Positive electrode material for sodium-ion battery, and preparation method therefor and use thereof

Abstract

A positive electrode material for a sodium-ion battery, and a preparation method therefor and the use thereof. The preparation method comprises: mixing an M source and a sodium source, and then sequentially subjecting same to primary sintering, a carbonization treatment, a high-entropy coating treatment and a secondary sintering treatment, so as to obtain a positive electrode material for a sodium-ion battery, wherein the M source is an M-containing compound, and M is selected from a combination of any three or more of Ni, Mn, Cu, Fe, Co, Ti, Mg, B, Al, Zn and Ca. The preparation method is simple to operate, and the obtained positive electrode material for a sodium-ion battery has the characteristics of a low surface alkalinity, few impurities, round and smooth morphology and a small specific surface area; and a battery prepared therefrom has a high capacity and good cycling stability.

Description

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

[0001] The present application belongs to the field of battery technology, and in particular relates to a sodium ion battery positive electrode material and a preparation method and application thereof. Background Art

[0002] Currently, energy crises and resource scarcity are becoming increasingly severe. China has therefore set the goal of achieving carbon neutrality and peak carbon emissions, urging the development of new energy sources. Facing this future, alkali metal ion secondary batteries have emerged as a promising technology, attracting attention from companies worldwide. Lithium-ion batteries offer the most mature technology and applications, but with market development, lithium resources are becoming increasingly scarce, leading to rising prices. Furthermore, the low natural abundance and uneven global distribution of lithium ore resources present significant obstacles to the development of new energy sources. In comparison, sodium, due to its abundant reserves and lower cost, as well as its similar operating principles and the high overlap in production technology and tools, will likely become a promising alternative to lithium-ion batteries in the future.

[0003] In sodium-ion batteries, the key to battery performance and cost advantages lies in the positive electrode material. In current research, sodium-ion battery positive electrode materials mainly include three types: layered transition metal oxides, polyanions and Prussian blue. Among various sodium-ion battery positive electrode materials, O3-phase layered transition metal oxide positive electrode materials have attracted widespread attention due to their ease of synthesis and excellent performance in capacity. Their theoretical gram capacity can reach 210mAh / g. However, it also has several problems that cannot be ignored. The main problem is that the residual alkali on the surface of the O3-phase layered sodium battery is high, resulting in a high pH, ​​easy gelation in the subsequent preparation process, and serious gas production; in addition, there is also the problem of poor cycle stability caused by the surface instability of the O3-phase layered sodium battery.

[0004] There is currently no effective solution to the above problems.

[0005] Application Contents

[0006] The purpose of this application is to overcome the shortcomings of the above-mentioned prior art and provide a sodium ion battery positive electrode material with low surface residual alkali content, high energy density and excellent cycle performance when used in batteries, as well as a preparation method and application thereof.

[0007] To achieve the above objectives, in a first aspect of the present application, the present application provides a method for preparing a positive electrode material for a sodium ion battery, the preparation method comprising the following steps:

[0008] The M source and the sodium source are mixed and sintered once to obtain a primary sintered product;

[0009] The primary sintered product is sequentially subjected to carbonization treatment, high entropy coating treatment, and secondary sintering treatment to obtain a positive electrode material for a sodium ion battery;

[0010] The M source is a compound containing M, and the M is selected from any three or more of Ni, Mn, Cu, Fe, Co, Ti, Mg, B, Al, Zn, and Ca;

[0011] The carbonization treatment comprises placing the primary sintered product in an environment with a carbon dioxide concentration of 20-99%, a relative humidity of 5-30%, and a temperature of 15-50° C. for carbonization to obtain a carbonized product;

[0012] The high entropy coating treatment comprises reacting the carbonized product with five or more metal ions whose ion radii differ by less than 15% to form a high entropy coating layer, wherein the high entropy coating layer accounts for 0.2-1.2% of the mass of the carbonized product.

[0013] In a preparation method of a sodium ion battery positive electrode material provided by the present application, a primary sintered product is sequentially subjected to carbonization treatment and high-entropy coating treatment, and the mass ratio of the high-entropy coating layer to the carbonization treatment product is controlled, thereby being able to solve the problem that conventional non-metallic and metal oxide coating of positive electrode materials fails to effectively solve the high surface residual alkali and poor cycle performance; the sodium ion battery positive electrode material obtained by the preparation method of the present application has a small specific surface area, a smooth, dense and stable surface coating, a low surface residual alkali, and a high-entropy coating layer of moderate thickness. When applied to a battery, it can reduce gas production during use of the battery cell, inhibit side reactions between the surface and the electrolyte, stabilize the internal structure of the positive electrode material particles, and reduce the dissolution of bulk sodium, thereby making the obtained battery have high energy density and excellent cycle performance.

[0014] Specifically, the residual alkali on the surface of the O3-phase layered sodium-ion battery cathode material is relatively high. The residual alkali mainly includes sodium hydroxide and sodium carbonate, and the content of sodium hydroxide is more prominent. By placing the product after the first sintering in a carbonization box with a specific carbon dioxide concentration, relative humidity, and temperature for carbonization treatment, the conversion of sodium hydroxide on the surface of the cathode material to sodium carbonate can be completed relatively quickly. Compared with the property that sodium hydroxide is more likely to absorb moisture and carbon dioxide in the air, which will further precipitate Na in the interlayer of the cathode material, sodium carbonate is more stable and can be used as a temporary coating layer to protect the cathode material. However, sodium carbonate also has a large specific surface area and will absorb water, and has an adverse effect on gas production. Therefore, after carbonization treatment, high-entropy coating treatment is combined to remove sodium carbonate. During the high-entropy coating treatment, 5 or more metal ions with an ionic radius difference of less than 15% are selected to react with sodium carbonate on the surface of the carbonization treatment product to form a high-entropy coating layer. This high-entropy coating layer is a high-entropy infinite solid solution coating layer, and the disordered metal ion occupancy in it can make the coating layer structure more stable, effectively isolating harmful substances from the cathode material, achieving the purpose of reducing surface sodium carbonate while forming a coating protection.

[0015] In one embodiment, the structural formula of the product after the first sintering is Na x MO2, where 0 < x ≤ 1, and M is selected from any combination of three or more of Ni, Mn, Cu, Fe, Co, Ti, Mg, B, Al, Zn, Ca.

[0016] In one embodiment, the M source is an oxide, hydroxide, or carbonate containing M.

[0017] In one embodiment, the sodium source is at least one of sodium carbonate, sodium hydroxide, or sodium acetate.

[0018] In one embodiment, the carbonization treatment is: placing the product after the first sintering in an environment with a carbon dioxide concentration of 40 - 90%, a relative humidity of 8 - 20%, and a temperature of 20 - 30°C for carbonization to obtain a carbonization treatment product.

[0019] In one embodiment, the carbonization treatment is: placing the product after the first sintering in an environment with a carbon dioxide concentration of 50 - 60%, a relative humidity of 10 - 15%, and a temperature of 20 - 30°C for carbonization to obtain a carbonization treatment product.

[0020] In one embodiment, the carbonization treatment time is 6 - 10d.

[0021] During the carbonization process, carbon dioxide can provide raw materials for the reaction. The reason for controlling a certain relative humidity is that the conversion of sodium hydroxide into sodium carbonate requires the participation of water. Otherwise, the reaction proceeds slowly and the efficiency is extremely low. By selecting carbonization in an environment of carbon dioxide concentration of 40-90%, relative humidity of 8-20%, and temperature of 20-30°C, especially when carbonization is carried out in an environment of carbon dioxide concentration of 50-60%, relative humidity of 10-15%, and temperature of 20-30°C, a more complete reaction can be achieved, that is, the sodium hydroxide content on the surface is lowered, and the precipitation of sodium between the positive electrode material layers is avoided, thereby stabilizing the formed positive electrode material.

[0022] In one embodiment, the high entropy coating layer accounts for 0.5-1% of the mass of the carbonization product.

[0023] As the mass percentage of the high entropy coating layer in the carbonization product increases, the residual alkali content on the surface of the obtained positive electrode material will show a gradually decreasing trend. However, when the mass percentage of the high entropy coating layer in the carbonization product continues to increase, the resulting residual alkali content has a limited downward trend, and on the contrary, due to the high entropy coating layer being too thick, it will affect the subsequent sodium ion deintercalation process during actual use of the battery, resulting in a decrease in capacity and even a significant decrease in cycle performance. Therefore, when the high entropy coating layer provided by the present invention accounts for 0.2-1.2% of the mass of the carbonization product, especially 0.5-1%, the overall performance of the obtained positive electrode material and the battery obtained by subsequent application is more excellent.

[0024] In one embodiment, the carbonized product is reacted with seven metal ions whose ionic radii differ by less than 15% to form a high entropy coating layer.

[0025] In one embodiment, the seven ions are manganese, titanium, magnesium, copper, scandium, iron, and tin.

[0026] In one embodiment, the molar ratio of manganese, titanium, magnesium, copper, scandium, iron and tin is manganese: titanium: magnesium: copper: scandium: iron: tin = (0.35-0.45): (0.05-0.15): (0.05-0.15) (0.05-0.15): (0.03-0.07): (0.15-0.25): (0.03-0.07).

[0027] During the high-entropy coating treatment, different high-entropy coating layers will be formed by reacting with different metal ions. The high-entropy coating layer is a multi-element metal oxide system. Different components in the system can be different crystal structures, thereby forming a stable solid solution, thereby stabilizing the material structure, and the introduction of metal ions can also increase the interlayer spacing of the sodium ion layer and improve the diffusion rate of sodium ions in the crystal structure; when the metal ions are further selected as manganese, titanium, magnesium, copper, scandium, iron and tin, especially when the molar ratio of the seven species is selected as manganese: titanium: magnesium: copper: scandium: iron: tin = (0.35-0.45): (0.05-0.15): (0.05-0.15) (0.05-0.15): (0.03-0.07): (0.15-0.25): (0.03-0.07), when the obtained positive electrode material is used in the preparation of a battery, the obtained battery has better cycle stability.

[0028] After the compounds of the above seven elements are selected to react with the sodium carbonate on the surface of the carbonized product, i.e., high entropy coating treatment is performed, the structural formula of the substance in the high entropy coating layer is NaMn a Cu b Fe c Mg d Ti e Sn f Sc g O2, where a:b:c:d:e:f:g = (0.35-0.45): (0.05-0.15): (0.15-0.25)(0.05-0.15): (0.05-0.15): (0.03-0.07): (0.03-0.07).

[0029] In one embodiment, the reaction in the high entropy coating process is performed by dry ball milling or wet ball milling;

[0030] The dry ball milling is to mix and ball mill the compounds containing the corresponding metal ions and then mix and ball mill with the carbonized product;

[0031] The wet ball milling method comprises mixing a compound containing corresponding metal ions with the carbonized product, dissolving the mixture in water, and ball milling the mixture, followed by drying after the ball milling.

[0032] In one embodiment, in the dry ball milling, the compound containing the corresponding metal ions is the corresponding metal oxide. For example, when the seven ions of manganese, titanium, magnesium, copper, scandium, iron and tin are selected, titanium oxide, manganese oxide, magnesium oxide, copper oxide, scandium oxide, iron oxide and tin oxide are mixed and ball milled, and then mixed and ball milled with the carbonization product.

[0033] In the wet ball milling, the compound containing the corresponding metal ions is the corresponding metal chloride or nitrate. For example, when the seven ions of manganese, titanium, magnesium, copper, scandium, iron and tin are selected, manganese nitrate, magnesium nitrate, copper nitrate, scandium nitrate, iron nitrate, titanium chloride and tin chloride are mixed with the carbonization treatment product, dissolved in water and ball milled, and dried after the ball milling is completed.

[0034] In one embodiment, in the dry ball milling, the ball milling speed is 300-400 r / min, and the ball milling time is 2-6 h;

[0035] In the wet ball milling, the ball milling speed is 300-400 r / min, and the ball milling time is 2-6 h.

[0036] In one embodiment, the M is Ni, Mn, Fe and Cu.

[0037] In one embodiment, the molar ratio of Ni, Mn, Fe and Cu is Ni:Mn:Fe:Cu=(0.20-0.28):(0.40-0.60):(0.10-0.20):(0.02-0.08).

[0038] Different primary sintering products are selected for subsequent treatment, resulting in different reductions in residual alkali, and different battery capacity and cycle performance levels when used in battery preparation. When M is further selected as Ni, Mn, Fe and Cu, especially when the molar ratio of Ni, Mn, Fe and Cu is Ni:Mn:Fe:Cu=(0.20-0.28):(0.40-0.60):(0.10-0.20):(0.02-0.08), the elements can interact with each other and jointly improve the stability of the product, resulting in excellent battery capacity and cycle performance.

[0039] In one embodiment, the primary sintering is performed at a temperature of 800-1000° C. for a time of 10-24 hours, and in an atmosphere of any one or two of air, oxygen, or nitrogen.

[0040] Illustratively, the primary sintering temperature may be 800°C, 850°C, 900°C, 950°C, or 1000°C, and the sintering time may be 10h, 11h, 12h, 13h, 14h, 15h, 16h, 17h, 18h, 19h, 20h, 21h, 22h, 23h, or 24h.

[0041] In one embodiment, the primary sintering is performed at a temperature of 900° C. for 15 hours in an air atmosphere.

[0042] In one embodiment, the secondary sintering is performed at a temperature of 900-1000° C. for 5-15 hours in an atmosphere of any one or two of oxygen, nitrogen or argon.

[0043] Illustratively, the primary sintering temperature may be 900° C., 950° C., or 1000° C., and the primary sintering time may be 5 h, 6 h, 7 h, 8 h, 9 h, 10 h, 11 h, 12 h, 13 h, 14 h, or 15 h.

[0044] In one embodiment, the primary sintering temperature is 930° C., the time is 6 hours, and the atmosphere is argon.

[0045] In a second aspect of the present application, the present application provides a sodium ion battery positive electrode material, which is prepared using the preparation method described in the present application.

[0046] In a third aspect of the present application, the present application provides a positive electrode plate, which comprises the sodium ion battery positive electrode material described in the present application.

[0047] In a fourth aspect of the present application, the present application provides a sodium ion battery, wherein the sodium ions comprise the positive electrode plate described in the present application.

[0048] Compared with the prior art, the present invention has the following advantages:

[0049] The sodium ion battery positive electrode material prepared by the preparation method provided in the present application has the characteristics of low surface alkalinity, few impurities, smooth and rounded morphology, and small specific surface area; in the process of slurrying the positive electrode material, the low alkaline surface is conducive to avoiding the jelly gel of the slurry, providing convenience for subsequent coating, and is conducive to the preparation of the positive electrode sheet of the battery; in addition, the less alkaline impurities on the surface and the stable solid solution coating layer reduce the gas production of the battery during use, inhibit the side reaction between the surface and the electrolyte, stabilize the internal structure of the positive electrode material particles, reduce the dissolution of bulk sodium, and can improve the cycle stability of the material. At the same time, the preparation method provided in the present application is simple to operate and is conducive to actual production. BRIEF DESCRIPTION OF THE DRAWINGS

[0050] FIG1 is a SEM image of the carbonized product in Example 1;

[0051] FIG2 is a SEM image of the positive electrode material in Example 1;

[0052] FIG3 is an XRD diagram of the positive electrode materials in Example 1 and Example 2;

[0053] FIG4 is a SEM image of the positive electrode material in Example 2. DETAILED DESCRIPTION

[0054] In order to better illustrate the purpose, technical solutions and advantages of this application, this application will be further described below in conjunction with specific embodiments.

[0055] Unless otherwise specified, the raw materials used in this application are conventional commercially available raw materials, and the raw materials used in the parallel examples or comparative examples in this application are consistent.

[0056] Example 1

[0057] The present invention provides a sodium ion battery cathode material, and a method for preparing the sodium ion battery cathode material comprises the following steps:

[0058] (1) Nickel oxide, manganese oxide, ferric oxide, copper oxide and sodium carbonate were mixed in a ratio of 0.20:0.15:0.60:0.05:0.95 among the elements Ni, Fe, Mn, Cu and Na, and then placed in a crucible. The mixture was then sintered at 900°C for 15 hours in an air atmosphere. After sintering, the mixture was crushed to obtain the primary sintered product: Na 0.95 Ni 0.20 Fe 0.15 Cu 0.05 Mn 0.60 O2;

[0059] (2) The primary sintered product was spread on a 50*50 cm tray and placed in a carbonization box. The temperature in the box was adjusted to 25°C, the relative humidity was 10%, and the carbon dioxide concentration was 50%. The primary sintered product was exposed to the carbonization box for 7 days to obtain a carbonized product, the morphology of which is shown in Figure 1.

[0060] (3) a high entropy infinite solid solution coating layer of 0.5% of the mass of the carbonized product and a stoichiometric ratio of the corresponding metal element nano-oxide raw materials (nano-titanium oxide, nano-manganese oxide, nano-magnesium oxide, nano-copper oxide, nano-scandium oxide, nano-iron oxide, nano-tin oxide, wherein the molar ratio of manganese, titanium, magnesium, copper, scandium, iron, and tin is 0.4:0.1:0.1:0.1:0.05:0.1:0.05) were first placed in a planetary ball mill and premixed at 360 rpm / min for 2 h, and then the carbonized product was added and dry-milled in the planetary ball mill at a speed of 360 r / min for 6 h;

[0061] (4) After the ball milling, the mixture was heated at 930℃ for 6 hours in an argon atmosphere for secondary sintering. After the sintering, Na 0.95 Ni 0.20 Fe 0.15 Cu 0.05 Mn 0.60 The morphology of the sodium ion positive electrode material of O2@ZMSCT-dry is shown in Figure 2, and its XRD is shown in Figure 3.

[0062] Example 2

[0063] The present embodiment provides a sodium ion battery cathode material. The preparation method of the sodium ion battery cathode material is different from that of Example 1 only in that step (4) is a wet coating method, specifically:

[0064] The carbonized product was dissolved in water with the corresponding stoichiometric weight of metal salts (manganese nitrate, magnesium nitrate, copper nitrate, scandium nitrate, iron nitrate, titanium chloride, and tin chloride, wherein the molar ratio of manganese, titanium, magnesium, copper, scandium, iron, and tin was 0.4:0.1:0.1:0.1:0.05:0.1:0.05) of a high entropy infinite solid solution coating layer of 0.5% of the carbonized product weight, and then dry-milled in a planetary ball mill at a speed of 360 rpm / min for 6 h. After the milling, the slurry was dried in a forced air drying oven at 90° C. for 2 h.

[0065] The sodium ion positive electrode material Na obtained in Example 2 0.95 Ni 0.20 Fe 0.15 Cu 0.05 Mn 0.60 The morphology of O2@ZMSCT-wet is shown in Figure 4, and the XRD pattern is shown in Figure 3.

[0066] Example 3

[0067] The embodiment of the present application provides a sodium ion battery positive electrode material. The only difference between the preparation method of the sodium ion battery positive electrode material and that of Example 1 is that the carbon dioxide concentration in step (2) is 60%.

[0068] Example 4

[0069] The embodiment of the present application provides a sodium ion battery positive electrode material. The only difference between the preparation method of the sodium ion battery positive electrode material and that of Example 1 is that the carbon dioxide concentration in step (2) is 40%.

[0070] Example 5

[0071] The embodiment of the present application provides a sodium ion battery positive electrode material. The only difference between the preparation method of the sodium ion battery positive electrode material and that of Example 1 is that the carbon dioxide concentration in step (2) is 90%.

[0072] Example 6

[0073] The embodiment of the present application provides a sodium ion battery positive electrode material. The only difference between the preparation method of the sodium ion battery positive electrode material and that of Example 1 is that the carbon dioxide concentration in step (2) is 20%.

[0074] Example 7

[0075] The embodiment of the present application provides a sodium ion battery positive electrode material. The only difference between the preparation method of the sodium ion battery positive electrode material and that of Example 1 is that the carbon dioxide concentration in step (2) is 99%.

[0076] Example 8

[0077] The embodiment of the present application provides a sodium ion battery positive electrode material. The only difference between the preparation method of the sodium ion battery positive electrode material and that of Example 1 is that the relative humidity in step (2) is 20%.

[0078] Example 9

[0079] The present embodiment provides a sodium ion battery positive electrode material. The only difference between the preparation method of the sodium ion battery positive electrode material and that of Example 1 is that the relative humidity in step (2) is 8%.

[0080] Example 10

[0081] The embodiment of the present application provides a sodium ion battery positive electrode material. The only difference between the preparation method of the sodium ion battery positive electrode material and that of Example 1 is that the relative humidity in step (2) is 25%.

[0082] Example 11

[0083] The embodiment of the present application provides a sodium ion battery positive electrode material. The only difference between the preparation method of the sodium ion battery positive electrode material and that of Example 1 is that the relative humidity in step (2) is 5%.

[0084] Example 12

[0085] The present embodiment provides a sodium ion battery positive electrode material. The only difference between the preparation method of the sodium ion battery positive electrode material and that of Example 1 is that the temperature in step (2) is 15°C.

[0086] Example 13

[0087] The present embodiment provides a sodium ion battery positive electrode material. The only difference between the preparation method of the sodium ion battery positive electrode material and that of Example 1 is that the temperature in step (2) is 50°C.

[0088] Example 14

[0089] The embodiment of the present application provides a sodium ion battery positive electrode material. The only difference between the preparation method of the sodium ion battery positive electrode material and that of Example 1 is that in step (3), the mass of the metal element nano-oxide raw materials calculated according to the stoichiometric ratio of the high-entropy infinite solid solution coating layer accounts for 1% of the mass of the carbonization treatment product.

[0090] Example 15

[0091] The embodiment of the present application provides a sodium ion battery positive electrode material. The only difference between the preparation method of the sodium ion battery positive electrode material and that of Example 1 is that in step (3), the mass of the metal element nano-oxide raw materials calculated according to the stoichiometric ratio of the high-entropy infinite solid solution coating layer accounts for 0.2% of the mass of the carbonization treatment product.

[0092] Example 16

[0093] The embodiment of the present application provides a sodium ion battery positive electrode material. The only difference between the preparation method of the sodium ion battery positive electrode material and that of Example 1 is that in step (3), the mass of the metal element nano-oxide raw materials calculated according to the stoichiometric ratio of the high-entropy infinite solid solution coating layer accounts for 1.2% of the mass of the carbonization treatment product.

[0094] Example 17

[0095] The present embodiment provides a sodium ion battery positive electrode material. The only difference between the preparation method of the sodium ion battery positive electrode material and that of Example 1 is that in step (1), the molar ratio of Ni, Fe, Mn, Cu, and Na elements is 0.20:0.15:0.55:0.10:0.95.

[0096] Example 18

[0097] The present embodiment provides a sodium ion battery positive electrode material. The only difference between the preparation method of the sodium ion battery positive electrode material and that of Example 1 is that in step (1), the molar ratio of Ni, Fe, Mn, Ti, and Na elements is 0.20:0.15:0.60:0.05:0.95.

[0098] Example 19

[0099] The embodiment of the present application provides a sodium ion battery positive electrode material. The only difference between the preparation method of the sodium ion battery positive electrode material and that of Example 1 is that in step (5), the molar ratio of manganese, titanium, magnesium, copper, scandium, iron, and tin is 0.48:0.1:0.02:0.1:0.05:0.1:0.05.

[0100] Example 20

[0101] The embodiment of the present application provides a sodium ion battery positive electrode material. The only difference between the preparation method of the sodium ion battery positive electrode material and that of Example 1 is that in step (5), the molar ratio of manganese, titanium, magnesium, copper, scandium and iron is 0.4:0.1:0.1:0.1:0.05:0.15.

[0102] Comparative Example 1

[0103] The comparative example of the present application provides a sodium ion battery positive electrode material. The only difference between the preparation method of the sodium ion battery positive electrode material and Example 1 is that the carbonization treatment in step (2) is not performed.

[0104] Comparative Example 2

[0105] The comparative example of the present application provides a sodium ion battery positive electrode material. The only difference between the preparation method of the sodium ion battery positive electrode material and Example 1 is that the high entropy coating treatment in step (3) is not performed.

[0106] Comparative Example 3

[0107] The comparative example of the present application provides a sodium ion battery positive electrode material. The only difference between the preparation method of the sodium ion battery positive electrode material and Example 1 is that the carbon dioxide concentration in step (2) is 100%.

[0108] Comparative Example 4

[0109] The comparative example of the present application provides a sodium ion battery positive electrode material. The only difference between the preparation method of the sodium ion battery positive electrode material and Example 1 is that the carbon dioxide concentration in step (2) is 10%.

[0110] Comparative Example 5

[0111] The comparative example of the present application provides a sodium ion battery positive electrode material. The only difference between the preparation method of the sodium ion battery positive electrode material and Example 1 is that the relative humidity in step (2) is 60%.

[0112] Comparative Example 6

[0113] The comparative example of the present application provides a sodium ion battery positive electrode material. The only difference between the preparation method of the sodium ion battery positive electrode material and that of Example 1 is that the relative humidity in step (2) is 3%.

[0114] Comparative Example 7

[0115] The comparative example of the present application provides a sodium ion battery positive electrode material. The only difference between the preparation method of the sodium ion battery positive electrode material and Example 1 is that in step (3), the mass of the metal element nano-oxide raw materials calculated according to the stoichiometric ratio of the high entropy infinite solid solution coating layer accounts for 1.5% of the mass of the carbonization treatment product.

[0116] Comparative Example 8

[0117] The comparative example of the present application provides a sodium ion battery positive electrode material. The only difference between the preparation method of the sodium ion battery positive electrode material and Example 1 is that in step (3), the mass of the metal element nano-oxide raw materials calculated according to the stoichiometric ratio of the high entropy infinite solid solution coating layer accounts for 0.1% of the mass of the carbonization treatment product.

[0118] Comparative Example 9

[0119] The comparative example of the present application provides a sodium ion battery positive electrode material. The only difference between the preparation method of the sodium ion battery positive electrode material and that of Example 1 is that in step (5), the molar ratio of potassium, titanium, magnesium, copper, scandium, iron and tin is 0.4:0.1:0.1:0.1:0.05:0.1:0.05.

[0120] Comparative Example 10

[0121] The comparative example of the present application provides a sodium ion battery positive electrode material. The only difference between the preparation method of the sodium ion battery positive electrode material and Example 1 is that in step (1), the molar ratio of Ni, Fe, Sn, Ti, and Na elements is 0.20:0.15:0.60:0.05:0.95.

[0122] Effect Example 1

[0123] The present application effect example tests the residual alkali content on the surface of the sodium ion positive electrode material prepared in Example 1-20 and Comparative Example 1-10. Specifically, 1 g of positive electrode material was taken from each sample and dissolved in 100 mL of ultrapure water in a conical flask. After the conical flask was closed and stirred for 30 minutes, it was immediately filtered to obtain a filtrate. 5 mL of the filtrate from each sample was transferred and titrated using a 0.05 mol / L standard hydrochloric acid solution on a potentiometric titrator to test the residual alkali content on the surface of the sample. The test results are shown in Table 1:

[0124] Table 1

[0125] As can be seen from Table 1, when the technical solution of the present application is adopted, the surface residual alkali content of the obtained sodium ion positive electrode material is low, wherein the sodium hydroxide content is below 2.0254%, the sodium carbonate content is below 1.2356%, and the sodium ion content is below 1.6141%;

[0126] It can be seen from Example 1 and Comparative Examples 1-2 that the sodium ion content on the surface of the obtained positive electrode material increases significantly regardless of whether the carbonization treatment or the high-entropy coating treatment is performed. Compared with Example 1, the sodium ion content increases by 84.80-115.87%. That is, only under the combined action of carbonization and coating treatment can the residual sodium be reduced to a low level, and the effect of a single treatment is not as good as the combined effect of the two.

[0127] It can be seen from Examples 1 and 2 that, compared with nanoscale dry coating, liquid-phase wet coating has more advantages in reducing residual alkali. On the one hand, this is because liquid-phase coating can form a more uniform high-entropy infinite solid solution coating layer on the surface, which more effectively prevents the loss of bulk Na. On the other hand, since the residual alkali can be dissolved in water in a liquid phase environment, a small amount of residual sodium can also be reduced during the ball milling stage.

[0128] It can be seen from Example 1, Examples 3-7, and Comparative Examples 3-4 that the concentration of carbon dioxide in the carbonization treatment affects the residual alkali content. When the carbon dioxide content gradually increases, the residual alkali content shows a trend of first decreasing and then increasing. When the carbon dioxide concentration in the carbonization treatment is further selected to be 40-90%, the sodium ion content in the obtained product is below 1.3585%;

[0129] It can be seen from Example 1, Examples 8-11, and Comparative Examples 5-6 that the relative humidity during carbonization treatment also affects the residual alkali content. When the humidity in Comparative Example 6 is too low, although the sodium carbonate content is low, the sodium hydroxide content is high, resulting in a high overall residual alkali content. This is because the humidity is too low and the surface sodium hydroxide cannot fully react. When the humidity in Comparative Example 5 is too high, the sodium ion content also increases by 132.75% compared with Example 1. This is because the increase in humidity leads to the precipitation of Na between the material layers, thereby causing a further increase in the surface residual alkali.

[0130] As can be seen from Example 1 and Examples 12-13, the temperature selection during the carbonization treatment also affects the residual alkali content. If the temperature is too low, the reaction rate slows down and the residual alkali increases to a certain extent. If the temperature is too high, more Na precipitates to a certain extent and the residual alkali is high.

[0131] It can also be seen from Example 1, Examples 14-16 and Comparative Examples 7-8 that the mass ratio of the high entropy coating layer to the carbonized product will also affect the surface residual alkali content of the product. If the mass ratio of the high entropy coating layer is too large, although more surface residual sodium will react, the electrical properties will be reduced due to the excessive thickness of the coating.

[0132] It can be seen from Example 1 and Examples 17-18 that the structural formulas of the primary sintered products are different, and the residual alkali content on the surface is also different. In Example 17, increasing the Cu content can improve the water stability of the material, but will cause a decrease in battery capacity; while in Example 18, replacing Cu with Ti will reduce the air stability and increase the residual alkali.

[0133] It can be seen from Example 1, Examples 19-20 and Comparative Example 9 that the metal ions selected in the high entropy coating treatment will also bring differences to the surface residual alkali content;

[0134] It can be seen from Example 1, Examples 17-18 and Comparative Example 10 that the type selection and ratio of M will also affect the surface residual alkali content.

[0135] In addition, the morphology of the carbonized product in Example 1 is shown in Figure 1, the morphology after secondary sintering is shown in Figure 2, and the XRD is shown in Figure 3. It can be seen from Figure 1 that after carbonization treatment, there are more sodium carbonate impurities on the surface of the positive electrode material. After coating and sintering treatment, the surface of the material becomes smooth as shown in Figures 2-3, and the impurities are greatly reduced; this shows that the present invention uses a carbonization box to convert sodium hydroxide on the surface of the positive electrode material into sodium carbonate, and then coats and removes it at a high temperature stage. It is a feasible solution and can achieve the effect of reducing the residual alkali on the surface.

[0136] Effect Example 2

[0137] The present application shows that the sodium ion positive electrode materials prepared in Examples 1-20 and Comparative Examples 1-10 are applied to batteries, and the performance of the resulting batteries is as follows: the positive electrode materials prepared in Examples 1-20 and Comparative Examples 1-10 are mixed with a binder and conductive carbon black in a ratio of 90:5:5, NMP solvent is added and stirred, the mixture is coated on a current collector, dried, and roll-pressed to obtain a positive electrode sheet, the positive electrode sheet and the sodium negative electrode sheet are used to make a sodium ion battery, and the performance test is carried out at 1.5 to 4.2 V. The test results are shown in Table 2;

[0138] Table 2

[0139] As can be seen from Table 1, when the technical solution of the present application is adopted, the obtained sodium ion battery has a high first-cycle discharge capacity of more than 151.5 mAh / g, and a high cycle retention rate of more than 91.7% after 50 cycles at 1C.

[0140] It can be seen from Example 1 and Comparative Examples 1-2 that, regardless of whether carbonization treatment or high-entropy coating treatment is performed, the first-cycle discharge capacity and 1C cycle retention rate of the obtained battery are significantly reduced; this is because both carbonization and coating play a role in reducing residual alkali, and reducing residual alkali will reduce surface side reactions, protect the internal structure of the particles, and improve the cycle performance of the material;

[0141] It can be seen from Example 1, Examples 3-7 and Comparative Examples 3-4 that the concentration of carbon dioxide in the carbonization treatment affects the first-cycle discharge capacity and the cycle retention rate of 1C cycles for 50 cycles of the battery. When the carbon dioxide content is too high, not only the residual alkali content on the surface of the obtained sodium ion positive electrode material increases, but the capacity and cycle performance of the obtained battery also show a downward trend; when the carbon dioxide content is too low, it is insufficient to convert sodium hydroxide, resulting in a significant deterioration in the performance of the obtained battery.

[0142] It can be seen from Example 1, Examples 8-11, and Comparative Examples 5-6 that the relative humidity during the carbonization treatment also affects the first-cycle discharge capacity and the 1C cycle 50-cycle retention rate of the battery. When the humidity in Comparative Example 6 is too low, the first-cycle discharge capacity and the 1C cycle 50-cycle retention rate of the battery are significantly lower than those in Example 1. When the humidity in Comparative Example 5 is too high, the first-cycle discharge capacity and the 1C cycle 50-cycle retention rate of the battery also show a significant downward trend compared to Example 1.

[0143] As can be seen from Examples 1 and 12-13, the temperature selection during the carbonization treatment also affects the first-cycle discharge capacity and the cycle retention rate of the battery after 50 cycles at 1C. Too high or too low a temperature will affect the reaction rate, resulting in differences in capacity and cycle retention rate.

[0144] It can also be seen from Example 1, Examples 14-16 and Comparative Examples 7-8 that the mass ratio of the high entropy coating layer to the carbonized product will also affect the first-cycle discharge capacity and the 1C cycle 50-cycle retention rate of the battery; although it was found in Effect Example 1 that the increase in the mass ratio of the high entropy coating layer to the carbonized product can effectively reduce the residual alkali content on the surface of the positive electrode material, as the mass ratio further increases, the effect of reducing the residual alkali content is not obvious, but the capacity of the battery will decrease significantly. If the mass ratio of the coating layer continues to increase, the cycle performance will also show a downward trend; this is because the large coating amount causes the coating layer on the surface of the material to be too thick, which affects the Na + The deintercalation process causes the capacity to decrease;

[0145] It can be seen from Example 1, Examples 17-18 and Comparative Example 10 that the structural formulas of the primary sintered products are different, and the first cycle discharge capacity and 1C cycle retention rate of the battery after 50 cycles are also different;

[0146] It can be seen from Example 1, Examples 19-20 and Comparative Example 9 that the metal ions selected in the high-entropy coating treatment will also bring differences to the first-cycle discharge capacity and the cycle retention rate of 1C cycles for 50 cycles of the battery.

Claims

1. A method for preparing a positive electrode material for a sodium ion battery, characterized in that: The preparation method comprises the following steps: The M source and the sodium source are mixed and then sintered once to obtain a primary sintered product; The primary sintered product is sequentially subjected to carbonization treatment, high entropy coating treatment, and secondary sintering treatment to obtain a positive electrode material for a sodium ion battery; The M source is a compound containing M, and the M is selected from any three or a combination of more than three of Ni, Mn, Cu, Fe, Co, Ti, Mg, B, Al, Zn, and Ca; The carbonization treatment comprises: placing the primary sintered product in an environment with a carbon dioxide concentration of 20-99%, a relative humidity of 5-30%, and a temperature of 15-50° C. for carbonization to obtain a carbonized product; The high entropy coating treatment is: reacting the carbonized product with 5 or more metal ions whose ion radii differ by less than 15% to form a high entropy coating layer, wherein the high entropy coating layer accounts for 0.2-1.2% of the mass of the carbonized product.

2. The preparation method according to claim 1, characterized in that: The carbonization treatment is as follows: placing the primary sintered product in an environment with a carbon dioxide concentration of 40-90%, a relative humidity of 8-20%, and a temperature of 20-30° C. for carbonization to obtain a carbonized product.

3. The preparation method according to claim 2, characterized in that: The carbonization treatment is as follows: placing the primary sintered product in an environment with a carbon dioxide concentration of 50-60%, a relative humidity of 10-15%, and a temperature of 20-30° C. for carbonization to obtain a carbonized product.

4. The preparation method according to claim 1, characterized in that: The high entropy coating layer accounts for 0.5-1% of the mass of the carbonization product.

5. The preparation method according to claim 1, characterized in that: The carbonized product is reacted with seven metal ions whose ionic radii differ by less than 15% to form a high entropy coating layer.

6. The preparation method according to claim 5, characterized in that: The seven ions are manganese, titanium, magnesium, copper, scandium, iron and tin.

7. The preparation method according to claim 6, characterized in that: The molar ratio of manganese, titanium, magnesium, copper, scandium, iron and tin is manganese: titanium: magnesium: copper: scandium: iron: tin = (0.35-0.45): (0.05-0.15): (0.05-0.15)(0.05-0.15): (0.03-0.07): (0.15-0.25): (0.03-0.07).

8. The preparation method according to claim 1, characterized in that: The reaction in the high entropy coating process is carried out by dry ball milling or wet ball milling; The dry ball milling is to mix and ball mill the compounds containing the corresponding metal ions and then mix and ball mill with the carbonization product; The wet ball milling is to mix the compound containing the corresponding metal ions with the carbonization product, dissolve the mixture in water and perform ball milling, and then dry the mixture after the ball milling is completed.

9. The preparation method according to claim 1, characterized in that: The M is Ni, Mn, Fe and Cu.

10. The preparation method according to claim 9, characterized in that: The molar ratio of Ni, Mn, Fe and Cu is Ni:Mn:Fe:Cu=(0.20-0.28):(0.40-0.60):(0.10-0.20):(0.02-0.08).

11. The preparation method according to claim 1, characterized in that: The primary sintering is carried out at a temperature of 800-1000° C. for a time of 10-24 hours in an atmosphere of any one or two of air, oxygen or nitrogen.

12. The preparation method according to claim 1, characterized in that: The secondary sintering is carried out at a temperature of 900-1000° C. for 5-15 hours in an atmosphere of any one or two of oxygen, nitrogen or argon.

13. A sodium ion battery positive electrode material, characterized in that: The sodium ion battery positive electrode material is prepared by the preparation method according to any one of claims 1 to 12.

14. A positive electrode sheet, characterized in that: The positive electrode sheet comprises the sodium ion battery positive electrode material as claimed in claim 13.

15. A sodium ion battery, characterized in that: The sodium ion battery comprises the positive electrode sheet as claimed in claim 14.

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