Amorphous lithium iron phosphate composite positive electrode material and preparation method and application thereof

Abstract

The invention belongs to the technical field related to batteries, and particularly discloses an amorphous lithium iron phosphate composite positive electrode material as well as a preparation method and application thereof. The composite positive electrode material comprises amorphous lithium iron phosphate and crystalline lithium iron phosphate, and the mass ratio of the amorphous lithium iron phosphate to the crystalline lithium iron phosphate is (0.01-0.1): (0.90-0.99). By introducing a certain amount of amorphous lithium iron phosphate into crystalline lithium iron phosphate, the gram capacity of the battery can be effectively improved while the characteristics of the original crystalline lithium iron phosphate are kept, the internal resistance of the battery is reduced, and the battery adapts to the high-rate charging performance of the battery; and the plateau voltage of the battery is improved, so that the electrochemical performance of the battery is improved. Meanwhile, the amorphous lithium iron phosphate is beneficial for inhibiting the formation of lithium dendrites and preventing the diaphragm from being punctured; and the lithium precipitation phenomenon can be effectively prevented by adjusting the use amount relationship between the crystalline lithium iron phosphate and the amorphous lithium iron phosphate.

Description

Technical Field

[0001] The present invention belongs to the technical field of batteries, and in particular relates to an amorphous lithium iron phosphate composite positive electrode material and a preparation method and application thereof. Background Art

[0002] Currently, the cathodes of commonly used consumer batteries are mostly made of crystalline materials such as pure ternary, mixed ternary, and lithium cobalt oxide. These materials are relatively expensive and often suffer from slow charging rates and low energy density. Consequently, these materials are increasingly unable to meet the growing demand for fast-charging and high-capacity batteries.

[0003] Compared to traditional crystalline metals, amorphous alloys possess long-range disorder and short-range order in their atomic arrangement. This unique microstructure endows amorphous alloys with numerous excellent physical and chemical properties. Due to their disordered structure, amorphous alloys lack dislocations and grain boundaries that are susceptible to corrosion, and possess an extremely high energy state, high strength and hardness, excellent corrosion resistance, and soft magnetic properties. These exceptional properties have made amorphous alloys a research hotspot at the intersection of multiple disciplines, including materials science, mechanics, physics, chemistry, and energy. Their excellent corrosion resistance in acidic and alkaline aqueous solutions, combined with their high energy storage capacity, makes amorphous materials promising for battery applications. However, their application in traditional electrode materials remains a significant challenge.

[0004] Therefore, how to improve the energy storage and charging capacity of electrode materials while reducing the cost is a technical problem that needs to be solved urgently in the battery field. Summary of the Invention

[0005] The present invention aims to address at least one of the technical problems existing in the above-mentioned prior art. To this end, the present invention provides an amorphous lithium iron phosphate composite positive electrode material, a preparation method, and applications thereof. This composite positive electrode material can increase battery capacity and reduce internal resistance during charge and discharge, adapt to high-rate charging performance, and prevent the formation of lithium dendrites and lithium plating.

[0006] To solve the above technical problems, the first aspect of the present invention provides a composite positive electrode material, which includes amorphous lithium iron phosphate and crystalline lithium iron phosphate, and the mass ratio of the amorphous lithium iron phosphate to the crystalline lithium iron phosphate is (0.01-0.1): (0.90-0.99).

[0007] Specifically, although traditional crystalline lithium iron phosphate has good specific capacity and long cycle life, its low conductivity and energy density limit its application in high-performance batteries. Amorphous lithium iron phosphate, as an amorphous material, has the characteristics of long-range order and short-range disorder, and has better conductivity and corrosion resistance than crystalline lithium iron phosphate. Therefore, amorphous lithium iron phosphate as a positive electrode material can increase the battery capacity during battery charging and discharging, while reducing the internal resistance of the battery and adapting to the high-rate charging performance of the battery. However, since most of the current commercial negative electrode materials are artificial graphite or silicon-carbon graphite, they cannot accommodate Li + The capacity of the battery is limited. When the content of amorphous lithium iron phosphate in the positive electrode material is too high, lithium deposition is likely to occur.

[0008] Based on this, the present invention introduces a certain amount of amorphous lithium iron phosphate into crystalline lithium iron phosphate, which not only helps to improve the mechanical strength of the electrode while retaining the original characteristics of the crystalline lithium iron phosphate, but also effectively improves the battery's gram capacity, while reducing the battery's internal resistance, adapting to the battery's charging performance at high rates; and helps to improve the battery's platform voltage, thereby improving the battery's electrochemical performance. At the same time, the energy state of amorphous lithium iron phosphate is higher, and the electrolyte has a better effect on the Li + Faster transport is beneficial to promote the crystalline Li + transfer to prevent excessive Li + Dendrites accumulate on the electrode surface and pierce the diaphragm. Therefore, the introduction of an appropriate amount of amorphous lithium iron phosphate can also help inhibit the formation of lithium dendrites and prevent the diaphragm from piercing. In addition, the present invention can prevent the occurrence of lithium precipitation by adjusting the dosage relationship between crystalline lithium iron phosphate and amorphous lithium iron phosphate; and without changing the existing negative electrode material, the battery cell can be designed to adjust the C / B value of the battery (the ratio of the anode to the cathode capacity).

[0009] In some embodiments of the present invention, the preparation process of the amorphous lithium iron phosphate is as follows: α-FePO4·2H2O is first heated under an inert atmosphere and rapidly cooled to obtain amorphous iron phosphate; the amorphous iron phosphate is then allowed to stand, heated for a second time, and dispersed in an organic solvent; a lithium source solution is then added and mixed to obtain a mixed solution; and the amorphous lithium iron phosphate is obtained by suction filtration.

[0010] Specifically, the present invention utilizes a thermal decomposition method to prepare amorphous lithium iron phosphate. Crystalline α-FePO4·2H2O is first heated and rapidly cooled to obtain amorphous iron phosphate. A liquid-phase synthesis method is then employed using the amorphous iron phosphate and a lithium source solution as raw materials to obtain the amorphous lithium iron phosphate. This preparation method yields high-purity amorphous lithium iron phosphate while minimizing the precipitation of crystalline lithium iron phosphate. Furthermore, the thermal decomposition method can effectively process large amounts of waste raw materials. Recycled raw materials generated during production can be reused as raw materials for preparing crystalline lithium iron phosphate, achieving resource reuse and further reducing production costs.

[0011] In some embodiments of the present invention, the temperature regime of the first heating is: heating to 100-1500° C. at a rate of 1-25° C. / min and keeping the temperature for 1-24 hours.

[0012] In some embodiments of the present invention, the standing time is 1-24 hours.

[0013] In some embodiments of the present invention, the second heating is performed to a temperature of 100-1200°C.

[0014] In some embodiments of the present invention, the lithium source solution includes n-butyllithium solution or sec-butyllithium solution; preferably n-butyllithium solution.

[0015] In some embodiments of the present invention, the concentration of the lithium source solution is 0.5-3.2 mol / L.

[0016] In some embodiments of the present invention, in the mixed solution, the molar ratio of the lithium source (such as n-butyl lithium or sec-butyl lithium) to the amorphous iron phosphate is (0.1-1.6):1.

[0017] In some embodiments of the present invention, the particle size of the composite positive electrode material is 30-100 nm.

[0018] In some embodiments of the present invention, the particle size of the amorphous lithium iron phosphate is 30-60 nm.

[0019] In some embodiments of the present invention, the particle size of the crystalline lithium iron phosphate is 40-100 nm.

[0020] The study found that by reducing the particle size of amorphous lithium iron phosphate and crystalline lithium iron phosphate, it is beneficial to improve the conductivity of the material and allow the negative electrode material to accommodate more Li + At the same time, finer positive electrode materials are easier to separate from the material surface and pass through the diaphragm, which speeds up the transmission efficiency of ions and better adapts to high-rate charging requirements.

[0021] In some embodiments of the present invention, the organic solvent is a hexane solution.

[0022] In some embodiments of the present invention, the stirring is performed at a rate of 200-3000 rpm for 1-24 hours.

[0023] A second aspect of the present invention provides a method for preparing the composite positive electrode material, comprising the following steps:

[0024] Amorphous lithium iron phosphate and crystalline lithium iron phosphate are mixed and ground to obtain the composite positive electrode material.

[0025] In some embodiments of the present invention, the grinding is performed by dry ball milling, the ball milling temperature is 50-700° C., and the ball milling time is 5-24 hours.

[0026] A third aspect of the present invention provides a positive electrode plate, wherein the raw materials for preparing the positive electrode plate include the above-mentioned composite positive electrode material or the composite positive electrode material prepared by the above-mentioned preparation method.

[0027] In some embodiments of the present invention, the raw materials for preparing the positive electrode plate further include a conductive agent, a binder and an additive.

[0028] In some embodiments of the present invention, the conductive agent may be a conventional conductive agent, preferably conductive carbon black.

[0029] In some embodiments of the present invention, the binder may be a conventional binder, preferably polyvinylidene fluoride (PVDF).

[0030] In some embodiments of the present invention, the additives include methyl pyrrolidone (NMP) and ethylene carbonate (EC) for slurry preparation.

[0031] In some embodiments of the present invention, the volume ratio of NMP to EC is (0.1-0.9): (0.2-1.2).

[0032] In some embodiments of the present invention, the mass ratio of the composite positive electrode material, the conductive agent, the binder and the additive is (8-9): (1-0.2): (0.9-0.3): (0.1-0.7).

[0033] A fourth aspect of the present invention provides a battery comprising the above-mentioned positive electrode plate.

[0034] Compared with the prior art, the above technical solution of the present invention has at least the following technical effects or advantages:

[0035] (1) The composite positive electrode material of the present invention comprises crystalline lithium iron phosphate and amorphous lithium iron phosphate. By introducing a certain amount of amorphous lithium iron phosphate into the crystalline lithium iron phosphate, the battery's gram capacity can be effectively increased while retaining the original characteristics of the crystalline lithium iron phosphate. At the same time, the battery's internal resistance can be reduced, adapting to the battery's high-rate charging performance; and it is also beneficial to improve the battery's platform voltage, thereby improving the battery's electrochemical performance. At the same time, amorphous lithium iron phosphate helps to inhibit the formation of lithium dendrites and prevent diaphragm puncture. By adjusting the amount of crystalline lithium iron phosphate and amorphous lithium iron phosphate, the occurrence of lithium precipitation can also be effectively prevented.

[0036] (2) The composite positive electrode material of the present invention is flexible in design and has high mechanical strength. Without changing the existing negative electrode material, the battery cell can be designed and the C / B value of the battery can be adjusted.

[0037] (3) When the cathode material of the present invention is applied to a battery, at a charging rate of 5C, the number of mutation cycles can reach 987-1201, the mutation cycle energy attenuation can reach 92.5-96.5%, and the platform voltage can reach 3.4-4.2V. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] Figure 1 XRD patterns of amorphous lithium iron phosphate prepared in Example 1 of the present invention at different glass transition temperatures;

[0039] Figure 2 Schematic diagram of the crystal structure of amorphous lithium iron phosphate (LPF) and crystalline lithium iron phosphate;

[0040] Figure 3 This is the XRD pattern of the amorphous lithium iron phosphate prepared in Example 1 of the present invention;

[0041] Figure 4 Schematic diagram of grain boundary structure before and after ball milling. DETAILED DESCRIPTION

[0042] The following will clearly and completely describe the concept of the present invention and the technical effects produced in conjunction with the embodiments, so as to fully understand the purpose, characteristics and effects of the present invention. Obviously, the embodiments described are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, other embodiments obtained by those skilled in the art without creative work are within the scope of protection of the present invention. Unless otherwise specified, the test methods used in the embodiments are all conventional methods; the materials, reagents, etc. used, unless otherwise specified, are reagents and materials obtained from commercial channels. Unless otherwise specified, the same parameter in each embodiment has the same value. The embodiments described below are exemplary and are only used to explain the present invention, and are not to be understood as limitations of the present invention.

[0043] Example 1

[0044] A method for preparing an amorphous lithium iron phosphate composite positive electrode material comprises the following steps:

[0045] (1) Preparation of amorphous lithium iron phosphate powder:

[0046] Commercial α-FePO4·2H2O was used as the raw material powder and heated in a Carbolite AAF 1200 furnace. The air in the heating tube was exhausted and argon was introduced. The temperature was raised to 600°C at a rate of 5°C / min, maintained for 12 hours, and then rapidly cooled to form amorphous iron phosphate. The amorphous iron phosphate powder was then cooled and allowed to stand for 12 hours. It was then heated to 600°C and dispersed in 50 mL of hexane solution. A 1.6 mol / L n-butyl lithium solution was slowly added to obtain a mixed solution (in the mixed solution, the molar ratio of n-butyl lithium to amorphous iron phosphate was 1:1.1). The mixture was stirred at 500 rpm for 10 hours and then filtered through the hexane solution to obtain amorphous lithium iron phosphate powder.

[0047] (2) Preparation of composite positive electrode materials:

[0048] The amorphous lithium iron phosphate powder prepared in step (1) and commercial crystalline lithium iron phosphate are mixed in a mass ratio of 0.07:0.93; the mixture is then added to a ball mill and milled for 20 hours at 500° C. in three steel ball bearings with a diameter of 0.4 cm and a ball mill with an inner diameter of 3.7 cm and a length of 6.2 cm to obtain a composite positive electrode material. The particle size of the crystalline lithium iron phosphate is 40-100 nm, and the particle size of the amorphous lithium iron phosphate is 30-60 nm.

[0049] A method for preparing a positive electrode sheet comprises the following steps:

[0050] The composite positive electrode material prepared in this embodiment was used as the active material, and was mixed with a conductive agent (conductive carbon black), a binder (PVDF) and an additive in a mass ratio of 8.5:0.75:0.75:0.25 to prepare a slurry; wherein the additives included NMP and EC in a volume ratio of 0.4:0.6; and then a wire rod machine was used to coat the copper foil with a coating thickness of 230 mm, followed by drying and rolling to obtain a positive electrode sheet.

[0051] Example 2

[0052] A method for preparing an amorphous lithium iron phosphate composite positive electrode material comprises the following steps:

[0053] (1) Preparation of amorphous lithium iron phosphate powder:

[0054] Commercial α-FePO4·2H2O was used as the raw material powder and heated in a Carbolite AAF 1200 furnace. The air in the heating tube was exhausted and argon was introduced. The temperature was raised to 1500°C at a rate of 1°C / min, maintained for 1 hour, and then rapidly cooled to form amorphous iron phosphate. The amorphous iron phosphate powder was then cooled and allowed to stand for 24 hours before being heated to 100°C. It was then dispersed in 120 mL of hexane solution, and a 0.5 mol / L n-butyl lithium solution was slowly added to obtain a mixed solution (in the mixed solution, the molar ratio of n-butyl lithium to amorphous iron phosphate was 1.6:1). The mixture was stirred at 3000 rpm for 1 hour and then filtered through the hexane solution to obtain amorphous lithium iron phosphate powder.

[0055] (2) Preparation of composite positive electrode materials:

[0056] The amorphous lithium iron phosphate powder prepared in step (1) and commercial crystalline lithium iron phosphate are mixed in a mass ratio of 0.01:0.99; the mixture is then added to a ball mill and milled at 700° C. for 5 hours in three steel ball bearings with a diameter of 0.4 cm and a ball mill with an inner diameter of 3.7 cm and a length of 6.2 cm to obtain a composite positive electrode material. The particle size of the crystalline lithium iron phosphate is 40-100 nm, and the particle size of the amorphous lithium iron phosphate is 30-60 nm.

[0057] A method for preparing a positive electrode sheet comprises the following steps:

[0058] The composite positive electrode material prepared in this embodiment was used as the active material, and was mixed with a conductive agent (conductive carbon black), a binder (PVDF) and an additive in a mass ratio of 8:1:0.3:0.7 to prepare a slurry; wherein the additives included NMP and EC in a volume ratio of 0.1:1.2; and then a wire rod machine was used to coat the copper foil with a coating thickness of 50 mm, followed by drying and rolling to obtain a positive electrode sheet.

[0059] Example 3

[0060] A method for preparing an amorphous lithium iron phosphate composite positive electrode material comprises the following steps:

[0061] (1) Preparation of amorphous lithium iron phosphate powder:

[0062] Commercial α-FePO4·2H2O was used as the raw material powder and heated in a Carbolite AAF 1200 furnace. The air in the heating tube was exhausted and argon was introduced. The temperature was raised to 100°C at a rate of 25°C / min, maintained for 24 hours, and then rapidly cooled to form amorphous iron phosphate. The amorphous iron phosphate powder was then cooled, allowed to stand for 1 hour, and then heated to 1200°C. It was then dispersed in 10 mL of hexane solution, and a 3.2 mol / L n-butyl lithium solution was slowly added to obtain a mixed solution (in the mixed solution, the molar ratio of n-butyl lithium to amorphous iron phosphate was 0.1:1). The mixture was stirred at 200 rpm for 24 hours and then filtered through the hexane solution to obtain amorphous lithium iron phosphate powder.

[0063] (2) Preparation of composite cathode materials:

[0064] The amorphous lithium iron phosphate powder prepared in step (1) and commercial crystalline lithium iron phosphate are mixed in a mass ratio of 0.1:0.9; the mixture is then added to a ball mill and milled for 24 hours at 50° C. using three steel ball bearings with a diameter of 0.4 cm and a ball mill with an inner diameter of 3.7 cm and a length of 6.2 cm to obtain a composite positive electrode material. The particle size of the crystalline lithium iron phosphate is 40-100 nm, and the particle size of the amorphous lithium iron phosphate is 30-60 nm.

[0065] A method for preparing a positive electrode sheet comprises the following steps:

[0066] The composite positive electrode material prepared in this embodiment was used as the active material, and was mixed with a conductive agent (conductive carbon black), a binder (PVDF) and an additive in a mass ratio of 9:0.2:0.9:0.1 to prepare a slurry; wherein: the additive included NMP and EC in a volume ratio of 0.9:0.2; then, a wire rod machine was used to coat the copper foil with a coating thickness of 40 mm, followed by drying and rolling to obtain a positive electrode sheet.

[0067] Example 4

[0068] The only difference between Example 4 and Example 1 is that the preparation method of the amorphous lithium iron phosphate powder in Example 4 is different, which specifically includes the following steps:

[0069] Commercial α-FePO4·2H2O was used as the raw material powder and heated in a Carbolite AAF 1200 furnace. The air in the heating tube was exhausted and argon was introduced. The temperature was raised to 600°C at a rate of 5°C / min, maintained for 12 hours, and then rapidly cooled to form amorphous iron phosphate. The amorphous iron phosphate powder was then cooled and allowed to stand for 12 hours. It was then heated to 600°C and dispersed in 50 mL of hexane solution. A 1.6 mol / L sec-butyl lithium solution was slowly added to obtain a mixed solution (in the mixed solution, the molar ratio of sec-butyl lithium to amorphous iron phosphate was 1:1.1). The mixture was stirred at 500 rpm for 10 hours and then filtered through the hexane solution to obtain amorphous lithium iron phosphate powder.

[0070] Comparative Example 1

[0071] The only difference between Comparative Example 1 and Example 1 is that the positive electrode material of Comparative Example 1 does not contain amorphous lithium iron phosphate, but is a single crystalline lithium iron phosphate. The preparation method thereof includes the following steps:

[0072] Commercial crystalline lithium iron phosphate was added to a ball mill and milled at 500°C for 24 hours in three steel ball bearings with a diameter of 0.4 cm and a ball mill with an inner diameter of 3.7 cm and a length of 6.2 cm to obtain a crystalline lithium iron phosphate positive electrode material with a particle size of 40-100 nm.

[0073] Comparative Example 2

[0074] The only difference between Comparative Example 2 and Example 1 is that the composite cathode material of Comparative Example 2 was not ball-milled during preparation, resulting in a larger particle size of the composite cathode material. Specifically, the particle size of the crystalline lithium iron phosphate was 120-300 nm, and the particle size of the amorphous lithium iron phosphate was 100-200 nm.

[0075] Comparative Example 3

[0076] The only difference between Comparative Example 3 and Example 1 is that the content of amorphous lithium iron phosphate powder in the composite positive electrode material of Comparative Example 3 is higher, that is, the mass ratio of amorphous lithium iron phosphate powder to commercial crystalline lithium iron phosphate is 0.15:0.85.

[0077] Performance Testing

[0078] The positive electrode sheets prepared in Examples 1-4 and Comparative Examples 1-3 were wound on a winding machine to form finished battery cells, top-sealed, liquid-filled, and then dissolved into different volumes. The finished battery cells were then allowed to stand for a while to prepare the finished battery cells. The finished battery cells were then tested according to the following steps:

[0079] (1) Shelf: time 10 minutes;

[0080] (2) Discharge at a constant current of 2C and a cut-off voltage of 4V;

[0081] (3) Shelf: time 10 minutes;

[0082] (4) Charge to 4V at 5C constant current and constant voltage, with a cut-off rate of 0.7C;

[0083] (5) Charge to 4.5V at 1.2C constant current and constant voltage, with a cut-off rate of 0.05C;

[0084] (6) Shelf: time 10 minutes;

[0085] (7) Repeat steps (3) to (6) 5000 times. When the Fading of the loop suddenly changes, end the loop.

[0086] The test results are shown in Table 1.

[0087] Table 1:

[0088]

[0089] As can be seen from Table 1, the composite positive electrode materials of Examples 1-3 contain 1-10wt% of amorphous lithium iron phosphate, respectively. At a charge rate of 5C, the number of sudden cycle turns is 987-1201, the sudden cycle energy decay is 92.5-96.5%, and the platform voltage is 3.4-4.2V. Compared with Comparative Example 1 which does not contain amorphous lithium iron phosphate, the charge rate, number of cycles, cycle energy decay and platform voltage are all better, indicating that adding an appropriate amount of amorphous lithium iron phosphate is beneficial to improving the cycle performance and energy storage performance of commercial 3C batteries.

[0090] Figure 1 The XRD patterns of amorphous lithium iron phosphate prepared in Example 1 at different glass transition temperatures are shown in Figure 1. The horizontal axis 2θ represents the diffraction angle, and the vertical axis Intersity represents the intensity of the diffraction peak. Figure 1 It can be seen that lithium iron phosphate shows an amorphous bun peak at different temperatures, and the bun peak formed at 600°C is more obvious. Because amorphous lithium iron phosphate has a long-range disordered and short-range ordered atomic arrangement, this special microstructure makes it free of dislocations and grain boundaries that are prone to corrosion. It has an extremely high energy state, high strength and hardness, good corrosion resistance and soft magnetic properties, etc., which provides better ionic conductivity for the battery positive electrode. The structural diagrams of amorphous lithium iron phosphate (a) and crystalline lithium iron phosphate (b) are shown in Figure 2. Figure 2 shown.

[0091] Example 4 Compared with Example 1, in the preparation of amorphous lithium iron phosphate powder, sec-butyl lithium was used as the lithium source. Since the synthesized amorphous lithium iron phosphate was impure, a small amount of single crystal lithium iron phosphate existed (see Figure 3), resulting in a decrease in electrochemical performance relative to Example 1.

[0092] In Example 1, compared with Comparative Example 2, the particle size of amorphous lithium iron phosphate is close to that of crystalline lithium iron phosphate, or even smaller, which effectively improves the charge rate performance of the material. The main reason is that the amorphous structure has good corrosion resistance, can adapt to various electrolytes more conveniently, and provides a better development environment for electrolyte development. The composite positive electrode material after ball milling can change the structure and grain morphology of the material, increase the defects between molecules, and thus improve the material's ability to release energy. Schematic diagram of the grain boundary structure of lithium iron phosphate before (a) and after (b) ball milling is shown in the figure. Figure 4 shown.

[0093] Comparative Example 3 has a higher content of amorphous lithium iron phosphate than Example 1. At a charge rate of 5C, a mutation occurs at 800 cycles, and the mutation cycle energy attenuation and platform voltage are lower than those in Example 1. The reasons may be: First, amorphous lithium iron phosphate has better lithium ion reaction activity and can achieve rapid reaction under the existing electrolyte, diaphragm and anode system; but the anode cannot quickly accommodate lithium ions, resulting in rupture of the anode carbon layer and lithium deposition on the diaphragm surface. Second, in the composite positive electrode material, as the content of amorphous lithium iron phosphate increases, the mechanical properties of the material are enhanced and the hard expansion increases, which leads to an increase in thickness after cycling and increased coating difficulty.

[0094] For those skilled in the art to which the present invention belongs, a number of simple deductions or substitutions can be made without departing from the concept of the present invention, without having to resort to creative work. Therefore, based on the disclosure of the present invention, simple improvements made by those skilled in the art to the present invention should be within the scope of protection of the present invention. The above embodiments are preferred embodiments of the present invention, and all processes similar to the present invention and equivalent changes made should fall within the scope of protection of the present invention.

Claims

1. A composite positive electrode material, characterized in that The composite positive electrode material comprises amorphous lithium iron phosphate and crystalline lithium iron phosphate, and the mass ratio of the amorphous lithium iron phosphate to the crystalline lithium iron phosphate is (0.01-0.1):(0.90-0.99).

2. The composite cathode material according to claim 1, characterized in that The preparation process of the amorphous lithium iron phosphate is as follows: first, α-FePO4·2H2O is heated for the first time under an inert atmosphere, and then rapidly cooled to obtain amorphous iron phosphate; then, the amorphous iron phosphate is allowed to stand, heated for a second time, and then dispersed in an organic solvent; then, a lithium source solution is added and mixed to obtain a mixed solution; and then, the amorphous lithium iron phosphate is obtained by suction filtration.

3. The composite cathode material according to claim 2, characterized in that The temperature system of the first heating is: heating to 100-1500° C. at a rate of 1-25° C. / min and keeping the temperature for 1-24 hours.

4. The composite cathode material according to claim 2, characterized in that The standing time is 1-24 hours; and / or the second heating is performed to 100-1200°C.

5. The composite cathode material according to claim 2, characterized in that The lithium source solution includes n-butyllithium solution or sec-butyllithium solution; and / or the concentration of the lithium source solution is 0.5-3.2 mol / L.

6. The composite cathode material according to claim 2 or 5, characterized in that In the mixed solution, the molar ratio of the lithium source to the amorphous iron phosphate is (0.1-1.6):

1.

7. The composite cathode material according to claim 1, characterized in that The particle size of the composite positive electrode material is 30-100 nm.

8. A method for preparing a composite positive electrode material according to any one of claims 1 to 7, characterized in that: The following steps are involved: Amorphous lithium iron phosphate and crystalline lithium iron phosphate are mixed and ground to obtain the composite positive electrode material.

9. A positive electrode plate, characterized in that: The raw material for preparing the positive electrode plate includes the composite positive electrode material according to any one of claims 1 to 7; or includes the composite positive electrode material prepared by the preparation method according to claim 8.

10. A battery, characterized in that: The battery comprises the positive electrode sheet according to claim 9.

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