CN112259734A

CN112259734A - Lithium ion battery negative electrode polymer binder and preparation method and application thereof

Info

Publication number: CN112259734A
Application number: CN202011133868.0A
Authority: CN
Inventors: 任玉荣; 胡贤超
Original assignee: Changzhou University
Current assignee: Changzhou University
Priority date: 2020-10-21
Filing date: 2020-10-21
Publication date: 2021-01-22

Abstract

The invention relates to a lithium ion battery cathode polymer binder and a preparation method and application thereof. The preparation method of the adhesive comprises the steps of preparing Oxidized Starch (OS) by hydrogen peroxide oxidation under alkaline conditions, and preparing OS-PAA by reacting polyacrylic acid (PAA) with the Oxidized Starch (OS) through a hydroxyl-carboxyl dehydration condensation reaction. The lithium ion battery cathode polymer binder has a three-dimensional network structure, and can relieve the powder falling phenomenon caused by the volume expansion of silicon particles, so that the cycle performance of the battery is enhanced.

Description

Lithium ion battery negative electrode polymer binder and preparation method and application thereof

Technical Field

The invention relates to a preparation method of a battery binder, in particular to a preparation method of a lithium ion battery cathode polymer binder, belonging to the technical field of lithium ion batteries.

Background

For LIBs, silicon is an anode material with great development potential, and the theoretical specific capacity of the silicon is up to 4200mAh g^-1，Li^-/Li⁺The electrochemical potential is between 0 and 0.4V, and the initial irreversible capacity is smaller than that of other metal or alloy anode materials. However, silicon has some practical problems in practical applications, in Li⁺During the insertion and removal process, the silicon undergoes severe volume changes (about300%), which causes the destruction and mechanical pulverization of the material structure, resulting in the separation between electrode materials and between the electrode materials and the current collector, thereby losing electrical contact, causing rapid capacity decay and deterioration of cycle performance. Although the mechanical strain generated by the volume change can be effectively relieved after the silicon-based material is coated and modified, the electrode deformation and the external battery expansion can still be caused due to the inherent volume change of the silicon. This large variation in cell volume is a major factor limiting the commercialization of silicon-based anode materials. For commercial use, various approaches have been taken, including binder development, to suppress severe volume changes of silicon.

In the lithium ion battery, the binder is a substance for maintaining the integrity of the pole piece and plays a crucial role in the cycle performance of the battery. The simple substance silicon is used as the cathode material, and has more strict requirements on the binder: firstly, the large volume expansion of the silicon material requires that the adhesion force between the binder and the copper foil of the current collector must be stronger than that of PVDF; secondly, the silicon material is easy to separate from the pole piece in the self-contraction process, so that the loss of the surrounding conductive agent is caused, and therefore, the adhesive has strong acting force with the surface of the silicon material. Therefore, the development of a high-performance adhesive suitable for a silicon negative electrode is a scientific problem to be solved urgently.

Disclosure of Invention

In order to solve the above technical problems, an object of the present invention is to provide a negative electrode binder for a lithium ion battery having high adhesion to silicon, mechanical strength and self-healing properties, and a method for preparing the same.

In order to solve the above technical problems, the present invention firstly provides a preparation method of a lithium ion battery negative electrode polymer binder, wherein the preparation method comprises:

adding copper sulfate and hydrogen peroxide into the starch emulsion, and reacting at 20-90 deg.C for 10-60 min to obtain a mixed solution; the addition amount of the copper sulfate is 0-0.05% (preferably 0.005-0.05%) of the mass content of the starch, and the addition amount of the hydrogen peroxide is 1-30% of the mass content of the starch;

adding sodium bisulfite into the mixed solution, stirring for 10min-30min, adjusting pH to 3-7, filtering, dehydrating, washing, oven drying, pulverizing, and sieving to obtain oxidized starch solid powder; the addition amount of the sodium bisulfite is 0.05 to 0.5 percent of the mass content of the starch;

adding polyacrylic acid into the oxidized starch solid powder, reacting for 4-16 h at 80-200 ℃ under the protection of inert gas, and freeze-drying to obtain a lithium ion battery negative electrode polymer binder; the mass ratio of the oxidized starch solid powder to the polyacrylic acid is 1 (0.5-5).

The preparation method of the lithium ion battery negative electrode polymer binder prepares Oxidized Starch (OS) through hydrogen peroxide oxidation under alkaline conditions, and prepares OS-PAA through a hydroxyl-carboxyl condensation reaction by reacting polyacrylic acid (PAA) with the Oxidized Starch (OS). The OS-PAA has a three-dimensional network structure, and can relieve the powder falling phenomenon caused by the volume expansion of silicon particles, thereby enhancing the cycle performance of the battery.

The preparation method of the adhesive comprises the step of preparing starch emulsion. Specifically, starch is prepared into starch emulsion, NaOH solution is added, and the pH value of the starch emulsion is adjusted to be alkaline.

In the present invention, the concentration is measured by a Bome viscometer, and the pH test is carried out by a pH test pen.

In one embodiment of the invention, the starch emulsion has a concentration of 15 Be-to 30 Be-at which starch oxidation is more readily carried out.

In one embodiment of the invention, the pH of the starch emulsion is from 7 to 10.

In one embodiment of the invention, a starch emulsion having a concentration of 15 Be-to 30 Be-and a pH of 7-10 is prepared by the steps of:

mixing starch and water to obtain starch emulsion with concentration of 15 Be-to 30Be-, and adjusting pH of the starch emulsion to 7-10 by adopting NaOH solution. Preferably, the NaOH solution is used in a concentration of 5% to 7% by mass, for example, the NaOH solution is used in a concentration of 6% by mass. The solution with the concentration is more easily controlled and the pH value is detected when the solution is dripped.

The method for preparing the binder of the present invention includes the step of preparing a mixed solution. Adding copper sulfate and hydrogen peroxide into starch emulsion, stirring and reacting for a period of time at a certain temperature to obtain a mixtureAnd (4) mixing the solution. Cu under alkaline conditions²⁺The structure of the starch is damaged, so that the hydroxyl groups are easier to oxidize. Wherein the addition amount of the copper sulfate is 0.01-0.05% of the mass content of the starch, and the addition amount of the hydrogen peroxide is 1-20% of the mass content of the starch; wherein the mass concentration of the adopted hydrogen peroxide is 30 percent.

In a specific embodiment of the invention, the copper sulfate and the hydrogen peroxide solution are added slowly and dropwise during the preparation of the mixed solution, and the total rate is preferably controlled to be 0.1g/min-0.5 g/min. Adopts a water bath heating mode.

The method for preparing the binder of the present invention comprises the step of preparing oxidized starch solid powder. Adding sodium bisulfite into the mixed solution, stirring for a period of time, adding dilute HCl to adjust the pH value of the solution to acidity, carrying out suction filtration and dehydration, washing and drying, crushing and screening to obtain oxidized starch solid powder.

In a specific embodiment of the invention, dilute HCl with the mass concentration of 5-10% is slowly dripped; the drying temperature for washing and drying is 30-60 ℃.

The preparation method of the adhesive comprises the step of preparing the adhesive. Specifically, solid powder is placed into a three-neck flask, water is added into the three-neck flask, the mixture is stirred for 1 hour to 3 hours, the mixture is uniformly stirred, polyacrylic acid is added, the mixture reacts for a period of time at a certain temperature under the protection of inert gas, and after the reaction is finished, the mixture is frozen and dried to obtain a solid material.

In one embodiment of the present invention, the inert gas is at least one of nitrogen, argon, and helium. The heating mode is oil bath heating.

In one embodiment of the present invention, polyacrylic acid is used having a number average molecular weight Mw of 750000-.

The invention also provides a lithium ion battery cathode polymer binder, which is prepared by the preparation method of the lithium ion battery cathode polymer binder.

The invention also provides a silicon-based negative electrode of the lithium ion battery, which comprises a negative electrode material, a conductive agent and a binder, wherein the binder is the polymer binder for the negative electrode of the lithium ion battery. The main improvement of the silicon-based negative electrode of the lithium ion battery is that the adhesive is adopted, and the specific types, the dosage and the like of the negative electrode material and the conductive agent can be the same as those of the prior art. For example, specific examples of the conductive agent include, but are not limited to: at least one of carbon black, graphene, carbon fiber, and graphite.

The invention also provides a lithium ion battery, wherein the negative electrode of the lithium ion battery is the silicon-based negative electrode of the lithium ion battery.

The invention also provides a product containing the lithium ion battery.

The polymer binder OS-PAA prepared by the preparation method of the lithium ion battery cathode polymer binder has a three-dimensional network structure and a reversible ionic bond reconstruction effect, and the special structure has higher adhesion, high mechanical strength and self-healing property on silicon, can effectively adapt to volume expansion and contraction of a silicon-based cathode material, can still keep structural stability after generating huge volume change, and can improve the cycling stability of a battery when being used as the lithium ion battery cathode binder.

Drawings

Fig. 1 is an FT-IR diagram of the lithium ion battery negative electrode binder prepared in example 1.

Fig. 2 is a TG of the lithium ion battery negative electrode binder prepared in example 1.

Fig. 3 is a DSC diagram of the lithium ion battery negative electrode binder prepared in example 1.

Fig. 4 is an SEM image of the negative electrode binder for lithium ion battery prepared in example 1 (panel a, panel b, panel c are SEM images of OS, PAA, OS-PAA, respectively, when not cycled; panel e, panel d, panel f are SEM images of OS, PAA, OS-PAA, respectively, after 100 weeks of cycling).

Fig. 5 is a TEM image of the negative electrode binder of the lithium ion battery prepared in example 1.

Fig. 6 is a CV diagram of the negative electrode binder for a lithium ion battery prepared in example 1.

Fig. 7 is a graph of battery cycle performance based on the lithium ion battery negative electrode binder prepared in example 1.

Fig. 8 is a battery rate performance graph based on the lithium ion battery negative electrode binder prepared in example 1.

Detailed Description

The preferred embodiments of the present invention will be described in detail below with reference to the accompanying drawings:

example 1

This example provides a method of preparing a polymeric binder, comprising the steps of:

a.10g of starch was added to 40mL of deionized water, stirred for 10min with a magnetic stirrer, 5% NaOH was added dropwise to adjust the pH to 8, and the temperature of the water bath was adjusted to 40 ℃.

b. Adding 0.001g of anhydrous copper sulfate, slowly adding 4mL of 30% hydrogen peroxide dropwise, reacting at 40 ℃ in a water bath for 30min, adding 0.02g of sodium bisulfite, and stirring for 10 min. Slowly dropwise adding 5% dilute hydrochloric acid to adjust the pH of the solution to 5.5-6.0. And (4) carrying out suction filtration and dehydration, washing the mixture by using deionized water, and putting the mixture into an oven to be dried for 6 hours at the drying temperature of 40 ℃. And (4) crushing and grinding the solid to obtain solid powder.

c. Putting 1g of oxidized starch into a three-neck flask, adding 50mL of deionized water, stirring for 2h, adding 1g of polyacrylic acid, adjusting the temperature of an oil bath to 120 ℃ under the protection of Ar gas, and reacting for 6 h. After the reaction is finished, the reaction solution is frozen and dried for 24 hours to obtain a solid product.

FIG. 1 is a FT-IR diagram of the obtained sample, wherein the oxidation of starch mainly occurs at the hydroxyl position on a starch chain, the influence on C-H is small, and the association peak formed by starch hydroxyl is 3550-3250cm^-1The strength of (a) is reduced, indicating that the content of alcoholic hydroxyl groups in the system is reduced. In addition, at 1660cm^-1Here, the yc ═ o asymmetric stretching vibration absorption peak of the carboxylate is strengthened, indicating that the COO-content in the system is increased. It can be seen that part of the alcoholic hydroxyl groups of the system are oxidized to carboxyl groups. Carboxyl groups are located from 1710cm at the C ═ O stretch band in PAA due to ester groups (COO-) formed by interchain crosslinking^-1Moved to 1730cm^-1. Furthermore, it can be clearly seen that the hydroxyl group is 3550-3250cm^-1Broad peaks, are significantly reduced by condensation reactions of the COOH groups of PAA with the OH groups of OS.

FIG. 2 is TGA of the resulting sample, and FIG. 3 is DSC of the resulting sample, and OS-PAA thermal stability and endothermic/exothermic behavior were determined by TG and DSC. It can be seen by TGA that the polymer had a small mass loss before 100 ℃, but this was due to the loss of moisture, and the polymer remained stable well before 200 ℃ overall, without any additional endothermic/exothermic peak in the DSC trace, indicating good thermal stability. Then, when used as a Si-based binder, the binder can maintain good stability during battery cycling.

Fig. 4 is an SEM image of the pole piece powder before and after different binder cycles. From fig. 4, it can be seen that the silicon electrode shows uniform particle distribution in the original state under different binders, and after 100 cycles, the Si-OS-PAA electrode maintains a relatively clear Si nanoparticle morphology and maintains a good stable porous structure without severe pulverization, while the Si-OS and Si-PAA electrodes show the silicon-pulverized nanoparticles aggregated together (panels e and f in fig. 4). The well-preserved original Si form retains the porous electrode structure and the relatively uniform particle distribution after circulation shows that the OS-PAA binder has enough toughness, can adapt to the large volume change of Si particles, maintains the original size electrode form (forms a thin and stable SEI layer) and maintains a conductive network and a mechanical network, and enables the silicon electrode to be kept complete in deep charge-discharge circulation.

FIG. 5 from TEM it can be seen that the OS-PAA polymer is partially hydrolyzed with the Si surface due to the polar carboxyl (-COOH)/hydroxyl (-OH) functional groups of the binder₂The layers have strong hydrogen bonding between them and can therefore be firmly anchored to the surface of the Si particles. The OS-PAA binder can ensure good coverage of silicon particles, and reduce the contact area of silicon active particles and electrolyte, thereby reducing the decomposition of the electrolyte on the silicon surface. In addition, the uniform adhesion of the OS-PAA layer to the Si surface can tightly bind the active material and conductive additives together, adhere to the current trap, and maintain the electromechanical integrity of the electrode over long cycling times. This stable electrode architecture and binder network structure can facilitate electrons and Li⁺The transport is permeated by the electrolyte。

And (3) carrying out battery assembly on the prepared cathode binder (testing the electrochemical performance of the material by adopting a 2032 type button cell): weighing 80% of negative active substance, 10% of binder and 10% of conductive agent according to the mass ratio, uniformly grinding, coating on a current collector, and finally placing in an oven at 60-120 ℃ for vacuum drying for 4-24 h; finally transferring the cut pole piece into a glove box filled with argon gas to assemble a battery, taking a metal lithium piece as a counter electrode and 1.0M LiPF₆And in EC, DMC, EMC 1:1:1 Vol%, FEC 10.0% is used as an electrolyte, Celgard2300 is used as a diaphragm, and the CR2032 button cell is prepared. The CV diagram was measured by an electrochemical tester, and the results are shown in FIG. 6, in which the performance of silicon-based anodes using OS, PAA and OS-PAA as binders was measured by cyclic voltammetry at 0.5mV/S in the voltage range of 0.01 to 1.5V. In the detection of three weeks of circulation, three oxidation peaks are provided, which are around 0.34V and 0.53V, which is similar to Li⁺Below 0.35V, the silicon particles undergo cathodic activation and the current increases sharply, which is related to the lithiation of the silicon particles, i.e. the process of intercalation of lithium, which coincides with the phenomenon of silicon-based materials. The redox peaks of the first cycle are separated and compared, and the values are 0.115V, 0.097V and 0.072V respectively. This shows that OS-PAA as the binder can effectively reduce the polarization phenomenon relative to the other two. Comparing their redox peak heights, we can see that the peak of OS-PAA is much higher than the other two, and the peak height is in comparison with Li⁺The higher the peak value is, the higher the migration rate is, which also explains that the three-dimensional network structure promotes Li⁺Is being migrated.

The charging and discharging test is performed on a LAND battery test system (CT2100A) and is set to be in a constant-current charging and discharging mode, the adopted current density is a set value, and the charging and discharging voltage range is set to be 0.01-1.5V, and the result is shown in the graph of figure 7 and figure 8. The first discharge specific capacity of OS-PAA is higher and can reach 3488mAh g^-1The first coulombic efficiency was 68.90% higher than 53.59% for PAA under an equivalent mating bar; at 200mA · g^-1The capacity after 100 cycles of the current density of (2) was also 1413.5mAh g^-1The capacity retention rate was 40.5%. The rate capability of the adhesive is better, and the adhesive passes through large currentAfter charging and discharging, at 200mAh g^-1The capacity was 2185.4mAh g at a current density of (1)^-1The capacity retention rate is 63.56%; in 1Ag^-1The capacity of the capacitor under the current density is 779mAh g^-1。

Example 2

This example provides a method for preparing a binder for a negative electrode of a lithium ion battery, which is substantially the same as in example 1, except that: in step (a), the alkaline pH was set to 7.

Example 3

This example provides a method for preparing a binder for a negative electrode of a lithium ion battery, which is substantially the same as in example 1, except that: the alkaline pH was set to 9 in step (a).

Example 4

This example provides a method for preparing a binder for a negative electrode of a lithium ion battery, which is substantially the same as in example 1, except that: in step (b), anhydrous copper sulfate is not added.

Example 5

This example provides a method for preparing a binder for a negative electrode of a lithium ion battery, which is substantially the same as in example 1, except that: in step (b), 0.002g of anhydrous copper sulfate was added.

Example 6

This example provides a method for preparing a binder for a negative electrode of a lithium ion battery, which is substantially the same as in example 1, except that: in step (b), 2mLH is added₂O₂。

Example 7

This example provides a method for preparing a binder for a negative electrode of a lithium ion battery, which is substantially the same as in example 1, except that: in step (b), 6mLH was added₂O₂。

Comparative example 1

This example provides a method of preparing a lithium ion battery negative binder, which is substantially the same as in example 1, except that: step (c) was not performed, and the OS of step 2 was used as a binder.

Comparative example 2

This example provides a method of preparing a lithium ion battery negative binder, which is substantially identical to the battery installation procedure of example 1, except that: commercial PAA was used directly as binder.

Electrochemical tests were performed on 2032 type button cells assembled using the lithium ion battery negative electrode binders of examples 1-7 and comparative examples 1-2, and the results are listed in table 1.

Table 1 performance table for 2032 type button cell assembled with binders of examples 1-7 and comparative examples 1-2

The above embodiments are merely illustrative of the technical ideas and features of the present invention, and the purpose thereof is to enable those skilled in the art to understand the contents of the present invention and implement the present invention, and not to limit the protection scope of the present invention. All equivalent changes and modifications made according to the spirit of the present invention should be covered within the protection scope of the present invention.

Claims

1. A preparation method of a polymer binder for a lithium ion battery negative electrode comprises the following steps:

adding copper sulfate and hydrogen peroxide into the starch emulsion, and reacting at 20-90 deg.C for 10-60 min to obtain a mixed solution; the addition amount of the copper sulfate is 0-0.05% of the mass content of the starch, and the addition amount of the hydrogen peroxide is 1-30% of the mass content of the starch;

adding sodium bisulfite into the mixed solution, stirring for 10min-30min, adjusting pH to 3-7, filtering, dehydrating, washing, drying, pulverizing, and sieving to obtain oxidized starch solid powder; the addition amount of the sodium bisulfite is 0.05 to 0.5 percent of the mass content of the starch;

2. The lithium ion battery negative electrode polymer binder of claim 1, wherein the starch emulsion has a concentration of 15Be "to 30 Be".

3. The lithium ion battery negative electrode polymer binder of claim 1 or 2, wherein the starch emulsion has a pH of 7-10.

4. The lithium ion battery negative electrode polymer binder of claim 3, wherein the starch emulsion is prepared by the following steps:

mixing starch and water to obtain starch emulsion, and adjusting the pH of the starch emulsion to 7-10 by adopting NaOH solution;

preferably, the mass concentration of the NaOH solution is 5-7%.

5. The lithium ion battery negative electrode polymer binder of claim 1, wherein the polyacrylic acid has a number average molecular weight Mw of 750000-.

6. The lithium ion battery negative electrode polymer binder of claim 1, wherein the mass concentration of the hydrogen peroxide is 30%;

preferably, the drying temperature for washing and drying is 30-60 ℃.

7. A lithium ion battery negative electrode polymer binder prepared by the method for preparing a lithium ion battery negative electrode polymer binder according to any one of claims 1 to 6.

8. A silicon-based negative electrode of a lithium ion battery, which comprises a negative electrode material, a conductive agent and a binder, wherein the binder is the negative electrode polymer binder of the lithium ion battery of claim 7.

9. A lithium ion battery, wherein the negative electrode of the lithium ion battery is the silicon-based negative electrode of the lithium ion battery according to claim 8.

10. A product comprising the lithium ion battery of claim 9.