Sodium-ion battery positive electrode material with high-entropy superlattice structure and preparation method of sodium-ion battery positive electrode material

Abstract

The invention relates to the technical field of battery materials, in particular to a sodium-ion battery positive electrode material with a high-entropy superlattice structure and a preparation method of the sodium-ion battery positive electrode material, and the general formula of the sodium-ion battery positive electrode material is Na < 0.67 > MnaNibFecLidCueTifO2, a < lt >; 0.6, 0.1 lt; blt; 0.3, 0.01 lt, 0.01 lt, 0.01 lt; clt; ct; 0, 0.2, 0.03 lt; dlt; 0, 0.2, 0.03 lt; lt, lt; 0.2, 0.01 lt, 0.01 lt, 0.01 lt; flt; 0.2, a + b + c + d + e + f = 1; according to the invention, a plurality of ions with similar sizes are introduced into the sodium ion layered oxide transition metal layer, so that a short-range disordered honeycomb-shaped high-entropy superlattice structure is formed; by means of the hysteresis diffusion effect of the high-entropy material, the oxidation-reduction reaction of oxygen anions activated by lithium is effectively regulated and controlled, and the phenomena of voltage decline and structure degradation caused by the migration process of manganese ions in the transition metal layer are inhibited.

Description

Technical Field

[0001] The present invention relates to the technical field of battery materials, and particularly to a cathode material for a sodium-ion battery with a high-entropy superlattice structure and a preparation method thereof. Background Art

[0002] With the continuous growth of global energy demand and the strengthening of environmental protection awareness, the utilization of renewable energy has received increasing attention. However, existing lithium-ion batteries have certain limitations in terms of resource distribution, cost, and environmental impact. Therefore, developing sodium-ion batteries with high performance, low cost, and environmental friendliness has become an important research direction for scientific researchers. The manganese-rich layered oxide has characteristics similar to the layered structure of the cathode material for lithium-ion batteries and can achieve reversible deintercalation and intercalation of sodium ions during charge and discharge processes. In addition, manganese is relatively abundant in the earth's crust, and the rich resources are conducive to cost reduction. Moreover, it has less impact on the environment during production and recycling processes, which is beneficial to sustainable development.

[0003] Although the manganese-rich layered oxide has many advantages, it still faces some challenges in practical applications, such as rapid capacity decay, structural changes, and phase transitions during cycling. Among them, the energy density of sodium-ion batteries is one of the key factors determining their practical application. Currently, the low specific capacity of the cathode material for sodium-ion batteries limits the improvement of the battery energy density. Therefore, exploring cathode materials with high specific capacity is of great significance for the early realization of large-scale industrialization of sodium-ion batteries. Research in recent years has shown that in some layered transition metal oxides, anionic oxygen can also participate in the electrochemical reaction process.

[0004] Therefore, the synergistic redox reaction based on transition metals and anionic oxygen provides the possibility to improve the specific capacity of layered cathode materials. In the manganese-rich layered oxide, the redox reaction of oxygen atoms has an important impact on the capacity and cycle stability of the battery. Generally, by introducing lithium elements to construct the Li-O-Na configuration, the redox reaction of oxygen anions can be activated. However, this approach will cause serious lattice oxygen loss problems in the high-voltage region of the layered oxide cathode material. The reason is the excessive oxidation of interlayer lattice oxygen and the irreversible migration of transition metals during the charging process. The serious loss of lattice oxygen will bring a series of problems.

[0005] First of all, the peroxide groups generated during high-voltage charging often cannot be effectively reduced back to lattice oxygen during discharge, and at the same time, lithium ions cannot migrate back to the transition metal (TM) layer position completely reversibly to form a stable interlayer structure. This situation will accelerate the degradation of the Li-O-TM configuration in the transition metal layer, thereby causing a serious attenuation of the capacity based on oxygen redox activity.

[0006] In addition, the loss of lattice oxygen and irreversible lithium migration will further exacerbate the irreversible migration of transition metal ions from the TM layer to the Na layer. At the same time, the in-layer migration of manganese will lead to the formation of a large number of oxygen clusters and vacancies. This process will further result in obvious structural rearrangement and drastic phase change, ultimately leading to the loss of lattice oxygen and the collapse of the layered structure, causing the energy density to rapidly decrease during the initial electrochemical cycle, resulting in a decline in battery performance and limiting its commercial application. Summary of the Invention

[0007] In order to solve the above technical problems, an embodiment of the present invention provides a cathode material for a sodium-ion battery with a high-entropy superlattice structure and a preparation method thereof.

[0008] To achieve the above object, the embodiments of the present invention adopt the following technical solutions:

[0009] On the one hand, the present invention provides a cathode material for a sodium-ion battery with a high-entropy superlattice structure, and the general formula of the cathode material for the sodium-ion battery is: Na 0.67 Mn a Ni b Fe c Li d Cu e Ti f O 2 , where

[0010] 0.3 < a < 0.6, 0.1 < b < 0.3, 0.01 < c < 0.2, 0.03 < d < 0.2, 0.03 < e < 0.2, 0.01 < f < 0.2, and a + b + c + d + e + f = 1.

[0011] In some embodiments, the cathode material for the sodium-ion battery is of the P2 type.

[0012] On the other hand, the present invention provides a preparation method for a cathode material for a sodium-ion battery, including the following steps:

[0013] Mix the sodium source, lithium source, iron source, nickel source, manganese source, copper source, and titanium source by ball milling uniformly, then press into tablets and calcine to obtain the cathode material for the sodium-ion battery.

[0014] In some embodiments, the molar ratio of the sodium source, manganese source, nickel source, iron source, lithium source, copper source, and titanium source is (6 - 7):(7 - 16):(2 - 6):(1 - 4):(1 - 4):(1 - 3):

[0015] (1 - 4).

[0016] In some embodiments, the sodium source includes NaOH, Na 2 CO 3 、Na 2 CO3 ·H 2 at least one of O;

[0017] The lithium source includes LiNO 3 , Li 2 CO 3 , LiOH·H 2 O; at least one of them;

[0018] The iron source includes FeO, Fe 2 O 3 , Fe 3 O 4 at least one of them;

[0019] The manganese source includes MnO, Mn(OH) 2 , MnO 2 , Mn 3 O 4 at least one of them;

[0020] The nickel source includes Ni(OH) 2 , NiO; at least one of them;

[0021] The copper source includes CuO, Cu 2 O; at least one of them;

[0022] The titanium source includes TiO 2 .

[0023] In some embodiments, the ball milling time is 12 - 20 h, and the sieving mesh size is 100 - 300 mesh.

[0024] In some embodiments, the pressure for tablet pressing is 10 - 50 MPa, and the thickness is 10 - 25 mm.

[0025] In some embodiments, the calcination temperature is 800 - 950 °C, and the heat preservation time is 10 - 15 h to obtain a single-phase P2-type structure.

[0026] In some embodiments, the heating rate of the calcination is 2 - 5 °C / min.

[0027] In some embodiments, the air humidity in the calcination atmosphere is lower than 35% to ensure that the product is not eroded by water vapor and other substances to occur side reactions.

[0028] Compared with the prior art, the present invention has at least the following beneficial effects:

[0029] In the present invention, by introducing a variety of ions with similar sizes into the transition metal layer of the sodium-ion layered oxide, a short-range disordered "honeycomb-like" high-entropy superlattice structure is formed. The "retarded diffusion" effect of the high-entropy material is utilized to effectively regulate the lithium-activated oxygen anion redox reaction and inhibit the voltage decay and structural degradation phenomena caused by the migration of manganese ions within the transition metal layer.

[0030] In the present invention, five 3d transition elements with similar sizes are utilized. Due to the obvious size difference between Li and the other introduced transition metal atoms, local short-range disordered superlattice units are formed at the microscopic atomic scale. At the same time, combined with the "retarded diffusion" effect of the high-entropy material, the problems of transition metal migration and lattice oxygen deficiency in the layered oxide at a relatively high charging voltage are fundamentally solved, and the structural stability of the positive electrode material for sodium-ion batteries is improved.

[0031] Among them, the transition metal sites TM in the synthesized high-entropy superlattice structure need to meet the following requirements:

[0032] Where R is the ideal gas constant, and x i represents the mole fraction of the i-component. The configurational entropy of the molecular transition metal composition system is calculated to satisfy 1.5R ≤ ΔS conf .

[0033] The present invention provides a method for using a high-entropy superlattice structure to solve the voltage decay and structural degradation generated during the lithium-activated oxygen anion redox reaction and the migration of manganese cations within the layer in the manganese-rich P2-type layered oxide. By introducing the high-entropy superlattice structure in the present invention, the retarded diffusion effect in the high-entropy material is utilized to effectively inhibit the in-layer migration of manganese, effectively inhibiting the phenomena of voltage decay and structural degradation of the layered oxide, improving the cycle stability and electrochemical performance of the material, and being applicable to electrochemical energy storage batteries such as high-performance sodium-ion batteries. The present invention designs and synthesizes a layered oxide positive electrode material with an inter-transition metal superlattice structure, improves the cycle stability of the material, and obtains a positive electrode material for sodium-ion batteries with excellent electrochemical performance through a simple and easy-to-implement preparation process combining ball milling and high-temperature solid-phase method, showing excellent comprehensive electrochemical performance, as well as a stable working voltage, excellent cycle stability, and being easy to scale up for industrial application, generating large-scale economic benefits. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 X-ray diffraction pattern of the high-entropy superlattice positive electrode material prepared in Example 1;

[0035] Figure 2 Charge and discharge curves of the high-entropy superlattice positive electrode material prepared in Example 1;

[0036] Figure 3Normalized average discharge voltage curve of the high-entropy superlattice cathode material prepared in Example 1 for the first 50 cycles;

[0037] Figure 4 Long cycle performance graph of the high-entropy superlattice cathode material prepared in Example 1;

[0038] Figure 5 In-situ oxygen partial pressure differential electrochemical mass spectrometry analysis graph of the high-entropy superlattice cathode material prepared in Example 1;

[0039] Figure 6 Charge and discharge curve graph of the high-entropy superlattice cathode material prepared in Example 2;

[0040] Figure 7 Cycle performance graph of the high-entropy superlattice cathode material prepared in Example 2;

[0041] Figure 8 Charge and discharge curve graph of the high-entropy superlattice cathode material prepared in Example 3;

[0042] Figure 9 Cycle performance graph of the high-entropy superlattice cathode material prepared in Example 3;

[0043] Figure 10 Charge and discharge curve graph of the high-entropy superlattice cathode material prepared in Example 4;

[0044] Figure 11 Cycle performance graph of the high-entropy superlattice cathode material prepared in Example 4;

[0045] Figure 12 Charge and discharge curve graph of the high-entropy superlattice cathode material prepared in Example 5;

[0046] Figure 13 Cycle performance graph of the high-entropy superlattice cathode material prepared in Example 5;

[0047] Figure 14 X-ray diffraction pattern of the non-high-entropy cathode material prepared in Comparative Example 1;

[0048] Figure 15 Charge and discharge curve graph of the non-high-entropy cathode material prepared in Comparative Example 1;

[0049] Figure 16 Normalized average discharge voltage curve graph of the non-high-entropy cathode material prepared in Comparative Example 1 for the first 50 cycles;

[0050] Figure 17 Cycle performance graph of the non-high-entropy cathode material prepared in Comparative Example 1;

[0051] Figure 18In-situ oxygen partial pressure differential electrochemical mass spectrometry analysis chart of the non-high-entropy cathode material prepared in Comparative Example 1. Detailed implementation manners

[0052] The technical solutions in some embodiments of the present disclosure will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the present disclosure, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments provided by the present disclosure fall within the protection scope of the present disclosure.

[0053] Example 1

[0054] (1) Synthesize the high-entropy superlattice cathode material Na 0.67 Mn 0.45 Ni 0.2 Fe 0.1 Li 0.07 Cu 0.05 Ti 0.13 O 2， Among them, the configurational entropy calculation of the transition metal sites in the synthesized high-entropy superlattice structure

[0055] S config =-R(0.2ln(0.2)+0.45ln(0.45)+0.1ln(0.1)+0.01ln(0.07)+0.05ln(0.05)+0.13ln(0.13)) = 1.51R ≥ 1.5R, which meets the definition of high entropy.

[0056] Weigh 0.75 g of anhydrous sodium carbonate, 0.78 g of manganese dioxide, 0.3 g of nickel oxide, 0.32 g of iron(III) oxide, 0.06 g of lithium hydroxide monohydrate, 0.08 g of copper oxide and 0.21 g of titanium dioxide in a molar ratio of 6.7:9:4:2:1.4:1:2.6, and pour them into a mortar in sequence for grinding and mixing evenly until the particle size reaches 200 mesh.

[0057] (2) Use a tablet press mold to press the above mixed raw materials into a powder tablet, and press it into a circular tablet with a diameter of 16 mm and a thickness of 10 mm under a pressure of 15 MPa, and transfer it to an alumina crucible.

[0058] (3) Place the alumina crucible in a tube furnace for calcination, heat it up at a rate of 5 °C / min, calcine it at 800 °C for 15 h, and the air humidity is 30%. After natural cooling, take out the active material tablet and immediately transfer it to a glove box for grinding into powder. The high-entropy superlattice cathode material Na 0.67 Mn 0.45 Ni 0.2 Fe 0.1 Li 0.07 Cu 0.05 Ti0.13 O 2 The X-ray powder diffraction test results of the material are as follows Figure 1 , the space group is P63 / mmc, the PDF card is JCPDS:#54-0894, and there are no impurities.

[0059] (4) To evaluate the electrochemical performance of the material, the electrode material was first assembled into a battery according to the following steps. The specific operation is as follows: taking the positive electrode material as the main component, mixing it according to the mass ratio of the conductive agent (acetylene black) and the binder (polyvinylidene fluoride PVDF) of 8:1:1, and using N-methylpyrrolidone NMP as the solvent to stir the mixture evenly. Subsequently, the mixture was coated on the aluminum foil and vacuum dried at 110 °C, and then cut into circular pieces with a diameter of 12 mm for use as the positive electrode plate. Metallic sodium was used as the negative electrode, and the glass fiber membrane was used as the separator material. The electrolyte was selected as 1.0 M NaClO 4 solution, in which 5 wt% of fluoroethylene carbonate (FEC) was added and used as the electrolyte for the sodium-ion battery. The entire battery assembly process was carried out in a glove box filled with argon.

[0060] (5) As Figure 2 shown, it has a relatively flat charge-discharge curve between 1.5 and 4.4 V, has a higher discharge platform compared with Comparative Example 1, and at the same time the capacity is also improved. Its normalized average discharge voltage curve is as Figure 3 shown, its discharge voltage hardly decays during 50 cycles, and the specific capacity cycle stability is as Figure 4 shown, at a rate of 100 mA g -1 , the initial discharge specific capacity is 149.5 mAh g -1 during long cycling, and it can still maintain 84.6% after 100 cycles, showing a significant improvement in cycle stability compared with non-high-entropy Comparative Example 1. At the same time, the Coulomb efficiency remains 99.3% during 100 cycles of long cycling, confirming its excellent electrochemical performance.

[0061] To illustrate its structural stability, Figure 5 in-situ oxygen partial pressure differential electrochemical mass spectrometry was used to analyze its charge-discharge process. During the entire initial voltage window of 1.5 V - 4.4 V, there is no significant change in oxygen partial pressure during the entire charge-discharge process, further confirming the structural stability of the high-entropy superlattice layered oxide during the sodium-ion insertion / extraction process.

[0062] Example 2

[0063] (1) Synthesis of the high-entropy superlattice positive electrode material Na 0.67 Mn 0.42 Ni 0.18 Fe 0.15 Li 0.05 Cu0.08 Ti 0.12 O 2， Calculation of configurational entropy of transition metal sites in the synthesized high-entropy superlattice structure

[0064] S config = -R(0.42ln(0.42) + 0.18ln(0.18) + 0.15ln(0.15) + 0.05ln(0.05) + 0.08ln(0.08) + 0.12ln(0.12)) = 1.56R ≥ 1.5R, which meets the definition of high entropy.

[0065] Weigh 0.75 g of anhydrous sodium carbonate, 0.73 g of manganese dioxide, 0.27 g of nickel oxide, 0.48 g of iron(III) oxide, 0.04 g of lithium hydroxide monohydrate, 0.13 g of copper oxide, and 0.19 g of titanium dioxide in a molar ratio of 6.7:8.4:3.6:3:1:1.6:2.4 and pour them into a mortar in sequence for grinding and mixing evenly until the particle size reaches 200 mesh.

[0066] (2) Use a tablet press mold to press the above mixed raw materials into a powder tablet, press it into a circular tablet with a diameter of 16 mm and a thickness of 20 mm under a pressure of 18 MPa, and transfer it to an alumina crucible.

[0067] (3) Place the alumina crucible in a tube furnace for calcination, heat it at a rate of 5 °C / min, calcine it at 900 °C for 15 h, and the air humidity is 30%. After natural cooling, take out the active material tablet and immediately transfer it to a glove box for grinding into powder. The high-entropy superlattice cathode material Na 0.67 Mn 0.42 Ni 0.18 Fe 0.15 Li 0.05 Cu 0.08 Ti 0.12 O 2 is obtained.

[0068] (4) To evaluate the electrochemical performance of the material, first assemble the electrode material into a battery according to the following steps. The specific operation is as follows: mainly using the cathode material, mix it with a conductive agent (acetylene black) and a binder (polyvinylidene fluoride PVDF) in a mass ratio of 8:1:1, and use N-methylpyrrolidone NMP as a solvent to stir the mixture evenly. Subsequently, coat the mixture on an aluminum foil and dry it under vacuum at 110 °C, and then cut it into a circular tablet with a diameter of 12 mm for use as the positive electrode plate. Metallic sodium is used as the negative electrode, and a glass fiber membrane is used as the separator material. The electrolyte is a 1.0 M NaClO 4 solution with 5 wt% fluoroethylene carbonate (FEC) added, which is used as the electrolyte of the sodium-ion battery. The entire battery assembly process is carried out in a glove box filled with argon.

[0069] (5) As Figure 6 shown, it has a relatively flat charge-discharge curve between 1.5 and 4.4 V, and the initial discharge specific capacity reaches 157.2 mAh g -1 . After 100 cycles of long-term cycling test, the discharge specific capacity remains 84.8%, showing a significant improvement compared with 52.3% of Comparative Example 1, which confirms its good cycle stability and further verifies the promoting effect of the high-entropy superlattice layered oxide on the electrochemical performance ( Figure 7 ).

[0070] Example 3

[0071] (1) Synthesize the high-entropy superlattice cathode material Na 0.67 Mn 0.45 Ni 0.15 Fe 0.12 Li 0.08 Cu 0.1 Ti 0.1 O 2， Among them, the configurational entropy of the transition metal sites in the synthesized high-entropy superlattice structure is calculated

[0072] S config =-R(0.42ln(0.42)+0.15ln(0.15)+0.12ln(0.12)+0.08ln(0.08)+0.1ln(0.1)+0.1ln(0.1)) = 1.56R ≥ 1.5R, which meets the definition of high entropy.

[0073] Weigh 0.75 g of anhydrous sodium carbonate, 0.96 g of manganese dioxide, 0.27 g of nickel oxide, 0.16 g of iron(III) oxide, 0.05 g of lithium hydroxide monohydrate, 0.11 g of copper oxide and 0.19 g of titanium dioxide in a molar ratio of 6.7:9:3:2.5:1.6:2:2, and pour them into a mortar in sequence for grinding and mixing evenly until the particle size reaches 200 mesh.

[0074] (2) Use a tablet press mold to press the above mixed raw materials into a powder tablet. Press it into a disc with a diameter of 16 mm and a thickness of 25 mm under a pressure of 15 MPa, and transfer it to an alumina crucible.

[0075] (3) Place the alumina crucible in a tube furnace for calcination. Heat it up at a rate of 5 °C / min and calcine it at 900 °C for 15 h with an air humidity of 30%. After natural cooling, take out the active material tablet and immediately transfer it to a glove box for grinding into powder. The obtained high-entropy superlattice cathode material Na 0.67 Mn 0.45 Ni 0.15 Fe 0.12 Li 0.08 Cu 0.1Ti 0.1 O 2 。

[0076] (4) To evaluate the electrochemical performance of the material, the electrode material was first assembled into a battery according to the following steps. The specific operation is as follows: taking the positive electrode material as the main component, mixing it according to the mass ratio of the conductive agent (acetylene black) to the binder (polyvinylidene fluoride PVDF) of 8:1:1, and using N-methylpyrrolidone NMP as the solvent to stir the mixture evenly. Subsequently, the mixture was coated on aluminum foil and vacuum dried at 110 °C, and then cut into circular sheets with a diameter of 12 mm for use as the positive electrode sheet. Metallic sodium was used as the negative electrode, and a glass fiber membrane was used as the separator material. The electrolyte was a 1.0 M NaClO 4 solution, in which 5 wt% of fluoroethylene carbonate (FEC) was added and used as the electrolyte for the sodium-ion battery. The entire battery assembly process was carried out in a glove box filled with argon.

[0077] (5) As Figure 8 shown, it has a relatively flat charge-discharge curve between 1.5 and 4.4 V, and the initial discharge specific capacity reaches 156.4 mAh g -1 . After 100 cycles of long-term cycling tests, the discharge specific capacity remained at 86.1%, showing a significant improvement compared to 52.3% of Comparative Example 1, confirming its good cycle stability and further confirming the promoting effect of the high-entropy superlattice layered oxide on the electrochemical performance ( Figure 9 ).

[0078] Example 4

[0079] (1) Synthesis of the high-entropy superlattice positive electrode material Na 0.67 Mn 0.48 Ni 0.17 Fe 0.1 Li 0.07 Cu 0.08 Ti 0.1 O 2， Among them, the configurational entropy of the transition metal sites in the synthesized high-entropy superlattice structure was calculated

[0080] S config = -R(0.48 ln(0.48) + 0.17 ln(0.17) + 0.1 ln(0.1) + 0.07 ln(0.07) + 0.08 ln(0.08) + 0.1 ln(0.1)) = 1.5R ≥ 1.5R, which meets the definition of high entropy.

[0081] Weigh 0.75 g of anhydrous sodium carbonate, 0.84 g of manganese dioxide, 0.26 g of nickel oxide, 0.32 g of iron(III) oxide, 0.06 g of lithium hydroxide monohydrate, 0.13 g of copper oxide and 0.16 g of titanium dioxide in a molar ratio of 6.7:9.6:3.4:2:1.4:1.6:2. Pour the samples into a mortar in sequence for grinding and mixing evenly until the particle size reaches 200 mesh.

[0082] (2) Use a tablet press mold to press the above mixed raw materials into a powder tablet. Press it into a circular tablet with a diameter of 16 mm and a thickness of 23 mm under a pressure of 18 MPa, and transfer it to an alumina crucible.

[0083] (3) Place the alumina crucible in a tube furnace for calcination. Heat it up at a rate of 5 °C / min and calcine it at 950 °C for 15 h with an air humidity of 30%. After natural cooling, take out the active material tablet and immediately transfer it to a glove box for grinding into powder. The high-entropy superlattice cathode material Na 0.67 Mn 0.48 Ni 0.17 Fe 0.1 Li 0.07 Cu 0.08 Ti 0.1 O 2 is obtained.

[0084] (4) To evaluate the electrochemical performance of the material, first assemble the electrode material into a battery according to the following steps. The specific operation is as follows: Take the cathode material as the main component, mix it with a conductive agent (acetylene black) and a binder (polyvinylidene fluoride PVDF) in a mass ratio of 8:1:1, and use N-methylpyrrolidone NMP as a solvent to stir the mixture evenly. Subsequently, coat the mixture on an aluminum foil and vacuum dry it at 110 °C, and then cut it into a circular piece with a diameter of 12 mm for use as the positive electrode plate. Metallic sodium is used as the negative electrode, and a glass fiber membrane is used as the separator material. The electrolyte is a 1.0 M NaClO 4 solution, in which 5 wt% of fluoroethylene carbonate (FEC) is added, and it is used as the electrolyte for the sodium-ion battery. The entire battery assembly process is carried out in a glove box filled with argon.

[0085] (5) As Figure 10 shown, it has a relatively flat charge-discharge curve between 1.5 and 4.4 V, and the initial discharge specific capacity reaches 162.7 mAh g -1 , showing a significant improvement compared to Comparative Example 1; the discharge specific capacity remains 82.3% after 100 cycles of long-term cycling tests, showing a significant improvement compared to 52.3% of Comparative Example 1, which confirms its good cycle stability and further confirms the improvement effect of the high-entropy superlattice layered oxide on the electrochemical performance ( Figure 11 ).

[0086] Example 5

[0087] (1) Synthesis of the high-entropy superlattice cathode material Na 0.67 Mn 0.48 Ni 0.15 Fe 0.12 Li 0.08 Cu 0.05 Ti 0.12 O 2， Among them, the configurational entropy calculation of the transition metal sites in the synthesized high-entropy superlattice structure

[0088] S config = -R(0.48ln(0.48) + 0.15ln(0.15) + 0.12ln(0.12) + 0.08ln(0.08) + 0.05ln(0.05) + 0.12ln(0.12)) = 1.5R ≥ 1.5R, which meets the definition of high entropy.

[0089] Weigh 0.75 g of anhydrous sodium carbonate, 0.84 g of manganese dioxide, 0.23 g of nickel oxide, 0.38 g of iron(III) oxide, 0.07 g of lithium hydroxide monohydrate, 0.08 g of copper oxide and 0.19 g of titanium dioxide in a molar ratio of 6.7:9.6:3:2.4:1.6:1:2.4, and pour them into a mortar in sequence for grinding and mixing evenly until the particle size reaches 200 mesh.

[0090] (2) Use a tablet press mold to press the above mixed raw materials into a powder tablet, and press it into a round tablet with a diameter of 16 mm and a thickness of 25 mm under a pressure of 35 MPa, and transfer it to an alumina crucible.

[0091] (3) Place the alumina crucible in a tube furnace for calcination, heat it up at a rate of 5 °C / min, calcine it at 900 °C for 15 h, and the air humidity is 30%. After natural cooling, take out the active material tablet and immediately transfer it to a glove box for grinding into powder. The high-entropy superlattice cathode material Na 0.67 Mn 0.48 Ni 0.15 Fe 0.12 Li 0.08 Cu 0.05 Ti 0.12 O 2 .

[0092] (4) To evaluate the electrochemical performance of the material, the electrode material was first assembled into a battery according to the following steps. The specific operation is as follows: taking the positive electrode material as the main component, mixing it with a conductive agent (acetylene black) and a binder (polyvinylidene fluoride PVDF) in a mass ratio of 8:1:1, and using N-methylpyrrolidone NMP as a solvent to stir the mixture evenly. Subsequently, the mixture was coated on aluminum foil and vacuum dried at 110 °C, and then cut into circular pieces with a diameter of 12 mm for use as the positive electrode plate. Metallic sodium was used as the negative electrode, and a glass fiber membrane was used as the separator material. The electrolyte was 1.0 M NaClO 4 solution, to which 5 wt% of fluoroethylene carbonate (FEC) was added, and it was used as the electrolyte for the sodium-ion battery. The entire battery assembly process was carried out in a glove box filled with argon.

[0093] (5) As Figure 12 shown, it has a relatively high discharge plateau between 1.5 and 4.4 V, and the initial discharge specific capacity reaches 153.5 mAh g -1 , showing a significant improvement compared to Comparative Example 1; the discharge specific capacity remains 79.4% after 100 cycles of long-term cycling tests, showing a significant improvement compared to 52.3% in Comparative Example 1, which confirms its good cycle stability and further confirms the improvement effect of the high-entropy superlattice layered oxide on the electrochemical performance ( Figure 13 ).

[0094] Comparative Example 1

[0095] (1) For the non-high-entropy positive electrode material Na 0.67 Li 0.2 Mn 0.8 O 2， where the configurational entropy calculation of the transition metal sites S config =-R(0.8ln(0.8)+0.2ln(0.2)) = 0.5R < 1.5R, which does not meet the definition of high entropy.

[0096] Na 2 CO 3 , Li 2 CO 3 , and MnO 2 powders were poured into a mortar in a molar ratio of 6.7:4:16 in sequence for grinding and mixing evenly until the particle size reached 200 mesh.

[0097] (2) The mixed oxide raw material powder was pressed into tablets using a tablet press mold at a pressure of 15 MPa. The precursor tablets were placed in a muffle furnace for calcination, heated at 5 °C / min, calcined at 900 °C for 15 h, with an air humidity of 30%, and cooled naturally to obtain the high-entropy superlattice positive electrode material Na 0.67 Li 0.2 Mn0.8 O 2 The X-ray powder diffraction test results of the material are as follows Figure 14 , the space group is P63 / mmc, and the PDF card is

[0098] JCPDS:#54-0894.

[0099] (3) To evaluate the electrochemical performance of the material, the electrode material was first assembled into a battery according to the following steps. The specific operation is as follows: taking the positive electrode material as the main component, mixing it according to the mass ratio of the conductive agent (acetylene black) to the binder (polyvinylidene fluoride PVDF) of 8:1:1, and using N-methylpyrrolidone NMP as the solvent to stir the mixture evenly. Subsequently, the mixture was coated on the aluminum foil and vacuum dried at 110 °C, and then cut into circular pieces with a diameter of 12 mm and used as the positive electrode plate. Metallic sodium was used as the negative electrode, and the glass fiber membrane was used as the separator material. The electrolyte was selected as 1.0 M NaClO 4 solution, in which 5 wt% of fluoroethylene carbonate (FEC) was added and used as the electrolyte for the sodium-ion battery.

[0100] (4) As Figure 15 shown, it has a lower discharge plateau at 1.5 - 4.4 V, and the average discharge voltage is relatively low, about 2.7 V. Its normalized average discharge voltage curve is as Figure 16 shown, and its discharge voltage shows an obvious attenuation during 50 cycles. The cycle stability of the discharge specific capacity is as Figure 17 shown. At a rate of 100 mA g -1 , the initial discharge specific capacity in the long cycle is 152.9 mAh g -1 , and only 52.3% remains after 100 cycles. To further make a comparison and highlight the structural advantages of constructing the high-entropy superlattice, Figure 18 in-situ oxygen partial pressure differential electrochemical mass spectrometry was used to analyze the charge-discharge process of the non-high-entropy cathode material Na 0.67 Li 0.2 Mn 0.8 O 2 . During the entire initial charging process, when the charging voltage exceeds 4 V, the change in oxygen partial pressure occurs. When charging to 4.4 V, the oxygen partial pressure reaches the peak value; entering the discharge stage, the oxygen partial pressure begins to gradually decrease, indicating the oxygen evolution of the non-high-entropy layered oxide at high charging voltages and revealing the phenomenon of its lattice oxygen loss.

[0101] In the description of this specification, specific features, structures, materials, or characteristics can be combined in a suitable manner in any one or more embodiments or examples.

[0102] As described above, it is only the specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Any person skilled in the art within the technical scope disclosed by the present invention can easily think of changes or substitutions, which should all be covered within the protection scope of the present invention. Therefore, the protection scope of the present invention shall be subject to the protection scope of the claims described above.

Claims

1. A sodium ion battery positive electrode material with a high entropy superlattice structure, characterized in that: The general formula of the sodium ion battery positive electrode material is: Na 0.67 Mn a Ni b Fe c Li d Cu e Ti f O2, of which 0.3 <a<0.6,0.1<b<0.3,0.01<c<0.2,0.03<d<0.2,0.03<e<0.2,0.01<f<0.2,a+b+c+d+e+f=1。 2. The sodium ion battery positive electrode material according to claim 1, characterized in that The sodium ion battery positive electrode material is of P2 type.

3. A method for preparing a positive electrode material for a sodium ion battery as claimed in claim 1 or 2, characterized in that: The following steps are involved: The sodium source, lithium source, iron source, nickel source, manganese source, copper source and titanium source are evenly mixed by ball milling, and then pressed into sheets and calcined to obtain the positive electrode material of the sodium ion battery.

4. The preparation method according to claim 3, characterized in that: The molar ratio of the sodium source, manganese source, nickel source, iron source, lithium source, copper source and titanium source is (6-7): (7-16): (2-6): (1-4)：(1-4)：(1-3)：(1-4)。 5. The preparation method according to claim 3, characterized in that: The sodium source includes at least one of NaOH, Na2CO3, and Na2CO3·H2O; The lithium source includes at least one of LiNO3, Li2CO3, and LiOH·H2O; The iron source includes at least one of FeO, Fe2O3, and Fe3O4; The manganese source includes at least one of MnO, Mn(OH)2, MnO2, and Mn3O4; The nickel source includes at least one of Ni(OH)2 and NiO; The copper source includes at least one of CuO and Cu2O; The titanium source includes TiO2.

6. The preparation method according to claim 3, characterized in that: The ball milling time is 12 to 20 hours, and the product is sieved with 100 to 300 meshes.

7. The preparation method according to claim 3, characterized in that: The tableting pressure is 10-50 MPa and the thickness is 10-25 mm.

8. The preparation method according to claim 3, characterized in that: The calcination temperature is 800-950° C. and the heat preservation time is 10-15 hours.

9. The preparation method according to claim 3, characterized in that: The heating rate of the calcination is 2-5°C / min.

10. The preparation method according to claim 3, characterized in that: The air humidity in the calcination atmosphere is lower than 35%.

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