Diameter-controllable one-dimensional lithium manganate nanorod as well as preparation method and application thereof

Abstract

The invention belongs to the technical field of lithium ion battery electrode materials, and particularly discloses a diameter-controllable one-dimensional lithium manganate nanorod as well as a preparation method and application thereof. The preparation method comprises the following steps: dispersing manganese sulfate, potassium permanganate, a structure-directing agent and a surfactant into a solvent, and carrying out hydrothermal reaction to obtain a black precipitate; sintering the black precipitate to obtain a manganese dioxide nanorod; and mixing the manganese dioxide nanorod with lithium hydroxide, and carrying out two-stage sintering to obtain the one-dimensional lithium manganate nanorod. The prepared lithium ion battery anode material is uniform in thickness and very small in surface energy, can effectively shorten the transmission path of lithium ions when being used as an anode material, is not easy to agglomerate, has good flexibility, can maintain the structural integrity in a large-current long-time service process, and is beneficial to improving the rate and cycle performance of an electrode. In addition, by adjusting the concentration of potassium permanganate and the hydrothermal reaction temperature, the diameter of manganese dioxide can be accurately adjusted, and controllable preparation of one-dimensional lithium manganate is realized.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium ion battery electrode materials, and in particular to a one-dimensional lithium manganate nanorod with controllable diameter, and a preparation method and application thereof. Background Art

[0002] Lithium-ion batteries are not only one of the important electrochemical energy storage devices, but are currently widely used in electric vehicles, hybrid vehicles, energy storage facilities, consumer electronic components and other fields. Among them, spinel-type LiMn2O4 cathode materials have a wide range of application prospects in the fields of 3C electronic products and low-speed electric vehicle batteries as an alternative to commercial cobalt-based and nickel-based cathode materials due to their relatively stable charging and discharging platform, excellent thermal stability, low production cost and no pollution to the environment.

[0003] However, the commercialized spinel LiMn2O4 cathode materials are all agglomerated particles of micron size or above. The paths of lithium ion diffusion and electron transmission during charge and discharge are long, which limits their further commercial application. Compared with micron-sized materials, one-dimensional spinel LiMn2O4 materials (such as nanowires, nanorods and nanotubes) can not only effectively shorten the Li + The diffusion distance and electron transmission distance are long, and it also has the characteristics of not easy to agglomerate and good flexibility. It can maintain its structural integrity during long-term service at high current. The resulting excellent electrochemical performance has good application prospects. However, traditional preparation methods make it difficult to accurately control the diameter size of one-dimensional materials and meet the specific needs of batteries.

[0004] Therefore, how to provide a one-dimensional lithium manganese oxide nanorod with controllable diameter and its preparation method and application is a difficult problem to be solved urgently in this field. Summary of the invention

[0005] In view of this, the present invention provides a one-dimensional lithium manganese oxide nanorod with controllable diameter and a preparation method and application thereof, which solves the problem that the traditional method of controlling the size of one-dimensional lithium manganese oxide is difficult and the size is uneven.

[0006] In order to achieve the above object, the present invention adopts the following technical solution:

[0007] A method for preparing one-dimensional lithium manganate nanorods with controllable diameter comprises the following steps:

[0008] 1) dispersing manganese sulfate, potassium permanganate, a structure directing agent and a surfactant in a solvent, and performing a hydrothermal reaction to obtain a black precipitate;

[0009] 2) sintering the black precipitate to obtain manganese dioxide nanorods;

[0010] 3) Mix manganese dioxide nanorods with lithium hydroxide and perform two-stage sintering to obtain one-dimensional lithium manganate nanorods;

[0011] In the system of the hydrothermal reaction described in step 1), the molar concentration of potassium permanganate is 0.06 - 0.15 mmol / L, and the temperature of the hydrothermal reaction is 120 - 160 °C;

[0012] The structure-directing agent includes polyethylene glycol.

[0013] Preferably, the molar ratio of manganese sulfate to potassium permanganate is 1:0.5 - 2;

[0014] The molar volume ratio of potassium permanganate to the structure-directing agent and the surfactant is 0.06 - 0.15 mmol:5 - 10 mL:5 - 10 mL.

[0015] Preferably, the surfactant includes one or more of ethanol, isopropanol, isobutanol, and n-pentanol;

[0016] The solvent is water.

[0017] Preferably, the time of the hydrothermal reaction described in step 1) is 8 - 12 h.

[0018] Preferably, the temperature of the sintering described in step 2) is 400 - 500 °C, and the time of the sintering is 2 - 4 h.

[0019] Preferably, the molar ratio of the manganese dioxide nanorods to lithium hydroxide in step 3) is 2:1 - 1.05.

[0020] Preferably, the two-stage sintering includes a first sintering and a second sintering;

[0021] The temperature of the first sintering is 400 - 500 °C, and the time of the sintering is 4 - 6 h;

[0022] The temperature of the second sintering is 650 - 750 °C, and the time of the sintering is 10 - 12 h.

[0023] Another object of the present invention is to provide one-dimensional lithium manganate nanorods prepared by the preparation method, and the diameter of the one-dimensional lithium manganate nanorods is 30 - 500 nm, and the length is 2 - 6 μm.

[0024] Another object of the present invention is to provide an application of one-dimensional lithium manganate nanorods as a cathode material.

[0025] It can be seen from the above technical solutions that compared with the prior art, the present invention has the following beneficial effects:

[0026] 1. The one-dimensional lithium manganese oxide nanorods prepared by the present invention have uniform thickness and very low surface energy. Manganese salts with different concentrations first form [MnO x structural units under hydrothermal conditions, and stable directional curling occurs under the action of the hydrothermal reaction temperature and structure-directing agent defined in the present invention, and manganese dioxide with uniform cross-sectional diameter can be obtained.

[0027] 2. By adjusting the concentration of potassium permanganate and the hydrothermal reaction temperature, the interface diameter of manganese dioxide can be accurately adjusted to achieve the controllable preparation of one-dimensional lithium manganese oxide.

[0028] 3. The one-dimensional lithium manganese oxide nanorods prepared by the method of the present invention have a smooth surface and uniform thickness dimensions. When used as a cathode material, it can effectively shorten the lithium ion transmission path, is not easy to agglomerate and has good flexibility, and can maintain the integrity of its structure during long-term service at high current, which is beneficial to improving the rate and cycle performance of the electrode.

[0029] 4. The LiMn2O4 cathode material prepared by the method of the present invention has a capacity that basically does not decay after 100 cycles at room temperature and remains higher than 90% after 100 cycles at 55 °C under 1C charge and discharge at 3.0V - 4.3V. The present invention has low requirements for synthesis equipment, is easy to operate, has no special requirements for the sintering process, and is environmentally friendly. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for use in the description of the embodiments or the prior art. Obviously, the drawings in the following description are only the embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained according to the provided drawings.

[0031] Figure 1 It is the XRD pattern of the one-dimensional lithium manganese oxide nanorods prepared in Examples 1 - 4 of the present invention;

[0032] Figure 2 It is the SEM pattern of the one-dimensional lithium manganese oxide nanorods prepared in Examples 1 - 4 of the present invention, where Figure 2 (a) is the SEM image of the one-dimensional lithium manganese oxide nanorods prepared in Example 1, Figure 2 (b) is the SEM image of the one-dimensional lithium manganese oxide nanorods prepared in Example 2, Figure 2 (c) is the SEM image of the one-dimensional lithium manganese oxide nanorods prepared in Example 3, Figure 2 (d) is the SEM image of the one-dimensional lithium manganese oxide nanorods prepared in Example 4;

[0033] Figure 3Electrochemical performance curves of the batteries assembled with the one-dimensional lithium manganese oxide nanorods prepared in Embodiments 1 to 4 of the present invention at different cycling rates. Detailed implementation manners

[0034] The present invention provides a method for preparing one-dimensional lithium manganese oxide nanorods with controllable diameter, comprising the following steps:

[0035] 1) Dispersing manganese sulfate, potassium permanganate, a structure-directing agent and a surfactant into a solvent, and performing a hydrothermal reaction to obtain a black precipitate;

[0036] 2) Sintering the black precipitate to obtain manganese dioxide nanorods;

[0037] 3) Mixing the manganese dioxide nanorods with lithium hydroxide, and performing two-stage sintering to obtain one-dimensional lithium manganese oxide nanorods.

[0038] In the present invention, in the system of the hydrothermal reaction in step 1), the molar concentration of potassium permanganate is 0.06 - 0.15 mmol / L, specifically, it can be 0.08 mmol / L, 0.1 mmol / L, 0.11 mmol / L, 0.12 mmol / L, 0.13 mmol / L, 0.14 mmol / L; the temperature of the hydrothermal reaction is 120 - 160 °C, specifically, it can be 125 °C, 130 °C, 135 °C, 140 °C, 145 °C, 150 °C, 155 °C.

[0039] In the present invention, the diameter of the one-dimensional lithium manganese oxide nanorods increases with the increase of the temperature of the hydrothermal reaction and increases with the increase of the concentration of potassium permanganate. The diameters of the one-dimensional lithium manganese oxide nanorods under different hydrothermal reaction temperatures and potassium manganate concentration conditions are shown in Table 1.

[0040] Table 1 Diameters of one-dimensional lithium manganese oxide nanorods at different temperatures and concentrations

[0041]

[0042] In the present invention, the structure-directing agent includes polyethylene glycol.

[0043] In the present invention, the molar ratio of manganese sulfate to potassium permanganate is 1:0.5 - 2, preferably 1:0.8 - 1.5, and further preferably 1:1.

[0044] In the present invention, the molar volume ratio of potassium permanganate to the structure-directing agent and the surfactant is 0.06 - 0.15 mmol:5 - 10 mL:5 - 10 mL, preferably 0.1 - 0.14 mmol:6 - 9 mL:6 - 9 mL, and further preferably 0.12 mmol:8 mL:8 mL.

[0045] In the present invention, the surfactant includes one or more of ethanol, isopropanol, isobutanol, and n-pentanol; the solvent is water.

[0046] In the present invention, in step 1), the hydrothermal reaction time is 8 to 12 h, specifically, it can be 8 h, 9 h, 10 h, 11 h, or 12 h.

[0047] In the present invention, before sintering, the black precipitate further includes the steps of washing, filtering, and freeze-drying in sequence.

[0048] In the present invention, in step 2), the sintering temperature is 400 to 500 °C, specifically, it can be 420 °C, 440 °C, 450 °C, 460 °C, or 480 °C; the sintering time is 2 to 4 h, specifically, it can be 2.2 h, 2.5 h, 2.8 h, 3 h, 3.2 h, 3.5 h, or 3.8 h.

[0049] In the present invention, in step 3), the molar ratio of manganese dioxide nanorods to lithium hydroxide is 2:1 to 1.05, preferably 2:1.01 to 1.04, and further preferably 2:1.02.

[0050] In the present invention, the two-stage sintering includes the first sintering and the second sintering.

[0051] In the present invention, the temperature of the first sintering is 400 to 500 °C, specifically, it can be 420 °C, 440 °C, 450 °C, 460 °C, or 480 °C; the sintering time is 4 to 6 h, specifically, it can be 4.2 h, 4.5 h, 4.8 h, 5 h, 5.2 h, 5.5 h, or 5.8 h; the temperature of the second sintering is 650 to 750 °C, specifically, it can be 660 °C, 680 °C, 700 °C, 720 °C, or 740 °C; the sintering time is 10 to 12 h, specifically, it can be 10 h, 10.5 h, 11 h, 11.5 h, or 12 h.

[0052] The present invention also provides a one-dimensional lithium manganese oxide nanorod prepared by the preparation method described above. The diameter of the one-dimensional lithium manganese oxide nanorod is 30 to 500 nm, specifically, it can be 40 nm, 50 nm, 80 nm, 100 nm, 150 nm, 200 nm, 250 nm, 300 nm, 350 nm, 400 nm, or 450 nm; the length is 2 to 6 μm, specifically, it can be 2 μm, 3 μm, 4 μm, 5 μm, or 6 μm.

[0053] The present invention also provides an application of the one-dimensional lithium manganese oxide nanorod as a cathode material.

[0054] The technical solutions in the embodiments of the present invention are described clearly and completely below. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0055] Example 1

[0056] Weigh 0.006mmol of KMnO4 and 0.008mmol of MnSO4·H2O in molar ratio and add them to a beaker. Then pour 100mL of water into the beaker, then add 0.5mL of polyethylene glycol and 0.5mL of isopropanol (the molar concentration of KMnO4 is 0.06mmol / L); place the beaker on a stirrer and stir to completely dissolve the solid. Move the mixed solution into the reactor, tighten the reactor and put it into a blast drying oven, set the temperature to 160℃, and the hydrothermal time is 8h. After the hydrothermal treatment, wash and filter the obtained black precipitate with deionized water and ethanol respectively, and then place the sample in a freeze dryer for drying. Place the obtained black powder in a muffle furnace and heat it to 400℃ at a rate of 5℃ / min for 2h, cool it in the furnace and take it out to obtain manganese dioxide nanorods. The obtained manganese dioxide nanorods and lithium hydroxide were fully mixed in a molar ratio of 2:1.05 and then placed in a muffle furnace for two-stage sintering at 5°C / min. First, sintering was performed at 450°C for 4 hours, and then the sintering temperature was increased to 750°C for 12 hours. After cooling in the furnace, the nanorods were taken out to obtain one-dimensional lithium manganate nanorods, which were recorded as LMO-1.

[0057] Example 2

[0058] Weigh 0.009mmol of KMnO4 and 0.008mmol of MnSO4·H2O in molar ratio and add them to a beaker. Then pour 100mL of water into the beaker, then add 0.5mL of polyethylene glycol and 0.5mL of isopropanol (the molar concentration of KMnO4 is 0.09mmol / L); place the beaker on a stirrer and stir to completely dissolve the solid. Move the mixed solution into the reactor, tighten the reactor and put it into a blast drying oven, set the temperature to 160℃, and the hydrothermal time is 8h. After the hydrothermal treatment, wash and filter the obtained black precipitate with deionized water and ethanol respectively, and then place the sample in a freeze dryer for drying. Place the obtained black powder in a muffle furnace and heat it to 400℃ at a rate of 2℃ / min for 2h, cool it in the furnace and take it out to obtain manganese dioxide nanorods. The obtained manganese dioxide nanorods and lithium hydroxide were fully mixed in a molar ratio of 2:1.05 and then placed in a muffle furnace for two-stage sintering at 5°C / min. First, sintering was performed at 400°C for 5 hours, and then the sintering temperature was increased to 700°C for 10 hours. After cooling in the furnace, the nanorods were taken out to obtain one-dimensional lithium manganate nanorods, which were recorded as LMO-2.

[0059] Example 3

[0060] Weigh 0.012mmol of KMnO4 and 0.008mmol of MnSO4·H2O in molar ratio and add them to a beaker. Then pour 100mL of water into the beaker, then add 0.5mL of polyethylene glycol and 0.5mL of isopropanol (the molar concentration of KMnO4 is 0.12mmol / L); place the beaker on a stirrer and stir to completely dissolve the solid. Move the mixed solution into the reactor, tighten the reactor and put it into a blast drying oven, set the temperature to 120℃, and the hydrothermal time is 12h. After the hydrothermal treatment, wash and filter the obtained black precipitate with deionized water and ethanol respectively, and then place the sample in a freeze dryer for drying. Place the obtained black powder in a muffle furnace and heat it to 450℃ at a rate of 4℃ / min for 2h, cool it in the furnace and take it out to obtain manganese dioxide nanorods. The obtained manganese dioxide nanorods and lithium hydroxide were fully mixed in a molar ratio of 2:1.05 and then placed in a muffle furnace for two-stage sintering at 4°C / min. First, sintering was performed at 500°C for 6 hours, and then the sintering temperature was increased to 650°C for 12 hours. After cooling in the furnace, the one-dimensional lithium manganate nanorods were taken out and recorded as LMO-3.

[0061] Example 4

[0062] Weigh 0.015mmol of KMnO4 and 0.008mmol of MnSO4·H2O in molar ratio and add them to a beaker. Then pour 100mL of water into the beaker, then add 0.5mL of polyethylene glycol and 0.5mL of isopropanol (the molar concentration of KMnO4 is 0.15mmol / L); place the beaker on a stirrer and stir to completely dissolve the solid. Move the mixed solution into the reactor, tighten the reactor and put it into a forced air drying oven, set the temperature to 140℃, and the hydrothermal time is 10h. After the hydrothermal treatment, wash and filter the obtained black precipitate with deionized water and ethanol respectively, and then place the sample in a freeze dryer for drying. Place the obtained black powder in a muffle furnace and heat it to 500℃ at a rate of 3℃ / min for 3h, cool it in the furnace and take it out to obtain manganese dioxide nanorods. The obtained manganese dioxide nanorods and lithium hydroxide were fully mixed in a molar ratio of 2:1.05 and then placed in a muffle furnace for two-stage sintering at 3°C / min. First, sintering was performed at 400°C for 6 hours, and then the sintering temperature was increased to 700°C for 10 hours. After cooling in the furnace, the nanorods were taken out to obtain one-dimensional lithium manganate nanorods, which were recorded as LMO-4.

[0063] The XRD patterns of the one-dimensional lithium manganate nanorods prepared in Examples 1 to 4 are as follows: Figure 1 As shown, through Figure 1 It can be seen that the diffraction peaks of all positive electrode materials correspond to LiMn2O4 (standard card number: PDF#35.0782) and have the Fd3m space group, indicating that the sample is high-purity LiMn2O4.

[0064] SEM pictures Figure 2 As shown, Figure 2 (a) is a SEM image of the one-dimensional lithium manganate nanorods prepared in Example 1. Figure 2 (b) is a SEM image of the one-dimensional lithium manganate nanorods prepared in Example 2. Figure 2 (c) is a SEM image of the one-dimensional lithium manganate nanorods prepared in Example 3. Figure 2 (d) is a SEM image of the one-dimensional lithium manganate nanorods prepared in Example 4. Figure 2 It can be seen that all samples have typical one-dimensional nanorod morphology, and the average diameters prepared in Examples 1 to 4 are about 30 to 60 nm, 60 to 100 nm, 100 to 140 nm and 140 to 180 nm, with uniform diameters, smooth surfaces and aspect ratios greater than 20:1.

[0065] The one-dimensional lithium manganese oxide nanorods prepared in Examples 1 to 4 were used as the cathode material for battery assembly respectively. The assembly method was as follows: A 2025-type button battery was used as the carrier for battery performance testing. LiMn2O4 was coated on a round aluminum foil as the cathode, and a lithium metal sheet was used as the anode. 1 mol / L LiPF6 (dissolved in a mixed solvent of dimethyl carbonate (DMC), ethylene carbonate (EC) and ethyl methyl carbonate (EMC) with a volume ratio of 1:1:1) was used as the battery electrolyte. The button battery was assembled in a glove box filled with argon in the order of the negative electrode case, gasket, lithium sheet, separator, positive electrode sheet, gasket, spring sheet, and positive electrode case, and was compactly sealed with a hydraulic button battery encapsulation machine to obtain a 2025-type button battery. The testing method was as follows: A Neware CT3008 battery tester was used to test the battery performance. The test voltage range was 3.0 - 4.5 V, and the charge and discharge currents were set respectively according to different test requirements. During the current setting process, the current density corresponding to the 1C rate of LiMn2O4 was 148 mAh·g -1 . When testing the rate performance, 5 cycles were carried out at the current densities of 0.1C, 1C, 2C, 5C, 10C, 20C and 0.1C respectively. The test results are as Figure 3 shown. It can be seen from Figure 3 that different one-dimensional lithium manganese oxide nanorods all showed good rate performance and cycle stability at high current densities. Among them, even at a high current density of 20C, the discharge capacity of the LMO-2 sample was still as high as 62 mAh·g -1 .

[0066] In this specification, each embodiment is described in a progressive manner. The key point of each embodiment is to illustrate the differences from other embodiments. For the same and similar parts among the embodiments, reference can be made to each other.

[0067] The above description of the disclosed embodiments enables those skilled in the art to implement or use the present invention. Various modifications to these embodiments will be obvious to those skilled in the art. The general principles defined herein can be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention will not be limited to these embodiments shown herein, but will be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A preparation method of one-dimensional lithium manganate nanorods with controllable diameter, characterized in that, It includes the following steps: 1) Disperse manganese sulfate, potassium permanganate, structure-directing agent and surfactant into a solvent, and carry out a hydrothermal reaction to obtain a black precipitate; 2) Sinter the black precipitate to obtain manganese dioxide nanorods; 3) Mix the manganese dioxide nanorods with lithium hydroxide and carry out two-stage sintering to obtain one-dimensional lithium manganate nanorods; In the system of the hydrothermal reaction in step 1), the molar concentration of potassium permanganate is 0.06 - 0.15 mmol / L, and the temperature of the hydrothermal reaction is 120 - 160 °C; The structure-directing agent includes polyethylene glycol.

2. The preparation method of a one-dimensional lithium manganate nanorod with controllable diameter according to claim 1, characterized in that, The molar ratio of manganese sulfate to potassium permanganate is 1:0.5 - 2; The molar volume ratio of potassium permanganate to the structure-directing agent and surfactant is 0.06 - 0.15 mmol:5 - 10 mL:5 - 10 mL.

3. The preparation method of a one-dimensional lithium manganate nanorod with controllable diameter according to claim 2, characterized in that, The surfactant includes one or more of ethanol, isopropanol, isobutanol and n-pentanol; The solvent is water.

4. A method for preparing a one-dimensional lithium manganese oxide nanorod with controllable diameter according to any one of claims 1 to 3, characterized in that, The time of the hydrothermal reaction in step 1) is 8 - 12 h.

5. The preparation method of a one-dimensional lithium manganate nanorod with controllable diameter according to claim 4, characterized in that The temperature of the sintering in step 2) is 400 - 500 °C, and the time of the sintering is 2 - 4 h.

6. The preparation method of a one-dimensional lithium manganate nanorod with controllable diameter according to claim 5, characterized in that, The molar ratio of the manganese dioxide nanorods to lithium hydroxide in step 3) is 2:1 - 1.

05.

7. The preparation method of a one-dimensional lithium manganate nanorod with controllable diameter according to claim 5 or 6, characterized in that, The two-stage sintering includes the first sintering and the second sintering; The temperature of the first sintering is 400 - 500 °C, and the time of the sintering is 4 - 6 h; The temperature of the second sintering is 650 - 750 °C, and the time of the sintering is 10 - 12 h.

8. The one-dimensional lithium manganate nanorods prepared by the preparation method according to any one of claims 1 to 7, characterized in that, The diameter of the one-dimensional lithium manganate nanorods is 30 - 500 nm, and the length is 2 - 6 μm.

9. Application of the one-dimensional lithium manganate nanorods according to claim 8 as a cathode material.

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