KR20230129759A - Binder composition, anode slurry comprising same, anode comprising same and secondary battery comprising same - Google Patents

Abstract

The present specification is a binder composition comprising a binder having a crosslinked structure and containing two or more selected from the group consisting of polyvinyl alcohol, polyacrylic acid, polyethylene glycol, polythiophene, polyacrylamide, and carboxymethyl cellulose, and a binder composition containing the same. It relates to a negative electrode slurry, a negative electrode containing the same, and a secondary battery containing the same.

Description

Binder composition, negative electrode slurry containing the same, negative electrode containing the same, and secondary battery containing the same {BINDER COMPOSITION, ANODE SLURRY COMPRISING SAME, ANODE COMPRISING SAME AND SECONDARY BATTERY COMPRISING SAME}

This specification relates to a binder composition, a negative electrode slurry containing the same, a negative electrode containing the same, and a secondary battery containing the same.

Recently, as the electric vehicle (EV) market has gradually expanded, the demand for secondary batteries capable of high energy density and fast charging is rapidly increasing.

As high-capacity materials are required to overcome the limitations (low theoretical capacity) of graphite, a currently commercialized anode active material, silicon-based anode materials are emerging.

However, when silicon reacts with lithium, not only does it generate a large initial irreversible capacity due to volume expansion of 100-400%, but also the structure of the active material collapses and detachment from the current collector occurs during charging and discharging, resulting in loss of electrical contact, thereby reducing electrode lifespan characteristics. There was a problem that caused the deterioration of .

Spherical rubber binders such as current SBR have limitations in maintaining the mechanical rigidity of the electrode.

Therefore, a new concept binder that helps maintain electrical contact during charging and discharging by buffering the volume expansion of silicon is absolutely necessary.

Korean Patent No. 10-1591712

This specification relates to a binder composition, an electrode containing the same, and a secondary battery containing the same.

One embodiment of the present invention is a binder composition comprising two or more selected from the group consisting of polyvinyl alcohol, polyacrylic acid, polyethylene glycol, polythiophene, polyacrylamide, and carboxymethyl cellulose, and a binder having a crosslinked structure. provides.

Additionally, an exemplary embodiment of the present invention provides a negative electrode slurry containing the binder composition.

In addition, an exemplary embodiment of the present invention includes a negative electrode current collector; and a negative electrode active material layer provided on the negative electrode current collector, wherein the negative electrode active material layer includes: a negative electrode active material; conductive materials; And it provides a negative electrode comprising the binder composition.

In addition, an exemplary embodiment of the present invention includes a negative electrode current collector; and a negative electrode active material layer provided on the negative electrode current collector, wherein the negative electrode active material layer includes: a negative electrode active material; conductive materials; And it provides a negative electrode comprising the binder composition.

Additionally, an exemplary embodiment of the present invention provides a secondary battery including the negative electrode.

When used in a negative electrode, the binder composition of the present specification can sufficiently control volume expansion/contraction of the negative electrode active material due to charging and discharging.

Additionally, when the binder composition of the present specification is used in a negative electrode, it can improve the lifespan characteristics of the negative electrode.

Hereinafter, this specification will be described in detail.

One embodiment of the present invention is a binder composition comprising two or more selected from the group consisting of polyvinyl alcohol, polyacrylic acid, polyethylene glycol, polythiophene, polyacrylamide, and carboxymethyl cellulose, and a binder having a crosslinked structure. provides.

When the binder composition is applied to a negative electrode, the volume expansion/contraction of the negative electrode active material can be controlled to a desirable level while providing flexibility to the electrode and improving the lifespan performance of the secondary battery.

In one embodiment of the present invention, the binder includes two or more selected from the group consisting of polyvinyl alcohol, polyacrylic acid, polyethylene glycol, polythiophene, polyacrylamide, and carboxymethyl cellulose. In this case, strong stress and high modulus can be achieved.

In one embodiment of the present invention, the cross-linked structure may be one or more selected from the group consisting of branched type, graft type, dendrimer type, and network type. It may be in a branched type or a graft type. In the case of the above structure, the structural stability of the binder polymer is improved and phase separation is prevented, so adhesion to the current collector is excellent and volume expansion of the active material can be effectively suppressed.

In one embodiment of the present invention, the cross-linked structure may be cross-linked by non-covalent bonds. In this case, when the binder composition is applied to the slurry, the long-term storage stability of the slurry is improved.

In one embodiment of the present invention, the cross-linked structure may be cross-linked through ionic bonds or hydrogen bonds.

In one embodiment of the present invention, the binder is a first group comprising polyacrylic acid; and a second group selected from the group consisting of polyvinyl alcohol, polyacrylic acid, polyethylene glycol, polyacrylamide, and carboxymethyl cellulose.

In one embodiment of the present invention, the binder may include a copolymer of polyacrylic acid and polyvinyl alcohol. At this time, strong stress may be exerted by hydrogen bonding or covalent bonding between the carboxyl group (-COOH) of polyacrylic acid and the hydroxyl group (-OH) of polyvinyl alcohol.

In one embodiment of the present invention, the binder may include a copolymer of polyacrylic acid and polyethylene glycol. The polyethylene glycol (PEG) can provide flexibility to the negative electrode, sufficiently controlling the volume expansion/contraction of the silicon-based active material, and securing electrode adhesion and excellent negative electrode flexibility.

In one embodiment of the present invention, the weight ratio of the first group and the second group may be 1:5 to 5:1. Preferably it may be 1:3 to 3:1 or 1:2 to 2:1.

In one embodiment of the present invention, the weight average molecular weight (Mw) of the binder may be 10,000 to 700,000. Or it may be 1,000 to 500,000, preferably 50,000 to 400,000, and more preferably 75,000 to 300,000. When it is within the above range, the adhesion and flexibility of the cathode can be further improved.

In one embodiment of the present invention, the glass transition temperature (Tg) of the binder may be 50°C or higher. Alternatively, it may be 70°C to 250°C, and the above range is preferable in that it can exhibit strong physical properties such as high tensile strength and high modulus.

In one embodiment of the present invention, a negative electrode slurry containing the above-described binder composition is provided.

In one embodiment of the present invention, a negative electrode current collector; and a negative electrode active material layer provided on the negative electrode current collector, wherein the negative electrode active material layer includes: a negative electrode active material; conductive materials; And it provides a negative electrode comprising the binder composition.

In one embodiment of the present invention, the binder of the binder composition may be included in the negative electrode active material layer in an amount of 1% to 10% by weight. Alternatively, it may be included at 2% by weight to 5% by weight, more preferably at 3% by weight to 4.5% by weight. When it is within the above range, the capacity characteristics of the cathode can be improved while sufficiently exhibiting the effect of improving the flexibility and electrode adhesion of the cathode.

In one embodiment of the present invention, the negative electrode current collector is not particularly limited as long as it has high conductivity without causing chemical changes in the battery. Specifically, the negative electrode current collector may be copper, stainless steel, aluminum, nickel, titanium, calcined carbon, copper or stainless steel surface treated with carbon, nickel, titanium, silver, etc., aluminum-cadmium alloy, etc. there is.

In one embodiment of the present invention, the negative electrode current collector may typically have a thickness of 3 to 100 μm.

In one embodiment of the present invention, the negative electrode current collector may form fine irregularities on the surface to strengthen the bonding force of the negative electrode active material. For example, the negative electrode current collector may be used in various forms such as films, sheets, foils, nets, porous materials, foams, and non-woven fabrics.

In one embodiment of the present invention, the negative electrode active material may include a silicon-based active material.

In one embodiment of the present invention, the silicon-based active material may include a compound represented by Formula 1 below. In the case of SiO ₂ , since it does not react with lithium ions and cannot store lithium, x is preferably within the above range, and more preferably contains oxygen to alleviate the volume expansion of the silicon-based active material to an appropriate level, and is preferably 0.01 It may be ≤x<2.

[Formula 1]

SiOx (0 < x < 2).

In one embodiment of the present invention, the average particle diameter (D ₅₀ ) of the silicon-based active material is adjusted to minimize side reactions with the electrolyte and reduce the effect of volume expansion of the silicon-based active material, including a negative electrode binder for binding the active material and the current collector. In terms of facilitating accessibility, the side may be 1㎛ to 15㎛, preferably 3㎛ to 10㎛.

In one embodiment of the present invention, the negative electrode active material may further include a carbon-based active material along with the silicon-based active material described above. The carbon-based active material can provide excellent cycle characteristics or battery life performance to the anode or secondary battery of the present invention.

In one embodiment of the present invention, the carbon-based active material is at least selected from the group consisting of artificial graphite, natural graphite, hard carbon, soft carbon, carbon black, acetylene black, Ketjen black, Super P, graphene, and fibrous carbon. It may include one type, and preferably may include at least one type selected from the group consisting of artificial graphite and natural graphite.

In one embodiment of the present invention, the average particle diameter (D ₅₀ ) of the carbon-based active material is 10㎛ to 30㎛, preferably 15㎛ to 15㎛ in terms of ensuring structural stability during charging and discharging and reducing side reactions with the electrolyte solution. It may be 25㎛.

In one embodiment of the present invention, it is preferable to use both the silicon-based active material and the carbon-based active material as the negative electrode active material in terms of simultaneously improving capacity characteristics and cycle characteristics. Specifically, the negative electrode active material includes the silicon-based active material and the carbon-based active material. It is preferable to include the carbon-based active material in a weight ratio of 5:95 to 40:60, preferably 10:90 to 25:75. The above range is desirable in terms of simultaneous improvement in capacity and cycle characteristics.

In one embodiment of the present invention, the negative electrode active material may be included in the negative electrode active material layer at 80% to 99% by weight, preferably 85% to 96% by weight.

In one embodiment of the present invention, the conductive material is not particularly limited as long as it has conductivity without causing chemical changes in the battery. For example, graphite such as natural graphite or artificial graphite; Carbon black, such as carbon black, acetylene black, Ketjen black, channel black, Paneth black, lamp black, and thermal black; Conductive fibers such as carbon fiber and metal fiber; Conductive tubes such as carbon nanotubes; Metal powders such as fluorocarbon, aluminum, and nickel powder; Conductive whiskers such as zinc oxide and potassium titanate; Conductive metal oxides such as titanium oxide; Conductive materials such as polyphenylene derivatives may be used.

In one embodiment of the present invention, the conductive material may be included in the negative electrode active material layer in an amount of 0.5% to 10% by weight, preferably 1% to 5% by weight, based on the total weight of the negative electrode active material layer.

In one embodiment of the present invention, the thickness of the negative electrode active material layer may be 10㎛ to 200㎛, preferably 50㎛ to 150㎛.

In one embodiment of the present invention, the negative electrode is manufactured by coating a negative electrode slurry containing a negative electrode active material, a binder, and a conductive material and/or a solvent for forming a negative electrode slurry on the negative electrode current collector, followed by drying and rolling. You can.

In one embodiment of the present invention, the solvent for forming the negative electrode slurry may include, for example, at least one selected from the group consisting of distilled water, ethanol, methanol, and isopropyl alcohol, preferably distilled water.

One embodiment of the present invention provides a secondary battery including the negative electrode. The secondary battery may be a lithium secondary battery.

An exemplary embodiment of the present invention includes an anode provided opposite to the cathode; A separator provided between the cathode and the anode; and a secondary battery containing an electrolyte.

In one embodiment of the present invention, the positive electrode includes a positive electrode current collector; It may include a positive electrode active material layer formed on the positive electrode current collector.

In one embodiment of the present invention, the positive electrode current collector is not particularly limited as long as it has high conductivity without causing chemical changes in the battery. Specifically, the negative electrode current collector may be copper, stainless steel, aluminum, nickel, titanium, calcined carbon, copper or stainless steel surface treated with carbon, nickel, titanium, silver, etc., aluminum-cadmium alloy, etc. there is.

In one embodiment of the present invention, the positive electrode current collector may typically have a thickness of 3 to 500 μm.

In one embodiment of the present invention, the positive electrode current collector may form fine irregularities on the surface to strengthen the bonding force of the negative electrode active material. For example, the negative electrode current collector may be used in various forms such as films, sheets, foils, nets, porous materials, foams, and non-woven fabrics.

In one embodiment of the present invention, the positive electrode active material layer may include a positive electrode active material.

In one embodiment of the present invention, the positive electrode active material is a compound capable of reversible intercalation and deintercalation of lithium, and specifically, at least one transition metal consisting of nickel, cobalt, manganese, and aluminum and lithium. It may include a lithium transition metal complex oxide containing, preferably a lithium transition metal complex oxide containing a transition metal containing nickel, cobalt and manganese, and lithium.

In one embodiment of the present invention, the lithium transition metal complex oxide includes lithium-manganese-based oxides (e.g., LiMnO ₂ , LiMn ₂ O ₄ , etc.), lithium-cobalt-based oxides (e.g., LiCoO _2, etc.) ), lithium-nickel-based oxide (for example, LiNiO _2, etc.), lithium-nickel-manganese-based oxide (for example, LiNi _1-Y Mn _Y O ₂ (where 0<Y<1), LiMn _{2 -z} Ni _z O ₄ (where 0<Z<2), etc.), lithium-nickel-cobalt-based oxide (for example, LiNi _1-Y1 Co _Y1 O ₂ (where 0<Y1<1), etc. ), lithium-manganese-cobalt-based oxide (for example, LiCo _1-Y2 Mn _Y2 O ₂ (where 0<Y2<1), LiMn _2-z1 Co _z1 O ₄ (where 0<Z1<2 ), etc.), lithium-nickel-manganese-cobalt-based oxide (for example, Li(Ni _p Co _q Mn _r1 )O ₂ (where 0<p<1, 0<q<1, 0<r1<1) , p+q+r1=1) or Li(Ni _p1 Co _q1 Mn _r2 )O ₄ (where 0<p1<2, 0<q1<2, 0＜r2＜2, p1+q1+r2=2 ), etc.), or lithium-nickel-cobalt-transition metal (M) oxide (e.g., Li(Ni _p2 Co _q2 Mn _r3 M _S2 )O ₂ (where M is Al, Fe, V, Cr, Ti) , Ta, Mg, and Mo, and p2, q2, r3, and s2 are each independent atomic fractions of elements, 0 < p2 < 1, 0 < q2 < 1, 0 < r3 < 1, 0 < s2 < 1, p2 + q2 + r3 + s2 = 1), etc., and any one or two or more of these compounds may be included. Among these, in that the capacity characteristics and stability of the battery can be improved, the lithium transition metal composite oxide is LiCoO ₂ , LiMnO ₂ , LiNiO ₂ , lithium nickel-manganese-cobalt oxide (for example, Li(Ni _0.6 Mn _0.2 Co _0.2 )O ₂ , Li(Ni _0.5 Mn _0.3 Co _0.2 )O ₂ , Li(Ni _0.7 Mn _0.15 Co _0.15 )O ₂ or Li(Ni _0.8 Mn _0.1 Co _0.1 )O ₂ etc.), or lithium nickel cobalt aluminum oxide (e.g. For example, it may be Li (Ni _0.8 Co _0.15 Al _0.05 )O ₂ , etc.), and considering the remarkable improvement effect due to control of the type and content ratio of the constituent elements forming the lithium transition metal complex oxide, the lithium transition metal The complex oxide is Li(Ni _0.6 Mn _0.2 Co _0.2 )O ₂ , Li(Ni _0.5 Mn _0.3 Co _0.2 )O ₂ , Li(Ni _0.7 Mn _0.15 Co _0.15 )O ₂ or Li(Ni _0.8 Mn _0.1 Co _0.1 )O ₂ etc., and any one or a mixture of two or more of these may be used.

In one embodiment of the present invention, the positive electrode active material may be included in the positive electrode active material layer at 80% to 99% by weight, preferably 92% to 98.5% by weight, considering sufficient capacity of the positive active material.

In one embodiment of the present invention, the positive electrode active material layer may further include a binder and/or a conductive material along with the positive electrode active material described above.

In one embodiment of the present invention, the binder is a component that assists the binding of the active material and the conductive material and the binding to the current collector, and specifically, polyvinylidene fluoride, polyvinyl alcohol, and carboxymethyl cellulose (CMC). ), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene terpolymer (EPDM), sulfonated EPDM, styrene-butadiene. It may include at least one selected from the group consisting of rubber and fluororubber, preferably polyvinylidene fluoride.

In one embodiment of the present invention, the binder may be included in an amount of 1% to 20% by weight, preferably 1.2% to 10% by weight, in the positive electrode active material layer in terms of sufficiently securing binding force between components such as the positive electrode active material. .

In one embodiment of the present invention, the conductive material can be used to assist and improve conductivity in a secondary battery, and is not particularly limited as long as it has conductivity without causing chemical changes. Specifically, the conductive material includes graphite such as natural graphite or artificial graphite; Carbon black, such as carbon black, acetylene black, Ketjen black, channel black, Paneth black, lamp black, and thermal black; Conductive fibers such as carbon fiber and metal fiber; Conductive tubes such as carbon nanotubes; Metal powders such as fluorocarbon, aluminum, and nickel powder; Conductive whiskers such as zinc oxide and potassium titanate; Conductive metal oxides such as titanium oxide; and polyphenylene derivatives, and may preferably include carbon black in terms of improving conductivity.

In one embodiment of the present invention, the separator separates the cathode and the anode and provides a passage for lithium ions to move. It can be used without particular restrictions as long as it is normally used as a separator in a lithium secondary battery, and in particular, it can be used for ion movement in the electrolyte. It is desirable to have low resistance and excellent electrolyte moisturizing ability. Specifically, porous polymer films, for example, porous polymer films made of polyolefin polymers such as ethylene homopolymer, propylene homopolymer, ethylene/butene copolymer, ethylene/hexene copolymer, and ethylene/methacrylate copolymer, or these. A laminated structure of two or more layers may be used. In addition, conventional porous non-woven fabrics, for example, non-woven fabrics made of high melting point glass fibers, polyethylene terephthalate fibers, etc., may be used. Additionally, a coated separator containing a ceramic component or polymer material may be used to ensure heat resistance or mechanical strength, and may optionally be used in a single-layer or multi-layer structure.

In one embodiment of the present invention, electrolytes used in the present invention include organic liquid electrolytes, inorganic liquid electrolytes, solid polymer electrolytes, gel-type polymer electrolytes, solid inorganic electrolytes, molten inorganic electrolytes, etc. that can be used in the manufacture of secondary batteries. Examples include, but are not limited to these.

In one embodiment of the present invention, the electrolyte may include an organic solvent and a lithium salt.

Hereinafter, the present invention will be described in more detail through examples.

<Examples and Comparative Examples>

<Example 1>

A first group comprising polyacrylic acid; and a second group selected from the group consisting of polyvinyl alcohol, polyacrylic acid, polyethylene glycol, polyacrylamide, and carboxymethyl cellulose. At this time, the binder was graft polymerized.

<Example 2>

A first group comprising polyacrylic acid; and a second group selected from the group consisting of polyvinyl alcohol, polyacrylic acid, polyethylene glycol, polyacrylamide, and carboxymethyl cellulose. At this time, polyethyleneimine was added during binder polymerization to induce non-covalent bonds.

<Comparative Example 1>

A carboxymethyl cellulose (CMC) binder was prepared as a linear single polymer.

<Comparative Example 2>

A polyacrylic acid (PAA) binder was prepared as a linear single polymer.

<Comparative Example 3>

A mixture of CMC binder and PAA binder was prepared.

<Comparative Example 4>

A copolymer of PAA and PVA was prepared.

<Comparative Example 5>

A copolymer crosslinked by covalent bonds was prepared by introducing an additive containing two or more hydroxy groups into PAA and heat treating it to induce covalent bonds.

<Experimental example>

An anode slurry was prepared by mixing the binder prepared in the above examples and comparative examples, a silicon anode active material, a conductive material, and a solvent. The negative electrode slurry was coated and rolled on a negative electrode current collector and dried to form a negative electrode active material layer, thereby preparing a half cell using this as a negative electrode.

The modulus of the binders of the examples and comparative examples was measured, and the solid content of the anode slurry was measured.

In addition, by conducting a peel test, electrode adhesion was measured and the electrode volume expansion rate compared to before battery operation was measured.

Cell lifespan was confirmed and recorded through the final 100 repeated cycles.

Binder Type Modulus (GPa) Slurry solid content (%) Electrode adhesion (gf/cm) Electrode volume expansion rate (%) Cell life (@100 cycle) Example 1 4.5 34 20 120 81 Example 2 5.5 35 20 115 84 Comparative Example 1 2.8 35 10 170 40 Comparative Example 2 3.5 30 10 130 70 Comparative Example 3 3.2 30 12 150 62 Comparative Example 4 2 33 15 170 67

From the above results, it was confirmed that the binder composition of the present invention has excellent mechanical strength (modulus) and excellent electrode adhesion. In addition, it was confirmed that cell life was significantly increased by keeping the electrode volume expansion rate low.

Claims (15)

Contains two or more selected from the group consisting of polyvinyl alcohol, polyacrylic acid, polyethylene glycol, polythiophene, polyacrylamide, and carboxymethyl cellulose,
A binder composition comprising a binder having a cross-linked structure. In claim 1,
The binder composition wherein the cross-linked structure is at least one selected from the group consisting of branched type, graft type, dendrimer type, and network type. In claim 1,
A binder composition in which the cross-linked structure is cross-linked by non-covalent bonds. In claim 1,
A binder composition in which the cross-linked structure is cross-linked through ionic bonds or hydrogen bonds. In claim 1,
The binder is a first group comprising polyacrylic acid; and
A binder composition comprising a second group selected from the group consisting of polyvinyl alcohol, polyacrylic acid, polyethylene glycol, polyacrylamide, and carboxymethyl cellulose. In claim 5,
A binder composition wherein the weight ratio of the first group and the second group is 1:5 to 5:1. In claim 1,
A binder composition wherein the binder has a weight average molecular weight (Mw) of 10,000 to 700,000. A binder composition wherein the binder has a glass transition temperature (Tg) of 50°C or higher. A negative electrode slurry containing the binder composition according to any one of claims 1 to 8. negative electrode current collector; and
It includes a negative electrode active material layer provided on the negative electrode current collector,
The negative electrode active material layer includes a negative electrode active material; conductive materials; And a negative electrode comprising the binder composition according to any one of claims 1 to 8. In claim 10,
A negative electrode in which the binder of the binder composition is included in an amount of 1% to 10% by weight in the negative electrode active material layer. In claim 10,
The negative electrode active material includes a silicon-based active material. In claim 12,
The silicon-based active material is a negative electrode containing a compound represented by the following formula (1):
[Formula 1]
SiOx (0 < x < 2). A secondary battery comprising a negative electrode according to claim 11. In claim 14,
an anode provided opposite the cathode;
A separator provided between the cathode and the anode; and
Secondary battery containing electrolyte.