CN111244460B

CN111244460B - Polymer-inorganic nano composite binder for lithium ion battery

Info

Publication number: CN111244460B
Application number: CN202010072772.1A
Authority: CN
Inventors: 韩伟强; 郭容男
Original assignee: Zhejiang University ZJU
Current assignee: Zhejiang University ZJU
Priority date: 2020-01-21
Filing date: 2020-01-21
Publication date: 2021-01-08
Anticipated expiration: 2040-01-21
Also published as: CN111244460A

Abstract

The invention discloses a polymer-inorganic nano composite binder for a lithium ion battery, which is formed by compounding a polymer and a layered inorganic nano material, wherein the monomer of the polymer is one or more of acrylic acid/acid salt, acrylamide, 6-acrylamidocaproic acid/acid salt, N-methacryloyl glycine/acid salt and 2-acrylamide-2-methylpropanesulfonic acid/acid salt, and at least one monomer contains a polar group; the inorganic nano material is synthesized laponite, montmorillonite, MXene or modified products thereof. The adhesive is prepared by in-situ polymerization of polymer monomers on the surface of a stripped layered inorganic nano material through physical and chemical double crosslinking, and has the characteristics of high adhesive strength and high lithium ion transmission rate. When the binder is applied to the lithium ion battery, the specific capacity, the cycling stability and the rate capability of the lithium ion battery can be simultaneously improved.

Description

Polymer-inorganic nano composite binder for lithium ion battery

Technical Field

The invention relates to the field of lithium ion batteries, in particular to a polymer-inorganic nano composite binder for a lithium ion battery and a preparation method thereof.

Background

The lithium ion battery has the advantages of high energy density, long cycle life, high working voltage and the like, so that the lithium ion battery is widely applied to systems such as a micro-grid, a smart grid and electronic products. However, the current commercial lithium ion battery cannot meet the requirements of hybrid power or pure electric vehicles and also cannot meet huge market requirements. The development of high-energy density and high-rate performance lithium ion batteries is imminent. The selection of active materials with high specific capacity is one way to increase the energy density of lithium ion batteries. However, most of high specific capacity active materials have the defects of large volume change in the lithium intercalation and deintercalation process, active material shedding, capacity attenuation and poor cycle stability. Meanwhile, most active materials with high specific capacity have poor ion conductivity, and the battery has serious polarization under high rate, so the rate performance is poor, and the requirement of quick charge of the battery can not be met. The binder is used in a small amount in a lithium ion battery, but plays an important role.

At present, the acting force between the commercial binder polyvinylidene fluoride (PVDF) and an active substance is weak, and the active substance is easy to fall off in the charging and discharging processes, so that the specific capacity and the cycling stability are reduced. In addition, PVDF is insulating to electrons and ions, which is not beneficial to improving the rate capability of the lithium ion battery. Therefore, PVDF as a binder for high specific capacity active materials cannot achieve satisfactory specific capacity, cycle performance, and rate capability.

In order to solve the above problems, it is necessary to develop a binder which has a strong force with an active material and is advantageous for improving the electrochemical performance of a lithium ion battery.

Disclosure of Invention

The invention aims to provide a polymer-inorganic nano composite binder for a lithium ion battery and a preparation method thereof, aiming at the defects of the prior art, the binder can be used for the anode or the cathode of the lithium ion battery, has strong binding power to active substances, can uniformly disperse the active substances and conductive agents in the electrode, is beneficial to ion transmission in the electrode, and can effectively improve the cycle stability and the rate capability of the lithium ion battery.

The technical scheme adopted by the invention is as follows:

a polymer-inorganic nano composite binder for a lithium ion battery is formed by compounding a polymer and a layered inorganic nano material, wherein the monomer of the polymer is one or more of acrylic acid/acid salt, acrylamide, 6-acrylamidocaproic acid/acid salt, N-methacryloyl glycine/acid salt and 2-acrylamide-2-methylpropanesulfonic acid/acid salt, and at least one monomer contains a polar group; the inorganic nano material is synthesized laponite, montmorillonite, MXene or modified products thereof.

The mass ratio of the inorganic nano material in the binder is 2-50%, and the mass ratio of the polymer is 98-50%. Preferably, the mass ratio of the inorganic nanomaterial in the binder is 25%.

The monomer of the polymer is preferably selected from 6-acrylamide lithium adipate, 2-acrylamide-2 lithium methyl propane sulfonate, N-acrylamide lithium glycinate and lithium polyacrylate.

The adhesive is prepared by in-situ polymerization of a polymer monomer on the surface of a stripped layered inorganic nano material, a chemical cross-linking agent N, N-methylene bisacrylamide needs to be added during in-situ polymerization, and the adhesive is obtained by double cross-linking through the combined action of physical cross-linking of the inorganic nano material and the added chemical cross-linking agent.

After the layered inorganic nano material is subjected to intercalation stripping by solvent molecules, the polymer monomer is adsorbed on the surface of a stripping layer of the inorganic nano material, an initiator is added or an initiator and a catalyst are simultaneously added, and the polymer monomer is subjected to in-situ polymerization. The initiator can adopt common initiators such as ammonium persulfate, potassium persulfate and the like, and the catalyst has no special requirement and only needs the common catalyst. The initiator can be adsorbed on the surface of the inorganic nano material to initiate polymerization on the surface of the inorganic nano material.

In the in-situ polymerization process of the binder, an electrode active substance and a conductive agent can be added, so that the battery anode or cathode slurry can be prepared by a one-step method. The positive active material can be any known positive material of a lithium ion battery, such as elemental sulfur, sulfur-based compound, lithium polysulfide, organic sulfide, lithium cobaltate, lithium manganate, lithium iron phosphate, and nickel cobalt manganese ternary material, but is not limited thereto; the active material in the negative electrode may be any known negative electrode active material of lithium ion batteries, such as graphite, hard carbon, soft carbon, silicon carbon, silicon-tin alloy, lithium titanate, tin carbon, and germanium, but is not limited thereto. The lithium ion battery can be a liquid lithium ion battery or a solid lithium ion battery.

The adhesive prepared by the invention has the characteristics of strong adhesive force, uniform dispersion of active substances and conductive agents, contribution to ion transmission and the like.

The invention has the beneficial effects that:

the invention utilizes the synergistic effect of the layered inorganic nano material and the specific polymer to improve the binding performance and the ion transmission rate of the binder to active substances, conductive agents and current collectors in the anode or the cathode. The binder can greatly improve the specific capacity, the cycling stability and the rate capability of the lithium ion battery.

The adhesive provided by the invention can be produced in large quantities.

Drawings

FIG. 1 is a graph of cycle performance of lithium ion batteries prepared in examples and comparative examples;

fig. 2 is a graph of rate performance of lithium ion batteries prepared in examples and comparative examples.

Detailed Description

The technical solution of the present invention will be described in more detail with reference to the following examples. The specific examples described herein are merely illustrative of the invention and the scope of the invention is not limited to these examples.

The sulfur loading in the electrode sheets in the following examples and comparative examples was 1mg/cm²。

Examples

6-acrylamidohexanoic acid (0.016g) and lithium hydroxide monohydrate (3.56mg) were dissolved in 0.4mL of deionized water to produce an aqueous solution of lithium 6-acrylamidohexanoate, followed by the addition of 0.1mL of ammonium persulfate solution (containing 0.2mg of ammonium persulfate) and 0.1mL of N, N-methylenebisacrylamide solution (containing 0.1mg of N, N-methylenebisacrylamide). This solution was mixed with a dispersion of deionized water containing 0.40g of synthetic laponite, and 0.160g of active material (sulfur-carbon complex) and 0.02g of carbon black conductive agent were added to the above dispersion. Introducing argon for 30min, adding 0.2ml of aqueous solution containing 0.4mg of catalyst N, N, N, N-tetramethylethylenediamine, and polymerizing at 40 ℃ for 24h to obtain the anode slurry. The whole polymerization process is carried out in an argon atmosphere. This slurry was coated on a carbon-coated aluminum foil and dried. And cutting the dried pole piece into small round pieces with the diameter of 14mm, and assembling the small round pieces into a 2032 button cell in a glove box by taking the lithium piece as a counter electrode and the prepared pole piece as a working electrode. Wherein the electrolyte is a solution of 1, 2-dimethoxyethane and 1, 3-dioxolane (volume ratio of 1:1) containing 1.0mol/L lithium bistrifluoromethanesulfonylimide.

Comparative example

PVDF was prepared as a 2 wt% N-methylpyrrolidone solution. 0.16g of sulfur-carbon composite material and 0.02g of conductive agent Super-P are ground and mixed uniformly, added into 1g of 2 wt% PVDF solution, and mechanically stirred to prepare uniform slurry. This slurry was coated on a carbon-coated aluminum foil and dried. And cutting the dried pole piece into small round pieces with the diameter of 14mm, and assembling the small round pieces into a 2032 button cell in a glove box by taking a lithium piece as a counter electrode and a pole piece prepared from PVDF (polyvinylidene fluoride) binder as a working electrode. The electrolyte used was the same as in the examples.

And (3) testing conditions are as follows: in the examples and the comparative examples, the blue cell test system for button cell (model: CT2001A) was charged and discharged at a constant current in a voltage range of 1.8 to 2.8V. Long cycling tests were performed at 0.5C (1C 1675mAh/g) with the first two rounds activated at 0.1C. When the rate performance is tested, the current density is respectively 0.1C, 0.2C, 0.5C, 1C, 2C, 3C and 4C. FIG. 1 is a graph of cycle performance for examples and comparative examples. The first charge specific capacity in the examples was 1195mAh/g, and in the comparative examples was 1005 mAh/g. After 500 cycles, the specific charge capacity of the example remained at 591mAh/g, while that of the comparative example was only 287 mAh/g. FIG. 2 is a graph of rate performance for examples and comparative examples. When the current density was as high as 3C and 4C, the specific charge capacities in the examples were 613 and 519mAh/g, respectively, while the specific charge capacities in the comparative examples were only 118 and 107 mAh/g. Fig. 1 and fig. 2 illustrate that the binder provided by the invention can effectively improve the first specific capacity, the cycling stability and the rate performance of the electrode.

Claims

1. A polymer-inorganic nano composite binder for lithium ion batteries is characterized in that: the adhesive is formed by compounding a polymer and a layered inorganic nano material, wherein the monomer of the polymer is one or more of acrylic acid/acid salt, acrylamide, 6-acrylamidocaproic acid/acid salt, N-methacryloyl glycine/acid salt and 2-acrylamide-2-methylpropanesulfonic acid/acid salt, and at least one monomer contains a polar group; the inorganic nano material is a synthetic laponite, montmorillonite, MXene or MXene modified product; the adhesive is prepared by in-situ polymerization of a polymer monomer on the surface of a stripped layered inorganic nano material, and a chemical cross-linking agent N, N-methylene bisacrylamide needs to be added during in-situ polymerization.

2. The polymer-inorganic nanocomposite binder for lithium ion batteries according to claim 1, characterized in that: the mass ratio of the inorganic nano material in the binder is 2-50%, and the mass ratio of the polymer is 98-50%.

3. The polymer-inorganic nanocomposite binder for lithium ion batteries according to claim 2, characterized in that: the mass ratio of the inorganic nano material in the adhesive is 25 percent.

4. The polymer-inorganic nanocomposite binder for lithium ion batteries according to claim 1, characterized in that: the monomer of the polymer is selected from 6-acrylamido lithium adipate, 2-acrylamide-2-methyl lithium propanesulfonate, N-acrylamido lithium glycinate or lithium polyacrylate.

5. The polymer-inorganic nanocomposite binder for lithium ion batteries according to claim 1, characterized in that: after the layered inorganic nano material is subjected to intercalation stripping by solvent molecules, the polymer monomer is adsorbed on the surface of a stripping layer of the inorganic nano material, an initiator is added or an initiator and a catalyst are simultaneously added, and the polymer monomer is subjected to in-situ polymerization.

6. A method for preparing electrode slurry for lithium ion batteries, characterized in that, electrode active material and conductive agent are added in the preparation process of the binding agent according to claim 4 or 5, and then positive electrode slurry or negative electrode slurry for lithium ion batteries is prepared in one step.