Novel sulfate sodium ion battery positive electrode material and calcination-free preparation method thereof

Abstract

The invention relates to the technical field of sodium-ion battery materials, discloses a novel sulfate sodium-ion battery positive electrode material and a non-calcination preparation method thereof, solves the problem that a Stanfieldite type Na2Fe (SO4) 2 material cannot be prepared, and verifies the electrochemical activity of the Stanfieldite type Na2Fe (SO4) 2 material. The average voltage of the original Na2Fe (SO4) 2 electrode material is 3.5 V (relative to Na / Na < + >, Fe < 2 + > / Fe < 3 + > redox pairs), and the Na2Fe (SO4) 2 electrode material has potential sodium ion battery application value.

Description

Technical Field

[0001] The invention relates to a novel sulfate sodium ion battery positive electrode material and a calcination-free preparation method thereof, belonging to the technical field of sodium ion batteries. Background Art

[0002] Due to the increasing environmental degradation caused by traditional fossil fuels, the need to explore and cultivate sustainable, renewable and clean energy alternatives has become increasingly prominent. Given the dispersion and sporadic distribution of these renewable resources, it is crucial to establish a large-scale energy storage system that can intelligently store and distribute energy. The main components of sodium-ion batteries are abundant and evenly distributed. Existing studies have found that sodium-ion batteries can provide better thermal safety and low-temperature electrochemical performance than lithium-ion batteries. Therefore, sodium-ion batteries are regarded as a strong competitor in the future large-scale energy storage market. The development of sodium-ion battery electrode materials with long cycle life and high energy density is one of the research focuses in the field of sodium-ion battery research.

[0003] At present, researchers have conducted extensive research on various polyanionic sulfate sodium ion battery cathode materials, such as Alluaudite-type Na 2 Fe 2 (SO 4 ) 3 , Eldfellite-type NaFe(SO 4 ) 2 Heating sulfate cathode materials at high temperatures causes the sulfate groups in the crystal lattice to violently decompose into SO x Gas, so sulfate materials cannot be coated and modified by traditional high-temperature pyrolysis process. The ideal goal of researchers is to find a new sulfate cathode material that can be prepared without calcination process and has electrochemical activity. 2 Fe 2 (SO 4 ) 3 and Eldfellite-type NaFe(SO 4 ) 2 It must be calcined at 350-400°C to obtain a phase with high crystallinity. 2 Fe(SO 4 ) 2 The electrode material is highly anticipated, but there is no report on its steady-state preparation and electrochemical performance. Specifically, even if the stoichiometric preparation conditions are adopted, the obtained product does not contain Na 2 Fe(SO 4 ) 2 phase, but completely Vanthoffite-type Na6 Fe(SO 4 ) 4 Mutually. Summary of the invention

[0004] The purpose of the present invention is to provide a novel sulfate sodium ion battery positive electrode material and a calcination-free preparation method thereof, which solves the problem of stable Stanfieldite-type Na 2 Fe(SO 4 ) 2 The material was difficult to prepare and further confirmed its excellent electrochemical activity and potential application value.

[0005] The purpose of the present invention can be achieved through the following technical solutions:

[0006] A sodium ion battery prepared from a novel sulfate sodium ion battery positive electrode material comprises the following steps:

[0007] Step 1. Weigh 70-80 parts of Na 2 Fe(SO 4 ) 2 Active material, 10-20 parts of conductive carbon black, 10 parts of binder are put into an agate mortar, dry-grinded for 10-30 minutes, and wet-grinded for 10-30 minutes with NMP to form a paste, which can form a positive electrode slurry for sodium ion batteries with good fluidity;

[0008] Step 2: Evenly coat the slurry onto aluminum foil and dry it in vacuum at 100°C for 12 hours, then use a cutting machine to cut it into round positive electrode material sheets.

[0009] Furthermore, the Na 2 Fe(SO 4 ) 2 The active material is obtained by two consecutive vacuum drying steps:

[0010] Step 3: Prepare a mixed aqueous solution of sodium sulfate and ferrous sulfate

[0011] Sodium sulfate and ferrous sulfate in a molar ratio of 1:1 were added to deionized water, and then stirred continuously for 1 to 2 hours to completely dissolve them. During this period, an appropriate amount of antioxidant was added to prevent Fe 2+ After hydrolysis, a light green mixed aqueous solution of sodium sulfate and ferrous sulfate with evenly dispersed solutes is obtained.

[0012] Step 4: Two-step continuous vacuum drying of a mixed aqueous solution of sodium sulfate and ferrous sulfate

[0013] The mixed aqueous solution of sodium sulfate and ferrous sulfate is first dried in a vacuum oven at low temperature to obtain a solid powder, and then dried at high temperature for 6 to 12 hours to obtain the Stanfieldite-type Na 2 Fe(SO 4 ) 2 .

[0014] Furthermore, in Step 3, the antioxidant is at least one of ascorbic acid, citric acid or reduced iron powder.

[0015] Furthermore, in Step 3, the antioxidant: Fe 2+ The molar ratio is 30-60:1.

[0016] Furthermore, in Step 4, the two-step continuous vacuum drying is divided into a two-step vacuum drying process of low temperature and high temperature.

[0017] Furthermore, in Step 4, the first vacuum drying temperature is 60-100°C and the drying time is 3-6 hours.

[0018] Furthermore, in Step 4, the secondary vacuum drying temperature is 150-200° C., and the drying time is 6-12 hours.

[0019] Beneficial Effects

[0020] The present invention discloses a novel sulfate Na 2 Fe(SO 4 ) 2 Sodium ion battery positive electrode material, the material preparation process adopts a two-step continuous vacuum drying process, effectively avoiding Stanfieldite-type Na 2 Fe(SO 4 ) 2 Transformed into Na 6 Fe(SO 4 ) 4 Based on the single electron reaction, the new Na 2 Fe(SO 4 ) 2 The average voltage of the positive electrode material is 3.5V (relative to Na / Na + , Fe 2+ / Fe 3+ The discharge capacity at 0.1C is about 40 mAh / g. In general, this work not only solves the problem of steady-state Na 2 Fe(SO 4 ) 2 The difficulty of preparation further reveals that Na 2 Fe(SO 4 )2 Crystal structure composition and electrochemical activity of sodium-ion battery cathode materials. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings required for describing the embodiments are briefly introduced below.

[0022] Figure 1 It is a Stanfieldite-type Na 2 Fe(SO 4 ) 2 XRD patterns of the materials.

[0023] Figure 2 It is a Stanfieldite-type Na 2 Fe(SO 4 ) 2 SEM images of the materials.

[0024] Figure 3 The Na prepared in Comparative Example 1 6 Fe(SO 4 ) 4 XRD patterns of mixed-phase materials.

[0025] Figure 4 The Na prepared in Comparative Example 1 6 Fe(SO 4 ) 4 SEM images of mixed phase materials.

[0026] Figure 5 is Na in Example 1 2 Fe(SO 4 ) 2 0.05C constant current charge and discharge performance of the positive electrode material.

[0027] Figure 6 is Na in Example 1 2 Fe(SO 4 ) 2 Rate performance test of positive electrode materials. Figure 7 is Na in Example 1 2 Fe(SO 4 ) 2 Nyquist plot of electrochemical impedance spectroscopy of positive electrode materials. DETAILED DESCRIPTION

[0028] The present invention is further described in detail below in conjunction with specific embodiments.

[0029] Example 1

[0030] Preparation of Stanfieldite-type Na 2 Fe(SO 4 ) 2 Material:

[0031] Step 1: Prepare a mixed aqueous solution of sodium sulfate and ferrous sulfate

[0032] Weigh sodium sulfate and ferrous sulfate in a molar ratio of 1:1 and add them into deionized water. Stir continuously for 1 to 2 hours to make them completely dissolved. During this period, add ascorbic acid:Fe 2+ An appropriate amount of ascorbic acid was added at a molar ratio of 30:1, and then a mixed aqueous solution of sodium sulfate and ferrous sulfate with a light green color and uniform dispersion of the solute was obtained.

[0033] Step 2: Two-step continuous vacuum drying of a mixed aqueous solution of sodium sulfate and ferrous sulfate

[0034] The mixed aqueous solution of sodium sulfate and ferrous sulfate was first dried in a vacuum drying oven at 100°C for 5 hours to obtain a solid powder, and then immediately heated to 200°C and continued to be vacuum dried for 10 hours. Finally, the dried powder was ground and collected to obtain Stanfieldite-type Na 2 Fe(SO 4 ) 2 Material.

[0035] Figure 1 Preparation of Na for Example 1 2 Fe(SO 4 ) 2 The XRD diagram of the material shows that the number and position of the main diffraction peaks of the material are similar to those of Na 2 Co(SO 4 ) 2 、Na 2 Ni(SO 4 ) 2 The standard card is consistent with that of the material, and the material only contains transition metal element Fe, which further proves that the prepared material is a new type of Stanfieldite-type Na 2 Fe(SO 4 ) 2 Material.

[0036] Figure 2 It is a Stanfieldite-type Na 2 Fe(SO 4 ) 2The SEM image of the material shows that the material has a rich porous structure, which is caused by the rapid loss of adsorbed water and crystal water during the two-step continuous vacuum drying process. The porous structure is conducive to the infiltration of the electrolyte. At the same time, a large number of isolated particles with a particle size of about 100-200nm can be seen, indicating that the prepared Stanfieldite-type Na 2 Fe(SO 4 ) 2 The material is of micro-nano size.

[0037] Comparative Example 1

[0038] Step 1: Prepare a mixed aqueous solution of sodium sulfate and ferrous sulfate

[0039] Weigh sodium sulfate and ferrous sulfate in a molar ratio of 1:1 and add them into deionized water. Stir continuously for 1 to 2 hours to make them completely dissolved. During this period, add ascorbic acid:Fe 2+ An appropriate amount of ascorbic acid was added at a molar ratio of 30:1, and then a mixed aqueous solution of sodium sulfate and ferrous sulfate with a light green color and uniform dispersion of the solute was obtained.

[0040] Step 2: Air drying of the mixed aqueous solution of sodium sulfate and ferrous sulfate

[0041] The mixed aqueous solution of sodium sulfate and ferrous sulfate is first dried in air at 80°C for 5 hours to obtain a solid powder, then immediately heated to 200°C and continued to dry for 10 hours. Finally, the dried powder is ground and collected to obtain a mixed phase material.

[0042] Figure 3 The XRD pattern of the material prepared in Comparative Example 1 shows that the material is Na 6 Fe(SO 4 ) 4 and FeSO 4 ·H 2 A two-phase mixture of O.

[0043] Figure 4 This is the SEM image of the prepared mixed phase material. It can be observed that the primary particles with a particle size of about 100 to 500 nm have obviously agglomerated, but no obvious pore structure is observed on the surface of the primary particles. The rapid loss of adsorbed water and crystallized water during the vacuum drying process cannot be achieved in air drying to generate a two-phase mixture.

[0044] Electrochemical activity test experiment

[0045] The Na prepared in Example 1 of the present invention 2 Fe(SO 4 ) 2The positive electrode material was coated on aluminum foil and after it was completely dried, it was cut into circular electrode sheets with a diameter of 11 mm using a cutting machine. It was used as the positive electrode of the sodium ion battery. The metal sodium sheet was used as the counter electrode, the glass fiber filter membrane was used as the diaphragm, and the sodium salt used in the electrolyte was 1M NaClO 4 The solvent used in the electrolyte is EC and PC in a volume ratio of 1:1, and FEC is added at a volume fraction of 5%. The button-type CR2032 battery was assembled in a glove box filled with argon, and then the electrochemical performance test including charge and discharge was carried out. The final electrochemical performance is as follows Figure 5 and Figure 6 shown.

[0046] from Figure 5 It can be seen that the sodium ion battery prepared in Example 1 has an initial discharge capacity of about 40 mAh / g at a current density of 5 mA / g, and an average operating voltage of about 3.5 V (vs. Na / Na + ), the charge-discharge curves are almost symmetrical, indicating that Na 2 Fe(SO 4 ) 2 The cathode material can indeed achieve Na + reversible deintercalation.

[0047] from Figure 6 It can be seen that the sodium ion battery prepared in Example 1 has a discharge specific capacity at current densities of 5 mA / g, 10 mA / g, 20 mA / g, and 50 mA / g, but the discharge specific capacity at higher current densities, such as 100 mA / g and 200 mA / g, is poor. The inherent low electronic conductivity of the polyanionic material limits the high-rate capacity.

[0048] from Figure 7 It can be seen that the ohmic impedance of the sodium ion battery prepared in Example 1 in the Nyquist spectrum is about 8.814Ω, and the charge transfer impedance is about 684.2Ω, which confirms that its electronic conductivity is indeed poor.

[0049] Combination Figure 5 , Figure 6 and Figure 7 It can be inferred that the original Stanfieldite-type Na 2 Fe(SO 4 ) 2 The material cannot fully utilize its discharge capacity due to the inherent low electronic conductivity of the polyanion structure, and further carbon modification or particle nano-sizing strategies are needed to further improve its electrochemical performance.

[0050] The above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit the same. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that the technical solutions described in the aforementioned embodiments may still be modified, or some of the technical features thereof may be replaced by equivalents. Such modifications or replacements will not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the various embodiments and comparative technical solutions of the present invention.

Claims

1. A novel sulfate sodium ion battery positive electrode material and a method for preparing the same without calcination, characterized in that: The sodium ion battery is prepared by the following steps: Step 1. Weigh 70-80 parts of Na2Fe(SO4)2 active material, 10-20 parts of conductive carbon black and 10 parts of binder by mass and put them into an agate mortar. Dry grind for 10-30 minutes. Add NMP and wet grind for 10-30 minutes. The resulting paste can form a sodium ion battery positive electrode slurry with good fluidity. Step 2: Evenly coat the slurry onto aluminum foil and dry it in vacuum at 100°C for 12 hours, then use a cutting machine to cut it into round positive electrode material sheets.

2. A novel sulfate sodium ion battery positive electrode material and a method for preparing the same without calcination according to claim 1, characterized in that: The novel sulfate sodium ion battery positive electrode material is prepared by the following steps: Step 3: Prepare a mixed aqueous solution of sodium sulfate and ferrous sulfate Sodium sulfate and ferrous sulfate in a molar ratio of 1:1 were added to deionized water, and then stirred continuously for 1-2 hours to completely dissolve them. During this period, an appropriate amount of antioxidant was added to prevent Fe 2+ After hydrolysis, a light green mixed aqueous solution of sodium sulfate and ferrous sulfate with evenly dispersed solutes is obtained. Step 4: Two-step continuous vacuum drying of a mixed aqueous solution of sodium sulfate and ferrous sulfate The mixed aqueous solution of sodium sulfate and ferrous sulfate is first vacuum dried in a vacuum drying oven at low temperature to obtain a solid powder, and then vacuum dried for a second time at high temperature for 6-12 hours to obtain the Stanfieldite-type Na2Fe(SO4)2.

3. A novel sulfate sodium ion battery positive electrode material and a method for preparing the same without calcination according to claim 2, characterized in that: The antioxidant in Step 3 is at least one of ascorbic acid, citric acid or reduced iron powder.

4. The novel sulfate sodium ion battery positive electrode material and the method for preparing the same without calcination according to claim 2, characterized in that: Antioxidant mentioned in Step 3: Fe 2+ The molar ratio is 30-60:

1.

5. The novel sulfate sodium ion battery positive electrode material and the non-calcining preparation method thereof according to claim 2, characterized in that: The two-step continuous vacuum drying described in Step 4 is divided into a two-step vacuum drying process of low temperature and high temperature.

6. A novel sulfate sodium ion battery positive electrode material and a method for preparing the same without calcination according to claim 2, characterized in that: The first vacuum drying temperature in Step 4 is 60-100° C., and the drying time is 3-6 hours.

7. A novel sulfate sodium ion battery positive electrode material and a method for preparing the same without calcination according to claim 2, characterized in that: The secondary vacuum drying temperature in Step 4 is 150-200° C., and the drying time is 6-12 hours.

Images