Blending type Prussian blue positive electrode material, preparation method thereof and sodium ion battery

Abstract

The invention relates to the field of sodium ion batteries, and discloses a blended Prussian blue positive electrode material, a preparation method thereof and a sodium ion battery. The positive electrode material comprises an eutectic formed by Na4Fe (CN) 6 and Na4Fe (SCN) 6, wherein the mass ratio of the Na4Fe (CN) 6 to the Na4Fe (SCN) 6 is 1: (0.5-3). Two materials with different coordination groups are mixed to form a eutectic structure, so that the problems of insufficient capacity and relatively poor rate capability of a Prussian blue positive electrode material caused by sodium ion diffusion limitation are effectively solved, in addition, the structural stability of the obtained positive electrode material is further enhanced, and the performance of the positive electrode material is improved. Therefore, the cycle life of the battery is prolonged, and finally, the specific capacity, the rate capability and the cycle life of the sodium ion battery containing the positive electrode material are improved and prolonged.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of sodium ion batteries, and specifically discloses a blended Prussian blue positive electrode material, a preparation method thereof, and a sodium ion battery. BACKGROUND

[0002] In recent years, the cost of lithium ion batteries has increased significantly, and low-cost sodium ion batteries have more advantages compared with lithium ion batteries. Because sodium resources are abundant, the cost is low, and the fluctuation is small, it is expected to replace lead-acid batteries or lithium iron phosphate batteries in the energy storage market in the future.

[0003] Sodium ion positive electrode material is one of the main raw materials of sodium ion battery. It is mainly divided into three categories of Prussian blue series, layered oxide series and polyanion and its derivative series. Because the Prussian blue series has the advantages of low cost, high specific capacity, high energy density, simple synthesis, etc., it has great industrialization prospect.

[0004] Although the Prussian blue material has good cycle stability, its specific capacity is relatively low, which is difficult to meet the requirement of higher energy density. In addition, due to the limited diffusion path of sodium ions in the Prussian blue positive electrode material, the sodium ion transmission efficiency is seriously hindered when fast charging and discharging, thereby affecting the rate performance of the positive electrode material, and the structure of the positive electrode material is easy to deform in the cycle process of the battery, resulting in the reduction of active sites of the positive electrode material after long-term use, and ultimately leading to the capacity attenuation of the battery. SUMMARY

[0005] The purpose of the present application is to overcome the above-mentioned problems of the prior art Prussian blue sodium ion, and to provide a blended Prussian blue sodium ion positive electrode material, a preparation method thereof, and a sodium ion battery. By mixing two materials with different coordination groups to form a eutectic structure, the problems of insufficient capacity and poor rate performance of the positive electrode material caused by the limitation of sodium ion diffusion of the Prussian blue positive electrode material are effectively solved. In addition, the structural stability of the positive electrode material obtained is further strengthened, thereby improving the cycle life of the battery, and ultimately improving and enhancing the specific capacity, rate performance and cycle life of the sodium ion battery containing the positive electrode material.

[0006] In order to achieve the above-mentioned purpose, the first aspect of the present application provides a blended Prussian blue positive electrode material, characterized in that the positive electrode material comprises a eutectic structure formed by Na4Fe(CN)6 and Na4Fe(SCN)6; wherein the mass ratio of Na4Fe(CN)6 to Na4Fe(SCN)6 is 1:0.5-3.

[0007] In the present application, the positive electrode material includes a eutectic crystal formed by Na4Fe(CN)6 and Na4Fe(SCN)6, and when the ratio of the two is controlled to meet the range defined in the present application, the two cooperate with each other to improve the structural stability of the positive electrode material, increase the active sites of the positive electrode material, and improve the diffusion rate of sodium ions in the positive electrode material, ultimately improving and enhancing the specific capacity, rate performance, and cycle life of the sodium ion battery containing the positive electrode material.

[0008] Specifically, the introduction of Na4Fe(SCN)6 provides additional active sites for the positive electrode material, inhibits the adverse reduction of the performance of the positive electrode material due to the reduction of active sites of the positive electrode material during the cycle process, and ultimately improves the specific capacity of the positive electrode material. When the mass ratio of Na4Fe(CN)6 and Na4Fe(SCN)6 is controlled to meet the above range, the eutectic crystal formed by the two can have a more stable structure, while improving the diffusion rate of sodium ions in the positive electrode material, ultimately improving the rate performance of the positive electrode material and the structural stability and capacity retention rate of the positive electrode material during long-term charge and discharge cycles.

[0009] In one specific embodiment of the present application, the mass ratio of Na4Fe(CN)6 to Na4Fe(SCN)6 is 1:1-2.

[0010] According to the present application, the average particle size of the positive electrode material is 100-300 nm.

[0011] According to the present application, the specific surface area of the positive electrode material is 30-60 g / m 2 .

[0012] In the present application, when the average particle size or specific surface area of the positive electrode material meets the above range, the positive electrode material can have efficient ion transport performance, thereby significantly improving the specific capacity, rate performance, and cycle life of the sodium ion battery containing the positive electrode material.

[0013] Further, the average particle size of the positive electrode material is 100-200 nm.

[0014] Further, the specific surface area of the positive electrode material is 40-60 m 2 / g.

[0015] According to the present application, the electrical conductivity of the positive electrode material is 1-8×10 -5 S / m.

[0016] In the present application, when the electrical conductivity of the positive electrode material meets the above range, the positive electrode material can have good electronic conductivity and high charge and discharge efficiency.

[0017] The second aspect of the present application provides a preparation method of the above-mentioned blended Prussian blue positive electrode material, characterized in that the preparation method comprises the following steps:

[0018] S1, Na4Fe(CN)6 and Na4Fe(SCN)6 are mixed with solvents respectively, then a complexing agent is added to obtain a Na4Fe(CN)6 precursor solution and a Na4Fe(SCN)6 precursor solution;

[0019] S2, the Na4Fe(CN)6 precursor solution and the Na4Fe(SCN)6 precursor solution are mixed in the presence of stirring, a precipitant is added, and a co-precipitation reaction is carried out, and then solid-liquid separation, washing and drying are carried out to obtain a blended Prussian blue positive electrode material precursor material;

[0020] S3, the blended Prussian blue positive electrode material precursor material is subjected to heat treatment in a protective atmosphere, and then is crushed and dried to obtain the blended Prussian blue positive electrode material.

[0021] In the present application, the Na4Fe(CN)6 precursor solution and the Na4Fe(SCN)6 precursor solution are mixed and subjected to a co-precipitation reaction in the presence of a precipitant, and then are subjected to heat treatment, Na4Fe(SCN)6 is introduced into Na4Fe(CN)6, and by controlling the ratio relationship of Na4Fe(CN)6 and Na4Fe(SCN)6, Na4Fe(CN)6 and Na4Fe(SCN)6 can form a eutectic structure, thereby significantly improving the structural stability and active sites of the positive electrode material thus prepared, so that the specific capacity, rate performance and cycle life of the sodium ion battery containing the positive electrode material are improved.

[0022] According to the present application, the complexing agent is selected from at least one of citric acid, tartaric acid and ethylenediaminetetraacetic acid.

[0023] In the present application, the amount of the complexing agent is not particularly limited, as long as the amount of the complexing agent can make the pH values of the Na4Fe(CN)6 precursor solution and the Na4Fe(SCN)6 precursor solution each independently be 4-5.

[0024] In the present application, controlling the pH values of the Na4Fe(CN)6 precursor solution and the Na4Fe(SCN)6 precursor solution each independently to meet the above-mentioned range can ensure that the Na4Fe(CN)6 precursor solution and the Na4Fe(SCN)6 precursor solution have excellent solution stability.

[0025] In a preferred embodiment of the present application, the complexing agent is citric acid.

[0026] In the present application, the kind of solvent is not particularly limited, and can be a conventional solvent in the art, for example, deionized water. In the present application, the amount of the solvent is not particularly limited, as long as it can ensure that Na4Fe(CN)6 and Na4Fe(SCN)6 are fully dissolved in the solvent to form a uniform precursor solution.

[0027] According to the present application, the stirring speed is 100-500 rpm.

[0028] In the present application, when the stirring speed is controlled to meet the above range, it can ensure that each component in the precursor solution is uniformly mixed.

[0029] Further, the stirring speed is 250-350 rpm.

[0030] In the present application, the conditions for mixing the Na4Fe(CN)6 precursor solution and the Na4Fe(SCN)6 precursor solution are not particularly limited, as long as the two precursor solutions can be fully mixed and uniform, for example, the mixing conditions include: the mixing temperature is 20-30℃, and the mixing time is 1-3h.

[0031] According to the present application, the conditions for the co-precipitation reaction include: the reaction temperature is 25-80℃, and the reaction time is 2-12h.

[0032] In the present application, under the above conditions, the co-precipitation reaction can be ensured to proceed fully, and the prepared precursor material has high uniformity of each element dispersion.

[0033] Further, the conditions for the co-precipitation reaction include: the reaction temperature is 30-60℃, and the reaction time is 4-8h.

[0034] According to the present application, the precipitant is selected from at least one of sodium hydroxide, ammonia, and potassium hydroxide.

[0035] In the present application, the specific amount of the precipitant is not particularly limited, as long as the amount of the precipitant makes the pH value of the solution after mixing the Na4Fe(CN)6 precursor solution and the Na4Fe(SCN)6 precursor solution be 7-8.

[0036] In the present application, when the pH value of the solution after mixing the Na4Fe(CN)6 precursor solution and the Na4Fe(SCN)6 precursor solution is controlled to meet the above range, the particle morphology and particle size of the precursor material in the co-precipitation process can be controlled, so that the precursor particles are uniform spherical and / or spheroid particles.

[0037] In one specific embodiment of the present application, in order to further control the morphology and particle size of the precursor, preferably, a precipitant solution is slowly added to the mixed solution after mixing the Na4Fe(CN)6 precursor solution and the Na4Fe(SCN)6 precursor solution.

[0038] In one preferred embodiment of the present application, the precipitant is sodium hydroxide.

[0039] In the present application, the method further comprises a step of solid-liquid separation of the product after the co-precipitation reaction.

[0040] In the present application, the method for solid-liquid separation is not particularly limited as long as it can separate the solid particles from the liquid phase in the product after the co-precipitation reaction, for example, the solid-liquid separation is a centrifugal separation method.

[0041] In the present application, the method further comprises a step of washing the solid phase obtained by solid-liquid separation. In the present application, the solvent for washing is not particularly limited, and a conventional solvent in the art can be used for washing, for example, deionized water.

[0042] In the present application, the drying conditions in steps S2 and S3 are not particularly limited as long as the material to be dried can be fully dried, for example, in steps S2 and S3, the drying conditions each independently include a drying temperature of 50-80℃ and a drying time of 6-12h.

[0043] According to the present application, the heat treatment conditions include a heat treatment temperature of 300-500℃ and a heat treatment time of 2-5h.

[0044] In the present application, the type of protective atmosphere is not particularly limited and can be a conventional protective atmosphere in the art, for example, nitrogen and / or argon.

[0045] In the present application, when the blended Prussian blue positive electrode material precursor material is heat treated under the above conditions, the crystal structure of the precursor material can be fully optimized, the eutectic structure of Na4Fe(CN)6 and Na4Fe(SCN)6 is promoted, which is beneficial to the conductivity and structural stability of the positive electrode material, and ultimately the specific capacity, rate performance and cycle life of the sodium ion battery containing the positive electrode material are improved.

[0046] Further, the heat treatment conditions include a heat treatment temperature of 350-500℃ and a heat treatment time of 2-4h.

[0047] In the present application, the equipment for sintering is not particularly limited as long as the sintering step can be achieved, for example, the sintering is carried out in a tube furnace.

[0048] In the present application, the pulverizing device is not particularly limited, and a conventional pulverizing device such as a ball mill can be used.

[0049] In the present application, the average particle size of the positive electrode material is 100-300 nm, preferably 100-200 m, by pulverizing and sieving.

[0050] In the present application, the drying device is not particularly limited, and a conventional drying device such as a vacuum drying oven can be used.

[0051] The third aspect of the present application provides a sodium ion battery, characterized in that the sodium ion battery comprises the above-mentioned blended Prussian blue positive electrode material.

[0052] Through the above technical solution, the blended Prussian blue positive electrode material, the preparation method and the application thereof provided by the present application have the following beneficial effects:

[0053] In the present application, the positive electrode material comprises a eutectic crystal formed by Na4Fe(CN)6 and Na4Fe(SCN)6, and when the ratio of the two is controlled to meet the range defined in the present application, the two cooperate with each other to improve the structural stability of the positive electrode material, increase the active sites of the positive electrode material, and improve the diffusion rate of sodium ions in the positive electrode material, ultimately improving and enhancing the specific capacity, rate performance, and cycle life of the sodium ion battery containing the positive electrode material.

[0054] Specifically, the introduction of Na4Fe(SCN)6 provides additional active sites for the positive electrode material, inhibits the adverse reduction of the performance of the positive electrode material due to the reduction of the active sites of the positive electrode material during the cycle process, and ultimately improves the specific capacity of the positive electrode material. When the mass ratio of Na4Fe(CN)6 and Na4Fe(SCN)6 is controlled to meet the above range, the eutectic crystal formed by the two has a more stable structure, while the diffusion rate of sodium ions in the positive electrode material is improved, ultimately improving the rate performance of the positive electrode material and the structural stability and capacity retention rate of the positive electrode material during long-term charge and discharge cycles. DETAILED DESCRIPTION

[0055] The endpoints of the ranges and any values disclosed herein are not to be understood as limited. It is explicitly contemplated that the ranges between any two endpoints are also disclosed. It is also explicitly contemplated that each point within a range is also disclosed. It is further explicitly contemplated that any value within a range is also disclosed. It is explicitly contemplated that the disclosure of a range should be interpreted as specifically disclosing all subrange values and any whole or fraction of a value within the range. The same applies to any numerical values recited herein.

[0056] The raw materials used in the following examples and comparative examples are commercially available.

[0057] In the present application, the composition of elements in the blended Prussian blue positive electrode material is measured by inductively coupled plasma (ICP) method.

[0058] In the present application, the average particle size of the blended Prussian blue positive electrode material is measured by a laser particle size analyzer.

[0059] In the present application, the specific surface area of the blended Prussian blue positive electrode material is measured by BET method.

[0060] In the present application, the electrical conductivity of the blended Prussian blue positive electrode material is measured by electrochemical impedance spectroscopy method.

[0061] Example 1

[0062] S1, 100g of Na4Fe(CN)6 and 100g of Na4Fe(SCN)6 were respectively dissolved in 500mL of deionized water, and citric acid was added as a complexing agent after ensuring complete dissolution, and the amount of citric acid was used to make the pH value of the Na4Fe(CN)6 precursor solution and the Na4Fe(SCN)6 precursor solution to 4.5.

[0063] S2, the two precursor solutions obtained in step S1 were uniformly mixed at room temperature (25℃), and a stirrer was used to stir at a speed of 300rpm for 2 hours, then a precipitant NaOH solution was added to maintain the pH value at about 7.5, wherein Fe(CN)6 and Fe(SCN)6 occur coprecipitation reaction, the reaction temperature is 30℃, and the reaction time is 5h. After the coprecipitation is completed, the blue precipitate is separated from the mother liquor by centrifugal separation method. The obtained precipitate is repeatedly washed with deionized water for 3-4 times to remove unreacted impurities and byproducts. The washed material is dried in a vacuum drying oven at 80℃ for 8 hours to obtain a blended Prussian blue positive electrode material precursor material.

[0064] S3, the blended Prussian blue positive electrode material precursor material is heat treated at 400℃ for 3 hours in an argon environment, and the material is crushed to an average particle size of 150nm by a ball milling method after heat treatment, and is dried in a vacuum drying treatment, the drying temperature is 80℃, and the drying time is 8 hours, to obtain the blended Prussian blue positive electrode material A1, wherein the mass ratio of Na4Fe(CN)6 to Na4Fe(SCN)6 is 1:1, the specific surface area is 55.0m 2 / g, and the electrical conductivity is 9.4×10 -5 S / m.

[0065] Example 2

[0066] The positive electrode material A2 is prepared according to the method of example 1, except that:

[0067] The amounts of Na4Fe(CN)6 and Na4Fe(SCN)6 were changed so that the mass ratio of Na4Fe(CN)6 to Na4Fe(SCN)6 was 1:3, the average particle size was 180 nm, the specific surface area was 52.0 m2 / g, the conductivity was 8.6 x 10-7 S / m. 2 -5 S / m.

[0068] Example 3

[0069] The positive electrode material A3 was prepared according to the method of Example 1, except that:

[0070] The amounts of Na4Fe(CN)6 and Na4Fe(SCN)6 were changed so that the mass ratio of Na4Fe(CN)6 to Na4Fe(SCN)6 was 1:0.5, the average particle size was 174 nm, the specific surface area was 54.0 m2 / g, the conductivity was 7.8 x 10-7 S / m. 2 -5 S / m.

[0071] Example 4

[0072] The positive electrode material A4 was prepared according to the method of Example 1, except that:

[0073] In step S1, the amounts of citric acid were such that the pH values of the Na4Fe(CN)6 precursor solution and the Na4Fe(SCN)6 precursor solution were 2.8 and 3.6, respectively, the average particle size was 170 nm, the specific surface area was 51.0 m2 / g, the conductivity was 6.5 x 10-7 S / m. 2 -5 S / m.

[0074] Example 5

[0075] In step S2, the amount of the precipitant NaOH solution was such that the pH value of the solution after mixing the Na4Fe(CN)6 precursor solution and the Na4Fe(SCN)6 precursor solution was 7, the average particle size was 168 nm, the specific surface area was 54.0 m2 / g, the conductivity was 9.2 x 10-7 S / m. 2 -5 S / m.

[0076] Example 6

[0077] The positive electrode material A6 was prepared according to the method of Example 1, except that:

[0078] In step S3, the heat treatment temperature was 300°C, the heat treatment time was 2 h, the average particle size was 190 nm, the specific surface area was 49.0 m2 / g, the conductivity was 6.8 x 10-7 S / m. 2 -5 S / m.

[0079] ​​​​​Example 7

[0080] The positive electrode material A7 was prepared according to the method of Example 1, except that:

[0081] In step S3, the heat treatment temperature was 500°C, the heat treatment time was 5h, the average particle size was 181nm, the specific surface area was 46.0m 2 / g, and the conductivity was 5.9x10 -5 S / m.

[0082] Example 8

[0083] The positive electrode material A7 was prepared according to the method of Example 1, except that:

[0084] In step S3, the heat treatment temperature was 250°C, the heat treatment time was 2h, the average particle size was 301nm, the specific surface area was 25.0m 2 / g, and the conductivity was 2.8x10 -5 S / m.

[0085] Comparative Example 1

[0086] The positive electrode material was prepared according to the method of Example 1, except that:

[0087] In step S1, Na4Fe(SCN)6 was not added. The positive electrode material D1 was prepared, with an average particle size of 341nm, a specific surface area of 15.0m 2 / g, and a conductivity of 7.5x10 -6 S / m.

[0088] Comparative Example 2

[0089] The positive electrode material D2 was prepared according to the method of Example 1, except that:

[0090] The amounts of Na4Fe(CN)6 and Na4Fe(SCN)6 were different from Example 1, so that the mass ratio of Na4Fe(CN)6 to Na4Fe(SCN)6 was 1:0.1, the average particle size was 325nm, the specific surface area was 18.0m 2 / g, and the conductivity was 8.4x10 -6 S / m.

[0091] Test Example

[0092] The prepared Fe(CN)6 and Fe(SCN)6 blended material was mixed with conductive carbon black and polyvinylidene fluoride (PVDF) at a ratio of 8:1:1, coated on an aluminum foil current collector to form a positive electrode sheet. Through drying and compaction, a positive electrode sheet for assembling a battery was obtained. A sodium ion half-battery was assembled using a glass fiber membrane as a separator, sodium metal as a counter electrode, and a 1M NaPF6 solution as an electrolyte. Constant current charge and discharge and cyclic voltammetry tests were performed. The test conditions were: constant current charge and discharge, charge and discharge current density was 1C and 5C, voltage range was 1.0-2.5V, and test temperature was 25℃.

[0093] The test results are shown in Table 1.

[0094] Table 1

[0095] 1C initial specific capacity mAh / g capacity retention % after 500 cycles 5C specific capacity mAh / g 150 93 120 145 89 115 140 85 110 138 83 105 148 92 118 135 78 95 140 79 99 130 70 89 130 90 105 79 63 59 75 52 58 78 57 57

[0096] The positive electrode material prepared in Example 1 has an initial specific capacity of 150 mAh / g at a 1C rate, and after 500 cycles at a 1C rate, the capacity retention rate reaches 93%, showing excellent cycle stability and rate performance. At a 5C rate, the specific capacity of the material can still reach 120 mAh / g, showing excellent rate performance.

[0097] The above describes the preferred embodiments of the present application, but the present application is not limited thereto. Within the technical concept of the present application, various simple modifications can be made to the technical solutions of the present application, including the combination of various technical features in any other suitable manner, and these simple modifications and combinations should also be considered as disclosed by the present application and fall within the protection scope of the present application.

Claims

1. A blend-type doped Prussian blue cathode material, characterized in that, The cathode material comprises a eutectic formed from Na4Fe(CN)6 and Na4Fe(SCN)6; The mass ratio of Na4Fe(CN)6 to Na4Fe(SCN)6 is 1:0.5-3.

2. The cathode material according to claim 1, wherein Na The mass ratio of 4Fe(CN)6 to Na4Fe(SCN)6 is 1:1-2.

3. The cathode material according to claim 1 or 2, wherein, The average particle size of the cathode material is 100-300 nm, preferably 100-200 nm; Preferably, the specific surface area of ​​the positive electrode material is 30-60 m². 2 / g; Preferably, the conductivity of the positive electrode material is 1×10⁻⁶. -5 -8×10 -5 S / m.

4. A method for preparing the blended Prussian blue cathode material according to any one of claims 1-3, characterized in that, The preparation method includes the following steps: S1. After mixing Na4Fe(CN)6 and Na4Fe(SCN)6 with solvents respectively, a complexing agent is added to obtain Na4Fe(CN)6 precursor solution and Na4Fe(SCN)6 precursor solution. S2. Under stirring, the Na4Fe(CN)6 precursor solution and the Na4Fe(SCN)6 precursor solution are mixed, a precipitant is added, and a co-precipitation reaction is carried out. After solid-liquid separation, washing and drying, a blended Prussian blue cathode material precursor material is obtained. S3. In a protective atmosphere, the blended Prussian blue cathode material precursor material is heat-treated, then pulverized and dried to obtain the blended Prussian blue cathode material.

5. The preparation method according to claim 4, wherein, The complexing agent is selected from at least one of citric acid, tartaric acid, and ethylenediaminetetraacetic acid, preferably citric acid; Preferably, the amount of citric acid used is such that the pH values ​​of the Na4Fe(CN)6 precursor solution and the Na4Fe(SCN)6 precursor solution are each independently 4-5.

6. The preparation method according to claim 4 or 5, wherein, The stirring speed is 100-500 rpm; Preferably, the conditions for the coprecipitation reaction include: a reaction temperature of 25-80℃ and a reaction time of 2-12h.

7. The preparation method according to any one of claims 4-6, wherein, The precipitant is selected from at least one of sodium hydroxide, ammonia, and potassium hydroxide; preferably sodium hydroxide. Preferably, the amount of precipitant used is such that the pH value of the solution after mixing the Na4Fe(CN)6 precursor solution and the Na4Fe(SCN)6 precursor solution is 7-8.

8. The method according to any one of claims 4-7, wherein, In steps S2 and S3, the drying conditions each independently include: a drying temperature of 50-80℃ and a drying time of 6-12h.

9. The method according to any one of claims 4-8, wherein, The heat treatment conditions include: a heat treatment temperature of 300-500℃ and a heat treatment time of 2-5 hours.

10. A sodium-ion battery, characterized in that, The sodium-ion battery includes the blended Prussian blue cathode material as described in any one of claims 1-3.