Manganese iron precursor, preparation method thereof and cathode material

Abstract

The application discloses a manganese-iron precursor, a preparation method thereof and a positive electrode material, and belongs to the technical field of positive electrode materials. x Mn y (OH)2, wherein 0.3<=x<=0.7, and x+y=1; a first coating layer coated on at least part of the surface of the inner core and composed of xanthate; and a second coating layer coated on at least part of the surface of the first coating layer and composed of M(OH)2, wherein M is one or more of Mg, Co, Zn, Al, Ti, Zr, Nb, La, Mo and W. The synergistic effect of the first coating layer and the second coating layer can make the sodium battery positive electrode material or the lithium iron phosphate positive electrode material prepared from the manganese-iron precursor have better comprehensive electrochemical performance.

Description

Technical Field

[0001] This invention belongs to the field of battery cathode material technology, specifically relating to a manganese-iron precursor and its preparation method, and cathode material. Background Technology

[0002] The cathode material is the core factor determining the battery's energy density, cycle life, and cost. Sodium-ion batteries (NIBs) use layered oxides (Na₂O₃). x TMO2) and lithium iron phosphate (LiMn) batteries (LIB) x Fe 1-x PO4 and LMFP are two promising cathode material systems. However, their performance is jointly limited by transition metal (TM) elements, especially the uniformity of Mn and Fe distribution in the material. Traditional solid-state methods are prone to elemental segregation and phase separation, leading to capacity decay and deterioration of cycle performance.

[0003] Coprecipitation is an effective method for preparing uniform precursors. Hydroxide coprecipitation is favored due to its mature process and low cost. However, most current research focuses on single material systems (such as NIB or LMFP), lacking a universal, precisely controllable precursor solution to simultaneously meet the preparation requirements of these two cathode materials. Furthermore, pure hydroxide precursors have limited ability to address the Jameer-Taylor effect in LMFP and the phase transition problem in NIB, resulting in poor electrochemical performance of the battery. Summary of the Invention

[0004] Therefore, the purpose of this invention is to provide a manganese-iron precursor, its preparation method, and a cathode material.

[0005] In a first aspect, the present invention provides a ferromanganese precursor having a core-shell structure, comprising:

[0006] The kernel, its composition is Fe x Mn y (OH)2, where: 0.3≤x≤0.7, and satisfy x+y=1;

[0007] A first coating layer, covering at least a portion of the surface of the core, is composed of xanthate;

[0008] The second coating layer covers at least a portion of the surface of the first coating layer and has the composition M(OH)2, wherein M is one or more of Mg, Co, Zn, Al, Ti, Zr, Nb, La, Mo, and W.

[0009] Preferably, the primary particles of the manganese-iron precursor are hexagonal flakes.

[0010] Preferably, the molar ratio of the second coating layer to the core is (1~5):(95~99).

[0011] Preferably, the particle size of the manganese-iron precursor is 4~7μm.

[0012] Secondly, the present invention provides a method for preparing a manganese-iron precursor, comprising the following steps:

[0013] A mixed solution containing xanthate, ammonia, ammonium sulfate, and ammonium acetate was used as the reaction substrate. Under an inert atmosphere, a mixed solution containing manganese salt and ferrous salt, along with ammonia, was simultaneously introduced into the reaction substrate to carry out a coprecipitation reaction. After the coprecipitation reaction was completed, the mixed solution containing manganese salt and ferrous salt was replaced with a coating solution containing M salt to continue the reaction. After the reaction was completed, the solution was aged to obtain the manganese-iron precursor.

[0014] Preferably, the xanthate is one or both of butyl xanthate and sodium butyl xanthate.

[0015] A further preferred embodiment is a combination of butyl xanthate and sodium butyl xanthate in a mass ratio of (0.5~0.8):1.

[0016] Preferably, the mass ratio of xanthate, ammonium sulfate and ammonium acetate in the reaction substrate is (1.5~2.5):(0.5~1.5):(0.5~1.5); ammonia water is added to adjust the pH of the reaction substrate to 9~9.5.

[0017] Preferably, the ratio of the mass of the xanthate to the total molar amount of Mn and Fe in the mixed solution containing manganese salt and ferrous salt is (10~20) g:(10~20) mol.

[0018] Preferably, the Mn in the mixed solution containing manganese salt and ferrous salt is... 2+ and Fe 2+ The total concentration is 1~3 mol / L; ammonia water is introduced to control the pH during the coprecipitation reaction to be 10~10.5.

[0019] Preferably, the concentration of M in the coating solution containing M salt is 0.5~1.5 mol / L, and the ratio of the molar amount of M introduced into the coating solution containing M salt to the total molar amount of Mn and Fe introduced into the mixed solution containing manganese salt and ferrous salt is (1~5):(95~99).

[0020] Preferably, during the continued reaction process, ammonia water is introduced to control the pH of the continued reaction to be 10.6~10.8.

[0021] Preferably, the rate at which the coating solution containing M salt is introduced is 1 / 3 to 1 / 2 of the rate at which the mixed solution containing manganese salt and ferrous salt is introduced.

[0022] Preferably, the aging time is 2 to 12 hours.

[0023] Preferably, after aging, the product is sequentially filtered, washed, and dried to obtain the manganese-iron precursor.

[0024] Thirdly, the present invention provides a sodium-ion battery cathode material, the raw materials of which include the aforementioned manganese-iron precursor.

[0025] Fourthly, the present invention provides a method for preparing a sodium-ion battery cathode material, comprising the following steps: mixing a manganese-iron precursor with a sodium source, and then sintering the mixture in an oxygen-containing atmosphere to obtain the sodium-ion battery cathode material.

[0026] Preferably, the sodium source and the manganese-iron precursor are mixed at a molar ratio of Na / (Mn+Fe+M) of 0.7 to 0.75.

[0027] Preferably, the sintering temperature is 750~950℃ and the sintering time is 4~15h.

[0028] Fifthly, the present invention provides a lithium manganese iron phosphate cathode material, the raw material of which includes the aforementioned manganese iron precursor.

[0029] In a sixth aspect, the present invention provides a method for preparing lithium manganese iron phosphate cathode material, comprising the following steps: mixing a manganese iron precursor, a lithium source, a phosphorus source and a carbon source, and then performing sand milling and spray drying to obtain a mixture; sintering the mixture under an inert atmosphere to obtain lithium manganese iron phosphate cathode material.

[0030] Preferably, the phosphorus source is one or more of ammonium dihydrogen phosphate and ammonium hydrogen phosphate; the carbon source is one or two of sucrose and glucose.

[0031] Preferably, the manganese-iron precursor, lithium source, and phosphorus source are mixed in a molar ratio of Li : (Mn+Fe+M) : P of (1~1.05):1 :(1~1.05), and the amount of carbon source added is 5~20% of the total mass of the manganese-iron precursor, lithium source, and phosphorus source.

[0032] Preferably, the sintering temperature is 600~750℃ and the sintering time is 8~20h.

[0033] Compared with the prior art, one or more of the above technical solutions can achieve at least one of the following beneficial effects:

[0034] In this invention, the manganese-iron precursor contains a xanthate first coating layer, which is beneficial for improving the stability of the sodium-ion cathode material and broadening the sodium ion migration pathway, thereby enhancing the electrochemical performance of the sodium-ion battery. The xanthate first coating layer can improve the conductivity of the lithium manganese iron phosphate cathode material, thus improving the electrochemical performance of the lithium-ion battery. The manganese-iron precursor in this invention also contains a M(OH)₂ second coating layer. The M(OH)₂ second coating layer can alleviate the Jam-Taylor effect of the lithium manganese iron phosphate cathode and the phase transition problem of the sodium-ion cathode, thereby improving the electrochemical performance of the battery. The synergistic effect of the two coating layers allows the sodium-ion cathode material or lithium iron phosphate cathode material prepared from the manganese-iron precursor to have better overall electrochemical performance.

[0035] The manganese iron precursor in this invention can be used as a cathode material for lithium manganese iron phosphate or as a precursor for sodium battery cathode materials. It has strong versatility and can reduce development and production costs. Attached Figure Description

[0036] Figure 1 This is a SEM image of the manganese-iron precursor in Example 1.

[0037] Figure 2 This is a SEM image of the sodium-ion cathode material in Example 6. Detailed Implementation

[0038] To facilitate understanding of the present invention, the present invention will be described more fully and in detail below with reference to the accompanying drawings and preferred embodiments, but the scope of protection of the present invention is not limited to the following specific embodiments.

[0039] Unless otherwise defined, all technical terms used herein have the same meaning as commonly understood by those skilled in the art. The technical terms used herein are for the purpose of describing particular embodiments only and are not intended to limit the scope of the invention.

[0040] As mentioned above, in a first aspect, the present invention provides a ferromanganese precursor having a core-shell structure, comprising:

[0041] The kernel, its composition is Fe x Mn y (OH)2, where: 0.3≤x≤0.7, and satisfy x+y=1;

[0042] A first coating layer, covering at least a portion of the surface of the core, is composed of xanthate;

[0043] The second coating layer covers at least a portion of the surface of the first coating layer and has the composition M(OH)2, wherein M is one or more of Mg, Co, Zn, Al, Ti, Zr, Nb, La, Mo, and W.

[0044] In this invention, the xanthate first coating layer of the manganese iron precursor can react with the lithium source to generate lithium sulfate during the synthesis of lithium manganese iron phosphate, thereby improving the electronic conductivity of the material. In addition, some sulfate groups are incorporated into the lattice in the form of anions, occupying oxygen sites and forming anion doping, which further enhances the structural stability of the lithium manganese iron phosphate cathode material.

[0045] In this invention, the xanthate first coating layer of the manganese-iron precursor reacts with the iron and sodium sources during the synthesis of sodium-ion battery cathode materials to form a sodium iron sulfate protective layer. This protective layer can inhibit the dissolution of elements in the cathode material under high voltage. At the same time, sulfur elements partially replace oxygen sites in the crystal lattice to form anion substitution, which broadens the migration path of sodium ions and thus improves the rate performance and cycle stability of sodium-ion batteries.

[0046] In this invention, the second coating layer of the manganese iron precursor diffuses into the interior of the material during the subsequent sintering process to prepare the cathode material, achieving gradient doping of the M element. At the same time, it forms a dense protective layer on the surface of the material, effectively inhibiting the dissolution of manganese, reducing surface side reactions and delaying structural degradation. This can alleviate the Ginger-Taylor effect or the phase transition problem of sodium-ion batteries in lithium manganese iron phosphate cathodes.

[0047] In some embodiments, the primary particles of the ferromanganese precursor are hexagonal flakes.

[0048] In this invention, the manganese-iron precursor is in the form of hexagonal sheets, which is beneficial for preparing sodium-ion cathode materials with single-crystal morphology.

[0049] In some implementations, the molar ratio of the second coating layer to the core is (1~5):(95~99), including but not limited to: 1:99, 2:98, 3:97, 4:96, 5:95, etc.

[0050] In some embodiments, the particle size of the manganese-iron precursor is 4~7μm, including but not limited to: 4μm, 5μm, 6μm, 7μm, etc.

[0051] Secondly, the present invention provides a method for preparing a manganese-iron precursor, comprising the following steps:

[0052] A mixed solution containing xanthate, ammonia, ammonium sulfate, and ammonium acetate was used as the reaction base solution. Under an inert atmosphere, a mixed solution containing manganese salt and ferrous salt, along with ammonia, was simultaneously introduced into the reaction base solution to carry out a coprecipitation reaction. After the coprecipitation reaction was completed, the mixed solution containing manganese salt and ferrous salt was replaced with a coating solution containing M salt to continue the reaction. After the reaction was completed, the solution was aged to obtain the manganese-iron precursor.

[0053] In the preparation method of this invention, the ammonium xanthate molecules in xanthate will preferentially and strongly adsorb onto the crystal face with a faster growth rate through the sulfur atoms at its hydrophilic end. Since the growth rate of different crystal faces is differentially suppressed, the final morphology of the generated manganese-iron precursor crystal is a hexagonal plate agglomerate particle with uniform particle size distribution.

[0054] In some embodiments, the xanthate is one or both of butyl xanthate and sodium butyl xanthate; more preferably, the xanthate is a combination of butyl xanthate and sodium butyl xanthate in a mass ratio of (0.5~0.8):1, including but not limited to: 0.5:1, 0.6:1, 0.7:1, 0.8:1, etc.

[0055] In some embodiments, the mass ratio of xanthate, ammonium sulfate, and ammonium acetate in the reaction substrate is (1.5~2.5):(0.5~1.5):(0.5~1.5), including but not limited to: 1.5:0.5:0.5, 1.5:1:0.5, 1.5:1.5:0.5, 1.5:0.5:1, 1.5:0.5:1.5, 1.5:1:1, 1.5:1:1.5, 1.5:1.5:1.5:1.5, 2:0.5:0.5, 2:1: 0.5, 2:1.5:0.5, 2:0.5:1, 2:0.5:1.5, 2:1:1, 2:1:1.5, 2:1.5:1, 2:1.5:1.5, 2.5:0.5:0.5, 2.5:1:0.5, 2.5:1.5:0.5, 2.5:0.5:1, 2.5:0.5:1.5, 2.5:1:1, 2.5:1:1.5, 2.5:1.5:1, 2.5:1.5:1.5, etc.; add ammonia water to adjust the pH of the reaction substrate to 9~9.5.

[0056] In some embodiments, the mass ratio of the xanthate to the total molar amount of Mn and Fe in the mixed solution containing manganese and ferrous salts is (10~20)g:(10~20)mol, including but not limited to: 10g:10mol, 15g:10mol, 20g:10mol, 10g:15mol, 20g:10mol, 10g:20mol, 15g:20mol, etc.

[0057] In some embodiments, the Mn in the mixed solution containing manganese salt and ferrous salt 2+ and Fe 2+ The total concentration is 1~3 mol / L, including but not limited to: 1 mol / L, 1.5 mol / L, 2 mol / L, 2.5 mol / L, 3 mol / L, etc.; ammonia water is introduced to control the pH of the coprecipitation reaction to be 10~10.5.

[0058] In some embodiments, the concentration of M in the coating solution containing M salt is 0.5~1.5 mol / L, including but not limited to: 0.5 mol / L, 0.8 mol / L, 1.0 mol / L, 1.2 mol / L, 1.5 mol / L, etc.; the ratio of the molar amount of M in the coating solution containing M salt to the total molar amount of Mn and Fe in the mixed solution containing manganese salt and ferrous salt is (1~5):(95~99), including but not limited to: 1:99, 2:98, 3:97, 4:96, 5:95, etc.

[0059] In some embodiments, during the continued reaction process, ammonia water is introduced to control the pH of the continued reaction to be 10.6-10.8.

[0060] In some embodiments, the rate at which the coating solution containing M salt is introduced is 1 / 3 to 1 / 2 of the rate at which the mixed solution containing manganese salt and ferrous salt is introduced.

[0061] In some embodiments, the aging time is 2 to 12 hours, including but not limited to: 2 hours, 3 hours, 4 hours, 5 hours, 6 hours, 7 hours, 8 hours, 9 hours, 10 hours, 11 hours, 12 hours, etc.

[0062] In some embodiments, after aging, the product is sequentially filtered, washed, and dried to obtain a manganese-iron precursor.

[0063] Thirdly, the present invention provides a sodium-ion battery cathode material, the raw materials of which include the aforementioned manganese-iron precursor.

[0064] Fourthly, the present invention provides a method for preparing a sodium-ion battery cathode material, comprising the following steps: mixing a manganese-iron precursor with a sodium source, and then sintering the mixture in an oxygen-containing atmosphere to obtain the sodium-ion battery cathode material.

[0065] In some embodiments, the sodium source and the manganese-iron precursor are mixed at a molar ratio of Na / (Mn+Fe+M) of 0.7 to 0.75.

[0066] In some embodiments, the sintering temperature is 750~950℃, including but not limited to: 750℃, 800℃, 850℃, 900℃, 950℃, etc.; the sintering time is 4~15h, including but not limited to: 4h, 5h, 6h, 7h, 8h, 9h, 10h, 11h, 12h, 13h, 14h, 15h, etc.

[0067] Fifthly, the present invention provides a lithium manganese iron phosphate cathode material, the raw material of which includes the aforementioned manganese iron precursor.

[0068] In a sixth aspect, the present invention provides a method for preparing lithium manganese iron phosphate cathode material, comprising the following steps: mixing a manganese iron precursor, a lithium source, a phosphorus source and a carbon source, and then performing sand milling and spray drying to obtain a mixture; sintering the mixture under an inert atmosphere to obtain lithium manganese iron phosphate cathode material.

[0069] In some embodiments, the phosphorus source is one or more of ammonium dihydrogen phosphate and ammonium hydrogen phosphate; the carbon source is one or two of sucrose and glucose.

[0070] In some embodiments, the manganese-iron precursor, lithium source, and phosphorus source are mixed in a molar ratio of Li : (Mn+Fe+M) : P of 1: 1: 1; the amount of carbon source added is 5-20% of the total mass of the manganese-iron precursor, lithium source, and phosphorus source, including but not limited to: 5%, 10%, 15%, 20%, etc.

[0071] In some embodiments, the sintering temperature is 600~750℃, including but not limited to: 600℃, 650℃, 700℃, 750℃, etc.; the sintering time is 8~20h, including but not limited to: 8h, 9h, 10h, 11h, 12h, 13h, 14h, 15h, 16h, 17h, 18h, 19h, 20h, etc.

[0072] Unless otherwise specified, all raw materials, reagents, instruments and equipment used in this invention can be purchased from the market or prepared by existing methods.

[0073] Example 1

[0074] In this embodiment, the manganese-iron precursor has a core-shell structure, and its core is: Mn 0.7 Fe 0.3 (OH)₂, the first coating layer is a combination of butyl xanthate and sodium butyl xanthate in a mass ratio of 0.6:1, and the second coating layer is Mg 0.5 Co 0.5 (OH)2; the mass ratio of the first coating layer to the total molar amount of Mn and Fe in the core is 20g:20mol, and the molar ratio of the second coating layer to the core is 0.03:0.97.

[0075] The specific preparation method is as follows:

[0076] (1) Under nitrogen protection, manganese sulfate (MnSO4·H2O) and ferrous sulfate (FeSO4·7H2O) were dissolved in deoxygenated and deionized water at a molar ratio of Mn:Fe = 0.7:0.3 to prepare a solution containing MnSO4·H2O. 2+ and Fe 2+ A mixed solution of metal salts with a total concentration of 2.0 mol / L.

[0077] Magnesium sulfate (MgSO4·7H2O) and cobalt sulfate (CoSO4·7H2O) were dissolved in deionized water at a molar ratio of Mg:Co = 1:1 to prepare a MgSO4·7H2O solution. 2+ With Co 2+ A composite coated salt solution with a total concentration of 1.0 mol / L.

[0078] The concentration of ammonia water is 10 mol / L.

[0079] The mass ratio of sodium butylxanthate, ammonium butylxanthate, ammonium sulfate, and ammonium acetate in the reaction substrate is 0.75:1.25:1:1 (the total amount of sodium butylxanthate and ammonium butylxanthate added to the reaction substrate is 20g). Then, ammonia water is added to adjust the pH of the reaction substrate to 9~9.5.

[0080] (2) Add the reaction base liquid to the reaction vessel; under a nitrogen atmosphere and at a temperature of 45°C, simultaneously introduce ammonia water and metal salt mixed solution into the reaction base liquid for co-precipitation reaction. During the co-precipitation reaction, control the flow rate of ammonia water to stabilize the pH of the reaction system at 10.3; the total amount of metal salt solution introduced during the co-precipitation reaction is 10L. After the introduction is completed (the D50 of the core in the reaction solution reaches 5.0μm), switch to introducing composite coated salt solution to continue the reaction, and control the flow rate of ammonia water to stabilize the pH of the reaction system at 10.8. The introduction rate of composite coated salt solution is 1 / 3 of the introduction rate of metal salt mixed solution. The total volume of the introduced composite coated salt solution is 0.619L. After the composite coated salt solution is introduced, stop introducing ammonia water, and then age for 6h. After aging, filter, wash the filter cake multiple times with deionized water and ethanol, and then vacuum dry at 80°C for 24h to obtain light brown spherical manganese iron precursor powder.

[0081] The SEM image of the manganese-iron precursor powder prepared in this embodiment is shown below. Figure 1 As shown, the primary particles are hexagonal plates, and the secondary particles have a diameter between 4 and 7 μm.

[0082] After filtration in step (2), the filtrate was subjected to ultraviolet testing. The total mass of sodium butyl xanthate and ammonium butyl xanthate remaining in the filtrate was only 2.88g, indicating that most of the xanthates were coated on the manganese-iron precursor.

[0083] Comparative Example 1

[0084] Preparation of conventional Mn 0.7 Fe 0.3 The (OH)₂ precursor is prepared as follows:

[0085] (1) Under nitrogen protection, manganese sulfate (MnSO4·H2O) and ferrous sulfate (FeSO4·7H2O) were dissolved in deoxygenated and deionized water at a molar ratio of Mn:Fe = 0.7:0.3 to prepare a mixed solution of metal salts with a total concentration of Mn ions and Fe ions of 2.0 mol / L.

[0086] The concentration of ammonia water is 10 mol / L.

[0087] The mass ratio of ammonium sulfate to ammonium acetate in the reaction substrate is 1:1 (the total amount of ammonium sulfate and ammonium acetate added is 20g). Then, ammonia water is added to adjust the pH of the reaction substrate to 9~9.5.

[0088] (2) Add the reaction base liquid to the reaction vessel; under a nitrogen atmosphere and at a temperature of 45°C, simultaneously introduce ammonia water and metal salt mixed solution into the reaction base liquid to carry out co-precipitation reaction. During the co-precipitation reaction, control the flow rate of ammonia water to stabilize the pH of the reaction system at 10.3; the total amount of metal salt solution introduced during the co-precipitation reaction is 10L. After the introduction is completed (the D50 of the core in the reaction solution reaches 5.0μm), age for 6h. After aging, filter, wash the filter cake with deionized water and ethanol several times, and then vacuum dry at 80°C for 24h to obtain light brown spherical manganese iron precursor powder.

[0089] Comparative Example 2

[0090] The method is basically the same as Example 1, except that there is no first coating layer and no sodium butyl xanthate or ammonium butyl xanthate is added to the reaction solution in the corresponding preparation method.

[0091] Comparative Example 3

[0092] The method is basically the same as in Example 1, except that there is no second coating layer. The corresponding preparation method step (2) is as follows:

[0093] (2) Add the reaction base liquid to the reaction vessel; under nitrogen atmosphere and at 45°C, simultaneously introduce ammonia water and metal salt mixed solution into the reaction base liquid for coprecipitation reaction. During the coprecipitation reaction, control the flow rate of ammonia water to stabilize the pH of the reaction system at 10.3; the total amount of metal salt solution introduced during the coprecipitation reaction is 10L. After the reaction is completed (the precursor particles D50 in the reaction solution reach 5.0μm), age for 6h. After aging, filter, wash the filter cake with deionized water and ethanol several times, and then vacuum dry at 80°C for 24h to obtain light brown spherical manganese iron precursor powder.

[0094] Example 2

[0095] The method is basically the same as in Example 1, except that the first coating material is butyl xanthate ammonium. In the corresponding preparation method, the composition of the reaction base solution is as follows: the mass ratio of butyl xanthate ammonium, ammonium sulfate and ammonium acetate in the reaction base solution is 2:1:1 (the amount of butyl xanthate ammonium added in the reaction base solution is 20g), and then ammonia water is added to adjust the pH of the reaction base solution to 9~9.5.

[0096] Example 3

[0097] The method is basically the same as in Example 1, except that the first coating material is sodium butylxanthate. In the corresponding preparation method, the composition of the reaction base solution is as follows: the mass ratio of sodium butylxanthate, ammonium sulfate and ammonium acetate in the reaction base solution is 2:1:1 (the amount of sodium butylxanthate added to the reaction base solution is 20g), and then ammonia water is added to adjust the pH of the reaction base solution to 9~9.5.

[0098] Example 4

[0099] In this embodiment, the manganese-iron precursor has a core-shell structure, and its core is: Mn 0.5 Fe 0.5 (OH)₂, the first coating layer is a combination of butyl xanthate and sodium butyl xanthate in a mass ratio of 0.8:1, and the second coating layer is Zn . (OH)2; the mass ratio of the first coating layer to the total molar amount of Mn and Fe in the core is 15g:10mol, and the molar ratio of the second coating layer to the core is 0.05:0.95.

[0100] The specific preparation method is as follows:

[0101] (1) Under nitrogen protection, manganese sulfate (MnSO4·H2O) and ferrous sulfate (FeSO4·7H2O) were dissolved in deoxygenated and deionized water at a molar ratio of Mn:Fe = 0.5:0.5 to prepare a mixed solution of metal salts with a total concentration of Mn ions and Fe ions of 1.0 mol / L.

[0102] Zinc sulfate (ZnSO4·7H2O) was dissolved in deionized water to prepare a composite coated salt solution with a concentration of 0.5 mol / L.

[0103] The concentration of ammonia water is 10 mol / L.

[0104] The mass ratio of sodium butyl xanthate, ammonium butyl xanthate, ammonium sulfate, and ammonium acetate in the reaction substrate is 0.67:0.83:1.5:0.5 (the total amount of sodium butyl xanthate and ammonium butyl xanthate added to the reaction substrate is 15g). Then, ammonia water is added to adjust the pH of the reaction substrate to 9~9.5.

[0105] (2) Add the reaction base liquid to the reaction vessel; under a nitrogen atmosphere and at a temperature of 45°C, simultaneously introduce ammonia water and a mixed solution of metal salt into the reaction base liquid to carry out a co-precipitation reaction. During the co-precipitation reaction, control the flow rate of ammonia water to stabilize the pH of the reaction system at 10.5. The total amount of metal salt solution introduced during the co-precipitation reaction is 10L. After the introduction is completed (the D50 of the core in the reaction solution reaches 4.8μm), switch to introducing a composite coated salt solution to continue the reaction. Control the flow rate of ammonia water to stabilize the pH of the reaction system at 10.7. The introduction rate of the composite coated salt solution is 1 / 2 of the introduction rate of the mixed solution of metal salt. The total volume of the introduced composite coated salt solution is 1.05L. After the composite coated salt solution is introduced, stop introducing ammonia water and then age for 3h. After aging, filter, wash the filter cake multiple times with deionized water and ethanol, and then vacuum dry at 80°C for 24h to obtain manganese iron precursor powder.

[0106] The microstructure of the manganese-iron precursor prepared in this embodiment is basically the same as that in Example 1. The primary particles have a hexagonal structure, and the secondary particles have a particle size of 4~6μm.

[0107] After filtration in step (2), the filtrate was subjected to ultraviolet testing. The total mass of sodium butyl xanthate and ammonium butyl xanthate remaining in the filtrate was only 1.5g, indicating that most of them were coated on the manganese-iron precursor.

[0108] Example 5

[0109] In this embodiment, the manganese-iron precursor has a core-shell structure, and its core is: Mn 0.3 Fe 0.7 (OH)₂, the first coating layer is a combination of butyl xanthate and sodium butyl xanthate in a mass ratio of 0.5:1, and the second coating layer is Ti . (OH)4. The mass ratio of the first coating layer to the total molar amount of Mn and Fe in the core is 15 g: 30 mol, and the molar ratio of the second coating layer to the core is 0.01:0.99.

[0110] The specific preparation method is as follows:

[0111] (1) Under nitrogen protection, manganese sulfate (MnSO4·H2O) and ferrous sulfate (FeSO4·7H2O) were dissolved in deoxygenated and deionized water at a molar ratio of Mn:Fe = 0.3:0.7 to prepare a mixed solution of metal salts with a total concentration of Mn ions and Fe ions of 3.0 mol / L.

[0112] Titanium oxysulfate (TiOSO4·8H2O) was dissolved in deionized water to prepare a composite coated salt solution with a concentration of 1.5 mol / L.

[0113] The concentration of ammonia water is 10 mol / L.

[0114] The mass ratio of sodium butylxanthate, ammonium butylxanthate, ammonium sulfate, and ammonium acetate in the reaction substrate is 0.83:1.67:0.5:1.5 (the total amount of sodium butylxanthate and ammonium butylxanthate added to the reaction substrate is 15g). Then, ammonia water is added to adjust the pH of the reaction substrate to 9~9.5.

[0115] (2) Add the reaction base liquid to the reaction vessel; under a nitrogen atmosphere and at a temperature of 45°C, simultaneously introduce ammonia water and a metal salt mixed solution into the reaction base liquid for co-precipitation reaction. During the co-precipitation reaction, control the flow rate of ammonia water to stabilize the pH of the reaction system at 10.3; the total amount of metal salt solution introduced during the co-precipitation reaction is 10L. After the introduction is completed (the D50 of the core in the reaction solution reaches 6.1μm), switch to introducing a composite coated salt solution to continue the reaction, and control the flow rate of ammonia water to stabilize the pH of the reaction system at 10.6. The introduction rate of the composite coated salt solution is 1 / 2 of the introduction rate of the metal salt mixed solution. The total volume of the introduced composite coated salt solution is 0.202L. After the composite coated salt solution is introduced, stop introducing ammonia water, and then age for 12h. After aging, filter, wash the filter cake multiple times with deionized water and ethanol, and then vacuum dry at 80°C for 24h to obtain manganese iron precursor powder.

[0116] The microstructure of the manganese-iron precursor prepared in this embodiment is basically the same as that in Example 1. The primary particles have a hexagonal plate-like structure, and the secondary particles have a particle size of 5~7μm.

[0117] After filtration in step (2), the filtrate was subjected to ultraviolet testing. The total mass of sodium butyl xanthate and ammonium butyl xanthate remaining in the filtrate was only 1.8g, indicating that most of them were coated on the manganese-iron precursor.

[0118] Example 6

[0119] The manganese-iron precursor from Example 1 was mixed with sodium carbonate at a molar ratio of Na / (Mn+Fe+Mg+Co)=0.75, and ball-milled for 2 hours to obtain a mixture. The mixture was placed in a muffle furnace and heated to 850°C at a rate of 5°C / min under an oxygen atmosphere, held at that temperature for 12 hours, and then cooled with the furnace to obtain a sodium-ion battery cathode material. The main component of the cathode material was Na. 0.67 [(Mn 0.7 Fe 0.3 ) 0.97 (Mg 0.5 Co 0.5 ) 0.03O2 / S. XRD analysis of the obtained cathode material confirmed it to be a P2-type layered structure. ICP analysis of the obtained cathode material revealed a sulfur content of 4265 ppm, indicating the presence of a trace sulfur-containing coating layer; therefore, S in the chemical formula represents the sulfur-containing coating layer.

[0120] The SEM image of the sodium-ion electrode material prepared in this embodiment is shown below. Figure 2 As shown, the sodium-ion cathode material also exhibits a hexagonal structure and a single-crystal morphology.

[0121] Comparative Example 4

[0122] This example is essentially the same as Example 6, except that the precursor is the manganese-iron precursor from Comparative Example 1, and the corresponding sodium-ion cathode material prepared is Na. 0.67 Mn 0.7 Fe 0.3 O2.

[0123] Comparative Example 5

[0124] This example is essentially the same as Example 6, except that the precursor is the manganese-iron precursor from Comparative Example 2, and the corresponding sodium-ion cathode material prepared is Na. 0.67 [(Mn 0.7 Fe 0.3 ) 0.97 (Mg 0.5 Co 0.5 ) 0.03 O2.

[0125] Comparative Example 6

[0126] This is basically the same as Example 6, except that the precursor is the manganese-iron precursor from Comparative Example 3, and the corresponding positive electrode is Na. 0.67 Mn 0.7 Fe 0.3 O2 / S.

[0127] Example 7

[0128] This is basically the same as Example 6, except that the precursor is the manganese-iron precursor from Example 2, and Na... 0.67 [(Mn 0.7 Fe 0.3 ) 0.97 (Mg 0.5 Co 0.5 ) 0.03 O2 / S.

[0129] Example 8

[0130] This is basically the same as Example 6, except that the precursor is the manganese-iron precursor from Example 3, and Na... 0.67[(Mn 0.7 Fe 0.3 ) 0.97 (Mg 0.5 Co 0.5 ) 0.03 O2 / S.

[0131] Example 9

[0132] The manganese iron precursor from Example 1 was mixed with lithium hydroxide, ammonium dihydrogen phosphate, and sucrose at a molar ratio of Li:(Mn+Fe+Mg+Co):P of 1:1.01:1.02, with sucrose comprising 15% of the total mass of the manganese iron precursor, lithium hydroxide, and ammonium dihydrogen phosphate, to obtain a mixture. The mixture was then sand-milled for 4 hours and spray-dried. The dried material was placed in a tube furnace and heated to 680°C at 3°C / min under an argon atmosphere, held at that temperature for 15 hours, and then naturally cooled to obtain a black powdered lithium manganese iron phosphate cathode material, Li[(Mn+Fe+Mg+Co):P. 0.7 Fe 0.3 ) 0.97 (Mg 0.5 Co 0.5 ) 0.03 ]PO4 / SC (in the chemical formula, S represents sulfur-containing coating and C represents carbon coating).

[0133] Comparative Example 7

[0134] This is essentially the same as Example 9, except that the manganese-iron precursor is the same as that in Comparative Example 1, corresponding to the prepared lithium manganese iron phosphate cathode material LiMn. 0.7 Fe 0.3 PO4 / SC.

[0135] Comparative Example 8

[0136] The process is basically the same as in Example 9, except that the manganese-iron precursor is the same as that in Comparative Example 2, corresponding to the prepared lithium manganese iron phosphate cathode material Li[(Mn 0.7 Fe 0.3 ) 0.97 (Mg 0.5 Co 0.5 ) 0.03 ]PO4 / C.

[0137] Comparative Example 9

[0138] This is basically the same as Example 9, except that the manganese iron precursor is the lithium manganese iron phosphate cathode material LiMn prepared from the manganese iron precursor in Comparative Example 3. 0.7 Fe 0.3 PO4 / SC.

[0139] Example 10

[0140] The manganese-iron precursor from Example 4 was mixed with sodium carbonate at a molar ratio of Na / (Mn+Fe+Mg+Co) / S=0.75. After ball milling for 2 hours, a mixture was obtained. The mixture was placed in a muffle furnace and heated to 750°C at a rate of 5°C / min under an oxygen atmosphere, held at that temperature for 15 hours, and then cooled with the furnace to obtain the sodium-ion battery cathode material Na. 0.67 [(Mn 0.7 Fe 0.3 ) 0.95 (Zn) 0.05 O2 / S.

[0141] Example 11

[0142] The manganese iron precursor from Example 5 was mixed with lithium hydroxide, ammonium dihydrogen phosphate, and glucose at a molar ratio of Li:(Mn+Fe+Mg+Co):P of 1.02:1:1.02, with glucose comprising 20% ​​of the total mass of the manganese iron precursor, lithium hydroxide, and ammonium dihydrogen phosphate, to obtain a mixture. The mixture was then milled in a sand mill for 4 hours and spray-dried. The dried material was placed in a tube furnace and heated to 750°C at a rate of 3°C / min under an argon atmosphere, held at that temperature for 8 hours, and then naturally cooled to obtain a black powdered lithium manganese iron phosphate cathode material, Li[(Mn+Fe+Mg+Co):P]. 0.7 Fe 0.3 ) 0.99 (Ti) 0.01 ]PO4 / SC.

[0143] The sodium-ion cathode materials prepared in Examples 6-8, Comparative Examples 4-6, and Example 10 were assembled into sodium-ion batteries. The specific assembly and testing methods are as follows:

[0144] Sodium-ion battery cathode material was mixed with SP (carbon black conductive agent), CNT (carbon nanotubes), and PVDF (polyvinylidene fluoride), wherein the mass ratio of the cathode material, SP+CNT, and PVDF was controlled at 90:5:5. Using NMP (N-methylpyrrolidone) as a solvent, the mixture was stirred for several hours to obtain a cathode slurry. This slurry was then used to prepare a cathode sheet. The cathode sheet, along with a sodium sheet, a polypropylene separator, and a sodium hexafluorophosphate electrolyte, was used to prepare a sodium-ion battery. Constant current charge-discharge tests were conducted within a voltage range of 2.0–4.0 V. The first three cycles were performed at a rate of 0.1C, followed by 1C, for a total of 150 cycles. The initial discharge capacity and capacity retention of the prepared sodium-ion battery were measured, and the test results are shown in Table 1.

[0145] Table 1

[0146]

[0147] As can be seen from the data in Table 1, the battery assembled with the sodium-ion cathode material without coating treatment in Comparative Example 4 exhibits poor cycle stability. The battery assembled with the sodium-ion cathode material prepared from the manganese-iron precursor with only a second coating layer in Comparative Example 5 shows a slight improvement in cycle stability compared to Comparative Example 4, but the effect is still not ideal. The battery assembled with the sodium-ion cathode material prepared from the manganese-iron precursor with only a xanthate coating layer in Comparative Example 6 shows a slight improvement in cycle stability compared to Comparative Example 4, but the effect is still not ideal. The battery assembled with the sodium-ion cathode material prepared from the manganese-iron precursor containing both a first and second xanthate coating layer in Example 6 exhibits significantly higher cycle stability than Comparative Examples 4-6. This may be due to a synergistic effect between the two coating layers, thus significantly improving the battery's cycle performance. In Examples 7 and 8, the first coating of the precursor consisted of only one type of xanthate: butylammonium xanthate or sodium butylxanthate. The cycle stability of the batteries assembled with the corresponding sodium-ion cathodes was slightly lower than that of Example 6. This may be because the combination of the two xanthates could further improve the structural stability of the manganese-iron precursor. Example 10 mainly adjusted the preparation process of the sodium-ion cathode. The cycle stability of the assembled batteries showed slight fluctuations, but still maintained good cycle stability.

[0148] The lithium manganese iron phosphate cathode materials prepared in Examples 9, 11 and Comparative Examples 7-9 were assembled into lithium batteries. The specific assembly method is as follows, and the test results are shown in Table 2.

[0149] Lithium manganese iron phosphate cathode material, acetylene black, and PVDF were mixed in a mass ratio of 8:1:1, and an appropriate amount of NMP was added. The mixture was stirred into a paste, coated onto aluminum foil, and dried to form the cathode sheet. A lithium metal sheet was used as the anode, and a polypropylene porous membrane was used as the separator. 2023-type button batteries were assembled in a glove box. The assembled batteries underwent constant current charge-discharge testing within a voltage range of 2.5~4.5V. The first three cycles were at a rate of 0.1C, followed by a rate of 1C, for a total of 500 cycles. The initial discharge capacity and capacity retention of the prepared lithium manganese iron phosphate batteries were tested, and the results are shown in Table 2.

[0150] Table 2

[0151]

[0152] As can be seen from the data in Table 2, the battery assembled with the uncoated lithium manganese iron phosphate cathode material in Comparative Example 7 exhibits poor specific capacity and cycle stability. The battery assembled with the lithium manganese iron phosphate cathode material prepared using only the second coating layer of the manganese iron precursor in Comparative Example 8 shows only a slight improvement in specific capacity and cycle stability compared to Comparative Example 7, and the improvement is very insignificant. The battery assembled with the lithium manganese iron phosphate cathode material prepared using only the xanthate coating layer of the manganese iron precursor in Comparative Example 9 shows a slight improvement in specific capacity and cycle stability compared to Comparative Example 8, and the improvement is very insignificant. The battery assembled with the lithium manganese iron phosphate cathode material prepared using the first and second xanthate coating layers in Example 9 shows significantly higher specific capacity and cycle stability than Comparative Examples 7-9. This may be due to a synergistic effect between the two coating layers, which significantly improves the battery's specific capacity and cycle stability. Example 11 mainly adjusted the preparation process of the lithium manganese iron phosphate cathode, resulting in slight fluctuations in the cycle stability of the assembled battery, but it still possesses good specific capacity and cycle stability.

[0153] The above embodiments are only for illustrating the technical concept and features of the present invention, and are intended to enable those skilled in the art to understand the content of the present invention and implement it accordingly. They should not be construed as limiting the scope of protection of the present invention. All equivalent changes or modifications made in accordance with the spirit and essence of the present invention should be covered within the scope of protection of the present invention.

Claims

1. A manganese-iron precursor, characterized in that, The manganese-iron precursor has a core-shell structure, comprising: The kernel, its composition is Fe x Mn y (OH)2, where: 0.3≤x≤0.7, and satisfy x+y=1; A first coating layer, covering at least a portion of the surface of the core, is composed of xanthate; The second coating layer covers at least a portion of the surface of the first coating layer, and its composition is M(OH)2 or Ti(OH)4, wherein M is one or more of Mg, Co, and Zn.

2. The manganese-iron precursor according to claim 1, characterized in that, The primary particles of the manganese-iron precursor are hexagonal flakes; And / or: The particle size of the manganese-iron precursor is 4~7μm.

3. The manganese-iron precursor according to claim 1 or 2, characterized in that, The molar ratio of the second coating layer to the core is (1~5):(95~99).

4. The method for preparing the manganese-iron precursor according to any one of claims 1 to 3, characterized in that, Includes the following steps: A mixed solution containing xanthate, ammonia, ammonium sulfate, and ammonium acetate was used as the reaction substrate. Under an inert atmosphere, a mixed solution containing manganese salt and ferrous salt, along with ammonia, was simultaneously introduced into the reaction substrate to carry out a coprecipitation reaction. After the coprecipitation reaction was completed, the mixed solution containing manganese salt and ferrous salt was replaced with a coating solution containing M salt to continue the reaction. After the reaction was completed, the solution was aged to obtain the manganese-iron precursor.

5. The method for preparing the manganese-iron precursor according to claim 4, characterized in that, The xanthate is one or both of butyl xanthate and sodium butyl xanthate; And / or: the mass ratio of xanthate, ammonium sulfate and ammonium acetate in the reaction substrate is (1.5~2.5):(0.5~1.5):(0.5~1.5); ammonia water is added to adjust the pH of the reaction substrate to 9~9.

5.

6. The method for preparing the manganese-iron precursor according to claim 5, characterized in that, Xanthate is a combination of butyl xanthate and sodium butyl xanthate in a mass ratio of (0.5~0.8):

1.

7. The method for preparing the manganese-iron precursor according to claim 4, characterized in that, The ratio of the mass of xanthate to the total molar amount of Mn and Fe in the mixed solution containing manganese and ferrous salts is (10~20) g:(10~20) mol; ammonia water is introduced to control the pH of the coprecipitation reaction to be 10~10.5; And / or: Mn in the mixed solution containing manganese salt and ferrous salt 2+ and Fe 2+ Total concentration 1~3 mol / L; And / or: the concentration of M in the coating solution containing M salt is 0.5~1.5 mol / L; And / or: the ratio of the molar amount of M in the coating solution containing M salt to the total molar amount of Mn and Fe in the mixed solution containing manganese salt and ferrous salt is (1~5):(95~99); And / or: During the continued reaction process, ammonia water is introduced to control the pH of the continued reaction to be 10.6~10.

8.

8. The method for preparing the manganese-iron precursor according to claim 4, characterized in that, The rate at which the coating solution containing M salt is introduced is 1 / 3 to 1 / 2 of the rate at which the mixed solution containing manganese salt and ferrous salt is introduced. And / or: The aging time is 2~12h.

9. A sodium-ion battery cathode material, characterized in that, The raw materials include the ferromanganese precursor as described in any one of claims 1 to 3, or the ferromanganese precursor prepared by the preparation method described in any one of claims 4 to 8.

10. A lithium manganese iron phosphate cathode material, characterized in that, The raw materials include the ferromanganese precursor as described in any one of claims 1 to 3, or the ferromanganese precursor prepared by the preparation method described in any one of claims 4 to 8.

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