High-entropy sodium battery cathode material, preparation method and application thereof

Abstract

The application belongs to the technical field of new energy, and particularly relates to a high-entropy sodium battery positive electrode material and a preparation method and application thereof. x Ni a Fe b Mn c Zn d Ti e L p O2, wherein, 0.95<=x<=1.10, 0.25<=a<=0.35, 0.25<=b<=0.40, 0.25<=c<=0.35, 0 The high-entropy sodium battery positive electrode material is doped with multiple elements and is surface-modified, so that the energy density, cycle stability and air stability of the high-entropy sodium battery positive electrode material are improved.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of new energy, and particularly relates to a high-entropy sodium battery positive electrode material and a preparation method and application thereof. BACKGROUND

[0002] Sodium-ion batteries, as an important alternative technology of lithium-ion batteries, have attracted widespread attention in recent years. The core advantages of sodium-ion batteries lie in the crust abundance of sodium resources (about 2.36%, much higher than 0.0017% of lithium), low cost (the price of sodium raw materials is only 1 / 10~1 / 5 of that of lithium), and environmental friendliness. In addition, sodium-ion batteries have similar "rocking chair" working principles as lithium-ion batteries, and can directly learn from the mature production equipment and process of lithium-ion batteries, so the industrialization threshold is low. However, although sodium-ion batteries have advantages in resources and cost, they have defects such as low capacity, insufficient energy density, and short cycle life, which lead to high unit energy cost (yuan / Wh) and make it difficult to compete with lithium-ion batteries, seriously restricting the application of sodium-ion batteries.

[0003] Currently, mainstream sodium battery positive electrode materials include layered oxides (such as NaNiO2, NaFeO2), polyanion compounds (such as Na3V2(PO4)3), and Prussian blue analogues. Among them, NaNiO2 has the highest theoretical capacity (about 275 mAh / g), but its actual capacity is only about 100 mAh / g, and its cycle life is short. 1 / 3 Fe 1 / 3 Mn 1 / 3 O2layered oxides are concerned due to their high theoretical capacity (≥160 mAh / g) and mature preparation process, but their actual performance still has low capacity and short cycle life. SUMMARY

[0004] Therefore, the technical problem to be solved by the present application is to overcome the defects of low specific capacity, low energy density, and poor cycle performance of existing sodium battery positive electrode materials, so as to provide a high-entropy sodium battery positive electrode material and a preparation method and application thereof.

[0005] To this end, the present application provides the following technical solutions:

[0006] The present application protects, in a first aspect, a high-entropy sodium battery positive electrode material, wherein the high-entropy sodium battery positive electrode material comprises a matrix and a coating layer coated on the matrix.

[0007] The general composition of the matrix is Na x Ni a Fe b Mn c Zn d Ti e L pO2, wherein, 0.95≤x≤1.10, 0.25≤a≤0.35, 0.25≤b≤0.40, 0.25≤c≤0.35, 0<d≤0.06, 0<e≤0.06, 0.001≤p≤0.005, a+b+c+d+e=1, L includes at least one of Cu, Mo, Sb, Sn, Nb, Li.

[0008] According to the application, the general formula of the base body is Na x Ni a Fe b Mn c Zn d Ti e L p O2, wherein, 1.00≤x≤1.05, 0.25≤a≤0.30, 0.35≤b≤0.40, 0.25≤c≤0.30, 0.03≤d≤0.05, 0.03≤e≤0.05, 0.001≤p≤0.003, a+b+c+d+e=1.

[0009] According to the application, the coating layer includes a metal oxide.

[0010] The second aspect of the application protects a preparation method of the aforementioned high-entropy sodium electrode positive material, wherein the preparation method comprises the following steps:

[0011] S1, mixing a sodium source, a Ni ɑ Fe β Mn γ Zn ε Ti δ (OH)2 precursor, a zinc source, a titanium source, and a dopant to obtain a first sintered product;

[0012] The Ni ɑ Fe β Mn γ Zn ε Ti δ (OH)2 precursor, wherein, 0.25≤ɑ≤0.35, 0.25≤β≤0.40, 0.25≤γ≤0.35, 0≤ε≤0.02, 0≤δ≤0.02; ɑ+β+γ+ε+δ=1;

[0013] The first sintering includes three independent temperature rising stages of a first stage, a second stage, and a third stage, and a fourth stage of temperature reduction; the first stage is to rise the temperature to 400-550℃ at a speed of 1-5℃ / min; the second stage is to rise the temperature to 750-850℃ at a speed of 1-5℃ / min; the third stage is to rise the temperature to 950-1050℃ at a speed of 1-5℃ / min;

[0014] S2, the first product, coating agent is mixed and then second sintering is carried out to obtain the high-entropy sodium battery positive electrode material.

[0015] In the present application, Ni ɑ Fe β Mn γ Zn ε Ti δ The (OH)2 precursor can be purchased or prepared, and when prepared, the preparation method in the art can be used, typically and non-limitingly, when Zn is 0 and Ti is 0, Ni ɑ Fe β Mn γ The preparation method of the (OH)2 precursor includes the following steps: dissolving a nickel source (typically and non-limitingly, the nickel source includes NiSO4), an iron source (typically and non-limitingly, the iron source includes FeSO4) and a manganese source (typically and non-limitingly, the manganese source includes MnSO4) into water in a molar ratio of (0.25-0.35):(0.25-0.40):(0.25-0.35) according to the metal elements, to obtain a mixed metal-containing solution with a total metal ion concentration of 2-3 mol / L, prepare an ammonia solution with a concentration of 20-30 wt%, and prepare a NaOH solution with a concentration of 2-3 mol / L; under a nitrogen atmosphere, the flow rate of nitrogen is 3-5 L / min, the mixed metal-containing solution and the ammonia solution are introduced into the reaction kettle for co-precipitation reaction at a flow rate of 8-12 L / h and 4-6 L / h, respectively, the reaction temperature is controlled at 55-60℃, the pH of the reaction system is controlled at 10.2-10.5 by using the NaOH solution, the reaction is carried out for 10-15 h, and then the (OH)2 precursor is obtained by filtration, washing and drying. ɑ Fe β Mn γ .

[0016] In the present application, when NiSO4, FeSO4 and MnSO4 (all in terms of metal elements) are prepared in a ratio of 0.33:0.33:0.33, the (OH)2 precursor obtained is Ni 1 / 3 Fe 1 / 3 Mn 1 / 3 (OH)2, because 1 / 3 cannot be divided, in order to facilitate calculation, it is also written in the form of Ni 0.33 Fe 0.33 Mn 0.33 (OH)2, it should be considered that the (OH)2 also satisfies the metal element subscript of 1. 0.33 Fe 0.33 Mn 0.33 (OH)2 also satisfies the metal element subscript of 1.

[0017] In the present application, the amount of zinc source and titanium source is added according to the need of the general formula of the high-entropy sodium battery positive electrode material matrix in the first part of the present application.

[0018] In the present application, the molar ratio of sodium element in the sodium source to the sum of metal elements in the Ni ɑ Fe β Mn γ Zn ε Ti δ The molar ratio of the sum of metal elements in the (OH)2 precursor to 1 is 0.95-1.10:1.

[0019] According to the present application, the sodium source, the Ni ɑ Fe β Mn γ Zn ε Ti δ The first sintering is performed after mixing the (OH)2 precursor, the zinc source, the titanium source, the iron source and the dopant.

[0020] In the present application, the amount of each of the iron source and the dopant and the type of the dopant are added according to the need of the general formula of the high-entropy sodium electric positive electrode material matrix in the first part of the present application.

[0021] According to the present application, the dopant includes at least one of an oxide of Cu, a sulfate of Cu, a chloride of Cu, an oxide of Mo, a sulfate of Mo, a chloride of Mo, an oxide of Sb, a sulfate of Sb, a chloride of Sb, an oxide of Sn, a sulfate of Sn, a chloride of Sn, an oxide of Nb, a sulfate of Nb, a chloride of Nb, an oxide of Li, a sulfate of Li, a chloride of Li, a hydrochloride of Li, and a carbonate of Li.

[0022] According to the present application, the dopant includes at least one of an oxide of Cu, an oxide of Mo, an oxide of Sb, an oxide of Sn, an oxide of Nb, a hydroxide of Li, and a carbonate of Li.

[0023] According to the present application, the dopant includes at least one of Sb2O5, Nb2O5, CuO, MoO3, SnO2, LiOH and Li2CO3.

[0024] According to the present application, the conditions of the first sintering include: in the first stage, the temperature is raised to 400-550℃ at a speed of 1-5℃ / min and the temperature is maintained for 2-5h; in the second stage, the temperature is raised to 750-850℃ at a speed of 1-5℃ / min and the temperature is maintained for 2-5h; in the third stage, the temperature is raised to 950-1050℃ at a speed of 1-5℃ / min and the temperature is maintained for 5-10h; in the fourth stage, the temperature is reduced to 800-950℃ at a speed of 2-5℃ / min and the temperature is maintained for 8-15h, and then the temperature is naturally cooled to room temperature (25-30℃).

[0025] In the present application, the first sintering and the second sintering are each independently performed in an air atmosphere or an oxygen atmosphere.

[0026] According to the application, the coating agent comprises a metal oxide and / or a metal carbon oxide, and optionally, the coating agent comprises at least one of B2O3, Al2O3, ZrO2, TiO2, NiO, CaO or CaCO3.

[0027] According to the application, the mass percentage of the coating agent is 0.5-3wt% based on the mass of the sintered product.

[0028] According to the application, the second sintering condition comprises: heating to 400-800℃ at a rate of 1-5℃ / min and holding for 3-8h.

[0029] In the application, a sieving and iron removing step is further performed after the second sintering.

[0030] The third aspect of the application protects a secondary battery, wherein the secondary battery comprises the aforementioned sodium battery positive electrode material or the high-entropy sodium battery positive electrode material prepared by the aforementioned preparation method.

[0031] The technical solution of the application has the following advantages:

[0032] 1. The application provides a high-entropy sodium battery positive electrode material, wherein the high-entropy sodium battery positive electrode material comprises a base body and a coating layer coated on the base body; the general composition of the base body is Na x Ni a Fe b Mn c Zn d Ti e L p O2, wherein 0.95≤x≤1.10, 0.25≤a≤0.35, 0.25≤b≤0.40, 0.25≤c≤0.35, 0<d≤0.06, 0<e≤0.06, 0.001≤p≤0.005, a+b+c+d+e=1, and L comprises at least one of Cu, Mo, Sb, Sn, Nb and Li; the high-entropy sodium battery positive electrode material of the application is prepared by multi-element high-entropy doping and surface modification, and the crystal structure phase transition and sodium precipitation side reaction are inhibited, so that the prepared sodium ion battery has excellent specific capacity, energy density, cycle stability and air stability; wherein, the inexpensive Fe is used to replace part of Ni, which not only reduces the cost of raw materials, but also forms Fe 3+ / Fe 4+ redox pairs, breaking through the capacity bottleneck of traditional Ni-Mn-based materials; although the O3-type sodium nickelate has a two-electron reaction (Ni 2+ / Ni 4+ ), the theoretical specific capacity is relatively high, but the Na +The phase transition will be accompanied by severe phase transition, resulting in rapid contraction and expansion of interlayer spacing, and eventually evolving into serious local strain, cracks and capacity decay. Therefore, the application adopts Zn, Ti and Fe element doping to regulate the phase transition path of the material, which shows a negative lattice expansion behavior in the desodium process (2.0-4.0V), realizing the stable cycle of high-entropy sodium battery positive electrode. Among them, the incorporation of Zn will induce the generation of P / O symbiotic phase, cause lattice contraction at high voltage, reduce the lattice expansion degree in the desodium process, and improve the specific capacity of the material; the incorporation of Ti will inhibit the Jahn-Teller distortion of [Ni 3+ O6], eliminate the rearrangement of Na + / hole, improve the structural stability during the cycle process; the incorporation of Fe can further improve the discharge voltage platform and improve the energy density; the trace doping of L element can further improve the configurational entropy of the material system, and at the same time, widen the sodium ion diffusion channel of the material, reduce the Na + migration energy barrier, thereby accelerating the diffusion of Na + , and the cycle stability is also effectively improved; the coating layer can improve the air stability of the material, improve the processing performance, and at the same time, reduce the residual alkali on the surface of the material, isolate the electrolyte corrosion, and reduce the occurrence of side reactions.

[0033] 2、In the application, the base general formula is further limited, wherein the Ni, Fe, Mn, Zn and Ti elements constitute a high-entropy sodium battery positive electrode material. Due to the cation disorder, the cation redox boundary can be disturbed, the formation of harmful O'3 phase is inhibited, and the cycle stability of the battery made of the high-entropy sodium battery positive electrode material is significantly improved. In addition, the synergistic effect of the multiple elements of the high-entropy sodium battery positive electrode material can further improve the energy density and cycle stability.

[0034] 3、The application provides a preparation method of a high-entropy sodium battery positive electrode material, wherein the preparation method comprises the following steps: S1, mixing a sodium source, a Ni ɑ Fe β Mn γ Zn ε Ti δ (OH)2 precursor, a zinc source, a titanium source and a dopant to perform first sintering, to obtain a first sintered product; the Ni ɑ Fe β Mn γ Zn ε Ti δ(OH)2 precursor, wherein 0.25≤ɑ≤0.35, 0.25≤β≤0.40, 0.25≤γ≤0.35, 0≤ε≤0.02, 0≤δ≤0.02; ɑ+β+γ+ε+δ=1; the first sintering includes three respective independent temperature rising stages of a first stage, a second stage and a third stage and a fourth stage of temperature falling; in the first stage, the temperature is raised to 400-550 DEG C at a speed of 1-5 DEG C / min; in the second stage, the temperature is raised to 750-850 DEG C at a speed of 1-5 DEG C / min; in the third stage, the temperature is raised to 950-1050 DEG C at a speed of 1-5 DEG C / min; S2, the first sintered product and the coating agent are mixed to carry out the second sintering to obtain the high-entropy sodium battery positive electrode material; the specific precursor, the zinc source and the titanium source in the application can optimize the electrochemical performance of the battery prepared from the high-entropy sodium battery positive electrode material in terms of specific capacity and cycle, the specific process of the first sintering independently raises the temperature in different stages, improves the crystal structure stability and electrochemical performance of the high-entropy sodium battery positive electrode material, and avoids damage or excessive reaction of the high-entropy sodium battery positive electrode material in the preparation process due to excessively high temperature.

[0035] 4、In the application, the specific content of the precursor is generally prepared by coprecipitation, and the coprecipitation reaction is not easy to control when Fe is excessive in the preparation process, so the iron source is further added in step S1 to further adjust the content of iron in the final product, and the addition of the iron source can also optimize the single crystal morphology.

[0036] 5、In the application, the specific temperature rising, holding temperature and time of the first sintering can further reduce the internal structure defects of the high-entropy sodium battery positive electrode material, eliminate the excessive expansion and shrinkage of the crystal lattice caused by internal stress, reduce the generation of microcracks, and further improve the cycle stability of the high-entropy sodium battery positive electrode material. BRIEF DESCRIPTION OF DRAWINGS

[0037] In order to more clearly illustrate the specific embodiments of the application or the technical solutions in the prior art, the drawings needed in the following specific embodiments or prior art description will be briefly introduced. Obviously, the drawings in the following description are some embodiments of the application, and other drawings can also be obtained by those skilled in the art without creative labor.

[0038] Figure 1 It is the SEM picture of the high-entropy sodium battery positive electrode material of Example 1;

[0039] Figure 2 It is the XRD spectrum of the high-entropy sodium battery positive electrode material of Example 1;

[0040] Figure 3 It is the SEM picture of the sodium battery positive electrode material of Comparative Example 1;

[0041] Figure 4is the XRD pattern of the sodium battery cathode material of Comparative Example 1;

[0042] Figure 5 is the specific capacity-discharge voltage graph of the high-entropy sodium battery cathode material of Example 1 and the sodium battery cathode material of Comparative Example 1;

[0043] Figure 6 is the cycle number-capacity retention rate graph of the high-entropy sodium battery cathode material of Example 1 and the sodium battery cathode material of Comparative Example 1;

[0044] Figure 7 is the air stability test column chart of the high-entropy sodium battery cathode material of Example 1 and the sodium battery cathode material of Comparative Example 1. DETAILED DESCRIPTION

[0045] The following examples are provided to better enable those skilled in the art to further understand the application, and are not intended to limit the content and scope of the application. Any person skilled in the art, under the guidance of the present application or by combining the present application with other prior art features, can obtain any product that is the same or similar to the present application, which falls within the scope of protection of the present application.

[0046] Unless specific experimental steps or conditions are specified in the examples, the operation or conditions can be carried out according to the conventional experimental steps described in the literature in the art. The reagents or instruments used are not specified by the manufacturer, and are conventional reagent products that can be obtained by purchase.

[0047] Example 1

[0048] The present embodiment provides a preparation method of a high-entropy sodium battery cathode material, comprising the following steps:

[0049] Preparation of the precursor

[0050] NiSO4, FeSO4and MnSO4(all in terms of metal elements) were dissolved in water in a molar ratio of 0.3:0.4:0.3 to obtain a mixed metal-containing solution with a total metal ion concentration of 2.5 mol / L, an ammonia solution with a concentration of 25 wt% was prepared, and a NaOH solution with a concentration of 2 mol / L was prepared; under a nitrogen atmosphere with a nitrogen flow rate of 4 L / min, the above-mentioned mixed metal-containing solution and ammonia solution were introduced into a reaction kettle at a flow rate of 10 L / h and 5 L / h, respectively, for co-precipitation reaction, the reaction temperature was controlled at 60°C, the pH of the reaction system was controlled at 10.2 by adding NaOH solution, and the reaction was carried out for 12 h. After filtration, washing and drying, a Ni 0.3 Fe 0.4 Mn 0.3 (OH)2precursor was obtained.

[0051] S1, Na2CO3and Ni0.3 Fe 0.4 Mn 0.3 (OH)2precursor, ZnO, TiO2and Sb2O5(all in metal elements) were mixed uniformly in a molar ratio of Na:Ni:Fe:Mn:Zn:Ti:Sb of 1:0.28:0.38:0.28:0.03:0.03:0.002, and then first sintering was performed in an air atmosphere: first stage, temperature was raised to 500°C at a rate of 2°C / min and maintained for 2h; second stage, temperature was raised to 800°C at a rate of 2°C / min and maintained for 4h; third stage, temperature was raised to 1000°C at a rate of 2°C / min and maintained for 8h; fourth stage, temperature was lowered to 900°C and maintained for 10h, and then the furnace was naturally cooled to room temperature. After crushing and sieving, NaNi 0.28 Fe 0.38 Mn 0.28 Zn 0.03 Ti 0.03 Sb 0.002 O2one-shot product was obtained.

[0052] S2, NaNi 0.28 Fe 0.38 Mn 0.28 Zn 0.03 Ti 0.03 Sb 0.002 O2one-shot product was mixed with coating agent TiO2and ZrO2, the mass percentage of TiO2was 0.5wt% and the mass percentage of ZrO2was 0.5wt% based on the mass of the one-shot product. After uniform mixing, the mixture was heated to 600°C at a rate of 2°C / min and maintained for 6h in an air atmosphere, and then cooled to room temperature. After sieving and removing iron, a high-entropy sodium electric positive electrode material was obtained, and the composition of the matrix was NaNi 0.28 Fe 0.38 Mn 0.28 Zn 0.03 Ti 0.03 Sb 0.002 O2. The SEM image of the high-entropy sodium electric positive electrode material is shown in Figure 1 , from which it can be seen that the particle size of the high-entropy sodium electric positive electrode material is uniform, has good dispersibility, and has a smooth surface. The XRD pattern is shown in Figure 2 , from which it can be seen that the high-entropy sodium electric positive electrode material prepared is a standard O3 phase.

[0053] Example 2

[0054] The present embodiment provides a preparation method of a high-entropy sodium electric positive electrode material, comprising the following steps:

[0055] Preparation of precursor

[0056] NiSO4, FeSO4 and MnSO4 (all in terms of metal elements) are dissolved in water in a molar ratio of 0.33:0.33:0.33 to obtain a mixed metal-containing solution with a total metal ion concentration of 3 mol / L, an ammonia solution with a concentration of 30 wt% is prepared, and a NaOH solution with a concentration of 3 mol / L is prepared; in a nitrogen atmosphere, the flow rate of nitrogen is 3 L / min, the mixed metal-containing solution, the ammonia solution, and the NaOH solution are introduced into the reactor at a flow rate of 8 L / h and 4 L / h, respectively, to carry out a co-precipitation reaction, the reaction temperature is controlled at 55°C, the pH of the reaction system is controlled at 10.3 by adding the NaOH solution, the reaction is carried out for 10 h, and then filtration, washing and drying are carried out to obtain a Ni 0.33 Fe 0.33 Mn 0.33 (OH)2 precursor;

[0057] S1, Na2CO3 and Ni 0.33 Fe 0.33 Mn 0.33 (OH)2 precursor, ZnO, TiO2, Fe2O3 and Sb2O5 (all in terms of metal elements) are uniformly mixed in a molar ratio of Na:Ni:Fe:Mn:Zn:Ti:Cu 0.95:0.25:0.40:0.25:0.05:0.05:0.005, and then a first sintering is carried out in an air atmosphere: in the first stage, the temperature is raised to 550°C at a rate of 5°C / min and kept for 3 h; in the second stage, the temperature is raised to 750°C at a rate of 5°C / min and kept for 3 h; in the third stage, the temperature is raised to 950°C at a rate of 5°C / min and kept for 10 h; in the fourth stage, the temperature is lowered to 850°C and kept for 15 h, and then the temperature is naturally lowered to room temperature, and then the product is crushed and sieved to obtain a Na 0.95 Ni 0.25 Fe 0.40 Mn 0.25 Zn 0.05 Ti 0.05 Cu 0.005 O2 sintered product;

[0058] S2, the Na 0.95 Ni 0.25 Fe 0.40 Mn 0.25 Zn 0.05 Ti 0.05 Cu 0.005 O2 sintered product is mixed with a coating agent CaCO3, the mass percentage of CaCO3 is 1 wt% based on the mass of the sintered product, and then uniformly mixed, and then the temperature is raised to 800°C at a rate of 5°C / min and kept for 4 h in an air atmosphere, and then cooled to room temperature, and then sieved and iron is removed to obtain a high-entropy sodium electric positive electrode material, and the composition of the matrix is Na 0.95 Ni 0.25 Fe0.40 Mn 0.25 Zn 0.05 Ti 0.05 Cu 0.005 O2.

[0059] Example 3

[0060] The embodiment provides a preparation method of a high-entropy sodium electric positive electrode material, and comprises the following steps:

[0061] Preparation of the precursor

[0062] NiSO4, FeSO4, MnSO4, ZnSO4 and TiOSO4 (all in terms of metal elements) are dissolved into water in a molar ratio of 0.29:0.38:0.29:0.02:0.02 to obtain a mixed metal-containing solution with a total metal ion concentration of 2 mol / L, an ammonia solution with a concentration of 20 wt% is prepared, and a NaOH solution with a concentration of 2 mol / L is prepared; in a nitrogen atmosphere, the flow rate of nitrogen is 5 L / min, the mixed metal-containing solution and the ammonia solution are introduced into a reaction kettle for a co-precipitation reaction at a flow rate of 12 L / h and 6 L / h respectively, the reaction temperature is controlled to be 60 DEG C, the pH of the reaction system is controlled to be 10.3 by adding NaOH, the reaction is performed for 15 h, and after filtration, washing and drying, a Ni 0.29 Fe 0.38 Mn 0.29 Zn 0.02 Ti 0.02 (OH)2 precursor is obtained.

[0063] S1, Na2CO3 and Ni 0.29 Fe 0.38 Mn 0.29 Zn 0.02 Ti 0.02 (OH)2 precursor, MoO3 and SnO2 (all in terms of metal elements) are uniformly mixed in a molar ratio of 1.05:0.29:0.38:0.29:0.02:0.02:0.002:0.002, and then first sintering is performed in an air atmosphere: in the first stage, the temperature is increased to 400 DEG C at a speed of 1 DEG C / min and kept for 2 h; in the second stage, the temperature is increased to 800 DEG C at a speed of 1 DEG C / min and kept for 4 h; in the third stage, the temperature is increased to 1000 DEG C at a speed of 1 DEG C / min and kept for 8 h; in the fourth stage, the temperature is decreased to 900 DEG C and kept for 10 h, and then the temperature is naturally decreased to room temperature along with the furnace temperature, and after crushing and sieving, a Na 1.05 Ni 0.29 Fe 0.38 Mn 0.29 Zn 0.02 Ti 0.02 Mo 0.002 Sn 0.002O2 - calcined product;

[0064] S2, mixing the Na 1.05 Ni 0.29 Fe 0.38 Mn 0.29 Zn 0.02 Ti 0.02 Mo 0.002 Sn 0.002 O2 - calcined product with coating agent Al2O3, the mass percentage of Al2O3 in the calcined product is 0.5wt%, after mixing uniformly, the temperature is raised to 500℃ at a speed of 2℃ / min under air atmosphere, and the temperature is kept for 6h, then the temperature is cooled to room temperature, sieved and de-ironed, to obtain a high-entropy sodium battery positive electrode material, the composition of the matrix is Na 1.0 5Ni 0.29 Fe 0.38 Mn 0.29 Zn 0.02 Ti 0.02 Mo 0.002 Sn 0.002 O2.

[0065] Example 4

[0066] The embodiment provides a preparation method of a high-entropy sodium battery positive electrode material, comprising the following steps:

[0067] Preparation of the precursor

[0068] NiSO4, FeSO4 and MnSO4 (all in terms of metal elements) are dissolved in water in a molar ratio of 0.3:0.4:0.3 to obtain a mixed metal-containing solution with a total metal ion concentration of 2.5mol / L, an ammonia solution with a concentration of 25wt% is prepared, and a NaOH solution with a concentration of 2mol / L is prepared; under a nitrogen atmosphere, the flow rate of nitrogen is 4L / min, the mixed metal-containing solution and the ammonia solution are introduced into a reaction kettle for co-precipitation reaction at a flow rate of 10L / h and 5L / h respectively, the reaction temperature is controlled to be 60℃, the pH of the reaction system is controlled to be 10.2 by adding the NaOH solution, the reaction is carried out for 12h, and then filtration, washing and drying are performed to obtain a Ni 0.3 Fe 0.4 Mn 0.3 (OH)2 precursor;

[0069] S1, mixing Na2CO3 and Ni 0.3 Fe 0.4 Mn 0.3The Na2CO3, Ni(NO3)2.9H2O, Fe(NO3)3.9H2O, Mn(NO3)2.4H2O, Zn(NO3)2.6H2O, TiO2 and Sb2O5 (all in terms of metal elements) are mixed uniformly in a molar ratio of Na:Ni:Fe:Mn:Zn:Ti:Sb = 1.02:0.25:0.40:0.25:0.06:0.06:0.004, and then first sintering is performed in an air atmosphere: first stage, temperature is raised to 500°C at a speed of 2°C / min and kept for 2h; second stage, temperature is raised to 800°C at a speed of 2°C / min and kept for 4h; third stage, temperature is raised to 1000°C at a speed of 2°C / min and kept for 8h; fourth stage, temperature is lowered to 900°C and kept for 10h, and then the furnace is naturally cooled to room temperature, and after crushing and sieving, a Na 1.02 Ni 0.25 Fe 0.40 Mn 0.25 Zn 0.06 Ti 0.06 Sb 0.004 O2 first sintered product is obtained.

[0070] S2, in the manner of step S2 in Example 1, a high-entropy sodium battery positive electrode material is obtained, and the composition of the substrate is Na 1.02 Ni 0.25 Fe 0.40 Mn 0.25 Zn 0.06 Ti 0.06 Sb 0.004 O2.

[0071] Example 5

[0072] The embodiment provides a preparation method of a high-entropy sodium battery positive electrode material, comprising the following steps:

[0073] In the manner of Example 1, except that in step S1, TiO2 is replaced by TiCl4, and Sb2O5 is replaced by SbCl3, and the molar amount of TiCl4 is equal to that of TiO2, and the molar amount of Sb2O5 is equal to that of SbCl3.

[0074] Example 6

[0075] The embodiment provides a preparation method of a high-entropy sodium battery positive electrode material, comprising the following steps:

[0076] In the manner of Example 1, except that in step S1, Na2CO3 and Ni 0.3 Fe 0.4 Mn 0.3The (OH)2precursor, ZnO, TiO2, and Sb2O5(all in terms of metal elements) are uniformly mixed in a molar ratio of Na:Ni:Fe:Mn:Zn:Ti:Sb of 1.0:0.28:0.38:0.28:0.03:0.03:0.005 to obtain a high-entropy sodium battery positive electrode material, and the composition of the substrate is NaNi 0.28 Fe 0.38 Mn 0.28 Zn 0.03 Ti 0.03 Sb 0.005 O2.

[0077] Comparative Example 1

[0078] The present comparative example provides a preparation method of a sodium battery positive electrode material, comprising the following steps:

[0079] NiSO4, FeSO4, and MnSO4(all in terms of metal elements) are dissolved in water in a molar ratio of 0.33:0.33:0.33 to obtain a mixed metal-containing solution with a total metal ion concentration of 2.5 mol / L, an ammonia solution with a concentration of 25 wt% is prepared, and a NaOH solution with a concentration of 2 mol / L is prepared; in a nitrogen atmosphere, the flow rate of nitrogen is 4 L / min, the mixed metal-containing solution, the ammonia solution, and the NaOH solution are introduced into the reactor at a flow rate of 10 L / h, 5 L / h, and 5 L / h respectively, the reaction temperature is controlled at 60°C, the pH of the reaction system is controlled at 10.2 by adding NaOH, and the reaction is carried out for 12 h; after filtration, washing, and drying, NaNi 0.33 Fe 0.33 Mn 0.33 (OH)2precursor is obtained.

[0080] S1, Na2CO3 and Ni 0.33 Fe 0.33 Mn 0.33 The (OH)2precursor (all in terms of metal elements) is uniformly mixed in a molar ratio of Na:Ni:Fe:Mn of 1:0.33:0.33:0.33, and then first sintering is carried out in an air atmosphere: first stage, heating to 500°C at a rate of 2°C / min and maintaining for 2 h; second stage, heating to 800°C at a rate of 2°C / min and maintaining for 4 h; third stage, heating to 1000°C at a rate of 2°C / min and maintaining for 8 h; fourth stage, cooling to 900°C and maintaining for 10 h, and then naturally cooling to room temperature with the furnace temperature, and then crushing and sieving to obtain NaNi 0.33 Fe 0.33 Mn 0.33 O2sintered product.

[0081] S2, NaNi 0.33 Fe0.33 Mn 0.33 The calcined product was mixed with coating agents TiO2 and ZrO2, with the mass percentages of TiO2 and ZrO2 being 0.5 wt% and 0.5 wt% respectively, based on the mass of the calcined product. After uniform mixing, the mixture was heated to 600℃ at a rate of 2℃ / min and held for 6 hours in air. After cooling to room temperature, the mixture was sieved and iron was removed to obtain the sodium-ion battery cathode material. The matrix composition was NaNi. 0.33 Fe 0.33 Mn 0.33 SEM images of O2 and sodium-ion cathode materials are shown below. Figure 3 As shown in the figure, it can be seen that the particle size of the cathode material varies greatly, its dispersibility is poor, and there are tiny particles attached to the surface. The XRD pattern is as follows. Figure 4 As shown in the figure, the prepared sodium-ion cathode material has a distinct NiO impurity phase.

[0082] Comparative Example 2

[0083] This comparative example provides a method for preparing a sodium-ion battery cathode material, comprising the following steps:

[0084] The method is the same as in Example 1, except that in step S1, Na2CO3 and Ni are... 0.30 Fe 0.40 Mn 0.30 (OH)₂ precursors (based on metal elements) were mixed uniformly in a molar ratio of Na:Ni:Fe:Mn of 1:0.30:0.40:0.30 to obtain sodium-ion cathode material. The matrix composition was NaNi. 0.30 Fe 0.40 Mn 0.30 O2.

[0085] Comparative Example 3

[0086] This comparative example provides a method for preparing a sodium-ion battery cathode material, comprising the following steps:

[0087] The method is the same as in Example 1, except that in step S1, Na2CO3 and Ni are... 0.3 Fe 0.4 Mn 0.3 (OH)₂ precursor, ZnO, and Sb₂O₅ (all based on metal elements) were mixed uniformly in a molar ratio of Na:Ni:Fe:Mn:Zn:Sb of 1:0.29:0.39:0.29:0.03:0.002 to obtain a sodium-ion cathode material with a matrix composition of NaNi. 0.29 Fe 0.39 Mn 0.29 Zn 0.03 Sb 0.002 O2.

[0088] Comparative Example 4

[0089] The present comparative example provides a preparation method of a sodium battery cathode material, comprising the following steps:

[0090] In the manner of Example 1, except that in step S1, Na2CO3 and Ni 0.3 Fe 0.4 Mn 0.3 (OH)2precursor, TiO2and Sb2O5(all in terms of metal elements) are uniformly mixed in a molar ratio of Na:Ni:Fe:Mn:Ti:Sb of 1:0.29:0.39:0.29:0.03:0.002 to obtain a sodium battery cathode material, and the composition of the matrix is NaNi 0.29 Fe 0.39 Mn 0.29 Ti 0.03 Sb 0.002 O2.

[0091] Comparative Example 5

[0092] The present comparative example provides a preparation method of a sodium battery cathode material, comprising the following steps:

[0093] In the manner of Example 1, except that in step S1, Na2CO3 and Ni 0.3 Fe 0.4 Mn 0.3 (OH)2precursor, ZnO, TiO2(all in terms of metal elements) are uniformly mixed in a molar ratio of Na:Ni:Fe:Mn:Zn:Ti of 1:0.28:0.38:0.28:0.03:0.03 to obtain a sodium battery cathode material, and the composition of the matrix is NaNi 0.28 Fe 0.38 Mn 0.28 Zn 0.03 Ti 0.03 O2.

[0094] Comparative Example 6

[0095] The present comparative example provides a preparation method of a high-entropy sodium battery cathode material, comprising the following steps:

[0096] In the manner of Example 1, except that the addition amount of ZnO and TiO2is adjusted to obtain a high-entropy sodium battery cathode material, and the composition of the matrix is NaNi 0.25 Fe 0.30 Mn 0.25 Zn 0.1 Ti 0.1 Sb 0.002 O2.

[0097] Comparative Example 7

[0098] The present comparative example provides a preparation method of a high-entropy sodium battery cathode material, comprising the following steps:

[0099] According to the manner of Example 1, the only difference is that NaNi 0.28 Fe 0.38 Mn 0.28 Zn 0.03 Ti 0.03 Sb 0.002 O2after calcination without step S2, a high-entropy sodium battery cathode material is obtained, and the composition of the matrix is NaNi 0.28 Fe 0.38 Mn 0.28 Zn 0.03 Ti 0.0 3Sb 0.002 O2.

[0100] Comparative Example 8

[0101] The present comparative example provides a preparation method of a sodium battery cathode material, comprising the following steps:

[0102] According to the manner of Example 1, the only difference is that in step S1, the first sintering is carried out in an air atmosphere: the first stage is to heat to 500°C at a speed of 2°C / min and keep for 4h; the second stage is to heat to 1000°C at a speed of 2°C / min and keep for 8h, a high-entropy sodium battery cathode material is obtained, and the matrix is the same as that of Example 1.

[0103] Test Example

[0104] Preparation method of CR2032 button cell: the material (high-entropy sodium battery cathode material or sodium battery cathode material) prepared in the examples and comparative examples is used as the positive active material, and polyvinylidene fluoride and carbon black are added in a mass ratio of 95:2.5:2.5, N-methyl pyrrolidone (NMP) is added, and the positive electrode slurry is obtained by mixing, the solid content of the positive electrode slurry is 52%, the positive electrode slurry is uniformly coated, the compaction density of the electrode sheet is 3.2 g / cm 3 , the electrode sheet is made, a lithium metal sheet is used as the counter electrode, a glass fiber is used as the separator, a 1 mol / L lithium hexafluorophosphate ethylene carbonate (EC) and dimethyl carbonate (DMC) solution (the volume ratio of EC to DMC is 1:1) is used as the electrolyte, a CR2032 button cell is assembled in an argon-filled glove box, and the electrical performance is tested in a blue cell test system.

[0105] Test method of charge and discharge capacity: the battery is charged to 4.0V at a rate of 0.1C, and the 0.1C charge specific capacity is obtained according to the battery mass; then discharged to 2.0V at a rate of 0.1C, and the 0.1C discharge specific capacity is obtained according to the battery mass.

[0106] The test method of capacity retention rate: at 25 DEG C, the battery is charged to 4.0V at 1C rate, then discharged to 2.0V at 1C rate, and cycled for 50 times, the capacity retention rate of the 50th cycle = the discharge capacity of the 50th cycle / the discharge capacity of the 1st cycle) * 100%.

[0107] 0.1C discharge energy density = 0.1C discharge specific capacity * discharge voltage at 0.1C, which can be directly read by the blue test software.

[0108] The test results are shown in Table 1;

[0109] Table 1

[0110]

[0111] From the data in the table, it can be seen that the high-entropy sodium electrode material prepared in the application has excellent charge and discharge capacity and cycle performance, the 0.1C charge specific capacity is greater than 160 mAh / g, and the capacity retention rate after 50 cycles is greater than 90%. Ni and Fe are used as main active elements, and the specific capacity is improved by the multi-electron reaction of the double active elements Ni 2+ / Ni 3+ / Ni 4+ , Fe 3+ / Fe 4+ , and the interlayer spacing is expanded by a small amount of non-active elements Zn and Ti, which accelerates the diffusion of sodium ions and inhibits the Jahn-Teller distortion of Mn 3+ , stabilizes the crystal structure, and further activates the Ni / Fe ion redox activity; the dopant enhances the electronic conductivity and reduces the interface impedance.

[0112] In comparison, in Comparative Example 1, the traditional NaNi 0.33 Fe 0.33 Mn 0.33 O2 material has a charge specific capacity of only 152.3mAh / g, and a capacity retention rate of only 70.3%, and has poor performance. After increasing the amount of Fe, the specific capacity of the electrode material in Comparative Example 2 is increased, but the Jahn-Teller distortion of Fe 3+ is serious, which affects the structural stability of the material, and the capacity retention rate is only 67.1%. In addition, single Zn or Ti doping or no Sb, Mo, Cu, Sn and other element doping, although the specific capacity and cycle performance are improved, it is difficult to achieve the optimal performance, and excessive Zn or Ti doping will also reduce the battery performance, and only Ti or Cu single element doping electrode material, although the specific capacity and cycle performance are improved, but it cannot meet the needs; in Comparative Example 5, excessive Ti is added, and during the charge and discharge process, Na +It is difficult to fully exfoliate, and the capacity gradually decays. In addition, the coating layer can isolate the active material from reacting with the electrolyte, thereby improving the cycle stability of the material.

[0113] The first sintering process is a specific temperature rising sintering process, which can reduce lattice stress and promote uniform distribution of elements. In Comparative Example 8, the material generates more internal stress due to improper sintering process, which is prone to deformation during charging and discharging, thereby damaging the cycle performance of the material.

[0114] From Figure 5 It can be seen that, under the same discharge voltage, the high-entropy sodium battery positive electrode material in Example 1 has higher specific capacity and voltage than Comparative Example 1; which means that the energy density of Example 1 is greater; and Comparative Example 1 has a clear discharge platform at 2.5V, which often accompanies the occurrence of irreversible phase transition of the material, which means that the structural reversibility of Comparative Example 1 is poor.

[0115] From Figure 6 It can be seen that, after 50 cycles, the capacity retention rate of the high-entropy sodium battery positive electrode material in Example 1 is still above 90%, while the capacity retention rate of the sodium battery positive electrode material in Comparative Example 1 is only about 70% after 50 cycles.

[0116] Air stability test method: The positive electrode materials prepared in the examples and comparative examples are tested for moisture content at a temperature of 25°C and an air humidity of 40% using a Karl Fischer moisture meter, and the moisture content is tested at the time of placement (0 days), 3 days, 5 days, 7 days and 14 days.

[0117] From Figure 7 It can be seen that, compared with Comparative Example 1, the high-entropy sodium battery positive electrode material in Example 1 has less increase in moisture content after being placed at a temperature of 25°C and an air humidity of 40% for 14 days. The moisture content of Example 1 is only 2037ppm, which is much lower than 3576ppm in Comparative Example 1, showing excellent air stability.

[0118] Obviously, the above examples are merely examples for clarity and do not limit the embodiments. For those skilled in the art, other different forms of changes or variations can be made on the basis of the above description. Here, it is not necessary and impossible to exhaust all embodiments. The obvious changes or variations derived therefrom are still within the protection scope of the present application.

Claims

1. A high-entropy sodium cathode material, characterized in that, The high-entropy sodium-ion cathode material includes a matrix and a coating layer covering the matrix; The matrix has the general formula Na. x Ni a Fe b Mn c Zn d Ti e L p O2, wherein 0.95≤x≤1.10, 0.25≤a≤0.35, 0.25≤b≤0.40, 0.25≤c≤0.35, 0<d≤0.06, 0<e≤0.06, 0.001≤p≤0.003, a+b+c+d+e=1, and L includes at least one of Cu, Mo, Sb, Sn, Nb, and Li.

2. The high-entropy sodium cathode material according to claim 1, characterized in that, The matrix has the general formula Na. x Ni a Fe b Mn c Zn d Ti e L p O2, where 1.00≤x≤1.05, 0.25≤a≤0.30, 0.35≤b≤0.40, 0.25≤c≤0.30, 0.03≤d≤0.05, 0.03≤e≤0.05, a+b+c+d+e=1; And / or, the coating layer comprises a metal oxide.

3. A method for preparing the high-entropy sodium cathode material as described in claim 1 or 2, characterized in that, The preparation method includes the following steps: S1, sodium source, Ni ɑ Fe β Mn γ Zn ε Ti δ The (OH)2 precursor, zinc source, titanium source, and dopant are mixed and then subjected to a first sintering to obtain a sintered product; The Ni ɑ Fe β Mn γ Zn ε Ti δ In the (OH)2 precursor; 0.25≤ɑ≤0.35, 0.25≤β≤0.40, 0.25≤γ≤0.35, 0≤ε≤0.02, 0≤δ≤0.02; ɑ+β+γ+ε+δ=1; The first sintering includes three independent heating stages: a first stage, a second stage, and a third stage, and a fourth stage of cooling. In the first stage, the temperature is increased to 400-550℃ at a rate of 1-5℃ / min; in the second stage, the temperature is increased to 750-850℃ at a rate of 1-5℃ / min; and in the third stage, the temperature is increased to 950-1050℃ at a rate of 1-5℃ / min. S2, after mixing the first sintered product and the coating agent, a second sintering is carried out to obtain a high-entropy sodium cathode material.

4. The preparation method according to claim 3, characterized in that, Sodium source, Ni ɑ Fe β Mn γ Zn ε Ti δ The (OH)2 precursor, zinc source, titanium source, iron source, and dopant are mixed and then subjected to a first sintering to obtain a sintered product.

5. The preparation method according to claim 3 or 4, characterized in that, The dopant includes at least one of the following: Cu oxide, Cu sulfate, Cu chloride, Mo oxide, Mo sulfate, Mo chloride, Sb oxide, Sb sulfate, Sb chloride, Sn oxide, Sn sulfate, Sn chloride, Nb oxide, Nb sulfate, Nb chloride, Li oxide, Li sulfate, Li chloride, Li hydrochloride, and Li carbonate.

6. The preparation method according to claim 5, characterized in that, The dopant includes at least one of the following: Cu oxide, Mo oxide, Sb oxide, Sn oxide, Nb oxide, Li hydroxide, and Li carbonate.

7. The preparation method according to claim 3, characterized in that, The conditions for the first sintering include: a first stage, heating to 400-550℃ at a rate of 1-5℃ / min and holding for 2-5 hours; a second stage, heating to 750-850℃ at a rate of 1-5℃ / min and holding for 2-5 hours; a third stage, heating to 950-1050℃ at a rate of 1-5℃ / min and holding for 5-10 hours; and a fourth stage, cooling to 800-950℃ at a rate of 2-5℃ / min and holding for 8-15 hours, followed by natural cooling to room temperature.

8. The preparation method according to claim 3, characterized in that, The coating agent includes metal oxides and / or metal carbon oxides; And / or, based on the mass percentage of a calcined product, the coating agent is 0.5-3 wt%.

9. The preparation method according to claim 3, characterized in that, The second sintering conditions include: heating to 400-800℃ at a rate of 1-5℃ / min and holding at that temperature for 3-8 hours.

10. A secondary battery, characterized in that, The secondary battery comprises the high-entropy sodium-ion cathode material as described in claim 1 or 2, or the high-entropy sodium-ion cathode material prepared by the preparation method described in any one of claims 3-9.

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