A sodium ion cathode material, its preparation method and uses

Abstract

The present disclosure provides a sodium-ion cathode material, a preparation method thereof and uses thereof. The general formula of the sodium-ion cathode material is Na x Ni y Fe z Mn t Cu h Zn m B n Al g Ce j Mg k Sr u O2, and the sodium-ion cathode material is in the O3 phase. The preparation method adds the sodium source in two steps for mixing and performs two-step sintering. In an increasing manner of the sodium source, a P2 / O3 mixed phase is first generated as an intermediate phase. The presence of the P2 phase can make the subsequent secondary sintering reaction more sufficient, the element diffusion more uniform, and the sodium ions are uniformly supplemented into the bulk phase. Finally, the prepared O3-phase finished product has lower surface residual sodium and has excellent air stability and rate cycling performance.

Description

Technical Field

[0001] The present disclosure belongs to the field of batteries, and relates to a sodium-ion cathode material, a preparation method thereof, and uses thereof. Background Art

[0002] As the most popular energy storage device, lithium-ion batteries are widely used in portable electronic products and electric vehicles, etc., profoundly affecting our daily life. However, due to reasons such as the difficult development, high cost, and weak supply capacity of lithium resources, China is highly dependent on lithium resources from other countries. Therefore, it is imperative to develop alternative or alternative energy storage technologies for lithium-ion batteries. Sodium-ion batteries, due to advantages such as abundant sodium resources, low cost, and similar physical and chemical properties to lithium-ion batteries, can be used as an important supplementary technology for lithium-ion batteries in the field of large-scale energy storage, and have important economic value and strategic significance, making them a new type of secondary battery that has received attention currently.

[0003] Sodium-ion batteries have a working principle similar to that of lithium-ion batteries, but have lower costs and higher safety, and are therefore considered to be a next-generation energy storage system that can replace lithium-ion batteries.

[0004] In sodium-ion batteries, the cathode material is an important factor restricting performance indicators such as the capacity, energy density, and safety of sodium-ion batteries. Layered transition metal oxide cathode materials have become an important type of cathode material in practical applications due to advantages such as simple preparation, high specific capacity, and high ionic conductivity. Usually, layered cathode materials can be divided into P2, P3, O2, and O3 phases according to the occupancy of sodium atoms and the stacking of oxygen layers, with P2 and O3 phases being more common. Among them, the O3 phase has a higher capacity due to a higher sodium content. At the same time, the high sodium content also makes the surface of the O3-phase sodium-ion cathode material more likely to generate residual alkalis (NaOH, Na 2 CO 3 ) with water or carbon dioxide in the air, that is, the air stability and water stability are poor, resulting in a decrease in active sodium in the sodium-ion cathode material, affecting the capacity performance during the charge-discharge process, and since the residual alkalis hinder the conduction of sodium ions during the charge-discharge process, the sodium-ion cathode material exhibits low specific capacity and low rate performance.

[0005] It can be seen that optimizing the material's own composition and structure as well as the preparation method plays an important role in improving the performance and stability of O3-phase sodium-ion cathode materials. Developing new O3-phase sodium-ion cathode materials and matching preparation methods is of great significance for promoting the development and application of sodium-ion batteries. Summary of the Invention

[0006] The following is an overview of the subject matter described in detail in this article. This overview is not intended to limit the scope of protection of the claims.

[0007] In view of the problems existing in the prior art, the purpose of the present disclosure is to provide a sodium ion cathode material, a preparation method and a use thereof. The general formula of the sodium ion cathode material is Na x Ni y Fe z Mn t Cu h Zn m B n Al g Ce j Mg k Sr u O 2 , and the sodium ion cathode material is of the O3 phase. The preparation method adds the sodium source in two steps, mixes them and conducts two-step sintering. In the way of increasing the sodium source step by step, a P2 / O3 mixed phase is first generated. The existence of the P2 phase can make the subsequent secondary sintering reaction more sufficient, the element diffusion more uniform, and the sodium ions are uniformly supplemented into the bulk phase. Finally, the prepared O3-phase finished product has lower surface residual sodium and has excellent air stability and rate cycling performance.

[0008] To achieve this purpose, the present disclosure adopts the following technical solutions:

[0009] In the first aspect, the present disclosure provides a kind of. The general formula of the sodium ion cathode material is Na x Ni y Fe z Mn t Cu h Zn m B n Al g Ce j Mg k Sr u O 2 , where 0.8 ≤ x ≤ 1.0, 0.1 ≤ y ≤ 0.5, 0.1 ≤ z ≤ 0.5, 0.3 ≤ t ≤ 0.7, 0.01 ≤ h ≤ 0.3, 0.01 ≤ m ≤ 0.2, y + z + t + h + m + n + g + j + k + u = 1, 0 ≤ n + g + j + k + u ≤ 0.05, and the sodium ion cathode material is of the O3 phase.

[0010] The present disclosure provides a new sodium ion cathode material, which has a specific composition. Among them, Cu, B and Ce improve the structural stability of the material, Zn and Mg can stabilize the sodium layer and improve the capacity, Sr improves the roundness of the material particles, Al improves the rate performance of the material, and the multi-element high-entropy doping synergistically improves the local entropy of the material, thereby improving the cycling performance.

[0011] In the present disclosure, 0.8 ≤ x ≤ 1.0, such as 0.8, 0.82, 0.84, 0.86, 0.88, 0.9, 0.92, 0.94, 0.96, 0.98 or 1, etc.; 0.1 ≤ y ≤ 0.5, such as 0.1, 0.12, 0.14, 0.16, 0.18, 0.2, 0.22, 0.24, 0.26, 0.28, 0.3, 0.32, 0.34, 0.36, 0.38, 0.4, 0.42, 0.44, 0.46, 0.48 or 0.5, etc.; 0.1 ≤ z ≤ 0.5, such as 0.1, 0.12, 0.14, 0.16, 0.18, 0.2, 0.22, 0.24, 0.26, 0.28, 0.3, 0.32, 0.34, 0.36, 0.38, 0.4, 0.42, 0.44, 0.46, 0.48 or 0.5, etc.; 0.3 ≤ t ≤ 0.7, such as 0.3, 0.32, 0.34, 0.36, 0.38, 0.4, 0.42, 0.44, 0.46, 0.48, 0.5, 0.52, 0.54, 0.56, 0.58, 0.6, 0.62, 0.64, 0.66, 0.68 or 0.7, etc.; 0.01 ≤ h ≤ 0.3, such as 0.01, 0.05, 0.08, 0.1, 0.12, 0.14, 0.16, 0.18, 0.2, 0.22, 0.24, 0.26, 0.28 or 0.3, etc.; 0.01 ≤ m ≤ 0.2, such as 0.01, 0.05, 0.08, 0.1, 0.12, 0.14, 0.16, 0.18 or 0.2, etc., y + z + t + h + m + n + g + j + k + u = 1, 0 ≤ n + g + j + k + u ≤ 0.05, such as 0.001, 0.005, 0.01, 0.015, 0.02, 0.025, 0.03, 0.035, 0.04, 0.045 or 0.05, etc., but not limited to the listed values, and other unlisted values within the above numerical ranges are equally applicable.

[0012] The following are alternative technical solutions of the present disclosure, but not limitations on the technical solutions provided by the present disclosure. Through the following technical solutions, the technical objectives and beneficial effects of the present disclosure can be better achieved.

[0013] As an alternative technical solution of the present disclosure, the general formula of the sodium ion cathode material is Na x Ni y Fe z Mn t Cu h Zn m B n Al g Ce j Mg k Sr u Q vO 2 , where Q is a doping element, and 0.8 ≤ x ≤ 1.0, 0.1 ≤ y ≤ 0.5, 0.1 ≤ z ≤ 0.5, 0.3 ≤ t ≤ 0.7, 0.01 ≤ h ≤ 0.3, 0.01 ≤ m ≤ 0.2, y + z + t + h + m + n + g + j + k + u + v = 1, and 0 ≤ n + g + j + k + u + v ≤ 0.05.

[0014] The present disclosure may optionally further dope the sodium ion cathode material, and use the doping element Q to further optimize and improve the properties of the obtained sodium ion cathode material.

[0015] In one embodiment, Q is selected from at least one of Li, Ca, S, Sc, Ti, V, Cr, Co, Ga, Ge, Se, Y, Zr, Nb, Mo, Tc, Ru, Rh, Pd, Ag, Cd, In, Sn, Sb, Te, La, Ta, Ir, or Bi. For example, it can be a combination of Li and Ca, a combination of S and Sc, a combination of Ti and V, a combination of Cr and Co, a combination of Ga and Ge, a combination of Se and Y, a combination of Zr and Nb, a combination of Mo and Tc, a combination of Ru and Rh, a combination of Pd and Ag, a combination of Cd and In, a combination of Sn and Sb, a combination of Te and La, or a combination of Ta and Ir

[0016] In one embodiment, 0.001 ≤ v ≤ 0.02, such as 0.001, 0.003, 0.005, 0.008, 0.01, 0.011, 0.012, 0.013, 0.014, 0.015, 0.016, 0.017, 0.018, 0.019, or 0.02, etc., but not limited to the listed values. Other unlisted values within the above numerical range are equally applicable.

[0017] In one embodiment, the particle size D50 of the sodium ion cathode material is 5 - 15 μm, such as 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm, 11 μm, 12 μm, 13 μm, 14 μm, or 15 μm, etc., but not limited to the listed values. Other unlisted values within the above numerical range are equally applicable.

[0018] In one embodiment, the specific surface area of the sodium ion cathode material is 0.2 - 0.5 m 2 / g, such as 0.2 m 2 / g, 0.25 m 2 / g, 0.3 m 2 / g, 0.35 m 2 / g, 0.4 m 2 / g, 0.45 m 2 / g, or 0.5 m 2 / g, etc., but not limited to the listed values, and other unlisted values within the above value ranges are equally applicable.

[0019] In one embodiment, in the X-ray diffraction pattern of the sodium ion cathode material, diffraction peaks of the following crystal planes are respectively included in the ranges of diffraction angles of 16° - 17°, 33° - 34°, 35° - 36°, 36° - 37.5°, 41° - 42.5°, 45° - 46°, 53° - 54.5°, 58° - 59°, 62 - 63.5°, 65 - 66°: (003), (006), (101), (012), (104), (015), (017), (018), (110), (113).

[0020] In one embodiment, the mass range of residual sodium measured by the aqueous method of the sodium ion cathode material is 0.5 - 1.5 wt%, such as 0.5 wt%, 0.6 wt%, 0.7 wt%, 0.8 wt%, 0.9 wt%, 1 wt%, 1.1 wt%, 1.2 wt%, 1.3 wt%, 1.4 wt% or 1.5 wt%, etc., and the mass range of residual sodium measured by the alcohol method is 0.01 - 0.2 wt%, such as 0.01 wt%, 0.03 wt%, 0.05 wt%, 0.08 wt%, 0.1 wt%, 0.11 wt%, 0.12 wt%, 0.13 wt%, 0.14 wt%, 0.15 wt%, 0.16 wt%, 0.17 wt%, 0.18 wt%, 0.19 wt% or 0.2 wt%, etc., but not limited to the listed values, and other unlisted values within the above value ranges are equally applicable.

[0021] In a second aspect, the present disclosure provides a preparation method of the sodium ion cathode material described in the first aspect, and the preparation method includes the following steps:

[0022] Mix a first Na source, a Ni source, a Fe source, a Mn source, and a Cu source, a Zn source, a B source, an Al source, a Ce source, a Mg source, and a Sr source, and obtain a first-fired material through a first sintering;

[0023] Mix a second Na source and the first-fired material, and obtain the sodium ion cathode material through a second sintering.

[0024] The present disclosure performs a first sintering using a first Na source to enable the material to form a P2 / O3 mixed phase. Since the P2 phase has a low sodium ion migration barrier and a large interlayer spacing, sodium ions are more likely to diffuse and migrate in the bulk phase, forming a uniform and consistent cathode material. The secondary sintering supplements the sodium source on the basis of the material obtained from the first sintering, so that the final sodium molar content in the prepared material reaches 80% to 100%, preferably 90% to 100%. The secondary sintering supplements the sodium source to generate the O3 phase. Due to the large interlayer spacing, sodium ions are more likely to enter the bulk phase, and at the same time, the fresh interfaces exposed due to the pulverization of the material after the first sintering are repaired.

[0025] That is, the present disclosure adopts a two-step sintering method to increase the sodium source. First, a P2 / O3 mixed phase is formed. The presence of the P2 phase can make the subsequent secondary sintering reaction more complete, the element diffusion more uniform, and sodium ions are uniformly supplemented into the bulk phase. The prepared O3-phase product has lower surface residual sodium and excellent air stability and rate cycling performance. In addition to making the sodium ion diffusion uniform, the P2 / O3 mixed phase can also cooperate with doping to reduce the energy barrier for doping elements to enter the bulk phase, so that each element is uniformly doped into the bulk phase. At the same time, the co-doping of each element further improves the rate and cycling performance of the material.

[0026] In summary, the sodium-ion cathode material obtained by using the preparation method has the characteristics of low residual sodium, excellent air stability, and excellent cycling rate performance.

[0027] As an optional technical solution of the present disclosure, both the first Na source and the second Na source include at least one of sodium carbonate, sodium bicarbonate, sodium hydroxide, sodium oxide, sodium oxalate, sodium acetate, and sodium peroxide. For example, the combination types that can be used but are not limited to are sodium carbonate and sodium bicarbonate, sodium hydroxide and sodium oxide, sodium oxalate and sodium acetate, sodium peroxide and sodium carbonate, sodium bicarbonate and sodium hydroxide, sodium oxide and sodium oxalate, or sodium acetate and sodium peroxide, etc.

[0028] In one embodiment, the second Na source is an oxide of sodium, and the oxide of sodium includes sodium oxide and / or sodium peroxide.

[0029] The present application limits the second Na source oxide, which can improve the uniformity of the secondary sintering and does not introduce other impurities.

[0030] In one embodiment, the molar content of sodium in the material obtained from the first sintering is 55% to 75%, but is not limited to the listed values, and other unlisted values within the above numerical range are equally applicable.

[0031] In the present disclosure, when the amount of the Na source used in the first sintering is too small, not only the P2 / O3 phase cannot be formed, but also more Na source needs to be supplemented during the second sintering, which easily leads to an incomplete second sintering reaction and a large amount of residual alkali.

[0032] As an alternative technical solution of the present disclosure, the Ni source, Fe source, and Mn source all include oxides of the corresponding elements, and NiFeMn hydroxide is used to replace the Ni source, Fe source, and Mn source; the chemical general formula of the NiFeMn hydroxide is Ni y Fe z Mn t (OH) 2 , where 0.1 ≤ y ≤ 0.5, 0.1 ≤ z ≤ 0.5, and 0.3 ≤ t ≤ 0.7.

[0033] Preferably, using NiFeMn hydroxide to replace the mixture of the separate Ni source, Fe source, and Mn source can greatly improve the uniformity of Ni, Fe, and Mn elements in the obtained sodium ion cathode material.

[0034] In one embodiment, the Cu source, Zn source, B source, Al source, Ce source, Mg source, and Sr source all include oxides of the corresponding elements.

[0035] In one embodiment, the mixing before the first sintering further includes a doping element Q source, and the Q source includes an oxide of the corresponding doping element.

[0036] As an alternative technical solution of the present disclosure, the first sintered material is a P2 / O3 mixed phase.

[0037] In one embodiment, the particle size D50 of the first sintered material is 2 - 5 μm, such as 2 μm, 2.2 μm, 2.4 μm, 2.6 μm, 2.8 μm, 3 μm, 3.2 μm, 3.4 μm, 3.6 μm, 3.8 μm, 4 μm, 4.2 μm, 4.4 μm, 4.6 μm, 4.8 μm, or 5 μm, etc., but not limited to the listed values, and other unlisted values within the above value range are equally applicable.

[0038] In one embodiment, the specific surface area of the first sintered material is 0.5 - 1 m 2 / g, such as 0.5 m 2 / g, 0.55 m 2 / g, 0.6 m 2 / g, 0.65 m 2 / g, 0.7 m 2 / g, 0.75 m 2 / g, 0.8 m 2 / g, 0.85 m 2 / g, 0.9 m 2 / g, 0.95 m 2 / g, or 1 m 2 / g, etc., but not limited to the listed values, and other unlisted values within the above value range are equally applicable.

[0039] In one embodiment, in the X-ray diffraction pattern of the first-fired material, diffraction peaks of the following crystal planes are respectively included in the ranges of diffraction angles of 15.5° - 16.5°, 16° - 17°, 32° - 32.5°, 33° - 34°, 35° - 36°, 36° - 37.5°, 39° - 40°, 41° - 42.5°, 43° - 44°, 45° - 46°, 53° - 54.5°, 58° - 59°, 62° - 63.5°, 65° - 66°: (002), (003), (004), (006), (101), (012), (102), (104), (103), (015), (017), (018), (110), (113).

[0040] As an alternative technical solution of the present disclosure, the temperature of the first sintering is 800 - 1000 °C, such as 800 °C, 820 °C, 840 °C, 860 °C, 880 °C, 900 °C, 920 °C, 940 °C, 960 °C, 980 °C or 1000 °C, etc., and the time is 2 - 10 h, such as 2 h, 2.5 h, 3 h, 3.5 h, 4 h, 4.5 h, 5 h, 5.5 h, 6 h, 6.5 h, 7 h, 7.5 h, 8 h, 8.5 h, 9 h, 9.5 h or 10 h, etc., but not limited to the listed values, and other unlisted values within the above numerical ranges are equally applicable.

[0041] In one embodiment, the temperature of the second sintering is 800 - 1000 °C, such as 800 °C, 820 °C, 840 °C, 860 °C, 880 °C, 900 °C, 920 °C, 940 °C, 960 °C, 980 °C or 1000 °C, etc., and the heat preservation time is 2 - 10 h, such as 2 h, 2.5 h, 3 h, 3.5 h, 4 h, 4.5 h, 5 h, 5.5 h, 6 h, 6.5 h, 7 h, 7.5 h, 8 h, 8.5 h, 9 h, 9.5 h or 10 h, etc., but not limited to the listed values, and other unlisted values within the above numerical ranges are equally applicable.

[0042] In the present disclosure, if the temperature of the first sintering is too low, it is difficult for the material to nucleate and grow; if the temperature is too high, the cost increases, and at the same time, the flaky particles are larger and are prone to cracking during subsequent processing; if the temperature of the second sintering is too low, the dissolution of bulk-phase sodium causes an increase in residual sodium, and if the temperature is too high, over-sintering occurs and the material decomposes. The temperature ranges of the second sintering and the first sintering are the same, both ensuring the decomposition of the Na source and its entry into the bulk phase. According to the actual experimental requirements, the temperature of the second sintering can be lower than that of the first sintering, but generally, in order to ensure the decomposition of residual sodium (sodium carbonate) into the bulk phase, the temperature is not lower than 800 °C.

[0043] In one embodiment, the sintering atmospheres of the first sintering and the second sintering both include an oxygen-containing atmosphere.

[0044] In one embodiment, the oxygen-containing atmosphere includes air and / or oxygen.

[0045] In one embodiment, the sintering atmosphere further includes an inert gas.

[0046] As an alternative technical solution of the present disclosure, the preparation method includes the following steps:

[0047] Mix a first Na source, NiFeMn hydroxide, and oxides of Cu, Zn, B, Al, Ce, Mg, Sr, and doping element Q, such that the molar content of sodium is 55% to 75%. Under an air atmosphere, perform a first sintering at 800 to 1000 °C for 2 to 10 h, and after cooling, crush and screen to obtain a first-sintered material.

[0048] The obtained first-sintered material is a P2 / O3 mixed phase, with a particle size D50 of 2 to 5 μm and a specific surface area of 0.5 to 1 m 2 / g. In the X-ray diffraction pattern of the first-sintered material, diffraction peaks of the following crystal planes are respectively included in the ranges of diffraction angles of 15.5° to 16.5°, 16° to 17°, 32° to 32.5°, 33° to 34°, 35° to 36°, 36° to 37.5°, 39° to 40°, 41° to 42.5°, 43° to 44°, 45° to 46°, 53° to 54.5°, 58° to 59°, 62° to 63.5°, and 65° to 66°: (002), (003), (004), (006), (101), (012), (102), (104), (103), (015), (017), (018), (110), (113);

[0049] Mix a second Na source and the first-sintered material, and perform a second sintering at 800 to 1000 °C for 2 to 10 h to obtain the sodium-ion cathode material, and the molar content in the obtained sodium-ion cathode material is 90% to 100%.

[0050] In a third aspect, the present disclosure provides a positive electrode sheet, and the positive electrode sheet contains the sodium-ion cathode material described in the first aspect.

[0051] In a fourth aspect, the present disclosure provides a sodium-ion battery, and the sodium-ion battery contains the positive electrode sheet described in the third aspect or contains the sodium-ion cathode material described in the first aspect or contains the sodium-ion cathode material obtained by the preparation method described in the second aspect.

[0052] Compared with the prior art solutions, the present disclosure has at least the following beneficial effects:

[0053] (1) The present disclosure provides a new sodium-ion cathode material with a specific composition. Among them, Cu, B, and Ce improve the structural stability of the material. Zn and Mg can stabilize the sodium layer and increase the capacity. Sr improves the roundness of the material particles. The multi-element high-entropy doping synergistically increases the local entropy of the material, thereby improving the cycling performance. The obtained sodium-ion cathode material has characteristics such as low residual sodium, excellent air stability, and cycling rate performance.

[0054] (2) The present disclosure adopts a two-step sintering method with an increasing sodium source. First, a P2 / O3 mixed phase is generated. The presence of the P2 phase enables a more complete subsequent secondary sintering reaction, more uniform element diffusion, and uniform replenishment of sodium ions into the bulk phase. The prepared O3-phase product has lower surface residual sodium, excellent air stability, and rate cycling performance. In addition to making the sodium ion diffusion uniform, the P2 / O3 intermediate phase can also act synergistically with doping to reduce the energy barrier for doping elements to enter the bulk phase, enabling each element to be uniformly doped into the bulk phase. At the same time, the co-doping of each element further improves the rate and cycling performance of the material.

[0055] Other aspects will be apparent after reading and understanding the drawings and the detailed description. Description of the Drawings

[0056] The drawings are used to provide a further understanding of the technical solutions herein, and constitute a part of the specification. Together with the embodiments of the present application, they are used to explain the technical solutions herein, and do not constitute a limitation to the technical solutions herein.

[0057] Figure 1 is the SEM image of the sodium-ion cathode material prepared in Example 1 of the present disclosure;

[0058] Figure 2 is the SEM image of the sodium-ion cathode material prepared in Comparative Example 1 of the present disclosure;

[0059] Figure 3 is the XRD pattern of the first-fired material obtained by the first sintering in Example 1 of the present disclosure;

[0060] Figure 4 is the XRD pattern of the sodium-ion cathode material obtained by the second sintering in Example 1 of the present disclosure. Detailed Embodiments

[0061] The following detailed embodiments are used to further illustrate the technical solutions of the present disclosure.

[0062] Those skilled in the art should understand that the embodiments are only for helping to understand the present disclosure and should not be regarded as specific limitations to the present disclosure.

[0063] Example 1

[0064] This embodiment provides a sodium-ion cathode material, and the preparation method of the sodium-ion cathode material is as follows:

[0065] (1) Mix Ni 0.3 Fe 0.2 Mn 0.33 (OH) 2 , copper oxide, zinc oxide, boron trioxide, aluminum trioxide, cerium oxide, magnesium hydroxide, strontium carbonate, and sodium carbonate evenly according to the molar ratio of Ni:Fe:Mn:Cu:Zn:B:Al:Ce:Mg:Sr:Na elements of 0.3:0.2:0.33:0.06:0.06:0.01:0.01:0.01:0.01:0.01:0.7, and conduct a primary sintering in an air atmosphere at a sintering temperature of 900 °C for 9 h. After the material is cooled, it is crushed and sieved to obtain a first-fired material;

[0066] (2) Add the first-fired material and sodium carbonate to a mixer according to the molar ratio of Ni:Na elements of 0.3:0.23 and mix evenly. Conduct a secondary sintering in an air atmosphere at a sintering temperature of 920 °C for 6 h. After the material is cooled, it is crushed and sieved to obtain the sodium-ion cathode material.

[0067] The SEM image of the sodium-ion cathode material obtained in this embodiment is as Figure 1 shown. It can be seen from the figure that the material particles have uniform and round particle sizes and good dispersibility; Figure 3 and Figure 4They are the XRD patterns of the once-sintered material and the sodium-ion cathode material obtained in this embodiment. It can be seen from the figures that the once-sintered material obtained has diffraction peaks of the following crystal planes in the ranges of diffraction angles of 15.5° - 16.5°, 16° - 17°, 32° - 32.5°, 33° - 34°, 35° - 36°, 36° - 37.5°, 39° - 40°, 41° - 42.5°, 43° - 44°, 45° - 46°, 53° - 54.5°, 58° - 59°, 62° - 63.5°, and 65° - 66° respectively: (002), (003), (004), (006), (101), (012), (102), (104), (103), (015), (017), (018), (110), (113); while the sodium-ion cathode material obtained has diffraction peaks of the following crystal planes in the ranges of diffraction angles of 16° - 17°, 33° - 34°, 35° - 36°, 36° - 37.5°, 41° - 42.5°, 45° - 46°, 53° - 54.5°, 58° - 59°, 62 - 63.5°, and 65 - 66° respectively: (003), (006), (101), (012), (104), (015), (017), (018), (110), (113), that is, the diffraction peaks at 15.5° - 16.5°, 32° - 32.5°, 39° - 40°, and 43° - 44° disappear.

[0068] Example 2

[0069] This example provides a sodium-ion cathode material. The preparation method of the sodium-ion cathode material uses nickel oxide, iron oxide, and manganese oxide to replace Ni 0.3 Fe 0.2 Mn 0.33 (OH) 2 , with the element molar ratios remaining unchanged. Except for this, other conditions are exactly the same as those in Example 1.

[0070] Example 3

[0071] This example provides a sodium-ion cathode material. The sodium-ion cathode material is further doped with a doping element Q, where Q is Ti. In the preparation method, titanium oxide is added to step (1) for mixing so that the molar ratio of Ti element is Ni:Ti = 0.3:0.005. Except for this, other conditions are exactly the same as those in Example 1.

[0072] Example 4

[0073] This example provides a sodium-ion cathode material. The preparation method of the sodium-ion cathode material adjusts the temperature of the first sintering from 900 °C to 770 °C. Except for this, other conditions are exactly the same as those in Example 1.

[0074] Example 5

[0075] This example provides a sodium ion cathode material. The preparation method of the sodium ion cathode material adjusts the temperature of the first sintering from 900 °C to 800 °C. Except for this, other conditions are exactly the same as those in Example 1.

[0076] Example 6

[0077] This example provides a sodium ion cathode material. The preparation method of the sodium ion cathode material adjusts the temperature of the first sintering from 900 °C to 1000 °C. Except for this, other conditions are exactly the same as those in Example 1.

[0078] Example 7

[0079] This example provides a sodium ion cathode material. The preparation method of the sodium ion cathode material adjusts the temperature of the first sintering from 900 °C to 1050 °C. Except for this, other conditions are exactly the same as those in Example 1.

[0080] Comparative Example 1

[0081] This comparative example provides a sodium ion cathode material. The preparation method of the sodium ion cathode material only performs one-step sintering. The preparation method is as follows:

[0082] Mix Ni 0.3 Fe 0.2 Mn 0.33 (OH) 2 , copper oxide, zinc oxide, boron trioxide, aluminum trioxide, cerium oxide, magnesium hydroxide, strontium carbonate and sodium carbonate evenly according to the molar ratio of Ni:Fe:Mn:Cu:Zn:B:Al:Ce:Mg:Sr:Na elements of 0.3:0.2:0.33:0.06:0.06:0.01:0.01:0.01:0.01:0.01:0.93. Sinter in an air atmosphere at a sintering temperature of 900 °C for 15 h. After the material is cooled, it is crushed and sieved to obtain an O3-phase sodium ion cathode material.

[0083] Figure 2 is the SEM image of the sodium ion cathode material obtained in this comparative example. It can be seen from the figure that the particle size distribution of the material prepared in Comparative Example 1 is wide, indicating poor reaction uniformity. At the same time, there are more debris on the surface, which also reflects that sodium may not easily enter the bulk phase.

[0084] Comparative Example 2

[0085] This comparative example provides a sodium-ion cathode material. Compared with Example 1, the sodium-ion cathode material in this comparative example does not contain Cu element, that is, the preparation method does not use Cu source copper oxide, and the molar content of Mn element is adjusted from 0.33 to 0.39 to replace part of the Cu element. Except for this, other conditions are exactly the same as those in Example 1.

[0086] Comparative Example 3

[0087] This comparative example provides a sodium-ion cathode material. Compared with Example 1, the sodium-ion cathode material in this comparative example does not contain Zn element, that is, the preparation method does not use Zn source zinc oxide, and the molar content of Mn element is adjusted from 0.33 to 0.39 to replace part of the Zn element. Except for this, other conditions are exactly the same as those in Example 1.

[0088] Comparative Example 4

[0089] This comparative example provides a sodium-ion cathode material. Compared with Example 1, the sodium-ion cathode material in this comparative example does not contain B element, that is, the preparation method does not use B source boron trioxide, and the molar content of Mn element is adjusted from 0.33 to 0.34 to replace part of the B element. Except for this, other conditions are exactly the same as those in Example 1.

[0090] Comparative Example 5

[0091] This comparative example provides a sodium-ion cathode material. Compared with Example 1, the sodium-ion cathode material in this comparative example does not contain Al element, that is, the preparation method does not use Al source aluminum oxide, and the molar content of Mn element is adjusted from 0.33 to 0.34 to replace part of the Al element. Except for this, other conditions are exactly the same as those in Example 1.

[0092] Comparative Example 6

[0093] This comparative example provides a sodium-ion cathode material. Compared with Example 1, the sodium-ion cathode material in this comparative example does not contain Ce element, that is, the preparation method does not use Ce source cerium oxide, and the molar content of Mn element is adjusted from 0.33 to 0.34 to replace part of the Ce element. Except for this, other conditions are exactly the same as those in Example 1.

[0094] Comparative Example 7

[0095] This comparative example provides a sodium-ion cathode material. Compared with Example 1, the sodium-ion cathode material in this comparative example does not contain Mg element, that is, the preparation method does not use Mg source magnesium hydroxide, and the molar content of Mn element is adjusted from 0.33 to 0.34 to replace part of the Mg element. Except for this, other conditions are exactly the same as those in Example 1.

[0096] Comparative Example 8

[0097] This comparative example provides a sodium-ion cathode material. Compared with Example 1, the sodium-ion cathode material in this comparative example has no Sr element, that is, the preparation method does not use Sr source strontium carbonate, and the molar content of Mn element is adjusted from 0.33 to 0.34 to replace part of the Sr element. Other conditions are exactly the same as those in Example 1.

[0098] Comparative Example 9

[0099] This comparative example provides a sodium-ion cathode material. Compared with Example 1, the sodium-ion cathode material in this comparative example has no Cu, Zn, B, Al, Ce, Mg, Sr elements, that is, the preparation method does not use Cu source copper oxide, Zn source zinc oxide, B source boron trioxide, Al source aluminum oxide, Ce source cerium oxide, Mg source magnesium hydroxide, Sr source strontium carbonate, and the molar content of Mn element is adjusted from 0.33 to 0.5. Other conditions and parameters are exactly the same as those in Example 1.

[0100] The sodium-ion cathode materials obtained in the examples and comparative examples were tested as follows:

[0101] Electrical performance test:

[0102] The cathode materials prepared in the examples and comparative examples were mixed with a binder and conductive carbon black in a ratio of 90:5:5, added with NMP solvent and stirred, coated on a current collector and dried and rolled to obtain a cathode electrode sheet. The anode was hard carbon, and a battery was made. Its cycle performance was tested. The test voltage was 1.5 - 4.2V, and the test conditions were 0.1C for two cycles, 0.33C for two cycles, and 1C for 100 cycles. The test results are shown in Table 1.

[0103] Residual sodium content test:

[0104] 30 g of the cathode materials prepared in the examples and comparative examples were taken, 100 ml of pure water was added, and stirred at 600 rpm for 30 min. After filtration, the filtrate was diluted to 250 ml, and 10 ml was taken to test the residual alkali Na + , and the test results are shown in Table 1.

[0105] Table 1

[0106]

[0107]

[0108] As can be seen from Table 1, from Example 1, it can be obtained that the battery prepared from the sodium-ion cathode material described in the present disclosure has a capacity retention rate of up to 92.86% after 100 cycles at 1C;

[0109] Comparing Example 1 with Comparative Example 1, it can be seen that during the preparation process of the sodium-ion cathode material described in the present disclosure, secondary sintering improves the air stability, rate performance, and cycling performance of the material;

[0110] Comparing Example 1, Comparative Example 1, and Comparative Example 2, it can be seen that during the preparation process of the sodium-ion cathode material described in the present disclosure, the doping element and multiple sinterings promote each other in improving the air stability;

[0111] Comparing Example 1 with Comparative Examples 2-9, it can be seen that during the preparation process of the sodium-ion cathode material described in the present disclosure, multi-element doping has a synergistic effect, improving the air stability and rate cycling performance of the material;

[0112] Comparing Example 1 with Example 4, it can be seen that using an oxide or hydroxide precursor can basically achieve the same effect;

[0113] Comparing Example 1 with Example 5, it can be seen that the doping element Q in the present disclosure has an optimizing effect on certain properties of the material, and doping optimization can be carried out according to different usage scenarios;

[0114] Comparing Example 1 with Examples 6-9, it can be seen that too high or too low sintering temperature has a great impact on the material properties, especially when the temperature is too low, resulting in insufficient reaction.

Claims

1. A preparation method of a sodium ion cathode material, the preparation method comprising the following steps: Mix a first Na source, a Ni source, a Fe source, a Mn source, and a Cu source, a Zn source, a B source, an Al source, a Ce source, a Mg source, and a Sr source, and perform a first sintering at a temperature of 820-1000 °C to obtain a first-sintered material; the obtained first-sintered material is a P2 / O3 mixed phase; Mix the second Na source and a sintering material, and obtain the sodium ion cathode material through secondary sintering; the general formula of the sodium ion cathode material is Na x Ni y Fe z Mn t Cu h Zn m B n Al g Ce j Mg k Sr u O 2 , where 0.8 ≤ x ≤ 1.0, 0.1 ≤ y ≤ 0.5, 0.1 ≤ z ≤ 0.5, 0.3 ≤ t ≤ 0.7, 0.01 ≤ h ≤ 0.3, 0.01 ≤ m ≤ 0.2, y + z + t + h + m + n + g + j + k + u = 1, n, g, j, k, and u are all 0.01, and the sodium ion cathode material is in the O3 phase.

2. The preparation method of the sodium ion cathode material according to claim 1, wherein, the particle size D50 of the sodium ion cathode material is 5-15 μm.

3. The preparation method of the sodium ion cathode material according to claim 1, wherein, the specific surface area of the sodium ion cathode material is 0.2-0.5 m² / g.

4. The preparation method of the sodium ion cathode material according to claim 1, wherein, in the X-ray diffraction pattern of the sodium ion cathode material, diffraction peaks of the following crystal planes are respectively included in the ranges of diffraction angles of 16°-17°, 33°-34°, 35°-36°, 36°-37.5°, 41°-42.5°, 45°-46°, 53°-54.5°, 58°-59°, 62-63.5°, 65-66°: (003), (006), (101), (012), (104), (015), (017), (018), (110), (113).

5. The preparation method of the sodium ion cathode material according to claim 1, wherein, the mass range of residual sodium measured by the water method of the sodium ion cathode material is 0.5-1 wt%.

6. The preparation method of the sodium ion cathode material according to claim 1, wherein, the first Na source includes at least one of sodium carbonate, sodium bicarbonate, sodium hydroxide, sodium oxide, sodium oxalate, sodium acetate, and sodium peroxide; the second Na source is an oxide of sodium, and the oxide of sodium includes sodium oxide and / or sodium peroxide.

7. The preparation method of the sodium ion cathode material according to claim 1, wherein, the molar content of sodium in the first-sintered material is 55%-75%.

8. The preparation method of the sodium ion cathode material according to claim 1, wherein, use NiFeMn hydroxide to replace the Ni source, the Fe source, and the Mn source.

9. The preparation method of the sodium ion cathode material according to claim 1, wherein, the time of the first sintering is 2-10 h; the temperature of the second sintering is 800-1000 °C, and the heat preservation time is 2-10 h.

10. A preparation method of a sodium ion cathode material, the preparation method comprising the following steps: Mix a first Na source, a Ni source, a Fe source, a Mn source, and a Cu source, a Zn source, a B source, an Al source, a Ce source, a Mg source, and a Sr source, and a doping element Q source, the Q source includes an oxygen-containing compound of the corresponding doping element, and perform a first sintering at a temperature of 820-1000 °C to obtain a first-sintered material; the obtained first-sintered material is a P2 / O3 mixed phase; Mix the second Na source and a sintering material, and obtain the sodium ion cathode material through secondary sintering; the general formula of the sodium ion cathode material is Na x Ni y Fe z Mn t Cu h Zn m B n Al g Ce j Mg k Sr u Q v O 2 , Q is Ti, where 0.8 ≤ x ≤ 1.0, 0.1 ≤ y ≤ 0.5, 0.1 ≤ z ≤ 0.5, 0.3 ≤ t ≤ 0.7, 0.01 ≤ h ≤ 0.3, 0.01 ≤ m ≤ 0.2, y + z + t + h + m + n + g + j + k + u = 1, n, g, j, k, and u are all 0.01, v = 0.005, and the sodium ion cathode material is of the O3 phase.

11. The preparation method of the sodium ion cathode material according to claim 10, wherein, the preparation method comprises the following steps: Mix the first Na source, NiFeMn hydroxide, and oxides of Cu, Zn, B, Al, Ce, Mg, Sr, and doping element Q so that the molar content of sodium is 55% - 75%. Under an air atmosphere, conduct a first sintering at 820 - 1000 °C for 2 - 10 h. After cooling, crush and screen to obtain a first-fired material; The obtained first-fired material is a P2 / O3 mixed phase with a particle size D50 of 2 - 5 μm and a specific surface area of 0.5 - 1 m² / g. In the X-ray diffraction pattern of the first-fired material, diffraction peaks of the following crystal planes are respectively included in the ranges of diffraction angles of 15.5° - 16.5°, 16° - 17°, 32° - 32.5°, 33° - 34°, 35° - 36°, 36° - 37.5°, 39° - 40°, 41° - 42.5°, 43° - 44°, 45° - 46°, 53° - 54.5°, 58° - 59°, 62° - 63.5°, 65° - 66°: (002), (003), (004), (006), (101), (012), (102), (104), (103), (015), (017), (018), (110), (113); Mix the second Na source and the first-fired material, and conduct a second sintering at 800 - 1000 °C for 2 - 10 h to obtain the sodium-ion positive electrode material, and the molar content in the obtained sodium-ion positive electrode material is 90% - 100%.

12. A sodium-ion positive electrode material, which is obtained by the preparation method according to any one of claims 1 - 11.

13. A sodium-ion battery, which contains the sodium-ion positive electrode material according to claim 12.

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