阅读说明：本技术 普鲁士蓝及其制备方法和应用 (Prussian blue and preparation method and application thereof ) 是由 伍攀羽 江辉 邹美靓 孔少锋 于 2021-06-10 设计创作，主要内容包括：本发明公开了一种普鲁士蓝及其制备方法和应用。普鲁士蓝是以铁氰化盐与二价铁盐作为铁源在柠檬酸盐、抗氧化剂存在的条件进行络合反应制备获得。普鲁士蓝晶型完整,空位和结构水少或不含空位和结构水,且在离子嵌脱过程中晶体结构稳定,赋予其高的可逆克容量,有利于离子扩散,具有在大电流下可呈现较好的容量保持率特性。普鲁士蓝的制备方法能够保证制备的普鲁士蓝结构和电化学性能稳定,而且效率高,节约生产成本,而且不产生有毒害成分,安全性高。因此,其能够作为正极材料中应用。(The invention discloses prussian blue and a preparation method and application thereof. The Prussian blue is prepared by carrying out complex reaction on ferricyanide and ferrous salt serving as iron sources in the presence of citrate and an antioxidant. The Prussian blue crystal has a complete crystal form, little or no vacancy and structural water, and a stable crystal structure in the ion intercalation and deintercalation process, so that the Prussian blue crystal is endowed with high reversible gram capacity, is beneficial to ion diffusion, and has the characteristic of presenting better capacity retention rate under large current. The preparation method of the Prussian blue can ensure that the prepared Prussian blue has stable structure and electrochemical performance, has high efficiency, saves the production cost, does not generate toxic and harmful components and has high safety. Therefore, it can be applied as a positive electrode material.)

1. Prussian blue, characterized in that: the Prussian blue is prepared by carrying out a complex reaction on ferricyanide and ferrous salt serving as iron sources in the presence of citrate and an antioxidant.

2. The prussian blue according to claim 1, characterized in that: the Prussian blue is in a cubic shape and is a nanoparticle.

3. The prussian blue according to claim 2, characterized in that: the particle size of the nanoparticles is 30-40 nm.

4. A preparation method of Prussian blue comprises the following steps:

preparing a mixed solution from citrate, an antioxidant and a ferrous salt;

adding ferricyanide salt into the mixed solution to carry out a precipitation reaction for generating Prussian blue;

and after the ferricyanide is added, aging the reaction mixture solution, and then carrying out solid-liquid separation to obtain the Prussian blue.

5. The method of claim 4, wherein: in the mixed solution, the concentration of the citrate is 0.154-0.192 mol/L; and/or

In the mixed solution, the molar concentration ratio of the ferrous salt to the antioxidant to the citrate is 0.05: 0.1: (0.154 to 0.192); and/or

The citrate salt contains the same metal ion species as the ferricyanide salt.

6. The production method according to claim 4 or 5, characterized in that: the ferricyanide salt comprises at least one of potassium ferricyanide and sodium ferricyanide; and/or

The ferrous salt comprises at least one of ferrous sulfate and ferrous chloride; and/or

The citrate comprises at least one of potassium citrate and sodium citrate; and/or

The antioxidant comprises at least one of ascorbic acid, tea polyphenol, butyl hydroxy anisol, dibutyl hydroxy toluene and tert-butyl hydroquinone.

7. The production method according to claim 4 or 5, characterized in that: the ferricyanide is added to the mixed solution in a manner of dropwise adding a ferricyanide salt solution; and/or

The aging treatment is to perform heat preservation treatment for 8 to 19 hours at the temperature of 35 to 55 ℃ of the mixture solution; and/or

And after the solid-liquid separation treatment, the method also comprises the step of carrying out vacuum freeze drying treatment on the filter residue.

8. The method of claim 7, wherein: the dropping rate of the ferricyanide salt solution is 1-1.3 ml/min; and/or

The freeze drying temperature of the vacuum freeze drying treatment is-45 to-60 ℃.

9. Use of the prussian blue according to any one of claims 1 to 3 or the prussian blue prepared by the preparation method according to any one of claims 4 to 8 as a battery positive electrode material.

10. A secondary battery comprising a positive electrode including a current collector and a positive electrode active layer bonded to a surface of the current collector, characterized in that: the positive electrode material in the positive electrode active layer includes the prussian blue according to any one of claims 1 to 3 or the prussian blue prepared by the preparation method according to any one of claims 4 to 8.

Technical Field

The invention belongs to the field of batteries, and particularly relates to Prussian blue and a preparation method and application thereof.

Background

With ternary positive electrode materials (LiNi)_xCo_yMn_zO₂X + y + z ═ 1) the nonrenewable lithium, cobalt and nickel ore that involve continuously consumes and the price sharply promotes, leads to the lithium ion battery cost to constantly improve, especially in the new forms of energy electric motor car, the cost of battery package accounts for whole car cost 40 ~ 60%. In addition, the safety of the high-nickel anode material is a difficult point which troubles researchers. At high temperature, oxygen in crystal lattices of the ternary cathode material is released, irreversible structural damage is generated, and phenomena such as thermal runaway, violent battery combustion and the like are also generated. The above problems severely limit the application of lithium ion batteries in the large-scale energy storage field. The search for a novel anode material with rich resources, high energy density, good safety performance and long cycle life is a research hotspot at present.

More recently prussian blue species (Fe)₄[Fe(CN₆)]₃]) The anode material has the advantages of stable frame structure, low cost, high working voltage, high specific energy, ultra-long cycle life and the like, and can be prepared by a normal-temperature liquid phase method, and the anode material receives wide attention of academia. Prussian blue analogue with cyanide ligand alternately connected with FeN₆And FeC₆Octahedra, a three-dimensional (3D) stable crystal framework structure is constructed. The theoretical capacity of the prussian blue analogue is about 140mAh/g when charging and discharging, wherein Fe is the electrochemically active site.

The existing common preparation methods of the Prussian blue comprise a simple precipitation method, a thermal decomposition method, a hydrothermal method, a single iron source method, a blue-sun method and the like, and materials obtained by adopting different methods are different in components, particle sizes, shapes and the like and also different in electrochemical properties. Compared with other methods, the simple precipitation method has the advantages of simple process, low cost, wide applicability, mass production and the like. But the traditional liquid phase precipitation method has rapid reaction speed, and crystal nuclei are easy to agglomerate and are not easy to grow; while Fe²⁺Is easy to oxidize in the air, and introduces a large amount of structural water to occupy active sites. The thermal decomposition method and the hydrothermal method have low production efficiency and yield, and the decomposition of ferrocyanide is easily caused in the synthesis process to generate toxic gas。

Therefore, the existing Prussian blue prepared has an imperfect crystal structure, so that a large number of vacancies exist in the crystal, and the vacancies can cause the collapse of the material structure in the process of the material intercalation and deintercalation of ions. The prepared Prussian blue also has a large amount of crystal water and coordination water, and simultaneously Fe²⁺Is easily oxidized. The existence of these problems reduces the reversible gram capacity of prussian blue, and the existence of structural water causes side reactions during charge and discharge, and causes lattice destruction and deterioration of cycle performance.

Disclosure of Invention

The invention aims to overcome the defects in the prior art and provide Prussian blue and a preparation method thereof so as to solve the technical problems of vacancy and structural water, low reversible gram capacity and the like of the existing Prussian blue crystal.

The invention also aims to provide Prussian blue and a secondary battery, so as to solve the technical problems of high cost and unsatisfactory safety of the existing high-nickel positive electrode material or unsatisfactory reversible gram capacity and cycle performance of the secondary battery taking the existing Prussian blue as the positive electrode material.

In order to achieve the above object, according to one aspect of the present invention, prussian blue is provided. The Prussian blue is prepared by carrying out complex reaction on ferricyanide and ferrous salt serving as iron sources in the presence of citrate and an antioxidant. The Prussian blue crystal of the invention has complete crystal form, little or no vacancy and structural water, stable crystal structure in the ion intercalation and deintercalation process, high reversible gram capacity, ion diffusion benefiting, and good capacity retention rate under high current.

Further, prussian blue is in a cubic morphology and is a nanoparticle.

Furthermore, the particle size of the nano-particles is 30-40 nm.

The Prussian blue crystal is completely formed into standard cubic nanoparticles, and when the Prussian blue crystal is used as a positive electrode material, the Prussian blue crystal is favorable for ion diffusion, and the capacity retention rate of the Prussian blue crystal can be improved under high current.

In another aspect of the invention, a preparation method of prussian blue is provided. The preparation method of the Prussian blue comprises the following steps:

preparing a mixed solution from citrate, an antioxidant and a ferrous salt;

adding ferricyanide salt into the mixed solution to carry out a precipitation reaction for generating Prussian blue;

and after the ferricyanide is added, aging the reaction mixture solution, and then carrying out solid-liquid separation to obtain the Prussian blue.

According to the preparation method of the Prussian blue, ferric ferricyanide and ferrous salt are subjected to complex precipitation reaction in a solution containing citric acid and an antioxidant, so that the formed Prussian blue has a complete crystal form, little or no vacancy and structural water exists, the crystal structure is stable in the ion intercalation and deintercalation process, high reversible gram capacity is endowed to the Prussian blue, ion diffusion is facilitated, and the Prussian blue has the characteristic of presenting a better capacity retention rate under a large current. In addition, the preparation method of the Prussian blue can ensure that the prepared Prussian blue has stable structure and electrochemical performance, has high efficiency, saves the production cost, does not generate toxic and harmful components, and has high safety.

Further, the concentration of the citrate is 0.154-0.192 mol/L.

Further, in the mixed solution, the molar concentration ratio of the ferrous salt, the ascorbic acid and the citrate is 0.05: 0.1: (0.154-0.192).

By controlling the high concentration of citrate in the mixed solution, the reaction rate of Prussian blue crystal nucleus is favorably reduced, the crystallinity is improved, the water content of crystal lattice is reduced, and a stable crystal lattice structure is formed. Controlling the concentration of the antioxidant to effectively avoid Fe²⁺Is oxidized. Therefore, a complex precipitation reaction system is constructed by controlling the concentration of components such as citrate, ferrous salt, ascorbic acid and the like in the mixed solution, so that the formation of Prussian blue crystals generated by precipitation reaction is favorably improved, the integrity of the crystals is improved, the content of vacancies and structural water is reduced, and the reversible gram capacity of Prussian blue is improved.

Further, the citrate salt contains the same kind of metal ions as those contained in the ferricyanide salt. By controlling the metal ions contained in the citrate, the metal ions irrelevant to the target product are prevented from being mixed, so that the purity of the Prussian blue is improved, the integrity of the Prussian blue crystal is improved, and the introduction of excessive metal ions is avoided.

Further, the ferricyanide salt includes at least one of potassium ferricyanide and sodium ferricyanide.

Further, the ferrous salt comprises at least one of ferrous sulfate and ferrous chloride.

Further, the citrate comprises at least one of potassium citrate and sodium citrate.

Further, the antioxidant comprises at least one of ascorbic acid, tea polyphenol, butyl hydroxy anisole, dibutyl hydroxy toluene and tert-butyl hydroquinone.

By controlling the types of citrate, ferric ferricyanide and divalent salt, the stability of the mixed solution is improved, the crystal integrity and purity of the Prussian blue are improved, and the content of vacancy and structural water is reduced.

Further, the ferricyanide salt is added to the mixed solution in such a manner that the ferricyanide salt solution is added dropwise thereto.

Furthermore, the dripping speed of the ferricyanide salt solution is 1-1.3 ml/min.

The adding speed is controlled by controlling the adding mode of the ferricyanide, so that the speed of the complex precipitation reaction of the ferricyanide in the mixed solution is controlled, the crystallinity of the Prussian blue crystal is improved, and the agglomeration phenomenon of crystal particles is reduced to improve the crystal integrity of the Prussian blue crystal.

Further, the aging treatment is to perform heat preservation treatment for 8 to 19 hours at the temperature of 35 to 55 ℃ of the mixture solution. Aging under the condition to ensure that Prussian blue crystal nucleus generated in the complex precipitation reaction has proper crystal growth time so as to improve the crystal integrity and reduce the content of crystal vacancy and structural water.

Further, after the solid-liquid separation treatment, the method also comprises the step of carrying out vacuum freeze drying treatment on the filter residue.

Furthermore, the freeze-drying temperature of the vacuum freeze-drying treatment is-45 to-60 ℃.

The precipitate is dried by a freeze vacuum drying method, so that Fe in Prussian blue is effectively avoided²⁺Oxidized to ensure that the reversible gram capacity of the Prussian blue is improved.

In another aspect of the present invention, an application of the prussian blue of the present invention or the prussian blue prepared by the prussian blue preparation method of the present invention as a battery positive electrode material is provided. The Prussian blue crystal is complete, the crystal vacancy and the structural water are low or not contained, or the Prussian blue crystal is further in a nano-particle shape, so that the Prussian blue crystal is high in reversible gram capacity and good in ion diffusion performance, and has the characteristic of presenting better capacity retention rate under high current and good cyclicity.

In still another aspect of the present invention, a secondary battery is provided. The secondary battery comprises a positive electrode, wherein the positive electrode comprises a current collector and a positive electrode active layer combined on the surface of the current collector, and a positive electrode material in the positive electrode active layer comprises the Prussian blue. The Prussian blue is contained in the secondary battery and is used as a positive electrode material, so that the secondary battery has high gram capacity, excellent cycle performance and high safety performance, and if the phenomenon of thermal runaway of the secondary battery at a high temperature of 200 ℃ is measured, the reversible gram capacity can be as high as 122 mAh/g.

Drawings

In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly described below, and it is obvious that the drawings in the following description are some embodiments of the present invention, and other drawings can be obtained by those skilled in the art without creative efforts.

FIG. 1 is a schematic flow chart of a method for preparing Prussian blue according to an embodiment of the present invention;

fig. 2 is a TEM image of prussian blue prepared in example 1 of the present invention;

FIG. 3 is a graph showing the thermogravimetric loss of Prussian blue prepared in example 1 of the present invention;

fig. 4 is a CV curve graph of a button cell containing prussian blue prepared according to example 1 of the present invention, wherein a is a scan rate of 0.1 mV/s; graph a is a graph of rate performance.

Detailed Description

In order to make the technical problems, technical solutions and advantageous effects to be solved by the present application more clearly apparent, the present application is further described in detail below with reference to the embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the present application and are not intended to limit the present application.

In this application, the term "and/or" describes an association relationship of associated objects, meaning that there may be three relationships, e.g., a and/or B, which may mean: a is present alone, A and B are present simultaneously, and B is present alone. Wherein A and B can be singular or plural. The character "/" generally indicates that the former and latter associated objects are in an "or" relationship.

In the present application, "at least one" means one or more, "a plurality" means two or more. "at least one of the following" or similar expressions refer to any combination of these items, including any combination of the singular or plural items. For example, "at least one (a), b, or c", or "at least one (a), b, and c", may each represent: a, b, c, a-b (i.e., a and b), a-c, b-c, or a-b-c, wherein a, b, and c may be single or plural, respectively.

It should be understood that, in various embodiments of the present application, the sequence numbers of the above-mentioned processes do not mean the execution sequence, some or all of the steps may be executed in parallel or executed sequentially, and the execution sequence of each process should be determined by its function and inherent logic, and should not constitute any limitation to the implementation process of the embodiments of the present application.

The terminology used in the embodiments of the present application is for the purpose of describing particular embodiments only and is not intended to be limiting of the application. As used in the examples of this application and the appended claims, the singular forms "a", "an", and "the" are intended to include the plural forms as well, unless the context clearly indicates otherwise.

The weight of the related components mentioned in the description of the embodiments of the present application may not only refer to the specific content of each component, but also represent the proportional relationship of the weight among the components, and therefore, the content of the related components is scaled up or down within the scope disclosed in the description of the embodiments of the present application as long as it is scaled up or down according to the description of the embodiments of the present application. Specifically, the mass described in the specification of the embodiments of the present application may be a mass unit known in the chemical industry field such as μ g, mg, g, kg, etc.

In one aspect, embodiments of the present invention provide a prussian blue with crystal perfection, little or no vacancies and structural water. The Prussian blue provided by the embodiment of the invention is prepared by carrying out a complex reaction on ferricyanide and ferrous salt serving as iron sources in the presence of citrate and an antioxidant. Through detection, the Prussian blue crystal form of the embodiment of the invention is complete, and a TEM picture of the Prussian blue crystal form is shown in FIG. 2. In addition, the Prussian blue crystal form of the embodiment of the invention has little or no vacancy and structural water, and has no thermal runaway phenomenon, as shown in figure 2. In addition, the Prussian blue provided by the embodiment of the invention has a stable crystal structure in the ion intercalation and deintercalation process, is endowed with high reversible gram capacity, is beneficial to ion diffusion, and has the characteristic of presenting better capacity retention rate under large current.

Further detection shows that the prussian blue crystal in the embodiment of the invention is cubic, and is shown in a TEM photograph in fig. 2. Further, as can be seen from fig. 2, in the examples, the particles are low in agglomeration phenomenon and are nanoparticles. In a further embodiment, the particle size of the prussian blue nanoparticles is 30-40 nm. In specific embodiments, the particle size of the nanoparticles is a typical but non-limiting particle size of 30nm, 31nm, 32nm, 33nm, 34nm, 35nm, 36nm, 37nm, 38nm, 39nm, 40nm, and the like. The Prussian blue crystal is completely formed into standard cubic nanoparticles, and when the Prussian blue crystal is used as a positive electrode material, the Prussian blue crystal is favorable for ion diffusion, and the capacity retention rate of the Prussian blue crystal can be improved under high current.

Accordingly, the embodiment of the invention provides a preparation method of the prussian blue in the embodiment of the invention. The process flow of the preparation method of prussian blue provided by the embodiment of the invention is shown in fig. 1, and the preparation method comprises the following steps:

s01: preparing a mixed solution from citrate, an antioxidant and a ferrous salt;

s02: adding ferricyanide salt into the mixed solution to carry out a precipitation reaction for generating Prussian blue;

s03: and after the ferricyanide is added, aging the reaction mixture solution, and then carrying out solid-liquid separation to obtain the Prussian blue.

In step S01, citrate is added to the mixed solution, which suppresses the precipitation reaction rate in step S02, reduces the rate of prussian blue nuclei formation, improves the prussian blue crystallinity, reduces the contents of lattice water and vacancies, and forms a stable lattice structure. In the embodiment, the concentration of citrate in the mixed solution is 0.154-0.192 mol/L, in the specific embodiment, the concentration of citrate is typical but not limiting concentrations such as 0.154mol/L, 0.160mol/L, 0.165mol/L, 0.170mol/L, 0.173mol/L, 0.180mol/L, 0.185mol/L, 0.190mol/L, 0.192mol/L, etc., wherein 0.173mol/L is relatively preferable in the embodiment of the present invention. The citrate is controlled to be in high concentration in the mixed solution, so that the precipitation reaction rate of the citrate is improved, the generation rate of Prussian blue crystal nuclei is reduced, the crystallinity of Prussian blue is improved, the contents of crystal lattice water and vacancies are reduced, and a stable crystal lattice structure is formed.

In an embodiment, the citrate salt comprises at least one of potassium citrate, sodium citrate. Of course, other alkali metal citrates are also possible in principle. In a further embodiment, the type of citrate salt is selected from citrate salts having the same type of metal ion as the type of metal ion contained in the salt of ferricyanide. By selecting the type of the citrate and preferably controlling the metal ions contained in the citrate, the metal ions irrelevant to the target product are prevented from being mixed, so that the purity of the Prussian blue is improved, and the integrity of Prussian blue crystals is improved. The introduction of excessive metal ions is avoided.

Adding into the mixed solutionAnd adding an antioxidant to ensure the stability of ferrous (ferrous) ions in the mixed solution and avoid oxidation. In the embodiment, the concentration of the antioxidant in the mixed solution can be controlled to be that the molar concentration ratio of the antioxidant to the citrate is 0.1: (0.154-0.192), in specific embodiments, the molar concentration ratio of the antioxidant to the citrate is 0.1: 0.154, 0.1: 0.160, 0.1: 0.165, 0.1: 0.170, 0.1: 0.173, 0.1: 0.180, 0.1: 0.185, 0.1: 0.190, 0.1: 0.192, etc., in a typical, but not limiting, ratio. That is, when the molar concentration of the citrate is in the range of 0.154-0.192 mol/L, the molar concentration of the antioxidant is controlled to be 0.1mol/L according to the concentration ratio of the citrate to the citrate. Controlling the concentration of antioxidant to increase the control of Fe²⁺The protection function is realized, the oxidation of the prussian blue crystal is avoided, and meanwhile, the precipitation reaction and the formation of prussian blue crystal are not influenced.

In an embodiment, the antioxidant comprises at least one of ascorbic acid, tea polyphenols, butyl hydroxy anisole, dibutyl hydroxy toluene, tert-butyl hydroquinone. The antioxidants can effectively remove oxygen in the mixed solution, prevent ferrous ions from being oxidized, and have no side effect on the generation of Prussian blue and the formation of crystals.

In the mixed solution, the ferrous salt provides an iron source required for preparing prussian blue, and in the embodiment, the concentration of the ferrous salt in the mixed solution can be controlled to be 0.05: (0.154-0.192). In specific examples, the molar concentration ratio of the ferrous salt to the citrate is 0.05: 0.154, 0.05: 0.160, 0.05: 0.165, 0.05: 0.170, 0.05: 0.173, 0.05: 0.180, 0.05: 0.185, 0.05: 0.190, 0.05: 0.192, etc., in a typical, but not limiting, ratio. That is, when the molar concentration of the citrate is in the range of 0.154-0.192 mol/L, the molar concentration of the ferrous salt is controlled to be 0.05mol/L according to the concentration ratio of the citrate and the citrate. In an embodiment, the ferrous salt comprises at least one of ferrous sulfate and ferrous chloride.

Based on the statement of each component in the mixed solution prepared in the above step S01, in the examples, the molar concentration ratio of the ferrous salt, the ascorbic acid and the citrate is 0.05: 0.1: (0.154-0.192). In the specific embodiment, the molar concentration ratio of the ferrous salt, the ascorbic acid and the citrate is 0.05: 0.1: 0.154, 0.05: 0.1: 0.160, 0.05: 0.1: 0.165, 0.05: 0.1: 0.170, 0.05: 0.1: 0.173, 0.05: 0.1: 0.180, 0.05: 0.1: 0.185, 0.05: 0.1: 0.190, 0.05: 0.1: 0.192, etc., in a typical, but not limiting, ratio. By controlling and optimizing the component types and the component concentrations of the mixed solution, on the basis of providing enough iron sources, the stability of diiron ions can be kept under the conditions of the existence of ascorbic acid and citrate and the concentration of the ascorbic acid and the citrate, a reaction system which is beneficial to reducing the generation rate of Prussian blue crystal nuclei, improving the crystallinity of Prussian blue and reducing the contents of crystal lattice water and vacant sites can be formed, and metal ions irrelevant to target products are prevented from being mixed, so that the purity of Prussian blue is improved, the integrity of Prussian blue crystals is improved, and the introduction of excessive metal ions is avoided. The system constructed by the method is beneficial to improving the formation of Prussian blue crystals generated by precipitation reaction, improving the integrity of the crystals, reducing the content of vacancies and structural water and improving the reversible gram capacity of Prussian blue.

In step S02, ferricyanide salt is added to the mixed solution, and a precipitation reaction proceeds to produce prussian blue. In the examples, the ferricyanide salt was added to the mixed solution in such a manner that the ferricyanide salt solution was added dropwise thereto. In a further embodiment, the dropwise addition rate of the ferricyanide salt solution is 1-1.3 ml/min. In specific examples, the salt solution of ferricyanide is added dropwise at a typical, but not limiting, rate of 1ml/min, 1.1ml/min, 1.2ml/min, 1.3ml/min, and the like. Among them, the rate of dropwise addition of the ferricyanide salt solution is 1.2ml/min, which is preferable in the embodiment of the present invention. The adding speed is controlled by controlling the adding mode of the ferricyanide, so that the speed of the complex precipitation reaction of the ferricyanide in the mixed solution is controlled, the precipitation reaction speed is prevented from being too high, the generated Prussian blue crystal has enough growth process, and agglomeration is avoided, so that the crystallinity of the Prussian blue crystal is improved, the content of Prussian blue crystal vacancy and less structural water is reduced, and the agglomeration phenomenon of blue crystal particles is reduced to improve the crystal integrity.

In addition, the ferricyanide salt should be added in a relatively sufficient amount to mix the two added in solution so that the precipitation reaction is complete. In specific examples, the molar ratio of potassium ferricyanide salt to the ferrous salt may be controlled to be, but not limited to, 2: 3. the proportion saves the using amount of potassium ferricyanide salt and reduces the cost on the basis of ensuring that the iron source is fully subjected to precipitation reaction to generate Prussian blue.

In step S03, the aging treatment enables the prussian blue nuclei generated by the precipitation reaction in step S02 to grow and perfect. The inventor finds in experiments that conditions such as aging temperature, aging time and the like have influence on the growth and perfection of the Prussian blue crystal lattice, and when the aging temperature is too high, the crystal growth is faster, which is not beneficial to the performance of the Prussian blue under a large multiplying power; the temperature is too low to be good for lattice perfection. Therefore, in the embodiment, the aging treatment is carried out by controlling the temperature of the mixture solution to be 35-55 ℃ and carrying out heat preservation treatment for 8-19 hours. In specific examples, the aging temperature is typically, but not limited to, 35 ℃, 36 ℃, 37 ℃, 38 ℃, 39 ℃, 40 ℃, 41 ℃, 42 ℃, 43 ℃, 44 ℃, 45 ℃, 46 ℃, 47 ℃, 48 ℃, 49 ℃, 50 ℃, 51 ℃, 52 ℃, 53 ℃, 54 ℃, 55 ℃ and the like. The heat preservation time in the aging treatment is further 5 h-9 h, in other specific examples, the heat preservation time is typical but not limiting aging time such as 8h, 9h, 10h, 11h, 12h, 13h, 14h, 15h, 16h, 17h, 18h, 19h and the like. Aging under the condition to ensure that Prussian blue crystal nucleus generated in the complex precipitation reaction has proper crystal growth time so as to improve the crystal integrity and reduce the content of crystal vacancy and structural water. Wherein, the control of the aging temperature can be controlled by adopting water bath heating but not only.

The solid-liquid separation in step S03 is for separating precipitates, and all separation methods that can achieve solid-liquid separation are within the scope disclosed in the examples of the present invention. In the specific embodiment, the solid-liquid separation treatment adopts a centrifugal method, wherein the rotating speed of the centrifugal machine is 8000r/min but not only 8000 r/min. During which time prussian blue was purified by washing three times with deionized water.

In the examples, the solids and liquids are treatedAfter the separation treatment, the method also comprises the step of carrying out vacuum freeze drying treatment on the filter residue. Wherein the freeze-drying temperature of the vacuum freeze-drying treatment is-45 to-60 ℃, and in specific examples, the freeze-drying temperature is-45 ℃, -46 ℃, -47 ℃, -48 ℃, -49 ℃, -50 ℃, -51 ℃, -52 ℃, -53 ℃, -54 ℃, -55 ℃, -56 ℃, -57 ℃, -58 ℃, -59 ℃, or-60 ℃ and the like. The freeze-drying treatment should be sufficient, for example, when the degree of vacuum is controlled to be 80KPa, the freeze-drying time is 18 h-36 h, in specific examples, the freeze-drying temperature is 18h, 20h, 22h, 24h, 26h, 28h, 30h, 32h, 34h, 36h, and other typical but not limiting freeze-drying time, wherein the freeze-drying time is 24h is preferred. The precipitate is dried by a freeze vacuum drying method, so that Fe in Prussian blue is effectively avoided²⁺Oxidized to ensure that the reversible gram capacity of the Prussian blue is improved.

Therefore, in the preparation method of prussian blue according to the embodiment of the present invention, the ferric cyanide and the ferrous salt are subjected to a complex precipitation reaction in the solution of citric acid and the antioxidant, so that the generated prussian blue has a complete crystal form, contains little or no vacancy and structural water, has a stable crystal structure in the ion intercalation and deintercalation process, gives high reversible gram capacity to the prussian blue, facilitates ion diffusion, and has a good capacity retention rate characteristic under a large current. In addition, the preparation method of the Prussian blue can ensure that the prepared Prussian blue has stable structure and electrochemical performance, has high efficiency, saves the production cost, does not generate toxic and harmful components, and has high safety.

On the other hand, based on the prussian blue and the preparation method thereof, and the prussian blue which has complete crystal form, little or no vacancy and structural water and stable crystal structure in the ion intercalation and deintercalation process, the prussian blue can be used as a positive electrode material of a battery, and endows the prussian blue positive electrode material with the characteristics of high reversible gram capacity, good ion diffusion performance, good capacity retention rate under high current and the like.

On the other hand, based on the prussian blue and the preparation method and the application thereof, the embodiment of the invention also provides a positive electrode and a secondary battery containing the positive electrode.

The positive electrode may be a conventional positive electrode of a secondary battery, such as a lithium ion battery, and includes a current collector and a positive active layer bonded to a surface of the current collector. The positive electrode active layer contains a positive electrode material, and generally contains a conductive agent, a binder, and the like. Wherein, the anode material comprises Prussian blue of the invention example. In an embodiment, the binder is a PVDF material. In other embodiments, the conductive agent material comprises one of super P, acetylene black, and Ketjen black. In addition, the mass ratio of the conductive agent and the binder to the positive electrode material such as prussian blue in the positive electrode active layer may be a conventional ratio, and in the embodiment of the present invention, the molar ratio of prussian blue to the conductive agent material to the binder is 8:1: 1. The Prussian blue cathode material can be fully exerted by controlling the mixing proportion of the Prussian blue, the conductive agent material and the binder.

The secondary battery of the embodiment of the invention contains the positive electrode. Of course, the secondary battery according to the embodiment of the present invention further includes necessary components such as a positive electrode, a separator, and an electrolyte, which are necessary for the secondary battery.

The secondary battery may be a lithium ion battery or a lithium metal battery.

Because the positive electrode and the secondary battery contain the Prussian blue as the positive electrode material, the cycle performance of the positive electrode is good, the gram capacity is high, so that the secondary battery is high in gram capacity, excellent in cycle performance and high in safety performance, for example, the phenomenon of thermal runaway of the secondary battery at a high temperature of 200 ℃ is measured, and the reversible gram capacity can be as high as 122 mAh/g.

The composite graphite anode material, the preparation method and the application thereof according to the embodiments of the present invention are illustrated by a plurality of specific examples.

1. Prussian blue and a preparation method thereof:

example 1

This example provides prussian blue and a method for preparing the same. The Prussian blue of the embodiment is prepared according to the following steps of the preparation method:

s1: weighing 3mmol of potassium ferricyanide, dissolving the potassium ferricyanide in 60ml of deionized solution, and fully stirring to form a clear and transparent solution A;

s2: weighing 4.5mmol of ferrous chloride, 4.5g of potassium citrate and 0.22g of ascorbic acid, and dissolving in 80ml of deionized water to form a clear and transparent solution B;

s3: the solution A was dropped into the solution B at a rate of 1.2ml/min, and the solution B was continuously stirred. White precipitate is rapidly generated after the A and the B are contacted;

s4: after the reaction is finished, the reaction bottle containing the solution B is placed in a water area at 45 ℃ for aging for 16 h.

S5: adjusting the centrifugal machine to 8000r/min, collecting the powder, and washing with water for three times.

S6: freezing the wet powder into block solid with liquid nitrogen, and drying in a freeze dryer for 24 hr. The temperature of the freeze dryer is controlled to be-45 to-60 ℃, and the vacuum degree is 80 KPa.

Example 2

This example provides prussian blue and a method for preparing the same. The Prussian blue of the embodiment is prepared according to the following steps of the preparation method:

s1: weighing 3mmol of potassium ferricyanide, dissolving the potassium ferricyanide in 60ml of deionized solution, and fully stirring to form a clear and transparent solution A;

s2: weighing 4.5mmol of ferrous sulfate, 4.5g of potassium citrate and 0.22g of ascorbic acid, and dissolving in 80ml of deionized water to form a clear and transparent solution B;

s3: the solution A was dropped into the solution B at a rate of 1.2ml/min, and the solution B was continuously stirred. White precipitate is rapidly generated after the A and the B are contacted;

s4: after the reaction is finished, the reaction bottle containing the solution B is placed in a water area at 45 ℃ for aging for 16 h.

S5: adjusting the centrifugal machine to 8000r/min, collecting the powder, and washing with water for three times.

S6: freezing the wet powder into block solid with liquid nitrogen, and drying in a freeze dryer for 24 hr. The temperature of the freeze dryer is controlled to be-45 to-60 ℃, and the vacuum degree is 80 KPa.

Example 3

This example provides prussian blue and a method for preparing the same. The Prussian blue of the embodiment is prepared according to the following steps of the preparation method:

s1: weighing 3mmol of sodium ferricyanide, dissolving the sodium ferricyanide in 60ml of deionized solution, and fully stirring to form a clear and transparent solution A;

s2: weighing 4.5mmol of ferrous chloride, 3.8g of sodium citrate and 0.22g of ascorbic acid, and dissolving in 80ml of deionized water to form a clear and transparent solution B;

s3: the solution A was dropped into the solution B at a rate of 1.3ml/min, and the solution B was continuously stirred. White precipitate is rapidly generated after the A and the B are contacted;

s4: after the reaction is finished, the reaction bottle containing the solution B is placed in a water area at 55 ℃ for aging for 12 hours.

S5: adjusting the centrifugal machine to 8000r/min, collecting the powder, and washing with water for three times.

S6: freezing the wet powder into block solid with liquid nitrogen, and drying in a freeze dryer for 24 hr. The temperature of the freeze dryer is controlled to be-45 to-60 ℃, and the vacuum degree is 80 KPa.

Example 4

This example provides prussian blue and a method for preparing the same. The Prussian blue of the embodiment is prepared according to the following steps of the preparation method:

s1: weighing 3mmol of potassium ferricyanide, dissolving the potassium ferricyanide in 60ml of deionized solution, and fully stirring to form a clear and transparent solution A;

s2: weighing 4.5mmol of ferrous chloride, 3.8g of potassium citrate and 0.22g of ascorbic acid, and dissolving in 80ml of deionized water to form a clear and transparent solution B;

s3: the solution A was dropped into the solution B at a rate of 1.1ml/min, and the solution B was continuously stirred. White precipitate is rapidly generated after the A and the B are contacted;

s4: after the reaction is finished, the reaction bottle containing the solution B is placed in a water area at 55 ℃ for aging for 8 hours.

S5: adjusting the centrifugal machine to 8000r/min, collecting the powder, and washing with water for three times.

S6: freezing the wet powder into block solid with liquid nitrogen, and drying in a freeze dryer for 24 hr. The temperature of the freeze dryer is controlled to be-45 to-60 ℃, and the vacuum degree is 80 KPa.

Example 5

This example provides prussian blue and a method for preparing the same. The Prussian blue of the embodiment is prepared according to the following steps of the preparation method:

s1: weighing 3mmol of potassium ferricyanide, dissolving the potassium ferricyanide in 60ml of deionized solution, and fully stirring to form a clear and transparent solution A;

s2: weighing 4.5mmol of ferrous chloride, 4.5g of potassium citrate and 0.22g of tea polyphenol, and dissolving in 80ml of deionized water to form a clear and transparent solution B;

s3: the solution A was dropped into the solution B at a rate of 1.2ml/min, and the solution B was continuously stirred. White precipitate is rapidly generated after the A and the B are contacted;

s4: after the reaction is finished, the reaction bottle containing the solution B is placed in a water area at 45 ℃ for aging for 16 h.

S5: adjusting the centrifugal machine to 8000r/min, collecting the powder, and washing with water for three times.

S6: freezing the wet powder into block solid with liquid nitrogen, and drying in a freeze dryer for 24 hr. The temperature of the freeze dryer is controlled to be-45 to-60 ℃, and the vacuum degree is 80 KPa.

Comparative example 1

The present comparative example 1 provides prussian blue and a preparation method thereof. The Prussian blue of the embodiment is prepared according to the following steps of the preparation method:

s1: weighing 3mmol of sodium ferrocyanide, dissolving in 50ml of deionized solution, and fully stirring to form a clear and transparent solution A;

s2: weighing 3.3mmol of ferrous chloride, 2g of ascorbic acid and 0.7g of potassium citrate, and dissolving in 50ml of deionized water to form a clear and transparent solution B;

s3: dripping the solution A and the solution B into deionized water simultaneously, and obtaining the suspension of the Prussian blue material through coprecipitation reaction

S4: and aging the suspension at 30 ℃ for 2 hours, and then cooling, washing, separating and vacuum-drying the suspension to obtain the micron-sized Prussian blue material.

2. The lithium ion battery comprises the following embodiments:

the prussian blue cathode materials provided in the above examples 1 to 5 were prepared into a cathode electrode and an assembled lithium ion battery, respectively, according to the following methods:

and (3) positive electrode: taking the prussian blue material provided in the above examples 1 to 5 as a positive electrode, the composite graphite negative electrode material and the composite graphite negative electrode material provided in the comparative example as negative electrodes, respectively preparing the negative electrodes according to the following methods;

and (3) positive electrode: mixing prussian blue, a conductive agent and a binder according to the weight ratio of 8:1:1, fully grinding and mixing, then adding a proper amount of NMP to prepare slurry with certain fluidity and viscosity, then coating the slurry on a carbon-sprayed aluminum foil current collector, and preparing a positive electrode according to a positive electrode preparation method;

negative electrode: li metal sheet

Electrolyte solution: 0.5mol/L LiPF₆EC + DMC (volume ratio 1: 1);

a diaphragm: two layers of Cellgard-2400 type polypropylene film;

assembling the lithium ion battery: and assembling the mixture into a button cell in a glove box filled with argon.

3. Correlation characteristic test

3.1 Prussian blue Material Property test

The prussian blue materials provided in examples 1 to 5 and comparative example 1 above were respectively subjected to transmission electron microscopy analysis, wherein a TEM image of the prussian blue material provided in example 1 is shown in fig. 2. Other embodiments provide TEM images of prussian blue material similar to fig. 2. Therefore, as can be seen from fig. 2, the prussian blue prepared by the embodiment of the invention has a nano size, a particle size of about 30-40 nm, a relatively complete crystal form, and an agglomeration phenomenon is significantly reduced. And the preparation method can ensure the stability of the appearance and the performance of the prepared Prussian blue. As can be seen from the TEM image of the prussian blue material in comparative example 1, the particle size of the prussian blue material is in the micrometer range, which is significantly larger than the particle size of the prussian blue material in examples 1 to 5, and the crystal form of the prussian blue material is significantly differentiated unevenly.

3.2 thermal weight loss Performance testing of Prussian blue Material

The prussian blue materials provided in the above examples 1 to 5 and comparative example 1 were subjected to a thermal weight loss property test at 200 ℃. Fig. 3 shows the thermal weight loss curve of the prussian blue material provided in example 1. The thermal weight loss curves of the prussian blue materials provided by other examples are similar to those of fig. 3. Therefore, as can be seen from fig. 3, the prussian blue prepared in the example of the present invention contains almost no structural water, and has a thermal weight loss of 2.23% at 200 ℃, without thermal runaway phenomenon. The slight mass loss is due to the evaporation of adsorbed water from the sample surface. The thermal weight loss performance test of the prussian blue material in the comparative example 1 shows that the thermal weight loss at 200 ℃ is obviously higher than 2.23%, so that the prussian blue material has a possible volatilization phenomenon of surface adsorbed water and simultaneously shows that the prussian blue material has a weight loss phenomenon, thereby showing that structural water exists in the prussian blue material particles in the comparative example 1 or the content of the structural water is obviously higher than that in the examples 1 to 5.

3.3 lithium ion Battery electrochemical Performance testing

The assembled button cell of section 2 above was tested for charge and discharge capacity and cycle life using the LandCT2001A battery test system manufactured by wuhanjinuo electronics ltd.

Wherein CV performance and cycling performance of the button cell battery containing the prussian blue material provided in example 1 are shown in fig. 4. As can be seen from FIG. 4, at a scanning speed of 0.1mV/s, the Prussian blue positive electrode exhibits two pairs of higher-potential charging and discharging plateaus, and the discharging voltages thereof are 3.83V and 3.2V. Meanwhile, the gram capacity exertion is tested at currents of 25, 50, 100, 200 and 500mA/g, and the gram capacity is respectively 122.2, 123.2, 120.3, 114.6 and 105.5 mAh/g. And the capacity recovery rate is 100 percent from 500mA/g current to 200mA/g current. The CV performance and cycling performance of the button cells containing other example prussian blue materials was similar to that of fig. 4. The charge-discharge capacity and cycle life test data show that the Prussian blue used as the lithium ion battery anode material has higher working potential, stable crystal structure and excellent cycle performance. Therefore, the crystal structure of the embodiment of the invention has complete crystal form, less or no vacancy and structural water, and the crystal structure is stable in the ion intercalation and deintercalation process, so that the crystal structure is endowed with high reversible gram capacity, the ion diffusion is facilitated, and the capacity retention rate characteristic can be better presented under large current. While the CV performance and cycling performance of the button cell containing the prussian blue material in comparative example 1 were significantly weaker than those of the button cell containing the prussian blue material in example 1.

The above description is only for the purpose of illustrating the preferred embodiments of the present invention and is not to be construed as limiting the invention, and any modifications, equivalents and improvements made within the spirit and principle of the present invention are intended to be included within the scope of the present invention.