Prussian blue-based sodium ion battery positive electrode material and its preparation method and application

Abstract

The present invention discloses a Prussian blue-based sodium-ion battery positive electrode material, a preparation method, and applications thereof. The method comprises: mixing sodium ferrocyanide, oxalate, and a non-aqueous solvent, subjecting the mixture to a ball-milling reaction, and washing the product after the ball-milling reaction to remove unreacted raw materials and a portion of sodium oxalate generated by the reaction, thereby obtaining the Prussian blue-based sodium-ion battery positive electrode material. The present invention can synthesize Prussian blue-based compounds with low defects and low interstitial water molecule content, thereby improving the sodium storage performance and capacity utilization of such materials; it also reduces the probability of side reactions in the electrolyte causing cell bloating. In addition, the use of oxalate-based raw materials can also generate a sodium oxalate-based positive electrode sodium supplement during the synthesis of the Prussian blue-based compound, thereby replenishing sodium ion loss caused by SEI film formation or other side reactions during the initial charge.

Description

Technical Field

[0001] The present invention belongs to the technical field of sodium ion batteries, and in particular relates to a Prussian blue-based sodium ion battery positive electrode material and a preparation method and application thereof. Background Art

[0002] Prussian blue and its analogues are a class of sodium-ion battery positive electrode materials with an open three-dimensional framework structure and abundant sodium storage sites. They can be produced on a large scale through the co-precipitation method and have received widespread attention.

[0003] However, the coprecipitation method for synthesizing Prussian blue and its analogs is difficult to control, and the resulting Prussian blue-based materials often contain numerous defects and interstitial water molecules (i.e., crystalline water) in their lattices. These defects can severely damage the Prussian blue framework, affecting electron transport during sodium storage. Interstitial water molecules can occupy sodium sites in the lattice, reducing the material's capacity utilization. Furthermore, during the electrochemical process of sodium-ion batteries, these interstitial water molecules can be lost to the electrolyte as sodium ions are inserted and removed, reacting with the electrolyte and causing bloating, a potential safety hazard. Summary of the Invention

[0004] The present invention aims to solve, at least to a certain extent, one of the technical problems in the related art. To this end, one object of the present invention is to provide a Prussian blue-based sodium-ion battery positive electrode material, a preparation method, and an application thereof. The present invention is capable of synthesizing Prussian blue-based compounds with low defects and low interstitial water molecule content, thereby improving the sodium storage performance of such materials and the capacity utilization rate of such materials; at the same time, it also reduces the probability of side reactions in the electrolyte causing bloating of the battery cell. In addition, the use of oxalate-based raw materials can also generate sodium oxalate-based positive electrode sodium supplements during the synthesis of Prussian blue-based compounds, thereby replenishing sodium ion losses caused by SEI film formation or other side reactions during the initial charge.

[0005] In one aspect of the present invention, a method for preparing a Prussian blue-based sodium ion battery cathode material is provided. According to an embodiment of the present invention, the method comprises:

[0006] Sodium ferrocyanide, oxalate and non-aqueous solvent are mixed and subjected to ball milling reaction;

[0007] The product after the ball milling reaction is washed to remove unreacted raw materials and part of the sodium oxalate generated by the reaction, thereby obtaining a Prussian blue-based sodium ion battery positive electrode material;

[0008] wherein the sodium ferrocyanide and / or the oxalate contain crystal water;

[0009] The molar ratio of the sodium ferrocyanide to the oxalate is 1:(0.5-1.5);

[0010] Based on the total mass of the sodium ferrocyanide and the oxalate, the amount of the non-aqueous solvent is 2 wt%-10 wt%;

[0011] The mass ratio of the total mass of the sodium ferrocyanide, the oxalate and the non-aqueous solvent to the ball milling beads is 1:(1-30).

[0012] According to the method for preparing a Prussian blue-based sodium ion battery positive electrode material according to an embodiment of the present invention, a Prussian blue-based compound with low defects and low interstitial water molecule content can be synthesized, which reduces the influence of defects on electron transport during sodium storage and the probability of interstitial water molecules occupying sodium sites in the crystal lattice, thereby improving the sodium storage performance of such materials and improving the capacity utilization of such materials; at the same time, it also reduces the probability of interstitial water molecules in the material being lost to the electrolyte as sodium ions are embedded and extracted, thereby reducing the probability of side reactions in the electrolyte causing flatulence in the battery cell. In addition, the use of oxalate raw materials can also generate sodium oxalate-based positive electrode sodium supplements during the synthesis of Prussian blue-based compounds, thereby supplementing the sodium ion loss caused by the formation of SEI film or other side reactions during the first charge, saving the process of adding sodium supplements to the sodium ion battery positive electrode material and saving costs.

[0013] In addition, the method for preparing a Prussian blue-based sodium ion battery cathode material according to the above embodiment of the present invention may also have the following additional technical features:

[0014] In some embodiments of the present invention, the oxalate comprises at least one compound of the general chemical formula MC2O4, wherein M is Ni, Fe, Mn, Co, Cu or Zn.

[0015] In some embodiments of the present invention, the non-aqueous solvent includes at least one of ethanol, ethylene glycol, and acetone.

[0016] In some embodiments of the present invention, the sodium ferrocyanide is Na4[Fe(CN)6]·10H2O.

[0017] In some embodiments of the present invention, the mass ratio of the total mass of the sodium ferrocyanide, the oxalate and the non-aqueous solvent to the ball milling beads is 1:(3-15).

[0018] In some embodiments of the present invention, the rotation speed of the ball mill is 200-1000 rpm, preferably 400-600 rpm.

[0019] In some embodiments of the present invention, the ball milling time is 1-24 hours, preferably 2-6 hours.

[0020] In a further aspect of the present invention, the present invention provides a Prussian blue-based sodium-ion battery cathode material. According to an embodiment of the present invention, the Prussian blue-based sodium-ion battery cathode material comprises a compound with the chemical general formula of Na x M[Fe(CN)6] y ·nH2O, where 1 < x ≤ 2, 0 < y ≤ 1, 0 < n < 14, and M is Ni, Fe, Mn, Co, Cu or Zn;

[0021] The content of interstitial water molecules in the Na x M[Fe(CN)6] y ·nH2O is not more than 5 wt%.

[0022] The Prussian blue-based sodium-ion battery cathode material according to an embodiment of the present invention comprises a Prussian blue-based compound Na x M[Fe(CN)6] y ·nH2O with low defects and low interstitial water molecule content, which reduces the probability of affecting electron transport during sodium storage due to the presence of defects and the probability of interstitial water molecules occupying sodium sites in the lattice, thereby improving the sodium storage performance of this type of material and the capacity utilization rate of this type of material; at the same time, it also reduces the probability of interstitial water molecules in the material leaking into the electrolyte with the insertion and extraction of sodium ions, thereby reducing the probability of side reactions occurring in the electrolyte and causing the battery cell to swell.

[0023] In addition, the Prussian blue-based sodium-ion battery cathode material according to the above embodiment of the present invention may further have the following additional technical features:

[0024] In some embodiments of the present invention, the Prussian blue-based sodium-ion battery cathode material further comprises sodium oxalate as a cathode sodium supplement agent.

[0025] In some embodiments of the present invention, based on the total mass of the Prussian blue-based sodium-ion battery cathode material, the content of the sodium oxalate cathode sodium supplement agent is 1 wt% - 5 wt%.

[0026] In a third aspect of the present invention, the present invention provides a positive electrode sheet. According to an embodiment of the present invention, the positive electrode sheet comprises a current collector and an active material layer, the active material layer is coated on the current collector, and the active material layer comprises the Prussian blue-based sodium-ion battery cathode material described in the above embodiments or the Prussian blue-based sodium-ion battery cathode material prepared by the method described in the above embodiments. Thereby, the sodium storage performance and capacity utilization rate of the active material in the positive electrode sheet are improved, and the probability of side reactions occurring in the battery where the positive electrode sheet is located and causing the battery cell to swell is reduced.

[0027] In a fourth aspect, the present invention provides a sodium-ion battery. According to an embodiment of the present invention, the sodium-ion battery includes the positive electrode sheet described in the above embodiment, thereby further increasing the capacity of the sodium-ion battery, improving the cycle performance and charge-discharge performance of the sodium-ion battery, and improving the safety performance of the sodium-ion battery, further meeting the needs of consumers.

[0028] In a fifth aspect of the present invention, an energy storage device is provided. According to an embodiment of the present invention, the energy storage device comprises the sodium-ion battery described in the above embodiment. Thus, the energy storage device has all the advantages of the sodium-ion battery, which will not be further elaborated here.

[0029] Additional aspects and advantages of the present invention will be set forth in part in the description which follows and, in part, will be obvious from the description which follows, or may be learned by practice of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] The above and / or additional aspects and advantages of the present invention will become apparent and readily understood from the following description of the embodiments with reference to the accompanying drawings, in which:

[0031] Figure 1 This is the XRD test pattern of the Prussian blue material prepared in step 3 of Example 1 of the present invention;

[0032] Figure 2 This is an XRD test pattern of the pure Prussian blue material prepared in step 3 of Example 1 of the present invention after multiple washings;

[0033] Figure 3 This is a scanning electron microscope image of the pure Prussian blue material prepared in step 3 of Example 1 of the present invention after multiple washings;

[0034] Figure 4 This is a thermogravimetric curve of the Prussian blue material prepared in step 3 of Example 1 of the present invention;

[0035] Figure 5 This is a charge and discharge curve diagram of the button battery prepared in Example 1 of the present invention;

[0036] Figure 6 This is a capacity retention curve of the button battery prepared in Example 1 of the present invention;

[0037] Figure 7 Thermogravimetric curves of the Prussian blue materials prepared in Examples 2-6 of the present invention;

[0038] Figure 8 This is a thermogravimetric curve of the Prussian blue material prepared in Comparative Example 1 of the present invention. DETAILED DESCRIPTION

[0039] The following describes embodiments of the present invention in detail, examples of which are shown in the accompanying drawings, wherein the same or similar reference numerals throughout represent the same or similar elements or elements having the same or similar functions. The embodiments described below with reference to the accompanying drawings are exemplary and are intended to be used to explain the present invention, and are not to be construed as limiting the present invention.

[0040] In the prior art, Prussian blue-based materials are generally synthesized by coprecipitation in aqueous solution. However, the solubility of the reaction raw materials, sodium ferrocyanide and oxalate, in aqueous solution is relatively large, resulting in very fast reaction kinetics (i.e., very fast reaction rate) in the aqueous solution. As a result, the resulting Prussian blue-based material often contains a large number of defects and interstitial water molecules (i.e., crystal water) in the lattice. Among them, the presence of defects can seriously damage the Prussian blue framework structure, affecting electron transport during sodium storage, and interstitial water molecules can occupy sodium sites in the lattice, reducing the material's capacity utilization. Moreover, during the electrochemical process of sodium-ion batteries, interstitial water molecules in the material will be lost to the electrolyte as sodium ions are embedded and extracted, reacting with the electrolyte side effects, causing battery cell bloating and posing a safety hazard.

[0041] In view of this, in one aspect of the present invention, a method for preparing a Prussian blue-based sodium ion battery positive electrode material is proposed. According to an embodiment of the present invention, the method comprises:

[0042] Sodium ferrocyanide, oxalate and a non-aqueous solvent are mixed (wherein the sodium ferrocyanide and / or the oxalate contain crystal water), subjected to ball milling reaction, and the product after the ball milling reaction is cleaned to remove unreacted raw materials and part of the sodium oxalate generated by the reaction, thereby obtaining a Prussian blue sodium ion battery positive electrode material. During the ball milling process, the interstitial water molecules (i.e., crystal water) contained in the sodium ferrocyanide and / or the oxalate are dissolved in the non-aqueous solvent to form a mixed solvent, while part of the sodium ferrocyanide Na4[Fe(CN)6] and oxalate are dissolved in the mixed solvent. The part of Na4[Fe(CN)6] dissolved in the mixed solvent and the oxalate can undergo a coordination reaction to generate Na x M[Fe(CN)6] y·nH2O and sodium oxalate, where 1 < x ≤ 2, 0 < y ≤ 1, 0 < n < 14. Compared with an aqueous solution, the solubility of the reaction raw materials sodium ferrocyanide and oxalate is relatively small in the above-mentioned mixed solvent. Therefore, the reaction rate of this reaction in the above-mentioned mixed solvent is relatively slow. Therefore, the Prussian blue-like compound prepared in the present invention has fewer defects and a lower content of interstitial water molecules, and its interstitial water molecule content is only below 5%, while the interstitial water molecule content of the Prussian blue-like material synthesized by the co-precipitation method is between 10% and 15%. Thus, this method can synthesize Prussian blue-like compounds with low defects and low interstitial water molecule content, reducing the probability of affecting electron transport during sodium storage due to the existence of defects and the probability of interstitial water molecules occupying sodium sites in the lattice, thereby improving the sodium storage performance of this type of material and the capacity utilization rate of this type of material; at the same time, it also reduces the probability that the interstitial water molecules in the material are lost into the electrolyte during the insertion and extraction of sodium ions, thereby reducing the probability of side reactions occurring in the electrolyte and causing the cell to swell. In addition, selecting oxalate raw materials can also generate sodium oxalate-based positive electrode sodium supplement agents during the synthesis of Prussian blue-like compounds, which can supplement the sodium ion loss caused by the formation of the SEI film or other side reactions during the first charging, saving the process of adding sodium supplement agents to the positive electrode material of sodium ion batteries and also saving costs.

[0043] In the embodiments of the present invention, the role of ball milling is to ball mill the reaction raw materials into particles with relatively small particle sizes (for example, the raw materials can be ball milled into the nanometer level), which is beneficial to their dissolution in the above-mentioned mixed solution, and at the same time fully mix sodium ferrocyanide, oxalate and non-aqueous solvent, so that the reaction between sodium ferrocyanide and oxalate can proceed completely.

[0044] In the embodiments of the present invention, the molar ratio of sodium ferrocyanide to oxalate is 1:(0.5 - 1.5), for example, it can be 1:0.5 / 0.6 / 0.7 / 0.8 / 0.9 / 1.0 / 1.1 / 1.2 / 13. / 1.4 / 1.5. By limiting the molar ratio of sodium ferrocyanide to oxalate within the above range, it can ensure that sodium ferrocyanide or oxalate can react fully. The molar ratio of sodium ferrocyanide to oxalate is preferably 1:1. Thus, it ensures that both sodium ferrocyanide and oxalate can react completely.

[0045] In the embodiments of the present invention, based on the total mass of sodium ferrocyanide and oxalate, the dosage of the non-aqueous solvent is 2wt% - 10wt%, for example, it can be 2 / 3 / 4 / 5 / 6 / 7 / 8 / 9 / 10wt%. By limiting the dosage of the non-aqueous solvent within the above range, it can ensure that the coordination reaction between sodium ferrocyanide and oxalate can proceed smoothly in the mixed solvent formed by the non-aqueous solvent and the crystal water contained in the raw materials. The inventor found that if the dosage of the non-aqueous solvent is too high, it may lead to uneven mixing of the raw materials and incomplete reaction.

[0046] In an embodiment of the present invention, the specific type of the non-aqueous solvent is not particularly limited as long as the non-aqueous solvent is miscible with the crystal water contained in the raw materials and the reaction raw materials are slightly soluble therein. As some preferred embodiments, the non-aqueous solvent includes at least one of ethanol, ethylene glycol, and acetone.

[0047] In an embodiment of the present invention, the sodium ferrocyanide may contain crystal water or may not contain crystal water, as long as at least one of the sodium ferrocyanide and the oxalate contains crystal water. As a specific example, the sodium ferrocyanide may be Na4[Fe(CN)6]·10H2O.

[0048] In an embodiment of the present invention, the oxalate may contain crystal water or may not contain crystal water, as long as at least one of the sodium ferrocyanide and the oxalate contains crystal water. As a specific example, the oxalate includes at least one of the compounds with the chemical general formula MC2O4, where the specific type of M is not particularly limited. Preferably, M may be Ni, Fe, Mn, Co, Cu, or Zn. Correspondingly, the general formula of the formed Prussian blue compound is Na x M[Fe(CN)6] y ·nH2O compound, where 1 < x ≤ 2, 0 < y ≤ 1, 0 < n < 14, and M is Ni, Fe, Mn, Co, Cu, or Zn. <00,00181>

[0049] In an embodiment of the present invention, the mass ratio of the total mass of the sodium ferrocyanide, the oxalate, and the non-aqueous solvent to the mass of the ball milling beads is 1:(1 - 30), preferably 1:(3 - 15). Thus, it is further beneficial to fully mix the sodium ferrocyanide, the oxalate, and the non-aqueous solvent, so that the reaction between the sodium ferrocyanide and the oxalate can proceed completely. Further, the rotation speed of the ball milling is 200 - 1000 rpm, preferably 400 - 600 rpm. Thus, it is further beneficial to fully mix the sodium ferrocyanide, the oxalate, and the non-aqueous solvent, so that the reaction between the sodium ferrocyanide and the oxalate can proceed completely. Further, the ball milling time is 1 - 24 h, preferably 2 - 6 h. Thus, it is further beneficial for the reaction between the sodium ferrocyanide and the oxalate to proceed completely.

[0050] In an embodiment of the present invention, the method further includes: washing the product after the ball milling reaction to remove unreacted raw materials and a part of sodium oxalate generated by the reaction, and drying to obtain a Prussian blue-based sodium ion battery cathode material. In an embodiment of the present invention, sodium ferrocyanide and oxalate react in a molar ratio of 1:1 in principle, and the unreacted raw materials can be removed by washing the product after the ball milling reaction. In addition, sodium oxalate-based sodium ion supplementing agents for the cathode can be generated during the synthesis of Prussian blue-based compounds, so that the sodium ion loss caused by the formation of the SEI film or other side reactions during the first charge can be supplemented, saving the process of adding sodium ion supplementing agents to the sodium ion battery cathode material and also saving costs. However, the molar ratio of the generated sodium oxalate to Na x M[Fe(CN)6] y ·nH2O is approximately 1:1, and the required content of the sodium ion supplementing agent for the cathode in the cathode material is approximately: based on the total mass of the Prussian blue-based sodium ion battery cathode material, the content of the sodium oxalate cathode sodium ion supplementing agent is 1 wt% - 5 wt%. Therefore, the generated sodium oxalate is in excess, and the excess sodium oxalate can also be removed by washing the product after the ball milling reaction. The number of washing times and the solvent used for washing can be determined through multiple experimental attempts, which can be easily achieved by those skilled in the art and will not be elaborated here. Preferably, the product after the ball milling reaction can be washed once with deionized water and once with absolute ethanol respectively.

[0051] In another aspect of the present invention, the present invention proposes a Prussian blue-based sodium ion battery cathode material. According to an embodiment of the present invention, the Prussian blue-based sodium ion battery cathode material includes a compound with the chemical general formula of Na x M[Fe(CN)6] y ·nH2O, where 1 < x ≤ 2, 0 < y ≤ 1, 0 < n < 14, and M is Ni, Fe, Mn, Co, Cu or Zn;

[0052] The content of interstitial water molecules in the Na x M[Fe(CN)6] y ·nH2O is not more than 5 wt%.

[0053] According to the Prussian blue-based sodium ion battery cathode material of the embodiment of the present invention, the cathode material includes a Prussian blue-based compound Na x M[Fe(CN)6] y ·nH2O with low defects and low interstitial water molecule content, and its interstitial water molecule content is only below 5%, while the interstitial water molecule content of the existing Prussian blue-based materials is between 10% and 15%. At the same time, the Prussian blue-based compound Na x M[Fe(CN)6] ynH2O has fewer defects (especially when 1≥y≥0.95, Na x M[Fe(CN)6] y nH2O has fewer defects). Thus, the Prussian blue compound Na x M[Fe(CN)6] y nH2O reduces the probability of defects affecting electron transport during sodium storage and the probability of interstitial water molecules occupying sodium sites in the crystal lattice, thereby improving the sodium storage performance and capacity utilization of such materials. It also reduces the probability of interstitial water molecules in the material being lost to the electrolyte with the insertion and extraction of sodium ions, thereby reducing the probability of side reactions in the electrolyte causing cell flatulence.

[0054] According to some specific embodiments of the present invention, the Prussian blue-based sodium-ion battery cathode material further includes a sodium oxalate cathode sodium supplement, thereby replenishing sodium ions lost due to SEI film formation or other side reactions during the initial charge. Furthermore, based on the total mass of the Prussian blue-based sodium-ion battery cathode material, the content of the sodium oxalate cathode sodium supplement is 1 wt% to 5 wt%.

[0055] In its third aspect, the present invention provides a positive electrode sheet. According to an embodiment of the present invention, the positive electrode sheet comprises a current collector and an active material layer, wherein the active material layer is coated on the current collector and comprises the Prussian blue-based sodium-ion battery positive electrode material described in the above embodiments, or a Prussian blue-based sodium-ion battery positive electrode material prepared using the method described in the above embodiments. This improves the sodium storage performance and capacity utilization of the active material in the positive electrode sheet, and reduces the probability of side reactions in the battery cell causing bloating.

[0056] In a fourth aspect, the present invention provides a sodium-ion battery. According to an embodiment of the present invention, the sodium-ion battery includes the positive electrode sheet described in the above embodiment, thereby further increasing the capacity of the sodium-ion battery, improving the cycle performance and charge-discharge performance of the sodium-ion battery, and improving the safety performance of the sodium-ion battery, further meeting the needs of consumers.

[0057] In a fifth aspect of the present invention, an energy storage device is provided. According to an embodiment of the present invention, the energy storage device comprises the sodium-ion battery described in the above embodiment. Thus, the energy storage device has all the advantages of the sodium-ion battery, which will not be further elaborated here.

[0058] The following embodiments of the present invention are described in detail. It should be noted that the following embodiments are illustrative and are intended only to explain the present invention and are not to be construed as limiting the present invention. In addition, unless otherwise expressly stated, all reagents used in the following embodiments are commercially available or can be synthesized according to methods described herein or known methods. Reaction conditions not listed are also readily available to those skilled in the art.

[0059] Example 1

[0060] This embodiment provides a method for preparing a Prussian blue-based sodium ion battery cathode material, comprising the following steps:

[0061] Step 1: Na4[Fe(CN)6]·10H2O and FeC2O4·2H2O were added into an agate ball mill at a molar ratio of 1:1, and 6 wt% of anhydrous ethanol was added based on the total mass of Na4[Fe(CN)6]·10H2O and FeC2O4·2H2O.

[0062] Step 2: Add zirconia beads in a ratio of 1:3 between the total mass of raw materials (Na4[Fe(CN)6]·10H2O, FeC2O4·2H2O and anhydrous ethanol) and ball milling beads, and ball mill at 580 rpm for 2 h.

[0063] Step 3: The ball-milled product was washed with deionized water and anhydrous ethanol to remove excess Na2C2O4, and then vacuum-dried at 170°C for 12 hours to obtain Prussian blue material.

[0064] Step 4: The Prussian blue material obtained in step 3, Ketjen black, carbon nanotubes, and polytetrafluoroethylene were mixed in a mass ratio of 90:2.5:2.5:5 and pressed onto a stainless steel mesh to form an electrode sheet, which was then punched into a disc electrode with a diameter of 10 mm;

[0065] Step 5: Stack the disc electrode obtained in Step 4, glass fiber (diameter 19 mm), and sodium metal sheet (diameter 15 mm) in a sandwich structure, add electrolyte (1M NaClO4 ethyl carbonate / diethyl carbonate solution), and encapsulate in a CR2032 button battery case.

[0066] The Prussian blue material prepared in step 3 was subjected to XRD test, and the test results are shown in the attached Figure 1 As mentioned above, Figure 1It can be seen that the diffraction peaks corresponding to the (200), (220), (400), (420), (422), (440), (600) and (620) crystal planes in the cubic phase structure of Prussian blue appear at 17.22°, 24.44°, 34.91°, 39.09°, 43.52°, 50.22°, 55.51° and 56.57°. In addition, the characteristic diffraction peaks of sodium oxalate also appear at 31.82°, 41.58°, 44.83° and 47.31°. Therefore, the Prussian blue material prepared in step 3 includes the Prussian blue compound Na x Fe[Fe(CN)6] y nH2O and sodium oxalate. The reaction product was washed again with deionized water and anhydrous ethanol several times to completely remove Na2C2O4, and then vacuum dried at 170℃ for 12h to obtain pure Prussian blue material. The pure Prussian blue material was subjected to XRD test. The test results are shown in the attached figure. Figure 2 As mentioned above, Figure 2 It can be seen that the characteristic diffraction peak of sodium oxalate in the product after multiple washings has completely disappeared, and only the Prussian blue compound Na x Fe[Fe(CN)6] y ·nH2O. At the same time, the pure Prussian blue material was scanned by electron microscope, as shown in the attached Figure 3 As shown in the attached Figure 3 It can be seen that the pure Prussian blue material Na x Fe[Fe(CN)6] y The microscopic morphology of nH2O is nanocubic blocks.

[0067] Prussian blue compounds Na x Fe[Fe(CN)6] y nH2O was subjected to thermogravimetric analysis, and the test results were as follows Figure 4 As shown in the test results, it can be seen that Prussian blue compounds Na x Fe[Fe(CN)6] y The water content of nH2O is 2.80%.

[0068] ICP elemental testing of Prussian blue compounds showed that the mass ratio of each element was Na:Fe=15.68:39.14;

[0069] In summary, the chemical formula for synthesizing the Prussian blue compound in this embodiment is Na 1.92 Fe[Fe(CN)6] 0.98 0.49H2O. It can be seen that the Prussian blue compound synthesized in this example has fewer defects and less water content.

[0070] The button cell prepared in this embodiment was subjected to electrochemical performance test. Figure 5 The figure shows the charge and discharge curve of the button battery at a rate of 0.2C. The charge cutoff voltage in the first cycle is set to 4.5V. The Na2C2O4 in the material can decompose in the high voltage range to replenish the sodium source consumed by SEI film formation and other side reactions. The charge cutoff voltage in the second and third cycles is set to 4.2V, which is within the normal working range of the iron-based Prussian blue material.

[0071] Attachment Figure 6 The capacity retention rate curve of the button battery prepared in this embodiment is shown in the attached figure. Figure 6 It can be seen that the capacity retention rate of the button battery prepared in this embodiment is relatively high, and it still maintains 98.46% after 50 cycles.

[0072] Example 2

[0073] The FeC2O4·2H2O in Example 1 was replaced by NiC2O4·2H2O, and the other contents were the same as those in Example 1.

[0074] The Prussian blue compound Na prepared in this example x Ni[Fe(CN)6] y nH2O for thermogravimetric analysis, as shown in the attached Figure 7 As shown, it can be calculated from the test results that Prussian blue compounds Na x Ni[Fe(CN)6] y The water content of nH2O is 3.15.

[0075] The Prussian blue compound prepared in this example was subjected to an ICP elemental test, and the test result showed that the mass ratio of each element was Na:Ni:Fe=15.14:20.64:19.03.

[0076] In summary, the chemical formula for synthesizing the Prussian blue compound in this embodiment is Na 1.87 Ni[Fe(CN)6] 0.97 0.55H2O. It can be seen that the Prussian blue compound synthesized in this example has fewer defects and less water content.

[0077] Example 3

[0078] The FeC2O4·2H2O in Example 1 was replaced by MnC2O4·2H2O, and the other contents were the same as those in Example 1.

[0079] The Prussian blue compound Na prepared in this example x Mn[Fe(CN)6] y nH2O for thermogravimetric analysis, as shown in the attached Figure 7As shown, it can be calculated from the test results that Prussian blue compounds Na x Mn[Fe(CN)6] y The water content of nH2O is 4.27%.

[0080] The Prussian blue compound prepared in this example was subjected to an ICP elemental test, and the test result showed that the mass ratio of each element was Na:Mn:Fe=16.37:21.86:20.98.

[0081] In summary, the chemical formula for synthesizing the Prussian blue compound in this embodiment is Na 1.79 Mn[Fe(CN)6] 0.94 0.73H2O. It can be seen that the Prussian blue compound synthesized in this example has fewer defects and less water content.

[0082] Example 4

[0083] The FeC2O4·2H2O in Example 1 was replaced by CuC2O4, and the other contents were the same as those in Example 1.

[0084] The Prussian blue compound Na prepared in this example x Cu[Fe(CN)6] y nH2O for thermogravimetric analysis, as shown in the attached Figure 7 As shown, it can be calculated from the test results that Prussian blue compounds Na x Cu[Fe(CN)6] y The water content of nH2O is 4.18%.

[0085] The Prussian blue compound prepared in this example was subjected to an ICP elemental test, and the test results showed that the mass ratio of each element was Na:Cu:Fe=14.88:22.29:18.71.

[0086] In summary, the chemical formula for synthesizing the Prussian blue compound in this embodiment is Na 1.85 Cu[Fe(CN)6] 0.96 0.75H2O. It can be seen that the Prussian blue compound synthesized in this example has fewer defects and less water content.

[0087] Example 5

[0088] The FeC2O4·2H2O in Example 1 was replaced by ZnC2O4·2H2O, and the other contents were the same as those in Example 1.

[0089] The Prussian blue compound Na prepared in this example x Zn[Fe(CN)6] y nH2O for thermogravimetric analysis, as shown in the attached Figure 7 As shown, it can be calculated from the test results that Prussian blue compounds Na x Zn[Fe(CN)6] y The water content of nH2O is 3.04%.

[0090] The Prussian blue compound prepared in this example was subjected to an ICP elemental test, and the test result showed that the mass ratio of each element was Na:Zn:Fe=15.54:23.56:19.68.

[0091] In summary, the chemical formula for synthesizing the Prussian blue compound in this embodiment is Na 1.87 Zn[Fe(CN)6] 0.98 0.56H2O. It can be seen that the Prussian blue compound synthesized in this example has fewer defects and less water content.

[0092] Example 6

[0093] The FeC2O4·2H2O in Example 1 was replaced by CoC2O4·2H2O, and the other contents were the same as those in Example 1.

[0094] The Prussian blue compound Na prepared in this example x Co[Fe(CN)6] y nH2O for thermogravimetric analysis, as shown in the attached Figure 7 As shown, it can be calculated from the test results that Prussian blue compounds Na x Co[Fe(CN)6] y The water content of nH2O is 3.12%.

[0095] The Prussian blue compound prepared in this example was subjected to an ICP elemental test, and the test results showed that the mass ratio of each element was Na:Co:Fe=15.63:21.74:20.11.

[0096] In summary, the chemical formula for synthesizing the Prussian blue compound in this embodiment is Na 1.84 Co[Fe(CN)6] 0.98 0.54H2O. It can be seen that the Prussian blue compound synthesized in this example has fewer defects and less water content.

[0097] Comparative Example 1

[0098] This comparative example provides a method for synthesizing Prussian blue by coprecipitation, comprising the following steps:

[0099] Step 1: Add 12.986 g of sodium citrate dihydrate and 2.503 g of ferrous sulfate hexahydrate to 150 mL of deionized water, stir at room temperature to dissolve, and obtain solution A;

[0100] Step 2: Add 2.905 g of sodium ferrocyanide decahydrate to 150 mL of deionized water and stir at room temperature to dissolve to obtain solution B;

[0101] Step 3: Slowly add solution A to solution B, stir at room temperature for 6 hours, and then stand for 24 hours to obtain a reaction product;

[0102] Step 4: The reaction product obtained in step 3 was centrifuged at 10,000 rpm for 10 minutes for separation and washing, and then vacuum dried at 170° C. for 12 hours to obtain a Prussian blue material. Other contents were the same as in Example 1.

[0103] The Prussian blue compound Na synthesized in this comparative example x Fe[Fe(CN)6] y nH2O was subjected to thermogravimetric analysis, and the test results were as follows Figure 8 As shown in the test results, it can be seen that Prussian blue compounds Na x Fe[Fe(CN)6] y The water content of nH2O is 11.74%.

[0104] ICP elemental analysis of Prussian blue compounds revealed a mass ratio of Na:Fe of 14.53:43.19.

[0105] In summary, the chemical formula of the Prussian blue compound synthesized in this comparative example is Na 1.54 Fe[Fe(CN)6] 0.88 2.06H2O. It can be seen that the defects and water content in the Prussian blue compound synthesized in this ratio are higher than those in Example 1.

[0106] In the description of this specification, the reference terms "one embodiment", "some embodiments", "example", "specific example", or "some examples" mean that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in any one or more embodiments or examples in a suitable manner. In addition, those skilled in the art can combine and combine different embodiments or examples described in this specification and features of different embodiments or examples without contradiction.

[0107] Although the embodiments of the present invention have been shown and described above, it will be understood that the above embodiments are illustrative and are not to be construed as limitations on the present invention. A person skilled in the art may change, modify, replace and modify the above embodiments within the scope of the present invention.

Claims

1. A method for preparing a Prussian blue-based sodium ion battery cathode material, characterized in that: include: Sodium ferrocyanide, oxalate and non-aqueous solvent are mixed and subjected to ball milling reaction; The product after the ball milling reaction is washed with deionized water and anhydrous ethanol respectively to remove unreacted raw materials and part of the sodium oxalate generated by the reaction, thereby obtaining a Prussian blue-based sodium ion battery positive electrode material; wherein the sodium ferrocyanide and / or the oxalate contain crystal water; The molar ratio of the sodium ferrocyanide to the oxalate is 1:(0.5-1.5); Based on the total mass of the sodium ferrocyanide and the oxalate, the amount of the non-aqueous solvent is 2 wt%-10 wt%; The mass ratio of the total mass of the sodium ferrocyanide, the oxalate and the non-aqueous solvent to the ball milling beads is 1:(3-15).

2. The method according to claim 1, characterized in that The sodium ferrocyanide is Na4[Fe(CN)6]·10H2O.

3. The method according to claim 1, characterized in that The oxalate comprises at least one compound having a general chemical formula of MC2O4, wherein M is Ni, Fe, Mn, Co, Cu or Zn.

4. A Prussian blue-based sodium ion battery cathode material prepared by the method according to any one of claims 1 to 3, characterized in that: The Prussian blue-based sodium-ion battery cathode material includes a compound with the chemical general formula Na x M[Fe(CN)6] y ·nH2O, where 1 < x ≤ 2, 0 < y ≤ 1, 0 < n < 14, and M is Ni, Fe, Mn, Co, Cu or Zn; The Na x M[Fe(CN)6] y The interstitial water molecule content of nH2O is not greater than 5wt%.

5. The Prussian blue-based sodium ion battery positive electrode material according to claim 4, characterized in that The Prussian blue-based sodium ion battery positive electrode material also includes sodium oxalate positive electrode sodium supplement.

6. The Prussian blue-based sodium ion battery cathode material according to claim 5, characterized in that Based on the total mass of the Prussian blue-based sodium ion battery positive electrode material, the content of the sodium oxalate positive electrode sodium supplement is 1wt%-5wt%.

7. A positive electrode sheet, characterized in that: The positive electrode sheet includes a current collector and an active material layer, the active material layer is coated on the current collector, and the active material layer includes the Prussian blue-based sodium ion battery positive electrode material according to any one of claims 4 to 6 or the Prussian blue-based sodium ion battery positive electrode material prepared by the method according to any one of claims 1 to 3.

8. A sodium ion battery, characterized in that: Including the positive electrode sheet according to claim 7.

9. An energy storage device, characterized in that: A sodium ion battery according to claim 8.

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