KR20220157095A - Multi-layered negative electrode and secondary battery comprising the same - Google Patents

Abstract

The present invention relates to a multi-layered negative electrode and a secondary battery including the same. The multi-layered negative electrode according to an embodiment of the present invention includes: a current collector; a first layer formed on one side or both sides of the current collector and including a first negative electrode active material, a first binder, and a conductive material; and a second layer formed on the first layer and including a second negative electrode active material and a second binder.

Description

A negative electrode having a multi-layer structure and a secondary battery including the same

The present invention relates to a multi-layered negative electrode and a secondary battery including the negative electrode.

In the case of lithium secondary batteries, demand as an energy source is rapidly increasing as technology development and demand for mobile devices increase. Recently, use as a power source for electric vehicles (EV) and hybrid electric vehicles (HEV) has been realized. , The use area is also expanding for purposes such as power auxiliary power through gridization. Lithium secondary batteries are far superior to existing small-sized lithium secondary batteries because they must be able to be used for more than 10 years under harsh conditions in which charging and discharging by high current are repeated in a short time, along with high energy density and high output characteristics in a short time. Safety and long life properties are inevitably required.

In this regard, a carbon-based compound capable of reversible intercalation and deintercalation of lithium ions while maintaining structural and electrical properties as an anode active material of a conventional lithium secondary battery has been mainly used.

However, carbon-based compounds have a theoretical maximum capacity of 372 mAh/g, which limits capacity increase, making it difficult to play a sufficient role as an energy source for rapidly changing next-generation mobile devices.

Accordingly, in recent years, there have been many studies on anode materials by Li alloy reaction using silicon (Si), germanium (Ge), tin (Sn), and aluminum (Al), away from conventional carbon-based anode materials. It's going on.

However, in the case of such an alloy-based anode material, since the lifespan characteristic is remarkably low due to the large volume change that occurs during charging and discharging, it has great limitations in its use. In the case of silicon-based negative electrode materials, they experience a large volume change (~270%) between charging and discharging due to the implementation of high capacity, so they experience many difficulties in practical use. Due to this volume change, the contact between the particles becomes unstable, and the electron transfer path is lost and detached, so that the capacity cannot be expressed. . As a way to overcome the problem of volume change, the size and shape of the material is adjusted, and a method of forming a composite material with other materials with excellent electrical conductivity, surface treatment of the material, and various methods such as a new binder, etc. Efforts have been made to improve longevity.

In the application of high-capacity alloy-based active materials, the most attention has been paid to carbon-coated silicon oxide (SiO _x ) and nano-silicon-carbon composites. In the case of silicon oxide, it is interpreted to be composed of amorphous SiO, nano Si clusters, and SiO ₂ inside. Although the silicon cluster is very small at the level of 10 nm, it has an advantage in life, but the initial efficiency is low due to side reactions that occur in the beginning. It has low downsides.

In the case of silicon-carbon composite materials, the efficiency is relatively excellent, but it is difficult to control the particle size of nano-silicon and uniformly disperse it within the composite material. It has the advantage of being large and has excellent efficiency, and it is possible to apply various methods of forming composite materials with carbon-based materials.

Since these two types of materials are still insufficient in performance to be used alone, methods of mixing a small amount with graphite, an existing anode active material, are being applied. To this end, it is important to control the shape and size of the silicon active material, and in order to apply the active material with a large volume change, many studies are being conducted on the application of new binders suitable for active materials with a large volume change. ), and a binder with strong binding force to the active material, but there is a phenomenon in which the electrode becomes hard, which causes a fatal problem in the electrode manufacturing and battery assembly process, so additional research on this is in progress.

Anode graphite shows stable life characteristics compared to low theoretical capacity, while silicon composite material has high capacity, but has the disadvantage of rapid decrease in life due to large volume expansion during charging and discharging processes. As the electrode is manufactured by mixing the silicon-based material and the conventional graphite material, the two types of active materials must be mixed in a homogeneous form, the same conductive material and binder must be applied, and the electrode must be composed of the same composition. However, since the silicon-based material has a large volume change, its performance cannot be properly realized by applying a conventional binder for graphite, so there is a limit to its performance, and the amount of silicon-based material used cannot be increased.

The foregoing background art is technical information that the inventor possessed for derivation of the present invention or acquired during the derivation process of the present invention, and cannot necessarily be said to be known art disclosed to the general public prior to filing the present invention.

The present invention is to solve the above problems, and an object of the present invention is to manufacture a high-capacity electrode by minimizing the volume expansion of the negative electrode active material, thereby improving the mechanical stability, operation reliability, and lifespan of the electrode. And to provide a secondary battery comprising the same.

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

A negative electrode having a multi-layer structure according to an embodiment of the present invention includes a current collector; a first layer formed on one side or both sides of the current collector and including a first negative electrode active material, a first binder, and a conductive material; and a second layer formed on the first layer and including a second negative electrode active material and a second binder.

A negative electrode having a multi-layer structure according to another embodiment of the present invention includes a current collector; a second layer formed on one side or both sides of the current collector and including a second negative electrode active material and a second binder; and a first layer formed on the second layer and including a first negative electrode active material, a first binder, and a conductive material.

In one embodiment, the first negative active material is silicon, silicon oxide, carbon-coated silicon oxide, tin (Sn), tin oxide (SnO, SnO ₂ ), germanium (Ge), aluminum (Al), and antimony. It may include at least one selected from the group consisting of (Sb).

In one embodiment, the aqueous binder of the first binder, carboxymethyl cellulose (CMC), methyl cellulose (MC), hydroxypropyl cellulose (HPC), methyl hydroxypropyl cellulose (methyl hydroxypropyl cellulose; MHPC), ethyl hydroxyethyl cellulose (EHEC), methyl ethylhydroxyethyl cellulose (MEHEC), cellulose gum, polyacrylic acid (PAA), A- It includes at least one selected from the group consisting of PAA (alkali-acrylate, A is an alkali element), PVA (polyvinyl alcohol), alginic acid, and alginate, and is an organic type of the first binder. The binder may include at least one selected from the group consisting of carboxymethyl cellulose (CMC), polyacrylic acid (PAA), and alginic acid.

In one embodiment, the weight ratio of the first negative active material: the first binder: the conductive material may be 50 to 95:2.5 to 30:2.5 to 20.

In one embodiment, the second negative electrode active material may include at least one selected from the group consisting of artificial graphite, natural graphite, hard carbon, soft carbon, and Li ₄ Ti ₅ O ₁₂ .

In one embodiment, the aqueous binder of the second binder includes styrene-butadiene rubber (SBR), carboxymethyl cellulose (CMC), or both, and the organic binder of the second binder includes polyvinylidene fluoride (PVdF), It may include a PVdF copolymer or both.

In one embodiment, the weight ratio of the second negative electrode active material to the second binder may be 80 to 98:1 to 10.

In one embodiment, the second layer may further include a conductive material, and the weight ratio of the second negative electrode active material: the second binder: the conductive material may be 80 to 98:1 to 10:1 to 10.

In one embodiment, the conductive material of the first layer and the conductive material of the second layer are at least one selected from the group consisting of graphite, carbon black, graphene, carbon nanotubes, carbon fibers, and carbon nanofibers, respectively. one carbon-based conductive material; and a metal-based conductive material including at least one perovskite material selected from the group consisting of tin, tin oxide, titanium oxide, LaSrCoO ₃ and LaSrMnO ₃ .

In one embodiment, the current collector has a thickness of 1 μm to 100 μm, the first layer has a thickness of 5 μm to 100 μm, and the second layer has a thickness of 5 μm to 300 μm it could be

In one embodiment, on the first layer or the second layer, a first layer/second layer; or a second layer; may further include.

In one embodiment, the multi-layered negative electrode may have 2 to 10 layers in total of the first layer and the second layer.

A secondary battery according to another embodiment of the present invention includes a multi-layered negative electrode according to one embodiment or a multi-layered negative electrode according to another embodiment; a separator formed on the cathode; and an anode formed on the separator.

Unlike the conventional case of manufacturing a mixture of a silicon-based material and a graphite-based material, the multi-layer negative electrode according to an embodiment of the present invention applies the use of a binder and electrode composition optimized for each active material, and a bi-layer or By configuring in the form of a multi-layered structure, it is possible to maximize mechanical stability, operational reliability, and cycle performance of a secondary battery by manufacturing a high-capacity electrode by minimizing volumetric expansion of the negative electrode active material.

1 is a cross-sectional view of a multi-layered cathode according to an embodiment of the present invention.
2 is a cross-sectional view of a multi-layered cathode according to another embodiment of the present invention.
3 is a cross-sectional view showing the respective electrode configurations of Comparative Examples 1 to 4 and Examples 1 and 2 of the present invention.
4 is a scanning electron micrograph of artificial graphite and c-SiO used in the present invention.
5 is a scanning electron micrograph of each electrode of Comparative Examples 1 to 4 and Examples 1 and 2 of the present invention.
6 is charge/discharge curves of coin cells manufactured using electrodes of (a) Comparative Example 1 and (b) Comparative Example 2 of the present invention.
7 is charge/discharge curves of coin cells manufactured using the electrodes of Comparative Example 3, Comparative Example 4, Example 1 and Example 2 of the present invention.
8 is a graph showing cycle characteristics of coin cells manufactured using electrodes of Comparative Examples 1 and 2 of the present invention.
9 is a graph showing cycle characteristics of coin cells manufactured using the electrodes of Comparative Example 3, Comparative Example 4, Example 1 and Example 2 of the present invention.
10 is electron micrographs of coin cells manufactured using the electrodes of Comparative Example 1 and Comparative Example 2 of the present invention before and after charging and discharging.
11 is electron micrographs before/after charging and discharging of coin cells manufactured using the electrodes of Comparative Example 4, Example 1, and Example 2 of the present invention.
12 is a graph showing cycle characteristics (0.2 C current) of coin full cells using electrodes prepared in Comparative Example 4, Example 1, and Example 2 of the present invention as negative electrodes.
13 is a graph showing cycle characteristics (1.0 C current) of coin full cells using the electrodes prepared in Comparative Example 4, Example 1, and Example 2 of the present invention as a negative electrode.

Hereinafter, embodiments will be described in detail with reference to the accompanying drawings. However, since various changes can be made to the embodiments, the scope of the patent application is not limited or limited by these embodiments. It should be understood that all changes, equivalents or substitutes to the embodiments are included within the scope of rights.

Terms used in the examples are used only for descriptive purposes and should not be construed as limiting. Singular expressions include plural expressions unless the context clearly dictates otherwise. In this specification, terms such as "include" or "have" are intended to designate that there is a feature, number, step, operation, component, part, or combination thereof described in the specification, but one or more other features It should be understood that the presence or addition of numbers, steps, operations, components, parts, or combinations thereof is not precluded.

Unless defined otherwise, all terms used herein, including technical or scientific terms, have the same meaning as commonly understood by a person of ordinary skill in the art to which the embodiment belongs. Terms such as those defined in commonly used dictionaries should be interpreted as having a meaning consistent with the meaning in the context of the related art, and unless explicitly defined in the present application, they should not be interpreted in an ideal or excessively formal meaning. don't

In addition, in the description with reference to the accompanying drawings, the same reference numerals are given to the same components regardless of reference numerals, and overlapping descriptions thereof will be omitted. In describing the embodiment, if it is determined that a detailed description of a related known technology may unnecessarily obscure the gist of the embodiment, the detailed description will be omitted.

In addition, in describing the components of the embodiment, terms such as first, second, A, B, (a), and (b) may be used. These terms are only used to distinguish the component from other components, and the nature, order, or order of the corresponding component is not limited by the term.

Components included in one embodiment and components having common functions will be described using the same names in other embodiments. Unless stated to the contrary, descriptions described in one embodiment may be applied to other embodiments, and detailed descriptions will be omitted to the extent of overlap.

Hereinafter, a multi-layer structured negative electrode and a secondary battery including the negative electrode of the present invention will be described in detail with reference to examples and drawings. However, the present invention is not limited to these examples and drawings.

A negative electrode having a multi-layer structure according to an embodiment of the present invention includes a current collector; a first layer formed on one side or both sides of the current collector and including a first negative electrode active material, a first binder, and a conductive material; and a second layer formed on the first layer and including a second negative electrode active material and a second binder.

1 is a cross-sectional view of a multi-layered cathode according to an embodiment of the present invention.

Referring to FIG. 1 , a negative electrode 100 having a multilayer structure according to an embodiment of the present invention includes a current collector 110 , a first layer 120 and a second layer 130 .

A negative electrode having a multi-layer structure according to another embodiment of the present invention includes a current collector; a second layer formed on one side or both sides of the current collector and including a second negative electrode active material and a second binder; and a first layer formed on the second layer and including a first negative electrode active material, a first binder, and a conductive material.

2 is a cross-sectional view of a multi-layered cathode according to another embodiment of the present invention.

Referring to FIG. 2 , a negative electrode 100a having a multilayer structure according to another embodiment of the present invention includes a current collector 110 , a second layer 130 and a first layer 120 .

In the multi-layered cathode 100 of FIG. 1 and the multi-layered cathode 100a of FIG. 2 , only the order of the first layer 120 and the second layer 130 is changed, and the rest is the same.

In one embodiment, the current collector 110 is selected from the group consisting of copper, stainless steel, aluminum, nickel, titanium, calcined carbon, carbon, nickel, titanium, silver and gold on the surface of copper or stainless steel. It may contain at least any one. It may preferably contain copper or a copper alloy.

In one embodiment, the current collector 110 may have a thickness of 1 μm to 100 μm.

In one embodiment, the first layer 120 may be formed on one or both surfaces of the current collector and include a first negative active material, a first binder, and a conductive material.

In one embodiment, the first negative active material may have a high capacity and a large volume change during charging and discharging.

In one embodiment, the first negative active material is silicon, silicon oxide, carbon-coated silicon oxide, tin (Sn), tin oxide (SnO, SnO ₂ ), germanium (Ge), aluminum (Al) and antimony ( Sb) may include at least one selected from the group consisting of.

In one embodiment, the first negative electrode active material is not limited as long as it is a material containing Si.

In one embodiment, the first negative active material is, for example, a Si—C composite, SiO _x (0<x<2), metal-doped SiO _x (0<x<2), or a metal oxide coating. To include at least one selected from the group consisting of SiO _x (0 <x <2), C-SiO _x (0 <x <2), pure Si (pure Si) and Si alloy (Si-alloy) can More specifically, x may be 0.1≤x≤1.2, and most specifically, x=1.

In one embodiment, silicon-based oxide slightly increases resistance compared to artificial graphite, but is included in the first negative electrode active material layer in the above content range, thereby improving thermal stability by applying Si, which is a ceramic material containing silicon-based oxide. In addition, during charging and discharging, SiO participates in the reaction before artificial graphite, so that rapid charging characteristics can be improved, resulting in excellent battery performance. The C-Si composite is, for example, a configuration in which carbon material is coated on the surface of the particle by heating in a state in which carbon is bonded to silicon or silicon oxide particles, or carbon is dispersed in an atomic state inside the silicon particle It may be a configuration, and it is possible without being limited as long as it is a configuration in which carbon and silicon materials form a composite. The C-SiO _x (0<x<2) includes a composite or coated structure of silicon oxide and carbon.

In one embodiment, the metal-doped SiO _x (0<x<2) is rjt doped with at least one metal selected from the group consisting of Li, Mg, Al, Ca, Fe, and Ti. can When doped as described above, the initial efficiency of the SiO _x material can be increased by reducing the irreversible SiO ₂ phase of the SiO _x material or converting it into an electrochemically inactive metal-silicate phase, more preferable

In one embodiment, the metal oxide-coated SiO _x (0<x<2) may be, for example, Al ₂ O ₃ or TiO ₂ coated.

In one embodiment, the Si alloy (Si-alloy) is that Si is alloyed with a metal containing at least one selected from the group consisting of Zn, Al, Mn, Ti, Fe and Sn, and Solid solutions, intermetallic compounds, eutectic alloys, and the like may be cited, but are not limited thereto.

In one embodiment, the first binder may be a water-based binder in the case of using a water-based process, or may be a polymer material having a high modulus.

In one embodiment, the aqueous binder of the first binder, carboxymethyl cellulose (CMC), methyl cellulose (MC), hydroxypropyl cellulose (HPC), methyl hydroxypropyl cellulose (methyl hydroxypropyl cellulose; MHPC), ethyl hydroxyethyl cellulose (EHEC), methyl ethylhydroxyethyl cellulose (MEHEC), cellulose gum, polyacrylic acid (PAA), A- PAA (alkali-acrylate, A is an alkali element such as Li, Na, K), PVA (polyvinyl alcohol), alginic acid (alginic acid) and alginate (alginate) containing at least one selected from the group consisting of can

In one embodiment, when the first binder is organic, a binder having a high modulus while being soluble in an organic solvent may be used.

In one embodiment, the organic binder of the first binder may include at least one selected from the group consisting of carboxymethyl cellulose (CMC), polyacrylic acid (PAA), and alginic acid. have.

In one embodiment, the first binder is not limited as long as it is a component that assists in the bonding of the first negative electrode active material and the conductive material and the bonding to the current collector.

In one embodiment, the weight ratio of the first negative active material: the first binder: the conductive material may be 50 to 95:2.5 to 30:2.5 to 20.

In one embodiment, the first layer may have a thickness of 5 μm to 100 μm.

In one embodiment, the second layer 130 may be formed on the first layer 120 and include a second negative electrode active material and a second binder.

In one embodiment, the second negative electrode active material may include a material with a small volume change during charging and discharging.

In one embodiment, the second negative electrode active material may include at least one selected from the group consisting of artificial graphite, natural graphite, hard carbon, soft carbon, and Li ₄ Ti ₅ O ₁₂ .

Preferably, the second negative electrode active material may include artificial graphite. Artificial graphite has relatively superior lifespan characteristics compared to natural graphite, and thus, it is possible to compensate for deterioration in electrode lifespan and stability due to the use of a silicon-based active material as the first anode active material.

In one embodiment, when the second negative active material includes both artificial graphite and natural graphite, the natural graphite:artificial graphite weight ratio may be in the range of about 20:80 to 80:20. Within the above range, it is possible to secure additional capacity/output improvement through natural graphite while improving mechanical stability of an anode or secondary battery through artificial graphite. Preferably, a larger amount of artificial graphite may be included to improve the mechanical and chemical stability of the anode.

In one embodiment, the aqueous binder of the second binder includes styrene-butadiene rubber (SBR), carboxymethyl cellulose (CMC), or both, and the organic binder of the second binder includes polyvinylidene fluoride (PVdF), It may include a PVdF copolymer or both.

In one embodiment, the second layer may further include a conductive material. Even if you use it at this time, use the minimum amount.

In one embodiment, the conductive material of the first layer and the conductive material of the second layer are at least one selected from the group consisting of graphite, carbon black, graphene, carbon nanotubes, carbon fibers, and carbon nanofibers, respectively. one carbon-based conductive material; and a metal-based conductive material including at least one perovskite material selected from the group consisting of tin, tin oxide, titanium oxide, LaSrCoO ₃ and LaSrMnO ₃ .

In one embodiment, the weight ratio of the second negative electrode active material to the second binder may be 80 to 95:1 to 10. If the content of the binder increases beyond the above range, the energy density of the battery is lowered and the flow of electrons is hindered, so that the speed characteristics of the battery may be lowered. When the content of the binder is reduced, the binding force of the electrode is reduced, and the electrode may be separated from the current collector and the first electrode, and active material and conductive material particles may be separated to generate dust, which may cause defects.

In one embodiment, the weight ratio of the second negative electrode active material: the second binder: the conductive material may be 80 to 95:1 to 10:1 to 10. If the content of the conductive material exceeds the above range, the energy density of the battery is lowered, and when the weight of the conductive material is reduced, the electrical conductivity is lowered, resulting in unfavorable rate characteristics. If the content of the binder is increased, the energy density of the battery is lowered and the flow of electrons is hindered, so that the speed characteristics of the battery may be lowered. When the content of the binder decreases, the binding force of the electrode decreases, and the electrode may be separated from the current collector and the first negative electrode, and active material and conductive material particles may be separated to generate dust, which may cause defects.

In one embodiment, the second layer may have a thickness of 5 μm to 300 μm. The second negative active material layer including the graphite does not need to be formed too thick because it only needs to exhibit an effect of improving a certain portion of the adhesion between the current collector and the active material, and when the content of graphite in the entire negative active material layer increases, output characteristics rather However, the overall performance of the secondary battery in terms of capacity and lifespan characteristics may be deteriorated, which is undesirable.

In one embodiment, on the first layer 120 or the second layer 130, the first layer / second layer; or a second layer; may further include. In the multi-layer structure cathode 100 of FIG. 1, the first layer/second layer on the second layer 130; or a second layer; and, in the multi-layered cathode 100a of FIG. 2, the first layer/second layer on the first layer 120; Or a second layer; may include.

Preferably, a first layer/second layer on the second layer 130; or a second layer; and may further include a second layer capable of minimizing volume expansion of the negative electrode active material during charging and discharging processes at the outermost part.

In one embodiment, the multi-layered negative electrode may have 2 to 10 layers in total of the first layer and the second layer. If the total is less than two layers, it becomes a single layer rather than a multilayer, and the effect of the present invention cannot be exhibited.

Unlike the conventional case of mixing a silicon-based material and a graphite-based material, the multi-layer negative electrode according to an embodiment of the present invention uses a binder optimized for each active material and applies an electrode composition to form a bi-layer or multi-layer structure. By configuring in the form of a structure, it is possible to maximize the cycle performance of the secondary battery.

A secondary battery according to another embodiment of the present invention includes a multi-layered negative electrode according to one embodiment or a multi-layered negative electrode according to another embodiment; a separator formed on the cathode; and an anode formed on the separator.

In one embodiment, the secondary battery may have a structure in which an electrode assembly including the negative electrode, the positive electrode, and the separator is embedded in a battery case together with an electrolyte solution.

In one embodiment, the positive electrode may be manufactured by, for example, applying a positive electrode mixture in which a positive electrode active material and a binder are mixed to a positive electrode current collector, and, if necessary, a conductive material and a filler as described in the negative electrode. can be added more.

In one embodiment, the cathode current collector is generally manufactured to a thickness of 3 μm to 100 μm, and is not particularly limited as long as it has high conductivity without causing chemical change to the battery. For example, stainless One selected from among steel, aluminum, nickel, titanium, and aluminum or stainless steel surface-treated with carbon, nickel, titanium, or silver may be used, and in detail, aluminum may be used. The current collector may form fine irregularities on its surface to increase the adhesion of the positive electrode active material, and may have various forms such as film, sheet, foil, net, porous material, foam, and non-woven fabric.

In one embodiment, the cathode active material may include, for example, a layered compound such as lithium cobalt oxide (LiCoO ₂ ) or lithium nickel oxide (LiNiO ₂ ) or a compound substituted with one or more metals; Formula Li _1+x Mn _2-x O ₄ (where x is 0 to 0.33), LiCoO ₂ , LiNiO ₂ , LiMn ₂ O ₄ , LiNi _0.5 Mn _1.5 O ₄ , LiNi _x Co _y Mn _z O ₂ (x +y+z=1), LiNi _x Co _y Al _z O ₂ (x+y+z=1), LiNi _x Co _y Mn _z Al _a O ₂ (x+y+z+a=1) and xLi ₂ MnO ₃ -(1-x)LiMO ₂ (0<x<1, M=including at least one of Mn, Ni, and Co), LiFePO ₄ , LiMnPO ₄ , LiMn _1-x Fe _x O ₄ (0<x< 1), lithium manganese oxides such as LiMnO ₃ , LiMn ₂ O ₃ , and LiMnO ₂ ; lithium copper oxide (Li ₂ CuO ₂ ); vanadium oxides such as LiV ₃ O ₈ , LiV ₃ O ₄ , V ₂ O ₅ , and Cu ₂ V ₂ O ₇ ; Ni site type lithium nickel oxide represented by the formula LiNi _1-x MxO ₂ , where M = Co, Mn, Al, Cu, Fe, Mg, B or Ga, and x = 0.01 to 0.3; Formula LiMn _2-x MxO ₂ where M = Co, Ni, Fe, Cr, Zn or Ta and x =0.01 to 0.1 or Li ₂ Mn ₃ MO ₈ where M = Fe, Co, Ni, a lithium manganese composite oxide represented by Cu or Zn; LiMn ₂ O ₄ in which Li part of the formula is substituted with an alkaline earth metal ion; disulfide compounds; Fe ₂ (MoO ₄ ) ₃ etc. are mentioned, but it is not limited only to these.

In one embodiment, examples of the binder, the conductive material, the filler, the thickener, and the like are the same as described in the multi-layered negative electrode according to an embodiment of the present invention.

In one embodiment, the separator is an insulating thin film having high ion permeability and mechanical strength. The pore diameter of the separator is generally 0.01 μm to 10 μm, and the thickness is generally 5 μm to 300 μm. Examples of such a separator include olefin-based polymers such as chemical-resistant and hydrophobic polyethylene and polypropylene; A sheet or non-woven fabric made of glass fiber, polyterephthalate, polyimide, cellulose, or the like is used. When a solid electrolyte such as a polymer is used as the electrolyte, the solid electrolyte may serve as a separation membrane. Alternatively, an SRS safety reinforced separator in which a mixture of inorganic particles and a binder is coated on at least one surface of an olefin-based polymer may be used.

In one embodiment, the electrolyte may be a lithium salt-containing non-aqueous electrolyte, the lithium salt-containing non-aqueous electrolyte is composed of a non-aqueous electrolyte and a lithium salt, and the non-aqueous electrolyte includes a non-aqueous organic solvent, an organic solid electrolyte, and an inorganic solid. Electrolytes and the like are used, but are not limited to these.

In one embodiment, the non-aqueous organic solvent includes, for example, ethyl methyl carbonate, N-methyl-2-pyrrolidinone, propylene carbonate, ethylene carbonate, butylene carbonate, Dimethyl carbonate, diethyl carbonate, gamma-butylolactone, 1,2-dimethoxyethane, tetrahydroxyfuran, 2-methyl tetrahydrofuran, dimethylsulfoxide, 1,3-dioxorane, form Amides, dimethylformamide, dioxolane, acetonitrile, nitromethane, methyl formate, methyl acetate, phosphoric acid triesters, trimethoxy methane, dioxorane derivatives, sulfolane, methyl sulfolane, 1,3-dimethyl-2 -At least one aprotic organic solvent selected from the group consisting of imidazolidinone, propylene carbonate derivative, tetrahydrofuran derivative, ether, methyl propionate and ethyl propionate may be used.

In one embodiment, the organic solid electrolyte includes, for example, polyethylene derivatives, polyethylene oxide derivatives, polypropylene oxide derivatives, phosphoric acid ester polymers, poly agitation lysine, polyester sulfide, polyvinyl alcohol, It may include at least one selected from the group consisting of polyvinylidene fluoride and a polymerization agent containing an ionic dissociation group.

In one embodiment, the inorganic solid electrolyte is, for example, 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 At least one selected from the group consisting of nitrides, halides, phosphides, sulfides and sulfates of Li may include

In one embodiment, the lithium salt is a material soluble in the nonaqueous electrolyte, for example, LiCl, LiBr, LiI, LiClO ₄ , LiBF ₄ , LiB ₁₀ Cl ₁₀ , LiPF ₆ , LiCF ₃ SO ₃ , LiCF3CO ₂ , LiAsF ₆ , LiSbF ₆ , LiAlCl ₄ , LiB(C ₂ O ₄ ) ₂ , LiB(C ₂ O ₄ )F ₂ , (FSO ₂ ) ₂ NLi, CH ₃ SO ₃ Li, (CF ₃ SO ₂ ) ₂ It may include at least one selected from the group consisting of NLi, lithium chloroborane, lithium lower aliphatic carbonate, lithium 4-phenyl borate, and imide.

In one embodiment, in the non-aqueous electrolyte, for the purpose of improving charge and discharge characteristics, flame retardancy, etc., for example, pyridine, triethylphosphite, triethanolamine, cyclic ether, ethylene diamine, n-glyme, hexa Triamides of phosphoric acid, nitrobenzene derivatives, sulfur, quinone imine dyes, N-substituted oxazolidinones, N,N-substituted imidazolidines, ethylene glycol dialkyl ethers, ammonium salts, pyrroles, 2-methoxyethanol, aluminum trichloride, etc. may be added. In some cases, halogen-containing solvents such as carbon tetrachloride and trifluoride ethylene may be further included to impart incombustibility, and carbon dioxide gas may be further included to improve high-temperature storage characteristics, and FEC (Fluoro-Ethylene carbonate), propene sultone (PRS), vinylene carbonate (VC), vinyl ethylene carbonate (VEC), and propane sultone (PS).

For example, lithium salts such as LiPF ₆ , LiClO ₄ , LiBF ₄ , LiN(SO ₂ CF ₃ ) ₂ are combined with cyclic carbonates of EC or PC, which are high dielectric solvents, and linear carbonates of DEC, DMC, or EMC, which are low-viscosity solvents. A lithium salt-containing non-aqueous electrolyte may be prepared by adding to a mixed solvent of

In one embodiment, the lithium secondary battery unit may be included as a power source of the device, or a battery module including the lithium secondary battery as a unit cell, a battery pack including the battery module, and the battery pack It can also be included as a power source.

In one embodiment, the device is, for example, a notebook computer, a netbook, a tablet PC, a mobile phone, an MP3 player, a wearable electronic device, a power tool, an electric vehicle (EV), a hybrid electric vehicle ( Hybrid Electric Vehicle (HEV), Plug-in Hybrid Electric Vehicle (PHEV), E-bike, E-scooter, electric golf cart; or It may be a power storage system, but is not limited thereto.

Since the structures and manufacturing methods of these battery modules, battery packs, and devices are well known in the art, a detailed description thereof is omitted in the present specification.

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

However, the following examples are only for illustrating the present invention, and the content of the present invention is not limited to the following examples.

[Comparative Example 1]

An anode was prepared using artificial graphite (AG). The composition of the electrode was composed of artificial graphite: conductive material (carbon black): binder (PVdF) = 93: 1: 6 ratio, and the loading level of the electrode was 5.4 mg / cm ² based on the active material. PVdF suitable for graphite materials was used as a binder and NMP (N-methyl-2-pyrrolidinone) was used as a solvent to prepare a slurry, which was then coated on copper foil as a current collector and dried in an oven at 120 °C.

[Comparative Example 2]

An anode was manufactured using carbon coated silicon monoxide (c-SiO). The composition of the electrode was composed of a ratio of c-SiO : conductive material (carbon black) : binder (CMC) = 60 : 30 : 10, and the loading level of the electrode was prepared at 0.9 mg/cm2 based on the active material. As a binder, CMC suitable for silicon-based materials was used, and as a solvent, a slurry was prepared using distilled water, and then coated on copper foil as a current collector and dried in an oven at 120 ° C.

[Comparative Example 3]

It is a result shown by combining the results obtained in Comparative Example 1 and Comparative Example 2. The results for the case where the electrodes of Comparative Example 1 and Comparative Example 2 were configured together were used. The ratio of graphite and c-SiO was configured as 5:1 in terms of mass ratio. The c-SiO ratio in the active material was adjusted to about 17%.

[Comparative Example 4]

An anode was prepared by mixing artificial graphite and carbon-coated silicon monoxide (c-SiO) together. The composition of the electrode was composed of artificial graphite: c-SiO: conductive material (carbon black): binder (PVdF) = 77.5: 15.5: 1: 6 ratio, and the loading level of the electrode was prepared at 6 mg / cm2. PVdF suitable for graphite materials was used as a binder and NMP (N-methyl-2-pyrrolidinone) was used as a solvent to prepare a slurry, which was then coated on copper foil as a current collector and dried in an oven at 120 °C.

[Example 1]

After preparing the electrode of Comparative Example 1, the electrode of Comparative Example 2 was coated again thereon to prepare an electrode. The electrode was composed of a bi-layer composed of two layers, graphite was made of a PVdF binder on the lower layer, and c-SiO was made of a CMC binder on the upper layer to form a bi-layer electrode.

[Example 2]

After preparing the electrode of Comparative Example 2, the electrode of Comparative Example 1 was coated again thereon to prepare an electrode. The electrode was composed of a bi-layer composed of two layers, c-SiO was made of CMC binder on the bottom layer, and graphite was made of PVdF binder on the top layer to form a bi-layer electrode.

3 is a cross-sectional view showing the respective electrode configurations of Comparative Examples 1 to 4 and Examples 1 and 2 of the present invention.

4 is a scanning electron micrograph of artificial graphite and c-SiO used in the present invention, and FIG. 5 is a scanning electron micrograph of each electrode of Comparative Examples 1 to 4 and Examples 1 and 2 of the present invention.

Referring to FIGS. 4 and 5 , Comparative Examples 1 and 2 show electrodes including graphite particles and c-SiO particles smaller than graphite. In the case of Comparative Example 4, graphite and c-SiO appeared together, and in Examples 1 and 2, c-SiO corresponding to the upper layer and the shape of the graphite electrode were observed in each layer.

[Production Example]

After pressing the dried electrode using a roll press, it was cut into a required size and dried in a vacuum oven at 120 °C for 8 hours or more to remove moisture. A 2032-size coin cell was fabricated inside an argon atmosphere glove box using the electrode thus prepared. At this time, lithium metal foil was used as the counter electrode, and as the electrolyte, 1 mol of LiPF ₆ /ethylene carbonate (EC): ethyl methyl carbonate (EMC) (volume ratio of 3: 7) was mixed with 5% by mass of FEC (fluoroethylene carbonate). It was prepared by adding, and an electrochemical cell was prepared using this. A PP separator was used as the separator.

[Evaluation Example 1]

A charge/discharge experiment was performed with a coin cell manufactured using the electrodes prepared in Comparative Examples 1 to 4 and Examples 1 to 2. Charging and discharging were performed in a constant current method to measure the reaction voltage and capacity of the battery. Constant current charging was performed from 0.0 to 1.5 V (vs. Li/Li ⁺ ) voltage range using a current of 100 mA/g based on the weight of the active material. This was repeated 50 times to conduct a 50 cycle experiment.

6 is charge/discharge curves of coin cells manufactured using electrodes of (a) Comparative Example 1 and (b) Comparative Example 2 of the present invention.

As shown in FIG. 6, graphite of Comparative Example 1 exhibited a capacity of about 330 mAh/g, and c-SiO exhibited a high reversible capacity of 1650 mAh/g.

7 is charge/discharge curves of coin cells manufactured using the electrodes of Comparative Example 3, Comparative Example 4, Example 1 and Example 2 of the present invention.

Referring to FIG. 7, since the graphite and c-SiO active material ratios were all set to 5:1, all capacities were around 520 mAh/g.

8 is a graph showing cycle characteristics of coin cells manufactured using electrodes of Comparative Examples 1 and 2 of the present invention.

As shown in FIG. 8, the cycle of Comparative Example 3 is calculated based on the case where the cycle characteristics of the coin cells manufactured using the electrodes of Comparative Examples 1 and 2 are manufactured at a standard mixing ratio of 6:1. did

9 is a graph showing cycle characteristics of coin cells manufactured using the electrodes of Comparative Example 3, Comparative Example 4, Example 1 and Example 2 of the present invention.

Referring to FIG. 9 , the performance of Comparative Example 4, which is a mixed electrode, was rapidly reduced, and Examples 1 and 2 showed greatly improved performance. In the case of Example 1, the performance was equivalent to that of Comparative Example 3 composed of the sum of the individual single-layer electrodes, and in the case of Example 2, the performance was further improved. This shows that the performance of each electrode is maintained to some extent even in the configuration of the multi-layer electrode, and the case where c-SiO, which deteriorates quickly, is in the upper layer shows equivalent performance to the case of each single-layer electrode. In addition, in Example 2, in which the graphite electrode having a small volume change is located on the upper side, more excellent cycle performance was obtained.

10 is electron micrographs before and after charging and discharging of coin cells manufactured using electrodes of Comparative Examples 1 and 2 of the present invention, and FIG. 11 is Comparative Example 4, Example 1 and Example 2 of the present invention It is an electron microscope picture before/after charging and discharging of a coin cell manufactured using the electrode of .

Referring to FIG. 10, the graphite of Comparative Example 1 showed no particular change even after 50 cycles, and in the case of Comparative Example 2, cracks were observed after 50 cycles, and the gaps were several microns in size.

Referring to FIG. 11, in the case of Comparative Example 4, which is a mixed electrode using a PVdF binder, the electrode was greatly damaged and cracked, and as a result, it was found that the performance rapidly deteriorated. In the case of Example 1, the c-SiO electrode was located on the upper layer, and its cracking was similar to that of Comparative Example 2. In the case of Example 2, cracks were not observed because the graphite layer was located on the upper layer. Through this, it can be expected that the graphite of the upper layer alleviates the damage of the electrode.

[Evaluation example 2]

A coin full cell was manufactured using the electrode prepared in Comparative Example 4, Example 1 and Example 2 as a negative electrode and evaluated. In the case of the anode, NMC622 (LiNi _0.6 Co _0.2 Mn _0.2 O ₂ ) was mixed with PVdF, a conductive material and binder, in a ratio of 90: 5: 5, and then an electrode was prepared with an NP ratio of 110%. After punching the anode to a diameter of 11 mm and the cathode to a diameter of 13 mm, a coin full cell was manufactured using the same electrolyte and separator as in Evaluation Example 1. This was charged and discharged in a constant current method to measure the reaction voltage and capacity of the battery. Constant current charging was performed from 3.0 to 4.3 V to 2.5 V using a current of 30 mA/g corresponding to about 0.2 C or 150 mA/g corresponding to 1.0 C based on the weight of the active material.

12 is a graph showing cycle characteristics (0.2 C current) of a coin full cell using the electrode prepared in Comparative Example 4, Example 1 and Example 2 of the present invention as a negative electrode, and FIG. 13 is Comparative Example 4 of the present invention, It is a graph showing cycle characteristics (1.0 C current) of coin full cells using the electrodes prepared in Examples 1 and 2 as cathodes.

As in the case of the half-cell, Comparative Example 4 exhibited rapid cycle degradation at a current of 0.2 C, but Examples 1 and 2 exhibited stable cycle characteristics up to 150 cycles or more. In the case of Example 2, 70% capacity was maintained up to 200 cycles.

The same result was shown even at a current of 1.0 C, which is a larger current, but the case of Example 2 showed better performance than Example 1.

As described above, although the embodiments have been described with limited drawings, those skilled in the art can apply various technical modifications and variations based on the above. For example, the described techniques may be performed in an order different from the method described, and/or components of the described system, structure, device, circuit, etc. may be combined or combined in a different form than the method described, or other components may be used. Or even if it is replaced or substituted by equivalents, appropriate results can be achieved.

Therefore, other implementations, other embodiments, and equivalents of the claims are within the scope of the following claims.

100, 100a: multi-layer cathode
110: entire collector
120: first layer
130: second layer

Claims (14)

current collector;
a first layer formed on one side or both sides of the current collector and including a first negative electrode active material, a first binder, and a conductive material; and
a second layer formed on the first layer and including a second negative electrode active material and a second binder;
including,
A cathode with a multi-layer structure.
current collector;
a second layer formed on one side or both sides of the current collector and including a second negative electrode active material and a second binder; and
a first layer formed on the second layer and including a first negative electrode active material, a first binder, and a conductive material;
including,
A cathode with a multi-layer structure.
According to claim 1 or 2,
The first negative active material is a group consisting of silicon, silicon oxide, carbon-coated silicon oxide, tin (Sn), tin oxide (SnO, SnO ₂ ), germanium (Ge), aluminum (Al), and antimony (Sb). Which includes at least one selected from
A cathode with a multi-layer structure.
According to claim 1 or 2,
The aqueous binder of the first binder is carboxymethyl cellulose (CMC), methyl cellulose (MC), hydroxypropyl cellulose (HPC), methyl hydroxypropyl cellulose (MHPC) ), ethyl hydroxyethyl cellulose (EHEC), methyl ethylhydroxyethyl cellulose (MEHEC), cellulose gum, PAA (polyacrylic acid), A-PAA (alkali-acrylate, A is an alkali element), PVA (polyvinyl alcohol), alginic acid (alginic acid), and at least one selected from the group consisting of alginate (alginate),
The organic binder of the first binder includes at least one selected from the group consisting of carboxymethyl cellulose (CMC), polyacrylic acid (PAA), and alginic acid,
A cathode with a multi-layer structure.
According to claim 1 or 2,
The weight ratio of the first negative active material: first binder: conductive material is 55 to 80: 10 to 40: 5 to 15,
A cathode with a multi-layer structure.
According to claim 1 or 2,
The second negative active material includes at least one selected from the group consisting of artificial graphite, natural graphite, hard carbon, soft carbon, and Li ₄ Ti ₅ O ₁₂ ,
A cathode with a multi-layer structure.
According to claim 1 or 2,
The aqueous binder of the second binder includes styrene-butadiene rubber (SBR), carboxymethyl cellulose (CMC) or both,
The organic binder of the second binder includes polyvinylidene fluoride (PVdF), a PVdF copolymer, or both,
A cathode with a multi-layer structure.
According to claim 1 or 2,
The weight ratio of the second negative electrode active material: the second binder is 80 to 95: 1 to 10,
A cathode with a multi-layer structure.
According to claim 1 or 2,
The second layer further includes a conductive material,
The weight ratio of the second negative active material: second binder: conductive material is 80 to 95: 1 to 10: 1 to 10,
A cathode with a multi-layer structure.
According to claim 9,
The conductive material of the first layer and the conductive material of the second layer may include at least one carbon-based conductive material selected from the group consisting of graphite, carbon black, graphene, and carbon nanotubes; and
a metal-based conductive material including at least one perovskite material selected from the group consisting of tin, tin oxide, titanium oxide, LaSrCoO ₃ and LaSrMnO ₃ ;
Which includes,
A cathode with a multi-layer structure.
According to claim 1 or 2,
The current collector has a thickness of 1 μm to 100 μm,
The first layer has a thickness of 5 μm to 100 μm,
Wherein the second layer has a thickness of 5 μm to 300 μm,
A cathode with a multi-layer structure.
According to claim 1 or 2,
on the first layer or the second layer, a first layer/second layer; Or a second layer; further comprising,
A cathode with a multi-layer structure.
According to claim 1 or 2,
In the multi-layered cathode, the total sum of the first layer and the second layer is 2 to 10 layers,
A cathode with a multi-layer structure.
Claim 1 or claim 2 of the multi-layer structure of the negative electrode;
a separator formed on the cathode; and
an anode formed on the separator;
including,
secondary battery.

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