WO2018176255A1

WO2018176255A1 - Binder-and anode-composition, methods for their preparation, and an anode and a lithium ion battery containing said anode composition

Info

Publication number: WO2018176255A1
Application number: PCT/CN2017/078552
Authority: WO
Inventors: Jun Yang; Zhixin XU; Yuqian DOU; Jingjing Zhang
Original assignee: Robert Bosch Gmbh
Priority date: 2017-03-29
Filing date: 2017-03-29
Publication date: 2018-10-04
Also published as: CN110461980A; DE112017007332T5; CN110461980B

Abstract

The present invention relates to a binder composition for lithium ion batteries and its preparation method, wherein said binder composition contains a carboxyl-containing binder and a silane coupling agent. The present invention further relates to an anode composition and its preparation method, wherein said anode composition contains a silicon-based electrode active material and said binder composition. The present invention further relates to an anode containing said anode composition, and to a lithium ion battery containing said anode.

Description

BINDER-AND ANODE-COMPOSITION, METHODS FOR THEIR PREPARATION, AND AN ANODE AND A LITHIUM ION BATTERY CONTAINING SAID ANODE COMPOSITION

Technical Field

Background Art

Silicon is a promising candidate anode material owing to its high theoretical specific capacity of 4200 mAh/g for Li_4.4Si. However, the cycling performance of silicon base anode is still not satisfied for industrial application. One of the biggest challenge is binder failure due to repeating volume change of silicon. Therefore, the binder network plays key role to reach good cycling performance. Among all kinds of binders, polyacrylic acid (PAA) is considered to be an advanced binder for Si-based anodes compared with polyvinylidene fluoride (PVDF) , sodium carboxymethyl cellulose (CMC) which are more used for traditional anode such as graphite-based. In addition to low swell ability in carbonates and good elasticity, PAA can be dissolved both in water and a variety of organic solvents, such as ethanol. And it also offers a much higher concentration of carboxyl groups which can form plenty of hydrogen bonds with silanol groups on the silicon surface.

Despite of the advantages of PAA, there are still two issues for PAA binder: 1) as non-chemical bond, hydrogen bonds formed between PAA binder and silicon active material is not strong enough. After repeated volume change, the connection between PAA binder and Si active materials may be easily lost. 2) PAA is a linear polymer； therefore, the binding network formed by PAA is not strong enough to maintain electrode integrity during long cycling.

Summary of Invention

The object of the present invention is to provide a cross-linked PAA based binder other than a pure PAA binder, wherein a 3D binding network is formed by covalent bonds. The enhanced binding network is beneficial for long cycling performance.

Said object, according to one aspect, can be achieved by a binder composition for lithium ion batteries, which contains:

a) a carboxyl-containing binder； and

b) a silane coupling agent prepared by free radical polymeriazation from the monomer of formula (1) :

Y- (CH₂) _n-Si-X₃ (1) ,

wherein

Y represents a non-hydrolyzable ethylenically unsaturated group, such as acryloxy, methacryloxy, vinyl, and propenyl group,

X can be identical or different, and each independently represents a hydroxyl group, or a hydrolyzable group selected from the group consisting of halogen atoms, alkoxy groups, ether groups and siloxy groups, preferably alkoxy group having 1 –3 carbon atoms,

n represents an integer of 0 –6, preferably 0 –3.

According to another aspect of the present invention, an anode composition is provided, which contains a silicon-based electrode active material and the binder composition according to the present invention.

Said object, according to another aspect, can be achieved by a method for preparing a binder composition for lithium ion batteries, including the following steps:

1) preparing a silane coupling agent by free radical polymeriazation from the monomer of formula (1) :

Y- (CH₂) _n-Si-X₃ (1) ,

wherein

n represents an integer of 0 –6, preferably 0 –3；

2) mixing the silane coupling agent with a carboxyl-containing binder to obtain the binder composition.

According to another aspect of the present invention, a method for preparing an anode composition for lithium ion batteries is provided, wherein a silicon-based electrode active material is mixed with the binder composition according to the present invention.

According to another aspect of the present invention, an anode for lithium ion batteries is provided, which contains the anode composition according to the present invention.

According to another aspect of the present invention, a lithium ion battery is provided, which contains the anode according to the present invention.

Brief Description of Drawings

Each aspect of the present invention will be illustrated in more detail in conjunction with the accompanying drawings, wherein :

Fig. 1 shows a schematic chemical structure of the PKH550-PAA-Si-based anode composition of Example 1 (E1) and Example 2 (E2) , and n ＝ 0, 1 or 2；

Fig. 2 shows the cycling performances of the anode compositions with PAA (CE) , PAA+5％PKH570 (E1) , PAA+10％PKH570 (E2) .

Detailed Description of Preferred Embodiments

All publications, patent applications, patents and other references mentioned herein, if not otherwise indicated, are explicitly incorporated by reference herein in their entirety for all purposes as if fully set forth.

Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. In case of conflict, the present specification, including definitions, will control.

When an amount, concentration, or other value or parameter is given as either a range, preferred range or a list of upper preferable values and lower preferable values, this is to be understood as specifically disclosing all ranges formed from any pair of any upper range limit or preferred value and any lower range limit or preferred value, regardless of whether ranges are separately disclosed. Where a range of numerical values is recited herein, unless otherwise stated, the range is intended to include the endpoints thereof, and all integers and fractions within the range.

The present invention, according to one aspect, relates to a binder composition for lithium ion batteries, which contains:

a) a carboxyl-containing binder； and

Y- (CH₂) _n-Si-X₃ (1) ,

wherein

n represents an integer of 0 –6, preferably 0 –3.

In accordance with an embodiment of the binder composition according to the present invention, the carboxyl-containing binder can be selected from the group consisting of polyacrylic acid, carboxymethyl cellulose, alginic acid, and polysaccharide, for example oxystarch, carrageenan, and xanthan gum.

In accordance with another embodiment of the binder composition according to the present invention, the monomer can be selected from the group consisting of vinyltrimethoxysilane, vinyltriethoxysilane, vinyltri (2-methoxyethoxy) silane and γ-methacryloxypropyl- trimethoxysilane. Thus, the corresponding silane coupling agents prepared by free radical polymeriazation from these monomers are polyvinyltrimethoxysilane, polyvinyltriethoxysilane, polyvinyltri (2-methoxyethoxy) silane and poly (γ-methacryloxy-propyltrimethoxysilane) , respectively.

For example, poly (γ-methacryloxypropyltrimethoxysilane) (PKH570) can be synthesized by free radical polymeriazation from γ-methacryloxypropyltrimethoxysilane (KH570) in tetrahydrofuran (THF) at an elevated temperature, for example at about 60℃ for 24 hours:

wherein the free radical polymeriazation can be initiated, for example, by azobisisobutyronitrile (AIBN) .

In accordance with another embodiment of the binder composition according to the present invention, the molecular weight Mw of the silane coupling agent can be 50,000 –200,000, preferably 80,000 –150,000.

In accordance with another embodiment of the binder composition according to the present invention, the content of the silane coupling agent can be 1 –20％, preferably 2 –10％, more preferably 3 –8％, based on the weight of the carboxyl-containing binder.

In accordance with another embodiment of the binder composition according to the present invention, the carboxyl-containing binder can be crosslinked with the silane coupling agent to form a 3D binding network. In addition, the binder composition according to the present invention can also form strong and flexible Si–O–Si bonds with Si particles, thus exhibiting a high mechanical strength of adhesion on Si. This binder composition can effectively accommodate the huge volume change of silicon anodes during lithiation/delithiation, with a better cycling stability and higher Coulombic efficiency than the pure PAA binder, even at a high current density and high coverage (3 mAh/cm²) . In view of simplicity in using this PAA-modified polymer binder, it is believed that this novel binder has a great potential to be commercialized with high capacity silicon anodes in next generation Li-ion batteries.

The present invention, according to another aspect, relates to an anode composition, which contains a silicon-based electrode active material and 2 –25％, preferably 5 –15％, of the binder composition according to the present invention, based on the total weight of the anode composition. The silicon-based electrode active material used here is not particularly limited. For example silicon nanoparticle can be used.

In accordance with an embodiment of the anode composition according to the present invention, the anode composition can optionally contain one or more carbon materials selected from the group consisting of carbon black, super P, acetylene black, Ketjen black, graphite, graphene, carbon nanotubes and vapour grown carbon fibers. The content of the carbon materials can be 0 to 85％, based on the total weight of the anode composition. In this case, other binders in addition to the above carboxyl-containing binders can also be used, for example hydroxypropyl methylcellulose (HPMC) , cellulose acetate, gelatin, chitosan, polyvinylidene fluoride (PVDF) , and styrene-butadiene rubber (SBR) .

The present invention, according to another aspect, relates to a method for preparing a binder composition for lithium ion batteries, including the following steps:

Y- (CH₂) _n-Si-X₃ (1) ,

wherein

n represents an integer of 0 –6, preferably 0 –3；

1) Preparing a silane coupling agent

A silane coupling agent can be prepared by free radical polymeriazation from the monomer of formula (1) .

In accordance with an embodiment of the method according to the present invention, the monomer can be selected from the group consisting of vinyltrimethoxysilane, vinyltriethoxysilane, vinyltri (2-methoxyethoxy) silane and γ-methacryloxypropyl-trimethoxysilane. Thus, the corresponding silane coupling agents prepared by free radical polymeriazation from these monomers are polyvinyltrimethoxysilane, polyvinyltriethoxysilane, polyvinyltri (2-methoxyethoxy) silane and poly (γ-methacryloxy-propyltrimethoxysilane) , respectively.

In accordance with another embodiment of the method according to the present invention, the molecular weight Mw of the silane coupling agent can be 50,000 –200,000, preferably 80,000 – 150,000.

In accordance with another embodiment of the method according to the present invention, the silane coupling agent can be used in an amout of 1 –20％, preferably 2 –10％, more preferably 3 –8％, based on the weight of the carboxyl-containing binder.

2) Mixing the silane coupling agent with a carboxyl-containing binder

The silane coupling agent can be mixed with a carboxyl-containing binder to obtain the binder composition.

In accordance with another embodiment of the method according to the present invention, the carboxyl-containing binder can be selected from the group consisting of polyacrylic acid, carboxymethyl cellulose, alginic acid, and polysaccharide, for example oxystarch, carrageenan, and xanthan gum.

In accordance with another embodiment of the method according to the present invention, the carboxyl-containing binder can be crosslinked with the silane coupling agent to form a 3D binding network.

The present invention, according to another aspect, relates to a method for preparing an anode composition for lithium ion batteries, wherein a silicon-based electrode active material can be mixed with 2 –25％, preferably 5 –15％, of the binder composition prepared according to the present invention, based on the total weight of the anode composition. The silicon-based electrode active material used here is not particularly limited. For example silicon nanoparticle can be used.

In accordance with an embodiment of the method according to the present invention, one or more carbon materials selected from the group consisting of carbon black, super P, acetylene black, Ketjen black, graphite, graphene, carbon nanotubes and vapour grown carbon fibers can be optionally mixed into the anode composition. The carbon materials can be used in an amout of 0 to 85％, based on the total weight of the anode composition. In this case, other binders in addition to the above carboxyl-containing binders can also be used, for example hydroxypropyl methylcellulose (HPMC) , cellulose acetate, gelatin, chitosan, polyvinylidene fluoride (PVDF) , and styrene-butadiene rubber (SBR) .

The present invention, according to another aspect, relates to an anode for lithium ion batteries, which contains the anode composition according to the present invention.

The present invention, according to further aspect, relates to a lithium ion battery, which contains the anode according to the present invention.

Example 1 (E1) :

A silane coupling agent poly (γ-methacryloxypropyltrimethoxysilane) (PKH570) was synthesized by free radical polymeriazation from γ-methacryloxypropyltrimethoxysilane (KH570) in tetrahydrofuran (THF) at about 60℃ for 24 hours in a glove box (MB-10 compact, MBRAUN) under an argon atmosphere containing less than 1 ppm water and O₂, wherein the free radical polymeriazation was initiated by azobisisobutyronitrile (AIBN) .

A carboxyl-containing binder polyacrylic acid (PAA) was in situ crosslinked by mixing the silane coupling agent (PKH570) with PAA in ethanol at room temperature to obtain a binder composition PAA-PKH570, wherein the silane coupling agent was used in an amout of 5％, based on the weight of the carboxyl-containing binder.

Cells assembling and electrochemical evaluation:

The electrochemical performance of the as-prepared composites was evaluated using two electrode coin-type cells. The working electrodes were prepared by pasting a mixture of active material (Silicon powder 50 nm/graphite, 7 : 9 by weight) , Super P conductive carbon black (40 nm, Timical) , and the binder at a weight ratio of 80 : 7 : 13. After coating the mixture onto Cu foil, the electrodes were dried, cut to Ф12 mm disks, pressed at 3 MPa, and finally dried at 60℃ in vacuum for 8 hours, the total loading was ca. 2.0 mg cm^-2. The CR2016 coin cells were assembled in an argon-filled glove box (MB-10 compact, MBraun) using 1M LiPF₆ in dimethyl carbonate (DMC) and ethylene carbonate (EC) mixed solvent of 1: 1 by volume, including 10 wt. ％fluoroethylene carbonate (FEC) as electrolyte, ENTEK ET 20-26 (PE, thickness: 20 μm) as separator, and lithium metal as counter electrode. The cycling performance was evaluated on a LAND-CT 2001A Battery test system (Wuhan, China) at room temperature with constant current densities. The cut-off voltage was 0.01 V versus Li⁺/Li for discharge (Li insertion) and 1.2 V versus Li⁺/Li for charge (Li extraction) . The specific capacity was calculated on the basis of the weight of Si-graphite composites. The cycling performance was evaluated at a rate of 0.3C at room temperature. The coin cell was discharged at 0.1C for the first four cycles and then at 0.3C in the following cycles.

Fig. 1 shows a schematic chemical structure of the PKH550-PAA-Si-based anode composition of Example 1 (E1) . Fig. 2 shows the cycling performance of the anode composition with PAA+5％PKH570 of Example 1 (E1) .

Example 2 (E2) :

Example 2 (E2) was carried out similar to Example 1, except that the silane coupling agent was used in an amout of 10％, based on the weight of the carboxyl-containing binder.

Fig. 1 shows a schematic chemical structure of the PKH550-PAA-Si-based anode composition of Example 2 (E2) . Fig. 2 shows the cycling performance of the anode composition with PAA+10％PKH570 of Example 2 (E2) .

Comparative Example (CE) :

Comparative Example (CE) was carried out similar to Example 1, except that unmodified polyacrylic acid (PAA) was used as the binder.

Fig. 2 shows the cycling performance of the anode composition with PAA of Comparative Example (CE) .

Potential applications of the electrode active material according to the present invention include, but are not limited to, high-energy-density lithium ion batteries with acceptable high power density for energy storage applications, such as power tools, photovoltaic cells and electric vehicles.

While certain embodiments have been described, these embodiments have been presented by way of example only, and are not intended to limit the scope of the inventions. The attached claims and their equivalents are intended to cover all the modifications, substitutions and changes as would fall within the scope and spirit of the invention.

Claims

A binder composition for lithium ion batteries, which contains:

a) a carboxyl-containing binder； and

b) a silane coupling agent prepared by free radical polymeriazation from the monomer of formula (1) :

Y- (CH₂) _n-Si-X₃ (1) ,

wherein

Y represents a non-hydrolyzable ethylenically unsaturated group, such as acryloxy, methacryloxy, vinyl, and propenyl group,

X can be identical or different, and each independently represents a hydroxyl group, or a hydrolyzable group selected from the group consisting of halogen atoms, alkoxy groups, ether groups and siloxy groups, preferably alkoxy group having 1–3 carbon atoms,

n represents an integer of 0–6, preferably 0–3.
The binder composition of claim 1, characterized in that the carboxyl-containing binder is selected from the group consisting of polyacrylic acid, carboxymethyl cellulose, alginic acid, and polysaccharide, for example oxystarch, carrageenan, and xanthan gum.
The binder composition of claim 1 or 2, characterized in that the monomer is selected from the group consisting of vinyltrimethoxysilane, vinyltriethoxysilane, vinyltri (2-methoxyethoxy) silane and γ-methacryloxypropyltrimethoxysilane.
The binder composition of any one of claims 1 to 3, characterized in that the molecular weight Mw of the silane coupling agent is 50,000–200,000, preferably 80,000–150,000.
The binder composition of any one of claims 1 to 4, characterized in that the content of the silane coupling agent is 1–20％, preferably 2–10％, more preferably 3–8％, based on the weight of the carboxyl-containing binder.
An anode composition, characterized in that said anode composition contains a silicon-based electrode active material and 2–25％, preferably 5–15％, of the binder composition of any one of claims 1 to 5, based on the total weight of the anode composition.
A method for preparing a binder composition for lithium ion batteries, including the following steps:

1) preparing a silane coupling agent by free radical polymeriazation from the monomer of formula (1) :

Y- (CH₂) _n-Si-X₃ (1) ,

wherein

Y represents a non-hydrolyzable ethylenically unsaturated group, such as acryloxy, methacryloxy, vinyl, and propenyl group,

X can be identical or different, and each independently represents a hydroxyl group, or a hydrolyzable group selected from the group consisting of halogen atoms, alkoxy groups, ether groups and siloxy groups, preferably alkoxy group having 1–3 carbon atoms,

n represents an integer of 0–6, preferably 0–3；

2) mixing the silane coupling agent with a carboxyl-containing binder to obtain the binder composition.
The method of claim 7, characterized in that the carboxyl-containing binder is selected from the group consisting of polyacrylic acid, carboxymethyl cellulose, alginic acid, and polysaccharide, for example oxystarch, carrageenan, and xanthan gum.
The method of claim 7 or 8, characterized in that the monomer is selected from the group consisting of vinyltrimethoxysilane, vinyltriethoxysilane, vinyltri (2-methoxy-ethoxy) silane and γ-methacryloxypropyltrimethoxysilane.
The method of any one of claims 7 to 9, characterized in that the molecular weight Mw of the silane coupling agent is 50,000–200,000, preferably 80,000–150,000.
The method of any one of claims 7 to 10, characterized in that the silane coupling agent is used in an amout of 1–20％, preferably 2–10％, more preferably 3–8％, based on the weight of the carboxyl-containing binder.
A method for preparing an anode composition for lithium ion batteries, wherein a silicon-based electrode active material is mixed with 2–25％, preferably 5–15％, of the binder composition prepared by the method of any one of claims 7 to 11, based on the total weight of the anode composition.
An anode for lithium ion batteries, characterized in that said anode contains the anode composition of claim6 or the anode composition prepared by the method of claim 12.
A lithium ion battery, characterized in that said lithium ion battery contains the anode of claim 13.