A negative electrode sheet and a lithium ion battery

Abstract

The application provides a negative electrode sheet and a lithium ion battery. The negative electrode sheet comprises a current collector and a coating layer, the coating layer comprises a first sub-coating layer, a second sub-coating layer and a third sub-coating layer, the first sub-coating layer, the second sub-coating layer and the third sub-coating layer are sequentially stacked, and the second sub-coating layer is located between the first sub-coating layer and the third sub-coating layer; the coating layer is coated on the surface of the current collector, and the first sub-coating layer is in contact with the current collector; the heat conduction capacity of the first sub-coating layer is greater than that of the second sub-coating layer, and the heat conduction capacity of the third sub-coating layer is greater than that of the second sub-coating layer. The negative electrode sheet provided by the application realizes temperature rise caused by the internal resistance of the battery by arranging multiple coating layers with different heat conduction performances on the negative electrode sheet, thereby improving the charging rate of the lithium ion battery.

Description

Technical Field

[0001] This invention relates to the field of lithium-ion batteries, and more particularly to a negative electrode and a lithium-ion battery. Background Technology

[0002] Batteries often experience a high temperature rise during high-rate charging. This is because there is a certain resistance from the current collector to the positive and negative electrodes, and the large current will generate heat in the electrodes, Q=I. 2 Rt. On the one hand, due to the non-uniformity of the electrode structure, the temperature rise in different parts of the electrode is not the same; on the other hand, when the battery is charged at a high rate, the fast charging performance will be limited to a certain extent by the dynamic capability, thus resulting in the problem of low charging rate of lithium-ion batteries. Summary of the Invention

[0003] This invention provides a negative electrode and a lithium-ion battery, which solves the problem of low charging rate of lithium-ion batteries.

[0004] In a first aspect, embodiments of the present invention provide a negative electrode sheet, comprising: a current collector and a paste layer, wherein the paste layer comprises a first sub-paste layer, a second sub-paste layer and a third sub-paste layer, wherein the first sub-paste layer, the second sub-paste layer and the third sub-paste layer are stacked sequentially, and the second sub-paste layer is located between the first sub-paste layer and the third sub-paste layer;

[0005] The paste layer is applied to the surface of the current collector, and the first sub-paste layer is in contact with the current collector;

[0006] The first sub-coating layer includes at least one of gold fiber, silver fiber, copper fiber, carbon fiber, and graphene;

[0007] And / or,

[0008] The third sub-coating layer includes at least one of gold fiber, silver fiber, copper fiber, carbon fiber, and graphene;

[0009] The second sub-coating layer includes a negative electrode active material and a thermally conductive substance;

[0010] The thermal conductivity of the first sub-coating layer is greater than that of the second sub-coating layer, and the thermal conductivity of the third sub-coating layer is greater than that of the second sub-coating layer.

[0011] Optionally, the first sub-coating layer, the second sub-coating layer, and the third sub-coating layer all have the same length along the electrode winding direction.

[0012] Optionally, the thickness of the second sub-coating layer is greater than the thickness of the first sub-coating layer, and the thickness of the second sub-coating layer is greater than the thickness of the third sub-coating layer.

[0013] Optionally, the thickness of the first sub-coating layer is in the range of 2μm to 5μm.

[0014] Optionally, the thickness of the third sub-coating layer is in the range of 2μm to 5μm.

[0015] Optionally, the thickness of the second sub-coating layer is in the range of 50 μm to 150 μm, and the proportion of the thermally conductive material in the second sub-coating layer is in the range of 1% to 3%.

[0016] Optionally, the thermally conductive material includes at least one of gold fiber, silver fiber, copper fiber, carbon fiber, and graphene.

[0017] Optionally, the negative electrode active material includes at least one of silicon-carbon, silicon-oxygen, graphite, metal oxide, and silicon-based alloy.

[0018] Optionally, a paste layer is provided on both opposite sides of the current collector.

[0019] In a second aspect, embodiments of the present invention provide a lithium-ion battery, the lithium-ion battery comprising a negative electrode as described in any one of the first aspects.

[0020] This invention provides a negative electrode sheet and a lithium-ion battery. The negative electrode sheet includes a current collector and a paste layer. The paste layer includes a first sub-paste layer, a second sub-paste layer, and a third sub-paste layer, which are sequentially stacked, with the second sub-paste layer located between the first and third sub-paste layers. The paste layer is coated on the surface of the current collector, and the first sub-paste layer is in contact with the current collector. The first sub-paste layer includes at least one of gold fiber, silver fiber, copper fiber, carbon fiber, and graphene; and / or, the third sub-paste layer includes at least one of gold fiber, silver fiber, copper fiber, carbon fiber, and graphene. The second sub-paste layer includes a negative electrode active material and a thermally conductive material. The thermal conductivity of the first sub-paste layer is greater than that of the second sub-paste layer, and the thermal conductivity of the third sub-paste layer is greater than that of the second sub-paste layer.

[0021] The negative electrode sheet provided in this embodiment of the invention comprises three sub-paste layers with different thermal conductivity on the negative electrode current collector. The first sub-paste layer is in contact with the negative electrode current collector and includes a thermally conductive material, which can uniformly transfer heat from the copper foil side to the second sub-paste layer of the negative electrode sheet. The third sub-paste layer also includes a thermally conductive material, which can uniformly conduct heat from the positive electrode side to the second sub-paste layer, which includes the negative electrode active material. The second sub-paste layer includes the negative electrode active material and a thermally conductive material and is disposed between the first and third sub-paste layers, which can uniformly transfer heat from both sides to the negative electrode active material, causing heat to accumulate in the second sub-paste layer. The negative electrode active material in the second sub-paste layer has a low internal resistance, so even when the heat is high, the temperature on the negative electrode side rises. By utilizing the temperature rise caused by the battery's internal resistance, the charging rate of the lithium-ion battery is improved, and the rate performance of the negative electrode is enhanced during high-current charging and discharging.

[0022] By designing the negative electrode structure, each of the three sub-coating layers contains thermally conductive material, forming a connected thermally conductive network with the negative electrode current collector (preferably copper foil). This enhances conductivity and allows the significant heat generated by the high internal resistance of the positive electrode during fast charging to be quickly conducted to the negative electrode active material through the thermally conductive network formed by the three-layer structure. This increases the temperature on the negative electrode side, improves the chemical reaction dynamics, and enhances the charging rate and rate performance of the negative electrode during high-current charging and discharging of the lithium-ion battery. Attached Figure Description

[0023] Figure 1 This is a schematic diagram of the structure of a negative electrode sheet provided in an embodiment of the present invention;

[0024] Figure 2 This is a schematic diagram of the structure of the coating layer in an embodiment of the present invention.

[0025] Figure 3 This is a schematic diagram of the cross-sectional structure of the current collector and the coating layer in an embodiment of the present invention;

[0026] Figure 4 This is a cross-sectional SEM image and an elemental distribution diagram of the cross-section of a negative electrode provided in an embodiment of the present invention. Detailed Implementation

[0027] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0028] Before discussing the exemplary embodiments in more detail, it should be noted that some exemplary embodiments are described as processes or methods depicted as flowcharts. Although the flowcharts describe the steps as sequential processes, many of these steps can be performed in parallel, concurrently, or simultaneously. Furthermore, the order of the steps can be rearranged. A process can be terminated when its operation is complete, but it may also have additional steps not included in the figures. A process can correspond to a method, function, procedure, subroutine, subroutine, etc.

[0029] Furthermore, the terms "first," "second," etc., may be used herein to describe various directions, actions, steps, or elements, but these directions, actions, steps, or elements are not limited by these terms. These terms are only used to distinguish a first direction, action, step, or element from another direction, action, step, or element. For example, without departing from the scope of this application, a first speed difference may be referred to as a second speed difference, and similarly, a second speed difference may be referred to as a first speed difference. Both the first speed difference and the second speed difference are speed differences, but they are not the same speed difference. The terms "first," "second," etc., should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of this invention, "a plurality of" means at least two, such as two, three, etc., unless otherwise explicitly specified.

[0030] like Figure 1 and Figure 2 As shown, Figure 1 This is a schematic diagram of the structure of a negative electrode sheet provided in an embodiment of the present invention. Figure 2 This is a schematic diagram of the structure of the paste layer 120 in an embodiment of the present invention. The embodiment of the present invention provides a negative electrode sheet, which includes a current collector 110 and a paste layer 120. The paste layer 120 includes a first sub-paste layer 121, a second sub-paste layer 122 and a third sub-paste layer 123. The first sub-paste layer 121, the second sub-paste layer 122 and the third sub-paste layer 123 are stacked sequentially, and the second sub-paste layer 122 is located between the first sub-paste layer 121 and the third sub-paste layer 123.

[0031] The paste layer 120 is coated on the surface of the current collector 110, and the first sub-paste layer 121 is in contact with the current collector 110;

[0032] The first sub-coating layer 121 includes at least one of gold fiber, silver fiber, copper fiber, carbon fiber and graphene;

[0033] And / or,

[0034] The third sub-coating layer 123 includes at least one of gold fiber, silver fiber, copper fiber, carbon fiber and graphene;

[0035] The second sub-coating layer 122 includes a negative electrode active material and a thermally conductive substance;

[0036] The thermal conductivity of the first sub-coating layer 121 is greater than that of the second sub-coating layer 122, and the thermal conductivity of the third sub-coating layer 123 is greater than that of the second sub-coating layer 122.

[0037] In this embodiment, due to the high internal resistance of the positive electrode material in the lithium-ion battery, a large amount of heat is generated under the action of high current during fast charging; the negative electrode material has a low internal resistance. During fast charging, the heat distribution caused by the temperature rise between the positive and negative electrodes is uneven. In order to effectively suppress the uneven temperature rise of the electrodes and transform it into a condition beneficial to fast charging, in this embodiment, the paste layer 120 of the negative electrode is set to three layers, thereby utilizing the temperature rise caused by the battery's internal resistance to improve the rate performance of the negative electrode during high current charging / discharging.

[0038] Specifically, in this embodiment, three layers of paste 120 are sequentially stacked on the current collector 110. The first sub-paste layer 121 is coated on the surface of the current collector and contains a thermally conductive functional material with good thermal conductivity. The second sub-paste layer 122 is coated on the surface of the first sub-paste layer 121 and contains both a thermally conductive functional material and an active material. The third sub-paste layer 123 is coated on the surface of the second sub-paste layer 122 and contains a thermally conductive functional material with good thermal conductivity. The thermal conductivity of the thermally conductive functional material is stronger than that of the active material. Optionally, the lengths of the first sub-paste layer 121, the second sub-paste layer 122, and the third sub-paste layer 123 are all the same.

[0039] In this embodiment, the first sub-coating layer 121, the second sub-coating layer 122, and the third sub-coating layer 123 have the same length along the electrode winding direction and are disposed flush on the current collector at both ends.

[0040] In this embodiment, the mass percentage of the thermally conductive material in the first sub-coating layer is 60% to 99%, preferably 95% to 99%. The mass percentage of the thermally conductive material in the second sub-coating layer is 0.1% to 5%, preferably 1% to 2%.

[0041] like Figure 3 As shown, Figure 3 This is a schematic diagram of the negative electrode interface in an embodiment of the present invention, wherein the first sub-coating layer 121 and the third sub-coating layer 123 are composed of thermally conductive materials, and the second sub-coating layer 122 is composed of negative electrode active materials.

[0042] It should be noted that, Figure 4Here are a cross-sectional SEM image and an energy dispersive spectroscopy (EDS) elemental distribution map of a negative electrode provided in this embodiment of the invention, such as... Figure 4 As shown, Figure 4 The top left corner shows the cross-sectional SEM image. Figure 4 The thickness of the first and third sub-coating layers is greater than the thickness of the second sub-coating layer. Figure 4 The upper right corner shows the elemental distribution of the first and third sub-coating layers, which mainly contain the element C. Figure 4 The bottom right corner shows the elemental distribution of the second sub-coating layer, which mainly contains Cu. Through cross-sectional SEM and energy dispersive spectroscopy analysis of the electrode, the negative electrode structure described above can be clearly seen, and thermally conductive material can be clearly detected in the middle second sub-coating layer.

[0043] This invention provides a negative electrode sheet and a lithium-ion battery. The negative electrode sheet includes a current collector and a paste layer. The paste layer includes a first sub-paste layer, a second sub-paste layer, and a third sub-paste layer, which are sequentially stacked, with the second sub-paste layer located between the first and third sub-paste layers. The paste layer is coated on the surface of the current collector, and the first sub-paste layer is in contact with the current collector. The thermal conductivity of the first sub-paste layer is greater than that of the second sub-paste layer, and the thermal conductivity of the third sub-paste layer is greater than that of the second sub-paste layer. The negative electrode sheet provided in this embodiment of the invention, by setting multiple paste layers with different thermal conductivity on the negative electrode sheet, achieves temperature rise caused by the battery's internal resistance, thereby improving the charging rate of the lithium-ion battery.

[0044] The negative electrode sheet provided in this embodiment of the invention comprises three sub-paste layers with different thermal conductivity on the negative electrode current collector. The first sub-paste layer is in contact with the negative electrode current collector and includes a thermally conductive material, which can uniformly transfer heat from the copper foil side to the second sub-paste layer of the negative electrode sheet. The third sub-paste layer also includes a thermally conductive material, which can uniformly conduct heat from the positive electrode side to the second sub-paste layer, which includes the negative electrode active material. The second sub-paste layer includes the negative electrode active material and a thermally conductive material and is disposed between the first and third sub-paste layers, which can uniformly transfer heat from both sides to the negative electrode active material, causing heat to accumulate in the second sub-paste layer. The negative electrode active material in the second sub-paste layer has a low internal resistance, so even when the heat is high, the temperature on the negative electrode side rises. By utilizing the temperature rise caused by the battery's internal resistance, the charging rate of the lithium-ion battery is improved, and the rate performance of the negative electrode is enhanced during high-current charging and discharging.

[0045] By designing the negative electrode structure, each of the three sub-coating layers contains thermally conductive material, forming a connected thermally conductive network with the negative electrode current collector (preferably copper foil). This enhances conductivity and allows the significant heat generated by the high internal resistance of the positive electrode during fast charging to be quickly conducted to the negative electrode active material through the thermally conductive network formed by the three-layer structure. This increases the temperature on the negative electrode side, improves the chemical reaction dynamics, and enhances the charging rate and rate performance of the negative electrode during high-current charging and discharging of the lithium-ion battery.

[0046] In other alternative embodiments, the thickness of the second sub-coating layer may be greater than the thickness of the first sub-coating layer, and the thickness of the second sub-coating layer may be greater than the thickness of the third sub-coating layer.

[0047] Specifically, the thickness of the first sub-coating layer is in the range of 2 μm to 5 μm. The thickness of the third sub-coating layer is in the range of 2 μm to 5 μm. The thickness of the second sub-coating layer is in the range of 50 μm to 150 μm, and the second sub-coating layer includes a thermally conductive material, wherein the thermally conductive material accounts for 1% to 3% of the total mass of the second sub-coating layer.

[0048] In this embodiment, the thicknesses of the first and third sub-coating layers can be the same or different, and the specific values ​​are determined according to the actual manufacturing process. In this embodiment, the thicknesses of the first and third sub-coating layers are in the range of 2μm to 5μm, such as 2μm, 3μm, 4μm, 5μm, etc., with 2μm being optimal. The thickness of the second sub-coating layer is in the range of 50μm to 150μm, and the proportion of thermally conductive material is in the range of 1% to 3%, such as 1%, 1.5%, 2%, 2.5%, 3%, etc., with 1.2% being optimal. Specifically, the thermally conductive material includes at least one of gold fiber, silver fiber, copper fiber, carbon fiber, graphene, etc.

[0049] It should be noted that the length is the direction of the paste application for the current collector, and the thickness direction is perpendicular to the direction of the paste application for the current collector.

[0050] Optionally, the first sub-coating layer includes at least one of gold fiber, silver fiber, copper fiber, carbon fiber, and graphene;

[0051] And / or,

[0052] The third sub-coating layer includes at least one of gold fiber, silver fiber, copper fiber, carbon fiber, and graphene.

[0053] Optionally, the thermally conductive material includes at least one of silicon-carbon, silicon-oxygen, graphite, metal oxides, and silicon-based alloys.

[0054] Optionally, the negative electrode active material includes at least one of silicon-carbon, silicon-oxygen, graphite, metal oxide, and silicon-based alloy.

[0055] In this embodiment, the first sub-coating layer is coated on the surface of the current collector and contains a thermally conductive material with good thermal conductivity. The third sub-coating layer may have the same or different composition as the first sub-coating layer. Specifically, the third sub-coating layer is coated on the surface of the second sub-coating layer and contains a thermally conductive material with good thermal conductivity. The second sub-coating layer is coated on the surface of the first sub-coating layer and contains both a thermally conductive material and a negative electrode active material, wherein the thermal conductivity of the thermally conductive material is stronger than that of the active material.

[0056] Optionally, a paste layer is provided on both opposite sides of the current collector.

[0057] In this embodiment, three sub-coating layers are symmetrically distributed on both sides of the current collector, and the current collector is disposed between the upper and lower three sub-coating layers.

[0058] This invention provides a negative electrode sheet and a lithium-ion battery. The negative electrode sheet includes a current collector and a paste layer. The paste layer includes a first sub-paste layer, a second sub-paste layer, and a third sub-paste layer, which are sequentially stacked, with the second sub-paste layer located between the first and third sub-paste layers. The paste layer is coated on the surface of the current collector, and the first sub-paste layer is in contact with the current collector. The first sub-paste layer includes at least one of gold fiber, silver fiber, copper fiber, carbon fiber, and graphene; and / or, the third sub-paste layer includes at least one of gold fiber, silver fiber, copper fiber, carbon fiber, and graphene. The second sub-paste layer includes a negative electrode active material and a thermally conductive material. The thermal conductivity of the first sub-paste layer is greater than that of the second sub-paste layer, and the thermal conductivity of the third sub-paste layer is greater than that of the second sub-paste layer.

[0059] The negative electrode sheet provided in this embodiment of the invention comprises three sub-paste layers with different thermal conductivity on the negative electrode current collector. The first sub-paste layer is in contact with the negative electrode current collector and includes a thermally conductive material, which can uniformly transfer heat from the copper foil side to the second sub-paste layer of the negative electrode sheet. The third sub-paste layer also includes a thermally conductive material, which can uniformly conduct heat from the positive electrode side to the second sub-paste layer, which includes the negative electrode active material. The second sub-paste layer includes the negative electrode active material and a thermally conductive material and is disposed between the first and third sub-paste layers, which can uniformly transfer heat from both sides to the negative electrode active material, causing heat to accumulate in the second sub-paste layer. The negative electrode active material in the second sub-paste layer has a low internal resistance, so even when the heat is high, the temperature on the negative electrode side rises. By utilizing the temperature rise caused by the battery's internal resistance, the charging rate of the lithium-ion battery is improved, and the rate performance of the negative electrode is enhanced during high-current charging and discharging.

[0060] By designing the negative electrode structure, each of the three sub-coating layers contains thermally conductive material, forming a connected thermally conductive network with the negative electrode current collector (preferably copper foil). This enhances conductivity and allows the significant heat generated by the high internal resistance of the positive electrode during fast charging to be quickly conducted to the negative electrode active material through the thermally conductive network formed by the three-layer structure. This increases the temperature on the negative electrode side, improves the chemical reaction dynamics, and enhances the charging rate and rate performance of the negative electrode during high-current charging and discharging of the lithium-ion battery.

[0061] In other embodiments, a lithium-ion battery is also provided, the lithium-ion battery comprising a negative electrode as described in any of the preceding embodiments.

[0062] In this embodiment, the manufacturing process of the lithium-ion battery is as follows:

[0063] Example 1

[0064] Preparation of the positive electrode sheet: The slurry composition of the positive electrode active material layer is as follows: lithium cobalt oxide, acetylene black and polyvinylidene fluoride are added to a mixing tank in a mass ratio of 96:1.2:1.5:1.3, N-methylpyrrolidone solvent is added and stirred, and then the mixture is passed through a 200-mesh sieve to prepare a slurry (positive electrode active material layer slurry) with a solid content of 70wt%.

[0065] The slurry is coated onto the positive electrode current collector (aluminum foil) using a coating machine, dried at 120℃, and then rolled to obtain the positive electrode sheet, the structure of which is as follows. Figure 2 As shown.

[0066] Preparation of negative electrode:

[0067] First functional slurry (first sub-coating layer slurry, third sub-coating layer slurry): Gold fiber, conductive carbon black and styrene-butadiene rubber are added to a mixing tank at a mass ratio of 96.1:1.9:2. After adding deionized water solvent and stirring, the mixture is passed through a 200-mesh sieve to prepare a first functional slurry with a solid content of 40wt%-45wt%.

[0068] The second functional slurry (second sub-coating layer slurry): The slurry composition of the negative electrode active material layer is: graphite, gold fiber, conductive carbon black, and styrene-butadiene rubber. These are added to a mixing tank at a mass ratio of 96:1.2:1.5:1.3. After adding deionized water and stirring, the mixture is passed through a 200-mesh sieve to prepare the negative electrode active material layer slurry, with a solid content of 42 wt%. The first sub-coating layer slurry, the second sub-coating layer slurry, and the third sub-coating layer slurry are sequentially coated onto a 5 μm thick negative electrode current collector (copper foil) using a transfer coating machine or an extrusion coating machine. The coating is dried at 120℃ and then rolled to obtain the negative electrode sheet.

[0069] After drying and rolling, the first sub-coating slurry forms a first sub-coating layer with a thickness of 2μm, the second sub-coating slurry forms a second sub-coating layer with a thickness of 65μm, and the third sub-coating slurry forms a third sub-coating layer with a thickness of 2μm.

[0070] Assemble the battery cell: The negative electrode sheet, positive electrode sheet and separator prepared above are wound together to form a core (width is 62mm), packaged with aluminum-plastic film, baked to remove moisture, injected with electrolyte, and hot-pressed to form the battery cell.

[0071] Example 2

[0072] The preparation steps of the lithium-ion battery in this embodiment are basically the same as those in Example 1, except that the gold fiber, which is a thermally conductive functional material in the first sub-coating layer, is replaced with silver fiber.

[0073] Example 3

[0074] The preparation steps of the lithium-ion battery in this embodiment are basically the same as those in Example 1, except that the gold fiber, which is a thermally conductive functional material in the first sub-coating layer, is replaced with copper fiber.

[0075] Example 4

[0076] The preparation steps of the lithium-ion battery in this embodiment are basically the same as those in Example 1. The difference is that the heat-conducting functional material gold fiber in the first sub-coating layer is replaced with graphene.

[0077] Example 5

[0078] The preparation steps of the lithium-ion battery in this embodiment are basically the same as those in Embodiment 1. The difference is that the thermally conductive functional material gold fiber in the first sub-coating layer is replaced with carbon fiber.

[0079] Example 6a

[0080] The preparation steps of the lithium-ion battery in this embodiment are basically the same as those in Example 1. The difference is that the first sub-coating layer includes 97.2% gold fiber, 1.5% conductive agent and 1.3% binder by mass percentage.

[0081] Example 6b

[0082] The preparation steps of the lithium-ion battery in this embodiment are basically the same as those in Example 1. The difference is that the second sub-coating layer includes 95.5% negative electrode active material, 1.5% gold fiber, 1.5% conductive agent and 1.3% binder by mass percentage.

[0083] Example 7a

[0084] The preparation steps of the lithium-ion battery in this embodiment are basically the same as those in Example 1. The difference is that the first sub-coating layer includes 94% gold fiber, 2.5% conductive agent and 3.5% binder by mass percentage.

[0085] Example 7b

[0086] The preparation steps of the lithium-ion battery in this embodiment are basically the same as those in Example 1. The difference is that the second sub-coating layer includes 96.5% negative electrode active material, 0.5% gold fiber, 1.5% conductive agent and 1.3% binder by mass percentage.

[0087] Example 8a

[0088] The preparation steps of the lithium-ion battery in this embodiment are basically the same as those in Example 1, except that the thickness of the first sub-coating layer is 1 μm.

[0089] Example 8b

[0090] The preparation steps of the lithium-ion battery in this embodiment are basically the same as those in Example 1, except that the thickness of the first sub-coating layer is 6 μm.

[0091] Comparative Example 1

[0092] The preparation steps of the lithium-ion battery in this embodiment are basically the same as those in Embodiment 1. The difference is that no thermally conductive material is added to the second sub-coating layer.

[0093] Comparative Example 2

[0094] The preparation steps of the lithium-ion battery in this embodiment are basically the same as those in Embodiment 1. The difference is that there is no first sub-coating layer and a third sub-coating layer. The second sub-coating layer is made of thermally conductive material and has a coating thickness of 65 μm.

[0095] Comparative Example 3

[0096] The preparation steps of the lithium-ion battery in this embodiment are basically the same as those in Embodiment 1. The difference is that there is no first sub-coating layer and a third sub-coating layer, and no thermally conductive material is added to the second sub-coating layer. The coating thickness is 65μm.

[0097] All lithium-ion battery positive and negative electrode sheets were fabricated into different cells, and the cell capacity was tested at 0.2C / 0.2C charge and discharge at 25℃. The energy density of the battery was calculated according to capacity * voltage / thickness / width / height. The cycle performance at 4C / 1C at 25℃ was also tested. The battery was disassembled after the same number of cycles to confirm the lithium deposition in the edge area of ​​the negative electrode sheet. The experimental results of the disassembly are shown in Table 1.

[0098]

[0099] Table 1

[0100] 1. Compared with Comparative Examples 1 and 3, the application of (thermal conductive functional material base coating + surface thermal conductive coating) can significantly improve the 4C rate fast charging performance of the battery cell; compared with Comparative Examples 2 and 3, the application of thermal conductive functional material mixed in the active material can also significantly improve the 4C rate fast charging performance of the battery cell; compared with Examples 1-8 and Comparative Examples 1 and 2, the application of thermal conductive functional material mixed in the active material and base coating on the current collector can further significantly improve the 4C rate fast charging performance of the battery cell;

[0101] 2. Comparing Examples 1 and 2, 3, 4 and 5, under the premise of basically the same energy density, the battery cell using gold fiber thermal conductive material has the best 4C rate fast charging performance.

[0102] 3. Comparing Example 1 and Example 6, the energy density is the highest when the optimal mixing ratio is used, and the 4C rate fast charging performance of the battery cell can be maximized.

[0103] 4. Comparing Example 1 and Example 7, when too little thermally conductive material is mixed in, the improvement effect on the 4C rate fast charging performance of the battery cell cannot meet the requirements.

[0104] 5. Comparing Example 1 and Example 8, the first and third sub-coating layers with thermal conductivity are too thin and fail to achieve the optimal lithium plating improvement effect; if they are too thick, the cell thickness will be increased and more energy density will be lost.

[0105] The capacity retention rate is calculated as follows: The battery is placed in a 25°C environment and charged at a constant current and constant voltage of 4C to 4.48V. It is then charged at 4.48V to the cutoff current of 0.05C. Afterward, it is allowed to stand for 15 minutes and discharged at a 1C current to 3V. The initial capacity is recorded as Q1, and the capacity after 500 cycles is recorded as Q2. The capacity retention rate after room temperature cycling is calculated using the following formula:

[0106] Capacity retention rate (%) = (Q2 / Q1) × 100%.

[0107] In summary, while prioritizing improved 4C fast charging performance, it is crucial to maintain a high energy density as much as possible. This leads to the optimal addition amount and type of thermally conductive material for both the first and second sub-coating layers, as well as the optimal thickness of the first sub-coating layer.

[0108] The negative electrode sheet provided in this embodiment of the invention comprises three sub-paste layers with different thermal conductivity on the negative electrode current collector. The first sub-paste layer is in contact with the negative electrode current collector and includes a thermally conductive material, which can uniformly transfer heat from the copper foil side to the second sub-paste layer of the negative electrode sheet. The third sub-paste layer also includes a thermally conductive material, which can uniformly conduct heat from the positive electrode side to the second sub-paste layer, which includes the negative electrode active material. The second sub-paste layer includes the negative electrode active material and a thermally conductive material and is disposed between the first and third sub-paste layers, which can uniformly transfer heat from both sides to the negative electrode active material, causing heat to accumulate in the second sub-paste layer. The negative electrode active material in the second sub-paste layer has a low internal resistance, so even when the heat is high, the temperature on the negative electrode side rises. By utilizing the temperature rise caused by the battery's internal resistance, the charging rate of the lithium-ion battery is improved, and the rate performance of the negative electrode is enhanced during high-current charging and discharging.

[0109] By designing the negative electrode structure, each of the three sub-coating layers contains thermally conductive material, forming a connected thermally conductive network with the negative electrode current collector (preferably copper foil). This enhances conductivity and allows the significant heat generated by the high internal resistance of the positive electrode during fast charging to be quickly conducted to the negative electrode active material through the thermally conductive network formed by the three-layer structure. This increases the temperature on the negative electrode side, improves the chemical reaction dynamics, and enhances the charging rate and rate performance of the negative electrode during high-current charging and discharging of the lithium-ion battery.

[0110] Note that the above description is merely a preferred embodiment of the present invention and the technical principles employed. Those skilled in the art will understand that the present invention is not limited to the specific embodiments described herein, and various obvious changes, readjustments, and substitutions can be made without departing from the scope of protection of the present invention. Therefore, although the present invention has been described in detail through the above embodiments, the present invention is not limited to the above embodiments, and may include many other equivalent embodiments without departing from the concept of the present invention, the scope of which is determined by the scope of the appended claims.

Claims

1. A negative electrode sheet, characterized in that, include: The current collector and the coating layer, wherein the coating layer includes a first sub-coating layer, a second sub-coating layer and a third sub-coating layer, wherein the first sub-coating layer, the second sub-coating layer and the third sub-coating layer are stacked sequentially, and the second sub-coating layer is located between the first sub-coating layer and the third sub-coating layer; The paste layer is applied to the surface of the current collector, and the first sub-paste layer is in contact with the current collector; The first sub-coating layer includes a thermally conductive material, which includes at least one of gold fiber, silver fiber, copper fiber, and carbon fiber. The third sub-coating layer includes a thermally conductive material, which includes at least one of gold fiber, silver fiber, copper fiber and carbon fiber. The second sub-coating layer includes a negative electrode active material and a thermally conductive substance; Wherein, the thermal conductivity of the first sub-coating layer is greater than that of the second sub-coating layer, and the thermal conductivity of the third sub-coating layer is greater than that of the second sub-coating layer. The mass percentage of the thermally conductive material in the first sub-coating layer is 60% to 99%, the mass percentage of the thermally conductive material in the second sub-coating layer is 0.1% to 5%, and the mass percentage of the thermally conductive material in the third sub-coating layer is 60% to 99%.

2. The negative electrode sheet according to claim 1, characterized in that, The first sub-coating layer, the second sub-coating layer, and the third sub-coating layer all have the same length along the electrode winding direction.

3. The negative electrode sheet according to claim 1, characterized in that, The thickness of the second sub-coating layer is greater than the thickness of the first sub-coating layer, and the thickness of the second sub-coating layer is greater than the thickness of the third sub-coating layer.

4. The negative electrode sheet according to claim 1, characterized in that, The thickness of the first sub-coating layer is in the range of 2μm to 5μm.

5. The negative electrode sheet according to claim 1, characterized in that, The thickness of the third sub-coating layer is in the range of 2μm to 5μm.

6. The negative electrode sheet according to claim 1, characterized in that... The thickness of the second sub-coating layer is in the range of 50μm to 150μm, and the thermally conductive material in the second sub-coating layer accounts for 1% to 3% of the total material content.

7. The negative electrode sheet according to claim 1, characterized in that, The second sub-coating layer includes at least one of the following thermally conductive materials: gold fiber, silver fiber, copper fiber, carbon fiber, and graphene.

8. The negative electrode sheet according to claim 1, characterized in that, The negative electrode active material includes at least one of silicon-carbon, silicon-oxygen, graphite, metal oxide, and silicon-based alloy.

9. The negative electrode sheet according to claim 1, characterized in that, A paste layer is provided on both sides of the current collector.

10. A lithium-ion battery, characterized in that, The lithium-ion battery includes a negative electrode sheet as described in any one of claims 1-9.

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