Negative electrode for secondary batteries and lithium secondary batteries containing the same

Abstract

To provide a negative electrode for secondary batteries and a lithium secondary battery having improved electrochemical properties. [Solution] A negative electrode for a secondary battery and a lithium secondary battery containing the same are provided. The negative electrode for the secondary battery includes a negative electrode current collector and a negative electrode active material layer containing alcohol, disposed on one surface of the negative electrode current collector. ¹H NMR analysis of the negative electrode active material layer, performed using CDCl3 solvent at room temperature and atmospheric pressure, with trimethoxybenzene as the reference material, and fixing the protons of the peak observed in the range of 6 ppm to 6.5 ppm to 3 to set the reference area, shows that the sum of the area of ​​the first peak observed in the range of 4 ppm to 4.5 ppm and the area of ​​the second peak observed in the range of 3.5 ppm to 4 ppm is greater than 0 and 0.15 or less, the area of ​​the third peak observed in the range of 1.5 ppm to 2 ppm is greater than 0 and 0.15 or less, and the area of ​​the fourth peak observed in the range of 1 ppm to 1.5 ppm is greater than 0 and 0.8 or less.

Description

[Technical Field]

[0001] This disclosure relates to a negative electrode for a secondary battery, a method for manufacturing the same, and a lithium secondary battery including the same. [Background technology]

[0002] Rechargeable batteries are batteries that can be repeatedly charged and discharged, and have been widely used as a power source for portable electronic communication devices such as camcorders, mobile phones, and laptop computers as the information and communication and display industries have developed. More recently, battery packs containing rechargeable batteries have also been developed and applied as power sources for environmentally friendly vehicles such as electric vehicles and hybrid vehicles.

[0003] Examples of secondary batteries include lithium-ion batteries, nickel-cadmium batteries, and nickel-metal hydride batteries. Among these, lithium-ion batteries are being actively developed and applied due to their high operating voltage and energy density per unit weight, as well as their advantages in terms of charging speed and weight reduction.

[0004] For example, a lithium secondary battery may include an electrode assembly comprising a positive electrode, a negative electrode, and a separator, and an electrolyte that impregnates the electrode assembly. The lithium secondary battery may further include an outer packaging material, for example, in the form of a pouch, that houses the electrode assembly and the electrolyte.

[0005] High-capacity lithium-ion secondary batteries with fast charge / discharge rates are being developed. Consequently, there is a need for the development of negative electrodes that can achieve improved efficiency and high capacity lithium-ion secondary batteries. [Overview of the Initiative] [Problems that the invention aims to solve]

[0006] One objective of this disclosure is to provide a negative electrode for a secondary battery having improved electrochemical properties.

[0007] One object of the present disclosure is to provide a lithium secondary battery having improved electrochemical properties.

Means for Solving the Problem

[0008] The negative electrode for a secondary battery according to the present disclosure includes a negative electrode current collector and a negative electrode active material layer disposed on one surface of the negative electrode current collector and containing alcohol. By 1H NMR analysis of the negative electrode active material layer using a CDCl3 solvent under normal temperature and normal pressure conditions, using trimethoxybenzene as a reference substance, and fixing the protons of the peak observed in the range of 6 ppm to 6.5 ppm to 3 and setting them to the reference area, the sum of the area of the first peak observed in the range of 4 ppm to 4.5 ppm and the area of the second peak observed in the range of 3.5 ppm to 4 ppm is greater than 0 and not more than 0.15, the area of the third peak observed in the range of 1.5 ppm to 2 ppm is greater than 0 and not more than 0.15, and the area of the fourth peak observed in the range of 1 ppm to 1.5 ppm is greater than 0 and not more than 0.8.

[0009] According to an exemplary embodiment, the area of the first peak may be 0.01 to 0.04.

[0010] According to an exemplary embodiment, the area of the second peak may be 0.03 to 0.08.

[0011] According to an exemplary embodiment, the area of the third peak may be 0.05 to 0.13.

[0012] According to an exemplary embodiment, the area of the fourth peak may be 0.3 to 0.6.

[0013] According to an exemplary embodiment, the alcohol may include a monohydric alcohol or a dihydric alcohol.

[0014] According to an exemplary embodiment, the alcohol may include a monohydric alcohol having 3 to 10 carbon atoms or a dihydric alcohol having 3 to 10 carbon atoms.

[0015] According to an exemplary embodiment, the loading amount of the negative electrode active material layer is 5 mg / cm 2 ~30 mg / cm 2 and may be such.

[0016] According to an exemplary embodiment, the negative electrode active material layer may include a graphite-based active material and a silicon-based active material.

[0017] According to an exemplary embodiment, in the total weight of the negative electrode active material layer, the ratio of the content of the graphite-based active material to the content of the silicon-based active material may be 5 to 30.

[0018] The lithium secondary battery according to the present disclosure includes the negative electrode for a secondary battery and a positive electrode facing the negative electrode.

Advantages of the Invention

[0019] The negative electrode for a secondary battery according to an exemplary embodiment of the present disclosure can have a low surface tension and can suppress the occurrence of curling and / or cracking in the manufacturing process of the negative electrode. As a result, the efficiency and productivity in the manufacturing process of the negative electrode can be improved. Further, the negative electrode for a secondary battery can have improved capacity and stability.

[0020] The lithium secondary battery according to an exemplary embodiment of the present disclosure can have improved life characteristics.

[0021] The negative electrode for a secondary battery and the lithium secondary battery according to the present disclosure can be widely applied in the fields of green technologies such as electric vehicles, battery charging stations, solar power generation, and wind power generation that utilize other batteries. Further, the negative electrode for a secondary battery and the lithium secondary battery according to the present disclosure can be used in environment-friendly electric vehicles (Electric Vehicle), hybrid vehicles, etc. for suppressing air pollution and greenhouse gas emissions to prevent climate change.

Brief Description of the Drawings

[0022] [Figure 1] Figure 1 is a schematic plan view showing a lithium secondary battery according to one embodiment. [Figure 2] Figure 2 is a schematic cross-sectional view showing a lithium secondary battery according to one embodiment. [Figure 3] Figure 3 is a graph showing the internal resistance of batteries as they undergo cycle counts in the reference example, the embodiment, and the comparative example. [Figure 4] Figure 4 is a graph showing the internal resistance of batteries as they undergo cycle counts in the reference example, the embodiment, and the comparative example. [Figure 5] Figure 5 is a graph showing the battery discharge capacity as a number of cycles for the reference example, the example, and the comparative example. [Figure 6] Figure 6 is a graph showing the battery discharge capacity as a number of cycles occurs for the reference example, the example, and the comparative example. [Modes for carrying out the invention]

[0023] This disclosure provides a negative electrode for a secondary battery that provides predetermined 1H NMR measurement characteristics. This disclosure also discloses a lithium secondary battery including the negative electrode for the secondary battery.

[0024] The present disclosure will be described in detail below with reference to examples and drawings. However, these embodiments are illustrative and not limiting to the present disclosure.

[0025] The negative electrode 130 for a secondary battery according to this disclosure (hereinafter sometimes abbreviated as "negative electrode") includes a negative electrode current collector 125 and a negative electrode active material layer 120 disposed on the surface of the negative electrode current collector. According to exemplary embodiments, the negative electrode active material layer 120 may be disposed on one or both sides of the negative electrode current collector 125, respectively (see Figure 2).

[0026] Non-limiting examples of the negative electrode current collector 125 include copper foil, nickel foil, stainless steel foil, titanium foil, nickel foam, copper foam, and polymer substrates coated with conductive metal. Non-limiting examples also include the thickness of the negative electrode current collector 125, for example, 4 μm to 50 μm.

[0027] The negative electrode active material layer 120 contains an alcohol. The alcohol has a lower surface tension than the solvent of the negative electrode slurry, such as water. This prevents curling and cracking that occur during the formation of the negative electrode active material layer 120 due to the difference in shrinkage rates between the negative electrode active material layer 120 and the negative electrode current collector 125.

[0028] According to exemplary embodiments, the surface tension of the alcohol may be 50 mN / m or less. This can lower the surface tension of the negative electrode surface and prevent the occurrence of cracks and / or curls during the formation of the negative electrode active material layer.

[0029] According to exemplary embodiments, the boiling point of the alcohol at atmospheric pressure may be 130°C or higher. This allows it to evaporate more slowly than water during the formation process of the negative electrode active material layer 120, thereby preventing damage to the negative electrode active material layer 120 due to excessive shrinkage during drying.

[0030] According to exemplary embodiments, the alcohol may include a monohydric alcohol or a dihydric alcohol. According to some embodiments, the alcohol may include a monohydric alcohol having 3 to 10 carbon atoms, or a dihydric alcohol having 3 to 10 carbon atoms.

[0031] For example, the alcohols include 1-propanol, 2-propanol, 1-butanol, 2-butanol, 1-pentanol, 2-pentanol, 3-pentanol, 1-hexanol, 2-hexanol, 3-hexanol, 1-heptanol, 2-heptanol, 3-heptanol, 4-heptanol, 1-octanol, 2-octanol, 3-octanol, 4-octanol, 1-nonanol, 2-nonanol, 3-nonanol, 4-nonanol, 5-nonanol, 1-decanol, 2-decanol, 3-decanol, 4-decanol, 5- Decanol, 1,1-propanediol, 1,2-propanediol, 2,2-propanediol, 1,3-propanediol, 1,1-butanediol, 1,2-butanediol, 1,3-butanediol, 1,4-butanediol, 2,2-butanediol, 2,3-butanediol, 1,1-pentanediol, 1,2-pentanediol, 1,3-pentanediol, 1,4-pentanediol, 1,5-pentanediol, 2,2-pentanediol, 2,3-pentanediol, 2,4-pentanediol, 3,3-pentanediol, 1 ,1-Hexanediol, 1,2-Hexanediol, 1,3-Hexanediol, 1,4-Hexanediol, 1,5-Hexanediol, 1,6-Hexanediol, 2,2-Hexanediol, 2,3-Hexanediol, 2,4-Hexanediol, 2,5-Hexanediol, 3,3-Hexanediol, 3,4-Hexanediol, 1,1-Heptanediol, 1,2-Heptanediol, 1,3-Heptanediol, 1,4-Heptanediol, 1,5-Heptanediol, 1,6-Heptanediol, 1,7-Heptanediol, 2 ,2-heptanediol, 2,3-heptanediol, 2,4-heptanediol, 2,5-heptanediol, 2,6-heptanediol, 3,3-heptanediol, 3,4-heptanediol, 3,5-heptanediol, 4,4-heptanediol, 1,1-octanediol, 1,2-octanediol, 1,3-octanediol, 1,4-octanediol, 1,5-octanediol, 1,6-octanediol, 1,7-octanediol, 1,8-octanediol, 2,2-octanediol, 2,3-octanediol, 2,4-octanediol, 2,5-octanediol, 2,6-octanediol, 2,7-octanediol, 3,3-octanediol, 3,4-octanediol, 3,5-octanediol, 3,6-octanediol, 4,4-octanediol, 4,5-octanediol, 1,1-nonanediol, 1,2-nonanediol, 1,3-nonanediol, 1,4-nonanediol, 1,5-nonanediol, 1,6-nonanediol , 1,7-nonanediol, 1,8-nonanediol, 1,9-nonanediol, 2,2-nonanediol, 2,3-nonanediol, 2,4-nonanediol, 2,5-nonanediol, 2,6-nonanediol, 2,7-nonanediol, 2,8-nonanediol, 3,3-nonanediol, 3,4-nonanediol, 3,5-nonanediol, 3,6-nonanediol, 3,7-nonanediol, 4,4-nonanediol, 4,5-nonanediol Diol, 4,6-nonanediol, 5,5-nonanediol, 1,1-decanediol, 1,2-decanediol, 1,3-decanediol, 1,4-decanediol, 1,5-decanediol, 1,6-decanediol, 1,7-decanediol, 1,8-decanediol, 1,9-decanediol, 1,10-decanediol, 2,2-decanediol, 2,3-decanediol, 2,4-decanediol, 2,5-decanediol, 2 ,6-decanediol, 2,7-decanediol, 2,8-decanediol, 2,9-decanediol, 3,3-decanediol, 3,4-decanediol, 3,5-decanediol, 3,6-decanediol, 3,7-decanediol, 3,8-decanediol, 4,4-decanediol, 4,5-decanediol, 4,6-decanediol, 4,7-decanediol, 5,5-decanediol, 5,6-decanediol, etc. These can be used alone or in combination of two or more.

[0032] According to exemplary embodiments, the negative electrode active material layer 120 may include a graphite-based active material and a silicon-based active material. The graphite-based active material may have high stability. The silicon-based active material may increase the capacity of the negative electrode.

[0033] The graphite-based active material can include graphite-based carbons such as natural graphite, artificial graphite, graphitized coke, graphitized MCMB, and graphitized MPCF.

[0034] According to an exemplary embodiment, the content of the graphite-based active material may be 50% to 95% by weight based on the total weight of the negative electrode active material layer 120. According to some embodiments, the content of the graphite-based active material may be 70% to 90% by weight based on the total weight of the negative electrode active material layer 120.

[0035] The silicon-based active material can include Si, SiOx (0 < x < 2), metal-doped SiOx (0 < x < 2), silicon-carbon composites, etc. The metal can include lithium and / or magnesium, and the metal-doped SiOx (0 < x < 2) can include metal silicate.

[0036] According to an exemplary embodiment, the content of the silicon-based active material may be 1% to 10% by weight based on the total weight of the negative electrode active material layer 120. According to an exemplary embodiment, the content of the silicon-based active material may be 2% to 7% by weight based on the total weight of the negative electrode active material layer 120.

[0037] In some embodiments, the negative electrode active material layer 120 can further include amorphous carbon, lithium metal, or a lithium alloy as the negative electrode active material.

[0038] Examples of the amorphous carbon include hard carbon, soft carbon, coke, mesocarbon microbeads (MCMB), mesophase pitch-based carbon fiber (MPCF), etc.

[0039] The lithium metal may include pure lithium metal or lithium metal with a protective layer formed on it for purposes such as inhibiting dendrite growth. In one embodiment, a lithium metal-containing layer deposited or coated on the negative electrode current collector 125 can be used as the negative electrode active material layer 120. In one embodiment, a lithium thin film layer can also be used as the negative electrode active material layer 120.

[0040] The elements contained in the lithium alloy include aluminum, zinc, bismuth, cadmium, antimony, silicon, lead, tin, gallium, or indium.

[0041] According to exemplary embodiments, the ratio of the content of the graphite-based active material to the content of the silicon-based active material in the total weight of the negative electrode active material layer 120 may be 5 to 30. According to some embodiments, the ratio of the content of the graphite-based active material to the content of the silicon-based active material in the total weight of the negative electrode active material layer 120 may be 7 to 20.

[0042] Within the aforementioned range, the stability of the high-capacity negative electrode 130 can be further improved.

[0043] According to exemplary embodiments, the negative electrode active material layer 120 may further include a binder, a conductive material, a thickener, and the like.

[0044] In some embodiments, the binder can be a styrene-butadiene rubber (SBR) binder, a carboxymethylcellulose (CMC) binder, a polyacrylic acid binder, a poly(3,4-ethylenedioxythiophene) (PEDOT) binder, or the like.

[0045] The conductive material may include, but is not limited to, carbon-based conductive materials such as graphite, carbon black, acetylene black, Ketjenblack, graphene, carbon nanotubes, vapor-grown carbon fiber (VGCF), and carbon fibers, and / or metallic conductive materials such as tin, tin oxide, titanium oxide, LaSrCoO3, and LaSrMnO3.

[0046] The thickness of the negative electrode active material layer 120 may be approximately 100 μm to 300 μm, but is not limited to this.

[0047] According to an exemplary embodiment, the load amount of the negative electrode active material layer 120 is 5 mg / cm³. 2 ~30 mg / cm³ 2 It may also be 10 mg / cm³. According to some embodiments, the load amount of the negative electrode active material layer is 10 mg / cm³. 2 ~20 mg / cm³ 2 That's fine.

[0048] Within the aforementioned range, a negative electrode 130 with a higher capacity can be realized.

[0049] According to an exemplary embodiment, ¹H NMR analysis of the negative electrode active material layer 120 reveals a first and / or second, third, and fourth peak. The first to fourth peaks may originate from the alcohol. The ¹H NMR analysis is performed using trimethoxybenzene as a reference material. The ¹H NMR analysis may reveal peaks originating from the reference material in the range of 6 ppm to 6.5 ppm. A reference area is set by fixing the protons of the peaks observed in the range of 6 ppm to 6.5 ppm to three, and the areas of the first to fourth peaks are shown.

[0050] The 1H NMR analysis may be performed, for example, under room temperature and atmospheric pressure conditions. Room temperature may refer to 20°C to 30°C, for example, 25°C. Atmospheric pressure may refer to 0.95 atm to 1.05 atm, for example, 1 atm.

[0051] The aforementioned 1H NMR analysis is performed using CDCl3 solvent.

[0052] The area of ​​the first to fourth peaks observed from the aforementioned 1H NMR analysis can be calculated. For example, the area of ​​the first to fourth peaks observed from the 1H NMR analysis of the negative electrode can be calculated using the 1H NMR analysis results of the aforementioned reference material as the reference area.

[0053] According to an exemplary embodiment, the sum of the area of ​​the first peak observed in the range of 4 ppm to 4.5 ppm and the area of ​​the second peak observed in the range of 3.5 ppm to 4 ppm is greater than 0 and less than or equal to 0.15.

[0054] According to some embodiments, the area of ​​the first peak may be 0.01 to 0.04. According to some embodiments, the area of ​​the second peak may be 0.03 to 0.08.

[0055] According to some embodiments, a first and / or second peak may be observed from 1H NMR analysis. Depending on the type of alcohol, the area of ​​the first or second peak may be zero.

[0056] According to exemplary embodiments, the area of ​​the third peak observed in the range of 1.5 ppm to 2 ppm is greater than 0 and less than or equal to 0.15. According to some embodiments, the area of ​​the third peak may be between 0.05 and 0.13.

[0057] According to exemplary embodiments, the area of ​​the fourth peak observed in the range of 1 ppm to 1.5 ppm is greater than 0 and less than or equal to 0.8. According to some embodiments, the area of ​​the fourth peak may be between 0.3 and 0.6.

[0058] Within the aforementioned range, when the battery including the negative electrode is repeatedly charged and discharged, a decrease in the capacity of the negative electrode and an increase in the internal resistance of the battery can be suppressed.

[0059] According to exemplary embodiments, a negative electrode slurry can be produced by mixing the aforementioned negative electrode active material and the aforementioned alcohol with a solvent.

[0060] The negative electrode slurry can be applied to the surface of the negative electrode current collector 125, dried, and rolled to form a negative electrode active material layer 120.

[0061] Non-limiting examples of the solvent for the negative electrode slurry include water, pure water, deionized water, and distilled water.

[0062] The aforementioned coating can be carried out by methods such as gravure coating, slot die coating, multilayer simultaneous die coating, imprinting, doctor blade coating, dip coating, bar coating, and casting, but is not limited to these.

[0063] In some embodiments, the alcohol content in the total weight of the negative electrode active material layer (e.g., residual alcohol content after drying and rolling) may be less than 400 ppm. Within this range, the aforementioned 1H NMR peak characteristics can be easily achieved.

[0064] In one embodiment, the alcohol content may be 350 ppm or less, or 300 ppm or less. For example, the alcohol content may be 50 ppm to 350 ppm, 50 ppm to 300 ppm, 100 ppm to 350 ppm, 100 ppm to 300 ppm, 200 ppm to 350 ppm, or 200 ppm to 300 ppm.

[0065] Figures 1 and 2 are schematic plan and cross-sectional views, respectively, of a lithium secondary battery according to an exemplary embodiment. For example, Figure 2 is a cross-sectional view along line I-I' in Figure 1.

[0066] Referring to FIGS. 1 and 2, the lithium secondary battery can include an electrode assembly 150 including a positive electrode 100, a negative electrode 130, and a separator 140 interposed between the positive electrode 100 and the negative electrode 130. The electrode assembly 150 can be housed in a case 160 together with an electrolytic solution and can be impregnated with the electrolytic solution.

[0067] The positive electrode 100 can include a positive electrode current collector 105 and a positive electrode active material layer 110 on the positive electrode current collector 105. The positive electrode active material layer 110 includes a positive electrode active material and can further include a positive electrode binder and a conductive material.

[0068] For example, the positive electrode active material may include a compound capable of reversibly intercalating and deintercalating lithium ions.

[0069] In an exemplary embodiment, the positive electrode active material can include a lithium-transition metal oxide. For example, the lithium-transition metal oxide can include nickel (Ni) and can further include at least one of cobalt (Co) and manganese (Mn).

[0070] For example, the lithium-transition metal oxide can include a layered structure represented by the following Chemical Formula 1.

[0071] [Chemical Formula 1] Li x Ni (1-a-b) Co[[ID=z7]] a M b O y

[0072] For example, in Chemical Formula 1, M includes at least one of Al, Zr, Ti, Cr, B, Mg, Mn, Ba, Si, Y, W, and Sr, and 0.9 ≦ x ≦ 1.2, 1.9 ≦ y ≦ 2.1, 0 ≦ a + b ≦ 0.5 may be satisfied.

[0073] In some embodiments, 0 <a+b≦0.4、0<a+b≦0.3、0<a+b≦0.2、0<a+b≦0.17、0<a+b≦0.15、0<a+b≦0.12、または0<a+b≦0.1であってもよい。

[0074] As shown in the chemical formula 1, the lithium-transition metal oxide has the highest content or molar ratio of Ni among Ni, Co, and M. Since Ni functions as a metal that substantially contributes to the output and / or capacity of lithium secondary batteries, having the highest amount of Ni among the transition metals makes it possible to achieve high capacity and high output of lithium secondary batteries.

[0075] When the Ni content in the positive electrode active material or lithium-transition metal oxide is high, the relative chemical stability, such as the high-temperature storage stability of the secondary battery, may deteriorate. Furthermore, due to surface damage to the positive electrode active material or side reactions with the electrolyte caused by repeated charging and discharging, the sufficient high power / high capacity characteristics resulting from a high Ni content may not be achieved.

[0076] In one embodiment, the lithium-transition metal oxide may further contain a coating element or a doping element. For example, the coating element or doping element may include Al, Ti, Ba, Zr, Si, B, Mg, P, Sr, W, La, or alloys thereof, or oxides thereof. In this case, a lithium secondary battery with improved lifespan characteristics can be realized.

[0077] A slurry can be produced by mixing and stirring the positive electrode active material with a binder, conductive material and / or dispersant in a solvent. After coating the positive electrode current collector 105 with the slurry, the positive electrode 100 can be produced by drying and compressing it.

[0078] The positive electrode current collector 105 can include, for example, stainless steel, nickel, aluminum, titanium, copper, or alloys thereof, and preferably, aluminum or an aluminum alloy.

[0079] The binder may include, for example, organic binders such as vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinylidene fluoride (PVDF), polyacrylonitrile, or polymethyl methacrylate, or aqueous binders such as styrene-butadiene rubber (SBR), and can be used together with a thickener such as carboxymethylcellulose (CMC).

[0080] For example, a PVDF-based binder can be used as the positive electrode binder. In this case, the amount of binder required to form the positive electrode active material layer can be reduced, and the amount of positive electrode active material can be relatively increased. This can improve the output and capacity of the secondary battery.

[0081] The conductive material may be added to promote electron transfer between active material particles. For example, the conductive material may include carbon-based conductive materials such as graphite, carbon black, graphene, and carbon nanotubes, and / or metallic conductive materials such as tin, tin oxide, titanium oxide, and perovskite materials such as LaSrCoO3 and LaSrMnO3.

[0082] A separation membrane 140 can be interposed between the positive electrode 100 and the negative electrode 130. The separation membrane 140 may include a porous polymer film made from polyolefin polymers such as ethylene homopolymer, propylene homopolymer, ethylene / butene copolymer, ethylene / hexene copolymer, or ethylene / methacrylate copolymer. The separation membrane 140 may also include a nonwoven fabric formed from high-melting-point glass fibers, polyethylene terephthalate fibers, etc.

[0083] In some embodiments, the area (e.g., contact area with the separation membrane 140) and / or volume of the negative electrode 130 may be larger than that of the positive electrode 100. This allows lithium ions generated from the positive electrode 100 to be smoothly transferred to the negative electrode 130 without, for example, precipitating along the way.

[0084] According to an exemplary embodiment, an electrode cell is defined by a positive electrode 100, a negative electrode 130, and a separator membrane 140, and by stacking multiple electrode cells, an electrode assembly 150 of the jelly roll type can be formed, for example. The electrode assembly 150 can be formed by winding, stacking, folding, etc., of the separator membrane 140.

[0085] A lithium secondary battery can be defined by housing the electrode assembly 150 together with the electrolyte in a case 160. According to some embodiments, a non-aqueous electrolyte can be used as the electrolyte.

[0086] The non-aqueous electrolyte contains a lithium salt, which is the electrolyte, and an organic solvent. The lithium salt is, for example, Li + X - It can be expressed as follows: The anion (X) of the lithium salt. - ) as 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 - , and (CF3CF2SO2)2N - These are some examples.

[0087] Examples of organic solvents that can be used 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, gamma-butyrolactone, propylene sulfite, and tetrahydrofuran. These can be used individually or in combination of two or more.

[0088] As shown in Figure 1, electrode tabs (positive electrode tab and negative electrode tab) can protrude from the positive electrode current collector 105 and the negative electrode current collector 125 belonging to each electrode cell and extend to one side of the case 160. These electrode tabs can be fused together with the aforementioned side of the case 160 to form electrode leads (positive electrode lead 107 and negative electrode lead 127) that extend or are exposed outside the case 160.

[0089] The lithium secondary battery may be manufactured, for example, in the form of a cylindrical, rectangular, pouch-type, or coin-type container using a can.

[0090] Hereinafter, embodiments of the present disclosure will be additionally described with reference to specific experimental examples. The examples and comparative examples included in the experimental examples are merely illustrative of the present disclosure and do not limit the scope of the appended claims. It is obvious to those skilled in the art that various changes and modifications can be made to these examples within the scope of the present disclosure and the scope of the technical idea, and it is natural that these modifications and changes belong to the scope of the appended claims.

[0091] Examples and Comparative Examples The content of 1,3 - butanediol was changed and added to a mixture containing 80 parts by weight of artificial graphite particles (D50: ~10 μm), 10 parts by weight of SiOx (0 < x < 2), 3 parts by weight of graphene as a conductive material, and 4 parts by weight of CMC / SBR as a binder, and it was dispersed in pure water as a solvent to produce a negative electrode slurry.

[0092] The negative electrode slurry was applied onto one surface of a copper foil (thickness 8 μm), completely dried at a temperature of 150 °C, and rolled to produce a negative electrode having a negative electrode active material layer with a thickness in the range of 100 μm to 250 μm (loading amount 10.2 mg / cm 2 ~15.6 mg / cm 2 ).

[0093] Specifically, in the examples, the content of 1,3 - butanediol in the total weight of the negative electrode active material layer (after drying and rolling) was adjusted within a range of less than 400 ppm. In the comparative examples, the content of 1,3 - butanediol in the weight of the negative electrode active material layer was adjusted within a range of more than 400 ppm.

[0094] The electrolyte used was a solution in which 10 wt% of fluoroethylene carbonate (FEC) was added to an EC / EMC / DEC (25 / 45 / 30, volume ratio) solution containing 1.2 M LiPF6 salt. A battery was manufactured using lithium metal as the counter electrode and reference electrode, and a polypropylene (PP) film as the separator.

[0095] Reference Example The negative electrode and battery were manufactured in the same manner as in the examples, except that 1,3-butanediol was not used. 1H NMR analysis was performed on the negative electrodes of the examples, comparative examples, and reference examples. The analysis was carried out using CDCl3 solvent under room temperature (approximately 25°C) and atmospheric pressure (approximately 1 atm). The reference area was calculated by fixing the protons of the trimethoxybenzene-derived peak observed in the range of 6 ppm to 6.5 ppm to three. The positions of the peaks observed in the ranges of 4 ppm to 4.5 ppm, 3.5 ppm to 4 ppm, 1.5 ppm to 2 ppm, and 1 ppm to 1.5 ppm were identified from the 1H NMR analysis results of the electrodes of the examples, comparative examples, and reference examples, and the area of ​​each peak was calculated. The measurement results are shown in Table 1 below.

[0096] [Table 1]

[0097] Experimental example The physical properties of the negative electrodes and batteries of the examples, comparative examples, and reference examples were evaluated as follows. The results are shown in Table 2.

[0098] (1) Evaluation of crack and curl occurrence In the negative electrode manufacturing processes of the examples, comparative examples, and reference examples, the occurrence of cracks in the negative electrode active material layer and curling of the negative electrode after coating and drying was visually inspected. For cracks, ○ indicated no occurrence and × indicated occurrence. For curling, ○ indicated no occurrence, △ indicated partial occurrence, and × indicated excessive occurrence.

[0099] (2) Evaluation of battery life characteristics For the batteries of the Examples, Comparative Examples, and Reference Examples, charging (CC / CV 1.0C 4.2V 0.05C CUT-OFF) and discharging (CC 1.0C 2.5V CUT-OFF) cycles were repeated 400 times, and the capacity and internal resistance (DCIR) were measured. The capacity retention rate was calculated as the percentage of the capacity after 400 cycles relative to the initial capacity, which was defined as the capacity after one cycle. Figures 3 and 4 are graphs showing the internal resistance of batteries as they undergo cycle counts in the reference example, the embodiment, and the comparative example. Figures 5 and 6 are graphs showing the battery discharge capacity as a reference example, an example, and a comparative example, based on the number of battery cycles.

[0100] [Table 2]

[0101] As shown in Figures 3 to 6 and Tables 1 and 2, in the examples where the area of ​​the first to fourth peaks in 1H NMR analysis was within the aforementioned range, the surface tension and contact angle of the negative electrode surface decreased, and curling and cracking did not occur during negative electrode manufacturing. Furthermore, batteries using the negative electrodes of the examples showed high capacity retention and low internal resistance.

[0102] On the other hand, in the comparative example's negative electrode, the peak areas in 1H NMR analysis increased excessively. As a result, the internal resistance of the battery increased excessively, and the battery life characteristics deteriorated compared to the battery in the example.

[0103] The above description is merely an example of applying the principles of this disclosure, and other configurations may be added without departing from the scope of this disclosure.

Claims

1. Negative electrode current collector and Displaced on the surface of the negative electrode current collector, it includes a negative electrode active material layer containing alcohol, CDCl under normal temperature and atmospheric pressure conditions ３ Using a solvent and trimethoxybenzene as a reference substance, the 1H NMR analysis of the negative electrode active material layer, in which the protons of the peak observed in the range of 6 ppm to 6.5 ppm were fixed to three and set as the reference area, was performed. The sum of the area of ​​the first peak observed in the range of 4 ppm to 4.5 ppm and the area of ​​the second peak observed in the range of 3.5 ppm to 4 ppm is greater than 0 and less than or equal to 0.

15. The area of ​​the third peak observed in the range of 1.5 ppm to 2 ppm is greater than 0 and less than or equal to 0.

15. A negative electrode for a secondary battery, wherein the area of ​​the fourth peak observed in the range of 1 ppm to 1.5 ppm is greater than 0 and less than or equal to 0.

8.

2. The negative electrode for a secondary battery according to claim 1, wherein the area of ​​the first peak is 0.01 to 0.

04.

3. The negative electrode for a secondary battery according to claim 1, wherein the area of ​​the second peak is 0.03 to 0.

08.

4. The negative electrode for a secondary battery according to claim 1, wherein the area of ​​the third peak is 0.05 to 0.

13.

5. The negative electrode for a secondary battery according to claim 1, wherein the area of ​​the fourth peak is 0.3 to 0.

6.

6. The negative electrode for a secondary battery according to claim 1, wherein the alcohol comprises a monohydric alcohol or a dihydric alcohol.

7. The negative electrode for a secondary battery according to claim 1, wherein the alcohol comprises a monohydric alcohol having 3 to 10 carbon atoms, or a dihydric alcohol having 3 to 10 carbon atoms.

8. The load amount of the negative electrode active material layer is 5 mg / cm². ２ ~30 mg / cm³ ２ The negative electrode for a secondary battery according to claim 1.

9. The negative electrode for a secondary battery according to claim 1, wherein the negative electrode active material layer comprises a graphite-based active material and a silicon-based active material.

10. The negative electrode for a secondary battery according to claim 9, wherein the ratio of the content of the graphite-based active material to the content of the silicon-based active material in the total weight of the negative electrode active material layer is 5 to 30.

11. The negative electrode for a secondary battery according to claim 1, A lithium secondary battery comprising a positive electrode facing the negative electrode.

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