Positive electrode active materials and their preparation methods, positive electrode sheets and sodium-ion batteries

Abstract

This application relates to the field of sodium-ion batteries, disclosing a positive electrode active material and its preparation method, a positive electrode sheet, and a sodium-ion battery. This application first prepares a precursor for the positive electrode active material using iron, manganese, nickel, titanium, and fluorine source raw materials. Then, a sodium source raw material is added, and the mixture is sintered to prepare an O3-type sodium-ion battery positive electrode active material doped with titanium and fluorine ions. The positive electrode active material described in this application uses fluorine doping to replace oxygen, which improves the crystallinity of the material, stabilizes the interface between the electrode material and the electrolyte, and improves the cycle performance of the material. Titanium doping enhances the structural stability of the material, thereby suppressing complex phase transitions during charging and discharging.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of sodium ion batteries, in particular to a positive electrode active material, a preparation method thereof, a positive electrode sheet and a sodium ion battery. BACKGROUND

[0002] Compared with lithium ion batteries, sodium ion batteries have advantages in cost and rate performance. Sodium and lithium are in the same group of the periodic table, have the same number of valence electrons, and have more active chemical properties. Since the atomic mass and radius of sodium are much larger than those of lithium, the energy density of sodium ion batteries is obviously difficult to compare with that of lithium ion batteries. However, the natural abundance of sodium is more than 1,000 times that of lithium, and the desolvation energy of sodium ions is much lower than that of lithium ions. In addition, in sodium ion batteries, sodium does not alloy with aluminum, so that the positive and negative electrode current collectors can use aluminum foil, avoiding the use of relatively expensive copper foil, which means that the same sodium ion battery has a natural price advantage.

[0003] At present, nickel-iron-manganese ternary positive electrode material is the most promising ternary positive electrode material. However, due to the complex phase change in the charging and discharging process and the complex side reaction between the surface and the electrolyte, the metal layered sodium ion battery positive electrode material containing nickel-iron-manganese ternary material is unstable in structure and has poor cycle performance as the voltage rises. SUMMARY

[0004] Therefore, the purpose of the present application is to provide a positive electrode active material and a preparation method thereof, so that the positive electrode active material has high cycle performance and specific capacity.

[0005] Another purpose of the present application is to provide the use of the above-mentioned positive electrode active material in the preparation of a positive electrode sheet and a sodium ion battery.

[0006] Another purpose of the present application is to provide a positive electrode sheet and a sodium ion battery based on the above-mentioned negative electrode active material.

[0007] In order to solve the above technical problems / achieve the above purposes or at least partially solve the above technical problems / achieve the above purposes, as a first aspect of the present application, a positive electrode active material is provided, with a chemical formula of Na z Ni (1 / 3)-x Fe 1 / 3Mn 1 / 3 Ti x O 2-y F y ; wherein 0.5≤z≤1.5, 0.01≤x≤0.07, 0.2≤y≤1.6.

[0008] As a second aspect of the present application, a preparation method of the positive electrode active material is provided, comprising:

[0009] The iron source, nickel source, manganese source, fluorine source and titanium source raw materials are weighed, mixed with water, and uniformly mixed, and then a precursor Ni (1 / 3)-x Fe 1 / 3 Mn 1 / 3 Ti x (OH) 2-y F y ;

[0010] The sodium source raw material and the precursor are mixed and sintered to obtain a positive active material Na z Ni (1 / 3)-x Fe 1 / 3 Mn 1 / 3Ti x O 2-y F y ; wherein 0.5≤z≤1.5, 0.01≤x≤0.07, 0.2≤y≤1.6.

[0011] Optionally, the molar mass ratio of the iron source, nickel source, manganese source, titanium source, fluorine source, and sodium source raw materials is (2.0-3.3):(2.3-3.3):(2.6-3.4):(0.2-0.7):(2-16):(10-25).

[0012] Optionally, the iron source, nickel source, manganese source, titanium source, and sodium source raw materials are sulfate salts, hydrochloride salts, nitrate salts, carbonate salts, acetate salts, oxides, or hydrates thereof.

[0013] Optionally, the fluorine source raw material is a metal ion fluoride or ammonium fluoride; further optionally, the metal ion is a sodium ion or a potassium ion.

[0014] Optionally, the sintering is sintered at a first rated rate to 300-600°C, and then sintered at a second rated rate to 800-1100°C; further optionally, the first rated rate and the second rated rate are independently selected from 2-5°C / min.

[0015] As a third aspect of the present application, a positive electrode tab is provided, comprising the positive active material according to any one of the preceding aspects of the present application, and a conductive agent, a binder, and a current collector.

[0016] As a fourth aspect of the present application, a sodium ion battery is also provided, comprising the positive electrode tab, a separator, an electrolyte, a tab, and a negative electrode tab. Optionally, the negative electrode tab can be an electrode tab with hard carbon as the active material.

[0017] Compared with existing sodium ion positive electrode active materials, the application first prepares a precursor of a positive electrode active material through iron source, manganese source, nickel source, titanium source and fluorine source raw materials, and then adds a sodium source raw material for sintering to prepare a titanium ion and fluorine ion doped O3 type sodium ion battery positive electrode active material. The positive electrode active material described in the application uses fluorine doping to replace oxygen to improve the crystallinity of the material, stabilize the interface between the electrode material and the electrolyte, and improve the cycle performance of the material. Titanium doping is used to improve the structural stability of the material, thereby inhibiting the complex phase change during charging and discharging. BRIEF DESCRIPTION OF DRAWINGS

[0018] Figure 1 The XRD results of the first embodiment of the positive electrode material described in the application are shown.

[0019] Figure 2 The SEM results of the first embodiment of the positive electrode material described in the application are shown. DETAILED DESCRIPTION

[0020] The application discloses a positive electrode active material, a preparation method thereof, a positive electrode sheet and a sodium ion battery. Those skilled in the art can refer to the content herein and appropriately improve the process parameters for implementation. It should be particularly pointed out that all similar replacements and changes are obvious to those skilled in the art, and they are all considered to be included in the application. The products, processes and applications described in the application have been described through preferred embodiments, and relevant personnel can obviously make changes or appropriate changes and combinations to the products, processes and applications described herein without departing from the content, spirit and scope of the application, to realize and apply the technology of the application. Obviously, the described embodiments are part of the embodiments of the application, rather than all the embodiments. Based on the embodiments in the application, all other embodiments obtained by those skilled in the art without creative labor belong to the scope of protection of the application.

[0021] It should be noted that, in the present document, relational terms such as "first" and "second", and "step 1" and "step 2", and "a" and "an", and "one" and "another" and the like are used solely to distinguish one entity or action from another entity or action, without necessarily requiring or implying any actual such relationship or order between such entities or actions. Moreover, the terms "comprises", "comprising", or any other variation thereof, are intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements does not include only those elements but can include other elements not expressly listed or inherent to such process, method, article, or apparatus. An element proceeded by "comprises... a", "comprising... a", or "comprises... one" does not, without more constraints, preclude the existence of additional identical elements in the process, method, article, or apparatus that comprises the element. The embodiments and features discussed herein can be combined with each other as mutually consistent, without conflicts.

[0022] In a first aspect of the present application, a positive electrode active material is provided, having a chemical formula of Na z Ni (1 / 3)-x Fe 1 / 3 Mn 1 / 3Ti x O 2-y F y ; wherein 0.5≤z≤1.5, 0.01≤x≤0.07, 0.2≤y≤1.6. In some embodiments of the present application, x is 0.01, 0.02, 0.03, 0.04, 0.05, 0.06, or 0.07, y is 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1.0, 1.1, 1.2, 1.3, 1.4, 1.5, or 1.6, and z is 0.5, 0.6, 0.7, 0.8, 0.9, 1.0, 1.1, 1.2, 1.3, 1.4, or 1.5; in some other embodiments of the present application, x, y, z in the positive electrode active material are selected as any one of the following cases:

[0023] (1) x = 0.02, y = 0.2, z = 1.0;

[0024] (2) x = 0.02, y = 0.4, z = 1.0;

[0025] (3) x = 0.02, y = 0.1, z = 1.0;

[0026] (4) x = 0.05, y = 0.4, z = 1.0.

[0027] In the second aspect of the present application, a preparation method of the positive electrode active material is provided. The iron source raw material, nickel source raw material, manganese source raw material, fluorine source raw material and titanium source raw material are mixed uniformly in water, and then prepared by co-precipitation method and added into a constant temperature reaction kettle, and then filtered and dried to obtain a precursor Ni (1 / 3)-x Fe 1 / 3 Mn 1 / 3 Ti x (OH) 2-y F y , and then mixed with a sodium source raw material and sintered at high temperature to obtain the positive electrode active material Na z Ni (1 / 3)-x Fe 1 / 3 Mn 1 / 3 Ti x O 2-y F y ; wherein 0.5≤z≤1.5, 0.01≤x≤0.07, 0.2≤y≤1.6. The amount of each raw material is determined according to the chemical formula of the final product.

[0028] In some embodiments of the present application, the molar mass ratio of the nickel source, iron source, manganese source, titanium source, fluorine source, and sodium source raw materials is (2.0-3.3):(2.3-3.3):(2.6-3.4):(0.2-0.7):(2-16):(10-25); in other embodiments of the present application, the molar mass ratio of the manganese source, nickel source, iron source, and titanium source in the metal source raw material is 3.3:3.1:3.3:0.2, and the molar mass ratio of the sodium source and fluorine source in the non-metal source raw material is 1:0.2.

[0029] In some embodiments of the present application, the iron source, nickel source, manganese source, titanium source, and sodium source raw materials are sulfate, hydrochloride, nitrate, carbonate, acetate, or oxide of each metal ion or its hydrate; the iron source includes ferrous ion and ferric ion; in other embodiments of the present application, the iron source raw material is selected from the sulfate, nitrate or hydrochloride of iron ion or ferrous ion, such as ferrous sulfate, ferric nitrate, ferric chloride, etc.; the nickel source raw material is selected from its oxide, nitrate or sulfate, such as nickel oxide, nickel sulfate or nickel nitrate of +2 valence nickel ion; the manganese source raw material is selected from its sulfate, nitrate or hydrochloride, such as manganese sulfate, manganese nitrate or manganese chloride of +2 valence manganese ion; the titanium source is selected from its oxide, such as +2 valence titanium oxide; the sodium source raw material is selected from its carbonate, acetate or nitrate, such as sodium carbonate, sodium acetate or sodium nitrate.

[0030] In some embodiments of the present application, the fluorine source raw material is a metal ion fluoride or ammonium fluoride; further optionally, the metal ion is sodium ion or potassium ion; in other embodiments of the present application, the fluorine source raw material is potassium fluoride, sodium fluoride or ammonium fluoride.

[0031] In some embodiments of the present application, ferrous sulfate, manganese sulfate, nickel sulfate, titanium oxide, sodium fluoride and sodium carbonate are used as raw materials for the preparation of the positive electrode active material.

[0032] In some embodiments of the present application, a hydroxide complexing agent, such as sodium hydroxide, is added during the coprecipitation reaction to form a complex small molecule with nickel ions, preventing the formation of nickel ion precipitates; in some other embodiments of the present application, a heavy metal complexing agent, such as ammonia, can also be added to further remove heavy metal impurities. Most impurity metal ions in the feed solution can be complexed by ammonia, and can be hydrolyzed to form the corresponding hydroxide, which is referred to as an alkaline salt precipitate.

[0033] In some embodiments of the present application, the sintering is performed by first sintering at a first predetermined rate to a temperature of 300-600°C, and then sintering at a second predetermined rate to a temperature of 800-1100°C. The first sintering temperature can be selected from 300°C, 400°C, 500°C or 600°C, and the second sintering temperature can be selected from 800°C, 900°C, 1000°C or 1100°C. In some other embodiments of the present application, the first sintering time is 4-12h, which can be selected from 4h, 6h, 8h, 10h or 12h, and the second sintering time is 10-24h, which can be selected from 10h, 12h, 14h, 16h, 18h, 20h, 22h or 24h. In some other embodiments of the present application, the first predetermined rate and the second predetermined rate are independently selected from 2-5°C / min, such as 2°C / min, 3°C / min, 4°C / min or 5°C / min. In some other embodiments of the present application, the sintering is performed by first sintering at a rate of 2-5°C / min to a temperature of 300-600°C for 4-12h, and then sintering at a rate of 2-5°C / min to a temperature of 800-1100°C for 10-24h.

[0034] In some embodiments of the present application, the positive electrode active material prepared by the preparation method of the present application has a particle size D 50 of 100-500nm, a pH value of 11.0-13.0, a specific surface area of 0.1-1.0m 2 / g, and is more concentrated in the range of 0.3-0.6m 2 / g.

[0035] In a third aspect of the present application, a positive electrode tab is provided, which comprises the positive electrode active material according to any one of the preceding schemes of the present application, and a conductive agent, a binder and a current collector. The positive electrode active material, the conductive agent and the binder form a positive electrode slurry, and the positive electrode tab is formed by coating the positive electrode slurry on the surface of the current collector.

[0036] In some embodiments of the present application, the mass percentage of the positive active material, the conductive agent and the binder in the positive electrode slurry is 95%-99%, 0.5%-3% and 1%-5% respectively, for example, 96% positive active material, 2% conductive agent and 2% binder.

[0037] In some embodiments of the present application, the conductive agent is carbon nanotube and / or conductive carbon black, and the binder is one or more of CMC (sodium carboxymethyl cellulose), SBR (styrene-butadiene rubber) and polyvinylidene fluoride (PVDF).

[0038] In some embodiments of the present application, the current collector is a metal foil, for example, an aluminum foil, a copper foil or the like.

[0039] In a fourth aspect of the present application, a sodium ion battery is provided, comprising the aforementioned positive electrode sheet, and a separator, an electrolyte, a tab and a negative electrode sheet.

[0040] In some embodiments of the present application, the negative electrode sheet uses hard carbon as the active material, and the separator, the tab, the conductive agent and the binder are selected from conventional materials.

[0041] In some embodiments of the present application, the sodium ion battery is prepared into a battery cell by the method of lamination, after baking the battery cell, a non-aqueous electrolyte is injected into the battery cell, and after formation and capacity determination, the sodium ion battery is prepared.

[0042] In each group of comparative experiments provided in the present application, unless otherwise specified, all other experimental conditions, materials, etc. remain the same to ensure comparability. Unless otherwise specified, the experimental materials and reagents used in the examples can be obtained from commercial channels.

[0043] Unless otherwise specified, "room temperature" used in the present application refers to the temperature measured by a Celsius thermometer in a normal laboratory, generally 20-30℃, preferably 25℃ (298.15K in Kelvin).

[0044] The following further describes a positive active material, a preparation method thereof, a positive electrode sheet and a sodium ion battery provided in the present application.

[0045] First embodiment: O3-type sodium ion battery positive active material (x=0.02, y=0.2, z=1.0) of the present application

[0046] (1) Take 102 parts of ferrous sulfate, 102 parts of manganese sulfate, 90 parts of nickel sulfate, 5 parts of titanium oxide, 10.7 parts of sodium fluoride, and add 160 parts of water, mix uniformly to obtain a mixed solution;

[0047] (2) Slowly add complexing agents ammonia and sodium hydroxide to the mixed solution, and the reaction time is 24h;

[0048] (3) After filtering the reaction product, dry it at 70-120℃ for 12-36h to obtain the precursor Ni 0.31 Fe 0.33 Mn 0.33 Ti 0.02 (OH) 1.8 F 0.2 ;

[0049] (4) Take 112 parts of sodium carbonate, mix and grind with the precursor prepared in the above (3), and then sinter, increase the temperature to 450℃ at a rate of 3℃ / min and keep for 5h, then increase the temperature to 900℃ at the same rate and keep for 12h to obtain the final product of sodium ion positive electrode material doped with titanium ions and fluorine ions, with the chemical formula of NaNi 0.31 Fe 0.33 Mn 0.33 Ti 0.02 O 1.8 F 0.2 .

[0050] Figure 1 The XRD results show that the NaNi 0.31 Fe 0.33 Mn 0.33 Ti 0.02 O 1.8 F 0.2 obtained in this embodiment is a pure phase, indicating that doping a small amount of fluorine ions and titanium ions will not affect the crystal structure of NaNi 0.31 Fe 0.33 Mn 0.33 Ti 0.02 O 1.8 F 0.2 ; Figure 2 The SEM results show that the particle size of the NaNi 0.31 Fe 0.33 Mn 0.33 Ti 0.02 O 1.8 F 0.2 prepared in this embodiment is about 5-8um, and the particle size is uniform.

[0051] Second embodiment: sodium ion battery positive electrode active material (x=0.02, y=0.4, z=1.0) of the application O3 type

[0052] (1) Take 102 parts of ferrous sulfate, 102 parts of manganese sulfate, 90 parts of nickel sulfate, 5 parts of titanium oxide, and 21.5 parts of sodium fluoride, add 160 parts of water, mix uniformly to obtain a mixed solution;

[0053] (2) Slowly add complexing agents ammonia and sodium hydroxide to the mixed solution A, and the reaction time is 24h;

[0054] (3) After the reaction product is filtered, the precursor Ni 0.31 Fe 0.33 Mn 0.33 Ti 0.02 (OH) 1.6 F 0.4 ;

[0055] (4) Take 112 parts of sodium carbonate, mix and grind with the precursor prepared in the above (3), and then sinter, increase the temperature to 450°C at a rate of 3°C / min and keep for 5h, and then increase the temperature to 900°C at the same rate and keep for 12h, to obtain the final product of sodium ion positive electrode material doped with titanium ions and fluorine ions, with the chemical formula NaNi 0.31 Fe 0.33 Mn 0.33 Ti 0.02 O 1.6 F 0.4 .

[0056] Similar to the XRD results and SEM results of the first embodiment, the NaNi 0.31 Fe 0.33 Mn 0.33 Ti 0.02 O 1.6 F 0.4 obtained in this embodiment is a pure phase, indicating that doping a small amount of fluorine ions and titanium ions will not affect the crystal structure of NaNi 0.31 Fe 0.33 Mn 0.33 Ti 0.0 2O 1.6 F 0.4 ; the particle size is about 5-8um, and the particle size is uniform.

[0057] Third embodiment: O3 type sodium ion battery positive electrode active material (x=0.02, y=0.1, z=1.0) of the application

[0058] (1) Take 102 parts of ferrous sulfate, 102 parts of manganese sulfate, 90 parts of nickel sulfate, 5 parts of titanium oxide, and 5.4 parts of sodium fluoride, add 160 parts of water, mix uniformly to obtain a mixed solution;

[0059] (2) Slowly add complexing agents ammonia and sodium hydroxide to the mixed solution, and the reaction time is 24h;

[0060] (3) After the reaction product is filtered, the precursor Ni 0.31 Fe 0.33 Mn 0.33 Ti 0.02 (OH)1.9 F 0.1 ;

[0061] (4) Take 112 parts of sodium carbonate, mix and grind with the precursor prepared in the above (3), then sinter, increase the temperature to 450℃ at a rate of 3℃ / min and keep for 5h, then increase the temperature to 900℃ at the same rate and keep for 12h, to obtain the final product of titanium ion and fluorine ion doped sodium ion positive electrode material, with the chemical formula of NaNi 0.31 Fe 0.33 Mn 0.33 Ti 0.02 O 1.9 F 0.1 .

[0062] Similar to the XRD results and SEM results of the first embodiment, the NaNi 0.31 Fe 0.33 Mn 0.33 Ti 0.02 O 1.9 F 0.1 obtained in this embodiment is a pure phase, indicating that doping a small amount of fluorine ion and titanium ion will not affect the crystal structure of NaNi 0.31 Fe 0.33 Mn 0.33 Ti 0.0 2O 1.9 F 0.1 ; The particle size is about 5-8um, and the particle size is uniform.

[0063] Fourth embodiment: the sodium ion battery positive active material of the application O3 type (x=0.05, y=0.4, z=1.0)

[0064] (1) Take 102 parts of ferrous sulfate, 102 parts of manganese sulfate, 89 parts of nickel sulfate, 6 parts of titanium oxide, and 21.5 parts of sodium fluoride, add 160 parts of water, mix uniformly to obtain a mixed solution;

[0065] (2) Slowly add complexing agents ammonia and sodium hydroxide to the mixed solution, and the reaction time is 24h;

[0066] (3) After filtering the reaction product, dry it at 70-120℃ for 12-36h to obtain the precursor Ni 0.27 Fe 0.33 Mn 0.33 Ti 0.05 (OH) 1.8 F 0.2 ;

[0067] (4) take weight of 112 parts of sodium carbonate, mixed with the precursor prepared in the above (3) grinding, and then sintering, to 450℃ at a rate of 3℃ / min for 5h, and then at the same rate to 900℃ for 12h, to obtain the final product of titanium ion and fluorine ion doped sodium ion positive electrode material, its chemical formula is NaNi 0.27 Fe 0.33 Mn 0.33 Ti 0.05 O 1.8 F 0.2 .

[0068] Similar to the XRD results and SEM results of the first embodiment, the NaNi 0.27 Fe 0.33 Mn 0.33 Ti 0.05 O 1.8 F 0.2 of the embodiment is a pure phase, indicating that a small amount of fluorine ion and titanium ion doping will not affect the crystal structure of NaNi 0.27 Fe 0.33 Mn 0.33 Ti 0.0 5O 1.8 F 0.2 ; the particle size is about 5-8um, and the particle size is uniform.

[0069] The first comparative example: undoped fluorine and titanium positive electrode active material (x=0, y=0, z=1.0)

[0070] (1) take 102 parts of ferrous sulfate, 102 parts of manganese sulfate, 92 parts of nickel sulfate, add 160 parts of water, mix uniformly to obtain a mixed solution;

[0071] (2) slowly add complexing agent ammonia and sodium hydroxide to the mixed solution, and the reaction time is 24h;

[0072] (3) filter the reaction product and dry at 70-120℃ for 12-36h to obtain the precursor Ni 0.33 Fe 0.33 Mn 0.33 (OH)2;

[0073] (4) take weight of 112 parts of sodium carbonate, mixed with the precursor prepared in the above (3) grinding, and then sintering, to 450℃ at a rate of 3℃ / min for 5h, and then at the same rate to 900℃ for 12h, to obtain the final product of titanium ion and fluorine ion doped sodium ion positive electrode material, its chemical formula is NaNi 0.33 Fe 0.33 Mn 0.33 O2.

[0074] Second Comparative Example: Undoped fluorine positive electrode active material (x = 0.02, y = 0, z = 1.0)

[0075] (1) Take 102 parts of ferrous sulfate, 102 parts of manganese sulfate, 90 parts of nickel sulfate, 5 parts of titanium oxide, add 160 parts of water, mix uniformly to obtain a mixed solution;

[0076] (2) Slowly add complexing agents ammonia and sodium hydroxide to the mixed solution, and the reaction time is 24h;

[0077] (3) After filtering the reaction product, dry it at 70-120°C for 12-36h to obtain the precursor Ni 0.31 Fe 0.33 Mn 0.33 Ti 0.02 (OH)2;

[0078] (4) Take 112 parts of sodium carbonate, mix and grind with the precursor prepared in the above (3), and then sinter, increase the temperature to 450°C at a rate of 3°C / min and keep for 5h, then increase the temperature to 900°C at the same rate and keep for 12h, to obtain the final product of titanium ion and fluorine ion doped sodium ion positive electrode material, whose chemical formula is NaNi 0.31 Fe 0.33 Mn 0.33 Ti 0.02 O2

[0079] Third Comparative Example: Undoped titanium positive electrode active material (x = 0, y = 0.2, z = 1.0)

[0080] (1) Take 102 parts of ferrous sulfate, 102 parts of manganese sulfate, 92 parts of nickel sulfate, 10.7 parts of sodium fluoride, add 160 parts of water, mix uniformly to obtain a mixed solution;

[0081] (2) Slowly add complexing agents ammonia and sodium hydroxide to the mixed solution, and the reaction time is 24h;

[0082] (3) After filtering the reaction product, dry it at 70-120°C for 12-36h to obtain the precursor Ni 0.33 Fe 0.33 Mn 0.33 (OH) 1.8 F 0.2 ;

[0083] (4) Take 112 parts of sodium carbonate, mix and grind with the precursor prepared in the above (3), and then sinter, increase the temperature to 450°C at a rate of 3°C / min and keep for 5h, then increase the temperature to 900°C at the same rate and keep for 12h, to obtain the final product of titanium ion and fluorine ion doped sodium ion positive electrode material, whose chemical formula is NaNi 0.33 Fe0.33 Mn 0.33 O 1.8 F 0.2 .

[0084] Fifth embodiment: preparation and performance test of sodium ion battery

[0085] 1. Preparation of sodium ion battery

[0086] (1) Preparation of positive electrode sheet

[0087] The sodium ion positive electrode active material is prepared by dissolving 96% positive electrode active material (based on the mass of the positive electrode), 2% PVDF (based on the mass of the positive electrode), 1% conductive carbon black (based on the mass of the positive electrode), and 1% carbon nanotubes (based on the mass of the positive electrode) in N-methyl pyrrolidone, stirring and dispersing in a blender under vacuum, to prepare a uniform bubble-free slurry, and uniformly coating on an aluminum foil to prepare a positive electrode sheet.

[0088] (2) Preparation of negative electrode sheet

[0089] The hard carbon is used as the negative electrode active material, and is prepared by dissolving 94% negative electrode active material (based on the mass of the negative electrode), 1.5% sodium carboxymethyl cellulose (based on the mass of the positive electrode), 2% conductive carbon black (based on the mass of the positive electrode), and 2.5% butyl rubber latex (based on the mass of the negative electrode) in deionized water, stirring and dispersing in a blender under vacuum, to prepare a uniform bubble-free slurry, and uniformly coating on an aluminum foil to prepare a negative electrode sheet.

[0090] (3) Packaging and formation

[0091] The positive electrode sheet, separator, and negative electrode sheet are used to prepare a battery cell by lamination, the battery cell has the same side tab, the tab and the current collector are welded together using an ultrasonic welding machine, and then the battery cell is packaged using an aluminum plastic film.

[0092] After the battery cell is baked, a non-aqueous electrolyte is injected into the battery cell, and after formation and capacity test, a 4Ah lithium ion battery is prepared for battery performance test.

[0093] 2. Performance detection method

[0094] Battery cycle performance test method:

[0095] (1) The experimental battery cell is placed at 25℃±3, and the battery cell is charged at 0.5C constant current and constant voltage to 4.0V, and the current is cut off at 0.02C;

[0096] (2) Standby for 30min;

[0097] (3) At 25℃±3, discharge at 1C constant current to 1.5V, and record the capacity D1 at this time;

[0098] (4) rest for 30 min;

[0099] (5) cycle (1)-(4), record cycle number and final discharge capacity D2;

[0100] Capacity retention rate D = D2 / D1*100%

[0101] Gravimetric capacity experimental method:

[0102] (1) The positive electrode material: SP: PVDF = 94:3:3 was prepared into a positive electrode, the negative electrode used metal sodium sheet, electrolyte (1 mol / L NaPF6+EC:DEC = 1:1+5% FEC), prepared into a button cell

[0103] (2) The experimental battery was placed at 25℃±3, and the cell was charged at 0.1C constant current and constant voltage to 4.0V, and the current was cut off at 0.02C;

[0104] (3) rest for 30 min;

[0105] (4) At 25℃±3, the cell was discharged at 0.1C constant current to 2.0V, and the capacity at this time was recorded.

[0106] Gravimetric capacity of the positive electrode.

[0107] 3. Experimental results

[0108] Table 1

[0109] Positive electrode specific capacity mAh / g Cycle number Capacity retention rate % First embodiment 137 200 95.4 Second embodiment 136 200 96.2 Third embodiment 136 200 95.5 Fourth embodiment 131 200 95.3 First comparative example 130 200 60.23 Second comparative example 134 200 70.15 Third comparative example 130 200 78.31

[0110] As can be seen from Table 1, the sodium ion battery assembled by the positive electrode active material of the application still has a capacity retention rate of more than 95% after 200 cycles, while the capacity retention rates of the sodium ion batteries of the comparative examples are all less than 80%, forming a significant difference;

[0111] Moreover, compared with the first embodiment and the three comparative examples (not doped with fluorine and / or titanium based on the first embodiment), the gravimetric capacity also decreases in the case of not doping fluorine and / or titanium, which affects the performance of the battery.

[0112] The above description is only a specific embodiment of the application, which enables those skilled in the art to understand or implement the application. Various modifications to these embodiments will be apparent to those skilled in the art, and the general principles defined herein can be implemented in other embodiments without departing from the spirit or scope of the application. Therefore, the application will not be limited to these embodiments shown herein, but will conform to the widest scope consistent with the principles and novel features applied herein.

Claims

1. A method for producing a positive electrode active material, characterized by, Comprising: Take iron source, nickel source, manganese source, fluorine source and titanium source raw materials, add water and mix uniformly, react through coprecipitation method to generate precursor Ni (1 / 3)-x Fe 1 / 3 Mn 1 / 3 Ti x (OH) 2-y F y ; Sintering after mixing sodium source raw material and the precursor to obtain positive active material Na z Ni (1 / 3)-x Fe 1 / 3 Mn 1 / 3 Ti x O 2- y F y ; wherein, 0.5≤z≤1.5, 0.01≤x≤0.07, 0.2≤y≤1.6; The sintering is sintering at a first rated rate to 300-600 DEG C, and then sintering at a second rated rate to 800-1100 DEG C.

2. The method of claim 1, wherein, The molar mass ratio of the iron source, nickel source, manganese source, titanium source, fluorine source, and sodium source raw materials is (2.0-3.3):(2.3-3.3):(2.6-3.4):(0.2-0.7):(2-16):(10-25).

3. The preparation method according to claim 2, characterized in that, The iron source, nickel source, manganese source, titanium source, and sodium source raw materials are each a sulfate, hydrochloride, nitrate, carbonate, acetate, oxide, or hydrate of a metal ion.

4. The preparation method according to claim 2, characterized in that, The fluorine source raw material is a metal ion fluoride or ammonium fluoride.

5. The preparation method according to claim 4, characterized in that, The metal ion is a sodium ion or potassium ion.

6. The method of claim 1, wherein the step of forming the first and second layers is performed by a process selected from the group consisting of: sputtering, evaporation, and chemical vapor deposition. The first rated rate and the second rated rate are independently selected from 2-5 DEG C / min.

7. A positive electrode sheet characterized by comprising: The positive electrode active material, a conductive agent, a binder, and a current collector according to any one of claims 1-6.

8. A sodium-ion battery, characterized in that, The positive electrode plate, a separator, an electrolyte, a tab, and a negative electrode plate according to claim 7.

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