CN114891136A - A kind of multi-branched structural adhesive and its preparation method and application - Google Patents

Abstract

The invention discloses a multi-branched structure binder and a preparation method and application thereof. Branched PAA was prepared. The graft-modified binder prepared by the invention provides more active sites and can generate multi-dimensional bonding with silicon particles, thereby improving the bonding strength, maintaining the integrity of the electrode structure and improving the battery cycle performance; At the same time, the binder can form a covalent bond on the surface of the nano-silicon particles, which has high strength, can inhibit the volume expansion of the silicon negative electrode, and can greatly improve the electrochemical performance of the silicon-based negative electrode of the lithium ion battery.

Description

A kind of multi-branched structural adhesive and its preparation method and application

technical field

The invention belongs to the technical field of chemical power sources, and in particular relates to a multi-branched structural adhesive and a preparation method and application thereof.

Background technique

Lithium-ion batteries stand out in people's sight due to their advantages such as high capacity, no memory effect, fast reversible charge and discharge, and high Coulomb efficiency. As 3C electronic products and electric vehicles have higher and higher requirements on the capacity and life of lithium-ion batteries, the commercially available traditional anode material graphite has been unable to meet the high-capacity requirements. People are beginning to focus on some new high-capacity electrode materials.

Silicon can store up to 22 lithiums (Li ₂₂ Si ₅ ) in 5 silicons during the intercalation and extraction of lithium ions, with a theoretical specific capacity of 4200mAh/g, abundant reserves and low cost. Therefore, silicon materials are considered to be the next generation high-efficiency materials. It is one of the most promising anode materials for energy density lithium-ion batteries. Silicon is combined with lithium through alloying reaction to obtain extremely high capacity, so co-intercalation of electrolyte solvent does not occur during the intercalation and deintercalation of lithium ions, and there is a wide selection range of electrolytes. In addition, silicon has a higher deintercalation potential than carbon materials, so that it can reduce or even avoid the precipitation of lithium when it is charged and discharged at a large rate, avoid the formation of lithium dendrites, and improve the safety of the battery.

However, silicon electrodes currently have the disadvantages of poor intrinsic conductivity and large volume expansion during charging and discharging. Among them, the volume expansion of silicon will make the performance of the electrode rapidly attenuate, and its main attenuation mechanism mainly includes three aspects: first, the repeated volume change of silicon causes looseness between particles and between particles and current collectors, which leads to silicon The particles lose electrical contact and the pole body detaches from the current collector. Second, the repeated volume change of silicon will destroy the original solid electrolyte interfacial layer (SEI), so that the silicon particles are in direct contact with the electrolyte, and an unstable thick SEI film is formed. This process continuously consumes lithium ions and electrolyte, thereby reducing the Coulombic efficiency of each cycle and eventually depleting the electrolyte. Third, most of the silicon particles are crushed because they cannot withstand the stress caused by volume expansion. These pulverized silicon particles are dispersed, resulting in electrical isolation and further growth of the SEI film due to the increased surface area. Therefore, the current research on silicon electrodes is mainly focused on how to solve the volume expansion of silicon.

At present, most of the measures taken for the volume effect of silicon are nano-sized silicon materials, hollow and porous structuring of silicon particles, or designing carbon-silicon composites with special structures (Wang X, Zhang Y, MaL, et al. .ActaChimica Sinica, 2019, 77(1): 24-40.), although these have certain effects on material modification, they cannot be applied in practice due to the complex preparation process and harsh preparation conditions. In practical applications, the binder, as one of the indispensable non-electrochemically active components in the electrode, can not only ensure the connection between particles and particles, but also maintain the close contact between the electrode and the current collector to prevent the The electrode falls off the current collector. Polymer binders play a very important role in the formation of SEI films and in maintaining the mechanical integrity and conductive network integrity of the electrodes. In addition, due to the volume effect, compared with other electrode materials, silicon needs a suitable binder to buffer and even constrain the volume expansion of silicon. Traditional PVDF and commonly used water-soluble binders (PAA, CMC, PVA, etc.) cannot withstand huge volume expansion, resulting in poor electrochemical performance of silicon electrodes. For this reason, researchers at home and abroad have made many modifications to the binder. work, but the synthesis of most modified binders involves polymerization, the reaction conditions are complex, the reaction process is cumbersome, and it is difficult to commercialize. Therefore, the development of a novel binder with simple synthesis, strong adhesion and good mechanical properties is very important for the development of Si-based anodes.

SUMMARY OF THE INVENTION

The purpose of this section is to outline some aspects of embodiments of the invention and to briefly introduce some preferred embodiments. Some simplifications or omissions may be made in this section and the abstract and title of the application to avoid obscuring the purpose of this section, abstract and title, and such simplifications or omissions may not be used to limit the scope of the invention.

The present invention has been made in view of the above and/or problems existing in the prior art.

Therefore, the purpose of the present invention is to overcome the deficiencies in the prior art and provide a preparation method of a multi-branched structural adhesive.

In order to solve the above-mentioned technical problems, the present invention provides the following technical solutions: including,

Preparation of precursor: adding polyacrylic acid into deionized water with magnetic stirring, then adding graft modifier, continuing to stir and heating to obtain a uniformly mixed precursor;

Preparation of multi-branched structural adhesive: react the precursor under vacuum and high temperature conditions, swell and freeze-dry after the reaction is completed to obtain the multi-branched structural adhesive.

As a preferred solution of the present invention, wherein: the graft modifier is one or more of glycine, glutamic acid, taurine, and citric acid.

As a preferred solution of the present invention, wherein: the mass ratio of the polyacrylic acid to the graft modifier is 1:0.05-0.2, wherein, in terms of the mass fraction of the adhesive, the polyacrylic acid and the graft The modifier mixture is 0 to 50 parts.

As a preferred solution of the present invention, wherein: in the preparation of the precursor, the heating temperature is 100-180°C, and the heating time is 2h-12h.

As a preferred solution of the present invention, wherein: in the preparation of the multi-branched structural adhesive, the swelling time is 1h-4h, and the freeze-drying time is 24-48h.

Another object of the present invention is to overcome the deficiencies in the prior art and provide a multi-branched structural adhesive.

Another object of the present invention is to overcome the deficiencies in the prior art and provide an application of a multi-branched structural adhesive.

In order to solve the above-mentioned technical problems, the present invention provides the following technical solutions: including,

The material containing the active material, the conductive agent, the multi-branched structure binder and the water is coated on the current collector, and after drying, a negative electrode sheet is prepared, and the obtained negative electrode sheet is applied to a lithium ion battery.

As a preferred solution of the present invention, wherein: the active material is nano-silicon, and the conductive agent is one or more of super P and acetylene black.

As a preferred solution of the present invention, wherein: the amount of the binder is 10-20 parts by mass of the negative electrode sheet.

As a preferred solution of the present invention, wherein: in the drying, the temperature is 100-180° C. and the time is 8-12 hours.

Beneficial effects of the present invention:

(1) The branched PAA binder disclosed in the present invention has excellent electrochemical performance as a lithium ion silicon-based negative electrode binder. Due to its multi-branched structure, the grafted molecules contain many functional groups, which can interact with the silicon surface. Multi-dimensional bonding is generated, thereby improving the adhesion with silicon, effectively alleviating the volume expansion of silicon, and maintaining the integrity of the electrode structure, which provides method support for the future research and application of lithium-ion battery silicon anode binders.

(2) The preparation process of the present invention is simple, and a modified binder with a multi-branched structure is generated by the method of grafting, and the obtained branched PAA binder is easily soluble in water, and itself is a kind of hydraulic gel. It exists in the form of glue, has the characteristics of environmental friendliness, can be produced on a large scale, and is pollution-free.

Description of drawings

In order to illustrate the technical solutions of the embodiments of the present invention more clearly, the following briefly introduces the accompanying drawings used in the description of the embodiments. Obviously, the drawings in the following description are only some embodiments of the present invention. For those of ordinary skill in the art, other drawings can also be obtained based on these drawings without any creative effort. in:

Fig. 1 is the FTIR spectrum of the binder prepared in Example 1 of the present invention.

2 is a 180-degree peel test chart of the adhesive prepared in Example 1 of the present invention.

FIG. 3 is a CV curve diagram of the binder prepared in Example 1 of the present invention.

FIG. 4 is a cycle performance diagram of the binder prepared in Example 1 of the present invention.

FIG. 5 is a graph of the rate performance of the adhesive prepared in Example 1 of the present invention.

FIG. 6 is a SEM image of the binder prepared in Example 1 of the present invention.

FIG. 7 is an initial SEM image of the electrode pad of the binder prepared in Example 1 of the present invention.

Detailed ways

In order to make the above objects, features and advantages of the present invention more obvious and easy to understand, the specific embodiments of the present invention will be described in detail below with reference to the embodiments of the specification.

Many specific details are set forth in the following description to facilitate a full understanding of the present invention, but the present invention can also be implemented in other ways different from those described herein, and those skilled in the art can do so without departing from the connotation of the present invention. Similar promotion, therefore, the present invention is not limited by the specific embodiments disclosed below.

Second, reference herein to "one embodiment" or "an embodiment" refers to a particular feature, structure, or characteristic that may be included in at least one implementation of the present invention. The appearances of "in one embodiment" in various places in this specification are not all referring to the same embodiment, nor are they separate or selectively mutually exclusive from other embodiments.

Example 1

Add 1 g of polyacrylic acid (PAA) to 4.725 mL of deionized water, stir magnetically, then add 0.05 g of citric acid in a water bath and heat to 60°C, and then keep at this temperature for 3 hours to form a uniformly mixed precursor;

The precursor was reacted under vacuum at 150 °C for 8 h, and the reaction product was swollen with deionized water for 2 h after natural cooling to obtain the modified binder CA-g-PAA.

Example 2

Add 1 g of polyacrylic acid (PAA) to 4.95 mL of deionized water, stir magnetically, then add 0.1 g of citric acid in a water bath and heat to 60°C, then keep at this temperature for 3 hours to form a well-mixed precursor;

The precursor was reacted under vacuum at 150 °C for 8 h, and the reaction product was swollen with deionized water for 2 h after natural cooling to obtain the modified binder CA-g-PAA.

Example 3

Add 1 g of polyacrylic acid (PAA) to 5.4 mL of deionized water, stir magnetically, then add 0.15 g of citric acid in a water bath and heat to 60°C, then keep at this temperature for 3 hours to form a well-mixed precursor;

The precursor was reacted under vacuum at 150 °C for 8 h, and the reaction product was swollen with deionized water for 2 h after natural cooling to obtain the modified binder CA-g-PAA.

Example 4

Add 1 g of polyacrylic acid (PAA) to 5.85 mL of deionized water, stir magnetically, then add 0.2 g of citric acid in a water bath and heat to 60°C, and then keep at this temperature for 3 hours to form a well-mixed precursor;

The precursor was reacted under vacuum at 150 °C for 8 h, and the reaction product was swollen with deionized water for 2 h after natural cooling to obtain the modified binder CA-g-PAA.

Comparative Example 1

Add 1 g of polyacrylic acid (PAA) to 5.4 mL of deionized water, stir magnetically, then add 0.15 g of glycine, heat to 60°C in a water bath, and keep at this temperature for 3 hours to form a well-mixed precursor;

The precursor was reacted under vacuum at 150 °C for 8 h, and after natural cooling, the reaction product was swollen with deionized water for 2 h to obtain a modified binder.

Comparative Example 2

Add 1 g of polyacrylic acid (PAA) to 5.4 mL of deionized water, stir magnetically, then add 0.15 g of glutamic acid, heat to 60°C in a water bath, and keep at this temperature for 3 hours to form a well-mixed precursor;

The precursor was reacted under vacuum at 150 °C for 8 h, and after natural cooling, the reaction product was swollen with deionized water for 2 h to obtain a modified binder.

Comparative Example 3

Add 1 g of polyacrylic acid (PAA) to 5.4 mL of deionized water, stir magnetically, then add 0.15 g of taurine, heat to 60°C in a water bath, and keep at this temperature for 3 hours to form a well-mixed precursor;

The precursor was reacted under vacuum at 150 °C for 8 h, and after natural cooling, the reaction product was swollen with deionized water for 2 h to obtain a modified binder.

Example 5

Electrochemical performance test:

The nano-silicon (negative electrode material), acetylene black (conductive carbon) and CA-g-PAA (binder) synthesized by the examples of the present invention and the comparative example were evenly mixed according to the mass ratio of 6:2:2, and coated on copper. On the foil, it was dried in a vacuum oven at 150 °C for 8 h, and after drying, it was pressed into a disc with a diameter of 14 mm.

The preparation of the lithium ion battery adopts the conventional methods in the art, that is, using metal lithium as the counter electrode; using 1 mol/L LiPF ₆ /EC:DMC:EMC (V:V:V=1:1:1) as the basic electrolyte, The additive is FEC, and the mass ratio in the electrolyte is 0-10 wt%; a button battery is assembled in a glove box protected by an argon atmosphere. The electrochemical performance was tested with a battery tester from Shenzhen Newwell Electronics Co., Ltd. The charging and discharging voltage range was 0.01V to 1.5V (vs. Li ⁺ /Li), and the test temperature was 25°C. At the same time, the CHI660E electrochemical workstation of Shanghai Chenhua Co., Ltd. was used for impedance test, and the test frequency was 0.01-100000Hz.

Table 1 is the electrochemical performance table of the negative electrode sheets of lithium ion batteries prepared in Examples 1-4 and Comparative Examples 1-3;

Table 1

As can be seen from Table 1, when the binder prepared by the present invention is applied to the silicon negative electrode of a lithium ion battery, it can have better mechanical properties and electrochemical properties. This is because the binder prepared by the present invention has multiple branches. Chain structure, because of its many branches, the groups on these branches (such as sulfonic acid groups, carboxylic acid groups, etc.) and the carboxylic acid groups on the PAA main chain can bond with silicon to form chemical bonds, resulting in The multi-dimensional bonding can firmly grasp the silicon particles, so it can alleviate the powdering of silicon during the process of silicon volume expansion and contraction, so as to better maintain the integrity of the electrode structure.

In the present invention, by controlling the amount of different grafting modifiers, the influence of different grafting degrees on its electrochemistry can be explored, so as to select suitable grafting modifiers and usage amounts. It can be seen that the grafting modification of the present invention The best technical effect is achieved when the mass ratio of the agent and the polyacrylic acid is selected as 0.1:1.

In addition, under the same grafting degree, the taurine graft-modified binder showed better electrochemical performance; by testing with different modifier binders, different graft modifications can be explored. The influence of the agent on the electrochemical performance of PAA, and then the appropriate graft modifier was selected to effectively improve the service life of the lithium-ion silicon-based anode battery.

Figure 1 is the FTIR spectrum of the prepared CA-g-PAA. It can be seen from the figure that the characteristic peak of the C=O bond on the carboxyl group on PAA appears at 1700cm ^-1 , but after modification with citric acid, the The -PAA spectrum shifted to a higher wavenumber of 1707cm ^-1 , which indicated that part of the carboxyl groups on PAA successfully formed bonds with the hydroxyl groups on citric acid to form ester groups, which proved that the target product was synthesized.

Figure 2 is the 180° peel test chart of the above-mentioned negative pole piece using CA-g-PAA and PAA as binders. As can be seen from the figure, the average peel strength of the uncycled silicon electrode containing CA-g-PAA binder is 4.07 N, while the average peel strength of the PAA adhesive is only 1.36N. The results show that the CA-g-PAA binder has higher bonding ability than the PAA binder.

Figure 3 is a cyclic voltammetry diagram of the button cell prepared with the above negative electrode, and redox peaks can be clearly observed, indicating that the modified binder has no effect on the electrochemical behavior. At the same time, the peak current of the redox peak gradually increased from the first to the fifth cycle of the scan, indicating that the electrode material is a gradually activated process during the initial electrochemical reaction.

FIG. 4 is a graph showing the charge-discharge cycle performance of the button battery prepared with the above negative electrode. It can be seen from the figure that at a current density of 840 mA g -1, the capacity of the silicon electrode composed of the citric acid-grafted PAA binder after 100 cycles is 2627.4 mAh g ^-1 , while the capacity of the silicon electrode composed of the PAA binder is 2627.4 mAh g ^-1 . The capacity is only 942.3mAh g ^-1 , indicating that the material has good cycle performance.

Figure 5 is a graph of the rate performance of the coin-type battery prepared above under different current densities. When the prepared battery was subjected to charge-discharge tests at The PAA/Si electrodes exhibited specific discharge capacities of 3596, 3189, 2744, 2023 and 1499 mAh g ^-1 , respectively. Even when the current density was restored to 0.2 C, the specific discharge capacity remained at 2897 mAh g ^-1 , indicating that the binder has high specific capacity and excellent rate capability when used in lithium-ion battery silicon anodes.

Figure 6 is the SEM image of the above-mentioned negative pole piece using CA-g-PAA and PAA as binders. It can be seen from the figure that all electrodes have no obvious difference before cycling, and all have flat surface morphology. After 5 cycles, micron-scale cracks were observed on the surface of the PAA/Si electrode, while no obvious cracks were found on the CA-g-PAA/Si electrode, indicating that the modified binder well maintained the integrity of the electrode structure. .

It should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit them. Although the present invention has been described in detail with reference to the preferred embodiments, those of ordinary skill in the art should understand that the technical solutions of the present invention can be Modifications or equivalent substitutions without departing from the spirit and scope of the technical solutions of the present invention should be included in the scope of the claims of the present invention.

Claims (10)

1. A preparation method of a multi-branching structure adhesive is characterized by comprising the following steps: comprises the steps of (a) preparing a mixture of a plurality of raw materials,

preparing a precursor: adding polyacrylic acid into deionized water, magnetically stirring, adding a grafting modifier, continuously stirring and heating to obtain a uniformly mixed precursor;

preparing a multi-branched structure binder: and (3) reacting the precursor under the conditions of vacuum and high temperature, and swelling for a period of time after the reaction is finished to obtain the adhesive with the multi-branched structure.

2. The method of preparing the multi-branched structure adhesive according to claim 1, wherein: the graft modifier is one or more of glycine, glutamic acid, taurine and citric acid.

3. The method of preparing the multi-branched structure adhesive according to claim 1, wherein: the mass ratio of the polyacrylic acid to the grafting modifier is 1: 0.05-0.2, wherein the mass portion of the adhesive is 0-50 parts of the mixture of polyacrylic acid and the grafting modifier.

4. The method of preparing the multi-branched structure adhesive according to claim 1, wherein: the precursor is prepared, wherein the heating temperature is 100-180 ℃, and the heating time is 2-12 h.

5. The method of preparing the multi-branched structure adhesive according to claim 1, wherein: the preparation method of the adhesive with the multi-branched structure is characterized in that the swelling time is 1-4 h.

6. The adhesive with a multi-branching structure prepared by the method for preparing the adhesive with a multi-branching structure as claimed in any one of claims 1 to 5.

7. The application of the adhesive with the multi-branching structure is characterized in that: the preparation method comprises the steps of coating a material containing an active material, a conductive agent, a multi-branched structure binder and water on a current collector, drying to obtain a negative plate, and applying the negative plate to a lithium ion battery.

8. Use of the multi-limbed structural adhesive according to claim 7 wherein: the active material is nano silicon, and the conductive agent is one or more of super P and acetylene black.

9. Use of the multi-limbed structural adhesive according to claim 7 wherein: the negative plate comprises, by mass, 10-20 parts of the binder.

10. Use of the multi-limbed structural adhesive according to claim 7 wherein: and drying, wherein the temperature is 100-180 ℃, and the time is 8-12 h.

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