Electrode precursor composition

Abstract

Disclosed is a method for preparing an electrode for an alkali metal ion secondary battery cell, the method comprising: a mixing step, comprising mixing polyacrylonitrile, or a copolymer of acrylonitrile and at least one other monomer, or a blend of any of the foregoing and one or more other polymers with a first organic solvent and an electrochemically active material to form an electrode precursor composition; an electrode precursor forming step in which the electrode precursor composition is formed as an electrode precursor; and an electrode forming step including exposing the electrode precursor to an alkali metal salt. The mixing step may be performed in the presence of between 0 and 1 wt% alkali metal salt. The electrode forming step may include exposing the electrode precursor to a solution or gel comprising an alkali metal salt. The solution comprising the alkali metal salt may comprise a second organic solvent, preferably wherein the second organic solvent is the same as the first organic solvent.

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 batteries 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 a method that avoids the use of sacrificial solvents is needed.

[0004] One way to avoid the use of sacrificial solvents is to prepare gel electrodes. These electrodes can be formed from a composition prepared by mixing the necessary components such as electrochemically active materials, polymers and solvents or liquid electrolytes, followed by heat treatment of the composition.

[0005] For example, using gels when preparing electrodes using heat treatment must balance two opposing requirements. On the one hand, the gel must be soft enough to form an electrode during the heat treatment process. On the other hand, the gel must have sufficient mechanical strength to be practical for use.

[0006] There is a need for a gel electrode precursor composition that meets the above criteria. Summary of the invention

[0007] In general, the present inventors propose to solve the above problems by exploiting the sensitivity of certain classes of polymers to their chemical environment, in particular their sensitivity to the presence of alkali metal salts.

[0008] The present invention is based on the discovery that, in the absence of alkali metal salts, polyacrylonitrile forms soft, flexible, viscous materials and that these materials become hard when alkali metal salts are subsequently added.

[0009] Electrode compositions containing polyacrylonitrile are known, for example from US 2017 / 162862 A1. However, these compositions do not appear to utilize the alkali metal salt sensitivity of polyacrylonitrile described herein.

[0010] Therefore, the general suggestion of the present invention is to prepare a processable electrode precursor composition, which comprises a polymer containing an acrylonitrile monomer having an alkali metal salt that is insufficient to cause hardening, such as in the absence of an alkali metal salt. Subsequently, once the electrode precursor composition is subjected to a heat treatment and formed into an electrode precursor, the electrode precursor can be hardened by exposure to an alkali metal salt. Using this general procedure, the inventors have found that the electrode precursor composition is highly processable while also forming an electrode with sufficient mechanical strength and energy density for practical applications.

[0011] A first aspect of the present invention relates to a method for preparing an electrode for an alkali metal ion secondary battery cell, the method comprising:

[0012] a mixing step comprising mixing polyacrylonitrile, or a copolymer of acrylonitrile and at least one other monomer, or a blend of any of the foregoing with one or more other polymers, with a first organic solvent and an electrochemically active material to form an electrode precursor composition;

[0013] an electrode precursor forming step, wherein the electrode precursor composition is formed into an electrode precursor; and

[0014] The electrode forming step includes exposing the electrode precursor to an alkali metal salt.

[0015] In the electrode forming step, the alkali metal salt can be provided in any suitable form. In some embodiments, the method may include exposing the electrode precursor to a solution comprising an alkali metal salt. In some embodiments, the method may include exposing the electrode precursor to a gel comprising an alkali metal salt.

[0016] As can be understood from the above, the electrode precursor composition prepared by the mixing step generally contains a small amount of alkali metal salt, so as to maintain the soft and flexible nature of the composition and facilitate processing into an electrode.

[0017] In some embodiments, the electrode precursor composition prepared by the mixing step is free (i.e., contains 0 wt %) or substantially free (i.e., contains 1 wt % or less, e.g., less than 0.5 wt % or less than 0.2 wt % or less than 0.1 wt %) of alkali metal salt within experimental accuracy.

[0018] In some embodiments, the electrode precursor composition comprises insufficient alkali metal salt to impart a final desired electrode hardness to the composition. In some embodiments, the electrode precursor composition comprises a final salt concentration between 0 and 25% of the desired electrode hardness.

[0019] In this way, the electrode precursor composition can be processed into a thin film electrode precursor, which in some embodiments can have gel-like properties. Subsequently, the electrode precursor is contacted with or exposed to an alkali metal salt, causing the electrode precursor to harden into a state of sufficient mechanical strength for practical use. In some embodiments, the electrode formed after exposure to the alkali metal salt has a gel-like property, i.e., a gel electrode.

[0020] In general, without wishing to be bound by theory, the inventors believe that the method of the present invention can avoid some of the limitations and compromises common in the field of electrode preparation, especially in the field of gel electrode preparation. For example, the inventors believe that the method can allow for higher effective capacity, or stronger mechanical strength electrodes than using prior art methods.

[0021] According to a second aspect, the present invention relates to an electrode precursor composition suitable for preparing a gel electrode, the composition comprising polyacrylonitrile, or a copolymer of acrylonitrile and at least one other monomer, or a blend of any of the above with one or more other polymers, an organic solvent and an electrochemically active material, the composition being free of or substantially free of alkali metal salts.

[0022] By "free or substantially free of alkali metal salts" we preferably mean that the composition is free (i.e. contains 0 wt%) or substantially free (i.e. contains less than 1 wt%, for example less than 0.5 wt% or less than 0.2 or 0.1 wt%) of alkali metal salts within experimental accuracy.

[0023] The electrode precursor composition of the second aspect may be suitably prepared by the mixing steps described in the method of the first aspect.

[0024] The electrode precursor composition of the second aspect may be suitably processed into an electrode precursor and / or an electrode by the electrode precursor forming and electrode forming steps respectively described in the method of the first aspect.

[0025] Other aspects relate to an electrode precursor prepared from the electrode precursor composition according to the present invention, an electrode for an alkali metal ion secondary battery prepared from the electrode precursor composition or method or electrode precursor according to the present invention, an electrochemical secondary battery including the electrode precursor or electrode according to the present invention, such as an alkali metal ion secondary battery cell, and an electrochemical energy storage device including the electrochemical battery according to the present invention. DETAILED DESCRIPTION

[0026] 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. Any preferred and / or optional features of any aspect may be combined with any aspect of the present invention individually or in combination, unless the context otherwise requires.

[0027] In the following, "electrode precursor composition" refers to both the electrode precursor composition of the second aspect and the electrode precursor composition that is the result of the mixing step in the method of the first aspect.

[0028] Similarly, an electrode precursor refers to the electrode precursor of the other aspect, as well as the electrode precursor formed in the method of the first aspect. Similarly, an electrode refers to the electrode of the other aspect, as well as the electrode formed in the method of the first aspect.

[0029] The present invention generally describes the use of specific polymers for forming electrode precursor compositions. The specific polymer is polyacrylonitrile, or a copolymer of acrylonitrile and at least one other monomer, or a blend of any of the above with one or more other polymers. Therefore, it can be seen that these specific polymers can generally be described as those polymers with acrylonitrile as a constituent monomer. In this article, we use "polymer containing acrylonitrile monomer" and "polyacrylonitrile, or a copolymer of acrylonitrile and at least one other monomer, or a blend of any of the above with one or more other polymers" interchangeably.

[0030] Thus, the polymer containing acrylonitrile monomers may be a homopolymer (when it is polyacrylonitrile) or a copolymer. The polymer containing acrylonitrile monomers may be present as part of a blend of polyacrylonitrile or a copolymer with one or more other polymers.

[0031] When the polymer containing acrylonitrile monomer is a copolymer, in addition to acrylonitrile monomer, the copolymer can contain one or more monomers. The copolymer can be a copolymer of any suitable type, such as a random copolymer, an alternating copolymer or a block copolymer, etc. One or more monomers except acrylonitrile monomer can be any suitable type, as long as they do not damage the effect of the present invention. In order to achieve the effect of the present invention, the inventor generally believes that based on the weight of the copolymer, a suitable copolymer comprises at least 20 wt % (weight percentage), such as at least 30 wt %, 50 wt % or at least 70 wt % of acrylonitrile monomer.

[0032] When the polymer containing acrylonitrile monomer is part of the blend, any other suitable polymers can be used to form the blend, as long as they do not impair the effects of the present invention. In order to achieve the effects of the present invention, the inventors generally believe that the suitable blend accounts for at least 20 volume %, such as at least 30 volume %, 50 volume % or at least 70 volume % of the blend.

[0033] Generally, in the present invention, it is preferred to use polyacrylonitrile alone or as part of a blend.

[0034] In some embodiments, polyacrylonitrile is not mixed with one or more other polymers as part of a blend, ie, it is used as the sole polymer component of the electrode precursor composition.

[0035] In some embodiments, the mixing step of the methods of the present invention includes mixing polyacrylonitrile with a first organic solvent and an electrochemically active material in the absence of an alkali metal salt to form an electrode precursor composition.

[0036] The amount of the polymer containing acrylonitrile monomer used in the electrode precursor composition can be any suitable amount. The lower limit is any value that achieves the effect of the present invention. The upper limit is determined by considering the processing properties: a polymer containing too much acrylonitrile monomer may have the disadvantage of being too soft.

[0037] In some embodiments, the volume ratio of polyacrylonitrile, or a copolymer of acrylonitrile and at least one other monomer, or a blend of any of the foregoing with one or more other polymers, to the organic solvent is at least 1:1, e.g., at least 1:2, at least 1:3, at least 1:4, at least 1:5, or at least 1:6.

[0038] In some embodiments, the volume ratio of polyacrylonitrile, or a copolymer of acrylonitrile and at least one other monomer, or a blend of any of the foregoing with one or more other polymers, to the organic solvent is up to 1:15, e.g., up to 1:13, up to 1:12, up to 1:11, up to 1:10, up to 1:9, or up to 1:8.

[0039] In some embodiments, the volume ratio of polyacrylonitrile, or a copolymer of acrylonitrile and at least one other monomer, or a blend of any of the foregoing with one or more other polymers to the organic solvent is between 1:1 and 1:15. Other combinations of the above values ​​can be combined to form a suitable range, for example, between 1:1 and 1:12, between 1:2 and 1:11, between 1:3 and 1:10, or between 1:4 and 1:8.

[0040] In some embodiments, polyacrylonitrile, or a copolymer of acrylonitrile and at least one other monomer, or a blend of any of the foregoing with one or more other polymers comprises at least 0.5 volume %, e.g., at least 1 volume %, at least 2 volume %, or at least 3 volume % of the electrode precursor composition.

[0041] In some embodiments, polyacrylonitrile, or a copolymer of acrylonitrile and at least one other monomer, or a blend of any of the foregoing with one or more other polymers comprises up to 15 vol %, e.g., up to 12 vol %, up to 10 vol %, or up to 8 vol % of the electrode precursor composition.

[0042] Therefore, in some embodiments, polyacrylonitrile, or a copolymer of acrylonitrile and at least one other monomer, or a blend of any of the foregoing with one or more other polymers, accounts for 0.5-15 volume percent of the organic solvent. Other combinations of the above values ​​can be combined to form a suitable range, such as between 1 and 12 volume %, between 1 and 10 volume %, between 2 and 8 volume %, or between 3 and 8 volume %.

[0043] Note that the total volume percentage of all components in the electrode precursor composition is 100 volume %.

[0044] In the method of the present invention, polyacrylonitrile or a copolymer of acrylonitrile and at least one other monomer or a blend of any of the foregoing and one or more other polymers is mixed with an organic solvent and an electrochemically active material to form an electrode precursor composition. Any suitable mixing method can be used. Generally, it is expected that the mixing step will produce a substantially uniform composition.

[0045] For example, a suitable method may include compounding using a twin-screw extruder. In this method, individual components are provided separately. They are then mixed at a desired temperature to form an electrode precursor composition. This method advantageously achieves mixing of all components in a single step.

[0046] The above desired temperature is not particularly limited. Generally speaking, the temperature is usually high enough to dissolve the components to be dissolved in each other, but not high enough to degrade the constituent components. Therefore, the selected temperature will depend on the properties of the components used in the electrode precursor composition.

[0047] The identity of the electrochemically active materials used in the present invention is not particularly important. The benefits of the present invention can be achieved for any active material that may be present in the electrode composition. The skilled person 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 can be used in the present invention.

[0048] The electrochemically active material is typically 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.

[0049] In some embodiments, the electrochemically active material may be a positive electrode active material. That is, the electrode functions as a cathode.

[0050] 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 comprising a mixed metal oxide of lithium and one or more transition metals, optionally further comprising one or more additional non-transition metals. In some embodiments, the positive electrode active material is a lithium transition metal oxide material comprising lithium and one or more transition metals selected from nickel, cobalt and manganese. In some embodiments, the positive electrode active material is selected from one or more of 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.

[0051] 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 optional lithiation to incorporate lithium into the oxide.

[0052] 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.

[0053] In some embodiments, the electrochemically active material comprises at least 55%, e.g., at least 56%, at least 57%, at least 58%, at least 59%, at least 60%, at least 61%, or at least 62% by volume of the electrode precursor composition.

[0054] In some embodiments, the electrochemically active material constitutes 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% of the electrode precursor composition.

[0055] In some embodiments, the electrochemically active material comprises 55-75% by volume of the electrode precursor composition. Other combinations of the above values ​​can be combined to form suitable ranges, 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.

[0056] 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.

[0057] 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, for example, a polymer containing acrylonitrile monomer and an electrochemically active material to form a solution.

[0058] In certain embodiments, organic solvent is non-aqueous.In certain embodiments, solvent comprises one or more cyclic or linear carbonate compounds.In certain embodiments, solvent comprises one or more cyclic carbonate compounds.In certain embodiments, solvent comprises one or more cyclic carbonate compounds.In certain embodiments, solvent comprises one or more in ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, ethyl carbonate-methyl ester, butylene carbonate, vinylene carbonate, fluoroethylene carbonate, fluoropropylene carbonate and gamma-butyrolactone.

[0059] The relative amounts of solvent and polymer containing acrylonitrile monomer are discussed above.

[0060] In some embodiments, the organic solvent constitutes at least 20 vol%, eg, at least 21 vol%, at least 22 vol%, at least 23 vol%, at least 24 vol%, or at least 25 vol% of the electrode precursor composition.

[0061] In some embodiments, the organic solvent constitutes up to 40 vol%, eg, up to 39 vol%, up to 38 vol%, up to 37 vol%, up to 36 vol%, or up to 35 vol% of the electrode precursor composition.

[0062] In some embodiments, the organic solvent comprises 20 to 40% by volume of the electrode precursor composition. Other combinations of the above values ​​can be combined to form suitable ranges, such as between 22 and 38% by volume, between 22 and 37% by volume, between 23 and 36% by volume, or between 25 and 35% by volume.

[0063] The present invention utilizes the sensitivity of polymers containing acrylonitrile monomers to alkali metal salts. Therefore, the electrode precursor composition contains little or no added alkali metal salt. Therefore, in some embodiments, the electrode precursor composition - prepared in the mixing step of the second aspect or in the method of the first aspect of the present invention - contains a small amount of alkali metal salt, such as 1 wt% or less, such as less than 0.5 wt%, less than 0.2 wt% or less than 0.1 wt% or substantially 0 wt%.

[0064] In some embodiments, the electrode precursor composition formed by the mixing step may include up to 25 wt %, such as up to 15 wt %, up to 10 wt %, or up to 5 wt % (total 100 wt %) of the total amount of alkali metal salt included in the electrode formed after the electrode forming step.

[0065] In some embodiments, the electrode precursor composition formed by the mixing step may include up to 1 wt % or 0 wt % of the total amount of alkali metal salt included in the electrode formed after the electrode forming step.

[0066] Thus, in some embodiments, the electrode precursor composition comprises 0 wt % to 25 wt % of the total amount of alkali metal salt in the electrode formed after the electrode forming step. Other combinations of the above values ​​can be combined to form suitable ranges, such as between 0 wt % and 15 wt %, between 0 wt % and 10 wt %, between 0 wt % and 5 wt %, or between 0 wt % and 1 wt %.

[0067] The alkali metal of the alkali metal salt may be any suitable alkali metal (Group I of the Periodic Table of Elements). Typically, the alkali metal may be lithium, sodium and potassium.

[0068] In some embodiments, the alkali metal of the alkali metal salt is lithium. In some embodiments, the alkali metal of the alkali metal salt that is not present in the mixing step and added in the electrode forming step is lithium.

[0069] The anion of the alkali metal salt can be any suitable anion. Typical anions are known to the skilled person and can be selected based on the type of alkali metal. In some embodiments, when the alkali metal is lithium, the anion of the alkali metal salt includes a halogen, such as fluorine. Examples include BF4 - PF6 - TFSI - 、FSI - and TDI - .

[0070] In some embodiments, the alkali metal salt comprises one or more lithium salts. In some embodiments, the lithium salt or each lithium salt is independently selected from: a lithium borate salt, a lithium imide salt, and a lithium imidazole salt.

[0071] In some embodiments, the liquid electrolyte includes 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), and 2-trifluoromethyl-4,5-dicyanoimidazole lithium (LiTDI). In some embodiments, the lithium salt is one or more of LiFSI, LiDFOB, and LiTDI. Examples of lithium salts are known to technicians, but include, for example, one or more of LiBF4, LiPF6, LiTFSI, LiFSI, and LiTDI.

[0072] 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.

[0073] In some embodiments, the electrode precursor composition further comprises an additive, such as a conductive additive. The conductive additive can be added to the electrode precursor composition at any suitable time and using any suitable method. For example, in the mixing step of the inventive method, the conductive additive can be suitably included with polyacrylonitrile, or a copolymer of acrylonitrile and at least one other monomer, or any of the aforementioned blends with one or more other polymers, the first organic solvent and the electrochemically active material. The conductive additive can be a particle conductive additive.

[0074] In some embodiments, the conductive additive comprises or consists of one or more of carbon black, carbon nanotubes (including multi-walled and single-walled carbon nanotubes), carbon fibers, and graphite. In some embodiments, the conductive additive comprises or consists of carbon black. Examples of commercially available carbon black include Ketjen Black and Super C65.

[0075] In some embodiments, the conductive additive is present in an amount of 0.5 vol % to 2.5 vol %, e.g., 0.5 vol % to 2.5 vol %, 0.5 vol % to 2.3 vol %, 0.5 vol % to 2.1 vol %, 0.7 vol % to 2.0 vol %, 0.7 vol % to 1.8 vol % or 0.7 vol % to 1.6 vol %, based on the total volume of the electrode precursor composition.

[0076] In the method of the present invention, the electrode precursor composition forms an electrode precursor.

[0077] In some embodiments, the electrode precursor forming step includes heat treatment. That is, the electrode precursor forming step includes a step of applying a high temperature during the fluid formation process.

[0078] In some embodiments, the thermal treatment comprises passing the electrode precursor composition through a roller assembly at a temperature of at least 50° C., e.g., 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 a roller assembly at a temperature of up to 150° C., e.g., up to 140° C., or up to 130° C. In some embodiments, the thermal treatment comprises passing the electrode precursor composition through a roller at a temperature of 50° C. to 150° C., e.g., 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.

[0079] 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.

[0080] In some embodiments, the heat treatment comprises extruding the electrode. In some embodiments, the heat treatment 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, the temperature of the die is at least 50°C, for example, 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, for example, up to 140°C or up to 130°C. For example, from 60°C to 150°C, from 70°C to 150°C, from 80°C to 150°C, from 80°C to 140°C, from 90°C to 140°C, from 100°C to 140°C or from 110°C to 130°C.

[0081] In some embodiments, the thickness of the electrode precursor 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 precursor 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.

[0082] In some embodiments, the electrode precursor 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 electrode precursor composition 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.

[0083] In some cases, the extruded electrode may form part of an extruded monolith that includes one or more other 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.

[0084] In some embodiments, in the electrode forming step, exposing the electrode precursor to an alkali metal salt includes exposing the electrode precursor to a solution or gel comprising an alkali metal salt.

[0085] In some embodiments, in the electrode forming step, exposing the electrode precursor to an alkali metal salt comprises exposing the electrode precursor to a lithium salt. In some embodiments, in the electrode forming step, exposing the electrode precursor to a solution or gel comprising an alkali metal salt comprises exposing the electrode precursor to a solution or gel comprising a lithium salt.

[0086] In some embodiments, the solution comprising an alkali metal salt comprises a second organic solvent, preferably wherein the second organic solvent is the same as the first organic solvent.Thus, all of the above discussion of organic solvents is applicable to the electrode precursor composition and the electrode forming step in the method of the present invention.

[0087] Particularly useful embodiments of the methods of the present invention include exposing the electrode precursor to an alkali metal salt in situ, such as in an alkali metal secondary battery cell. For example, the alkali metal salt may be (contained in) a liquid electrolyte.

[0088] In this way, hardening of the electrode can be performed at a desired time without the need to handle an already hardened electrode.

[0089] In some embodiments, the electrode film has a thickness of 500 to 700 μm.

[0090] In some embodiments, the method of the present invention further comprises shaping and / or cutting the electrode precursor and / or the electrode to form an electrode precursor or an electrode of a predetermined size.

[0091] 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.

[0092] In some embodiments, the temperature during the heat treating step is from 100 to 140°C.

[0093] As an aspect of the present invention, an electrode prepared by the method of the present invention or by the electrode precursor composition of the present invention is also provided herein. An 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. Preferably, the battery cell is a lithium ion secondary battery cell. In some embodiments, the electrochemical secondary battery cell comprises a first electrode according to the present invention, wherein the first electrode is a cathode, and a second electrode according to the present invention, wherein the second electrode is an anode, and an electrolyte between the cathode and the anode. In some embodiments, the electrolyte is a liquid electrolyte. In some embodiments, the liquid electrolyte includes or is a solution comprising an alkali metal salt as described herein.

[0094] 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.

[0095] 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.

[0096] Example

[0097] The following is an exemplary electrode precursor composition according to the present invention:

[0098]

Claims

1. A method for preparing an electrode for an alkali metal ion secondary battery cell, the method comprising: a mixing step comprising mixing polyacrylonitrile, or a copolymer of acrylonitrile and at least one other monomer, or a blend of any of the foregoing and one or more other polymers with a first organic solvent and an electrochemically active material to form an electrode precursor composition; an electrode precursor forming step, wherein the electrode precursor composition is formed into an electrode precursor; and The electrode forming step includes exposing the electrode precursor to an alkali metal salt.

2. The method of claim 1, wherein the mixing step is performed in the presence of between 0 and 1 wt% of an alkali metal salt.

3. A method according to any one of the preceding claims, wherein the electrode forming step comprises exposing the electrode precursor to a solution or gel comprising the alkali metal salt.

4. The method according to claim 3, wherein the solution comprising the alkali metal salt comprises a second organic solvent, preferably wherein the second organic solvent is the same as the first organic solvent.

5. The method of any one of the preceding claims, wherein the mixing step comprises mixing polyacrylonitrile with the first organic solvent and the electrochemically active material to form the electrode precursor composition.

6. A method according to any one of the preceding claims, wherein the electrode precursor forming step comprises a heat treatment.

7. A method according to any one of the preceding claims, wherein in the mixing step, the volume ratio of polyacrylonitrile, or a copolymer of acrylonitrile and at least one other monomer, or a blend of any of the foregoing and one or more other polymers, to the organic solvent is between 1:1 and 1:

15.

8. A method according to any one of the preceding claims, wherein the mixing step is performed in the absence of a lithium salt and / or in the electrode forming step, the alkali metal salt comprises a lithium salt.

9. The method of any one of the preceding claims, wherein the electrode forming step is performed in an alkali metal ion secondary battery cell.

10. The method according to any one of the preceding claims, wherein the organic solvent comprises a carbonate.

11. An electrode precursor composition suitable for preparing a gel electrode, the composition comprising polyacrylonitrile, or a copolymer of acrylonitrile and at least one other monomer, or a blend of any of the foregoing substances and one or more other polymers; an organic solvent; and an electrochemically active material, the composition containing no or substantially no alkali metal salt.

12. The electrode precursor composition according to claim 11, wherein the volume ratio of the polyacrylonitrile, or a copolymer of acrylonitrile and at least one other monomer, or a blend of any of the foregoing substances and one or more other polymers to the organic solvent is between 1:1 and 1:

15.

13. The electrode precursor composition according to claim 11 or 12, wherein the composition contains no or substantially no lithium salt.

14. The electrode precursor composition according to any one of claims 11 to 13, wherein the organic solvent comprises a carbonate.

15. The electrode precursor composition according to any one of claims 11 to 14, wherein the polyacrylonitrile, or a copolymer of acrylonitrile and at least one other monomer, or a blend of any of the foregoing and one or more other polymers is present in an amount between 1-10 volume % based on the total volume of the electrode precursor composition. 16 . The electrode precursor composition according to claim 11 , wherein the organic solvent is present in an amount of at least 20% by volume based on the total volume of the electrode precursor composition.

17. The electrode precursor composition according to any one of claims 11 to 16, wherein the electrochemically active material is present in an amount of at least 60 volume % based on the total volume of the electrode precursor composition.

18. The electrode precursor composition according to any one of claims 11 to 17, further comprising a conductive additive.

19. The electrode precursor composition of claim 18, wherein the conductive additive is present in an amount between 0.1 wt% and 3 wt% based on the total weight of the electrode precursor composition.

20. The electrode precursor composition of any one of claims 11 to 19, wherein the composition comprises polyacrylonitrile.

21. The electrode precursor composition of any one of claims 11 to 20, wherein the electrochemically active material comprises a positive electrode active material.

22. The electrode precursor composition of any one of claims 11 to 21, wherein the electrochemically active material comprises a lithium transition metal oxide material.

23. An electrode precursor prepared from the electrode precursor composition according to any one of claims 11 to 22.

24. An electrode for an alkali metal ion secondary battery cell, the electrode being prepared according to the electrode precursor composition of any one of claims 11 to 22, or being prepared by the method of any one of claims 1 to 10, or being prepared from the electrode precursor of claim 23.

25. An electrochemical secondary battery cell, such as an alkali metal ion secondary battery cell, comprising an electrode precursor according to claim 23 or an electrode according to claim 24.

26. The electrochemical secondary battery cell of claim 23, comprising a liquid electrolyte.

27. An electrochemical energy storage device comprising an electrochemical cell according to claim 24 or 25.

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