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CN116995222B - Sodium ion positive electrode material with low residual alkali content and preparation method and application thereof - Google Patents

Sodium ion positive electrode material with low residual alkali content and preparation method and application thereof Download PDF

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CN116995222B
CN116995222B CN202311244623.9A CN202311244623A CN116995222B CN 116995222 B CN116995222 B CN 116995222B CN 202311244623 A CN202311244623 A CN 202311244623A CN 116995222 B CN116995222 B CN 116995222B
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positive electrode
electrode material
sodium ion
ion positive
sodium
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CN116995222A (en
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赵建明
蔡伟华
郭启涛
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Shenzhen Huaxin Material Co ltd
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Shenzhen Huaxin Material Co ltd
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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/48—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides
    • H01M4/50—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of manganese
    • H01M4/505—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of manganese of mixed oxides or hydroxides containing manganese for inserting or intercalating light metals, e.g. LiMn2O4 or LiMn2OxFy
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M10/00—Secondary cells; Manufacture thereof
    • H01M10/05—Accumulators with non-aqueous electrolyte
    • H01M10/054—Accumulators with insertion or intercalation of metals other than lithium, e.g. with magnesium or aluminium
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/362—Composites
    • H01M4/366—Composites as layered products
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/48—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides
    • H01M4/52—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of nickel, cobalt or iron
    • H01M4/525—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of nickel, cobalt or iron of mixed oxides or hydroxides containing iron, cobalt or nickel for inserting or intercalating light metals, e.g. LiNiO2, LiCoO2 or LiCoOxFy
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/62—Selection of inactive substances as ingredients for active masses, e.g. binders, fillers
    • H01M4/628—Inhibitors, e.g. gassing inhibitors, corrosion inhibitors
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M2004/021—Physical characteristics, e.g. porosity, surface area
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M2004/026—Electrodes composed of, or comprising, active material characterised by the polarity
    • H01M2004/028—Positive electrodes
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
    • Y02E60/10—Energy storage using batteries

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Abstract

The invention relates to a sodium ion positive electrode material with low residual alkali content, and a preparation method and application thereof. According to the invention, the non-metal element is adopted to coat the sodium ion positive electrode material, meanwhile, the crushing and screening treatment is carried out under the environment of specific humidity and carbon dioxide concentration, and a small amount of specific doping elements are added, so that the residual alkali content on the surface of the material can be obviously reduced, the residual alkali content on the surface can be further obviously reduced after the subsequent high-temperature treatment process, the structural stability and the processability of the material are improved, the irreversible removal of sodium ions and the release of lattice oxygen are inhibited, the gram capacity, the energy density, the multiplying power performance, the cycle life and the safety of the positive electrode material can be obviously improved, and the gas production is reduced.

Description

Sodium ion positive electrode material with low residual alkali content and preparation method and application thereof
Technical Field
The invention relates to the technical field of materials, in particular to a sodium ion positive electrode material with low residual alkali content, and a preparation method and application thereof.
Background
Since the commercialization of lithium ion batteries in 1991, lithium ion battery technology has been rapidly developed, while contemporary sodium ion batteries have been slowly developed. The lithium ion battery has the advantages of high energy density, no memory effect, good cycle performance, good multiplying power performance and the like, has been widely used in the fields of various portable equipment, electric automobiles and the like, occupies more than 90% of the novel energy storage market, and is developed at a high speed. The limited global lithium resource reserves are insufficient for supporting the electric vehicle and the energy storage market simultaneously, novel markets such as an electric airplane and a ship are not included, lithium resources are unevenly distributed, so that the price fluctuation of the lithium ion battery is large, and the industry development is not facilitated.
The sodium and lithium are the same, the sodium ion battery principle is the same as that of the lithium ion battery, most materials and battery equipment can be used commonly, the sodium resource storage in the crust is high, the distribution is uniform, the cost is far lower than that of the lithium, and therefore, the expected cost of the sodium ion battery is only lower than 70% of that of the lithium ion battery, and the market space is wide.
Compared with polyanion compounds and Prussian blue positive electrode materials, the layered oxide positive electrode material has higher specific capacity and meets the market demand of needing higher energy density. Iron-based and manganese-based oxide cathode materials have received wide attention due to their high theoretical gram capacity, low cost, and environmental protection. But the iron-based actual reversible gram capacity is very low; the manganese-based oxide anode material has the problems of complex phase change, JT effect, metal dissolution and the like, so that the capacity of the material is fast attenuated and cannot be applied. The surface of the material contains a large amount of residual alkali, including sodium oxide, sodium hydroxide, sodium carbonate and sodium bicarbonate, after the sodium oxide and the water react to form sodium hydroxide after contacting water and carbon dioxide in the air, bulk sodium migrates outwards, sodium carbonate and sodium bicarbonate are generated by the reaction of sodium hydroxide and carbon dioxide, and the negative effects of capacity reduction, resistance increase, poor processability, gas production increase, circulation performance reduction and the like of the positive electrode material are caused. Post-treatment processes such as washing and heat treatment means increase costs. Therefore, there is a strong market demand for positive electrode materials with high reversible capacity, long cycle life, low cost, high rate capability, high voltage plateau, excellent processability.
Disclosure of Invention
The invention aims to solve the problems of overhigh residual alkali content on the surface of a sodium ion positive electrode material and increased residual alkali content in the processing process in the prior art, thereby providing the sodium ion battery oxide positive electrode material, which has obviously reduced residual alkali content on the surface, high reversible specific capacity, good rate capability, high safety, long cycle life, low cost, high voltage platform, good processing performance and environment-friendly process.
In order to solve the technical problems, the invention is realized by the following technical scheme.
The first aspect of the invention provides a sodium ion positive electrode material with low residual alkali content, the molecular formula of which is Na 1-x [Mn y M z ]M’ a R b O 2-c X c The method comprises the steps of carrying out a first treatment on the surface of the Wherein M is selected from Li, mg, ca, al, ni, cu, zn, zr, nb, co, ti, Y, sc, fe, cr, W,One or more of La, mo and Sr; m' is selected from one or more of Mg, ca, al, cu, zn, ni, zr, nb, co, ti, Y, sc, sr, ce, fe, cr, W, la, mo and Sr; r is selected from one or more of nonmetallic elements; x is selected from one or more of halogen elements;
the surface residual alkali content of the sodium ion positive electrode material meets the following conditions:
（1）m（NaOH、Na 2 O）/m（Na 2 CO 3 、NaHCO 3 ）＜1；
（2）m（Na 2 CO 3 、NaHCO 3 ）＜3400ppm；
（3）m（NaOH、Na 2 O）＜1000ppm。
preferably, the surface residual alkali content of the sodium ion positive electrode material satisfies the following conditions:
（1）m（NaOH、Na 2 O）/m（Na 2 CO 3 、NaHCO 3 ）＜0.5；
（2）m（Na 2 CO 3 、NaHCO 3 ）＜2000ppm；
（3）m（NaOH、Na 2 O）＜750ppm。
preferably, the M is selected from one or more of Cu, zn and Mg; most preferably, the M is selected from Mg.
Preferably, the M' is selected from one or more of Ca, ce and Fe; most preferably, the M' is selected from Ca.
Preferably, the nonmetallic element is selected from one or more of B, N, P, S, si; most preferably, the nonmetallic element is selected from one or more of B, P.
Preferably, the halogen element is selected from one or more of F, cl, br, I.
Preferably, -0.1.ltoreq.x.ltoreq. 0.4,0.2.ltoreq.y.ltoreq. 0.8,0.1.ltoreq.z.ltoreq.0.8, 0.ltoreq.a.ltoreq.0.1, 0 < b.ltoreq.0.1, 0.ltoreq.c.ltoreq.0.2.
It is to be understood that x, y, z, a, b, c and the like in the context of the present invention represent the elements of a sodium ion positive electrode material unless otherwise specifiedThe relative proportions of the amounts of the element substances, for example, when x=0.2, y=0.48, z=0.5, a=0.02, b=0.1, c=0.05, the molecular formula of the sodium ion positive electrode material is Na 0.8 [Mn 0.48 M 0.5 ]M’ 0.02 R 0.1 O 1.95 X 0.05 。
Preferably, the tap density of the sodium ion positive electrode material is more than or equal to 1.3g/cm 3 The compaction density is more than or equal to 2.4g/cm 3 The method comprises the steps of carrying out a first treatment on the surface of the More preferably, the tap density of the sodium ion positive electrode material is more than or equal to 1.4g/cm 3 The compaction density is more than or equal to 2.9g/cm 3 The method comprises the steps of carrying out a first treatment on the surface of the Most preferably, the tap density of the sodium ion positive electrode material is more than or equal to 1.9g/cm 3 The compaction density is more than or equal to 3.0g/cm 3 。
Preferably, the specific surface area BET of the sodium ion positive electrode material is: 0.1m 2 /g≤BET≤3m 2 /g; most preferably, the specific surface area BET of the sodium ion positive electrode material is: 0.15m 2 /g≤BET≤1.5m 2 /g。
Preferably, the particle size D50 of the sodium ion positive electrode material is: d50 is more than 0.5 mu m and less than 20 mu m; most preferably, the particle size D50 of the sodium ion positive electrode material is: d50 is more than 2 μm and less than 12 μm.
Preferably, the residual alkali content of the sodium ion positive electrode material after high-temperature treatment meets the following conditions: 0 << 1; wherein,
；/>is the total content of soluble alkali on the surface of the sodium ion positive electrode material before high-temperature treatment; />Total content of surface soluble alkali of the treated sodium ion positive electrode material.
As a preferred alternative to this,＜0.9。
preferably, the temperature of the high temperature treatment is 550-950 ℃.
The second aspect of the invention provides a preparation method of the sodium ion positive electrode material with low residual alkali content, which comprises the following steps:
(1) Preparing a precursor material from a sodium source, a manganese source, an M source and an M' source;
(2) The method comprises the steps of performing primary sintering on a precursor material, cooling to room temperature, and sequentially crushing and screening to obtain a primary sintered product; wherein, the environmental humidity is less than or equal to 0.5 (1+x) (1.5-y) RH% and the carbon dioxide content is less than or equal to 100 (1+x) (1.5-y) ppm in the crushing and screening processes;
(3) Uniformly mixing the first sintering product with an R source, performing secondary sintering, cooling to room temperature, and then crushing and screening to obtain the composite material; wherein, the environmental humidity is less than or equal to 0.3 (1+x) (1.5-y) RH% and the carbon dioxide content is less than or equal to 50 (1+x) (1.5-y) ppm in the process of crushing and sieving.
Preferably, the precursor material in the step (1) may be prepared by one or more of a solid phase method and a liquid phase method.
Preferably, the solid phase method specifically comprises the following steps:
uniformly mixing a sodium source, a manganese source, an M source and an M' source according to a proportion to prepare the precursor material.
Preferably, the sodium source is selected from one or more of sodium hydroxide, sodium carbonate, sodium bicarbonate, sodium acetate, sodium manganate, sodium nitrate, sodium sulfate, sodium oxalate, sodium chloride, sodium dihydrogen phosphate, sodium phosphate, disodium hydrogen phosphate, sodium borate, sodium citrate, and sodium fluoride.
Preferably, the manganese source is selected from one or more of oxides of manganese, hydroxides of manganese, carbonates of manganese.
Preferably, the M source is selected from one or more of oxides, hydroxides, carbonates of element M.
Preferably, the source of M 'is selected from one or more of the oxides, hydroxides, carbonates, oxyhydroxides, phosphates, fluorides, borides and oxalates of element M'.
Preferably, a solvent is optionally added during the mixing of the sodium source, the manganese source, the M source, and the M' source.
Preferably, the solvent is selected from ethanol.
The method has the advantages of simple operation, easy adjustment of the composition proportion and high compaction density of the prepared positive electrode material by mixing the raw materials in a solid form, so that the prepared precursor of the positive electrode material containing the sodium ferromanganese has the good effects of low price, easy preparation, easy adjustment of the composition, high compaction density and the like; wherein, the addition of solvents such as ethanol and the like is helpful for improving the mixing uniformity degree of each component.
Preferably, the liquid phase method specifically comprises the following steps:
(a) Preparing manganese salt and M salt to obtain mixed salt solution; preparing a precipitant solution and a complexing agent solution respectively;
(b) The mixed salt solution, the precipitator solution and the complexing agent solution are flowed into a reaction kettle to carry out coprecipitation reaction, a solid-liquid mixture is obtained and then filtered, and a filter cake is dried and screened to obtain an intermediate;
(c) And uniformly mixing the intermediate with a sodium source and an M' source.
Preferably, the manganese salt in step (a) is selected from one or more of manganese nitrate, manganese sulfate, manganese carbonate, manganese acetate and halogenated manganese.
Preferably, the salt of M in step (a) is selected from one or more of nitrate, sulfate, carbonate, acetate, halo salts of element M.
Preferably, the temperature of the coprecipitation reaction in step (b) is 20-60 ℃, the pH value is 4-11, the rotational speed of the reaction is 400-1000rpm, and the reaction time is 10-25h.
Preferably, the sodium source in step (c) is selected from one or more of sodium hydroxide, sodium carbonate, sodium bicarbonate, sodium acetate, sodium manganate, sodium nitrate, sodium sulfate, sodium oxalate, sodium dihydrogen phosphate, sodium phosphate, disodium hydrogen phosphate, sodium borate, sodium chloride, sodium citrate and sodium fluoride.
Preferably, the source of M 'in step (c) is selected from one or more of the oxides, hydroxides, carbonates, oxyhydroxides, phosphates, fluorides, borides and oxalates of the element M'.
According to the method, the raw materials are subjected to coprecipitation in a solution mode to obtain the intermediate, and the intermediate, the sodium source and the M' source are uniformly mixed, so that the element distribution is more uniform, the activity of the precursor is high, the morphology is controllable, and the prepared precursor of the sodium-ferromanganese-containing anode material has good effects of easiness in high-temperature reaction, easiness in morphology control and the like. It should be understood that the precipitants and complexing agents used are all of the type commonly used in liquid phase processes in the art, e.g., sodium hydroxide is selected as the precipitant, ammonia is selected as the complexing agent, etc., and the concentration thereof can be selected and adjusted by those skilled in the art.
Preferably, the environmental humidity in the crushing and sieving process in the step (2) is less than or equal to 0.3 (1+x) (1.5-y) RH, and the carbon dioxide content is less than or equal to 50 (1+x) (1.5-y) ppm.
Preferably, the temperature of the first sintering in step (2) is T1, wherein T1 satisfies the following condition: 350 (1-x) (1.5-y) T1 is less than or equal to 850 (1-x) (3-y) and the unit is the temperature; most preferably, T1 satisfies the following condition: 500 (1-x) (1.5-y) T1 is less than or equal to 800 (1-x) (3-y) and the unit is the temperature.
Preferably, the time of the first sintering in the step (2) is 6 to 20 hours.
Preferably, in the step (2), dry air is also introduced during the first sintering, and the introduced amount of the dry air is 0.1-1m 3 The humidity of the dry air is less than or equal to 1.5 RH%/h/kg; most preferably, the air quantity is 0.15-0.8m 3 And/h/kg, wherein the humidity of the dry air is less than or equal to 1.2RH percent.
Preferably, the environmental humidity in the crushing and sieving process in the step (3) is less than or equal to 0.2 (1+x) (1.5-y) RH, and the carbon dioxide content is less than or equal to 40 (1+x) (1.5-y) ppm.
Preferably, the temperature of the second sintering in step (3) is T2, wherein T2 satisfies the following condition: 400 (1-x) (1.5-y) T2 is less than or equal to 800 (1-x) (3-y) and the unit is the temperature. Most preferably, T2 satisfies the following condition: 500 (1-x) (1.5-y) T2 is less than or equal to 750 (1-x) (3-y) and the unit is the temperature.
Preferably, the time of the second sintering in the step (3) is 4-15h.
Preferably, in the second sintering process in the step (3), drying air is also introduced, wherein the introduced amount of the drying air is 0.01-0.5m 3 The humidity of the dry air is less than or equal to 0.5RH percent; most preferably, the air is introduced in an amount of 0.05-0.4m 3 And/h/kg, wherein the humidity of the dry air is less than or equal to 0.4RH percent.
Preferably, the R source is selected from one or more of oxides, hydroxides, salts of the element R.
The third aspect of the invention provides a positive plate, which comprises the sodium ion positive material with low residual alkali content and/or the sodium ion positive material with low residual alkali content prepared by the preparation method.
Preferably, the sodium ion positive electrode material with low residual alkali content and/or the sodium ion positive electrode material with low residual alkali content prepared by the preparation method account for 80% wt of the total mass of the positive electrode sheet; more preferably, the sodium ion positive electrode material with low residual alkali content and/or the sodium ion positive electrode material with low residual alkali content prepared by the preparation method accounts for 85% wt of the total mass of the positive electrode sheet; most preferably, the sodium ion positive electrode material with low residual alkali content and/or the sodium ion positive electrode material with low residual alkali content prepared by the preparation method account for 95% wt of the total mass of the positive electrode sheet.
Preferably, the positive electrode sheet further includes an auxiliary agent. The auxiliary agent is of the type commonly used in the art, such as a conductive agent, a binder, and the like; the type and amount of the auxiliary are not particularly limited, and those skilled in the art can routinely select and adjust the auxiliary according to the need.
Preferably as a result ofThe density of the positive plate is more than or equal to 2.9g/cm 3 The method comprises the steps of carrying out a first treatment on the surface of the More preferably, the pole piece density of the positive pole piece is more than or equal to 3g/cm 3 The method comprises the steps of carrying out a first treatment on the surface of the Most preferably, the pole piece density of the positive pole piece is more than or equal to 3.0g/cm 3 . The electrode plate density of the positive electrode plate is measured by weighing the mass of the electrode plate active substance and dividing the mass by the electrode plate area.
The fourth aspect of the invention provides a sodium ion positive electrode material with low residual alkali content and/or application of the sodium ion positive electrode material with low residual alkali content prepared by the preparation method in a sodium ion battery.
Coating the positive electrode material is one of the common means in the art for reducing soluble alkali and improving the stability of the material. In the prior art, a metal element coating layer material is generally used for coating the positive electrode material, which can indeed reduce the soluble alkali on the surface of the positive electrode material to a certain extent, and improve the structural stability of the material, however, the improvement of the performance is still very limited. According to the invention, a large amount of researches show that the non-metal elements, especially P, B and other elements are adopted as the coating layer to coat the sodium ion positive electrode material, so that the surface soluble alkali content of the prepared positive electrode material is further reduced, and the charge-discharge capacity, the circulation multiplying power, the circulation service life and the safety performance of the sodium ion battery prepared from the positive electrode material are further improved. In the high-temperature calcination process, the nonmetallic element can react with residual alkali on the surface of the positive electrode material, so that sodium ions on the surface of the material migrate inwards, the lattice structure of the positive electrode material is further perfected, the residual alkali content is reduced, the surface structure of the positive electrode material is stabilized, the crystal face structure among primary particles can be stabilized in secondary particles, the reaction of the positive electrode material and electrolyte and the dissolution of metallic elements of the positive electrode material are inhibited, the sodium ion transmission capacity of interfaces among the primary particles and between the particles and the electrolyte of the material is improved, the charge-discharge capacity, the high cycle multiplying power, the good processing performance, the long cycle life and the excellent safety performance of the positive electrode material are improved.
Meanwhile, the invention discovers that the environmental humidity and the carbon dioxide content in the crushing and screening processes after the preparation and the coating of the precursor of the sodium ion positive electrode material have important influence on the residual alkali on the surface of the material, and the environmental humidity and the carbon dioxide content have direct relevance with the content of sodium and manganese elements. The method is characterized in that the environmental humidity and the carbon dioxide concentration in the smashing and sieving processes are controlled, the method is favorable for further reducing the content of soluble alkali on the surface of the positive electrode material, more importantly, the positive electrode material obtained through smashing and sieving under specific humidity and carbon dioxide concentration can generate a proper crystal structure in the subsequent processing, especially high-temperature sintering processes, the content of residual alkali on the surface is further greatly reduced, the migration of the soluble alkali into the material is avoided, the processing performance is remarkably improved, the charge-discharge capacity, the circulation multiplying power, the circulation service life, the safety performance and the like of a sodium ion battery containing the positive electrode material are improved, and the cost for preparing the positive electrode material and the performance index of the prepared positive electrode material can be considered.
Besides, the invention adds proper first main element M and doping element M' on the basis of Mn element, wherein the addition of a small amount of doping element is helpful to promote the high-temperature solid phase reaction of sodium ions and metal oxide or metal hydroxide, reduce the residual sodium content on the surface of the positive electrode material, inhibit the decomposition of residual alkali to produce gas and the reaction of residual alkali and electrolyte, inhibit the interface reaction and excessive metal dissolution of the positive electrode material, improve the lattice structure stability and the particle strength of the material, and improve the rate performance and the cycle life of the battery prepared from the positive electrode material.
Compared with the prior art, the invention has the following beneficial effects:
(1) According to the invention, the sodium ion positive electrode material is coated by adopting nonmetallic elements, and crushing and screening treatment is carried out under the environment of specific humidity and carbon dioxide concentration, so that the content of sodium oxide, sodium hydroxide, sodium carbonate and sodium bicarbonate residual alkali on the surface of the material can be obviously reduced, the content of the surface residual alkali is further obviously reduced after the subsequent high-temperature treatment process, the structural stability and the processability of the material are improved, the irreversible removal of sodium ions and the release of lattice oxygen are inhibited, the gram capacity, the energy density, the multiplying power performance, the cycle life and the safety of the positive electrode material can be obviously improved, and the gas production is reduced.
(2) The sodium ion battery anode material provided by the invention has low residual alkali content on the surface, can prevent reversible deintercalation sodium ions from being reduced and reversible specific capacity from being reduced in the charging and discharging process of the sodium ion battery caused by high residual alkali on the surface of the anode material, reduces electronic conductivity and ionic conductivity of the surface interface of the anode material, improves electrochemical reaction kinetics, improves the conductivity of the material, and further improves the multiplying power performance of the material; the decomposition reaction of sodium carbonate and sodium bicarbonate at high voltage in the charge and discharge process of the material is reduced, sodium oxide and sodium hydroxide react with electrolyte, the cycle life and the safety of the sodium ion battery are improved, and the gas production of the battery is reduced.
(3) According to the invention, a small amount of doping elements are added into the positive electrode material of the sodium ion battery, so that the high-temperature solid-phase reaction of sodium ions and precursor metal carbonate, metal hydroxide or/and metal oxide can be effectively promoted, the residual sodium content on the surface of the positive electrode material is reduced, the decomposition and gas production of residual alkali on the surface and the reaction of residual alkali and electrolyte are inhibited, the interface reaction and excessive metal dissolution of the positive electrode material are inhibited, the lattice structure stability and the particle strength of the material are improved, and the rate performance and the cycle life of the battery prepared from the positive electrode material are improved.
Drawings
Fig. 1 is an SEM image of the sodium ion positive electrode material of example 1.
Fig. 2 is an SEM image of the sodium ion positive electrode material of example 2.
Fig. 3 is an SEM image of the sodium ion positive electrode material of comparative example 1.
Detailed Description
In order to make the objects, technical solutions and effects of the present invention more clear and clear, the present invention will be described in further detail with reference to examples. It should be understood that the specific embodiments described herein are for purposes of illustration only and are not intended to limit the scope of the invention. The raw materials, equipment, consumables and the like used in the context of the present invention are commercially available without any particular explanation.
Example 1
The preparation method of the sodium ion positive electrode material with low residual alkali content comprises the following steps:
(1) According to the mol ratio of the element Na, mn, fe, ni, mg of 10:3.2:3.2:3.2: and 0.2, weighing sodium carbonate, manganese hydroxide, ferric oxide, nickel carbonate and magnesium oxide, and uniformly mixing to prepare the precursor material.
(2) Placing the precursor material in a muffle furnace, sintering for 12h at 950 ℃ for the first time, continuously introducing dry air with humidity of 0.3RH% into the muffle furnace in the first sintering process, wherein the introducing amount is 0.5m 3 /h/kg; then cooling to room temperature, and sequentially crushing and screening to obtain a first sintered product; wherein the environmental humidity is 0.22RH% and the carbon dioxide content is 30ppm in the process of crushing and sieving.
(3) Uniformly mixing the first sintering product with phosphorus pentoxide and aluminum oxide according to a proportion, placing the mixture in a muffle furnace, and performing secondary sintering at 850 ℃ for 8 hours, wherein dry air with humidity of 0.1RH% is continuously introduced in the secondary sintering process, and the introduced amount is 0.1m 3 /h/kg; then cooling to room temperature, and then crushing and screening to obtain the product; wherein the environmental humidity is 0.1RH% and the carbon dioxide content is 40ppm in the process of crushing and sieving. The molecular formula of the obtained sodium ion positive electrode material is Na 1.0 Mn 0.32 Fe 0.32 Ni 0.32 Al 0.02 Mg 0.02 P 0.03 O 2 。
Example 2
The preparation method of the sodium ion positive electrode material with low residual alkali content comprises the following steps:
(1) According to the mol ratio of the element Na, mn, fe, ni, cu, ca of 9.8:3.4:2:2:2: and 0.2, weighing sodium carbonate, sodium fluoride, sodium dihydrogen phosphate, manganese hydroxide, ferric oxide, nickel oxide, copper oxide and calcium oxide, and uniformly mixing to prepare the precursor material.
(2) Placing the precursor material in a muffle furnace, sintering for 12h at 900 ℃ for the first time, continuously introducing dry air with humidity of 0.3RH% into the muffle furnace in the first sintering process, wherein the introducing amount is 0.5m 3 /h/kg; then cooling to room temperature, and sequentially crushing and screening to obtain a first sintered product; wherein the environmental humidity is 0.3RH% and the carbon dioxide content is 50ppm in the process of crushing and sieving.
（3）Uniformly mixing the first sintering product with phosphorus pentoxide, cobalt carbonate and aluminum oxide according to a proportion, placing the mixture in a muffle furnace, and performing secondary sintering at 850 ℃ for 5 hours, wherein dry air with humidity of 0.1RH% is continuously introduced in the secondary sintering process, and the introduced amount is 0.1m 3 /h/kg; then cooling to room temperature, and then crushing and screening to obtain the product; wherein the environmental humidity is 0.1RH% and the carbon dioxide content is 40ppm in the process of crushing and sieving. The molecular formula of the obtained sodium ion positive electrode material is Na 0.98 Mn 0.34 Fe 0.2 Ni 0.2 Cu 0.2 Co 0.02 Al 0.02 Ca 0.02 P 0.03 O 1.95 F 0.05 。
Example 3
The preparation method of the sodium ion positive electrode material with low residual alkali content comprises the following steps:
(1) According to the mol ratio of the element Na, mn, cu, ca of 9.5:5:5: and 0.2, weighing sodium carbonate, manganese dioxide, copper oxide and calcium oxide, and uniformly mixing to obtain the precursor material.
(2) Placing the precursor material in a muffle furnace, sintering for 12h at 950 ℃ for the first time, continuously introducing dry air with humidity of 0.25RH% into the muffle furnace in the first sintering process, wherein the introducing amount is 0.5m 3 /h/kg; then cooling to room temperature, and sequentially crushing and screening to obtain a first sintered product; wherein the environmental humidity is 0.2RH% and the carbon dioxide content is 40ppm in the process of crushing and sieving.
(3) Uniformly mixing the first sintering product and phosphoric acid according to a proportion, placing the mixture in a muffle furnace, performing secondary sintering at 800 ℃ for 5 hours, and continuously introducing dry air with humidity of 0.1RH% into the furnace in the secondary sintering process, wherein the introducing amount is 0.1m 3 /h/kg; then cooling to room temperature, and then crushing and screening to obtain the product; wherein the environmental humidity is 0.1RH% and the carbon dioxide content is 30ppm in the process of crushing and sieving. The molecular formula of the obtained sodium ion positive electrode material is Na 0.95 Mn 0.5 Cu 0.5 Ca 0.02 P 0.04 O 2 。
Example 4
The preparation method of the sodium ion positive electrode material with low residual alkali content comprises the following steps:
(1) According to the mole ratio of Mn and Mg of 8:1.9 weighing manganese nitrate and magnesium sulfate to prepare a mixed salt solution with the concentration of 2mol/L, preparing a sodium hydroxide solution with the concentration of 2mol/L as a precipitator, and preparing an ammonia water solution with the concentration of 2.5mol/L as a complexing agent; and (3) adding the mixed salt solution, the precipitator and the complexing agent into a reaction kettle in parallel, reacting for 20 hours at 35 ℃ under the conditions of pH of 10 and stirring rotation speed of 700rpm, then carrying out filter pressing and washing on the slurry, drying a filter cake at 120 ℃, and screening to obtain an intermediate. Uniformly mixing sodium carbonate, selenium dioxide and an intermediate to obtain a precursor material, wherein the molar ratio of elements Na, ce and Mn is 0.75:0.01:0.8.
(2) Placing the precursor material in a muffle furnace, sintering for 12h at 1000 ℃ for the first time, continuously introducing dry air with humidity of 0.3RH% into the muffle furnace in the first sintering process, wherein the introducing amount is 0.5m 3 /h/kg; then cooling to room temperature, and sequentially crushing and screening to obtain a first sintered product; wherein the environmental humidity is 0.15RH% and the carbon dioxide content is 25ppm in the process of crushing and sieving.
(3) Uniformly mixing the first sintering product and phosphoric acid according to a proportion, placing the mixture in a muffle furnace, performing secondary sintering at 850 ℃ for 5 hours, and continuously introducing dry air with humidity of 0.1RH% into the furnace in the secondary sintering process, wherein the introducing amount is 0.1m 3 /h/kg; then cooling to room temperature, and then crushing and screening to obtain the product; wherein the environmental humidity during the crushing and sieving process is about 0.05RH% and the carbon dioxide content is 20ppm. The molecular formula of the obtained sodium ion positive electrode material is Na 0.75 Mn 0.8 Mg 0.19 Ce 0.01 P 0.02 O 2 。
Example 5
The preparation method of the sodium ion positive electrode material with low residual alkali content comprises the following steps:
(1) According to the mole ratio of elements Mn, fe and Ni of 3.2:3.2:3.2 weighing manganese nitrate, ferrous sulfate and nickel sulfate to prepare a mixed salt solution with the concentration of 2mol/L, preparing a sodium hydroxide solution with the concentration of 2mol/L as a precipitator, and preparing an ammonia water solution with the concentration of 2.5mol/L as a complexing agent; and (3) adding the mixed salt solution, the precipitator and the complexing agent into a reaction kettle in parallel, reacting for 20 hours at 35 ℃ under the conditions of pH of 10 and stirring rotation speed of 700rpm, then carrying out filter pressing and washing on the slurry, drying a filter cake at 120 ℃, and screening to obtain an intermediate. Uniformly mixing sodium carbonate, calcium oxide and an intermediate to obtain a precursor material, wherein the molar ratio of elements Na, ca and Mn is 0.98:0.02:0.32.
(2) Placing the precursor material in a muffle furnace, sintering for 12h at 900 ℃ for the first time, continuously introducing dry air with humidity of 0.3RH% into the muffle furnace in the first sintering process, wherein the introducing amount is 0.5m 3 /h/kg; then cooling to room temperature, and sequentially crushing and screening to obtain a first sintered product; wherein the environmental humidity is 0.25RH% and the carbon dioxide content is 50ppm in the process of crushing and sieving.
(3) Uniformly mixing the first sintering product with boron oxide and cobalt oxyhydroxide according to a proportion, placing the mixture in a muffle furnace, performing secondary sintering at 850 ℃ for 5 hours, and continuously introducing dry air with humidity of 0.1RH% into the furnace for 0.1m in the secondary sintering process 3 /h/kg; then cooling to room temperature, and then crushing and screening to obtain the product; wherein the environmental humidity is 0.1RH% and the carbon dioxide content is 40ppm in the process of crushing and sieving. The molecular formula of the obtained sodium ion positive electrode material is Na 0.98 Mn 0.32 Fe 0.32 Ni 0.32 Ca 0.02 Co 0.02 B 0.03 O 2 。
Comparative example 1
The preparation method of the sodium ion positive electrode material comprises the following steps:
(1) According to the mol ratio of the element Na, mn, fe, ni, mg of 10:3.2:3.2:3.2: and 0.4, weighing sodium carbonate, manganese hydroxide, ferric oxide, nickel carbonate and magnesium oxide, and uniformly mixing to prepare the precursor material.
(2) Sintering the precursor material in a muffle furnace at 950 ℃ for 12h, continuously introducing dry air with humidity of 0.3RH% into the furnace during the sintering process, wherein the introducing amount is 0.5m 3 /h/kg; then cooled to room temperatureCrushing and screening the mixture to obtain a sintered product; wherein the environmental humidity is 0.22RH% and the carbon dioxide content is 30ppm in the process of crushing and sieving. The molecular formula of the obtained sodium ion positive electrode material is Na 1.0 Mn 0.32 Fe 0.32 Ni 0.32 Mg 0.04 O 2 。
Comparative example 2
The preparation method of the sodium ion positive electrode material comprises the following steps:
(1) According to the mol ratio of the element Na, mn, fe, ni, mg of 10:3.2:3.2:3.2: and 0.2, weighing sodium carbonate, manganese hydroxide, ferric oxide, nickel carbonate and magnesium oxide, and uniformly mixing to prepare the precursor material.
(2) Placing the precursor material in a muffle furnace, sintering for 12h at 950 ℃ for the first time, continuously introducing dry air with humidity of 0.3RH% into the muffle furnace in the first sintering process, wherein the introducing amount is 0.5m 3 /h/kg; then cooling to room temperature, and sequentially crushing and screening to obtain a first sintered product; wherein the environmental humidity is 0.22RH% and the carbon dioxide content is 30ppm in the process of crushing and sieving.
(3) Uniformly mixing the first sintering product with phosphorus pentoxide and aluminum oxide according to a proportion, placing the mixture in a muffle furnace, and performing secondary sintering at 850 ℃ for 8 hours, wherein dry air with humidity of 0.1RH% is continuously introduced in the secondary sintering process, and the introduced amount is 0.1m 3 /h/kg; then cooling to room temperature, and then crushing and screening to obtain the product; wherein the environmental humidity is 10RH% and the carbon dioxide content is 140ppm in the crushing and sieving processes. The molecular formula of the obtained sodium ion positive electrode material is Na 1.0 Mn 0.32 Fe 0.32 Ni 0.32 Al 0.02 Mg 0.02 P 0.03 O 2 。
Comparative example 3
The preparation method of the sodium ion positive electrode material comprises the following steps:
(1) According to the mol ratio of the element Na, mn, fe, ni, mg of 10:3.2:3.2:3.2: and 0.2, weighing sodium carbonate, manganese hydroxide, ferric oxide, nickel carbonate and magnesium oxide, and uniformly mixing to prepare the precursor material.
(2) Placing the precursor material in a muffle furnace, sintering for 12h at 950 ℃ for the first time, continuously introducing dry air with humidity of 0.3RH% into the muffle furnace in the first sintering process, wherein the introducing amount is 0.5m 3 /h/kg; then cooling to room temperature, and sequentially crushing and screening to obtain a first sintered product; wherein the environmental humidity is 30RH% and the carbon dioxide content is 235ppm in the process of crushing and sieving.
(3) Uniformly mixing the first sintering product with phosphorus pentoxide and aluminum oxide according to a proportion, placing the mixture in a muffle furnace, and performing secondary sintering at 500 ℃ for 8 hours, wherein dry air with humidity of 0.2RH% is continuously introduced in the secondary sintering process, and the introduced amount is 0.1m 3 /h/kg; then cooling to room temperature, and then crushing and screening to obtain the product; wherein the environmental humidity is 55RH% and the carbon dioxide content is 267ppm in the crushing and sieving processes. The molecular formula of the obtained sodium ion positive electrode material is Na 1.0 Mn 0.32 Fe 0.32 Ni 0.32 Al 0.02 Mg 0.02 P 0.03 O 2 。
Verification example 1
The sodium ion positive electrode materials prepared in examples 1 to 5 and comparative examples 1 to 3 were prepared by a conventional method in the art, and the surface-soluble alkali (m (Na 2CO3, naHCO 3), m (NaOH, na 2O)) content (ppm), the particle size D50 (μm), the specific surface area (m 2 Per gram), tap density (g/cm) 3 ) Density of compaction (g/cm) 3 ) The same physicochemical properties were tested, while the soluble alkali content (ppm) of each material was tested at high temperature calcinationThe variation, wherein the high temperature calcination temperatures are all 800 ℃,>calculated by the following formula:
is the total content of soluble alkali on the surface of the sodium ion positive electrode material before high-temperature treatment; />Total content of surface soluble alkali of the treated sodium ion positive electrode material.
Wherein the residual alkali (Na) 2 CO 3 、NaHCO 3 ) The content of (2) is detected by an aqueous solution titration method, and residual alkali (NaOH and Na) on the surface of the positive electrode material 2 The content of O) is detected by absolute ethanol titration, and the instrument used is a potentiometric titrator (Metretolterodine G10S); specific surface area BET was measured by nitrogen physisorption using a specific surface area tester (Micromertics, tristar II 3020); the tap density is detected by a tap density tester (Baite, BT-30); the compacted density was measured by a compacted density tester (Mitsubishi chemical, MCP-PD 51); thermal stability was checked by thermogravimetric analysis tester (mertler, TGA-DSC 3); the morphology of the material was detected by scanning electron microscopy (HITACHI, S-4800). The detection results are shown in the following table 1.
TABLE 1 physicochemical Property test results of examples 1 to 5 and comparative examples 1 to 3
m（Na2CO3、NaHCO3）（ppm） m（NaOH、Na2O）（ppm） BET（m2/g） Tap density (g/cm 3) Compaction Density (g/cm 3) ∆β
Example 1 660 350 0.22 2.2 3.2 0.75
Example 2 950 170 0.35 2.1 3.15 0.68
Example 3 720 220 0.25 2.0 3.05 0.55
Example 4 1230 420 0.30 2.25 3.0 0.72
Example 5 530 320 0.26 2.25 3.2 0.81
Comparative example 1 2370 1670 0.35 2.2 3.2 0
Comparative example 2 7600 2000 0.52 2.2 3.2 -1.43
Comparative example 3 8900 4100 0.57 2.2 3.2 -0.08
As can be seen from Table 1, examples 1 to 5 have significantly lower m (Na 2 CO 3 、NaHCO 3 ）+m（NaOH、Na 2 O) content, illustrating the present inventionThe sodium oxide-containing positive electrode material provided by the method has lower surface soluble alkali content, and not only can reduce NaCO 3 And NaOH content, and also can reduce NaHCO 3 And Na (Na) 2 The content of O; compared with comparative examples 1-3, examples 1-5 have smaller specific surface area, which shows that the surface interface of the anode material provided by the invention has less side reaction, improves the cycle performance of the sodium ion battery, and reduces the gas production; examples 1-5 have higher tap and compacted densities than comparative examples 1-3, demonstrating that the sodium oxide-containing positive electrode material provided by the invention is conducive to preparing positive electrode sheets with high electrode density and improving the energy density of the battery. Meanwhile, compared with comparative examples 1-3, the surface soluble alkali content of examples 1-5 is further remarkably reduced after high temperature heat treatment, the migration of soluble alkali into the material is avoided, the processing performance is remarkably improved, the charge and discharge capacity, the circulation rate, the circulation service life, the safety performance and the like of a sodium ion battery containing the positive electrode material are improved, and the cost for preparing the positive electrode material and the performance index of the prepared positive electrode material can be considered.
Morphological analysis of the sodium ion positive electrode materials prepared in example 1, example 2 and comparative example 1 shows that the sodium ion positive electrode material prepared in example 1 is uniform in distribution, smooth in surface and good in crystallinity; the sodium ion positive electrode material obtained in the embodiment 2 is in a spherical shape, is uniformly distributed and has good sphericity; the sodium ion positive electrode material obtained in comparative example 1 had uneven distribution of particles, a rough surface, a large amount of residual alkali, and poor crystallinity (see fig. 1 to 3).
Further, the positive electrode materials of sodium ion batteries prepared in examples 1 to 5 and comparative examples 1 to 3 were respectively taken and respectively mixed with conductive carbon black (SuperP) and vinylidene fluoride (PVDF) according to a mass ratio of 80:10:10 pulping in N-methylpyrrolidone (NMP) solution, coating on aluminum foil, vacuum drying, cutting into 12mm diameter pole pieces (carrying 5-10 mg/cm) 2 ) NaPF with metal sodium flake as negative electrode and 1mol/L 6 Polycarbonate (PC): ethylene Carbonate (EC): dimethyl carbonate (DMC) (volume ratio 1:1:1) +5% FEC solution is used as electrolyte, glass fiber diaphragm, and CR2032 button cell is assembled in an argon glove box. Taking and preparingThe obtained button cell tests electrochemical performances such as 0.1C discharge gram capacity (mAh/g), initial effect (0.1C,%), multiplying power performance (1C/0.1C gram capacity), cycle performance (1C, 50 circles,%), thermal reaction temperature (full electricity, DEGC) and the like, wherein the voltage ranges of the charge-discharge capacity test and the initial effect test are 1.5-4.3V. The detection results are shown in the following table 2.
TABLE 2 electrochemical performance test results for examples 1-5 and comparative examples 1-3
0.1C discharge gram Capacity (mAh/g) First effect (%) Multiplying power performance (0.1C/1C) Cycle performance (%) Thermal reaction temperature (. Degree. C.)
Example 1 143 95.2 95.8 99.1 286
Example 2 135 96.2 95.5 98.5 299
Example 3 152 97.5 92.3 98.2 273
Example 4 160 90.4 91.7 92.4 265
Example 5 142 95.4 95.3 98.6 286
Comparative example 1 138 93.3 93.5 93.6 275
Comparative example 2 135 90.6 91.5 92.3 268
Comparative example 3 134 90.1 90.7 89.3 262
From the above results, it is understood that the positive electrode sheets prepared from the positive electrode materials provided in examples 1 to 5 have higher gram capacity, energy density, specific discharge capacity, and better rate performance and cycle stability than those of comparative examples 1 to 3. In addition, examples 1-5 have higher thermal decomposition temperatures than comparative examples 1-3, demonstrating the higher safety of the sodium oxide-containing cathode materials provided by the present invention.
The above detailed description describes the analysis method according to the present invention. It should be noted that the above description is only intended to help those skilled in the art to better understand the method and idea of the present invention, and is not intended to limit the related content. Those skilled in the art may make appropriate adjustments or modifications to the present invention without departing from the principle of the present invention, and such adjustments and modifications should also fall within the scope of the present invention.

Claims (12)

1. A sodium ion positive electrode material with low residual alkali content is characterized in that the molecular formula is Na 1-x [Mn y M z ]M’ a R b O 2- c X c The method comprises the steps of carrying out a first treatment on the surface of the Wherein M is selected from one or more of Li, mg, ca, al, ni, cu, zn, zr, nb, co, ti, Y, sc, fe, cr, W, la, mo and Sr; m' is selected from one or more of Mg, ca, al, cu, zn, ni, zr, nb, co, ti, Y, sc, sr, ce, fe, cr, W, la, mo and Sr; the sodium ion positive electrode material with low residual alkali content comprises a coating layer, wherein the coating layer comprises an element R, and R is one or more selected from B, N, P, S, si; x is selected from one or more of halogen elements; and-0.1 to less than or equal tox≤0.4，0.2≤y≤0.8，0.1≤z≤0.8，0＜a≤0.1，0＜b≤0.1，0≤c≤0.2
The surface residual alkali content of the sodium ion positive electrode material meets the following conditions:
（1）m（NaOH、Na 2 O）/m（Na 2 CO 3 、NaHCO 3 ）＜1；
（2）m（Na 2 CO 3 、NaHCO 3 ）＜3400ppm；
（3）m（NaOH、Na 2 O）＜1000ppm。
2. the sodium ion positive electrode material according to claim 1, wherein the tap density of the sodium ion positive electrode material is not less than 1.3g/cm 3 The compaction density is more than or equal to 2.4g/cm 3 。
3. The sodium ion positive electrode material according to claim 1, wherein the specific surface area BET of the sodium ion positive electrode material is: 0.1m 2 /g≤BET≤3m 2 /g。
4. The sodium ion positive electrode material according to claim 1, wherein the particle size D50 of the sodium ion positive electrode material is: 0.5 μm < D50 < 20 μm.
5. The sodium ion positive electrode material according to any one of claims 1 to 4, wherein the residual alkali content of the sodium ion positive electrode material after high temperature treatment satisfies the following condition: 0 << 1; wherein,
；
is a sodium ion positive electrode material before high-temperature treatmentTotal surface soluble alkali content; />The total content of soluble alkali on the surface of the sodium ion positive electrode material after high-temperature treatment;
the temperature of the high-temperature treatment is 550-950 ℃.
6. The method for preparing a sodium ion positive electrode material with low residual alkali content according to any one of claims 1 to 5, comprising the steps of:
(1) Preparing a precursor material from a sodium source, a manganese source, an M source and an M' source;
(2) The method comprises the steps of performing primary sintering on a precursor material, cooling to room temperature, and sequentially crushing and screening to obtain a primary sintered product; wherein, the environmental humidity is less than or equal to 0.5 (1+x) (1.5-y) RH% and the carbon dioxide content is less than or equal to 100 (1+x) (1.5-y) ppm in the crushing and screening processes;
(3) Uniformly mixing the first sintering product with an R source, performing secondary sintering, cooling to room temperature, and then crushing and screening to obtain the composite material; wherein, the environmental humidity is less than or equal to 0.3 (1+x) (1.5-y) RH% and the carbon dioxide content is less than or equal to 50 (1+x) (1.5-y) ppm in the process of crushing and sieving.
7. The method according to claim 6, wherein the temperature of the first sintering in the step (2) is T1, wherein T1 satisfies the following condition: 350 (1-x) (1.5-y) T1 is less than or equal to 850 (1-x) (3-y) and the unit is the temperature.
8. The method according to claim 7, wherein the first sintering process in step (2) is further conducted with a dry air, and the quantity of the dry air is 0.1-1m 3 And/h/kg, wherein the humidity of the dry air is less than or equal to 1.5RH percent.
9. The method according to claim 6, wherein the temperature of the second sintering in the step (3) is T2, wherein T2 satisfies the following condition: 400 (1-x) (1.5-y) T2 is less than or equal to 800 (1-x) (3-y) and the unit is the temperature.
10. The method according to claim 9, wherein the second sintering step (3) is performed by introducing dry air in an amount of 0.01-0.5m 3 And/h/kg, wherein the humidity of the dry air is less than or equal to 0.5RH percent.
11. A positive electrode sheet comprising the sodium ion positive electrode material with low residual alkali content according to any one of claims 1 to 5 and/or the sodium ion positive electrode material with low residual alkali content prepared by the preparation method according to any one of claims 6 to 10.
12. Use of the low residual alkali content sodium ion positive electrode material according to any one of claims 1-5 and/or the low residual alkali content sodium ion positive electrode material prepared according to any one of claims 6-10 in sodium ion batteries.
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