NaCaNiFeMnCuZn high-entropy oxide (at) MnOz (at) Al2O3-n composite material and preparation and application thereof

Abstract

The invention belongs to the field of sodium ion battery positive electrode materials, and particularly relates to a NaCaNiFeMnCuZn high-entropy oxide (at) MnOz (at) Al2O3-n composite material which comprises a matrix, a middle layer coating the matrix and an outer layer containing the middle layer. The invention also provides a preparation method and application of the material. The material disclosed by the invention has the characteristics of excellent high rate performance, long cycle life, high voltage retention rate and low gas production.

Description

Technical Field

[0001] The present invention relates to the field of cathode materials for sodium-ion batteries, and particularly to a field of cathode materials for sodium-ion batteries. Background Art

[0002] Lithium-ion batteries have become the best choice for electrochemical energy storage due to their high energy density and long service life, and are widely used in fields such as power batteries and large-scale energy storage. However, due to the drastic fluctuations in lithium prices and the severe uneven distribution of lithium resources, the development of lithium-ion batteries is restricted. Sodium-ion batteries with rich resources, stable prices, and a similar energy storage mechanism to lithium-ion batteries have become an important future research and development direction. Sodium-ion batteries mainly include a cathode, an anode, an electrolyte, a separator, and other auxiliary materials, among which the cathode is the key part that determines the cost and performance of sodium-ion batteries. The cathode materials for sodium-ion batteries mainly include oxide cathode materials, polyanion cathode materials, and Prussian blue cathode materials. Oxide cathode materials have been industrialized first due to their mature and simple synthesis process and relatively high specific capacity.

[0003] Oxide cathode materials include various structures such as tunnel type, P2 type, and O3 type, with the general formula Na x MO2. Currently, the M of the mainstream commercial layered oxide cathode materials includes Ni, Fe, Cu, Mn, etc. Among them, Ni has relatively high electrochemical activity and can undergo multiple redox reactions of Ni 2+ / Ni 3+ / Ni 4+ during charge and discharge, contributing a relatively high capacity. Therefore, in order to achieve a high specific capacity, oxide cathode materials usually contain a relatively high content of nickel. However, the price of nickel is relatively expensive compared with other transition metal elements, resulting in a relatively high cost of nickel-based oxide cathode materials and being unable to meet the development needs of sodium-ion batteries. To reduce the nickel content, it is imperative to lower the nickel content of oxide cathode materials.

[0004] In order to improve the performance of active materials, it is expected to improve the performance of materials by constructing high-entropy cathode materials with multi-metal references. Some related technologies have also been disclosed in the prior art. For example, the Chinese patent document with the publication number CN118472236A discloses a biphasic high-entropy layered oxide sodium-ion battery cathode material and its preparation method, which has a P2 / O3 biphasic composite structure, and the chemical general formula is Na x Ni y Fe z Mn w Cu a Zn b Ti 1-y-z-w-a-bO2. For another example, the Chinese patent document with the publication number CN118198347A discloses a high-entropy layered oxide, a single-crystal high-entropy cathode material, and their preparation methods and applications. The chemical general formula of the high-entropy layered oxide is: NaxFeaMnbM1y1M2y2…MiyiO2, and the configurational entropy ΔSconfig > 1.5R; where 0.8 ≤ x ≤ 1, 0.1 ≤ a, 0.4 ≤ b, a + b + y1 + y2 + … + yi = 1, i ≥ 3; M1, M2, …, Mi are each selected from one of Li, Mg, Al, K, Ca, Ti, V, Cr, Ni, Co, Cu, Zn, Zr, Nb, Mo, Sn, Ta, W, Sb, and La.

[0005] In addition, in order to improve the performance of the material, some coating methods have also been reported in the prior art. For example, the Chinese patent document with the publication number CN117897360A discloses a sodium-ion battery cathode material and its preparation method and application, specifically reporting a coating scheme with a high-entropy material. The Chinese patent document with the publication number CN116093326A discloses a sodium-ion battery cathode material and its preparation method and application, specifically recording a coating scheme of a solid electrolyte coating a high-entropy type layered transition metal oxide.

[0006] In summary, although the prior art has disclosed some high-entropy and coating technologies for sodium-ion oxide cathode materials, there is still room for improvement in aspects such as material cost, high-rate performance, long-cycle performance, and voltage stability in the prior art, especially the lack of effective means for the gas generation problem. Summary of the Invention

[0007] To solve the above technical problems, the present invention proposes a NaCaNiFeMnCuZn high-entropy oxide @MnO z @Al2O 3-n composite material, aiming to provide a new material that takes into account excellent high-rate performance, long cycle life, high voltage retention rate, and low gas generation.

[0008] The second object of the present invention is to provide a preparation method of the NaCaNiFeMnCuZn high-entropy oxide @MnO z @Al2O 3-n composite material and its application in sodium-ion batteries.

[0009] The third object of the present invention is to provide a sodium-ion battery containing the NaCaNiFeMnCuZn high-entropy oxide @MnOz@Al2O3 composite material, as well as its cathode and cathode material.

[0010] Low-nickel cathode materials have a high cost advantage, but they face problems such as low capacity, poor cycle stability, and unremarkable comprehensive cost advantages. Therefore, the present invention provides a solution idea of high entropy of NiFeMnCuZn in the industry. However, early research shows that due to the further activation of cationic redox, the voltage decay and transition metal dissolution problems of NiFeMnCuZn high-entropy materials will be more obvious. In addition, the introduction of highly catalytic active elements Cu and Zn will exacerbate the side reaction problems of the electrolyte and cause serious gas generation. In view of the problems faced by NiFeMnCuZn high-entropy materials, the present invention provides the following improvement ideas:

[0011] A NaCaNiFeMnCuZn high-entropy oxide@MnO z @Al2O 3-n composite material, wherein the matrix is a NaCaNiFeMnCuZn high-entropy oxide with internal stress, and its chemical formula is Na x Ca y Ni a Fe b Mn c Cu d Zn e M 1-a-b-c-d-e O 2-m , where M is one or more of Li, K, Sc, Ti, V, Zr, Nb, Mo, W, Ta, Sr, 0.6 < x < 1.05, 0 < y < 0.05, 0.05 ≤ a ≤ 0.25, 0.2 ≤ b ≤ 0.6, 0.1 ≤ c ≤ 0.6, 0.01 ≤ d ≤ 0.2, 0.05 ≤ e ≤ 0.2, 0 < m ≤ 0.2;

[0012] The material of the intermediate layer is oxygen vacancy manganese oxide (MnO z , 1 ≤ z ≤ 2);

[0013] The material of the outer layer is oxygen vacancy aluminum oxide (Al2O 3-n , 0 < n ≤ 0.5).

[0014] Research in the present invention shows that innovatively using a NaCaNiFeMnCuZn high-entropy oxide with internal stress as the matrix, successively coating an oxygen-deficient manganese oxide (MnO z ) intermediate layer and an oxygen-deficient aluminum oxide layer (Al2O 3-n ), in this way, based on the combination of composition, the structural relationship between components, the internal stress core, and the double oxygen vacancy structure, synergy can be achieved, and the capacity, rate, cycle, voltage, air stability, and low gas generation characteristics of the material can be strengthened.

[0015] The material described in this invention exhibits internal stress within the matrix and abundant oxygen vacancies on the matrix surface, intermediate layer, and outer layer. Through the combined control of composition and hierarchical relationships, the material can strengthen the matrix structure, suppress phase transitions, increase the energy barrier for interlayer migration of transition metal ions, enhance stability and long-term performance, and improve the material's rate capability, cycling performance, and voltage retention.

[0016] In the present invention, abundant oxygen vacancies are formed on the surface of the substrate and in the middle and outer layers, which can accelerate surface electron transport and improve the rate performance of the material; more importantly, it can inhibit the nucleophilic attack of the electrolyte, reduce the side reactions of the electrolyte, and inhibit the gas production of the battery; in addition, the presence of surface oxygen vacancies forms an electric field barrier layer, which inhibits the dissolution of transition metal ions, reduces the content of transition metal ions deposited on the negative electrode, reduces the crosstalk effect, and also reduces the decomposition and gas production of the electrolyte on the negative electrode side.

[0017] In the present invention, Na x Ca y Ni a Fe b Mn c Cu d Zn e M 1-a-b-c-d-e O 2-m wherein M is one or more of Zr, Mo, Ta, and Sr. Preferably, x is 0.9 to 0.99, preferably 0.94 to 0.96; y is 0.01 to 0.03; a is 0.1 to 0.15; b is 0.4 to 0.5; c is 0.2 to 0.3; d is 0.1 to 0.15; and e is 0.05 to 0.1.

[0018] Preferably, the weight ratio of the matrix, the intermediate layer and the outer layer is 1:(0.005-0.05):(0.001-0.02).

[0019] The present invention also provides a NaCaNiFeMnCuZn high entropy oxide @MnO z @Al2O 3-n The preparation method of the composite material comprises preparing a mixed raw material according to the stoichiometric ratio of the matrix, and sintering the mixed raw material in an oxygen-rich atmosphere to obtain a matrix; the oxygen-rich atmosphere is an atmosphere with an oxygen content of more than 40v%.

[0020] The substrate and the Mn source are mixed and subjected to a first stage coating sintering in an oxygen-deficient atmosphere to obtain a first stage coating material; the oxygen-deficient atmosphere refers to an atmosphere with an oxygen content between 2 and 15% by volume;

[0021] Mixing the first-stage coating material and the Al source and performing the second-stage coating sintering to obtain the second-stage coating material;

[0022] The two-stage coating material is subjected to a third-stage sintering under atmosphere A, and then the third-stage sintered product is brought into contact with a cooling medium for quenching treatment to obtain the described NaCaNiFeMnCuZn high-entropy oxide @MnO z @Al2O 3-n composite material; the atmosphere A includes at least one of nitrogen, noble gas, and hydrogen;

[0023] the cooling medium includes at least one of gas, liquid nitrogen, and dry ice.

[0024] In order to successfully prepare the material of the present invention, the present invention innovatively prepares the matrix under a rich oxygen atmosphere in advance. This not only helps to improve the phase and mixing entropy of the material, but also helps to provide sites for subsequent coating. Then, combined with the first-stage coating sintering and the second-stage sintering under a lean oxygen atmosphere, the matrix and the layer-by-layer coated material can be prepared, and the interfaces and phases of each layer of material can be optimized. In addition, by combining the sintering under atmosphere A and the subsequent quenching treatment, internal stress and abundant surface oxygen vacancies can be formed inside the material. The research of the present invention shows that the new material with excellent capacity, rate performance, stability, and low gas generation can be prepared by using the described preparation method.

[0025] In the present invention, the rich oxygen atmosphere is an atmosphere with an oxygen content of 40-80 v%.

[0026] In the present invention, the matrix sintering process includes a first-stage sintering process at temperature T1 and a second-stage sintering process at temperature T2.

[0027] Among them, temperature T1 is 400-750 °C (further 500-600 °C); temperature T2 is 800-1100 °C (further 900-1050 °C).

[0028] Preferably, the holding time t1 at temperature T1 is 3-8 hours, and the holding time t2 at temperature T2 is 8-15 hours.

[0029] In the present invention, the Mn source can be at least one of manganese oxides, carbonates, and hydroxides.

[0030] In the present invention, the weight ratio of the base material to the Mn source is 100:0.5-5; preferably 100:2-4.

[0031] In the present invention, the temperature of the first-stage coating sintering is 500-850 °C (further 600-800 °C). The holding time is 5-12 hours. The heating rate is 3-5 °C / min.

[0032] In the present invention, the Al source can be at least one of aluminum oxides, carbonates, and hydroxides.

[0033] In the present invention, the atmosphere of the second covering stage can be air.

[0034] In the present invention, the weight ratio of the base material to the Al source is 100:0.1-2, preferably 100:1-1.5.

[0035] In the present invention, the temperature of the second stage coating sintering is 300-650°C (further 400-550°C), the holding time is 3-6 hours, and the heating rate is 3-5°C / min.

[0036] In the present invention, the temperature of the third sintering treatment is 600-1050°C (further 900-1000°C), the holding time is 0.5-2 hours, and the heating rate is 10-15°C / min.

[0037] In the present invention, the rare gas in the atmosphere A is, for example, a Group 8 gas such as Ar.

[0038] In the present invention, atmosphere A is a hydrogen-argon mixture with a hydrogen content of 1-5% by volume. Research has shown that performing the third sintering process under the preferred atmosphere further optimizes the material's internal stress and double oxygen vacancy coating interface, further enhancing the material's rate capability, capacity, and voltage stability, and further controlling gas production.

[0039] In the present invention, after the third stage of calcination is completed, a quenching treatment is performed while the material is in contact with a cooling medium while still hot; this can assist in building the internal stress and hierarchical oxygen vacancies of the material.

[0040] In the present invention, in the cooling medium, the gas may be air.

[0041] Preferably, the cooling medium is dry ice or liquid nitrogen. Studies have shown that the optimal quenching process optimizes the internal stress of the material and the double oxygen vacancy coating interface, which helps to further enhance the material's rate capability, capacity, and voltage stability, and also helps to further control gas production.

[0042] In the present invention, when the cooling medium is dry ice or liquid nitrogen, the product of the third stage sintering can be cooled to 400-700° C. in advance and then brought into contact with the cooling medium for quenching.

[0043] The present invention also provides a positive electrode material for a sodium ion battery, including a positive electrode active material, wherein the positive electrode active material includes the NaCaNiFeMnCuZn high entropy oxide @MnO z @Al2O 3-n Composite materials.

[0044] In the present invention, the NaCaNiFeMnCuZn high entropy oxide@MnO z@Al2O 3-n The composite material is used as a positive electrode active material to prepare the required sodium ion battery and its associated components and materials (such as positive electrode, positive electrode material, etc.).

[0045] For example, as the same inventive concept, the present invention also provides a positive electrode material for a sodium ion battery, including a positive electrode active material, wherein the positive electrode active material includes the NaCaNiFeMnCuZn high entropy oxide@MnO z @Al2O 3-n Composite materials.

[0046] Preferably, in the positive electrode active material, the NaCaNiFeMnCuZn high entropy oxide @MnO z @Al2O 3-n The content of the composite material is above 50wt.%; furthermore, it can be the NaCaNiFeMnCuZn high entropy oxide@MnO z @Al2O 3-n Composite materials.

[0047] In the present invention, the positive electrode material may further include a conductive agent and a binder. The conductive agent and binder may be materials known in the industry. For example, the conductive agent may be a carbonaceous conductive agent known in the industry. The binder may be PVDF, CMC, etc.

[0048] In the present invention, in the positive electrode material, the content of the conductive agent is less than 15 wt.% (for example, 5 to 15 wt.%); the content of the binder is less than 15 wt.% (for example, 5 to 15 wt.%).

[0049] The present invention also provides a positive electrode of a sodium ion battery, comprising a current collector and a positive electrode material composited on the surface of the current collector, wherein the positive electrode material is the positive electrode material of the present invention.

[0050] The present invention also provides a sodium ion battery, comprising a positive electrode and a negative electrode, and a barrier material arranged between the positive electrode and the negative electrode, characterized in that the positive electrode is the positive electrode described in the present invention.

[0051] Beneficial effects

[0052] The present invention shows that the novel high entropy oxide NaCaNiFeMnCuZn with internal stress is used as the matrix, and oxygen vacancy manganese oxide MnO is coated in sequence. z Intermediate layer and oxygen vacancy aluminum oxide Al2O 3-nlayers. Thus, based on the combination of components and the structural relationships between components, synergy can be achieved, strengthening the capacity, rate performance, cycle performance, voltage stability, air stability, and low gas generation characteristics of the material.

[0053] The material described in the present invention can endow and facilitate the internal stress of the matrix, strengthen the matrix structure, inhibit the degree of phase change, and increase the interlayer migration energy barrier of transition metal ions. In addition, it can improve the hierarchical interface and further cooperate with the oxygen vacancy layer-by-layer coating layer described above to achieve synergy, accelerate surface electron transfer, and improve the rate performance of the material. More importantly, it can inhibit the nucleophilic attack of the electrolyte, reduce side reactions of the electrolyte, and inhibit gas generation in the battery. In addition, the presence of surface oxygen vacancies forms an electric field barrier layer, inhibiting the dissolution of transition metal ions, reducing the content of transition metal ions deposited on the negative electrode, reducing the crosstalk effect, and also reducing the decomposition and gas generation of the electrolyte on the negative electrode side.

[0054] In order to successfully prepare the material described in the present invention, the present invention innovatively prepares the matrix in an oxygen-rich atmosphere in advance. This not only helps to improve the phase and mixing entropy of the material, but also provides sites for subsequent coating. Then, in combination with the first-stage coating sintering, second-stage coating sintering, third-stage sintering treatment, and subsequent quenching treatment in an oxygen-deficient atmosphere, the matrix and the layer-by-layer coated material can be prepared, forming internal stress and abundant surface oxygen vacancies, and optimizing the interfaces and phases of each layer of the material. The research of the present invention shows that the new material with excellent capacity, rate performance, stability, and low gas generation can be prepared by using the described preparation method. BRIEF DESCRIPTION OF THE DRAWINGS

[0055] Figure 1 XRD pattern of the low-nickel oxide cathode material prepared in Example 1;

[0056] Figure 2 SEM image of the low-nickel oxide cathode material prepared in Example 1;

[0057] Figure 3 Charge-discharge curve of the low-nickel oxide cathode material prepared in Example 1;

[0058] Figure 4 Cycling performance of the low-nickel oxide cathode material prepared in Example 1;

[0059] Figure 5 SEM image of the low-nickel oxide cathode material prepared in Example 2B; DETAILED DESCRIPTION OF THE EMBODIMENTS

[0060] The technical solutions of the present invention will be further described below in conjunction with specific embodiments, but not limited thereto.

[0061] A NaCaNiFeMnCuZn high-entropy oxide @MnOz @Al2O 3-n The composite material comprises a matrix, an intermediate layer covering the matrix, and an outer layer including the intermediate layer; the matrix is a NaCaNiFeMnCuZn high entropy oxide with internal stress, and its chemical formula is Na x Ca y Ni a Fe b Mn c Cu d Zn e M 1-a-b-c-d-e O 2-m , where M is one or more of Li, K, Sc, Ti, V, Zr, Nb, Mo, W, Ta, Sr, 0.6 <x<1.05,0<y<0.05,0.05≤a≤0.25,0.2≤b≤0.6,0.1≤c≤0.6,0.01≤d≤0.2,0.05≤e≤0.2,0<m≤0.2;

[0062] The morphology of the substrate is single crystal or polycrystalline, and the crystal structure is P2 type, O3 type or P2 / O3 composite phase;

[0063] The material of the intermediate layer is oxygen vacancy manganese oxide, and its chemical formula is MnO z (oxygen vacancy manganese oxide), 1≤z≤2;

[0064] The material of the outer layer is oxygen vacancy Al2O 3-n (oxygen vacancy alumina), 0 <n≤0.5。

[0065] The weight ratio of the substrate, the middle layer and the outer layer is 1: (0.005-0.05): (0.001-0.02);

[0066] The present invention also provides a NaCaNiFeMnCuZn high entropy oxide @MnO z @Al2O 3-n Preparation steps of composite materials:

[0067] S1: A sodium source, a calcium source, a nickel source, an iron source, a manganese source, a copper source, a zinc source, and an M source are uniformly mixed to obtain a mixture A, A is subjected to high-temperature sintering in an oxygen-rich atmosphere according to a certain sintering schedule, and a matrix material B is obtained after cooling, crushing, and screening;

[0068] S2: After the base material B and the manganese source are evenly mixed, the first stage of coating sintering is carried out in an oxygen-deficient atmosphere, and the first stage of coating material C is obtained after cooling, crushing and screening;

[0069] S3: After uniformly mixing the first-stage coating material C with the aluminum source, performing the second-stage coating sintering, cooling, crushing, and screening to obtain the second-stage coating material D;

[0070] S4: Sinter the secondary coating material D in atmosphere A and then perform a quenching treatment to obtain the described NaCaNiFeMnCuZn high-entropy oxide@MnOz@Al2O 3-n composite material.

[0071] The sodium source described in step S1 includes, but is not limited to, one or more of sodium carbonate, sodium bicarbonate, sodium hydroxide, and sodium acetate; preferably, one or more of sodium carbonate or sodium hydroxide; more preferably, sodium carbonate;

[0072] The calcium source described in step S1 includes, but is not limited to, one or more of calcium oxide, calcium carbonate, calcium acetate, and calcium citrate; preferably, calcium oxide or calcium carbonate;

[0073] The nickel source, iron source, manganese source, copper source, zinc source, and M source described in step S1 include, but are not limited to, one or more of their oxides, hydroxides, carbonates, sulfates, and nitrates, as well as mixed oxides, hydroxides, and carbonates; preferably, one or more of oxides, hydroxides, carbonates, or mixed oxides, hydroxides, and carbonates;

[0074] The manganese source described in step S2 includes, but is not limited to, one or more of Mn3O4, MnO, and MnO2;

[0075] The particle size D50 of the manganese source in step S2 < 10 μm; preferably, the particle size D50 of the manganese source < 2 μm;

[0076] The aluminum source described in step S3 includes, but is not limited to, one or more of Al2O3, aluminum isopropoxide, and aluminum hydroxide;

[0077] The particle size D50 of the aluminum source in step S3 < 10 μm;

[0078] The mixing methods described in steps S1, S2, and S3 include, but are not limited to, one or more of mechanical mixing method, ball milling method, sol-gel method, co-precipitation method, hydrothermal method, sand milling method, and combined method of sand milling and spraying;

[0079] The sintering atmosphere described in step S1 is an oxygen-rich atmosphere with an oxygen content higher than 40 v%; among them, in addition to containing oxygen, the remaining gas can be nitrogen, argon, air, etc. In the following cases, unless otherwise stated, the gas other than oxygen can be nitrogen or argon.

[0080] Increasing the oxygen content in the sintering atmosphere of the cathode material can improve the lattice integrity of the material, inhibit the formation of impurity phases, and reduce the content of residual sodium on the surface;

[0081] The sintering atmosphere in step S2 is an oxygen-poor atmosphere with an oxygen content between 2% and 15% by volume;

[0082] The atmosphere A in step S4 is an inert atmosphere, or a hydrogen-Ar mixed gas.

[0083] The sintering system described in step S1 is a two-stage sintering, that is, after heating from room temperature to the first holding temperature T1 and holding for t1 hour, heating to the second holding temperature T2 and holding for t2 hours, the first holding temperature T1 is 400-750°C, the first holding time t1 is 3-8 hours, the second holding temperature T2 is 800-1100°C, the first holding time t2 is 8-15 hours, and the heating rate is 3-5°C / min;

[0084] The sintering system described in step S2 is a one-stage sintering, that is, heating from room temperature to a holding temperature T3 for t3 hours, the holding temperature T3 is 500-850°C, the holding time t3 is 5-12 hours, and the heating rate is 3-5°C / min;

[0085] The sintering system described in step S3 is a one-stage sintering, that is, heating from room temperature to a holding temperature T4 for t4 hours, the holding temperature T4 is 300-650°C, the holding time t4 is 3-6 hours, and the heating rate is 3-5°C / min;

[0086] The sintering system described in step S3 is a one-stage sintering, that is, heating from room temperature to a holding temperature T5 for t5 hours, the holding temperature T5 is 600-1050°C, the holding time t5 is 0.5-2 hours, and the heating rate is 10-15°C / min;

[0087] The cooling method in steps S1, S2 and S3 is slow cooling with the furnace or air cooling;

[0088] The cooling method in step S4 is quenching, and the cooling medium is cold dry air or liquid nitrogen; more preferably, liquid nitrogen.

[0089] Sudden cooling can accelerate cooling, form built-in stress in the crystal, improve the stability of the crystal structure during long cycles, and inhibit the migration and dissolution of transition metals.

[0090] The crushing method in steps S1, S2 and S3 includes but is not limited to one or more of jaw crushing, roller crushing and air flow crushing; preferably, it is a combination of roller crushing and air flow crushing;

[0091] The mesh size of the sieve in the screening process described in steps S1, S2 and S3 is 80-800 mesh.

[0092] Example 1

[0093] A NaCaNiFeMnCuZn high entropy oxide@MnOz @Al2O 3-n Preparation method of composite material, comprising the following steps:

[0094] (S1) According to the chemical formula of Na 0.95 Ca 0.01 Ni 0.1 Fe 0.4 Mn 0.3 Cu 0.1 Zn 0.08 Ta 0.01 Sr 0.01 O2, weigh sodium carbonate, calcium oxide, nickel hydroxide, iron oxide, manganese tetraoxide, copper oxide, zinc oxide, tantalum oxide, strontium oxide, and obtain mixture A after uniform sand grinding in an aqueous medium and spray drying. Sinter mixture A in an oxygen-rich atmosphere with an oxygen content of 50%. The sintering regime is to rise from room temperature to 500°C (marked as T1) at a heating rate of 3°C / min and hold for 5 hours, then continue to rise to 950°C (marked as T2) at a heating rate of 3°C / min and hold for 11 hours. After slow cooling to room temperature with the furnace, obtain matrix material B after roller pressing and air flow crushing and screening through a 200-mesh sieve;

[0095] (S2) After uniformly mixing MnO2 and matrix material B with a weight ratio of 0.025:1, heat from room temperature to 750°C (marked as temperature T3) at a heating rate of 3°C / min in a lean oxygen atmosphere (oxygen-Ar mixture) with an oxygen content of 5% and hold for 7 hours. After slow cooling to room temperature with the furnace, obtain a first-stage coating material C after roller pressing and air flow crushing and screening through a 200-mesh sieve;

[0096] (S3) After uniformly mixing Al2O3 and the first-stage coating material C with a weight ratio of 0.01:1, heat from room temperature to 450°C (marked as temperature T4) at a heating rate of 3°C / min in a dry air atmosphere and hold for 4.5 hours. Then, immediately introduce air (cooling medium) while it is hot. After cooling to room temperature, obtain a second-stage coating material D after roller pressing and air flow crushing and screening through a 200-mesh sieve.

[0097] (S4) Heat the second-stage coating material D from room temperature to 1000°C (marked as temperature T5) at a heating rate of 12°C / min in a hydrogen-argon mixture (atmosphere A) with a hydrogen content of 4% and hold for 1 hour. Then, cool to 400 - 600°C with the furnace and immediately contact with liquid nitrogen for quenching treatment to obtain the internal stress NaCaNiFeMnCuZn high-entropy oxide @MnO z @Al2O 3-n composite material.

[0098] Example 2

[0099] Group A: Compared with Example 1, the only difference is that the chemical formula of the matrix material in S1 is changed to Na 0.95 Ca 0.01 Ni 0.1 Fe 0.4 Mn 0.3 Cu 0.1 Zn 0.08 Mo 0.01 Zr 0.01 O2;

[0100] Group B: Compared with Example 1, the only difference is that the chemical formula of the matrix material in S1 is changed to Na 0.90 Ca 0.03 Ni 0.1 2Fe 0.48 Mn 0.2 Cu 0.12 Zn 0.05 Ta 0.02 Sr 0.01 O2;

[0101] Group C: Compared with Example 1, the only difference is that during the sintering process of S1, the temperature T1 is 600 °C, and the holding time at this temperature is 4 h; the temperature T2 is 1050 °C, and the holding time at this temperature is 9 h; the heating rates for heating to temperature T1 and heating to temperature T2 are 5 °C / min; the sintering atmosphere is an oxygen-rich atmosphere with an oxygen content of 70%;

[0102] All other operations and parameters are the same as in Example 1.

[0103] Example 3

[0104] Compared with Example 1, the only difference is that in step S2, the weight ratio of the matrix material:MnO2 is 1:0.04; the temperature T3 is 650 °C, and the holding time at this temperature is 10 h; and the sintering atmosphere is a lean oxygen atmosphere (oxygen-nitrogen mixture) with an oxygen content of 10%;

[0105] All other operations and parameters are the same as in Example 1.

[0106] Example 4

[0107] Compared with Example 1, the only difference is that the weight ratio of the first-stage coating material:Al2O3 in S3 is changed to 1:0.015; the temperature of temperature T4 is 500 °C, and the holding time at this temperature is 4 h; all other operations and parameters are the same as in Example 1.

[0108] Example 5

[0109] Group A: Compared with Example 1, the only difference is that the atmosphere of the three-stage sintering treatment in S4 is changed to a hydrogen-argon mixture with a hydrogen content of 1%; the temperature T5 is 900 °C, the heating rate during the treatment is 10 °C / min; the holding time is 1.5 h;

[0110] Group B: Compared with Example 1, the only difference is that the atmosphere A of the three-stage sintering treatment in S4 is changed to nitrogen;

[0111] Group C: Compared with Example 1, the only difference is that the quenching cooling medium after the three-stage sintering in S4 is changed to cold dry air;

[0112] All other operations and parameters are the same as those in Example 1.

[0113] Comparative Example 1

[0114] Group A: Compared with Example 1, the only difference is that the chemical formula of the matrix material in S1 is changed to Na 0.95 Ni 0.1 Fe 0.4 Mn 0.3 Cu 0.1 Zn 0.08 Ta 0.01 Sr 0.01 O2;

[0115] Group B: Compared with Example 1, the only difference is that the chemical formula of the matrix material in S1 is changed to Na 0.95 Ca 0.01 Ni 0.2 Fe 0.4 Mn 0.3 O2;

[0116] Group C: Compared with Example 1, the only difference is that the sintering atmosphere of the matrix material in S1 is changed to air;

[0117] All other operations and parameters are the same as those in Example 1.

[0118] Comparative Example 2

[0119] Compared with Example 1, the only difference is that the atmosphere of the one-stage coating sintering in S2 is changed to air;

[0120] All other operations and parameters are the same as those in Example 1.

[0121] Comparative Example 3

[0122] Compared with Example 1, the only difference is that the atmosphere of the three-stage sintering treatment in S4 is changed to air. All other operations and parameters are the same as those in Example 1.

[0123] Comparative Example 4

[0124] Compared with Example 1, the only difference is that step S2 is omitted, and the material obtained in S1 is directly subjected to the second-stage coating sintering in S3; other operations and parameters are the same as in Example 1.

[0125] Comparative Example 5

[0126] Compared with Example 1, the only difference is that step S3 is omitted, and the material obtained in S2 is directly subjected to the three-stage sintering treatment in S4; other operations and parameters are the same as in Example 1.

[0127] Comparative Example 6

[0128] Compared with Example 1, the only difference is that step S4 is omitted and the product obtained in S3 is directly used as the positive electrode material; other operations and parameters are the same as those in Example 1.

[0129] Comparative Example 7

[0130] Compared with Example 1, the only difference is that after S1 is completed, step S4 is performed first, and then steps S2 and S3 are performed; other operations and parameters are the same as in Example 1.

[0131] Comparative Example 8

[0132] Compared with Example 1, the only difference is that steps S2 and S3 are carried out simultaneously, that is, MnO2 and Al2O3 are mixed with the matrix material at the same time, and the temperature is raised from room temperature to 450°C at a heating rate of 3°C / min in a dry air atmosphere and kept warm for 4.5 hours. After air cooling to room temperature, the second-stage coating material D is obtained after being crushed by rollers and air flow crushing and then sieved with 200 mesh, and then S4 is carried out.

[0133] Other operations and parameters are the same as in Example 1.

[0134] Sodium secondary battery performance test:

[0135] The active materials (freshly prepared or stored in an Ar atmosphere) obtained in each of the above cases, acetylene black (AB), and polyvinylidene fluoride (PVDF) were added to an n-methyl-2-pyrrolidone (NMP) solution in a molar ratio of 8:1:1. After grinding and dispersion, the slurry was evenly coated on aluminum foil and dried in a vacuum oven at 80°C for more than 10 hours to form a positive electrode sheet. Acetylene black was used as a conductive additive, polyvinylidene fluoride was used as a binder, and aluminum foil was used as a current collector. The positive electrode surface loading was approximately 2.5 mg / cm. 2 .

[0136] In a glove box filled with argon, where the concentrations of H2O and O2 are below 0.1 ppm, 2032 button cells were assembled. The electrolyte is a solution of 1 M NaPF6 in propylene carbonate (PC) and 5% fluoroethylene carbonate (FEC). A sodium metal foil was used as the negative electrode, and a glass fiber membrane was used as the separator for the half-cell, and a CR2032 button cell was assembled. The constant current charge-discharge mode was used for testing. The temperature of the test cabinet was 25 °C (cycling test temperature), the charge cut-off voltage was 4.0 V, the discharge cut-off voltage was 2.0 V, activated for 3 cycles at 0.1 C, cycled 500 times at 1 C or a 5 C charge-discharge test was carried out. The active materials finally prepared in each of the above cases were loaded into a special in-situ cell, and the gas generation behavior was tested and recorded by DEMs. The results are shown in Table 1.

[0137] Table 1 Comparison table of electrochemical performance of examples and comparative examples

[0138]

[0139]

[0140]

[0141] Figures 1 to 4 XRD pattern, SEM image, charge-discharge curve and cycling performance graph of Example 1. It can be seen that the product of Example 1 is of the O3 type, has a good crystal structure, a secondary spherical morphology, a smooth surface, a high capacity and excellent cycling performance.

[0142] Figure 5 SEM image of Example 2B. It can be seen that the product of Example 2 has a secondary spherical morphology and a smooth surface.

[0143] From each of the examples and comparative examples of the present invention, it is innovatively based on the NaCaNiFeMnCuZn high-entropy oxide with internal stress as the matrix, and successively coated with oxygen vacancy manganese oxide MnO z intermediate layer and oxygen vacancy aluminum oxide Al2O 3-n layer. In this way, based on the combination of the composition and the structural relationship between the components, synergy can be achieved, and the capacity, rate, cycling, voltage, air stability and low gas generation characteristics of the material can be strengthened.

[0144] In addition, from Examples 1 and 5, it can be seen that by using the hydrogen-containing atmosphere of the present invention for the third-stage heat treatment and cooperating with rapid quenching in liquid nitrogen, it is expected to further construct an internal stress double oxygen vacancy material, which can further improve its various performances.

Claims

1. A NaCaNiFeMnCuZn high-entropy oxide @MnO z @Al2O 3-n composite material, comprising a matrix, an intermediate layer coating the matrix, and an outer layer containing the intermediate layer; characterized in that, The substrate is a NaCaNiFeMnCuZn high-entropy oxide with internal stress, and its chemical formula is Na x Ca y Ni a Fe b Mn c Cu d Zn e M 1-a-b-c-d-e O 2-m , where M is one or more of Li, K, Sc, Ti, V, Zr, Nb, Mo, W, Ta, Sr, 0.6 < x < 1.05, 0 < y < 0.05, 0.05 ≤ a ≤ 0.25, 0.2 ≤ b ≤ 0.6, 0.1 ≤ c ≤ 0.6, 0.01 ≤ d ≤ 0.2, 0.05 ≤ e ≤ 0.2, 0 < m ≤ 0.2; The material of the middle layer is oxygen vacancy manganese oxide; The material of the outer layer is oxygen vacancy aluminum oxide.

2. The NaCaNiFeMnCuZn high-entropy oxide @MnO z @Al2O 3-n composite material according to claim 1, characterized in that There is internal stress inside the substrate, and there are oxygen vacancies on the surface of the substrate, the middle layer and the outer layer; Preferably, the weight ratio of the substrate, the middle layer and the outer layer is 1:(0.005 - 0.05):(0.001 - 0.02).

3. Preparation method of the NaCaNiFeMnCuZn high-entropy oxide @MnO₂@Al₂O₃ composite material according to any one of claims 1 to 2, characterized in that, 3-n Mixing raw materials according to the stoichiometric ratio of the substrate, and sintering the mixed raw materials in an oxygen-rich atmosphere to obtain the substrate; the oxygen-rich atmosphere refers to an atmosphere with an oxygen content of more than 40 v%; ​ Mixing the substrate and the Mn source and performing the first-stage coating sintering in an oxygen-deficient atmosphere to obtain the first-stage coated material; the oxygen-deficient atmosphere refers to an atmosphere with an oxygen content between 2 and 15 v%; Mixing the first-stage coated material and the Al source and performing the second-stage coating sintering to obtain the second-stage coated material; The two-stage coating material is subjected to a third-stage sintering under atmosphere A, and then the third-stage sintered product is brought into contact with a cooling medium for quenching treatment to obtain the NaCaNiFeMnCuZn high-entropy oxide @MnO z @Al2O 3-n composite material; the atmosphere A includes at least one of nitrogen, noble gas, and hydrogen; The cooling medium includes at least one of gas, liquid nitrogen, and dry ice.

4. The preparation method of the NaCaNiFeMnCuZn high-entropy oxide @MnO₂@Al₂O 3-n composite material, characterized in that The substrate sintering process includes a first-stage sintering process at temperature T1 and a second-stage sintering process at temperature T2; Among them, temperature T1 is 400 - 750 °C; temperature T2 is 800 - 1100 °C; Preferably, the heat preservation time t1 at temperature T1 is 3 - 8 hours, and the heat preservation time t2 at temperature T2 is 8 - 15 hours.

5. Preparation method of the NaCaNiFeMnCuZn high-entropy oxide@MnO₂@Al₂O₃ 3-n composite material, characterized in that, The temperature of the first-stage coating sintering is 500 - 850 °C, and the heat preservation time is preferably 5 - 12 hours.

6. The preparation method of the NaCaNiFeMnCuZn high-entropy oxide @MnO₂@Al₂O 3-n composite material, characterized in that The temperature of the second-stage coating sintering is 300 - 650 °C, and the heat preservation time is preferably 3 - 6 hours.

7. The preparation method of the NaCaNiFeMnCuZn high-entropy oxide @MnO z @Al2O 3-n composite material, characterized in that Atmosphere A is preferably a hydrogen-argon mixed gas with a hydrogen content of 1 - 5 v%; Preferably, the temperature of the third-stage sintering is 600 - 1050 °C, and the heat preservation time is preferably 0.5 - 2 hours; Preferably, the cooling medium is dry ice or liquid nitrogen.

8. A positive electrode material for a sodium-ion battery, comprising a positive electrode active material, characterized in that, The positive electrode active material described above includes the NaCaNiFeMnCuZn high-entropy oxide@MnO composite material according to any one of claims 1 to 2 or the NaCaNiFeMnCuZn high-entropy oxide@MnO z @Al2O 3-n composite material prepared by the preparation method according to any one of claims 3 to 7 z @Al2O 3-n composite material.

9. The positive electrode of a sodium-ion battery, comprising a current collector and a positive electrode material compounded on its surface, is characterized in that The positive electrode material is the positive electrode material described in claim 8.

10. A sodium-ion battery, comprising a positive electrode, a negative electrode, and a barrier material disposed between the positive electrode and the negative electrode, characterized in that, The positive electrode is the positive electrode described in claim 9.

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