A composite adhesive and its preparation method and application

Abstract

The present invention discloses a composite binder and its preparation method and application, which is prepared by mixing polyacrylic acid with an alkaline polymer, wherein the mass ratio of the polyacrylic acid to the alkaline polymer is 40:1-40:4, and the mixing is physical blending. The composite binder of the present invention can not only adapt to the huge volume change of silicon-based materials during charge and discharge to a certain extent, but also improve the charge transfer between active particles and conductive agents, thereby improving the cycle and rate performance of lithium-ion batteries. Compared with the chemical polymerization method in which the preparation process is relatively cumbersome and the reaction degree is difficult to control, the present invention adopts a physical blending method to compound PAA and alkaline polymer in a certain proportion to obtain a PAA-based binder. The preparation method has the advantages of simple process, safety, environmental protection and low cost, and is suitable for large-scale commercial production and practical application.

Description

Technical Field

[0001] The present invention belongs to the technical field of lithium-ion batteries and relates to a composite binder, in particular to a composite binder prepared based on a physical blending method, a preparation method thereof and an application thereof. Background Art

[0002] Polyacrylic acid (PAA) is a water-soluble polymer with abundant and evenly distributed carboxyl groups in its molecular chain. These groups form strong hydrogen bonds with active materials and current collectors, and are easily modified. Furthermore, PAA exhibits excellent electrochemical stability, electrolyte compatibility, safety, non-toxicity, and low cost. Therefore, PAA is considered an ideal binder for silicon-based anodes, promising for the commercialization of high-capacity silicon anodes. However, linear PAA homopolymers exhibit poor elasticity and chain mobility, necessitating modification through grafting of small molecules, soft polymers, or cross-linked polymers to form a cross-linked three-dimensional network structure and enhance its mechanical strength and mobility. This mitigates the significant volume changes experienced by silicon-based materials during lithium insertion and extraction, maintaining the integrity of the electrode structure.

[0003] For silicon-based negative electrode systems, since silicon-based materials react with lithium to produce a large amount of irreversible products during the first lithium insertion process, the lithium loss is more serious than that of traditional graphite electrodes. In order to improve the first coulombic efficiency of silicon-based negative electrodes, one of the existing technologies is to pre-lithiate silicon-based materials. The principle of pre-lithiation is mainly to first react silicon-based materials with metallic lithium under certain conditions to generate substances such as silicates and lithium oxides to reduce the loss of active lithium. Although pre-lithiated silicon-based negative electrode materials have a certain lithium replenishment effect, since some alkaline substances will inevitably remain in the pre-lithiation process, it will seriously affect the bonding performance of the PAA binder, causing problems such as negative electrode material shedding and poor cycle performance. Therefore, improving the alkali resistance of the PAA binder is of great significance to the commercialization of silicon-based negative electrodes. Summary of the Invention

[0004] In order to solve the above problems, the present invention provides a composite binder prepared based on a physical blending method, which can not only adapt to the huge volume changes of silicon-based materials during the charging and discharging process to a certain extent, but also improve the charge transfer between active particles and conductive agents, thereby enhancing the cycle and rate performance of lithium-ion batteries; in addition, the composite binder has a certain alkali resistance and can be applied to pre-lithiation silicon-based material systems; and the synthesis process is simple and low-cost, suitable for large-scale commercial production and practical applications.

[0005] The present invention also provides a preparation method and application of the composite adhesive.

[0006] In order to achieve the above object, the present invention adopts the following technical solutions:

[0007] First, the present invention provides a composite adhesive, which is prepared by mixing polyacrylic acid and an alkaline polymer, wherein the mass ratio of the polyacrylic acid to the alkaline polymer is 40:1-40:4, and the mixing is physical blending.

[0008] In the present invention, a polyacrylic acid (PAA)-based composite adhesive is prepared, which is compounded by PAA and a basic polymer through a simple physical blending method.

[0009] PAA is a water-soluble polymer with abundant and evenly distributed carboxyl groups in its molecular chain. This patent utilizes a PAA system as a binder for silicon-based anode materials. Firstly, PAA has excellent adhesion properties, forming strong hydrogen bonds with the silicon-based material and the current collector. Secondly, the high density of carboxyl groups on the PAA chain makes it easy to modify. Thirdly, PAA offers excellent electrochemical stability and electrolyte compatibility, and is safe, non-toxic, and low-cost.

[0010] High-capacity pre-lithiation silicon-based negative electrode materials can seriously affect the bonding performance of PAA due to the residual alkaline substances, leading to problems such as negative electrode material shedding and poor cycle performance. To solve the above problems, the present invention introduces polymers containing alkaline functional groups that can form hydrogen bonds with PAA, such as polyaniline (PANI), polyethyleneimine (PEI), polyacrylamide (PAM) and chitosan (CTS), to enhance the alkali resistance of PAA-based binders, thereby effectively inhibiting the shedding of active materials during the cycle and maintaining the integrity of the electrode structure. On the other hand, the nitrogen element in the above-mentioned alkaline polymer has lone pairs of electrons and can undergo complexation and decomplexation reactions with lithium ions under the action of an electric field, which is conducive to the rapid migration of lithium ions and improves the rate performance of the battery.

[0011] As a preferred embodiment of the present invention, the basic polymer includes one or more combinations of polyaniline, polyethyleneimine, polyacrylamide or chitosan.

[0012] As a preferred embodiment of the present invention, the molecular weight of the polyacrylic acid is 20-60w.

[0013] As a preferred solution of the present invention, the solid content of the composite binder is 2-5%.

[0014] Secondly, the present invention provides a method for preparing the above-mentioned composite adhesive, which comprises the following steps:

[0015] 1) Weighing polyacrylic acid and a solvent, placing them in a container, stirring and fully dissolving them to obtain a colorless and transparent polyacrylic acid solution;

[0016] 2) Weighing an alkaline polymer and adding it to the polyacrylic acid solution obtained in step 1), stirring and dispersing the solution for a period of time, and then placing the solution in an oil bath and continuing to stir the solution to obtain a uniform polyacrylic acid-based composite binder solution.

[0017] As a preferred embodiment of the present invention, in step 1), the solvent is DMSO or water, the stirring temperature is 15-35° C., and the stirring time is 4-6 h.

[0018] As a preferred embodiment of the present invention, in step 2), after the basic polymer is added, the mixture is first stirred at 15-35° C. for 4-6 hours, and then stirred in an oil bath at 50-70° C. for 1-3 hours.

[0019] Finally, the present invention provides an application of the above-mentioned composite binder, wherein the composite binder is used in the field of lithium-ion batteries, wherein the negative electrode material of the lithium-ion battery is a mixture of pre-lithiated silicon-based material and graphite, and the mass ratio of the pre-lithiated silicon-based material to the graphite is 1:9 to 4:6.

[0020] As a preferred solution of the present invention, the addition amount of the composite binder is 5-10%.

[0021] Compared with the prior art, the present invention has the following beneficial effects:

[0022] 1) The composite binder of the present invention can not only adapt to the huge volume change of silicon-based materials during the charge and discharge process to a certain extent, but also improve the charge transfer between active particles and conductive agents, thereby improving the cycle and rate performance of lithium-ion batteries.

[0023] 2) Compared with chemical polymerization methods, which have a more complex preparation process and difficult to control the reaction rate, the present invention uses a physical blending method to compound PAA and a basic polymer in a certain ratio to obtain a PAA-based binder. This preparation method has the advantages of simplicity, safety, environmental protection, and low cost, making it suitable for large-scale commercial production and practical applications. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 is a SEM photograph of the PAA-PANI composite adhesive prepared in Example 1.

[0025] Figure 2 This is the room temperature rate performance of Example 1 using PAA-PANI as the binder.

[0026] Figure 3 This is the room temperature 0.2°C cycle performance of Example 1 using PAA-PANI as the binder. DETAILED DESCRIPTION

[0027] In order to make the technical means, creative features, purpose and efficacy of the present invention easy to understand, the present invention is further described below in conjunction with specific examples, but the following examples are only preferred embodiments of the present invention, not all. Based on the examples in the embodiments, other embodiments obtained by those skilled in the art without making creative work are within the scope of protection of the present invention. The experimental methods in the following examples, unless otherwise specified, are conventional methods, and the materials, reagents, etc. used in the following examples, unless otherwise specified, can be obtained from commercial channels.

[0028] In the present invention, the pre-lithiated silicon-based material is pre-lithiated silicon oxide, which can be purchased from the market.

[0029] Example 1

[0030] This embodiment provides the preparation of a composite adhesive, comprising:

[0031] Weigh 0.31g of polyacrylic acid (PAA) and 10g of DMSO solvent in a beaker and stir at 25°C for 6h to dissolve completely to obtain a colorless and transparent PAA-DMSO solution. Then add 0.0232g of polyaniline (PANI) to the above PAA-DMSO solution, stir and disperse at 25°C for 4h, and then place in a 50°C oil bath and stir for 1h to obtain a uniform PAA-PANI composite adhesive solution. The SEM photo of the PAA-PANI composite adhesive is shown in Figure 1 As can be seen from the figure, the PAA-PANI composite is composed of uniform discs and there is no obvious phase separation, indicating that PAA and PANI form a homogeneous composite after physical blending.

[0032] To test the ionic conductivity of the binder, the PAA-PANI solution prepared in this example was slowly poured into a polytetrafluoroethylene mold to ensure uniform distribution, and then transferred to a forced air drying oven and dried at 70°C for 12 hours to form a transparent PAA-PANI film with a thickness of 100 μm. Before the test, the binder film was first soaked in electrolyte in a glove box for 12 hours, and then sandwiched between two stainless steel gaskets to assemble a symmetrical blocked button cell. The cell was subjected to electrochemical impedance spectroscopy testing with a frequency range of 2M to 0.1Hz and an amplitude of 10mV. The bulk resistance of the binder was determined based on the Z′ intercept of the obtained Nyquist curve in the high frequency range, and the room temperature ionic conductivity of the PAA-PANI binder was calculated to be 3.60×10 -5 S / cm.

[0033] In order to characterize the electrochemical properties of the binder, a mixture of pre-lithiated silicon dioxide and graphite was used as the negative electrode material, and the PAA-PANI composite prepared in this example was used as the binder. The negative electrode plate was prepared according to the mass ratio of negative electrode material: conductive agent carbon black: binder = 91:2:7. The above-mentioned plate was used as the working electrode, and the lithium sheet was used as the counter electrode to assemble into a button-type half-cell. The assembled half-cell was then subjected to a room temperature rate performance test, and was charged and discharged at different rates from 0.05C, 0.1C, 0.2C, 0.5C to 1.0C. Each rate was cycled for 5 weeks, and finally a charge and discharge test was performed at 0.05C. The results are shown in the figure. Figure 2 The discharge capacity of the electrode at a rate of 0.5C reached 305mAh / g, and the discharge capacity at a rate of 1.0C was still 206mAh / g, which were 58% and 39% of the initial capacity respectively. After further charge and discharge cycles at a rate of 0.05C, the discharge capacity of the electrode can be restored to about 365mAh / g. In addition, a room temperature 0.2C charge and discharge cycle performance test was also carried out, and the results are shown in Figure 3 The initial specific capacity is 402 mAh / g, and the capacity retention rate after 100 cycles is 67%.

[0034] Example 2

[0035] This embodiment provides the preparation of a composite adhesive, comprising:

[0036] Weigh 0.465g of polyacrylic acid (PAA) and 15g of DMSO solvent into a beaker and stir at 25°C for 6 hours to completely dissolve, yielding a colorless, transparent PAA-DMSO solution. Then, add 0.03g of polyethyleneimine (PEI) to the PAA-DMSO solution and stir at 25°C for 4 hours. The mixture is then placed in a 50°C oil bath and stirred for 1 hour to yield a uniform PAA-PEI composite binder solution.

[0037] The PAA-PEI adhesive film was prepared in the same manner as in Example 1, and the ionic conductivity was tested. According to the obtained AC impedance spectrum, the room temperature ionic conductivity of the PAA-PEI adhesive was calculated to be 9.14×10 -6 S / cm.

[0038] A coin-shaped half-cell using PAA-PEI as the silicon-based negative electrode binder was assembled using the same method as in Example 1. Cycling performance was tested at room temperature and 0.2C rates. The electrode exhibited a discharge capacity of 139 mAh / g at a 0.5C rate and 60 mAh / g at a 1.0C rate, representing 27% and 12% of the initial capacity, respectively. After further charge-discharge cycling at a 0.05C rate, the electrode's discharge capacity recovered to approximately 315 mAh / g. Furthermore, the capacity retention rate after 100 cycles at room temperature and 0.2C was 62%.

[0039] Example 3

[0040] This embodiment provides the preparation of a composite adhesive, comprising:

[0041] Weigh 0.62g of polyacrylic acid (PAA) and 20g of DMSO solvent into a beaker and stir at 25°C for 6 hours to completely dissolve, yielding a colorless, transparent PAA-DMSO solution. Then, add 0.05g of polyacrylamine (PAM) to the PAA-DMSO solution and stir and disperse at 25°C for 4 hours. The mixture is then placed in a 50°C oil bath and stirred for 1 hour to yield a uniform PAA-PAM composite binder solution.

[0042] The PAA-PAM adhesive film was prepared in the same manner as in Example 1, and the ionic conductivity was tested. Based on the obtained AC impedance spectrum, the room temperature ionic conductivity of the PAA-PAM adhesive was calculated to be 1.26×10 -5 S / cm.

[0043] A coin-shaped half-cell using PAA-PAM as the silicon-based negative electrode binder was assembled using the same method as in Example 1. Cycling performance was tested at room temperature and 0.2C rates. The electrode exhibited a discharge capacity of 200 mAh / g at a 0.5C rate and 105 mAh / g at a 1.0C rate, representing 40% and 21% of the initial capacity, respectively. After further charge-discharge cycling at a 0.05C rate, the electrode's discharge capacity recovered to approximately 335 mAh / g. Furthermore, the capacity retention rate after 100 cycles at room temperature and 0.2C was 60%.

[0044] Example 4

[0045] This embodiment provides the preparation of a composite adhesive, comprising:

[0046] Weigh 0.31g of polyacrylic acid (PAA) and 20g of DMSO solvent into a beaker and stir at 35°C for 6 hours to completely dissolve, yielding a colorless, transparent PAA-DMSO solution. Then, add 0.0232g of chitosan (CTS) to the PAA-DMSO solution and disperse with stirring at 25°C for 4 hours. The mixture is then placed in a 70°C oil bath and stirred for 1 hour to yield a uniform PAA-CTS composite binder solution.

[0047] The PAA-CTS adhesive film was prepared in the same manner as in Example 1, and the ionic conductivity was tested. Based on the obtained AC impedance spectrum, the room temperature ionic conductivity of the PAA-CTS adhesive was calculated to be 1.42×10 -5 S / cm.

[0048] A coin-shaped half-cell using PAA-CTS as a silicon-based binder was assembled using the same method as in Example 1. Cycling performance was tested at room temperature and 0.2C rates. The electrode exhibited a discharge capacity of 280 mAh / g at a 0.5C rate and 190 mAh / g at a 1.0C rate, representing 55% and 37% of the initial capacity, respectively. After further charge-discharge cycling at a 0.05C rate, the electrode's discharge capacity recovered to approximately 350 mAh / g. Furthermore, the capacity retention rate after 100 cycles at room temperature and 0.2C was 64%.

[0049] Comparative Example 1

[0050] The same method as in Example 1 was used to prepare a pure PAA adhesive film, and the ionic conductivity was tested. According to the obtained AC impedance spectrum, the room temperature ionic conductivity of the PAA adhesive was calculated to be 8.35×10 -6 S / cm.

[0051] A coin-shaped half-cell using PAA as the silicon-based negative electrode binder was assembled using the same method as in Example 1, and performance was tested at room temperature and 0.2C rates. The electrode exhibited a discharge capacity of 57 mAh / g at a 0.5C rate and 4 mAh / g at a 1.0C rate, representing only 13% and 0.9% of the initial capacity, respectively. After further charge-discharge cycling at a 0.05C rate, the electrode's discharge capacity recovered to approximately 255 mAh / g. Furthermore, the capacity retention after 100 cycles at room temperature and 0.2C was only 25%.

[0052] The above description is only a preferred embodiment of the present invention and does not limit the present invention in any form or substance. It should be pointed out that ordinary technicians in this technical field can make several improvements and supplements without departing from the method of the present invention. These improvements and supplements should also be regarded as the scope of protection of the present invention. Any equivalent changes, modifications and evolutions made by technicians familiar with this profession without departing from the spirit and scope of the present invention by using the technical content disclosed above are all equivalent embodiments of the present invention; at the same time, any equivalent changes, modifications and evolutions made to the above embodiments based on the essential technology of the present invention are still within the scope of the technical solution of the present invention.

Claims

1. An application of a composite adhesive, characterized in that: The composite binder is used in the field of lithium-ion batteries. The negative electrode material of the lithium-ion battery is a mixture of a pre-lithiated silicon-based material and graphite, and the mass ratio of the pre-lithiated silicon-based material to the graphite is 1:9 to 4:

6. The composite binder is prepared by mixing polyacrylic acid and an alkaline polymer, and the mass ratio of the polyacrylic acid to the alkaline polymer is 40:1-40:

4. The alkaline polymer includes one or more combinations of polyaniline, polyethyleneimine, polyacrylamide, or chitosan. The molecular weight of the polyacrylic acid is 20-60w. The mixing is physical blending. The preparation method of the composite binder comprises the following steps: 1) Weigh polyacrylic acid and solvent into a container, stir and dissolve thoroughly to obtain a colorless and transparent polyacrylic acid solution; 2) Weighing an alkaline polymer, adding it to the polyacrylic acid solution obtained in step 1), stirring and dispersing it for a period of time, and then placing it in an oil bath and continuing to stir it to obtain a uniform polyacrylic acid-based composite binder solution.

2. The use of a composite adhesive according to claim 1, characterized in that: The addition amount of the composite binder is 5-10%.

3. The use of a composite adhesive according to claim 1, characterized in that: The solid content of the composite binder is 2-5%.

4. The use of a composite adhesive according to claim 1, characterized in that: In the preparation method of the composite adhesive, in step 1), the solvent is DMSO or water, the stirring temperature is 15-35° C., and the stirring time is 4-6 hours.

5. The use of the composite adhesive according to claim 1, characterized in that: In the preparation method of the composite binder, in step 2), after the alkaline polymer is added, the mixture is first stirred at 15-35° C. for 4-6 hours, and then stirred in an oil bath at 50-70° C. for 1-3 hours.

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