Sodium-ion positive electrode material, and preparation method therefor and use thereof

Abstract

Provided are a sodium-ion positive electrode material, and a preparation method therefor and the use thereof. The general formula of the sodium-ion positive electrode material is NaxNiyFezMntCuhZnmBnAlgCejMgkSruO2, and the sodium-ion positive electrode material is an O3-phase material. In the preparation method, by adding and mixing a sodium source in two steps and performing two-step sintering, a P2 / O3 mixed phase is first generated to serve as an intermediate phase in a manner that the sodium source gradually increases, wherein the presence of a P2 phase can make the subsequent secondary sintering reaction more sufficient and the diffusion of elements more uniform and enables sodium ions to be uniformly supplemented into a bulk phase, resulting in an O3 phase finished product ultimately prepared having a lower content of surface residual sodium, good stability in air and good rate cycle performance.

Description

A sodium ion positive electrode material and its preparation method and use Technical Field

[0001] The present invention relates to the field of batteries and relates to a sodium ion positive electrode material and a preparation method and application thereof. Background Art

[0002] Lithium-ion batteries, the most popular energy storage device, are widely used in portable electronics and electric vehicles, profoundly impacting our daily lives. However, the difficulty, high cost, and limited supply of lithium resources have led to my country's heavy reliance on lithium resources from other countries. Therefore, the development of alternative or backup energy storage technologies to lithium-ion batteries is imperative. Sodium-ion batteries, with their abundant sodium resources, low cost, and similar physical and chemical properties to lithium-ion batteries, can serve as an important complementary technology to lithium-ion batteries in large-scale energy storage. They possess significant economic value and strategic significance, making them a new and exciting type of secondary battery.

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

[0004] In sodium-ion batteries, the cathode material is a key factor limiting performance indicators such as capacity, energy density, and safety. Layered transition metal oxide cathode materials have become an important class of cathode materials for practical applications due to their advantages such as simple preparation, high specific capacity, and high ionic conductivity. Layered cathode materials are generally classified into P2, P3, O2, and O3 phases based on the occupancy of sodium atoms and the stacking of oxygen layers, with the P2 and O3 phases being more common. The O3 phase exhibits higher capacity due to its higher sodium content. However, the high sodium content also makes the surface of the O3 phase sodium-ion cathode material more susceptible to forming residual alkali (NaOH, Na2CO3) by reacting with water or carbon dioxide in the air. This results in poor air and water stability, resulting in reduced active sodium in the sodium-ion cathode material, affecting its capacity during charge-discharge. Furthermore, the residual alkali hinders the conduction of sodium ions during charge-discharge, leading to low specific capacity and low rate performance.

[0005] It can be seen that the optimization of 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 positive electrode materials. The development of new O3 phase sodium ion positive electrode materials and matching preparation methods are of great significance to promoting the development and application of sodium ion batteries.

[0006] Summary of the Invention

[0007] The following is a summary of the subject matter described in detail herein. This summary is not intended to limit the scope of the claims.

[0008] In view of the problems existing in the prior art, the purpose of the present disclosure is to provide a sodium ion positive electrode material and its preparation method and use. The general formula of the sodium ion positive electrode 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, the sodium ion positive electrode material is an O3 phase. The preparation method comprises adding a sodium source in two steps and performing two-step sintering, thereby first generating a P2 / O3 mixed phase by increasing the sodium source. The presence of the P2 phase enables a more complete subsequent secondary sintering reaction, more uniform element diffusion, and uniform sodium ion replenishment into the bulk phase. The resulting O3 phase product has lower surface residual sodium and exhibits excellent air stability and rate cycling performance.

[0009] To achieve this goal, the present disclosure adopts the following technical solutions:

[0010] In the first aspect, the present disclosure provides a sodium ion positive electrode material having the general formula of Na x Ni y Fe z Mn t Cu h Zn m B n Al g Ce j Mg k Sr u O2, wherein 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 positive electrode material is an O3 phase.

[0011] The present disclosure provides a new sodium ion positive electrode material having a specific composition, wherein Cu, B, and Ce improve the structural stability of the material, Zn and Mg stabilize the sodium layer and increase the capacity, Sr improves the roundness of the material particles, and Al improves the rate performance of the material. Multi-element high-entropy doping synergistically increases the local entropy of the material, thereby improving the cycle performance.

[0012] The present disclosure states that 0.8≤x≤1.0, for example, 0.8, 0.82, 0.84, 0.86, 0.88, 0.9, 0.92, 0.94, 0.96, 0.98 or 1, and 0.1≤y≤0.5, for example, 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, for example, 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, for example, 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, for example, 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 are not limited to the listed values, and other values ​​not listed within the above numerical range are equally applicable.

[0013] The following are optional technical solutions of the present disclosure, but are not intended to limit 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 and realized.

[0014] As an optional technical solution of the present disclosure, the general formula of the sodium ion positive electrode 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 vO2, Q are doping elements, wherein 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, 0≤n+g+j+k+u+v≤0.05.

[0015] The present disclosure may optionally further dope the sodium ion cathode material, using the doping element Q to further optimize and improve the properties of the resulting sodium ion cathode material.

[0016] 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, and may be, for example, 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.

[0017] In one embodiment, 0.001≤v≤0.02, for example, 0.001, 0.003, 0.005, 0.008, 0.01, 0.011, 0.012, 0.013, 0.014, 0.015, 0.016, 0.017, 00.018, 0.019 or 0.02, etc., but is not limited to the listed values, and other unlisted values ​​within the above numerical range are also applicable.

[0018] In one embodiment, the particle size D50 of the sodium ion positive electrode material is 5 to 15 μm, for example, 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 is not limited to the listed values, and other unlisted values ​​within the above numerical range are also applicable.

[0019] In one embodiment, the specific surface area of ​​the sodium ion positive electrode material is 0.2 to 0.5 m 2 / g, for example 0.2m 2 / g, 0.25m 2 / g, 0.3m 2 / g, 0.35m 2 / g, 0.4m 2 / g, 0.45m 2 / g or 0.5m 2 / g, etc., but are not limited to the listed values, and other values ​​not listed within the above numerical range are also applicable.

[0020] In one embodiment, the X-ray diffraction pattern of the sodium ion positive electrode material contains diffraction peaks of the following crystal planes within the range of diffraction angles of 16° to 17°, 33° to 34°, 35° to 36°, 36° to 37.5°, 41° to 42.5°, 45° to 46°, 53° to 54.5°, 58° to 59°, 62 to 63.5°, and 65 to 66°, respectively: (003), (006), (101), (012), (104), (015), (017), (018), (110), and (113).

[0021] In one embodiment, the mass range of residual sodium measured by water method of the sodium ion positive electrode material is 0.5-1.5wt%, such as 0.5wt%, 0.6wt%, 0.7wt%, 0.8wt%, 0.9wt%, 1wt%, 1.1wt%, 1.2wt%, 1.3wt%, 1.4wt% or 1.5wt%, and the mass range of residual sodium measured by alcohol method is 0.01-0.2wt%, such as 0.01wt%, 0.03wt%, 0.05wt%, 0.08wt%, 0.1wt%, 0.11wt%, 0.12wt%, 0.13wt%, 0.14wt%, 0.15wt%, 0.16wt%, 0.17wt%, 0.18wt%, 0.19wt% or 0.2wt%, etc., but is not limited to the listed values, and other values ​​not listed within the above numerical range are equally applicable.

[0022] In a second aspect, the present disclosure provides a method for preparing the sodium ion positive electrode material according to the first aspect, the preparation method comprising the following steps:

[0023] Mixing a first Na source, a Ni source, a Fe source, a Mn source, a Cu source, a Zn source, a B source, an Al source, a Ce source, a Mg source, and a Sr source, and sintering the mixture once to obtain a single-fired material;

[0024] The second Na source and the first sintered material are mixed and sintered twice to obtain the sodium ion positive electrode material.

[0025] The present invention discloses a primary sintering using a first Na source in order to generate a P2 / O3 mixed phase in the material. Since the P2 phase has a low sodium ion migration energy barrier and a large interlayer spacing, sodium ions can more easily diffuse and migrate in the bulk phase to form a uniform and consistent positive electrode material. The secondary sintering is performed to supplement the sodium source on the basis of the primary sintered material, so that the sodium molar content in the prepared material eventually reaches 80% to 100%, preferably 90% to 100%. The secondary sintering supplements the sodium source in order to generate an O3 phase. Due to the large interlayer spacing, sodium ions can more easily enter the bulk phase, and at the same time repair the fresh interface exposed due to the crushing of the material after the primary sintering.

[0026] That is, the present disclosure adopts a two-step sintering method of increasing the sodium source to first generate a P2 / O3 mixed phase, wherein the presence of the P2 phase can make the subsequent secondary sintering reaction more complete, the element diffusion more uniform, and the sodium ions are uniformly supplemented 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 ions diffuse evenly, the P2 / O3 mixed phase can also synergize with doping to reduce the energy barrier of the doping elements entering the bulk phase, so that each element is uniformly doped into the bulk phase. At the same time, the synergistic doping of each element further improves the rate and cycle performance of the material.

[0027] In summary, the sodium ion positive electrode material obtained using the preparation method has the characteristics of low residual sodium, air stability, and excellent cycle rate performance.

[0028] As an optional technical solution of the present disclosure, the first Na source and the second Na source both 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 include sodium carbonate and sodium bicarbonate, sodium hydroxide and sodium oxide, sodium oxalate and sodium acetate, peroxide and sodium carbonate, sodium bicarbonate and sodium hydroxide, sodium oxide and sodium oxalate or sodium acetate and sodium peroxide, etc.

[0029] In one embodiment, the second Na source is sodium oxide, and the sodium oxide includes sodium oxide and / or sodium peroxide.

[0030] The present application limits the second Na source oxide to improve the uniformity of the secondary sintering without introducing other impurities.

[0031] In one embodiment, the molar content of sodium in the calcined material is 55% to 75%, but is not limited to the listed values, and other values ​​not listed within the above numerical range are also applicable.

[0032] In the present disclosure, when the amount of Na source used in the first sintering is too small, not only can the P2 / O3 phase not be formed, but more Na source needs to be added during the second sintering, which can easily lead to insufficient second sintering reaction and a large amount of residual alkali.

[0033] As an optional technical solution of the present disclosure, the Ni source, Fe source and Mn source all include oxides of corresponding elements, and NiFeMn hydroxide is used to replace the Ni source, Fe source and Mn source; the chemical formula of the NiFeMn hydroxide is Ni y Fe z Mn t (OH)2, 0.1≤y≤0.5, 0.1≤z≤0.5, 0.3≤t≤0.7.

[0034] It is preferred to use NiFeMn hydroxide instead of a mixture of a single Ni source, Fe source and Mn source, which can greatly improve the uniformity of Ni, Fe and Mn elements in the obtained sodium ion positive electrode material.

[0035] In one embodiment, the Cu source, the Zn source, the B source, the Al source, the Ce source, the Mg source, and the Sr source each include oxides of the corresponding elements.

[0036] In one embodiment, the mixture before the primary sintering further includes a doping element Q source, wherein the Q source includes an oxide of the corresponding doping element.

[0037] As an optional technical solution of the present disclosure, the sintered material is a P2 / O3 mixed phase.

[0038] In one embodiment, the particle size D50 of the sintered material is 2 to 5 μm, for example, 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 is not limited to the listed values. Other values ​​not listed within the above numerical range are also applicable.

[0039] In one embodiment, the specific surface area of ​​the calcined material is 0.5 to 1 m 2 / g, for example 0.5m 2 / g, 0.55m 2 / g, 0.6m 2 / g, 0.65m 2 / g, 0.7m 2 / g, 0.75m 2 / g, 0.8m 2 / g, 0.85m 2 / g, 0.9m 2 / g, 0.95m 2 / g or 1m 2 / g, etc., but are not limited to the listed values, and other values ​​not listed within the above numerical range are also applicable.

[0040] In one embodiment, the X-ray diffraction pattern of the sintered material contains diffraction peaks of the following crystal planes within the diffraction angle range 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°, respectively: (002), (003), (004), (006), (101), (012), (102), (104), (103), (015), (017), (018), (110), and (113).

[0041] As an optional technical solution disclosed in the present invention, the temperature of the primary sintering is 800-1000°C, for example, 800°C, 820°C, 840°C, 860°C, 880°C, 900°C, 920°C, 940°C, 960°C, 980°C or 1000°C, and the time is 2-10h, for example, 2h, 2.5h, 3h, 3.5h, 4h, 4.5h, 5h, 5.5h, 6h, 6.5h, 7h, 7.5h, 8h, 8.5h, 9h, 9.5h or 10h, but is not limited to the listed values, and other values ​​not listed within the above numerical range are also applicable.

[0042] In one embodiment, the secondary sintering temperature is 800-1000°C, for example, 800°C, 820°C, 840°C, 860°C, 880°C, 900°C, 920°C, 940°C, 960°C, 980°C or 1000°C, and the holding time is 2-10h, for example, 2h, 2.5h, 3h, 3.5h, 4h, 4.5h, 5h, 5.5h, 6h, 6.5h, 7h, 7.5h, 8h, 8.5h, 9h, 9.5h or 10h, but is not limited to the listed values, and other values ​​not listed within the above numerical range are also applicable.

[0043] In the present disclosure, if the primary sintering temperature is too low, the material will be difficult to nucleate and grow; if the temperature is too high, the cost will increase, and the flaky particles will be larger and easy to break during subsequent processing; if the secondary sintering temperature is too low, the bulk sodium will dissolve, causing an increase in residual sodium, and if the temperature is too high, it will cause over-sintering and material decomposition. The secondary sintering temperature is in the same range as the primary sintering temperature, both of which ensure that the Na source decomposes and enters the bulk phase. According to actual experimental requirements, the secondary sintering temperature can be lower than the primary sintering temperature, but generally, in order to ensure that the residual sodium (sodium carbonate) decomposes and enters the bulk phase, the temperature is not lower than 800°C.

[0044] In one embodiment, the sintering atmospheres of the primary sintering and the secondary sintering both include an oxygen-containing atmosphere.

[0045] In one embodiment, the oxygen-containing atmosphere comprises air and / or oxygen.

[0046] In one embodiment, the sintering atmosphere further includes an inert gas.

[0047] As an optional technical solution of the present disclosure, the preparation method includes the following steps:

[0048] A first Na source, NiFeMn hydroxide, and oxides of Cu, Zn, B, Al, Ce, Mg, Sr, and a doping element Q are mixed so that the molar content of sodium is 55% to 75%, and the mixture is sintered at 800 to 1000° C. for 2 to 10 hours in an air atmosphere. After cooling, the mixture is crushed and sieved to obtain a sintered material.

[0049] The obtained calcined 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, the X-ray diffraction pattern of the sintered material comprises diffraction peaks of the following crystal planes within the diffraction angle range 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°, respectively: (002), (003), (004), (006), (101), (012), (102), (104), (103), (015), (017), (018), (110), and (113);

[0050] The second Na source and the primary sintered material are mixed and secondary sintered at 800-1000° C. for 2-10 hours to obtain the sodium ion positive electrode material, wherein the molar content of the obtained sodium ion positive electrode material is 90%-100%.

[0051] In a third aspect, the present disclosure provides a positive electrode plate, which contains the sodium ion positive electrode material described in the first aspect.

[0052] In a fourth aspect, the present disclosure provides a sodium ion battery, which contains the positive electrode sheet described in the third aspect, or the sodium ion positive electrode material described in the first aspect, or the sodium ion positive electrode material obtained by the preparation method described in the second aspect.

[0053] Compared with the existing technical solutions, the present disclosure has at least the following beneficial effects:

[0054] (1) The present disclosure provides a new sodium-ion cathode material having a specific composition, wherein Cu, B, and Ce improve the structural stability of the material, Zn and Mg stabilize the sodium layer and increase the capacity, Sr improves the roundness of the material particles, and multi-element high-entropy doping synergistically increases the local entropy of the material, thereby improving the cycling performance. The resulting sodium-ion cathode material has the characteristics of low residual sodium, excellent air stability, and excellent cycling rate performance.

[0055] (2) The present invention adopts a two-step sintering method of increasing the sodium source to first generate a P2 / O3 mixed phase, wherein the presence of the P2 phase can make the subsequent secondary sintering reaction more complete, the element diffusion more uniform, and the sodium ions are uniformly supplemented into the bulk phase. The prepared O3 phase product has lower surface residual sodium and has excellent air stability and rate cycling performance; in addition to making the sodium ions diffuse evenly, the P2 / O3 intermediate phase can also synergize with doping to reduce the energy barrier of the doping elements entering the bulk phase, so that each element is uniformly doped into the bulk phase. At the same time, the synergistic doping of each element further improves the rate and cycle performance of the material.

[0056] Still other aspects will become apparent upon reading and understanding the accompanying drawings and detailed description. BRIEF DESCRIPTION OF THE DRAWINGS

[0057] The accompanying drawings are used to provide a further understanding of the technical solution of this article and constitute a part of the specification. Together with the embodiments of this application, they are used to explain the technical solution of this article and do not constitute a limitation on the technical solution of this article.

[0058] FIG1 is a SEM image of the sodium ion positive electrode material prepared in Example 1 of the present disclosure;

[0059] FIG2 is a SEM image of the sodium ion positive electrode material prepared in Comparative Example 1 of the present disclosure;

[0060] FIG3 is an XRD pattern of a single-fired material obtained by single-fired sintering in Example 1 of the present disclosure;

[0061] FIG4 is an XRD diagram of the sodium ion positive electrode material obtained by secondary sintering in Example 1 of the present disclosure. DETAILED DESCRIPTION

[0062] The following specific implementation methods are used to further illustrate the technical solutions of the present disclosure.

[0063] It should be apparent to those skilled in the art that the embodiments are only intended to help understand the present disclosure and should not be considered as specific limitations of the present disclosure.

[0064] Example 1

[0065] This embodiment provides a sodium ion positive electrode material, and the preparation method of the sodium ion positive electrode material is as follows:

[0066] (1) Ni0.3 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 are uniformly mixed according to the molar ratio of Ni:Fe:Mn:Cu:Zn:B:Al:Ce:Mg:Sr:Na of 0.3:0.2:0.33:0.06:0.06:0.01:0.01:0.01:0.01:0.01:0.7, and sintered once in an air atmosphere at a sintering temperature of 900°C for 9 hours. After cooling, the material is crushed and sieved to obtain a single-fired material;

[0067] (2) The primary sintered material and sodium carbonate were added to a mixer in a molar ratio of Ni:Na of 0.3:0.23 and mixed evenly. The secondary sintering was carried out in an air atmosphere at a sintering temperature of 920°C for 6 hours. After the material was cooled, it was crushed and sieved to obtain a sodium ion positive electrode material.

[0068] The SEM image of the sodium ion positive electrode material obtained in this embodiment is shown in FIG1 , from which it can be seen that the material particles have uniform and rounded particle size and good dispersibility; FIG3 and FIG4 are XRD patterns of the calcined material and the sodium ion positive electrode material obtained in this embodiment, respectively. It can be seen from the figure that the calcined material contains the following diffraction peaks of each crystal plane in the range 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°, respectively: (002), (003), (004), (006), (101), (007), (102), (103), (104), (105), (106), (107), (108), (109), (110), (111), (112), (113), (114), (115), (116), (117), (118), (119), (120), (121), (122), (123), (124), (125 12), (102), (104), (103), (015), (017), (018), (110), (113); and the obtained sodium ion positive electrode material has a diffraction angle of 16°~17°, 33°~34°, 35°~36°, 36°~37.5°, 41°~42.5°, 45°~46°, 53°~54.5°, 58°~59°, The ranges of 62-63.5° and 65-66° contain the diffraction peaks of the following crystal planes: (003), (006), (101), (012), (104), (015), (017), (018), (110), and (113), respectively. That is, the diffraction peaks at 15.5-16.5°, 32-32.5°, 39-40°, and 43-44° disappear.

[0069] Example 2

[0070] This embodiment provides a sodium ion positive electrode material. The preparation method of the sodium ion positive electrode material uses nickel oxide, iron oxide and manganese oxide instead of Ni. 0.3 Fe 0.2 Mn 0.33 (OH)2, the molar ratio of the elements remains unchanged, and other conditions are exactly the same as those in Example 1.

[0071] Example 3

[0072] This embodiment provides a sodium ion positive electrode material, which is further doped with a doping element Q, where Q is Ti. The preparation method adds titanium oxide to step (1) and mixes them so that the molar ratio of the Ti element is Ni:Ti=0.3:0.005. Apart from this, the other conditions are exactly the same as those in Example 1.

[0073] Example 4

[0074] This embodiment provides a sodium ion positive electrode material. The preparation method of the sodium ion positive electrode material adjusts the primary sintering temperature from 900° C. to 770° C. Apart from this, other conditions are exactly the same as those in Example 1.

[0075] Example 5

[0076] This embodiment provides a sodium ion positive electrode material. In the preparation method of the sodium ion positive electrode material, the primary sintering temperature is adjusted from 900° C. to 800° C. Apart from this, other conditions are exactly the same as those in Example 1.

[0077] Example 6

[0078] This embodiment provides a sodium ion positive electrode material. In the preparation method of the sodium ion positive electrode material, the primary sintering temperature is adjusted from 900° C. to 1000° C. Apart from this, other conditions are exactly the same as those in Example 1.

[0079] Example 7

[0080] This embodiment provides a sodium ion positive electrode material. In the preparation method of the sodium ion positive electrode material, the primary sintering temperature is adjusted from 900° C. to 1050° C. Apart from this, other conditions are exactly the same as those in Example 1.

[0081] Comparative Example 1

[0082] This comparative example provides a sodium ion positive electrode material. The preparation method of the sodium ion positive electrode material only performs one-step sintering. The preparation method is as follows:

[0083] 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 are mixed uniformly according to the molar ratio of Ni:Fe:Mn:Cu:Zn:B:Al:Ce:Mg:Sr:Na of 0.3:0.2:0.33:0.06:0.06:0.01:0.01:0.01:0.01:0.01:0.93, sintered in an air atmosphere at a sintering temperature of 900°C, kept warm for 15 hours, and after cooling, the material was crushed and sieved to obtain O3 phase sodium ion positive electrode material.

[0084] Figure 2 is an SEM image of the sodium ion positive electrode 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, the presence of more debris on the surface also reflects that sodium may not easily enter the bulk phase.

[0085] Comparative Example 2

[0086] This comparative example provides a sodium ion positive electrode material. Compared with Example 1, the sodium ion positive electrode material in this comparative example does not contain the Cu element, that is, the preparation method does not use Cu source copper oxide, and the molar content of the Mn element is adjusted from 0.33 to 0.39, thereby replacing part of the Cu element. Other than this, the other conditions are exactly the same as those in Example 1.

[0087] Comparative Example 3

[0088] This comparative example provides a sodium ion positive electrode material. Compared with Example 1, the sodium ion positive electrode material in this comparative example does not contain the Zn element, that is, the preparation method does not use Zn source zinc oxide, and the molar content of the Mn element is adjusted from 0.33 to 0.39, thereby replacing part of the Zn element. Other than this, the other conditions are exactly the same as those in Example 1.

[0089] Comparative Example 4

[0090] This comparative example provides a sodium ion positive electrode material. Compared with Example 1, the sodium ion positive electrode material in this comparative example does not contain the B element, that is, the preparation method does not use the B source boron trioxide, and the molar content of the Mn element is adjusted from 0.33 to 0.34, thereby replacing part of the B element. Other than this, the other conditions are exactly the same as those in Example 1.

[0091] Comparative Example 5

[0092] This comparative example provides a sodium ion positive electrode material. Compared with Example 1, the sodium ion positive electrode material in this comparative example does not contain Al element, that is, the preparation method does not use Al source alumina, and the molar content of the Mn element is adjusted from 0.33 to 0.34, thereby replacing part of the Al element. Other than this, the other conditions are exactly the same as those in Example 1.

[0093] Comparative Example 6

[0094] This comparative example provides a sodium ion positive electrode material. Compared with Example 1, the sodium ion positive electrode material in this comparative example does not contain the Ce element, that is, the preparation method does not use Ce source cerium oxide, and the molar content of the Mn element is adjusted from 0.33 to 0.34, thereby replacing part of the Ce element. Other than this, the other conditions are exactly the same as those in Example 1.

[0095] Comparative Example 7

[0096] This comparative example provides a sodium ion positive electrode material. Compared with Example 1, the sodium ion positive electrode 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, thereby replacing part of the Mg element. Other than this, the other conditions are exactly the same as those in Example 1.

[0097] Comparative Example 8

[0098] This comparative example provides a sodium ion positive electrode material. Compared with Example 1, the sodium ion positive electrode material in this comparative example does not contain the Sr element, that is, the preparation method does not use the Sr source strontium carbonate, and the molar content of the Mn element is adjusted from 0.33 to 0.34, thereby replacing part of the Sr element. Other than this, the other conditions are exactly the same as those in Example 1.

[0099] Comparative Example 9

[0100] This comparative example provides a sodium ion positive electrode material. Compared with Example 1, the sodium ion positive electrode material in this comparative example does not contain Cu, Zn, B, Al, Ce, Mg, and 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 trioxide, Ce source cerium oxide, Mg source magnesium hydroxide, and Sr source strontium carbonate. The molar content of the Mn element is adjusted from 0.33 to 0.5, and the other conditions and parameters are exactly the same as in Example 1.

[0101] The sodium ion positive electrode materials obtained in the examples and comparative examples were subjected to the following tests:

[0102] Electrical performance test:

[0103] The positive electrode material prepared in the embodiment and the comparative example was mixed with a binder and conductive carbon black in a ratio of 90:5:5, NMP solvent was added and stirred, coated on a current collector, dried, and rolled to obtain a positive electrode sheet. The negative electrode was hard carbon. A battery was made and its cycle performance was tested. The test voltage was 1.5-4.2 V, 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.

[0104] Residual sodium test:

[0105] Take 30g of the positive electrode material prepared in the embodiment and the comparative example, add 100ml of pure water, stir at 600rpm for 30min, filter and dilute the filtrate to 250ml, take 10ml and test the residual alkali Na with a potentiometric titrator. + , the test results are shown in Table 1.

[0106] Table 1

[0107] As can be seen from Table 1, according to Example 1, the battery made of the sodium ion positive electrode material disclosed in the present invention has a capacity retention rate of up to 92.86% after 100 cycles at 1C;

[0108] From the comparison between Example 1 and Comparative Example 1, it can be seen that during the preparation of the sodium ion positive electrode material disclosed in the present invention, the secondary sintering improves the air stability, rate capability and cycle performance of the material;

[0109] From the comparison between Example 1, Comparative Example 1 and Comparative Example 2, it can be seen that in the preparation process of the sodium ion positive electrode material disclosed in the present invention, the improvement of air stability by doping elements and multiple sintering is mutually promoted;

[0110] From the comparison between Example 1 and Comparative Examples 2-9, it can be seen that in the preparation process of the sodium ion positive electrode material disclosed in the present invention, multi-element doping has a synergistic effect, which improves the air stability and rate cycling performance of the material;

[0111] From the comparison between Example 1 and Example 4, it can be seen that the use of oxide or hydroxide precursors can basically achieve the same effect;

[0112] From the comparison between Example 1 and Example 5, it can be seen that the doping element Q in the present disclosure has an optimization effect on certain properties of the material, and doping optimization can be performed according to different usage scenarios;

[0113] From the comparison between Example 1 and Examples 6-9, it can be seen that a sintering temperature that is too high or too low has a significant impact on the material properties, especially a temperature that is too low, which leads to an incomplete reaction.

Claims

1. A sodium ion positive electrode material, the general formula of which is Na x Ni y Fe z Mn t Cu h Zn m B n Al g Ce j Mg k Sr u O2, wherein 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 positive electrode material is O3 phase.

2. The sodium ion positive electrode material according to claim 1, wherein The sodium ion positive electrode material further includes a doping element Q. The general formula of the sodium ion positive electrode 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 O2, y+z+t+h+m+n+g+j+k+u+v=1, 0≤n+g+j+k+u+v≤0.

05.

3. The sodium ion positive electrode material according to claim 2, wherein The doping element 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.

4. The sodium ion positive electrode material according to claim 2 or 3, wherein 0.001≤v≤0.02。 5. The sodium ion positive electrode material according to any one of claims 1 to 4, wherein: The particle size D50 of the sodium ion positive electrode material is 5 to 15 μm.

6. The sodium ion positive electrode material according to any one of claims 1 to 5, wherein: The specific surface area of ​​the sodium ion positive electrode material is 0.2 to 0.5 m 2 / g.

7. The sodium ion positive electrode material according to any one of claims 1 to 6, wherein In the X-ray diffraction spectrum of the sodium ion positive electrode material, the diffraction angles are in the range of 16° to 17°, 33° to 34°, 35° to 36°, 36° to 37.5°, 41° to 42.5°, 45° to 46°, 53° to 54.5°, 58° to 59°, 62° to 63.5°, and 65° to 66°, respectively, containing the diffraction peaks of the following crystal planes: (003), (006), (101), (012), (104), (015), (017), (018), (110), and (113).

8. The sodium ion positive electrode material according to any one of claims 1 to 7, wherein: The mass range of residual sodium in the sodium ion positive electrode material measured by water method is 0.5-1.5wt%.

9. A method for preparing the sodium ion positive electrode material according to any one of claims 1 to 8, the method comprising the following steps: The first Na source, Ni source, Fe source, Mn source, Cu source, Zn source, B source, Al source, Ce source, Mg source and Sr source are mixed and sintered once to obtain a sintered material; Mixing the second Na source and the first sintered material, and performing secondary sintering to obtain the sodium ion positive electrode material; Optionally, the mixture before the primary sintering further includes a doping element Q source, wherein the Q source includes an oxygen-containing compound corresponding to the doping element.

10. The method for preparing a sodium ion positive electrode material according to claim 9, wherein: The first Na source and the second Na source both include at least one of sodium carbonate, sodium bicarbonate, sodium hydroxide, sodium oxide, sodium oxalate, sodium acetate and sodium peroxide; the second Na source is sodium oxide, and the sodium oxide includes sodium oxide and / or sodium peroxide.

11. The method for preparing a sodium ion positive electrode material according to claim 9 or 10, wherein: The molar content of sodium in the calcined material is 55% to 75%.

12. The method for preparing a sodium ion positive electrode material according to any one of claims 9 to 11, wherein: NiFeMn hydroxide is used instead of the Ni source, Fe source and Mn source.

13. The method for preparing a sodium ion positive electrode material according to any one of claims 9 to 12, wherein: The temperature of the primary sintering is 800-1000° C., and the time is 2-10 hours; the temperature of the secondary sintering is 800-1000° C., and the heat preservation time is 2-10 hours.

14. The method for preparing a sodium ion positive electrode material according to claim 9, wherein: The preparation method comprises the following steps: A first Na source, NiFeMn hydroxide, and oxides of Cu, Zn, B, Al, Ce, Mg, Sr and doping element Q are mixed so that the molar content of sodium is 55% to 75%, and a sintering is performed at 800 to 1000° C. for 2 to 10 hours in an air atmosphere, and after cooling, the mixture is crushed and sieved to obtain a sintered material; The obtained calcined 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, the X-ray diffraction spectrum of the sintered material comprises diffraction peaks of the following crystal planes in the range 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°, respectively: (002), (003), (004), (006), (101), (012), (102), (104), (103), (015), (017), (018), (110), and (113); The second Na source and the first sintered material are mixed, and secondary sintering is performed at 800-1000° C. for 2-10 hours to obtain the sodium ion positive electrode material, wherein the molar content of the obtained sodium ion positive electrode material is 90%-100%.

15. A sodium ion battery, comprising the sodium ion positive electrode material according to any one of claims 1 to 8 or the sodium ion positive electrode material obtained by the preparation method according to any one of claims 9 to 14.

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