Quick-charge type high-specific-capacity negative electrode plate, preparation method thereof and lithium ion battery

Abstract

The invention belongs to the technical field of lithium ion batteries, and particularly relates to a fast-charging type high-specific-capacity negative electrode plate, a preparation method thereof and a lithium ion battery. The invention provides a fast-charging type high-specific-capacity negative electrode plate. The fast-charging type high-specific-capacity negative electrode plate comprises a current collector, inner layers close to the two sides of the current collector and outer layers far away from the two sides of the current collector, the inner layer contains high-energy graphite and a silicon-containing material, and the outer layer contains high-power graphite and a fast charging material. The negative plate has a double-layer structure, the specific capacity of the negative plate is improved by using the high-energy graphite and the silicon-containing material in the inner layer, and the conductivity and the ion transmission performance of the negative plate are improved by using the high-power graphite and the fast charging material in the outer layer, so that the high specific capacity and the fast charging performance of the negative plate are realized.

Description

Technical Field

[0001] This invention belongs to the field of lithium-ion battery technology, specifically relating to a fast-charging high-specific-capacity negative electrode sheet, its preparation method, and a lithium-ion battery. Background Technology

[0002] With the continuous development of consumer electronics, users have placed higher demands on the functionality and convenience of devices. Modern electronic products not only pursue powerful hardware and software performance but also require devices to be lightweight and portable. Against this backdrop, batteries, as the core component of electronic products, face increasingly higher performance requirements. Especially with limited battery compartment space and increasingly demanding device sealing, balancing battery size and performance has become a key design issue.

[0003] Currently, most lithium-ion batteries on the market face the following challenges: High energy density requirements: As devices become increasingly powerful, especially high-performance electronic products such as smartphones and laptops, the demand for battery energy density is rising. Batteries need to store more energy within a limited space to meet the needs of devices operating for extended periods. Fast charging capability: With the development of fast charging technology, users' demands for charging speed are constantly increasing. However, traditional lithium-ion batteries tend to generate significant heat at high charging rates, leading to anxiety and discomfort during charging. Improving charging capability while maintaining battery safety and efficiency during fast charging is a major challenge for lithium-ion battery technology. Summary of the Invention

[0004] The present invention aims to at least partially solve one of the technical problems in related technologies. To this end, embodiments of the present invention propose a fast-charging high-specific-capacity negative electrode.

[0005] The fast-charging high-capacity negative electrode sheet of this invention includes a current collector, an inner layer close to both sides of the current collector, and an outer layer away from both sides of the current collector.

[0006] The inner layer contains high-energy graphite and silicon-containing materials, while the outer layer contains high-power graphite and fast-charging materials.

[0007] The fast-charging high-specific-capacity negative electrode sheet of this invention adopts a double-layer design. The inner layer uses high-energy graphite and silicon-containing materials to improve the specific capacity of the negative electrode sheet, while the outer layer uses high-power graphite and fast-charging materials to improve the conductivity and ion transport performance of the negative electrode sheet, thereby achieving high specific capacity and fast-charging performance of the negative electrode sheet.

[0008] In some embodiments, the high-energy graphite includes at least one of high-energy artificial graphite or high-energy natural graphite;

[0009] And / or, the silicon-containing material includes at least one of silicon-carbon composite materials or silicon-oxygen materials.

[0010] In some embodiments, the high-power graphite includes at least one of high-power artificial graphite or high-power natural graphite;

[0011] And / or, the fast-charging material includes at least one of soft carbon or hard carbon.

[0012] In some embodiments, the inner layer further contains a conductive agent and an adhesive, and the outer layer further contains a conductive agent and an adhesive.

[0013] In some embodiments, the inner layer contains 30-70 wt% high-energy graphite, 20-60 wt% silicon-containing material, 1-10 wt% conductive agent, and 1-5 wt% binder.

[0014] In some embodiments, the outer layer contains 40–95 wt% high-power graphite, 5–40 wt% fast-charging material, 0.5–8 wt% conductive agent, and 0.5–4 wt% binder.

[0015] In some embodiments, the conductive agent includes at least one of carbon black, carbon fiber, carbon nanotubes, or graphene.

[0016] And / or, the adhesive comprises at least one of polyacrylic acid, styrene-butadiene rubber, or sodium carboxymethyl cellulose.

[0017] In some embodiments, the thickness ratio of the inner layer to the outer layer is 1:(0.5-2), the total thickness of the inner and outer layers is 100-200 μm, and the compaction density of the negative electrode sheet is 1.2-1.7 g / cm³. 3 ;

[0018] And / or, the current collector comprises copper foil, and the thickness of the current collector is 4 to 9 μm.

[0019] This invention also provides a method for preparing the above-mentioned fast-charging high-specific-capacity negative electrode, comprising the following steps:

[0020] (1) High-energy graphite, silicon-containing materials, conductive agents and binders are uniformly dispersed in deionized water to obtain inner negative electrode slurry; high-power graphite, fast-charging materials, conductive agents and binders are uniformly dispersed in deionized water to obtain outer negative electrode slurry;

[0021] (2) The inner negative electrode slurry is evenly coated on both sides of the current collector, and the outer negative electrode slurry is evenly coated on the inner negative electrode slurry on both sides. After drying in an oven, the negative electrode sheet is obtained.

[0022] This invention also provides a lithium-ion battery, comprising the fast-charging high-specific-capacity negative electrode sheet described above or the fast-charging high-specific-capacity negative electrode sheet prepared by the above method. Attached Figure Description

[0023] Figure 1 This is a schematic diagram of the fast-charging high specific capacity negative electrode sheet prepared in Embodiment 1 of the present invention. Detailed Implementation

[0024] Embodiments of the present invention are described in detail below, examples of which are illustrated in the accompanying drawings. The embodiments described below with reference to the accompanying drawings are exemplary and intended to explain the present invention, and should not be construed as limiting the present invention.

[0025] like Figure 1 As shown, the fast-charging high-capacity negative electrode sheet of this embodiment includes a current collector, an inner layer close to both sides of the current collector, and an outer layer away from both sides of the current collector.

[0026] The inner layer contains high-energy graphite and silicon-containing materials, while the outer layer contains high-power graphite and fast-charging materials.

[0027] The fast-charging high-specific-capacity negative electrode sheet of this invention adopts a double-layer design. The inner layer uses high-energy graphite and silicon-containing materials to improve the specific capacity of the negative electrode sheet, while the outer layer uses high-power graphite and fast-charging materials to improve the conductivity and ion transport performance of the negative electrode sheet, thereby achieving high specific capacity and fast-charging performance of the negative electrode sheet.

[0028] In some embodiments, preferably, the high-energy graphite includes at least one of high-energy artificial graphite or high-energy natural graphite;

[0029] And / or, the silicon-containing material includes at least one of silicon-carbon composite materials or silicon-oxygen materials.

[0030] In some embodiments, preferably, the high-power graphite includes at least one of high-power artificial graphite or high-power natural graphite;

[0031] And / or, the fast-charging material includes at least one of soft carbon or hard carbon.

[0032] In some embodiments, preferably, the inner layer further contains a conductive agent and an adhesive, and the outer layer further contains a conductive agent and an adhesive.

[0033] In some embodiments, preferably, the inner layer contains 30-70 wt% high-energy graphite, 20-60 wt% silicon-containing material, 1-10 wt% conductive agent, and 1-5 wt% binder.

[0034] In this embodiment of the invention, the preferred content of high-energy graphite and silicon-containing materials in the inner layer can improve the energy density of the battery cell while ensuring the cycle performance of the battery cell. If the amount of high-energy graphite is too high, the amount of silicon-containing materials will inevitably be too low, which will not effectively improve the specific energy of the negative electrode. If the amount of high-energy graphite is too low, the amount of silicon-containing materials will inevitably be too high. Due to the large expansion of silicon materials, repeated stress will cause the negative electrode to pulverize, resulting in a low cycle life.

[0035] In some embodiments, preferably, the outer layer contains 40-95 wt% high-power graphite, 5-40 wt% fast-charging material, 0.5-8 wt% conductive agent, and 0.5-4 wt% binder.

[0036] In this embodiment of the invention, the preferred content of high-power graphite and fast-charging material in the outer layer can improve the power performance of the battery cell while ensuring the energy density of the battery cell. If the amount of high-power graphite is too high, it will inevitably lead to a low content of fast-charging material, thereby reducing the power performance of the negative electrode. If the amount of high-power graphite is too low, it will inevitably lead to a high content of fast-charging material. Since the specific capacity of fast-charging material is low, excessive use of fast-charging material will reduce the energy density of the battery cell.

[0037] In some embodiments, preferably, the conductive agent includes at least one of carbon black, carbon fiber, carbon nanotubes, or graphene.

[0038] And / or, the adhesive comprises at least one of polyacrylic acid, styrene-butadiene rubber, or sodium carboxymethyl cellulose.

[0039] In some embodiments, preferably, the thickness ratio of the inner layer to the outer layer is 1:(0.5-2), the total thickness of the inner and outer layers is 100-200 μm, and the compaction density of the negative electrode sheet is 1.2-1.7 g / cm³. 3 ;

[0040] And / or, the current collector comprises copper foil, and the thickness of the current collector is 4 to 9 μm.

[0041] This invention also provides a method for preparing a fast-charging high-specific-capacity negative electrode, comprising the following steps:

[0042] (1) High-energy graphite, silicon-containing materials, conductive agents and binders are uniformly dispersed in deionized water to obtain inner negative electrode slurry; high-power graphite, fast-charging materials, conductive agents and binders are uniformly dispersed in deionized water to obtain outer negative electrode slurry;

[0043] (2) The inner negative electrode slurry is evenly coated on both sides of the current collector, and the outer negative electrode slurry is evenly coated on the inner negative electrode slurry on both sides. After drying in an oven, the negative electrode sheet is obtained.

[0044] This invention also provides a lithium-ion battery, comprising the fast-charging high-specific-capacity negative electrode sheet described above or the fast-charging high-specific-capacity negative electrode sheet prepared by the above method.

[0045] The technical solution of the present invention will now be described in detail with reference to specific embodiments and accompanying drawings.

[0046] Example 1

[0047] (1) High-energy artificial graphite, silicon-carbon composite material, carbon black, sodium carboxymethyl cellulose and polyacrylic acid are uniformly dispersed in deionized water to obtain inner negative electrode slurry; high-power artificial graphite, soft carbon, carbon black, sodium carboxymethyl cellulose and polyacrylic acid are uniformly dispersed in deionized water to obtain outer negative electrode slurry.

[0048] (2) The inner negative electrode slurry is evenly coated on both sides of the current collector, and the outer negative electrode slurry is evenly coated on the inner negative electrode slurry on both sides. After drying in an oven, the negative electrode sheet is obtained.

[0049] In the inner layer of the fast-charging high-specific-capacity negative electrode sheet prepared in this embodiment, the content of high-energy artificial graphite is 50wt%, the content of silicon-carbon composite material is 46wt%, the content of carbon black is 1wt%, the content of sodium carboxymethyl cellulose is 0.8wt%, and the content of polyacrylic acid is 2.2wt%; in the outer layer, the content of high-power artificial graphite is 70wt%, the content of soft carbon is 25wt%, the content of carbon black is 3wt%, the content of sodium carboxymethyl cellulose is 1wt%, and the content of polyacrylic acid is 1wt%.

[0050] The thickness ratio of the inner layer to the outer layer is 1:1, and the electrode compaction density is 1.59 g / cm³. 3 The total thickness of the inner and outer layers is 150 μm.

[0051] The structure of the negative electrode sheet prepared in this embodiment is as follows: Figure 1 As shown.

[0052] Example 2

[0053] The preparation method of this embodiment is the same as that of Embodiment 1, except that: in the inner layer of the obtained fast-charging high specific capacity negative electrode sheet, the content of high-energy artificial graphite is 65wt%, the content of silicon oxide material is 30wt%, the content of carbon black is 2wt%, the content of sodium carboxymethyl cellulose is 1wt%, the content of styrene-butadiene rubber is 1wt%, and the content of polyacrylic acid is 1wt%; in the outer layer, the content of high-power natural graphite is 80wt%, the content of soft carbon is 15wt%, the content of carbon black is 1wt%, the content of carbon fiber is 2wt%, the content of sodium carboxymethyl cellulose is 0.7wt%, the content of styrene-butadiene rubber is 0.8wt%, and the content of polyacrylic acid is 0.5wt%.

[0054] The thickness ratio of the inner layer to the outer layer is 1:1.5, and the electrode compaction density is 1.60 g / cm³. 3 The total thickness of the inner and outer layers is 150 μm.

[0055] Comparative Example 1

[0056] The preparation method of this comparative example is the same as that of Example 1, except that in the inner layer of the obtained negative electrode sheet, the content of high-energy artificial graphite is 95wt%, the content of carbon black is 2wt%, the content of sodium carboxymethyl cellulose is 1wt%, and the content of styrene-butadiene rubber is 2wt%; in the outer layer, the content of high-power artificial graphite is 96wt%, the content of carbon black is 1wt%, the content of sodium carboxymethyl cellulose is 1.5wt%, and the content of styrene-butadiene rubber is 1.5wt%.

[0057] The thickness ratio of the inner layer to the outer layer is 1:1, and the electrode compaction density is 1.62 g / cm³. 3 The total thickness of the inner and outer layers is 150 μm.

[0058] Comparative Example 2

[0059] The preparation method of this comparative example is the same as that of Example 1, except that the negative electrode obtained in this comparative example has only one material layer. In this material layer, the content of high-energy artificial graphite is 94wt%, the content of carbon black is 3wt%, the content of sodium carboxymethyl cellulose is 1.5wt%, the content of styrene-butadiene rubber is 1.5wt%, and the electrode compaction density is 1.65 g / cm³. 3 The thickness of the material layer is 150μm.

[0060] Comparative Example 3

[0061] The preparation method of this comparative example is the same as that of Example 1, except that: in the inner layer of the negative electrode sheet prepared in this comparative example, the content of high-energy artificial graphite is 50wt%, the content of soft carbon is 46wt%, the content of carbon black is 1wt%, the content of sodium carboxymethyl cellulose is 0.8wt%, and the content of polyacrylic acid is 2.2wt%; in the outer layer, the content of high-power artificial graphite is 70wt%, the content of silicon-carbon composite material is 25wt%, the content of carbon black is 3wt%, the content of sodium carboxymethyl cellulose is 1wt%, and the content of polyacrylic acid is 1wt%.

[0062] Comparative Example 4

[0063] The preparation method of this comparative example is the same as that of Example 1, except that: in the inner layer of the negative electrode sheet prepared in this comparative example, the content of high-energy artificial graphite is 50wt%, the content of silicon-carbon composite material is 36wt%, the content of soft carbon is 10wt%, the content of carbon black is 1wt%, the content of sodium carboxymethyl cellulose is 0.8wt%, and the content of polyacrylic acid is 2.2wt%; in the outer layer, the content of high-power artificial graphite is 70wt%, the content of soft carbon is 25wt%, the content of carbon black is 3wt%, the content of sodium carboxymethyl cellulose is 1wt%, and the content of polyacrylic acid is 1wt%.

[0064] The negative electrode sheets prepared in Examples 1-2 and Comparative Examples 1-4 were assembled with lithium iron phosphate positive electrode sheets, PE ceramic coated separators and lithium hexafluorophosphate electrolyte to form battery cells. After the battery cells were successfully manufactured, their energy density, constant current-constant voltage ratio during 5C charging and whether there was lithium plating after full charging at 5C fast charging were tested. The test results are shown in Table 1.

[0065] Table 1

[0066]

[0067] As can be seen from the data in Table 1, the battery cells obtained using the negative electrode sheets prepared in Examples 1 and 2 exhibit good fast-charging performance while maintaining the battery cell's energy density. Specifically, Example 1 features a high outer layer soft carbon content, resulting in good battery cell power performance, and a high inner layer silicon-carbon content, leading to increased battery cell energy density. Example 2, with a lower outer layer soft carbon content, uses natural graphite with a larger interlayer spacing as the active material and adds carbon fibers with good conductivity. While the battery cell power performance is slightly worse than in Example 1, the energy density is lower due to the reduced silicon-oxygen content and the reduced proportion of the high-specific-capacity inner layer material thickness.

[0068] Compared with Example 1, Comparative Example 1 does not contain silicon-containing materials in the inner layer and does not contain fast-charging materials in the outer layer, resulting in reduced energy density and significantly reduced fast-charging performance.

[0069] Compared with Example 1, Comparative Example 2 changed from double-layer coating to single-layer coating, and only high-energy graphite was used as the active material. In order to improve power performance, the proportion of conductive agent was relatively high, but the power performance was still poor and lithium plating was present. Although the specific capacity of high-energy graphite was high and the compaction was large, the energy density of the cell was comparable to that of Comparative Example 1 due to the reduced proportion of active material.

[0070] Compared with Example 1, Comparative Example 3 removed the soft carbon fast-charging material from the outer layer and replaced it with a silicon-carbon composite material in the same proportion. The inner layer also removed the silicon-carbon composite material and replaced it with a soft carbon fast-charging material in the same proportion. After the substitution, the proportion of soft carbon fast-charging material increased, while the proportion of silicon-carbon composite material decreased, resulting in a decrease in the cell's energy density. During charging, lithium ions first diffuse through the outer layer to the inner layer. Due to the low ion diffusion coefficient of the silicon-carbon composite material, lithium ions cannot quickly enter the silicon-carbon composite material, leading to a high lithium ion concentration in the outer layer. This congestion of lithium ions in the outer layer prevents them from quickly entering the inner layer, resulting in increased concentration polarization and high polarization resistance. Consequently, the cell's power performance decreases. Since the lithium intercalation potential of the silicon-carbon negative electrode is relatively high (approximately 0.4-0.5V), lithium plating did not occur at the negative electrode.

[0071] Compared with Example 1, Comparative Example 4 added soft carbon fast-charging material to the inner layer, reduced the content of silicon-carbon composite material, and reduced the energy density of the battery cell. Since the soft carbon is in the inner layer, the improvement in power performance is not obvious.

[0072] In this invention, the terms "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., refer to a specific feature, structure, material, or characteristic described in connection with that embodiment or example, which is included in at least one embodiment or example of the invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.

[0073] Although the above embodiments have been shown and described, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Any changes, modifications, substitutions and variations made to the above embodiments by those skilled in the art are within the protection scope of the present invention.

Claims

1. A fast-charging high-specific-capacity negative electrode, characterized in that, It includes the current collector, the inner layer near both sides of the current collector, and the outer layer away from both sides of the current collector; The inner layer contains high-energy graphite and silicon-containing materials, while the outer layer contains high-power graphite and fast-charging materials.

2. The fast-charging high-specific-capacity negative electrode sheet according to claim 1, characterized in that, The high-energy graphite includes at least one of high-energy artificial graphite or high-energy natural graphite; And / or, the silicon-containing material includes at least one of silicon-carbon composite materials or silicon-oxygen materials.

3. The fast-charging high-specific-capacity negative electrode sheet according to claim 1, characterized in that, The high-power graphite includes at least one of high-power artificial graphite or high-power natural graphite. And / or, the fast-charging material includes at least one of soft carbon or hard carbon.

4. The fast-charging high-specific-capacity negative electrode sheet according to claim 1, characterized in that, The inner layer also contains a conductive agent and a binder, and the outer layer also contains a conductive agent and a binder.

5. The fast-charging high-specific-capacity negative electrode sheet according to claim 4, characterized in that, The inner layer contains 30-70 wt% high-energy graphite, 20-60 wt% silicon-containing material, 1-10 wt% conductive agent, and 1-5 wt% binder.

6. The fast-charging high-specific-capacity negative electrode sheet according to claim 4, characterized in that, The outer layer contains 40–95 wt% high-power graphite, 5–40 wt% fast-charging material, 0.5–8 wt% conductive agent, and 0.5–4 wt% binder.

7. The fast-charging high-specific-capacity negative electrode sheet according to any one of claims 4 to 6, characterized in that, The conductive agent includes at least one of carbon black, carbon fiber, carbon nanotubes, or graphene. And / or, the adhesive comprises at least one of polyacrylic acid, styrene-butadiene rubber, or sodium carboxymethyl cellulose.

8. The fast-charging high-specific-capacity negative electrode according to claim 1, characterized in that, The thickness ratio of the inner layer to the outer layer is 1:(0.5-2), the total thickness of the inner and outer layers is 100-200 μm, and the compaction density of the negative electrode sheet is 1.2-1.7 g / cm³. 3 ; And / or, the current collector comprises copper foil, and the thickness of the current collector is 4 to 9 μm.

9. The method for preparing a fast-charging high-specific-capacity negative electrode sheet according to any one of claims 1 to 8, characterized in that, Includes the following steps: (1) High-energy graphite, silicon-containing materials, conductive agents and binders are uniformly dispersed in deionized water to obtain inner negative electrode slurry; high-power graphite, fast-charging materials, conductive agents and binders are uniformly dispersed in deionized water to obtain outer negative electrode slurry; (2) The inner negative electrode slurry is evenly coated on both sides of the current collector, and the outer negative electrode slurry is evenly coated on the inner negative electrode slurry on both sides. After drying in an oven, the negative electrode sheet is obtained.

10. A lithium-ion battery, characterized in that, Includes the fast-charging high specific capacity negative electrode sheet according to any one of claims 1 to 8 or the fast-charging high specific capacity negative electrode sheet prepared by the preparation method according to claim 9.

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