A layered sodium ferromanganate cathode material, its molten salt preparation method and application

Abstract

This invention relates to the field of sodium-ion battery technology, and particularly to a sodium iron manganese oxide layered cathode material, its molten salt preparation method, and its application. The preparation method includes: weighing sodium source, manganese source, iron source, and potassium chloride molten salt according to stoichiometric ratios; adding anhydrous ethanol and ball milling to obtain a precursor; pressing the dried precursor powder and calcining it; grinding the calcined material into a fine powder; filtering and washing with deionized water and anhydrous ethanol; drying; and then annealing to obtain the sodium iron manganese oxide layered cathode material. The cathode material prepared using the molten salt method exhibits an initial discharge capacity of 214 mAh / g at 0.1C, a discharge capacity of 175 mAh / g at 1C, and a discharge capacity retention rate of 64.91% after 100 cycles. This invention has a simple preparation method, high safety, and is suitable for large-scale industrial production, and can be widely applied in the field of layered cathodes for sodium-ion batteries.

Description

TECHNICAL FIELD

[0001] The application relates to the technical field of sodium ion batteries, in particular to a sodium ferrimanganate layered positive electrode material and a molten salt preparation method and application thereof. BACKGROUND

[0002] Due to the continuous consumption of fossil energy and the resulting severe environmental problems, green energy generation is increasingly favored worldwide. However, due to the geographical and time limitations, energy storage devices are needed. Secondary batteries are widely used due to their stable storage, safety and efficiency. Among them, the most representative lithium ion battery has been widely used in 3C electronic field and power automobile field due to its high energy density, long cycle life and other advantages. However, the development of lithium ion batteries is limited by poor cycle stability, poor rate performance, narrow working temperature range and other problems, and in recent years, the price of lithium ore is rising, and the distribution of lithium resources is uneven in the world, which hinders the further development of lithium ion batteries. Therefore, sodium, which is abundant in the earth's crust and also belongs to the first main group of the periodic table, has been re-attacked by researchers since the 1970s.

[0003] Sodium ion batteries have the advantages of low cost, abundant raw materials, good safety, good performance at high and low temperatures, and have great development potential and broad market prospects in the field of energy storage and power. However, the sodium ion battery positive electrode material also faces two key problems that need to be solved urgently - poor cycle life and low energy density.

[0004] The molten salt method is usually used as a method for preparing positive electrode materials, which provides a molten liquid environment at high temperature, changes the grain growth from a simple single-phase mechanism to a two-phase mechanism, and reduces the energy required in the mass transfer process. At the same time, due to the dissolution and recrystallization mechanism, the primary particles in the precursor are almost not aggregated together, which is more conducive to the formation of regular, uniform and good grain morphology, and is beneficial to the improvement of the electrochemical performance of the positive electrode material. The existing molten salt method is generally used for the preparation of ternary lithium ion battery positive electrode materials, and the grain morphology of the ternary lithium ion battery positive electrode material is controlled. The selected molten salt generally uses lithium salt with a lower melting point, such as LiOH, LiSO4, etc. In the document with the application number "CN202410127517.0", an "O3-type nickel-iron-manganese-based sodium battery positive electrode material and a preparation method thereof" is provided. The method prepares a sodium ion battery positive electrode material through pre-sintering and secondary sintering. The problem is that the material prepared by the traditional pre-sintering and secondary sintering method has a low first discharge specific capacity and an unsatisfactory electrochemical performance. SUMMARY

[0005] The application aims to provide a sodium ion battery sodium ferrimanganate layered positive electrode material and a molten salt preparation method and application thereof. 0.67 Mn 0.5 Fe 0.5 O2 grain morphology, low initial specific capacity and poor cycle stability.

[0006] To achieve the application purposes, the application provides a molten salt preparation method of a sodium ferrimanganate layered positive electrode material, which comprises the following steps:

[0007] Step one, sodium source, manganese source and iron source are weighed according to stoichiometric ratio, and a certain amount of potassium chloride is added as a molten salt, the added amount of potassium chloride is x:1 in atomic ratio with the added sodium, and the value range of x is 0.5<=x<=5;

[0008] Step two, the weighed powder is added into a proper amount of anhydrous ethanol, and then is uniformly mixed by a planetary ball mill, and is transferred to a blast drying oven for overnight drying;

[0009] Step three, after drying, the sodium ferrimanganate positive electrode material mixed with KCl molten salt is obtained by pressing through a tablet press and high-temperature sintering;

[0010] Step four, the fine powder is obtained by grinding, and is washed by deionized water and anhydrous ethanol, and then the sample is placed into a blast drying oven for drying;

[0011] Step five, the powder after washing by filtration is subjected to secondary calcination annealing treatment, and the sodium ferrimanganate layered positive electrode material is obtained.

[0012] Further, in the above step one, the sodium source is one or more of sodium carbonate, anhydrous sodium acetate and sodium sulfate, the manganese source is manganese dioxide or manganese acetate tetrahydrate, and the iron source is diiron trioxide.

[0013] Further, in the above step two, the rotation speed of the planetary ball mill for ball milling mixing is 400-600 rpm, and the ball milling time is 6-8 h.

[0014] Further, in the above step three, the pressing pressure is 10-12 MPa, the high-temperature sintering temperature is 900-1000 DEG C, the starting temperature is room temperature, the temperature is increased by 3-5 DEG C per minute, the temperature is maintained for 10-20 hours, after the temperature maintaining is completed, the sample is naturally cooled to room temperature with the furnace, and the whole heat treatment process is in air.

[0015] Further, in the above step five, the annealing temperature is 500-700 DEG C, and the time is 5-10 hours.

[0016] Further, in the above-mentioned step four, the vacuum filtration uses an organic filter membrane, and deionized water is repeatedly filtered 3-5 times to sufficiently remove residual potassium chloride molten salt, and then anhydrous ethanol is repeatedly filtered 3-5 times.

[0017] Further, in the above-mentioned steps two and four, the temperature of the air oven is 60-80 DEG C, and the drying time is 10-12h.

[0018] Further, the sodium ferrimanganate layered positive electrode material prepared by the above-mentioned molten salt preparation method.

[0019] Further, the application of the sodium ferrimanganate sodium ion positive electrode material prepared by the above-mentioned molten salt preparation method in the field of sodium ion batteries.

[0020] Compared with the prior art, the application has the beneficial effects that:

[0021] 1. The application combines the molten salt method and the solid phase reaction method for the first time to synthesize Na 0.67 Mn 0.5 Fe 0.5 O2 positive electrode material, improves the dispersity of the sodium ion battery positive electrode material particles, and the selected KCl molten salt has low cost, and the potassium ion radius in the molten state is large and not easy to be embedded into the sodium ion layer, and has low influence on the sodium ion battery positive electrode material. The existence of the molten salt provides a molten liquid environment for the precursor under high temperature conditions, changes the grain growth from a single phase mechanism to a two-phase mechanism, and reduces the energy required in the mass transfer process. At the same time, due to the dissolution and recrystallization mechanism, the primary particles in the precursor are almost not aggregated together, and it is easier to form a good grain morphology and reduce the surface residual alkali, and finally the first discharge specific capacity and the cycle stability of the sodium ion battery positive electrode material are improved. 0.67 Mn 0.5 Fe 0.5 O2 positive electrode material, for example, in the voltage window of 1.5-4.3 V and under the charge-discharge rate of 0.1C, the first discharge capacity of the material without using KCl as the molten salt is 178mAh / g, the first discharge capacity of the Na 0.67 Mn 0.5 Fe 0.5 O2 positive electrode material prepared by the molten salt method is as high as 214mAh / g. In the 1C rate, the first discharge capacity of the material without using KCl as the molten salt is 133mAh / g, and the discharge capacity retention rate after 100 cycles is 55.22%. In the 1C rate, the first discharge capacity of the Na 0.67 Mn 0.5 Fe 0.5 O2 positive electrode material prepared by the molten salt method is 175mAh / g, and the discharge capacity retention rate after 100 cycles is 64.91%.

[0022] 2、The preparation method of the application: the method of mixing the precursor and the molten salt in one step by mechanical ball milling is simple and easy to synthesize; the used molten salt KCl material is cheap in price and is not easy to be embedded in the material crystal lattice in high temperature calcination, and is easy to separate from the material subsequently, which is suitable for large-scale industrial production;

[0023] 3、The prepared positive electrode material can be widely applied in the field of sodium ion battery layered positive electrode. BRIEF DESCRIPTION OF DRAWINGS

[0024] Figure 1 is the XRD pattern of the sodium iron manganese acid prepared in Example 1 and the comparative example;

[0025] Figure 2 is the micro-morphology diagram of the sodium iron manganese acid prepared in Example 1 and the comparative example;

[0026] Figure 3 is the charge-discharge curve comparison diagram of the sodium iron manganese acid positive electrode material prepared in Example 1 and the comparative example at 0.1C rate;

[0027] Figure 4 is the cycle performance of the sodium iron manganese acid positive electrode material prepared in Example 1 and the comparative example under the charge-discharge rate condition of 1C;

[0028] Figure 5 is the rate performance diagram of the sodium iron manganese acid prepared in Example 1 and the comparative example;

[0029] Figure 6 is the 1C, 100 cycle median voltage diagram of the sodium iron manganese acid prepared in Example 1 and the comparative example;

[0030] Figure 7 is the GITT diagram of the sodium iron manganese acid prepared in Example 1 and the comparative example; DETAILED DESCRIPTION

[0031] The application will be described in detail below with reference to the drawings and examples.

[0032] Example 1, a sodium iron manganese acid layered positive electrode material and a molten salt preparation method thereof, is prepared by the following synthesis method:

[0033] 1) According to the chemical formula Na 0.67 Mn 0.5 Fe 0.5 O2, the stoichiometric ratio of Na2CO3, MnO2, Fe2O3 and KCl with the atomic ratio of 1:1 is weighed;

[0034] 2) Add an appropriate amount of anhydrous ethanol, mix uniformly by wet grinding through a planetary ball mill, and then transfer to a drum oven for overnight drying; the rotation speed of the planetary ball mill for ball milling mixing is 600 rpm, the ball milling time is 6 h, and the mixed powder is obtained by drying at 80 ℃ for 10 h;

[0035] 3) 1.6 g of the mixed powder is pressed by a tablet press at 12 MPa, and then heated at a temperature rise of 3 ℃ per minute from room temperature as the starting temperature, and kept at 950 ℃ for 15 h; after the heat preservation is completed, the sample is naturally cooled to room temperature with the furnace, and air is continuously pumped into the muffle furnace by an air pump throughout the whole heat treatment process to provide sufficient oxygen for the reaction process;

[0036] 4) The calcined powder is ground into fine powder and washed by filtration with deionized water and anhydrous ethanol, and then the sample is placed in a drum oven for drying after the filtration is completed;

[0037] The organic filter membrane is used for vacuum filtration, and the residual potassium chloride molten salt is removed by repeatedly filtering with deionized water for 5 times, and then the subsequent drying speed is increased and the continuous influence of deionized water on the positive electrode material powder is reduced by repeatedly filtering with anhydrous ethanol for 3 times; after the excess KCl molten salt is washed away, the sample is dried at 80 ℃ for 10 h;

[0038] 5) The dried powder is annealed at 600 ℃ for 5 h to obtain a sodium iron-manganese layered positive electrode material.

[0039] Example 2, a sodium iron-manganese layered positive electrode material and a molten salt preparation method thereof, is prepared by the following synthesis method:

[0040] 1) The stoichiometric ratio of Na2CO3, MnO2, Fe2O3 and KCl with a Na atom ratio of 1:1 is weighed according to the chemical formula Na 0.67 Mn 0.5 Fe 0.5 O2;

[0041] 2) An appropriate amount of anhydrous ethanol is added, and the mixture is uniformly mixed by wet grinding through a planetary ball mill, and then transferred to a drum oven for overnight drying; the rotation speed of the planetary ball mill for ball milling mixing is 400 rpm, the ball milling time is 8 h, and the mixed powder is obtained by drying at 80 ℃ for 10 h;

[0042] 3) 1.6 g of the mixed powder is pressed by a tablet press at 12 MPa, and then heated at a temperature rise of 3 ℃ per minute from room temperature as the starting temperature, and kept at 950 ℃ for 15 h; after the heat preservation is completed, the sample is naturally cooled to room temperature with the furnace, and air is continuously pumped into the muffle furnace by an air pump throughout the whole heat treatment process to provide sufficient oxygen for the reaction process;

[0043] 4) The calcined powder is ground into fine powder and washed by filtration with deionized water and anhydrous ethanol, and then the sample is placed in a drum oven for drying after the filtration is completed;

[0044] Vacuum filtration uses organic filter membrane, first use deionized water repeatedly filtered 3 times to fully remove residual potassium chloride molten salt, then use anhydrous ethanol repeatedly filtered 5 times to increase the subsequent drying speed, reduce the continuous influence of deionized water on the positive material powder; after washing the excess KCl molten salt, drying at 80℃ for 10h;

[0045] 5) The dried powder is annealed at 600℃ for 5h to obtain a sodium iron-manganese layered positive material.

[0046] Example 3, a sodium iron-manganese layered positive material and its molten salt preparation method, which is prepared by the following synthesis method:

[0047] 1) According to the chemical formula Na 0.67 Mn 0.5 Fe 0.5 O2, weigh the stoichiometric ratio of Na2CO3, CH3COONa, Na2SO4, MnO2, Fe2O3 (wherein each sodium source provides 1 / 3 of the total amount of sodium), and KCl with a Na atom ratio of 1:1;

[0048] 2) Add an appropriate amount of anhydrous ethanol, mix uniformly by planetary ball mill, then transfer to a forced air oven and dry overnight; the rotation speed of the planetary ball mill is 400rpm, the ball milling time is 6h, and the mixed powder is obtained by drying at 80℃ for 10h;

[0049] 3) Press 1.6g of the mixed powder through a tablet press at 12MPa, then heat from room temperature to 950℃ at a rate of 3℃ per minute, and calcine for 15h; after the heat treatment is completed, the sample is naturally cooled to room temperature in the furnace, and air is continuously pumped into the muffle furnace throughout the heat treatment process to provide sufficient oxygen for the reaction process;

[0050] 4) Grind the calcined powder into fine powder and wash it with deionized water and anhydrous ethanol, then dry the sample in a forced air oven after the filtration is completed;

[0051] Vacuum filtration uses organic filter membrane, first use deionized water repeatedly filtered 5 times to fully remove residual potassium chloride molten salt, then use anhydrous ethanol repeatedly filtered 5 times to increase the subsequent drying speed, reduce the continuous influence of deionized water on the positive material powder; after washing the excess KCl molten salt, drying at 80℃ for 10h;

[0052] 5) The dried powder is annealed at 600℃ for 5h to obtain a sodium iron-manganese layered positive material.

[0053] Example 4, a sodium iron-manganese layered positive material and its molten salt preparation method, which is prepared by the following synthesis method:

[0054] 1) According to the chemical formula Na0.67 Mn 0.5 Fe 0.5 O2weighed stoichiometric ratio of Na2CO3, (CH3COO)2Mn · 4H2O, Fe2O3 and KCl with Na atom ratio of 1:1;

[0055] 2) A proper amount of anhydrous ethanol was added, and the mixture was uniformly mixed by a planetary ball mill and then transferred to a blast oven for overnight drying; the rotation speed of the planetary ball mill for mixing was 600 rpm, the ball milling time was 8 h, and the mixture was dried at 60 ℃ for 12 h to obtain a mixed powder;

[0056] 3) 1.6 g of the mixed powder was pressed by a tablet machine at 10 MPa, and then heated at a temperature rise of 5 ℃ per minute from room temperature to 950 ℃ and kept for 15 h; after the heat preservation, the sample was naturally cooled to room temperature in the furnace; air was continuously pumped into the muffle furnace during the whole heat treatment process to provide sufficient oxygen for the reaction process;

[0057] 4) The calcined powder was ground into fine powder and washed by filtration with deionized water and anhydrous ethanol; after the filtration, the sample was placed in a blast oven for drying;

[0058] The organic filter membrane was used for vacuum filtration; deionized water was repeatedly filtered for 3 times to sufficiently remove residual KCl molten salt, and then anhydrous ethanol was repeatedly filtered for 3 times to increase the subsequent drying speed and reduce the continuous influence of deionized water on the positive electrode material powder; after the excess KCl molten salt was washed away, the sample was dried at 60 ℃ for 12 h;

[0059] 5) The dried powder was annealed at 700 ℃ for 8 h to obtain a sodium ferrimanganate layered positive electrode material.

[0060] Comparative Example, preparation of Na 0.67 Mn 0.5 Fe 0.5 O2positive electrode material by the following synthesis method:

[0061] 1) weighed stoichiometric ratio of Na2CO3, MnO2 and Fe2O3 according to the chemical formula Na 0.67 Mn 0.5 Fe 0.5 O2;

[0062] 2) the uniformly mixed precursor was dried at 80 ℃ for 10 h to obtain a mixed powder;

[0063] 3) the mixed powder was heated at a temperature rise of 3 ℃ per minute from room temperature to 950 ℃ and kept for 15 h; after the heat preservation, the sample was naturally cooled to room temperature in the furnace; air was continuously pumped into the muffle furnace during the whole heat treatment process to provide sufficient oxygen for the reaction process.

[0064] In the above examples, Na was prepared by adding sodium carbonate, manganese dioxide, and diiron trioxide to KCl with a Na atom ratio of 1:1 according to Example 1 0.67 Mn 0.5 Fe 0.5 The O2 positive electrode material had the highest discharge capacity, which was the best example.

[0065] The test results are as follows:

[0066] As Figure 1 shown, the XRD patterns of the comparative example and Example 1 showed that the structures of the two samples both belonged to the P2 phase. Compared with the comparative example, the diffraction peak intensity of Example 1 was stronger, indicating that the crystallinity of Example 1 was better. Example 1 absorbed water during storage, and a peak representing the hydrated phase was generated at a low angle.

[0067] As Figure 2 shown, the scanning electron microscope patterns of the comparative example and Example 1 showed that the grain agglomeration phenomenon of Example 1 was very small, the grains were in a near-hexagonal sheet structure, and the grain size was above 1 μm. The grain agglomeration phenomenon of the comparative example was serious, many grains were bonded together to form a particle colony, the grain shape was irregular, and the size of the single small grain was mostly in the range of 500-600 nm.

[0068] As Figure 3 shown, the first discharge specific capacity of the comparative example and Example 1 was 178.17 mAh / g and 214.03 mAh / g, respectively, and the first coulombic efficiency was 201.51 % and 243.00 %, respectively, under a voltage window of 1.5-4.3 V and a current of 0.1C. The first discharge capacity and the first coulombic efficiency of Example 1 were higher than those of the comparative example, because the use of KCl as a molten salt provided a molten environment for the growth of grains in a high-temperature environment, which made the grain growth more uniform under a two-phase mechanism, and avoided the agglomeration of large sizes, thereby improving the first discharge capacity.

[0069] As Figure 4 shown, after the comparative example and Example 1 were both charged and discharged for 100 cycles under a wide voltage window of 1.5-4.3 V and a large current of 1C, the discharge specific capacity of the comparative example and Example 1 was 73.52 mAh / g and 113.85 mAh / g, respectively, and the corresponding capacity retention rate was 55.22 % and 64.91 %, respectively, and the capacity retention rate was improved by 9.69 %. The improvement in the capacity retention rate was due to the fact that the positive electrode particles with more uniform grain sizes had a more uniform volume change under a wide voltage window, resulting in less stress, which greatly inhibited the generation of intergranular cracks and avoided further side reactions between the positive electrode material and the electrolyte.

[0070] As Figure 5The graph shows the rate performance of the comparative example and Example 2 under a wide voltage window of 1.5-4.3 V and currents of 0.1 C, 1 C, 3 C, 5 C, 10 C, and 0.1 C. The initial discharge specific capacity of the comparative example at currents of 0.1 C, 1 C, 3 C, 5 C, 10 C, and 0.1 C are 170.54 mAh / g, 116.88 mAh / g, 91.08 mAh / g, 78.16 mAh / g, 54.18 mAh / g, and 148.42 mAh / g, respectively. The initial discharge specific capacity of Example 1 at currents of 0.1 C, 1 C, 3 C, 5 C, 10 C, and 0.1 C are 200.69 mAh / g, 158.63 mAh / g, 125.46 mAh / g, 106.64 mAh / g, 77.09 mAh / g, and 188.95 mAh / g. In Example 1, the discharge specific capacity at different rates was increased by 30.15 mAh / g, 41.75 mAh / g, 34.38 mAh / g, 28.48 mAh / g, 22.91 mAh / g, and 40.53 mAh / g, respectively, compared to the comparative example.

[0071] like Figure 6 As shown, the median voltages of the comparative example and Example 1 after 100 cycles at a current of 1.5–4.3 V and a voltage of 1C, respectively, were 2.313 V and 2.329 V, with voltage decay per cycle of 2.06 mV and 1.15 mV, respectively. This indicates that a more uniform grain size suppresses the formation of intergranular cracks, stabilizes the layered structure of the material, and hinders further undesirable side reactions at the electrolyte-particle interface, thereby suppressing voltage decay.

[0072] like Figure 7 As shown, the comparative example and Example 1 were activated once at 0.1 C under 1.5-4.3 V, followed by charging or discharging under a constant current pulse of 0.1 C for 30 min, and then relaxed for 2 h to achieve a GITT curve close to equilibrium. The sodium ion diffusion coefficient (Dc) of the comparative example is shown. Na+ ) in 10 -6.9 cm 2 S -1 Within the range, the sodium ion diffusion coefficient (D) of Example 1 Na+ ) in 10 -6.7 cm 2 S -1 Within the specified range, the sodium ion diffusion coefficient of the cathode material prepared using the molten salt method is larger than that of the cathode material prepared without the molten salt method, indicating better sodium ion migration kinetics.

[0073] It is to be understood that the above description is intended to be illustrative, and not restrictive. Many other embodiments will be apparent to those of skill in the art upon reading the above description. The scope of the application should, therefore, be determined not with reference to the above description, but should instead be determined with reference to the appended claims, along with their full scope of equivalents.

Claims

1. A method for the molten salt preparation of sodium iron-manganese layered cathode material, characterized in that, It comprises the following steps: Step one, weigh the sodium source, manganese source and iron source according to the stoichiometric ratio, and then add a certain amount of potassium chloride as a molten salt, the addition amount of potassium chloride is x:1 with the added sodium atom ratio, wherein the value range of x is 0.5≤x≤5; Step two, add the weighed powder to a proper amount of anhydrous ethanol, mix uniformly by wet milling with a planetary ball mill, and then transfer to a blast drying oven overnight; Step three, after drying, press through a tablet press, high temperature sintering, obtain a sodium iron manganate positive electrode material mixed with KCl molten salt; Step four, grind into fine powder and wash with deionized water and anhydrous ethanol, and then put the sample into a blast drying oven after the filtration is completed; Step five, the powder after filtration and washing is subjected to secondary calcination annealing treatment, and a sodium iron manganate layered positive electrode material is obtained.

2. The method according to claim 1, wherein the method is characterized by, In step one, the sodium source is one or more of sodium carbonate, anhydrous sodium acetate and sodium sulfate, the manganese source is manganese dioxide or manganese acetate tetrahydrate, and the iron source is diiron trioxide.

3. The method according to claim 1, wherein the method is characterized by, In step two, the rotation speed of the planetary ball mill for ball milling mixing is 400-600 rpm, and the ball milling time is 6-8 h.

4. The method according to claim 1, wherein the method is characterized by, In step three, the pressure for pressing is 10-12 MPa, the high temperature sintering temperature is 900-1000℃, the starting temperature is room temperature, the temperature is raised by 3-5℃ per minute, the temperature is maintained for 10-20 hours, after the temperature maintaining is completed, the sample is naturally cooled to room temperature with the furnace, and the whole heat treatment is in air.

5. The method according to claim 1, wherein the method is characterized by, In step five, the annealing temperature is 500-700℃, and the time is 5-10 hours.

6. The method according to claim 1, wherein the method is characterized by, In step four, the filter membrane used for vacuum filtration is organic, and the residual potassium chloride molten salt is removed by repeatedly filtering with deionized water for 3-5 times, and then filtering with anhydrous ethanol for 3-5 times.

7. The method according to claim 1, wherein the method is characterized by, In steps two and four, the temperature of the blast drying oven is 60-80℃, and the drying time is 10-12 h.

8. A sodium iron manganate layered positive electrode material prepared by the molten salt preparation method of claim 1.

9. The application of the sodium iron manganate layered positive electrode material prepared by the molten salt preparation method of claim 1 in the field of sodium ion batteries.

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