Layered positive electrode material and preparation method thereof, and sodium ion battery

Abstract

The present application is applicable to the field of material technology, and provides a layered positive electrode material and a preparation method thereof, and a sodium ion battery, wherein the layered positive electrode material comprises a core and a coating layer located on the surface of the core; wherein the chemical formula of the core is [NaM b ][Ni x Fe y Mn z N k O2],0

Description

Technical Field

[0001] The present application belongs to the field of material technology, and in particular relates to a layered positive electrode material and a preparation method thereof, and a sodium ion battery. Background Art

[0002] Lithium-ion batteries, with their high energy density, long lifespan, and excellent rate capability, dominate the portable electronic device market and also show great promise in electric vehicles. However, global lithium resources are unevenly distributed, and lithium prices have fluctuated significantly in recent years, limiting their application in large-scale energy storage. Sodium shares similar physical and chemical properties with lithium and is abundant, making sodium-ion batteries (Na-ion batteries) even more promising. Layered oxide materials are considered the most promising cathode materials for Na-ion batteries due to their ease of preparation and high theoretical capacity. However, when used as cathodes in Na-ion batteries, these materials suffer from unstable crystal structures and are prone to phase transitions during charge and discharge, resulting in poor performance. Furthermore, during the high-temperature solid-phase reaction between the nickel-iron-manganese ternary precursor and the sodium source, some sodium ions are released from the bulk of the material and remain on the surface of the particles, ultimately forming residual alkali (in the form of Na2CO3 and NaOH). The presence of this surface residual alkali can impair the cycling stability of the cathode material and lead to capacity decay.

[0003] Therefore, improving the structural stability of the material and reducing the residual alkali on the surface to prepare a sodium-ion battery cathode with excellent cycle performance and safety is of great significance for the large-scale application of sodium-ion batteries. As an effective modification method, ion doping can improve the stability of the crystal structure and inhibit the occurrence of harmful phase changes, thereby improving the material's cycle performance and rate capability. For example, CN115924999A discloses a copper-ion-doped nickel-iron-manganese-based ternary precursor, a preparation method, and its application. By introducing copper elements in the preparation process of the nickel-iron-manganese ternary precursor, the cyclic stability and air stability of the material are significantly improved. For example, CN112864389B discloses a sodium-ion positive electrode material doped with at least one of Mn, Fe, Zn, Ag, Zr, Mo, Nb, Cu, Cr, and Ti, which improves the cycle performance and rate performance of the material, and significantly improves the charge and discharge capacity, specific capacity, cycle stability, and service life of the sodium-ion battery. For example, CN116885140A discloses a dual-point doping modification method, which dopes and modifies the sodium layer and the transition metal layer respectively, significantly improving the structural stability of the sodium-ion positive electrode material, and thus significantly improving the cycle performance of the sodium-ion positive electrode material. Coating modification is also an effective modification method that can stabilize the crystal structure of the material, prevent the shedding of particles on the surface of the material, and thus improve the cycle stability of the battery. For example, CN116169268A double-coated the surface of a layered oxide positive electrode material with a metal oxide and carbon. By double-coating the layered oxide, the conductivity of the material is enhanced while improving its stability in the electrolyte, reducing the leaching of transition metal elements, and thus improving the cyclic stability of the material. However, some of the above methods only use a single sodium layer doping or transition metal doping. Even if double-point doping can improve the stability of the material structure, it is difficult to solve the problems of high residual alkali on the surface of the material and the susceptibility to side reactions with the electrolyte, resulting in prominent problems of thermal stability and gas production of the material. While only single metal oxide coating can effectively reduce the residual alkali on the surface and prevent the occurrence of side reactions with the electrolyte, it cannot suppress the problem of unstable internal structure of the material during long-cycle charge and discharge, resulting in poor cycle performance. Summary of the Invention

[0004] The purpose of the embodiments of the present application is to provide a layered positive electrode material, which aims to effectively combine doping and coating modification methods to achieve all-round targeted modification of sodium ion battery positive electrode materials, and solve the problems existing in the prior art such as high residual alkali on the material surface, easy side reactions with the electrolyte, poor thermal stability of the material, or poor cycle performance.

[0005] The embodiment of the present application is implemented as follows: a layered positive electrode material, the layered positive electrode material comprising a core and a coating layer located on the surface of the core;

[0006] Among them, the chemical general formula of the core is [NaM b [Ni x Fe y Mn z N k O2], where 0 < b ≤ 0.1, 0.1 ≤ x ≤ 0.5, 0.1 ≤ y ≤ 0.5, 0.2 ≤ z ≤ 0.6, 0 < k ≤ 0.1, x + y + z = 1, M is a sodium layer doping element; N is a transition metal layer doping element; the coating layer is a metal oxide.

[0007] Preferably, M is one or more of Ca, Mg, Sr, La, K, Zn; N is one or more of Ti, Zr, Sb, Sc, Y, La, Ce, Sm, Ho, Ta.

[0008] Preferably, the metal oxide is one or more of zirconia, titanium oxide, tin oxide, magnesium oxide, tungsten oxide.

[0009] Preferably, the metal element in the metal oxide accounts for 0.05% - 0.5% of the mass of the core.

[0010] The embodiment of the present application also provides a preparation method of the above-mentioned layered cathode material, including:

[0011] Uniformly mixing the pre-sintered nickel iron manganese hydroxide with a sodium source, a sodium layer doping element, and a transition metal layer doping element, and performing a first sintering treatment to obtain a first-sintered sample;

[0012] After crushing the first-sintered sample, uniformly mixing it with a metal oxide, and performing a second sintering treatment to obtain a layered cathode material.

[0013] The embodiment of the present application also provides a sodium ion battery, and the sodium ion battery includes the above-mentioned layered cathode material.

[0014] The layered cathode material provided by the embodiment of the present application realizes double-site doping through the sodium layer and the transition metal layer and surface coating with a synergistic metal oxide, achieving the following effects: 1) The sodium layer doping element plays a supporting role in the sodium layer, stabilizing the layer spacing of the sodium layer before and after charge and discharge, making the charge and discharge curve of the battery smoother, and improving the cycling performance of the material; 2) By doping high-valence elements in the transition metal layer, the phase change (O3’→P3’) of the material during charge and discharge can be inhibited, improving the stability of the material, and further improving the cycling performance of the material; 3) Coating the metal oxide on the surface of the material reduces the residual alkali on the surface of the cathode material, effectively inhibiting the occurrence of side reactions with the electrolyte, and further improving the cycling performance of the material; in addition, the coating layer provides a protective layer to prevent the cathode material from directly contacting and reacting with moisture and carbon dioxide in the air, improving the air stability of the material; 4) The process is simple and controllable, and is easy to mass-produce. Brief Description of the Drawings

[0015] Figure 1 SEM image of nickel-iron-manganese hydroxide provided in Embodiment 1 of the present application;

[0016] Figure 2 SEM image of the layered cathode material provided in Embodiment 1 of the present application. Detailed Description of the Embodiments

[0017] In order to make the objectives, technical solutions and advantages of the present application more clear and understandable, the present application will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present application and are not used to limit the present application.

[0018] The embodiment of the present application provides a layered cathode material, and the layered cathode material includes a core and a coating layer located on the surface of the core;

[0019] Among them, the chemical general formula of the core is [NaM b [Ni x Fe y Mn z N k O2], 0 < b ≤ 0.1, 0.1 ≤ x ≤ 0.5, 0.1 ≤ y ≤ 0.5, 0.2 ≤ z ≤ 0.6, 0 < k ≤ 0.1, x + y + z = 1, M is a sodium layer doping element; N is a transition metal layer doping element; the coating layer is a metal oxide.

[0020] Among them, 0.1 ≤ x ≤ 0.5, for example, it can be 0.1, 0.3 or 0.5; 0.1 ≤ y ≤ 0.5, for example, it can be 0.1, 0.3 or 0.5; 0.2 ≤ z ≤ 0.6, for example, it can be 0.2, 0.4 or 0.6, 0.4 ≤ a ≤ 1.2, for example, it can be 0.4, 0.6, 0.8, 1.0 or 1.2; 0 < b ≤ 0.1, for example, it can be 0.01, 0.05 or 0.1, preferably 0 < b ≤ 0.02; however, the above x, y, z, b are not limited to the listed values, and other unlisted values within the numerical range are equally applicable.

[0021] Among them, 0 < k ≤ 0.1, for example, it can be 0.0005, 0.001, 0.005, 0.01, 0.05 or 0.1, but not limited to the listed values, and other unlisted values within the numerical range are equally applicable, preferably 0 < k ≤ 0.01. The present application represents the doping amount k of the doping element in the transition metal layer, preferably 0 < k ≤ 0.01. If k is too large, the specific capacity of the material will be significantly reduced.

[0022] In an optional embodiment of the present application, the sodium layer doping element M is any one or a combination of at least two metal elements with a radius close to that of sodium ions, such as one or more of Ca, Mg, Sr, La, K, and Zn, more preferably one or more of Ca, Mg, and Sr.

[0023] In an optional embodiment of the present application, the N is any one or a combination of at least two of high-valent elements such as Ti, Zr, Sb, Sc, Y, La, Ce, Ta, etc., more preferably one or more of Ti, Zr, and Sb.

[0024] In an optional embodiment of the present application, the metal oxide is one or more of zirconium oxide, titanium oxide, tin oxide, magnesium oxide, and tungsten oxide, more preferably one or more of zirconium oxide, titanium oxide, and magnesium oxide.

[0025] In an optional embodiment of the present application, the metal element in the metal oxide accounts for 0.05%-0.5% of the mass of the core, preferably 0.05%-0.3%.

[0026] The present application also provides a method for preparing the above-mentioned layered positive electrode material, comprising:

[0027] The pre-sintered nickel-iron-manganese hydroxide is uniformly mixed with a sodium source, a sodium layer doping element, and a transition metal layer doping element, and subjected to a single sintering process to obtain a single-fired sample;

[0028] The first-fired sample is crushed, uniformly mixed with metal oxides, and subjected to a second sintering treatment to obtain a layered positive electrode material.

[0029] In an optional embodiment of the present application, the precursor material nickel iron manganese hydroxide is subjected to a pre-sintering treatment, the pre-sintering temperature is 350-750° C., and the pre-sintering time is 3-9 hours.

[0030] In an optional embodiment of the present application, the sodium source is one or more of sodium carbonate, sodium bicarbonate, sodium hydroxide, sodium nitrate, sodium acetate, and sodium citrate, and the molar ratio of the sodium element in the sodium source to the sum of the nickel, iron, and manganese elements in the nickel-iron-manganese hydroxide is (1-1.04):1.

[0031] In an optional embodiment of the present application, the nickel-iron-manganese hydroxide after pre-sintering treatment is uniformly mixed with a sodium source, a sodium layer doping element and a transition metal layer doping element, and subjected to a single sintering treatment to obtain a single-fired sample. The temperature of the single sintering treatment is 850-950°C, and the sintering time is 10-20h; the sintering atmosphere includes one or more of air and oxygen.

[0032] In an optional embodiment of the present application, the calcined sample is crushed, uniformly mixed with metal oxides, and subjected to a secondary sintering treatment to obtain a layered positive electrode material. The secondary sintering treatment temperature is 500-700°C, and the sintering time is 7-13h; the sintering atmosphere includes one or more of air and oxygen.

[0033] The following examples describe the layered cathode material, its preparation method, and sodium-ion battery in detail. The experimental methods used in the following examples are conventional methods unless otherwise specified. Materials and reagents used are commercially available unless otherwise specified.

[0034] Example 1

[0035] This embodiment provides a double-site doping and metal oxide coating synergistically modified O3 sodium layered cathode material, the double-site doping and metal oxide coating synergistically modified O3 sodium layered cathode material chemical formula is [NaCa 0.001 ][Ni 0.333 Fe 0.333 Mn 0.334 Ti 0.001 ]O2, wherein Ca is a doping element for the sodium layer, Ti is a doping element for the transition metal layer, and the coating layer comprises zirconium oxide;

[0036] The preparation method of the double-point doping and metal oxide coating synergistically modified O3 sodium layered cathode material comprises the following steps:

[0037] Step S1: nickel iron manganese hydroxide Ni 0.333 Fe 0.333 Mn 0.334 (OH)2 was pre-calcined in air atmosphere at a temperature of 550°C, a heating rate of 3°C / min, and a holding time of 6h to obtain a pre-calcined material;

[0038] Step S2, the pre-calcined material obtained in step 1 is mixed with sodium carbonate, calcium oxide, and titanium oxide in a high-speed mixer to obtain a high-mix material, wherein the sodium content is 3% in excess, the calcium metal content is one thousandth of the sodium content, and the titanium metal content is one thousandth of the transition metal content. The high-mix material is placed in a box furnace, and under an air atmosphere with an air flow rate of 16 L / min, the temperature is first increased to 900° C. at a rate of 3° C. / min, maintained for 15 hours, and then naturally cooled to room temperature to obtain a fired material. The fired material is mechanically crushed and vibrated to obtain a fired sample;

[0039] Step S3, weigh 100kg of the burned sample [NaCa 0.001 ][Ni 0.333 Fe 0.333 Mn 0.334 Ti0.001 ]O2 and 0.3kg zirconium oxide were added into a high-speed mixer and mixed at 3000r / min for 15min. The mixture was placed in a box furnace and heated to 650℃ at a heating rate of 3℃ / min under an oxygen atmosphere. The mixture was kept warm for 6h and naturally cooled to room temperature. The mixture was sieved through a 300-mesh sieve to obtain the sodium layered positive electrode material A1.

[0040] The SEM test of the sodium nickel iron manganate cathode material prepared in this embodiment was carried out, and the results were as follows: Figure 1 shown.

[0041] Example 2

[0042] This embodiment provides a double-site doping and metal oxide coating synergistically modified O3 sodium layered cathode material, the double-site doping and metal oxide coating synergistically modified O3 sodium layered cathode material chemical formula is [NaMg 0.002 ][Ni 0.333 Fe 0.333 Mn 0.334 Zr 0.002 ]O2, wherein Mg is a doping element for the sodium layer, Zr is a doping element for the transition metal layer, and the coating layer comprises titanium oxide;

[0043] The preparation method of the double-point doping and metal oxide coating synergistically modified O3 sodium layered cathode material comprises the following steps:

[0044] Step S1: nickel iron manganese hydroxide Ni 0.333 Fe 0.333 Mn 0.334 (OH)2 was pre-calcined in air at a temperature of 600°C, a heating rate of 3°C / min, and a holding time of 5h to obtain a pre-calcined material;

[0045] Step S2, the pre-calcined material obtained in step 1 is mixed with sodium carbonate, magnesium oxide, and zirconium oxide in a high-speed mixer to obtain a high-mix material, wherein the sodium content is 3% in excess, the magnesium metal content is 0.2% of the sodium content, and the titanium metal content is 0.2% of the transition metal content. The high-mix material is placed in a box furnace, and in an air atmosphere with an air flow rate of 16 L / min, the temperature is first increased to 920° C. at a rate of 3° C. / min, kept at this temperature for 13 hours, and then naturally cooled to room temperature to obtain a first-fired material. The first-fired material is mechanically crushed and vibrated to obtain a first-fired sample.

[0046] Step S3, weigh 100kg of the burned sample [NaMg 0.002 ][Ni 0.333 Fe 0.333 Mn 0.334 Zr 0.002]O2 and 0.35kg of titanium oxide were added into a high-speed mixer and mixed at 3000r / min for 15min. The mixture was placed in a box furnace and heated to 600℃ at a heating rate of 3℃ / min under an oxygen atmosphere. The mixture was kept warm for 8h and naturally cooled to room temperature. The mixture was sieved through a 300-mesh sieve to obtain the sodium layered positive electrode material A2.

[0047] Example 3

[0048] This embodiment provides a double-site doping and metal oxide coating synergistically modified O3 sodium layered cathode material, the double-site doping and metal oxide coating synergistically modified O3 sodium layered cathode material chemical formula is [NaSr 0.002 ][Ni 0.333 Fe 0.333 Mn 0.334 Sb 0.001 ]O2, wherein Sr is a doping element for the sodium layer, Sb is a doping element for the transition metal layer, and the coating layer comprises magnesium oxide;

[0049] The preparation method of the double-point doping and metal oxide coating synergistically modified O3 sodium layered cathode material comprises the following steps:

[0050] Step S1: nickel iron manganese hydroxide Ni 0.333 Fe 0.333 Mn 0.334 (OH)2 was pre-calcined in air at a temperature of 500°C, a heating rate of 3°C / min, and a holding time of 8h to obtain a pre-calcined material;

[0051] Step S2, the pre-calcined material obtained in step 1 is mixed with sodium carbonate, strontium oxide, and antimony oxide in a high-speed mixer to obtain a high-mix material, wherein the sodium content is 3% in excess, the calcium metal content is 0.2% of the sodium content, and the titanium metal content is 0.1% of the transition metal content. The high-mix material is placed in a box furnace, and in an air atmosphere with an air flow rate of 16 L / min, the temperature is first raised to 880° C. at a rate of 3° C. / min, kept at this temperature for 20 hours, and then naturally cooled to room temperature to obtain a fired material. The fired material is mechanically crushed and vibrated to obtain a fired sample;

[0052] Step S3, weigh 100kg of the calcined sample [NaSr 0.002 ][Ni 0.333 Fe 0.333 Mn 0.334 Sb 0.001]O2 and 0.25kg magnesium oxide were added into a high-speed mixer and mixed at 3000r / min for 15min. The mixture was placed in a box furnace and heated to 700℃ at a heating rate of 3℃ / min under an oxygen atmosphere. The mixture was kept warm for 5h and naturally cooled to room temperature. The mixture was sieved through a 300-mesh sieve to obtain the sodium layered positive electrode material A3.

[0053] Comparative Example 1

[0054] The sodium layered cathode material B1 provided in this comparative example is not subjected to double-site doping and metal oxide coating. The chemical formula of the O3 sodium layered cathode material is NaNi 0.333 Fe 0.333 Mn 0.334 O2.

[0055] The preparation method of the O3 sodium layered positive electrode material comprises the following steps:

[0056] Step S1: nickel iron manganese hydroxide Ni 0.333 Fe 0.333 Mn 0.334 (OH)2 was pre-calcined in air atmosphere at a temperature of 550°C, a heating rate of 3°C / min, and a holding time of 6h to obtain a pre-calcined material;

[0057] Step S2: The pre-burned material obtained in step 1 is mixed with sodium carbonate in a high-speed mixer to obtain a high-mix material, wherein the sodium content is 3% in excess. The high-mix material is placed in a box furnace under an air atmosphere with an air flow rate of 16 L / min, and the temperature is first raised to 900°C at a rate of 3°C / min, kept warm for 15 hours, and then naturally cooled to room temperature to obtain a fired material. The fired material is mechanically crushed and vibrated to obtain sample B1.

[0058] Comparative Example 2

[0059] This comparative example provides a double-point doped O3 sodium layered positive electrode material, the chemical formula of the double-point doped O3 sodium layered positive electrode material is [NaCa 0.001 ][Ni 0.333 Fe 0.333 Mn 0.334 Ti 0.001 ]O2, wherein Ca is the doping element for the sodium layer and Ti is the doping element for the transition metal layer.

[0060] The preparation method of the double-point doped O3 sodium layered positive electrode material comprises the following steps:

[0061] Step S1: nickel iron manganese hydroxide Ni 0.333 Fe 0.333 Mn 0.334(OH)2 was pre-calcined in air atmosphere at a temperature of 550°C, a heating rate of 3°C / min, and a holding time of 6h to obtain a pre-calcined material;

[0062] Step S2, the pre-burned material obtained in step 1 is mixed with sodium carbonate, calcium oxide, and titanium oxide by a high-speed mixer to obtain a high-mix material, wherein the sodium content is 3% in excess, the calcium metal content is one thousandth of the sodium content, and the titanium metal content is one thousandth of the transition metal content. The high-mix material is placed in a box furnace, under an air atmosphere with an air flow rate of 16 L / min, and the temperature is first increased to 900°C at a heating rate of 3°C / min, kept warm for 15 hours, and then naturally cooled to room temperature to obtain a fired material, and the fired material is mechanically crushed and vibrated to obtain a B2 sample.

[0063] Comparative Example 3

[0064] This comparative example provides a metal oxide coated synergistically modified O3 sodium layered positive electrode material, the metal oxide coated modified O3 sodium layered positive electrode material chemical formula NaNi 0.333 Fe 0.333 Mn 0.334 O2, the coating layer includes zirconium oxide.

[0065] The preparation method of the metal oxide coated modified O3 sodium layered positive electrode material comprises the following steps:

[0066] Step S1: nickel iron manganese hydroxide Ni 0.333 Fe 0.333 Mn 0.334 (OH)2 was pre-calcined in air atmosphere at a temperature of 550°C, a heating rate of 3°C / min, and a holding time of 6h to obtain a pre-calcined material;

[0067] Step S2, the pre-calcined material obtained in step 1 is mixed with sodium carbonate in a high-speed mixer to obtain a high-mix material, wherein the sodium content is 3% in excess, the high-mix material is placed in a box furnace, and under an air atmosphere, the air flow rate is 16 L / min, and the temperature is first increased to 900° C. at a rate of 3° C. / min, kept at this temperature for 15 hours, and then naturally cooled to room temperature to obtain a first-fired material, and the first-fired material is mechanically crushed and vibrated to obtain a first-fired sample;

[0068] Step S3: weigh 100 kg of NaNi sample and burn it. 0.333 Fe 0.333 Mn 0.334 O2 and 0.3 kg of zirconium oxide were added into a high-speed mixer and mixed at 3000 r / min for 15 min. The mixture was placed in a box furnace and heated to 650 ° C at a heating rate of 3 ° C / min under an oxygen atmosphere. The mixture was kept warm for 6 hours and naturally cooled to room temperature. The mixture was sieved through a 300 mesh sieve to obtain the sodium layered positive electrode material B3.

[0069] Comparative Example 4

[0070] This comparative example provides a sodium layer doped modified O3 sodium layered positive electrode material, the sodium layer doped modified O3 sodium layered positive electrode material chemical formula [NaCa 0.001 ][Ni 0.333 Fe 0.333 Mn 0.334 ]O2, where Ca is the sodium layer doping element.

[0071] The preparation method of the sodium layer point doped modified O3 sodium layered positive electrode material comprises the following steps:

[0072] Step S1: nickel iron manganese hydroxide Ni 0.333 Fe 0.333 Mn 0.334 (OH)2 was pre-calcined in air atmosphere at a temperature of 550°C, a heating rate of 3°C / min, and a holding time of 6h to obtain a pre-calcined material;

[0073] Step S2: The pre-burned material obtained in step 1 is mixed with sodium carbonate and calcium oxide in a high-speed mixer to obtain a high-mix material, wherein the sodium content is 3% in excess and the calcium metal content is one thousandth of the sodium content. The high-mix material is placed in a box furnace under an air atmosphere with an air flow rate of 16 L / min, and the temperature is first increased to 900° C. at a rate of 3° C. / min, kept warm for 15 hours, and then naturally cooled to room temperature to obtain a fired material. The fired material is mechanically crushed and vibrated to obtain a fired sample B4.

[0074] Comparative Example 5

[0075] The difference between this comparative example and the embodiment is that the sodium electrode layered positive electrode material B5 provided in this comparative example is only doped with the transition metal layer.

[0076] This comparative example provides a transition metal layer doped modified O3 sodium layered positive electrode material, the transition metal layer doped modified O3 sodium layered positive electrode material chemical formula is Na[Ni 0.333 Fe 0.333 Mn 0.334 Ti 0.001 ]O2, wherein Ti is the doping element of the transition metal layer.

[0077] The preparation method of the transition metal layer doped modified O3 sodium layered positive electrode material comprises the following steps:

[0078] Step S1: nickel iron manganese hydroxide Ni 0.333 Fe 0.333 Mn 0.334(OH)2 was pre-calcined in air atmosphere at a temperature of 550°C, a heating rate of 3°C / min, and a holding time of 6h to obtain a pre-calcined material;

[0079] Step S2: The pre-burned material obtained in step 1 is mixed with sodium carbonate and titanium oxide in a high-speed mixer to obtain a high-mix material, wherein the sodium content is 3% in excess and the titanium metal content is one thousandth of the transition metal content. The high-mix material is placed in a box furnace under an air atmosphere with an air flow rate of 16 L / min. The temperature is first raised to 900°C at a rate of 3°C / min, kept warm for 15 hours, and then naturally cooled to room temperature to obtain a fired material. The fired material is mechanically crushed and vibrated to obtain a fired sample B5.

[0080] The sodium nickel iron manganate positive electrode materials prepared in Examples 1-3 and Comparative Examples 1-5 were subjected to pH and residual alkali tests, wherein the surface residual alkali test of the materials used water as the solvent. The results are shown in Table 1.

[0081] Table 1

[0082]

[0083]

[0084] Furthermore, at 25°C, the sodium cathode materials prepared in Examples 1-3 and Comparative Examples 1-5 were prepared into cathode sheets, which were assembled with the sodium metal anode sheet into CR2016 button cells. The discharge current density was 150 mAg / s in the voltage range of 2.00-4.00 V. -1 The electrochemical performance test was carried out under , and the test results of the capacity retention rate after 200 cycles are shown in Table 2 below.

[0085] Table 2

[0086] cathode materials Capacity retention after 200 cycles (%) Example 1 A1 92.88 Example 2 A2 90.78 Example 3 A3 90.88 Comparative Example 1 B1 73.65 Comparative Example 2 B2 85.39 Comparative Example 3 B3 84.22 Comparative Example 4 B4 82.45 Comparative Example 5 B5 82.06

[0087] According to Tables 1 and 2 above, the residual alkali of the layered sodium ion positive electrode material coated with a single metal oxide has decreased to varying degrees, and the effect is particularly obvious. The residual alkali has also decreased after double-point doping modification, but the relative decrease is not obvious, indicating that coating is the most effective means to reduce the residual alkali. It can be seen from Example 1 and Comparative Examples 1-3 that if no modification work is performed, or only a single double-point doping and a single metal oxide coating work is performed, the performance of the material cannot reach the optimal performance. Examples 1-3 achieve synergistic modification of double-point doping and metal oxide coating, and the performance of the material can be greatly improved.

[0088] In summary, the present application realizes double-point doping and coordinated metal oxide surface coating through the sodium layer and the transition metal layer, achieving the following effects: 1) The doping elements in the sodium layer play a supporting role in the sodium layer, stabilizing the interlayer spacing of the sodium layer before and after charge and discharge, making the charge and discharge curve of the battery smoother, and improving the cycle performance of the material; 2) By incorporating high-valent elements into the transition metal layer, the phase change of the material (O3'→P3') during the charge and discharge process can be suppressed, the stability of the material can be improved, and the cycle performance of the material can be improved; 3) The metal oxide is coated on the surface of the material, so that the surface residual alkali of the positive electrode material is reduced, and the occurrence of side reactions with the electrolyte is effectively suppressed, thereby improving the cycle performance of the material. The coating layer provides a protective layer to prevent the positive electrode material from directly contacting and reacting with moisture and carbon dioxide in the air, thereby improving the air stability of the material. 4) The process is simple and controllable, and easy to mass produce.

[0089] The above-described embodiments merely represent several implementation methods of the present application. While the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the present invention. It should be noted that a person of ordinary skill in the art may make various modifications and improvements without departing from the spirit of the present invention, all of which fall within the scope of protection of the present invention. Therefore, the scope of protection of the present invention shall be determined by the appended claims.

[0090] The above description is only a preferred embodiment of the present application and is not intended to limit the present application. Any modifications, equivalent replacements and improvements made within the spirit and principles of the present application should be included in the scope of protection of the present application.

Claims

1. A layered positive electrode material, characterized in that The layered positive electrode material includes a core and a coating layer located on the surface of the core; Among them, the chemical general formula of the core is [NaM b [Ni x Fe y Mn z N k O2], where 0 < b ≤ 0.1, 0.1 ≤ x ≤ 0.5, 0.1 ≤ y ≤ 0.5, 0.2 ≤ z ≤ 0.6, 0 < k ≤ 0.1, x + y + z = 1, M is a sodium layer doping element; N is a transition metal layer doping element; the coating layer is a metal oxide.

2. The layered cathode material according to claim 1, wherein The sodium layer doping element is any one or a combination of at least two metal elements having a radius close to that of sodium ions.

3. The layered positive electrode material according to claim 1, characterized in that The M is one or more of Ca, Mg, Sr, La, K, and Zn; and the N is one or more of Ti, Zr, Sb, Sc, Y, La, Ce, Sm, Ho, and Ta.

4. The layered cathode material according to claim 1, wherein 0 <b≤0.02;0<k≤0.01。 5. The layered cathode material according to claim 1, wherein The metal oxide is one or more of zirconium oxide, titanium oxide, tin oxide, magnesium oxide, and tungsten oxide.

6. The layered positive electrode material according to claim 1 or 5, characterized in that The metal elements in the metal oxide account for 0.05% to 0.5% of the mass of the core.

7. A method for preparing the layered positive electrode material according to claim 1, characterized in that: include: The pre-sintered nickel-iron-manganese hydroxide is uniformly mixed with a sodium source, a sodium layer doping element, and a transition metal layer doping element, and subjected to a single sintering process to obtain a single-fired sample; The first-fired sample is crushed, uniformly mixed with metal oxides, and subjected to a second sintering treatment to obtain a layered positive electrode material.

8. The method for preparing a layered positive electrode material according to claim 7, wherein: The sodium source is one or more of sodium carbonate, sodium bicarbonate, sodium hydroxide, sodium nitrate, sodium acetate, and sodium citrate; the molar ratio of the sodium element in the sodium source to the sum of the nickel, iron, and manganese elements in the nickel-iron-manganese hydroxide is (1-1.04):

1.

9. The method for preparing a layered cathode material according to claim 7, wherein: The temperature of the pre-sintering treatment is 350-750°C, and the pre-sintering time is 3-9 hours; the temperature of the primary sintering treatment is 850-950°C, and the sintering time is 10-20 hours; the temperature of the secondary sintering treatment is 500-700°C, and the sintering time is 7-13 hours.

10. A sodium ion battery, characterized in that: The sodium ion battery comprises the layered positive electrode material according to any one of claims 1 to 6.

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