Dual-tubular reactor, as well as nano-level manganese ferrite and lithium battery cathode material and preparation method thereof

Abstract

A dual-tubular reactor relates to the technical field of the preparation of cathode materials for lithium-ion batteries. It includes two tubular reactors arranged in series. This dual-tubular reactor can be used to prepare nanoscale manganese ferrite precursors, match the reaction process of manganese ferrite, and achieve controllable continuous production. In addition, the embodiment of the present invention also provides a continuous preparation method of nanoscale manganese ferrite. It uses the above-mentioned dual-tubular reactor, which is simple and convenient to operate, and can efficiently prepare a pure-phase nanoscale manganese ferrite precursor with a spinel structure to solve the problems of the mixing uniformity and stability of manganese sources and iron sources existing in the preparation process of lithium iron phosphate. The cathode material for lithium batteries prepared from this nanoscale manganese ferrite has a high tap density, good electrical properties, and can effectively inhibit manganese dissolution.

Description

Technical Field

[0001] The present invention relates to the technical field of the preparation of cathode materials for lithium-ion batteries. Specifically, the present invention relates to a double-tube reactor, as well as nano-scale manganese ferrite, a cathode material for lithium batteries, and a preparation method thereof. Background Art

[0002] Lithium manganese iron phosphate (LiMn x Fe 1-x PO4, abbreviated as LMFP) is a cathode material for olivine-type lithium-ion batteries, which combines the safety of LiFePO4 (LFP) and the high-voltage advantage of LiMnPO4 (LMP), and is considered to be one of the core materials for the next generation of high-energy-density and low-cost power batteries.

[0003] In the synthesis process of lithium manganese iron phosphate (LiMn x Fe 1-x PO4), the homogenization mixing of manganese source and iron source and the stability problem of the precursor have become the key technical bottlenecks restricting industrialization. In the prior art, there are mainly two ways to achieve the uniform mixing of manganese source and iron source. One is to synthesize manganese iron hydroxide as a precursor by liquid-phase precipitation of manganese source and iron source. However, divalent manganese in manganese iron hydroxide is extremely unstable, and Mn3O4 and Fe2O3 two phases will be formed during the filtration, drying, packaging, storage, and grinding stages. The other way is to mix the manganese source and iron source by solid-phase grinding or liquid phase, and then form Fe x Mn 2- x O3 as a precursor through high-temperature calcination. This process is relatively complex, and manganese in Fe x Mn 2-x O3 is trivalent, which is prone to disproportionation reaction, and it is difficult to obtain a stable pure phase. Moreover, the high-temperature calcination method has high energy consumption and is not conducive to industrialization. Summary of the Invention

[0004] The purpose of the present invention is to provide a double-tube reactor, which is simple to operate and convenient to use, and can be used to produce nano-scale manganese ferrite precursor.

[0005] The second purpose of the present invention is to provide a nano-scale manganese ferrite and a preparation method thereof, which can prepare a stable pure-phase manganese ferrite precursor, reduce the occurrence of manganese dissolution phenomenon, and improve production efficiency.

[0006] The third purpose of the present invention is to provide a cathode material for lithium batteries, which is prepared from the above-mentioned nano-scale manganese ferrite as a manganese source and an iron source, and has excellent battery performance.

[0007] The embodiments of the present invention are implemented as follows:

[0008] A double-tube reactor, which comprises two tube reactors arranged in series. The tube reactor includes a shell and a reaction chamber inside the shell. The shell is provided with a first feed pipe and a discharge pipe, and the first feed pipe and the discharge pipe penetrate through the shell and communicate with the reaction chamber. A stirring shaft is arranged in the reaction chamber along the length direction of the reaction chamber. The stirring shaft is a tubular structure, including a tube wall and a feed channel inside the tube wall. The tube wall is provided with a plurality of feed holes, and the feed holes penetrate through the tube wall to communicate the feed channel and the reaction chamber. One end of the stirring shaft penetrates through the shell and is connected to a second feed pipe.

[0009] The two tube reactors are respectively a first tube reactor and a second tube reactor, and the discharge pipe of the first tube reactor is communicated with the second feed pipe of the second tube reactor.

[0010] Further, in other preferred embodiments of the present invention, a sandwich layer is arranged inside the shell of the tube reactor, and the sandwich layer is provided with a hot water inlet and a hot water outlet; the hot water outlet of the first tube reactor is communicated with the hot water inlet of the second tube reactor.

[0011] Further, in other preferred embodiments of the present invention, the stirring shaft includes a feed section, the length of the feed section is 1 / 3 - 1 / 2 of the stirring shaft, and it is arranged close to the second feed pipe; a plurality of feed holes are all located in the feed section and are evenly distributed along the length direction of the stirring shaft.

[0012] Further, in other preferred embodiments of the present invention, a propeller blade is connected to the outside of the stirring shaft; a plurality of baffles are arranged inside the shell, and the plurality of baffles are arranged at intervals along the length direction of the reaction chamber.

[0013] The embodiment of the present invention also provides a continuous preparation method of nano-level iron manganese tetraoxide, which uses the above double-tube reactor, and includes:

[0014] S1. Adding lye into the reaction chamber from the first feed pipe of the first tube reactor; adding ferrous ion solution and manganese ion solution into the reaction chamber from the second feed pipe of the first tube reactor.

[0015] S2. The lye, ferrous ion solution and manganese ion solution carry out a coprecipitation reaction in the reaction chamber to obtain a reaction solution; discharging the reaction solution from the discharge pipe of the first tube reactor.

[0016] S3. Adding hydrogen peroxide into the reaction chamber from the first feed pipe of the second tube reactor, and adding the reaction solution into the reaction chamber from the second feed pipe of the second tube reactor.

[0017] S4. The reaction solution and hydrogen peroxide are mixed and oxidized to obtain a solid suspension of iron manganese tetraoxide.

[0018] Among them, the reaction formula of the coprecipitation reaction is as follows:

[0019]

[0020] Mn²⁺ and Fe²⁺ coordinate with water molecules under strong alkaline conditions (pH > 12) to form [M(H2O)6] 2+ (M = Mn, Fe), and then hydroxyl groups replace water molecules to generate M(OH)2M(OH)2 precipitate. Due to the coprecipitation synergistic effect of manganese and iron ions, Mn²⁺ and Fe²⁺ form a heteronuclear complex [MnFe(OH)4] through electrostatic interaction 0 , which can inhibit the crystallization of single hydroxides and generate amorphous composite precipitates.

[0021] The reaction formula of the oxidation reaction is as follows:

[0022]

[0023] Hydrogen peroxide decomposes under alkaline conditions: H2O2 + OH - →HO2 - +H2O, HO2 - →O2 2- +H + ; due to the influence of the potential difference, Fe is preferentially selectively oxidized 2+ , FeMn(OH)2 serves as a precipitation platform, and an interfacial electron transfer occurs between the Fe 2+ site and the adsorbed HO2⁻; Mn / Fe is connected by sharing OH⁻ at the edge / corner and dehydroxylates at a certain temperature (neutralized with locally released H + ) to form manganese ferrite, that is, Mn x Fe 3-x O4. Among them, the value range of x can be adjusted according to the feeding ratio of manganese and iron. When 1 > x > 0, manganese is divalent and iron is a mixture of divalent and trivalent; when x = 1, manganese is divalent and iron is trivalent; when 3 > x > 1, part of the manganese is further oxidized to tetravalent and iron is trivalent. It is speculated to be the Fenton reaction mechanism, but FeMn(OH)2 causes the reaction to stagnate due to metal precipitation, ineffective decomposition of H2O2 and radical quenching in a strong alkaline environment.

[0024] It should be noted that, compared with the prior art that prepares the precursor by high-temperature calcination, the chemical formula of its oxide is Fe x Mn 2-x O3, which is based on the corundum structure of Fe2O3 as a template, and Mn 3+ replaces part of the Fe in some unit cells 3+ , and it is difficult to obtain a pure phase due to the instability of Mn 3 + . In the present invention, the chemical formula of the oxide is Mn x Fe 3-xO4 uses the spinel structure of Fe3O4 as a template and utilizes Mn 2+ to replace part of Fe 2+ . Once the crystal of the spinel structure is formed, further oxidizing Mn 2+ to Mn 4+ will not destroy the crystal structure, enabling it to always maintain a pure phase. The use of a double-tube reactor ensures a uniform reaction between hydrogen peroxide and the manganese-iron composite precipitate, allowing Fe 2+ to be preferentially oxidized in each local area and form crystals according to the spinel structure, thus enabling the acquisition of pure-phase oxides.

[0025] Furthermore, in other preferred embodiments of the present invention, the ferrous ion solution includes a solution prepared from at least one of ferrous sulfate, ferrous nitrate, and ferrous chloride; the manganese ion solution includes a solution prepared from at least one of manganese sulfate, manganese nitrate, and manganese chloride. Optionally, the metal ion concentrations of both the ferrous ion solution and the manganese ion solution are 0.5 mol / L to 2 mol / L. Within this range, the ion concentration is moderate, and better reactivity can be obtained.

[0026] Furthermore, in other preferred embodiments of the present invention, the ferrous ion solution and the manganese ion solution are fed in a Mn / Fe molar ratio of 0.1 to 10. The value of x in manganese iron tetraoxide can be effectively regulated through the feed ratio. Optionally, a three-way pipe can be added at the second feed pipe of the first tubular reactor to allow the ferrous ion solution and the manganese ion solution to be fed separately, making it more convenient to flexibly adjust the feed ratio. In addition, considering that this manganese iron tetraoxide is used as a manganese source and an iron source in the preparation of lithium iron manganese phosphate, the Mn / Fe molar ratio can be set to 6:4, so that no additional manganese source or iron source needs to be added during the preparation of lithium iron manganese phosphate.

[0027] Furthermore, in other preferred embodiments of the present invention, the reaction temperatures of both the coprecipitation reaction and the oxidation reaction are 50°C to 80°C. The temperature is controlled by introducing a heating medium into the jacket of the tubular reactor.

[0028] Furthermore, in other preferred embodiments of the present invention, after the oxidation reaction, the solid suspension of manganese iron tetraoxide is filtered and dried at 100°C to 120°C for 6 h to 10 h. During actual operation, a filter is provided at the discharge pipe of the second tubular reactor, and the solid suspension of manganese iron tetraoxide is directly introduced into the filter for filtration.

[0029] Further, in other preferred embodiments of the present invention, in the first tubular reactor, the feeding rate of the first feed pipe is 110 L / h to 120 L / h, and the feeding rate of the second feed pipe is 90 L / h to 100 L / h; in the second tubular reactor, the feeding rate of the first feed pipe is 10 L / h to 20 L / h, and the feeding rate of the second feed pipe is 190 L / h to 200 L / h.

[0030] Further, the embodiment of the present invention also provides a nano-level iron manganese tetraoxide, which is prepared by the above continuous preparation method, is a pure phase with a stable structure, has a uniform ion distribution, and can be used to prepare a high-performance cathode material for lithium batteries.

[0031] Further, the embodiment of the present invention also provides a cathode material for lithium batteries, which is prepared by using the above nano-level iron manganese tetraoxide as a manganese source and an iron source. It has a high tap density, good electrical properties, and can effectively inhibit manganese dissolution.

[0032] The beneficial effects of the embodiment of the present invention are:

[0033] The embodiment of the present invention provides a double-tubular reactor, which includes two tubular reactors arranged in series. The double-tubular reactor can be used to prepare a nano-level iron manganese tetraoxide precursor, match the reaction process of iron manganese tetraoxide, and achieve controllable continuous production. In addition, the present invention also provides a continuous preparation method of nano-level iron manganese tetraoxide, which uses the above double-tubular reactor. Its operation is simple and convenient, and it can efficiently prepare a pure-phase nano-level iron manganese tetraoxide precursor with a spinel structure to solve the problems of the mixing uniformity and stability of the manganese source and the iron source in the existing preparation process of lithium iron phosphate manganese. The cathode material for lithium batteries prepared with this nano-level iron manganese tetraoxide has a high tap density, good electrical properties, and can effectively inhibit manganese dissolution. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings required for use in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of the present invention, and therefore should not be regarded as limiting the scope. For those of ordinary skill in the art, other related drawings can be obtained based on these drawings without creative efforts.

[0035] Figure 1 It is a schematic diagram of a double-tubular reactor provided in Embodiment 1 of the present invention;

[0036] Figure 2 It is an electron microscope image of iron manganese tetraoxide provided in Embodiment 2 of the present invention;

[0037] Figure 3XRD pattern comparison diagram of iron manganese tetraoxide provided in Example 2 of the present invention and the standard spectrum of MnFe2O4;

[0038] Figure 4 XRD pattern of iron manganese tetraoxide in the prior art;

[0039] Figure 5 Infrared spectrum of iron manganese tetraoxide in the prior art;

[0040] Figure 6 Electron micrograph of manganese iron oxide provided in Comparative Example 1 of the present invention;

[0041] Figure 7 XRD pattern comparison diagram of manganese iron oxide provided in Comparative Example 1 of the present invention and the standard spectra of Mn3O4 and Fe2O3;

[0042] Figure 8 Electron micrograph of manganese iron oxide provided in Comparative Example 2 of the present invention;

[0043] Figure 9 Electron micrographs of each lithium iron manganese phosphate provided in the test example of the present invention (upper left: Example 1, upper right: Control Example 1, middle left: Control Example 2, middle right: Control Example 3, lower left: Control Example 4, lower right: Control Example 5);

[0044] Figure 10 0.1C charge-discharge capacity test diagram of each lithium iron manganese phosphate provided in the test example of the present invention.

[0045] Icon: 10 - double-tube reactor; 100 - tube reactor; 1001 - first tube reactor; 1002 - second tube reactor; 110 - housing; 111 - first feed pipe; 112 - discharge pipe; 113 - interlayer; 114 - hot water inlet; 115 - hot water outlet; 116 - baffle; 120 - reaction chamber; 130 - stirring shaft; 131 - pipe wall; 132 - feed channel; 133 - feed hole; 134 - propeller blade; 135 - second feed pipe. Detailed implementation mode

[0046] To make the objectives, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention. Apparently, the described embodiments are only a part rather than all of the embodiments of the present invention. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the scope of protection of the present invention. Therefore, the detailed description of the embodiments of the present invention provided in the accompanying drawings is not intended to limit the scope of the claimed present invention, but merely represents selected embodiments of the present invention. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the scope of protection of the present invention.

[0047] In the description of the present invention, it should be understood that the terms "center", "longitudinal", "lateral", "length", "width", "thickness", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", "clockwise", "counterclockwise", etc. indicate the orientation or positional relationship based on the orientation or positional relationship shown in the drawings. It is only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and thus should not be construed as a limitation to the present invention.

[0048] In addition, the terms "first" and "second" are only used for descriptive purposes and should not be construed as indicating or implying relative importance or implicitly specifying the quantity of the indicated technical features. Thus, the features defined with "first" and "second" may explicitly or implicitly include one or more of such features. In the description of the present invention, "a plurality" means two or more unless otherwise specifically defined.

[0049] In the present invention, unless otherwise clearly defined and limited, the terms "mounted", "connected", "coupled", "fixed", etc. shall be construed in a broad sense. For example, it may be a fixed connection, a detachable connection, or integrated; it may be directly connected or indirectly connected through an intermediate medium, and it may be the internal communication of two elements or the interaction relationship between two elements. For those of ordinary skill in the art, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0050] In the present invention, unless otherwise clearly specified and defined, the first feature being "on" or "under" the second feature may include direct contact between the first and second features, or may include the first and second features not being in direct contact but in contact through additional features therebetween. Moreover, the first feature being "above", "over" and "on top of" the second feature includes the first feature being directly above and obliquely above the second feature, or merely indicating that the first feature has a higher horizontal height than the second feature. The first feature being "under", "beneath" and "underneath" the second feature includes the first feature being directly below and obliquely below the second feature, or merely indicating that the first feature has a lower horizontal height than the second feature. Example 1

[0051] This embodiment provides a double-tube reactor 10. Referring to Figure 1 as shown, it includes two tubular reactors 100 arranged in series.

[0052] Among them, the tubular reactor 100 includes a housing 110 and a reaction chamber 120 inside the housing 110. The housing 110 is provided with a first feed pipe 111 and a discharge pipe 112. The first feed pipe 111 and the discharge pipe 112 penetrate the housing 110 and communicate with the reaction chamber 120; a stirring shaft 130 is arranged in the reaction chamber 120 along the length direction of the reaction chamber 120. The stirring shaft 130 is a tubular structure, including a pipe wall 131 and a feed channel 132 inside the pipe wall 131. The pipe wall 131 is provided with a plurality of feed holes 133. The feed holes 133 penetrate the pipe wall 131 to communicate the feed channel 132 and the reaction chamber 120; one end of the stirring shaft 130 penetrates the housing 110 and is connected to a second feed pipe 135.

[0053] The two tubular reactors 100 are respectively a first tubular reactor 1001 and a second tubular reactor 1002. The discharge pipe 112 of the first tubular reactor 1001 is communicated with the second feed pipe 135 of the second tubular reactor 1002. A feed pump is arranged between the first tubular reactor 1001 and the second tubular reactor 1002 for transporting the reaction liquid between the two.

[0054] Furthermore, a sandwich layer 113 is arranged inside the housing 110 of the tubular reactor 100. The sandwich layer 113 is provided with a hot water inlet 114 and a hot water outlet 115; the hot water outlet 115 of the first tubular reactor 1001 is communicated with the hot water inlet 114 of the second tubular reactor 1002. By introducing a heat medium into the sandwich layer 113, the reaction liquid in the reaction chamber 120 can be heated.

[0055] As Figure 1As shown in the figure, the stirring shaft 130 includes a feeding section. The length of the feeding section is 1 / 3 - 1 / 2 of the stirring shaft 130 and is arranged close to the second feeding pipe 135. A plurality of feeding holes 133 are all located in the feeding section and are evenly distributed along the length direction of the stirring shaft 130. Through such an arrangement, the raw materials can have sufficient reaction time after feeding, making the reaction more complete.

[0056] A propeller blade 134 is connected to the outside of the stirring shaft 130; a plurality of baffles 116 are arranged inside the housing 110, and the plurality of baffles 116 are arranged at intervals along the length direction of the reaction chamber 120. The propeller blade 134 is used to stir the reaction liquid in the reaction chamber 120, and the design of the baffles 116 can cause the reaction liquid to form a vortex during the forward process, making the mixing between the raw materials more complete. It should be noted that the height of the baffle 116 is designed according to the diameter of the propeller blade 134, mainly to prevent the rotation of the propeller blade 134 from being hindered. At the same time, the coverage range of each baffle 116 is 1 / 5 - 1 / 4 of the circumferential direction of the housing 110. The plurality of baffles 116 are arranged at intervals along the length direction of the housing 110, and adjacent two baffles 116 are staggered from each other, that is, the orthographic projections in the length direction of the housing 110 do not overlap. Example 2

[0057] This example provides a continuous preparation method of nano-level iron manganese tetroxide, which uses the above-mentioned double-tube reactor 10 and includes:

[0058] S1. Add the alkali solution (NaOH, 30wt%) from the first feeding pipe 111 of the first tubular reactor 1001 into the reaction chamber 120; add the ferrous ion solution (FeSO4, 1mol / L) and the manganese ion solution (MnSO4, 1mol / L) from the second feeding pipe 135 of the first tubular reactor 1001 into the reaction chamber 120.

[0059] Among them, the pumping speed of the alkali solution is 120L / h, and the total pumping speed of the ferrous ion solution and the manganese ion solution (Mn / Fe molar ratio is 6:4) is 100L / h. At this time, the front end of the double-tube reactor 10 maintains a positive pressure state, P ≤ 100kpa.

[0060] S2. The alkali solution, the ferrous ion solution and the manganese ion solution carry out a coprecipitation reaction in the reaction chamber 120. Hot water at 60°C is introduced into the interlayer 113 to maintain the reaction at a constant temperature, and a reaction liquid is obtained; the reaction liquid is discharged from the discharge pipe 112 of the first tubular reactor 1001.

[0061] S3. Add hydrogen peroxide (30%) to the reaction chamber 120 from the first feed pipe 111 of the second tubular reactor 1002, and add the reaction solution to the reaction chamber 120 from the second feed pipe 135 of the second tubular reactor 1002; wherein, the pumping speed of hydrogen peroxide is 20 L / h, and the pumping speed of the reaction solution is 200 L / h.

[0062] S4. The reaction solution and hydrogen peroxide are mixed and oxidized to obtain a solid suspension of iron manganese tetraoxide.

[0063] S5. Discharge the solid suspension of iron manganese tetraoxide from the discharge pipe 112 of the second tubular reactor 1002, transport it to a filter for filtration, and the pumping speed is 200 L / h. The precipitate obtained by filtration is washed with appropriate pure water, and the washing temperature is 60 °C.

[0064] S7. Dry the precipitate at 105 °C for 8 h to obtain iron manganese tetraoxide.

[0065] The microscopic morphology of the obtained iron manganese tetraoxide is as Figure 2 shown. It can be seen that microscopically, the particle size distribution of the iron manganese tetraoxide in this example is relatively uniform, and the average particle size is below 200 nm. It is extremely easy to grind during the synthesis of lithium iron manganese phosphate, improving the production efficiency.

[0066] The obtained iron manganese tetraoxide is subjected to X-ray diffraction, and its XRD pattern is as Figure 3 shown. Its peak pattern completely coincides with that of MnFe2O4 in the standard library, and there are no impurity peaks, proving that the reaction has obtained a pure phase with a spinel structure.

[0067] However, from the reference (N. Dogan, et. Al, Manganese doped-iron oxide nanoparticles and their potential as tracer agents for magnetic particle imaging (MPI), Journal of Magnetism and Magnetic Materials , 561, 2022,169654), it can be seen that for manganese iron oxides with a spinel structure, their XRD patterns ( Figure 4 ) and infrared spectra ( Figure 5 ) do not change with the change of the manganese iron ratio. Therefore Figure 1 the XRD pattern can only show the crystal structure of the product obtained in this example, but cannot characterize the manganese iron ratio.

[0068] Furthermore, after sampling and dissolving the iron manganese tetraoxide, analyze the main content and other trace elements of the iron manganese tetraoxide by elemental analysis, and the analysis results are shown in Table 1.

[0069] Table 1: Main content and other trace elements of iron manganese tetraoxide

[0070]

[0071] It can be seen that after converting the mass percentage of ferromanganese into a molar ratio, it is 1.517, which is basically consistent with the molar ratio of 6 / 4 of the raw materials. The manganese ferrite in this example is characterized as Mn 1.8 Fe 1.2 O4, in which Fe is completely oxidized to +3 valence, while Mn is partially oxidized to +4 valence.

[0072] Examples 3 to 5

[0073] Examples 3 to 5 respectively provide a continuous preparation method of nano-scale manganese ferrite, and its operation steps are basically the same as those of Example 2, and the differences are shown in Table 2.

[0074] Table 2. Continuous preparation parameters of nano-scale manganese ferrite

[0075]

[0076] After dissolving the prepared manganese ferrite, elemental analysis was carried out, and the measured Mn and Fe contents are as follows:

[0077] Table 3. Composition analysis of nano-scale manganese ferrite

[0078]

[0079] As can be seen from Table 3, the Mn / Fe feeding ratio of the raw materials is basically matched with the Mn / Fe molar ratio in the product. In Example 3, the iron content is relatively high, and the generated product is Mn 0.3 Fe 2.7 O4, in which Mn is +2 valence and Fe is partially oxidized to +3 valence. In Example 4, the manganese to iron ratio just reaches 1:2, and the generated product is MnFe2O4, in which Mn is +2 valence and Fe is +3 valence. In Example 5, the manganese content is relatively high, and the generated product is Mn 2.7 Fe 0.3 O4, in which Fe is all oxidized to +3 valence and Mn is partially oxidized to +4 valence.

[0080] Comparative Example 1

[0081] This comparative example provides a preparation method of manganese iron oxide, including:

[0082] S1. Add lye (NaOH, 30 wt%) and ferrous ion solution (FeSO4, 1 mol / L), manganese ion solution (MnSO4, 1 mol / L) into the reaction kettle according to the Mn / Fe molar ratio of 6:4 and co-precipitate at 60 °C to obtain a reaction solution.

[0083] S2. Filter the reaction solution to obtain ferromanganese hydroxide precipitate.

[0084] S3. Calcinate the ferromanganese hydroxide precipitate at high temperature to obtain ferromanganese oxide.

[0085] The microstructure of the ferromanganese oxide is as Figure 6 shown. Its particle size shows an irregular distribution, and the size reaches the micron level.

[0086] Furthermore, it can be seen from the XRD pattern ( Figure 7 ) that the peak pattern is relatively complex. By comparing with the standard pattern, it shows that there are two components, Mn3O4 and Fe2O3, present simultaneously.

[0087] Comparative Example 2

[0088] This comparative example provides a method for preparing ferromanganese oxide, including:

[0089] S1. Add lye (NaOH, 30 wt%) and ferrous ion solution (FeSO4, 1 mol / L), manganese ion solution (MnSO4, 1 mol / L) into the reaction kettle according to the Mn / Fe molar ratio of 6:4 and co-precipitate at 60 °C to obtain a reaction solution.

[0090] S2. Add hydrogen peroxide (30%) to the reaction solution and continue to stir and react at 60 °C to obtain a solid suspension of ferromanganese tetraoxide.

[0091] S3. Filter the solid suspension of ferromanganese tetraoxide and dry it at 105 °C for 8 h to obtain ferromanganese tetraoxide.

[0092] This comparative example uses a conventional reaction kettle to replace the double-tube reactor 10, and can also obtain a ferromanganese tetraoxide product with a spinel structure. However, there are a large number of small miscellaneous peaks in the XRD pattern, and a pure-phase product cannot be obtained. Moreover, the relevant miscellaneous peaks cannot find corresponding substances in the standard library, making it difficult to analyze. The microstructure of ferromanganese tetraoxide is as Figure 8 shown. Compared with Example 1, the degree of particle uniformity is significantly reduced, but the size is significantly smaller than that of Comparative Example 1.

[0093] Test Example

[0094] Use the nanoscale ferromanganese tetraoxide prepared in Example 2 as the manganese source and iron source to prepare lithium iron manganese phosphate. Use different iron sources and manganese sources as Comparative Examples 1 - 5, and compare their various performances. The raw material selection and performance comparison are shown in Table 4.

[0095] Table 4. Raw material selection and performance comparison of lithium iron manganese phosphate

[0096]

[0097] Figure 9 shows the SEM images of lithium iron manganese phosphate of Example 1 and Comparative Examples 1 - 5. From Table 4 and Figure 9 it can be seen that the lithium iron manganese phosphate synthesized using the nanoscale manganese iron tetraoxide precursor provided in Example 1 has a tap density of 2.45 g / cc. In terms of microstructure, the particle size is uniform and the packing is tight, which is significantly better than that of lithium iron manganese phosphate prepared from conventional raw materials. This is because the uniform ion distribution of the spinel precursor reduces particle agglomeration during the sintering process, forming a dense packing; and reduces the grain boundary pores caused by Mn / Fe phase separation.

[0098] In addition, Figure 10 shows the 0.1C charge - discharge capacity test diagrams of different lithium iron manganese phosphate materials. From Table 4 and Figure 10 it can be seen that the lithium iron manganese phosphate synthesized using the nanoscale manganese iron tetraoxide precursor provided in Example 1 can reach 154.83 mAh / g at 0.1C. The atomic - level mixing of Mn / Fe shortens the Li ⁺ diffusion path, reduces the interfacial polarization between the two phases, and synergistically with the electron conduction network (Fe 3+ enhances the electron conductivity, Mn 2+ promotes Li + diffusion) to reduce the voltage hysteresis; the induced (010) crystal plane preferred orientation promotes the rapid insertion / extraction of Li ⁺ along the one - dimensional channel.

[0099] For the lithium iron manganese phosphate synthesized using the nanoscale manganese iron tetraoxide precursor provided in Example 1, the manganese dissolution is only 0.38 ppm, and the inhibition effect is significant. This is because Mn²⁺ (A - site) and Fe³⁺ (B - site) form a strong Mn - O - Fe covalent bond network through the spinel oxygen bridge (Mn - O - Fe), stabilizing the lattice oxygen, reducing the oxidative dissolution of Mn ions by the electrolyte (weakening of Jahn - Teller distortion), and after sintering, it is transformed into a stable framework of Mn²⁺ - O - P - Fe³⁺ in LMFP, inhibiting the migration and dissolution of Mn / Fe.

[0100] In summary, a dual - tube reactor 10 includes two tube reactors 100 arranged in series. This dual - tube reactor 10 can be used to prepare a nanoscale manganese iron tetraoxide precursor, matching the reaction process of manganese iron tetraoxide to achieve controllable continuous production. In addition, the embodiment of the present invention also provides a continuous preparation method for nanoscale manganese iron tetraoxide. Using the above - mentioned dual - tube reactor 10, its operation is simple and convenient, and it can efficiently prepare a pure - phase nanoscale manganese iron tetraoxide precursor with a spinel structure to solve the problems of the mixing homogeneity and stability of the manganese source and iron source in the existing preparation process of lithium iron manganese phosphate.

[0101] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A continuous preparation method of nano-scale iron manganate, characterized in that, A double-tube reactor is adopted. The double-tube reactor includes two tubular reactors arranged in series. The tubular reactor includes a shell and a reaction chamber inside the shell. The shell is provided with a first feed pipe and a discharge pipe. The first feed pipe and the discharge pipe penetrate the shell and communicate with the reaction chamber. A stirring shaft is arranged in the reaction chamber along the length direction of the reaction chamber. The stirring shaft is of a tubular structure and includes a pipe wall and a feed channel inside the pipe wall. The pipe wall is provided with a plurality of feed holes. The feed holes penetrate the pipe wall to communicate the feed channel and the reaction chamber. One end of the stirring shaft penetrates the shell and is connected to a second feed pipe. The two tubular reactors are respectively a first tubular reactor and a second tubular reactor. The discharge pipe of the first tubular reactor is communicated with the second feed pipe of the second tubular reactor. The continuous preparation method includes: Adding an alkali solution into the reaction chamber from the first feed pipe of the first tubular reactor; adding a ferrous ion solution and a manganese ion solution into the reaction chamber from the second feed pipe of the first tubular reactor. The alkali solution, the ferrous ion solution and the manganese ion solution carry out a coprecipitation reaction in the reaction chamber to obtain a reaction solution; discharging the reaction solution from the discharge pipe of the first tubular reactor. Adding hydrogen peroxide into the reaction chamber from the first feed pipe of the second tubular reactor, and adding the reaction solution into the reaction chamber from the second feed pipe of the second tubular reactor. The reaction solution and the hydrogen peroxide are mixed and subjected to an oxidation reaction to obtain a solid suspension of iron manganate tetroxide.

2. The continuous preparation method according to claim 1, wherein The ferrous ion solution includes a solution prepared from at least one of ferrous sulfate, ferrous nitrate, and ferrous chloride; the manganese ion solution includes a solution prepared from at least one of manganese sulfate, manganese nitrate, and manganese chloride.

3. The continuous preparation method according to claim 2, characterized in that, The ferrous ion solution and the manganese are fed in according to a Mn / Fe molar ratio of 0.1 to 10.

4. The continuous preparation method according to claim 1, characterized in that, The reaction temperatures of both the coprecipitation reaction and the oxidation reaction are 50 to 80 °C.

5. The continuous preparation method according to claim 1, characterized in that, A sandwich layer is arranged inside the shell of the tubular reactor. The sandwich layer is provided with a hot water inlet and a hot water outlet. The hot water outlet of the first tubular reactor is communicated with the hot water inlet of the second tubular reactor.

6. The continuous preparation method according to claim 5, characterized in that The stirring shaft includes a feed section. The length of the feed section is 1 / 3 to 1 / 2 of the stirring shaft and is arranged close to the second feed pipe. A plurality of the feed holes are all located in the feed section and are evenly distributed along the length direction of the stirring shaft.

7. The continuous preparation method according to claim 6, wherein A propeller blade is connected to the outside of the stirring shaft; a plurality of baffles are arranged on the inner side of the shell. The plurality of baffles are arranged at intervals along the length direction of the reaction chamber.

8. A nano-scale manganese ferrite tetroxide, characterized in that, Prepared by the continuous preparation method according to any one of claims 1 to 7.

9. A cathode material for a lithium battery, characterized in that, It is prepared from the nano-scale iron manganate tetroxide as a manganese source and an iron source according to claim 8.

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