Compositions and preparation methods for negative electrode undercoating, negative electrode electrodes, electrochemical devices, and electrical devices.

Abstract

This application discloses a composition and preparation method for a negative electrode undercoating, a negative electrode electrode, an electrochemical device, and an electrical device. The composition, by mass percentage, comprises the following components: molybdate, 5%–25%; conductive agent, 0.5%–10%; binder, 0.3%–1.5%; and graphite particles, 70%–90%. The conductive undercoating formed by drying the composition for the negative electrode undercoating in this application has a certain roughness, which allows for a tighter bond between the undercoating and the negative electrode material, thereby indirectly enhancing the adhesion between the negative electrode material and the copper foil, effectively improving the technical problem of film removal. Simultaneously, utilizing the high ionic conductivity of molybdate, the thickness of the graphite layer used as the negative electrode material can be appropriately reduced, minimizing the increase in electrode thickness and energy density loss caused by electrode expansion and internal stress release, effectively reducing battery impedance, and improving the battery's energy density, cycle life, and rate performance.

Description

Technical Field

[0001] This application belongs to the field of lithium battery material technology, and particularly relates to a composition and preparation method for a negative electrode undercoating, a negative electrode, an electrochemical device, and an electrical device. Background Technology

[0002] Currently, the negative electrode sheet of power lithium-ion secondary batteries is generally made by directly coating the negative electrode slurry onto a smooth copper foil. The surface of the copper foil is relatively smooth, and the adhesion strength between the copper foil and the negative electrode slurry is relatively weak. During the production process and subsequent battery cycles, as the electrode sheet expands and internal stress is released, the negative electrode is prone to demolding, causing battery failure.

[0003] Existing technologies typically involve adding an adhesive coating between the negative electrode material and the copper foil to improve the film removal problem, but this also increases the thickness of the negative electrode sheet and reduces energy density. This application aims to propose an improvement to address this issue. Summary of the Invention

[0004] This application provides a composition for a negative electrode undercoating, which can improve the problem of film separation between the negative electrode material and the copper foil without increasing or decreasing the thickness of the negative electrode and without causing a loss of energy density.

[0005] In a first aspect, this application provides a composition for a negative electrode undercoating, comprising, by weight percentage, the following components:

[0006] Molybdate, 5%–25%;

[0007] Conductive agent, 0.5%–10%;

[0008] Adhesive, 0.3%–1.5%;

[0009] Graphite particles, 70%–90%.

[0010] Molybdates possess high electronic conductivity and specific capacity (≥600 mAh / g). Combined with the aforementioned conductive agents and graphite particles, they can effectively accept some lithium ions, increasing battery energy density while reducing the negative electrode's bulk impedance, thus improving the battery's rate performance and cycle performance. Furthermore, the composition used for the negative electrode undercoat, after modifying the undercoat slurry, results in a conductive undercoat layer with a certain degree of roughness after drying. This allows for a tighter bond between the undercoat layer and the negative electrode material, indirectly enhancing the adhesion between the negative electrode material and the copper foil.

[0011] In the composition of the negative electrode undercoat in this application embodiment, graphite particles act as an excipient, and when mixed with molybdate, they can form a dense undercoat. If the undercoat is simply a molybdate coating, the coating is brittle and easily peels off.

[0012] In one embodiment of this application, the composition for the negative electrode undercoat further comprises, by weight percentage, the following components:

[0013] Dispersant, 0.05%–0.1%.

[0014] In one embodiment of this application, the dispersant is lithium carboxymethyl cellulose.

[0015] The content of the dispersant is preferably 0.06% to 0.08%.

[0016] In one embodiment of this application, the content of molybdate is preferably 5% to 20%, more preferably 5% to 10%.

[0017] In one embodiment of this application, the molybdate is selected from alkali metal salts, alkaline earth metal salts, iron salts, or combinations thereof.

[0018] In one embodiment of this application, the alkali metal salt of the molybdate is selected from Li₂MoO₄, Na₂MoO₄, K₂MoO₄, or a combination thereof; and / or

[0019] The alkaline earth metal salt of molybdate is MgMoO4; and / or

[0020] The iron salts of molybdates are selected from LiFe(MoO4)2, KFe(MoO4)2, or combinations thereof.

[0021] In one embodiment of this application, the combination of alkali metal salts is Li2MoO4 and Na2MoO4, or Li2MoO4 and K2MoO4.

[0022] In one embodiment of this application, the conductive agent is selected from conductive carbon black, Ketjen black, carbon nanotubes, or combinations thereof.

[0023] In one embodiment of this application, the composition for the negative electrode undercoat contains 1% to 5% of a conductive agent, which is conductive carbon black.

[0024] In one embodiment of this application, the composition for the negative electrode undercoat contains 1% to 3% of a conductive agent, wherein the conductive agent is Ketjen Black.

[0025] In some embodiments, the conductive carbon black is Super-P Li, and the Ketjen black is ECP.

[0026] In one embodiment of this application, the composition for the negative electrode undercoat contains 0.5% to 2.0% of a conductive agent, wherein the conductive agent is carbon nanotubes.

[0027] In one embodiment of this application, the adhesive is selected from styrene-butadiene rubber, polytetrafluoroethylene, polystyrene ester, or a combination thereof.

[0028] In one embodiment of this application, the composition for the negative electrode undercoat contains 0.3% to 1.4% of a binder, the binder being independently selected from styrene-butadiene rubber, polytetrafluoroethylene, and polyacrylate.

[0029] In one embodiment of this application, the graphite particles have a graphitization degree ≥90% and an average particle size D90 of 15 micrometers to 30 micrometers. The graphite particles are natural graphite or synthetic graphite.

[0030] The composition for the negative electrode undercoating of this application embodiment is used to prepare the undercoating of the negative electrode of a lithium-ion battery.

[0031] Secondly, embodiments of this application provide a method for preparing the above-described composition for a negative electrode undercoating, comprising:

[0032] S1. Preparation of adhesive solution: Mix part of the adhesive with deionized water or mix the dispersant and part of the adhesive with deionized water thoroughly to obtain adhesive solution A;

[0033] S2. Thoroughly mix the conductive agent and molybdate with adhesive A to obtain solution B containing the conductive agent and molybdate;

[0034] S3. Mix the graphite particles with the remaining binder to obtain slurry C;

[0035] S4. Thoroughly mix slurry C with solution B to obtain a composition for the undercoating of the negative electrode.

[0036] In one embodiment of this application, the step of preparing the adhesive solution includes thoroughly mixing a portion of the binder with deionized water, or mixing a dispersant and a portion of the binder with deionized water at a mass ratio of 1:10 to 1000. Preferably, a portion of the binder, or a portion of the dispersant and a portion of the binder, is thoroughly mixed with deionized water at a mass ratio of 1:80 to 500. More preferably, a portion of the binder, or a portion of the dispersant and a portion of the binder, is thoroughly mixed with deionized water at a mass ratio of 1:120 to 180.

[0037] Thirdly, embodiments of this application provide a negative electrode, comprising:

[0038] current collector;

[0039] A base coating layer is applied to at least one surface of the current collector, the base coating layer being formed from the composition described above for a negative electrode base coating layer;

[0040] A layer of negative electrode active material is disposed on the base coating.

[0041] In one embodiment of this application, the current collector is selected from copper foil, platinum sheet; and / or

[0042] The negative electrode active material layer is selected from graphite materials or silicon negative electrode materials.

[0043] For example, the graphite material is natural graphite or artificial graphite; the silicon anode material is silicon suboxide.

[0044] Fourthly, embodiments of this application provide a method for preparing a negative electrode, comprising:

[0045] The composition for the negative electrode undercoat was prepared according to the above-described method.

[0046] It provides layered current collectors and negative electrode active materials;

[0047] The obtained composition for the negative electrode undercoat is applied onto the current collector to form the undercoat.

[0048] A negative electrode active material layer is coated on the back surface opposite to the current collector layer, that is, the negative electrode active material is coated on the base layer to obtain the negative electrode electrode.

[0049] The composition for the negative electrode undercoat of this application uses deionized water as the undercoat solvent. The amount of the undercoat solvent added can be adjusted according to the needs of the coating operation of the composition for the negative electrode undercoat. The thickness of the undercoat of the composition for the negative electrode undercoat is 1 micrometer to 3 micrometers.

[0050] Fifthly, embodiments of this application provide an electrochemical device, comprising:

[0051] positive electrode;

[0052] Separating membrane;

[0053] The above-mentioned negative electrode containing a composition for a negative electrode undercoat.

[0054] Sixthly, embodiments of this application also provide an electrical device, including the electrochemical device described above.

[0055] The composition for the negative electrode undercoat of this application has a certain roughness in the conductive undercoat formed after drying. This allows the conductive undercoat composed of the composition for the negative electrode undercoat to bond more tightly with the negative electrode material, thereby indirectly enhancing the adhesion between the negative electrode material and the copper foil and effectively improving the technical problem of film removal. At the same time, by utilizing the high ionic conductivity of molybdate, the thickness of the graphite layer can be appropriately reduced, reducing the increase in electrode thickness and energy density loss caused by electrode expansion and internal stress release. This also effectively reduces the battery impedance and improves the battery's energy density, cycle life, and rate performance. Attached Figure Description

[0056] To more clearly illustrate the technical solutions of the embodiments of this application, the accompanying drawings used in the embodiments of this application will be briefly introduced below. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0057] Figure 1 This is a schematic flowchart illustrating a method for preparing a composition for a negative electrode undercoating according to an embodiment of this application;

[0058] Figure 2 This is a schematic diagram of the structure of a negative electrode containing a composition for a negative electrode undercoating, according to another embodiment of this application.

[0059] Figure 3 This is a graph showing the capacity retention rate-cycle count test results of the undercoating compositions for negative electrode undercoatings provided in Example 2 and Comparative Example 1 in the battery cell system.

[0060] Explanation of reference numerals in the attached figures:

[0061] 1. Graphite layer; 2. Undercoat containing a composition for the negative electrode undercoat; 3. Copper foil as a current collector. Detailed Implementation

[0062] The features and exemplary embodiments of various aspects of this application will be described in detail below. To make the objectives, technical solutions, and advantages of this application clearer, the application will be further described in detail below with reference to the accompanying drawings and specific embodiments. It should be understood that the specific embodiments described herein are only intended to explain this application and not to limit it. For those skilled in the art, this application can be implemented without some of these specific details. The following description of the embodiments is merely to provide a better understanding of this application by illustrating examples.

[0063] It should be noted that, in this document, relational terms such as "first" and "second" are used merely to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitations, an element defined by the phrase "comprising..." does not exclude the presence of additional identical elements in the process, method, article, or apparatus that includes said element.

[0064] As described in the background section, while existing technologies improve the problem of negative electrode material and copper foil delamination, they also cause an increase in the thickness of the negative electrode sheet and a loss of energy density.

[0065] Meanwhile, due to the presence of the passivation film on the surface of the metal foil, the contact resistance between the simple battery slurry coating and graphite coating and the copper foil is relatively large, that is, the contact resistance between the base coating and the current collector is relatively large, which leads to poor conductivity between the battery slurry coating and the copper foil, affecting the performance of the battery.

[0066] To address the problems of the prior art, this application provides a composition for a negative electrode undercoating and a method for preparing the same. The method for preparing the composition for a negative electrode undercoating provided in this application will be described first.

[0067] Example 1: This example provides a composition for a negative electrode undercoat, comprising, by weight percentage: 5% lithium iron molybdate, 0.50% conductive agent, the conductive agent being a mixture of 0.4% conductive carbon black and 0.1% carbon nanotubes, 1.30% binder styrene-butadiene rubber, and 93.2% natural graphite.

[0068] Example 2: This example provides a composition for a negative electrode undercoating, comprising, by weight percentage: 10% lithium iron molybdate, 0.50% conductive agent, the conductive agent being a mixture of 0.4% conductive carbon black and 0.1% carbon nanotubes, 1.30% binder styrene-butadiene rubber, and 88.2% natural graphite.

[0069] Comparative Example 1: This comparative example provides a composition for a negative electrode undercoating, comprising, by weight percentage: 0% lithium iron molybdate, 0.50% conductive agent, the conductive agent being a mixture of 0.4% conductive carbon black and 0.1% carbon nanotubes, 1.30% binder styrene-butadiene rubber, and 98.2% natural graphite.

[0070] The compositions of Examples 1 and 2 and the comparative example are shown in Table 1 below:

[0071] Table 1. Composition of the negative electrode undercoat coating of Comparative Example 1 and Examples 1 and 2

[0072]

[0073] Figure 1 A schematic flowchart of a method for preparing a composition for a negative electrode undercoat provided in one embodiment of this application is shown.

[0074] The compositions for negative electrode undercoating of Examples 1 and 2 and Comparative Example 1 were prepared according to the preparation method of the composition for negative electrode undercoating to obtain the corresponding compositions for negative electrode undercoating.

[0075] Example 3: This example uses the composition for preparing the negative electrode undercoating of Example 1 as an example to provide a method for preparing the composition for preparing the negative electrode undercoating, including:

[0076] It provides 5% lithium iron molybdate, 0.5% conductive agent, which is a mixture of 0.4% conductive carbon black Super-P Li and 0.1% carbon nanotubes, 1.3% styrene-butadiene rubber, 98.2% natural graphite and deionized water;

[0077] Preparation of adhesive solution: Mix 1 / 3 of the 1.3% styrene-butadiene rubber binder with deionized water thoroughly to obtain adhesive solution A; wherein the mass of deionized water is 100 times the mass of styrene-butadiene rubber.

[0078] Preparation of conductive liquid: Mix 0.5% conductive agent with adhesive A thoroughly to form a conductive liquid with a conductive network;

[0079] Mixing of molybdates: Add 5% lithium iron molybdate to a conductive liquid to obtain solution B;

[0080] Natural graphite with a content of 98.2% was mixed with the remaining 2 / 3 of styrene-butadiene rubber to obtain slurry C;

[0081] The slurry C and solution B are thoroughly mixed to obtain a lithium iron molybdate doped composition.

[0082] In this embodiment, only one order of adding the conductive agent and molybdate is given as an example. The conductive agent and molybdate can also be added to the adhesive A at the same time, or the molybdate can be added first and then the conductive agent can be added to obtain a solution B containing the conductive agent and molybdate.

[0083] The compositions for negative electrode undercoating of Example 2 and Comparative Example 1 were prepared into their respective compositions for negative electrode undercoating by the same preparation method as in Example 3.

[0084] Example 4: This example provides a negative electrode containing a composition for a negative electrode undercoating, such as... Figure 2 As shown, the negative electrode includes:

[0085] Current collector, the current collector is copper foil 3;

[0086] A base coating 2 is applied to at least one surface of the current collector, the base coating being formed from the composition for the negative electrode base coating of Example 3;

[0087] A negative electrode active material layer is provided on the base coating layer; in this embodiment, it is graphite layer 1.

[0088] The negative electrode of this embodiment, containing a composition for a negative electrode undercoat, is prepared according to the following method, including:

[0089] The slurry-like composition for the negative electrode undercoat prepared in Example 3 above is coated on one side surface of the current collector copper foil 3 to form an undercoat 2 with a thickness of 3 micrometers. Then, a negative electrode material layer graphite layer 1 is coated on the undercoat 2 to obtain a negative electrode containing the composition for the negative electrode undercoat.

[0090] Performance testing

[0091] 1. Cyclic Voltmeter-Ampere Performance Test

[0092] The compositions for the negative electrode undercoating of Example 2 and Comparative Example 1 were prepared into negative electrode electrodes containing the compositions for the negative electrode undercoating using the same preparation method as in Example 4, and applied to the following cell systems:

[0093] Square aluminum-cased battery, dimensions: 52*148*106 mm, test voltage: 2.8V~4.35V;

[0094] Negative electrode: Graphite negative electrode prepared in Examples 1 and 2 and Comparative Example 1;

[0095] Positive electrode: NCM613;

[0096] Electrolyte: Lithium salt is LiPF6, and diluent is 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether;

[0097] Lithium salt LiPF6 was dissolved in a non-aqueous solvent to obtain a lithium salt solution with a molar concentration of 4 mol / L. The non-aqueous solvent was a mixture of ethylene carbonate and dimethyl carbonate in a volume ratio of 1:3.

[0098] Add a diluent to the lithium salt solution to dilute the lithium salt molar concentration to 0.5 mol / L to obtain the battery electrolyte.

[0099] The cell systems of Comparative Example 1 and Examples 1 and 2 were subjected to cycle performance tests under the same test conditions. Their electrode film internal resistance, energy density, DC internal resistance, cycle capacity retention, and room temperature 2C rate discharge capacity retention were tested. The test results of the cycle voltage-current performance are recorded in Table 2 below.

[0100] 2. Electrode bonding performance test

[0101] The negative electrode electrodes prepared in Examples 1 and 2, as well as Comparative Example 1, were subjected to electrode adhesion tests. The specific test steps were as follows:

[0102] Several rectangular negative electrode samples with a length of 260 mm and a width of 37 mm were made from the rolled negative electrode film. Double-sided adhesive tape with a length and width of 10 mm was attached to the negative electrode head of the sample (tape model: NITTO.5000NS0). The sample to be tested was placed in the tensile testing device of an electronic universal testing machine to measure the peel force between the tape and the graphite layer, and to obtain the adhesion force between the graphite of the negative electrode material and the substrate. The tensile testing device had a lifting speed of 50 mm / min, a tensile displacement of 150 mm, an accuracy of ±0.1 N for the tensile sensor in the tensile testing device, and a tensile direction of 60°. The test results of the adhesion performance were recorded in Table 2 below.

[0103] 3. Diaphragm internal resistance test method

[0104] The rolled negative electrode film was cut into 60mm x 80mm diameter pieces to serve as the negative electrode. These pieces were placed between the two electrodes of the film resistance meter. The test pressure was set to 0.6MPa and the holding time to 15 seconds on the MRMS testing software. The test was then started, and the MRMS software automatically read the film thickness and resistance value, recording them in Table 2 below. The film resistance meter used for the test was a BER1300, purchased from IEST Yuaneng Technology (Xiamen) Co., Ltd.

[0105] Table 2. Performance test results of the negative electrode undercoat coating in the battery cell system for Comparative Example 1 and Examples 1 and 2.

[0106] Electrode adhesion strength (N / m) 8 12 14 Electrode diaphragm internal resistance (Ω) 3 2.61 2.43 Energy density (Wh / kg) 249 252 255 Graphite layer thickness (μm) 131 129 127 DC internal resistance (mΩ) 0.82 0.779 0.72 Cyclic capacity retention (1C / 1C) 800cys / 90% 800 cys / 91.3% 800 cys / 91.7% Capacity retention rate at room temperature 2C rate discharge 95.40％ 96.10％ 97.20％

[0107] From the test data in Table 2, we can conclude that:

[0108] Compared to a negative electrode cell system that does not contain a composition for the negative electrode undercoating, when the negative electrode contains a composition for the negative electrode undercoating, and with the increase of the molybdate content in the composition for the negative electrode undercoating, the cycle performance of the battery significantly and gradually improves. The capacity retention rate after 800 cycles increases from 90% in the cell system without the composition for the negative electrode undercoating in Comparative Example 1 to 91.3% and 91.7% in the cell systems with the composition for the negative electrode undercoating in Examples 1 and 2, respectively, representing an improvement in cycle performance of 1.3% to 1.7%. The comparison results of the capacity retention rate after 800 cycles between the cell systems of Example 2 and Comparative Example 1 are as follows: Figure 3 As shown;

[0109] The capacity retention rate at room temperature 2C rate discharge was increased from 95.4% in the battery cell system without the negative electrode undercoating in Comparative Example 1 to 96.10% and 97.2% in the battery cell systems with the negative electrode undercoating in Examples 1 and 2, respectively, with a rate discharge performance improvement of 0.7% to 1.8%.

[0110] Meanwhile, the energy density was increased from 249 Wh / kg in the battery cell system without the negative electrode undercoating in Comparative Example 1 to 252 Wh / kg and 255 Wh / kg in the battery cell systems with the negative electrode undercoating in Examples 1 and 2, respectively, with the battery cell energy density increasing by 1.2% to 2.4%.

[0111] The DC internal resistance of the cell system also decreased from 0.82mΩ to 0.779mΩ and 0.72mΩ, and the internal resistance of the electrode film also decreased from 3Ω in the negative electrode of Comparative Example 1 without the composition for the negative electrode undercoat to 2.61Ω and 2.43Ω in the negative electrode of the composition for the negative electrode undercoat, reducing the internal resistance of the negative electrode by 5% to 10%. The above test results show that the molybdate-doped undercoat can effectively improve the battery impedance and cycle performance.

[0112] Furthermore, Table 2 shows that the electrode adhesion strength increased from 8 N / m in the negative electrode of Comparative Example 1 without the composition for the negative electrode undercoat to 12 N / m and 14 N / m in Examples 1 and 2, respectively, representing increases of 50% and 75%. This indicates that the composition used for the negative electrode undercoat in this application can effectively improve the problem of negative electrode delamination and enhance the adhesion strength between the negative electrode material and the copper foil.

[0113] The negative electrode sheet of Comparative Example 1 requires a graphite layer thickness of 131 μm. Compared with the negative electrode sheet of Comparative Example 1, which does not contain molybdate and is used for the negative electrode sheet undercoat, the graphite layer thickness of the negative electrode sheet using the molybdate-containing composition of this application for the negative electrode sheet undercoat can be reduced to 127 μm to 129 μm. The negative electrode sheets of Examples 1 and 2 of this application, with a lower graphite layer thickness, can achieve a higher energy density than the higher graphite layer thickness of Comparative Example 1. This shows that the composition of this application for the negative electrode sheet undercoat can take advantage of the high ionic conductivity of molybdate to appropriately reduce the thickness of the graphite layer, so as to avoid the increase in electrode thickness and the loss of energy density caused by electrode sheet expansion and the release of internal stress.

[0114] The above description is merely a specific implementation of this application. Those skilled in the art will clearly understand that, for the sake of convenience and brevity, the specific working processes of the systems, modules, and units described above can be referred to the corresponding processes in the foregoing method embodiments, and will not be repeated here. It should be understood that the protection scope of this application is not limited thereto. Any person skilled in the art can easily conceive of various equivalent modifications or substitutions within the technical scope disclosed in this application, and these modifications or substitutions should all be covered within the protection scope of this application.

Claims

1. A composition for a negative electrode undercoating, characterized in that, Components included in the following amounts as a percentage by mass: Molybdate, 5%–25%, wherein the molybdate is selected from iron salts of molybdate, combinations of iron salts of molybdate and alkali metal salts, combinations of iron salts of molybdate and alkaline earth metal salts, and combinations of iron salts of molybdate and alkali metal salts and alkaline earth metal salts. Conductive agent, 0.5%–10%; Adhesive, 0.3%–1.5%; Graphite particles, 70%–90%.

2. The composition according to claim 1, characterized in that, The composition for the negative electrode undercoat also includes, by weight percentage, the following components: Dispersant, 0.05%–0.1%.

3. The composition according to claim 2, characterized in that, The dispersant is lithium carboxymethyl cellulose.

4. The composition according to claim 1, characterized in that... The alkali metal salt of the molybdate is selected from Li2MoO4, Na2MoO4, K2MoO4 or a combination thereof.

5. The composition according to claim 1, characterized in that, The alkaline earth metal salt of the molybdate is MgMoO4; and / or The iron salt is selected from LiFe(MoO4)2, KFe(MoO4)2, or a combination thereof.

6. The composition according to any one of claims 1-3, characterized in that, The conductive agent is selected from conductive carbon black, Ketjen black, carbon nanotubes, or combinations thereof.

7. The composition according to claim 6, characterized in that, The composition contains 1% to 5% of a conductive agent, wherein the conductive agent is conductive carbon black; or The composition contains 1% to 3% of a conductive agent, wherein the conductive agent is Ketjen Black; or The composition contains 0.5% to 2.0% of a conductive agent, wherein the conductive agent is carbon nanotubes.

8. The composition according to any one of claims 1-3, characterized in that, The composition contains 0.3% to 1.4% of a binder, which is independently selected from styrene-butadiene rubber, polytetrafluoroethylene, and polyacrylate.

9. The composition according to any one of claims 1-3, characterized in that, The graphite particles have a graphitization degree of ≥90%.

10. The composition according to claim 9, characterized in that, The average particle size D90 of the graphite particles is 15 micrometers to 30 micrometers.

11. A method for preparing a composition for a negative electrode undercoating as described in any one of claims 1-10, characterized in that, include: Preparation of adhesive solution: Mix a portion of the adhesive with deionized water or mix the dispersant and a portion of the adhesive with deionized water thoroughly to obtain adhesive solution A; The conductive agent and molybdate are thoroughly mixed with the adhesive solution A to obtain solution B containing the conductive agent and molybdate; The graphite particles are mixed with the remaining portion of the binder to obtain slurry C; Slurry C and solution B are thoroughly mixed to obtain a composition for the undercoat of the negative electrode.

12. A negative electrode, characterized in that, include: current collector; A base coating on at least one surface of a current collector, said base coating being formed from the composition for a negative electrode base coating as described in any one of claims 1-10; A negative electrode active material layer is disposed on the base coating.

13. The negative electrode according to claim 12, characterized in that, The current collector is selected from copper foil, platinum sheet; and / or The negative electrode active material layer is selected from graphite materials, silicon negative electrode materials, or a combination thereof.

14. An electrochemical device, characterized in that, include: positive electrode; Separating membrane; The negative electrode as described in claim 12 or 13.

15. An electrical appliance, characterized in that, Includes the electrochemical device as described in claim 14.

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