Positive electrode active material, method for manufacturing the same, positive electrode sheet, and sodium-ion battery

Abstract

The application relates to the field of sodium ion batteries, and discloses a positive electrode active material, a preparation method thereof, a positive electrode sheet and a sodium ion battery. The application first prepares a precursor of the positive electrode active material through iron source, manganese source, nickel source and magnesium source raw materials, then adds sodium source raw materials for sintering, and finally prepares a novel sodium ion battery positive electrode active material through magnesium salt coating, prevents the material from directly contacting with electrolyte, and obviously improves the cycle performance, the rate performance and gas production inhibition.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of sodium ion batteries, in particular to a positive electrode active material, a preparation method thereof, a positive electrode sheet and a sodium ion battery. BACKGROUND

[0002] Compared with lithium ion batteries, sodium ion batteries have the following advantages: (1) sodium salt raw materials are abundant in reserves and low in price, and the use of iron-manganese-nickel-based positive electrode materials can reduce the raw material cost by half compared with ternary positive electrode materials of lithium ion batteries; (2) due to the characteristics of sodium salt, low-concentration electrolyte can be used to reduce cost (the conductivity of sodium salt is about 20% higher than that of lithium electrolyte at the same electrolyte concentration); (3) sodium ions do not form alloys with aluminum, and the negative electrode can use aluminum foil as the current collector, which can further reduce the cost by about 8% and the weight by about 10%;

[0003] At present, nickel-iron-manganese ternary positive electrode materials are the most promising ternary positive electrode materials, but the complex phase change during charging and discharging and the complex side reaction between the surface and the electrolyte can lead to a decrease in cycle performance.

[0004] In patent CN 110416521 A, Mn is used for doping to improve the structural stability, but the cycle performance is poor. SUMMARY

[0005] Therefore, the purpose of the present application is to provide a positive electrode active material and a preparation method thereof, so that the positive electrode active material can have high cycle performance and rate performance.

[0006] Another purpose of the present application is to provide the use of the above-mentioned positive electrode active material in the preparation of a positive electrode sheet and a sodium ion battery.

[0007] Another purpose of the present application is to provide a positive electrode sheet and a sodium ion battery based on the above-mentioned negative electrode active material.

[0008] In order to solve the above technical problems / achieve the above purposes or at least partially solve the above technical problems / achieve the above purposes, as a first aspect of the present application, a positive electrode active material is provided, which comprises a core layer material and a coating layer material, the core layer material has a chemical formula of Na 2 / 3 Ni (2 / 5)-x Fe 1 / 5 Mn 2 / 5 Mg x O2, 0.01≤x≤0.07; and the coating layer material is magnesium oxide.

[0009] As a second aspect of the present application, a preparation method of the positive electrode active material is provided, which comprises:

[0010] The nickel source, manganese source, iron source and magnesium source raw materials are weighed, mixed with water, and uniformly mixed, and a precursor Ni (2 / 5)-x Fe 1 / 5 Mn 2 / 5 Mg x (OH)2 is obtained by sintering after mixing the sodium source raw material with the precursor.

[0011] The core layer material Na 2 / 3 Ni (2 / 5)-x Fe 1 / 5 Mn 2 / 5 Mg x O2 is obtained by sintering after mixing the sodium source raw material with the precursor.

[0012] The sintered Na 2 / 3 Ni (2 / 5)-x Fe 1 / 5 Mn 2 / 5 Mg x O2 and heavy metal complexing agent are added to the magnesium salt solution and mixed uniformly, stirred, washed, filtered, and dried to obtain a positive electrode active material with a magnesium oxide coating layer and a Na 2 / 3 Ni (2 / 5)-x Fe 1 / 5 Mn 2 / 5 Mg x O2 core layer.

[0013] Optionally, the nickel source, manganese source, sodium source and iron source are sulfate, nitrate, carbonate, hydrochloride, phosphate or hydrate of each metal ion.

[0014] Optionally, the concentration of magnesium salt in the magnesium salt solution is 0.01-0.03 mol / L; further optionally, the magnesium salt in the magnesium salt solution is one or more of magnesium sulfate, magnesium chloride, and magnesium acetate.

[0015] Optionally, the magnesium source raw material is magnesium oxide.

[0016] Optionally, the concentration of heavy metal complexing agent is 1-2 mol / L; further optionally, the heavy metal complexing agent is ammonia.

[0017] Optionally, the sintering is performed at a first rated rate to 300-500°C for 2-10 hours, and then at a second rated rate to 800-1100°C for 8-20 hours; further optionally, the first rated rate and the second rated rate are independently selected from 1-10°C / min.

[0018] In view of the problem that the existing metal layered sodium-ion battery cathode material is unstable in structure and has poor cycle performance as the voltage rises, the application provides a cathode active material suitable for a sodium-ion battery, which can greatly increase the structural stability of the material and improve the cycle performance and rate performance of the battery. Therefore, as a third aspect of the application, a cathode sheet is provided, which comprises the cathode active material according to any one of the preceding aspects of the application, and a conductive agent, a binder and a current collector.

[0019] As a fourth aspect of the application, a sodium-ion battery is also provided, which comprises the cathode sheet described above, a separator, an electrolyte, a tab and a negative electrode sheet.

[0020] Compared with the existing sodium-ion cathode active material, the application first prepares a precursor of the cathode active material by using iron source, manganese source, nickel source and magnesium source raw materials, then adds sodium source raw materials for sintering, and finally prepares a new type of sodium-ion battery cathode active material through magnesium salt coating, which prevents the material from directly contacting the electrolyte and significantly improves the cycle performance, rate performance and gas production inhibition. BRIEF DESCRIPTION OF DRAWINGS

[0021] Figure 1 The XRD results of the cathode material of Example 1 of the application are shown;

[0022] Figure 2 The SEM results of the cathode material of Example 1 of the application are shown;

[0023] Figure 3 The comparison chart of the room temperature cycle performance of the cathode material of Example 1 of the application and the cathode material of Comparative Example 1 is shown. DETAILED DESCRIPTION

[0024] The application discloses a cathode active material, a preparation method thereof, a cathode sheet and a sodium-ion battery. Those skilled in the art can refer to the content herein and appropriately improve the process parameters for implementation. It should be particularly pointed out that all similar substitutions and changes are obvious to those skilled in the art, and they are all regarded as included in the application. The products, processes and applications described in the application have been described by preferred embodiments, and relevant personnel can obviously make changes or appropriate changes and combinations to the products, processes and applications described herein without departing from the content, spirit and scope of the application, to realize and apply the technology of the application. Obviously, the described embodiments are part of the embodiments of the application, rather than all the embodiments. Based on the embodiments in the application, all other embodiments obtained by those skilled in the art without creative labor are within the scope of protection of the application.

[0025] It should be noted that, in this document, relational terms such as "first" and "second," "step 1" and "step 2," and "(1)" and "(2)" are used merely to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitations, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element. Moreover, the embodiments and features described in this application can be combined with each other without conflict.

[0026] In the first aspect of this application, a positive electrode active material is provided, wherein the core layer is a magnesium-doped sodium-ion metal layered oxide, which is an O3 type material with the chemical formula Na. 2 / 3 Ni (2 / 5)-x Fe 1 / 5 Mn 2 / 5 Mg x O2, where 0.01 ≤ x ≤ 0.07; the coating layer is magnesium oxide. In some embodiments of this application, x is 0.01, 0.02, 0.03, 0.04, 0.05, 0.06 or 0.07.

[0027] In a second aspect of this application, a method for preparing the positive electrode active material is provided, comprising adding manganese source material, nickel source material, iron source material, and magnesium source material for doping to water, mixing them evenly, and then adding the mixture to a constant-temperature reaction vessel by co-precipitation, filtering and drying to obtain the precursor Ni. (2 / 5)-x Fe 1 / 5 Mn 2 / 5 Mg x (OH)2, then dry-mixed with sodium source raw materials and sintered at high temperature to obtain core material Na. 2 / 3 Ni (2 / 5)-x Fe 1 / 5 Mn 2 / 5 Mg x O2, 0.01≤x≤0.07, where the value of x is determined by the amount of magnesium source material used for doping; finally, the sintered Na... 2 / 3 Ni (2 / 5)-x Fe 1 / 5 Mn 2 / 5 Mg x O2 and a heavy metal complexing agent were added to a magnesium salt solution and mixed thoroughly. The mixture was then stirred, washed, filtered, and dried to obtain a magnesium oxide-coated core layer containing Na.2 / 3 Ni (2 / 5)-x Fe 1 / 5 Mn 2 / 5 Mg x The positive electrode active material for O2. The amount of each raw material is determined according to the chemical formula of the final product. The concentration of magnesium salt in the coated magnesium salt solution is 0.01mol / L-0.03mol / L, which can be selected as 0.01mol / L, 0.02mol / L or 0.03mol / L.

[0028] In some embodiments of this application, the magnesium salt in the magnesium salt solution is one or more of magnesium sulfate, magnesium chloride, and magnesium acetate; in other embodiments of this application, the magnesium salt solution is a 0.01 mol / L magnesium chloride solution, a 0.02 mol / L magnesium chloride solution, a 0.03 mol / L magnesium chloride solution, or a 0.03 mol / L magnesium sulfate solution.

[0029] In some embodiments of this application, the nickel, manganese, sodium, and iron sources are sulfates, nitrates, carbonates, hydrochlorides, phosphates, or hydrates of various metal ions, and the iron source includes ferrous ions and ferric ions. In other embodiments of this application, the iron source is selected from sulfates, nitrates, carbonates, phosphates, or hydrochlorides of ferric or ferrous ions, such as ferrous sulfate, ferric nitrate, ferric chloride, etc.; the nickel source is selected from its nitrates or sulfates, such as nickel sulfate or nickel nitrate of +2 valent nickel ions; the manganese source is selected from its sulfates, nitrates, or hydrochlorides, such as manganese sulfate, manganese nitrate, or manganese chloride of +2 valent manganese ions; and the sodium source is selected from its carbonates, acetates, or nitrates, such as sodium carbonate, sodium acetate, or sodium nitrate.

[0030] In some embodiments of this application, the magnesium source material is magnesium oxide; in other embodiments of this application, the magnesium oxide is magnesium oxide.

[0031] In some other embodiments of this application, the mass ratio of nickel sulfate, manganese sulfate, ferrous sulfate, magnesium oxide, and sodium carbonate is 200-227:200-220:100-123:40-50:240-266.

[0032] In some embodiments of the present application, a hydroxide complexing agent, such as sodium hydroxide, is added in the co-precipitation reaction to form a complex small molecule with nickel ions, thereby preventing the formation of nickel ion precipitates; in some other embodiments of the present application, 824.5 g of NaOH and 2473.5 g of water are mixed to prepare a sodium hydroxide solution. In some other embodiments of the present application, a heavy metal complexing agent, such as ammonia, can also be added to further remove heavy metal impurities. Most of the impurity metal ions in the feed solution can be complexed by ammonia, which can be hydrolyzed to form the corresponding hydroxide, which is referred to as an alkaline salt precipitate. The concentration of the ammonia can be selected to be 0.1-1 mol / L.

[0033] In some embodiments of the present application, the sintering is performed by increasing the temperature to 300-500°C at a first predetermined rate, and then increasing the temperature to 800-1100°C at a second predetermined rate; in some other embodiments of the present application, the sintering is performed by increasing the temperature to 300-500°C at a first predetermined rate and maintaining the temperature for 2-10 h, and then increasing the temperature to 800-1100°C at a second predetermined rate and maintaining the temperature for 8-20 h. The first predetermined rate and the second predetermined rate are independently selected from 1-10°C / min, such as 1°C / min, 2°C / min, 3°C / min, 4°C / min, 5°C / min, 6°C / min, 7°C / min, 8°C / min, 9°C / min or 10°C / min. In some other embodiments of the present application, the sintering is performed by increasing the temperature to 300-500°C at a rate of 2-5°C / min and maintaining the temperature for 4-6 h, and then increasing the temperature to 800-1100°C at a rate of 2-5°C / min and maintaining the temperature for 10-15 h.

[0034] In some embodiments of the present application, the concentration of the heavy metal complexing agent during the coating of the magnesium salt solution is 1-2 mol / L; in some other embodiments of the present application, the concentration of the heavy metal complexing agent during the coating of the magnesium salt solution is 1 mol / L, 1.2 mol / L, 1.5 mol / L or 1.8 mol / L; in some other embodiments of the present application, the heavy metal complexing agent during the coating of the magnesium salt solution is ammonia.

[0035] In some embodiments of the present application, the stirring temperature during the coating of the magnesium salt solution is 60-90°C, and the stirring time is 3-9 h; the drying temperature is 500-900°C, and the time is 18-36 h.

[0036] In a third aspect of the present application, a positive electrode sheet is provided, which comprises the positive electrode active material according to any one of the preceding schemes of the present application, and a conductive agent, a binder and a current collector. The positive electrode active material, the conductive agent and the binder form a positive electrode slurry, and the positive electrode sheet is formed by coating the positive electrode slurry on the surface of the current collector.

[0037] In some embodiments of the present application, the mass percentage of the positive active material, the conductive agent and the binder in the positive electrode slurry is 95%-99%, 0.5%-3% and 1%-5% in turn, for example, 96% positive active material, 2% conductive agent and 2% binder.

[0038] In some embodiments of the present application, the conductive agent is carbon nanotube and / or conductive carbon black, and the binder is one or more than two of CMC (sodium carboxymethyl cellulose), SBR (styrene-butadiene latex) and polyvinylidene fluoride (PVDF).

[0039] In some embodiments of the present application, the current collector is a metal foil, for example, an aluminum foil, a copper foil or the like.

[0040] In the fourth aspect of the present application, a sodium ion battery is provided, comprising the aforementioned positive electrode tab, and a separator, an electrolyte, a tab and a negative electrode tab.

[0041] In some embodiments of the present application, the negative electrode tab uses hard carbon as the active material, and the separator, the tab, the conductive agent and the binder are selected from conventional materials.

[0042] In some embodiments of the present application, the sodium ion battery is prepared into a battery cell by the method of lamination, after baking the battery cell, a non-aqueous electrolyte is injected into the battery cell, and after formation and capacity determination, the sodium ion battery is prepared.

[0043] In each group of comparative experiments provided in the present application, unless otherwise specified, the experimental conditions, materials and the like remain the same except for the differences indicated by each group, so as to have comparability. The experimental materials and reagents used in the examples can be obtained from the market unless otherwise specified.

[0044] Unless otherwise specified, "room temperature" used in the present application refers to the temperature measured by a Celsius thermometer in a normal laboratory, generally 20-30℃, preferably 25℃ (298.15K in Kelvin).

[0045] The following further describes a positive active material, a preparation method thereof, a positive electrode tab and a sodium ion battery provided in the present application.

[0046] First embodiment:

[0047] A magnesium-rich sodium ion battery O3-type ternary positive active material, the core layer material has a chemical formula of Na 2 / 3 Ni (2 / 5)- x Fe 1 / 5 Mn 2 / 5 Mg x O2, wherein x=0.05, and the preparation process specifically comprises:

[0048] Take 227 g of nickel sulfate, 220 g of manganese sulfate, 123 g of ferrous sulfate, 45 g of magnesium oxide, and add 5000 mL of deionized water to stir for half an hour to obtain a uniformly mixed solution;

[0049] Take 824.5 g of NaOH and 2473.5 g of deionized water, mix uniformly to prepare a sodium hydroxide solution;

[0050] Slowly add the above mixed solution to the constant temperature reaction kettle, add 5000 mL of deionized water as the bottom liquid to the reaction kettle, and then slowly add 80 mL of NH3·H2O (0.1-1 mol / L) and the prepared sodium hydroxide solution to the reaction kettle, and react in the constant temperature reaction kettle for 12 h, and then filter and dry to obtain the precursor Ni (2 / 5)-x Fe 1 / 5 Mn 2 / 5 Mg x (OH)2;

[0051] Take 266 g of sodium carbonate and mix with the prepared precursor;

[0052] After mixing, sintering is carried out, and the temperature is raised to 450°C at a rate of 3°C / min and maintained for 5 h, and then the temperature is raised to 900°C at the same rate and maintained for 12 h to obtain the product, MgO-doped Na 2 / 3 Ni (2 / 5)-x Fe 1 / 5 Mn 2 / 5 Mg x O2, wherein x=0.05.

[0053] Coating: prepare a 0.01 mol / L magnesium chloride solution, add the sintered MgO-doped Na 2 / 3 Ni (2 / 5)-x Fe 1 / 5 Mn 2 / 5Mg x O2 to the solution and mix uniformly, pass 1 mol / L ammonia solution, stir at 70°C for 4 h, wash with distilled water, filter, and dry at 500°C for 24 h to obtain the positive electrode active material of MgO-coated Na 2 / 3 Ni (2 / 5)-x Fe 1 / 5 Mn 2 / 5 Mg x O2, wherein x=0.05. The particle size of the prepared positive electrode active material is about 5 μm, the specific surface area is about 0.68 m 2 / g, and the XRD pattern of the target product is shown in Figure 1 From the Figure 1 XRD pattern, it can be seen that the obtained product has no impurity phase peak and has an O3 structure, and the diffraction peak of MgO is not shown in the XRD pattern, which is due to the too small amount of MgO and the too low peak intensity. The SEM image of the target product is shown in Figure 2, from Figure Two It can be seen that the product has uniform particle size.

[0054] Second embodiment:

[0055] A magnesium-rich sodium-ion battery O3-type ternary positive electrode active material has a chemical formula of Na 2 / 3 Ni (2 / 5)-x Fe 1 / 5 Mn 2 / 5Mg x O2, wherein x = 0.03, and a preparation process thereof specifically comprises:

[0056] Take 227g of nickel sulfate, 220g of manganese sulfate, 123g of ferrous sulfate, 40g of magnesium oxide, and add 5000mL of deionized water and stir for half an hour to obtain a uniformly mixed mixed solution;

[0057] Take 824.5g of NaOH and 2473.5g of deionized water, mix uniformly to prepare a sodium hydroxide solution;

[0058] Slowly add the above mixed solution to the constant temperature reaction kettle, add 5000mL of deionized water as the bottom liquid in the reaction kettle, and then slowly add 80mL of NH3·H2O (0.1-1mol / L) and the prepared sodium hydroxide solution to the reaction kettle, and react in the constant temperature reaction kettle for 12h, and then filter and dry to obtain the precursor Ni (2 / 5)-x Fe 1 / 5 Mn 2 / 5 Mg x (OH)2;

[0059] Take 266g of sodium carbonate and mix with the prepared precursor;

[0060] After mixing, sintering is performed, and the temperature is increased to 450℃ at a rate of 3℃ / min and maintained for 5h, and then increased to 900℃ at the same rate and maintained for 12h to obtain the product, MgO-doped Na 2 / 3 Ni (2 / 5)-x Fe 1 / 5 Mn 2 / 5 Mg x O2, wherein x = 0.03.

[0061] Coating: prepare a 0.01mol / L magnesium chloride solution, mix the sintered MgO-doped Na 2 / 3 Ni (2 / 5)-x Fe 1 / 5 Mn 2 / 5Mg x O2 into the solution, and then uniformly mix, pass 1mol / L ammonia solution, stir at 70℃ for 4h, wash with distilled water, filter, and dry at 500℃ for 24h to obtain MgO-coated Na 2 / 3 Ni(2 / 5)-x Fe 1 / 5 Mn 2 / 5 Mg x O2, wherein x = 0.03. The prepared positive electrode active material has a particle size of about 5 μm and a specific surface area of about 0.68 m 2 / g. The XRD pattern and SEM pattern of the target product are similar to those of the first embodiment. The product has a uniform particle size, no impurity phase peak appears, has an O3 structure, and no diffraction peak of MgO is shown in the XRD pattern, which is due to too little amount of MgO and too low peak contrast.

[0062] Third embodiment:

[0063] A Mg-rich Na-ion battery O3-type ternary positive electrode active material has a chemical formula of Na 2 / 3 Ni (2 / 5)-x Fe 1 / 5 Mn 2 / 5Mg x O2, wherein x = 0.07, and the preparation process specifically comprises:

[0064] Take 227 g of nickel sulfate, 220 g of manganese sulfate, 123 g of ferrous sulfate, 50 g of magnesium oxide, and add 5000 mL of deionized water to stir for half an hour to obtain a uniformly mixed mixed solution;

[0065] Take 824.5 g of NaOH and 2473.5 g of deionized water, mix uniformly to prepare a sodium hydroxide solution;

[0066] Slowly add the above mixed solution to the constant temperature reaction kettle, add 5000 mL of deionized water as the bottom liquid in the reaction kettle, and then slowly add 80 mL of NH3·H2O (0.1-1 mol / L) and the prepared sodium hydroxide solution to the reaction kettle. React in the constant temperature reaction kettle for 12 h, filter and dry to obtain a precursor Ni (2 / 5)-x Fe 1 / 5 Mn 2 / 5 Mg x (OH)2;

[0067] Take 266 g of sodium carbonate and mix with the prepared precursor;

[0068] After mixing, sintering is performed, and the temperature is increased to 450°C at a rate of 3°C / min and maintained for 5 h, and then increased to 900°C at the same rate and maintained for 12 h to obtain the product, MgO-doped Na 2 / 3 Ni (2 / 5)-x Fe 1 / 5 Mn 2 / 5 Mg x O2, wherein x = 0.07.

[0069] Coating: 0.01 mol / L magnesium chloride solution was prepared, and the sintered MgO-doped Na 2 / 3 Ni (2 / 5)-x Fe 1 / 5 Mn 2 / 5Mg x O2 was added into the solution and mixed uniformly, 1 mol / L ammonia solution was introduced, stirring was carried out at 70°C for 4 h, distilled water was used for cleaning and filtering, and drying was carried out at 500°C for 24 h, so as to obtain a positive electrode active material of Na 2 / 3 Ni (2 / 5)-x Fe 1 / 5 Mn 2 / 5 Mg x O2, wherein x=0.07. The particle size of the prepared positive electrode active material is about 5 μm, and the specific surface area is about 0.68 m 2 / g. The XRD pattern and SEM pattern of the target product are similar to those of the first embodiment, the product has uniform particle size, no impurity phase peak appears, has an O3 structure, and no diffraction peak of MgO is shown in the XRD pattern, which is caused by too small amount of MgO and too low peak contrast.

[0070] Fourth embodiment:

[0071] A Mg-rich Na-ion battery O3-type ternary positive electrode active material has a chemical formula of Na 2 / 3 Ni (2 / 5)-x Fe 1 / 5 Mn 2 / 5Mg x O2, wherein x=0.05, and the preparation process specifically comprises the following steps:

[0072] 227 g of nickel sulfate, 220 g of manganese sulfate, 123 g of ferrous sulfate, and 45 g of magnesium oxide were weighed and added into 5000 mL of deionized water and stirred for half an hour to obtain a mixed solution which is uniformly mixed;

[0073] 824.5 g of NaOH and 2473.5 g of deionized water were weighed and mixed uniformly to prepare a sodium hydroxide solution;

[0074] The above mixed solution was slowly added into a constant-temperature reaction kettle, 5000 mL of deionized water was added into the reaction kettle as a bottom liquid, and 80 mL of NH3·H2O (0.1-1 mol / L) and the prepared sodium hydroxide solution were slowly added into the reaction kettle, and reaction was carried out in the constant-temperature reaction kettle for 12 h, and the precursor Ni (2 / 5)-x Fe 1 / 5 Mn 2 / 5 Mg x (OH)2;

[0075] 266 g of sodium carbonate was taken and mixed with the prepared precursor;

[0076] After mixing, sintering is performed, with a rate of 3°C / min to 450°C for 5h, and then with the same rate to 900°C for 12h, to obtain the product, MgO-doped Na 2 / 3 Ni (2 / 5)-x Fe 1 / 5 Mn 2 / 5 Mg x O2, wherein x=0.05.

[0077] Coating: a 0.02mol / L magnesium chloride solution is prepared, and the sintered MgO-doped Na 2 / 3 Ni (2 / 5)-x Fe 1 / 5 Mn 2 / 5Mg x O2 is added into the solution and mixed uniformly, 1mol / L ammonia water solution is introduced, stirred at 70°C for 4h, washed with distilled water, filtered, and dried at 500°C for 24h, to obtain the MgO-coated Na 2 / 3 Ni (2 / 5)-x Fe 1 / 5 Mn 2 / 5 Mg x O2 positive electrode active material, wherein x=0.05. The prepared positive electrode active material has a particle size of about 5μm and a specific surface area of about 0.68m 2 / g. The XRD pattern and SEM pattern of the target product are similar to those of the first embodiment, the obtained product has uniform particle size, no impurity phase peak appears, has an O3 structure, and no diffraction peak of MgO is shown in the XRD pattern, which is due to too small amount of MgO and too low peak contrast.

[0078] Fifth embodiment:

[0079] A Mg-rich Na-ion battery O3-type ternary positive electrode active material has a chemical formula of Na 2 / 3 Ni (2 / 5)-x Fe 1 / 5 Mn 2 / 5Mg x O2, wherein x=0.05, and the preparation process specifically includes:

[0080] 227g of nickel sulfate, 220g of manganese sulfate, 123g of ferrous sulfate, and 45g of magnesium oxide are weighed and added into 5000mL of deionized water and stirred for half an hour to obtain a mixed solution;

[0081] 824.5g of NaOH and 2473.5g of deionized water are weighed and mixed uniformly to prepare a sodium hydroxide solution;

[0082] The mixed solution is slowly added into a constant temperature reaction kettle, 5000 mL of deionized water is added into the reaction kettle as a bottom liquid, and 80 mL of NH3·H2O (0.1-1 mol / L) and the prepared sodium hydroxide solution are slowly added into the reaction kettle. The reaction is carried out in the constant temperature reaction kettle for 12 h, and the precursor Ni (2 / 5)-x Fe 1 / 5 Mn 2 / 5 Mg x (OH)2.

[0083] 266 g of sodium carbonate is mixed with the prepared precursor;

[0084] After mixing, sintering is carried out, the temperature is increased to 450°C at a rate of 3°C / min and maintained for 5 h, and then the temperature is increased to 900°C at the same rate and maintained for 12 h to obtain the product, MgO-doped Na 2 / 3 Ni (2 / 5)-x Fe 1 / 5 Mn 2 / 5 Mg x O2, wherein x=0.05.

[0085] Coating: a 0.03 mol / L magnesium chloride solution is prepared, the sintered MgO-doped Na 2 / 3 Ni (2 / 5)-x Fe 1 / 5 Mn 2 / 5Mg x O2 is added into the solution and uniformly mixed, 1 mol / L ammonia water solution is introduced, stirring is carried out at 70°C for 4 h, the product is washed with distilled water, filtered, and dried at 500°C for 24 h to obtain a positive electrode active material of Na 2 / 3 Ni (2 / 5)-x Fe 1 / 5 Mn 2 / 5 Mg x O2 coated with MgO, wherein x=0.05. The prepared positive electrode active material has a particle size of about 5 μm and a specific surface area of about 0.68 m 2 / g. The XRD pattern and SEM pattern of the target product are similar to those of the first embodiment, the obtained product has uniform particle size, no impurity phase peak appears, has an O3 structure, and no diffraction peak of MgO is shown in the XRD pattern, which is caused by too small amount of MgO and too low peak contrast.

[0086] Sixth embodiment:

[0087] A Mg-rich Na-ion battery O3-type ternary positive electrode active material has a chemical formula Na 2 / 3 Ni (2 / 5)-x Fe 1 / 5 Mn 2 / 5Mg x O2, wherein x=0.05, and the preparation process specifically comprises:

[0088] Take 227 g of nickel sulfate, 220 g of manganese sulfate, 123 g of ferrous sulfate, 45 g of magnesium oxide, and add 5000 mL of deionized water and stir for half an hour to obtain a uniformly mixed solution;

[0089] Take 824.5 g of NaOH and 2473.5 g of deionized water, mix uniformly to obtain a sodium hydroxide solution;

[0090] Slowly add the above solution into a constant temperature reactor, add 5000 mL of deionized water as a bottom liquid into the reactor, and then slowly add 80 mL of NH3·H2O (0.1-1 mol / L) and the prepared sodium hydroxide solution into the reactor, react in the constant temperature reactor for 12 h, filter and dry to obtain the precursor Ni (2 / 5)-x Fe 1 / 5 Mn 2 / 5 Mg x (OH)2;

[0091] Take 266 g of sodium carbonate and mix with the prepared precursor;

[0092] After mixing, sintering is performed, with a rate of 3 ℃ / min to 450 ℃ for 5 h, and then with the same rate to 900 ℃ for 12 h to obtain the product, MgO-doped Na 2 / 3 Ni (2 / 5)-x Fe 1 / 5 Mn 2 / 5 Mg x O2, wherein x=0.05.

[0093] Coating: prepare a 0.03 mol / L magnesium sulfate solution, add the sintered MgO-doped Na 2 / 3 Ni (2 / 5)-x Fe 1 / 5 Mn 2 / 5Mg x O2 into the solution and mix uniformly, pass 1 mol / L ammonia solution, stir at 70 ℃ for 4 h, wash with distilled water, filter, and dry at 500 ℃ for 24 h to obtain the positive electrode active material of MgO-coated Na 2 / 3 Ni (2 / 5)-x Fe 1 / 5 Mn 2 / 5 Mg x O2, wherein x=0.05. The prepared positive electrode active material has a particle size of about 5 μm and a specific surface area of about 0.68 m 2 / g. The XRD pattern and SEM pattern of the target product are similar to those of the first embodiment, the obtained product has uniform particle size, no impurity phase peak appears, has an O3 structure, and no diffraction peak of MgO is shown in the XRD pattern, which is due to the too small amount of MgO and too low peak intensity.

[0094] First Comparative Example:

[0095] A magnesium-rich sodium-ion battery O3-type ternary positive electrode active material, chemical formula Na 2 / 3 Ni (2 / 5)-x Fe 1 / 5 Mn 2 / 5Mg x O2, wherein x = 0.05, the preparation process specifically includes:

[0096] Take 227g of nickel sulfate, 220g of manganese sulfate, 123g of ferrous sulfate, 45g of magnesium oxide, and add 5000mL of deionized water and stir for half an hour to obtain a uniform mixture;

[0097] Take 824.5g of NaOH and 2473.5g of deionized water, mix well to prepare a sodium hydroxide solution;

[0098] Slowly add the above mixture to the constant temperature reaction kettle, add 5000mL of deionized water as the bottom liquid to the reaction kettle, and then slowly add 80mL of NH3·H2O (0.1-1mol / L) and the prepared sodium hydroxide solution to the reaction kettle, and react in the constant temperature reaction kettle for 12h, then filter and dry to obtain the precursor Ni (2 / 5)-x Fe 2 / 5 Mn 2 / 5 Mg x (OH)2;

[0099] Take 266g of sodium carbonate and mix with the prepared precursor;

[0100] After mixing, sintering is carried out, and the temperature is raised to 450℃ at a rate of 3℃ / min and maintained for 5h, and then the temperature is raised to 900℃ at the same rate and maintained for 12h to obtain the product, MgO-doped Na 2 / 3 Ni (2 / 5)-x Fe 1 / 5 Mn 2 / 5 Mg x O2, wherein x = 0.05, the prepared positive electrode active material has a particle size of about 5μm and a specific surface area of about 0.68m 2 / g.

[0101] Second Comparative Example:

[0102] A magnesium-rich sodium-ion battery O3-type ternary positive electrode active material, chemical formula Na 2 / 3 Ni (2 / 5)-x Fe 1 / 5 Mn 2 / 5Mg x O2, wherein x = 0.05, the preparation process specifically includes:

[0103] Take 227 g of nickel sulfate, 220 g of manganese sulfate, 123 g of ferrous sulfate, 45 g of magnesium oxide, and add 5000 mL of deionized water and stir for half an hour to obtain a uniformly mixed solution;

[0104] Take 824.5 g of NaOH and 2473.5 g of deionized water, mix uniformly to prepare a sodium hydroxide solution;

[0105] Slowly add the above mixed solution to the constant temperature reaction kettle, add 5000 mL of deionized water as the bottom liquid in the reaction kettle, and then slowly add 80 mL of NH3·H2O (0.1-1 mol / L) and the prepared sodium hydroxide solution to the reaction kettle, and react in the constant temperature reaction kettle for 12 h, and then filter and dry to obtain the precursor Ni (2 / 5)-x Fe 2 / 5 Mn 2 / 5 Mg x (OH)2;

[0106] Take 266 g of sodium carbonate and mix with the prepared precursor;

[0107] After mixing, sintering is performed, with a rate of 13℃ / min to 450℃ for 5h, and then the same rate to 900℃ for 12h to obtain the product, MgO-doped Na 2 / 3 Ni (2 / 5)-x Fe 1 / 5 Mn 2 / 5 Mg x O2, wherein x=0.05.

[0108] Coating: prepare a 0.03 mol / L magnesium chloride solution, add the sintered MgO-doped Na 2 / 3 Ni (2 / 5)-x Fe 1 / 5 Mn 2 / 5Mg x O2 to the solution and mix uniformly, pass 1 mol / L ammonia solution, stir at 80℃ for 4h, wash with distilled water, filter, and dry at 600℃ for 24h to obtain a positive electrode active material of MgO-coated Na 2 / 3 Ni (2 / 5)-x Fe 1 / 5 Mn 2 / 5 Mg x O2, wherein x=0.05, and the prepared positive electrode active material has a particle size of about 6μm and a specific surface area of about 0.63m 2 / g.

[0109] Third Comparative Example:

[0110] A Mg-rich Na-ion battery O3-type ternary positive electrode active material has a chemical formula Na 2 / 3 Ni (2 / 5)-x Fe1 / 5 Mn 2 / 5Mg x O2, wherein x = 0.05, and the preparation process specifically comprises:

[0111] Take 227 g of nickel sulfate, 220 g of manganese sulfate, 123 g of ferrous sulfate, 45 g of magnesium oxide, and add 5000 mL of deionized water and stir for half an hour to obtain a uniformly mixed solution;

[0112] Take 824.5 g of NaOH and 2473.5 g of deionized water, mix well to prepare a sodium hydroxide solution;

[0113] Slowly add the above mixed solution to the constant temperature reaction kettle, add 5000 mL of deionized water as the bottom liquid to the reaction kettle, and then slowly add 80 mL of NH3·H2O (0.1-1 mol / L) and the prepared sodium hydroxide solution to the reaction kettle, and react in the constant temperature reaction kettle for 12 h, then filter and dry to obtain the precursor Ni (2 / 5)-x Fe 2 / 5 Mn 2 / 5 Mg x (OH)2;

[0114] Take 266 g of sodium carbonate and mix it with the prepared precursor;

[0115] After mixing, sintering is performed, with a rate of 3°C / min to 450°C for 5 h, and then the same rate to 700°C for 12 h to obtain the product, MgO-doped Na 2 / 3 Ni (2 / 5)-x Fe 1 / 5 Mn 2 / 5 Mg x O2, wherein x = 0.05.

[0116] Coating: prepare a 0.03 mol / L magnesium chloride solution, and add the sintered MgO-doped Na 2 / 3 Ni (2 / 5)-x Fe 1 / 5 Mn 2 / 5Mg x O2 into the solution and mix well, pass 2 mol / L ammonia solution, stir at 80°C for 4 h, wash with distilled water, filter, and dry at 600°C for 30 h to obtain MgO-coated Na 2 / 3 Ni (2 / 5)-x Fe 1 / 5 Mn 2 / 5 Mg x O2 positive electrode active material, wherein x = 0.05, and the prepared positive electrode active material has a particle size of about 4 μm and a specific surface area of about 0.72 m 2 / g.

[0117] Example 4:

[0118] A magnesium-rich sodium-ion battery O3-type ternary positive electrode active material, chemical formula Na 2 / 3 Ni (2 / 5)-x Fe 1 / 5 Mn 2 / 5Mg x O2, wherein x = 0.05, the preparation process specifically includes:

[0119] Take 227g of nickel sulfate, 220g of manganese sulfate, 123g of ferrous sulfate, 45g of magnesium oxide, and add 5000mL of deionized water and stir for half an hour to obtain a uniformly mixed mixture;

[0120] Take 824.5g of NaOH and 2473.5g of deionized water, mix well to prepare a sodium hydroxide solution;

[0121] Slowly add the above mixture to a constant temperature reaction kettle, add 5000mL of deionized water as a bottom liquid to the reaction kettle, and then slowly add 80mL of NH3·H2O (0.1-1mol / L) and the prepared sodium hydroxide solution to the reaction kettle, and react in the constant temperature reaction kettle for 12h, then filter and dry to obtain the precursor Ni (2 / 5)-x Fe 2 / 5 Mn 2 / 5 Mg x (OH)2;

[0122] Take 266g of sodium carbonate and mix with the prepared precursor;

[0123] After mixing, sintering is performed, with a rate of 3℃ / min to 250℃ for 5h, and then the same rate to 900℃ for 12h to obtain the product, MgO-doped Na 2 / 3 Ni (2 / 5)-x Fe 1 / 5 Mn 2 / 5 Mg x O2, wherein x = 0.05.

[0124] Coating: prepare a 0.03mol / L magnesium chloride solution, mix the sintered MgO-doped Na 2 / 3 Ni (2 / 5)-x Fe 1 / 5 Mn 2 / 5Mg x O2 into the solution and mix well, pass 2mol / L ammonia solution, stir at 70℃ for 4h, wash with distilled water, filter, and dry at 700℃ for 26h to obtain MgO-coated Na 2 / 3 Ni (2 / 5)-x Fe 1 / 5 Mn 2 / 5 Mg xO2, the prepared positive electrode active material has a particle size of about 8 μm and a specific surface area of about 0.80 m 2 / g.

[0125] Fifth Comparative Example:

[0126] A magnesium-rich sodium-ion battery O3-type ternary positive electrode active material has a chemical formula of Na 2 / 3 Ni (2 / 5)-x Fe 1 / 5 Mn 2 / 5Mg x O2, wherein x = 0.05, and the preparation process specifically comprises the following steps.

[0127] Take 227 g of nickel sulfate, 220 g of manganese sulfate, 123 g of ferrous sulfate, 45 g of magnesium oxide, and 5000 mL of deionized water, and stir for half an hour to obtain a uniformly mixed mixed solution;

[0128] Take 824.5 g of NaOH and 2473.5 g of deionized water, and mix uniformly to obtain a sodium hydroxide solution;

[0129] Slowly add the above mixed solution into a constant temperature reaction kettle, add 5000 mL of deionized water as a bottom liquid into the reaction kettle, and then slowly add 80 mL of NH3·H2O (0.1-1 mol / L) and the prepared sodium hydroxide solution into the reaction kettle, and react in the constant temperature reaction kettle for 12 h, and then filter and dry to obtain a precursor Ni (2 / 5)-x Fe 2 / 5 Mn 2 / 5 Mg x (OH)2.

[0130] Take 266 g of sodium carbonate and mix with the prepared precursor B;

[0131] After mixing, sintering is performed, the temperature is increased to 450°C at a rate of 3°C / min and maintained for 5 h, and then the temperature is increased to 900°C at the same rate and maintained for 6 h to obtain a product, MgO-doped Na 2 / 3 Ni (2 / 5)-x Fe 1 / 5 Mn 2 / 5 Mg x O2, wherein x = 0.05.

[0132] Coating: prepare a 0.03 mol / L magnesium chloride solution, and coat the sintered MgO-doped Na 2 / 3 Ni (2 / 5)-x Fe 1 / 5 Mn 2 / 5Mg xO2 was added to the solution and mixed uniformly, 1.5 mol / L ammonia water solution was passed, stirred at 65°C for 4h, washed with distilled water, filtered, and dried at 650°C for 26h to obtain Na 2 / 3 Ni (2 / 5)-x Fe 1 / 5 Mn 2 / 5 Mg x O2 positive active material, wherein x = 0.05, the prepared positive active material has a particle size of about 3pm and a specific surface area of about 0.82m 2 / g.

[0133] Seventh embodiment: preparation and performance test of sodium ion battery

[0134] 1. Preparation of sodium ion battery

[0135] (1) Preparation of positive electrode sheet

[0136] The sodium ion positive active material was prepared, and 96% of the positive active material (based on the mass of the positive electrode), 2% of PVDF (based on the mass of the positive electrode), 1% of conductive carbon black (based on the mass of the positive electrode), and 1% of carbon nanotubes (based on the mass of the positive electrode) were dissolved in N-methyl pyrrolidone, vacuum stirred and dispersed in a blender, and a uniform bubble-free slurry was prepared. The positive electrode sheet was prepared by uniformly coating the aluminum foil.

[0137] (2) Preparation of negative electrode sheet

[0138] The hard carbon was used as the negative active material, and 94% of the negative active material (based on the mass of the negative electrode), 1.5% of sodium carboxymethyl cellulose (based on the mass of the positive electrode), 2% of conductive carbon black (based on the mass of the positive electrode), and 2.5% of butyl benzene latex (based on the mass of the negative electrode) were dissolved in deionized water, vacuum stirred and dispersed in a blender, and a uniform bubble-free slurry was prepared. The negative electrode sheet was prepared by uniformly coating the aluminum foil.

[0139] (3) Packaging and formation

[0140] The positive electrode sheet, separator, and negative electrode sheet were used to prepare the battery cell by lamination, and the battery cell had the same side of the tab. The tab and the current collector were welded together using an ultrasonic welding machine, and then the battery cell was packaged using an aluminum plastic film.

[0141] After the battery cell was baked, the non-aqueous electrolyte was injected into the battery cell, and after formation and capacity test, a 4Ah lithium ion battery was prepared for battery performance test.

[0142] 2. Performance detection method

[0143] Battery cycle performance test method:

[0144] (1) The experimental battery was charged at 25°C±3 to 4.0V at 0.5C constant current and constant voltage, and the current was cut off at 0.02C;

[0145] (2) Rest for 30min;

[0146] (3) Discharge at 1C constant current to 1.5V at 25°C±3, and record the capacity D1 at this time;

[0147] (4) Rest for 30min;

[0148] (5) Cycle (1)-(4), record the cycle number and the final discharge capacity D2;

[0149] Capacity retention rate D=D2 / D1*100%

[0150] Battery rate performance test method:

[0151] (1) The experimental battery was charged at 25°C±3 to 4.0V at 0.5C constant current and constant voltage, and the current was cut off at 0.02C;

[0152] (2) Rest for 30min;

[0153] (3) Discharge at 1C constant current to 2.0V at 25°C±3, and record the capacity D1 at this time;

[0154] (4) Rest for 30min;

[0155] (5) The experimental battery was charged at 25°C±3 to 4.0V at 0.5C constant current and constant voltage, and the current was cut off at 0.02C;

[0156] (6) Rest for 30min;

[0157] (7) Discharge at 5C constant current to 2.0V at 25°C±3, and record the capacity D2 at this time;

[0158] Capacity retention rate D=D2 / D1*100%

[0159] 3. Experimental results

[0160] The positive active materials of the second embodiment and the first comparative example were prepared into sodium ion batteries, and the two groups of batteries were subjected to battery cycle performance detection under the same conditions, and the results are shown in Figure 3 ;

[0161] According to Figure 3It can be clearly seen that when the number of cycles reaches 200, the battery capacity retention rate prepared by the positive electrode active material in the second embodiment is still close to 100%, while the capacity retention rate of the sodium-ion battery in the first comparative example has decreased to about 95%. In addition, the cycle performance of the positive electrode active material of this application is also significantly better than the 86% effect described in the prior art patent CN110416521A.

[0162] In addition, this application also compares the electrochemical performance of the sixth embodiment and the second to fifth comparative examples, as shown in Table 1 below;

[0163] Table 1

[0164] Particle diameter Specific surface area 5C rate discharge capacity retention rate 1C cycle 200 cycles cycle retention rate First embodiment 5 um 0.68m 2 / g]] 98.45％ 99.6％ First comparative example 5 um 0.68m 2 / g]] 95.21％ 95.21％ Second comparative example 6 um 0.63 m 2 / g]] 98.3％ 93.4％ Third comparative example 4 um 0.72m 2 / g]] 98.1％ 92.26％ Fourth comparative example 8 um 0.80 m 2 / g]] 93.2％ 95.1％ Fifth comparative example 3 um 0.82m 2 / g]] 80.1％ 87.5％

[0165] As shown in Table 1, 1. Comparing the first embodiment and the first comparative example, the first embodiment, after being coated with magnesium oxide, showed improved cycle and rate performance, while the first comparative example, lacking magnesium oxide coating, exhibited a significant decrease in rate and cycle performance. 2. Comparing the particle size and specific surface area of ​​the first embodiment and the other comparative examples under different sintering process conditions (heating frequency, temperature, and sintering time) for the core material, the influence of specific surface area and particle size is significant. It is speculated that reducing the particle size increases the specific surface area, thereby increasing the contact area with the electrolyte, increasing side reactions, and deteriorating electrochemical performance.

[0166] The above description is merely a specific embodiment of this application, enabling those skilled in the art to understand or implement this application. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of this application. Therefore, this application is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features claimed herein.

Claims

1. A positive electrode active material, characterized by, comprising a core material of formula Na 2 / 3 Ni (2 / 5)-x Fe 1 / 5 Mn 2 / 5 Mg x O2, 0.01≤x≤0.07; and a cladding material of magnesium oxide. The preparation method of the positive electrode active material comprises: The nickel source, manganese source, iron source and magnesium source raw materials are weighed, water is added and mixed uniformly, a precursor Ni (2 / 5)-x Fe 1 / 5 Mn 2 / 5 Mg x (OH)2is generated by co-precipitation reaction. Sintering after mixing the sodium source raw material and the precursor to obtain the core layer material Na 2 / 3 Ni (2 / 5)-x Fe 1 / 5 Mn 2 / 5 Mg x O2; wherein, 0.01≤x≤0.07; After sintering, Na 2 / 3 Ni (2 / 5)-x Fe 1 / 5 Mn 2 / 5 Mg x O2 and heavy metal complexing agent are added to the magnesium salt solution and mixed uniformly, stirred, washed, filtered, and dried to obtain a positive electrode active material with a magnesium oxide coating layer and a Na 2 / 3 Ni (2 / 5)-x Fe 1 / 5 Mn 2 / 5 Mg x O2 core layer.

2. The method of producing the positive electrode active material according to claim 1, characterized by, The preparation method of the positive electrode active material comprises: The nickel source, manganese source, iron source and magnesium source raw materials are weighed, water is added and mixed uniformly, a precursor Ni (2 / 5)-x Fe 1 / 5 Mn 2 / 5 Mg x (OH)2is generated by co-precipitation reaction. Sintering after mixing the sodium source raw material and the precursor to obtain the core layer material Na 2 / 3 Ni (2 / 5)-x Fe 1 / 5 Mn 2 / 5 Mg x O2; wherein, 0.01≤x≤0.07; After sintering, Na 2 / 3 Ni (2 / 5)-x Fe 1 / 5 Mn 2 / 5 Mg x O2 and heavy metal complexing agent are added to the magnesium salt solution and mixed uniformly, stirred, washed, filtered, and dried to obtain a positive electrode active material with a magnesium oxide coating layer and a Na 2 / 3 Ni (2 / 5)-x Fe 1 / 5 Mn 2 / 5 Mg x O2 core layer.

3. The preparation method according to claim 2, characterized in that, The nickel source, the manganese source, the sodium source and the iron source are each a sulfate, a nitrate, a carbonate, a hydrochloride, a phosphate or a hydrate thereof of a metal ion.

4. The preparation method according to claim 2, characterized in that, The concentration of the magnesium salt in the magnesium salt solution is 0.01-0.03 mol / L.

5. The preparation method according to claim 2 or 4, characterized in that, The magnesium salt in the magnesium salt solution is one or more of magnesium sulfate, magnesium chloride and magnesium acetate.

6. The preparation method according to claim 2, characterized in that, The magnesium source is a magnesium oxide.

7. The preparation method according to claim 2, characterized in that, The concentration of the heavy metal complexing agent is 1-2 mol / L.

8. The preparation method according to claim 2 or 7, characterized in that, The heavy metal complexing agent is ammonia.

9. The preparation method according to claim 2, characterized in that, The sintering is performed at a first rate to 300-500 DEG C, holding for 2-10 hours, and then at a second rate to 800-1100 DEG C, holding for 8-20 hours.

10. The preparation method according to claim 9, characterized in that, The first rate and the second rate are independently selected from 1-10 DEG C / min.

11. A positive electrode sheet characterized by comprising: The positive electrode active material, a conductive agent, a binder and a current collector.

12. A sodium-ion battery, characterized in that, The positive electrode active material, a separator, an electrolyte, a tab and a negative electrode active material.

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