A sodium positive electrode active material, a preparation method thereof, a sodium ion battery, and an electric device

Abstract

The application provides a sodium positive electrode active material, a preparation method thereof, a sodium ion battery and a power utilization device. The sodium positive electrode active material meets the following conditions: pH1-pH2<=1.0, and both pH1 and pH2 are less than or equal to 13.0; wherein pH1 is a pH value of the sodium positive electrode active material tested by dissolving in water; and pH2 is a pH value of the sodium positive electrode active material tested by dissolving in an alcohol organic solvent. The sodium positive electrode active material is selected according to the pH difference in water and the alcohol organic solvent, so that the positive electrode active material with a stable layered structure, less reaction with water and being beneficial to battery processing can be more accurately screened, and a sodium ion battery material with good cycle performance and initial discharge specific capacity can be prepared.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of battery materials, and particularly relates to a sodium positive electrode active material, a preparation method thereof, a sodium ion battery and an electric device. BACKGROUND

[0002] With the rapid development of new energy vehicles and power grid energy storage, the consumption of lithium resources is increasing. Under this background, sodium ion batteries, which have the same working principle and similar battery components as lithium ion batteries, have attracted attention again. Sodium ion batteries not only have the advantages of abundant sodium resources, wide distribution, low cost, environmental friendliness and compatibility with existing lithium ion battery production equipment, but also have good power characteristics, wide temperature range adaptability, safety performance and no over-discharge problem. At the same time, by virtue of the feature that both the positive electrode and the negative electrode can adopt aluminum foil current collector to construct bipolar battery, the energy density of the sodium ion battery can be further improved, so that the sodium ion battery moves towards the direction of low cost, long life, high specific energy and high safety. Therefore, in some fields, sodium ion batteries are ideal energy technologies to replace lithium ion batteries, and in recent years, they have become a research hotspot in the academic and industrial fields.

[0003] Among sodium ion battery positive electrode active materials, layered materials have two-dimensional transmission channels, and sodium ions are transmitted faster. In addition, the compaction density of the layered material is higher, so that the sodium ion battery can have higher energy density and be applied more widely, and is a relatively ideal positive electrode material.

[0004] However, the layered material of the sodium ion battery also has some problems. The stability of the synthesized material in the air is poor, especially in humid air, which will further exacerbate the influence. The main problem is that the unstable layered material will react with water to generate more NaOH through Na-H exchange reaction. Because of the generation of a large amount of alkaline impurities, the pH of the material will increase significantly, and the water absorption will become serious, resulting in gelation of the slurry during the processing process, which makes it difficult to coat. In the subsequent electrochemical reaction process, the impurities will react with the electrolyte to increase the gas production, which seriously affects the cycle performance and safety performance.

[0005] Therefore, it is necessary to provide a sodium positive electrode active material with stable structure and poor water absorption to improve the processing performance and electrochemical performance of the battery. SUMMARY

[0006] The sodium positive electrode active material provided by the present application has a stable structure and is not easy to absorb water, and the difference between the pH value measured when the sodium positive electrode active material is dissolved in water and the pH value measured when the sodium positive electrode active material is dissolved in an alcohol organic solvent is less than or equal to 1.0, and the pH value measured when the sodium positive electrode active material is dissolved in an alcohol organic solvent and the pH value measured when the sodium positive electrode active material is dissolved in water are both less than 13. The sodium positive electrode active material provided by the present application has a stable layered structure, has less reaction with water, is beneficial to battery processing, can improve the cycle stability, reduces the safety risk, and can further improve the initial discharge specific capacity of the battery prepared by the sodium positive electrode active material.

[0007] Another object of the present application is to provide a preparation method of the sodium positive electrode active material.

[0008] Another object of the present application is to provide a sodium ion battery prepared by the sodium positive electrode active material.

[0009] Another object of the present application is to provide a power utilization device comprising the sodium ion battery.

[0010] To achieve the above object, the present application adopts the following technical solutions.

[0011] A sodium positive electrode active material, the sodium positive electrode active material comprising a layered metal oxide, the sodium positive electrode active material satisfying the following conditions:

[0012] pH1-pH2≤1.0, and both pH1 and pH2 are less than or equal to 13.0;

[0013] wherein pH1 is the pH value measured when the sodium positive electrode active material is dissolved in water; and pH2 is the pH value measured when the positive electrode active material is dissolved in an alcohol organic solvent.

[0014] The present application has found that, if the difference between the pH values measured when the prepared positive electrode active material is dissolved in water and in an alcohol organic solvent satisfies the above conditions, the layered structure of the positive electrode active material is relatively stable; the present inventors have also found that, if the pH of the positive electrode active material in the above two solvents is too high (e.g. greater than 13), the changeable pH value of water embedded in the molecule is limited, and the material with high alkalinity has a great impact on the battery performance, the gas production is intensified, and the cycle stability is sharply decreased. Therefore, within the above suitable pH range and with a small pH difference in the above two solvents, the structure of the positive electrode active material satisfying the above conditions is more stable, so that the sodium ion battery prepared by using the positive electrode active material has good cycle performance and initial discharge specific capacity.

[0015] It should be noted that the sodium positive electrode active material inevitably contains a certain amount of free sodium element, and these free metal ions will form alkali with OH - in water to increase the alkalinity of the material in aqueous solution. In addition, the undoped metal oxides (including sodium oxide, doped element oxides, etc.) will also absorb water and react to form alkali, further increasing the pH of the material in water. However, the sodium positive electrode active material is relatively stable in alcohol organic solvents and will not generate alkali to affect the pH of the solution, so it can reflect the properties of the active material itself. Therefore, the pH of the sodium positive electrode active material tested in water in the present application can reflect the content of water-absorbing impurities (such as free sodium ions and metal oxides) in the positive electrode active material to a certain extent. The smaller the pH difference of the active material in the two solvents, the less the content of water-absorbing impurities in the active material, the less the reaction of the material with water, and the more stable the layered structure of the positive electrode active material.

[0016] The pH difference of the active material in water and alcohol organic solvents can more accurately reflect the water absorption performance of the positive electrode active material. On the one hand, alcohol organic solvents will not react with free sodium or water-absorbing impurities such as sodium oxide and metal oxides to form alkali, and on the other hand, alcohol organic solvents will not ionize H + to affect the pH of the sodium positive electrode active material in its solution.

[0017] The pH test method of the solution includes but is not limited to titration and pH meter test.

[0018] Preferably, the pH1 of the positive electrode active material dissolved in water is 11.5-12.5, and the pH2 of the positive electrode active material dissolved in alcohol organic solvent is 11.0-12.5. If the pH value is too large, it indicates that the content of residual alkali (such as NaOH) in the positive electrode active material is high, which is easy to absorb water. During the preparation of the electrode active slurry, the binder PVDF will react with the residual alkali (i.e. free sodium) on the surface of the positive electrode active material, i.e. OH - in the residual alkali will undergo nucleophilic reaction with PVDF, and then rearrange to form conjugated polyenes. The conjugated double bonds in the polyenes will further undergo nucleophilic reaction with OH - , and the double bonds will be oxidized to carbonyl and hydroxyl groups. Finally, PVDF is degraded, and water is also generated in the process, causing PVDF to agglomerate and gel in water. The gelation of the slurry will cause the active slurry to form a non-uniform surface during coating. If the pH value is small, it indicates that there is less free sodium, the alkalinity of the material is weaker, and the water absorption is weaker, which will greatly reduce the reaction between the active material and the binder PVDF during stirring, and is beneficial to the stirring and coating of the electrode piece to form a uniform electrode piece and improve the cycle stability of the battery.

[0019] Preferably, the alcohol organic solvent comprises at least one of anhydrous methanol, anhydrous ethanol, and further preferably anhydrous ethanol.

[0020] Preferably, the content of water in the positive electrode active material is <1000 ppm. The size of solid water reflects the water absorption degree of the material, and when the water absorption is too much, the structure of the material will be destroyed, and the battery preparation process will be disturbed, which seriously affects the cycle performance and safety performance. In the present application, the water content is tested by Karl Fischer titration method in the standard "GB / T 24533-2019", and the equipment adopts Karl Fischer titrator, wherein 1 g of powder sample is heated at 200°C for 5 min, the gas flow rate is 50 mL / min, and the water content is obtained by the data displayed by the titrator.

[0021] The powder resistivity of the positive electrode active material under 20 kN is in the range of 3000-1000000 Ω·cm, which can meet the use of the battery, but the powder resistivity value of the positive electrode active material reflects the kinetic performance of the material, and is important for the process stability of the material and the resistance estimation of the finished battery. The powder resistance is too large, which affects the rate performance and causes low capacity. Therefore, the powder resistivity of the positive electrode active material under 20 kN is preferably 8000-35000 Ω·cm. In the present application, the powder resistivity is tested by four-probe method in the standard "GB / T 30835-2014", and the equipment adopts resistivity tester, wherein 10 g of powder sample is introduced into the mold, and then 20 KN pressure is applied to read the powder resistance by the instrument.

[0022] Preferably, the true density of the positive electrode active material is 4.2-4.4 g / cm 3 . For example, the true density can be 4.2 g / cm 3 , 4.3 g / cm 3 , 4.4 g / cm 3 , or a range composed of any two numerical values, and the true density is further preferably 4.3-4.4 g / cm 3 The true density is equal to the ratio of the mass of the positive electrode active material to the true volume of the positive electrode active material, wherein the true volume is the actual volume of the solid substance, and the true density affects the compaction density of the material, and further affects the energy density, initial discharge energy and other electrochemical performances of the battery. In the present application, the true density is tested by the method in the standard "GB / T 24533-2019", and the equipment adopts true density tester, wherein the volume of the sample cell is 10 cm 3 , and the sample cell is filled with not less than 2 / 3 of the sample amount, and the value is read by the true density instrument.

[0023] Optionally, the layered metal oxide comprises sodium nickel iron manganese oxide containing element Me, wherein the element Me comprises at least one of Zr, Mo, Al, Sr, Mg, W, Y, Nb, Ru, Ti or Ca element. The doping element can effectively enhance the structural stability of the material, and improve the cycle performance and safety performance. Ni, Fe and Mn elements are main elements constituting the layered metal oxide.

[0024] Preferably, the layered metal oxide comprises a compound of structural formula Na q Ni x Fe y Mn z Me p O2, wherein 0.67

[0025] Preferably, in the Na q Ni x Fe y Mn z Me p O2, 0.95 In the sodium positive electrode active material of the present application, a large amount of Na element is contained, and the increase of the content of Na element is beneficial to improve the energy density of the battery, and further improve the initial discharge capacity and other performances of the battery.

[0026] The preparation method of the sodium positive electrode active material comprises the following steps:

[0027] S1. Preparation of sodium positive electrode active material precursor

[0028] The salt solution of the main element metal, the precipitating agent and the complexing agent are mixed to obtain a mixed solution, under inert atmosphere, the pH of the mixed solution is controlled to be 11.0-12.0, after reaction at 50-60℃ for 12-48h, drying is performed to obtain the sodium positive electrode active material precursor;

[0029] S2. The sodium positive electrode active material precursor obtained in step S1., sodium salt and doping element oxide are uniformly mixed, and then pre-calcination is performed at 450-500℃ for 2-3h, and then calcination is performed at 800-900℃ for 10-14h, to obtain the sodium positive electrode active material.

[0030] In the present application, a suitable process is selected to prepare the precursor material, and then the prepared precursor material is calcined with sodium salt and doping elements: on the one hand, more sodium elements can be doped, more sodium elements can generate sodium-rich phases, which can provide more de-embeddable sodium ions for electrochemical reaction, and the capacity will be higher, thereby improving the energy density of the battery; on the other hand, the precursor element distribution is more uniform, the morphology is more regular, and the reaction activity is higher, which can more firmly fix the generated sodium oxide in the precursor material, reduce the content of free sodium and free sodium oxide in the sodium positive electrode active material, and improve the stability of the material.

[0031] Preferably, the base metal salt in the base metal salt solution is at least one of a sulfate, a nitrate, an acetate, an oxalate or a chloride of the base metal.

[0032] The sodium salt includes but is not limited to at least one of sodium carbonate, sodium nitrate, sodium sulfate, sodium acetate or sodium oxalate.

[0033] Both conventional precipitants and complexing agents can be used in the present application. The precipitant includes but is not limited to sodium hydroxide; the complexing agent includes but is not limited to ammonia.

[0034] The inert atmosphere is an atmosphere formed by mixing at least one of nitrogen, argon or helium.

[0035] Preferably, the calcination in step S2 is carried out in an atmosphere containing oxygen, the temperature of the calcination is 800-900℃, the time of the calcination is 10-14h, and the heating rate of the calcination is 3-5℃ / min.

[0036] The present application also protects a sodium ion battery prepared from the above-mentioned sodium positive electrode active material. The sodium ion battery comprises a positive electrode sheet, the positive electrode sheet comprises a positive electrode current collector and a sodium positive electrode active material layer arranged on the positive electrode current collector, and the sodium positive electrode active material layer comprises the above-mentioned sodium positive electrode active material.

[0037] A power utilization device comprising the sodium ion battery is also within the protection scope of the present application.

[0038] Compared with the prior art, the present application has the following beneficial effects:

[0039] The present application selects the pH difference of the sodium positive electrode active material in water and alcohol organic solvents for screening, which can more accurately screen the positive electrode active material with stable layered structure, less reaction with water and being beneficial to battery processing, and can prepare a sodium ion battery material with good cycle performance and initial discharge specific capacity. BRIEF DESCRIPTION OF DRAWINGS

[0040] Figure 1SEM image of the sodium positive electrode active material prepared for Example 1;

[0041] Figure 2 SEM image of the sodium positive electrode active material prepared for Comparative Example 4. DETAILED DESCRIPTION

[0042] For the purpose of better illustrating the object, technical scheme and advantages of the present application, the present application will be further described below in conjunction with specific examples and drawings, but the examples do not limit the present application in any form. Unless otherwise specified, the reagents, methods and devices used in the present application are conventional reagents, methods and devices in the technical field. Unless otherwise specified, the reagents and materials used in the present application are commercially available.

[0043] Example 1

[0044] The present embodiment provides a sodium positive electrode active material with the chemical formula Na(Ni 0.33 Fe 0.33 Mn 0.33 ) 0.998 Zr 0.002 O2, and the preparation method comprises the following steps:

[0045] S1. Preparation of sodium positive electrode active material precursor

[0046] Nickel nitrate, ferrous nitrate and manganese nitrate were configured into a mixed metal salt solution with a concentration of 2 mol / L according to a molar ratio of 0.33:0.33:0.33; a sodium hydroxide solution with a concentration of 4 mol / L was configured; and an ammonia water solution with a concentration of 6 mol / L was configured;

[0047] Equal volumes of the mixed metal salt solution, the precipitant sodium hydroxide solution and the complexing agent ammonia water solution were synchronously added into a reaction kettle, the stirring speed was controlled at 300 rpm during the reaction, the temperature was controlled at 55°C, the pH was maintained at 11.5, the reaction was carried out for 36 h, nitrogen gas was continuously introduced as a protective gas to prevent metal oxidation during the reaction, the nitrogen gas flow rate was 15 m 3 / h, and the precursor Ni 0.33 Fe 0.33 Mn 0.33 (OH)2was prepared after washing and drying after the reaction.

[0048] S2. The sodium positive electrode active material precursor obtained in step S1., sodium carbonate and ZrO2were mixed uniformly according to a molar ratio of 0.998:1.03:0.002 (sodium excess to prevent trace sodium loss during high-temperature calcination), and then placed in an oxygen furnace for calcination, the oxygen flow rate was 10 m 3 / h, preheated from room temperature (25°C) to 450°C at a temperature increase rate of 3°C / min, kept for 3h, then continued to heat to 800°C, calcined at this temperature for 12h, after calcination, naturally cooled to room temperature, then crushed and classified to obtain the sodium positive electrode active material Na(Ni 0.33 Fe 0.33 Mn 0.33 ) 0.998 Zr 0.002 O2.

[0049] Example 2

[0050] This example provides a sodium positive electrode active material, chemical formula is Na(Ni 0.33 Fe 0.33 Mn 0.33 ) 0.998 Zr 0.002 O2, the difference between the preparation method and example 1 is that the reaction time in step S1. is 24h, and the temperature increase rate in step S2. is 5°C / min.

[0051] Example 3

[0052] This example provides a sodium positive electrode active material, chemical formula is Na(Ni 0.33 Fe 0.33 Mn 0.33 ) 0.998 Zr 0.002 O2, the difference between the preparation method and example 1 is that the reaction time in step S1. is 48h.

[0053] Example 4

[0054] This example provides a sodium positive electrode active material, chemical formula is Na(Ni 0.33 Fe 0.33 Mn 0.33 ) 0.998 Zr 0.002 O2, the difference between the preparation method and example 1 is that the reaction temperature in step S1. is 50°C.

[0055] Example 5

[0056] This example provides a sodium positive electrode active material, chemical formula is Na(Ni 0.33 Fe 0.33 Mn 0.33 ) 0.998 Zr 0.002 O2, the difference between the preparation method and example 1 is that the reaction temperature in step S1. is 60°C.

[0057] Example 6

[0058] The present embodiment provides a sodium positive electrode active material with a chemical formula of Na(Ni 0.33 Fe 0.33 Mn 0.33 ) 0.998 Zr 0.002 O2, the difference between the preparation method and embodiment 1 is that the pH of the mixed solution in step S1. is 11.0.

[0059] Embodiment 7

[0060] The present embodiment provides a sodium positive electrode active material with a chemical formula of Na(Ni 0.33 Fe 0.33 Mn 0.33 ) 0.998 Zr 0.002 O2, the difference between the preparation method and embodiment 1 is that the pH of the mixed solution in step S1. is 12.0.

[0061] Embodiments 8-13

[0062] The type and proportion of the doping elements are changed, and the sodium positive electrode active materials are prepared according to the method of embodiment 1, the chemical formula of the sodium positive electrode active materials of embodiments 8-13 is shown in Table 1:

[0063] Table 1 Chemical composition of the sodium positive electrode active materials of embodiments 8-13

[0064] Examples Doping elements Chemical formula Example 8 [ZrO2, SrO2] Na(Ni 0.33 Fe 0.33 Mn 0.33 ) 0.998 Sr 0.001 Zr 0.001 O2]]> Example 9 Zr02, Mo03, Ce02 Na(Ni 0.33 Fe 0.33 Mn 0.33 ) 0.996 Zr 0.002 Mo 0.001 Ce 0.001 O2]]> Example 10 [WO3, SrO2, Nb2O3] Na(Ni 0.33 Fe 0.33 Mn 0.33 ) 0.992 W 0.004 Sr 0.002 Nb 0.002 O2]]> Example 11 Zr02, MgO, AI2O3 Na(Ni 0.33 Fe 0.33 Mn 0.33 ) 0.990 Zr 0.003 Mg 0.004 Al 0.003 O2]]> Example 12 CaO2, RuO2 Na(Ni 0.6 Fe 0.2 Mn 0.2 ) 0.996 Ca 0.002 Ru 0.002 O2]]> Example 13 [Zr02, Y02, MgO] Na(Ni 0.6 Fe 0.2 Mn 0.2 ) 0.996 Zr 0.002 Y 0.001 Mg 0.001 O2]]>

[0065] Comparative example 1

[0066] The present comparative example provides a sodium positive electrode active material, which is prepared according to the method of embodiment 1, the difference between the present comparative example and embodiment 1 is that the pH of the mixed solution in step S1. is 13.0.

[0067] Comparative example 2

[0068] The present comparative example provides a sodium positive electrode active material, which is prepared according to the method of embodiment 1, the difference between the present comparative example and embodiment 1 is that the calcination time at 800℃ in step S2. is 8h.

[0069] Comparative example 3

[0070] The present comparative example provides a sodium positive electrode active material, which is prepared according to the method of embodiment 1, the difference between the present comparative example and embodiment 1 is that the calcination temperature in step S2. is 700℃.

[0071] Comparative example 4

[0072] The comparative example provides a sodium positive electrode active material, which is prepared according to the method of Example 1, and is different from Example 1 in that no pre-calcination is performed in step S2, but is directly heated to 800°C for calcination for 15h.

[0073] Comparative Example 5

[0074] The comparative example provides a sodium positive electrode active material, which is prepared according to the method of Example 1, and is different from Example 1 in that the pre-calcination temperature in step S2 is 400°C.

[0075] Performance test

[0076] The performance of the sodium positive electrode active materials obtained in the above examples and comparative examples and the sodium ion batteries prepared therefrom is tested, and the specific test items, test methods and results are as follows:

[0077] 1. Physical property parameter characterization of the sodium positive electrode active material:

[0078] 1) The sodium positive electrode active material is dissolved in deionized water to prepare a solution with a concentration of 0.1 g / mL, and the pH of the solution is tested by a pH meter, which is recorded as pH1; the sodium positive electrode active material is dissolved in anhydrous ethanol to prepare a solution with a concentration of 0.1 g / mL, and the pH of the solution is tested by a pH meter, which is recorded as pH2;

[0079] 2) Powder resistivity (Ω·cm): tested by the four-probe method in GB / T 30835-2014, and the resistivity tester is used, wherein 10 g of the powder sample is introduced into a mold, and then a pressure of 20 KN is applied to read the powder resistivity by the instrument;

[0080] 3) True density (denoted as ρ 真 , g / cm 3 ): tested according to the method in the standard GB / T 24533-2019, and the true density tester is used, wherein the volume of the sample cell is 10 cm 3 , and not less than 2 / 3 of the sample is loaded in the sample cell, and the value is read by the true density tester;

[0081] 4) Solid moisture content (ppm): tested by the Karl Fischer titration method in the standard GB / T 24533-2019, and the Karl Fischer titrator is used, wherein 1 g of the powder sample is heated at a temperature of 200°C for 5 min, and the air flow rate is 50 mL / min, and the moisture content is obtained by the data displayed by the titrator;

[0082] 5) Morphology characterization: the surface morphology of the obtained positive electrode active material is characterized by a scanning electron microscope (SEM), and the test results are shown in Figure 1 and Figure 2It can be seen from the figure that when the pH value is low, the obtained positive electrode material is uniformly dispersed, and the fine powder is less (such as Figure 1 The active material of embodiment 1 shown in the figure), which is beneficial to improve the cycle stability of the material.

[0083] The test results are shown in Table 2.

[0084] 2. Battery performance test:

[0085] The sodium positive electrode active material, the conductive agent conductive carbon black and the binder polyvinylidene fluoride (PVDF) are mixed in a mass ratio of 95:3:2, a solvent N-methyl pyrrolidone (NMP) is added and stirring is performed in a vacuum stirrer, a uniform positive electrode slurry is prepared after the stirring is completed, the positive electrode slurry is uniformly coated on an aluminum foil positive electrode current collector with a thickness of 16 microns, drying is performed in an oven at 100 DEG C after the coating is completed, then the positive electrode sheet is prepared after rolling, slitting and cutting.

[0086] The stability of the positive electrode slurry is also tested, and the discharge viscosity and the viscosity after standing for 24 hours are compared for evaluation, wherein the test method of the viscosity (mPa.s) is as follows: the viscosity is tested by using a viscosity tester, 500 mL of the positive electrode slurry is taken into a beaker, then the corresponding rotor is put in, the parameters are set for testing, and the viscosity value is read through the display on the tester;

[0087] The resistivity (Ω.cm) of the positive electrode sheet is tested by using a diaphragm resistance tester, the sheet is placed on a workbench, the test area is 1540mm 2 , the sampling time is 15s, the test number is 20 times, the reading is read through the display on the tester, and then the average value is taken, that is, the resistivity (Ω.cm) of the positive electrode sheet.

[0088] The hard carbon, sodium carboxymethyl cellulose, conductive carbon black and butadiene-styrene rubber are mixed in a mass ratio of 96.5:1.5:1.5:0.5, then water is added to mix uniformly to prepare a negative electrode slurry, and the negative electrode slurry is coated on the surface of a negative electrode current collector to obtain a negative electrode sheet.

[0089] The positive electrode sheet, the separator (PP film) and the negative electrode sheet prepared above are stacked in order, the separator is just between the positive electrode and the negative electrode to play a role of isolating the two electrodes, then the bare cell is wound into an aluminum plastic film, is baked at 80 DEG C to remove water, after the water is removed, an electrolyte (1 mol / L sodium hexafluorophosphate is dissolved in an organic solvent (volume ratio EC:DMC:DEC = 1:1:1), 10wt% of fluoroethylene carbonate (FEC) is added as an electrolyte, then after sealing, hot and cold pressing, formation and capacity, a sodium ion battery is obtained.

[0090] In the performance test of the battery, the first charge is 0.1C constant current charging to 3.9V, and the first discharge is 0.1C constant current discharging to 1.5V: 1) the cycle performance test is the cycle number (the maximum cycle number that the capacity retention rate can maintain 80%) at 25℃ / 45℃ constant temperature, the voltage interval is 1.5-3.8V, and 1C constant current constant voltage charging (the cutoff current is 0.05C when the constant voltage is cut off) and constant current discharging are used; 2) the initial discharge specific capacity (mAh / g) test: first use 0.1C to charge the soft package cell at room temperature (constant current constant voltage charging, the cutoff current is 0.02C when the constant voltage is cut off), the upper limit of the voltage is 3.9V, and then use 0.1C to discharge after standing for 5min, the lower limit of the voltage is 1.5V. The test results are shown in Table 2.

[0091] Table 2 Performance test results of sodium positive active material battery

[0092]

[0093] From the above results, it can be seen that:

[0094] When the pH value is low, and the difference between the test pH values obtained by different test methods is small, the structural stability of the material is improved, and the cycle performance of the battery is improved; however, when the pH value is large to a certain extent (such as the pH of Comparative Examples 1-3 is greater than 13), even if the difference between the test values obtained by different solvents is very small, the cycle performance of the battery is still poor, which is mainly because there is too much residual alkali on the surface of the material, and the structure is already very unstable, and the solvent, whether it is water or ethanol, will dissolve more alkali, and the gas production will be intensified, so the cycle stability will also be severely deteriorated.

[0095] Finally, it should be noted that the above examples are only used to illustrate the technical solutions of the present application and not to limit the protection scope of the present application. Although the present application has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solutions of the present application can be modified or replaced by equivalents without departing from the essence and scope of the technical solutions of the present application.

Claims

1. A sodium positive electrode active material comprising a layered metal oxide, characterized in that, The layered metal oxide comprises sodium nickel iron manganese oxide containing element Me, the element Me comprising at least one of Zr, Mo, Al, Sr, Mg, W, Y, Nb, Ru, Ti or Ca element; the sodium positive electrode active material satisfies the following conditions: pH1-pH2≤1.0, and both pH1 and pH2 are less than or equal to 13.0; pH2 is 11.0-12.5; wherein, pH1 is the pH value of the sodium positive electrode active material tested by dissolving in water; pH2 is the pH value of the sodium positive electrode active material tested by dissolving in an alcohol organic solvent; The sodium positive electrode active material is dissolved in deionized water to prepare a solution with a concentration of 0.1 g / mL, a pH meter is used to test the pH of the solution, which is recorded as pH1; the sodium positive electrode active material is dissolved in anhydrous ethanol to prepare a solution with a concentration of 0.1 g / mL, a pH meter is used to test the pH of the solution, which is recorded as pH2.

2. The sodium positive electrode active material according to claim 1, characterized in that The pH1 of the sodium positive electrode active material tested by dissolving in water is 11.5-12.

5.

3. The sodium positive electrode active material of claim 1, wherein The layered metal oxide comprises a compound of formula Na q Ni x Fe y Mn z Me p O2, wherein 0.67 < q < 1.1, 0 < x < 0.5, 0 < y < 0.5, 0 < z < 0.5, 0 < p < 0.05, x + y + z + p = 1.

4. The sodium positive electrode active material of claim 1, wherein The content of water in the sodium positive electrode active material is <1000 ppm.

5. The sodium positive electrode active material of claim 1, wherein The powder resistivity of the sodium positive electrode active material is 8000-35000 Ω·cm under 20 kN.

6. The sodium cathode active material of claim 1, wherein The true density of the sodium positive electrode active material is 4.3-4.4 g / cm 3 .

7. The method of producing a sodium positive electrode active material according to any one of claims 1 to 6, characterized by, Comprising the following steps: S1. Preparing a sodium positive electrode active material precursor Mixing a salt solution of main element metal, a precipitating agent and a complexing agent to obtain a mixed solution, controlling the pH of the mixed solution to be 11.0-12.0 under an inert atmosphere, drying after reacting at 50-60℃ for 12-48 h to obtain a sodium positive electrode active material precursor; S2. Mixing the sodium positive electrode active material precursor obtained in step S1., sodium salt and doped element oxide uniformly, then pre-calcining at 450-500℃ for 2-3 h, and then calcining at 800-900℃ for 10-14 h to obtain the sodium positive electrode active material.

8. A sodium-ion battery comprising a positive electrode sheet, characterized by, The positive electrode sheet comprises a positive electrode current collector and a sodium positive electrode active material layer arranged on the positive electrode current collector, and the sodium positive electrode active material layer comprises the sodium positive electrode active material according to any one of claims 1-6.

9. An electrical device, characterized by The sodium ion battery comprising the sodium positive electrode active material according to claim 8.

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