Method for manufacturing sodium or potassium ion battery cells

Abstract

This disclosure generally relates to a method for producing a sodium or potassium ion battery cell containing a Prussian blue analog (PBA) as a cathode active material. This disclosure also relates to a sodium or potassium ion battery produced by this method.

Description

[Technical Field]

[0001] This disclosure generally relates to a method for producing sodium or potassium ion battery cells containing a Prussian blue analog (PBA) as a cathode active material. This disclosure also relates to sodium or potassium ion battery cells produced by this method. [Background technology]

[0002] Lithium-ion batteries dominate the rechargeable battery market. However, this technology has drawbacks, particularly due to the relatively limited availability of lithium resources. Although superior to previous generations of secondary battery technology, lithium-ion batteries are not considered environmentally friendly and are costly from a recycling perspective.

[0003] These drawbacks have triggered the search for alternatives to lithium-ion batteries. Sodium or potassium-ion batteries present an attractive alternative and are also a viable means of supporting renewable energy sources for the purposes of load leveling and storing excess energy.

[0004] The performance of sodium or potassium ion batteries largely depends on the properties of the electrode materials.

[0005] A typical process for manufacturing electrodes, such as cathodes, involves mixing an active material with a solvent, conductive additives, and a binder to form a slurry. The slurry is then coated onto a current collector to form the cathode. The cathode may then be assembled with an anode and any other components used to form a battery, such as a separator.

[0006] In conventional battery manufacturing, all processes typically need to be carried out in a dry room. A dry room is a room where the moisture content of the air is controlled to a specific level. If a battery or any of its components are exposed to moisture during assembly, it can lead to a decrease in quality, such as a reduction in charge capacity and overall performance.

[0007] Prussian blue analog (PBA) cathode materials stand out as promising cathode materials for use in sodium or potassium ion batteries. Prussian blue analogs have a unique crystalline structure with an open three-dimensional framework and large interstitial voids, allowing them to store sodium (and potassium) ions.

[0008] When PBA is used as a cathode active material, drying is particularly important in battery cells because it is necessary to remove any water present in the PBA structure in order for the active material to fully utilize its capacity. The presence of water can adversely affect the electrochemical potential and cycle stability of battery cells containing PBA as a cathode material.

[0009] Therefore, when used in final battery cells, it is essential to remove any water present in the PBA material. However, even after the water has been removed from the PBA material, it still retains a strong affinity for water. PBA is extremely hygroscopic and can rapidly transition from anhydrous to hydrated upon exposure to air or moisture.

[0010] Therefore, the manufacture of battery cells containing PBA-containing cathodes is a cumbersome and difficult task.

[0011] While conventional battery manufacturing can utilize dry rooms, dry rooms such as those used in lithium-ion battery manufacturing are not always sufficient to guarantee that the PBA material remains in its anhydrous form, resulting in an increased risk of cathode decomposition.

[0012] Furthermore, dry rooms are generally not a convenient environment for personnel to work in.

[0013] Therefore, there is a need to provide an improved method for manufacturing sodium or potassium ion batteries that is simple, inexpensive, and more convenient from the perspective of the working environment. Furthermore, this method should be suitable for the manufacture of large-scale sodium or potassium ion batteries. Summary of the Invention

[0014] In view of the above and other drawbacks of the prior art, an object of the present disclosure is to provide improvements related to sodium or potassium ion batteries, particularly, a simple and inexpensive manufacturing method for manufacturing such batteries on a large industrial scale.

[0015] According to a first aspect of the present disclosure, a method for manufacturing a sodium or potassium ion battery cell, comprising: a) providing a slurry containing a Prussian blue analog, the Prussian blue analog may exist in a first hydrated phase and a second dehydrated phase, and the slurry contains the first hydrated phase of the Prussian blue analog; 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 analog to convert from the first hydrated phase to the second dehydrated phase; e) placing the electrode stack in a battery casing; f) adding an electrolyte to the battery casing; g) sealing the battery casing to form a battery cell; and where steps e) to g) are performed in an atmosphere with a dew point temperature in the range of -40°C to -80°C, and the process time for performing steps e) to g) is less than 7 hours, preferably less than 5 hours. A method is provided.

[0016] Prussian blue analogs (PBA) can exist in a hydrated phase, i.e., a hydrated phase, or in a dehydrated phase, i.e., an anhydrous phase from which water has been removed. The inventors have found that steps e) to g) of a method for producing sodium or potassium ion battery cells can be significantly improved by performing the steps in an atmosphere where the dew point temperature is within the above range.

[0017] This makes it possible to maintain the Prussian blue analog in the second dehydrated phase throughout steps e) to g) of this method. Therefore, undesirable conversions between the dehydrated phase and the hydrated phase are prevented.

[0018] In the first hydration phase of the Prussian blue analog, the material has a monoclinic crystalline structure. PBA material generally exists in a monoclinic structure in the slurry and in the processes preceding the drying process.

[0019] In the second dehydration phase, the PBA material has a rhombohedral crystal structure. In battery applications, it is preferable to utilize the dehydrated rhombohedral phase of PBA to maximize the energy density and cycle stability of the battery cell.

[0020] The transition from the first to the second phase involves distortion of the monoclinic crystal lattice and a significant change in volume. This phase transition is associated with a substantial increase in sensitivity to moisture. The dehydrated rhombohedral crystal structure of Prussian blue analogs is highly susceptible to reversion to the first hydrated phase, i.e., the monoclinic structure. However, such reversion is undesirable because it can significantly impair the PBA structure, making the material unsuitable for use in battery cells. Furthermore, a considerable amount of sodium or potassium may be lost during such reversion.

[0021] Therefore, it is important that the PBA material remains in the second dehydrated phase after transitioning to it, that is, maintains its rhombohedral crystal structure throughout the rest of the process. This is achieved by the method of this disclosure.

[0022] An atmosphere with a dew point temperature in the range of -40°C to -80°C is substantially free of moisture or water molecules that can react with the PBA material.

[0023] The process times in steps e) to g) are also factors that can affect the ability of the PBA material to be maintained in the second dehydration phase. Therefore, process times can also affect the possibility of cathode decomposition during manufacturing.

[0024] When the dew point temperature is in a higher range (e.g., -40°C to -50°C), the time required for steps e) to g) should generally be shorter. Longer process times between the drying step and the final sealing step can adversely affect the final battery cell (due to undesirable PBA conversion and cathode decomposition).

[0025] When the dew point temperature is in a lower range (e.g., -70°C to -80°C), the process time is similarly less sensitive, and longer process times are possible.

[0026] However, the process time is less than 7 hours, preferably less than 5 hours. The process time may be, for example, between 10 minutes and less than 5 hours.

[0027] This is also advantageous from a working environment perspective. As mentioned above, exposure to an atmosphere with a dew point temperature within the aforementioned range is preferably kept as short as possible. An atmosphere with a dew point within the above range is extremely dry and essentially contains no water molecules.

[0028] A further advantage of this method is that there are no specific process requirements for the steps preceding the drying process.

[0029] For example, steps a) to c) of this method may be carried out under ambient conditions.

[0030] This is beneficial from a work environment perspective. It significantly reduces the amount of time personnel need to be exposed to a low-dew-point atmosphere.

[0031] Significant improvements in capacity and cycle performance have been observed with the method described herein. Therefore, a simple and cost-effective method suitable for large-scale battery manufacturing is provided.

[0032] In exemplary embodiments, steps e) to g) are carried out in an atmosphere with a dew point temperature in the range of -45°C to -70°C, preferably -50°C to -70°C.

[0033] The process time for carrying out steps e) to g) of this method is less than 7 hours, preferably less than 5 hours.

[0034] Preferably, the process time for carrying out steps e) to g) may be 5 minutes to less than 3 hours, preferably 15 minutes to 2.5 hours.

[0035] This timing is suitable for avoiding undesirable conversions of the PBA structure and preventing cathode degradation. It also places less demand on personnel during the manufacturing of battery cells.

[0036] As mentioned above, steps a) to c) of this method may be carried out under ambient conditions.

[0037] Therefore, personnel can work and operate under normal (and not so "extreme") conditions during these steps of the method.

[0038] Slurries containing Prussian blue analogs are typically aqueous slurries. Therefore, the Prussian blue analogs can be retained in the primary hydration phase within the slurry.

[0039] The Prussian blue analog is preferably present in the first hydration phase in steps a) to c) of this method.

[0040] The inventors have found that it is desirable to keep the Prussian blue analog in the first hydrated phase until the drying step (step d), that is, until the phase transition occurs. In this way, undesirable transitions between the first and second phases are avoided, and only one phase transition occurs (during the drying step).

[0041] This allows the processes preceding the drying process to be carried out under ambient conditions. This is a significant advantage compared to conventional battery manufacturing techniques, which typically require all process steps to be performed in a dry room.

[0042] 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 carried out under ambient conditions. During these stages of the process, the PBA material is less susceptible because it has not yet been converted to the second dehydrated phase.

[0043] In an exemplary embodiment, drying step d) is performed at a drying temperature t1 of 110 to 300°C.

[0044] For example, drying step d) can be carried out at a drying temperature t1 of 150 to 300°C, preferably 160 to 250°C.

[0045] The drying time can be between 15 minutes and 20 hours.

[0046] These drying conditions are suitable for enabling the phase transition from the first hydrated phase of the Prussian blue analog to the second dehydrated phase of PBA. Furthermore, these drying conditions allow for the removal of any water present in the first phase of the PBA material, as well as any water potentially present in any other part of the battery cell. Moreover, these drying conditions do not adversely affect the PBA structure or any other components of the battery cell.

[0047] When the drying temperature t1 is within the range of 150 to 300 °C, the drying time can be significantly shortened. A drying time of less than 4 hours may be sufficient for an efficient conversion from the first hydrated PBA phase to the second dehydrated PBA phase at that time.

[0048] In an exemplary embodiment, the drying step d) is performed at a pressure below ambient pressure.

[0049] Since the drying time can be shortened, it is desirable to utilize a vacuum.

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

[0051] The separator prevents an electrical short circuit between the negative electrode and the positive electrode and provides mechanical stability to the battery cell. The separator material may include any material that is chemically stable and electrically insulating. The separator is preferably thermally stable at a temperature of 170 °C to 320 °C, such as 200 °C to 270 °C.

[0052] In an exemplary embodiment, the Prussian blue analog has the formula A a M b [M’ c (CN)6] d where A is sodium or potassium, 1 < a ≤ 2, M and M’ are transition metals, preferably selected from iron and / or manganese, 0 < b < 2, 1 < c < 2, and 1 < d < 2.

[0053] Preferably, the Prussian blue analog is Prussian white having the formula A a Fe[Fe(CN)6], where A is sodium or potassium, 1.8 < a ≤ 2, preferably 1.9 < a ≤ 2.

[0054] Prussian white is associated with a high battery capacity and an improvement in the storage capacity of sodium (and potassium) ions. Prussian white is also environmentally friendly and can be manufactured at a low cost.

[0055] In an exemplary embodiment, the step of applying the slurry to the current collector includes coating the current collector with the slurry at a coating weight of 5 mg / cm 2 ~70 mg / cm 2 , preferably 10 mg / cm 2 ~40 mg / cm 2 .

[0056] 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 may be in the range of 50 μm to 500 μm, such as 100 μm to 250 μm.

[0057] Next, the electrode can be cut into a desired shape by techniques well known in the art.

[0058] The cathode may be assembled with the anode by laminating or winding the electrode together with the separator.

[0059] According to another aspect, a sodium or potassium ion battery cell manufactured according to the foregoing method is provided.

[0060] In an exemplary embodiment, the battery cell has an electrochemical cycle curve with no voltage plateau above 3.7 V with respect to Na + / Na or K + / K.

[0061] The absence of a voltage plateau above 3.7 V indicates that water has been removed from the battery cell and that the PBA material is present in a second dehydrated phase. Such battery cells exhibit stable behavior during subsequent charge and discharge and have a high initial Coulombic efficiency. A voltage plateau above 3.7 V (versus Na + / Na or versus K + / K) is associated with water extraction and indicates that the PBA material contains the first hydrated phase of the PBA material.

[0062] In an exemplary embodiment, the battery cell is Na+ / against Na or K + The electrochemical cycle curve exhibits a single voltage plateau between 3.2 and 3.7V for a given K, and there are no additional voltage plateaus in the electrochemical cycle curve.

[0063] The presence of a clear voltage plateau within the range described above indicates that the battery cell lacks water and that no side reactions caused by water or moisture occur.

[0064] In an exemplary embodiment, the energy efficiency of the battery cell is at least 80% over the first 25 cycles.

[0065] Therefore, the battery cell has stable battery cycle performance.

[0066] Further features and advantages of this disclosure will become apparent when considering the attached claims and the following description. Those skilled in the art will understand that it is possible to combine different features of this disclosure without departing from the scope of this disclosure to create embodiments other than those described below.

[0067] Various aspects of this disclosure, including specific features and advantages, will be readily apparent from the following detailed description and accompanying drawings. [Brief explanation of the drawing]

[0068] [Figure 1] This diagram schematically illustrates the steps of the method described herein. [Figure 2] This figure schematically illustrates a sodium or potassium ion battery according to an exemplary embodiment of the present disclosure. [Figure 3a] This graph shows the cycle data of a sodium-ion battery cell manufactured by an exemplary embodiment of the method of the present disclosure, with a dew point temperature of -48°C and a process time of 3 hours for steps e) to g). [Figure 3b]This graph shows the cycle data of a sodium-ion battery cell manufactured by an exemplary embodiment of the method of this disclosure, manufactured under the same conditions as the battery cell in Figure 3a, except that the process time for steps e) to g) was 30 minutes. [Figure 3c] This graph shows the energy efficiency with respect to the number of cycles of a sodium-ion battery cell manufactured by an exemplary embodiment of the method of the present disclosure, with a dew point temperature of -48°C and a process time of 3 hours for steps e) to g). [Figure 3d] This graph shows the energy efficiency with respect to cycle count of a sodium-ion battery cell manufactured according to an exemplary embodiment of the method of this disclosure, manufactured under the same conditions as the battery cell in Figure 3a, except that the process time for steps e) to g) was 30 minutes. [Modes for carrying out the invention]

[0069] This disclosure is described more fully below with reference to the accompanying drawings illustrating currently preferred embodiments of this disclosure. However, this disclosure may be embodied in many different forms and should not be construed as being limited to the embodiments described herein. Rather, these embodiments are provided for thoroughness and completeness and fully convey the scope of this disclosure to those skilled in the art.

[0070] Figure 1a schematically outlines the steps of the method (100) for manufacturing a sodium or potassium ion battery cell according to the present disclosure.

[0071] This method involves the following steps in a sequential order: a) To provide a slurry containing a Prussian blue analog, wherein the Prussian blue analog can exist in a first hydration phase and a second dehydration phase, and the slurry contains the first hydration phase of the Prussian blue analog (step 101), b) Applying the slurry to the current collector to form a cathode (step 102), c) Assembling the cathode with the anode and separator to form an electrode stack (step 103), d) Drying the electrode stack under conditions that allow the Prussian blue analog to be converted from the first hydrated phase to the second dehydrated phase (step 104), e) Placing the electrode stack inside the battery casing (step 105), f) Adding an electrolyte to the battery casing (step 106), g) sealing the battery casing to form the battery cell (step 107) Includes, Steps e) to g) are carried out in an atmosphere with a dew point temperature in the range of -40°C to -80°C, and the process time for carrying out steps e) to g) is less than 7 hours, preferably less than 5 hours.

[0072] A key feature of the method of this disclosure is that steps e) to g) are carried out under conditions that prevent the reaction and undesirable transformation of the PBA material and allow the Prussian blue analog to be maintained in the second dehydrated phase throughout steps e) to g) of the method. This is achieved by carrying out these steps for a period of less than 7 hours, preferably less than 5 hours, in an atmosphere where the dew point temperature is within the range defined above.

[0073] It is important to ensure that the electrode stack is not exposed to moisture or air during the process following drying step d). The process of this disclosure ensures that only one phase transition occurs between the first hydrated phase and the second dehydrated phase of the PBA analog. Thus, undesirable backflow between the first and second phases of the PBA material, which could result in expansion and damage to the material, is prevented.

[0074] The Prussian blue analog "may exist" in the first hydrated phase and the second dehydrated phase. In other words, the Prussian blue analog may exist, or present, in two different phases under different conditions. In step a), the Prussian blue analog exists in the first hydrated phase (in the slurry). During step d), a phase transition occurs from the first hydrated phase to the second dehydrated phase. In the remaining steps e) to g), the Prussian blue analog exists in the second dehydrated phase.

[0075] As used herein, the term “dew point temperature” means the temperature at which air must be cooled to the point of saturation with water vapor (assuming constant air pressure and moisture content). The dew point temperature is a measure of the water vapor content in a gas. The dew point is used as a measure of atmospheric moisture.

[0076] The atmosphere typically has a relative humidity (RH) of less than 20%.

[0077] The inventors have found that battery cells manufactured according to the method of this disclosure exhibit significant improvements in capacity and cycle performance. Battery cells with stable cycle performance are obtained, and undesirable side reactions caused by wet exposure are avoided.

[0078] Personnel can still perform work and operations under normal conditions throughout the first step of this method, and can perform steps e) to g) in a dew-point controlled atmosphere (compared to, for example, conventional lithium-ion battery manufacturing where all steps are performed in a dry room).

[0079] Preferably, steps e) to g) are carried out in an atmosphere with a dew point temperature in the range of -45°C to -70°C.

[0080] The process time required to carry out steps e) to g) may range from 5 minutes to less than 5 hours.

[0081] Preferably, the process time for carrying out steps e) to g) is 10 minutes to less than 3 hours, preferably 15 minutes to 2.5 hours.

[0082] If the dew point temperature is in the range of -40°C to -50°C, the process time for performing e) to g) may be between 5 minutes and less than 3 hours, for example, between 10 minutes and 2.5 hours.

[0083] If the dew point temperature is in the range of -50°C to -80°C, the process time for performing e) to g) may be between 5 minutes and less than 5 hours, for example, between 10 minutes and 4 hours.

[0084] Preferably, steps a) to c) of this method are carried out under ambient conditions.

[0085] As used herein, “ambient conditions” means the general temperature and relative humidity under which the process is carried out. Steps a) to c) may be carried out at relative humidity (RH) levels related to room temperature (e.g., 40–60% RH). The process is not limited to any specific requirements or equipment in these first steps of the Method.

[0086] The first step of this method, i.e., steps a) to c) (steps 101 to 103), may be carried out at room temperature.

[0087] The Prussian blue analog is preferably present in the first hydration phase in steps a) to c) of this method.

[0088] Therefore, in the method of this disclosure, only one phase conversion occurs, and personnel only need to perform the final steps (steps e) to g)) of the method in a low dew point temperature atmosphere.

[0089] The step of providing a slurry (step 101) may include mixing a Prussian blue analog in powder form with a conductive additive and a binder.

[0090] The mixing can be carried out by stirring and / or mixing for at least one hour.

[0091] The conductive additive can be any type of conductive additive known to those skilled in the art. For example, various types of carbon compounds, such as super P, C65, C45, and carbon black, such as Ketjenblack, can be used.

[0092] The binder is not limited to any particular type. For example, arginate, carboxymethylcellulose (CMC), styrene-butadiene rubber (SBR), and polyvinylidene fluoride (PVdF) can be used.

[0093] Prussian blue analog (PBA) powder can be prepared by means known in the art.

[0094] Slurries containing Prussian blue analogs are typically aqueous slurries. Therefore, the Prussian blue analogs exist in the first hydration phase of the slurry.

[0095] The step (102) of applying the slurry to the current collector is 5 mg / cm 2 ~70 mg / cm³ 2 Preferably 10 mg / cm³ 2 ~40 mg / cm³ 2 The coating may include coating the current collector with a slurry at a coating weight.

[0096] The slurry is preferably applied uniformly to at least one surface of the current collector. The current collector is typically a metal foil or metal sheet.

[0097] The current collector may be coated on one or two surfaces. When coated on two surfaces, the coating weight can be increased. In this case, for example, the coating weight may be 30-50 mg / cm³. 2 That's fine.

[0098] The coating process is not limited to a specific coating technique, and any means for coating the current collector with slurry can be used. For example, slot die coating can be used. Preferably, the coating is uniformly distributed on at least one surface of the current collector.

[0099] The thickness of the coating on the current collector may vary depending on the specific application and purpose. For example, the thickness of the PBA coating may be in the range of 50 μm to 500 μm, for example, 100 μm to 250 μm.

[0100] Subsequently, the coated PBA active material may be pressed and compressed on the current collector by calendering, for example, using a roller press calender. Thus, a coating of consistent thickness and density can be achieved.

[0101] Next, the electrodes can be cut into the desired shape using techniques well known in this field. For example, any type of slitting machine can be used.

[0102] In step 103, the cathode is assembled with the anode by stacking or winding electrodes together with a separator. Any technique known in the art can be used.

[0103] As mentioned above, the separator prevents electrical short circuits between the negative and positive electrodes and provides mechanical stability to the battery cell. The separator material may include any material that is chemically stable and electrically insulating.

[0104] The separator has a melting temperature t2 that is higher than the drying temperature t1.

[0105] The separator is preferably thermally stable at temperatures between 170°C and 320°C, for example, between 200°C and 270°C.

[0106] The separator may include any chemically stable and electrically insulating material, such as polymer films including polypropylene, polyethylene, or combinations thereof.

[0107] In step 104, the electrode stack is dried. The drying temperature t1 may be between 110 and 300°C.

[0108] Drying time may vary depending on the temperature used during drying.

[0109] In an exemplary embodiment, step d) of drying the electrode stack can be performed at a drying temperature t1 of 150°C to 300°C, for example, 170°C to 250°C.

[0110] The drying time can be between 15 minutes and 20 hours.

[0111] If the drying temperature t1 is in the range of 150-300°C, for example, 170-250°C, the drying time can be significantly reduced. A drying time of less than 4 hours may be sufficient for the efficient conversion from the first hydrated PBA phase to the second dehydrated PBA phase.

[0112] Preferably, the drying process is carried out at a pressure below ambient temperature.

[0113] Preferably, the drying process is carried out under vacuum. This is beneficial in reducing the drying time required for the phase transition of the PBA analog.

[0114] The drying process is 10 -3 This can be done at a pressure of ~100 mbar. For example, the pressure may be 0.01 to 1 mbar.

[0115] However, the pressure is highly dependent on the temperature used in the drying process. Therefore, the pressure can vary depending on the temperature used during drying.

[0116] It is important that the drying process ensures the removal of all water present in the PBA active material, as well as any potentially present water in any other part of the battery cell.

[0117] Dehydrated PBA material means that the PBA material does not contain water, which affects the electrochemical behavior of battery cells containing the PBA material.

[0118] The drying process (step d)) may be carried out in a drying apparatus such as a closed drying chamber.

[0119] The drying step d) may be carried out in an atmosphere with a dew point temperature in the range of -40°C to -80°C.

[0120] The drying chamber may be placed in the room where steps e) to g) are performed. This is to prevent the battery cell components from being exposed to a humid or ambient atmosphere.

[0121] The drying step d) may be carried out under inert conditions.

[0122] As used herein, the term “inert conditions” means an atmosphere in which oxygen and water are absent. Step d) may be carried out in the presence of an inert gas.

[0123] After the drying process (step 104), the battery cells are placed inside the battery casing (step 105).

[0124] Battery casings can vary depending on the intended application and preferences. The battery casing encloses and seals the battery cells, acting as a barrier against the penetration of any air or moisture into or out of the battery cells.

[0125] The battery casing may be a pouch cell or a cylindrical cell.

[0126] Typically, battery casings are pouch cells. Pouch cells may be formed from flexible materials such as foil. Therefore, battery casings are flexible, lightweight, and can be made in a variety of sizes and shapes.

[0127] For example, the pouch cell may include a polymer-coated metal foil. The metal foil may have a polymer coating on one or both sides.

[0128] Once the electrode stack is inserted into the pouch cell, the pouch cell can be partially sealed.

[0129] This method further includes a step of adding an electrolyte to the battery casing (step 106).

[0130] In exemplary embodiments, step f) (step 106) may be carried out under inert conditions. Thus, step f) is carried out in an atmosphere where oxygen and water are absent.

[0131] For example, step f) (step 106) may be performed in an electrolyte infusion device such as a glove box. The glove box is a closed device for electrolyte infusion, which may be equipped with sealed gloves. The glove box may be filled with an inert gas, such as argon (Ar) gas.

[0132] Since the electrolyte may contain organic solvents that are potentially harmful to personnel handling the electrolyte injection, it may be beneficial to perform step f) (step 106) of adding the electrolyte to the battery casing in an inert, sealed atmosphere such as a glove box.

[0133] The methods disclosed herein are not limited to the use of specific electrolytes.

[0134] Preferably, the electrolyte is a non-aqueous electrolyte. The non-aqueous electrolyte prevents water from interfering with the PBA-coated cathode. Furthermore, the non-aqueous electrolyte provides a larger potential window compared to an aqueous electrolyte. Also, since the battery cell is dried and the PBA is dehydrated, water is substantially absent in the PBA active material or in the battery cell that could interfere with the non-aqueous electrolyte.

[0135] The non-aqueous electrolyte typically includes a solvent or blend of solvents and at least one dissolved salt.

[0136] 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.

[0137] In an exemplary embodiment, the non-aqueous electrolyte includes an alkali metal bis(oxalato)borate salt, and the alkali metal ion is selected from sodium (Na + ), and potassium (K + ). Such non-aqueous electrolytes are fluoride-free, environmentally friendly, safe, and have high ionic conductivity and electrochemical stability.

[0138] Thereafter, the battery casing is sealed (step 107).

[0139] In an exemplary embodiment, the Prussian blue analog has the formula A a M b [M’ c (CN)6] d where A is sodium or potassium, 1 < a ≦ 2, M and M’ are transition metals, preferably selected from iron and / or manganese, 0 < b < 2, 1 < c < 2, and 1 < d < 2.

[0140] In one embodiment, the Prussian blue analog has the formula Aa Prussian white having Fe[Fe(CN)6], wherein A is sodium or potassium, 1.8 < a ≦ 2, preferably 1.9 < a ≦ 2.

[0141] Prussian white is associated with high battery capacity and improved storage ability of sodium (and potassium) ions. Prussian white is also environmentally friendly and can be manufactured at low cost.

[0142] In embodiments where the Prussian blue analog is a Prussian white material, this material can be prepared according to the method described in International Publication No. WO 2018 / 056890 assigned to Altris AB.

[0143] According to another aspect, a sodium or potassium ion battery cell manufactured according to the aforementioned method is provided.

[0144] Figure 2 shows the schematic principle of a sodium or potassium ion battery 200 that uses sodium or potassium ions 201 as charge carriers. The battery stores energy in the chemical bonds of the negative electrode, i.e., the anode 202. When the battery 200 is charged, Na + or K + ions 201 are forcibly deintercalated from the positive electrode, i.e., the cathode 203, and move towards the anode 202. During discharge, the process is reversed. When the circuit is completed, electrons return from the anode 202 to the cathode 203, and Na + or K + ions 201 return to the cathode 203. During discharge of the battery, as shown in Figure 2, oxidation occurs at the anode 202 while reduction occurs at the cathode 203. The flow of current is determined by the potential difference between the cathode 203 and the anode 202, the cell voltage.

[0145] The two electrodes are separated by a separator 205 infiltrated with an electrolyte 204.

[0146] As used herein, the term "battery" means a device containing one or more battery cells.

[0147] A "battery cell" includes a positive electrode, or cathode, a negative electrode, or anode, and a separator. In a battery cell, chemical energy is converted into electricity through reduction and oxidation (redox) reactions at the electrodes.

[0148] The cathode 203 used in the sodium or potassium ion battery of this disclosure includes a current collector coated with the Prussian blue analog material described above.

[0149] The negative electrode material, i.e., anode 202, is not particularly limited as long as it is a material capable of storing / releasing sodium 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 materials, and hard carbon. The anode may also be a metal foil coated with an anode active material.

[0150] Preferably, the battery cell is Na + / Na or K + The electrochemical cycle curve exhibits no voltage plateau above 3.7V relative to / K. Such a voltage plateau is associated with water extraction and indicates that PBA has not fully transitioned from the first hydration phase to the second dehydration phase.

[0151] When used herein, "Na + / against Na or K + The phrase "no voltage plateau above 3.7V relative to / K" means that there is no additional capacitance after 3.7V. Therefore, Na + / against Na or K +There are no moisture-induced reactions above 3.7V relative to / K. This is shown in Figure 3b by the vertically upward-sloping electrochemical cycle curve. The anode used in the electrochemical cycle test is typically a carbon-based anode (hard carbon). The electrochemical cycle tests shown in Figures 3a and 3b were constant-current cycles using a Neware BTS4000 galvanostat to charge / discharge a full cell under controlled conditions. During the first cycle of the measurement, a constant current equal to 0.1C was used with voltage cutoff limits set to 4.2V and 1.3V. During the second and third cycles, a constant current equal to 0.1C was used with voltage cutoff limits set to 3.8V–1.3V.

[0152] The presence of water, or the presence of side reactions caused by water or moisture, + / against Na or K + This can be proven by a slope curve greater than 3.7V for / K. This can also be proven by the presence of two or more voltage plateaus in the electrochemical cycle curve (see Figure 3a).

[0153] The battery cell is Na + / against Na or K + The electrochemical cycle curve may have one voltage plateau between 3.2 and 3.7V for a given K, and there may be no additional voltage plateaus in the electrochemical cycle curve.

[0154] Therefore, a stable and high-performance battery cell is achieved in the absence of water.

[0155] Preferably, the energy efficiency of the battery cell is at least 80% over the first 25 cycles.

[0156] As used herein, “energy efficiency” means the amount of energy extracted from a battery relative to the energy used to charge the battery means. Energy efficiency is the ratio of the sodiumization capacity, multiplied by the average voltage of its sodiumization cycle, to the desodiumization capacity, multiplied by the average voltage of its desodiumization cycle. The higher the energy efficiency per cycle, the more stable the system.

[0157] A battery cell that maintains at least 80% energy efficiency over the first 25 cycles has stable cycle performance. [Examples]

[0158] Example 1 To remove all water from the electrodes, place the Prussian white electrodes in a high vacuum oven (2 × 10 -2 The electrodes were dried at 170°C for 12 hours under conditions of less than mBar. After drying, the electrodes were placed in an argon-filled glove box (1m). 3 The electrode was directly introduced into the glove box. The foil was then sealed in a Ziploc bag. To control moisture and thus the dew point of the glove box, water was absorbed with tissue paper and placed near the glove box's circulation. The moisture content of the glove box was controlled so that the dew point temperature inside the glove box was maintained at -48°C. Once the moisture content and dew point temperature inside the glove box were stable, the electrode was removed from the Ziploc bag and exposed to the moisture inside the glove box for 3 hours. After that, the electrode was transferred to another argon-filled glove box (O2 < 1 ppm, H2O < 1 ppm), and then a separator, a carbon-containing anode, and 12 mg / cm³ of argon were added. 2 The electrode mass load was stacked onto a prototype Prussian white full cell. The cell stack was then transferred to a pouch cell casing under an inert atmosphere for electrolyte injection and sealing. Subsequently, the electrolyte was injected into the cell stack and sealed without exposure to the ambient atmosphere.

[0159] A Neware BTS4000 galvanostat was used to charge / discharge a full cell under controlled conditions using a constant current cycle. During the first cycle of measurement, a constant current equal to 0.1C was used with voltage cutoff limits set to 4.2 and 1.3V. During the second and third cycles, a constant current equal to 0.1C was used, and the voltage cutoff limits were set to 3.8–1.3V.

[0160] The cycle data in Figure 3a shows that the electrode stack contains both the anhydrous and hydrated phases of Prussian white, i.e., both rhombohedral and monoclinic crystal structures. This is clearly demonstrated by the voltage plateau above 3.7V that appears at the end of charging and is associated with the extraction of water from the cathode. The water content in the cell caused gas generation within the cell, making discharge impossible.

[0161] Furthermore, the energy efficiency of the battery cells with respect to the number of cycles was evaluated (see Figure 3c). Energy efficiency refers to the amount of energy extracted from the battery relative to the energy used to charge it. Compared to Coulomb efficiency, which represents current efficiency, energy efficiency can provide an indicator of the charge / discharge C rate, and therefore power. Energy efficiency is the ratio of the sodiumization capacity, obtained by multiplying its sodiumization cycle's average voltage by the sodiumization capacity, to the desodiumization capacity, obtained by multiplying its desodiumization cycle's average voltage by the desodiumization capacity. Energy efficiency can be calculated from the cycle data. The higher the energy efficiency with respect to the number of cycles, the more stable the system. In Figure 3c, the energy efficiency is approximately 60%. The cycles were performed using a Neware BTS4000 galvanostat. The cells were charged using constant current / constant voltage (CC-CV), where a constant current corresponding to 0.25C was used until an upper voltage cutoff of 3.6V was reached, followed by constant voltage charging until a current cutoff of 0.1C was reached. Then, constant current discharge was performed with a current corresponding to 0.25C until a voltage cutoff of 1.8V was reached. The cyclical procedure was repeated multiple times.

[0162] Example 2 An electrochemical cycle evaluation similar to that described in Example 1 was performed. However, this test differed from Example 1 in that the process time for steps e) to g) was shorter, namely 30 minutes.

[0163] The cycle data in Figure 3b shows that the electrode stack contains only the anhydrous phase of Prussian white, i.e., the rhombohedral phase. This is clearly demonstrated by the absence of a voltage plateau above 3.7 volts at the end of charging (such voltage plateaus are associated with the extraction of water from the cathode).

[0164] Furthermore, the energy efficiency of the battery cells with respect to the number of cycles was evaluated (see Figure 3d). The energy efficiency was approximately 95%, indicating stable battery cycling.

[0165] The terms, definitions, and embodiments of all aspects of this disclosure shall apply mutatis mutandis to other aspects of this disclosure.

[0166] While this disclosure has been described with reference to specific exemplary embodiments, many different changes, modifications, etc., will be apparent to those skilled in the art.

[0167] Variations of the disclosed embodiments can be understood and achieved by those skilled in the art when implementing the disclosure, based on a review of the drawings, disclosures, and appended claims. Furthermore, in the claims, the word “including” does not exclude other elements or steps, and the indefinite article “a” or “an” does not exclude the plural.

Claims

1. A method for manufacturing a sodium or potassium ion battery cell, a) To provide a slurry containing a Prussian blue analog, wherein the Prussian blue analog may be present in a first hydration phase and a second dehydration phase, and the slurry contains the first hydration phase of the Prussian blue analog. b) Applying the slurry to the current collector to form a cathode, c) Assembling the cathode with the anode and separator to form an electrode stack, d) Drying the electrode stack under conditions that allow the Prussian blue analog to convert from the first hydrated phase to the second dehydrated phase, e) Placing the electrode stack inside the battery casing, f) Adding an electrolyte to the battery casing, g) sealing the battery casing to form a battery cell Includes, A method wherein steps e) to g) are carried out in an atmosphere with a dew point temperature in the range of -40°C to -80°C, and the process time for carrying out steps e) to g) is less than 7 hours, preferably less than 5 hours.

2. The method according to claim 1, wherein steps e) to g) are performed in an atmosphere with a dew point temperature in the range of -45°C to -70°C.

3. The method according to any one of claims 1 and 2, wherein the process time for carrying out steps e) to g) is 10 minutes to less than 3 hours, preferably 15 minutes to 2.5 hours.

4. The method according to any one of claims 1 to 3, wherein steps a) to c) of the above method are performed under ambient conditions.

5. The method according to any one of claims 1 to 4, wherein the Prussian blue analog is present in the first hydrated phase in steps a) to c) of the method.

6. The method according to any one of claims 1 to 5, wherein the drying step d) is performed at a drying temperature t1 of 110 to 300°C.

7. The method according to any one of claims 1 to 6, wherein the drying step d) is performed at a pressure less than the ambient pressure.

8. The process according to any one of claims 1 to 7, wherein the separator has a melting temperature t2 that is higher than the drying temperature t1.

9. The Prussian blue analog mentioned above is formula A ａ M ｂ [M' ｃ (CN) ６ ] ｄ The formula has the following characteristics, where A is sodium or potassium: The method according to any one of claims 1 to 8, wherein 1 < a ≤ 2, M and M' are transition metals, preferably selected from iron and / or manganese, and 0 < b < 2, 1 < c < 2, and 1 < d < 2.

10. The Prussian blue analog is, Formula A ａ Fe[Fe(CN) ６ The method according to any one of claims 1 to 9, wherein Prussian white having ], where A is sodium or potassium, and 1.8 < a ≤ 2, preferably 1.9 < a ​​≤ 2.

11. The step of applying the slurry to the current collector is 5 mg / cm ２ to 70 mg / cm ２ , preferably 10 mg / cm ２ to 40 mg / cm ２ in coating weight, and coating the slurry on the current collector, the method according to any one of claims 1 to 10.

12. A sodium or potassium ion battery cell manufactured according to the method described in any one of claims 1 to 11.

13. The aforementioned battery cell is Na ＋ / against Na or K ＋ A sodium or potassium ion battery cell according to claim 12, having an electrochemical cycle curve in which there is no voltage plateau above 3.7V with respect to / K.

14. The aforementioned battery cell is Na ＋ / against Na or K ＋ A sodium or potassium ion battery cell according to claim 12 or 13, having an electrochemical cycle curve that shows one voltage plateau between 3.2 and 3.7 V with respect to / K, and having no additional voltage plateaus in the electrochemical cycle curve.

15. The sodium or potassium ion battery cell according to any one of claims 12 to 14, wherein the energy efficiency of the battery cell is at least 80% over the first 25 cycles.

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