Method for manufacturing sodium-or potassium-ion battery cell

Abstract

The present disclosure generally relates to a method for manufacturing a sodium or potassium ion battery cell comprising a Prussian blue analogue (PBA) as an active cathode material. The present disclosure also relates to sodium or potassium ion batteries produced by the method.

Description

Technical Field

[0001] The present disclosure generally relates to a method for manufacturing a sodium or potassium ion battery cell, the sodium or potassium ion battery cell including a Prussian blue analogue (PBA) as an active cathode material. The present disclosure also relates to a sodium or potassium ion battery cell produced by the method. Background Art

[0002] Lithium-ion-based batteries dominate the market for rechargeable batteries. However, this technology also has drawbacks, at least in part due to the relatively scarce lithium resources. Although lithium-ion batteries are better than previous generations of secondary battery technologies, lithium-ion-based batteries are not considered environmentally friendly and are also costly from a recycling perspective.

[0003] These drawbacks have triggered an exploration of alternatives to lithium-ion batteries. Sodium or potassium ion batteries represent attractive alternatives and also represent a viable approach to support renewable energy for load balancing and storing excess energy purposes.

[0004] The performance of sodium or potassium ion batteries depends to a large extent on the performance of the electrode materials.

[0005] A typical process for manufacturing an electrode (such as a cathode) is to mix an active material with a solvent, a conductive additive, and a binder to form a slurry. The slurry is then coated on a current collector to form a cathode. The cathode is then assembled with an anode and any other components (such as a separator) used to form a battery.

[0006] In traditional battery production, all steps of the process typically have to be carried out in a drying chamber. A drying chamber refers to a chamber in which the air humidity is controlled at a certain level. If a battery or any component of the battery is exposed to moisture during assembly, this may result in impaired quality, such as reduced charge capacity and reduced overall performance.

[0007] Prussian blue analogue (PBA) cathode materials stand out as promising cathode materials for sodium or potassium ion batteries. Prussian blue analogues have a unique crystal structure with an open three-dimensional framework and large interstitial vacancies and are capable of storing sodium (and potassium) ions.

[0008] When PBA is used as an active cathode material, drying is particularly important because any water present in the PBA structure must be removed to enable the material to fully utilize its capacity in the battery cell. The presence of water may have a negative impact on the electrochemical potential and cycle stability in a battery cell including PBA as the cathode material.

[0009] Therefore, when the PBA material is used in the final battery cell, any water present in the PBA material must be removed. However, once the water is removed from the PBA material, the PBA material still has a strong affinity for water. PBA has extremely strong hygroscopicity and may rapidly change from an anhydrous state to a hydrated state once exposed to air or moisture.

[0010] Therefore, the utilization of a drying chamber is an important part in the process of preparing sodium-ion or potassium-ion batteries using Prussian blue analogue cathode materials. In addition, the drying time is typically long.

[0011] However, there are various disadvantages in using a drying chamber in battery production. First, the drying chamber requires a high investment cost. In addition, due to the need to control the temperature and dry a large amount of air, the energy demand is very high. Another disadvantage of the drying chamber is that it is not a convenient working environment for the personnel working in the drying chamber.

[0012] Therefore, there is a need to provide an improved method for manufacturing sodium-ion or potassium-ion batteries, which is simple, inexpensive and does not require the use of a drying chamber. In addition, the method should also be applicable to the production of large-scale sodium-ion or potassium-ion batteries. Summary of the Invention

[0013] In view of the above and other disadvantages of the prior art, the object of the present disclosure is to provide improvements related to sodium-ion or potassium-ion batteries, particularly to provide a simple and inexpensive manufacturing method for large-scale industrial production of such batteries.

[0014] According to a first aspect of the present invention, there is provided a method for manufacturing a sodium-ion or potassium-ion battery, the method comprising:

[0015] a) providing a slurry comprising a Prussian blue analogue, wherein the Prussian blue analogue can exist in a first hydrated phase and a second dehydrated phase, and wherein the slurry comprises the Prussian blue analogue in the first hydrated phase,

[0016] b) applying the slurry to a current collector to form a cathode,

[0017] c) assembling the cathode with an anode and a separator to form an electrode stack,

[0018] d) drying the electrode stack under conditions that allow the Prussian blue analogue to transform from the first hydrated phase to the second dehydrated phase, wherein the drying is carried out at a drying temperature t1 from 150 °C to 300 °C and a drying time from 1 minute to less than 4 hours,

[0019] e) disposing the electrode stack in a battery housing,

[0020] f) adding an electrolyte to the battery housing, and

[0021] g) Seal the battery housing to form a battery cell, wherein steps e) to g) in this method are carried out under conditions that allow the Prussian blue analogue to remain in the second dehydrated phase throughout steps e) to g).

[0022] Prussian blue analogues (PBAs) can exist in the following forms: hydrated (i.e., aqueous phase); and dehydrated (i.e., anhydrous phase); in the dehydrated phase, water has been removed. The inventors have found that if the conversion of the Prussian blue analogue in the first hydrated phase to the second dehydrated phase is carried out in the final stage of the process and the converted dehydrated phase is maintained throughout the steps of the process, the method of manufacturing sodium or potassium ion battery cells can be greatly improved. Thus, an undesired conversion between the dehydrated phase and the hydrated phase can be prevented.

[0023] In the Prussian blue analogue in the first hydrated phase, the material has a monoclinic crystal structure. PBA materials typically exist in their monoclinic structure in slurries and in steps prior to the drying step.

[0024] In the second dehydrated phase, the PBA material has a rhombohedral crystal structure. For battery applications, it is desirable to utilize the dehydrated rhombohedral phase of PBA to maximize the energy density and cycle stability of the battery cell.

[0025] During the transition from the first phase to the second phase, the lattice of the monoclinic structure is distorted, resulting in a significant change in volume. The phase transition is associated with a significant increase in sensitivity to moisture. The dehydrated rhombohedral structure of the Prussian blue analogue is extremely prone to reverting to the first hydrated phase, i.e., the monoclinic structure. However, this is undesirable because such a reversal may cause significant damage to the PBA structure, rendering the material unsuitable for use in a battery cell. In addition, a significant amount of sodium or potassium may be lost during such a reversal.

[0026] Therefore, it is important that the PBA material remains in the second dehydrated phase after being converted thereto; i.e., its rhombohedral crystal structure is maintained in the remaining steps of the method. This is achieved by means of the method disclosed herein.

[0027] In an exemplary embodiment, steps e) to g) are carried out under inert conditions.

[0028] Therefore, these steps are carried out in an atmosphere without oxygen and water.

[0029] Therefore, after the drying step (step d), the Prussian blue analogue (PBA) will remain in the second dehydrated phase, preventing an undesired conversion between the dehydrated and hydrated phases of the PBA material.

[0030] Typically, the drying step (step d) is also carried out under inert conditions.

[0031] In an exemplary embodiment, steps e) to g) are performed in the same device or multiple connected devices, wherein one or more of the devices include an inert gas or dry air with a water content of less than 50 ppm H2O.

[0032] Dry air substantially does not include moisture that can react with the PBA material.

[0033] By performing these steps in the same device or multiple connected devices, the atmosphere within these devices is controlled, and it is ensured that the Prussian blue analogue (PBA) remains in the second dehydrated phase and an undesired phase change is avoided. The staff can still work and operate under normal conditions (in contrast, for example, it is less convenient for personnel working in a drying chamber).

[0034] Typically, the drying step (step d) is also performed in the same device or multiple connected devices.

[0035] Thus, in an exemplary embodiment, steps d) to g) are performed in the same device or multiple connected devices, wherein one or more of the devices include an inert gas or dry air with a water content of less than 50 ppm H2O.

[0036] Furthermore, the inventors have found that if the drying temperature t1 is in the range of 150 °C to 300 °C, the drying time can be significantly shortened. A drying time of less than 4 hours is sufficient to achieve an effective conversion from the first hydrated PBA phase to the second dehydrated PBA phase. Thus, the method of the present disclosure brings a great improvement to the large-scale industrial production of sodium-ion batteries and potassium-ion batteries. A fast, efficient and simplified method is provided.

[0037] In an exemplary embodiment, steps a) to c) of the method are performed under ambient conditions.

[0038] The slurry including the Prussian blue analogue is typically an aqueous slurry. Thus, the Prussian blue analogue can be maintained in the first hydrated phase in the slurry.

[0039] The inventors have found that it is desirable to maintain the Prussian blue analogue in the first hydrated phase until the drying step (step d) (i.e., the step of phase change). This avoids an undesired transition between the first and second phases and only one phase change is performed (during the drying step).

[0040] This allows the steps before the drying step to be performed under ambient conditions. This is a significant advantage compared to traditional battery manufacturing techniques, which typically require all method steps to be performed in a drying chamber.

[0041] Therefore, the steps of providing the PBA slurry (step a), applying the slurry to the current collector (step b), and assembling the cathode with additional battery components (step c) can be performed under ambient conditions. At these stages of the process, the PBA material is less vulnerable because it has not yet been converted into the second dehydrated phase.

[0042] The Prussian blue analogue preferably exists in the first hydrated phase in steps a) to c) of the method.

[0043] Using the method of the present disclosure, significant improvements in capacity and cycling performance have been observed. Even exposure to ambient atmosphere for a very short time can lead to undesirable PBA conversion and impair battery performance (see Example 2).

[0044] The method of the present disclosure does not require the use of a drying chamber during any step of battery production. Therefore, a simple and cost-effective method suitable for large-scale battery production is provided.

[0045] In an exemplary embodiment, step d) of drying the electrode stack is performed at a drying temperature t1 ranging from 170 °C to 250 °C.

[0046] As confirmed in the examples, the inventors have found that drying temperatures within this range allow for high-capacity battery cells to be obtained even during relatively short drying times (i.e., as low as 30 minutes) (see Example 1).

[0047] These drying conditions are suitable for enabling the first hydrated phase of the Prussian blue analogue to transform into the second dehydrated phase of PBA. In addition, these drying conditions allow for the removal of any water present in the first phase of the PBA material as well as any water that may be present in any other part of the battery cell. Furthermore, these drying conditions do not have an adverse effect on the PBA structure or any other components of the battery cell.

[0048] In an exemplary embodiment, the drying time ranges from 5 minutes to 2 hours.

[0049] Such short drying times offer significant advantages for the large-scale production of sodium-ion and potassium-ion batteries.

[0050] In an exemplary embodiment, the separator has a melting temperature t2 that is higher than the drying temperature t1.

[0051] The separator prevents electrical short circuits between the negative and positive electrodes and provides mechanical stability to the battery cell. The separator material can include any chemically stable and electrically insulating material. The separator is preferably thermally stable at temperatures ranging from 170 °C to 320 °C, such as from 200 °C to 270 °C.

[0052] Despite the relatively high temperature during drying, the short drying time achieved by the processes of the present disclosure places less demand on the separator.

[0053] In an exemplary embodiment, the drying step d) is performed at a pressure below ambient pressure.

[0054] The use of a vacuum is desirable as it can further shorten the drying time.

[0055] In an exemplary embodiment, the Prussian blue analogue has the formula A a M b [M' c (CN)6] d , where A is sodium or potassium and 1 < a ≤ 2, where M and M' are transition metals, preferably the transition metals are selected from iron and / or manganese, where 0 < b < 2, 1 < c < 2, and where 1 < d < 2.

[0056] Preferably, the Prussian blue analogue is Prussian white having the formula A a Fe[Fe(CN)6], where A is sodium or potassium and where 1.8 < a ≤ 2, preferably where 1.9 < a ≤ 2.

[0057] Prussian white is associated with high battery capacity and enhanced sodium (and potassium) ion storage capabilities. Prussian white is also environmentally friendly and can be produced at low cost.

[0058] In an exemplary embodiment, the battery housing is a pouch cell or a cylindrical cell.

[0059] Typically, the housing is a pouch cell.

[0060] A pouch cell can be formed from a flexible material such as a foil. Thus, the battery housing is flexible and lightweight and can be made in various sizes and shapes.

[0061] The sealed battery housing encloses and seals the battery cell and acts as a barrier to prevent any air or moisture from infiltrating or exfiltrating the battery cell.

[0062] In an exemplary embodiment, the step of applying the slurry to the current collector includes coating the current collector with a coating weight of the slurry from 5 mg / cm 2 to 70 mg / cm 2 , preferably the step of applying the slurry to the current collector includes coating the current collector with a coating weight of the slurry from 10 mg / cm 2 to 40 mg / cm 2 .

[0063] The thickness coated on the current collector can vary depending on the specific application and purpose. For example, the thickness of the PBA coating can range from 50 μm to 500 μm, such as from 100 μm to 250 μm.

[0064] Then, the electrodes can be cut into the desired shape by techniques well known in the art.

[0065] The cathode and anode can be assembled by stacking or winding the electrodes with a separator.

[0066] According to another aspect, a sodium or potassium ion battery cell produced by the method described above is provided.

[0067] In an exemplary embodiment, the battery cell has the following electrochemical cycling curve: for Na + / Na, the electrochemical cycling curve has no voltage plateau above 3.9 V, or for K + / K, the electrochemical cycling curve has no voltage plateau above 4.1 V.

[0068] The absence of a voltage plateau above 3.9 V (Na + / Na) and above 4.1 V (K + / K) respectively indicates that water has been removed from the battery cell and the PBA material exists in a second dehydrated phase. Such a battery cell is associated with stable behavior during subsequent charge and discharge and such a battery cell has a high initial Coulombic efficiency. The voltage plateau above 3.9 V (Na + / Na) and above 4.1 V (K + / K) respectively is associated with water extraction, and this voltage plateau indicates that the PBA material includes the PBA material in the first hydrated phase.

[0069] In an exemplary embodiment, the battery cell has the following electrochemical cycling curve, for Na + / Na, the electrochemical cycling curve shows a voltage plateau between 3.0 V and 3.9 V, or for K + / K, the electrochemical cycling curve shows a voltage plateau between 3.8 V and 4.1 V, and wherein the electrochemical cycling curve has no additional voltage plateau.

[0070] The presence of an obvious voltage plateau within the above range indicates that the battery cell contains no water and no side reactions caused by water or moisture occur.

[0071] Other features and advantages of the present disclosure will become apparent when studying the appended claims and the following description. Those skilled in the art will recognize that, without departing from the scope of the present disclosure, different features of the present disclosure can be combined to create embodiments other than those described below. BRIEF DESCRIPTION OF THE DRAWINGS

[0072] Aspects of the present disclosure, including its specific features and advantages, will be readily understood from the following detailed description and the accompanying drawings, in which:

[0073] Figure 1 Steps in the method of the present disclosure are schematically illustrated.

[0074] Figure 2 A sodium ion or potassium ion battery according to an exemplary embodiment of the present disclosure is schematically illustrated.

[0075] Figure 3a Cycling data for a sodium ion battery cell produced according to an exemplary embodiment of the method of the present disclosure is shown.

[0076] Figure 3b Is shown in connection with Figure 3a Cycling data for a sodium ion battery cell produced under the same conditions as the battery cell of, but differing in that the step of arranging the electrode stack in the battery housing (step e) is carried out under ambient conditions.

[0077] Figure 3c Is shown in connection with Figure 3a Cycling data for a sodium ion battery produced under the same conditions as the battery cell in, but differing with respect to the drying temperature and drying time utilized. DETAILED DESCRIPTION

[0078] The present disclosure will now be described more fully hereinafter with reference to the accompanying drawings, in which currently preferred embodiments of the present disclosure are shown. However, the present disclosure may be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided for thoroughness and completeness and to fully convey the scope of the present disclosure to those skilled in the art.

[0079] Figure 1 a schematically outlines the steps of a method (100) for manufacturing a sodium ion or potassium ion battery cell of the present disclosure.

[0080] The method includes the following steps in a continuous sequence:

[0081] a) providing a slurry comprising a Prussian blue analogue, wherein the Prussian blue analogue is capable of existing in a first hydrated phase and a second dehydrated phase, and wherein the slurry comprises the Prussian blue analogue in the first hydrated phase (step 101),

[0082] b) Apply the slurry to the current collector to form a cathode (step 102),

[0083] c) Assemble the cathode with the anode and the separator to form an electrode stack (step 103),

[0084] d) Dry the electrode stack under conditions that allow the Prussian blue analogue to transform from a first hydrated phase to a second dehydrated phase, wherein the drying is carried out at a drying temperature t1 from 150 °C to 300 °C and a drying time from 1 minute to less than 4 hours (step 104),

[0085] e) Dispose the electrode stack in a battery housing (step 105),

[0086] f) Add an electrolyte to the battery housing (step 106), and

[0087] g) Seal the battery housing to form a battery cell (step 107), wherein steps e) to g) are carried out under conditions that allow the Prussian blue analogue to remain in the second dehydrated phase throughout steps e) to g) of the method.

[0088] A key feature of the disclosed method is that steps e) to g) are carried out under conditions that prevent reactions and unwanted transformations of the PBA material.

[0089] It is important to ensure that the electrode stack is not exposed to moisture or air during the steps following the drying step d). The process of the present disclosure ensures that only one phase change occurs between the first hydrated phase and the second dehydrated phase of the PBA analogue. Thus, unwanted reversals between the first and second phases of the PBA material can be prevented, which may cause swelling and damage of the material.

[0090] In an exemplary embodiment, steps e) to g) (steps 105 to 107) can be carried out under inert conditions.

[0091] As used herein, the term "inert conditions" means an atmosphere free of oxygen and water.

[0092] Preferably, the drying step (step d) is also carried out under inert conditions.

[0093] In an exemplary embodiment, steps e) to g) (steps 105 to 107) are carried out in the same device or in a plurality of connected devices, wherein one or more of the devices comprise an inert gas or dry air with a water content of less than 50 ppm H2O (such as less than 30 ppm H2O).

[0094] Dry air essentially does not contain moisture that can react with the PBA material.

[0095] Preferably, the drying step (step d) is also carried out in the same device or in a plurality of connected devices.

[0096] Therefore, steps d) to g), i.e., steps 104 to 107 of the method, can be carried out in the same device or in a plurality of connected devices.

[0097] In steps e) to g), preferably in steps d) to g), one or more closed chambers filled with inert gas or dry air can be used, the inert gas or dry air having a water content of less than 50 ppm H2O, for example less than 30 ppm H2O.

[0098] For example, step f) (step 106) can be carried out in an electrolyte injection device (such as a glove box). A glove box is an enclosed device for electrolyte injection, and the enclosed device can include built-in sealed gloves. In an exemplary embodiment, the glove box is filled with an inert gas, such as argon (Ar). In an alternative embodiment, the glove box is filled with dry air having a water content below 50 ppm H2O.

[0099] Step e) (step 105) and / or step g) (step 107) can be carried out in an electrolyte injection device or in a separate device directly connected to the electrolyte injection device.

[0100] The drying step (step d)) can be carried out in a drying device (such as an enclosed drying chamber). The drying device can be connected to the electrolyte injection device or integrated in the electrolyte injection device. The drying device can include means for applying a vacuum.

[0101] By carrying out these steps in the same device or in a plurality of connected devices, the atmosphere inside these devices is controlled, thus ensuring that the electrode stack is not undesirably exposed to moisture and ambient air. Therefore, after the transition from the first hydrated phase, the Prussian blue analogue (PBA) can remain in the second dehydrated phase of the Prussian blue analogue. In addition, undesired phase transitions are avoided. The staff can still work and operate under normal conditions (in contrast, for example, it is less convenient for the personnel working in a drying chamber).

[0102] The inventors have found that the battery cells produced by the method according to the present disclosure have obtained significant improvements in capacity and cycling performance. Battery cells with stable cycling performance have been obtained, and undesired side reactions due to exposure to ambient air have been avoided (see respectively Figure 3a and Figure 3b ).

[0103] The step of providing the slurry (step 101) may include mixing a Prussian blue analogue in powder form with a conductive additive and a binder.

[0104] The mixing may be carried out by stirring and / or mixing for at least one hour.

[0105] The conductive additive may be any type of conductive additive known to those skilled in the art. For example, various types of carbon compounds may be used, such as Super P, C65, C45, carbon black (such as Ketjen black).

[0106] The binder is not limited to a specific binder. For example, alginate, carboxymethyl cellulose (CMC), styrene-butadiene rubber (SBR), polyvinylidene fluoride (PVdF) may be used.

[0107] The Prussian blue analogue (PBA) powder may be prepared by methods known in the art.

[0108] The slurry comprising the Prussian blue analogue is typically an aqueous slurry. Thus, the Prussian blue analogue exists in the first hydrated phase of the Prussian blue analogue in the slurry.

[0109] The step of applying the slurry to the current collector (102) may include using the slurry to coat the current collector with a coating weight from 5 mg / cm 2 to 70 mg / cm 2 Preferably, the step of applying the slurry to the current collector (102) may include using the slurry to coat the current collector with a coating weight from 10 mg / cm 2 to 40 mg / cm 2 of the coating weight.

[0110] Preferably, the slurry is uniformly applied to at least one side of the current collector. The current collector is typically a metal foil or a metal sheet.

[0111] The current collector may be coated on one side or both sides. When coated on both sides, the coating weight will increase. For example, the coating weight may thus be 30 mg / cm 2 to 50 mg / cm 2 ).

[0112] The coating step is in no way limited to a specific coating technique, but any method for coating the slurry on the current collector may be utilized. For example, slit extrusion coating may be utilized. Preferably, the coating is uniformly distributed on at least one side of the current collector.

[0113] The thickness of the coating on the current collector can vary depending on the specific application and purpose. For example, the thickness of the PBA coating can range from 50 μm to 500 μm, such as from 100 μm to 250 μm.

[0114] Subsequently, the coated active PBA material can be pressed and compacted onto the current collector, for example, by calendering (such as by means of a roller calender). Thus, a consistent coating thickness and coating density can be achieved.

[0115] Then, the electrodes can be cut into the desired shape by techniques well known in the art. For example, any type of slitter can be utilized.

[0116] In step 103, the cathode and anode are assembled by stacking or winding the electrodes with a separator. Any technique known in the art can be utilized.

[0117] As previously mentioned, the separator prevents electrical short - circuiting between the negative and positive electrodes and provides mechanical stability to the battery cell. The separator material can include any chemically stable and electrically insulating material.

[0118] The separator has a melting temperature t2, which is higher than the drying temperature t1.

[0119] The separator is preferably thermally stable at temperatures from 170 °C to 320 °C, such as from 200 °C to 270 °C.

[0120] The separator can include any chemically stable and electrically insulating material, such as a polymer membrane, such as a membrane comprising polypropylene, polyethylene, or a combination thereof.

[0121] The first steps of the method, i.e., steps a) to c) (steps 101 to 103), can be carried out under ambient conditions.

[0122] Steps a) to c) (steps 101 to 103) can be carried out at room temperature.

[0123] As used herein, "ambient conditions" means the current air temperature and relative humidity at which the process occurs. Steps a) to c) can be carried out at a relative humidity (RH) level related to room temperature (e.g., 40% to 60% RH). The process is not limited to any specific requirements or equipment in these first steps of the method.

[0124] Preferably, in steps a) to c) of the method, the Prussian blue analogue exists in a first hydrated phase.

[0125] In step 104, the electrode stack is dried. The drying temperature t1 is from 150 °C to 300 °C, and the drying time is from 1 minute to less than 4 hours.

[0126] These conditions allow the Prussian blue analogue to transform from the first hydrated phase to the second dehydrated phase.

[0127] Preferably, the drying step is carried out at a temperature in the range from 170 °C to 250 °C, such as from 190 °C to 230 °C. Preferably, the drying time is from 5 minutes to 2 hours, more preferably from 20 minutes to 1.5 hours.

[0128] Thus, sodium or potassium ion batteries with improved capacity and cycling performance can be obtained. In addition, these drying conditions do not have an adverse effect on the PBA structure.

[0129] Preferably, the drying step is carried out under a pressure below ambient temperature.

[0130] Preferably, the drying step is carried out under vacuum.

[0131] This is beneficial for reducing the drying time required for the phase transition of the PBA analogue.

[0132] The drying step can be carried out at a pressure from 10 -3 mbar to 100 mbar. For example, the pressure can be from 0.01 mbar to 1 mbar.

[0133] However, the pressure depends to a large extent on the temperature utilized in the drying step. Thus, the pressure can vary depending on the temperature used during drying.

[0134] Importantly, the drying step ensures the removal of any water present in the active PBA material, as well as any water that may be present in any other part of the battery cell.

[0135] The dehydrated PBA material means that the PBA material does not include water that affects the electrochemical behavior of the battery cell including the PBA material.

[0136] After the drying step (step 104), the battery cell is arranged in a battery housing (step 105).

[0137] The battery housing can vary depending on the intended use and preference. The battery housing surrounds and seals the battery cell and acts as a barrier to prevent any air or moisture from infiltrating or exuding from the battery cell.

[0138] Preferably, the battery housing is a pouch cell. In other words, the battery housing can be in the form of a pouch formed from a flexible material such as a foil. Thus, the housing is flexible and lightweight, and the housing can be made in various sizes and shapes.

[0139] For example, a pouch cell may include a polymer-coated metal foil. The metal foil may include a polymer coating on one or both of its sides.

[0140] When the electrode stack is inserted into the pouch cell, the pouch cell may be partially sealed.

[0141] The method further includes the step of adding an electrolyte to the battery housing (step 106).

[0142] The method of the present disclosure is not limited to the use of a specific electrolyte.

[0143] Preferably, the electrolyte is a non-aqueous electrolyte. The non-aqueous electrolyte can prevent water from interfering with the cathode coated with PBA. In addition, compared with an aqueous electrolyte, the non-aqueous electrolyte provides a larger voltage window. Further, since the battery cell has been dried and the PBA has been dehydrated, there is substantially no water in the active PBA material or the battery cell that may interfere with the non-aqueous electrolyte.

[0144] The non-aqueous electrolyte solution typically includes a solvent or a mixture of solvents and at least one dissolved salt.

[0145] For example, the non-aqueous electrolyte may include, for example, ethylene carbonate, diethyl carbonate, dimethyl carbonate, and / or any mixture thereof. The non-aqueous electrolyte may include salts such as sodium hexafluorophosphate (NaPF6) or sodium tetrafluoroborate (NABF4). The non-aqueous electrolyte may also include additives.

[0146] In an exemplary embodiment, the non-aqueous electrolyte contains an alkali metal bis(oxalato)borate, wherein the alkali metal ion is selected from sodium (Na + ) and potassium (K + ). Such a non-aqueous electrolyte solution is fluorine-free, environmentally friendly, safe, and such a non-aqueous electrolyte has a high ionic conductivity and electrochemical stability.

[0147] Thereafter, the battery housing is sealed (step 107).

[0148] In an exemplary embodiment, the Prussian blue analogue has the formula A a M b [M' c (CN)6] d , wherein A is sodium or potassium, and 1 < a ≤ 2, wherein M and M' are transition metals, preferably, the transition metals are selected from iron and / or manganese, wherein 0 < b < 2, 1 < c < 2, and wherein 1 < d < 2.

[0149] In an embodiment, the Prussian blue analogue is of the formula A aPrussian white of Fe[Fe(CN)6], where A is sodium or potassium, and where 1.8 < a ≤ 2, preferably where 1.9 < a ≤ 2.

[0150] Prussian white is associated with high battery capacity and enhanced sodium (and potassium) ion storage capabilities. Prussian white is also environmentally friendly, and Prussian white can be produced at low cost.

[0151] In embodiments where the Prussian blue analogue is a Prussian white material, the material can be prepared according to the method described in WO2018 / 056890 assigned to Altris AB.

[0152] According to another aspect, a sodium ion or potassium ion battery cell produced according to the method described above is provided.

[0153] Figure 2 The schematic principle of a sodium ion or potassium ion battery 200 utilizing sodium ions or potassium ions 201 as charge carriers is shown. The battery stores energy in the chemical bonds of the negative electrode (i.e., anode 202). Charging the battery 200 forces Na + ions or K + ions 201 to be deintercalated from the positive electrode (i.e., cathode 203) and migrate towards the anode 202. During discharge, the process is reversed. Once the circuit is complete, electrons are transferred from the anode 202 back to the cathode 203, and Na + ions or K + ions 201 travel back to the cathode 203. During battery discharge, as Figure 2 shown, oxidation occurs at the anode 202, while reduction occurs at the cathode 203. The current is determined by the potential difference (cell voltage) between the cathode 203 and the anode 202.

[0154] The two electrodes are separated by a separator 205 permeated with an electrolyte 204.

[0155] As used herein, the term "battery" means a device comprising one or more battery cells.

[0156] A "battery cell" includes a positive electrode (i.e., cathode), a negative electrode (i.e., anode), and a separator. In a battery cell, chemical energy is converted into electrical energy through reduction and oxidation (redox) reactions on the electrodes.

[0157] The cathode 203 used in the sodium ion or potassium ion battery of the present disclosure includes a current collector coated with a Prussian blue analogue material as described above.

[0158] The negative electrode material (i.e., anode 202) is not particularly limited as long as it is a material capable of storing / releasing sodium ions or potassium ions. Examples include metal composite oxides, sodium metal, sodium alloys, silicon, silicon-based alloys, tin-based alloys, bismuth-based alloys, metal oxides, conductive polymers, Na-Co-Ni-based materials, hard carbon, etc. The anode can be a metal foil coated with an active anode material.

[0159] Preferably, the battery cell has the following electrochemical cycling curve: for Na + / Na, the electrochemical cycling curve has no voltage plateau above 3.9 V, or for K + / K, the electrochemical cycling curve has no voltage plateau above 4.1 V. Such voltage plateaus are associated with water extraction, and such voltage plateaus indicate that the PBA has not fully transformed from the first hydrated phase to the second dehydrated phase.

[0160] As used herein, the term "for Na + / Na, having no voltage plateau above 3.9 V, or for K + / K, having no voltage plateau above 4.1 V" means having no additional capacity after 3.9 V and 4.1 V, respectively. Thus, for Na + / Na, above 3.9 V, or for K + / K, above 4.1 V, there is no reaction caused by moisture. This is illustrated by the Figure 3b vertically upward electrochemical cycling curve in. The anode typically used in the electrochemical cycling test is a carbon-based anode (hard carbon). Figures 3a to 3c The shown electrochemical cycling test was conducted at a C-rate of 0.05C, where the voltage cut-off limits were set to 4.2 V and 2.0 V, respectively, during three charge / discharge cycles.

[0161] The presence of water or side reactions caused by water or moisture can be demonstrated by the sloping curve for Na + / Na above 3.9 V (see Figure 3b ), or the presence of water or side reactions caused by water or moisture can be demonstrated by the sloping curve for K + / K above 4.1 V. This can also be demonstrated by the presence of more than one voltage plateau in the electrochemical cycling curve.

[0162] The battery cell can have the following electrochemical cycling curve: for Na+ / Na, the electrochemical cycling curve shows a voltage plateau between 3.0 V and 3.9 V, or for K+ / K, the electrochemical cycling curve shows a voltage plateau between 3.9 V and 4.1 V, and wherein the electrochemical cycling curve has no any additional voltage plateau.

[0163] Thus, a stable and high-performance battery cell without water is achieved.

[0164] An important advantage of the method of the present disclosure is that no drying chamber is required at any step of battery production. Thus, the method is greatly simplified, low-cost and suitable for large-scale battery production.

[0165] Example :

[0166] Example 1

[0167] The prototype Prussian white half-cell was stacked with a heat-resistant separator and an electrode mass loading of 12 mg / cm 2 The stacked prototype was dried at 210 °C for 0.5 h under the conditions of a high vacuum (<2×10 -2 mBar) oven to remove all water from the electrode. After drying, the battery stack was transferred from the oven to a pouch cell housing while electrolyte injection and sealing were carried out under an inert atmosphere. After drying, the battery stack was injected with electrolyte and sealed without being exposed to the ambient atmosphere.

[0168] Constant current cycling was performed using a Neware BTS4000 constant current instrument to charge / discharge the half-cell under controlled conditions. During the measurement, the current was kept constant at 0.05 C, where the voltage cut-off limits were set to 4.2 V and 2.0 V, respectively. A total of three charge / discharge cycles were recorded.

[0169] Figure 3a The cycling data in shows that the electrode stack only contains the anhydrous phase of Prussian white, i.e., the rhombohedral phase. This is clearly demonstrated by the absence of a voltage plateau above 3.9 V at the end of charging (such a voltage plateau is associated with water extraction from the cathode).

[0170] Example 2

[0171] The prototype Prussian white half-cell was stacked with a heat-resistant separator and an electrode mass loading of 12 mg / cm 2 The stacked prototype was dried at 210 °C for 0.5 h under the conditions of a high vacuum (<2×10 -2 mBar) oven to remove all water from the electrode. After drying, the battery stack was transferred from the oven to a pouch cell housing. This operation included exposing the electrode stack to ambient conditions for a short period (less than three minutes), and then transferring it back to an inert atmosphere for electrolyte injection and sealing.

[0172] Figure 3bThe cyclic data therein shows that the electrode stack contains both the anhydrous phase of Prussian white and the hydrated phase of Prussian white, i.e., both the rhombohedral and monoclinic structures. The appearance of a voltage plateau at above 3.9 V at the end of charging clearly proves this, and this voltage plateau is associated with water extraction from the cathode. The water content in the battery causes gas generation inside the battery and makes discharging impossible.

[0173] Example 3

[0174] Perform a similar electrochemical cycle evaluation as described in Example 1. However, this test is different from Example 1 in that the temperature used for drying the stacked prototype is 130 °C and the drying time is 15 hours.

[0175] As Figure 3c shown, a voltage plateau appears at above 3.9 V at the end of charging, and this voltage plateau is associated with water extraction from the cathode. The water content in the battery causes gas generation inside the battery and makes discharging impossible. Therefore, similar to the results in Example 2, the electrode stack contains both the anhydrous phase of Prussian white and the hydrated phase of Prussian white, i.e., both the rhombohedral and monoclinic structures.

[0176] The terms, definitions, and embodiments of all aspects of the present disclosure apply to other aspects of the present disclosure with necessary modifications.

[0177] Although the present disclosure has been described with reference to specific exemplary embodiments of the present disclosure, many different changes, modifications, etc. will become apparent to those skilled in the art.

[0178] When practicing the present disclosure, those skilled in the art can understand and implement variations of the disclosed embodiments by studying the drawings, the present disclosure, and the appended claims. In addition, in the claims, the word "comprising" does not exclude other elements or steps, and the indefinite article "a" or "an" does not exclude a plurality.

Claims

1. A method for manufacturing a sodium or potassium ion battery cell, the method comprising a) Providing a slurry comprising a Prussian blue analogue, wherein, The Prussian blue analogue can exist in a first hydrated phase and a second dehydrated phase, wherein the slurry comprises the Prussian blue analogue in the first hydrated phase, b) applying the slurry to a current collector to form a cathode, c) assembling the cathode with an anode and a separator to form an electrode stack, d) drying the electrode stack under conditions that allow the Prussian blue analogue to transform from the first hydrated phase to the second dehydrated phase, wherein the drying is carried out at a drying temperature t1 from 150 °C to 300 °C and a drying time from 1 minute to less than 4 hours, e) disposing the electrode stack in a battery housing, f) adding an electrolyte to the battery housing, and g) sealing the battery housing to form a battery cell, wherein, Steps e) to g) are carried out under conditions that allow the Prussian blue analogue to remain in the second dehydrated phase throughout steps e) to g) of the method.

2. The method according to claim 1, wherein, Steps e) to g) are carried out under inert conditions.

3. The method according to claim 1 or 2, wherein Steps e) to g) are carried out in the same device or a plurality of connected devices, wherein one or more of the devices comprise an inert gas or dry air with a water content of less than 50 ppm H2O.

4. The method according to any one of the preceding claims, wherein, Steps a) to c) of the method are carried out under ambient conditions.

5. The process according to any one of the preceding claims, wherein, Step d) of drying the electrode stack is carried out at a drying temperature t1 from 170 °C to 250 °C.

6. The process according to any one of the preceding claims, wherein, The drying time is from 5 minutes to 2 hours.

7. The process according to any one of the preceding claims, wherein, The separator has a melting temperature t2, and the melting temperature t2 is higher than the drying temperature t1.

8. The method according to any one of the preceding claims, wherein, Step d) of drying is carried out under a pressure lower than ambient pressure.

9. The method according to any one of the preceding claims, wherein, The Prussian blue analogue has the formula A a M b [M' c (CN)6] d , where A is sodium or potassium and 1 < a ≤ 2, where M and M' are transition metals, preferably the transition metals are selected from iron and / or manganese, where 0 < b < 2, 1 < c < 2, and where 1 < d < 2.

10. The method according to any one of the preceding claims, wherein, The Prussian blue analogue has the formula A a Prussian white of Fe[Fe(CN)6], where A is sodium or potassium, and where 1.8 < a ≤ 2, preferably where 1.9 < a ≤ 2.

11. The method according to any one of the preceding claims, wherein, The battery housing is a pouch cell.

12. The method according to any one of the preceding claims, wherein, The step of applying the slurry to the current collector includes using the slurry to coat the current collector with a coating weight ranging from 5 mg / cm 2 to 30 mg / cm 2 Preferably, the step of applying the slurry to the current collector includes using the slurry to coat the current collector with a coating weight ranging from 10 mg / cm 2 to 40 mg / cm 2 of the current collector.

13. A sodium or potassium ion battery cell produced by the method according to any one of claims 1 to 12.

14. The sodium ion or potassium ion battery cell according to claim 13, wherein, The battery cell has the following electrochemical cycling curve: for Na + / Na, the electrochemical cycling curve has no voltage plateau at voltages higher than 3.9 V, or for K + / K, the electrochemical cycling curve has no voltage plateau at voltages higher than 4.1 V.

15. The sodium ion or potassium ion battery cell according to claim 13 or 14, wherein, The battery cell has the following electrochemical cycling curve: for Na + / Na, the electrochemical cycling curve shows a voltage plateau between 3.0 V and 3.9 V, or for K + / K, the electrochemical cycling curve shows a voltage plateau between 3.8 V and 4.1 V, and wherein the electrochemical cycling curve has no additional voltage plateau.

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