Positive electrode material, preparation method and application thereof, sodium ion battery

Abstract

The present invention relates to the technical field of sodium ion batteries, and in particular to a positive electrode material, a preparation method thereof, and an application thereof, and a sodium ion battery containing the positive electrode material. The positive electrode material has a core-shell structure, consisting of a core and a shell; the core has a composition shown in Formula I: Na a Fe 1‑b M 1 b O2, formula I, 0.6≤a≤1.05, 0<b≤0.1, M 1 At least one selected from Sn, V, Y, Ti, Zr and Nb; the shell has a composition shown in formula II: Na c Mn x Ni 1‑x‑ d M 2 d O2, formula II, 0.6≤c≤1.05, 0<x≤0.5, 0<d<0.5, M 2 At least one selected from Si, Sr, B and Cu; in the positive electrode material, M 1 and M 2 The sodium ion battery containing the above cathode material has high rate performance and capacity retention rate, as well as low Fe dissolution amount.

Description

Technical Field

[0001] The present invention relates to the technical field of sodium ion batteries, and in particular to a positive electrode material, a method for preparing the positive electrode material, an application of the positive electrode material, and a sodium ion battery containing the positive electrode material. Background Art

[0002] In recent years, the large-scale development of renewable clean energy sources such as solar and wind power, as well as the widespread use of electric vehicles, has driven the rapid development of electrochemical energy storage. Lithium-ion batteries, with their high energy density and long cycle life, are widely used in electrochemical energy storage systems. However, due to the limited and uneven distribution of global lithium resources, future applications in large-scale energy storage will inevitably face bottlenecks in the supply of raw materials. Elemental sodium and lithium are in the same main group and have very similar physical and chemical properties. Furthermore, sodium is much more abundant on Earth than lithium. Therefore, sodium-ion batteries hold great potential as future large-scale energy storage systems.

[0003] Among the many types of sodium-ion battery cathode materials, layered oxide systems have become the focus of development in the industry due to their high energy density and similar synthesis process to lithium-ion battery layered oxide cathode materials. However, at this stage, layered oxide systems still have problems such as poor cycle performance and severe metal dissolution, which can usually be improved through doping, coating, etc. Conventional inert coatings can usually reduce metal dissolution to a certain extent, but they will also hinder the transmission of sodium ions, affecting capacity and rate performance. Summary of the Invention

[0004] The purpose of the present invention is to overcome the above technical problems and provide a positive electrode material and its preparation method and application, and a sodium ion battery, wherein the positive electrode material is limited to a core of NaFeO2 phase containing Fe and a shell of NaMn phase containing Mn. x Ni 1-x The O2 phase and the doping elements are distributed in a gradient, so that the positive electrode material has high capacity, high structural stability and high cycle stability; at the same time, the sodium ion battery containing the positive electrode material has high rate performance and capacity retention rate.

[0005] In order to achieve the above object, the first aspect of the present invention provides a positive electrode material, wherein the positive electrode material has a core-shell structure, consisting of a core and a shell; wherein the core has a composition shown in Formula I: Na a Fe 1-b M 1 b O2, formula I, wherein 0.6≤a≤1.05, 0<b≤0.1, M 1 At least one selected from Sn, V, Y, Ti, Zr and Nb; the shell has a composition shown in formula II: Nac Mn x Ni 1-x-d M 2 d O2, formula II, wherein 0.6≤c≤1.05, 0<x≤0.5, 0<d<0.5, M 2 At least one selected from Si, Sr, B and Cu;

[0006] Among them, in the positive electrode material, M 1 and M 2 They are distributed in gradients.

[0007] Preferably, in the positive electrode material, M 1 The distribution is gradient decreasing from the core to the interface, M 2 The distribution is gradient increasing from the interface to the surface.

[0008] Preferably, in the positive electrode material, M 1 The decreasing rate from the core to the interface is 0.001-0.5 mol% / μm, preferably 0.1-0.3 mol% / μm; M 2 The increasing rate from the interface to the surface is 0.001-0.5 mol% / μm, preferably 0.002-0.015 mol% / μm.

[0009] Preferably, in the positive electrode material, based on the molar amount of the core in terms of Fe, M 1 The doping amount is 0.01-2 mol%, preferably 0.05-0.5 mol%; based on the molar amount of the shell layer calculated as Mn and Ni, M 2 The doping amount is 0.01-2 mol%, preferably 0.05-0.5 mol%.

[0010] Preferably, the mass ratio of the core to the shell is 0.2-10:1, preferably 0.5-4:1.

[0011] Preferably, in the XRD diffraction patterns of the core and the shell obtained independently under CuKa radiation, a characteristic diffraction peak of the (003) crystal plane appears at 15.7-18° 2θ.

[0012] Preferably, the average particle size d1 of the primary particles in the core and the average particle size d2 of the primary particles in the shell satisfy Formula III: d2=n×d1+200, Formula III, wherein 0<n≤5.

[0013] Preferably, the particle size distribution of the positive electrode material is selected from normal distribution or non-normal distribution.

[0014] Preferably, when the particle size distribution of the positive electrode material is a normal distribution, the average particle size D50 of the positive electrode material is 2-15 μm; or, when the particle size distribution of the positive electrode material is a non-normal distribution, the d50 within the distribution peak of the positive electrode material is 2-15 μm. peak 2-15μm.

[0015] A second aspect of the present invention provides a method for preparing a positive electrode material, the method comprising:

[0016] (1) In a non-oxidizing atmosphere, a solution containing an Fe source and a solution containing an M 1 The solution of the source, the first precipitant solution and the first complexing agent solution are mixed and subjected to a first coprecipitation reaction, and the M-containing 1 The feed rate of the solution of the source is 1:1 to obtain slurry A;

[0017] (2) In a non-oxidizing atmosphere, a solution containing a Mn source, a solution containing a Ni source, a solution containing M 2 The solution of the source, the second precipitant solution and the second complexing agent solution are mixed with the slurry A and subjected to a second coprecipitation reaction, and the M-containing 2 The feed rate of the solution of the source is 1:1 to obtain slurry B;

[0018] (3) aging, washing, filtering and drying the slurry B in sequence to obtain a precursor comprising a matrix and a coating layer;

[0019] (4) mixing the precursor and a Na source, and sintering the resulting mixture in an oxygen-containing atmosphere to obtain a positive electrode material having a normal distribution;

[0020] Wherein, the matrix has a composition shown in Formula IV: Fe 1-m M 1 m (OH)2, Formula IV, 0<m≤0.1, M 1 At least one selected from Sn, V, Y, Ti, Zr and Nb; the coating layer has a composition shown in formula V: (Mn y Ni 1-y-n M 2 n )(OH)2, formula V, 0<y≤0.5, 0<n<0.5, M 2 At least one selected from Si, Sr, B and Cu.

[0021] Preferably, the cathode material is composed of a core having formula I and a shell having formula II, Na a Fe 1-b M 1 b O2, formula (I), Na c Mn x Ni1-x-d M 2 d O2, formula (II), and M 1 and M 2 They are distributed in gradients respectively;

[0022] Wherein, in formula I, 0.6≤a≤1.05, 0<b≤0.1, M 1 At least one selected from Sn, V, Y, Ti, Zr and Nb; in Formula II, 0.6≤c≤1.05, 0<x≤0.5, 0<d<0.5, M 2 At least one element selected from Si, Sr, B and Cu.

[0023] Preferably, the method further comprises:

[0024] S1, cycling steps (1)-(4), and controlling the time of the first coprecipitation reaction in step (1) and the second coprecipitation reaction in step (2) during each cycle to obtain different particles of positive electrode materials;

[0025] S2. Mixing the different granular positive electrode materials to obtain a positive electrode material with a non-normal distribution.

[0026] Compared with the prior art, the present invention has the following advantages:

[0027] (1) The positive electrode material provided by the present invention is limited to a core of Na a Fe 1-b M 1 b O2, ensuring that the positive electrode material has high capacity; limiting the shell to Na c Mn x Ni 1-x-d M 2 d O2, effectively stabilizes the outer layer structure of the cathode material and inhibits Fe dissolution; and limits the doping elements (i.e., M 1 and M 2 ) is distributed in a gradient within the cathode material, and in particular, the rate of change of the gradient distribution is further limited, which can more effectively alleviate the stress deformation of the core-shell layer during the charge and discharge process, and further improve the cycle stability;

[0028] Specifically, the doping element M 1 Using elements that prevent grain boundary growth, M 2 By using fluxing elements, the particle size d1' of the primary particles in the core constituting the interface and the particle size d2' of the primary particles in the shell constituting the interface are made to differ by ≤±10% through gradient distribution, thereby avoiding stress deformation caused by excessive difference in particle size during charge and discharge; and the M in the shell 2Doping with elements can also play a role in supporting the material structure, stabilizing the bulk structure of the material during charging and discharging, and preventing the dissolution of transition metals;

[0029] (2) The method provided by the present invention is to control the M-containing 1 The solution of the source and the M 2 The feed rate of the source solution is such that the doping element M 1 and M 2 There is a gradient distribution inside the cathode material, especially M 1 The distribution is gradient decreasing from the core to the interface, M 2 The main elements of the core and shell of the positive electrode material are evenly distributed in a gradient distribution from the interface to the surface, combined with the technical means of co-precipitation reaction, thereby obtaining a positive electrode material with a normal distribution; preferably, by regulating the conditions of the co-precipitation reaction, different particles of positive electrode materials are obtained, and the different particles of positive electrode materials are proportioned to obtain a positive electrode material with a non-normal distribution;

[0030] (3) The positive electrode material provided by the present invention is used in sodium ion batteries, which can effectively improve the electrochemical performance of sodium ion batteries, especially have higher rate performance and capacity retention rate, and effectively reduce the amount of Fe dissolution. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 This is a cross-sectional line scanning distribution diagram of Ti and Cu elements in the positive electrode material S1 prepared in Example 1;

[0032] Figure 2 XRD patterns of the core and shell of the cathode material S1 prepared in Example 1;

[0033] Figure 3 This is a cross-sectional line scanning distribution diagram of the Ti element of the positive electrode material DS1 prepared in Comparative Example 1;

[0034] Figure 4 This is a graph showing the 1C cycle performance of button batteries assembled with the positive electrode materials prepared in Example 1 and Comparative Example 1. DETAILED DESCRIPTION

[0035] The endpoints of the ranges and any values disclosed herein are not limited to the precise ranges or values, and these ranges or values should be understood to include values close to these ranges or values. For numerical ranges, the endpoints of each range, the endpoints of each range and individual point values, and the individual point values can be combined with each other to obtain one or more new numerical ranges, which should be considered to be specifically disclosed herein.

[0036] In the present invention, unless otherwise specified, the terms "first" and "second" do not indicate a sequential order or limit the materials or steps. They are merely used to distinguish or indicate that they are not the same material or step. For example, the terms "first" and "second" in "first precipitant solution" and "second precipitant solution" are merely used to indicate that they are not the same precipitant solution; similarly, the terms "first" and "second" in "first coprecipitation reaction" and "second coprecipitation reaction" are merely used to indicate that they are not the same coprecipitation reaction.

[0037] The first aspect of the present invention provides a positive electrode material having a core-shell structure, consisting of a core and a shell; wherein the core has a composition shown in Formula I: Na a Fe 1-b M 1 b O2, formula I, wherein 0.6≤a≤1.05, 0<b≤0.1, M 1 At least one selected from Sn, V, Y, Ti, Zr and Nb; the shell has a composition shown in formula II: Na c Mn x Ni 1-x- d M 2 d O2, formula II, wherein 0.6≤c≤1.05, 0<x≤0.5, 0<d<0.5, M 2 At least one selected from Si, Sr, B and Cu;

[0038] Among them, in the positive electrode material, M 1 and M 2 They are distributed in gradients.

[0039] In the present invention, unless otherwise specified, the positive electrode material has a core-shell structure, and being composed of a core and a shell means that the positive electrode material includes a core and a shell layer covering the core.

[0040] The inventors of the present invention have found that in the positive electrode material, the core is limited to the Fe-containing NaFeO2 phase (i.e., Na a Fe 1- b M 1 b O2), ensuring that the positive electrode material has high capacity; limiting the shell to NaMn containing Mn x Ni 1-x O2 phase (i.e., Na c Mn x Ni 1-x- d M 2 dO2), effectively stabilizes the outer layer structure of the cathode material and inhibits Fe dissolution; at the same time, M 1 Doping of elements, in the phase formation process M 1 The element has the effect of refining the grains. Therefore, when the sintering is still carried out at the same temperature after adding the doping element, the primary particle size of the core formed is smaller. 1 The elements are distributed in a gradient, especially from the inside to the outside, so that the primary particle size outside the core is close to that of the shell, thereby avoiding stress deformation caused by excessive difference in particle size during charge and discharge; M in the shell 2 The doping of elements mainly plays a role in fluxing and supporting the material structure, stabilizing the bulk structure of the material during charge and discharge, avoiding the dissolution of transition metals, and the shell primary particles are small, which can effectively ensure the initial capacity and rate performance of the material. 2 The gradient distribution of elements, especially the increasing gradient distribution, can ensure that the outer structure of the material is more stable and further improve the cycle performance.

[0041] In some embodiments of the present invention, preferably, in the positive electrode material, M 1 The distribution is gradient decreasing from the core to the interface, M 2 The distribution is gradient increasing from the interface to the surface.

[0042] In the present invention, unless otherwise specified, the core is the center of the positive electrode material, the interface is the junction between the inner core and the shell, and the surface is the outermost layer of the positive electrode material.

[0043] In some embodiments of the present invention, preferably, in the positive electrode material, M 1 The decreasing rate from the core to the interface is 0.001-0.5 mol% / μm, for example, 0.001 mol% / μm, 0.005 mol% / μm, 0.01 mol% / μm, 0.1 mol% / μm, 0.15 mol% / μm, 0.196 mol% / μm, 0.2 mol% / μm, 0.25 mol% / μm, 0.3 mol% / μm, 0.5 mol% / μm, and any value in a range consisting of any two values, preferably 0.1-0.3 mol% / μm, and most preferably 0.196 mol% / μm; M 2The increasing rate from the interface to the surface is 0.001-0.5 mol% / μm, for example, 0.001 mol% / μm, 0.002 mol% / μm, 0.004 mol% / μm, 0.008 mol% / μm, 0.01 mol% / μm, 0.012 mol% / μm, 0.015 mol% / μm, 0.2 mol% / μm, 0.5 mol% / μm, and any value in the range of any two values, preferably 0.002-0.015 mol% / μm, most preferably 0.004 mol% / μm. Wherein, M 1 The decreasing rate from the core to the interface and M 2 The calculation method of the increasing rate from the interface to the surface is M per μm. 1 or M 2 The difference in mole percentage.

[0044] In the present invention, the doping element M of the core 1 and the shell doping element M 2 The rate of change of the gradient distribution is within the above-mentioned limited range, which can further maintain the stress deformation of the positive electrode material in the charge and discharge process within a controllable range. 1 and M 2 When the gradient distribution changes too quickly, the difference in volume expansion coefficient between the inside and outside of the material will become larger. During the charge and discharge process, the unit cell volume of the positive electrode material will frequently expand and contract, causing stress deformation of the core-shell layer and irreversible deterioration of the cycle performance. 1 and M 2 If the gradient distribution change rate is too slow, the gradient distribution formed is not obvious, and the improvement of the material performance is insufficient. Therefore, it is necessary to control the doping element M 1 and M 2 The gradient distribution change rate is within the above range, reducing the doping element M 1 and M 2 Effect of gradient distribution on the cycle performance of cathode materials.

[0045] In some embodiments of the present invention, preferably, in the positive electrode material, based on the molar amount of the core calculated as Fe, M 1 The doping amount is 0.01-2 mol%, for example, 0.01 mol%, 0.05 mol%, 0.1 mol%, 0.2 mol%, 0.3 mol%, 0.4 mol%, 0.5 mol%, 1 mol%, 2 mol%, and any value in the range of any two values, preferably 0.05-0.5 mol%; based on the molar amount of the shell layer calculated as Mn and Ni, M 2The doping amount is 0.01-2 mol%, for example, 0.01 mol%, 0.05 mol%, 0.1 mol%, 0.2 mol%, 0.3 mol%, 0.4 mol%, 0.5 mol%, 1 mol%, 2 mol%, and any value in a range consisting of any two values, preferably 0.05-0.5 mol%. Within this range, the doping element can enter the crystal lattice and play a role in refining the grains.

[0046] In some embodiments of the present invention, preferably, the particle size of the core is 1-10 μm, for example, 1 μm, 2 μm, 5 μm, 8 μm, 10 μm, and any value in the range consisting of any two values, preferably 2-8 μm; the thickness of the shell is 1-10 μm, for example, 1 μm, 2 μm, 5 μm, 8 μm, 10 μm, and any value in the range consisting of any two values, preferably 2-8 μm.

[0047] In some embodiments of the present invention, the core-to-shell ratio is preferably 0.2-10:1, for example, 0.2:1, 0.5:1, 1:1, 2:1, 3:1, 4:1, 5:1, 8:1, 10:1, and any value in a range consisting of any two of these values, preferably 0.5-4:1. Within this range, the positive electrode material capacity and cycle performance can be properly achieved.

[0048] In some embodiments of the present invention, in Formula I, 0.6≤a≤1.05, for example, 0.6, 0.7, 0.8, 0.9, 1, 1.03, 1.05, and any value in the range of any two values, preferably 0.7≤a≤1.03; 0<b≤0.1, for example, 0.001, 0.005, 0.01, 0.02, 0.05, 0.1, and any value in the range of any two values, 0<b≤0.02; M 1 At least one selected from Sn, V, Y, Ti, Zr and Nb, preferably selected from Ti and / or Zr.

[0049] In some embodiments of the present invention, in Formula II, 0.6≤c≤1.05, for example, 0.6, 0.7, 0.8, 0.9, 1, 1.03, 1.05, and any value in a range consisting of any two values, preferably 0.7≤c≤1.03; 0<x≤0.5, for example, 0.001, 0.1, 0.198, 0.2, 0.3, 0.4, 0.499, 0.5, and any value in a range consisting of any two values, preferably 0.198≤x≤0.5; 0<d<0.5, for example, 0.001, 0.002, 0.005, 0.01, 0.02, 0.03, 0.04, 0.1, 0.2, 0.5, and any value in a range consisting of any two values, 0.002≤d≤0.04; M 2 At least one selected from Si, Sr, B and Cu, preferably at least one selected from Si, Sr and Cu.

[0050] In some embodiments of the present invention, preferably, in the XRD diffraction patterns obtained independently of the core and the shell under CuKa radiation, a characteristic diffraction peak of the (003) crystal plane appears at 15.7-18° at 2θ. In the present invention, when the 2θ angle of the core and the shell has a characteristic diffraction peak within the above range, it indicates that both the core and the shell are O3 phase crystal structures, which can ensure that the positive electrode material has a high specific capacity, wherein the core is mainly NaFeO2 phase containing Fe, which can further ensure the high capacity of the positive electrode material, and the shell is mainly NaMn containing Mn. x Ni 1-x The O2 phase can effectively stabilize the outer structure of the positive electrode material and inhibit the dissolution of Fe.

[0051] In some embodiments of the present invention, preferably, the core and shell are each independently secondary particles formed by agglomeration of primary particles. Further preferably, the average particle size d1 of the primary particles in the core and the average particle size d2 of the primary particles in the shell satisfy Formula III: d2 = n × d1 + 200, where 0 < n ≤ 5. In the present invention, when d1 and d2 satisfy this relationship, stress deformation caused by large particle size differences during charge and discharge can be avoided while effectively ensuring the initial capacity and rate performance of the material.

[0052] In some embodiments of the present invention, preferably, the average particle size d1 of the primary particles in the core is ≤300 nm; and the average particle size d2 of the primary particles in the shell is ≥500 nm.

[0053] In the present invention, the kernel M 1 It has the effect of refining grains, and M in the shell 2This has the effect of promoting flux and grain growth, and the main elements are evenly distributed within the core and shell. For example, the concentrations of Fe in the core and Mn and Ni in the shell are essentially unchanged. This further ensures that the primary particles in the core increase in size from the core to the interface, while the primary particles in the shell increase in size from the interface to the surface. Preferably, the particle size d1' of the primary particles in the core increases from the core to the interface, while the particle size d2' of the primary particles in the shell increases from the interface to the surface.

[0054] In this application, M 1 The use of elements that prevent grain boundary growth, when doped, has a gradient distribution, and the effect on grain refinement is also gradient, so the grain size can be controlled; M 2 The use of elements that promote grain growth can promote the fusion of small grains when doping, and the particle size of the shell layer formed when sintering is still at the same temperature is larger.

[0055] In the present invention, a doping element M is provided in the core of the positive electrode material. 1 , while the shell is provided with a doping element M 2 , where the doping element M 1 The ionic radius of the doping element M is different from that of the main element Fe in the core. 2 The ionic radius of the main elements Mn and Ni in the shell is different, but based on the doping element M 1 With M 2 It has the opposite gradient change trend as described above. Therefore, at the interface between the core and the shell, the content of the doping element is the lowest value, so the interface is least affected by the doping element, so that the size of the primary particles of the core layer close to the interface and the primary particles of the shell layer close to the interface can be close. During the charge and discharge process, the structural stability of the positive electrode material can be maintained to a certain extent, avoiding stress deformation caused by the large difference in particle size between the core layer and the shell layer during charge and discharge, thereby improving the cycle performance. At the same time, the setting of the shell layer can further reduce the dissolution of Fe elements in the matrix.

[0056] In some embodiments of the present invention, preferably, in the positive electrode material, the particle size d1' of the primary particles in the inner core constituting the interface and the particle size d2' of the primary particles in the shell constituting the interface differ by ≤±10%, for example, 0, ±1%, ±2%, ±3%, ±4%, ±5%, ±10%, and any value in the range consisting of any two numerical values, preferably ≤±5%.

[0057] In some embodiments of the present invention, preferably, the particle size distribution of the positive electrode material is selected from normal distribution or non-normal distribution. In the present invention, the non-normal distribution refers to the presence of multiple particle size distribution peaks.

[0058] In some embodiments of the present invention, preferably, when the particle size distribution of the positive electrode material is a normal distribution, the average particle size D50 of the positive electrode material is 2-15 μm; or, when the particle size distribution of the positive electrode material is a non-normal distribution, the d50 within the distribution peak of the positive electrode material is 2-15 μm. peak 2-15μm.

[0059] In the present invention, unless otherwise specified, the particle size distribution of the positive electrode material may be either normal or non-normal. Regardless of the distribution, the average particle size D50 of the positive electrode material or the particle size distribution within the distribution peak may be peak The value range of is 2-15μm. In the present invention, if the particle size is larger than 15μm, the capacity and rate performance will deteriorate; if the particle size is smaller than 2μm, excessive gas will be generated, which will have an adverse effect on the material's performance such as circulation.

[0060] In the present invention, unless otherwise specified, the average particle size D50 is measured using a laser particle size method, and the d peak Measured by XRD diffraction method.

[0061] In some embodiments of the present invention, preferably, the compaction density PD of the positive electrode material is ≥ 3 g / cm 3 , for example, 3g / cm 3 , 3.1g / cm 3 、3.2g / cm 3 , 3.3g / cm 3 、3.4g / cm 3 , 3.5g / cm 3 、3.6g / cm 3 , and any value in the range of any two values, preferably 3-3.6 g / cm 3 In the present invention, when the compaction density satisfies the above value range, it can be ensured that the positive electrode material has a higher capacity and energy density.

[0062] In the present invention, unless otherwise specified, the pressure density PD is measured by a powder compaction method.

[0063] A second aspect of the present invention provides a method for preparing a positive electrode material, characterized in that the preparation method comprises:

[0064] (1) In a non-oxidizing atmosphere, a solution containing an Fe source and a solution containing an M 1 The solution of the source, the first precipitant solution and the first complexing agent solution are mixed and subjected to a first coprecipitation reaction, and the M-containing 1 The feed rate of the solution of the source is 1:1 to obtain slurry A;

[0065] (2) In a non-oxidizing atmosphere, a solution containing a Mn source, a solution containing a Ni source, a solution containing M 2 The solution of the source, the second precipitant solution and the second complexing agent solution are mixed with the slurry A and subjected to a second coprecipitation reaction, and the M-containing 2 The feed rate of the solution from the source to obtain slurry B;

[0066] (3) aging, washing, filtering and drying the slurry B in sequence to obtain a precursor comprising a matrix and a coating layer;

[0067] (4) mixing the precursor and a Na source, and sintering the resulting mixture in an oxygen-containing atmosphere to obtain a positive electrode material having a normal distribution;

[0068] Wherein, the matrix has a composition shown in Formula IV: Fe 1-m M 1 m (OH)2, Formula IV, 0<m≤0.1, M 1 At least one selected from Sn, V, Y, Ti, Zr and Nb; the coating layer has a composition shown in formula V: (Mn y Ni 1-y-n M 2 n )(OH)2, formula V, 0<y≤0.5, 0<n<0.5, M 2 At least one selected from Si, Sr, B and Cu.

[0069] In some embodiments of the present invention, preferably, the cathode material is composed of a core having formula I and a shell having formula II, Na a Fe 1-b M 1 b O2, formula (I), Na c Mn x Ni 1-x-d M 2 d O2, formula (II), and M 1 and M 2 They are distributed in a gradient; wherein, in formula I, 0.6≤a≤1.05, 0<b≤0.1, M 1 At least one selected from Sn, V, Y, Ti, Zr and Nb; in Formula II, 0.6≤c≤1.05, 0<x≤0.5, 0<d<0.5, M 2 At least one element selected from Si, Sr, B and Cu.

[0070] In some embodiments of the present invention, in Formula I, 0.6≤a≤1.05, for example, 0.6, 0.7, 0.8, 0.9, 1, 1.03, 1.05, and any value in the range of any two values, preferably 0.7≤a≤1.03; 0<b≤0.1, for example, 0.001, 0.005, 0.01, 0.02, 0.05, 0.1, and any value in the range of any two values, 0<b≤0.02; M 1 At least one selected from Sn, V, Y, Ti, Zr and Nb, preferably selected from Ti and / or Zr.

[0071] In some embodiments of the present invention, in Formula II, 0.6≤c≤1.05, for example, 0.6, 0.7, 0.8, 0.9, 1, 1.03, 1.05, and any value in a range consisting of any two values, preferably 0.7≤c≤1.03; 0<x≤0.5, for example, 0.001, 0.1, 0.198, 0.2, 0.3, 0.4, 0.492, 0.499, 0.4993, 0.5, and any value in a range consisting of any two values, preferably 0.198≤x≤0.5; 0<d<0.5, for example, 0.001, 0.002, 0.005, 0.01, 0.02, 0.03, 0.04, 0.1, 0.2, 0.5, and any value in a range consisting of any two values, preferably 0.002≤d≤0.04; M 2 At least one selected from Si, Sr, B and Cu, preferably at least one selected from Si, Sr and Cu.

[0072] In the present invention, unless otherwise specified, the non-oxidizing atmosphere includes but is not limited to nitrogen, helium, argon, neon, etc., preferably nitrogen.

[0073] In the present invention, step (1), the first coprecipitation reaction is to combine the solution containing the Fe source and the solution containing M 1 Fe and M in the solution of the source 1 Co-precipitation and ensuring uniform distribution of Fe element. Preferably, the conditions of the first co-precipitation reaction include: temperature of 40-85°C, preferably 50-80°C; time of 10-40h, preferably 15-30h; pH value of 8-11, preferably 8.5-10.

[0074] In the present invention, step (1) is to regulate the M-containing 1 The feeding rate of the source solution is intended to make the core of the positive electrode material M 1 In a gradient distribution, especially in a gradient decreasing distribution. Preferably, the M-containing 1The feeding rate of the source solution includes: an initial rate of 0.1-5mmol / min, for example, 0.1mmol / min, 0.5mmol / min, 1mmol / min, 2mmol / min, 3mmol / min, 4mmol / min, 5mmol / min, and any value in the range consisting of any two numerical values, preferably 2-4mmol / min; an acceleration of -1.5 to 0mmol / min, for example, -1.5mmol / min, -1mmol / min, -0.5mmol / min, -0.1mmol / min, -0.05mmol / min, -0.01mmol / min, -0.005mmol / min, -0.001mmol / min, 0mmol / min, and any value in the range consisting of any two numerical values, preferably -0.5 to -0.001mmol / min.

[0075] In some embodiments of the present invention, preferably, the solution containing the Fe source and the solution containing the M 1 The amount ratio of the source solution satisfies n(Fe):n(M 1 ), where 0.9≤n(Fe)<1, 0<n(M 1 )≤0.1; further preferably, 0.98≤n(Fe)<1,0<n(M 1 )≤0.02.

[0076] In the present invention, unless otherwise specified, in step (1), the solute of the solution containing the Fe source is the Fe source, and the solvent is water; similarly, the solution containing M 1 The solutes of the source solution, the first precipitant solution and the first complexing agent solution are M 1 The source, the first precipitant and the first complexing agent, and the solvent are all water.

[0077] In some embodiments of the present invention, preferably, the concentration of the solution containing the Fe source in terms of Fe is 0.5-5 mol / L, for example, 0.5 mol / L, 1 mol / L, 2 mol / L, 5 mol / L, and any value in the range of any two values; 1 M 1The concentration of the source solution is 0.5-5mol / L, for example, 0.5mol / L, 1mol / L, 2mol / L, 5mol / L, and any value in the range consisting of any two values; the concentration of the first precipitant solution is 0.5-5mol / L, for example, 0.5mol / L, 1mol / L, 2mol / L, 5mol / L, and any value in the range consisting of any two values; the concentration of the first complexing agent solution is 0.5-5mol / L, for example, 0.5mol / L, 1mol / L, 2mol / L, 5mol / L, and any value in the range consisting of any two values.

[0078] In a specific embodiment of the present invention, preferably, the Fe source in the solution containing the Fe source is selected from at least one of sulfate, nitrate, alkoxide and oxide containing Fe; 1 The M of the source solution 1 The source is selected from the 1 At least one of carbonates, sulfates, nitrates, alkoxides and oxides, including but not limited to TiO2, niobium oxide, niobium ethoxide, zirconium oxide, and niobium oxalate; the first precipitant in the first precipitant solution is selected from sodium hydroxide and / or potassium hydroxide; the first complexing agents in the first complexing agent solution are independently selected from at least one of ammonia water, disodium edetate, ammonium nitrate, ammonium chloride and ammonium sulfate.

[0079] In some embodiments of the present invention, preferably, the solid content of the slurry A is 20-50wt%, for example, 20wt%, 25wt%, 30wt%, 40wt%, 50wt%, and any value in the range consisting of any two values.

[0080] In the present invention, step (2), the second coprecipitation reaction is to prepare a solution containing a Mn source, a solution containing a Ni source, a solution containing M 2 Mn, Ni and M in the solution of the source 2 Co-precipitate on the particle surface of slurry A, and ensure that Mn and Ni are evenly distributed. Preferably, the conditions of the second co-precipitation reaction include: temperature of 40-85°C, preferably 50-80°C; time of 10-40 hours, preferably 15-30 hours; pH value of 8-11, preferably 8.5-10.

[0081] In the present invention, step (2) is to regulate the M-containing 2 The feeding rate of the solution of the source is intended to make the shell layer of the positive electrode material M 2 In a gradient distribution, especially in a gradient increasing distribution. Preferably, the M-containing 2The feeding rate of the source solution includes: an initial rate of 0.1-5mmol / min, for example, 0.1mmol / min, 0.5mmol / min, 1mmol / min, 2mmol / min, 3mmol / min, 4mmol / min, 5mmol / min, and any value in the range consisting of any two numerical values, preferably 2-4mmol / min; an acceleration of 0-1.5mmol / min, for example, 0mmol / min, 0.001mmol / min, 0.005mmol / min, 0.01mmol / min, 0.05mmol / min, 0.1mmol / min, 0.2mmol / min, 0.5mmol / min, 1mmol / min, 1.5mmol / min, and any value in the range consisting of any two numerical values, preferably 0.001-0.5mmol / min.

[0082] In some embodiments of the present invention, preferably, in step (2), the solution containing a Mn source, the solution containing a Ni source, the solution containing M 2 The amount ratio of the source solution satisfies n(Mn):n(Ni):n(M 2 ), where 0<n(Mn)≤0.5, 0<n(Ni)<1, 0<n(M 2 )<0.5; further preferably, 0.198≤n(Mn)≤0.5, 0.46≤n(Ni)≤0.8, 0.002≤n(M 2 )≤0.04.

[0083] In the present invention, unless otherwise specified, in step (2), the solute of the solution containing the Mn source is the Mn source, and the solvent is water; similarly, the solution containing the Ni source, the solution containing the Mn source, 2 The solutes of the source solution, the second precipitant solution and the second complexing agent solution are Ni source, M 2 The source, the second precipitant and the second complexing agent are all water as the solvent.

[0084] In some embodiments of the present invention, preferably, the concentration of the solution containing the Mn source in terms of Mn is 0.5-5 mol / L, for example, 0.5 mol / L, 1 mol / L, 2 mol / L, 5 mol / L, and any value in a range consisting of any two values; the concentration of the solution containing the Ni source in terms of Ni is 0.5-5 mol / L, for example, 0.5 mol / L, 1 mol / L, 2 mol / L, 5 mol / L, and any value in a range consisting of any two values; 2 M 2The concentration of the source solution is 0.5-5mol / L, for example, 0.5mol / L, 1mol / L, 2mol / L, 5mol / L, and any value in the range consisting of any two values; the concentration of the second precipitant solution is 0.5-5mol / L, for example, 0.5mol / L, 1mol / L, 2mol / L, 5mol / L, and any value in the range consisting of any two values; the concentration of the second complexing agent solution is 0.5-5mol / L, for example, 0.5mol / L, 1mol / L, 2mol / L, 5mol / L, and any value in the range consisting of any two values.

[0085] In a specific embodiment of the present invention, preferably, the Mn source in the solution containing the Mn source is selected from at least one of sulfates, nitrates, alkoxides and oxides containing Mn; the Ni source in the solution containing the Ni source is selected from at least one of sulfates, nitrates, alkoxides and oxides containing Ni; 2 The M of the source solution 2 The source is selected from the 2 at least one of carbonates, sulfates, nitrates, alcoholates and oxides, including but not limited to CuSO4, strontium carbonate, and silicon oxide; the second precipitant in the second precipitant solution is selected from sodium hydroxide and / or potassium hydroxide; the second complexing agents in the second complexing agent solution are independently selected from at least one of ammonia water, disodium edetate, ammonium nitrate, ammonium chloride and ammonium sulfate.

[0086] In some embodiments of the present invention, preferably, the solid content of the slurry B is 20-50wt%, for example, 20wt%, 25wt%, 30wt%, 40wt%, 50wt%, and any value in the range consisting of any two values.

[0087] In some embodiments of the present invention, preferably, in step (3), the aging conditions include: temperature of 30-70°C, preferably 40-60°C; time of 5-25h, preferably 10-15h.

[0088] In the present invention, in step (3), the washing is intended to remove residual impurities in the aged product. Preferably, the washing process comprises: washing the aged product with water to obtain a washed product. The washing equipment is selected from common washing and separation equipment such as a filter press, a centrifuge, and a positive pressure filter.

[0089] In the present invention, in step (3), the filtration is intended to remove the washing product and obtain a filtered product through solid-liquid separation.

[0090] In the present invention, in step (3), the drying is to remove the residual moisture in the product. Preferably, the drying conditions include: a temperature of 70-120°C, preferably 80-110°C; and a time of 5-30 hours, preferably 10-20 hours.

[0091] In some embodiments of the present invention, preferably, in step (4), the molar ratio of the precursor calculated as total metal to the Na source calculated as Na is 0.6-1.05:1, for example, 0.6:1, 0.7:1, 0.8:1, 0.9:1, 0.95:1, 0.98:1, 1:1, 1.03:1, 1.05:1, and any value in the range of any two values, preferably 0.7-1.03:1. This range can ensure that the O3 phase is generated on the sample surface and the residual sodium on the surface is within a reasonable range. In the present invention, the total metal includes not only Fe and M in the matrix (Formula IV) of the precursor, but also Fe and M in the matrix (Formula IV) of the precursor. 1 , further comprising Mn, Ni and M in the coating layer (Formula V) of the precursor 2 .

[0092] In the present invention, there is a wide range of choices for the type of the Na source. Preferably, the Na source is selected from at least one of sodium carbonate, sodium hydroxide, sodium bicarbonate and sodium nitrate.

[0093] In the present invention, unless otherwise specified, the oxygen content in the oxygen-containing atmosphere is 20-100% by volume, including but not limited to oxygen, air, etc.

[0094] In some embodiments of the present invention, preferably, in step (4), the sintering conditions include: a temperature of 750-1100° C., for example, 750° C., 800° C., 900° C., 1000° C., 1100° C., and any value in a range consisting of any two values, preferably 800-1000° C., more preferably 900° C.; a time of 6-30 h, for example, 6 h, 10 h, 15 h, 20 h, 30 h, and any value in a range consisting of any two values, preferably 10-20 h, more preferably 15 h. Under these conditions, the formation of the O3 phase can be ensured and the residual sodium on the surface is within a reasonable range.

[0095] In some embodiments of the present invention, the method preferably further comprises: crushing the sintered product to obtain the positive electrode material having an average particle size D50 of 2-15 μm. In the present invention, a wide range of equipment can be selected for the crushing, including but not limited to a colloid mill, a mechanical mill, a jet mill, etc.

[0096] In some embodiments of the present invention, preferably, when the cathode material has a non-normal distribution, the method further comprises:

[0097] S1, cycling steps (1)-(4), and controlling the time of the first coprecipitation reaction in step (1) and the second coprecipitation reaction in step (2) during each cycle to obtain different particle positive electrode materials;

[0098] S2. Mixing the different granular positive electrode materials to obtain a positive electrode material with a non-normal distribution.

[0099] In the present invention, in step S1, during the first cycle, the time of the first coprecipitation reaction in step (1) and the second coprecipitation reaction in step (2) is controlled to obtain a first particle positive electrode material; during the second cycle, the time of the first coprecipitation reaction in step (1) and the second coprecipitation reaction in step (2) is controlled to obtain a second particle positive electrode material; ... and so on; during the Nth cycle, the time of the first coprecipitation reaction in step (1) and the second coprecipitation reaction in step (2) is controlled to obtain an Nth particle positive electrode material, wherein the particle sizes of the first particle positive electrode material, the second particle positive electrode material ... and the Nth particle positive electrode material are different. That is, the present invention regulates the particle size of the positive electrode material by regulating the conditions of the first coprecipitation reaction and the second coprecipitation reaction.

[0100] In some embodiments of the present invention, preferably, the different particle cathode materials include: large particle cathode materials and small particle cathode materials. In the present invention, large particle cathode materials and small particle cathode materials are relative.

[0101] In some embodiments of the present invention, preferably, the average particle size D50 of the large-particle positive electrode material is 8-16μm, for example, 8μm, 10μm, 12μm, 14μm, 16μm, and any value in the range consisting of any two numerical values; the average particle size D50 of the small-particle positive electrode material is 2-8μm, for example, 2μm, 4μm, 5μm, 6μm, 8μm, and any value in the range consisting of any two numerical values.

[0102] In some embodiments of the present invention, preferably, the mass ratio of the large-particle positive electrode material to the small-particle positive electrode material is 0.1-10:1, for example, 0.1:1, 0.5:1, 1:1, 2:1, 3:1, 4:1, 5:1, 8:1, 10:1, and any value in the range of any two numerical values, preferably 1-4:1.

[0103] The third aspect of the present invention provides a use of the positive electrode material provided in the first aspect, or the positive electrode material prepared by the method provided in the second aspect, in a sodium ion battery.

[0104] A fourth aspect of the present invention provides a sodium ion battery, which contains the positive electrode material provided by the first aspect, or the positive electrode material prepared by the method provided by the second aspect.

[0105] In some embodiments of the present invention, preferably, under the test conditions of 2-4 V, the 0.1C discharge specific capacity of the sodium ion battery is ≥130 mAh / g, preferably 140-150 mAh / g; the capacity retention rate after 100 cycles at 1C is ≥91%, preferably 91-98%; after 100 cycles at 1C, the Fe dissolution amount on the negative electrode side is ≤1500 ppm, preferably ≤500 ppm, and more preferably ≤100 ppm.

[0106] Example 1

[0107] (1) Fe source (FeSO4), M 1 The Fe source (TiO2) was dissolved in water to obtain a 2 mol / L FeSO4 solution and a 2 mol / L TiO2 solution; wherein the Fe source in terms of Fe and the TiO2 in terms of M 1 M 1 The molar ratio of the source is 0.999:0.001;

[0108] In a nitrogen atmosphere, the 2 mol / L FeSO4 solution, the 2 mol / L TiO2 solution, the 5 mol / L NaOH aqueous solution, and the 5 mol / L ammonia aqueous solution were mixed and subjected to a first coprecipitation reaction (temperature 55°C, time 15 h, pH 9.5), while controlling the feed rate of the TiO2 solution (initial rate 4 mmol / min, acceleration of -0.2 mmol / min) to obtain a slurry A with a solid content of 30 wt%;

[0109] (2) Mn source (MnSO4), Ni source (NiSO4) and M 2 The source (CuSO4) was dissolved in water to obtain 2 mol / L MnSO4 solution, 2 mol / L NiSO4 solution and 2 mol / L CuSO4 solution respectively; wherein, the Mn source in terms of Mn, the Ni source in terms of Ni and the CuSO4 solution in terms of Mn were respectively ... 2 M 2 The molar ratio of the source is 0.499:0.499:0.002;

[0110] In a nitrogen atmosphere, the 2 mol / L MnSO4 solution, 2 mol / L NiSO4 solution, 2 mol / L CuSO4 solution, 5 mol / L NaOH aqueous solution, and 5 mol / L ammonia aqueous solution were mixed with the slurry A and subjected to a second coprecipitation reaction (temperature 55°C, time 15 h, pH 9.5). The feed rate of the CuSO4 solution was controlled (initial rate 0.2 mmol / min, acceleration 0.01 mmol / min) to obtain a slurry B with a solid content of 30 wt%;

[0111] (3) aging the slurry B at 50°C for 10 h, and washing the purified product with water, filtering, and drying at 80°C to obtain a precursor with a core-shell structure;

[0112] The above-mentioned precursor includes a matrix and a coating layer, and the general formula of the matrix is Fe 0.999 Ti 0.001 (OH)2, the general formula of the coating layer is (Mn 0.499 Ni 0.499 Cu 0.002 )(OH)2;

[0113] (4) Considering that the Na source will have a certain volatilization loss during the sintering process, the above precursor calculated as the total metal and the Na source (Na2CO3) calculated as Na were mixed at a molar ratio of 1.03:1. The resulting mixture was sintered in an oxygen atmosphere (temperature of 900 ° C, time of 15 h). The sintered product was crushed to obtain a positive electrode material S1 with a normal distribution and core-shell structure (average particle size of 3 μm);

[0114] The process parameters of the positive electrode material S1 are listed in Table 1, and the composition and physical properties of the positive electrode material S1 are listed in Table 2.

[0115] Among them, the cross-sectional line scanning distribution diagram of Ti and Cu elements in the positive electrode material S1 is as follows: Figure 1 As shown by Figure 1 It can be seen that the Ti content in the core of the positive electrode material S1 is distributed in a gradient decreasing manner from the core to the interface, and the Cu content in the shell is distributed in a gradient increasing manner from the interface to the surface.

[0116] Among them, the XRD patterns of the core and shell of the positive electrode material S1 are as follows: Figure 2 As shown by Figure 2 It can be seen that in the XRD diffraction pattern of the core and shell of the positive electrode material S1 obtained under CuKa radiation, the characteristic diffraction peak of the (003) crystal plane appears at 15.7-18° 2θ, that is, both the core and the shell have O3 phase.

[0117] Example 2

[0118] According to the method of Example 1, the difference is that

[0119] In step (1), the time of the first coprecipitation reaction is replaced with 25 h;

[0120] In step (2), the time of the second coprecipitation reaction is replaced with 10 h.

[0121] The other conditions were the same, and a positive electrode material S2 with a normal distribution (average particle size of 7 μm) was obtained.

[0122] The process parameters of the positive electrode material S2 are listed in Table 1, and the composition and physical properties of the positive electrode material S2 are listed in Table 2.

[0123] Example 3

[0124] According to the method of Example 1, the difference is that

[0125] In step (1), the time of the first coprecipitation reaction is replaced with 10 h;

[0126] In step (2), the time of the second coprecipitation reaction is replaced with 35 h;

[0127] The other conditions were the same, and a positive electrode material S3 with a normal distribution (average particle size of 10 μm) was obtained.

[0128] The process parameters of the positive electrode material S3 are listed in Table 1, and the composition and physical properties of the positive electrode material S3 are listed in Table 2.

[0129] Example 4

[0130] According to the method of Example 1, the difference is that

[0131] In step (1), the time of the first coprecipitation reaction is replaced with 25 h;

[0132] In step (2), the time of the second coprecipitation reaction is replaced with 25 h;

[0133] The other conditions were the same, and a positive electrode material S4 with a normal distribution (average particle size of 14 μm) was obtained.

[0134] The process parameters of the positive electrode material S4 are listed in Table 1, and the composition and physical properties of the positive electrode material S4 are listed in Table 2.

[0135] Example 5

[0136] The method of Example 1 is as follows, except that

[0137] In step (1), M 1 The type of source is replaced by NbSO4;

[0138] In step (2), M2 The source type was replaced with SiO2, and the acceleration of the SiO2 solution was controlled to be 0.001mmol / min;

[0139] The other conditions were the same, and a positive electrode material S5 with a normal distribution (average particle size of 3 μm) was obtained.

[0140] The process parameters of the positive electrode material S5 are listed in Table 1, and the composition and physical properties of the positive electrode material S5 are listed in Table 2.

[0141] Example 6

[0142] According to the method of Example 2, the difference is that

[0143] In step (1), M 1 The source type was replaced with ZrSO4, and the acceleration of the ZrSO4 solution was controlled to -0.001mmol / min;

[0144] In step (2), M 2 The source type was replaced with SrSO4, and the acceleration of the SrSO4 solution was controlled to be 0.001mmol / min;

[0145] The other conditions were the same, and a positive electrode material S6 with a normal distribution (average particle size of 7 μm) was obtained.

[0146] The process parameters of the positive electrode material S6 are listed in Table 1, and the composition and physical properties of the positive electrode material S6 are listed in Table 2.

[0147] Example 7

[0148] The method of Example 3 is followed, except that

[0149] In step (1), M 1 The type of source is replaced by ZrSO4;

[0150] In step (2), M 2 The type of source is replaced by SiO2;

[0151] The other conditions were the same, and a positive electrode material S7 with a normal distribution (average particle size of 10 μm) was obtained.

[0152] The process parameters of the positive electrode material S7 are listed in Table 1, and the composition and physical properties of the positive electrode material S7 are listed in Table 2.

[0153] Example 8

[0154] According to the method of Example 1, the difference is that

[0155] In step (1), M 1The source type was replaced with NbSO4, and the acceleration of the NbSO4 solution was controlled to -0.5mmol / min;

[0156] In step (2), M 2 The source was replaced with boric acid, and the acceleration of the boric acid solution was controlled to be 0.5 mmol / min;

[0157] The other conditions were the same, and a positive electrode material S8 with a normal distribution (average particle size of 3 μm) was obtained.

[0158] The process parameters of the positive electrode material S8 are listed in Table 1, and the composition and physical properties of the positive electrode material S8 are listed in Table 2.

[0159] Example 9

[0160] The method of Example 1 is as follows, except that

[0161] In step (2), M 2 The type of source was replaced by CuO;

[0162] The other conditions were the same, and a positive electrode material S9 with a normal distribution (average particle size of 3 μm) was obtained.

[0163] The process parameters of the positive electrode material S9 are listed in Table 1, and the composition and physical properties of the positive electrode material S9 are listed in Table 2.

[0164] Example 10

[0165] The method of Example 1 is as follows, except that

[0166] In step (1), adjust the solution containing Fe source and the solution containing M 1 The amount of solution of the source, that is, the Fe source in terms of Fe and the M 1 M 1 The molar ratio of the source is 0.99:0.01;

[0167] The other conditions were the same, and a positive electrode material S10 with a normal distribution (average particle size of 3 μm) was obtained.

[0168] The process parameters of the positive electrode material S10 are listed in Table 1, and the composition and physical properties of the positive electrode material S10 are listed in Table 2.

[0169] Example 11

[0170] The method of Example 1 is as follows, except that

[0171] In step (2), the solution containing the Mn source, the solution containing the Ni source, the solution containing the M 2 The amount of the solution of the source, i.e., the Mn source calculated as Mn, the Ni source calculated as Ni and the M2 M 2 The molar ratio of the source is 0.19:0.8:0.01,

[0172] The other conditions were the same, and a positive electrode material S11 with a normal distribution (average particle size of 3 μm) was obtained.

[0173] The process parameters of the positive electrode material S11 are listed in Table 1, and the composition and physical properties of the positive electrode material S11 are listed in Table 2.

[0174] Example 12

[0175] According to the method of Example 1, the difference is that

[0176] In step (1), the feeding acceleration of the TiO2 solution is regulated to be -1 mmol / min;

[0177] The other conditions were the same, and a positive electrode material S12 with a normal distribution (average particle size of 3 μm) was obtained.

[0178] Among them, the process parameters of the positive electrode material S12 are listed in Table 1, and the composition and physical properties of the positive electrode material S12 are listed in Table 2.

[0179] Example 13

[0180] According to the method of Example 1, the difference is that

[0181] In step (2), the feeding acceleration of the CuSO4 solution is regulated to be 1 mmol / min;

[0182] The other conditions were the same, and a positive electrode material S13 with a normal distribution (average particle size of 3 μm) was obtained.

[0183] Among them, the process parameters of the positive electrode material S13 are listed in Table 1, and the composition and physical properties of the positive electrode material S13 are listed in Table 2.

[0184] Example 14

[0185] The positive electrode material S1 prepared in Example 1 and the positive electrode material S4 prepared in Example 4 were mixed at a mass ratio of 1:4 to obtain a positive electrode material S14 having a non-normal distribution.

[0186] Among them, the composition and physical properties of the positive electrode material S14 are listed in Table 2.

[0187] Example 15

[0188] The positive electrode material S1 prepared in Example 1 and the positive electrode material S4 prepared in Example 4 were mixed at a mass ratio of 1:0.25 to obtain a positive electrode material S15 having a non-normal distribution.

[0189] The composition and physical properties of the positive electrode material S15 are listed in Table 2.

[0190] Example 16

[0191] The method of Example 1 is as follows, except that

[0192] In step (2), the Mn source calculated as Mn, the Ni source calculated as Ni and the M 2 M 2 The molar ratio of the source is 0.4993:0.4993:0.0004;

[0193] In a nitrogen atmosphere, the 2 mol / L MnSO4 solution, 2 mol / L NiSO4 solution, 2 mol / L CuSO4 solution, 5 mol / L NaOH aqueous solution, and 5 mol / L ammonia aqueous solution were mixed with the slurry A and subjected to a second coprecipitation reaction (temperature 55°C, time 15 h, pH 9.5). The feed rate of the CuSO4 solution was controlled (initial rate 0.04 mmol / min, acceleration 0.01 mmol / min) to obtain a slurry B with a solid content of 30 wt%;

[0194] The slurry B is treated according to step (3) of Example 1 to obtain a precursor having a core-shell structure; wherein the precursor comprises a matrix and a coating layer, and the general formula of the matrix is Fe 0.999 Ti 0.001 (OH)2, the general formula of the coating layer is (Ni 0.4993 Mn 0.4993 Cu 0.0004 )(OH)2;

[0195] The above precursor was treated according to step (4) of Example 1 to obtain a positive electrode material S16 with a normal distribution (average particle size of 3 μm).

[0196] Among them, the process parameters of the positive electrode material S16 are listed in Table 1, and the composition and physical properties of the positive electrode material S16 are listed in Table 2.

[0197] Example 17

[0198] The method of Example 1 is as follows, except that

[0199] In step (2), the Mn source calculated as Mn, the Ni source calculated as Ni and the M 2 M 2 The molar ratio of the source is 0.492:0.492:0.006;

[0200] In a nitrogen atmosphere, the 2 mol / L MnSO4 solution, 2 mol / L NiSO4 solution, 2 mol / L CuSO4 solution, 5 mol / L NaOH aqueous solution, and 5 mol / L ammonia aqueous solution were mixed with the slurry A and subjected to a second coprecipitation reaction (temperature 55°C, time 15 h, pH 9.5). The feed rate of the CuSO4 solution was controlled (initial rate 0.2 mmol / min, acceleration 0.01 mmol / min) to obtain a slurry B with a solid content of 30 wt%;

[0201] The slurry B is treated according to step (3) of Example 1 to obtain a precursor having a core-shell structure; wherein the precursor comprises a matrix and a coating layer, and the general formula of the matrix is Fe 0.999 Ti 0.001 (OH)2, the general formula of the coating layer is (Ni 0.492 Mn 0.492 Cu 0.006 )(OH)2;

[0202] The above precursor was treated according to step (4) of Example 1 to obtain a positive electrode material S17 with a normal distribution (average particle size of 3 μm).

[0203] Among them, the process parameters of the positive electrode material S17 are listed in Table 1, and the composition and physical properties of the positive electrode material S17 are listed in Table 2.

[0204] Comparative Example 1

[0205] The method of Example 1 is followed, except that M is not doped 2 source; that is,

[0206] In step (1), the time of the first coprecipitation reaction is replaced with 35 h;

[0207] In step (2), in a nitrogen atmosphere, the 2 mol / L MnSO4 solution, the 2 mol / L NiSO4 solution, the 5 mol / L NaOH aqueous solution and the 5 mol / L ammonia aqueous solution were mixed with the slurry A and subjected to a second coprecipitation reaction (temperature of 55° C., time of 30 h, pH of 9.5) to obtain a slurry B having a solid content of 30 wt%;

[0208] The molar ratio of the Mn source calculated as Mn to the Ni source calculated as Ni is 0.5:0.5;

[0209] The slurry B is treated according to step (3) of Example 1 to obtain a precursor having a core-shell structure; wherein the precursor comprises a matrix and a coating layer, and the general formula of the matrix is Fe 0.999 Ti 0.001 (OH)2, the general formula of the coating layer is (Mn0.5 Ni 0.5 )(OH)2;

[0210] The above precursor is subjected to step (4) of Example 1 to obtain the positive electrode material DS1;

[0211] The process parameters of the positive electrode material DS1 are listed in Table 1, and the composition and physical properties of the positive electrode material DS1 are listed in Table 2.

[0212] Among them, the cross-sectional line scanning distribution diagram of the Ti element of the positive electrode material DS1 is as follows: Figure 3 As shown by Figure 3 It can be seen that the Ti content in the core of the positive electrode material DS1 does not show a gradient distribution.

[0213] Comparative Example 2

[0214] The method of Example 1 is followed, except that M is not doped 1 source; that is,

[0215] In step (1), in a nitrogen atmosphere, the above-mentioned 2 mol / L FeSO4 solution, 5 mol / L NaOH aqueous solution and 5 mol / L ammonia aqueous solution were mixed and subjected to a first coprecipitation reaction (temperature 55°C, time 35 hours, pH value 9.5) to obtain slurry A with a solid content of 30 wt%;

[0216] In step (2), the second coprecipitation reaction time was replaced with 30 h to obtain slurry B with a solid content of 30 wt%;

[0217] The slurry B is treated according to step (3) of Example 1 to obtain a precursor having a core-shell structure; wherein the precursor comprises a matrix and a coating layer, the general formula of the matrix is Fe(OH)2, and the general formula of the coating layer is (Mn 0.499 Ni 0.499 Cu 0.002 )(OH)2;

[0218] The above precursor was treated according to step (4) of Example 1 to obtain the positive electrode material DS2;

[0219] The process parameters of the positive electrode material DS2 are listed in Table 1, and the composition and physical properties of the positive electrode material DS2 are listed in Table 2.

[0220] Comparative Example 3

[0221] According to the method of Example 1, the difference is that

[0222] In step (1), the feeding rate of the TiO2 solution is not controlled;

[0223] In step (2), the feeding rate of the CuSO4 solution is not controlled;

[0224] The other conditions were the same to obtain the positive electrode material DS3.

[0225] The process parameters of the positive electrode material DS3 are listed in Table 1, and the composition and physical properties of the positive electrode material DS3 are listed in Table 2.

[0226] Table 1

[0227]

[0228] Table 1

[0229]

[0230] Table 1

[0231]

[0232]

[0233] Table 1

[0234]

[0235] Table 1

[0236]

[0237] Table 2

[0238]

[0239]

[0240] Note: 1-mass ratio of the core to the shell.

[0241] Table 2

[0242]

[0243]

[0244] Note: 2- average particle size d1 of the primary particles in the core, nm; 3- average particle size d2 of the primary particles in the shell, nm.

[0245] Table 2

[0246]

[0247] According to the data in Table 1-2, compared with Comparative Examples 1-3, the positive electrode material prepared by the method provided by the present invention has a core-shell structure, and the core has Na a Fe 1-b M 1b The general formula of O2, the shell has Na c Mn x Ni 1-x-d M 2 d The general formula of O2; At the same time, the doping elements in the core and shell (M 1 and M 2 ) is distributed in a gradient inside the cathode material, that is, M 1 The distribution is gradient decreasing from the core to the interface, M 2 The gradient distribution from the interface to the surface can more effectively alleviate the stress deformation of the core-shell layer during the charging and discharging process, and further improve the cycle stability.

[0248] Test Example 1

[0249] The positive electrode materials (S1-S17 and DS1-DS3) prepared in Examples 1-17 and Comparative Examples 1-3 were subjected to electrochemical performance tests.

[0250] Assembling a sodium-ion battery:

[0251] (1) The positive electrode materials (S1-S17 and DS1-DS3), acetylene black and polyvinylidene fluoride (PVDF) were mixed in a mass ratio of 90:5:5, coated on aluminum foil and dried, and then stamped into positive electrode sheets with a diameter of 12 mm and a thickness of 120 μm using a pressure of 100 MPa. The positive electrode sheets were then placed in a vacuum drying oven at 120°C and dried for 12 h.

[0252] (2) The negative electrode used a Na metal sheet with a diameter of 17 mm and a thickness of 1 mm; the separator used a Celgard 2400 porous membrane with a thickness of 25 μm; the blotting paper used glass fiber, and the electrolyte used a mixture of equal parts of 1 mol / L NaPF6, ethylene carbonate (EC), and diethyl carbonate (DEC);

[0253] (3) The positive electrode sheet, separator, blotting paper, negative electrode sheet and electrolyte were assembled into 2025 button cells (Q1-Q17 and DQ1-DQ3) in sequence in an Ar gas glove box with a water content and an oxygen content of less than 5 ppm.

[0254] Test conditions: The assembled button cell was tested for capacity at a rate of 0.1C at 25°C, and its capacity retention was tested at a rate of 1C for 100 cycles. After 100 cycles, the cell was disassembled, the blotting paper was removed, and dissolved in aqua regia. The dissolved solution was placed in an ICP instrument to test the Fe content. The test data are listed in Table 3.

[0255] The button cell assembled with the positive electrode materials prepared in Example 1 and Comparative Example 1 has a 1C cycle performance as shown in the figure below. Figure 4 As shown by Figure 4 It can be seen that compared with Comparative Example 1, the button battery assembled with the positive electrode material prepared in Example 1 has higher discharge specific capacity and cycle retention rate.

[0256] Table 3

[0257]

[0258] As shown in Table 3, compared to Comparative Examples 1-3, the coin-type batteries assembled using the positive electrode materials of Examples 1-17 exhibited a 0.1C discharge specific capacity of 140-150 mAh / g, a capacity retention rate of 91-98% after 100 cycles at 1C, and Fe dissolution from the negative electrode of ≤100 ppm after 100 cycles at 1C. This indicates that the positive electrode materials provided by the present invention exhibit higher rate performance and capacity retention, as well as lower Fe dissolution, in sodium-ion batteries.

[0259] The preferred embodiments of the present invention have been described in detail above, but the present invention is not limited thereto. Within the technical concept of the present invention, various simple variations of the technical solution of the present invention may be made, including combining the various technical features in any other appropriate manner. These simple variations and combinations should also be regarded as disclosed in the present invention and fall within the scope of protection of the present invention.

Claims

1. A positive electrode material, characterized in that The positive electrode material has a core-shell structure, consisting of a core and a shell; wherein the core has a composition shown in Formula I: Na a Fe 1-b M 1 b O2, formula I, where 0.6≤ a ≤1.05,0< b ≤0.1, M 1 At least one selected from Sn, V, Y, Ti, Zr and Nb; the shell has a composition shown in formula II: Na c Mn x Ni 1-x-d M 2 d O2, formula II, where 0.6≤ c ≤1.05,0< x ≤0.5,0< d <0.5, M 2 At least one selected from Si, Sr, B and Cu; Among them, in the positive electrode material, M 1 and M 2 They are distributed in gradients, M 1 The distribution is gradient decreasing from the core to the interface, M 2 The distribution is gradient increasing from the interface to the surface.

2. The positive electrode material according to claim 1, wherein M 1 The decreasing rate from the core to the interface is 0.001-0.5mol% / μm; M 2 The increasing rate from the interface to the surface is 0.001-0.5 mol% / μm.

3. The positive electrode material according to claim 2, wherein M 1 The decreasing rate from the core to the interface is 0.1-0.3mol% / μm; M 2 The increasing rate from the interface to the surface is 0.002-0.015mol% / μm.

4. The positive electrode material according to claim 1, wherein In the positive electrode material, based on the molar amount of the core calculated as Fe, M 1 The doping amount is 0.01-2 mol%; based on the molar amount of the shell layer calculated as Mn and Ni, M 2 The doping amount is 0.01-2mol%; And / or, the particle size of the core is 1-10 μm; the thickness of the shell is 1-10 μm; And / or, the mass ratio of the core to the shell is 0.2-10:

1.

5. The positive electrode material according to claim 4, wherein In the positive electrode material, based on the molar amount of the core calculated as Fe, M 1 The doping amount is 0.05-0.5 mol%; based on the molar amount of the shell layer calculated as Mn and Ni, M 2 The doping amount is 0.05-0.5mol%; And / or, the particle size of the core is 2-8 μm; the thickness of the shell is 2-8 μm; And / or, the mass ratio of the core to the shell is 0.5-4:

1.

6. The positive electrode material according to claim 1, wherein In formula I, 0.7≤ a ≤1.03,0< b ≤0.02, M 1 Selected from Ti and / or Zr; And / or, in Formula II, 0.7≤ c ≤1.03,0.198≤ x ≤0.5,0.002≤ d ≤0.04, M 2 At least one selected from Si, Sr and Cu.

7. The positive electrode material according to claim 1, wherein In the XRD diffraction patterns of the core and the shell obtained independently under CuKa radiation, a characteristic diffraction peak of the (003) crystal plane appears at 15.7-18° 2θ.

8. The positive electrode material according to claim 1, wherein The core and shell are each independently a secondary particle formed by agglomeration of primary particles; The average particle size d1 of the primary particles in the core and the average particle size d2 of the primary particles in the shell satisfy Formula III: d2=n×d1+200, Formula III, wherein 0<n≤5.

9. The positive electrode material according to claim 8, wherein The average particle size d1 of the primary particles in the core is ≤300nm; the average particle size d2 of the primary particles in the shell is ≥500nm; And / or, in the positive electrode material, the particle size d1' of the primary particles in the core constituting the interface and the particle size d2' of the primary particles in the shell constituting the interface differ by ≤±10%.

10. The positive electrode material according to claim 9, wherein The difference between the particle size d1' of the primary particles in the core constituting the interface and the particle size d2' of the primary particles in the shell constituting the interface is ≤±5%.

11. The positive electrode material according to claim 1, wherein The particle size distribution of the positive electrode material is selected from normal distribution or non-normal distribution; When the particle size distribution of the positive electrode material is a normal distribution, the average particle size D50 of the positive electrode material is 2-15 μm; or, when the particle size distribution of the positive electrode material is a non-normal distribution, the d peak 2-15μm; And / or, the compaction density PD of the positive electrode material is ≥3g / cm 3 .

12. The positive electrode material according to claim 11, wherein The compaction density PD of the positive electrode material is 3-3.6 g / cm 3 .

13. A method for preparing a positive electrode material, characterized in that: The preparation method comprises: (1) In a non-oxidizing atmosphere, a solution containing an Fe source and a solution containing M 1 The solution of the source, the first precipitant solution and the first complexing agent solution are mixed and subjected to a first coprecipitation reaction, and the M-containing 1 The feed rate of the solution of the source is 1:1 to obtain slurry A; (2) In a non-oxidizing atmosphere, a solution containing a Mn source, a solution containing a Ni source, a solution containing 2 The solution of the source, the second precipitant solution and the second complexing agent solution are mixed with the slurry A and subjected to a second coprecipitation reaction, and the M-containing 2 The feed rate of the solution of the source is 1:1 to obtain slurry B; (3) aging, washing, filtering and drying the slurry B in sequence to obtain a precursor comprising a matrix and a coating layer; (4) mixing the precursor and a Na source, and sintering the resulting mixture in an oxygen-containing atmosphere to obtain a positive electrode material having a normal distribution; Wherein, the M-containing 1 The feeding rate of the solution containing M includes: an initial rate of 0.1-5 mmol / min, an acceleration of -1.5 to -0.001 mmol / min; 2 The feed rate of the source solution includes: an initial rate of 0.1-5 mmol / min and an acceleration rate of 0.001-1.5 mmol / min; The matrix has a composition shown in Formula IV: Fe 1-m M 1 m (OH)2, formula IV, 0< m ≤0.1, M 1 At least one selected from Sn, V, Y, Ti, Zr and Nb; the coating layer has a composition shown in formula V: (Mn y Ni 1-y-n M 2 n )(OH)2, formula V, 0< y ≤0.5,0< n <0.5, M 2 At least one selected from Si, Sr, B and Cu.

14. The method according to claim 13, wherein The positive electrode material is composed of a core having formula I and a shell having formula II, Na a Fe 1-b M 1 b O2, formula (I), Na c Mn x Ni 1-x-d M 2 d O2, formula (II), and M 1 and M 2 They are distributed in gradients respectively; Wherein, in formula I, 0.6≤ a ≤1.05,0< b ≤0.1, M 1 At least one selected from Sn, V, Y, Ti, Zr and Nb; in Formula II, 0.6≤ c ≤1.05,0< x ≤0.5,0< d <0.5, M 2 At least one element selected from Si, Sr, B and Cu.

15. The method according to claim 14, wherein In formula I, 0.7≤ a ≤1.03,0< b ≤0.02, M 1 Selected from Ti and / or Zr; And / or, in Formula II, 0.7≤ c ≤1.03,0.198≤ x ≤0.5,0.002≤ d ≤0.04, M 2 At least one selected from Si, Sr and Cu.

16. The method according to claim 13, wherein: In step (1), the conditions of the first coprecipitation reaction include: temperature of 40-85°C; time of 10-40h; pH value of 8-11; And / or, the M-containing 1 The feed rate of the source solution includes: an initial rate of 2-4 mmol / min; an acceleration rate of -0.5 to -0.001 mmol / min; And / or, the solution containing Fe source and the solution containing M 1 The amount ratio of the source solution satisfies n(Fe):n(M 1 ), where 0.9≤n(Fe)<1, 0<n(M 1 )≤0.1; And / or, the solid content of the slurry A is 20-50wt%.

17. The method according to claim 16, wherein In step (1), the conditions of the first coprecipitation reaction include: temperature of 50-80°C; time of 15-30h; pH value of 8.5-10; And / or, the solution containing Fe source and the solution containing M 1 The amount ratio of the source solution satisfies n(Fe):n(M 1 ), where 0.98≤n(Fe)<1, 0<n(M 1 )≤0.

02.

18. The method according to claim 13, wherein In step (2), the conditions of the second coprecipitation reaction include: temperature of 40-85°C; time of 10-40h; pH value of 8-11; And / or, the M-containing 2 The feed rate of the source solution includes: an initial rate of 2-4 mmol / min; an acceleration rate of 0.001-0.5 mmol / min; And / or, the solution containing a Mn source, the solution containing a Ni source, the solution containing M 2 The amount ratio of the source solution satisfies n(Mn):n(Ni):n(M 2 ), where 0<n(Mn)≤0.5, 0<n(Ni)<1, 0<n(M 2 )<0.5; And / or, the solid content of the slurry B is 20-50wt%.

19. The method according to claim 18, wherein In step (2), the conditions of the second coprecipitation reaction include: temperature of 50-80°C; time of 15-30h; pH value of 8.5-10; And / or, the solution containing a Mn source, the solution containing a Ni source, the solution containing M 2 The amount ratio of the source solution satisfies n(Mn):n(Ni):n(M 2 ), where 0.198≤n(Mn)≤0.5, 0.46≤n(Ni)≤0.8, 0.002≤n(M 2 )≤0.

04.

20. The method according to claim 13, wherein In step (4), the molar ratio of the precursor calculated as total metal to the Na source calculated as Na is 0.6-1.05:1; And / or, the Na source is selected from at least one of sodium carbonate, sodium hydroxide, sodium bicarbonate, and sodium nitrate; And / or, the sintering conditions include: temperature of 750-1100° C.; time of 6-30 hours; And / or, the method further comprises: crushing the sintered product to obtain the positive electrode material with an average particle size D50 of 2-15 μm.

21. The method according to claim 20, wherein In step (4), the molar ratio of the precursor calculated as total metal to the Na source calculated as Na is 0.7-1.03:1; And / or, the sintering conditions include: temperature of 800-1000° C.; time of 10-20 hours.

22. The method according to claim 13, wherein The method further comprises: S1, cycling steps (1) to (4), and controlling the time of the first coprecipitation reaction in step (1) and the second coprecipitation reaction in step (2) during each cycle to obtain different particle positive electrode materials; S2. mixing the different granular positive electrode materials to obtain a positive electrode material with a non-normal distribution; The different particle positive electrode materials include: large particle positive electrode materials and small particle positive electrode materials; The mass ratio of the large-particle positive electrode material to the small-particle positive electrode material is 0.1-10:

1.

23. The method according to claim 22, wherein The average particle size D50 of the large-particle positive electrode material is 8-16 μm, and the average particle size D50 of the small-particle positive electrode material is 2-8 μm; And / or, the mass ratio of the large-particle positive electrode material to the small-particle positive electrode material is 1-4:

1.

24. Use of the positive electrode material according to any one of claims 1 to 12, or the positive electrode material prepared by the method according to any one of claims 13 to 23, in a sodium ion battery.

25. A sodium ion battery, characterized in that: The sodium ion battery contains the positive electrode material according to any one of claims 1 to 12, or the positive electrode material prepared by the method according to any one of claims 13 to 23.

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