Polyimide binder for negative electrode material of secondary battery

Abstract

The present invention relates to a polyimide binder for a negative electrode material of a secondary battery, capable of improving the charging and discharging efficiency of a battery and increasing the content of silicon.

Description

Polyimide binder for secondary battery anode materials

[0001] The present invention relates to a polyimide binder for a secondary battery negative electrode material.

[0002] Various methods are being explored to increase the energy density of lithium-ion batteries. Silicon theoretically has 10 times the capacity of conventional graphite anode materials, allowing for a significant increase in energy density compared to existing lithium-ion batteries. However, during charge and discharge of lithium-ion batteries, silicon continuously expands by more than four times in volume. This causes silicon particles to pulverize and become finer, detaching or continuously forming a SEI layer on the fresh anode surface due to finer particle size, which reduces battery performance and lifespan. Therefore, while approximately 5% silicon is currently added to graphite for mass production, the addition of large amounts of silicon is necessary to increase the capacity of lithium-ion batteries.

[0003] In order to increase the silicon content, development is also underway to control the volume expansion of silicon itself, but the development of a high-performance aqueous binder is an urgent task to control the volume expansion of silicon to improve the life of the battery, secure adhesion between the negative electrode layer and the Cu current collector, and bind between particles.

[0004] Currently, CMC / SBR-based binders are used in graphite anode materials, but they fail to increase the silicon content. Recently, many researchers have been developing polyacrylic acid-based binders, but they are unable to control the volume expansion of silicon, so they are unable to secure the charge / discharge characteristics of lithium-ion batteries and improve the lifespan of batteries.

[0005] The problem to be solved by the present invention is to provide a polyimide binder for a secondary battery negative electrode material that can improve the charge / discharge efficiency of a battery and increase the silicon content.

[0006] One aspect of the present invention is a polyimide binder for a secondary battery negative electrode material, which comprises a repeating unit represented by the following chemical formula 1.

[0007] [Chemical Formula 1]

[0008]

[0009] In the above chemical formula 1, X is a group derived from an aromatic anhydride, a substituted or unsubstituted aromatic group having 6 to 30 carbon atoms, or a substituted or unsubstituted alicyclic group having 4 to 30 carbon atoms, Y is a substituted or unsubstituted aromatic group having 6 to 30 carbon atoms containing at least one aromatic group, or a substituted or unsubstituted alicyclic group having 4 to 30 carbon atoms containing at least one ring, Z is a substituted or unsubstituted aromatic group having 6 to 30 carbon atoms containing at least one aromatic group, or a substituted or unsubstituted alicyclic group having 4 to 30 carbon atoms containing at least one ring, and m and n are positive integers.

[0010] In the present invention, m may be 4 or more, and the molar ratio of m and n may be 1:1 to 5.

[0011] In the present invention, the X may be one or more selected from the following.

[0012] and .

[0013] In the present invention, the Y may be one or more selected from the following.

[0014] and

[0015] In the present invention, Z may be one or more selected from the following.

[0016] and

[0017] In the present invention, the polyimide may be manufactured by reacting an acid anhydride, a diamine, and a carbonyl chloride.

[0018] In the present invention, the molar content of the acid anhydride and carbonyl chloride may be 20 to 60 mol and 40 to 80 mol, respectively, relative to 100 mol of diamine.

[0019] In the present invention, the acid anhydride may be one or more selected from the following.

[0020] and .

[0021] In the present invention, the diamine may be one or more selected from the following.

[0022] and

[0023] In the present invention, the carbonyl chloride may be one or more selected from the following.

[0024] and

[0025] In the present invention, the polyimide may be soluble in water.

[0026] Another aspect of the present invention is a negative electrode for a secondary battery comprising the polyimide binder for the negative electrode material.

[0027] Another aspect of the present invention is a secondary battery including the negative electrode for the secondary battery.

[0028] The polyimide binder for a negative electrode material according to the present invention can increase the silicon content, thereby improving the charge / discharge efficiency of a secondary battery and extending its lifespan.

[0029] The polyimide according to the present invention can be dissolved in water, and thus can be applied to conventional processes for manufacturing negative electrode slurry and negative electrode plate.

[0030] In addition, the polyimide binder for a cathode material according to the present invention can improve the electrochemical stability and mechanical stability of the electrode by improving the adhesion and interaction with the metal surface, thereby securing high initial capacity and excellent life characteristics.

[0031] Hereinafter, the present invention will be described in more detail with reference to exemplary embodiments, examples, etc. so that those skilled in the art can easily implement the present invention. However, the present invention may be implemented in various different forms and is not limited to the embodiments, examples, etc. described herein.

[0032] In this specification, the phrase "substituted or unsubstituted" means that a substituent is substituted by an arbitrary or specific functional group, and is not substituted. The case of being substituted means that an arbitrary or specific functional group is bonded to one or more carbons of the substituent.

[0033] Specifically, it may mean that one or more hydrogen atoms in the functional group are substituted with one or more substituents selected from the group consisting of a halogen atom (F, Cl, Br, I), a C1~C10 alkyl group, a C1~C10 alkoxy group, a C1~C10 halogenated alkyl group, a C3~C20 cycloalkyl group, a C3~C20 cycloalkenyl group, a C6~C30 aryl group, a hydroxyl group, an amine group, a carboxylic acid group, an aldehyde group, etc., but is not necessarily limited thereto.

[0034] The polyimide binder for a cathode material according to the present invention does not form a network structure within the polymer, and unlike conventional CMC / SBR, it can secure excellent adhesive strength by performing pre-adhesion rather than point-adhesion.

[0035]

[0036] The present invention is described in detail below.

[0037] One aspect of the present invention is a polyimide binder for a secondary battery negative electrode material, which comprises a repeating unit represented by the following chemical formula 1.

[0038] In the present invention, the polyimide is soluble in water, and up to 15% by weight of the polyimide can be completely dissolved, and preferably up to 10% by weight of the polyimide can be completely dissolved. By dissolving the polyimide in water, a negative electrode slurry can be prepared in an aqueous system and a negative electrode plate can be manufactured, as in a conventional method.

[0039] In the present invention, the polyimide can be represented by the following chemical formula 1.

[0040] [Chemical Formula 1]

[0041]

[0042] In the above chemical formula 1, X is a group derived from an aromatic anhydride, a substituted or unsubstituted aromatic group having 6 to 30 carbon atoms, or a substituted or unsubstituted alicyclic group having 4 to 30 carbon atoms, Y is a substituted or unsubstituted aromatic group having 6 to 30 carbon atoms containing at least one aromatic group, or a substituted or unsubstituted alicyclic group having 4 to 30 carbon atoms containing at least one ring, Z is a substituted or unsubstituted aromatic group having 6 to 30 carbon atoms containing at least one aromatic group, or a substituted or unsubstituted alicyclic group having 4 to 30 carbon atoms containing at least one ring, and m and n are positive integers.

[0043] Additionally, in the present invention, the chemical formula 1 may further include a monovalent cation.

[0044] Specifically, in X, the aromatic anhydride may include an aromatic anhydride derivative, and the aromatic anhydride derivative may be used without limitation as long as it is an aromatic anhydride derivative widely used in the art in the production of polyimide.

[0045] In X, the aromatic group may be a benzene group, a naphthalene group, an anthracene group, a phenanthrene group, a fluorene group, a fluoranthene group, etc., and the alicyclic group may be a cyclopropyl group, a cyclobutyl group, a cyclopentyl group, a cyclohexyl group, a 4-tert-butylcyclohexyl group, an isobornyl group, a norbornenyl group, a mensyl group, an adamantyl group, etc.

[0046] In Y, the aromatic group may be a benzene group, a naphthalene group, an anthracene group, a phenanthrene group, a fluorene group, a fluoranthene group, etc., and the alicyclic group may be a cyclopropyl group, a cyclobutyl group, a cyclopentyl group, a cyclohexyl group, a 4-tert-butylcyclohexyl group, an isobornyl group, a norbornenyl group, a mensyl group, an adamantyl group, etc.

[0047] In Z, the aromatic group may be a benzene group, a naphthalene group, an anthracene group, a phenanthrene group, a fluorene group, a fluoranthene group, etc., and the alicyclic group may be a cyclopropyl group, a cyclobutyl group, a cyclopentyl group, a cyclohexyl group, a 4-tert-butylcyclohexyl group, an isobornyl group, a norbornenyl group, a mensyl group, an adamantyl group, etc.

[0048] In addition, m and n are positive integers, m may be 4 or more, and the molar ratio of m and n may be 1:1 to 5, preferably 1:1.2 to 2, and most preferably 1:1.5. If m is less than 4, the produced polyimide may not dissolve in water, so the above range is preferred.

[0049] In the present invention, the X may be one or more selected from the following, and the polyimide thus manufactured may be dissolved in water:

[0050] and .

[0051] In the present invention, Y may be one or more selected from the following:

[0052] and

[0053] Preferably, the above Y is It can be, and the above Y When present, it may further contain a monovalent cation.

[0054] In the present invention, Z may be one or more selected from the following:

[0055] and

[0056] Preferably, the above Z is It could be.

[0057] In the present invention, the polyimide may be manufactured by reacting an acid anhydride, a diamine, and a carbonyl chloride.

[0058] The molar contents of the acid anhydride and carbonyl chloride may be 20 to 60 mol and 40 to 80 mol, respectively, relative to 100 mol of diamine, and preferably 30 to 50 mol and 50 to 70 mol, respectively, relative to 100 mol of diamine. If the contents of the acid anhydride and carbonyl chloride are outside the above range, the solubility of the produced polyimide may decrease, and therefore the above range is preferred.

[0059] In the present invention, the molar content of the acid anhydride may be equal to or less than the content of carbonyl chloride, and the molar ratio of the acid anhydride and carbonyl chloride may be 1:1 to 5, preferably 1:1.2 to 2. If the molar ratio of the acid anhydride and carbonyl chloride is outside the above range, the solubility of the produced polyimide may be reduced, so the above range is preferred.

[0060] In the present invention, the acid anhydride may be one or more selected from the following, and the polyimide produced thereby may be dissolved in water:

[0061] and .

[0062] In the present invention, the diamine may be one or more selected from the following:

[0063] and

[0064] Preferably, the diamine is It could be.

[0065] In the present invention, the carbonyl chloride may be one or more selected from the following.

[0066] and

[0067] Preferably, the carbonyl chloride is It could be.

[0068] In the present invention, the polyimide may preferably be represented by the following chemical formula 2-1 or 2-2.

[0069] [Chemical Formula 2-1]

[0070]

[0071] In the above chemical formula 2-1, m and n are positive integers, m may be 4 or more, the molar ratio of m and n may be 1:1 to 5, preferably 1:1.2 to 2, and most preferably 1:1.5, and may further include a monovalent cation.

[0072] [Chemical Formula 2-2]

[0073]

[0074] In the above chemical formula 2-2, m and n are positive integers, m may be 4 or more, the molar ratio of m and n may be 1:1 to 5, preferably 1:1.2 to 2, and most preferably 1:1.5, and may further include a monovalent cation.

[0075] Another aspect of the present invention is a negative electrode for a secondary battery comprising the polyimide binder for the negative electrode material described above.

[0076] The negative electrode can be manufactured by coating a negative electrode slurry containing a negative electrode active material, a binder, a conductive material, a solvent, etc. on a negative electrode current collector, and then drying and rolling.

[0077] The negative electrode current collector may have a thickness of 3 to 500 μm. The negative electrode current collector is not particularly limited as long as it has high conductivity and does not cause chemical changes in the lithium secondary battery. For example, the negative electrode current collector may be made of copper, stainless steel, aluminum, nickel, titanium, calcined carbon, etc., or may be made of copper or stainless steel surface-treated with carbon, nickel, titanium, silver, etc., or may be made of an aluminum-cadmium alloy. In addition, like the positive electrode current collector, the negative electrode current collector may have fine unevenness on its surface to improve bonding strength with the negative electrode active material. The negative electrode collector may be made in the form of a film, sheet, foil, net, porous body, foam, non-woven fabric, etc.

[0078] Additionally, the negative electrode active material is lithium metal, a compound capable of reversibly intercalating and deintercalating lithium ions. The negative electrode active material may be selected from the group consisting of carbon materials, metals or alloys of these metals and lithium, metal composite oxides, materials capable of doping and dedoping lithium, and transition metal oxides.

[0079] As a carbon material, any carbon-based negative electrode active material commonly used in lithium-ion secondary batteries may be used without particular restrictions. For example, crystalline carbon, amorphous carbon, or a mixture thereof may be used as the carbon material. As the crystalline carbon, graphite such as natural graphite or artificial graphite in an amorphous, plate-like, flake-like, spherical, or fibrous form may be used, and as the amorphous carbon, soft carbon (low-temperature calcined carbon), hard carbon, mesophase pitch carbide, calcined coke, etc. may be used.

[0080] Metal complex oxides include PbO, PbO2, Pb2O3, Pb3O4, Sb2O3, Sb2O4, Sb2O5, GeO, GeO2, Bi2O3, Bi2O4, Bi2O5, LixFe2O3(0≤x≤1), LixWO2(0≤x≤1), and SnxMe1-xMe'yOz (Me: Mn, Fe, Pb, Ge; Me': Al, B, P, Si, elements of group 1, 2, and 3 of the periodic table, halogens; 0 <x≤1; 1≤y≤3; 1≤z≤8) 로 이루어진 군에서 선택되는 것이 사용될 수 있다.

[0081] Si, SiOx(0) as a material capable of doping and dedoping lithium <x≤2), Si-Y 합금(상기 Y는 알칼리 금속, 알칼리토금속, 13족 원소, 14족 원소, 전이금속, 희토류 원소 및 이들의 조합으로 이루어진 군에서 선택되는 원소이며, Si은 아님), Sn, SnO2, Sn-Y(상기 Y는 알칼리 금속, 알칼리 토금속, 13족 원소, 14족 원소, 전이 금속, 희토류 원소 및 이들의 조합으로 이루어진 군에서 선택되는 원소이며, Sn은 아님) 등이 사용될 수 있고, 이들 중 적어도 하나와 SiO2를 혼합하여 사용될 수 있다. 원소 Y로 Mg, Ca, Sr, Ba, Ra, Sc, Y, Ti, Zr, Hf, Rf, V, Nb, Ta, Db, 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, Ge, P, As, Sb, Bi, S, Se, Te, Po 및 이들의 조합으로 이루어진 군에서 선택된 원소가 사용될 수 있다.

[0082] Transition metal oxides that can be used include lithium-containing titanium composite oxide (LTO), vanadium oxide, and lithium vanadium oxide.

[0083] The negative electrode active material may be included in an amount of 80 wt% to 99 wt% based on the total weight of the solid content in the negative electrode slurry.

[0084] The binder includes the polyimide binder for the secondary battery negative electrode material described above.

[0085] A conductive agent is a component that further enhances the conductivity of the negative electrode active material and can be added in an amount of 1 to 20 wt% based on the total weight of the solid content in the negative electrode slurry. The conductive agent may be the same as or different from the conductive agent used in the manufacture of the positive electrode. For example, the conductive agent may include carbon powder, conductive fiber, metal powder, graphite powder, conductive whiskers, conductive metal oxides, and polyphenylene derivatives.

[0086] Carbon powders such as carbon black, acetylene black (or Denka black), Ketjen black, channel black, furnace black, lamp black, or thermal black can be used. Graphite powders such as natural graphite, artificial graphite, or graphite with highly developed crystal structures can be used. Carbon fibers or metal fibers can be used as conductive fibers. Fluorinated carbon, aluminum, or nickel powders can be used as metal powders. Zinc oxide, potassium titanate, etc. can be used as conductive whiskers. Titanium oxide, etc. can be used as conductive metal oxides.

[0087] The negative active material slurry may further include a solvent. The solvent may be water or an organic solvent such as NMP or alcohol, and may be used in an amount that provides a desirable viscosity when including the negative active material and a binder or conductive agent. For example, the solvent may be included so that the solids concentration in the slurry including the negative active material and the binder or conductive agent is 50 wt% to 95 wt%, preferably 70 wt% to 90 wt%.

[0088] Another aspect of the present invention is a secondary battery including the aforementioned negative electrode for a secondary battery.

[0089] A lithium secondary battery according to one aspect of the present invention can be usefully used in portable devices such as mobile phones, laptop computers, and digital cameras, and in electric vehicles such as hybrid electric vehicles (HEVs).

[0090] The lithium secondary battery of the present invention can be manufactured by applying and curing a solid electrolyte composition on a positive electrode and then laminating the negative electrode of the present invention.

[0091] The positive electrode includes a positive electrode active material. The positive electrode can be manufactured by coating a positive electrode slurry containing a positive electrode active material, a binder, a conductive agent, a solvent, etc. on a positive electrode current collector, followed by drying and rolling.

[0092] The cathode current collector is not particularly limited, as long as it is conductive and does not induce chemical changes in the lithium secondary battery. For example, stainless steel, aluminum, nickel, titanium, calcined carbon, etc., or aluminum or stainless steel with a surface treated with carbon, nickel, titanium, silver, etc., may be used as the cathode current collector.

[0093] In addition, the positive electrode active material is a compound capable of reversible intercalation and deintercalation of lithium. Specifically, the positive electrode active material may include a lithium composite metal oxide containing lithium and one or more metals such as cobalt, manganese, nickel, or aluminum. The lithium composite metal oxide is a lithium-manganese oxide (e.g., LiMnO2, LiMn2O4, etc.), a lithium-cobalt oxide (e.g., LiCoO2, etc.), a lithium-nickel oxide (e.g., LiNiO2, etc.), a lithium-nickel-manganese oxide (e.g., LiNi1 - Y Mn Y O2 (here, 0 <Y<1), LiMn2 -z Ni z O4 (where 0<Z<2), etc.), lithium-nickel-cobalt oxides (e.g., LiNi1 -Y1CoY1O2(here, 0 <Y1<1) 등), 리튬-망간-코발트계 산화물(예를 들면, LiCo1 -Y2 Mn Y2 O2 (here, 0 <Y2<1), LiMn2 - 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, respectively, such that 0<p2<1, 0<q2<1, 0<r3<1, 0<s2<1, p2+q2+r3+s2=1).

[0094] In terms of being able to improve the capacity characteristics and stability of the battery, the lithium composite metal oxide may be LiCoO2, LiMnO2, LiNiO2, lithium nickel manganese cobalt oxide (e.g., Li(Ni1 / 3Mn1 / 3Co1 / 3)O2, Li(Ni0.6Mn0.2Co0.2)O2, Li(Ni0.5Mn0.3Co0.2)O2, Li(Ni0.7Mn0.15Co0.15)O2, and Li(Ni0.8Mn0.1Co0.1)O2, or lithium nickel cobalt aluminum oxide (e.g., Li(Ni0.8Co0.15Al0.05)O2, etc.).

[0095] The positive electrode active material may be included in an amount of 80 wt% to 99 wt% based on the total weight of the solid content in the positive electrode slurry.

[0096] A binder is a component that facilitates bonding between a conductive material, an active material, and a current collector. The binder is added in an amount of 1 to 30 wt% based on the total weight of the solid content in the positive electrode slurry. For example, polyvinylidene fluoride (PVDF), polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinyl pyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene terephthalate monomer (EPDM), sulfonated EPDM, styrene-butadiene rubber, fluoroelastomer, etc. can be used as a binder.

[0097] The conductive material is added in an amount of 1 to 30 wt% based on the total weight of the solids in the positive electrode slurry. The conductive material is not particularly limited as long as it is conductive and does not induce chemical changes in the lithium secondary battery. Examples of conductive materials that can be used include carbon powder, conductive fiber, metal powder, graphite powder, conductive whiskers, conductive metal oxides, and polyphenylene derivatives.

[0098] Carbon powders such as carbon black, acetylene black (or Denka black), Ketjen black, channel black, furnace black, lamp black, or thermal black can be used. Graphite powders such as natural graphite, artificial graphite, or graphite with highly developed crystal structures can be used. Carbon fibers or metal fibers can be used as conductive fibers. Fluorinated carbon, aluminum, or nickel powders can be used as metal powders. Zinc oxide, potassium titanate, etc. can be used as conductive whiskers. Titanium oxide, etc. can be used as conductive metal oxides.

[0099] The positive electrode slurry may include a solvent. The solvent may include an organic solvent such as NMP (Nmethyl-2-pyrrolidone). The solvent may be used in an amount that provides a desirable viscosity when including the positive electrode active material and the binder or conductive material. For example, the solvent may be included so that the solid content of the slurry including the positive electrode active material and the binder or conductive material is 50 wt% to 95 wt%, preferably 70 wt% to 90 wt%.

[0100] The cathode is the same as described above and is therefore omitted.

[0101] Hereinafter, the present invention will be described in more detail by way of preferred embodiments thereof.

[0102]

[0103] The compounds used are as follows:

[0104]

[0105] Diamine

[0106] DABA: 3,5-diaminobenzoic acid

[0107] ODA: 4,4'-oxydianiline

[0108] m-PDA:m-phenylenediamine

[0109] MBAA: 5,5'-methylene bis(anthranilic acid)

[0110]

[0111] acid anhydride

[0112] BPADA: 2,2-bis[(3,4-dicarboxyphenoxy)phenyl]propane dianhydride

[0113] BTDA: 3,3',4,4'-Benzophenonetetracarboxylic acid dihydrochloride

[0114] BPDA: Biphenyltetracarboxylic dianhydride

[0115] PMDA: Pyromellitic dianhydride

[0116] ODPA: Oxydiphthalic dianhydride

[0117] DSDA: Diphenylsulfone-3,4,3',4'-tetracarboxylic dianhydride

[0118] 6-FDA: 2-Bis(3,4-dicarboxyphenyl)hexafluoropropane dianhydride

[0119]

[0120] carbonyl chloride

[0121] TPC: Terephthaloyl Chloride

[0122] IPC: Isophthaloyl chloride

[0123]

[0124] <Examples and Comparative Examples>

[0125] In a 500 mL separable reactor, 300 mL of dimethylacetamide (DMAc) solvent is added, diamine is added, and stirred to dissolve completely. Afterwards, acid anhydride is added and polymerization is performed while maintaining the temperature at 10℃. Afterwards, 1.2 equivalents of propylene oxide relative to carbonyl chloride are added, carbonyl chloride is added, and polymerization is performed for 4 hours through stirring. For the imidization reaction, 2.5 equivalents of pyridine relative to acid anhydride and 2.5 equivalents of acetic anhydride relative to acid anhydride are added, and stirring is performed at a temperature of 80℃ for 1 hour. Afterwards, a polymer precipitate is obtained using methanol, and the polymer in the form of a powder is obtained by vacuum drying. In order to dissolve the obtained polymer in water, 2.5 equivalents of 2-Dimethylaminoethanol per acid anhydride are added to distilled water and stirred to make it uniform, and then the obtained polymer is added so that the solid content becomes 8 wt%, stirred at a temperature of 60°C for 7 hours, and completely dissolved to prepare an aqueous binder. Table 1 below shows the molar ratios of the added diamine, acid anhydride, and carbonyl chloride, and Table 2 below shows the solubility of the manufactured polyimide polymer. The solubility was evaluated by visually confirming the undissolved polymer.

[0126]

[0127] Diamine (mol) Acid anhydride (mol) Carbonyl chloride (mol) DABAMBAAODAm-PDA6FDAOPDABPADABPDAPMDADSDABTDATPCIPC Example 1 100 60 40 Example 2 100--50------50 Example 3 100--40------60 Example 4 100--30------70 Example 5 100 20 80 Example 6 100--40------60 Example 7 100 50 50 Example 8 100 40 60 Example 9 100 30 70 Example 10 100 20 80 Example 11 100 50 50 Example 12 100 40 60 Example 13 100 30 70 Example 141005050Example 151004060Example 161003070Comparative Example 1100--------5050Comparative Example 2100---30-----70-Comparative Example 3100---40-----60-Comparative Example 4100---50-----50-Comparative Example 5100----10----90-Comparative Example 6100----5----95-Comparative Example 7100-----40---60-Comparative Example 8100-----30---70-Comparative Example 9100-----20---80-Comparative Example 10100------40--60Comparative Example 11100------30--70-Comparative Example 12100------20--80-Comparative Example 13100-------40-60-Comparative Example 14100--------4060-Comparative Example 15-100---100------Comparative Example 16-100----100-----Comparative Example 17-5050--100------Comparative Example 18--100--50----50-Comparative Example 199010-30------70-Comparative Example 209010-40------60-Comparative Example 218020-30------70-Comparative Example 228020-40------60-

[0128]

[0129] Distinctive Solubility Example 1○ Example 2○ Example 3○ Example 4○ Example 5△ Example 6○ Example 7○ Example 8○ Example 9○ Example 10△ Example 11○ Example 12○ Example 13○ Example 14○ Example 15○ Example 16○ Comparative Example 1X Comparative Example 2X Comparative Example 3X Comparative Example 4X Comparative Example 5X Comparative Example 6X Comparative Example 7X Comparative Example 8X Comparative Example 9X Comparative Example 10X Comparative Example 11X Comparative Example 12X Comparative Example 13X Comparative Example 14X Comparative Example 15X Comparative Example 16X Comparative Example 17X Comparative Example 18X Comparative Example 19X Comparative Example 20X Comparative Example 21X Comparison Example 22X

[0130]

[0131] In order to dissolve polyimide in water, it is necessary to use a bulky substance such as an acid anhydride to increase the free volume of the polymer chain, and to form a structure with an ionic salt within the polymer chain so that it can be dissolved in water.

[0132] Referring to Table 2, it can be confirmed that a water-soluble polyimide can be manufactured using a material capable of forming an ionic salt, such as DABA or MBAA, based on an acid anhydride having a structure such as 6FDA or BPADA, as in the present invention.

[0133] In addition, in the present invention, when the content of the acid anhydride and the content of the amine having an ionic salt structure are within the range of the present invention, it can be confirmed that a water-soluble polyimide can be manufactured, and when the content is outside the range of the present invention, it does not dissolve in water and exists in a dispersed form.

[0134]

[0135] Comparative Example 23

[0136] Polyacrylic acid (PAA) is a commercially available product from Sigma-Aldrich. It has a weight average molecular weight of 250,000 and a solid content of 35%.

[0137]

[0138] Exam example

[0139] Using the binder prepared in Example 23 and Comparative Example 23 dissolved in water, the charge / discharge and current-rate recovery rates were evaluated as follows, and the results are shown in Tables 3 and 4 below. PAA was used as a control.

[0140] [Half-cell manufacturing]

[0141] 10 wt% of the negative electrode binder composition obtained in the Examples and Comparative Examples, 80 wt% of the silicon negative electrode material, and 10 wt% of carbon black Super-P were added, and mixed uniformly while adding water to prepare a slurry. The slurry was applied to a copper foil, dried, and rolled to prepare a negative electrode. Lithium metal having a thickness of 1,000 μm was used as the counter electrode of the negative electrode. An electrolyte (PuriEL) was used in which 1.0 M LiPF6 was added to a solvent containing 3 wt% of fluoroethylene carbonate (FEC) mixed with a 1:1 mixture of ethylene carbonate (EC) and diethyl carbonate (DEC).

[0142] A half-cell was manufactured using the above cathode, its counter electrode, and the above electrolyte.

[0143]

[0144] [measurement method]

[0145] Charge / Discharge: The half-cell manufactured by the above method is mounted on a battery charger / discharger, and a first charge and discharge are performed at 0.1C, followed by another charge / discharge at 0.2C to stabilize the half-cell. Then, the charge is performed at 0.5C and the discharge is performed at 1.0C, and the capacity (mAh / g) at each cycle is measured.

[0146]

[0147] Current-Rate Recovery Rate: As in the previous charge / discharge test, charge / discharge is performed at 0.1C and 0.2C respectively to stabilize the initial half-cell, and then the C-rate of the charge / discharge is changed as follows (0.1C → 0.2C → 1.0C → 2.0C → 3.0C → 5.0C → 3.0C → 2.0C → 1.0C → 0.2C) to check the capacity at each C-rate, and set the initial 1.0C capacity as “100” as the standard, and display the capacity at each C-rate as a value converted to this.

[0148]

[0149] Classification Capacity (mAh / g) 1st Cycle 5th 10th 15th 20th 25th Example 11 28 21 1 20 10 10 0 0 9 5 9 9 0 Example 21 28 11 1 0 0 10 4 0 10 3 21 0 2 1 1 0 0 0 Example 31 28 0 1 ...71 28 0 1 1 0 10 8 0 10 5 5 10 4 0 10 2 0 1 0 2 0 1 0 10 2 0 1 0 0 0 Example 91 28 3 1 1 1 0 10 5 0 10 2 0 1 0 10 0 0 Comparative Example 231 1 3 0 10 0 0 9 5 0 8 0 0 7 0 0 6 0

[0150]

[0151] Classification 0.1C0.2C1.0C2.0C3.0C5.0C3.0C2.0C1.0C0.2CExample 1105103100989897989899101Example 2105102100989896989899102Example 3105102100989896989899102Example 7105103100989896989899102Example 8105102100989896989898101Example 9105102100989896989899102Comparative Example 2310510310098959394959598

[0152]

[0153] Referring to Tables 3 and 4 above, it can be confirmed that when the binder of Example 23 is used, the charge-discharge performance is stable even if volume expansion occurs during charge-discharge of the silicon negative electrode material due to the high mechanical properties of the polyimide.

[0154] In addition, the current-rate recovery rate shows excellent recovery rate when returning to 1.0C after a high C-rate charge / discharge.

[0155] The polyimide binder for a negative electrode material according to the present invention can increase the silicon content, thereby improving the charge / discharge efficiency of a secondary battery and extending its lifespan.

Claims

1. A polyimide binder for a secondary battery negative electrode material, comprising a repeating unit represented by the following chemical formula 1: [Chemical Formula 1] In the above chemical formula 1, X is a group derived from an aromatic anhydride, a substituted or unsubstituted aromatic group having 6 to 30 carbon atoms, or a substituted or unsubstituted alicyclic group having 4 to 30 carbon atoms, Y is a substituted or unsubstituted aromatic group having 6 to 30 carbon atoms including at least one aromatic group, or a substituted or unsubstituted alicyclic group having 4 to 30 carbon atoms including at least one ring, Z is a substituted or unsubstituted aromatic group having 6 to 30 carbon atoms including at least one aromatic group, or a substituted or unsubstituted alicyclic group having 4 to 30 carbon atoms including at least one ring, and m and n are positive integers.

2. In paragraph 1, A polyimide binder for a secondary battery negative electrode material, wherein the above m is 4 or more and the molar ratio of m and n is 1:1 to 5.

3. In paragraph 1, A polyimide binder for a secondary battery negative electrode material, wherein the above X is at least one selected from the following: , .

4. In paragraph 1, A polyimide binder for a secondary battery negative electrode material, wherein the above Y is at least one selected from the following: and 5. In paragraph 1, A polyimide binder for a secondary battery negative electrode material, wherein the above Z is at least one selected from the following: and 6. In paragraph 1, The above polyimide is a polyimide binder for secondary battery negative electrode materials, manufactured by the reaction of an acid anhydride, diamine, and carbonyl chloride.

7. In paragraph 5, A polyimide binder for a secondary battery negative electrode material, wherein the molar contents of the above acid anhydride and carbonyl chloride are 20 to 60 mol and 40 to 80 mol, respectively, with respect to 100 mol of diamine.

8. In paragraph 5, A polyimide binder for a secondary battery negative electrode material, wherein the acid anhydride is at least one selected from the following: and .

9. In paragraph 5, A polyimide binder for a secondary battery negative electrode material, wherein the above diamine is at least one selected from the following: and 10. In paragraph 5, A polyimide binder for a secondary battery negative electrode material, wherein the carbonyl chloride is at least one selected from the following: and 11. In paragraph 1, The above polyimide is a polyimide binder for secondary battery negative electrode materials that is soluble in water.

12. A negative electrode for a secondary battery comprising a polyimide binder for negative electrode material according to any one of claims 1 to 11.

13. A secondary battery including the negative electrode for a secondary battery of Article 12.

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