Positive electrode slurry, positive electrode, and secondary battery

Abstract

Provided is a positive electrode slurry that provides improved lifespan and rate characteristics of a positive electrode. According to one aspect of the present invention, provided is a positive electrode slurry comprising: a polysaccharide binder; an organic acid; a positive electrode active material; a conductive material; and an aqueous solvent, wherein the organic acid comprises a carboxyl group and a sulfonic acid group.

Description

Cathode slurry, cathode and secondary battery

[0001] The present invention relates to a cathode slurry, and more particularly, to a cathode slurry, a cathode, and a secondary battery.

[0002] As the application range of secondary batteries as power sources expands, development is focused on high-energy batteries, including the search for active materials with high theoretical capacity and a wider operating voltage range. At the same time, there is a growing demand for batteries that operate stably across a wide temperature range. Consequently, ensuring cycle life and safety is becoming increasingly challenging.

[0003] Meanwhile, for positive electrodes, which exhibit low volumetric expansion during charge and discharge, the resistance and chemical stability of the binder significantly influence battery characteristics, rather than binding properties, compared to negative electrodes. Therefore, development directions may differ significantly. For example, applying an aqueous binder directly to the positive electrode could lead to increased resistance and oxidation degradation due to coating properties.

[0004] Accordingly, it has been difficult to change the binder from a non-aqueous to an aqueous one to improve cycle characteristics, and a slurry of polyvinylidene fluoride (PVDF) dispersed in N-methyl-2-pyrrolidone (NMP) is still used. However, this also has problems with gas generation and electrode peeling due to PVDF decomposition during charge / discharge cycles under high temperature and high voltage, and NMP used as a solvent has problems with being harmful to the human body.

[0005] An object of the present invention is to provide a cathode slurry capable of solving the Li leaching problem and the collector corrosion problem that may occur in a cathode slurry containing an aqueous solvent.

[0006] Another object of the present invention is to provide a positive electrode slurry that is harmless to the human body using an aqueous solvent.

[0007] Another object of the present invention is to provide a positive electrode capable of lowering the resistance of the electrode and extending the life of a secondary battery.

[0008] Another object of the present invention is to provide a positive electrode having excellent electrochemical performance.

[0009] Another object of the present invention is to provide a secondary battery including the positive electrode.

[0010] The purposes of the present invention are not limited to those mentioned above, and other unmentioned purposes and advantages of the present invention can be understood through the following description and will be more clearly understood through the embodiments of the present invention. Furthermore, it will be readily apparent that the purposes and advantages of the present invention can be realized by the means and combinations thereof set forth in the claims.

[0011] According to a first aspect of the present invention for achieving the above object, a positive electrode slurry is provided, comprising: a polysaccharide binder; an organic acid; a positive electrode active material; a conductive agent; and an aqueous solvent; wherein the organic acid comprises a carboxyl group and a sulfonic acid group.

[0012] According to the second aspect of the present invention, the weight average molecular weight (M) of the polysaccharide binder in the first aspect w ) may be 90,000 to 1,500,000 g / mol. Alternatively or additionally, the degree of substitution (DS) of the polysaccharide binder may be 0.6 to 1.2, 0.7 to 1.1, or 0.7 to 0.9. For example, the degree of substitution may mean the average number of substituted carboxymethyl groups per anhydroglucose unit.

[0013] According to a third aspect of the present invention, in the first or second aspect, the number of carboxyl groups and sulfonic acid groups in one molecule of the organic acid may be the same.

[0014] According to a fourth aspect of the present invention, in any one of the first to third aspects, the organic acid may be a compound represented by the following general formula 1.

[0015] [General Formula 1]

[0016]

[0017] In the general formula 1 above, R includes a hydrogen atom or -R1-COOH, and R1 may include a substituted or unsubstituted main skeletal linking group having 1 to 5 carbon atoms.

[0018] According to a fifth aspect of the present invention, in any one of the first to fourth aspects, the organic acid may be any one selected from the group consisting of sulfosuccinic acid, sulfoacetic acid, and combinations thereof.

[0019] According to a sixth aspect of the present invention, in any one of the first to fifth aspects, the content of the organic acid may be 0.1 to 2 wt% based on the weight of the total solid content included in the positive electrode slurry.

[0020] According to the seventh aspect of the present invention, a cathode slurry further comprising a dispersant can be provided.

[0021] According to an eighth aspect of the present invention, a positive electrode is provided, comprising: a current collector; and a positive electrode active material layer on the current collector; wherein the positive electrode active material layer comprises a polysaccharide binder including at least one side chain, a positive electrode active material, and a conductive material, wherein the at least one side chain includes an ester group and a sulfonic acid group.

[0022] According to the ninth aspect of the present invention, in the eighth aspect, the one or more side chains may further include a carboxyl group.

[0023] According to a tenth aspect of the present invention, a secondary battery is provided, comprising: a positive electrode according to the eighth or ninth aspect; a negative electrode; a separator interposed between the positive electrode and the negative electrode; and an electrolyte.

[0024] The solutions to the above problems do not enumerate all features of the present invention. The various features of the present invention, along with their corresponding advantages and effects, can be understood in more detail by referring to the specific examples below.

[0025] According to one aspect of the present invention, the Li leaching problem and the collector corrosion problem that may occur in a cathode slurry containing an aqueous solvent can be solved.

[0026] According to another aspect of the present invention, a positive electrode capable of lowering the resistance of an electrode and extending the life of a secondary battery can be provided.

[0027] According to another aspect of the present invention, an anode that is harmless to the human body and has excellent electrochemical performance can be provided.

[0028] In addition to the effects described above, specific effects of the present invention are described below while explaining specific details for carrying out the invention.

[0029] Figure 1a is a structural formula of a polysaccharide binder-organic acid according to one embodiment of the present invention. Figure 1b is a structural formula of the polysaccharide binder of Figure 1a. Figure 1c is a structural formula of the organic acid of Figure 1a.

[0030] Figure 2a shows the discharge capacity according to the cycle of the half-cell according to Example 1 and the reference example under the conditions of a cut-off voltage of 4.5 V and 0.5 C.

[0031] Figure 2b shows 0.5C and 2 nd The specific capacity according to the potential of the half-cell according to Example 1 and Reference Example under cycle conditions is shown.

[0032] Figure 3 shows the specific capacity and coulombic efficiency of half-cells according to Example 1 and Reference Example according to the number of cycles.

[0033] Figure 4a shows the specific capacity according to the number of cycles of the half-cells according to Example 1 and the reference example.

[0034] Figure 4b shows the discharge capacity according to the number of cycles of the half-cells according to Example 1 and the reference example.

[0035] Figure 5 shows the discharge capacity according to the number of cycles of half cells according to Examples 1 and 2, Comparative Examples 1 to 3, and Reference Example.

[0036] Figure 6a shows the discharge capacity of half cells according to Examples 1, 3, and 4 and the reference example.

[0037] Figure 6b shows the specific capacity according to the potential of the half-cells according to the reference example and examples 1, 3 and 4.

[0038] Figure 7a is a SEM (Scanning Electron Microscope) photograph of the surface of an anode manufactured by a method according to a reference example.

[0039] Figure 7b is an SEM photograph of the surface of the anode manufactured by the method according to Example 5.

[0040] Figure 7c is an SEM photograph of the surface of the anode manufactured by the method according to Example 1.

[0041] Figure 7d is an SEM photograph of the surface of the anode manufactured by the method according to Example 6.

[0042] Figure 8 shows the FT-IR (Fourier Transform Infrared Spectroscopy) of the polysaccharide binder-organic acid manufactured by the method according to Example 1 when the drying temperatures of the positive electrode slurry were 60°C and 120°C, respectively.

[0043] Figure 9 shows a peeling test of the positive electrode active material layer on the current collector in a positive electrode manufactured by the method according to Reference Example and Example 1.

[0044] Figure 10a shows each TM-O peak when the concentration of the polysaccharide binder is 1, 2, and 5 wt% based on the total weight of the solid in a positive electrode manufactured by the method according to Example 1. Figure 10b shows each TM-O peak when the concentration of the polysaccharide binder is 1, 2, and 5 wt% based on the total weight of the solid in a positive electrode manufactured by the method according to the reference example.

[0045] Fig. 11a is a graph of the impedance imaginary part Z`` according to the impedance real part Z` of the pristine electrode according to Example 1 and the reference example. Fig. 11b is a graph of the impedance imaginary part Z`` according to the impedance real part Z` of the electrode according to Example 1 and the reference example according to the number of cycles.

[0046] In this specification, singular expressions include plural expressions unless the context clearly indicates otherwise.

[0047] The numerical range indicated by the term "to" in this specification refers to a numerical range that includes the values ​​described before and after the term as the lower limit and the upper limit, respectively. When multiple numerical values ​​are disclosed as the upper and lower limits of an arbitrary numerical range, the numerical range disclosed in this specification can be understood as an arbitrary numerical range that includes any one of the multiple lower limit values ​​and any one of the multiple upper limit values ​​as the lower limit and the upper limit, respectively.

[0048] As used herein, "polysaccharide binder-organic acid" may be defined as a single compound in which a polysaccharide and an organic acid are chemically bonded to each other. For example, a hydroxyl group contained in one or more side chains of the polysaccharide may react with a carboxyl group of the organic acid to form an ester bond.

[0049] According to one aspect of the present invention, a positive electrode slurry is provided, comprising: a polysaccharide binder; an organic acid; a positive electrode active material; and an aqueous solvent; wherein the organic acid comprises a carboxyl group and a sulfonic acid group.

[0050] According to one aspect of the present invention, by adding an organic acid containing a carboxyl group and a sulfonic acid group to a positive electrode slurry containing an aqueous solvent, the coverage of the polysaccharide binder-organic acid on the surface of the positive electrode active material can be increased. Accordingly, a CEI (Cathode Electrolyte Interphase) with excellent performance can be formed, thereby reducing the resistance of the electrode and improving the life characteristics of the secondary battery. Specifically, the carboxyl group of the organic acid can increase the bonding force between the current collector and the positive electrode active material layer, and the sulfonic acid group of the organic acid can implement excellent lithium ion conductivity. According to another aspect of the present invention, the combination of the carboxyl group and the sulfonic acid group of the organic acid can remove residual lithium on the surface of the positive electrode active material, thereby suppressing Li leaching, and adjusting the pH of the positive electrode slurry to an appropriate level, thereby solving the corrosion problem of the current collector. If an organic acid containing only a carboxyl group; Alternatively, if an organic acid containing only sulfonic acid is added to the cathode slurry, the above performances may not be sufficiently achieved.

[0051] Below, the configuration of the present invention is described in more detail.

[0052] 1. Positive slurry

[0053] The positive electrode slurry according to the present invention includes a polysaccharide binder to increase the bonding strength between positive electrode active material particles and between the positive electrode active material layer and the current collector.

[0054] The polysaccharide binder according to the present invention may include a polymer chain having a ring structure forming a main skeleton and one or more side chains bonded to the main skeleton. Specifically, one or more side chains of the polysaccharide binder may include a hydroxyl group.

[0055] For example, the polysaccharide binder may include at least one selected from the group consisting of alginic acid, carboxymethyl cellulose or a salt thereof, carboxymethyl starch, carboxymethyl guar gum, carboxymethyl xanthane gum, carboxymethyl tara gum, low methoxyl pectin, carrageenan, cellulose, amylose, chitosan, glucose, sucrose, maltose, lactose, starch, and glycogen.

[0056] According to one embodiment of the present invention, the weight average molecular weight of the polysaccharide binder may be 90,000 to 1,500,000 g / mol, 90,000 to 1,200,000 g / mol, 150,000 to 850,000 g / mol, 450,000 to 850,000 g / mol, or 500,000 to 800,000 g / mol. When the weight average molecular weight of the polysaccharide binder is less than the above numerical range, a problem may arise in that the bonding force between the current collector and the positive electrode active material layer is not sufficiently increased, and when it exceeds the above numerical range, a problem may arise in that the viscosity of the positive electrode slurry increases, blocking the ion transfer path.

[0057] The content of the polysaccharide binder according to the present invention may be 0.5 to 10 wt%, specifically 1.0 to 5.0 wt%, based on the weight of the total solid content included in the positive electrode slurry. Specifically, when the content of the polysaccharide binder satisfies the above numerical range, sufficient bonding force between the current collector and the positive electrode active material layer can be realized.

[0058] The organic acid according to the present invention can increase the coverage of the cathode binder on the surface of the cathode active material. This can form a high-performance cathode electrolyte interphase (CEI), thereby reducing electrode resistance and improving the lifespan of the secondary battery. Furthermore, the organic acid according to another aspect of the present invention can suppress Li leaching by removing residual lithium and, by adjusting the pH of the cathode slurry to an appropriate level, resolve the problem of current collector corrosion.

[0059] The organic acid according to the present invention contains a carboxyl group (-COOH) and a sulfonic acid group (-SO3H). Specifically, the carboxyl group of the organic acid can enhance the bonding strength between the current collector and the positive electrode active material layer, and the sulfonic acid group of the organic acid can realize excellent lithium ion conductivity. If an organic acid containing only a carboxyl group or an organic acid containing only a sulfonic acid group is added to the positive electrode slurry, the electrochemical performance and life characteristics of the secondary battery may not be sufficiently achieved.

[0060] The organic acid according to the present invention can be bound by reacting with a functional group bonded to a side chain of a polysaccharide when the positive electrode slurry is dried at a high temperature (e.g., 120°C). For example, the functional group bonded to the side chain of the polysaccharide may be a hydroxyl group. Here, the hydroxyl group can react with a carboxyl group of the organic acid to form an ester group (COO). According to some embodiments of the present invention, the bonding strength of the positive electrode active material layer to the positive electrode current collector can be significantly increased by reacting the organic acid and the polysaccharide binder to form an ester group.

[0061] According to one embodiment of the present invention, the number of carboxyl groups and sulfonic acid groups within one molecule of the organic acid may be the same. According to one embodiment of the present invention, by controlling the number of carboxyl groups and sulfonic acid groups within one molecule to be the same, long-term cycle stability can be sufficiently achieved.

[0062] According to some embodiments of the present invention, the organic acid may be a compound represented by the following general formula 1.

[0063] [General Formula 1]

[0064]

[0065] In the general formula 1 above, R includes a hydrogen atom, -R1-COOH, and the R1 may include a substituted or unsubstituted main skeletal linking group having 1 to 5 carbon atoms. Here, the substituted or unsubstituted main skeletal linking group having 1 to 5 carbon atoms may include a main skeletal structure composed of, for example, -(CH2)n- (n is an integer from 1 to 5). Here, since the number of carbon atoms 1 to 5 is the number of carbon atoms of the "main skeletal linking group", the total number of carbon atoms of R may exceed 5 depending on the substituted structure. Specifically, the functional group substituted on the linking group having 1 to 5 carbon atoms may be defined as one in which at least one hydrogen atom bonded to the main skeletal structure is replaced by any one selected from the group consisting of an alkylthiol group, an alkoxy group, an ether group, an acetal group, a linear or branched alkyl group, a linear or branched alkenyl group, a cycloalkyl group, a heterocycloalkyl group, an allyl group, a benzyl group, an aryl group, a heteroaryl group, derivatives thereof, and combinations thereof.

[0066] For example, the organic acid may be any one selected from the group consisting of sulfosuccinic acid, sulfoacetic acid, and combinations thereof.

[0067] The content of the organic acid according to the present invention may be 0.1 to 2.0 wt%, 0.3 to 1.6 wt%, 0.4 to 1.3 wt%, 0.5 to 1.2 wt%, 0.6 to 1.1 wt%, 0.7 to 1.0 wt%, 0.8 to 0.9 wt%, or 0.80 to 0.85 wt%, based on the weight of the total solid content included in the positive electrode slurry. Specifically, when the content of the organic acid satisfies the numerical range, the bonding force between the positive electrode active material layer and the positive electrode current collector can be sufficiently increased, and the life characteristics and electrochemical performance of the secondary battery can be excellent.

[0068] Figure 1a is a structural formula of a polysaccharide binder-organic acid according to one embodiment of the present invention. Figure 1b is a structural formula of the polysaccharide binder of Figure 1a. Figure 1c is a structural formula of the organic acid of Figure 1a.

[0069] Referring to Figures 1a to 1c, under high drying temperature conditions of the positive electrode slurry, the -CH2OH group bonded to one side chain of the polysaccharide and the carboxyl group (COOH) of the organic acid can react with each other to form an ester bond (-COO-).

[0070] The cathode slurry according to the present invention comprises a cathode active material capable of providing lithium ions. For example, the cathode active material may comprise a lithium transition metal oxide containing nickel, cobalt, and manganese. The lithium transition metal oxide may be, for example, Li x1 CoO2(0.5 <x1<1.3), Li x2 NiO2(0.5 <x2<1.3), Li x3 MnO2(0.5 <x3<1.3), Li x4 Mn2O4(0.5 <x4<1.3), Li x5 (Ni a1 Co b1 Mn c1 )O2(0.5 <x5<1.3, 0<a1<1, 0<b1<1, 0<c1<1, a1+b1+c1=1), Li x6 Ni 1-y1 Co y1 O2(0.5 <x6<1.3, 0<y1<1), Li x7 Co 1-y2 Mn y2 O2(0.5 <x7<1.3, 0혏2<1), Li x8 Ni 1-y3 Mn y3 O2(0.5 <x8<1.3, O혏3<1), Li x9 (Ni a2 Co b2 Mn c2 )O4(0.5 <x9<1.3, 0<a2<2, 0<b2<2, 0<c2<2, a2+b2+c2=2), Li x10 Mn 2-z1 Niz1 O4(0.5 <x10<1.3, 0<z1<2) 및 Li x11 Mn 2-z2 Co z2 O4(0.5 <x11<1.3, 0<z2<2)로 이루어진 군에서 선택되는 하나 이상일 수 있다.

[0071] For example, the positive electrode active material may include a lithium transition metal phosphate. The lithium transition metal phosphate may be, for example, Li x12 FePO4(0.5 <x12<1.3), Li x13 CoPO4(0.5 <x13<1.3), Li x14 Mn 1-w1 Fe w1 PO4(0.5 <x14<1.3, 0.15<w1<0.85), Li x15 Mn a3 Fe b3 Al c3 PO4(0.5 <x15<1.3, a3+b3+c3=1), Li x16 Mn a4 Fe b4 Mg c4 PO4(0.5 <x16<1.3, a4+b4+c41), Li x17 Mn a5 Fe b5 Zn c5 PO4(0.5 <x17<1.3, a5+b5+c5=1) 및 Li x18 Mn a6 Fe b6 V c6 PO4(0.5 <x18<1.3, a6+b6+c6=1)로 이루어진 군에서 선택되는 하나 이상일 수 있다.

[0072] In another example, the positive electrode active material may include a lithium transition metal oxide containing aluminum. Specifically, the positive electrode active material may include Li x19 (Ni a7 Co b7 Al c7 )O2(0.5 <x19<1.3, 0<a7<1, 0<b7<1, 0<c7<0.15, a7+b7+c7=1), Li x20 (Nia8 Mn b8 Al c8 )O2(0.5 <x20<1.3, 0<a8<1, 0<b8<1, 0<c8<0.15, a8+b8+c8=1), Li x21 (Co a9 Mn b9 Al c9 )O2(0.5 <x21<1.3, 0<a9<1, 0<b9<1, 0<c9<0.15, a9+b9+c9=1), Li x22 (Ni 1-y4 Al y4 )O2(0.5 <x22<1.3, 0≤y4<0.15), Li x23 (Co 1-y5 Al y5 )O2(0.5 <x23<1.3, 0≤y5<0.15), Li x24( Mn 1-y6 Al y6 )O2(0.5 <x24<1.3, 0≤y6<0.15), 및 Li x25 (Ni a10 Co b10 Mn c10 Al d10 )O2(0.5 <x25<1.3, 0<a10<1, 0<b10<1, 0<c10<1, 0<d10<0.15, a10+b10+c10+d10=1)로 이루어진 군에서 선택되는 하나 이상일 수 있다.

[0073] For example, the content of the positive electrode active material may be 80 wt% or more, or 80 to 97 wt%, based on the total weight of the positive electrode slurry.

[0074] The cathode slurry according to the present invention includes a conductive agent to improve conductivity between cathode active material particles or with the cathode current collector and to compensate for the binder acting as an insulator.

[0075] For example, the conductive material may be a mixture of one or more conductive materials selected from the group consisting of graphite, carbon black, carbon fiber, metal fiber, metal powder, conductive whisker, conductive metal oxide, activated carbon, and polyphenylene derivatives, and more specifically, may be a mixture of one or more conductive materials selected from the group consisting of natural graphite, artificial graphite, Super-p, acetylene black, Ketjen black, channel black, furnace black, lamp black, summer black, Denka black, aluminum powder, nickel powder, zinc oxide, potassium titanate, and titanium oxide.

[0076] For example, the content of the conductive material may be 1 to 30 wt% based on the total weight of the positive electrode slurry.

[0077] The cathode slurry according to the present invention comprises an aqueous solvent that is harmless to the human body in order to replace organic solvents that are harmful to the human body, such as NMP. For example, the aqueous solvent may comprise water.

[0078] In general, in the case of a cathode slurry containing an aqueous solvent, there have been problems of Li leaching and easy corrosion of a current collector composed of a metal material. According to one aspect of the present invention, by adding an organic acid containing a carboxyl group and a sulfonic acid group to a cathode slurry containing an aqueous solvent, residual lithium on the surface of the cathode active material can be removed, thereby suppressing Li leaching, and the problem of corrosion of the current collector can be solved by adjusting the pH of the cathode slurry to an appropriate level.

[0079] According to another embodiment of the present invention, the positive electrode slurry may further include a dispersant. For example, the dispersant may be an anionic component containing one or more salts selected from the group consisting of carboxylates, phosphates, sulfonates, and sulfates, or a cationic component containing an ammonium salt. The dispersant may be determined based on the surface charge of the positive electrode active material.

[0080] According to another embodiment of the present invention, the drying temperature of the positive electrode slurry may be 100°C or higher, 110°C or higher, or 120°C or higher. Specifically, when the drying temperature of the positive electrode slurry satisfies the above numerical range, the ester bond formation reaction between the organic acid and the polysaccharide binder can proceed well.

[0081] 2. Bipolar

[0082] According to another aspect of the present invention, a positive electrode is provided, comprising: a current collector; and a positive electrode active material layer on the current collector; wherein the positive electrode active material layer comprises a polysaccharide binder including at least one side chain, a positive electrode active material, and a conductive material, wherein the at least one side chain includes an ester group and a sulfonic acid group.

[0083] The above positive electrode active material is a compound capable of reversible lithiation and de-lithiation of lithium, and specifically may include a lithium composite metal oxide containing lithium and one or more metals such as cobalt, manganese, nickel, or aluminum. More specifically, the lithium composite metal oxide may be a lithium-manganese oxide (e.g., LiMnO2, LiMn2O 4　 etc.), lithium-cobalt oxides (e.g., LiCoO2, etc.), lithium-nickel oxides (e.g., LiNiO2, etc.), lithium-nickel-manganese oxides (e.g., LiNi 1-Y Mn Y O2 (here, 0 <Y<1), LiMn 2-z Ni zO4 (where 0<Z<2), etc.), lithium-nickel-cobalt oxides (e.g., LiNi 1-Y1 Co Y1 O2 (here, 0 <Y1<1) 등), 리튬-망간-코발트계 산화물(예를 들면, LiCo 1-Y2 Mn Y2 O2 (here, 0 <Y2<1), LiMn 2-z1 Co z1 O4 (wherein, 0<Z1<2) etc.), lithium-nickel-manganese-cobalt oxides (e.g., Li(Ni p Co q Mn r1 )O2(wherein, 0<p<1, 0<q<1, 0<r1<1, p+q+r1=1) or Li(Ni p1 Co q1 Mn r2 )O4 (wherein, 0<p1<2, 0<q1<2, 0<r2<2, p1+q1+r2=2) etc.), or lithium-nickel-cobalt-transition metal (M) oxide (e.g., Li(Ni p2 Co q2 Mn r3 M S2 )O2 (wherein, M is selected from the group consisting of Al, Fe, V, Cr, Ti, Ta, Mg, and Mo, and p2, q2, r3, and s2 are atomic fractions of independent elements, 0<p2<1, 0<q2<1, 0<r3<1, 0<s2<1, p2+q2+r3+s2=1)), and one or more compounds of these may be included.

[0084] Among these, the lithium composite metal oxides are LiCoO2, LiMnO2, LiNiO2, lithium nickel manganese cobalt oxide (e.g., Li(Ni)) in that they can improve the capacity characteristics and stability of the battery. 1 / 3 Mn 1 / 3 Co 1 / 3 )O2, Li(Ni 0.6 Mn 0.2 Co 0.2 )O2, Li(Ni 0.5 Mn 0.3 Co0.2 )O2, Li(Ni 0.7 Mn 0.15 Co 0.15 )O2 and Li(Ni 0.8 Mn 0.1 Co 0.1 )O2, etc.), or lithium nickel cobalt aluminum oxide (e.g., Li(Ni 0.8 Co 0.15 Al 0.05 )O2, etc.) may be.

[0085] The above positive electrode active material is a compound capable of reversible lithiation and de-lithiation of lithium, and specifically may include a lithium composite metal phosphate containing lithium and a metal such as manganese, nickel, aluminum, magnesium, zinc, vanadium, and iron or cobalt. More specifically, the lithium composite metal phosphate is a lithium iron phosphate phosphate (e.g., LiFePO 4　 etc.), lithium cobalt phosphate phosphate (e.g., LiCoPO4), lithium manganese phosphate-iron phosphate phosphate (e.g., LiMn 1-Y Fe Y PO4 (0.15 here <Y<0.85 등), 리튬인산전이금속-인산망간-인산철계 인산화물(예를 들면, LiMn p Fe q M r PO4 (wherein, M is selected from the group consisting of Al, Mg, Zn and V, and 0 <p<1, 0<q<1, 0<r<1, p+q+r=1) 등) 등을 들 수 있으며, 이들 중 어느 하나 또는 둘 이상의 화합물이 포함될 수 있다.

[0086] Among these, the lithium composite metal phosphate is LiFePO4, LiCoPO4, or lithium manganese iron phosphate (e.g., LiMn) in that it can improve the capacity characteristics and stability of the battery. 0.8 Fe 0.2 PO4, LiMn 0.6 Fe 0.4 PO4, LiMn 0.5 Fe 0.5PO4, etc.), or lithium manganese iron aluminum phosphate (e.g., LiMn 0.45 Fe 0.5 Al 0.05 It could be PO4, etc.

[0087] Meanwhile, according to some embodiments of the present invention, by including an ester group and a sulfonic acid group in the one or more side chains, the covering rate of the polysaccharide binder-organic acid on the surface of the positive electrode active material can be increased. Accordingly, by forming a CEI (Cathode Electrolyte Interphase) with excellent performance, the resistance of the electrode can be reduced, and the life characteristics of the secondary battery can be improved. Specifically, the ester group can increase the bonding force between the current collector and the positive electrode active material layer, and the sulfonic acid group can implement excellent lithium ion conductivity. According to another aspect of the present invention, by combining the ester group and the sulfonic acid group, the residual lithium on the surface of the positive electrode active material can be removed, thereby suppressing Li leaching, and the pH of the positive electrode slurry can be adjusted to an appropriate level, thereby solving the corrosion problem of the current collector.

[0088] Specifically, the ester group included in the one or more side chains may be formed by a reaction between a hydroxyl group (-OH) included in one side chain of the polysaccharide and a carboxyl group (-COOH) of an organic acid under high temperature and drying temperature conditions of the positive electrode slurry.

[0089] For example, the current collector is not particularly limited as long as it has high conductivity without causing chemical changes in the battery. Specifically, the positive electrode current collector may be made of copper, stainless steel, aluminum, nickel, titanium, calcined carbon, copper or stainless steel surface-treated with carbon, nickel, titanium, silver, or the like, an aluminum-cadmium alloy, or the like. The positive electrode current collector may typically have a thickness of 6 to 20 μm.

[0090] According to another embodiment of the present invention, the one or more side chains may further include a carboxyl group. Here, the carboxyl group may be an unreacted functional group that does not react with the polysaccharide binder.

[0091] According to another embodiment of the present invention, the positive electrode may further include a rubber-based polymer. In order to increase the energy density of a battery including the positive electrode of the present invention, it is necessary to increase the amount of active material loaded onto the current collector. However, loading a large amount of positive electrode active material onto the current collector increases the hardness of the electrode, which is disadvantageous in the subsequent battery assembly process. In this case, by additionally including the rubber-based polymer in the positive electrode slurry, the hardness of the electrode can be somewhat alleviated, and the processability of the battery assembly process can be improved.

[0092] For example, the rubber-based polymer may specifically include one or more compounds of latex rubber having an acrylate functional group containing fluorine, styrene butadiene rubber (SBR), butadiene rubber (BR), styrene ethylene butylene copolymer (SEBS), nitrile butadiene rubber (NBR), and ethyl cellulose.

[0093] According to an embodiment of the present invention, the content of the rubber-based polymer may be 50 to 100 wt% based on the total weight of the polysaccharide binder included in the positive electrode.

[0094] 3. Secondary batteries

[0095] According to another aspect of the present invention, a secondary battery is provided, comprising: a positive electrode; a negative electrode; a separator interposed between the positive electrode and the negative electrode; and an electrolyte, according to some embodiments. A description of the positive electrode is omitted as it has been described above.

[0096] cathode

[0097] The negative electrode according to the present invention may include 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 may include a negative electrode active material, a conductive material, and a negative electrode binder.

[0098] The above-described negative electrode current collector can serve as a passage to transfer electrons from the outside to cause an electrochemical reaction in the negative electrode active material or to receive electrons from the negative electrode active material and send them to the outside. For example, the negative electrode current collector may be made of copper, stainless steel, aluminum, nickel, titanium, calcined carbon, or aluminum or stainless steel surface-treated with carbon, nickel, titanium, silver, etc. Specifically, a transition metal that adsorbs carbon well, such as copper or nickel, may be used as the current collector. For example, the thickness of the negative electrode current collector may be 6 μm to 20 μm, but the thickness of the negative electrode current collector is not limited thereto.

[0099] The above-mentioned negative active material can store or release lithium ions and generate electricity. For example, the above-mentioned negative active material may include at least one of silicon-based active material particles and graphite-based active material particles.

[0100] The above silicon-based active material particles are Si, SiO x (0 <x 2), at least one selected from the group consisting of Si-C composites and Si-Y alloys (Y is any one element selected from the group consisting of alkali metals, alkaline earth metals, transition metals, group 13 elements, group 14 elements, and rare earth elements) may be used.

[0101] The above graphite-based active material particles may include at least one selected from the group consisting of artificial graphite, natural graphite, graphitized carbon fibers, and graphitized mesocarbon microbeads.

[0102] The content of the negative electrode active material may be 80 to 97 wt% based on the total solid content included in the negative electrode active material layer.

[0103] The conductive material can improve conductivity between active material particles in the electrode or with the metal current collector and prevent the binder from acting as an insulator. The conductive material can be, for example, a mixture of one or two or more conductive materials selected from the group consisting of graphite, carbon black, carbon fiber, metal fiber, metal powder, conductive whisker, conductive metal oxide, activated carbon, and polyphenylene derivatives, and more specifically, a mixture of one or two or more conductive materials selected from the group consisting of natural graphite, artificial graphite, super-p, acetylene black, Ketjen black, channel black, furnace black, lamp black, summer black, Denka black, aluminum powder, nickel powder, zinc oxide, potassium titanate, and titanium oxide.

[0104] The above-mentioned negative electrode binder can suppress separation between negative electrode active material particles or between the negative electrode and the current collector. A polymer commonly used in electrodes in the relevant technical field can be used as the above-mentioned negative electrode binder. These negative electrode binders include, but are not limited to, poly(vinylidene fluorideco-hexafluoropropylene), poly(vinylidene fluoride-co-trichloroethylene), poly(methylmethacrylate), poly(ethylhexylacrylate), poly(butylacrylate), poly(acrylonitrile), poly(vinylpyrrolidone), poly(vinyl acetate), poly(ethylene-co-vinyl acetate), poly(ethylene oxide), polyacrylate, cellulose acetate, cellulose acetate butyrate. Examples of such polymers include, but are not limited to, cellulose acetate propionate, cyano ethyl pullulan, cyano ethyl poly(vinylalcohol), cyanoethylcellulose, cyano ethylsucrose, pullulan, and carboxyl methyl cellulose.

[0105] membrane

[0106] The separator according to the present invention includes a porous substrate to electrically insulate the cathode and the anode to prevent short circuits.

[0107] Any organic or inorganic material having electrical insulation properties may be used as a constituent material of the porous substrate without particular limitation. The porous substrate may include, for example, at least one selected from the group consisting of polyolefin, polyethylene terephthalate, polybutylene terephthalate, polyacetal, polyamide, polycarbonate, polyimide, polyetheretherketone, polyethersulfone, polyphenylene oxide, polyphenylene sulfide, and polyethylene naphthalene, and may specifically include polyolefin. Polyolefin not only has excellent coatability but also increases the ratio of the electrode active material layer in the battery by making the separator thin, thereby increasing the capacity per volume. Specifically, the weight average molecular weight (M) of the polyolefin w ) may be 100,000 to 500,000 g / mol. If the weight average molecular weight of the polyolefin is less than the above numerical range, it may be difficult to secure sufficient mechanical properties, and if it exceeds the above numerical range, the shutdown function may not be implemented or molding may become difficult. The shutdown function refers to the function of blocking the movement of ions and preventing thermal runaway of the battery by melting the thermoplastic resin and closing the pores of the porous substrate when the temperature of the secondary battery increases.

[0108] The thickness of the porous substrate may be, for example, 3 to 12 μm or 5 to 12 μm. If the thickness of the porous substrate is less than the numerical range, the function of the conductive barrier may not be sufficient, and if it exceeds the numerical range, the resistance of the separator may excessively increase.

[0109] The average diameter of the pores included in the porous substrate may be, for example, 10 to 100 nm. The pores included in the porous substrate have a structure that is interconnected with each other, so that gas or liquid can pass from one side of the porous substrate to the other side.

[0110] According to some embodiments of the present invention, a coating layer may be disposed on at least one surface of the porous substrate. Specifically, the coating layer may improve the mechanical strength and heat resistance of the separator and increase the ionic conductivity within the secondary battery.

[0111] The coating layer according to the present invention may include a binder polymer and inorganic particles.

[0112] The binder polymer according to the present invention can connect inorganic particles and stably fix them. The binder polymer may be, for example, polyvinylidene fluoride-co-hexafluoropropylene, polyvinylidene fluoride-co-trichloroethylene, polymethylmethacrylate, polyacrylonitrile, polyvinylpyrrolidone, polyvinylacetate, poly(ethylene-co-vinyl acetate), polyethylene oxide, cellulose acetate, cellulose acetate butyrate, cellulose acetate propionate, cyanoethylpullulan, One or more selected from the group consisting of cyanoethylpolyvinylalcohol, cyanoethylcellulose, cyanoethylsucrose, pullulan, carboxyl methyl cellulose, acrylonitrile-styrene butadiene copolymer, and polyimide may be used in combination.

[0113] According to another embodiment of the present invention, the weight ratio of the inorganic particles and the binder polymer (inorganic particles: binder polymer) may be 50:50 to 99:1, specifically 70:30 to 95:5. If the content ratio of the inorganic particles to the binder polymer is less than the above numerical range, the content of the binder polymer may increase, thereby deteriorating the thermal safety improvement performance of the separator, and the pore size and porosity may decrease due to a decrease in the empty space formed between the inorganic particles, thereby causing a deterioration in the performance of the final battery, and if the content of the binder polymer is exceeded, the content of the binder polymer may be too small, thereby weakening the peeling resistance of the coating layer.

[0114] The inorganic particles according to the present invention can contribute to improving the mechanical strength and heat resistance of a separator for a secondary battery. Specifically, the inorganic particles are not particularly limited as long as they are electrochemically stable. That is, the inorganic particles that can be used in the present invention can be used within the operating voltage range of the secondary battery to which they are applied (e.g., Li / Li). + There are no special restrictions as long as no oxidation and / or reduction reaction occurs at a voltage of 0 to 5 V (as a standard).

[0115] For example, when using inorganic particles with a high dielectric constant as inorganic particles, the degree of dissociation of electrolyte salts, such as lithium salts, in a liquid electrolyte can be increased, thereby improving the ionic conductivity of the electrolyte. For the reasons described above, the inorganic particles may be inorganic particles having a dielectric constant of 5 or higher, inorganic particles having lithium ion transport capabilities, or a mixture thereof.

[0116] The inorganic particles having the dielectric constant of 5 or more are Al2O3, SiO2, ZrO2, AlO(OH), Al(OH)3, Mg(OH)2, BaSO4, TiO2, BaTiO3, Pb(Zr x Ti 1-x )O3(PZT, where 0 <x<1), Pb 1-x La x Zr 1-y Tiy O3(PLZT, where 0 < x < 1, 0 < y < 1), (1-x)Pb(Mg 1 / 3 Nb 2 / 3 )O 3-x It may be a mixture of one or more selected from the group consisting of PbTiO3 (PMN-PT, where 0 < x < 1), HfO2, SrTiO3, SnO2, CeO2, MgO, NiO, CaO, ZnO, and SiC.

[0117] The inorganic particles having the above lithium ion transfer capability include lithium phosphate (Li3PO4), lithium titanium phosphate (Li x Ti y (PO4)3, 0< x < 2, 0 < y < 3), lithium aluminum titanium phosphate (Li x Al y Ti z (PO4)3, 0 < x < 2, 0 < y < 1, 0 < z < 3), (LiAlTiP) x O y Series glass (0 < x < 4, 0 < y < 13), lithium lanthanum titanate (Li x La y TiO3, 0 < x < 2, 0 < y < 3), lithium germanium thiophosphate (Li x Ge y P z S w , 0 < x < 4, 0 < y < 1, 0 < z < 1, 0 < w < 5), lithium nitride (Li x N y , 0 < x <4, 0 < y < 2), SiS2 series glass(Li x Si y S z , 0 < x < 3, 0 < y < 2, 0 < z < 4) and P2S5 series glass(Li x P y S z, 0 < x < 3, 0 < y < 3, 0 < z < 7) may be a mixture of one or more selected from the group consisting of:

[0118] For example, the average particle diameter (D) of the above inorganic particles 50 ) may be 1 nm to 10 μm, specifically 10 nm to 2 μm, and more specifically 50 nm to 1 μm, for forming a coating layer of uniform thickness and an appropriate porosity. The "average particle diameter (D50)" refers to the particle diameter at the 50% point of the cumulative distribution of the number of particles according to particle diameter. The average particle diameter can be measured using a laser diffraction method. Specifically, after dispersing the target powder in a dispersion medium, it is introduced into a commercially available laser diffraction particle size measuring device (e.g., Microtrac S3500) and measuring the difference in diffraction pattern according to particle size when the particles pass through a laser beam, thereby calculating the particle size distribution.

[0119] electrolyte

[0120] The electrolyte according to the present invention may include a solvent and a lithium salt.

[0121] The solvent according to the present invention may be, for example, one or a mixture of two or more selected from the group consisting of propylene carbonate (PC), ethylene carbonate (EC), diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), dimethyl sulfoxide, acetonitrile, dimethoxyethane, diethoxyethane, tetrahydrofuran, N-methyl-2-pyrrolidone (NMP), ethyl methyl carbonate (EMC), gamma butyrolactone (GBL), fluoroethylene carbonate (FEC), methyl formate, ethyl formate, propyl formate, methyl acetate, ethyl acetate, propyl acetate, pentyl acetate, methyl propionate, ethyl propionate, ethyl propionate, and butyl propionate.

[0122] Lithium salt according to the present invention is, for example, NO3- , F - , Cl - , Br - , I - , PF6 - It may contain anions such as:

[0123] The electrolyte according to the present invention may further include an additive, and specifically, may include a compound containing a fluorine atom. For example, the additive may include at least one selected from the group consisting of LiBF4, LiTFSI, and LiFSI. Here,

[0124] LiTFSI and LiFSI can increase the conductivity of lithium ions by forming a lithium fluoride (LiF)-rich passive film on the surface of lithium metal through corrosion.

[0125] Application

[0126] The secondary battery according to the present invention may be a cylindrical, square, or pouch-shaped secondary battery, but is not particularly limited as long as it corresponds to a charging / discharging device.

[0127] Another embodiment of the present invention can provide a battery module including the secondary battery as a unit cell and a battery pack including the same. The battery pack can be used as a power source for one or more medium- to large-sized devices selected from the group consisting of, for example, power tools; electric vehicles including electric vehicles (EVs), hybrid electric vehicles (HEVs), and plug-in hybrid electric vehicles (PHEVs); or power storage systems.

[0128] Hereinafter, embodiments of the present invention will be described in detail so that those skilled in the art can easily implement the present invention. However, this is merely an example, and the scope of the present invention is not limited by the following contents.

[0129] [Manufacturing Example 1: Preparation of positive electrode slurry]

[0130] Examples 1 and 2

[0131] Cathode active material (LiNi) 0.8 Co 0.1 Mn 0.1 O2, LiNi 0.6 Co 0.2 Mn 0.2 O2), a conductive agent (Super-P), and carboxymethyl cellulose (CMC) were mixed in a weight ratio of 96:2:2, and the organic acid (0.8 wt% based on the total solid content contained in the positive electrode slurry) and solvent (water) described in Table 1 below were added to prepare a positive electrode slurry having a total solid content of 73.5 wt%.

[0132] Examples 3 to 6

[0133] A cathode slurry was prepared in the same manner as in Example 1, except that the content of the organic acid was adjusted to the content described in Table 1 below.

[0134] Comparative Examples 1 to 3

[0135] A positive electrode slurry was prepared in the same manner as in Example 1, but the type of organic acid or inorganic acid was changed to those described in Table 1 below. At this time, the content of the inorganic acid was set based on the weight of the total solid content included in the positive electrode slurry.

[0136] Reference example

[0137] For reference, the positive electrode active material (LiNi 0.8 Co 0.1 Mn 0.1 O2, LiNi 0.6 Co 0.2 Mn 0.2 A cathode slurry having a total solid content of 61.8 wt% was prepared by adding a solvent (NMP) to a mixture of O2, a conductive agent (Super-P), and PVDF in a weight ratio of 96:2:2.

[0138] Classification Organic acid Polysaccharide Binder Example 1 (CMC-SSA 0.8 wt%) Sulfosuccinic acid (SSA) CMC Example 2 (CMC-SAA 0.8 wt%) Sulfoacetic acid (SAA) CMC Example 3 (CMC-SSA 0.6 wt%) Sulfosuccinic acid (SSA) CMC Example 4 (CMC-SSA 1.6 wt%) Sulfosuccinic acid (SSA) CMC Example 5 (CMC-SSA 0.3 wt%) Sulfosuccinic acid (SSA) CMC Example 6 (CMC-SSA 1.3 wt%) Sulfosuccinic acid (SSA) CMC Comparative Example 1 Succinic acid (ScA) CMC Comparative Example 2 Ethane disulfonic acid (EDSA) CMC Comparative Example 3 Sulfuric acid (SfA) CMC Reference Example - PVDFCMC: 0.7 to Binder PVDF having a degree of substitution of 0.9 and a weight average molecular weight of 90,000 to 1,200,000 g / mol: Weight average molecular weight (M w ) polyvinylidene fluoride having a molecular weight of 500,000 g / mol

[0139] [Manufacturing Example 2: Manufacturing of the anode]

[0140] The positive electrode slurry according to each of the above manufacturing examples 1 was applied to a 20㎛ thick aluminum film using a doctor blade, and then dried (overnight) at 120°C to manufacture the positive electrode.

[0141] [Manufacturing Example 3: Manufacturing a Half-Battery]

[0142] Preparation of cathode and anode

[0143] Lithium metal (Li metal) with a thickness of 450㎛ was prepared as the negative electrode, and each positive electrode according to the above manufacturing example 2 was prepared as the positive electrode.

[0144] Preparation of membrane

[0145] A porous substrate (thickness: 15㎛) made of polyolefin material was prepared.

[0146] Electrolyte solution

[0147] After stacking the cathode, separator, and anode in that order, an electrode assembly was manufactured by lamination.

[0148] Manufacturing of half-cells

[0149] After the above electrode assembly was placed in a battery case, an electrolyte was injected to manufacture a half-cell. Here, the electrolyte used was an electrolyte in which 1 M LiPF6 was dissolved in a mixed solvent of ethylene carbonate and dimethyl carbonate at a volume ratio of 1:1.

[0150] [Experimental Example 1: Electrochemical Performance Evaluation of Half-Cells]

[0151] Figure 2a compares the life performance of half-cells according to Example 1 and Reference Example under conditions of a cut-off voltage of 4.5 V and 0.5 C.

[0152] Referring to Fig. 2a, it can be confirmed that the half-cell according to Example 1 has a higher discharge capacity than the half-cell according to the reference example.

[0153] Figure 2b shows 0.5C and 2 nd Voltage-capacity curves of half-cells according to Example 1 and Reference Example under cycling conditions are shown.

[0154] Referring to FIG. 2b, it can be confirmed that the half-cell according to Example 1 has a lower overpotential than the half-cell according to the reference example.

[0155] [Experimental Example 2: Evaluation of the Lifespan Characteristics of Half-Batteries]

[0156] Figure 3 compares the life performance and coulombic efficiency of half-cells according to Example 1 and Reference Example according to the number of cycles. Specifically, for Experimental Example 2, each half-cell was charged and discharged at 0.5 C, high voltage (4.7 V cut-off voltage), and high temperature (60 °C).

[0157] Referring to Figure 3, it can be confirmed that the half-cell according to Example 1 not only exhibits higher Coulombic efficiency compared to the half-cell according to the Reference Example, but also exhibits superior life performance. This confirms that the life performance is significantly improved by using a polysaccharide binder-organic acid.

[0158] [Experimental Example 3: Evaluation of the Speed ​​Characteristics of Half-Batteries]

[0159] Figure 4a shows the life performance of half-cells according to Example 1 and Reference Example. Specifically, Experimental Example 3 was conducted under conditions of a 4.5 V cut-off voltage and 2 C.

[0160] Referring to FIG. 4a, it can be confirmed that the half-cell according to Example 1 not only exhibits higher coulombic efficiency compared to the half-cell according to the reference example, but also exhibits better life performance.

[0161] Figure 4b compares the rate characteristics of half-cells according to Example 1 and Reference Example. The discharge capacity test was conducted under a cut-off voltage condition of 4.5 V.

[0162] Referring to Fig. 4b, it can be confirmed that the discharge capacity of the half-cell according to Example 1 is generally higher than that of the half-cell according to the Reference Example even when the charge / discharge rate is varied from 0.1 C to 20 C. Through this, it can be inferred that excellent rate characteristics are realized by using a polysaccharide binder-organic acid.

[0163] [Experimental Example 4: Evaluation of Discharge Capacity of Half-Cells According to Type of Binder or Organic Acid]

[0164] Figure 5 compares the life performance of half cells according to Examples 1 and 2, Comparative Examples 1 to 3, and Reference Example. Specifically, the discharge capacity test was conducted under conditions of a cut-off voltage of 3.0 to 4.5 V and 0.5 C.

[0165] Referring to FIG. 5, it can be confirmed that the half-cells according to Examples 1 and 2 exhibit superior life performance compared to the half-cells according to Comparative Examples 1 to 3 and the Reference Example.

[0166] In addition, when comparing Examples 1 and 2 from the perspective of the type of organic acid, it can be confirmed that the half-cell according to Example 2 exhibits superior life performance compared to the half-cell according to Example 1 by including one carboxyl group and one sulfonic acid functional group in the molecule of the organic acid.

[0167] [Experimental Example 5: Evaluation of Electrochemical Performance of Half-Cells According to Organic Acid Content]

[0168] Figure 6a shows the discharge capacity of half cells according to Examples 1, 3, and 4 and the reference example.

[0169] Referring to Fig. 6a, it can be confirmed that the half-cell according to Example 1, in which the concentration of sulfosuccinic acid (SSA) was 0.8 wt% based on the total weight of the electrode (= total solid content of the positive electrode slurry), exhibits superior life performance compared to the half-cell according to the reference example and the half-cells according to Examples 3 and 4. Considering the above experimental results, it can be inferred that there is an optimized content of organic acid that can realize superior life performance of the cell.

[0170] [Experimental Example 6: SEM image of the electrode surface]

[0171] Fig. 7a is an SEM photograph of the surface of an anode manufactured by the method according to the reference example. Fig. 7b is an SEM photograph of the surface of an anode manufactured by the method according to Example 5. Fig. 7c is an SEM photograph of the surface of an anode manufactured by the method according to Example 1. Fig. 7d is an SEM photograph of the surface of an anode manufactured by the method according to Example 6.

[0172] Referring to FIGS. 7a to 7d, it can be confirmed that residual lithium is well removed from the surface of the positive electrode active material included in the positive electrode manufactured by the method according to Example 1.

[0173] [Experimental Example 7: FT-IR of Polysaccharide Binder-Organic Acid]

[0174] Figure 8 shows the FT-IR of the polysaccharide binder-organic acid manufactured by the method according to Example 1 when the drying temperatures of the positive electrode slurry were 60°C and 120°C, respectively.

[0175] Referring to Figure 8, it can be confirmed that the organic acid forms an ester bond with the polysaccharide binder as the positive electrode slurry is dried at 120°C.

[0176] [Experimental Example 8: Evaluation of Bonding Strength with the Collector]

[0177] Figure 9 shows a peeling test of the positive electrode active material layer on the current collector in a positive electrode manufactured by the method according to Reference Example and Example 1.

[0178] Referring to FIG. 9, in the case of the positive electrode manufactured by the method according to Example 1, it can be confirmed that the positive electrode manufactured by the method according to Example 1 in which the drying temperature of the positive electrode slurry was set to 60°C and 120°C both exhibited a higher bonding force to the current collector compared to the positive electrode manufactured by the method according to the reference example.

[0179] Specifically, when the drying temperature of the positive electrode slurry is 120°C, the bonding strength of the positive electrode active material layer to the current collector is significantly enhanced due to the formation of ester bonds between the polysaccharide and the organic acid. This suggests that the interaction between the current collector and the binder is not hindered by residual organic acid molecules, resulting in a stronger bonding strength.

[0180] [Experimental Example 9: Measurement of the surface coverage of positive electrode active materials according to the type and content of binder]

[0181] Figure 10a shows each TM-O peak when the concentration of the polysaccharide binder is 1, 2, and 5 wt% based on the total weight of the solid in the positive electrode manufactured by the method according to Example 1. Figure 10b shows each TM-O peak when the concentration of the polysaccharide binder is 1, 2, and 5 wt% based on the total weight of the solid in the positive electrode manufactured by the method according to the reference example. In order to analyze the TM-O peak, the beamline X-ray absorption spectrometry of the Pohang Accelerator Laboratory was used as the analysis equipment, and the analysis conditions were soft X-ray, ultra-high vacuum (~10 -9 The evaluation was conducted under the bar.

[0182] Referring to FIGS. 10a and 10b, it can be confirmed that the positive electrode manufactured by the method according to Example 1 has a lower TM-O peak detected compared to the positive electrode manufactured by the method according to the Reference Example. This suggests that when a positive electrode manufactured with a polysaccharide binder-organic acid is used, the surface coverage of the binder increases.

[0183] [Experimental Example 10: Evaluation of Interfacial Resistance According to the Number of Cycles]

[0184] Fig. 11a is a graph showing electrochemical impedance measurements of a pristine electrode according to Example 1 and a reference example. Fig. 11b is a graph showing electrochemical impedance measurements of an electrode according to Example 1 and a reference example.

[0185] Referring to Figures 11a and 11b, the pristine electrode is an electrode before the CEI (Cathode Electrolyte Interphase) is formed, and the pristine electrode according to Example 1 was measured to have a higher resistance than the pristine electrode according to the Reference Example. However, in the case of Example 1, it can be inferred that as the CEI is formed, the high coverage of the polysaccharide binder-organic acid suppresses side reactions of the electrolyte, thereby forming a CEI with better performance. Accordingly, it was confirmed that the resistance of the electrode was reduced.

[0186] In comprehensive consideration of the above experimental results, according to one aspect of the present invention, by including a structure derived from an organic acid having a carboxyl group and a sulfonic acid group in one side chain of the polysaccharide binder, the covering rate of the polysaccharide binder-organic acid on the surface of the positive electrode active material can be increased. Accordingly, by forming a CEI (Cathode Electrolyte Interphase) with excellent performance, the resistance of the electrode can be reduced, and the life characteristics of the secondary battery can be improved. Specifically, the carboxyl group of the organic acid can increase the bonding force between the current collector and the positive electrode active material layer, and the sulfonic acid group of the organic acid can implement excellent lithium ion conductivity. By combining the carboxyl group and the sulfonic acid group of the organic acid, the residual lithium on the surface of the positive electrode active material can be removed, thereby suppressing Li leaching, and the pH of the positive electrode slurry can be adjusted to an appropriate level, thereby solving the corrosion problem of the current collector.

[0187] Although the preferred embodiments of the present invention have been described in detail above, the scope of the present invention is not limited thereto, and various modifications and improvements made by those skilled in the art using the basic concept of the present invention defined in the following claims also fall within the scope of the present invention.

[0188]

[0189] [National Research and Development Project Supporting This Invention]

[0190] [Project ID]1711192947

[0191] [Assignment Number] 2020M3H4A3081889

[0192] [Ministry Name] Ministry of Science and ICT

[0193] [Name of Project Management (Specialist) Institution] National Research Foundation of Korea

[0194] [Research Project Name] Nanomaterial Technology Development

[0195] [Research Project Name] Development of Binder and Electrode Manufacturing Technology for High-Voltage / High-Capacity Secondary Battery Anodes

[0196] [Contribution rate] 1 / 2

[0197] [Name of Project Performing Organization] Korea Institute of Science and Technology

[0198] [Research Period] May 15, 2020 - December 31, 2024

[0199]

[0200] [National Research and Development Project Supporting This Invention]

[0201] [Project ID]1711185103

[0202] [Assignment Number] 2021M3H4A3A02086100

[0203] [Ministry Name] Ministry of Science and ICT

[0204] [Name of Project Management (Specialist) Institution] National Research Foundation of Korea

[0205] [Research Project Name] Nanomaterial Technology Development

[0206] [Research Project Name] Research on Binder and Electrode Technology for High-Capacity Silicon Anodes

[0207] [Contribution rate] 1 / 2

[0208] [Name of the project performing organization] Korea Institute of Ceramic Engineering and Technology

[0209] [Research Period] May 15, 2021 - December 31, 2023

Claims

1. Polysaccharide binder; organic acid; positive electrode active material; Challenge; and containing an aqueous solvent; The above organic acid contains a carboxyl group and a sulfonic acid group. Bipolar slurry.

2. In paragraph 1, The weight average molecular weight (M) of the above polysaccharide binder w ) is 90,000 to 1,500,000 g / mol, Bipolar slurry.

3. In paragraph 1, Within one molecule of the above organic acid The number of the carboxyl group and the sulfonic acid group is the same, Bipolar slurry.

4. In paragraph 1, The above organic acid is a compound represented by the following general formula 1: Positive slurry: [General Formula 1] In the above general formula 1, R contains a hydrogen atom, or -R1-COOH, The above R1 comprises a substituted or unsubstituted main skeletal linking group having 1 to 5 carbon atoms.

5. In paragraph 1, The above organic acid is, Any one selected from the group consisting of sulfosuccinic acid, sulfoacetic acid, and combinations thereof, Bipolar slurry.

6. In paragraph 1, The content of the organic acid is 0.1 to 2 wt% based on the weight of the total solid content included in the positive electrode slurry. Bipolar slurry.

7. In paragraph 1, further comprising a dispersant; Bipolar slurry.

8. In paragraph 1, Rubber-based polymers; further comprising, Bipolar slurry.

9. The entire house; and A positive electrode active material layer on the above-mentioned collector; The above positive electrode active material layer is, A polysaccharide binder comprising one or more side chains, Positive active material and Including challenges, wherein said one or more side chains comprise an ester group and a sulfonic acid group, anode.

10. In paragraph 9, wherein said one or more side chains further comprise a carboxyl group, anode.

11. In paragraph 9, The above positive electrode active material layer further comprises a rubber-based polymer; anode.

12. In paragraph 9, The above positive electrode active material is Li x1 CoO2(0.5 <x1<1.3), Li x2 NiO2(0.5 <x2<1.3), Li x3 MnO2(0.5 <x3<1.3), Li x4 Mn2O4(0.5 <x4<1.3), Li x5 (Ni a1 Co b1 Mn c1 )O2(0.5 <x5<1.3, 0<a1<1, 0<b1<1, 0<c1<1, a1+b1+c1=1), Li x6 Ni 1-y1 Co y1 O2(0.5 <x6<1.3, 0<y1<1), Li x7 Co 1-y2 Mn y2 O2(0.5 <x7<1.3, 0혏2<1), Li x8 Ni 1-y3 Mn y3 O2(0.5 <x8<1.3, O혏3<1), Li x9 (Ni a2 Co b2 Mn c2 )O4(0.5 <x9<1.3, 0<a2<2, 0<b2<2, 0<c2<2, a2+b2+c2=2), Li x10 Mn 2-z1 Ni z1 O4(0.5 <x10<1.3, 0<z1<2), Li x11 Mn 2-z2 Co z2 O4(0.5 <x11<1.3, 0<z2<2), Li x12 FePO4(0.5 <x12<1.3), Li x13 CoPO4(0.5 <x13<1.3), Li x14 Mn 1-w1 Fe w1 PO4(0.5 <x14<1.3, 0.15<w1<0.85), Li x15 Mn a3 Fe b3 Al c3 PO4(0.5 <x15<1.3, a3+b3+c3=1), Li x16 Mn a4 Fe b4 Mg c4 PO4(0.5 <x16<1.3, a4+b4+c4=1), Li x17 Mr a5 Feb b5 Zn c5 PO4(0.5 <x17<1.3, a5+b5+c5=1), Li x18 Mr a6 Feb b6 V c6 PO4(0.5 <x18<1.3, a6+b6+c6=1), Li x19 (Ni a7 Co b7 Al c7 )O2(0.5 <x19<1.3, 0<a7<1, 0<b7<1, 0<c7<0.15, a7+b7+c7=1), Li x20 (Ni a8 Mr b8 Al c8 )O2(0.5 <x20<1.3, 0<a8<1, 0<b8<1, 0<c8<0.15, a8+b8+c8=1), Li x21 (Co a9 Mr b9 Al c9 )O2(0.5 <x21<1.3, 0<a9<1, 0<b9<1, 0<c9<0.15, a9+b9+c9=1), Li x22 (Ni 1-y4 Al y4 )O2(0.5 <x22<1.3, 0≤y4<0.15), Li x23 (Co 1-y5 Al y5 )O2(0.5 <x23<1.3, 0≤y5<0.15), Li x24( Mr 1-y6 Al y6 )O2(0.5 <x24<1.3, 0≤y6<0.15), 및 Li x25 (Ni a10 Co b10 Mr c10 Al d10 )O2(0.5 <x25<1.3, 0<a10<1, 0<b10<1, 0<c10<1, 0<d10<0.15, a10+b10+c10+d10=1)로 이루어진 군에서 선택되는 하나 이상인, anode.

13. The anode according to Article 9; cathode; a separator interposed between the positive electrode and the negative electrode; and containing an electrolyte; Secondary battery.

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