Electrode precursor composition

Abstract

Disclosed is an electrode precursor composition suitable for preparing a gel electrode, the composition comprising an organic solvent, an alkali metal salt, and two or more polymers including at least an electrically insulating polymer and an electrically conductive polymer, where the electrically conductive polymer is present at a smaller volume fraction than the electrically insulating polymer. The conductive polymer may be present in the electrode precursor composition in an amount of between 1 and 20 vol% based on the total volume of the electrode precursor composition. The conductive polymer may be present in the electrode precursor composition in an amount of up to 8% by volume based on the total volume of the electrode precursor composition. The conductive polymer may be redox active.

Description

Technical Field

[0001] The present invention relates to an electrode precursor composition for an alkali metal ion secondary battery cell, an electrode, a battery cell and an energy storage device made from the precursor composition, and a method for preparing an electrode for an alkali metal ion secondary battery cell. Background Art

[0002] Lithium-ion secondary battery cells are the leading battery technology used today in applications ranging from small personal devices to electric vehicles. Lithium-ion batteries are favored for their high energy density and long cycle life. They contain multiple lithium-ion secondary battery cells.

[0003] Conventional lithium-ion battery components such as electrodes are made by a solvent casting process that uses sacrificial solvents. This is an energy-expensive step, so there is a need for processes that avoid the use of sacrificial solvents.

[0004] One way to avoid the use of sacrificial solvents is to prepare gel electrodes. These electrodes can be formed from a composition that is prepared by mixing the necessary components, such as an electrochemically active material, a polymer (usually an electrically insulating polymer), and a solvent or liquid electrolyte, and then processing the composition, such as extrusion, to form an electrode.

[0005] The use of gels in the preparation of electrodes using such processing must balance at least two opposing requirements. On the one hand, the electrode must have a sufficiently high electronic conductivity to be practical to use. To this end, a higher solids content (higher content of electrochemically active material) is generally required to provide the material with a useful electronic conductivity. On the other hand, the gel must be soft enough to be handled to form an electrode. To this end, a lower solids content (lower content of electrochemically active material) is ideal so that the material exhibits sufficient fluidity to be handleable.

[0006] There is a need for electrode precursor compositions that meet the above criteria. Summary of the invention

[0007] In general, the inventors propose to solve the above problems by utilizing a conductive polymer as part of the electrode precursor composition. In particular, the inventors generally suggest replacing a portion of the conventional electrically insulating polymer with a conductive polymer. Generally, electrically insulating polymers are considered to have some structural functions and are generally expandable. In the present invention, the volume fraction of the conductive polymer should be less than the volume fraction of the electrically insulating polymer.

[0008] In this way, the inventors believe that the electronic conductivity of the gel electrode can be increased compared to a corresponding gel electrode without a conductive polymer. For example, if the electrode precursor composition requires a reduced amount of electrochemically active material for processability, then the presence of the conductive polymer can at least partially compensate for the expected corresponding decrease in electronic conductivity. Similarly, if the electrode precursor composition does not require a reduced amount of electrochemically active material for processability, then the use of a conductive polymer can increase capacity and result in an electrode having a higher electronic conductivity than expected for a gel electrode without a conductive polymer. The present invention is based on this discovery.

[0009] The use of conductive polymers in electrodes is known, for example, as discussed by Poizot et al. (Chem. Rev. 2020, 120, 14, 6490-6557). For example, Duc et al. (ACS Appl. Polym. Mater. 2020, 2, 6, 2366-2379) disclose a long-range electronic conductor based on PEO and PEDOT:PSS. The authors report that extrusion of these blends introduces phase separation phenomena, requiring acidic post-treatment to restore electronic conductivity. US 9,722,249 B2 and DE 102012022976 A1 disclose a composition comprising a complex of polythiophene and a polyanion, at least one lithium-containing compound and at least one solvent, wherein based on 1g of polythiophene, the composition comprises less than 1g of a material comprising elemental carbon, or does not comprise a material comprising elemental carbon at all. JP 2004-158286 A discloses an electrode comprising PEDOT and PVDF as a binder produced by molding. JP 2011-100594 A discloses a composition comprising: a conductive polymer formed by polymerizing ethylenedioxythiophene or a derivative in the presence of at least one polymer sulfonic acid selected from polystyrene sulfonic acid, sulfonated polyester and phenolsulfonic acid novolac resin, the novolac resin containing the polymer sulfonic acid as a dopant; and an organic solvent and a carbonaceous conductive material, and an electrode mixture composition further comprising a binder and an electrode active material.

[0010] However, these documents do not describe the concept of increasing the electronic conductivity of a gel electrode by using a conductive polymer that is present in the composition at a volume fraction less than that of the electrically insulating polymer. The present inventors used a conductive polymer to generate high electronic conductivity throughout the medium used to prepare the gel electrode, and in this way, the electrode can be prepared directly from the electrode precursor composition.

[0011] Therefore, the overall proposal of the present invention is to provide a processable gel electrode precursor composition comprising a conductive polymer, an electrically insulating polymer, an alkali metal salt and an organic solvent. The composition can then be combined with an electrochemically active material and a conductive additive before further processing to form an electrode. Using this general process, the inventors have found that the electrode precursor composition is highly processable while also forming an electrode with sufficient electronic conductivity for practical use. The electrically insulating polymer and the conductive polymer can provide sufficient conductivity for the electrode, and in this case, a reduced amount of conductive carbon-based additive can be advantageously used. Therefore, with the same degree of processability, the loading of the electrochemically active material can be increased.

[0012] The first aspect of the present invention relates to an electrode precursor composition suitable for preparing a gel electrode, the composition comprising an organic solvent, an alkali metal salt and two or more polymers, the two or more polymers comprising at least an electrically insulating polymer and a conductive polymer, wherein the conductive polymer is present in a smaller volume fraction than the electrically insulating polymer.

[0013] The resulting electrode precursor composition generally comprises a polymer gel matrix phase. As such, the electrode precursor composition generally has gel-like properties and can be processed into a thin film electrode.

[0014] According to a second aspect, the present invention relates to a method for preparing an electrode for an alkali metal ion secondary battery cell, the method comprising:

[0015] A providing step comprises providing an electrode precursor composition according to the first aspect; and

[0016] The processing step includes processing the electrode precursor composition to form an electrode.

[0017] Further aspects relate to electrodes for alkali metal ion secondary battery cells prepared from the electrode precursor composition or method according to the invention, electrochemical secondary battery cells such as alkali metal ion secondary battery cells comprising electrodes according to the invention, electrochemical energy storage devices comprising electrochemical battery cells according to the invention, and the use of conductive polymers in methods for preparing electrodes for alkali metal ion secondary battery cells using a high temperature processing step. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 Schematic diagrams of theoretical electrodes with (a), (b) nearly ideal filling of electrochemically active materials and (c), (d) non-ideal filling of electrochemically active materials. DETAILED DESCRIPTION

[0019] The preferred and / or optional features of the present invention will now be described. Unless the context otherwise requires, any aspect of the present invention may be combined with any other aspect of the present invention. Unless the context otherwise requires, any preferred and / or optional features of any aspect may be combined with any aspect of the present invention individually or in combination.

[0020] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which the present disclosure belongs. Methods and materials for use in the present disclosure are described herein; other suitable methods and materials known in the art may also be used. The materials, methods, and examples are illustrative only and not restrictive. All publications, patent applications, patents, and other references mentioned herein are incorporated herein by reference in their entirety. In the event of a conflict, the present specification (including definitions) shall prevail.

[0021] The methods described herein generally employ typical laboratory ambient temperature, usually between 20 and 30°C, preferably about 25°C, at atmospheric pressure, unless different conditions are defined herein or are more general for, e.g., a particular apparatus.

[0022] The present invention generally describes the use of conductive polymers in electrode precursor compositions, and such electrode precursor compositions are particularly suitable for preparing electrodes using processing steps including one or more of extrusion and thermal treatment. Conductive polymers, also known as intrinsically conductive polymers, are organic polymers that conduct electricity. Typically, these polymers have conjugated double bonds, which allow electrons to flow through the polymer backbone. Depending on the properties of the conductive polymer, dopants can be used to achieve practical and useful conductivity.

[0023] Useful conductivity of the conductive polymers for use in the present invention is at least 0.01 S / cm, preferably higher, such as at least 0.1 S / cm, at least 0.5 S / cm, at least 1.0 S / cm or at least 2 S / cm.

[0024] Conductivity testers are available and can be used to measure the conductivity of the conductive polymers used in the present invention. An exemplary method of measuring conductivity includes applying a sample to a substrate and using a conductivity probe attached to the conductivity tester. During operation, the conductivity tester will apply a small current to the pins of the conductivity probe and calculate a resistance correction factor based on the parameters entered by the user. An example of a suitable conductivity tester is the Loresta-GP MCP-T610.

[0025] It should be understood that the content of the conductive polymer in the electrode precursor composition should be sufficient to achieve the desired increase in electronic conductivity. Therefore, in some embodiments, the conductive polymer is present in the electrode precursor composition in an amount of at least 1 volume %, such as at least 2 volume %, at least 3 volume %, or at least 5 volume %, based on the total volume of the electrode precursor composition.

[0026] In addition, the conductive polymer is present in the electrode precursor composition in a smaller volume fraction than the electrically insulating polymer. Thus, in some embodiments, the conductive polymer is present in the electrode precursor composition in an amount up to 20 volume %, such as up to 18 volume %, up to 15 volume %, up to 10 volume %, or up to 8 volume %, based on the total volume of the electrode precursor composition.

[0027] Therefore, in some embodiments, the conductive polymer is present in the electrode precursor composition in an amount between 1 and 20 volume %, based on the total volume of the electrode precursor composition. Other combinations of the above values ​​can be combined to form a suitable range, such as between 2 and 18 volume %, between 2 and 10 volume %, or between 5 and 8 volume %.

[0028] Note that the total volume % of all ingredients in the electrode precursor composition is 100 volume %.

[0029] In a particularly advantageous embodiment, the conductive polymer is also redox-active. Redox-active polymers are polymers that are able to undergo reversible oxidation and reduction processes. They therefore represent a particularly useful subclass of conductive polymers because they have the additional ability to store charge.

[0030] By using a redox-active polymer, the inventors believe that the energy density of the electrode can be increased compared to a corresponding electrode without the redox-active polymer. For example, if the electrode precursor composition requires a reduced amount of electrochemically active material for processability, then the presence of the redox-active polymer can at least partially compensate for the expected corresponding decrease in energy density. Similarly, if the electrode precursor composition does not require a reduced amount of electrochemically active material for processability, then the use of a redox-active polymer can increase capacity and result in an electrode having a higher electronic conductivity than expected for an electrode without the redox-active polymer.

[0031] In this way, a compensation or improvement of the energy density of the electrode and a simultaneous improvement of the processability are achieved using conductive and redox-active polymers.

[0032] This principle is Figure 1 , where (a) shows a nearly ideal electrode with nearly complete filling of electrochemically active particles.

[0033] Theoretically, this has >73% solids filling (close to ideal), with about 68% volume of electrochemically active material (black circles), with the intervening space filled with gel (white). This can result in about 210 mAhg -1 Active material capacity, and about 183mAhg -1 The same electrode as (a) is shown in (b), but the redox-active conductive polymer (grey) is contained in the gel in the pores, which can be represented by, for example, PEDOT. When other values ​​remain unchanged, the electrode capacity can be increased to 186 mAhg -1 .

[0034] A similar trend can be seen at lower filling efficiencies. Figure 1 (c) shows a non-ideal electrode, such as that more typically achieved by an extrusion process. This electrode has <73% solid filling and incomplete filling of electrochemically active particles (black circles) of about 63% volume, with the intervening spaces filled with gel (white). This can result in a charge of about 210 mAhg -1 Active material capacity and 177mAhg -1 The same electrode as (c) is shown in (d), but with a redox-active conductive polymer such as PEDOT (grey) in the pores. When other values ​​remain unchanged, the electrode capacity can be increased to 181 mAhg -1 . It can therefore be seen that replacing some of the gel polymer with a redox-active polymer can compensate to some extent for the loss of volumetric capacity and provide increased electronic conductivity. As a result, higher energies can be achieved. This is particularly important for non-ideal examples, which already have lower energy densities and present greater challenges in ensuring long-range electronic conductivity.

[0035] In each of (a) to (d), other components such as conductive additives and electrically insulating polymers are not shown.

[0036] At the cathode, charge is stored by anion insertion. That is, compensation of energy density is achieved by anion doping reactions. The skilled person will be familiar with electrochemical storage mechanisms using redox-active organics; in this regard, further reference is made to Figure 9 and Table 1 of Poizot et al. (Chem. Rev. 2020, 120, 14, 6490-6557). Figure 9a of Poizot et al. shows an example of anion compensation for a p-type system, where a polymer containing conjugated double bonds (shown as ) can be used with anion A - Reversibly doped. The process is shown as two reversible doping steps (n=2). Each doping step involves the polymer losing one electron.

[0037] Thus, in embodiments using a redox-active polymer that undergoes anion doping reactions, the gel electrode can include up to 8 vol% of the redox-active polymer, such as up to 7 vol%, up to 6 vol%, or up to 5 vol% of the redox-active polymer to avoid effective consumption of anions, thereby maintaining battery performance.

[0038] Many conductive polymers and polymers that are both conductive and redox-active are known to the skilled person. In fact, several conductive polymers are also redox-active. Such conductive and optionally redox-active polymers can be used in the present invention alone or in combination. By way of example only and not limitation, conductive polymers suitable for use in the present invention include one or more of the following: thiophene-containing polymers, such as polythiophene and poly(3,4-phenylenedioxythiophene) (PEDOT); aniline-containing polymers, such as polyaniline (PANI); pyrrole-containing polymers, such as polypyrrole (PPy); acetylene-containing polymers, such as polyacetylene; organic sulfur polymers, including organic disulfide polymers, such as 2,5-dithio-1,3,4-thiadiazole, poly(2,2'-dithiodiphenylamine), sulfur-polyacrylonitrile, poly(sulfur-random-1,3-diisopropenylbenzene) (poly(Sr-DIB)); amine-containing polymers, such as poly(methyl methacrylate); 2,2,6,6-tetramethylpiperidinyloxy-4-yl acrylate (PTMA) and triphenylamine-containing polymers, such as polytriphenylamine (PTPA), poly(3-vinyl-N-methylphenothiazine) (PVMPT); quinone-containing polymers, such as polydopamine, calix[4]quinone, pillar[5]quinone, poly(benzoquinone-based sulfide) (PBQS) and poly(2,5-dihydro-p-benzoquinone-based sulfide) (PDBS); anthraquinone-containing polymers, such as P14AQ and its lithium derivatives, such as Li2PDBS and poly-LiDHAQS, poly(benzo[1,2-b:4,5-b']-dithiophene-4,8-dione-2,6-diyl) (PBD imide-containing polymers, such as poly{[N,N'-bis(2-octyldodecyl)-1,4,5,8-naphthalene dicarboximide-2,6-diyl]-alt-5,5'-(2,2'-bithiophene)} (P(NDI2OD-T2)) and poly(ethylene-pyromellitic acid diimide) (PPDIE); and poly(4-glycidyloxy-2,2,6,6-tetramethylpiperidin-1-oxy) (PTEO).

[0039] Also suitable for use in the present invention are conductive polymers that are doped derivatives of any of these conductive polymers, such as poly(3,4-ethylenedioxythiophene)-polystyrene sulfonate (PEDOT-PSS).

[0040] In some embodiments, the conductive polymer comprises one or more of the following: polythiophene, PEDOT; PANI; PPy; polyacetylene; PTPA, polydopamine, PBQS, PDBS; and PEDOT-PSS. In some embodiments, the conductive polymer comprises one or more of the following: polythiophene, PEDOT PANI; PPy; and PEDOT-PSS.

[0041] The electrode precursor composition of the present invention also comprises an electrically insulating polymer. These polymers are not essentially conductive polymers and are non-conductive or have negligible conductivity. Typically, these polymers are substantially free of conjugated double bonds that allow electrons to flow through the polymer backbone.

[0042] The electrically insulating polymer used for the present electrode precursor composition is a polymer commonly used to prepare a gel electrode. They are generally swellable. They can be used alone or in combination in the present invention. Many are known to the technician. By way of example only and not limitation, the electrically insulating polymer suitable for the present invention includes one or more of the following: polyvinylidene fluoride (PVDF), polyethylene oxide (PEO), polymethyl methacrylate (PMMA) and polyacrylonitrile.

[0043] In some embodiments, the electrically insulating polymer is present in the electrode precursor composition in an amount of at least 5 vol%, such as at least 7 vol%, at least 10 vol%, or at least 15 vol%, based on the total volume of the electrode precursor composition.

[0044] In some embodiments, the electrically insulating polymer is present in the electrode precursor composition in an amount up to 30 vol %, such as up to 28 vol %, up to 25 vol %, or up to 20 vol %, based on the total volume of the electrode precursor composition.

[0045] Therefore, in some embodiments, the electrically insulating polymer is present in the electrode precursor composition in an amount between 5 and 30 volume %, based on the total volume of the electrode precursor composition. Other combinations of the above values ​​can be combined to form a suitable range, such as between 5 and 28 volume %, between 7 and 25 volume %, or between 10 and 20 volume %.

[0046] The electrode precursor composition of the present invention comprises at least one alkali metal salt.

[0047] The alkali metal of the at least one alkali metal salt can be any suitable alkali metal (Group I of the periodic table of elements). Typically, it can be lithium, sodium and potassium. In some embodiments, the alkali metal of the at least one alkali metal salt is lithium, which may be preferred in all embodiments of the present invention.

[0048] The anion of the at least one alkali metal salt may be any suitable anion. Typical anions are known to the skilled person and may be selected based on the nature of the alkali metal. In some embodiments, when the at least one alkali metal is lithium, the anion of the or each alkali metal salt is independently selected from: lithium borate salts, lithium imide salts, and lithium imidazole salts, or comprises a halogen, such as fluorine. Examples include BF4 - , PF6 - , TFSI - , FSI - and TDI - .

[0049] Thus, in some embodiments, at least one alkali metal salt comprises one or more of lithium bis(oxalate)borate, lithium tetrafluoroborate, lithium difluoro(oxalate)borate (LiDFOB), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium bis(fluorosulfonyl)imide (LiFSI), lithium 2-trifluoromethyl-4,5-dicyanoimidazole (LiTDI), and lithium hexafluorophosphate (LiPF6).

[0050] In some embodiments, the at least one alkali metal salt includes one or more of LiFSI, LiDFOB, and LiTDI.

[0051] In some particularly useful embodiments, the at least one alkali metal salt comprises one or more of LiBF4, LiPF6, LiTFSI, LiFSI, and LiTDI.

[0052] According to the present invention, one or more alkali metal salts may be used. Typically, but not exclusively, when more than one alkali metal salt is used, they share a common alkali metal cation. Typically, but not exclusively, when more than one salt is present, they are each a lithium salt.

[0053] The organic solvent used in the present invention is an organic solvent generally used for manufacturing electrodes of alkali metal secondary battery cells. The organic solvent should be able to be appropriately mixed with the polymer of the electrode precursor composition, for example, to form a solution.

[0054] In some embodiments, the organic solvent is non-aqueous. In some embodiments, the solvent includes one or more cyclic or linear carbonates, ethers or nitrile compounds. In some embodiments, the solvent includes one or more cyclic or linear carbonate compounds.

[0055] In certain embodiments, one or more linear or cyclic carbonate compounds include one or more cyclic carbonate compounds. In certain embodiments, the solvent includes one or more of: ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, ethyl carbonate-methyl ester, butylene carbonate, vinylene carbonate, fluoroethylene carbonate, fluoropropylene carbonate and gamma-butyrolactone.

[0056] In some embodiments, the alkali metal salt and the organic solvent together are present in an amount of at least 5 vol%, such as at least 7 vol%, at least 10 vol%, or at least 15 vol%, based on the total volume of the electrode precursor composition.

[0057] In some embodiments, the alkali metal salt and the organic solvent are present in an amount up to 35 vol %, such as up to 32 vol %, up to 30 vol %, or up to 25 vol %, based on the total volume of the electrode precursor composition.

[0058] Therefore, in some embodiments, based on the total volume of the electrode precursor composition, the alkali metal salt and the organic solvent are present in an amount between 5 and 35 volume %. Other combinations of the above values ​​can be combined to form a suitable range, such as between 7 and 32 volume %, between 10 and 30 volume %, or between 15 and 30 volume %.

[0059] The skilled artisan will be aware of a large number of possible electrochemically active materials, including cathode active materials (also known as positive electrode active materials) and anode active materials (also known as negative electrode active materials), which may be used in the present invention.

[0060] The electrochemically active material is a particulate material, ie a material consisting of a plurality of discrete particles. The particles may include primary particles and / or secondary particles formed by the aggregation of a plurality of primary particles.

[0061] In some embodiments, the electrochemically active material is a positive electrode active material. That is, the electrode functions as a cathode.

[0062] In some embodiments, the positive electrode active material is a lithium transition metal oxide material. In some embodiments, the positive electrode active material is a lithium transition metal oxide material, or a lithium transition metal phosphate material, or a lithium transition metal sulfide material. These respectively contain mixed metal oxides, phosphates or sulfides of lithium and one or more transition metals, optionally further containing one or more other non-transition metals. In some embodiments, the positive electrode active material is a lithium transition metal oxide, phosphate or sulfide material containing lithium and one or more transition metals selected from nickel, cobalt and manganese. In some embodiments, the positive electrode active material is a lithium transition metal oxide material, which contains a mixed metal oxide of lithium and one or more transition metals, optionally further containing one or more other non-transition metals. In some embodiments, the positive electrode active material is selected from one or more of the following: lithium cobalt oxide (LCO), lithium manganese oxide (LMO), lithium nickel cobalt oxide (NCO), aluminum-doped lithium nickel cobalt oxide (NCA), lithium nickel manganese cobalt oxide (NMC), lithium nickel oxide (LNO), lithium nickel manganese oxide (LNMO), lithium iron phosphate (LFP), lithium manganese iron phosphate (LFP) and lithium nickel vanadate (LNV). In some embodiments, the positive electrode active material is lithium nickel manganese cobalt oxide (NMC), optionally doped with another metal, such as aluminum.

[0063] Such electrochemically active materials are commercially available or can be made by methods known to those skilled in the art, for example by precipitation of a mixed metal hydroxide intermediate from a reaction mixture containing various precursor metal salts, followed by calcination to form a mixed metal oxide, and optionally lithiation to incorporate lithium into the oxide.

[0064] The electrochemically active material may be undoped or uncoated, or may include one or more dopants and / or coatings. For example, the electrochemically active material may be doped with a small amount of one or more metallic elements. The electrochemically active material may include a carbon coating on the surface of the material particles.

[0065] In some embodiments, the electrochemically active material is present in an amount of at least 55 vol%, e.g., at least 56 vol%, at least 57 vol%, at least 58 vol%, at least 59 vol%, at least 60 vol%, at least 61 vol%, or at least 62 vol%, based on the total volume of the electrode precursor composition.

[0066] In some embodiments, the electrochemically active material is present in an amount up to 75 vol%, e.g., up to 74 vol%, up to 73 vol%, up to 72 vol%, up to 71 vol%, up to 70 vol%, up to 69 vol%, or up to 68 vol%, based on the total volume of the electrode precursor composition.

[0067] In some embodiments, the electrochemically active material is present in an amount of 55 to 75% by volume based on the total volume of the electrode precursor composition. Other combinations of the above values ​​can be combined to form a suitable range, such as 55 to 70% by volume, 55 to 69% by volume, 55 to 68% by volume, 58 to 68% by volume, or 60 to 68% by volume.

[0068] In some embodiments, the electrochemically active material comprises 62 to 75 volume %, eg, 62 to 70 volume %, 62 to 69 volume %, 62 to 68 volume %, or 62 to 69 volume % of the electrode precursor composition.

[0069] In some embodiments, the electrochemically active material is present in an amount of 62 to 75 volume %, eg, 60 to 75 volume %, 60 to 72 volume %, 60 to 70 volume %, or 60 to 68 volume % of the electrode precursor composition.

[0070] In some embodiments, the electrode precursor composition further comprises a conductive additive, preferably conductive carbon. The conductive additive may be a particle.

[0071] In some embodiments, the conductive additive comprises one or more of carbon black, carbon nanotubes, graphene and graphite or consists thereof. In some embodiments, the conductive additive comprises carbon black or graphite, preferably carbon black, or consists thereof. Examples of commercially available carbon black include Ketjen Black and Super C65.

[0072] In some embodiments, the conductive additive is present in an amount of at least 1 volume %, such as at least 2 volume %, at least 3 volume %, or at least 4 volume %, based on the total volume of the precursor composition.

[0073] In some embodiments, the conductive additive is present in an amount up to 10 vol %, such as up to 9 vol %, up to 8 vol %, or up to 7 vol %, based on the total volume of the electrode precursor composition.

[0074] Therefore, in some embodiments, the conductive additive is present in an amount between 1 and 10 volume %, based on the total volume of the electrode precursor composition. Other combinations of the above values ​​can be combined to form a suitable range, such as between 1 and 9 volume %, between 1 and 8 volume %, between 2 and 8 volume %, or between 3 and 7 volume %.

[0075] In embodiments where the composition comprises a conductive polymer (in an amount of q volume %), an electrically insulating polymer (in an amount of z volume %), an alkali metal salt, an organic solvent, and an electrochemically active material (together in an amount totaling x volume %), and a conductive additive (in an amount of y volume %), then x + y + z + q = 100 volume %.

[0076] In some such embodiments, typically (x+y)>(q+z).

[0077] In some such embodiments, q / (q+z) is typically at least 0.25, such as at least 0.27 or at least 0.30. In further examples, q / (q+z) can be at least 0.32, at least 0.35 or at least 0.40. In some such embodiments, q / (q+z) is typically less than 0.5, such as up to 0.49, up to 0.47, up to 0.45 or up to 0.40. Therefore, in some such embodiments, when x+y>70% by volume, then q / (q+z) is typically between 0.25 and less than 0.50. Other combinations of the above values ​​can be combined to form a suitable range, such as between 0.27 and less than 0.50, between 0.27 and 0.49, or between 0.30 and 0.45.

[0078] Also provided herein is a method for making an electrode precursor composition as described herein. Typically, the method comprises mixing a conductive polymer, an electrically insulating polymer, an alkali metal salt and an organic solvent. Typically, this blend forms a gel. Without wishing to be bound by theory, it is believed that cooling provides sufficient mechanical strength for the gel. These ingredients can be mixed in any suitable manner, simultaneously or in any suitable order, for any suitable time. For example, each of the appropriate amounts can be added and mixed simultaneously.

[0079] Subsequently, the organic solvent, alkali metal salt, electrically insulating polymer and conductive polymer blend are mixed with electrochemically active materials and conductive additives and optionally any other components. The electrochemically active materials and conductive additives can be combined with the blend simultaneously or in any suitable order, at any suitable time, and in any suitable manner.

[0080] Typically, the components are mixed together using various standard mixing equipment such as planetary mixing to ensure good dispersion of the components. The mixture is then passed through a twin-screw extruder at high temperature (>110°C), which can combine the polymer and liquid into a viscous gel. Alternatively, each component can be fed into the extruder individually through a separate feeder and mixed inside the extruder. The material can then be extruded directly into a sheet through a die, or it can be roughly extruded before being calendered into a film. The film can be adhered to a metal foil and then assembled into a battery.

[0081] Any suitable equipment for preparing electrode precursor compositions can be used to prepare the electrode precursor compositions herein, such as standard mixing equipment.

[0082] The electrode precursor composition can then be processed into an electrode as described herein.

[0083] Also provided herein is a method for preparing an electrode for an alkali metal ion secondary battery cell. Typically, the method includes a providing step and a processing step, the providing step including providing an electrode precursor composition as described herein, and the processing step including processing the electrode precursor composition to form an electrode. Therefore, it should be understood that the electrode precursor composition as described herein is used to prepare an electrode according to the present invention. Therefore, the steps for preparing the electrode precursor composition described elsewhere herein are also applicable to the providing step of the method for preparing an electrode.

[0084] In some embodiments, the processing step includes one or more of extrusion and heat treatment.

[0085] In some embodiments, the treatment step includes at least heat treatment. That is, the treatment step includes a step of applying high temperature during the fluidization process.

[0086] In some embodiments, the thermal treatment comprises passing the electrode precursor composition through a roller assembly at a temperature of at least 50° C., such as at least 60° C., at least 70° C., at least 80° C., at least 90° C., or at least 100° C. In some embodiments, the thermal treatment comprises passing the electrode precursor composition through rollers at a temperature of up to 150° C., such as up to 140° C. or up to 130° C. In some embodiments, the thermal treatment comprises passing the electrode precursor composition through rollers at a temperature of 50° C. to 150° C., such as 60° C. to 150° C., 70° C. to 150° C., 80° C. to 150° C., 80° C. to 140° C., 90° C. to 140° C., 100° C. to 140° C., or 110° C. to 130° C.

[0087] The roller assembly may include two rollers separated by a small distance so that the electrode precursor composition is pressed into a thin film as it passes over the rollers.

[0088] In some embodiments, the processing step comprises at least extruding the electrode, or extruding. In some embodiments, the processing step comprises extruding the electrode using an extrusion device, the extrusion device comprising one or more screw feed sections and an extrusion die. In some embodiments, extrusion is achieved using a twin screw extruder.

[0089] In some embodiments where extrusion and heat treatment are used in the treating step, the temperature of the die is at least 50° C., such as at least 60° C., at least 70° C., at least 80° C., at least 90° C., or at least 100° C. In some embodiments, the temperature of the die is up to 150° C., such as up to 140° C. or up to 130° C. In some embodiments, the temperature of the die is from 50° C. to 150° C., such as from 60° C. to 150° C., 70° C. to 150° C., 80° C. to 150° C., 80° C. to 140° C., 90° C. to 140° C., 100° C. to 140° C., or 110° C. to 130° C.

[0090] In some embodiments, the thickness of the electrode is less than 150 μm, such as less than 100 μm, less than 90 μm, less than 80 μm, or less than 70 μm. In some embodiments, the thickness of the electrode is 40 to 150 μm, such as 40 to 100 μm, 40 to 90 μm, 40 to 80 μm, 40 to 70 μm, or 50 to 70 μm. In a specific embodiment, the thickness of the electrode is 40 to 100 μm.

[0091] In some embodiments, the electrode has a thickness of 40 to 150 μm, e.g., 40 to 100 μm, 40 to 90 μm, 40 to 80 μm, 40 to 70 μm, or 50 to 70 μm, and comprises 60 to 75% by volume of the electrochemically active material, e.g., 60 to 70% by volume, 60 to 69% by volume, 60 to 68% by volume, or 62 to 69% by volume of the electrode precursor composition.

[0092] In some cases, the extruded electrode may form part of an extruded monolith that includes one or more additional layers present in an electrochemical cell. For example, the monolith may include a separator layer, and / or may include another electrode (i.e., the extruded monolith may include a cathode and an anode). Different layers may be coextruded and have different compositions from each other.

[0093] In some embodiments, the methods of the present invention further comprise shaping and / or cutting the electrode to form an electrode of a predetermined size.

[0094] In some embodiments, the electrode film has a thickness of 500 to 700 μm. In some embodiments, the method of the present invention further comprises performing a second heat treatment step on the cut film to reduce the thickness of the film to a range of 50 to 70 μm.

[0095] In some embodiments, the temperature during the heat treating step is 100 to 140°C.

[0096] As an aspect of the present invention, an electrode prepared by the method of the present invention or from the electrode precursor composition of the present invention is also provided herein. Typically, the electrode obtained by the method of the present invention is a gel electrode.

[0097] In some embodiments, the electrode prepared by the method of the present invention has a porosity of less than 10%, such as a porosity of less than 8%, a porosity of less than 5%, a porosity of less than 3%, or a porosity of less than 1%. In some embodiments, the electrode prepared by the method of the present invention has a porosity of 0%.

[0098] For example, electrode porosity can be determined by comparing theoretical density to observed density. That is, a technician can calculate the theoretical density of the electrode and then measure the actual electrode density using a suitable method. Subsequently, the actual density is subtracted from the theoretical density to obtain the porosity.

[0099] Without wishing to be bound by theory, the inventors believe that lower porosity is generally advantageous because it reduces the tortuosity of ions (e.g., lithium ions) moving through the electrode gel. Therefore, the initial rate performance of the electrode is expected to be higher than that of an electrode with higher porosity. For similar reasons, it is expected that electronic conductivity may be similarly affected. Therefore, the inventors expect that energy density is related to porosity.

[0100] One aspect of the present invention also provides an electrochemical secondary battery cell comprising such an electrode. The battery cell may be an alkali metal ion secondary battery cell, such as a sodium ion secondary battery cell or a lithium ion secondary battery cell. In some embodiments, the battery cell is a lithium ion secondary battery cell.

[0101] In some embodiments, the electrochemical secondary battery cell comprises a first electrode according to the present invention and an anode, wherein the first electrode is a cathode. In some embodiments, the electrochemical secondary battery cell comprises a second electrode according to the present invention and a cathode, wherein the second electrode is an anode. In some embodiments, the electrochemical secondary battery cell comprises a first and a second electrode according to the present invention, wherein the first electrode is a cathode and the second electrode is an anode. In each of these embodiments, the electrochemical secondary battery cell further comprises an electrolyte between the cathode and the anode. In some embodiments, the electrolyte is a liquid electrolyte. In some embodiments, the liquid electrolyte comprises or is a solution containing an alkali metal salt as described herein.

[0102] In some embodiments, an electrochemical secondary battery cell includes an electrode according to the present invention laminated with a current collector such as a metal foil.

[0103] As an aspect of the present invention, an electrochemical energy storage device comprising an electrochemical secondary battery cell of the present invention is also provided herein. In some embodiments, the electrochemical energy storage device is a battery. In some embodiments, the electrochemical energy storage device is a lithium ion battery.

[0104] As one aspect of the present invention, the present invention also provides the use of a conductive polymer in a method for preparing an electrode for an alkali metal ion secondary battery cell, the method using at least one of a heat treatment step or an extrusion step. The conductive polymer of this aspect is preferably a conductive polymer for the first aspect as described herein. The method for preparing the electrode of this aspect is preferably the method of the second aspect as described herein.

[0105] In some embodiments, such use provides the electrode with increased conductivity compared to a corresponding electrode without the conductive polymer. In some embodiments, such use provides the electrode with increased energy density compared to a corresponding electrode without the conductive redox-active polymer.

[0106] Example

[0107] The following are exemplary electrode precursor compositions for use in the present invention:

[0108]

Claims

1. An electrode precursor composition suitable for preparing a gel electrode, the composition comprising an organic solvent, an alkali metal salt and two or more polymers, The two or more polymers include at least an electrically insulating polymer and a conductive polymer, wherein the conductive polymer is present in a smaller volume fraction than the electrically insulating polymer.

2. The electrode precursor composition according to claim 1, wherein The conductive polymer is present in the electrode precursor composition in an amount between 1 and 20 volume % based on the total volume of the electrode precursor composition.

3. The electrode precursor composition according to claim 2, wherein The conductive polymer is present in the electrode precursor composition in an amount of up to 8 volume % based on the total volume of the electrode precursor composition.

4. An electrode precursor composition according to any one of the preceding claims, wherein The conductive polymer is also redox active.

5. An electrode precursor composition according to any one of the preceding claims, wherein The conductive polymer comprises one or more selected from the group consisting of poly(3,4-ethylenedioxythiophene), polyaniline, polypyrrole and doped derivatives thereof, such as poly(3,4-ethylenedioxythiophene)-polystyrene sulfonate.

6. An electrode precursor composition according to any one of the preceding claims, wherein The electrically insulating polymer comprises one or more selected from the group consisting of polyvinylidene fluoride, polyethylene oxide, polymethyl methacrylate and polyacrylonitrile.

7. The electrode precursor composition according to claim 6, wherein The electrically insulating polymer is present in the electrode precursor composition in an amount between 5 and 30 volume % based on the total volume of the electrode precursor composition.

8. An electrode precursor composition according to any one of the preceding claims, wherein The alkali metal salt includes a lithium salt.

9. The electrode precursor composition according to claim 8, wherein The lithium salt includes one or more of LiBF4, LiPF6, LiTFSI, LiFSI or LiTDI.

10. An electrode precursor composition according to any one of the preceding claims, wherein The organic solvent comprises one or more of carbonate, ether or nitrile.

11. An electrode precursor composition according to any one of the preceding claims, further comprising an electrochemically active material.

12. The electrode precursor composition according to claim 11, wherein The electrochemically active material includes a positive electrode active material.

13. The electrode precursor composition according to claim 10 or 11, wherein The electrochemically active material is present in the electrode precursor composition in an amount of at least 60 volume % based on the total volume of the electrode precursor composition.

14. The electrode precursor composition of any one of the preceding claims, further comprising an additive comprising conductive carbon.

15. The electrode precursor composition according to claim 14, wherein The conductive carbon includes one or more of carbon black, carbon nanotubes, graphene and graphite.

16. The electrode precursor composition according to claim 14 or 15, wherein The conductive carbon is present in the electrode precursor composition in an amount between 1 and 10 volume % based on the total volume of the electrode precursor composition.

17. A method for preparing an electrode for an alkali metal ion secondary battery cell, the method comprising: A providing step, comprising providing an electrode precursor composition according to any one of claims 1 to 16; as well as The processing step includes processing the electrode precursor composition to form an electrode.

18. The method according to claim 17, wherein: The processing step includes one or more of extrusion and heat treatment.

19. The method according to claim 17 or 18, wherein: The providing step comprises providing an electrode precursor composition according to any one of claims 1 to 10, followed by combining the electrode precursor composition with an electrochemically active material and conductive carbon.

20. The method according to any one of claims 16 to 19, wherein: The electrodes are gel electrodes.

21. An electrode for an alkali metal ion secondary battery cell, prepared from the electrode precursor composition according to any one of claims 1 to 16, or prepared by the method according to any one of claims 17 to 20.

22. An electrochemical secondary battery cell comprising the electrode according to claim 21.

23. An electrochemical energy storage device comprising the electrochemical cell according to claim 22.

24. Use of a conductive polymer in a method for preparing an electrode for an alkali metal ion secondary battery cell, the method using at least one of a heat treatment step or an extrusion step.

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