Preparation method of A-site doped Prussian blue sodium ion battery positive electrode material

Abstract

A preparation method of an A-site doped Prussian blue sodium ion battery positive electrode material belongs to the field of new energy batteries, and the specific scheme comprises the following steps: step 1, adding Prussian blue prepared by a traditional process into an A'solution, stirring for 5-20 hours, and filtering to obtain a Prussian blue solution A '; wherein the A'solution comprises one or a combination of more of alkaline earth metal ions, transition metal ions and main group metal ions; and 2, after stirring is finished, centrifuging, collecting Prussian blue, washing and carrying out vacuum drying to obtain the A-site doped Prussian blue sodium ion battery positive electrode material. The invention relates to a method for partially replacing A-site ions with metal ions A'through cation exchange in a liquid phase environment to achieve an A-site doping effect. In the charging and discharging process, the metal ion A'is not separated and can be used as a support column in a Prussian blue lattice channel, so that the structure collapse in the Na < + > deintercalation process is prevented, and the long cycle performance of the sodium ion battery is improved.

Description

Technical Field

[0001] The invention belongs to the field of new energy batteries and relates to sodium ion batteries, and specifically to a method for preparing an "A-site doped" Prussian blue sodium ion battery positive electrode material. Background Art

[0002] At present, lithium-ion batteries are widely used in human life, but the global shortage of lithium resources has led to rising costs, which has restricted the development of lithium-ion batteries. However, the global sodium resources are abundant, and the working principles and production processes of sodium-ion batteries and lithium-ion batteries are similar, so sodium-ion batteries are expected to become a substitute for lithium-ion batteries.

[0003] There are three main types of positive electrode materials for sodium ion batteries: Prussian blue and its analogs, layered oxide series, and polyanions and their derivatives. Among them, Prussian blue and its analogs have low production costs, high theoretical energy density, and an open three-dimensional framework structure, which is conducive to the rapid insertion and extraction of sodium ions, and have attracted widespread attention. The chemical formula of Prussian blue and its analogs is A x M y [M'(CN)6] z □ 1-z ·nH2O, (A=Na + or K + , M / M'=Mn 2+ , Fe 2+ ,Co 2+ , Ni 2+ etc.). However, during the sodium ion extraction and insertion process, the three-dimensional framework collapses, resulting in poor long-cycle performance of the sodium ion battery. Element doping, as a basic method for adjusting capacity, life, rate performance and production cost, has been widely used in Prussian blue materials and is one of the most effective methods at present. Through literature research, Prussian blue can be used as a positive electrode material for other alkaline earth metal ion, transition metal ion, and main group metal ion batteries, but the gram capacity is not high, indicating that alkaline earth metal ions, transition metal ions, and main group metal ions can diffuse in the Prussian blue lattice, but the selectivity is lower than that of monovalent ions. Among them, the invention patent application with publication number CN109728295A proposes that the A position of Prussian blue is one or more of alkali metal ions and alkaline earth metal ions; the invention patent application with publication number CN109728296B proposes that the A position of Prussian blue is alkali metal ions, alkaline earth metal cations, Zn 2+ 、Al 3+At present, the research on Prussian blue A-site doping mainly focuses on adding the ions to be doped at the synthesis end. However, since the mother liquor at the synthesis end contains a large amount of sodium ions, the amount of ions doped into the A-site is small; at the same time, most synthesis methods use trisodium citrate as a complexing agent, resulting in a large amount of citrate ions in the mother liquor at the synthesis end, and alkaline earth metal ions Mg 2+ and Ca 2+ 、Main group metal ions Al 3+ They will all complex with it (calcium citrate is insoluble in water), further hindering the doping of alkaline earth metal ions or main group metal ions into the A position. Summary of the invention

[0004] In order to solve the problems existing in the background technology, the present invention provides a method for preparing an "A-site doped" Prussian blue sodium ion battery positive electrode material.

[0005] In order to achieve the above object, the present invention adopts the following technical solutions:

[0006] A method for preparing an "A-site doped" Prussian blue sodium ion battery positive electrode material comprises the following steps:

[0007] Step 1, adding Prussian blue prepared by conventional process into A' solution and stirring, wherein A' solution comprises one or more combinations of alkaline earth metal ions, transition metal ions and main group metal ions;

[0008] Step 2: After stirring, centrifuge, collect Prussian blue, wash and vacuum dry to obtain "A-site doped" Prussian blue-based sodium ion battery positive electrode material.

[0009] In step 1, the stirring time is 5-12 hours.

[0010] In step 1, the concentration of metal ions in the A' solution is 0.01-5M.

[0011] In step 1, the stirring parameters of the stirring process are 100-800 r / min, and nitrogen or argon is introduced at a flow rate of 20-120 ml / min throughout the process.

[0012] In step 1, the conventional method for preparing Prussian blue includes liquid-liquid method, solid-solid method, and solid-liquid method. The chemical formula of the prepared Prussian blue is A x T y M 1-y [Fe(CN)6] z □ 1-z nH2O, 0<x≤2, 0≤y≤1, 0<z<1, where T and M are independently selected Mn 2+ , Fe 2+ ,Co2+ , Ni 2+ , Zn 2+ , V 3+ , VO 2+ , Cu 2+ ,Cr 3+ One or a combination of the following, with the A-site ion being Na + .

[0013] In step 1, the alkaline earth metal ions include Ca 2+ , Sr. 2+ ,Mg 2+ , Ba 2+ One or more combinations of; the main group metal ions include Al 3+ , Ga 3+ ,In 3+ , Sn 2+ One or more combinations of, the transition metal ion is Zn 2 + .

[0014] In step 2, the vacuum drying temperature is 80-120° C., and the vacuum drying time is 9-12 hours.

[0015] A sodium ion battery, comprising an "A-site doped" Prussian blue-based sodium ion battery positive electrode material prepared by the preparation method.

[0016] Compared with the prior art, the present invention has the following beneficial effects:

[0017] Compared with the traditional A-site doping method, the present invention chooses to immerse Prussian blue in a liquid environment, and at the same time selects alkaline earth metal ions, transition metal ions or main group metal ions A' with lower selectivity as doping ions. The present invention immerses the Prussian blue synthesized by the traditional method in an alkaline earth metal ion, transition metal ion or main group metal ion solution. Since the solution does not contain sodium ions, the sodium ions in the Prussian blue lattice diffuse unidirectionally into the solution, and the alkaline earth metal ions, transition metal ions or main group metal ions A' in the corresponding solution are filled into the Prussian blue lattice, so that A' partially replaces the A-site ions, thereby achieving the effect of A-site doping. During the charge and discharge process, the alkaline earth metal ions, transition metal ions or main group metal ions A' do not escape, and can serve as "pillars" in the Prussian blue lattice channels to prevent Na + The structure collapses during the deintercalation process, thereby improving the long cycle performance of the sodium ion battery. The present invention is simple to operate, low in cost, and suitable for large-scale production. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 It is a schematic diagram of the reaction device of the present invention;

[0019] Figure 2 It is the capacity retention rate graph of PB1, PBA3, PBA1, and PBA2. DETAILED DESCRIPTION

[0020] The technical solution of the present invention will be clearly and completely described below in conjunction with the drawings and embodiments. Obviously, the described embodiments are only part of the embodiments of the invention, rather than all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0021] Embodiment 1:

[0022] A method for preparing an "A-site doped" Prussian blue sodium ion battery positive electrode material comprises the following steps:

[0023] Step 1: Weigh 58g of sodium ferrocyanide decahydrate and dissolve it in deoxygenated deionized water to prepare 600ml of solution A. Weigh 16.85g of ferrous sulfate heptahydrate, 10.24g of manganese sulfate monohydrate, and 90g of sodium citrate dihydrate and dissolve them in deoxygenated deionized water to prepare 600ml of solution B. Weigh 90g of sodium citrate dihydrate and dissolve it in deoxygenated deionized water to prepare 600ml of solution C.

[0024] Step 2: Add solution A and solution B to solution C at the same time for co-precipitation reaction. Continue the reaction for 11 hours after the addition is complete. Centrifuge after the reaction is complete, wash three times with deionized water, and collect Prussian blue.

[0025] Step 3: Add the above Prussian blue material into a clean container C, then add 900 ml of 0.6 M CaCl2 solution into container C, and stir at 500 r / min for 16 hours;

[0026] Step 4: centrifuge, wash three times with deionized water, and dry under vacuum at 80° C. for 12 h to obtain A-site doped Prussian blue (PBA1).

[0027] The coprecipitation reaction was carried out using the device shown in Figure a, wherein container A was filled with solution A, container B was filled with solution B, and container C was filled with solution C. A peristaltic pump was used to control the flow rate of 2 mL / min so that solution A and solution B were simultaneously added dropwise to solution C through a silicone tube in equal volumes. The speed of the stirrer in container C was controlled at 500 r / min. N2 was introduced into the solution at a flow rate of 60 mL / min during the reaction and immersion doping processes. The temperature of the solution was maintained at 25°C during the reaction and immersion doping processes.

[0028] Example 2

[0029] The difference from Example 1 is that the CaCl2 solution in step 3 is changed to 0.9M MgSO4 solution to obtain A-site doped Prussian blue (PBA2), and the rest is the same as Example 1.

[0030] Comparative Example 1

[0031] The difference from Example 1 is that the soaking step in step 3 and step 4 are omitted, the Prussian blue collected in step 2 is placed in a vacuum drying oven at 80° C. and dried for 12 hours to obtain Prussian blue (PB1), and the rest is the same as Example 1.

[0032] Comparative Example 2

[0033] The difference from Example 1 is that the preparation method of solution A in step 1 is changed to: weigh 58g of sodium ferrocyanide decahydrate and dissolve 20.48g of anhydrous magnesium sulfate in deoxygenated deionized water to prepare 600ml of solution A. Steps 3 and 4 are eliminated. The Prussian blue collected in step 2 is placed in a vacuum drying oven at 80°C for 12h to obtain Prussian blue doped at the A position (PBA3). The rest is the same as in Example 1.

[0034] Battery Assembly:

[0035] The Prussian blue material prepared in Example 1-2 and Comparative Example 1-2 was mixed with Super P conductive carbon black and polyvinylidene fluoride in a mass ratio of 7:2:1, and then N-methyl-2-pyrrolidone was added and mixed to form a positive electrode slurry. The prepared positive electrode slurry was coated on a clean aluminum foil, dried in a coating machine, rolled by an electric roller machine, and then cut into circular pole pieces with a diameter of 14 mm by a slicer to obtain a positive electrode sheet; the sodium sheet was placed in the center of the negative electrode shell of the button battery, 40 μL of electrolyte was dripped, and a glass fiber diaphragm was placed and then 40 μL of electrolyte was dripped, and then the positive electrode sheet, gasket, spring and positive electrode shell were placed in turn, and then sealed with a sealing machine to prepare a button battery.

[0036] Test method:

[0037] Table 1: After the assembled button cell was left to stand for 12 hours, the electrochemical performance test was carried out at a test temperature of 25°C, a voltage range of 2.0 to 3.8 V, and a rate of 1.0C. The test results are shown in the following table.

[0038] Case Particle size (D50 / um) Gram capacity (mAh / g) 25℃ Capacity retention rate (400 cycles) Comparative Example 1 10.896 145.3 87.29％ Comparative Example 2 10.121 141.7 87.70％ Example 1 10.285 122.1 91.06％ Example 2 10.597 132.9 91.04％

[0039] ICP analysis was used to quantitatively analyze the content of metal Ca and Mg in the A-doped Prussian blue material. The results are shown in the following table:

[0040] Ca(ppm) Mg(ppm) Comparative Example 2 ______________ 289.97 Example 1 568.96 ______________ Example 2 ______________ 675.22

[0041] in conclusion:

[0042] From the test data, it can be seen that compared with Comparative Example 2, the Mg doped into the A position in Example 2 2+ The amount is larger, indicating that the synthesis end mother liquor contains a large amount of sodium ions and citrate ions, which is not conducive to Mg 2+ Doping into the A position. By comparing the comparative examples with each other, the cycle performance of comparative example 2 has no obvious improvement. Compared with comparative example 1, the cycle performance of embodiments 1 and 2 are improved (compared with comparative example 1, after 400 cycles, the capacity retention rate of embodiment 1 is increased by 3.83%, and the capacity retention rate of embodiment 2 is increased by 3.81%). This shows that after eliminating the interference of other ions, the present invention can successfully dope alkaline earth metal, transition metal ion or main group metal ion A' into the A position by using the immersion method, and A' can play a "pillar" role in the Prussian blue lattice channel and in the Na + It does not come out during the embedding and de-embedding process, thus inhibiting the structural collapse during the cycle and improving the cycle stability of sodium-ion batteries.

[0043] In addition, it should be understood that although the present specification is described according to implementation modes, not every implementation mode contains only one independent technical solution. This description of the specification is only for the sake of clarity. Those skilled in the art should regard the specification as a whole. The technical solutions in each embodiment may also be appropriately combined to form other implementation modes that can be understood by those skilled in the art.

Claims

1. A method for preparing a "A-site doped" Prussian blue sodium ion battery positive electrode material, characterized in that: The following steps are involved: Step 1, adding Prussian blue prepared by conventional process into A' solution and stirring, wherein A' solution comprises one or more combinations of alkaline earth metal ions, transition metal ions and main group metal ions; Step 2: After stirring, centrifuge, collect Prussian blue, wash and vacuum dry to obtain "A-site doped" Prussian blue-based sodium ion battery positive electrode material.

2. The preparation method according to claim 1, characterized in that: In step 1, the stirring time is 5-12 hours.

3. The preparation method according to claim 1, characterized in that: In step 1, the concentration of metal ions in the A' solution is 0.01-5M.

4. The preparation method according to claim 1, characterized in that: In step 1, the stirring parameters of the stirring process are 100-800 r / min, and nitrogen or argon is introduced at a flow rate of 20-120 ml / min throughout the process.

5. The preparation method according to claim 1, characterized in that: In step 1, the conventional method for preparing Prussian blue includes liquid-liquid method, solid-solid method and solid-liquid method. The chemical formula of the prepared Prussian blue is A x T y M 1-y [Fe(CN)6] z □ 1-z nH2O, 0<x≤2, 0≤y≤1, 0<z<1, where T and M are independently selected Mn 2+ , Fe 2+ ,Co 2+ , Ni 2+ , Zn 2+ , V 3+ , VO 2+ , Cu 2+ ,Cr 3+ One or a combination of A-site ion is Na + .

6. The preparation method according to claim 1, characterized in that: In step 1, the alkaline earth metal ions include Ca 2 + , Sr. 2+ ,Mg 2+ , Ba 2+ One or more combinations of; the main group metal ions include Al 3+ , Ga 3+ ,In 3+ , Sn 2+ One or more combinations of, the transition metal ion is Zn 2+ .

7. The preparation method according to claim 1, characterized in that: In step 2, the vacuum drying temperature is 80-120° C., and the vacuum drying time is 9-12 hours.

8. A sodium ion battery, characterized in that: The sodium ion battery comprises an "A-site doped" Prussian blue-based sodium ion battery positive electrode material prepared by the preparation method described in any one of claims 1 to 6.

Images