A method for manufacturing a prussian white compound

Abstract

The present disclosure generally relates to a method for manufacturing a Prussian White compound comprising: a) reacting a first precursor selected from NaCN and KCN with a salt selected from the group consisting of CoSO4, Co3(PO4)2, Co(CH3CO2)2, Co(HCO2)2, CoC2O4, CoCl2, CrSO4, Cr3(PO4)2, Cr(CH3CO2)2, Cr(HCO2)2, CrC2O4, CrCl2, FeSO4, Fe3(PO4)2, Fe(CH3CO2)2, Fe(HCO2)2, FeC2O4, FeCl2, MnSO4, Mn3(PO4)2, Mn(CH3CO2)2, Mn(HCO2)2, MnC2O4, MnCl2, and combinations thereof to form a second precursor defined by the formula A4X1(CN)6 and a third precursor defined by the formula A4X2(CN)6, wherein A is Na or K, and wherein X1 and X2 are individually selected from Co, Cr, Fe, and Mn; b) reacting the second and third precursors with an acid selected from the group consisting of H2SO4, H4C2O2, H2C2O4, H2CO2, H3PO4, H3PO3, HCl, and HClO2 under conditions that allow for a Prussian White compound to be formed, wherein the Prussian White compound is defined by the formula AaX1[X2(CN)6]1-y, wherein 1.8 < a ≤ 2, and 0 ≤ y ≤ 0.2, wherein step a) is performed at a pH of from 9 to 14, preferably from 10 to 13. The present disclosure also relates to a system for manufacturing a Prussian White compound.

Description

[0001]A METHOD FOR MANUFACTURING A PRUSSIAN WHITE COMPOUND TECHNICAL FIELD The present disclosure generally relates to a method for manufacturing aPrussian white compound and to a system for manufacturing the Prussian white compound.BACKGROUND To date, lithium-ion based batteries (LIB) dominate the market for rechargeable batteries. However, the technology is associated with drawbacks, particularly since the availability of lithium resources is limited. Furthermore, the disposal of spent LIBsis challenging both from a recycling and waste management perspective. Specific precautionsare typically required to handle spent LIBs in a safe manner, and improper disposal may have a negative environmental impact. Sodium ion batteries (SIBs) have emerged as attractive alternatives to LIBs. SIBs offer environmental advantages due to the abundance of sodium resources and the reduced environmental impact associated with sodium extraction and processing. The performance of a sodium ion battery is largely dependent on theproperties of the cathode material. Prussian White (PW) is an environmentally friendly cathode material, whichhas gained considerable attention due to its high theoretical capacity and rate performance.Prussian White has a crystal structure with an open three-dimensional framework and largeinterstitial voids, which makes it capable of storing sodium ions in an efficient manner.Prussian White may be synthesized via co-precipitation, in which an aqueous solution of precursor salts, e.g. sodium ferrocyanide (Na4Fe(CN)6) and iron sulfate (FeSO4)are mixed and reacted under conditions that lead to the formation of an insoluble product,Prussian White, to precipitate out of the solution. Alternatively, Prussian White may be synthesized via acid decomposition, as described in e.g. WO2018 / 056890A1. Acid decomposition involves treating a transition metal cyanide-containingprecursor, e.g. sodium ferrocyanide (Na4Fe(CN)6) with an acid under conditions leading todecomposition of the precursor. Common to the known methods of synthesizing Prussian White is the challenge of providing a high yield of the Prussian White material, and in particular a high yield of a high-quality Prussian White material. The acid decomposition synthesis route is typically associated with theprovision of Prussian White with a high sodium (or potassium) content (compared to co-precipitation). However, this synthesis route typically requires lengthy drying and recoveringsteps, separate sodium enrichment steps, and the use of complex mechanochemical post- synthetic modifications, all of which may be regarded as inconvenient for large scale production. Furthermore, in the synthesis of Prussian White, large amounts of virgin starting materials are typically consumed, which is associated with high costs and high energy demands. In view of this, there is a need to provide an improved and facilitated method tosynthesize Prussian White via the acid decomposition route, which is cost-efficient, sustainable, and suitable for large scale production. SUMMARY In view of the above-mentioned and other drawbacks of the prior art, it is anobject of the present disclosure to provide improvements in relation to synthesizing a highyield of Prussian White material in a facilitated, sustainable and cost-efficient manner.According to a first aspect of the present disclosure, there is providedmethod for manufacturing a Prussian White compound comprising: a) reacting a first precursor selected from NaCN and KCN with a salt selected from the group consisting of CoSO4, Co3(PO4)2, Co(CH3CO2)2, Co(HCO2)2, CoC2O4, CoCl2,CrSO4, Cr3(PO4)2, Cr(CH3CO2)2, Cr(HCO2)2, CrC2O4, CrCl2, FeSO4, Fe3(PO4)2,Fe(CH3CO2)2, Fe(HCO2)2, FeC2O4, FeCl2, MnSO4, Mn3(PO4)2, Mn(CH3CO2)2, Mn(HCO2)2,MnC2O4, MnCl2, and combinations thereof to form a second precursor defined by the formulaA4X1(CN)6and a third precursor defined by the formula A4X2(CN)6, wherein A is Na or K,and wherein X1 and X2 are individually selected from Co, Cr, Fe, and Mn;b) reacting the second and third precursors with an acid selected from thegroup consisting of H2SO4, H4C2O2, H2C2O4, H2CO2, H3PO4, H3PO3, HCl, and HClO2 underconditions that allow for a Prussian White compound to be formed, wherein the PrussianWhite compound is defined by the formula AaX1[X2(CN)6]1-y, wherein 1.8 < a ≤ 2, and 0 ≤ y≤ 0.2, wherein step a) is performed at a pH of from 9 to 14, preferably from 10 to 13.The method of the present disclosure is associated with a significantlyimproved efficiency in synthesizing Prussian White via acid decomposition. Steps a) and b)of the method may be performed in a streamlined, uninterrupted manner, which allows for the continuous formation of high-quality Prussian White; i.e. Prussian White with a highsodium (or potassium) content. The method may be performed in-line. Hence, time-consuming and labor-intensive separation intermediate recrystallization and recovery steps ofthe second and third precursors can be avoided. Drying, separation, washing, and recoveringsteps of crystallized second and third precursors can thus be avoided. Accordingly, PrussianWhite may be manufactured in a significantly facilitated manner. Furthermore, the method ofthe present disclosure is associated with reduced energy demands as well as consumption ofvirgin material. The method of the present disclosure is suitable for large-scale production of Prussian White. Typically, steps a) and b) are performed in-line without interruption or intermediate processing. The inventors have further found that the reaction of step a) is exothermal. This advantageously allows for a more cost-effective and environmentally friendly method sinceless, or sometimes no additional heat needs to be supplied from an external heat source toobtain optimized reaction conditions in step b). An external heat source may for example be ahot plate, an oil bath, an oven, or an electrical heat tracing system. The Prussian White material, obtainable by the method described hereinabove,is associated with a high sodium content, as evidenced by XRD characterization (seeExample section). Step a) is performed at a pH of from 9 to 14, preferably from 10 to 13. This pH range is beneficial to improve the quality and yield of the second andthird precursors, which is important for producing Prussian White with a high sodium (orpotassium) content. At pH levels below 9, the second and third precursors can still form,however, undesirable co-precipitation of “poor-quality” Prussian White as well as theformation of unwanted iron solids (e.g. iron hydroxide and iron oxyhydroxide) may alsooccur, which may lead to reduced material performance and a decreased yield.By performing step a) of the method at a pH level of from 9 to 14, preferably from 10 to 13, the potentially formed Prussian White is unstable, and the second and thirdprecursors become the dominant species, ensuring a high yield and superior product quality.The second precursor, defined by the formula A4X1(CN)6 may be the same as the third precursor defined by the formula A4X2(CN)6. This will be the case if the cation ofthe salts used in step a) are the same, or if only one salt, such as FeSO4 is used in step a).Accordingly, in the Prussian White compound formed in step b), defined by AaX1[X2(CN)6]1-y, X1 and X2 will be the same, e.g. Fe. For example, step b) may comprise the reaction: 2Na4Fe(CN)6 + 3 H2SO4 ^ Na2Fe[Fe(CN)6] + 6 HCN + 3 Na2SO4Alternatively, the second precursor, defined by the formula A4X1(CN)6 may be different from the third precursor defined by the formula A4X2(CN)6. This will be the case ifthe cations of the salts used in the reactions are different, e.g. if two different salts areutilized, such as FeSO4 and CoSO4 in step a). Accordingly, in the Prussian White compoundformed in step b), defined by AaX1[X2(CN)6]1-y, X1 and X2 will be different, e.g. Fe, and Co,respectively. For example, step b) may comprise the reaction: Na4Fe(CN)6 + Na4Mn(CN)6 + 3 H2SO4 ^ Na2Mn[Fe(CN)6] + 6 HCN + 3Na2SO4. In exemplary embodiments, step a) may be performed in a first reactor vessel,and wherein step b) may be performed in a second reactor vessel arranged downstream ofand in fluid communication with the first reactor vessel.This is beneficial since the reaction conditions of step a) may differ from the reaction conditions of step b), particularly with respect to pH. Hence, the reaction conditions for steps a), and b), respectively may be optimized in the first, and second reactor vessel, respectively. Furthermore, undesired co-precipitation of poor-quality Prussian White isavoided. This may occur if the pH level is shifted between an alkaline pH (in step a) and anacidic pH (in step b) in the same reactor vessel.In exemplary embodiments, step b) is performed at a pH of from 1.8 to 4.5, preferably from 2 to 3.5. The inventors have found that performing step b) in this pH range significantlyimproves the decomposition rate of the second and third precursors and also results in theformation of high-quality Prussian white with a high sodium content. The specific pH rangefurther advantageously decreases the risk of unwanted side-reactions which may lead to a decreased yield of Prussian white compound. In exemplary embodiments, step b) is performed at a temperature of from 65 to 95^C, preferably from 75 to 95^C. A temperature in this range triggers acid decomposition of the second andthird precursors. Accordingly, an improved yield of high-quality Prussian White may beobtained.The salt in step a) may be defined by a first cation and a first anion; the acid instep b) being defined by a second cation and a second anion, wherein the second anion of theacid corresponds to the first anion of the salt.Preferably, the anion of the salt (“first anion”) matches the anion of the acid (“second anion”). A consistent chemical environment is thus provided, which secures that thedecomposition reaction proceeds efficiently, and that unwanted by-products or side reactions(with e.g. foreign anions) are not formed. In exemplary embodiments, the first precursor may be reacted with the salt instep a) in the presence of an alkaline additive, preferably wherein the alkaline additive isselected from the group consisting of NH4OH, NaOH, Na3PO4, Na2CO3, KOH, and K2CO3,preferably from NaOH and KOH.The inclusion of an alkaline additive serves to elevate and stabilize the pHduring the reaction in step a). The alkaline additives mentioned hereinabove are substantiallynot consumed during the reaction, which ensures a relatively high pH throughout step a). Asmentioned hereinbefore, maintaining an alkaline environment is important for preventing theformation of poor-quality Prussian White and achieving a high yield of the second and third precursors. In exemplary embodiments, steps a) and b) are performed in an atmospherecomprising argon and / or nitrogen. Accordingly, steps a) and b) are performed in an inert atmosphere. This isbeneficial to prevent unwanted side reactions. An argon or nitrogen atmosphere prevents thePrussian White precursor from degrading or from reacting with oxygen in the air.In exemplary embodiments, steps a) and step b) are conducted in the presenceof water, preferably in an aqueous solution.In other words, the second and third precursors can be formed in an aqueoussolution during step a) and reacted in the aqueous solution during step b). Accordingly, stepsof time-consuming purification and crystallization of the second and third precursors may beavoided. In addition, this advantageously allows for an environmentally friendly process as the use of costly and toxic organic solvents may be avoided. Furthermore, water has a relatively good heat / thermal storage capacity. Thus, the heat generated from the reaction in step a) heats the aqueous solution and may be substantially maintained and consequently benefit the reaction of step b). During the acid decomposition step b), hydrogen cyanide (HCN) may be formed as a by-product. The acidic environment and the specific reaction conditions cause the cyanide groups of the transition metal cyanide-containing precursor, e.g. sodium ferrocyanide (Na4Fe(CN)6, to dissociate from the ferrocyanide precursor and combine with hydrogen ions (H+) to form HCN gas. The remaining free metal ions then react with residual transition metal cyanide-containing precursor to form Prussian white. The production of HCN gas during synthesis is associated with several challenges. HCN is toxic and requires stringent safety measures for handling and disposal. Furthermore, improper management of HCN can lead to severe environmental risks. Hence, in step b) HCN may be formed as a by-product, and wherein the methodmay further comprise: c) recycling the HCN by reacting NaOH or KOH with the HCN to form the first precursor, and d) introducing the first precursor into step a). Accordingly, HCN formed during the acid decomposition of the second andthird precursors may be reacted with NaOH or KOH to form the first precursor. The formedfirst precursor may then be re-introduced into step a) for subsequent manufacturing ofadditional second and third precursors, and eventually additional Prussian white. In thisregard, the efficiency is increased and less virgin first precursor is consumed.The HCN is recycled in the method and utilized for continuous Prussian Whitesynthesis. Accordingly, the manufacturing method is environmentally friendly, and cost-effective. Furthermore, time-consuming and labor-intensive recovery, destructions steps,and / or waste packaging and transporting steps of the formed HCN may be avoided.The HCN produced during acid decomposition is scrubbed using NaOH (orKOH) to form NaCN (or KCN); i.e. first precursor. In this regard, the method of the present disclosure may decrease strenuous handling and disposal of toxic HCN. Accordingly, a safer, less hazardous, and more sustainable method to synthesize Prussian White is provided. In exemplary embodiments, step c) may be performed in a scrubbing devicearranged in fluid communication with the first and / or the second reactor vessel. This allows for an efficient transport of fluids to and from the first reactorvessel, and the second reactor vessel (if present), and the scrubbing device. The arrangementincreases the safety as it allows for avoiding steps of extracting fluids to separate transport vessels and, e.g. manually moving such transport vessels within a factory or to an external facility. Step d) of introducing the first precursor into step a) may comprise:i) collecting the first precursor in an aqueous solution in the scrubbing device;and ii) introducing the aqueous solution comprising the first precursor into the firstreaction vessel. This advantageously allows for avoiding separate steps of time-consuming andcost-intensive steps of crystallizing the first precursor prior to introducing the first precursorinto the first reaction vessel. Furthermore, by conducting step i) and ii) it is relatively easy to maintain a closed system, thereby avoiding unwanted reactions with ambient air. According to another aspect, there is provided a system for manufacturing aPrussian White compound comprising a reactor unit configured to: -conduct a first reaction of a first precursor selected from NaCN and KCNwith a salt selected from the group consisting of CoSO4, Co3(PO4)2, Co(CH3CO2)2,Co(HCO2)2, CoC2O4, CoCl2, CrSO4, Cr3(PO4)2, Cr(CH3CO2)2, Cr(HCO2)2, CrC2O4, CrCl2,FeSO4, Fe3(PO4)2, Fe(CH3CO2)2, Fe(HCO2)2, FeC2O4, FeCl2, MnSO4, Mn3(PO4)2,Mn(CH3CO2)2, Mn(HCO2)2, MnC2O4, MnCl2, and combinations thereof to form a secondprecursor defined by the formula A4X1(CN)6, and a third precursor defined by the formulaA4X2(CN)6, wherein A is Na or K, and wherein X1 and X2 are individually selected from Co,Cr, Fe, and Mn; and- conduct a second reaction of the second and third precursors with an acidselected from the group consisting of H2SO4, H4C2O2, H2C2O4, H2CO2, H3PO4, H3PO3, HCl,and HClO2under conditions that allow for a Prussian White compound to be formed, wherein the Prussian White compound is defined by the formula AaX1[X2(CN)6]1-y, wherein1.8 < a ≤ 2, and 0 ≤ y ≤ 0.2, wherein the first reaction is performed at a pH of from 9 to 14,preferably from 10 to 13. In exemplary embodiments, step a) is performed in a first reactor vessel of the reactor unit, and wherein step b) is performed in a second reactor vessel of the reactor unitarranged downstream of and in fluid communication with the first reactor vessel.Accordingly, the reaction conditions of the respective steps a), and b) may be optimized. In exemplary embodiments, the system may further comprise a scrubbingdevice arranged in fluid communication with the reactor unit, wherein the scrubbing device isconfigured to conduct a third reaction of NaOH or KOH with HCN formed as a by-product inthe second reaction to form the first precursor, and wherein the scrubbing device isconfigured to feed the first precursor into the reactor unit. As mentioned hereinbefore, HCN may be formed as a by-product in the second reaction. Hence, the system may further comprise a scrubbing device arranged in fluidcommunication with the reactor unit; the scrubbing device being configured to conduct athird reaction of NaOH or KOH with HCN to form the first precursor, and wherein thescrubbing device is further configured to feed the first precursor into the reactor unit.The effects and features of the second aspect are analogous to those described above in connection with the first aspect. Embodiments mentioned in relation to the first aspect are compatible with the second aspect. It is further noted that the inventive concept relate to all possible combinations of features unless explicitly stated otherwise. Further features of, and advantages with, the present disclosure will become apparent when studying the appended claims and the following description. The skilled addressee realizes that different features of the present disclosure may be combined to create embodiments other than those described in the following, without departing from the scope of the present disclosure. BRIEF DESCRIPTION OF THE DRAWINGS The various aspects of the present disclosure, including its particular features and advantages, will be readily understood from the following detailed description and the accompanying drawings, in which: Figure 1 shows a flowchart explaining the steps of a method in accordancewith exemplary embodiments of the present disclosure; Figure 2 schematically illustrates a system in accordance with exemplaryembodiments of the present disclosure; Figures 3a-e illustrate the XRD patterns obtained for the Prussian white particles produced in Example 1; Figure 4 illustrates the XRD pattern obtained for the Prussian white particles produced in Example 2. The figures are not necessarily to scale, and generally only show parts that are necessary in order to elucidate the inventive concept, wherein other parts may be omitted or merely suggested. DETAILED DESCRIPTION The present disclosure will now be described more fully hereinafter with reference to the accompanying drawings. The present disclosure may, however, 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 fully convey the scope of the present disclosure to the skilled person. Figure 1 is a flow-chart schematically illustrating the various steps of themethod of the present disclosure. The method for manufacturing a Prussian White compoundcomprises: a) reacting a first precursor selected from NaCN and KCN with a salt selected from the group consisting of CoSO4, Co3(PO4)2, Co(CH3CO2)2, Co(HCO2)2, CoC2O4, CoCl2,CrSO4, Cr3(PO4)2, Cr(CH3CO2)2, Cr(HCO2)2, CrC2O4, CrCl2, FeSO4, Fe3(PO4)2,Fe(CH3CO2)2, Fe(HCO2)2, FeC2O4, FeCl2, MnSO4, Mn3(PO4)2, Mn(CH3CO2)2, Mn(HCO2)2,MnC2O4, MnCl2, and combinations thereof to form a second precursor defined by the formulaA4X1(CN)6and a third precursor defined by the formula A4X2(CN)6, wherein A is Na or K,and wherein X1 and X2 are individually selected from Co, Cr, Fe, and Mn(denoted 101 in figure 1); b) reacting the second and third precursors with an acid selected from thegroup consisting of H2SO4, H4C2O2, H2C2O4, H2CO2, H3PO4, H3PO3, HCl, and HClO2 underconditions that allow for a Prussian White compound to be formed, wherein the PrussianWhite compound is defined by the formula AaX1[X2(CN)6]1-y, wherein 1.8 < a ≤ 2, and 0 ≤ y≤ 0.2, wherein step a) is performed at a pH of from 9 to 14, preferably from 10 to 13.(denoted 102 in figure 1).As used herein, the term “precursor” refers to a compound or substance that precedes and partakes in the formation of another compound during a chemical reaction. The salt in step a) is preferably FeSO4, FeCl2, MnSO4, or MnCl2, morepreferably FeSO4. As used herein, the term “salt” refers to a compound comprising positively charged ions (cations) and negatively charged ions (anions) that are ionically bonded. In a dissolved state the cation(s) and the anion(s) of the salt are dissociated into individual ions. Salt and dissolved salt are known to the person skilled in the art. As used herein, the term “reactor vessel” means a container or chamber inwhich chemical reactions are conducted. The reactor vessel is configured to contain andcontrol chemical reactions under specific conditions of pressure, temperature, and chemical environment. The reactor vessel(s) is / are typically constructed from materials resistant to the chemicals involved and capable of withstanding the operational conditions, including, e.g. pressures and temperatures. Suitable materials for withstanding at least two cycles are known to the person skilled in the art. The reactions of step a) and step b) may be performed in the same first reactor vessel. Preferably, the reaction of step a) is performed in a first reactor vessel, and wherein the reaction of step b) is performed in a second reactor vessel arranged downstream of and influid communication with the first reactor vessel.Accordingly, the method of the present disclosure may be conducted batch-wiseor semi-continuous / continuous. Furthermore, the reaction conditions of the respective steps a) and b) may be optimized. This is beneficial to prevent undesired co-precipitation of poor- quality Prussian White. As used herein, the term “fluid” includes liquid and gas. That the second reactor vessel is arranged in “fluid communication” with thefirst reactor vessel means that the connection between the reactor vessels allow for the flow or transfer of fluid (liquids or gases) between them. The connection may be direct or through conduits, pipes, channels, or passages. The fluid communication may be facilitated using valves, pumps, seals, and other mechanisms to regulate flow rates, pressure, and direction. CoSO4, Co3(PO4)2, Co(CH3CO2)2, Co(HCO2)2, CoC2O4, CoCl2, CrSO4,Cr3(PO4)2, Cr(CH3CO2)2, Cr(HCO2)2, CrC2O4, CrCl2, FeSO4, Fe3(PO4)2, Fe(CH3CO2)2,Fe(HCO2)2, FeC2O4, FeCl2, MnSO4, Mn3(PO4)2, Mn(CH3CO2)2, Mn(HCO2)2, MnC2O4, andMnCl2are also known as cobolt(II) sulfate, cobolt(II) phosphate, cobolt(II) acetate, cobolt(II)oxalate, cobolt(II) formate, cobolt chloride, chromium(II) sulfate, chromium(II) phosphate,chromium(II) acetate, chromium(II) oxalate, chromium(II) formate, chromium chloride,ferrous sulfate, ferrous phosphate, ferrous acetate, ferrous formate, ferrous oxalate, ferrouschloride, manganese(II) sulfate, manganese(II) phosphate, manganese(II) acetate,manganese(II) oxalate, manganese(II) formate, and manganese chloride, respectively.H2SO4, H4C2O2, H2C2O4, H2CO2, H3PO4, H3PO3, HCl, and HClO2are also known as sulfuric acid, acetic acid, oxalic acid, formic acid, phosphoric acid, phosphorous acid, hydrochloric acid, and chlorous acid respectively. NaCN and KCN are also known as sodium cyanide and potassium cyanide, respectively. Reacting the second and third precursors with an acid “under conditions thatallow for a Prussian White compound to be formed” means performing step b) at atemperature of from 75 to 98°C, preferably from 80 to 95°C, preferably from 85 to 95°C andat a pH of from 1.8 to 4.5, preferably from 2 to 3.5. Step b) may be performed during 1 to 24hours, such as 2 to 20 hours, preferably 3 to 12 hours, more preferably 4 to 8 hours. It is contemplated that such conditions trigger acid decomposition of the second and thirdprecursors, whereby the Prussian White compound is formed. Reacting the second and thirdprecursors with an acid may thus be an acid decomposition reaction. Expressed differently,the conditions of step b) allow for acid decomposition of the second and third precursors. Typically, steps a) and b) are performed in-line without interruption and intermediate processing. As used herein, the term “in-line” means that steps a) and b) are carried out ina sequential order such that the output stream from step a) is directly transferred into step b)without decoupling or interrupting the process. This may be accomplished through interconnected reactor vessels, pipes or conduits. The term “intermediate processing” refers to any handling, treatment, oroperation performed between steps a) and b), including but not limited to isolation,separation, filtration, drying, crystallization, enrichment, or recovery of intermediatecompounds. The method of the present disclosure is an in-line method. This is beneficialsince it allows for the entire process to be performed continuously without interruption. Thiseliminates the need for intermediate recovery, drying, or sodium enrichment steps, whichsignificantly reduces processing time and energy consumption. Additionally, the in-lineconfiguration minimizes handling and contamination risks, enhancing both efficiency andproduct quality, making it highly suitable for large-scale production. Furthermore, the use oftoxic and costly organic solvents can be avoided. The obtained Prussian White compound hasa high sodium content, and is suitable for use as the active material of a cathode in a sodium or potassium ion battery cell. The Prussian White compound when used as a cathode active materialfacilitates the intercalation and deintercalation of sodium (or potassium) ions during thecharging and discharging cycles. This process is crucial for the movement of ions that generates electrical current in a battery. The open Prussian White framework allows for easy movement of ions, thereby contributing to an improved cycling stability and capacity of the battery cell. In particular, the Prussian White obtained by the method of the present disclosure has a very high sodium (or potassium) content which advantageously allows for improved specific capacity. Furthermore, the Prussian White obtained is associated with a low vacancy content. A high vacancy content may compromise the structural integrity of the material making it more prone to structural degradation and / or collapsing during cycling in battery applications. Furthermore, with increasing vacancy content the material’s capacity for storing sodium (or potassium) is reduced as the charge balance must be maintained in the material. As illustrated in figure 1, the method may comprise a step of drying thePrussian White compound obtained in step b) (denoted 105 in figure 1).The method may comprise the steps of: -separating the Prussian White compound obtained in step b);- drying the Prussian White compound.The separation step may for example be performed using a filter press or a centrifuge. The step of drying may be performed by means known to the skilled person. The step of drying may for example be performed using a rotary dryer, a fluidized bed dryer, a spray dryer, a vacuum dryer, or a conveyor dryer. The term “Prussian White compound” means a compound defined by the formula AaX1[X2(CN)6]1-y, wherein A is Na or K, 1.8 < a ≤ 2, 0 ≤ y ≤ 0.2, X1and X2areindividually selected from Co, Cr, Fe, and Mn. Preferably, X1 and X2 are selected from Feand Mn. The Prussian White compound comprises iron (Fe), manganese (Mn), cobolt (Co),or chromium (Cr) ions which are linked through cyanide (CN) bridges, forming a three-dimensional framework. The framework forms a cubic-like arrangement, in which each iron, manganese, cobolt or chromium ion is surrounded by six cyanide groups. Sodium orpotassium ions reside within the cavities or interstitial sites of the cubic arrangement formedby e.g. Fe[Fe(CN)6] or Mn[Mn(CN)6] units. Herein, Prussian white compound encompassesboth hydrated and dehydrated Prussian white compounds. Hydrated Prussian white compounds may be understood as Prussian white compounds having water molecules arranged in voids and / or interstitial spaces of the crystalstructure. The water molecules may be bonded through a hydrogen bond with the nitrogen ofthe (CN)6, a metal-ligand bond with one of the transition metal cations, or an ion-dipole bond with sodium. Dehydrated Prussian white compounds may be understood as Prussian white compounds substantially free of water molecules arranged in voids and / or interstitial spaces of the crystal structure. The amount of water molecules arranged in voids and / or interstitial spaces of the crystal structure may be determined using Thermogravimetric Analysis (TGA). In some embodiments, X1and X2are Fe. Preferably, X1and X2are Fe, and A is Na. The method of the present disclosure may yield Prussian white compounds defined by the formula AaX1[X2(CN)6]1-y, wherein A is Na, 1.8 < a ≤ 2, 0 ≤ y ≤ 0.2, X1and X2are Fe. In particular, such a Prussian White compound obtained from the method of the presentdisclosure is associated with a high-quality, and has a high degree of crystallinity.The chemical composition of the Prussian white compound may be measured by methods known in the art. For example, an inductively coupled plasma (ICP) spectrometer (e.g. PerkinElmer Avio 200), CHNOS elemental analysis and / or Mössbauer spectrometry(e.g. an MS 96 spectrometer) may be used to measure a content of element(s) in a sample ofthe Prussian white compound. The Prussian white compound is a solid and may be in the form of particles, i.e., discrete portions of solid matter. Typically, the particles have a DV50 value of from 1 to 50μm, preferably from 10 to 45μm, more preferably in the range of from 12 to 30μm, as determined according to ISO 13320:2009. Herein, the term “DV50 value” refers to a particle diameter below which 50% of the sample volume exists. The DV50 value may also be understood as the median particle size by volume or the volumetric particle size distribution. DV50 as such is known to the person skilled in the art. A DV50 value of a sample volume (a plurality of particles) may bemeasured using, e.g. a PSA 1090 L / D (Anton Paar) instrument. The DV50 may be determinedaccording to ISO 13320:2009 and / or ASTM B822-20.Typically, steps a) and step b) of the method are conducted in the presence ofwater, e.g. in an aqueous solution. Step a) of the method is performed at a pH of from 9 to 14, preferably from 10 to 13. The alkaline pH may be controlled by performing step a) in the presence of analkaline additive. Hence, in step a), the first precursor may be reacted with the salt in thepresence of an alkaline additive, preferably wherein the alkaline additive is selected from thegroup consisting of NH4OH, NaOH, Na3PO4, Na2CO3, KOH, and K2CO3.Controlling the pH within this range is advantageous for obtaining a high yield of high-quality Prussian White without the interference of lower quality co-precipitates. NH4OH, NaOH, Na3PO4, Na2CO3, KOH, and K2CO3are also known as ammonium hydroxide, sodium hydroxide, trisodium phosphate, sodium carbonate, potassium hydroxide, and potassium carbonate, respectively. Step b) of the method is preferably performed at a pH of from 1.8 to 4.5, preferably from 2 to 3.5. Preferably, step b) of the method is performed at a temperature of from 65 to 95^C, preferably from 75 to 95^C. The inventors have found that a pH and / or temperature in these rangessignificantly improves the decomposition of the second and third precursors (in step b) andresults in the formation of Prussian white having a high sodium (and potassium) content.The salt in step a) may be defined by a first cation and a first anion; the acid in step b) being defined by a second cation and a second anion, wherein the second anion of the acid corresponds to the first anion of the salt. This advantageously allows for a cost-effective process since only one type ofanion (and any accompanying by-products thereof) stemming from the first and second anion must be handled during down-stream processing steps such as effluent treatment. Having different anions of the acid and the salt may lead to two types of residual anions and / or the formation of (at least) one more by-product which may need to be separated and / or processedusing different and more complex methods.In other words, a consistent chemical environment is provided, which secures that the formation of Prussian White compound proceeds efficiently, and that unwanted by- products or side reactions (with e.g. foreign anions) are not formed. In other words, if the salt in step a) is FeSO4 or MnSO4, the acid in step b) is preferably H2SO4. If the salt in step a) is FePO4 or Mn3(PO4)2, the acid in step b) is preferably H3PO4. Steps a) and b) are preferably performed in an atmosphere comprising argonor nitrogen. Accordingly, the precursor reacts with the acid and / or salt in an inert atmosphere, which prevents undesired exposure to ambient air (which could yield undesired side-reactions). As illustrated in figure 1, the method may further comprise additional step(s). As mentioned hereinbefore, the reaction of step b) typically involves the formation of HCN as a by-product. Accordingly, when HCN is formed as a by-product in step b), the method may further comprise: c) recycling the HCN by reacting NaOH or KOH with the HCN to form thefirst precursor (denoted 103 in figure 1), andd) introducing the first precursor into step a) (denoted 104 in figure 1).This is advantageous since it enhances the efficiency of the method. Less virgin first precursor is required as the recycling of HCN secures that additional first precursor material can be continuously re-introduced into the process. Furthermore, the problems associated with toxic HCN are overcome and various hazardous waste management or destruction steps can be avoided. The term "virgin first precursor material" refers a first precursor material which has not been recycled through the process of the present disclosure. Virgin NaCN (or KCN) may for example be produced by reacting HCN with NaOH (or KOH). The term “recycling” refers to the process of recovering and treating by- products to produce compounds which may be entered into a production cycle. The term “by-product” refers to a secondary product or substance that is produced during a chemical reaction or manufacturing process but is not the primary intended product. In other words, by-products are generated alongside the primary intended product. Step c) (denoted 103 in figure 1) may be performed in a scrubbing devicearranged in fluid communication with the first and / or the second reactor vessel.Herein, the term “scrubbing device” refers to an apparatus adapted to remove,contaminants or specific compounds in a gas or liquid stream. In particular, a scrubbingdevice refers to a device configured to house / facilitate a reaction between HCN andNaOH / KOH to form NaCN / KCN. The scrubbing device may be a venturi scrubber, apacked-bed scrubber, or a spray tower scrubber. These scrubbing devices are known to the skilled person. The scrubbing device may comprise two or more scrubber units independently selected from a venturi scrubber, a packed bed scrubber, or a spray tower. This advantageously allows for combining characteristic features of different types of scrubberunits. In the example of the two or more scrubber units, the scrubber units may be arranged inseries and / or in parallel. Preferably, at least two scrubber units are arranged in series and at least one of the scrubber units is a venturi scrubber configured to receive HCN from the first and / or second reactor vessel. HCN formed in step b) may be directed to the scrubbing device by a carrieragent or by providing a pressure differential between the scrubbing device and the first and / orsecond reactor vessel.Directing the HCN formed in step b) to the scrubbing device by a carrier agentor by providing a pressure differential between the scrubbing device and the first and / orsecond reactor vessel advantageously allows for relatively rapidly moving the HCN from the first and / or second reactor vessel to the scrubbing device. Thereby the risk of unwanted HCNpolymerization, on e.g., reactor vessel walls or pipes, is reduced. Additionally, this decreasesthe amount of HCN (in gas phase) in a headspace in the first and / or second reactor vessel. In other words, the partial pressure of the HCN in the headspace is decreased allowing for moreHCN to be released from, e.g., a reactor liquid and be transported to the scrubbing device.The carrier agent may be an inert gas, such as nitrogen gas or argon gas,preferably nitrogen gas. Utilizing an inert gas is advantageous since substantially nounwanted side reactions between the HCN and the carrier agent molecules occur, and oxidation of the Prussian white compound is prevented. Alternatively or in addition, a pressure differential may be provided by applyinga vacuum or by providing a lower pressure in the scrubbing device relative to the first and / orsecond reactor vessel. Step d) of introducing the first precursor into step a) may comprise:i) collecting the first precursor in an aqueous solution in the scrubbing device;and ii) introducing the aqueous solution comprising the first precursor into the firstreaction vessel. In embodiments wherein the salt in step a) is FeSO4, step a) comprisesreacting: NaCN with FeSO4 to form Na4Fe(CN)6, orKCN with FeSO4 to form K4Fe(CN)6.Step a) may comprise the reaction: 6NaCN + FeSO4 ^ Na4Fe(CN)6 + Na2SO4, or6 KCN + FeSO4 ^ K4Fe(CN)6 + K2SO4.In embodiments wherein the salt in step a) is Fe3(PO4)2, step a) comprises reacting: NaCN with Fe3(PO4)2 to form Na4Fe(CN)6, orKCN with Fe3(PO4)2 to form K4Fe(CN)6.Step a) may comprise the reaction: 18 KCN + Fe3(PO4)2 ^ 3 K4Fe(CN)6 + 2 K3PO4. In embodiments wherein the salt in step a) is Fe(CH3CO2)2, step a) comprises reacting: NaCN with Fe(CH3CO2)2 to form Na4Fe(CN)6, orKCN with Fe(CH3CO2)2 to form K4Fe(CN)6.Step a) may comprise the reaction: 6NaCN + Fe(CH3CO2)2 ^ Na4Fe(CN)6 + 2 NaH3C2O2, or6 KCN + Fe(CH3CO2)2 ^ K4Fe(CN)6 + 2 KH3C2O2.In embodiments wherein the salt in step a) is Fe(HCO2)2, step a) comprises reacting: NaCN with Fe(HCO2)2 to form Na4Fe(CN)6, orKCN with Fe(HCO2)2 to form K4Fe(CN)6.Step a) may comprise the reaction: 6NaCN + Fe(HCO2)2 ^ Na4Fe(CN)6 + 2 NaHCO2, or6 KCN + Fe(HCO2)2 ^ K4Fe(CN)6 + 2 KHCO2.In embodiments wherein the salt in step a) is FeC2O2, step a) comprisesreacting: NaCN with FeC2O2 to form Na4Fe(CN)6, orKCN with FeC2O2 to form K4Fe(CN)6.Step a) may comprise the reaction: 6NaCN + FeC2O2 ^ Na4Fe(CN)6 + Na2C2O2, or6 KCN + FeC2O2 ^ K4Fe(CN)6 + K2C2O2.In embodiments wherein the salt in step a) is FeCl2, step a) comprises reacting:NaCN with FeCl2 to form Na4Fe(CN)6, orKCN with FeCl2 to form K4Fe(CN)6.Step a) may comprise the reaction: 6NaCN + FeCl2 ^ Na4Fe(CN)6 + 2 NaCl, or6 KCN + FeCl2 ^ K4Fe(CN)6 + 2 KCl.In embodiments wherein the salt in step a) is MnSO4, step a) comprisesreacting: NaCN with MnSO4 to form Na4Mn(CN)6, orKCN with MnSO4 to form K4Mn(CN)6.Step a) may comprise the reaction: 6NaCN + MnSO4 ^ Na4Mn(CN)6 + Na2SO4, or6 KCN + MnSO4 ^ K4Mn(CN)6 + K2SO4.In embodiments wherein the salt in step a) is Mn3(PO4)2, step a) comprisesreacting: NaCN with Mn3(PO4)2 to form Na4Mn(CN)6, orKCN with Mn3(PO4)2 to form K4Mn(CN)6.Step a) may comprise the reaction: 18 NaCN + Mn3(PO4)2 ^3 Na4Mn(CN)6 + 2 Na3PO4, or In embodiments wherein the salt in step a) is Mn(CH3CO2)2, step a) comprises reacting: NaCN with Mn(CH3CO2)2 to form Na4Mn(CN)6, orKCN with Mn(CH3CO2)2 to form K4Mn(CN)6.Step a) may comprise the reaction: 6NaCN + Mn(CH3CO2)2 ^ Na4Mn(CN)6 + 2 NaH3C2O2, or6 KCN + Mn(CH3CO2)2 ^ K4Mn(CN)6 + 2 KH3C2O2.In embodiments wherein the salt in step a) is Mn(HCO2)2, step a) comprisesreacting: NaCN with Mn(HCO2)2 to form Na4Mn(CN)6, orKCN with Mn(HCO2)2 to form K4Mn(CN)6.Step a) may comprise the reaction: 6NaCN + Mn(HCO2)2 ^ Na4Mn(CN)6 + 2 NaHCO2, or6 KCN + Mn(HCO2)2 ^ K4Mn(CN)6 + 2 KHCO2.In embodiments wherein the salt in step a) is MnC2O2, step a) comprisesreacting: NaCN with MnC2O2 to form Na4Mn(CN)6, orKCN with MnC2O2 to form K4Mn(CN)6.Step a) may comprise the reaction: 6NaCN + MnC2O2 ^ Na4Mn(CN)6 + Na2C2O2, or6 KCN + MnC2O2 ^ K4Mn(CN)6 + K2C2O2.In embodiments wherein the salt in step a) is MnCl2, step a) comprisesreacting: NaCN with MnCl2 to form Na4Mn(CN)6, orKCN with MnCl2 to form K4Mn(CN)6.Step a) may comprise the reaction: 6NaCN + MnCl2 ^ Na4Mn(CN)6 + 2 NaCl, or6 KCN + MnCl2 ^ K4Mn(CN)6 + 2 KCl.Both the second and third precursors may be Na4Fe(CN)6, or K4Fe(CN)6, and wherein step b) may comprise reacting: Na4Fe(CN)6 with H2SO4 to form NaaFe[Fe(CN)6] and HCN, or K4Fe(CN)6 with H2SO4 to form KaFe[Fe(CN)6] and HCN, wherein 1.8 < a ≤ 2.Step b) may comprise the reaction: 2Na4Fe(CN)6 + 3 H2SO4 ^ Na2Fe[Fe(CN)6] + 6 HCN + 3 Na2SO4, or2 K4Fe(CN)6 + 3 H2SO4 ^ K2Fe[Fe(CN)6] + 6 HCN + 3 K2SO4.Both the second and third precursors may be Na4Fe(CN)6, or K4Fe(CN)6, andstep b) may comprise reacting: Na4Fe(CN)6 with H4C2O2 to form NaaFe[Fe(CN)6] and HCN, orK4Fe(CN)6 with H4C2O2 to form KaFe[Fe(CN)6] and HCN, wherein 1.8 < a ≤ 2.Step b) may comprise the reaction: 2Na4Fe(CN)6 + 3 H4C2O2 ^ Na2Fe[Fe(CN)6] + 6 HCN + 3 Na2C2O4, or Both the second and third precursors may be Na4Fe(CN)6, or K4Fe(CN)6, andstep b) may comprise reacting: Na4Fe(CN)6 with H2C2O4 to form NaaFe[Fe(CN)6] and HCN, orK4Fe(CN)6 with H2C2O4 to form KaFe[Fe(CN)6] and HCN, wherein 1.8 < a ≤ 2.Step b) may comprise the reaction: 2Na4Fe(CN)6 + 3 H2C2O4 ^ Na2Fe[Fe(CN)6] + 6 HCN + 3 Na2C2O4, or Both the second and third precursors may be Na4Fe(CN)6, or K4Fe(CN)6, andstep b) may comprise reacting:Na4Fe(CN)6 with H2CO2 to form NaaFe[Fe(CN)6] and HCN, orK4Fe(CN)6 with H2CO2 to form KaFe[Fe(CN)6] and HCN, wherein 1.8 < a ≤ 2.Step b) may comprise the reaction: 2Na4Fe(CN)6 + 6 H2CO2 ^ Na2Fe[Fe(CN)6] + 6 HCN + 6 NaHCO2, or Both the second and third precursors may be Na4Fe(CN)6, or K4Fe(CN)6, andstep b) may comprise reacting: Na4Fe(CN)6 with H3PO4 to form NaaFe[Fe(CN)6] and HCN, orK4Fe(CN)6 with H3PO4 to form KaFe[Fe(CN)6] and HCN, wherein 1.8 < a ≤ 2.Step b) may comprise the reaction:2 K4Fe(CN)6 + 6 H3PO4 ^ K2Fe[Fe(CN)6] + 6 HCN + 6 KH2PO4.Both the second and third precursors may be Na4Fe(CN)6, or K4Fe(CN)6, andstep b) may comprise reacting:Na4Fe(CN)6 with H3PO3 to form NaaFe[Fe(CN)6] and HCN, orK4Fe(CN)6 with H3PO3 to form KaFe[Fe(CN)6] and HCN, wherein 1.8 < a ≤ 2.Step b) may comprise the reaction: Both the second and third precursors may be Na4Fe(CN)6, or K4Fe(CN)6, andstep b) may comprise reacting: Na4Fe(CN)6 with HCl to form NaaFe[Fe(CN)6] and HCN, orK4Fe(CN)6 with HCl to form KaFe[Fe(CN)6] and HCN, wherein 1.8 < a ≤ 2.Step b) may comprise the reaction: 2Na4Fe(CN)6 + 6 HCl ^ Na2Fe[Fe(CN)6] + 6 HCN + 6 NaCl, or Step c) (denoted 103 in figure 1) comprises the reaction: The products NaCN or KCN obtained in step c) are introducible into step a) ofthe method according to the present disclosure. This step is illustrated by the arrow 104 in figure 1. The formed product water (H2O) is environmentally friendly and may, in some embodiments, be introduced in the method of the present disclosure. Figure 2 schematically illustrates a system according to a second aspect of thepresent disclosure. According to the second aspect, there is provided a system 200 formanufacturing a Prussian White compound comprising a reactor unit 201 configured to:- conduct a first reaction of a first precursor selected from NaCN and KCNwith a salt selected from the group consisting of CoSO4, Co3(PO4)2, Co(CH3CO2)2,Co(HCO2)2, CoC2O4, CoCl2, CrSO4, Cr3(PO4)2, Cr(CH3CO2)2, Cr(HCO2)2, CrC2O4, CrCl2,FeSO4, Fe3(PO4)2, Fe(CH3CO2)2, Fe(HCO2)2, FeC2O4, FeCl2, MnSO4, Mn3(PO4)2,Mn(CH3CO2)2, Mn(HCO2)2, MnC2O4, MnCl2, and combinations thereof to form a secondprecursor defined by the formula A4X1(CN)6 and a third precursor defined by the formulaA4X2(CN)6, wherein A is Na or K, and wherein X1 and X2 are individually selected from Co,Cr, Fe, and Mn; and- conduct a second reaction of the second and third precursors with an acidselected from the group consisting of H2SO4, H4C2O2, H2C2O4, H2CO2, H3PO4, H3PO3, HCl,and HClO2 under conditions that allow for a Prussian White compound to be formed, wherein the Prussian White compound is defined by the formula AaX1[X2(CN)6]1-y, wherein1.8 < a ≤ 2, and 0 ≤ y ≤ 0.2, wherein the first reaction is performed at a pH of from 9 to 14,preferably from 10 to 13. The first reaction may be performed in a first reactor vessel of the reactor unit201, and wherein step b) may be performed in a second reactor vessel of the reactor unit 201arranged downstream of and in fluid communication with the first reactor vessel.Herein, a device, such as a reactor unit, configured to conduct a reaction, refers to a device able to facilitate and control chemical and / or physical reactions under specified conditions. The device is equipped with the necessary structural, mechanical, and controlcomponents known in the art. The reactor unit may comprise one or more than one reactorvessels. Hence, the reactor unit may also be referred to as a reactor assembly. The reactorunit may be configured for batch or continuous processing. As mentioned hereinbefore, HCN may be formed as a by-product in the second reaction. Hence, the system may further comprise a scrubbing device 202 arranged influid communication with the reactor unit 201; the scrubbing device 202 being configured toconduct a third reaction of NaOH or KOH with HCN to form the first precursor, and whereinthe scrubbing device 202 is further configured to feed the first precursor into the reactor unit201. EXAMPLES Example 1: Synthesis of Prussian white compound and recycling of HCN Cycle 1 A first aqueous solution comprising 202.66 g of a first precursor being virgin NaCN (aq) was prepared and arranged in a reactor. The volume of the first aqueous solution was 720 ml, and the pH was about 12. A total amount of about 191.66 g of FeSO4⋅7H2O (s) was added to the first aqueous solution over a period of one (1) hour (also referred to as addition period). The NaCN was reacted with the (now dissolved) FeSO4 (aq) to form a second aqueous solution comprising (dissolved) Na4Fe(CN)6(aq). The first aqueous solution was agitated using an over-head stirrer throughout the addition period and a subsequent 10- minute-long aging period. The temperature of the first aqueous solution before the addition of FeSO4⋅7H2O was 20 °C and the resulting second aqueous solution had an increased temperature. After the aging period, the second aqueous solution was filtered to produce a filtrate substantially free from solids, i.e., by-products, such as iron hydroxides. The filtrate was arranged in a reactor. An acid decomposition reaction of the Na4Fe(CN)6 present in thefiltrate was instigated by heating the filtrate to a temperature of about 85 °C and introducingsulfuric acid to reach a pH of about 2.9 to form a slurry. The slurry was maintained at thetemperature and the pH for about six (6) hours. The slurry was agitated and a flow of N2 gaswas used as carrier agent for the HCN and was directed through the headspace in the reactor in order to minimize oxidation of the formed Prussian white compounds. After the six (6)hours of reaction, a solid-liquid separation (filtering step) was carried out on the slurry toobtain a filter cake. the filter cake was washed with deionized water and subsequently dried,thereby obtaining Prussian white compounds in the form of particles. During the above-mentioned acid decomposition reaction HCN was formed as a by-product. The HCN in gas phase was transported to a scrubber system where it was contacted with an aqueous solution comprising NaOH. This led to the formation of a scrubber solution comprising NaCN (l) (also referred to as recycled NaCN). Cycle 2-5 Cycle 2 was carried out in a similar manner to Cycle 1. In Cycle 2, virgin NaCNwas introduced into the scrubber solution obtained from Cycle 1 to reach a targetconcentration of (dissolved) NaCN of about 341.27 g / L. The remaining steps of Cycle 1 wererepeated to obtain a new set of Prussian white particles and scrubber solution comprising recycled NaCN (l). Cycle 3 was conducted in a similar fashion to Cycle 2 with the main differencebeing using the scrubber solution from Cycle 2 instead of Cycle 1. Cycle 4 and 5 wereconducted following the same pattern. The amounts of reactants used in each of the cycles as well as the amount of Prussian white produced are presented in table 1.Cycle # FeSO4⋅7H2O [g] Virgin NaCNRecycled NaCN Obtained [g] [g] Prussian white [g] 1191.6 202.66 N / A 106.32 191.6 160.3 42.0 73.13 191.6 161.6 41.0 85.04 191.6 187.37 15.5 102.05 191.6 122.35 79.6 102.1Table 1: Summary of amount of virgin reactants used, recycled NaCN used, and Prussian white obtained. Example 2: Synthesis and characterization of Prussian white compound A first aqueous solution comprising NaCN and NaOH was prepared and arranged in a reactor. The volume of the first aqueous solution was 1.05 L, and the pH was above 12. In the first aqueous solution, the concentration of (dissolved) NaCN was 45.8 g / L and (dissolved) NaOH was 36.0 g / L. A total amount of about 77 g of FeSO4*7H2O (s) was added to the first aqueous solution over a period of one (1) hour (also referred to as addition period). The NaCN was reacted with the (now dissolved) FeSO4 to form a second aqueous solution comprising (dissolved) Na4Fe(CN)6. The first aqueous solution was agitated using a magnetic stirrer throughout the addition period. The temperature of the first aqueous solution before the addition of FeSO4⋅7H2O was 20 °C and the resulting second aqueous solution had an increased temperature. After the addition period, the second aqueous solution was filtered to produce a filtrate substantially free from solids, i.e., by-products, such as iron hydroxides. The filtrate was arranged in a reactor. An acid decomposition reaction of the Na4Fe(CN)6present in thefiltrate was instigated by heating the filtrate to a temperature of about 85 °C and introducingsulfuric acid to reach a pH of about 2.9 to form a slurry. The slurry was maintained at thetemperature for about 12 hours. The slurry was agitated and a flow of N2gas was used through the head space in the reactor in order to minimize oxidation of the formed Prussian white compounds. After the 12 hours of reaction, a solid-liquid separation (filtering step) wascarried out on the filtrate to obtain a filter cake. the filter cake was washed with deionizedwater and subsequently dried, thereby obtaining Prussian white compounds in the form of particles. X-ray diffraction XRD and Rietveld refinement was conducted to determine the crystal structure of the Prussian white particles obtained from each of the cycles 1-5 of Example 1 and the Prussian white particles of Example 2. The XRD was conducted using a Bruker D8 Advance diffractometer equipped with a Cu Kα (λ1 = 1.540596 Å, λ2 = 1.544390 Å) source and a LYNXEYE XE-T detector over the range of 10-120 (2^) with a scanning step of 0.021°. The resulting X-ray diffractograms of the Prussian white particles from Cycles 1-5 are shown inFigure 3a-d, respectively, and the Prussian white particles of Example 2 are shown in Figure4. The Prussian white particles of Cycle 1-5 and Example 2 were concluded to be crystalline. The Prussian white particle of Cycle 1-5 had a hydrated rhombohedral crystalstructure with an R3^ space group symmetry. The Prussian white particles had a combinationof hydrated rhombohedral crystal structure with an R3^ space group symmetry and hydratedmonoclinic phase with a P21 / n space group symmetry. It is understood that as a plurality of particles are measured at the same time. It is contemplated that some particles may consist ofthe hydrated rhombohedral crystal, some of the hydrated monoclinic phase, and some acombination thereof. Such Prussian white particles have been found to be a promising cathode active material due to a high sodium content and low Fe(CN)6 vacancy content. The high sodium content allows for producing battery cells having a high specific capacity (milliampere hours / gram). The rhombohedral crystal structure and the particular monoclinic structure identified through XRD indicate a high sodium content. Particle Size Analysis Particle size distribution (PSD), Dv50 (volumetric particle size distribution), of the Prussian white particles from Cycle 1-5 was measured using a PSA 1090 L / D (Anton Paar). The results of the Particle Analysis are presented in table 2. Cycle # DV50 [µm]1 13.22 16.93 14.24 10.65 11.2 Table 2: Summary of the volumetric particle size distribution of the Prussian white particles obtained in Cycles 1-5. Clearly, in view of Example 1 and 2, the method of the present disclosure advantageously allows for an environmentally friendly and cost-effective way of manufacturing Prussian white particles. The Prussian white particles obtained in each ofExamples 1 and 2 have a high sodium content, making them particularly suitable for use ascathode active material in battery cells. The examples also demonstrate the successful recycling of the by-product HCN to form a precursor which can be used in a subsequent synthesis cycle. Terms, definitions and embodiments of all aspects of the present disclosure apply mutatis mutandis to the other aspects of the present disclosure. Even though the present disclosure has been described with reference to specific exemplifying embodiments thereof, many different alterations, modifications and the like will become apparent for those skilled in the art. Variations to the disclosed embodiments can be understood and effected by the skilled addressee in practicing the present disclosure, from a study of the drawings, the disclosure, and the appended claims. Furthermore, 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

CLAIMS 1. A method for manufacturing a Prussian White compound comprising: a) reacting a first precursor selected from NaCN and KCN with a salt selected from the group consisting of CoSO4, Co3(PO4)2, Co(CH3CO2)2, Co(HCO2)2, CoC2O4, CoCl2,CrSO4, Cr3(PO4)2, Cr(CH3CO2)2, Cr(HCO2)2, CrC2O4, CrCl2, FeSO4, Fe3(PO4)2,Fe(CH3CO2)2, Fe(HCO2)2, FeC2O4, FeCl2, MnSO4, Mn3(PO4)2, Mn(CH3CO2)2, Mn(HCO2)2,MnC2O4, MnCl2, and combinations thereof to form a second precursor defined by the formulaA4X1(CN)6 and a third precursor defined by the formula A4X2(CN)6, wherein A is Na or K,and wherein X1 and X2 are individually selected from Co, Cr, Fe, and Mn;b) reacting said second and third precursors with an acid selected from thegroup consisting of H2SO4, H4C2O2, H2C2O4, H2CO2, H3PO4, H3PO3, HCl, and HClO2 underconditions that allow for a Prussian White compound to be formed, wherein said PrussianWhite compound is defined by the formula AaX1[X2(CN)6]1-y, wherein 1.8 < a ≤ 2, and 0 ≤ y≤ 0.2, wherein said step a) is performed at a pH of from 9 to 14, preferably from 10 to 13.

2. The method according to claim 1, wherein said steps a) and b) are performed in-linewithout interruption or intermediate processing.

3. The method according to claim 1 or claim 2, wherein said step a) is performed in a firstreactor vessel, and wherein said step b) is performed in a second reactor vessel arrangeddownstream of and in fluid communication with said first reactor vessel.

4. The method according to any one of the preceding claims, wherein said step b) isperformed at a pH of from 1.8 to 4.5, preferably from 2 to 3.5.

5. The method according to any one of the preceding claims, wherein said step b) isperformed at a temperature of from 65 to 95^C, preferably from 75 to 95^C.

6. The method according to according to any one of the preceding claims, wherein said salt insaid step a) is defined by a first cation and a first anion; said acid in said step b) being definedby a second cation and a second anion, wherein said second anion of said acid corresponds tosaid first anion of said salt.

7. The method according to any one of the preceding claims, wherein said first precursor isreacted with the salt in said step a) in the presence of an alkaline additive, preferably whereinsaid alkaline additive is NH4OH, NaOH, Na3PO4, Na2CO3, KOH, or K2CO3.

8. The method according to any one of the preceding claims, wherein said steps a) and b) areperformed in an atmosphere comprising argon or nitrogen.

9. The method according to any one of the preceding claims, wherein said steps a) and b) areconducted in the presence of water, preferably in an aqueous solution.

10. The method according to any one of the preceding claims, wherein in said step b), HCNis formed as a by-product, and wherein said method further comprises:c) recycling said HCN by reacting NaOH or KOH with said HCN to form saidfirst precursor, and d) introducing said first precursor into said step a).

11. The method according to claim 10, wherein said step c) is performed in a scrubbingdevice arranged in fluid communication with said first and / or said second reactor vessel.

12. The method according to claim 10 or claim 11, wherein said step d) of introducing saidfirst precursor into said step a) comprises:i) collecting said first precursor in an aqueous solution in said scrubbingdevice; and ii) introducing said aqueous solution comprising said first precursor into saidfirst reaction vessel.

13. The method according to any one of the preceding claims, wherein said salt in said step a)is FeSO4, and wherein said step a) comprises the reaction:6 NaCN + FeSO4 ^ Na4Fe(CN)6 + Na2SO4, or6 KCN + FeSO4 ^ K4Fe(CN)6 + K2SO4.

14. A system (200) for manufacturing a Prussian White compound comprising a reactor unit (201) configured to:- conduct a first reaction of a first precursor selected from NaCN and KCNwith a salt selected from the group consisting of CoSO4, Co3(PO4)2, Co(CH3CO2)2,Co(HCO2)2, CoC2O4, CoCl2, CrSO4, Cr3(PO4)2, Cr(CH3CO2)2, Cr(HCO2)2, CrC2O4, CrCl2,FeSO4, Fe3(PO4)2, Fe(CH3CO2)2, Fe(HCO2)2, FeC2O4, FeCl2, MnSO4, Mn3(PO4)2,Mn(CH3CO2)2, Mn(HCO2)2, MnC2O4, MnCl2, and combinations thereof to form a secondprecursor defined by the formula A4X1(CN)6 and a third precursor defined by the formulaA4X2(CN)6, wherein A is Na or K, and wherein X1 and X2 are individually selected from Co,Cr, Fe, and Mn; and- conduct a second reaction of said second and third precursors with an acidselected from the group consisting of H2SO4, H4C2O2, H2C2O4, H2CO2, H3PO4, H3PO3, HCl,and HClO2under conditions that allow for a Prussian White compound to be formed, wherein said Prussian White compound is defined by the formula AaX1[X2(CN)6]1-y, wherein1.8 < a ≤ 2, and 0 ≤ y ≤ 0.2, wherein said first reaction is performed at a pH of from 9 to 14,preferably from 10 to 13.

15. The system (200) according to claim 14, wherein said step a) is performed in a firstreactor vessel of said reactor unit (201), and wherein said step b) is performed in a second reactor vessel of said reactor unit (201) arranged downstream of and in fluid communicationwith said first reactor vessel.

16. The system (200) according to claim 14 or claim 15, wherein HCN is formed as a by-product in said second reaction, and wherein said system (200) further comprises a scrubbingdevice (202) arranged in fluid communication with said reactor unit (201); said scrubbingdevice (202) being configured to conduct a third reaction of NaOH or KOH with said HCN toform said first precursor, and wherein said scrubbing device (202) is further configured tofeed said first precursor into said reactor unit (201).

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