Sodium-ion battery with sodium metal anode and method of making a sodium-ion battery

Abstract

A sodium-ion battery has a cathode comprising a cathode active material and a sodium metal anode, wherein the cathode active material has been at least partially desodiumified prior to the first discharge and / or charging process of the sodium-ion battery. A method for preparing the sodium-ion battery is also proposed.

Description

Technical Field

[0001] This invention relates to a sodium-ion battery having a sodium metal anode and a method for preparing a sodium-ion battery. Background Technology

[0002] In the following text, the term "sodium-ion battery" is used as a synonym for all names commonly used 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 rechargeable battery. This includes, in particular, rechargeable batteries (secondary batteries). The terms "battery" and "electrochemical cell" are also used as synonyms for the term "sodium-ion battery." Sodium-ion batteries can also be solid-state batteries, such as inorganic, ceramic, gel-based, or polymer-based solid-state batteries.

[0003] To meet the demand for electrochemical energy storage devices for stationary and mobile applications, lithium-free galvanic elements or systems are increasingly returning to the forefront. Sodium-ion batteries are essentially the only known alternative to lithium-based compound-based electrochemical storage devices in the prior art.

[0004] Sodium-ion batteries have at least two distinct electrodes: a positive electrode (cathode) and a negative electrode (anode). Each of these electrodes has at least one active material (correspondingly referred to as cathode active material or anode active material), optionally along with additives (such as electrode binders and conductivity additives, such as conductive carbon black).

[0005] For a general description of sodium-ion technology, see 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 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).

[0006] In sodium-ion batteries, both the cathode active material and the anode active material must be able to reversibly accept or release sodium ions.

[0007] Currently, in existing technologies, sodium-ion batteries are assembled and assembled in a completely uncharged state. This corresponds to a state where sodium ions are fully inserted (i.e., embedded) into the cathode, while the anode typically does not have active (i.e., reversibly cyclic) sodium ions.

[0008] Similar to lithium-ion batteries with an anode formed of metallic lithium, sodium-ion batteries using metallic sodium as the anode (also known as "sodium metal anodes") are also known. Recyclable sodium, contained in the cathode active material after assembly, can be deposited on the sodium metal anode used during the charging process of such a sodium-ion battery and then detached again during the discharging process.

[0009] Here, typically, a thin layer of sodium metal is used on the anode (on which the cyclic sodium of the cathode is deposited). This "excess" serves as a substrate for metal deposition, but also improves the lifespan of such electrochemical cells because the excess can be used for cycling in the event of a side reaction that consumes sodium.

[0010] One drawback of this type of sodium-ion battery is that the sodium metal anode installed in the battery must have a relatively small thickness of about 10 μm in order to minimize the excess sodium metal for cost reasons and to minimize the energy density loss caused by the excess sodium metal. For this purpose, a rolling process is typically used. However, such rolling processes are time-consuming, labor-intensive, and expensive, with costs increasing disproportionately as the thickness decreases.

[0011] In addition, it is not permissible to fully predict the volume changes that may occur due to the cyclic sodium deposited on the anode in every case, which may adversely affect the dimensional accuracy and lifespan of the sodium-ion battery due to the unexpected expansion effect of the anode during charging.

[0012] In the known cell manufacturing process in the prior art, sodium-ion batteries are first assembled in an uncharged state, and then formed, which involves the first charge and discharge cycles. Formation (or Formierung) is an extremely cost-intensive process because it requires specialized equipment and adherence to the highest safety standards, especially in terms of fire prevention. Summary of the Invention

[0013] The object of this invention is to provide a sodium-ion battery with a long service life and which can be manufactured at a low cost. A further object of this invention is to provide a low-cost method for providing such sodium-ion batteries.

[0014] According to the present invention, the objective is achieved by a sodium-ion battery having a cathode and a sodium metal anode, the cathode comprising a cathode active material, wherein the cathode active material is at least partially desodiumified prior to the first discharge and / or charging process of the sodium-ion battery.

[0015] According to the present invention, at least partially desodiumized active materials have a degree of sodiumization of less than 1, while sodiumized or presodiumized active materials have a degree of sodiumization of greater than 0.

[0016] The term "sodium saturation" refers to the ratio of the amount of sodium (in the form of sodium ions, metallic sodium, and / or sodium alloys) that can be reversibly recycled for each chemical unit of the active material to the maximum amount of sodium that can be reversibly recycled in the active material. In other words, sodium saturation is a measure of the percentage of recyclable sodium, given in advance by the chemical unit of the active material, embedded or intercalated within the structure of the active material.

[0017] A degree of sodiumization of 1 here refers to a fully sodium-modified active material, while a degree of sodiumization of 0 indicates a fully desodium-modified active material.

[0018] It goes without saying that the amount of sodium capable of reversible cycling depends on the voltage range in which the sodium-ion battery is intended to operate. Accordingly, the chemical formula of the active material may contain sodium that is not reversibly cyclic within the voltage range envisioned in each case, even if said sodium might be reversibly cyclic when the voltage range is extended to relatively high voltages. In this case, the degree of sodiumization only relates to the proportion of sodium that is reversibly cyclic within the selected voltage range.

[0019] The voltage range is specifically defined by a maximum voltage of up to 5.0 V, preferably up to 4.5 V, and particularly preferably up to 4.3 V.

[0020] For example, when the voltage range has a maximum voltage of up to 4.3 V, especially when the voltage range has a voltage in the range of 2.0 V to 4.3 V, the degree of sodicity is equal to 1 in sodium vanadium fluorophosphate (NVPF) with the chemical formula unit Na3V2(PO4)F3 in stoichiometry, and equal to 0 in the desodiumized related compound NaV2(PO4)F3.

[0021] Alternatively, the degree of sodiumization can be given as a percentage by multiplying the corresponding sodiumization value by 100%. Thus, for example, a sodiumization of 1 corresponds to 100% sodiumization, a sodiumization of 0.5 corresponds to 50% sodiumization, and a sodiumization of 0 corresponds to 0% sodiumization.

[0022] According to the present invention, prior to the first discharge and / or charging process of the sodium-ion battery, the cathode active material has been at least partially desodiumized. The term "desodiumized" or "sodium-free" means that, prior to the first discharge and / or charging process of the sodium-ion battery, sodium has been at least partially removed from the structure of the cathode active material compared to a fully sodium-free cathode active material, i.e., the degree of sodium-freeing is less than 1. The amount of recyclable sodium missing due to the desodiumization of the cathode active material is correspondingly provided by a sodium metal anode in which metallic sodium is present.

[0023] Thus, prior to the first discharge and / or charge process, the sodium-ion battery according to the invention is at least partially charged, i.e., has a state of charge (SoC) greater than 0%. This allows the sodium-ion battery to be ready for use immediately after assembly or assembly.

[0024] The initial discharge and / or charge process can be performed directly in the envisioned application, such as at the end user. Alternatively, individual electrochemical cells can be connected into a battery module first, followed by the initial discharge and / or charge.

[0025] This method eliminates the pre-charging and formation steps (i.e., the initial charge of the sodium-ion battery) in the manufacturing process, thereby shortening production time. Furthermore, it reduces current consumption during manufacturing and the scale and operation of necessary production facilities.

[0026] Another advantage of the sodium-ion battery according to the invention is that the volume change that occurs during charging of the sodium-ion battery relative to its volume during cell assembly can be minimized or even completely suppressed, because the installed sodium metal anode has already provided an amount of sodium corresponding to the degree of desodiumification of the cathode active material. This improves the dimensional accuracy of the sodium-ion battery and thus enhances its reliability and lifespan.

[0027] Furthermore, the thickness of the sodium metal anode, which must be considered and processed during the assembly or assembly of the sodium-ion battery (while maintaining the same energy content in the finished sodium-ion battery), can be selected to be greater than the thickness when using a fully sodium-based cathode active material. This eliminates the need for additional processing steps, such as additional rolling steps, during the fabrication of the sodium metal anode, thereby reducing the manufacturing cost of the sodium-ion battery.

[0028] The sodium metal anode has, for example, a thickness of up to 75 µm, preferably in the range of 20 to 50 µm.

[0029] In this regard, the thickness refers to the thickness of the sodium metal anode prior to the first discharge and / or charging process of the sodium-ion battery.

[0030] It goes without saying that when the sodium-ion battery is charged to a SoC higher than that obtained directly after assembling the sodium-ion battery, the thickness of the sodium metal anode can be further increased, and when the sodium-ion battery is discharged to a SoC lower than that obtained directly after assembling the sodium-ion battery, the thickness of the sodium metal anode can be further reduced.

[0031] Prior to the first discharge and / or charge process of the sodium-ion battery, the cathode active material may have a sodium saturation of up to 0.50, preferably up to 0.25. As the sodium saturation of the cathode active material gradually decreases, the SoC of the sodium-ion battery obtained directly after assembly increases, and this can be attributed to the sodium metal anode having a gradually increasing thickness.

[0032] In one variant, the cathode active material has been completely desodiumified prior to the first discharge and / or charge cycle of the sodium-ion battery. In other words, apart from unavoidable impurities, there is no recyclable sodium within the cathode active material prior to the first discharge and / or charge cycle of the sodium-ion battery.

[0033] Therefore, in this variant, the degree of sodiumization of the cathode active material is zero before the first discharge and / or charging process, and the SoC of the sodium-ion battery is 100% immediately after assembly. In this way, a sodium metal anode with a thickness corresponding to the maximum thickness of the sodium-ion battery during operation can be used to obtain a sodium-ion battery with particularly accurate dimensions.

[0034] Furthermore, this design of sodium-ion batteries is particularly advantageous when it is easier to synthesize a fully sodium-free cathode active material than to synthesize a partially sodium-free cathode active material.

[0035] Partially or completely desodiumized cathode active materials are commercially available or can be obtained by electrochemically extracting sodium from fully or partially sodiumized cathode active materials.

[0036] Sodium can also be chemically extracted from fully or partially sodium-modified cathode active materials by using acids, such as sulfuric acid (H2SO4), to dissolve sodium.

[0037] Another possibility is to synthesize formulations that a priori have the desired degree of sodicity by means of solid-state synthesis.

[0038] The cathode active material can be selected from the group consisting of Prussian blue analogues (Preußisch-Blau-Analoga), polyanionic cathode active materials, layered oxides and combinations thereof, and preferably from the group consisting of Prussian blue analogues, polyanionic cathode active materials and combinations thereof.

[0039] Prussian blue analogues and polyanionic cathode active materials are fully compatible with commonly used electrode binders, electrolyte compositions, and conductivity additives (such as conductive carbon black) and with commonly used cathode active material preparation processes, such as mixing, coating, calendering, stamping, cutting, winding, stacking, and laminating processes.

[0040] Prussian blue analogues (also known as "PBA") are known as active materials for sodium-ion batteries. The term "Prussian blue analogue" is understood to refer to compounds whose crystal structure is equal to or substantially equal to that of Prussian blue. For example, when desodiumning is used to obtain compounds with the chemical formula unit Na... 2-x When desodium-modified analogues of Fe[Fe(CN)6] (where 0 < x ≤ 2), the structure of Prussian white Na2Fe[Fe(CN)6] remains unchanged.

[0041] The types of Prussian blue analogues are essentially not further restricted, provided that at least a partially desodiumized form of the corresponding cathode active material is available or can be prepared or produced.

[0042] General prior art concerning Prussian blue analogues used in sodium-ion batteries is exemplarily referenced to WO2018 / 209653 A1 and WO 2022 / 121570 A1.

[0043] Prussian blue analogues are particularly selected from compounds Na x M[M' (CN)6] 1-y The group of z H2O, wherein 0 ≤ x < 2, 0 ≤ y < 1 and z ≥ 0, and wherein M and M' are selected from the group of transition metals, preferably from the group consisting of iron, manganese, chromium, nickel, cobalt and copper.

[0044] Preferably, M and M' are selected from the group consisting of iron, manganese, and chromium, respectively. Correspondingly, the Prussian blue analogue is preferably free of nickel and cobalt.

[0045] Particularly preferred is the combination of M and M' (M / M') selected from the group consisting of Fe and Fe (Fe / Fe), Fe and Mn (Fe / Mn) and manganese and manganese (Mn / Mn).

[0046] Possible synthetic routes for preparing suitable cathode active materials based on Prussian blue analogues are described, for example, in Cheryldine QX Lim and Zhi-Kuang Tan, “Prussian White with Near-Maximum Specific Capacity in Sodium-ion Batteries” (ACS Appl. Energy Mater. 2021, 4, pp. 6214-6220, doi: 10.1021 / acsaem.1c00987) and Brant et al., “Selective Control of Composition in Prussian White for Enhanced Material Properties” (Chem. Mater. 2019, 31, pp. 7203-7211, doi: 10.1021 / acs.chemmater.9b01494).

[0047] Polyanionic cathode active materials are also known as active materials for sodium-ion batteries. For general prior art regarding the use of polyanionic cathode active materials in sodium-ion batteries, exemplarily refer to 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).

[0048] The types of polyanionic cathode active materials are essentially not further restricted, provided that at least a partially desodiumized form of the corresponding cathode active material is available or can be prepared or produced.

[0049] The polyanionic cathode active material is particularly selected from phosphates, sulfates, silicates, and combinations thereof. Corresponding polyphosphates, polysulfates, and polysilicates are included within this option.

[0050] Preferably, the polyanionic cathode active material is selected from compounds having NASICON, Tavorit, olivine, or sodium manganese phosphate structures, layered compounds, and combinations thereof. Such compounds are capable of reversibly accepting and releasing sodium ions while the basic structure of the cathode active material remains substantially unchanged. This reduces the stress exerted on the cathode material during charge and discharge cycles and thereby improves the lifespan of the sodium-ion battery.

[0051] In this respect, the term "layered compound" does not simultaneously include compounds that have oxygen anions and can be expressed using the general formula Na. x MO2 describes the so-called "layered oxide" or "layered oxide", where M represents a transition metal.

[0052] The polyanionic cathode active material may contain a transition metal, which is selected from the group consisting of iron, manganese, vanadium, and combinations thereof.

[0053] For example, the polyanionic cathode active material is selected from the following group of compounds: Na 1-x FePO4 (NFP), Na 2-x' Fe3(PO4)3, Na 2-x' FeP2O7, Na 1-x MnPO4, Na 2-x' MnP2O7, Na 2-x' MnP2O7, Na 2-x' MnPO4F, Na 4-x''' (Fe,Mn)3(PO4)2(P2O7), Na 3-x'' V2(PO4)3 (NVP), Na 3-x'' V2(PO4)2F3 (NVPF), Na 3-x'' V 2-y (VO) y (PO4)2F 3-y Na 2-x' Fe2(SO4)3, Na 2+2z-x'' Fe 2-z (SO4)3, Na 2-x' Mn2(SO4)3, Na 2-x' Fe2(SiO4)3, Na 2-x' Mn2(SiO4)3, Na 2-x' FeSiO4, Na 2-x' MnSiO4 and its combinations, wherein 0 ≤ x < 1, 0 ≤ x' < 2, 0 ≤ x'' < 3, 0 ≤ x''' < 4, 0 ≤ y < 3 and 0 ≤ z < 2.

[0054] The layered oxide (also known as "layered oxide") can be of the general formula Na. x Compounds of MO2, where M represents a transition metal and 0 ≤ x ≤ 1.

[0055] For example, the layered oxide is selected from the compound Na. x MO2, where M is selected from the group consisting of manganese, iron, cobalt, nickel, aluminum, copper, titanium, zinc or combinations thereof and 0 ≤ x ≤ 1.

[0056] Alternatively, the cathode active material may be doped, wherein the element used for doping partially replaces the transition metal.

[0057] For example, M and M', respectively, Prussian blue analogues of Fe, can be doped with elements selected from the group consisting of manganese, chromium, nickel, cobalt, and copper. In the case of a polyanionic cathode active material comprising a transition metal selected from the group consisting of iron, manganese, vanadium, and combinations thereof, the cathode active material can be doped with elements selected from the group consisting of manganese, chromium, nickel, cobalt, copper, and combinations thereof.

[0058] "Doping" is understood to mean that, relative to the total weight of the polyanionic cathode active material, the content of the corresponding element is at most 5% by weight, and especially at most 1% by weight.

[0059] The cathode active material can have a particle size in the range of 0.1 to 35 μm, preferably 1 to 20 μm. Such a particle size is optimally suited for blending the cathode active material with other particles, especially with conductive carbon black. This results in a uniform and highly dense cathode coating material that can be used in the cathode of a sodium-ion battery.

[0060] In addition to the cathode active material, the cathode may also contain additives, such as binders and conductivity additives.

[0061] The binder (also known as the electrode binder) is particularly 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), styrene-butadiene rubber (SBR), polyisobutylene (PIB), and mixtures thereof.

[0062] Electrical conductivity additives (also known as conductive additives) may be selected from the group consisting of conductive carbon black, carbon nanotubes (CNTs), graphene, graphite, expanded graphite and carbon nanofibers, porous carbon (such as those described in EP 2 528 879 B1 and DE10 2013 106 114 A1), vapor-grown carbon nanofibers (also known as “VGCF”, which stands for “vapour grown carbon fibers” in English) and combinations thereof.

[0063] The anode is a sodium metal anode, wherein metallic sodium is used as the active material and also as the matrix, and recyclable sodium is bound thereto.

[0064] The sodium metal anode may have at least one modification, such as metal doping, carbon addition, or stabilizing elements, as applied to the framework structure of the sodium metal anode.

[0065] However, the anode contains, in particular, no anodic active materials other than metallic sodium, such as hard carbon, soft carbon, synthetic graphite, natural graphite, graphene, mesophase carbon, doped carbon, tin, tin oxide, phosphorus, antimony, antimony oxide, Prussian blue analogues and mixtures thereof.

[0066] In one variant, the sodium-ion battery is a solid-state battery. The unique feature of solid-state batteries is that they eliminate the need for a liquid electrolyte. This suppresses undesirable side reactions between the electrolyte and the sodium metal anode, and simplifies the design of the sodium-ion battery.

[0067] In order to provide sufficient ionic conductivity in a sodium-ion battery without a liquid electrolyte, the cathode may include a solid electrolyte (also referred to as a cathode solid electrolyte).

[0068] The choice of the cathode solid electrolyte is essentially unrestricted, as long as it provides sufficient sodium ion conductivity and can be processed together with the remaining components of the cathode into a uniform cathode coating material.

[0069] For example, the cathode solid electrolyte is a ceramic solid electrolyte, especially a β-alumina compound, a compound having a NASICON structure, rare earth sodium silicate, a chalcogenide-based compound such as Na3PSe4, or a combination thereof.

[0070] It goes without saying that compounds with a NASICON structure that can be used as cathode solid electrolytes are different from polyanionic cathode active materials with a NASICON structure.

[0071] In particular, compounds with a NASICON structure suitable for use as cathode solid electrolytes exhibit higher sodium ion conductivity than polyanionic cathode active materials with a NASICON structure. Exemplary compounds with a NASICON structure that can be used as cathode solid electrolytes are described in Von Alpen et al.: “Compositional dependence of the electrochemical and structural parameters in the Nasiconsystem (Na…”). 1+x Si x Zr2P 3-x O 12 (Nasicon system (Na)) 1+x Si x Zr2P 3-x O 12 Composition dependence of electrochemical and structural parameters in (Solid State Ionics, Vol. 3-4, 1981, pp. 215-218, doi: 10.1016 / 0167-2738(81)90085-0).

[0072] In particular, an additional solid electrolyte is arranged between the cathode and the sodium metal anode of the sodium-ion battery. This additional solid electrolyte also serves as a membrane and is thus also referred to as a membrane solid electrolyte.

[0073] The membrane solid electrolyte may be selected from the same compound as the cathode solid electrolyte, wherein the membrane solid electrolyte and the cathode solid electrolyte may be the same or different from each other.

[0074] The object of the present invention is also achieved by a method for preparing a sodium-ion battery, the method comprising the steps of: providing a cathode active material, wherein the cathode active material has been at least partially desodiumized; providing a sodium metal anode; the cathode active material being disposed in a cathode, and the cathode and the sodium metal anode being assembled into a sodium-ion battery.

[0075] The various components of the sodium-ion battery prepared in the method of the present invention are made, in particular, of the materials described above for the sodium-ion battery of the present invention.

[0076] Correspondingly, the sodium-ion battery of the present invention described above can be obtained in particular by the method of the present invention.

[0077] The at least partially desodiumized cathode active material can be provided by solid synthesis or by pre-sodiumization of a completely desodiumized cathode active material.

[0078] The cathode active material can be pre-sodium-treated, in particular, by techniques known in the prior art, to prepare a sodium-containing active material.

[0079] For example, a mixture of the cathode active material and metallic sodium can be prepared. This mixture formed from the cathode 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, sodium can be incorporated into the cathode active material, thereby obtaining a pre-sodiumized, i.e., partially desodiumized, cathode active material.

[0080] In one variant, the cathode active material can be pre-sodiumized by mixing it with a sodium precursor and subsequently converting the sodium precursor into metallic sodium.

[0081] In another variant, the cathode active material can be pre-sodium-treated by pressing sodium into it.

[0082] In another variant, the cathode active material can be pre-sodiumed by depositing sodium onto it.

[0083] Prior to assembly, the sodium metal anode can be adjusted to a maximum thickness of 75 µm, preferably in the range of 20 to 50 µm. The selected thickness is particularly matched to the desodiuming of the cathode active material, wherein a thicker sodium metal anode can be used as the cathode active material is further desodiumed.

[0084] The thickness of the sodium metal anode can be adjusted by means of rolling, compression, sputtering, or vapor deposition using physical vapor deposition.

[0085] Preferably, the sodium metal anode is rolled to the desired thickness prior to assembly. Rolling is a relatively inexpensive process and requires the necessary rolling equipment for testing in battery production facilities.

[0086] Following the assembly step and prior to the first discharge and / or charge process of the sodium-ion battery, the sodium-ion battery can have a state of charge (SoC) of at least 50%, preferably at least 75%. Accordingly, the prepared sodium-ion battery is suitable for direct use in the envisioned application scenarios.

[0087] In one variant, after assembly, the sodium-ion battery is discharged to a target state of charge (target SoC). The target SoC is specifically selected to give the sodium-ion battery the desired state of charge for transporting the sodium-ion battery.

[0088] The electrical energy generated when the sodium-ion battery is discharged can be used to operate the production equipment used to manufacture the sodium-ion battery and / or can be fed into the power grid. This optimizes the energy requirements of the production equipment.

[0089] It is also possible that the discharge of the sodium-ion battery is decoupled from the assembly steps in time so that the electrical energy generated during the discharge of the sodium-ion battery can be used at times when there is increased energy demand from this source, such as when electrical energy from renewable sources is only available in limited quantities, such as during dark and windless periods or at night.

[0090] Other advantages and features of the invention will become apparent from the following description and the embodiments, which should not be construed as limiting. Detailed Implementation

[0091] Table 1 lists the substances and materials used in the examples.

[0092] Table 1: Substances and materials used.

[0093]

[0094] Example 1 (Reference Example)

[0095] At 20°C, a mixture consisting of 75 wt% Prussian white (Na2Fe[Fe(CN)6]), 3.5 wt% PVdF, 3.5 wt% conductive carbon black, and 18 wt% solid electrolyte was suspended in NMP using a dissolving mixer under high shear. A uniform cathode coating material was obtained, which was then coated onto an aluminum carrier foil rolled to a thickness of 15 μm. After NMP removal, a cathode material with a concentration of 24.4 mg / cm³ was obtained. 2 The composite cathode membrane per unit area weight.

[0096] As the anode, a 10 μm thick sodium layer is applied onto a 15 μm thick rolled aluminum carrier foil, for example, by rolling over.

[0097] When using this anode and diaphragm solid electrolyte, the cathode with the cathode membrane is installed with a diameter of 25 cm. 2 An electrochemical cell with an active electrode area is packaged and sealed in a highly refined aluminum composite foil (thickness: 0.12 mm). This produces a pouch cell with external dimensions of approximately 0.5 mm × 6.4 mm × 4.3 mm.

[0098] The battery cell is initially charged to 3.8 V (C / 10), and then discharged to 2.2 V using C / 10.

[0099] The initial charge capacity is 70.6 mAh and the initial discharge capacity is 68.5 mAh. This results in a formation efficiency of approximately 97% for the entire cell, meaning a formation loss of approximately 3%.

[0100] Example 2 (Sodium-ion battery according to the present invention)

[0101] At 20°C, a mixture of the same substances and quantities as in Example 1 was suspended in NMP at high shear using a dissolve-mixer, but with completely desodiumed Prussian white (Fe[Fe(CN)6]) instead of the fully sodium-modified Prussian white in Example 1. A uniform cathode coating material was obtained, which was then scraped onto an aluminum current collector foil rolled to a thickness of 15 μm. After NMP removal, a cathode coating material with a concentration of 21.7 mg / cm³ was obtained. 2 The cathode film weight per unit area. Under the same mass, Prussian white with complete desodiumification achieved a reduced weight per unit area, the mass of sodium that is absent compared to fully sodiumified Prussian white is not included.

[0102] The cathode active material used therefore has a sodium content of 0.

[0103] As the anode, a 35 μm thick sodium layer is applied onto a 15 μm thick rolled aluminum carrier foil, for example by rolling over.

[0104] When using this anode and diaphragm solid electrolyte, the cathode with the cathode membrane is installed with a diameter of 25 cm. 2 An electrochemical cell with an active electrode area is packaged and sealed in a highly refined aluminum composite foil (thickness: 0.12 mm). This produces a pouch cell with external dimensions of approximately 0.5 mm × 6.4 mm × 4.3 mm.

[0105] After final sealing of the cell according to the invention, it has an open-circuit voltage of approximately 3.25 to 3.5 V, which is generated by the potential difference between the cathode with desodiumized cathode active material and the sodium metal anode. The nominal capacity of the sodium-ion battery is 68.5 mAh, and the sodium-ion battery has 100% state of charge (SoC) immediately after fabrication.

[0106] The sodium-ion battery according to the present invention has the same nominal capacity as the sodium-ion battery of the comparative embodiment. Because a cathode having desodium-treated cathode active material is used to prepare the sodium-ion battery according to the present invention, the sodium-ion battery according to the present invention can be used directly after the assembly step.

[0107] In addition, a 35 μm thick sodium foil can be used in the anode for this purpose. The anode can be formed more simply and at a lower cost during the rolling process than for a 10 μm thick sodium foil, because fewer rolling steps are required to obtain a sodium foil of such thickness.

[0108] Furthermore, the sodium-ion battery is fabricated while the electrodes and the entire sodium-ion battery are fully expanded. That is, the sodium-ion battery already possesses the aforementioned external dimensions when fully charged, thereby avoiding mechanical stress caused by the subsequent expansion of the anode during charging.

[0109] Furthermore, after assembling the sodium-ion battery, it can be at least partially discharged, thereby reducing the system-on-chip (SoC) to the target SoC, enabling particularly safe transport of the sodium-ion battery. The electrical energy discharged during this process can be sustainably used directly in the cell manufacturing plant or fed into the power grid.

Claims

1. A sodium-ion battery having a cathode comprising a cathode active material, and a sodium metal anode, wherein the cathode active material has been at least partially desodiated prior to a first discharge and / or charge process of the sodium-ion battery.

2. The sodium-ion battery according to claim 1, wherein the sodium metal anode has a thickness of at most 75 pm, preferably a thickness in the range of 20 to 50 pm.

3. The sodium-ion battery according to claim 1 or 2, wherein the cathode active material has a sodiation degree of at most 0.50, preferably at most 0.25, prior to a first discharge and / or charge process of the sodium-ion battery.

4. The sodium-ion battery according to claim 3, wherein the cathode active material has been completely desodiated prior to a first discharge and / or charge process of the sodium-ion battery.

5. The sodium-ion battery according to any of the preceding claims, wherein the cathode active material is selected from the group consisting of Prussian Blue analogues, polyanionic cathode active materials, layered oxides, and combinations thereof.

6. The sodium-ion battery according to any of the preceding claims, wherein the sodium-ion battery is a solid-state battery.

7. A method of preparing a sodium-ion battery, comprising the steps of: - providing a cathode active material, wherein the cathode active material has been at least partially desodiated; - providing a sodium metal anode; - incorporating the cathode active material in a cathode; and - assembling the cathode and the sodium metal anode into a sodium-ion battery.

8. The method according to claim 7, wherein prior to the assembling the sodium metal anode is conditioned to a thickness of at most 50 pm, preferably a thickness in the range of 40 to 50 pm.

9. The method according to claim 7 or 8, wherein immediately after the assembling step, prior to a first discharge and / or charge process of the sodium-ion battery, the sodium-ion battery has a state of charge (SoC) of at least 50%, preferably at least 75%.

10. The method according to any of claims 7 to 9, wherein after the assembling the sodium-ion battery is discharged to a target state of charge (target SoC).

Images