A battery negative electrode sheet, a battery

Abstract

The application provides a battery negative plate and a battery, the battery negative plate comprising a silicon-based negative active material and a binder, the binder being a product obtained by cross-linking a polyacrylic compound modified by a phenylboronic acid compound and a hydroxylated carbon nanotube, and the silicon-based negative active material comprising at least one of a silicon material, a silicon oxide material, a silicon-carbon material and a silicon alloy material. The application provides a battery negative plate adopting a three-dimensional conductive network binder based on cross-linking of a polyacrylic compound modified by a phenylboronic acid compound and a hydroxylated carbon nanotube and a silicon-based negative material. The network structure provides excellent mechanical strength and flexibility for the negative electrode, and due to the excellent mechanical strength and flexibility, the silicon negative electrode exhibits excellent cycle stability, high reversible capacity and stable electrochemical impedance in battery tests.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of lithium ion batteries, in particular to a battery negative plate and a battery. BACKGROUND

[0002] In the rapid development of current energy storage technology, lithium ion batteries (LIBs) have become the preferred power source for portable electronic devices and electric vehicles due to their high energy density, long cycle life and environmental friendliness. However, as the demand for higher energy density and faster charging speed continues to grow, the existing graphite negative electrode material is gradually approaching its theoretical capacity limit, which limits the further improvement of the performance of LIBs. Therefore, the development of new high-capacity negative electrode materials has become the key to promoting the development of battery technology.

[0003] Silicon (Si) as a new negative electrode material, due to its extremely high theoretical specific capacity (about 4200mAh g -1 -1), which is an order of magnitude higher than traditional graphite materials, is widely considered as a strong candidate for improving the energy density of lithium ion batteries. However, the silicon negative electrode will undergo significant volume expansion (up to 400%) during charging and discharging, and this volume change can lead to the crushing of active materials, the destruction of electrode structure and the continuous consumption of electrolyte, resulting in increased internal resistance of the battery, rapid capacity decay and decreased cycle stability, which seriously limits the commercialization process of silicon negative electrodes. In order to solve these problems, the electrochemical performance of the above battery can be improved by selecting a suitable binder system. The binder is an important component of the lithium battery negative electrode material, and the binder adheres the conductive agent and active material to the current collector, ensuring the conductive path of the electrode structure, thereby improving the overall electrochemical performance of the negative electrode. Currently, traditional binders such as polyvinylidene fluoride (PVDF), polyacrylic acid (PAA) and carboxymethyl cellulose (CMC) are not sufficient to adapt to the influence of the volume expansion of silicon-based materials on the cycle stability, reversible capacity and electrochemical impedance of the battery due to their poor intermolecular interaction and brittleness. SUMMARY

[0004] The present application is aimed at the above-mentioned problems, and makes up for the deficiencies of the prior art, and provides a lithium battery negative plate and a battery.

[0005] In a first aspect, the present application provides a battery negative plate, comprising a silicon-based negative electrode active material and a binder, the binder being a product obtained by cross-linking a polyacrylic compound modified with a phenylboronic compound and a hydroxylated carbon nanotube, and the silicon-based negative electrode active material comprising at least one of a silicon material, a silicon oxide material, a silicon-carbon material and a silicon alloy material.

[0006] The application provides a battery negative electrode sheet, which adopts a three-dimensional conductive network binder based on phenylboronic acid compound modified polyacrylic compound and hydroxylated carbon nanotube crosslinking and a silicon-based negative electrode material. On one hand, the phenylboronic acid groups of the binder can be in-situ crosslinked with the hydroxyl groups (-OH) on the surface of the hydroxylated carbon nanotube (OHCNT) to form borate ester, on the other hand, the phenylboronic acid can also react with the hydroxyl groups on the surface of the negative electrode active material to form borate ester, and the phenylboronic acid can also be self-crosslinked to form boroxin structure to form a special three-dimensional conductive network. The network structure provides excellent mechanical strength and flexibility for the negative electrode, and the silicon negative electrode shows excellent cycle stability, high reversible capacity and stable electrochemical impedance in the battery test; the phenylboronic acid groups in the binder can form a more stable electrolyte interface (SEI) film, increase the migration rate of lithium ions (Li + ) and thus reduce the consumption of electrolyte, and show excellent rate performance.

[0007] Specifically, in some embodiments of the application, the mass ratio of the phenylboronic acid compound to the polyacrylic compound is 0.19-1.33; more specifically, the mass ratio of the phenylboronic acid compound to the polyacrylic compound is 0.19, 0.38, 0.57, 0.76, 0.95, 1.14, 1.33; preferably, the mass ratio of the phenylboronic acid compound to the polyacrylic compound is 0.57-0.95.

[0008] Specifically, in some embodiments of the application, the mass ratio of the phenylboronic acid compound modified polyacrylic compound to the hydroxylated carbon nanotube is 1.0-6.0, more specifically, the mass ratio of the phenylboronic acid compound modified polyacrylic compound to the hydroxylated carbon nanotube is 1.0, 1.5, 2.0, 2.5, 3.0, 3.5, 4.0, 4.5, 5.0, 5.5, 6.0; preferably, the mass ratio of the phenylboronic acid compound modified polyacrylic compound to the hydroxylated carbon nanotube is 2.0-3.0.

[0009] In the application, if the mass ratio of the phenylboronic acid compound modified polyacrylic compound to the hydroxylated carbon nanotube is too large, the crosslinking density will be too large, the polymer network will be complex, the slurry viscosity will be too large and the slurry cannot be uniformly dispersed. If the mass ratio is too small, the polymer cannot adapt to the expansion of the silicon negative electrode, and the cycle performance of the battery will be poor.

[0010] Specifically, in some embodiments of the application, the phenylboronic acid compound is at least one of 3-aminophenylboronic acid, 2-aminophenylboronic acid, 4-aminophenylboronic acid, [3-(2-aminoethyl)phenyl]boronic acid and 3-aminomethylphenylboronic acid.

[0011] Specifically, in some embodiments of the present application, the polyacrylic compound includes at least one of polyacrylic acid, polymethacrylic acid, sodium polyacrylate, lithium polyacrylate, sodium polymethacrylate, and lithium polymethacrylate.

[0012] Specifically, in some embodiments of the present application, the polyacrylic compound is modified by the phenyl boronic acid compound to crosslink with the hydroxylated carbon nanotube, including:

[0013] S1: dissolving the polyacrylic compound and the base in water, and adding the aqueous solution of the phenyl boronic acid compound to obtain a mixed solution, cooling the mixed solution to 2-7℃, and adding an activator to react for 10-14 hours to obtain the phenyl boronic acid compound modified polyacrylic compound;

[0014] S2: adding the hydroxylated carbon nanotube and the dispersant to water and ultrasonicating for 1-3 hours to obtain a dispersion liquid, and mixing the dispersion liquid with the phenyl boronic acid compound modified polyacrylic compound to obtain the adhesive.

[0015] Compared with the traditional adhesive preparation process, the present application uses aqueous solvent, thereby simplifying the synthesis process, improving the preparation efficiency, and showing the potential of direct industrial application of the component formula of the adhesive and the conductive agent combined into one.

[0016] Specifically, in some embodiments of the present application, the silicon material is nano-silicon or micro-silicon material;

[0017] The silicon oxide material is SiO x , wherein 0≤x≤2;

[0018] The silicon-carbon material is a silicon-based material containing silicon and carbon material and / or a silicon-based material containing SiO y and carbon material, wherein 0≤y≤2.

[0019] Specifically, in some embodiments of the present application, the mass ratio of the silicon-based negative electrode active material to the adhesive is 85:15-97:3, more specifically, the mass ratio of the silicon-based negative electrode active material to the adhesive is 85:15, 90:10, 91:9, 92:8, 93:7, 94:6, 95:5, 97:3, and preferably, the mass ratio of the silicon-based negative electrode active material to the adhesive is 92:8-95:5.

[0020] Specifically, in some embodiments of the present application, the base is at least one of lithium hydroxide, sodium hydroxide, and potassium hydroxide.

[0021] Specifically, in some embodiments of the present application, the activating agent is at least one of 1-ethyl-(3-dimethylaminopropyl) carbodiimide, dicyclohexyl carbodiimide, N,N'-diisopropyl carbodiimide.

[0022] In a second aspect, the present application also provides a method for preparing a battery negative electrode sheet, comprising the following steps: mixing the negative electrode active material and the binder uniformly by using a stirrer to obtain a negative electrode slurry, coating the negative electrode slurry on the surface of the current collector by using a coating machine, and obtaining the battery negative electrode sheet after drying and cutting, wherein the active material loading is about 2.0-5.0 mg·cm -2 .

[0023] The present application also provides a battery comprising the above battery negative electrode sheet, wherein the battery is a lithium ion battery, a semi-solid battery or a solid-state battery.

[0024] Compared with the prior art, the present application has the following beneficial effects:

[0025] The present application provides a battery negative electrode sheet, which selects a silicon-based negative electrode active material and uses a binder cross-linked with hydroxylated carbon nanotubes based on phenylboronic acid compounds modified polyacrylic compounds and a silicon-based negative electrode material. On the one hand, the phenylboronic acid groups of the binder can be in-situ cross-linked with the hydroxyl groups (-OH) on the surface of the hydroxylated carbon nanotubes (OHCNT) to form borate esters, on the other hand, the phenylboronic acid can also react with the hydroxyl groups on the surface of the negative electrode active material to form borate esters, and the phenylboronic acid can also be self-cross-linked to form a boroxin structure, forming a special three-dimensional conductive network. This network structure provides excellent mechanical strength and flexibility for the negative electrode, and the silicon negative electrode shows excellent cycle stability, high reversible capacity and stable electrochemical impedance in battery tests; the phenylboronic acid groups in the binder can form a more stable solid electrolyte interface film (SEI), increase the migration rate of lithium ions (Li + ), and thus reduce the consumption of electrolyte, and show excellent rate performance. BRIEF DESCRIPTION OF DRAWINGS

[0026] Figure 1 Synthesis principle diagram of 3-aminophenylboronic acid modified polyacrylic compound in Example 1;

[0027] Figure 2 Synthesis principle diagram of the binder in Example 1;

[0028] Figure 3 Infrared detection spectrum of the phenylboronic acid compound modified polyacrylic compound;

[0029] Figure 4 Infrared detection spectrum of the binder. DETAILED DESCRIPTION

[0030] The technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the drawings in the present application. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by a person of ordinary skill in the art without creative effort belong to the protection scope of the present application.

[0031] Embodiment 1

[0032] The present embodiment provides a battery negative electrode sheet, comprising a nano-silicon active material and a binder, wherein the binder is a product obtained by cross-linking a polyacrylic compound modified by a phenylboronic acid compound and a hydroxylated carbon nanotube.

[0033] Preparation of the binder:

[0034] S1: 1g of polyacrylic acid (PAA) and 0.05g of LiOH were dissolved in 20g of water, 0.76g of 3-aminophenylboronic acid (APBA) was added to obtain a mixed solution, the mixed solution was cooled to 4℃, 1.06g of 1-ethyl-(3-dimethylaminopropyl) carbonyldiimide was added and kept at 4℃ for 12 hours, and 3-aminophenylboronic acid modified polyacrylic acid was obtained by purification through dialysis, and the synthesis principle is as shown in Figure 1 .

[0035] S2: 0.3g of hydroxylated carbon nanotube (OHCNT) and 0.33g of dispersant were added to 15.75g of water and ultrasonically treated for 2 hours to obtain a hydroxylated carbon nanotube dispersion. 0.75g of 3-aminophenylboronic acid modified polyacrylic acid was mixed with the hydroxylated carbon nanotube dispersion, and the mass ratio of 3-aminophenylboronic acid modified polyacrylic acid to hydroxylated carbon nanotube (OHCNT) was 5:2 to obtain a binder (PBO), and the synthesis principle is as shown in Figure 2 .

[0036] Preparation of the negative electrode sheet: according to the weight parts, the nano-silicon active material and the binder were mixed and stirred uniformly by a stirrer at a mass ratio of 93:7 to obtain a negative electrode slurry with suitable viscosity, the slurry was coated on a copper current collector by using a coating machine, and after vacuum drying at 120℃ for 12 hours, the negative electrode was cut into a circular sheet with a diameter of 12mm, and the active material loading was about 3.0mg·cm -2 .

[0037] Preparation of the half battery: the electrochemical performance was evaluated by using CR2025 type half batteries, which were assembled by sandwiching a separator (about 25μm) between a working electrode based on the above binder and a lithium foil counter electrode.

[0038] Preparation of the full battery: LiNi 0.8 Co 0.1 Mn0.1 O2(NCM811) positive electrode and the above negative electrode were assembled to obtain a full battery, and the loading amount of NCM811 was 3.5 mAh·cm -2 .

[0039] In this embodiment, the infrared detection results of 3-aminobenzenboronic acid modified polyacrylic acid are shown in Table 1. Figure 3 The absorption peak at 2877 cm -1 represents the stretching vibration of the benzene ring C-H bond, the absorption peak at 1465 cm -1 is the in-plane deformation vibration of N-H bond, and the absorption peak at 1350 cm -1 represents the stretching vibration of B-O bond, which proves that 3-aminobenzenboronic acid successfully modifies polyacrylic acid.

[0040] The infrared detection results of the binder are shown in Table 1. Figure 4 The absorption peak at 1231 cm -1 represents the stretching vibration of B-O-C, and the absorption peak at 735 cm -1 represents the stretching vibration of B-O-B, which proves that 3-aminobenzenboronic acid modified polyacrylic acid is successfully combined with OH-CNT.

[0041] Example 2-27

[0042] This embodiment is used to compare and illustrate the lithium ion battery disclosed in the present application, which includes most of the operation steps in Example 1 described above, and the difference lies in: the synthesis conditions, components, mass and mass ratio of the negative active material, the benzene boronic acid compound modified polyacrylic acid compound and the binder.

[0043] Comparative Example 1

[0044] Compared with Example 1, the binder used in this comparative example directly mixes polyacrylic acid with hydroxylated carbon nanotubes, and the rest is consistent with Example 1.

[0045] Table 1

[0046]

[0047]

[0048] The performance detection method of the lithium ion battery of Examples 1-27 and Comparative Example 1 is as follows: half-cell performance test

[0049] Experiment one,

[0050] Cycling performance test: discharge at 0.2C rate to 0.01V, then charge at 0.2C rate to 2V at 25℃, this is one charge-discharge cycle, repeat 400 times. Capacity retention after 400 cycles = discharge capacity after 400th cycle / discharge capacity after 1st cycle x 100%, test results are shown in Table 2.

[0051] Experiment two,

[0052] Rate performance test: charge at 0.2C, 0.5C, 1C, 2C rate to 2V at 25℃, test results are shown in Table 2.

[0053] Full cell performance detection experiment

[0054] Experiment three,

[0055] Cycling performance test: full cell first activated at 0.05C (1C = 200mAh g- 1 ) for 2 cycles, then activated at 0.1C for 2 cycles, capacity retention after 200 cycles at 2.5V to 4.25V and 0.5C current density, test results are shown in Table 2.

[0056] Experiment four,

[0057] Electrochemical impedance test: connect EIS electrochemical workstation, set frequency 10 -2 -10 -6 Hz, amplitude 5mVRMS; EIS impedance after 2 cycles and EIS impedance after 100 cycles of full cell, test results are shown in Table 2.

[0058] Table 2

[0059]

[0060]

[0061] As can be seen from the data in Table 2: from the battery performance test results of Examples 1-27 and Comparative Example 1, it can be seen that the battery prepared by using the binder based on the phenylboronic acid compound modified polyacrylic compound cross-linked with the hydroxylated carbon nanotube and the silicon-based negative electrode material in the present application is superior to the battery prepared by using the polyacrylic acid as the binder in Comparative Example 1 in the cycle stability, the charge capacity and the electrochemical impedance stability, indicating that the phenylboronic acid groups of the binder in the present application can be cross-linked with the hydroxyl groups (-OH) on the surface of the hydroxylated carbon nanotube (OHCNT) in situ to form the borate ester, the phenylboronic acid can also react with the hydroxyl groups on the surface of the negative electrode active material to form the borate ester, and the phenylboronic acid can also be self-cross-linked to form the boroxin structure, forming a special three-dimensional conductive network, and this network structure provides the negative electrode with excellent mechanical strength and flexibility, and the silicon negative electrode exhibits excellent cycle stability, high reversible capacity and stable electrochemical impedance in the battery test; from the battery performance test results of Examples 1-5 and Examples 6-7, it can be seen that when the mass ratio of the phenylboronic acid compound / polyacrylic compound is in the range of 0.19-1.33, the cycle stability, the charge capacity and the electrochemical impedance stability of the battery are more superior; from the battery performance test results of Examples 1, Examples 8-10 and Examples 11-12, it can be seen that when the mass of the phenylboronic acid compound modified polyacrylic compound and the hydroxylated carbon nanotube is in the range of 1.0-6.0, the cycle stability, the charge capacity and the electrochemical impedance stability of the battery are more superior.

[0062] The above has further described the present application by means of specific examples, but it should be understood that the specific description herein should not be understood as limiting the spirit and scope of the present application, and various modifications made to the above examples by those skilled in the art after reading the present specification all belong to the scope of the present application.

Claims

1. A battery negative electrode sheet, characterized by, The negative electrode active material includes at least one of a silicon material, a silicon oxide material, a silicon-carbon material and a silicon alloy material.

2. The battery negative electrode sheet according to claim 1, wherein The mass ratio of the phenyl boronic acid compound to the polyacrylic compound is 0.19-1.

33.

3. The battery negative electrode sheet according to claim 1, wherein The mass ratio of the phenyl boronic acid compound modified polyacrylic compound to the hydroxylated carbon nanotube is 1.0-6.

0.

4. The battery negative electrode sheet according to claim 1, wherein The phenyl boronic acid compound is at least one of 3-aminophenyl boronic acid, 2-aminophenyl boronic acid, 4-aminophenyl boronic acid, [3-(2-aminoethyl) phenyl] boronic acid and 3-aminomethylphenyl boronic acid.

5. The battery negative electrode sheet according to claim 1, wherein The polyacrylic compound includes at least one of polyacrylic acid, polymethyl acrylic acid, sodium polyacrylate, lithium polyacrylate, sodium polymethyl acrylate and lithium polymethyl acrylate.

6. The negative electrode sheet according to any one of claims 1 to 5, wherein The phenyl boronic acid compound modified polyacrylic compound is crosslinked with the hydroxylated carbon nanotube, including: S1: dissolving a polyacrylic compound and a base in water, adding a phenyl boronic acid compound aqueous solution to obtain a mixed solution, cooling the mixed solution to 2-7℃, adding an activator and reacting for 10-14 hours to obtain a phenyl boronic acid compound modified polyacrylic compound; S2: adding a hydroxylated carbon nanotube and a dispersant to water and ultrasonicating for 1-3 hours to obtain a dispersion liquid, mixing the dispersion liquid with the phenyl boronic acid compound modified polyacrylic compound to obtain a binder.

7. The battery negative electrode sheet according to claim 1, wherein the silicon material is a nano-silicon or micro-silicon material. The mass ratio of the silicon-based negative electrode active material to the binder is 85:15-97:

3. The silicon oxide material is SiO x Material, wherein 0≤x≤2; The silicon-carbon material is a silicon-based material containing a silicon and carbon material and / or a silicon-based material containing SiO y and a carbon material, wherein 0 < y < 2.

8. The battery negative electrode sheet according to claim 1, wherein The battery is a lithium ion battery, a semi-solid battery or a solid-state battery.

9. A battery, characterized by ​

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