Manganese iron oxalate with in-situ carbon-coated core-shell structure and preparation method thereof

Abstract

The application relates to a manganese iron oxalate with an in-situ carbon-coated core-shell structure and a preparation method thereof, and the technical scheme points are as follows: manganese source, iron source and carbon source are weighed according to the stoichiometric ratio, and are added into deionized water to prepare manganese solution, iron solution and carbon source solution with certain concentrations; the manganese solution is quickly added into an oxalic acid solution containing a particle inhibitor and is continuously stirred at high speed; then the iron solution and the carbon source solution are added into the oxalic acid solution immediately when manganese oxalate fine particles are formed, the ferrous oxalate crystal nucleus continues to grow on the surface of the manganese oxalate particles, the ferrous oxalate wraps the manganese oxalate, the manganese iron oxalate core-shell structure is formed, and carbon coating is performed on the surface of the manganese iron oxalate core-shell structure. The generated manganese iron oxalate is filtered, washed and dried to obtain the manganese iron oxalate powder with the carbon-coated core-shell structure. The application enhances the electronic conductivity of the manganese iron lithium phosphate and improves the electrochemical performance.

Description

Technical Field

[0001] This invention relates to the field of inorganic fine chemical technology, specifically to an in-situ carbon-coated core-shell structure of manganese iron oxalate and its preparation method. Background Technology

[0002] With the continuous development of science and technology, energy and environmental problems are becoming increasingly serious. The reduction of traditional energy sources such as coal, oil, and natural gas, and the environmental and climate pollution caused by exhaust emissions, make the development of environmentally friendly new energy sources and the research on high-performance environmentally friendly energy storage and conversion materials important topics in energy research today.

[0003] Lithium manganese iron phosphate (LFP) combines the safety and low cost of lithium iron phosphate (LFP) while increasing energy density by 10-20%, making it a potential replacement for LFP batteries in power applications. LFP is an upgraded version of LFP, increasing voltage through manganese solution, thereby improving energy density (up to 21%), but this compromises cycle and rate performance. In terms of application, LFP can be mixed with high-nickel ternary lithium batteries to obtain products that combine safety and high energy density, forming a series of range solutions. However, using LFP alone is more economical, and it is expected to become a long-term trend once the material technology matures. However, LFP has poor conductivity and is prone to manganese leaching during high-temperature cycling, requiring atomic-level mixing and high crystallinity. To address these issues, this invention provides an in-situ carbon-coated core-shell structure of manganese iron oxalate and its preparation method to solve the problems of poor conductivity and manganese ion leaching in LFP. Summary of the Invention

[0004] The purpose of this invention is to provide an in-situ carbon-coated core-shell structure of manganese iron oxalate and its preparation method, so as to solve the problems of poor conductivity and manganese ion dissolution in the prior art of lithium manganese iron phosphate.

[0005] To achieve the above objectives, the present invention provides the following technical solution:

[0006] The first aspect of this invention provides a method for preparing in-situ carbon-coated core-shell structured manganese iron oxalate, comprising the following steps:

[0007] Step (1): Weigh a certain amount of iron salt and manganese salt solids according to the chemical molar ratio, add an appropriate amount of deionized water to dissolve them, and obtain iron solution and manganese solution respectively. The concentration of the metal solution is 0.1-3.0 mol / L.

[0008] Step (2): Weigh a certain amount of carbon source and add it to the iron solution, and stir it evenly. The concentration of carbon source is 0.1-100 g / L.

[0009] Step (3): According to the molar ratio of metal solution to precipitant of 1:1 to 1.5, weigh a certain mass of precipitant and particle inhibitor, add deionized water to dissolve and obtain a mixed solution. The concentration of precipitant solution is 0.1 to 3.0 mol / L, and the amount of particle inhibitor is 0.5% to 20% of the sum of the amounts of iron salt and manganese salt.

[0010] Step (4): Add the prepared precipitant and particle inhibitor into the reactor, seal it, and then bubble it to remove oxygen.

[0011] Step (5): The prepared manganese solution is added dropwise to the mixed solution of precipitant and particle inhibitor at a certain flow rate;

[0012] Step (6): Under inert gas protection, react at room temperature for 1.0-60 min to obtain a fine-particle manganese oxalate suspension;

[0013] Step (7): When fine manganese oxalate particles are generated in the solution, the mixed solution of iron and carbon source is quickly added dropwise to the mixed solution of precipitant and particle inhibitor at a certain flow rate, and the heating is turned on.

[0014] Step (8): Under inert gas protection, the reaction is carried out at a constant temperature for 0.5-48 hours to obtain a suspension of manganese iron oxalate precursor with a core-shell structure.

[0015] Step (9): After the reaction is completed, the manganese ferric oxalate suspension is taken out from the reactor and successively filtered, washed and dried to obtain manganese ferric oxalate precursor powder.

[0016] Preferably, in step (1), the molar ratio of iron salt to manganese salt is 1:1 to 5, and the concentrations of the two metal solutions are 0.1 to 3.0 mol / L, respectively.

[0017] Preferably, the particle inhibitor in step (3) is one or more of polyvinylpyrrolidone, polyacrylamide, and ethylene glycol; the amount of the particle inhibitor is 0.5% to 20% of the sum of the amounts of iron salt and manganese salt.

[0018] Preferably, in step (3), the molar ratio of the metal solution to the precipitant is 1:1 to 1.5; and the concentration of the precipitant solution is 0.1 to 3.0 mol / L.

[0019] Preferably, the metal solution is added at a rate of 0.01 to 1.0 L / min in step (5).

[0020] Preferably, in step (7), the metal solution is added at a rate of 0.01 to 1.0 L / min and the reaction temperature is 20 to 100 °C.

[0021] Preferably, the bubbling gas in step (8) is one of argon, nitrogen, or helium, the reaction temperature is 20–100°C, and the reaction time is 0.5–48 h.

[0022] A second aspect of the present invention provides an in-situ carbon-coated core-shell structure of ferromanganese oxalate, wherein the ferromanganese oxalate is prepared by the method described in the first aspect of the present invention.

[0023] The present invention has at least the following beneficial effects:

[0024] (1) The present invention provides an in-situ carbon-coated core-shell structure of manganese iron oxalate and its preparation method. The manganese iron oxalate synthesized by liquid phase co-precipitation method can effectively solve the problems of poor conductivity and manganese ion dissolution of lithium manganese iron phosphate, realize atomic-level mixing of manganese iron elements and have good crystallinity, enhance the electronic conductivity of lithium manganese iron phosphate and improve electrochemical performance.

[0025] (2) The present invention provides an in-situ carbon-coated core-shell structure of manganese iron oxalate and its preparation method, which effectively avoids the dissolution of manganese ions and their reaction with the electrolyte, thereby improving the cycle life of the battery. Attached Figure Description

[0026] Figure 1 Mn obtained in Example 1 0.6 Fe 0.4 X-ray (XRD) image of C2O4·2H2O@GO;

[0027] Figure 2 Mn obtained in Example 1 0.6 Fe 0.4 Scanning electron microscope (SEM) image of C2O4·2H2O@GO. Detailed Implementation

[0028] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0029] The technical solution of this invention is as follows: Manganese source, iron source, and carbon source are weighed according to stoichiometric ratios. Deionized water is added to prepare manganese solution, iron solution, and carbon source solution of specific concentrations. The manganese solution is rapidly added to an oxalic acid solution containing a particle inhibitor while continuously stirring at high speed. Subsequently, as fine manganese oxalate particles are formed, the iron solution and carbon source solution are immediately added to the oxalic acid solution, allowing ferrous oxalate crystal nuclei to continue growing on the surface of the manganese oxalate particles, achieving the encapsulation of manganese oxalate by ferrous oxalate, thereby forming a manganese-iron core-shell structure. Carbon is then applied to the surface of the manganese-iron core-shell structure. The generated manganese-iron oxalate is filtered, washed, and dried to obtain carbon-coated manganese-iron oxalate powder with a core-shell structure.

[0030] The specific steps are as follows:

[0031] Step (1): Weigh a certain amount of iron salt and manganese salt solids according to the chemical molar ratio, add an appropriate amount of deionized water to dissolve them, and obtain iron solution and manganese solution respectively. The concentration of the metal solution is 0.1-3.0 mol / L.

[0032] Step (2): Weigh a certain amount of carbon source and add it to the iron solution, and stir it evenly. The concentration of carbon source is 0.1-100 g / L.

[0033] Step (3): According to the molar ratio of metal solution to precipitant of 1:1 to 1.5, weigh a certain mass of precipitant and particle inhibitor, add deionized water to dissolve and obtain a mixed solution. The concentration of precipitant solution is 0.1 to 3.0 mol / L, and the amount of particle inhibitor is 0.5% to 20% of the sum of the amounts of iron salt and manganese salt.

[0034] Step (4): Add the prepared precipitant and particle inhibitor into the reactor, seal it, and then bubble it to remove oxygen.

[0035] Step (5): The prepared manganese solution is added dropwise to the mixed solution of precipitant and particle inhibitor at a certain flow rate;

[0036] Step (6): Under inert gas protection, react at room temperature for 1.0-60 min to obtain a fine-particle manganese oxalate suspension;

[0037] Step (7): When fine manganese oxalate particles are generated in the solution, the mixed solution of iron and carbon source is quickly added dropwise to the mixed solution of precipitant and particle inhibitor at a certain flow rate, and the heating is turned on.

[0038] Step (8): Under inert gas protection, the reaction is carried out at a constant temperature for 0.5-48 hours to obtain a suspension of manganese iron oxalate precursor with a core-shell structure.

[0039] Step (9): After the reaction is completed, the manganese ferric oxalate suspension is taken out from the reactor and successively filtered, washed and dried to obtain manganese ferric oxalate precursor powder.

[0040] The iron salt in step (1) includes, but is not limited to, one or more of ferrous nitrate, ferrous sulfate, ferrous acetate, and ferrous chloride; the ferrous sulfate can be anhydrous ferrous sulfate or hydrated ferrous sulfate, specifically one or more of anhydrous ferrous sulfate, ferrous sulfate monohydrate, and ferrous sulfate heptahydrate.

[0041] The manganese salt in step (1) includes, but is not limited to, one or more of manganese nitrate, manganese sulfate, manganese acetate, and manganese chloride; manganese sulfate can be ahydrous manganese sulfate or hydrated manganese sulfate, specifically one or more of anhydrous manganese sulfate, manganese sulfate monohydrate, and manganese sulfate tetrahydrate.

[0042] In step (1), the molar ratio of iron salt to manganese salt is 1:1 to 5, and the concentrations of the two metal solutions are 0.1 to 3.0 mol / L, respectively.

[0043] In step (2), the carbon source is one or more of glucose, phenolic resin, citric acid, and graphene, with a concentration of 0.1 to 100 g / L.

[0044] In step (3), the precipitant is oxalate, and examples of oxalate include, but are not limited to, one or more of oxalic acid, potassium oxalate, and sodium oxalate.

[0045] In step (3), the particle inhibitor is one or more of polyvinylpyrrolidone, polyacrylamide, and ethylene glycol, and the amount of particle inhibitor used is 0.5% to 20% of the sum of the amounts of iron salt and manganese salt.

[0046] In step (3), the molar ratio of metal solution to precipitant is 1:1 to 1.5, and the concentration of precipitant solution is 0.1 to 3.0 mol / L.

[0047] The bubbling gas used in step (4) is one of argon, nitrogen, or helium.

[0048] In step (5), the metal solution is added at a rate of 0.01 to 1.0 L / min.

[0049] In step (6), the inert gas is one of argon, nitrogen, or helium, and the reaction time is 1.0-60 min.

[0050] In step (7), the metal solution is added at a rate of 0.01 to 1.0 L / min and the reaction temperature is 20 to 100 °C.

[0051] The bubbling gas used in step (8) is one of argon, nitrogen, or helium, the reaction temperature is 20-100℃, and the reaction time is 0.5-48h.

[0052] This invention uses a liquid-phase co-precipitation method to synthesize an in-situ carbon-coated core-shell structured manganese iron oxalate, which is then used as a raw material to synthesize lithium manganese iron phosphate. This method effectively solves the problems of poor conductivity and manganese ion dissolution in lithium manganese iron phosphate, achieving atomic-level mixing of manganese and iron elements with good crystallinity, thereby improving electrochemical performance.

[0053] Based on the above methods, the present invention provides the following partial embodiments:

[0054] Unless otherwise specified, the raw materials, reagents or devices used in the following examples are available from conventional commercial sources or can be obtained by existing known methods.

[0055] Example 1:

[0056] A carbon-coated core-shell structured manganese iron oxalate with the molecular formula Mn 0.6 Fe 0.4 The preparation method of C2O4·2H2O@GO includes the following steps:

[0057] Step 1: Weigh 27.8g of ferrous sulfate heptahydrate according to the stoichiometric ratio and dissolve it in 200mL of deionized water. Weigh 25.35g of manganese sulfate monohydrate and dissolve it in 300mL of deionized water to obtain iron and manganese solutions with a concentration of 0.5mol / L.

[0058] Step 2: Weigh 5.32g of graphene and add it to the iron solution and mix well to obtain a graphene solution with a concentration of 26.6g / L.

[0059] Step 3: Weigh 31.52g of oxalic acid dihydrate into a beaker, add 500mL of deionized water to dissolve it, and obtain an oxalic acid solution with a concentration of 0.5mol / L. Then weigh 1.06g of polyacrylamide into the oxalic acid solution and stir to mix evenly.

[0060] Step 4: Pour the dissolved oxalic acid solution and particle inhibitor solution into the reactor, start stirring at 400 r / min, and continuously bubble to remove oxygen for 10 min under nitrogen protection.

[0061] Step 5: Slowly add the manganese solution dropwise at a rate of 0.1 L / min into the reaction vessel containing the oxalic acid solution and the particle inhibitor. After the manganese solution is added, react for 2 minutes, and then fine manganese oxalate particles are immediately generated in the reaction vessel.

[0062] Step 6: When a large number of fine manganese oxalate particles are generated in the reaction vessel and the reaction is complete, under nitrogen protection, a mixed solution of iron and graphene is added dropwise to the reaction vessel at a rate of 0.5 L / min, the temperature is raised to 40℃, and the reaction is kept at a constant temperature for 8 hours to obtain graphene-coated core-shell structured iron manganese oxalate.

[0063] Step 7: After the reaction is complete, the entire manganese ferric oxalate mixed solution is collected from the reaction vessel, filtered under reduced pressure, and repeatedly washed with deionized water until the filtrate is clear. The filter cake is then dried under vacuum at 80°C for 12 hours to obtain manganese ferric oxalate precursor powder.

[0064] Example 2:

[0065] A carbon-coated core-shell structured manganese iron oxalate with the molecular formula Mn 0.7 Fe 0.3 The preparation method of C2O4·2H2O@GO includes the following steps:

[0066] Step 1: Weigh out 41.7g of ferrous sulfate heptahydrate according to the stoichiometric ratio and dissolve it in 300mL of deionized water. Weigh out 59.16g of manganese sulfate monohydrate and dissolve it in 700mL of deionized water to obtain iron and manganese solutions with a concentration of 0.5mol / L.

[0067] Step 2: Weigh 7.98g of graphene and add it to the iron solution and mix well to obtain a graphene solution of 26.6g / L.

[0068] Step 3: Weigh 63.04g of oxalic acid dihydrate into a beaker, add 1000mL of deionized water to dissolve it, and obtain an oxalic acid solution with a concentration of 0.5mol / L. Then weigh 2.02g of polyacrylamide into the oxalic acid solution and stir to mix evenly.

[0069] Step 4: Pour the dissolved oxalic acid solution and particle inhibitor solution into the reactor, start stirring at 400 r / min, and continuously bubble to remove oxygen for 10 min under nitrogen protection.

[0070] Step 5: Slowly add the manganese solution dropwise at a rate of 0.1 L / min into the reaction vessel containing the oxalic acid solution and the particle inhibitor. After the manganese solution is added, react for 2 minutes, and then fine manganese oxalate particles are immediately generated in the reaction vessel.

[0071] Step 6: When a large number of fine manganese oxalate particles are generated in the reaction vessel and the reaction is complete, under nitrogen protection, a mixed solution of iron and graphene is added dropwise to the reaction vessel at a rate of 0.5 L / min, the temperature is raised to 40℃, and the reaction is kept at a constant temperature for 8 hours to obtain graphene-coated core-shell structured iron manganese oxalate.

[0072] Step 7: After the reaction is complete, the entire manganese ferric oxalate mixed solution is collected from the reaction vessel, filtered under reduced pressure, and repeatedly washed with deionized water until the filtrate is clear. The filter cake is then dried under vacuum at 80°C for 12 hours to obtain manganese ferric oxalate precursor powder.

[0073] Example 3:

[0074] A carbon-coated core-shell structured manganese iron oxalate with the molecular formula Mn 0.8 Fe 0.2 The preparation method of C2O4·2H2O@GO includes the following steps:

[0075] Step 1: Weigh 27.8g of ferrous sulfate heptahydrate according to the stoichiometric ratio and dissolve it in 200mL of deionized water. Weigh 67.61g of manganese sulfate monohydrate and dissolve it in 800mL of deionized water to obtain iron and manganese solutions with a concentration of 0.5mol / L.

[0076] Step 2: Weigh 5.32g of graphene and add it to the iron solution and mix well to obtain a graphene solution with a concentration of 26.6g / L.

[0077] Step 3: Weigh 63.04g of oxalic acid dihydrate into a beaker, add 1000mL of deionized water to dissolve it, and obtain an oxalic acid solution with a concentration of 0.5mol / L. Then weigh 1.91g of polyacrylamide into the oxalic acid solution and stir to mix evenly.

[0078] Step 4: Pour the dissolved oxalic acid solution and particle inhibitor solution into the reactor, start stirring at 400 r / min, and continuously bubble to remove oxygen for 10 min under nitrogen protection.

[0079] Step 5: Slowly add the manganese solution dropwise at a rate of 0.1 L / min into the reaction vessel containing the oxalic acid solution and the particle inhibitor. After the manganese solution is added, react for 2 minutes, and then fine manganese oxalate particles are immediately generated in the reaction vessel.

[0080] Step 6: When a large number of fine manganese oxalate particles are generated in the reaction vessel and the reaction is complete, under nitrogen protection, a mixed solution of iron and graphene is added dropwise to the reaction vessel at a rate of 0.5 L / min, the temperature is raised to 40℃, and the reaction is kept at a constant temperature for 8 hours to obtain graphene-coated core-shell structured iron manganese oxalate.

[0081] Step 7: After the reaction is complete, the entire manganese ferric oxalate mixed solution is collected from the reaction vessel, filtered under reduced pressure, and repeatedly washed with deionized water until the filtrate is clear. The filter cake is then dried under vacuum at 80°C for 12 hours to obtain manganese ferric oxalate precursor powder.

[0082] The product prepared in Example 1 above was subjected to XRD and SEM analysis, and the results are as follows: Figure 1-2 As shown.

[0083] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above, and that the invention can be implemented in other specific forms without departing from its spirit or basic characteristics. Therefore, the embodiments should be considered exemplary and non-limiting in all respects, and the scope of the invention is defined by the appended claims rather than the foregoing description. Thus, it is intended that all variations falling within the meaning and scope of equivalents of the claims be included within the present invention.

[0084] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A method for preparing in-situ carbon-coated core-shell structured manganese iron oxalate, characterized in that, Includes the following steps: Step (1): Weigh a certain amount of iron salt and manganese salt solids according to the chemical molar ratio, add an appropriate amount of deionized water to dissolve them, and obtain iron solution and manganese solution respectively. The concentration of the metal solution is 0.1-3.0 mol / L. Step (2): Weigh a certain amount of carbon source and add it to the iron solution, and stir it evenly. The concentration of carbon source is 0.1-100 g / L. Step (3): According to the molar ratio of metal solution to precipitant of 1:1 to 1.5, weigh a certain mass of precipitant and particle inhibitor, add deionized water to dissolve and obtain a mixed solution. The concentration of precipitant solution is 0.1 to 3.0 mol / L, and the amount of particle inhibitor is 0.5% to 20% of the sum of the amounts of iron salt and manganese salt. Step (4): Add the prepared precipitant and particle inhibitor into the reactor, seal it, and then bubble it to remove oxygen. Step (5): The prepared manganese solution is added dropwise to the mixed solution of precipitant and particle inhibitor at a certain flow rate; Step (6): Under inert gas protection, react at room temperature for 1.0-60 min to obtain a fine-particle manganese oxalate suspension; Step (7): When fine manganese oxalate particles are generated in the solution, the mixed solution of iron and carbon source is quickly added dropwise to the mixed solution of precipitant and particle inhibitor at a certain flow rate, and the heating is turned on. Step (8): Under inert gas protection, the reaction is carried out at a constant temperature for 0.5-48 hours to obtain a suspension of manganese iron oxalate precursor with a core-shell structure. Step (9): After the reaction is completed, the manganese ferric oxalate suspension is taken out from the reactor and successively filtered, washed and dried to obtain manganese ferric oxalate precursor powder.

2. The method for preparing in-situ carbon-coated core-shell structured manganese iron oxalate according to claim 1, characterized in that, In step (1), the molar ratio of iron salt to manganese salt is 1:1 to 5, and the concentrations of the two metal solutions are 0.1 to 3.0 mol / L, respectively.

3. The method for preparing in-situ carbon-coated core-shell structured ferromanganate according to claim 1, characterized in that, In step (3), the particle inhibitor is one or more of polyvinylpyrrolidone, polyacrylamide, and ethylene glycol; the amount of the particle inhibitor is 0.5% to 20% of the sum of the amounts of iron salt and manganese salt.

4. The method for preparing in-situ carbon-coated core-shell structured ferric manganese oxalate according to claim 1, characterized in that, In step (3), the molar ratio of the metal solution to the precipitant is 1:1 to 1.5; the concentration of the precipitant solution is 0.1 to 3.0 mol / L.

5. The method for preparing in-situ carbon-coated core-shell structured ferromanganate according to claim 1, characterized in that, In step (5), the metal solution is added at a rate of 0.01 to 1.0 L / min.

6. The method for preparing in-situ carbon-coated core-shell structured ferromanganate according to claim 1, characterized in that, In step (7), the metal solution is added at a rate of 0.01 to 1.0 L / min and the reaction temperature is 20 to 100 °C.

7. The method for preparing in-situ carbon-coated core-shell structured manganese iron oxalate according to claim 1, characterized in that, In step (8), the bubbling gas is one of argon, nitrogen, or helium, the reaction temperature is 20–100°C, and the reaction time is 0.5–48 h.

8. A type of in-situ carbon-coated core-shell structured manganese iron oxalate, characterized in that, The manganese ferric oxalate is prepared by the method described in any one of claims 1 to 7.

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