Negative pole piece and preparation method thereof, lithium ion battery, battery pack and electronic equipment

Abstract

The invention relates to the field of battery negative electrodes, and discloses a negative electrode plate and a preparation method thereof, a lithium ion battery, a battery pack and electronic equipment. The negative pole piece comprises a columnar current collector, active material layers and coating layers, the outer surface of the columnar current collector is alternately coated with the active material layers and the coating layers, the first layer coating the outer surface of the columnar current collector is the active material layers, the number of the active material layers and the number of the coating layers are both at least two, the total thickness of the active material layers is 1-5 microns, and the total thickness of the coating layers is 1-5 microns. And the total thickness of the coating layer is 50 nm to 300 nm. The negative pole piece can improve the dynamic performance of the battery, and can effectively restrain the volume expansion problem caused by the charging and discharging process of the battery.

Description

Technical Field

[0001] The present invention relates to the field of battery anodes, and particularly to a negative electrode sheet, a preparation method thereof, a lithium ion battery, a battery pack, and an electronic device. Background Art

[0002] In recent years, with the development of lithium ion batteries, the market demand for high energy density batteries has become increasingly strong. Substances such as silicon, germanium, and tin are regarded as the most promising anode materials for lithium batteries due to their high specific capacity advantages. However, these materials will cause problems such as poor conductivity, poor strength of the electrode sheet, poor adhesion, and obvious volume expansion in the use process of lithium ion batteries, thus reducing the electrochemical performance of lithium ion batteries.

[0003] Based on this, the performance of the negative electrode active material layer can be improved by coating a layer of substance on the active material layer. However, due to the relatively thick active material layer, a relatively thick coating layer needs to be set to achieve the effect of complete coating, but this leads to an increase in the thickness of the negative electrode sheet, thereby increasing the transmission resistance of ions and electrons, and adversely affecting the kinetic performance of the battery; in addition, although single-layer coating can alleviate the volume expansion during the charge and discharge process of the battery, it is difficult to effectively solve the problem of the shedding of active substances caused by expansion, thereby adversely affecting the electrochemical performance of the battery. Summary of the Invention

[0004] Embodiments of the present invention disclose a negative electrode sheet, a preparation method thereof, a lithium ion battery, a battery pack, and an electronic device, so as to solve the problem in the prior art that the thickness of the negative electrode sheet and the coating layer is relatively thick, resulting in the obstruction of the kinetic performance of the battery, and it is difficult to effectively alleviate the volume expansion caused by the charge and discharge process of the battery.

[0005] In the first aspect, embodiments of the present application provide a negative electrode sheet, 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. 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.

[0006] Further, 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.

[0007] Further, the thicknesses of adjacent active material layers are the same, and the single-layer thickness of any active material layer is 0.1 μm to 2.5 μm; the thicknesses of adjacent coating layers are the same, and the single-layer thickness of any coating layer is 5 nm to 150 nm.

[0008] Further, 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.

[0009] Further, the active material of the active material layer is at least one of silicon, silicon oxide, carbon, germanium, tin, germanium oxide, and tin oxide.

[0010] Further, 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.

[0011] Further, the structure of the negative electrode sheet includes the columnar current collector, the first active material layer, the first coating layer, the second active material layer, and the second coating layer. The active material is silicon, 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.

[0012] Further, the negative electrode sheet further includes a transition layer disposed 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.

[0013] Further, 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.

[0014] Further, the transition material of the transition layer is at least one of titanium, nickel, chromium, or stainless steel.

[0015] Further, the active material is silicon or silicon oxide, and the coating material is a ceramic oxide.

[0016] Further, the diameter of the columnar current collector is 5 μm to 50 μm.

[0017] Further, the columnar current collector is at least one of copper, nickel, stainless steel, or a conductive carbon-based material.

[0018] Further, at least one of chemical vapor deposition, physical vapor deposition, spraying, electroplating, coating, or ball milling is used to prepare the active material layer, and at least one of chemical vapor deposition, physical vapor deposition, spraying, electroplating, coating, or ball milling is used to prepare the coating layer.

[0019] In a second aspect, an embodiment of the present application provides a method for preparing the negative electrode sheet as described in the first aspect. The preparation method includes the following steps:

[0020] Provide the columnar current collector;

[0021] The active material and the coating material are alternately coated on the outer surface of the columnar current collector in sequence by a magnetron sputtering method to form the active material layer and the coating layer.

[0022] In a third aspect, the present application provides a lithium-ion battery, and the lithium-ion battery includes the negative electrode tab described in the first aspect.

[0023] In a fourth aspect, the present application provides a battery pack, and the battery pack includes a box body and the lithium-ion battery described in the third aspect placed in the box body.

[0024] In a fifth aspect, the present application provides an electronic device, and the electronic device includes an electronic device body and the lithium-ion battery described in the third aspect for supplying power to the electronic device body.

[0025] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0026] The embodiment of the present application provides a negative electrode tab, 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. Among them, the total thickness of the active material layer is 1 μm to 5 μm, the total thickness of the coating layer is 50 nm to 300 nm, and the number of layers of the active material layer and the coating layer is at least 2 layers. This design method is beneficial to suppressing the volume expansion during the charge and discharge process of the battery, reducing the risk of active material shedding, improving the transmission resistance of ions and electrons, increasing the kinetic performance of the battery, and improving the electrochemical performance of the battery.

[0027] On the one hand, for the negative electrode tab provided by the present application, the coating material can be selectively targeted 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 certain, and the multi-layer alternating coating method is adopted. Compared with the single-layer coating, the multi-layer alternating coating method makes the number of layers of the active material layer more, and the thickness of any active material layer becomes thinner. Therefore, the coating difficulty is reduced, the coating uniformity of the coating layer is improved, and the phenomenon of uneven coating of the coating layer caused by the relatively thick active material layer during the coating process is avoided; and because the coating material has an optimizing effect on 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 coating material on the active material and improving the electrochemical performance of the battery; in addition, since the coating layer has a certain strength, such an alternating coating method is adopted, and the expansion degree of the single-layer active material layer is reduced. Therefore, the coating layer can greatly inhibit the expansion of the active material layer and reduce the risk of active material shedding, thereby improving the electrochemical performance of the battery; and adopting such a coating method does not increase the thickness of the negative electrode tab, and the multi-layer structure is also beneficial to improving the transmission paths of ions and electrons and increasing the kinetic performance of the battery. Brief Description of the Drawings

[0028] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the drawings required for use in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can be obtained based on these drawings.

[0029] Figure 1 is a cross-sectional view of a negative electrode plate with two layers of active material layer and coating layer provided by an embodiment of the present application;

[0030] Figure 2 is a cross-sectional view of a negative electrode plate with a single layer of coating layer and active material layer in the prior art provided by an embodiment of the present application;

[0031] Figure 3 is an electrochemical performance test chart provided by Embodiment 1 and Comparative Example 1 of the present application;

[0032] Figure 4 is an electron microscope image of the negative electrode plate provided by Embodiment 6 of the present application.

[0033] Reference Signs: 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 of the Embodiments

[0034] The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, rather than all embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts belong to the scope of protection of the present invention.

[0035] In the present invention, the terms "upper", "lower", "left", "right", "front", "rear", "top", "bottom", "inner", "outer", "middle", "vertical", "horizontal", "lateral", "longitudinal", etc. indicate the orientation or positional relationship based on the orientation or positional relationship shown in the drawings. These terms are mainly used to better describe the present invention and its embodiments, and are not used to limit that the indicated device, element or component must have a specific orientation or be constructed and operated in a specific orientation.

[0036] Moreover, in addition to being used to indicate orientation or positional relationship, some of the above terms may also be used to represent other meanings. For example, the term "upper" may also be used to represent a certain attachment relationship or connection relationship in some cases. For those of ordinary skill in the art, the specific meanings of these terms in the present invention can be understood according to specific circumstances.

[0037] In addition, terms such as "first", "second", etc. are mainly used to distinguish different devices, components or constituent parts (the specific types and structures may be the same or different), and are not used to indicate or imply the relative importance and quantity of the indicated devices, components or constituent parts. Unless otherwise specified, the meaning of "a plurality" is two or more.

[0038] The technical solution provided by the present invention will be further described below in conjunction with embodiments and drawings.

[0039] With the development of lithium-ion batteries, lithium-ion batteries have been widely used in products such as laptop computers, mobile phones, Bluetooth headsets, and new energy vehicles. The market demand for lithium-ion batteries has increased, and higher requirements have been put forward for the performance of lithium-ion batteries. However, there are problems such as poor conductivity and high expansibility in the anode material, which have an adverse impact on the performance of lithium-ion batteries.

[0040] In order to further improve the performance of the anode material, surface coating modification is one of the effective means. Generally, the surface coating layer can be tough or flexible. It not only needs to be able to buffer stress, but also has excellent conductivity to provide a fast transport channel for lithium ions and electrolytes. At the same time, it has high stability, which can keep the silicon anode relatively independent and protect the silicon anode 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 anode structure. At the same time, it can ensure the stable existence of the surface SEI film. However, although the primary coating can improve the conductivity of the anode material and inhibit volume expansion, due to the relatively high thickness of the active material layer, the impedance of the anode electrode is relatively high. And when the relatively thick active material layer needs to be completely coated, the thickness of the coating layer is relatively large, increasing the thickness of the anode electrode, increasing the transport distance, hindering the transport of ions and electrons, and making the kinetic performance of the battery blocked, which has an adverse impact on the electrochemical performance of lithium-ion batteries.

[0041] Based on this, the embodiments of the present application provide an anode electrode, which solves the problems of poor conductivity and easy volume expansion during cycling when materials such as silicon are used as the anode by alternately coating an active material layer and a coating layer on the current collector. At the same time, the coating effect is improved, the coating uniformity is increased, and further the electrochemical performance of the lithium-ion battery is optimized.

[0042] In a 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. 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.

[0043] In the embodiment of the present application, the active material layer and the coating layer are directly coated on the outer surface of the columnar current collector. Among them, 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. Considering the selection of the coating material, since the selection of the coating material has a certain optimization effect on the active material, and as the number of coating layers increases, the contact area between the active material layer and the coating layer is larger, so it is beneficial to improve the optimization effect of the coating material on the active material. Structurally speaking, by adopting the alternating coating method, the number of coating layers increases, but in fact the total thickness of the active material layer and the coating layer does not change. Therefore, the thickness of a single active material layer and a single coating layer is relatively low, which is beneficial to improving the uniformity of the coating layer; and for 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. Therefore, the expansion effect of the active material layer is dispersed, so that the inhibitory effect of the coating layer on the expansion of the active material layer is enhanced, effectively reducing the occurrence of the expansion phenomenon during the battery cycle and improving the electrochemical performance of the lithium-ion battery; in addition, due to the adoption 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, so it helps to improve the kinetic performance of the battery.

[0044] It should be emphasized that the number of layers of the active material layer is the same as that of the coating layer, 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 as the coating material that improves the conductivity of the electrode plate; if it is necessary to improve the adhesion of the active material layer, the coating material of the coating layer can be selected as the coating material that improves the adhesion of the electrode plate; it is also possible to select the coating material that can improve the conductivity or adhesion of the electrode plate at the same time.

[0045] Compared with the method of directly coating the active material and then directly coating the obtained composite active material on the current collector, directly coating on the current collector in the present application not only reduces the difficulty of the process of manufacturing the negative electrode plate and improves the processing efficiency of the negative electrode plate, but also avoids that in the process of rolling the composite active material, if the stability of the particle structure is poor, it will cause serious particle deformation and damage to the coating layer, and the structure of the composite active material coated on the electrode plate is uneven, resulting in differences in the performance of each region of the negative electrode plate, thus having an adverse impact on the electrochemical performance of the lithium-ion battery.

[0046] When the total thickness of the active material layer 2 and the total thickness of the coating layer 3 are the same, as Figure 1 shown, Figure 1 Figure Figure 1 shows a negative electrode plate in which both the active material layer 2 and the coating layer 3 are two layers. The negative electrode plate 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 that are alternately coated on the outer surface of the columnar current collector 1. Among them, 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 plate. Moreover, in this multi-layer structure with alternating coating, as the interface between the coating layer 3 and the active material layer 2 increases, it is beneficial to improve the kinetic performance of the battery. In addition, the volume expansion phenomenon of the first active material layer 21 is not only restricted 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 plate during the battery cycle is effectively improved. As Figure 2 shown, Figure 2 Figure Figure 2 shows a single-layer coating structure, which is manifested as an active material layer 2 and a coating layer 3 that are sequentially coated on the outer surface of the columnar current collector 1. Among them, the contact area between the active material layer 2 and the coating layer 3 is small, and the number of its interfaces is low, so the improvement of the performance of the negative electrode plate is small, and the effect of suppressing volume expansion is limited. That is to say, the multi-layer alternating coating method adopted in this application can effectively improve the conductivity of the negative electrode plate, suppress the volume expansion phenomenon, and improve the kinetic performance of the battery.

[0047] Furthermore, 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.

[0048] Within this range of the number of layers, it ensures that the coating uniformity of the coating layer on the active material layer is better. It 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 phenomenon of the active material layer, reduce the thickness of the active material layer, which is beneficial to reducing the impedance of the battery and improving the electrochemical performance of the battery. If the number of layers is higher than this range, it will increase the difficulty and cost of the process preparation, and it is difficult to ensure the coating uniformity; if the number of layers is lower than this range, the effect of suppressing the volume expansion of the negative electrode plate is poor, and the impedance of the battery is increased, and the kinetic performance of the battery is limited. Exemplarily, the number of layers of the coating layer is 2 layers, 4 layers, 6 layers, 8 layers, 10 layers, etc., and the number of layers of the active material layer is 2 layers, 4 layers, 6 layers, 8 layers, 10 layers, etc.

[0049] Furthermore, the thicknesses of adjacent active material layers are the same, and the thickness of any active material layer is 0.1 μm to 2.5 μm; the thicknesses of adjacent coating layers are the same, and the thickness of any coating layer is 5 nm to 150 nm.

[0050] From the perspective of process preparation, since the thickness of the adjacent coating layer and the active material layer is the same, when preparing a single-layer active material layer or coating layer, the preparation parameters are consistent, and the preparation process is relatively easy to control, reducing the process difficulty, which is conducive to large-scale production and development. Moreover, the thickness of the single-layer active material layer within this range can provide a rich lithium storage space, reducing the risk of lithium plating, which is beneficial to improving 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 accordingly, resulting in an increase in the migration distance of electrons and ions, and the kinetic performance of the battery is hindered; if the thickness of the active material layer is too low, the lithium storage space provided by the active material is limited, and the phenomenon of lithium plating is likely to occur in the battery. When the thickness of the coating layer is within this range, it can not only make the content of the coating material relatively high, fully contact with the active material layer, and significantly improve the conductivity of the battery; 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 sheet increases, which is not conducive to the improvement of the battery kinetic performance.

[0051] It should be noted that if the number of layers of the active material layer is 3, the adjacent ones refer to the same thickness of the first active material layer and the second active material layer, and the same thickness of the second active material layer and the third active material layer, that is, the first active material layer, the second active material layer, and the third active material layer have the same thickness, which means that the thickness of the single-layer active material layer is the same. Here, the meaning of the adjacent coating layer is the same as that of the adjacent active material layer, referring to the same thickness of the single-layer coating layer.

[0052] 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.

[0053] Within this ratio range, the coating layer can completely cover the outer surface of the active material, with a high matching degree with the active material layer, so it can effectively inhibit the volume expansion phenomenon during charge and discharge in the battery cycle, thereby improving the electrochemical performance of the battery. If it is lower than this range, the uniformity of the coating layer coating is poor, which is not conducive to inhibiting the volume expansion phenomenon of the battery; if it is higher than this range, the thickness of the finally prepared negative electrode sheet is too high, increasing the distance of ion and electron transmission, which is not conducive to the improvement of the battery kinetic performance. Exemplarily, the ratio of the single-layer thickness of the active material layer to the single-layer thickness of the coating layer is 25:1, 15:1, 10:1, 5:1, 4:1, etc.

[0054] 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.

[0055] The selection of the active material of the active material layer determines the performance of the active material layer of the negative electrode sheet, so that the coating material can be selected specifically, which is beneficial to improving the electrochemical performance of the battery. Exemplarily, the active material is silicon, silicon oxide, or silicon oxide and carbon, or germanium, tin, and germanium oxide, etc.

[0056] Further, 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.

[0057] When silicon or silicon oxide is selected as the active material, the conductivity of the active material is poor at this time. In order to further improve the conductive effect of the active material layer, carbon, germanium, tin, germanium oxide, or tin oxide is 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.

[0058] Further, the structure of the negative electrode sheet 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, the coating material is carbon, the thicknesses of the first active material layer and the second active material layer are both 0.5 μm, and the thicknesses of the first coating layer and the second coating layer are both 100 nm.

[0059] Selecting silicon as the active material and carbon as the coating material, and the number of layers of both the coating layer and the active material layer is 2, which increases the contact area between the active material layer and the coating layer, thereby helping to improve the conductive performance of the negative electrode sheet. The thickness of the active material layer is 0.5 μm, and the thickness of the coating layer is 100 nm, which ensures the uniformity of the coating of the coating layer and also helps to improve the degree of suppression of the volume expansion of the active material layer by the coating layer during the charge and discharge process of the negative electrode sheet.

[0060] Further, the negative electrode sheet 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.

[0061] As the number of alternating coating layers increases, the adhesion between the coating layer and the active material layer may be poor. By introducing the design of the transition layer, the adhesion between the active material layer and the coating layer is improved, and the influence of the multi-layer coating on the adhesion of the electrode sheet is reduced. And the sum of the thicknesses of the transition layer and the coating layer is within this range, and the total thickness of the electrode sheet does not change, ensuring the uniformity of the coating of the transition layer and the coating layer, and will not have a great impact on the performance of the battery. Instead, due to the existence of the transition layer, the adhesion of the electrode sheet is higher, avoiding the adverse impact on the battery caused by the shedding of the active material during the battery cycle. Exemplarily, the sum of the total thicknesses of the transition layer and the coating layer is 50 nm, 100 nm, 150 nm, 200 nm, 250 nm, 300 nm.

[0062] Further, 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.

[0063] 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 lower than this range, the uniformity of the coating of the transition layer is poor, and there are some areas that are not coated, which is not conducive to improving the adhesion of the battery; if it is higher than this range, the coating thickness of the transition layer is too high, resulting in too low a thickness of the coating layer, resulting in poor coating uniformity of the coating layer and difficulty in effectively improving the performance of the negative electrode sheet. Exemplarily, 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.

[0064] Further, the transition material of the transition layer is at least one of titanium, nickel, chromium, or stainless steel.

[0065] Since the active material of the active material layer is silicon and the coating material of the coating layer is carbon, the above substances are selected as the transition material of the transition layer. The coefficient of thermal expansion of the transition material is between that of silicon and carbon, which can make the combination of silicon and carbon stronger, thereby improving the bonding force of the negative electrode sheet, reducing the influence of multi-layer coating on the adhesion of the sheet, and improving the electrochemical performance of the battery during the cycling process. Exemplarily, the transition materials are titanium, nickel, and chromium, nickel, chromium, and stainless steel, etc.

[0066] Further, the active material is silicon or silicon oxide, and the coating material is a ceramic oxide.

[0067] When silicon or silicon oxide is selected as the active material, the expansion phenomenon during the charge and discharge process of the battery is more obvious at this time, and the silicon element will react with the fluorine element in the electrolyte, affecting the formation of the solid electrolyte membrane, thereby having an adverse impact on the electrochemical performance of the battery. At this time, by coating a ceramic oxide with high strength, not only can the volume expansion phenomenon of the negative electrode material be inhibited, reducing the occurrence of battery safety risks, but also the reaction between the negative electrode active material and the fluorine element can be blocked, promoting the formation of a stable solid electrolyte membrane.

[0068] Further, the diameter of the columnar current collector is 5 μm to 50 μm.

[0069] If the diameter of the columnar current collector is too thin, the strength of the electrode sheet is low, and the current collector is prone to deformation and fracture, resulting in safety problems; since the current collector is a non-active component in the battery and does not participate in the reaction, if the columnar current collector is too thick at this time, the proportion of non-active substances in the lithium-ion battery increases, and the electron impedance increases, which is not conducive to the improvement of the battery energy density. Exemplarily, the diameter of the columnar current collector is 5 μm, 10 μm, 15 μm, 20 μm, 25 μm, 30 μm, 40 μm, 45 μm, 50 μm, etc.

[0070] Further, the columnar current collector is at least one of copper, nickel, stainless steel, and conductive carbon-based materials.

[0071] When the columnar current collector is a metal material, the negative electrode active material layer is in direct contact with the metal, which not only helps to improve the conductivity of the battery, but also increases the structural strength of the negative electrode sheet. Exemplarily, the columnar current collector is copper, or nickel, or stainless steel and conductive carbon-based materials, etc. 。

[0072] Furthermore, 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.

[0073] 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 includes the following steps:

[0074] Provide a columnar current collector;

[0075] Use the magnetron sputtering method to alternately coat the active material and the coating material on the outer surface of the columnar current collector to form an active material layer and a coating layer.

[0076] Using the magnetron sputtering method to prepare the coating layer and the active material layer has a simple preparation process and high controllability. It can also avoid the phenomenon that when continuously depositing the active material layer and the coating layer, there will be a large thermal stress and easy film cracking. By dividing the active material layer or the coating layer into multiple layers with a small single-layer thickness, the stress during the preparation process is reduced, and the occurrence of film cracking is minimized, thereby improving the thickness uniformity of the active material layer and the coating layer.

[0077] In a third aspect, an embodiment of the present application provides a lithium-ion battery, which includes the negative electrode sheet as described in the first aspect.

[0078] In a fourth aspect, an embodiment of the present application provides a battery pack, which includes the lithium-ion battery as described in the third aspect.

[0079] In a fourth aspect, an embodiment of the present application provides an electronic device, which includes an electronic device body and the lithium-ion battery as described in the third aspect for powering the electronic device body.

[0080] In order to further illustrate the technical solutions and technical effects of the present application in more detail, the following will further illustrate the embodiments of the present application through more specific examples, application examples, and performance test results.

[0081] Example 1

[0082] 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 that are alternately coated on the outer surface of the columnar current collector. Among them, 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.

[0083] In this negative electrode plate, the diameter of the columnar current collector is 5 μm. The active material of the active material layer is silicon, and the coating material of the coating layer is carbon. The thicknesses of the first active material layer and the second active material layer are 0.5 μm, and the thicknesses of the first coating layer and the second coating layer are 100 nm.

[0084] The preparation process of this negative electrode plate:

[0085] Adopt the magnetron sputtering process, use a silicon target as the working target, and keep the power of the silicon target (12 KW) and the carbon target power (10 KW) unchanged during the deposition process to deposit the active material layer and the coating layer.

[0086] Provide a columnar current collector:

[0087] Deposit a first active material layer with a thickness of 0.5 μm on the columnar current collector using a silicon target as the working target;

[0088] Deposit a first coating layer with a thickness of 100 nm on the first active material layer using a carbon target as the working target;

[0089] Deposit a second active material layer with a thickness of 0.5 μm on the first coating layer using a silicon target as the working target;

[0090] Deposit a second coating layer with a thickness of 100 nm on the second active material layer using a carbon target as the working target.

[0091] Example Two

[0092] The difference between this example and Example One is only that the total thickness of the coating layer in this example is 50 nm, and the thicknesses of the first coating layer and the second coating layer are 25 nm.

[0093] Example Three:

[0094] The difference between this example and Example One is only that the total thickness of the coating layer in this example is 100 nm, and the thicknesses of both the first coating layer and the second coating layer are 50 nm.

[0095] Example Four:

[0096] The difference between this example and Example One is only that the total thickness of the coating layer in this example is 250 nm, and the thicknesses of both the first coating layer and the second coating layer are 125 nm.

[0097] Example 5:

[0098] The difference between this example and Example 1 is only that the total thickness of the coating layer in this example is 100 nm, the total thickness of the active material layer is 2.5 μm, the thicknesses of the first coating layer and the second coating layer are both 50 nm, and the thicknesses of the first active material layer and the second active material layer are 1.25 μm.

[0099] Example 6:

[0100] The difference between this example and Example 1 is only that the total thickness of the coating layer in this example is 164 nm, the total thickness of the active material layer is 3.6 μm, the thicknesses of the first coating layer and the second coating layer are both 82 nm, and the thicknesses of the first active material layer and the second active material layer are 1.8 μm.

[0101] Example 7:

[0102] The difference between this example and Example 1 is only that the number of layers of the coating layer in this example 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.

[0103] Example 8:

[0104] The difference between this example and Example 1 is only that the number of layers of the coating layer in this example is 10, the total thickness of the active material layer is 1 μm, and the total thickness of the coating layer is 50 nm.

[0105] Example 9:

[0106] The difference between this example and Example 1 is only that the number of layers of the coating layer in this example is 15, the total thickness of the active material layer is 5 μm, and the total thickness of the coating layer is 300 nm.

[0107] Example 10:

[0108] The difference between this example and Example 1 is only that this example 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 200 nm, and the thicknesses of the first transition layer and the second transition layer are both 50 nm, and the thicknesses of the first coating layer and the second coating layer are both 50 nm.

[0109] Example 11:

[0110] The difference between this example and Example 1 is only that the coating material of the coating layer in this example is alumina.

[0111] Comparative Example 1:

[0112] The difference between this comparative example and Example 1 is only that the number of layers of the coating layer in this comparative example is 1 layer.

[0113] Comparative Example 2:

[0114] The difference between this comparative example and Example 1 is only 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.

[0115] Comparative Example 3:

[0116] The difference between this comparative example and Example 1 is only that the total thickness of the coating layer in this comparative example is 10 nm.

[0117] Test Data 1:

[0118] The negative electrode plates of Examples 1 to 11 and Comparative Examples 1 to 3 were assembled with other conventional lithium secondary battery materials into coin cells for electrochemical testing, and the results are shown in Table 1.

[0119] Table 1 Electrochemical Test Data

[0120]

[0121]

[0122] Analyzing the data of Example 1 and Comparative Example 1 and Figure 3 it can be seen 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 Comparative Example 1, and the thickness of a single layer is lower, so it is beneficial to the transmission of lithium ions, improving the kinetic performance of the battery. Moreover, this multi-layer coating method makes the contact area between the coating layer and the active material layer higher, and the improvement effect on the performance of the active material layer is better, resulting in a higher initial capacity and better cycle stability of the battery.

[0123] Analyzing the data of Examples 1 to 11 and Comparative Example 2, it can be seen that the capacity retention rate and the first-cycle Coulombic efficiency of the examples are higher than those of Comparative Example 2. This is because the total thickness of the active material layer in 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. Therefore, the hindrance to the migration of lithium ions is smaller, which is beneficial to the improvement of the battery kinetic performance, resulting in better cycle performance and higher first-cycle Coulombic efficiency of the battery.

[0124] Analysis of the data of Examples 1 to 4 and Comparative Example 3 shows that, under the condition of the same number of layers and the same single-layer thickness of the active material layer, 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 in Examples 1 to 4 is relatively high, which is beneficial to improving the volume expansion phenomenon during the battery cycle and improving the conductivity of the active material layer, thereby resulting in higher initial capacity, first-week Coulomb efficiency, and capacity retention rate of the battery. Analysis of the data of Examples 1 to 4 shows that the electrical performance data of Example 4 is better than those of Examples 1 to 3. This is because the thickness of the coating layer in Example 4 is relatively high, and its improvement effect on the conductivity of the active material layer is more obvious, and its improvement effect on the volume expansion phenomenon during the battery cycle is more obvious. Therefore, it shows a higher cycle effect.

[0125] Analysis of the data of Example 1 and Examples 5 to 6 shows that, under the same number of coating layers, the capacity retention rate of Example 1 is higher than those of Examples 5 to 6. This is because the thickness of the coating layer in Example 1 is relatively high and the thickness of the active material layer is relatively low, indicating that the coating degree of the coating layer in Example 1 is relatively high, which is beneficial to suppressing the volume expansion phenomenon during the battery cycle, reducing the risk of active material shedding, and improving the cycle service life of the battery.

[0126] Analysis of the data of Example 1 and Examples 7 to 9 shows that the capacity retention rate of Example 1 is slightly higher than those of Examples 7 and 9, and the capacity retention rate of Example 8 is higher than that of Example 1. This shows that with the increase in the number of layers, the phenomenon of the coating layer suppressing volume expansion is not adversely affected, which further indicates that the preparation method of the present application is applicable to 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 those of Examples 7 to 9. This is because the first-week Coulomb efficiency of silicon, which is used as the active material, is relatively low, and 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 relatively low, indicating that Examples 7 to 9 have higher kinetic performance, that is, with the increase in the number of layers, the kinetic performance of the battery is not adversely affected.

[0127] Analysis of the data of Example 1 and Example 10 shows that the cycling performance of Example 10 is the best. This is because there is also a transition layer in Example 10, and the transition layer material can improve the adhesion between the active material layer and the coating layer, thereby effectively reducing the risk of active material shedding and improving the cycling performance of the battery. Analysis of the data of Example 1 and Example 11 shows that the cycling performance of Example 11 is relatively good. This is because Example 11 uses alumina as the coating material, and such materials can improve the adhesion of the negative electrode sheet and reduce the probability of active material shedding during cycling, thus improving the cycling performance of the battery. Analysis of the data of Example 10 and Example 11 shows that the initial capacity and the first-week Coulombic efficiency of Example 10 are both better than those of Example 11. This is because the coating material of Example 10 is carbon, which can effectively improve the conductivity of the negative electrode sheet, thereby increasing the initial capacity and the first-week Coulombic efficiency of the battery.

[0128] Test data two:

[0129] As Figure 4 shown, Figure 4 This is the electron microscope cross-section test diagram of Example 6 of the present application. The thicknesses of the first coating layer and the second coating layer in Example 6 are uniform, both being 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.

[0130] The negative electrode sheet, the preparation method, the lithium-ion battery, the battery pack, and the electronic device disclosed in the embodiments of the present application have been introduced in detail above. Specific examples are used in this article to elaborate on the principles and implementation manners of the present application. The descriptions of the above embodiments are only used to help understand the negative electrode sheet, the preparation method, the lithium-ion battery, the battery pack, and the electronic device: At the same time, for those of ordinary skill in the art, according to the idea of the present invention, there will be changes in the specific implementation manners and application scopes. In summary, the content of this specification should not be construed as a limitation of the present invention.

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, characterized in that, 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, wherein, 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, characterized in that, 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, wherein 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 the active material and the 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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