Lithium ion battery negative electrode and preparation method thereof, lithium ion battery and electric device

Abstract

The present application belongs to the field of lithium battery, and particularly relates to a lithium ion battery negative electrode and a preparation method thereof, a lithium ion battery and an electric device. The preparation method of the lithium ion battery negative electrode comprises the following steps: S1: preparing a graphite-SiOx composite negative electrode slurry; S2: sequentially and uniformly coating the surface layer negative electrode slurry and the inner layer negative electrode slurry obtained in step S1 on the surface of a current collector. The present application is aimed at the silicon negative electrode material, and by adopting a double-layer coating process, SiO x is distributed more in the inner layer. The volume expansion of SiO x is effectively inhibited by the graphite in the surface layer, and the overall conductive performance of the negative electrode material is improved. Meanwhile, more binder and conductive agent are distributed in the inner layer, the adhesion of the composite negative electrode is increased, and the contact resistance between the electrode powders and between the electrode powders / current collector is reduced, so that the cycle performance and rate performance of the lithium ion battery are further improved.

Description

Technical Field

[0001] This invention belongs to the field of lithium batteries, specifically relating to a lithium-ion battery negative electrode and its preparation method, a lithium-ion battery, and electrical equipment. Background Technology

[0002] The energy landscape is gradually shifting from traditional petroleum-based energy sources to new energy sources. Lithium-ion batteries, with their long cycle life and high energy density, are widely used in digital products, electric vehicles, and energy storage. In the production of lithium-ion batteries, electrode coating is a crucial process. Currently, the most common coating process for preparing the negative electrode of lithium-ion batteries is the traditional single-layer coating process. However, when dealing with materials with high volume expansion effects (such as silicon), structural collapse due to volume expansion is highly likely during cycling, affecting cycle life. Therefore, there is an urgent need to develop new processes that can solve these problems. Summary of the Invention

[0003] The purpose of this invention is to overcome the shortcomings of the prior art and provide a lithium-ion battery negative electrode and its preparation method, a lithium-ion battery, and an electrical device.

[0004] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0005] A method for preparing a lithium-ion battery negative electrode includes the following steps:

[0006] S1: Preparation of graphite-SiOx composite negative electrode slurry: The graphite-SiOx composite negative electrode slurry includes a surface negative electrode slurry and an inner negative electrode slurry; the SiOx in the surface negative electrode slurry... x The content is less than that of SiO in the inner negative electrode slurry. x Content; wherein, in SiOx, 1≤x≤2; the inner layer in this application specifically refers to the layer close to the current collector, and the surface layer is the layer relatively far from the current collector compared to the inner layer. Figure 1 (as shown);

[0007] S2: The inner negative electrode slurry and the outer negative electrode slurry obtained in step S1 are sequentially and uniformly coated on the surface of the current collector.

[0008] The graphite content and SiO content in graphite-SiOx composite negative electrode slurry x The content ratio is 2-6:1;

[0009] The graphite content and SiO content in the surface negative electrode slurry mentioned in step S1 x The content ratio is 3-9:0-1, preferably 9:1;

[0010] Preferably, the graphite content in the inner negative electrode slurry is related to the SiO content. xThe ratio of the contents is 1-9:1, preferably 3:1.

[0011] In step S2, the inner layer coating amount is 1-20 mg / cm². 2 The surface coating amount is 1-20 mg / cm². 2 The ratio of the surface coating amount to the inner coating amount is 1:2 to 2:1, preferably 1:2.

[0012] The preparation process of the graphite-SiOx composite negative electrode slurry in step S1 is as follows: the binder and conductive agent are thoroughly stirred in a high-speed mixer to achieve uniform dispersion of the conductive agent in the slurry, thus obtaining a conductive slurry; then, SiOx is added to the conductive slurry according to... x Adding SiO to graphite at different mass ratios x The mixture was thoroughly stirred with graphite; finally, deionized water was added to adjust the solid content and viscosity of the slurry, ultimately yielding graphite-SiO₂. x Composite negative electrode slurry;

[0013] Preferably, graphite-SiO x The solid content of the composite negative electrode slurry is 20%-80%, and the viscosity is 2000-8000 mPa·s.

[0014] The present invention also includes a lithium-ion battery negative electrode, comprising a current collector, and an inner active material layer and a surface active material layer sequentially disposed on the surface of the current collector.

[0015] Both the inner active material layer and the outer active material layer contain graphite and SiOx, wherein 1≤x≤2 in SiOx;

[0016] The SiOx content in the surface active material layer is less than the SiOx content in the inner active material layer.

[0017] The ratio of the total graphite content to the total SiOx content in the inner active material layer and the outer active material layer is 2-6:1;

[0018] Preferably, the ratio of graphite content to SiOx content in the inner active material layer is 1-9:1;

[0019] Preferably, the ratio of graphite content to SiOx content in the surface active material layer is 3-9:0-1;

[0020] Preferably, the ratio of SiOx content in the surface active material layer to SiOx content in the inner active material layer is 0-2.5:1-5.

[0021] Graphite content refers to the mass percentage of graphite in the dry basis material of the negative electrode slurry, i.e., the electrode powder (the same applies below). SiO x The content is SiO xThe dry basis material in the negative electrode slurry, i.e., the electrode powder, is expressed as a percentage by mass (hereinafter the same). Unless otherwise specified, all contents in this application refer to mass content.

[0022] The inner active material layer also includes an adhesive, the mass of which accounts for 1%-50% of the total mass of the inner active material layer;

[0023] Preferably, the adhesive is one or a combination of at least two of sodium carboxymethyl cellulose, styrene-butadiene rubber, polyacrylic acid, or sodium alginate;

[0024] Preferably, the inner active material layer further includes a conductive agent, the mass of which accounts for 0.1%-50% of the total mass of the inner active material layer;

[0025] Preferably, the conductive agent is one or a combination of at least two of carbon black, carbon nanotubes, carbon fibers, or graphene.

[0026] The surface active material layer also includes a binder, the mass of which accounts for 1%-100% of the total mass of the surface active material layer;

[0027] Preferably, the adhesive is one or a combination of at least two of sodium carboxymethyl cellulose, styrene-butadiene rubber, polyacrylic acid, or sodium alginate;

[0028] Preferably, the surface active material layer further includes a conductive agent, the mass of which accounts for 0.1%-100% of the total mass of the surface active material layer;

[0029] Preferably, the conductive agent is one or a combination of at least two of carbon black, carbon nanotubes, carbon fibers, or graphene.

[0030] The present invention also includes a lithium-ion battery negative electrode obtained by the preparation method described above.

[0031] The present invention also includes a lithium-ion battery, comprising the negative electrode of the lithium-ion battery.

[0032] Preferably, the lithium-ion battery includes the lithium-ion battery negative electrode, positive electrode, separator, battery casing, and electrolyte.

[0033] The positive electrode consists of active materials, a positive electrode current collector, a conductive agent, and a binder. The active material is a nickel-cobalt-manganese ternary positive electrode material. Based on 100% of the total weight of the dry powder of the positive electrode active material, the mass percentage of lithium nickel oxide is 30-99%, the mass percentage of lithium cobalt oxide is 0-40%, and the mass percentage of lithium manganese oxide is 1-40%.

[0034] The positive electrode current collector is a single-sided, double-sided, or carbon-coated aluminum foil. The conductive agent is one or more of single-walled carbon nanotubes, multi-walled carbon nanotubes, carbon fibers, carbon black, graphite, and graphene. Based on 100% of the total dry-based raw materials used to prepare the positive electrode active layer, the conductive agent's mass percentage in the electrode material is 0.01-10%. The positive electrode binder includes, but is not limited to, PVDF, and its mass percentage in the electrode material is 0.1-10%. The separator is a polymer multilayer separator or a single-layer or double-layer ceramic separator; the electrolyte used in the lithium-ion battery is a ternary lithium battery-specific electrolyte.

[0035] Compared with the prior art, the beneficial effects of the present invention are:

[0036] The lithium-ion battery anode provided by this invention employs a double-layer coating process to make SiO x More of it is distributed in the inner layers; using surface graphite can effectively suppress SiO2. x The volume expansion (the average thickness growth rate after 300 cycles at room temperature was 33.23% lower than that of the control group);

[0037] The lithium-ion battery anode provided by this invention can improve the overall conductivity of the anode material, distribute more binder and conductive agent in the inner layer, increase the adhesion of the composite anode, and reduce the contact resistance between electrode powders and between electrode powder / current collector, thereby further improving the cycle performance and rate performance of the lithium-ion battery (compared with the control group, the cycle performance of the lithium-ion battery is improved by 10% and the 0.5C rate discharge performance is improved by 7% by using the double-layer coating process). Attached Figure Description

[0038] Figure 1 The graphite-SiO in Embodiment 1 of the present invention x Scanning electron microscope images of composite negative electrode slurry;

[0039] Figure 2 These are the room temperature cycling performance curves of Examples 1-6 and Comparative Example 1 of the present invention. Detailed Implementation

[0040] To enable those skilled in the art to better understand the technical solution of the present invention, the present invention will be further described in detail below with reference to the accompanying drawings and preferred embodiments.

[0041] Example 1: A lithium-ion battery was prepared using the following steps:

[0042] S1: Preparation of graphite-SiOx composite negative electrode slurry; the graphite-SiOx composite negative electrode slurry includes a surface negative electrode slurry and an inner negative electrode slurry; the graphite-SiOx composite negative electrode slurry includes a binder, carbon black conductive agent, graphite, and SiO2.x And water; in SiOx, 1≤x≤2;

[0043] The CMC / SBR (sodium carboxymethyl cellulose / styrene-butadiene rubber) composite binder and carbon black conductive agent were thoroughly stirred in a high-speed mixer to achieve uniform dispersion of the conductive agent in the adhesive solution. In the inner negative electrode slurry, the CMC / SBR composite binder accounted for 3.0% of the inner dry base material by mass, and the carbon black conductive agent accounted for 0.75% of the inner dry base material by mass. SiO₂ x The remaining portion of the inner dry base material is supplemented with graphite; in the surface negative electrode slurry, the CMC / SBR composite binder accounts for 1.5% of the surface dry base material by mass, and the carbon black conductive agent accounts for 0.3% of the surface dry base material by mass; SiO x Use graphite to fill in the remaining portion of the surface dry base material;

[0044] Then add SiO to the conductive adhesive solution x And graphite (total graphite content and SiO2) x The content ratio is 4:1, where the surface graphite content is higher than that of SiO2. x The content ratio is 9:1, and the content of inner layer graphite is related to SiO₂. x The content ratio is 3:1, with surface SiO₂ x Content and inner layer SiO x The content ratio is 1:2.5) and the mixture is stirred thoroughly; finally, deionized water is added to adjust the solid content and viscosity of the slurry (solid content is 45-50%, viscosity is 2000-3000 mPa·s), and finally graphite-SiO is obtained. x Composite negative electrode slurry.

[0045] S2: Double-layer coating; the double-layer coating process uses a double-layer die coating machine. The inner layer negative electrode slurry and the outer layer negative electrode slurry are sequentially and evenly coated onto the surface of the copper foil current collector, achieving layered distribution of the slurry on the current collector. The coating amount on one side of the inner layer is 6.0 mg / cm². 2 The surface coating amount on one side is 3.0 mg / cm². 2 After drying, it is rolled (rolled density 1.7 g / cm³). 3 The negative electrode sheet is obtained by slitting, cutting, and stamping.

[0046] S3: Preparation of lithium batteries; high-nickel NCM (nickel-cobalt-manganese) ternary materials are dispersed with conductive agents and binders in NMP (N-methylpyrrolidone), and after thorough stirring, they are uniformly coated on aluminum foil. After drying, rolling, slitting, and punching, positive electrode sheets are obtained. The negative electrode sheets, positive electrode sheets, and separators are assembled into batteries using a fully automated stacking machine (the number of negative electrode stacking layers is 23). After casing, electrolyte injection (the electrolyte is a ternary special electrolyte, with an injection volume of 2g / Ah), encapsulation, and formation, a soft-pack lithium-ion battery based on a high-capacity negative electrode is obtained.

[0047] The differences between Examples 2-6 and Example 1 are shown in Table 1.

[0048] Table 1

[0049]

[0050]

[0051] Comparative Example 1 involves the preparation of a lithium-ion battery using the following steps:

[0052] S1: Preparation of graphite-SiOx composite negative electrode slurry; the graphite-SiOx composite negative electrode slurry includes a surface negative electrode slurry and an inner negative electrode slurry;

[0053] The CMC / SBR composite binder and carbon black conductive agent were thoroughly stirred in a high-speed mixer to achieve uniform dispersion of the conductive agent in the adhesive solution. The CMC / SBR composite binder accounted for 2.5% of the total dry base material by mass, and the carbon black conductive agent accounted for 0.5% of the total dry base material by mass. Then, SiO2 was added to the conductive adhesive solution. x And graphite (total graphite content: SiO) x The mixture was thoroughly stirred at a content ratio of 4:1; finally, deionized water was added to adjust the solid content and viscosity of the slurry (solid content 45-50%, viscosity 2000-3000 mPa·s), ultimately yielding graphite-SiO₂. x Composite negative electrode slurry.

[0054] S2: The negative electrode coating process uses a traditional single-layer die coating machine. The negative electrode slurry is uniformly coated onto the surface of the copper foil current collector, with a single-sided coating amount of 9.0 mg / cm². 2 After drying, it is rolled (rolled density 1.7 g / cm³). 3 ( ), slitting, punching, to obtain negative electrode sheets.

[0055] S3: High-nickel NCM ternary material, conductive agent, and binder are dispersed in NMP, thoroughly stirred, and then uniformly coated on aluminum foil. After drying, rolling, slitting, and punching, a positive electrode sheet is obtained. The negative electrode sheet, positive electrode sheet, and separator are assembled into a battery using a fully automatic stacking machine (the negative electrode stacking layer is 23 layers). After casing, electrolyte injection (the electrolyte is a ternary special electrolyte, with an injection volume of 2g / Ah), encapsulation, and formation, a soft-pack lithium-ion battery based on a high-capacity negative electrode is obtained.

[0056] The performance test results of Examples 1-6 and Comparative Example 1 are shown in Table 2. The room temperature cycling performance of Examples 1-6 and Comparative Example 1 is as follows: Figure 2 As shown.

[0057] Test methods: (1) Capacity, energy density and first-efficiency test: The battery is charged / discharged at 0.2C / 0.2C rate, with a voltage range of 2.5-4.25V, and the test is conducted at room temperature.

[0058] (2) Room temperature cycle performance: The battery was charged / discharged at a rate of 0.5C / 0.5C, with a voltage range of 3.0-4.2V, and tested at 25℃.

[0059] (3) Rate discharge performance: The voltage range is 2.5-4.25V. The battery is charged at a rate of 0.2C and discharged at a rate of 0.1C / 0.2C / 0.33C / 0.5C. The test is conducted at 25℃.

[0060] Table 2

[0061]

[0062] Table 2 and Figure 2 The performance data of Examples 1-6 and Comparative Example 1 are recorded in the document. Figure 2 The best results in terms of capacity retention were found in Example 1, followed by Examples 3, 6, 4, 5, 2, and Comparative Example 1.

[0063] As can be seen from Example 2 (Comparative Example 2), when the total graphite content is: SiO x When the content ratio is 4:1, SiO x The surface layer has a higher mass percentage than the inner layer, making it impossible to suppress SiO2 during cycling. x The volume expansion ultimately leads to a decrease in cycle performance and rate performance.

[0064] Compared with Comparative Examples 1 and 2 (Comparative Example 2), Examples 1 and 3-6 showed a 33.23% decrease in the average thickness growth rate after 300 cycles at room temperature compared with the control group. It can be seen that the lithium-ion battery anode provided by the present invention, by adopting a double-layer coating process, allows more SiOx to be distributed in the inner layer, and the surface graphite can effectively suppress the volume expansion of SiOx.

[0065] Compared to the traditional single-layer coating method used in Comparative Example 1, the graphite-SiO2 prepared using the double-layer coating process in Examples 1-6... x The composite anode material and lithium-ion battery showed superior performance compared to Comparative Example 1 in terms of capacity, charge-discharge efficiency, cycle performance, and rate discharge, indicating that the novel double-layer coating process has a significant effect on improving the performance of silicon-based anodes and lithium-ion batteries.

[0066] In Examples 3 and 4, the inner layer SiO x The relatively increased content resulted in poor rate performance; in Example 5, SiO was added. x The mass percentage can significantly improve the battery's capacity and energy density, but due to the inner SiO layer... x Excessive amounts of graphite on the surface prevent it from effectively suppressing SiO₂. x The volume expansion of SiO2 will reduce the cycle performance of the battery; in Example 6, SiO2... x The reduced mass percentage leads to lower battery capacity, energy density, and rate discharge performance, but the increased graphite content effectively suppresses silicon volume expansion, resulting in better cycle performance. In Example 1, a larger amount of SiO2 was used. x The graphite distributed in the inner layer and the graphite on the surface effectively suppress the SiO₂ in the inner layer. x The volume expansion significantly improves the battery's cycle performance, while also maintaining high capacity and rate discharge performance.

[0067] In other words, the graphite content in the surface negative electrode slurry described in step S1 of Examples 1, 3, and 6 is: SiO x The content ratio is 9:1; the graphite content in the inner layer negative electrode slurry is: SiO x The content ratio is 2.5-5:1; the surface coating amount: inner coating amount is 1:2, and the surface SiO content is... x Content and inner layer SiO x With a content ratio of 1:1.5-3, the cycle performance is better, while the graphite content in the surface negative electrode slurry described in step S1 of Example 1 is: SiO₂ x The content ratio is 9:1; the graphite content in the inner layer negative electrode slurry is: SiO x The content ratio is 3:1; the surface coating amount: inner coating amount is 1:2, and the surface SiO content is 3:1. x Content and inner layer SiOx The best cycle performance is achieved when the content ratio is 1:2.5.

[0068] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for preparing a lithium-ion battery negative electrode, characterized in that, Includes the following steps: S1: preparing a graphite-SiOx composite negative electrode slurry: the graphite-SiOx composite negative electrode slurry includes a surface layer negative electrode slurry and an inner layer negative electrode slurry; the content of SiO x in the surface layer negative electrode slurry is less than the content of SiO x in the inner layer negative electrode slurry; wherein 1≤x≤2 in SiOx. Graphite-SiOx composite negative electrode slurry graphite content and SiO x content ratio of 4:1; The ratio of the content of graphite to the content of SiO x 9:

1. The ratio of the content of graphite to the content of SiO x 3:

1. S2: sequentially and uniformly coating the inner layer negative electrode slurry and the surface layer negative electrode slurry obtained in step S1 on the surface of the current collector; the inner layer coating amount is 1-20 mg / cm 2 , the surface layer coating amount is 1-20 mg / cm 2 ; the ratio of the surface layer coating amount to the inner layer coating amount is 1:

2.

2. The method for preparing a lithium-ion battery negative electrode according to claim 1, characterized in that, The preparation process of the graphite-SiOx composite negative electrode slurry in step S1 is as follows: the binder and conductive agent are thoroughly stirred in a high-speed mixer to achieve uniform dispersion of the conductive agent in the slurry, thus obtaining a conductive slurry; then, SiOx is added to the conductive slurry according to... x Adding SiO to graphite at different mass ratios x The mixture was thoroughly stirred with graphite; finally, deionized water was added to adjust the solid content and viscosity of the slurry, ultimately yielding graphite-SiO₂. x Composite negative electrode slurry.

3. The method for preparing a lithium-ion battery negative electrode according to claim 2, characterized in that, Graphite-SiO x The solid content of the composite negative electrode slurry is 20%-80%, and the viscosity is 2000-8000 mPa·s.

4. A lithium-ion battery negative electrode, characterized in that, It is obtained by the preparation method according to any one of claims 1-3.

5. The lithium-ion battery negative electrode according to claim 4, characterized in that, The inner negative electrode slurry also includes a binder, the mass of which accounts for 1%-50% of the total mass of the inner negative electrode slurry; The adhesive is one or a combination of at least two of sodium carboxymethyl cellulose, styrene-butadiene rubber, polyacrylic acid, or sodium alginate. The inner negative electrode slurry also includes a conductive agent, the mass of which accounts for 0.1%-50% of the total mass of the inner negative electrode slurry; The conductive agent is one or a combination of at least two of carbon black, carbon nanotubes, carbon fibers, or graphene.

6. The lithium-ion battery negative electrode according to claim 4, characterized in that, The surface negative electrode slurry also includes a binder, the mass of which accounts for 1%-1.5% of the total mass of the surface negative electrode slurry; The adhesive is one or a combination of at least two of sodium carboxymethyl cellulose, styrene-butadiene rubber, polyacrylic acid, or sodium alginate. The surface negative electrode slurry also includes a conductive agent, the mass of which accounts for 0.1%-0.3% of the total mass of the surface active material layer; The conductive agent is one or a combination of at least two of carbon black, carbon nanotubes, carbon fibers, or graphene.

7. A lithium-ion battery, comprising the lithium-ion battery negative electrode as described in any one of claims 5-6.

8. An electrical device comprising the lithium-ion battery of claim 7.

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