Lithium secondary batteries

Abstract

This invention discloses a lithium secondary battery comprising a negative electrode, the negative electrode including a negative electrode current collector and a negative electrode active material layer formed thereon, the negative electrode active material layer including an acryloyl binder; a positive electrode opposite to the negative electrode; a negative electrode tab electrically connected to the negative electrode; and a positive electrode tab electrically connected to the positive electrode. The content of the acryloyl binder and the distance between the positive electrode tab and the negative electrode tab satisfy a predetermined relationship to provide a lithium secondary battery with improved mechanical stability and battery performance.

Description

[0001] Cross-reference and priority claims of related applications

[0002] This application claims priority to Korean Patent Application No. 10-2020-0091043, filed on July 22, 2020 with the Korean Intellectual Property Office (KIPO), the entire disclosure of which is incorporated herein by reference. Technical Field

[0003] This invention relates to lithium secondary batteries. More specifically, this invention relates to a lithium secondary battery with improved stability and lifespan characteristics. Background Technology

[0004] With the development of information and display technologies, rechargeable and dischargeable secondary batteries have been widely used as power sources for mobile electronic devices such as portable cameras, mobile phones, and laptops. Recently, battery packs incorporating secondary batteries have also been developed and applied to environmentally friendly vehicles, such as hybrid vehicles, as their power source.

[0005] Secondary batteries include, for example, lithium-ion batteries, nickel-cadmium batteries, and nickel-metal hydride batteries. Lithium-ion batteries have attracted much attention due to their high operating voltage and energy density per unit weight, high charge rate, and compact size.

[0006] For example, a lithium secondary battery may include an electrode assembly comprising a positive electrode, a negative electrode, and a separator layer (separator); and an electrolyte immersing the electrode assembly. The lithium secondary battery may further include a casing having, for example, a pouch shape.

[0007] Recently, with the expansion of lithium-ion battery applications, lithium-ion batteries with higher power and higher capacity are being developed. For example, research is being conducted on cathodes or active materials that can provide higher capacity.

[0008] For example, alternative materials for negative electrodes that can replace traditional carbon-based materials are being researched. When the negative electrode active material is changed, the binder that may come into contact with or react with the negative electrode active material also needs to be changed or redesigned. However, binders can cause mechanical deformation of the negative electrode and may also lead to a deterioration in the stability and lifespan of the negative electrode or the battery.

[0009] For example, Korean patent registration number 10-1764072 discloses an adhesive for coating carbon-coated lithium iron phosphate electrodes. Summary of the Invention

[0010] According to one aspect of the present invention, a lithium secondary battery with improved mechanical stability and operational reliability is provided.

[0011] According to an exemplary embodiment, a lithium secondary battery includes a negative electrode comprising a negative electrode current collector and a negative electrode active material layer formed thereon, the negative electrode active material layer comprising an acryloyl binder; a positive electrode opposite to the negative electrode; a negative electrode tab electrically connected to the negative electrode; and a positive electrode tab electrically connected to the positive electrode. The lithium secondary battery satisfies Formula 1.

[0012] [Formula 1]

[0013] 3.6 M / 重量％ +95.1≤D T / mm

[0014] In Formula 1, M is the content of the acryloyl binder, expressed as a weight percentage (wt%) based on the total weight of the negative electrode active material layer, and D... T M is the distance between the negative and positive electrodes, expressed in millimeters (mm), and 1 ≤ M ≤ 4.

[0015] In some implementations, the negative electrode active material layer may include a silicon-based negative electrode active material.

[0016] In some embodiments, the silicon-based anode active material may include at least one selected from silicon (Si), silicon alloys, silicon oxides, silicon-carbon (Si-C) composites, and silicon alloy-carbon composites.

[0017] In some implementations, the negative electrode active material layer may further include a carbon-based negative electrode active material.

[0018] In some embodiments, the carbon-based negative electrode active material may include at least one selected from artificial graphite, natural graphite, amorphous carbon, carbon fiber, coke, and pyrolytic carbon.

[0019] In some implementations, the content of silicon-based anode active material can be from 3% to 40% by weight, based on the total weight of the anode active material layer.

[0020] In some embodiments, the acryloyl adhesive may include at least one polymer selected from acrylic polymers, lithium-based polymers, and acrylonitrile polymers.

[0021] In some implementations, the positive and negative electrode tabs may protrude in the same direction.

[0022] In some implementations, an electrode assembly may be defined including a positive electrode tab and a negative electrode tab, and the electrode assembly may include multiple electrode assemblies.

[0023] In some implementations, the volume expansion rate of the negative electrode during full charging can be less than 40%.

[0024] As described above, in the lithium secondary battery according to the exemplary embodiment, the content of the acryloyl binder and the distance between the electrode tabs can be adjusted to satisfy a predetermined relationship, thereby suppressing electrode wrinkling and reducing the volume expansion rate. Therefore, the stability and lifespan of the lithium secondary battery can be improved.

[0025] In an exemplary embodiment, the negative electrode active material layer of the lithium secondary battery may include a silicon-based negative electrode active material to improve the power / capacity of the lithium secondary battery while enhancing the mechanical and chemical stability as described above. Attached Figure Description

[0026] Figure 1 A schematic top plan view is provided to illustrate a lithium secondary battery according to an exemplary embodiment.

[0027] Figure 2 A schematic cross-sectional view is provided to illustrate a lithium secondary battery according to an exemplary embodiment.

[0028] Figure 3 An image of the electrode surface of the lithium secondary battery of Example 1 after electrode wrinkling evaluation is shown.

[0029] Figure 4 An image of the electrode surface of the lithium secondary battery of Comparative Example 1 after electrode wrinkling evaluation is shown.

[0030] Figure 5 An image of the electrode surface of the lithium secondary battery of Comparative Example 4 after electrode wrinkling evaluation is shown. Detailed Implementation

[0031] According to an exemplary embodiment of the present invention, a lithium secondary battery is provided, which includes an acryloyl binder and provides improved mechanical stability and operability.

[0032] The invention will now be described in detail with reference to the accompanying drawings. However, those skilled in the art will understand that these embodiments described with reference to the drawings are provided to further understand the spirit of the invention and do not limit the scope of the detailed description and the subject matter disclosed in the appended claims.

[0033] Figure 1 This is a schematic top plan view illustrating a lithium secondary battery according to an exemplary embodiment.

[0034] Reference Figure 1 The lithium secondary battery 200 may include a positive electrode 100 and a negative electrode 130 opposite to each other, with a separator layer 140 inserted therebetween.

[0035] exist Figure 1For ease of description, only a positive electrode 100 on the upper surface and a negative electrode 130 on the lower surface of the separator layer 140 are shown, but multiple unit cells, each including a positive electrode 100, a separator layer 140, and a negative electrode 130, can be stacked repeatedly.

[0036] The positive electrode 100 may include a positive electrode current collector 105 and a positive electrode active material layer 110 formed on the surface of the positive electrode current collector 105.

[0037] The positive current collector 105 may comprise stainless steel, nickel, aluminum, titanium, copper, or alloys thereof. Preferably, aluminum or alloys thereof may be used.

[0038] The positive electrode active material layer 110 may be formed on at least one of the upper and lower surfaces of the positive electrode current collector 105. In an exemplary embodiment, the positive electrode active material layer 110 may be formed on each of the upper and lower surfaces of the positive electrode current collector 105.

[0039] For example, the positive electrode active material can be mixed and stirred with a positive electrode binder, conductive agent and / or dispersant in a solvent to form a positive electrode slurry. The positive electrode slurry can be coated onto the positive electrode current collector 105 and dried and pressed to form a positive electrode active material layer 110.

[0040] Positive electrode active materials may include compounds that enable reversible intercalation and de-intercalation of lithium ions.

[0041] In an exemplary embodiment, the positive electrode active material may include a lithium transition metal oxide. For example, the lithium transition metal oxide may include nickel (Ni), and may further include at least one of cobalt (Co) and manganese (Mn).

[0042] For example, lithium transition metal oxides can be represented by the following chemical formula 1.

[0043] [Chemical Formula 1]

[0044] Li 1+a Ni 1-(x+y) Co x M y O2

[0045] In chemical formula 1, -0.05≤α≤0.15, 0.01≤x≤0.3, 0.01≤y≤0.3, and M may include at least one element selected from Mn, Mg, Sr, Ba, B, Al, Si, Ti, Zr and W.

[0046] The positive electrode binder may include organic-based binders, such as polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinylidene fluoride (PVDF), polyacrylonitrile, polymethyl methacrylate, etc., or water-based binders, such as styrene-butadiene rubber (SBR), which can be used with thickeners such as carboxymethyl cellulose (CMC).

[0047] For example, PVDF-based binders can be used as positive electrode binders. In this case, the amount of binder used to form the positive electrode active material layer 110 can be reduced, and the amount of positive electrode active material can be relatively increased. Therefore, the capacity and power of the lithium secondary battery can be further improved.

[0048] Conductive agents can be added to promote electron migration between active material particles. For example, conductive agents may include carbon-based materials such as graphite, carbon black, graphene, carbon nanotubes (CNTs), and / or metal-based materials such as tin, tin oxide, titanium oxide, perovskite minerals such as LaSrCoO3 or LaSrMnO3, etc.

[0049] The negative electrode 130 may include a negative electrode current collector 125 and a negative electrode active material layer 120 formed on the surface of the negative electrode current collector 125.

[0050] The negative electrode current collector 125 may include, for example, gold, stainless steel, nickel, aluminum, titanium, copper or alloys thereof, preferably copper or copper alloys.

[0051] The negative electrode active material layer 120 may be formed on at least one of the upper and lower surfaces of the negative electrode current collector 125. In an exemplary embodiment, the negative electrode active material layer 120 may be formed on each of the upper and lower surfaces of the negative electrode current collector 125.

[0052] For example, a negative electrode slurry can be prepared by mixing and stirring the negative electrode active material with a negative electrode binder, a conductive agent, and / or a dispersant in a solvent. The negative electrode slurry can be coated onto a negative electrode current collector 125, then dried and pressed to form a negative electrode active material layer 120.

[0053] In an exemplary embodiment, the negative electrode active material may include a silicon (Si)-based negative electrode active material. For example, the silicon-based negative electrode active material may include at least one of silicon (Si), silicon alloy, silicon oxide, silicon-carbon (Si-C) composite, and silicon alloy-carbon composite.

[0054] Traditionally, carbon-based active materials have been primarily used as anode active materials, but the theoretical capacity obtained from carbon-based active materials can be limited to around 370 mAh / g. However, according to an exemplary embodiment of the present invention, silicon-based materials with a theoretical capacity more than ten times that of graphite (e.g., a theoretical capacity of approximately 4200 mAh / g) can be included in the anode active material layer to significantly enhance the power and capacity characteristics of the secondary battery.

[0055] In an exemplary embodiment, the silicon-based negative electrode active material may be included in an amount of 3% to 40% by weight, based on the total weight of the negative electrode active material layer.

[0056] If the weight percentage of silicon-based active material is less than about 3% by weight, the effect of increasing capacity / power through silicon-based active material may not be fully realized. If the weight percentage of silicon-based active material exceeds about 40% by weight, excessive volume changes may occur during charging and discharging due to lithium-ion insertion and removal, resulting in expansion of the negative electrode of the secondary battery and reducing the stability of the secondary battery.

[0057] In an exemplary embodiment, the negative electrode active material layer 120 may further include a carbon-based negative electrode active material. For example, the carbon-based negative electrode active material may include at least one of artificial graphite, natural graphite, amorphous carbon, carbon fiber, coke, and pyrolytic carbon. In some embodiments, graphite-based materials may be used as the carbon-based negative electrode active material, and preferably, artificial graphite or a mixture of natural and artificial graphite may be used.

[0058] Carbon-based active materials can be used in conjunction with silicon-based active materials, which can mitigate excessive electrode expansion of silicon-based active materials during repeated charging and discharging.

[0059] For example, a mixture or blend of silicon-based and carbon-based active materials can include a silicon-carbon-based active material. This silicon-carbon-based active material can include, for example, silicon carbide (SiC) or silicon-carbon particles with a core-shell structure. Silicon-carbon particles can be formed, for example, by depositing a silicon layer on the surface of a graphite core.

[0060] In one embodiment, silicon layers can be coated onto commercially available graphite particles using a chemical vapor deposition (CVD) process employing silicon precursor compounds such as silyl compounds to form silicon-carbon particles.

[0061] In an exemplary embodiment, the negative electrode active material layer 120 may include an acryloyl binder. For example, the acryloyl binder may include at least one polymer selected from acrylic polymers, lithium acrylate polymers, and acrylonitrile polymers.

[0062] Acryloyl-based binders possess relatively high tensile strength (modulus), thus suppressing the expansion / contraction of silicon-based active materials to prevent their decomposition and collapse. Therefore, even when the silicon-based active material expands, it prevents peeling, lifting, cracking, and voiding of the negative electrode active material layer 120, and maintains stable capacity and power of the secondary battery for extended periods, even when repeated charging / discharging is possible.

[0063] In some embodiments, the acryloyl adhesive may include polyacrylic acid (PAA) and / or polyacrylamide. For example, an SEI (solid electrolyte interface) layer can be formed on the surface of the silicone-based active material by the interaction of the electrolyte with the carboxyl groups of polyacrylic acid or the amide groups of polyacrylamide.

[0064] Therefore, excessive expansion of silicon-based active materials can be suppressed while preventing irreversible decomposition of the electrolyte. For example, acryloyl-based adhesives can be used by mixing with polyvinyl alcohol (PVA). Polyvinyl alcohol can be included to further promote the formation of the SEI layer through hydrophilic interactions.

[0065] In an exemplary embodiment, the acryloyl binder may be included in an amount of about 1 wt% to 5 wt% based on the total weight of the negative electrode active material layer 120. For example, based on the solids content of the negative electrode slurry, the amount of negative electrode active material may be about 90 wt% to 98 wt%, the amount of negative electrode binder may be about 1 wt% to 5 wt%, and the amount of conductive agent may be about 0.5 wt% to 5 wt%.

[0066] Within the aforementioned range, the thickening effect and improved adhesion of the adhesive can be effectively achieved.

[0067] For example, conductive agents may include carbon-based materials such as graphite, carbon black, graphene, carbon nanotubes, etc., and / or metal-based materials such as tin, tin oxide, titanium oxide, perovskite minerals such as LaSrCoO3 or LaSrMnO3, etc.

[0068] As described above, the negative electrode active material layer 120 may contain silicon-based active materials to improve the power and capacity of the secondary battery. Furthermore, the negative electrode active material layer 120 may contain an acryloyl-based binder with high tensile strength, thereby suppressing or reducing repeated expansion and contraction caused by the silicon-based active material during charging and discharging.

[0069] When repeatedly charged / discharged, the acryloyl adhesive may have high tensile strength, causing electrode wrinkles in relatively weak areas of the electrode. However, according to an exemplary embodiment, the distance between the positive electrode tab 107 and the negative electrode tab 127 can be adjusted to prevent electrode deformation and improve the stability of the lithium secondary battery.

[0070] like Figure 1 As shown, the lithium secondary battery may include a positive electrode tab 107 electrically connected to a positive electrode 100 and a negative electrode tab 127 electrically connected to a negative electrode 130. For example, the positive electrode tab 107 and the negative electrode tab 127 may protrude from each of the positive current collector 105 and the negative current collector 125 to extend to one end of the housing 160. The positive electrode tab 107 and the negative electrode tab 127 may be welded to one end of the housing 160 to form electrode leads (positive leads and negative leads), which may protrude or may be exposed outside the housing 160.

[0071] In an exemplary embodiment, the distance between the positive electrode tab 107 and the negative electrode tab 127 can be adjusted according to the content of the acryloyl binder contained in the negative electrode active material layer 120 to satisfy the following formula 1.

[0072] [Formula 1]

[0073] 3.6 M / 重量％ +95.1≤D T / mm

[0074] In Equation 1 above, M represents the content (wt%) of acryloyl binder based on the total weight of the negative electrode active material layer, and D... T It is the distance (mm) between the negative electrode tab and the positive electrode tab, and 1≤M≤4.

[0075] For example, if the content of acryloyl adhesive is less than 2% by weight, D T It can be approximately 102 mm or more. If the content of the acryloyl adhesive is 2.5% to 4% by weight, D T It can be approximately 120mm or more.

[0076] The content of acryloyl adhesive as shown in Formula 1 and D T The formula can prevent damage and failure of the negative electrode 130 due to electrode expansion and contraction, and can suppress electrode wrinkling while achieving overall adhesion of the negative electrode active material layer 120. Therefore, it can improve the mechanical and chemical stability of lithium secondary batteries, and can also increase battery life while achieving high-density electrodes.

[0077] For example, M in Formula 1, which represents the content (wt%) of acryloyl binder relative to the total weight of the negative electrode active material layer, can be adjusted to a value between 1 and 4. Within the above range, the lifespan characteristics of lithium secondary batteries can be effectively achieved.

[0078] In an exemplary embodiment, the positive electrode tab 107 and the negative electrode tab 127 may protrude in the same direction. For example, the electrode tabs and electrode leads may be formed in a single or monodirectional manner. Therefore, when multiple electrode assemblies are stacked, space efficiency can be improved, and the energy density of the negative electrode 130 can be increased.

[0079] In a single unidirectional battery that satisfies Formula 1 as described above, volume expansion and physical deformation of the negative electrode 130 caused by silicon-based active material and acryloyl-based binder can be prevented.

[0080] Specifically, it can prevent electrode wrinkling caused by the interference and overlap of stress in the area around the tab during charging and discharging, and can reduce local stress to reduce the volume expansion rate of the electrode.

[0081] In an exemplary embodiment, when Equation 1 is satisfied, the expansion rate of the negative electrode in the fully charged state can be less than 40%. Therefore, taking into account the volume expansion rate in the fully charged state, a pouch casing can be appropriately designed, and a lithium secondary battery with a compact size can be provided.

[0082] The membrane layer 140 may include a porous polymer membrane, which is prepared from, for example, a polyolefin-based polymer, such as ethylene homopolymer, propylene homopolymer, ethylene / butene copolymer, ethylene / hexene copolymer, ethylene / methacrylate copolymer, etc. The membrane layer 140 may also be formed from a nonwoven fabric including high-melting-point glass fiber, polyethylene terephthalate fiber, etc.

[0083] In some embodiments, the area and / or volume of the negative electrode 130 (e.g., the contact area with the separator layer 140) can be larger than the area and / or volume of the positive electrode 100. Therefore, lithium ions generated from the positive electrode 100 can be readily transferred to the negative electrode 130 without loss through, for example, precipitation or sedimentation. Thus, utilizing silicon-based active materials can effectively improve power and capacity.

[0084] In an exemplary embodiment, an electrode unit may be defined by a positive electrode 100, a negative electrode 130, and a separator layer 140, and multiple electrode units may be stacked to form an electrode assembly having, for example, a jelly roll shape. For example, the electrode assembly may be formed by winding, laminating, or folding the separator layer 140. In some embodiments, the lithium secondary battery may include multiple electrode assemblies.

[0085] Figure 2 This is a schematic cross-sectional view illustrating a lithium secondary battery according to an exemplary embodiment. For example, Figure 2 Along the thickness direction of the lithium secondary battery Figure 1 The cross-sectional view shown is taken along line I-I'.

[0086] Reference Figure 2 The lithium secondary battery 200 can be housed in the casing 160 and may include, as shown in the reference... Figure 1 The electrode assembly described.

[0087] The electrode assembly can be housed together with the electrolyte in the housing 160 to form a lithium secondary battery. In an exemplary embodiment, the electrolyte may include a non-aqueous electrolyte.

[0088] Non-aqueous electrolytes can include lithium salts and organic solvents. Lithium salts can be derived from Li... + X - This indicates that the lithium salt anion X - This can include, for example, F - Cl - ,Br - I - NO3 - N(CN)2 - BF4 - ClO4 - PF6 - (CF3)2PF4 - (CF3)3PF3 - (CF3)4PF2 - (CF3)5PF - (CF3)6P - CF3SO3 - CF3CF2SO3 - (CF3SO2)2N - (FSO2)2N - CF3CF2(CF3)2CO - (CF3SO2)2CH - (SF5)3C - (CF3SO2)3C -CF3(CF2)7SO3 - CF3CO2 - CH3CO2 - SCN - (CF3CF2SO2)2N - wait.

[0089] Organic solvents may include propylene carbonate (PC), ethylene carbonate (EC), diethyl carbonate (DEC), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), methyl propyl carbonate, dipropyl carbonate, dimethyl sulfoxide, acetonitrile, dimethoxyethane, diethoxyethane, vinylene carbonate, sulfolane, γ-butyrolactone, propylene sulfite, tetrahydrofuran, etc. These organic solvents can be used alone or in combination.

[0090] Lithium-ion batteries can be manufactured in various shapes, including cylindrical (canned), triangular (prismatic), pouch, and coin-shaped.

[0091] Preferred embodiments are presented below to describe the invention in more detail. However, the following examples are given only to illustrate the invention, and those skilled in the art will clearly understand that various changes and modifications are possible within the scope and spirit of the invention. Such changes and modifications are suitably included in the appended claims.

[0092] Example 1

[0093] Li[Ni] will be used as the positive electrode active material 0.88 Co 0.1 Mn 0.02 O2, carbon black as a conductive agent, and polyvinylidene fluoride (PVdF) as a binder were mixed in a weight ratio of 96.5:2:1.5 to prepare the positive electrode. The positive electrode slurry was uniformly coated onto an aluminum foil with a thickness of 12 μm, and then vacuum dried and pressed at 130 °C to prepare the positive electrode of the lithium secondary battery.

[0094] Based on the total solids content of the negative electrode slurry, 8 parts by weight of silicon (Si), 1.5 parts by weight of acryloyl binder, 0.5 parts by weight of carbon nanotubes (CNTs) as a conductive agent, and 90 parts by weight of carbon-based active material were mixed to prepare the negative electrode slurry. The negative electrode slurry was uniformly coated on a copper foil with a thickness of 8 μm, and then vacuum dried at 130 °C and pressed to form the negative electrode.

[0095] The positive and negative electrodes obtained as described above are cut to suitable sizes and stacked. A separator (polyethylene, thickness: 13 μm) is inserted between the positive and negative electrodes to form an electrode unit. The respective tab portions of the positive and negative electrodes are welded. The distance between the positive and negative electrode tabs (D) is... TIt is formed to be 102mm.

[0096] The welded positive / separator / negative electrode assembly is inserted into the flexible package, and the three sides of the package, except for the electrolyte injection side, are sealed. The tab portion is also included in the sealed portion. Electrolyte is injected through the electrolyte injection side, and then the electrolyte injection side is also sealed. Subsequently, the above structure is immersed for more than 12 hours.

[0097] The solution was prepared by dissolving 1M LiPF6 in a mixed solvent of EC / EMC / DEC (25 / 45 / 30; volume ratio), followed by the addition of 1% by weight vinylene carbonate, 0.5% by weight 1,3-propenyl sulfonyl lactone (PRS) and 0.5% by weight lithium bis(oxalate)borate (LiBOB).

[0098] Example 2

[0099] The secondary battery was manufactured using the same method as in Example 1, except that the binder content of the negative electrode slurry was changed to 2.5 parts by weight, the carbon-based active material content was changed to 89 parts by weight, and the distance between the positive and negative electrode tabs (D) was changed. T It is formed to be 120mm.

[0100] Example 3

[0101] The secondary battery was manufactured using the same method as in Example 1, except that the binder content of the negative electrode slurry was changed to 3.5 parts by weight, the carbon-based active material content was changed to 88 parts by weight, and the distance between the positive and negative electrode tabs (D) was changed. T It is formed to be 185mm.

[0102] Comparative Example 1

[0103] Besides the distance between the positive and negative electrode tabs (D) T The secondary battery is formed to a diameter of 60 mm and manufactured using the same method as in Example 1.

[0104] Comparative Example 2

[0105] Besides the distance between the positive and negative electrode tabs (D) T The secondary battery is formed to a diameter of 89 mm and manufactured using the same method as in Example 1.

[0106] Comparative Example 3

[0107] The secondary battery was manufactured using the same method as in Example 1, except that the binder content of the negative electrode slurry was changed to 2.5 parts by weight, and the distance between the positive and negative electrode tabs (D) was also changed. TIt is formed to be 102mm.

[0108] Comparative Example 4

[0109] The secondary battery was manufactured using the same method as in Example 1, except that the Si content was changed to 16 parts by weight, the binder content of the negative electrode slurry was changed to 2.5 parts by weight, the carbon-based active material content was changed to 81 parts by weight, and the distance between the positive and negative electrode tabs (D) was changed. T It is formed to be 60mm.

[0110] Comparative Example 5

[0111] The secondary battery was manufactured using the same method as in Example 1, except that the binder content of the negative electrode slurry was changed to 3.5 parts by weight, and the distance between the positive and negative electrode tabs (D) was also changed. T It is formed to be 120mm.

[0112] Comparative Example 6

[0113] The secondary battery was manufactured using the same method as in Example 1, except that the binder content of the negative electrode slurry was changed to 4.5 parts by weight, and the distance between the positive and negative electrode tabs (D) was also changed. T It is formed to be 185mm.

[0114] Experimental Example

[0115] (1) Evaluation of electrode wrinkles

[0116] The lithium secondary batteries of the examples and comparative examples were each fully charged (CC / CV 0.5C 4.3V 0.05C cutoff), and then the negative electrode surface was visually observed according to the following criteria to evaluate electrode wrinkles. Figures 3 to 5 Electrode surface images from Example 1, Comparative Example 1, and Comparative Example 4 are shown respectively.

[0117] <Wrinkle Assessment Criteria>

[0118] ×: No wrinkles observed

[0119] ○: Local wrinkles were observed on the electrode surface.

[0120] ◎: Wrinkles appear on the entire electrode surface.

[0121] (2) Evaluation of negative electrode expansion rate

[0122] For each negative electrode prepared in the above-described embodiments and comparative examples, the volume expansion rate of the electrode was calculated by comparing the thickness of the negative electrode after full charging with the thickness of the negative electrode after pressurization.

[0123] (3) Charging / discharging efficiency

[0124] The secondary battery was charged (CC / CV 1 / 3C 4.2V 0.05C cutoff) and discharged (CC 1 / 3C 2.5V cutoff) according to the embodiments and comparative examples, and the initial charge capacity and initial discharge capacity were measured.

[0125] Charge-discharge efficiency is measured as a percentage obtained by dividing the initial discharge capacity by the initial charge capacity.

[0126] The results are shown in Table 1 below.

[0127] [Table 1]

[0128]

[0129] Referring to Table 1, in the embodiments that satisfy Formula 1, electrode wrinkling and volume expansion are prevented, thereby providing improved electrical performance.

[0130] In the comparative example, wrinkles were detected around the tab, and the negative electrode volume expansion suppression effect and charge / discharge efficiency were also reduced.

Claims

1. A lithium secondary battery, comprising: The negative electrode includes a negative electrode current collector and a negative electrode active material layer formed thereon, the negative electrode active material layer including a silicon-based negative electrode active material and an acryloyl binder; The positive electrode opposite to the negative electrode; The negative electrode tab is electrically connected to the negative terminal; and The positive electrode tab is electrically connected to the positive terminal. The positive electrode tab and the negative electrode tab protrude in the same direction. The lithium secondary battery described therein satisfies Equation 1: [Formula 1] 3.6 M / 重量 %+95.1≤D T / mm In Formula 1, M is the content of the acryloyl binder as a weight percentage based on the total weight of the negative electrode active material layer, and D... T The distance between the negative electrode tab and the positive electrode tab is expressed in millimeters, and 1 ≤ M ≤ 4.

2. The lithium secondary battery according to claim 1, wherein the silicon-based negative electrode active material comprises at least one selected from silicon, silicon alloy, silicon oxide, silicon-carbon composite and silicon alloy-carbon composite.

3. The lithium secondary battery according to claim 1, wherein the negative electrode active material layer further comprises a carbon-based negative electrode active material.

4. The lithium secondary battery according to claim 3, wherein the carbon-based negative electrode active material comprises at least one selected from artificial graphite, natural graphite, amorphous carbon, carbon fiber, coke, and pyrolytic carbon.

5. The lithium secondary battery according to claim 1, wherein the content of the silicon-based negative electrode active material is from 3% to 40% by weight, based on the total weight of the negative electrode active material layer.

6. The lithium secondary battery according to claim 1, wherein the acryloyl binder comprises at least one polymer selected from acrylic polymers, lithium acrylate polymers, and acrylonitrile polymers.

7. The lithium secondary battery of claim 1, wherein an electrode assembly including the positive electrode tab and the negative electrode tab is defined, and the lithium secondary battery includes a plurality of electrode assemblies.

8. The lithium secondary battery according to claim 1, wherein the volume expansion rate of the negative electrode during full charging is less than 40%.

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