Negative electrode sheet of lithium-ion battery, preparation method thereof, lithium-ion battery, and vehicle

Abstract

The present invention provides a negative electrode sheet for a lithium-ion battery, a preparation method thereof, a lithium-ion battery, and a vehicle. The negative electrode sheet includes a substrate, a modified functional layer covering the substrate, and a negative electrode active material layer covering the modified functional layer; the substrate material includes copper, and the modified functional layer includes a polymer compound containing a catechol structure; wherein, the polymer compound containing a catechol structure is used to prevent the oxidation of the substrate and prevent the dissolution or precipitation of the substrate when charging the lithium-ion battery in an over-discharged state; the negative electrode active material layer is used to provide an insertion / extraction channel for lithium ions. So that when charging the lithium-ion battery in an over-discharged state, the negative electrode sheet can still maintain a normal state, so that the negative electrode sheet can be applied to the situation of over-discharging of the lithium-ion battery, broadening the voltage range that the lithium-ion battery can use, and reducing the abnormal situation of the lithium-ion battery being locked due to over-discharging.

Description

Technical Field

[0001] The present invention relates to the field of batteries, and particularly to a negative electrode sheet of a lithium-ion battery, a preparation method of a negative electrode sheet of a lithium-ion battery, a lithium-ion battery, and a vehicle. Background Art

[0002] Generally speaking, when a lithium-ion battery is used as a backup energy source, or when an electronic device containing a lithium-ion battery has not been used for a long time, it is possible that the lithium-ion battery is stored for many years without being used. If the battery is not properly maintained, due to reasons such as battery self-discharge, the requirements of the Battery Management System (BMS), and parasitic loads, the voltage of the lithium-ion battery may continuously decrease. When the discharge voltage is lower than the redox potential of the negative electrode sheet, it may cause the negative electrode sheet to dissolve and precipitate, thus potentially leading to safety hazard problems.

[0003] In order to avoid the problem of dissolution and precipitation of the negative electrode sheet, usually, a lower limit of the prohibited charging voltage can be set in the battery management system. The prohibited charging voltage is usually higher than the redox potential of the negative electrode sheet to avoid the dissolution and precipitation of the negative electrode sheet. If the voltage of the lithium-ion battery is lower than the prohibited charging voltage, the battery management system can lock the battery. However, when the redox potential of the negative electrode sheet is relatively high, it is easy to cause the available voltage range of the lithium-ion battery to become narrow, and the lithium-ion battery is prone to being locked. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to provide a negative electrode sheet of a lithium-ion battery, a preparation method of a negative electrode sheet of a lithium-ion battery, a lithium-ion battery, and a vehicle, so that the negative electrode sheet can be normally used at a low voltage and the available voltage range of the lithium-ion battery is broadened.

[0005] To solve the above problems, the present invention provides a negative electrode sheet of a lithium-ion battery, including:

[0006] The negative electrode sheet includes a substrate, a modified functional layer covering the substrate, and a negative electrode active material layer covering the modified functional layer; the substrate material includes copper, and the modified functional layer includes a polymer compound containing a catechol structure;

[0007] Wherein, the polymer compound containing a catechol structure is used to prevent the oxidation of the substrate and prevent the dissolution or precipitation of the substrate when charging the lithium-ion battery in an over-discharged state;

[0008] The negative electrode active material layer is used to provide an insertion / extraction channel for lithium ions.

[0009] Optionally, the polymer compound containing catechol structure includes polydopamine.

[0010] Optionally, the negative electrode plate further includes a conductive layer disposed between the modification functional layer and the negative electrode active material layer, and the conductive layer includes at least one of polypyrrole, polyacetylene, polyaniline, polythiophene, and polyurethane; the conductive layer is used to protect and shield the substrate and increase the corrosion potential of the substrate.

[0011] Optionally, the negative electrode active material layer includes a negative electrode active material and a first binder, or the negative electrode active material layer includes a negative electrode active material, a first binder, and a first conductive agent; the negative electrode active material includes at least one of graphite, soft carbon, hard carbon, and mesocarbon microbeads.

[0012] Optionally, the first binder includes polydopamine, and the first conductive agent includes at least one of polypyrrole, polyacetylene, polyaniline, polythiophene, and polyurethane.

[0013] Optionally, the thickness of the modification functional layer is 0.5 to 5 μm.

[0014] Optionally, the thickness of the conductive layer is 0.1 to 10 μm.

[0015] An embodiment of the present invention further provides a method for preparing a negative electrode plate of a lithium-ion battery, and the method includes:

[0016] Obtain a substrate; the substrate material includes copper;

[0017] Coat a modification functional layer on the surface of the substrate; the modification functional layer includes a polymer compound containing catechol structure, and the polymer compound containing catechol structure is used to prevent the substrate from oxidizing and prevent the substrate from dissolving or precipitating when charging the lithium-ion battery in an over-discharged state;

[0018] Coat a negative electrode active material layer on the surface of the modification functional layer to obtain a negative electrode plate; the negative electrode active material layer is used to provide an insertion / extraction channel for lithium ions.

[0019] Optionally, the step of coating a negative electrode active material layer on the surface of the modification functional layer to obtain a negative electrode plate includes:

[0020] Coat a conductive layer on the surface of the modification functional layer, and the conductive layer is used to protect and shield the substrate and increase the corrosion potential of the substrate;

[0021] Coat a negative electrode active material layer on the surface of the conductive layer to obtain a negative electrode plate.

[0022] An embodiment of the present invention also provides a lithium-ion battery, which includes a negative electrode sheet as described in the embodiment of the present invention, or a negative electrode sheet prepared by the preparation method as described in the embodiment of the present invention.

[0023] Optionally, the lithium-ion battery further includes a positive electrode sheet and an electrolyte; the positive electrode sheet includes lithium nickel cobalt manganese oxide, a second binder, and a second conductive agent; the electrolyte includes a lithium salt and a solvent, and the solvent includes at least one of ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, and ethyl methyl carbonate.

[0024] An embodiment of the present invention also provides a vehicle, which includes the lithium-ion battery as described in the embodiment of the present invention.

[0025] Compared with the prior art, the present invention has the following advantages:

[0026] For the negative electrode sheet of the lithium-ion battery in the embodiment of the present invention, by providing a modified functional layer containing a polymer compound with a catechol structure, the catechol structure complexes the copper ions generated due to over-discharge of the lithium-ion battery, preventing the copper ions from further dissolving into the electrolyte, and even preventing the copper ions from being oxidized and reduced to copper metal during charging, thus avoiding the situation where the substrate of the negative electrode sheet is oxidized, dissolved, or precipitated. When charging is carried out after over-discharging of the lithium-ion battery, the negative electrode sheet can still maintain a normal state, so that the negative electrode sheet can be applied to the situation of over-discharging of the lithium-ion battery, broadening the voltage range available for the lithium-ion battery and reducing the abnormal situation of the lithium-ion battery being locked due to over-discharging. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 is a schematic cross-sectional structure view of a negative electrode sheet provided by an embodiment of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS:

[0029] 1 - Substrate, 2 - Modified functional layer, 3 - Conductive layer, 4 - Negative electrode active material layer. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0030] To make the above objects, features, and advantages of the present invention more obvious and understandable, the present invention will be further described in detail below with reference to the drawings and specific embodiments.

[0031] The present invention provides a negative electrode sheet for a lithium-ion battery, including:

[0032] The negative electrode sheet includes a substrate, a modified functional layer covering the substrate, and a negative electrode active material layer covering the modified functional layer; the substrate material includes copper, and the modified functional layer includes a polymer compound containing a catechol structure;

[0033] Among them, the high molecular compound containing a catechol structure is used to prevent the oxidation of the substrate, and when charging the lithium-ion battery in an over-discharged state, it prevents the substrate from dissolving or precipitating;

[0034] The negative electrode active material layer is used to provide an insertion / extraction channel for lithium ions.

[0035] Specifically, for the negative electrode sheet of a lithium-ion battery, copper is usually used as the substrate. Copper has good electrical conductivity and is relatively stable in air and hardly reacts in dry air. However, copper has a relatively high redox potential. In the case of over-discharging of a lithium-ion battery, if the lithium-ion battery is charged, it is easy to cause the copper substrate to be oxidized, dissolved or precipitated.

[0036] Therefore, in order to avoid the situation that the substrate of the negative electrode sheet is easily oxidized, dissolved or precipitated when charging the lithium-ion battery after over-discharging to 0V, a modified functional layer covering the substrate can be provided. The modified functional layer can include a high molecular compound containing a catechol structure, which can effectively complex the copper ions (Cu + / Cu 2+ ) generated by the over-discharging of the lithium-ion battery, prevent the copper ions from further dissolving into the electrolyte, and even prevent the copper ions from being oxidized and reduced to copper metal during charging, thereby avoiding the situation that the substrate of the negative electrode sheet is oxidized, dissolved or precipitated. When charging the lithium-ion battery during over-discharging, the negative electrode sheet can still maintain a normal state, so that the negative electrode sheet can be suitable for the situation of over-discharging of the lithium-ion battery, broadening the voltage range available for the lithium-ion battery and reducing the abnormal situation of the lithium-ion battery being locked due to over-discharging.

[0037] Thereafter, a negative electrode active material layer can be coated on the surface of the modified functional layer. The negative electrode active material layer can be used to provide an insertion / extraction channel for lithium ions, so that lithium ions can move between the positive electrode and the negative electrode, thereby realizing the charging and discharging of the lithium-ion battery.

[0038] In an embodiment of the present invention, the high molecular compound containing a catechol structure includes polydopamine.

[0039] Specifically, the high molecular compound containing a catechol structure can include polydopamine. Polydopamine has a catechol structure and can complex copper ions. At the same time, it also has strong adhesion performance and can be used as an adhesive, so that materials such as the negative electrode active layer in the negative electrode sheet can be more tightly adhered to the surface of the substrate, improving the stability of the negative electrode sheet, further reducing the dissolution or precipitation of the substrate of the negative electrode sheet, and improving the safety of use of the lithium-ion battery in an over-discharged state.

[0040] In one embodiment of the present invention, the negative electrode sheet further includes a conductive layer disposed between the modification functional layer and the negative electrode active material layer, and the conductive layer includes at least one of polypyrrole, polyacetylene, polyaniline, polythiophene, and polyurethane; the conductive layer is used to protect and shield the substrate and increase the corrosion potential of the substrate.

[0041] Specifically, in order to form better protection for the negative electrode sheet, a conductive layer can be further disposed between the modification functional layer and the negative electrode active material layer. The conductive layer can include at least one of polypyrrole, polyacetylene, polyaniline, polythiophene, and polyurethane. Conductive agents such as polypyrrole, polyacetylene, polyaniline, polythiophene, and polyurethane used in the conductive layer can have excellent conductivity, thereby forming shielding and protection for the negative electrode sheet, and at the same time can increase the corrosion potential of the copper substrate to a certain extent, making it more difficult for the copper substrate to be oxidized, dissolved, or precipitated.

[0042] In one embodiment of the present invention, the negative electrode active material layer includes negative electrode active material and a first binder, or the negative electrode active material layer includes negative electrode active material, a first binder, and a first conductive agent; the negative electrode active material includes at least one of graphite, soft carbon, hard carbon, and mesophase carbon microspheres.

[0043] Among them, the first binder includes polydopamine, and the first conductive agent includes at least one of polypyrrole, polyacetylene, polyaniline, polythiophene, and polyurethane

[0044] Specifically, the negative electrode active material layer can include negative electrode active material and a first binder, or can include negative electrode active material, a first binder, and a first conductive agent. Among them, the first binder can be used to bond the negative electrode active material so that the negative electrode active material can adhere to the modification functional layer or the conductive layer. The first binder can include binders that can be used in negative electrode sheets such as styrene-butadiene latex, polytetrafluoroethylene latex, and aqueous polyacrylate latex, or polydopamine can also be used as the binder. Thus, the negative electrode active material layer can also have the function of complexing copper ions to avoid dissolution or precipitation of the substrate, further improving the stability of the substrate of the negative electrode sheet. The first conductive agent can include at least one of polypyrrole, polyacetylene, polyaniline, polythiophene, and polyurethane, so that the negative electrode active material layer can also provide protection and shielding for the copper substrate, and can further improve the use safety of the battery.

[0045] The negative electrode active material can include at least one of graphite, soft carbon, hard carbon, and mesophase carbon microspheres. Graphite, soft carbon, hard carbon, and mesophase carbon microspheres can all provide good insertion and extraction channels for lithium ions, so that the overall lithium ion battery can have good electrochemical performance.

[0046] In an embodiment of the present invention, the thickness of the modification functional layer is 0.5 - 5 μm, and the thickness of the conductive layer is 0.1 - 10 μm.

[0047] Specifically, with appropriate thicknesses, the modification functional layer and the conductive layer can better coat the copper substrate, protecting the substrate from oxidation, dissolution, or precipitation. At the same time, they can maintain good electrochemical performance of the negative electrode sheet, resulting in better overall performance of the lithium-ion battery.

[0048] As a specific example of the present invention, Figure 1 It is a schematic cross-sectional structure diagram of a negative electrode sheet according to an embodiment of the present invention. Among them, modification functional layers 2 are coated on both the front and back surfaces of a substrate 1 made of copper. A conductive layer 3 is coated on the surface of the modification functional layer 2, and a negative electrode active material layer 4 can be coated on the surface of the conductive layer 3. Thus, the modification functional layer 2 can better wrap the substrate 1, preventing the substrate from dissolving or precipitating. Subsequently, the conductive layer 2 can further coat the substrate, forming shielding and protection for the negative electrode sheet. Then, a negative electrode active material layer can be coated on the surface of the conductive layer 2, providing an insertion / extraction channel for lithium ions, so that lithium ions can move between the positive electrode and the negative electrode, thereby realizing the charging and discharging of the lithium-ion battery.

[0049] For the negative electrode sheet of the lithium-ion battery according to the embodiment of the present invention, by setting a modification functional layer containing a polymer compound with a catechol structure, the catechol structure can complex copper ions generated due to over-discharge of the lithium-ion battery, preventing copper ions from further dissolving into the electrolyte, and even preventing copper ions from being oxidized and reduced to copper metal during charging, thus avoiding the situation where the substrate of the negative electrode sheet is oxidized, dissolved, or precipitated. When charging is carried out during over-discharge of the lithium-ion battery, the negative electrode sheet can still maintain a normal state, so that the negative electrode sheet can be applicable to the situation of over-discharge of the lithium-ion battery, broadening the available voltage range of the lithium-ion battery and reducing abnormal situations where the lithium-ion battery is locked due to over-discharge.

[0050] The embodiment of the present invention also provides a method for preparing a negative electrode sheet of a lithium-ion battery, the method comprising:

[0051] Step 101, obtaining a substrate; the substrate material includes copper;

[0052] For the negative electrode sheet of a lithium-ion battery, copper is usually used as the substrate. Copper has good electrical conductivity and is relatively stable in air, hardly reacting in dry air. However, copper has a relatively high oxidation-reduction potential. In the case of over-discharge of the lithium-ion battery, if the lithium-ion battery is charged, it is easy to cause the copper substrate to be oxidized, dissolved, or precipitated.

[0053] Step 102, coat a modified functional layer on the surface of the substrate; the modified functional layer includes a polymer compound containing a catechol structure, and the polymer compound containing a catechol structure is used to prevent the substrate from oxidizing and, when charging the lithium-ion battery in an over-discharged state, prevent the substrate from dissolving or precipitating;

[0054] Specifically, in order to avoid the substrate from being oxidized, dissolved, or precipitated, a functional modified layer can be coated on the surface of the substrate. The modified functional layer can include a polymer compound containing a catechol structure, which can effectively complex the copper ions (Cu+ / Cu2+) generated by the lithium-ion battery due to over-discharge, prevent the copper ions from further dissolving into the electrolyte, and even prevent the copper ions from being oxidized and reduced to copper metal during charging, thereby avoiding the situation where the substrate of the negative electrode sheet is oxidized, dissolved, or precipitated. When charging the lithium-ion battery in an over-discharged state, the negative electrode sheet can still maintain a normal state, so that the negative electrode sheet can be applied to the situation of over-discharged lithium-ion batteries, broadening the usable voltage range of the lithium-ion battery and reducing the abnormal situation of the lithium-ion battery being locked due to over-discharge.

[0055] In a specific implementation, during the coating process, equipment such as a coater can be used to perform double-sided coating on the substrate, so that both the front and back sides of the substrate are coated with a polymer compound containing a catechol structure, so that the polymer compound containing a catechol structure can better coat the substrate.

[0056] Step 103, coat a negative electrode active material layer on the surface of the modified functional layer to obtain a negative electrode sheet; the negative electrode active material layer is used to provide an insertion / extraction channel for lithium ions.

[0057] After the coating of the modified functional layer is completed, a negative electrode active material layer can be further coated on the surface of the modified functional layer to provide an insertion / extraction channel for lithium ions and obtain a negative electrode sheet.

[0058] In a specific implementation, after the coating of the modified functional layer is completed, equipment such as a coater and a sprayer can be further used to perform double-sided coating on the substrate coated with the modified functional layer, so that both the front and back sides of the substrate are coated with the negative electrode active material. Specifically, in order to enable the negative electrode active material to be better coated on the modified functional layer, the negative electrode active material can be first mixed with a first binder, and then the mixture of the negative electrode active material and the first binder can be coated on the modified functional layer. It is also possible to mix the negative electrode active material, the first binder, and a first conductive agent, and then coat the mixture of the negative electrode active material, the first binder, and the first conductive agent on the modified functional layer.

[0059] In an embodiment of the present invention, the step of coating a negative electrode active material layer on the surface of the modified functional layer to obtain a negative electrode sheet includes:

[0060] S11. Coat a conductive layer on the surface of the modification functional layer. The conductive layer is used to protect and shield the substrate and increase the corrosion potential of the substrate.

[0061] Specifically, in order to further improve the stability of the negative electrode plate, a conductive layer can be coated on the surface of the modification functional layer. The conductive layer can include at least one of polypyrrole, polyacetylene, polyaniline, polythiophene, and polyurethane. Thus, the conductive layer can protect and shield the substrate and increase the corrosion potential of the substrate through its good electrical conductivity.

[0062] In a specific implementation, after the coating of the modification functional layer is completed, equipment such as a coater and a sprayer can be further used to perform double-sided coating on the substrate coated with the modification functional layer, so that both the front and back sides of the substrate are coated with the conductive layer.

[0063] S12. Coat a negative electrode active material layer on the surface of the conductive layer to obtain a negative electrode plate.

[0064] Specifically, after the coating of the conductive layer is completed, a negative electrode active material layer can be coated on the surface of the conductive layer to provide an insertion / extraction channel for lithium ions, thereby obtaining a negative electrode plate.

[0065] In a specific implementation, after the coating of the conductive layer is completed, equipment such as a coater and a sprayer can be further used to perform double-sided coating on the substrate coated with the modification functional layer and the conductive layer, so that both the front and back sides of the substrate are coated with the negative electrode active material.

[0066] Through the method for preparing the negative electrode plate of the lithium-ion battery according to the present invention, during the preparation of the negative electrode plate, a modification functional layer is coated on the surface of the substrate. The modification functional layer contains a polymer compound with a catechol structure, and the polymer compound with a catechol structure is used to prevent the oxidation of the substrate and prevent the dissolution or precipitation of the substrate when charging the lithium-ion battery in an over-discharged state. When charging the lithium-ion battery during over-discharge, the negative electrode plate can still maintain a normal state, so that the negative electrode plate can be applicable to the situation of over-discharge of the lithium-ion battery, expanding the usable voltage range of the lithium-ion battery and reducing the abnormal situation of the lithium-ion battery being locked due to over-discharge.

[0067] The embodiment of the present invention further provides a lithium-ion battery, which includes the negative electrode plate as described in the embodiment of the present invention, or includes the negative electrode plate prepared by the preparation method as described in the embodiment of the present invention. Among them, the specific structural form and preparation method of the negative electrode plate have been described in detail in the foregoing embodiments and will not be elaborated here.

[0068] In an embodiment of the present invention, the lithium-ion battery further includes a positive electrode plate and an electrolyte; the positive electrode plate includes lithium nickel cobalt manganese oxide, a second binder, and a second conductive agent; the electrolyte includes a lithium salt and a solvent, and the solvent includes at least one of ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, and ethyl methyl carbonate.

[0069] Specifically, the positive electrode plate of the lithium-ion battery can mainly use lithium nickel cobalt manganese oxide (NCM) as the base material. Lithium nickel cobalt manganese oxide is a positive electrode material with high safety developed on the basis of lithium cobaltate. It can have high capacity, good thermal stability, and excellent electrochemical properties such as a wide charge-discharge voltage range. Using lithium nickel cobalt manganese oxide as the positive electrode material of the lithium-ion battery can better improve the electrochemical performance of the lithium-ion battery.

[0070] Among them, the positive electrode plate can also include a second binder and a second conductive agent. The second binder can include polyvinylidene fluoride (PVDF). The second conductive agent can include substances such as graphite, acetylene black, and carbon nanotubes that can be used to improve the conductivity of the positive electrode plate.

[0071] The electrolyte can include a lithium salt and a solvent. The lithium salt can include lithium perchlorate, lithium hexafluorophosphate, lithium tetrafluoroborate, etc. The solvent includes at least one of ethylene carbonate (EC), propylene carbonate (PC), dimethyl carbonate (DMC), diethyl carbonate (DEC), and ethyl methyl carbonate (EMC). Among them, the ratio of the solvent can be determined according to the needs of the actual use environment. Usually, a high dielectric constant solvent and a low viscosity solvent can be mixed and used. For example, propylene carbonate and diethyl carbonate are mixed and used; ethylene carbonate and dimethyl carbonate are mixed and used; ethylene carbonate, diethyl carbonate, and ethyl methyl carbonate are mixed and used, etc.

[0072] Through the lithium-ion battery of the present invention, a substrate coated with a modified functional layer containing a polymer compound with a catechol structure is used. The polymer compound with a catechol structure is used to prevent the oxidation of the substrate and prevent the dissolution or precipitation of the substrate when charging the lithium-ion battery in an over-discharged state. When charging the lithium-ion battery during over-discharge, the negative electrode plate can still maintain a normal state, so that the negative electrode plate can be applicable to the situation of over-discharge of the lithium-ion battery, broadening the voltage range that the lithium-ion battery can use and reducing the abnormal situation of the lithium-ion battery being locked due to over-discharge.

[0073] The embodiment of the present invention also provides a vehicle, and the vehicle includes the lithium-ion battery as described in the embodiment of the present invention. Among them, the specific structural form of the lithium-ion battery has been described in detail in the foregoing embodiments and will not be elaborated here.

[0074] With the vehicle of the present invention, the negative electrode plate in the lithium-ion battery uses a substrate coated with a modified functional layer of a polymer compound containing a catechol structure. The polymer compound containing a catechol structure is used to prevent the substrate from oxidizing, and when charging the lithium-ion battery in an over-discharged state, it prevents the substrate from dissolving or precipitating. When charging the lithium-ion battery during over-discharge, the negative electrode plate can still maintain a normal state, so that the negative electrode plate can be applied to the situation of over-discharge of the lithium-ion battery, broadening the voltage range that the lithium-ion battery can use and reducing the abnormal situation of the lithium-ion battery being locked due to over-discharge.

[0075] To enable those skilled in the art to better understand the present invention, the following describes the preparation method of the negative electrode plate of the lithium-ion battery of the present invention through multiple specific embodiments.

[0076] Example 1

[0077] (1) Obtain a copper substrate;

[0078] (2) Coat 0.5 μm thick polydopamine on both the front and back surfaces of the substrate to form a modified functional layer on the substrate surface;

[0079] (3) Mix graphite, polypyrrole, and polydopamine in a mass ratio of 96:2:2 to obtain a negative electrode active mixture;

[0080] (4) Coat the negative electrode active mixture on both the front and back surfaces of the substrate coated with the modified functional layer to form a negative electrode active material layer on the surface of the substrate coated with the modified functional layer, and obtain a negative electrode plate.

[0081] Example 2

[0082] (1) Obtain a copper substrate;

[0083] (2) Coat 0.5 μm thick polydopamine on both the front and back surfaces of the substrate to form a modified functional layer on the substrate surface;

[0084] (3) Coat 0.1 μm thick polypyrrole on both the front and back surfaces of the substrate coated with the modified functional layer to form a conductive layer on the surface of the substrate coated with the modified functional layer;

[0085] (4) Mix graphite, polypyrrole, and polydopamine in a mass ratio of 96:2:2 to obtain a negative electrode active mixture;

[0086] (5) Coat the negative electrode active mixture on both the front and back surfaces of the substrate coated with the modified functional layer and the conductive layer to form a negative electrode active material layer on the surface of the substrate coated with the modified functional layer and the conductive layer, and obtain a negative electrode plate.

[0087] Example 3

[0088] (1) Obtain a copper substrate;

[0089] (2) Coat polydopamine with a thickness of 5 μm on both the front and back surfaces of the substrate to form a modified functional layer on the substrate surface.

[0090] (3) Coat polypyrrole with a thickness of 5 μm on both the front and back surfaces of the substrate coated with the modified functional layer to form a conductive layer on the substrate surface coated with the modified functional layer.

[0091] (4) Mix graphite, polypyrrole, and polydopamine in a mass ratio of 96:2:2 to obtain a negative electrode active mixture.

[0092] (5) Coat the negative electrode active mixture on both the front and back surfaces of the substrate coated with the modified functional layer and the conductive layer to form a negative electrode active material layer on the substrate surface coated with the modified functional layer and the conductive layer, thereby obtaining a negative electrode plate.

[0093] Example 4

[0094] (1) Obtain a copper substrate.

[0095] (2) Coat polydopamine with a thickness of 5 μm on both the front and back surfaces of the substrate to form a modified functional layer on the substrate surface.

[0096] (3) Coat polyacetylene with a thickness of 10 μm on both the front and back surfaces of the substrate coated with the modified functional layer to form a conductive layer on the substrate surface coated with the modified functional layer.

[0097] (4) Mix graphite, polyacetylene, and polydopamine in a mass ratio of 96:2:2 to obtain a negative electrode active mixture.

[0098] (5) Coat the negative electrode active mixture on both the front and back surfaces of the substrate coated with the modified functional layer and the conductive layer to form a negative electrode active material layer on the substrate surface coated with the modified functional layer and the conductive layer, thereby obtaining a negative electrode plate.

[0099] Example 5

[0100] (1) Obtain a copper substrate.

[0101] (2) Coat polydopamine with a thickness of 0.1 μm on both the front and back surfaces of the substrate to form a modified functional layer on the substrate surface.

[0102] (3) Coat polypyrrole with a thickness of 10 μm on both the front and back surfaces of the substrate coated with the modified functional layer to form a conductive layer on the substrate surface coated with the modified functional layer.

[0103] (4) Mix graphite, polypyrrole, and polydopamine in a mass ratio of 96:2:2 to obtain a negative electrode active mixture.

[0104] (5) Coating the positive and negative surfaces of the substrate coated with the modified functional layer and the conductive layer with the negative active mixture, forming a negative active material layer on the surface of the substrate coated with the modified functional layer and the conductive layer, and obtaining a negative electrode plate.

[0105] Example 6

[0106] (1) Obtain a copper substrate;

[0107] (2) Coating the positive and negative surfaces of the substrate with 0.5 μm thick polydopamine to form a modified functional layer on the surface of the substrate;

[0108] (3) Coating the positive and negative surfaces of the substrate coated with the modified functional layer with 10 μm thick polyaniline and polythiophene to form a conductive layer on the surface of the substrate coated with the modified functional layer;

[0109] (4) Mixing graphite, polyaniline, polythiophene and polydopamine according to a mass ratio of 96:2:2 to obtain a negative active mixture;

[0110] (5) Coating the positive and negative surfaces of the substrate coated with the modified functional layer and the conductive layer with the negative active mixture, forming a negative active material layer on the surface of the substrate coated with the modified functional layer and the conductive layer, and obtaining a negative electrode plate.

[0111] Example 7

[0112] (1) Obtain a copper substrate;

[0113] (2) Coating the positive and negative surfaces of the substrate with 2 μm thick polydopamine to form a modified functional layer on the surface of the substrate;

[0114] (3) Coating the positive and negative surfaces of the substrate coated with the modified functional layer with 8 μm thick polypyrrole to form a conductive layer on the surface of the substrate coated with the modified functional layer;

[0115] (4) Mixing graphite, polyurethane and polydopamine according to a mass ratio of 96:2:2 to obtain a negative active mixture;

[0116] (5) Coating the positive and negative surfaces of the substrate coated with the modified functional layer and the conductive layer with the negative active mixture, forming a negative active material layer on the surface of the substrate coated with the modified functional layer and the conductive layer, and obtaining a negative electrode plate.

[0117] Example 8

[0118] (1) Obtain a copper substrate;

[0119] (2) Coating the positive and negative surfaces of the substrate with 1 μm thick polydopamine to form a modified functional layer on the surface of the substrate;

[0120] (3) Apply a 0.5-μm-thick polyurethane coating on both the front and back surfaces of the substrate coated with the modification functional layer to form a conductive layer on the surface of the substrate coated with the modification functional layer;

[0121] (4) Mix graphite, polyacetylene, polyaniline, and polydopamine in a mass ratio of 96:2:2 to obtain a negative electrode active mixture;

[0122] (5) Apply the negative electrode active mixture on both the front and back surfaces of the substrate coated with the modification functional layer and the conductive layer to form a negative electrode active material layer on the surface of the substrate coated with the modification functional layer and the conductive layer, thereby obtaining a negative electrode plate.

[0123] Comparative Example 1

[0124] (1) Obtain a copper substrate;

[0125] (2) Mix graphite, polypyrrole, and polydopamine in a mass ratio of 96:2:2 to obtain a negative electrode active mixture;

[0126] (3) Apply the negative electrode active mixture on both the front and back surfaces of the substrate to form a negative electrode active material layer on the surface of the substrate, thereby obtaining a negative electrode plate.

[0127] The following uses specific experimental data to illustrate some advantages of the embodiments of the present invention compared with the prior art.

[0128] Prepare the negative electrode plates obtained in the above Examples 1-8 and Comparative Example 1 into soft-pack batteries. Among them, the positive electrode plate of the soft-pack battery includes lithium nickel cobalt manganese oxide, a second binder, and a second conductive agent. Among them, the second binder can be polyvinylidene fluoride (PVDF). The second conductive agent can be substances such as graphite, acetylene black, and carbon nanotubes that can be used to improve the conductivity of the positive electrode plate. The electrolyte can be a mixed solution of ethylene carbonate, diethyl carbonate, and ethyl methyl carbonate containing a lithium salt.

[0129] Perform performance tests on the prepared soft-pack batteries. To simulate the influence of battery self-discharge on voltage, the method of the performance test includes: at room temperature (25 °C), fully charge the battery at a current of 1 / 3C. After full charge, discharge the battery at a current of 1 mA to 0 V. Observe whether the battery bulges after the voltage drops to 0 V. Then, fully charge the battery at a current of 1 / 3C again and disassemble the interface. Observe whether copper elements appear on the interface of the positive or negative electrode plate through EDS (X-ray energy dispersive spectrometer).

[0130] The test results are shown in Table 1:

[0131] Table 1

[0132] Battery appearance when over-discharged to 0V Full charge interface after over-discharging to 0V Example 1 Slight swelling Slight copper deposition Example 2 Flat appearance No copper deposition Example 3 Flat appearance No copper deposition Example 4 Flat appearance No copper deposition Example 5 Flat appearance No copper deposition Example 6 Flat appearance No copper deposition Example 7 Flat appearance No copper deposition Example 8 Flat appearance No copper deposition Comparative Example 1 Severe swelling Severe copper deposition

[0133] It can be seen that, compared with Comparative Example 1 without the modification functional layer and the conductive layer, Examples 1-8 can all be charged after over-discharging to 0V, and the copper deposition phenomenon after discharging to 0V is significantly alleviated compared with that obtained in Comparative Example 1. Among them, Example 1 with the modification functional layer added can better alleviate the copper deposition phenomenon. And Examples 2-8 with both the modification functional layer and the conductive layer added provide good protection and shielding for the copper substrate through the synergistic effect of the modification functional layer and the conductive layer, avoiding the dissolution and precipitation of copper in the case of over-discharging of the lithium-ion battery. At the same time, the overall structure of the present invention is simple, the preparation process is simple, and the impact on the battery capacity is small. While effectively reducing the safety risk of the battery during over-discharge, it is applicable to actual production.

[0134] The above has introduced in detail a negative electrode sheet of a lithium-ion battery, a preparation method of a negative electrode sheet of a lithium-ion battery, a lithium-ion battery, and a vehicle provided by the present invention. Specific examples are used in this article to elaborate on the principle and implementation manner of the present invention. The description of the above examples is only used to help understand the method and its core idea of the present invention; 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 manner and application scope. In summary, the content of this specification should not be construed as a limitation to the present invention.

Claims

1. A negative electrode sheet of a lithium-ion battery, characterized in that, The lithium-ion battery is used for charging after discharging to 0V. The negative electrode sheet includes: a substrate, a modified functional layer coating the substrate, and a negative electrode active material layer coating the modified functional layer; the substrate material includes copper, and the modified functional layer includes a polymer compound containing a catechol structure; wherein, the polymer compound containing a catechol structure is used to prevent the oxidation of the substrate and prevent the dissolution or precipitation of the substrate when charging the lithium-ion battery in an over-discharged state; the negative electrode active material layer is used to provide an insertion / extraction channel for lithium ions; wherein, the negative electrode sheet further includes a conductive layer disposed between the modified functional layer and the negative electrode active material layer, and the conductive layer includes at least one of polypyrrole, polyacetylene, polyaniline, polythiophene, and polyurethane; the conductive layer is used to protect and shield the substrate and increase the corrosion potential of the substrate.

2. The negative electrode sheet according to claim 1, characterized in that, The polymer compound containing a catechol structure includes polydopamine.

3. The negative electrode sheet according to claim 1 or 2, characterized in that The negative electrode active material layer includes a negative electrode active material and a first binder, or the negative electrode active material layer includes a negative electrode active material, a first binder, and a first conductive agent; the negative electrode active material includes at least one of graphite, soft carbon, hard carbon, and mesocarbon microbeads.

4. The negative electrode sheet according to claim 3, characterized in that, The first binder includes polydopamine, and the first conductive agent includes at least one of polypyrrole, polyacetylene, polyaniline, polythiophene, and polyurethane.

5. A method for preparing a negative electrode sheet of a lithium-ion battery, characterized in that, The lithium-ion battery is used for charging after discharging to 0V. The method includes: obtaining a substrate; the substrate material includes copper; coating a modified functional layer on the surface of the substrate; the modified functional layer includes a polymer compound containing a catechol structure, and the polymer compound containing a catechol structure is used to prevent the oxidation of the substrate and prevent the dissolution or precipitation of the substrate when charging the lithium-ion battery in an over-discharged state; coating a conductive layer on the surface of the modified functional layer; the conductive layer includes at least one of polypyrrole, polyacetylene, polyaniline, polythiophene, and polyurethane; the conductive layer is used to protect and shield the substrate and increase the corrosion potential of the substrate; coating a negative electrode active material layer on the surface of the conductive layer to obtain a negative electrode sheet; the negative electrode active material layer is used to provide an insertion / extraction channel for lithium ions.

6. A lithium-ion battery, characterized in that, The lithium-ion battery includes the negative electrode sheet according to any one of claims 1 to 4, or includes the negative electrode sheet prepared by the preparation method according to claim 5.

7. The lithium ion battery according to claim 6, wherein The lithium-ion battery further includes a positive electrode sheet and an electrolyte; the positive electrode sheet includes lithium nickel cobalt manganese oxide, a second binder, and a second conductive agent; the electrolyte includes a lithium salt and a solvent, and the solvent includes at least one of ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, and ethyl methyl carbonate.

8. A vehicle, characterized in that, The vehicle includes the lithium-ion battery according to claim 6 or 7.

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