CN116779839A

CN116779839A - Positive electrode material for sodium secondary battery, preparation method thereof, positive electrode for sodium secondary battery and sodium secondary battery

Info

Publication number: CN116779839A
Application number: CN202310741190.1A
Authority: CN
Inventors: 戴腾远; 张洁; 邵洪源; 周春鹏; 陈玉超; 张玉军; 涂文哲; 高桐
Original assignee: Wanhua Chemical Yantai Battery Material Technology Co ltd
Current assignee: Wanhua Chemical Yantai Battery Material Technology Co ltd
Priority date: 2023-06-21
Filing date: 2023-06-21
Publication date: 2023-09-19

Abstract

The invention belongs to the technical field of sodium secondary batteries, and particularly relates to a positive electrode material for a sodium secondary battery, a preparation method thereof, a positive electrode for the sodium secondary battery and the sodium secondary battery; the positive electrode material is a non-stoichiometric P3/O3 phase hybridization layered oxide with a single crystal morphology; the preparation method of the positive electrode material comprises the following steps: the mixed salt solution containing nickel salt, ferric salt, manganese salt, morphology control agent and optional fluorine-containing surfactant is mixed with the precipitation solution to prepare a nickel-iron-manganese ternary precursor, then the nickel-iron-manganese ternary precursor is subjected to plasma ball milling together with doping agent, water and sodium source, and the mixture obtained by ball milling is subjected to heat treatment. The sodium secondary battery prepared from the positive electrode material obtained by the method has high average discharge voltage, high rate and quick charge and long cycle performance.

Description

Positive electrode material for sodium secondary battery, preparation method thereof, positive electrode for sodium secondary battery and sodium secondary battery

Technical Field

The invention belongs to the technical field of sodium secondary batteries, and particularly relates to a positive electrode material for a sodium secondary battery, a preparation method of the positive electrode material, a positive electrode for the sodium secondary battery and the sodium secondary battery.

Background

Currently, lithium ion batteries are the primary power source for electric vehicles due to their high energy density, excellent rate capability, and long cycle life. With the rapid development of energy storage systems of electric automobiles and power grids, the demands of the market for lithium ion batteries are growing increasingly, however, the demands are limited by the limitation of lithium ore resource reserves, the prices of lithium carbonate and lithium hydroxide serving as lithium raw materials are rising, and people have to search for novel batteries with energy density comparable to that of lithium batteries and richer resource reserves to replace the existing lithium ion batteries. Therefore, similar to the working mechanism of lithium ion batteries, industrialization of sodium ion batteries with more abundant raw material reserves has been developed.

The layered transition metal oxide in the positive valence material of the sodium ion battery becomes a research and development hot spot of the positive electrode material of the sodium ion battery due to the advantages of stable structure, high capacity, long cycle life and the like. Wherein, the O3 phase, P2 phase and P3 phase layered oxides of the sodium ferronickel manganate are the materials with the best comprehensive performance and the most widely applied materials. The O3 phase has the highest reversible capacity, and the possible capacity of the O3 phase can reach 240mAh/g based on a nickel-iron-manganese 111 system, but the diffusion of sodium ions in the surface sharing tetrahedral sites in the sodium removal/intercalation process often induces one or more complex phase change reactions, so that the cycle and rate performance of the O3 phase are relatively poor. The P2 phase benefits from the direct diffusion of sodium ions at the triangular prism sites, which have better multiplying power and cycling performance, but because it is a sodium-poor phase, its reversible capacity and coulombic efficiency are relatively low in practical batteries. The same P3 is a sodium-poor phase and has similar electrochemical activity with the P2 phase, but because the same has a similar crystal structure with the O3 phase, the inter-phase conversion between the P3 phase and the O3 phase is easy to realize through the inter-layer sliding of the transition metal layer, and meanwhile, the P3 phase has a large sodium interlayer spacing compared with the P2 phase and has a trigonal system superstructure of 2 ∈3ax2 ∈ 3ax2c.

In addition, the atomic mass of sodium ions is higher than that of lithium ions, which makes the mass specific capacity of sodium ion batteries lower than that of lithium ion batteries; the radius of sodium ions is about 25% than that of lithium ions, the migration in the electrode material needs higher electrode potential, larger volume strain can be generated in the charge-discharge phase change process, and the charging voltage is usually not more than 3.8-4.0V in order to inhibit the irreversible phase change; meanwhile, the redox potential of sodium ions is 0.3V lower than that of lithium ions, thereby further reducing the energy density, which also makes the average discharge voltage of the sodium ion battery lower than 3.0 to 3.1V.

However, for the working conditions of systems such as electric bicycles, automobiles, energy storage and the like, the batteries are required to drive an electric appliance with constant power, so that the high capacity of the used batteries is required, and meanwhile, the high average voltage is required to be ensured so as to reduce the thermal effect caused by high current; the reason is that on the basis of ensuring the high capacity of the positive electrode material of the sodium ion battery, how to increase the charging voltage threshold value, the discharging platform and the average voltage become the keys for playing the advantages of multiplying power performance, processing cost and safety performance and partially replacing the lithium ion battery.

In view of this, how to prepare a positive material of sodium ion battery with high average discharge voltage, high rate and fast charge and long cycle performance at the same time becomes a research-worthy direction.

Disclosure of Invention

The invention aims at providing a positive electrode material for a sodium secondary battery, a preparation method thereof, a positive electrode for the sodium secondary battery and a sodium secondary battery, aiming at the difficulties and challenges of the positive electrode material of the sodium ion battery in the prior art; the positive electrode material is a non-stoichiometric ratio phase hybridization layered oxide with a single crystal morphology, and the sodium secondary battery prepared from the positive electrode material has high average discharge voltage, high-rate quick charge and long cycle performance.

In order to achieve the above object, the present invention provides the following technical solutions:

in a first aspect, there is provided a positive electrode material for a sodium secondary battery, the positive electrode material being a non-stoichiometric P3/O3 phase hybrid layered oxide having a single crystalline morphology;

the chemical formula of the positive electrode material is shown as a formula (I): na (Na) _x Ni _a Fe _b Mn _c M _d O _2-2y F _y Wherein:

m is a metal cation with oxygen ion regulation capability and oxygen reduction reaction characteristic,

0.67.ltoreq.x.ltoreq.1.00 (e.g., x is 0.68, 0.7, 0.75, 0.8, 0.85, 0.9, 0.94, 0.96, 0.98), preferably 0.95.ltoreq.x.ltoreq.0.99;

0.20.ltoreq.a.ltoreq.0.4 (e.g., a is 0.21, 0.24, 0.25, 0.3, 0.32, 0.35, 0.38), 0.20.ltoreq.b.ltoreq.0.4 (e.g., b is 0.21, 0.24, 0.25, 0.3, 0.32, 0.35, 0.38), 0.20.ltoreq.c.ltoreq.0.4 (e.g., c is 0.21, 0.24, 0.25, 0.3, 0.32, 0.35, 0.38), a+b+c+d=1; preferably, a=b=c;

0.ltoreq.y.ltoreq.0.05 (e.g., y is 0.001, 0.005, 0.01, 0.015, 0.02, 0.025, 0.03, 0.035, 0.04, 0.045); preferably, 0.01.ltoreq.y.ltoreq.0.04.

According to the positive electrode material provided by the present invention, in some embodiments, in the formula (I), 0.01.ltoreq.d.ltoreq.0.1 (e.g., d is 0.012, 0.015, 0.02, 0.025, 0.03, 0.035, 0.04, 0.045, 0.05, 0.06, 0.07, 0.08, 0.09), preferably 0.03.ltoreq.d.ltoreq.0.07.

In some embodiments, the M is selected from one or more of cobalt ion, titanium ion, cerium ion, and copper ion.

In the invention, the bulk phase of the positive electrode material is a layered O3 phase, and an amorphous nano P3 phase is embedded and doped at the grain boundary of the O3 phase. The O3 phase and the P3 phase are respectively sodium nickel iron manganate doped with metal cations or respectively sodium nickel iron manganate doped with metal cations and fluorine anions; for example, the bulk phase of the O3 phase sodium nickel iron manganese oxide is doped with metal cations, and the amorphous P3 phase nano phase is rich in doped metal cations; or, the bulk phase of the O3-phase sodium nickel iron manganese oxide is co-doped with metal cations and fluoride ions, and the amorphous P3-phase nano phase is rich in the metal cations and simultaneously co-doped with fluoride anions.

In some embodiments, the positive electrode material comprises: metal cation doped O3 phase sodium nickel iron manganate, and metal cation rich amorphous P3 phase nanophase pinned at the O3 phase grain boundaries; alternatively, the positive electrode material includes: the metal cations and fluoride ions co-doped O3 phase sodium nickel iron manganate, and the amorphous fluorine doped P3 phase nanophase of the doped metal cation rich which is pinned at the O3 phase grain boundaries.

In some embodiments, the doping amount of fluorine is 0 to 5mol% (e.g., 0.001mol%, 0.01mol%, 0.05mol%, 0.1mol%, 0.5mol%, 1mol%, 1.5mol%, 2mol%, 2.5mol%, 3mol%, 3.5mol%, 4.5 mol%), preferably 1 to 4 mol%) based on the total molar amount of oxygen atoms and fluorine atoms in the single crystal cathode material.

In some embodiments, the amount of doping of the cation M is 1 to 10mol% (e.g., 1.5mol%, 2mol%, 4mol%, 5mol%, 6mol%, 8mol%, 9 mol%) based on the total molar amount of nickel, iron, manganese, and the cation M in the single crystal positive electrode material, preferably 3 to 7mol%.

In some embodiments, the positive electrode material consists of an O3 phase and a P3 phase, wherein the O3 phase comprises 95 to 100mol%, e.g., 95.5mol%, 96.5mol%, 97mol%, 97.5mol%, 98.5mol%, 99mol%, 99.5mol%, preferably 96 to 98mol%, of the layered oxide phase (e.g., based on the layered oxide phase).

In some embodiments, the P3 phase is doped in an amount of 0 to 5mol% (e.g., 0.01mol%, 0.05mol%, 0.1mol%, 0.5mol%, 1mol%, 1.5mol%, 2mol%, 2.5mol%, 3mol%, 3.5mol%, 4.5 mol%) based on the total moles of the layered oxide phases, preferably 2 to 4mol%.

In some embodiments, the positive electrode material having a single crystal morphology is in the form of spheroid-like particles having a median particle size of 4 to 15 μm (e.g., 5 μm, 6 μm, 9 μm, 10 μm, 14 μm), preferably 8 to 12 μm.

In some embodiments, the P3 phase is an amorphous nanophase rich in doped metal cations or an amorphous fluorine doped nanophase rich in doped metal cations, and the P3 phase is mosaiced distributed at grain boundaries of the O3 phase particles.

In some embodiments, the P3 phase is in the form of amorphous particles having a particle size of 3 to 100nm (e.g., 4nm, 10nm, 20nm, 40nm, 60nm, 80 nm), preferably 5 to 50nm.

In a second aspect, there is provided a method for preparing the positive electrode material as described above, comprising the steps of:

1) Preparation of ternary nickel-iron-manganese precursor

1a) Uniformly mixing water and the precipitation solution in a reaction kettle to obtain reaction base solution, and introducing inert protective gas;

1b) Dissolving nickel salt, ferric salt and manganese salt which are used as transition metal salts, a morphology control agent and an optional fluorine-containing surfactant in water, and uniformly mixing to obtain a mixed salt solution;

Adding the prepared mixed salt solution into a reaction kettle at a flow rate of 0.5-1.5L/min (e.g., 0.55L/min, 0.7L/min, 0.8L/min, 0.9L/min, 1.0L/min, 1.2L/min and 1.4L/min), stirring to uniformly mix materials in the reaction kettle, controlling the pumping amount of the mixed salt solution to maintain the pH of the system after the materials in the reaction kettle are mixed to be 10-11 (e.g., 10.5), reacting for 8-12 h (e.g., 9h, 10h and 11 h), and stopping the reaction;

1c) Collecting the discharge of the reaction kettle, washing, and suction filtering, and vacuum drying the obtained filter cake at 100-120 ℃ (such as 110 ℃) to obtain a nickel-iron-manganese ternary precursor;

2) Plasma ball milling mixing

Adding the nickel-iron-manganese ternary precursor prepared in the step 1) together with a doping agent, water and a sodium source into a plasma ball mill, and performing ball milling and mixing in an inert atmosphere to obtain a mixture;

3) And 2) carrying out heat treatment on the mixture obtained in the step 2) until the reaction is completed, and obtaining the positive electrode material.

According to the preparation method provided by the invention, in some embodiments, in the step 1), the nickel salt is selected from one or more of nickel sulfate, nickel nitrate, nickel hydrochloride, nickel acetate and nickel acetylacetonate, preferably nickel nitrate.

In some embodiments, in step 1), the iron salt is selected from one or more of iron sulfate, iron nitrate, iron hydrochloride, iron acetate and iron acetylacetonate, preferably iron nitrate.

In some embodiments, in step 1), the manganese salt is selected from one or more of a manganese sulfate, a manganese nitrate, a manganese hydrochloride, a manganese acetate and a manganese acetylacetonate, preferably a manganese nitrate.

In some embodiments, in step 1), the morphology control agent is selected from one or more of urea, sodium citrate, citric acid, sodium carbonate, sodium bicarbonate, sodium phosphate, and sodium hydrogen phosphate, preferably urea.

In some embodiments, in step 1), the fluorosurfactant is selected from one or more of sodium fluoride, ammonium fluoride, potassium fluoride, and calcium fluoride, preferably ammonium fluoride.

In some embodiments, in step 1), the precipitation solution is selected from one or more of aqueous ammonia, aqueous or alcoholic sodium hydroxide solution, aqueous or alcoholic potassium hydroxide solution, preferably aqueous sodium hydroxide solution.

In some embodiments, in step 1), the total concentration of transition metal salts in the mixed salt solution is 0.03 to 0.2mol/L (e.g., 0.06mol/L, 0.1mol/L, 0.14mol/L, 0.18 mol/L), preferably 0.05 to 0.15mol/L.

In some embodiments, in step 1), the fluorosurfactant concentration in the mixed salt solution is 0-0.4 mol/L (e.g., 0.01mol/L, 0.02mol/L, 0.05mol/L, 0.06mol/L, 0.1mol/L, 0.2mol/L, 0.25mol/L, 0.35 mol/L), preferably 0.1-0.3 mol/L.

In some embodiments, in step 1), the concentration of the morphology control agent in the mixed salt solution is from 0.1 to 0.8mol/L (e.g., 0.15mol/L, 0.25mol/L, 0.3mol/L, 0.5mol/L, 0.7 mol/L), preferably from 0.2 to 0.6mol/L.

In some embodiments, in step 1), the concentration of the precipitation solution in the reaction base solution is 0.5 to 5mol/L (e.g., 0.55mol/L, 0.6mol/L, 1.2mol/L, 1.5mol/L, 2mol/L, 4 mol/L), more preferably 1 to 3mol/L. The amount of the precipitation solution can be controlled, for example, by maintaining the pH range of the system after the materials in the reaction kettle are mixed by the pumping amount of the mixed salt solution.

In some embodiments, in step 1), the nickel salt in the mixed salt solution: iron salt: the molar ratio of the manganese salt is 1:1:1.

In some embodiments, for the solution of step 1) to add fluorosurfactant, the molar ratio of total moles of transition metal salt to fluorosurfactant in the mixed salt solution is 1:1-4 (e.g., 1:2, 1:3, 1:3.5), preferably 1:1.5-2.5.

In some embodiments, the molar ratio of the total moles of transition metal salt in the mixed salt solution to the morphology control agent is from 1:1 to 10 (e.g., 1:1.5, 1:3, 1:4, 1:5, 1:8), preferably from 1:2 to 6.

In some embodiments, in step 1 b), the mixed salt solution is pumped into the reaction vessel by peristaltic pump at a flow rate of 0.6 to 1L/min, e.g., 0.7L/min, 0.8L/min, 0.9L/min.

In some embodiments, in step 1 b), the stirring rate is controlled to be 600-1000 rpm (e.g., 800rpm, 900 rpm) to uniformly mix the materials in the reaction kettle. In some embodiments, the agitation time is 1 to 5 minutes (e.g., 1.5 minutes, 2.5 minutes, 3.5 minutes), preferably 2 to 4 minutes.

In some embodiments, in step 1 b), the reaction temperature is 50 to 90 ℃ (e.g., 70 ℃, 85 ℃), preferably 60 to 80 ℃.

In some embodiments, in step 1 c), the washing, suction filtration, etc. process is a conventional operation in the art; for example, the washing process is to alternately wash with water and ethanol, for example, the washing process can be performed for 4 to 6 times; the specific process conditions and equipment for vacuum drying are conventional in the art and will not be described in detail herein. The drying time may be, for example, 4 to 10 hours (e.g., 5 hours, 9 hours), preferably 6 to 8 hours.

In some embodiments, in step 2), the dopant is selected from one or more of cobalt oxide, cobaltosic oxide, titanium trioxide, cerium oxide, cerium trioxide, cerium fluoride, copper oxide, cuprous chloride, cuprous bromide and cuprous iodide, preferably from one or more of cobaltosic oxide, titanium trioxide, cerium oxide and cuprous oxide.

In some embodiments, the sodium source is selected from one or more of sodium oxide, sodium hydroxide, sodium carbonate, sodium fluoride, sodium phosphate, and sodium dihydrogen phosphate, preferably from one or more of sodium carbonate and sodium hydroxide.

In some embodiments, the mass ratio of the ternary nickel iron manganese precursor to the sodium source is 1:0.495-0.615 (e.g., 1:0.5, 1:0.53, 1:0.54, 1:0.55, 1:0.56, 1:0.58, 1:0.6), preferably 1:0.525-0.585.

In some embodiments, the molar ratio of the ferronickel manganese ternary precursor to dopant is 9-199:1 (e.g., 10:1, 15:1, 20:1, 25:1, 30:1, 35:1, 40:1, 50:1, 60:1, 65:1, 70:1, 80:1, 100:1, 120:1, 150:1, 180:1, 190:1), and may preferably be 19-100:1.

In some embodiments, the molar ratio of the ternary nickel iron manganese precursor to water is 1:0.5-3 (e.g., 1:0.6, 1:0.75, 1:1, 1:1.5, 1:2, 1:2.5).

In some embodiments, when the material is ball milled in a plasma ball mill, the plasma ball milling process conditions include: the mass ratio of the materials to the ball-milling beads is 10-30:1 (e.g. 12:1, 15:1, 20:1, 25:1); the ball milling speed is 200-800 rpm (e.g. 300rpm, 500rpm, 600rpm, 750 rpm), the ball milling time is 20-60 min (e.g. 30min, 40min, 50 min), the excitation voltage is 5-15 kV (e.g. 6kV, 10kV, 14 kV), and the pressure value is 0.01-0.05 MPa (e.g. 0.02MPa, 0.03MPa, 0.04 MPa).

In some embodiments, in step 3), the atmosphere of the heat treatment is selected from one or more of nitrogen, argon, air and vacuum, preferably air.

In some embodiments, the process conditions of the heat treatment include:

the temperature programming rate of the first stage is 10-50 ℃/min (e.g. 15 ℃/min, 30 ℃/min, 45 ℃/min), preferably 20-40 ℃/min;

the temperature programming in the first stage is raised to 650-900 deg.c, preferably 800-900 deg.c, such as 700 deg.c and 850 deg.c;

the heat preservation time in the first stage is 0.5-5 h (e.g. 1.5h, 2h, 4 h), preferably 1-3 h;

the temperature programming rate of the second stage is 0.5-5 ℃/min (e.g., 0.6 ℃/min, 1.5 ℃/min, 2 ℃/min, 4 ℃/min), preferably 1-3 ℃/min;

the temperature programming in the second stage is raised to 850-1000 ℃ (e.g. 950 ℃), preferably 900-1000 ℃;

the heat preservation time in the second stage is 6-15 h (e.g. 7.5h, 10h, 14 h), preferably 8-12 h.

After the heat treatment, cooling is performed; for example, the cooling rate is 50 to 150℃per hour (e.g., 60℃per hour, 80℃per hour, 120℃per hour), preferably 75 to 125℃per hour.

In some preferred embodiments, the method for preparing a positive electrode material as described above comprises the steps of:

1) Preparation of fluorine doped ferronickel manganese ternary precursor

1b) Dissolving nickel salt, ferric salt and manganese salt which are used as transition metal salts, a morphology control agent and a fluorine-containing surfactant in water, and uniformly mixing to obtain a mixed salt solution;

1c) Collecting the discharge of the reaction kettle, washing, and suction filtering, and vacuum drying the obtained filter cake at 100-120 ℃ (such as 110 ℃) to obtain a fluorine doped nickel-iron-manganese ternary precursor;

2) Plasma ball milling mixing

Adding the fluorine-doped nickel-iron-manganese ternary precursor prepared in the step 1) into a plasma ball mill together with a doping agent, water and a sodium source, and performing ball milling and mixing in an inert atmosphere to obtain a mixture;

In a third aspect, there is provided a positive electrode for a sodium secondary battery, which is prepared from the positive electrode material as described above or prepared from the positive electrode material prepared by the preparation method as described above.

In a fourth aspect, there is provided a sodium secondary battery comprising the positive electrode as described above, preferably the sodium secondary battery is a sodium ion battery or a sodium battery.

According to the invention, a novel dispersing mode at the grain boundary is adopted to prepare the non-stoichiometric O3 phase doped sodium nickel iron manganese oxide monocrystal anode material with an amorphous P3 nano phase dispersed at the grain boundary, namely, the amorphous heterogeneous nano P3 phase is anchored and doped at the grain boundary of the traditional O3 phase sodium nickel iron manganese oxide monocrystal material, and meanwhile, the bulk phase is doped with cations; the structure is favorable for rapid transmission of sodium ions, improves the stability of a unit cell structure and the mechanical strength of crystals, inhibits monoclinic phase change, enhances the electron delocalization degree, further improves the high-voltage high-rate charging performance of the material, improves the average discharging voltage, and improves the energy density and the cycle performance of a battery system. Because the amorphous heterogeneous nano P3 phase is dispersedly anchored at the crystal boundary of the O3 phase, the amorphous structure is beneficial to the rapid diffusion of sodium ions, the rate performance of the material is improved, the stress strain caused by phase change in the charge and discharge process is buffered, and the cycle performance of the material is improved; the reversible capacity of the layered oxide is mainly derived from O3/P3 reversible phase change, and the prepared amorphous heterogeneous nano P3 phase/O3 phase region improves the phase change reversibility, inhibits the P3 monoclinic irreversible phase change and improves the discharge platform voltage. In addition, in some preferred embodiments, the co-doping of the oxygen reducing cations and fluorine anions not only further facilitates bulk doping, but also improves the electrical properties of the material, enhances the ionic nature of the TM-O bond, and facilitates delocalized distribution of electrons; meanwhile, fluorine doping stabilizes crystal lattice oxygen vacancies, and doping of cations with oxygen reducing capability promotes dynamic balance of oxygen vacancies in the redox process of charge-discharge transition metal ions, so that redox potential is improved, and average discharge voltage is further improved.

In the preparation method, the precursor is crushed and penetrated by adopting a plasma ball milling step and high-energy ball milling, so that the precursor is easy to form a monocrystal appearance in a subsequent sintering process; cu (provided by dopant) ⁺ /Cu ²⁺ 、Ti ³⁺ /Ti ⁴⁺ The synergistic effect of the equal redox electron pair and oxygen vacancy and electron density disturbance induced by high-energy plasma ball milling induces the formation of a non-stoichiometric ratio P3/O3 phase hybrid phase; meanwhile, the doping of the heterogeneous phase causes a difference in ion diffusion rates between grain boundaries and the inside of grains during sintering, which promotes pinning enrichment of the doped P3 phase at the O3 phase grain boundaries. In addition, aiming at the technical scheme of co-doping cations and fluoride anions, in the step of preparing the fluorine-doped nickel-iron-manganese ternary precursor, fluoride ions in the fluorine-containing surfactant and transition metal cations in transition metal salts form complex ions, ions generated after hydrolysis of morphology control agents (such as urea is hydrolyzed to generate carbonate ions and ammonium ions) induce the nickel-iron-manganese precursor to radially grow along a (001) crystal face, and meanwhile, the fluoride anions can enter the nickel-iron-manganese precursor in the form of intercalation anionsThe hydrotalcite structural layers of the precursor further promote bulk doping.

The high-energy plasma ball milling step realizes the effective mixing of the precursor, the sodium source and the doping source and the crushing and granulating of the monocrystal precursor by means of mechanical force, and simultaneously, defects and vacancies caused in the mixing process are beneficial to the appearance of finished monocrystal, the formation of specific P3/O3 hybrid phase and the reduction of sintering temperature, and the processing energy consumption and cost are reduced; for the technical scheme of co-doping of cations and fluoride ions, a non-corrosive fluorine-containing surfactant (which can play a role of a surfactant and has a certain shape control function) is used as a fluorine source in the precursor synthesis process, so that the method is simple and easy to operate, low in cost and small in pollution, and fluorine can enter an oxygen skeleton lattice through intercalation anions by adopting the method, so that atomic-level dispersion is realized in the sintering process.

Therefore, the preparation method provided by the invention is simple and convenient to operate, strong in feasibility and high in safety; the invention can prepare the non-stoichiometric O3 phase doped sodium nickel iron manganese oxide monocrystal anode material with amorphous P3 nano phase dispersed at the grain boundary, improves the high-voltage high-rate charging performance of the obtained material, improves the average discharging voltage, and improves the energy density and the cycle performance of a battery system.

Drawings

FIG. 1 is an SEM photograph of a single crystal positive electrode material prepared in example 1 of the present invention;

FIG. 2 is an SEM photograph of a single crystal positive electrode material prepared in example 2 of the present invention;

FIG. 3 is an SEM photograph of a single crystal positive electrode material prepared in example 3 of the present invention;

FIG. 4 is an SEM photograph of a single crystal positive electrode material prepared in example 4 of the present invention;

FIG. 5 is an SEM photograph of a single crystal positive electrode material prepared in comparative example 1 of the present invention;

fig. 6 is an SEM photograph of the single crystal cathode material prepared in comparative example 2 of the present invention;

FIG. 7 is an SEM photograph of a single crystal positive electrode material prepared according to comparative example 3 of the present invention;

FIG. 8 is a high resolution TEM photograph of a single crystal positive electrode material prepared according to example 1 of the present invention;

FIG. 9 is an SEM Mapping chart of a single crystal positive electrode material prepared in example 1 of the present invention;

fig. 10 is an XRD pattern of the single crystal cathode materials prepared in examples 1 to 4, comparative examples 1 to 3 according to the present invention.

Detailed Description

So that the technical features and content of the present invention can be understood in detail, preferred embodiments of the present invention will be described in more detail below. While the preferred embodiments of the present invention have been described in the examples, it should be understood that the present invention may be embodied in various forms and should not be limited to the embodiments set forth herein.

< source of raw materials >

The raw materials used in each of the examples and comparative examples are common commercial raw materials, which are commercially available, and will not be described in detail herein.

Example 1

The preparation method of the hybridized phase single crystal positive electrode material comprises the following steps:

1) Preparation of fluorine-doped ternary nickel-iron-manganese precursor

Accurately weighing nickel nitrate, ferric nitrate, manganese nitrate, ammonium fluoride and urea according to the stoichiometric ratio of 1:1:1:6:12, and then dissolving the weighed nickel nitrate, ferric nitrate, manganese nitrate, ammonium fluoride and urea in pure water to uniformly mix to prepare a mixed salt solution; in the mixed salt solution, the total concentration of transition metal salts containing nickel ions, iron ions and manganese ions is 0.1mol/L, the concentration of fluorine ions is 0.2mol/L, and the concentration of urea is 0.4mol/L;

under the protection of inert atmosphere, injecting the mixed salt solution into a reaction kettle which is prepared in advance and takes sodium hydroxide aqueous solution with the concentration of 2mol/L as reaction base solution at the flow rate of 1L/min by adopting a peristaltic pump, keeping the stirring rate of 800rpm, controlling the pumping amount of the mixed salt solution to maintain the pH=10.5 of the system, and stirring for 3min to ensure that materials in the reaction kettle are uniformly mixed; controlling the reaction temperature at 70 ℃, standing and aging for 10 hours, and stopping the reaction;

collecting the discharge of the reaction kettle, alternately washing the precipitate obtained by the reaction by pure water and ethanol, centrifugally filtering at least 3 times, and vacuum drying and drying the obtained filter cake for 8 hours at 120 ℃ to obtain the required fluorine-doped nickel-iron-manganese hydroxide ternary precursor;

2) Plasma ball milling mixing

Accurately weighing the fluorine-doped nickel-iron-manganese hydroxide precursor obtained in the step 1) and cuprous oxide with water according to the stoichiometric ratio of 38:1:38, adding the fluorine-doped nickel-iron-manganese hydroxide precursor and sodium carbonate into a plasma ball mill together according to the mass ratio of 1:0.555, and then adding zirconium dioxide ball milling beads, wherein the mass ratio of the materials to the ball milling beads is 15:1; firstly, ball milling is carried out for 2min at the ball milling rotation speed of 200rpm for premixing, then inert gas is introduced, the excitation voltage is 10kV, the pressure is 0.03MPa, and ball milling is carried out for 40min at the ball milling rotation speed of 600rpm for mixing until the mixture is uniformly mixed, thus obtaining a mixture;

3) Carrying out sintering heat treatment on the mixture obtained in the step 2), namely, heating to 850 ℃ at a heating rate of 30 ℃/min in an air atmosphere, and preserving heat for 2 hours; then the temperature is programmed to 950 ℃ at the temperature rising rate of 2 ℃/min, and the temperature is kept for 10 hours; then naturally cooling to obtain a copper ion and fluorine ion co-doped sodium nickel iron manganese oxide hybrid phase monocrystal anode material; XRD and ICP characterization confirm that the composition is Na _0.984 Ni _0.317 Fe _0.316 Mn _0.317 Cu _0.05 O _1.984 F _0.03 。

The single crystal positive electrode material consists of 3.2mol% of P3 phase and 96.8mol% of O3 phase.

Fig. 1 is an SEM photograph of the single crystal positive electrode material prepared in this example, and it can be seen that the positive electrode material has a high sphericity single crystal morphology with a particle size of 9 to 10 μm.

Fig. 8 is a high-resolution TEM photograph of the prepared positive electrode material, and it can be seen that the P3 phase is an amorphous phase having a particle size of 5 to 50nm, uniformly dispersed at the O3 phase grain boundary.

Fig. 9 is an SEM Mapping diagram of the prepared positive electrode material, na, ni, fe, mn, O elements are distributed in a bulk O3 phase, F elements are uniformly doped in a crystal lattice, and Cu elements are distributed in a P3 phase doped in a grain boundary in a punctiform manner.

The contents of the P3 phase and the O3 phase are calculated by the sodium content (1 mol of Na element in the P3 phase is 0.5mol,1mol of Na element in the O3 phase is 1 mol), and the sodium content is obtained by an inductively coupled plasma-atomic emission spectrum test.

Example 2

1) Preparation of fluorine-doped ternary nickel-iron-manganese precursor

2) Plasma ball milling mixing

Accurately weighing the fluorine-doped nickel-iron-manganese hydroxide precursor obtained in the step 1) and cerium oxide and water according to the stoichiometric ratio of 19:1:19, and adding the fluorine-doped nickel-iron-manganese hydroxide precursor and sodium carbonate into a plasma ball mill according to the mass ratio of 1:0.555, and then adding zirconium dioxide ball milling beads, wherein the mass ratio of the materials to the ball milling beads is 15:1; firstly, ball milling is carried out for 2min at the ball milling rotation speed of 200rpm for premixing, then inert gas is introduced, the excitation voltage is 10kV, the pressure is 0.03MPa, and ball milling is carried out for 40min at the ball milling rotation speed of 600rpm for mixing until the mixture is uniformly mixed, thus obtaining a mixture;

3) Mixing the mixture obtained in the step 2)Sintering heat treatment, namely, heating to 850 ℃ in an air atmosphere at a heating rate of 30 ℃/min, and preserving heat for 2 hours; then the temperature is programmed to 950 ℃ at the temperature rising rate of 2 ℃/min, and the temperature is kept for 10 hours; then naturally cooling to obtain cerium ion and fluorine ion co-doped sodium nickel iron manganese oxide hybrid phase monocrystal anode material; XRD and ICP characterization confirm that the composition is Na _0.985 Ni _0.316 Fe _0.317 Mn _0.317 Ce _0.05 O _1.985 F _0.03 。

Fig. 2 is an SEM photograph of the single crystal positive electrode material prepared in this example, and it can be seen that the positive electrode material has a high sphericity single crystal morphology with a particle size of 9 to 10 μm.

The single crystal positive electrode material consists of 3.0mol% of P3 phase and 97.0mol% of O3 phase. The contents of the P3 phase and the O3 phase are calculated by the sodium content (1 mol of Na element in the P3 phase is 0.5mol,1mol of Na element in the O3 phase is 1 mol), and the sodium content is obtained by an inductively coupled plasma-atomic emission spectrum test.

Example 3

1) Preparation of fluorine-doped ternary nickel-iron-manganese precursor

2) Plasma ball milling mixing

Accurately weighing the fluorine-doped nickel-iron-manganese hydroxide precursor obtained in the step 1) and titanium oxide with water according to the stoichiometric ratio of 38:1:38, adding the fluorine-doped nickel-iron-manganese hydroxide precursor and sodium carbonate into a plasma ball mill together according to the mass ratio of 1:0.555, and then adding zirconium dioxide ball milling beads, wherein the mass ratio of the materials to the ball milling beads is 15:1; firstly, ball milling is carried out for 2min at the ball milling rotation speed of 200rpm for premixing, then inert gas is introduced, the excitation voltage is 10kV, the pressure is 0.03MPa, and ball milling is carried out for 40min at the ball milling rotation speed of 600rpm for mixing until the mixture is uniformly mixed, thus obtaining a mixture;

3) Carrying out sintering heat treatment on the mixture obtained in the step 2), namely, heating to 850 ℃ at a heating rate of 30 ℃/min in an air atmosphere, and preserving heat for 2 hours; then the temperature is programmed to 950 ℃ at the temperature rising rate of 2 ℃/min, and the temperature is kept for 10 hours; then naturally cooling to obtain a titanium ion and fluorine ion co-doped sodium nickel iron manganese oxide hybrid phase monocrystal anode material; XRD and ICP characterization confirm that the composition is Na _0.985 Ni _0.316 Fe _0.317 Mn _0.317 Ti _0.05 O _1.985 F _0.03 。

Fig. 3 is an SEM photograph of the single crystal positive electrode material prepared in this example, and it can be seen that the positive electrode material has a high sphericity single crystal morphology with a particle size of 9 to 10 μm.

Example 4

1) Preparation of fluorine-doped ternary nickel-iron-manganese precursor

2) Plasma ball milling mixing

Accurately weighing the fluorine-doped nickel-iron-manganese hydroxide precursor obtained in the step 1) and high cobalt oxide and water according to the stoichiometric ratio of 38:1:38, adding the fluorine-doped nickel-iron-manganese hydroxide precursor and sodium carbonate into a plasma ball mill together according to the mass ratio of 1:0.555, and then adding zirconium dioxide ball milling beads, wherein the mass ratio of the materials to the ball milling beads is 15:1; firstly, ball milling is carried out for 2min at the ball milling rotation speed of 200rpm for premixing, then inert gas is introduced, the excitation voltage is 10kV, the pressure is 0.03MPa, and ball milling is carried out for 40min at the ball milling rotation speed of 600rpm for mixing until the mixture is uniformly mixed, thus obtaining a mixture;

3) Carrying out sintering heat treatment on the mixture obtained in the step 2), namely, heating to 850 ℃ at a heating rate of 30 ℃/min in an air atmosphere, and preserving heat for 2 hours; then the temperature is programmed to 950 ℃ at the temperature rising rate of 2 ℃/min, and the temperature is kept for 10 hours; then naturally cooling to obtain cobalt ion and fluorine ion co-doped sodium nickel iron manganese oxide hybrid phase monocrystal anode material; XRD and ICP characterization confirm that the composition is Na _0.985 Ni _0.317 Fe _0.317 Mn _0.316 Co _0.05 O _1.985 F _0.03 。

Fig. 4 is an SEM photograph of the single crystal positive electrode material prepared in this example, and it can be seen that the positive electrode material has a high sphericity single crystal morphology with a particle size of 9 to 10 μm.

Example 5

The preparation procedure of the hybrid phase single crystal positive electrode material was as described in example 1, except that no fluoride ion was doped, namely:

in the process of preparing the ternary nickel-iron-manganese precursor, ammonium fluoride is not added, and nickel nitrate, ferric nitrate, manganese nitrate and urea are accurately weighed according to the stoichiometric ratio of 1:1:1:12 and then are dissolved in pure water to be uniformly mixed, so that a mixed salt solution is prepared. The remaining steps were the same as in example 1.

Finally, the copper ion doped sodium nickel iron manganese oxide hybrid phase monocrystal anode material is obtained; XRD and ICP characterization confirm that the composition is Na _0.987 Ni _0.316 Fe _0.317 Mn _0.317 Cu _0.05 O _1.998 Consists of 2.5mol% of P3 phase and 97.5mol% of O3 phase.

Example 6

The preparation procedure of the hybrid phase single crystal positive electrode material is described with reference to example 2, except that no fluoride ion doping, namely:

In the process of preparing the ternary nickel-iron-manganese precursor, ammonium fluoride is not added, and nickel nitrate, ferric nitrate, manganese nitrate and urea are accurately weighed according to the stoichiometric ratio of 1:1:1:12 and then are dissolved in pure water to be uniformly mixed, so that a mixed salt solution is prepared. The remaining steps were the same as in example 2.

Finally, the cerium ion doped sodium nickel iron manganese oxide hybridized phase monocrystal anode material is obtained; XRD and ICP characterization confirm that the composition is Na _0.988 Ni _0.316 Fe _0.317 Mn _0.317 Ce _0.05 O _1.998 Consists of 2.3mol% of P3 phase and 97.7mol% of O3 phase.

Example 7

The preparation procedure of the hybrid phase single crystal positive electrode material was as described in example 3, except that no fluoride ion was doped, namely:

in the process of preparing the ternary nickel-iron-manganese precursor, ammonium fluoride is not added, and nickel nitrate, ferric nitrate, manganese nitrate and urea are accurately weighed according to the stoichiometric ratio of 1:1:1:12 and then are dissolved in pure water to be uniformly mixed, so that a mixed salt solution is prepared. The remaining steps were the same as in example 3.

Finally, the titanium ion doped sodium nickel iron manganese oxide hybrid phase monocrystal anode material is obtained; XRD and ICP characterization confirm that the composition is Na _0.988 Ni _0.316 Fe _0.317 Mn _0.317 Ti _0.05 O _1.998 Consists of 2.3mol% of P3 phase and 97.7mol% of O3 phase.

Example 8

The preparation procedure of the hybrid phase single crystal positive electrode material was as described in example 4, except that no fluoride ion was doped, namely:

In the process of preparing the ternary nickel-iron-manganese precursor, ammonium fluoride is not added, and nickel nitrate, ferric nitrate, manganese nitrate and urea are accurately weighed according to the stoichiometric ratio of 1:1:1:12 and then are dissolved in pure water to be uniformly mixed, so that a mixed salt solution is prepared. The remaining steps were the same as in example 4.

Finally, the cobalt ion doped sodium nickel iron manganese oxide hybrid phase monocrystal anode material is obtained; XRD and ICP characterization confirm that the composition is Na _0.988 Ni _0.317 Fe _0.317 Mn _0.316 Co _0.05 O _1.998 Consists of 2.3mol% of P3 phase and 97.7mol% of O3 phase.

Example 9

The preparation procedure of the hybrid phase single crystal positive electrode material was as described in example 5, except that the doping amount of copper ions was changed, namely:

in the plasma ball milling process of the step 2), accurately weighing the obtained nickel-iron-manganese hydroxide precursor, cuprous oxide and water according to the stoichiometric ratio of 194:3:194 and the mass ratio of 1:0.555 of the nickel-iron-manganese hydroxide precursor to sodium carbonate, adding the obtained mixture into a plasma ball mill, and then adding zirconium dioxide ball milling beads, wherein the mass ratio of the material to the ball milling beads is 15:1; firstly, ball milling is carried out for 2min at the ball milling rotation speed of 200rpm, then inert gas is introduced, the excitation voltage is 10kV, the pressure is 0.03MPa, and the ball milling is carried out for 40min at the ball milling rotation speed of 600rpm, so that the mixture is obtained. The remaining steps were the same as in example 5.

Finally, the copper ion doped sodium nickel iron manganese oxide hybrid phase monocrystal anode material is obtained; XRD and ICP characterization confirm that the composition is Na _0.989 Ni _0.324 Fe _0.323 Mn _0.323 Cu _0.03 O ₂ Consists of 2.1mol% of P3 phase and 97.9mol% of O3 phase.

Example 10

in the plasma ball milling process of the step 2), accurately weighing the obtained nickel-iron-manganese hydroxide precursor, cuprous oxide and water according to the stoichiometric ratio of 186:7:186 and the mass ratio of 1:0.555 of the nickel-iron-manganese hydroxide precursor to sodium carbonate, adding the obtained mixture into a plasma ball mill, and then adding zirconium dioxide ball milling beads, wherein the mass ratio of the material to the ball milling beads is 15:1; firstly, ball milling is carried out for 2min at the ball milling rotation speed of 200rpm, then inert gas is introduced, the excitation voltage is 10kV, the pressure is 0.03MPa, and the ball milling is carried out for 40min at the ball milling rotation speed of 600rpm, so that the mixture is obtained. The remaining steps were the same as in example 5.

Finally, the copper ion doped sodium nickel iron manganese oxide hybrid phase monocrystal anode material is obtained; XRD and ICP characterization confirm that the composition is Na _0.986 Ni _0.31 Fe _0.31 Mn _0.31 Cu _0.07 O _1.998 Consists of 2.6mol% of P3 phase and 97.4mol% of O3 phase.

Comparative example 1

The preparation method of the single crystal positive electrode material comprises the following steps:

1) Preparation of fluorine-doped ternary nickel-iron-manganese precursor

collecting the discharge of the reaction kettle, alternately washing the precipitate obtained by the reaction by pure water and ethanol, centrifugally filtering at least 3 times, and vacuum drying and drying the obtained filter cake for 8 hours at 120 ℃ to obtain the required fluorine-doped nickel-iron-manganese hydroxide precursor;

2) Plasma ball milling mixing

Accurately weighing the fluorine-doped nickel-iron-manganese hydroxide precursor and sodium carbonate obtained in the step 1) according to the mass ratio of 1:0.555, adding the precursor and water into a plasma ball mill according to the molar ratio of 1:1, and then adding zirconium dioxide ball milling beads, wherein the mass ratio of the material to the ball milling beads is 15:1; firstly, ball milling is carried out for 2min at the ball milling rotation speed of 200rpm for premixing, then inert gas is introduced, the excitation voltage is 10kV, the pressure is 0.03MPa, and ball milling is carried out for 40min at the ball milling rotation speed of 600rpm for mixing until the mixture is uniformly mixed, thus obtaining a mixture;

3) Carrying out sintering heat treatment on the mixture obtained in the step 2), namely, heating to 850 ℃ at a heating rate of 30 ℃/min in an air atmosphere, and preserving heat for 2 hours; then the temperature is programmed to 950 ℃ at the temperature rising rate of 2 ℃/min, and the temperature is kept for 10 hours; then naturally cooling to obtain a fluorine doped sodium nickel iron manganese oxide hybridized phase monocrystal anode material; XRD and ICP characterization prove that the composition is Na _0.993 Ni _0.33 Fe _0.33 Mn _0.33 O _1.987 F _0.027 。

Compared with the example 1, the comparative example has no oxygen to adjust the metal cation doping, and the obtained product is the positive electrode material of fluorine doped nickel iron sodium manganate.

FIG. 5 is an SEM photograph of a single crystal positive electrode material prepared according to the comparative example, which was composed of 1.3mol% of P3 phase and 98.7mol% of O3 phase.

Comparative example 2

1) Preparation of ternary nickel-iron-manganese precursor

Accurately weighing nickel nitrate, ferric nitrate, manganese nitrate and urea according to the stoichiometric ratio of 1:1:1:12, and then dissolving the weighed nickel nitrate, ferric nitrate, manganese nitrate and urea in pure water to uniformly mix the weighed nickel nitrate, the ferric nitrate, the manganese nitrate and the urea to prepare a mixed salt solution; in the mixed salt solution, the total concentration of transition metal salts containing nickel ions, iron ions and manganese ions is 0.1mol/L, and the concentration of urea is 0.4mol/L;

collecting the discharge of the reaction kettle, alternately washing the precipitate obtained by the reaction by pure water and ethanol, centrifugally filtering at least 3 times, and vacuum drying the obtained filter cake at 120 ℃ for 8 hours to obtain the required nickel-iron-manganese hydroxide precursor;

2) Conventional ball milling mixing

Accurately weighing the precursor of the nickel-iron-manganese hydroxide obtained in the step 1) and cuprous oxide according to the stoichiometric ratio of 38:1, adding the precursor and sodium carbonate into a ball mill according to the mass ratio of 1:0.555, and then adding zirconium dioxide ball milling beads, wherein the mass ratio of the material to the ball milling beads is 15:1; firstly, ball milling for 2min at the ball milling rotating speed of 200rpm for premixing, and then ball milling for 40min at the ball milling rotating speed of 600rpm for mixing until the materials are uniformly mixed to obtain a mixture;

3) Carrying out sintering heat treatment on the mixture obtained in the step 2), namely, heating to 850 ℃ at a heating rate of 30 ℃/min in an air atmosphere, and preserving heat for 2 hours; then the temperature is programmed to 950 ℃ at the temperature rising rate of 2 ℃/min, and the temperature is kept for 10 hours; then naturally cooling to obtain a copper ion doped sodium nickel iron manganese oxide hybrid phase monocrystal anode material; XRD and ICP characterization confirm that the composition is Na _0.999 Ni _0.317 Fe _0.316 Mn _0.317 Cu _0.05 O ₂ 。

Compared with the example 1, the comparative example adopts conventional ball milling and mixing, and the obtained product is the cathode material of fluorine doped sodium ferronickel manganate.

FIG. 6 is an SEM photograph of a single crystal positive electrode material prepared according to the comparative example, which was composed of 0.2mol% of P3 phase and 99.8mol% of O3 phase.

Comparative example 3

The preparation method of the positive electrode material comprises the following steps:

1) Preparation of fluorine-doped ternary nickel-iron-manganese precursor

2) Conventional ball milling mixing

Accurately weighing the nickel-iron-manganese hydroxide precursor obtained in the step 1) and sodium carbonate according to the mass ratio of 1:0.555, adding into a ball mill, and then adding zirconium dioxide ball milling beads, wherein the mass ratio of the materials to the ball milling beads is 15:1; firstly, ball milling for 2min at the ball milling rotating speed of 200rpm for premixing, and then ball milling for 40min at the ball milling rotating speed of 600rpm for mixing until the materials are uniformly mixed to obtain a mixture;

3) Carrying out sintering heat treatment on the mixture obtained in the step 2), namely, heating to 850 ℃ at a heating rate of 30 ℃/min in an air atmosphere, and preserving heat for 2 hours; then the temperature is programmed to 950 ℃ at the temperature rising rate of 2 ℃/min, and the temperature is kept for 10 hours; then naturally cooling to obtain an unmodified nickel iron sodium manganate monocrystal anode material; XRD and ICP characterization prove that the composition is NaNi _0.33 Fe _0.33 Mn _0.33 O ₂ 。

Compared with the example 1, the comparative example adopts conventional ball milling and mixing, has no fluoride ion and no cation doping, and the obtained product is the nickel iron sodium manganate positive electrode material.

Fig. 7 is an SEM photograph of the single crystal positive electrode material prepared in this comparative example, which is composed of 0mol% of P3 phase and 100mol% of O3 phase.

Fig. 10 shows XRD patterns of single crystal cathode materials prepared in examples 1 to 4, comparative examples 1 to 3 of the present invention.

Test case

The positive electrode materials prepared in examples 1 to 10 and comparative examples 1 to 3 were all matched with the same negative electrode, electrolyte and separator to prepare sodium ion 2032 button cell or 18650 cylindrical cell of the same specification (but the phase hybridization layered oxide single crystal positive electrode material prepared by the method of the invention is not limited to be used for preparing sodium ion 2032 button cell), and electrical performance test was performed under the following test conditions:

(1) 0.5C charge and discharge test at 25 ℃;

(2) 0.5C/2.0C rate charge and discharge test at 25 ℃;

(3) 5.0C/1.0C cycling test at 25 ℃.

The test results are shown in Table 1.

Table 1: sodium ion battery performance test results

As can be seen from the data in Table 1, compared with the conventional sodium electric single crystal material, which has a discharge equalizing voltage of only about 3.13V, the phase-hybridized single crystal positive electrode material prepared by the method has better high-rate rapid charge and discharge performance, higher discharge average voltage and better high-rate cycle performance under the conditions of equivalent 0.5C initial discharge capacity, 2.0C discharge capacity and initial discharge efficiency. This demonstrates that the non-stoichiometric P3/O3 phase hybrid single crystal positive electrode material prepared by the method of the invention, oxygen-regulated cation doping induces the generation of non-stoichiometric phase hybridization; meanwhile, charge disturbance caused by oxygen vacancies introduced by plasma high-energy ball milling and doping of cations with oxygen regulation capability induce the formation of a doped cation-rich amorphous P3 phase in a bulk phase O3 phase grain boundary, and the doped cation-rich amorphous P3 phase serves as an O3-P3 phase change seed crystal in a cyclic process, so that irreversible phase change is inhibited; the grain boundary doping of the P3 phase and the bulk doping of the oxygen regulating cations enhance the ionic property of TM-O bonds of the layered structure, and improve the electronic conductivity and the phase change energy of the material. Therefore, the single crystal positive electrode material prepared by the invention has improved discharge voltage equalizing performance, rate capability and high rate cycle performance.

In addition, as can be seen from the comparison of examples 1-4 and examples 5-8, the co-doping of cations and fluoride ions can further enhance the degree of phase hybridization by the synergistic effect, further improve the performance of the single crystal positive electrode material, such as obviously improving the discharge voltage equalizing of the material to above 3.21V, and the capacity cycle of the material is at least 200 circles without attenuation.

The foregoing description of embodiments of the invention has been presented for purposes of illustration and description, and is not intended to be exhaustive or limited to the embodiments disclosed. Many modifications and variations will be apparent to those of ordinary skill in the art without departing from the spirit of the invention.

Claims

1. A positive electrode material for a sodium secondary battery, characterized in that the positive electrode material is a non-stoichiometric P3/O3 phase hybrid layered oxide having a single crystal morphology;

x is more than or equal to 0.67 and less than or equal to 1.00, preferably, x is more than or equal to 0.95 and less than or equal to 0.99;

a is more than or equal to 0.20 and less than or equal to 0.4,0.20, b is more than or equal to 0.4,0.20, c is more than or equal to 0.4, and a+b+c+d=1; preferably, a=b=c;

y is more than or equal to 0 and less than or equal to 0.05; preferably, 0.01.ltoreq.y.ltoreq.0.04.

2. The positive electrode material according to claim 1, wherein in formula (I), 0.01.ltoreq.d.ltoreq.0.1, preferably 0.03.ltoreq.d.ltoreq.0.07;

preferably, the M is selected from one or more of cobalt ion, titanium ion, cerium ion and copper ion.

3. The positive electrode material according to claim 1, characterized in that the positive electrode material comprises: metal cation doped O3 phase sodium nickel iron manganate, and metal cation rich amorphous P3 phase nanophase pinned at the O3 phase grain boundaries; alternatively, the positive electrode material includes: metal cation and fluoride ion co-doped O3 phase sodium nickel iron manganate, and a metal cation-rich amorphous fluorine doped P3 phase nanophase pinned at the O3 phase grain boundaries;

preferably, the positive electrode material is composed of an O3 phase and a P3 phase, wherein the O3 phase accounts for 95-100 mol%, preferably 96-98 mol%, of the layered oxide phase;

preferably, the positive electrode material with single crystal morphology is in a sphere-like particle shape, and the median particle diameter is 4-15 μm, more preferably 8-12 μm;

preferably, the P3 phase is an amorphous nanophase rich in doped metal cations or an amorphous fluorine doped nanophase rich in doped metal cations, and the P3 phase is inlaid and distributed at the grain boundaries of the O3 phase particles;

Preferably, the P3 phase is in the form of amorphous particles having a particle size of 3 to 100nm, more preferably 5 to 50nm.

4. A method for producing the positive electrode material according to any one of claims 1 to 3, comprising the steps of:

1) Preparation of ternary nickel-iron-manganese precursor

adding the prepared mixed salt solution into a reaction kettle at a flow rate of 0.5-1.5L/min, stirring to uniformly mix materials in the reaction kettle, controlling the pumping amount of the mixed salt solution to maintain the pH value of a system after the materials in the reaction kettle are mixed to be 10-11, reacting for 8-12 h, and stopping the reaction;

1c) Collecting the discharge of the reaction kettle, washing, and suction filtering, and vacuum drying the obtained filter cake at 100-120 ℃ to obtain a nickel-iron-manganese ternary precursor;

2) Plasma ball milling mixing

5. The method according to claim 4, wherein in step 1), the nickel salt is selected from one or more of a sulfate of nickel, a nitrate of nickel, a hydrochloride of nickel, an acetate of nickel and an acetylacetonate of nickel, preferably a nitrate of nickel;

the iron salt is selected from one or more of sulfate of iron, nitrate of iron, hydrochloride of iron, acetate of iron and acetylacetonate of iron, preferably nitrate of iron;

the manganese salt is selected from one or more of manganese sulfate, manganese nitrate, manganese hydrochloride, manganese acetate and manganese acetylacetonate, preferably manganese nitrate;

the morphology control agent is selected from one or more of urea, sodium citrate, citric acid, sodium carbonate, sodium bicarbonate, sodium phosphate and sodium hydrogen phosphate, preferably urea;

the fluorine-containing surfactant is selected from one or more of sodium fluoride, ammonium fluoride, potassium fluoride and calcium fluoride, preferably ammonium fluoride;

the precipitation liquid is one or more selected from ammonia water, aqueous solution or ethanol solution of sodium hydroxide, aqueous solution or ethanol solution of potassium hydroxide, preferably aqueous solution of sodium hydroxide;

Preferably, the total concentration of the transition metal salt in the mixed salt solution is 0.03 to 0.2mol/L, more preferably 0.05 to 0.15mol/L;

preferably, the concentration of the fluorosurfactant in the mixed salt solution is 0-0.4 mol/L, more preferably 0.1-0.3 mol/L;

preferably, the concentration of the morphology control agent in the mixed salt solution is 0.1-0.8 mol/L, more preferably 0.2-0.6 mol/L;

preferably, the concentration of the precipitate in the reaction base liquid is 0.5 to 5mol/L, more preferably 1 to 3mol/L.

6. The method according to claim 4, wherein in step 1), the nickel salt in the mixed salt solution: iron salt: the molar ratio of the manganese salt is 1:1:1;

preferably, the molar ratio of the total moles of transition metal salt in the mixed salt solution to the fluorosurfactant is 1:1-4, more preferably 1:1.5-2.5;

preferably, the molar ratio of the total moles of transition metal salt in the mixed salt solution to the morphology control agent is 1:1-10, more preferably 1:2-6;

preferably, in the step 1 b), the mixed salt solution is pumped into a reaction kettle through a peristaltic pump, and the flow rate of the mixed salt solution is 0.6-1L/min;

preferably, in the step 1 b), the stirring speed is controlled to be 600-1000 rpm so as to uniformly mix materials in the reaction kettle;

Preferably, in step 1 b), the reaction temperature is 50 to 90 ℃, more preferably 60 to 80 ℃.

7. The method according to claim 4, wherein in step 2), the dopant is selected from one or more of cobalt oxide, tricobalt tetraoxide, cobalt oxide, titanium oxide, cerium fluoride, copper oxide, copper chloride, copper bromide and copper iodide, preferably from one or more of cobalt oxide, titanium oxide, cerium oxide and copper oxide;

the sodium source is selected from one or more of sodium oxide, sodium hydroxide, sodium carbonate, sodium fluoride, sodium phosphate and sodium dihydrogen phosphate, preferably from one or more of sodium carbonate and sodium hydroxide;

preferably, the mass ratio of the ferronickel manganese ternary precursor to the sodium source is 1:0.495-0.615, more preferably 1:0.525-0.585;

preferably, the molar ratio of the ferronickel manganese ternary precursor to the doping agent is 9-199:1;

preferably, the molar ratio of the nickel-iron-manganese ternary precursor to water is 1:0.5-3;

preferably, when the material is ball-milled in a plasma ball mill, the plasma ball milling process conditions include: the mass ratio of the materials to the ball-milling beads is 10-30:1; the ball milling rotating speed is 200-800 rpm, the ball milling time is 20-60 min, the exciting voltage is 5-15 kV, and the pressure value is 0.01-0.05 MPa.

8. The method of any one of claims 4 to 7, wherein in step 3) the heat-treated atmosphere is selected from one or more of nitrogen, argon, air and vacuum, preferably air; and/or

The process conditions of the heat treatment include:

the temperature programming rate in the first stage is 10-50 ℃/min, preferably 20-40 ℃/min;

the temperature programming in the first stage is raised to 650-900 ℃, preferably 800-900 ℃;

the heat preservation time in the first stage is 0.5-5 h, preferably 1-3 h;

the temperature programming rate of the second stage is 0.5-5 ℃/min, preferably 1-3 ℃/min;

the temperature programming in the second stage is increased to 850-1000 ℃, preferably 900-1000 ℃;

the heat preservation time in the second stage is 6-15 h, preferably 8-12 h.

9. A positive electrode for a sodium secondary battery, which is prepared from the positive electrode material according to any one of claims 1 to 3 or prepared from the positive electrode material prepared by the preparation method according to any one of claims 4 to 8.

10. A sodium secondary battery comprising the positive electrode according to claim 9, preferably the sodium secondary battery is a sodium ion battery or a sodium battery.