KR20220125482A - Lithium secondary battery - Google Patents

Abstract

The present invention relates to a negative electrode for a lithium secondary battery and a lithium secondary battery including the same. The negative electrode for a lithium secondary battery, according to embodiments of the present invention, comprises: a negative electrode current collector; a negative electrode active material layer including a first negative electrode active material layer, and a second negative electrode active material layer sequentially positioned on at least one surface of the negative electrode current collector; and a binder layer positioned on the second negative electrode active material layer. The second negative electrode active material layer comprises: a silicon-based active material, and the binder layer comprises: at least one binder selected from a group consisting of polyacrylic acid, polyvinyl alcohol, polyacrylonitrile, polyacrylamide, and polyvinyl acetate. Therefore, the lifespan characteristics of a battery can be improved by mitigating the expansion and contraction of the silicon-based active material during charging and discharging, and excellent cycle characteristics can be secured.

Description

Anode for lithium secondary battery and lithium secondary battery including same

The present invention relates to a negative electrode for a lithium secondary battery and a lithium secondary battery including the same. More particularly, it relates to an anode for a lithium secondary battery in which a binder layer is laminated on one surface of an anode active material layer, and a lithium secondary battery including the same.

A secondary battery is a battery that can be repeatedly charged and discharged, and is widely applied as a power source for portable electronic communication devices such as camcorders, mobile phones, and notebook PCs with the development of information communication and display industries. In addition, recently, as a power source for an eco-friendly vehicle such as a hybrid vehicle, a battery pack including a secondary battery has been developed and applied.

Examples of the secondary battery include a lithium secondary battery, a nickel-cadmium battery, a nickel-hydrogen battery, and the like, and among them, the lithium secondary battery has high operating voltage and energy density per unit weight, and is advantageous for charging speed and weight reduction. It is being actively developed and applied in this respect.

For example, a lithium secondary battery may include an electrode assembly including a positive electrode, a negative electrode, and a separator (separator), and an electrolyte impregnating the electrode assembly. The lithium secondary battery may further include, for example, a pouch-type casing accommodating the electrode assembly and the electrolyte.

Recently, with the development of the electric vehicle industry, a lithium secondary battery having a high energy density is being developed so that a long-distance operation is possible with a single charge. Typically, a silicon-based anode active material is used, but compared to a carbon-based anode active material, lifespan characteristics due to volume expansion are inferior.

Therefore, research for the development of a silicon-based anode with improved high energy density and lifespan characteristics is being actively conducted. For example, Korean Patent Application Laid-Open No. 10-2020-0055448 discloses a multi-layered anode including a silicon-based compound, but there is a limit in ensuring sufficient lifespan characteristics and stability of the anode according to volume expansion.

Korean Patent Publication No. 10-2020-0055448

One object of the present invention is to provide a negative electrode for a lithium secondary battery having improved high energy density and lifespan characteristics.

One object of the present invention is to provide a lithium secondary battery including a negative electrode for a lithium secondary battery having improved high energy density and lifespan characteristics.

A negative electrode for a lithium secondary battery according to exemplary embodiments includes a negative electrode current collector; an anode active material layer including a first anode active material layer and a second anode active material layer sequentially positioned on at least one surface of the anode current collector; and a binder layer positioned on the second anode active material layer, wherein the second anode active material layer includes a silicone-based active material, and the binder layer includes polyacrylic acid, polyvinyl alcohol, polyacrylonitrile, polyacrylamide and At least one binder selected from the group consisting of polyvinyl acetate may be included.

In some embodiments, the first anode active material layer and the second anode active material layer each include a silicon-based active material, and the content of the silicon-based active material in the total weight of the first anode active material layer is the total weight of the second anode active material layer. It may be less than the content of the silicon-based active material.

In some embodiments, the first anode active material layer and the second anode active material layer may include a blend of the carbon-based active material and the silicon-based active material, respectively.

In some embodiments, the first anode active material layer may be formed of a carbon-based active material.

In some embodiments, the silicon-based negative active material includes silicon (Si), a silicon alloy, silicon oxide, a silicon-carbon (Si-C) composite, a silicon alloy (Si-alloy)-based-carbon composite, or a mixture thereof. can do.

In some embodiments, the content of the binder included in the binder layer may be 0.1 to 5 wt% based on the total weight of the negative electrode.

In some embodiments, the binder layer may be formed of a binder slurry including a binder and a solvent.

In some embodiments, the binder slurry may not include an additive.

In some embodiments, the viscosity of the binder slurry may be 100 to 3,000 cp.

A lithium secondary battery according to example embodiments may include a positive electrode, the negative electrode, and a separator interposed between the positive electrode and the negative electrode.

The negative electrode for a lithium secondary battery according to the above-described embodiments of the present invention may include a negative active material layer having a multi-layer structure. The anode active material layer includes a first anode active material layer and a second anode active material layer sequentially stacked on an anode current collector, and the content of the silicon-based anode active material of the first anode active material layer is the silicon-based anode active material of the second anode active material layer. may be less than the amount. Accordingly, the energy density of the battery can be improved.

According to example embodiments, by including a binder layer on one surface of the anode active material layer, the adhesion of the electrode and the lifespan characteristics of the battery may be improved.

According to exemplary embodiments, the negative active material layer includes only the PAA-based water-based binder in the binder layer to relieve expansion and contraction of the silicon-based active material during charging and discharging, thereby improving battery life characteristics and securing excellent cycle characteristics. can do.

1 is a schematic cross-sectional view illustrating a negative electrode of a lithium secondary battery according to exemplary embodiments.
2 and 3 are schematic plan and cross-sectional views, respectively, of lithium secondary batteries according to exemplary embodiments.

The negative electrode for a lithium secondary battery according to embodiments of the present invention includes a negative electrode current collector, a negative electrode active material layer including a multilayer structure formed on one surface of the negative electrode current collector, and an aqueous binder layer formed on one surface of the negative electrode active material layer. It is possible to improve the energy density, lifespan characteristics, and cycle characteristics while securing a high energy density.

Hereinafter, with reference to the drawings, an embodiment of the present invention will be described in more detail. However, the following drawings attached to the present specification illustrate preferred embodiments of the present invention, and serve to further understand the technical spirit of the present invention together with the above-described content of the present invention, so the present invention is described in such drawings It should not be construed as being limited only to the matters.

The terms "first" and "second" used herein do not limit the number or order of the objects modified by "first" and "second", but refer to different modified objects. used to distinguish

1 is a schematic cross-sectional view illustrating a negative electrode of a lithium secondary battery according to exemplary embodiments.

Referring to FIG. 1 , the negative electrode 130 includes the negative electrode active material layer 120 positioned on at least one surface of the negative electrode current collector 125 . Furthermore, the anode active material layer 120 may be formed on both surfaces (eg, upper and lower surfaces) of the anode current collector 125 .

The negative electrode current collector 125 may include, for example, stainless steel, nickel, aluminum, titanium, copper, or an alloy thereof, preferably aluminum or an aluminum alloy.

In an embodiment, the anode active material layer 120 may include a first anode active material layer 122 and a second anode active material layer 124 . That is, the anode active material layer 120 may have a multilayer structure (eg, a double layer structure) in which a plurality of anode active material layers are stacked. Accordingly, it is possible to secure better cycle characteristics than when the anode active material layer 120 is a single layer.

As shown in FIG. 1 , the first negative active material layer 122 may be stacked on at least one surface of the negative electrode current collector 125 , and a second negative active material layer on the upper surface of the first negative active material layer 122 . 124 may be sequentially stacked. Also, a binder layer 126 may be stacked on the second anode active material layer 124 . Accordingly, it is possible to secure cycle characteristics while securing electrode adhesion, thereby improving lifespan characteristics.

In addition, it may be formed in direct contact with each of the upper and lower surfaces of the negative electrode current collector 125 .

In an embodiment, the first anode active material layer 122 and the second anode active material layer 124 each include a silicon-based active material to significantly improve output and capacity characteristics of the secondary battery.

In particular, the content of the silicon-based active material of the first anode active material layer 122 may be less than the content of the silicon-based active material of the second anode active material layer 124 . In this case, the same material or different materials may be used for the silicon-based active material of the first negative active material layer 122 and the silicon-based active material of the second negative active material layer 124 .

In a preferred embodiment, the silicon-based active material of the second anode active material layer 124 includes more than the silicon-based active material content of the first anode active material layer 122 to directly contact the second anode active material layer 124 and Since the binder layer 126 in the present invention can further suppress the expansion of the silicon-based active material, it is possible to improve the disadvantage of deterioration of lifespan characteristics due to volume expansion, and it can help to increase the energy density of the electrode.

In some embodiments, the first negative active material layer 122 and the second negative active material layer 124 may include a blend of a carbon-based active material and a silicon-based active material, respectively. Accordingly, while increasing the capacity characteristics of the lithium secondary battery through the silicon-based active material, it is possible to buffer the excessive expansion of the electrode due to the silicon-based active material through the carbon-based active material.

For example, artificial graphite and natural graphite may be used together as the carbon-based active material. The artificial graphite has relatively superior lifespan characteristics compared to the natural graphite, and thus may compensate for the decrease in electrode lifespan due to the use of the silicon-based active material. The natural graphite has a smaller particle roughness than the artificial graphite, and may be blended with the artificial graphite to control the sphericity of the carbon-based active material.

In some embodiments, the carbon-based active material may be included in an amount of about 80 to 97% by weight, and the silicon-based active material may be included in a range of about 3 to 20% by weight of the total weight of the negative active material, preferably the total weight of the negative active material Among the carbon-based active material is 85 to 94% by weight, the silicon-based active material may contain 6 to 15% by weight. Within the above range, it is possible to significantly increase capacity and output while ensuring adhesion and mechanical stability of the anode active material.

In a preferred embodiment, in the case of the first negative active material layer 122, the carbon-based active material may be included in an amount of about 90 to 97% by weight, and the silicon-based active material in an amount of about 3 to 10% by weight of the total weight of the negative active material. In the case of the second anode active material layer 124 , the carbon-based active material may be included in an amount of about 80 to 91 wt%, and the silicon-based active material may be included in an amount of about 9 to 20 wt% of the total weight of the anode active material.

In some embodiments, the first anode active material layer 122 may not include a silicon-based active material. In this case, the first anode active material layer 122 may be formed of only a carbon-based active material.

In some embodiments, the silicon-based active material may include silicon (Si), a silicon alloy, a silicon oxide, a silicon-carbon (Si-C) composite, a silicon alloy-based-carbon composite, or a mixture thereof. have. For example, in the case of the silicon oxide, SiO _X (0<x<2) may be included.

A slurry may be prepared by mixing and stirring the first negative active material with a binder, a conductive material, and/or a dispersing material in a solvent. After the slurry is applied on at least one surface of the negative electrode current collector 125 , it is dried and compressed to prepare the first negative electrode active material layer 122 . Thereafter, the second anode active material layer 124 on at least one surface of the first anode active material layer 122 may be coated, dried and compressed in the same order. In addition, a binder and conductive material substantially the same as or similar to those used in the formation of the first anode active material layer 122 may also be used for the second anode active material layer 124 .

In addition, the binder included in the negative active material layer 120 may include an organic binder, an aqueous binder, or a mixture thereof.

Examples of the organic binder include vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinylidenefluoride (PVDF), polyacrylonitrile, polymethylmethacrylate ) may be included, and the aqueous binder may include, for example, styrene-butadiene rubber (SBR). In addition, if necessary, it may be used together with a thickener such as carboxymethyl cellulose (CMC).

For example, a PVDF-based binder may be used as a binder for forming the negative electrode. In this case, the output and capacity of the secondary battery can be improved by reducing the amount of the binder for forming the anode active material layer 120 and relatively increasing the amount of the anode active material.

In addition, the conductive material may be included to promote electron movement between the particles of the active material. For example, the conductive material may be a carbon-based conductive material such as graphite, carbon black, graphene, or carbon nanotubes and/or a perovskite material such as tin, tin oxide, titanium oxide, LaSrCoO ₃ , and LaSrMnO ₃ . It may include a metal-based conductive material including the like.

In an embodiment, a binder layer 126 may be stacked on the upper surface of the second anode active material layer 124 , and a binder layer is a last layer among the anode active material layers sequentially stacked in the anode current collector 125 . 126 may be stacked.

In one embodiment, the binder layer 126 may include a PAA-based binder, at least one selected from the group consisting of polyacrylic acid, polyvinyl alcohol, polyacrylonitrile, polyacrylamide and polyvinyl acetate. It may include a binder. Therefore, mechanical strength can be improved and electrode volume expansion can be efficiently controlled, and the existing brittle disadvantages can be supplemented.

In an embodiment, the binder layer 126 may be formed of a binder slurry including a binder and an aqueous solvent. In the case of the aqueous solvent, water, distilled water, pure water, ultrapure water, etc. may be provided. Preferably, the binder slurry may include a binder and an aqueous solvent, and may not include additional additives. Accordingly, when the binder slurry is applied to the upper surface of the second anode active material layer 14 to manufacture an electrode, the formed binder layer 126 is composed of only 100% binder and may not include other additives.

In some embodiments, the viscosity of the binder slurry may be 3,000 cp or less. Preferably, 100 or more to 3,000 cp or less may be provided. When the slurry viscosity exceeds 3,000cp, it is difficult to provide a uniform surface thickness of the binder layer, and when the slurry is unevenly coated on the surface of the binder layer, it causes partial deterioration of the electrode and reduces the capacity of the battery, making it difficult to secure cycle characteristics. lifespan may be shortened. When the slurry viscosity is less than 100cp, it may be difficult to secure rheological properties suitable for coating, so that it may be difficult to apply a certain amount or more to the surface of the active material layer. That is, if the slurry concentration is too low and a large amount is applied to coat the slurry at a certain level, the pre-coated active material layer may be damaged.

The binder layer 126 may be prepared by coating the binder slurry on one surface of the anode active material layer 120, and in the case of coating, slot die coating may be performed, casting by doctor blade coating, or It may be carried out by a general coating method such as spray coating, but is not necessarily limited to the above-described coating process.

As described above, the negative active material layer 120 may include the above-described organic binder, water-based binder, or a mixture thereof as a binder, and may further include a thickener as necessary to provide excellent adhesion and dispersibility.

In one embodiment, the binder content included in the binder layer 126 may be 0.1 to 5 wt% based on the total weight of the negative electrode.

In the case of the aqueous solvent contained in the binder slurry in the formed binder layer 126, it evaporates during the manufacturing process of the electrode, and the finally formed binder layer 126 is composed of only the binder. In this case, the binder content included in the binder layer 126 may be 0.1 to 5 wt% based on the total weight of the negative electrode. The content is the amount relative to the total weight of the negative electrode by adjusting the concentration of the binder with respect to the aqueous solvent during the preparation of the binder slurry or by adjusting the coating amount of the binder slurry applied to the second negative active material layer 124, the slurry concentration or the viscosity, etc. can control

If the binder content included in the binder layer 126 is less than 1 wt % based on the total weight of the negative electrode, there may be a slightly weak problem to prevent volume expansion, and if it exceeds 5 wt %, there may be a problem of strong brittleness. have.

The thickness of the binder layer 126 may be, for example, 0.1 to 20 nm. If the coating layer is too thin, it may be difficult to suppress the volume expansion of the electrode, and if it is too thick, resistance may occur due to them, so the above thickness range is preferable.

In addition, the standard deviation of the thickness of the negative electrode 130 for a lithium secondary battery may be 1.1 or less. Accordingly, a coated electrode having a uniform thickness can be provided, and cycle performance and lifespan characteristics of the electrode can be improved.

Hereinafter, a lithium secondary battery including the above-described negative electrode 130 for a lithium secondary battery will be described.

In one embodiment, the lithium secondary battery includes an electrode assembly 150 including a positive electrode 100 , the above-described negative electrode 130 , and a separator 140 interposed between the positive electrode 100 and the negative electrode 130 . may include The electrode assembly 150 may be accommodated and impregnated with an electrolyte in the case 160 .

The positive electrode 100 may include a positive electrode active material layer 110 formed by applying a positive electrode active material to the positive electrode current collector 105 . The positive active material may include a compound capable of reversibly intercalating and deintercalating lithium ions.

In example embodiments, the positive active material may include a lithium-transition metal oxide. For example, the lithium-transition metal oxide may include nickel (Ni) and at least one of cobalt (Co) and manganese (Mn). For example, the lithium-transition metal oxide may be represented by Formula 1 below.

[Formula 1]

Li _1+a Ni _1-(x+y) Co _x M _y O ₂

In Formula 1, -0.05≤α≤0.15, 0.01≤x≤0.3, 0.01≤y≤0.3, and M is selected from Mn, Mg, Sr, Ba, B, Al, Si, Ti, Zr, and W It may be one or more elements.

For example, nickel (Ni) may be provided as a metal associated with the output and/or capacity of the lithium secondary battery. Therefore, by employing lithium metal oxide as the positive electrode active material and forming the positive electrode active material layer in contact with the positive electrode current collector, high output and high capacity through the positive electrode can be effectively obtained.

For example, manganese (Mn) may be provided as a metal related to mechanical and electrical stability of a lithium secondary battery. For example, cobalt (Co) may be a metal associated with conductivity or resistance of a lithium secondary battery.

In addition, in the case of the above-mentioned positive electrode active material, it may be formed through a co-precipitation method of a metal precursor. The metal precursor solution may include metal precursors to be included in the positive electrode active material. For example, the metal precursor may include a lithium precursor (eg, lithium oxide), a nickel precursor, a manganese precursor, and a cobalt precursor. In addition, the metal precursor may exist in the form of a metal halide, oxide, hydroxide, acid salt, or the like.

A positive electrode slurry may be prepared by mixing and stirring the above-described positive active material with a binder, a conductive material and/or a dispersing material in a solvent. After the positive electrode slurry is coated on the positive electrode current collector 105 , it is dried and compressed to form the positive electrode active material layer 110 .

2 and 3 are schematic plan and cross-sectional views, respectively, of lithium secondary batteries according to exemplary embodiments. Specifically, FIG. 3 is a cross-sectional view taken along the line I-I' of FIG. 2 in the thickness direction of the lithium secondary battery.

2 and 3 , the lithium secondary battery may include an electrode assembly 150 accommodated in a case 160 . As shown in FIG. 3 , the electrode assembly 150 may include the positive electrode 100 , the negative electrode 130 , and the separator 140 repeatedly stacked.

In particular, the negative electrode 130 may include the negative electrode active material layer 120 on at least one surface of the negative electrode current collector 105 . Although not shown in detail in FIG. 3 , as described with reference to FIG. 1 , the negative active material layer 120 may include a stacked structure of the first negative active material layer 122 and the second negative active material layer 124 . Furthermore, a binder layer 126 positioned on the second anode active material layer 124 may be included.

That is, the negative electrode 130 has a multi-layer structure in which the content of the silicon-based active material included in the first negative active material layer 122 is less than that of the silicon-based active material in the second negative active material layer 124, and the second negative active material layer ( 124), when a PAA-based water-based binder layer in contact with the upper layer is further laminated, excellent cycle characteristics can be secured to improve the lifespan characteristics of the battery.

A separator 140 may be interposed between the anode 100 and the cathode 130 . The separator 140 may include a porous polymer film made of a polyolefin-based polymer such as an ethylene homopolymer, a propylene homopolymer, an ethylene/butene copolymer, an ethylene/hexene copolymer, or an ethylene/methacrylate copolymer. The separator 140 may include a nonwoven fabric formed of high-melting-point glass fiber, polyethylene terephthalate fiber, or the like.

In some embodiments, an area (eg, a contact area with the separator 140 ) and/or a volume of the negative electrode 130 may be larger than that of the positive electrode 100 . Accordingly, lithium ions generated from the positive electrode 100 may be smoothly moved to the negative electrode 130 without being precipitated in the middle, for example. Accordingly, the effect of simultaneously improving the output and stability of the above-described positive electrode active material layer 112 can be more easily realized.

According to exemplary embodiments, an electrode cell is defined by the positive electrode 100 , the negative electrode 130 , and the separator 140 , and a plurality of electrode cells are stacked to form, for example, a jelly roll electrode. Assembly 150 may be formed. For example, the electrode assembly 150 may be formed by winding, lamination, or folding of the separator 140 .

The electrode assembly 150 may be accommodated together with the electrolyte in the case 160 to define a lithium secondary battery. According to exemplary embodiments, a non-aqueous electrolyte may be used as the electrolyte.

The non-aqueous electrolyte includes a lithium salt serving as an electrolyte and an organic solvent, and the lithium salt is, for example, represented by Li ⁺ X ⁻ and F ⁻ , Cl ⁻ , Br ⁻ , I ⁻ , NO as an anion (X ⁻ ) of the lithium salt. ₃ ^- , N(CN) ₂ ^- , BF ₄ ^- , ClO ₄ ^- , PF ₆ ^- , (CF ₃ ) ₂ PF ₄ ^- , (CF ₃ ) ₃ PF ₃ ^- , (CF ₃ ) ₄ PF ₂ ^- , ( CF ₃ ) ₅ PF ^- , (CF ₃ ) ₆ P ^- , CF ₃ SO ₃ ^- , CF ₃ CF ₂ SO ₃ ^- , (CF ₃ SO ₂ ) ₂ N ^- , (FSO ₂ ) ₂ N ^- _, CF ₃ CF ₂ (CF ₃ ) ₂ CO ^- , (CF ₃ SO ₂ ) ₂ CH ^- , (SF ₅ ) ₃ C ^- , (CF ₃ SO ₂ ) ₃ C ^- , CF ₃ (CF ₂ ) ₇ SO ₃ ^- , CF ₃ CO ₂ ^- , CH ₃ CO ₂ ^- , SCN ⁻ and (CF ₃ CF ₂ SO ₂ ) ₂ N ⁻ and the like can be exemplified.

As the organic solvent, for example, propylene carbonate (PC), ethylene carbonate (EC), diethyl carbonate (DEC), dimethyl carbonate (DMC), ethylmethyl carbonate (EMC) ), methylpropyl carbonate, dipropyl carbonate, dimethylsulfuroxide, acetonitrile, dimethoxyethane, diethoxyethane, vinylene carbonate, sulfolane, gamma-butyrolactone, propylene sulfite and tetrahydrofuran can be used. . These may be used alone or in combination of two or more.

As shown in FIG. 2 , electrode tabs (positive electrode tab and negative electrode tab) protrude from each of the positive current collector 105 and the negative current collector 125 belonging to each electrode cell, so that one end of the case 160 is can be extended up to The electrode tabs may be fused together with the one end of the case 160 to be connected to the electrode leads (positive lead 107 and negative lead 127 ) that are extended or exposed to the outside of the case 160 .

In FIG. 2 , the positive lead 107 and the negative lead 127 are illustrated to protrude from the upper side of the case 160 in the planar direction, but the positions of the electrode leads are not limited thereto. For example, the electrode leads may protrude from at least one of both side sides of the case 160 , or may protrude from a lower side of the case 160 . Alternatively, the positive lead 107 and the negative lead 127 may be formed to protrude from different sides of the case 160 , respectively.

The lithium secondary battery may be manufactured, for example, in a cylindrical shape, a square shape, a pouch type, or a coin type using a can.

The lithium secondary battery according to the exemplary embodiments may provide a battery having good electrode adhesion and improved high energy density and lifespan characteristics according to the above-described negative electrode structure.

Hereinafter, preferred embodiments are presented to help the understanding of the present invention, but these examples are merely illustrative of the present invention and do not limit the appended claims, and are within the scope and spirit of the present invention. It is obvious to those skilled in the art that various changes and modifications are possible, and it is natural that such variations and modifications fall within the scope of the appended claims.

Example 1

(1) Preparation of anode comprising a binder layer

94.05 wt% of graphite as a first negative active material, 3 wt% of silicon oxide (SiO _X ), 0.25 wt% of carbon nanotubes (CNT) as a conductive material, 1.5 wt% of styrene-butadiene rubber (SBR) as a binder, and carboxymethyl as a thickener A first negative electrode slurry was prepared including 1.2 wt% of cellulose (CMC). The first negative electrode slurry was applied on a copper substrate, dried and pressed to prepare a first negative electrode active material layer.

88.05 wt% of graphite as a second negative active material, 9 wt% of silicon oxide (SiO _X ), 0.25 wt% of carbon nanotubes (CNT) as a conductive material, 1.5 wt% of styrene-butadiene rubber (SBR) as a binder, and carboxymethyl as a thickener A second negative electrode slurry was prepared including 1.2 wt% of cellulose (CMC). The second negative electrode slurry was applied on the first negative electrode slurry, dried and pressed to prepare a second negative electrode active material layer.

A binder slurry for preparing a binder layer was prepared by dissolving 1 wt% of polyacrylic acid (PAA) in pure water (H ₂ O). Thereafter, a negative electrode including a binder layer was prepared by coating, drying, and rolling a bar of binder slurry (viscosity of 3,000 cp) on one surface of the second negative active material layer prepared in (1) above.

(2) Preparation of anode

A positive electrode mixture was prepared by mixing NCM as a positive electrode active material, CNT as a conductive material, and PVDF as a binder in a mass ratio of 98:1:1, respectively, after coating on an aluminum current collector, followed by pressing and drying to form a positive electrode. .

(3) manufacture of secondary battery

The negative electrode and the positive electrode prepared in (1) and (2) are each notched to a predetermined size and laminated, and a separator (polyethylene, thickness 15 μm) is interposed between the positive electrode and the negative electrode to form an electrode cell. , the tabs of the positive and negative electrodes were welded, respectively. The welded anode/separator/cathode assembly was placed in a pouch and three sides were sealed except for the electrolyte injection side. At this time, the part with the electrode tab was included in the sealing part. Electrolyte was injected through the remaining surfaces except for the sealing part, and the remaining surfaces were sealed and impregnated for more than 12 hours.

The electrolyte solution was prepared by dissolving 1M LiPF ₆ in a mixed solvent of EC/EMC/DEC (25/45/30; volume ratio), then vinylene carbonate (VC) 1wt%, 1,3-propensultone (PRS) 0.5wt% and 0.5 wt% of lithium bis(oxalato)borate (LiBOB) was used.

Example 2-6

As shown in Table 1, a lithium secondary battery was manufactured in the same manner as in Example 1, except that the binder content included in the binder layer was adjusted.

Examples 7-8

A lithium secondary battery was prepared in the same manner as in Example 3, except that the viscosity of the binder slurry was adjusted as shown in Table 1.

Comparative Example 1

91.05 wt% of artificial graphite, silicon oxide (SiO _X ) for the preparation of negative electrode active material slurry A negative electrode slurry was prepared including 6 wt%, 1.5 wt% of styrene-butadiene rubber (SBR) as a binder, 1.2 wt% of carboxymethyl cellulose (CMC), and 0.25 wt% of carbon nanotubes (CNT) as a conductive material. The negative electrode slurry was applied as a single layer on a copper substrate, dried and pressed to prepare a single layer negative electrode without a binder layer.

The positive electrode and the secondary battery were prepared in the same manner as in Example 1 (2) preparation of the positive electrode and (3) preparation of the secondary battery.

Comparative Example 2

91.05 wt% of artificial graphite, silicon oxide (SiO _X ) for the preparation of negative electrode active material slurry 6% by weight, polyacrylic acid (PAA) 2.7% by weight as a binder, and carbon nanotubes (CNT) 0.25% by weight as a conductive material to prepare a negative electrode slurry. The negative electrode slurry was applied as a single layer on a copper substrate, dried and pressed to prepare a single layer negative electrode without a binder layer.

The positive electrode and the secondary battery were prepared in the same manner as in Example 1 (2) preparation of the positive electrode and (3) preparation of the secondary battery.

Comparative Example 3

A lithium secondary battery was prepared in the same manner as in Example 3, except that 3 wt% of Na-CMC was included as the binder of the binder layer.

Comparative Example 4

A lithium secondary battery was prepared in the same manner as in Comparative Example 1, except that 3wt% of Na-CMC was included as the binder of the binder layer.

Comparative Example 5

A lithium secondary battery was prepared in the same manner as in Example 1 except that the binder layer was not included.

Coating conditions of the binder layer binder layer
The presence or absence bookbinder
type Binder content in binder layer (wt%) binder slurry
Viscosity (cp) Example 1 ○ PAA 0.1 3,000 Example 2 ○ PAA One 3,000 Example 3 ○ PAA 3 3,000 Example 4 ○ PAA 4 3,000 Example 5 ○ PAA 5 3,000 Example 6 ○ PAA 7 3,000 Example 7 ○ PAA 3 10,000 Example 8 ○ PAA 3 90 Comparative Example 1 X - - - Comparative Example 2 X - - - Comparative Example 3 ○ Na-CMC 3 3,000 Comparative Example 4 ○ Na-CMC 3 3,000 Comparative Example 5 X - - -

Experimental example

(1) Viscosity

Viscosity was measured at 25°C and 30 rpm using a viscometer (viscometer TV-22, manufactured by TOKI).

(2) overall electrode thickness standard deviation

The electrode thickness was measured using a micrometer. The standard deviation of the total electrode thickness was calculated by measuring the thickness of the electrode 20 times or more. The measurement results are shown in Table 2 below.

(3) Measurement of electrode adhesion

After attaching the double-sided tape to the adhesive force measuring jig, the current collector side of the positive electrode prepared in Examples and Comparative Examples was placed on the tape, and then the roller was reciprocated 10 times to attach it. Then, the tape was cut to a width of 18 mm and attached to the center of the measuring jig with the tape side facing down.

The adhesive force of the second anode active material layer to the surface of the first anode active material layer was measured while the second anode active material layer was peeled off from the first anode active material layer while the adhesive force meter was moved at a speed of 300 rpm.

From the positive electrode from which the second negative active material layer was removed, the first negative active material layer was peeled off from the current collector under the same conditions, and the adhesive force of the first negative active material layer to the current collector surface was measured. The measurement results are shown in Table 2 below.

(4) Dose ratio evaluation

The discharge capacity of each cycle was measured while charging and discharging the secondary batteries according to the above-described Examples and Comparative Examples at 0.1 C (total of 3 cycles). Thereafter, the measured discharge capacity was measured while repeating charging and discharging at 0.3C. The ratio (%) of the 0.3C discharge capacity (third time) to the 0.1C discharge capacity was calculated based on the discharge capacity, respectively, and the results are shown in Table 2 below.

(5) Capacity retention rate evaluation

After repeating charging (CC-CV 0.3 C 4.2V 0.05C CUT-OFF) and discharging (CC 0.3C 2.5V CUT-OFF) 200 times with the lithium secondary battery according to the above-described embodiment and comparative examples, 200 times The capacity retention rate was measured by calculating the discharge capacity in % of the one-time discharge capacity.

Electrode properties Cell characteristics Total electrode thickness standard deviation adhesion ratio
(N/18mm) 0.3C/0.1C
Capacity ratio (%) Cycle retention
(200 ^th ) Example 1 0.5 0.45±0.5 93.9 76.5 Example 2 0.5 0.45±0.5 93.7 78.7 Example 3 0.6 0.45±0.5 93.9 80.2 Example 4 0.7 0.45±0.5 93.8 80.2 Example 5 0.7 0.45±0.5 94.0 80.4 Example 6 0.8 0.45±0.5 90.5 75.1 Example 7 1.1 0.45±0.5 93.7 68.9 Example 8 0.8 0.45±0.5 88.4 78.7 Comparative Example 1 0.5 0.45±0.5 94.1 71.4 Comparative Example 2 0.5 0.2±1.0 94.4 75.6 Comparative Example 3 0.8 0.45±0.5 88.4 78.7 Comparative Example 4 0.8 0.45±0.5 88.3 74.8 Comparative Example 5 0.5 0.45±0.5 94.1 71.4

Referring to Table 2, the examples of the present invention include a PAA-based water-based binder layer, the negative active material layer is a single layer, and compared to Comparative Examples 1 and 2 that does not include a separate binder layer, the cycle characteristics while securing electrode adhesion. It was confirmed that it can be obtained.

However, in the case of capacity characteristics, Comparative Examples 1 and 2 were measured to be somewhat higher than those of Examples. This is determined to be due to the fact that in Comparative Examples 1 and 2, when the active material layer not including the binder layer is a single layer, the resistance of the electrode is small. On the other hand, it can be confirmed that it is difficult to guarantee the lifespan characteristics compared to the examples through the remarkably low cycle characteristics.

In particular, in the case of Comparative Example 2, even if the PAA-based binder layer is used, it can be confirmed that the adhesive strength is lowered when applied to a single layer of an anode active material rather than a surface layer.

In light of the results of Comparative Example 3, even when the anode active material layer has a multilayer structure, it can be confirmed that the use of the Na-CMC binder layer has inferior capacity characteristics and cycle characteristics compared to the case of using the PAA-based binder layer.

In the case of Comparative Example 4, although the negative active material layer was a single layer, not a multi-layer active material layer, even including a binder layer, the effect on a slight cycle improvement was confirmed. Able to know. This means that in order to maximize the effect of the binder layer, it should be applied to the multi-layered active material layer.

In the case of Comparative Example 5, even though the negative active material layer had a multilayer structure, it was confirmed that cycle characteristics were deteriorated when the binder layer was not included.

In light of the comprehensive results of Examples and Comparative Examples, the content of the silicon-based active material of the first anode active material layer is less than the content of the silicon-based active material of the second anode active material layer In the case of including a PAA-based aqueous binder layer in the active material layer of a multilayer structure , it can be confirmed that the lifespan characteristics of the battery can be improved by securing excellent cycle characteristics while improving thermal adhesion, which can be a problem when using a conventional aqueous binder.

In addition, in light of the results of Example 6, when the binder content included in the binder layer contains 0.1 to 5% by weight based on the total weight of the electrode, in the case of Examples 1 to 5, the capacity ratio and capacity retention rate of the electrode are improved, and the electrode lifespan characteristics are improved. can be improved.

In addition, in light of the results of Examples 7 and 8, when the viscosity of the binder slurry exceeds 3,000 cp when forming the binder layer, it is difficult to secure cycle characteristics by reducing the capacity of the battery, and when it is less than 100 cp, it is also difficult to secure the thickness of the electrode. It can be seen that it is difficult to guarantee cycle characteristics.

100: positive electrode 105: positive electrode current collector
110: positive active material layer 120: negative active material layer
122: first anode active material layer 124: second anode active material layer
125: negative electrode current collector 126: binder layer
130: negative electrode 140: separator
150: electrode assembly 160: case

Claims (10)

negative electrode current collector;
an anode active material layer including a first anode active material layer and a second anode active material layer sequentially positioned on at least one surface of the anode current collector; and
a binder layer positioned on the second anode active material layer;
The second anode active material layer includes a silicon-based active material,
The binder layer comprises at least one binder selected from the group consisting of polyacrylic acid, polyvinyl alcohol, polyacrylonitrile, polyacrylamide and polyvinyl acetate, a negative electrode for a lithium secondary battery. The method according to claim 1, wherein the first anode active material layer and the second anode active material layer each comprises a silicon-based active material,
The content of the silicon-based active material in the total weight of the first anode active material layer is less than the content of the silicon-based active material in the total weight of the second anode active material layer, a negative electrode for a lithium secondary battery. The negative electrode for a lithium secondary battery according to claim 2, wherein the first negative active material layer and the second negative active material layer each include a blend of a carbon-based active material and the silicon-based active material. The negative electrode for a lithium secondary battery according to claim 1, wherein the first negative active material layer is made of a carbon-based active material. The method according to claim 1, wherein the silicon-based negative active material is silicon (Si), silicon alloy, silicon oxide, silicon-carbon (Si-C) composite, silicon alloy (Si-alloy)-based lithium containing a carbon composite or mixtures thereof. Anode for secondary batteries. The negative electrode for a lithium secondary battery according to claim 1, wherein the binder content in the binder layer is 0.1 to 5 wt% based on the total weight of the negative electrode. The negative electrode for a lithium secondary battery according to claim 1, wherein the binder layer is formed of a binder slurry including a binder and an aqueous solvent. The negative electrode for a lithium secondary battery according to claim 7, wherein the binder slurry does not contain an additive. The negative electrode for a lithium secondary battery according to claim 7, wherein the binder slurry has a viscosity of 100 to 3,000 cp. anode;
The negative electrode according to claim 1; and
A lithium secondary battery comprising a separator interposed between the positive electrode and the negative electrode.

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