CN115636402A

CN115636402A - Lithium manganese iron phosphate material and preparation method and application thereof

Info

Publication number: CN115636402A
Application number: CN202211343289.8A
Authority: CN
Inventors: 刘厅; 万远鑫; 李意能; 陈燕玉; 薛山; 王鹏
Original assignee: Shenzhen Dynanonic Co ltd
Current assignee: Shenzhen Dynanonic Co ltd
Priority date: 2022-10-28
Filing date: 2022-10-28
Publication date: 2023-01-24
Anticipated expiration: 2042-10-28
Also published as: CN115636402B

Abstract

The application discloses a lithium iron manganese phosphate material and a preparation method and application thereof. The lithium iron manganese phosphate material is a graphene-like two-dimensional structure, and compared with the current granular shape, the two-dimensional structure can effectively shorten the diffusion path of lithium ions and improve the reaction kinetics of the lithium iron manganese phosphate material; meanwhile, the Hall effect of the two-dimensional structure can also effectively improve the conductivity of the material, and the compaction density is high. The preparation method can ensure that the prepared lithium manganese iron phosphate material has stable electrochemical performance, is high in efficiency and saves the production cost.

Description

Lithium manganese iron phosphate material and preparation method and application thereof

Technical Field

The application belongs to the technical field of electrode materials, and particularly relates to a lithium iron manganese phosphate material and a preparation method and application thereof.

Background

Lithium ion batteries are widely applied to 3C electronic products, power automobiles, energy storage power stations and other fields due to high energy density, small self-discharge, no memory effect and long cycle life, and are a research hotspot in current new energy storage and conversion systems.

The positive electrode material has the highest cost ratio and mass ratio in the battery, and thus has a very important influence on the performance and cost of the battery. Among them, lithium manganese iron phosphate having an olivine structure has an olivine structure of a phosphate material and has safety performance equivalent to that of lithium iron phosphate, and therefore, in recent years, the market share of power batteries is increasing. More importantly, the reaction potential of the lithium iron phosphate is greatly improved by adding the manganese element. Meanwhile, the manganese element is rich in earth resources and low in cost, and has great competitive advantages in the future environment of the trend of energy conservation and cost reduction of power batteries.

However, lithium iron manganese phosphate also has certain defects, the conductivity of the material is reduced due to the introduction of manganese, and meanwhile, the olivine structure causes poor power diffusion and the rate capability of the battery is low. Therefore, how to improve the conductivity of the material and the dynamic diffusion energy thereof is a key for expanding the large-scale commercial use of the lithium iron manganese phosphate material, and is also a technical problem which is attempted to be solved in the field.

Disclosure of Invention

The purpose of the present application is to overcome the above disadvantages in the prior art, and provide a lithium iron manganese phosphate material and a preparation method thereof, so as to solve the technical problem that the existing lithium iron manganese phosphate has poor conductivity and poor dynamic diffusion performance.

Another object of the present application is to provide a positive electrode and a secondary battery including the same, so as to solve the technical problem that the rate capability of the existing lithium iron manganese phosphate secondary battery is low.

In order to achieve the above object, a first aspect of the present application provides a lithium iron manganese phosphate material. The lithium iron manganese phosphate material is of a two-dimensional structure similar to graphene.

In some embodiments, the lithium iron manganese phosphate material has at least one of the following characteristics:

the thickness of the nanosheet of the lithium iron manganese phosphate material is 2-20nm;

the single-layer thickness of the nanosheet of the lithium iron manganese phosphate material is 0.5-2nm;

the number of the nanosheet layers of the lithium iron manganese phosphate material is 1-10;

the radial size of the nano-sheet of the lithium iron manganese phosphate material is 18-55 mu m.

In some embodiments, the lithium iron manganese phosphate material has a compacted density of 2.396-2.582g/cm ³ 。

In some embodiments, the conductivity of the lithium iron manganese phosphate material is 5.68 × 10 ^-12 -32.8×10 ^-11 mS/cm。

In a second aspect of the present application, a method for preparing a lithium iron manganese phosphate material is provided. The preparation method of the lithium iron manganese phosphate material comprises the following steps:

dispersing a lithium iron manganese phosphate precursor in a hydrophobic ligand solvent to prepare a mixed ligand solution;

carrying out gelling reaction on the mixed ligand solution to obtain a mixture colloid;

and sintering the mixture colloid to obtain the lithium manganese iron phosphate material, wherein the lithium manganese iron phosphate material is of a graphene-like two-dimensional structure.

In some embodiments, the dispersing of the lithium iron manganese phosphate precursor in the hydrophobic ligand solvent is performed according to a ratio of a molar concentration of a lithium source contained in the lithium iron manganese phosphate precursor in the mixed ligand solution of 0.1 to 6 mol/L.

In some embodiments, a method of dispersing a lithium iron manganese phosphate precursor in a hydrophobic ligand solvent comprises the steps of:

respectively dispersing a lithium source, a manganese source, an iron source and a phosphorus source contained in a lithium iron manganese phosphate precursor into a hydrophobic ligand solvent to respectively prepare a lithium source ligand solution, a manganese source ligand solution, an iron source ligand solution and a phosphorus source ligand solution;

and mixing the lithium iron manganese phosphate ligand solution, the manganese source ligand solution, the iron source ligand solution and the phosphorus source ligand solution according to the element metering ratio to obtain a mixed ligand solution.

In further embodiments, the gelling reaction temperature is from 30 to 100 ℃.

In a further embodiment, the viscosity of the mixture colloid is from 400 to 8000cp.

In a further embodiment, the method for performing gel-forming reaction on the mixed ligand solution comprises the following steps:

and heating the mixed ligand solution to the gelling reaction temperature, and continuously stirring until the mixed ligand solution undergoes the gelling reaction and forms a colloid.

In some embodiments, the hydrophobic ligand solvent comprises at least one of oleic acid, oleylamine, trioctylphosphine, and trioctylphosphine oxide.

In some embodiments, the temperature of the sintering process is 200-800 ℃.

In some embodiments, the sintering process is ramped up to the sintering process temperature at a ramp rate of 1-15 ℃/min.

In a third aspect of the present application, a positive electrode is provided. The positive pole of this application includes the mass flow body and combines the anodal active layer on the mass flow body, and the anodal active material that contains of anodal active layer includes text application lithium iron manganese phosphate material.

In a fourth aspect of the present application, a secondary battery is provided. The present application includes a positive electrode, which is the present application positive electrode.

Compared with the prior art, the method has the following technical effects:

the lithium iron manganese phosphate material is of a graphene-like two-dimensional structure, namely, has a layered structure, and compared with the current granular shape, the two-dimensional structure can effectively shorten the diffusion path of lithium ions and improve the reaction kinetics of the lithium iron manganese phosphate material; meanwhile, the two-dimensional Hall effect can also effectively improve the conductivity of the material, and the compaction density is high.

According to the preparation method of the lithium manganese iron phosphate material, a hydrophobic ligand solvent is adopted to prepare a lithium manganese iron phosphate precursor into a colloid, so that when lithium manganese iron phosphate is formed by sintering, a hydrophobic alkane molecule ligand modified on the surface of a lithium manganese iron phosphate crystal can play a role in modifying a nanocrystal for the lithium manganese iron phosphate through a sulfydryl-alkene click chemical reaction, the lithium manganese iron phosphate crystal can be regulated and controlled to directionally grow into a two-dimensional lamellar structure along the (100) and (010) crystal plane directions during high-temperature nucleation, the prepared lithium manganese iron phosphate is endowed with a graphene-like two-dimensional structure, and the prepared lithium manganese iron phosphate is endowed with a short lithium ion diffusion path and high conductivity and compaction density. In addition, the preparation method of the lithium iron manganese phosphate material can ensure that the prepared lithium iron manganese phosphate material has stable electrochemical performance, is high in efficiency and saves the production cost.

The positive electrode contains the lithium iron manganese phosphate material, so that the positive electrode has high ion diffusion efficiency and rate performance.

The secondary battery contains the positive electrode, so that the secondary battery has high rate capability and charge and discharge performance.

Drawings

In order to more clearly illustrate the detailed description of the present application or the technical solutions in the prior art, the drawings used in the detailed description or the prior art description will be briefly described below, and it is obvious that the drawings in the following description are some embodiments of the present application, and other drawings can be obtained by those skilled in the art without creative efforts.

Fig. 1 is a schematic flow chart of a preparation method of a lithium iron manganese phosphate material according to an embodiment of the present application;

fig. 2 is an electron microscope image of the lithium iron manganese phosphate material in embodiment A1 of the present application; wherein, a in fig. 2 is a Transmission Electron Microscope (TEM) image of the lithium iron manganese phosphate material, b is a Scanning Electron Microscope (SEM) image of the lithium iron manganese phosphate material in liquid phase, and c is an SEM image of the lithium iron manganese phosphate material powder;

fig. 3 is an X-ray diffraction (XRD) pattern of the lithium iron manganese phosphate material in example A4 of the present application;

FIG. 4 is a graph showing a discharge curve of a lithium secondary battery in example B1 of the present application.

Detailed Description

In order to make the technical problems, technical solutions and advantageous effects to be solved by the present application more clearly apparent, the present application is further described in detail below with reference to the embodiments. It should be understood that the specific embodiments described herein are merely illustrative of and not restrictive on the broad application.

In this application, the term "and/or" describes an association relationship of associated objects, meaning that there may be three relationships, e.g., a and/or B, which may mean: a is present alone, A and B are present simultaneously, and B is present alone. Wherein A and B can be singular or plural. The character "/" generally indicates that the former and latter associated objects are in an "or" relationship.

In the present application, "at least one" means one or more, "a plurality" means two or more. "at least one of the following" or similar expressions refer to any combination of these items, including any combination of the singular or plural items. For example, "at least one (a), b, or c", or "at least one (a), b, and c", may each represent: a, b, c, a-b (i.e. a and b), a-c, b-c, or a-b-c, wherein a, b, and c can be single or multiple respectively.

It should be understood that, in various embodiments of the present application, the sequence numbers of the foregoing processes do not imply an execution sequence, some or all of the steps may be executed in parallel or executed sequentially, and the execution sequence of each process should be determined by its function and inherent logic, and should not limit the implementation process of the embodiments of the present application.

The terminology used in the embodiments of the present application is for the purpose of describing particular embodiments only and is not intended to be limiting of the application. As used in the examples of this application and the appended claims, the singular forms "a", "an", and "the" are intended to include the plural forms as well, unless the context clearly indicates otherwise.

The weight of the related components mentioned in the specification of the embodiments of the present application may not only refer to the specific content of each component, but also refer to the proportional relationship of the weight of each component, and therefore, the proportional enlargement or reduction of the content of the related components according to the specification of the embodiments of the present application is within the scope disclosed in the specification of the embodiments of the present application. Specifically, the mass described in the specification of the examples of the present application may be a mass unit known in the chemical field such as μ g, mg, g, kg, etc.

The terms "first" and "second" are used for descriptive purposes only and are used for distinguishing purposes such as substances from one another, and are not to be construed as indicating or implying relative importance or implying any number of technical features indicated. For example, a first XX may also be referred to as a second XX, and similarly, a second XX may also be referred to as a first XX, without departing from the scope of embodiments of the present application. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature.

In a first aspect, an embodiment of the present application provides a lithium iron manganese phosphate material. The lithium iron manganese phosphate material is of a two-dimensional structure similar to graphene, namely the lithium iron manganese phosphate material is of a two-dimensional lamellar structure.

Because the lithium iron manganese phosphate material in the embodiment of the application is of a specific graphene-like two-dimensional structure, compared with the current granular shape, the two-dimensional structure can effectively shorten the diffusion path of lithium ions and improve the reaction kinetics of the lithium iron manganese phosphate material; meanwhile, the two-dimensional Hall effect can also effectively improve the conductivity of the material.

The inventor further characterizes the lithium iron manganese phosphate material in the embodiment of the present application, and the lithium iron manganese phosphate material in the embodiment of the present application has at least one of the following characteristics:

in some embodiments, the nanoplatelets of lithium iron manganese phosphate material have a thickness of 2-20nm.

In some embodiments, the number of nanosheet layers of the lithium iron manganese phosphate material is 1-10. Therefore, in combination with the thickness of the nanosheets of the lithium iron manganese phosphate material, the thickness of the single-layer nanosheets of the lithium iron manganese phosphate material may be 0.5-2nm.

In some embodiments, the nanoplatelets of lithium iron manganese phosphate material have a radial dimension of 18-55 μm.

Because the lithium iron manganese phosphate material in the embodiment of the application has the size, the lithium iron manganese phosphate material has a lithium ion diffusion path, good conductivity and high compaction density. As further detected by the inventor, the compacted density of the lithium iron manganese phosphate material in the embodiment of the application can be as high as 2.396-2.582g/cm ³ The conductivity of the lithium iron manganese phosphate material can reach 5.68 multiplied by 10 ^-12 -32.8×10 ^-11 mS/cm。

In other embodiments, the lithium iron manganese phosphate material of the embodiments may be chemical LiMn _x Fe _1-x PO ₄ The lithium manganese iron phosphate of (1). Wherein x may be 0.1 to 0.9.

In a further embodiment, the lithium iron manganese phosphate material in each of the above embodiments may also be doped lithium iron manganese phosphate. Wherein, the doping element can be at least one of titanium, magnesium, vanadium, aluminum, potassium, sodium, zinc, copper, silver, fluorine and chlorine, and the doping content can be 400-6000ppm.

In a second aspect, an embodiment of the present application further provides a preparation method of the above lithium iron manganese phosphate material. The preparation method of the lithium iron manganese phosphate material in the embodiment of the application has a process flow as shown in fig. 1, and comprises the following steps:

s01: dispersing a lithium iron manganese phosphate precursor in a hydrophobic ligand solvent to prepare a mixed ligand solution;

s02: carrying out gelling reaction on the mixed ligand solution to obtain a mixture colloid;

s03: and sintering the mixture colloid to obtain the lithium manganese iron phosphate material, wherein the lithium manganese iron phosphate material is of a graphene-like two-dimensional structure.

Thus, in the preparation method of the lithium manganese iron phosphate material in the embodiment of the application, the lithium manganese iron phosphate precursor is prepared into colloid by using a hydrophobic ligand solvent, so that the hydrophobic alkane molecular ligand modified on the surface of the lithium manganese iron phosphate generated in sintering can play a role in modifying the lithium manganese iron phosphate by a thiol-ene click chemical reaction, the lithium manganese iron phosphate crystal can be controlled to directionally grow into a graphene-like two-dimensional lamellar structure along the (100) and (010) crystal plane directions during high-temperature nucleation, the prepared lithium manganese iron phosphate is endowed with the graphene-like two-dimensional structure, and the prepared lithium manganese iron phosphate is endowed with a short lithium ion diffusion path and high conductivity and compaction density. In addition, the preparation method of the lithium iron manganese phosphate material in the embodiment of the application can ensure that the prepared lithium iron manganese phosphate material has stable electrochemical performance and high efficiency, and saves the production cost.

Step S01

In step S01, after dispersing the lithium manganese iron phosphate precursor in the hydrophobic ligand solvent, the hydrophobic ligand solvent can form a ligand compound with each component of the lithium manganese iron phosphate precursor, so that each precursor can form a ligand sol.

Thus, in some embodiments, the hydrophobic ligand solvent comprises at least one of oleic acid, oleylamine, trioctylphosphine and trioctylphosphine oxide. The hydrophobic ligand solvents can form stable ligands with each component of the lithium iron manganese phosphate precursor, so that the lithium iron manganese phosphate precursor forms uniformly dispersed and stable sol.

In some embodiments, the step S01 of dispersing the lithium iron manganese phosphate precursor in the hydrophobic ligand solvent is a dispersing treatment according to a ratio of a molar concentration of a lithium source contained in the lithium iron manganese phosphate precursor in the mixed ligand solution of 0.1 to 6 mol/L. By controlling the concentration of the lithium iron manganese phosphate precursor in the hydrophobic ligand solvent, the components of the lithium iron manganese phosphate precursor and the hydrophobic ligand solvent can form sol, so that the dispersion uniformity of the lithium iron manganese phosphate precursor is improved.

In an exemplary embodiment, the method for dispersing the lithium iron manganese phosphate precursor in the hydrophobic ligand solvent in step S01 includes the following steps:

s011: respectively dispersing a lithium source, a manganese source, an iron source and a phosphorus source contained in a lithium iron manganese phosphate precursor in a hydrophobic ligand solvent to respectively prepare a lithium source ligand solution, a manganese source ligand solution, an iron source ligand solution and a phosphorus source ligand solution;

s012: and mixing the lithium iron manganese phosphate ligand solution, the manganese source ligand solution, the iron source ligand solution and the phosphorus source ligand solution according to the element metering ratio to obtain a mixed ligand solution.

In step S011, a lithium source ligand solution, a manganese source ligand solution, an iron source ligand solution, and a phosphorus source are prepared from a lithium source, a manganese source, an iron source, and a phosphorus source contained in the lithium iron manganese phosphate precursor and the hydrophobic ligand solvent, respectively, so that components contained in the lithium iron manganese phosphate precursor can be sufficiently dispersed in the hydrophobic ligand solvent, and each component can form a sol with the hydrophobic ligand solvent, respectively.

The concentrations of the prepared lithium source ligand solution, manganese source ligand solution, iron source ligand solution and phosphorus source ligand solution can be adjusted according to actual conditions, but at least the components contained in the prepared lithium source ligand solution, manganese source ligand solution, iron source ligand solution and phosphorus source ligand solution can be fully dispersed, namely the components can fully form sol with hydrophobic ligand solvent.

In addition, in order to improve the dispersibility of the components in each solution of the lithium source ligand solution, the manganese source ligand solution, the iron source ligand solution, and the phosphorus source ligand solution, ultrasonic treatment may be combined.

In a specific embodiment, the lithium source in step S011 can include one or more of lithium hydroxide, lithium carbonate, lithium nitrate, lithium sulfate, lithium chloride, lithium phosphate, lithium acetate, and the like. The manganese source may include one or more of manganese acetate, manganese nitrate, manganese sulfate, manganese carbonate, manganese chloride, and the like. The iron source may include one or more of ferrous oxalate, ferrous sulfate, ferrous nitrate, ferrous phosphate, and ferrous carbonate. The phosphorus source may include one or more of monoammonium phosphate, monopotassium phosphate, monosodium phosphate, and monosodium phosphate.

In step S012, the stoichiometric ratio of each element may be a molar ratio of the elements contained in the lithium manganese iron phosphate, or a mass ratio or other ratios converted from the molar ratio of the elements. In an embodiment, the precursor of the lithium iron manganese phosphate may be a precursor of lithium iron manganese phosphate having a chemical general formula shown in the lithium iron manganese phosphate in the embodiment of the above application. Therefore, the molar ratio of the elements contained in the lithium manganese iron phosphate may be the stoichiometric ratio of the elements in the above chemical formula shown in the lithium manganese iron phosphate. When the lithium manganese iron phosphate is doped lithium manganese iron phosphate, the precursor of the lithium manganese iron phosphate further comprises a doping element source.

In the embodiment, in the process of mixing the lithium source ligand solution, the manganese source ligand solution, the iron source ligand solution and the phosphorus source ligand solution, the lithium source ligand solution and the phosphorus source ligand solution may be first prepared into a first mixed solution, the manganese source ligand solution and the iron source ligand solution may be prepared into a second mixed solution, and then the first mixed solution and the second mixed solution may be mixed. By controlling the preparation sequence, the uniform and stable dispersion of the lithium iron manganese phosphate precursor in the finally prepared mixed ligand solution is improved.

The mixing treatment including the lithium source ligand solution, the manganese source ligand solution, the iron source ligand solution, and the phosphorus source ligand solution may be stirring treatment, ultrasonic treatment, or the like, and any mixing treatment method that can uniformly mix the respective solutions is within the scope disclosed in the present embodiment.

Step S02

In step S02, the mixed ligand solution in step S01 undergoes gelling reaction, and then the mixed ligand solution forms gel. Thus, in the examples, the gelling reaction temperature is between 30 and 100 ℃. The temperature can improve the efficiency of the gelling reaction and the stability of the formed mixture colloid, thereby improving the stability of the performance of the lithium iron manganese phosphate material. Of course, the gelling reaction time should be sufficient, as in the example, the gelling reaction time at 30-100 ℃ is 10min-24h.

In the embodiment, the viscosity of the mixture colloid can be 400-8000cp, and further 400-6000cp. The viscosity number is the value at the temperature during the gelling reaction. The degree of gelling reaction can be indirectly judged by detecting the viscosity of the mixture colloid, and the stability of the mixture colloid is improved.

As in the embodiment, the method for performing gel-forming reaction on the mixed ligand solution in step S02 includes the following steps:

During the treatment by warming and continuous stirring, the consistency of the mixed ligand solution gradually increases until finally a gel is formed.

Step S03

And sintering the mixture colloid to form the lithium manganese iron phosphate by sintering the lithium manganese iron phosphate precursor. Due to the fact that the hydrophobic ligand solvent exists in the mixture colloid, the hydrophobic ligand solvent can modify the surface of the lithium manganese iron phosphate crystal, a nanocrystalline modification effect can be achieved on the lithium manganese iron phosphate through a mercapto-alkene click chemical reaction, the lithium manganese iron phosphate crystal can be controlled to directionally grow into a two-dimensional lamellar structure along the (100) and (010) crystal plane directions during high-temperature nucleation, the prepared lithium manganese iron phosphate is endowed with the two-dimensional structure of the graphene-like of the lithium manganese iron phosphate material in the embodiment of the above application, and therefore the prepared lithium manganese iron phosphate is endowed with a short lithium ion diffusion path and high conductivity and compaction density.

In some embodiments, the temperature of the sintering process is 200-800 ℃. The sintering treatment at the temperature can effectively enable the lithium manganese iron phosphate precursor to generate the lithium manganese iron phosphate, and can improve the stability of the two-dimensional structure of the lithium manganese iron phosphate. Of course, the time of the sintering treatment should be sufficient, as in the illustrated example, the time of the sintering treatment at 200-800 ℃ is 1-48h.

In some embodiments, the sintering process is ramped up to the sintering process temperature at a ramp rate of 1-15 ℃/min. By controlling the heating rate of the sintering treatment, the size and the stability of the generated lithium iron manganese phosphate two-dimensional structure can be effectively controlled and adjusted.

In addition, the sintering process in step S02 may be performed in a protective atmosphere, and in an exemplary case, the protective atmosphere may be a protective atmosphere of a lithium manganese iron phosphate preparation method, such as an inert atmosphere including nitrogen, argon, helium, and the like.

In a third aspect, an embodiment of the present application further provides a positive electrode. The positive electrode of the embodiment of the application comprises a positive electrode current collector and a positive electrode active layer combined on the positive electrode current collector.

The positive electrode current collector of the positive electrode may be, but not limited to, any one of a copper foil and an aluminum foil.

The positive active layer of the positive electrode includes positive active material, binder, conductive agent and other components.

The positive electrode active material in the positive electrode active layer is a lithium iron manganese phosphate material in the embodiment of the above application. Therefore, the positive electrode in the embodiment of the application has high rate capability and quick charge characteristic, and the active layer has high compaction density and high capacity density. In an embodiment, the lithium iron manganese phosphate material in the embodiment of the present application may be controlled to account for 90% -95% of the mass of the positive active layer.

In an embodiment, the content of the binder in the positive electrode active layer may be 2% to 5% by mass in the positive electrode active layer. In a specific embodiment, the binder comprises one or more of polyvinylidene chloride, soluble polytetrafluoroethylene, styrene butadiene rubber, hydroxypropyl methylcellulose, carboxymethylcellulose, polyvinyl alcohol, acrylonitrile copolymer, sodium alginate, chitosan, and chitosan derivatives.

In an embodiment, the content of the conductive agent in the positive electrode active layer may be 1wt% to 5wt% in the positive electrode active layer. In particular embodiments, the conductive agent includes one or more of graphite, carbon black, acetylene black, graphene, carbon fibers, C60, and carbon nanotubes.

In an embodiment, the preparation process of the positive electrode may be: mixing the positive active material, the conductive agent and the binder to obtain electrode slurry, coating the electrode slurry on a current collector, and drying, rolling, die cutting and the like to obtain the positive electrode.

In a fourth aspect, embodiments of the present application further provide a secondary battery. The secondary battery of the embodiment of the present application includes necessary components such as a positive electrode, a negative electrode, a separator, and an electrolyte, and of course, includes other necessary or auxiliary components. The positive electrode is the positive electrode in the embodiment of the present application, that is, the positive active layer included in the positive electrode contains the lithium iron manganese phosphate material in the embodiment of the present application. Because the secondary battery in the embodiment of the application contains the lithium iron manganese phosphate material in the embodiment of the application, the secondary battery in the embodiment of the application has high energy density, rate capability and quick charge characteristic.

The lithium iron manganese phosphate material and the preparation method thereof according to the embodiments of the present application are described below by way of examples.

1. The embodiment of the lithium iron manganese phosphate material and the preparation method thereof comprises the following steps:

example A1

The embodiment provides a lithium iron manganese phosphate material and a preparation method thereof. The lithium iron manganese phosphate material is LiFe _0.8 Mn _0.2 PO ₄ It is a graphene-like two-dimensional layered structure.

The preparation method of the lithium iron manganese phosphate material comprises the following steps:

s1: dispersing 0.05mol of lithium carbonate in 20ml of oleylamine to prepare oleylamine solution of lithium carbonate;

dispersing 0.02mol of manganese acetate in 10ml of oleic acid to prepare an oleylamine solution of manganese acetate;

dispersing 0.08mol of ferrous oxalate in 15ml of trioctylphosphine to prepare a trioctylphosphine solution of the ferrous oxalate;

0.1mol of ammonium dihydrogen phosphate is dispersed in 20ml of oleylamine to prepare oleylamine solution of ammonium dihydrogen phosphate;

s2: mixing the oleylamine solution of lithium carbonate and the oleylamine solution of ammonium dihydrogen phosphate, and recording the mixed solution as A; mixing the oleylamine solution of manganese acetate and the trioctylphosphine solution of ferrous oxalate together, and recording the mixed solution as B; slowly adding the mixed solution B into the mixed solution A drop by drop; meanwhile, continuously stirring for 3h in the dropping process, and simultaneously heating the temperature from room temperature to 40 ℃; in the process of heating and stirring, the viscosity of the mixed solution is gradually increased along with the gradual addition of the mixed solution B, and finally, brown gel is formed;

s3: cooling the gel to room temperature, transferring the gel to a high-temperature tube furnace, heating to 450 ℃ at a heating rate of 5 ℃/min, preserving heat for 12h under the protective atmosphere of argon/hydrogen, and performing solid-phase sintering on the precursorGradually nucleating to generate the lithium manganese iron phosphate with the graphene-like two-dimensional structure, and recording a sample as LiFe _0.8 Mn _0.2 PO ₄ 。

Through detection, the thickness of the lithium iron manganese phosphate nanosheet is about 5nm, the maximum radial dimension is about 20 mu m, and the compacted density of the powder is 2.486g/cm ³ The powder has a conductivity of 2.56X 10 ^-12 ms/cm。

Example A2

The embodiment provides a lithium iron manganese phosphate material and a preparation method thereof. The lithium iron manganese phosphate material is LiFe _0.5 Mn _0.5 PO ₄ It is a graphene-like two-dimensional layered structure.

s1: dispersing 0.1mol of lithium sulfate in 35ml of oleylamine to prepare oleylamine solution of lithium sulfate;

dispersing 0.1mol of manganese chloride in 20ml of trioctylphosphine oxide to prepare trioctylphosphine oxide solution of manganese chloride;

dispersing 0.1mol of ferrous nitrate in 20ml of oleic acid to prepare an oleic acid solution of the ferrous nitrate;

dispersing 0.2mol of ammonium dihydrogen phosphate in 35ml of trioctylphosphine oxide to prepare a trioctylphosphine oxide solution of ammonium dihydrogen phosphate;

s2: the oleylamine solution of lithium sulfate and trioctylphosphine of ammonium dihydrogen phosphate were mixed together in solution, and the mixture was designated as A. Mixing the trioctylphosphine solution of manganese chloride and the oleic acid solution of ferrous nitrate together, and recording the mixed solution as B; slowly adding the mixed solution B into the mixed solution A dropwise, and simultaneously continuously stirring for 8 hours during the dropwise adding process, and simultaneously raising the temperature from room temperature to 70 ℃; in the process of heating and stirring, the viscosity of the mixed solution is gradually increased along with the gradual addition of the mixed solution B, and finally brown gel is formed;

s3: cooling the gel to room temperature, transferring the gel into a high-temperature tube furnace, heating to 600 ℃ at a heating rate of 2 ℃/min, preserving the heat for 18h under the protective atmosphere of nitrogen/hydrogen, and gradually nucleating the precursor to generate the like in the solid-phase sintering processLithium manganese iron phosphate with a two-dimensional structure of graphene, and a sample is recorded as LiFe _0.5 Mn _0.5 PO ₄ 。

Through detection, the thickness of the lithium iron manganese phosphate nanosheet is about 2nm, the maximum radial dimension is about 35 mu m, and the compacted density of the powder is 2.582g/cm ³ The powder has a conductivity of 3.28X 10 ^-11 ms/cm。

Example A3

The embodiment provides a lithium iron manganese phosphate material and a preparation method thereof. The lithium iron manganese phosphate material is LiFe _0.2 Mn _0.8 PO ₄ It is a graphene-like two-dimensional layered structure.

s1: dispersing 0.15mol of lithium acetate in 35ml of oleylamine to prepare oleylamine solution of lithium acetate;

dispersing 0.24mol of manganese carbonate in 30ml of trioctylphosphine to prepare a trioctylphosphine solution of manganese carbonate;

dispersing 0.06mol of ferrous carbonate in 10ml of oleic acid to prepare an oleic acid solution of the ferrous carbonate;

dispersing 0.3mol of potassium dihydrogen phosphate in 35ml of trioctylphosphine to prepare a trioctylphosphine solution of potassium dihydrogen phosphate;

s2: mixing the oleylamine solution of lithium acetate and the trioctylphosphine solution of potassium dihydrogen phosphate, and recording the mixed solution as A; mixing the trioctylphosphine solution of the manganese carbonate and the oleic acid solution of the ferrous carbonate together, and recording the mixed solution as B; slowly adding the mixed solution B into the mixed solution A dropwise, and simultaneously continuously stirring for 15h during the dropwise adding process, and simultaneously raising the temperature from room temperature to 80 ℃; in the process of heating and stirring, the viscosity of the mixed solution is gradually increased along with the gradual addition of the mixed solution B, and finally brown gel is formed;

s3: cooling the gel to room temperature, transferring the gel to a high-temperature tube furnace, heating to 700 ℃ at a heating rate of 1 ℃/min, and preserving heat for 35 hours under the protective atmosphere of argon/hydrogen; in the solid phase sintering process, the precursor gradually nucleates to generate the phosphoric acid with the two-dimensional structure similar to grapheneLithium iron manganese, sample is recorded as LiFe _0.2 Mn _0.8 PO ₄ 。

Through detection, the thickness of the lithium iron manganese phosphate nanosheet is about 8nm, the maximum radial dimension is about 18 mu m, and the compacted density of the powder is 2.396g/cm ³ The powder has a conductivity of 1.76X 10 ^-11 mS/cm。

Example A4

The embodiment provides a lithium iron manganese phosphate material and a preparation method thereof. The lithium iron manganese phosphate material is LiFe _0.3 Mn _0.7 PO ₄ It is a graphene-like two-dimensional layered structure.

s1: dispersing 0.05mol of lithium chloride in 10ml of trioctylphosphine to prepare a trioctylphosphine solution of the lithium chloride;

0.07mol of manganese sulfate is dispersed in 10ml of oleylamine to prepare oleylamine solution of manganese sulfate;

0.03mol of ferrous nitrate is dispersed in 5ml of oleic acid to prepare oleylamine solution of the ferrous nitrate;

0.1mol of sodium dihydrogen phosphate is dispersed in 20ml of trioctylphosphine to prepare a trioctylphosphine solution of sodium dihydrogen phosphate;

s2: mixing the trioctylphosphine solution of lithium chloride and the trioctylphosphine solution of sodium dihydrogen phosphate, and marking the mixed solution as A; mixing the oleylamine solution of manganese sulfate and the oleylamine solution of ferrous nitrate together, and recording the mixed solution as B; slowly adding the mixed solution B into the mixed solution A dropwise, and simultaneously continuously stirring for 10 hours during the dropwise adding process, and simultaneously raising the temperature from room temperature to 60 ℃; in the process of heating and stirring, the viscosity of the mixed solution is gradually increased along with the gradual addition of the mixed solution B, and finally, brown gel is formed;

s3: after cooling the gel to room temperature, transferring the gel to a high-temperature tube furnace, raising the temperature to 500 ℃ at a heating rate of 1 ℃/min, and preserving the temperature for 26h under the protective atmosphere of nitrogen/hydrogen. In the solid-phase sintering process, the precursor is gradually nucleated to generate the lithium manganese iron phosphate with the graphene-like two-dimensional structure, and a sample is recorded as LiFe _0.3 Mn _0.7 PO ₄ 。

Through detection, the thickness of the lithium iron manganese phosphate nanosheet is about 12nm, the maximum radial dimension is about 35 mu m, and the compacted density of the powder is 2.476g/cm ³ The powder has a conductivity of 1.056X 10 ^-12 mS/cm。

Example A5

The embodiment provides a lithium iron manganese phosphate material and a preparation method thereof. The lithium iron manganese phosphate material is LiFe _0.6 Mn _0.4 PO ₄ It is a graphene-like two-dimensional layered structure.

s1: dispersing 0.2mol of lithium hydroxide in 10ml of trioctylphosphine oxide to prepare a trioctylphosphine oxide solution of the lithium hydroxide;

0.16mol of manganese nitrate is dispersed in 10ml of oleylamine to prepare oleylamine solution of manganese nitrate;

0.24mol of ferrous sulfate is dispersed in 5ml of trioctylphosphine oxide to prepare trioctylphosphine solution of ferrous sulfate;

0.4mol of potassium monohydrogen phosphate is dispersed in 20ml of oleylamine to prepare oleylamine solution of potassium monohydrogen phosphate;

s2: mixing the trioctylphosphine solution of lithium hydroxide and the oleylamine solution of potassium monohydrogen phosphate, and recording the mixed solution as A; mixing the oleylamine solution of manganese nitrate and the trioctylphosphine solution of ferrous sulfate nitrate together, and recording the mixed solution as B; slowly adding the mixed solution B into the mixed solution A dropwise, and simultaneously continuously stirring for 23 hours during the dropwise adding process, and simultaneously raising the temperature from room temperature to 90 ℃; in the process of heating and stirring, the viscosity of the mixed solution is gradually increased along with the gradual addition of the mixed solution B, and finally brown gel is formed;

s3: cooling the gel to room temperature, transferring the gel to a high-temperature tube furnace, heating to 800 ℃ at a heating rate of 8 ℃/min, and preserving heat for 36 hours under the protective atmosphere of argon/hydrogen; in the solid-phase sintering process, the precursor gradually nucleates to generate graphene-like lithium manganese iron phosphate with a two-dimensional structure, and a sample is recorded as LiFe _0.6 Mn _0.4 PO ₄ 。

Through detection, the thickness of the lithium iron manganese phosphate nanosheet is about 20nm, the maximum radial dimension is about 55 mu m, and the compacted density of the powder is 2.546g/cm ³ The powder has a conductivity of 5.68X 10 ^-12 mS/cm。

Comparative example A1

The comparative example provides a lithium iron manganese phosphate material and a preparation method thereof. The lithium iron manganese phosphate material is LiFe _0.6 Mn _0.4 PO ₄ It is in the form of granules.

s1: dispersing 0.2mol of lithium hydroxide, 0.16mol of manganese nitrate, 0.24mol of ferrous sulfate and 0.4mol of ammonium dihydrogen phosphate in 50ml of alcohol, and carrying out ball milling and mixing for 8 hours;

s2: transferring the mixed precursor to a tubular furnace for high-temperature calcination, raising the temperature rise rate to 600 ℃ at the speed of 5 ℃/min, preserving the heat for 18h under the protective atmosphere of nitrogen/hydrogen, and recording the sample as LiFe _0.6 Mn _0.4 PO ₄ 。

The detection shows that the lithium manganese iron phosphate is granular, the grain diameter is about 5 mu m, and the compacted density of the powder is 2.18g/cm ³ The powder had a conductivity of 3.58X 10 ^-14 mS/cm。

2. The lithium ion battery comprises the following embodiments:

examples B1 to B5 and comparative examples B1 to B2 each provide a lithium ion battery. The lithium ion batteries are assembled into the lithium ion battery by the following method:

1) Positive plate:

lithium iron manganese phosphate materials provided by examples A1 to A5 and comparative example A1 are used as positive electrode active materials of lithium ion batteries of examples B1 to B5 and comparative example B1, respectively, under the same conditions, according to NMP: lithium manganese iron phosphate material: super P: PVDF, the four are mixed according to the mass ratio of 100; the rotation speed is set to be 30Hz; the anode plates are respectively prepared by the operations of homogenate, coating, drying and cutting, and are baked in a vacuum oven at 100 ℃ to remove trace water.

2) And (3) negative plate: a metallic lithium plate.

3) A diaphragm: a Polyethylene (PE) separator was used.

4) Electrolyte solution: liPF with electrolyte of 1mol/L ₆ The solvent consists of EC (ethylene carbonate) and DEC (diethyl carbonate) in a volume ratio of 1.

5) Assembling the secondary battery:

and assembling the positive plate, the negative plate, the electrolyte and the diaphragm into the lithium ion soft package battery according to the lithium ion battery assembly requirement.

3. Characterization of lithium iron manganese phosphate and electrochemical performance of the lithium ion battery:

3.1 characterization of lithium manganese iron phosphate

Scanning Electron Microscope (SEM) analysis was performed on lithium iron manganese phosphates containing examples A1 to A1 and comparative example A1, wherein the details of example A1 are shown in fig. 2.

As can be seen from fig. 2, the lithium iron manganese phosphate provided in embodiment A1 of the present invention has a typical two-dimensional layered structure.

X-ray diffraction (XRD) analysis was performed on lithium iron manganese phosphates containing examples A1 to A5 and comparative example A1, wherein the details of example A2 are shown in fig. 3.

As can be seen from fig. 2, the lithium iron manganese phosphate provided in embodiment A2 of the present invention is in the form of an obvious two-dimensional sheet, the sheet size of which reaches the micron level, and the transparent thickness of which indicates that the sheet is only several nm thick. The radial ratio of the graphene material tends to be similar to the graphene structure, so that the Hall effect is caused to remarkably improve the conductivity of the material. Meanwhile, as can be seen from the SEM image of fig. 3, the material maintains a good laminar two-dimensional structure even in the non-dispersed state, and no significant re-stacking occurs.

3.2 characterization of lithium manganese iron phosphate

The electrochemical performance of the lithium secondary batteries comprising examples B1 to B5 and comparative example B1 was subjected to the relevant performance tests as in table 1 below, the test conditions being determined according to the industry standard test methods. Wherein, the discharge test conditions of the battery are as follows:

the results of the relevant electrochemical performance test of the lithium secondary battery are shown in table 1 below. The embodiment B4 is specifically shown in figure 4.

As can be seen from FIG. 4, the lithium secondary battery provided in example B4 of the present invention has excellent electrochemical properties, and the capacity thereof can not only reach 146mAhg ^-1 And a significant high voltage plateau appears around 4.1V, which can significantly improve the energy density of the electrode.

TABLE 1

As can be seen from table 1, compared with the lithium manganese iron phosphate material synthesized in the comparative example B1 and having a common particle structure, the electrode material assembled by lithium manganese iron phosphate having a graphene-like two-dimensional nanosheet morphology structure has significantly improved electrochemistry, mainly because the two-dimensional structure can effectively shorten the diffusion distance of lithium ions and enhance the diffusion energy level of the material. Meanwhile, the quantum Hall effect of the two-dimensional structure can effectively improve the conductivity of the material, so that the rate capability of the material is greatly improved, and the performance advantage of the material in quick charge is obvious compared with that of the comparative example B1.

The above examples only express several embodiments of the present application, and the description thereof is more specific and detailed, but not construed as limiting the scope of the present application. It should be noted that, for a person skilled in the art, several variations and modifications can be made without departing from the concept of the present application, which falls within the scope of protection of the present application. Therefore, the protection scope of the present patent shall be subject to the appended claims.

Claims

1. A lithium iron manganese phosphate material is characterized in that: the lithium iron manganese phosphate material is of a two-dimensional structure similar to graphene.

2. The lithium iron manganese phosphate material of claim 1, wherein: the lithium iron manganese phosphate material has at least one of the following characteristics:

the single-layer thickness of the nanosheets of the lithium iron manganese phosphate material is 0.5-2nm;

the number of the layers of the nano sheets of the lithium iron manganese phosphate material is 1-10;

the radial size of the nanosheet of the lithium iron manganese phosphate material is 18-55 microns.

3. The lithium iron manganese phosphate material of claim 1 or 2, wherein: the compacted density of the lithium iron manganese phosphate material is 2.396-2.582g/cm ³ (ii) a And/or

The conductivity of the lithium iron manganese phosphate material is 5.68 multiplied by 10 ^-12 -32.8×10 ^-11 mS/cm。

4. The preparation method of the lithium iron manganese phosphate material is characterized by comprising the following steps of:

5. The method of claim 4, wherein: dispersing the lithium iron manganese phosphate precursor in a hydrophobic ligand solvent according to the proportion that the molar concentration of a lithium source contained in the lithium iron manganese phosphate precursor in the mixed ligand solution is 0.1-6 mol/L;

and/or

The method for dispersing the lithium iron manganese phosphate precursor in the hydrophobic ligand solvent comprises the following steps:

respectively dispersing a lithium source, a manganese source, an iron source and a phosphorus source contained in the lithium iron manganese phosphate precursor into the hydrophobic ligand solvent to respectively prepare a lithium source ligand solution, a manganese source ligand solution, an iron source ligand solution and a phosphorus source ligand solution;

and mixing the lithium source ligand solution, the manganese source ligand solution, the iron source ligand solution and the phosphorus source ligand solution according to the element metering ratio of the lithium manganese iron phosphate to obtain the mixed ligand solution.

6. The method of claim 4, wherein: the temperature of the gelling reaction is 30-100 ℃; and/or

The viscosity of the mixture colloid is 400-8000cp; and/or

The method for carrying out the gel-forming reaction on the mixed ligand solution comprises the following steps:

7. The production method according to any one of claims 4 to 6, characterized in that: the hydrophobic ligand solvent includes at least one of oleic acid, oleylamine, trioctylphosphine and trioctylphosphine oxide.

8. The production method according to any one of claims 4 to 6, characterized in that: the temperature of the sintering treatment is 200-800 ℃; and/or

The sintering treatment is carried out by heating to the sintering treatment temperature at the heating rate of 1-15 ℃/min.

9. A positive electrode characterized in that: the lithium iron manganese phosphate material comprises a current collector and a positive active layer combined on the current collector, wherein a positive active material contained in the positive active layer comprises the lithium iron manganese phosphate material in any one of claims 1 to 3 or the lithium iron manganese phosphate material prepared by the preparation method in any one of claims 4 to 8.

10. A secondary battery comprising a positive electrode, characterized in that: the positive electrode according to claim 9.