A composite positive electrode material and its preparation method and application

Abstract

The present invention provides a composite cathode material, a preparation method thereof and an application. The preparation method includes: mixing a phosphorus source, a lithium source and Li x M y N z and calcining to obtain the composite cathode material; wherein, 0 ≤ x < 2, 0.8 ≤ y ≤ 2, 0.5 < z < 0.8; M is a metal ion, N is a ligand ion containing a cyanide ion, and the mixture formed after mixing is acidic. In the present invention, the phosphorus source, the lithium source and L ix M y N z are mixed and calcined. The carbide decomposed by L ix M y N z reacts with the phosphorus source to generate elemental carbon, thereby realizing the atomic-level mixing of M element, C element and Li element, and thus forming a carbon-coated composite cathode material. The process of the present invention is simple, can achieve uniform carbon coating and form a conductive network inside the particles, and effectively improves the electrochemical performance of the composite cathode material.

Description

Technical Field

[0001] The present invention belongs to the field of electrode materials, and in particular relates to a composite positive electrode material and a preparation method and application thereof. Background Art

[0002] In recent years, China has strongly supported the development of the electric vehicle industry, leading to increasing demands from automakers on battery companies. High-energy-density, long-life, and low-cost cathode materials and batteries are urgently needed. Lithium-ion batteries, with their advantages of high operating voltage, high energy density, long cycle life, and low pollution, have attracted considerable attention from battery companies. Phosphate cathode materials, due to their structural stability, cost-effectiveness, and environmental friendliness, have attracted considerable attention as potential alternatives to commercial layered cathode materials.

[0003] Among them, lithium manganese iron phosphate is a phosphate positive electrode material that has attracted much attention. However, the poor conductivity of the material itself is a major defect. Carbon-coated lithium manganese iron phosphate is usually used to improve the conductivity of the material. The current synthesis method mainly mixes various iron salts, phosphoric acid, and manganese sources to prepare a precursor, and then mixes it with a lithium source and a carbon source to form carbon-coated lithium manganese iron phosphate.

[0004] For example, CN105762335A discloses a two-step calcination method for preparing a carbon-coated lithium manganese iron phosphate material, which includes: placing the raw material of lithium manganese iron phosphate in air for a first 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 calcination on 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.

[0005] 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, which are configured according to the molar ratio of Mn and Fe, are simultaneously added dropwise to a reactor 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 doping metal compound are added, and the carbon-coated lithium manganese iron phosphate positive electrode material is calcined under inert atmosphere protection.

[0006] CN102249208A discloses a hydrothermal synthesis method for lithium manganese iron phosphate, a positive electrode material for lithium ion batteries, wherein the process steps of the method are as follows: a first step, a hydrothermal synthesis reaction is performed to prepare LiMnxFe 1-xPO4: lithium hydroxide aqueous solution, 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 at a pressure of 0.48-1.0 MPa for 0.5-4 hours, cooled to below 80 ° C, and filtered; the second step is to mix with organic matter and dry: the wet filter cake is mixed with soluble carbon source organic matter, spray dried or flash dried; the third step is carbon coating treatment: LiMnxFe 1-x The PO4 carbon source composite powder is calcined at 600-750°C for 4-6 hours under inert gas conditions and cooled to below 150°C to obtain a carbon-coated lithium manganese iron phosphate lithium ion battery positive electrode material.

[0007] However, the above process is complex, has little effect on the conductivity inside the material particles, and is difficult to achieve uniform carbon coating. Moreover, 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.

[0008] Therefore, how to design a simple preparation process to achieve uniform carbon coating and improve the electrical conductivity inside the material particles and enhance the electrochemical properties of the material is a technical problem that needs to be solved urgently. Summary of the Invention

[0009] In view of the shortcomings of the prior art, the present invention aims to provide a composite positive electrode material and its preparation method and application. x M y N z Mixed calcination, Li x M y N z The calcined and decomposed carbides react with a phosphorus source to produce elemental carbon, thereby achieving atomic-level mixing of the M, C, and Li elements, thereby forming a carbon-coated composite cathode material. This simple process forms a uniform carbon coating and a conductive network within the particles, effectively improving the electrochemical performance of the composite cathode material.

[0010] In order to achieve the purpose of the invention, the present invention adopts the following technical solutions:

[0011] In a first aspect, the present invention provides a method for preparing a composite positive electrode material, characterized in that the preparation method comprises:

[0012] Phosphorus source, lithium source and Li x M y N z Mixing and calcining to obtain the composite positive electrode material;

[0013] Among them, 0≤x<2, 0.8≤y≤2, 0.5 <z<0.8;

[0014] M is a metal ion, N is a ligand ion containing a cyanide ion, and the mixture formed after mixing is acidic.

[0015] In the present invention, a phosphorus source, a lithium source and Li x M y N z are mixed and calcined. Li x M y N z The carbide generated by calcination decomposition reacts with the phosphorus source in an acidic environment to generate metal ion phosphates and elemental carbon. Thus, atomic-level mixing of M element, C element and Li element can be achieved, and a carbon-coated composite cathode material is formed. By using the preparation method of the present invention, a uniform carbon coating layer and a conductive network inside the particles can be formed, effectively improving the electrochemical performance of the cathode material. In addition, doping elements can be introduced at the M site in the raw materials to achieve uniform doping of the doping elements.

[0016] In the present invention, 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.

[0017] In the present invention, 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.

[0018] In the present invention, 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.

[0019] In the present invention, if the mixture formed after mixing is not acidic, then Li x M y N z it is difficult for the carbide generated by calcination decomposition to react with the phosphorus source, and it is difficult to achieve atomic-level mixing of M element, C element and Li element.

[0020] As a preferred technical solution, the ligand ion containing a cyanide 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.

[0021] Preferably, 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 more preferably manganese ion.

[0022] Preferably, 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.

[0023] In the present invention, 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.

[0024] As a preferred technical solution, the phosphorus source includes phosphoric acid and / or phosphate. Exemplarily, the phosphate can be lithium phosphate, ammonium dihydrogen 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.

[0025] Preferably, the Li x M y N z The molar ratio of phosphorus to phosphorus source is 1:(2-5), for example, it can be 1:2, 1:.2.5, 1:3, 1:3.5, 1:4, 1:4.5 or 1:5, etc.

[0026] In the present invention, if Li x M y N z If the molar ratio of Li to phosphorus source is too small, the reaction will be insufficient, the gram capacity will be low, and the proportion of active ingredients will be reduced; if Li x M y N z If the molar ratio to the phosphorus source is too large, pyrophosphate with no electrochemical activity will be produced, which will also lead to a decrease in the proportion of active ingredients.

[0027] Preferably, the lithium source includes lithium hydroxide and / or lithium carbonate.

[0028] As a preferred technical solution of the present invention, the mixing method is ball milling.

[0029] Preferably, 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.

[0030] Preferably, 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.

[0031] Preferably, 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.

[0032] Preferably, the calcination time is 8-20 h, for example, 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.

[0033] Preferably, the calcination atmosphere is an inert atmosphere, and the gas in the inert atmosphere includes nitrogen and / or helium.

[0034] Preferably, the calcination is carried out in a roller kiln.

[0035] As a preferred technical solution of the present invention, the Li x M y N z The preparation method comprises:

[0036] The N source and the M source are mixed and reacted in liquid phase to obtain the Li x M y N z ;

[0037] Wherein, the N source contains lithium element.

[0038] Preferably, the nitrogen source includes any one of lithium ferrocyanide, lithium manganese cyanide or lithium cobalt cyanide, or a combination of at least two thereof.

[0039] Preferably, the M source includes any one of manganese sulfate, manganese nitrate, zirconium sulfate or manganese chloride, or a combination of at least two thereof.

[0040] Preferably, 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.

[0041] As a preferred technical solution, the mixing method includes: passing the M source into the N source at a certain flow rate.

[0042] Preferably, the certain flow rate is 0.5-3 mL / min, for example, 0.5 mL / min, 1 mL / min, 1.5 mL / min, 2 mL / min, 2.5 mL / min or 3 mL / min.

[0043] Preferably, 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.

[0044] In the present invention, 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 specific capacity; if the temperature of the liquid phase reaction is too low, the production efficiency will be affected.

[0045] Preferably, the liquid phase reaction time is 10-14 h, for example, 10 h, 10.5 h, 11 h, 11.5 h, 12 h, 12.5 h, 13 h, 13.5 h or 14 h.

[0046] Preferably, the pH of the liquid phase reaction is 6.5-9, for example, 6.5, 7, 7.5, 8, 8.5 or 9.

[0047] In the present invention, the pH of the liquid phase reaction is in the range of 6.5-9, which can make the prepared Li x M y N z Stable existence.

[0048] As a preferred technical solution, the preparation method comprises the following steps:

[0049] (1) The M source is introduced into the reaction vessel containing the N source containing lithium at a flow rate of 0.5-3 mL / min for mixing, and the liquid phase reaction is carried out at pH 6.5-9 and 50-90° C. for 10-14 h to obtain the Li x M y N z ;

[0050] Among them, 0≤x<2, 0.8≤y≤2, 0.5 <z<0.8;

[0051] (2) Phosphorus source, lithium source and Li x M y N z ball milling at 300-600 rpm for 1-10 hours, and then transferring the ball milled product to a roller kiln and calcining it in an inert atmosphere at 450-900° C. for 8-20 hours to obtain the composite positive electrode material;

[0052] Among them, phosphorus source and Li x M y N z The molar ratio is (2-5):1.

[0053] In a second aspect, the present invention 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;

[0054] Wherein, the carbon coating layer contains M element.

[0055] The preparation method adopted by the present invention 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 elements 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.

[0056] In a third aspect, the present invention provides a lithium-ion battery, wherein the positive electrode of the lithium-ion battery comprises the composite positive electrode material as described in the second aspect.

[0057] The numerical range described in the present invention includes not only the point values ​​listed above, but also any point values ​​between the above numerical ranges that are not listed. Due to space limitations and for the sake of simplicity, the present invention no longer exhaustively lists the specific point values ​​included in the range.

[0058] Compared with the prior art, the present invention has the following beneficial effects:

[0059] (1) The present invention combines a phosphorus source, a lithium source and Li x M y N z Mixed calcination, Li x M y N z The calcined and decomposed carbides react with a phosphorus source to produce elemental carbon, thereby achieving atomic-level mixing of the M, C, and Li elements, thereby forming a carbon-coated composite cathode material. This simple process forms a uniform carbon coating and a conductive network within the particles, effectively improving the electrochemical performance of the composite cathode material.

[0060] (2) In the preparation method provided by the present invention, doping elements can be introduced into the raw materials through the M position to achieve uniform doping of the doping elements. BRIEF DESCRIPTION OF THE DRAWINGS

[0061] Figure 1 This is an SEM image of the composite positive electrode material provided in Example 1 of the present invention.

[0062] Figure 2 This is a charge and discharge curve diagram of the composite positive electrode material provided in Example 1 of the present invention. DETAILED DESCRIPTION

[0063] The technical solution of the present invention is further described below by way of specific embodiments. It should be understood by those skilled in the art that the embodiments are merely to help understand the present invention and should not be regarded as specific limitations of the present invention.

[0064] Example 1

[0065] This embodiment provides a method for preparing a composite positive electrode material, the preparation method comprising the following steps:

[0066] (1) 100 mL of 1 mol / L lithium ferrocyanide aqueous solution was placed in a reactor, and 100 mL of 1 mol / L manganese sulfate solution was added to the reactor at 1 mL / min by a peristaltic pump. The reaction was carried out at a pH of 8 and a temperature of 60°C for 12 h, and the mixture was filtered and dried to obtain Li 1.4 Mn 0.8 [Fe(CN)6] 0.75 ;

[0067] Among them, the ratio of y to z is 1.07:1;

[0068] (2) Take 60g of the above 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 at 600 ° C in a nitrogen atmosphere for 12 h to obtain a carbon-coated lithium manganese iron phosphate positive electrode material;

[0069] Among them, Li 1.4 Mn 0.8 [Fe(CN)6] 0.75 The molar ratio of phosphoric acid solution is 1:3.

[0070] Figure 1 The SEM image of the composite positive electrode material provided in this embodiment is shown. It can be seen from the figure that the particles of the lithium manganese iron phosphate positive electrode material prepared in this embodiment are complete and have a uniform particle size distribution.

[0071] Figure 2 The charge and discharge curve of the composite positive electrode material provided in this embodiment is shown. 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.

[0072] Example 2

[0073] This embodiment provides a method for preparing a composite positive electrode material, the preparation method comprising the following steps:

[0074] (1) 100 mL of 1 mol / L lithium ferrocyanide aqueous solution was placed in a reactor, and 100 mL of 1 mol / L manganese sulfate solution was added to the reactor at 1 mL / min by a peristaltic pump. The reaction was carried out at a pH of 7 and a temperature of 60°C for 12 h, and the reaction was carried out after filtration and drying to obtain Li 0.9 Mn 0.75 [Fe(CN)6] 0.6 ;

[0075] Among them, the ratio of y to z is 1.25:1;

[0076] (2) Take 60g of the above 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 milled 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;

[0077] Among them, Li 1.4 Mn 0.8 [Fe(CN)6] 0.6 The molar ratio of phosphoric acid solution is 1:4.

[0078] Example 3

[0079] This embodiment provides a method for preparing a composite positive electrode material, the preparation method comprising the following steps:

[0080] (1) 100 mL of 1 mol / L lithium ferrocyanide aqueous solution was placed in a reactor, and 100 mL of 1 mol / L manganese sulfate solution (which also contained 0.05 mol / L zirconium sulfate) was added to the reactor at 1 mL / min by a peristaltic pump. The reaction was carried out at a pH of 9 and a temperature of 60°C for 12 h, and the mixture was filtered and dried to obtain Li 1.4 Mn 0.76 Zr 0.04 [Fe(CN)6] 0.77 ;

[0081] Among them, the ratio of y to z is 1.04:1;

[0082] (2) Take 60g of the above Li 1.4 Mn 0.76 Zr 0.04 [Fe(CN)6] 0.77100 mL of 4 mol / L phosphoric acid solution (pH 5) and 0.72 g of lithium hydroxide were placed in a ball mill and ball-milled 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;

[0083] Among them, Li 1.4 Mn 0.76 Zr 0.04 [Fe(CN)6] 0.77 The molar ratio of phosphoric acid solution is 1:3.5.

[0084] Example 4

[0085] This embodiment provides a method for preparing a composite positive electrode material, the preparation method comprising the following steps:

[0086] (1) 100 mL of 1 mol / L lithium manganese cyanide aqueous solution was placed in a reactor, and 100 mL of 0.5 mol / L nickel nitrate solution was added to the reactor at 0.5 mL / min by a peristaltic pump. The reaction was carried out at a pH of 6.5 and a temperature of 50°C for 14 h, and the mixture was filtered and dried to obtain Li 0.6 Ni[Mn(CN)6] 0.65 ;

[0087] Among them, the ratio of y to z is 1.54:1;

[0088] (2) Take 60g of the above Li 0.6 Ni[Mn(CN)6] 0.65 100 mL of 4 mol / L ammonium dihydrogen 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;

[0089] Among them, Li 0.6 Ni[Mn(CN)6] 0.65 The molar ratio of phosphate solution is 1:2.

[0090] Example 5

[0091] This embodiment provides a method for preparing a composite positive electrode material, the preparation method comprising the following steps:

[0092] (1) 100 mL of 1 mol / L ammonium ferrocyanide aqueous solution was placed in a reactor, and 100 mL of 2 mol / L manganese sulfate solution was added to the reactor at 3 mL / min by a peristaltic pump. The reaction was carried out at a pH of 8 and a temperature of 90°C for 10 h, and the mixture was filtered and dried to obtain Mn 1.5[Fe(CN)6] 0.75 ;

[0093] Among them, the ratio of y to z is 2:1;

[0094] (2) 60 g of the above-mentioned Mn2[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 at 600 rpm for 1 h. After ball milling, the mixture was transferred to a roller kiln and calcined in a nitrogen atmosphere at 900 ° C for 8 h to obtain a carbon-coated lithium manganese iron phosphate positive electrode material;

[0095] The molar ratio of Mn2[Fe(CN)6] to phosphoric acid solution is 1:5.

[0096] Example 6

[0097] The difference between this embodiment and embodiment 1 is that Li x M y N z The chemical formula is Li 1.4 Mn 0.5 [Fe(CN)6] 0.6 , where the ratio of y to z is 0.83:1.

[0098] The rest of the preparation methods and parameters remained the same as in Example 1.

[0099] Example 7

[0100] The difference between this embodiment and embodiment 1 is that Li 1.4 Mn 0.8 [Fe(CN)6] 0.75 The molar ratio of phosphoric acid solution is 1:1.

[0101] The rest of the preparation methods and parameters remained the same as in Example 1.

[0102] Example 8

[0103] The difference between this embodiment and embodiment 1 is that Li 1.4 Mn 0.8 [Fe(CN)6] 0.75 The molar ratio of phosphoric acid solution is 1:10.

[0104] The rest of the preparation methods and parameters remained the same as in Example 1.

[0105] Example 9

[0106] 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 .

[0107] The rest of the preparation methods and parameters remained the same as in Example 1.

[0108] Comparative Example 1

[0109] This comparative example uses commercially available lithium manganese iron phosphate, whose chemical formula is LiMn 0.75 Fe 0.25 PO4.

[0110] Comparative Example 2

[0111] 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.

[0112] Performance Testing

[0113] The composite positive electrode materials provided in Examples 1-9 and Comparative Examples 1-2 were mixed with the conductive agent acetylene black and the binder polyvinylidene fluoride (PVDF) in a mass ratio of 8:1:1, and a certain amount of organic solvent N-methylpyrrolidone (NMP) was added. After stirring, the mixture was coated on aluminum foil to form a positive electrode sheet. A lithium-ion half-cell was assembled in a glove box using copper foil as the negative electrode, PE as the separator, and an ethylene carbonate / diethyl carbonate solution of lithium hexafluorophosphate as the electrolyte. Charge and discharge tests were performed at an operating voltage of 2-4.35 V and different current densities.

[0114] The test results are shown in Table 1.

[0115] Table 1

[0116]

[0117]

[0118] analyze:

[0119] 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 by the present invention is significantly improved.

[0120] 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 capacity of the material will be improved, its voltage platform will be reduced.

[0121] From the comparison of 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 is produced, which reduces the proportion of active materials and affects the gram capacity.

[0122] 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 specific capacity.

[0123] 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 by the present invention is more excellent.

[0124] From the comparison of the data results of Example 1 and Comparative Example 2, it can be seen that the carbon coating achieved by the preparation method provided by the present invention can significantly improve the electrochemical performance of the positive electrode material.

[0125] The applicant states that while the above-described embodiments illustrate the process of the present invention, the present invention is not limited to the above-described process steps, nor does it imply that the present invention must rely on the above-described process steps for implementation. Those skilled in the art will appreciate that any improvements to the present invention, equivalent substitutions for the raw materials used, additions of auxiliary components, and selection of specific methods, etc., fall within the scope of protection and disclosure of the present invention.

Claims

1. A method for preparing a composite positive electrode material, characterized in that: The preparation method comprises: Phosphorus source, lithium source and Li x M y N z Mixing 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 cyanide-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 thereof; The M is a transition metal ion, and the transition metal ion includes any one of nickel ion, cobalt ion, manganese ion, zinc ion, zirconium ion or chromium ion, or a combination of at least two thereof.

2. The preparation method according to claim 1, characterized in that The transition metal ion is a manganese ion.

3. The preparation method according to claim 1, characterized in that The ratio of y to z is (1-2):

1.

4. The preparation method according to claim 1, characterized in that The phosphorus source includes phosphoric acid and / or phosphate, and the pH of the phosphorus source is 3-5.

5. The preparation method according to claim 1, characterized in that The Li x M y N z The molar ratio of phosphorus source is 1:(2-5).

6. The preparation method according to claim 1, characterized in that The lithium source includes lithium hydroxide and / or lithium carbonate.

7. The preparation method according to claim 1, characterized in that The mixing method is ball milling.

8. The preparation method according to claim 7, characterized in that The ball milling speed is 300-600 rpm.

9. The preparation method according to claim 7, characterized in that The ball milling time is 1-10 hours.

10. The preparation method according to claim 9, characterized in that The ball milling time is 2-6 hours.

11. The preparation method according to claim 1, characterized in that The calcination temperature is 450-900°C.

12. The preparation method according to claim 1, characterized in that The calcination time is 8-20 hours.

13. The preparation method according to claim 12, characterized in that The calcination time is 12-16 hours.

14. The preparation method according to claim 1, characterized in that The calcination atmosphere is an inert atmosphere, and the gas in the inert atmosphere includes nitrogen and / or helium.

15. The preparation method according to claim 1, characterized in that The calcination is carried out in a roller kiln.

16. The preparation method according to claim 1, characterized in that The Li x M y N z The preparation method comprises: The N source and the M source are mixed and reacted in liquid phase to obtain the Li x M y N z ; Wherein, the N source contains lithium element.

17. The preparation method according to claim 16, characterized in that The nitrogen source includes any one of lithium ferrocyanide, lithium manganese cyanide, and lithium cobalt cyanide, or a combination of at least two of them.

18. The preparation method according to claim 16, characterized in that The M source includes any one of manganese sulfate, manganese nitrate, zirconium sulfate or manganese chloride, or a combination of at least two thereof.

19. The preparation method according to claim 16, characterized in that The molar concentration ratio of the N source to the M source is 1:(0.5-2).

20. The preparation method according to claim 16, characterized in that The mixing method includes: passing the M source into the N source at a certain flow rate.

21. The preparation method according to claim 20, characterized in that The certain flow rate is 0.5-3 mL / min.

22. The preparation method according to claim 16, characterized in that The temperature of the liquid phase reaction is 50-90°C.

23. The preparation method according to claim 16, characterized in that The liquid phase reaction time is 10-14 hours.

24. The preparation method according to claim 16, characterized in that The pH of the liquid phase reaction is 6.5-9.

25. The preparation method according to claim 16, characterized in that The preparation method comprises the following steps: (1) The M source is introduced into the reaction vessel containing the N source containing lithium at a flow rate of 0.5-3 mL / min for mixing, and the liquid phase reaction is carried out at pH 6.5-9 and 50-90° C. for 10-14 h to obtain the Li x M y N z ; Among them, 0≤x<2, 0.8≤y≤2, 0.5 <z<0.8; (2) Phosphorus source, lithium source and Li x M y N z ball milling at 300-600 rpm for 1-10 hours, and then transferring the ball milled product to a roller kiln and calcining it in an inert atmosphere at 450-900° C. for 8-20 hours to obtain the composite positive electrode material; Among them, phosphorus source and Li x M y N z The molar ratio is (2-5):

1.

26. A composite positive electrode material prepared by the preparation method according to any one of claims 1 to 25, characterized in that: 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.

27. A lithium ion battery, characterized in that: The positive electrode of the lithium-ion battery includes the composite positive electrode material as claimed in claim 26.

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