Carbon-coated lithium manganese iron phosphate material, and preparation method and application thereof

Abstract

To provide a carbon-coated lithium manganese iron phosphate material having a stable hierarchical structure, featuring high uniformity of lithium manganese iron phosphate element distribution, with metal doping, providing a dense and uniform carbon-coated layer, and capable of effectively improving the electrochemical performance of the material; and to provide a method for preparing a carbon-coated lithium manganese iron phosphate material, which has a simple process flow and is suitable for application in large-scale industrial production.SOLUTION: The present disclosure provides a carbon-coated lithium manganese iron phosphate material having a composition of: LiFe1-x-yMnxMyPO4@C, where M includes at least one of Mg, V, Zr, Nb, In, Al, Co and Ni, 0.5≤x≤0.8, 0<y≤0.02, and C is a carbon coating.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to the technical field of batteries, more particularly to a carbon-coated lithium manganese iron phosphate material, a manufacturing method and application of the carbon-coated lithium manganese iron phosphate material. [Background technology]

[0002] As the representative of the secondary battery with the best overall performance at present, the commercialization of lithium-ion batteries can be traced back to the 1990s. After many years of research, carbon-coated lithium manganese iron phosphate materials have become a technology roadmap with good performance in the field of lithium-ion batteries today.

[0003] Conventional methods for preparing lithium manganese iron phosphate and its precursor include high-temperature solid-state method, sol-gel method, co-precipitation method, etc., and the precursor or carbon-coated lithium manganese iron phosphate material prepared by a conventional single preparation method has low compaction density and low electrochemical specific capacity applied to positive electrode materials and corresponding batteries, which cannot meet the high performance application needs.

[0004] At present, a method for producing carbon-coated lithium manganese iron phosphate material by a two-stage precursor production method is known, but the method includes an additional grinding process for producing particle precursors with different particle sizes, which increases the process complexity and makes it difficult to ensure the uniformity of the material. In fact, it is still impossible to obtain a carbon-coated lithium manganese iron phosphate material that meets the high performance requirements. Summary of the Invention [Problem to be solved by the invention]

[0005] In view of the above, the present invention aims to solve at least one of the technical problems existing in the prior art. For this reason, the present invention provides a carbon-coated lithium iron manganese phosphate material, a manufacturing method, and a lithium ion battery. According to the carbon-coated lithium iron manganese phosphate material and its manufacturing method of the present invention, it has a stable hierarchical structure, high uniformity of the lithium iron manganese phosphate element distribution, is doped with metal, and a dense and uniform carbon coating layer can be obtained, which can preferably improve the electrochemical performance of the material. In addition, the manufacturing method of the carbon-coated lithium iron manganese phosphate material has a simple process flow and is suitable for application in large-scale industrial production.

Means for Solving the Problem

[0006] For this reason, in a first aspect, an embodiment of the present invention provides a carbon-coated lithium iron manganese phosphate material composed of LiFe 1-x-y Mn x M y PO 4 @C, where M includes at least one of Mg, V, Zr, Nb, In, Al, Co, and Ni, 0.5 ≦ x ≦ 0.8, 0 < y ≦ 0.02, and C is coated carbon.

[0007] In a second aspect, an embodiment of the present invention provides a manufacturing method of a carbon-coated lithium iron manganese phosphate material for manufacturing the lithium iron manganese phosphate material described in the first aspect. The manufacturing method includes Mixing and dissolving an iron source, a manganese source, phosphoric acid, and deionized water at a certain ratio to produce a lithium iron manganese phosphate precursor by a liquid phase coprecipitation method, and subjecting the lithium iron manganese phosphate precursor to a first sintering in an inert atmosphere to remove crystal water to obtain an anhydrous lithium iron manganese phosphate precursor in step S10; Mixing two sets of anhydrous lithium iron manganese phosphate precursors, lithium phosphate, a carbon source, a dopant, and deionized water at a certain ratio, stirring and dispersing them, performing wet grinding, spray drying, and a second sintering to obtain two sets of carbon-coated lithium iron manganese phosphate intermediates in step S20, where the first sintering of the first set is performed at a first temperature, the second sintering of the second set is performed at a second temperature, and the first temperature and the second temperature are different in step S20; and step S30 of mixing two sets of the carbon-coated lithium manganese iron phosphate intermediate, a carbon source, a dopant and deionized water in a certain ratio, stirring to disperse, and then wet-grinding, spray-drying and third sintering to obtain a carbon-coated lithium manganese iron phosphate material.

[0008] Preferably, the first temperature is set to 400° C. to 500° C., the second temperature is set to 670° C. to 760° C., and the sintering time is set to 4 hours to 6 hours.

[0009] Preferably, the manganese source comprises at least one of manganese sulfate, manganese chloride, manganese oxalate, manganese acetate, and / or The iron source includes at least one of ferrous sulfate, ferrous chloride, ferrous oxalate, and ferrous acetate.

[0010] Preferably, the iron manganese phosphate precursor has a molar ratio of iron manganese to phosphorus (Fe+Mn) / P of 1.45 to 1.465, and a molar ratio of lithium to iron manganese (Li / (Fe+Mn)) of 1.02 to 1.05.

[0011] Preferably, the carbon source includes at least one of glucose, polyethylene glycol, citric acid, and modified graphite, and the mass ratio of the carbon source to the carbon-coated lithium manganese iron phosphate material is 1.5 wt% to 2.0 wt%; and / or The dopant includes at least one compound of Mg, V, Zr, Nb, In, Al, Co, and Ni.

[0012] Preferably, the mixing ratio of the two sets of carbon-coated lithium manganese iron phosphate intermediates is (1-9):(9-1).

[0013] Preferably, the grain size D50 is controlled to 0.3 μm to 0.6 μm during the wet polishing, and / or For the spray drying, the intake air temperature is 220°C to 280°C and the exhaust air temperature is 90°C to 110°C, and / or In the third sintering, the sintering temperature is set to 700° C. to 800° C., and the sintering time is set to 6 hours to 12 hours.

[0014] In a third aspect, embodiments of the present invention further provide a carbon coated lithium manganese iron phosphate material produced by the method described in the second aspect above.

[0015] In a fourth aspect, embodiments of the present invention further provide a lithium-ion battery comprising a battery cathode fabricated from the carbon-coated lithium manganese iron phosphate material according to the first or third aspect above. Effect of the Invention

[0016] In the carbon-coated lithium manganese iron phosphate material and its preparation method according to the embodiment of the present invention, the sintering process for preparing the doped carbon-coated lithium manganese iron phosphate intermediate is performed at different temperatures to form carbon-coated lithium manganese iron phosphate intermediates of different shapes, and the doped carbon coating is sintered to form layers of the carbon-coated lithium manganese iron phosphate intermediates of different shapes, and a dense and uniform carbon coating layer is formed, so that the layers of the different carbon-coated lithium manganese iron phosphate intermediates are closely bonded to obtain high compression density and excellent electrochemical performance, and the lithium ion battery prepared using the carbon-coated lithium manganese iron phosphate material as the positive electrode material can also obtain excellent performance. In addition, the preparation method has a simple process flow, low equipment requirements, and is suitable for large-scale industrial production. [Brief description of the drawings]

[0017] [Figure 1] FIG. 2 is a SEM image of a carbon-coated lithium manganese iron phosphate material according to one embodiment of the present invention. [Diagram 2] 1 is a flow chart of a method for manufacturing a carbon-coated lithium manganese iron phosphate material according to one embodiment of the present invention. [Diagram 3] FIG. 2 is an XRD diagram of the carbon-coated lithium manganese iron phosphate material prepared in Example 1 of the present invention. [Figure 4]It is a charge-discharge characteristic curve diagram of a carbon-coated lithium iron manganese phosphate material manufactured in Example 1 of the present invention.

Mode for Carrying Out the Invention

[0018] Hereinafter, embodiments of the present invention will be described in detail. Examples of the above embodiments are shown in the drawings, and throughout, the same or similar reference numerals indicate the same or similar parts, or parts having the same or similar functions. The embodiments described below with reference to the drawings are exemplary and are to be construed as illustrative of the present invention and should not be understood as limiting the present invention.

[0019] The following disclosure provides many different embodiments or examples for implementing different structures of the present invention. To simplify the disclosure of the present invention, the members and installations of specific examples are described below. Of course, these are merely exemplary and not intended to limit the present invention. Also, the present invention can repeatedly use reference numerals and / or reference alphabets in different examples. Such repetition is for the purpose of simplification and clarification and does not itself indicate the relationship between various embodiments and / or installations considered. Also, the present invention provides examples of various specific processes and materials, but those skilled in the art can be aware of the applicability of other processes and / or the use of other materials.

[0020] As shown in FIG. 1, in the first aspect, the carbon-coated lithium iron manganese phosphate material according to the embodiment of the present invention is LiFe 1-x-y Mn x M y PO 4 @C, where M includes at least one of Mg, V, Zr, Nb, In, Al, Co, and Ni, 0.5 ≦ x ≦ 0.8, 0 < y ≦ 0.02, and C is coated carbon. In this embodiment, the carbon-coated lithium iron manganese phosphate material includes hierarchical material particles of a first particle size and material particles of a second particle size, the particle gaps are small, the layers are tightly bonded, and the compression density of the material is 2.4 g / cm 3 or more.

[0021] As shown in FIG. 2, in the second aspect, the method for producing the carbon-coated lithium manganese iron phosphate material according to the first aspect of the present invention includes the steps of: A step S10 of mixing and dissolving an iron source, a manganese source, phosphoric acid, and deionized water in a certain ratio, producing an iron manganese phosphate precursor by a liquid phase coprecipitation method, and sintering the iron manganese phosphate precursor for the first time in an inert atmosphere to remove water of crystallization to obtain an anhydrous iron manganese phosphate precursor; Step S20: mixing two sets of anhydrous iron manganese phosphate precursor, lithium phosphate, carbon source, dopant and deionized water in a certain ratio, stirring to disperse, wet grinding, spray drying and second sintering to obtain two sets of carbon-coated lithium iron manganese phosphate intermediates, where the first set of sintering is performed at a first temperature and the second set of sintering is performed at a second temperature, and the first temperature and the second temperature are different; and step S30 of mixing two sets of the carbon-coated lithium manganese iron phosphate intermediates, a carbon source, a dopant and deionized water in a certain ratio, stirring to disperse, and then carrying out wet grinding, spray drying and third sintering to obtain a carbon-coated lithium manganese iron phosphate material.

[0022] Furthermore, the first temperature is set to 400° C. to 500° C., the second temperature is set to 670° C. to 760° C., and the sintering time is set to 4 hours to 6 hours.

[0023] Further, the manganese source includes at least one of manganese sulfate, manganese chloride, manganese oxalate, and manganese acetate.

[0024] Further, the iron source includes at least one of ferrous sulfate, ferrous chloride, ferrous oxalate, and ferrous acetate.

[0025] Furthermore, the molar ratio (Fe+Mn) / P of iron manganese to phosphorus in the iron manganese phosphate precursor is set to 1.45 to 1.465, and the molar ratio Li / (Fe+Mn) of lithium to iron manganese is set to 1.02 to 1.05.

[0026] Furthermore, the carbon source includes at least one of glucose, polyethylene glycol, citric acid, and modified graphite, and the mass ratio of the carbon source to the carbon-coated lithium manganese iron phosphate material produced is 1.5 wt% to 2.0 wt%.

[0027] Furthermore, the dopant includes at least one compound of Mg, V, Zr, Nb, In, Al, Co, and Ni.

[0028] Furthermore, the mixing ratio of the two sets of carbon-coated lithium manganese iron phosphate intermediates is set to (1-9):(9-1).

[0029] Furthermore, the grain size D50 is controlled to 0.3 μm to 0.6 μm during the wet polishing.

[0030] Furthermore, for the above spray drying, the intake air temperature is set to 220°C to 280°C, and the exhaust air temperature is set to 90°C to 110°C.

[0031] Furthermore, in the third sintering, the sintering temperature is set to 700° C. to 800° C., and the sintering time is set to 6 h to 12 h.

[0032] In a third aspect, a carbon coated lithium manganese iron phosphate material according to an embodiment of the present invention is produced by the method described in the second aspect above.

[0033] In a fourth aspect, a lithium-ion battery according to an embodiment of the present invention comprises a battery cathode made of the carbon-coated lithium manganese iron phosphate material according to the first or third aspect above.

[0034] In the embodiment of the present invention, the manganese ferromanganese source precursor is synthesized by co-precipitation, which makes it easy to control the reaction conditions in the reaction process, effectively improves the phase uniformity of the material, and has high reproducibility of the material.

[0035] In the embodiment of the present invention, the lithium manganese iron phosphate / carbon composite positive electrode material synthesized by coprecipitation-tertiary sintering can improve the compression density of the material by controlling the primary sintering temperature and the mass ratio of the primary sintering materials with different primary sintering temperatures and adjusting the size of the hierarchical structure between particles, and the compression density of the material is 2.4 g / cm 3 Reaches more than.

[0036] In the embodiment of the present invention, the method of secondary carbon coating and ion doping is used to favor the movement of electrons and ions, thus improving the charge and discharge characteristics of the battery.

[0037] The specific process and effects of the method for producing the carbon-coated lithium manganese iron phosphate material of the present invention will be described in more detail below with reference to other specific examples, but the scope of protection of the present invention is not limited thereto.

[0038] Example 1 In this example, a carbon-coated lithium manganese iron phosphate material was produced, specifically: Ferrous sulfate, manganese sulfate, phosphoric acid, and deionized water were mixed and dissolved, and the mixture was co-precipitated to prepare a manganese iron phosphate precursor (Mn 0.6 Fe 0.4 )2(PO 4 ) 3 6H 2 Get O and N 2 (1) sintering the mixture in an atmosphere at a sintering temperature of 525° C. for 5 hours, and then cooling the mixture to room temperature and removing the mixture to obtain an anhydrous iron manganese phosphate precursor; Step (2) of mixing 754.5 g of the anhydrous iron manganese phosphate precursor obtained in step (1) with 252.9 g of lithium phosphate, 9.6 g of glucose, 9.6 g of polyethylene glycol, 9.6 g of citric acid, 4.8 g of ammonium metavanadate and deionized water to control the solid content to 45%, dispersing in a ball mill for 30 minutes, and then polishing in a sand mill to control the final polishing particle size D50 to 0.5 μm; The paste obtained in step (2) is spray-dried, and the intake temperature is controlled at 220°C and the exhaust temperature is controlled at 100°C. Then, N2 (3) sintering in an atmosphere at 400°C and 720°C, respectively, for a sintering time of 6h, and cooling to room temperature after sintering to obtain primary sintered materials of different temperatures; 500g of the 720 ° C primary sintered material obtained in step (3), 500g of the 400 ° C primary sintered material, 47.5g of glucose, 47.5g of polyethylene glycol, 8g of modified graphite, 15g of magnesium acetate tetrahydrate and deionized water are mixed, the solid content is controlled to 42%, and the mixture is ball milled for 30 minutes and then ground in a sand mill, and the final ground particle size D50 is controlled to 0.5 μm; and The paste obtained in step (4) is spray-dried and then N 2 and (5) sintering the mixture in an atmosphere at a sintering temperature of 760°C for a sintering time of 10 hours, cooling the mixture to room temperature after sintering, and then passing the mixture through airflow pulverization to control the particle size so that D10≧0.30 μm, D50 is 0.8-1.1 μm, and D90≦12 μm, thereby obtaining a carbon-coated lithium manganese iron phosphate material with high compressed density.

[0039] FIG. 1 is a SEM image of the carbon-coated lithium manganese iron phosphate material with high pressed density produced in Example 1. As can be seen from FIG. 1, the primary particles are distributed with different particle sizes, with the particle size range of 11 nm to 1200 nm, and the primary particles are closely connected to each other.

[0040] FIG. 3 is the XRD diagram of the carbon-coated lithium manganese iron phosphate material with high compaction density prepared in Example 1. As can be seen from FIG. 3, the spectral peak position is consistent with the standard PDF file of lithium manganese iron phosphate, there is no heterogeneous phase, and the purity of the material is high.

[0041] FIG. 4 is a charge / discharge characteristic curve diagram of the carbon-coated lithium manganese iron phosphate material prepared in Example 1 at a 0.1C rate within a voltage range of 2.5-4.5V. As can be seen from FIG. 4, the discharge specific capacity reaches 156mAh / g. Compared with Li+ / Li, the material shows two typical charge / discharge voltage plateaus at about 4.1V and 3.5V, respectively. 3+ / Mn2+ and Fe 3+ / Fe 2+ This corresponds to the oxidation-reduction reaction

[0042] Example 2 In this example, a carbon-coated lithium manganese iron phosphate material was produced, specifically: Ferrous sulfate, manganese sulfate, phosphoric acid, and deionized water were mixed and dissolved, and the mixture was co-precipitated to prepare a manganese iron phosphate precursor (Mn 0.6 Fe 0.4 )2(PO 4 ) 3 6H 2 Get O and N 2 (1) sintering the mixture in an atmosphere at a sintering temperature of 525° C. for 5 hours, and then cooling the mixture to room temperature and removing the mixture to obtain an anhydrous iron manganese phosphate precursor; Step (2) of mixing 754.5 g of the anhydrous iron manganese phosphate precursor obtained in step (1) with 252.9 g of lithium phosphate, 11.5 g of glucose, 11.5 g of polyethylene glycol, 9.6 g of citric acid, 4.8 g of ammonium metavanadate and deionized water to control the solid content to 45%, dispersing in a ball mill for 30 minutes, and then polishing in a sand mill to control the final polishing particle size D50 to 0.5 μm; The paste obtained in step (2) is spray-dried, and the intake temperature is controlled at 220°C and the exhaust temperature is controlled at 100°C. Then, N 2 (3) sintering in an atmosphere at 400°C and 740°C, respectively, for a sintering time of 6h, and cooling to room temperature after sintering to obtain primary sintered materials of different temperatures; 500g of the 740 ° C primary sintered material obtained in step (3), 500g of the 400 ° C primary sintered material, 47.5g of glucose, 47.5g of polyethylene glycol, 8g of modified graphite, 15g of magnesium acetate tetrahydrate and deionized water are mixed, the solid content is controlled to 42%, and the mixture is ball milled for 30 minutes and then ground in a sand mill, and the final ground particle size D50 is controlled to 0.5 μm; and The paste obtained in step (4) is spray-dried and then N 2and (5) sintering the mixture in an atmosphere at a sintering temperature of 760°C for a sintering time of 10 hours, cooling the mixture to room temperature after sintering, and then passing the mixture through airflow pulverization to control the particle size so that D10≧0.30 μm, D50 is 0.8-1.1 μm, and D90≦12 μm, thereby obtaining a carbon-coated lithium manganese iron phosphate material with high compressed density.

[0043] Example 3 In this example, a carbon-coated lithium manganese iron phosphate material was produced, specifically: Ferrous sulfate, manganese sulfate, phosphoric acid, and deionized water were mixed and dissolved, and the mixture was co-precipitated to prepare a manganese iron phosphate precursor (Mn 0.6 Fe 0.4 )2(PO 4 ) 3 6H 2 Get O and N 2 (1) sintering the mixture in an atmosphere at a sintering temperature of 525° C. for 5 hours, and then cooling the mixture to room temperature and removing the mixture to obtain an anhydrous iron manganese phosphate precursor; Step (2) of mixing 754.5 g of the anhydrous iron manganese phosphate precursor obtained in step (1) with 252.9 g of lithium phosphate, 11.5 g of glucose, 11.5 g of polyethylene glycol, 9.6 g of citric acid, 4.8 g of ammonium metavanadate and deionized water to control the solid content to 45%, dispersing in a ball mill for 30 minutes, and then polishing in a sand mill to control the final polishing particle size D50 to 0.5 μm; The paste obtained in step (2) is spray-dried, and the intake temperature is controlled to 220°C and the exhaust temperature is controlled to 100°C. After that, N 2 (3) sintering in an atmosphere at 400°C and 740°C, respectively, for a sintering time of 6h, and cooling to room temperature after sintering to obtain primary sintered materials of different temperatures; 500g of the 740 ° C primary sintered material obtained in step (3), 500g of the 400 ° C primary sintered material, 47.5g of glucose, 47.5g of polyethylene glycol, 8g of modified graphite, 15g of magnesium acetate tetrahydrate and deionized water are mixed, the solid content is controlled to 42%, and the mixture is ball milled for 30 minutes and then ground in a sand mill, and the final ground particle size D50 is controlled to 0.45 μm; and The paste obtained in step (4) is spray-dried and then N 2 and (5) sintering the mixture in an atmosphere at a sintering temperature of 760°C for a sintering time of 10 hours, cooling the mixture to room temperature after sintering, and then passing the mixture through airflow pulverization to control the particle size so that D10≧0.30 μm, D50 is 0.8-1.1 μm, and D90≦12 μm, thereby obtaining a carbon-coated lithium manganese iron phosphate material with high compressed density.

[0044] Example 4 In this example, a carbon-coated lithium manganese iron phosphate material was produced, specifically: Ferrous sulfate, manganese sulfate, phosphoric acid, and deionized water were mixed and dissolved, and the mixture was co-precipitated to prepare a manganese iron phosphate precursor (Mn 0.6 Fe 0.4 )2(PO 4 ) 3 6H 2 Get O and N 2 (1) sintering the mixture in an atmosphere at a sintering temperature of 525° C. for 5 hours, and then cooling the mixture to room temperature and removing the mixture to obtain an anhydrous iron manganese phosphate precursor; Step (2) of mixing 754.5 g of the anhydrous iron manganese phosphate precursor obtained in step (1) with 252.9 g of lithium phosphate, 11.5 g of glucose, 11.5 g of polyethylene glycol, 9.6 g of citric acid, 4.8 g of ammonium metavanadate and deionized water to control the solid content to 45%, dispersing in a ball mill for 30 minutes, and then polishing in a sand mill to control the final polishing particle size D50 to 0.5 μm; The paste obtained in step (2) is spray-dried, and the intake temperature is controlled at 220°C and the exhaust temperature is controlled at 100°C. Then, N 2(3) sintering in an atmosphere at 400°C and 740°C, respectively, for a sintering time of 6h, and cooling to room temperature after sintering to obtain primary sintered materials of different temperatures; 700g of the 740 ° C primary sintered material obtained in step (3), 300g of the 400 ° C primary sintered material, 47.5g of glucose, 47.5g of polyethylene glycol, 8g of modified graphite, 15g of magnesium acetate tetrahydrate and deionized water are mixed, the solid content is controlled to 42%, and the mixture is ball milled for 30 minutes and then ground in a sand mill, and the final ground particle size D50 is controlled to 0.45 μm; and The paste obtained in step (4) is spray-dried and then N 2 and (5) sintering the mixture in an atmosphere at a sintering temperature of 760°C for a sintering time of 10 hours, cooling the mixture to room temperature after sintering, and then passing the mixture through airflow pulverization to control the particle size so that D10≧0.30 μm, D50 is 0.8-1.1 μm, and D90≦12 μm, thereby obtaining a carbon-coated lithium manganese iron phosphate material with high compressed density.

[0045] Comparative Example 1 In this comparative example, a carbon-coated lithium manganese iron phosphate material was produced, specifically: Ferrous sulfate, manganese sulfate, phosphoric acid, and deionized water were mixed and dissolved, and the mixture was co-precipitated to prepare a manganese iron phosphate precursor (Mn 0.6 Fe 0.4 )2(PO 4 ) 3 6H 2 Get O and N 2 (1) sintering the mixture in an atmosphere at a sintering temperature of 525° C. for 5 hours, and then cooling the mixture to room temperature and removing the mixture to obtain an anhydrous iron manganese phosphate precursor; Step (2) of mixing 754.5 g of the anhydrous iron manganese phosphate precursor obtained in step (1) with 252.9 g of lithium phosphate, 9.6 g of glucose, 9.6 g of polyethylene glycol, 9.6 g of citric acid, 4.8 g of ammonium metavanadate and deionized water to control the solid content to 45%, dispersing in a ball mill for 30 minutes, and then polishing in a sand mill to control the final polishing particle size D50 to 0.5 μm; The paste obtained in step (2) is spray-dried and dried with N 2 (3) sintering in an atmosphere at a sintering temperature of 400° C. for 6 hours, and then cooling to room temperature to obtain a primary sintered material; 1000g of the 400 ° C. primary sintered material obtained in step (3), 47.5g of glucose, 47.5g of polyethylene glycol, 8g of modified graphite, 15g of magnesium acetate tetrahydrate and deionized water are mixed, the solid content is controlled to 42%, and the mixture is ball milled for 30 minutes, then put into a sand mill for grinding, and the final grinding particle size D50 is controlled to 0.5 μm; and The paste obtained in step (4) is spray-dried and then N 2 and (5) sintering the mixture in an atmosphere at a sintering temperature of 760°C for a sintering time of 10 hours, cooling to room temperature after sintering, and subjecting the mixture to airflow pulverization to control the particle size so that D10≧0.30 μm, D50 is 0.8-1.1 μm, and D90≦12 μm, thereby obtaining a lithium manganese iron phosphate / carbon composite material with high compressed density.

[0046] Comparative Example 2 In this comparative example, a carbon-coated lithium manganese iron phosphate material was produced, specifically: Ferrous sulfate, manganese sulfate, phosphoric acid, and deionized water were mixed and dissolved, and the mixture was co-precipitated to prepare a manganese iron phosphate precursor (Mn 0.6 Fe 0.4 )2(PO 4 ) 3 6H 2 Get O and N 2 (1) sintering the mixture in an atmosphere at a sintering temperature of 525° C. for 5 hours, and then cooling the mixture to room temperature and removing the mixture to obtain an anhydrous iron manganese phosphate precursor; Step (2) of mixing 754.5 g of the anhydrous iron manganese phosphate precursor obtained in step (1) with 252.9 g of lithium phosphate, 9.6 g of glucose, 9.6 g of polyethylene glycol, 9.6 g of citric acid, 4.8 g of ammonium metavanadate and deionized water to control the solid content to 45%, dispersing in a ball mill for 30 minutes, and then polishing in a sand mill to control the final polishing particle size D50 to 0.5 μm; The paste obtained in step (2) is spray-dried and dried with N 2 (3) sintering in an atmosphere at a sintering temperature of 720° C. for 6 hours, and then cooling to room temperature to obtain a primary sintered material; 1000g of the 720 ° C. primary sintered material obtained in step (3), 47.5g of glucose, 47.5g of polyethylene glycol, 8g of modified graphite, 15g of magnesium acetate tetrahydrate and deionized water are mixed, the solid content is controlled to 45%, and the mixture is ball milled for 30 minutes, then put into a sand mill for grinding, and the final grinding particle size D50 is controlled to 0.5 μm; and The paste obtained in step (4) is spray-dried and then N 2 and (5) sintering the mixture in an atmosphere at a sintering temperature of 760°C for a sintering time of 10 hours, cooling the mixture to room temperature after sintering, and then passing the mixture through airflow pulverization to control the particle size so that D10≧0.30 μm, D50 is 0.8-1.1 μm, and D90≦12 μm, thereby obtaining a carbon-coated lithium manganese iron phosphate material with high compressed density.

[0047] Comparing the comparative example with the example 1, the difference is that the controlled first sintering temperature in the comparative example is a single sintering temperature, and a single sintering temperature primary sintering material is used in the secondary polishing process.

[0048] Furthermore, the carbon content, powder compression, and specific discharge capacity at 0.1 C and 1 C of the products obtained in Examples 1 to 4 and Comparative Examples 1 and 2 were measured. The results are shown in Table 1.

[0049] Regarding the measurement method, the relevant physicochemical and electrochemical performances were measured in accordance with GB / T 30835 2014, “Carbon composite lithium iron phosphate cathode material for lithium ion batteries”, and a button battery (with a mass ratio of active material, conductive agent and binder of 90:5:5, and a charge / discharge voltage range of 2.0-4.5V) was manufactured.

[0050] [Table 1] Electrochemical results

[0051] As can be seen from the above results, when the carbon contents of the materials are essentially the same, the primary particles of different particle sizes produced at different first sintering temperatures in the examples of the present invention are mixed in different mass ratios and then subjected to secondary sintering, and the powder compaction density and electrical performance of the resulting lithium manganese iron phosphate composite materials are both higher than those of the carbon-coated lithium manganese iron phosphate materials produced at a single primary sintering temperature.

[0052] In the carbon-coated lithium manganese iron phosphate material and its preparation method according to the embodiment of the present invention, the sintering process for preparing the doped carbon-coated lithium manganese iron phosphate intermediate is performed at different temperatures to form carbon-coated lithium manganese iron phosphate intermediates of different shapes, and the doped carbon coating is sintered to form layers of the carbon-coated lithium manganese iron phosphate intermediates of different shapes, and a dense and uniform carbon coating layer is formed, so that the layers of the different carbon-coated lithium manganese iron phosphate intermediates are closely bonded to obtain high compression density and excellent electrochemical performance, and the lithium ion battery prepared using the carbon-coated lithium manganese iron phosphate material as the positive electrode material can also obtain excellent performance. In addition, the preparation method has a simple process flow, low equipment requirements, and is suitable for large-scale industrial production.

[0053] In the description of this specification, a description referring to the terms "one embodiment", "several embodiments", "examples", "specific examples", "several examples", etc. means that the specific features, structures, materials or characteristics described in the combination of the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the exemplary expressions of the above terms are not necessarily limited to the same embodiment or example. In addition, the specific features, structures, materials or characteristics described can be appropriately combined in any one or more embodiments or examples. In addition, if not mutually inconsistent, a person skilled in the art can combine or combine different embodiments or examples described in this specification and features of different embodiments or examples.

[0054] Although embodiments of the present invention have been shown and described, those skilled in the art will understand that various changes, modifications, substitutions and variations can be made to these embodiments without departing from the principles and objectives of the present invention, and that the scope of the present invention is limited by the claims and their equivalents.

Claims

1. LiFe １－ｘ－ｙ Mn ｘ M ｙ P.O. ４ @C, wherein M comprises at least one of Mg, V, Zr, Nb, In, Al, Co, and Ni, 0.5≦x≦0.8, 0<y≦0.02, and C is a coating carbon. Carbon-coated lithium manganese iron phosphate material.

2. a step S10 of mixing and dissolving an iron source, a manganese source, phosphoric acid, and deionized water in a certain ratio, producing an iron manganese phosphate precursor by a liquid phase coprecipitation method, and sintering the iron manganese phosphate precursor for the first time in an inert atmosphere to remove water of crystallization to obtain an anhydrous iron manganese phosphate precursor; S20: mixing two sets of anhydrous iron manganese phosphate precursor, lithium phosphate, carbon source, dopant and deionized water in a certain ratio, stirring to disperse, wet grinding, spray drying and second sintering to obtain two sets of carbon-coated lithium iron manganese phosphate intermediates, where the first set of sintering is performed at a first temperature and the second set of sintering is performed at a second temperature, and the first temperature and the second temperature are different; and a step S30 of mixing two sets of the carbon-coated lithium manganese iron phosphate intermediate, a carbon source, a dopant and deionized water in a certain ratio, dispersing by stirring, wet grinding, spray drying and third sintering to obtain a carbon-coated lithium manganese iron phosphate material. A method for producing a carbon-coated lithium manganese iron phosphate material.

3. The first temperature is 400°C to 500°C, the second temperature is 670°C to 760°C, and the sintering time is 4h to 6h. A method for producing the carbon coated lithium manganese iron phosphate material of claim 2.

4. The manganese source comprises at least one of manganese sulfate, manganese chloride, manganese oxalate, manganese acetate, and / or The iron source includes at least one of ferrous sulfate, ferrous chloride, ferrous oxalate, and ferrous acetate. A method for producing the carbon coated lithium manganese iron phosphate material of claim 2.

5. The iron manganese phosphate precursor has a molar ratio of iron manganese to phosphorus (Fe+Mn) / P of 1.45 to 1.465, and a molar ratio of lithium to iron manganese (Li / (Fe+Mn)) of 1.02 to 1.

05. A method for producing the carbon coated lithium manganese iron phosphate material of claim 2.

6. The carbon source includes at least one of glucose, polyethylene glycol, citric acid, and modified graphite, and the mass ratio of the carbon source to the carbon-coated lithium manganese iron phosphate material is 1.5 wt % to 2.0 wt %; and / or The dopant includes at least one compound selected from the group consisting of Mg, V, Zr, Nb, In, Al, Co, and Ni. A method for producing the carbon coated lithium manganese iron phosphate material of claim 2.

7. The mixing ratio of the two sets of carbon-coated lithium manganese iron phosphate intermediates is (1 to 9):(9 to 1). A method for producing the carbon coated lithium manganese iron phosphate material of claim 2.

8. Controlling the grain size D50 to 0.3 μm to 0.6 μm during the wet polishing, and / or For the spray drying, the inlet air temperature is between 220°C and 280°C and the exhaust air temperature is between 90°C and 110°C, and / or The third sintering is performed at a sintering temperature of 700° C. to 800° C. for a sintering time of 6 h to 12 h. A method for producing the carbon coated lithium manganese iron phosphate material of claim 2.

9. Produced by the production method according to any one of claims 2 to 8. Carbon-coated lithium manganese iron phosphate material.

10. 10. A battery comprising a positive electrode made of the carbon-coated lithium manganese iron phosphate material according to claim 1 or 9. Lithium-ion battery.

Images