Prussian blue positive electrode material and preparation method and application thereof

Abstract

The invention relates to the technical field of battery materials, and discloses a Prussian blue positive electrode material and a preparation method and application thereof. Researchers find that the specific water content and distribution ensure the structural stability of the material in the battery cell preparation process in the test, and the battery cell does not generate gas and does not fall off during circulation. Therefore, according to the Prussian blue type positive electrode material provided by the invention, the mass content ratio of coordination water Xa to interstitial water Xb to adsorbed water Xc is (0.2-5): 1, and the mass content ratio of Xc: Xa is (0.1-5): 1, so that the stability of water distribution of the Prussian blue type positive electrode material in the pole piece drying process is avoided, the stability of the material structure is kept, and meanwhile, the advantage of certain interstitial water for improving circulation is exerted; and shedding of the positive electrode material caused by the volume effect of phase change during circulation of the material with extremely low water content is avoided, so that the battery prepared from the material as the positive electrode material has excellent cycle stability.

Description

Technical Field

[0001] This invention relates to the field of battery materials technology, and in particular to a Prussian blue-based cathode material, its preparation method, and its application. Background Technology

[0002] With the continuous expansion of global demand for large-scale energy storage, resource-rich and environmentally friendly battery technologies have become a research hotspot. Seeking and developing high-capacity electrode materials with rapid sodium insertion / extraction capabilities is crucial for battery development. Prussian blue-based cathode materials possess advantages such as high capacity, low cost, and good conductivity, and have broad application prospects in the field of electrochemical energy storage.

[0003] Prussian blue cathode materials have attracted increasing research attention due to their significant advantages. However, as research progresses, several related problems have emerged. For example, moisture control in Prussian blue cathode materials is difficult, and the properties of water are unclear, which can lead to numerous side reactions in the battery. Furthermore, Prussian blue cathode materials are highly hygroscopic, making their structure and properties prone to change. Additionally, high water content can cause gas generation during cell cycling. These water-related issues hinder the reliable application of Prussian blue cathode materials.

[0004] Regarding the problems caused by water in Prussian blue cathode materials, existing technologies primarily employ solutions such as reducing the water content of Prussian blue and improving its hygroscopicity. These solutions include coating it with different materials, treating it with organic solvents to remove water and inhibit moisture absorption, and surface modification. However, since the properties of water in Prussian blue cathode materials are currently unclear, the current approach of eliminating water-related problems by simply reducing moisture is a short-sighted solution. This approach simultaneously abandons the potential benefits that water can bring to Prussian blue cathode materials. Furthermore, the process of controlling the water content of Prussian blue cathode materials to a low level is complex and costly in practical applications.

[0005] In the prior art, Chinese patent application number 2017110426381 proposes a positive electrode sheet, its preparation method, and a sodium-ion battery. This patent controls the water content of the positive electrode active material layer within a certain range, specifically 100μg / g to 5000μg / g. This ensures that water is not electrolyzed during charging and discharging, and the probability of side reactions between water and electrolyte is low. This prevents severe gas expansion during charging and discharging of the sodium-ion battery, allowing for normal charging and discharging. It also avoids structural collapse caused by the drying out of coordinated water in the crystal structure of Prussian blue-like materials, giving the sodium-ion battery both good charge-discharge performance and cycle performance. The patented cathode material maintains a low moisture content to avoid a series of problems caused by water in the cathode material. However, obtaining a cathode material with a water content of 100μg / g to 5000μg / g requires strict control of the process. Furthermore, ensuring that the water content meets the requirements in the later stages of cell production is difficult to control. In today's fierce competition among companies in this field, this production process is unlikely to meet the requirements for rapid mass production.

[0006] Therefore, in summary, there is an urgent need in this field for an effective and feasible method to solve the problems caused by moisture in current Prussian blue cathode materials. Summary of the Invention

[0007] In order to improve the electrical performance of Prussian blue cathode materials, this invention specifically addresses the shortcomings of difficult moisture control and poor battery electrical performance caused by moisture in the cathode, by providing a Prussian blue cathode material, its preparation method, and its application.

[0008] The specific technical solution of this invention is as follows: In a first aspect, the present invention provides a Prussian blue-based cathode material with the molecular formula A. x M[M'(CN)6] y ·zH2O, where: A is an alkali metal, M is a transition metal, M' is a transition metal, 1 <x≤2,0.8≤y<1,0<z≤3; In Prussian blue-type cathode materials, the interstitial water content is X b and coordination water X a The mass content ratio is 0.2~5:1, and the adsorbed water X c and coordination water X a The mass content ratio is 0.1~5:1.

[0009] Prussian blue cathode materials are prone to structural and property changes due to water content, leading to poor battery cycle stability. Current technologies typically address these issues by reducing water content. However, the properties of water in Prussian blue cathode materials are unclear, and research on water content and the distribution of different water types is scarce. Therefore, the current approach of uniformly removing water introduces other problems.

[0010] Among them, coordinated water X a Interstitial water (X) occupies vacancy [M'(CN)6] sites in Prussian blue cathode materials. These vacancy sites are strongly bound to the material's lattice, and their removal causes a change in the lattice structure. b Water molecules occupying interstitial sites in Prussian blue-based cathode materials exert strong binding forces on the lattice, causing changes in the lattice structure upon removal. Adsorbed water X c These are water molecules that adhere to the Prussian blue cathode material through adsorption. They have a weak binding force with the material and do not participate in the formation of the crystal lattice. The removal of adsorbed water does not cause a change in the crystal structure. The three types of water molecules have different binding forces to the material's crystal lattice, and therefore require different temperatures to be removed from the lattice.

[0011] The researchers of this invention discovered in experiments that specific water content and distribution can ensure the structural stability of the material during the cell fabrication process, preventing gas generation and material loss during cell cycling. Therefore, through numerous experiments, this invention discovered that the interstitial water content X in Prussian blue-based cathode materials... b and coordination water X a The mass content ratio is 0.2~5:1, adsorbed water X c and coordination water X a The mass content ratio is 0.1~5:1, which can avoid the problem of conversion between different types of water in Prussian blue cathode materials, improve the structural stability of Prussian blue cathode materials, and make the batteries prepared by using it as cathode materials have excellent cycle stability.

[0012] The Prussian blue cathode material of this invention possesses excellent stability, which depends on the interstitial water X b and coordination water X a The mass content ratio is 0.2~5:1, adsorbed water X c and coordination water X a The mass content ratio is 0.1~5:1. When there is too much coordinated water in the Prussian blue cathode material, it will affect the electronic conductivity; when there is too little, there will be a problem of cathode material falling off the electrode sheet. When there is too much interstitial water, the ionic conductivity will deteriorate and there will be a problem of gas generation. When there is too little interstitial water, the crystal structure will easily change and the battery cycle will be poor. When there is too much adsorbed water, the processing performance will be poor; when there is too little, there will be a problem of water absorption during processing.

[0013] As a preferred cathode material, the Prussian blue-based cathode material contains interstitial water X b and coordination water X a The mass content ratio is 0.5~2:1, and the adsorbed water X c and coordination water X a The mass content ratio is 0.1~2:1.

[0014] The Prussian blue cathode material provided by this invention exhibits excellent electrical properties based on its specific water content and distribution. Through multiple experimental verifications, this invention has found that when interstitial water X b and coordination water X a The mass content ratio is 0.5~2:1, adsorbed water X c and coordination water X a The mass content ratio is 0.1~2:1, which can further improve the stability of the Prussian blue cathode material structure.

[0015] As a preferred cathode material, the total water content is 0.1wt%~15wt%.

[0016] Further optimization, coordination water X a The content is 0.05wt%~5wt%.

[0017] In Prussian blue-type cathode materials, coordinated water X a It occupies lattice sites in its coordination structure vacancy, and the coordination water X a The content needs to be controlled within a certain range to prevent the positive electrode from shedding material under the condition of optimal ionic conductivity.

[0018] As a preferred cathode material, A is selected from one or more of Na, K, and Li.

[0019] As a preferred cathode material, M is selected from one or more of Mn, Fe, Co, Ni, Cu, Zn, V and Cr.

[0020] As a preferred cathode material, M' is selected from one or more of Mn, Fe, Co, Ni, Cu, Zn, V, and Cr.

[0021] Secondly, this invention provides a method for preparing a Prussian blue-based cathode material, comprising the following steps: Step S1: Prepare the reaction base solution, a first solution containing a hexacyano alkali metal salt of transition metal M', and a second solution containing a salt of transition metal M; Step S2: Add the first solution and the second solution to the base liquid to react and obtain a reaction slurry; Step S3: Separate and wash the reaction slurry to obtain solid material, and dry the solid material until the interstitial water content in the solid material is reduced by X. b and coordination water X a The mass content ratio is 0.2~5:1, adsorbed water X c and coordination water X a The mass content ratio is 0.1~5:1; The solid material obtained after drying has the molecular formula A. x M[M'(CN)6] y ·zH2O.

[0022] To achieve a specific water content and distribution, this invention provides a method for preparing Prussian blue-based cathode materials as described above. Specifically, through steps S1 to S3, this invention achieves a co-precipitation reaction using a hexacyanoalkali metal salt of transition metal M' and a salt of transition metal M as reactants, and further, through drying, obtains a Prussian blue-based cathode material with a specific water content and distribution. This avoids the problem of water conversion between different types in the Prussian blue-based cathode material. Because the water content and distribution of this Prussian blue-based cathode material are suitable, the structural stability of the Prussian blue-based cathode material can be improved, resulting in excellent cycle stability of the battery prepared using this cathode material.

[0023] Specifically, the transition metal M is selected from one or more of Mn, Fe, Co, Ni, Cu, Zn, V and Cr, the transition metal M' is selected from one or more of Mn, Fe, Co, Ni, Cu, Zn, V and Cr, and the alkali metal is selected from one or more of Na, K and Li.

[0024] As a preferred embodiment of the above preparation method, in step S2, the reaction temperature is 10~100℃ and the reaction time is 0.5~24h.

[0025] As a preferred embodiment of the above preparation method, the drying method is selected from at least one of forced-air drying, vacuum drying, and drying under a specific atmosphere. The specific atmosphere refers to an inert atmosphere or a reducing atmosphere. More preferably, the drying method includes a controlled section with a temperature of 80~250℃ and a duration of 1~32h.

[0026] The reaction substrate is preferably water, and further preferred, a sodium supplement and a complexing agent are added to the water.

[0027] Thirdly, the present invention provides an electrochemical energy storage device, comprising: a positive electrode sheet including a positive current collector and a positive electrode membrane disposed on the positive current collector and containing a positive electrode material; a negative electrode sheet; and a separator. Specifically, the positive electrode material is the Prussian blue-based positive electrode material provided by the present invention.

[0028] Compared with the prior art, the present invention has the following technical effects: (1) This invention provides a Prussian blue-type cathode material, wherein the interstitial water X b and coordination water X a The mass content ratio is 0.2~5:1, adsorbed water X c and coordination water X a The mass content ratio is 0.1~5:1, which avoids the problem of conversion between different types of water in Prussian blue cathode materials, and can improve the structural stability of Prussian blue cathode materials, so that the batteries prepared by using it as cathode material have excellent cycle stability.

[0029] (2) In the prior art, the problem of poor material structural stability caused by water content in Prussian blue cathode materials is solved by reducing the water content. However, if the water content is too low, the volume change during cycling will be significant, which will lead to material shedding and worsen the internal resistance. This invention optimizes the content and distribution of different types of water in Prussian blue cathode materials to avoid the problem of poor material structural stability caused by water content in Prussian blue cathode materials, and can also take into account the role of a certain water content in ensuring volume stability during cycling. Detailed Implementation

[0030] The present invention will be further described below with reference to embodiments. Those skilled in the art will be able to implement the present invention based on these descriptions. Furthermore, the embodiments of the present invention described below are generally only some, not all, of the embodiments of the present invention. Therefore, all other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort should fall within the scope of protection of the present invention.

[0031] The total mass content of water, coordinated water, interstitial water, and adsorbed water in the Prussian blue cathode material of this invention were obtained through analysis of thermogravimetric analysis (TGA) results. Based on the obtained thermogravimetric curve (TG) and the decomposition temperature of the Prussian blue cathode material, the total amount of water removed before decomposition of the sample can be analyzed. Differential TG is used to obtain the derivative thermogravimetric curve (DTG). Based on the minimum weight loss rate point of the DTG curve and the physical meaning of different types of water, temperature curves corresponding to the removal of different types of water are divided, thus obtaining the content of different types of water.

[0032] General Implementation Examples This embodiment provides a Prussian blue-based cathode material with the molecular formula A. x M[M'(CN)6] y ·zH2O, where: A is an alkali metal, M is a transition metal, M' is a transition metal, 1 <x≤2,0.8≤y<1,0<z≤3; In the Prussian blue-type cathode material, the interstitial water content is X b and coordination water X a The mass content ratio is 0.2~5:1, and the adsorbed water X c and coordination water X a The mass content ratio is 0.1~5:1.

[0033] Among them, coordinated water X a Interstitial water (X) occupies vacancy [M'(CN)6] sites in Prussian blue cathode materials. These vacancy sites are strongly bound to the material's lattice, and their removal causes a change in the lattice structure. b Water molecules occupying interstitial sites in Prussian blue-based cathode materials exert strong binding forces on the lattice, causing changes in the lattice structure upon removal. Adsorbed water X c These are water molecules that adhere to the Prussian blue cathode material through adsorption. They have a weak binding force with the material and do not participate in the formation of the crystal lattice. The removal of adsorbed water does not cause a change in the crystal structure. The three types of water molecules have different binding forces to the material's crystal lattice, and therefore require different temperatures to be removed from the lattice.

[0034] This embodiment utilizes the interstitial water X in the Prussian blue-type cathode material. b and coordination water X a The mass content ratio is 0.2~5:1, adsorbed water X c and coordination water X a The mass content ratio is 0.1~5:1 to avoid the problem of conversion between different types of water in Prussian blue cathode materials, improve the structural stability of Prussian blue cathode materials, and make the batteries prepared by using them as cathode materials have excellent cycle stability.

[0035] As a preferred embodiment, in the Prussian blue-type cathode material, the interstitial water content is X b and coordination water X a The mass content ratio is 0.5~2:1, and the adsorbed water X c and coordination water X a The mass content ratio is 0.1~2:1.

[0036] The Prussian blue cathode material provided in this embodiment exhibits excellent electrical performance due to its specific water content and distribution. This embodiment, through multiple experimental verifications, has found that when interstitial water X b and coordination water X a The mass content ratio is 0.5~2:1, adsorbed water X c and coordination water X aThe mass content ratio is 0.1~2:1, which can further improve the stability of the Prussian blue cathode material structure.

[0037] As a preferred embodiment, the total water content is 0.1wt% to 15wt%.

[0038] Further optimization, coordination water X a The content is 0.05wt%~5wt%.

[0039] As a preferred embodiment, A is selected from one or more of Na, K, and Li.

[0040] As a preferred embodiment, M is selected from one or more of Mn, Fe, Co, Ni, Cu, Zn, V and Cr.

[0041] As a preferred embodiment, M' is selected from one or more of Mn, Fe, Co, Ni, Cu, Zn, V and Cr.

[0042] Example 1 This embodiment provides a Prussian blue-based cathode material, which is prepared according to the following steps: 484 g of Na₄Fe(CN)₆·10H₂O was dissolved in 5000 mL of water to obtain the first solution. 278 g of FeSO₄·7H₂O was dissolved in 2000 mL of water to obtain the second solution. 1 mol of complexing agent sodium citrate and 1 mol of sodium chloride supplement were mixed and dissolved in 2000 mL of water to obtain the reaction base solution. The reaction base solution was placed in a reaction vessel, and the temperature was controlled at 25℃. The first and second solutions were added to the base solution with stirring, and the reaction time was controlled at 6 h. After the reaction was completed, the reaction slurry was separated and washed to obtain a solid material. The solid material was vacuum dried at 200℃ for 16 h to obtain the target product, whose molecular formula is Na₂Fe(CN)₆·10H₂O. 1.95 Fe[Fe(CN)6] 0.98 ·zH2O.

[0043] Example 2 This embodiment provides a Prussian blue-based cathode material, which is prepared according to the following steps: 484 g of Na₄Fe(CN)₆·10H₂O was dissolved in 5000 mL of water to obtain the first solution. 278 g of FeSO₄·7H₂O was dissolved in 2000 mL of water to obtain the second solution. 1 mol of complexing agent sodium citrate and 0.5 mol of sodium chloride supplement were mixed and dissolved in 2000 mL of water to obtain the reaction base solution. The reaction base solution was placed in a reaction vessel, and the temperature was controlled at 25℃. The first and second solutions were added to the base solution with stirring, and the reaction time was controlled at 6 h. After the reaction was completed, the reaction slurry was separated and washed to obtain the solid material. The solid material was vacuum dried at 200℃ for 16 h to obtain the target product, whose molecular formula is Na₂Fe(CN)₆·10H₂O. 1.90 Fe[Fe(CN)6] 0.98 ·zH2O.

[0044] Example 3 This embodiment provides a Prussian blue-based cathode material, which is prepared according to the following steps: 484 g of Na₄Fe(CN)₆·10H₂O was dissolved in 5000 mL of water to obtain the first solution. 278 g of FeSO₄·7H₂O was dissolved in 2000 mL of water to obtain the second solution. 1 mol of complexing agent sodium citrate and 1 mol of sodium chloride supplement were mixed and dissolved in 2000 mL of water to obtain the reaction base solution. The reaction base solution was placed in a reaction vessel, and the temperature was controlled at 25℃. The first and second solutions were added to the base solution with stirring, and the reaction time was controlled at 6 h. After the reaction was completed, the reaction slurry was separated and washed to obtain a solid material. The solid material was vacuum dried at 200℃ for 24 h to obtain the target product, whose molecular formula is Na₂Fe(CN)₆·10H₂O. 1.95 Fe[Fe(CN)6] 0.98 ·zH2O.

[0045] Example 4 This embodiment provides a Prussian blue-based cathode material, which is prepared according to the following steps: 484 g of Na₄Fe(CN)₆·10H₂O was dissolved in 5000 mL of water to obtain the first solution. 278 g of FeSO₄·7H₂O was dissolved in 2000 mL of water to obtain the second solution. 1 mol of complexing agent sodium citrate and 0.5 mol of sodium chloride supplement were mixed and dissolved in 2000 mL of water to obtain the reaction base solution. The reaction base solution was placed in a reaction vessel, and the temperature was controlled at 25℃. The first and second solutions were added to the base solution with stirring, and the reaction time was controlled at 6 h. After the reaction was completed, the reaction slurry was separated and washed to obtain a solid material. The solid material was vacuum dried at 210℃ for 24 h to obtain the target product, whose molecular formula is Na₂Fe(CN)₆·10H₂O. 1.95Fe[Fe(CN)6] 0.98 ·zH2O.

[0046] Comparative Example 1 This embodiment provides a Prussian blue-based cathode material, the preparation method of which differs from that of Example 1 in that: the complexing agent is reduced to 0.5 mol, and the sodium supplement is increased to 2 mol, thus increasing the X content of the Prussian blue-based cathode material obtained in this comparative example. b :X a =0.1:1.

[0047] Comparative Example 2 This embodiment provides a Prussian blue-based cathode material, the preparation method of which differs from that of Example 1 in that: no sodium supplement is added, and the drying temperature is reduced to 120°C, thus increasing the X content of the Prussian blue-based cathode material obtained in this comparative example. b :X a =6:1.

[0048] Comparative Example 3 This embodiment provides a Prussian blue-based cathode material, the preparation method of which differs from that of Example 1 in that: the complexing agent is increased to 2 mol, the sodium supplement agent is increased to 3 mol, and the drying temperature is increased to 230°C, thus increasing the X content of the Prussian blue-based cathode material obtained in this comparative example. c :X a =0.05:1.

[0049] Comparative Example 4 This embodiment provides a Prussian blue-based cathode material, the preparation method of which differs from that of Example 1 in that: the sodium supplement is reduced to 0.5 mol, and the drying temperature is reduced to 110°C, thus improving the X content of the Prussian blue-based cathode material obtained in this comparative example. c :X a =6:1.

[0050] Comparative Example 5 This embodiment provides a Prussian blue-based cathode material. The preparation method differs from that of Example 1 in that the complexing agent is increased to 3 mol, the sodium supplement agent is increased to 2 mol, the reaction time is extended to 24 h, and the drying temperature is increased to 240 °C, so that the total water content in the Prussian blue-based cathode material obtained in this comparative example is 0.08 wt%.

[0051] Comparative Example 6 This embodiment provides a Prussian blue cathode material, the preparation method of which differs from that of Example 1 in that the reaction time is shortened to 3 hours and the drying temperature is reduced to 80°C, so that the total water content in the Prussian blue cathode material obtained in this comparative example is 18 wt%.

[0052] Comparative Example 7 This embodiment provides a Prussian blue cathode material, the preparation method of which differs from that of Example 1 in that: the complexing agent is increased to 3 mol, the sodium supplement agent is increased to 3 mol, the reaction time is extended to 36 h, and the drying temperature is increased to 240 °C, so that the coordinated water in the Prussian blue cathode material obtained in this comparative example is 0.04 wt%.

[0053] Comparative Example 8 This embodiment provides a Prussian blue cathode material, the preparation method of which differs from that of Example 1 in that: the complexing agent is reduced to 0.5 mol, the sodium supplement is reduced to 0.5 mol, the reaction time is shortened to 3 h, and the drying temperature is reduced to 120 °C, so that the coordinated water in the Prussian blue cathode material obtained in this comparative example is 7 wt%.

[0054] Performance testing Prussian blue cathode materials obtained in Examples 1-5 and Comparative Examples 1-8 were used as cathode materials to prepare batteries. The capacity, cycle performance and average voltage of the Prussian blue cathode materials were tested to characterize the cycle stability of the Prussian blue cathode materials. The results are shown in Table 1. The capacity retention rate (%) is the capacity retention rate after 100n cycles at 2C. The test method is as follows: (1) Prussian blue positive electrode material, conductive carbon black and binder PVDF are weighed and mixed in a mass ratio of 7:2:1, and NMP solvent is added and mixed evenly to obtain positive electrode slurry. The positive electrode slurry is coated on aluminum foil and dried to obtain positive electrode sheet; (2) Battery is assembled using a 2032 battery case, the negative electrode is a sodium metal sheet, the fiber separator is used (model Whatman Grade GF / D), and the electrolyte is 1mol / L NaPF6 (EC:PC=1:1, 5%FEC); (3) The battery is left to stand for 12 hours, the rated capacity is set to 150mA / g to determine the current density, the 0.1C charge and discharge program is set to test the capacity, the 2C charge and discharge program is tested for cycles, and the voltage range is 2.0V~4.0V.

[0055] Table 1 Example Total water content (wt%) <![CDATA[X a (wt%)]]> <![CDATA[X b :X a ]]> <![CDATA[X c :X a ]]> Capacity retention rate (%) Example 1 4.2 1.2 0.5 2.0 91% Example 2 4.8 1.2 1.0 2.0 93% Example 3 3.0 1.2 0.5 1.0 93% Example 4 3.0 1.0 1.0 1.0 94% Comparative Example 1 3.2 1.0 0.1 0.5 88% Comparative Example 2 12.0 1.0 6.0 5.0 82% Comparative Example 3 0.58 0.4 0.4 0.05 83% Comparative Example 4 10.0 1.0 3.0 6.0 77% Comparative Example 5 0.08 0.05 0.3 0.3 81% Comparative Example 6 18.0 4.0 1.5 2.0 78% Comparative Example 7 0.12 0.04 1.0 1.0 76% Comparative Example 8 18.0 6.0 1.0 1.0 73% Data Analysis: (1) As can be seen from the characterization data of Examples 1 to 4, the present invention achieves this by making the interstitial water X in the Prussian blue cathode material b and coordination water X a The mass content ratio is 0.2~5:1, adsorbed water X c and coordination water X aThe mass content ratio of water is 0.1~5:1 to avoid the conversion between different types of water in Prussian blue cathode materials, which can improve the structural stability of Prussian blue cathode materials and make the batteries prepared from them have excellent cycle stability. With appropriate content and ratio of different types of water, the stability of water distribution during electrode drying can be ensured, maintaining the stability of the material structure. At the same time, the advantage of interstitial water in improving cycle performance is utilized, avoiding the volume effect of phase changes during cycling that could cause cathode material detachment in materials with low water content.

[0056] Furthermore, a comparative analysis of Examples 2-4 with Example 1 shows that the structure of the Prussian blue cathode material can be optimized by controlling the content and distribution of different types of water in the Prussian blue cathode material, thereby improving the stability of the obtained Prussian blue cathode material structure and obtaining a cathode material with excellent battery cycle stability.

[0057] (2) Comparative analysis of Comparative Examples 1-8 and Example 1 shows that the required coordination water X in the Prussian blue cathode material a Interstitial water X b and adsorbed water X c Without proper content and ratio, the cycle stability of the battery will deteriorate to varying degrees. Therefore, the Prussian blue cathode material provided by this invention preferably contains interstitial water X... b and coordination water X a The mass content ratio is 0.2~5:1, adsorbed water X c and coordination water X a The mass content ratio is 0.1~5:1, and the total water content is preferably 0.1wt%~15wt%, further preferably coordinated water X. a The content is 0.05wt%~5wt%.

[0058] Unless otherwise specified, the raw materials and equipment used in this invention are all commonly used in the field; unless otherwise specified, the methods used in this invention are all conventional methods in the field.

[0059] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Any simple modifications, alterations, and equivalent transformations made to the above embodiments based on the technical essence of the present invention shall still fall within the protection scope of the present invention.

Claims

1. A Prussian blue-based cathode material, characterized in that: The molecular formula is A x M[M'(CN)6] y ·zH2O, where: A is an alkali metal, M is a transition metal, M' is a transition metal, 1 <x≤2,0.8≤y<1,0<z≤3; In Prussian blue-type cathode materials, the interstitial water content is X b and coordination water X a The mass content ratio is 0.2~5:1, and the adsorbed water X c and coordination water X a The mass content ratio is 0.1~5:

1.

2. The Prussian blue-based cathode material as described in claim 1, characterized in that: In Prussian blue-type cathode materials, the interstitial water content is X b and coordination water X a The mass content ratio is 0.5~2:1, and the adsorbed water X c and coordination water X a The mass content ratio is 0.1~2:

1.

3. The Prussian blue-based cathode material as described in claim 1, characterized in that: The total water content is 0.1wt%~15wt%.

4. The Prussian blue-based cathode material as described in claim 3, characterized in that: Coordination waterX a The content is 0.05wt%~5wt%.

5. The Prussian blue-based cathode material as described in claim 1, characterized in that: A is selected from one or more of Na, K, and Li.

6. The Prussian blue-based cathode material as described in claim 1, characterized in that: M is selected from one or more of Mn, Fe, Co, Ni, Cu, Zn, V, and Cr.

7. The Prussian blue-based cathode material as described in claim 1, characterized in that: M' is selected from one or more of Mn, Fe, Co, Ni, Cu, Zn, V, and Cr.

8. A method for preparing a Prussian blue-based cathode material, characterized in that: Includes the following steps: Step S1: Prepare the reaction base solution, a first solution containing a hexacyano alkali metal salt of transition metal M', and a second solution containing a salt of transition metal M; Step S2: Add the first solution and the second solution to the base liquid to react and obtain a reaction slurry; Step S3: Separate and wash the reaction slurry to obtain solid material, and dry the solid material until the interstitial water content in the solid material is reduced by X. b and coordination water X a The mass content ratio is 0.2~5:1, adsorbed water X c and coordination water X a The mass content ratio is 0.1~5:1; The solid material obtained after drying has the molecular formula A. x M[M'(CN)6] y ·zH2O.

9. The preparation method according to claim 8, characterized in that: In step S2, the reaction temperature is 10~100℃ and the reaction time is 0.5~24h.

10. An electrochemical energy storage device, comprising: A positive electrode sheet includes a positive current collector and a positive electrode membrane disposed on the positive current collector and containing a positive electrode material; Negative electrode plate; And the separating membrane; Its features are: The cathode material includes any one of the Prussian blue cathode materials according to claims 1 to 7, or the Prussian blue cathode material prepared by the preparation method according to any one of claims 8 to 9.