Sodium ion battery, method for producing a sodium ion battery and use of a sodium ion battery

Abstract

The invention relates to a sodium ion battery comprising a cathode which has a composite cathode active material, and an anode which has an anode active material. The composite cathode active material comprises at least a first cathode active material and a second cathode active material, wherein the first cathode active material and / or the second cathode active material is a polyanionic cathode active material, and wherein, prior to the first discharging and / or charging process of the sodium ion battery, the first cathode active material is fully sodiated and the second cathode active material is fully desodiated. The anode active material is pre-sodiated prior to the first discharging and / or charging process of the sodium ion battery. The invention also relates to a method for producing a sodium ion battery of this type and a use of a sodium ion battery of this type.

Description

[0001] Sodium ion battery, method for producing a sodium ion battery and use of a sodium ion battery

[0002] The invention relates to a sodium ion battery, a method for producing a sodium ion battery and the use of a sodium ion battery.

[0003] In the following, the term "sodium-ion battery" is used synonymously for all commonly used terms in the prior art for sodium-containing galvanic elements and cells, such as sodium battery, sodium cell, sodium ion cell, sodium polymer cell, sodium ion polymer cell, and sodium ion accumulator. This particularly includes rechargeable batteries (secondary batteries). The terms "battery" and "electrochemical cell" are also used synonymously with the term "sodium ion battery." The sodium ion battery can also be a solid-state battery, for example, an inorganic, ceramic, gel-based, or polymer-based solid-state battery.

[0004] To meet the demand for electrochemical energy storage devices for stationary and mobile applications, lithium-free electrolytic cells and systems are increasingly coming into focus. Sodium-ion batteries are a fundamentally well-known alternative to electrochemical storage devices based on lithium-containing compounds.

[0005] A sodium-ion battery has at least two different electrodes: a positive electrode (cathode) and a negative electrode (anode). Each of these electrodes contains at least one active material, referred to as a cathode active material or anode active material, respectively, optionally together with additives such as electrode binders and electrical conductivity additives, such as conductive carbon black.

[0006] A general description of sodium-ion technology can be found in Chen et al.: "Readiness Level of Sodium-Ion Battery Technology: A Materials Review" (Adv. Sustainable Syst. 2018, 2, 1700153, doi: 10.1002 / adsu.201700153) and in Hasa et al.: "Challenges of today for Na-based batteries of the future: From materials to cell metrics" (Journal of Power Sources, 2021, 282, 22872, doi: 10.1016 / j.jpowsour.2020.228872). In sodium-ion batteries, both the cathode active material and the anode active material must be able to reversibly absorb or release sodium ions.

[0007] Sodium-ion batteries offer several advantages over other known systems. For example, sodium-ion batteries allow the use of hard carbon instead of graphite as the anode active material. Hard carbon can be produced at lower temperatures than synthetic graphite and, thanks to its more mechanically stable particles, can be calendered or compacted more effectively than synthetic or natural graphite. Furthermore, a cathode active material can be used that is not based on nickel and cobalt and is inexpensive. Furthermore, sodium, as an active ion—that is, an ion that is reversibly absorbed and released—is significantly cheaper than lithium and is virtually unlimited in supply. Since sodium does not alloy with aluminum, it is also possible to use aluminum-based current collectors or carrier foils in sodium-ion batteries instead of copper in the anode, which significantly reduces costs.Furthermore, the materials used in sodium-ion batteries are generally more chemically stable than the components used in lithium-ion batteries and can be processed, particularly in contact with air and moisture, which can simplify process control in the manufacturing process, which in turn results in cost reduction.

[0008] Sodium-ion batteries are currently assembled and manufactured in a completely uncharged state. This corresponds to a state in which the sodium ions are completely intercalated, i.e., stored, in the cathode, while the anode typically contains no active, i.e., reversibly cyclable, sodium ions.

[0009] During the initial charging process of a sodium-ion battery, also known as "formation," the sodium ions leave the cathode and deposit themselves in the anode. This initial charging process involves complex processes with numerous reactions taking place between the various components of the sodium-ion battery.

[0010] Of particular importance is the formation of an interface between the negative active material, i.e., the anode active material, and the electrolyte of the sodium-ion battery on the anode. This interface is also referred to as the "solid electrolyte interphase" or "SEI." The formation of the SEI, which can also be seen as a protective layer, is essentially attributed to decomposition reactions between the electrolyte and the surface of the anode active material and is sodium ion-conductive.

[0011] However, sodium is required to form the SEI, which is no longer available for cycling during the charge and discharge process. The difference between the capacity after the first charge and the capacity after the first discharge, relative to the charge capacity, is referred to as formation loss and can range from approximately 5 to 40%, depending on the cathode and anode active materials used.

[0012] The cathode active material must therefore be oversized, i.e., provided in larger quantities, to achieve the desired nominal capacity of the finished sodium-ion battery even after formation loss. This increases manufacturing costs and reduces the battery's specific energy. This also increases the demand for potentially toxic and / or limited metals and compounds that are necessary for the production of the cathode active material or that arise during its processing, for example, in recycling processes.

[0013] In the state-of-the-art cell manufacturing process, sodium-ion batteries are first assembled in an uncharged state and then formed. Formation is an extremely cost-intensive process, as it requires both specialized equipment and compliance with the highest safety standards, particularly with regard to fire protection.

[0014] The object of the invention is to provide a sodium-ion battery that has a high specific energy and service life, as well as a cost-effective method for producing such a sodium-ion battery. A further object of the invention is to realize a simplified manufacturing process for the sodium-ion battery, in which, in particular, the pre-charge or forming process is eliminated. The "pre-charge process" in this context refers to an initial charging of the cell in order to form an SEI and ensure a stable cell voltage. This object is achieved according to the invention by a sodium-ion battery with a cathode comprising a composite cathode active material and an anode comprising an anode active material.The composite cathode active material comprises at least a first cathode active material and a second cathode active material, wherein the first cathode active material and / or the second cathode active material is a polyanionic cathode active material, and wherein the first cathode active material is fully sodiated and the second cathode active material is fully deodiated before the first discharge and / or charge process of the sodium-ion battery. The anode active material is pre-sodiated before the first discharge and / or charge process of the sodium-ion battery.

[0015] According to the invention, a fully sodiated active material has a sodiation degree of 1 and a fully deodiated active material has a sodiation degree of 0, while a sodiated or pre-sodiated active material has a sodiation degree of greater than 0.

[0016] The term "degree of sodiation" refers to the content of reversibly cyclable sodium, in the form of sodium ions, metallic sodium, and / or sodium alloys, per formula unit of the active material relative to the maximum content of reversibly cyclable sodium in the active material. In other words, the degree of sodiation is a measure of the percentage of the cyclable sodium specified by the formula unit of the active material that is intercalated or intercalated within the structure of the active material.

[0017] It is understood that the amount of reversibly cyclable sodium depends on the voltage range in which the sodium-ion battery is intended to be operated. Accordingly, the formula unit of the active material may contain sodium that is not reversibly cyclable in the respective intended voltage range, even if it would be reversibly cyclable if the voltage range were expanded to comparatively higher voltages. In this case, the degree of sodiation refers only to the proportion of sodium that is reversibly cyclable in the selected voltage range.

[0018] In particular, the voltage range is limited by a maximum voltage of at most 5.0 V, preferably of at most 4.5 V, particularly preferably of at most 4.3 V. For example, in a stoichiometric sodium vanadium phosphate fluoride (NVPF) with the formula unit NasV2(PO4)F3 the degree of sodiation is 1 and in the deodiated associated compound Na 2(PO4)Fs the degree of sodiation is 0 if the voltage range has a maximum voltage of at most 4.3 V, in particular if the voltage range has a voltage in the range from 2.0 V to 4.3 V.

[0019] It is also possible to specify the sodiation degree as a percentage by multiplying the respective sodiation degree value by 100%. For example, a sodiation degree of 1 corresponds to a sodiation degree of 100%, a sodiation degree of 0.5 corresponds to a sodiation degree of 50%, and a sodiation degree of 0 corresponds to a sodiation degree of 0%.

[0020] Formation loss occurs almost exclusively during the first discharge and / or charge cycle. Therefore, the initial state of the cathode active material and the anode active material in particular influences the prevention of formation losses.

[0021] According to the invention, the cathode comprises a composite cathode active material that represents a combination of a fully sodiated first cathode active material and a fully deodiated second cathode active material. This combination makes it particularly easy to obtain a partially deodiated composite cathode material with a desired overall degree of sodiation before the first discharge and / or charge process of the sodium-ion battery by using a blend of the first cathode active material and the second cathode active material.

[0022] In particular, the use of only partially deodized cathode active materials, whose production is complex and expensive, can be avoided. Furthermore, this approach also allows the use of cathode active materials that cannot be produced in a partially deodized state, while still achieving a total degree of sodification that is neither 0 nor 1.

[0023] The term “total sodification degree” indicates the total resulting sodification degree of all components of the active material, taking into account both the respective sodification degree of the components and the respective weight and capacity share of the components in the composite cathode active material.

[0024] The capacity fraction depends on the specific capacity of the respective cathode active materials, i.e. the specific capacity of the first cathode active material and the second cathode active material, as well as on the weight fractions of the first cathode active material and the second cathode active material in the composite cathode active material.

[0025] For example, in a composite cathode active material consisting of 50 wt.% first cathode active material and 50 wt.% second cathode active material, wherein the first cathode active material has a specific capacity twice as high as the second cathode active material, the total sodification degree S is 0.33.

[0026] If the first cathode active material and the second cathode active material have the same specific capacity, the total degree of sodification of the composite cathode active material depends accordingly only on the respective weight proportion of the first cathode active material and the second cathode active material in the composite cathode active material.

[0027] For example, in this case, in a composite cathode active material consisting of 70 wt.% first cathode active material with a sodiation degree a of 1 and 30 wt.% second cathode active material with a sodiation degree b of 0, the total sodiation degree S is 0.7.

[0028] In other words, the total degree of sodification S in this case is the sum of the products of the weight fraction and the degree of sodification of all components of the active material.

[0029] Since the sodium ions are also incorporated into the second cathode active material after filling with electrolyte, and in particular during the first discharge cycle, the ratio of the degree of sodiation of the first and second cathode active materials after filling with electrolyte and / or after the first discharge and / or charge process of the sodium-ion battery can equalize from the initial state in the composite cathode active material. However, since formation loss occurs almost exclusively during the first discharge and / or charge process, the initial state of the composite cathode active material is particularly important to avoid formation losses. Therefore, the information regarding the degrees of sodiation of the first and second cathode active materials in the composite cathode active material according to the invention refers to the state before the first discharge and / or charge process and in particular before filling with electrolyte.

[0030] According to the invention, the anode active material is pre-sodium-treated before the first discharge and / or charge process of the sodium-ion battery. The term "pre-sodium-treated" or "pre-sodium treatment" indicates that at least some sodium is present, in particular adsorbed or incorporated, in the structure of the anode active material before the first discharge and / or charge process of the sodium-ion battery.

[0031] The sodium used for pre-sodium treatment can be used later as a sodium reserve during the charge and discharge cycles of the sodium-ion battery, or it can be used to form a SEI before or during the first discharge and / or charge cycle of the sodium-ion battery. Thus, pre-sodium treatment can at least partially offset the formation losses that would otherwise occur. In this way, the amount of costly and potentially toxic cathode active materials or toxic compounds potentially generated during the processing of the cathode active materials can be minimized and / or the energy density of the cell can be increased.

[0032] Furthermore, the reactions for the formation of the SEI do not have to take place during the first discharge and / or charging process of the assembled sodium-ion battery, but can at least partially be carried out during the production of the anode active material and / or the anode, in particular after filling the electrolyte.

[0033] By combining an at least partially deodiated composite cathode active material and an optionally substoichiometrically pre-sodium-ionized anode active material, the sodium-ion battery is at least partially charged directly after assembly and is therefore immediately ready for use.

[0034] The first discharge and / or charge process can therefore take place directly in the intended application, for example, at the end customer's site. Individual electrochemical cells can also be connected to form a battery module and then discharged and / or charged for the first time.

[0035] This eliminates the pre-charge and formation steps—the initial charging of the sodium-ion battery—during the manufacturing process, shortening production time. It also reduces power consumption during production, as well as the size and operation of the required production facilities.

[0036] In particular, the composite cathode active material has a total sodification degree of 0.99 or less, preferably 0.95 or less, particularly preferably 0.75 or less, further preferably 0.5 or less, before the first discharge and / or charge process of the sodium ion battery.

[0037] The composite cathode active material may further have a total degree of sodification of greater than 0, preferably of at least 0.25, particularly preferably of at least 0.5, before the first discharge and / or charging process of the sodium ion battery.

[0038] Fully deodiated cathode active materials are commercially available or can be obtained by electrochemical extraction of sodium from fully or partially sodiated cathode active materials.

[0039] Chemical extraction of sodium from fully or partially sodiated cathode active materials is also possible, in which the sodium is dissolved out using acids, for example sulfuric acid (H2SO4).

[0040] Another possibility is to obtain deodiated cathode active materials by means of solid-state synthesis or precipitation reactions.

[0041] According to the invention, the first cathode active material and / or the second cathode active material is a polyanionic cathode active material.

[0042] Polyanionic cathode active materials are known as active materials for sodium-ion batteries. For the general state of the art on the use of polyanionic cathode active materials in sodium-ion batteries, see, for example, EP 3 933 997 A1 and Hasa et al.: "Challenges of today for Na-based batteries of the future: From materials to cell metrics" (Journal of Power Sources, 2021, 282, 22872, doi: 10.1016 / j.jpowsour.2020.228872).

[0043] The type of polyanionic cathode active material is fundamentally not further restricted.

[0044] Polyanionic cathode active materials are fully compatible with common electrode binders, electrolyte compositions and conductivity additives, such as conductive carbon black, as well as with common manufacturing processes for cathode active materials, such as mixing, coating, calendering, punching, cutting, winding, stacking, vacuuming, drying and lamination processes as well as electrolyte filling.

[0045] In particular, polyanionic cathode active materials with a particle size in the range of 0.1 to 35 pm, preferably 1 to 20 pm, can be used. Such particle sizes are ideal for blending the cathode active material with other particles, especially conductive carbon black. This allows a homogeneous cathode coating composition to be obtained, which, after drying a carrier solvent and compaction, can be used as a composite cathode in the sodium-ion battery.

[0046] Particularly preferably, the composite cathode active material consists of a first cathode active material which is a fully sodiated polyanionic cathode active material and a second cathode active material which is a fully deodiated polyanionic cathode active material.

[0047] The polyanionic cathode active material is selected in particular from the group of phosphates, sulfates, silicates, and combinations thereof. This selection includes corresponding polyphosphates, polysulfates, and polysilicates.

[0048] The polyanionic cathode active material is preferably selected from compounds with a NASICON structure, tavorite structure, olivine structure, alluaudite structure, layered compounds, and combinations thereof. Such compounds are capable of reversibly absorbing and releasing sodium ions while essentially preserving the basic structure of the cathode active material. This reduces stress on the cathode material during charge and discharge cycles and thus increases the service life of the sodium-ion battery.

[0049] In this context, the term “layered compounds” does not include so-called “layered oxides” which contain oxygen anions and have the general formula Na x MO2, where M denotes a transition metal.

[0050] The polyanionic cathode active material may contain a transition metal selected from the group consisting of iron, manganese, vanadium and combinations thereof.

[0051] For example, the polyanionic cathode active material is selected from the group of compounds Nai- x FePO4 (NFP), Naz- x Fe3(PO4)3, Naz-xFePzO?, Nai- x MnPO4, Naz-xMnPzO?, Naz-xMnPzO?, Naz- x MnPO4F, Na4- x .(Fe,Mn)3(PO4)2(P2O7), Na3- x V2(PO4)3 (NVP), Na3^V2(PO4)2F3(NVPF), Na3^V2. y(VO) y (PO4)2F3-y, Naz- x Fe(SO4)3, Na2+2z- X “Fe2-z(SO4)3, Na2- x Mn2(SO4)3, Naz- x Fez(SiO4)3, Naz- x Mnz(SiO4)3, Naz- x FeSiO4, Naz- xMnSiO4 and combinations thereof, where 0 < y < 3 and 0 < z < 2, and where, in the case of a fully deodiated cathode active material, x is 1, x' is 2, x" is 3 and x"' is 4, and where, in the case of a fully sodiated cathode active material, x, x', x" and x"' are 0.

[0052] It is also possible for the polyanionic cathode active material to be doped, with the element used for doping partially replacing the respective transition metal present in the active material. For example, a polyanionic cathode active material containing a transition metal selected from the group consisting of iron, manganese, vanadium, and combinations thereof can be doped with an element selected from the group consisting of manganese, chromium, nickel, cobalt, copper, and combinations thereof.

[0053] Doping is understood to mean a content of the respective element in a proportion of no more than 5 percent by weight, based on the total weight of the polyanionic cathode active material, in particular in a proportion of no more than 1 percent by weight. In one variant, the first cathode active material is a polyanionic cathode active material, and the second cathode active material is selected from the group of sodium layer oxides, sodium spinels, and Prussian blue analogues (PBA).

[0054] In a further variant, the first cathode active material is selected from the group of sodium layer oxides, sodium spinels and Prussian blue analogues (PBA) and the second cathode active material is a polyanionic cathode active material.

[0055] The Prussian Blue analogue is particularly selected from the group of compounds Na x M[M'(CN)6]i- y* z H2O, where 0 < y < 1 and z > 0, and where M and M' are each selected from the group of transition metals, preferably from the group consisting of iron, manganese, chromium, nickel, cobalt, and copper. If the Prussian Blue analogue is fully sodiated, x is in particular equal to 2. If the Prussian Blue analogue is fully deodiated, x is in particular equal to 0.

[0056] Preferably, M and M' are each selected from the group consisting of iron, manganese, and chromium. Accordingly, the Prussian Blue analogue is preferably free of nickel and cobalt.

[0057] Particularly preferred is the combination of M and M' (M / M') selected from the group Fe and Fe (Fe / Fe), Fe and Mn (Fe / Mn) and manganese and manganese (Mn / Mn).

[0058] In principle, the ratio of the weight fractions of the first cathode active material and the second cathode active material in the composite cathode active material can be chosen arbitrarily.

[0059] The second cathode active material is preferably present in a proportion of 1 to 50 wt.%, based on the total weight of the first cathode active material and the second cathode active material, preferably in a proportion of 5 to 30 wt.%.

[0060] In addition to the cathode active material, the cathode may further comprise additives such as binders and electrical conductivity additives. The binder (also referred to as electrode binder) is in particular selected from the group consisting of polyethylene oxide (PEO), polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVdF), polyvinylidene fluoride-hexafluoropropylene copolymer (PVdF-HFP), cellulose, acrylates (e.g., polymethyl methacrylate), polyvinylpyrrolidone (PVP), styrene-butadiene rubber (SBR), polyisobutene (PIB), polyethylene (PE), polypropylene (PP), and mixtures thereof.

[0061] The electrical conductivity additive (also referred to as electrical conductivity additive) can be selected from the group consisting of conductive carbon black, carbon nanotubes (CNT), graphene, graphite, expanded graphite and carbon nanofibers, porous carbons (as described, for example, in EP 2 528 879 B1 and DE 10 2013 106 114 A1), gas-phase produced carbon nanofibers (also referred to as “VGCF” for English “vapour grown carbon fibers”) and combinations thereof.

[0062] The anode active material can be selected from the group consisting of hard carbon, soft carbon, synthetic graphite, natural graphite, graphene, mesocarbon, doped carbon, tin, tin oxide, phosphorus, antimony, antimony oxide, Prussian blue analogues and mixtures thereof.

[0063] The Prussian Blue analogue in the anode active material can be selected analogously to the Prussian Blue analogues described for the composite cathode active material, but where 0 < x < 2.

[0064] Hard carbon is particularly preferred as the anode active material.

[0065] In particular, the hard carbon can be a hard carbon that has been industrially produced from renewable materials through appropriate carbonization. Such hard carbon types are marketed, for example, by Stora Enso under the name Lignode®.

[0066] The anode active material is, in particular, pre-sodium-treated to such an extent that, before the first discharge and / or charge process of the sodium-ion battery, more sodium is present than is required to form the SEI during anode production and / or the formation of the sodium-ion battery. Preferably, the anode active material has a degree of sodification greater than 0 and, in addition, a stable SEI before the first discharge and / or charge process of the sodium-ion battery.

[0067] The anode active material is pre-sodium-stoichiometrically pre-sodium-containing, particularly before the first discharge and / or charge process. This means that the degree of sodium-containing of the anode active material is, in particular, less than 1.

[0068] In particular, the degree of sodiation of the anode active material before the first discharge and / or charge process can be in the range from 0.01 to 1, preferably in the range from 0.05 to 0.6, particularly preferably from 0.1 to 0.5.

[0069] If the anode active material already contains sodium, which cannot participate in the cyclization because it cannot be extracted electrochemically, i.e. is not active sodium, this proportion of sodium is not considered as a component of the pre-sodium treatment according to the invention.

[0070] In addition to the anode active material, the anode may contain further components and additives, such as a carrier, a binder, and / or an electrically conductive additive. All conventional compounds and materials known in the art, as well as the compounds previously described for the cathode, can be used as further components and additives.

[0071] Preferably, the anode active material is pre-sodium-treated before the first discharge and / or charge process of the sodium ion battery to such an extent that the sodium ion battery has a state of charge (SoC) in the range from 1 to 100%, preferably from 5 to 60%, particularly preferably from 10 to 50%, before the first discharge and / or charge process.

[0072] The SoC indicates the remaining available capacity of the sodium-ion battery in relation to the maximum capacity of the sodium-ion battery and can be easily determined, for example, via the voltage and / or current flow of the sodium-ion battery.

[0073] The amount of sodium required to pre-sodium the anode active material to achieve a specific SoC before the first discharge and / or charge of the sodium-ion battery depends on whether an SEI has already formed on the anode active material before the first discharge and / or charge of the sodium-ion battery. If an SEI has not yet formed on the anode active material, the anode active material should be pre-sodium-treated to such an extent that the added sodium is sufficient both to form the SEI and to achieve the corresponding capacity of the sodium-ion battery. The amount of sodium required to form the SEI can be estimated based on the anode active materials used.

[0074] The SoC of the sodium-ion battery before the first discharge and / or charge process can be adjusted not only by the pre-sodination of the anode active material, but also by the total sodination degree of the composite cathode active material.

[0075] The total sodification level of the composite cathode active material can be adjusted to match the pre-sodification level of the anode active material. In other words, the total sodification level of the composite cathode active material can be reduced by the amount of sodium used for pre-sodification of the anode active material. In this way, the energy density or open cell voltage of the sodium-ion battery is further optimized.

[0076] The anode active material can also be pre-sodium-treated to such an extent that a sodium excess results in the sodium-ion battery, while at the same time maintaining a SoC in the aforementioned ranges before the first discharge and / or charge of the sodium-ion battery. An excess of sodium can serve to improve the service life of the sodium-ion battery.

[0077] Between the cathode and the anode, the sodium ion battery according to the invention has a separator which separates the two electrodes from each other, i.e. the cathode and the anode.

[0078] The separator is permeable to sodium ions but non-conductive to electrons.

[0079] Polymers can be used as the separator, in particular a polymer selected from the group consisting of polyesters, in particular polyethylene terephthalate, polyolefins, in particular polyethylene and / or polypropylene, polyacrylonitriles, polyvinylidene fluoride, polyvinylidene hexafluoropropylene, polyetherimide, polyimide, aramid, polyether, polyether ketone, synthetic spider silk (as described, for example, in DE 10 2018 205484 A1), or mixtures thereof. The separator can optionally be additionally coated with a ceramic material, for example, with SiO2 or Al2O3.

[0080] In addition, the sodium-ion battery has an electrolyte that is conductive to sodium ions and can be either a solid electrolyte or a liquid comprising an electrolyte solvent and at least one sodium conducting salt dissolved therein, for example, sodium hexafluorophosphate (NaPFe). Other possible sodium conducting salts can be: sodium triflate (NaCFsSCh), sodium tetraborate (NaBF4), sodium bis(trifluoromethylsulfonyl)amide (NaTFSI), sodium bis(trifluoromethylsulfonyl)amide (NaFSI), and sodium bis(oxalato)borate (NaBOB).

[0081] The electrolyte solvent is preferably inert. Suitable electrolyte solvents include organic solvents such as ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), fluoroethylene carbonate (FEC), vinylene carbonate (VC), sulfolane, 2-methyltetrahydrofuran, acetonitrile, and 1,3-dioxolane.

[0082] In one variant, two or more of the above-mentioned liquids can be used.

[0083] Preferred sodium conducting salts are sodium salts that contain inert anions and are preferably non-toxic. Suitable sodium salts are, in particular, sodium hexafluorophosphate (NaPFe), sodium tetrafluoroborate (NaBF4), and mixtures of these salts.

[0084] If the electrolyte is liquid, the separator is particularly soaked or wetted with the electrolyte.

[0085] The object of the invention is further achieved by a method for producing a sodium-ion battery, comprising the following steps: A composite cathode active material is provided by mixing a first cathode active material and a second cathode active material, wherein the first cathode active material and / or the second cathode active material is a polyanionic cathode active material, and wherein the first cathode active material is fully sodiated and the second cathode active material is fully deodiated. An anode active material is provided. The composite cathode active material is installed in a cathode and the anode active material is installed in an anode, and the cathode and the anode are assembled to form a sodium-ion battery. The anode active material is pre-sodiated before or after the anode active material is installed in the anode.

[0086] The individual components of the sodium ion battery produced in the process according to the invention are made in particular from the materials previously described for the sodium ion battery according to the invention.

[0087] Accordingly, the sodium ion battery according to the invention described above is obtainable in particular by the process according to the invention.

[0088] According to the invention, the composite cathode active material is obtained by mixing the first and second cathode active materials. In other words, the composite cathode active material is, in particular, a blend of the first cathode active material and the second cathode active material. Thus, a composite cathode active material with a desired total sodification level can be obtained particularly easily.

[0089] The pre-sodium treatment of the anode active material can be carried out in particular by the techniques known in the prior art for the production of sodium-containing active materials.

[0090] For example, a mixture of the anode active material with metallic sodium can be prepared. The mixture of anode active material can be stored for a period of up to two weeks, preferably up to one week, and particularly preferably up to five days. During this period, the sodium can be incorporated into the anode active material, thus obtaining a pre-sodium-treated anode active material.

[0091] In one variant, the pre-sodium treatment of the anode active material can be carried out by mixing the anode active material with a sodium precursor and subsequently converting the sodium precursor to metallic sodium. In another variant, the pre-sodium treatment of the anode active material can be carried out by injecting sodium into the anode active material and / or the anode.

[0092] In a further variant, the pre-sodium plating of the anode active material can be carried out by vapor deposition of sodium onto the anode active material and / or the anode.

[0093] By storing the anode in an electrolyte for a predetermined period of time, for example, 2 minutes to 14 days, a stable SEI can be built up on the anode.

[0094] Finally, it is possible to pre-sodium the anode active material by electrochemically treating it in a sodium-containing electrolyte. In this way, the SEI can be formed on the anode during pre-sodium treatment. By storing the anode in the electrolyte, the SEI can be further completed and kinetically stabilized.

[0095] In order to produce a sodium-ion battery that is ready for immediate use, the sodium-ion battery can have a state-of-charge (SoC) in the range of > 1% immediately after the assembly step, before a first discharge and / or charge process of the sodium-ion battery.

[0096] The object of the invention is further achieved by the use of a sodium-ion battery as described above in a vehicle, a stationary energy storage device, or a portable device. The portable device can, in particular, be a smartphone, a power tool, a tablet, or a wearable device. The sodium-ion battery is preferably used in a vehicle, for example, a hybrid or electric vehicle.

[0097] Further advantages and features of the invention will become apparent from the following description and examples, which are not to be understood in a limiting sense.

[0098] Table 1 lists the substances and materials used in the examples. Table 1: Substances and materials used. Example 1 (Reference example)

[0099] A mixture of 94 wt.% sodium iron phosphate (NaFePO4, NFP), 3 wt.% PVdF, and 3 wt.% conductive carbon black is suspended in NMP at 20 °C using a high-shear dissolver mixer. This results in a homogeneous cathode coating mass, which is doctored onto a 15 μm thick aluminum carrier foil. After removing the NMP, a composite cathode film with a basis weight of 19.5 mg / cm is obtained. 2 .

[0100] Analogously, an anode coating composition with a composition of 94 wt.% hard carbon, 2 wt.% SBR, 2 wt.% CMC, and 2 wt.% Super C65 is prepared and applied to a 15 μm thick rolled aluminum carrier foil. The resulting anode film has a basis weight of 5.7 mg / cm 2 .

[0101] The cathode with the cathode film is assembled into an electrochemical cell with 25 cm using an anode with the anode film, a separator (thickness: 25 pm) made of polypropylene (PP) and a liquid electrolyte of a 1 M solution of NaPFe in EC / DMC (3:7 w / w). 2 The active electrode surface is packaged and sealed in a high-quality aluminum composite foil (thickness: 0.12 mm). The result is a pouch cell with external dimensions of approximately 0.5 mm x 6.4 mm x 4.3 mm.

[0102] The cell is first charged to 3.5 V (C / 10) and then discharged with C / 10 to 2.0 V.

[0103] The capacity of the first charge is 52.5 mAh and the capacity of the first discharge is 38.5 mAh. This results in a formation efficiency of approximately 73.3% for the entire cell, which corresponds to a formation loss of approximately 26.7%.

[0104] Example 2 (Sodium ion battery according to the invention)

[0105] A mixture of 65.8 wt.% sodium iron phosphate (NaFePO4), 28.2 wt.% FePO4, 3 wt.% PVdF, and 3 wt.% conductive carbon black is suspended in NMP at 20 °C using a high-shear mixing device. A homogeneous cathode coating mass is obtained, which is doctored onto an aluminum collector carrier foil rolled to a thickness of 15 μm. After removing the NMP, a cathode film with a basis weight of 19.5 mg / cm is obtained. 2 .

[0106] Analogously, an anode coating composition with a composition of 94 wt.% hard carbon, 2 wt.% SBR, 2 wt.% CMC, and 2 wt.% Super C65 is prepared and applied to a 15 μm rolled aluminum collector carrier foil. The resulting anode film has a basis weight of 7.5 mg / cm 2 .

[0107] This anode film is pre-sodium-treated with 30.8 mAh of sodium prior to cell assembly. Approximately 15.7 mAh of sodium forms a SEI protective layer, and approximately 15.1 mAh of sodium remains as cyclable sodium in the hard carbon.

[0108] 30.8 mAh sodium corresponds to about 1.15 mmol or about 26.5 mg sodium.

[0109] The cathode with the cathode film is combined with an anode with the anode film, a separator (25 pm) and an electrolyte of a 1 M solution of NaPFe in EC / DMC (3:7 w / w) to form an electrochemical cell with 25 cm 2 The electrode surface is packaged and sealed in aluminum foil (thickness: 0.12 mm). This results in a pouch cell with external dimensions of approximately 0.5 mm x 6.4 mm x 4.3 mm.

[0110] After dosing the electrolyte and final sealing of the cell according to the invention, it has an open voltage of approximately 2.3 to 2.9 V, resulting from the potential difference between the partially deodized cathode and the pre-sodium-treated anode. The nominal capacity of the sodium-ion battery is 50.4 mAh, so the sodium-ion battery has a state-of-charge (SoC) of 30% immediately after production.

[0111] The cell is initially charged to 3.5 V (C / 10) and then discharged at C / 10 to 2.0 V. Since the cell already has a SoC of 30% after assembly and activation with liquid electrolyte, a charge of 35.3 mAh is observed during further formation at C / 10, while the first C / 10 discharge is 50.4 mAh.

[0112] The sodium-ion battery according to the invention accordingly has a 31% higher nominal capacity with an identical total cathode load and a 32% higher anode load compared to the reference example. In a further embodiment, the anode load could alternatively be kept constant compared to the reference example and the cathode load reduced, resulting in a similar nominal capacity, but with significantly reduced cathode material usage. Since an anode with pre-sodium-treated anode active material and partially deoxidized composite cathode active material is used to manufacture the sodium-ion battery, the sodium-ion battery according to the invention can be used immediately after the manufacturing step.

Claims

Patent claims 1. A sodium ion battery having a cathode comprising a composite cathode active material and an anode comprising an anode active material, wherein the composite cathode active material comprises at least a first cathode active material and a second cathode active material, wherein the first cathode active material and / or the second cathode active material is a polyanionic cathode active material, wherein the first cathode active material is fully sodiated and the second cathode active material is fully deodiated before the first discharge and / or charge process of the sodium ion battery, and wherein the anode active material is pre-sodiated before the first discharge and / or charge process of the sodium ion battery.

2. Sodium ion battery according to one of the preceding claims, wherein the polyanionic cathode active material is selected from the group of phosphates, sulfates, silicates and combinations thereof.

3. A sodium ion battery according to claim 2, wherein the polyanionic cathode material is selected from compounds having a NASICON structure, a tavorite structure, an olivine structure, an alluaudite structure, layered compounds, and combinations thereof.

4. A sodium ion battery according to claim 2 or 3, wherein the polyanionic cathode material contains a transition metal selected from the group consisting of iron, manganese, vanadium, and combinations thereof.

5. Sodium ion battery according to one of the preceding claims, wherein the second cathode active material is present in a proportion of 1 to 50 wt.%, based on the total weight of the first cathode active material and the second cathode active material, preferably in a proportion of 5 to 30 wt.%.

6. Sodium ion battery according to one of the preceding claims, wherein the anode active material is selected from the group consisting of hard carbon, soft carbon, synthetic graphite, natural graphite, graphene, Mesocarbon, doped carbon, tin, tin oxide, phosphorus, antimony, antimony oxide, Prussian blue analogues and mixtures thereof.

7. Sodium ion battery according to one of the preceding claims, wherein the anode active material is pre-sodium-treated before the first discharge and / or charge process of the sodium ion battery to such an extent that the sodium ion battery has a state of charge (SoC) in the range from 1 to 100%, preferably from 5 to 60%, particularly preferably from 10 to 50%, before the first discharge and / or charge process.

8. A method for producing a sodium ion battery, comprising the following steps: - Providing a composite cathode active material by mixing a first cathode active material and a second cathode active material, wherein the first cathode active material and / or the second cathode active material is a polyanionic cathode active material, and wherein the first cathode active material is fully sodiated and the second cathode active material is fully deodiated; - Providing an anode active material; - incorporating the composite cathode active material in a cathode and the anode active material in an anode; and - Assembling the cathode and the anode to form a sodium-ion battery; wherein the anode active material is pre-sodium-treated before or after the anode active material is incorporated into the anode.

9. The method according to claim 7, wherein the sodium ion battery has a state of charge (SoC) in the range of > 1% immediately after the assembly step, before a first discharge and / or charge process of the sodium ion battery.

10. Use of a sodium ion battery according to one of claims 1 to 7 in a vehicle, a stationary energy storage device or a portable device.

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