Sodium ion battery positive electrode material, preparation method thereof and battery

Abstract

The application belongs to the technical field of batteries, and provides a sodium ion battery positive electrode material, a preparation method thereof and a battery. x N y Fe b Mn c A d Cu f M z O2, wherein, 0.5≤x≤0.72, 0.01≤y≤0.05, 0.2≤b≤0.5, 0.5≤c≤0.8, 0.05≤d≤0.2, 0.05≤f≤0.2, 0.01≤z≤0.12, b+c+d+f+z=1, 0.8≤(d+f) / z≤3.0, 1 / 3≤b / c≤0.9. The sodium ion battery positive electrode material solves a series of problems existing in iron-manganese-based P2-phase positive electrode materials by selecting appropriate valence elements for doping and controlling the values of (d+f) / z and b / c.

Description

Technical Field

[0001] This invention belongs to the field of battery technology, and relates to a sodium-ion battery cathode material, its preparation method, and the battery itself. Background Technology

[0002] With the increasing demand for high-performance, low-cost, and environmentally friendly rechargeable batteries in fields such as energy storage systems, new energy vehicles, and portable electronic devices, lithium-ion batteries have widely occupied the mainstream market for rechargeable batteries due to their advantages such as high energy density and long cycle life. However, lithium resources are scarce in the Earth's crust (approximately 20 ppm), unevenly distributed, and have high mining costs. Therefore, finding low-cost and abundant lithium alternative battery technologies has become a research hotspot.

[0003] Sodium-ion batteries are considered the most promising alternative to lithium-ion batteries due to the high abundance of sodium resources in the Earth's crust (approximately 23,600 ppm), their wide distribution, low mining and processing costs, and their "rocking chair" charging and discharging mechanism similar to that of lithium-ion batteries. They also possess superior low-temperature performance, higher safety, and better rate capability. They are particularly suitable for cost-sensitive scenarios and applications with moderate energy density requirements, such as large-scale energy storage, low-speed electric vehicles, and backup power supplies for base stations.

[0004] As a core component of sodium-ion batteries, cathode materials directly determine the battery's energy density, cycle life, rate performance, and safety performance. They are a key bottleneck restricting the practical application of sodium-ion batteries, and their performance and cost directly impact the development of the entire sodium-ion battery industry. Currently, sodium-ion battery cathode materials are mainly divided into three categories: layered oxides, polyanionic compounds, and Prussian blue analogues. Among these, layered oxides, due to their advantages of high energy density, high voltage platform, and simple preparation process, have become one of the current research and development priorities and the preferred direction for industrialization. P2-type layered oxides, with their unique crystal structure, stand out among many layered oxides.

[0005] The crystal structure of P2-type layered oxides consists of alternating layers of transition metal (TM) oxygen octahedrons and sodium ions. "P" represents prismatic coordination, and "2" indicates that there are two sodium ion layers between every two transition metal layers. The interlayer spacing can reach 5.58 Å, providing a wide diffusion channel for sodium ion migration. The sodium ion diffusion rate is about 3 times higher than that of other layered structures such as O3, which provides a basis for excellent kinetic performance. At the same time, the voltage and capacity can be flexibly optimized by adjusting the transition metal composition. The theoretical capacity of P2-type layered oxides can reach 190 mAh / g, showing outstanding energy density potential.

[0006] In the composition design of P2-type layered oxides, iron-manganese-based P2-type cathode materials have become a core focus of current research and industrialization due to their unique comprehensive advantages. Iron (Fe) and manganese (Mn), two transition metals, are extremely abundant in the Earth's crust, inexpensive, and environmentally friendly, avoiding the use of more expensive metals such as cobalt and nickel. This significantly reduces the manufacturing cost of cathode materials, meeting the cost requirements of large-scale industrialization. Meanwhile, Fe... 3+ / Fe 4+ With Mn 3+ / Mn 4+ The synergistic effect of the redox pair can achieve a higher voltage plateau (approximately 3.3V for the Fe-Mn system vs. Na). + With its combination of reversible capacity and energy density, iron-manganese-based P2 cathode materials can further improve the overall performance of batteries compared to P2 materials with a single transition metal.

[0007] However, in the existing technology, iron-manganese based P2 phase sodium cathode materials still have the following drawbacks:

[0008] 1) Prone to phase transitions, unstable crystal structure: ① When the battery is charged to >4.0V (vs. Na + When / Na), a large amount of Na + Desorption triggers oxygen layer slip, resulting in an irreversible P2→O2 phase transition. This is accompanied by lattice volume shrinkage and lattice stress, leading to pulverization of cathode material particles, collapse of the layered structure, and decreased cycle performance. ② Jahn-Teller (JT) distortion (Mn) exists. 3+ Dominant): Mn 3+ (d) 4 Octahedral symmetry breaking leads to MnO6 distortion, severe c-axis stretching (>5%), interlayer slip, and microcracks, causing continuous lattice stress accumulation, structural integrity destruction, and rapid capacity and voltage decay in the cathode material during cycling. ③ Transition metal (TM) migration and interlayer mixing: Fe under high voltage 3+ and Mn 3+ It easily migrates to the Na layer, forming rock salt phase, which blocks Na. + Diffusion channels cause degradation of the rate performance of cathode materials, permanent loss of reversible capacity, and collapse of cycle stability.

[0009] 2) Interface and chemical stability issues: ① Sensitivity to air and humidity: Surface alkaline sites (Na+) + O 2- ① It readily reacts with CO2 and H2O in the air to form passivation layers such as Na2CO3 and NaOH, resulting in increased pH of the material, poor slurry stability, difficulty in electrode processing, and low initial coulombic efficiency (<85%). ② The positive electrode-electrolyte interface (CEI) side reactions are severe: under high voltage, high-valence Fe... 4+and Mn 4+ Catalytic electrolyte oxidation and decomposition leads to the formation of an unstable CEI film, resulting in a continuous increase in impedance, electrolyte consumption, gas production, increased safety risks, and accelerated cycle degradation. ③ Transition metal (Fe / Mn) dissolution and migration: Mn in acidic electrolytes 2+ and Fe 2 + It is easily dissolved, migrates to the negative electrode and deposits, destroys the SEI, blocks the negative electrode channel, causing dual degradation of the positive and negative electrodes, soaring battery internal resistance, and a significant decrease in capacity and cycle life.

[0010] Based on the above research, there is a need to provide a sodium-ion battery cathode material that addresses the shortcomings of the aforementioned iron-manganese-based P2 phase cathode materials. Summary of the Invention

[0011] The purpose of this invention is to provide a sodium-ion battery cathode material, its preparation method, and the battery. The sodium-ion battery cathode material is doped with sodium and transition metal sites, and elements with appropriate valence states are selected for doping. By controlling the molar amounts of A, M, and Cu to satisfy a specific relationship, and finally by controlling the appropriate iron-manganese content ratio, a series of problems existing in iron-manganese-based P2 phase cathode materials are solved.

[0012] To achieve this objective, the present invention employs the following technical solution:

[0013] In a first aspect, the present invention provides a sodium-ion battery cathode material, wherein the sodium-ion battery cathode material includes a matrix material, the matrix material having the general chemical formula Na. x N y Fe b Mn c A d Cu f M zO2, wherein 0.5≤x≤0.72, for example, can be 0.5, 0.55, 0.6, 0.65, 0.7 or 0.72; 0.01≤y≤0.05, for example, can be 0.01, 0.02, 0.03, 0.04 or 0.05; 0.2≤b≤0.5 (preferably 0.2≤b≤0.3), for example, can be 0.2, 0.3, 0.4 or 0.5; 0.5≤c≤0.8 (preferably 0.5≤c≤0.6), for example, can be 0.5, 0.6, 0.7 or 0.8; 0.05≤d≤0.2 (preferably 0.05≤d≤0.72). 1) For example, it can be 0.05, 0.1, 0.15 or 0.2, 0.05≤f≤0.2 (preferably 0.05≤f≤0.1), for example, it can be 0.05, 0.1, 0.15 or 0.2, 0.01≤z≤0.12 (preferably 0.05≤z≤0.1), for example, it can be 0.01, 0.03, 0.05, 0.07, 0.09, 0.1 or 0.12, b+c+d+f+z=1, N is selected from monovalent metal elements and / or divalent metal elements, M is selected from divalent metal elements, and A is selected from trivalent metal elements and / or tetravalent metal elements.

[0014] The d, f, and z satisfy the following relationship: 0.8≤(d+f) / z≤3.0 (preferably 1≤(d+f) / z≤3.0), for example, it can be 0.8, 1, 1.5, 2, 2.5 or 3, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0015] The values ​​of b and c satisfy the following relationship: 1 / 3 ≤ b / c ≤ 0.9 (preferably 1 / 3 ≤ b / c ≤ 0.6). For example, they can be 1 / 3, 0.4, 0.6, 0.8 or 0.9, but are not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0016] The matrix material described in this invention is a P2 type material, wherein N is a sodium site dopant, and M and A are transition metal site dopants. M and A are selected from metals of different valence states. The selection of M and A as dopant elements has the following effects: ① By doping with elements of different valence states, they occupy lattice interstices, replace some transition metal sites, enhance interlayer forces, form a lattice pinning effect, forcibly suppress oxygen layer slip, and thus stabilize the material's crystal structure; ② Reduce the Mn content in the system. 3+ The concentration of high-valence ions can suppress Jahn-Teller distortion, thereby enhancing the overall lattice stability, increasing the covalentity of TM-O bonds, and reducing the driving force for metal dissolution.

[0017] In this invention, among the various doping elements, A serves as a high-valence framework element, working with Cu to ensure rigid lattice construction and stable Mn valence. M acts as interlayer support and charge balance. This invention controls the molar amounts d, f, and z of A, M, and Cu to satisfy specific relationships, preventing the sodium-ion battery cathode material from becoming too strong and causing Na+ to degrade. + Diffusion is hindered, and the problem of disorder in the transition metal layer due to excessive supporting elements is avoided. The P2 phase structure is synergistically controlled so that the P2→O2 phase transition does not occur under high voltage.

[0018] Meanwhile, in the sodium-ion battery cathode material described in this invention, the molar ratio of iron to manganese is controlled at 1 / 3 ≤ b / c ≤ 0.9, which achieves an optimal synergistic balance between capacity, voltage, structural stability, cycle life, and kinetic performance. The reasons are as follows: ①Fe 3+ / Fe 4+ With Mn 3+ / Mn 4+ The two redox pairs work synergistically, with Mn providing a higher operating voltage and contributing the main capacity, while Fe supplements the additional capacity and increases the average voltage. Secondly, it significantly suppresses Jahn-Teller distortion and improves structural stability; when b / c ≥ 1 / 3, Fe can effectively dilute Mn. 3+ The concentration is reduced to decrease the density of distortion centers within the unit cell, thereby weakening structural distortion at its source and ensuring the integrity of the crystal structure during long cycles. At the same time, the b / c ratio is controlled to be ≤0.9 (preferably ≤0.6) to avoid problems such as lattice disorder, transition metal mixing, and phase structure instability caused by excessive Fe.

[0019] Preferably, in the XRD pattern of the matrix material, the interlayer spacing corresponding to the (002) crystal plane is d. 002 The d 002 y and z satisfy the following relationship:

[0020] d 002 =n1+n2×(y+z);

[0021] Wherein, 5.25≤n1≤5.55, for example, it can be 5.25, 5.35, 5.45 or 5.55; 2≤n2≤3, for example, it can be 2, 2.25, 2.5, 2.75 or 3; and 5.6Å≤d 002 ≤5.8Å, for example, it can be 5.6Å, 5.65Å, 5.7Å, 5.75Å or 5.8Å, but is not limited to the listed values. Other unlisted values ​​within the range also apply.

[0022] In this invention, nitrogen (N) directly expands the interlayer spacing through the ionic radius expansion effect, while nitrogen (M) indirectly expands the interlayer spacing through the lattice distortion transfer effect. Therefore, by directly controlling the content of nitrogen (N) and nitrogen (M), this invention optimizes the interlayer spacing of the sodium layer in the prepared sodium-ion battery cathode material, precisely controls the interlayer spacing of the sodium layer, improves its dynamic performance, and balances the structural stability and rate performance of the cathode material.

[0023] Preferably, the average valence state of Mn in the matrix material is 3.5 to 3.8, for example, it can be 3.5, 3.55, 3.6, 3.65, 3.7, 3.75 or 3.8, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0024] For example, the average valence state of Mn in this invention can be calculated after testing XPS.

[0025] Preferably, N is selected from any one or a combination of at least two of Li, K, or Ca.

[0026] Preferably, M is selected from any one or a combination of at least two of Mg, Zn, Ni or Sr.

[0027] Preferably, A is selected from any one or a combination of at least two of Al, Ti, Y or Zr.

[0028] Preferably, the sodium-ion battery cathode material further includes a coating layer covering the surface of the substrate material, the coating layer comprising Na x’ Ni 1 / 3-y’-z’ Fe 1 / 3 Mn 1 / 3 Cu y’ M' z’ O2, wherein 0.99≤x'≤1.02, for example, can be 0.99, 1.0, 1.01 or 1.02; 0.05≤y'≤0.1, for example, can be 0.05, 0.06, 0.07, 0.08, 0.09 or 0.1; 0.01≤z'≤0.03, for example, can be 0.01, 0.02 or 0.03; and M' is selected from any one or at least a combination of two of Al, Y, Ti, Ta, Zn, Zr, Sr, Sb, W, Mo, Nb, Co, Ca, Mg, B or Sc.

[0029] The surface of the matrix material described in this invention is further coated with a quaternary copper-containing cathode material. The coating layer not only acts as a physical barrier to isolate the material from direct contact with the electrolyte, reducing electrolyte oxidation, HF corrosion and metal dissolution, and lowering charge transfer impedance from an interfacial dynamics perspective to stabilize CEI, but also has a mechanical constraint effect, absorbing the stress generated by volume changes during cycling and preventing particle crack propagation.

[0030] Preferably, the content of the coating layer in the sodium-ion battery cathode material is 1wt% to 3wt%, for example, it can be 1wt%, 1.5wt%, 2wt%, 2.5wt% or 3wt%, but it is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0031] Secondly, the present invention provides a method for preparing a sodium-ion battery cathode material as described in the first aspect, the method comprising the following steps:

[0032] According to the formula, sodium source, nitrogen source, iron source, manganese source, a source, copper source and M source are first blended to obtain a mixture;

[0033] The mixture is sintered once to obtain the sodium-ion battery cathode material.

[0034] Preferably, the temperature of the first sintering is 920℃~1000℃, for example, 920℃, 930℃, 940℃, 950℃, 960℃, 970℃, 980℃, 990℃ or 1000℃, the time is 10h~14h, for example, 10h, 11h, 12h, 13h or 14h, and the heating rate is 3℃ / min~8℃ / min, for example, 3℃ / min, 5℃ / min, 7℃ / min or 8℃ / min, but is not limited to the listed values, and other unlisted values ​​within the range are also applicable.

[0035] Preferably, the atmosphere for the first sintering is an air atmosphere with a ventilation rate of 300 m³ / s. 3 / h-400m 3 / h, for example, could be 300m 3 / h, 325m 3 / h, 350m 3 / h、375m 3 / h or 400m 3 / h, but not limited to the listed values, other unlisted values ​​within the range also apply.

[0036] Preferably, after the first sintering, a crushing is performed to obtain a first-burned crushed material. Then, according to the formula, the first-burned crushed material, sodium source, nickel-iron-manganese-copper precursor material and M' source are sequentially subjected to a second blending, a second sintering, and a second crushing.

[0037] Preferably, the secondary sintering temperature is 600℃~800℃, for example, 600℃, 650℃, 700℃, 750℃ or 800℃, the time is 8h~12h, for example, 8h, 9h, 10h, 11h or 12h, and the heating rate is 3℃ / min~8℃ / min, for example, 3℃ / min, 5℃ / min, 7℃ / min or 8℃ / min, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0038] Preferably, the atmosphere for the secondary sintering is an air atmosphere with a ventilation rate of 300 m³ / s. 3 / h-400m 3 / h, for example, could be 300m 3 / h, 325m 3 / h, 350m 3 / h、375m 3 / h or 400m 3 / h, but not limited to the listed values, other unlisted values ​​within the range also apply.

[0039] Preferably, the first blend and the second blend are each performed independently 2 to 4 times, for example, 2, 3 or 4 times.

[0040] Preferably, the first blend and the second blend each independently include a first blend, a second blend, a third blend and a fourth blend performed sequentially, wherein the rotational speed of the fourth blend is greater than the rotational speed of the third blend, the rotational speed of the second blend and the rotational speed of the first blend.

[0041] Preferably, the rotation speed of the first mixing is 100 rpm to 300 rpm, for example, 100 rpm, 150 rpm, 200 rpm, 250 rpm or 300 rpm, and the time is 1 min to 3 min, for example, 1 min, 1.5 min, 2 min, 2.5 min or 3 min, but not limited to the listed values, other unlisted values ​​within the range are also applicable.

[0042] Preferably, the rotation speed of the second mixing is 400 rpm to 600 rpm, for example, 400 rpm, 450 rpm, 500 rpm, 550 rpm or 600 rpm, and the time is 1 min to 3 min, for example, 1 min, 1.5 min, 2 min, 2.5 min or 3 min, but not limited to the listed values, other unlisted values ​​within the range are also applicable.

[0043] Preferably, the rotation speed of the third mixing is 800 rpm to 1200 rpm, for example, 800 rpm, 900 rpm, 1000 rpm, 1100 rpm or 1200 rpm, and the time is 3 min to 5 min, for example, 3 min, 3.5 min, 4 min, 4.5 min or 5 min, but not limited to the listed values, other unlisted values ​​within the range are also applicable.

[0044] Preferably, the rotation speed of the fourth mixing is 1300 rpm to 1800 rpm, for example, 1300 rpm, 1500 rpm, 1700 rpm or 1800 rpm, and the time is 1 min to 3 min, for example, 1 min, 1.5 min, 2 min, 2.5 min or 3 min, but not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0045] Preferably, the primary crushing method includes airflow crushing and / or mechanical crushing, wherein the primary crushing results in a particle size D50 of 6μm to 7μm, for example, 6μm, 6.2μm, 6.4μm, 6.6μm, 6.8μm or 7μm, but is not limited to the listed values, and other unlisted values ​​within the range are also applicable.

[0046] Preferably, the secondary crushing method includes airflow crushing and / or mechanical crushing, and the secondary crushing results in a particle size D50 of 6μm to 8μm, for example, 6μm, 6.5μm, 7μm, 7.5m or 8μm, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0047] Preferably, the sodium source includes any one or a combination of at least two of sodium carbonate, trisodium phosphate, sodium hydroxide, sodium citrate, or sodium oxalate.

[0048] Preferably, the nickel-iron-manganese-copper precursor material can be a carbonate precursor, a hydroxide precursor, or an oxide precursor. The carbonate precursor and the hydroxide precursor can be prepared by co-precipitation, and the oxide precursor can be prepared by solid-phase mixing and calcination.

[0049] Preferably, the N source, iron source, manganese source, A source, copper source, M source, and M' source are each independently selected from the oxides and / or salts of the corresponding metals.

[0050] Thirdly, the present invention provides a battery comprising the sodium-ion battery cathode material as described in the first aspect.

[0051] Compared with the prior art, the present invention has the following beneficial effects:

[0052] This invention first involves doping with elements of different valence states to occupy interstitial spaces in the crystal lattice, replacing some transition metal sites, enhancing interlayer forces, forming a lattice pinning effect, forcibly suppressing oxygen layer slip, thereby stabilizing the material's crystal structure and reducing the Mn content in the system. 3+ The concentration of A, M, and Cu is controlled to suppress Jahn-Teller distortion, improve the covalentity of TM-O bonds, and reduce the driving force for metal dissolution. Secondly, this invention controls the molar amounts d, f, and z of A, M, and Cu to satisfy specific relationships, ensuring that the sodium-ion battery cathode material does not cause Na+ dissolution due to an excessively strong framework. + Diffusion is hindered, preventing the disorder of the transition metal layer due to excessive supporting elements. This synergistic control prevents the P2 phase structure from undergoing the P2→O2 phase transition under high voltage. Furthermore, by controlling the molar ratio of iron to manganese within the range of 1 / 3≤b / c≤0.9, this invention achieves an optimal synergistic balance between capacity, voltage, structural stability, cycle life, and kinetic performance, thus solving a series of problems existing in P2 phase cathode materials. Attached Figure Description

[0053] Figure 1 The figures show the charge and discharge curves of batteries prepared from the sodium-ion battery cathode material described in Example 1 and Comparative Example 1 of this invention. The figures include the charging and discharging curves corresponding to Example 1 and Comparative Example 1.

[0054] Figure 2 The images show the XRD patterns of the sodium-ion battery cathode materials described in Example 1 and Comparative Example 1 of this invention.

[0055] Figure 3 This is a magnified XRD pattern of the (002) peak of the sodium-ion battery cathode material described in Example 1 and Comparative Example 1 of the present invention. Detailed Implementation

[0056] The technical solution of the present invention will be further illustrated below through specific embodiments. Those skilled in the art should understand that the embodiments described are merely illustrative of the present invention and should not be construed as limiting the invention in any way.

[0057] Example 1

[0058] This embodiment provides a sodium-ion battery cathode material, which includes a matrix material and a coating layer on the surface of the matrix material. The chemical formula of the matrix material is Na. 0.7 Ca y Fe b Mn c Ti d Cu f Mg zO2, where y is 0.02, b is 0.3, c is 0.5, d is 0.05, f is 0.1, z is 0.05, (d+f) / z is 3, and b / c is 0.6;

[0059] In the XRD pattern of the matrix material, the interlayer spacing corresponding to the (002) crystal plane is d. 002 The d 002 y and z satisfy the following relationship: d 002 =5.525 + 2.5 × (y + z) = 5.70 Å;

[0060] In the matrix material, the average valence state of Mn is 3.72;

[0061] In the sodium-ion battery cathode material, the content of the coating layer is 2 wt%, and the chemical formula of the coating layer is NaNi. 0.22 Fe 1 / 3 Mn 1 / 3 Cu 0.1 Ti 0.01 Y 0.01 O2;

[0062] The method for preparing the sodium-ion battery cathode material includes the following steps:

[0063] (1) According to the formula amount of the matrix material chemical formula, Na2CO3, Fe2O3, Mn3O4, CuO, CaO, MgO and TiO2 are mixed twice to obtain a first mixture. The first mixing includes mixing at 200 rpm for 2 min, mixing at 500 rpm for 2 min, mixing at 1000 rpm for 4 min, and finally mixing at 1500 rpm for 2 min.

[0064] (2) The first mixture is packed into a bowl at a rate of 3.5 kg / bowl, and then placed in an air atmosphere furnace (air flow rate of 350 m³ / h). 3 The temperature was increased to 980℃ at a rate of 5℃ / min and sintered for 12 hours. After natural cooling, the material was pulverized by airflow milling until the particle size D50 was 6.5μm to obtain the matrix material.

[0065] (3) According to the formulation amount (the content of the coating layer and the chemical formula of the coating layer), the matrix material and Ni are added. 0.23 Fe 1 / 3 Mn 1 / 3 Cu 0.1(OH)2, titanium dioxide and yttrium oxide are blended twice to obtain a second mixture. The second blending includes mixing at 200 rpm for 2 min, then at 500 rpm for 2 min, then at 1000 rpm for 4 min, and finally at 1500 rpm for 2 min.

[0066] (4) Place the second mixture in an air atmosphere furnace (air flow rate of 350 m³ / h). 3 The temperature was increased to 700℃ at a rate of 5℃ / min and sintered for 12 hours. After natural cooling, the material was pulverized by airflow to a particle size D50 of 7μm to obtain the sodium-ion battery cathode material.

[0067] Example 2

[0068] This embodiment provides a sodium-ion battery cathode material, which includes a matrix material and a coating layer on the surface of the matrix material. The chemical formula of the matrix material is Na. 0.55 Ca y Fe b Mn c Ti d Cu f Mg z O2, where y is 0.01, b is 0.3, c is 0.5, d is 0.05, f is 0.05, z is 0.1, (d+f) / z is 1, and b / c is 0.6;

[0069] In the XRD pattern of the matrix material, the interlayer spacing corresponding to the (002) crystal plane is d. 002 The d 002 y and z satisfy the following relationship: d 002 =5.31+2.64×(y+z)=5.60Å;

[0070] In the matrix material, the average valence state of Mn is 3.55;

[0071] In the sodium-ion battery cathode material, the content of the coating layer is 1 wt%, and the chemical formula of the coating layer is Na. 1.02 Ni 0.27 Fe 1 / 3 Mn 1 / 3 Cu 0.05 Ti 0.01 O2;

[0072] The method for preparing the sodium-ion battery cathode material includes the following steps:

[0073] (1) According to the formula amount of the matrix material chemical formula, Na2CO3, Fe2O3, Mn3O4, CuO, CaO, MgO and TiO2 are first blended four times to obtain the first mixture. The first blending includes mixing at 100 rpm for 3 min, mixing at 600 rpm for 1 min, mixing at 1200 rpm for 3 min, and finally mixing at 1300 rpm for 3 min.

[0074] (2) The first mixture is packed into a bowl at a rate of 3.5 kg / bowl, and then placed in an air atmosphere furnace (air flow rate of 300 m³ / h). 3 The temperature was increased to 1000℃ at a rate of 8℃ / min and sintered for 10h. After natural cooling, the material was pulverized by airflow milling until the particle size D50 was 7μm, thus obtaining the matrix material.

[0075] (3) According to the formulation amount (the content of the coating layer and the chemical formula of the coating layer), the matrix material and Ni are added. 0.28 Fe 1 / 3 Mn 1 / 3 Cu 0.05 (OH)2 and titanium dioxide are blended three times to obtain a second mixture. The second blending includes mixing at 300 rpm for 1 min, mixing at 600 rpm for 1 min, mixing at 800 rpm for 5 min, and finally mixing at 1300 rpm for 3 min.

[0076] (4) Place the second mixture in an air atmosphere furnace (air flow rate of 300 m³ / h). 3 The temperature was increased to 600℃ at a rate of 3℃ / min and sintered for 12 hours. After natural cooling, the material was pulverized by airflow to a particle size D50 of 6μm to obtain the sodium-ion battery cathode material.

[0077] Example 3

[0078] This embodiment provides a sodium-ion battery cathode material, which includes a matrix material and a coating layer on the surface of the matrix material. The chemical formula of the matrix material is Na. 0.6 Ca y Fe b Mn c Al d Cu f Zn z O2, where y is 0.05, b is 0.2, c is 0.5, d is 0.1, f is 0.1, z is 0.1, (d+f) / z is 2, and b / c is 0.4;

[0079] In the XRD pattern of the matrix material, the interlayer spacing corresponding to the (002) crystal plane is d. 002 The d 002 y and z satisfy the following relationship: d 002 =5.42 + 2.53 × (y + z) = 5.80 Å;

[0080] In the matrix material, the average valence state of Mn is 5.61.

[0081] In the sodium-ion battery cathode material, the content of the coating layer is 3 wt%, and the chemical formula of the coating layer is Na. 1.02 Ni 0.27 Fe 1 / 3 Mn 1 / 3 Cu 0.05 Ti 0.01 O2;

[0082] The method for preparing the sodium-ion battery cathode material includes the following steps:

[0083] (1) According to the formula amount of the matrix material chemical formula, Na2CO3, Fe2O3, Mn3O4, CuO, CaO, ZnO and Al2O3 are first blended four times to obtain the first mixture. The first blending includes mixing at 300 rpm for 1 min, mixing at 400 rpm for 3 min, mixing at 800 rpm for 5 min, and finally mixing at 1800 rpm for 1 min.

[0084] (2) The first mixture is packed into a bowl at a rate of 3.5 kg / bowl, and then placed in an air atmosphere furnace (air flow rate of 400 m³ / h). 3 The temperature was increased to 950℃ at a rate of 3℃ / min and sintered for 14h. After natural cooling, the material was pulverized by airflow milling until the particle size D50 was 6μm to obtain the matrix material.

[0085] (3) According to the formulation amount (the content of the coating layer and the chemical formula of the coating layer), the matrix material and Ni are added. 0.28 Fe 1 / 3 Mn 1 / 3 Cu 0.05 (OH)2 and titanium dioxide are blended four times to obtain a second mixture. The second blending includes mixing at 100 rpm for 3 min, mixing at 400 rpm for 3 min, mixing at 1200 rpm for 3 min, and finally mixing at 1800 rpm for 1 min.

[0086] (4) Place the second mixture in an air atmosphere furnace (air flow rate of 400 m³ / h). 3The temperature was increased to 800℃ at a rate of 8℃ / min and sintered for 8 hours. After natural cooling, the material was pulverized by airflow to a particle size D50 of 8μm to obtain the sodium-ion battery cathode material.

[0087] Example 4

[0088] This embodiment provides a sodium-ion battery cathode material. Except for the matrix material, which is adapted to the parameter values ​​in Table 1, the sodium-ion battery cathode material is the same as that in Embodiment 1.

[0089] The preparation method of the sodium-ion battery cathode material is the same as that in Example 1, except that the formulation amount of the matrix material chemical formula is adapted to the changes.

[0090] Example 5

[0091] This embodiment provides a sodium-ion battery cathode material, which is the same as that in Embodiment 1 except that it does not contain a coating layer.

[0092] The preparation method of the sodium-ion battery cathode material is the same as that in Example 1, except that steps (3) and (4) are not performed.

[0093] Example 6

[0094] This embodiment provides a sodium-ion battery cathode material. Except for the matrix material, which is adapted to the parameter values ​​in Table 1, the sodium-ion battery cathode material is the same as that in Embodiment 1.

[0095] The preparation method of the sodium-ion battery cathode material is the same as that in Example 1, except that the formulation amount of the matrix material chemical formula is adapted to the changes.

[0096] Comparative Examples 1-5

[0097] Comparative Examples 1-5 provide a sodium-ion battery cathode material, wherein the sodium-ion battery cathode material is the same as that in Example 1, except that the matrix material is adapted to the parameter values ​​in Table 1.

[0098] The preparation methods of the sodium-ion battery cathode materials described in Comparative Examples 1-5 are the same as those in Example 1, except that the formulation amount of the matrix material is adapted according to the chemical formula.

[0099] In the above embodiments and comparative examples, b, c, b / c, d, f, z, (d+f) / z, y, and d 002 As shown in Table 1:

[0100] Table 1

[0101]

[0102] The sodium-ion battery cathode material, CNT (carbon nanotubes), SP (conductive carbon black), and PVDF (polyvinylidene fluoride) of the above embodiments and comparative examples were mixed in a molar ratio of 94:1:2:3 to obtain a mixture. Then, the mixture and N-methylpyrrolidone were stirred in a homogenizer at 2000 rpm for 8 minutes to form a viscous slurry. This slurry was then evenly coated onto aluminum foil and vacuum-baked at 80°C. The dried electrode was then rolled and finally cut into cathode sheets with a diameter of 14 mm, wherein the areal density of the cathode sheet was 9 mg / cm³. 2 The compaction density of the positive electrode is 2.2 g / cm³. 3 Then, using a 15mm diameter pure sodium sheet as the negative electrode, ENA 18 from Tianci as the electrolyte, and a Whatman glass fiber separator, the sodium-ion battery was assembled with the obtained positive electrode in an argon-filled glove box.

[0103] The obtained sodium-ion battery was subjected to electrochemical performance testing under the following conditions:

[0104] 1) Charge / discharge cycle: Voltage range of 2.0-4.25V; constant temperature test at 25℃;

[0105] 2) Cyclic test: 0.5C charging, 1.0C discharging, 50 cycles;

[0106] 3) Capacity test: 0.1C charging and 0.1C discharging test the first charge and discharge capacity;

[0107] 4) Rate test: Two cycles of charging and discharging at 0.1C, charging at 0.5C, and discharging at 0.5C / 1C / 2C / 3C / 4C. The test results are shown in Table 2.

[0108] The charge-discharge curves of the batteries prepared from the sodium-ion battery cathode material described in Example 1 and Comparative Example 1 of this invention are shown below. Figure 1 As shown, by Figure 1 It can be seen that the sodium-ion battery of Example 1 has superior performance; the XRD patterns of the sodium-ion battery cathode materials described in Example 1 and Comparative Example 1 are as follows. Figure 2 As shown, a magnified view of a local XRD pattern is as follows. Figure 3 As shown, by Figure 2 and Figure 3 It can be seen that the crystal structure of the product after doping has not changed, and the (002) peak of Example 1 is shifted to the left compared with the (002) peak of Comparative Example 1, indicating that the interlayer spacing of sodium layers has increased.

[0109] Table 2

[0110]

[0111] As can be seen from Tables 1 and 2 above:

[0112] As can be seen from Examples 1-4 and Comparative Examples 1-5, the present invention achieves optimal doping effect by doping sodium sites and transition metal sites, and controlling d, f, and z to satisfy specific relationships, and b and c to satisfy specific relationships. It also achieves optimal synergistic balance among capacity, voltage, structural stability, cycle life, and kinetic performance, resulting in a sodium-ion battery with excellent comprehensive electrochemical performance. As can be seen from Examples 1 and 5, the coating layer of the present invention further improves the stability of the material, reduces charge transfer impedance, and enhances the performance of the sodium-ion battery. As can be seen from Examples 1, 6, and Comparative Example 5, the present invention controls the interlayer spacing d corresponding to the (002) crystal plane. 002 The specific relationship between y and z ensures that the interlayer spacing of the sodium layer in the prepared sodium-ion battery cathode material is optimally designed, and balances the structural stability and rate performance of the cathode material, resulting in a sodium-ion battery with excellent comprehensive electrochemical performance.

[0113] The above description is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention fall within the protection and disclosure scope of the present invention.

Claims

1. A sodium-ion battery cathode material, characterized in that, The sodium-ion battery cathode material includes a matrix material, the general chemical formula of which is Na. x N y Fe b Mn c A d Cu f M z O2, where 0.5≤x≤0.72, 0.01≤y≤0.05, 0.2≤b≤0.5, 0.5≤c≤0.8, 0.05≤d≤0.2, 0.05≤f≤0.2, 0.01≤z≤0.12, b+c+d+f+z=1, N is selected from monovalent and / or divalent metal elements, M is selected from divalent metal elements, and A is selected from trivalent and / or tetravalent metal elements; The d, f, and z satisfy the following relationship: 0.8 ≤ (d + f) / z ≤ 3.0; The relationship between b and c is as follows: 1 / 3 ≤ b / c ≤ 0.9; In the XRD pattern of the matrix material, the interlayer spacing corresponding to the (002) crystal plane is d. 002 The d 002 y and z satisfy the following relationship: d 002 =n1+n2×(y+z); Where, 5.25≤n1≤5.55, 2≤n2≤3, 5.6Å≤d 002 ≤5.8Å.

2. The sodium-ion battery cathode material according to claim 1, characterized in that, The chemical formula of the matrix material is Na. x N y Fe b Mn c A d Cu f M z O2, where 0.5≤x≤0.72, 0.01≤y≤0.05, 0.2≤b≤0.3, 0.5≤c≤0.6, 0.05≤d≤0.1, 0.05≤f≤0.1, 0.05≤z≤0.1, b+c+d+f+z=1; The d, f, and z satisfy the following relationship: 1 ≤ (d + f) / z ≤ 3.0; The relationship between b and c is as follows: 1 / 3 ≤ b / c ≤ 0.

6.

3. The sodium-ion battery cathode material according to claim 1 or 2, characterized in that, In the matrix material, the average valence state of Mn is 3.5 to 3.

8. And / or, the N is selected from any one or at least a combination of two of Li, K or Ca; And / or, M is selected from any one or at least a combination of two of Mg, Zn, Ni or Sr; And / or, the A is selected from any one or at least a combination of two of Al, Ti, Y or Zr.

4. The sodium-ion battery cathode material according to claim 1 or 2, characterized in that, The sodium-ion battery cathode material also includes a coating layer covering the surface of the matrix material; The coating layer includes Na. x’ Ni 1 / 3-y’-z’ Fe 1 / 3 Mn 1 / 3 Cu y’ M' z’ O2, wherein 0.99≤x'≤1.02, 0.05≤y'≤0.1, 0.01≤z'≤0.03, and M' is selected from any one or at least two of Al, Y, Ti, Ta, Zn, Zr, Sr, Sb, W, Mo, Nb, Co, Ca, Mg, B or Sc; In the sodium-ion battery cathode material, the content of the coating layer is 1wt%~3wt%.

5. A method for preparing a sodium-ion battery cathode material as described in any one of claims 1-4, characterized in that, The preparation method includes the following steps: According to the formula, sodium source, nitrogen source, iron source, manganese source, a source, copper source and M source are first blended to obtain a mixture; The mixture is sintered once to obtain the sodium-ion battery cathode material.

6. The preparation method according to claim 5, characterized in that, The temperature of the first sintering is 920℃~1000℃, the time is 10h~14h, and the heating rate is 3℃ / min~8℃ / min; And / or, the atmosphere for the first sintering is an air atmosphere with a ventilation rate of 300 m³ / s. 3 / h-400m 3 / h.

7. The preparation method according to claim 5, characterized in that, After the first sintering, a crushing process was carried out to obtain a first-burned crushed material. Then, according to the formula, the first-burned crushed material, sodium source, nickel-iron-manganese-copper precursor material and M' source were sequentially subjected to a second blending, a second sintering and a second crushing.

8. The preparation method according to claim 7, characterized in that, The secondary sintering temperature is 600℃~800℃, the time is 8h~12h, and the heating rate is 3℃ / min~8℃ / min; And / or, the atmosphere for the secondary sintering is an air atmosphere with a ventilation rate of 300 m³ / h. 3 / h-400m 3 / h.

9. A battery, characterized in that, The battery includes the sodium-ion battery cathode material as described in any one of claims 1-4.

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