Ferromanganese phosphate precursor with high compaction density and preparation method thereof

Abstract

The invention discloses a high-compaction-density ferromanganese phosphate precursor and a preparation method thereof, and belongs to the technical field of lithium batteries, and the provided preparation method comprises the following steps: step 1, respectively dissolving a manganese source, an iron source and a phosphorus source in water to form solutions; 2, adding a complexing agent into the iron source solution to form a complexing iron salt solution; step 3, mixing the complexing ferric salt solution, the manganese source solution and the phosphorus source solution, adding an oxidizing agent and alkali liquor, keeping the pH value of the system to be 5.5-8, heating and stirring for reaction, and synchronously introducing oxygen for bubbling during reaction; and 4, after the reaction is finished, carrying out solid-liquid separation, and drying and roasting to obtain the ferromanganese phosphate precursor. According to the method, under the action of the complexing agent, the homogeneity of iron-manganese coprecipitation is improved, oxygen is introduced for bubbling in the reaction process, and excessive growth of crystals is inhibited while the oxidation condition is ensured, so that the ferromanganese phosphate precursor is proper in particle size and uniform in distribution, and the positive electrode material prepared from the precursor has high compaction density and excellent electrochemical performance.

Description

Technical Field

[0001] The invention belongs to the technical field of lithium batteries, and in particular relates to a high compaction density ferromanganese phosphate precursor and a preparation method thereof. Background Art

[0002] As a high-voltage (3.4-4.1V) phosphate material, lithium iron manganese phosphate is an upgraded product of the phosphate material lithium iron phosphate. Under the same specific capacity, the energy density of lithium iron manganese phosphate battery is 10%-20% higher than that of lithium iron phosphate battery. Compared with ternary materials, lithium iron manganese phosphate has similar energy density, but higher safety and relatively lower price. Therefore, lithium iron manganese phosphate is expected to become a new generation of high-energy density power battery positive electrode material, and its precursor iron manganese phosphate is also receiving more and more attention.

[0003] The composition, structure, particle size, morphology and other performance indicators of ferromanganese phosphate play a vital role in the electrochemical performance of the synthesized lithium iron manganese phosphate material. Therefore, studying the synthesis technology of ferromanganese phosphate is of great significance to improving the electrochemical performance of lithium iron manganese phosphate cathode materials and promoting their industrial application.

[0004] The preparation method of ferromanganese phosphate precursor material is similar to that of iron phosphate, mainly including coprecipitation, hydrothermal method, high temperature solid phase reaction method, spray drying method, etc. In the manufacture of lithium-ion batteries, compaction density has a great influence on battery performance, and compaction density is related to the particle size and uniformity of the particles. Studies have shown that the appropriate average particle size and small distribution range of ferromanganese phosphate materials are helpful to improve the electrochemical reaction activity of the positive electrode material. The selection of different synthesis methods has a very important influence on the particle size and morphology of ferromanganese phosphate, which in turn determines the electrochemical performance of lithium ferromanganese phosphate positive electrode materials to a certain extent.

[0005] The co-precipitation method has a simple process, low synthesis temperature, low equipment requirements, and low investment cost. It is easy to realize industrial production, and compared with other preparation methods, the particle size of the prepared product is more uniform. However, there is also an uneven distribution of elements caused by inconsistent iron and manganese sedimentation rates, which affects the quality of the prepared ferromanganese phosphate. The use of co-precipitation to prepare ferromanganese phosphate precursor materials with suitable and uniform particle size and uniform composition distribution has become an urgent problem to be solved for its application in large-scale production. Summary of the invention

[0006] The purpose of the present invention is to provide a high compaction density ferromanganese phosphate precursor and a preparation method thereof, which overcomes the problem of uneven distribution of iron and manganese in ferromanganese phosphate due to different iron and manganese precipitation rates, and optimizes the preparation process to obtain high-quality ferromanganese phosphate precursor.

[0007] The purpose of the present invention can be achieved through the following technical solutions:

[0008] The present invention provides a method for preparing a ferromanganese phosphate precursor with a high compaction density, comprising the following steps:

[0009] Step 1, dissolving a manganese source, an iron source, and a phosphorus source in water to form a solution;

[0010] Step 2, adding a complexing agent to the iron source solution to form a complex iron salt solution;

[0011] Step 3: Mix the complex iron salt solution, manganese source solution and phosphorus source solution according to the molar ratio of Fe:Mn:PO4=(0.1-0.6):(0.4-0.9):(1.03-1.06), add oxidant and alkali solution, keep the system pH=5.5-8.0, heat and stir to react, and simultaneously introduce oxygen bubbling during the reaction;

[0012] Step 4: After the reaction is completed, solid-liquid separation is performed, and the ferromanganese phosphate precursor is obtained after drying and calcination.

[0013] Further, the manganese source is at least one of manganese sulfate, manganese acetate, manganese nitrate and manganese chloride;

[0014] and / or the iron source is at least one of ferric sulfate, ferric acetate, ferric nitrate and ferric chloride;

[0015] And / or the phosphorus source is at least one of diammonium phosphate and phosphoric acid.

[0016] Furthermore, in step 1, the manganese source, iron source and phosphorus source are dissolved in water at a concentration of 0.5-1 mol / L to form a solution.

[0017] Further, the complexing agent is at least one of citric acid, L-tartaric acid, and malic acid;

[0018] In step 2, the complexing agent is added to the iron source solution at a molar ratio of the complexing agent to iron of 1:1-4.

[0019] Furthermore, the oxidant is at least one of hydrogen peroxide and ammonium persulfate, and the amount of the oxidant added is 5%-10% of the total mass of the complex iron salt solution, the manganese source solution and the phosphorus source solution.

[0020] Furthermore, the alkali solution is at least one of aqueous ammonia, sodium carbonate and sodium hydroxide.

[0021] Furthermore, the heating and stirring reaction temperature is 30-50°C, and the reaction time is 4-7h.

[0022] Furthermore, the oxygen bubbling gas velocity is 1-3 cm / s.

[0023] Furthermore, the calcination temperature is 300-600° C., and the calcination time is 3-8 hours.

[0024] The present invention also provides a ferromanganese phosphate precursor obtained by the method for preparing the ferromanganese phosphate precursor with high compaction density as described above.

[0025] Beneficial effects of the present invention:

[0026] (1) The present invention utilizes a chelating agent and an iron salt to form a complex, which is then mixed with a manganese source solution and a phosphorus source solution for reaction. The reaction of trivalent iron with phosphoric acid to form a precipitate requires overcoming the coordination effect of the complex, which slows down the precipitation rate compared to the direct reaction of the iron salt and phosphoric acid. By controlling the amount of the chelating agent and the reaction conditions, the uniformity of the iron-manganese co-precipitation is improved, the uniformity of the iron-manganese distribution in the manganese iron phosphate is improved, and the electrochemical performance of the prepared positive electrode material is enhanced.

[0027] (2) In the present invention, oxygen is bubbled during the reaction process. On the one hand, oxygen can ensure oxidation conditions and inhibit the generation of divalent metal ions. On the other hand, the bubbling effect causes instability of the precipitation in the solution and inhibits excessive growth of crystals in the precipitation. The prepared ferromanganese phosphate precursor has an appropriate particle size and uniform distribution, and the prepared positive electrode material has a high compaction density. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] The present invention will be further described below in conjunction with the accompanying drawings.

[0029] Figure 1 This is a SEM image of the ferromanganese phosphate precursor prepared in Example 1 of the present invention. DETAILED DESCRIPTION

[0030] The following will be combined with the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0031] Example 1

[0032] Step 1, dissolving manganese sulfate, ferric sulfate and ammonium dihydrogen phosphate in water to form solutions, wherein the concentration of the solutions is 0.5 mol / L;

[0033] Step 2, adding citric acid to the ferric sulfate solution in a molar ratio of citric acid to Fe of 1:4 to form a complex iron salt solution;

[0034] Step 3: Mix the complex iron salt solution, manganese sulfate solution and ammonium dihydrogen phosphate solution according to the molar ratio of Fe:Mn:PO4=0.6:0.4:1.03, add 30% hydrogen peroxide solution according to 10% of the total mass of the complex iron salt solution, manganese sulfate solution and ammonium dihydrogen phosphate solution, and then add 25% ammonia water, keep the system pH=5.5, heat to 30°C and stir to react for 7h, and simultaneously introduce oxygen bubbling during the reaction at a gas velocity of 1cm / s;

[0035] Step 4: After the reaction is completed, the reaction mixture is filtered and the solid is washed with deionized water after solid-liquid separation, and then filtered and dried at 100° C. for 6 h. After drying, the mixture is calcined at 300° C. for 8 h to obtain a manganese iron phosphate precursor.

[0036] Example 2

[0037] The only difference from Example 1 is that the molar ratio of citric acid to Fe is adjusted to 1:3, and the other conditions and steps are the same as Example 1.

[0038] Example 3

[0039] The only difference from Example 1 is that the molar ratio of citric acid to Fe is adjusted to 1:1, and the other conditions and steps are the same as Example 1.

[0040] Example 4

[0041] The only difference from Example 2 is that the complex iron salt solution, manganese sulfate solution and diammonium phosphate solution are mixed in a molar ratio of Fe:Mn:PO4=0.4:0.6:1.03, and the other conditions and steps are the same as Example 2.

[0042] Example 5

[0043] The only difference from Example 2 is that the complex iron salt solution, manganese sulfate solution and diammonium phosphate solution are mixed in a molar ratio of Fe:Mn:PO4=0.1:0.9:1.03, and the other conditions and steps are the same as Example 2.

[0044] Example 6

[0045] The only difference from Example 4 is that in step 3, the system pH is maintained at 6.0, and the other steps and conditions are the same as in Example 4.

[0046] Example 7

[0047] The only difference from Example 4 is that in step 3, the system pH is maintained at 8.0, and the other steps and conditions are the same as in Example 4.

[0048] Example 8

[0049] The only difference from Example 6 is that in step 3, the mixture is heated to 40° C. and stirred for reaction for 5 h. The other steps and conditions are the same as those in Example 6.

[0050] Example 9

[0051] The only difference from Example 6 is that in step 3, the mixture is heated to 50° C. and stirred for reaction for 4 h. The other steps and conditions are the same as those in Example 6.

[0052] Example 10

[0053] The only difference from Example 6 is that the gas velocity of oxygen bubbling in step 3 is 2 cm / s, and the other steps and conditions are the same as Example 6.

[0054] Embodiment 11

[0055] The only difference from Example 6 is that the gas velocity of oxygen bubbling in step 3 is 3 cm / s, and the other steps and conditions are the same as Example 6.

[0056] Comparative Example 1

[0057] Compared with Example 1, citric acid is not added in step 2 of this comparative example, and the specific steps are as follows:

[0058] Step 1, dissolving manganese sulfate, ferric sulfate and ammonium dihydrogen phosphate in water to form solutions, wherein the concentration of the solutions is 0.5 mol / L;

[0059] Step 3: Mix the ferric sulfate solution, manganese sulfate solution and diammonium phosphate solution according to the molar ratio of Fe:Mn:PO4=0.6:0.4:1.03, add 30% hydrogen peroxide solution according to 10% of the total mass of the ferric sulfate solution, manganese sulfate solution and diammonium phosphate solution, and then add 25% ammonia water, keep the system pH=5.5, heat to 30°C and stir to react for 7h, and simultaneously introduce oxygen bubbling during the reaction at a gas velocity of 1cm / s;

[0060] Step 4: After the reaction is completed, the reaction mixture is filtered and the solid is washed with deionized water after solid-liquid separation, and then filtered and dried at 100° C. for 6 h. After drying, the mixture is calcined at 300° C. for 8 h to obtain a manganese iron phosphate precursor.

[0061] Comparative Example 2

[0062] Compared with Example 1, oxygen bubbling is not introduced in step 3 of this comparative example, and the specific steps are as follows:

[0063] Step 1, dissolving manganese sulfate, ferric sulfate and ammonium dihydrogen phosphate in water to form solutions, wherein the concentration of the solutions is 0.5 mol / L;

[0064] Step 2, adding citric acid to the ferric sulfate solution in a molar ratio of citric acid to Fe of 1:4 to form a complex iron salt solution;

[0065] Step 3: Mix the complex iron salt solution, manganese sulfate solution and diammonium phosphate solution according to the molar ratio of Fe:Mn:PO4=0.6:0.4:1.03, add 30% hydrogen peroxide solution according to 10% of the total mass of the complex iron salt solution, manganese sulfate solution and diammonium phosphate solution, and then add 25% ammonia water, keep the system pH=5.5, heat to 30°C and stir to react for 7h;

[0066] Step 4: After the reaction is completed, the reaction mixture is filtered and the solid is washed with deionized water after solid-liquid separation, and then filtered and dried at 100° C. for 6 h. After drying, the mixture is calcined at 300° C. for 8 h to obtain a manganese iron phosphate precursor.

[0067] The performance of the precursors prepared in Example 1 to Example 11 and Comparative Example 1 to Comparative Example 2 was tested, and the results are shown in Table 1.

[0068] The precursors prepared in Examples 1 to 11 and Comparative Examples 1 to 2 and lithium carbonate were mixed at a molar ratio of (Fe+Mn): Li=1:1.05 to obtain a mixture, glucose accounting for 10% of the mass of the mixture was added, and water accounting for 60% of the total mass was added after mixing, and the mixture was stirred and spray-dried after being evenly mixed, calcined at 750° C. for 12 hours under a nitrogen atmosphere, cooled to room temperature, and passed through a 200-mesh sieve to obtain a lithium manganese iron phosphate positive electrode material. The prepared positive electrode material was subjected to performance testing, and the results are shown in Table 2.

[0069] Table 1

[0070]

[0071] Table 2

[0072]

[0073] As can be seen from Table 1, since no oxygen bubbling was introduced in Comparative Example 2, crystal growth was difficult to control during the precipitation process, resulting in a larger particle size of the prepared precursor than in Example 1. In Example 8 and Example 9, the reaction temperature and duration were adjusted on the basis of Example 6, and the corresponding temperature was increased, the reaction time was shortened, and the precipitate was rapidly formed in a short time, resulting in a wide distribution of the particle size of the prepared precursor particles. In Example 10 and Example 11, the gas velocity of bubbling was gradually increased on the basis of Example 6. The increase in gas velocity increased the fluidity of the reaction solution. Too high a gas velocity would cause turbulence in the solution and make it difficult to form a precipitate. In Example 10, the gas velocity was appropriately increased to create oxidation conditions while suppressing the excessive growth of precipitated crystals, and the particle size of the prepared precursor particles was uniformly distributed.

[0074] As can be seen from Table 2, the increase in the amount of complexing agent in Examples 1 to 3 balances the precipitation rate of iron and manganese, making the precipitation components more uniform, but the amount of complexing agent in Example 3 is too much, resulting in a too slow precipitation rate of iron phosphate, a decrease in the uniformity of the precursor components, and a corresponding decrease in its capacity. No complexing agent was added in Comparative Example 1, resulting in uneven precursor components. The electrochemical performance of the positive electrode material prepared using the precursor of Comparative Example 1 is significantly inferior to that of Example 1. The difference between Example 4 and Example 5 and Example 1 is that the ratio of iron and manganese is adjusted. Excessive manganese content will lead to the John-Teller effect of manganese, which reduces the capacity of the material. In Example 6, the reaction pH is adjusted to 6.0, and the electrochemical performance of the positive electrode material prepared by this precursor is better than that prepared by other reaction pH values.

[0075] It should be noted that, in this article, relational terms such as first and second, etc. are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Moreover, the terms "include", "comprise" or any other variants thereof are intended to cover non-exclusive inclusion, so that a process, method, article or device including a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, method, article or device.

[0076] Although embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions and variations may be made to the embodiments without departing from the principles and spirit of the present invention, and that the scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A method for preparing a ferromanganese phosphate precursor with a high compaction density, characterized in that: The following steps are involved: Step 1, dissolving a manganese source, an iron source, and a phosphorus source in water to form a solution; Step 2, adding a complexing agent to the iron source solution to form a complex iron salt solution; Step 3: Mix the complex iron salt solution, manganese source solution and phosphorus source solution according to the molar ratio of Fe:Mn:PO4=(0.1-0.6):(0.4-0.9):(1.03-1.06), add oxidant and alkali solution, keep the system pH=5.5-8, heat and stir to react, and simultaneously introduce oxygen bubbling during the reaction; Step 4: After the reaction is completed, solid-liquid separation is performed, and the ferromanganese phosphate precursor is obtained after drying and calcination.

2. The method for preparing a ferromanganese phosphate precursor with a high compaction density according to claim 1, characterized in that: The manganese source is at least one of manganese sulfate, manganese acetate, manganese nitrate and manganese chloride; and / or the iron source is at least one of ferric sulfate, ferric acetate, ferric nitrate and ferric chloride; And / or the phosphorus source is at least one of diammonium phosphate and phosphoric acid.

3. The method for preparing a ferromanganese phosphate precursor with a high compaction density according to claim 1, characterized in that: In step 1, a manganese source, an iron source, and a phosphorus source are dissolved in water at a concentration of 0.5-1 mol / L to form a solution.

4. The method for preparing a ferromanganese phosphate precursor with a high compaction density according to claim 1, characterized in that: The complexing agent is at least one of citric acid, L-tartaric acid and malic acid; In step 2, the complexing agent is added to the iron source solution at a molar ratio of the complexing agent to iron of 1:1-4.

5. The method for preparing a ferromanganese phosphate precursor with a high compaction density according to claim 1, characterized in that: The oxidant is at least one of hydrogen peroxide and ammonium persulfate, and the added amount of the oxidant is 5%-10% of the total mass of the complex iron salt solution, the manganese source solution and the phosphorus source solution.

6. The method for preparing a ferromanganese phosphate precursor with a high compaction density according to claim 1, characterized in that: The alkali solution is at least one of ammonia water, sodium carbonate and sodium hydroxide.

7. The method for preparing a ferromanganese phosphate precursor with a high compaction density according to claim 1, characterized in that: The heating and stirring reaction temperature is 30-50° C., and the reaction time is 4-7 hours.

8. The method for preparing a ferromanganese phosphate precursor with a high compaction density according to claim 1, characterized in that: The gas velocity of the oxygen bubbling is 1-3 cm / s.

9. The method for preparing a ferromanganese phosphate precursor with high compaction density according to claim 1, characterized in that: The calcination temperature is 300-600° C., and the calcination time is 3-8 hours.

10. A high compaction density ferromanganese phosphate precursor, characterized in that: The ferromanganese phosphate precursor is prepared by the method for preparing a ferromanganese phosphate precursor with a high compaction density as described in any one of claims 1 to 9.

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