Nickel-iron-manganese cathode material precursor and preparation method thereof, cathode material and sodium ion battery

Abstract

The present application provides a nickel-iron-manganese cathode material precursor and its preparation method, cathode material and sodium ion battery, which relate to the field of new energy technology. The precursor is a core-shell structure, including a core and a shell coated outside the core, and the core and the shell are both basic carbonates containing nickel, iron and manganese. By regulating the pH value in the co-precipitation method to control the different ratios of hydroxide and carbonate in the core and the shell, precursors with different morphologies of the core and the shell and different ratios of hydroxide and carbonate are obtained. The core is loose and has a small proportion, and its hydroxide content is high. The shrinkage ratio during sintering is relatively small, which avoids the internal hollowness from collapsing and cracking, and improves the cycle performance; the shell is dense and has a large proportion, and its carbonate content is high. The shrinkage ratio during sintering is relatively large. While retaining the energy density, reserving a certain amount of evenly distributed pores can reduce Na + Volume strain during the intercalation and deintercalation process, crack prevention, and balanced capacity performance and cycle performance.

Description

Technical Field

[0001] The present application relates to the field of new energy technology, and in particular to a nickel-iron-manganese cathode material precursor and a preparation method thereof, a cathode material, and a sodium ion battery. Background Art

[0002] With the rapid development of the new energy industry, lithium-ion batteries have always dominated with their performance advantages such as good safety performance, high energy density and high operating voltage. However, the high prices of lithium and cobalt, the raw materials of lithium-ion batteries, make lithium-ion batteries more expensive. Compared with lithium-ion batteries, sodium-ion batteries have obvious cost advantages. The working principle of sodium-ion batteries is the same as that of lithium-ion batteries, and the production process is also highly overlapping with that of lithium-ion batteries. In addition, sodium resources are 400 times that of lithium ore, are unrestricted and easy to mine, and can ensure the supply of the industrial chain. At the same time, sodium-ion batteries have stronger thermal stability, no over-discharge risk, great potential for fast charging and discharging, and are safer than lithium-ion batteries. They are expected to replace lithium batteries and be used.

[0003] The working principle of sodium-ion batteries is similar to that of lithium-ion batteries. Sodium salts are cheaper than lithium salts, but due to the large mass and radius of sodium ions, their migration speed is slow, which limits the improvement of the rate performance of sodium-ion batteries and also leads to lower mass and volume energy density of sodium-ion batteries. At the same time, although compared with products prepared from pure hydroxide systems, the raw material production cost of products containing carbonate systems is lower, which has cost advantages. However, a large amount of water vapor and carbon dioxide escape during sintering, and the internal porosity is higher, indicating that the compaction density inherited from this structure is low, resulting in lower mass and volume energy density of sodium-ion batteries, affecting the battery capacity performance. In addition, the shrinkage ratio of carbonate system products is large, and the interior is prone to hollow collapse. The positive electrode material inheriting this structure is more prone to cracking, resulting in poor cycle performance.

[0004] How to combine the advantages of carbonate systems and hydroxide systems to develop a new preparation method so that the prepared sodium ion battery positive electrode material precursor is not easy to collapse hollowly and crack after sintering, and has a relatively high tap density, thereby improving the rate performance, capacity performance and cycle performance of the sodium ion battery, and at a relatively low cost is an urgent problem that technicians in this field need to solve. Summary of the Invention

[0005] The purpose of this application is to provide a nickel-iron-manganese positive electrode material precursor and its preparation method, positive electrode material and sodium ion battery, aiming to solve the problems of low battery capacity caused by low mass and volume energy density of existing sodium ion batteries, poor cycle performance caused by easy cracking, and rate performance caused by slow sodium ion migration.

[0006] To achieve the above objectives, the first aspect of the present application provides a nickel-iron-manganese positive electrode material precursor, which has a core-shell structure, including a core and an outer shell coated outside the core, and the core and the shell are both basic carbonates containing nickel, iron and manganese.

[0007] Preferably, the chemical formula of the precursor, core and shell is Ni x Fe y Mn(CO3) a (OH) b , where 0<x<1, 0<y<1, 0<z<1, x+y+z=1; 0<a<1, 0<b<1, b=2(1-a), 0<b / a<1.5; and the b / a value of the inner core is greater than the b / a value of the outer shell;

[0008] Preferably, 0.1≤x≤0.5, 0.2≤z≤0.5;

[0009] Preferably, the chemical formula of the precursor core satisfies: 0<b / a<1.5, the chemical formula of the precursor shell satisfies: 0<b / a<1, and the chemical formula of the precursor satisfies: 0<b / a<1.

[0010] Preferably, the shell thickness is 3 to 10 μm and the core diameter is 1 to 6 μm;

[0011] More preferably, the shell thickness is 3 to 5 μm and the core diameter is 1 to 3 μm.

[0012] Preferably, the overall porosity of the precursor is 0.05% to 2.0%, wherein the porosity of the inner core is 3% to 20%, and the porosity of the outer shell is 0.02% to 1.3%.

[0013] Preferably, the nickel-iron-manganese precursor satisfies at least one of the following conditions:

[0014] C. The primary particles of the core are flake-shaped, and multiple primary particles of the core are arranged in a honeycomb shape;

[0015] Here, "plurality" refers to two or more.

[0016] D. The primary particles of the shell are granular and densely arranged;

[0017] E. The shell is a single-layer structure;

[0018] F. The outer shell is a multi-layer structure.

[0019] Here, "multi-layer" refers to two or more layers.

[0020] Preferably, the nickel-iron-manganese cathode material precursor satisfies at least one of the following conditions (1) to (4):

[0021] (1) The secondary particle size D50 of the precursor is 7 to 26 μm;

[0022] Preferably, the secondary particle size D50 of the precursor is 7 to 13 μm;

[0023] (2) Particle size distribution of the precursor: Span = (D90-D10) / D50 = 0.4-0.9;

[0024] (3) The BET surface area of ​​the precursor is 50 to 120 m 2 / g;

[0025] (4) The tap density TD of the precursor is 1.0 to 1.6 g / cm 3 ;

[0026] Preferably, the tap density TD of the precursor is 1.2 to 1.6 g / cm 3 .

[0027] The second aspect of the present application also provides a method for preparing the above-mentioned nickel-iron-manganese positive electrode material precursor, comprising:

[0028] adding water and a precipitant, and mixing to obtain a reaction base liquid;

[0029] Adding a mixed metal solution including nickel, iron and manganese, a precipitant and a complexing agent to the reaction base liquid to carry out a coprecipitation reaction;

[0030] Washing, centrifuging, and drying to obtain a nickel-iron-manganese cathode material precursor;

[0031] Among them, the coprecipitation reaction is divided into the first coprecipitation reaction and the second coprecipitation reaction.

[0032] Preferably, the specific steps of the coprecipitation reaction are: first, adding a mixed metal solution including nickel, iron, and manganese, a precipitant, and a complexing agent to the reaction base liquid to carry out a first coprecipitation reaction until the core is obtained, and then adding a mixed metal solution including nickel, iron, and manganese, a precipitant, and a complexing agent to carry out a second coprecipitation reaction until the precursor is obtained;

[0033] The reaction base liquid satisfies at least one of the following conditions a to d:

[0034] a. The reaction base solution also includes a complexing agent;

[0035] b. The pH value of the reaction base solution is 6.0-11.0;

[0036] c. The ammonium concentration of the reaction base solution is ≤10g / L;

[0037] Among them, the calculation method of ammonium concentration is: according to NH4 + Calculation of mass concentration in solution; the same below,

[0038] d. The reaction mixture was heated to 30°C to 50°C and the stirring speed was controlled at 700r / min to 900r / min;

[0039] The coprecipitation reaction satisfies at least one of the following conditions e to l:

[0040] e. The pH value of the coprecipitation reaction process is controlled at 6.5-10.0;

[0041] f. The ammonium concentration during the coprecipitation reaction is controlled to be ≤6 g / L, and the final ammonium concentration is controlled to be ≤0.5 g / L;

[0042] g. During the coprecipitation reaction, adjust the stirring speed to 200r / min~400r / min;

[0043] h. The complexing agent is one or more of ammonium bicarbonate, ammonium carbonate, ammonium sulfate, ammonium bisulfate, ammonia water, and ammonium chloride;

[0044] i. The precipitant is one or more of sodium carbonate, sodium bicarbonate, and sodium hydroxide;

[0045] j. The feed flow ratio of the mixed metal solution, precipitant, and complexing agent is controlled at 1:(1.2-2.5):(0-1.5), and the flow rate of the mixed metal solution is 10-60% / h of the available reactor volume;

[0046] k. During the first coprecipitation reaction, the feed flow ratio of the mixed metal solution, precipitant, and complexing agent is controlled at 1:(1.5-2.5):(0-1.5), and the flow rate of the mixed metal solution is 10-30% / h of the available reactor volume;

[0047] During the second coprecipitation reaction, the feed flow ratio of the mixed metal solution, the precipitant, and the complexing agent is controlled at 1:(1.2-1.8):(0-0.8), and the flow rate of the mixed metal solution is 30-60% / h of the available reactor volume;

[0048] l. The diameter of the core formed by the first coprecipitation reaction is 1 to 6 μm; the secondary particle size D50 of the precursor formed by the second coprecipitation reaction is 7 to 26 μm.

[0049] The third aspect of the present application also provides a sodium ion battery positive electrode material, which is prepared using the above-mentioned nickel-iron-manganese positive electrode material precursor.

[0050] The fourth aspect of the present application also provides a method for preparing a positive electrode material for a sodium ion battery, which is prepared by reacting the above-mentioned nickel-iron-manganese positive electrode material precursor with a sodium source.

[0051] Preferably, the molar ratio of the sum of nickel, iron and manganese to the sodium source in the nickel-iron-manganese positive electrode material precursor is 1:(1.00-1.05);

[0052] Preferably, the reaction is calcined using programmed temperature:

[0053] Specifically, the temperature is raised to 820-920° C. at a heating rate of 2-4° C. / min and calcined for 10-20 hours.

[0054] The fifth aspect of the present application also provides a sodium ion battery, comprising the above-mentioned sodium ion battery positive electrode material.

[0055] Compared with the prior art, the advantages of this application include:

[0056] The nickel-iron-manganese cathode material precursor provided in the present application is synthesized by a co-precipitation method, and the ratio of hydroxide to carbonate in the core and shell is regulated by regulating the pH through the flow of the precipitant to obtain a precursor of a core-shell structure. The core is relatively loose due to the influence of the process, and its hydroxide content is relatively high and accounts for a small proportion. The shrinkage ratio during sintering is relatively small, and a reticular skeleton with a smaller area can be formed to avoid the internal hollow from collapsing and cracking, thereby improving the cycle performance. The loose honeycomb structure of the core is conducive to the infiltration and reaction of the electrolyte, thereby improving the capacity performance; the shell is dense and accounts for a large proportion, and its carbonate content is relatively high. The shrinkage ratio during sintering is relatively large. While retaining the energy density, reserving a certain amount of evenly distributed pores can reduce Na + Volume strain during intercalation and deintercalation, crack prevention, and balanced capacity performance and cycle stability.

[0057] More preferably, the shell is multi-layered and in the shape of annual rings, and its primary particles are small and consistent, densely arranged, and the elements are evenly distributed. The stacked "annual ring-shaped" structure can reduce the damage to the electrode material structure caused by stress during the charge and discharge cycle, reduce the dissolution of metal ions during the charge and discharge cycle, and improve the cycle stability. BRIEF DESCRIPTION OF THE DRAWINGS

[0058] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the following is a brief introduction to the drawings required for use in the embodiments. It should be understood that the following drawings only show certain embodiments of the present application and therefore should not be regarded as limiting the scope of the present application.

[0059] Figure 1 This is a local SEM image of the surface of the core of the nickel-iron-manganese cathode material precursor of Example 1;

[0060] Figure 2 This is a surface SEM image of the nickel-iron-manganese cathode material precursor of Example 1;

[0061] Figure 3 This is a cross-sectional SEM image of the nickel-iron-manganese cathode material precursor of Example 1;

[0062] Figure 4This is a local SEM image of the surface of the core of the nickel-iron-manganese cathode material precursor of Example 2;

[0063] Figure 5 This is a surface SEM image of the nickel-iron-manganese cathode material precursor of Example 2;

[0064] Figure 6 This is a cross-sectional SEM image of the nickel-iron-manganese cathode material precursor of Example 2;

[0065] Figure 7 This is a local SEM image of the surface of the core of the nickel-iron-manganese cathode material precursor of Example 3;

[0066] Figure 8 This is a surface SEM image of the nickel-iron-manganese cathode material precursor of Example 3;

[0067] Figure 9 This is a cross-sectional SEM image of the nickel-iron-manganese cathode material precursor of Example 3;

[0068] Figure 10 This is a local SEM image of the surface of the core of the nickel-iron-manganese cathode material precursor of Comparative Example 1;

[0069] Figure 11 This is a surface SEM image of the carbonate system nickel-iron-manganese positive electrode material precursor of Comparative Example 1;

[0070] Figure 12 This is a cross-sectional SEM image of the carbonate system nickel-iron-manganese cathode material precursor of Comparative Example 1;

[0071] Figure 13 This is a surface SEM image of the carbonate system nickel-iron-manganese positive electrode material precursor of Comparative Example 2;

[0072] Figure 14 This is a cross-sectional SEM image of the carbonate system nickel-iron-manganese cathode material precursor of Comparative Example 2;

[0073] Figure 15 This is a surface SEM image of the nickel-iron-manganese cathode material precursor of Comparative Example 3;

[0074] Figure 16 This is a cross-sectional SEM image of the nickel-iron-manganese cathode material precursor of Comparative Example 3;

[0075] Figure 17 This is a surface SEM image of the nickel-iron-manganese cathode material precursor of Comparative Example 4;

[0076] Figure 18 This is a cross-sectional SEM image of the nickel-iron-manganese cathode material precursor of Comparative Example 4;

[0077] Figure 19This is the XRD pattern of the positive electrode material prepared from the nickel-iron-manganese positive electrode material precursor of Example 1. DETAILED DESCRIPTION

[0078] As used herein:

[0079] "Prepared from" is synonymous with "comprising." As used herein, the terms "comprising," "including," "having," "containing," or any other variations thereof, are intended to cover a non-exclusive inclusion. For example, a composition, process, method, article, or apparatus that comprises the listed elements is not necessarily limited to only those elements but may include other elements not expressly listed or inherent to such composition, process, method, article, or apparatus.

[0080] When an amount, concentration, or other value or parameter is expressed as a range, a preferred range, or a range defined by a series of upper preferred values ​​and lower preferred values, this should be understood as specifically disclosing all ranges formed by any pairing of any range upper limit or preferred value with any range lower limit or preferred value, regardless of whether the range is disclosed alone. For example, when a range of "1 to 5" is disclosed, the described range should be interpreted as including the range "1 to 4", "1 to 3", "1 to 2", "1 to 2 and 4 to 5", "1 to 3 and 5", etc. When a numerical range is described herein, unless otherwise stated, the range is intended to include its end values ​​and all integers and fractions within the range.

[0081] In these examples, parts and percentages are by mass unless otherwise indicated.

[0082] In a first aspect, the present application provides a nickel-iron-manganese cathode material precursor, which has a core-shell structure, including a core and an outer shell covering the core, wherein both the core and the outer shell are basic carbonates containing nickel, iron, and manganese.

[0083] Among them, the chemical formula of the precursor, core and shell is Ni x Fe y Mn z (CO3) a (OH) b , where 0<x<1, 0<y<1, 0<z<1, x+y+z=1; 0<a<1, 0<b<1, b=2(1-a), 0<b / a<1.5; and the b / a value of the inner core is greater than the b / a value of the outer shell, that is, the hydroxide content of the inner core is higher than the hydroxide content of the outer shell.

[0084] Within the above range, x, y, z, a, and b can be, for example, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9 or 0.95, respectively, or any value greater than 0 and less than 1; b / a can be, for example, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 0.95, 1.0, 1.1, 1.2, 1.3, 1.4 or 1.45, or any value greater than 0 and less than 1.5.

[0085] Preferably, in the chemical formula of the nickel-iron-manganese cathode material precursor, 0.1≤x≤0.5, 0.2≤z≤0.5.

[0086] Among them, the chemical formula Ni x Fe y Mn Z (CO3) a (OH) b It can represent the chemical formula of any part of the nickel-iron-manganese cathode material precursor, that is, the chemical composition of the nickel-iron-manganese cathode material precursor is Ni x Fe y Mn Z (CO3) a (OH) b , and it cannot be understood that the nickel iron manganese cathode material precursor includes Ni x 、Fe y 、Mn Z 、(CO3) a and (OH) b , nor can it be understood that the nickel iron manganese cathode material precursor includes Ni x Fe y Mn Z (CO3) a and Ni x Fe y Mn Z (OH) b .

[0087] The method for determining the values ​​of a and b in the above chemical formula is as follows: a certain amount of nickel-iron-manganese cathode material precursor solid is taken, washed several times with cold pure water, filtered and dried, and then dried at 120°C for 3 hours. The main metal content of the dried material is determined by potentiometric titration and ICP testing, and the values ​​of a and b are calculated based on the determined metal total amount Me (wt%). The specific calculation is as follows:

[0088] Me(wt%)=M / (M+60×a+17×b)×100;

[0089] b=2(1-a);

[0090] Where Me is the total metal content of nickel, iron and manganese in basic carbonate,

[0091] M is the sum of the products of the relative atomic mass and corresponding molar ratio of the three metal elements nickel, iron and manganese. When the chemical formula of the nickel iron manganese cathode material precursor is Ni x Fe y Mn Z (CO3) a (OH) b When M=M Ni ×x+M Fe ×y+M Mn ×z.

[0092] It is understandable that the chemical formula of any part of the nickel-iron-manganese cathode material precursor is Ni x Fe y Mn Z (CO3) a (OH) b However, the carbonate content and hydroxide content in different parts, that is, the a and b values, can be different, thereby adjusting the basic carbonate content in different parts.

[0093] In a preferred embodiment, the chemical formula of the precursor core is Ni x Fe y Mn Z (CO3) a (OH) b Satisfies: 0<b / a<1.5, the chemical formula of the precursor shell is Ni x Fe y Mn Z (CO3) a (OH) b Satisfies: 0<b / a<1, the chemical formula of the precursor is Ni x Fe y Mn Z (CO3) a (OH) b Satisfies: 0<b / a<1.

[0094] On the basis of the above embodiment, the shell thickness of the nickel-iron-manganese positive electrode material precursor is 3 to 10 μm, for example, it can be 6 to 10 μm, or 3 to 5 μm, or 7 to 10 μm, or 4 to 8 μm, and more specifically, it can be 3 μm, 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm or 10 μm, or any value in the range of 3 to 10 μm; the core diameter of the nickel-iron-manganese positive electrode material precursor is 1 to 6 μm, for example, it can be 1 to 3 μm, or 2 to 4 μm, or 3 to 6 μm, or 1 to 5 μm, and more specifically, it can be 1 μm, 2 μm, 3 μm, 4 μm, 5 μm or 6 μm, or any value in the range of 1 to 6 μm.

[0095] Preferably, the shell thickness is 3 to 5 μm, and the core diameter is 1 to 3 μm. The core of the nickel-iron-manganese cathode material precursor accounts for a relatively small proportion, while the shell accounts for a relatively large proportion.

[0096] Further preferably, the nickel-iron-manganese cathode material precursor has a loose core and a compact shell structure, and the overall porosity is 0.05% to 2.0%, for example, 0.05% to 0.1%, or 0.1% to 0.5%, or 0.5% to 1%, or 0.8% to 1.3%, or 1.3% to 2.0%, and more specifically, for example, 0.06%, 0.07%, 0.08%, 0.09%, 0.1%, 0.2%. , 0.4%, 0.6%, 0.8%, 1.0%, 1.1%, 1.2%, 1.3%, 1.4%, 1.5%, 1.6%, 1.7%, 1.8%, 1.9% or 2.0%, or any value in the range of 0.05% to 2.0%; wherein the porosity of the core of the nickel-iron-manganese positive electrode material precursor is 3% to 20%, for example, it can be 3% to 6%, or 6% to 12%, or 12% to 20%, more preferably Specifically, for example, it can be 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19% or 20%, or any value between 3% and 20%; the porosity of the shell of the nickel-iron-manganese positive electrode material precursor is 0.02% to 1.3%, for example, it can be 0.02% to 0.08%, or 0.08% to 0.1%, or 0.1% to 0.3%, or 0.3% to 0.8%, or 0.8% to 1.3%, more specifically, for example, it can be 0.02%, 0.04%, 0.06%, 0.08%, 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1.0%, 1.1%, 1.2% or 1.3%, or any value between 0.02% and 1.3%.

[0097] Among them, the porosity is the value obtained by image analysis of the cross section of the secondary particles of the precursor using Image-Pro Plus software using a scanning electron microscope (SEM), and is expressed as [(area of ​​pores inside the secondary particles / cross-sectional area of ​​the secondary particles) × 100] (%).

[0098] The inner core of the nickel-iron-manganese cathode material precursor is relatively loose due to the influence of the process, and its hydroxide content is high and accounts for a small proportion. The shrinkage ratio during sintering is relatively small, which can form a network skeleton in a smaller area, avoiding the internal hollowness from collapsing and cracking, thereby improving the cycle performance.

[0099] The shell of the nickel-iron-manganese cathode material precursor is dense and accounts for a large proportion, and its carbonate content is high. The shrinkage ratio during sintering is relatively large. While retaining the energy density, reserving a certain amount of evenly distributed pores can reduce the Na + Volume strain during intercalation and deintercalation, crack prevention, and balanced capacity performance and cycle stability.

[0100] Preferably, the primary particles of the inner core are in the form of flakes, and a plurality of the primary particles of the inner core are arranged in a honeycomb shape, thereby making them in a loose state; the primary particles of the outer shell are in the form of granules, and are densely arranged, thereby making them in a dense state.

[0101] The outer shell can be a single-layer or multi-layer structure. In a preferred embodiment, the multi-layered outer shell has a tree-ring-like structure. The outer shell's primary particles are small and uniform, ensuring uniform distribution of elements. This stacked "tree-ring-like" structure can reduce stress damage to the electrode material structure during charge-discharge cycles, reduce metal ion dissolution during charge-discharge cycles, and improve cycle stability.

[0102] Preferably, the secondary particle size D50 of the nickel-iron-manganese positive electrode material precursor is 7 to 26 μm, for example, 7 to 20 μm, or 10 to 25 μm, or 10 to 20 μm, or 15 to 26 μm, or 15 to 20 μm, or 13 to 26 μm, more specifically, for example, 7 μm, 8 μm, 9 μm, 10 μm, 11 μm, 12 μm, 13 μm, 14 μm, 15 μm, 16 μm, 17 μm, 18 μm, 19 μm, 20 μm, 21 μm, 22 μm, 23 μm, 24 μm, 25 μm or 26 μm, or any value in the range of 7 to 26 μm;

[0103] More preferably, the secondary particle size D50 of the precursor is 7 to 13 μm;

[0104] The particle size distribution of the nickel-iron-manganese positive electrode material precursor is Span=(D90-D10) / D50=0.4-0.9, for example, it can be 0.4-0.8, or 0.5-0.9, or 0.6-0.9, or 0.4-0.7, or 0.5-0.8, and more specifically, it can be 0.40, 0.45, 0.50, 0.55, 0.60, 0.65, 0.70, 0.75, 0.80, 0.85 or 0.90, or any value in the range of 0.4-0.9;

[0105] The specific surface area of ​​nickel-iron-manganese cathode material precursor is 50-120m 2 / g, for example, 50 to 100 m 2 / g, or 60-110m 2 / g, or 70-100m 2 / g, or 80-120m 2 / g, or 80-100m 2 / g, more specifically, for example, 50m 2 / g, 60m 2 / g、70m 2 / g、80m 2 / g、90m 2 / g、100m 2 / g、110m 2 / g or 120m 2 / g, or 50-120m 2 Any value in / g;

[0106] The tap density TD of the nickel-iron-manganese cathode material precursor is 1.0-1.6 g / cm 3 , for example, it can be 1.0 to 1.5 g / cm 3 , or 1.2~1.6g / cm 3 , or 1.1~1.4g / cm 3 , or 1.0~1.3g / cm 3 , more specifically, it can be 1.0 g / cm 3 , 1.1g / cm 3 , 1.2g / cm 3 , 1.3g / cm 3 , 1.4g / cm 3 , 1.5g / cm 3 or 1.6 g / cm 3 , or 1.0~1.6g / cm 3 Any value in ;

[0107] Preferably, the tap density TD of the precursor is 1.2 to 1.6 g / cm 3 .

[0108] The second aspect of the present application also provides a method for preparing the above-mentioned nickel-iron-manganese positive electrode material precursor, comprising:

[0109] Step 1: Add water and precipitant, mix to obtain reaction base liquid.

[0110] The reaction base liquid may further include a complexing agent, and the reaction base liquid may be a mixture of water, a precipitant, and a complexing agent, or a mixture of water and a precipitant. The complexing agent may be one or more of ammonium bicarbonate, ammonium carbonate, ammonium sulfate, ammonium bisulfate, ammonia water, and ammonium chloride; and the precipitant may be one or more of sodium carbonate, sodium bicarbonate, and sodium hydroxide. The sodium carbonate concentration in the sodium carbonate solution may be 100-300 g / L; the sodium bicarbonate concentration in the sodium bicarbonate solution may be 100-300 g / L; the ammonium bicarbonate concentration in the ammonium bicarbonate solution may be 2.3-2.7 mol / L; the ammonium sulfate concentration in the ammonium sulfate solution may be 100-300 g / L; and the ammonium chloride concentration in the ammonium chloride solution may be 80-250 g / L.

[0111] The pH value of the reaction base solution is 6.0-11.0, for example, it can be 6.0, 7.0, 8.0, 9.0, 10.0, or 11.0, or it can be 6.0-7.0, or 6.5-7.5, or 7.5-8.5, or 8.5-9.5, or 9.0-11.0, or any value in the range of 6.0-11.0; the ammonium concentration of the reaction base solution is ≤10 g / L, for example, it can be an ammonium-free solution, an ammonium concentration of 0.1 g / L, 0.5 g / L, 1 g / L, 2 g / L, 3 g / L, 4 g / L, 5 g / L, 6 g / L, 7 g / L, 8 g / L, 9 g / L or 10 g / L, or any value in the range of 0-10 g / L, wherein when no complexing agent is added to the reaction base solution, the ammonium concentration of the reaction base solution is 0 g / L;

[0112] The calculation method of the above ammonium concentration is: according to NH4 + Calculation of mass concentration in solution; the same below.

[0113] The reaction base liquid is heated to 30°C to 50°C, for example, 30°C, 32°C, 35°C, 37°C, 39°C, 40°C, 41°C, 43°C, 44°C, 45°C, 48°C or 50°C, and the stirring speed is controlled at 700r / min to 900r / min, for example, 700r / min, 710r / min, 720r / min, 730r / min, 740r / min, 750r / min, 760r / min, 770r / min, 800r / min, 810r / min, 820r / min, 830r / min, 850r / min, 860r / min, 880r / min or 900r / min.

[0114] Step 2: Adding a mixed metal solution including nickel, iron, and manganese, a precipitant, and a complexing agent to the reaction base liquid to carry out a co-precipitation reaction. The co-precipitation reaction is divided into a first co-precipitation reaction and a second co-precipitation reaction. Specifically, the first co-precipitation reaction is carried out by adding the mixed metal solution including nickel, iron, and manganese, a precipitant, and a complexing agent to the reaction base liquid until an inner core with a diameter of 1 to 6 μm is obtained. Then, the flow rate of the mixed metal solution including nickel, iron, and manganese, the precipitant, and the complexing agent is adjusted to carry out a second co-precipitation reaction until a precursor with a secondary particle size D50 of 7 to 26 μm is obtained.

[0115] After the feeding conditions are met, a mixed metal solution including nickel, iron and manganese, a precipitant and a complexing agent are pumped in at the same time. The pH and ammonium concentration of the reaction process are controlled by controlling the feed flow rates of the mixed metal solution, the precipitant and the complexing agent, so that the pH of the coprecipitation reaction process is controlled to be reduced to 6.5-10.0, for example, it can be 6.5, 7.0, 7.5, 8.0, 8.5, 9.0, 9.5, 10.0, or it can be 6.5-7.2, 7.2-7.5, or 7.5-9.0, or 7.5-8.5, or 8.5-10.0. The pH value of the reaction process is reduced relative to the pH value of the reaction base liquid, and the inner core is synthesized during the reduction process, and the outer shell is synthesized after the pH stabilizes.

[0116] During the coprecipitation reaction, the ammonium concentration is controlled to be ≤6 g / L, and ultimately to be ≤0.5 g / L. In the case where no complexing agent is added to the reaction base solution, the ammonium concentration needs to be gradually increased and then gradually decreased to ≤0.5 g / L during the reaction process. In the case where a complexing agent is added to the reaction base solution, the ammonium concentration needs to be directly and gradually decreased to ≤0.5 g / L during the reaction process.

[0117] During the coprecipitation reaction, the stirring speed is adjusted to 200 r / min to 400 r / min, for example, 200 r / min, 250 r / min, 300 r / min, 350 r / min or 400 r / min;

[0118] The feed flow ratio of the mixed metal solution, the precipitant and the complexing agent is controlled at 1:(1.2-2.5):(0-1.5), and the flow rate of the mixed metal solution is 10-60% / h of the available reactor volume.

[0119] During the first coprecipitation reaction, the feed flow ratio of the mixed metal solution, the precipitant, and the complexing agent is controlled at 1:(1.5-2.5):(0-1.5), and the flow rate of the mixed metal solution is 10-30% / h of the available reactor volume;

[0120] During the second coprecipitation reaction, the feed flow ratio of the mixed metal solution, the precipitant, and the complexing agent is controlled at 1:(1.2-1.8):(0-0.8), and the flow rate of the mixed metal solution is 30-60% / h of the available reactor volume;

[0121] The diameter of the inner core formed by the first coprecipitation reaction is 1 to 6 μm; the diameter D50 of the secondary particles of the precursor formed by the second coprecipitation reaction is 7 to 26 μm.

[0122] Step 3: Wash, centrifuge and dry to obtain nickel-iron-manganese cathode material precursor.

[0123] The third aspect of the present application also provides a sodium ion battery positive electrode material, which is prepared using the above-mentioned nickel-iron-manganese positive electrode material precursor.

[0124] The fourth aspect of the present application also provides a method for preparing a positive electrode material for a sodium ion battery, which is prepared by reacting the above-mentioned nickel-iron-manganese positive electrode material precursor with a sodium source.

[0125] Preferably, the molar ratio of the sum of nickel, iron and manganese to the sodium source in the nickel-iron-manganese positive electrode material precursor is 1:(1.00-1.05);

[0126] Preferably, the reaction is calcined using programmed temperature:

[0127] Specifically, the temperature is raised to 820-920° C. at a heating rate of 2-4° C. / min and calcined for 10-20 hours.

[0128] The fifth aspect of the present application also provides a sodium ion battery, comprising the above-mentioned sodium ion battery positive electrode material.

[0129] The present application controls the different ratios of hydroxide to carbonate in the core and shell of the nickel-iron-manganese cathode material precursor by indirectly controlling the pH value by regulating the flow rate of the precipitant in the co-precipitation method, thereby obtaining precursors with different core and shell morphologies and different ratios of hydroxide to carbonate. The core is relatively loose due to the influence of the process, and its hydroxide content is high and accounts for a small proportion. The shrinkage ratio during sintering is relatively small, and a small area of ​​​​network skeleton can be formed to avoid the internal hollowness from collapsing and cracking, thereby improving the cycle performance; the shell is dense and accounts for a large proportion, and its carbonate content is high. The shrinkage ratio during sintering is relatively large. While retaining the energy density, a certain amount of evenly distributed pores can be reserved to reduce Na + Volume strain during intercalation and deintercalation, crack prevention, and balanced capacity performance and cycle stability.

[0130] The primary particles that constitute the shell are preferably small and consistent, and densely arranged, and the elements inside are evenly distributed. The stacked "annual ring-like" structure can reduce the damage to the electrode material structure caused by stress during the charge and discharge cycle, reduce the dissolution of metal ions during the charge and discharge cycle, and improve the cycle stability.

[0131] The embodiments of the present application will be described in detail below in conjunction with specific examples, but it will be understood by those skilled in the art that the following examples are merely illustrative of the present application and should not be considered as limiting the scope of the present application. In the examples, if specific conditions are not specified, the conditions are carried out according to conventional conditions or manufacturer recommendations. The reagents or instruments used are not specified by the manufacturer and are conventional products that can be purchased commercially.

[0132] Example 1

[0133] Prepare a chemical formula of Ni 0.25 Fe 0.30 Mn 0.45 (CO3) 0.9 (OH) 0.2 Nickel iron manganese cathode material precursor, wherein the core chemical formula is Ni 0.25 Fe 0.30 Mn 0.45 (CO3) 0.72 (OH) 0.56 , the shell chemical formula is Ni 0.25 Fe 0.30 Mn 0.45 (CO3) 0.9 (OH) 0.2 , its specific preparation method is as follows:

[0134] ① Dissolve nickel sulfate, ferrous sulfate, and manganese sulfate crystals into a mixed metal solution with a nickel: iron: manganese molar ratio of 25:30:45 and a total metal concentration of 2 mol / L, prepare a sodium carbonate solution with a concentration of 150 g / L, and prepare an ammonium sulfate solution with a concentration of 140 g / L;

[0135] ② Add pure water and sodium carbonate solution to the reactor to prepare the reaction base liquid, control the pH value of the reaction base liquid to 8.5-8.7, introduce nitrogen protection, heat the reactor to 40°C, and control the stirring speed at 800r / min;

[0136] ③ After the feeding conditions are met, a pump is used to simultaneously pump in the mixed metal solution, sodium carbonate solution, and ammonium sulfate solution. The feed flow ratio of the mixed metal solution: sodium carbonate solution: ammonium sulfate solution is controlled at 1: (1.8-2.0): (0.8-1.1), and the flow rate of the mixed metal solution is 15-25% / h of the available reactor volume. Samples are taken when the kernel D50 is in the range of 1.0-1.5 μm. At the same time, the feed flow ratio of the mixed metal solution: sodium carbonate solution: ammonium sulfate solution is adjusted to be controlled at 1: (1.4-1.6): (0-0.5), and the flow rate of the mixed metal solution is 40-60% / h of the available reactor volume. During the reaction process, the pH is gradually reduced to 7.3-7.7, and the ammonium concentration is gradually increased to 3.5-4.5 g / L, and then reduced to ≤0.5 g / L. The stirring speed is gradually adjusted to 300 r / min, and the weight of the material in the reactor is adjusted. The co-precipitation time is 67 hours to reach the target particle size;

[0137] ④ After the synthesis stage, the material was put into a centrifuge and washed with cold pure water for 30 minutes to obtain a centrifugal material; the centrifugal material was put into an oven and dried at 140°C for 10 hours in an air atmosphere to obtain a dry sample, and the dry sample was sieved with a 200-mesh sieve to obtain the nickel-iron-manganese cathode material precursor of Example 1. The core and the precursor after the reaction were taken for inspection, the same below. The surface local SEM image, surface SEM image and cross-section SEM image of the core are shown as follows: Figure 1 、 Figure 2 and Figure 3 The SEM image is a scanning electron microscope image.

[0138] Example 2

[0139] Prepare a chemical formula of Ni 0.33 Fe 0.33 Mn 0.34 (CO3) 0.7 (OH) 0.6 Nickel iron manganese cathode material precursor, wherein the core chemical formula is Ni 0.33 Fe 0.33 Mn 0.34 (CO3) 0.6 (OH) 0.8 , the shell chemical formula is Ni 0.33 Fe 0.33 Mn 0.34 (CO3) 0.7 (OH) 0.6 , its specific preparation method is as follows:

[0140] ① Dissolve nickel sulfate, ferrous sulfate, and manganese sulfate crystals into a mixed metal solution with a nickel: iron: manganese molar ratio of 33:33:34 and a total metal concentration of 2 mol / L, prepare a sodium carbonate solution with a concentration of 150 g / L, prepare an ammonium bicarbonate solution with a concentration of 200 g / L, and prepare a sodium hydroxide solution with a concentration of 32%;

[0141] ② Add pure water, ammonium bicarbonate solution, sodium carbonate solution, and sodium hydroxide solution to the reactor to prepare the reaction base solution. Control the pH value of the reaction base solution to 8.9-9.1 and the ammonium concentration to 2.5-3.5 g / L. Pass nitrogen protection. Heat the reactor to 40°C and control the stirring speed to 800 r / min.

[0142] ③ After the feeding conditions are met, a pump is used to simultaneously pump in the mixed metal solution and sodium carbonate solution. The feed flow ratio of the mixed metal solution: sodium carbonate solution is controlled at 1: (1.8-2.0), and the flow rate of the mixed metal solution is 15-25% / h of the available reactor volume. Samples are taken when the kernel D50 is in the range of 2.0-2.5 μm. At the same time, the feed flow ratio of the mixed metal solution: sodium carbonate solution is adjusted to 1: (1.4-1.6), and the flow rate of the mixed metal solution is 40-60% / h of the available reactor volume. During the reaction process, the pH is controlled to be reduced to 7.2-7.8, and the ammonium concentration is reduced to ≤0.5 g / L. The stirring speed is gradually adjusted to 300 r / min, and the weight of the material in the reactor is adjusted. The co-precipitation time is 75 hours to reach the target particle size;

[0143] ④ After the synthesis stage, the material was centrifuged and washed with cold pure water for 30 min to obtain a centrifuged material; the centrifuged material was put into an oven and dried at 140 ° C for 10 h in an air atmosphere to obtain a dried sample. The dried sample was sieved with a 200-mesh sieve to obtain the nickel-iron-manganese cathode material precursor of Example 2, and the surface local SEM image, surface SEM image and cross-sectional SEM image of the kernel were shown as follows: Figure 4 、 Figure 5 and Figure 6 shown.

[0144] Example 3

[0145] Prepare a chemical formula of Ni 0.30 Fe 0.22 Mn 0.48 (CO3) 0.8 (OH) 0.4 Nickel iron manganese cathode material precursor, the core chemical formula is Ni 0.30 Fe 0.22 Mn 0.48 (CO3) 0.78 (OH) 0.44 , the shell chemical formula is Ni 0.30 Fe 0.22 Mn0.48 (CO3) 0.8 (OH) 0.4 , its specific preparation method is as follows:

[0146] ① Dissolve nickel sulfate, ferrous sulfate, and manganese sulfate crystals into a mixed metal solution with a nickel: iron: manganese molar ratio of 30:22:48 and a total metal concentration of 2 mol / L, and prepare a sodium carbonate solution with a concentration of 150 g / L;

[0147] ② Add pure water, sodium carbonate solution, and ammonia water to the reactor to prepare the reaction base liquid. Control the pH value of the reaction base liquid to 9.5-9.7 and the ammonium concentration to 4.5-5.5 g / L. Pass nitrogen protection. Heat the reactor to 45°C and control the stirring speed to 800 r / min.

[0148] ③ After the feeding conditions are met, a pump is used to simultaneously pump in the mixed metal solution, sodium carbonate solution, and ammonia water. The feed flow ratio of the mixed metal solution: sodium carbonate solution: ammonia water is controlled at 1: (1.8-2.0): (0.04-0.06), and the flow rate of the mixed metal solution is 15-25% of the available reactor volume / h. The reaction is performed until the kernel D50 is in the range of 1.0-1.5 μm. Samples are taken, and at the same time, the feed flow ratio of the mixed metal solution: sodium carbonate solution: ammonia water is adjusted to be controlled at 1: (1.4-1.6): (0-0.04), and the flow rate of the mixed metal solution is 40-60% of the available reactor volume / h. During the reaction process, the pH is gradually reduced to 7.8-8.4, and the ammonium concentration is gradually reduced to ≤0.5 g / L. The stirring speed is gradually adjusted to 300 r / min, and the weight of the material in the reactor is adjusted. The co-precipitation time is 53 hours to reach the target particle size;

[0149] ④ After the synthesis stage, the material was centrifuged and washed with cold pure water for 30 min to obtain a centrifuged material; the centrifuged material was put into an oven and dried at 140 ° C for 10 h in an air atmosphere to obtain a dried sample. The dried sample was sieved with a 200-mesh sieve to obtain the nickel-iron-manganese cathode material precursor of Example 3, and the surface local SEM image, surface SEM image and cross-sectional SEM image of the kernel were shown as follows: Figure 7 、 Figure 8 and Figure 9 shown.

[0150] Comparative Example 1

[0151] Prepare a chemical formula of Ni 0.33 Fe 0.33 Mn 0.34 The specific preparation method of the nickel-iron-manganese positive electrode material precursor of the CO3 carbonate system is as follows:

[0152] ① Dissolve nickel sulfate, ferrous sulfate, and manganese sulfate crystals into a mixed metal solution with a nickel: iron: manganese molar ratio of 33:33:34 and a total metal concentration of 2 mol / L, and prepare a sodium carbonate solution with a concentration of 150 g / L;

[0153] ② Add pure water to the reactor, prepare the reactor bottom liquid, control the pH value of the reaction bottom liquid to 7.0±0.5, introduce nitrogen protection, heat the reactor to 45°C, and control the stirring speed at 600r / min;

[0154] ③ After the feeding conditions are met, a pump is used to simultaneously pump in the mixed metal solution and sodium carbonate solution. The feed flow ratio of the mixed metal solution: sodium carbonate solution is controlled at 1:(1.7-1.8), and the flow rate of the mixed metal solution is 15-25% / h of the available reactor volume. Samples are taken when the kernel D50 is in the range of 2.5-3.0 μm. At the same time, the feed flow ratio of the mixed metal solution: sodium carbonate solution is adjusted to 1:(1.4-1.5), and the flow rate of the mixed metal solution is 40-60% / h of the available reactor volume. The pH of the reaction process is controlled at 6.8-7.2, and the stirring speed is gradually adjusted to 300 r / min. The weight of the material in the reactor is adjusted, and the co-precipitation time is 71 hours to reach the target particle size.

[0155] ④ After the synthesis stage, the material was put into a centrifuge and washed with cold pure water for 30 minutes to obtain a centrifugal material; the centrifugal material was put into an oven and dried at 140°C for 10 hours in an air atmosphere to obtain a dry sample. The dry sample was sieved with a 200-mesh sieve to obtain a nickel-iron-manganese positive electrode material precursor of the carbonate system of Comparative Example 1, and the surface local SEM image, surface SEM image and cross-sectional SEM image of the kernel were shown as follows: Figure 10 、 Figure 11 and Figure 12 shown.

[0156] Comparative Example 2

[0157] Prepare a chemical formula of Ni 0.19 Fe 0.04 Mn 0.77 The specific preparation method of the nickel-iron-manganese positive electrode material precursor of the CO3 carbonate system is as follows:

[0158] ① Dissolve nickel sulfate, ferrous sulfate, and manganese sulfate crystals into a mixed metal solution with a nickel: iron: manganese molar ratio of 19:4:77 and a total metal concentration of 2 mol / L, and prepare a sodium carbonate solution with a concentration of 150 g / L;

[0159] ② Add pure water to the reactor, prepare the reactor bottom liquid, control the pH value of the reaction bottom liquid to 6.5-7.5, heat the reactor to 40°C, and control the stirring speed at 800r / min;

[0160] ③ After the feeding conditions are met, use a pump to pump in the mixed metal liquid, control the pH to gradually drop to 3.3-3.7, then stop feeding the metal liquid, switch to sodium carbonate solution, control the pH to gradually rise to 7.3-7.7, stir for 1 hour, and then use a pump to pump in the mixed metal solution and sodium carbonate solution at the same time. The feed flow rate of mixed metal solution: sodium carbonate solution is controlled at 1: (1.5-2.0), and the flow rate of the mixed metal solution is 30-50% / h of the available reactor volume. During the reaction process, the pH is controlled at 7.3-7.7, and the stirring speed is gradually adjusted to 300r / min. The weight of the material in the reactor is adjusted. The co-precipitation time is 77h to reach the target particle size;

[0161] ④ After the synthesis stage, the material was centrifuged and washed with cold pure water for 30 min to obtain a centrifuged material; the centrifuged material was put into an oven and dried at 140 ° C for 10 h in an air atmosphere to obtain a dried sample. The dried sample was sieved with a 200-mesh sieve to obtain a nickel-iron-manganese positive electrode material precursor of the carbonate system of Comparative Example 2, and its surface SEM image and cross-section SEM image were shown as follows: Figure 13 and Figure 14 shown.

[0162] Comparative Example 3

[0163] Prepare a chemical formula of Ni 0.33 Fe 0.33 Mn 0.34 (CO3) 0.6 (OH) 0.8 The specific preparation method of the nickel-iron-manganese cathode material precursor is as follows:

[0164] ① Dissolve nickel sulfate, ferrous sulfate, and manganese sulfate crystals into a mixed metal solution with a nickel: iron: manganese molar ratio of 33:33:34 and a total metal concentration of 2 mol / L, and prepare a sodium carbonate solution with a concentration of 150 g / L;

[0165] ② Add pure water and sodium carbonate solution to the reactor to prepare the reactor bottom liquid, control the pH value of the reaction bottom liquid to 8.5-9.5, heat the reactor to 45°C, and control the stirring speed at 800r / min;

[0166] ③ After the feeding conditions are met, use a pump to pump in the mixed metal solution and sodium carbonate solution. The feed flow rate of the mixed metal solution: sodium carbonate solution is controlled at 1: (1.6-1.8). The flow rate of the mixed metal solution is 20-40% / h of the available reactor volume. During the reaction process, the pH is controlled at 7.9-8.3. The stirring speed is gradually adjusted to 300r / min, and the weight of the material in the reactor is adjusted. The co-precipitation time is 55h to reach the target particle size.

[0167] ④ After the synthesis stage, the material was put into a centrifuge and washed with cold pure water for 30 minutes to obtain a centrifugal material; the centrifugal material was put into an oven and dried at 140°C for 10 hours in an air atmosphere to obtain a dry sample. The dry sample was sieved with a 200-mesh sieve to obtain a nickel-iron-manganese positive electrode material precursor of Comparative Example 3, whose surface SEM image and cross-section SEM image are shown as follows: Figure 15 and Figure 16 shown.

[0168] Comparative Example 4

[0169] Prepare a chemical formula of Ni 0.30 Fe 0.30 Mn 0.40 (CO3) 0.8 (OH) 0.4 Nickel iron manganese cathode material precursor, the core chemical formula is Ni 0.30 Fe 0.30 Mn 0.40 (CO3) 0.84 (OH) 0.32 , the shell chemical formula is Ni 0.30 Fe 0.30 Mn 0.40 (CO3) 0.77 (OH) 0.46 , its specific preparation method is as follows:

[0170] ① Dissolve nickel sulfate, ferrous sulfate, and manganese sulfate crystals into a mixed metal solution with a nickel: iron: manganese molar ratio of 30:30:40 and a total metal concentration of 2 mol / L, and prepare a sodium carbonate solution with a concentration of 150 g / L;

[0171] ② Add pure water to the reactor and prepare the reactor bottom liquid. Control the pH value of the reaction bottom liquid to 7.0±0.5. Heat the reactor to 40°C and control the stirring speed at 800r / min.

[0172] ③ After the feeding conditions are met, use a pump to pump in the mixed metal solution and sodium carbonate solution. The feed flow rate of the mixed metal solution: sodium carbonate solution is controlled at 1: (1.5-1.7), and the flow rate of the mixed metal solution is 15-25% / h of the available reactor volume. Samples are taken when the kernel D50 is within the range of 5.0-5.5 μm. At the same time, the feed mixed metal solution: sodium carbonate solution flow rate ratio is adjusted to 1: (1.8-2.0), and the flow rate of the mixed metal solution is 40-60% / h of the available reactor volume.

[0173] During the reaction process, the pH was gradually increased to 8.3-8.7, the stirring speed was gradually adjusted to 300 r / min, the weight of the material in the reactor was adjusted, and the co-precipitation time was 62 h to reach the target particle size;

[0174] ④ After the synthesis stage, the material was centrifuged and washed with cold pure water for 30 minutes to obtain a centrifuged material; the centrifuged material was put into an oven and dried at 140°C for 10 hours in an air atmosphere to obtain a dried sample. The dried sample was sieved with a 200-mesh sieve to obtain a nickel-iron-manganese positive electrode material precursor of Comparative Example 4, whose surface SEM image and cross-section SEM image are shown as follows: Figure 17 and Figure 18 shown.

[0175] Battery performance test

[0176] The obtained ternary precursor was mixed with sodium carbonate in an element molar ratio of (Ni+Mn+Fe):Na=1:1.02 and then calcined in a muffle furnace at a heating rate of 3°C / min to 850°C for 15 hours. After cooling, it was sieved to obtain a positive electrode material. The XRD pattern of the positive electrode material prepared from the nickel-iron-manganese positive electrode material precursor of Example 1 is shown in FIG. Figure 19 As shown, from Figure 19 It can be seen that there is no phase change within 30 days, indicating that the positive electrode material prepared by the nickel-iron-manganese positive electrode material precursor and sodium salt has good storage performance.

[0177] Electrochemical performance testing was conducted using a button-type semi-battery: The aforementioned positive electrode material, conductive carbon black, and binder polyvinylidene fluoride were mixed into a slurry at a ratio of 8:1:1 and coated onto aluminum foil to form the positive electrode sheet. A metallic lithium sheet was used as the negative electrode, and the electrolyte was a 1 mol / L LiPF6 / EC:DMC (volume ratio 1:1). In a vacuum glove box, the battery case, positive and negative electrode sheets, separator, spring, and gasket were assembled into a button-type cell. Electrochemical performance testing was conducted using a Blue Electric test system.

[0178] The test results of Examples 1 to 3 and Comparative Examples 1 to 4 are shown in Table 1.

[0179] Table 1 Precursor indicators and performance parameters of sodium ion batteries in various embodiments and comparative examples

[0180]

[0181] Note: The seed crystals (i.e., core) and nickel-iron-manganese cathode material precursors of each embodiment and comparative example were taken for inspection, and the metal content of the core and the precursor were measured, and then the b / a value of the shell was calculated.

[0182] According to Table 1, the precursor cores prepared in Examples 1-3 all have a honeycomb structure; the shells all have a multi-layer structure, the primary particles of the shell are granular, densely arranged, and have low porosity, and the ratio of hydroxide to carbonate in the core is controlled to be higher than the ratio of hydroxide to carbonate in the shell, thereby achieving the effect of indirectly controlling the internal and external pore size and porosity of the positive electrode material that inherits the performance of the structure, while effectively improving the capacity and the first-effect performance. At the same time, the molar content of hydroxide in the core region is higher than the molar content of carbonate, which avoids the generation of internal hollowness after sintering of the material, effectively improves the particle strength of the positive electrode material and the tap density of the product, brings beneficial effects on the processing performance of the positive electrode material, and also improves the cycle performance of the product.

[0183] The precursor prepared in Comparative Example 1 is a carbonate with a core-shell structure, and the precursor prepared in Comparative Example 2 is a carbonate with a monolithic structure. The internal molecular formulas of the two are the same. The battery prepared from the positive electrode material inheriting the structural performance has poor characterization data such as rate, capacity, first effect, and cycle, which are significantly different from those in Example 2. The reasons may be: the positive electrode material obtained by sintering the carbonate has too high a porosity and too low a compaction density, which affects the capacity performance; and it is more prone to cracking, resulting in poor cycle performance. Comparative Example 2 is worse than Comparative Example 1 in electrochemical performance characterization data, and the reasons may be: Comparative Example 2 is a monolithic structure, and the radial structure of the shell of Comparative Example 1 may be conducive to the infiltration reaction of the electrolyte and improve the capacity performance; Comparative Example 2 is a monolithic structure, which may be more likely to produce large cracks that penetrate during charge and discharge, resulting in poor cycle performance.

[0184] The precursor prepared in Comparative Example 3 is a basic carbonate with a monolithic structure and the same internal molecular formula. The electrochemical characterization data of the battery prepared from the positive electrode material inheriting the structural performance are all poor, and are significantly different from those in Example 2. The reasons may be: the tap density and specific surface area of ​​the product in Comparative Example 3 are lower than those in Example 2, affecting the capacity performance; and the monolithic structure may make it easier to produce large cracks during charge and discharge, resulting in poor cycling. However, the electrochemical data of the battery prepared in Comparative Example 3 are better than those in Comparative Examples 1-2. The reasons may be: compared with carbonates, when basic carbonates are sintered into positive electrode materials, the porosity decreases, the compaction density is improved, and the capacity and cycle are improved to a certain extent.

[0185] Comparative Example 4 is a core-shell structure, and the ratio of hydroxide to carbonate in the core is lower than that in the shell. The cycle data of the battery prepared by the positive electrode material inheriting the structural performance are all poor, and there are significant differences compared with Example 3. The reasons may be that the shell in Example 3 is dense and accounts for a large proportion, and its carbonate content is high. The shrinkage ratio during sintering is relatively large. While retaining the energy density, reserving a certain amount of evenly distributed pores can reduce Na +Volume strain during the intercalation and deintercalation process prevents cracking, which is beneficial for balancing capacity performance and cycle stability. Comparative Example 4, on the other hand, has a loose, flaky shell structure with a large contact surface with the electrolyte, which is beneficial for the intercalation and deintercalation of sodium ions in the material and has good rate performance. However, due to the large contact surface, side reactions are more likely to occur, leading to changes in the material structure and collapse, resulting in poor cycle performance.

[0186] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present application, rather than to limit them. Although the present application has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some or all of the technical features therein. These modifications or replacements do not deviate the essence of the corresponding technical solutions from the scope of the technical solutions of the embodiments of the present application.

[0187] Furthermore, those skilled in the art will appreciate that although some embodiments herein include certain features included in other embodiments but not others, combinations of features from different embodiments are intended to be within the scope of this application and to form distinct embodiments. For example, in the claims above, any of the claimed embodiments may be used in any combination. The information disclosed in this background section is intended solely to enhance understanding of the overall background of this application and should not be construed as an admission or any implication that such information constitutes prior art known to those skilled in the art.

Claims

1. A nickel-iron-manganese cathode material precursor, characterized in that: The precursor is a core-shell structure, comprising a core and a shell covering the core, wherein both the core and the shell are basic carbonates containing nickel, iron, and manganese; The chemical formula of the precursor, the core and the shell is Ni x Fe y Mn z (CO3) a (OH) b , wherein, 0<x<1, 0<y<1, 0<z<1, x+y+z=1; 0<a<1, 0<b<1, b=2(1-a), 0<b / a<1.5; and the b / a value of the inner core is greater than the b / a value of the outer shell.

2. The nickel-iron-manganese cathode material precursor according to claim 1, characterized in that 0.1≤x≤0.5, 0.2≤z≤0.5; And / or, the chemical formula of the precursor core satisfies: 0<b / a<1.5, the chemical formula of the precursor shell satisfies: 0<b / a<1, and the chemical formula of the precursor satisfies: 0<b / a<1.

3. The nickel-iron-manganese cathode material precursor according to claim 1 or 2, characterized in that: The nickel-iron-manganese cathode material precursor satisfies at least one of the following conditions A to B: A. The shell thickness is 3-10 μm, and the core diameter is 1-6 μm; B. The overall porosity of the precursor is 0.05% to 2.0%; wherein the porosity of the core is 3% to 20%, and the porosity of the shell is 0.02% to 1.3%.

4. The nickel-iron-manganese cathode material precursor according to claim 3, characterized in that The shell has a thickness of 3-5 μm and the core has a diameter of 1-3 μm.

5. The nickel-iron-manganese cathode material precursor according to claim 1 or 2, characterized in that: The nickel-iron-manganese cathode material precursor satisfies at least one of the following C~F conditions: C. The core primary particles are in the form of flakes, and a plurality of the core primary particles are arranged in a honeycomb shape; D. the shell primary particles are granular; E. The shell is a single-layer structure; F. The shell is a multi-layer structure.

6. The nickel-iron-manganese cathode material precursor according to claim 1, characterized in that The nickel-iron-manganese cathode material precursor satisfies at least one of the following conditions (1) to (4): (1) The secondary particle size D50 of the precursor is 7 to 26 μm; (2) The particle size distribution of the precursor is Span = (D90-D10) / D50 = 0.4~0.9; (3) The BET specific surface area of ​​the precursor is 50~120m 2 / g; (4) The tap density TD of the precursor is 1.0~1.6g / cm 3 .

7. The nickel-iron-manganese cathode material precursor according to claim 6, characterized in that: The secondary particle size D50 of the precursor is 7-13 μm; and / or the tap density TD of the precursor is 1.2-1.6 g / cm 3 .

8. A method for preparing a nickel-iron-manganese cathode material precursor according to any one of claims 1 to 7, characterized in that: include: adding water and a precipitant, and mixing to obtain a reaction base liquid; Adding a mixed metal solution including nickel, iron, and manganese, a precipitant, and a complexing agent to the reaction base liquid to perform a coprecipitation reaction; Washing, centrifuging, and drying to obtain the nickel-iron-manganese cathode material precursor; Wherein, the coprecipitation reaction is divided into a first coprecipitation reaction and a second coprecipitation reaction; The specific steps of the co-precipitation reaction are: first, add the mixed metal solution including nickel, iron, and manganese, the precipitant, and the complexing agent to the reaction base liquid to carry out the first co-precipitation reaction until the inner core is obtained; then add the mixed metal solution including nickel, iron, and manganese, the precipitant, and the complexing agent to carry out the second co-precipitation reaction until the precursor is obtained.

9. The method for preparing a nickel-iron-manganese cathode material precursor according to claim 8, wherein: The reaction base liquid satisfies at least one of the following conditions a to d: a. The reaction base liquid further comprises a complexing agent; b. The pH value of the reaction bottom solution is 6.0-11.0; c. The ammonium concentration of the reaction solution is ≤10 g / L; d. The reaction mixture was heated to 30°C~50°C and the stirring speed was controlled at 700r / min~900r / min; The coprecipitation reaction satisfies at least one of the following conditions e to l: e. The pH value during the coprecipitation reaction was controlled to be 6.5-10.0; f. The ammonium concentration is controlled during the coprecipitation reaction to be ≤6 g / L, and the ammonium concentration is finally controlled to be ≤0.5 g / L; g. During the coprecipitation reaction, the stirring speed was adjusted to 200 r / min~400 r / min; h. The complexing agent is one or more of ammonium bicarbonate, ammonium carbonate, ammonium sulfate, ammonium bisulfate, ammonia, and ammonium chloride; i. The precipitating agent is one or more of sodium carbonate, sodium bicarbonate, and sodium hydroxide; j. The feed flow ratio of the mixed metal solution, the precipitant, and the complexing agent is controlled at 1: (1.2-2.5): (0-1.5), and the flow rate of the mixed metal solution is 10-60% / h of the available reactor volume; k. During the first coprecipitation reaction, the feed flow ratio of the mixed metal solution, the precipitant, and the complexing agent is controlled at 1: (1.5-2.5): (0-1.5), and the flow rate of the mixed metal solution is 10-30% / h of the available reactor volume; During the second coprecipitation reaction, the feed flow ratio of the mixed metal solution, the precipitant, and the complexing agent is controlled at 1: (1.2-1.8): (0-0.8), and the flow rate of the mixed metal solution is 30-60% / h of the available reactor volume; l. The diameter of the core formed by the first coprecipitation reaction is 1~6μm; the secondary particle size D50 of the precursor formed by the second coprecipitation reaction is 7~26μm.

10. A sodium ion battery cathode material, characterized in that: It is prepared using the nickel-iron-manganese positive electrode material precursor described in any one of claims 1 to 7.

11. A sodium ion battery, characterized in that: Including the sodium ion battery positive electrode material according to claim 10.

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