阅读说明：本技术 一种钠离子电池正极材料及其制备方法和钠离子电池 (Sodium-ion battery positive electrode material, preparation method thereof and sodium-ion battery ) 是由 马紫峰 冯凡 陈苏莉 车海英 廖建平 马思堃 于 2020-04-14 设计创作，主要内容包括：本发明公开了一种钠离子电池正极材料及其制备方法和钠离子电池,制备方法包括以下步骤：步骤一,将包括亚铁氰化钠、有机弱酸和络合剂的反应物混合均匀,得溶液A；步骤二,将溶液A在80-160℃的温度下保温8-16小时,冷却,洗涤产物,干燥即可。本发明制备的钠离子电池正极材料在未使用任何导电材料包覆的情况下,制成的电池在1A g<Sup>-1</Sup>电流密度下,其首次放电容量为117.8mAg<Sup>-1</Sup>,经过200次充放电循环后,其容量维持率高达88.9％,电化学性能十分优异。(The invention discloses a sodium ion battery anode material, a preparation method thereof and a sodium ion battery, wherein the preparation method comprises the following steps: step one, uniformly mixing reactants including sodium ferrocyanide, organic weak acid and a complexing agent to obtain a solution A; and step two, preserving the temperature of the solution A at 80-160 ℃ for 8-16 hours, cooling, washing a product, and drying. Under the condition that the positive electrode material of the sodium-ion battery prepared by the invention is not coated by any conductive material, the prepared battery is 1A g ‑1 The first discharge capacity is 117.8mAg under the current density ‑1 After 200 times of charge-discharge cycles, the capacity maintenance rate is as high as 88.9%, and the electrochemical performance is very excellent.)

1. A preparation method of a positive electrode material of a sodium-ion battery is characterized by comprising the following steps:

step one, uniformly mixing reactants including sodium ferrocyanide, organic weak acid and complexing agent to obtain solution A, wherein the ionization equilibrium constant of the organic weak acid is 3 x 10^-5-3*10^-3The pH value of the solution A is 2-4;

and step two, preserving the temperature of the solution A at 80-160 ℃ for 8-16 hours, cooling, washing a product, and drying.

2. The method for preparing the positive electrode material of the sodium-ion battery according to claim 1, wherein the weak organic acid is an aliphatic polycarboxylic acid;

alternatively, the weak organic acid is citric acid and/or ascorbic acid.

3. The method for preparing the positive electrode material of the sodium-ion battery according to claim 1, wherein the complexing agent is an organic weak acid salt complexing agent, and the complexing agent is mixed with Fe²⁺A stability constant lg β of 5.5-16.5;

or the complexing agent is an aliphatic polycarboxylic acid complexing agent;

or the complexing agent is a sodium citrate complexing agent.

4. The method for preparing the positive electrode material of the sodium-ion battery as claimed in claim 1, wherein the temperature is 100-140 ℃;

alternatively, the temperature is 120 ± 2 ℃;

or the heat preservation time is 10-14 hours;

or the heat preservation time is 12 plus or minus 0.5 hour.

5. The method for preparing a positive electrode material for a sodium-ion battery according to claim 1, wherein in the first step, the reactants are vigorously stirred until uniform;

or, stirring the reactants to be uniform by a violent magnetic force;

and/or in the second step, sealing the solution A and then preserving the heat for 8-16 hours at the temperature of 80-160 ℃;

and/or, the cooling is rapid cooling to room temperature;

and/or, the step of washing the product comprises centrifuging the washed product with deionized water and ethanol to a neutral pH;

and/or, the step of drying comprises vacuum drying at 60-100 ℃.

6. A positive electrode material for a sodium-ion battery, which is prepared by the preparation method of any one of claims 1 to 5.

7. The positive electrode material of the sodium-ion battery is characterized by being in a cubic crystal form, and the chemical formula of the positive electrode material of the sodium-ion battery is Na_xFe[Fe(CN)₆]_y·□_1-yWherein x is more than or equal to 1.72 and less than or equal to 1.95, y is more than or equal to 0.975 and less than or equal to 0.995, □ represents vacancy, and the average particle size D50 of the positive electrode material of the sodium-ion battery is 3.76-9.67 mu m.

8. The positive electrode material for sodium-ion batteries according to claim 7, wherein the average particle diameter D50 is 5.91 to 8.28 μm;

and/or, x is more than or equal to 1.91 and less than or equal to 1.95;

and/or, y is more than or equal to 0.990 and less than or equal to 0.995.

9. A sodium-ion battery, characterized in that it is made of a conductive agent, a binder, a current collector, an electrolyte and the positive electrode material of the sodium-ion battery according to any one of claims 6 to 8.

10. The sodium-ion battery of claim 9, wherein the conductive agent is one or more of SuperP, acetylene black, carbon nanotubes, or graphene;

and/or the binder is one or more of PVDF, PTFE or CMC + SBR;

and/or the current collector is one or more of aluminum foil, copper foil, stainless steel mesh, nickel foil or titanium foil;

and/or the electrolyte is one or more of NaPF6, NaClO4 or NaTFSI;

and/or the solvent of the electrolyte is one or more of PC, EC, DMC, DEC, EMC or FEC;

and/or the mass concentration of the electrolyte is 0.1M-2.0M.

Technical Field

The invention relates to the technical field of batteries, in particular to a sodium-ion battery positive electrode material, a preparation method thereof and a sodium-ion battery.

Background

The lithium ion battery has the advantages of long cycle life, high energy density, no memory effect, high charging and discharging speed, environmental friendliness and the like, and is widely applied to production and life. But the limited lithium resources and the increasing price of lithium will also become important factors limiting the further development of lithium ion batteries. The metal sodium and lithium being elements of the same main group, Na/Na⁺Potential of standard electrode of-2.71V, and Li/Li⁺The standard potential is approximate to-3.04V, and sodium ions are inserted and extracted between the positive electrode and the negative electrode of the battery as lithium ions in the charging and discharging processes to form the sodium ion battery. Compared with lithium element, sodium element has the advantages of wide source, low cost and the like, so that the sodium ion battery becomes a new research focus in recent years and is expected to replace lithium ion batteries or lead-acid batteries in the fields of low-speed electric vehicles, mobile power systems and large-scale energy storage in the future.

The electrode material is an important component of the sodium ion battery, plays a key role in the process of sodium ion intercalation and deintercalation and plays a decisive role in the electrochemical performance of the battery. Since sodium ions have a larger ion radius than lithium ions, and thus require a larger ion channel, conventional lithium storage electrode materials are not necessarily suitable for storage of sodium ions. The currently commonly used positive electrode materials of the sodium-ion battery comprise transition metal oxides with a layered structure, polyanion compounds and prussian blue compounds. Layered structure Na based on readily variable-valence iron_xFeMO₂And open frame structure Na₂MFe(CN)₆(M is transition metal such as Fe, Co, Ni, Mn and the like) is a hot spot of research and development at present. Preparation process (such as coprecipitation, precipitation, crystallization, high-temperature sintering, etc.) and its applicationThe process parameters have great influence on the structure and performance of the anode material.

Na with special open frame structure₂MFe(CN)₆The compound has small acting force with interstitial cations and is suitable for the rapid migration of alkali metal ions. When M is Fe, the compound is called Fe-based Prussian blue (FeHCF for short). The common synthetic methods of FeHCF include a single iron source method and a double iron source method, wherein the single iron source method is widely applied due to simple synthetic method and good product crystallization. At present, sodium ferrocyanide (Na) such as hydrochloric acid is generally used in the single iron source method₄Fe(CN)₆) Decomposing to generate ferrous iron ions and ferrous cyanide ions, and reacting the ferrous iron ions with the ferrous cyanide ions to generate FeHCF precipitates. However, the crystals produced in the prior art have a high number of vacancies (above 4%, for example j. mater. chem. a,2016,4, 6036). Excessive vacancies can cause the collapse of the material structure in the process of rapid sodium ion intercalation and deintercalation, and a large amount of coordinated water also exists in the prepared material, and the coordinated water can seriously affect the electrochemical performance of the material. The maximum amount of Na contained per mole of FeHCF is 1.70 moles (2 moles theoretical) due to defects and the presence of coordinated water, as reported in the literature, e.g., Liu Y, Qiao Y, Zhang W, et al, sodium storage in Na-rich NaxFeFe (CN)6 nanocubes [ J]Nano Energy,2015,12: 386-. In addition, it has been reported in the literature that FeHCF crystals prepared by the prior art (hydrochloric acid as an acid source) are generally small in size, as in Energy environ. sci.,2014,7,1643, and the FeHCF particles are between 300 and 600 nanometers.

Disclosure of Invention

The invention aims to overcome the defect that FeHCF crystals in the prior art have more defects, and provides a sodium ion battery positive electrode material, a preparation method thereof and a sodium ion battery.

The invention solves the technical problems through the following technical scheme:

a preparation method of a positive electrode material of a sodium-ion battery comprises the following steps:

step one, uniformly mixing reactants including sodium ferrocyanide, organic weak acid and complexing agent to obtain solution A, wherein the ionization equilibrium constant of the organic weak acid is 3 x 10^-5-3*10^-3The pH value of the solution A is 2-4.

And step two, preserving the temperature of the solution A at 80-160 ℃ for 8-16 hours, cooling, washing a product, and drying.

In the preparation method of the invention, the following reaction occurs:

Na₄Fe(CN)₆+6H⁺→Fe²⁺+4Na⁺+6HCN

Na₄Fe(CN)₆+Fe²⁺→Na₂FeFe(CN)₆+2Na⁺

to make (Na)₄Fe(CN)₆) The invention finds that the strength of acidity has a great influence on the vacancy in the crystal through research. The hydrochloric acid is more acidic, so that ferrous ions are rapidly generated to cause Prussian blue to precipitate more quickly, and more vacancies are generated. But too weak and insufficient to be acidic (Na)₄Fe(CN)₆) And (5) decomposing. This creates a technical dilemma. The research team of the invention obtains the use of organic weak acid and complexation through a large amount of theoretical calculation and scientific experimentsThe agent has the cooperation effect, which can not only slow down the speed of generating ferrous ions, but also promote (Na)₄Fe(CN)₆) And (5) decomposing. The reaction of the present invention is a single iron source reaction, [ Fe (CN) ]₆]^4-And H⁺Reaction to release Fe²⁺，Fe²⁺Then with [ Fe (CN)₆]^4-And reacting to generate FeHCF crystals. Besides providing an acidic reducing environment, the organic weak acid also has a complexing effect, which is equivalent to forming double complexing effect with a complexing agent. By setting the reaction temperature and time and adopting organic weak acid and complexing agent, Na is created₂FeFe(CN)₆(i.e., FeHCF crystals) are extremely favorable crystallization conditions. Thereby obtaining Na with less vacancy₂FeFe(CN)₆And (4) crystals. The sodium ion battery prepared by the crystal has excellent performance under the condition of high current working condition.

The weak organic acid employed in the present invention may be a weak organic acid conventional in the art. Specifically, the weak organic acid may be, for example, one or more of citric acid, ascorbic acid, and succinic acid. Preferably, the weak organic acid is an aliphatic polycarboxylic acid. The aliphatic polycarboxylic acid is usually a weak acid and has ionization balance, so the reaction speed of the aliphatic polycarboxylic acid and sodium ferrocyanide is not too fast, divalent iron ions can be slowly generated, and the speed of the reaction of the divalent iron ions and ferricyanide radicals to generate precipitates is slower, and the formed crystal defects are less. In addition, the acid radical of the aliphatic polycarboxylic acid generally has complexation effect, and can be complexed with ferrous ions, so that the crystallization speed is further reduced, and perfect crystals are formed.

Further preferably, the weak organic acid is citric acid and/or ascorbic acid. Citric acid/ascorbic acid are two aliphatic polycarboxylic acids which are relatively easy to obtain, and the two acids have certain reducibility and can prevent the generated ferrous ions from being oxidized.

The complexing agent employed in the present invention may be one that is conventional in the art. Preferably, the complexing agent is with Fe²⁺The stable constant lg β is 5.5-16.5, such as EDTA or sodium citrate, preferably, the complexing agent is weak organic acid salt complexing agent, and the weak organic acid salt complexing agent has moderate complexing capacity and can effectively react with ironThe ion complexation does not hinder the combination of iron ions and ferrocyanide because of too strong complexation ability.

Further preferably, the complexing agent is an aliphatic polycarboxylic acid complexing agent. The aliphatic polycarboxylic acid complexing agent is a type of organic weak acid complexing agent with moderate complexing capability, and is suitable to be used as a complexing agent.

Further preferably, the complexing agent is a sodium citrate complexing agent. The sodium citrate is easy to obtain, and in addition, the sodium citrate structurally contains hydroxyl groups, so that the sodium citrate has relatively obvious reducibility and can prevent ferrous ions from being oxidized.

Preferably, the mass ratio of the sodium ferrocyanide to the weak organic acid is from 1:2 to 1:20, such as 1:2, 1:4, 1:5, 1:10 or 1: 20. Further preferably, the mass ratio of the sodium ferrocyanide to the weak organic acid is 1:4 to 1: 10. Further preferably, the mass ratio of the sodium ferrocyanide to the weak organic acid is 1:4 to 1: 10.

Preferably, the mass ratio of the sodium ferrocyanide to the complexing agent is from 1:2 to 1:20, such as 1:2, 1:4, 1:5, 1:10 or 1: 20. Further preferably, the mass ratio of the sodium ferrocyanide to the complexing agent is 1:5 to 1: 10.

The temperature may be 80 ℃, 100 ℃, 120 ℃, 140 ℃ or 160 ℃. Preferably, the temperature is 100-. The proper ionization level of weak acid can be maintained at the temperature of 100-140 ℃, and the proper reaction rate is maintained, so that the product defects are maintained at a lower level.

Further preferably, the temperature is 120 ± 2 ℃. The reaction temperature is 120 +/-2 ℃, so that the reaction can be completed in a short time, and the crystal defects of the product can be kept at a lower level.

The incubation time may be 8 hours, 10 hours, 12 hours, 14 hours, or 16 hours. Preferably, the incubation time is 10-14 hours. The use of energy and the balance of crystal defects can be achieved by selecting 10-14 hours. The reaction can be complete, the crystals are not easy to agglomerate, and the crystal defects are few.

Further preferably, the incubation time is 12 ± 0.5 hours. The reaction time is 12 +/-0.5 hours, so that the reaction is completely carried out, agglomeration among product crystals is avoided, and the crystal defects are fewer.

Preferably, in step one, the reactants are vigorously stirred to homogeneity.

Further preferably, the reactants are stirred to homogeneity by a vigorous magnetic force. The violent magnetic stirring can make the reactant dissolve more quickly and stir evenly to form a solution with better dispersibility.

Preferably, in step two, the solution A is sealed and then is kept at the temperature of 80-160 ℃ for 8-16 hours.

Preferably, the cooling is a rapid cooling to room temperature. The room temperature here is a room temperature generally understood in the chemical field, and is generally 25 ℃. The crystal can not continue to grow in the quick cooling process, the formed crystal is relatively independent, and if the temperature is slowly reduced, the crystal continues to grow, and the formed crystals are different in size due to different growth speeds.

Preferably, the step of washing the product comprises centrifuging the washed product with deionized water and ethanol to a neutral pH. Neutral is herein understood to be neutral as commonly understood in the chemical art, and generally means a pH of 6.5-7.5.

Preferably, the drying step comprises vacuum drying at 60-100 ℃.

The products after vacuum drying can be gathered into blocks, and for the convenience of later characterization, battery installation on a coated electrode plate and the like, the block products can be slowly ground into fine powder to prevent the crystal structure from being damaged.

The positive electrode material of the sodium-ion battery is prepared by the preparation method.

The positive electrode material of the sodium-ion battery is in a cubic crystal form, and the chemical formula of the positive electrode material of the sodium-ion battery is Na_xFe[Fe(CN)₆]_y·□_1-yWherein x is more than or equal to 1.72 and less than or equal to 1.95, y is more than or equal to 0.975 and less than or equal to 0.995, □ represents vacancy, and the average particle size D50 of the positive electrode material of the sodium-ion battery is 3.76-9.67 mu m. Wherein, x can be 1.72, 1.77, 1.78, 1.84, 1.86, 1.91, 1.92 or 1.95; y may be specifically 0975, 0.980, 0.981, 0.986, 0.989, 0.990 or 0.995; d50 may specifically be 3.76, 4.98, 5.62, 5.91, 6.98, 7.86, 8.28 or 9.67.

Preferably, 1.91. ltoreq. x.ltoreq.1.95.

Preferably, 0.990. ltoreq. y.ltoreq.0.995.

Preferably, the average particle diameter D50 is 5.91-8.28. mu.m.

The sodium ion battery is prepared from a conductive agent, a binder, a current collector, an electrolyte and the positive electrode material of the sodium ion battery.

Preferably, the conductive agent can be one or more of Super P, acetylene black, carbon nanotubes or graphene.

Preferably, the binder may be one or more of PVDF, PTFE or CMC + SBR.

Preferably, the current collector used may be one or more of aluminum foil, copper foil, stainless steel mesh, nickel foil or titanium foil.

Preferably, the electrolyte is one or more of NaPF6, NaClO4, or NaTFSI.

Preferably, the solvent of the electrolyte is one or more of PC, EC, DMC, DEC, EMC or FEC.

Preferably, the mass concentration of the electrolyte is 0.1M to 2.0M.

On the basis of the common knowledge in the field, the above preferred conditions can be combined randomly to obtain the preferred embodiments of the invention.

The positive progress effects of the invention are as follows: the invention provides a preparation method of a FeHCF sodium ion battery positive electrode material with low cost, high yield and high performance, which uses sodium ferrocyanide, organic weak acid and sodium citrate as raw materials to obtain a product with very low crystal water content and defect content through hydrothermal reaction, and simultaneously overcomes the defect that Na is caused by sodium ferrocyanide₄Fe(CN)₆The low conductivity of the FeHCF material can cause the application limitation of the sodium ion battery anode material, and the FeHCF with a perfect lattice structure can be prepared through simple hydrothermal reaction, and the FeHCF material has higher capacity and better cycle performance. The sodium ion battery anode material FeHCF prepared by the invention does not use any conductive material packageUnder the condition of coating, the prepared sodium ion battery is coated with 1Ag^-1The first discharge capacity is 117.8mAg under the current density^-1After 200 times of charge-discharge cycles, the capacity maintenance rate is as high as 88.9%, and the electrochemical performance is very excellent.

Drawings

FIG. 1 is a scanning electron microscope image of FeHCF crystal prepared by the prior art magnified 20000 times.

FIG. 2 is a scanning electron micrograph of a FeHCF crystal prepared by the prior art magnified 10000 times.

FIG. 3 is a scanning electron microscope image of FeHCF crystal prepared by the present invention magnified 5000 times.

FIG. 4 is a scanning electron microscope image of the FeHCF crystal prepared by the invention with 14000 times magnification.

Fig. 5 is an XRD spectrum of a FeHCF crystal prepared in the prior art.

Fig. 6 is an XRD spectrum of the FeHCF crystal prepared in the present invention.

FIG. 7 is a graph comparing the charge and discharge cycle performance of the cell made of FeHCF material prepared in example 1, with a voltage range of 2.0-4.5V and 1mol/L NaPF electrolyte₆EMC FEC (49:49:2) with a charging and discharging current of 1A g^-1。

FIG. 8 is a graph at 1A g showing a cell made of the FeHCF material prepared in example 1^-1Lower discharge curve.

FIG. 9 shows a cell at 0.1A g for FeHCF material prepared in example 1^-1Lower discharge curve.

Detailed Description

The invention is further illustrated by the following examples, which are not intended to limit the scope of the invention.

Interpretation of terms:

FeHCF: prussian blue ferrous iron sodium cyanide serving as the positive electrode material of the sodium ion battery, and the chemical formula of the Prussian blue ferrous iron sodium cyanide is Na₂FeFe(CN)₆。