode current collector, and improving the processability of the negative electrode current collector.

[0036] By increasing the thickness of the first surface layer (H) 01 ), thickness of the second surface layer (H) 02 ) and the thickness of the central layer (H) C Controlling the temperature within the aforementioned range helps to better suppress Fe dissolution and can better balance the strength and ductility of the negative electrode current collector, which is beneficial to improving the cycle performance of the secondary battery.

[0037] By using the percentage of the thickness of the first surface layer relative to the iron-containing alloy layer (F) H1 ) and the percentage of the thickness of the second surface layer relative to the iron-containing alloy layer (F H2 Controlling the temperature within the aforementioned range helps to better suppress Fe dissolution and can better balance the strength and ductility of the negative electrode current collector, which is beneficial to improving the cycle performance of the secondary battery.

[0038] By adjusting the mass concentration of Fe element in the first surface layer (C F1 ) and the mass concentration of Fe element in the second surface layer (C F2 Controlling the temperature within the aforementioned range helps to better suppress Fe dissolution and can better balance the strength and ductility of the negative electrode current collector, which is beneficial to improving the cycle performance of the secondary battery.

[0039] By summing the mass concentrations of Ni and Cr elements in the first surface layer (C 21 The sum of the mass concentrations of Ni and Cr elements in the second surface layer (C) 22 Controlling the current collector within the aforementioned range helps to ensure both ductility and higher strength in the negative electrode current collector, which is beneficial for improving the cycle performance of the secondary battery.

[0040] By measuring the mass concentration of Fe in the central layer (C C By controlling one or both of the parameters, including the sum of the mass concentrations of Ni and Cr elements in the central layer, within the aforementioned range, the strength and ductility of the negative electrode current collector can be better balanced, which is beneficial to improving the cycle performance of the secondary battery.

[0041] In some embodiments, the concentration of Fe in the iron-containing alloy layer decreases from the center towards both sides along the longitudinal direction. This helps to better balance the strength, ductility, and corrosion resistance of the negative electrode current collector, and thus improves the cycle life of the secondary battery.

[0042] In some embodiments, the iron-containing alloy layer comprises multiple structural sublayers, wherein any two adjacent structural sublayers contain different concentrations of Fe; the iron-containing alloy layer comprises a central layer and a first surface layer and a second surface layer located on opposite sides of the iron-containing alloy layer.

[0043] The negative electrode current collector satisfies one or more of the following characteristics:

[0044] (d1) The number of structural sublayers in the iron-containing alloy layer is greater than or equal to 3, and in the longitudinal direction, the concentration of Fe element in the multiple structural sublayers decreases from the center to the two sides respectively.

[0045] (d2) The iron-containing alloy layer further includes a first intermediate layer and a second intermediate layer; wherein the first intermediate layer is located between the first surface layer and the central layer, and the second intermediate layer is located between the second surface layer and the central layer; the mass concentration of Fe element in the first intermediate layer and the second intermediate layer is denoted as C. M1 and C M2 C F1 <C M1 <C C And C F2 <C M2 <C C .

[0046] In some embodiments, the negative electrode current collector satisfies one or more of the following characteristics:

[0047] (d1') The number of structural sublayers in the iron-containing alloy layer is 2n+1, where n is an integer greater than or equal to 2. In the longitudinal direction, the concentration of Fe element in the multiple structural sublayers decreases from the center to both sides of the surface.

[0048] Optionally, each structural sublayer from the first surface layer to the second surface layer is denoted as layer 1, layer 2, layer 3, ..., layer 2n and layer 2n+1, respectively; wherein the mass concentration difference of Fe element in layer i and layer 2n+2-i is 0 to 20%, optionally 0 to 5%; wherein 1 ≤ i ≤ n;

[0049] (d2') The iron-containing alloy layer further includes a first intermediate layer and a second intermediate layer; the difference in mass concentration of Fe element in the first surface layer and the second surface layer is 0 to 20%, optionally 0 to 5%; the difference in mass concentration of Fe element in the first intermediate layer and the second intermediate layer is 0 to 20%, optionally 0 to 5%.

[0050] When the iron-containing alloy layer includes multiple structural sublayers (e.g., the number of structural sublayers is ≥3, or even 2n+1, n≥2), the concentration distribution gradient of Fe element in the longitudinal direction can be controlled. By controlling the concentration of Fe element in multiple structural sublayers to decrease from the center to both sides, it is beneficial to better balance the strength, ductility and corrosion resistance of the negative electrode current collector, and to better improve the cycle life of the secondary battery.

[0051] When the iron-containing alloy layer also includes a first intermediate layer and a second intermediate layer, by controlling C F1 <C M1 <C C And C F2 <C M2 <C C This is beneficial for better balancing the strength, ductility, and corrosion resistance of the negative electrode current collector, and for improving the cycle life of the secondary battery.

[0052] By controlling the difference in the mass concentration of Fe element between the i-th layer and the 2n+2-i-th layer (1≤i≤n) within the aforementioned range, it is beneficial to better eliminate the internal stress of the iron-containing alloy layer and better suppress the warping of the negative electrode current collector.

[0053] By controlling the difference in the mass concentration of Fe element between the first and second surface layers and between the first and second intermediate layers to be within the aforementioned range, it is beneficial to better eliminate the internal stress of the iron-containing alloy layer and better suppress the warping of the negative electrode current collector.

[0054] In some embodiments, the negative electrode current collector satisfies one or more of the following characteristics:

[0055] (e1) The thickness of the iron-containing alloy layer is 3μm to 8μm, and can be 4μm to 6μm;

[0056] (e2) The thickness of the conductive layer is 0.5 μm to 2 μm, and can be selected as 0.5 μm to 1.5 μm;

[0057] (e3) The thickness of the iron-containing alloy layer is 42% to 86% of the thickness of the negative electrode current collector, and can be 60% to 86%;

[0058] (e4) The negative electrode current collector further includes an isolation layer, which is located between the iron-containing alloy layer and the conductive layer; the isolation layer satisfies one or more of the following features (f1) and (f2): (f1) The isolation layer includes one or more of a nickel layer, a nickel alloy layer, a chromium layer and a chromium alloy layer; (f2) The thickness of the isolation layer is 0.1 μm to 1 μm.

[0059] In some embodiments, the negative electrode current collector satisfies one or more of the following characteristics:

[0060] (e1') The thickness of the iron-containing alloy layer is 4μm to 6μm;

[0061] (e2') The thickness of the conductive layer is 0.5 μm to 1.5 μm;

[0062] (e3') The thickness of the iron-containing alloy layer is 60% to 86% of the thickness of the negative electrode current collector.

[0063] By controlling one or both of the parameters, namely the thickness of the iron-containing alloy layer and the percentage of the thickness of the iron-containing alloy layer relative to the thickness of the negative electrode current collector, within the aforementioned range, it is beneficial to better utilize the iron-containing alloy layer to improve the mechanical properties of the negative electrode current collector, enhance corrosion resistance, suppress Fe dissolution, and better improve the cycle performance of the secondary battery.

[0064] By setting an isolation layer between the iron-containing alloy layer and the conductive layer, the protective effect of the isolation layer can better suppress Fe dissolution and improve the cycle performance of the secondary battery.

[0065] In some embodiments, the negative electrode active layer includes a negative electrode active material, which includes a silicon-based material;

[0066] Optionally, the negative electrode sheet satisfies one or more of the following characteristics:

[0067] (g1) The silicon-based material accounts for more than or equal to 10% of the mass of the negative electrode active material, and can be selected from 10% to 80%, or from 40% to 70%;

[0068] (g2) The silicon-based material includes one or more of elemental silicon, silicon-carbon composite materials, silicon-oxygen materials, silicon-nitrogen composite materials, and silicon alloys;

[0069] (g3) The negative electrode active material further includes a carbon-based material, wherein the mass ratio of the carbon-based material and the silicon-based material in the negative electrode active material is 90% to 100%;

[0070] (g4) The secondary battery is a lithium-ion secondary battery.

[0071] When the negative electrode active material includes silicon-based materials, the volume expansion of the negative electrode sheet during charging is large, resulting in large volume changes during charge-discharge cycles. In this case, by introducing an iron-containing alloy layer with the aforementioned structural design into the negative electrode current collector, the strength of the negative electrode current collector can be significantly improved, and the ductility and corrosion resistance can be well balanced, which can significantly improve the cycle life of the secondary battery.

[0072] In some embodiments, the secondary battery is a lithium-ion secondary battery.

[0073] According to some embodiments of the second aspect, a negative electrode sheet is provided, which is the negative electrode sheet in the secondary battery described in the first aspect of this application.

[0074] The aforementioned iron-containing alloy layer is introduced into the negative electrode current collector of this negative electrode sheet, which has high strength, good ductility, and good corrosion resistance. It can effectively suppress Fe dissolution, and the cycle performance of the secondary battery including this negative electrode sheet can be significantly improved.

[0075] According to some embodiments of the third aspect, a negative electrode current collector is provided, which is the negative electrode current collector in the secondary battery described in the first aspect of this application.

[0076] This negative electrode current collector has high strength and good ductility, as well as good corrosion resistance. It can effectively suppress Fe dissolution. By introducing a negative electrode sheet containing this negative electrode current collector into the secondary battery, the cycle performance of the secondary battery can be significantly improved.

[0077] According to some embodiments of the fourth aspect, a method for preparing a negative electrode sheet is provided, which includes the following steps:

[0078] A negative electrode current collector is prepared; wherein the negative electrode current collector includes an iron-containing alloy layer and a conductive layer located on at least one side of the iron-containing alloy layer; the iron-containing alloy layer is a structural layer including a reinforcing element and an Fe element, wherein the reinforcing element includes at least one of Ni and Cr; the conductive layer includes at least one of Cu and a metallic element M2, wherein the metallic element M2 is a conductive metallic element different from Cu and Fe; the thickness direction of the negative electrode current collector is denoted as the longitudinal direction; in the longitudinal direction, the concentration of Fe element on the surface of the iron-containing alloy layer is lower than the concentration of Fe element inside the iron-containing alloy layer;

[0079] A negative electrode active layer is provided on at least one side of the negative electrode current collector.

[0080] The negative electrode sheet prepared by the aforementioned method introduces an iron-containing alloy layer of reinforcing elements and Fe elements into the negative electrode current collector. The Fe element has a differential concentration distribution in the thickness direction of the negative electrode current collector, and the Fe concentration on the surface of the iron-containing alloy layer is lower than the Fe concentration inside. This gives the negative electrode current collector both high strength and good ductility, which can better resist the volume change of the negative electrode sheet, improve the structural stability of the negative electrode sheet, reduce the risk of breakage of the negative electrode current collector and the risk of battery capacity drop, and the negative electrode current collector also has good corrosion resistance, which can effectively inhibit Fe dissolution and significantly improve the cycle performance of the secondary battery including this negative electrode sheet.

[0081] In some embodiments, the negative electrode sheet of the secondary battery described in the first aspect of this application is prepared;

[0082] Optionally, the negative electrode current collector is prepared by a method comprising the following steps:

[0083] The iron-containing alloy layer is prepared by electroplating, such that the anode current density corresponding to the preparation of the surface layer of the iron-containing alloy layer is higher than the anode current density corresponding to the preparation of the internal structural layer of the iron-containing alloy layer.

[0084] The conductive layer is formed on at least one side of the iron-containing alloy layer by electroplating.

[0085] When preparing an iron-containing alloy layer by electroplating deposition, the concentration distribution of Fe in the iron-containing alloy layer is mainly controlled by diffusion, while the concentration distribution of reinforcing elements (such as Ni and / or Cr) in the iron-containing alloy layer is mainly controlled by electrochemical deposition. The higher the anode current density during electroplating deposition, the lower the Fe concentration at the corresponding layer thickness. By controlling the anode current density corresponding to the preparation of the surface layer to be higher than that corresponding to the preparation of the internal structural layer, the Fe concentration in the surface layer can be lower than that in the internal structural layer.

[0086] In some embodiments, the iron-containing alloy layer includes a central layer and a first surface layer and a second surface layer located on opposite sides of the iron-containing alloy layer, respectively.

[0087] The method for preparing the negative electrode sheet satisfies one or more of the following characteristics:

[0088] (h1) The iron-containing alloy layer includes multiple structural sublayers, and the concentration of Fe element in any two adjacent structural sublayers is different; in the longitudinal direction, the anode plate current density during the preparation of the multiple structural sublayers decreases from the central layer to the two side surface layers respectively;

[0089] (h2) First, the first surface layer is prepared by electroplating deposition, then the central layer is prepared by electroplating deposition, and then the second surface layer is prepared by electroplating deposition;

[0090] (h3) In the longitudinal direction, the anode plate current density during the fabrication of the plurality of structural sub-layers decreases and then increases from the first surface layer to the central layer and then to the second surface layer. It can be selected as a linear distribution or a curve distribution, and can be further selected as a normal distribution.

[0091] (h4) The equipment used to prepare the iron-containing alloy layer by electroplating includes a cathode roller and an anode combination plate arranged opposite to each other. The anode combination plate is composed of multiple anode sub-plates spliced ​​together in sequence, and the current density of each of the multiple anode sub-plates is controlled independently.

[0092] In some embodiments, the negative electrode sheet described in the second aspect of this application is prepared.

[0093] According to some embodiments of the fifth aspect, an electrical device is provided, comprising at least one of the secondary battery described in the first aspect of this application, the negative electrode sheet described in the second aspect of this application, the negative current collector described in the third aspect of this application, and the negative electrode sheet prepared by the method for preparing the negative electrode sheet described in the fourth aspect of this application.

[0094] Details of one or more embodiments or examples 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

[0095] To better describe and illustrate the embodiments, examples, or models 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, examples, or models, or the best mode of these applications as currently understood. Furthermore, the same reference numerals denote the same parts throughout the drawings. It should also be noted that the drawings are drawn in a simplified form and are only intended to facilitate and clarify the illustration of this application. The various dimensions of each part shown in the drawings are arbitrarily shown and may be precise or not drawn to scale. For example, the dimensions of parts are appropriately exaggerated in some places in the drawings to make the illustration clearer. Unless otherwise specified, the parts in the drawings are not drawn to scale. This application does not limit every dimension of every part.

[0096] In the attached diagram:

[0097] Figure 1 This is a schematic diagram of the structure of the iron alloy layer in one embodiment of this application.

[0098] Figure 2 This is a schematic diagram of the negative electrode current collector in one embodiment of this application.

[0099] Figure 3 This is a schematic diagram of the negative electrode sheet in one embodiment of this application.

[0100] Figure 4 This is a schematic diagram of the negative electrode sheet in one embodiment of this application.

[0101] Figure 5 This is a schematic diagram of a battery cell according to one embodiment of this application.

[0102] Figure 6 for Figure 5 An exploded view of a battery cell according to one embodiment of this application is shown.

[0103] Figure 7 This is a schematic diagram of a battery device according to one embodiment of this application.

[0104] Figure 8 This is a schematic diagram of a battery pack according to one embodiment of this application.

[0105] Figure 9 for Figure 8 An exploded view of a battery pack according to one embodiment of this application is shown.

[0106] 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.

[0107] Explanation of reference numerals in the attached figures:

[0108] 10, Negative electrode sheet; 110, Negative current collector; 130, Iron alloy layer; 111, Central layer; 129, First surface layer; 149, Second surface layer; 101, Reinforcing element; 102, Iron (Fe); 160, Conductive layer; 120, Negative active layer; 180, Separator layer; 1, Battery pack; 2, Upper casing; 3, Lower casing; 4, Battery assembly; 5, Battery cell; 51, Battery casing; 52, Electrode assembly; 53, Cover plate; 6, Electrical device. Detailed Implementation

[0109] The following describes in detail some embodiments and examples of the secondary battery, preparation method, and power-using device of this application with appropriate reference to the accompanying drawings. However, some unnecessary detailed descriptions may be omitted. For example, detailed descriptions of well-known matters and repetitive descriptions of actually identical structures may be omitted. This is to avoid making the following description unnecessarily lengthy and to facilitate understanding by those skilled in the art. Furthermore, the accompanying drawings and the following description are provided to enable those skilled in the art to fully understand this application and are not intended to limit the subject matter of the claims.

[0110] 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 included or excluded independently and can be combined arbitrarily; 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 ​​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" and "5" have been listed in this article; "0-5" is simply a shortened representation of these numerical combinations. Furthermore, when describing a parameter as an integer ≥ 2, it is equivalent to listing integers such as 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, and 12 for that parameter. For instance, when describing a parameter as an integer selected from "2-10", it is equivalent to listing the integers 2, 3, 4, 5, 6, 7, 8, 9, and 10.

[0111] In this application, the term "numerical value" includes the number itself and its reasonable approximations. The definition of "numerical value" can apply to discrete numerical points or to the endpoints of a numerical range. Unless otherwise specified, the term "approximation" covers a numerical interval based on a reasonable range of fluctuations of the number itself. This reasonable range of fluctuations can vary depending on the type and magnitude of the number. This reasonable range of fluctuations can be reasonably determined based on the accuracy of the testing or measurement method. Therefore, when referring to a numerical value or a numerical range, unless otherwise specified, it should be understood that the numerical value includes its reasonable approximation, and the numerical range includes reasonable approximations at both endpoints. Those skilled in the art will understand that acceptable fluctuation ranges of the relevant approximations can be included within the definition of the numerical value or the numerical range. In this application, unless otherwise specified, "N1" can be reasonably understood as "about N1," and "N1~N2" can be reasonably understood as "about N1 to about N2," where N1 and N2 are two unequal numerical values.

[0112] In this application, unless otherwise specified, "about" means within a reasonable range above and below the stated number, and the range of fluctuation may vary depending on the type and value of the stated number. For example, a range of ±10%, ±5%, ±2%, ±1%, etc., may be allowed. For example, taking "about 20°C" and its approximation as ±1°C, approximate values ​​such as 19°C, 19.5°C, etc., within the approximation range indicated by "about 20°C" should also be included in the range indicated by "about 20°C".

[0113] In this application, the terms "multiple," "various," "multiple items," "several," etc., unless otherwise specified, refer to a quantity greater than or equal to 2. For example, "one or more" means one or more (greater than or equal to) two. It can be understood that when "any number of" items are involved, it refers to any suitable combination of multiple items, that is, a combination of "any number of" items in a manner that does not conflict and enables the implementation of this application.

[0114] Unless otherwise specified, all embodiments and optional embodiments of this application can be combined to form new technical solutions.

[0115] 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.

[0116] Those skilled in the art will understand that, unless otherwise specified, the order in which the steps are written in the various embodiments or methods of this application 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 in this application can be performed sequentially or randomly, but are preferably performed sequentially. For example, "method M includes steps (a) and (b)" means that method M may include steps (a) and (b) performed sequentially, or it may include steps (b) and (a) performed sequentially. As another example, "method M may also include step (c)" means that step (c) can be added to method M in any order.

[0117] In this application, open-ended technical features or solutions described using terms such as "containing," "including," or "comprising" do not exclude additional members beyond those listed unless otherwise specified. They can be considered as providing both closed-ended features or solutions comprised of the listed members and open-ended features or solutions that include additional members beyond the listed members. For example, if A includes a1, a2, and a3, it may also include other members or exclude additional members unless otherwise specified. This can be considered as providing both features or solutions where "A consists of a1, a2, and a3" or "A is selected from a1, a2, and a3," and features or solutions where "A includes not only a1, a2, and a3, but also other members."

[0118] 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.

[0119] In this application, "optionally," "optionally," and "optional" mean that something is optional, that is, it is selected from either "with" or "without." If multiple "options" appear in a technical solution, unless otherwise specified and there are no contradictions or mutual constraints, each "option" is independent. Unless otherwise specified, the descriptions such as "optionally include" and "optionally contain" in this application, taking "optionally include" as an example, mean "may include or not include."

[0120] In this application, unless otherwise specified, the features or solutions corresponding to "and / or" include any one of two or more of the related listed items, as well as any and all combinations of the related listed items. These arbitrary and all combinations include any two related listed items, any more related listed items, or a combination of all related listed items. For example, "A and / or B" represents a group consisting of A, B, and "a combination of A and B". "Containing A and / or B" can mean "containing A, containing B, and containing A and B", or "containing A, containing B, or containing A and B", and can be appropriately understood according to the context.

[0121] The terms “combinations of,” “any combination of,” and “any combination of” used in this article include all suitable combinations of any two or more of the listed items.

[0122] In this document, the term "suitable" as used in "suitable combination", "suitable method", "any suitable method", etc., refers to the technical solution that enables the implementation of this application.

[0123] In this document, terms such as "preferred," "better," "more suitable," "ideal," "good," and "superior" are merely descriptions of more effective implementation methods or embodiments, and should be understood not to limit the scope of protection of this application. If multiple "preferred" terms appear in a technical solution, unless otherwise specified and there are no contradictions or mutual constraints, each "preferred" term shall be independent.

[0124] In this application, terms such as "further," "even more," "especially," "for example," "as," "example," and "exemplary" are used for descriptive purposes to indicate differences in content, but should not be construed as limiting the scope of protection of this application.

[0125] In this application, the terms "first aspect," "second aspect," "third aspect," "fourth aspect," etc., are used for descriptive purposes only and should not be construed as indicating or implying relative importance or quantity, nor should they be construed as implicitly indicating the importance or quantity of the indicated technical features. Moreover, "first," "second," "third," "fourth," etc., serve only as a non-exhaustive enumeration and should be understood not to constitute a closed limitation on quantity.

[0126] In this application, unless otherwise expressly specified and limited, terms such as "connected" and "joined" in relation to mechanical structures should be interpreted broadly, for example, they can refer to a fixed connection, a detachable connection, or an integral part. Those skilled in the art can understand the meaning of the above terms in this application according to the circumstances.

[0127] In the description of this application, it should be understood that the terms "length", "width", "thickness", "height", "upper", "lower", "vertical", "horizontal", "top", "bottom", "inner", "outer", etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings, and are only for the convenience of describing this application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of this application.

[0128] In this application, unless otherwise expressly specified and limited, the phrase "above" or "below" the second feature can mean that the first and second features are in direct contact, or that the first and second features are in indirect contact through an intermediate medium. In this application, unless otherwise expressly specified and limited, the phrase "above" or "below" the second feature can indicate a horizontal positional relationship, or it can simply indicate the existence of an attachment relationship without specifying a horizontal positional relationship.

[0129] In this application, the term "room temperature" generally refers to 4℃ to 35℃, and may refer to 20℃ ± 5℃. In some embodiments or examples of this application, room temperature refers to 20℃ to 30℃.

[0130] In this application, when a unit is specified for a data range, if it is only followed by the right endpoint, it indicates that the units for the left and right endpoints are the same. For example, 3~5μm or 3-5μm both mean that the units for the left endpoint "3" and the right endpoint "5" are both μm (micrometers), and have the same meaning as 3μm~5μm. Furthermore, similar descriptions of other parameters such as temperature and current density are interpreted in the same way.

[0131] In this application, "greater than or equal to", "greater than or equal to", and "≥" have the same meaning and can be used interchangeably; "less than or equal to", "less than or equal to", and "≤" have the same meaning and can be used interchangeably; "greater than" can be equivalently represented as ">", and "less than" can be equivalently represented as "<". In this application, unless otherwise specified, "greater than or equal to" and "≥" can be considered as providing two additional solutions: "greater than" and "equal to". In this application, unless otherwise specified, "less than or equal to" and "≤" can be considered as providing two additional solutions: "less than" and "equal to".

[0132] In this application, the exemplary descriptions such as "in some implementations (or embodiments)" and "in one implementation (or embodiment)" may cover, but are not limited to, the following meanings: these solutions can be combined with other solutions in a suitable manner to form new technical solutions.

[0133] Unless otherwise stated, the improvements described in this application are not intended to be limited to any theoretical constraints.

[0134] During the charge-discharge cycle of a secondary battery, the reversible insertion and extraction of active ions on the negative electrode causes repeated volume expansion and contraction changes. The negative electrode current collector needs to have sufficient strength to withstand the stress during these volume changes, preventing tearing and affecting battery life. For batteries experiencing significant volume changes during charge-discharge, the strength provided by traditional copper foil is limited, posing a risk of current collector breakage and capacity reduction, severely impacting battery cycle life. While using pure nickel or pure chromium layers significantly improves strength, their toughness and ductility are insufficient.

[0135] According to various embodiments and examples of this application, this application provides a secondary battery, a preparation method, and an electrical device, and further provides a secondary battery, a negative electrode sheet, a negative electrode current collector, a preparation method, and an electrical device. This secondary battery has improved cycle life.

[0136] The secondary battery includes a negative electrode sheet, which includes a negative current collector. The negative current collector includes an iron-containing alloy layer and a conductive layer located on at least one side of the iron-containing alloy layer. The iron-containing alloy layer is a structural layer including reinforcing elements and Fe elements. The thickness direction of the negative current collector is denoted as the longitudinal direction. In the longitudinal direction, the concentration of Fe elements on the surface of the iron-containing alloy layer is lower than the concentration of Fe elements inside the iron-containing alloy layer. The secondary battery has improved cycle life.

[0137] In some implementations, the reinforcing element includes at least one of Ni and Cr.

[0138] In some embodiments, the electric layer includes at least one of Cu and metal element M2, wherein the metal element M2 is a conductive metal element different from Cu and Fe.

[0139] In some embodiments, the secondary battery includes a positive electrode, a negative electrode, and an electrolyte, with a separator provided between the positive and negative electrodes.

[0140] Typically, a secondary battery includes 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 extracting. The electrolyte acts as a conductor between the positive and negative electrodes. A separator is placed between the positive and negative electrodes; its primary function is to prevent short circuits between the positive and negative electrodes while allowing ions to pass through. The active ions are not particularly limited and can include one or more of lithium ions, sodium ions, and potassium ions. Without limitation, the active ions can be lithium ions, in which case it corresponds to a lithium-ion secondary battery. The term "lithium-ion secondary battery" refers to a secondary battery in which the active ions include lithium ions.

[0141] In this application, unless otherwise specified, "electrode active material layer" includes at least one of the positive active material layer of the positive electrode sheet and the negative active material layer of the negative electrode sheet. Depending on the specific circumstances, the electrode active material layer may refer to either the positive active material layer or the negative active material layer. It is understood that the positive active material layer contains positive active material, and the negative active material layer contains negative active material. In this application, "electrode active material layer" may also be referred to as "active material layer," "positive active material layer" may also be referred to as "positive active layer," and "negative active material layer" may also be referred to as "negative active layer."

[0142] In this application, the terms "electrode sheet" and "electrode plate" have the same meaning and can be used interchangeably. An electrode sheet can be a positive electrode sheet or a negative electrode sheet, and the "active material" or "active substance" in the electrode sheet has the ability to reversibly insert and extract active ions.

[0143] In this application, the term "positive electrode sheet" includes a positive electrode active layer, and the positive electrode active layer includes a positive electrode active material. The term "positive electrode active material" refers to a material used in a positive electrode sheet that is capable of reversibly extracting and inserting active ions.

[0144] In this application, unless otherwise specified, "positive electrode sheet" includes a positive current collector. A "positive current collector" refers to a structure responsible for collecting and conducting electrons at the positive electrode. In the positive electrode sheet, the positive active layer is located on at least one side of the positive current collector, and may be located on one or both sides of the positive current collector.

[0145] In this application, the term "negative electrode sheet" includes a negative electrode active layer, which includes a negative electrode active material. The term "negative electrode active material" refers to a material used in a negative electrode sheet that is capable of reversibly inserting and de-inserting active ions.

[0146] In this application, unless otherwise specified, "negative electrode sheet" includes a negative electrode current collector. A "negative electrode current collector" refers to a structure responsible for collecting and conducting electrons at the negative electrode. In the negative electrode sheet, the negative electrode active layer is located on at least one side of the negative electrode current collector, and may be located on one or both sides of the negative electrode current collector.

[0147] In this application, unless otherwise specified, "separation membrane" and "diaphragm" have the same meaning and can be used interchangeably.

[0148] According to some embodiments of the first aspect, a secondary battery is provided, comprising a negative electrode sheet, the negative electrode sheet including a negative current collector, the negative current collector including an iron-containing alloy layer and a conductive layer located on at least one side of the iron-containing alloy layer. This secondary battery has improved cycle life.

[0149] In some embodiments, a secondary battery is provided, which includes a negative electrode sheet, the negative electrode sheet including a negative current collector and a negative active layer located on at least one side of the negative current collector;

[0150] The negative electrode current collector includes an iron-containing alloy layer and a conductive layer located on at least one side of the iron-containing alloy layer; the iron-containing alloy layer is a structural layer including a reinforcing element and an Fe element, wherein the reinforcing element includes at least one of Ni and Cr elements; the conductive layer includes at least one of Cu and a metallic element M2, wherein the metallic element M2 is a conductive metallic element different from Cu and Fe; the thickness direction of the negative electrode current collector is denoted as the longitudinal direction; in the longitudinal direction, the concentration of Fe element on the surface of the iron-containing alloy layer is lower than the concentration of Fe element inside the iron-containing alloy layer.

[0151] In this application, unless otherwise specified, "reinforcing element" refers to an element with higher strength relative to the strength of the conductive layer; unless otherwise specified, "reinforcing element" is a metallic element. Unless otherwise specified, the reinforcing element is a metallic element with higher strength than Cu and Fe. If a tensile test is performed on samples of the same size, and the tensile strength of a test sample of a "metallic element" is higher than that of Cu and Fe samples, then that metallic element can be considered to be within the scope of reinforcing elements. In some embodiments, the reinforcing element includes at least one of nickel (Ni) and chromium (Cr).

[0152] In this application, unless otherwise specified, the thickness direction of the negative electrode current collector is referred to as "longitudinal," and the direction perpendicular to the longitudinal direction is defined as "transverse." Typically, the thickness direction of the negative electrode current collector coincides with the thickness direction of the iron-containing alloy layer.

[0153] In this application, unless otherwise specified, "iron-containing alloy layer" refers to an alloy layer containing reinforcing elements and iron (Fe). The reinforcing elements in the iron-containing alloy layer can improve the strength of the negative electrode current collector, and the introduction of Fe serves to balance strength and toughness / ductility. For example, the toughness and ductility of the iron-containing alloy layer are significantly improved compared to materials such as pure nickel or pure chromium. In the "iron-containing alloy layer" used herein, the Fe element has a vertically varying concentration, with the Fe concentration on the surface of the iron-containing alloy layer being lower than that inside the iron-containing alloy layer.

[0154] In this application, unless otherwise specified, "conductive layer" refers to a structural layer capable of collecting and conducting electrons. It is understood that the conductive layer may include conductive metal elements known in the art as suitable for negative electrode current collectors. In some embodiments, the conductive layer includes at least one of copper (Cu) and metal element M2. Unless otherwise specified, "metal element M2" is a conductive metal element other than Cu and Fe. In some embodiments, metal element M2 includes a suitable rare metal element. In some embodiments, the metal element includes one or more of Ag, Ti, and Ni.

[0155] In this application, unless otherwise specified, the concentration of Fe element in the iron-containing alloy layer, at a certain location therein, or in a certain structural sublayer therein can be either mass concentration or mass-volume concentration; in some embodiments, it refers to mass concentration.

[0156] By introducing an iron-containing alloy layer, including reinforcing elements (at least one of Ni and Cr) and Fe, into the negative electrode current collector of the negative electrode sheet, and further controlling the distribution difference of Fe in the thickness direction (denoted as the longitudinal direction) of the negative electrode current collector, the concentration of Fe on the surface of the iron-containing alloy layer is lower than that inside the iron-containing alloy layer. This iron-containing alloy layer can balance strength and ductility. The high concentration of reinforcing elements on the surface is beneficial to providing higher strength, while the high concentration of Fe inside is beneficial to providing better ductility. This allows the negative electrode current collector to better resist volume changes of the negative electrode sheet, improve the structural stability of the negative electrode sheet, reduce the risk of breakage of the negative electrode current collector and the risk of battery capacity drop, and improve the cycle stability and cycle life of the secondary battery. Furthermore, by reducing the distribution concentration of Fe on the surface of the iron-containing alloy layer, the corrosion resistance of the iron-containing alloy layer can be improved, Fe dissolution can be inhibited, and the damage of potentially dissolved Fe ions to the negative electrode solid electrolyte interface (SEI) film can be reduced. Based on the aforementioned multiple effects, but not limited to the aforementioned theory, the secondary battery can be endowed with improved cycle life.

[0157] Unless otherwise specified in this application, the structure and chemical composition of the negative electrode current collector can be tested and analyzed using the following method: disassemble the battery cell, remove the negative electrode sheet, remove the negative electrode active layer, obtain the cross-section of the negative electrode current collector, and perform scanning electron microscopy (SEM) to observe the cross-sectional morphology. Exemplary SEMs include ZEISS Sigma 300, JEOL SEM, and Axia ChemiSEM. By performing SEM scanning on the cross-section of the negative electrode current collector and combining it with energy-dispersive spectroscopy (EDS) analysis, the thickness, element types, and content of each structural sublayer in the negative electrode current collector can be determined. Unless otherwise specified, the cross-section of the negative electrode current collector refers to the section along its thickness direction, i.e., the longitudinal section.

[0158] In some implementations, the secondary battery satisfies one or more of the following characteristics:

[0159] (a1) The mass concentration of Fe in the iron-containing alloy layer (which can be denoted as C) Fe It can be greater than or equal to 30%, and can be selected from 30% to 65%, or from 30% to 50%. It can also be any of the following percentages or a range composed of any two of the following percentages: 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, etc.

[0160] (a2) Mass concentration of reinforcing elements in iron-containing alloy layers (can be denoted as C) Q It can be greater than or equal to 35%, and can be selected from 35% to 70%, and further selected from 50% to 70%. It can also be any of the following percentages or a range selected from any two of the following percentages: 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, etc.

[0161] (a3) The mass percentage of Ni and Cr elements in the reinforcing elements (which can be denoted as F) 12 The percentage can be 95% to 100%, optionally 98% to 100%, or any of the following percentages or a range selected from any two of the following percentages: 95%, 96%, 97%, 98%, 99%, 100%, etc.; further optionally, the iron alloy layer is a nickel-iron binary alloy layer, a chromium-iron binary alloy layer, or a nickel-chromium-iron ternary alloy layer.

[0162] (a4) The conductive layer is a copper layer.

[0163] For composite alloy layers including reinforcing elements and Fe, when the mass concentration of Fe in the alloy layer is high, if the reinforcing elements and Fe are prepared as a single-layer composite alloy layer, poor corrosion resistance is likely to occur, leading to deterioration of cycle performance. When the iron content in the single-layer composite alloy layer is high, rust is also easily formed on the surface of the negative electrode current collector, deteriorating long-term storage performance. When using traditional methods, such as surface anti-oxidation treatment to improve the corrosion resistance of single-layer composite alloy layers, surface passivation has limited effect on improving corrosion resistance.

[0164] When the mass concentration of Fe element in the iron-containing alloy layer (which can be denoted as C) Fe When the content of iron is greater than or equal to 30% (or even 30% to 65%), by introducing an iron-containing alloy layer with the aforementioned structural design into the negative electrode current collector, the corrosion resistance of the iron-containing alloy layer and the negative electrode current collector can be significantly improved, the leaching of Fe can be significantly reduced, and the cycle life of the secondary battery can be significantly improved.

[0165] By controlling the mass concentration of reinforcing elements in the iron-containing alloy layer (which can be denoted as C), Q Within the aforementioned range, it is beneficial to improve the strength of the negative electrode current collector while taking into account both its strength and ductility.

[0166] When controlling C Fe and C Q Meanwhile, within the aforementioned range, by introducing an iron-containing alloy layer with the aforementioned structural design into the negative electrode current collector, the strength and ductility of the negative electrode current collector can be well balanced, Fe dissolution can be significantly reduced, and the cycle life of the secondary battery can be significantly improved.

[0167] When controlling the mass ratio of Ni and Cr elements in the reinforcing elements (which can be denoted as F), 12 Within the aforementioned range, the negative electrode current collector can achieve a good balance between strength and ductility.

[0168] In some embodiments, the iron-containing alloy layer is a nickel-iron binary alloy layer, a chromium-iron binary alloy layer, or a nickel-chromium-iron ternary alloy layer.

[0169] In some embodiments, the iron-containing alloy layer is a nickel-iron binary alloy layer. Ni has better ductility than Cr. Compared to a chromium-iron binary alloy layer, a nickel-iron binary alloy layer is more beneficial for improving the ductility of the negative electrode current collector.

[0170] In some embodiments, the iron-containing alloy layer is a chromium-iron binary alloy layer. Compared to Ni, Cr is more conducive to the formation of a denser oxide. Compared to nickel-iron binary alloy layers, chromium-iron binary alloy layers are more conducive to improving strength, corrosion resistance, and inhibiting Fe dissolution.

[0171] In this application, a "nickel-iron binary alloy layer" refers to an alloy layer primarily composed of nickel and iron, allowing for unavoidable impurities introduced during the preparation process. The sum of the mass concentrations of Ni and Fe in the nickel-iron binary alloy layer can be considered to be approximately 100%. A "chromium-iron binary alloy layer" refers to an alloy layer primarily composed of chromium and iron, allowing for unavoidable impurities introduced during the preparation process. The sum of the mass concentrations of Cr and Fe in the chromium-iron binary alloy layer can be considered to be approximately 100%. A "nickel-chromium-iron ternary alloy layer" refers to an alloy layer primarily composed of nickel, chromium, and iron, allowing for unavoidable impurities introduced during the preparation process. The sum of the mass concentrations of Ni, Cr, and Fe in the chromium-iron ternary alloy layer can be considered to be approximately 100%.

[0172] In some embodiments, the conductive layer includes one or more of Cu, Ag, Ti, and Ni elements.

[0173] In some implementations, the conductive layer is a copper layer.

[0174] In some implementations, the negative electrode current collector satisfies one or more of the following characteristics:

[0175] (t1) The iron alloy layer is a nickel-iron binary alloy layer, a chromium-iron binary alloy layer, or a nickel-chromium-iron ternary alloy layer;

[0176] (t2) The conductive layer is a copper layer.

[0177] When the iron-containing alloy layer is a nickel-iron binary alloy layer, a chromium-iron binary alloy layer, or a nickel-chromium-iron ternary alloy layer, the negative electrode current collector can better balance strength and ductility, thus improving the cycle life of the secondary battery.

[0178] In some embodiments, the iron-containing alloy layer 130 includes a central layer 111 and a first surface layer 129 and a second surface layer 149 located on opposite sides of the iron-containing alloy layer, as described in [reference]. Figure 1 Furthermore, the first surface layer 129, the second surface layer 149, and the central layer 111 each independently include reinforcing element 101 and iron element 102.

[0179] In some embodiments, the iron-containing alloy layer includes a central layer and a first surface layer and a second surface layer located on opposite sides of the iron-containing alloy layer, respectively.

[0180] The mass concentration of Fe in the first surface layer, the central layer, and the second surface layer is denoted as C. F1 C C and C F2 C F1 <C C And C F2<C C .

[0181] By controlling C F1 <C C And C F2 <C C It can effectively improve the corrosion resistance of iron-containing alloy layers, reduce Fe leaching, and improve the cycle life of secondary batteries.

[0182] In some embodiments, the thickness of the first surface layer and the second surface layer is less than the thickness of the central layer. In this case, the thickness ratio of the first surface layer to the central layer and the thickness ratio of the second surface layer to the central layer are both less than 1.

[0183] In some embodiments, the areal density of Fe in the first and second surface layers is less than that in the central layer. In this case, the ratio of the areal density of Fe in the first surface layer to that in the central layer, and the ratio of the areal density of Fe in the second surface layer to that in the central layer, are each independently less than 1 per unit area in the transverse direction of the iron-containing alloy layer.

[0184] In this application, "the areal density of Fe in a certain structural sublayer of an iron-containing alloy layer" refers to the ratio of the mass of Fe in that structural sublayer to the area of ​​that structural sublayer. This can be determined based on the SEM and EDS test results of the negative electrode current collector sample, according to the mass M of Fe in a structural sublayer of a certain area (e.g., S0). Fe Calculate the corresponding areal density = M Fe / S0.

[0185] In some implementations, the negative electrode current collector satisfies one or more of the following characteristics:

[0186] (b1) The thickness ratio of the first surface layer to the central layer (R) H1 ) and the thickness ratio of the second surface layer to the central layer (R H2 Each value is independently less than 1, and can be selected from 0.05 to 0.8, further selected from 0.05 to 0.5, or can be any of the following values ​​or a range selected from any two of the following values: 0.05, 0.06, 0.08, 0.1, 0.12, 0.14, 0.15, 0.16, 0.18, 0.2, 0.25, 0.3, 0.35, 0.4, 0.45, 0.5, 0.6, 0.65, 0.7, 0.75, 0.8, etc.;

[0187] (b2) The ratio of the areal density of Fe in the first surface layer to the areal density in the central layer, per unit area in the transverse direction of the iron-containing alloy layer (R ρ1) and the ratio of the areal density of Fe in the second surface layer to its areal density in the central layer (R ρ2 Each value is independently less than 1, and can be selected from 0.01 to 0.5, further selected from 0.02 to 0.3, or can be any of the following values ​​or a range composed of any two of the following values: 0.01, 0.02, 0.04, 0.05, 0.06, 0.08, 0.1, 0.12, 0.14, 0.15, 0.16, 0.18, 0.2, 0.25, 0.3, 0.35, 0.4, 0.45, 0.5, etc.; where horizontal is the direction perpendicular to vertical.

[0188] By comparing the thickness ratio (R) of either the first surface layer or the second surface layer with respect to the central layer H12 Controlling the temperature within the aforementioned range helps to better suppress Fe dissolution and can better balance the strength and ductility of the negative electrode current collector, which is beneficial to improving the cycle life of the secondary battery.

[0189] Based on the transverse unit area of ​​the iron-containing alloy layer, the ratio of the areal density of Fe element in the first or second surface layer to the areal density in the central layer (R) is used. ρ12 Controlling the temperature within the aforementioned range helps to better suppress Fe dissolution and can better balance the strength and ductility of the negative electrode current collector, which is beneficial to improving the cycle life of the secondary battery.

[0190] By R H and R ρ Controlling one or both of these factors within the aforementioned range is also beneficial for improving the corrosion resistance of the negative electrode current collector, inhibiting rust formation, and improving the long-term storage performance of the secondary battery, but it is not limited to the aforementioned theories.

[0191] Without limitation, the difference in mass concentration of Fe element between the first and second surface layers (which can be denoted as Δ) C12 The percentage can be 0-30%, optionally 0-25%, further optionally 0-20%, even further optionally 0-10%, even further optionally 0-5%, and can also be any of the following percentages or a range selected from any two of the following percentages: 0, 0.1%, 0.5%, 1%, 2%, 4%, 5%, 6%, 8%, 10%, 15%, 20%, 25%, 30%, etc.

[0192] Without limitation, the thickness difference between the first surface layer and the second surface layer (which can be denoted as Δ) H12The value can be 0–1 μm, optionally 0–0.5 μm, further optionally 0–0.25 μm, further optionally 0–0.2 μm, or any of the following values ​​or a range consisting of any two of the following values: 0 μm, 0.01 μm, 0.02 μm, 0.04 μm, 0.05 μm, 0.06 μm, 0.08 μm, 0.1 μm, 0.15 μm, 0.2 μm, 0.25 μm, 0.3 μm, 0.35 μm, 0.4 μm, 0.45 μm, 0.5 μm, etc.

[0193] By the difference in mass concentration of Fe element in the first surface layer and the second surface layer (Δ C12 ) and the thickness difference (Δ) between the first surface layer and the second surface layer H12 Controlling one or both of these factors within the aforementioned range is beneficial for reducing the internal stress of the iron-containing alloy layer, reducing or avoiding curling and / or warping problems of the negative electrode current collector, and improving the processability of the negative electrode current collector.

[0194] Coating curling and / or warping are external manifestations of unbalanced internal stress in the coating. Common methods to address internal stress in the coating include changing the plating solution additives or performing heat treatment. However, adjusting the type and amount of softener in the plating solution cannot solve the coating warping problem because the stress direction provided by the softener is consistent with the direction of coating warping; increasing the amount of softener actually increases the degree of coating warping. Taking nickel-iron binary alloy coatings as an example, heat treatment leads to segregation of the nickel-iron foil and sulfur embrittlement, significantly reducing the tensile strength and ductility of the coating and significantly increasing its brittleness.

[0195] Non-limitingly, the thickness of the first surface layer and the second surface layer can each be independently 0.1 μm to 2 μm, optionally 0.1 μm to 1 μm, further optionally 0.2 μm to 1 μm, and can also be any of the following values ​​or a range selected from any two of the following values: 0.1 μm, 0.15 μm, 0.2 μm, 0.25 μm, 0.3 μm, 0.35 μm, 0.4 μm, 0.45 μm, 0.5 μm, 0.6 μm, 0.7 μm, 0.8 μm, 0.9 μm, 1 μm, 1.2 μm, 1.4 μm, 1.5 μm, 1.6 μm, 1.8 μm, 2 μm, etc.

[0196] By increasing the thickness of the first surface layer (H) 01 ) and the thickness of the second surface layer (H) 02 Controlling the temperature within the aforementioned range is beneficial for better suppressing Fe dissolution and for better improving the cycle performance of the secondary battery.

[0197] Non-limitingly, the thickness of the core layer can be 2μm to 6μm, optionally 2μm to 4μm, or any of the following values ​​or a range selected from any two of the following values: 2μm, 2.2μm, 2.4μm, 2.5μm, 3μm, 3.2μm, 3.5μm, 4μm, 4.5μm, 5μm, 5.5μm, 5.6μm, 5.8μm, 6μm, etc.

[0198] By increasing the thickness of the central layer (H) C Controlling the strength and ductility of the negative electrode current collector within the aforementioned range is beneficial for better balancing the strength and ductility of the negative electrode current collector and for improving the cycle performance of the secondary battery.

[0199] In some embodiments, the thicknesses of the first and second surface layers are each independently 0.1 μm to 2 μm, and the thickness of the central layer is 2 μm to 6 μm. 01 H 02 and H C You may also refer to any suitable numerical value or range in the context. For example, the thickness of the first surface layer and the second surface layer are each independently 0.1 μm to 1 μm, and the thickness of the central layer is 2 μm to 4 μm.

[0200] By increasing the thickness of the first surface layer (H) 01 ), thickness of the second surface layer (H) 02 ) and the thickness of the central layer (H) C When both are controlled within the aforementioned range, it is beneficial to better suppress Fe dissolution and to better balance the strength and ductility of the negative electrode current collector, which is beneficial to better improve the cycle performance of the secondary battery.

[0201] Non-limiting, the percentage of the thickness of the first surface layer relative to the iron-containing alloy layer (which may be denoted as F) H1 ) and the percentage of the thickness of the second surface layer relative to the iron alloy layer (which can be denoted as F) H2 Each percentage can be independently 1% to 35%, optionally 3% to 30%, or even 4% to 25%. It can also be any of the following percentages or a range composed of any two of the following percentages: 1%, 2%, 3%, 4%, 5%, 6%, 8%, 10%, 12%, 14%, 15%, 16%, 18%, 20%, 25%, 30%, 35%, etc.

[0202] By using the percentage of the thickness of the first surface layer relative to the iron-containing alloy layer (F) H1 ) and the percentage of the thickness of the second surface layer relative to the iron-containing alloy layer (F H2 Controlling the temperature within the aforementioned range helps to better suppress Fe dissolution and can better balance the strength and ductility of the negative electrode current collector, which is beneficial to improving the cycle performance of the secondary battery.

[0203] Without limitation, the mass concentration of Fe element in the first surface layer (which can be denoted as C) F1 And the mass concentration of Fe in the second surface layer (which can be denoted as C) F2 Each percentage can be less than 40% (can be greater than or equal to 20% and less than 40%), or less than or equal to 30%, and can be selected from 20% to 30%. It can also be any of the following percentages or a range composed of any two of the following percentages: 20%, 21%, 22%, 23%, 24%, 25%, 26%, 27%, 28%, 29%, 30%, 34%, 35%, 37%, etc.

[0204] By adjusting the mass concentration of Fe element in the first surface layer (C F1 ) and the mass concentration of Fe element in the second surface layer (C F2 Controlling the temperature within the aforementioned range helps to better suppress Fe dissolution and can better balance the strength and ductility of the negative electrode current collector, which is beneficial to improving the cycle performance of the secondary battery.

[0205] In some implementations, the added element is Ni (corresponding to a nickel-iron binary alloy layer), C F1 and C F2 Each percentage can be less than or equal to 30%, can be selected from 20% to 30%, or can be any of the following percentages or a range composed of any two of the following percentages: 20%, 21%, 22%, 23%, 24%, 25%, 26%, 27%, 28%, 29%, 30%, etc.

[0206] In some implementations, the added element is Cr (corresponding to the ferrochrome binary alloy layer), C F1 and C F2 Each percentage can be less than 40% independently, and can be greater than or equal to 20% and less than 40%. It can also be any of the following percentages or a range consisting of any two of the following percentages: 20%, 21%, 22%, 23%, 24%, 25%, 26%, 27%, 28%, 29%, 30%, 34%, 35%, 37%, etc.

[0207] Without limitation, the mass concentration of Fe in the central layer (which can be denoted as C) C It can be greater than or equal to 30%, and can be selected from 30% to 60%, further selected from 35% to 60%, and can also be any of the following percentages or a range selected from any two of the following percentages: 30%, 35%, 40%, 45%, 50%, 55%, 60%, etc.

[0208] Non-limitingly, the sum of the mass concentrations of Ni and Cr elements in the central layer may be less than or equal to 70%, optionally 40% to 70%, further optionally 40% to 65%, and may also be any of the following percentages or a range selected from any two of the following percentages: 40%, 45%, 50%, 55%, 60%, 65%, 70%, etc.

[0209] By measuring the mass concentration of Fe in the central layer (C C By controlling one or both of the parameters, including the sum of the mass concentrations of Ni and Cr elements in the central layer, within the aforementioned range, the strength and ductility of the negative electrode current collector can be better balanced, which is beneficial to improving the cycle performance of the secondary battery.

[0210] Without limitation, the sum of the mass concentrations of Ni and Cr elements in the first surface layer (which can be denoted as C) 21 The sum of the mass concentrations of Ni and Cr elements in the second surface layer (which can be denoted as C) 22 Each percentage can be greater than or equal to 70%, and can be selected from 70% to 80%. It can also be any of the following percentages or a range composed of any two of the following percentages: 70%, 71%, 72%, 73%, 74%, 75%, 76%, 77%, 78%, 79%, 80%, etc.

[0211] By summing the mass concentrations of Ni and Cr elements in the first surface layer (C 21 The sum of the mass concentrations of Ni and Cr elements in the second surface layer (C) 22 Controlling the current collector within the aforementioned range helps to ensure both ductility and higher strength in the negative electrode current collector, which is beneficial for improving the cycle performance of the secondary battery.

[0212] In some implementations, the negative electrode current collector satisfies one or more of the following characteristics (any numerical parameter of the following characteristics may also be selected from any suitable value or range in the context):

[0213] (c1) The difference in mass concentration of Fe element between the first surface layer and the second surface layer is 0-30%, optionally 0-25%, further optionally 0-20%, even further optionally 0-10%, and even further optionally 0-5%;

[0214] (c2) The thickness difference between the first surface layer and the second surface layer is 0 to 1 μm, optionally 0 to 0.5 μm, and further optionally 0 to 0.25 μm;

[0215] (c3) The thickness of the first surface layer and the second surface layer are each independently 0.1 μm to 2 μm, and can be selected as 0.1 μm to 1 μm; the thickness of the central layer is 2 μm to 6 μm, and can be selected as 2 μm to 4 μm;

[0216] (c4) The thickness percentage of the first surface layer relative to the iron-containing alloy layer and the thickness percentage of the second surface layer relative to the iron-containing alloy layer are each independently 1% to 35%, optionally 3% to 30%, and even more preferably 4% to 25%;

[0217] (c5) The mass concentration of Fe in the first surface layer and the mass concentration of Fe in the second surface layer are each independently less than 40% (may be greater than or equal to 20% and less than 40%), and may also be less than or equal to 30%, and may further be 20% to 30%;

[0218] (c6) The mass concentration of Fe element in the central layer is greater than or equal to 30%, which can be selected as 30% to 60%, and further selected as 35% to 60%;

[0219] (c7) The sum of the mass concentrations of Ni and Cr elements in the first surface layer and the sum of the mass concentrations of Ni and Cr elements in the second surface layer are each independently greater than or equal to 70%, and can be selected as 70% to 80%.

[0220] (c8) The sum of the mass concentrations of Ni and Cr elements in the central layer is less than or equal to 70%, and can be selected as 40% to 70%, or more preferably 40% to 65%.

[0221] In some embodiments, the concentration of Fe in the iron-containing alloy layer decreases longitudinally from the center towards both sides. This helps to better balance the strength, ductility, and corrosion resistance of the negative electrode current collector, and thus improves the cycle life of the secondary battery.

[0222] In some embodiments, the iron-containing alloy layer comprises multiple structural sublayers. Furthermore, the difference between any two adjacent structural sublayers may be due to a difference in one or both parameters: Fe concentration and thickness.

[0223] In some embodiments, each structural sublayer of the iron-containing alloy layer independently includes reinforcing elements and iron.

[0224] In some embodiments, the iron-containing alloy layer includes multiple structural sublayers, and any two adjacent structural sublayers contain different concentrations of Fe element; further, the iron-containing alloy layer includes a central layer and a first surface layer and a second surface layer located on both sides of the iron-containing alloy layer, that is, the multiple structural sublayers include a first surface layer, a central layer and a second surface layer.

[0225] In some implementations, the negative electrode current collector satisfies one or more of the following characteristics:

[0226] (d1) The number of structural sublayers in the iron-containing alloy layer is greater than or equal to 3. In the vertical direction, the concentration of Fe element in multiple structural sublayers decreases from the center to both sides of the surface.

[0227] (d2) The iron-containing alloy layer further includes a first intermediate layer and a second intermediate layer; wherein, the first intermediate layer is located between the first surface layer and the central layer, and the second intermediate layer is located between the second surface layer and the central layer; the mass concentration of Fe element in the first intermediate layer and the second intermediate layer is denoted as C, respectively. M1 and C M2 C F1 <C M1 <C C And C F2 <C M2 <C C .

[0228] In some implementations, the negative electrode current collector satisfies one or more of the following characteristics:

[0229] (d1') The number of structural sublayers in the iron-containing alloy layer is 2n+1, where n is an integer greater than or equal to 2. In the vertical direction, the concentration of Fe element in multiple structural sublayers decreases from the center to both sides of the surface.

[0230] Optionally, each structural sublayer from the first surface layer to the second surface layer is denoted as layer 1, layer 2, layer 3, ..., layer 2n and layer 2n+1, respectively; wherein the difference in mass concentration of Fe element between layer i and layer 2n+2-i is 0 to 20%, optionally 0 to 10%, and further optionally 0 to 5%; wherein 1 ≤ i ≤ n;

[0231] (d2') The iron-containing alloy layer further includes a first intermediate layer and a second intermediate layer; the difference in mass concentration of Fe element between the first surface layer and the second surface layer is 0 to 20%, optionally 0 to 10%, and further optionally 0 to 5%; the difference in mass concentration of Fe element between the first intermediate layer and the second intermediate layer is 0 to 20%, optionally 0 to 10%, and further optionally 0 to 5%.

[0232] In some implementations, n is an integer selected from 2 to 10, which can be 2, 3, 4, 5, 6, 7, 8, 9, or 10, or it can be selected from any two of the aforementioned integers. In some implementations, n is 2.

[0233] Unless otherwise specified, i in the 2n+2-i level is an integer selected from 1 to n.

[0234] In some embodiments, the structural sublayers from the first surface layer to the second surface layer are respectively denoted as layer 1, layer 2, layer 3, ..., layer 2n and layer 2n+1; wherein the difference in mass concentration of Fe element in layer i and layer 2n+2-i is 0 to 20%, optionally 0 to 10%, further optionally 0 to 5%, and may also be any of the following percentages or a range selected from any two of the following percentages: 0, 1%, 2%, 3%, 4%, 5%, 6%, 8%, 10%, 12%, 14%, 15%, 16%, 18%, 20%, etc.; wherein 1≤i≤n.

[0235] In some embodiments, the mass concentration difference of Fe element in the first surface layer and the second surface layer is 0-30%, optionally 0-25%, further optionally 0-20%, even further optionally 0-10%, even further optionally 0-5%, and may also be any of the following percentages or a range selected from any two of the following percentages: 0, 1%, 2%, 3%, 4%, 5%, 6%, 8%, 10%, 12%, 14%, 15%, 16%, 18%, 20%, 25%, 30%, etc.; the mass concentration difference of Fe element in the first intermediate layer and the second intermediate layer is 0-20%, optionally 0-10%, further optionally 0-5%, and may also be any of the following percentages or a range selected from any two of the following percentages: 0, 1%, 2%, 3%, 4%, 5%, 6%, 8%, 10%, 12%, 14%, 15%, 16%, 18%, 20%, etc.

[0236] In some embodiments, the mass concentration difference of Fe element in the first surface layer and the second surface layer is 0-20%, optionally 0-10%, and more preferably 0-5%; the mass concentration difference of Fe element in the first intermediate layer and the second intermediate layer is 0-20%, optionally 0-10%, and more preferably 0-5%.

[0237] When the iron-containing alloy layer includes multiple structural sublayers (e.g., the number of structural sublayers is ≥3, or even 2n+1, n≥2), the concentration distribution gradient of Fe element in the longitudinal direction can be controlled. By controlling the concentration of Fe element in multiple structural sublayers to decrease from the center to both sides, it is beneficial to better balance the strength, ductility and corrosion resistance of the negative electrode current collector, and to better improve the cycle life of the secondary battery.

[0238] When the iron-containing alloy layer also includes a first intermediate layer and a second intermediate layer, by controlling C F1 <C M1 <C C And C F2 <C M2 <C CThis is beneficial for better balancing the strength, ductility, and corrosion resistance of the negative electrode current collector, and for improving the cycle life of the secondary battery.

[0239] By controlling the difference in the mass concentration of Fe element between the i-th layer and the 2n+2-i-th layer (1≤i≤n) within the aforementioned range, it is beneficial to better eliminate the internal stress of the iron-containing alloy layer and better suppress the warping of the negative electrode current collector.

[0240] By controlling the difference in the mass concentration of Fe element between the first and second surface layers and between the first and second intermediate layers to be within the aforementioned range, it is beneficial to better eliminate the internal stress of the iron-containing alloy layer and better suppress the warping of the negative electrode current collector.

[0241] In some implementations, the negative electrode current collector satisfies one or more of the following characteristics (any numerical parameter of the following characteristics may also be selected from any suitable value or range in the context):

[0242] (e1) The thickness of the iron alloy layer is 3μm to 8μm, and can be selected from 4μm to 6μm. It can also be any of the following values ​​or a range selected from any two of the following values: 3μm, 3.5μm, 4μm, 4.5μm, 5μm, 5.5μm, 6μm, 6.5μm, 7μm, 7.5μm, 8μm, etc.

[0243] (e2) The thickness of the conductive layer is 0.5μm to 2μm, and can be selected from 0.5μm to 1.5μm. It can also be any of the following values ​​or a range selected from any two of the following values: 0.5μm, 0.6μm, 0.7μm, 0.8μm, 0.9μm, 1μm, 1.2μm, 1.4μm, 1.5μm, 1.6μm, 1.8μm, 2μm, etc.

[0244] (e3) The thickness of the iron alloy layer relative to the thickness of the negative electrode current collector is 42% to 86%, optionally 50% to 86%, further optionally 60% to 86%, and may also be any of the following percentages or a range selected from any two of the following percentages: 42%, 43%, 44%, 45%, 46%, 48%, 50%, 52%, 54%, 55%, 56%, 58%, 60%, 65%, 70%, 75%, 80%, 82%, 84%, 85%, 86%, etc.

[0245] By controlling one or both of the parameters, namely the thickness of the iron-containing alloy layer and the percentage of the thickness of the iron-containing alloy layer relative to the thickness of the negative electrode current collector, within the aforementioned range, it is beneficial to better utilize the iron-containing alloy layer to improve the mechanical properties of the negative electrode current collector, enhance corrosion resistance, suppress Fe dissolution, and better improve the cycle performance of the secondary battery.

[0246] In some embodiments, the negative electrode current collector further includes an isolation layer located between the iron-containing alloy layer and the conductive layer.

[0247] Unless otherwise stated, the "isolation layer" in this application may be used to prevent Fe leaching.

[0248] In some embodiments, the insulating layer includes one or more of Ni and Cr elements. Non-limitingly, the sum of the mass concentrations of Ni and Cr elements in the insulating layer can be 95% to 100%, optionally 98% to 100%, or any of the following percentages or a range selected from any two of the following percentages: 95%, 96%, 97%, 98%, 99%, 100%, etc.

[0249] Without limitation, the isolation layer may satisfy one or more of the following characteristics (f1) and (f2):

[0250] (f1) The isolation layer includes one or more of the following: a nickel layer, a nickel alloy layer, a chromium layer, and a chromium alloy layer;

[0251] (f2) The thickness of the isolation layer is 0.1μm to 1μm, and may also be any of the following values ​​or a range selected from any two of the following values: 0.1μm, 0.15μm, 0.2μm, 0.25μm, 0.3μm, 0.35μm, 0.4μm, 0.45μm, 0.5μm, 0.6μm, 0.7μm, 0.8μm, 0.9μm, 1μm, etc.

[0252] By setting an isolation layer between the iron-containing alloy layer and the conductive layer, the protective effect of the isolation layer can better suppress Fe dissolution and improve the cycle performance of the secondary battery.

[0253] In some embodiments, the negative electrode active layer includes a negative electrode active material, which includes a silicon-based material. Non-limitingly, the silicon-based material may constitute 10% or more by mass in the negative electrode active material, optionally from 10% to 80%, further optionally from 40% to 70%, and may also be any of the following percentages or a range selected from any two of the following percentages: 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 60%, 65%, 70%, 75%, 80%, etc.

[0254] When the negative electrode active material includes silicon-based materials, the volume expansion of the negative electrode sheet during charging is large, resulting in large volume changes during charge-discharge cycles. In this case, by introducing an iron-containing alloy layer with the aforementioned structural design into the negative electrode current collector, the strength of the negative electrode current collector can be significantly improved, and the ductility and corrosion resistance can be well balanced, which can significantly improve the cycle life of the secondary battery.

[0255] Non-limitingly, silicon-based materials may include one or more of elemental silicon, silicon-carbon composites, silicon-oxygen materials, silicon-nitrogen composites, and silicon alloys. In some embodiments, the silicon-carbon composite includes a porous carbon matrix containing elemental silicon located within the pores of the porous carbon matrix; further, the elemental silicon within the pores of the porous carbon matrix is ​​nano-elemental silicon.

[0256] In some implementations, the negative electrode active material includes a carbon-based material.

[0257] In some embodiments, the negative electrode active material includes carbon-based materials and silicon-based materials. Carbon-based materials may include, but are not limited to, one or more of graphite, soft carbon, and hard carbon. Graphite materials may include one or more of artificial graphite and natural graphite.

[0258] Non-limitingly, the mass percentage of carbon-based materials and silicon-based materials in the negative electrode active material can be 90% to 100%, optionally 95% to 100%, or any of the following percentages or a range selected from any two of the following percentages: 90%, 91%, 92%, 94%, 95%, 96%, 97%, 98%, 99%, 100%, etc.

[0259] In some implementations, the negative electrode sheet satisfies one or more of the following characteristics (any numerical parameter of the following characteristics may also be selected from any suitable value or range in the context):

[0260] (g1) The mass percentage of silicon-based material in the negative electrode active material is greater than or equal to 10%, which can be selected as 10% to 80%, and further can be selected as 40% to 70%.

[0261] (g2) Silicon-based materials include one or more of elemental silicon, silicon-carbon composite materials, silicon-oxygen materials, silicon-nitrogen composite materials, and silicon alloys;

[0262] (g3) The negative electrode active material also includes carbon-based materials, and the mass ratio of carbon-based materials and silicon-based materials in the negative electrode active material is 90% to 100%;

[0263] (g4) The secondary battery is a lithium-ion secondary battery.

[0264] Those skilled in the art can identify the components in the negative electrode active layer using one or more of the following detection methods known in the art, including but not limited to: Fourier transform infrared (FT-IR) spectroscopy, ultraviolet spectroscopy, 1H nuclear magnetic resonance (1H NMR) spectroscopy, gel permeation chromatography (GPC), high performance liquid chromatography (HPLC), mass spectrometry, X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), Raman spectroscopy, single crystal X-ray diffraction (SCXRD), inductively coupled plasma optical emission spectrometry (ICP), energy dispersive spectroscopy (EDS), etc. The sample preparation and testing methods for these methods are known to those skilled in the art, and the test parameters can be appropriately adjusted according to the structure of the material or substance and the characteristics of the sample.

[0265] As a non-limiting example, EDS can be used to distinguish between carbon and silicon, and thus between carbon-based and silicon-based materials.

[0266] In some implementations, the secondary battery is a lithium-ion secondary battery.

[0267] The following is a description of the positive electrode sheet.

[0268] The positive electrode includes a positive current collector and a positive active layer disposed on at least one surface of the positive current collector, the positive active layer including a positive active material.

[0269] Without limitation, the weight percentage of the positive electrode active material in the positive electrode active layer may be greater than or equal to 80 wt%, further greater than or equal to 90 wt%, and even further greater than or equal to 92 wt%.

[0270] As a non-limiting example, the positive current collector has two surfaces that are opposite to 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.

[0271] In some embodiments, the positive electrode current collector may be a metal foil or a composite current collector. For example, aluminum foil may be used as the metal foil. In the positive electrode current collector, 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. In the positive electrode current collector, the composite current collector may 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 at least one of aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy. Non-limitingly, in the positive electrode current collector, the polymer material substrate may include one or more of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), and polyethylene (PE).

[0272] In some embodiments, the positive electrode active material may be a positive electrode active material known in the art for use in batteries.

[0273] In some embodiments, the positive electrode active material may be a positive electrode active material known in the art for use in lithium-ion secondary batteries.

[0274] In some embodiments, the positive electrode active material includes lithium-ion materials. "Lithium-ion materials" refers to positive electrode active materials capable of providing active lithium ions for lithium-ion secondary batteries.

[0275] Without limitation, the positive electrode active material may include one or more of lithium transition metal oxide positive electrode materials and lithium phosphate active materials.

[0276] In this application, unless otherwise specified, "lithium transition metal oxide cathode material" refers to a cathode active material containing lithium, transition metal elements, and oxygen. Therefore, lithium transition metal oxide cathode materials include non-lithium metal elements, and these non-lithium metal elements include transition metal elements. Non-limitingly, in lithium transition metal oxide cathode materials, the molar percentage of transition metal elements relative to non-lithium metal elements can be 90% to 100%, and can also be any of the following percentages or a range selected from any two of the following percentages: 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, 100%, etc.

[0277] In this application, unless otherwise specified, "non-lithium metal element" refers to a metal element that is not lithium (Li).

[0278] In some embodiments, lithium transition metal oxide cathode materials have a layered crystal structure.

[0279] In this application, unless otherwise specified, "lithium phosphate-containing cathode material" refers to a class of cathode active materials containing lithium iron phosphate components, and more specifically, includes lithium, transition metal elements, and phosphate ions (PO4). 3- The positive electrode active material is lithium phosphate. Unless otherwise specified, "lithium phosphate positive electrode material" may be olivine structure.

[0280] As a non-limiting example, the positive electrode active material may include one or more 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 positive electrode active materials for batteries may also be used. These positive electrode active materials may be used alone or in combination of two or more. Among them, examples of lithium transition metal oxides may include, but are not limited to, one or more of lithium cobalt oxide, lithium nickel oxide, lithium manganese oxide, lithium nickel cobalt oxide, lithium manganese cobalt oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, and their modified compounds. 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 manganese iron phosphate, and lithium manganese iron phosphate and carbon composites. Non-limiting examples of lithium cobalt oxides may include LiCoO2; non-limiting examples of lithium nickel oxides may include LiNiO2; non-limiting examples of lithium manganese oxides may include LiMnO2, LiMn2O4, etc.; non-limiting examples of lithium nickel cobalt manganese oxides may include LiNi 1 / 3Co 1 / 3 Mn 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 Examples of lithium nickel cobalt aluminum oxides include LiNi, etc. 0.80 Co 0.15 Al 0.05 O2. Examples of lithium iron phosphate include LiFePO4. Examples of lithium manganese phosphate include LiMnPO4.

[0281] In some embodiments, the positive electrode active material may be a positive electrode active material known in the art for sodium-ion secondary batteries.

[0282] In some embodiments, the positive electrode active material includes a sodium-ion material. "Sodium-ion material" refers to a positive electrode active material capable of providing active sodium ions for a sodium-ion secondary battery.

[0283] In a non-limiting manner, the positive electrode active material may include one or more of the following: sodium transition metal oxide positive electrode materials, polyanionic compounds, and Prussian blue compounds. However, this application is not limited to these materials, and other conventionally known materials or substances that can be used as positive electrode active materials in sodium-ion batteries may also be used.

[0284] Taking lithium-ion secondary batteries as an example, it is understandable that lithium (Li) will be intercalated and deintercalated and consumed during the charging and discharging process. The Li content in the positive electrode sheet will vary depending on the state of discharge. In the exemplary description of the positive electrode active material in this application, unless otherwise specified, the Li content can be the initial state of the material or a non-initial state after charge-discharge cycles. When the positive electrode active material is applied to the positive electrode in a battery system, the Li content in the positive electrode active material at the positive electrode will usually change after charge-discharge cycles. The Li content can be measured in atomic molar content, but is not limited to this. Regarding "Li content is the initial state of the material", the initial state of the material refers to the state before it is formed into the positive electrode active layer. It is understood that new materials or substances obtained by appropriately modifying the listed positive electrode active materials are also within the scope of positive electrode active materials. The aforementioned appropriate modification refers to an acceptable modification method for the positive electrode active material, and non-limiting examples include one or more of coating modification and doping modification.

[0285] In the exemplary description of the positive electrode active material in this application, the oxygen (O) content is only a theoretical value. Lattice oxygen release will cause changes in the atomic molar content of oxygen, and the actual O content will fluctuate. The O content can be measured in atomic molar content, but is not limited to this.

[0286] In some embodiments, the positive electrode active layer optionally includes 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. Typically, the binder may constitute 0–10 wt% of the weight of the positive electrode active layer, more commonly 0–8 wt%, and even more commonly 1 wt%–5 wt%, based on the total weight of the positive electrode active layer.

[0287] In some embodiments, the positive electrode active layer optionally includes 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. Typically, the weight percentage of the conductive agent in the positive electrode active layer can be 0–10 wt%, more commonly 0–8 wt%, and even more commonly 0–5 wt%, based on the total weight of the positive electrode active layer.

[0288] 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. Further, the positive electrode slurry is coated onto at least one surface of the positive current collector, and after drying, cold pressing, and other processes, the positive electrode sheet is obtained. Cold pressing can be performed using a cold rolling mill. The solvent in the positive electrode slurry can be, but is not limited to, any of the solvents described in the foregoing embodiments, for example, it can include N-methylpyrrolidone (NMP), and more specifically, NMP. The surface of the positive current collector coated with the positive electrode slurry can be a single surface of the positive current collector or both surfaces of the positive current collector. The solid content of the positive electrode slurry can be 40 wt% to 80 wt%. The viscosity of the positive electrode slurry at room temperature can be adjusted to 5000 mPa·s to 25000 mPa·s.

[0289] In some embodiments, the positive electrode active material includes a lithium composite metal oxide-based positive electrode material. Further, the mass percentage of the lithium composite metal oxide-based positive electrode material in the positive electrode active material can be greater than or equal to 50%, and more preferably 95% to 100%, but is not limited thereto. When coating the positive electrode slurry, the coating areal density (based on the coating areal density of one side) on a dry weight basis (excluding solvent) can be (0.05 to 0.6) g / 1540.25 mm². 2 The optional value is (0.1~0.3)g / 1540.25mm. 2 The compaction density of the positive electrode sheet can be 3.0 g / cm³. 3 ~4.2g / cm 3 3.3g / cm³ is an option. 3 ~3.8g / cm 3 .

[0290] In some embodiments, the positive electrode active material includes a lithium phosphate-based positive electrode material. Further, the mass percentage of the lithium phosphate-based positive electrode material in the positive electrode active material can be greater than or equal to 50%, and more specifically, can be 95% to 100%, but is not limited thereto. When coating the positive electrode slurry, the coating areal density (based on dry weight, minus solvent) (based on the coating areal density of one side) can also be (0.1 to 0.5) g / 1540.25 mm². 2However, this is not the only possibility. The compaction density of the positive electrode sheet can be 2.0 g / cm³. 3 ~2.8g / cm 3 2.3g / cm³ is an option. 3 ~2.6g / cm 3 .

[0291] The term "compacted density" as used in this application has a meaning known in the art and is one of the reference indicators for the energy density of materials. In this application, unless otherwise specified, the compacted density of the positive electrode refers to the ratio of the mass of the positive electrode active layer to its volume, and the compacted density of the negative electrode refers to the ratio of the mass of the negative electrode active layer to its volume.

[0292] The following is a description of the negative electrode plate.

[0293] The negative electrode sheet includes a negative current collector and a negative active layer disposed on at least one surface of the negative current collector, the negative active layer including a negative active material.

[0294] Without limitation, the weight percentage of the negative electrode active material in the negative electrode active layer may be greater than or equal to 80 wt%, and may further be greater than or equal to 90 wt%.

[0295] As a non-limiting example, the negative electrode current collector has two surfaces that are opposite to 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.

[0296] The structure and composition of the negative electrode current collector can be found in the context description of this application.

[0297] The types of negative electrode active materials in the negative electrode sheet can be found in the description in the context of this application. Without limitation, other types of negative electrode active materials may also be introduced into the negative electrode active material. These negative electrode active materials may be used alone or in combination of two or more.

[0298] In some embodiments, the negative electrode active layer optionally includes a binder. Non-limitingly, 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). Non-limitingly, the weight percentage of the binder in the negative electrode active layer may be 0 wt% to 20 wt%, more further 0 wt% to 10 wt%, even further 0 to 5 wt%, even further 1 wt% to 5 wt%, and even more preferably 1 wt% to 3 wt%.

[0299] In some embodiments, the negative electrode active layer optionally includes a conductive agent. Non-limitingly, 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. Non-limitingly, the weight percentage of the conductive agent in the negative electrode active layer may be 0 wt% to 15 wt%, more preferably 0 wt% to 10 wt%, and even more preferably 0 wt% to 5 wt%.

[0300] In some embodiments, the negative electrode active layer may optionally include other additives, such as thickeners (e.g., sodium carboxymethyl cellulose (CMC-Na)). Non-limitingly, the weight percentage of other additives in the negative electrode active layer may be 0 wt% to 15 wt%, more preferably 0 wt% to 10 wt%, even more preferably 0 wt% to 5 wt%, even more preferably 0 wt% to 3 wt%, and even more preferably 0 wt% to 2 wt%.

[0301] 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. Further, the negative electrode slurry is coated onto at least one surface of the negative electrode current collector, and after drying, cold pressing, and other processes, the negative electrode sheet is obtained. Cold pressing can be performed using a cold rolling mill. 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 30wt% to 70wt%, optionally 40wt% to 60wt%. The viscosity of the negative electrode slurry at room temperature can be adjusted to 2000 mPa·s to 10000 mPa·s, optionally 3000 mPa·s to 10000 mPa·s. When coating the negative electrode slurry, the coating surface density (excluding solvent) can be 75 g / m² on a dry weight basis. 2 ~220g / m 2 The optional value is (0.12~0.2)g / 1540.25mm. 2 Based on the surface density of the coating on one side, the compacted density of the negative electrode sheet can be 1.0 g / cm³. 3 ~2.0g / cm 3 1.0g / cm can be selected. 3 ~1.85g / cm 3 .

[0302] The electrolyte is described below as an example.

[0303] The electrolyte serves to conduct ions between the positive and negative electrodes. The electrolyte is a non-aqueous electrolyte. It includes electrolyte salts and non-aqueous solvents.

[0304] In some embodiments, the molar volume concentration of the electrolyte salt in the electrolyte is typically 0.5 mol / L to 5 mol / L, and may be 0.5 mol / L to 2 mol / L.

[0305] In some embodiments, the secondary battery is a lithium-ion secondary battery, and the electrolyte salt may include an electrolyte lithium salt.

[0306] In some embodiments, the electrolyte salt includes an electrolyte lithium salt, and may further be an electrolyte lithium salt.

[0307] Non-limitingly, the electrolyte lithium 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).

[0308] Non-limitingly, the non-aqueous solvent in the electrolyte may include one or more of carbonate solvents, carboxylic acid ester solvents, and sulfone solvents. Carbonate solvents may include one or more of cyclic carbonates and linear carbonates. Cyclic carbonates may include, but are not limited to, one or more of ethylene carbonate (EC), propylene carbonate (PC), butenyl carbonate (BC), and fluoroethylene carbonate (FEC). Linear carbonates may include, but are not limited to, one or more of ethyl methyl carbonate (EMC), diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), and ethyl propyl carbonate (EPC). Non-limitingly, the number of carbon atoms in the linear carbonate may be 3 to 9, optionally 3 to 7, and may also be 3, 4, 5, 6, 7, 8, or 9, or selected from any range of two of the aforementioned values. Carboxylic acid ester solvents may include one or more of linear carboxylic acid esters and cyclic carboxylic acid esters. Chain carboxylic acid esters may include, but are not limited to, one or more of methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, and ethyl butyrate. Non-limitingly, the number of carbon atoms in the chain carboxylic acid ester may be 2 to 8, optionally 3 to 8, or may be 2, 3, 4, 5, 6, 7, or 8, or selected from any range of two of the aforementioned numbers. Cyclic carboxylic acid esters may include, but are not limited to, 1,4-butyrolactone. Sulfone solvents may include, but are not limited to, one or more of sulfolane, dimethyl sulfone, methyl ethyl sulfone, and diethyl sulfone.

[0309] 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.

[0310] In some embodiments, the additives in the electrolyte may include, but are not limited to, one or more of fluoroethylene carbonate (FEC), 1,3-propanesulfonate lactone (PS), and succinic anhydride.

[0311] The following is an exemplary description of the separator membrane.

[0312] 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.

[0313] 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.

[0314] In some embodiments, the thickness of the separator can be 6μm to 40μm, and optionally 6μm to 20μm.

[0315] In some implementations, the positive electrode, negative electrode, and separator can be fabricated into an electrode assembly using a winding or stacking process.

[0316] 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.

[0317] 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-type soft pack. The material of the soft pack can be plastic; further, non-limiting examples of plastic may include one or more of polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0318] A secondary battery includes at least one battery cell. A secondary battery may include one or more battery cells.

[0319] In this application, unless otherwise specified, "cell battery" refers to the basic unit capable of converting chemical energy into electrical energy. Typically, a cell battery includes 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 extracting. The electrolyte acts as a conductor of ions between the positive and negative electrodes. The separator is positioned between the positive and negative electrodes; its primary function is to prevent short circuits between the positive and negative electrodes while allowing ions to pass through.

[0320] 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, Figure 5 The example shown is a square-structured battery cell 5.

[0321] In some of these implementations, reference is made to... Figure 6 The outer packaging may include a battery casing 51 and a cover plate 53. The battery casing 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 battery casing 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. Positive electrode sheets, negative electrode sheets, and a separator can be formed into electrode assemblies 52 through a winding process or a stacking process. The electrode assemblies 52 are encapsulated within the receiving cavity. The electrode assemblies 52 are immersed in an electrolyte. The number of electrode assemblies 52 contained in a single battery cell 5 can be one or more, which can be selected by those skilled in the art according to actual needs. In some embodiments, the electrolyte injection coefficient is greater than or equal to 1.6 g / Ah.

[0322] The secondary battery can be either battery device 4 or battery pack 1.

[0323] The battery device includes at least one battery cell. The number of battery cells in the battery device can be one or more, and those skilled in the art can select an appropriate number according to the application and capacity of the battery device.

[0324] Figure 7 This is battery device 4, used as an example. (See reference...) Figure 7 In the battery assembly 4, multiple battery cells 5 can be arranged sequentially along the length of the battery assembly 4. Of course, they can also be arranged in any other manner. Furthermore, the multiple battery cells 5 can be fixed in place using fasteners.

[0325] Optionally, the battery device 4 may also include a housing with a receiving space in which multiple battery cells 5 are received.

[0326] 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.

[0327] 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 devices 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 devices 4. The multiple battery devices 4 can be arranged in any manner within the battery box.

[0328] According to some embodiments of the second aspect, a negative electrode sheet is provided, which is the negative electrode sheet in the secondary battery described in the first aspect of this application.

[0329] The aforementioned iron-containing alloy layer is introduced into the negative electrode current collector of this negative electrode sheet, which has high strength, good ductility, and good corrosion resistance. It can effectively suppress Fe dissolution, and the cycle performance of the secondary battery including this negative electrode sheet can be significantly improved.

[0330] In some embodiments, the negative electrode sheet 10 includes a negative current collector 110 and a negative active layer 120 located on at least one side of the negative current collector 110. The negative current collector 110 includes an iron-containing alloy layer 120 and conductive layers 160 located on both sides of the iron-containing alloy layer 130; further, the iron-containing alloy layer 130 includes a central layer 111 and a first surface layer 129 and a second surface layer 149 located on both sides of the iron-containing alloy layer. In some embodiments, the negative active layer 120 is located on both sides of the negative current collector 110, as can be seen in the following references. Figure 3 .

[0331] In some embodiments, the negative electrode current collector 110 further includes an isolation layer 180 located between the iron alloy layer 130 and the conductive layer 160.

[0332] In some embodiments, an insulating layer 180 is provided between the first surface layer 129 and the conductive layer 160, and between the second surface layer 149 and the conductive layer 160. (See also...) Figure 4 .

[0333] According to some embodiments of the third aspect, a negative electrode current collector is provided, which is the negative electrode current collector in the secondary battery described in the first aspect of this application.

[0334] This negative electrode current collector has high strength and good ductility, as well as good corrosion resistance. It can effectively suppress Fe dissolution. By introducing a negative electrode sheet containing this negative electrode current collector into the secondary battery, the cycle performance of the secondary battery can be significantly improved.

[0335] The negative electrode current collector includes an iron-containing alloy layer and a conductive layer located on at least one side of the iron-containing alloy layer. The conductive layer may be located on one or both sides of the iron-containing alloy layer.

[0336] In some embodiments, the negative electrode current collector 110 includes an iron-containing alloy layer 120 and conductive layers 160 located on both sides of the iron-containing alloy layer 130; further, the iron-containing alloy layer 130 includes a central layer 111 and a first surface layer 129 and a second surface layer 149 located on both sides of the iron-containing alloy layer. Further, the first surface layer 129, the second surface layer 149, and the central layer 111 each independently include a reinforcing element 101 and an iron element 102. See also... Figure 2 .

[0337] In some embodiments, the negative electrode current collector 110 includes a central layer 111 and a first surface layer 129 and a second surface layer 149 located on both sides of the central layer. The negative electrode current collector 110 also includes conductive layers 160 located on both sides of the central layer 111. The first surface layer 129 and the second surface layer 149 are located between the conductive layers on both sides and the central layer, respectively.

[0338] According to some embodiments of the fourth aspect, a method for preparing a negative electrode sheet is provided, which can be used to prepare the negative electrode sheet described in the second aspect of this application.

[0339] In some embodiments, a method for preparing a negative electrode sheet is provided, which includes the following steps:

[0340] S100: Prepare a negative electrode current collector; wherein the negative electrode current collector includes an iron-containing alloy layer and a conductive layer located on at least one side of the iron-containing alloy layer; the definition of the iron-containing alloy layer can be found in the context of this application; exemplaryly, the iron-containing alloy layer is a structural layer including a reinforcing element and an Fe element, the reinforcing element including at least one of Ni and Cr elements; the conductive layer includes at least one of Cu and a metal element M2, the metal element M2 being a conductive metal element different from Cu and Fe; the thickness direction of the negative electrode current collector is denoted as the longitudinal direction; in the longitudinal direction, the concentration of Fe element on the surface of the iron-containing alloy layer is lower than the concentration of Fe element inside the iron-containing alloy layer;

[0341] S200: A negative electrode active layer is provided on at least one side of the negative electrode current collector.

[0342] The negative electrode sheet prepared by the aforementioned method introduces an iron-containing alloy layer of reinforcing elements and Fe elements into the negative electrode current collector. The Fe element has a differential concentration distribution in the thickness direction of the negative electrode current collector, and the Fe concentration on the surface of the iron-containing alloy layer is lower than the Fe concentration inside. This gives the negative electrode current collector both high strength and good ductility, which can better resist the volume change of the negative electrode sheet, improve the structural stability of the negative electrode sheet, reduce the risk of breakage of the negative electrode current collector and the risk of battery capacity drop, and the negative electrode current collector also has good corrosion resistance, which can effectively inhibit Fe dissolution and significantly improve the cycle performance of the secondary battery including this negative electrode sheet.

[0343] In some embodiments, the negative electrode current collector is prepared by a method comprising the following steps:

[0344] S110: The iron-containing alloy layer is prepared by electroplating, so that the anode current density corresponding to the preparation of the surface layer of the iron-containing alloy layer is higher than the anode current density corresponding to the preparation of the internal structural layer of the iron-containing alloy layer.

[0345] S120: A conductive layer is formed on at least one side of the iron alloy layer by electroplating.

[0346] When preparing an iron-containing alloy layer by electroplating deposition, the concentration distribution of Fe in the iron-containing alloy layer is mainly controlled by diffusion, while the concentration distribution of reinforcing elements (such as Ni and / or Cr) in the iron-containing alloy layer is mainly controlled by electrochemical deposition. The higher the anode current density during electroplating deposition, the lower the Fe concentration at the corresponding layer thickness. By controlling the anode current density corresponding to the preparation of the surface layer to be higher than that corresponding to the preparation of the internal structural layer, the Fe concentration in the surface layer can be lower than that in the internal structural layer.

[0347] Those skilled in the art can select appropriate electrolyte composition and electroplating conditions based on the elemental composition of the target iron-containing alloy layer. For example, the electroplating solution may consist of solvent water, a main salt, a conductive salt, a buffer, and additives. Additives may include one or more of complexing agents, antioxidants, primary brighteners, secondary brighteners, and wetting agents. The pH of the electroplating solution is 1.5–4, for example, pH 1.5, pH 2, pH 2.5, pH 3, pH 3.5, pH 4, etc., and may also be selected from any two of the aforementioned pH ranges. The main salt includes at least an iron source.

[0348] Taking the preparation of a nickel-iron binary alloy layer as an example, the main salt is composed of an iron source and a nickel source.

[0349] Taking the preparation of a chromium-iron binary alloy layer as an example, the main salt is composed of an iron source and a chromium source.

[0350] The iron source may be a water-soluble ferrous salt. Non-limiting examples of iron sources may include one or more of ferrous sulfate and its hydrates.

[0351] The nickel source may be a water-soluble nickel salt. Non-limiting examples of nickel sources may include one or more of nickel sulfate and its hydrates.

[0352] The chromium source may be a water-soluble chromium salt. Non-limiting examples of chromium sources may include one or more of chromium sulfate and its hydrate, chromium chloride and its hydrate.

[0353] In some implementations, the iron source is FeSO4·7H2O.

[0354] Non-limiting examples of conductive salts may include sodium chloride.

[0355] In a non-limiting sense, the buffer may include boric acid.

[0356] Non-limiting examples of complexing agents may include one or more of sodium citrate, citric acid, sodium gluconate, gluconic acid, glycine, etc. Appropriate types of complexing agents can be selected based on the type of reinforcing element and the differences in the composition of the electroplating solution.

[0357] Non-limiting examples of antioxidants may include one or more of catechol, hydroquinone, ascorbic acid, etc.

[0358] Non-limiting examples of a primary light-generating agent may include one or more of saccharin, sodium benzenesulfonate, sodium toluenesulfonate, sodium benzenesulfinate, diphenylsulfonylimide, etc.

[0359] Non-limiting examples of secondary brighteners may include one or more of 1,4-butynediol and its derivatives, pyridine derivatives, etc.

[0360] Non-limiting examples of wetting agents may include one or more of sodium dodecyl sulfate, sodium dodecylbenzene sulfonate, etc.

[0361] Taking the preparation of a nickel-iron binary alloy layer as an example, the electrodeposition process involves the deposition of iron (Fe) and nickel (Ni) elements. Fe deposition is mainly controlled by diffusion, while Ni deposition is mainly controlled by electrochemical reduction. The iron content in the coating can be affected by changing the iron content in the diffusion layer on the cathode surface. Methods for changing the iron content in the diffusion layer or coating include altering one or more parameters such as the main salt concentration, stirring rate, pH value, and current density. Generally, higher iron concentration in the main salt, more vigorous stirring, lower pH value, and lower current density result in a higher iron content in the coating. In the process of preparing nickel-iron foil using a foil-making machine, the current density can be adjusted by setting rectifier parameters to achieve differences in current density at different anode plate positions during the foil-making process. This results in a nickel-iron ratio deposited on the cathode roller at the corresponding anode plate position, leading to an inconsistent nickel-iron ratio along the foil thickness direction during foil production, and obtaining a nickel-iron foil (i.e., a nickel-iron binary alloy layer) with a gradient distribution of Fe content along the thickness direction.

[0362] In some implementations, during the preparation of the iron-containing alloy layer by electroplating, the surface diffusion layer can be affected by controlling the main salt concentration, current density, stirring, etc., thereby controlling the deposition ratio of reinforcing elements and iron elements in each structural sublayer.

[0363] In some implementations, the current density gradient distribution of the anode plates at different positions of the foil-making machine is mainly controlled to achieve a gradient distribution of Fe element content in the thickness direction (longitudinal direction) of the alloy layer.

[0364] Taking the preparation of a nickel-iron binary alloy layer as an example, in some embodiments, the anode plate current density during the preparation of the first surface layer and the second surface layer can be independently set to 20 A / dm². 2 ~30A / dm 2 .

[0365] Taking the preparation of a nickel-iron binary alloy layer as an example, in some embodiments, the current density during the preparation of the central layer can be 5 A / dm. 2 ~15A / dm 2 .

[0366] Taking the preparation of a nickel-iron binary alloy layer as an example, in some embodiments, the iron-containing alloy layer further includes a first intermediate layer and a second intermediate layer; wherein, the first intermediate layer is located between the first surface layer and the central layer, and the second intermediate layer is located between the second surface layer and the central layer; the anode plate current density during the preparation of the first surface layer and the second surface layer can each be independently 20 A / dm². 2 ~30A / dm 2 The anode current density during the fabrication of the first and second intermediate layers can each be independently 15 A / dm². 2 ~20A / dm 2 .

[0367] The current density of the anode plate can be controlled using a rectifier.

[0368] In some embodiments, the iron-containing alloy layer includes a central layer and a first surface layer and a second surface layer located on opposite sides of the iron-containing alloy layer, respectively.

[0369] The preparation method of the negative electrode sheet satisfies one or more of the following characteristics:

[0370] (h1) The iron-containing alloy layer includes multiple structural sublayers, and the concentration of Fe element in any two adjacent structural sublayers is different; in the longitudinal direction, the anode plate current density decreases from the central layer to the two surface layers when multiple structural sublayers are prepared.

[0371] (h2) First, the first surface layer is prepared by electroplating deposition, then the central layer is prepared by electroplating deposition, and then the second surface layer is prepared by electroplating deposition.

[0372] (h3) In the vertical direction, the current density of the anode plate when preparing multiple structural sublayers decreases and then increases from the first surface layer to the center layer and then to the second surface layer. It can be selected as a linear distribution or a curve distribution, and can be further selected as a normal distribution.

[0373] (h4) The equipment used to prepare the iron-containing alloy layer by electroplating includes a cathode roller and an anode combination plate arranged opposite each other. The anode combination plate is composed of multiple anode sub-plates spliced ​​together in sequence, and the current density of each anode sub-plate is controlled independently.

[0374] In some embodiments, the negative electrode sheet described in the second aspect of this application is prepared.

[0375] In another aspect of this application, a method for preparing a secondary battery is provided.

[0376] In some embodiments, a method for preparing a secondary battery is provided, comprising the following steps: placing an electrode assembly including a positive electrode, a separator, and a negative electrode in a battery casing; injecting an electrolyte into the battery casing; allowing the electrolyte to wet the electrode assembly and form, thereby preparing a secondary battery. In the electrode assembly, a separator is disposed between the positive and negative electrode.

[0377] According to some embodiments of the fifth aspect, an electrical device is provided, comprising at least one of the secondary battery described in the first aspect of this application, the negative electrode sheet described in the second aspect of this application, the negative current collector described in the third aspect of this application, and the negative electrode sheet prepared by the method for preparing the negative electrode sheet described in the fourth aspect of this application.

[0378] Electrical devices that include the aforementioned secondary batteries can have the advantages of the aforementioned secondary batteries.

[0379] In some embodiments, the electrical device includes a secondary battery of any of the embodiments provided in this application.

[0380] Secondary batteries can be used as a power source for electrical devices or as energy storage units within electrical devices. Electrical devices can include, but are not limited to, mobile devices, electric vehicles, electric trains, ships and satellites, energy storage systems, etc. Mobile devices can include, for example, mobile phones and laptops; electric vehicles can include, for example, pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, electric motorcycles, power tools, etc., but are not limited to these. This electrical device can also be applied in aerospace and other fields, and can also be used in energy storage power systems such as hydroelectric, thermal, wind, and solar power plants.

[0381] As an electrical device, a rechargeable battery can be selected based on its usage requirements.

[0382] Figure 10 Here is 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 device or battery pack can be used.

[0383] Another example device could be a mobile phone, tablet, or laptop. These devices typically require a slim and lightweight design and can use a rechargeable battery as their power source.

[0384] The following describes some embodiments of this application. The described embodiments are only a part of the embodiments of this application, and not all of them. The embodiments described below are exemplary and are only used to explain this application, and should not be construed as limiting this application and 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.

[0385] Unless otherwise specified in the examples, the procedures described above, or those described in the literature in this field, or those described in the product instructions, shall be followed. Reagents or instruments whose manufacturers are not specified are all commercially available conventional products, or products that can be synthesized using conventional methods from commercially available products.

[0386] In the following examples, room temperature refers to 20°C to 30°C.

[0387] The following examples are non-limiting examples of using lithium-ion secondary batteries as secondary batteries.

[0388] I. Preparation of negative electrode current collector, negative electrode sheet and lithium-ion secondary battery.

[0389] In the following examples, the electroplating equipment includes columnar cathode rollers and curved anode combination plates arranged opposite each other. The curved anode combination plate is composed of multiple curved anode sub-plates spliced ​​together. The number of anode sub-plates in the curved anode combination plate is consistent with the number of structural sub-layers in the iron alloy layer. The electroplating deposition thickness at different positions of the alloy layer and the element ratio of different metal elements in the coating are mainly controlled by adjusting the current density of each anode sub-plate.

[0390] In the following examples, unless otherwise specified, the electroplating temperature for preparing the nickel-iron binary alloy layer is 45℃~65℃, and the electroplating temperature for preparing the chromium-iron binary alloy layer is room temperature.

[0391] In the following examples, the same acidic electroplating solution was used to prepare the nickel-iron binary alloy layer. The composition of the electroplating solution used to prepare the nickel-iron binary alloy layer was: FeSO4·7H2O (60g / L), NiSO4·6H2O (180g / L), sodium chloride (30g / L), buffer boric acid, and additives. The additives used included complexing agents, antioxidants, primary brighteners, secondary brighteners, and wetting agents. Boric acid was used to control the pH in the range of 1.5 to 4.

[0392] The electroplating solution used to prepare the ferrochrome binary alloy layer consisted of: chromium chloride (160 g / L), ferrous chloride (20 g / L), potassium bromide (20 g / L), ammonium chloride (20 g / L), buffer boric acid, and additives, including complexing agent glycine and antioxidant ascorbic acid. The pH was controlled within the range of 1.5 to 3.0, and the pH in Example 8 was 2.

[0393] Those skilled in the art can also use other electroplating solutions, as long as they can combine the control of parameters such as current density to obtain the Fe concentration and thickness control of each structural sublayer of the iron-containing alloy layer shown in Table 1-2, and can also achieve the same or similar technical effects as those in Table 1-2.

[0394] Example 1.

[0395] 1. Preparation of negative electrode current collector.

[0396] (1) Preparation of iron-containing alloy layers, taking nickel-iron binary alloy layers as an example.

[0397] Electroplating parameters: Electroplating temperature is 55℃, with a total of 3 anode sub-plates from the unwinding side (corresponding to the first surface layer) to the winding side (corresponding to the second surface layer), and current densities of 20A / dm². 2 10A / dm 2 20A / dm 2 The arc length ratio of each anode plate is 1:6:1, and they are used sequentially to form the first surface layer, the central layer, and the second surface layer. Current density is measured in amperes per square decimeter (A / dm²). 2 ).

[0398] In this example, the iron-containing alloy layer formed is a nickel-iron binary alloy layer, which consists of a first surface layer (thickness of 0.8 μm, Fe content of 29%), a central layer (thickness of 2.4 μm, Fe content of 41%), and a second surface layer (thickness of 0.8 μm, Fe content of 29%).

[0399] (2) Set the copper layer.

[0400] The electroplating temperature was 25℃, using a commercially available copper foil plating solution (JRM copper plating solution), with a pH value less than 1 and a current density of 5A / dm³. 2 .

[0401] A copper layer with a thickness of 1 μm is formed on both sides of the iron-containing alloy layer to prepare a negative electrode current collector.

[0402] In this example, the structure and preparation parameters of the negative electrode current collector can also be found in Table 1.

[0403] 2. Preparation of secondary batteries

[0404] (1) Preparation of positive electrode sheet

[0405] LiNi, the positive electrode active material 0.8 Co 0.1 Mn 0.1 O2 (NCM811), conductive agent acetylene black, and binder polyvinylidene fluoride (PVDF) were dissolved in N-methylpyrrolidone (NMP) at a weight ratio of 90:5:5 and thoroughly mixed to obtain a positive electrode slurry. The positive electrode slurry was then uniformly coated onto both sides of the positive electrode current collector, followed by drying, cold pressing, and slitting to obtain the positive electrode sheet. During the coating process, the surface area density of the coating on one side of the positive electrode current collector, based on dry weight (excluding solvent), was 0.3 g / 1540.25 mm². 2 The compaction density of the positive electrode sheet is 3.5 g / cm³. 3 .

[0406] (2) Preparation of negative electrode sheet

[0407] A negative electrode slurry was prepared by dissolving silicon-carbon composite material (negative electrode active material), graphite, acetylene black (conductive agent), styrene-butadiene rubber (SBR) (binder), and sodium carboxymethyl cellulose (CMC-Na) (thickener) in deionized water at a weight ratio of 48:40:2:8:2. The slurry was then uniformly mixed and coated onto both sides of the prepared negative electrode current collector. After drying, a negative electrode film was obtained, which was then cold-pressed and slit to obtain the negative electrode sheet. When coating the negative electrode slurry, the areal density per unit area on one side of the negative electrode current collector (dry weight, after deducting solvent) was 0.09 g / 1540.25 mm². 2The compaction density of the negative electrode sheet is 1.4 g / cm³. 3 .

[0408] In this example, the mass ratio of silicon to carbon in the silicon-carbon composite material is 1:1.

[0409] (3) Preparation of electrolyte

[0410] In an argon-atmospheric glove box (H2O < 0.1 ppm, O2 < 0.1 ppm), fluoroethylene carbonate (FEC), ethylene carbonate (EC), and ethyl methyl carbonate (EMC) were mixed uniformly at a mass ratio of 1:2:7. 12.5 wt% of lithium LiPF6 salt was added and stirred until dissolved. Then, 1,3-propanesulfonate lactone and succinic anhydride were added as additives, and the mixture was stirred until homogeneous to obtain the electrolyte. The additive concentrations in the electrolyte were: 0.5 wt% 1,3-propanesulfonate lactone and 0.5 wt% succinic anhydride.

[0411] (4) Separating membrane

[0412] Polypropylene film is used as the separator.

[0413] (5) Assemble and prepare lithium-ion secondary batteries

[0414] The positive electrode, separator, and negative electrode are stacked in sequence, with the separator positioned between the positive and negative electrodes to provide isolation. The electrodes are then wound to obtain the electrode assembly. The electrode assembly is placed in the battery casing, dried, and then injected with electrolyte. After formation and settling processes, a lithium-ion battery is obtained.

[0415] Examples 2-7. The negative electrode current collector, negative electrode sheet and secondary battery were prepared using the same method as in Example 1. The difference is that the negative electrode current collector is different. The negative electrode current collector with the structure and elemental composition shown in Table 1 was prepared by adjusting the current density of each anode subplate.

[0416] In Examples 2-6, a total of 5 anode sub-plates are used from the unwinding side (corresponding to the first surface layer) to the winding layer (corresponding to the second surface layer) to form the first surface layer, the first intermediate layer, the center layer, the second intermediate layer, and the second surface layer in sequence.

[0417] In Example 7, three anode sub-plates are used sequentially from the unwinding side (corresponding to the first surface layer) to the winding layer (corresponding to the second surface layer) to form the first surface layer, the central layer, and the second surface layer.

[0418] Comparative Example 1. Copper foil was used.

[0419] The negative electrode current collector, negative electrode sheet and secondary battery were prepared using the same method as in Example 1, except that a copper foil with a thickness of 6 μm was used as the negative electrode current collector.

[0420] Comparative Example 2. A single-layer nickel-iron alloy layer.

[0421] The negative electrode current collector, negative electrode sheet and secondary battery were prepared using the same method as in Example 1, except that a single anode plate was used instead of the curved anode combination plate to prepare a single-layer nickel-iron alloy layer.

[0422] The structure and preparation parameters of the negative electrode current collector in Examples 1-7 and Comparative Examples 1-2 can also be found in Table 1.

[0423] Example 8. A chromium-iron binary alloy layer is used.

[0424] The negative electrode current collector, negative electrode sheet and secondary battery were prepared using the same method as in Example 1, except that a chromium-iron binary alloy layer was used instead of a nickel-iron binary alloy layer.

[0425] Electroplating method: The electroplating temperature is room temperature; a total of 3 anode sub-plates are used to form the first surface layer, the central layer and the second surface layer from the unwinding side (corresponding to the first surface layer) to the winding side (corresponding to the second surface layer).

[0426] The structure and preparation parameters of the negative electrode current collector in Example 8 can also be found in Table 2.

[0427] II. Testing and Analysis Methods

[0428] (I) Iron-containing alloy layer and negative electrode current collector

[0429] 1. Detection of the thickness and elemental composition of each structural sublayer in the iron-containing alloy layer.

[0430] Instrument: Sigma 300 scanning electron microscope from ZEISS GmbH, Germany.

[0431] Thickness of each structural sublayer: The thickness of each substructure layer was determined by testing the longitudinal section SEM and using line scanning.

[0432] Elemental composition: Based on the longitudinal section EDS results, the types and proportions of each metallic element in each structural layer are determined, as well as the total mass and mass concentration of each element in each structural sublayer. Combined with thickness test results, the areal density of Fe and reinforcing elements in each structural sublayer is calculated or compared. See also the method description above.

[0433] 2. Mechanical properties

[0434] Sample to be tested: Negative electrode current collector.

[0435] The tensile strength of the sample under test at room temperature can be obtained by testing the tensile fracture curve of the sample under test.

[0436] Detailed testing methods can be found in GB / T5230-1995 "Electrolytic Copper Foil" standard. As an example, at least four test specimens with a length of 200±0.5 mm, a width of 15±0.25 mm, and a gauge length of 50±5 mm should be cut. The specimens should be continuously loaded at a tensile speed of 50±0.5 mm / min at room temperature until fracture. The tensile strength of the specimen is calculated by dividing the tensile stress at fracture by the tensile cross-sectional area, expressed in MPa. At least four specimens should be tested, and the average value should be taken as the tensile strength of the test specimen. The elongation at fracture is calculated as: Elongation at fracture = L2 / L0 × 100%, where L0 is the initial length and L2 is the length at fracture.

[0437] Higher tensile strength indicates higher strength; higher elongation at break indicates better ductility.

[0438] 3. Fe leaching resistance test

[0439] Sample to be tested: a sheet with an area of ​​30mm × 100mm.

[0440] Test method: Dry in a vacuum oven at 80°C for 1 hour. Take 20g of electrolyte (with the same composition as the electrolyte in Example 1), seal it with aluminum-plastic film, and store it at 25°C and 60°C for 30 days respectively. Then, test the Fe content in the electrolyte by inductively coupled plasma atomic absorption spectrometry (ICP). The unit is ppm (mass content), which means parts per million.

[0441] The test results can be found in Table 1-2.

[0442] 4. Warpage Height Test

[0443] Test method: Place a foil of approximately 500mm in length flat on a glass plate. Measure the warping height of the copper foil edge with a steel ruler perpendicular to the plate at a 90° angle. The test results can be found in Table 3.

[0444] (II) Battery Performance Testing

[0445] Cycling performance: Capacity retention rate after capacity decay to 500 cycles at 25°C.

[0446] At 25℃, the battery under test was charged to 3.65V at a constant current of 1C, then charged to a cutoff current of 0.05C at a constant voltage of 3.65V, left to rest for 10 minutes, and then discharged to 2.5V at a constant current of 1C, left to rest for 5 minutes. This constitutes one charge-discharge cycle. The discharge capacity at this point is recorded as C0. This charge-discharge cycle is repeated for the same battery, and the discharge capacity C of the first, second, ..., nth cycle is recorded. n The number of cycles must be at least 500.

[0447] Record the battery's cycle capacity retention rate P500 = C after 500 cycles. 500 / C0×100%. Test results can be found in Table 1-2, "Capacity Retention Rate after 500 Cycles at 25℃". A higher test value indicates a longer cycle life.

[0448] III. Test Results and Analysis

[0449] The test results for each embodiment and comparative example can be found in Tables 1-3.

[0450] The negative electrode current collectors of Examples 1-8 of this application all incorporate an iron-containing alloy layer, achieving a balance between strength and ductility. Compared to the copper foil negative electrode current collector (Comparative Example 1), Examples 1-8 exhibit significantly improved tensile strength, higher elongation at break, and lower Fe dissolution. The cycle life of Examples 1-8 is also significantly extended compared to Comparative Example 1. Exemplarily, the iron-containing alloy layer in Examples 1-7 is a nickel-iron binary alloy layer, and in Example 8, a chromium-iron binary alloy layer is used.

[0451] Compared to the single-layer nickel-iron alloy layer (Comparative Example 2), the tensile strength and elongation at break of Examples 1-7 were significantly improved, the Fe dissolution was significantly reduced, and the cycle life was significantly improved.

[0452] Furthermore, the warping problem in each of the embodiments 1-7 is well controlled, as can be seen in Table 3.

[0453] Table 1. Preparation process, structure, and chemical composition of the iron-containing alloy layer, as well as performance test results of the negative electrode current collector and battery cell.

[0454]

[0455] In Table 1, the "Fe content" of each structural sublayer of the iron alloy layer represents the mass concentration of Fe element in that structural sublayer.

[0456] Table 2.

[0457]

[0458] Table 3. Warpage Height Test

[0459] Test metrics Example 1 Example 2 Example 3 Example 4 Warpage height (mm) 2 2 1 2

[0460] When the first and second surface layers use the same current density, the iron content of the first surface layer, which is closer to the cathode roller, may be slightly higher than that of the second surface layer due to the influence of the cathode roller grains.

[0461] Table 4. Summary results based on Table 1

[0462]

[0463] In Table 4, the two surface layers refer to the first surface layer and the second surface layer; "concentration difference" refers to the difference in mass concentration.

[0464] The descriptions of the various implementation methods and embodiments above tend to emphasize the differences between them. Similarities or resemblances can be referenced interchangeably, and for the sake of brevity, they will not be repeated here. The technical features of the implementation methods and embodiments described above can be combined arbitrarily. For the sake of brevity, not all possible combinations of the technical features in the above embodiments have been described. However, as long as the combinations of these technical features do not contradict each other, they should be considered within the scope of this specification.

[0465] It should be noted that this application is not limited to the above-described embodiments and examples. The above-described embodiments and examples are merely examples, and any embodiments and examples that have the same structure and achieve the same effect as the technical concept within the scope of this application are included in the technical scope of this application. The embodiments and examples described above only illustrate several embodiments and examples of this application, and although the descriptions are relatively detailed, they should not be construed as limiting the scope of the patent. Furthermore, various modifications that can be conceived by those skilled in the art to the embodiments or examples, and other ways of constructing embodiments or examples by combining some of the constituent elements of the embodiments or examples, are also included in the scope of this application without departing from the spirit of this application.

Claims

1. A secondary battery, characterized in that, It includes a negative electrode sheet, the negative electrode sheet including a negative current collector and a negative active layer located on at least one side of the negative current collector; The negative electrode current collector includes an iron-containing alloy layer and a conductive layer located on at least one side of the iron-containing alloy layer; the iron-containing alloy layer is a structural layer including a reinforcing element and an Fe element, wherein the reinforcing element includes at least one of Ni and Cr elements; the conductive layer includes at least one of Cu and a metallic element M2, wherein the metallic element M2 is a conductive metallic element different from Cu and Fe; the thickness direction of the negative electrode current collector is denoted as the longitudinal direction; in the longitudinal direction, the concentration of Fe element on the surface of the iron-containing alloy layer is lower than the concentration of Fe element inside the iron-containing alloy layer.

2. The secondary battery according to claim 1, characterized in that, It meets one or more of the following characteristics: (a1) The mass concentration of Fe element in the iron-containing alloy layer is greater than or equal to 30%, and can be selected as 30% to 65%; (a2) The mass concentration of the reinforcing element in the iron-containing alloy layer is greater than or equal to 35%, optionally 35% to 70%, and more preferably 50% to 70%; (a3) The mass percentage of Ni and Cr elements in the reinforcing elements is 95% to 100%, and optionally 98% to 100%; further optionally, the iron-containing alloy layer is a nickel-iron binary alloy layer, a chromium-iron binary alloy layer, or a nickel-chromium-iron ternary alloy layer. (a4) The conductive layer is a copper layer.

3. The secondary battery according to claim 1 or 2, characterized in that, The iron-containing alloy layer includes a central layer and a first surface layer and a second surface layer located on both sides of the iron-containing alloy layer, respectively. The mass concentrations of Fe in the first surface layer, the central layer, and the second surface layer are denoted as C. F1 C C and C F2 C F1 <C C And C F2 <C C ; Optionally, the negative electrode current collector satisfies one or more of the following characteristics: (b1) The thickness ratio of the first surface layer to the central layer and the thickness ratio of the second surface layer to the central layer are each independently less than 1, and can be selected as 0.05 to 0.8, or more preferably 0.05 to 0.5; (b2) The ratio of the areal density of Fe in the first surface layer to the areal density in the central layer and the ratio of the areal density of Fe in the second surface layer to the areal density in the central layer are each independently less than 1, optionally 0.01 to 0.5, and more preferably 0.02 to 0.3, per unit area in the transverse direction of the iron alloy layer; wherein, transverse direction is the direction perpendicular to the longitudinal direction.

4. The secondary battery according to claim 3, characterized in that, The negative electrode current collector satisfies one or more of the following characteristics: (c1) The difference in mass concentration of Fe element between the first surface layer and the second surface layer is 0-30%, optionally 0-20%, and further optionally 0-5%; (c2) The thickness difference between the first surface layer and the second surface layer is 0 to 1 μm, and can be selected as 0 to 0.5 μm; (c3) The thickness of the first surface layer and the second surface layer are each independently 0.1 μm to 2 μm, and can be selected as 0.1 μm to 1 μm; the thickness of the central layer is 2 μm to 6 μm, and can be selected as 2 μm to 4 μm; (c4) The thickness percentage of the first surface layer relative to the iron-containing alloy layer and the thickness percentage of the second surface layer relative to the iron-containing alloy layer are each independently 1% to 35%, and optionally 4% to 25%; (c5) The mass concentration of Fe in the first surface layer and the mass concentration of Fe in the second surface layer are each independently less than 40%, and can be greater than or equal to 20% and less than 40%, and can be further selected as 20% to 30%; (c6) The mass concentration of Fe element in the central layer is greater than or equal to 30%, optionally 30% to 60%, and more preferably 35% to 60%; (c7) The sum of the mass concentrations of Ni and Cr elements in the first surface layer and the sum of the mass concentrations of Ni and Cr elements in the second surface layer are each independently greater than or equal to 70%, and can be selected as 70% to 80%. (c8) The sum of the mass concentrations of Ni and Cr elements in the central layer is less than or equal to 70%, and can be selected from 40% to 70%, or from 40% to 65%.

5. The secondary battery according to any one of claims 1 to 4, characterized in that, The iron-containing alloy layer comprises multiple structural sublayers, and any two adjacent structural sublayers contain different concentrations of Fe element; the iron-containing alloy layer comprises a central layer and a first surface layer and a second surface layer located on both sides of the iron-containing alloy layer respectively. The negative electrode current collector satisfies one or more of the following characteristics: (d1) The number of structural sublayers in the iron-containing alloy layer is greater than or equal to 3, and in the longitudinal direction, the concentration of Fe element in the multiple structural sublayers decreases from the center to the two sides respectively. Optionally, the number of structural sublayers in the iron-containing alloy layer is 2n+1, where n is an integer greater than or equal to 2, and in the longitudinal direction, the concentration of Fe element in the multiple structural sublayers decreases from the center to both sides of the surface. Further optionally, each structural sublayer from the first surface layer to the second surface layer is denoted as layer 1, layer 2, layer 3, ..., layer 2n and layer 2n+1, respectively; wherein the mass concentration difference of Fe element in layer i and layer 2n+2-i is 0 to 20%, optionally 0 to 5%; wherein 1 ≤ i ≤ n; (d2) The iron-containing alloy layer further includes a first intermediate layer and a second intermediate layer; wherein the first intermediate layer is located between the first surface layer and the central layer, and the second intermediate layer is located between the second surface layer and the central layer; the mass concentration of Fe element in the first intermediate layer and the second intermediate layer is denoted as C. M1 and C M2 C F1 <C M1 <C C And C F2 <C M2 <C C； Optionally, the difference in mass concentration of Fe element between the first surface layer and the second surface layer is 0-20%, optionally 0-5%; the difference in mass concentration of Fe element between the first intermediate layer and the second intermediate layer is 0-20%, optionally 0-5%.

6. The secondary battery according to any one of claims 1 to 5, characterized in that, The negative electrode current collector satisfies one or more of the following characteristics: (e1) The thickness of the iron-containing alloy layer is 3μm to 8μm, and can be 4μm to 6μm; (e2) The thickness of the conductive layer is 0.5 μm to 2 μm, and can be selected as 0.5 μm to 1.5 μm; (e3) The thickness of the iron-containing alloy layer is 42% to 86% of the thickness of the negative electrode current collector, and can be 60% to 86%; (e4) The negative electrode current collector further includes an isolation layer, which is located between the iron-containing alloy layer and the conductive layer; the isolation layer satisfies one or more of the following features (f1) and (f2): (f1) The isolation layer includes one or more of a nickel layer, a nickel alloy layer, a chromium layer and a chromium alloy layer; (f2) The thickness of the isolation layer is 0.1 μm to 1 μm.

7. The secondary battery according to any one of claims 1 to 6, characterized in that, The negative electrode active layer includes a negative electrode active material, and the negative electrode active material includes a silicon-based material; Optionally, the negative electrode sheet satisfies one or more of the following characteristics: (g1) The silicon-based material accounts for more than or equal to 10% of the mass of the negative electrode active material, and can be selected from 10% to 80%, or from 40% to 70%; (g2) The silicon-based material includes one or more of elemental silicon, silicon-carbon composite materials, silicon-oxygen materials, silicon-nitrogen composite materials, and silicon alloys; (g3) The negative electrode active material further includes a carbon-based material, wherein the mass ratio of the carbon-based material and the silicon-based material in the negative electrode active material is 90% to 100%; (g4) The secondary battery is a lithium-ion secondary battery.

8. A method for preparing a negative electrode sheet, characterized in that, Includes the following steps: A negative electrode current collector is prepared; wherein the negative electrode current collector includes an iron-containing alloy layer and a conductive layer located on at least one side of the iron-containing alloy layer; the iron-containing alloy layer is a structural layer including a reinforcing element and an Fe element, wherein the reinforcing element includes at least one of Ni and Cr; the conductive layer includes at least one of Cu and a metallic element M2, wherein the metallic element M2 is a conductive metallic element different from Cu and Fe; the thickness direction of the negative electrode current collector is denoted as the longitudinal direction; in the longitudinal direction, the concentration of Fe element on the surface of the iron-containing alloy layer is lower than the concentration of Fe element inside the iron-containing alloy layer; A negative electrode active layer is provided on at least one side of the negative electrode current collector.

9. The method for preparing the negative electrode sheet according to claim 8, characterized in that, The negative electrode sheet of the secondary battery according to any one of claims 2 to 7 is prepared; The negative electrode current collector is prepared by a method comprising the following steps: The iron-containing alloy layer is prepared by electroplating, such that the anode current density corresponding to the preparation of the surface layer of the iron-containing alloy layer is higher than the anode current density corresponding to the preparation of the internal structural layer of the iron-containing alloy layer. The conductive layer is formed on at least one side of the iron-containing alloy layer by electroplating.

10. An electrical device, characterized in that, It includes at least one of the secondary batteries according to any one of claims 1 to 7 and the negative electrode sheet prepared by the method of preparing the negative electrode sheet according to claim 8 or 9.

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