WO2024124694A1

WO2024124694A1 - Composite positive electrode material, as well as preparation method therefor, and use thereof

Info

Publication number: WO2024124694A1
Application number: PCT/CN2023/078032
Authority: WO
Inventors: 余海军; 李长东; 谢英豪; 李爱霞
Original assignee: 广东邦普循环科技有限公司; 湖南邦普循环科技有限公司
Priority date: 2022-12-15
Filing date: 2023-02-24
Publication date: 2024-06-20
Also published as: CN115832256A; FR3143871A1

Abstract

Provided in the present application are a composite positive electrode material, as well as a preparation method therefor, and the use thereof. The preparation method comprises: mixing a phosphorus source, a lithium source and Li_xM_yN_z, and calcining same to obtain the composite positive electrode material, wherein 0≤x<2, 0.8≤y≤2, 0.5<z<0.8, the M is a metal ion, the N is a complex ion containing a cyanide ion, and the mixture formed after mixing is acidic. The present application mixes the phosphorus source, the lithium source and the L_ixM_yN_z and calcines same, and a carbide obtained by means of calcination and decomposition of the L_ixM_yN_z reacts with the phosphorus source to generate elementary carbon, thereby achieving atomic-scale mixing of the M element, C element and Li element, and thus forming a carbon-coated composite positive electrode material. The present application involves a simple process, and can achieve uniform coating of carbon and formation of a conductive network in particles, thus effectively improving the electrochemical properties of the composite positive electrode material.

Description

A composite positive electrode material and its preparation method and application

Technical Field

The present application belongs to the field of electrode materials, and specifically relates to a composite positive electrode material and a preparation method and application thereof.

Background technique

In recent years, the country has strongly supported the development of the electric vehicle industry, and as a result, car companies have increasingly higher requirements for battery companies. High specific energy, long life, low-cost cathode materials and batteries are urgently needed. Lithium-ion batteries are selected by battery companies for their advantages such as high operating voltage, high specific energy, long cycle life, and low pollution. Phosphate cathode materials have attracted considerable attention as potential alternatives to commercial layered cathode materials due to their advantages in structural stability, cost-effectiveness, and environmental friendliness.

Among them, lithium iron manganese phosphate is a phosphate positive electrode material that has attracted much attention. However, the poor conductivity of the material itself is an important defect. Carbon-coated lithium iron manganese phosphate is usually used to improve the conductivity of the material. The current synthesis method is mainly to mix various iron salts, phosphoric acid, and manganese sources to prepare a precursor, and then mix it with a lithium source and a carbon source to form a carbon-coated lithium iron manganese phosphate.

For example, CN105762335A discloses a method for preparing a carbon-coated lithium manganese iron phosphate material by two-step calcination, the method comprising: placing the raw material of lithium manganese iron phosphate in the air for a first step of calcination; mixing the air calcination product with a carbon source organic matter in a dispersion medium and drying it to obtain an intermediate product; then performing a second step of calcining the intermediate product under the protection of an inert atmosphere or a weak reducing atmosphere to finally obtain a carbon-coated lithium manganese iron phosphate material.

CN111900344A discloses a method for preparing a carbon-coated lithium manganese iron phosphate positive electrode material. First, a transition metal salt solution A, a phosphorus solution B and an ammonia solution C are simultaneously added dropwise to a reaction kettle according to a molar ratio of Mn and Fe to prepare a lithium manganese iron phosphate positive electrode material precursor; then the precursor is prepared with a lithium source according to a molar ratio, and a coating carbon source and a doped metal compound are added, and calcined under an inert atmosphere to obtain a carbon-coated lithium manganese iron phosphate. Lithium cathode material.

CN102249208A discloses a hydrothermal synthesis method for lithium iron manganese phosphate, a positive electrode material for a lithium ion battery. The process steps of the method are as follows: the first step is to prepare LiMnxFe1 _- _xPO4 by hydrothermal synthesis reaction: a lithium hydroxide aqueous solution, a ferrous sulfate aqueous solution and phosphoric acid are mixed under stirring conditions, sealed, heated to 150-180°C within 0.5-2.0 hours, reacted for 0.5-4 hours under a pressure of 0.48-1.0Mpa, cooled to below 80°C, and filtered; the second step is to mix with organic matter and dry: a wet filter cake is mixed with a soluble carbon source organic matter, spray dried or flash dried; the third step is carbon coating treatment: the LiMnxFe1 _-xPO4 _carbon source composite powder is calcined at 600-750°C for 4-6 hours under inert gas conditions, cooled to below 150°C, and a carbon-coated lithium iron manganese phosphate lithium ion battery positive electrode material is obtained.

However, the above process is complicated, has little effect on the conductivity inside the material particles, and is difficult to achieve uniform carbon coating. In addition, the above process is difficult to achieve uniform mixing of Li, Fe and Mn elements, cannot fully exert the performance of the material, and the improvement of electrochemical performance is limited.

Therefore, how to design a simple preparation process to achieve uniform carbon coating and improve the conductivity inside the material particles and improve the electrochemical properties of the material is a technical problem that needs to be solved urgently.

Summary of the invention

The following is a summary of the subject matter described in detail herein. This summary is not intended to limit the scope of the claims.

In view of the deficiencies of the prior art, the purpose of the present application is to provide a composite positive electrode material and its preparation method and application. In the present application, a phosphorus source, a lithium source and Li _x M _y N _z are mixed and calcined, and the carbide decomposed by the calcination of Li _x M _y N _z reacts with the phosphorus source to produce elemental carbon, thereby achieving atomic-level mixing of M element, C element and Li element, thereby forming a carbon-coated composite positive electrode material. The present application has a simple process, can form a uniform carbon coating layer and a conductive network inside the particles, and effectively improve the electrochemical performance of the composite positive electrode material.

In order to achieve the purpose of this application, this application adopts the following technical solutions:

In a first aspect, the present application provides a method for preparing a composite positive electrode material, wherein the preparation method comprises:

Mixing a phosphorus source, a lithium source and Li _x My _y N _z , and calcining to obtain the composite positive electrode material;

Among them, 0≤x<2, 0.8≤y≤2, 0.5<z<0.8;

The M is a metal ion, the N is a complex ion containing a cyanide ion, and the mixture formed after the mixing is acidic.

The present application mixes and calcines a phosphorus source, a lithium source and Li _x M _y N _z , and the carbide produced by the calcination and decomposition of Li _x M _y N _z reacts with the phosphorus source in an acidic environment to produce phosphates of metal ions and elemental carbon, thereby achieving atomic-level mixing of M elements, C elements and Li elements to form a carbon-coated composite positive electrode material. The preparation method of the present application can form a uniform carbon coating layer and a conductive network inside the particles, effectively improving the electrochemical performance of the positive electrode material. In addition, doping elements can be introduced into the raw materials through the M position to achieve uniform doping of the doping elements.

In the present application, 0≤x<2, for example, it can be 0, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8 or 1.9, etc.

In the present application, 0.8≤y≤2, for example, it can be 0.8, 0.9, 1, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9 or 2, etc.

In the present application, 0.5<z<0.8, for example, it can be 0.52, 0.55, 0.6, 0.65, 0.7, 0.75 or 0.78, etc.

In the present application, if the mixture formed after mixing is not acidic, the carbide produced by calcining and decomposing Li _x M _y N _z is difficult to react with the phosphorus source, and atomic-level mixing of the M element, the C element and the Li element is difficult to achieve.

As a preferred technical solution, the cyanide ion-containing complex ion includes a central ion, and the central ion includes any one of ferrous ion, manganous ion, divalent nickel ion or divalent cobalt ion, or a combination of at least two of them.

Optionally, the M is a transition metal ion, and the transition metal ion preferably includes any one or a combination of at least two of nickel ion, cobalt ion, manganese ion, zinc ion, zirconium ion or chromium ion, and is more preferably a manganese ion.

Optionally, the ratio of y to z is (1-2):1, for example, it can be 1:1, 1.2:1, 1.3:1, 1:1.4, 1.5:1, 1.6:1, 1.7:1, 1.8:1, 1.9:1 or 2:1, etc.

In the present application, if the ratio of y to z is too large, that is, the content of y is too high, the conductivity of the material will be reduced; if the ratio of y to z is too small, that is, the content of y is too low, the voltage platform will be reduced.

As a preferred technical solution, the phosphorus source includes phosphoric acid and/or phosphate. Exemplarily, the phosphate may be lithium phosphate, diammonium phosphate or sodium phosphate, and the pH of the phosphorus source is 3-5, for example, 3, 3.3, 3.6, 3.9, 4.2, 4.5, 4.8 or 5.

Optionally, the molar ratio of Li _x _My N _z to the phosphorus source is 1:(2-5), for example, 1:2, 1:.2.5, 1:3, 1:3.5, 1:4, 1:4.5 or 1:5, etc.

In the present application, if _the molar ratio _of _LixMyNz to the phosphorus source is _too small, it will lead to insufficient reaction, low gram capacity, and reduced proportion of active ingredients; if the molar ratio _of _LixMyNz to the phosphorus source is too large, pyrophosphate with no electrochemical activity will be produced, which will also lead to a reduced proportion of active ingredients.

Optionally, the lithium source includes lithium hydroxide and/or lithium carbonate.

As a preferred technical solution of the present application, the mixing method is ball milling.

Optionally, the ball milling speed is 300-600 rpm, for example, 300 rpm, 350 rpm, 400 rpm, 450 rpm, 500 rpm, 550 rpm or 600 rpm.

Optionally, the ball milling time is 1-10 h, for example, 1 h, 3 h, 5 h, 7 h, 9 h or 10 h, etc., preferably 2-6 h.

Optionally, the calcination temperature is 450-900°C, for example, 450°C, 500°C, 550°C, 600°C, 650°C, 700°C, 750°C, 800°C, 850°C or 900°C.

Optionally, the calcination time is 8-20 h, for example, it can be 8 h, 9 h, 10 h, 11 h, 12 h, 13 h, 14 h, 15 h, 16 h, 17 h, 18 h, 19 h or 20 h, etc., preferably 12-16 h.

Optionally, the calcination atmosphere is an inert atmosphere, and the gas in the inert atmosphere includes nitrogen and/or helium.

Optionally, the calcination is carried out in a roller kiln.

As a preferred technical solution of the present application, the preparation method of Li _x M _y N _z comprises:

Mixing the N source and the M source, and reacting them in a liquid phase to obtain the Li _x _My N _z ;

Wherein, the N source contains lithium element.

Optionally, the N source includes any one of lithium ferrocyanide, lithium manganese cyanide or lithium cobalt cyanide, or a combination of at least two of them.

Optionally, the M source includes any one of manganese sulfate, manganese nitrate, zirconium sulfate or manganese chloride, or a combination of at least two thereof.

Optionally, the molar concentration ratio of the N source to the M source is 1:(0.5-2), for example, it can be 1:0.5, 1:0.6, 1:0.7, 1:0.8, 1:0.9, 1:1, 1:1.1, 1:1.2, 1:1.3, 1:1.4, 1:1.5, 1:1.6, 1:1.7, 1:1.8, 1:1.9 or 1:2, etc.

As a preferred technical solution, the mixing method includes: passing the M source into the N source at a certain flow rate.

Optionally, the certain flow rate is 0.5-3 mL/min, for example, it can be 0.5 mL/min, 1 mL/min, 1.5 mL/min, 2 mL/min, 2.5 mL/min or 3 mL/min.

Optionally, the temperature of the liquid phase reaction is 50-90°C, for example, 50°C, 55°C, 60°C, 65°C, 70°C, 75°C, 80°C, 85°C or 90°C.

In the present application, if the temperature of the liquid phase reaction is too high, the reaction will be too fast, which will lead to a decrease in the content of ferrocyanide and lithium in the product, thereby reducing the conductivity and gram capacity; if the temperature of the liquid phase reaction is too high, the reaction will be too fast. If it is low, it will affect the production efficiency.

Optionally, the liquid phase reaction time is 10-14 h, for example, it can be 10 h, 10.5 h, 11 h, 11.5 h, 12 h, 12.5 h, 13 h, 13.5 h or 14 h.

Optionally, the pH of the liquid phase reaction is 6.5-9, for example, 6.5, 7, 7.5, 8, 8.5 or 9.

In the present application, the pH of the liquid phase reaction is in the range of 6.5-9 so that the prepared Li _x M _y N _z can exist stably.

As a preferred technical solution, the preparation method comprises the following steps:

(1) introducing the M source into a reaction vessel containing the N source containing the lithium element at a flow rate of 0.5-3 mL/min to mix, and reacting in a liquid phase at pH 6.5-9 and 50-90° C. for 10-14 h to obtain the Li _x _My N _z ;

Among them, 0≤x<2, 0.8≤y≤2, 0.5<z<0.8;

(2) ball-milling the phosphorus source, lithium source and Li _x M _y N _z at 300-600 rpm for 1-10 h, transferring the ball-milled product to a roller kiln and calcining the product in an inert atmosphere at 450-900° C. for 8-20 h to obtain the composite positive electrode material;

Wherein, the molar ratio of the phosphorus source to Li _x _My N _z is (2-5):1.

In a second aspect, the present application provides a composite positive electrode material prepared by the preparation method described in the first aspect, wherein the composite positive electrode material comprises a positive electrode material core and a carbon coating layer located on the surface of the core;

Wherein, the carbon coating layer contains M element.

The preparation method adopted in the present application can achieve atomic-level mixing of M, C and Li to form a carbon-coated composite positive electrode material. The composite positive electrode material contains M element not only in the core but also in the carbon coating layer. In addition, doping elements can be introduced into the raw materials through the M position to achieve uniform doping of the doping elements.

In a third aspect, the present application provides a lithium-ion battery, wherein the positive electrode of the lithium-ion battery includes the composite positive electrode material as described in the second aspect.

The numerical range described in this application includes not only the point values listed above, but also any point values between the above numerical ranges that are not listed. Due to limited space and for the sake of brevity, this application no longer exhaustively lists the specific point values included in the range.

Compared with the prior art, this application has the following beneficial effects:

(1) In the present application, a phosphorus source, a lithium source and Li _x M _y N _z are mixed and calcined, and the carbide decomposed by the calcination of Li _x M _y N _z reacts with the phosphorus source to produce elemental carbon, thereby achieving atomic-level mixing of M element, C element and Li element, thereby forming a carbon-coated composite positive electrode material. The present application has a simple process, can form a uniform carbon coating layer and a conductive network inside the particles, and effectively improves the electrochemical performance of the composite positive electrode material.

(2) In the preparation method provided in the present application, doping elements can be introduced into the raw materials through the M position to achieve uniform doping of the doping elements.

Other aspects will be apparent upon reading and understanding the drawings and detailed description.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings are used to provide further understanding of the technical solution of this article and constitute a part of the specification. Together with the embodiments of the present application, they are used to explain the technical solution of this article and do not constitute a limitation on the technical solution of this article.

FIG. 1 is a SEM image of the composite positive electrode material provided in Example 1 of the present application.

FIG. 2 is a charge and discharge curve diagram of the composite positive electrode material provided in Example 1 of the present application.

Detailed ways

The technical solution of the present application is further described below through specific implementation methods. Those skilled in the art should understand that the embodiments are only to help understand the present application and should not be regarded as specific limitations of the present application.

Example 1

This embodiment provides a method for preparing a composite positive electrode material, the preparation method comprising the following steps:

(1) 100 mL of 1 mol/L lithium ferrocyanide aqueous solution was placed in a reaction kettle, and 100 mL of 1 mol/L manganese sulfate solution was added to the reaction kettle at 1 mL/min by a peristaltic pump, and the mixture was reacted for 12 h at a pH of 8 and a temperature of 60° C., and then filtered and dried to obtain Li _1.4 Mn _0.8 [Fe(CN) ₆ ] _0.75 ;

Among them, the ratio of y to z is 1.07:1;

(2) 60 g of the above-mentioned Li _1.4 Mn _0.8 [Fe(CN) ₆ ] _0.75 , 100 mL of 4 mol/L phosphoric acid solution (pH 4) and 0.72 g of lithium hydroxide were placed in a ball mill and milled at 450 rpm for 3 h. After ball milling, the mixture was transferred to a roller kiln and calcined in a nitrogen atmosphere at 600° C. for 12 h to obtain a carbon-coated lithium manganese iron phosphate positive electrode material;

The molar ratio of Li _1.4 Mn _0.8 [Fe(CN) ₆ ] _0.75 to the phosphoric acid solution is 1:3.

FIG1 shows a SEM image of the composite positive electrode material provided in this embodiment. As can be seen from the image, the particles of the lithium manganese iron phosphate positive electrode material prepared in this embodiment are complete and have a uniform particle size distribution.

FIG2 shows a charge and discharge curve of the composite positive electrode material provided in this embodiment. As can be seen from the figure, the gram capacity of the lithium manganese iron phosphate positive electrode material prepared in this embodiment can reach 158.5 mAh/g.

Example 2

(1) 100 mL of 1 mol/L lithium ferrocyanide aqueous solution was placed in a reaction kettle, and 100 mL of 1 mol/L manganese sulfate solution was added to the reaction kettle at 1 mL/min by a peristaltic pump, and the mixture was reacted for 12 h at a pH of 7 and a temperature of 60° C., and then filtered and dried to obtain Li _0.9 Mn _0.75 [Fe(CN) ₆ ] _0.6 ;

Among them, the ratio of y to z is 1.25:1;

(2) 60 g of the above-mentioned Li _0.9 Mn _0.75 [Fe(CN) ₆ ] _0.6 , 100 mL of 4 mol/L phosphoric acid solution (pH 3) and 2.4 g of lithium hydroxide were placed in a ball mill and mixed at 500 rpm for 2 h. After ball milling, the mixture was transferred to a roller kiln and calcined in a nitrogen atmosphere at 600° C. for 12 h to obtain a carbon-coated lithium manganese iron phosphate positive electrode material;

The molar ratio of Li _1.4 Mn _0.8 [Fe(CN) ₆ ] _0.6 to the phosphoric acid solution is 1:4.

Example 3

(1) 100 mL of 1 mol/L lithium ferrocyanide aqueous solution was placed in a reaction kettle, and 100 mL of 1 mol/L manganese sulfate solution (including 0.05 mol/L zirconium sulfate) was added to the reaction kettle at 1 mL/min by a peristaltic pump, and the reaction was carried out at a pH of 9 and a temperature of 60° C. for 12 h, and then filtered and dried to obtain Li _1.4 Mn _0.76 Zr _0.04 [Fe(CN) ₆ ] _0.77 ;

Among them, the ratio of y to z is 1.04:1;

(2) 60 g of the above-mentioned Li _1.4 Mn _0.76 Zr _0.04 [Fe(CN) ₆ ] _0.77 , 100 mL of 4 mol/L phosphoric acid solution (pH 5) and 0.72 g of lithium hydroxide were placed in a ball mill and mixed at 400 pm for 6 h. After ball milling, the mixture was transferred to a roller kiln and calcined at 600° C. in a nitrogen atmosphere for 12 h to obtain a carbon-coated lithium manganese iron phosphate positive electrode material;

The molar ratio of Li _1.4 Mn _0.76 Zr _0.04 [Fe(CN) ₆ ] _0.77 to the phosphoric acid solution is 1:3.5.

Example 4

(1) placing 100 mL of 1 mol/L lithium manganese cyanide aqueous solution in a reaction kettle, adding 100 mL of 0.5 mol/L nickel nitrate solution into the reaction kettle at 0.5 mL/min through a peristaltic pump, reacting for 14 h at a pH of 6.5 and a temperature of 50° C., filtering and drying to obtain Li _0.6 Ni[Mn(CN) ₆ ] _0.65 ;

Among them, the ratio of y to z is 1.54:1;

(2) 60 g of the above-mentioned Li _0.6 Ni[Mn(CN) ₆ ] _0.65 , 100 mL of 4 mol/L diammonium phosphate solution (pH 4) and 10 g of lithium carbonate were placed in a ball mill and milled at 300 rpm for 10 h. After ball milling, the mixture was transferred to a roller kiln and calcined in a helium atmosphere at 450° C. for 20 h to obtain a carbon-coated nickel manganese lithium phosphate positive electrode material;

The molar ratio of Li _0.6 Ni[Mn(CN) ₆ ] _0.65 to the phosphate solution is 1:2.

Example 5

(1) 100 mL of 1 mol/L ammonium ferrocyanide aqueous solution was placed in a reaction kettle, and 100 mL of 2 mol/L manganese sulfate solution was added to the reaction kettle at 3 mL/min by a peristaltic pump, and the mixture was reacted for 10 h at a pH of 8 and a temperature of 90° C., and then filtered and dried to obtain Mn _1.5 [Fe(CN) ₆ ] _0.75 ;

Among them, the ratio of y to z is 2:1;

(2) 60 g of the above-mentioned Mn ₂ [Fe(CN) ₆ ], 100 mL of 4 mol/L phosphoric acid solution (pH 4) and 12 g of lithium hydroxide were placed in a ball mill and mixed at 600 rpm for 1 h. After ball milling, the mixture was transferred to a roller kiln and calcined at 900° C. in a nitrogen atmosphere for 8 h to obtain a carbon-coated lithium manganese iron phosphate positive electrode material;

The molar ratio of Mn ₂ [Fe(CN) ₆ ] to the phosphoric acid solution is 1:5.

Example 6

The difference between this embodiment and embodiment 1 is that the chemical formula of Li _x M _y N _z is Li _1.4 Mn _0.5 [Fe(CN) ₆ ] _0.6 , wherein the ratio of y to z is 0.83:1.

The rest of the preparation methods and parameters were the same as those in Example 1.

Example 7

The difference between this embodiment and embodiment 1 is that the molar ratio of Li _1.4 Mn _0.8 [Fe(CN) ₆ ] _0.75 and the phosphoric acid solution is 1:1.

Example 8

The difference between this embodiment and embodiment 1 is that the molar ratio of Li _1.4 Mn _0.8 [Fe(CN) ₆ ] _0.75 to the phosphoric acid solution is 1:10.

Example 9

The difference between this embodiment and embodiment 1 is that the reaction temperature in step (1) is 95° C., and the product obtained in step (1) is Li _1.2 Mn _0.8 [Fe(CN) ₆ ] _0.55 .

Comparative Example 1

This comparative example uses commercially available lithium manganese iron phosphate, whose chemical formula is LiMn _0.75 Fe _0.25 PO ₄ .

Comparative Example 2

The lithium manganese iron phosphate provided in Comparative Example 1 was mixed with 10% by mass of starch solid phase, and the mixture was calcined to obtain a carbon-coated lithium manganese iron phosphate positive electrode material.

Performance Testing

The composite positive electrode material provided in Examples 1-9 and Comparative Examples 1-2 was mixed with a conductive agent, acetylene black, and a binder, polyvinylidene fluoride (PVDF), in a mass ratio of 8:1:1, and a certain amount of organic solvent N-methylpyrrolidone (NMP) was added, and the mixture was coated on an aluminum foil after stirring to prepare a positive electrode sheet; a lithium ion half-cell was assembled in a glove box using copper foil as a negative electrode, PE as a separator, and an ethylene carbonate/diethyl carbonate solution of lithium hexafluorophosphate as an electrolyte, and charge and discharge tests were carried out at an operating voltage of 2-4.35 V and different current densities.

The test results are shown in Table 1.

Table 1

analyze:

It can be seen from the data results of Examples 1-5 that the electrochemical performance of the lithium manganese iron phosphate positive electrode material prepared in the present application is significantly improved.

From the comparison of the data results of Example 1 and Example 6, it can be seen that when the ratio of y to z is too low, although the discharge specific capacity of the material will be improved, its voltage platform will be reduced.

By comparing the data results of Example 1 and Examples 7-8, it can be seen that when the amount of phosphoric acid used is insufficient, the reaction cannot be fully carried out and the gram capacity is reduced; when the amount of phosphoric acid used is too much, pyrophosphate with no electrochemical activity will be produced, which will reduce the proportion of active materials and affect the gram capacity.

From the comparison of the data results of Example 1 and Example 9, it can be seen that preparing lithium manganese ferrocyanide at a higher temperature will lead to a decrease in the content of ferrocyanide and lithium in the product, thereby resulting in a decrease in conductivity and gram capacity.

From the comparison of the data results of Example 1 and Comparative Example 1, it can be seen that compared with the commercially available positive electrode materials, the electrochemical performance of the composite positive electrode material prepared by the preparation method provided in the present application is more excellent.

From the comparison of the data results of Example 1 and Comparative Example 2, it can be seen that the preparation method provided by the present application Carbon coating can significantly improve the electrochemical performance of positive electrode materials.

The applicant declares that the present application uses the above-mentioned embodiments to illustrate the process method of the present application, but the present application is not limited to the above-mentioned process steps, that is, it does not mean that the present application must rely on the above-mentioned process steps to be implemented. The technicians in the relevant technical field should understand that any improvement to the present application, the equivalent replacement of the raw materials selected in the present application, the addition of auxiliary components, the selection of specific methods, etc., all fall within the scope of protection and disclosure of the present application.

Claims

A method for preparing a composite positive electrode material, wherein the preparation method comprises:

Mixing a phosphorus source, a lithium source and Li x My y N z , and calcining to obtain the composite positive electrode material;

Among them, 0≤x<2, 0.8≤y≤2, 0.5<z<0.8;

The M is a metal ion, the N is a complex ion containing a cyanide ion, and the mixture formed after the mixing is acidic.
The preparation method according to claim 1, wherein the cyanide ion-containing complex ion includes a central ion, and the central ion includes any one or a combination of at least two of ferrous ion, manganous ion, divalent nickel ion or divalent cobalt ion;
The preparation method according to claim 1, wherein optionally, M is a transition metal ion, and the transition metal ion preferably includes any one or a combination of at least two of nickel ions, cobalt ions, manganese ions, zinc ions, zirconium ions or chromium ions, and is further preferably a manganese ion;
The preparation method according to claim 1, wherein optionally, the ratio of y to z is (1-2):1.
The preparation method according to claim 1, 2, 3 or 4, wherein the phosphorus source comprises phosphoric acid and/or phosphate, and the pH of the phosphorus source is 3-5;

Optionally, the molar ratio of Li x M y N z to the phosphorus source is 1:(2-5);

Optionally, the lithium source includes lithium hydroxide and/or lithium carbonate.
The preparation method according to any one of claims 1 to 5, wherein the mixing method is ball milling;

Optionally, the ball milling speed is 300-600 rpm;

Optionally, the ball milling time is 1-10h, preferably 2-6h;

Optionally, the calcination temperature is 450-900°C;

Optionally, the calcination time is 8-20h, preferably 12-16h;

Optionally, the calcination atmosphere is an inert atmosphere, and the gas in the inert atmosphere includes nitrogen and/or helium;

Optionally, the calcination is carried out in a roller kiln.
The preparation method according to any one of claims 1 to 6, wherein the preparation method of Li x My N z comprises:

Mixing the N source and the M source, and reacting them in a liquid phase to obtain the Li x My N z ;

Wherein, the N source contains lithium element.
The preparation method according to claim 7, wherein the N source comprises any one of lithium ferrocyanide, lithium manganese cyanide or lithium cobalt cyanide, or a combination of at least two thereof;

Optionally, the M source includes any one or a combination of at least two of manganese sulfate, manganese nitrate, zirconium sulfate or manganese chloride;

Optionally, the molar concentration ratio of the N source to the M source is 1:(0.5-2);
The preparation method according to claim 7 or 8, wherein the mixing method comprises: passing the M source into the N source at a certain flow rate;

Optionally, the certain flow rate is 0.5-3 mL/min;

Optionally, the temperature of the liquid phase reaction is 50-90°C;

Optionally, the liquid phase reaction time is 10-14h;

Optionally, the pH of the liquid phase reaction is 6.5-9.
The preparation method according to any one of claims 7 to 9, wherein the preparation method comprises the following steps:

(1) introducing the M source into a reaction vessel containing the N source containing the lithium element at a flow rate of 0.5-3 mL/min to mix, and reacting in a liquid phase at pH 6.5-9 and 50-90° C. for 10-14 h to obtain the Li x My N z ;

Among them, 0≤x<2, 0.8≤y≤2, 0.5<z<0.8;

(2) ball-milling the phosphorus source, lithium source and Li x M y N z at 300-600 rpm for 1-10 h, transferring the ball-milled product to a roller kiln and calcining the product in an inert atmosphere at 450-900° C. for 8-20 h to obtain the composite positive electrode material;

Wherein, the molar ratio of the phosphorus source to Li x My N z is (2-5):1.
A composite positive electrode material prepared by the preparation method according to any one of claims 1 to 10, wherein the composite positive electrode material comprises a positive electrode material core and a carbon coating layer located on the surface of the core;

Wherein, the carbon coating layer contains M element.
A lithium-ion battery, wherein the positive electrode of the lithium-ion battery comprises the composite positive electrode material as claimed in claim 11.