KR102223989B1 - Slurry including the elastic binder for secondary battery electrode, electrodes including the slurry for secondary battery, and secondary battery including the electrode - Google Patents

Abstract

The present invention relates to a slurry for a secondary battery electrode including an elastic binder that enables high dispersibility of a slurry for manufacturing a high-performance secondary battery electrode and a binding force of the electrode, a secondary battery electrode including the same, and a secondary battery.

Description

Slurry for secondary battery electrode including the elastic binder for secondary battery electrode, and electrode for secondary battery and secondary battery including the same TECHNICAL FIELD [Slurry including the elastic binder for secondary battery electrode, electrodes including the slurry for secondary battery, and secondary battery including the electrode}

The present invention relates to a slurry for a secondary battery electrode including an elastic binder for a secondary battery electrode, an electrode for a secondary battery including the same, and a secondary battery, and more particularly, a secondary battery including an elastic binder for a layered lithium transition metal oxide electrode It relates to an electrode slurry, an electrode for a secondary battery including the same, and a secondary battery.

Recently, due to environmental pollution problems, interest in electric vehicles that can reduce carbon dioxide and pollutant factors is increasing rapidly. In this respect, lithium secondary batteries, which are the core energy sources of electric vehicles, are expected to play a very important role in the development of electric vehicles because they have a higher energy density than other energy storage devices.

In particular, the layered oxide material containing lithium nickel manganese cobalt (LiNi _0.8 Mn _0.1 Co _0.1 O ₂ ) with a high nickel content is secondary for electric vehicles due to its high energy density, low material cost, environmental friendliness, and excellent stability. It is a material that has received a lot of attention as a battery cathode material. However, a layered oxide material having a high nickel content has a problem of performance degradation due to inherent low electrical conductivity and an exchange phenomenon between nickel and lithium.

To solve this problem, the existing researchers tried to solve the problem of low electrical conductivity by substituting heterogeneous elements or synthesizing nano-sized materials. However, in the case of the existing approach, it may take a lot of cost for material synthesis, and since it may have a low electrode density, there is a big limitation in terms of commercialization.

However, recently, research contents have been published that existing problems can be improved through a change in a binder, which is a component of a secondary battery electrode. In the case of a binder material, although it has a low content in the secondary battery electrode, it is a key factor that affects the overall electrode performance. In particular, in the case of previously published studies, the performance of a layered oxide electrode with a high nickel composition was improved by applying an environmentally friendly and low process cost water-based binder. However, when the water-based binder process is applied, a lithium ion corrosion problem of a positive electrode material and a corrosion problem of an aluminum current collector may occur, which is still a big limitation in terms of commercialization.

In addition, in the case of the current organic solvent-based commercial PVDF binder, there is a problem of aggregation of the active material and low adhesion to the current collector due to the high molecular weight. Therefore, in order to manufacture a layered oxide electrode having a high nickel content with excellent properties, an organic solvent-based polymer that is not only electrochemically stable but can be immediately applied to commercial processes must be discovered, and the dispersibility of the slurry can be improved. In addition, it is necessary to discover a multifunctional polymer that protects the interface of the electrode and has high adhesion.

Korean Patent Registration No. 10-1320381

The present invention is to solve the above-described problem, it is possible to improve the dispersibility of the slurry in order to improve the performance of the secondary battery electrode, a slurry for a secondary battery electrode comprising an elastic binder having a function of protecting the electrode interface with high adhesion , To provide a secondary battery electrode and a secondary battery including the same.

To achieve the above object,

The present invention is a slurry for a secondary battery electrode comprising a binder, an active material and a conductive material,

The binder includes a copolymer polymer including a hard segment capable of hydrogen bonding in an electrode and a soft segment having a polyol structure,

The slurry for secondary battery electrodes is characterized in that shearing stress is generated in the slurry during the mixing process at a shear rate in the range of ^{0.1 to 1,000 s -1, and a binder is applied to the surface of the active material.} to provide.

In addition, the present invention provides a secondary battery electrode, characterized in that the slurry for secondary battery electrode is applied to a current collector.

In addition, the present invention, a secondary battery electrode; And

It includes a non-aqueous electrolyte, and the non-aqueous electrolyte provides a secondary battery, characterized in that it contains a compound of the following formula (3):

[Formula 3]

.

.

The slurry for a secondary battery electrode according to the present invention includes an elastic binder, and the elastic binder has a hard segment capable of hydrogen bonding with a layered lithium transition metal oxide, conductive carbon, and a current collector material. It has high adhesion between the whole and has excellent mechanical properties. In addition, since the binder material has a polyol-type soft segment, it is well dispersed during the slurry production process, thereby reducing the amount of the organic solvent used and minimizing the aggregation of the material.

More specifically, the slurry for a secondary battery electrode according to the present invention has a shearing stress in the slurry during the mixing process at a shear rate in the range of ^{0.1 to 1,000 s -1, and due to the elasticity of the binder, the active material surface} The binder can be applied evenly.

In particular, during the mixing process of the secondary battery electrode slurry, a binder is uniformly applied to the surface of the active material, thereby providing a secondary battery with improved speed characteristics due to improved conductivity, and prevents direct contact between the electrode and the electrolyte as the cycle progresses. Therefore, deterioration caused by the electrolyte is suppressed, and the lifespan characteristics of the secondary battery may be improved.

1 is a view showing the structure of a copolymer polymer according to an embodiment of the present invention.
Figure 2(a) is a molecular structure of a copolymer polymer of an elastic binder according to the present invention and a bonding structure with an aluminum current collector, and Figure (b) shows the results of molecular functional group analysis through Fourier transform infrared spectroscopy (FT-IR). It is a drawing.
3 is a view showing the results of evaluation of the life of a secondary battery using the secondary batteries prepared in Example 1 and Comparative Example 1 of the present invention.
4 is a diagram showing a stress-strain curve of the binders according to Example 1 and Comparative Example 1. FIG.
5 is a view showing the results of a peeling test of cross-sections of electrodes according to Example 1 and Comparative Example 1. FIG.
6 is a view showing photographs taken by SEM of the electrode surfaces prepared in Example 1 and Comparative Example 1. FIG.
7 is a view showing an XRD graph of the electrode surfaces prepared in Example 1 and Comparative Example 1.
8(a) is a graph showing the change in specific capacity of the lithium secondary batteries of Example 1 and Comparative Example 1 when the charge/discharge rate changes, and FIG. 8(b) is a secondary battery electrode of Example 1 and Comparative Example 1 This is a graph showing the results of cyclic voltammetry analysis.
9 is a view showing the impedance analysis results of the secondary batteries prepared in Example 1 and Comparative Example 1.
10 is a graph showing capacity retention characteristics at room temperature and high temperature during long-term driving of the secondary batteries prepared in Example 1 and Comparative Example 1 ((a) 25°C, (b) 50°C).
11 is a graph showing the results of XPS spectral analysis in order to evaluate the components of the electrode interface before/after the electrochemical experiment for the electrodes of Example 1 and Comparative Example 1 ((a), (b) Comparative Example 1 and Example 1 Before the electrochemical cycle of the electrode, (c), (d) after the cycle of the Comparative Example 1 and Example 1 electrodes).
12 is a view showing a photograph of the electrode of Example 1 and Comparative Example 1 taken by SEM before/after an electrochemical experiment ((a), (b) of the electrode of Comparative Example 1 and Example 1) Before the electrochemical cycle, (c), (d) after the cycle of the electrode in Comparative Example 1 and Example 1).

In the present invention, various modifications may be made and various embodiments may be provided, and specific embodiments will be illustrated in the drawings and described in detail in the detailed description.

However, this is not intended to limit the present invention to a specific embodiment, it should be understood to include all changes, equivalents, and substitutes included in the spirit and scope of the present invention. In describing the present invention, when it is determined that a detailed description of a related known technology may obscure the subject matter of the present invention, a detailed description thereof will be omitted.

The terms used in the present application are only used to describe specific embodiments, and are not intended to limit the present invention. Singular expressions include plural expressions unless the context clearly indicates otherwise.

In the present invention, terms such as "comprises" or "have" are intended to designate the presence of features, numbers, steps, actions, components, parts, or combinations thereof described in the specification, but one or more other features. It is to be understood that the presence or addition of elements, numbers, steps, actions, components, parts, or combinations thereof, does not preclude in advance the possibility of the presence or addition.

The present invention relates to a slurry for a secondary battery electrode including an elastic binder for a secondary battery electrode, an electrode for a secondary battery, and a secondary battery including the same.

Conventionally, in the case of a commercial PVDF binder, there is a problem of aggregation of an active material and low adhesion to a current collector due to a high molecular weight. Therefore, in order to manufacture a secondary battery electrode with excellent properties, it is necessary to discover an organic solvent-based polymer that is not only electrochemically stable, but can be immediately applied to commercial processes. In particular, it is possible to improve the dispersibility of the slurry and have high adhesion. There is a need for research on multifunctional polymers with

Accordingly, the present invention provides a slurry comprising a binder, which is a copolymer polymer including a hard segment capable of hydrogen bonding in an electrode and a soft segment having a polyol structure, and in particular, the slurry has a shear rate in the range of ^{0.1 to 1,000 s -1.} During the mixing process, shearing stress is generated in the slurry, and a binder is applied to the surface of the active material, thereby providing a slurry for a secondary battery electrode.

Furthermore, it provides an electrode for a secondary battery and a secondary battery including the slurry.

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

The present invention is a slurry for a secondary battery electrode comprising a binder, an active material and a conductive material,

The binder includes a copolymer polymer including a hard segment capable of hydrogen bonding in an electrode and a soft segment having a polyol structure,

The slurry for secondary battery electrodes is characterized in that shearing stress is generated in the slurry during the mixing process at a shear rate in the range of ^{0.1 to 1,000 s -1, and a binder is applied to the surface of the active material.} to provide.

The slurry for a secondary battery electrode can be prepared by mixing a copolymer polymer of a binder, an active material, and a conductive material in an organic solvent, and the slurry for a secondary battery electrode in the mixing process of the slurry is at a shear rate ^{of 0.1 to 1,000 s -1.} , Shearing stress in the range of 20 to 1100 Pa on average may be generated, and the slurry for secondary battery electrode is at the shearing stress in the range of 20 to 1100 Pa, elastic binder for secondary battery electrode on the surface of the positive electrode active material. Can be applied. More specifically, at a shear rate of 1 to 500 s ^-1 , shear stress in the range of 63 to 660 Pa on average may occur, and ^{at a shear rate of 10 to 100 s -1} , shear stress in the range of 111 to 224 Pa on average Can occur. For example, a shear stress of 141.1 Pa is generated at a shear rate of 46.4 s ^-1 , and a binder may be applied to the surface of the active material. On the other hand, if the shear stress is less than the minimum value of the range, the active material surface coating function of the binder may be weakened and the dispersion degree of the slurry may be lowered.If the shear stress exceeds the maximum value, the active material particles collide with the reactor wall, the active material A problem of damage to the structure of the active material occurs due to collision between the cells or overheating of the slurry.

In a specific embodiment, it may be applied in the form of a polymer film film on the surface of the active material due to the functional group included in the copolymer polymer of the elastic binder described above by the strong binding force with the active material and the elongation (elastic force) of the elastic binder. In addition, due to these properties, the binder can be evenly dispersed in the slurry.

Furthermore, the viscosity of the slurry for secondary battery electrodes according to the present invention is characterized in that at 25° C., in the range of 500 to 250,000 cP. The viscosity of the slurry for secondary battery electrodes may be in the range of 500 to 250,000 cP, 1,000 to 240,000 cP, 10,000 to 220,000 cP, 50,000 to 200,000 cP, or 130,000 to 180,000 cP. On the other hand, when the viscosity of the slurry is less than 500 cP, the coated electrode is weak in binding to the current collector, there is a limit to increasing the electrode thickness, and when the viscosity of the slurry exceeds 250,000 cP, the viscosity is too high to the components in the slurry. The dispersibility of them can be significantly deteriorated.

That is, the slurry for a secondary battery electrode according to the present invention may maintain a slurry viscosity within the above-described range, and may have an appropriate viscosity in a slurry mixing process. In addition, the binding force may be improved in the subsequent rolling process.

On the other hand, when the slurry is applied to the electrode, the polymer film film on the surface of the active material can act as a protective layer, and as the cycle progresses, it prevents direct contact between the electrode and the electrolyte, so that deterioration due to the electrolyte is suppressed and the lifespan It is possible to provide a secondary battery with improved characteristics and the like.

The binder is an elastic binder, a copolymer polymer comprising a hard segment capable of hydrogen bonding in an electrode and a soft segment of a polyol structure, and a copolymer polymer having a modulus of elasticity of 100 MPa or less and an elongation of 50% or more. It characterized in that it includes.

In the present invention, "elastic binder" refers to a polymer binder for secondary battery electrodes having a predetermined elastic modulus, and more specifically, a secondary battery comprising a copolymer polymer having an elastic modulus of 100 MPa or less and an elongation of 50% or more. It may mean a polymeric binder for electrodes.

More specifically, the modulus of elasticity of the copolymer polymer is in the range of 500 kPa to 100 MPa, 600 kPa to 80 MPa, 800 kPa to 60 MPa, 1 to 40 MPa, 1 to 25 MPa, or 2 to 10 MPa. I can. In particular, the elastic binder for an electrode includes a copolymer polymer having the above-described elastic modulus, and may have very excellent elongation. More specifically, the elongation of the copolymer polymer may be 50% or more, and may be in the range of 50 to 1000% or 50 to 950%.

The modulus of elasticity and elongation may be obtained from a stress-strain curve through a tensile stress test under a condition of 5 mm/min after the binder is prepared as a specimen of JIS K-6301 TYPE 1. Specifically, after filming the copolymer polymer, when the average thickness of the film is 80 to 95 µm, and 0.3 cm in width and 2.7 cm in length, the elastic modulus of the film is 500 kPa to 100 MPa, and the elongation is 50 to It can be in the range of 950%. For example, under the above conditions, the modulus of elasticity may be about 4 MPa, and the elongation may be about 920%.

In the present invention, the "modulus of elasticity" refers to the degree of strain occurring when an elastic material is subjected to stress, and refers to the degree to which the material resists pressure. That is, an elastic material that is easily deformed may have a lower elastic modulus value.

1 is a view showing the structure of a copolymer polymer according to an embodiment of the present invention.

Referring to FIG. 1, the elastic polymer binder according to the present invention is a copolymer polymer including a hard segment capable of hydrogen bonding in an electrode and a soft segment having a polyol structure.

The electrode containing the copolymer polymer may react with the compound of Formula 3 below or the electrolyte in the electrolyte to form a polycarbonate-based electrode interface film.

[Formula 3]

.

.

Alternatively, the electrode containing the copolymer polymer is at least selected from the group consisting of _{Li x} PF _y and Li _x PO _y F _z by the reaction of the compound of Formula 3 above or lithium salt in the electrolyte during an electrochemical reaction. It is characterized by forming an electrode interface film of one component.

The number average molecular weight of the copolymer polymer may be ^{140,000 to 1,000,000 g mol -1.}

The hard segment includes an aromatic urethane and an aromatic urea bond, and the soft segment may ^{use an aliphatic polyol compound having a weight average molecular weight of 1,000 to 3,000 g mol -1} , and the aliphatic polyol is polyethylene glycol, polytetramethylene ether glycol , Polypropylene glycol, polycarbonate diol, polycaprolactone diol, and ethylene-propylene glycol may be one or more selected from the group consisting of a copolymer.

2(a) is a view showing the molecular structure of the copolymer polymer of the elastic binder according to the present invention, and FIG. 2(b) is a view showing the results of molecular functional group analysis through Fourier transform infrared spectroscopy (FT-IR). Referring to FIG. 2, the polymer is a structure capable of being phase-separated into soft-hard segments, and a structure capable of hydrogen bonding with an electrode active material through urea and urethane functional groups of the hard segment.

In addition, the active material may include at least one lithium metal oxide selected from the group consisting of the following Chemical Formulas 1 and 2:

[Formula 1]

LiNi _x Mn _y Co _z Al _w O ₂

In Formula 1, 0≤x≤1, y is 0≤y≤1, 0≤z≤1, w is 0≤w≤0.15, and x+y+z+w=1.

[Formula 2]

LiFe _x Mn _y PO ₄

In Formula 2, 0≤x≤1, 0≤y≤1, and x+y=1.

More specifically, the active material may be a layered lithium transition metal oxide (LiNi _x Mn _y Co _z Al _w O ₂ ), or an olivine-based iron phosphate (LiFe _x Mn _y PO ₄ ), or the layer It may be a combination of an upper lithium transition metal oxide and an olivine-based iron phosphate. As an example, the lithium transition metal oxide may be LiNi _0.8 Co _0.1 Mn _0.1 O ₂ or LiNi _0.6 Co _0.2 Mn _0.2 O ₂ , but is not limited thereto.

Meanwhile, the binder may contain 0.2 to 15% by weight based on the total weight of the active material. More specifically, the binder may be 0.2 to 15% by weight, 1.2 to 10% by weight, 1.4 to 5% by weight, 1.5 to 3% by weight, or 1.6 to 3.1% by weight based on the total weight of the active material, or 3.0% by weight, Or 2.0% by weight. On the other hand, when the binder is in the above weight range, a secondary battery having high efficiency can be implemented.

In addition, the present invention provides a secondary battery electrode, characterized in that the slurry for secondary battery electrode is applied to a current collector. Specifically, the positive electrode of the electrode may be coated with a slurry including a positive electrode active material on the positive electrode current collector.

In particular, the binder applied on the surface of the electrode can protect the interface of the electrode, thereby suppressing performance degradation.

In the present invention, the positive electrode active material may include at least one lithium metal oxide selected from the group consisting of the following Chemical Formulas 1 and 2:

[Formula 1]

LiNi _x Mn _y Co _z Al _w O ₂

In Formula 1, 0≤x≤1, y is 0≤y≤1, 0≤z≤1, w is 0≤w≤0.15, and x+y+z+w=1.

[Formula 2]

LiFe _x Mn _y PO ₄

In Formula 2, 0≤x≤1, 0≤y≤1, and x+y=1.

More specifically, the active material may be a layered lithium transition metal oxide (LiNi _x Mn _y Co _z Al _w O ₂ ), or an olivine-based iron phosphate (LiFe _x Mn _y PO ₄ ), or the layer It may be a combination of an upper lithium transition metal oxide and an olivine-based iron phosphate.

As the positive electrode binder, the copolymer binder may be used.

As the positive electrode current collector, any one that can be used as a current collector in the art may be used, and specifically, it is preferable to use an aluminum foil, foamed aluminum, foamed nickel, or the like having excellent conductivity.

The conductive material may be porous. Therefore, if the conductive material has porosity and conductivity, it may be used without limitation, and for example, a carbon-based material having porosity may be used. As such a carbon-based material, carbon black, graphite, graphene, activated carbon, carbon fiber, carbon nanotubes, and the like may be used. Further, metallic fibers such as metal mesh, metallic powders such as copper, silver, nickel, aluminum, or organic conductive materials such as polyphenylene derivatives can also be used. The conductive materials may be used alone or in combination.

The positive electrode as described above may be manufactured according to a conventional method, and specifically, a slurry for forming a positive electrode active material layer prepared by mixing a positive electrode active material, the conductive material, and the binder in an organic solvent is applied and dried on a current collector, Optionally, in order to improve the electrode density, it may be manufactured by pressing the current collector. At this time, as the organic solvent, a positive electrode active material, a binder, and a conductive material may be uniformly dispersed, and it is preferable to use an easily evaporated one. Specifically, N-methyl-2-pyrrolidone, acetonitrile, methanol, ethanol, tetrahydrofuran, isopropyl alcohol, and the like can be used.

In addition, in the present invention, the negative electrode in the battery includes a negative electrode active material formed on the negative electrode current collector.

The negative electrode current collector may be specifically selected from the group consisting of copper, stainless steel, titanium, silver, palladium, nickel, alloys thereof, and combinations thereof. The stainless steel may be surface-treated with carbon, nickel, titanium or silver, and an aluminum-cadmium alloy may be used as the alloy. In addition, calcined carbon, a non-conductive polymer surface-treated with a conductive material, or a conductive polymer may be used.

As the negative active ^{material, a material capable of reversibly intercalating or deintercalating lithium ions (Li +} ), a material capable of reversibly forming a lithium-containing compound by reacting with lithium ions, a lithium metal or a lithium alloy Can be used. The material capable of reversibly occluding or releasing lithium ions (Li ⁺ ) may be, for example, crystalline carbon, amorphous carbon, lithium titanium oxide, or a mixture thereof. A material capable of reversibly forming a lithium-containing compound by reacting with the lithium ions (Li ⁺ ) may be, for example, tin oxide, titanium nitrate, silicon, silicon oxide, or a silicon-carbon composite. The lithium alloy is, for example, lithium (Li) and sodium (Na), potassium (K), rubidium (Rb), cesium (Cs), francium (Fr), beryllium (Be), magnesium (Mg), calcium ( It may be an alloy of a metal selected from the group consisting of Ca), strontium (Sr), barium (Ba), radium (Ra), aluminum (Al), and tin (Sn).

The negative electrode may further include a binder for bonding of the negative active material and the conductive material to the current collector, and specifically, the binder is the same as described above for the binder of the positive electrode.

The separator is a physical separator having a function of physically separating an electrode, and if it is used as a conventional separator, it can be used without particular limitation. In particular, it is preferable that the separator has low resistance against ion migration of the electrolyte and has excellent electrolyte moisture-moisturizing ability.

In addition, the separator separates or insulates the anode and the cathode from each other, while allowing lithium ions to be transported between the anode and the cathode. The separator may be made of a porous, non-conductive or insulating material, and the separator may be an independent member such as a film, or a coating layer added to an anode and/or a cathode.

Specifically, a porous polymer film, for example, a porous polymer film made of polyolefin-based polymers such as ethylene homopolymer, propylene homopolymer, ethylene/butene copolymer, ethylene/hexene copolymer, and ethylene/methacrylate copolymer. It may be used alone or by stacking them, or a nonwoven fabric made of a conventional porous nonwoven fabric such as high melting point glass fiber, polyethylene terephthalate fiber, etc. may be used, but is not limited thereto.

In addition, the present invention provides a secondary battery comprising the secondary battery electrode and a non-aqueous electrolyte.

The non-aqueous electrolyte solution includes a compound represented by the following formula (3).

[Formula 3]

.

.

The content of Formula 3 may be 0.1 to 15.0% by weight of the non-aqueous electrolyte.

In addition, the non-aqueous electrolyte solution contains a lithium salt and is composed of a lithium salt and a solvent, and a non-aqueous organic solvent, an organic solid electrolyte, and an inorganic solid electrolyte may be used as the solvent.

The lithium salt is a material that can be easily dissolved in a non-aqueous organic solvent, for example, LiCl, LiBr, LiI, LiClO ₄ , LiBF ₄ , LiB ₁₀ Cl ₁₀ , LiB(Ph) ₄ , LiC ₄ BO ₈ , LiPF ₆ , _{LiCF 3 SO 3, LiCF 3 CO} 2, LiAsF 6, LiSbF 6, LiAlCl 4, LiSO 3 CH 3, LiSO 3 CF 3, LiSCN, LiC (CF 3 SO 2) 3, LiN (CF 3 SO 2) 2, LiN (C ₂ F ₅ SO ₂ ) ₂ , LiN(SO ₂ F) ₂ , lithium chloroborane, lithium lower aliphatic carboxylic acid, lithium 4 phenyl borate, it may be at least one selected from the group consisting of imide.

The concentration of the lithium salt is 0.1 to 6.0, depending on several factors such as the exact composition of the electrolyte mixture, the solubility of the salt, the conductivity of the dissolved salt, the charging and discharging conditions of the battery, the working temperature and other factors known in the lithium-sulfur battery field. M, preferably 0.5M to 2.0M. If the concentration of the lithium salt is less than the above range, the conductivity of the electrolyte may be lowered and battery performance may be degraded, and if the concentration of the lithium salt is greater than the above range, the viscosity of the electrolyte may increase and ^{the mobility of lithium ions (Li +} ) may decrease. It is desirable to select an appropriate concentration from.

The non-aqueous organic solvent is a material capable of dissolving a lithium salt well, preferably N-methyl-2-pyrrolidone, propylene carbonate, ethylene carbonate, butylene carbonate, dimethyl carbonate , Diethyl carbonate, ethylmethyl carbonate, gamma-butyllolactone, 1,2-dimethoxy ethane, 1,2-diethoxy ethane, 1-ethoxy-2-methoxy ethane, tetraethylene glycol dimethyl ether, Tetrahydroxy franc (franc), 2-methyl tetrahydrofuran, dimethyl sulfoxide, 1,3-dioxolane, 4-methyl-1,3-dioxene, diethyl ether, formamide, dimethylformamide, dioxolane , Acetonitrile, nitromethane, methyl formate, methyl acetate, phosphoric acid tryster, trimethoxy methane, dioxolane derivative, sulfolane, methyl sulfolane, 1,3-dimethyl-2-imidazolidinone, propylene carbonate Aprotic organic solvents such as derivatives, tetrahydrofuran derivatives, ethers, methyl propionate and ethyl propionate may be used, and one or two or more of them may be used in the form of a mixed solvent.

The organic solid electrolyte is preferably a polyethylene derivative, a polyethylene oxide derivative, a polypropylene oxide derivative, a phosphate ester polymer, a poly etch lysine, a polyester sulfide, a polyvinyl alcohol, a polyvinylidene fluoride, an ionic A polymer or the like containing a dissociation group can be used.

As the inorganic solid electrolyte of the present invention, preferably, Li ₃ N, LiI, Li ₅ NI ₂ , Li ₃ N-LiI-LiOH, LiSiO ₄ , LiSiO ₄ -LiI-LiOH, Li ₂ SiS ₃ , Li ₄ SiO ₄ , Li ₄ SiO ₄ -LiI-LiOH, Li ₃ PO ₄ -Li ₂ S-SiS ₂ It is possible to use nitrides, halides, and sulfates of Li such as S-SiS 2.

The copolymer polymer of the binder may react with the compound of Formula 3 to form a polycarbonate-based electrode interface layer, and the binder may be 0.2 to 15% by weight of the electrode.

Alternatively, the electrode including the copolymer polymer of the binder may form an electrode interface film of at least one component selected from the group consisting of _{Li x} PF _y and Li _x PO _y F _z by a reaction in which the compound of Formula 3 or lithium salt participates. Can be formed.

Hereinafter, the present invention will be described in more detail by examples and experimental examples.

However, the following Examples and Experimental Examples are merely illustrative of the present invention, and the contents of the present invention are not limited to the following Examples and Experimental Examples.

<Example>

Example 1.

(Preparation of slurry for secondary battery electrode)

The copolymer polymer disclosed in FIG. 1 was prepared by inducing urethane and urea bond formation through condensation polymerization between aromatic diisocyanate, glycol, and diamine. _{In addition, LiNi 0.8} Co _0.1 Mn _0.1 O ₂ (NCM811) as a positive electrode active material, carbon black (Super P) as a conductive material, and the binder of Example 1 were used in a weight ratio of 94:4:2, and the solvent was N-methyl- It was added to 2-pyrrolidone (NMP) to prepare a positive electrode slurry. Meanwhile, during the mixing process, the mixture ^{was mixed at a rate of 0.1 to 1,000 s -1} , and at this time, a shear stress of 21.1 to 1,071 Pa was generated.

(Electrode manufacturing)

The positive electrode slurry was coated on one surface of an aluminum thin film of a positive electrode current collector, dried, and pressed to prepare a single-sided positive electrode having an active material layer having a thickness of 95 μm.

(Manufacture of secondary battery)

A secondary battery including the electrode prepared above was manufactured. At this time, the configuration of the used secondary battery is shown in Table 1 below.

Working electrode NCM811/super P/(PVDF or Elastic binder) Counter electrode Lithium metal Electrolyte 1 M LiPF ₆ in EC/DMC (v/v=1/1) + 10 wt.% FEC separator PE

Comparative Example 1.

An electrode was manufactured in the same manner as in Example 1, except that PVDF was used as a binder.

<Experimental Example>

Experimental Example 1. Stability evaluation according to the type and composition of the binder

Using the secondary battery electrode prepared in Example 1 and Comparative Example 1, stability evaluation of the electrode was performed.

At this time, loading of the active material was carried out at ^{14 mg cm -2.} During the experiment, the first cycle was performed at 0.1C, and from the next cycle, current was supplied at 0.5C. Accordingly, cycle retention was calculated based on the capacity of the second cycle and the last cycle. And, the results are shown in FIG. 3.

The voltage range of the experimental results shown in FIG. 3 was 2.8 to 4.3V, and when the cut-off voltage was set from 4.5 to 4.7V, it was confirmed that the cycle retention reduction phenomenon was added (not shown).

Experimental Example 2. Comparison of Slurry Properties According to Binder

The viscosity and shear stress of the slurries in Example 1 and Comparative Example 1 were measured. Viscosity measurement was performed by installing a small sample adapter and a thermostat to a viscometer (HBDV II+, Brookfield, USA) to keep the temperature constant at 22°C, and then measuring the shear rate with a spindle. And, the results are shown in Table 2 below.

Shear rate (s ^-1 )
[0.1 ~ 1,000] Viscosity (cP) Shear stress (Pa) Slurry of Example 1 1,071 ~ 211,000 21.1 ~ 1,071 Slurry of Comparative Example 1 521 ~ 122,700 12.27 ~ 521.8 * Shear stress = viscosity × shear rate
* Weight ratio between electrode solids when preparing slurry, NCM811: Carbon Black (Super P): Binder = 94:4:2
* When preparing a slurry, the type of solvent = N-methyl-2-pyrrolidone (NMP)
* When preparing a slurry, the ratio of the total solid content of the electrode and the weight of the solvent, the total solid content of the electrode: solvent = 1.72:1

Referring to Table 2, it can be seen that the viscosity and shear stress of the slurry of Example 1 are superior to that of the slurry of Comparative Example 1. These results show that the binder of Example 1 is well dispersed during the slurry preparation process, thereby reducing the amount of use of the organic solvent and is advantageous in exerting a binding force between solids.

Experimental Example 3. Measurement of the elastic modulus and elongation of the binder

In order to measure the physical properties of the binder, the binders of Example 1 and Comparative Example 1 were prepared as a specimen of JIS K-6301 TYPE 1 (0.3 cm × 2.7 cm), and then the tensile speed (Grip Separation Speed) The elastic modulus and elongation were measured under tension under the condition of 5 mm/min. 4 is a diagram showing a stress-strain curve of the binders according to Example 1 and Comparative Example 1. FIG.

Then, the elastic modulus was derived from the stress-strain curve.

Referring to FIG. 4, the elastic modulus and elongation of the binders of Example 1 and Comparative Example 1 can be known. Specifically, it was found that the binder of Example 1 has excellent elasticity and high elongation. On the other hand, the binder of Comparative Example 1 had high rigidity, and the elongation was very low (less than 50%), and the binder of Comparative Example 1 was fractured at a stress of 35 MPa or more. That is, in Comparative Example 1, the stress-strain curve was very unstable.

Experimental Example 4. Measurement of adhesion of electrode cross-section

After the electrode cross-sections prepared in Example 1 and Comparative Example 1 were prepared as specimens having a width of 25 mm × 30 mm, the electrode cross-section, 3M tape, and a glass substrate were sequentially stacked, and then 10 using a 2 kg roll. It was rolled twice.

The specimen was subjected to a peeling test at a rate of 25 mm/min, and the results are shown in FIG. 5.

5 is a view showing the results of a peeling test of cross-sections of electrodes according to Example 1 and Comparative Example 1. FIG.

Referring to FIG. 5, it was confirmed that the adhesive strength of Example 1 was superior to that of Comparative Example 1. It is believed that the binder of Example 1 includes an electrode active material, conductive carbon, and a hard segment capable of hydrogen bonding with a current collector material, and thus provides high adhesion between materials and between the active material layer and the current collector. In addition, it is judged that the high binding force of Example 1 is caused by evenly applying the binder to the surface of the active material during slurry stirring.

Experimental Example 5. Surface analysis according to the binder

The surfaces of the electrodes prepared in Example 1 and Comparative Example 1 were measured with a scanning electron microscope (SEM). And, it is shown in Figure 6.

6 is a view showing photographs taken by SEM of the electrode surfaces prepared in Example 1 and Comparative Example 1. FIG. Referring to FIG. 6, it can be seen that the electrode surface of Example 1 is smoother than that of Comparative Example 1. This is due to the excellent interaction between the binder and the active material and the even dispersion of the binder.

Experimental Example 6. XRD analysis according to the binder

The electrodes prepared in Example 1 and Comparative Example 1 were subjected to X-ray diffraction analysis using CuKα. X-ray diffraction analysis was performed using a Rigaku RINT2200HF+ diffractometer using Cu Kαradiation (1.540598Å).

The slurries of Example 1 and Comparative Example 1 were analyzed by X-ray diffraction to obtain a ratio (I ₀₀₃ /I ₁₀₄ ) of peaks representing (before/after) (003) planes and (104) planes before and after battery operation. The results are shown in Fig. 7 and Table 3.

I ₍₀₀₃₎ /I ₍₁₀₄₎ Comparative Example 1 before 1.11 Comparative Example 1 after 0.75 Example 1 before 1.07 Example 1 after 1.02

According to the results of FIG. 7 and Table 3, in Example 1, the _{value of I 003} /I ₁₀₄ decreased very small before and after driving, whereas in Comparative Example 1, the _{value of I 003} /I ₁₀₄ decreased very significantly after the same driving. This means that in the case of Comparative Example 1, the mixture of cations in the layered oxide structure was severe, so that the layered structure was transformed into a spinel or rock salt structure. This structural change accelerates the elution of the transition metal into the electrolyte and side reactions on the electrode surface. In the same vein, the electrode surface protection function of the binder of Example 1 suppressed such a structural change, and maintained a _{high I 003} /I _{104 value even after the battery was operated.}

Experimental Example 7. Analysis of electrochemical properties according to the binder

The electrochemical properties of the battery according to the type of binder were evaluated. And, the results are shown in FIG. 8. 8(a) is a graph showing the change in specific capacity of the lithium secondary batteries of Example 1 and Comparative Example 1 when the charge/discharge rate changes, and FIG. 8(b) is a secondary battery electrode of Example 1 and Comparative Example 1 This is the result of cyclic voltammetry analysis of at various scan rates

Referring to FIG. 8(a), it can be seen that the secondary battery of Example 1 compared to Comparative Example 1 maintains excellent electrochemical properties. In particular, in the case of Example 1, it was confirmed that the specific capacity of the electrode was maintained high under the condition of increasing the C-rate.

9 is a view showing the impedance analysis results of the secondary batteries prepared in Example 1 and Comparative Example 1. In the process of driving the battery, Example 1 showed lower impedance than Comparative Example 1. This means that the high rate characteristics are good, and it is due to the decrease in the interface resistance due to the interface protection function of the binder.

10 is a graph showing capacity retention characteristics of the secondary batteries prepared in Example 1 and Comparative Example 1 during long-term driving. ((a) 25°C, (b) 50°C). Referring to FIG. 10, it can be seen that Example 1 has excellent lifespan characteristics compared to Comparative Example 1 regardless of the driving temperature condition of the secondary battery. That is, it means that the binder can suppress the deterioration of the electrolyte solution due to the interface protection function even at high temperatures due to thermal stability. In addition, as the dispersion of the binder of Example 1 is excellent, the dispersion of the conductive material is increased, so that the conductivity inside the electrode is improved, so that the specific capacity is maintained high throughout the life measurement period.

Experimental Example 8. Surface analysis of secondary battery electrodes according to the type of binder

(Material properties)

Using the lithium secondary batteries prepared in Example 1 and Comparative Example 1, the electrode surface functional groups according to the electrochemical cycle were analyzed. And, the results are shown in FIG. 11. 11 is a graph showing the results of XPS spectral analysis for the electrodes of Example 1 and Comparative Example 1 to determine the components of the electrode interface before/after the electrochemical experiment ((a), (b) Comparative Example 1 and implementation) Example 1 Before the electrochemical cycle of the electrode, (c), (d) after the cycle of the Comparative Example 1 and Example 1 electrodes).

As a result of the electrode surface analysis, when the copolymer binder of the present invention was used, peaks related to _{Li x} PF _y or Li _x PO _y F _{z increased.} Due to the active material interface protection function of the binder, deterioration caused by the electrolyte during an electrochemical reaction is suppressed, _{reducing the tendency of the lithium salt, LiPF 6} , ^{to be finally decomposed to F-} ions in the electrolyte, reducing the ratio of forming the electrode interface film of LiF. Due to that. As a result, it was confirmed that an electrode interface film containing _{Li x} PF _y or Li _x PO _y F _z , which is an intermediate decomposition product of the lithium salt in the electrolyte solution or a reaction product of Formula 3 and the lithium salt in the electrolyte solution, as a main component was formed.

(Surface analysis according to the binder)

Using the lithium secondary batteries prepared in Example 1 and Comparative Example 1, the surface of the electrode according to the electrochemical cycle was analyzed with a scanning electron microscope (SEM). And, it is shown in Figure 12.

12 is a view showing a photograph of the electrode of Example 1 and Comparative Example 1 taken by SEM before/after an electrochemical experiment ((a), (b) of the electrode of Comparative Example 1 and Example 1) Before the electrochemical cycle, (c), (d) after the cycle of the electrode in Comparative Example 1 and Example 1). Referring to FIG. 12, it can be seen that the electrode surface of Example 1 is smoother before and after the cycle than the electrode surface of Comparative Example 1. This is due to the excellent interaction between the binder and the active material and even solid dispersion.

Claims (14)

As a slurry for a secondary battery electrode comprising a binder, an active material and a conductive material,
The binder includes a copolymer polymer including a hard segment capable of hydrogen bonding in an electrode and a soft segment having a polyol structure,
When the slurry for secondary battery electrodes ^{is mixed at a shear rate in the range of 1 to 1,000 s -1} , shearing stress is generated in the slurry, so that a binder is applied to the surface of the active material,
The active material is a slurry for a secondary battery electrode comprising at least one lithium metal oxide or lithium metal phosphate selected from the group consisting of the following Chemical Formulas 1 and 2:
[Formula 1]
LiNi _x Mn _y Co _z Al _w O ₂
In Formula 1, 0≤x≤1, y is 0≤y≤1, 0≤z≤1, w is 0≤w≤0.15, x+y+z+w=1,
[Formula 2]
LiFe _x Mn _y PO ₄
In Formula 2, 0≤x≤1, 0≤y≤1, and x+y=1.
The method of claim 1,
The slurry for secondary battery electrodes is characterized in that a shearing stress in the range of 63 to 1,100 Pa is generated on average at a shear rate in the range of ^{1 to 1,000 s -1.}
The method of claim 1,
A slurry for a secondary battery electrode, characterized in that the viscosity of the slurry for a secondary battery electrode is in the range of 500 to 250,000 cP.
The method of claim 1,
A slurry for secondary battery electrodes, characterized in that the copolymer polymer has a modulus of elasticity of 100 MPa or less and an elongation of 50% or more.
The method of claim 1,
After filming the copolymer polymer, when the average thickness of the film is 80 to 95 µm, and the width is 0.3 cm and the length is 2.7 cm,
The film has an elastic modulus of 500 kPa to 100 MPa, and an elongation of 50 to 950%.
The method of claim 1,
The number average molecular weight of the copolymer polymer is a slurry for a secondary battery electrode, characterized in that the range of ^{140,000 to 1,000,000 g mol -1.}
The method of claim 1,
The hard segment contains aromatic urethane and aromatic urea bonds,
The soft segment is a slurry for a secondary battery electrode, characterized in that the weight average molecular weight is ^{an aliphatic polyol compound in the range of 1,000 to 3,000 g mol -1.}
The method of claim 1,
The aliphatic polyol is at least one selected from the group consisting of polyethylene glycol, polytetramethylene ether glycol, polypropylene glycol, polycarbonate diol, polycaprolactone diol, and ethylene-propylene glycol copolymer.
delete The method of claim 1,
The binder is a slurry for a secondary battery electrode comprising 0.2 to 15% by weight based on the total weight of the active material.
An electrode, characterized in that the slurry for a secondary battery electrode according to any one of claims 1 to 8 and 10 is applied to a current collector.
The secondary battery electrode according to claim 11; And
A secondary battery comprising a non-aqueous electrolyte, wherein the non-aqueous electrolyte comprises a compound represented by the following formula (3):
[Formula 3]

.
The method of claim 12,
A secondary battery, characterized in that the electrode of the secondary battery reacts with a non-aqueous electrolyte solution, a compound of Formula 3, or a combination thereof to form a polycarbonate-based electrode interface film.
The method of claim 12,
The electrode of the secondary battery is characterized by forming an electrode interface film of at least one component selected from the group consisting of _{Li x} PF _y and Li _x PO _y F _z by reacting with the compound of Formula 3 or the lithium salt in the electrolyte or a combination thereof. Secondary battery.

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