Preparation method and application of high manganese Prussian white material

Abstract

The present invention discloses a high manganese Prussian white material and a preparation method and application thereof. The Mn in the high manganese Prussian white material has both +2 valence and +1 valence; the chemical formula satisfies: Na 6‑2x‑y A x [B y (CN) 6]·zH2O; A is Mn 2+ , x is the number of atoms of A in the chemical formula; B is Mn + , y is the number of atoms of B in the chemical formula; z is the number of atoms of H2O in the chemical formula; 0.5≤x+y≤3, 0<x≤1. The Prussian white material of the present invention partially replaces +2-valent Mn with +1-valent Mn, increasing the manganese content compared to conventional Prussian white. This increases the number of active sodium sites in the Prussian white material, thereby improving the specific capacity and energy density of the electrode material. A moderate increase in manganese content helps improve crystal integrity, maintaining the stability of the material structure and electrochemical performance. This solves the problems of low specific capacity, energy density, and poor stability associated with high-manganese Prussian white materials in the prior art.

Description

Technical Field

[0001] The present invention relates to the technical field of sodium ion batteries, and in particular to a high-manganese Prussian white material and a preparation method and application thereof. Background Art

[0002] The crystal structure of Prussian compounds is composed of transition metals and Fe elements respectively with CN - The unique three-dimensional open framework structure is formed by connecting N and C in the lattice. The crystal structure is face-centered cubic, and the transition metal ions and CN - A hexacoordinate system is formed, with the alkali metal ions located in a three-dimensional channel structure and coordination pores. Due to the unique electronic structure of the cyanide double coordination, as well as its unique open framework and three-dimensional macroporous structure, it is suitable for the migration and storage of sodium ions, and has the advantages of structural stability, fast insertion and extraction rates, and high specific capacity. The actual energy density of a full battery composed of Prussian compounds and hard carbon can reach 130 Wh / kg to 160 Wh / kg, and the theoretical energy density is 500 Wh / kg to 600 Wh / kg, but it still lags behind the energy density of lithium-ion batteries. Summary of the Invention

[0003] In view of the above analysis and in view of the deficiencies in the prior art, the present invention aims to provide a preparation method and application of a high manganese Prussian white material to solve at least one of the problems existing in the prior art, such as low specific capacity and energy density, and poor stability.

[0004] The purpose of the present invention is mainly achieved through the following technical solutions:

[0005] A high-manganese Prussian white material, wherein Mn in the high-manganese Prussian white material has both a +2 valence and a +1 valence.

[0006] Preferably, the chemical formula of the high manganese Prussian white material satisfies: Na 6-2x-y A x [B y (CN) 6]·zH2O; A is Mn 2 + , x is the number of atoms of A in the chemical formula; B is Mn + , y is the number of atoms of B in the chemical formula; z is the number of atoms of H2O in the chemical formula; 0.5≤x+y≤3, 0<x≤1.

[0007] Preferably, x and y satisfy: 1≤x+y≤2, 0.5≤x≤1.

[0008] Preferably, the manganese content in the high manganese Prussian white material is 31 wt% to 34 wt%; preferably, the manganese content is 33 wt% to 34 wt%.

[0009] Preferably, the chemical formula of the high manganese Prussian white material satisfies: Na3A[B(CN)6]·zH2O; A is Mn 2+ , B is Mn + ; z is the number of H2O atoms in the chemical formula.

[0010] Preferably, z satisfies: 0.2≤z≤0.4.

[0011] A method for preparing a high manganese Prussian white material, which is used to prepare the above-mentioned high manganese Prussian white material, comprising: using NaH as a reducing agent to reduce the Mn in the raw material 2+ Reduced to Mn + , prepare high manganese Prussian white.

[0012] Preferably, it includes:

[0013] Using NaH as a reducing agent, Mn in the first divalent manganese salt 2+ Reduced to Mn + , prepare insoluble manganese sodium complex salt;

[0014] The manganese sodium complex salt and a second divalent manganese salt are co-precipitated to prepare high manganese Prussian white having lower solubility than the manganese sodium complex salt.

[0015] Preferably, the method for preparing the high manganese Prussian white material further comprises:

[0016] The reaction temperature and reaction time during the co-precipitation of the sodium manganese complex salt and the second divalent manganese salt are controlled so that the crystal water in the high manganese Prussian white material meets the target range.

[0017] An application of a high-manganese Prussian white material for preparing battery electrodes and rechargeable batteries, using the high-manganese Prussian white material or the high-manganese Prussian white material prepared by the above-mentioned preparation method.

[0018] Compared with the prior art, the present invention can achieve at least one of the following beneficial effects:

[0019] (1) The Prussian white material of the present invention partially replaces +2-valent Mn with +1-valent Mn, which increases the manganese content compared to conventional Prussian white, thereby increasing the number of active sodium sites in the Prussian white material and thereby improving the specific capacity and energy density of the electrode material. A moderate increase in the manganese content helps improve the crystallization integrity and maintain the stability of the material structure and electrochemical properties. This solves the problems of low specific capacity and energy density and poor stability of high-manganese Prussian white materials in the prior art. The specific capacity of high-manganese Prussian white is 186.2 mAh / g to 196.4 mAh / g, preferably 192.4 mAh / g to 196.4 mAh / g. The capacity retention rate after 100 cycles of the battery is 90.4% to 94.6%, preferably 93.8% to 94.6%.

[0020] (2) The present invention uses NaH as a strong reducing agent to reduce the Mn 2+ Reduced to Mn + And no new impurities are introduced; the +2-valent Mn in the Prussian white material is partially replaced by +1-valent Mn, thereby improving the long-life cycle capability and stability of the sodium-ion battery, the specific capacity and energy density of the electrode material.

[0021] (3) The present invention achieves full contact and reduction of divalent manganese salt by NaH in an anhydrous environment by dropping a divalent manganese salt aqueous solution into a molten NaH / NaOH solution, while avoiding the introduction of impurities. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] The accompanying drawings are only used for the purpose of illustrating specific embodiments and are not to be considered as limiting the present invention. Throughout the drawings, the same reference symbols denote the same components.

[0023] Figure 1 This is the cycle performance diagram of the Prussian white material in Example 1. DETAILED DESCRIPTION

[0024] In order to make the technical problems, technical solutions and beneficial effects solved by the present invention more clearly understood, the present invention is further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0025] Technical terms:

[0026] Specific capacity: refers to the amount of charge that a battery material can provide per unit mass or unit volume, usually expressed in mAh / g (mass specific capacity) or mAh / cm³ (volume specific capacity).

[0027] Energy density: refers to the energy stored in a battery per unit mass or unit volume, usually expressed in Wh / kg (mass energy density) or Wh / L (volume energy density).

[0028] Energy density is the joint result of specific capacity and voltage: energy density depends not only on specific capacity, but also on the discharge platform voltage of the battery; under the same voltage, the greater the specific capacity, the greater the energy density.

[0029] In one aspect, the present invention discloses a high manganese Prussian white material comprising:

[0030] The Mn in the high manganese Prussian white material has both a valence of +2 and a valence of +1.

[0031] The applicant's research found that partially reducing the +2-valent Mn to +1-valent Mn in the Prussian white material and introducing a high proportion of sodium can help improve the first coulombic efficiency, improve the long-life cycle capability, and further improve the stability and first coulombic efficiency of the sodium-ion battery.

[0032] Compared to the prior art, the Prussian white material of this invention partially replaces the +2-valent Mn with +1-valent Mn, increasing the manganese content compared to conventional Prussian white. This increases the number of active sodium sites, thereby improving the specific capacity and energy density of the electrode material. A moderate increase in manganese content helps improve crystallization integrity, maintaining the stability of the material structure and electrochemical performance. The high-manganese Prussian white has a specific capacity of 186.2 mAh / g to 196.4 mAh / g, preferably 192.4 mAh / g to 196.4 mAh / g. The capacity retention rate after 100 cycles is 90.4% to 94.6%, preferably 93.8% to 94.6%.

[0033] Preferably, the chemical formula of the high manganese Prussian white material satisfies: Na 6-2x-y A x [B y (CN) 6]·zH2O; A is Mn 2 + , x is the number of atoms of A in the chemical formula; B is Mn + , y is the number of atoms of B in the chemical formula; z is the number of atoms of H2O in the chemical formula; 0.5≤x+y≤3, 0<x≤1.

[0034] More preferably, 1≤x+y≤2, 0.5≤x≤1.

[0035] It should be noted that Prussian white material has a cubic structure, Mn + Although it can replace Na + Constitute a cubic structure, but Mn +The diameter is larger than Na + , excessive Mn + Although it can improve the specific capacity and energy density of electrode materials, it is not conducive to maintaining the crystal integrity of the cubic structure and maintaining the stability of the material structure and electrochemical properties.

[0036] Preferably, the manganese content in the high manganese Prussian white material is 31 wt% to 34 wt%; it can be 31.0 wt%, 31.2 wt%, 31.3 wt%, 31.4 wt%, 31.6 wt%, 31.8 wt%, 32.0 wt%, 32.2 wt%, 32.04 wt%, 32.5 wt%, 32.6 wt%, 32.7 wt%, 32.8 wt%, 33.0 wt%, 33.2 wt%, 33.4 wt%, 33.5 wt%, 33.6 wt%, 33.8 wt% or 34.0 wt%.

[0037] It should be noted that when the manganese content is greater than 34wt%, Prussian white will be more likely to induce Taylor effect during the charge and discharge process, causing the material particles to corrode and dissolve, intergranular cracks to form, the interface impedance to continue to increase, and the bulk structure to seriously degrade, thereby affecting the cycle stability of the material; at the same time, the electrode material cannot play a good role in replenishing sodium during the cycle, resulting in reduced conductivity, poor rate performance, and decreased cycle performance; when the manganese content is less than 31wt%, the proportion of Mn+2 valence state is reduced, and during the first charge, only a small part of Mn 2+ Will be reduced to Mn + , resulting in a lower first discharge specific capacity; the manganese content accounts for 31 wt% ~34 wt%, which is conducive to obtaining better cycle performance and first discharge specific capacity.

[0038] Preferably, the manganese content is 33 wt% to 34 wt%.

[0039] Preferably, the chemical formula of the high manganese Prussian white material satisfies: Na3A[B(CN)6]·zH2O; A is Mn + , B is Mn 2+ ; z is the number of H2O atoms in the chemical formula, 0.2≤z≤0.4.

[0040] It should be noted that when z is less than 0.2, it is difficult for the Prussian white material to maintain a cubic structure; when z is greater than 0.4, there is too much crystalline water in the Prussian white material, which penetrates into the electrolyte during the charge and discharge process, reacts with the electrolyte, and affects the stable use of the battery; 0.2≤z≤0.4 is conducive to obtaining better cycle performance.

[0041] Preferably, the average particle size of the Prussian white material is 20 μm to 60 μm, for example, it can be 20 μm, 22 μm, 24 μm, 26 μm, 28 μm, 30 μm, 32 μm, 34 μm, 36 μm, 38 μm, 40 μm, 42 μm, 44 μm, 45 μm, 46 μm, 47 μm, 48 μm, 50 μm, 52 μm, 54 μm, 55 μm, 56 μm, 58 μm, or 60 μm.

[0042] It should be noted that the particle size of the electrode material has the following effects on the electrode performance: if the particle size is too large, the ion transmission distance in the material is large, the rate performance is poor; if the particle size is too small, the conductive properties of the material are affected and the electrode performance decreases; if the particle size is too small, the material is difficult to disperse.

[0043] On the other hand, the present invention discloses a method for preparing a high manganese Prussian white material, comprising: using NaH as a reducing agent to reduce the Mn in the raw material to 2+ Reduced to Mn + , prepare high manganese Prussian white.

[0044] It should be noted that Mn 2+ The valence of Mn determines that its number cannot be increased indefinitely when it is complexed with cyanate in Prussian white; + Able to replace Na in cubic Prussian white + , high manganese Prussian white is obtained, which increases the manganese content compared to conventional Prussian white, thereby improving the specific capacity and energy density of the electrode material; a moderate increase in manganese content helps to improve the crystal integrity and maintain the stability of the material structure and electrochemical properties.

[0045] Compared with the prior art, the present invention uses NaH as a strong reducing agent to reduce Mn in the raw material. 2+ Reduced to Mn + And no new impurities are introduced; the +2-valent Mn in the Prussian white material is partially replaced by +1-valent Mn, thereby improving the long-life cycle capability and stability of the sodium ion battery, the specific capacity and energy density of the electrode material, and the high manganese Prussian white has a specific capacity of 186.2 mAh / g ~196.4 mAh / g, preferably, the specific capacity is 192.4 mAh / g ~ 196.4 mAh / g; the capacity retention rate of the battery after 100 cycles is 90.4% ~ 94.6%, preferably, the capacity retention rate of the battery after 100 cycles is 93.8% ~ 94.6%.

[0046] Specifically, the method for preparing the high manganese Prussian white material comprises:

[0047] Using NaH as a reducing agent, Mn in the first divalent manganese salt 2+ Reduced to Mn+ , prepare insoluble manganese sodium complex salt;

[0048] The manganese sodium complex salt and a second divalent manganese salt are co-precipitated to prepare high manganese Prussian white having lower solubility than the manganese sodium complex salt.

[0049] It should be noted that the crystalline water content of Prussian white as an electrode material has a significant impact on the electrical properties and stability: if there is too little crystalline water, for example, when z is less than 0.2, the Prussian white material is difficult to maintain a cubic structure; if there is too much crystalline water, for example, when z is greater than 0.4, it will penetrate into the electrolyte during the charge and discharge process, react with the electrolyte, and affect the stable use of the battery; 0.2≤z≤0.4 is conducive to obtaining better cycle performance.

[0050] In order to control the crystal water in the high manganese Prussian white material to be within the range of 0.2≤z≤0.4, the method for preparing the high manganese Prussian white material further includes:

[0051] The reaction temperature and reaction time during the co-precipitation of the sodium manganese complex salt and the second divalent manganese salt are controlled so that the crystal water in the high manganese Prussian white material meets the target range.

[0052] Specifically, the manganese sodium complex salt can be sodium manganous cyanide.

[0053] Specifically, the coprecipitation reaction temperature is 50°C to 60°C, and can be 50°C, 52°C, 53°C, 54°C, 55°C, 56°C, 58°C or 60°C.

[0054] Preferably, the coprecipitation reaction temperature is 55°C to 60°C.

[0055] It should be noted that at lower temperatures, the solubility of raw materials is poor and the ion transfer rate is poor; at higher temperatures, although it is beneficial to reduce the formation of crystal water, it affects the Mn + The stability of high manganese Prussian white material Mn + Below expectations.

[0056] Specifically, the coprecipitation reaction time is 10 h to 20 h, and can be 10 h, 11 h, 12 h, 13 h, 14 h, 15 h, 16 h, 17 h, 18 h, 19 h or 20 h.

[0057] It should be noted that the coprecipitation reaction is the process of preparing high manganese Prussian white with lower solubility from manganese sodium complex salt. + Mn 2+ Replacement, longer coprecipitation reaction time is beneficial to Na + Mn 2+ Fully replaceable.

[0058] Specifically, the preparation method of high manganese Prussian white material includes:

[0059] Step 1) dissolving a reducing agent NaH in molten NaOH to prepare a precursor solution A;

[0060] Step 2) dispersing the first divalent manganese salt and sodium cyanide in an acidic solution to obtain a precursor solution B;

[0061] Step 3) adding precursor liquid B to precursor liquid A to obtain sodium manganese cyanide precipitate;

[0062] Step 4) dispersing sodium manganese cyanide in deionized water to obtain a precursor solution C;

[0063] Step 5) dissolving the second divalent manganese salt and the complexing agent in deionized water to obtain a precursor solution D;

[0064] Step 6) Precursor liquid C is slowly added to precursor liquid D to co-precipitate high manganese Prussian white.

[0065] Specifically, step 1) is an inert gas environment, and the reaction temperature is 320° C. to 350° C., which can ensure that NaOH is fully melted.

[0066] Specifically, in step 1), the mass ratio of NaH to NaOH is 1:3-12, and can be 1:3, 1:4, 1:5, 1:6, 1:7, 1:8, 1:9, 1:10, 1:11 or 1:12.

[0067] It should be noted that if the NaH ratio is too high, it cannot be completely dissolved in the molten NaOH liquid. If the NaH ratio is too low, the addition of divalent manganese salt later cannot fully reduce Mn. 2+ , causing the product to have a mixed phase.

[0068] Specifically, the pH of the acidic solution in step 2) is 3-6, which can inhibit the hydrolysis of sodium cyanide and is conducive to the cyanate ions in the sodium cyanide remaining free and participating in the coordination reaction.

[0069] Specifically, the acidic solution in step 2) can be one or more of citric acid solution, acetic acid solution, hydrocyanic acid solution and dilute sulfuric acid solution.

[0070] Specifically, in step 2), the molar ratio of the first divalent manganese salt to NaCN is 1:6.1 to 6.5, satisfying a slight excess of NaCN.

[0071] Specifically, in step 3), the volume ratio of precursor liquid A to precursor liquid B is (1-1.5):2, which can be 1:2, 1.1:2, 1.2:2, 1.3:2, 1.4:2 or 1.5:2.

[0072] It should be noted that in step 3), precursor liquid B needs to be dropped into precursor liquid A at a high temperature to ensure that the water in precursor liquid B evaporates at high temperature and cannot react with NaH in precursor liquid A. At the same time, molten NaOH can serve as a good reaction solvent, allowing the first divalent manganese salt in precursor liquid B to fully contact and react with sodium hydride.

[0073] Compared with the prior art, the present invention achieves full contact and reduction of the divalent manganese salt by NaH in an anhydrous environment by dripping the divalent manganese salt aqueous solution into the molten NaH / NaOH solution, while avoiding the introduction of impurities.

[0074] Preferably, the precursor liquid C in step 4) comprises 3 wt% to 10 wt% of ascorbic acid as an antioxidant and 10 wt% to 50 wt% of sodium manganous cyanide.

[0075] Specifically, the first divalent manganese salt in step 2) and the second divalent manganese salt in step 5) are one or more of manganese sulfate, manganese chloride, manganese nitrate, and manganese acetate; the first divalent manganese salt and the second divalent manganese salt may be the same or different.

[0076] Specifically, in step 5), the complexing agent is one or more of sodium nitrilotriacetate, disodium ethylenediaminetetraacetate, tetrasodium ethylenediaminetetraacetate, and diethylenetriamine pentacarboxylate.

[0077] Specifically, the mass proportion of the complexing agent in the precursor liquid D is 0.5% to 2%, which can be 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1.0%, 1.1%, 1.2%, 1.3%, 1.4%, 1.5%, 1.6%, 1.7%, 1.8%, 1.9% or 2.0%.

[0078] Specifically, the mass proportion of the second divalent manganese salt in the precursor liquid D is 10wt% to 50wt%.

[0079] Specifically, the high manganese Prussian white material prepared in step 6) is dried at a temperature not higher than 180°C.

[0080] It should be noted that the water content of high-manganese Prussian white material includes interstitial water and coordinated water. Interstitial water is free water that is physically adsorbed and remains between atoms in the high-manganese Prussian white material, not participating in the formation of the high-manganese Prussian white crystal structure. Coordinated water is water molecules that participate in the formation of the high-manganese Prussian white crystal structure through chemical bonds. The water of crystallization in high-manganese Prussian white material refers to coordinated water. Drying at temperatures below 180°C will cause the high-manganese Prussian white material to lose interstitial water, but will not affect the coordinated water in the high-manganese Prussian white crystal structure.

[0081] Regarding step 6), it should be noted that the present invention can adjust the amount of Mn in the precursor liquid C added to the reaction system.+ and Mn in precursor fluid D 2+ Total amount, adjust the Mn content of the product + 、Mn 2+ Proportion.

[0082] For example, when preparing Na3A[B(CN)6]·0.2H2O, the Mn content in the precursor solution C is controlled. + and Mn in precursor fluid D 2+ The total amount is 1:1.

[0083] In a third aspect, the present invention discloses an application of a high manganese Prussian white material for preparing battery electrodes and rechargeable batteries, using the high manganese Prussian white material or the high manganese Prussian white material prepared by the above preparation method.

[0084] Specifically, Na3A[B(CN)6]·0.2H2O, where A is Mn 2+ , B is Mn + , conductive carbon black, and binder (PVDF) were added to a certain volume of NMP solvent in a ratio of 8:1:1, stirred and mixed evenly, and the slurry was coated on the surface of aluminum foil (thickness 20μm) to prepare the positive electrode sheet with a coating thickness of 50μm;

[0085] Cut the electrode sheet into 5 pieces of 1 cm 2 The circular electrode is used as the positive electrode, the sodium sheet is used as the negative electrode, the separator is made of PP material, and the electrolyte is NaPF6. The button battery is assembled in a glove box;

[0086] The button battery was left to stand for 48 hours and then subjected to electrochemical performance testing: the specific capacity of the high manganese Prussian white was 186.2 mAh / g ~ 196.4 mAh / g, preferably, the specific capacity was 192.4 mAh / g ~ 196.4 mAh / g; the capacity retention rate of the battery after 100 cycles was 90.4% ~ 94.6%, preferably, the capacity retention rate of the battery after 100 cycles was 93.8% ~ 94.6%.

[0087] In order to better illustrate the technical solution of the present invention, the following examples and comparative examples are further provided:

[0088] Example 1

[0089] This embodiment discloses a high-manganese Prussian white material: Na3A[B(CN)6]·0.2H2O; A is Mn 2+ , B is Mn + .

[0090] The preparation method comprises:

[0091] Under argon protection, 15 g of NaOH was weighed and heated to 325°C to melt, and then 3 g of NaH was weighed and dissolved in the molten NaOH liquid to obtain precursor liquid A;

[0092] Weigh 0.2 g of acetic acid and dissolve it in 20 mL of deionized water to prepare a weak acid solution with a pH of 4.2. Then, weigh 1.42 g of MnCl2 and 6.05 g of NaCN and dissolve them in the weak acid solution. Stir in a closed container for 50 minutes to obtain precursor solution B.

[0093] Precursor liquid B was slowly added to precursor liquid A, stirred and mixed, and then allowed to stand for 15 hours. After separation and precipitation, it was washed with deionized water and dried under vacuum at 90°C for 35 hours to prepare sodium manganous cyanide (Na5Mn(CN)6).

[0094] Weigh 4 g of Na5Mn(CN)6 and 0.15 g of ascorbic acid and dissolve them in 15 mL of deionized water. Stir well to obtain precursor solution C.

[0095] Weigh 1.86 g of MnSO4 and 0.02 g of disodium ethylenediaminetetraacetate and dissolve them in 10 mL of deionized water to obtain precursor solution D;

[0096] Precursor liquid C was slowly added to precursor liquid D to carry out a co-precipitation reaction. The reaction temperature was set at 40°C. After standing for 20 hours, it was washed and vacuum-dried at 90°C for 30 hours to obtain cubic high-manganese Prussian white, namely Na3A[B(CN)6]·0.2H2O.

[0097] The crystalline water content in the high manganese Prussian white product is calculated as follows:

[0098] The high manganese Prussian white product was weighed for the first time, dried at 190°C for 8 hours, and then weighed a second time. Drying was continued, and the high manganese Prussian white was weighed again every hour. When the weight change between the two weighings was less than 0.1%, it was determined that all crystal water had been removed from the high manganese Prussian white. The crystal water content of the high manganese Prussian white product was calculated based on the weight of the high manganese Prussian white weighed for the last time and the weight of the first time. The calculated crystal water content in the high manganese Prussian white product of the present invention, z=0.2012, was substantially the same as the theoretical value. The structural formula of the high manganese Prussian white product satisfied Na3A[B(CN)6]·0.2H2O, and the manganese content accounted for 33.28%.

[0099] Na3A[B(CN)6]·0.2H2O, where A is Mn 2+ , B is Mn + , conductive carbon black, and binder (PVDF) were added to a certain volume of NMP solvent in a ratio of 8:1:1, stirred and mixed evenly, and the slurry was coated on the surface of aluminum foil (thickness 20μm) to prepare the positive electrode sheet with a coating thickness of 50μm;

[0100] Cut the electrode sheet into 5 pieces of 1 cm 2 The circular electrode is used as the positive electrode, the sodium sheet is used as the negative electrode, the separator is made of PP material, and the electrolyte is NaPF6. The button battery is assembled in a glove box;

[0101] The button battery was left standing for 48 hours before undergoing electrochemical performance testing. The test current density was 50 mA / g. Based on the mass of the positive electrode active material, the specific capacity was 192.4 mAh / g. This material has a high specific capacity. After 100 cycles, the capacity retention rate was 93.8%.

[0102] Example 2

[0103] This embodiment discloses a high-manganese Prussian white material: Na3A[B(CN)6]·0.35H2O; A is Mn 2+ , B is Mn + .

[0104] The preparation method comprises:

[0105] Under argon protection, 21 g of NaOH was weighed and heated to 325°C to melt, and then 4 g of NaH was weighed and dissolved in the molten NaOH liquid to obtain precursor liquid A;

[0106] Weigh 0.25 g of citric acid and dissolve it in 20 mL of deionized water to prepare a weak acid solution with a pH of 4.2. Then, weigh 2.2 g of MnSO4 and 4.45 g of NaCN and dissolve them in the weak acid solution. Stir in a closed container for 35 minutes to obtain precursor solution B.

[0107] Precursor liquid B was slowly added to precursor liquid A, stirred and mixed, and then allowed to stand for 12 hours. After separation and precipitation, it was washed with deionized water and dried under vacuum at 110°C for 40 hours to prepare sodium manganous cyanide (Na5Mn(CN)6).

[0108] Weigh 4 g of Na5Mn(CN)6 and 0.15 g of ascorbic acid and dissolve them in 15 mL of deionized water. Stir well to obtain precursor solution C.

[0109] Weigh 2.2 g of MnSO4 and 0.03 g of sodium nitrilotriacetate and dissolve them in 14 mL of deionized water to obtain precursor solution D;

[0110] Precursor liquid C was slowly added to precursor liquid D to perform a coprecipitation reaction. The reaction temperature was set at 75°C. After standing for 15 hours, it was washed and vacuum-dried at 90°C for 24 hours to obtain cubic high-manganese Prussian white, namely Na3A[B(CN)6]·0.35H2O.

[0111] The same method as in Example 1 was used to detect z=0.4998 in the high manganese Prussian white product. The high manganese Prussian white product was consistent with Na3A[B(CN)6]·0.35H2O, and the manganese content accounted for 33.03%.

[0112] Na3A[B(CN)6]·0.35H2O, conductive carbon black, and binder (PVDF) were added to a certain volume of NMP solvent in a ratio of 8:1:1, stirred and mixed evenly, and the slurry was coated on the surface of aluminum foil (thickness 20μm) to prepare the positive electrode sheet with a coating thickness of 50μm;

[0113] Cut the electrode sheet into 5 pieces of 1 cm 2 The circular electrode is used as the positive electrode, the sodium sheet is used as the negative electrode, the separator is made of PP material, and the electrolyte is NaPF6. The button battery is assembled in a glove box;

[0114] The button battery was left standing for 48 hours before undergoing electrochemical performance testing. The test current density was 50 mA / g. Based on the mass of the positive electrode active material, the specific capacity was 189.7 mAh / g. This material has a high specific capacity. After 100 cycles, the capacity retention rate was 94.6%.

[0115] Example 3

[0116] This embodiment discloses a high manganese Prussian white material: Na 2.5 A 1.5 [B 0.5 (CN)6]·0.2H2O.

[0117] The difference between the preparation method and Example 1 is:

[0118] The divalent manganese salt is replaced with an equal molar amount of MnCl2; disodium ethylenediaminetetraacetate is selected as the complexing agent;

[0119] Adjust the ratio of precursor liquid C to precursor liquid D so that Mn + The molar ratio of MnCl2 to precursor liquid D is 3:1.

[0120] The prepared high manganese Prussian white was tested in the same manner as in Example 1, and z=0.1988 was obtained. The high manganese Prussian white product met the Na 2.5 A 1.5 [B 0.5 (CN)6]·0.2H2O, with a manganese content of 33.32%.

[0121] Will Na 2.5 A 1.5 [B 0.5 (CN)6]·0.2H2O, A is Mn + , B is Mn 2+, conductive carbon black, and binder (PVDF) were added to a certain volume of NMP solvent in a ratio of 8:1:1, stirred and mixed evenly, and the slurry was coated on the surface of aluminum foil (thickness 20μm) to prepare the positive electrode sheet with a coating thickness of 50μm;

[0122] Cut the electrode sheet into 5 pieces of 1 cm 2 The circular electrode is used as the positive electrode, the sodium sheet is used as the negative electrode, the separator is made of PP material, and the electrolyte is NaPF6. The button battery is assembled in a glove box;

[0123] The button battery was left standing for 48 hours before undergoing electrochemical performance testing. The test current density was 50 mA / g. Based on the mass of the positive electrode active material, the specific capacity was 196.4 mAh / g. This material has a high specific capacity. After 100 cycles, the capacity retention rate was 90.4%.

[0124] Example 4

[0125] This embodiment discloses a high manganese Prussian white material: Na 3.5 A 0.5 [B 1.5 (CN)6]·0.2H2O.

[0126] The difference between the preparation method and Example 1 is:

[0127] Adjust the ratio of precursor liquid C to precursor liquid D so that Mn + The molar ratio of MnCl2 to precursor liquid D is 1:3.

[0128] The prepared high manganese Prussian white was tested in the same manner as in Example 1, and z=0.1988 was obtained. The high manganese Prussian white product met the Na 3.5 A 0.5 [B 1.5 (CN)6]·0.2H2O, with a manganese content of 35.59%.

[0129] Will Na 3.5 A 0.5 [B 1.5 (CN)6]·0.2H2O, A is Mn + , B is Mn 2+ , conductive carbon black, and binder (PVDF) were added to a certain volume of NMP solvent in a ratio of 8:1:1, stirred and mixed evenly, and the slurry was coated on the surface of aluminum foil (thickness 20μm) to prepare the positive electrode sheet with a coating thickness of 50μm;

[0130] Cut the electrode sheet into 5 pieces of 1 cm 2 The circular electrode is used as the positive electrode, the sodium sheet is used as the negative electrode, the separator is made of PP material, and the electrolyte is NaPF6. The button battery is assembled in a glove box;

[0131] The button battery was left standing for 48 hours before undergoing electrochemical performance testing. The test current density was 50 mA / g. Based on the mass of the positive electrode active material, the specific capacity was 186.2 mAh / g. This material has a high specific capacity. After 100 cycles, the capacity retention rate was 93.2%.

[0132] Comparative Example 1

[0133] This comparative example discloses a method for preparing a high-manganese Prussian white material. Compared with Example 1, the mass ratio of NaH to NaOH in this comparative example is 30:75, and the amount of NaOH used is 15 g, the same as in Example 1. The amount of NaH used exceeds the scope of protection of the present invention.

[0134] The method for preparing electrodes and batteries is the same as that in Example 1. The button battery is allowed to stand for 48 hours before undergoing electrochemical performance testing. The test current density is 50 mA / g. Based on the mass of the positive electrode active material, the specific capacity is 158.1 mAh / g. The material has a high specific capacity, and the capacity retention rate is 85.7% after 100 cycles.

[0135] Comparative Example 2

[0136] This comparative example discloses a high-manganese Prussian white material: Na2A2[B(CN)6]·0.2H2O.

[0137] The difference between the preparation method and Example 1 is:

[0138] Adjust the ratio of precursor liquid C to precursor liquid D so that Mn + The molar ratio of MnCl2 to precursor liquid D is 1:3:

[0139] Dissolve 1g Na5Mn(CN)6) and 0.15g ascorbic acid in 15mL deionized water and stir to obtain precursor solution C.

[0140] Weigh 1.395 g of MnSO4 and 0.015 g of disodium ethylenediaminetetraacetate and dissolve them in 10 mL of deionized water to obtain precursor solution D.

[0141] The prepared high manganese Prussian white was detected in the same manner as in Example 1, and z=0.1988 was obtained. The high manganese Prussian white product satisfied the requirements of Na2A2[B(CN)6]·0.2H2O, and the manganese content accounted for 44.68%.

[0142] The method for preparing electrodes and batteries is the same as that in Example 1. The button battery is left to stand for 48 hours before undergoing electrochemical performance testing. The test current density is 50 mA / g. Based on the mass of the positive electrode active material, the specific capacity is 234.6 mAh / g. The material has a high specific capacity, and the capacity retention rate is 78.2% after 100 cycles.

[0143] Comparative Example 3

[0144] This comparative example discloses a method for preparing a high-manganese Prussian white material. Compared with Example 1, the pH of the weak acid solution in this comparative example is 6.52; the pH of the weak acid solution is higher than the protection range of the present invention, which affects the formation of sodium manganous cyanide.

[0145] The electrode and battery preparation methods were the same as in Example 1. The button battery was allowed to stand for 48 hours before electrochemical performance testing. The test current density was 50 mA / g. Based on the mass of the positive electrode active material, the product had insufficient manganese, and the specific capacity was reduced to 152.9 mAh / g. The material had a high specific capacity, and the capacity retention rate was 86.7% after 100 cycles.

[0146] Comparative Example 4

[0147] This comparative example discloses a method for preparing a high-manganese Prussian white material. Compared with Example 1, the co-precipitation reaction temperature in this comparative example is 80° C., which is higher than the protection scope of the present invention.

[0148] The prepared high manganese Prussian white was tested in the same manner as in Example 1, and z=0.88 was obtained. The product did not conform to the requirements of Na3A[B(CN)6]·0.2H2O.

[0149] The method for preparing electrodes and batteries from high manganese Prussian white was the same as in Example 1. The button battery was allowed to stand for 48 hours before undergoing electrochemical performance testing. The test current density was 50 mA / g. Based on the mass of the positive electrode active material, the specific capacity was 184.5 mAh / g. The material had a high specific capacity, and after 100 cycles, the capacity retention rate was 84.9%.

[0150] Comparative Example 5

[0151] This comparative example discloses a method for preparing a high-manganese Prussian white material. Compared with Example 1, the co-precipitation reaction time in this comparative example is 5 hours, which is below the protection scope of the present invention.

[0152] The prepared high manganese Prussian white was tested in the same manner as in Example 1, and z=0.5 was obtained. The product did not conform to the requirements of Na3A[B(CN)6]·0.2H2O.

[0153] The method for preparing electrodes and batteries was the same as in Example 1. The button battery was allowed to stand for 48 hours before undergoing electrochemical performance testing. The test current density was 50 mA / g. Based on the mass of the positive electrode active material, the specific capacity was 182.1 mAh / g. The material had a high specific capacity, and after 100 cycles, the capacity retention rate was 86.3%.

[0154] From the above, it can be seen that the high manganese Prussian white prepared in Examples 1-4 of the present invention has a specific capacity of 186.2 mAh / g to 196.4 mAh / g, preferably, the specific capacity is 192.4 mAh / g to 196.4 mAh / g; the capacity retention rate of the battery after 100 cycles is 90.4% to 94.6%, preferably, the capacity retention rate of the battery after 100 cycles is 93.8% to 94.6%.

[0155] If the amount of NaH used, the proportion of manganese content in the product, the pH of the weak acid solution, the coprecipitation reaction temperature, and the coprecipitation reaction time are not within the protection range, it will have a negative impact on the specific capacity and battery cycle stability.

[0156] The above description is only a preferred specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any changes or substitutions that can be easily thought of by any technician familiar with this technical field within the technical scope disclosed by the present invention should be covered by the scope of protection of the present invention.

Claims

1. A method for preparing high manganese Prussian white material, characterized in that: include: Using NaH as reducing agent, Mn 2+ Reduced to Mn + , preparation of high manganese Prussian white; The Mn in the high manganese Prussian white material has both +2 valence and +1 valence; The preparation of high manganese Prussian white includes: Using NaH as a reducing agent, Mn in the first divalent manganese salt of the raw material 2+ Reduced to Mn + , prepare sodium manganous cyanide precipitate; Sodium manganese cyanide precipitate is co-precipitated with a second divalent manganese salt to prepare high manganese Prussian white which has lower solubility than sodium manganese cyanide precipitate. The preparation of sodium manganous cyanide precipitate comprises: Step 1) dissolving the reducing agent NaH in molten NaOH to prepare precursor liquid A; the mass ratio of NaH to NaOH is 1:3-12; Step 2) dispersing the first divalent manganese salt and sodium cyanide in an acidic solution to obtain a precursor solution B; the pH of the acidic solution is 3-6; Step 3) Precursor liquid B is slowly dripped into precursor liquid A to obtain sodium manganese cyanide precipitate, so that the water in precursor liquid B evaporates at high temperature and cannot react with NaH in precursor liquid A.

2. The method for preparing high manganese Prussian white material according to claim 1, characterized in that: The chemical formula of the high manganese Prussian white material satisfies: Na 6-2x-y A x [B y (CN) 6]·zH2O; A is Mn 2+ , x is the number of atoms of A in the chemical formula; B is Mn + , y is the number of atoms of B in the chemical formula; z is the number of atoms of H2O in the chemical formula; 0.5≤x+y≤3, 0<x≤1.

3. The method for preparing high manganese Prussian white material according to claim 2, wherein: x and y satisfy: 1≤x+y≤2, 0.5≤x≤1.

4. The method for preparing high manganese Prussian white material according to claim 3, characterized in that: The manganese content in the high manganese Prussian white material is 31 wt% to 34 wt%.

5. The method for preparing high manganese Prussian white material according to claim 4, characterized in that: The chemical formula of the high manganese Prussian white material satisfies: Na3A[B(CN)6]·zH2O; A is Mn 2+ , B is Mn + ; z is the number of H2O atoms in the chemical formula.

6. The method for preparing high manganese Prussian white material according to claim 5, characterized in that: z satisfies: 0.2≤z≤0.

4.

7. The method for preparing high manganese Prussian white material according to claim 6, characterized in that: The method for preparing the high manganese Prussian white material further comprises: The reaction temperature and reaction time during the co-precipitation of sodium manganous cyanide precipitation and the second divalent manganese salt are controlled so that the crystal water in the high manganese Prussian white material meets the target range.

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