Negative electrode and secondary battery containing the same

Abstract

The present invention provides a negative electrode comprising: a negative electrode current collector; a first negative electrode active material layer disposed on at least one surface of the negative electrode current collector and including a first negative electrode active material; and a second negative electrode active material layer disposed on a second surface of the negative electrode current collector, the first negative electrode active material layer including side portions defined on both sides and a central portion defined excluding the side portions, the side portions being inclined toward a surface of the negative electrode current collector; the second negative electrode active material layer disposed on at least a part of the side portions; and a maximum height of the second negative electrode active material layer based on the surface of the negative electrode current collector is equal to or less than a maximum height of the first negative electrode active material layer.

Description

[Technical Field]

[0001] [Cross-reference of related applications] This application claims priority based on Korean Patent Application No. 10-2021-0097021, filed on 23 July 2021, and all content disclosed in the said Korean Patent Application is incorporated herein as part of this specification.

[0002] This invention relates to a negative electrode and a secondary battery including the same. [Background technology]

[0003] Recently, with the development of the information society, personal IT devices and computer networks have advanced, leading to an increased reliance on electrical energy in society as a whole. This has created a demand for the development of battery technologies to efficiently store and utilize electrical energy.

[0004] In particular, with growing interest in solving environmental problems and realizing a sustainable, circular society, research into energy storage devices such as lithium-ion batteries and electric double-layer capacitors is being conducted extensively. Among these, lithium-ion secondary batteries are attracting attention as the battery system with the theoretically highest energy density among battery technologies.

[0005] The lithium secondary battery generally includes a positive electrode, a negative electrode, a separation membrane interposed between the positive and negative electrodes, an electrolyte, an organic solvent, etc. Furthermore, the positive and negative electrodes may have active material layers formed on a current collector, containing either a positive electrode active material or a negative electrode active material.

[0006] In particular, the negative electrode active material layer is generally manufactured by adding negative electrode active material and the like to a solvent for forming the negative electrode slurry, and then coating, drying, and rolling the resulting negative electrode slurry onto a negative electrode current collector. However, due to the fluid properties of the negative electrode slurry, the negative electrode active material layer may develop a slope at its end, making it difficult to achieve the desired capacity or negative electrode loading amount. Furthermore, the sloped end may not be able to adequately accept lithium from the opposing positive electrode, leading to lithium deposition. This can result in insufficient capacity, reduced charge-discharge efficiency, and reduced lifespan characteristics of the lithium secondary battery.

[0007] Japanese Patent Publication No. 2020-167066 discloses a positive electrode for lithium-ion secondary batteries, a positive electrode sheet for lithium-ion secondary batteries, and a method for manufacturing the same, but it has not been able to present an alternative to the above-mentioned problem. [Prior art documents] [Patent Documents]

[0008] [Patent Document 1] Japanese Patent Publication No. 2020-167066 [Overview of the project] [Problems that the invention aims to solve]

[0009] One objective of the present invention is to provide a negative electrode that can improve the negative electrode capacity, prevent the problem of lithium deposition on the negative electrode side, and thereby improve the negative electrode capacity, charge / discharge efficiency, and life characteristics.

[0010] Another objective of the present invention is to provide a secondary battery including the negative electrode described above. [Means for solving the problem]

[0011] The present invention provides a negative electrode including a negative electrode current collector, a first negative electrode active material layer disposed on at least one surface of the negative electrode current collector and containing a first negative electrode active material, and a second negative electrode active material layer containing a second negative electrode active material. The first negative electrode active material layer includes side portions partitioned on both sides and a central portion partitioned excluding the side portions. The side portions have an inclination toward the surface of the negative electrode current collector. The second negative electrode active material layer is disposed on at least a part of the side portions, and the maximum height of the second negative electrode active material layer is equal to or less than the maximum height of the first negative electrode active material layer with reference to the surface of the negative electrode current collector.

[0012] The present invention also provides a lithium secondary battery including the above-described negative electrode, a positive electrode, a separator interposed between the negative electrode and the positive electrode, and an electrolyte.

Advantages of the Invention

[0013] The negative electrode according to the present invention includes a first negative electrode active material layer including side portions inclined toward the surface of the negative electrode current collector, and a second negative electrode active material layer disposed on at least a part of the side portions. With reference to the surface of the negative electrode current collector, the maximum height of the second negative electrode active material layer is equal to or less than the maximum height of the first negative electrode active material layer. The negative electrode according to the present invention forms a second negative electrode active material layer on the inclined side portions, thereby compensating for the insufficient capacity of the negative electrode and the loading amount of the negative electrode due to the inclination of the side portions, and preventing the problem of precipitation of uninserted lithium, improving the capacity of the negative electrode, and improving the charge-discharge efficiency and life characteristics of the negative electrode and the lithium secondary battery including the same.

Brief Description of the Drawings

[0014] [Figure 1] It is a side view for schematically explaining the negative electrode of the present invention. [Figure 2] It is a plan view for schematically explaining the negative electrode of the present invention.

Embodiments for Carrying Out the Invention

[0015] The present invention will be described in more detail below to aid in understanding the invention. In this specification and in the claims, terms and words used should not be interpreted in a manner limited to their ordinary or dictionary meanings, but rather in a manner consistent with the technical idea of ​​the invention, in accordance with the principle that inventors may appropriately define the concepts of terms in order to best describe their invention.

[0016] Furthermore, in this specification, terms such as “includes,” “equip,” or “possess” are intended to specify the existence of implemented features, figures, stages, components, or combinations thereof, and should be understood not to preemptively exclude the possibility of the existence or addition of one or more other features, figures, stages, components, or combinations thereof.

[0017] In this specification, average particle size D 50 This can be defined as the particle size corresponding to 50% of the cumulative volume in the particle size distribution curve. The average particle size D 50 This can be measured, for example, using the laser diffraction method. The laser diffraction method can generally measure particle sizes from the submicron region to several millimeters in size, and can obtain highly reproducible and high-resolution results.

[0018] The negative electrode of the present invention will be described in detail below with reference to the drawings. Specifically, Figure 1 is a side view illustrating the negative electrode of the present invention, and Figure 2 is a top view illustrating the negative electrode of the present invention. When assigning reference numerals to the components in each drawing, identical components may be given the same reference numeral whenever possible, even if they are shown in other drawings. Furthermore, when describing the present invention, if it is determined that a specific description of a related known configuration or function may obscure the gist of the present invention, such detailed description may be omitted.

[0019] negative electrode The present invention provides a negative electrode 10. Specifically, the negative electrode 10 may be a negative electrode for a lithium secondary battery.

[0020] The negative electrode 10 according to the present invention includes a negative electrode current collector 100, a first negative electrode active material layer 200 containing a first negative electrode active material and disposed on at least one surface of the negative electrode current collector 100, and second negative electrode active material layers 300a and 300b containing a second negative electrode active material, wherein the first negative electrode active material layer 200 includes side portions 210a and 210b partitioned on both sides, and a central portion 220 partitioned excluding the side portions 210a and 210b, the side portions 210a and 210b are inclined toward the surface of the negative electrode current collector 100, the second negative electrode active material layers 300a and 300b are disposed on at least a portion of the side portions 210a and 210b, and the maximum height of the second negative electrode active material layers 300a and 300b is less than or equal to the maximum height of the first negative electrode active material layer 200 with respect to the surface of the negative electrode current collector 100.

[0021] Generally, the negative electrode active material layer contained in the negative electrode is manufactured by adding negative electrode active material and other components to a solvent for forming the negative electrode slurry, and then applying, drying, and rolling the resulting slurry onto the negative electrode current collector. In this case, since the negative electrode slurry has fluid properties, the formed negative electrode active material layer will have sides or ends that slope toward the surface of the negative electrode current collector. Because the negative electrode active material layer is not sufficiently loaded into these sloped sides, it not only leads to insufficient negative electrode capacity but also causes lithium ions that have moved from the positive electrode to not be sufficiently inserted, resulting in lithium deposition on the outside. Such lithium deposition not only reduces the charge and discharge efficiency of the lithium secondary battery but also significantly reduces its lifespan.

[0022] To solve these problems, the present invention includes a first negative electrode active material layer including a side portion inclined toward the surface of the negative electrode current collector, and a second negative electrode active material layer disposed on at least a part of the side portion, wherein the maximum height of the second negative electrode active material layer is less than or equal to the maximum height of the first negative electrode active material layer with respect to the surface of the negative electrode current collector. The negative electrode according to the present invention, by forming the second negative electrode active material layer on the inclined side portion, compensates for the insufficient capacity and loading amount of the negative electrode due to the inclination of the side portion, prevents the problem of uninserted lithium precipitation, thereby preventing cell degradation and improving the charge-discharge efficiency and life characteristics of the negative electrode and the lithium secondary battery containing it.

[0023] The negative electrode current collector 100 is not particularly limited as long as it has high conductivity without inducing a chemical change in the battery. Specifically, the negative electrode current collector 100 may include at least one selected from the group consisting of copper, stainless steel, aluminum, nickel, titanium, calcined carbon, and aluminum-cadmium alloy, and may specifically include copper.

[0024] The negative electrode current collector 100 can typically have a thickness of 3 to 500 μm.

[0025] The negative electrode current collector 100 can also have fine irregularities formed on its surface to strengthen the bonding force of the negative electrode active material. For example, the negative electrode current collector can be used in a variety of forms, such as a film, sheet, foil, net, porous material, foam, or nonwoven fabric.

[0026] The first negative electrode active material layer 200 is disposed on at least one surface of the negative electrode current collector 100. Specifically, the first negative electrode active material layer 200 can be disposed on one or both surfaces of the negative electrode current collector 100.

[0027] The first negative electrode active material layer may include side portions 210a and 210b partitioned on both sides, and a central portion 220 partitioned excluding the side portions 210a and 210b. In this specification, the side portions 210a and 210b and the central portion 220 may be abstractly partitioned to identify the formation locations of the second negative electrode active material layers 300a and 300b, which will be described later, as shown in Figures 1 and 2. For example, the side portions 210a and 210b and the central portion 220 may have the same composition or may be manufactured from the same negative electrode slurry.

[0028] As shown in Figure 1, the side portions 210a and 210b may have an inclination toward the surface of the negative electrode current collector 100. Such inclination of the side portions 210a and 210b may be formed, for example, by the fluid properties of the negative electrode slurry when the negative electrode slurry is applied for the manufacture of the first negative electrode active material layer. Such inclination of the side portions may lead to insufficient loading amount and capacity of the negative electrode, and insufficient insertion of lithium ions that have moved from the positive electrode, potentially causing problems such as a decrease in negative electrode capacity, a decrease in charge / discharge efficiency, and a decrease in lifespan characteristics. However, the presence of the second negative electrode active material layers 300a and 300b, described later, prevents such problems and makes it possible to achieve improvements in negative electrode capacity, charge / discharge efficiency, and lifespan characteristics.

[0029] The inclination angle, width, etc., of the side portions 210a and 210b can be determined by, for example, the viscosity of the negative electrode slurry for manufacturing the first negative electrode active material layer, the coating conditions, the drying conditions, etc., and are not particularly limited.

[0030] The central portion 200 may be a region partitioned from the side portions 210a and 210b of the first negative electrode active material layer. Specifically, the central portion 200 may be substantially flat or form a flat surface.

[0031] The first negative electrode active material layer 200 may contain the first negative electrode active material.

[0032] The first negative electrode active material is a material that allows for lithium insertion / deinsertion and may include at least one selected from carbon-based active materials and (semi)metallic active materials.

[0033] The carbon-based active material may include at least one selected from the group consisting of artificial graphite, natural graphite, hard carbon, soft carbon, carbon black, graphene, and fibrous carbon.

[0034] The (semi)metallic active material is an alloy of lithium with at least one (semi)metal selected from the group consisting of Li, Cu, Ni, Na, K, Rb, Cs, Fr, Be, Mg, Ca, Sr, Si, Sb, Pb, In, Zn, Ba, Ra, Ge, Al, V, Ti, and Sn; or an alloy of lithium with at least one (semi)metal selected from the group consisting of Cu, Ni, Na, K, Rb, Cs, Fr, Be, Mg, Ca, Sr, Si, Sb, Pb, In, Zn, Ba, Ra, Ge, Al, V, Ti, and Sn; or a alloy of lithium with at least one (semi)metal selected from the group consisting of Cu, Ni, Na, K, It may include a composite of carbon with at least one (semi)metallic element selected from the group consisting of Rb, Cs, Fr, Be, Mg, Ca, Sr, Si, Sb, Pb, In, Zn, Ba, Ra, Ge, Al, V, Ti, and Sn; and at least one selected from the group consisting of an oxide of at least one (semi)metallic element selected from the group consisting of Li, Cu, Ni, Na, K, Rb, Cs, Fr, Be, Mg, Ca, Sr, Si, Sb, Pb, In, Zn, Ba, Ra, Ge, Al, V, Ti, and Sn.

[0035] The first negative electrode active material layer may contain the first negative electrode active material in an amount of 60% by weight or more, specifically 60% to 99% by weight.

[0036] The first negative electrode active material layer 200 may include, together with the first negative electrode active material, at least one selected from a binder and a conductive material.

[0037] The binder is used to improve the adhesion between the negative electrode active material layer and the negative electrode current collector, thereby improving the performance of the battery. For example, it may contain at least one selected from the group consisting of polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinylidene fluoride (PVDF), polyacrylonitrile, polymethyl methacrylate, polyvinyl alcohol, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, polyacrylic acid, ethylene-propylene-diene monomer (EPDM), sulfonated EPDM, styrene-butadiene rubber (SBR), fluororubber, and substances in which the hydrogen atoms of these substances are substituted with Li, Na, or Ca, and may also contain a variety of copolymers thereof.

[0038] The binder can be included in the first negative electrode active material layer in an amount of 0.5% to 20% by weight.

[0039] The conductive material is not particularly limited as long as it is conductive without inducing a chemical change in the battery, and for example, graphite such as natural graphite or artificial graphite; carbon black such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, and thermal black; conductive fibers such as carbon fibers and metal fibers; conductive tubes such as carbon nanotubes; fluorocarbons; metal powders such as 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 can be used.

[0040] The conductive material can be included in the first negative electrode active material layer in an amount of 0.5% to 20% by weight.

[0041] The height or thickness of the first negative electrode active material layer, relative to the surface of the negative electrode current collector, may be 10 μm to 300 μm, preferably 50 μm to 150 μm.

[0042] The second negative electrode active material layers 300a and 300b can be arranged on at least a portion of the side portions 210a and 210b. Specifically, the second negative electrode active material layers 300a and 300b can be arranged on the side portions 210a and 210b along the inclined surfaces of the side portions 210a and 210b.

[0043] The arrangement of the second negative electrode active material layer prevents insufficient loading and capacity of the negative electrode due to the inclination of the side portions 210a and 210b of the first negative electrode active material layer 200, and prevents the problem of lithium deposition on the side portions, thereby achieving improvements in the negative electrode's capacity, charge / discharge efficiency, and lifespan characteristics.

[0044] In the present invention, the maximum height H2 of the second negative electrode active material layers 300a and 300b can be less than or equal to the maximum height H1 of the first negative electrode active material layer, with respect to the surface of the negative electrode current collector 100. Specifically, with respect to the surface of the negative electrode current collector, the maximum height H2 of the second negative electrode active material layer can be the same as the maximum height H1 of the first negative electrode active material layer, or less than the maximum height H1 of the first negative electrode active material layer. That is, the maximum distance between the second negative electrode active material layers 300a and 300b formed or arranged on the side portions 210a and 210b and the surface of the negative electrode current collector 100 does not have to exceed the maximum distance between the first negative electrode active material layer 200 and the surface of the negative electrode current collector 100. This realizes overall flatness of the negative electrode and prevents the problem of the structural stability of the negative electrode decreasing due to the maximum height of the second negative electrode active material layer exceeding the maximum height of the first negative electrode active material layer.

[0045] In this specification, "surface reference of the negative electrode current collector" means the surface of the negative electrode current collector where it is in contact with the first negative electrode active material layer, as shown in Figure 1.

[0046] The second negative electrode active material layers 300a and 300b may contain the second negative electrode active material.

[0047] The second negative electrode active material is a material that allows for lithium insertion / deinsertion and may include at least one selected from carbon-based active materials and (semi)metallic active materials.

[0048] The carbon-based active material may include at least one selected from the group consisting of artificial graphite, natural graphite, hard carbon, soft carbon, carbon black, graphene, and fibrous carbon.

[0049] The (semi)metallic active material is an alloy of lithium with at least one (semi)metal selected from the group consisting of Li, Cu, Ni, Na, K, Rb, Cs, Fr, Be, Mg, Ca, Sr, Si, Sb, Pb, In, Zn, Ba, Ra, Ge, Al, V, Ti, and Sn; or an alloy of lithium with at least one (semi)metal selected from the group consisting of Cu, Ni, Na, K, Rb, Cs, Fr, Be, Mg, Ca, Sr, Si, Sb, Pb, In, Zn, Ba, Ra, Ge, Al, V, Ti, and Sn; or a alloy of lithium with at least one (semi)metal selected from the group consisting of Cu, Ni, Na, K, It may include a composite of carbon with at least one (semi)metallic element selected from the group consisting of Rb, Cs, Fr, Be, Mg, Ca, Sr, Si, Sb, Pb, In, Zn, Ba, Ra, Ge, Al, V, Ti, and Sn; and at least one selected from the group consisting of an oxide of at least one (semi)metallic element selected from the group consisting of Li, Cu, Ni, Na, K, Rb, Cs, Fr, Be, Mg, Ca, Sr, Si, Sb, Pb, In, Zn, Ba, Ra, Ge, Al, V, Ti, and Sn.

[0050] More specifically, the second negative electrode active material is SiO x The material may include (0≦x<2) and at least one silicon-based active material selected from silicon-carbon composites. Since the silicon-based active material has excellent capacity, it can more preferably realize the above-mentioned capacity improvement effect of the negative electrode.

[0051] On the other hand, the second negative electrode active material may contain lithium titanium oxide (LTO), which is preferable because it can improve the capacity of the negative electrode and increase the ionic conductivity of the second negative electrode active material layer, thereby mitigating lithium deposition.

[0052] The second negative electrode active material may be the same as or different from the first negative electrode active material described above.

[0053] More specifically, the capacity per unit weight of the second negative electrode active material may be larger than the capacity per unit weight of the first negative electrode active material. In this case, the capacity deficiency or insufficient loading amount of the negative electrode due to the inclination of the side portion of the first negative electrode active material layer can be compensated to an even more favorable level.

[0054] If the capacity per unit weight of the second negative electrode active material is greater than the capacity per unit weight of the first negative electrode active material, the maximum height H2 of the second negative electrode active material layers 300a and 300b may be less than the maximum height H1 of the first negative electrode active material layer 200, with respect to the surface of the negative electrode current collector 100. Specifically, if the capacity per unit weight of the second negative electrode active material is greater than the capacity per unit weight of the first negative electrode active material, the degree of volume expansion of the second negative electrode active material due to lithium insertion may be greater than the degree of volume expansion of the first negative electrode active material. Therefore, by adjusting the maximum height H2 of the second negative electrode active material layer to less than the maximum height H1 of the first negative electrode active material layer, it is possible to prevent a decrease in the structural stability of the negative electrode due to volume expansion of the second negative electrode active material layer during negative electrode charging and discharging.

[0055] For example, if the first negative electrode active material includes the carbon-based active material and the second negative electrode active material includes the silicon-based active material, the maximum height H2 of the second negative electrode active material layers 300a and 300b may be 99% or less of the maximum height H1 of the first negative electrode active material layer 200, specifically 10% to 99%, and more specifically 40% to 95%.

[0056] The second negative electrode active material layers 300a and 300b may contain the second negative electrode active material in an amount of 60% by weight or more, specifically 60% to 99% by weight.

[0057] The second negative electrode active material layers 300a and 300b may include, together with the second negative electrode active material, at least one selected from a binder and a conductive material.

[0058] The binder is used to improve the adhesion between the negative electrode active material layer and the negative electrode current collector, thereby improving the performance of the battery. For example, it may contain at least one selected from the group consisting of polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinylidene fluoride (PVDF), polyacrylonitrile, polymethyl methacrylate, polyvinyl alcohol, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, polyacrylic acid, ethylene-propylene-diene monomer (EPDM), sulfonated EPDM, styrene-butadiene rubber (SBR), fluororubber, and substances in which the hydrogen atoms of these substances are substituted with Li, Na, or Ca, and may also contain a variety of copolymers thereof.

[0059] The binder can be included in the second negative electrode active material layer in an amount of 0.5% to 20% by weight.

[0060] The conductive material is not particularly limited as long as it is conductive without inducing a chemical change in the battery, and for example, graphite such as natural graphite or artificial graphite; carbon black such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, and thermal black; conductive fibers such as carbon fibers and metal fibers; conductive tubes such as carbon nanotubes; fluorocarbons; metal powders such as 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 can be used.

[0061] The conductive material can be included in the second negative electrode active material layer in an amount of 0.5% to 20% by weight.

[0062] In the present invention, the negative electrode current collector may include blank portions 110a and 110b. The blank portions 110a and 110b may be those on which a negative electrode active material layer (first negative electrode active material layer and second negative electrode active material layer) is not disposed.

[0063] Specifically, as shown in Figures 1 and 2, the negative electrode current collector is located on both sides and includes blank portions 110a and 110b where the first negative electrode active material layer 200 and the second negative electrode active material layers 300a and 300b are not arranged, the side portions 210a and 210b are adjacent to the blank portions 110a and 110b, and the central portion 220 can be separated from the blank portions 110a and 110b.

[0064] Furthermore, the present invention provides a method for manufacturing the negative electrode described above.

[0065] Specifically, the method for manufacturing a negative electrode of the present invention may include the steps of: applying a first negative electrode slurry containing a first negative electrode active material and a solvent for forming a negative electrode slurry onto a negative electrode current collector; and forming a second negative electrode active material layer on the side portion of the applied first negative electrode slurry.

[0066] The first negative electrode slurry may further include, together with the first negative electrode active material, at least one selected from a binder and a conductive material.

[0067] The solvent for forming the negative electrode slurry may include at least one selected from the group consisting of N-methylpyrrolidone (NMP), distilled water, ethanol, methanol, and isopropyl alcohol, preferably distilled water.

[0068] The formation of the second negative electrode active material layer can be performed simultaneously with the application of the first negative electrode slurry or after the application of the first negative electrode slurry.

[0069] If the formation of the second negative electrode active material layer is performed after the application of the first negative electrode slurry, the formation of the second negative electrode active material layer can be performed after the application of the first negative electrode slurry but before drying, or after the application and drying of the first negative electrode slurry.

[0070] The formation of the second negative electrode active material can be carried out by first manufacturing a second negative electrode slurry containing the second negative electrode active material and a solvent for forming the negative electrode slurry, and then applying the second negative electrode slurry to the side portion of the coated first negative electrode slurry. The application method is not particularly limited and may include spray coating, slot die coating, gravure coating, curtain coating, etc. On the other hand, the second negative electrode active material layer can also be formed by first manufacturing a film using the second negative electrode slurry and then transferring the film to the side portion of the coated first negative electrode slurry.

[0071] Lithium-ion battery Furthermore, the present invention provides a lithium secondary battery including the negative electrode described above.

[0072] Specifically, the lithium secondary battery includes the negative electrode, the positive electrode, a separation membrane interposed between the negative electrode and the positive electrode, and an electrolyte.

[0073] The positive electrode can include a positive electrode current collector and a positive electrode active material layer formed on the positive electrode current collector.

[0074] The positive electrode current collector is not particularly limited as long as it has conductivity without inducing a chemical change in the battery. For example, stainless steel, aluminum, nickel, titanium, fired carbon, or those obtained by surface treatment of the surface of aluminum or stainless steel with carbon, nickel, titanium, silver, etc. can be used.

[0075] The positive electrode current collector can generally have a thickness of 3 μm to 500 μm.

[0076] The positive electrode active material layer is formed on the positive electrode current collector and contains a positive electrode active material.

[0077] The positive electrode active material is a compound capable of reversible intercalation and deintercalation of lithium. Specifically, it can include a lithium composite metal oxide containing one or more metals such as cobalt, manganese, nickel, or aluminum and lithium. More specifically, the lithium composite metal oxide is a lithium-manganese-based oxide (e.g., LiMnO2, LiMn2O4, etc.), a lithium-cobalt-based oxide (e.g., LiCoO2, etc.), a lithium-nickel-based oxide (e.g., LiNiO2, etc.), a lithium-nickel-manganese-based oxide (e.g., LiNi 1-Y Mn Y O2 (where 0 < Y < 1), LiMn 2-z Ni z O4 (where 0 < Z < 2), etc.), a lithium-nickel-cobalt-based oxide (e.g., LiNi<​​​​​​​​​​O4 (where 0 < Z1 < 2, etc.), lithium-nickel-manganese-cobalt oxide (e.g., Li(Ni p Co q Mn r1 )O2 (where 0 < p < 1, 0 < q < 1, 0 < r1 < 1, p + q + r1 = 1), or Li(Ni p1 Co q1 Mn r2 )O4 (where 0 < p1 < 2, 0 < q1 < 2, 0 < r2 < 2, p1 + q1 + r2 = 2), etc., or lithium-nickel-cobalt-transition metal (M) oxide (e.g., Li(Ni p2 Co q2 Mn r3 M S2 )O2 (where M is selected from the group consisting of Al, Fe, V, Cr, Ti, Ta, Mg, and Mo, and p2, q2, r3, and s2 are the atomic fractions of the respective independent elements, 0 < p2 < 1, 0 < q2 < 1, 0 < r3 < 1, 0 < s2 < 1, and p2 + q2 + r3 + s2 = 1), etc.) etc. can be mentioned, and one or two or more of these compounds can be included. Among these, in terms of being able to enhance the capacity characteristics and stability of the battery, the lithium composite metal oxide is LiCoO2, LiMnO2, LiNiO2, lithium nickel manganese cobalt oxide (e.g., Li(Ni 0.6 Mn 0.2 Co 0.2 )O2, Li(Ni 0.5 Mn 0.3 Co 0.2 )O2, or Li(Ni 0.8 Mn 0.1 Co 0.1 )O2, etc.), or lithium nickel cobalt aluminum oxide (e.g., Li(Ni 0.8 Co 0.15 Al 0.05 )O2, etc.).

[0078] The positive electrode active material can be contained at 80% to 99% by weight based on the total weight of the positive electrode active material layer.

[0079] In addition to the positive electrode active material described above, the positive electrode active material layer may further contain at least one additive selectively selected from the group consisting of binders and conductive materials.

[0080] The binder is a component that helps to bond the active material to the conductive material and to the current collector, and is usually added at a concentration of 1 to 30% by weight based on the total weight of the positive electrode active material layer. Examples of such binders include polyvinylidene fluoride, polyvinyl alcohol, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-dientelpolymer (EPDM), sulfonated EPDM, styrene-butadiene rubber, fluororubber, and various copolymers.

[0081] The conductive material is not particularly limited as long as it is conductive without inducing a chemical change in the battery. Examples of such materials include graphite; carbon-based substances such as carbon black, acetylene black, Ketjenblack, channel black, furnace black, lamp black, and thermal black; conductive fibers such as carbon fibers and metal fibers; metal powders such as carbon fluoride, aluminum, and nickel powder; conductive whiskers such as zinc oxide and titanium potassium; conductive metal oxides such as titanium oxide; and conductive materials such as polyphenylene derivatives. Specific examples of commercially available conductive materials include acetylene black-based products from Chevron Chemical Company, Denka Singapore Private Limited, and Gulf Oil Company, as well as Ketjenblack, EC-based products (Armak Company products), Vulcan XC-72 (Cabot Company products), and Super P (Timcal products).

[0082] The conductive material may be included in an amount of 1 to 30% by weight based on the total weight of the positive electrode active material layer.

[0083] The positive electrode active material layer can be manufactured by adding a positive electrode active material and additives selectively containing a binder and / or conductive material to a solvent to produce a positive electrode slurry, which is then coated onto the positive electrode current collector, rolled, and dried.

[0084] The solvent may include organic solvents such as NMP (N-methyl-2-pyrrolidone) and can be used in an amount that results in a desirable viscosity when the positive electrode active material and selectively include a binder and conductive material. For example, the concentration of solids containing the positive electrode active material and selectively including a binder and conductive material can be 50% to 95% by weight, preferably 70% to 90% by weight.

[0085] In the lithium secondary battery described above, the separation membrane separates the negative electrode and the positive electrode and provides a passage for lithium ions to move. Any membrane commonly used as a separation membrane in lithium secondary batteries can be used without special restrictions, and those with low resistance to ion movement of the electrolyte while having excellent electrolyte moisture absorption capacity are particularly preferred. Specifically, porous polymer films, such as porous polymer films made from polyolefin polymers such as ethylene homopolymer, propylene homopolymer, ethylene / butene copolymer, ethylene / hexene copolymer, and ethylene / methacrylate copolymer, or laminated structures of two or more layers thereof can be used. Ordinary porous nonwoven fabrics, such as nonwoven fabrics made from high-melting-point glass fiber or polyethylene terephthalate fiber, can also be used. Furthermore, coated separation membranes containing ceramic components or polymeric substances to ensure heat resistance or mechanical strength can be used, and can be selectively used in single-layer or multi-layer structures.

[0086] Furthermore, examples of electrolytes used in the present invention include, but are not limited to, organic liquid electrolytes, inorganic liquid electrolytes, solid polymer electrolytes, gel-type polymer electrolytes, solid inorganic electrolytes, and molten inorganic electrolytes that can be used in the manufacture of lithium secondary batteries.

[0087] Specifically, the electrolyte may include an organic solvent and a lithium salt.

[0088] The aforementioned organic solvent can be used without any special restrictions, as long as it can act as a medium through which ions involved in the electrochemical reaction of the battery can move. Specifically, the organic solvents that can be used include ester solvents such as methyl acetate, ethyl acetate, gamma-butyrolactone, and ε-caprolactone; ether solvents such as dibutyl ether or tetrahydropyran; ketone solvents such as cyclohexanone; aromatic hydrocarbon solvents such as benzene and fluorobenzene; carbonate solvents such as dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), ethylene carbonate (EC), and propylene carbonate (PC); alcohol solvents such as ethyl alcohol and isopropyl alcohol; nitriles such as R-CN (where R is a C2-C20 linear, branched, or cyclic hydrocarbon group, and may include a double-bonded aromatic ring or ether bond); amides such as dimethylformamide; dioxolanes such as 1,3-dioxolane; or sulfolanes. Among these, carbonate-based solvents are preferred, and more preferably, a mixture of a cyclic carbonate (e.g., ethylene carbonate or propylene carbonate) having high ionic conductivity and high dielectric constant, which can improve the charge and discharge performance of the battery, and a low-viscosity linear carbonate compound (e.g., ethyl methyl carbonate, dimethyl carbonate, or diethyl carbonate). In this case, using a mixture of cyclic carbonate and linear carbonate in a volume ratio of approximately 1:1 to approximately 1:9 may result in superior electrolyte performance.

[0089] The lithium salt can be any compound capable of providing lithium ions for use in lithium secondary batteries, without any special limitations. Specifically, the lithium salt can be LiPF6, LiClO4, LiAsF6, LiBF4, LiSbF6, LiAlO4, LiAlCl4, LiCF3SO3, LiC4F9SO3, LiN(C2F5SO3)2, LiN(C2F5SO2)2, LiN(CF3SO2)2, LiCl, LiI, or LiB(C2O4)2, etc. The lithium salt is preferably used in a concentration range of 0.1 to 2.0 M. When the lithium salt concentration falls within this range, the electrolyte exhibits excellent electrolyte performance due to having appropriate conductivity and viscosity, and lithium ions can move effectively.

[0090] As described above, the secondary battery according to the present invention is useful in portable devices such as mobile phones, laptop computers, and digital cameras, as well as in the field of electric vehicles such as hybrid electric vehicles (HEVs), and can be preferably used as a component battery in medium- and large-sized battery modules. Therefore, the present invention also provides a medium- and large-sized battery module that includes the secondary battery described above as a unit battery.

[0091] Such medium- and large-sized battery modules are preferably applied to power sources that require high output and large capacity, such as electric vehicles, hybrid electric vehicles, and power storage devices.

[0092] As described above, embodiments of the present invention have been explained. Based on these embodiments, a person with ordinary skill in the art can modify and change the present invention in various ways by adding, changing, deleting, or adding components, without departing from the essential technical concept of the present invention as described in the claims, and this is also included within the scope of the rights of the present invention. [Explanation of symbols]

[0093] 10: Negative electrode; 100: Negative electrode current collector; 110a, 110b: Plain part; 200: first negative electrode active material layer; 210a, 210b: Side sections; 220: central part; 300a, 300b: second negative electrode active material layer; H1: Maximum height of the first negative electrode active material layer relative to the surface of the negative electrode current collector; H2: Maximum height of the second negative electrode active material layer relative to the surface of the negative electrode current collector.

Claims

1. Negative electrode current collector; Distributed on at least one surface of the negative electrode current collector, a first negative electrode active material layer containing a first negative electrode active material, and It includes a second negative electrode active material layer containing a second negative electrode active material, The first negative electrode active material layer includes side portions partitioned on both sides and a central portion partitioned excluding the side portions. The side portion has an inclination toward the surface of the negative electrode current collector, The second negative electrode active material layer is arranged in at least a portion of the side portion, With respect to the surface of the negative electrode current collector, the maximum height of the second negative electrode active material layer is 40% to 95% of the maximum height of the first negative electrode active material layer. The capacity per unit weight of the second negative electrode active material is larger than the capacity per unit weight of the first negative electrode active material. A negative electrode in which the first negative electrode active material contains a carbon-based active material and the second negative electrode active material contains a silicon-based active material.

2. The anode according to claim 1, wherein the carbon-based active material comprises at least one selected from the group consisting of artificial graphite, natural graphite, hard carbon, soft carbon, carbon black, graphene, and fibrous carbon.

3. The aforementioned silicon-based active material is SiO ｘ The negative electrode according to claim 1, comprising (0 ≤ x < 2) and at least one selected from silicon-carbon composites.

4. The negative electrode current collector is located on both sides and includes blank areas where the first negative electrode active material layer and the second negative electrode active material layer are not disposed. The negative electrode according to claim 1, wherein the side portion is adjacent to the plain portion and the central portion is separated from the plain portion.

5. The negative electrode according to any one of claims 1 to 4, positive electrode, A release film interposed between the negative electrode and the positive electrode, and A secondary battery containing an electrolyte.

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