KR20170034724A - 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 including: (i) an active material portion having an active material layer formed therein; and (ii) a plain portion where the active material layer is not formed, wherein the active material portion and the plain portion are formed on a current collector. According to the present invention, the negative electrode for a lithium secondary battery has the active material portion where the active material layer is formed on the current collector, other than the active material portion where the active material layer is formed, thereby accepting a volume change in the gas and negative active material generated when the lithium secondary battery is charged or discharged, thus improving deterioration in the performance of a battery.

Description

TECHNICAL FIELD [0001] The present invention relates to a negative electrode for a lithium secondary battery including a non-coated portion and a lithium secondary battery including the negative electrode. [0002]

The present invention relates to a negative electrode for a lithium secondary battery including a non-coated portion and a lithium secondary battery including the same. More particularly, the present invention relates to a negative electrode capable of coping with changes in the volume of a gas and an active material generated during charging / discharging of the battery, To a negative electrode for a lithium secondary battery and a lithium secondary battery including the negative electrode.

As technology development and demand for mobile devices have increased, there has been a rapid increase in demand for secondary batteries as energy sources. Among such secondary batteries, lithium secondary batteries, which exhibit high energy density and operating potential, long cycle life, Batteries have been commercialized and widely used.

In recent years, there has been a growing interest in environmental issues, and as a result, electric vehicles (EVs) and hybrid electric vehicles (HEVs), which can replace fossil-fueled vehicles such as gasoline vehicles and diesel vehicles, And the like. Although a nickel metal hydride (Ni-MH) secondary battery is mainly used as a power source for such an electric vehicle (EV) and a hybrid electric vehicle (HEV), a lithium secondary battery having a high energy density, a high discharge voltage, Research is being actively carried out, and some are commercialized.

On the other hand, 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 the positive electrode of the lithium secondary battery. Examples of the negative electrode active material constituting the negative electrode include metal lithium, a carbon based meterial such as graphite or activated carbon or a material such as silicon oxide (SiO _x ) is used. Among the above-mentioned negative electrode active materials, metal lithium is mainly used. However, as charging and discharging cycles are progressed, lithium atoms are grown on the surface of the 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 in that the theoretical capacity is only about 400 mAh / g and the capacity is small.

Accordingly, various studies have been made to replace the carbonaceous material with silicon (Si) having a high theoretical capacity (4,200 mAh / g) as the negative electrode active material. The reaction formula when lithium is inserted into silicon is as follows:

[Reaction Scheme 1]

₂₂ Li + ₅ Si = Li ₂₂ Si ₅

However, the carbonaceous material and the negative electrode active material such as silicon are expanded in volume depending on the degree of filling, and the structure thereof is changed, and the twisting phenomenon of the electrode due to the volumetric expansion may occur, There is a problem that gas is generated during charging and discharging, and adhesion between the electrode contact and the active material becomes poor, which adversely affects battery performance.

Particularly, in the case of the above-mentioned silicon, the silicon volume is expanded up to 300% by the lithium insertion, thereby causing the negative electrode to be destroyed and the high cycle characteristic can not be exhibited. In addition, in the case of silicon, as the cycle continues, the lithium insertion causes a volume expansion and causes contact losses with pulverization, conducting agents, and current collectors, and unstable solid - can exhibit a fading mechanism such as solid-electrolyte-interphase (SEI) formation.

Therefore, when graphite or silicon is to be used as the negative electrode active material, consideration should be given to the influence of gas generation due to charging and discharging and the degree of volume expansion due to the structural change of graphite or silicon depending on the degree of filling.

Therefore, there is still a need to develop a technology capable of improving degradation of battery performance due to a change in the volume of a gas and an anode active material generated during charging and discharging of a lithium secondary battery, which is a problem that may occur when the anode active material such as graphite or silicon is used. .

Disclosure of the Invention A problem to be solved by the present invention is to provide a lithium secondary battery capable of improving the deterioration of battery performance by accommodating changes in volume of a gas and an anode active material generated during charging and discharging of a lithium secondary battery through a non- Thereby providing a negative electrode for a battery.

It is another object of the present invention to provide a lithium secondary battery including the negative electrode for a lithium secondary battery, wherein the degradation problem of the battery performance is improved.

In order to solve the above problems,

(I) an active material layer on which an active material layer is formed, and (ii) an uncoated portion on which no active material layer is formed, on a current collector.

Further, in order to solve the above-mentioned other problems,

And a negative electrode for the lithium secondary battery.

Since the negative electrode for a lithium secondary battery according to the present invention is formed with an uncoated portion in which an active material layer is not formed in addition to an active material portion having an active material layer formed on the current collector, the volume of the negative electrode active material It is possible to accommodate the change, thereby improving the deterioration problem of the battery performance.

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

Hereinafter, the present invention will be described in detail in order to facilitate understanding of the present invention.

The terms and words used in the present specification and claims should not be construed as limited to ordinary or dictionary terms and the inventor may appropriately define the concept of the term in order to best describe its invention It should be construed as meaning and concept consistent with the technical idea of the present invention.

The negative electrode for a lithium secondary battery of the present invention is formed with an active material portion having (i) an active material layer formed thereon and (ii) an uncoated portion having no active material layer formed thereon.

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

The negative electrode for a lithium secondary battery according to the present invention is divided into an active material layer by an uncoated portion in which the active material layer is not formed and an active material portion in which an active material layer is formed and an uncoated portion in which an active material layer is not formed.

The non-coated portion may be a portion in which the active material layer is not formed and the current collector is exposed to the outside through the non-coated portion. That is, since the non-coated portion corresponds to a void space existing between the active material layers (active material portions), it can serve as a passage through which the gas generated in the active material layer is trapped and moved, and also the volume change of the active material layer The degradation problem of the battery performance due to the volume change of the gas and the active material layer can be improved.

The non-coated portion separates the active material layer from the uncoated portion by two or more, so that the negative electrode for a lithium secondary battery according to an exemplary embodiment of the present invention may include two or more active material portions.

In addition, the negative electrode for a lithium secondary battery may include at least one uncoated portion, 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 the non-coated portion includes two or more, the active material portion may include three or more.

The non-coated portion may be adjacent to two or more active material portions. Specifically, since the uncoated portion divides the active material layer as described above, the divided active material layer is positioned on both sides and is in the form of being adjacent to two or more active material portions. Therefore, the shape in which the uncoated portion is adjacent to only one active material portion, that is, the shape in which the active material portion is located only on one side of the uncoated portion is not included because the uncoated portion is positioned on the rim of the current collector. In the case where the unoccluded portion is located on the rim of the current collector as described above, there is no particular difference from the case where the active material portion is located on the rim of the current collector and the side surface of the active material portion is exposed to the outside, It is difficult to expect additional effects.

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 non-coated portion may have a shape such as a narrow width and a long strip. The shape of the non-coated portion is not particularly limited, but the non-coated portion may include a straight line, a curved line, and a wave curve , And the like.

Particularly, the non-coated portion may include a wave curved shape. When the non-coated portion includes a wave form, the contact surface between the non-coated portion and the adjacent active material portion can be widened, The generated gas or the volume change of the active material layer can be more effectively accepted.

At least two of the non-coated portions may intersect with each other. Accordingly, the negative electrode for a lithium secondary battery according to an exemplary embodiment of the present invention may include at least one intersection where two or more of the non-coated portions intersect with each other. In this case, the active material portion formed on the current collector may be adjacent to at least two unoccupied portions regardless of the position.

The negative electrode for a lithium secondary battery according to an exemplary embodiment of the present invention is characterized in that, with respect to one uncoated portion, a cross point at which two or more uncoated portions cross each other at different positions May include two or more. In this case, the active material portion adjacent to the intersection, that is, the one uncoated portion that is a reference and the two or more uncoated portions that intersect with the one uncoated portion, may be formed of the one uncoated portion and the two or more uncoated portions That is, three or more uncoated portions. Since the negative electrode for a rechargeable lithium battery according to an embodiment of the present invention may include two or more active materials adjacent to three or more non-positive portions, since the active material of this type may further exist symmetrically around one non- have. In the case where two or more non-pattern portions cross each other at different positions relative to the one non-pattern portion on the current collector side, if there are two or more non-pattern portions, Two or more intersecting unoccupied portions may enclose one active material portion. Therefore, in one embodiment of the present invention, the negative electrode for a lithium rechargeable battery may include at least one active material portion adjacent to four or more uncoated portions.

The thickness of the active material layer formed on the current collector may be in the range of the thickness of a typical active material layer but is preferably 0.01 to 0.2 mm, more specifically 0.05 to 0.1 mm, And the volume change of the active material layer can be accepted by the ignition portion.

The active material portion may have a width of 3 to 200 mm, and may have a width of 5 to 50 mm, and more specifically, a width of 10 to 30 mm. In this case, 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, the width of the active material portion is measured along the length direction of the electrode.

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

The width of the non-coated portion indicates the width in the direction perpendicular to the longitudinal direction of the non-coated portion. That is, the width of the non-coated portion in the direction perpendicular to the longitudinal direction of the non- And the length is measured.

The width of the active material portion and the width of the non-coated portion may have a ratio of 2: 1 to 50: 1, and more 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, the non-coated portion can smoothly receive the gas generated from the active material and the volume change of the active material, If the width of the active material portion and the width of the non-coated portion are 50: 1 or less, the change in volume of the gas and the active material from the active material can be smoothly received by the non-coated portion.

In an embodiment of the present invention, the area ratio of the active material portion to the non-coated portion may be 1.4: 1 to 40: 1, and more preferably 1.6: 1 to 1: 30: 1, more specifically 3.5: 1 to 15: 1.

When the area ratio of the active material portion to the non-coated portion is 1.4: 1 or more, the uncoated portion can smoothly receive the gas generated from the active material and the volume change of the active material, And when the area ratio of the active material portion and the non-coated portion is 40: 1 or less, the change in the volume of the gas and the active material generated from the active material can be appropriately accepted.

As the active material that can be included in the negative electrode for a lithium secondary battery, that is, a negative electrode active material, a carbon material capable of occluding and releasing lithium ions, lithium metal, silicon or tin may be used. Preferably, carbon materials can be used, and carbon materials such as low-crystalline carbon and highly-crystalline carbon can be used. Examples of the low crystalline carbon include soft carbon and hard carbon. Examples of highly crystalline carbon include natural graphite, kish graphite, pyrolytic carbon, liquid crystal pitch carbon fiber mesophase pitch based carbon fiber, meso-carbon microbeads, mesophase pitches, and petroleum or coal tar pitch derived cokes. The silicon-based furnace can 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 contains a carbonaceous active material as an active material, particularly when a graphite-based active material is included as a carbonaceous material, the volume change is relatively small and gas generation is relatively small during charging and discharging, For example, the area ratio of the active material portion to the non-coated portion may be 3.5: 1 to 40: 1, specifically 3.5: 1 to 30: 1, more specifically 7: 1 to 30: 1 Lt; / RTI &gt;

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

When the active material layer contains a silicon-based active material as an active material, considering that the silicon-based active material has a relatively large volume change and a large amount of gas generation at the time of charging and discharging, it is preferable that the non- , And at least one intersection point where two or more non-negative portions of the negative electrode for a lithium secondary battery cross each other. Further, the non-land portion may be configured to include a shape of a wave curve.

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

The stacked lithium secondary battery may be a lithium secondary battery including an electrode assembly manufactured by vertically stacking a cathode, a separator, and an anode. The stacked and folded lithium secondary battery may include a positive electrode / separator / A bicell of a full-cell structure or a positive electrode (cathode) / separator / cathode (anode) / separator / anode (cathode) structure is manufactured by using a long- And a lithium secondary battery including an electrode assembly.

In the stacked or stacked type lithium rechargeable battery, the anode and the anode each have an active material layer formed on the current collector, and the current collector has an area of 100 to 200% Specifically, it may be 100 to 110%. In this case, in the case of the negative electrode, the area of the active material portion and the non-coated portion corresponds to the area of the active material layer.

Hereinafter, the negative electrode for a lithium secondary battery of the present invention will be described in 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 illustrative purposes and may differ from the size actually applied.

1 is a cross-sectional view schematically showing a conventional negative electrode for a lithium secondary battery. Referring to FIG. 1, a negative electrode for a lithium secondary battery is formed such that an active material layer 20 is formed on a current collector 10.

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

2 and 3, a negative electrode for a lithium secondary battery according to an exemplary embodiment of the present invention includes an active material portion 200 having an active material layer formed on a current collector 100, and a non-coated portion 300 having no active material layer Is formed.

Since the non-coated portion 300 is a portion where no active material layer is formed, the current collector 100 may be exposed to the outside through the non-coated portion 300. The non-coated portion 300 is an empty space existing between the active material portions 200. The non-coated portion 300 can serve as a passage through which the gas generated in the active material layer of the active material portion 200 is collected and moved. It can serve as a buffer capable of absorbing the volume change.

As can be seen from FIGS. 2 and 3, the active material layer is divided into two or more by one uncoated portion 300, so that two or more active material portions 200 may be included. In addition, when two or more non-coated portions 300 are included, the active material layer is divided by the non-coated portion 300, so that three or more active material portions 200 may be included.

As shown in FIG. 3, the non-coated portion 300 has a shape in which the divided active material layer is located on both sides and is adjacent to two or more active material portions 200. Further, since the non-coated portion 300 divides the active material layer, the active material portion 200 may be adjacent to the at least one non-coated portion 300.

4 is a front view schematically showing a negative electrode for another type lithium secondary battery. 4, since the non-coated portion 300 divides the active material layer into two or more boundaries with the boundaries of the non-coated portion 300, the non-coated portion 300 has one active material portion 200 The shape of the active material part 200 being located only on one side of the non-coated part 300 by placing the non-coated part 300 on the edge of the current collector 100 is included in the example of the present invention It does not.

Referring again to FIG. 3, the non-coated portion 300 has a narrow and long-band shape. Although the shape of the non-coated portion 300 is not particularly limited, it may include at least one shape selected from the group consisting of a straight line, a curved line, and a wave curve when the electrode, that is, the face of the current collector is viewed from above vertically.

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

5, when the non-coated portion 300 includes a wave curved shape, the non-coated portion 300 includes a wave curved shape. When the non-coated portion 300 includes a wave curved shape, The contact surface with the active layer 200 can be widened, so that 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 front views schematically showing a cathode for a lithium secondary battery according to another example of the present invention, respectively.

Referring to FIG. 6, two or more non-printed portions 310, 321, and 322 may intersect with each other, and one or more intersections 331 and 332 at which two or more non-printed portions 310, 321, . In this case, the active material portion 200 formed on the current collector is adjacent to two or more uncoated portions 310, 321, and 322 irrespective of positions.

In addition, the non-printed portion may be formed by tracing a single non-printed portion 310 by a plurality of non-printed portions 321 and 322. As shown in FIG. 6, when two unoccupied portions 321 and 322 cross one uncoated portion 310 at different positions from each other, two intersections 331 and 332, . In this case, the active material portion 201, which is adjacent to the intersection points 331 and 332, that is, the reference uncoated portion 310 and the two uncoated portions 321 and 322 intersecting with each other, The non-printed portion 310 is adjacent to the two non-printed portions 321 and 322, that is, the three non-printed portions 310, 321 and 322, which intersect with the non-printed portion 310. In addition, there is a further symmetrical addition of this type of active material portion 202 around the non-coated portion 310 as a reference. Accordingly, two or more of the active material portions 201 and 202 adjacent to the three or more non-coated portions may be included.

As shown in Fig. 7, there exist two shapes in which three unoccupied portions 321, 322, and 323 intersect each other at different positions with respect to one unoccupied portion 311 and 312 on the current collector Two uncoated portions 311 and 312 and three uncoated portions 321 and 322 and 323 which intersect with each other may surround one active material portion 202 as a reference of intersection, The active material portion 203 is adjacent to the four plain portions 311, 312, 322, and 323.

The present invention also provides a lithium secondary battery including 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. 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 cathode, a separator, and an anode. The stacked and folded lithium secondary battery may include a positive electrode / separator / A bicell of a full-cell structure or a positive electrode (cathode) / separator / cathode (anode) / separator / anode (cathode) structure is manufactured by using a long- And a lithium secondary battery including an electrode assembly.

The anode may be prepared by a conventional method known in the art. For example, a slurry may be prepared by mixing and stirring a solvent, a binder, a conductive material, and a dispersant as necessary in a cathode active material, and then coating (coating) the mixture on a current collector of a metal material, have.

The current collector of the metal material is a metal having high conductivity and is a metal which can easily adhere to the slurry of the cathode active material and is not particularly limited as long as it has high conductivity without causing chemical change in the battery in the voltage range of the battery But not limited to, stainless steel, aluminum, nickel, titanium, sintered carbon, or aluminum or stainless steel surface treated with carbon, nickel, titanium, silver, or the like. In addition, fine unevenness may be formed on the surface of the current collector to increase the adhesive force of the positive electrode active material. The current collector may be used in various forms such as a film, a sheet, a foil, a net, a porous body, a foam, and a nonwoven fabric, and may have a thickness of 3 to 500 μm.

The cathode active material is preferably 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)], compound; Lithium manganese oxides such as LiMnO ₃ , LiMn ₂ O ₃ , or [Li _x MnO ₂ (0.5 <x <1.3)], such as Li _{1 + x} Mn _{2 - x} O ₄ where x is 0 to 0.33; Lithium copper oxide (Li ₂ CuO ₂ ); Vanadium oxides such as LiV ₃ O ₈ , LiFe ₃ O ₄ , V ₂ O ₅ , or Cu ₂ V ₂ O ₇ ; A 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, and Zn, or Ta, x = 0.01 to 0.1 Im) or Li ₂ Mn ₃ MO ₈ (where, M = Fe, Co, Ni, Cu, or Zn); LiMn ₂ O _{4 in} which a part of Li in the formula is substituted with an alkaline earth metal ion; 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-methylpyrrolidone), DMF (dimethylformamide), acetone, and dimethylacetamide, and water. These solvents may be used alone or in combination of two or more Can be mixed and used. The amount of the solvent used is sufficient to dissolve and disperse the cathode 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), polyvinylidene fluoride, polyacrylonitrile, polymethylmethacrylate, Polyvinyl alcohol, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated 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 in which hydrogen is substituted with Li, Na, or Ca, or Various kinds of binder polymers such as various copolymers can be used.

The conductive material is not particularly limited as long as it has electrical conductivity without causing chemical changes in the battery, and examples thereof include graphite such as natural graphite and artificial graphite; Carbon black such as acetylene black, Ketjen black, channel black, panes black, lamp black, and thermal black; Conductive fibers such as carbon fiber and metal fiber; Conductive tubes such as carbon nanotubes; Metal powders such as fluorocarbon, aluminum and nickel powder; Conductive whiskers such as zinc oxide and potassium titanate; Conductive metal oxides such as titanium oxide; Conductive materials such as polyphenylene derivatives and the like can be used. The conductive material may be used in an amount of 1 wt% to 20 wt% based on the total weight of the positive electrode slurry.

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

The negative electrode may be prepared by a conventional method known in the art. For example, the negative electrode active material, additives such as a binder and a conductive material are mixed and stirred to prepare an anode active material slurry, which is then applied to an anode current collector, Followed by compression.

The binder may be used to bind the negative electrode active material particles to maintain the formed body. Any conventional binder used in preparing the slurry for the negative electrode active material is not particularly limited, and examples thereof include polyvinyl alcohol, carboxymethyl cellulose, Polyvinylidene fluoride (PTFE), polyvinylidene fluoride (PVdF), polyethylene or polypropylene, and the like can be used. In addition, an acrylic resin such as acrylic resin (polyvinyl chloride), polyvinyl pyrrolidone, polytetrafluoroethylene Acrylonitrile-butadiene rubber, styrene-butadiene rubber, styrene-butadiene rubber, and acrylic rubber, or a mixture of two or more thereof. The aqueous binders are economical, environmentally friendly, harmless to the health of workers, and are superior to non-aqueous binders, and have a better binding effect than non-aqueous binders. Thus, the ratio of the active materials of the same volume can be increased and the capacity of the aqueous binders can be increased. Preferably styrene-butadiene rubber can be used.

The binder may be contained in an amount of 10 wt% or less, specifically 0.1 wt% to 10 wt%, based on the total weight of the slurry for the negative electrode active material. If the content of the binder is less than 0.1 wt%, the effect of the binder is insufficient, which is undesirable. If the content of the binder is more than 10 wt%, the relative content of the active material may decrease to increase the binder content. not.

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

The negative electrode collector used in the negative electrode according to an embodiment of the present invention may have a thickness of 3 to 500 mu m. The negative electrode current collector is not particularly limited as long as it has electrical conductivity without causing a chemical change in the battery. The negative electrode current collector may be formed on the surface of copper, gold, stainless steel, aluminum, nickel, titanium, sintered carbon, Carbon, nickel, titanium, silver or the like, an aluminum-cadmium alloy, or the like can be used. In addition, fine unevenness can be formed on the surface to enhance the bonding force of the negative electrode active material, and it can be used in various forms such as a film, a sheet, a foil, a net, a porous body, a foam, and a nonwoven fabric.

As the separator, a conventional porous polymer film conventionally used as a separator, such as a polyolefin-based polymer such as an ethylene homopolymer, a propylene homopolymer, an ethylene-butene copolymer, an ethylene-hexene copolymer and an ethylene-methacrylate copolymer Porous nonwoven fabric such as high melting point glass fiber, polyethylene terephthalate fiber or the like may be used as the nonwoven fabric, but the present invention is not limited thereto.

The lithium salt that can be used as the electrolyte used in the present invention may be any of those commonly used in electrolytes for lithium secondary batteries, and examples thereof include 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 ^- , 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-based liquid electrolyte, an inorganic liquid electrolyte, a solid polymer electrolyte, a gel-type polymer electrolyte, a solid inorganic electrolyte, and a molten inorganic electrolyte that can be used in the production of 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, a coin shape, or the like using a can.

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

Preferable examples of the above medium and large-sized devices include, but are not limited to, electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, and electric power storage systems.

Example

Hereinafter, the present invention will be described in more detail with reference to Examples and Experimental Examples, but the present invention is not limited by these Examples and Experimental Examples. The embodiments according to the present invention can be modified into various other 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 enable those skilled in the art to more fully understand the present invention.

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

A negative electrode mixture slurry was prepared by adding 96 wt% of natural graphite, 1 wt% of Denka black (conductive agent), 2 wt% of SBR (binder), and 1 wt% of CMC (thickener) as an anode active material to water.

A masking tape (2210A, manufactured by 3M Co.) was applied to a region of the current collector on which a non-coated portion was to be formed, and then the slurry was coated After drying, the masking tape was removed to form an uncoated portion, followed by rolling to form an active material portion having a thickness of 70 μm. The negative electrode was formed by punching the active material portion to a predetermined size.

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

cathode Width of active material
X (mm) Width of plain weave
Y (mm) Area ratio of the active material portion and the non- 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

94% by weight of Li (Li _0.2 Co _0.1 Ni _0.1 Mn _0.6 ) O ₂ as a cathode active material, 3% by weight of carbon black as a conductive agent and 3% by weight of PVdF as a binder were dissolved in N-methyl-2-pyrrolidone NMP) to prepare a positive electrode mixture slurry. The positive electrode mixture slurry was coated on an aluminum (Al) thin film having a thickness of about 20 탆, which was a positive current collector, and dried to produce a positive electrode, followed by roll pressing.

A polyethylene porous membrane having a thickness of 17 탆 was interposed between each of the negative electrodes prepared in Examples 1 to 12 and the prepared positive electrode, and ethylene carbonate (EC) and diethyl carbonate (DEC) were mixed at a volume ratio of 30:70 Was injected into a solvent mixed with 1M LiPF ₆ to prepare coin type half cells.

Experimental Example 1: Cycle Characterization Experiment

Electrochemical evaluation experiments were carried out as follows to confirm the cycle characteristics of the coin-shaped half-cells obtained in Examples 12 to 24, respectively.

Specifically, the coin-shaped half-cells obtained in each of Examples 12 to 24 were charged at a constant current (CC) of 4.2 C at a constant current of 0.8 C at 25 캜 and then charged at a constant voltage (CV) cut-off current). After that, it was left for 20 minutes and then discharged at a constant current (CC) of 0.8 C until it reached 2.5 V. [ This was repeated in 1 to 100 cycles. The measurement results of the capacity retention rate of the battery after 100 cycles are shown in Fig.

Referring to FIG. 10, it can be seen that as the width of the active material increases, the capacity retention ratio after 100 cycles of the battery becomes lower than that of the non-coated portion. Specifically, the results of Examples 12 to 14 indicate that the negative electrodes having the same width of uncoated portions are used in Examples 12 to 14. However, as the width of the active material portion increases, the capacity retention ratio after 100 cycles of the battery gradually decreases have.

On the other hand, in the case of the electrode in which the non-ionized portions cross each other, the electrode retention ratio is higher than that of the electrode. Specifically, the negative electrode (area ratio of the active material portion to the non-coated portion) of Example 4 was higher than that of the negative electrode of Example 8 (area ratio of the active material portion to the non-coated portion was 7.26: 1) , And the cell of Example 16 using the negative electrode of Example 4 had a lower capacity retention rate after 100 cycles than the cell of Example 20 using the negative electrode of Example 8.

As a result, the capacity retention ratio after 100 cycles of the battery is increased as the width of the non-woven portion is widened and the area of the non-woven portion with respect to the area of the active material portion is widened. It was confirmed that the capacity retention rate after 100 cycles of the battery was increased.

10: collector 20: active material layer
100: House full
200, 201, 202, 203: active material part
300, 310, 311, 312, 321, 322, 323:
X: Width of the active material portion
Y: Width of plain weave

Claims (27)

(I) an active material layer on which an active material layer is formed, and (ii) an uncoated portion on which no active material layer is formed.
The method according to claim 1,
Wherein the non-coated portion is a portion in which the active material layer is not formed and the current collector is exposed to the outside through the non-coated portion.
The method according to claim 1,
Wherein the non-coated portion divides the active material layer by two or more with the non-coated portion as a boundary.
The method according to claim 1,
Wherein the negative electrode for a lithium secondary battery comprises at least two active material portions.
The method according to claim 1,
Wherein the negative electrode for a lithium secondary battery comprises two or more uncoated portions.
The method according to claim 1,
Wherein the non-coated portion is adjacent to two or more active material portions.
The method according to claim 1,
Wherein the active material portion is adjacent to at least one uncoated portion.
The method according to claim 1,
Wherein the non-coated portion includes at least one shape selected from the group consisting of a straight line, a curved line, and a wave curve.
The method according to claim 1,
Wherein the non-coated portion includes a shape of a wave curve.
The method according to claim 1,
Wherein the negative electrode for a lithium secondary battery comprises at least one intersection where two or more of the non-negative portions cross each other.
11. The method of claim 10,
Wherein the active material portion is adjacent to two or more non-coated portions.
The method according to claim 1,
Wherein the negative electrode for a lithium secondary battery includes two or more intersections where two or more non-negative portions cross each other at different positions with respect to one non-positive portion.
13. The method of claim 12,
Wherein the negative electrode for a lithium secondary battery comprises two or more active materials adjacent to three or more non-coated portions.
13. The method of claim 12,
Wherein the negative electrode for a lithium secondary battery comprises at least one non-coated portion and at least one active material portion adjacent to the negative electrode portion for the lithium secondary battery.
The method according to claim 1,
And the thickness of the active material portion is 0.01 to 0.2 mm.
The method according to claim 1,
The active material portion has a width of 3 to 200 mm,
Wherein a width of the active material portion indicates a width in a direction parallel to a longitudinal direction of the negative electrode.
The method according to claim 1,
The non-coated portion has a width of 0.1 to 5 mm,
Wherein a width of the non-coated portion indicates a width in a direction perpendicular to a length direction of the non-coated portion.
The method according to claim 1,
The width of the active material portion and the width of the non-coated portion have a ratio of 2: 1 to 50: 1,
Wherein a width of the active material portion indicates a width in a direction parallel to the length direction of the negative electrode and a width of the non-coated portion indicates a width in a direction perpendicular to the length direction of the non-coated portion.
The method according to claim 1,
Wherein an area ratio of the active material portion to the non-coated portion is from 1.4: 1 to 40: 1.
The method according to claim 1,
Wherein the active material is a carbon material, lithium metal, silicon or tin, and an anode for a lithium secondary battery.
The method according to claim 1,
Wherein the active material layer includes a carbonaceous active material as an active material,
Wherein an area ratio of the active material portion to the non-coated portion is 3.5: 1 to 40: 1.
The method according to claim 1,
Wherein the active material layer contains a silicon-based active material as an active material,
In this case, an area ratio of the active material portion to the non-coated portion is 1.4: 1 to 30: 1.
23. The method of claim 22,
Wherein the negative electrode for a lithium secondary battery comprises at least one intersection where two or more of the non-negative portions cross each other.
23. The method of claim 22,
Wherein the non-coated portion includes a shape of a wave curve.
The method according to claim 1,
The negative electrode for a lithium secondary battery according to claim 1, wherein the negative electrode for a lithium secondary battery is a stack type or stack and folding type negative electrode for a lithium secondary battery.
A lithium secondary battery comprising a negative electrode for a lithium secondary battery according to any one of claims 1 to 25.
27. The method of claim 26,
Wherein the lithium secondary battery is a stack type or stack and folding type battery.

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