Binder composition, negative electrode for secondary battery containing said binder composition, and lithium secondary battery

Abstract

The present invention provides a binder composition, a negative electrode for a secondary battery including the binder composition, and a lithium secondary battery. The binder composition of the present invention includes a first binder resin, a second binder resin, and water, wherein the first binder resin includes a lithium-substituted polyacrylic acid having a weight-average molecular weight (Mw) of 300,000 g / mol to 1,500,000 g / mol, and the second binder resin includes a lithium-substituted carboxymethyl cellulose having a weight-average molecular weight (Mw) of 300,000 g / mol to 1,500,000 g / mol.

Description

[Technical Field]

[0001] This application claims the benefit of priority based on Korean Patent Application No. 10-2023-0103197, filed August 7, 2023, and Korean Patent Application No. 10-2024-0102770, filed August 1, 2024, and all contents disclosed in the documents of said Korean patent applications are incorporated herein by reference.

[0002] The present invention relates to a binder composition, a secondary battery negative electrode containing the binder composition, and a lithium secondary battery. Specifically, the present invention relates to a binder composition capable of suppressing volume expansion of a negative electrode, a secondary battery negative electrode containing the binder composition, and a lithium secondary battery containing the binder composition and thereby exhibiting improved cycle characteristics. [Background technology]

[0003] With the development of mobile device technology and the increase in demand, the demand for secondary batteries as an energy source is rapidly increasing. Among these secondary batteries, lithium secondary batteries, which have high energy density, voltage, and long cycle life, have been commercialized and are widely used.

[0004] A lithium secondary battery includes a positive electrode, a negative electrode, a separator interposed between the positive electrode and the negative electrode to separate them, and an electrolyte in electrochemical communication with the positive electrode and the negative electrode.

[0005] Such lithium secondary batteries are typically manufactured using lithium-intercalated compounds such as LiCoO2 or LiMn2O4 in the positive electrode and carbon-based materials without lithium intercalated in the negative electrode. During charging, lithium ions intercalated in the positive electrode move to the negative electrode via the electrolyte, and during discharging, lithium ions move from the negative electrode to the positive electrode again, thereby operating.

[0006] On the other hand, carbon-based materials such as graphite used as anode materials have excellent stability and plasticity but are limited in terms of capacity. Therefore, in order to meet the demand for high capacity in applications such as EVs, active research has been conducted to use silicon (Si)-based materials, which are non-carbon-based materials with high theoretical capacity.

[0007] The silicon (Si)-based material is abundant in nature and has a theoretical specific capacity of 4,200 mAh / g, which is higher than that of a commercial graphite anode (372 mAh / g). -1 ), and is attracting great interest as a next-generation anode material for high-energy-density lithium-ion batteries. In addition, silicon-based materials have the advantages of being low cost, non-toxic, environmentally friendly, and having a low operating voltage (<0.5V vs. Li + / Li).

[0008] However, silicon-based materials have the disadvantages of high initial irreversible capacity, rapid lithium depletion, and lower initial efficiency compared to carbon-based anode active materials. In particular, silicon-based materials experience rapid volume expansion (≥300%) due to changes in their crystalline structure caused by the insertion and extraction of lithium ions during charge and discharge, which can lead to localized short-circuiting (isolation) or damage to the electrode, increasing resistance and causing a rapid capacity decrease in the secondary battery, making it difficult to ensure stable output and cycle characteristics.

[0009] Therefore, in order to apply silicon-based materials as negative electrode active materials, research and development is required to solve the problem of deterioration due to volume expansion of silicon-based materials and to ensure durability and charge / discharge efficiency. Summary of the Invention [Problem to be solved by the invention]

[0010] The present invention provides a binder composition having a specific composition, which, when used in combination with a silicon-based negative electrode active material, can alleviate the problem of deterioration due to volume expansion of the silicon-based negative electrode active material, while ensuring excellent electrode adhesion and providing an anode for a secondary battery with excellent durability and charge / discharge efficiency. The present invention also provides a lithium secondary battery containing the anode for a secondary battery, which has improved output characteristics and cycle characteristics. [Means for solving the problem]

[0011] [1] The present invention provides a binder composition comprising a first binder resin, a second binder resin, and water, The binder composition includes, as the first binder resin, a lithium-substituted polyacrylic acid having a weight-average molecular weight (Mw) of 300,000 g / mol to 1,500,000 g / mol, and as the second binder resin, a lithium-substituted carboxymethyl cellulose having a weight-average molecular weight (Mw) of 50,000 g / mol to 1,000,000 g / mol.

[0012] [2] The present invention provides the binder composition according to [1] above, wherein the weight average molecular weight (Mw) of the first binder resin is 500,000 g / mol to 1,500,000 g / mol.

[0013] [3] The present invention provides the binder composition according to the above [1] or [2], wherein the weight average molecular weight (Mw) of the second binder resin is 100,000 g / mol to 1,000,000 g / mol.

[0014] [4] The present invention provides a binder composition according to at least one of the above [1] to [3], wherein the total content of the first binder resin and the second binder resin is 0.2 wt % to 5.0 wt % of the total content of the binder composition.

[0015] [5] The present invention provides the binder composition according to at least one of the above [1] to [4], wherein the weight ratio of the first binder resin to the second binder resin is 3:7 to 5:5.

[0016] [6] The present invention provides a binder composition according to at least one of the above items [1] to [5], wherein the viscosity of the binder composition is 500 cP to 50,000 cP at 25°C in a 2.5 wt% aqueous solution state.

[0017] [7] The present invention provides a negative electrode active material slurry containing a silicon-based negative electrode active material and the binder composition according to [1] above.

[0018] [8] The present invention provides the negative electrode active material slurry according to [7], wherein the negative electrode active material slurry further contains a carbon-based negative electrode active material.

[0019] [9] The present invention provides the negative electrode active material slurry according to the above [7] or [8], wherein the weight ratio of the carbon-based negative electrode active material to the silicon-based negative electrode active material is 80:20 to 99:1.

[0020]

[10] The present invention provides a negative electrode active material slurry according to at least one of the above [7] to [9], wherein the binder composition is contained in an amount of 0.1 wt % to 5.0 wt % based on the total weight of the negative electrode active material slurry.

[0021]

[11] The present invention provides the negative electrode active material slurry in at least one of the above items [7] to

[10] , wherein the negative electrode active material slurry further contains a third binder resin.

[0022]

[12] The present invention provides the negative electrode active material slurry according to at least one of the above items [7] to

[11] , wherein the third binder resin is styrene-butadiene rubber.

[0023]

[13] The present invention provides the negative electrode active material slurry according to at least one of the above [7] to

[12] , wherein the third binder resin is contained in an amount of 0.1 wt % to 5.0 wt % based on the total weight of the negative electrode active material slurry.

[0024]

[14] The present invention provides, in at least one of the above items [7] to

[13] , the negative electrode active material slurry further containing a conductive material.

[0025]

[15] The present invention provides the negative electrode active material slurry according to at least one of the above [7] to

[14] , wherein the conductive material is at least one of SWCNT (single-walled carbon nanotube), TWCNT (thin-walled carbon nanotube), MWCNT (multi-walled carbon nanotube), carbon fiber, and graphene.

[0026]

[16] The present invention provides a negative electrode comprising: a negative electrode current collector; and a negative electrode active material layer disposed on at least one surface of the negative electrode current collector, the negative electrode active material layer being formed by applying the negative electrode active material slurry according to [7] above.

[0027]

[17] The present invention provides a negative electrode according to

[16] above, wherein the negative electrode has an adhesive strength of 23.2 gf / 20 mm to 25 gf / 20 mm and an energy efficiency of 96% or more in a life evaluation of 100 cycles.

[0028]

[18] The present invention provides a lithium secondary battery comprising the negative electrode according to

[16] . [Effects of the Invention]

[0029] The binder composition of the present invention contains a lithium-substituted polyacrylic acid having a weight-average molecular weight (Mw) of 300,000 g / mol to 1,500,000 g / mol and a lithium-substituted carboxymethyl cellulose having a weight-average molecular weight (Mw) of 50,000 g / mol to 1,000,000 g / mol in a specific composition ratio. This effectively suppresses volume expansion of the silicon-based active material, preventing cracks on the negative electrode surface and improving adhesion between the negative electrode active material layer and the current collector, thereby improving lithium ion mobility and enabling the production of negative electrodes with superior durability and charge / discharge efficiency. Therefore, the use of such a negative electrode of the present invention can realize lithium secondary batteries with improved power and cycle characteristics. DETAILED DESCRIPTION OF THE INVENTION

[0030] The terms and words used in this specification and claims should not be interpreted as being limited to their ordinary or dictionary meanings, but should be interpreted as having meanings and concepts that are consistent with the technical idea of ​​the present invention, based on the principle that inventors can appropriately define the concepts of terms in order to best explain their inventions.

[0031] Meanwhile, in this specification, "weight average molecular weight" can be measured using a gel permeation chromatography (GPC) device. Specifically, in the present invention, measurement is performed under GPC conditions using a 1200 series manufactured by Agilent Corporation, and the column used in this measurement can be a PL mixed B column manufactured by Agilent Corporation, and THF or DMF can be used as the solvent. Meanwhile, in this specification, unless otherwise specified, molecular weight can mean weight average molecular weight.

[0032] In addition, in this specification, the "viscosity" can be measured using a test sample in the state of a 2.5 wt% aqueous solution with a B-type viscometer (VISCOMETER, TOKIMEC) or a rheometer (Rheometer, TA instruments). Specifically, in the present invention, the "viscosity" can be measured using a test sample in the state of a 2.5 wt% aqueous solution with a B-type viscometer (VISCOMETER, TOKIMEC) (25°C, 12 rpm).

[0033] Conventionally, when manufacturing lithium secondary batteries, binders such as a mixture of styrene-butadiene rubber (SBR) and carboxymethyl cellulose (CMC) or polyvinylidene fluoride (PVDF) have been mainly used as negative electrode binders.

[0034] Styrene-butadiene rubber has the advantage of not significantly affecting conductivity when used as a binder, but its relatively weak binding strength necessitates the use of an excessive amount of binder to maintain binding strength, resulting in low electrical conductivity and significantly reduced cycle characteristics. Carboxymethyl cellulose (CMC), a thickener used in combination with styrene-butadiene rubber (SBR), has the advantage of being inexpensive and easy to manufacture, but has the disadvantage of being difficult to form a strong SEI coating due to its weak binding strength with the surface of silicon-based negative electrode active materials and by-products generated by decomposition of the electrolyte salt. Furthermore, polyvinylidene fluoride has little expansion and excellent binding strength, but has the disadvantage of expanding upon reaction with most organic electrolytes, such as propylene carbonate, and damaging parts of the negative electrode. In particular, the binder cannot effectively suppress the volume expansion of the silicon-based active material in the negative electrode containing the silicon-based active material during charge and discharge, which causes structural destruction, peeling, and deformation of the negative electrode, resulting in a problem of reduced capacity and cycle characteristics of the secondary battery.

[0035] Therefore, the present inventors conducted extensive research to develop a binder that can ensure excellent adhesive strength between negative electrode active material particles and / or between the negative electrode active material and the current collector, and can also effectively suppress volume expansion of the silicon-based negative electrode active material. As a result, they discovered that when a lithium-substituted polyacrylic acid having a specific weight-average molecular weight range and a lithium-substituted carboxymethyl cellulose having a specific weight-average molecular weight range are mixed in a specific composition ratio, excellent electrode adhesive strength (bonding strength) can be ensured, lithium ion mobility can be improved, and a strong coating can be formed on the surface of the silicon-based negative electrode active material, thereby suppressing volume expansion, and thus completed the present invention.

[0036] The present invention will now be described in more detail.

[0037] The binder composition, the negative electrode active material slurry and the negative electrode including the binder composition, and the lithium secondary battery according to the present invention may include at least one of the following configurations, and may include any technically feasible combination of the following configurations.

[0038] <Binder composition> The binder composition according to the present invention a first binder resin, a second binder resin, and water; The first binder resin includes a lithium-substituted polyacrylic acid having a weight average molecular weight (Mw) of 300,000 g / mol to 1,500,000 g / mol, The second binder resin may include lithium-substituted carboxymethyl cellulose having a weight average molecular weight (Mw) of 50,000 g / mol to 1,000,000 g / mol.

[0039] (1-1) First binder resin The first binder resin may include lithium-substituted polyacrylic acid.

[0040] The lithium-substituted polyacrylic acid may be one kind of lithium-substituted polyacrylic acid, or two or more kinds of lithium-substituted polyacrylic acids having different molecular weights may be used in combination.

[0041] In the past, when non-lithiated polyacrylic acid was used as a binder resin for negative electrode active material slurries, hydrogen gas generated by the polyacrylic acid increased the withstand voltage during charging and discharging, which could lead to cell swelling. Furthermore, a Lewis acid (HF) was formed through a side reaction between the generated hydrogen and fluorine decomposed from the electrolyte salt, which reduced the SEI formation effect and could lead to side reactions such as corrosion of the electrode current collector and the inside of the cell.

[0042] To solve this problem, in the present invention, lithium-substituted polyacrylic acid is used as the first binder resin instead of the lithium-unsubstituted polyacrylic acid, thereby suppressing hydrogen gas generation from polyacrylic acid and preventing battery swelling. Furthermore, the lithium-substituted polyacrylic acid has a terminal -COO - The functional groups form a coating on the surface of the silicon-based active material (SiOx) that can suppress volume expansion, thereby preventing cracks from occurring, and also ensures the bonding strength between the silicon-based active material (SiOx) and the adhesive strength between the silicon-based active material and the surface of the current collector, preventing the silicon-based negative electrode active material from detaching from the surface of the current collector, thereby reducing short circuits and peeling of the negative electrode. + The anion component of the group decomposed from the electrolyte salt, for example, PF6 decomposed from LiPF6 or LiFSI, etc. - or FSI -The lithium-substituted polyacrylic acid reacts with anionic components such as lithium ions to form a strong coating containing a fluorine component on the surface of the negative electrode, effectively suppressing volume expansion of the silicon-based negative electrode during repeated charge and discharge. Furthermore, the lithium-substituted polyacrylic acid has higher electrical conductivity than non-lithium-substituted polyacrylic acid within the same content range, and exhibits more efficient charge and discharge characteristics. Thus, in the present invention, by using a binder composition containing lithium-substituted polyacrylic acid as the first binder resin, a lithium secondary battery that achieves excellent charge and discharge capacity and cycle life (capacity retention rate) can be realized.

[0043] Meanwhile, the lithium-substituted polyacrylic acid of the present invention has all the hydrogen atoms of the carboxyl groups (COOH) in its structure substituted with lithium. It can be formed by adding lithium hydroxide (LiOH) to polyacrylic acid and then neutralizing it. Specifically, the lithium-substituted polyacrylic acid can be formed by adding lithium hydroxide so that the molar ratio of the carboxyl groups in the polyacrylic acid to the lithium is 1:1, and then completely neutralizing the polyacrylic acid by stirring at room temperature (25°C) for 12 hours. If the amount of lithium hydroxide added is too small, the polyacrylic acid may not be completely neutralized, and side reactions may occur due to hydrogen generated from the polyacrylic acid during charging and discharging. Furthermore, if the amount of lithium hydroxide added is too large, the -OH functional groups of the lithium hydroxide that do not participate in the neutralization reaction may bond to the surface of the silicon-based negative electrode active material, causing a side reaction that interferes with the bonding of the -COO functional groups. This prevents the formation of a strong SEI coating on the negative electrode surface, potentially reducing battery life.

[0044] The neutralized lithium-substituted polyacrylic acid may have a pH of 6 to 9.

[0045] In particular, the weight-average molecular weight (Mw) of the lithium-substituted polyacrylic acid of the present invention may be 300,000 g / mol to 1,500,000 g / mol, specifically 500,000 g / mol to 1,500,000 g / mol, and more specifically 500,000 g / mol to 1,000,000 g / mol. Preferably, the weight-average molecular weight (Mw) of the lithium-substituted polyacrylic acid of the present invention may be 600,000 g / mol to 800,000 g / mol. If the weight-average molecular weight of the lithium-substituted polyacrylic acid is less than 300,000 g / mol, the adhesive strength with the active material or current collector may be insufficient, and the improvement in the adhesive properties of the electrode and the cycle characteristics of the battery may be minimal. Furthermore, if the weight-average molecular weight of the lithium-substituted polyacrylic acid exceeds 1,500,000 g / mol, the viscosity of the binder composition increases, making it difficult to manufacture an electrode sheet. Furthermore, the adhesive strength of the electrode increases excessively, acting as a resistance in the electrode, which may reduce the mobility of lithium ions. Furthermore, the additional manufacturing costs required to improve the processability of the lithium-substituted polyacrylic acid may result in an increased unit price for the entire cell.

[0046] The present invention may use a single lithium-substituted polyacrylic acid as the first binder resin. Alternatively, two or more lithium-substituted polyacrylic acids with different weight-average molecular weights may be used in combination to improve adhesive strength and processability and to suppress the volume expansion of silicon-based materials. A lithium-substituted polyacrylic acid with a relatively high molecular weight can help increase the adhesive strength of the binder and improve the battery life stability. A lithium-substituted polyacrylic acid with a relatively low molecular weight can increase the solids content during slurry preparation, thereby improving the fluidity of the slurry and improving the processability of the binder. Specifically, the present invention may use a combination of a first lithium-substituted polyacrylic acid with a relatively low molecular weight (weight-average molecular weight (Mw): 300,000 g / mol to less than 1,000,000 g / mol) and a second lithium-substituted polyacrylic acid with a relatively high molecular weight (weight-average molecular weight (Mw): 1,000,000 g / mol to 1,500,000 g / mol).

[0047] (1-2) Second binder resin In the present invention, the second binder resin may include lithium-substituted carboxymethyl cellulose.

[0048] When lithium-unsubstituted carboxymethyl cellulose (CMC-Na) is used as a binder resin as in the past, the sodium (Na + ) ions act as impurities, impeding the movement of lithium ions and increasing resistance within the electrode, thereby reducing battery life and power output characteristics.

[0049] In order to solve this problem, in the present invention, when the second binder resin contains lithium-substituted carboxymethyl cellulose (CMC-Li) instead of the lithium-unsubstituted carboxymethyl cellulose (CMC-Na), Na + This prevents an increase in resistance due to ions, facilitates lithium desorption / insertion at the negative electrode during charging and discharging, and improves the battery's lifespan.

[0050] In particular, the lithium-substituted carboxymethyl cellulose (CMC-Li) contains many cellulose functional groups with excellent adhesive strength within its structure. Therefore, when lithium-substituted carboxymethyl cellulose (CMC-Li) is used as the second binder resin, the bonding strength between silicon-based active materials (SiOx) or the adhesive strength between silicon-based active materials and current collectors, which is reduced due to the influence of the acrylic acid groups contained in the first binder, can be further secured. During charging and discharging, the -COO-Li contained within the structure + The functional groups react with the anions generated by decomposition of the electrolyte salt to form a stronger coating on the surface of the negative electrode, which effectively suppresses the expansion of the silicon-based negative electrode active material during charge and discharge.

[0051] On the other hand, the lithium-substituted carboxymethyl cellulose (CMC-Na) has a sodium (Na + ) element is substituted with lithium, and can be prepared by adding lithium hydroxide to carboxymethyl cellulose and neutralizing it. Specifically, the lithium-substituted carboxymethyl cellulose can be prepared by adding lithium hydroxide to carboxymethyl cellulose (CMC-Na) so that the molar ratio of the carboxyl groups to the lithium is 1:1, and then completely neutralizing the carboxymethyl cellulose (CMC-Na) by stirring at room temperature (25°C) for 12 hours. If the amount of lithium hydroxide added is small, the carboxymethyl cellulose will not be completely neutralized, and the sodium (Na) contained in the carboxymethyl cellulose (CMC-Na) structure will be dissolved. + ) ions remain partially unsubstituted. +As described above, the lithium ions dissociate in the electrolyte during battery operation and act as impurities, remaining on the surface of the negative electrode and in the lithium pathways, hindering the movement of lithium ions. This can result in increased resistance and decreased conductivity within the electrode, potentially reducing the battery's lifespan. Furthermore, if a slight excess of lithium hydroxide is added during the neutralization reaction, the remaining lithium hydroxide can cause the negative electrode active material slurry to have a high pH. This can lead to increased aggregation within the negative electrode active material slurry, increasing the roughness of the negative electrode surface, and thus reducing the battery's lifespan.

[0052] In particular, the weight-average molecular weight (Mw) of the lithium-substituted carboxymethyl cellulose (CMC-Li) of the present invention may be 50,000 g / mol to 1,000,000 g / mol, specifically 100,000 g / mol to 1,000,000 g / mol, and more specifically 100,000 g / mol to 500,000 g / mol. Preferably, the weight-average molecular weight (Mw) of the lithium-substituted carboxymethyl cellulose (CMC-Li) of the present invention may be 100,000 g / mol to 300,000 g / mol. If the weight-average molecular weight of the lithium-substituted carboxymethyl cellulose (CMC-Li) is less than 50,000 g / mol, the viscosity of the binder composition decreases, increasing the drying temperature and drying time, which may cause wrinkles and cracks on the surface of the electrode. Furthermore, the binding strength between the negative electrode active material and the current collector is reduced, resulting in reduced adhesion, which may lead to detachment of the negative electrode active material. In addition, if the weight average molecular weight of the lithium-substituted carboxymethyl cellulose (CMC-Li) exceeds 1,000,000 g / mol, not only does the viscosity of the binder composition increase, making it difficult to manufacture an electrode sheet, but it also excessively increases the adhesive strength of the electrode, acting as a binder within the electrode and potentially reducing the mobility of lithium ions.

[0053] (1-3) Solvent Meanwhile, unless otherwise specified, the remainder of the binder composition of the present invention other than the first binder resin and the second binder resin may contain a solvent, and such a solvent may include water.

[0054] Meanwhile, in the binder composition of the present invention, the total content of the first binder resin and the second binder resin may be 0.2% by weight to 5.0% by weight based on the total content of the binder composition.

[0055] When the total content of the first binder resin and the second binder resin satisfies the above range, the formulation stability of the binder composition can be maintained and the adhesive strength of the binder and battery performance can be improved. When the total content of the first binder resin and the second binder resin is 0.2 wt % or more, the adhesive strength (binding strength) of the binder and the cycle performance of the battery can be improved. When the total content of the first binder resin and the second binder resin is 5.0 wt % or less, an increase in the viscosity of the binder composition can be prevented, and dispersibility can be improved during the preparation of an electrode slurry, preventing aggregation of the electrode slurry or a decrease in activity.

[0056] Specifically, the total content of the first binder resin and the second binder resin can be 0.2% by weight to 3.0% by weight, more specifically 0.2% by weight to 1.0% by weight, based on the total content of the binder composition.

[0057] Meanwhile, in the binder composition of the present invention, the first binder resin and the second binder resin may be mixed and used in a weight ratio of 3:7 to 5:5, or in a weight ratio of 4:6 to 5:5.

[0058] When the weight ratio of the first binder resin to the second binder resin satisfies the above range, the bonding strength (adhesion strength) of the silicon-based negative electrode active material is improved, thereby +It is possible to improve ion and electron mobility and enhance conductivity, suppress cracks caused by volume expansion of the silicon-based negative electrode active material, and prevent the silicon-based negative electrode active material from detaching from the surface of the current collector, thereby reducing short circuits and peeling of the negative electrode, and form a stronger coating on the surface of the negative electrode, ensuring excellent charge / discharge capacity and cycle life characteristics.

[0059] If the ratio of the second binder resin to the first binder resin is less than 5 by weight, the adhesive strength may be relatively reduced due to the reduced cellulose content, and the effects of suppressing volumetric expansion of the silicon-based active material, preventing short circuits in the negative electrode, and forming a coating may be relatively small. Furthermore, if the ratio of the second binder resin to the first binder resin is greater than 7 by weight, for example, if the content of lithium-substituted carboxymethyl cellulose in the binder composition exceeds this range, the effect of forming a fluorine-containing coating on the surface of the silicon-based negative electrode active material may be reduced due to the influence of some hydroxy groups (—OH) present in the lithium-substituted carboxymethyl cellulose structure. This may result in particle cracks occurring in the silicon-based active material during charging and discharging, which may cause a decrease in conductivity and volumetric expansion, resulting in a slight decrease in battery life.

[0060] Meanwhile, the viscosity of the binder composition of the present invention, in a 2.5 wt % aqueous solution state at a temperature of 25° C., may be 500 cP to 50,000 cP, specifically 1,000 cP to 50,000 cP, more specifically 1,000 cP to 10,000 cP, and preferably 3,000 cP to 5,000 cP. When the viscosity of the binder composition of the present invention satisfies the above range, the formulation stability of the binder composition can be maintained and excellent binder adhesive strength can be ensured, and dispersibility can be improved during the production of electrode slurry, preventing aggregation of the electrode slurry and achieving improved battery performance.

[0061] <Negative electrode active material slurry> According to another embodiment, the present invention provides a negative electrode active material slurry containing a silicon-based negative electrode active material and the binder composition of the present invention. The negative electrode active material slurry of the present invention can further contain a carbon-based negative electrode active material as needed. Further, the negative electrode active material slurry of the present invention can further contain a third binder resin and / or a conductive material as needed.

[0062] (2-1) Silicon-based negative electrode active material Since the silicon-based negative electrode active material exhibits higher capacity characteristics than the carbon-based negative electrode active material, better capacity characteristics can be obtained compared to the carbon-based negative electrode active material.

[0063] Such silicon-based negative electrode active materials include, as typical examples, metallic silicon (Si), silicon oxide (SiO x , where 0 < x < 2), silicon carbide (SiC), and Si-Y alloys (where Y is an element selected from the group consisting of alkali metals, alkaline earth metals, Group 13 elements, Group 14 elements, transition metals, rare earth elements, and combinations thereof, and is not Si). The element Y can be selected from the group consisting of Mg, Ca, Sr, Ba, Ra, Sc, Y, Ti, Zr, Hf, Rf, V, Nb, Ta, Db (dubnium), Cr, Mo, W, Sg, Tc, Re, Bh, Fe, Pb, Ru, Os, Hs, Rh, Ir, Pd, Pt, Cu, Ag, Au, Zn, Cd, B, Al, Ga, Sn, In, Ti, Ge, p, As, Sb, Bi, S, Se, Te, Po, and combinations thereof.

[0064] (2-2) Carbon-based negative electrode active material Meanwhile, the negative electrode active material slurry of the present invention may further include a carbon-based negative electrode active material, if necessary. Examples of such carbon-based negative electrode active materials include various carbon-based negative electrode active materials commonly used in the art, such as graphite-based materials such as natural graphite, artificial graphite, and Kish graphite; pyrolytic carbon, mesophase pitch-based carbon fiber, mesophase pitch microbeads, mesophase pitches, and high-temperature-calcined carbons such as petroleum or coal tar pitch-derived cokes; soft carbon; and hard carbon. The shape of the carbon-based negative electrode active material is not particularly limited, and may be amorphous, plate-like, flake-like, spherical, or fibrous.

[0065] Meanwhile, when the carbon-based negative electrode active material and the silicon-based negative electrode active material are used in combination, the weight ratio of the carbon-based negative electrode active material to the silicon-based negative electrode active material may be 80:20 to 99:1, or 85:15 to 95:5, and more specifically, 97:3 to 99:1.

[0066] When the mixing ratio of the silicon-based negative electrode active material to the carbon-based negative electrode active material satisfies the above range, the capacity characteristics are improved and the volume expansion of the silicon-based negative electrode active material is suppressed, thereby ensuring excellent cycle performance.

[0067] Meanwhile, the total content of the negative electrode active materials may be 80 wt % to 99 wt % based on the total weight of the negative electrode active material slurry. When the total content of the negative electrode active materials satisfies this range, excellent capacity characteristics and electrochemical characteristics can be obtained.

[0068] (2-3) Binder composition The description of the binder composition contained in the negative electrode active material slurry of the present invention overlaps with the above description, and therefore will be omitted.

[0069] However, with regard to the content of the binder composition, the binder composition may be included in an amount of 0.1 wt % to 5.0 wt %, or 0.1 wt % to 3.0 wt %, based on the total weight of the negative electrode active material slurry of the present invention.

[0070] When the binder composition is included within the above content range, high capacity design is possible and improved life characteristics can be achieved. Specifically, when the binder composition is included in an amount less than 0.1 wt %, not only is the effect of suppressing volume expansion of the silicon-based negative electrode active material during charge and discharge minimal, but the adhesion between the current collector and the active material cannot be ensured, which may result in detachment of the active material. Furthermore, when the binder composition is included in an amount greater than 5.0 wt %, the capacity is reduced due to a decrease in the content of the positive electrode active material caused by a slightly higher content of the binder composition, and the life characteristics may be reduced due to the resistance effect within the electrode caused by the binder.

[0071] (2-4) Third binder resin Meanwhile, the negative electrode active material slurry of the present invention may further include a third binder resin to improve the flexibility of the negative electrode.

[0072] The third binder resin may include styrene-butadiene rubber.

[0073] The third binder resin may be included in an amount of 0.1 wt % to 5.0 wt % based on the total weight of the negative electrode active material slurry.

[0074] When the third binder resin is contained within the above content range, it is possible to improve the flexibility of the negative electrode and suppress cracking of the electrode during assembly or repeated charge / discharge. Specifically, when the third binder resin is contained in an amount less than 0.1 wt %, the electrode flexibility is not ensured, and cracking of the electrode due to volume expansion during assembly or charge / discharge may occur. Furthermore, when the content of the third binder resin exceeds 5.0 wt %, the battery capacity decreases due to a decrease in the content of the negative electrode active material, and the resistance within the electrode increases, which may cause side reactions that deteriorate the battery's life characteristics.

[0075] (2-5) Conductive materials The negative electrode active material slurry of the present invention may further include a conductive material to further improve the conductivity of the negative electrode active material.

[0076] The conductive material is not particularly limited as long as it does not cause a chemical change in the battery and has conductivity, and representative examples thereof include at least one of SWCNT (single-walled carbon nanotube), TWCNT (thin-walled carbon nanotube), MWCNT (multi-walled carbon nanotube), carbon fiber, and graphene.

[0077] Such a conductive material can be contained in an amount of 1.0 to 30% by weight, preferably 1.0 to 20% by weight, and more preferably 1.0 to 10% by weight, relative to the total weight of the negative electrode active material layer.

[0078] On the other hand, if the conductive material is contained in an amount less than 1.0 wt%, it is difficult to expect an improvement in electrical conductivity or the electrochemical characteristics of the battery may be deteriorated. Also, if the conductive material is contained in an amount more than 20.0 wt%, the ratio of the silicon-based negative electrode active material to the binder may be relatively reduced, which may result in a decrease in battery capacity and energy density.

[0079] (2-6) Solvent Meanwhile, the negative electrode active material slurry of the present invention may contain a solvent.

[0080] Such a solvent may include water or an organic solvent such as NMP or alcohol, and may be used in an amount that provides a desired viscosity when the negative electrode active material, binder composition, and optionally a conductive material are included. For example, the solvent may be added so that the solids concentration in the negative electrode active material slurry is 50 wt % to 75 wt %, preferably 40 wt % to 70 wt %.

[0081] Unless otherwise specified, the remainder of the negative electrode active material slurry of the present invention, other than the silicon-based negative electrode active material, binder composition, carbon-based negative electrode active material, third binder resin, conductive material, etc., may contain a solvent.

[0082] Meanwhile, the negative electrode active material slurry of the present invention can be prepared by dissolving or dispersing the silicon-based negative electrode active material, the binder composition, and optionally at least one of a carbon-based negative electrode active material, a third binder resin, and a conductive material in the solvent.

[0083] <Negative electrode> In yet another embodiment, the present invention provides a negative electrode comprising: a negative electrode current collector; and a negative electrode active material layer disposed on at least one surface of the negative electrode current collector, the negative electrode active material layer being formed by applying the negative electrode active material slurry of the present invention.

[0084] The negative electrode current collector generally has a thickness of 3 μm to 500 μm. Such a negative electrode current collector is not particularly limited as long as it does not cause chemical changes in the battery and has high conductivity, and examples of such a negative electrode current collector include copper, stainless steel, aluminum, nickel, titanium, calcined carbon, copper or stainless steel surfaces that have been surface-treated with carbon, nickel, titanium, silver, etc., and aluminum-cadmium alloys. Furthermore, similar to the positive electrode current collector, the surface can be formed with fine irregularities to strengthen the binding force of the negative electrode active material, and the negative electrode current collector can be used in various forms such as a film, sheet, foil, mesh, porous material, foam, and nonwoven fabric.

[0085] Meanwhile, the anode of the present invention may be manufactured by a method known in the art, for example, by coating the anode active material slurry on an anode current collector, rolling and drying the coating to form an anode active material layer, or by casting the anode active material layer using the anode active material slurry on a separate support, peeling off the support, and laminating the resulting film on the anode current collector.

[0086] Such a negative electrode of the present invention has an adhesive strength of 24 gf / 20 mm to 25 gf / 20 mm, and can have an energy efficiency of 96% or more in a life evaluation of 100 cycles.

[0087] The adhesive strength was measured by cutting the rolled electrodes into a size of 15 cm x 2 cm, attaching the electrode surface to a glass slide with double-sided tape, and laminating three samples for a peel test. Each sample was then loaded into a UTM (Universal Testing Machine) and subjected to a 90° peel test to measure the peel resistance (gf / cm), and calculating the adhesiveness of each electrode.

[0088] <Secondary battery> In yet another embodiment of the present invention, there is provided a lithium secondary battery including the negative electrode of the present invention.

[0089] Specifically, the lithium secondary battery includes a positive electrode, a negative electrode, a separator interposed between the positive electrode and the negative electrode, and an electrolyte, and the negative electrode can include the negative electrode of the present invention.

[0090] Here, since the negative electrode of the present invention has been described above, the description thereof will be omitted, and hereinafter, other components will be described.

[0091] (3-1) Positive electrode The positive electrode according to the present invention can include a positive electrode active material layer containing a positive electrode active material, and if necessary, the positive electrode active material layer can further include a conductive material and / or a binder.

[0092] The positive electrode active material is a compound capable of reversible intercalation and deintercalation of lithium, and specifically, it can include a lithium metal oxide containing one or more metals such as cobalt, manganese, nickel, or aluminum and lithium.

[0093] Specifically, the positive electrode active material is a lithium-cobalt-based oxide (e.g., LiCoO2, etc.), a lithium-manganese-based oxide (e.g., LiMnO2, LiMn2O4, etc.), a lithium-nickel-based oxide (e.g., LiNiO2, etc.), a lithium-nickel-manganese-based oxide (e.g., LiNi 1-Y Mn Y O2 (where 0 < Y < 1), LiMn 2-z Ni z O4 (where 0 < Z < 2), etc.), a lithium-nickel-cobalt-based oxide (e.g., LiNi 1-Y1 Co Y1 O2 (where 0 < Y1 < 1), etc.), a lithium-manganese-cobalt-based oxide (e.g., LiCo 1-Y2 Mn Y2 O2 (where 0 < Y2 < 1), LiMn 2-z1 Co z1 O4 (where 0 < Z1 < 2), etc.), a lithium-nickel-manganese-cobalt-based oxide (e.g., Li(Nip Co q Mn r1 )O2 (where 0 < p < 1, 0 < q < 1, 0 < r1 < 1, p + q + r1 = 1) or Li(Ni p1 Co q1 Mn r2 )O4 (where 0 < p1 < 2, 0 < q1 < 2, 0 < r2 < 2, p1 + q1 + r2 = 2), etc.), lithium-nickel-cobalt-transition metal (M) oxides (e.g., Li(Ni p2 Co q2 Mn r3 M S2 )O2 (where M is selected from the group consisting of Al, Fe, V, Cr, Ti, Ta, Mg, and Mo, and p2, q2, r3, and s2 are the atomic fractions of the respective independent elements, 0 < p2 < 1, 0 < q2 < 1, 0 < r3 < 1, 0 < s2 < 1,and p2 + q2 + r3 + s2 = 1)), etc. can be included, and any one or two or more of these compounds can be included.

[0094] Among them, in terms of being able to enhance the capacity characteristics and stability of the battery, the positive electrode active material can include at least one selected from the group consisting of lithium-cobalt oxide, lithium-manganese-based oxide, lithium-nickel-manganese-cobalt-based oxide, and lithium-nickel-cobalt-transition metal (M) oxide.

[0095] Specifically, the positive electrode active material can include at least one selected from lithium-nickel-manganese-cobalt-based oxide with a nickel content of 55 atm% or more and lithium-nickel-cobalt-transition metal (M) oxide with a nickel content of 55 atm% or more. Specifically, the positive electrode active material can include a lithium-nickel-manganese-cobalt-based oxide represented by the following Chemical Formula 1.

[0096] [Chemical Formula 1] Li(Ni a Co b Mn c M d )O2

[0097] In the above Chemical Formula 1, M is W, Cu, Fe, V, Cr, Ti, Zr, Zn, Al, In, Ta, Y, La, Sr, Ga, Sc, Gd, Sm, Ca, Ce, Nb, Mg, B or Mo; a, b, c, and d are the atomic fractions of each independent element, 0.55≦a<1, 0 <b≦0.3、0<c≦0.3、0≦d≦0.1、a+b+c+d=1である。

[0098] Specifically, the a, b, c, and d may be in the ranges 0.60≦a≦0.95, 0.01≦b≦0.20, 0.01≦c≦0.20, and 0≦d≦0.05, respectively.

[0099] More specifically, a, b, c, and d can be 0.80≦a≦0.95, 0.02≦b≦0.15, 0.02≦c≦0.15, and 0≦d≦0.03, respectively.

[0100] Specifically, the positive electrode active material is, for example, Li(Ni 0.6 Mn 0.2 Co 0.2 )O2, Li(Ni 0.65 Mn 0.2 Co 0.15 )O2, Li(Ni 0.7 Mn 0.2 Co 0.1 )O2, Li(Ni 0.8 Mn 0.1 Co 0.1 )O2, Li(Ni 0.85 Co 0.05 Mn 0.08 Al 0.02 )O2 and Li(Ni 0.93 Co 0.02 Mn 0.03 Al 0.02 ) O2.

[0101] The positive electrode active material may be contained in an amount of 80 wt% to 99 wt%, specifically 90 wt% to 99 wt%, based on the total weight of the solid content of the positive electrode active material layer. If the content of the positive electrode active material is less than 80 wt%, the energy density may be reduced, and the capacity may be reduced.

[0102] The conductive material is not particularly limited as long as it does not cause a chemical change in the battery and has conductivity, and examples of the conductive material that can be used include carbon black such as carbon black, acetylene black, ketjen black, channel black, furnace black, lamp black, and thermal black; graphite powder such as natural graphite, artificial graphite, or graphite with a highly developed crystal structure; conductive fibers such as carbon fiber and metal fiber; conductive powders such as carbon fluoride powder, aluminum powder, and nickel powder; conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; and conductive materials such as polyphenylene derivatives.

[0103] The conductive material is usually added in an amount of 1 to 30% by weight based on the total weight of the solid content in the positive electrode active material layer.

[0104] The binder, which functions to improve adhesion between positive electrode active material particles and between the positive electrode active material and the current collector, is typically added in an amount of 1 to 30 wt% based on the total weight of the solids in the positive electrode active material layer. Examples of such binders include fluororesin-based binders including polyvinylidene fluoride (PVDF) or polytetrafluoroethylene (PTFE); rubber-based binders including styrene butadiene rubber (SBR), acrylonitrile butadiene rubber, and styrene-isoprene rubber; cellulose-based binders including carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, and regenerated cellulose; polyalcohol-based binders including polyvinyl alcohol; polyolefin-based binders including polyethylene and polypropylene; polyimide-based binders; polyester-based binders; and silane-based binders.

[0105] The positive electrode of the present invention may be manufactured by a method well known in the art. For example, the positive electrode may be manufactured by dissolving or dispersing a positive electrode active material, a binder, and / or a conductive material in a solvent to prepare a positive electrode slurry, which is then coated on a positive electrode current collector, followed by drying and rolling to form a positive electrode active material layer, or by casting the positive electrode active material layer on a separate support, peeling off the support, and laminating the resulting film on a positive electrode current collector.

[0106] The positive electrode current collector is not particularly limited as long as it does not cause a chemical change in the battery and has conductivity. For example, stainless steel, aluminum, nickel, titanium, baked carbon, or aluminum or stainless steel whose surface has been treated with carbon, nickel, titanium, silver, or the like can be used.

[0107] The solvent may include an organic solvent such as NMP (N-methyl-2-pyrrolidone), and may be used in an amount that provides a desired viscosity when the positive electrode active material and, optionally, a binder and a conductive material are included. For example, the solvent may be included so that the solids concentration in the active material slurry containing the positive electrode active material and, optionally, a binder and a conductive material, is 10 wt % to 90 wt %, preferably 30 wt % to 80 wt %.

[0108] (3-2) Separator The separator included in the lithium secondary battery of the present invention may be a commonly used conventional porous polymer film, for example, a porous polymer film made of a polyolefin polymer such as an ethylene homopolymer, a propylene homopolymer, an ethylene / butene copolymer, an ethylene / hexene copolymer, or an ethylene / methacrylate copolymer, either alone or in a laminate thereof, or a conventional porous nonwoven fabric, for example, a nonwoven fabric made of a high-melting point glass fiber, polyethylene terephthalate fiber, or the like, but is not limited thereto.

[0109] (3-3) Electrolyte The electrolyte used in the present invention is not particularly limited to a particular type, and various electrolytes that can be used in lithium secondary batteries, such as organic liquid electrolytes, inorganic liquid electrolytes, solid polymer electrolytes, gel-type polymer electrolytes, solid inorganic electrolytes, and molten inorganic electrolytes, can be used.

[0110] Specifically, the electrolyte may include an organic solvent and a lithium salt.

[0111] The organic solvent may be any solvent that can act as a medium through which ions involved in the electrochemical reaction of the battery can move. Specifically, examples of the organic solvent include ester solvents such as methyl acetate, ethyl acetate, γ-butyrolactone, and ε-caprolactone; ether solvents such as dibutyl ether and tetrahydrofuran; ketone solvents such as cyclohexanone; aromatic hydrocarbon solvents such as benzene and fluorobenzene; dimethylcarbonate (DMC), diethylcarbonate (DEC), methylethylcarbonate (MEC), ethylmethylcarbonate (EMC), ethylene carbonate (EC), and propylene carbonate. Examples of solvents that can be used include carbonate-based solvents such as ethylene carbonate (PC), alcohol-based solvents such as ethyl alcohol and isopropyl alcohol, nitriles such as R-CN (where R is a C2-C20 linear, branched, or cyclic hydrocarbon group that may contain a double-bonded aromatic ring or an ether bond), amides such as dimethylformamide, dioxolanes such as 1,3-dioxolane, and sulfolanes. Among these, carbonate-based solvents are preferred, and mixtures of cyclic carbonates (e.g., ethylene carbonate or propylene carbonate) with high ionic conductivity and a high dielectric constant, which can improve the charge / discharge performance of batteries, and low-viscosity linear carbonate compounds (e.g., ethyl methyl carbonate, dimethyl carbonate, or diethyl carbonate) are more preferred.

[0112] The lithium salt can be any compound that can provide lithium ions used in lithium secondary batteries without any particular limitations. Specifically, the lithium salt can include at least one of LiPF and LiN(SOF) (lithium bis(fluorosulfonyl)imide, LiFSI).

[0113] The lithium salt may further include at least one of LiClO4, LiAsF6, LiBF4, LiSbF6, LiAlO4, LiAlCl4, LiCF3SO3, LiC4F9SO3, LiN(C2F5SO3)2, LiN(C2F5SO2)2, LiN(CF3SO2)2, LiCl, LiI, and LiB(C2O4)2.

[0114] The lithium salt is preferably used at a concentration within the range of 0.1 M to 5.0 M, and more preferably 0.1 M to 3.0 M. When the lithium salt concentration is within this range, the electrolyte has appropriate conductivity and viscosity, and therefore can exhibit excellent electrolyte performance, allowing lithium ions to migrate effectively.

[0115] In addition to the essential components of the electrolyte, the electrolyte may further contain other additives for the purposes of improving the life characteristics of the battery, suppressing a decrease in the capacity of the battery, improving the discharge capacity of the battery, and the like.

[0116] Representative examples of such other additives include at least one selected from the group consisting of cyclic carbonate-based compounds, halogen-substituted carbonate-based compounds, sultone-based compounds, sulfate-based compounds, borate-based compounds, nitrile-based compounds, benzene-based compounds, amine-based compounds, silane-based compounds, and lithium salt-based compounds different from the lithium salt contained in the electrolyte.

[0117] Specifically, the other additives include vinylene carbonate (VC), vinylethylene carbonate, fluoroethylene carbonate (FEC), 1,3-propane sultone (PS), 1,4-butane sultone, ethene sultone, 1,3-propene sultone (PRS), 1,4-butene sultone, 1-methyl-1,3-propene sultone, ethylene sulfate (Esa), trimethylene sulfate (TMS), methyl trimethylene sulfate (Mt), sulfate; MTMS), tetraphenylborate, lithium oxalyl difluoroborate, succinonitrile, adiponitrile, acetonitrile, propionitrile, butyronitrile, valeronitrile, caprylonitrile, heptanenitrile, cyclopentanecarbonitrile, cyclohexanecarbonitrile, 2-fluorobenzonitrile, 4-fluorobenzonitrile, difluorobenzonitrile, trifluorobenzonitrile, phenylacetonitrile, 2-fluorophenylacetonitrile, 4-fluorophenylacetonitrile, fluorobenzene, triethanolamine, ethylenediamine, tetravinylsilane, LiN(SO2F)2 (Lithium bis(fluorosulfonyl)imide, LiFSI), LiN(SO2CF3)2 (lithium bis(trifluoromethane sulfonyl)imide, LiTFSI), LiPO2F2, LiODFB, LiBOB (lithium bisoxalatoborate (LiB(C2O4)2)), and LiBF4.

[0118] The other additives may be included in an amount of 0.01 wt % to 20 wt %, preferably 0.05 wt % to 5.0 wt %, based on the total weight of the electrolyte. If the content of the other additives is less than 0.01 wt %, the effects of improving the low-temperature output, high-temperature storage characteristics, and high-temperature life characteristics of the battery are minimal. If the content of the other additives is more than 20 wt %, excessive side reactions may occur in the electrolyte during battery charge and discharge. In particular, if the SEI film-forming additive is added in excess, it may not be sufficiently decomposed at high temperatures and may remain unreacted or precipitated in the electrolyte at room temperature. This may result in side reactions that reduce the life or resistance characteristics of the secondary battery.

[0119] The shape of the lithium secondary battery of the present invention is not particularly limited, but may be a cylindrical shape using a can, a square shape, a pouch shape, or a coin shape.

[0120] Hereinafter, the present invention will be described in detail with reference to examples. However, the examples according to the present invention may be modified into various other forms, and the scope of the present invention should not be construed as being limited to the examples detailed below. The examples of the present invention are provided to more completely explain the present invention to those skilled in the art.

[0121] [Example] I. Binder resin production Production example 1. Polyacrylic acid (Sigma-Aldrich, weight-average molecular weight: 750,000 g / mol) and lithium hydroxide (Sigma-Aldrich, LiOH·HO) were placed in a mixer in a 1:1 molar ratio and dissolved in water at 25°C. The mixture was then stirred until the pH reached 7, producing a lithium-substituted polyacrylic acid (weight-average molecular weight: 750,000 g / mol) binder.

[0122] Production example 2. Carboxymethylcellulose (Sigma-Aldrich, weight-average molecular weight: 250,000 g / mol) and lithium hydroxide (Sigma-Aldrich, LiOH·HO) were placed in a mixer in a 1:1 molar ratio and dissolved in water at 50°C. The mixture was then stirred until the pH reached 7, producing lithium-substituted carboxymethylcellulose (weight-average molecular weight: 250,000 g / mol).

[0123] Production example 3. Polyacrylic acid (Sigma-Aldrich, weight-average molecular weight: 290,000 g / mol) and lithium hydroxide (Sigma-Aldrich, LiOH·HO) were placed in a mixer in a 1:1 molar ratio and dissolved in water at 25°C. The mixture was then stirred until the pH reached 7, producing a lithium-substituted polyacrylic acid (weight-average molecular weight: 290,000 g / mol) binder.

[0124] Production example 4. Polyacrylic acid (Sigma-Aldrich, weight-average molecular weight: 1,600,000 g / mol) and lithium hydroxide (Sigma-Aldrich, LiOH·HO) were placed in a mixer in a 1:1 molar ratio and dissolved in water at 25°C. The mixture was then stirred until the pH reached 7, producing a lithium-substituted polyacrylic acid (weight-average molecular weight: 1,600,000 g / mol) binder.

[0125] Production example 5. Carboxymethylcellulose (Sigma-Aldrich, weight-average molecular weight: 40,000 g / mol) and lithium hydroxide (Sigma-Aldrich, LiOH·HO) were placed in a mixer in a 1:1 molar ratio and dissolved in water at 50°C. The mixture was then stirred until the pH reached 7, producing lithium-substituted carboxymethylcellulose (weight-average molecular weight: 40,000 g / mol).

[0126] Production Example 6. Carboxymethylcellulose (Sigma-Aldrich, weight-average molecular weight: 1,100,000 g / mol) and lithium hydroxide (Sigma-Aldrich, LiOH·HO) were placed in a mixer in a 1:1 molar ratio and dissolved in water at 50°C. The mixture was then stirred until the pH reached 7, producing lithium-substituted carboxymethylcellulose (weight-average molecular weight: 1,100,000 g / mol).

[0127] II. Secondary battery manufacturing Example 1 (Production of binder composition) The lithium-substituted polyacrylic acid (weight average molecular weight: 750,000 g / mol) prepared in Preparation Example 1 as the first binder resin and the lithium-substituted carboxymethyl cellulose (weight average molecular weight: 250,000 g / mol) prepared in Preparation Example 2 as the second binder resin were dissolved in water in a weight ratio of 3:7 to prepare a 1.0 wt % binder composition (viscosity: 3,000 cP, Brookfield viscometer (VISCOMETER, TOKIMEC), 25°C, 2.5 wt % aqueous solution).

[0128] (Manufacturing of negative electrodes) The negative electrode active material (graphite and SiO = 95:5 weight ratio), the prepared binder composition, styrene-butadiene rubber as a third binder resin, and conductive material (carbon black) were added to water as a solvent in a weight ratio of 97:1:1:1 to prepare a negative electrode slurry (solid content: 60 wt%). The negative electrode slurry was applied (13 mg / cm) to a copper (Cu) thin film as a negative electrode current collector with a thickness of 10 μm. 2 After drying, the negative electrode was prepared by roll pressing.

[0129] (Cathode manufacturing) Positive electrode active material particles (Li(Ni 0.93 Co 0.02 Mn 0.03 Al 0.02)O2), carbon black as a conductive material and polyvinylidene fluoride as a binder were added to N-methyl-2-pyrrolidone (NMP) as a solvent in a weight ratio of 98:0.8:1.2 to prepare a positive electrode slurry (solid content 75.0 wt%). The positive electrode slurry was applied (25 mg / cm) to a 15 μm-thick positive electrode current collector (Al thin film). 2 ), followed by drying and roll pressing to prepare a positive electrode.

[0130] (Secondary battery manufacturing) A porous polypropylene separator was interposed between the prepared positive electrode and negative electrode to prepare an electrode assembly, which was then housed in a battery case. An electrolyte (EC:EMC:DMC=20:10:70 volume ratio, 0.6M LiPF6, 0.6M LiFSI) was then injected to prepare a lithium secondary battery.

[0131] Example 2. (Production of binder composition) The lithium-substituted polyacrylic acid (weight average molecular weight: 750,000 g / mol) prepared in Preparation Example 1 as the first binder resin and the lithium-substituted carboxymethyl cellulose (weight average molecular weight: 250,000 g / mol) prepared in Preparation Example 2 as the second binder resin were dissolved in water in a weight ratio of 5:5 to prepare a 1.0 wt % binder composition (viscosity: 3,000 cP, Brookfield viscometer (VISCOMETER, TOKIMEC), 25°C, 2.5 wt % aqueous solution).

[0132] (Secondary battery manufacturing) A negative electrode and a lithium secondary battery including the same were manufactured in the same manner as in Example 1, except that the binder composition prepared above was used in manufacturing the negative electrode.

[0133] Example 3. (Production of binder composition) The lithium-substituted polyacrylic acid (weight average molecular weight: 750,000 g / mol) prepared in Preparation Example 1 as the first binder resin and the lithium-substituted carboxymethyl cellulose (weight average molecular weight: 250,000 g / mol) prepared in Preparation Example 2 as the second binder resin were dissolved in water in a weight ratio of 2:8 to prepare a 1.0 wt % binder composition (viscosity: 3,500 cP, Brookfield viscometer (VISCOMETER, TOKIMEC), 25°C, 2.5 wt % aqueous solution).

[0134] (Secondary battery manufacturing) A negative electrode and a lithium secondary battery including the same were manufactured in the same manner as in Example 1, except that the binder composition prepared above was used in manufacturing the negative electrode.

[0135] Example 4. (Production of binder composition) The lithium-substituted polyacrylic acid (weight average molecular weight: 750,000 g / mol) prepared in Preparation Example 1 as the first binder resin and the lithium-substituted carboxymethyl cellulose (weight average molecular weight: 250,000 g / mol) prepared in Preparation Example 2 as the second binder resin were dissolved in water in a weight ratio of 6:4 to prepare a 1.0 wt % binder composition (viscosity: 3,400 cP, Brookfield viscometer (VISCOMETER, TOKIMEC), 25°C, 2.5 wt % aqueous solution).

[0136] (Secondary battery manufacturing) A negative electrode and a lithium secondary battery including the same were manufactured in the same manner as in Example 1, except that the binder composition prepared above was used in manufacturing the negative electrode.

[0137] Comparative Example 1 (Production of binder composition) The lithium-substituted polyacrylic acid prepared in Preparation Example 1 was dissolved alone in water to prepare a 2.5 wt % binder composition (viscosity: 2,400 cP).

[0138] (Secondary battery manufacturing) A negative electrode and a lithium secondary battery including the same were manufactured in the same manner as in Example 1, except that the binder composition prepared above was used in manufacturing the negative electrode.

[0139] Comparative Example 2 (Production of binder composition) The lithium-substituted carboxymethyl cellulose prepared in Preparation Example 2 was dissolved alone in water to prepare a 2.5 wt % binder composition (viscosity: 3,000 cP).

[0140] (Secondary battery manufacturing) A negative electrode and a lithium secondary battery including the same were manufactured in the same manner as in Example 1, except that the binder composition prepared above was used in manufacturing the negative electrode.

[0141] Comparative Example 3. (Production of binder composition) A 1.0 wt % binder composition was prepared by dissolving lithium-substituted polyacrylic acid (manufactured by Aldrich, weight-average molecular weight: 750,000 g / mol) as the first binder resin and lithium-substituted carboxymethyl cellulose (weight-average molecular weight: 250,000 g / mol) prepared in Preparation Example 2 as the second binder resin in water in a weight ratio of 5:5 (viscosity: 2,800 cP, Brookfield viscometer (VISCOMETER, TOKIMEC), 25°C, 2.5 wt % aqueous solution).

[0142] (Secondary battery manufacturing) A negative electrode and a lithium secondary battery including the same were manufactured in the same manner as in Example 1, except that the binder composition prepared above was used in manufacturing the negative electrode.

[0143] Comparative Example 4. (Production of binder composition) The lithium-substituted polyacrylic acid (weight average molecular weight: 750,000 g / mol) prepared in Preparation Example 1 as the first binder resin and lithium-unsubstituted carboxymethyl cellulose (manufactured by LG Ensol, weight average molecular weight: 250,000 g / mol) as the second binder resin were dissolved in water in a weight ratio of 5:5 to prepare a 1.0 wt % binder composition (viscosity: 3,100 cP, Brookfield viscometer (VISCOMETER, TOKIMEC), 25°C, 2.5 wt % aqueous solution).

[0144] (Secondary battery manufacturing) A negative electrode and a lithium secondary battery including the same were manufactured in the same manner as in Example 1, except that the binder composition prepared above was used in manufacturing the negative electrode.

[0145] Comparative Example 5. (Production of binder composition) The lithium-substituted polyacrylic acid (weight average molecular weight: 290,000 g / mol) prepared in Preparation Example 3 as the first binder resin and the lithium-substituted carboxymethyl cellulose (weight average molecular weight: 250,000 g / mol) prepared in Preparation Example 2 as the second binder resin were dissolved in water in a weight ratio of 5:5 to prepare a 1.0 wt % binder composition (viscosity: 2,100 cP, Brookfield viscometer (VISCOMETER, TOKIMEC), 25°C, 2.5 wt % aqueous solution).

[0146] (Secondary battery manufacturing) A negative electrode and a lithium secondary battery including the same were manufactured in the same manner as in Example 1, except that the binder composition prepared above was used in manufacturing the negative electrode.

[0147] Comparative Example 6. (Production of binder composition) The lithium-substituted polyacrylic acid (weight average molecular weight: 1,600,000 g / mol) prepared in Preparation Example 4 as the first binder resin and the lithium-substituted carboxymethyl cellulose (weight average molecular weight: 250,000 g / mol) prepared in Preparation Example 2 as the second binder resin were dissolved in water in a weight ratio of 5:5 to prepare a 1.0 wt % binder composition (viscosity: 3,400 cP, Brookfield viscometer (VISCOMETER, TOKIMEC), 25°C, 2.5 wt % aqueous solution).

[0148] (Secondary battery manufacturing) A negative electrode and a lithium secondary battery including the same were manufactured in the same manner as in Example 1, except that the binder composition prepared above was used in manufacturing the negative electrode.

[0149] Comparative Example 7. (Production of binder composition) The lithium-substituted polyacrylic acid (weight average molecular weight: 750,000 g / mol) prepared in Preparation Example 1 as the first binder resin and the lithium-substituted carboxymethyl cellulose (weight average molecular weight: 40,000 g / mol) prepared in Preparation Example 5 as the second binder resin were dissolved in water in a weight ratio of 5:5 to prepare a 1.0 wt % binder composition (viscosity: 2,200 cP, Brookfield viscometer (VISCOMETER, TOKIMEC), 25°C, 2.5 wt % aqueous solution).

[0150] (Secondary battery manufacturing) A negative electrode and a lithium secondary battery including the same were manufactured in the same manner as in Example 1, except that the binder composition prepared above was used in manufacturing the negative electrode.

[0151] Comparative Example 8. (Production of binder composition) The lithium-substituted polyacrylic acid (weight average molecular weight: 750,000 g / mol) prepared in Preparation Example 1 as the first binder resin and the lithium-substituted carboxymethyl cellulose (weight average molecular weight: 1,100,000 g / mol) prepared in Preparation Example 6 as the second binder resin were dissolved in water in a weight ratio of 5:5 to prepare a 1.0 wt % binder composition (viscosity: 2,700 cP, Brookfield viscometer (VISCOMETER, TOKIMEC), 25°C, 2.5 wt % aqueous solution).

[0152] (Secondary battery manufacturing) A negative electrode and a lithium secondary battery including the same were manufactured in the same manner as in Example 1, except that the binder composition prepared above was used in manufacturing the negative electrode.

[0153] [Experimental Example] Experimental Example 1: Evaluation of negative electrode adhesive strength The negative electrodes prepared in Examples 1 and 2 and the negative electrodes prepared in Comparative Examples 1, 3 to 5, and 7 were cut into a size of 15 cm x 2 cm, and then the electrode surfaces were attached to slide glasses with double-sided tape attached, and three samples for each were prepared for a peel test by lamination.

[0154] The samples were loaded onto the UTM at 20 mm intervals and subjected to a 90° peel test (propagation speed: 300 mm / min) to measure the peel resistance (gf / cm). From this, the adhesiveness of each electrode was calculated, and the results are shown in Table 1 below.

[0155] [Table 1]

[0156] Referring to Table 1, it can be seen that the adhesive strength of the negative electrodes prepared using the binder compositions of Examples 1 and 2 was 23.2 gf or more, whereas the adhesive strength of the negative electrodes prepared using the binder compositions of Comparative Examples 1, 3 to 5, and 7 was inferior to that of Examples 1 and 2.

[0157] Experimental Example 2: Evaluation of cycle characteristics The lithium secondary batteries manufactured in Examples 1 to 4 and the lithium secondary batteries manufactured in Comparative Examples 2 to 8 were subjected to constant current-constant voltage charging at a 0.3 CC rate up to 4.2 V, constant voltage charging until the current reached 1 / 20 C, and then initial charging by discharging at a 0.5 CC rate down to 2.85 V was performed, and the initial capacity was measured.

[0158] Next, the battery was charged at a constant current and constant voltage up to 4.2 V at a rate of 0.3 CC, and then charged at a constant voltage until the current reached 1 / 20 C. After that, the battery was discharged at a rate of 0.5 CC down to 2.85 V, which was defined as one cycle. After 100 cycles, the capacity after 100 cycles was measured.

[0159] Next, the capacity retention rate after 100 cycles was calculated, and the results are shown in Table 2 below.

[0160] [Table 2]

[0161] Referring to Table 2, it can be seen that the lithium secondary batteries of Comparative Examples 2 to 8 had deteriorated cycle characteristics compared to Examples 1 to 4.

Claims

1. a first binder resin, a second binder resin, and water; The first binder resin includes a lithium-substituted polyacrylic acid having a weight average molecular weight (Mw) of 300,000 g / mol to 1,500,000 g / mol, The binder composition includes, as the second binder resin, a lithium-substituted carboxymethyl cellulose having a weight average molecular weight (Mw) of 50,000 g / mol to 1,000,000 g / mol.

2. The binder composition according to claim 1, wherein the weight average molecular weight (Mw) of the first binder resin is 500,000 g / mol to 1,500,000 g / mol.

3. The binder composition according to claim 1, wherein the weight average molecular weight (Mw) of the second binder resin is 100,000 g / mol to 1,000,000 g / mol.

4. The binder composition according to claim 1 , wherein the total content of the first binder resin and the second binder resin is 0.2% by weight to 5.0% by weight based on the total content of the binder composition.

5. The binder composition according to claim 1 , wherein a weight ratio of the first binder resin to the second binder resin is 3:7 to 5:

5.

6. 2. The binder composition according to claim 1, wherein the binder composition has a viscosity of 500 cP to 50,000 cP at 25° C. in a 2.5 wt % aqueous solution state.

7. A negative electrode active material slurry comprising a silicon-based negative electrode active material and the binder composition according to claim 1.

8. The negative electrode active material slurry of claim 7 , further comprising a carbon-based negative electrode active material.

9. 9. The negative electrode active material slurry according to claim 8, wherein a weight ratio of the carbon-based negative electrode active material to the silicon-based negative electrode active material is 80:20 to 99:

1.

10. The negative electrode active material slurry according to claim 7, wherein the binder composition is contained in an amount of 0.1 wt % to 5.0 wt % based on the total weight of the negative electrode active material slurry.

11. The negative electrode active material slurry of claim 7 , further comprising a third binder resin.

12. The negative electrode active material slurry according to claim 11 , wherein the third binder resin is styrene-butadiene rubber.

13. The negative electrode active material slurry of claim 11, wherein the third binder resin is contained in an amount of 0.1 wt % to 5.0 wt % based on the total weight of the negative electrode active material slurry.

14. The negative electrode active material slurry of claim 7 , further comprising a conductive material.

15. 15. The negative electrode active material slurry of claim 14, wherein the conductive material is at least one of a single-walled carbon nanotube (SWCNT), a thin-walled carbon nanotube (TWCNT), a multi-walled carbon nanotube (MWCNT), a carbon fiber, and graphene.

16. a negative electrode current collector; a negative electrode active material layer disposed on at least one surface of the negative electrode current collector, The negative electrode active material layer is formed by applying the negative electrode active material slurry according to claim 7 .

17. 17. The anode of claim 16, wherein the anode has an adhesive strength of 23.2 gf / 20 mm to 25 gf / 20 mm and an energy efficiency of 96% or greater with a life rating of 100 cycles.

18. A lithium secondary battery comprising the negative electrode according to claim 16.

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