CN115954482A

CN115954482A - Layered oxide composite material, preparation method thereof, positive plate and sodium ion battery

Info

Publication number: CN115954482A
Application number: CN202310249455.6A
Authority: CN
Inventors: 董英男; 王迪; 张继宗; 蒋绮雯
Original assignee: Jiangsu Zenergy Battery Technologies Co ltd
Current assignee: Jiangsu Zenergy Battery Technologies Co ltd
Priority date: 2023-03-15
Filing date: 2023-03-15
Publication date: 2023-04-11
Anticipated expiration: 2043-03-15
Also published as: CN115954482B

Abstract

The invention discloses a layered oxide composite material, the molecular formula of which is Na _x Ni _i Fe _j Mn _k M _m O ₂ /KFeF ₃ Wherein: m is Li ⁺ 、B ³⁺ 、Mg ²⁺ 、Al ³⁺ 、K ⁺ 、Ca ²⁺ 、Ti ⁴⁺ 、Co ³⁺ 、V ³⁺ 、V ⁴⁺ 、Cr ³⁺ 、Cu ²⁺ 、Zn ²⁺ 、Zr ⁴⁺ 、Nb ⁵⁺ And Sn ⁴⁺ One or more of; 0.8<x≤1，0<i≤0.4，0<j≤0.5，0<k≤0.6，0<m is less than or equal to 0.2, and i + j + k + m =1. The invention also discloses a preparation method of the layered oxide composite material, and a positive plate and a sodium ion battery prepared from the layered oxide composite material. The layered oxide composite material improves the structural stability of the existing O3 phase layered oxide and improves the cycle performance and the rate capability of a sodium ion battery.

Description

Layered oxide composite material, preparation method thereof, positive plate and sodium ion battery

Technical Field

The invention relates to the technical field of sodium ion batteries, in particular to a layered oxide composite material, a preparation method thereof, a positive plate and a sodium ion battery.

Background

Among various cathode materials for sodium ion batteries, O3 phase layered oxides have received much attention due to their advantages of sufficient sodium in the full cell, high electrochemical activity, high theoretical specific capacity, and easy synthesis. However, the structural stability of the O3 phase layered oxide material is poor, which leads to the cycle performance and rate capability of the material to be affected to a certain extent, and further limits the practical application of the O3 phase layered oxide.

Therefore, how to improve the cycle performance and rate capability of the O3 phase layered oxide cathode material becomes one of the key problems in the related art of the sodium ion battery.

Disclosure of Invention

The technical problem to be solved by the invention is to provide a layered oxide composite material to improve the structural stability of the layered oxide, and further improve the cycle performance and the rate capability of a sodium ion battery.

In order to solve the technical problems, the invention provides the following technical scheme:

the invention provides in a first aspect a layered oxide composite material having the molecular formula Na _x Ni _i Fe _j Mn _k M _m O ₂ /KFeF ₃ Wherein: m is Li ⁺ 、B ³⁺ 、Mg ²⁺ 、Al ³⁺ 、K ⁺ 、Ca ²⁺ 、Ti ⁴⁺ 、Co ³⁺ 、V ³⁺ 、V ⁴⁺ 、Cr ³⁺ 、Cu ²⁺ 、Zn ²⁺ 、Zr ⁴⁺ 、Nb ⁵⁺ And Sn ⁴⁺ One or more of; 0.8<x≤1，0<i≤0.4，0<j≤0.5，0<k≤0.6，0<m is less than or equal to 0.2, and i + j + k + m =1.

Further, in the layered oxide composite material, na _x Ni _i Fe _j Mn _k M _m O ₂ Is O3 phase layered oxide.

The second aspect of the present invention provides a method for preparing a layered oxide composite material, comprising the steps of:

na is mixed with _x Ni _i Fe _j Mn _k M _m O ₂ Powder, KFeF ₃ Ball-milling and mixing the precursor powder, and sintering in a protective atmosphere to obtain the layered oxide composite material Na _x Ni _i Fe _j Mn _k M _m O ₂ /KFeF ₃ ；

Wherein M is Li ⁺ 、B ³⁺ 、Mg ²⁺ 、Al ³⁺ 、K ⁺ 、Ca ²⁺ 、Ti ⁴⁺ 、Co ³⁺ 、V ³⁺ 、V ⁴⁺ 、Cr ³⁺ 、Cu ²⁺ 、Zn ²⁺ 、Zr ⁴⁺ 、Nb ⁵⁺ And Sn ⁴⁺ One or more of; 0.8<x≤1，0<i≤0.4，0<j≤0.5，0<k≤0.6，0<m is less than or equal to 0.2, and i + j + k + m =1.

Further, na _x Ni _i Fe _j Mn _k M _m O ₂ Powder and KFeF ₃ The mass ratio of the precursor powder is 9-9.5: 1-0.5;

and/or the rotation speed of the ball milling is 250 to 500r/min, and the ball milling time is 2 to 8h;

and/or the protective atmosphere is selected from one or more of nitrogen and inert gas;

and/or the sintering temperature is 350-650 ℃, and the sintering time is 2-6 h.

Further, the Na _x Ni _i Fe _j Mn _k M _m O ₂ The preparation method of the powder comprises the following steps:

a. mixing Ni _i Fe _j Mn _k M _m (OH) ₂ The precursor and a sodium source are ball-milled and mixed uniformly;

b. b, sintering the mixture obtained in the step a to obtain the productNa _x Ni _i Fe _j Mn _k M _m O ₂ And (3) powder.

Further, in step a, the sodium source comprises one or more of sodium carbonate, sodium hydroxide, sodium acetate, sodium oxalate and sodium nitrate;

and/or, the sodium source and Ni _i Fe _j Mn _k M _m (OH) ₂ The molar ratio of the precursor is 0.01 to 1.25: 0.01 to 1;

and/or the rotation speed of the ball milling is 300 to 800r/min, and the ball milling time is 0.5 to 5h;

in the step b, the sintering comprises presintering and high-temperature solid-phase sintering; the presintering temperature is 200 to 550 ℃, and the presintering time is 1 to 8h; the temperature of the high-temperature solid phase sintering is 750 to 1100 ℃, and the time of the high-temperature solid phase sintering is 4 to 20h.

Further, the KFeF ₃ The preparation method of the precursor powder comprises the following steps:

c. under the condition of stirring, dropwise adding the solution A and the solution B into an oil phase solvent containing an emulsifier to obtain a microemulsion;

d. centrifugally separating the microemulsion, collecting precipitate, washing, drying and grinding to obtain the KFeF ₃ Precursor powder;

wherein the solution A contains K ⁺ And Fe ²⁺ The solution B is an aqueous solution containing F ^- An aqueous solution of (a).

Further, in step c: the emulsifier comprises at least one of cetyl trimethyl ammonium bromide, N-dodecyl dimethylamine and polyoxyethylene ether;

and/or the oil phase solvent comprises at least one of isooctanol, n-butanol and octane;

and/or the mass ratio of the emulsifier to the oil phase solvent is 1 to 1.5: 6 to 8;

and/or the solution A is KNO ₃ And FeCl ₂ Dissolved in water, said solution B being obtained from NH ₄ F is obtained by dissolving in water;

and/or the volume ratio of the solution A to the solution B is 4 to 6.5: 1.5 to 3;

and/or in the microemulsion, the molar ratio of potassium nitrate, ferrous chloride and ammonium fluoride is 1;

and/or the speed of centrifugal separation is 2000 to 3000r/min, and the centrifugal time is 0.5 to 1.5 hours;

and/or the washing solution is absolute ethyl alcohol;

and/or the drying temperature is 80 to 120 ℃, and the drying time is 5 to 15h.

The invention provides a positive plate, which comprises the layered oxide composite material or the layered oxide composite material prepared by the method.

The invention provides a sodium-ion battery, which comprises the positive plate.

Compared with the prior art, the invention has the beneficial effects that:

1. the invention introduces the KFeF with the perovskite structure into the layered oxide material ₃ KFeF of perovskite structure ₃ Can be used as a nail to nail the layered structure, so that the layered oxide keeps the structural stability in the process of sodium removal, and the harmful structural phase change is reduced, thereby improving the structural stability of the layered oxide.

2. KFeF incorporated in the layered oxide composite material of the invention ₃ The sodium ion storage structure is an excellent sodium storage structure, has a three-dimensional rapid ion channel, is very convenient for ion transportation, and is introduced with KFeF ₃ The characteristic of high-rate charge and discharge of the material is enhanced, and the rate performance of the material is greatly improved.

Drawings

FIG. 1 shows the layered oxide NaNi prepared in example 1 _0.15 Fe _0.15 Mn _0.65 Mg _0.05 O ₂ Scanning Electron Microscopy (SEM);

FIG. 2 is KFeF prepared in example 1 ₃ Scanning electron microscope images of (a);

FIG. 3 shows NaNi prepared in example 1 _0.15 Fe _0.15 Mn _0.65 Mg _0.05 O ₂ /KFeF ₃ Scanning electron micrographs of the material;

FIG. 4 shows NaNi prepared in example 1 _0.15 Fe _0.15 Mn _0.65 Mg _0.05 O ₂ /KFeF ₃ X-ray diffraction pattern (XRD) of the material.

Detailed Description

Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. The terminology used in the description of the invention herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. As used herein, the term "and/or" includes any and all combinations of one or more of the associated listed items.

As one of the important positive electrode materials of the sodium ion battery, O3 phase layered oxide has the problems of poor structural stability and the like, so that the cycle performance and the rate capability are influenced to a certain extent, and the practical application of the layered oxide is limited. At present, the prior art adopts means such as element doping and cladding to modify the O3 phase layered oxide, and although the means improves the cycle performance and rate capability of the layered oxide to a certain extent, the problem of poor structural stability cannot be solved.

In order to solve the above problems of the layered oxide, the present invention provides a method for modifying a layered oxide by introducing KFeF having a perovskite structure ₃ The compound improves the structural stability of the layered oxide, thereby improving the cycle performance and rate capability of the battery.

Specifically, the molecular formula of the layered oxide composite material provided by the invention is Na _x Ni _i Fe _j Mn _k M _m O ₂ /KFeF ₃ Wherein: m is Li ⁺ 、B ³⁺ 、Mg ²⁺ 、Al ³⁺ 、K ⁺ 、Ca ²⁺ 、Ti ⁴⁺ 、Co ³⁺ 、V ³⁺ 、V ⁴⁺ 、Cr ³⁺ 、Cu ²⁺ 、Zn ²⁺ 、Zr ⁴⁺ 、Nb ⁵⁺ And Sn ⁴⁺ One or more of; 0.8<x≤1，0<i≤0.4，0<j≤0.5，0<k≤0.6，0<m is less than or equal to 0.2, and i + j + k + m =1.

In the present invention, na _x Ni _i Fe _j Mn _k M _m O ₂ M in (A) may be either an element, e.g. NaNi _0.15 Fe _0.15 Mn _0.65 Mg _0.05 O ₂ 、NaNi _0.3 Fe _0.15 Mn _0.5 Ti _0.05 O ₂ 、NaNi _0.15 Fe _0.25 Mn _0.55 Cu _0.05 O ₂ Or a plurality of elements, e.g. NaNi _0.22 Fe _0.18 Mn _0.56 Mg _0.02 Zr _0.02 O ₂ . When M is a plurality of elements, the resulting layered oxide composite has a similar technical effect to that when M is one element. Further preferably, na _x Ni _i Fe _j Mn _k M _m O ₂ Is O3 phase layered oxide.

Na _x Ni _i Fe _j Mn _k M _m O ₂ Is a typical layered metal oxide, and is accompanied with the intercalation and deintercalation of sodium ions during the charge and discharge of the battery. Local lattice distortion usually occurs during the insertion and extraction process, and local structural distortion aggravates Na ⁺ The migration of (2) causes irreversible phase change, finally causes mechanical fatigue of the structure, and in severe cases, cracks appear on the surface of the material, so that the performance of the battery is seriously reduced. KFeF ₃ Is a compound with a perovskite structure, and is prepared by adding Na into a layered oxide _x Ni _i Fe _j Mn _k M _m O ₂ KFeF with perovskite structure introduced therein ₃ The layered oxide can be used as a nail to pin a layered structure, so that the stability of the structure can be maintained in the process of removing sodium from the layered oxide, the harmful structural phase change is reduced, and a mechanical stable structure is formed; secondly, the perovskite structure is a combination of a layered structure and a rock salt structure, and thus Na of the layered structure _x Ni _i Fe _j Mn _k M _m O ₂ Has good adaptability, and eliminates the introduction of KFeF ₃ The complexity of the additional structure arises; third, KFeF of perovskite structure ₃ Structural features with zero strain introduced intoThe layered oxide can avoid large volume change in the circulation process, and further stabilizes the structure of the composite material; finally, KFeF ₃ The sodium ion storage structure is an excellent sodium storage structure, has a three-dimensional fast ion channel, is very convenient for ion transportation, and introduces KFeF ₃ The characteristic of the composite material of high-rate charge and discharge is strengthened, and the rate capability of the material is greatly improved.

The invention also discloses a preparation method of the layered oxide composite material, which comprises the following steps:

mixing Na _x Ni _i Fe _j Mn _k M _m O ₂ Powder, KFeF ₃ Mixing the precursor powder, and sintering in a protective atmosphere to obtain the layered oxide composite material Na _x Ni _i Fe _j Mn _k M _m O ₂ /KFeF ₃ (ii) a Wherein M is Li ⁺ 、B ³⁺ 、Mg ²⁺ 、Al ³⁺ 、K ⁺ 、Ca ²⁺ 、Ti ⁴⁺ 、Co ³ ⁺ 、V ³⁺ 、V ⁴⁺ 、Cr ³⁺ 、Cu ²⁺ 、Zn ²⁺ 、Zr ⁴⁺ 、Nb ⁵⁺ And Sn ⁴⁺ One or more of (a); 0.8<x≤1，0<i≤0.4，0<j≤0.5，0<k≤0.6，0<m is less than or equal to 0.2, and i + j + k + m =1.

In the above preparation method, na _x Ni _i Fe _j Mn _k M _m O ₂ Powder and KFeF ₃ The mass ratio of the precursor powder is preferably 9 to 9.5: 1 to 0.5, and may be, for example, from 9. The mixing is preferably performed by means of ball milling, which can improve the uniformity of powder mixing. The rotation speed of the ball milling is preferably 250 to 500r/min, such as 250 r/min, 300r/min, 350 r/min, 400 r/min, 450 r/min, 500r/min and the like; the time for ball milling is preferably 2 to 8h, for example, 2h, 3h, 4h, 5h, 6h, 7h, 8h, and the like.

After the powders are mixed uniformly, the mixture is placed in a sintering furnace (such as a tube furnace) and sintered under a protective atmosphere. The protective atmosphere may be one of nitrogen, inert gas (e.g., he, ne, ar), or a mixed atmosphere of a plurality of these gases. The same effect can be achieved when the protective atmosphere is one gas or a mixed gas composed of a plurality of gases. The sintering process can be carried out at a relatively low temperature, and the temperature rise rate of the sintering furnace can be 1 to 10 ℃/min, such as 1 ℃/min, 2 ℃/min, 3 ℃/min, 4 ℃/min, 5 ℃/min, 6 ℃/min, 7 ℃/min, 8 ℃/min, 9 ℃/min, 10 ℃/min, and the like. The sintering temperature is preferably 350 to 650 ℃, for example 350 ℃, 360 ℃, 380 ℃, 400 ℃, 420 ℃, 440 ℃, 450 ℃, 460 ℃, 480 ℃, 500 ℃, 520 ℃, 540 ℃, 550 ℃, 560 ℃, 5980 ℃, 600 ℃, 620 ℃, 640 ℃, 650 ℃ and the like; the sintering time is preferably 2 to 6h, for example, 2h, 3h, 4h, 5h, 6h, etc.

In the above preparation method, na _x Ni _i Fe _j Mn _k M _m O ₂ The preparation method of the powder comprises the following steps:

a. mixing Ni _i Fe _j Mn _k M _m (OH) ₂ Uniformly mixing the precursor with a sodium source;

b. sintering the mixture obtained in the step a to obtain the Na _x Ni _i Fe _j Mn _k M _m O ₂ And (3) powder.

In the step a, the sodium source is various sodium-containing compounds, including but not limited to one or more of sodium carbonate, sodium hydroxide, sodium acetate, sodium oxalate and sodium nitrate. Wherein, when the sodium source is one or more, na can be obtained by sintering _x Ni _i Fe _j Mn _k M _m O ₂ And (3) powder.

In the step a, the sodium source and Ni _i Fe _j Mn _k M _m (OH) ₂ The precursor is according to Na _x Ni _i Fe _j Mn _k M _m O ₂ （0.8<x≤1，0<i≤0.4，0<j≤0.5，0<k≤0.6，0<m is less than or equal to 0.2, and i + j + k + m = 1). In some embodiments, the sodium source is in contact with Ni _i Fe _j Mn _k M _m (OH) ₂ The molar ratio of the precursor is 0.01-1.25: 0.01-1.

In the above step a, ni _i Fe _j Mn _k M _m (OH) ₂ The precursor and the sodium source are preferably mixed in a ball milling mode, and the rotation speed of the ball milling is preferably 300 to 800r/min, such as 300r/min, 350 r/min, 400 r/min, 450 r/min, 500r/min, 550 r/min, 600 r/min, 650 r/min, 700 r/min, 750 r/min, 800r/min and the like; the time for ball milling is preferably 0.5 to 5h, for example, 0.5h, 1h, 2h, 3h, 4h, 5h, etc.

In the step b, the ball-milled mixture is placed in a sintering furnace (such as a muffle furnace) and sintered by heating. The heating rate is preferably 1 to 10 ℃/min, for example, 1 ℃/min, 2 ℃/min, 3 ℃/min, 4 ℃/min, 5 ℃/min, 6 ℃/min, 7 ℃/min, 8 ℃/min, 9 ℃/min, 10 ℃/min, or the like. The sintering process preferably includes two stages, pre-sintering and high temperature solid phase sintering. Wherein the pre-sintering temperature is preferably 200 to 550 ℃, such as 200 ℃, 250 ℃, 300 ℃, 350 ℃, 400 ℃, 450 ℃, 500 ℃, 550 ℃ and the like; the time for the pre-sintering is preferably 1 to 8h, for example, 1h, 2h, 3h, 4h, 5h, 6h, 7h, 8h, and the like. The temperature of the high-temperature solid phase sintering is preferably 750 to 1100 ℃, such as 750 ℃, 800 ℃, 850 ℃, 900 ℃, 950 ℃, 1000 ℃, 1050 ℃, 1100 ℃ and the like; the time for high-temperature solid-phase sintering is preferably 4 to 20h, for example, 4h, 5h, 6h, 8h, 10h, 12h, 15h, 16 h, 18 h, 20h and the like.

In the preparation method, the KFeF ₃ The preparation method of the precursor powder comprises the following steps:

d. centrifugally separating the microemulsion, collecting precipitate, washing, drying and grinding to obtain the KFeF ₃ And (3) precursor powder.

In the step c, the solution A contains K ⁺ And Fe ²⁺ The solution B is an aqueous solution containing F ^- An aqueous solution of (a). Under the condition of continuous stirring, the solution A and the solution B (namely water phase) are dripped into an oil phase solvent (oil phase) containing an emulsifier to form uniform and transparent microemulsion; after the microemulsion is formed, stirring is continued for a period of time to make the droplets formAre in mutual contact to generate chemical reaction to generate KFeF ₃ And (4) precipitating. Wherein, the emulsifier includes but is not limited to at least one of cetyl trimethyl ammonium bromide, N-dodecyl dimethylamine and polyoxyethylene ether; the oil phase solvent comprises at least one of isooctanol, n-butanol and octane. The mass ratio of the emulsifier to the oil phase solvent is 1 to 1.5: 6 to 8, for example, 1. The volume ratio of the solution A to the solution B is 4 to 6.5: 1.5 to 3, for example, 4:3, etc., preferably 5.

Preferably, the solution A is KNO ₃ And FeCl ₂ Obtained by dissolving in water, said solution B being obtained from NH ₄ F is obtained by dissolving in water. In the microemulsion, the molar ratio of potassium nitrate, ferrous chloride and ammonium fluoride is 1.

And d, in the step d, the microemulsion is subjected to centrifugal separation to separate out a precipitate. The speed of the centrifugal separation is preferably 2000 to 3000r/min, such as 2000r/min, 2200 r/min, 2400 r/min, 2500 r/min, 2600 r/min, 2800 r/min, 3000r/min and the like; the centrifugation time is preferably 0.5 to 1.5 hours, for example, 0.5 hour, 0.6 hour, 0.8 hour, 1.0 hour, 1.2 hours, 1.5 hours, etc. After the precipitate is collected, washing is performed, and the solvent for washing is preferably absolute ethyl alcohol. When drying, the mixture is preferably dried in a forced air drying oven, and the drying temperature is preferably 80 to 120 ℃, such as 80 ℃, 90 ℃, 100 ℃, 110 ℃, 120 ℃ and the like; the drying time is preferably 5 to 15h, for example, 5h, 6h, 7h, 8h, 9h, 10h, 11 h, 12h, 13 h, 14 h, 15h, or the like. Grinding the dried precipitate to obtain KFeF ₃ And (3) precursor powder.

On the basis of the layered oxide composite material, the invention also provides a sodium ion battery which comprises a positive plate, a negative plate, a diaphragm and an electrolyte, wherein the diaphragm is arranged to isolate the positive plate from the negative plate.

In the sodium ion battery, the positive plate can be prepared by adopting a plate preparation process commonly used in the field. The preparation method is schematically as follows: and mixing the layered oxide composite material, the conductive agent and the binder to prepare slurry, coating the slurry on at least one side surface of the positive current collector, and drying and tabletting to obtain the positive plate.

In the preparation method of the positive plate, the type and the content of the conductive agent are not particularly limited and can be selected according to actual requirements. In some embodiments, the conductive agent includes at least one of conductive carbon black, carbon nanotubes, acetylene black, graphene, ketjen black, carbon nanofibers, and the like. It is understood that other conductive agents capable of performing the functions of the present application may be selected according to specific needs without departing from the spirit of the present application, and are not limited thereto.

In the preparation method of the positive plate, the type and the content of the binder are not particularly limited and can be selected according to actual requirements. In some embodiments, the binder comprises at least one of polyacrylonitrile, polyvinylidene fluoride, polyvinyl alcohol, sodium carboxymethylcellulose, polymethacrylic acid, polyacrylic acid, sodium polyacrylate, polyacrylamide, polyamide, polyimide, polyacrylate, styrene butadiene rubber, sodium alginate, chitosan, polyethylene glycol, guar gum, and the like.

The kind of the positive electrode current collector is not particularly limited, and may be selected according to actual requirements, for example, the positive electrode current collector may be an aluminum foil, a nickel foil, or a polymer conductive film, and preferably, the positive electrode current collector is an aluminum foil.

In the sodium ion battery, the type of the separator is not particularly limited, and any separator material conventionally used in batteries may be used, for example, polyethylene, polypropylene, polyvinylidene fluoride, nonwoven fabric, multilayer composite films thereof, and modified separators obtained by modifying the separator with ceramic, PVDF, or the like, but the present invention is not limited thereto.

In the sodium ion battery, the electrolyte may be one or more of an organic liquid electrolyte, an organic solid electrolyte, a solid ceramic electrolyte and a gel electrolyte. Preferably, the electrolyte is an organic liquid electrolyte obtained by dissolving a sodium salt in a non-aqueous organic solvent; wherein the sodium salt may comprise sodium difluorophosphate (NaPO) ₂ F ₂ ) Sodium hexafluorophosphate (NaPF) ₆ ) Sodium bis (fluorosulfonyl) imide (NaFSI), sodium bis (trifluoromethanesulfonyl) imide (Na)TFSi), and sodium oxalyldifluoroborate (NaDFOB). The non-aqueous organic solvent may include one or more of cyclic carbonate, chain carbonate and carboxylate. Wherein, the cyclic carbonate can be selected from one or more of Ethylene Carbonate (EC), propylene Carbonate (PC), butylene carbonate and gamma-butyrolactone; the chain carbonate may be selected from one or more of dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl Methyl Carbonate (EMC), methyl Propyl Carbonate (MPC), methyl Acetate (MA), ethyl Acetate (EA), ethyl Propionate (EP).

In some embodiments, the organic liquid electrolyte may further include a certain amount of additives. The additive may comprise one or more of Vinylene Carbonate (VC), vinyl Ethylene Carbonate (VEC), vinyl sulfate (DTD), vinyl sulfite (ES), methylene Methanedisulfonate (MMDS), 1, 3-Propane Sultone (PS), propylene sultone (PES), propylene sulfate (TMS), trimethylsilylphosphate (TMSP), trimethylsilylborate (TMSB), fluoroethylene carbonate (FEC).

The present invention is further described below in conjunction with the following figures and specific examples so that those skilled in the art may better understand the present invention and practice it, but the examples are not intended to limit the present invention.

The experimental methods used in the following examples are conventional methods unless otherwise specified, and materials, reagents and the like used therein are commercially available without otherwise specified.

1. XRD test method

Grinding the prepared powder material, transferring the powder material to a glass slide objective table, transferring the glass slide objective table to an X-ray diffractometer, and carrying out scanning test, wherein the scanning range is 10-80 degrees, and the scanning speed is 5 degrees/min.

2. Sodium ion battery assembly and testing

Uniformly grinding a positive electrode material, a conductive agent Super P and a binder PVDF according to the mass ratio of 8; then, the anode plate was cut into a 14mm circular anode plate by a cutter. A CR2032 button cell is assembled in a glove box filled with high-purity argon by using a sodium metal sheet with the diameter of 14mm and the thickness of 0.2mm as a negative electrode, using 0.1mol/L sodium perchlorate solution as electrolyte (solvent is ethylene carbonate and dimethyl carbonate with the volume ratio of 1).

The assembled CR2032 button cell was charge and discharge tested at a current density of 0.1C using a constant current charge and discharge mode. The test items include: first cycle charge and discharge, rate capability and capacity retention rate of 100 cycles of 1C charge and discharge.

Example 1

(1) According to a molar ratio of 1 _0.15 Fe _0.15 Mn _0.65 Mg _0.05 (OH) ₂ The precursor and sodium acetate are placed in a ball milling tank with the rotating speed of 300r/min, and are subjected to ball milling for 2 hours to be fully mixed. Placing the mixed powder in a muffle furnace, pre-sintering at 200 ℃ for 3h at a heating rate of 5 ℃/min, then increasing the temperature to 800 ℃ for high-temperature solid-phase sintering for 10h, naturally cooling and grinding to obtain a layered oxide material NaNi _0.15 Fe _0.15 Mn _0.65 Mg _0.05 O ₂ The black powder of (1).

(2) Adding cetyl trimethyl ammonium bromide into isooctyl alcohol, and mixing to prepare a solution C; adding potassium nitrate and ferrous chloride into deionized water, and mixing to prepare a solution A; adding ammonium fluoride into deionized water, and mixing to prepare a solution B; wherein in the solution C, the mass ratio of the hexadecyl trimethyl ammonium bromide to the isooctyl alcohol is 1; in the solution A, the molar ratio of potassium nitrate to ferrous chloride is 1. And then, under the condition of continuous stirring, adding the solution A and the solution B into the solution C drop by drop to form uniform and transparent microemulsion, and continuously stirring for a period of time. In the microemulsion, the molar ratio of potassium nitrate, ferrous chloride and ammonium fluoride is 1. Separating the obtained microemulsion for 0.5h at the centrifugal speed of 2000 r/min; washing the precipitate with anhydrous ethanol, drying in a forced air drying oven at 120 deg.C for 10 hr, and grinding to obtain KFeF ₃ Precursor of (2)A bulk powder.

(3) According to the mass ratio of 9.3 _0.15 Fe _0.15 Mn _0.65 Mg _0.05 O ₂ Black powder and KFeF ₃ The precursor powder is put into a ball mill with the rotating speed of 500r/min for ball milling for 2 hours, and the precursor powder and the ball mill are mixed evenly. Then placing the mixed powder into a tube furnace, heating to 500 ℃ at the heating rate of 5 ℃/min, and sintering for 4h in an inert atmosphere to obtain the NaNi _0.15 Fe _0.15 Mn _0.65 Mg _0.05 O ₂ /KFeF ₃ A material.

Example 2

(1) According to a molar ratio of 1 _0.3 Fe _0.15 Mn _0.5 Ti _0.05 (OH) ₂ The precursor and sodium nitrate are placed in a ball milling tank with the rotating speed of 800r/min, and are subjected to ball milling for 0.5h to be fully mixed. Placing the mixed powder in a muffle furnace, pre-sintering at 400 ℃ for 5h at the heating rate of 5 ℃/min, then increasing the temperature to 900 ℃ for high-temperature solid phase sintering for 12h, naturally cooling and grinding to obtain the layered oxide material NaNi _0.3 Fe _0.15 Mn _0.5 Ti _0.05 O ₂ The black powder of (1).

(2) Adding cetyl trimethyl ammonium bromide into isooctyl alcohol, and mixing to prepare a solution C; adding potassium nitrate and ferrous chloride into deionized water, and mixing to prepare a solution A; adding ammonium fluoride into deionized water, and mixing to prepare a solution B; wherein in the solution C, the mass ratio of the hexadecyl trimethyl ammonium bromide to the isooctyl alcohol is 1; in the solution a, the molar ratio of potassium nitrate to ferrous chloride is 1. And then, under the condition of continuous stirring, adding the solution A and the solution B into the solution C drop by drop to form uniform and transparent microemulsion, and continuously stirring for a period of time. In the microemulsion, the molar ratio of potassium nitrate, ferrous chloride and ammonium fluoride is 1. Separating the obtained microemulsion for 0.5h at the centrifugal speed of 2000 r/min; washing the precipitate with anhydrous ethanol, drying in a forced air drying oven at 120 deg.C for 10 hr, and grinding to obtain KFeF ₃ The precursor powder of (1).

(3) According to a mass ratio of 9.5The obtained NaNi _0.3 Fe _0.15 Mn _0.5 Ti _0.05 O ₂ Black powder and KFeF ₃ The precursor powder is put into a ball mill with the rotating speed of 500r/min for ball milling for 2 hours, and the precursor powder and the ball mill are mixed evenly. Then placing the mixed powder into a tube furnace, heating to 600 ℃ at the heating rate of 5 ℃/min, and sintering for 2h in inert atmosphere to obtain the NaNi _0.3 Fe _0.15 Mn _0.5 Ti _0.05 O ₂ /KFeF ₃ A material.

Example 3

(1) According to a molar ratio of 1 _0.15 Fe _0.25 Mn _0.55 Cu _0.05 (OH) ₂ The precursor and sodium nitrate are placed in a ball milling tank with the rotating speed of 500r/min, and are subjected to ball milling for 1.5h to be fully mixed. Placing the mixed powder in a muffle furnace, pre-sintering at 400 ℃ for 5h at the heating rate of 5 ℃/min, then increasing the temperature to 1100 ℃ for high-temperature solid phase sintering for 20h, and naturally cooling and grinding to obtain the layered oxide material NaNi _0.15 Fe _0.25 Mn _0.55 Cu _0.05 O ₂ The black powder of (1).

(2) Adding cetyl trimethyl ammonium bromide into isooctyl alcohol, and mixing to prepare a solution C; adding potassium nitrate and ferrous chloride into deionized water, and mixing to prepare a solution A; adding ammonium fluoride into deionized water, and mixing to prepare a solution B; wherein in the solution C, the mass ratio of the hexadecyl trimethyl ammonium bromide to the isooctyl alcohol is 1; in the solution a, the molar ratio of potassium nitrate to ferrous chloride is 1. And then, under the condition of continuous stirring, adding the solution A and the solution B into the solution C drop by drop to form uniform and transparent microemulsion, and continuously stirring for a period of time. In the microemulsion, the molar ratio of potassium nitrate, ferrous chloride and ammonium fluoride is 1. Separating the obtained microemulsion for 0.5h at the centrifugal speed of 2000 r/min; washing the precipitate with anhydrous ethanol, drying in a forced air drying oven at 120 deg.C for 10 hr, and grinding to obtain KFeF ₃ The precursor powder of (4).

(3) The obtained NaNi was mixed at a mass ratio of 9.7 _0.15 Fe _0.25 Mn _0.55 Cu _0.05 O ₂ Black powder and KFeF ₃ The precursor powder is put into a ball mill with the rotating speed of 500r/min, and is ball-milled for 2 hours, so that the precursor powder and the ball mill are uniformly mixed. Then placing the mixed powder in a tube furnace, heating to 600 ℃ at the heating rate of 5 ℃/min, and sintering for 2h in an inert atmosphere to obtain the NaNi _0.15 Fe _0.25 Mn _0.55 Cu _0.05 O ₂ /KFeF ₃ A material.

Example 4

(1) According to a molar ratio of 1 _0.22 Fe _0.18 Mn _0.56 Mg _0.02 Zr _0.02 (OH) ₂ The precursor and sodium nitrate are placed in a ball milling tank with the rotating speed of 500r/min, and are subjected to ball milling for 2 hours to be fully mixed. Placing the mixed powder in a muffle furnace, pre-sintering at 300 ℃ for 4h at the heating rate of 5 ℃/min, then increasing the temperature to 900 ℃ for high-temperature solid phase sintering for 12h, naturally cooling and grinding to obtain the layered oxide material NaNi _0.22 Fe _0.18 Mn _0.56 Mg _0.02 Zr _0.02 O ₂ Black powder of (2).

(2) Adding cetyl trimethyl ammonium bromide into isooctyl alcohol, and mixing to prepare a solution C; adding potassium nitrate and ferrous chloride into deionized water, and mixing to prepare a solution A; adding ammonium fluoride into deionized water, and mixing to prepare a solution B; wherein in the solution C, the mass ratio of the hexadecyl trimethyl ammonium bromide to the isooctyl alcohol is 1; in the solution A, the molar ratio of potassium nitrate to ferrous chloride is 1. And then, under the condition of continuous stirring, adding the solution A and the solution B into the solution C dropwise to form uniform and transparent microemulsion, and continuously stirring for a period of time. In the microemulsion, the molar ratio of potassium nitrate, ferrous chloride and ammonium fluoride is 1. Separating the obtained microemulsion for 0.5h at the centrifugal speed of 2000 r/min; washing the precipitate with anhydrous ethanol, drying in a forced air drying oven at 120 deg.C for 10 hr, and grinding to obtain KFeF ₃ The precursor powder of (1).

(3) According to the mass ratio of 9.5 _0.22 Fe _0.18 Mn _0.56 Mg _0.02 Zr _0.02 O ₂ Black colorPowder and KFeF ₃ The precursor powder is put into a ball mill with the rotating speed of 500r/min for ball milling for 2 hours, and the precursor powder and the ball mill are mixed evenly. Then placing the mixed powder into a tube furnace, heating to 600 ℃ at the heating rate of 5 ℃/min, and sintering for 2h in inert atmosphere to obtain the NaNi _0.22 Fe _0.18 Mn _0.56 Mg _0.02 Zr _0.02 O ₂ /KFeF ₃ A material.

Comparative example 1

According to a molar ratio of 1 _0.15 Fe _0.15 Mn _0.65 Mg _0.05 (OH) ₂ The precursor and sodium acetate are placed in a ball milling tank with the rotating speed of 300r/min, and are subjected to ball milling for 2 hours to be fully mixed. Placing the mixed powder in a muffle furnace, presintering for 3h at the temperature of 200 ℃ at the heating rate of 5 ℃/min, then increasing the temperature to 800 ℃ for high-temperature solid phase sintering for 10h, and naturally cooling and grinding to obtain the layered oxide material NaNi _0.15 Fe _0.15 Mn _0.65 Mg _0.05 O ₂ The black powder of (1).

Comparative example 2

According to a molar ratio of 1 _0.3 Fe _0.15 Mn _0.5 Ti _0.05 (OH) ₂ The precursor and sodium nitrate are placed in a ball milling tank with the rotating speed of 800r/min, and are subjected to ball milling for 0.5h to be fully mixed. Placing the mixed powder in a muffle furnace, pre-sintering at 400 ℃ for 5h at the heating rate of 5 ℃/min, then increasing the temperature to 900 ℃ for high-temperature solid phase sintering for 12h, naturally cooling and grinding to obtain the layered oxide material NaNi _0.3 Fe _0.15 Mn _0.5 Ti _0.05 O ₂ The black powder of (1).

Comparative example 3

According to a molar ratio of 1 _0.15 Fe _0.25 Mn _0.55 Cu _0.05 (OH) ₂ The precursor and sodium nitrate are placed in a ball milling tank with the rotating speed of 500r/min, and are subjected to ball milling for 1.5h to be fully mixed. Placing the mixed powder in a muffle furnace, pre-sintering at 400 ℃ for 5h at the heating rate of 5 ℃/min, then increasing the temperature to 1100 ℃ for high-temperature solid phase sintering for 20h, and naturally cooling and grinding to obtain the layered oxide material NaNi _0.15 Fe _0.25 Mn _0.55 Cu _0.05 O ₂ Black powder of (2).

Comparative example 4

According to a molar ratio of 1 _0.22 Fe _0.18 Mn _0.56 Mg _0.02 Zr _0.02 (OH) ₂ The precursor and sodium nitrate are placed in a ball milling tank with the rotating speed of 500r/min, and are subjected to ball milling for 2 hours to be fully mixed. Placing the mixed powder in a muffle furnace, pre-sintering at 300 ℃ for 4h at the heating rate of 5 ℃/min, then increasing the temperature to 900 ℃ for high-temperature solid phase sintering for 12h, naturally cooling and grinding to obtain the layered oxide material NaNi _0.22 Fe _0.18 Mn _0.56 Mg _0.02 Zr _0.02 O ₂ The black powder of (1).

The following is directed to the NaNi prepared in example 1 _0.15 Fe _0.15 Mn _0.65 Mg _0.05 O ₂ /KFeF ₃ The material was subjected to characterization testing.

FIGS. 1 to 3 are each NaNi _0.15 Fe _0.15 Mn _0.65 Mg _0.05 O ₂ 、KFeF ₃ And NaNi _0.15 Fe _0.15 Mn _0.65 Mg _0.05 O ₂ /KFeF ₃ Scanning Electron Micrographs (SEM) of the material. As can be seen from the figure, the layered oxide NaNi _0.15 Fe _0.15 Mn _0.65 Mg _0.05 O ₂ The surface is relatively smooth, and NaNi _0.15 Fe _0.15 Mn _0.65 Mg _0.05 O ₂ /KFeF ₃ The surface of the material is coated with irregular coating and becomes rough, which shows that the layered oxide NaNi is coated with the coating _0.15 Fe _0.15 Mn _0.65 Mg _0.05 O ₂ In the KFeF with perovskite structure ₃ 。

FIG. 4 shows NaNi _0.15 Fe _0.15 Mn _0.65 Mg _0.05 O ₂ /KFeF ₃ The XRD diffraction pattern of the material can be seen, and the material is basically consistent with the standard peak of an O3 phase layered oxide standard card; in addition, diffraction peaks appear at 31 degrees and 45 degrees in the diffraction pattern of the material, and the diffraction peaks are KFeF ₃ Characteristic peak of (2) indicatesThe KFeF is successfully introduced into the layered oxide ₃ 。

The electrochemical test results of the batteries of the respective examples and comparative examples under the conditions of a discharge cut-off voltage of 2.0V and a charge cut-off voltage of 4.0V are shown in table 1.

TABLE 1

Group of	0.1C first cycle discharge capacity (mAh/g)	1C discharge Capacity (mAh/g)	2C discharge capacity (mAh/g)	5C discharge capacity (mAh/g)	1C 100 Ring Capacity Retention ratio (%)
						Example 1	128.6	122.4	112.1	98.4	95.6
Example 2	137.3	129.3	120.9	103.6	94.5
						Example 3	130.1	124.5	112.1	99.8	96.8
Example 4	133.5	127.1	115.6	100.5	94.6
						Comparative example 1	132.3	119.3	107.2	87.1	86.9
Comparative example 2	141.5	120.2	112.1	79.6	85.1
						Comparative example 3	133.6	120.6	109.1	90.2	88.9
Comparative example 4	137.2	122.4	110.4	78.8	83.6

The main materials of examples 1 to 4 and comparative examples 1 to 4 are all layered metal oxides, and the types and the preparation methods are the same. As can be seen from the results in Table 1, in examples 1 to 4, KFeF having perovskite structure was used ₃ Incorporated into the layered metal oxide, while the perovskite structure KFeF ₃ Does not contain sodium ions, and thus shows a phenomenon that the gram capacity is slightly decreased. However, na _x Ni _i Fe _j Mn _k M _m O ₂ /KFeF ₃ The rate capability and the cycling stability of the material are both greatly improved, and the gram capacity playing advantage of the material is very obvious under the condition of high-rate charge and discharge.

In conclusion, the perovskite structure is introduced into the layered oxide by low-temperature sintering, so that the structure of the material is stabilized, the ionic conductivity of the material is improved, and the cycling stability and the rate capability of the material are greatly improved.

The above-mentioned embodiments are merely preferred embodiments for fully illustrating the present invention, and the scope of the present invention is not limited thereto. The equivalent substitution or change made by the technical personnel in the technical field on the basis of the invention is all within the protection scope of the invention. The protection scope of the invention is subject to the claims.

Claims

1. A layered oxide composite material, characterized in that the molecular formula of the layered oxide composite material is Na _x Ni _i Fe _j Mn _k M _m O ₂ /KFeF ₃ Wherein: m is Li ⁺ 、B ³⁺ 、Mg ²⁺ 、Al ³⁺ 、K ⁺ 、Ca ²⁺ 、Ti ⁴⁺ 、Co ³⁺ 、V ³⁺ 、V ⁴⁺ 、Cr ³⁺ 、Cu ²⁺ 、Zn ²⁺ 、Zr ⁴⁺ 、Nb ⁵⁺ And Sn ⁴⁺ One or more of; 0.8<x≤1，0<i≤0.4，0<j≤0.5，0<k≤0.6，0<m is less than or equal to 0.2, and i + j + k + m =1.

2. The layered oxide composite of claim 1, wherein the layered oxide composite comprises Na _x Ni _i Fe _j Mn _k M _m O ₂ Is O3 phase layered oxide.

3. A method for preparing a layered oxide composite, comprising the steps of:

mixing Na _x Ni _i Fe _j Mn _k M _m O ₂ Powder, KFeF ₃ Ball-milling and mixing the precursor powder, and sintering in a protective atmosphere to obtain the layered oxide composite material Na _x Ni _i Fe _j Mn _k M _m O ₂ /KFeF ₃ ；

Wherein M is Li ⁺ 、B ³⁺ 、Mg ²⁺ 、Al ³⁺ 、K ⁺ 、Ca ²⁺ 、Ti ⁴⁺ 、Co ³⁺ 、V ³⁺ 、V ⁴⁺ 、Cr ³⁺ 、Cu ²⁺ 、Zn ²⁺ 、Zr ⁴⁺ 、Nb ⁵⁺ And Sn ⁴⁺ One or more of (a); 0.8<x≤1，0<i≤0.4，0<j≤0.5，0<k≤0.6，0<m is less than or equal to 0.2, and i + j + k + m =1.

4. The method of claim 3, wherein Na is added to the layered oxide composite _x Ni _i Fe _j Mn _k M _m O ₂ Powder and KFeF ₃ The mass ratio of the precursor powder is 9-9.5: 1-0.5;

5. The method for producing a layered oxide composite material according to claim 3, characterized in that the Na is _x Ni _i Fe _j Mn _k M _m O ₂ The preparation method of the powder comprises the following steps:

6. The method according to claim 5, wherein the layered oxide composite is prepared by a method comprising the steps of,

in the step a, the sodium source comprises one or more of sodium carbonate, sodium hydroxide, sodium acetate, sodium oxalate and sodium nitrate;

in the step b, the sintering comprises pre-sintering and high-temperature solid-phase sintering; the temperature of the pre-sintering is 200 to 550 ℃, and the time of the pre-sintering is 1 to 8h; the temperature of the high-temperature solid phase sintering is 750 to 1100 ℃, and the time of the high-temperature solid phase sintering is 4 to 20h.

7. The method of claim 3, wherein the KFeF is selected from the group consisting of ₃ The preparation method of the precursor powder comprises the following steps:

d. will be provided withThe microemulsion is centrifugally separated, precipitates are collected, washed, dried and ground to obtain the KFeF ₃ Precursor powder;

8. The method for preparing a layered oxide composite material according to claim 7, wherein in step c: the emulsifier comprises at least one of cetyl trimethyl ammonium bromide, N-dodecyl dimethylamine and polyoxyethylene ether;

and/or the washing solution is absolute ethyl alcohol;

9. A positive electrode sheet comprising the layered oxide composite material according to claim 1 or 2 or the layered oxide composite material produced by the production method according to any one of claims 3 to 8.

10. A sodium ion battery comprising the positive electrode sheet according to claim 9.