Duplex tubular reactor, nanoscale ferromanganese tetroxide, lithium battery positive electrode material and preparation method of lithium battery positive electrode material

Abstract

A duplex tubular reactor relates to the technical field of lithium ion battery positive electrode material preparation, and comprises two tubular reactors connected in series, and the duplex tubular reactor can be used for preparing and producing a nanoscale ferromanganese tetroxide precursor, is matched with the reaction process of ferromanganese tetroxide, and can realize controllable continuous production. In addition, the embodiment of the invention also provides a continuous preparation method of the nanoscale ferromanganese tetroxide, which adopts the duplex tubular reactor, is simple and convenient to operate, can efficiently prepare the pure-phase nanoscale ferromanganese tetroxide precursor with a spinel structure, and can be used for preparing the pure-phase nanoscale ferromanganese tetroxide precursor with the spinel structure. The problems of mixing uniformity and stability of a manganese source and an iron source in the existing lithium manganese iron phosphate preparation process are solved. The lithium battery positive electrode material prepared from the nanoscale ferromanganese tetroxide has relatively high compaction density and relatively good electrical properties, and meanwhile, the dissolution of manganese can be effectively inhibited.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium ion battery positive electrode material preparation, and in particular to a double-tube reactor, nano-scale manganese iron tetroxide, lithium battery positive electrode material and a preparation method thereof. Background Art

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

[0003] In lithium manganese iron phosphate (LiMn x Fe 1-x In the synthesis process of PO4, the homogenization of manganese source and iron source and the stability of precursors have become the key technical bottlenecks restricting industrialization. In the existing technology, there are two main ways to achieve uniform mixing of manganese source and iron source. One is to synthesize ferromanganese hydroxide as a precursor by liquid phase precipitation of manganese source and iron source. However, the divalent manganese in ferromanganese hydroxide is extremely unstable. During the filtration, drying, packaging, storage and grinding stages, Mn3O4 and Fe2O3 will be generated. The other way is to grind the manganese source and iron source in solid phase or liquid phase, and then calcine at high temperature to form Fe x Mn 2- x O3 is used as a precursor, the process is relatively complicated, and Fe x Mn 2-x The manganese in O3 is trivalent and easily undergoes disproportionation reaction, making it difficult to obtain a stable pure phase. In addition, the high-temperature calcination method consumes a lot of energy, which is not conducive to industrialization. Summary of the invention

[0004] The object 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 a nano-scale manganese ferrotetroxide precursor.

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

[0006] The third object of the present invention is to provide a lithium battery positive electrode material, which is prepared by using the above-mentioned nano-scale manganese iron tetroxide as a manganese source and an iron source and has excellent battery performance.

[0007] The embodiment of the present invention is achieved as follows: A double-tube reactor, comprising two tube reactors arranged in series, the tube reactor comprising a shell and a reaction chamber inside the shell, the shell being provided with a first feed pipe and a discharge pipe, the first feed pipe and the discharge pipe penetrating the shell and being connected with the reaction chamber; a stirring shaft arranged along the length direction of the reaction chamber is provided in the reaction chamber, the stirring shaft is a tubular structure, comprising a tube wall and a feed channel inside the tube wall, the tube wall being provided with a plurality of feed holes, the feed holes penetrating the tube wall to connect the feed channel with the reaction chamber; one end of the stirring shaft penetrating the shell is connected with the second feed pipe; The two tubular reactors are respectively a first tubular reactor and a second tubular reactor, and the discharge pipe of the first tubular reactor is communicated with the second feed pipe of the second tubular reactor.

[0008] Furthermore, in other preferred embodiments of the present invention, an interlayer is provided in the shell of the tubular reactor, and the interlayer is provided with a hot water inlet and a hot water outlet; the hot water outlet of the first tubular reactor is connected to the hot water inlet of the second tubular reactor.

[0009] Furthermore, in other preferred embodiments of the present invention, 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; multiple feed holes are located in the feed section and are evenly distributed along the length direction of the stirring shaft.

[0010] Furthermore, in other preferred embodiments of the present invention, a propeller blade is connected to the outer side of the stirring shaft; a plurality of baffles are arranged on the inner side of the shell, and the plurality of baffles are arranged at intervals along the length direction of the reaction chamber.

[0011] The embodiment of the present invention further provides a continuous preparation method of nano-sized manganese ferrotetroxide, which adopts the above-mentioned double-tube reactor and comprises: S1. The alkali solution is added to the reaction chamber from the first feed pipe of the first tubular reactor; the ferrous ion solution and the manganese ion solution are added to the reaction chamber from the second feed pipe of the first tubular reactor; S2. Alkaline solution, ferrous ion solution and manganese ion solution are coprecipitated in the reaction chamber to obtain a reaction solution; the reaction solution is discharged from the discharge pipe of the first tubular reactor; S3. The hydrogen peroxide is added to the reaction chamber from the first feed pipe of the second tubular reactor, and the reaction solution is added to the reaction chamber from the second feed pipe of the second tubular reactor; S4. The reaction solution is mixed with hydrogen peroxide and subjected to oxidation reaction to obtain a solid suspension of manganese iron tetroxide.

[0012] The reaction formula of the coprecipitation reaction is as follows:

[0013] Mn²⁺ and Fe²⁺ coordinate with water molecules under strong alkaline conditions (pH>12) to form [M(H2O)6] 2+ (M = Mn, Fe), and then the hydroxyl group replaces the water molecule to generate M(OH)2M(OH)2 precipitate. Due to the synergistic effect of the co-precipitation 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.

[0014] The oxidation reaction equation is as follows:

[0015] 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 oxidized 2+ , FeMn(OH)2 as precipitation platform, Fe 2+ The interfacial electron transfer occurs between the sites and the adsorbed HO2⁻; Mn / Fe shares OH⁻ connections through edges / corners and removes hydroxyl groups at a certain temperature (with the locally released H + Neutralization) to form manganese iron tetroxide, i.e. Mn x Fe 3-x O4, where the value range of x can be adjusted according to the feed ratio of manganese and iron. When 1>x>0, manganese is divalent, while iron is a mixture of divalent and trivalent; when x=1, manganese is divalent and iron is trivalent; when 3>x>1, part of manganese is further oxidized to tetravalent, while iron is trivalent. It is speculated to be a Fenton reaction mechanism, but the reaction of FeMn(OH)2 stagnates due to metal precipitation, ineffective decomposition of H2O2 and quenching of free radicals in a strong alkaline environment.

[0016] It should be noted that, compared with the high temperature calcination method used in the prior art to prepare the precursor, the oxide chemical formula is Fe x Mn 2-x O3, is based on the corundum structure of Fe2O3, Mn 3+ Replace part of the Fe in the unit cell 3+ , the product due to Mn 3 + The instability of the oxide makes it difficult to obtain a pure phase. In the present invention, the oxide chemical formula is Mn x Fe 3-x O4, is based on the spinel structure of Fe3O4, using Mn 2+ Replacement of part of Fe 2+Once the spinel crystal is formed, further addition of Mn 2+ Oxidized to Mn 4+ The use of a double-tube reactor ensures a uniform reaction between hydrogen peroxide and ferromanganese composite precipitation, so that each local area can be Fe 2+ It is preferentially oxidized to form crystals according to the spinel structure, making it possible to obtain pure phase oxides.

[0017] Further, in other preferred embodiments of the present invention, the ferrous ion solution includes a solution composed of at least one of ferrous sulfate, ferrous nitrate, and ferrous chloride; the manganese ion solution includes a solution composed of at least one of manganese sulfate, manganese nitrate, and manganese chloride. Optionally, the metal ion concentrations of the ferrous ion solution and the manganese ion solution are both 0.5 mol / L to 2 mol / L, and within this range, the ion concentration is moderate, and better reactivity can be obtained.

[0018] Further, in other preferred embodiments of the present invention, the ferrous ion solution and the manganese ion solution are fed according to a Mn / Fe molar ratio of 0.1 to 10. The value of x in ferromanganese tetroxide can be effectively regulated by the feed ratio. Optionally, a three-way pipe can be added at the second feed pipe of the first tubular reactor so that the ferrous ion solution and the manganese ion solution can be fed separately, which is more convenient for flexible adjustment of the feed ratio. In addition, considering that the ferromanganese tetroxide is used as a manganese source and an iron source in the preparation of lithium ferromanganese phosphate, the Mn / Fe molar ratio can be set to 6:4, so that no additional manganese source or iron source is required when preparing lithium ferromanganese phosphate.

[0019] Furthermore, in other preferred embodiments of the present invention, the reaction temperatures of the coprecipitation reaction and the oxidation reaction are both 50° C. to 80° C. The temperature is controlled by introducing a heating medium into the interlayer of the tubular reactor.

[0020] Further, in other preferred embodiments of the present invention, after the oxidation reaction, the solid suspension of manganese ferrotetroxide is filtered and dried at 100° C. to 120° C. for 6 h to 10 h. In actual operation, a filter is provided at the discharge pipe of the second tubular reactor, and the solid suspension of manganese ferrotetroxide is directly introduced into the filter for filtration treatment.

[0021] Furthermore, in other preferred embodiments of the present invention, in the first tubular reactor, the feed rate of the first feed pipe is 110 L / h~120 L / h, and the feed rate of the second feed pipe is 90 L / h~100 L / h; in the second tubular reactor, the feed rate of the first feed pipe is 10 L / h~20 L / h, and the feed rate of the second feed pipe is 190 L / h~200 L / h.

[0022] Furthermore, an embodiment of the present invention also provides a nano-scale manganese ferrotetroxide, which is prepared by the above-mentioned continuous preparation method. It is a pure phase with a stable structure and a uniform ion distribution, and can be used to prepare a high-performance lithium battery positive electrode material.

[0023] Furthermore, the present invention also provides a lithium battery positive electrode material, which is prepared by using the above-mentioned nano-scale manganese iron tetroxide as a manganese source and an iron source, and has a high compaction density, good electrical properties, and can effectively inhibit manganese dissolution.

[0024] The beneficial effects of the embodiments of the present invention are: The embodiment of the present invention provides a double-tube reactor, which includes two tubular reactors arranged in series. The double-tube reactor can be used to prepare and produce nano-scale manganese iron tetroxide precursors, match the reaction process of manganese iron tetroxide, and achieve controllable continuous production. In addition, the present invention also provides a continuous preparation method of nano-scale manganese iron tetroxide, which adopts the above-mentioned double-tube reactor, is simple and convenient to operate, and can efficiently prepare a pure phase nano-scale manganese iron tetroxide precursor with a spinel structure, so as to solve the problems of uniformity and stability of mixing of manganese source and iron source in the existing preparation process of lithium manganese iron phosphate. The positive electrode material of a lithium battery prepared by the nano-scale manganese iron tetroxide has a higher compaction density and better electrical properties, and can effectively inhibit manganese dissolution. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings required for use in the embodiments are briefly introduced below. It should be understood that the following drawings only show certain embodiments of the present invention and therefore should not be regarded as limiting the scope. For ordinary technicians in this field, other related drawings can be obtained based on these drawings without creative work.

[0026] Figure 1 A schematic diagram of a double-tube reactor provided in Example 1 of the present invention; Figure 2 This is an electron microscope image of ferromanganese tetroxide provided in Example 2 of the present invention; Figure 3 A comparison chart of the XRD spectrum of ferromanganese tetroxide provided in Example 2 of the present invention and the standard spectrum of MnFe2O4; Figure 4 is the XRD pattern of ferromanganese tetroxide in the prior art; Figure 5 is the infrared spectrum of ferromanganese tetroxide in the prior art; Figure 6 This is an electron microscope image of the ferromanganese oxide provided in Comparative Example 1 of the present invention; Figure 7 A comparison chart of the XRD spectrum of the manganese iron oxide provided in Comparative Example 1 of the present invention and the standard spectrum of Mn3O4 and Fe2O3; Figure 8 This is an electron microscope image of the manganese iron oxide provided in Comparative Example 2 of the present invention; Fig. 9 Electron microscope images of various lithium manganese iron phosphates provided for the test examples 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); Fig.10 This is a test chart of the charge and discharge capacity of each lithium manganese iron phosphate at 0.1C provided in the test examples of the present invention.

[0027] Icons: 10-double tubular reactor; 100-tubular reactor; 1001-first tubular reactor; 1002-second tubular reactor; 110-shell; 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-tube wall; 132-feed channel; 133-feed hole; 134-propeller blade; 135-second feed pipe. DETAILED DESCRIPTION

[0028] In order to make the purpose, 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 in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention. Therefore, the following detailed description of the embodiments of the present invention provided in the drawings is not intended to limit the scope of the invention claimed for protection, but merely represents the selected embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0029] In the description of the present invention, it should be understood that the terms "center", "longitudinal", "lateral", "length", "width", "thickness", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", "clockwise", "counterclockwise" and the like indicate orientations or positional relationships based on the orientations or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the referred device or element must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be understood as a limitation on the present invention.

[0030] In addition, the terms "first" and "second" are used for descriptive purposes only and should not be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Therefore, the features defined as "first" and "second" may explicitly or implicitly include one or more of the features. In the description of the present invention, the meaning of "plurality" is two or more, unless otherwise clearly and specifically defined.

[0031] In the present invention, unless otherwise clearly specified and limited, the terms "installed", "connected", "connected", "fixed" and the like should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be directly connected or indirectly connected through an intermediate medium, it can be the internal connection of two elements or the interaction relationship between two elements. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0032] In the present invention, unless otherwise clearly specified and limited, a first feature being "above" or "below" a second feature may include that the first and second features are in direct contact, or may include that the first and second features are not in direct contact but are in contact through another feature between them. Moreover, a first feature being "above", "above" and "above" a second feature includes that the first feature is directly above and obliquely above the second feature, or simply indicates that the first feature is higher in level than the second feature. A first feature being "below", "below" and "below" a second feature includes that the first feature is directly below and obliquely below the second feature, or simply indicates that the first feature is lower in level than the second feature. Example 1

[0033] This embodiment provides a double-tube reactor 10, referring to Figure 1 As shown, it comprises two tubular reactors 100 arranged in series.

[0034] Among them, the tubular reactor 100 includes a shell 110 and a reaction chamber 120 inside the shell 110. The shell 110 is provided with a first feed pipe 111 and a discharge pipe 112. The first feed pipe 111 and the discharge pipe 112 pass through the shell 110 and are connected to the reaction chamber 120; the reaction chamber 120 has a stirring shaft 130 arranged along the length direction of the reaction chamber 120. The stirring shaft 130 is a tubular structure, including a tube wall 131 and a feed channel 132 inside the tube wall 131. The tube wall 131 is provided with a plurality of feed holes 133. The feed holes 133 pass through the tube wall 131 to connect the feed channel 132 and the reaction chamber 120; one end of the stirring shaft 130 passes through the shell 110 and is connected to the second feed pipe 135.

[0035] The two tubular reactors 100 are respectively a first tubular reactor 1001 and a second tubular reactor 1002, and the discharge pipe 112 of the first tubular reactor 1001 is connected to the second feed pipe 135 of the second tubular reactor 1002. A feed pump is provided between the first tubular reactor 1001 and the second tubular reactor 1002 for transporting the reaction liquid between the two.

[0036] Furthermore, an interlayer 113 is provided in the shell 110 of the tubular reactor 100, and the interlayer 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 connected to the hot water inlet 114 of the second tubular reactor 1002. By introducing a heat medium into the interlayer 113, the reaction liquid in the reaction chamber 120 can be heated.

[0037] like Figure 1 As shown, the stirring shaft 130 includes a feeding section, the length of which is 1 / 3 to 1 / 2 of the stirring shaft 130 and is arranged close to the second feeding pipe 135; the 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. With such an arrangement, the raw materials can have sufficient reaction time after feeding, so that the reaction is more complete.

[0038] The outside of the stirring shaft 130 is connected to a propeller blade 134; the inside of the shell 110 is provided with a plurality of baffles 116, 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 baffle 116 allows the reaction liquid to form a vortex during the forward process, so that the mixing between the raw materials is 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 so as not to hinder the rotation of the propeller blade 134. At the same time, the coverage range of each baffle 116 is 1 / 5 to 1 / 4 of the circumferential direction of the shell 110, and the plurality of baffles 116 are arranged at intervals along the length direction of the shell 110, and the adjacent two baffles 116 are staggered from each other, that is, the orthographic projections in the length direction of the shell 110 do not overlap. Example 2

[0039] This embodiment provides a continuous preparation method of nano-sized manganese ferrotetroxide, which uses the above-mentioned double-tube reactor 10 and includes: S1. Alkali solution (NaOH, 30 wt%) is added into the reaction chamber 120 from the first feed pipe 111 of the first tubular reactor 1001 ; ferrous ion solution (FeSO4, 1 mol / L) and manganese ion solution (MnSO4, 1 mol / L) are added into the reaction chamber 120 from the second feed pipe 135 of the first tubular reactor 1001 .

[0040] The pumping speed of the alkali solution is 120 L / h, and the total pumping speed of the ferrous ion solution and the manganese ion solution (Mn / Fe molar ratio is 6:4) is 100 L / h. At this time, the front end of the double-tube reactor 10 maintains a positive pressure state, P≤100 kpa.

[0041] S2. The alkali solution, ferrous ion solution and manganese ion solution are co-precipitated in the reaction chamber 120 , and 60° C. hot water is introduced into the interlayer 113 to maintain the reaction constant temperature to obtain a reaction solution; the reaction solution is discharged from the discharge pipe 112 of the first tubular reactor 1001 .

[0042] S3. Add hydrogen peroxide (30%) into the reaction chamber 120 from the first feed pipe 111 of the second tubular reactor 1002, and add the reaction liquid into the reaction chamber 120 from the second feed pipe 135 of the second tubular reactor 1002; wherein the pumping speed of the hydrogen peroxide is 20 L / h, and the pumping speed of the reaction liquid is 200 L / h.

[0043] S4. The reaction solution is mixed with hydrogen peroxide and subjected to oxidation reaction to obtain a solid suspension of manganese iron tetroxide.

[0044] S5. The solid suspension of manganese ferrotetroxide is discharged from the discharge pipe 112 of the second tubular reactor 1002 and transported to the filter for filtration at a pumping speed of 200 L / h. The filtered precipitate is washed with appropriate pure water at a washing temperature of 60°C.

[0045] S7. Dry the precipitate at 105°C for 8 h to obtain manganese iron tetroxide.

[0046] The microstructure of the obtained manganese iron tetroxide is as follows Figure 2 As shown, it can be seen that at the microscopic level, the particle size distribution of the manganese iron tetroxide in this embodiment is relatively uniform, and the average particle size is below 200 nm. It is very easy to grind during the synthesis of lithium manganese iron phosphate, which improves production efficiency.

[0047] The obtained manganese ferrotetroxide was subjected to X-ray diffraction, and its XRD pattern is as follows Figure 3As shown, its peak shape is completely consistent with that of MnFe2O4 in the standard library, and there is no impurity peak, proving that the reaction obtained a pure phase of spinel structure.

[0048] According to the references (N. Dogan, et. Al, Manganese doped-iron oxidenanoparticles and their potential as tracer agents for magnetic particleimaging (MPI) , Journal of Magnetism and Magnetic Materials , 561, 2022,169654) It can be seen that the XRD spectrum of spinel-structured manganese iron oxide ( Figure 4 ) and infrared spectrum ( Figure 5 ) does not change with the change of manganese iron ratio, so 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.

[0049] Furthermore, after the manganese ferrotetroxide was sampled and dissolved, the main content of manganese ferrotetroxide and other trace elements were analyzed by elemental analysis. The analysis results are shown in Table 1.

[0050] Table 1: Main content of manganese iron tetroxide and other trace elements

[0051] It can be seen that the mass percentage of ferromanganese converted into a molar ratio is 1.517, which is basically consistent with the molar ratio of the raw material 6 / 4. The ferromanganese tetroxide in this embodiment is characterized by Mn 1.8 Fe 1.2 O4, in which Fe is completely oxidized to +3, and Mn is partially oxidized to +4.

[0052] Embodiment 3~embodiment 5 Examples 3 to 5 respectively provide a continuous preparation method for nano-sized manganese ferrotetroxide, and the operation steps are basically the same as those of Example 2, with the differences shown in Table 2.

[0053] Table 2. Continuous preparation parameters of nano-sized manganese ferrotetroxide

[0054] After dissolving the prepared ferromanganese tetroxide, elemental analysis was performed, and the Mn and Fe contents were measured as follows: Table 3. Composition analysis of nano-sized manganese iron tetroxide

[0055] It can be seen from Table 3 that the Mn / Fe ratio of the raw material is basically matched with the Mn / Fe molar ratio of the product. 0.3 Fe 2.7 O4, where Mn is +2 and Fe is partially oxidized to +3. In Example 4, the ratio of manganese to iron is just 1:2, and the product is MnFe2O4, where Mn is +2 and Fe is +3. In Example 5, the manganese content is higher, and the product is Mn 2.7 Fe 0.3 O4, in which Fe is completely oxidized to +3 and Mn is partially oxidized to +4.

[0056] Comparative Example 1 This comparative example provides a method for preparing ferromanganese oxide, comprising: S1. Alkaline solution (NaOH, 30wt%), ferrous ion solution (FeSO4, 1mol / L), and manganese ion solution (MnSO4, 1mol / L) were added into a reactor at a Mn / Fe molar ratio of 6:4 and co-precipitated at 60°C to obtain a reaction solution.

[0057] S2. Filter the reaction solution to obtain manganese iron hydroxide precipitate.

[0058] S3. Calcine the ferromanganese hydroxide precipitate at high temperature to obtain ferromanganese oxide.

[0059] The microstructure of the manganese iron oxide is as follows Figure 6 As shown, the particle size is irregularly distributed and reaches the micron level.

[0060] Further analysis of the XRD spectrum ( Figure 7 ) It can be seen that the peak shape is relatively complex. By comparing with the standard spectrum, it is shown that there are two components, Mn3O4 and Fe2O3.

[0061] Comparative Example 2 This comparative example provides a method for preparing ferromanganese oxide, comprising: S1. Alkaline solution (NaOH, 30wt%), ferrous ion solution (FeSO4, 1mol / L), and manganese ion solution (MnSO4, 1mol / L) were added into a reactor at a Mn / Fe molar ratio of 6:4 and co-precipitated at 60°C to obtain a reaction solution.

[0062] S2. Add hydrogen peroxide (30%) to the reaction solution, continue stirring and reacting at 60°C to obtain a solid suspension of manganese iron tetroxide.

[0063] S3. The solid suspension of manganese ferric oxide was filtered and dried at 105° C. for 8 h to obtain manganese ferric oxide.

[0064] In this comparative example, a conventional reactor is used to replace the double-tube reactor 10, and a spinel-structured ferromanganese tetroxide product can also be obtained. However, there are a large number of small impurity peaks in the XRD spectrum, and a pure phase product cannot be obtained. In addition, the relevant impurity peaks cannot find corresponding substances in the standard library, making it difficult to analyze. The microstructure of ferromanganese tetroxide is shown in FIG. Figure 8 As shown, compared with Example 1, the uniformity of the particles is significantly reduced, but the size is significantly smaller than that of Comparative Example 1.

[0065] Test example The nano-sized manganese iron tetroxide prepared in Example 2 was used as a manganese source and an iron source to prepare lithium manganese iron phosphate, and various properties were compared using different iron sources and manganese sources as control examples 1 to 5. The raw material selection and performance comparison are shown in Table 4.

[0066] Table 4. Lithium manganese iron phosphate raw material selection and performance comparison

[0067] Fig. 9 The SEM images of lithium manganese iron phosphate of Example 1 and Comparative Examples 1 to 5 are shown. Fig. 9 It can be seen that the lithium manganese iron phosphate synthesized using the nano-sized manganese iron tetroxide precursor provided in Example 1 has a compacted density of 2.45 g / cc. In terms of microstructure, the particles are uniform in size and densely packed, which is significantly better than the lithium manganese iron phosphate prepared from conventional raw materials. This is because the uniform ion distribution of the spinel precursor reduces the agglomeration of particles during sintering, forming a dense stacking; and reduces the grain boundary pores caused by Mn / Fe phase separation.

[0068] also, Fig.10 The test graphs of different lithium manganese iron phosphate materials at 0.1C charge and discharge capacity are shown in Table 4 and Fig.10 It can be seen that the lithium manganese iron phosphate synthesized using the nano-manganese iron tetroxide precursor provided in Example 1 can reach 154.83 mAh / g at 0.1C, and the Mn / Fe atomic-level mixing shortens the Li ⁺ Diffusion path, reducing the polarization of the two-phase interface, and coordinating the electronic conduction network (Fe 3+ Enhanced electronic conductivity, Mn 2+ Promote Li + diffusion) reduces voltage hysteresis; the induced (010) crystal plane preferential orientation promotes Li ⁺ Rapid embedding / ejection along a one-dimensional channel.

[0069] The manganese dissolution of lithium iron manganese phosphate synthesized by using the nano-manganese iron tetroxide precursor provided in Example 1 is only 0.38ppm, and the inhibition effect is significant. This is because Mn²⁺ (A position) and Fe³⁺ (B position) form a strong Mn-O-Fe covalent bond network through the spinel oxygen bridge (Mn-O-Fe) to stabilize the lattice oxygen, reduce the oxidation and dissolution of Mn ions by the electrolyte (Jahn-Teller distortion weakening), and after sintering, it is converted into the Mn²⁺-OP-Fe³⁺ stable framework in LMFP, which inhibits the migration and dissolution of Mn / Fe.

[0070] In summary, a double-tube reactor 10, which includes two tubular reactors 100 arranged in series, can be used to prepare and produce nano-scale manganese iron tetroxide precursors, match the reaction process of manganese iron tetroxide, and achieve controllable continuous production. In addition, an embodiment of the present invention also provides a continuous preparation method of nano-scale manganese iron tetroxide, which adopts the above-mentioned double-tube reactor 10, is simple and convenient to operate, and can efficiently prepare a pure-phase nano-scale manganese iron tetroxide precursor with a spinel structure, so as to solve the problems of uniformity and stability of mixing of manganese source and iron source in the existing preparation process of lithium manganese iron phosphate.

[0071] The above description is only a preferred embodiment of the present invention and is 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 in the protection scope of the present invention.

Claims

1. A double-tube reactor, characterized in that: The invention comprises two tubular reactors arranged in series, wherein the tubular reactor comprises a shell and a reaction chamber inside the shell, wherein the shell is provided with a first feed pipe and a discharge pipe, wherein the first feed pipe and the discharge pipe penetrate the shell and are connected with the reaction chamber; wherein the reaction chamber is provided with a stirring shaft arranged along the length direction of the reaction chamber, wherein the stirring shaft is a tubular structure, comprising a tube wall and a feed channel inside the tube wall, wherein the tube wall is provided with a plurality of feed holes, wherein the feed holes penetrate the tube wall to connect the feed channel with the reaction chamber; wherein one end of the stirring shaft penetrates the shell and is connected with the second feed pipe; The two tubular reactors are respectively a first tubular reactor and a second tubular reactor, and the discharge pipe of the first tubular reactor is connected to the second feed pipe of the second tubular reactor.

2. The double-tube reactor according to claim 1, characterized in that: An interlayer is arranged in the shell of the tubular reactor, and the interlayer is provided with a hot water inlet and a hot water outlet; the hot water outlet of the first tubular reactor is connected with the hot water inlet of the second tubular reactor.

3. The double-tube reactor according to claim 2, characterized in that: The stirring shaft includes a feeding section, the length of which is 1 / 3 to 1 / 2 of the stirring shaft and is arranged close to the second feeding pipe; the multiple feeding holes are all located in the feeding section and are evenly distributed along the length direction of the stirring shaft.

4. The double-tube reactor according to claim 3, characterized in that: The outer side of the stirring shaft is connected with a propeller blade; the inner side of the shell is provided with a plurality of baffles, and the plurality of baffles are arranged at intervals along the length direction of the reaction chamber.

5. A continuous preparation method of nano-sized ferromanganese tetroxide, characterized in that: The double-tube reactor according to any one of claims 1 to 4 is used, comprising: Adding alkali solution into the reaction chamber from the first feeding pipe of the first tubular reactor; adding ferrous ion solution and manganese ion solution into the reaction chamber from the second feeding pipe of the first tubular reactor; The alkali solution, the ferrous ion solution and the manganese ion solution are subjected to a co-precipitation reaction in the reaction chamber to obtain a reaction solution; and the reaction solution is discharged from a 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 liquid into the reaction chamber from the second feed pipe of the second tubular reactor; The reaction solution and the hydrogen peroxide are mixed and oxidized to obtain a solid suspension of manganese ferrotetroxide.

6. The continuous preparation method according to claim 5, characterized in that: The ferrous ion solution includes a solution composed of at least one of ferrous sulfate, ferrous nitrate, and ferrous chloride; the manganese ion solution includes a solution composed of at least one of manganese sulfate, manganese nitrate, and manganese chloride.

7. The continuous preparation method according to claim 6, characterized in that: The ferrous ion solution and the manganese ions are fed according to a Mn / Fe molar ratio of 0.1-10.

8. The continuous preparation method according to claim 5, characterized in that: The reaction temperatures of the coprecipitation reaction and the oxidation reaction are both 50°C to 80°C.

9. A nano-sized ferromanganese tetroxide, characterized in that: The method is prepared by the continuous preparation method according to any one of claims 5 to 8.

10. A positive electrode material for a lithium battery, characterized in that: It is prepared by using the nano-sized manganese ferrotetroxide as claimed in claim 9 as a manganese source and an iron source.

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