Negative pole piece and preparation method therefor, lithium-ion battery, battery pack, and electronic device

Abstract

A negative pole piece and a preparation method therefor, a lithium-ion battery, a battery pack, and an electronic device. The negative pole piece comprises: a columnar current collector, as well as an active material layer and a coating layer which are alternately coated on an outer surface of the columnar current collector. A first layer coated on the outer surface of the columnar current collector is the active material layer, there are at least two layers of both the active material layer and the coating layer, the total thickness of the active material layers is 1 μm to 5 μm, and the total thickness of the coating layers is 50 nm to 300 nm. The described negative pole piece can improve the dynamic performance of a battery, and can effectively inhibit the problem of volume expansion caused by the charging and discharging processes of the battery.

Description

Negative electrode sheet and preparation method thereof, lithium-ion battery, battery pack, and electronic equipment

[0001] Related cross-references

[0002] This disclosure claims priority to the Chinese patent application filed with the China Patent Office on December 25, 2023, with application number 2023117982232 and application name “Negative electrode sheet and preparation method thereof, lithium-ion battery, battery pack, electronic device”, the entire contents of which are incorporated by reference in this disclosure. Technical Field

[0003] The present application relates to the field of battery negative electrodes, and in particular to a negative electrode sheet and a preparation method thereof, a lithium-ion battery, a battery pack, and an electronic device. Background Art

[0004] In recent years, with the development of lithium-ion batteries, the market demand for high-energy-density batteries has become increasingly strong. Silicon, germanium, and tin, due to their high gram capacity, are considered the most promising lithium-ion battery anode materials. However, during use, these materials can cause lithium-ion batteries to suffer from poor conductivity, weak electrode strength, poor adhesion, and significant volume expansion, thereby reducing the electrochemical performance of lithium-ion batteries.

[0005] Based on this, the performance of the negative electrode active material layer can be improved by coating it with a layer of material. However, due to the thickness of the active material layer, a thicker coating layer is required to achieve complete coverage. This increases the thickness of the negative electrode sheet, thereby increasing the transport resistance of ions and electrons, which adversely affects the battery's dynamic performance. In addition, while a single-layer coating can alleviate the volume expansion of the battery during the charge and discharge process, it is difficult to effectively solve the problem of active material shedding caused by this expansion, which has an adverse effect on the battery's electrochemical performance.

[0006] Summary of the Invention

[0007] The embodiments of the present application disclose a negative electrode plate and a preparation method thereof, a lithium-ion battery, a battery pack, and an electronic device to solve the problem in the prior art that the thickness of the negative electrode plate and the coating layer is relatively thick, which hinders the dynamic performance of the battery and makes it difficult to effectively alleviate the volume expansion caused by the battery charging and discharging process.

[0008] In the first aspect, an embodiment of the present application provides a negative electrode plate, which includes a columnar current collector, an active material layer and a coating layer alternately coated on the outer surface of the columnar current collector, wherein the first layer coated on the outer surface of the columnar current collector is the active material layer, the number of layers of the active material layer and the coating layer is at least two, the total thickness of the active material layer is 1μm to 5μm, and the total thickness of the coating layer is 50nm to 300nm.

[0009] Furthermore, the number of the coating layer is 2 to 10 layers, and the number of the active material layer is 2 to 10 layers.

[0010] Furthermore, the thicknesses of adjacent active material layers are the same, and the thickness of a single layer of the active material layer in any layer is 0.1 μm to 2.5 μm; the thicknesses of adjacent coating layers are the same, and the thickness of a single layer of the coating layer in any layer is 5 nm to 150 nm.

[0011] Furthermore, the ratio of the single layer thickness of the active material layer to the single layer thickness of the coating layer is 25:1 to 4:1.

[0012] Furthermore, the active material of the active material layer is at least one of silicon, silicon oxide, carbon, germanium, tin, germanium oxide, and tin oxide.

[0013] Furthermore, the active material is silicon or silicon oxide, and the coating material of the coating layer is carbon, germanium, tin, germanium oxide, or tin oxide.

[0014] Furthermore, the structure of the negative electrode plate includes the columnar current collector, a first active material layer, a first coating layer, a second active material layer, and a second coating layer. The active material is silicon, the coating material is carbon, the thickness of the first active material layer and the second active material layer are both 0.5 μm, and the thickness of the first coating layer and the second coating layer are both 100 nm.

[0015] Furthermore, the negative electrode plate further includes a transition layer provided between the active material layer and the coating layer, and the sum of the total thickness of the transition layer and the coating layer is 50 nm to 300 nm.

[0016] Furthermore, the ratio of the single layer thickness of the transition layer to the single layer thickness of the coating layer is 1:25 to 1:1.

[0017] Furthermore, the transition material of the transition layer is at least one of titanium, nickel, chromium or stainless steel.

[0018] Furthermore, the active material is silicon or silicon oxide, and the coating material is ceramic oxide.

[0019] Furthermore, the diameter of the columnar current collector is 5 μm to 50 μm.

[0020] Furthermore, the columnar current collector is at least one of copper, nickel, stainless steel, and a conductive carbon-based material.

[0021] Furthermore, the active material layer is prepared by at least one of chemical vapor deposition, physical vapor deposition, spraying, electroplating, coating, and ball milling, and the coating layer is prepared by at least one of chemical vapor deposition, physical vapor deposition, spraying, electroplating, coating, and ball milling.

[0022] In a second aspect, an embodiment of the present application provides a method for preparing a negative electrode sheet as described in the first aspect, the preparation method comprising the following steps:

[0023] providing the columnar current collector;

[0024] The active material and the coating material are alternately coated on the outer surface of the columnar current collector in sequence by using a magnetron sputtering method to form the active material layer and the coating layer.

[0025] In a third aspect, the present application provides a lithium-ion battery, comprising the negative electrode sheet described in the first aspect.

[0026] In a fourth aspect, the present application provides a battery pack, comprising a box and a lithium-ion battery as described in the third aspect placed in the box.

[0027] In a fifth aspect, the present application provides an electronic device, comprising an electronic device body and a lithium-ion battery as described in the third aspect for powering the electronic device body.

[0028] Compared with the prior art, the present invention has the following advantages:

[0029] The present invention provides a negative electrode plate comprising a columnar current collector, an active material layer and a coating layer alternately coated on the outer surface of the columnar current collector. The active material layer has a total thickness of 1 μm to 5 μm, the coating layer has a total thickness of 50 nm to 300 nm, and the active material layer and coating layer have at least two layers. This design helps suppress volume expansion during battery charge and discharge, reduces the risk of active material shedding, improves ion and electron transport resistance, increases battery kinetic performance, and enhances battery electrochemical performance.

[0030] On the one hand, the negative electrode provided by the present application can select the coating material in a targeted manner according to the properties of the active material in the active material layer, so that the coating material can optimize and improve the active material, thereby improving the electrochemical performance of the lithium-ion battery; on the other hand, since the total thickness of the active material layer and the coating layer is constant, and a multi-layer alternating coating method is adopted, compared with a single-layer coating, the multi-layer alternating coating method makes the number of active material layers larger, and the thickness of any active material layer becomes thinner, thereby reducing the difficulty of coating, improving the uniformity of coating, and avoiding the phenomenon of uneven coating of the coating layer caused by a thick active material layer during the coating process; and since the coating material The material optimizes the performance of the active material. The multi-layer coating method makes the contact area between the coating layer and the active material layer higher, thereby improving the degree of optimization of the active material by the coating material and improving the electrochemical performance of the battery. In addition, since the coating layer has a certain strength, the expansion of the single-layer active material layer is reduced by adopting this alternating coating method, so that the coating layer can largely inhibit the expansion of the active material layer, reducing the risk of active material falling off, thereby improving the electrochemical performance of the battery. Moreover, the use of this coating method does not increase the thickness of the negative electrode sheet, and the multi-layer structure is also conducive to improving the transmission path of ions and electrons, thereby increasing the kinetic performance of the battery. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the following briefly introduces the drawings required for use in the embodiments. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0032] FIG1 is a cross-sectional view of a negative electrode sheet having two layers of active material layer and coating layer provided in an embodiment of the present application;

[0033] FIG2 is a cross-sectional view of a negative electrode sheet in which the coating layer and the active material layer are single layers according to the prior art provided by an embodiment of the present application;

[0034] FIG3 is an electrochemical performance test diagram provided by Example 1 and Comparative 1 of the present application;

[0035] FIG4 is an electron microscope image of the negative electrode sheet provided in Example 6 of the present application.

[0036] Icon: 1. Columnar current collector; 2. Active material layer; 21. First active material layer; 22. Second active material layer; 3. Coating layer; 31. First coating layer; 32. Second coating layer. DETAILED DESCRIPTION

[0037] The following will be combined with the drawings in the embodiments of this application to clearly and completely describe the technical solutions in the embodiments of this application. Obviously, the embodiments described are only part of the embodiments of this application, not all of the embodiments. Based on the embodiments in this application, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of this application.

[0038] In this application, terms such as "upper," "lower," "left," "right," "front," "back," "top," "bottom," "inner," "outer," "center," "vertical," "horizontal," "transverse," and "longitudinal" indicate positions or locations based on the positions or locations shown in the accompanying drawings. These terms are primarily intended to better describe this application and its embodiments and are not intended to limit the devices, elements, or components indicated to having a specific orientation, or to being constructed or operated in a specific orientation.

[0039] Furthermore, some of the above terms may be used to express other meanings besides indicating a position or location. For example, the term "on" may also be used to indicate a dependency or connection in certain circumstances. Those skilled in the art will understand the specific meanings of these terms in this application based on the specific circumstances.

[0040] Furthermore, the terms "first," "second," etc., are primarily used to distinguish between different devices, elements, or components (which may or may not be of the same type and configuration), and are not intended to indicate or imply the relative importance or quantity of the devices, elements, or components indicated. Unless otherwise specified, "plurality" means two or more.

[0041] The technical solution provided in this application will be further described below with reference to the embodiments and drawings.

[0042] With the development of lithium-ion batteries, they have been widely used in products such as laptops, mobile phones, Bluetooth headsets, and new energy vehicles. The market demand for lithium-ion batteries has increased, and higher performance requirements have been placed on lithium-ion batteries. However, negative electrode materials have problems such as poor conductivity and high expansion, which have a negative impact on the performance of lithium-ion batteries.

[0043] In order to further improve the performance of negative electrode materials, surface coating modification is one of the effective means. Usually, the surface coating layer can be tough or flexible. It not only needs to be able to buffer stress, but also has excellent conductivity, providing a fast transport channel for lithium ions and electrolytes, and has high stability, which can keep the silicon negative electrode relatively independent and protect the silicon negative electrode from the influence of the electrolyte. The surface coating layer needs to effectively relieve the mechanical stress caused by the huge volume expansion to improve the stability of the negative electrode structure. At the same time, it can ensure that the surface SEI film can exist stably. However, although a single coating can improve the conductivity of the negative electrode material and inhibit volume expansion, the thickness of the active material layer is relatively high, resulting in a higher impedance of the negative electrode sheet. When the thick active material layer needs to be fully coated, the thickness of the coating layer is large, which increases the thickness of the negative electrode sheet, increases the transmission distance, and hinders the transmission of ions and electrons, which hinders the kinetic performance of the battery and has an adverse effect on the electrochemical performance of the lithium-ion battery.

[0044] Based on this, an embodiment of the present application provides a negative electrode plate, which solves the problems of poor conductivity and easy volume expansion during cycling when materials such as silicon are used as negative electrodes by alternately coating active material layers and coating layers on the current collector. At the same time, it improves the coating effect and increases the uniformity of the coating, thereby further optimizing the electrochemical performance of the lithium-ion battery.

[0045] In the first aspect, an embodiment of the present application provides a negative electrode plate, which includes a columnar current collector, an active material layer alternately coated on the outer surface of the columnar current collector, and a coating layer, wherein the first layer coated on the outer surface of the columnar current collector is an active material layer, the number of layers of the active material layer and the coating layer are at least two, the total thickness of the active material layer is 1μm to 5μm, and the total thickness of the coating layer is 50nm to 300nm.

[0046] In the embodiments of this application, active material layers and coating layers are directly coated on the outer surface of a columnar current collector. The first layer coated on the outer surface of the columnar current collector is the active material layer, and the number of coating layers is at least two. From the perspective of coating material selection, since the selection of the coating material has a certain optimization effect on the active material, as the number of coating layers increases, the contact area between the active material layer and the coating layer increases, which helps to enhance the coating material's optimization effect on the active material. From a structural point of view, the alternating coating method increases the number of coating layers, but in fact the total thickness of the active material layer and the coating layer does not change. Therefore, the thickness of the single-layer active material layer and the single-layer coating layer is relatively low, which is conducive to improving the uniformity of the coating layer coating; and the alternating coating structure, due to the increase in the number of layers, the thickness of the active material layer coated by the coating layer is relatively low, so the expansion effect of the active material layer is dispersed, thereby enhancing the inhibitory effect of the coating layer on the expansion effect of the active material layer, effectively reducing the occurrence of battery expansion during the cycle, and improving the electrochemical performance of the lithium-ion battery; in addition, due to the use of this alternating coating form, as the interface between the active material layer and the coating layer increases, the transmission resistance of the electron and ion transmission process decreases, which helps to improve the kinetic performance of the battery.

[0047] It should be emphasized that the number of active material layers is consistent with the number of coating layers, and the coating material of the coating layer can be selected according to the properties of the active material in the active material layer. If it is necessary to improve the conductivity of the active material layer, the coating material of the coating layer can be selected to improve the conductivity of the electrode; if it is necessary to improve the adhesion of the active material layer, the coating material of the coating layer can be selected to improve the adhesion of the electrode; or a coating material that can simultaneously improve the conductivity or adhesion of the electrode can be selected.

[0048] Compared with the method of directly coating the active material and then directly coating the composite active material obtained after coating on the current collector, the direct coating on the current collector in the present application not only reduces the difficulty of the negative electrode plate manufacturing process and improves the processing efficiency of the negative electrode plate, but also avoids the composite active material in the rolling process. If the particle structure stability is poor, it will cause serious particle deformation and damage to the coating layer. The composite active material coated on the plate has an uneven structure, resulting in differences in performance of different regions of the negative electrode plate, thereby adversely affecting the electrochemical performance of the lithium-ion battery.

[0049] When the total thickness of the active material layer 2 and the total thickness of the coating layer 3 are the same, as shown in Figure 1, Figure 1 shows a negative electrode sheet in which both the active material layer 2 and the coating layer 3 are two layers, and the negative electrode sheet includes a columnar current collector 1, a first active material layer 21, a first coating layer 31, a second active material layer 22, and a second coating layer 32 alternately coated on the outer surface of the columnar current collector 1, wherein the contact area between the active material layer 2 and the coating layer 3 is large, which can effectively improve the performance of the negative electrode sheet, and this alternatingly coated multi-layer structure, as the interface between the coating layer 3 and the active material layer 2 increases, is conducive to improving the dynamic performance of the battery. In addition, the volume expansion phenomenon of the first active material layer 21 is not only limited by the first coating layer 31, but also constrained by the second active material layer 22 and the second coating layer 32, so that the volume expansion phenomenon of the negative electrode sheet during the battery cycle is effectively improved. As shown in Figure 2, a single-layer coating structure is shown, showing an active material layer 2 and a coating layer 3 sequentially coated on the outer surface of a columnar current collector 1. The contact area between the active material layer 2 and the coating layer 3 is small, and the number of interfaces is low. Therefore, the performance improvement of the negative electrode sheet is small, and the effect of suppressing volume expansion is limited. In other words, the multi-layer alternating coating method adopted in this application can effectively improve the conductivity of the negative electrode sheet, suppress volume expansion, and improve the dynamic performance of the battery.

[0050] Furthermore, the number of the coating layer is 2 to 10 layers, and the number of the active material layer is 2 to 10 layers.

[0051] Within this range of the number of layers, the coating uniformity of the active material layer is ensured, which is not only beneficial to the improvement of the properties of the active material layer by the coating layer, but also helps to suppress the volume expansion of the active material layer, reduce the thickness of the active material layer, and thus help to reduce the impedance of the battery and improve the electrochemical performance of the battery. If the number of layers is higher than this range, the difficulty and cost of the process preparation increase, and it is difficult to ensure the uniformity of the coating; if the number of layers is lower than this range, the effect of suppressing the volume expansion of the negative electrode sheet is poor, and the impedance of the battery is increased, and the dynamic performance of the battery is limited. Exemplarily, the number of coating layers is 2 layers, 4 layers, 6 layers, 8 layers, 10 layers, etc., and the number of active material layers is 2 layers, 4 layers, 6 layers, 8 layers, 10 layers, etc.

[0052] Furthermore, adjacent active material layers have the same thickness, and the thickness of any active material layer is 0.1 μm to 2.5 μm; adjacent coating layers have the same thickness, and the thickness of any coating layer is 5 nm to 150 nm.

[0053] From the perspective of process preparation, since the thickness of adjacent coating layers and active material layers is the same, when preparing a single layer of active material layer or coating layer, the preparation parameters are consistent, the preparation process is easier to control, and the process difficulty is reduced, which is conducive to large-scale production and development. In addition, the thickness of the single layer of active material layer within this range can provide abundant lithium storage space, reduce the risk of lithium plating, and thus improve the electrochemical performance of the battery. If the thickness of the active material layer is too high, in order to ensure the uniformity of the coating, the thickness of the coating layer will also increase, resulting in an increase in the migration distance of electrons and ions and hindering the kinetic performance of the battery. If the thickness of the active material layer is too low, the lithium storage space provided by the active material is limited, and the battery is prone to lithium plating. The thickness of the coating layer within this range can not only ensure a high content of the coating material, but also fully contact the active material layer, so that the conductivity of the battery is significantly improved. If the thickness of the coating layer is too low, it is difficult to ensure the uniformity of the coating. If the thickness of the coating layer is too high, the thickness of the electrode increases, which is not conducive to improving the kinetic performance of the battery.

[0054] It should be noted that if there are three active material layers, "adjacent" means that the thickness of the first active material layer is the same as that of the second active material layer, and the thickness of the second active material layer is the same as that of the third active material layer. That is, the thickness of the first active material layer, the second active material layer, and the third active material layer are the same, which means that the thickness of each single active material layer is the same. The meaning of "adjacent coating layers" here is consistent with the meaning of "adjacent active material layers," meaning that the thickness of each single coating layer is the same.

[0055] Furthermore, the ratio of the single layer thickness of the active material layer to the single layer thickness of the coating layer is 25:1 to 4:1.

[0056] Within this ratio range, the coating layer can completely coat the outer surface of the active material, with a high degree of match to the active material layer. This effectively suppresses volume expansion during charge and discharge during battery cycling, thereby improving the battery's electrochemical performance. Below this range, the coating layer's uniformity is poor, hindering the suppression of battery volume expansion. Above this range, the resulting negative electrode sheet becomes too thick, increasing the distance for ion and electron transport and hindering improvements in battery kinetic performance. For example, the ratio of the active material layer's single-layer thickness to the coating layer's single-layer thickness is 25:1, 15:1, 10:1, 5:1, 4:1, and the like.

[0057] Furthermore, the active material of the active material layer is at least one of silicon, silicon oxide, carbon, germanium, tin, germanium oxide, and tin oxide.

[0058] The choice of active material for the active material layer determines the performance of the negative electrode active material layer, allowing for targeted selection of coating materials to improve the electrochemical performance of the battery. Exemplary active materials include silicon, silicon oxide, silicon oxide and carbon, or germanium, tin, and germanium oxide.

[0059] Furthermore, the active material is silicon or silicon oxide, and the coating material of the coating layer is carbon, germanium, tin, germanium oxide, or tin oxide.

[0060] When silicon or silicon oxide is selected as the active material, the conductivity of the active material is relatively poor. In order to further improve the conductive effect of the active material layer, carbon, germanium, tin, germanium oxide, and tin oxide are selected as the coating material of the coating layer, which can further improve the conductive effect of silicon or silicon oxide, thereby improving the electrochemical performance of the battery.

[0061] Furthermore, the structure of the negative electrode plate includes a columnar current collector, a first active material layer, a first coating layer, a second active material layer, and a second coating layer. The active material is silicon, and the coating material is carbon. The thickness of the first active material layer and the second active material layer is 0.5 μm, and the thickness of the first coating layer and the second coating layer is 100 nm.

[0062] Silicon is chosen as the active material and carbon as the coating material, with two layers of coating and active material each. This increases the contact area between the active material layer and the coating layer, thereby improving the conductivity of the negative electrode. The thickness of the active material layer is 0.5μm, and the coating layer is 100nm, ensuring uniform coating and helping to improve the degree to which the coating layer suppresses the volume expansion of the active material layer during the charge and discharge process of the negative electrode.

[0063] Furthermore, the negative electrode plate further includes a transition layer provided between the active material layer and the coating layer, and the total thickness of the transition layer and the coating layer is 50 nm to 300 nm.

[0064] As the number of alternating coating layers increases, the adhesion between the coating layer and the active material layer may become poor. By introducing a transition layer design, the adhesion between the active material layer and the coating layer is improved, reducing the impact of multi-layer coating on the electrode adhesion. Moreover, within this range, the total thickness of the electrode does not change, ensuring the uniformity of the transition layer and coating layer coating. This will not have a significant impact on the performance of the battery. On the contrary, the presence of the transition layer will increase the adhesion of the electrode, preventing the active material from falling off during the battery cycle and causing adverse effects on the battery. For example, the sum of the total thickness of the transition layer and the coating layer is 50nm, 100nm, 150nm, 200nm, 250nm, and 300nm.

[0065] Furthermore, the ratio of the single layer thickness of the transition layer to the single layer thickness of the coating layer is 1:25 to 1:1.

[0066] Within this ratio range, the coating layer can completely cover the outer surface of the transition layer, and the transition layer can completely cover the outer surface of the active material layer. If it is below this range, the uniformity of the transition layer coating is poor, and some areas may not be coated, which is not conducive to improving the adhesion of the battery. If it is above this range, the coating thickness of the transition layer is too high, resulting in a low coating thickness, which leads to poor coating uniformity and difficulty in effectively improving the performance of the negative electrode sheet. For example, the ratio of the single layer thickness of the transition layer to the single layer thickness of the coating layer is 1:25, 1:15, 1:10, 1:5, 1:1, etc.

[0067] Furthermore, the transition material of the transition layer is at least one of titanium, nickel, chromium or stainless steel.

[0068] Since the active material layer is silicon and the coating layer is carbon, the transition material for the transition layer is selected from the aforementioned materials. The transition material's thermal expansion coefficient is between that of silicon and carbon, strengthening the bond between silicon and carbon. This improves the bonding strength of the negative electrode, reduces the impact of multi-layer coating on electrode adhesion, and enhances the battery's electrochemical performance during cycling. Exemplary transition materials include titanium, nickel and chromium, or nickel, chromium, and stainless steel.

[0069] Furthermore, the active material is silicon or silicon oxide, and the coating material is ceramic oxide.

[0070] When silicon or silicon oxide is used as the active material, the battery expands significantly during charge and discharge. Furthermore, silicon reacts with fluorine in the electrolyte, affecting the formation of the solid electrolyte membrane and thus adversely affecting the battery's electrochemical performance. However, coating the negative electrode with a high-strength ceramic oxide not only suppresses the volume expansion of the negative electrode material, reducing battery safety risks, but also prevents the reaction between the negative electrode active material and fluorine, promoting the formation of a stable solid electrolyte membrane.

[0071] Furthermore, the diameter of the columnar current collector is 5 μm to 50 μm.

[0072] If the diameter of the columnar current collector is too thin, the strength of the pole piece will be low, and the current collector will easily deform and fracture, leading to safety issues. Since the current collector is an inactive component in the battery and does not participate in the reaction, if the columnar current collector is too thick, the proportion of inactive material in the lithium-ion battery will increase, increasing the electronic impedance and hindering the improvement of the battery's energy density. For example, the diameter of the columnar current collector is 5μm, 10μm, 15μm, 20μm, 25μm, 30μm, 40μm, 45μm, 50μm, etc.

[0073] Furthermore, the columnar current collector is at least one of copper, nickel, stainless steel, and a conductive carbon-based material.

[0074] When the columnar current collector is made of a metal material, the negative electrode active material layer is in direct contact with the metal, which not only improves the battery's conductivity but also increases the structural strength of the negative electrode sheet. Exemplarily, the columnar current collector is made of copper, nickel, stainless steel, or a conductive carbon-based material.

[0075] Furthermore, the active material layer is prepared by at least one of chemical vapor deposition, physical vapor deposition, spraying, electroplating, coating, and ball milling, and the coating layer is prepared by at least one of chemical vapor deposition, physical vapor deposition, spraying, electroplating, coating, and ball milling.

[0076] In a second aspect, an embodiment of the present application provides a method for preparing a negative electrode sheet as in the first aspect, the method comprising the following steps:

[0077] providing a columnar current collector;

[0078] The active material and the coating material are alternately coated on the outer surface of the columnar current collector by a magnetron sputtering method to form an active material layer and a coating layer.

[0079] The coating layer and active material layer are prepared by magnetron sputtering. The preparation process is simple and highly controllable. It can also avoid the phenomenon of large thermal stress and easy film collapse caused by continuous deposition of active material layer and coating layer.

[0080] Dividing the active material layer or coating layer into multiple layers with a smaller thickness of a single layer reduces the stress during the preparation process and the occurrence of film collapse, thereby improving the uniformity of the thickness of the active material layer and the coating layer.

[0081] In a third aspect, an embodiment of the present application provides a lithium-ion battery, which includes the negative electrode plate as described in the first aspect.

[0082] In a fourth aspect, an embodiment of the present application provides a battery pack, which includes the lithium-ion battery of the third aspect.

[0083] In a fifth aspect, an embodiment of the present application provides an electronic device, which includes an electronic device body and a lithium-ion battery as described in the third aspect for powering the electronic device body.

[0084] In order to provide a more detailed description of the technical solution and technical effects of the present application, the embodiments of the present application will be further described below through more specific embodiments, application examples and performance test results.

[0085] Example 1

[0086] An embodiment of the present application provides a negative electrode plate, which includes: a columnar current collector, a first active material layer, a first coating layer, a second active material layer, and a second coating layer alternately coated on the outer surface of the columnar current collector, wherein the first layer coated on the outer surface of the columnar current collector is the first active material layer, the number of layers of the active material layer and the coating layer is two, the total thickness of the active material layer is 1 μm, and the total thickness of the coating layer is 200 nm.

[0087] In this negative electrode sheet, the diameter of the columnar current collector is 5μm, the active material of the active material layer is silicon, the coating material of the coating layer is carbon, the thickness of the first active material layer and the second active material layer is 0.5μm, and the thickness of the first coating layer and the second coating layer is 100nm.

[0088] Preparation process of the negative electrode sheet:

[0089] The magnetron sputtering process is adopted, with silicon target and carbon target as working targets. During the deposition process, the power of silicon target (12KW) and carbon target (10KW) is kept unchanged to deposit the active material layer and the coating layer.

[0090] providing a columnar current collector;

[0091] A first active material layer with a thickness of 0.5 μm is deposited on the columnar current collector using a silicon target as a working target;

[0092] Depositing a first coating layer with a thickness of 100 nm on the first active material layer using a carbon target as a working target;

[0093] Using a silicon target as a working target, a second active material layer with a thickness of 0.5 μm is deposited on the first coating layer;

[0094] A second coating layer with a thickness of 100 nm was deposited on the second active material layer using a carbon target as a working target.

[0095] Example 2:

[0096] The only difference between this embodiment and the first embodiment is that the total thickness of the coating layer in this embodiment is 50 nm, and the thickness of the first coating layer and the second coating layer is 25 nm.

[0097] Example 3:

[0098] The only difference between this embodiment and the first embodiment is that the total thickness of the coating layer in this embodiment is 100 nm, and the thickness of the first coating layer and the second coating layer are both 50 nm.

[0099] Example 4:

[0100] The only difference between this embodiment and the first embodiment is that the total thickness of the coating layer in this embodiment is 250 nm, and the thickness of the first coating layer and the second coating layer are both 125 nm.

[0101] Embodiment 5:

[0102] The only difference between this embodiment and embodiment 1 is that the total thickness of the coating layer in this embodiment is 100 nm, the total thickness of the active material layer is 2.5 μm, the thickness of the first coating layer and the second coating layer are both 50 nm, and the thickness of the first active material layer and the second active material layer is 1.25 μm.

[0103] Example 6:

[0104] The only difference between this embodiment and embodiment 1 is that the total thickness of the coating layer in this embodiment is 164 nm, the total thickness of the active material layer is 3.6 μm, the thickness of the first coating layer and the second coating layer are both 82 nm, and the thickness of the first active material layer and the second active material layer is 1.8 μm.

[0105] Embodiment seven:

[0106] The only difference between this embodiment and the first embodiment is that the number of coating layers in this embodiment is 5, the total thickness of the active material layer is 2.5 μm, and the total thickness of the coating layer is 250 nm.

[0107] Embodiment 8:

[0108] The only difference between this embodiment and the first embodiment is that the number of coating layers in this embodiment is 10, the total thickness of the active material layer is 1 μm, and the total thickness of the coating layer is 50 nm.

[0109] Embodiment 9:

[0110] The only difference between this embodiment and the first embodiment is that the number of coating layers in this embodiment is 15, the total thickness of the active material layer is 5 μm, and the total thickness of the coating layer is 300 nm.

[0111] Embodiment 10:

[0112] The only difference between this embodiment and embodiment 1 is that this embodiment further includes a transition layer, the transition material of the transition layer is nickel, the total thickness of the coating layer and the transition layer is 200nm, wherein the thickness of the first transition layer and the second transition layer are both 50nm, and the thickness of the first coating layer and the second coating layer are both 50nm.

[0113] Example 11:

[0114] The only difference between this embodiment and the first embodiment is that the coating material of the coating layer in this embodiment is aluminum oxide.

[0115] Comparative Example 1:

[0116] The only difference between this comparative example and Example 1 is that the number of the coating layers in this comparative example is one.

[0117] Comparative Example 2:

[0118] The only difference between this comparative example and Example 1 is that the total thickness of the active material in this comparative example is 10 μm, and the total thickness of the coating layer is 500 nm.

[0119] Comparative Example 3:

[0120] The only difference between this comparative example and Example 1 is that the total thickness of the coating layer in this comparative example is 10 nm.

[0121] Test data 1:

[0122] The negative electrode sheets of Examples 1 to 11 and Comparative Examples 1 to 3 were assembled into button batteries with other conventional lithium secondary battery materials, and electrochemical tests were performed. The results are shown in Table 1.

[0123] Table 1 Electrochemical test data

[0124] Analysis of the data of Example 1 and Comparative Example 1 and Figure 3 shows that when the total thickness of the coating layer and the total thickness of the active material layer are the same, the initial capacity and cycle stability of Example 1 are better than those of Comparative Example 1. This is because the number of coating layers in Example 1 is more than that in the comparative example, and the thickness of the single layer is lower, which is conducive to the transmission of lithium ions and improves the kinetic performance of the battery. In addition, this multi-layer coating method increases the contact area between the coating layer and the active material layer, and has a better performance improvement effect on the active material layer, thereby making the battery have a higher initial capacity and better cycle stability.

[0125] Analysis of the data of Examples 1 to 11 and Comparative Example 2 shows that the capacity retention rate and the first-week coulombic efficiency of the examples are higher than those of Comparative Example 2. This is because the total thickness of the active material layers of Examples 1 to 11 is lower, and the total thickness of the coating layer is lower, that is, the thickness of the prepared negative electrode plate is lower than that of Comparative Example 2, so the migration of lithium ions is less hindered, which is beneficial to the improvement of the battery kinetic performance, thereby making the battery cycle effect better and the first-week coulombic efficiency higher.

[0126] Analysis of the data of Examples 1 to 4 and Comparative Example 3 shows that, when the number of layers is the same and the thickness of the single layer of the active material layer is the same, the electrochemical performance of Examples 1 to 4 is better than that of Comparative Example 3. This is because the thickness of the coating layer of Examples 1 to 4 is higher, which is beneficial to improving the volume expansion phenomenon during the battery cycle and improving the conductivity of the active material layer, thereby making the battery have higher initial capacity, first-week coulombic efficiency and capacity retention rate.

[0127] Analysis of the data of Examples 1 to 4 shows that the electrical performance data of Example 4 is better than that of Examples 1 to 3. This is because the thickness of the coating layer of Example 4 is higher, which has a more obvious improvement on the conductive effect of the active material layer and a more obvious improvement on the volume expansion phenomenon during the battery cycle, so it exhibits a higher cycling effect.

[0128] Analysis of the data of Example 1, Example 5 to Example 6 shows that, under the same number of coating layers, the capacity retention rate of Example 1 is higher than that of Examples 5 to 6. This is because the thickness of the coating layer of Example 1 is higher and the thickness of the active material layer is lower, indicating that the degree of coating of Example 1 is higher, which is beneficial to suppressing the volume expansion phenomenon during the battery cycle, reducing the risk of active material shedding, and improving the cycle life of the battery.

[0129] Analysis of the data of Example 1, Example 7 to Example 9 shows that the capacity retention rate of Example 1 is slightly higher than that of Example 7 and Example 9, and the capacity retention rate of Example 8 is higher than that of Example 1, indicating that as the number of layers increases, the phenomenon of the coating layer suppressing volume expansion is not adversely affected, and further indicating that the preparation method of the present application is suitable for a multi-layer coating structure. In addition, analysis of the data of the first-week coulomb efficiency shows that the first-week coulomb efficiency of Example 1 is higher than that of Examples 7 to 9. This is because the silicon substance as the active material has a lower first-week coulomb efficiency. The higher the content participating in the reaction, the lower the first efficiency of the battery. Therefore, the reaction sufficiency of the active material silicon in Example 1 is lower, indicating that Examples 7 to 9 have higher kinetic performance, that is, as the number of layers increases, the kinetic performance of the battery is not adversely affected.

[0130] Analysis of the data of Example 1 and Example 10 shows that Example 10 has the best cycle effect. This is because Example 10 also has a transition layer, and the transition layer material can improve the adhesion between the active material layer and the coating layer, thereby effectively improving the risk of active material shedding and improving the cycle effect of the battery; Analysis of the data of Example 1 and Example 11 shows that Example 11 has a better cycle effect. This is because Example 11 uses alumina as the coating material. Such materials can improve the adhesion of the negative electrode sheet, reduce the probability of active material shedding during the cycle, and improve the cycle effect of the battery; Analysis of the data of Example 10 and Example 11 shows that the initial capacity and first-week coulombic efficiency of Example 10 are better than those of Example 11. This is because the coating material of Example 10 is carbon, which can effectively improve the conductive effect of the negative electrode sheet, thereby improving the initial capacity and first-week coulombic efficiency of the battery.

[0131] Test data 2:

[0132] As shown in Figure 4, Figure 4 is an electron microscope cross-sectional test diagram of Example 6 of the present application. The thickness of the first coating layer and the second coating layer in Example 6 are uniform, both of which are 82.17 nm, and the thickness difference between the first active material layer and the second active material layer is small, indicating that the coating density of the negative electrode sheet prepared by the preparation method of the present application is high and the coating uniformity is good.

[0133] The above is a detailed introduction to the negative electrode sheet and preparation method, lithium-ion battery, battery pack, and electronic device disclosed in the embodiments of the present application. Specific examples are used herein to illustrate the principles and implementation methods of the present application. The description of the above embodiments is only used to help understand the negative electrode sheet and preparation method, lithium-ion battery, battery pack, and electronic device: At the same time, for general technical personnel in this field, based on the ideas of this application, there will be changes in the specific implementation methods and application scope. In summary, the content of this specification should not be understood as a limitation on this application.

Claims

1. A negative electrode plate, characterized in that, The negative electrode plate includes: a columnar current collector, an active material layer alternately coated on the outer surface of the columnar current collector, and a coating layer. Among them, the first layer coated on the outer surface of the columnar current collector is the active material layer, and the number of layers of both the active material layer and the coating layer is at least two. The total thickness of the active material layer is 1 μm to 5 μm, and the total thickness of the coating layer is 50 nm to 300 nm.

2. The negative electrode sheet according to claim 1, wherein, The number of layers of the coating layer is 2 to 10 layers, and the number of layers of the active material layer is 2 to 10 layers.

3. The negative electrode sheet according to claim 2, wherein The thicknesses of adjacent active material layers are the same, and the single-layer thickness of any one of the active material layers is 0.1 μm to 2.5 μm; the thicknesses of adjacent coating layers are the same, and the single-layer thickness of any one of the coating layers is 5 nm to 150 nm.

4. The negative electrode sheet according to claim 3, characterized in that, The ratio of the single-layer thickness of the active material layer to the single-layer thickness of the coating layer is 25:1 to 4:

1.

5. The negative electrode sheet according to claim 1, characterized in that, The active material of the active material layer is at least one of silicon, silicon oxide, carbon, germanium, tin, germanium oxide, and tin oxide.

6. The negative electrode sheet according to claim 5, wherein, The active material is silicon or silicon oxide, and the coating material of the coating layer is carbon, germanium, tin, germanium oxide, or tin oxide.

7. The negative electrode sheet according to claim 6, characterized in that, The structure of the negative electrode plate includes the columnar current collector, a first active material layer, a first coating layer, a second active material layer, and a second coating layer. The active material is silicon, and the coating material is carbon. The thicknesses of both the first active material layer and the second active material layer are 0.5 μm, and the thicknesses of both the first coating layer and the second coating layer are 100 nm.

8. The negative electrode sheet according to any one of claims 1 to 5, characterized in that, The negative electrode plate further includes a transition layer provided between the active material layer and the coating layer, and the sum of the total thickness of the transition layer and the coating layer is 50 nm to 300 nm.

9. The negative electrode sheet according to claim 8, wherein The ratio of the single-layer thickness of the transition layer to the single-layer thickness of the coating layer is 1:25 to 1:

1.

10. The negative electrode sheet according to claim 9, wherein, The transition material of the transition layer is at least one of titanium, nickel, chromium, or stainless steel.

11. The negative electrode sheet according to claim 5, wherein, The active material is silicon or silicon oxide, and the coating material is a ceramic oxide.

12. The negative electrode sheet according to any one of claims 1 to 11, characterized in that, The diameter of the columnar current collector is 5 μm to 50 μm.

13. The negative electrode sheet according to claim 12, characterized in that, The columnar current collector is at least one of copper, nickel, stainless steel, and a conductive carbon-based material.

14. The negative electrode sheet according to claim 1, characterized in that, At least one of chemical vapor deposition, physical vapor deposition, spraying, electroplating, coating, and ball milling is used to prepare the active material layer, and at least one of chemical vapor deposition, physical vapor deposition, spraying, electroplating, coating, and ball milling is used to prepare the coating layer.

15. A method for preparing a negative electrode sheet according to any one of claims 1 to 14, characterized in that, The preparation method includes the following steps: Provide the columnar current collector; Use a magnetron sputtering method to alternately coat an active material and a coating material on the outer surface of the columnar current collector to form the active material layer and the coating layer.

16. A lithium-ion battery, characterized in that, The lithium-ion battery includes the negative electrode plate according to any one of claims 1 to 14.

17. A battery pack, characterized in that, The battery pack includes a box body and the lithium-ion battery according to claim 16 placed in the box body.

18. An electronic device, characterized in that, The electronic device includes an electronic device body and the lithium-ion battery according to claim 16 used to supply power to the electronic device body.

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