KR20230041565A - Cellulose derivative composition for all-solid-state secondary battery binder - Google Patents

Abstract

The present invention relates to a cellulose derivative composition for an all-solid-state secondary battery binder. The cellulose derivative composition for an all-solid-state secondary battery binder of the present invention includes a compound represented by chemical formula 1. The present invention can maintain high solubility in an aqueous phase. Therefore, the present invention can reduce the formation of microgel, thereby improving the electrical characteristics of an all-solid-state secondary battery.

Description

Cellulose derivative composition for all-solid-state secondary battery binder {Cellulose derivative composition for all-solid-state secondary battery binder}

The present invention relates to a cellulose derivative composition for an all-solid secondary battery binder, and more particularly, to a cellulose derivative composition in which metal ions are substituted in multiples.

Since the lithium secondary battery has a high energy density compared to other batteries and can be reduced in size and weight, it is highly likely to be used as a power source for portable electronic devices and the like. Compared to other energy storage devices such as capacitors and fuel cells, it exhibits high storage capacity, excellent charging and discharging characteristics, and high processability, making it suitable for use in wearable devices, electric vehicles, and energy storage systems (ESS: energy storage). system) is receiving great attention as a next-generation energy storage device.

A lithium secondary battery may include a positive electrode, a negative electrode, and an electrolyte. In general, as a liquid electrolyte, a carbonate-based solvent in which lithium salt (LiPF ₆ ) is dissolved is widely used. Liquid electrolytes exhibit excellent electrochemical properties due to high mobility of lithium ions, but have safety problems due to explosion due to high flammability, volatility, and leakage.

Accordingly, research on an all-solid-state secondary battery using a solid electrolyte instead of a liquid electrolyte is being conducted. Since all-solid-state secondary batteries can secure stability and mechanical strength, they are attracting attention in various application systems requiring high safety, such as electric vehicles, energy storage systems, and wearable devices.

An object to be solved by the present invention is to provide a binder having improved solubility in an aqueous solution and conductivity of lithium ions.

The problem to be solved by the present invention is not limited to the above-mentioned problems, and other problems not mentioned will be clearly understood by those skilled in the art from the following description.

A cellulose derivative composition for an all-solid secondary battery binder including a compound represented by Formula 1 according to the concept of the present invention may be included.

[Formula 1]

In Formula 1, R ₁ , R ₁ ', R ₂ , R ₂ ', R ₃ , R ₃ 'are independently any one of a carboxymethyl group substituted with a monovalent metal, a sulfur substituent, a phosphorus substituent, or hydrogen,

A carboxymethyl group corresponding to R ₁ , R ₂ , and R ₃ is -CH ₂ COOX, and X may be sodium (Na), potassium (K), rubidium (Rb), or cesium (Cs). A carboxymethyl group corresponding to R ₁ ', R ₂ ', and R ₃ ' is -CH ₂ COOY, and Y may be lithium (Li).

Sulfur substituents corresponding to R ₁ , R ₂ , and R ₃ are —SO ₃ X, and X may be any one of sodium (Na), potassium (K), and cesium (Cs) among rubidium (Rb). A sulfur substituent corresponding to R ₁ ', R ₂ ', and R ₃ ' is -SO ₃ Y, and Y may be lithium (Li).

The phosphorus substituent corresponding to R ₁ , R ₂ , R ₃ is -PO ₃ X or -PO ₃ X ₂ , where X is any one of sodium (Na), potassium (K), and cesium (Cs) among rubidium (Rb). can be A phosphorus substituent corresponding to R ₁ ', R ₂ ', and R ₃ ' is -PO ₃ Y or -PO ₃ Y ₂ , where Y may be lithium (Li).

According to the present invention, since monovalent metal ions are substituted into the cellulose derivative composition, hydrophobic properties due to attraction between cellulose polymers can be suppressed and high solubility in an aqueous solution can be maintained. As a result, it is possible to reduce the formation of microgel and improve the electrical characteristics of the all-solid-state secondary battery.

Also, according to the present invention, the cellulose derivative composition may include a substituent in which lithium ion is substituted. Accordingly, lithium ion conduction characteristics are improved, and even when an electrolyte component is excluded from the electrode, a lithium ion transfer path is provided through the binder, thereby lowering interfacial resistance inside the secondary battery and enabling rapid lithium ion transport. As a result, electrical characteristics of the all-solid-state secondary battery can be improved.

The effects of the present invention are not limited to the effects mentioned above, and other effects not mentioned will be clearly understood by those skilled in the art from the description below.

1 is a cross-sectional view showing an all-solid-state secondary battery including a cellulose derivative composition for an all-solid-state secondary battery binder according to an embodiment of the present invention.
2 is a flowchart illustrating a method of manufacturing a negative electrode of an all-solid-state secondary battery according to an embodiment of the present invention.
3 is a graph showing the number of microgels in binder solutions in Examples 1 to 3 and Comparative Example 1.
4 is a graph showing charge and discharge capacities of negative electrodes in Examples 4 to 6 and Comparative Example 2.
5 is a graph showing life characteristics of negative electrodes in Examples 7 to 9 and Comparative Example 3.

Advantages and features of the present invention, and methods of achieving them, will become clear with reference to the detailed description of the following embodiments taken in conjunction with the accompanying drawings. However, the present invention is not limited to the embodiments disclosed below, but may be implemented in various different forms, and only the present embodiments allow the disclosure of the present invention to be complete, and the common knowledge in the art to which the present invention belongs. It is provided to fully inform the holder of the scope of the invention, and the present invention is only defined by the scope of the claims. Like reference numbers designate like elements throughout the specification.

Terminology used herein is for describing the embodiments and is not intended to limit the present invention. In this specification, singular forms also include plural forms unless specifically stated otherwise in a phrase. As used herein, 'comprises' and/or 'comprising' means that a stated component, step, operation, and/or element is the presence of one or more other components, steps, operations, and/or elements. or do not rule out additions.

In addition, the embodiments described in this specification will be described with reference to cross-sectional views and/or plan views, which are ideal exemplary views of the present invention. In the drawings, the thicknesses of films and regions are exaggerated for effective explanation of technical content. Accordingly, the shape of the illustrative drawings may be modified due to manufacturing techniques and/or tolerances. Therefore, embodiments of the present invention are not limited to the specific shapes shown, but also include changes in shapes generated according to manufacturing processes. Accordingly, the regions illustrated in the drawings have schematic properties, and the shapes of the regions illustrated in the drawings are intended to illustrate a specific shape of a region of a device and are not intended to limit the scope of the invention.

Terms used in the embodiments of the present invention may be interpreted as meanings commonly known to those skilled in the art unless otherwise defined.

1 is a cross-sectional view showing an all-solid-state secondary battery including a cellulose derivative composition for an all-solid-state secondary battery binder according to an embodiment of the present invention.

Referring to FIG. 1 , an all-solid-state secondary battery 10 according to an embodiment of the present invention may include a positive electrode 100, a negative electrode 200, and a solid electrolyte layer 300. The positive electrode 100 and the negative electrode 200 may be disposed to face each other with the solid electrolyte layer 300 interposed therebetween.

The all-solid-state secondary battery 10 may be, for example, a lithium secondary battery. The cathode 100 may include a cathode active material. The cathode active material may include at least one of sulfur, LiCoO ₂ , LiNiO ₂ , LiNi _x Co _y Mn _z O ₂ (x+y+z=1), LiMn ₂ O ₄ , and LiFePO ₄ .

The positive electrode 100 may further include a conductive material. The conductive material may improve electrical conductivity of the positive electrode 100 . For example, the conductive material may include at least one of conductive amorphous carbon, carbon nanotubes, and graphene.

The anode 200 may include an anode active material. The anode active material is a high-capacity anode material coated with an electronic conductive layer such as graphite, hard carbon, soft carbon, carbon nanotube, graphene, redox graphene, carbon fiber, amorphous carbon, silicon-carbon composite (SiC), or carbon ( At least one of silicon or silicon oxide (SiO _X ), tin (Si), cobalt oxide (CoO _X ), and iron oxide (FeO _X )) may be included.

The positive electrode 100 and the negative electrode 200 may not include an electrolyte. In general, an electrolyte may be added to the positive electrode 100 and the negative electrode 200 of the all-solid secondary battery 10 . Even when the electrolyte is not added to the positive electrode 100 and the negative electrode 200 by including the cellulose derivative composition according to an embodiment of the present invention according to an embodiment of the present invention described later is not secured, the binder through the binder An additional lithium ion transport path may be provided to lower interfacial resistance inside the secondary battery and enable fast lithium ion transport.

The negative electrode 200 may further include a mixed binder composition. The mixed binder composition may include a cellulose derivative composition and a styrene-butadiene rubber (SBR) emulsion. Accordingly, the mixed binder composition may be a mixed aqueous binder.

The cellulose derivative composition may include a compound represented by Formula 1 below.

[Formula 1]

In the compound, R ₁ , R ₁ ', R ₂ , R ₂ ', R ₃ , and R ₃ ', which are present in the polymer structure, are functional groups of repeating units, and are independently of the first monovalent metal (X) or second metal (X). The monovalent metal (Y) may have a structure of any one of a substituted carboxymethyl group, a sulfur substituent, a phosphorus substituent, or hydrogen.

A carboxymethyl group corresponding to R ₁ , R ₂ , and R ₃ is -CH ₂ COOX, and X may be sodium (Na), potassium (K), rubidium (Rb), or cesium (Cs). A carboxymethyl group corresponding to R ₁ ', R ₂ ', and R ₃ ' is -CH ₂ COOY, and Y may be lithium (Li).

Sulfur substituents corresponding to R ₁ , R ₂ , and R ₃ are —SO ₃ X, and X may be any one of sodium (Na), potassium (K), and cesium (Cs) among rubidium (Rb). A sulfur substituent corresponding to R ₁ ', R ₂ ', and R ₃ ' is -SO ₃ Y, and Y may be lithium (Li).

The phosphorus substituent corresponding to R ₁ , R ₂ , R ₃ is -PO ₃ X or -PO ₃ X ₂ , where X is any one of sodium (Na), potassium (K), and cesium (Cs) among rubidium (Rb). can be A phosphorus substituent corresponding to R ₁ ', R ₂ ', and R ₃ ' is -PO ₃ Y or -PO ₃ Y ₂ , where Y may be lithium (Li).

Functional groups corresponding to R ₁ , R ₂ , and R ₃ may include a first monovalent metal, and functional groups corresponding to R ₁ ', R ₂ ', and R ₃ ' may include a second monovalent metal. . Here, the first monovalent metal may be any one of sodium (Na), potassium (K), and cesium (Cs) among rubidium (Rb), and the second monovalent metal may be lithium (Li). Each of the first monovalent metal and the second monovalent metal may be an alkali metal. That is, the cellulose derivative composition may be a composition in which alkali metal ions are substituted in multiple numbers.

In the conventional binder composition, due to the strong hydrophobicity of the cellulose polymer, a large number of aggregated microgels may be formed without being sufficiently dissolved in the aqueous solution. If these microgels still remain during the preparation of the electrode slurry, scratches are formed on the electrode plate during coating, or the thickness of the electrode is partially thickened in the microgel aggregation portion, thereby increasing the possibility of short circuit or leakage current. That is, electrical characteristics of the all-solid-state secondary battery may be deteriorated.

According to embodiments of the present invention, by substituting the monovalent metal ions in the cellulose derivative composition, it is possible to maintain high solubility in an aqueous solution by suppressing strong hydrophobic properties between cellulose polymers. As a result, it is possible to reduce the formation of microgels, thereby solving the above-mentioned problems.

In addition, the cellulose derivative composition according to embodiments of the present invention may include a substituent in which lithium ions are substituted. Accordingly, lithium ion conduction characteristics are improved, and even when an electrolyte component is excluded from the electrode, a lithium ion transfer path is provided through the binder, thereby lowering interfacial resistance inside the secondary battery and enabling rapid lithium ion transport. As a result, the electrochemical performance of the all-solid secondary battery electrode can be improved.

The cellulose derivative composition includes cellulose, methyl cellulose, ethyl cellulose, butyl cellulose, hydroxypropyl cellulose, cellulose nitrate, cellulose acetate ( cellulose acetate), cellulose acetate propionate, cellulose acetate butyrate, or carboxymethyl cellulose, including a derivative of at least one of Xanthan Gum, Pectin, Guar Gum, and Dextran can do. The cellulose derivative composition may include a structure in which carboxylic acid, sulfonic acid, phosphoric acid, or the like is substituted in the cellulose derivative structure.

The weight ratio of the active material particles in the negative electrode 200 may be 80 wt% to 99 wt%, preferably 90 wt% to 99 wt%. In the mixed binder composition, the weight ratio between the cellulose derivative and the SBR emulsion may be 99:1 to 1:99, preferably 90:10 to 60:40. The cellulose derivative composition may also be applied to the positive electrode 100 .

A solid electrolyte layer 300 may be disposed between the anode 100 and the cathode 200 . The solid electrolyte layer 300 may serve to deliver ions to the positive electrode 100 and the negative electrode 200 .

The solid electrolyte layer 300 may include at least one of oxide-based, phosphate-based, sulfide-based, and polymer-based materials. The inorganic solid electrolyte layer 300 may be formed in the form of a film having a certain thickness (30 to 2000 μm) through a cold or high temperature sintering process. The solid electrolyte layer 300 made of a polymer-based material or made of a composite electrolyte mixed with an inorganic solid electrolyte may be formed in the form of a film having a certain thickness (30 to 1000 μm) through a coating method. For example, the solid electrolyte layer 300 may further include at least one of a polymer binder, an organic scaffold, and an inorganic scaffold. A polymer binder, an organic scaffold, or an inorganic scaffold may increase mechanical strength of the solid electrolyte layer 300 . The polymeric binder may include, for example, polytetrafluoroethylene, polyvinylidene fluoride, poly(ethylene oxide), polyacrylonitrile, It may include at least one of hydroxypropyl cellulose, carboxymethyl cellulose, styrene-butadiene, and nitrile-butadiene rubber. As another example, the solid electrolyte layer 300 may not include a polymer binder, an organic scaffold, or an inorganic scaffold.

For example, the oxide-based material of the solid electrolyte layer 300 may include a garnet-type material having a composition of Li _7-3x+yz A _x La _3-y B _y Zr _2-z C _z O ₁₂ . Here, A is any one of aluminum (Al) and gallium (Ga), B is any one of calcium (Ca), strontium (Sr), barium (Ba), C is tantalum (Ta), niobium (Nb), anti It may be any one of mony (Sb) and bismuth (Bi). In particular, in the case of an oxide-based material having a Li _7-x A _x La ₃ Zr ₂ O ₁₂ structure, elements such as aluminum and gallium are used as doping elements at the Li site (0-0.3 mol ratio), and niobium and tantalum are used at the Zr site. A material doped with an element such as a doping element (0 to 0.3 mol ratio) may be used. As another example, the oxide-based material is a perovskite structure material, and Li _3x La _(2/3)-x □ _(1/3)-2x TiO ₃ (LLTO, 0<x<0.16, □ : vacancy) may be included.

The phosphate-based material of the solid electrolyte layer 300 may include, for example, a material having a NAISICON structure such as Li _1+x Al _x Ti _2-x (PO ₄ ) ₃ (x=0 to 0.4). there is.

The sulfide-based material of the solid electrolyte layer 300 is, for example, Li _10±1 MP ₂ X ₁₂ (where M is germanium (Ge), silicon (Si), tin (Sn), aluminum (Al) or phosphorus (P)). Any one of them, X may be any one of sulfur (S) or selenium (Se).) may include a material of the composition. For example, materials such as Li ₁₀ SnP ₂ S ₁₂ , Li _4-x Sn _1-x As _x S ₄ (x=0~100), thio―lithium superionic conductor (thio-LISICON) group Li _3.25 Ge _0.25 P _0.75 S ₄ , Li ₁₀ GeP ₂ S ₁₂ and other substances, Li-argyrodite Li ₆ PS ₅ X (where X is any one of chlorine (Cl), bromine (Br) or iodine (I)) group Li ₆ PS ₅ Cl materials such as glass-ceramic structures, materials selected from Li ₂ S·P ₂ S ₅ (xLi ₂ S·(100-x)P ₂ S ₅ , x=0~100) group, glass structure Groups with Li ₂ P ₂ S ₅ , Li ₂ S SiS ₂ Li ₃ N, Li ₂ S P ₂ S ₅ LiI, Li ₂ S SiS ₂ Li _x MO _y , Li ₂ S GeS ₂ , Li ₂ S·B ₂ S ₃ ·LiI, and the like, may be any one material selected from the group of compounds that basically contain a chalcogenide element and lithium.

The polymer material of the solid electrolyte layer 300 is, for example, polyethylene oxide (PEO), polyvinyl chloride (PVC), polyacrylonitrile (PAN), poly(methyl methacrylate) (PMMA), polyvinylidene fluoride (PVDF), polyvinylidene fluoride-hexafluoropropylene (P(VDF-HFP)) may include at least one of copolymers. At this time, the lithium salt included in the polymeric material is LiCl, LiBr, LiI, LiClO4, LiBF ₄ , LiB ₁₀ Cl ₁₀ , LiPF ₆ , LiCF ₃ SO ₃ , LiCF ₃ CO ₂ , LiAsF ₆ , LiSbF ₆ , LiAlCl ₄ , CH ₃ SO ₃ Li, CF ₃ SO ₃ Li, LiSCN, LiC(CF ₃ SO ₂ ) ₃ , (CF ₃ SO ₂ ) ₂ NLi, LiFSI, LiTFSI, LiBETI, LiBPB, LiCTFSI, LiTDI, and LiPDI. can

2 is a flowchart illustrating a method of manufacturing a negative electrode of an all-solid-state secondary battery according to an embodiment of the present invention.

Referring to FIG. 2 , a method of manufacturing the negative electrode 200 of the all-solid-state secondary battery 10 according to an embodiment of the present invention will be described. In this embodiment, a method of manufacturing the negative electrode 200 is described, but the process described below may be applied to the positive electrode 100 as well as the negative electrode 200 .

The method for manufacturing the negative electrode 200 of the all-solid-state secondary battery 10 according to an embodiment of the present invention is to prepare a cellulose derivative composition in which multiple metal ions are substituted through a cation exchange reaction (S1), Preparing a binder solution including a substituted cellulose derivative composition (S2), preparing a primary negative electrode slurry by stirring the electrode active material and the binder solution (S3), adding SBR emulsion to the primary negative electrode slurry and then stirring It may include preparing a final negative electrode slurry (S4), and applying the final negative electrode slurry to a negative electrode of an all-solid-state secondary battery by coating it on a current collector (S5).

A cellulose derivative composition in which multiple metal ions are substituted can be prepared through a cation substitution reaction (S1). _For example, sodium/lithium cations ( A cellulose derivative composition in which metal ions are substituted can be prepared by inducing a Na+/Li+) substitution reaction.

A binder solution containing a cellulose derivative composition substituted with multiple metal ions can be prepared (S2). For example, a (Na+Li)-CMC binder may be synthesized by inducing a sodium/lithium cation (Na+/Li+) substitution reaction and using a vacuum filtering and vacuum drying process for a cellulose derivative composition in which metal ions are substituted. A binder solution may be prepared by dissolving the (Na+Li)-CMC binder in a solvent (eg, water).

A primary negative electrode slurry may be prepared by stirring the electrode active material and the binder solution (S3). The electrode active material applied to the negative electrode is a material that is advantageous to mechanical deformation and has high electronic conductivity (more than 2S / cm), such as graphite, hard carbon, soft carbon, carbon nanotube, graphene, redox graphene, carbon fiber, amorphous Carbon, silicon-carbon composite (SiC), high-capacity anode material coated with an electron conductive layer such as carbon (silicon or silicon oxide (SiO _X ), tin (Si), cobalt oxide (CoO _X ), iron oxide (FeO _X ))) At least one of them may be included.

Specifically, a primary negative electrode slurry may be formed by uniformly mixing the binder solution with the electrode active material. Here, the weight ratio of the electrode active material and the binder solution may be between 80:20 and 99:1, preferably between 90:10 and 99:1.

A final anode slurry may be prepared by adding the SBR emulsion to the first anode slurry and then stirring it (S4). Specifically, the weight ratio between the cellulose derivative composition of the first anode slurry and the SBR emulsion may be 99:1 to 1:99, preferably 90:10 to 60:40.

By coating the final negative electrode slurry on the current collector, it can be applied to the negative electrode of the all-solid-state secondary battery (S5). Specifically, the final anode slurry is coated on a current collector as a thick film. For slurry coating, gravure coater method, small diameter gravure coater method, reverse roll coater method, transfer roll coater method, kiss coater method, dip coater method, knife coater method, air doctor blade coater method, blade coater method, bar coater method, die Thickening processes such as a coater method, a screen printing method, and a spray coating method may be applied. After application, solvent components of the final anode slurry are removed through high-temperature drying and vacuum drying processes. In the process of applying the slurry, the thickness of the negative electrode 200 may be adjusted between several micrometers and hundreds of micrometers. During drying, the temperature is between 80 and 120 ° C, and drying is performed in a vacuum state for about 10 to 20 hours to satisfy the residual solvent content of several ppm or less. Next, contact between coated electrode active material particles is improved through a compression process at a pressure of 100 to 200 MPa. For example, a hot-press process may be performed at a temperature between 100 and 300° C. to reduce porosity. The pore density of the electrode after pressing is about 10 to 20%, preferably 5% or less.

A solid electrolyte layer 300 and a counter electrode may be formed on the electrode. For example, the electrode may be the cathode 200 and the counter electrode may be the anode 100 . The current collector may be formed of a material such as lithium, sodium, magnesium, or potassium in a foil or powder form. The positive electrode 100 and the negative electrode 200 may include the current collector. The electrode and the counter electrode may be electrodes manufactured through the processes of S1 to S5 described above.

Finally, the all-solid secondary battery composed of the electrode/solid electrolyte layer/counter electrode is compressed at a pressure of 50 to 100 MPa to form a completely bonded electrode/electrolyte interface. If the final pressure process is not applied, high interfacial resistance may occur due to unstable contact between electrodes/electrolyte, which may hinder battery characteristics.

In order to evaluate the solubility of the cellulose derivative composition in an aqueous solution, a binder solution (1-2 wt% de-ionized water) was prepared and coated on a transparent sheet with a doctor blade method to analyze the number of microgels (Examples 1 to 20 below). Example 3 and Comparative Example 1). When preparing the binder solution, a mixing process was applied at 1500 to 2000 rpm using a mixer, and the time of the mixing process was between 30 and 60 minutes. At this time, for accurate comparison, when comparing the number of microgels according to the type of cellulose derivative composition, a binder solution having the same concentration was prepared and coated with the same thickness while applying the same mixing time. The doctor blade gap was adjusted between 100 and 200 μm.

Example 1

(Na+Li)-CMC binder was synthesized from sodium CMC (Na-CMC). Na-CMC binder was added to 150ml of ethanol/de-ionized water (90:10, volume ratio) mixture solution containing 7g of Lithium hydroxide monohydrate (LiOH H ₂ O) and reacted for 1 hour to allow sodium/lithium A cation (Na+/Li+) substitution reaction was induced. Then, (Na+Li)-CMC binder was synthesized through vacuum filtering and vacuum drying process for 24 hours. A binder solution (1 wt% in water) was prepared using the (Na+Li)-CMC binder prepared for the measurement of the number of microgels. At this time, the binder was dissolved in the solvent by stirring at 1500 rpm for 30 minutes using a mixer, and the binder solution was coated on a transparent sheet through a doctor blade method with a gap of 100 μm. The number of microgels was measured with the naked eye in an area of 5 × 5 cm ² .

Example 2

Na-CMC was added to a mixed solution of hydrochloric acid/ethanol (15:85, volume ratio) and reacted for 3 hours to synthesize carboxylic acid (H-CMC), which was then collected by vacuum filtration. Next, add 150ml of ethanol/water (de-ionized water) (90:10, volume ratio) mixed solution containing 7g Potassium hydroxide (KOH) and react for 1 hour to induce potassium/lithium cation (K+/Li+) substitution reaction. did. Then, a (K+Li)-CMC binder was synthesized through vacuum filtering and vacuum drying for 24 hours. Measurement of the number of microgels was the same as in Example 1 except that the (K+Li)-CMC binder was used.

Example 3

(Rb+Li)-CMC binder was prepared in the same process as in Example 2, except that an aqueous solution of Rubidium hydroxide monohydrate (RbOH H ₂ O) was used as a substitution solution instead of the aqueous solution of potassium hydroxide (KOH) in Example 2. synthesized. Measurement of the number of microgels was the same as in Example 1 except that the (Rb+Li)-CMC binder was used.

Comparative Example 1

In order to compare the multiple metal ion substitution effects of Examples 1 to 3, Na-CMC was selected as a comparative example and the number of microgels was measured in the same manner as in Example 1.

Figure 3 shows the results of measuring the number of microgels in the binder solution (1 wt% in de-ionized water) in Examples 1 to 3 and Comparative Example 1. It was observed that the number of microgels decreased in the order of (Na + Li), (K + Li), and (Rb + Li), and in the case of (Na + Li), the number of microgels was similar to or greater than that of pure Na.

According to an embodiment of the present invention, formation of microgel can be reduced by multiple substitution of metal ions in the cellulose derivative composition, and lithium ion conduction properties can be improved by including a substituent in which lithium ions are substituted.

FIG. 4 shows a graph comparing charge and discharge capacities of negative electrodes according to types of cellulose derivative compositions in which metal ions are polysubstituted (Examples 4 to 6 and Comparative Example 2 below).

Example 4

Using natural graphite as the electrode active material, a mixed binder of (Na+Li)-CMC and Styrene-butadiene rubber (SBR) as the binder, and de-ionized water as the solvent, the electrode is free of electrolyte components through a slurry process. was manufactured. The composition of the electrode is natural graphite:(Na+Li)-CMC:SBR=97:2:1 by weight. In order to precisely mix the slurry, it was mixed in the range of 1000 to 2000 rpm using a planetary mixer. To prepare the electrode slurry, first, natural graphite and (Na+Li)-CMC binder solution (1.5 wt% in deionized water) were mixed at 1500 rpm for 10 minutes. Next, an additional SBR emulsion solution (40wt%) was added and mixed again for 10 minutes. Electrodes were coated on nickel foil in a doctor blade method. After coating, initial drying was performed at 100 ° C, vacuum drying was performed at 90 ° C for 10 to 15 hours, and the density of the electrode was increased through a compression process. As a counter electrode, a lithium foil with a thickness of 300 μm was used to construct a graphite/lithium half-cell. As a solid electrolyte layer between both electrodes, Li ₆ PS ₅ Cl (LPSCl) was used. In order to manufacture an all-solid-state secondary battery, first, the LPSCl solid electrolyte layer was pre-pressurized at a pressure of 50 Mpa to a thickness of 1000 μm. Next, a (Na+Li)-CMC binder-based graphite electrode was brought into contact with one side of LPSCl, and a close interface was formed at 350 MPa pressure. Then, after contacting lithium foil on the opposite side of LPSCl, a 50Mpa pressure was applied to complete an all-solid-state secondary battery.

Based on the CC-CV mode, the charging rate of 0.1C and the cut-off current were set to 1/10 in the voltage range of 0.01 to 2V, and then the charge and discharge characteristics of the all-solid-state secondary battery were measured. In addition, in order to improve the ion diffusion rate in the relatively slow electrode, all charge and discharge tests were measured at 60 °C.

Example 5

The same process as in Example 4 was applied except for using the (K+Li)-CMC binder synthesized in Example 2.

Example 6

The same process as in Example 4 was applied except for using the (Rb+Li)-CMC binder synthesized in Example 3.

Comparative Example 2

In Comparative Example 2, the same process as in Example 4 was applied, except that an all-solid-state secondary battery was manufactured using Na-CMC, a non-ionic conductive binder.

Referring to FIG. 4, the case where Li was included showed a higher capacity than the case where pure Na was included, and the capacity decreased in the order of (Na + Li), (K + Li), and (Rb + Li).

That is, the electrical characteristics of the all-solid-state secondary battery can be improved by the cellulose derivative composition according to the embodiment of the present invention. This is because, as described with reference to FIG. 3 , formation of microgels is reduced and lithium ion transport properties are improved by including substituents in which lithium ions are substituted.

5 shows a graph comparing lifespan characteristics of negative electrodes according to types of cellulose derivative compositions in which metal ions are substituted multiple times (Examples 7 to 9 and Comparative Example 3 below).

Example 7

In order to analyze the lifespan characteristics of an all-solid-state secondary battery to which (Na+Li)-CMC binder is applied, a charging rate of 0.1C and a cut-off current of 1/10 are set in the voltage range of 0.01 to 2 V based on the CC-CV mode. After that, 50 charge/discharge cycles were performed.

Example 8

The same process as in Example 7 was applied except for using the (K+Li)-CMC binder synthesized in Example 2.

Example 9

The same process as in Example 7 was applied except for using the (Rb+Li)-CMC binder synthesized in Example 3.

Comparative Example 3

In Comparative Example 3, the same process as in Example 7 was applied, except that an all-solid-state secondary battery was manufactured using Na-CMC, a non-ion conductive binder.

Referring to FIG. 5, the case in which Li was included showed higher lifespan characteristics than the case in which pure Na was included, and the capacity retention characteristics were higher in the order of (Na+Li), (K+Li), and (Rb+Li).

That is, the electrical characteristics of the all-solid-state secondary battery can be improved by the cellulose derivative composition according to the embodiment of the present invention. This is because, as described with reference to FIG. 3 , formation of microgels is reduced and lithium ion transport properties are improved by including substituents in which lithium ions are substituted.

Although the embodiments of the present invention have been described with reference to the accompanying drawings, those skilled in the art can implement the present invention in other specific forms without changing its technical spirit or essential features. You will understand that there is Therefore, it should be understood that the embodiments described above are illustrative in all respects and not restrictive.

10: All-solid secondary battery
100: anode
200: cathode
300: solid electrolyte layer

Claims (1)

A cellulose derivative composition for an all-solid secondary battery binder comprising a compound represented by Formula 1 below:
[Formula 1]

In Formula 1, R ₁ , R ₁ ', R ₂ , R ₂ ', R ₃ , R ₃ 'are independently any one of a carboxymethyl group substituted with a monovalent metal, a sulfur substituent, a phosphorus substituent, or hydrogen,
A carboxymethyl group corresponding to R ₁ , R ₂ , and R ₃ is -CH ₂ COOX, and X may be sodium (Na), potassium (K), rubidium (Rb), or cesium (Cs). A carboxymethyl group corresponding to R ₁ ', R ₂ ', and R ₃ ' is -CH ₂ COOY, and Y may be lithium (Li).
Sulfur substituents corresponding to R ₁ , R ₂ , and R ₃ are —SO ₃ X, and X may be any one of sodium (Na), potassium (K), and cesium (Cs) among rubidium (Rb). A sulfur substituent corresponding to R ₁ ', R ₂ ', and R ₃ ' is -SO ₃ Y, and Y may be lithium (Li).
The phosphorus substituent corresponding to R ₁ , R ₂ , R ₃ is -PO ₃ X or -PO ₃ X ₂ , where X is any one of sodium (Na), potassium (K), and cesium (Cs) among rubidium (Rb). can be A phosphorus substituent corresponding to R ₁ ', R ₂ ', and R ₃ ' is -PO ₃ Y or -PO ₃ Y ₂ , where Y may be lithium (Li).

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