Flaky lithium manganate, preparation method therefor and use thereof

Abstract

The present application provides flaky lithium manganate, a preparation method therefor and a use thereof. The preparation method comprises the following steps: (1) mixing an oil phase substance, an emulsifier and a divalent manganese salt with water to obtain an O / W emulsion; (2) mixing a permanganate solution with the O / W emulsion, and carrying out stirring for a reaction to obtain flaky trimanganese tetraoxide; and (3) mixing the flaky trimanganese tetraoxide with a lithium source, and carrying out sintering treatment to obtain the flaky lithium manganate. According to the present application, an emulsion method is utilized to prepare flaky lithium manganate having a stable structure; and the flaky lithium manganate can greatly shorten the transport pathway of lithium ions, improve the lithium ion extraction efficiency, increase the specific surface area of an electrode material, promote sufficient contact between lithium ions in an electrolyte and the electrode material, and further promote the transport of lithium ions.

Description

A kind of flaky lithium manganese oxide and its preparation method and application Technical Field

[0001] The present application relates to the technical field of lithium extraction from salt lakes, for example, a flaky lithium manganese oxide and its preparation method and application. Background Art

[0002] To meet the growing global demand for lithium, selective extraction of lithium from brines has attracted widespread attention. LiMn2O4-based electrochemical lithium recovery systems are one of the best candidates for commercial applications due to their high selectivity and low energy consumption. However, the low ionic diffusion coefficient of lithium manganese oxide (LiMnO4) limits the further development of electrochemical lithium recovery systems.

[0003] CN113896244A discloses a porous, disc-shaped lithium manganate electrode for lithium extraction from salt lakes and a preparation method thereof. The method comprises the following steps: adding acetylacetone to a manganese salt aqueous solution, and then adding polyvinyl pyrrolidone to form a transparent solution; adding hydrazine hydrate under stirring conditions to form a yellow precipitate, and the precipitate is centrifuged and dried to obtain a yellow precursor; calcining the obtained precursor in air to obtain Mn5O8, and then mixing Mn5O8 with a lithium salt and calcining it at high temperature in a temperature-controlled muffle furnace, and naturally cooling to obtain a porous, disc-shaped lithium manganate.

[0004] CN112875760A discloses a method for preparing lithium manganese oxide for lithium ion sieves, which uses a manganese source compound and a lithium source compound as raw materials and prepares lithium manganese oxide for lithium ion sieves suitable for extracting lithium from low-concentration solutions through dynamic sintering.

[0005] The lithium manganate prepared by the above scheme has problems such as low adsorption capacity and poor selectivity, and cannot improve the lithium extraction efficiency.

[0006] Summary of the Invention

[0007] The following is a summary of the subject matter described in detail herein. This summary is not intended to limit the scope of the claims.

[0008] The present application provides a flaky lithium manganese oxide and its preparation method and application. The present application adopts an emulsion method to prepare a structurally stable flaky lithium manganese oxide. The flaky lithium manganese oxide can greatly shorten the transmission path of lithium ions, improve the extraction efficiency of lithium ions, increase the specific surface area of ​​the electrode material, promote the full contact between lithium ions in the electrolyte and the electrode material, and further promote the transmission of lithium ions.

[0009] In a first aspect, the present application provides a method for preparing flaky lithium manganese oxide, the preparation method comprising the following steps:

[0010] (1) mixing an oil phase substance, an emulsifier, and a divalent manganese salt with water to obtain an O / W emulsion;

[0011] (2) mixing the permanganate solution with the O / W emulsion, stirring and reacting to obtain flaky manganese tetraoxide;

[0012] (3) mixing the flaky manganese tetraoxide with a lithium source and sintering the mixture to obtain the flaky lithium manganate;

[0013] Wherein, the emulsifier includes an ionic surfactant and a non-ionic surfactant containing a reducing hydrophilic group.

[0014] The present application adopts an emulsion method to prepare flaky manganese tetraoxide. The structure of the droplets in the O / W emulsion is a shell with reducing and hydrophilic groups (provided by the hydrophilic end of the functional emulsifier and the ionic surfactant) and a hydrophobic core (provided by the hydrophobic end of the functional emulsifier and the ionic surfactant and the oil phase). The divalent manganese ions are coordinated with the oxygen on the shell and enriched on the surface of the droplets; permanganate is added as an oxidant to undergo an oxidation-reduction reaction with the divalent manganese and the functional groups on the shell, thereby generating a large number of manganese oxide nanosheets at the emulsion interface; in the post-treatment process, as the oil phase material is removed, dispersed flaky nano-manganese oxide is obtained. The flaky structure of the manganese tetraoxide is the prerequisite for the lithium manganate electrode material to be flaky. The flaky manganese tetraoxide described in the present application has a stable structure and still maintains a flaky structure after mixing with a lithium source and calcining.

[0015] In one embodiment, the oil phase substance in step (1) comprises any one of pentane, isooctane, n-hexane, n-heptane, ether, ethyl acetate, cyclopentane or cyclohexane, or a combination of at least two thereof.

[0016] In one embodiment, the mass ratio of the oil phase material to water is 1:(80-100), for example, 1:80, 1:85, 1:90, 1:95 or 1:100.

[0017] In one embodiment, the emulsifier includes an ionic surfactant and / or a nonionic surfactant containing a reducing hydrophilic group, and can be selected from an ionic surfactant and a nonionic surfactant containing a reducing hydrophilic group.

[0018] In one embodiment, the ionic surfactant comprises alkyl sulfonate and / or fatty acid salt.

[0019] In one embodiment, the alkyl sulfonate comprises sodium hexadecyl sulfonate and / or sodium dodecyl sulfonate.

[0020] In one embodiment, the fatty acid salt comprises sodium laurate and / or sodium stearate.

[0021] In one embodiment, the hydrophilic group of the nonionic surfactant containing a reducing hydrophilic group includes an aldehyde group and / or a carbonyl group.

[0022] In one embodiment, the nonionic surfactant containing a reducing hydrophilic group includes any one of nonanedial, suberic dialdehyde, heptanedialdehyde, 2-nonanone, 2-heptanone, or 2,4-nonanedione, or a combination of at least two thereof.

[0023] In one embodiment, the mass ratio of the nonionic surfactant containing reducing hydrophilic groups to the ionic surfactant is (1-2):1, for example: 1:1, 1.2:1, 1.5:1, 1.8:1 or 2:1.

[0024] In one embodiment, the divalent manganese salt includes any one of manganese nitrate, manganese chloride, manganese sulfate, or manganese acetate, or a combination of at least two thereof.

[0025] In one embodiment, the mass ratio of the oil phase substance to the emulsifier in step (1) is 1:(0.02-0.05), for example: 1:0.02, 1:0.025, 1:0.03, 1:0.04 or 1:0.05, etc.

[0026] In one embodiment, the mass ratio of the divalent manganese salt to the nonionic surfactant containing a reducing hydrophilic group is (1-2):1, for example: 1, 1.2, 1.5, 1.8 or 2.

[0027] In one embodiment, the particle size of the O / W emulsion is 0.4 to 2 μm, for example, 0.4 μm, 0.8 μm, 1 μm, 1.5 μm or 2 μm.

[0028] The particle size of the O / W emulsion described in this application directly affects the microscopic morphology of the product manganese oxide. If the emulsion diameter is too small, flaky crystals cannot be obtained, but granular crystals. If the particle size of the emulsion is greater than 2 μm, the larger the emulsion diameter, the worse the stability, and the emulsion is easily demulsified under the action of divalent manganese salt to obtain an emulsion with a smaller diameter.

[0029] In one embodiment, the permanganate solution in step (2) is prepared by the following method:

[0030] Barium permanganate is added to deionized water, and sulfuric acid solution is added, the mixture is stirred, and solid barium sulfate precipitate is separated by centrifugation to obtain the permanganate solution.

[0031] In one embodiment, the mixing method in step (2) comprises adding the permanganate solution dropwise into the O / W emulsion.

[0032] In one embodiment, the molar ratio of permanganic acid in the permanganic acid solution to divalent manganese in the O / W emulsion is 1:(1-2), for example, 1:1, 1:1.5, 1:2, etc.

[0033] In one embodiment, the stirring reaction temperature is 20-30°C, for example, 20°C, 22°C, 25°C, 28°C or 30°C.

[0034] In one embodiment, the stirring reaction time is 20 to 30 hours, for example, 20 hours, 22 hours, 25 hours, 28 hours or 30 hours.

[0035] In one embodiment, the stirring reaction is followed by washing, centrifugation and drying.

[0036] In one embodiment, the drying temperature is 50-80°C, for example, 50°C, 55°C, 60°C, 70°C or 80°C.

[0037] In one embodiment, the lithium source in step (3) includes any one of lithium chloride, lithium nitrate, lithium sulfate, lithium carbonate or lithium hydroxide, or a combination of at least two thereof.

[0038] In one embodiment, the sintering temperature is 600-800°C, for example, 600°C, 650°C, 700°C, 750°C or 800°C.

[0039] In one embodiment, the sintering treatment time is 8 to 12 hours, for example, 8 hours, 9 hours, 10 hours, 11 hours or 12 hours.

[0040] In a second aspect, the present application provides a flaky lithium manganese oxide, which is prepared by the method described in the first aspect.

[0041] The flaky lithium manganese oxide prepared in the present application can greatly shorten the transmission path of lithium ions, improve the extraction efficiency of lithium ions, promote the full contact between lithium ions in the electrolyte and the electrode material, and further promote the transmission of lithium ions.

[0042] In a third aspect, the present application provides a lithium manganate extraction electrode, wherein the lithium manganate extraction electrode comprises the flaky lithium manganate as described in the second aspect.

[0043] In a fourth aspect, the present application provides a method for preparing a lithium manganate electrode as described in the third aspect, the preparation method comprising the following steps:

[0044] Mixing the flaky lithium manganate, the conductive agent, and the binder as described in the second aspect with a solvent to obtain a slurry;

[0045] The slurry is coated on the surface of a graphite sheet to obtain the lithium manganate lithium extraction electrode.

[0046] In one embodiment, the conductive agent includes acetylene black.

[0047] In one embodiment, the binder includes polyvinylidene fluoride.

[0048] In one embodiment, the solvent comprises N-methylpyrrolidone.

[0049] In one embodiment, the coating amount of the slurry is 8 to 12 mg / cm 2 , for example: 8mg / cm 2 , 9mg / cm 2 、10mg / cm 2 、11mg / cm 2 or 12 mg / cm 2 wait.

[0050] Compared with the related art, this application has the following beneficial effects:

[0051] (1) This application adopts an emulsion method to prepare a structurally stable sheet of lithium manganese oxide. The sheet of lithium manganese oxide can greatly shorten the transmission path of lithium ions, improve the extraction efficiency of lithium ions, increase the specific surface area of ​​the electrode material, promote the full contact between lithium ions in the electrolyte and the electrode material, and further promote the transmission of lithium ions. The sheet of lithium manganese oxide made into a lithium extraction electrode has high selectivity and adsorption capacity for lithium ions.

[0052] (2) The extraction capacity Q of the electrode made of lithium manganate prepared by the method described in this application e It can reach above 18.72 mg / g.

[0053] Still other aspects will become apparent upon reading and understanding the accompanying drawings and detailed description. BRIEF DESCRIPTION OF THE DRAWINGS

[0054] The accompanying drawings are used to provide a further understanding of the technical solution of this article and constitute a part of the specification. Together with the embodiments of this application, they are used to explain the technical solution of this article and do not constitute a limitation on the technical solution of this article.

[0055] FIG1 is a SEM image of lithium manganate prepared in Example 1 of the present application.

[0056] FIG2 is an XRD diagram of the lithium manganate prepared in Example 1 of the present application and the manganese tetraoxide during the preparation process.

[0057] FIG3 is an XRD diagram of manganese oxide obtained during the preparation of lithium manganate in Comparative Example 1 and Comparative Example 2.

[0058] FIG4 is an XRD diagram of manganese oxide obtained during the preparation of lithium manganate in Comparative Example 4.

[0059] FIG5 is a SEM image of lithium manganate obtained in Comparative Example 5.

[0060] FIG6 is a curve showing the change in concentration of various ions in the electrolyte during the lithium ion extraction process of the lithium manganate prepared in Example 1 of the present application. DETAILED DESCRIPTION

[0061] The technical solution of the present application is further described below through specific implementation methods. Those skilled in the art should understand that the embodiments are only used to help understand the present application and should not be regarded as specific limitations of the present application.

[0062] Example 1

[0063] This embodiment provides a flaky lithium manganese oxide, and the preparation method of the flaky lithium manganese oxide is as follows:

[0064] (1) Sodium hexadecylsulfonate and nonanedial were dispersed in deionized water and stirred until homogeneous and clear. Then, n-heptane (the mass ratio of n-heptane to deionized water was 1:100) was slowly added and stirred at 150 rpm to obtain a milky white O / W emulsion. Manganese chloride was then added and stirred until the metal salt was completely dissolved. The droplet size of the emulsion was observed under an optical microscope, and the average particle size was calculated to be 1.21 μm. The mass ratio of n-heptane, sodium hexadecylsulfonate, and nonanedial was 1:0.02:0.02, and the ratio of manganese chloride to nonanedial was 1.5:1.

[0065] (2) Weighing barium permanganate and adding it to deionized water, adding 98 wt % sulfuric acid at a molar ratio of sulfuric acid to barium permanganate of 1.05:1, stirring and mixing, centrifuging to separate the solid barium sulfate precipitate, thereby obtaining permanganic acid, and adding the permanganic acid solution dropwise to the O / W emulsion at a molar ratio of permanganic acid to manganese chloride of 2:3, stirring and reacting at room temperature for 24 h, washing the obtained dark brown oil with ethanol and water three times each and centrifuging, and then drying at 60° C. to constant weight, thereby obtaining flaky manganese tetraoxide;

[0066] (3) The obtained manganese tetraoxide and lithium carbonate were mixed at a ratio of Li / Mn = 1.05:2, placed in a crucible, and heated to 700°C in a muffle furnace at a rate of 5°C / min for 10 hours. After natural cooling, the flaky lithium manganate LiMn2O4 was obtained. The flaky lithium manganate had an average diameter of 212 nm and a thickness of 0.6 nm.

[0067] The SEM image of the flaky lithium manganese oxide is shown in FIG1 . As can be seen from FIG1 , the lithium manganese oxide prepared in the present application has a flaky structure. The two-dimensional flaky structure shortens the transmission channel of lithium ions, thereby improving the lithium ion extraction efficiency.

[0068] The XRD patterns of the flaky lithium manganate and manganese manganese oxide during the preparation process are shown in FIG2 . As can be seen from the XRD pattern, the diffraction peak intensity of the product is high and consistent with the peak position of the standard card of LiMn2O4 (PDF#35-0782), indicating that the product is a spinel-type lithium manganate with high crystallinity and high purity.

[0069] Example 2

[0070] This embodiment provides a flaky lithium manganese oxide, and the preparation method of the flaky lithium manganese oxide is as follows:

[0071] (1) Sodium laurate and pimelic acid dialdehyde were dispersed in deionized water, stirred until homogeneous and clear, and then ether (the mass ratio of ether to deionized water was 1:100) was slowly added. The mixture was stirred at 200 rpm to obtain a milky white O / W emulsion. Manganese sulfate was then added and the stirring was continued until the metal salt was completely dissolved. The droplet size of the emulsion was observed under an optical microscope, and the average particle size was calculated to be 0.47 μm. The mass ratio of ether to sodium laurate and pimelic acid dialdehyde was 1:0.02:0.02, and the mass ratio of manganese sulfate to pimelic acid dialdehyde was 1.5:1.

[0072] (2) Weighing barium permanganate and adding it to deionized water, adding 98 wt % sulfuric acid at a molar ratio of sulfuric acid to barium permanganate of 1.05:1, stirring and mixing, centrifuging to separate the solid barium sulfate precipitate, thereby obtaining permanganic acid, and adding the permanganic acid solution dropwise to the O / W emulsion at a molar ratio of permanganic acid to manganese chloride of 2:3, stirring and reacting at room temperature for 24 h, and washing the resulting dark brown oil with ethanol and water three times each and centrifuging, and then drying at 60° C. to constant weight, thereby obtaining flaky manganese tetraoxide;

[0073] (3) The obtained manganese tetraoxide and lithium carbonate were mixed at a ratio of Li / Mn = 1.05:2, placed in a crucible, and heated to 600°C in a muffle furnace at 5°C / min for 12 hours. After natural cooling, the flaky lithium manganate LiMn2O4 was obtained. The flaky lithium manganate had an average diameter of 157 nm and a thickness of 0.5 nm.

[0074] Example 3

[0075] This embodiment provides a flaky lithium manganese oxide, and the preparation method of the flaky lithium manganese oxide is as follows:

[0076] (1) Sodium stearate and suberaldehyde were dispersed in deionized water, stirred until homogeneous and clear, and then ethyl acetate (the mass ratio of ethyl acetate to deionized water was 1:80) was slowly added and stirred at 150 rpm to obtain a milky white O / W emulsion. Manganese sulfate was then added and stirred until the metal salt was completely dissolved. The droplet size of the emulsion was observed under an optical microscope, and the average particle size was calculated to be 1.82 μm. The mass ratio of ethyl acetate, sodium stearate, and suberaldehyde was 1:0.015:0.015, and the mass ratio of manganese chloride to suberaldehyde was 2:1.

[0077] (2) Weighing barium permanganate and adding it to deionized water, adding 98 wt % sulfuric acid at a molar ratio of sulfuric acid to barium permanganate of 1.05:1, stirring and mixing, centrifuging to separate the solid barium sulfate precipitate, thereby obtaining permanganic acid, and adding the permanganic acid solution dropwise to the O / W emulsion at a molar ratio of permanganic acid to manganese chloride of 1:1, stirring and reacting at room temperature for 24 h, washing the resulting dark brown oil with ethanol and water three times each and centrifuging, and then drying at 60° C. to constant weight, thereby obtaining flaky manganese tetraoxide;

[0078] (3) The obtained manganese tetraoxide and lithium carbonate were mixed at a ratio of Li / Mn = 1.05:2, placed in a crucible, and heated to 800°C in a muffle furnace at a rate of 5°C / min for 8 hours. After natural cooling, the flaky lithium manganate LiMn2O4 was obtained. The flaky lithium manganate had an average diameter of 186 nm and a thickness of 0.8 nm.

[0079] Example 4

[0080] This embodiment provides a flaky lithium manganese oxide, and the preparation method of the flaky lithium manganese oxide is as follows:

[0081] (1) Sodium laurate and pimelic acid dialdehyde were dispersed in deionized water, stirred until homogeneous and clear, and then ether (the mass ratio of ether to deionized water was 1:100) was slowly added. The mixture was stirred at 200 rpm to obtain a milky white O / W emulsion. Manganese sulfate was then added and the stirring was continued until the metal salt was completely dissolved. The droplet size of the emulsion was observed under an optical microscope, and the average particle size was calculated to be 1.95 μm. The mass ratio of ether to sodium laurate and pimelic acid dialdehyde was 1:0.01:0.01, and the mass ratio of manganese sulfate to pimelic acid dialdehyde was 1:1.

[0082] (2) Weighing barium permanganate and adding it to deionized water, adding 98 wt % sulfuric acid at a molar ratio of sulfuric acid to barium permanganate of 1.05:1, stirring and mixing, centrifuging to separate the solid barium sulfate precipitate, thereby obtaining permanganic acid, and adding the permanganic acid solution dropwise to the O / W emulsion at a molar ratio of permanganic acid to manganese chloride of 1:2, stirring and reacting at room temperature for 24 h, washing the obtained dark brown oil with ethanol and water three times each and centrifuging, and then drying at 60° C. to constant weight, thereby obtaining flaky manganese tetraoxide;

[0083] (3) The obtained manganese tetraoxide and lithium carbonate were mixed at a ratio of Li / Mn = 1.05:2, placed in a crucible, and heated to 600°C in a muffle furnace at 5°C / min for 12 hours. After natural cooling, the flaky lithium manganate LiMn2O4 was obtained. The flaky lithium manganate had an average diameter of 174 nm and a thickness of 0.3 nm.

[0084] Example 5

[0085] This embodiment provides a flaky lithium manganese oxide, and the preparation method of the flaky lithium manganese oxide is as follows:

[0086] (1) Sodium stearate and suberaldehyde were dispersed in deionized water, stirred until homogeneous and clear, and then ethyl acetate (the mass ratio of ethyl acetate to deionized water was 1:80) was slowly added and stirred at 150 rpm to obtain a milky white O / W emulsion. Manganese sulfate was then added and stirred until the metal salt was completely dissolved. The droplet size of the emulsion was observed under an optical microscope, and the average particle size was calculated to be 0.87 μm. The mass ratio of ethyl acetate, sodium stearate, and suberaldehyde was 1:0.017:0.033, and the mass ratio of manganese chloride to suberaldehyde was 2:1.

[0087] (2) Weighing barium permanganate and adding it to deionized water, adding 98 wt % sulfuric acid at a molar ratio of sulfuric acid to barium permanganate of 1.05:1, stirring and mixing, centrifuging to separate the solid barium sulfate precipitate, thereby obtaining permanganic acid, and adding the permanganic acid solution dropwise to the O / W emulsion at a molar ratio of permanganic acid to manganese chloride of 1:1, stirring and reacting at room temperature for 24 h, washing the resulting dark brown oil with ethanol and water three times each and centrifuging, and then drying at 60° C. to constant weight, thereby obtaining flaky manganese tetraoxide;

[0088] (3) The obtained manganese tetraoxide and lithium carbonate were mixed at a ratio of Li / Mn = 1.05:2, placed in a crucible, and heated to 800°C in a muffle furnace at a rate of 5°C / min for 8 hours. After natural cooling, the flaky lithium manganate LiMn2O4 was obtained. The flaky lithium manganate had an average diameter of 129 nm and a thickness of 0.6 nm.

[0089] Example 6

[0090] The only difference between this embodiment and embodiment 1 is that the mass ratio of the oil phase substance (n-heptane) to the emulsifier (sodium hexadecylsulfonate and nonanedial) is 1:0.01, and the other conditions and parameters are exactly the same as those in embodiment 1.

[0091] Example 7

[0092] The only difference between this embodiment and embodiment 1 is that the mass ratio of the oil phase substance (n-heptane) to the emulsifier (sodium hexadecylsulfonate and nonanedial) is 1:0.08, and the other conditions and parameters are exactly the same as those in embodiment 1.

[0093] Example 8

[0094] The only difference between this embodiment and embodiment 1 is that the mass ratio of the divalent manganese salt (manganese chloride) to the nonionic surfactant containing a reducing hydrophilic group (nonanedial) is 0.5:1, and the other conditions and parameters are exactly the same as those in embodiment 1.

[0095] Example 9

[0096] The only difference between this embodiment and embodiment 1 is that the mass ratio of the divalent manganese salt (manganese chloride) to the nonionic surfactant containing a reducing hydrophilic group (nonanedial) is 2.5:1, and the other conditions and parameters are exactly the same as those in embodiment 1.

[0097] Comparative Example 1

[0098] The only difference between this comparative example and Example 1 is that potassium permanganate solution is used instead of the permanganic acid solution in step (2), that is, the molar ratio of potassium permanganate to manganese chloride is 2:3. Other conditions and parameters are exactly the same as those in Example 1.

[0099] The XRD pattern of the product obtained in step (2) is shown in FIG3 . The XRD results show that the product of step (2) is non-spinel MnO 2 .

[0100] Furthermore, MnO2 is mixed with a lithium source and calcined to obtain flaky lithium manganate powder.

[0101] Comparative Example 2

[0102] The only difference between this comparative example and Example 1 is that no nonanedialdehyde is added, that is, the mass of sodium hexadecylsulfonate is 4% of the mass of n-heptane, and the mass of manganese chloride is 75% of the mass of sodium hexadecylsulfonate. Other conditions and parameters are exactly the same as those in Example 1.

[0103] The XRD pattern of the product obtained in step (2) is shown in FIG3 . The XRD results show that the product of step (2) is non-spinel MnO 2 .

[0104] Furthermore, MnO2 is mixed with a lithium source and calcined to obtain lithium manganate powder.

[0105] Comparative Example 3

[0106] The only difference between this comparative example and Example 1 is that sodium hexadecyl sulfate is not added, and the other conditions and parameters are exactly the same as those in Example 1. Granular manganese tetraoxide is obtained.

[0107] Comparative Example 4

[0108] The only difference between this comparative example and Example 1 is that manganese chloride is not added, the feeding amount of permanganic acid is determined according to nonanedial, the feeding molar ratio of permanganic acid to nonanedial is 1:1.05, and the other conditions and parameters are exactly the same as those in Example 1.

[0109] The XRD pattern of the product obtained in step (2) is shown in FIG4 . The XRD results show that the product of step (2) is Mn2O3.

[0110] Furthermore, Mn2O3 is mixed with a lithium source and calcined to obtain flaky lithium manganate powder.

[0111] Comparative Example 5

[0112] The only difference between this comparative example and Example 1 is that granular Mn3O4 is used to prepare lithium manganate, and spherical particles of Mn3O4 with an average particle size of 500 nm are purchased. Other conditions and parameters are exactly the same as those in Example 1.

[0113] The SEM image of the prepared lithium manganate is shown in FIG5 .

[0114] Performance testing:

[0115] (1) The lithium manganate, acetylene carbon black (conductive agent) and polyvinylidene fluoride (binder) prepared in the examples and comparative examples were mixed with N-methylpyrrolidone (NMP) in a weight ratio of 8:1:1 to prepare a slurry for the working electrode. The slurry was then added to a 10 mg / cm 2 The lithium manganese oxide electrode was loaded on a graphite sheet and dried at 80°C for 10 hours. The lithium capture experiment was carried out in a two-electrode system consisting of a lithium manganese oxide electrode as a working electrode and Ag as a counter electrode. The whole process consists of two steps: extraction and release. In the capture process (discharge process), the electrolyte is 40mL of 100mM LiCl solution, and in the release process (charge process), the electrolyte is 0.01M LiCl solution. The applied current density is 150mA.g -1 The charge and discharge time was 60 min. The Li selectivity of the electrode material was tested in simulated saline (30 mM LiCl, NaCl, KCl, MgCl2, CaCl2), with other conditions being the same. Before changing the electrolyte, the electrode was carefully rinsed with deionized water. The concentration of each ion was analyzed by ICP-OES, and the Li + Extraction capacity (Qe).

[0116] Where Q e (mg / g) is the extraction capacity; C0 (mg / L) is Li + The initial concentration of C e (mg / L) is Li + The final concentration is: V(L) is the volume of the solution; m(g) is the mass of lithium manganate. The test results are shown in Table 1:

[0117] Table 1

[0118] As can be seen from Table 1, from Examples 1-5, the extraction capacity Q of the electrode made of lithium manganate prepared by the method described in this application is e It can reach above 18.72 mg / g.

[0119] A comparison of Example 1 and Examples 6-7 shows that during the preparation of the flaky lithium manganate described in the present application, the mass ratio of the oil phase substance to the emulsifier affects its performance. When the mass ratio of the oil phase substance to the emulsifier is controlled at 1:(0.02-0.05), the flaky lithium manganate obtained has better performance. When the amount of emulsifier exceeds 5% of the oil phase substance, the performance of the product is not significantly improved because the size of the emulsion droplets does not change with the increase in the amount of emulsifier. If the amount of emulsifier added is too small, the droplet size formed is too large, the stability of the emulsion droplets decreases, and demulsification occurs.

[0120] By comparison of Example 1 and Examples 8-9, it can be seen that in the preparation process of the flaky lithium manganate described in the present application, the mass ratio of the divalent manganese salt and the non-ionic surfactant containing a reducing hydrophilic group affects its performance. When the mass ratio of the divalent manganese salt and the non-ionic surfactant containing a reducing hydrophilic group is controlled at (1-2):1, the performance of the flaky lithium manganate obtained is better. If the amount of divalent manganese salt added is too large, the thickness of the product is too large, resulting in a decrease in the lithium extraction effect; if the amount of divalent manganese salt added is too small, it cannot be enriched on the surface of the emulsion droplets, and it is difficult to generate manganese oxide at the emulsion interface.

[0121] From the comparison between Example 1 and Comparative Example 1, it can be seen that potassium permanganate is used instead of permanganic acid for oxidation, K + It will enter the crystal lattice and affect the crystal shape.

[0122] From the comparison between Example 1 and Comparative Example 2, it can be seen that in the absence of a non-ionic surfactant containing a reducing hydrophilic group, it is equivalent to the redox reaction between permanganate and divalent manganese ions in a uniform aqueous environment, thereby obtaining MnO2.

[0123] From the comparison between Example 1 and Comparative Example 3, it can be seen that in the absence of an ionic surfactant, the emulsion stability is poor, it is difficult to form a stable oil-water interface, and therefore manganese oxide cannot be generated at the interface.

[0124] From the comparison between Example 1 and Comparative Example 4, it can be seen that in the absence of divalent manganese ions, the reduction product obtained is flaky Mn2O3, which is equivalent to the oxidation of nonanedial on the surface of the emulsion droplets by permanganate.

[0125] By comparing Example 1 and Comparative Example 5, it can be seen that the flaky lithium manganese oxide prepared in the present application can greatly shorten the transmission path of lithium ions, improve the extraction efficiency of lithium ions, promote the full contact between lithium ions in the electrolyte and the electrode material, and further promote the transmission of lithium ions, compared with granular lithium manganese oxide.

[0126] The curve of the change in the concentration of various ions in the electrolyte during the lithium ion extraction process of the lithium manganate prepared in Example 1 of the present application is shown in Figure 6. As can be seen from Figure 6, after 10 cycles of extraction, the lithium ion concentration in the electrolyte decreased by 6.86mmol / L, and the concentrations of other coexisting ions remained almost unchanged. At a current density of 150mA / g, the amount of lithium ions extracted after 1h of discharge was 18.7mg / g, and almost no other coexisting ions were extracted. This shows that the porous disc-shaped lithium manganate electrode has high selectivity and adsorption capacity for lithium ions.

[0127] The applicant declares that the above is only a specific implementation method of the present application, but the protection scope of the present application is not limited thereto. Technical personnel in the relevant technical field should understand that any changes or substitutions that can be easily thought of by technical personnel in the relevant technical field within the technical scope disclosed in this application fall within the protection scope and disclosure scope of this application.

Claims

1. A preparation method of flaky lithium manganate, which comprises the following steps: (1) Mix an oil-phase substance, an emulsifier and a divalent manganese salt with water to obtain an O / W emulsion; (2) Mix a permanganic acid solution with the O / W emulsion, and stir and react to obtain flaky manganese tetroxide; (3) Mix the flaky manganese tetroxide with a lithium source, and perform a sintering treatment to obtain the flaky lithium manganate; wherein, the emulsifier includes an ionic surfactant and a non-ionic surfactant containing a reducing hydrophilic group.

2. The preparation method according to claim 1, wherein, The oil-phase substance in step (1) includes any one or a combination of at least two of pentane, isooctane, n-hexane, n-heptane, diethyl ether, ethyl acetate, cyclopentane or cyclohexane.

3. The preparation method according to claim 1 or 2, wherein The mass ratio of the oil-phase substance to water is 1∶(80 - 100).

4. The preparation method according to any one of claims 1-3, wherein, The ionic surfactant includes alkyl sulfonate and / or fatty acid salt; Optionally, the alkyl sulfonate includes sodium hexadecyl sulfonate and / or sodium dodecyl sulfonate; Optionally, the fatty acid salt includes sodium laurate and / or sodium stearate.

5. The preparation method according to any one of claims 1-4, wherein, The hydrophilic group of the non-ionic surfactant containing a reducing hydrophilic group includes aldehyde group and / or carbonyl group; Optionally, the non-ionic surfactant containing a reducing hydrophilic group includes any one or a combination of at least two of nonanedial, octanedial, heptanedial, 2-nonanone, 2-heptanone or 2,4-nonanedione.

6. The preparation method according to any one of claims 1-5, wherein, The mass ratio of the non-ionic surfactant containing a reducing hydrophilic group to the ionic surfactant is (1 - 2)∶1; Optionally, the divalent manganese salt includes any one or a combination of at least two of manganese nitrate, manganese chloride, manganese sulfate or manganese acetate.

7. The preparation method according to any one of claims 1-6, wherein, The mass ratio of the oil-phase substance to the emulsifier in step (1) is 1∶(0.02 - 0.05); Optionally, the mass ratio of the divalent manganese salt to the non-ionic surfactant containing a reducing hydrophilic group is (1 - 2)∶1; Optionally, the particle size in the O / W emulsion is 0.4 - 2 μm.

8. The preparation method according to any one of claims 1-7, wherein, The permanganic acid solution in step (2) is prepared by the following method: Add barium permanganate to deionized water, add sulfuric acid solution, stir and mix, and centrifuge to separate the solid barium sulfate precipitate, then the permanganic acid solution is obtained.

9. The preparation method according to any one of claims 1-8, wherein, The mixing method in step (2) includes dropping the permanganic acid solution into the O / W emulsion; Optionally, the molar ratio of permanganic acid in the permanganic acid solution to divalent manganese in the O / W emulsion is 2∶(1 - 5).

10. The preparation method according to any one of claims 1-9, wherein, The temperature of the stirring reaction is 20 - 30 °C; Optionally, the time of the stirring reaction is 20 - 30 h; Optionally, after the stirring reaction, washing, centrifuging and drying treatments are carried out; Optionally, the drying temperature is 50 - 80 °C.

11. The preparation method according to any one of claims 1-10, wherein, The lithium source in step (3) includes any one or a combination of at least two of lithium chloride, lithium nitrate, lithium sulfate, lithium carbonate or lithium hydroxide; Optionally, the temperature of the sintering treatment is 600 - 800 °C; Optionally, the time of the sintering treatment is 8 - 12 h.

12. A sheet-like lithium manganate, wherein, The flaky lithium manganate is prepared by the method according to any one of claims 1 - 11.

13. A lithium-extracting electrode for lithium manganate, wherein, The lithium extraction electrode of lithium manganate contains the flaky lithium manganate according to claim 12.

14. A method for preparing a lithium extraction electrode of lithium manganate as described in claim 13, comprising the following steps: Mixing the flaky lithium manganate, conductive agent and binder as described in claim 12 with a solvent to obtain a slurry; Coating the slurry on the surface of a graphite sheet to obtain the lithium extraction electrode of lithium manganate.

15. The preparation method according to claim 14, wherein, The conductive agent includes acetylene black; Optionally, the binder includes polyvinylidene fluoride; Optionally, the solvent includes N-methylpyrrolidone; Optionally, the coating amount of the slurry is 8 to 12 mg / cm 2 .

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