Negative plate and preparation method thereof, cylindrical battery cell and cylindrical battery
By optimizing the pore consistency of different thicknesses in the negative electrode coating, the electrolyte infiltration and polarization problems caused by the increase of pore impedance are solved, and the battery efficiency and rate performance of lithium batteries are improved.
Patent Information
- Application Number
- CN202510501417.4
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-04-21
- Publication Date
- 2025-07-18
AI Technical Summary
In the prior art, the process of increasing the energy density of lithium batteries by increasing the coating surface density, the pore impedance increases, affecting the electrolyte infiltration and polarization, and reducing battery efficiency and rate performance.
By optimizing the pore consistency of different thicknesses in the negative electrode coating, adjusting the pore consistency deviation, reducing pore impedance, improving the degree of material particles, and improving the pore impedance and polarization performance of the battery.
Effectively reduce pore impedance, improve electrolyte infiltration, reduce closed pores, and improve battery efficiency and rate performance.
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Figure CN120341236A_ABST
Abstract
Description
Technical Field
[0001] This application relates to the technical field of cylindrical batteries, and particularly relates to a negative electrode sheet, a preparation method thereof, a cylindrical battery cell, and a cylindrical battery. Background Art
[0002] Currently, lithium batteries have advantages such as high energy density, long cycle life, low self-discharge rate, and no memory effect. They can be used as an efficient and environmentally friendly energy storage device and have been widely applied in fields such as consumer electronics, power tools, electric vehicles, and energy storage systems.
[0003] In a lithium-ion battery, the performance of its battery cell affects the performance of the battery. During the manufacturing process of the battery cell, active materials are generally evenly coated on aluminum foil or copper foil. Among them, to further improve the energy density of the battery, the coating surface density is generally increased in related technologies.
[0004] In the process of implementing the embodiments of the present disclosure, it is found that at least the following problems exist in related technologies:
[0005] By increasing the energy density of the battery in the above manner, during the cold pressing process of the electrode sheet, a greater cold pressing pressure is required. In this way, more closed pores will be formed in the electrode sheet, resulting in an increase in its pore impedance, which is not conducive to the infiltration of the electrolyte. In addition, a greater cold pressing pressure will also increase the degree of fragmentation of the material particles, thereby increasing the amount of SEI film formation and reducing the battery efficiency. At the same time, the increase in pore impedance will also increase the polarization, thereby affecting the rate performance of the battery.
[0006] It should be noted that the information disclosed in the above background art section is only used to enhance the understanding of the background of this application. Therefore, it may include information that does not constitute the prior art known to those of ordinary skill in the art. Summary of the Invention
[0007] To have a basic understanding of some aspects of the disclosed embodiments, a simple summary is given below. This summary is not a general review, nor is it intended to identify key / important constituent elements or delineate the protection scope of these embodiments. Instead, it serves as a preface to the subsequent detailed description.
[0008] The embodiments of the present disclosure provide a negative electrode sheet, a preparation method thereof, a cylindrical battery cell, and a cylindrical battery. By optimizing the porosity consistency of different thicknesses within the negative electrode coating, the pore impedance of the negative electrode sheet is greatly reduced, thereby improving the rate performance of the battery.
[0009] In some embodiments, it includes a negative electrode current collector and a negative electrode coating coated on at least one surface of the negative electrode current collector. The negative electrode coating includes a negative electrode active material, and the negative electrode active material includes a graphite material and a silicon-based material; wherein, the weight percentage of the graphite material is 70% to 97%, and the weight percentage of the silicon-based material is 3% to 30%; the sum of the weight percentages of the graphite material and the silicon-based material is less than 97%; the negative electrode coating further includes a continuous first negative electrode coating region, a second negative electrode coating region, and a third negative electrode coating region; wherein, the porosity uniformity rate M of the first negative electrode coating region, the second negative electrode coating region, and the third negative electrode coating region is different, and the deviation N of the porosity uniformity rate at different thicknesses is <0.03.
[0010] In some embodiments, the porosity uniformity rate M at different thicknesses within the negative electrode coating is calculated by the following formula:
[0011] M = |A - B|;
[0012] wherein, A is the ratio of the pore particle area in the upper half of the negative electrode coating, and B is the ratio of the pore particle area in the lower half of the negative electrode coating.
[0013] In some embodiments, the deviation N of the porosity uniformity rate at different thicknesses within the negative electrode coating is determined by the following method:
[0014] Partial coating units in the first negative electrode coating region, the second negative electrode coating region, and the third negative electrode coating are respectively taken, and the porosity uniformity rate of each coating unit is calculated; and the deviation N of the porosity uniformity rate at different thicknesses within the negative electrode coating is calculated by the following formula:
[0015] N = (|M1 - R| + |M2 - R| + |M3 - R|) / R;
[0016] wherein, M1 is the porosity uniformity rate of the coating unit in the first negative electrode coating region, M2 is the porosity uniformity rate of the coating unit in the second negative electrode coating region, M3 is the porosity uniformity rate of the coating unit in the third negative electrode coating region, and R is the average value of the porosity uniformity rates of the three coating units.
[0017] In some embodiments, at a state of charge (SOC) of 0%, the porosity uniformity rate M at different thicknesses within the second negative electrode coating region is <0.03.
[0018] In some embodiments, the pore impedance value Z of the second negative electrode coating region is <5, and the pore impedance value Z of the second negative electrode coating region is calculated by the following formula:
[0019] Z = e M-1 +1;
[0020] wherein, e is a constant.
[0021] In some embodiments, the average pore impedance Y of the negative electrode coating and the pore impedance value Z of the second negative electrode coating region satisfy the following condition:
[0022] (Z - Y) / Y ≤ 0.03;
[0023] Wherein, at a state of charge (SOC) of 0%, partial coating units are taken from the first negative electrode coating region, the second negative electrode coating region, and the third negative electrode coating region respectively, and the pore impedance of each coating unit is calculated to determine the average pore impedance values of the three coating units, and the average pore impedance value of the three coating units is used as the average pore impedance Y of the negative electrode coating.
[0024] In some embodiments, the areal density of the negative electrode sheet ranges from 4 g / cm 2 to 11 g / cm 2 .
[0025] In some embodiments, the areal density of the negative electrode sheet ranges from 6 g / cm 2 to 9 g / cm 2 .
[0026] In some embodiments, the tap density of the negative electrode sheet ranges from 1.2 g / cc to 1.9 g / cc.
[0027] In some embodiments, the tap density of the negative electrode sheet ranges from 1.4 g / cc to 1.7 g / cc.
[0028] In some embodiments, the method for preparing the negative electrode sheet includes the following steps:
[0029] Mix the negative electrode coating material, coat it on at least one surface of the negative electrode current collector, and obtain a negative electrode sheet with a first thickness D1 after drying and cold pressing;
[0030] Perform a first cold pressing on the first surface of the negative electrode sheet to obtain a negative electrode sheet with a second thickness D2;
[0031] Perform a second cold pressing on the first surface of the negative electrode sheet to obtain a negative electrode sheet with a third thickness D3;
[0032] Wherein, the first thickness D1, the second thickness D2, and the third thickness D3 satisfy the following relationship:
[0033] D2 = D1 - (D1 - D3)k;
[0034] Wherein, the value range of k is 50% to 90%.
[0035] In some embodiments, the cylindrical battery cell includes a positive electrode sheet, the negative electrode sheet as described in the foregoing embodiments, and a separator located therebetween.
[0036] In some embodiments, the cylindrical battery includes a housing and the cylindrical battery cell described in the foregoing embodiments, and the cylindrical battery cell is encapsulated in the housing.
[0037] The negative electrode sheet, its preparation method, the cylindrical battery cell, and the cylindrical battery provided by the embodiments of the present disclosure can achieve the following technical effects:
[0038] In this application, by optimizing the porosity consistency rates of the first negative electrode coating region, the second negative electrode coating region, and the third negative electrode coating region, and adjusting the porosity consistency rate deviation at different thicknesses, the pore impedance value of the coating on the surface of the negative electrode current collector is effectively adjusted. In this way, the pore impedance can be effectively reduced, which is beneficial to the infiltration of the electrolyte. In addition, during the process of optimizing the porosity consistency at different thicknesses within the negative electrode coating, the degree of fragmentation of the material particles is also improved, resulting in fewer closed pores in the negative electrode sheet, smaller pore impedance, and improved battery efficiency. On this basis, the reduction of pore impedance will reduce polarization, thereby improving the rate performance of the battery.
[0039] The above general description and the following description are only exemplary and explanatory, and are not used to limit this application. BRIEF DESCRIPTION OF THE DRAWINGS
[0040] One or more embodiments are exemplarily illustrated by corresponding drawings. These exemplary illustrations and the drawings do not constitute a limitation on the embodiments. Elements with the same reference numerals in the drawings are shown as similar elements. The drawings do not constitute a scale limitation, and among them:
[0041] Figure 1 is a schematic structural diagram of a cylindrical battery provided by an embodiment of the present disclosure;
[0042] Figure 2 is a schematic structural diagram of a cylindrical battery cell provided by an embodiment of the present disclosure;
[0043] Figure 3 is a developed schematic diagram of a cylindrical battery cell provided by an embodiment of the present disclosure;
[0044] Figure 4 is a schematic diagram of pores and particles with different thicknesses in the negative electrode coating provided by an embodiment of the present disclosure.
[0045] REFERENCE SIGNS:
[0046] 1 - positive electrode end; 10 - cylindrical battery cell; 11 - positive electrode post; 12 - negative electrode end; 2 - housing; 3 - negative electrode sheet; 4 - separator; 5 - positive electrode sheet. DETAILED DESCRIPTION OF THE EMBODIMENTS
[0047] In order to understand the features and technical content of the embodiments of the present disclosure in more detail, the implementation of the embodiments of the present disclosure will be described in detail below with reference to the accompanying drawings. The accompanying drawings are only for reference and explanation, and are not used to limit the embodiments of the present disclosure. In the following technical description, for the sake of explanation, numerous details are provided to give a thorough understanding of the disclosed embodiments. However, one or more embodiments may still be implemented without these details. In other cases, well-known structures and devices may be shown in a simplified manner to simplify the drawings.
[0048] In the specification and claims of the embodiments of the present disclosure and the above-mentioned accompanying drawings, terms such as "first" and "second" are used to distinguish similar objects, and are not necessarily used to describe a specific order or sequence. It should be understood that such data can be interchanged under appropriate circumstances so as to implement the embodiments of the present disclosure described herein. In addition, the terms "comprising" and "having" and any variations thereof are intended to cover non-exclusive inclusion.
[0049] In the embodiments of the present disclosure, the orientation or positional relationship indicated by terms such as "upper", "lower", "inner", "middle", "outer", "front", and "rear" is based on the orientation or positional relationship shown in the accompanying drawings. These terms are mainly used to better describe the embodiments of the present disclosure and their embodiments, and are not used to limit that the indicated devices, elements, or components must have a specific orientation or be constructed and operated in a specific orientation. And, in addition to being able to represent an orientation or positional relationship, some of the above terms may also be used to represent other meanings. For example, the term "upper" may also be used to represent a certain attachment relationship or connection relationship in some cases. For those of ordinary skill in the art, the specific meanings of these terms in the embodiments of the present disclosure can be understood according to specific circumstances.
[0050] In addition, the terms "arranged", "connected", and "fixed" should be understood in a broad sense. For example, "connected" can be a fixed connection, a detachable connection, or an integral structure; it can be a mechanical connection or an electrical connection; it can be directly connected, or indirectly connected through an intermediate medium, or there can be internal communication between two devices, elements, or components. For those of ordinary skill in the art, the specific meanings of the above terms in the embodiments of the present disclosure can be understood according to specific circumstances.
[0051] Unless otherwise specified, the term "plurality" means two or more.
[0052] In the embodiments of the present disclosure, the character " / " indicates that the objects before and after are in an "or" relationship. For example, A / B means: A or B.
[0053] The term "and / or" is an associative relationship describing objects, indicating that there can be three relationships. For example, A and / or B means: A or B, or, A and B these three relationships.
[0054] It should be noted that, without conflict, the embodiments in the present disclosure and the features in the embodiments may be combined with each other.
[0055] In the silicon-containing batteries in the related art, as the energy density continuously increases, the areal density of the negative electrode coating also increases accordingly. In this way, the internal resistance of the cylindrical battery product becomes larger, resulting in a large amount of heat generated during the charging and discharging process of the battery, and the energy utilization rate is low.
[0056] In addition, when the areal density of the negative electrode coating increases, the cold pressing difficulty of the electrode sheet also becomes higher, and a greater pressure is required for the first cold pressing. Therefore, under the action of a greater pressure, more closed pores will be formed in the negative electrode sheet, resulting in a larger pore impedance, which is not conducive to the infiltration of the electrolyte. In addition, a greater cold pressing pressure will also increase the degree of fragmentation of the material particles, thereby increasing the film formation amount of the SEI film and reducing the battery efficiency. At the same time, the increase in pore impedance will also increase the polarization, thereby affecting the rate performance of the battery.
[0057] Therefore, to further improve the rate performance of the battery, the embodiments of the present disclosure provide a negative electrode sheet. By optimizing the porosity consistency of different thicknesses in the negative electrode coating, the pore impedance of the negative electrode sheet is greatly reduced, thereby improving the rate performance of the battery. Specifically, the negative electrode sheet includes a negative electrode current collector and a negative electrode coating coated on at least one surface of the negative electrode current collector. The negative electrode coating includes a negative electrode active material, and the negative electrode active material includes a graphite material and a silicon-based material; wherein, the weight percentage of the graphite material is 70% to 97%, and the weight percentage of the silicon-based material is 3% to 30%; the sum of the weight percentages of the graphite material and the silicon-based material is less than 97%; the negative electrode coating further includes a continuous first negative electrode coating region, a second negative electrode coating region, and a third negative electrode coating region; wherein, the porosity consistency M of the first negative electrode coating region, the second negative electrode coating region, and the third negative electrode coating region is different, and the deviation N of the porosity consistency at different thicknesses is < 0.03.
[0058] By using the negative electrode sheet provided by the embodiments of the present disclosure, the present application optimizes the porosity consistency of the first negative electrode coating region, the second negative electrode coating region, and the third negative electrode coating region, and adjusts the deviation of the porosity consistency at different thicknesses, thereby effectively adjusting the pore impedance value of the coating on the surface of the negative electrode current collector. In this way, the pore impedance can be effectively reduced, which is beneficial to the infiltration of the electrolyte. In addition, during the process of optimizing the porosity consistency of different thicknesses in the negative electrode coating, the degree of fragmentation of the material particles is also improved, so that the closed pores of the negative electrode sheet become fewer, its pore impedance becomes smaller, and the battery efficiency is improved. On this basis, the reduction of the pore impedance will reduce the polarization, thereby improving the rate performance of the battery.
[0059] In the embodiments of the present disclosure, the first negative electrode coating region and the third negative electrode coating region refer to the coatings on both sides of the negative electrode coating; the second negative electrode coating region refers to the coating in the middle region of the negative electrode coating.
[0060] In some embodiments, the porosity consistency rate M of different thicknesses in the negative electrode coating is calculated by the following formula:
[0061] M = |A - B|;
[0062] where A is the ratio of the pore particle area in the upper half of the negative electrode coating, and B is the ratio of the pore particle area in the lower half of the negative electrode coating.
[0063] In the embodiments of the present disclosure, the pore particle area ratio refers to the ratio of the pore area to the particle area in the second negative electrode coating region. Here, reference can be made to Figure 4 , where a is the pore and particle distribution of the upper half thickness, and b is the pore and particle distribution of the lower half thickness.
[0064] In some embodiments, the porosity consistency rate M1 of different thicknesses in the first negative electrode coating region is calculated by the following formula:
[0065] M1 = |A1 - B1|;
[0066] where A1 is the ratio of the pore particle area in the upper half of the first negative electrode coating region, and B1 is the ratio of the pore particle area in the lower half of the first negative electrode coating region.
[0067] In some embodiments, the porosity consistency rate M2 of different thicknesses in the second negative electrode coating region is calculated by the following formula:
[0068] M2 = |A2 - B2|;
[0069] where A2 is the ratio of the pore particle area in the upper half of the middle electrode coating region, and B2 is the ratio of the pore particle area in the lower half of the middle electrode coating region.
[0070] In some embodiments, the porosity consistency rate M3 of different thicknesses in the third negative electrode coating region is calculated by the following formula:
[0071] M3 = |A3 - B3|;
[0072] where A3 is the ratio of the pore particle area in the upper half of the third negative electrode coating region, and B3 is the ratio of the pore particle area in the lower half of the third negative electrode coating region.
[0073] In some embodiments, the porosity consistency rate deviation N of different thicknesses in the negative electrode coating is determined by the following method:
[0074] Take partial coating units in the first negative electrode coating area, the second negative electrode coating area, and the third negative electrode coating respectively, and calculate the porosity consistency rate of each coating unit; and calculate the porosity consistency rate deviation N of different thicknesses in the negative electrode coating through the following formula:
[0075] N = (|M1 - R| + |M2 - R| + |M3 - R|) / R;
[0076] Among them, R is the average value of the porosity consistency rates of the three coating units.
[0077] In the embodiments of the present disclosure, by calculating the average value of the porosity consistency rates of three different regions and comparing it with the porosity consistency rate of each region, the porosity consistency rate deviation N of different thicknesses in the negative electrode coating can be obtained; and when the porosity consistency rate deviation N of different thicknesses in the negative electrode coating meets the above conditions, it indicates that the overall consistency of the negative electrode sheet is good, that is, the difference in the porosity consistency rate between the first negative electrode coating area and the third negative electrode coating area and the second negative electrode coating area is small, thereby ensuring that the overall pore impedance becomes smaller and improving the battery efficiency.
[0078] In some embodiments, at a state of charge (SOC) of 0%, the porosity consistency rate M2 of different thicknesses in the second negative electrode coating area is < 0.03.
[0079] In the embodiments of the present disclosure, when the porosity consistency rate M2 of different thicknesses in the second negative electrode coating area meets the above conditions, it indicates that the porosity bending degree and complexity of the upper and lower parts of the negative electrode sheet are low. In this way, it is beneficial to reduce the pore impedance of the negative electrode sheet.
[0080] In some embodiments, the pore impedance value Z of the second negative electrode coating area is < 5, and the pore impedance value Z of the second negative electrode coating area is calculated through the following formula:
[0081] Z = e M-1 +1;
[0082] Among them, e is a constant.
[0083] In some embodiments, the average pore impedance value Y of the negative electrode coating and the pore impedance value Z of the second negative electrode coating area meet the following conditions:
[0084] (Z - Y) / Y ≤ 0.03;
[0085] Among them, at a state of charge (SOC) of 0%, take partial coating units in the first negative electrode coating area, the second negative electrode coating area, and the third negative electrode coating area respectively, and calculate the pore impedance of each coating unit to determine the average pore impedance value of the three coating units, and use the average pore impedance value of the three coating units as the average pore impedance value Y of the negative electrode coating.
[0086] In the embodiments of the present disclosure, when the average pore impedance Y of the negative electrode coating and the pore impedance value Z of the second negative electrode coating region satisfy the above conditions, it indicates that the calculated pore impedance has a small difference from the actually measured pore impedance, so that the pore impedance can be ensured to become smaller and the battery efficiency can be improved.
[0087] In some embodiments, the areal density of the negative electrode sheet ranges from 4 g / cm 2 to 11 g / cm 2 .
[0088] In the embodiments of the present disclosure, the areal density of the negative electrode sheet refers to the mass of the negative electrode material per unit area.
[0089] In some embodiments, the areal density of the negative electrode sheet ranges from 6 g / cm 2 to 9 g / cm 2 .
[0090] In some embodiments, the tap density of the negative electrode sheet ranges from 1.2 g / cc to 1.9 g / cc.
[0091] In the embodiments of the present disclosure, the tap density of the negative electrode sheet refers to the mass or density per unit volume of the negative electrode sheet after being roll-pressed. Among them, the tap density affects the energy density, charge-discharge performance, and cycle life of the battery.
[0092] In some embodiments, the tap density of the negative electrode sheet ranges from 1.4 g / cc to 1.7 g / cc.
[0093] In some embodiments, the method for preparing the negative electrode sheet includes the following steps:
[0094] Mix the negative electrode coating material, coat it on at least one surface of the negative electrode current collector, and obtain a negative electrode sheet with a first thickness D1 after drying and cold pressing;
[0095] Perform a first cold pressing on the first surface of the negative electrode sheet to obtain a negative electrode sheet with a second thickness D2;
[0096] Perform a second cold pressing on the first surface of the negative electrode sheet to obtain a negative electrode sheet with a third thickness D3;
[0097] Among them, the first thickness D1, the second thickness D2, and the third thickness D3 satisfy the following relationship:
[0098] D2 = D1 - (D1 - D3)k;
[0099] Among them, the value range of k is 50% to 90%.
[0100] The embodiments of the present disclosure also disclose a cylindrical battery cell, including a positive electrode sheet, a negative electrode sheet as described in the foregoing embodiments, and a separator located between the two.
[0101] Among them, the specific structure of the negative electrode sheet refers to the above-mentioned embodiment. Since this cylindrical battery cell adopts all the technical solutions of the above-mentioned embodiments, it has at least all the technical effects brought by the technical solutions of the above-mentioned embodiments, which will not be elaborated one by one here.
[0102] An embodiment of the present disclosure also discloses a cylindrical battery, including a housing and the cylindrical battery cell described in the foregoing embodiment, and the cylindrical battery cell is encapsulated in the housing. The specific structure of the cylindrical battery cell refers to the above-mentioned embodiment. Since this cylindrical battery adopts all the technical solutions of the above-mentioned embodiments, it has at least all the technical effects brought by the technical solutions of the above-mentioned embodiments, which will not be elaborated one by one here.
[0103] Combined with Figures 1 to 3 As shown, the cylindrical battery specifically includes a cylindrical housing 2, the interior of which is used to accommodate the cylindrical battery cell, the top is the positive electrode end 1, the bottom is the negative electrode end 12, and a positive electrode post 11 is provided on the positive electrode end 1. Specifically, Figure 2 shows a schematic structural diagram of the cylindrical battery cell in the present application, Figure 3 shows a developed schematic diagram of the cylindrical battery cell in the present application. Among them, the positive electrode sheet 5, the negative electrode sheet 3 and the separator 4 are stacked as Figure 3 shown, and then wound to form Figure 2 the cylindrical battery cell 10 shown. The end of the electrode sheet at the initial stage of winding is the end of the electrode sheet at the axis of the cylinder, and the end of the electrode sheet at the end of winding is the end of the electrode sheet on the outer surface of the cylinder. Among them, the positive electrode sheet 5 includes a strip-shaped positive electrode foil, a positive electrode coating and a first empty foil area coated on the surface of the strip-shaped positive electrode foil. The negative electrode sheet 3 includes a strip-shaped negative electrode foil, a negative electrode coating and a second empty foil area coated on the surface of the strip-shaped negative electrode foil. The first empty foil area and the second empty foil area are perpendicular to the winding direction, and the top end face or the bottom end face of the cylindrical battery is formed by methods such as ironing or cutting and laminating.
[0104] On this basis, an embodiment of the present disclosure provides a method for manufacturing a cylindrical battery, including:
[0105] Preparing a positive electrode sheet: mixing positive electrode coating materials, coating on at least one side surface of the aluminum foil, and obtaining the positive electrode sheet after drying and cold pressing;
[0106] Preparing a negative electrode sheet: mixing negative electrode coating materials, coating on at least one side surface of the aluminum foil, and obtaining the negative electrode sheet after drying and cold pressing;
[0107] Preparing a cylindrical battery cell: respectively subjecting the positive electrode sheet and the negative electrode sheet to rolling and slitting, and then winding them together with the separator to obtain the cylindrical battery cell;
[0108] Assembling the cylindrical battery: welding the tabs of the cylindrical battery cell to the electrical connection sheet, installing it into the battery housing, and performing electrolyte injection, sealing and forming processes to obtain the cylindrical battery.
[0109] In addition, an embodiment of the present disclosure provides an electrical device, including a cylindrical battery for providing power as described in this application.
[0110] The following continues to further explain the present invention with embodiments.
[0111] Embodiment 1
[0112] In Embodiment 1, a method for preparing a negative electrode sheet is provided, including the following steps:
[0113] Coat the negative electrode paste on the surface of the negative electrode foil to obtain an initial negative electrode sheet with a first thickness D1. The initial negative electrode sheet includes a first surface and a second surface arranged opposite to each other.
[0114] Place the first surface of the initial negative electrode sheet facing upward, and perform a first cold pressing on the initial negative electrode sheet through a rolling device to obtain a negative electrode sheet with a second thickness D2.
[0115] After the first cold pressing, within 10 minutes, place the first surface of the negatively electrode sheet after the first cold pressing facing upward, and perform a second cold pressing on it through a rolling device to obtain a negative electrode sheet with a third thickness D3.
[0116] Among them, the first thickness D1, the second thickness D2, and the third thickness D3 satisfy the following relationship: D2 = D1 - (D1 - D3)k, and k is 60%.
[0117] Embodiment 2
[0118] In Embodiment 2, a method for preparing a negative electrode sheet is provided, including the following steps:
[0119] Coat the negative electrode paste on the surface of the negative electrode foil to obtain an initial negative electrode sheet with a first thickness D1. The initial negative electrode sheet includes a first surface and a second surface arranged opposite to each other.
[0120] Place the first surface of the initial negative electrode sheet facing upward, and perform a first cold pressing on the initial negative electrode sheet through a rolling device to obtain a negative electrode sheet with a second thickness D2.
[0121] After the first cold pressing, within 10 minutes, place the first surface of the negatively electrode sheet after the first cold pressing facing upward, and perform a second cold pressing on it through a rolling device to obtain a negative electrode sheet with a third thickness D3.
[0122] Among them, the first thickness D1, the second thickness D2, and the third thickness D3 satisfy the following relationship: D2 = D1 - (D1 - D3)k, and k is 70%.
[0123] Embodiment 3
[0124] In Embodiment 3, a method for preparing a negative electrode sheet is provided, including the following steps:
[0125] Coat the negative electrode paste on the surface of the negative electrode foil to obtain an initial negative electrode sheet with a first thickness D1. The initial negative electrode sheet includes a first surface and a second surface that are oppositely arranged;
[0126] Place the first surface of the initial negative electrode sheet upward, and perform the first cold pressing on the initial negative electrode sheet through a rolling device to obtain a negative electrode sheet with a second thickness D2;
[0127] After the first cold pressing, within 10 minutes, place the first surface of the negative electrode sheet after the first cold pressing upward, and perform the second cold pressing on it through a rolling device to obtain a negative electrode sheet with a third thickness D3;
[0128] Among them, the first thickness D1, the second thickness D2, and the third thickness D3 satisfy the following relationship: D2 = D1 - (D1 - D3)k, and k is 80%.
[0129] Example 4
[0130] In Example 4, a method for preparing a negative electrode sheet is provided, including the following steps:
[0131] Coat the negative electrode paste on the surface of the negative electrode foil to obtain an initial negative electrode sheet with a first thickness D1. The initial negative electrode sheet includes a first surface and a second surface that are oppositely arranged;
[0132] Place the first surface of the initial negative electrode sheet upward, and perform the first cold pressing on the initial negative electrode sheet through a rolling device to obtain a negative electrode sheet with a second thickness D2;
[0133] After the first cold pressing, within 10 minutes, place the first surface of the negative electrode sheet after the first cold pressing upward, and perform the second cold pressing on it through a rolling device to obtain a negative electrode sheet with a third thickness D3;
[0134] Among them, the first thickness D1, the second thickness D2, and the third thickness D3 satisfy the following relationship: D2 = D1 - (D1 - D3)k, and k is 90%.
[0135] Comparative Example 1:
[0136] In Comparative Example 1, a method for preparing a negative electrode sheet is provided, including the following steps:
[0137] Coat the negative electrode paste on the surface of the negative electrode foil to obtain an initial negative electrode sheet with a first thickness D1. The initial negative electrode sheet includes a first surface and a second surface that are oppositely arranged;
[0138] Place the first surface of the initial negative electrode sheet upward, and perform the first cold pressing on the initial negative electrode sheet through a rolling device to obtain a negative electrode sheet with a second thickness D2, and the second thickness D2 is the target thickness.
[0139] Comparative Example 2:
[0140] In Comparative Example 2, a method for preparing a negative electrode sheet is provided, including the following steps:
[0141] Coat the negative electrode slurry on the surface of the negative electrode foil to obtain an initial negative electrode sheet with a first thickness D1, where the initial negative electrode sheet includes a first surface and a second surface arranged opposite to each other;
[0142] Place the first surface of the initial negative electrode sheet facing upward, and perform a first cold pressing on the initial negative electrode sheet through a rolling device to obtain a negative electrode sheet with a second thickness D2;
[0143] After the first cold pressing, within 10 minutes, place the first surface of the negatively electrode sheet after the first cold pressing facing upward, and perform a second cold pressing through a rolling device to obtain a negative electrode sheet with a third thickness D3;
[0144] Among them, the first thickness D1, the second thickness D2, and the third thickness D3 satisfy the following relationship: D2 = D1 - (D1 - D3)k, and k is 40%.
[0145] Perform corresponding tests on the negative electrode sheets of Examples 1 to 4, and Comparative Examples 1 and 2.
[0146] This example provides a method for preparing a test battery, which is prepared by the following method:
[0147] Prepare a positive electrode sheet: including a positive electrode current collector aluminum foil and positive electrode coatings coated on both surfaces of the aluminum foil; among them, calculated by weight percentage, the ratio of the positive electrode active material, conductive carbon black, and binder polyvinylidene difluoride (PVDF) in the positive electrode coating is 96:1:3. After being fully stirred and mixed evenly in N-methylpyrrolidone (NMP), it is coated on a 12-μm aluminum foil, and after drying and cold pressing, a positive electrode sheet is obtained.
[0148] Prepare a negative electrode sheet, including a negative electrode current collector copper foil and negative electrode coatings coated on both surfaces of the copper foil; among them, calculated by weight percentage, the negative electrode coating includes 90% artificial graphite, 6% silicon-carbon material, 1% conductive agent acetylene black, 1% thickener carboxymethyl cellulose (CMC), and 2% negative electrode binder polyacrylic acid (PAA). Add the above substances to deionized water and stir to form a negative electrode slurry with a solid content of 40%, and coat it on the negative electrode current collector to form a negative electrode sheet.
[0149] Preparation of electrolyte: Ethylene carbonate (EC), fluoroethylene carbonate (FEC), ethyl methyl carbonate (EMC), and dimethyl carbonate (DMC) were mixed in a ratio of 15:15:20:50 to obtain an organic solvent. Then, the thoroughly dried lithium salt LiPF6 was dissolved in the mixed organic solvent to prepare an electrolyte with a concentration of 1 mol / L.
[0150] Preparation of separator: A polyethylene porous separator with a thickness of 12 μm was selected.
[0151] Assembly of cylindrical test battery: After the positive electrode sheet and the negative electrode sheet were respectively roll-pressed and slit, they were wound together with the separator to obtain a cylindrical battery core in a cylindrical shape. Subsequently, after the cylindrical battery core was welded to the electrical connection sheet, it was placed into the battery case. After completing the processes of injecting electrolyte, sealing, and formation, the test battery of this embodiment was obtained. The case of this test battery is a cylinder.
[0152] This embodiment also provides a test method for pore impedance, which is specifically obtained through the following method:
[0153] Preparation of symmetric soft-pack battery: A circular hole with a diameter of 14 mm was cut out from the middle part of the high-temperature insulating tape. The negative electrode sheet, separator, high-temperature insulating tape, and negative electrode sheet were stacked in sequence, and the negative electrode tab was welded to obtain an electrode assembly.
[0154] Among them, the number of layers of the negative electrode current collector is two, the number of layers of the separator is one, and the number of layers of the high-temperature insulating tape is one. The electrode assembly was placed in an outer packaging aluminum-plastic film to obtain a symmetric soft-pack battery.
[0155] Pore impedance test method: An electrochemical workstation was used to test the electrochemical impedance spectrum (EIS) of the above symmetric soft-pack battery in the test frequency range of 1 Hz to 100 kHz, and the pore impedance of the above symmetric soft-pack battery was obtained through the electrochemical impedance spectrum (EIS).
[0156] This embodiment also provides a test method for rate performance. Specifically, the cylindrical battery was placed in a constant-temperature oven at 25°C for 4 h and tested according to the following steps:
[0157] (1) Under the condition of 0.1C, charge at constant current and constant voltage to 4.2V and stand for 10 min;
[0158] (2) Under the condition of 0.1C, discharge at constant current until cutoff at 2.5V and stand for 10 min;
[0159] (3) Under the condition of 0.5C, charge at constant current and constant voltage to 4.2V and stand for 10 min;
[0160] (4) Under the condition of 0.1C, discharge at constant current until cutoff at 2.5V and stand for 10 min;
[0161] (5) Under the condition of 1C, charge at constant current and constant voltage to 4.2V and stand for 10 min;
[0162] (6) Under the condition of 0.1C, discharge at constant current until cutoff at 2.5V and stand for 10 min;
[0163] (7) Under the condition of 2C, charge at constant current and constant voltage to 4.2V and stand for 10 min;
[0164] (8) Under the condition of 0.1C, discharge at constant current until cutoff at 2.5V and stand for 10 min;
[0165] (9) Under the condition of 3C, charge at constant current and constant voltage to 4.2V and stand for 10 min;
[0166] (10) Under the condition of 0.1C, discharge at constant current until cutoff at 2.5V and stand for 10 min;
[0167] (11) Under the condition of 4C, charge at constant current and constant voltage to 4.2V and stand for 10 min;
[0168] (12) Under the condition of 0.1C, discharge at constant current until cutoff at 2.5V and stand for 10 min;
[0169] (13) Under the condition of 5C, charge at constant current and constant voltage to 4.2V and stand for 10 min;
[0170] (14) Under the condition of 0.1C, discharge at constant current until cutoff at 2.5V and stand for 10 min;
[0171] (15) Under the condition of 6C, charge at constant current and constant voltage to 4.2V and stand for 10 min;
[0172] (16) Under the condition of 0.1C, discharge at constant current until cutoff at 2.5V and stand for 10 min.
[0173] This embodiment also provides a method for testing the pore-to-particle area ratio. The negative electrode sheets of Examples 1 to 4, and Comparative Examples 1 and 2 are prepared into cross-sectional slices of the negative electrode sheets by argon ion polishing technology, and their cross-sections are photographed by a scanning electron microscope (SEM), and the ratio of the pore area to the particle area is statistically calculated for one of the surfaces.
[0174] Among them, the relevant parameter settings in Examples 1 to 4, as well as Comparative Examples 1 and 2, are as shown in Table 1 below:
[0175] Positive electrode Negative electrode Z <![CDATA[Y(Ωcm 2 )]]> A(％) B(％) M(％) N(％) Example 1 <![CDATA High nickel ternary]]> <![CDATA[Graphite, Silicon oxide > 2.83 2.89 7.31 9.18 1.87 2.12 Example 2 <![CDATA High nickel ternary]]> <![CDATA[Graphite, Silicon oxide > 3.39 3.45 7.16 9.42 2.26 2.33 Example 3 <![CDATA High nickel ternary]]> <![CDATA[Graphite, Silicon oxide > 3.99 4.08 6.75 9.33 2.58 2.57 Example 4 <![CDATA High nickel ternary]]> <![CDATA[Graphite, Silicon oxide > 4.66 4.58 6.49 9.36 2.87 2.88 Comparative example 1 <![CDATA High nickel ternary]]> <![CDATA[Graphite, Silicon oxide > 19.13 6.43 5.3 10.48 5.18 4.12 Comparative example 2 <![CDATA High nickel ternary]]> <![CDATA[Graphite, Silicon oxide > 6.39 5.56 6.25 9.68 3.43 3.34
[0176] Table 1
[0177] Correspondingly, the relevant data on the capacity retention rate in Examples 1 to 4, as well as Comparative Examples 1 and 2, are as shown in Table 2 below:
[0178]
[0179] Table 2
[0180] By comparing Examples 1 to 4, as well as Comparative Examples 1 and 2, it can be seen that by optimizing the pore particle area ratio of the negative electrode through secondary cold pressing, the consistency rate of pores with different thicknesses in the negative electrode coating becomes smaller, thereby effectively reducing the pore impedance, improving the rate performance of the battery, and enhancing the comprehensive performance of the battery.
[0181] At the same time, as can be seen from Table 2 above, in the negative electrode sheet, the larger the pore particle area ratio of the upper half and the lower half, the more uneven the pores in the upper half and the lower half, which may make the bending and complexity of the pores higher, thereby affecting the pore impedance.
[0182] In the embodiments of the present disclosure, during the charging and discharging process of the battery, lithium ions need to be transported between the positive electrode and the negative electrode through the electrolyte and the pores in the electrode material. Among them, the pore impedance of the negative electrode sheet mainly comes from the resistance suffered by lithium ions during transmission in the pores. Therefore, if the pore impedance is low, lithium ions can pass through the pores of the negative electrode sheet more smoothly, and can be quickly inserted into and extracted from the negative electrode material at different charge and discharge rates, so that the battery can adapt to a higher charge and discharge current and exhibit good rate performance. On the contrary, if the pore impedance is high, the transmission of lithium ions is blocked. During high-rate charge and discharge, lithium ions cannot reach or leave the negative electrode material in time, which will lead to an aggravation of the battery polarization phenomenon and the battery voltage deviating from the equilibrium voltage, thereby reducing the charge and discharge efficiency and rate performance of the battery.
[0183] On the other hand, a lower pore impedance helps to improve the kinetic process of the electrode reaction. The main reason is that lithium ions can be quickly transported to the active sites of the negative electrode material, enabling the electrode reaction to proceed more quickly and maintaining a high reaction rate even during high-rate charge and discharge, which is beneficial to improving the rate performance of the battery. While a higher pore impedance will cause lithium ions to consume more time and energy during transmission, resulting in a slowdown of the electrode reaction kinetic process and limiting the charge and discharge ability of the battery at high rates.
[0184] In summary, through the negative electrode sheet provided by the present application, by optimizing the porosity consistency of different thicknesses within the negative electrode coating, the pore impedance of the negative electrode sheet is greatly reduced, thereby improving the rate performance of the battery.
[0185] The above description and the drawings fully illustrate the embodiments of the present disclosure so that those skilled in the art can practice them. Other embodiments may include structural and other changes. Embodiments merely represent possible variations. Unless explicitly required, individual components and functions are optional, and the order of operations may vary. Parts and features of some embodiments may be included in or substituted for parts and features of other embodiments. The embodiments of the present disclosure are not limited to the structures already described and shown in the drawings, and various modifications and changes can be made without departing from its scope. The scope of the present disclosure is limited only by the appended claims.
Claims
1. A negative electrode sheet, characterized in that, It includes a negative electrode current collector and a negative electrode coating applied on at least one surface of the negative electrode current collector. The negative electrode coating includes negative electrode active materials, and the negative electrode active materials include graphite materials and silicon-based materials. Among them, the weight percentage of the graphite materials is 70% to 97%, and the weight percentage of the silicon-based materials is 3% to 30%. The sum of the weight percentages of the graphite materials and the silicon-based materials is less than 97%. The negative electrode coating further includes a continuous first negative electrode coating region, a second negative electrode coating region, and a third negative electrode coating region. Among them, the pore consistency rate M of the first negative electrode coating region, the second negative electrode coating region, and the third negative electrode coating region is different, and the deviation N of the pore consistency rate at different thicknesses is < 0.
03.
2. The negative electrode sheet according to claim 1, wherein The pore consistency rate M at different thicknesses within the negative electrode coating is calculated by the following formula: M = |A - B|; Among them, A is the pore particle area ratio of the upper half of the negative electrode coating, and B is the pore particle area ratio of the lower half of the negative electrode coating.
3. The negative electrode sheet according to claim 1, wherein The deviation N of the pore consistency rate at different thicknesses within the negative electrode coating is determined by the following method: Partial coating units are respectively taken from the first negative electrode coating region, the second negative electrode coating region, and the third negative electrode coating, and the pore consistency rate of each coating unit is calculated. And the deviation N of the pore consistency rate at different thicknesses within the negative electrode coating is calculated by the following formula: N = (|M1 - R| + |M2 - R| + |M3 - R|) / R; Among them, M1 is the pore consistency rate of the coating unit within the first negative electrode coating region, M2 is the pore consistency rate of the coating unit within the second negative electrode coating region, M3 is the pore consistency rate of the coating unit within the third negative electrode coating region, and R is the average value of the pore consistency rates of the three coating units.
4. The negative electrode sheet according to any one of claims 1 to 3, characterized in that, At the state of charge (SOC) of 0%, the pore consistency rate M at different thicknesses within the second negative electrode coating region is < 0.
03.
5. The negative electrode sheet according to any one of claims 1 to 3, characterized in that, The pore impedance value Z of the second negative electrode coating region is < 5, and the pore impedance value Z of the second negative electrode coating region is calculated by the following formula: Z = e M-1 + 1; Among them, e is a constant.
6. The negative electrode sheet according to claim 5, wherein The average pore impedance value Y of the negative electrode coating and the pore impedance value Z of the second negative electrode coating region satisfy the following conditions: (Z - Y) / Y ≤ 0.03; Among them, at the state of charge (SOC) of 0%, partial coating units are respectively taken from the first negative electrode coating region, the second negative electrode coating region, and the third negative electrode coating region, and the pore impedance of each coating unit is calculated to determine the average pore impedance value of the three coating units, and the average pore impedance value of the three coating units is used as the average pore impedance value Y of the negative electrode coating.
7. The negative electrode sheet according to any one of claims 1 to 3, characterized in that, The areal density of the negative electrode sheet ranges from 4 g / cm 2 to 11 g / cm 2 .
8. A method for preparing a negative electrode sheet according to any one of claims 1 to 7, characterized in that, It includes the following steps: Mix the negative electrode coating material, apply it on at least one surface of the negative electrode current collector, and obtain a negative electrode sheet with a first thickness D1 after drying and cold pressing. Perform the first cold pressing on the first surface of the negative electrode sheet to obtain a negative electrode sheet with a second thickness D2. Perform the second cold pressing on the first surface of the negative electrode sheet to obtain a negative electrode sheet with a third thickness D3. Among them, the first thickness D1, the second thickness D2, and the third thickness D3 satisfy the following relationship: D2 = D1 - (D1 - D3)k; Among them, the value range of k is 50% to 90%.
9. A cylindrical battery cell, characterized in that, It includes a positive electrode sheet, the negative electrode sheet according to any one of claims 1 to 7, and a separator located between the two.
10. A cylindrical battery, characterized in that, It includes a housing and the cylindrical battery cell according to claim 9, and the cylindrical battery cell is encapsulated in the housing.