Lithium manganate material, preparation method therefor, and use thereof

Abstract

A lithium manganate material, a preparation method therefor, and a use thereof, relating to the technical field of lithium manganate materials. The lithium manganate material comprises aluminum-doped lithium manganate and a layered structure formed by self-assembly of functionalized graphene, wherein the aluminum-doped lithium manganate is loaded at an interlayer position of the layered structure, and the functionalized graphene is graphene grafted with glycan on the surface. The lithium manganate material has relatively high lithium ion capacity, lithium ion extraction efficiency and cycling performance. The preparation thereof comprises: mixing functionalized graphene, a lithium source, and an aluminum source, then reacting the materials with a manganese source, and further carrying out a heating reaction and calcination. The lithium manganate material can be prepared into an electrode for use in lithium extraction.

Description

A lithium manganate material and its preparation method and application Technical Field

[0001] The present disclosure relates to the technical field of lithium manganate materials, and in particular to a lithium manganate material and a preparation method and application thereof. Background Art

[0002] Lithium manganese oxide (LMO) has the advantages of easy preparation and low cost, and is one of the most promising materials for lithium extraction from salt lakes. Spinel lithium manganese oxide (LMO) is used as an active material for electrochemical lithium extraction, in which Mn 3+ Due to its special 3d orbital electron configuration (t 2g 3 -e g 1 ), which will cause the Jahn-Teller effect when used, resulting in severe distortion of the octahedral MnO6 structure, causing manganese capacity loss, and further leading to lithium ion sieve in Li + The stability and lithium extraction efficiency during the extraction / intercalation process are reduced. What is more serious is that the large amount of manganese dissolved in water will cause serious water pollution during industrial production.

[0003] Conventional methods typically involve coating and doping to improve manganese loss and, to a certain extent, lithium extraction efficiency. However, the micromorphology and pore structure of lithium manganese oxide also affect its lithium extraction efficiency and cycling performance. Currently, no lithium manganese oxide material has been found that can simultaneously achieve high lithium extraction rates and cycling stability.

[0004] In view of this, the present disclosure is proposed.

[0005] Summary of the Invention

[0006] The purpose of the present disclosure is to provide a lithium manganate material and its preparation method and application to solve or improve the above technical problems.

[0007] The present disclosure can be implemented as follows:

[0008] In a first aspect, the present disclosure provides a lithium manganate material comprising a layered structure formed of functionalized graphene and aluminum-doped lithium manganate, wherein the aluminum-doped lithium manganate is loaded at the interlayer positions of the layered structure;

[0009] Among them, the functionalized graphene is graphene with polysaccharide grafted on the surface.

[0010] In an alternative embodiment, the aluminum-doped lithium manganate is in situ generated from a manganese source, an aluminum source, and a lithium source at an interlayer position of the layered structure.

[0011] In an optional embodiment, the lithium manganate material includes at least one of the following features:

[0012] Feature 1: The specific surface area of ​​lithium manganate material is 8m 2 / g-9m 2 / g;

[0013] Feature 2: The average pore size of lithium manganese oxide material is 15nm-20nm.

[0014] In a second aspect, the present disclosure provides a method for preparing a lithium manganate material as described in any of the aforementioned embodiments, comprising the following steps: mixing functionalized graphene, a lithium source, and an aluminum source to obtain a mixed solution; reacting the mixed solution with a manganese source to obtain a reaction solution; heating the reaction solution to react to obtain a flake; and grinding the flake and then calcining it.

[0015] In an optional embodiment, the preparation of functionalized graphene includes reacting an epoxy-modified graphene solution with polysaccharide.

[0016] In an optional embodiment, the preparation of functionalized graphene includes at least one of the following features:

[0017] Feature 1: The mass ratio of epoxy-modified graphene to polysaccharide in the epoxy-modified graphene solution is 1:0.2 to 1:0.4;

[0018] Feature 2: The reaction temperature of the epoxy-modified graphene solution and polysaccharide is 80°C-120°C;

[0019] Feature 3: The reaction time of epoxy-modified graphene solution and polysaccharide is 6h-10h;

[0020] Feature 4: The solvent used in the epoxy-modified graphene solution includes N,N-dimethylformamide;

[0021] Feature 5: The ratio of the solvent used in the epoxy-modified graphene solution to the epoxy-modified graphene is 300 mL:1 g to 400 mL:1 g.

[0022] In an optional embodiment, the polysaccharide includes at least one of carboxymethyl cellulose and its salts, alginic acid and its salts, hyaluronic acid and its salts, and carboxymethyl chitosan.

[0023] In an optional embodiment, the preparation of epoxy-modified graphene includes: mixing and reacting a graphene oxide solution with an epoxy silane coupling agent.

[0024] In an optional embodiment, the preparation of epoxy-modified graphene includes at least one of the following features:

[0025] Feature 1: The mass ratio of graphene oxide to epoxy silane coupling agent in the graphene oxide solution is 0.1:2 to 0.1:2.5;

[0026] Feature 2: The reaction temperature of the graphene oxide solution and the epoxy silane coupling agent is 60°C-80°C;

[0027] Feature 3: The reaction time of graphene oxide solution and epoxy silane coupling agent is 5h-8h;

[0028] Feature 4: The solvent used in the graphene oxide solution includes anhydrous ethanol;

[0029] Feature 5: The ratio of the solvent to graphene oxide used in the graphene oxide solution is 90g:0.1g to 100g:0.1g.

[0030] In an optional embodiment, the epoxy silane coupling agent includes at least one of 3-glycidoxypropyltriethoxysilane, epoxybutyltrimethoxysilane, 5,6-epoxyhexyltriethoxysilane, 3-glycidoxypropylmethyldiethoxysilane and 3-(2,3-epoxypropoxy)propyltrimethoxysilane.

[0031] In an optional embodiment, the mass ratio of the functionalized graphene to the manganese source is 1:8 to 1:10, and the molar ratio of the lithium source, the aluminum source, and the manganese source is 1:(0.2-0.5):(1.5-1.8).

[0032] In alternative embodiments, the lithium source comprises a lithium salt; and / or the aluminum source comprises an aluminum salt; and / or the manganese source comprises permanganate or a salt thereof.

[0033] In an optional embodiment, the lithium salt includes at least one of lithium chloride, lithium nitrate and lithium acetate;

[0034] and / or, the aluminum salt comprises at least one of aluminum nitrate and aluminum chloride;

[0035] And / or, the manganese source includes at least one of permanganic acid and potassium permanganate.

[0036] In an optional embodiment, the mixing temperature of the functionalized graphene, the lithium source and the aluminum source is 45°C-55°C.

[0037] In an optional embodiment, the manganese source is added to the mixed solution in a dropwise manner.

[0038] In an optional embodiment, the reaction of the mixed solution with the manganese source is carried out at 45° C.-55° C. for 10 min-30 min.

[0039] In an optional embodiment, the heating reaction is carried out at 150° C.-200° C. for 5 h-7 h.

[0040] In an alternative embodiment, the calcination includes at least one of the following features:

[0041] Feature 1: Calcination is carried out in an oxygen-containing atmosphere;

[0042] Feature 2: Calcination temperature is 600℃-700℃;

[0043] Feature 3: Calcination time is 3h-6h.

[0044] In a third aspect, the present disclosure provides an electrode, the raw materials for preparing the electrode include the lithium manganate material of any one of the aforementioned embodiments.

[0045] In a fourth aspect, the present disclosure provides a use of a lithium manganate material according to any one of the aforementioned embodiments or an electrode according to the aforementioned embodiments in lithium extraction.

[0046] The beneficial effects of the present disclosure include:

[0047] The lithium manganate material provided by the present disclosure includes aluminum-doped lithium manganate and a layered structure formed by self-assembly of functionalized graphene. The interlayer positions of the layered structure are loaded with aluminum-doped lithium manganate, and the functionalized graphene is graphene with polysaccharide grafted on the surface.

[0048] On the one hand, polysaccharide grafting can make the surface of graphene grafted with a large number of carboxyl groups and hydroxyl groups with high degree of freedom, which can react with Al 3+ Coordination, Al 3+ By coordinating with carboxyl and hydroxyl groups, it can act as a binder to allow functionalized graphene to self-assemble into a layered ordered structure. On the other hand, the permanganate used to form lithium manganate enters the interlayer position of the layered structure and undergoes redox reaction with polysaccharide as a reducing agent. At the same time, the permanganate can also react with Al 3+ and Li for forming lithium manganate + The reaction generates aluminum-doped lithium manganate in situ.

[0049] The present invention discloses a method for preparing a 3D ... 3+ The lithium extraction capacity, lithium extraction rate, and Li + By loading aluminum-doped lithium manganate between the layers of the layered structure, the large-diameter pores in the material can be reduced and the mesopores can be increased, thereby increasing the lithium extraction rate and reducing the manganese loss. BRIEF DESCRIPTION OF THE DRAWINGS

[0050] In order to more clearly illustrate the technical solutions of the embodiments of the present disclosure, the following briefly introduces the drawings required for use in the embodiments. It should be understood that the following drawings only illustrate certain embodiments of the present disclosure and therefore should not be regarded as limiting the scope. For ordinary technicians in this field, other relevant drawings can be obtained based on these drawings without creative work.

[0051] FIG1 is an XRD pattern of lithium manganate materials prepared in Example 1 and Comparative Examples 1-4;

[0052] FIG2 is a SEM image of the lithium manganate material prepared in Example 1;

[0053] Figure 3 is an enlarged view of Figure 2;

[0054] FIG4 is a SEM image of the lithium manganate material prepared in Comparative Example 4;

[0055] FIG5 is an infrared spectrum of the lithium manganate materials prepared in Example 1 and Comparative Example 1;

[0056] FIG6 shows the lithium capacity E of Example 1 and Comparative Examples 1-4. Li Graph of the changing relationship over time. DETAILED DESCRIPTION

[0057] To make the purpose, technical solutions, and advantages of the embodiments of the present disclosure more clear, the technical solutions in the embodiments of the present disclosure are described clearly and completely below. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer were followed. Reagents or instruments used where the manufacturer is not specified are conventional products that can be purchased commercially.

[0058] The lithium manganate material provided by the present disclosure, its preparation method and application are described in detail below.

[0059] The present disclosure provides a lithium manganate material, which includes a layered structure formed by functionalized graphene and aluminum-doped lithium manganate, and the interlayer positions of the layered structure are loaded with aluminum-doped lithium manganate; wherein the functionalized graphene is graphene with polysaccharide grafted on the surface.

[0060] In some embodiments, the aluminum-doped lithium manganate is in situ generated from a manganese source, an aluminum source, and a lithium source at an interlayer position of the layered structure.

[0061] As for the functionalized graphene, on the one hand, polysaccharide modification can graft a large number of carboxyl groups and hydroxyl groups with high degree of freedom onto the graphene surface, which can react with Al 3+ Coordination, Al 3+ By coordinating with carboxyl and hydroxyl groups, it can act as a binder to allow functionalized graphene to self-assemble into a layered ordered structure. On the other hand, the permanganate used to form lithium manganate enters the interlayer position of the layered structure and undergoes redox reaction with polysaccharides as a reducing agent. At the same time, the permanganate can also react with Al 3+ and Li for forming lithium manganate + The reaction generates aluminum-doped lithium manganate in situ.

[0062] The present invention discloses a method for preparing a 3D ... 3+The lithium extraction capacity, lithium extraction rate, and Li + By loading aluminum-doped lithium manganate between the layers of the layered structure, the material's macropores are reduced and mesopores are increased, thereby increasing the lithium extraction rate and reducing manganese loss. "Mesopores" refers to pores with a diameter of 2-50nm, and "macropores" refers to pores with a diameter greater than 50nm.

[0063] In some embodiments, the specific surface area of ​​the lithium manganate material provided by the present disclosure can be 8m 2 / g-9m 2 / g, such as 8.27m 2 In some embodiments, the average pore size of the lithium manganate material provided by the present disclosure may be 15 nm to 20 nm, such as 15.24 nm.

[0064] Accordingly, the present disclosure also provides a method for preparing the above-mentioned lithium manganate material, which may include the following steps: mixing functionalized graphene, a lithium source, and an aluminum source to obtain a mixed solution; reacting the mixed solution with a manganese source to obtain a reaction solution; heating the reaction solution to react to obtain a flake; and grinding the flake and then calcining it.

[0065] It should be noted that if the functionalized graphene, lithium source, aluminum source and manganese source are mixed and reacted simultaneously, a layered lithium manganate material cannot be obtained in the end.

[0066] For reference, the preparation of the functionalized graphene may include reacting an epoxy-modified graphene solution with polysaccharide.

[0067] The solvent used in the epoxy-modified graphene solution may include N,N-dimethylformamide (DMF), or other solvents capable of dissolving the epoxy-modified graphene. For example, the amount ratio of the solvent used in the epoxy-modified graphene solution to the epoxy-modified graphene may be 300 mL:1 g to 400 mL:1 g, such as 300 mL:1 g, 350 mL:1 g, or 400 mL:1 g, or any other value within the range of 300 mL:1 g to 400 mL:1 g.

[0068] The mass ratio of epoxy-modified graphene to polysaccharide in the epoxy-modified graphene solution can be 1:0.2 to 1:0.4, such as 1:0.2, 1:0.25, 1:0.3, 1:0.35 or 1:0.4, or any other value within the range of 1:0.2 to 1:0.4.

[0069] If the amount of polysaccharide is too little, it is not conducive to Al 3+ It is difficult to form a layered structure with it; if the amount of polysaccharide is too much, the polysaccharide as a reducing agent will further reduce the manganese element, making the Mn in the lithium manganese oxide3+ Too much will increase manganese loss.

[0070] The reaction temperature of the epoxy-modified graphene solution and the polysaccharide can be 80°C-120°C, such as 80°C, 85°C, 90°C, 95°C, 100°C, 105°C, 110°C, 115°C or 120°C, or any other value within the range of 80°C-120°C.

[0071] The reaction time of the epoxy-modified graphene solution and the polysaccharide can be 6 h-10 h, such as 6 h, 6.5 h, 7 h, 7.5 h, 8 h, 8.5 h, 9 h, 9.5 h or 10 h, or any other value within the range of 6 h-10 h.

[0072] The polysaccharide may illustratively but not limitatively include at least one of carboxymethyl cellulose and its salts, alginic acid and its salts, hyaluronic acid and its salts, and carboxymethyl chitosan.

[0073] By the above method, graphene with polysaccharide grafted on the surface can be obtained.

[0074] In some embodiments, the epoxy-modified graphene can be ultrasonically dispersed in DMF, and then the polysaccharide is added and ultrasonically dissolved until it is completely dissolved. The temperature is raised to 80°C-120°C and stirred for reaction for 6h-10h. After the reaction is completed, vacuum filtration is performed, and the mixture is washed multiple times with deionized water and ethanol, and then dried at 60°C to obtain functionalized graphene.

[0075] For reference, the preparation of the epoxy-modified graphene may include: mixing a graphene oxide solution with an epoxy silane coupling agent for reaction.

[0076] Graphene oxide can be prepared by existing methods in the prior art, such as electrolysis, Brodie method, or Hummers method. The present disclosure does not limit the preparation method of graphene oxide. In some embodiments, the above-mentioned graphene oxide can be prepared according to the improved Hummers method. For details, please refer to Marcano DC, Kosynkin DV, Berlin JM, et al. Improved Synthesis of Graphene Oxide [J]. Acs Nano, 2010, 4(8): 4806-4814.

[0077] In the present disclosure, the solvent used in the graphene oxide solution may include anhydrous ethanol or other solvents capable of dissolving or dispersing graphene oxide. The ratio of the solvent to graphene oxide used in the graphene oxide solution may be 90 g:0.1 g to 100 g:0.1 g, such as 90 g:0.1 g, 95 g:0.1 g, or 100 g:0.1 g, or any other value within the range of 90 g:0.1 g to 100 g:0.1 g.

[0078] The mass ratio of graphene oxide to epoxy silane coupling agent in the graphene oxide solution can be 0.1:2 to 0.1:2.5, such as 0.1:2, 0.1:2.1, 0.1:2.2, 0.1:2.3, 0.1:2.4 or 0.1:2.5, or any other value within the range of 0.1:2 to 0.1:2.5.

[0079] The reaction temperature of the graphene oxide solution and the epoxy silane coupling agent can be 60°C-80°C, such as 60°C, 65°C, 70°C, 75°C or 80°C, or any other value within the range of 60°C-80°C.

[0080] The reaction time of the graphene oxide solution and the epoxy silane coupling agent can be 5 h to 8 h, such as 5 h, 5.5 h, 6 h, 6.5 h, 7 h, 7.5 h or 8 h, or any other value within the range of 5 h to 8 h.

[0081] The epoxysilane coupling agent may illustratively but not limitatively include at least one of 3-glycidoxypropyltriethoxysilane, epoxybutyltrimethoxysilane, 5,6-epoxyhexyltriethoxysilane, 3-glycidoxypropylmethyldiethoxysilane and 3-(2,3-epoxypropoxy)propyltrimethoxysilane.

[0082] In some embodiments, graphene oxide can be ultrasonically dispersed in anhydrous ethanol, an epoxy silane coupling agent is added and stirred evenly, and then the temperature is raised to 60°C-80°C and stirred under reflux for 5h-8h. After the reaction is completed, vacuum filtration is performed, and the mixture is washed multiple times with deionized water and anhydrous ethanol, and dried at 60°C to obtain epoxy-modified graphene.

[0083] The mass ratio of the functionalized graphene to the manganese source used in the preparation of the lithium manganate material disclosed herein can be 1:8 to 1:10, such as 1:8, 1:8.5, 1:9, 1:9.5 or 1:10, or any other value within the range of 1:8 to 1:10. The molar ratio of the lithium source, the aluminum source and the manganese source can be 1:(0.2-0.5):(1.5-1.8), such as 1:0.2:1.5, 1:0.2:1.6, 1:0.2:1.7, 1:0.2:1.8, 1:0.3:1.5, 1:0.3:1.6, 1:0.3:1.7, 1:0.3:1.8, 1:0.4:1.5, 1:0.4:1.6, 1:0.4:1.7, 1:0.4:1.8, 1:0.5:1.5, 1:0.5:1.6, 1:0.5:1.7 or 1:0.5:1.8, or it can be any other value within the range of 1:(0.2-0.5):(1.5-1.8).

[0084] For reference, the lithium source may include a lithium salt, the aluminum source may include an aluminum salt, and the manganese source may include permanganate or a salt thereof. The lithium salt may, for example but not limited to, include at least one of lithium chloride, lithium nitrate, and lithium acetate; the aluminum salt may, for example but not limited to, include at least one of aluminum nitrate and aluminum chloride; and the manganese source may, for example but not limited to, include at least one of permanganate and potassium permanganate.

[0085] The functionalized graphene, the lithium source, and the aluminum source may be mixed at a temperature of 45° C. to 55° C. (eg, 45° C., 48° C., 50° C., 52° C., or 55° C.).

[0086] By mixing functionalized graphene, lithium source and aluminum source first, the Al in the aluminum source can be 3+ Coordinate with the carboxyl and hydroxyl groups grafted onto the surface of functionalized graphene, thereby enriching it on the surface of functionalized graphene. 3+ It can act as an adhesive to enable functionalized graphene to self-assemble into a layered ordered structure.

[0087] The manganese source can be added to the mixed solution in a dropwise manner, for example, at a rate of 1 drop / 2 seconds.

[0088] The reaction of the mixed solution and the manganese source can be carried out at 45°C-55°C (such as 45°C, 48°C, 50°C, 52°C or 55°C) for 10 min-30 min (such as 10 min, 15 min, 20 min, 25 min or 30 min).

[0089] In some embodiments, the temperature at which the functionalized graphene, the lithium source, and the aluminum source are mixed is recorded as T1, and the reaction temperature of the mixture with the manganese source is recorded as T2, where T1=T2.

[0090] By reacting the mixed solution with a manganese source, the manganese source undergoes an oxidation-reduction reaction with the polysaccharide at the interlayer position of the layered structure. At the same time, the manganese source can also undergo a hydrothermal reaction with the surrounding lithium source and aluminum source to generate lithium manganate.

[0091] The reaction solution may be heated in a resistance furnace. For example, the heating reaction may be carried out at 150° C. to 200° C. (e.g., 150° C., 160° C., 170° C., 180° C., 190° C., or 200° C.) for 5 to 7 hours (e.g., 5 hours, 5.5 hours, 6 hours, 6.5 hours, or 7 hours).

[0092] Through the above heating reaction, the corresponding elements enter the crystal lattice of the material and form lithium manganese oxide with a spinel structure.

[0093] In some embodiments, the functionalized graphene can be dispersed in deionized water, lithium salt and aluminum salt added, heated to 50°C, and stirred evenly. Permanganate or its salt solution is then added dropwise while maintaining the temperature and stirring. After the addition is complete, the reaction is allowed to incubate for 10-30 minutes. The reaction solution is then transferred to a porcelain crucible and placed in a resistance furnace at 150-200°C for 5-7 hours before drying to obtain a black flake.

[0094] After obtaining the flakes, they can be ground, for example, until the particles are substantially uniform as seen by visual inspection.

[0095] In the present disclosure, calcination can be performed in an oxygen-containing atmosphere. In some embodiments, calcination is performed in an air atmosphere.

[0096] For reference, the calcination temperature may be 600°C-700°C, such as 600°C, 620°C, 650°C, 680°C or 700°C, or any other value within the range of 600°C-700°C.

[0097] The calcination time can be 3 h to 6 h, such as 3 h, 3.5 h, 4 h, 4.5 h, 5 h, 5.5 h or 6 h, etc., or any other value within the range of 3 h to 6 h.

[0098] Through the above calcination step, the material can be activated and made active.

[0099] If the calcination temperature is lower than 600° C. or higher than 700° C., it is not conducive to the formation of aluminum-doped spinel lithium manganese oxide.

[0100] In addition, the present disclosure also provides an electrode, the raw materials for preparing the electrode include the above-mentioned lithium manganate material.

[0101] For reference, the preparation of the electrode can refer to: mixing the above-mentioned lithium manganese oxide material with a conductive agent, a binder and a solvent to obtain an electrode slurry; coating the electrode slurry on a current collector and drying.

[0102] The conductive agent may, for example but not limited to, carbon black and graphene. The binder may, for example but not limited to, polyvinylidene fluoride. The solvent may, for example but not limited to, N-methylpyrrolidone. The current collector may, for example but not limited to, carbon fiber cloth.

[0103] It should be noted that by using the lithium manganate material provided by the present disclosure, the Al3+ doped therein can reduce the usage of polymer adhesives such as polyvinylidene fluoride, which is beneficial to reducing production costs.

[0104] In some embodiments, lithium manganate material, carbon black, polyvinylidene fluoride and N-methylpyrrolidone (NMP) are mixed in a weight ratio of 7:2:1 to prepare a slurry for the working electrode. 2 The resulting lithium-rich electrode was loaded onto a carbon fiber cloth and dried at 80°C for 10 hours. Furthermore, the prepared lithium-rich electrode was used as the anode and the Ag / AgCl electrode as the cathode. The two electrodes were electrochemically treated in a 0.05 mol / L KCl solution at a constant potential of 1.0 V for 2 hours to obtain a lithium-poor electrode.

[0105] In addition, the present disclosure also provides an application of the above-mentioned lithium manganate material or the above-mentioned electrode in lithium extraction.

[0106] Illustratively, the above-mentioned lithium manganate material or electrode can be used to extract lithium from salt lakes, and can have good lithium ion selectivity and high lithium ion extraction efficiency.

[0107] The features and performance of the present disclosure are further described in detail below with reference to the embodiments.

[0108] Example 1

[0109] This embodiment provides a lithium manganate material, the preparation method of which includes:

[0110] S1: Preparation of epoxy-modified graphene.

[0111] Graphene oxide was ultrasonically dispersed in anhydrous ethanol, epoxy silane coupling agent was added and stirred evenly, then the temperature was raised to 60°C and stirred under reflux for 8 hours. After the reaction was completed, vacuum filtration was performed, and the mixture was washed three times with deionized water and anhydrous ethanol, and dried at 60°C to obtain epoxy-modified graphene.

[0112] Graphene oxide was prepared according to Marcano DC, Kosynkin DV, Berlin JM, et al. Improved Synthesis of Graphene Oxide [J]. Acs Nano, 2010, 4(8): 4806-4814. The epoxy silane coupling agent was 3-glycidoxypropyltriethoxysilane. The ratio of graphene oxide to anhydrous ethanol and epoxy silane coupling agent was 0.1 g:90 g:2 g.

[0113] S2: Preparation of functionalized graphene.

[0114] The epoxy-modified graphene was ultrasonically dispersed again in DMF, and then polysaccharide was added and ultrasonically dissolved until it was completely dissolved. The temperature was raised to 80°C and stirred for reaction for 10 hours. After the reaction was completed, vacuum filtration was performed, and the mixture was washed three times with deionized water and ethanol, and then dried at 60°C to obtain functionalized graphene.

[0115] The polysaccharide is carboxymethyl chitosan, and the feeding ratio of epoxy-modified graphene, DMF and polysaccharide is 1 g:400 mL:0.2 g.

[0116] S3: preparing lithium manganate flakes.

[0117] The above-mentioned functionalized graphene was dispersed in deionized water, lithium salt and aluminum salt were added, and the mixture was heated to 50°C and stirred evenly. Then, potassium permanganate solution was added dropwise under heat preservation and stirring conditions. After the addition was completed, the mixture was kept warm for 30 minutes. The reaction solution was then transferred to a porcelain crucible and reacted in a resistance furnace at 200°C for 6 hours. Black flakes were obtained after drying.

[0118] The lithium salt is lithium chloride, the aluminum salt is aluminum chloride, the mass ratio of functionalized graphene to potassium permanganate is 1g:10g, and the molar ratio of lithium salt, aluminum salt, and permanganate is 1:0.5:1.5. The potassium permanganate solution is added at a rate of 1 drop per 2 seconds.

[0119] S4: preparing lithium manganese oxide material.

[0120] The black flakes were ground and calcined at 600° C. in air for 5 h to obtain a layered aluminum-doped lithium manganate-graphene composite material (i.e., lithium manganate material, denoted as LAMO@GO).

[0121] Example 2

[0122] This embodiment provides a lithium manganate material, the preparation method of which includes:

[0123] S1: Preparation of epoxy-modified graphene.

[0124] Graphene oxide was ultrasonically dispersed in anhydrous ethanol, epoxy silane coupling agent was added and stirred evenly, then the temperature was raised to 80°C and stirred under reflux for 5 hours. After the reaction was completed, vacuum filtration was performed, and the mixture was washed three times with deionized water and anhydrous ethanol, and dried at 60°C to obtain epoxy-modified graphene.

[0125] The graphene oxide is the same as that in Example 1. The epoxy silane coupling agent is epoxybutyltrimethoxysilane. The feeding ratio of graphene oxide, anhydrous ethanol and epoxy silane coupling agent is 0.1g:90g:2.5g.

[0126] S2: Preparation of functionalized graphene.

[0127] The epoxy-modified graphene was re-ultrasonic dispersed in DMF, and then polysaccharide was added and ultrasonically dissolved until it was completely dissolved. The temperature was raised to 120°C and stirred for reaction for 8 hours. After the reaction was completed, vacuum filtration was performed, and the mixture was washed three times with deionized water and ethanol, and then dried at 60°C to obtain functionalized graphene.

[0128] The polysaccharide is carboxymethyl cellulose, and the feeding ratio of epoxy-modified graphene, DMF, and polysaccharide is 1 g:400 mL:0.4 g.

[0129] S3: preparing lithium manganate flakes.

[0130] The above-mentioned functionalized graphene was dispersed in deionized water, lithium salt and aluminum salt were added, and the mixture was heated to 50°C and stirred evenly. Then, permanganate solution was added dropwise under heat preservation and stirring conditions. After the addition was completed, the mixture was kept warm for 10 minutes. The reaction solution was then transferred to a porcelain crucible and reacted in a resistance furnace at 200°C for 6 hours. Black flakes were obtained after drying.

[0131] The lithium salt is lithium nitrate, the aluminum salt is aluminum nitrate, the mass ratio of functionalized graphene to permanganate is 1g:8g, and the molar ratio of lithium salt, aluminum salt, and permanganate is 1:0.5:1.5. The potassium permanganate solution is added at a rate of 1 drop per 2 seconds.

[0132] S4: preparing lithium manganese oxide material.

[0133] The black flakes were ground and then calcined at 700° C. in an air atmosphere for 3 h to obtain a layered aluminum-doped lithium manganate-graphene composite material (i.e., lithium manganate material).

[0134] Example 3

[0135] This embodiment provides a lithium manganate material, the preparation method of which includes:

[0136] S1: Preparation of epoxy-modified graphene.

[0137] Graphene oxide was ultrasonically dispersed in anhydrous ethanol, epoxy silane coupling agent was added and stirred evenly, then the temperature was raised to 70°C and stirred under reflux for 7 hours. After the reaction was completed, vacuum filtration was performed, and the mixture was washed three times with deionized water and anhydrous ethanol, and dried at 60°C to obtain epoxy-modified graphene.

[0138] The graphene oxide is the same as that in Example 1. The epoxy silane coupling agent is 3-glycidyloxypropylmethyldiethoxysilane. The feeding ratio of graphene oxide, anhydrous ethanol and epoxy silane coupling agent is 0.1g:100g:2.2g.

[0139] S2: Preparation of functionalized graphene.

[0140] The epoxy-modified graphene was ultrasonically dispersed again in DMF, and then polysaccharide was added and ultrasonically dissolved until it was completely dissolved. The temperature was raised to 100°C and stirred for reaction for 8 hours. After the reaction was completed, vacuum filtration was performed, and the mixture was washed three times with deionized water and ethanol, and then dried at 60°C to obtain functionalized graphene.

[0141] The polysaccharide is sodium hyaluronate, and the feeding ratio of epoxy-modified graphene, DMF, and polysaccharide is 1 g:300 mL:0.3 g.

[0142] S3: preparing lithium manganate flakes.

[0143] The above-mentioned functionalized graphene was dispersed in deionized water, lithium salt and aluminum salt were added, and the mixture was heated to 50°C and stirred evenly. Then, potassium permanganate solution was added dropwise under heat preservation and stirring conditions. After the addition was completed, the mixture was kept warm for 20 minutes. The reaction solution was then transferred to a porcelain crucible and reacted in a resistance furnace at 150°C for 6 hours. Black flakes were obtained after drying.

[0144] The lithium salt is lithium acetate, the aluminum salt is aluminum nitrate, the mass ratio of functionalized graphene to potassium permanganate is 1g:10g, and the molar ratio of lithium salt, aluminum salt, and permanganate is 1:0.3:1.7. The potassium permanganate solution is added at a rate of 1 drop per 2 seconds.

[0145] S4: preparing lithium manganese oxide material.

[0146] The black flakes were ground and then calcined at 700° C. in an air atmosphere for 5 h to obtain a layered aluminum-doped lithium manganate-graphene composite material (i.e., lithium manganate material).

[0147] Example 4

[0148] The difference between this embodiment and embodiment 1 is that the molar ratio of lithium salt, aluminum salt and permanganate is 1:0.2:1.8.

[0149] Comparative Example 1

[0150] This comparative example provides a lithium manganate material, the preparation method of which is as follows: lithium chloride and carboxymethyl chitosan are dispersed in deionized water, heated to 50°C, and stirred uniformly. Then, a potassium permanganate solution is added dropwise while maintaining the temperature and stirring. After the addition is complete, the solution is kept warm and reacted for 30 minutes. The reaction solution is then transferred to a porcelain crucible and reacted in a resistance furnace at 200°C for 6 hours. After drying, a black powder is obtained. The black powder is ground and calcined at 600°C in air for 5 hours to obtain a lithium manganate material, which is designated as LMO.

[0151] The molar ratio of lithium chloride to potassium permanganate is 1:2, and the mass ratio of carboxymethyl chitosan to potassium permanganate is 0.5 g:10 g.

[0152] Comparative Example 2

[0153] The difference between this comparative example and Example 1 is that no aluminum salt is added to S3, the molar ratio of lithium salt to potassium permanganate is 1:2, and the product is recorded as LMO-GO.

[0154] Comparative Example 3

[0155] This comparative example provides a lithium manganate material, the preparation method of which is as follows: lithium chloride, aluminum chloride, and carboxymethyl chitosan are dispersed in deionized water, heated to 50°C, and stirred uniformly. Then, a potassium permanganate solution is added dropwise while maintaining the temperature and stirring. After the addition is complete, the solution is kept warm and reacted for 30 minutes. The reaction solution is then transferred to a porcelain crucible and reacted in a resistance furnace at 200°C for 6 hours. After drying, a black powder is obtained. The black powder is ground and calcined at 600°C in air for 5 hours to obtain an aluminum-doped lithium manganate material, denoted as LAMO.

[0156] The molar ratio of lithium chloride, aluminum chloride, and permanganate is 1:0.2:1.8, and the mass ratio of functionalized graphene to potassium permanganate is 0.5 g:10 g.

[0157] Comparative Example 4

[0158] This comparative example provides a lithium manganate material, prepared by the following method: graphene oxide is dispersed in deionized water, lithium chloride, aluminum chloride, and carboxymethyl chitosan are added, and the mixture is heated to 50°C and stirred until uniform. A potassium permanganate solution is then added dropwise while maintaining the temperature and stirring. After completion of the addition, the mixture is kept warm for 30 minutes. The reaction solution is then transferred to a porcelain crucible and reacted in a resistance furnace at 200°C for 6 hours. After drying, black flakes are obtained. The resulting black flakes are ground and calcined at 600°C in air for 5 hours. The product is designated as LAMO-GO.

[0159] The mass ratio of graphene oxide, carboxymethyl chitosan, and potassium permanganate was 0.85 g:0.15:10 g, and the molar ratio of lithium chloride, aluminum chloride, and potassium permanganate was 1:0.2:1.8.

[0160] Comparative Example 5

[0161] The difference between this comparative example and Example 1 is that in S3, the functionalized graphene is dispersed in deionized water, and lithium salt, aluminum salt and permanganate solution are added at the same time. The mixture is heated to 50°C and stirred evenly, and then kept warm for 10 minutes. The reaction solution is then transferred to a porcelain crucible and reacted in a resistance furnace at 200°C for 6 hours. Black flakes are obtained after drying.

[0162] Test example

[0163] Performance testing:

[0164] ① The lithium manganate materials prepared in Example 1 and Comparative Examples 1-4 were subjected to the following analysis: X-ray powder diffractometer (XRD, Rigaku D / max-2600PC, Japan) was used to investigate the crystalline phase and structure of the materials. The test was performed using Cu Kα radiation with a wavelength λ of 0.154056 nm, a voltage of 40 kV, a current of 40 mA, and a scanning range 2θ of 10° to 80°. The XRD test results were analyzed using Jade6 software, as shown in FIG1 .

[0165] As can be seen from Figure 1, the lithium manganate material samples prepared in each group are all spinel-type LiMn2O4.

[0166] ② The microstructure of the lithium manganate materials prepared in Example 1 and Comparative Example 4 was observed using a JEOL JSM-6490LV scanning electron microscope. The results are shown in Figures 2 to 4.

[0167] It can be seen from FIG2 and FIG3 that the lithium manganese oxide material prepared in Example 1 has a layered structure formed by functionalized graphene, and the interlayer positions of the layered structure are loaded with aluminum-doped lithium manganese oxide.

[0168] As can be seen from FIG4 , the LAMO-GO material prepared in Comparative Example 4 does not have a layered structure.

[0169] ③. Taking the lithium manganate materials prepared in Example 1 and Comparative Example 1 as an example, the electrode material samples were detected using a VERTEX 70 Fourier transform infrared spectrometer using the KBr pellet method, and the Mn-O bond peak position was analyzed to determine the effect of aluminum doping on the spinel LMO. The results are shown in Figure 5.

[0170] As can be seen from Figure 5: 650-600cm -1 and 550-500cm-1 The two characteristic peaks in the range are caused by the asymmetric stretching vibration of the Mn-O bond in the MnO6 octahedron. In the infrared spectra of both samples, two obvious absorption peaks can be observed. For LMO, the peak positions of the two absorption peaks are 616.54 cm -1 and 503.24cm -1 , while the absorption peak position of LAMO@GO shifts to a higher wave number (618.47 cm -1 and 505.41cm -1 On the one hand, this indicates that Al is successfully incorporated into the spinel structure of LMO; on the other hand, the incorporation of Al causes the asymmetric stretching vibration peak of the Mn-O bond to blue-shift, indicating that the Mn-O bond strength is increased. This suggests that the introduction of aluminum reduces the average bond length of the Mn-O bond, which is beneficial to improving the stability of the spinel structure.

[0171] ④. Taking the lithium manganate materials obtained in Examples 1-4 and Comparative Examples 1-5 as examples, the following performance tests were performed:

[0172] A. The lithium extraction performance of the sample was investigated using a lithium-rich electrode combined with a lithium-poor electrode system (electrochemical deintercalation method). Specifically, the lithium-rich electrode was used as the anode, the lithium-poor electrode was used as the cathode, and the anode chamber and the cathode chamber were separated by an anion exchange membrane. The electrolyte (recovery solution) in the anode chamber was a 0.05 mol / L KCl solution, and the electrolyte (extraction solution) in the cathode chamber was a mixed solution of 0.05 mol / L LiCl and 1 mol / L MgCl2. The electrode spacing was 4.5 cm, and the voltage was constant at 1 V. The lithium-poor electrode obtained after delithiation with Ag as the counter electrode was used as the cathode to extract Li, and then it was turned into the anode for delithiation under this system. Samples were taken from the recovery pool at certain times and Li was analyzed using ICP-OES. + Mg 2+ , Mn ion concentration, calculate the lithium extraction capacity E Li (mg / g), lithium extraction rate r E (mg / g·min), separation coefficient α Li / Mg , manganese dissolution rate E Mn (mg / g) and other indicators, the calculation formulas are shown in (1), (2), (3) and (4).

[0173] Where, and Li in the recovered liquid + The final mass concentration and volume, and are the Li ion mass concentration and volume sampled at a certain time, t is the sampling time, and are the Li in the recovered liquid at time t + Mg 2+ The molar concentration of and The Li in the recovery solution at time 0 is + Mg 2+ The molar concentration of . and is the final mass concentration and volume of Mn ions in the recovered solution, and are the Mn ion mass concentration and volume sampled at a certain time, respectively, and m (g) is the mass of the lithium ion sieve precursor.

[0174] B. Cyclic stability evaluation: The lithium-poor electrode material is used as a cathode to extract lithium and then as an anode to remove lithium for one cycle (one cycle is 120 minutes). The lithium extraction capacity after 10 cycles is tested.

[0175] The results are shown in Table 1 and Figure 6.

[0176] Table 1 Test results

[0177] As can be seen from Table 1:

[0178] Compared with Comparative Example 1 and Comparative Example 3, Al doping can reduce manganese dissolution loss, thereby improving the cycle performance of the electrode, but has little effect on lithium extraction efficiency and Li ion selectivity, and even reduces them.

[0179] Compared with Comparative Example 1 and Comparative Example 2, compounding with graphene can improve the lithium extraction efficiency, selectivity for Li ions and cycle stability of the electrode material.

[0180] Compared with Comparative Example 3, Comparative Example 4 has improved performance in all aspects, indicating that graphene and Al doping can synergistically improve the cycle performance and lithium extraction rate of the electrode material.

[0181] However, compared with Comparative Example 4, Example 1 further improves the performance in all aspects, indicating that the microscopic bonding mode of graphene and LAMO also has a great influence on the performance of the material. The layered alternating structure makes the two more closely bonded, reducing the number of large pores, thereby helping to reduce the manganese dissolution rate without reducing the lithium extraction rate.

[0182] ⑤. The lithium manganate materials prepared in Example 1 and Comparative Example 4 were subjected to the following tests: a high-performance specific surface and micropore analyzer BSD-PM1 was used to measure the nitrogen adsorption-desorption curve of the powder material to obtain its internal micropore structure information. The results are shown in Table 2.

[0183] Table 2 Test results

[0184] In summary, the lithium manganate material provided by the present disclosure has a high lithium ion capacity and a high lithium ion extraction efficiency, and excellent cycle performance. Industrial Applicability

[0185] The lithium manganate material provided by the present invention has high lithium extraction capacity, lithium extraction rate, Li + The lithium manganese oxide material has fewer macropores and more mesopores, which helps reduce manganese loss. This lithium manganese oxide material can be used to extract lithium from salt lakes to improve the extraction efficiency.

Claims

1. A lithium manganate material, characterized in that, The lithium manganate material includes a layered structure formed by functionalized graphene and aluminum-doped lithium manganate, and the aluminum-doped lithium manganate is loaded at the interlayer position of the layered structure; Among them, the functionalized graphene is graphene grafted with polysaccharide on the surface.

2. The lithium manganate material according to claim 1, wherein The aluminum-doped lithium manganate is in-situ generated from a manganese source, an aluminum source, and a lithium source at the interlayer position of the layered structure.

3. The lithium manganate material according to claim 1 or 2, characterized in that, The lithium manganate material includes at least one of the following characteristics: Feature 1: The specific surface area of the lithium manganate material is 8 m 2 / g - 9 m 2 / g; Characteristic two: The average pore size of the lithium manganate material is 15nm - 20nm.

4. A method for preparing a lithium manganate material according to any one of claims 1-3, characterized in that, It includes the following steps: Mix the functionalized graphene, the lithium source, and the aluminum source to obtain a mixed solution; React the mixed solution with the manganese source to obtain a reaction solution; Heat-react the reaction solution to obtain flakes; Grind and calcine the flakes.

5. The preparation method according to claim 4, characterized in that, The preparation of the functionalized graphene includes: Reacting an epoxy-modified graphene solution with polysaccharide.

6. The preparation method according to claim 5, wherein The preparation of the functionalized graphene includes at least one of the following characteristics: Characteristic one: The mass ratio of the epoxy-modified graphene in the epoxy-modified graphene solution to the polysaccharide is 1:0.2 to 1:0.4; Characteristic two: The reaction temperature of the epoxy-modified graphene solution and the polysaccharide is 80°C - 120°C; Characteristic three: The reaction time of the epoxy-modified graphene solution and the polysaccharide is 6h - 10h; Characteristic four: The solvent used in the epoxy-modified graphene solution includes N,N-dimethylformamide; Characteristic five: The ratio of the solvent used in the epoxy-modified graphene solution to the amount of epoxy-modified graphene is 300mL:1g to 400mL:1g.

7. The preparation method according to claim 5 or 6, characterized in that, The polysaccharide includes at least one of carboxymethyl cellulose and its salts, alginic acid and its salts, hyaluronic acid and its salts, and carboxymethyl chitosan.

8. The preparation method according to any one of claims 5-7, characterized in that, The preparation of the epoxy-modified graphene includes: Mixing and reacting a graphene oxide solution with an epoxy silane coupling agent.

9. The preparation method according to claim 8, characterized in that, The preparation of the epoxy-modified graphene includes at least one of the following characteristics: Characteristic one: The mass ratio of the graphene oxide in the graphene oxide solution to the epoxy silane coupling agent is 0.1:2 to 0.1:2.5; Characteristic two: The reaction temperature of the graphene oxide solution and the epoxy silane coupling agent is 60°C - 80°C; Characteristic three: The reaction time of the graphene oxide solution and the epoxy silane coupling agent is 5h - 8h; Characteristic four: The solvent used in the graphene oxide solution includes absolute ethanol; Characteristic five: The ratio of the solvent used in the graphene oxide solution to the amount of graphene oxide is 90g:0.1g to 100g:0.1g.

10. The preparation method according to claim 8 or 9, characterized in that, The epoxy silane coupling agent includes at least one of 3-glycidoxypropyltriethoxysilane, epoxybutyltrimethoxysilane, 5,6-epoxyhexyltriethoxysilane, 3-glycidoxypropylmethyldiethoxysilane, and 3-(2,3-epoxypropoxy)propyltrimethoxysilane.

11. According to the preparation method described in claim 4, characterized in that, The mass ratio of the functionalized graphene to the manganese source is 1:8 to 1:10, and the molar ratio of the lithium source, the aluminum source, and the manganese source is 1:(0.2 - 0.5):(1.5 - 1.8).

12. The preparation method according to any one of claims 4-11, characterized in that, The lithium source includes lithium salts; and / or, the aluminum source includes aluminum salts; and / or, the manganese source includes permanganic acid or its salts.

13. The preparation method according to claim 12, characterized in that, The lithium salt includes at least one of lithium chloride, lithium nitrate, and lithium acetate; and / or, the aluminum salt includes at least one of aluminum nitrate and aluminum chloride; and / or, the manganese source includes at least one of permanganic acid and potassium permanganate.

14. The preparation method according to any one of claims 4-13, characterized in that, The mixing temperature of the functionalized graphene, the lithium source, and the aluminum source is 45°C - 55°C.

15. The preparation method according to any one of claims 4-14, characterized in that, The manganese source is added to the mixed solution in a dropwise manner.

16. The preparation method according to any one of claims 4-15, characterized in that, The reaction of the mixed solution with the manganese source is carried out at 45°C - 55°C for 10 min - 30 min.

17. The preparation method according to any one of claims 4-16, characterized in that, The heating reaction is carried out at 150°C - 200°C for 5 h - 7 h.

18. The preparation method according to any one of claims 4-17, characterized in that, The calcination includes at least one of the following characteristics: Characteristic one: The calcination is carried out in an oxygen-containing atmosphere; Characteristic two: The calcination temperature is 600°C - 700°C; Characteristic three: The calcination time is 3 h - 6 h.

19. An electrode, characterized in that, The preparation raw materials of the electrode include the lithium manganate material according to any one of claims 1 - 3.

20. Use of a lithium manganate material according to any one of claims 1 - 3 or an electrode according to claim 19 in lithium extraction.

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