CN109994703A - Battery electrode binders, electrodes and lithium-ion batteries - Google Patents

Abstract

The invention discloses a battery electrode binder, an electrode and a lithium ion battery, and belongs to the technical field of lithium ion battery electrode bonding and electrode preparation. The battery electrode binder includes hard polymers and their monomers, soft polymers and their monomers, and additives, and the additives can activate the hard polymers and their monomers, and soft polymers and their monomers. interpenetrating polymerization. The invention solves the problems of high cost of the binder for battery electrodes, poor electrode cycle performance and low electrode surface energy density.

Description

Battery electrode binders, electrodes and lithium-ion batteries

technical field

The invention belongs to the technical field of lithium ion battery electrode bonding and electrode preparation. In particular, it relates to a high viscoelastic binder formed from soft and hard polymers to form interpenetrating polymers, and electrodes and lithium ion batteries prepared by using the binder.

Background technique

Among many chemical power sources, lithium-ion batteries have the characteristics of high energy density, long cycle life, low preparation cost and good environmental compatibility. They are the most commonly used portable energy storage power sources and are widely used in portable devices such as smartphones and small power tools. . In the future, with the promotion of electric vehicles and the popularization of smart grids, lithium-ion batteries, as the most favorable competitors for large-scale energy storage units, will face application upgrades, facing higher energy density, longer cycle life, and more Low manufacturing cost development. At present, the most direct way to improve battery energy density and reduce cost is to use active materials with high specific capacity and increase the loading of electrode paste. For example, the anode material of lithium-ion battery is mainly graphite, but its limited theoretical specific capacity cannot meet the requirements for energy density of lithium-ion battery in the future. As a substitute for graphite anode material, silicon has a theoretical specific capacity ten times higher than that of graphite anode material (4200mAh/g vs. 372mAh/g). Silicon materials are commonly used to prepare lithium-ion battery anodes, which will greatly improve the energy density and power performance of lithium-ion batteries. However, the preparation of lithium battery negative electrodes with silicon materials still faces key problems. The severe volume expansion and contraction of silicon during the charging and discharging process will destroy the electrode structure, lead to electrode pulverization, and result in poor electrode cycle performance, which is difficult to be practically applied.

In the existing patents, there have been some methods to solve the cycle performance of silicon electrodes, which are mainly divided into the construction of silicon-based composites and the application of high viscoelastic binders. In the construction of silicon-based composite materials, the surface of silicon material particles is coated with heterogeneous materials, and at the same time, structural modification is performed on the silicon-based material, such as carbon or metal oxides, to realize the preparation of silicon-based composite materials. These coating materials can limit the volume expansion of silicon and improve its cycle performance, such as Chinese patent applications CN104254490A and CN103618074A. Such methods lead to an increase in the fabrication cost of silicon-based composites. In addition, because the coating material does not have the function of lithium storage, the specific capacity of the silicon-based composite material is low, and it is difficult to greatly improve the energy density of the lithium battery negative electrode.

Another method is to use a high viscoelastic binder to strengthen the mechanical strength in the electrode and improve the cycle performance of the electrode, such as Chinese patents CN104934609A, CN104877593A, CN103762367A. In the above-mentioned patent, the composite binder used is only simply mechanically mixed, which cannot form an effective bonding network. Although the cycle performance of the silicon electrode has been improved, it is all tested under low loading of active materials. . The energy areal density of silicon electrodes is less than 5mAh/cm ² , even lower than the current energy areal density of graphite negative electrodes. At high loadings, it is difficult for the above-mentioned binders to ensure cycle performance. From the existing research results, silicon electrodes need a high viscoelastic binder to ensure the integrity of silicon electrodes. Stiffness ensures the integrity of the electrodes, but at the same time requires an appropriate amount of elastic material to maintain microscopic local links.

SUMMARY OF THE INVENTION

The purpose of the present invention is: in view of the problems of poor cycle performance and low surface energy density of the existing lithium ion battery electrodes, the present invention provides a battery electrode binder, which can perform interpenetrating polymerization to form an interpenetrating The electrode prepared by the binder has good cycle performance and high areal specific capacity, and combined with the positive electrode of the lithium ion battery, the assembled lithium ion battery has a high energy density.

To achieve the above object, the present invention adopts the following technical solutions:

A battery electrode binder, the battery electrode binder includes hard polymers and their monomers, soft polymers and their monomers, and additives, and the additives can excite the hard polymers and their monomers, soft polymers Interpenetration polymerization of polymers and their monomers.

Wherein, the hard polymer and its monomers, soft polymers and its monomers and additives can all be dissolved in water or an organic solvent.

Wherein, the hard polymer is selected from polymeric materials with hardening properties, including epoxy resin, acrylic resin, polyfurfuryl alcohol, polyester resin, phenolic resin, amino resin and polyaniline.

Wherein, the soft polymer is selected from elastomers with deformation recovery ability, including polyacrylate materials, polyamine materials, styrene-butadiene rubber, polyvinyl alcohol, cis-butadiene rubber, isoprene rubber, ethylene-propylene rubber, Butyl, Neoprene and Nitrile.

Wherein, the additive is selected from a catalyst or an initiator, wherein the catalyst can provide a protonic acid for catalysis.

Wherein, the catalyst is selected from one or more of formic acid, acetic acid, oxalic acid, hydrochloric acid, sulfuric acid or nitric acid.

Wherein, the initiator is a compound that can provide free radicals, initiate free radical polymerization or copolymerization reaction, and can promote the addition reaction of hard polymers or soft polymers to achieve mutual crosslinking and interpenetrating polymerization purposes.

Wherein, the initiator is selected from organic peroxide initiators, inorganic peroxide initiators, azo initiators, and redox initiators.

Wherein, the initiator is selected from the group consisting of dibenzoyl peroxide, potassium persulfate, ammonium persulfate, azobisisobutyronitrile, hydrogen peroxide/ferrous sulfate.

Wherein, the weight ratio between the hard polymer or its monomer, the soft polymer or its monomer and the additive is 3:1-3:0.3.

An electrode liquid-phase slurry includes electrode active material and an appropriate amount of solvent, and also includes the above-mentioned battery electrode binder.

Wherein, the electrode active material is selected from a positive electrode active material or a negative electrode active material.

Wherein, the solvent is selected from water solvent or organic solvent; Wherein, the organic solvent is selected from N-methylpyrrolidone, tetrahydrofuran, N,N-dimethylformamide, dimethyl sulfoxide, cyclohexane, acetone , one or several mixtures of isopropanol, ethanol and furfural.

Wherein, the electrode liquid phase slurry further includes a conductive agent.

An electrode includes an electrode current collector and an electrode paste formed from the above-mentioned electrode liquid phase slurry.

A preparation method of the above-mentioned electrode, comprising the following preparation steps:

Step 1), disperse and dissolve the hard polymer or its monomer, soft polymer or its monomer in a solvent with an appropriate ratio, add additives, and stir for 10-300 minutes to form a homogeneous colloidal solution;

Step 2), in the above-mentioned uniform colloidal solution, add electrode active material and conductive agent, mix and stir for 1-60 minutes to obtain uniform electrode paste;

Wherein, the added amount of the electrode active material is 60%-90% of the total mass of the electrode paste, the added amount of the conductive agent is 5%-20% of the total mass of the electrode paste, and the homogeneous colloidal solution is The dosage is 5%-20% of the total mass of the electrode paste;

Step 3), coating or spraying the obtained electrode paste on the electrode current collector, the heating temperature is 60-150°C, and the heating time is 30-120 minutes, and the heating process promotes the additive to exert its catalytic polymerization function.

Wherein, in step 1), the dissolution temperature is selected from 30-60°C.

Wherein, in step 1), the glass transition temperature of the binder is 100-140°C.

Wherein, in step 2), the speed during the stirring is selected from 100-6000 rpm, and the stirring time is selected from 1-30 minutes.

Wherein, in step 3), the heating temperature is selected from 100-140°C.

Wherein, in step 3), the molecular weight range of the resin polymer obtained after catalytic polymerization is 1000-20000, and the thermal stabilization temperature is 0-400°C.

Wherein, in step 3), the spraying is to spray the electrode paste on both sides of the electrode current collector, and the spraying rate is 2-1000 mg/(min·m ² ).

A lithium ion battery comprising the above-mentioned electrode.

Compared with the published lithium battery electrode preparation technology, the binder of the present invention ensures the cycle performance and the areal specific capacity of the electrode. The binder can prepare electrode liquid phase slurry together with various positive active materials and negative active materials in the prior art, so as to further prepare positive or negative plates and lithium ion batteries, and the prepared lithium ion batteries have good performance . The following takes silicon material as an example to describe the beneficial effects of the present invention in detail:

(1) The interpenetrating polymeric binder of the present invention is applied to the lithium ion battery negative electrode of silicon-based material, which effectively solves the problem of poor cycle performance of traditional silicon-based electrodes. The binder makes the 100-cycle capacity retention rate of the silicon-based electrode 90%, and the 500-cycle capacity retention rate is 80%. The cycle performance of the above-mentioned silicon-based electrodes is comparable to that of the current graphite anodes, and can be fully applied to lithium-ion batteries.

(2) The silicon-based negative electrode prepared with the interpenetrating polymeric binder of the present invention has a surface specific capacity as high as 10 mAh/cm ² , which is the highest value among the existing published patents. The high-loaded silicon-based electrodes maintained a good charge-discharge specific capacity during cycling. At present, with a high-load silicon-based electrode and a lithium-ion battery ternary positive electrode, the energy density of the whole battery can reach 400Wh/kg, which fully meets the second-stage goal of the national "2025 Manufacturing" plan.

(3) Using the interpenetrating polymer binder of the present invention, the preparation process of the electrode slurry and the pole piece is also improved compared with the traditional method. wettability. Excellent wettability can improve the mixing efficiency of the material and the liquid phase, reduce the stirring time, avoid adding other surfactants and other materials, and provide a technical guarantee for the rapid paste mixing process. Compared to the published electrode preparation process, which requires hours of mixing time only at the slurry and paste stage, the binder of the present invention has a huge time advantage.

(4) The rigid polymer is solid at room temperature and exhibits certain hardness and brittleness. As the skeleton inside the interpenetrating polymeric binder, it has a certain mechanical strength to cope with the volume change of the silicon-based composite material, which is The silicon-based composite material sets a certain limited space, which will not affect the integrity of the overall silicon-based electrode. The nanoindentation test technology and the electrolyte soaking experiment show that the mechanical strength is improved after adding the hard polymer in the viscous body, indicating that its resistance to variable energy is enhanced. At the same time, the rigid polymer has good chemical stability and thermal stability: acid resistance, alkali resistance, corrosion resistance, insolubility in organic solvent systems and high resistance to thermal decomposition temperature, and it is also integrated into the interpenetrating polymer binder. Make it better to deal with the complex environment inside the lithium-ion battery.

(5) The soft polymer is solid at room temperature, but exhibits extremely high elasticity and has a large deformation recovery ability. Soft polymers are beneficial to relieve the microscopic local expansion stress, stabilize the deformation scale of the composite material, and ensure the mechanical integrity of the electrode. Since hard polymers face the disadvantage of brittleness, soft polymers mitigate the mechanical impact of the volume change of silicon-based materials on hard polymers. At the same time, the research shows that the addition of soft polymer to the binder has a good promoting effect on the formation of SEI film on the surface of silicon matrix composites. Due to the elasticity of the soft polymer, during the charging and discharging process, the viscous body forms a good contact environment with the surface of the silicon-based material. The stability of the surface of the silicon-based material is promoted, which is beneficial to the improvement of the Coulomb efficiency of the electrode.

Description of drawings

The accompanying drawings are used to provide a further understanding of the present invention, and constitute a part of the specification, and are used to explain the present invention together with the embodiments of the present invention, and do not constitute a limitation to the present invention. In the attached image:

FIG. 1 is a graph showing the cycle performance of silicon-based electrodes prepared with the binders in Example 1 and Comparative Example 1. FIG.

2 is a graph showing the cycle performance of silicon-based electrodes prepared with the binders in Example 2 and Comparative Examples 2-3.

FIG. 3 is a graph showing the cycle performance of the silicon-based electrode prepared with the binder in Example 3. FIG.

FIG. 4 is a photograph of the microscopic morphology of the silicon pole piece in Example 3. FIG.

5-6 are the results of nanoindentation test at 2000 μN performed on the silicon pole pieces prepared in Example 3 and Comparative Examples 2-3.

Detailed ways

The following examples facilitate a better understanding of the present invention, but do not limit the present invention. The experimental methods in the following examples are conventional methods unless otherwise specified. The test materials used in the following examples are commercially available unless otherwise specified. The quantitative tests in the following examples are all set to repeat the experiments three times, and the results are averaged.

The binder of the present invention comprises a hard polymer and its monomer, a soft polymer and its monomer, and an additive, wherein the additive is a catalyst for stimulating the interpenetrating polymerization of the hard polymer, the soft polymer and their monomers or initiator.

The rigid polymer can be used as a frame structure inside the electrode to strengthen the mechanical strength of the electrode and maintain the integrity of the electrode. The soft polymer relieves the microscopic local expansion stress and maintains the contact and transfer between particles. The presence of additives can stimulate the interpenetration polymerization of hard polymers, soft polymers and their monomers. Through the interpenetrating polymerization process between polymers, between polymers and monomers, or between monomers and monomers, soft polymers and hard polymers are promoted to form an interpenetrating polymer network, forming a highly viscoelastic polymer. binder. At the same time, the synthesis of the interpenetrating polymeric binder and the preparation process of the electrode sheet are completed at the same time, so that a good bonding force is formed between the binder and the active material, the conductive agent and the metal current collector.

Hard polymers, soft polymers, their monomers and additives are all soluble in water or organic solvents, and their mixed solutions have good wettability on the surface of active materials. This facilitates the adhesion of the binder on the active material and strengthens the binding force between the binder and the active material.

The rigid polymer is selected from polymeric materials with hardening properties, including epoxy resins, acrylic resins, polyfurfuryl alcohol, polyester resins, phenolic resins, amino resins and polyanilines.

The hardening characteristic means that the polymer formed after the polymerization of the monomer has high mechanical strength, exhibits an r-type curve in the tensile test, and the polymer has poor deformability.

The soft polymer is selected from elastomers with deformation recovery ability, including polyacrylate materials, polyamine materials, styrene-butadiene rubber, polyvinyl alcohol, cis-butadiene rubber, isoprene rubber, ethylene-propylene rubber, butyl rubber, Neoprene and Nitrile.

The requirements for the number-average molecular weight and weight-average molecular weight of hard polymers and soft polymers are: 100-20,000.

The weight ratio of the hard polymer or its monomer, the soft polymer or its monomer, and the additive needs to satisfy the following relationship: 3:1-3:0.3. At this time, a silicon-based active material high surface capacity electrode can be realized. preparation. The optimal weight ratio range of the three is: hard polymer or its monomer: soft polymer or its monomer: additive=3:1-2:0.3, and the optimal weight ratio of the three is: rigid polymer polymer or its monomer: soft polymer or its monomer: additive = 3:1:0.3.

The catalyst is a catalytic system providing a protic acid, selected from one or more of formic acid, acetic acid, oxalic acid, hydrochloric acid, sulfuric acid or nitric acid.

The initiator is a compound that provides free radicals, initiates free radical polymerization or copolymerization reaction, and promotes the addition reaction of hard polymers or soft polymers to achieve mutual crosslinking and interpenetrating polymerization. Among them, organic peroxide initiators, inorganic peroxide initiators, azo initiators, and redox initiators are included. The initiator can be selected from one of dibenzoyl peroxide, potassium persulfate, ammonium persulfate, azobisisobutyronitrile, hydrogen peroxide/ferrous sulfate.

The electrode liquid phase slurry according to one embodiment includes an electrode active material and an appropriate amount of solvent, and further includes the above-mentioned binder.

The electrode active material is selected from a positive electrode active material or a negative electrode active material.

The positive electrode and negative electrode active materials are not particularly limited, and positive electrode active materials and negative electrode active materials commonly used in related fields can be selected. Examples of positive active materials include, without limitation, lithium-containing metal oxides, phosphates, fluorides, sulfur-based materials; examples of negative active materials include, without limitation, graphite, carbon materials, metal oxides, Silicon-based materials, tin-based materials. For example, silicon-based composite materials include but are not limited to silicon carbon composite materials, silicon metal oxide composite materials, and silicon alloy composite materials, wherein the mass content of silicon in the composite materials is 1-85 wt.%. For example, metal oxides, including but not limited to iron oxide, lithium titanate, copper oxide, etc., are regarded as all metal oxides capable of de-intercalating lithium and storing lithium. For example, phosphates include lithium iron phosphate, lithium manganese phosphate, and lithium vanadium phosphate. For example, lithium-containing metal oxides include lithium cobaltate and lithium manganate.

The solvent is selected from water solvent or organic solvent, wherein the organic solvent is selected from N-methylpyrrolidone, tetrahydrofuran, N,N-dimethylformamide, dimethyl sulfoxide, cyclohexane, acetone, isopropanol, ethanol, One of furfural.

The electrode liquid phase slurry also includes a conductive agent, and any conductive agent commonly used in lithium batteries can be used. Examples of the conductive agent include carbon-based substances such as carbon black, acetylene black, Ketjen black, and carbon fibers (such as vapor-grown carbon fibers), metal Metal powders and metal fibers such as copper, nickel, aluminum and silver; conductive polymers such as polyphenylene derivatives and mixtures thereof. The amount of the conductive agent can be appropriately adjusted.

An electrode according to one embodiment includes an electrode current collector and an electrode paste formed from the above-mentioned electrode liquid-phase slurry. The obtained electrode paste is coated or sprayed on the surface of the electrode current collector, cured by heating, and the biomass monomer material is in-situ cross-linked and polymerized.

The thickness of the negative electrode current collector is usually about 3 μm to about 100 μm. The current collector is not limited as long as it is conductive without causing chemical changes to the lithium battery, examples of current collectors include copper, stainless steel, nickel, titanium, sintered carbon, those with carbon, nickel, titanium or silver treated surfaces Copper or stainless steel, aluminum-cadmium alloy, etc. Alternatively, the binding force of the negative active material can be increased by forming minute roughness on the surface of the current collector, and the current collector can have any of the following different shapes, such as film, sheet, foil, mesh, porous, foam and non-woven.

The thickness of the positive electrode current collector is about 3 μm to about 100 μm, and is not particularly limited as long as the current collector has high conductivity without causing chemical changes to the lithium battery. Examples of current collectors include stainless steel, aluminum, nickel, titanium, sintered carbon, or aluminum or stainless steel with carbon, nickel, titanium, or silver treated surfaces. Alternatively, the adhesion strength of the positive active material can be increased by forming minute roughness on the surface of the current collector, which can have any of the following different shapes, such as film, sheet, foil, mesh, porous, foam, and Nonwoven.

The preparation method of the electrode includes the following steps:

Step 1), prepare the binder: hard polymer or its monomer, soft polymer or its monomer and additives, hard polymer or its monomer, soft polymer or its monomer, in an appropriate amount. Disperse and dissolve in the solvent, add additives and stir for 10-300 minutes to form a homogeneous colloidal solution;

The weight ratio of the hard polymer or its monomer, the soft polymer or its monomer and the additive needs to satisfy the following relationship: 3:1-3:0.3;

The amount of the solvent is required to be able to disperse the hard polymer or its monomer, the soft polymer or its monomer and additive materials, and the purpose is to completely dissolve the solute and stir to form a homogeneous colloidal solution.

The dissolving temperature is selected from 30-60°C, and within this temperature range, it has the effect of accelerating the process of dissolving the solute by the solvent but reducing the volatilization of the solvent.

The glass transition temperature of the binder is 100-140°C. If the glass transition temperature is too high, it is easy to cause the pole piece to be hard and brittle, that is, the binder is prone to cracking during the coating process, many streaks appear after cold pressing, the edge is decarburized when cutting the piece, and the extremely high temperature during the winding process. The phenomenon of powder dropping at the bending place of the sheet has poor processing performance, which seriously restricts its application in batteries.

Step 2), adding an electrode active material and a conductive agent to the above-mentioned homogeneous colloidal solution. After mixing and stirring for 1-60 minutes at a certain stirring speed of a high-speed homogenizer, a uniform electrode paste is obtained;

The added amount of the electrode active material is 60%-90% of the total mass of the electrode paste, the added amount of the conductive agent is 5%-20% of the total mass of the electrode paste, and the amount of the homogeneous colloidal solution is the electrode paste. 5%-20% of the total body mass.

The stirring speed can be selected from 100-6000 rpm, and the stirring time can be selected from 1-30 minutes. Under the stirring speed and stirring time, a uniform electrode paste can be obtained.

Step 3), coating or spraying the obtained electrode paste on the electrode current collector, the heating temperature is 60-150 ° C, the heating time is 30-120 minutes, and the heating process promotes the additive to exert its catalytic polymerization function, and the obtained resin The molecular weight of the polymer is in the range of 1000-20000, and the thermal stability temperature is 0-400°C.

The heating temperature is preferably 100-140° C., within this temperature range, the mechanical properties of the polymer obtained by polymerizing the monomers can be better ensured.

The spraying is to spray the electrode paste on both sides of the electrode current collector, and the spraying rate is 2-1000 mg/(min·m ² ).

A lithium ion battery according to one embodiment includes the above-described electrode.

The preparation of lithium-ion batteries is known, so the details are not described here.

Embodiments will be described in more detail with reference to the following examples and comparative examples. The following examples are for illustrative purposes only and are not intended to limit the scope of the embodiments.

Example 1

Preparation of silicon-based negative electrode sheet

Step 1), hard polymer or its monomer, soft polymer or its monomer, disperse and dissolve in a solvent with a mass ratio of 1:1, add 10wt.% mass fraction of additives, and stir for 30 minutes , forming a homogeneous colloidal solution.

Step 2), in the above-mentioned homogeneous colloidal solution, add silicon-based active material and electrode conductive agent, the total amount of binder and conductive agent is 40% of the total mass of the electrode paste, and the amount of conductive agent added is 20%, After mixing and stirring at a stirring speed of 2500 rpm for 10 minutes by a high-speed homogenizer, a uniform electrode paste was obtained.

Step 3), coating or spraying the obtained electrode paste on the electrode current collector, and promoting the additive to exert its catalytic polymerization function through the heating process, the heating temperature is 140° C., and the heating time is 60 minutes.

In the present embodiment, the rigid polymer selects polyfurfuryl alcohol (PFA) with a weight-average molecular weight of 14000;

The soft polymer selects polyvinyl alcohol (PVA) with a weight average molecular weight of 16000;

The additive is oxalic acid;

The solvent is water;

The electrode conductive agent is made of conductive carbon black.

It is determined that the content of the generated binder in the negative electrode sheet is about 20% by mass.

Comparative Example 1

The polyvinylidene fluoride (PVdF) binding system and paste are used, and the mass ratio of the binder and the active material is referred to the quality of each component in Example 1.

1. Dissolve 20 wt.% PVdF binder in 10 ml of organic solvent N-hydroxymethylpyrrolidone, add silicon-based composite material, and stir for 10 hours.

2. Coat the evenly mixed paste on the metal current collector and vacuum dry to complete the preparation of the silicon-based electrode sheet.

The comparison results of Example 1 and Comparative Example 1 are shown in Figure 1 .

FIG. 1 is a graph showing the cycle performance of silicon-based electrodes prepared with the binders in Example 1 and Comparative Example 1. FIG.

By comparing the electrochemical properties of the above-mentioned silicon-based electrode sheets with different binders, it can be seen that the silicon-based electrode prepared with the binder in Example 1 exhibits good cycle stability.

Example 2

Preparation of silicon-based negative electrode sheet

Step 1), a soft polymer or its monomer, a hard polymer or its monomer, with a mass ratio of 1:2, disperse and dissolve in a solvent, add 10 wt.% mass fraction of additives, and stir for 30 minutes , forming a homogeneous colloidal solution.

Step 2), in the above-mentioned homogeneous colloidal solution, add silicon-based active material and electrode conductive agent, the total amount of binder and conductive agent is 40% of the total mass of the electrode paste, and the amount of conductive agent added is 20%, After mixing and stirring for 10 minutes at a stirring speed of 2500 rpm in a high-speed homogenizer, a uniform electrode paste was obtained;

Step 3), coating or spraying the obtained electrode paste on the electrode current collector, and promoting the additive to exert its catalytic polymerization function through the heating process, the heating temperature is 140° C., and the heating time is 60 minutes.

In the present embodiment, the rigid polymer selects polyfurfuryl alcohol with a weight-average molecular weight of 14000;

The soft polymer selects polyvinyl alcohol with a weight-average molecular weight of 16,000;

The additive is oxalic acid;

The solvent is water;

The electrode conductive agent is made of conductive carbon black.

It is determined that the content of the generated binder in the negative electrode sheet is about 20% by mass.

Comparative Example 2

Only the PVA binding system and paste are used, and the mass ratio of the binding agent and the active substance refers to the quality of each component in Example 2.

Comparative Example 3

Only the polyfurfuryl alcohol binding system and paste are used, and the mass ratio of the binding agent and the active substance refers to the quality of each component in Example 2.

2 is a graph showing the cycle performance of silicon-based electrodes prepared with the binders in Example 2 and Comparative Examples 2-3.

Compared with Example 1, the cycle performance of the silicon-based electrode in Example 2 is further improved. At the same time, it can be seen from the samples in Comparative Example 2 that only the PVA binder cannot effectively bond the silicon-based active material, because PVA, as an elastomer, belongs to a soft polymer. Therefore, in the application of silicon materials, a binder lacking a rigid polymer cannot establish a frame structure and maintain the mechanical strength of the electrode. Although the elasticity of the electrode reaches the maximum value, the chemical stability and thermodynamic stability of the soft polymer are not as good as that of the hard polymer, so the cycle performance of the silicon-based electrode is difficult to guarantee.

As seen by the samples in Comparative 3, the use of rigid polymeric binders alone cannot effectively bond silicon-based active materials. Although the hard polymer has good hardness and can be used as the internal framework of the electrode, its brittleness is not enough to stabilize the volume expansion of the silicon material, resulting in the cracking and powdering of the hard polymer, and the poor cycle performance of the electrode. In the hard polymer, adding a small amount of soft polymer will relieve the stress inside the electrode and improve the cycle performance of the electrode, as in Example 2.

Example 3

Preparation of silicon-based negative electrode sheet

Step 1), the soft polymer or its monomer, the hard polymer or its monomer, with a mass ratio of 1:3, disperse and dissolve in a solvent, add 10wt.% mass fraction of additives, stir for 30 minutes to form a homogeneous colloidal solution.

Step 2), in the above-mentioned homogeneous colloidal solution, add silicon-based active material and electrode conductive agent, the total amount of binder and conductive agent is 40% of the total mass of the electrode paste, and the amount of conductive agent added is 20%, After mixing and stirring at a stirring speed of 2500 rpm for 10 minutes by a high-speed homogenizer, a uniform electrode paste was obtained.

Step 3), coating or spraying the obtained electrode paste on the electrode current collector, and promoting the additive to exert its catalytic polymerization function through the heating process, the heating temperature is 140° C., and the heating time is 60 minutes.

In the present embodiment, the rigid polymer selects polyfurfuryl alcohol with a weight-average molecular weight of 14000;

The soft polymer selects polyvinyl alcohol with a weight-average molecular weight of 16,000;

The additive is oxalic acid;

The solvent is water;

The electrode conductive agent is made of conductive carbon black.

It is determined that the content of the generated binder in the negative electrode sheet is about 20% by mass.

FIG. 3 is a graph showing the cycle performance of the silicon-based electrode prepared with the binder in Example 3. FIG.

It can be seen from the samples in Example 3 that after optimization, the cycle performance of the high-capacity silicon electrode is further improved, indicating that optimizing the ratio of soft and hard polymers can indirectly improve the cycle performance of the silicon electrode.

Examples 1-3 and Comparative Examples 1-3 illustrate that the use of a viscous network of soft-hard interpenetrating polymerization, the synergistic effect of the hard polymer and the soft polymer, can well stabilize the cycle performance of the silicon material. Compared with the existing bonding technology, the viscous body network greatly improves the areal specific capacity and stabilizes the cycle performance of the electrode.

Example 4

Preparation of negative electrode sheet for lithium ion battery

Step 1), the epoxy resin with a number-average molecular weight of 11,000 and styrene-butadiene rubber with a number-average molecular weight of 15,000, with a mass ratio of 1:1, dispersed and dissolved in acetone, and added 20wt.% of potassium persulfate mass fraction , and stirred for 60 minutes to form a homogeneous colloidal solution.

Step 2), in the above-mentioned homogeneous colloidal solution, add silicon-based composite material and carbon black, the total amount of binder and carbon black is 20% of the total mass of the electrode paste, and the amount of carbon black is 20%. The high-speed homogenizer was mixed and stirred for 10 minutes at a stirring speed of 2000 rpm to obtain a uniform electrode paste.

Step 3), coating the obtained electrode paste on the electrode current collector, and promoting potassium persulfate to exert its catalytic polymerization function through the heating process, the heating temperature is 140° C., and the heating time is 60 minutes.

The silicon-based composite material is a silicon-carbon composite material, and the mass content of silicon in the composite material is 60 wt.%.

Example 5

Preparation of negative electrode sheet for lithium ion battery

Step 1), acrylic resin with a number-average molecular weight of 7000 and isoprene rubber with a number-average molecular weight of 8000, with a mass ratio of 1:1, dispersed and dissolved in cyclohexane, and added 10 wt.% mass fraction of acetic acid , and stirred for 300 minutes to form a homogeneous colloidal solution.

Step 2), in the above-mentioned homogeneous colloidal solution, add silicon-based composite material, pure silicon material and Ketjen black, the total amount of binder and Ketjen black is 5% of the total mass of the electrode paste, and the amount of Ketjen black is 5%. The addition amount is 10%, and the mixture is mixed and stirred for 10 minutes at a stirring speed of 6000 rpm through a high-speed homogenizer to obtain a uniform electrode paste.

Step 3), spray the obtained electrode paste on the electrode current collector, and promote the acetic acid to exert its catalytic polymerization function through the heating process, the heating temperature is 130° C., and the heating time is 70 minutes.

The silicon-based composite material is a silicon metal oxide composite material, and the mass content of silicon in the composite material is 1 wt.%.

Example 6

Preparation of negative electrode sheet for lithium ion battery

Step 1), a phenolic resin with a number average molecular weight of 8000 and an ethylene-propylene rubber with a number average molecular weight of 4000, with a mass ratio of 1:1, dispersed and dissolved in tetrahydrofuran, and added 30wt.% massfraction of azodiiso nitrile and stirred for 10 minutes to form a homogeneous gummy solution.

Step 2), in the above-mentioned homogeneous colloidal solution, add tin-based composite material and acetylene black, the total amount of binder and acetylene black is 30% of the total mass of the electrode paste, and the amount of acetylene black is 10%. The high-speed homogenizer was mixed and stirred at a stirring speed of 700 rpm for 60 minutes to obtain a uniform electrode paste.

Step 3), coating the obtained electrode paste on the electrode current collector, and promoting the azobisisobutyronitrile to exert its catalytic polymerization function through the heating process, the heating temperature is 60° C., and the heating time is 120 minutes.

Example 7

Preparation of negative electrode sheet for lithium ion battery

Step 1), the amino resin with a number-average molecular weight of 1000 and a nitrile-butadiene rubber with a number-average molecular weight of 15,000 are dispersed and dissolved in N-methylpyrrolidone with a mass ratio of 1:1, and 15wt.% mass fraction of Sulfuric acid, the concentration of sulfuric acid was 5%, and stirred for 20 minutes to form a homogeneous colloidal solution.

Step 2), in the above-mentioned homogeneous colloidal solution, add iron oxide and vapor-grown carbon fiber, the total amount of binder and vapor-grown carbon fiber is 20% of the total mass of the electrode paste, and the addition of vapor-grown carbon fiber is 5%, After mixing and stirring at a stirring speed of 1000 rpm for 45 minutes by a high-speed homogenizer, a uniform electrode paste was obtained.

Step 3), spray the obtained electrode paste on the electrode current collector, and promote the sulfuric acid to exert its catalytic polymerization function through the heating process, the heating temperature is 90° C., and the heating time is 100 minutes.

Example 8

Preparation of negative electrode sheet for lithium ion battery

Step 1), acrylic resin with a number-average molecular weight of 9000 and cis-butadiene rubber with a number-average molecular weight of 17,000, with a mass ratio of 1:1, dispersed and dissolved in dimethyl sulfoxide, and added 10wt.% mass fraction of Oxalic acid and 5 wt.% hydrochloric acid were stirred for 200 minutes to form a homogeneous colloidal solution.

Step 2), in the above-mentioned homogeneous colloidal solution, add graphite active material and carbon black, the total amount of binder and carbon black is 30% of the total mass of the electrode paste, and the amount of carbon black is 10%. The homogenizer was mixed and stirred for 3 minutes at a stirring speed of 3000 rpm to obtain a uniform electrode paste.

Step 3), coating the obtained electrode paste on the electrode current collector, and promoting the oxalic acid and hydrochloric acid to exert their catalytic polymerization function through the heating process, the heating temperature is 120° C., and the heating time is 70 minutes.

Example 9

Preparation of positive electrode sheet for lithium ion battery

Step 1), the amino resin with a number average molecular weight of 100 and a cis-butadiene rubber with a number average molecular weight of 7000 are dispersed and dissolved in ethanol with a mass ratio of 1:1, and 25wt.% of ammonium persulfate is added. , and stirred for 30 minutes to form a homogeneous colloidal solution.

Step 2), in the above-mentioned homogeneous colloidal solution, add lithium iron phosphate and polyphenylene derivatives, the total amount of the binder and the polyphenylene derivatives is 15% of the total mass of the electrode paste, and the polyphenylene derivatives The addition amount of 5% is passed through a high-speed homogenizer at a stirring speed of 3500 rpm for 10 minutes to obtain a uniform electrode paste.

Step 3), coating the obtained electrode paste on the electrode current collector, and promoting the ammonium persulfate to exert its catalytic polymerization function through the heating process, the heating temperature is 110° C., and the heating time is 50 minutes.

Example 10

Preparation of positive electrode sheet for lithium ion battery

Step 1), phenolic resin with a number average molecular weight of 2000 and isoprene rubber with a number average molecular weight of 6000, in a mass ratio of 1:1, dispersed and dissolved in a mixed solution of ethanol and acetone, and added 10 to 30wt.% The mass fraction of dibenzoyl peroxide was stirred for 150 minutes to form a homogeneous colloidal solution. The mass ratio of ethanol and acetone is 1:1.

Step 2), in the above-mentioned mixed solution, add sulfur-based composite material and Ketjen black, the total amount of binder and Ketjen black is 30% of the total mass of the electrode paste, and the addition of Ketjen black is 10%, After a high-speed homogenizer was mixed for 45 minutes at a stirring speed of 2000 rpm, a uniform electrode paste was obtained.

Step 3), spray the obtained electrode paste on the electrode current collector, and promote dibenzoyl peroxide to exert its catalytic polymerization function through the heating process, the heating temperature is 100° C., and the heating time is 60 minutes.

Example 11

Preparation of positive electrode sheet for lithium ion battery

Step 1), polyaniline with a number-average molecular weight of 7000 and a polyacrylate material with a number-average molecular weight of 12,000, with a mass ratio of 1:1, dispersed and dissolved in isopropanol, and added 25wt. Azisobutyronitrile was stirred for 180 minutes to form a homogeneous gummy solution.

Step 2), in the above-mentioned homogeneous colloidal solution, add lithium manganate and acetylene black, the total amount of binder and acetylene black is 35% of the total mass of the electrode paste, and the amount of acetylene black is 5%. The homogenizer was mixed and stirred at a stirring speed of 1000 rpm for 55 minutes to obtain a uniform electrode paste.

Step 3), coating the obtained electrode paste on the electrode current collector, and promoting the azobisisobutyronitrile to exert its catalytic polymerization function through the heating process, the heating temperature is 120° C., and the heating time is 70 minutes.

Example 12

Evaluation of battery performance

1. The lithium ion batteries prepared in Examples 1-11 and Comparative Examples 1-3 are respectively tested for cycle performance.

Normal temperature cycle performance test: in the voltage range of 0.01-1V, the working electrode was charged and discharged at a rate of 0.5C, and the interval between charging and discharging was 300 seconds. The test results are shown in Table 1.

Table 1 Lithium-ion battery cycle performance test results

2. The surface specific capacity of the opposite pole piece and the energy density of the whole battery after matching it into a lithium battery were tested. The test process is: the positive electrode is matched with a lithium-rich material, and the electrolyte is 1M LiPF6 dissolved in EC/DEC/FEC Solvent (1:1:0.25 volume ratio), the test results are shown in Table 2.

Table 2 The areal specific capacity of the pole piece and the energy density of the full cell

Example 13

Mechanical Properties Evaluation

1. Conduct electrolyte soaking experiments on the silicon pole pieces prepared in Example 3 and Comparative Example 4 respectively.

FIG. 4 is a photograph of the microscopic morphology of the silicon pole piece in Example 3. FIG. It can be seen from this that the PFA/PVA composite binder system can well bond the silicon electrode and bond the silicon material.

2. Perform a nanoindentation test of 2000 μN on the silicon pole pieces prepared in Example 3 and Comparative Examples 2-3 respectively.

5-6 are the results of nanoindentation test at 2000 μN performed on the silicon pole pieces prepared in Example 3 and Comparative Examples 2-3. It can be seen from the data chart that the PFA/PVA composite binder system exhibits low hardness and moderate reduction modulus value, which can well constrain the volume expansion of silicon materials, maintain the structural stability of silicon electrodes, and improve adhesion. Live silicon material.

Finally, it should be noted that the above descriptions are only preferred embodiments of the present invention, and are not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, for those skilled in the art, the The technical solutions described in the foregoing embodiments may be modified, or some technical features thereof may be equivalently replaced. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims (23)

1. battery electrode binder, it is characterised in that: the battery electrode binder includes rigid polymer and monomer, soft Polymer and monomer, additive, the additive can excite rigid polymer and monomer, soft polymer and monomer mutual Wear polymerization.

2. battery electrode binder according to claim 1, it is characterised in that: the rigid polymer and monomer, soft Matter polymer and monomer and additive may be dissolved in water or organic solvent.

3. battery electrode binder according to claim 1 or 2, it is characterised in that: the rigid polymer, which is selected from, to be had The polymeric material of hardening characteristics, including epoxy resin, acrylic resin, poly furfuryl alcohol, polyester resin, phenolic resin, ammonia Base resin and polyaniline.

4. battery electrode binder according to claim 1-3, it is characterised in that: the soft polymer is selected from Elastomer with deformation recovery capability, including polyacrylate material, polyamines material, butadiene-styrene rubber, polyvinyl alcohol, Butadiene rubber, isoprene rubber, EP rubbers, butyl rubber, neoprene and nitrile rubber.

5. battery electrode binder according to claim 1-4, it is characterised in that: the additive is selected from catalysis Agent or initiator, wherein the catalyst can provide Bronsted acid to be catalyzed.

6. battery electrode binder according to claim 5, it is characterised in that: the catalyst is selected from formic acid, acetic acid, grass One of acid, hydrochloric acid, sulfuric acid or nitric acid are a variety of.

7. battery electrode binder according to claim 5 or 6, it is characterised in that: the initiator is to provide freely Base, causing free radical polymerization perhaps the compound of copolyreaction and can promote the addition of rigid polymer or soft polymer Reaction, reach be cross-linked with each other and interpenetrating polymerization purpose.

8. battery electrode binder according to claim 7, it is characterised in that: the initiator is selected from organic peroxide Initiator, inorganic peroxide initiator, azo-initiator, redox initiator.

9. battery electrode binder according to claim 8, it is characterised in that: the initiator is selected from diphenyl peroxide first Acyl, potassium peroxydisulfate, ammonium persulfate, azodiisobutyronitrile, one of hydrogen peroxide/sulfuric acid ferrous iron.

10. -9 described in any item battery electrode binders according to claim 1, it is characterised in that: the rigid polymer or Weight ratio between monomer, soft polymer or monomer and additive is 3:1-3:0.3.

11. a kind of electrode liquid phase slurry, including electrode active material and suitable solvent, it is characterised in that: further include that right is wanted Seek the described in any item battery electrode binders of 1-10.

12. electrode liquid phase slurry according to claim 11, it is characterised in that: it is living that the electrode active material is selected from anode Property material or negative electrode active material.

13. electrode liquid phase slurry according to claim 11 or 12, it is characterised in that: the solvent is selected from aqueous solvent or has Solvent；Wherein, the organic solvent is selected from N-Methyl pyrrolidone, tetrahydrofuran, n,N-Dimethylformamide, dimethyl Asia Sulfone, one of hexamethylene, acetone, isopropanol, ethyl alcohol, furfural or its several mixture.

14. the described in any item electrode liquid phase slurries of 1-13 according to claim 1, it is characterised in that: the electrode liquid phase slurry It further include conductive agent.

15. a kind of electrode, including electrode current collecting body, it is characterised in that: further include by the described in any item electricity of claim 11-14 The electrode pastes that pole liquid phase slurry is formed.

16. a kind of preparation method of electrode as claimed in claim 15, it is characterised in that: including following preparation step:

Step 1), by rigid polymer or monomer, soft polymer or monomer, with suitable proportion dispersing and dissolving in solvent In, and additive is added, it stirs 10-300 minutes, forms uniform colloidal solution, obtain binder；

Step 2), in above-mentioned uniform colloidal solution, electrode active material and conductive agent is added, is mixed 1-60 minutes, obtains To uniform electrode pastes；

Wherein, the additional amount of the electrode active material is the 60%-90% of electrode pastes gross mass, the addition of the conductive agent Amount is the 5%-20% of electrode pastes gross mass, and the additional amount of the binder is the 5%-20% of electrode pastes gross mass；

The electrode obtained lotion is coated with or sprays on electrode current collecting body by step 3), and heating temperature is 60-150 DEG C, when heating Between be 30-120 minutes, promote additive to play the function of its catalytic polymerization by heating process.

17. the preparation method of electrode according to claim 16, it is characterised in that: in step 1), the solution temperature choosing From 30-60 DEG C.

18. the preparation method of electrode according to claim 16 or 17, it is characterised in that: in step 1), the binder Glass transition temperature be 100-140 DEG C.

19. the preparation method of the described in any item electrodes of 6-18 according to claim 1, it is characterised in that: described to stir in step 2) Speed when mixing is selected from 100-6000 revs/min, and mixing time is selected from 1-30 minutes.

20. the preparation method of the described in any item electrodes of 6-19 according to claim 1, it is characterised in that: described to add in step 3) Hot temperature is selected from 100-140 DEG C.

21. the preparation method of the described in any item electrodes of 6-20 according to claim 1, it is characterised in that: in step 3), catalysis is poly- The molecular weight ranges of the resinous polymer obtained after conjunction are 1000-20000, and thermal stable temperature is 0-400 DEG C.

22. the preparation method of electrode according to claim 16, it is characterised in that: in step 3), the spraying is will be electric Pole lotion be sprayed on electrode current collecting body it is two-sided on, injection rate be 2-1000mg/ (minm²)。

23. a kind of lithium ion battery, it is characterised in that: include the electrode described in claim 15.