Negative electrode for lithium secondary battery and lithium secondary battery including the same

Abstract

To provide a lithium secondary battery negative electrode exhibiting high energy density and excellent high rate charge / discharge characteristics, and a lithium secondary battery including the negative electrode.SOLUTION: In a lithium secondary battery negative electrode and a lithium secondary battery including the same, the negative electrode includes a current collector and a negative electrode active material layer positioned on the current collector, and the negative electrode active material layer includes a plurality of holes with a hole density of 90pt / mm2 or more.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a negative electrode for a lithium secondary battery and a lithium secondary battery including the same.

Background Art

[0002] Recently, with the rapid spread of electronic devices using batteries such as mobile phones, notebook computers, and electric vehicles, the demand for small, lightweight, and relatively high-capacity secondary batteries has been rapidly increasing. In particular, lithium secondary batteries have attracted attention as a driving power source for portable devices because of their light weight and high energy density.

[0003] A lithium secondary battery is a battery including a positive electrode and a negative electrode containing an active material capable of intercalation and deintercalation of lithium ions, and an electrolytic solution, and produces electrical energy by oxidation and reduction reactions when lithium ions are intercalated / deintercalated in the positive electrode and the negative electrode.

[0004] As the positive electrode active material of a lithium secondary battery, transition metal compounds such as lithium cobalt oxide, lithium nickel oxide, and lithium manganate are mainly used. As the negative electrode active material, crystalline carbon materials such as natural graphite and artificial graphite, or amorphous carbon materials are used.

[0005] In order to increase the energy density of such a lithium secondary battery, it is essential to increase the thickness and density. In addition, in order to solve the problem that the cycle life rapidly deteriorates, it is necessary to suppress the shape deformation (deforming) and swelling phenomenon due to shrinkage and expansion during charge and discharge.

[0006] Therefore, research on a battery structure having an adhesive function at the interface between the electrode and the separator has been underway. However, there is a problem that the adhesive polymer used to impart the adhesive function is inserted into the fine pores on the surface of the active material layer, reducing the lithium ion path and increasing the resistance.

Summary of the Invention

Problems to be Solved by the Invention

[0007] One embodiment provides a negative electrode for a lithium secondary battery that exhibits high energy density and excellent high-rate charge and discharge characteristics.

[0008] Another embodiment provides a lithium secondary battery including the negative electrode.

Means for Solving the Problems

[0009] One embodiment includes a current collector; and a negative electrode active material layer located on the current collector, the negative electrode active material layer including a plurality of holes at a hole density of 90 pt / mm 2 or more, and provides a negative electrode for a lithium secondary battery.

[0010] The hole density can be 90 pt / mm 2 to 625 pt / mm 2 and can be.

[0011] The depth of the holes can be 5 μm to 40 μm, and according to one embodiment, the depth of the holes can be 5 μm to 20 μm.

[0012] The negative electrode active material layer can include the holes at a pitch of 100 μm or less, and can include the holes at a pitch of 40 μm to 100 μm.

[0013] The negative electrode may further include an adhesive layer including a plurality of holes on the negative electrode active material layer.

[0014] The thickness of the adhesive layer can be 1 μm to 5 μm.

[0015] The adhesive layer can include an acrylic polymer, polyvinyl alcohol, a fluorine-based polymer, or a combination thereof.

[0016] The negative electrode can have a load level of 15 mg / cm 2 or more.

[0017] According to another embodiment, a lithium secondary battery including the negative electrode, the positive electrode, and the electrolyte is provided.

Advantages of the Invention

[0018] The negative electrode according to one embodiment can exhibit a high energy density and excellent cycle life characteristics.

Brief Description of the Drawings

[0019]

Figure 1

Figure 2

Modes for Carrying Out the Invention

[0020] Hereinafter, embodiments of the present invention will be described in detail. However, this is presented as an example, and the present invention is not limited thereby, and the present invention is defined only by the scope of the claims described later.

[0021] The terms used herein are used only for explaining exemplary embodiments and are not intended to limit the present invention. Singular expressions include plural expressions unless the context clearly indicates a different meaning.

[0022] “These combinations” means a mixture, laminate, composite, copolymer, alloy, blend, reaction product, etc. of components.

[0023] Terms such as “include,” “comprise,” or “have” are used to specify the presence of implemented features, numbers, steps, components, or combinations thereof, and should be understood not to preclude the possibility of the presence or addition of one or more other features, numbers, steps, components, or combinations thereof in advance.

[0024] To clearly show multiple layers and regions in the drawings, the thickness is enlarged and shown, and the same drawing reference numerals are given to similar parts throughout the specification. When a part such as a layer, film, region, plate, etc. is "on" or "above" another part, this includes not only the case where it is "immediately above" the other part, but also the case where there are other parts in between. Conversely, when a part is "immediately above" another part, it means that there are no other parts in between.

[0025] "Layer" includes not only the shape formed on the entire surface when observed in a plan view, but also the shape formed on a part of the surface.

[0026] "Thickness" can be measured, for example, from a photograph taken with an optical microscope such as a scanning electron microscope.

[0027] The negative electrode for a lithium secondary battery according to one embodiment includes a current collector and a negative electrode active material layer located on this current collector, and this negative electrode active material layer includes a plurality of holes.

[0028] The negative electrode active material layer may include the holes at a hole density of 90 pt / mm 2 or more. According to one embodiment, it can also include the holes at a hole density of 90 pt / mm 2 to 625 pt / mm 2 In this specification, "pt" means the number. That is, 90 or more holes can be formed per unit area mm 2 in the negative electrode active material layer, 90 to 625 holes can be formed, 90 to 400 holes can be formed, 90 to 300 holes can also be formed, and 100 to 300 holes can also be formed.

[0029] When holes are formed in the negative electrode active material at the hole density, the problem of the negative electrode active material layer falling off from the current collector during charge and discharge can be avoided, the charging and discharging rate can be improved, and the characteristics of rapid charge and discharge can be improved. If the hole density is less than 90 pt / mm 2 it is not appropriate because the increase in the charging and discharging rate is very small.

[0030] Referring to FIG. 1 schematically showing the negative electrode 1 according to one embodiment, a plurality of holes 7 are formed in the negative electrode active material layers 3a and 3b, and such holes 7 are 90 or more per square millimeter 2 According to one embodiment, 90 to 625, 90 to 400 can be formed, and those formed with 90 to 300, or 100 to 300.

[0031] The depth of the holes formed in the negative electrode active material layer can be 5 μm to 40 μm, and can be 5 μm to 20 μm. The depth of the holes means h in FIG. 1, and in one embodiment, the depth of the holes means the distance from the surface of the negative electrode active material layer in the direction of the current collector 5.

[0032] When the depth of the holes is within the above range, the decrease in cycle life characteristics occurring during rapid charge and discharge can be more effectively suppressed.

[0033] Generally, due to the overvoltage during rapid charge and discharge, a phenomenon may occur in which lithium is not inserted between the active materials, and lithium is plated on the surface of the active material layer. Therefore, a side reaction between a part of the deposited lithium and the electrolytic solution may occur, lithium ions may be inactivated, and the cycle life characteristics may deteriorate.

[0034] When holes are formed in the negative electrode active material layer with a depth within the above range as in one embodiment, lithium can be favorably inserted into the inside of the active material layer through the holes, and a charge and discharge reaction can occur uniformly throughout the active material layer. Therefore, the rapid charge and discharge characteristics can be more effectively improved.

[0035] In one embodiment, the depth of the holes is a value that is not adjusted according to the thickness of the active material layer, and it is appropriate that the holes are formed with a depth of 5 μm to 40 μm even when the thickness of the active material layer changes. Further, since the minimum depth of the holes is 5 μm, even when the thickness of the active material layer becomes thinner, it cannot be made thinner than 5 μm so as not to penetrate the active material layer. That is, in one embodiment, the holes do not penetrate the active material layer.

[0036] In one embodiment, the negative electrode active material layer may include the holes at a pitch of 100 μm or less. The pitch means the distance between the center points of the holes located at the closest distance. Therefore, the pitch is a value that is not linked to the diameter of the holes, is the length between the unprocessed portions, and is a value different from the interval that varies according to the size of the holes. According to another embodiment, the pitch may be 40 μm to 100 μm, may be 40 μm to 80 μm, and may be 40 μm to 75 μm.

[0037] When the pitch is within the above range, the cycle life characteristics during rapid charging can be further improved. If the pitch is greater than 100 μm, the effect of improving the cycle life characteristics during rapid charging is not so great, and there may be cases where actual application is difficult.

[0038] The shape of the holes can be any shape such as circular, elliptical, or square in plan view, and any shape such as columnar or conical on its side surface, and there is no particular need for limitation. According to one embodiment, the shape of the holes may have a conical side surface, may be a concave cone with a concave tip, or may be a cone with a rounded tip. According to another embodiment, the shape of the holes may be a concave cone with a concave tip, such that the bottom surface is located on the surface side of the active material layer like an ice cream cone, and the concave end is located in the direction of the current collector.

[0039] The holes may be regularly arranged or irregularly arranged, and there is no need to limit the arrangement form.

[0040] The holes may have an average diameter of 1 μm to 35 μm, or may be 3 μm to 35 μm. When the average diameter of the holes is within the above range, the battery capacity and the strength of the negative electrode active material layer can be well maintained, and the cycle life characteristics during rapid charging can be further improved. The average diameter may be the average particle size (D50), and unless otherwise defined in this specification, the average particle diameter (D50) means the diameter of the particles with a cumulative volume of 50% in the particle size distribution.

[0041] The measurement of the average particle size (D50) can be measured by methods widely known to those skilled in the art. For example, it can be measured with a particle size analyzer, or it can also be measured from a transmission electron microscope photograph or a scanning electron microscope photograph. As another method, it can be measured using a measuring device that uses the dynamic light-scattering method, and after performing data analysis to count the number of particles for each particle size range, the average particle size (D50) value can be obtained based on this.

[0042] In one embodiment, the negative electrode may further include an adhesive layer including a plurality of holes on the negative electrode active material layer.

[0043] When further including the adhesive layer, problems of volume expansion and contraction of the negative electrode active material layer that may occur during charge and discharge can be effectively suppressed.

[0044] Also, as described above, since the active material layer and the adhesive layer include a plurality of holes, insertion and extraction of lithium ions can be effectively performed without a decrease in energy density.

[0045] Therefore, the negative electrode according to one embodiment can exhibit all of the improvement in lithium ion insertion and extraction due to the formation of holes in the negative electrode active material layer, the effect of a uniform charge and discharge reaction, and the improvement effect of the deformation of the electrode shape and swelling characteristics due to having the adhesive layer.

[0046] The thickness of the adhesive layer can be 1 μm to 5 μm, and according to one embodiment, it can be 1 μm to 2 μm. When the thickness of the adhesive layer is within this range, problems of volume expansion and contraction of the negative electrode active material layer caused by forming the adhesive layer can be more effectively suppressed.

[0047] The adhesive layer can include a vinyl-based or acrylic-based polymer, polyvinyl alcohol, a fluorine-based polymer, or a polymer containing a combination thereof.

[0048] The vinyl-based or acrylic-based polymer can be, for example, poly(meth)acrylic acid, poly(meth)acrylate, polymethyl(meth)acrylate, polyacrylonitrile, acrylonitrile-styrene-butadiene copolymer, or a combination thereof. The "(meth)" means that it may or may not contain a methyl group. For example, poly(meth)acrylic acid means polymethacrylic acid or polyacrylic acid.

[0049] The fluorine-based polymer can be a vinylidene fluoride homopolymer, such as polyvinylidene fluoride, a vinylidene fluoride-hexafluoropropylene copolymer, a vinylidene fluoride-trichloroethylene copolymer, a vinylidene fluoride-tetrafluoroethylene copolymer, a vinylidene fluoride-trifluoroethylene copolymer, a vinylidene fluoride-trifluorochloroethylene copolymer, a vinylidene fluoride-ethylene copolymer, or a combination thereof.

[0050] In one embodiment, the negative electrode active material can be a material capable of reversibly intercalating / deintercalating lithium ions, lithium metal, an alloy of lithium metal, a material dopable and dedopable with lithium, or a transition metal oxide.

[0051] Examples of substances capable of reversibly intercalating / deintercalating lithium ions include carbon substances, that is, carbon-based negative electrode active materials generally used in lithium secondary batteries. Representative examples of carbon-based negative electrode active materials include crystalline carbon, amorphous carbon, or a combination of these. Examples of the crystalline carbon include graphite such as amorphous, plate-like, flaky, spherical, or fibrous natural graphite or artificial graphite, and examples of the amorphous carbon include soft carbon, hard carbon, mesophase pitch carbide, calcined coke, and the like.

[0052] As the alloy of the lithium metal, an alloy of lithium and a metal selected from the group consisting of Na, K, Rb, Cs, Fr, Be, Mg, Ca, Sr, Si, Sb, Pb, In, Zn, Ba, Ra, Ge, Al, and Sn can be used.

[0053] Examples of substances capable of doping and undoping lithium include Si, SiO x (0 < x < 2), Si-Q alloys (where Q is an element selected from the group consisting of alkali metals, alkaline earth metals, Group 13 elements, Group 14 elements, Group 15 elements, Group 16 elements, transition metals, rare earth elements, and combinations thereof, and is not Si), Si-carbon composites, Sn, SnO2, Sn-R alloys (where R is an element selected from the group consisting of alkali metals, alkaline earth metals, Group 13 elements, Group 14 elements, Group 15 elements, Group 16 elements, transition metals, rare earth elements, and combinations thereof, and is not Sn), Sn-carbon composites, and the like. Also, at least one of these can be mixed with SiO2 and used. As the elements Q and R, those selected from the group consisting of Mg, Ca, Sr, Ba, Ra, Sc, Y, Ti, Zr, Hf, Rf, V, Nb, Ta, Db, Cr, Mo, W, Sg, Tc, Re, Bh, Fe, Pb, Ru, Os, Hs, Rh, Ir, Pd, Pt, Cu, Ag, Au, Zn, Cd, B, Al, Ga, Sn, In, Ge, P, As, Sb, Bi, S, Se, Te, Po, and combinations thereof can be used.

[0054] As the transition metal oxide, lithium titanate can be used.

[0055] The Si-carbon composite can contain silicon and crystalline carbon. At this time, the average particle diameter (D50) of the silicon particles can be 10 nm to 200 nm. The Si-C composite can further contain an amorphous carbon layer formed on at least a part thereof. Unless otherwise defined in this specification, the average particle diameter (D50) means the diameter of particles with a cumulative volume of 50% by volume in the particle size distribution.

[0056] The measurement of the average particle size (D50) can be performed by methods widely known to those skilled in the art. For example, it can be measured with a particle size analyzer, or it can also be measured from a transmission electron microscope photograph or a scanning electron microscope photograph. As another method, it can be measured using a measuring device using the dynamic light-scattering method, data analysis is performed to count the number of particles for each particle size range, and then the average particle diameter (D50) value can be obtained based on this.

[0057] In one embodiment, as the negative electrode active material, the silicon-based negative electrode active material and the carbon-based negative electrode active material can also be included. When the silicon-based negative electrode active material and the carbon-based negative electrode active material are used together, the mixing ratio of the silicon-based negative electrode active material and the carbon-based negative electrode active material can be a weight ratio of 1:99 to 50:50. More specifically, the mixing ratio of the silicon-based negative electrode active material and the carbon-based negative electrode active material can be a weight ratio of 5:95 to 20:80.

[0058] In the negative electrode active material layer, the content of the negative electrode active material can be 90% by weight to 98% by weight, and can be 92% by weight to 97% by weight, based on 100% by weight of the entire negative electrode active material layer.

[0059] The negative electrode active material layer may further contain a conductive material. When the negative electrode active material layer further contains a binder, the negative electrode active material layer may contain 90% to 98% by weight of the negative electrode active material, 1% to 5% by weight of the binder, and 1% to 5% by weight of the conductive material.

[0060] The binder serves to make the negative electrode active material particles adhere well to each other and also to make the negative electrode active material adhere well to the current collector. As the binder, a non-aqueous binder, an aqueous binder, or a combination thereof can be used.

[0061] Examples of the non-aqueous binder include ethylene propylene copolymer, polyacrylonitrile, polystyrene, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, polyamideimide, polyimide, or a combination thereof.

[0062] Examples of the aqueous binder can be styrene-butadiene rubber (SBR), acrylated styrene-butadiene rubber (ABR), acrylonitrile-butadiene rubber, acrylic rubber, butyl rubber, fluororubber, a polymer containing ethylene oxide, polyvinylpyrrolidone, polypropylene, polyepichlorohydrin, polyphosphazene, ethylene propylene diene copolymer, polyvinylpyridine, chlorosulfonated polyethylene, latex, polyester resin, acrylic resin, phenol resin, epoxy resin, polyvinyl alcohol, or a combination thereof.

[0063] When using an aqueous binder as the negative electrode binder, a cellulose-based compound capable of imparting viscosity can be further included as a thickener. As this cellulose-based compound, one or more of carboxymethyl cellulose, hydroxypropyl methyl cellulose, methyl cellulose, or alkali metal salts thereof can be mixed and used. As the alkali metal, Na, K, or Li can be used. The content of such a thickener used can be 0.1 to 3 parts by weight with respect to 100 parts by weight of the negative electrode active material.

[0064] The conductive material is used to impart conductivity to the electrode, and in the configured battery, any material can be used as long as it is an electron conductive material that does not cause a chemical change. Examples of the conductive material include carbon-based substances such as natural graphite, artificial graphite, carbon black, acetylene black, ketjen black, and carbon fiber; metal-based substances such as metal powders or metal fibers of copper, nickel, aluminum, silver, etc.; conductive polymers such as polyphenylene derivatives; or conductive materials containing mixtures thereof can be used.

[0065] As the current collector, one selected from the group consisting of copper foil, nickel foil, stainless steel foil, titanium foil, nickel foam, copper foam, a polymer substrate coated with a conductive metal, and combinations thereof can be used.

[0066] The negative electrode can have a composite density of 1.5 g / cm 3 or more. For example, it can have a composite density of 1.5 g / cm 3 to 2.0 g / cm 3 .

[0067] Also, the negative electrode can have a load level of 15 mg / cm 2 or more, preferably 18 mg / cm 2 or more. When the load level of the negative electrode is 15 mg / cm 2In the above case, the effect of forming holes according to the hole density of one embodiment can be obtained more effectively. That is, the effect of hole formation can appear more effectively when applied to a negative electrode having such a high load level. The load level of the negative electrode is 15 mg / cm 2 or more is appropriate, so there is no need to limit the upper limit value. For example, 18 mg / cm 2 ~36 mg / cm 2 is possible.

[0068] The thickness of the negative electrode active material layer can be 100 μm or more and 200 μm or less. The thickness of the negative electrode active material layer means the thickness of one side. When the thickness of the negative electrode active material layer is within the above range, an appropriate battery capacity can be shown.

[0069] The negative electrode according to one embodiment can be manufactured by forming a negative electrode active material layer on a current collector and then forming holes. Further, the negative electrode can also form holes after forming an adhesive layer on the negative electrode active material layer.

[0070] Any method can be used for the hole formation method as long as holes can be formed. Examples include needle punching, laser, etc.

[0071] The formation of the negative electrode active material layer can be carried out by a usual method of applying, drying and rolling a negative electrode active material layer composition containing a negative electrode active material, a binder, optionally a conductive material and a solvent onto a current collector. The solvent can be N-methylpyrrolidone, water or a combination thereof. When a water-soluble binder is used as the binder, water can be used.

[0072] The formation process of the adhesive layer can be carried out by a usual method of applying, drying and rolling an adhesive layer composition containing a vinyl-based or acrylic-based polymer, polyvinyl alcohol, a fluorine-based polymer or a combination thereof and a solvent onto the negative electrode active material layer.

[0073] The solvent can be water.

[0074] Another embodiment provides a lithium secondary battery including the negative electrode, the positive electrode, and the electrolytic solution.

[0075] The positive electrode includes a current collector and a positive electrode active material layer formed on the current collector.

[0076] As the positive electrode active material, a compound capable of reversible intercalation and deintercalation of lithium (lithiated intercalation compound) can be used. Specifically, one or more of composite oxides of metals selected from cobalt, manganese, nickel, and combinations thereof with lithium can be used. As a more specific example, a compound represented by any one of the following chemical formulas can be used. Li a A 1-b X b D2(0.90 ≦ a ≦ 1.8, 0 ≦ b ≦ 0.5); Li a A 1-b X b O 2-c D c (0.90 ≦ a ≦ 1.8, 0 ≦ b ≦ 0.5, 0 ≦ c ≦ 0.05); Li a E 1-b X b O 2-c D c (0.90 ≦ a ≦ 1.8, 0 ≦ b ≦ 0.5, 0 ≦ c ≦ 0.05); Li a E 2-b X b O 4-c D c (0.90 ≦ a ≦ 1.8, 0 ≦ b ≦ 0.5, 0 ≦ c ≦ 0.05); Li a Ni 1-b-c Co b X c D α (0.90 ≦ a ≦ 1.8, 0 ≦ b ≦ 0.5, 0 ≦ c ≦ 0.5, 0 < α ≦ 2); Li a Ni 1-b-c Co b X c O 2-α T α (0.90 ≦ a ≦ 1.8, 0 ≦ b ≦ 0.5, 0 ≦ c ≦ 0.5, 0 < α < 2); Li a Ni1-b-c Co b X c O 2-α T2(0.90 ≦ a ≦ 1.8, 0 ≦ b ≦ 0.5, 0 ≦ c ≦ 0.5, 0 < α < 2); Li a Ni 1-b-c Mn b X c D α (0.90 ≦ a ≦ 1.8, 0 ≦ b ≦ 0.5, 0 ≦ c ≦ 0.5, 0 < α ≦ 2); Li a Ni 1-b-c Mn b X c O 2-α T α (0.90 ≦ a ≦ 1.8, 0 ≦ b ≦ 0.5, 0 ≦ c ≦ 0.05, 0 < α < 2); Li a Ni 1-b-c Mn b X c O 2-α T2(0.90 ≦ a ≦ 1.8, 0 ≦ b ≦ 0.5, 0 ≦ c ≦ 0.5, 0 < α < 2); Li a Ni b E c G d O2(0.90 ≦ a ≦ 1.8, 0 ≦ b ≦ 0.9, 0 ≦ c ≦ 0.5, 0.001 ≦ d ≦ 0.1); Li a Ni b Co c Mn d G e O2(0.90 ≦ a ≦ 1.8, 0 ≦ b ≦ 0.9, 0 ≦ c ≦ 0.5, 0 ≦ d ≦ 0.5, 0 ≦ e ≦ 0.1); Li a Ni b Co c Al d G e O2(0.90 ≦ a ≦ 1.8, 0 ≦ b ≦ 0.9, 0 ≦ c ≦ 0.5, 0 ≦ d ≦ 0.5, 0 ≦ e ≦ 0.1); Li a Ni b Co c Mn d G e O2(0.90 ≦ a ≦ 1.8, 0 ≦ b ≦ 0.9, 0 ≦ c ≦ 0.5, 0 ≦ d ≦ 0.5, 0.001 ≦ e ≦ 0.1); Li a NiG b O2(0.90 ≦ a ≦ 1.8, 0.001 ≦ b ≦ 0.1); Li a CoG bO2(0.90 ≤ a ≤ 1.8, 0.001 ≤ b ≤ 0.1); Li a Mn 1-b G b O2(0.90 ≤ a ≤ 1.8, 0.001 ≤ b ≤ 0.1); Li a Mn2G b O4(0.90 ≤ a ≤ 1.8, 0.001 ≤ b ≤ 0.1); Li a Mn 1-g G g PO4(0.90 ≤ a ≤ 1.8, 0 ≤ g ≤ 0.5); QO2; QS2; LiQS2; V2O5; LiV2O5; LiZO2; LiNiVO4; Li (3-f) J2(PO4)3(0 ≤ f ≤ 2); Li (3-f) Fe2(PO4)3(0 ≤ f ≤ 2); Li a FePO4(0.90 ≤ a ≤ 1.8)

[0077] In the above chemical formula, A is selected from the group consisting of Ni, Co, Mn, and combinations thereof; X is selected from the group consisting of Al, Ni, Co, Mn, Cr, Fe, Mg, Sr, V, rare earth elements, and combinations thereof; D is selected from the group consisting of O, F, S, P, and combinations thereof; E is selected from the group consisting of Co, Mn, and combinations thereof; T is selected from the group consisting of F, S, P, and combinations thereof; G is selected from the group consisting of Al, Cr, Mn, Fe, Mg, La, Ce, Sr, V, and combinations thereof; Q is selected from the group consisting of Ti, Mo, Mn, and combinations thereof; Z is selected from the group consisting of Cr, V, Fe, Sc, Y, and combinations thereof; J is selected from the group consisting of V, Cr, Mn, Co, Ni, Cu, and combinations thereof.

[0078] Of course, those having a coating layer on the surface of this compound can also be used, or the compound having a coating layer can be mixed with the said compound and used. This coating layer can contain at least one coating element compound selected from the group consisting of oxides of coating elements, hydroxides of coating elements, oxyhydroxides of coating elements, oxycarbonates of coating elements, and hydroxycarbonates of coating elements. The compounds forming these coating layers can be amorphous or crystalline. As the coating elements contained in the said coating layer, Mg, Al, Co, K, Na, Ca, Si, Ti, V, Sn, Ge, Ga, B, As, Zr, or mixtures thereof can be used. The coating layer formation process can use any coating method as long as such elements can be used for the said compound in a way that does not adversely affect the physical properties of the positive electrode active material (for example, spray coating, dipping method, etc.). This is well understood by those skilled in the art, so detailed description is omitted.

[0079] In the said positive electrode, the content of the positive electrode active material can be 90% to 98% by weight based on the total weight of the positive electrode active material layer.

[0080] In one embodiment, the positive electrode active material layer can further contain a binder and a conductive material. At this time, the contents of the binder and the conductive material can each be 1% to 5% by weight based on the total weight of the positive electrode active material layer.

[0081] The binder serves to well adhere the positive electrode active material particles to each other and also to well adhere the positive electrode active material to the current collector. As typical examples of the binder, polyvinyl alcohol, carboxymethyl cellulose, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, a polymer containing ethylene oxide, polyvinyl pyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, styrene-butadiene rubber, acrylated styrene-butadiene rubber, epoxy resin, nylon, etc. can be used, but it is not limited thereto.

[0082] The conductive material is used to impart conductivity to the electrode, and in the battery to be configured, any material may be used as long as it is an electron conductive material that does not cause a chemical change. Examples of the conductive material include carbon-based substances such as natural graphite, artificial graphite, carbon black, acetylene black, ketjen black, and carbon fiber; metal-based substances such as metal powders or metal fibers of copper, nickel, aluminum, silver, etc.; conductive polymers such as polyphenylene derivatives; or conductive materials containing mixtures thereof.

[0083] Al can be used as the current collector, but it is not limited thereto.

[0084] The electrolyte contains a non-aqueous organic solvent and a lithium salt.

[0085] The non-aqueous organic solvent serves as a medium through which ions involved in the electrochemical reaction of the battery can move.

[0086] As the non-aqueous organic solvent, carbonate-based, ester-based, ether-based, ketone-based, alcohol-based, or aprotic solvents can be used.

[0087] As the carbonate solvent, dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), methyl ethyl carbonate (MEC), ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), etc. can be used. As the ester solvent, methyl acetate, ethyl acetate, n-propyl acetate, dimethyl acetate, methyl propionate, ethyl propionate, decanolide, mevalonolactone, caprolactone, etc. can be used. As the ether solvent, dibutyl ether, tetraglyme, diglyme, dimethoxyethane, 2-methyltetrahydrofuran, tetrahydrofuran, etc. can be used. Further, as the ketone solvent, cyclohexanone, etc. can be used. Also, as the alcohol solvent, ethyl alcohol, isopropyl alcohol, etc. can be used, and as the aprotic solvent, nitriles such as R-CN (R is a linear, branched, or cyclic hydrocarbon group having 2 to 20 carbon atoms and can contain a double bond aromatic ring or an ether bond), amides such as dimethylformamide, dioxolanes such as 1,3-dioxolane, sulfolane, etc. can be used.

[0088] The organic solvent can be used alone or in a mixture of one or more. When used in a mixture of one or more, the mixing ratio can be appropriately adjusted according to the intended battery performance, which can be widely understood by those skilled in the art.

[0089] Also, in the case of the carbonate solvent, it is better to use a mixture of cyclic carbonate and chain carbonate. In this case, by mixing cyclic carbonate and chain carbonate in a volume ratio of 1:1 to 1:9, excellent electrolyte performance can be exhibited.

[0090] The organic solvent may further contain an aromatic hydrocarbon-based organic solvent in the carbonate-based solvent. At this time, the carbonate-based solvent and the aromatic hydrocarbon-based organic solvent can be mixed at a volume ratio of 1:1 to 30:1.

[0091] As the aromatic hydrocarbon-based organic solvent, an aromatic hydrocarbon-based compound represented by the following Chemical Formula 1 can be used.

[0092]

Chemical Formula

[0093] (In the Chemical Formula 1, R1 to R6 are the same as or different from each other and are selected from the group consisting of hydrogen, halogen, an alkyl group having 1 to 10 carbon atoms, a haloalkyl group, and combinations thereof.)

[0094] Specific examples of the aromatic hydrocarbon organic solvent include benzene, fluorobenzene, 1,2-difluorobenzene, 1,3-difluorobenzene, 1,4-difluorobenzene, 1,2,3-trifluorobenzene, 1,2,4-trifluorobenzene, chlorobenzene, 1,2-dichlorobenzene, 1,3-dichlorobenzene, 1,4-dichlorobenzene, 1,2,3-trichlorobenzene, 1,2,4-trichlorobenzene, iodobenzene, 1,2-diiodobenzene, 1,3-diiodobenzene, 1,4-diiodobenzene, 1,2,3-triiodobenzene, 1,2,4-triiodobenzene, toluene, fluorotoluene, 2,3-difluorotoluene, 2,4-difluorotoluene, 2,5-difluorotoluene, 2,3,4-trifluorotoluene, 2,3,5-trifluorotoluene, chlorotoluene, 2,3-dichlorotoluene, 2,4-dichlorotoluene, 2,5-dichlorotoluene, 2,3,4-trichlorotoluene, 2,3,5-trichlorotoluene, iodotoluene, 2,3-diiodotoluene, 2,4-diiodotoluene, 2,5-diiodotoluene, 2,3,4-triiodotoluene, 2,3,5-triiodotoluene, xylene, and those selected from the group consisting of combinations thereof.

[0095] In order to improve the battery life, the electrolyte can further contain vinyl ethyl carbonate, vinylene carbonate or an ethylene carbonate compound of the following Chemical Formula 2 as a life improvement additive.

[0096]

Chemical formula

[0097] (In Chemical Formula 2, R7 and R8 are the same as or different from each other, and are selected from the group consisting of hydrogen, a halogen group, a cyano group (CN), a nitro group (NO2), and a fluorinated alkyl group having 1 to 5 carbon atoms, and at least one of R7 and R8 is selected from the group consisting of a halogen group, a cyano group (CN), a nitro group (NO2), and a fluorinated alkyl group having 1 to 5 carbon atoms, provided that R7 and R8 are not all hydrogen.)

[0098] Typical examples of the ethylene carbonate-based compound include difluoroethylene carbonate, chloroethylene carbonate, dichloroethylene carbonate, bromoethylene carbonate, dibromoethylene carbonate, nitroethylene carbonate, cyanoethylene carbonate, or fluoroethylene carbonate. When such a life-improving additive is further used, its usage amount can be adjusted as appropriate.

[0099] The lithium salt is dissolved in an organic solvent, acts as a source of lithium ions in the battery to enable the operation of a basic lithium secondary battery, and plays a role in promoting the movement of lithium ions between the positive electrode and the negative electrode. Typical examples of such lithium salts include LiPF6, LiBF4, LiSbF6, LiAsF6, LiN(SO2C2F5)2, Li(CF3SO2)2N, LiN(SO3C2F5)2, Li(FSO2)2N (lithium bis(fluorosulfonyl)imide: LiFSI), LiC4F9SO3, LiClO4, LiAlO2, LiAlCl4, LiPO2F2, LiN(C x F 2x+1 SO2)(C y F 2y+1SO2) (where x and y are natural numbers, for example, integers from 1 to 20), lithium difluoro(bisoxolato) phosphate, LiCl, LiI, LiB(C2O4)2 (lithium bis(oxalato) borate: LiBOB) and lithium difluoro(oxalato) borate (LiDFOB), and includes one or more selected from the group as a supporting electrolyte salt. The concentration of the lithium salt is preferably used within the range of 0.1M to 2.0M. When the concentration of the lithium salt is within the above range, the electrolyte has appropriate conductivity and viscosity, so it can exhibit excellent electrolyte performance, and lithium ions can move effectively.

[0100] Depending on the type of lithium secondary battery, a separator can also be present between the positive electrode and the negative electrode. As such a separator, polyethylene, polypropylene, polyvinylidene fluoride, or a multilayer film of two or more layers thereof can be used. Of course, mixed multilayer films such as polyethylene / polypropylene two-layer separator, polyethylene / polypropylene / polyethylene three-layer separator, polypropylene / polyethylene / polypropylene three-layer separator, etc. can be used.

[0101] Fig. 2 shows an exploded perspective view of a lithium secondary battery according to an embodiment of the present invention. The lithium secondary battery according to an embodiment will be described by taking the case of being rectangular as an example, but the present invention is not limited thereto, and it can be applied to batteries in various forms such as cylindrical and pouch types.

[0102] Referring to Fig. 2, a lithium secondary battery 100 according to an embodiment can include an electrode assembly 40 wound with a separator 30 interposed between a positive electrode 10 and a negative electrode 20, and a case 50 in which the electrode assembly 40 is incorporated. The positive electrode 10, the negative electrode 20, and the separator 30 can be impregnated with an electrolyte solution (not shown).

[0103] Hereinafter, examples and comparative examples of the present invention will be described. Such a single example below is one example of the present invention, and the present invention is not limited to the single example below.

[0104] <Battery Configuration Change Experiment> (Example 1) 96% by weight of artificial graphite negative electrode active material, 1% by weight of styrene-butadiene rubber binder, 1% by weight of carboxymethyl cellulose thickener, and 2% by weight of carbon black conductive material were mixed in an aqueous solvent to produce a negative electrode active material layer slurry.

[0105] The negative electrode active material layer slurry was coated on a copper foil current collector, dried, and rolled to form a negative electrode active material layer on the current collector.

[0106] The obtained product was needle punched to form holes with a hole depth of 20 μm and a hole diameter of 20 μm at a hole density of 100 pt / mm 2 and a hole pitch of 100 μm to produce a negative electrode having a negative electrode active material layer including holes. The composite density of the produced negative electrode was 1.45 g / cm 3 and the one-side thickness of the negative electrode active material layer was 124 μm, and the one-side load level (L / L) was 18.0 mg / cm 2 .

[0107] 95% by weight of LiCoO2 positive electrode active material, 3% by weight of polyvinylidene fluoride binder, and 2% by weight of Ketjen black conductive material were mixed in an N-methylpyrrolidone solvent to produce a positive electrode active material slurry. This was coated on an aluminum current collector, dried, and rolled to produce a positive electrode.

[0108] Using the negative electrode, polyethylene / polypropylene separator, the positive electrode, and the electrolyte, a lithium secondary battery with a current density of 3 mA / cm 2 was produced in a normal method. As the electrolyte, a mixed solvent of ethylene carbonate and diethyl carbonate (50:50 volume ratio) in which 1.0 M LiPF6 was dissolved was used.

[0109] (Example 2) The composite material density is 1.5 g / cm 3 A negative electrode was produced in the same manner as in Example 1 except that the density was 1.5 g / cm and the single-sided thickness of the negative electrode active material layer was 120 μm. Using the negative electrode thus obtained, a lithium secondary battery was produced in the same manner as in Example 1.

[0110] (Example 3) The composite material density is 1.53 g / cm 3 A negative electrode was produced in the same manner as in Example 1 except that the density was 1.53 g / cm and the single-sided thickness of the negative electrode active material layer was 118 μm. Using the negative electrode thus obtained, a lithium secondary battery was produced in the same manner as in Example 1.

[0111] (Example 4) The composite material density is 1.58 g / cm 3 A negative electrode was produced in the same manner as in Example 1 except that the density was 1.58 g / cm and the single-sided thickness of the negative electrode active material layer was 114 μm. Using the negative electrode thus obtained, a lithium secondary battery was produced in the same manner as in Example 1.

[0112] (Example 5) The composite material density is 1.53 g / cm 3 A negative electrode was produced in the same manner as in Example 1 except that the density was 1.53 g / cm, the thickness of the negative electrode active material layer on one side was 106 μm, and the one-sided load level (L / L) was 16.2 mg / cm 2 Using the negative electrode thus obtained, the separator, positive electrode, and electrolyte of Example 1, a lithium secondary battery with a current density of 2.7 mA / cm 2 was produced by a conventional method.

[0113] (Example 6) The composite material density is 1.53 g / cm 3 A negative electrode was produced in the same manner as in Example 1 except that the density was 1.53 g / cm, the thickness of the negative electrode active material layer on one side was 137 μm, and the one-sided load level (L / L) was 21.0 mg / cm 2 Using the negative electrode thus obtained, the separator, positive electrode, and electrolyte of Example 1, a lithium secondary battery with a current density of 3.5 mA / cm 2 was produced by a conventional method.

[0114] (Comparative Example 1) A negative electrode with a composite material density of 1.45 g / cm³, a one-sided thickness of the negative electrode active material layer of 124 μm, and a one-sided load level (L / L) of 18.0 mg / cm² was produced by carrying out the same procedures as in Example 1 except that the needle punching process was not performed. Using the negative electrode, a lithium secondary battery was produced in the same manner as in Example 1. 3 ³, a one-sided thickness of the negative electrode active material layer of 124 μm, and a one-sided load level (L / L) of 18.0 mg / cm² 2 ² was produced by carrying out the same procedures as in Example 1 except that the needle punching process was not performed. Using the negative electrode, a lithium secondary battery was produced in the same manner as in Example 1.

[0115] (Comparative Example 2) A negative electrode with a composite material density of 1.5 g / cm³, a one-sided thickness of the negative electrode active material layer of 120 μm, and a one-sided load level (L / L) of 18.0 mg / cm² was produced by carrying out the same procedures as in Example 2 except that the needle punching process was not performed. Using the negative electrode, a lithium secondary battery was produced in the same manner as in Example 2. 3 ³, a one-sided thickness of the negative electrode active material layer of 120 μm, and a one-sided load level (L / L) of 18.0 mg / cm² 2 ² was produced by carrying out the same procedures as in Example 2 except that the needle punching process was not performed. Using the negative electrode, a lithium secondary battery was produced in the same manner as in Example 2.

[0116] (Comparative Example 3) A negative electrode with a composite material density of 1.53 g / cm³, a one-sided thickness of the negative electrode active material layer of 118 μm, and a one-sided load level (L / L) of 18.0 mg / cm² was produced by carrying out the same procedures as in Example 3 except that the needle punching process was not performed. Using the negative electrode, a lithium secondary battery was produced in the same manner as in Example 3. 3 ³, a one-sided thickness of the negative electrode active material layer of 118 μm, and a one-sided load level (L / L) of 18.0 mg / cm² 2 ² was produced by carrying out the same procedures as in Example 3 except that the needle punching process was not performed. Using the negative electrode, a lithium secondary battery was produced in the same manner as in Example 3.

[0117] (Comparative Example 4) A negative electrode with a composite material density of 1.58 g / cm³, a one-sided thickness of the negative electrode active material layer of 114 μm, and a one-sided load level (L / L) of 18.0 mg / cm² was produced by carrying out the same procedures as in Example 4 except that the needle punching process was not performed. Using the negative electrode, a lithium secondary battery was produced in the same manner as in Example 4. 3 ³, a one-sided thickness of the negative electrode active material layer of 114 μm, and a one-sided load level (L / L) of 18.0 mg / cm² 2 ² was produced by carrying out the same procedures as in Example 4 except that the needle punching process was not performed. Using the negative electrode, a lithium secondary battery was produced in the same manner as in Example 4.

[0118] (Comparative Example 5) Except for not performing the needle punching process, the procedure was the same as in Example 5, and the composite material density was 1.53 g / cm 3 , the one-side thickness of the negative electrode active material layer was 106 μm, and the one-side load level (L / L) was 16.2 mg / cm 2 . A negative electrode was manufactured. Using the negative electrode, the separator of Example 1, the positive electrode, and the electrolyte, a lithium secondary battery with a current density of 2.7 mA / cm 2 was manufactured in a conventional manner.

[0119] (Comparative Example 6) Except for not performing the needle punching process, the procedure was the same as in Example 6, and the composite material density was 1.53 g / cm 3 , the one-side thickness of the negative electrode active material layer was 137 μm, and the one-side load level (L / L) was 21.0 mg / cm 2 . A negative electrode was manufactured. Using the negative electrode, the separator of Example 1, the positive electrode, and the electrolyte, a lithium secondary battery with a current density of 3.5 mA / cm 2 was manufactured in a conventional manner.

[0120] (Example 7) 25% by weight of polyacrylic acid and 75% by weight of polyvinylidene fluoride were mixed in an aqueous solvent to produce an adhesive layer slurry.

[0121] The negative electrode active material layer slurry of Example 1 was coated on a copper foil current collector, dried, and rolled to form a negative electrode active material layer on the current collector. Next, the adhesive layer slurry was coated on the negative electrode active material layer, dried, and rolled to form an adhesive layer.

[0122] The product with the negative electrode active material layer and the adhesive layer formed was needle punched, and holes with a hole depth of 20 μm and a hole diameter of 20 μm were formed at a hole density of 100 pt / mm 2 and a hole pitch of 100 μm to manufacture a negative electrode having a negative electrode active material layer containing holes. The composite material density of the manufactured negative electrode was 1.45 g / cm 3 , the one-side thickness of the negative electrode active material layer was 124 μm, and the one-side load level (L / L) was 18.0 mg / cm 2It was

[0123] 95% by weight of LiCoO₂ cathode active material, 3% by weight of polyvinylidene fluoride binder, and 2% by weight of Ketjenblack conductive material are mixed in an N-methylpyrrolidone solvent to produce a cathode active material slurry. This is coated on an aluminum current collector, dried, and rolled to produce a cathode.

[0124] Using the anode, polyethylene / polypropylene separator, the cathode, and the electrolyte, a lithium secondary battery with a current density of 3 mA / cm² was manufactured in a normal method. 2 A lithium secondary battery with a current density of 3 mA / cm² was manufactured. As the electrolyte, a mixed solvent of ethylene carbonate and diethyl carbonate (50:50 volume ratio) in which 1.0 M LiPF₆ was dissolved was used.

[0125] (Example 8) The composite material density is 1.5 g / cm³, and an anode was manufactured in the same manner as in Example 7 except that the thickness of one side of the anode active material layer is 120 μm. Using the anode, a lithium secondary battery was manufactured in the same manner as in Example 7. 3 The composite material density is 1.5 g / cm³, and an anode was manufactured in the same manner as in Example 7 except that the thickness of one side of the anode active material layer is 120 μm. Using the anode, a lithium secondary battery was manufactured in the same manner as in Example 7.

[0126] (Example 9) The composite material density is 1.53 g / cm³, and an anode was manufactured in the same manner as in Example 7 except that the thickness of one side of the anode active material layer is 118 μm. Using the anode, a lithium secondary battery was manufactured in the same manner as in Example 7. 3 The composite material density is 1.53 g / cm³, and an anode was manufactured in the same manner as in Example 7 except that the thickness of one side of the anode active material layer is 118 μm. Using the anode, a lithium secondary battery was manufactured in the same manner as in Example 7.

[0127] (Example 10) The composite material density is 1.58 g / cm³, and an anode was manufactured in the same manner as in Example 7 except that the thickness of one side of the anode active material layer is 114 μm. Using the anode, a lithium secondary battery was manufactured in the same manner as in Example 7. 3 The composite material density is 1.58 g / cm³, and an anode was manufactured in the same manner as in Example 7 except that the thickness of one side of the anode active material layer is 114 μm. Using the anode, a lithium secondary battery was manufactured in the same manner as in Example 7.

[0128] (Example 11) The composite material density is 1.53 g / cm³ 3and the thickness of the negative electrode active material layer is 106 μm on one side, and the one-sided load level (L / L) is 16.2 mg / cm 2 A negative electrode was produced in the same manner as in Example 7 except for the above. Using the negative electrode, the separator, positive electrode, and electrolyte of Example 7, a lithium secondary battery having a current density of 2.7 mA / cm 2 was produced by a normal method.

[0129] (Example 12) The composite material density is 1.53 g / cm 3 and the thickness of the negative electrode active material layer is 137 μm on one side, and the one-sided load level (L / L) is 21.0 mg / cm 2 A negative electrode was produced in the same manner as in Example 7 except for the above. Using the negative electrode, the separator, positive electrode, and electrolyte of Example 7, a lithium secondary battery having a current density of 3.5 mA / cm 2 was produced by a normal method.

[0130] (Comparative Example 7) A negative electrode having a composite material density of 1.45 g / cm 3 was produced in the same manner as in Example 7 except that the needle punching process was not performed, the one-sided thickness of the negative electrode active material layer was 124 μm, and the one-sided load level (L / L) was 18.0 mg / cm 2 Using the negative electrode, a lithium secondary battery was produced in the same manner as in Example 7.

[0131] (Comparative Example 8) A negative electrode having a composite material density of 1.5 g / cm 3 was produced in the same manner as in Example 8 except that the needle punching process was not performed, the one-sided thickness of the negative electrode active material layer was 120 μm, and the one-sided load level (L / L) was 18.0 mg / cm 2 Using the negative electrode, a lithium secondary battery was produced in the same manner as in Example 8.

[0132] (Comparative Example 9) A negative electrode having a composite material density of 1.53 g / cm3 and a negative electrode having a single-sided thickness of the negative electrode active material layer of 118 μm and a single-sided load level (L / L) of 18.0 mg / cm 2 was manufactured. Using the negative electrode, a lithium secondary battery was manufactured in the same manner as in Example 9.

[0133] (Comparative Example 10) Except that the needle punching process was not carried out, the same procedure as in Example 10 was carried out, and the composite material density was 1.58 g / cm 3 and a negative electrode having a single-sided thickness of the negative electrode active material layer of 114 μm and a single-sided load level (L / L) of 18.0 mg / cm 2 was manufactured. Using the negative electrode, a lithium secondary battery was manufactured in the same manner as in Example 10.

[0134] (Comparative Example 11) Except that the needle punching process was not carried out, the same procedure as in Example 11 was carried out, and the composite material density was 1.53 g / cm 3 and a negative electrode having a single-sided thickness of the negative electrode active material layer of 106 μm and a single-sided load level (L / L) of 16.2 mg / cm 2 was manufactured. Using the negative electrode, the separator, the positive electrode, and the electrolyte of Example 7, a lithium secondary battery having a current density of 2.7 mA / cm 2 was manufactured in a conventional manner.

[0135] (Comparative Example 12) Except that the needle punching process was not carried out, the same procedure as in Example 12 was carried out, and the composite material density was 1.53 g / cm 3 and a negative electrode having a single-sided thickness of the negative electrode active material layer of 137 μm and a single-sided load level (L / L) of 21.0 mg / cm 2 was manufactured. Using the negative electrode, the separator, the positive electrode, and the electrolyte of Example 7, a lithium secondary battery having a current density of 3.5 mA / cm 2 was manufactured in a conventional manner.

[0136] The battery configurations of Examples 1 to 12 and Comparative Examples 1 to 12 are tabulated and shown in Table 1 below.

[0137] Experimental Example 1) Adhesion Evaluation For the negative electrodes produced according to Examples 1 to 12 and Comparative Examples 1 to 12 above, the presence or absence of shedding of the active material layer was measured by the following method.

[0138] After cutting the negative electrode into a circle with a diameter of 36 mm, the powder that fell off during this process was removed by air blowing, and the weight of the cut negative electrode was measured as the initial negative electrode weight.

[0139] The cut negative electrode was folded in half in the longitudinal direction, and the folded part was pressed once with a metal roll (500 g). Then, it was flattened and folded in half horizontally, and the folded part was pressed once with a metal roll (500 g). Next, the negative electrode was flattened, the falling powder was removed, and the weight of the flattened negative electrode was measured and taken as the final negative electrode weight.

[0140] The amount of shedding was determined as shown in the following formula (1). When the active material layer did not shed (within 10% of the shedding amount), it was rated as OK, and when it shed (exceeding 10% of the shedding amount), it was rated as NG. The results are shown in Table 2 below.

[0141] [Formula 1] Shedding amount (%) = [(Initial negative electrode weight - Final negative electrode weight) / Initial negative electrode weight] * 100

[0142] Experimental Example 2) Capacity Evaluation The lithium secondary batteries produced according to Examples 1 to 12 and Comparative Examples 1 to 12 above were charged and discharged once at 0.1C to obtain the discharge capacity. The results are shown in Table 2 below as the battery capacity.

[0143] Experimental Example 3) Capacity Retention Rate Evaluation The lithium secondary batteries produced according to Examples 1 to 12 and Comparative Examples 1 to 12 above were charged and discharged 200 times at 3C. The 200th discharge capacity consumption relative to the first discharge capacity was determined, and the results are shown in Table 2 below.

[0144] Experimental Example 4) Swelling Characteristic Evaluation The lithium secondary batteries manufactured according to Examples 1 to 12 and Comparative Examples 1 to 12 were charged and discharged 200 times at 3C. The battery thickness after 200 charge-discharge cycles was measured with respect to the battery thickness before the charge-discharge cycles, and the increase rate (%) of the battery thickness after 200 charge-discharge cycles with respect to 100% of the thickness before discharge was determined. The results are shown in Table 2 below as swelling.

[0145] Experimental Example 5) Resistance Characteristic Evaluation After the lithium secondary batteries manufactured according to Examples 1 to 12 and Comparative Examples 1 to 12 were subjected to 200 charge-discharge cycles at 3C, the resistance was measured. The results are shown in Table 2 below.

[0146] [Table 1]

[0147] [Table 2]

[0148] As shown in Table 2 above, in the case of Examples 1 to 12 in which a plurality of holes were formed in the active material layer at a hole density of 100 pt / mm 2 or more, it can be seen that the capacity retention rate was improved compared to Comparative Examples 1 to 12 at the same load level. It can also be seen that the capacity retention rate was improved at the same composite density even when an adhesive layer was formed together with the holes (Examples 7 to 12).

[0149] Furthermore, in the case of Examples 1 to 12, it can be seen that the swelling characteristics are superior to those of Comparative Examples 1 to 12 (that is, the swelling is less) and the resistance is lower than that of Comparative Examples 1 to 12.

[0150] <Hole Density Change Experiment - Using a Needle Punch> (Comparative Examples 13 to 16, Examples 13 to 20, and Reference Examples 1 to 3) The obtained product was needle-punched and carried out in the same manner as in Example 9 except that the density of the holes, the pitch of the holes, the depth of the holes, and the diameter of the holes were changed as shown in Table 3 below, to produce a negative electrode having a negative electrode active material layer and an adhesive layer.

[0151] Using the negative electrode, the separator, the positive electrode, and the electrolyte of Example 9, a lithium secondary battery having the current density shown in Table 3 below was produced by a normal method.

[0152] The battery characteristics of Examples 13 to 20, Comparative Examples 13 to 16, and Reference Examples 1 to 3 were carried out in the same manner as in Experimental Examples 1 to 5. The results are shown in Table 4 below. Also, for comparison, the results of Comparative Examples 9 and 12 and the results of Example 9 are shown together in Table 4 below.

[0153]

Table 3

[0154]

Table 4

[0155] As shown in Table 4 above, in the case of Examples 9, 13 to 20 in which holes were formed at an appropriate hole density, at the same load level, it can be seen that excellent capacity retention, excellent swelling characteristics, and low resistance were shown. On the other hand, in the case where no holes were formed (Comparative Examples 9, 12, and 15), or in the case of Comparative Examples 13, 14, and 16 where the hole density was excessively low even though holes were formed, at the same load level, low capacity retention, deteriorated swelling characteristics, and high resistance were shown. Furthermore, in the case of Reference Examples 1 to 3 where the hole density was excessively high at 800 pt / mm 2 excessive weak adhesion and peeling problems occurred.

[0156] <Experiment on changing hole density - using laser processing> (Comparative Examples 17 to 19, Examples 21 to 29) The obtained product was subjected to laser processing using a WS-FLEX IR femtosecond laser workstation, and a negative electrode having a negative electrode active material layer and an adhesive layer was manufactured in the same manner as in Example 9 except that the hole density, hole pitch, hole depth, and hole diameter were changed as shown in Table 5 below.

[0157] Using the negative electrode, the separator, positive electrode, and electrolyte of Example 9, a lithium secondary battery having the current density shown in Table 5 below was manufactured by a conventional method.

[0158] The battery characteristics of Examples 21 to 29 and Comparative Examples 17 to 19 were measured in the same manner as in Experimental Examples 1 to 5. The results are shown in Table 6 below. For comparison, the results of Comparative Examples 9, 12, and 15 are also shown in Table 6 below.

[0159]

Table 5

[0160]

Table 6

[0161] As shown in Table 6 above, in the case of Examples 21 to 29 where holes were formed with an appropriate hole density, at the same load level, it can be seen that they exhibited excellent capacity retention and swelling characteristics and low resistance. On the other hand, in the case of Comparative Examples 9, 12, and 15 where no holes were formed, or in Comparative Examples 17 to 20 where the hole density was excessively low even though holes were formed, at the same load level, they exhibited low capacity retention, deteriorated swelling characteristics, and high resistance.

[0162] <Hole Depth Change Experiment - Using Needle Punch> (Examples 30 to 41) The obtained product was subjected to needle punch processing, and a negative electrode having a negative electrode active material layer and an adhesive layer was manufactured in the same manner as in Example 9 except that the hole density, hole pitch, hole depth, and hole diameter were changed as shown in Table 7 below.

[0163] Using the negative electrode, the separator, the positive electrode, and the electrolytic solution of Example 9, a lithium secondary battery with a current density of 3 mA / cm 2 was manufactured in a normal manner.

[0164] The battery characteristics of Examples 30 to 41 were carried out in the same manner as in Experimental Examples 1 to 5. The results are shown in Table 8 below. For comparison, the results of Comparative Examples 9, 12, and 15 are also shown in Table 8 below.

[0165]

Table 7

[0166]

Table 8

[0167] In the case of Examples 30 to 41 in which holes were formed with an appropriate hole density and an appropriate hole depth as shown in Table 8, it can be seen that at the same load level, excellent capacity retention and swelling characteristics were shown, and low resistance was exhibited. On the contrary, when no holes were formed (Comparative Examples 9, 12, and 15), at the same load level, low capacity retention, deteriorated swelling characteristics, and high resistance were shown.

[0168] <Hole Depth Change Experiment - Using Laser Processing> (Examples 42 to 51 and Reference Examples 4 to 9) The obtained product was laser processed using a WS-FLEX IR femtosecond laser workstation, and except for changing the hole density, hole pitch, hole depth, and hole diameter as shown in Table 9 below, it was carried out in the same manner as in Example 9 to manufacture a negative electrode having a negative electrode active material layer and an adhesive layer.

[0169] Using the negative electrode, the separator, the positive electrode, and the electrolytic solution of Example 9, a lithium secondary battery with a current density of 3 mA / cm 2 was manufactured in a normal manner.

[0170] The battery characteristics of Examples 42 to 53 and Reference Examples 4 to 9 were carried out in the same manner as in Experimental Examples 1 to 5. The results are shown in Table 10 below. For comparison, the results of Examples 22 and 25 and Comparative Examples 9, 12, and 15 are also shown in Table 10 below.

[0171] [Table 9]

[0172] [Table 10]

[0173] As shown in Table 10 above, in the case of Examples 42 to 51 in which holes were formed with an appropriate hole density and an appropriate hole depth, it can be seen that at the same load level, excellent capacity retention, excellent swelling characteristics, and low resistance were exhibited. On the contrary, when no holes were formed (Comparative Examples 9, 12, and 15), low capacity retention, deteriorated swelling characteristics, and high resistance were shown at the same load level. Also, in the case of Reference Examples 5, 7, and 9 in which the holes were formed too deeply even though holes were formed, a problem occurred in that the adhesive force was excessively weak and peeling off occurred.

[0174] <Hole diameter change experiment - using needle punch> (Examples 52 to 60 and Reference Examples 10 to 12) The obtained product was subjected to needle punching, and except for changing the hole density, hole pitch, hole depth, and hole diameter as shown in Table 11 below, it was carried out in the same manner as in Example 9 above to produce a negative electrode having a negative electrode active material layer and an adhesive layer.

[0175] Using the negative electrode, the separator, positive electrode, and electrolyte of Example 9 above, a lithium secondary battery having the current density shown in Table 11 below was produced by a normal method.

[0176] The battery characteristics of Examples 52 to 60 and Reference Examples 10 to 12 were measured in the same manner as in Experimental Examples 1 to 5. The results are shown in Table 12 below. For comparison, the results of Comparative Examples 9, 12, and 15 are also shown in Table 12 below.

[0177]

Table 11

[0178]

Table 12

[0179] As shown in Table 12, in the case of Examples 52 to 60 in which holes were formed with an appropriate hole density and an appropriate hole diameter, it can be seen that at the same load level, excellent capacity retention, excellent swelling characteristics, and low resistance were exhibited. On the other hand, when no holes were formed (Comparative Examples 9, 12, and 15), a low capacity retention was shown. In addition, in the case of Reference Examples 10 to 12 in which holes were formed with an excessively large hole diameter even though holes were formed, there was a problem that the adhesive force was excessively weak and peeling occurred.

[0180] As described above, the preferred embodiments of the present invention have been described. However, the present invention is not limited thereto, and various modifications can be made within the scope of the claims, the detailed description of the invention, and the accompanying drawings, and it is natural that these also belong to the scope of the present invention.

Explanation of Reference Numerals

[0181] 1 Negative electrode 3a Negative electrode active material layer 3b Negative electrode active material layer 5 Current collector 7 Hole 10 Positive electrode 20 Negative electrode 30 Separator 40 Electrode assembly 50 Case

Claims

1. A current collector; A negative electrode active material layer located on the current collector; and An adhesive layer located on the negative electrode active material layer, The negative electrode active material layer and the adhesive layer contain a plurality of holes at a hole density of 200 pt / mm ２ to 625 pt / mm ２ and are included in the hole density of wherein the "pt" means the number, A negative electrode for a lithium secondary battery, wherein the diameters of the plurality of holes are 35 μm or less.

2. The negative electrode for a lithium secondary battery according to Claim 1, wherein the depth of the hole is 5 μm to 40 μm.

3. The negative electrode for a lithium secondary battery according to Claim 1, wherein the depth of the hole is 5 μm to 20 μm.

4. The negative electrode for a lithium secondary battery according to Claim 1, wherein the negative electrode active material layer contains the holes at a pitch of 100 μm or less.

5. The negative electrode for a lithium secondary battery according to Claim 1, wherein the negative electrode active material layer contains the holes at a pitch of 40 μm to 100 μm.

6. The negative electrode for a lithium secondary battery according to Claim 1, wherein the thickness of the adhesive layer is 1 μm to 5 μm.

7. The negative electrode for a lithium secondary battery according to Claim 1, wherein the adhesive layer contains a vinyl-based or acrylic-based polymer, polyvinyl alcohol, a fluorine-based polymer, or a combination thereof.

8. The negative electrode has a load level of 15 mg / cm ２ or higher, and is the negative electrode for a lithium secondary battery according to claim 1.

9. A negative electrode according to any one of Claims 1 to 8; A positive electrode; and A lithium secondary battery including an electrolyte.

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