A lithium manganate positive electrode material with a conductive protective layer and a preparation method thereof

Abstract

The present invention belongs to the technical field of lithium-ion batteries and provides a lithium manganate positive electrode material having a conductive protective layer and a preparation method thereof. The present invention comprises mixing manganese carbonate and lithium carbonate, followed by ball milling, primary sintering, and secondary sintering to produce a lithium manganate positive electrode material. The lithium manganate positive electrode material is then mixed with an acidic solution, followed by a hydrothermal reaction, drying, and sintering to produce a lithium manganate positive electrode material having a conductive protective layer. The preparation method of the present invention is simple and low-cost, and the conductive protective layer of the present invention can improve the low conductivity of the oxide protective layer while inhibiting electrolyte erosion of the positive electrode material.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium electronic batteries, and in particular to a lithium manganate positive electrode material with a conductive protective layer and a preparation method thereof. Background Art

[0002] Lithium-ion batteries (LIBs) play an important role in energy storage due to their advantages such as high volume / weight density, long cycle life, and green environmental protection. The positive electrode material accounts for a large proportion of the entire lithium-ion battery, which determines the energy density, voltage and service life of the entire lithium-ion battery. Therefore, the research and development of high-performance lithium-ion batteries mainly focuses on improving the energy density and cycle stability of the positive electrode material. Lithium manganese oxide positive electrode materials have faster lithiation and delithiation kinetics due to their inherent 3-D lithium ion diffusion channels, and therefore show good rate performance. However, due to the manganese dissolution (disproportionation reaction) and structural transformation (Jahn-Teller effect) of the lithium manganese oxide positive electrode material itself, it is prone to capacity attenuation during long cycles, especially at high temperature and high pressure, which limits its further practical application.

[0003] Therefore, it is of great significance to study and obtain a lithium manganese oxide positive electrode material with a conductive protective layer and a preparation method thereof, which can effectively inhibit the corrosion of the electrolyte on the positive electrode material while improving the conductivity of the protective layer. Summary of the Invention

[0004] In view of this, the present invention provides a lithium manganese oxide positive electrode material with a conductive protective layer and a preparation method thereof, the purpose of which is to solve the problems of manganese dissolution and Jahn-Teller effect faced by the lithium manganese oxide positive electrode material prepared in the prior art.

[0005] In order to achieve the above object, the present invention adopts the following technical solutions:

[0006] The present invention provides a method for preparing a lithium manganate positive electrode material having a conductive protective layer, comprising the following steps:

[0007] (1) mixing manganese carbonate and lithium carbonate, and then performing ball milling, primary sintering, and secondary sintering in sequence to prepare a lithium manganate positive electrode material;

[0008] (2) The lithium manganate positive electrode material is mixed with an acidic solution and subjected to hydrothermal reaction, drying and sintering in sequence to obtain a lithium manganate positive electrode material with a conductive protective layer.

[0009] Preferably, the molar ratio of manganese carbonate to lithium carbonate in step (1) is 2:1.0-1.1.

[0010] Preferably, the ball-to-material ratio of the ball milling in step (1) is 1:8-12, the ball milling speed is 500-700 r / min, and the ball milling time is 1.5-2.5 h.

[0011] Preferably, the temperature of the first sintering in step (1) is 400-550°C, the time of the first sintering is 3-6 hours, the temperature of the second sintering is 750-900°C, the time of the second sintering is 10-14 hours, and the heating rates of the first sintering and the second sintering are independently 1.5-3°C / min.

[0012] Preferably, the acidic solution in step (2) is a boric acid solution or a polyacrylic acid solution.

[0013] Preferably, the concentration of the boric acid solution or the polyacrylic acid solution in step (2) is independently 0.2-1.6 mg / mL, the mixing speed is 750-850 r / min, and the mixing time is 0.25-0.75 h.

[0014] Preferably, the temperature of the hydrothermal reaction in step (2) is 140-160° C., and the time of the hydrothermal reaction is 4-6 hours.

[0015] Preferably, the drying temperature in step (2) is 70-90° C., and the drying time is 20-25 h.

[0016] Preferably, the sintering temperature in step (2) is 450-550° C., the sintering time is 4.5-6 hours, and the heating rate to the sintering temperature is 1-4° C. / min.

[0017] The present invention also provides a lithium manganate positive electrode material with a conductive protective layer prepared by the method for preparing the lithium manganate positive electrode material with a conductive protective layer.

[0018] It can be seen from the above technical solution that compared with the prior art, the beneficial effects of the present invention are as follows:

[0019] (1) The preparation method of the present invention is simple, low in cost, has low requirements for synthesis equipment, is easy to operate, has no special requirements for the production process, is environmentally friendly, and is suitable for industrial production;

[0020] (2) The present invention constructs a conductive protective layer on the surface of the positive electrode material through a solvation hydrothermal method; this conductive protective layer is superior to other inert protective layers, and can improve the problem of low conductivity of the oxide protective layer while inhibiting the corrosion of the electrolyte on the positive electrode material; this protective layer can inhibit the capacity decay caused by the dissolution of the transition metal due to the disproportionation reaction.

[0021] (3) The lithium manganate positive electrode material obtained by the preparation method of the present invention has excellent electrochemical properties. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are merely embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on the provided drawings without paying any creative work.

[0023] Figure 1 The XRD patterns of the products obtained in Examples 3 and 7 of the present invention and the unmodified lithium manganate positive electrode material (original sample) in Example 3;

[0024] Figure 2 TEM images of the products obtained in Examples 3 and 7 of the present invention, wherein (A) is Example 3 and (B) is Example 7;

[0025] Figure 3 Graph showing the electrochemical performance of the products obtained in Examples 3 and 7 of the present invention and the unmodified lithium manganate positive electrode material (original sample) in Example 3. DETAILED DESCRIPTION

[0026] The present invention provides a method for preparing a lithium manganate positive electrode material having a conductive protective layer, comprising the following steps:

[0027] (1) mixing manganese carbonate and lithium carbonate, and then performing ball milling, primary sintering, and secondary sintering in sequence to prepare a lithium manganate positive electrode material;

[0028] (2) The lithium manganate positive electrode material is mixed with an acidic solution and subjected to hydrothermal reaction, drying and sintering in sequence to obtain a lithium manganate positive electrode material with a conductive protective layer.

[0029] In the present invention, a conductive protective layer is in-situ constructed on the surface of the lithium manganate positive electrode material by a solvation hydrothermal method. The protective layer has a standard cubic spinel structure and belongs to the Fd3m space group.

[0030] In the present invention, the molar ratio of manganese carbonate to lithium carbonate in step (1) is preferably 2:1.0-1.1, more preferably 2:1.03-1.08, and even more preferably 2:1.05-1.07.

[0031] In the present invention, the ball-to-material ratio of the ball milling in step (1) is preferably 1:8-12, more preferably 1:9-11, and more preferably 1:10. The rotation speed of the ball milling is preferably 500-700 r / min, more preferably 550-650 r / min, and more preferably 580-620 r / min. The ball milling time is preferably 1.5-2.5 h, more preferably 1.8-2.3 h, and more preferably 2-2.1 h.

[0032] In the present invention, the temperature of the primary sintering in step (1) is preferably 400-550°C, more preferably 420-520°C, more preferably 450-500°C, the time of the primary sintering is preferably 3-6h, more preferably 3.5-5.5h, more preferably 3.8-4h, the temperature of the secondary sintering is preferably 750-900°C, more preferably 780-880°C, more preferably 800-850°C, the time of the secondary sintering is preferably 10-14h, more preferably 11-13h, more preferably 11.5-12h, and the heating rates of the primary sintering and the secondary sintering are independently preferably 1.5-3°C / min, more preferably 1.8-2.8°C / min, more preferably 2-2.5°C / min.

[0033] In the present invention, the atmosphere for the primary sintering and the secondary sintering is preferably an oxygen atmosphere.

[0034] In the present invention, the acidic solution in step (2) is preferably a boric acid solution or a polyacrylic acid solution.

[0035] In the present invention, the mass volume ratio of the lithium manganate positive electrode material to the acidic solution is preferably 1 g:45-55 mL, more preferably 1 g:47-53 mL, and even more preferably 1 g:50-51 mL.

[0036] In the present invention, the concentration of the boric acid solution or the polypropylene solution in step (2) is preferably independently 0.2 to 1.6 mg / mL, more preferably 0.5 to 1.3 mg / mL, and more preferably 0.8 to 1 mg / mL. The mixing speed is preferably 750 to 850 r / min, more preferably 780 to 820 r / min, and more preferably 790 to 800 r / min. The mixing time is preferably 0.25 to 0.75 h, more preferably 0.35 to 0.65 h, and more preferably 0.45 to 0.55 h.

[0037] In the present invention, the temperature of the hydrothermal reaction in step (2) is preferably 140-160°C, more preferably 145-155°C, more preferably 150°C, and the time of the hydrothermal reaction is preferably 4-6h, more preferably 4.5-5.5h, more preferably 5h.

[0038] In the present invention, the drying temperature in step (2) is preferably 70-90°C, more preferably 75-85°C, more preferably 78-82°C, and the drying time is preferably 20-25h, more preferably 21-24h, more preferably 22-23h.

[0039] In the present invention, the sintering temperature in step (2) is preferably 450-550°C, more preferably 470-520°C, more preferably 485-500°C, and the sintering time is preferably 4.5-6h, more preferably 4.7-5.8h, more preferably 5-5.2h; the heating rate to the sintering temperature is preferably 1-4°C / min, more preferably 1.5-3°C / min, more preferably 2°C / min.

[0040] The present invention also provides a lithium manganate positive electrode material with a conductive protective layer prepared by the method for preparing the lithium manganate positive electrode material with a conductive protective layer.

[0041] The technical solutions provided by the present invention are described in detail below with reference to the embodiments, but they should not be construed as limiting the scope of protection of the present invention.

[0042] Example 1

[0043] Manganese carbonate and lithium carbonate were placed in a ball mill (with zirconium oxide grinding balls) in a molar ratio of 2:1, with a ball-to-material ratio of 1:11, and a rotation speed of 600 r / min. The mixture was ball-milled for 2.2 h to obtain a mixture, which was then placed in a crucible and placed in a tube furnace for two-stage sintering under an oxygen atmosphere. The temperature was increased to 480°C at a heating rate of 2.2°C / min and kept at this temperature for 4 h, and then increased to 780°C at the same heating rate and kept at this temperature for 13 h. The mixture was cooled in the furnace to obtain a lithium manganate positive electrode material.

[0044] 1 g of lithium manganate positive electrode material was stirred and mixed with 45 mL of boric acid aqueous solution (concentration of 0.2 mg / mL) at a speed of 820 r / min for 0.4 h, and then transferred to a reactor. The reactor was placed in a blast drying oven and reacted at 150°C for 5 h to obtain a black precipitate. After the black precipitate was dried in a drying oven at 85°C for 20 h, the precipitate was placed in a tubular furnace, heated to 550°C at a rate of 2°C / min, and tempered at 550°C for 5.5 h to obtain a lithium manganate positive electrode material with a conductive protective layer.

[0045] Example 2

[0046] Manganese carbonate and lithium carbonate were placed in a ball mill (with zirconium oxide grinding balls) at a molar ratio of 2:1.03, a ball-to-material ratio of 1:10, and a rotation speed of 600 r / min. The mixture was ball-milled for 2 h to obtain a mixture, which was then placed in a crucible and placed in a tube furnace under an oxygen atmosphere for two-stage sintering. The temperature was increased to 500° C. at a heating rate of 2° C. / min and kept at this temperature for 5 h, and then increased to 850° C. at the same heating rate and kept at this temperature for 12 h. The lithium manganate positive electrode material was obtained after cooling in the furnace.

[0047] 1 g of lithium manganate positive electrode material was stirred and mixed with 46 mL of boric acid aqueous solution (concentration of 0.6 mg / mL) at a speed of 800 r / min for 0.4 h, and then transferred to a reactor. The reactor was placed in a blast drying oven and reacted at 150°C for 5 h to obtain a black precipitate. The black precipitate was dried in a drying oven at 80°C for 24 h, and then the precipitate was placed in a tubular furnace, heated to 500°C at a rate of 2°C / min, and tempered at 500°C for 5 h to obtain a lithium manganate positive electrode material with a conductive protective layer.

[0048] Example 3

[0049] Manganese carbonate and lithium carbonate were placed in a ball mill (with zirconium oxide grinding balls) at a molar ratio of 2:1.05, a ball-to-material ratio of 1:8, and a rotation speed of 500 r / min. The mixture was ball-milled for 1.8 h to obtain a mixture, which was then placed in a crucible and placed in a tube furnace under an oxygen atmosphere for two-stage sintering. The temperature was increased to 430°C at a heating rate of 1.8°C / min and kept at this temperature for 3 h, and then increased to 800°C at the same heating rate and kept at this temperature for 10 h. The lithium manganate positive electrode material was obtained after cooling in the furnace.

[0050] 1 g of lithium manganate positive electrode material was stirred and mixed with 50 mL of boric acid aqueous solution (concentration of 1 mg / mL) at a speed of 800 r / min for 0.6 h, and then transferred to a reactor. The reactor was placed in a blast drying oven and reacted at 145°C for 4 h to obtain a black precipitate. The black precipitate was dried in a drying oven at 70°C for 24 h, and then the precipitate was placed in a tubular furnace, heated to 480°C at a rate of 4°C / min, and tempered at 480°C for 6 h to obtain a lithium manganate positive electrode material with a conductive protective layer.

[0051] Example 4

[0052] Manganese carbonate and lithium carbonate were placed in a ball mill (with zirconium oxide grinding balls) at a molar ratio of 2:1.1, a ball-to-material ratio of 1:12, and a rotation speed of 500 r / min. The mixture was ball-milled for 1.8 h to obtain a mixture, which was then placed in a crucible and placed in a tube furnace under an oxygen atmosphere for two-stage sintering. The temperature was increased to 430°C at a heating rate of 1.8°C / min and kept at this temperature for 3 h, and then increased to 880°C at the same heating rate and kept at this temperature for 10 h. The mixture was cooled in the furnace to obtain a lithium manganate positive electrode material.

[0053] 1 g of lithium manganate positive electrode material was stirred and mixed with 52 mL of boric acid aqueous solution (concentration of 1.6 mg / mL) at a speed of 800 r / min for 0.6 h, and then transferred to a reactor. The reactor was placed in a blast drying oven and reacted at 145°C for 4 h to obtain a black precipitate. The black precipitate was dried in a drying oven at 70°C for 24 h, and then the precipitate was placed in a tubular furnace, heated to 500°C at a rate of 4°C / min, and tempered at 500°C for 6 h to obtain a lithium manganate positive electrode material with a conductive protective layer.

[0054] Example 5

[0055] The 0.2 mg / mL boric acid aqueous solution in Example 1 was replaced with a 0.2 mg / mL polyacrylic acid aqueous solution, and the remaining steps were the same as in Example 1.

[0056] Example 6

[0057] The 0.6 mg / mL boric acid aqueous solution in Example 2 was replaced with a 0.6 mg / mL polyacrylic acid aqueous solution, and the remaining steps were the same as in Example 2.

[0058] Example 7

[0059] The 1 mg / mL boric acid aqueous solution in Example 3 was replaced with a 1 mg / mL polyacrylic acid aqueous solution, and the remaining steps were the same as in Example 3.

[0060] Example 8

[0061] The 1.6 mg / mL boric acid aqueous solution in Example 4 was replaced with a 1.6 mg / mL polyacrylic acid aqueous solution, and the remaining steps were the same as in Example 4.

[0062] The electrochemical performance curves of the products obtained in Example 3 and Example 7 and the unmodified lithium manganate positive electrode material (original sample) in Example 3 are shown in FIG. Figure 3 As shown. Figure 3 It can be seen that the preparation method of the present invention can effectively improve the conductivity of the protective layer, thereby improving the electrochemical performance of the lithium manganese oxide positive electrode material.

[0063] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principles of the present invention. These improvements and modifications should also be regarded as within the scope of protection of the present invention.

Claims

1. A method for preparing a lithium manganate positive electrode material having a conductive protective layer, characterized in that: The following steps are involved: (1) Mixing manganese carbonate and lithium carbonate, and then performing ball milling, primary sintering, and secondary sintering in sequence to prepare lithium manganate positive electrode material; (2) mixing the lithium manganate positive electrode material with an acidic solution and sequentially performing a hydrothermal reaction, drying, and sintering to obtain a lithium manganate positive electrode material with a conductive protective layer; The acidic solution in step (2) is a boric acid solution or a polyacrylic acid solution; In step (2), the concentration of the boric acid solution or the polyacrylic acid solution is independently 0.2-1.6 mg / mL, the mixing speed is 750-850 r / min, and the mixing time is 0.25-0.75 h; The temperature of the hydrothermal reaction in step (2) is 140-160° C., and the time of the hydrothermal reaction is 4-6 hours.

2. The method for preparing a lithium manganate positive electrode material with a conductive protective layer according to claim 1, characterized in that: The molar ratio of manganese carbonate to lithium carbonate in step (1) is 2:1.0~1.

1.

3. The method for preparing a lithium manganate positive electrode material with a conductive protective layer according to claim 2, characterized in that: The ball-to-material ratio of the ball mill in step (1) is 1:8-12, the rotation speed of the ball mill is 500-700 r / min, and the ball milling time is 1.5-2.5 h.

4. The method for preparing a lithium manganate positive electrode material with a conductive protective layer according to claim 2 or 3, characterized in that: In step (1), the primary sintering temperature is 400-550°C, the primary sintering time is 3-6 hours, the secondary sintering temperature is 750-900°C, the secondary sintering time is 10-14 hours, and the heating rates of the primary sintering and the secondary sintering are independently 1.5-3°C / min.

5. The method for preparing a lithium manganate positive electrode material with a conductive protective layer according to claim 1, characterized in that: The drying temperature in step (2) is 70-90° C., and the drying time is 20-25 h.

6. The method for preparing a lithium manganate positive electrode material with a conductive protective layer according to claim 5, characterized in that: The sintering temperature in step (2) is 450-550°C, and the sintering time is 4.5-6 hours; the heating rate to the sintering temperature is 1-4°C / min.

7. A lithium manganate positive electrode material with a conductive protective layer obtained by the method for preparing a lithium manganate positive electrode material with a conductive protective layer according to any one of claims 1 to 6.

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