Modified lithium ferric manganese phosphate positive electrode material, preparation method thereof and lithium ion battery

Abstract

The invention provides a modified lithium ferric manganese phosphate positive electrode material, a preparation method thereof and a lithium ion battery. The preparation method of the modified lithium ferric manganese phosphate positive electrode material comprises the following steps: S1, mixing a lithium source, an iron source, a manganese source, a phosphorus source and a carbon source with a solvent to obtain slurry; wherein the iron source is a mixture of an iron phthalocyanine compound and an inorganic iron compound, the manganese source is a mixture of immobilized manganese porphyrin and an inorganic manganese compound, and the immobilized manganese porphyrin comprises an alumina carrier and manganese porphyrin loaded on the surface of the alumina carrier; s2, performing spray drying treatment on the slurry to obtain a precursor; and S3, sintering the precursor in an inert atmosphere to obtain the modified lithium ferric manganese phosphate positive electrode material.

Description

Technical Field

[0001] The present invention relates to the technical field of positive electrode material preparation, and in particular to a modified lithium iron manganese phosphate positive electrode material, a preparation method thereof and a lithium ion battery. Background Art

[0002] Lithium-ion batteries have attracted much attention due to their high specific energy, long cycle life, and no memory effect, and have been widely used in daily life. In lithium-ion batteries, the positive electrode material restricts the battery performance and price, so the research on positive electrode materials for lithium-ion batteries is of far-reaching significance. Among the existing lithium-ion positive electrode materials, olivine-type phosphate positive electrode materials have the advantages of high energy density, large discharge specific capacity, and high voltage platform, and are expected to be used in high-end fields. Lithium iron manganese phosphate materials have gradually been favored by the lithium battery industry due to their high voltage and high safety performance. Under the same conditions, their energy density is 10% to 20% higher than that of lithium iron phosphate. However, due to the unique manganese dissolution characteristics of lithium iron manganese phosphate materials, their cycle performance is significantly inferior to that of iron lithium materials. How to design the structure based on the intrinsic characteristics of the material, inhibit manganese dissolution, and improve the stability of the material is of great research significance. Summary of the invention

[0003] The main purpose of the present invention is to provide a modified lithium iron manganese phosphate positive electrode material, a preparation method thereof and a lithium ion battery, so as to solve the problem that the lithium iron manganese phosphate positive electrode material in the prior art has poor structural stability and transition metal elements are easily dissolved during the charge and discharge process, resulting in poor cycle performance of lithium ion batteries.

[0004] In order to achieve the above-mentioned purpose, the present invention provides a method for preparing a modified lithium iron manganese phosphate positive electrode material on the one hand, and the method for preparing the modified lithium iron manganese phosphate positive electrode material comprises: step S1, mixing a lithium source, an iron source, a manganese source, a phosphorus source and a carbon source with a solvent to obtain a slurry; wherein the iron source is a mixture of an iron phthalocyanine compound and an inorganic iron compound, and the manganese source is a mixture of a solid-supported manganese porphyrin and an inorganic manganese compound, and the solid-supported manganese porphyrin comprises an alumina carrier and the manganese porphyrin loaded on the surface of the alumina carrier; step S2, spray drying the slurry to obtain a precursor; step S3, sintering the precursor in an inert atmosphere to obtain a modified lithium iron manganese phosphate positive electrode material.

[0005] The technical scheme of the present invention is applied. The iron source used in this application is a mixture of an iron phthalocyanine compound and an inorganic iron compound, and the manganese source is a mixture of a solid-supported manganese porphyrin and an inorganic manganese compound. The above-mentioned iron source and manganese source are mixed with a lithium source, a phosphorus source, and a carbon source and a solvent to obtain a slurry. The precursor is obtained by spray drying technology and then sintered to obtain a modified lithium iron manganese phosphate positive electrode material. Compared with the traditional method using an inorganic manganese compound as a manganese source and an inorganic iron compound as an iron source, the above-mentioned preparation method of this application can decompose part of the carboxyl groups on the iron phthalocyanine compound during the sintering process to generate local oxygen-containing substances, and manganese porphyrin will rapidly catalyze the reaction when it encounters oxygen-containing substances, prompting the carbon source to develop in the direction of a high degree of graphitization, improving the final carbon coating effect, and making the carbon coated on the surface of the lithium iron manganese phosphate primary particles. At the same time, aluminum oxide is coated on the surface of the lithium iron manganese phosphate primary particles and interspersed in the carbon coating layer, thereby improving the structural stability of the modified lithium iron manganese phosphate positive electrode material and inhibiting the dissolution of transition metal elements.

[0006] Moreover, iron phthalocyanine compounds coordinate with free manganese, thereby promoting the atomic-level combination of manganese atoms and iron atoms in the modified lithium iron manganese phosphate positive electrode material, thereby significantly improving the overall consistency of the modified lithium iron manganese phosphate positive electrode material and the cycle stability during the subsequent use of the battery cell.

[0007] Furthermore, the molar ratio of the Li element in the lithium source, the Fe element in the iron source, the Mn element in the manganese source, and the P element in the phosphorus source is (1.0-1.15):(0.3-0.5):(0.7-0.5):1.

[0008] The molar ratio of the Li element in the lithium source, the Fe element in the iron source, the Mn element in the manganese source, and the P element in the phosphorus source includes but is not limited to the above range. Limiting it within the above range is beneficial to preparing a modified lithium iron manganese phosphate positive electrode material of the corresponding crystal form of lithium iron manganese phosphate, improving the utilization rate of raw materials, and thus is beneficial to improving the electrochemical properties such as the charge and discharge specific capacity of the modified lithium iron manganese phosphate positive electrode material.

[0009] Furthermore, the molar ratio of the immobilized manganese porphyrin to the inorganic manganese compound is 1:(3-6).

[0010] The molar ratio of the immobilized manganese porphyrin to the inorganic manganese compound includes but is not limited to the above range. Limiting it within the above range is conducive to better exerting the role of manganese porphyrin in promoting the carbon source to develop in the direction of a high degree of graphitization, which is beneficial to improving the final carbon coating effect, thereby helping to improve the structural stability of the modified lithium iron manganese phosphate positive electrode material and inhibiting the dissolution of transition metals.

[0011] Further, the inorganic manganese compound is selected from one or more of the group consisting of manganese carbonate, dimanganese trioxide and trimanganese tetraoxide.

[0012] The inorganic manganese compound in the present application may be a material commonly used in the art.

[0013] Furthermore, the preparation method further comprises: subjecting the activated alumina and the manganese porphyrin to a hydrothermal reaction to obtain the immobilized manganese porphyrin.

[0014] The manganese porphyrin can be loaded on the activated alumina by hydrothermal reaction with activated alumina and manganese porphyrin as raw materials, thereby obtaining immobilized manganese porphyrin.

[0015] Furthermore, the weight ratio of activated alumina to manganese porphyrin is (0.1-0.9):100.

[0016] The weight ratio of activated alumina to manganese porphyrin includes but is not limited to the above range. Limiting it within the above range is beneficial to increasing the loading amount of manganese porphyrin, thereby facilitating better utilization of manganese porphyrin to improve the efficiency of carbon coating and inhibit the dissolution of transition metals.

[0017] Furthermore, the D50 of the activated alumina is 350 to 550 nm.

[0018] The D50 of activated alumina includes but is not limited to the above range. Limiting it within the above range is beneficial to improving the coating effect of alumina on the surface of lithium manganese iron phosphate, inhibiting the dissolution of transition metals, and facilitating the loading of manganese porphyrin.

[0019] Furthermore, the temperature of the hydrothermal reaction is 60-80° C., and the time is 6-8 hours.

[0020] The temperature and time of the hydrothermal reaction include but are not limited to the above ranges. Limiting them within the above ranges is beneficial to increasing the loading amount of manganese porphyrin, thereby facilitating better utilization of the efficiency of manganese porphyrin in improving carbon coating and inhibiting the dissolution of transition metals.

[0021] Furthermore, the molar ratio of the iron phthalocyanine compound to the inorganic iron compound is 1:(4-5.5).

[0022] The molar ratio of the iron phthalocyanine compound to the inorganic iron compound includes but is not limited to the above range. Limiting it within the above range is beneficial to the decomposition of some carboxyl groups on the iron phthalocyanine compound during the sintering process to generate local oxygen-containing substances, and manganese porphyrin will rapidly undergo a catalytic reaction when encountering oxygen-containing substances, prompting the carbon source to develop in the direction of a high degree of graphitization, which is beneficial to improving the final carbon coating effect.

[0023] Furthermore, the iron phthalocyanine compound is selected from tetracarboxyl iron phthalocyanine and / or octacarboxyl iron phthalocyanine.

[0024] The use of the above-mentioned iron phthalocyanine compounds facilitates the provision of more easily decomposable carboxyl groups and iron elements.

[0025] Further, the inorganic iron compound is selected from one or more of the group consisting of ferric oxide, ferric phosphate and ferrous oxalate.

[0026] The inorganic iron compound in the present application may be any commonly used type in the art.

[0027] Furthermore, the lithium source is selected from one or more of the group consisting of lithium carbonate, lithium dihydrogen phosphate, dilithium hydrogen phosphate and lithium hydroxide.

[0028] The use of the above-mentioned types of lithium sources is beneficial to providing lithium elements, thereby providing electrochemical capacity for the modified lithium iron manganese phosphate positive electrode material.

[0029] Further, the phosphorus source is selected from one or more of the group consisting of lithium dihydrogen phosphate, ammonium dihydrogen phosphate and iron phosphate.

[0030] Compared with other types, the use of the above-mentioned phosphorus source is beneficial to providing phosphorus elements for the modified lithium iron manganese phosphate positive electrode material, thereby helping to improve the charge and discharge specific capacity of the modified lithium iron manganese phosphate positive electrode material.

[0031] Furthermore, the solvent is water.

[0032] The use of the above-mentioned types of solvents is beneficial to improving the dispersibility and compatibility of the raw materials, thereby facilitating the improvement of the uniformity of the slurry and facilitating subsequent spray drying.

[0033] Furthermore, the carbon source is selected from one or more of the group consisting of glucose, sucrose, starch and graphyne.

[0034] Compared with other types, the above-mentioned types of carbon sources are easily carbonized to form a carbon coating layer after sintering and coated on the surface of the lithium iron manganese phosphate primary particles, which is beneficial to improve the structural stability of the modified lithium iron manganese phosphate positive electrode material and further improve the cycle stability of the lithium-ion battery.

[0035] Furthermore, based on the total weight of the lithium source, the iron source, the manganese source and the phosphorus source, the weight percentage of the carbon source is 0.8-1.8 wt %.

[0036] The weight percentage of the carbon source includes but is not limited to the above range. Limiting it within the above range is beneficial to further improve the structural stability of the modified lithium iron manganese phosphate positive electrode material, thereby further improving the cycle stability of the lithium ion battery.

[0037] Furthermore, the solid content of the slurry is 20-45wt%.

[0038] The solid content of the slurry includes but is not limited to the above range. Limiting it within the above range is beneficial to improving the processability of the slurry and facilitating subsequent spray drying.

[0039] Furthermore, the mixing process in step S1 is grinding, and the grinding time is 1 to 3 hours. Preferably, after the grinding, the D50 of the solid matter in the slurry is 300 to 550 nm.

[0040] The above-mentioned mixing method is beneficial to improving the mixing uniformity of the raw materials in step S1.

[0041] Furthermore, the spray drying process is carried out at a temperature of 200 to 300° C. and for a time of 30 to 60 minutes.

[0042] The temperature, time and pressure of the spray drying process include but are not limited to the above ranges. Limiting them within the above ranges is beneficial to improving the spray drying efficiency, thereby improving the distribution uniformity of each element.

[0043] Furthermore, the D50 of the precursor is 2000-5000 nm.

[0044] The D50 of the precursor includes but is not limited to the above range. Limiting it within the above range is beneficial to improving the treatment effect of the subsequent sintering treatment, thereby helping to improve the structural stability of the modified lithium iron manganese phosphate positive electrode material, and further helping to inhibit the dissolution of transition metals during the charge and discharge process.

[0045] Furthermore, the sintering process includes a first stage sintering and a second stage sintering, the first stage sintering temperature is 400-600°C, the time is 4-6 hours, and the second stage sintering temperature is 700-800°C, the time is 6-12 hours.

[0046] In the present application, the sintering process can be a two-stage programmed temperature treatment. Compared with other ranges, limiting the temperature and time of the first two stages of sintering within the above range is conducive to improving the sintering treatment effect, facilitating the coating of aluminum oxide and carbon on the surface of the lithium iron manganese phosphate primary particles, thereby improving the structural stability of the modified lithium iron manganese phosphate positive electrode material.

[0047] Furthermore, the preparation method further comprises: crushing the sintered product after the sintering treatment is completed to obtain a modified lithium iron manganese phosphate positive electrode material; preferably, the D50 of the modified lithium iron manganese phosphate positive electrode material is 1000 to 3000 nm.

[0048] The sintered product is crushed to facilitate the application of the modified lithium iron manganese phosphate positive electrode material in the positive electrode preparation process.

[0049] In order to achieve the above-mentioned purpose, another aspect of the present invention further provides a modified lithium iron manganese phosphate positive electrode material, which is prepared by the preparation method of the modified lithium iron manganese phosphate positive electrode material provided in the present application.

[0050] Compared with the traditional method of using inorganic manganese compounds as manganese sources and inorganic iron compounds as iron sources, the above-mentioned preparation method of the present application can decompose some carboxyl groups on the iron phthalocyanine compounds during the sintering process to generate local oxygen-containing substances, and manganese porphyrin will rapidly catalyze the reaction when encountering oxygen-containing substances, prompting the carbon source to develop in the direction of high graphitization, improving the final carbon coating effect, so that the carbon is coated on the surface of the primary particles of lithium iron manganese phosphate, and at the same time, aluminum oxide is coated on the surface of the primary particles of lithium iron manganese phosphate, and interspersed in the carbon coating layer, thereby improving the structural stability of the modified lithium iron manganese phosphate positive electrode material and inhibiting the dissolution of transition metal elements. Moreover, the iron phthalocyanine compound is coordinated with free manganese, thereby promoting the manganese and iron atoms in the modified lithium iron manganese phosphate positive electrode material to reach atomic level combination, thereby significantly improving the overall consistency of the modified lithium iron manganese phosphate positive electrode material and the cycle stability during the use of the later battery core. In short, the modified lithium iron manganese phosphate positive electrode material prepared by the above-mentioned preparation method of the present application has excellent structural stability, and the transition metal elements are difficult to dissolve during the charge and discharge process.

[0051] Another aspect of the present invention provides a lithium-ion battery, comprising a positive electrode, a negative electrode, an electrolyte and a separator arranged between the positive electrode and the negative electrode, wherein the positive electrode comprises the modified lithium iron manganese phosphate positive electrode material provided in the present application.

[0052] The modified lithium iron manganese phosphate positive electrode material provided in the present application has excellent structural stability, and the transition metal elements are difficult to dissolve during the charge and discharge process. The application of the modified lithium iron manganese phosphate positive electrode material in lithium ion batteries can significantly improve the capacity retention rate and cycle stability of lithium ion batteries. BRIEF DESCRIPTION OF THE DRAWINGS

[0053] The drawings constituting a part of the present application are used to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation of the present invention. In the drawings:

[0054] Figure 1 The SEM image of the modified lithium iron manganese phosphate positive electrode material prepared in Example 1 of the present application is shown;

[0055] Figure 2 The SEM image of the lithium iron manganese phosphate positive electrode material prepared in Comparative Example 1 of the present application is shown. DETAILED DESCRIPTION

[0056] It should be noted that, in the absence of conflict, the embodiments and features in the embodiments of the present application can be combined with each other. The present invention will be described in detail below in conjunction with the embodiments.

[0057] As described in the background technology, the existing lithium iron manganese phosphate positive electrode material has poor structural stability, and transition metal elements are easily dissolved during the charge and discharge process, resulting in poor cycle performance of lithium ion batteries. In order to solve the above technical problems, the present application provides a method for preparing a modified lithium iron manganese phosphate positive electrode material, and the method for preparing the modified lithium iron manganese phosphate positive electrode material comprises: step S1, mixing a lithium source, an iron source, a manganese source, a phosphorus source and a carbon source with a solvent to obtain a slurry; wherein the iron source is a mixture of an iron phthalocyanine compound and an inorganic iron compound, and the manganese source is a mixture of a solid-supported manganese porphyrin and an inorganic manganese compound, and the solid-supported manganese porphyrin includes an alumina carrier and a manganese porphyrin loaded on the surface of the alumina carrier; step S2, spray drying the slurry to obtain a precursor; step S3, sintering the precursor in an inert atmosphere to obtain a modified lithium iron manganese phosphate positive electrode material.

[0058] The iron source used in this application is a mixture of iron phthalocyanine compounds and inorganic iron compounds, and the manganese source is a mixture of solid-supported manganese porphyrin and inorganic manganese compounds. The above iron source and manganese source are mixed with a lithium source, a phosphorus source, and a carbon source and a solvent to obtain a slurry. The precursor is obtained by spray drying technology and then sintered to obtain a modified lithium iron manganese phosphate positive electrode material. Compared with the traditional method using an inorganic manganese compound as a manganese source and an inorganic iron compound as an iron source, the above-mentioned preparation method of this application can decompose part of the carboxyl groups on the iron phthalocyanine compound during the sintering process to generate local oxygen-containing substances, and manganese porphyrin will rapidly catalyze the reaction when it encounters oxygen-containing substances, prompting the carbon source to develop in the direction of a high degree of graphitization, improving the final carbon coating effect, and making the carbon coated on the surface of the primary particles of lithium iron manganese phosphate. At the same time, aluminum oxide is coated on the surface of the primary particles of lithium iron manganese phosphate and interspersed in the carbon coating layer, thereby improving the structural stability of the modified lithium iron manganese phosphate positive electrode material and inhibiting the dissolution of transition metal elements.

[0059] Moreover, iron phthalocyanine compounds coordinate with free manganese, thereby promoting the atomic-level combination of manganese atoms and iron atoms in the modified lithium iron manganese phosphate positive electrode material, thereby significantly improving the overall consistency of the modified lithium iron manganese phosphate positive electrode material and the cycle stability during the subsequent use of the battery cell.

[0060] In a preferred embodiment, the molar ratio of the Li element in the lithium source, the Fe element in the iron source, the Mn element in the manganese source, and the P element in the phosphorus source is (1.0-1.15): (0.3-0.5): (0.7-0.5): 1. The molar ratio of the Li element in the lithium source, the Fe element in the iron source, the Mn element in the manganese source, and the P element in the phosphorus source includes but is not limited to the above range. Limiting it within the above range is conducive to preparing a modified lithium iron manganese phosphate positive electrode material of the corresponding crystal form of lithium iron manganese phosphate, improving the utilization rate of raw materials, and thus helping to improve the electrochemical properties such as the charge and discharge specific capacity of the modified lithium iron manganese phosphate positive electrode material.

[0061] In a preferred embodiment, the molar ratio of the immobilized manganese porphyrin to the inorganic manganese compound is 1:(3-6). The molar ratio of the immobilized manganese porphyrin to the inorganic manganese compound includes but is not limited to the above range. Limiting it within the above range is conducive to better exerting the role of manganese porphyrin in promoting the carbon source to develop in the direction of a high degree of graphitization, which is conducive to improving the final carbon coating effect, thereby improving the structural stability of the modified lithium iron manganese phosphate positive electrode material and inhibiting the dissolution of transition metals.

[0062] The inorganic manganese compound in the present application may be a material commonly used in the art. In a preferred embodiment, the inorganic manganese compound includes but is not limited to one or more of the group consisting of manganese carbonate, dimanganese trioxide and trimanganese tetraoxide.

[0063] In a preferred embodiment, the preparation method further comprises: performing a hydrothermal reaction on activated alumina and manganese porphyrin to obtain immobilized manganese porphyrin. Performing a hydrothermal reaction with activated alumina and manganese porphyrin as raw materials can load manganese porphyrin on activated alumina, thereby obtaining immobilized manganese porphyrin.

[0064] In order to increase the loading amount of manganese porphyrin, thereby facilitating better utilization of the efficiency of manganese porphyrin in improving carbon coating and inhibiting the dissolution of transition metals, preferably, the weight ratio of activated alumina to manganese porphyrin is (0.1-0.9):100.

[0065] In order to improve the coating effect of aluminum oxide on the surface of lithium manganese iron phosphate and inhibit the dissolution of transition metals, and to facilitate the loading of manganese porphyrin, preferably, the D50 of the activated aluminum oxide is 350-550 nm.

[0066] In a preferred embodiment, the temperature of the hydrothermal reaction is 60-80°C and the time is 6-8h. The temperature and time of the hydrothermal reaction include but are not limited to the above ranges, and limiting them within the above ranges is conducive to increasing the loading amount of manganese porphyrin, thereby facilitating better utilization of the efficiency of manganese porphyrin in improving carbon coating and inhibiting the dissolution of transition metals.

[0067] In a preferred embodiment, the molar ratio of the iron phthalocyanine compound to the inorganic iron compound is 1:(4-5.5). The molar ratio of the iron phthalocyanine compound to the inorganic iron compound includes but is not limited to the above range. Limiting it within the above range is conducive to the decomposition of some carboxyl groups on the iron phthalocyanine compound during the sintering process to generate local oxygen-containing substances, and manganese porphyrin will rapidly undergo a catalytic reaction when encountering oxygen-containing substances, prompting the carbon source to develop in the direction of a high degree of graphitization, which is conducive to improving the final carbon coating effect.

[0068] In order to provide more easily decomposable carboxyl groups and provide iron elements, preferably, the iron phthalocyanine compound includes but is not limited to tetracarboxyl iron phthalocyanine and / or octacarboxyl iron phthalocyanine.

[0069] The inorganic iron compound in the present application may be any of the commonly used ones in the art. In a preferred embodiment, the inorganic iron compound includes but is not limited to one or more of the group consisting of ferric oxide, ferric phosphate and ferrous oxalate.

[0070] In a preferred embodiment, the lithium source includes, but is not limited to, one or more of the group consisting of lithium carbonate, lithium dihydrogen phosphate, lithium dihydrogen phosphate and lithium hydroxide. The above types of lithium sources are beneficial for providing lithium elements, thereby providing electrochemical capacity for the modified lithium iron manganese phosphate positive electrode material.

[0071] In a preferred embodiment, the phosphorus source includes but is not limited to one or more of the group consisting of lithium dihydrogen phosphate, ammonium dihydrogen phosphate and iron phosphate. Compared with other types, the use of the above phosphorus sources is conducive to providing phosphorus elements for the modified lithium iron manganese phosphate positive electrode material, thereby facilitating the improvement of the charge and discharge specific capacity of the modified lithium iron manganese phosphate positive electrode material.

[0072] In order to improve the dispersibility and compatibility of the raw materials, thereby improving the uniformity of the slurry and facilitating subsequent spray drying, in a preferred embodiment, the solvent is water.

[0073] In a preferred embodiment, the carbon source includes but is not limited to one or more of the group consisting of glucose, sucrose, starch and graphyne. Compared with other types, the above types of carbon sources are easy to be carbonized after sintering to form a carbon coating layer and coated on the surface of the lithium iron manganese phosphate primary particles, thereby facilitating the structural stability of the modified lithium iron manganese phosphate positive electrode material, thereby improving the cycle stability of the lithium ion battery.

[0074] In order to further improve the structural stability of the modified lithium iron manganese phosphate positive electrode material, and further improve the cycle stability of the lithium ion battery, preferably, the weight percentage of the carbon source is 0.8-1.8wt% based on the total weight of the lithium source, iron source, manganese source and phosphorus source.

[0075] In a preferred embodiment, the solid content of the slurry is 20-45 wt %. The solid content of the slurry includes but is not limited to the above range, and limiting it within the above range is conducive to improving the processability of the slurry and facilitating subsequent spray drying.

[0076] In order to improve the mixing uniformity of the raw materials in step S1, preferably, the mixing process in step S1 is grinding, and the grinding time is 1 to 3 hours. Preferably, the D50 of the solid matter in the slurry after grinding is 300 to 550 nm.

[0077] In a preferred embodiment, the temperature of the spray drying process is 200-300°C and the time is 30-60 minutes. The temperature, time and pressure of the spray drying process include but are not limited to the above ranges, and limiting them within the above ranges is conducive to improving the spray drying efficiency, thereby improving the distribution uniformity of each element.

[0078] In a preferred embodiment, the D50 of the precursor is 2000-5000 nm. The D50 of the precursor includes but is not limited to the above range, and limiting it within the above range is conducive to improving the treatment effect of the subsequent sintering treatment, thereby improving the structural stability of the modified lithium iron manganese phosphate positive electrode material, and further conducive to inhibiting the dissolution of transition metals during the charge and discharge process.

[0079] In the present application, the sintering treatment can be a two-stage programmed temperature treatment. In a preferred embodiment, the sintering treatment includes a first stage sintering and a second stage sintering, the temperature of the first stage sintering is 400-600°C, the time is 4-6h, and the temperature of the second stage sintering is 700-800°C, and the time is 6-12h. Compared with other ranges, limiting the temperature and time of the two stages of sintering within the above range is conducive to improving the sintering treatment effect, facilitating the coating of alumina and carbon on the surface of the lithium iron manganese phosphate primary particles, thereby improving the structural stability of the modified lithium iron manganese phosphate positive electrode material.

[0080] In order to subsequently apply the modified lithium iron manganese phosphate positive electrode material to the preparation of the positive electrode, preferably, the above preparation method also includes: crushing the sintered product after the sintering treatment is completed to obtain the modified lithium iron manganese phosphate positive electrode material.

[0081] In order to further facilitate the application of the modified lithium iron manganese phosphate positive electrode material in the positive electrode preparation process, preferably, the D50 of the modified lithium iron manganese phosphate positive electrode material is 1000-3000nm.

[0082] The second aspect of the present application also provides a modified lithium iron manganese phosphate positive electrode material, which is prepared by the preparation method of the modified lithium iron manganese phosphate positive electrode material provided by the present application. Compared with the traditional method using inorganic manganese compounds as manganese sources and inorganic iron compounds as iron sources, the above-mentioned preparation method of the present application can decompose some carboxyl groups on the iron phthalocyanine compounds during the sintering process to generate local oxygen-containing substances, and manganese porphyrin will rapidly catalyze the reaction when encountering oxygen-containing substances, prompting the carbon source to develop in the direction of high graphitization, improving the final carbon coating effect, so that carbon is coated on the surface of the lithium iron manganese phosphate primary particles, and at the same time, aluminum oxide is coated on the surface of the lithium iron manganese phosphate primary particles and interspersed in the carbon coating layer, thereby improving the structural stability of the modified lithium iron manganese phosphate positive electrode material and inhibiting the dissolution of transition metal elements. Moreover, the iron phthalocyanine compounds coordinate with the free manganese, thereby promoting the atomic-level combination of manganese and iron atoms in the modified lithium iron manganese phosphate positive electrode material, thereby significantly improving the overall consistency of the modified lithium iron manganese phosphate positive electrode material and the cycle stability during the later use of the battery cell. In short, the modified lithium iron manganese phosphate positive electrode material prepared by the above-mentioned preparation method of the present application has excellent structural stability, and the transition metal elements are difficult to dissolve during the charge and discharge process. It should be noted that due to the particularity of the material field and the limitations of existing test characterization methods, it is difficult to comprehensively and quantitatively characterize the complex microstructure of the modified lithium iron manganese phosphate positive electrode material prepared above, but experiments show that the modified lithium iron manganese phosphate positive electrode material obtained in the present application has excellent structural stability, and the transition metal elements are difficult to dissolve during the charge and discharge process.

[0083] The third aspect of the present application also provides a lithium-ion battery, comprising a positive electrode, a negative electrode, an electrolyte and a separator arranged between the positive electrode and the negative electrode, wherein the positive electrode comprises the modified lithium iron manganese phosphate positive electrode material provided by the present application. The modified lithium iron manganese phosphate positive electrode material provided by the present application has excellent structural stability, and transition metal elements are difficult to dissolve during the charge and discharge process. Applying it in a lithium-ion battery can significantly improve the capacity retention rate and cycle stability of the lithium-ion battery.

[0084] The present application is further described in detail below in conjunction with specific embodiments. These embodiments should not be construed as limiting the scope of protection claimed in the present application.

[0085] Example 1

[0086] A method for preparing a modified lithium iron manganese phosphate positive electrode material, comprising:

[0087] (1) weighing manganese porphyrin and manganese tetraoxide as manganese sources in a molar ratio of 1:4, weighing tetracarboxyferrophthalocyanine and iron phosphate as iron sources in a molar ratio of 1:5, weighing lithium carbonate, iron source, manganese source and diammonium phosphate in a molar ratio of Li element:Fe element:Mn element:P element=1.08:0.4:0.6:1, and weighing activated alumina and manganese porphyrin in a weight ratio of 100:5, wherein the D50 of the activated alumina is 400 nm;

[0088] (2) subjecting activated alumina and manganese porphyrin in a weight ratio of 0.5:100 to a hydrothermal reaction at 70° C., transferring the mixture to a mixing tank after reacting for 1.5 h, adding water, glucose, lithium carbonate, an iron source, a manganese source and a phosphorus source to the mixing tank, mixing for 2 h and then grinding the mixture to obtain a slurry; controlling the D50 of the solid matter in the slurry after grinding to be 400 nm; wherein the weight percentage of glucose, based on the total weight of the lithium source, the iron source, the manganese source and the phosphorus source, is 1.2 wt %, and the solid content of the slurry is 30 wt %;

[0089] (3) spray drying the slurry to obtain a precursor with a D50 of 2000 nm; wherein the spray drying temperature is 280° C. and the time is 45 min;

[0090] (4) The precursor was sintered at 500° C. for 5 h and 750° C. for 9 h under high-purity nitrogen. The material was crushed and the particle size D50 was controlled to be 2000 nm to obtain a modified lithium iron manganese phosphate positive electrode material.

[0091] The SEM image of the modified lithium iron manganese phosphate positive electrode material prepared in Example 1 is as follows: Figure 1 As shown, the material particles have good roundness and good dispersion.

[0092] Example 2

[0093] A method for preparing a modified lithium iron manganese phosphate positive electrode material, comprising:

[0094] (1) weighing manganese porphyrin and manganese tetraoxide as manganese sources in a molar ratio of 1:3, weighing tetracarboxyferrophthalocyanine and iron phosphate as iron sources in a molar ratio of 1:4, weighing lithium carbonate, iron source, manganese source and diammonium phosphate in a molar ratio of Li element:Fe element:Mn element:P element=1.0:0.3:0.7:1, and weighing activated alumina and manganese porphyrin in a weight ratio of 100:1, wherein the D50 of the activated alumina is 350 nm;

[0095] (2) subjecting activated alumina and manganese porphyrin in a weight ratio of 0.1:100 to a hydrothermal reaction at 60° C., transferring the mixture to a mixing tank after reacting for 1 hour, adding water, glucose, lithium carbonate, an iron source, a manganese source and a phosphorus source to the mixing tank, mixing for 1 hour and then grinding the mixture to obtain a slurry; controlling the D50 of the solid matter in the slurry after grinding to be 300 nm; wherein, based on the total weight of the lithium source, the iron source, the manganese source and the phosphorus source, the weight percentage of glucose is 0.8 wt %, and the solid content of the slurry is 20 wt %;

[0096] (3) spray drying the slurry to obtain a precursor with a D50 of 2000 nm; wherein the spray drying temperature is 200° C. and the time is 30 min;

[0097] (4) The precursor was sintered at 400° C. for 4 h and 700° C. for 6 h under high-purity nitrogen, and the material was crushed and the crushing particle size D50 was controlled to be 1000 nm to obtain a modified lithium iron manganese phosphate positive electrode material.

[0098] Example 3

[0099] A method for preparing a modified lithium iron manganese phosphate positive electrode material, comprising:

[0100] (1) weighing manganese porphyrin and manganese tetraoxide as manganese sources at a molar ratio of 1:6, weighing tetracarboxyl iron phthalocyanine and iron phosphate as iron sources at a molar ratio of 1:5.5, weighing lithium carbonate, iron source, manganese source and diammonium phosphate at a molar ratio of Li element:Fe element:Mn element:P element=1.15:0.5:0.5:1, weighing activated alumina and manganese porphyrin at a weight ratio of 100:0.9, wherein the D50 of the activated alumina is 550 nm;

[0101] (2) subjecting activated alumina and manganese porphyrin in a weight ratio of 0.9:100 to a hydrothermal reaction at 80° C., transferring the mixture to a mixing tank after reacting for 2 hours, adding water, glucose, lithium carbonate, an iron source, a manganese source and a phosphorus source to the mixing tank, mixing for 3 hours and then grinding the mixture to obtain a slurry; controlling the D50 of the solid matter in the slurry after grinding to be 550 nm; wherein, based on the total weight of the lithium source, the iron source, the manganese source and the phosphorus source, the weight percentage of glucose is 0.8 wt %, and the solid content of the slurry is 45 wt %;

[0102] (3) spray drying the slurry to obtain a precursor with a D50 of 2000 nm; wherein the spray drying temperature is 300° C. and the time is 60 min;

[0103] (4) The precursor was sintered at 600° C. for 6 h and 800° C. for 12 h under high-purity nitrogen. The material was crushed and the particle size D50 was controlled to be 3000 nm to obtain a modified lithium iron manganese phosphate positive electrode material.

[0104] Example 4

[0105] The difference from Example 1 is that in step (1), the molar ratio of the immobilized manganese porphyrin to manganese tetraoxide is 1:3.

[0106] Example 5

[0107] The difference from Example 1 is that in step (1), the molar ratio of the immobilized manganese porphyrin to manganese tetraoxide is 1:6.

[0108] Example 6

[0109] The difference from Example 1 is that in step (1), the molar ratio of the immobilized manganese porphyrin to manganese tetraoxide is 1:8.

[0110] Example 7

[0111] The difference from Example 1 is that in step (2), the weight ratio of activated alumina to manganese porphyrin is 0.1:100.

[0112] Example 8

[0113] The difference from Example 1 is that in step (2), the weight ratio of activated alumina to manganese porphyrin is 0.9:100.

[0114] Example 9

[0115] The difference from Example 1 is that in step (2), the weight ratio of activated alumina to manganese porphyrin is 1.2:100.

[0116] Example 10

[0117] The difference from Example 1 is that the D50 of the activated alumina is 350 nm.

[0118] Embodiment 11

[0119] The difference from Example 1 is that the D50 of the activated alumina is 350 nm.

[0120] Example 12

[0121] The difference from Example 1 is that the D50 of the activated alumina is 550 nm.

[0122] Embodiment 13

[0123] The difference from Example 1 is that in step (2), the temperature of the hydrothermal reaction is 60° C. and the time is 8 h.

[0124] Embodiment 14

[0125] The difference from Example 1 is that in step (2), the temperature of the hydrothermal reaction is 80° C. and the time is 6 hours.

[0126] Embodiment 15

[0127] The difference from Example 1 is that in step (2), the temperature of the hydrothermal reaction is 40° C. and the time is 3 h.

[0128] Example 16

[0129] The difference from Example 1 is that the molar ratio of tetracarboxyl iron phthalocyanine to iron phosphate is 1:5.5.

[0130] Embodiment 17

[0131] The difference from Example 1 is that the molar ratio of tetracarboxyl iron phthalocyanine to iron phosphate is 1:7.

[0132] Embodiment 18

[0133] The difference from Example 1 is that the weight percentage of glucose is 0.8 wt % based on the total weight of the lithium source, the iron source, the manganese source and the phosphorus source.

[0134] Embodiment 19

[0135] The difference from Example 1 is that the weight percentage of glucose is 1.8 wt % based on the total weight of the lithium source, the iron source, the manganese source and the phosphorus source.

[0136] Comparative Example 1

[0137] (1) Lithium carbonate, iron phosphate, manganese tetraoxide and ammonium dihydrogen phosphate were weighed according to the stoichiometric ratio of Li element:Fe element:Mn element:P element=1.08:0.4:0.6:1; glucose was weighed according to 1.2% of the total mass ratio of the above raw materials and added to a mixing tank filled with deionized water, and then the weighed lithium source, iron source, manganese source and phosphorus source were added to the mixing tank in turn, mixed for 2 hours and ground to obtain a slurry; after grinding, the D50 of the solid matter in the slurry was controlled to be 400nm;

[0138] (2) spray drying the slurry to obtain a precursor; wherein the spray drying temperature is 280° C. and the time is 45 min;

[0139] (3) The precursor was sintered at 500° C. for 5 h and 750° C. for 9 h under high-purity nitrogen, and the material was crushed and the crushing particle size D50 was controlled to be 2000 nm to obtain a lithium iron manganese phosphate positive electrode material.

[0140] The SEM image of the lithium iron manganese phosphate positive electrode material prepared in Comparative Example 1 is as follows: Figure 2 shown.

[0141] Comparative Example 2

[0142] The difference from Example 1 is that in step (2), no glucose is added.

[0143] The lithium iron manganese phosphate positive electrode material prepared in Comparative Example 2 is not coated with a carbon coating layer.

[0144] The modified lithium iron manganese phosphate positive electrode materials prepared in all the above Examples 1 to 19, and the lithium iron manganese phosphate positive electrode materials obtained in Comparative Examples 1 and 2 were respectively used as positive electrode materials, battery-grade lithium sheets were used as negative electrode materials, and lithium hexafluorophosphate as the main component was used as the electrolyte to assemble simulated batteries, and relevant performance tests were carried out. The initial charge and discharge capacity was tested at 0.2C, and the discharge capacity was tested at 1C, 2C, and 5C in turn. Under the condition of 1C charge and discharge, the capacity retention rate was tested after 300 cycles, and the test results are listed in Table 1.

[0145] Table 1

[0146]

[0147]

[0148] From the above description, it can be seen that the above embodiments of the present invention achieve the following technical effects:

[0149] The iron source used in this application is a mixture of iron phthalocyanine compounds and inorganic iron compounds, and the manganese source is a mixture of solid-supported manganese porphyrin and inorganic manganese compounds. The above iron source and manganese source are mixed with a lithium source, a phosphorus source, and a carbon source and a solvent to obtain a slurry. The precursor is obtained by spray drying technology and then sintered to obtain a modified lithium iron manganese phosphate positive electrode material. Compared with the traditional method using an inorganic manganese compound as a manganese source and an inorganic iron compound as an iron source, the above-mentioned preparation method of this application can decompose part of the carboxyl groups on the iron phthalocyanine compound during the sintering process to generate local oxygen-containing substances, and manganese porphyrin will rapidly catalyze the reaction when it encounters oxygen-containing substances, prompting the carbon source to develop in the direction of a high degree of graphitization, improving the final carbon coating effect, and making the carbon coated on the surface of the primary particles of lithium iron manganese phosphate. At the same time, aluminum oxide is coated on the surface of the primary particles of lithium iron manganese phosphate and interspersed in the carbon coating layer, thereby improving the structural stability of the modified lithium iron manganese phosphate positive electrode material and inhibiting the dissolution of transition metal elements.

[0150] Moreover, iron phthalocyanine compounds coordinate with free manganese, thereby promoting the atomic-level combination of manganese atoms and iron atoms in the modified lithium iron manganese phosphate positive electrode material, thereby significantly improving the overall consistency of the modified lithium iron manganese phosphate positive electrode material and the cycle stability during the subsequent use of the battery cell.

[0151] It should be noted that the terms "first", "second", etc. in the specification and claims of the present application are used to distinguish similar objects, and are not necessarily used to describe a specific order or sequence. It should be understood that the terms used in this way can be interchangeable where appropriate, so that the embodiments of the present application described herein can be implemented in an order other than those described herein, for example.

[0152] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A method for preparing a modified lithium iron manganese phosphate positive electrode material, characterized in that: The preparation method of the modified lithium iron manganese phosphate positive electrode material comprises: Step S1, mixing a lithium source, an iron source, a manganese source, a phosphorus source and a carbon source with a solvent to obtain a slurry; wherein the iron source is a mixture of an iron phthalocyanine compound and an inorganic iron compound, the manganese source is a mixture of a solid-supported manganese porphyrin and an inorganic manganese compound, and the solid-supported manganese porphyrin includes an alumina carrier and the manganese porphyrin supported on the surface of the alumina carrier; Step S2, spray drying the slurry to obtain a precursor; Step S3, sintering the precursor in an inert atmosphere to obtain the modified lithium iron manganese phosphate positive electrode material.

2. The method for preparing the modified lithium iron manganese phosphate positive electrode material according to claim 1, characterized in that: The molar ratio of the Li element in the lithium source, the Fe element in the iron source, the Mn element in the manganese source, and the P element in the phosphorus source is (1.0-1.15):(0.3-0.5):(0.7-0.5):

1.

3. The method for preparing the modified lithium iron manganese phosphate positive electrode material according to claim 1 or 2, characterized in that: The molar ratio of the immobilized manganese porphyrin to the inorganic manganese compound is 1:(3-6); Preferably, the inorganic manganese compound is selected from one or more of the group consisting of manganese carbonate, dimanganese trioxide and trimanganese tetraoxide; Preferably, the preparation method further comprises: performing a hydrothermal reaction on activated alumina and manganese porphyrin to obtain the immobilized manganese porphyrin; More preferably, the weight ratio of the activated alumina to the manganese porphyrin is (0.1-0.9):100; More preferably, the D50 of the activated alumina is 350 to 550 nm; More preferably, the temperature of the hydrothermal reaction is 60-80° C., and the time is 6-8 hours.

4. The method for preparing the modified lithium iron manganese phosphate positive electrode material according to any one of claims 1 to 3, characterized in that: The molar ratio of the iron phthalocyanine compound to the inorganic iron compound is 1:(4-5.5); Preferably, the iron phthalocyanine compound is selected from tetracarboxyl iron phthalocyanine and / or octacarboxyl iron phthalocyanine; Preferably, the inorganic iron compound is selected from one or more of the group consisting of ferric oxide, ferric phosphate and ferrous oxalate.

5. The method for preparing the modified lithium iron manganese phosphate positive electrode material according to claim 4, characterized in that: The lithium source is selected from one or more of the group consisting of lithium carbonate, lithium dihydrogen phosphate, dilithium hydrogen phosphate and lithium hydroxide; Preferably, the phosphorus source is selected from one or more of the group consisting of lithium dihydrogen phosphate, ammonium dihydrogen phosphate and iron phosphate; Preferably, the solvent is water; Preferably, the carbon source is selected from one or more of the group consisting of glucose, sucrose, starch and graphyne; Preferably, based on the total weight of the lithium source, the iron source, the manganese source and the phosphorus source, the weight percentage of the carbon source is 0.8-1.8 wt %.

6. The method for preparing the modified lithium iron manganese phosphate positive electrode material according to any one of claims 1 to 5, characterized in that: The solid content of the slurry is 20-45wt%; Preferably, the mixing process in step S1 is grinding, and the grinding time is 1 to 3 hours. Preferably, after the grinding is completed, the D50 of the solid matter in the slurry is 300 to 550 nm.

7. The method for preparing the modified lithium iron manganese phosphate positive electrode material according to claim 6, characterized in that: The spray drying process is performed at a temperature of 200 to 300°C and a time of 30 to 60 minutes; Preferably, the D50 of the precursor is 2000-5000 nm.

8. The method for preparing the modified lithium iron manganese phosphate positive electrode material according to claim 7, characterized in that: The sintering process includes a first stage sintering and a second stage sintering, wherein the first stage sintering is performed at a temperature of 400-600°C for 4-6 hours, and the second stage sintering is performed at a temperature of 700-800°C for 6-12 hours; Preferably, the preparation method further comprises: crushing the sintered product after the sintering treatment is completed to obtain the modified lithium iron manganese phosphate positive electrode material; preferably, the D50 of the modified lithium iron manganese phosphate positive electrode material is 1000-3000nm.

9. A modified lithium iron manganese phosphate positive electrode material, characterized in that: The modified lithium iron manganese phosphate positive electrode material is prepared by the preparation method of the modified lithium iron manganese phosphate positive electrode material according to any one of claims 1 to 8.

10. A lithium ion battery comprising a positive electrode, a negative electrode, an electrolyte and a separator arranged between the positive electrode and the negative electrode, characterized in that: The positive electrode comprises the modified lithium iron manganese phosphate positive electrode material according to claim 9.

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