Polyanionic sodium ion battery positive electrode material precursor, preparation method and application

Abstract

The invention discloses a polyanion type sodium ion battery positive electrode material precursor, a preparation method and application, the precursor is iron-based phosphate, and the porosity of the polyanion type sodium ion battery positive electrode material precursor is 15%-46%. When the polyanionic sodium-ion battery positive electrode material precursor is used as a raw material to prepare the positive electrode material, at least part of the pore structure of the polyanionic sodium-ion battery positive electrode material precursor can be inherited, more abundant three-dimensional through pore channels can be provided due to proper porosity, more sufficient ion deintercalation is realized in the charging and discharging process, and the service life of the positive electrode material is prolonged. The capacity of the polyanion type sodium ion battery positive electrode material can be improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of sodium ion battery cathode material, in particular to a polyanion type sodium ion battery cathode material precursor, a preparation method and application thereof. BACKGROUND

[0002] Sodium ion batteries have become an important supplement to lithium ion batteries due to their abundant resources, low cost, excellent low-temperature performance, high safety and other characteristics, and have shown broad application prospects in low-speed electric vehicles, electric ships, household / industrial energy storage systems, 5G communication base stations, data centers, large-scale renewable energy grid-connected and smart grids and other fields. By reducing or avoiding the use of expensive elements such as lithium, cobalt and nickel, sodium ion batteries can significantly reduce energy storage costs, making them have a significant competitive advantage in the field of grid energy storage, and are expected to become a good alternative to lithium ion batteries and a new force in the field of secondary battery technology.

[0003] The cathode material is one of the core elements that determine the key performance of sodium ion batteries, such as cycle stability, capacity and voltage. Specifically, oxide cathode materials have high theoretical specific capacity and are suitable for developing high-energy-density secondary batteries; and polyanion cathode materials are more suitable for building long-life battery systems due to their outstanding structural stability, but their capacity performance still needs to be further improved and optimized.

[0004] In view of this, the present application is proposed. SUMMARY

[0005] The purpose of the present application is to provide a polyanion type sodium ion battery cathode material precursor, a preparation method and application thereof, to improve the capacity of the cathode material prepared from the polyanion type sodium ion battery cathode material precursor.

[0006] The present application is realized as follows:

[0007] In a first aspect, the present application provides a polyanion type sodium ion battery cathode material precursor, which is an iron-based phosphate, and the porosity of the polyanion type sodium ion battery cathode material precursor is 15%-46%.

[0008] In an optional embodiment, the polyanion type sodium ion battery cathode material precursor comprises secondary particles composed of primary particles, the secondary particles comprise an inner core and an outer layer, and the porosity of the outer layer is less than the porosity of the inner core.

[0009] And / or, the porosity of the outer layer is 5%-35%;

[0010] And / or, the porosity of the inner core is 10%-60%;

[0011] And / or, the primary particles in the outer layer are arranged radially;

[0012] And / or, the general chemical formula of the polyanionic sodium-ion battery cathode material precursor is Na. q M m+n Mˋ w P x O y ·zH₂O; where M is one or more of Fe, Ni, Co, and Mn; Mˋ is one or more of transition metal elements other than M, Mg, Ca, Sr, and Al; m represents M 2+ The content of M, n represents M 3+ The content of , and the values ​​of q, m, n, w, x, y are such that the chemical formula can maintain charge balance.

[0013] In an optional embodiment, the values ​​of q, m, n, w, x, and y in the general chemical formula satisfy the following requirements: 0 ≤ m / (m+n) ≤ 0.35, 0 ≤ w / (m+n) ≤ 0.1, 0.32 ≤ q / (m+n+w) ≤ 0.70, 0.70 ≤ (m+n+w) / x ≤ 0.82, and 0 ≤ z / (m+n+w) ≤ 10;

[0014] Optionally, the general chemical formula of the polyanionic sodium-ion battery cathode material precursor is Na. q Fe m+n Mˋ w P x O y ·zH2O.

[0015] In an optional embodiment, the secondary particles are spherical; optionally, the sphericity of the secondary particles is ≥0.85.

[0016] In an optional embodiment, the D50 of the secondary particles is 5μm-50μm;

[0017] And / or, the outer layer thickness is 8%-50% of the secondary particle radius.

[0018] In an optional embodiment, the Span value of the polyanionic sodium-ion battery cathode material precursor is 0.8-1.4;

[0019] And / or, the specific surface area of ​​the polyanionic sodium-ion battery cathode material precursor is 5 m². 2 / g-18m 2 / g;

[0020] And / or, the tap density of the polyanionic sodium-ion battery cathode material precursor is 1 g / cm³. 3 -1.5g / cm 3 ;

[0021] In a second aspect, the present application provides a preparation method of a polyanionic sodium-ion battery cathode material precursor, comprising:

[0022] adding a first phosphorus source and a metal source to the reactor A containing the first bottom liquid at a preset speed to perform a first coprecipitation, collecting the overflow material to obtain slurry A when the reactor A starts to overflow, the first phosphorus source comprising pyrophosphate and / or phosphate, and the metal element of the metal source being selected from one or more of transition metal elements, Mg, Ca, Sr, and Al;

[0023] collecting part of the slurry A and placing it in the reactor B as a second bottom liquid;

[0024] adding the slurry A, a second phosphorus source, an oxidizing agent, and a pH adjuster to the reactor B containing the second bottom liquid at a preset speed to perform a second coprecipitation, collecting the overflow material to obtain slurry B when the reactor B starts to overflow, the second phosphorus source comprising pyrophosphate and / or phosphate, and the first phosphorus source or the second phosphorus source comprising Na + ;

[0025] performing solid-liquid separation, washing, and drying on the slurry B to obtain the polyanionic sodium-ion battery cathode material precursor.

[0026] In optional embodiments, the preparation method of the polyanionic sodium-ion battery cathode material precursor satisfies at least one of the following characteristics:

[0027] a. the temperature of the first coprecipitation is 50-60°C;

[0028] b. the pH of the first coprecipitation reaction is 4.2-6.2;

[0029] c. the first coprecipitation is performed under stirring at a speed of 250-500 rpm;

[0030] d. the temperature of the second coprecipitation is 50-60°C;

[0031] e. the pH of the second coprecipitation reaction is 2.5-3.5;

[0032] f. the second coprecipitation is performed under stirring at a speed of 300-600 rpm;

[0033] g. the concentration of phosphorus elements in the first phosphorus source is 19-40 g / L;

[0034] h. the concentration of metal ions in the metal source is 50-110 g / L;

[0035] i. the concentration of phosphorus element in the second phosphorus source is 19 g / L-40 g / L;

[0036] j. the oxidizing agent is selected from hydrogen peroxide solution, and optionally, the mass fraction of hydrogen peroxide in the hydrogen peroxide solution is 25wt%-27wt%;

[0037] k. the pH regulator is sulfuric acid solution, and optionally, the concentration of the sulfuric acid solution is 100 g / L-120 g / L;

[0038] l. the ratio of the flow rate of the metal source to the flow rate of the first phosphorus source is 1:1.4-1.7;

[0039] m. in the secondary co-precipitation, the flow rate of slurry A is the sum of the flow rates of the first phosphorus source and the metal source in the primary co-precipitation step.

[0040] In an optional embodiment, the preparation method of the polyanionic sodium ion battery cathode material precursor satisfies at least one of the following characteristics:

[0041] A. the flow rate of the first phosphorus source is 14-16% of the volume of reactor A per hour;

[0042] B. the ratio of the flow rate of the second phosphorus source to the flow rate of the first phosphorus source is 0.2-0.4;

[0043] C. the flow rate of the oxidizing agent is 0.8% / h-2.0% / h of the volume of reactor B;

[0044] D. the metal element is selected from one or more of Fe, Ni, Co, Mn, Mg, Ca, Sr, and Al.

[0045] In a third aspect, the present application provides a polyanionic sodium ion battery cathode material, wherein the raw material of the sodium ion battery cathode material comprises the polyanionic sodium ion battery cathode material precursor or the sodium ion battery cathode material precursor prepared by the preparation method of the polyanionic sodium ion battery cathode material precursor according to any one of the preceding embodiments.

[0046] In a fourth aspect, the present application provides a sodium ion battery comprising the polyanionic sodium ion battery cathode material according to the preceding embodiments.

[0047] The present application has the following beneficial effects:

[0048] The poly-anionic sodium ion battery cathode material precursor in the application is used as a raw material to prepare a cathode material, which can inherit at least part of the pore structure of the poly-anionic sodium ion battery cathode material precursor, the pores in the sodium ion battery cathode material serve as "channels" for ion transmission, which can shorten the diffusion path of sodium ions (Na+) in the material, and appropriate porosity can provide more three-dimensional through holes, so that Na+ can quickly penetrate into the deep active sites of the material, reduce the concentration polarization, and thus realize more complete ion deintercalation in the charging and discharging process, thereby improving the capacity of the poly-anionic sodium ion battery cathode material. BRIEF DESCRIPTION OF DRAWINGS

[0049] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the drawings needed in the embodiments will be briefly introduced as follows, and it should be understood that the following drawings only show some embodiments of the present application, and therefore should not be regarded as a limitation on the scope. For those skilled in the art, other related drawings can also be obtained without creative labor on the basis of these drawings.

[0050] Figure 1 The CP graph of the poly-anionic sodium ion battery cathode material precursor prepared in Example 1 is shown in Figure 1.

[0051] Figure 2 The CP graph of the poly-anionic sodium ion battery cathode material precursor prepared in Example 2 is shown in Figure 2. DETAILED DESCRIPTION

[0052] In order to make the purpose, technical solutions and advantages of the embodiments of the present application more clear, the technical solutions in the embodiments of the present application will be described clearly and completely. The specific conditions in the embodiments are not specified, and are carried out according to conventional conditions or manufacturer's recommended conditions. The reagents or instruments used are not specified by the manufacturer, and are conventional products that can be purchased on the market.

[0053] In the present application, the morphology of the poly-anionic sodium ion battery cathode material precursor is characterized by a scanning electron microscope (SEM); the internal structure of the poly-anionic sodium ion battery cathode material precursor is characterized by ion beam milling and a scanning electron microscope.

[0054] In the present application, the particle size D50 refers to the particle size corresponding to the cumulative particle size distribution percentage of 50% of the precursor.

[0055] In this application, the porosity of the precursor refers to the internal porosity of the secondary particles of the precursor, which is measured using porosity statistical software. The porosity testing method is as follows: the pore area and cross-sectional area of ​​the CP profile are directly calculated using image analysis software, and the porosity of different regions is calculated by "internal porosity = area of ​​pore region inside the secondary particle cross-section / area of ​​cross-sectional region of the secondary particle × 100%". All porosities in this paper are characterized by this method.

[0056] In this application, sphericity is calculated by the ratio of the pseudo-circular radius to the minimum circumscribed circle radius. The pseudo-circular radius is the ratio of the area of ​​the secondary particle detected in the SEM image to pi, and the square root of the ratio is taken. The minimum circumscribed circle radius is the radius of the smallest circle that can enclose the secondary particle.

[0057] In this application, the span and particle size were tested using a Malvern 3000 laser particle size analyzer, with reference to standard GB / T19077-2016.

[0058] In this application, the test reference standard for TD is GB / T 5162-2021 Determination of tap density of metal powder.

[0059] In this application, the specific surface area is determined according to GB / T 19587-2017 Gas Adsorption BET Method for the determination of solid substances.

[0060] In this application, the core and outer layer can be distinguished by the clear boundary identifiable by the CP diagram of the secondary particle. The longest distance between the two points on the outer periphery of the secondary particle is selected as its major axis, with the midpoint of the major axis as the center O. The lengths OAi of the lines connecting i (i≥1) points Ai on the outer boundary to the center O are calculated, and the average value of OAi is the radius R of the secondary particle. The length of the line connecting the point Bi where OAi intersects the core boundary to Ai is the outer layer thickness BiAi, and the average value of BiAi is the outer layer thickness L of the secondary particle. The outer layer thickness is the ratio of L to R.

[0061] This application provides a polyanionic sodium-ion battery cathode material precursor, wherein the precursor is an iron-based phosphate, and the porosity of the polyanionic sodium-ion battery cathode material precursor is 15%-46%, for example, it can be any value between 15%, 20%, 25%, 30%, 35%, 40%, 45%, 46%, or 15%-46%. Using the polyanionic sodium-ion battery cathode material precursor of this application as a raw material to prepare cathode materials can inherit at least part of the pore structure of the polyanionic sodium-ion battery cathode material precursor. The pores in the sodium-ion battery cathode material act as "channels" for ion transport, shortening the diffusion path of sodium ions (Na+) inside the material. A suitable porosity can provide richer three-dimensional interconnected channels, allowing Na+ to quickly penetrate to deep active sites in the material, reducing concentration polarization, thereby achieving more complete ion insertion / extraction during charging and discharging, and improving the capacity of the polyanionic sodium-ion battery cathode material.

[0062] If the porosity of the precursor of the polyanionic sodium-ion battery cathode material is too low, the polyanionic sodium-ion battery cathode material prepared from it will hinder ion transport due to the low porosity, thus leading to a decrease in capacity. Conversely, if the porosity of the precursor of the polyanionic sodium-ion battery cathode material is too high, the polyanionic sodium-ion battery cathode material prepared from it will lead to structural instability and an increase in side reactions due to the high porosity, thus leading to excessively rapid capacity decay.

[0063] In an optional embodiment, the polyanionic sodium-ion battery cathode material precursor includes secondary particles composed of primary particles. The secondary particles include a core and an outer layer, and the porosity of the outer layer is less than that of the core. The lower porosity of the outer layer compared to the core can improve electrolyte wetting and ion transport efficiency, reduce the direct contact area between the electrolyte and the active material, reduce side reactions, and maintain particle mechanical strength.

[0064] In an optional embodiment, the outer layer porosity is 5%-35%; for example, it can be any value between 5%, 7%, 8%, 10%, 12%, 15%, 18%, 20%, 25%, 30%, 32%, 34%, 35%, or 5%-35%; optionally, the outer layer porosity is 8%-35%.

[0065] In optional embodiments, the kernel porosity is 10%-60%; for example, it can be any value between 10%, 15%, 20%, 21%, 22%, 24%, 25%, 30%, 32%, 34%, 35%, 34%, 40%, 45%, 50%, 55%, 56%, 60%, or 10%-60%; optionally, the kernel porosity is 20%-56%.

[0066] In an optional embodiment, the primary particles in the outer layer are arranged in a radial manner; the primary particles arranged in a radial manner can shorten the diffusion path of sodium ions (Na+) in the material, facilitate the rapid penetration of sodium ions to the active sites in the deep layer of the material, facilitate the deintercalation of sodium ions, and improve the rate performance. The primary particles arranged in a radial manner refer to that, in the cross section of the secondary particles, the primary particles are arranged along the radial direction of the secondary particles or similar to the radial direction of the secondary particles.

[0067] In an optional embodiment, the chemical formula of the polyanionic sodium ion battery positive electrode material precursor is Na q M m+n M` w P x O y ·zH2O; wherein M is one or more of Fe, Ni, Co, and Mn; M` is one or more of transition metal elements other than M, Mg, Ca, Sr, and Al; m represents the content of M 2+ , n represents the content of M 3+ , and the values of q, m, n, w, x, and y can make the chemical formula charge balanced;

[0068] In an optional embodiment, the values of q, m, n, w, x, and y in the chemical formula satisfy the following requirements: 0≤m / (m+n)≤0.35, 0≤w / (m+n)≤0.1, 0.32≤q / (m+n+w)≤0.70, 0.70≤(m+n+w) / x≤0.82, and 0≤z / (m+n+w)≤10.

[0069] In an optional embodiment, the chemical formula of the polyanionic sodium ion battery positive electrode material precursor is Na q Fe m+n M` w P x O y ·zH2O.

[0070] In an optional embodiment, the secondary particles are spherical; optionally, the sphericity of the secondary particles is ≥0.85, for example, it can be 0.85, 0.87, 0.89, 0.91, 0.93, 0.95, 0.97, 0.99, 1.0, or any value greater than 0.85; the spherical secondary particles are more tightly packed, which can improve the tap density.

[0071] In an optional embodiment, the D50 of the secondary particles is 5 μm-50 μm, for example, it can be 5 μm, 10 μm, 15 μm, 20 μm, 25 μm, 30 μm, 35 μm, 40 μm, 45 μm, 50 μm, or any value between 5 μm and 50 μm; optionally, the D50 of the secondary particles is 20 μm-50 μm.

[0072] In an optional embodiment, the outer layer thickness is 8-50% of the radius of the secondary particle, for example, it can be 8%, 10%, 12%, 15%, 18%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, or any value between 8% and 50%, optionally, the outer layer thickness is 8-35% of the radius of the secondary particle. The primary particles in the outer layer are arranged radially, and the thickness of the outer layer accounts for a suitable range, which is beneficial to the transmission of sodium ions and ensures the strength of the particles, so that the prepared positive electrode material has good cycle performance and rate performance.

[0073] In an optional embodiment, the Span value of the polyanionic sodium ion battery positive electrode material precursor is 0.8-1.4, for example, it can be 0.8, 0.9, 1.0, 1.1, 1.2, 1.3, 1.4, or any value between 0.8 and 1.4. Under this condition, the polyanionic sodium ion battery positive electrode material precursor particles are packed more tightly, and the tap density is higher, which is beneficial to the preparation of polyanionic sodium ion battery positive electrode material with high tap density, and further improves the capacity of the positive electrode material.

[0074] In an optional embodiment, the specific surface area of the polyanionic sodium ion battery positive electrode material precursor is 5m 2 / g-18m 2 / g, for example, it can be 5m2 / g, 7m2 / g, 9m2 / g, 11m2 / g, 13m2 / g, 15m2 / g, 17m2 / g, 18m2 / g, or any value between 5m 2 / g and 18m 2 / g; the polyanionic sodium ion battery positive electrode material prepared therefrom can have a suitable specific surface area, provide more Na+adsorption sites, and be beneficial to the capacity.

[0075] In an optional embodiment, the tap density of the polyanionic sodium ion battery positive electrode material precursor is 1g / cm 3 -1.5g / cm 3 , for example, it can be 1.0g / cm3, 1.1g / cm3, 1.2g / cm3, 1.3g / cm3, 1.4g / cm3, 1.5g / cm3, or any value between 1g / cm 3 -1.5g / cm 3 , the improvement of the tap density is beneficial to the increase of the energy density of the battery.

[0076] The embodiment of the present application also provides a preparation method of a polyanionic sodium ion battery positive electrode material precursor, comprising:

[0077] adding a first phosphorus source and a metal source to the reactor A containing the first bottom solution at a preset speed to carry out a first co-precipitation, when the reactor A starts to overflow, collecting the overflow material to obtain slurry A, the first phosphorus source comprising pyrophosphate and / or phosphate, and the metal element of the metal source being selected from one or more of transition metal elements, Mg, Ca, Sr, Al;

[0078] collecting part of the slurry A and placing it in the reactor B as a second bottom solution;

[0079] adding the slurry A, a second phosphorus source, an oxidizing agent and a pH adjuster to the reactor B containing the second bottom solution at a preset speed to carry out a second co-precipitation, when the reactor B starts to overflow, collecting the overflow material to obtain slurry B, the second phosphorus source comprising pyrophosphate and / or phosphate, and the first phosphorus source or the second phosphorus source comprising Na + ;

[0080] carrying out solid-liquid separation, washing and drying on the slurry B to obtain the polyanionic sodium-ion battery cathode material precursor.

[0081] In the present application, the polyanionic sodium-ion battery cathode material precursor is prepared by the way of flow adding material to cooperate co-precipitation, and the polyanionic sodium-ion battery cathode material precursor with suitable porosity can be obtained.

[0082] In optional embodiments, at least one of the following features is met:

[0083] a. the temperature of the first co-precipitation is 50-60℃, for example, 50℃, 51℃, 52℃, 53℃, 54℃, 55℃, 56℃, 57℃, 58℃, 59℃, 60℃, or any value between 50-60℃;

[0084] b. the pH of the first co-precipitation reaction is 4.2-6.2, for example, 4.2, 4.4, 4.6, 4.8, 5.0, 5.2, 5.4, 5.6, 5.8, 6.0, 6.2, or any value between 4.2-6.2;

[0085] c. the first co-precipitation is carried out under stirring condition, and the rotation speed is 250-500rpm, for example, 250rpm, 280rpm, 310rpm, 340rpm, 370rpm, 400rpm, 430rpm, 460rpm, 490rpm, 500rpm, or any value between 250-500rpm;

[0086] d. the temperature of the second co-precipitation is 50-60℃, for example, 50℃, 51℃, 52℃, 53℃, 54℃, 55℃, 56℃, 57℃, 58℃, 59℃, 60℃, or any value between 50-60℃;

[0087] e. the pH of the secondary co-precipitation reaction is 2.5-3.5, for example 2.5, 2.6, 2.7, 2.8, 2.9, 3.0, 3.1, 3.2, 3.3, 3.4, 3.5 or any value between 2.5 and 3.5;

[0088] f. the secondary co-precipitation is carried out under stirring at a rotation speed of 300 rpm-600 rpm, for example 300 rpm, 340 rpm, 380 rpm, 420 rpm, 460 rpm, 500 rpm, 540 rpm, 580 rpm, 600 rpm or any value between 300 rpm and 600 rpm;

[0089] g. the concentration of phosphorus element in the first phosphorus source is 19 g / L-40 g / L, for example 19 g / L, 25 g / L, 30 g / L, 35 g / L, 40 g / L or any value between 19 g / L and 40 g / L;

[0090] h. the concentration of metal ions in the metal source is 50 g / L-110 g / L, for example 50 g / L, 60 g / L, 70 g / L, 80 g / L, 90 g / L, 100 g / L, 110 g / L or any value between 50 g / L and 110 g / L;

[0091] i. the concentration of phosphorus element in the second phosphorus source is 19 g / L-40 g / L, for example 19 g / L, 25 g / L, 30 g / L, 35 g / L, 40 g / L or any value between 19 g / L and 40 g / L;

[0092] j. the oxidizing agent is selected from hydrogen peroxide solution, optionally, the mass fraction of hydrogen peroxide in the hydrogen peroxide solution is 25wt%-27wt%, for example 25wt%, 25.2wt%, 25.4wt%, 25.6wt%, 25.8wt%, 26wt%, 26.2wt%, 26.4wt%, 26.6wt%, 26.8wt%, 27wt% or any value between 25wt% and 27wt%;

[0093] k. the pH regulator is sulfuric acid solution, optionally, the concentration of the sulfuric acid solution is 100 g / L-120 g / L, for example 100 g / L, 102 g / L, 104 g / L, 106 g / L, 108 g / L, 110 g / L, 112 g / L, 114 g / L, 116 g / L, 118 g / L, 120 g / L or any value between 100 g / L and 120 g / L;

[0094] l. the ratio of the flow rate of the metal source to the first phosphorus source is 1:1.4-1.7, for example 1:1.4, 1:1.55, 1:1.56, 1:1.57, 1:1.58, 1:1.59, 1:1.60, 1:1.61, 1:1.62, 1:1.63, 1:1.64, 1:1.65, 1:1.7, or any value between 1:1.4-1.7;

[0095] m. in the secondary co-precipitation, the flow rate of slurry A is the sum of the flow rates of the first phosphorus source and the metal source in the primary co-precipitation step.

[0096] In the present application, the first phosphorus source is selected from at least one of sodium pyrophosphate, ammonium dihydrogen phosphate, sodium dihydrogen phosphate, disodium hydrogen phosphate, and trisodium phosphate, the second phosphorus source is selected from at least one of sodium pyrophosphate, ammonium dihydrogen phosphate, sodium dihydrogen phosphate, disodium hydrogen phosphate, and trisodium phosphate, and the first phosphorus source and the second phosphorus source can be the same or different.

[0097] Within the above-mentioned scope of the present application, the pH of the primary co-precipitation and the secondary co-precipitation has a great influence on the precipitation rate, and a suitable pH is conducive to improving the precipitation rate, and in turn is conducive to obtaining a relatively loose and porous structure; controlling the stirring speed of the co-precipitation within a suitable range is conducive to obtaining a precursor with a suitable particle size and Span value; the comprehensive regulation of the pH, stirring speed, reaction temperature, and feed flow rate of the co-precipitation can prepare a polyanion-type sodium ion battery cathode material precursor with a porosity and specific surface area within a suitable range.

[0098] In optional embodiments, the preparation method satisfies at least one of the following characteristics:

[0099] A. the flow rate of the first phosphorus source is 14-16% per hour of the volume of reactor A, for example 14% per hour, 14.2% per hour, 14.4% per hour, 14.6% per hour, 14.8% per hour, 15% per hour, 15.2% per hour, 15.4% per hour, 15.6% per hour, 15.8% per hour, 16% per hour, or any value between 14-16% per hour;

[0100] B. the ratio of the flow rate of the second phosphorus source to the flow rate of the first phosphorus source is 0.2-0.4, for example 0.2, 0.22, 0.24, 0.26, 0.28, 0.30, 0.32, 0.34, 0.36, 0.38, 0.40, or any value between 0.2-0.4;

[0101] C. the flow rate of the oxidizing agent is 0.8% / h-2.0% / h of the volume of the reactor B, for example 0.8% / h, 0.84% / h, 0.88% / h, 0.92% / h, 0.96% / h, 1.0% / h, 1.04% / h, 1.08% / h, 1.12% / h, 1.16% / h, 1.2% / h or any value between 0.8% / h and 2.0% / h;

[0102] D. the N element is selected from one or more of transition metal elements, Mg, Ca, Sr, Al; optionally, the N element is selected from one or more of Fe, Ni, Co, Mn, Mg, Ca, Sr, Al.

[0103] In the embodiments of the present application, the inner core of the secondary particles is obtained by one-time co-precipitation, and the outer layer of the secondary particles is obtained by two-time co-precipitation. Meanwhile, by adjusting the concentration, flow rate and ratio of each raw material, and combining the stirring speed, temperature and pH of the reaction, the structure of the secondary particles can be adjusted.

[0104] In the embodiments of the present application, the thickness ratio of the outer layer can be adjusted by the flow rate of the second phosphorus source and the flow rate of the first phosphorus source.

[0105] The embodiments of the present application also provide a polyanionic sodium ion battery positive electrode material, raw materials of the sodium ion battery positive electrode material comprising the polyanionic sodium ion battery positive electrode material precursor or the polyanionic sodium ion battery positive electrode material precursor prepared by the preparation method of the polyanionic sodium ion battery positive electrode material precursor according to any one of the preceding embodiments.

[0106] The embodiments of the present application also provide a sodium ion battery comprising the polyanionic sodium ion battery positive electrode material according to the preceding embodiments.

[0107] The features and performances of the present application are further described in detail below in combination with examples.

[0108] Example 1

[0109] The embodiments provide a preparation method of a polyanionic sodium ion battery positive electrode material precursor, comprising the following steps:

[0110] A ferrous sulfate solution with a ferrous element concentration of 86g / L, a sodium pyrophosphate solution with a phosphorus concentration of 28g / L, a 26.5wt% hydrogen peroxide solution and a dilute sulfuric acid solution with a concentration of 110g / L are prepared.

[0111] In the reaction kettle A, 50L of clean water is added, the reaction temperature is set to 55℃, the stirring speed is 300r / min, and nitrogen is used as the protective gas. The prepared ferrous sulfate solution and sodium pyrophosphate solution are pumped into the reaction kettle at a flow rate of 1:1.6, wherein the flow rate of the sodium pyrophosphate solution is 16% of the volume of the reaction kettle A per hour, and the pH value of the reaction is controlled at 5.2±1.0. After the co-precipitation reaction, a slurry A with a certain solid content is formed. When the slurry in the reaction kettle A reaches the upper limit of the volume, it starts to overflow into the reaction kettle B. When the volume of the reaction kettle B reaches 50L, the prepared sodium pyrophosphate solution, hydrogen peroxide solution and dilute sulfuric acid solution are pumped into the reaction kettle B, wherein the flow rate of the sodium pyrophosphate solution is 3.2% of the volume of the reaction kettle B per hour, and the flow rate of the hydrogen peroxide solution is 1% of the volume of the reaction kettle B per hour. At the same time, the liquid is aerated, the reaction temperature is maintained at 55℃, the stirring speed is 600r / min, and the liquid pH is adjusted to 3.5 by adding dilute sulfuric acid solution to form slurry B. When the slurry B reaches 80L, it is overflowed into the material barrel. After filtration and washing, the overflowed material is dried, crushed and packaged to obtain a polyanionic sodium-ion battery positive electrode material precursor. The precursor CP diagram is shown in Figure 1 The precursor includes an inner core and an outer layer, and the porosity of the outer layer is less than that of the inner core. The porosity of the inner core is 20.61% and the porosity of the outer layer is 5.4% measured by an instrument. The thickness of the outer layer is 8% of the radius of the secondary particles.

[0112] Example 2:

[0113] The present embodiment provides a preparation method of a polyanionic sodium-ion battery positive electrode material precursor, comprising the following steps:

[0114] A ferrous sulfate solution with a concentration of 86g / L, a sodium pyrophosphate solution with a concentration of 28g / L, a hydrogen peroxide solution with a concentration of 26.5wt%, and a dilute sulfuric acid solution with a concentration of 110g / L are prepared.

[0115] The reaction kettle A is added with 50 L of clean water, the reaction temperature is set to 60 ℃, the stirring speed is 300 r / min, and nitrogen is used as the protective gas. The prepared ferrous sulfate solution and sodium pyrophosphate solution are pumped into the reaction kettle at a flow rate of 1:1.6, wherein the flow rate of the sodium pyrophosphate solution is 15% of the volume of the reaction kettle A per hour, and the pH value of the reaction is controlled at 5.2±1.0. After the co-precipitation reaction, a slurry A with a certain solid content is formed. When the slurry in the reaction kettle A reaches the upper limit of the volume, it starts to overflow into the reaction kettle B. When the volume of the reaction kettle B reaches 50 L, the prepared sodium pyrophosphate solution, hydrogen peroxide solution and dilute sulfuric acid solution are pumped into the reaction kettle B at a certain flow rate, wherein the flow rate of the sodium pyrophosphate solution is 4.2% of the volume of the reaction kettle B per hour, and the flow rate of the hydrogen peroxide solution is 1% of the volume of the reaction kettle B per hour. At the same time, the air above the liquid is opened, the reaction temperature is maintained at 60 ℃, the stirring speed is 500 r / min, and the pH value of the reaction process is adjusted to 3.5. The slurry B is formed, and when the slurry B reaches 80 L, it is overflowed into the material barrel. After filtration and washing, the overflowed material is dried, crushed and packaged to obtain a polyanionic sodium-ion battery positive electrode material precursor. The precursor CP diagram is shown in Figure 2 The precursor includes a core and an outer layer, and the porosity of the outer layer is less than that of the core. The porosity of the core is 32.44% and the porosity of the outer layer is 7.25% as measured by an instrument, and the thickness of the outer layer is 15% of the radius of the secondary particles.

[0116] Example 3

[0117] The present embodiment provides a preparation method of a polyanionic sodium-ion battery positive electrode material precursor, which comprises the following steps:

[0118] A ferrous sulfate solution with a concentration of 86 g / L, a sodium pyrophosphate solution with a concentration of 28 g / L, a hydrogen peroxide solution with a concentration of 26.5 wt%, and a dilute sulfuric acid solution with a concentration of 110 g / L are prepared.

[0119] In the reaction kettle A, 50L of clean water is added, the reaction temperature is set to 50℃, the stirring speed is 300r / min, and nitrogen is used as the protective gas. The prepared ferrous sulfate solution and sodium pyrophosphate solution are pumped into the reaction kettle at a flow rate of 1:1.6, wherein the flow rate of the sodium pyrophosphate solution is 14% of the volume of the reaction kettle A per hour, and the reaction pH is controlled at 5.2±1.0. After the co-precipitation reaction, a slurry A with a certain solid content is formed. When the slurry in the reaction kettle A reaches the upper limit of the volume, it starts to overflow into the reaction kettle B. When the volume of the reaction kettle B reaches 50L, the prepared sodium pyrophosphate solution, hydrogen peroxide solution and dilute sulfuric acid solution are pumped into the reaction kettle B at a certain flow rate, wherein the flow rate of the sodium pyrophosphate solution is 5.2% of the volume of the reaction kettle B per hour, and the flow rate of the hydrogen peroxide solution is 1% of the volume of the reaction kettle B per hour. At the same time, the air above the liquid is opened, the reaction temperature is maintained at 50℃, the stirring speed is 300r / min, and the reaction pH is adjusted to 2.5. Slurry B is formed. When the slurry B reaches 80L, it is overflowed into the material barrel. After filtration and washing, the overflowed material is dried, crushed and packaged to obtain a polyanionic sodium ion battery positive material precursor. The precursor includes an inner core and an outer layer, and the porosity of the outer layer is less than that of the inner core. The porosity of the inner core is 55.87% and the porosity of the outer layer is 34.89% by instrument measurement. The thickness of the outer layer is 35% of the radius of the secondary particles.

[0120] Example 4:

[0121] The present embodiment provides a preparation method of a polyanionic sodium ion battery positive material precursor, comprising the following steps:

[0122] A ferrous sulfate solution with a concentration of 86g / L, a sodium pyrophosphate solution with a concentration of 28g / L, a hydrogen peroxide solution with a concentration of 26.5wt%, and a dilute sulfuric acid solution with a concentration of 110g / L are prepared.

[0123] In the reaction kettle A, 50L of clean water was added, the reaction temperature was set to 55℃, the stirring speed was 250r / min, and nitrogen was introduced as a protective gas. The prepared ferrous sulfate solution and sodium pyrophosphate solution were pumped into the reaction kettle at a flow rate of 1:1.6, wherein the flow rate of the sodium pyrophosphate solution was 16% of the volume of the reaction kettle A per hour, and the reaction pH value was controlled at 5.2±1.0. After the co-precipitation reaction, a slurry A with a certain solid content was formed. When the slurry in the reaction kettle reached the upper limit of the volume, it began to overflow into the reaction kettle B. When the volume in the reaction kettle B reached 50L, the prepared sodium pyrophosphate solution, hydrogen peroxide solution and dilute sulfuric acid solution were pumped into the reaction kettle B at a certain flow rate, wherein the flow rate of the sodium pyrophosphate solution was 3.2% of the volume of the reaction kettle B per hour, and the flow rate of the hydrogen peroxide solution was 1% of the volume of the reaction kettle B per hour. At the same time, the liquid air was turned on, the reaction temperature was maintained at 55℃, the reaction speed was 300r / min, and the reaction process pH was adjusted to 3.5 to form slurry B. When the slurry B reached 80L, it overflowed into the material barrel. After filtering and washing the overflowed material, the poly-anionic sodium-ion battery positive electrode material precursor was obtained through the processes of drying, crushing and packaging.

[0124] Example 5:

[0125] The present embodiment provides a preparation method of a poly-anionic sodium-ion battery positive electrode material precursor, which comprises the following steps:

[0126] A ferrous sulfate solution with a concentration of 86g / L, a sodium pyrophosphate solution with a concentration of 28g / L, a hydrogen peroxide solution with a concentration of 26.5wt%, and a dilute sulfuric acid solution with a concentration of 110g / L were prepared.

[0127] In the reaction kettle A, 50L of clean water was added, the reaction temperature was set to 55℃, the stirring speed was 250r / min, and nitrogen was introduced as a protective gas. The prepared ferrous sulfate solution and sodium pyrophosphate solution were pumped into the reaction kettle at a flow rate of 1:1.6, wherein the flow rate of the sodium pyrophosphate solution was 16% of the volume of the reaction kettle A per hour, and the reaction pH value was controlled at 5.2±1.0. After the co-precipitation reaction, a slurry A with a certain solid content was formed. When the slurry in the reaction kettle reached the upper limit of the volume, it began to overflow into the reaction kettle B. When the volume in the reaction kettle B reached 50L, the prepared sodium pyrophosphate solution, hydrogen peroxide solution and dilute sulfuric acid solution were pumped into the reaction kettle B at a certain flow rate, wherein the flow rate of the sodium pyrophosphate solution was 3.2% of the volume of the reaction kettle B per hour, and the flow rate of the hydrogen peroxide solution was 1% of the volume of the reaction kettle B per hour. At the same time, the liquid air was turned on, the reaction temperature was maintained at 55℃, the reaction speed was 300r / min, and the reaction process pH was adjusted to 3.5 to form slurry B. When the slurry B reached 80L, it overflowed into the material barrel. After filtering and washing the overflowed material, the poly-anionic sodium-ion battery positive electrode material precursor was obtained through the processes of drying, crushing and packaging.

[0128] Comparative Example 1:

[0129] This comparative example provides a method for preparing a precursor of a polyanionic sodium-ion battery cathode material, including the following steps:

[0130] Prepare a ferrous sulfate solution with an iron concentration of 86 g / L, a sodium pyrophosphate solution with a phosphorus concentration of 28 g / L, a hydrogen peroxide solution of 26.5 wt%, and a dilute sulfuric acid solution of 110 g / L.

[0131] 50L of clean water was added to reactor A, and the reaction temperature was set to 55℃ and the reaction speed to 500r / min. The prepared ferrous sulfate solution and sodium pyrophosphate solution were pumped into the reactor at a flow rate of 1:1.6, with the flow rate of the sodium pyrophosphate solution being 16% / h of the volume of reactor A. At the same time, hydrogen peroxide solution and dilute sulfuric acid solution were pumped into reactor A, and the pH value of the reaction was controlled to be 3.5±1.0. The flow rate of the hydrogen peroxide solution was 1% / h of the volume of reactor B. After co-precipitation reaction, a slurry with a certain solid content was generated. When the slurry in the reactor reached the upper limit of the volume, it began to overflow into the material tank. The overflow material was filtered and washed, and then dried, crushed, and packaged to obtain the precursor of polyanionic sodium-ion battery cathode material.

[0132] Comparative Example 2:

[0133] This comparative example provides a method for preparing a precursor of a polyanionic sodium-ion battery cathode material, including the following steps:

[0134] Prepare a ferrous sulfate solution with an iron concentration of 86 g / L, a sodium pyrophosphate solution with a phosphorus concentration of 28 g / L, a hydrogen peroxide solution of 26.5 wt%, and a dilute sulfuric acid solution of 110 g / L.

[0135] Add 50L of clean water to reactor A. Pump the prepared ferrous sulfate, sodium pyrophosphate solution, hydrogen peroxide solution, and dilute sulfuric acid solution into the reactor at a ratio of 1:1.9:0.1:0.08. At the same time, turn on the liquid air and maintain the reaction temperature at 55℃, the stirring speed at 500r / min, and the pH of the solution at about 2.5 to form a slurry with a certain solid content. After the slurry reaches the maximum volume of the reactor, it overflows into the material tank. After filtering and washing the overflow material, it is dried, crushed, and packaged to obtain the precursor of polyanionic sodium-ion battery cathode material.

[0136] Test case

[0137] The polyanionic sodium-ion battery cathode material precursors prepared in the above embodiments and comparative examples were tested, and the results are shown in Table 1. Simultaneously, cathode materials were prepared using these precursors and assembled into batteries. The battery performance was then tested, specifically including the following steps:

[0138] Preparation of the positive electrode material: the poly-anionic sodium-ion battery positive electrode material precursor prepared in each example and comparative example was mixed with a sodium source and a carbon source in a ratio of n(Na) / n( precursor) = 1.01 and m( carbon source) / m( precursor) = 0.1, and then sintered at 500°C for 10h at a temperature increasing rate of 2°C / min under a nitrogen atmosphere, so that sodium was inserted into the original crystal nucleus to form a sodium iron pyrophosphate phosphate positive electrode material.

[0139] The positive electrode material was mixed with polyvinylidene fluoride and acetylene black in a mass ratio of 9:0.5:0.5, N-methyl-pyrrolidone was added, and then uniformly coated on an aluminum foil current collector as a positive electrode. After drying, a CR2032 button cell was assembled in a glove box with a metal sodium sheet as a negative electrode, a 1 mol / L NaClO4 solution as an electrolyte, and glass fiber as a separator. First, it was activated by charging and discharging at a current density of 0.1C (1C = 150mAh / g) for 3 weeks, and finally charged and discharged at a current density of 1C for 50 weeks, with a charge cut-off voltage of 4.2V and a discharge cut-off voltage of 2.0V. The test results are shown in Table 2.

[0140] Table 1 Performance parameters of poly-anionic sodium-ion battery positive electrode material precursor

[0141]

[0142]

[0143] Table 2 Electrical performance of poly-anionic sodium-ion battery positive electrode material precursor

[0144]

[0145] According to Tables 1 and 2, the porosity of the poly-anionic sodium-ion battery positive electrode material precursor in Examples 1-5 is 15%-46%, and the capacity and rate performance are significantly better than those of Comparative Examples 1 and 2, whose porosity is not in this range.

[0146] The sphericity of Examples 1-4 is higher than that of Example 5, so the rate performance of Examples 1-4 is higher than that of Example 5.

[0147] The above only describes the preferred embodiments of the present application and is not intended to limit the present application. Those skilled in the art can make various modifications and changes to the present application. Any modification, equivalent replacement, improvement, etc. made within the spirit and principles of the present application shall be included in the protection scope of the present application.

Claims

1. A polyanionic sodium-ion battery cathode material precursor, characterized in that, The polyanionic sodium-ion battery cathode material precursor is an iron-based phosphate, and the porosity of the polyanionic sodium-ion battery cathode material precursor is 15% to 46%.

2. The polyanionic sodium-ion battery cathode material precursor of claim 1, wherein, The polyanionic sodium-ion battery cathode material precursor comprises secondary particles composed of primary particles, and the secondary particles comprise an inner core and an outer layer, and the porosity of the outer layer is less than the porosity of the inner core; And / or, the porosity of the outer layer is 5% to 35%; And / or, the porosity of the inner core is 10% to 60%; And / or, the primary particles in the outer layer are arranged in a radial manner; And / or, the chemical formula of the polyanionic sodium-ion battery cathode material precursor is Na q M m+n Mˋ w P x O y ·zH2O; wherein, M is one or more of Fe, Ni, Co, Mn; M' is one or more of transition metal elements other than M, Mg, Ca, Sr, Al; m represents the content of M 2+ , n represents the content of M 3+ , and the values of q, m, n, w, x, y can make the chemical formula keep charge balance; Optionally, the values of q, m, n, w, x, and y in the chemical formula satisfy the following requirements: 0≤m / (m+n)≤0.35, 0≤w / (m+n)≤0.1, 0.32≤q / (m+n+w)≤0.70, 0.70≤(m+n+w) / x≤0.82, and 0≤z / (m+n+w)≤10. Optionally, the poly-anionic sodium-ion battery cathode material precursor has a chemical formula of Na q Fe m+n Mˋ w P x O y ·zH2O.

3. The polyanionic sodium-ion battery cathode material precursor of claim 2, wherein, The secondary particles are spherical; optionally, the sphericity of the secondary particles is greater than or equal to 0.

85.

4. The polyanionic sodium-ion battery cathode material precursor of claim 2, wherein, The D50 of the secondary particles is 5 μm to 50 μm; And / or, the thickness of the outer layer is 8% to 50% of the radius of the secondary particles.

5. The polyanionic sodium-ion battery cathode material precursor of claim 1, wherein, The Span value of the polyanionic sodium-ion battery cathode material precursor is 0.8 to 1.

4. And / or, the specific surface area of the polyanionic sodium-ion battery cathode material precursor is 5m 2 / g-18m 2 / g; And / or, the tap density of the polyanionic sodium-ion battery cathode material precursor is 1 g / cm 3 -1.5 g / cm 3 .

6. A method for preparing a polyanionic sodium-ion battery cathode material precursor, characterized in that, Comprise: A first phosphorus source and a metal source are added to a reaction kettle A containing a first bottom liquid at a preset speed to perform a first coprecipitation, and when the reaction kettle A starts to overflow, the overflow material is collected to obtain slurry A, the first phosphorus source comprises pyrophosphate and / or phosphate, and the metal elements of the metal source are selected from one or more of transition metal elements, Mg, Ca, Sr, and Al; Part of the slurry A is collected and placed in a reaction kettle B as a second bottom liquid; The slurry A, the second phosphorus source, the oxidizing agent and the pH regulator are added into the reactor B containing the second bottom solution at a preset speed to carry out the secondary co-precipitation, and when the reactor B starts to overflow, the overflow material is collected to obtain the slurry B, the second phosphorus source comprises pyrophosphate and / or phosphate, and the first phosphorus source or the second phosphorus source comprises Na + ; The slurry B is subjected to solid-liquid separation, washing, and drying to obtain the polyanionic sodium-ion battery cathode material precursor.

7. The method for preparing the precursor of the polyanionic sodium-ion battery cathode material according to claim 6, characterized in that, At least one of the following characteristics is satisfied: a. The temperature of the first coprecipitation is 50°C to 60°C; b. The pH of the first coprecipitation reaction is 4.2 to 6.2; c. The first coprecipitation is performed under stirring at a speed of 250 rpm to 500 rpm; d. The temperature of the second coprecipitation is 50°C to 60°C; e. The pH of the second coprecipitation reaction is 2.5 to 3.5; f. The second coprecipitation is performed under stirring at a speed of 300 rpm to 600 rpm; g. The concentration of phosphorus elements in the first phosphorus source is 19 g / L to 40 g / L; h. The concentration of metal ions in the metal source is 50 g / L to 110 g / L; i. The concentration of phosphorus elements in the second phosphorus source is 19 g / L to 40 g / L; j. The oxidizing agent is selected from a hydrogen peroxide solution, and optionally, the mass fraction of hydrogen peroxide in the hydrogen peroxide solution is 25 wt% to 27 wt%; k. The pH regulator is a sulfuric acid solution, and optionally, the concentration of the sulfuric acid solution is 100 g / L to 120 g / L; l. The ratio of the flow rate of the metal source to the first phosphorus source is 1:1.4 to 1.7; m. The flow rate of slurry A in the secondary co-precipitation is the sum of the flow rates of the first phosphorus source and the metal source in the primary co-precipitation step.

8. The method for preparing the precursor of the polyanionic sodium-ion battery cathode material according to claim 6, characterized in that, The preparation method satisfies at least one of the following characteristics: A. The flow rate of the first phosphorus source is 14-16% of the volume of reactor A per hour; B. The ratio of the flow rate of the second phosphorus source to the flow rate of the first phosphorus source is 0.2-0.4; C. The flow rate of the oxidizing agent is 0.8%-2.0% of the volume of reactor B per hour; D. The metal element is selected from one or more of Fe, Ni, Co, Mn, Mg, Ca, Sr, and Al.

9. A polyanionic sodium-ion battery cathode material, characterized in that, The raw material of the sodium ion battery cathode material includes the polyanionic sodium ion battery cathode material precursor of any one of claims 1-5 or the precursor prepared by the preparation method of the polyanionic sodium ion battery cathode material precursor of any one of claims 6-8.

10. A sodium-ion battery, characterized in that, The polyanionic sodium ion battery cathode material includes the polyanionic sodium ion battery cathode material of claim 9.

Images