KR102103895B1 - Negative electrode for lithium secondary battery comprising active material-non-coated portion and lithium secondary battery comprising the same - Google Patents

Abstract

The present invention relates to a negative electrode for a lithium secondary battery, wherein (i) an active material portion in which an active material layer is formed, and (ii) an uncoated portion in which an active material layer is not formed is formed on a current collector, and the lithium secondary according to the present invention Since the negative electrode for a battery is formed of a non-active part having an active material layer formed in addition to an active material part in which an active material layer is formed on the current collector, it accommodates changes in the volume of gas and negative active material generated during charging and discharging of the lithium secondary battery, thereby It is possible to improve the degradation of battery performance.

Description

A negative electrode for a lithium secondary battery containing an uncoated portion and a lithium secondary battery containing the same {NEGATIVE ELECTRODE FOR LITHIUM SECONDARY BATTERY COMPRISING ACTIVE MATERIAL-NON-COATED PORTION AND LITHIUM SECONDARY BATTERY COMPRISING THE SAME}

The present invention relates to a negative electrode for a lithium secondary battery including an uncoated portion and a lithium secondary battery including the same, and more particularly, to an unrecognized portion that can cope with changes in the volume of gases and active materials generated during charging and discharging of the battery, resulting in the battery The present invention relates to a lithium secondary battery negative electrode capable of suppressing performance degradation and a lithium secondary battery comprising the same.

With the development of technology and demand for mobile devices, the demand for secondary batteries as an energy source is rapidly increasing, and among such secondary batteries, lithium secondary with high energy density and operating potential, long cycle life, and low self-discharge rate Batteries have been commercialized and widely used.

In addition, in recent years, as interest in environmental problems has increased, electric vehicles (EVs) and hybrid electric vehicles (HEVs) that can replace fossil-fueled vehicles, such as gasoline vehicles and diesel vehicles, are one of the main causes of air pollution. A lot of research has been conducted on the back. As a power source such as an electric vehicle (EV) or a hybrid electric vehicle (HEV), a nickel metal hydride (Ni-MH) secondary battery is mainly used, but a lithium secondary battery having high energy density, high discharge voltage and output stability is used. Research is actively underway, and some are commercialized.

Meanwhile, a metal oxide such as LiCoO ₂ , LiMnO ₂ , LiMn ₂ O ₄ or LiCrO ₂ is used as a positive electrode active material constituting a positive electrode of a lithium secondary battery, and metal lithium, graphite as a negative electrode active material constituting the negative electrode Carbon-based meters such as (graphite) or activated carbon, or materials such as silicon oxide (SiO _x ) are used. Among the negative electrode active materials, metal lithium was mainly used initially, but as charging and discharging cycles progress, lithium atoms grow on the surface of metal lithium to damage the separator and damage the battery. Recently, carbon-based materials are mainly used. However, the carbon-based material has a disadvantage that the theoretical capacity is only about 400 mAh / g, so the capacity is small.

Accordingly, various studies have been conducted to replace the carbon-based material by using silicon (Si) having a high theoretical capacity (4,200 mAh / g) as a negative electrode active material. The reaction formula when lithium is incorporated in silicon is as follows:

[Scheme 1]

22Li + 5Si = Li ₂₂ Si ₅

However, the carbon-based material and the negative electrode active material such as silicon expands in volume according to the degree of filling, and its structure changes, and the electrode may be distorted due to the volume expansion, so that the life and performance of the battery may be significantly reduced. In addition, there is a problem in that gas is generated during charging and discharging, and adhesion between the electrode contactor and the active material is poor, which adversely affects battery performance.

Particularly, in the case of the silicon, the silicon volume expands up to 300% by lithium intercalation, and thus the negative electrode may be destroyed, and thus, a high cycle characteristic may not be exhibited. In addition, in the case of silicon, volume expansion occurs due to the lithium insertion as the cycle continues, pulverization, contact losses with conducting agents and current collectors, and unstable solids It can exhibit a fading mechanism such as the formation of a solid-electrolyte-interphase (SEI).

Therefore, when applying the graphite or silicon as a negative electrode active material, it is necessary to consider the effect of gas generation due to charging and discharging, and the degree of volume expansion due to a change in the structure of graphite or silicon according to the filling degree.

Accordingly, there is still a need to develop a technology capable of improving the deterioration of battery performance due to changes in the volume of gases and negative electrode active materials generated during charging and discharging of lithium secondary batteries, which are problems that may occur when using negative electrode active materials such as graphite or silicon. It is becoming.

The problem to be solved of the present invention is to accommodate the change in the volume of the gas and the negative electrode active material generated during charging and discharging of the lithium secondary battery through the uncoated portion formed on the current collector, thereby improving the deterioration of battery performance. It is to provide a negative electrode for a battery.

Another problem to be solved of the present invention is to provide a lithium secondary battery with improved deterioration of battery performance, including the negative electrode for a lithium secondary battery.

In order to solve the above problems, the present invention

An anode for a lithium secondary battery is provided on the current collector, wherein (i) an active material portion in which an active material layer is formed and (ii) an uncoated portion in which an active material layer is not formed are formed.

In addition, the present invention to solve the above other problems,

It provides a lithium secondary battery comprising the negative electrode for the lithium secondary battery.

The negative electrode for a lithium secondary battery according to the present invention is formed of a non-active part having no active material layer formed in addition to the active material portion in which the active material layer is formed on the current collector, so that the volume of gas and negative electrode active material generated during charging and discharging of the lithium secondary battery By accepting the change, it is possible to improve the problem of deterioration of battery performance.

1 is a cross-sectional view schematically showing a negative electrode for a conventional lithium secondary battery.
2 and 3 are cross-sectional and front views schematically showing a negative electrode for a lithium secondary battery according to an example of the present invention, respectively.
4 is a front view schematically showing a negative electrode for another type of lithium secondary battery.
5 is a front view schematically showing a negative electrode for a lithium secondary battery according to another example of the present invention.
6 and 7 are each a front view schematically showing a negative electrode for a lithium secondary battery according to another example of the present invention.
8 and 9 are front views schematically showing a negative electrode for a lithium secondary battery according to an embodiment of the present invention, respectively.
10 is a graph showing a result of measuring a capacity retention rate of a battery after 100 cycles for a lithium secondary battery according to an embodiment of the present invention.

Hereinafter, the present invention will be described in more detail to aid understanding of the present invention.

The terms or words used in the specification and claims should not be interpreted as being limited to ordinary or lexical meanings, and the inventor can appropriately define the concept of terms in order to best describe his or her invention. Based on the principle that it should be interpreted as meanings and concepts consistent with the technical spirit of the present invention.

The negative electrode for a lithium secondary battery according to the present invention is one in which (i) an active material portion in which an active material layer is formed and (ii) an uncoated portion in which an active material layer is not formed is formed on a current collector.

The active material portion corresponds to an active material layer containing a negative electrode active material in a conventional lithium secondary battery negative electrode.

The negative electrode for a lithium secondary battery of the present invention is divided into the active material layer by the non-coated portion where the active material layer is not formed, whereby the active material layer is formed and the active material layer is not formed.

The plain portion may be a portion in which the current collector is exposed to the outside through the plain portion because no active material layer is formed. That is, since the non-coated portion corresponds to an empty space existing between the active material layers (active material portion), gas generated in the active material layer can serve as a passage for collecting and moving the gas, and also change the volume of the active material layer. Since it can serve as an absorbable buffer, it is possible to improve the deterioration of battery performance due to the volume change of the gas and the active material layer.

The active material layer is divided into two or more bordered by the uncoated portion by the uncoated portion, whereby the negative electrode for a lithium secondary battery according to an example of the present invention may include two or more active material portions.

In addition, the negative electrode for a lithium secondary battery may include one or more of the uncoated portions, and specifically, the negative electrode for a lithium secondary battery may include two or more uncoated portions. Since the active material layer is divided by the non-coated portion, when two or more non-coated portions are included, three or more active material portions may be included.

The plain portion may be adjacent to two or more active material portions. Specifically, since the non-coated portion divides the active material layer as described above, the divided active material layers are positioned on both sides to form a shape adjacent to two or more active material portions. Therefore, the form in which only one active material part is adjacent to each other, that is, the position where the active material part is located on only one side of the non-coated part is not included by positioning the non-coated part on the edge of the current collector. As described above, when the plain portion is located on the border of the current collector, since the active material portion is located on the border of the current collector, there is no particular difference from the case where the side surface of the active material portion is exposed to the outside, so that the plain portion is formed. It is difficult to expect additional effects due to.

In addition, since the uncoated portion divides the active material layer as described above, the active material portion may be adjacent to one or more uncoated portions.

The plain portion may have a narrow width and a long belt-like shape, and the shape is not particularly limited. However, the plain portion is a straight line, a curved line, and a wave curve when the face of the current collector is viewed vertically from above. It may include one or more shapes selected from the group consisting of.

In particular, the non-coated portion may include a shape made of a wave curve, and when the non-coated portion includes a shape made of a wave curve, the contact surface between the non-coated portion and an active material portion adjacent to it can be widened. The volume change of the generated gas or the active material layer can be more effectively accepted.

Meanwhile, two or more of the non-coated portions may cross each other, and thus, a negative electrode for a lithium secondary battery according to an example of the present invention may include at least one crossing point where two or more of the non-coated portions cross each other. In this case, the active material part formed on the current collector may be adjacent to two or more plain parts regardless of the position.

In addition, the uncoated portion may cross a single uncoated portion with multiple uncoated portions, and thus, the negative electrode for a lithium secondary battery according to an example of the present invention crosses at least two uncoated portions at different locations with respect to one uncoated portion. It may contain two or more. In this case, the active material portion that is located adjacent to the intersection, that is, the reference portion of the one and the two or more non-parts that intersect it, the one and the two or more non-parts that cross the part. That is, it may be adjacent to three or more ignorance. Since the active material part of this type may additionally exist symmetrically around one uncoated part serving as the reference, the negative electrode for a lithium secondary battery according to an example of the present invention may include two or more active material parts adjacent to three or more uncoated parts. have. In addition, on the current collector, when there are two or more side-by-side forms in which two or more non-parts cross each other at different positions, for the one non-part, each of the two non-plain parts serving as a criterion for crossing, respectively, Two or more non-coated crossing parts may surround one active material part, and thus, in one example of the present invention, the negative electrode for a lithium secondary battery may include one or more active material parts adjacent to four or more non-coated parts.

The thickness of the active material portion formed on the current collector may be in the range of the thickness of a typical active material layer, specifically, 0.01 to 0.2 mm, more specifically 0.05 to 0.1 mm, more effectively the gas generated in the active material layer It can be discharged to the plain portion, and can also accept the volume change of the active material layer.

The active material part may have a width of 3 to 200 mm, specifically 5 to 50 mm, and more specifically 10 to 30 mm. At this time, the width of the active material portion indicates a width in a direction parallel to the longitudinal direction of the electrode, that is, when the active material portion is positioned on the electrode, it represents a value measured by measuring the width of the active material portion along the length direction of the electrode.

The plain portion may have a width of 0.1 to 5 mm, specifically, may have a width of 0.5 to 3 mm, and more specifically, may have a width of 1 to 2 mm.

At this time, the width of the plain portion indicates a width in a direction perpendicular to the length direction of the plain portion, that is, a width that is a direction perpendicular to the length direction of the plain portion, which may have a narrow, long strip-like shape. The value of the length is measured.

The width of the active material portion and the width of the plain portion may have a ratio of 2: 1 to 50: 1, and specifically, a ratio of 2.5: 1 to 20: 1.

When the width of the active material portion and the width of the non-coated portion are 2: 1 or more, while the volume of the active material and the volume of the active material and the volume of the active material can be smoothly received, the proportion of the non-coated portion becomes excessively large. The capacity may not be reduced, and when the width of the active material portion and the width of the non-coated portion are 50: 1 or less, the volume change of the gas and the active material generated from the active material may be smoothly accepted.

The ratio of the active material portion and the non-coated portion may also be represented by an area ratio, and in an example of the present invention, an area ratio of the active material portion and the non-coated portion may be 1.4: 1 to 40: 1, and specifically 1.6: 1 to 30: 1, and more specifically 3.5: 1 to 15: 1.

When the area ratio of the active material portion and the non-coated portion is 1.4: 1 or more, while the volume of the gas and the active material generated from the active material can smoothly accommodate the non-coated portion, the proportion of the non-coated portion becomes excessively large, and thus the capacity of the entire battery This may not be reduced, and when the area ratio of the active material portion and the non-coated portion is 40: 1 or less, the volume change of the gas and the active material generated from the active material may be appropriately accepted.

As the active material that may be included in the negative electrode for the lithium secondary battery, that is, as the negative electrode active material, a carbon material, lithium metal, silicon-based, tin, or the like, which can normally absorb and release lithium ions, may be used. Preferably, a carbon material can be used, and both low-crystalline carbon and high-crystalline carbon may be used as the carbon material. Soft carbon and hard carbon are typical examples of low crystalline carbon, and natural graphite, kish graphite, pyrolytic carbon, and liquid crystal pitch-based carbon fibers include high crystalline carbon. and high-temperature calcined carbons such as (mesophase pitch based carbon fiber), meso-carbon microbeads, mesophase pitches, and petroleum or coal tar pitch derived cokes. Examples of the silicon system include silicon, silicon oxide particles (SiO _x , 0 <x≤2), Si-metal alloys, and alloys of Si and silicon oxide particles (SiO _x , 0 <x≤2).

When the active material layer includes a carbon material active material as an active material, particularly when a graphite-based active material is included as a carbon material, the volume change during charging and discharging is relatively small, and gas generation is relatively small. It may be small, for example, the area ratio of the active material portion and the plain portion may be 3.5: 1 to 40: 1, specifically 3.5: 1 to 30: 1, and more specifically 7: 1 to 30: 1 Can be

When the active material layer includes a silicon-based active material as an active material, since the volume change is relatively large during charging and discharging, and gas generation tends to be large, it is necessary to increase the area of the non-coated part relatively, for example, the active material part and the plain material. The area ratio of the portion may be 1.4: 1 to 30: 1, specifically 1.5: 1 to 17: 1, and more specifically 1.6: 1 to 15: 1.

When the active material layer includes a silicon-based active material as an active material, considering that the silicon-based active material has a relatively large volume change during charging and discharging and a large amount of gas generation, the non-fat part can effectively accept the volume change and gas. , The lithium secondary battery negative electrode may be configured to include at least one crossing point where two or more of the uncoated sections cross each other. In addition, it may be configured to include a shape consisting of the above-described non-additive wave curve.

The negative electrode for a lithium secondary battery may be a stack type or a stack and folding type lithium secondary battery negative electrode.

The stacked lithium secondary battery may be a lithium secondary battery including an electrode assembly manufactured by vertically stacking a negative electrode, a separator, and a positive electrode, and the stack and folding type lithium secondary battery may have a positive electrode / separator / It is manufactured by rolling or folding a full cell of a cathode structure or a bicell of a cathode (cathode) / separator / cathode (anode) / separator / anode (cathode) structure using a continuous separation film of a long length. It may be a lithium secondary battery including an electrode assembly.

In the stack-type or stack-and-folding lithium secondary battery, the negative electrode and the positive electrode are each formed with an active material layer on the current collector, and the area of the current collector is 100 to 200% based on the area of the active material layer, Specifically, it may be 100 to 110%. At this time, in the case of the negative electrode, the area of the active material portion and the non-coated portion combined is the area of the active material layer.

Hereinafter, the negative electrode for a lithium secondary battery of the present invention will be described in more detail with reference to the drawings, but the drawings are only for illustrating the present invention and the scope of the present invention is not limited thereto. In the drawings of the present invention, the size of each component may be exaggerated for explanation, and may be different from the size actually applied.

1 is a sectional view schematically showing a negative electrode for a conventional lithium secondary battery. Referring to FIG. 1, the negative electrode for a lithium secondary battery is formed in a form in which the active material layer 20 is formed on the current collector 10.

In contrast, the negative electrode for a lithium secondary battery according to an example of the present invention includes an uncoated portion in addition to the active material layer. 2 and 3 respectively show a cross-sectional view and a front view schematically showing a negative electrode for a lithium secondary battery according to an example of the present invention.

2 and 3, the negative electrode for a lithium secondary battery according to an example of the present invention includes an active material part 200 on which an active material layer is formed on the current collector 100, and a solid part 300 on which an active material layer is not formed. ) Is formed.

Since the plain portion 300 is a portion in which an active material layer is not formed, the current collector 100 may be exposed to the outside through the plain portion 300. The plain part 300 is an empty space that exists between the active material parts 200, and can serve as a passage through which gases generated in the active material layer of the active material part 200 are collected and moved, and also the active material layer It can serve as a buffer that can absorb changes in volume.

2 and 3, the active material layer is divided into two or more by one plain portion 300, and accordingly, two or more active material portions 200 may be included. In addition, when two or more plain parts 300 are included, since the active material layer is divided by the plain parts 300, three or more active material parts 200 may be included.

As shown in FIG. 3, the uncoated portion 300 has a divided active material layer positioned at both sides, thereby being adjacent to two or more active material portions 200. In addition, since the uncoated portion 300 divides the active material layer, the active material portion 200 may be adjacent to one or more uncoated portions 300.

4 is a front view schematically showing another type of lithium secondary battery negative electrode. Referring to FIG. 4, since the uncoated portion 300 divides the active material layer into two or more borders of the uncoated portion 300, as shown in FIG. 4, one active material portion 200 in the uncoated portion 300 ), The form in which the active material portion 200 is located on only one side of the plain portion 300 is included in an example of the present invention. Does not work.

Referring to FIG. 3 again, the plain portion 300 has a narrow width and a long belt-like shape. The shape of the non-coated portion 300 is not particularly limited, but may include one or more shapes selected from the group consisting of a straight line, a curved line, and a wave curve when vertically looking down the surface of the electrode, that is, the current collector.

5 is a front view schematically showing a negative electrode for a lithium secondary battery according to another example of the present invention.

Referring to FIG. 5, the uncoated portion 300 includes a shape made of a wave curve, and thus, when the uncoated portion 300 includes a shape made of a wave curve, the active material portion adjacent to the uncoated portion 300 Since the contact surface with the 200 can be widened, the volume change of the gas or the active material layer generated in the active material layer can be more effectively accepted.

6 and 7 are each a front view schematically showing a negative electrode for a lithium secondary battery according to another example of the present invention.

Referring to FIG. 6, two or more non-parts 310, 321 and 322 may cross each other, and one or more intersections 331 and 332 where two or more non-parts 310, 321 and 322 cross each other. It can contain. In this case, the active material portion 200 formed on the current collector is adjacent to the two or more non-coated portions 310, 321, and 322 regardless of the position.

In addition, the uncoated portion may cross one uncoated portion 310 with multiple uncoated portions 321 and 322. As shown in FIG. 6, when two or more uncoated parts 321 and 322 cross one uncoated part 310 at different positions, the two intersections 331 and 332 where the uncoated parts cross each other are shown. Will be included. In this case, the active material portion 201 that is located adjacent to the intersections 331 and 332, that is, the reference plain portion 310 and the two plain portions 321 and 322 that intersect it, is one. The uncoated portion 310 and the two uncoated portions 321 and 322 intersecting it, that is, adjacent to the three uncoated portions 310, 321 and 322. In addition, the active material portion 202 of this type is additionally symmetrically centered on the plain portion 310 as a reference. Accordingly, two or more active material parts 201 and 202 adjacent to three or more non-coated parts may be included.

In addition, as shown in FIG. 7, on the current collector, for one uncoated portion 311, 312, two forms in which three uncoated portions 321, 322, and 323 cross each other at different positions exist side by side. In this case, two respective uncoated portions 311 and 312, which are the basis of crossing, and three uncoated portions 321, 322, and 323 crossing each of them may surround one active material portion 202. The active material portion 203 is adjacent to the four non-coated portions 311, 312, 322, and 323.

In addition, the present invention provides a lithium secondary battery comprising the negative electrode for a lithium secondary battery.

The lithium secondary battery may include a positive electrode, a negative electrode, and a separator interposed between the positive electrode and the negative electrode, and the lithium secondary battery may be a stack type or a stack and folding type lithium secondary battery. have.

The stacked lithium secondary battery may be a lithium secondary battery including an electrode assembly manufactured by vertically stacking a negative electrode, a separator, and a positive electrode, and the stack and folding type lithium secondary battery may have a positive electrode / separator / It is manufactured by rolling or folding a full cell of a cathode structure or a bicell of a cathode (cathode) / separator / cathode (anode) / separator / anode (cathode) structure using a continuous separation film of a long length. It may be a lithium secondary battery including an electrode assembly.

The positive electrode can be produced by a conventional method known in the art. For example, a mixture of a solvent, a binder, a conductive material, and a dispersant may be mixed with a positive electrode active material, if necessary, to prepare a slurry, and then coated (coated) on a current collector of a metal material, compressed, and dried to produce a positive electrode. have.

The current collector of the metal material is a metal having high conductivity, and is a metal to which the slurry of the positive electrode active material can be easily adhered, and is particularly limited as long as it has high conductivity without causing a chemical change in the battery in a voltage range of the battery. For example, stainless steel, aluminum, nickel, titanium, calcined carbon, or a surface treated with carbon, nickel, titanium, silver, or the like on the surface of aluminum or stainless steel may be used. In addition, it is also possible to increase the adhesion of the positive electrode active material by forming fine irregularities on the surface of the current collector. The current collector can be used in various forms such as a film, sheet, foil, net, porous body, foam, nonwoven fabric, and may have a thickness of 3 to 500 μm.

The positive electrode active material may be substituted with a layered compound such as lithium cobalt oxide [Li _x CoO ₂ (0.5 <x <1.3)], lithium nickel oxide [Li _x NiO ₂ (0.5 <x <1.3)] or an additional transition metal. compound; Lithium manganese oxides such as the formula Li _{1 + x} Mn _{2 - x} O ₄ (where x is 0 to 0.33), LiMnO ₃ , LiMn ₂ O ₃ , or [Li _x MnO ₂ (0.5 <x <1.3)]; Lithium copper oxide (Li ₂ CuO ₂ ); Vanadium oxide such as LiV ₃ O ₈ , LiFe ₃ O ₄ , V ₂ O ₅ , or Cu ₂ V ₂ O ₇ ; Ni-site type lithium nickel oxide represented by the formula LiNi _{1 - x} M _x O ₂ (where M = Co, Mn, Al, Cu, Fe, Mg, B or Ga, and x = 0.01 to 0.3); Formula LiMn _{2 - x} M _x O ₂ (where M = Co, Ni, Fe, Cr, Zn or Ta, x = 0.01 to 0.1) or Li ₂ Mn ₃ MO ₈ (where M = Fe, Co, Ni, Cu or Zn) lithium manganese composite oxide; LiMn ₂ O _{4 in} which a part of Li in the formula is substituted with alkaline earth metal ions; Disulfide compounds; Fe ₂ (MoO ₄ ) _{3 and the} like.

Examples of the solvent for forming the positive electrode include organic solvents such as NMP (N-methyl pyrrolidone), DMF (dimethyl formamide), acetone, and dimethyl acetamide or water, and these solvents may be used alone or in combination of two or more. Can be used in combination. The amount of the solvent used is sufficient to dissolve and disperse the positive electrode active material, the binder, and the conductive material in consideration of the coating thickness of the slurry and the production yield.

Examples of the binder include polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinylidenefluoride, polyacrylonitrile, polymethylmethacrylate, Polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, recycled cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, polyacrylic acid, ethylene-propylene-diene monomer (EPDM), Sulfonated EPDM, styrene butadiene rubber (SBR), fluorine rubber, poly acrylic acid and polymers substituted with hydrogen, Li, Na or Ca, or Various types of binder polymers such as various copolymers can be used.

The conductive material is not particularly limited as long as it has conductivity without causing a chemical change in the battery. For example, graphite such as natural graphite or artificial graphite; Carbon blacks such as acetylene black, ketjen black, channel black, panes black, lamp black, and thermal black; Conductive fibers such as carbon fibers and metal fibers; Conductive tubes such as carbon nanotubes; Metal powders such as fluorocarbon, aluminum, and nickel powders; Conductive whiskers such as zinc oxide and potassium titanate; Conductive metal oxides such as titanium oxide; Conductive materials such as polyphenylene derivatives may be used. The conductive material may be used in an amount of 1% to 20% by weight relative to the total weight of the positive electrode slurry.

The dispersant may be an aqueous dispersant or an organic dispersant such as N-methyl-2-pyrrolidone.

The negative electrode may be prepared by a conventional method known in the art, for example, by mixing and stirring the negative electrode active material and additives such as a binder and a conductive material to prepare a negative electrode active material slurry, and then apply it to the negative electrode current collector and dry it. After compression can be prepared.

The binder may be used to maintain the molded body by binding the negative electrode active material particles, and is not particularly limited as long as it is a conventional binder used in preparing a slurry for the negative electrode active material, for example, non-aqueous binders such as polyvinyl alcohol, carboxymethyl cellulose, and hydroxy Propylene cellulose, diacetylene cellulose, polyvinyl chloride, polyvinylpyrrolidone, polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVdF), polyethylene or polypropylene, etc. can be used, and acrylic as an aqueous binder. Any one selected from the group consisting of ronitrile-butadiene rubber, styrene-butadiene rubber and acrylic rubber, or a mixture of two or more of them can be used. Aqueous binders are more economical and eco-friendly than non-aqueous binders, are harmless to workers' health, and have a better binding effect than non-aqueous binders, so that the ratio of active materials per volume can be increased, making it possible to increase capacity. Preferably, styrene-butadiene rubber can be used.

The binder may be included in an amount of 10% by weight or less in the total weight of the slurry for a negative electrode active material, specifically 0.1% by weight to 10% by weight. If the content of the binder is less than 0.1% by weight, the effect of using the binder is insignificant and undesirable, and if it exceeds 10% by weight, the capacity per volume may be lowered due to the decrease in the relative content of the active material due to the increase in the binder content. not.

The conductive material is not particularly limited as long as it has conductivity without causing a chemical change in the battery, and examples of the conductive material include graphite such as natural graphite and artificial graphite; Carbon blacks such as acetylene black, ketjen black, channel black, furnace black, lamp black, and summer black; Conductive fibers such as carbon fibers and metal fibers; Metal powders such as carbon fluoride powder, aluminum powder, and nickel powder; Conductive whiskers such as zinc oxide and potassium titanate; Conductive metal oxides such as titanium oxide; Or conductive materials such as polyphenylene derivatives. The conductive material may be used in an amount of 1% by weight to 9% by weight relative to the total weight of the slurry for a negative electrode active material.

The negative electrode current collector used in the negative electrode according to an embodiment of the present invention may have a thickness of 3 μm to 500 μm. The negative electrode current collector is not particularly limited as long as it has conductivity without causing a chemical change in the battery, for example, copper, gold, stainless steel, aluminum, nickel, titanium, calcined carbon, copper or stainless steel. Carbon, nickel, titanium, silver, or the like, aluminum-cadmium alloy, or the like may be used. In addition, it is possible to form fine irregularities on the surface to enhance the bonding force of the negative electrode active material, and may be used in various forms such as films, sheets, foils, nets, porous bodies, foams, and nonwoven fabrics.

Further, as the separator, conventional porous polymer films conventionally used as separators, such as ethylene homopolymer, propylene homopolymer, ethylene-butene copolymer, ethylene-hexene copolymer, and ethylene-methacrylate copolymer, etc. The porous polymer film produced by can be used alone or by laminating them, or a conventional porous nonwoven fabric, such as a high melting point glass fiber, a polyethylene terephthalate fiber, or the like, may be used, but is not limited thereto.

A lithium salt which can be included as an electrolyte used in the present invention can be used without limitation, those which are commonly used in a lithium secondary battery electrolyte, for example the lithium salt of the anion is ^{F -, Cl -, Br -} , I -, NO 3 _{^{-, N (CN) 2 -}} , BF 4 -, ClO 4 -, PF 6 -, (CF 3) 2 PF 4 -, (CF 3) 3 PF 3 -, (CF 3) 4 PF 2 -, (CF ^{_{3) 5 PF -, (CF}} 3) 6 P -, CF 3 SO 3 -, CF 3 CF 2 SO 3 -, (CF 3 SO 2) 2 N -, (FSO 2) 2 N -, CF 3 CF 2 ^{_{(CF 3) 2 CO -,}} (CF 3 SO 2) 2 CH -, (SF 5) 3 C -, (CF 3 SO 2) 3 C -, CF 3 (CF 2) 7 SO 3 -, CF 3 CO ^₂ may be any one selected from the group consisting of _{^{-, CH 3 CO 2 -,}} SCN - , and _{(CF 3 CF 2 SO 2)} 2 N.

Examples of the electrolyte used in the present invention include an organic liquid electrolyte, an inorganic liquid electrolyte, a solid polymer electrolyte, a gel polymer electrolyte, a solid inorganic electrolyte, a molten inorganic electrolyte, and the like, which can be used in manufacturing a lithium secondary battery. no.

The external shape of the lithium secondary battery of the present invention is not particularly limited, but may be a cylindrical shape, a square shape, a pouch shape or a coin shape using a can.

The lithium secondary battery according to the present invention can be used not only for a battery cell used as a power source for a small device, but also as a unit battery in a medium-to-large battery module including a plurality of battery cells.

Preferred examples of the medium-to-large device include, but are not limited to, electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, and power storage systems.

Example

Hereinafter, examples and experimental examples will be described in more detail to specifically describe the present invention, but the present invention is not limited by these examples and experimental examples. Embodiments according to the present invention can be modified in many different forms, and the scope of the present invention should not be construed as being limited to the embodiments described below. The embodiments of the present invention are provided to more fully describe the present invention to those skilled in the art.

Examples 1 to 12: Preparation of a negative electrode for a lithium secondary battery

As a negative electrode active material, 96% by weight of natural graphite, 1% by weight of Denka black (conductive agent) and 2% by weight of SBR (binder), and 1% by weight of CMC (thickener) were added to water to prepare a negative electrode mixture slurry.

The prepared negative electrode mixture slurry was coated on one surface of the copper current collector to a thickness of 100 μm, but first, a masking tape (2210A, manufactured by 3M) was applied to the area to be formed on the current collector, and then the slurry was coated. After drying it, the masking tape was removed to form an uncoated portion, and then rolled to form an active material portion having a thickness of 70 μm, and punched it to a certain size to prepare a negative electrode.

At this time, the width of the active material portion and the width of the non-coated portion were as shown in Table 1 below, and the shapes are shown in FIGS. 8 (Examples 1 to 6) and 9 (Examples 7 to 12). On the other hand, in Examples 1 to 6, the width of the current collector was fixed to 100 mm.

cathode Width of active material
X (mm) Plain width
Y (mm) Area ratio of active material part and plain material part battery Example 1 5 One 7.5: 1 Example 13 Example 2 10 One 15: 1 Example 14 Example 3 20 One 30: 1 Example 15 Example 4 5 2 3.75: 1 Example 16 Example 5 10 2 7.5: 1 Example 17 Example 6 20 2 15: 1 Example 18 Example 7 5 One 3.52: 1 Example 19 Example 8 10 One 7.26: 1 Example 20 Example 9 20 One 14.75: 1 Example 21 Example 10 5 2 1.65: 1 Example 22 Example 11 10 2 3.52: 1 Example 23 Example 12 20 2 7.26: 1 Example 24

Example  13 to 24: Preparation of lithium secondary battery

As a positive electrode active material, Li (Li _0.2 Co _0.1 Ni _0.1 Mn _0.6 ) O ₂ 94 wt%, 3 wt% carbon black as a conductive agent, and 3 wt% PVdF as a binder, N-methyl-2 pyrrolidone as a solvent ( NMP) to prepare a positive electrode mixture slurry. The positive electrode mixture slurry was coated on a thin film of aluminum (Al), which is a positive electrode current collector having a thickness of about 20 μm, and dried to prepare a positive electrode, followed by roll press.

After interposing a porous membrane made of polyethylene having a thickness of 17 µm between each of the negative electrodes prepared in Examples 1 to 12 and the prepared positive electrode, the volume ratio of ethylene carbonate (EC) and diethyl carbonate (DEC) was 30:70. Coin-type half cells were prepared by injecting 1 M LiPF ₆ dissolved electrolyte into a mixed solvent.

Experimental Example 1: Cycle characteristic evaluation experiment

The electrochemical evaluation experiments were performed as follows to confirm the cycle characteristics of the coin-type half cells obtained in Examples 12 to 24, respectively.

Specifically, the coin-type half cells obtained in Examples 12 to 24 were charged at 25 ° C. with a constant current (CC) of 0.8 C until 4.25 V, and then charged with a constant voltage (CV) to obtain a charging current of 0.005 C ( The first charging was performed until it became cut-off current). Then, it was allowed to stand for 20 minutes, and then discharged to a constant current (CC) of 0.8 C until 2.5 V was reached. This was repeated in 1 to 100 cycles. The results of measuring the capacity retention rate of the battery after 100 cycles are shown in FIG. 10.

Referring to FIG. 10, it can be seen that the capacity retention rate after 100 cycles of the battery decreases as the width of the active material portion increases as compared to the non-coated portion. Specifically, when looking at the results of Examples 12 to 14, Examples 12 to 14 used the negative electrode having the same width of the uncoated portion, but it can be seen that the capacity retention rate after 100 cycles of the battery gradually decreased as the width of the active material portion increased. have.

On the other hand, in the case of an electrode in which the plain parts intersect each other, the electrode retention rate was higher. Specifically, the negative electrode of Example 4 (area ratio of the active material portion and the non-coated portion 3.75: 1) had a higher ratio of the area of the non-coated portion to the area of the active material portion than the negative electrode of Example 8 (area ratio of the active material portion and the non-coated portion 7.26: 1). , The battery of Example 16 using the negative electrode of Example 4 had a lower capacity retention rate after 100 cycles than the battery of Example 20 using the negative electrode of Example 8.

Through this, as the width of the plain portion becomes wider and the area of the plain portion relative to the area of the active material portion increases, the capacity retention rate after 100 cycles of the battery increases, and the plain portion has a form that crosses each other, so that there are more plain regions adjacent to the active material portion. It was confirmed that the capacity retention rate increased after 100 cycles of the battery.

10: current collector 20: active material layer
100: current collector
200, 201, 202, 203: active material part
300, 310, 311, 312, 321, 322, 323: plain
X: width of the active material
Y: width of the plain

Claims (27)

On the current collector, (i) an active material portion in which an active material layer is formed, and (ii) an uncoated portion in which an active material layer is not formed, and two or more of the uncoated portions different from each other in one location In each containing at least two crossing points, the active material layer includes a silicon-based active material as an active material, the plain portion has a width of 0.1 to 5 mm, and divides the active material layer into two or more bordering the plain portion, A negative electrode for a lithium secondary battery, wherein the width of the active material portion and the width of the non-coated portion have a ratio of 2.5: 1 to 20: 1, and an area ratio of the active material portion and the non-coated portion is 1.6: 1 to 15: 1;
anode; And
Includes; a separator interposed between the negative electrode for the lithium secondary battery and the positive electrode,
The width of the active material portion indicates a width in a direction parallel to the longitudinal direction of the cathode,
The width of the plain portion is a lithium secondary battery indicating a width in a direction perpendicular to the longitudinal direction of the plain portion.
delete delete delete delete According to claim 1,
The non-coated portion is a lithium secondary battery adjacent to two or more active material portions.
delete According to claim 1,
The lithium secondary battery comprising at least one shape selected from the group consisting of a straight line, a curved line, and a wave curve.
delete delete According to claim 1,
The active material portion is a lithium secondary battery adjacent to two or more non-coated portions.
delete delete delete According to claim 1,
The thickness of the active material portion is a lithium secondary battery of 0.01 to 0.2 mm.
According to claim 1,
The active material portion has a width of 3 to 200 mm,
At this time, the width of the active material portion is a lithium secondary battery showing a width in a direction parallel to the longitudinal direction of the negative electrode.
delete delete delete delete delete delete delete delete According to claim 1,
The lithium secondary battery is a stack (stack) or stack and folding (stack and folding) of the lithium secondary battery. delete delete

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