Silicon-based binder for negative electrode materials

Abstract

The present invention relates generally to blends of polyacrylic acid (PAA) and polyacrylamide (PAM) and their use as binders in negative electrodes of lithium ion batteries.

Description

[Technical Field]

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS This application claims priority to U.S. Provisional Patent Application No. 63 / 052924, filed July 16, 2020, and European Patent Application No. 20210786.8, filed November 30, 2020, the entire contents of which are incorporated herein by reference for all purposes.

[0002] The present invention relates generally to blends of polyacrylic acid (PAA) and polyacrylamide (PAM) and their use as binders in negative electrodes of lithium ion batteries. [Background technology]

[0003] Current lithium-ion batteries are limited in their storage of charge by the capacity of the anode. The overall picture is that the most direct route to creating next-generation energy storage systems is to significantly increase the storage capacity of lithium-ion batteries by incorporating silicon into graphite anodes. Silicon can reversibly store much more lithium than graphite, and small amounts are currently blended into anodes to significantly increase capacity. However, current binders only allow limited silicon loadings (up to 10 wt%) before battery life significantly degrades due to reduced charge cycle stability. Further capacity improvement is limited because silicon particles expand and contract significantly as large amounts of lithium are stored and released during charge and discharge. This creates mechanical stresses that lead to cracking and particle attrition, hindering the movement of ions within the cell, which in turn reduces battery performance over time.

[0004] Currently, there is a great deal of activity dedicated to the development of new binders for silicon-containing anodes that will enable greater energy density storage.

[0005] The binder, typically an organic polymer, acts as a binding matrix that maintains contact between the active material throughout the anode layer and the current collector onto which the anode is deposited during fabrication.

[0006] Many approaches are being pursued to develop next generation binders compatible with silicon anodes.

[0007] It is generally recognized that chemical functional groups that provide favorable surface interactions with both the active material and the current collector substrate are necessary. Furthermore, chemical compatibility with the liquid electrolyte and other additives is a prerequisite for any binder, regardless of the active material composition. One approach to overcoming the unique challenges associated with silicon is to create a self-healing mechanism within the binder matrix by incorporating weak bonding interactions that allow for a degree of reversibility. These unstable bonds can break under stress, but can reform upon relaxation without irreparable damage to the active material particles and the resulting electrode due to loss of interparticle contact and electrode inactivity.

[0008] Carboxymethyl cellulose (CMC) is a well-documented example of this, where hydrogen bonding occurs between pendant acid groups and silanol groups on the silicon surface.

[0009] There are several polycarboxylate binders and derivatives being pursued, including polyacrylic acid, polyamic acid, polyacrylamide, and other hydrogen-bonding structures.

[0010] Miranda, A. et al. (“A Comprehensive Study of Hydrolyzed Polyacrylamide as a Binder for Silicon Anodes” Appl. Mater. Interfaces, 2019, 11, 44090-44100) discloses the use of partially hydrolyzed polyacrylamide in the fabrication of composite silicon anodes with good adhesion, high strength, and high electrochemical storage capacity.

[0011] Despite current strategies to prevent the degradation of silicon-rich anodes, their effectiveness appears to be limited, and there has yet to be a clear breakthrough to reach the higher levels of silicon required to achieve meaningful progress in this field. Numerous disclosures exist of mixed binder systems that utilize intermolecular cooperative effects to enhance binder performance.

[0012] U.S. Pat. No. 6,399,246 (Eveready Battery Company Inc.) generally relates to water-soluble binders containing polyacrylamide and at least one copolymer selected from carboxylated styrene-butadiene copolymers and styrene-acrylate copolymers.

[0013] Novel binders based on polyacrylic acid (PAA) and carboxymethyl cellulose with styrene butadiene (CMC-SBR) have been investigated, however, they are still found to be brittle and create fracture points within the binder matrix itself.

[0014] It is also well documented that for polycarboxylates, particularly polyacrylic acid, there is an advantage to first converting them to their lithium salts by neutralization with a base such as lithium hydroxide, primarily to avoid trapping of lithium ions by free acid groups in the cell, which could reduce initial capacity.

[0015] Applicants have unexpectedly discovered that a combination of two materials in a single binder formulation, specifically a mixture of polyacrylamide (PAM) and polyacrylic acid metal salt (PAA salt), in a low-cost, environmentally friendly solvent such as water, can be used as a binder for electrodes, particularly for silicon-rich anodes, that exhibit high cycling and electrochemical stability. Summary of the Invention

[0016] The object of the present invention is to provide an aqueous electrode-forming composition [composition (C)] for use in the preparation of an electrode for an electrochemical device, comprising: a) a i ) at least one polyacrylamide (PAM) having a number average molecular weight (Mn) of up to 1,600,000 g / mol, and a ii ) at least one polyacrylic acid metal salt (PAA salt) A binder composition [binder (B)] comprising b) an electrode active material; c) an aqueous solvent; d) optionally at least one conductivity-imparting additive; and The aqueous electrode-forming composition [composition (C)] is characterized by comprising:

[0017] Another object of the present invention is to provide a method for producing an electrode [electrode (E)], comprising the steps of: (i) providing a metal substrate having at least one surface; (ii) providing composition (C) as defined above; (iii) applying the composition (C) prepared in step (ii) onto the at least one surface of the metal substrate prepared in step (i), thereby obtaining an assembly comprising a metal substrate coated with the composition (C) on at least one surface; (iv) drying the assembly obtained in step (iii); (v) subjecting the dried assembly obtained in step (iv) to a compression step to obtain the electrode (E) of the present invention; The method includes:

[0018] In a further aspect, the present invention relates to an electrode [electrode (E)] obtainable by the process of the present invention.

[0019] In yet another object, the present invention relates to an electrochemical device comprising at least one electrode (E) of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0020] In the context of the present invention, the term "weight percent" (wt%) indicates the content of a particular component in a mixture, calculated as the ratio between the weight of the component and the total weight of the mixture. When referring to the total solids content (TSC) of a liquid composition, weight percent (wt%) indicates the ratio between the weights of all non-volatile components in the liquid.

[0021] The term "electrochemical cell" is intended herein to mean an electrochemical cell comprising a positive electrode, a negative electrode and a liquid electrolyte, with a single or multi-layer separator attached to at least one surface of one of the electrodes.

[0022] Non-limiting examples of electrochemical cells include batteries, preferably secondary batteries, and electric double layer capacitors, among others.

[0023] For purposes of the present invention, "secondary battery" is intended to mean a rechargeable battery. Non-limiting examples of secondary batteries include alkaline or alkaline earth secondary batteries, among others.

[0024] As is known in the art, an electrode-forming composition is a composition, typically a fluid composition, in which solid components are dissolved or dispersed in a liquid, that can be applied to a metal substrate and then dried to form an electrode in which the metal substrate acts as a current collector. Electrode-forming compositions typically include at least an electrode active material and at least a binder.

[0025] The electrode-forming composition of the present invention [composition (C)] contains at least one polyacrylamide (PAM) that functions as a binder and at least one metal salt of polyacrylic acid (PAA salt).

[0026] The preparation of the electrode-forming composition involves the preparation of an aqueous binder composition which is then added with the powdered electrode material.

[0027] Binder (B) The binder composition [binder (B)] contains at least one polyacrylamide (PAM) and at least one metal salt of polyacrylic acid (PAA salt).

[0028] Without being bound by any particular theory, we believe that attractive interactions occur between the metal ions of the PAA salt and the amide functional groups of the PAM. The two polymers, polymer PAM and PAA salt, are linked through metal ion bridges between the carboxylate groups of the PAA and the amide groups of the PAM. This attractive ion-dipole interaction forms a copolymer network strong enough to hold the anode matrix together, yet dissociates under stress without damaging the active material. These dynamic bonds within this system provide a new type of self-healing mechanism that is particularly suited to lithium-ion battery applications.

[0029] Polyacrylamide (PAM) is a water-soluble polymer that is believed to improve the smoothness and uniformity of the binder mixture, thereby positively affecting the rheological properties of the binder mixture.

[0030] PAMs include any polymer or copolymer of acrylamide and methacrylamide-based monomers, including acrylamide, n-methylolacrylamide, n-butoxymethylacrylamide, methacrylamide, n-methylolmethacrylamide, and n-butoxymethylmethacrylamide. Useful monomers that can be used to form copolymers with acrylamide-based monomers include, for example, unsaturated carboxylic acid-based monomers.

[0031] In some embodiments, the PAM has a number average molecular weight (Mn) of at least 2,000 g / mol, preferably at least 10,000 g / mol, and more preferably at least 150,000 g / mol. In some embodiments, the PAM has a number average molecular weight (Mn) of up to 1,600,000 g / mol.

[0032] Methods for preparing suitable PAMs are well known, and PAMs of various number average molecular weights are commercially available.

[0033] Polyacrylic acid (PAA) includes any polymer or copolymer of acrylic acid or methacrylic acid or derivatives thereof, where at least about 50 mol%, at least about 60 mol%, at least about 70 mol%, at least about 80 mol%, or at least about 90 mol% of the copolymer is made using acrylic acid or methacrylic acid. Useful monomers that can be used to form these copolymers include, for example, alkyl esters of acrylic or methacrylic acid having alkyl groups having 1 to 12 carbon atoms (branched or unbranched), acrylonitrile, hydroxyl (meth)alkyl acrylates, and the like.

[0034] The homopolymers and copolymers of acrylic acid and methacrylic acid useful in the present invention may have a number average molecular weight (Mn) of at least 2,000 g / mol, preferably at least 90,000 g / mol, and more preferably at least 250,000 g / mol. In some embodiments, the PAA salts have a number average molecular weight (Mn) of at most 4,000,000 g / mol, preferably at most 1,250,000 g / mol, and more preferably at most 450,000 g / mol.

[0035] Methods for preparing suitable PAA salts are well known in the art.

[0036] The PAA salts used in the present invention can be prepared from the corresponding polyacrylic acid (PAA) by neutralizing the acid groups with a salt containing a monovalent cation, preferably an alkali metal salt [salt (S)], in a suitable solvent.

[0037] The binder (B) may comprise one or more PAA salts as defined above.

[0038] The salt (S) can be any salt capable of neutralizing an acid group. In some embodiments, the salt (S) is a lithium salt selected from the group consisting of lithium carbonate, lithium hydroxide, lithium bicarbonate, and combinations thereof, preferably lithium carbonate. In some embodiments, the lithium salt does not contain lithium hydroxide.

[0039] The solvent used in the step of salting PAA to obtain a PAA salt can be any solvent that can dissolve the salt (S) and the resulting PAA salt. Preferably, the solvent is selected from at least one of water, NMP, and aqueous solvents such as alcohols, for example, methanol, isopropanol, and ethanol. More preferably, the solvent is an aqueous solvent. Even more preferably, the solvent is water.

[0040] Preferably, the content of the salt (S) in the solvent is in the range of 0.5 to 10% by weight, preferably 1 to 5% by weight, based on the total weight of the solvent and the salt (S).

[0041] In some embodiments where the salt (S) is a lithium salt, the concentration of the lithium salt in the solvent provides at least 0.25, 0.5, 1, 1.5, 2, 2.5, 3, 4 equivalents of lithium relative to the acid groups, hi some embodiments, the concentration of the lithium salt in the solvent provides at most 5, preferably at most 4 equivalents of lithium relative to the acid groups.

[0042] The content of the PAA salt in the solution after being converted into a salt form is in the range of 0.5 to 40% by weight, preferably 5 to 30% by weight, and more preferably 10 to 30% by weight, based on the total weight of the solvent and the PAA salt.

[0043] After being converted into a salt form, the PAA salt can be isolated from the solution as a solid and optionally stored for later use. The solid PAA salt can also be dissolved (or redissolved) in water to prepare the electrode-forming composition described below. However, preferably, the solution containing the PAA salt after being converted into a salt form is an aqueous solution that can be used directly, optionally with further dilution with water, in preparing the binder composition described below.

[0044] In a preferred embodiment, the lithium salt of PAA (Li-PAA) was prepared by adding an amount of LiOH sufficient to completely neutralize an aqueous solution containing approximately 10 wt% PAA. The resulting solution had a pH in the range of 6.5-7.5 and contained approximately 10 wt% Li-PAA.

[0045] The PAA salt / PAM binder [binder (B)] can be suitably prepared as a solution in an aqueous solvent by mixing various amounts of the PAA salt, either as a solid powder or as a solution, obtained as described above with PAM, either as a solid powder or as a solution in an aqueous solvent.

[0046] The binders of the present invention are advantageously used in aqueous binder solutions comprising an aqueous solvent, preferably water, at least one PAM, and at least one PAA salt. The term "solution" as used herein is intended to encompass not only true solutions in which the polymer is uniformly dispersed at the molecular level, but also colloidal solutions.

[0047] The binder (B) in the form of an aqueous solution as detailed above contains the PAA salt / PAM mixture in an amount ranging from 1 to 30 parts by weight, particularly from 5 to 10 parts by weight, in 100 parts by weight of the aqueous solvent.

[0048] The preferred amount of PAM to PAA salt in binder (B) is from about 3:1 to about 1:3, more preferably from about 2:1 to about 1:2, on a dry weight basis.

[0049] Electrode forming composition [composition (C)] The amount of the binder (B) that can be used in the electrode-forming composition (C) is affected by various factors. One such factor is the surface area and amount of the electroactive material, as well as the surface area and amount of the conductivity-imparting additive added to the electrode-forming composition. These factors are considered important because the binder particles provide a bridge between the conductive material particles and the electroconductive material particles and keep them in contact.

[0050] The electrode-forming composition [composition (C)] of the present invention contains one or more electrode active materials. For the purposes of the present invention, the term "electrode active material" is intended to mean a compound that incorporates or inserts alkali or alkaline earth metal ions into its structure during the charging and discharging stages of an electrochemical device and can then substantially release them. The electrode active material preferably can incorporate or insert lithium ions and release them.

[0051] The properties of the electrode active material in the electrode-forming composition (C) of the present invention differ depending on whether the composition is used in the manufacture of a negative electrode (anode) or a positive electrode (cathode).

[0052] When forming a positive electrode for a lithium-ion secondary battery, the electrode active material can include a composite metal chalcogenide of the formula LiMQ2 (where M is at least one metal selected from transition metals such as Co, Ni, Fe, Mn, Cr, and V, and Q is a chalcogen such as O or S). Among these, it is preferable to use a lithium-based composite metal oxide of the formula LiMO2 (where M is the same as defined above). Preferred examples of these include LiCoO2, LiNiO2, LiNi x Co 1-x O2 (0 < x < 1) and spinel-structured LiMn2O4.

[0053] As an alternative form, when forming a positive electrode for a lithium-ion secondary battery, furthermore, the electrode active material has the formula M1M2(JO4) f E 1-f(wherein M1 is lithium and may be partially substituted by another alkali metal corresponding to less than 20% of the M1 metal; M2 is a transition metal having an oxidation level of +2 selected from Fe, Mn, Ni or a mixture thereof and may be partially substituted by one or more additional metals having an oxidation level of +1 to +5, inclusive, corresponding to less than 35% of the M2 metal; JO4 is any oxyanion; J is any of P, S, V, Si, Nb, Mo or a combination thereof; E is a fluoride, hydroxide or chloride anion; and f is the mole fraction of the JO4 oxyanion, typically comprised between 0.75 and 1.

[0054] M1M2(JO4) as defined above f E 1-f The electroactive material is preferably phosphate-based and may have an ordered or modified olivine structure.

[0055] More preferably, the electrode active material when forming a positive electrode is a compound represented by the formula Li 3-x M' y M'' 2-y (JO4)3, where 0≦x≦3, 0≦y≦2, M′ and M″ are the same or different metals, at least one of which is a transition metal, JO4 is preferably PO4 which may be partially substituted with another oxyanion, and J is any of S, V, Si, Nb, Mo, or a combination thereof. More preferably, the electrode active material has the formula Li(Fe x Mn 1-x )PO4 (where 0≦x≦1, and x is preferably 1), i.e., lithium iron phosphate of formula LiFePO4.

[0056] When forming a negative electrode for a lithium ion secondary battery, the electrode active material may preferably include one or more carbon-based materials and / or one or more silicon-based materials.

[0057] In some embodiments, the carbon-based material may be selected from graphite, such as natural or artificial graphite, graphene, or carbon black. These materials may be used alone or as a mixture of two or more thereof.

[0058] The carbon-based material is preferably graphite.

[0059] The silicon-based compound can be one or more selected from the group consisting of chlorosilanes, alkoxysilanes, aminosilanes, fluoroalkylsilanes, silicon, silicon chloride, silicon carbide, and silicon oxide.

[0060] More specifically, the silicon-based compound may be silicon oxide or silicon carbide.

[0061] When present in the electrode active material, the silicon-based compound is included in an amount ranging from 1 to 60% by weight, preferably from 5 to 30% by weight, based on the total weight of the electroactive compound.

[0062] One or more optional conductivity-imparting additives may be added to improve the conductivity of the resulting electrodes made from the compositions of the present invention. Conductive agents for batteries are known in the art.

[0063] Examples of these may include: carbon-based materials such as carbon black, graphite fine powder, carbon nanotubes, graphene, or fibers, or fine powders or fibers of metals such as nickel or aluminum. The optional conductive agent is preferably carbon black. Carbon black is available, for example, under the brand names Super P® or Ketjenblack®.

[0064] If present, the conductive agent is different from the carbon-based material described above.

[0065] The amount of the optional conductive agent is preferably 0 to 30 wt % of the total solids in the electrode-forming composition. In particular, for cathode-forming compositions, the optional conductive agent is typically 0 to 10 wt %, more preferably 0 to 5 wt %, of the total solids in the composition.

[0066] For anode-forming compositions that do not include a silicon-based electroactive compound, the optional conductive agent is typically present in an amount of from 0% to 5% by weight, more preferably from 0% to 2% by weight, of the total solids in the composition, while for anode-forming compositions that include a silicon-based electroactive compound, it has been found beneficial to incorporate a larger amount of optional conductive agent, typically from 0.5 to 30% by weight, of the total solids in the composition.

[0067] The total solids content (TSC) of the composition (C) of the present invention is typically comprised between 15 and 70% by weight, preferably between 40 and 60% by weight, based on the total weight of the composition (C). The total solids content of the composition (C) is understood to be the sum of all nonvolatile components thereof, including in particular the PAA salt, the PAM, the electrode active material, and any solid nonvolatile additional additives.

[0068] When the aqueous binder solution is prepared separately and then combined with the electrode active material, optional conductive material, and other additives to prepare composition (C), a sufficient amount of water is used to form a stable solution. The amount of water used can range from the minimum amount required to form a stable solution to the amount required to achieve the desired total solids content in the electrode mixture after the electrode active material, optional conductive material, and other solid additives have been added.

[0069] Electrode (E) The electrode-forming composition (C) of the present invention can be used in a process for producing an electrode [electrode (E)], and the process comprises the steps of: (i) providing a metal substrate having at least one surface; (ii) providing an electrode-forming composition [composition (C)] as defined above; (iii) applying the composition (C) prepared in step (ii) onto the at least one surface of the metal substrate prepared in step (i), thereby obtaining an assembly including a metal substrate coated with the composition (C) on at least one surface; (iv) drying the assembly obtained in step (iii); (v) carrying out a compression step on the dried assembly obtained in step (iv) to obtain the electrode (E) of the present invention; Includes.

[0070] The metal substrate is generally a foil, mesh or net made of a metal such as copper, aluminum, iron, stainless steel, nickel, titanium or silver.

[0071] Under step (iii) of the process of the present invention, the electrode-forming composition (C) is typically applied onto at least one surface of the metal substrate by any suitable procedure, such as casting, printing, and roll coating.

[0072] Optionally, step (iii) may be repeated, typically one or more times, by applying the electrode-forming composition (C) prepared in step (ii) onto the assembly prepared in step (iv).

[0073] In step (iv) of the process of the present invention, drying can be carried out either under atmospheric pressure or under vacuum. Alternatively, drying can be carried out under a modified atmosphere, such as under an inert gas, typically specifically devoid of moisture (water vapor content less than 0.001% v / v).

[0074] The drying temperature will be selected to achieve evaporative removal of the aqueous medium from the electrode (E) of the present invention.

[0075] In step (v), the dried assembly obtained in step (iv) can be subjected to a compression step, such as a calendering process, to achieve the target porosity and density of the electrode (E) of the present invention.

[0076] Preferably, the dried assembly obtained in step (iv) is hot pressed, the temperature during the pressing step being comprised between 25°C and 130°C, preferably about 60°C.

[0077] The preferred target density of the electrode (E) is comprised between 1.4 and 2 g / cc, preferably 1.55 g / cc or more. The density of the electrode (E) is calculated as the sum of the products of the densities of the electrode's constituents multiplied by their mass ratio in the electrode formulation.

[0078] In a further aspect, the present invention relates to an electrode [electrode (E)] obtainable by the process of the present invention.

[0079] Therefore, the present invention provides a metal substrate having at least one surface; - at least one layer adhered directly onto at least one surface of said metal substrate; Electrode (E), wherein said at least one layer comprises: a) a i ) at least one polyacrylamide (PAM), and a ii ) at least one polyacrylic acid metal salt (PAA salt); A binder composition [binder (B)] comprising b) an electrode active material; c) an aqueous solvent; d) optionally at least one conductivity-imparting additive; and The present invention relates to an electrode (E) comprising a composition comprising:

[0080] The composition directly adhered onto at least one surface of the metal substrate corresponds to the electrode-forming composition (C) of the present invention from which the aqueous medium has been at least partially removed during the electrode manufacturing process, for example in step (iv) (drying) and / or in the compacting step (v). Accordingly, all preferred embodiments described with respect to the electrode-forming composition (C) of the present invention are also applicable to the composition directly adhered onto at least one surface of the metal substrate in the electrode of the present invention, except for the aqueous medium that is removed during the manufacturing process.

[0081] In a preferred embodiment of the present invention, the electrode (E) is a negative electrode. More preferably, the negative electrode contains a silicon-based electrode active material.

[0082] In a further preferred embodiment, the present invention provides a method for manufacturing a semiconductor device comprising, based on the total weight of the electrode: 0.5 to 15% by weight, preferably 0.5 to 10% by weight, of a binder (B); 45 to 95% by weight, preferably 70 to 90% by weight, of a carbonaceous material; 3 to 50% by weight, preferably 10 to 50% by weight, of silicon-based materials; 0 to 5 wt. %, preferably 0.5 to 2.5 wt. %, more preferably about 1 wt. % of a conductivity-imparting additive; The present invention relates to a negative electrode comprising:

[0083] The electrode (E) of the present invention is particularly suitable for use in electrochemical devices, in particular in secondary batteries.

[0084] The secondary battery of the present invention is preferably an alkaline secondary battery or an alkaline earth secondary battery.

[0085] The secondary battery of the present invention is more preferably a lithium ion secondary battery.

[0086] Electrochemical devices according to the present invention can be fabricated by standard methods known to those skilled in the art.

[0087] To the extent that the disclosure of any patents, patent applications, and publications incorporated herein by reference contradicts the statements of this application to the extent that the term may be unclear, the statements of this application shall control.

[0088] The invention will now be described with reference to the following examples, the purposes of which are merely illustrative and are not intended to limit the scope of the invention.

[0089] Experimental section Materials and Methods Polyacrylic acid (PAA) available from Sigma-Aldrich (Mn: 250000); Polyacrylamide (PAM) available from Sigma-Aldrich (Mn: 150000); lithium hydroxide available from Sigma-Aldrich; silicon oxide, KSC-1064, commercially available from Shin-Etsu Chemical Co., Ltd., with a theoretical capacity of approximately 2100 mAh / g; graphite, including oxalatoborate of ACTILION2 from Imerys SA; carbon black available as SC45 from Imerys SA; carboxymethyl cellulose (CMC), available as MAC 500LC from Nippon Paper; a styrene butadiene rubber (SBR) suspension (40 wt. % aqueous solution) available from Nippon Zeon Co., Ltd. as Zeon® BM-480B; Solvionic electrolyte mixture of 1 M LiPF6 in EC / DMC 1 / 1 v / v containing 2 wt% VC and 10 wt% F1EC.

[0090] Basic procedure for preparing aqueous solutions of Li-PAA 35 wt% PAA (71.5 grams) was diluted with deionized water (178.5 grams) and mixed in a beaker using a magnetic stir plate to give 250 grams, to which 10 wt% LiOH (5 grams) was slowly added to bring the final pH to approximately 6.5.

[0091] General procedure for preparing Li-PAA / PAM blend solutions PAM (10 grams) was added to deionized water (90 grams), and the suspension was stirred and heated until completely dissolved to obtain a 10 wt% solution. The 10 wt% PAM solution (80 grams) was combined with the 10 wt% Li-PAA solution (40 grams) to obtain the final binder solution for electrode fabrication.

[0092] Preparation of electrode-forming composition and negative electrode The electrode-forming compositions and negative electrodes were prepared as detailed below using the following equipment: Mechanical mixers: Planetary mixers (Speedmixers) and Dispermat® series high shear mechanical mixers with flat PTFE lightweight dispersing impellers; Film Coater / Doctor Blade: Elcometer® 4340 Electric / Automatic Film Applicator; Vacuum oven: BINDER APT line VD 53 vacuum oven; Roll press: Precision 4-inch hot rolling press / calendering up to 100°C.

[0093] Example 1: An aqueous composition was prepared by mixing 28.0 g of a 10 wt % aqueous solution of Li-PAA / PAM, 18.8 g of deionized water, 10.53 g of silicon oxide, 42.11 g of graphite, and 0.56 g of carbon black.

[0094] The mixture was homogenized by gentle stirring with a planetary mixer for 10 minutes and then mixed again by gentle stirring for 1 hour.

[0095] After mixing for about 1 hour, the shear is reduced and the slurry is mixed again by stirring slowly for 1 hour.

[0096] The binder composition thus obtained was cast onto a copper foil with a thickness of 18.5 μm using a doctor blade, and the coating layer was dried in an oven at a temperature of 90°C for about 70 minutes to obtain a negative electrode. The thickness of the dried coating layer was about 70 μm. The electrode was then hot-pressed in a roll press at 60°C to obtain a target density of 1.6 g / cc. The resulting negative electrode had the following composition: 18.8 wt% silicon oxide, 75.2 wt% graphite, 5 wt% Li-PAA / PAM, and 1 wt% carbon black. Electrode E1 was thus obtained.

[0097] Comparative Example: Anode containing only polyacrylic acid (PAA) An aqueous composition was prepared by mixing 27.5 g of a 10 wt % aqueous solution of Li-PAA, 20.25 g of deionized water, 10.34 g of silicon oxide, 41.36 g of graphite, and 0.55 g of carbon black.

[0098] The mixture was homogenized by gentle stirring with a planetary mixer for 10 minutes and then mixed again by gentle stirring for 1 hour.

[0099] After mixing for about 1 hour, the shear is reduced and the slurry is mixed again by stirring slowly for 1 hour.

[0100] At the end of the stirring, the slurry had severe precipitation, and it was not possible to obtain an electrode CE1 having the following composition: 18.8 wt % silicon oxide, 75.2 wt % graphite, 5 wt % Li-PAA, and 1 wt % carbon black.

[0101] Comparative Example: Anode containing polyacrylic acid (PAA) and carboxymethyl cellulose (CMC) The aqueous composition was prepared by mixing 27.0 g of a 2 wt % CMC aqueous solution, 21.6 g of a 10 wt % Li-PAA aqueous solution, 0.1 g of deionized water, 10.15 g of silicon oxide, 40.61 g of graphite, and 0.56 g of carbon black.

[0102] The mixture was homogenized by gentle stirring with a planetary mixer for 10 minutes, and then mixed again by gentle stirring for 1 hour. After approximately 1 hour of mixing, the shear force was reduced and the slurry was mixed again by slow stirring for 1 hour.

[0103] The binder composition thus obtained was cast onto a copper foil with a thickness of 18.5 μm using a doctor blade, and the coating layer was dried in an oven at a temperature of 90°C for about 70 minutes to obtain a negative electrode. The thickness of the dried coating layer was about 55 μm. The electrode was then hot-pressed in a roll press at 60°C to obtain a target density of 1.6 g / cc. The resulting negative electrode had the following composition: 18.8 wt% silicon oxide, 75.2 wt% graphite, 4 wt% PAA, 1 wt% CMC, and 1 wt% carbon black. Electrode CE2 was thus obtained.

[0104] Comparative Example: Anode containing styrene butadiene rubber (SBR) and carboxymethyl cellulose (CMC) An aqueous composition was prepared by mixing 35.0 g of a 2 wt % aqueous solution of CMC, 21.41 g of deionized water, 7.90 g of silicon oxide, 31.58 g of graphite, and 0.42 g of carbon black.

[0105] The mixture was homogenized by gentle stirring with a planetary mixer for 10 minutes and then mixed again by gentle stirring for 1 hour.

[0106] After mixing for approximately 1 hour, 3.69 g of SBR suspension was added to the composition and mixed again for 1 hour on low agitation.

[0107] The binder composition thus obtained was cast onto a copper foil with a thickness of 18.5 μm using a doctor blade, and the coating layer was dried in an oven at a temperature of 90°C for about 70 minutes to obtain a negative electrode. The thickness of the dried coating layer was about 62 μm. The electrode was then hot-pressed in a roll press at 60°C to obtain a target density of 1.6 g / cc. The resulting negative electrode had the following composition: 18.8 wt% silicon oxide, 75.2 wt% graphite, 3 wt% SBR, 2% CMC, and 1 wt% carbon black. Electrode CE3 was thus obtained.

[0108] Battery manufacturing Coin cells (CR2032 type, 20 mm diameter) were fabricated in a glove box under Ar gas atmosphere by stamping small disks of the negative electrodes prepared according to Examples 1, CE1, CE2, and CE3 together with equilibrated NMC positive electrode disks purchased from CUSTOMCELLS. The electrolyte used to fabricate the coin cells was a 1 M LiPF6 mixture in EC / DMC 1 / 1 v / v containing 2 wt% VC and 10 wt% F1EC from Solvionic. Polyethylene separators (commercially available from Tonen Chemical Co., Ltd.) were used as received.

[0109] Capacity retention test Cycling stability of full cells at a C-rate of 1C (open capacity measured three times and shown in Table 1 below):

[0110] [Table 1]

Claims

1. An aqueous electrode-forming composition [composition (C)] for use in fabricating an electrode for an electrochemical device, comprising: a) a ｉ ) at least one polyacrylamide (PAM) having a number average molecular weight (Mn) of up to 1,600,000 g / mol; and a ｉｉ ) at least one polyacrylic acid metal salt (PAA salt); A binder composition [binder (B)] comprising: b) an electrode active material; and c) an aqueous solvent; An aqueous electrode-forming composition [composition (C)] comprising:

2. d) at least one conductivity-imparting additive The composition of claim 1 further comprising:

3. The composition according to claim 1, wherein the total solid content of the composition (C) is 15 to 70% by weight, based on the total weight of the composition (C).

4. 3. The composition of claim 1 or 2, wherein the amount of PAM to PAA salt is from 3:1 to 1:3 on a dry weight basis.

5. The composition according to any one of claims 1 to 4, wherein the electrode active material comprises one or more carbon-based materials and / or one or more silicon-based materials.

6. 6. The composition of claim 5, wherein the carbon-based material is selected from at least one of graphite and graphene, and the silicon-based material is selected from at least one of silicon, alkoxysilanes, aminosilanes, silicon carbide, and silicon oxide.

7. The composition of claim 2 wherein the conductivity-imparting additive is carbon black.

8. The composition of any one of claims 1 to 7, wherein the at least one polyacrylic acid metal salt (PAA salt) is a lithium salt of PAA (Li-PAA).

9. A method for producing an electrode [electrode (E)], comprising the steps of: (i) providing a metal substrate having at least one surface; (ii) preparing an electrode-forming composition [composition (C)] according to any one of claims 1 to 8; (iii) applying the composition (C) prepared in step (ii) onto the at least one surface of the metal substrate prepared in step (i), thereby obtaining an assembly comprising a metal substrate coated on at least one surface with the composition (C); (iv) drying the assembly obtained in step (iii); (v) subjecting the dried assembly obtained in step (iv) to a compression step; A method comprising:

10. The electrode has, based on the total weight of the electrode, 0.5 to 15% by weight of a binder (B); 45 to 95% by weight of a carbon-based material; 3 to 50% by weight of a silicon-based material; 0 to 5 wt. % of a conductivity-imparting additive; 10. The method of claim 9, comprising:

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