Modified lithium iron manganese phosphate cathode material, preparation method thereof and lithium ion battery

Abstract

The application provides a modified lithium iron manganese phosphate positive electrode material, a preparation method thereof and a lithium ion battery. The preparation method of the modified lithium iron 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 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 comprises an alumina carrier and a manganese porphyrin supported on the surface of the alumina carrier; S2, performing spray drying treatment on the slurry to obtain a precursor; and S3, performing sintering treatment on the precursor in an inert atmosphere to obtain the modified lithium iron manganese phosphate positive electrode material.

Description

Technical Field

[0001] This invention relates to the field of cathode material preparation technology, and more specifically, to a modified lithium iron manganese phosphate cathode material, its preparation method, and a lithium-ion battery. Background Technology

[0002] Lithium-ion batteries have attracted much attention and are widely used in daily life due to their high specific energy, long cycle life, and lack of memory effect. In lithium-ion batteries, the cathode material restricts battery performance and price, making research on lithium-ion battery cathode materials of profound significance. Among existing lithium-ion cathode materials, olivine-type phosphate cathode materials have advantages such as 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 are gradually gaining popularity in the lithium battery industry due to their high voltage and high safety performance, with an energy density 10% to 20% higher than lithium iron phosphate under the same conditions. However, due to the unique manganese leaching characteristics of lithium iron manganese phosphate materials, their cycle performance is significantly inferior to that of lithium iron phosphate materials. Therefore, how to design the structure based on the intrinsic properties of the material to suppress manganese leaching and improve material stability is of great research significance. Summary of the Invention

[0003] The main objective of this invention is to provide a modified lithium iron manganese phosphate cathode material, its preparation method, and a lithium-ion battery, in order to solve the problems of poor structural stability of lithium iron manganese phosphate cathode materials in the prior art, the easy dissolution of transition metal elements during charging and discharging, and the resulting poor cycle performance of lithium-ion batteries.

[0004] To achieve the above objectives, the present invention provides a method for preparing a modified lithium iron manganese phosphate cathode material, comprising: 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 iron phthalocyanine compounds and inorganic iron compounds, and the manganese source is a mixture of supported manganese porphyrin and inorganic manganese compounds, wherein the supported manganese porphyrin includes an alumina support and manganese porphyrin loaded on the surface of the alumina support; step S2, spray drying the slurry to obtain a precursor; and step S3, sintering the precursor in an inert atmosphere to obtain the modified lithium iron manganese phosphate cathode material.

[0005] Applying the technical solution of this invention, 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 supported manganese porphyrin and inorganic manganese compounds. The above-mentioned iron and manganese sources are mixed with lithium, phosphorus, and carbon sources and a solvent to obtain a slurry. A precursor is obtained using spray drying technology, followed by sintering to obtain the modified lithium iron manganese phosphate cathode material. Compared to traditional methods that use inorganic manganese compounds as the manganese source and inorganic iron compounds as the iron source, the preparation method of this application allows some carboxyl groups on the iron phthalocyanine compounds to decompose during sintering, generating locally oxygen-containing substances. The manganese porphyrin reacts rapidly with these oxygen-containing substances, promoting the carbon source towards a higher degree of graphitization, improving the final carbon coating effect, and ensuring that carbon coats the surface of the primary lithium iron manganese phosphate particles. Simultaneously, alumina coats the surface of the primary lithium iron manganese phosphate particles and is interspersed within the carbon coating layer, thereby improving the structural stability of the modified lithium iron manganese phosphate cathode material and inhibiting the dissolution of transition metal elements.

[0006] Moreover, iron phthalocyanine compounds coordinate with free manganese, thereby promoting the atomic-level bonding of manganese and iron atoms in the modified lithium iron manganese phosphate cathode material, which significantly improves the overall consistency of the modified lithium iron manganese phosphate cathode material and the cycle stability during the later use of the battery cell.

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

[0008] The molar ratios of Li in the lithium source, Fe in the iron source, Mn in the manganese source, and P in the phosphorus source are not limited to the ranges mentioned above. Limiting these ratios to the ranges is beneficial for obtaining modified lithium iron phosphate cathode materials with the corresponding crystal form of lithium manganese iron phosphate, improving raw material utilization, and thus improving the electrochemical performance of modified lithium iron phosphate cathode materials, such as charge-discharge specific capacity.

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

[0010] The molar ratio of supported manganese porphyrin to inorganic manganese compounds includes, but is not limited to, the ranges mentioned above. Limiting it to these ranges helps to better leverage the role of manganese porphyrin in promoting the development of carbon sources towards a higher degree of graphitization, which is beneficial to improving the final carbon coating effect. This, in turn, helps to improve the structural stability of the modified lithium iron manganese phosphate cathode material and inhibit the dissolution of transition metals.

[0011] Furthermore, the inorganic manganese compound is selected from one or more of the group consisting of manganese carbonate, manganese trioxide, and manganese tetroxide.

[0012] The inorganic manganese compound used in this application can be a material commonly used in the field.

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

[0014] Hydrothermal reaction using activated alumina and manganese porphyrin as raw materials enables the loading of manganese porphyrin onto activated alumina, 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 ranges mentioned above. Limiting it to these ranges helps to increase the loading of manganese porphyrin, thereby facilitating better utilization of manganese porphyrin to improve carbon coating efficiency and inhibit the dissolution of transition metals.

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

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

[0019] Furthermore, the hydrothermal reaction is carried out at a temperature of 60–80°C for 6–8 hours.

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

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

[0022] The molar ratio of iron phthalocyanine compounds to inorganic iron compounds includes, but is not limited to, the range mentioned above. Limiting it to the range mentioned above is beneficial for the decomposition of some carboxyl groups on the iron phthalocyanine compounds during the sintering process, generating local oxygen-containing substances. When manganese porphyrin encounters oxygen-containing substances, it will undergo a rapid catalytic reaction, promoting the carbon source to develop in the direction of high graphitization, which is beneficial to improving the final carbon coating effect.

[0023] Furthermore, the iron phthalocyanine compounds are selected from tetracarboxylated iron phthalocyanine and / or octacarboxylated iron phthalocyanine.

[0024] Using the above-mentioned types of iron phthalocyanine compounds makes it easier to provide more carboxyl groups that are prone to decomposition and to provide iron.

[0025] Furthermore, 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 used in this application can be of a type commonly used in the field.

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

[0028] Using the above-mentioned types of lithium sources is beneficial for providing lithium elements, thereby providing electrochemical capacity for modified lithium iron manganese phosphate cathode materials.

[0029] Furthermore, 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 to other types, using the above-mentioned phosphorus source is beneficial for providing phosphorus to the modified lithium iron manganese phosphate cathode material, thereby improving the charge-discharge specific capacity of the modified lithium iron manganese phosphate cathode material.

[0031] Furthermore, the solvent is water.

[0032] Using the above-mentioned solvents helps to improve the dispersibility and compatibility of the raw materials, thereby facilitating the improvement of the slurry uniformity and 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 to other types, the carbon sources of the above types are more likely to carbonize after sintering, forming a carbon coating layer that coats the surface of the primary lithium manganese iron phosphate particles. This helps to improve the structural stability of the modified lithium iron manganese phosphate cathode material, thereby improving the cycle stability of lithium-ion batteries.

[0035] Furthermore, the carbon source comprises 0.8 to 1.8 wt% of the total weight of the lithium, iron, manganese, and phosphorus sources.

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

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

[0038] The solid content of the slurry includes, but is not limited to, the range mentioned above. Limiting it to the 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, the D50 of the solid substances in the slurry after grinding is 300 to 550 nm.

[0040] Using the above mixing method is beneficial to improving the uniformity of the mixing of each raw material in step S1.

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

[0042] The temperature, time, and pressure of spray drying are not limited to the ranges mentioned above. Limiting them to these ranges is beneficial to improving spray drying efficiency, thereby improving the uniformity of the distribution 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 range described above. Limiting it to the range described above is beneficial to improving the processing effect of subsequent sintering, thereby improving the structural stability of the modified lithium iron manganese phosphate cathode material, and further helping to suppress the dissolution of transition metals during charging and discharging.

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

[0046] In this application, the sintering process can be a two-stage programmed temperature rise process. Compared with other ranges, limiting the temperature and time of the first two stages of sintering within the above range is beneficial to improving the sintering effect, making it easier for alumina and carbon to coat the surface of the primary lithium iron phosphate particles, thereby improving the structural stability of the modified lithium iron phosphate cathode material.

[0047] Furthermore, the above preparation method also includes: pulverizing the sintered product after sintering treatment to obtain modified lithium iron manganese phosphate cathode material; preferably, the D50 of the modified lithium iron manganese phosphate cathode material is 1000-3000 nm.

[0048] Pulverizing the sintered products facilitates the application of modified lithium iron manganese phosphate cathode materials in the cathode preparation process.

[0049] To achieve the above objectives, another aspect of the present invention provides a modified lithium iron manganese phosphate cathode material, which is prepared using the preparation method of the modified lithium iron manganese phosphate cathode material provided in this application.

[0050] Compared to traditional methods that use inorganic manganese compounds as the manganese source and inorganic iron compounds as the iron source, the preparation method described in this application allows for the decomposition of some carboxyl groups on the iron phthalocyanine compounds during sintering, generating localized oxygen-containing substances. Manganese porphyrin rapidly catalyzes these oxygen-containing substances, promoting the carbon source towards a higher degree of graphitization, thus improving the final carbon coating effect. This results in carbon coating on the surface of the primary lithium iron manganese phosphate particles, while alumina coats the surface of the primary lithium iron manganese phosphate particles and is interspersed within the carbon coating layer. This enhances the structural stability of the modified lithium iron manganese phosphate cathode material and inhibits the dissolution of transition metal elements. Furthermore, the iron phthalocyanine compounds coordinate with free manganese, promoting atomic-level bonding of manganese and iron atoms in the modified lithium iron manganese phosphate cathode material, significantly improving the overall consistency of the modified lithium iron manganese phosphate cathode material and its cycle stability during subsequent cell use. In summary, the modified lithium iron manganese phosphate cathode material prepared using the method described in this application exhibits excellent structural stability and exhibits low dissolution of transition metal elements during charge and discharge.

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

[0052] The modified lithium iron manganese phosphate cathode material provided in this application exhibits excellent structural stability, and transition metal elements are difficult to dissolve during charge and discharge. Its application in lithium-ion batteries can significantly improve the capacity retention and cycle stability of lithium-ion batteries. Attached Figure Description

[0053] The accompanying drawings, which form part of this application, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an undue limitation of the invention. In the drawings:

[0054] Figure 1 The SEM image of the modified lithium iron manganese phosphate cathode material prepared in Example 1 of this application is shown.

[0055] Figure 2 The SEM image of the lithium iron manganese phosphate cathode material prepared in Comparative Example 1 of this application is shown. Detailed Implementation

[0056] It should be noted that, unless otherwise specified, the embodiments and features described in this application can be combined with each other. The present invention will now be described in detail with reference to the embodiments.

[0057] As described in the background section, existing lithium iron manganese phosphate cathode materials suffer from poor structural stability and the easy dissolution of transition metal elements during charge and discharge, resulting in poor cycle performance of lithium-ion batteries. To address these technical problems, this application provides a method for preparing a modified lithium iron manganese phosphate cathode material. This method includes: 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 iron phthalocyanine compounds and inorganic iron compounds, and the manganese source is a mixture of supported manganese porphyrin and inorganic manganese compounds, wherein the supported manganese porphyrin includes an alumina support and manganese porphyrin loaded on the surface of the alumina support; 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 cathode 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 supported manganese porphyrin and inorganic manganese compounds. The iron and manganese sources are mixed with lithium, phosphorus, and carbon sources and a solvent to obtain a slurry. A precursor is obtained using spray drying technology, followed by sintering to obtain the modified lithium iron manganese phosphate cathode material. Compared to traditional methods that use inorganic manganese compounds as the manganese source and inorganic iron compounds as the iron source, the preparation method in this application allows some carboxyl groups on the iron phthalocyanine compounds to decompose during sintering, generating locally oxygen-containing substances. The manganese porphyrin reacts rapidly with these oxygen-containing substances, promoting the carbon source towards a higher degree of graphitization, improving the final carbon coating effect, and ensuring carbon coating on the surface of the primary lithium iron manganese phosphate particles. Simultaneously, alumina coats the surface of the primary lithium iron manganese phosphate particles and is interspersed within the carbon coating layer, thereby improving the structural stability of the modified lithium iron manganese phosphate cathode material and inhibiting the dissolution of transition metal elements.

[0059] Moreover, iron phthalocyanine compounds coordinate with free manganese, thereby promoting the atomic-level bonding of manganese and iron atoms in the modified lithium iron manganese phosphate cathode material, which significantly improves the overall consistency of the modified lithium iron manganese phosphate cathode material and the cycle stability during the later use of the battery cell.

[0060] In a preferred embodiment, the molar ratio of Li in the lithium source, Fe in the iron source, Mn in the manganese source, and P in the phosphorus source is (1.0–1.15):(0.3–0.5):(0.7–0.5):1. The molar ratio of Li in the lithium source, Fe in the iron source, Mn in the manganese source, and P in the phosphorus source includes, but is not limited to, the above range. Limiting it to this range is beneficial for obtaining modified lithium iron phosphate cathode materials with the corresponding crystal form of lithium manganese iron phosphate, improving raw material utilization, and thus improving the electrochemical performance of the modified lithium iron phosphate cathode material, such as its charge-discharge specific capacity.

[0061] In a preferred embodiment, the molar ratio of supported manganese porphyrin to inorganic manganese compound is 1:(3-6). The molar ratio of supported manganese porphyrin to inorganic manganese compound includes, but is not limited to, the range described above. Limiting it to this range helps to better utilize the role of manganese porphyrin in promoting the development of the carbon source towards a higher degree of graphitization, which is beneficial for improving the final carbon coating effect. This, in turn, helps to improve the structural stability of the modified lithium iron manganese phosphate cathode material and inhibits the dissolution of transition metals.

[0062] The inorganic manganese compound used in this application can 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, manganese trioxide, and manganese tetroxide.

[0063] In a preferred embodiment, the preparation method further includes: performing a hydrothermal reaction between activated alumina and manganese porphyrin to obtain immobilized manganese porphyrin. Using activated alumina and manganese porphyrin as raw materials for a hydrothermal reaction allows manganese porphyrin to be loaded onto the activated alumina, thereby obtaining immobilized manganese porphyrin.

[0064] To increase the loading of manganese porphyrin and thus better utilize its efficiency in improving carbon coating and inhibiting the dissolution of transition metals, the weight ratio of activated alumina to manganese porphyrin is preferably (0.1-0.9):100.

[0065] To improve the coating effect of alumina on the surface of lithium manganese iron phosphate, inhibit the dissolution of transition metals, and facilitate the loading of manganese porphyrin, the D50 of the active alumina is preferably 350-550 nm.

[0066] In a preferred embodiment, the hydrothermal reaction temperature is 60–80°C, and the time is 6–8 hours. The hydrothermal reaction temperature and time include, but are not limited to, the above ranges. Limiting them to the above ranges is beneficial to increasing the loading of manganese porphyrin, thereby facilitating better utilization of manganese porphyrin to improve carbon coating efficiency and inhibit 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 range described above. Limiting it to this range facilitates the decomposition of some carboxyl groups on the iron phthalocyanine compound during sintering, generating locally oxygen-containing substances. When manganese porphyrin encounters these oxygen-containing substances, it undergoes a rapid catalytic reaction, promoting the carbon source towards a higher degree of graphitization, which is beneficial for improving the final carbon coating effect.

[0068] In order to provide more easily decomposed carboxyl groups and iron, iron phthalocyanine compounds are preferably including, but not limited to, tetracarboxylated iron phthalocyanine and / or octacarboxylated iron phthalocyanine.

[0069] The inorganic iron compound used in this application can be of types commonly used 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 aforementioned types of lithium sources are advantageous in providing lithium elements, thereby providing electrochemical capacity for the modified lithium iron manganese phosphate cathode 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 to other types, using the above-mentioned phosphorus source is beneficial for providing phosphorus to the modified lithium iron manganese phosphate cathode material, thereby improving the charge-discharge specific capacity of the modified lithium iron manganese phosphate cathode material.

[0072] In order to improve the dispersibility and compatibility of the raw materials, thereby facilitating the improvement of the slurry uniformity and 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 graphylene. Compared to other types, the carbon sources described above are more likely to carbonize after sintering to form a carbon coating layer that coats the surface of the lithium iron phosphate primary particles, thereby improving the structural stability of the modified lithium iron phosphate cathode material and thus enhancing the cycle stability of the lithium-ion battery.

[0074] To further improve the structural stability of the modified lithium iron manganese phosphate cathode material, and thus further improve the cycle stability of the lithium-ion battery, preferably, the carbon source has a weight percentage of 0.8 to 1.8 wt% 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. Limiting it to the above range is beneficial to improving the processability of the slurry and facilitating subsequent spray drying.

[0076] To improve the uniformity of the mixing of 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 substances in the slurry after grinding is 300 to 550 nm.

[0077] In a preferred embodiment, the spray drying temperature is 200–300°C, and the time is 30–60 min. The temperature, time, and pressure of the spray drying process include, but are not limited to, the above ranges. Limiting them within these ranges is beneficial for improving spray drying efficiency, thereby improving the uniformity of the distribution of various elements.

[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. Limiting it to the above range is beneficial to improving the processing effect of subsequent sintering, thereby improving the structural stability of the modified lithium iron manganese phosphate cathode material, and further helping to suppress the dissolution of transition metals during charging and discharging.

[0079] In this application, the sintering process can be a two-stage programmed temperature rise process. In a preferred embodiment, the sintering process includes a first-stage sintering and a second-stage sintering. The temperature of the first-stage sintering is 400–600°C, and the time is 4–6 hours. The temperature of the second-stage sintering is 700–800°C, and the time is 6–12 hours. Compared to other ranges, limiting the temperature and time of the first two-stage sintering to the above range is beneficial to improving the sintering effect, facilitating the coating of alumina and carbon onto the surface of the lithium iron phosphate primary particles, thereby improving the structural stability of the modified lithium iron phosphate cathode material.

[0080] In order to subsequently apply the modified lithium iron manganese phosphate cathode material to the preparation of cathodes, preferably, the above preparation method further includes: pulverizing the sintered product after sintering treatment to obtain the modified lithium iron manganese phosphate cathode material.

[0081] To further facilitate the application of modified lithium iron manganese phosphate cathode materials in the cathode preparation process, preferably, the D50 of the modified lithium iron manganese phosphate cathode material is 1000-3000 nm.

[0082] The second aspect of this application also provides a modified lithium iron manganese phosphate cathode material, which is prepared using the preparation method described above. Compared to traditional methods that use inorganic manganese compounds as the manganese source and inorganic iron compounds as the iron source, the preparation method described above allows some carboxyl groups on the iron phthalocyanine compounds to decompose during sintering, generating locally oxygen-containing substances. Manganese porphyrins then undergo a rapid catalytic reaction upon encountering these oxygen-containing substances, promoting the carbon source towards a higher degree of graphitization and improving the final carbon coating effect. This results in carbon coating on the surface of the primary lithium iron manganese phosphate particles, while alumina coats the surface of the primary lithium iron manganese phosphate particles and is interspersed within the carbon coating layer, thereby improving the structural stability of the modified lithium iron manganese phosphate cathode material and inhibiting the dissolution of transition metal elements. Furthermore, the iron phthalocyanine compounds coordinate with free manganese, thereby promoting atomic-level bonding of manganese and iron atoms in the modified lithium iron manganese phosphate cathode material. This significantly improves the overall consistency of the modified lithium iron manganese phosphate cathode material and its cycle stability during later cell use. In summary, the modified lithium iron manganese phosphate cathode material prepared by the above-described method of this application exhibits excellent structural stability, and transition metal elements are difficult to dissolve during charge and discharge. It should be noted that due to the special nature of the materials field and the limitations of existing testing and characterization methods, it is difficult to comprehensively and quantitatively characterize the complex microstructure of the modified lithium iron manganese phosphate cathode material prepared above. However, experiments show that the modified lithium iron manganese phosphate cathode material obtained in this application has excellent structural stability, and transition metal elements are difficult to dissolve during charge and discharge.

[0083] A third aspect of this application also provides a lithium-ion battery, including a positive electrode, a negative electrode, an electrolyte, and a separator disposed between the positive and negative electrodes. The positive electrode includes the modified lithium iron manganese phosphate positive electrode material provided in this application. The modified lithium iron manganese phosphate positive electrode material provided in this application exhibits excellent structural stability, and transition metal elements are difficult to dissolve during charge and discharge. Its application in lithium-ion batteries can significantly improve the capacity retention and cycle stability of lithium-ion batteries.

[0084] The present application will be further described in detail below with reference to specific embodiments, which 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 cathode material includes:

[0087] (1) Manganese porphyrin and manganese tetroxide are weighed in a molar ratio of 1:4 as manganese source, tetracarboxylated iron phthalocyanine and iron phosphate are weighed in a molar ratio of 1:5 as iron source, lithium carbonate, iron source, manganese source and ammonium dihydrogen phosphate are weighed in a molar ratio of Li:Fe:Mn:P = 1.08:0.4:0.6:1, and activated alumina and manganese porphyrin are weighed in a weight ratio of 100:5, wherein the D50 of activated alumina is 400 nm;

[0088] (2) Active alumina and manganese porphyrin with a weight ratio of 0.5:100 were subjected to a hydrothermal reaction at 70°C. After the reaction was carried out for 1.5 h, the mixture was transferred to a mixing tank. Water, glucose, lithium carbonate, iron source, manganese source and phosphorus source were added to the mixing tank. After mixing for 2 h, the mixture was ground to obtain a slurry. The D50 of the solids in the slurry after grinding was controlled to be 400 nm. Among them, based on the total weight of lithium source, iron source, manganese source and phosphorus source, the weight percentage of glucose was 1.2 wt%, and the solid content of the slurry was 30 wt%.

[0089] (3) The above slurry was spray-dried to obtain a precursor with a D50 of 2000 nm; wherein the spray drying temperature was 280℃ and the time was 45 min.

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

[0091] The SEM image of the modified lithium iron manganese phosphate cathode material prepared in Example 1 is shown below. Figure 1 As shown, the material particles have good roundness and excellent dispersibility.

[0092] Example 2

[0093] A method for preparing a modified lithium iron manganese phosphate cathode material includes:

[0094] (1) Weigh manganese porphyrin and manganese tetroxide as manganese source in a molar ratio of 1:3, weigh tetracarboxylated iron phthalocyanine and iron phosphate as iron source in a molar ratio of 1:4, weigh lithium carbonate, iron source, manganese source and ammonium dihydrogen phosphate in a molar ratio of Li:Fe:Mn:P = 1.0:0.3:0.7:1, and weigh activated alumina and manganese porphyrin in a weight ratio of 100:1, wherein the D50 of activated alumina is 350 nm;

[0095] (2) Active alumina and manganese porphyrin with a weight ratio of 0.1:100 were subjected to a hydrothermal reaction at 60°C. After the reaction was carried out for 1 hour, the mixture was transferred to a mixing tank. Water, glucose, lithium carbonate, iron source, manganese source and phosphorus source were added to the mixing tank. After mixing for 1 hour, the mixture was ground to obtain a slurry. The D50 of the solids in the slurry after grinding was controlled to be 300 nm. Among them, based on the total weight of lithium source, iron source, manganese source and phosphorus source, the weight percentage of glucose was 0.8 wt%, and the solid content of the slurry was 20 wt%.

[0096] (3) The above slurry was spray-dried to obtain a precursor with a D50 of 2000 nm; wherein the spray drying temperature was 200℃ and the time was 30 min.

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

[0098] Example 3

[0099] A method for preparing a modified lithium iron manganese phosphate cathode material includes:

[0100] (1) Manganese porphyrin and manganese tetroxide are weighed in a molar ratio of 1:6 as manganese source, tetracarboxylated iron phthalocyanine and iron phosphate are weighed in a molar ratio of 1:5.5 as iron source, lithium carbonate, iron source, manganese source and ammonium dihydrogen phosphate are weighed in a molar ratio of Li:Fe:Mn:P = 1.15:0.5:0.5:1, and activated alumina and manganese porphyrin are weighed in a weight ratio of 100:0.9, wherein the D50 of activated alumina is 550 nm;

[0101] (2) Active alumina and manganese porphyrin with a weight ratio of 0.9:100 were subjected to a hydrothermal reaction at 80°C. After 2 hours of reaction, the mixture was transferred to a mixing tank. Water, glucose, lithium carbonate, iron source, manganese source and phosphorus source were added to the mixing tank. After mixing for 3 hours, the mixture was ground to obtain a slurry. The D50 of the solids in the slurry after grinding was controlled to be 550 nm. The weight percentage of glucose was 0.8 wt% based on the total weight of lithium source, iron source, manganese source and phosphorus source, and the solid content of the slurry was 45 wt%.

[0102] (3) The above slurry was spray-dried to obtain a precursor with a D50 of 2000 nm; wherein the spray drying temperature was 300℃ and the time was 60 min.

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

[0104] Example 4

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

[0106] Example 5

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

[0108] Example 6

[0109] The difference from Example 1 is that in step (1), the molar ratio of supported manganese porphyrin to manganese tetroxide 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] Example 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] Example 13

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

[0124] Example 14

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

[0126] Example 15

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

[0128] Example 16

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

[0130] Example 17

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

[0132] Example 18

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

[0134] Example 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, iron source, manganese source and phosphorus source.

[0136] Comparative Example 1

[0137] (1) Weigh lithium carbonate, iron phosphate, manganese tetroxide and ammonium dihydrogen phosphate according to the stoichiometric ratio of Li:Fe:Mn:P = 1.08:0.4:0.6:1; then weigh glucose at 1.2% of the total mass of the above raw materials and add it to a mixing tank containing deionized water. Then add the weighed lithium source, iron source, manganese source and phosphorus source to the mixing tank in sequence, mix for 2 hours and then grind to obtain a slurry; control the D50 of the solids in the slurry to be 400nm after grinding.

[0138] (2) The above slurry was spray-dried to obtain the precursor; wherein the spray drying temperature was 280℃ and the time was 45min.

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

[0140] The SEM image of the lithium iron manganese phosphate cathode material prepared in Comparative Example 1 is shown below. Figure 2 As shown.

[0141] Comparative Example 2

[0142] The difference from Example 1 is that glucose was not added in step (2).

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

[0144] The modified lithium iron manganese phosphate cathode materials prepared in all Examples 1 to 19 above, and the lithium iron manganese phosphate cathode materials obtained in Comparative Examples 1 and 2 were used as cathode materials, and a simulated battery was assembled with battery-grade lithium sheet as the anode material and lithium hexafluorophosphate as the electrolyte as the main component. 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 sequence. Under the condition of 1C charge and discharge, the capacity retention rate after 300 cycles was tested, and the test results are listed in Table 1.

[0145] Table 1

[0146]

[0147]

[0148] As can be seen from the above description, the 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 supported manganese porphyrin and inorganic manganese compounds. The iron and manganese sources are mixed with lithium, phosphorus, and carbon sources and a solvent to obtain a slurry. A precursor is obtained using spray drying technology, followed by sintering to obtain the modified lithium iron manganese phosphate cathode material. Compared to traditional methods that use inorganic manganese compounds as the manganese source and inorganic iron compounds as the iron source, the preparation method in this application allows some carboxyl groups on the iron phthalocyanine compounds to decompose during sintering, generating locally oxygen-containing substances. The manganese porphyrin reacts rapidly with these oxygen-containing substances, promoting the carbon source towards a higher degree of graphitization, improving the final carbon coating effect, and ensuring carbon coating on the surface of the primary lithium iron manganese phosphate particles. Simultaneously, alumina coats the surface of the primary lithium iron manganese phosphate particles and is interspersed within the carbon coating layer, thereby improving the structural stability of the modified lithium iron manganese phosphate cathode material and inhibiting the dissolution of transition metal elements.

[0150] Moreover, iron phthalocyanine compounds coordinate with free manganese, thereby promoting the atomic-level bonding of manganese and iron atoms in the modified lithium iron manganese phosphate cathode material, which significantly improves the overall consistency of the modified lithium iron manganese phosphate cathode material and the cycle stability during the later use of the battery cell.

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

[0152] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for preparing a modified lithium iron manganese phosphate cathode material, characterized in that, The preparation method of the modified lithium iron manganese phosphate positive electrode material comprises the following steps: In step S1, a lithium source, an iron source, a manganese source, a phosphorus source and a carbon source are mixed 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 comprises an alumina carrier and a manganese porphyrin supported on the surface of the alumina carrier; In step S2, the slurry is subjected to a spray drying treatment to obtain a precursor; In step S3, the precursor is subjected to a sintering treatment 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 cathode material according to claim 1, characterized in that, The molar ratio of Li element in the lithium source, Fe element in the iron source, Mn element in the manganese source and P element in the phosphorus source is (1.0-1.15):(0.3-0.5):(0.7-0.5):

1.

3. The method of claim 1, wherein the modified lithium iron manganese phosphate cathode material is prepared by the steps of: The molar ratio of the solid-supported manganese porphyrin to the inorganic manganese compound is 1:(3-6). ​ 4. The method for preparing the modified lithium iron manganese phosphate cathode material according to claim 3, characterized in that, The inorganic manganese compound is selected from one or more of the group consisting of manganese carbonate, manganese sesquioxide and trimanganese tetraoxide.

5. The method for preparing the modified lithium iron manganese phosphate cathode material according to claim 1, characterized in that, The preparation method further comprises: subjecting active alumina and manganese porphyrin to a hydrothermal reaction to obtain the solid-supported manganese porphyrin.

6. The method for preparing the modified lithium iron manganese phosphate cathode material according to claim 5, characterized in that, The weight ratio of the active alumina to the manganese porphyrin is (0.1-0.9):

100.

7. The method for preparing the modified lithium iron manganese phosphate cathode material according to claim 5, characterized in that, The D50 of the active alumina is 350-550 nm.

8. The method for preparing the modified lithium iron manganese phosphate cathode material according to claim 5, characterized in that, The temperature of the hydrothermal reaction is 60-80°C, and the time is 6-8 h.

9. The method of producing a modified lithium iron manganese phosphate cathode material according to any one of claims 1 to 8, characterized in that, The molar ratio of the iron phthalocyanine compound to the inorganic iron compound is 1:(4-5.5).

10. The method of claim 9, wherein the modified lithium iron manganese phosphate cathode material is prepared by the steps of: mixing a lithium source, an iron source, a manganese source, and a phosphorus source; and heating the mixture to a temperature of 600-800 °C for 6-24 hours in a non-oxidizing atmosphere. The iron phthalocyanine compound is selected from tetracarboxy iron phthalocyanine and / or octacarboxy iron phthalocyanine; and / or, the inorganic iron compound is selected from one or more of the group consisting of diiron trioxide, iron phosphate and ferrous oxalate.

11. The method of claim 9, wherein the modified lithium iron manganese phosphate cathode material is prepared by the steps of: mixing a lithium source, an iron source, a manganese source, and a phosphorus source; and heating the mixture to a temperature of 600-800°C for 6-24 hours in a non-oxidizing atmosphere. The lithium source is selected from one or more of the group consisting of lithium carbonate, lithium dihydrogen phosphate, lithium hydrogen phosphate and lithium hydroxide; and / or, The phosphorus source is selected from one or more of the group consisting of lithium dihydrogen phosphate, ammonium dihydrogen phosphate and iron phosphate; and / or, The solvent is water; and / or, The carbon source is selected from one or more of the group consisting of glucose, sucrose, starch and graphdiyne.

12. The method for preparing the modified lithium iron manganese phosphate cathode material according to claim 11, characterized in that, The weight percentage content of the carbon source is 0.8-1.8 wt% based on the total weight of the lithium source, the iron source, the manganese source and the phosphorus source.

13. The method for preparing the modified lithium iron manganese phosphate cathode material according to claim 1, characterized in that, The solid content of the slurry is 20-45 wt%.

14. The method for preparing the modified lithium iron manganese phosphate cathode material according to claim 1, characterized in that, The mixing process in step S1 is grinding, the grinding time is 1-3 h, and the D50 of the solid substance in the slurry after the grinding is completed is 300-550 nm.

15. The method of claim 1, wherein the modified lithium iron manganese phosphate cathode material is prepared by the steps of: The temperature of the spray drying treatment is 200-300°C, and the time is 30-60 min; and / or, ​ The D50 of the precursor is 2000-5000 nm.

16. The method of claim 1, wherein the modified lithium iron manganese phosphate cathode material is prepared by the steps of: The sintering treatment comprises a first-stage sintering and a second-stage sintering, the temperature of the first-stage sintering is 400-600°C, and the time is 4-6 h, the temperature of the second-stage sintering is 700-800°C, and the time is 6-12 h. ​ 17. The method for preparing the modified lithium iron manganese phosphate cathode material according to claim 1, characterized in that, 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; and the D50 of the modified lithium iron manganese phosphate positive electrode material is 1000-3000 nm.

18. A modified lithium iron manganese phosphate cathode 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 1-17.

19. A lithium-ion battery comprising a positive electrode, a negative electrode, an electrolyte, and a separator disposed between the positive electrode and the negative electrode, wherein, The positive electrode comprises the modified lithium iron manganese phosphate positive electrode material according to claim 18.

Images