POSITIVE ELECTRODE MATERIAL AND PREPARATION METHOD THEREFOR, AND LITHIUM-ION BATTERY

Abstract

The present disclosure provides a cobalt-free and nickel-free positive electrode material and a preparation method therefor, and a battery. The preparation method includes: preparing a cobalt-free and nickel-free matrix material, and mixing the cobalt-free and nickel-free matrix material, a lithium source, and a divalent manganese compound for reaction to obtain the cobalt-free and nickel-free positive electrode material. By adding the divalent manganese compound, the generation of lamellar LiMnO.sub.2 and spinel LiMn.sub.2O.sub.4 is inhibited, the generation of lamellar Li.sub.2MnO.sub.3 is promoted, and the cycle performance of the material is improved.

Claims

1. A preparation method for a cobalt-free and nickel-free positive electrode material, comprising: preparing a cobalt-free and nickel-free matrix material, and mixing the cobalt-free and nickel-free matrix material, a lithium source, and a divalent manganese compound for reaction to obtain the cobalt-free and nickel-free positive electrode material.

2. The preparation method according to claim 1, wherein a general formula of the cobalt-free and nickel-free matrix material is Na.sub.xLi.sub.yMn.sub.0.75O.sub.2, wherein 0.8?x?1, and 0?y?0.35.

3. The preparation method according to claim 1, wherein a preparation method for the cobalt-free and nickel-free matrix material comprises: mixing a lithium salt, a manganese salt, and a sodium salt, wherein a molar ratio of lithium in the lithium salt, sodium in the sodium salt, and manganese in the manganese salt is (0.2-0.3): (0.9-1.1): (0.65-0.85); and heating the mixture to obtain the cobalt-free and nickel-free matrix material.

4. The preparation method according to claim 3, wherein a temperature of the heating in the preparation method for the cobalt-free and nickel-free matrix material is 500-800? C., and time for the heating is 8-12 h.

5. The preparation method according to claim 1, wherein a temperature of the heating in the preparation method for the cobalt-free and nickel-free matrix material is 500-800? C., and time for the heating is 8-12 h.

6. The preparation method according to claim 1, wherein the cobalt-free and nickel-free matrix material, the divalent manganese compound, and the lithium source are mixed to obtain a mixture, and a molar ratio of lithium to manganese in the mixture is (0.8-1.5):1.

7. The preparation method according to claim 6, wherein the divalent manganese compound comprises one of or a combination of at least two of MnO, Mn.sub.3O.sub.4, or MnCO.sub.3.

8. The preparation method according to claim 6, wherein the mixing reaction is a melting reaction, a temperature of the mixing reaction is 400-800? C., and time for the mixing reaction is 4-8 h.

9. The preparation method according to claim 1, wherein the divalent manganese compound comprises one of or a combination of at least two of MnO, Mn.sub.3O.sub.4, or MnCO.sub.3.

10. The preparation method according to claim 1, wherein the mixing reaction is a melting reaction, a temperature of the mixing reaction is 400-800? C., and time for the mixing reaction is 4-8 h.

11. The preparation method according to claim 1, wherein the cobalt-free and nickel-free positive electrode material obtained after the mixing reaction is further coated, and a method for the coating comprises the following steps: mixing the cobalt-free and nickel-free positive electrode material obtained by the reaction with AlPO.sub.4, and performing primary calcination to obtain an AlPO.sub.4-coated positive electrode material; and mixing the AlPO.sub.4-coated positive electrode material with TiO.sub.2, and performing secondary calcination to obtain an AlPO.sub.4- and TiO.sub.2-coated cobalt-free and nickel-free positive electrode material.

12. The preparation method according to claim 11, wherein a temperature of the primary calcination is 300-800? C., time for the primary calcination is 5-8 h, and an atmosphere for the primary calcination is air or oxygen.

13. The preparation method according to claim 11, wherein a temperature of the secondary calcination is 300-800? C., time for the secondary calcination is 5-8 h, and an atmosphere for the secondary calcination is air or oxygen.

14. The preparation method according to claim 11, wherein based on a total mass of the cobalt-free and nickel-free positive electrode material, a coating amount of the AlPO.sub.4 is 500-5000 ppm, and a coating amount of the TiO.sub.2 is 500-5000 ppm.

15. The preparation method according to claim 1, wherein based on a total mass of the cobalt-free and nickel-free positive electrode material, a coating amount of the AlPO.sub.4 is 500-5000 ppm, and a coating amount of the TiO.sub.2 is 500-5000 ppm.

16. A cobalt-free and nickel-free positive electrode material prepared by the preparation method according to claim 1, wherein the cobalt-free and nickel-free positive electrode material comprises lamellar LiMnO.sub.3, spinel LiMn.sub.2O.sub.4, and lamellar Li.sub.2MnO.sub.3.

17. The cobalt-free and nickel-free positive electrode material according to claim 16, wherein a molar ratio of the lamellar Li.sub.2MnO.sub.3 in the cobalt-free and nickel-free positive electrode material is 50-90%.

18. A battery, comprising a positive electrode, a negative electrode, and a separator, wherein the cobalt-free and nickel-free positive electrode material is used in the positive electrode.

19. The battery according to claim 18, wherein the cobalt-free and nickel-free positive electrode material comprises lamellar LiMnO.sub.3, spinel LiMn.sub.2O.sub.4, and lamellar Li.sub.2MnO.sub.3.

20. The battery according to claim 19, wherein a molar ratio of the lamellar Li.sub.2MnO.sub.3 in the cobalt-free and nickel-free positive electrode material is 50-90%.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0038] The accompanying drawings are used to provide a further understanding of the technical solutions of the present disclosure, constitute a part of the specification, are used together with the embodiments of the present application to explain the technical solutions of the present disclosure, and do not constitute limitations on the technical solutions of the present disclosure.

[0039] FIG. 1 is a scanning electron microscope image of a cobalt-free and nickel-free positive electrode material prepared in one embodiment of the present disclosure at a magnification of 2000 times;

[0040] FIG. 2 is a scanning electron microscope image of a cobalt-free and nickel-free positive electrode material prepared in one embodiment of the present disclosure at a magnification of 3000 times;

[0041] FIG. 3 is an XRD graph of a cobalt-free and nickel-free positive electrode material prepared in one embodiment of the present disclosure;

[0042] FIG. 4 is a curve graph of charging and discharging of a cobalt-free and nickel-free positive electrode material prepared in Comparative Example 1 of the present disclosure in 1.sup.st and 2.sup.nd weeks; and

[0043] FIG. 5 is a curve graph of charging and discharging of a cobalt-free and nickel-free positive electrode material prepared in one embodiment of the present disclosure in 1.sup.st, 2.sup.nd, and 51.sup.th weeks.

DETAILED DESCRIPTION OF EMBODIMENTS

[0044] The technical solutions of the present disclosure will be further illustrated below with reference to the accompanying drawings and through specific examples.

Example 1

[0045] A preparation method for a cobalt-free and nickel-free positive electrode material included the following steps: [0046] (I) Lithium carbonate, sodium carbonate, and manganese carbonate were mixed with a molar ratio of lithium, sodium, and manganese of 0.25:1:0.75, and heated at 750? C. for 10 h in an air atmosphere with an air flow rate of 7.5 L/min to obtain a cobalt-free and nickel-free matrix material, a general formula of which was NaLi.sub.0.25Mn.sub.0.75O.sub.2, [0047] (II) The cobalt-free and nickel-free matrix material prepared in step (I), lithium carbonate, and MnO were mixed to obtain a mixture in which a molar ratio of lithium to manganese was 1.2:1, a melting reaction was performed at 600? C. for 6 h, water was added in a mass twice that of the material after reaction to the material, and the material was stirred and washed for 10 min and then dried; and [0048] (III) The dried cobalt-free and nickel-free positive electrode material was mixed with AlPO.sub.4, and primary calcination was performed at 550? C. in the air atmosphere for 6.5 h to coat AlPO.sub.4 with a coating amount of 500 ppm; and the material was mixed with TiO.sub.2, a secondary calcination was performed at 550? C. in an oxygen atmosphere for 6.5 h to coat TiO.sub.2 with a coating amount of 500 ppm to obtain the cobalt-free and nickel-free positive electrode material.

[0049] A chemical formula of the cobalt-free and nickel-free positive electrode material prepared in this example was Li.sub.0.92Mn.sub.0.76O.sub.2, where a molar ratio of lamellar Li.sub.2MnO.sub.3 was 70%.

[0050] It can be seen from FIG. 1 and FIG. 2 that the cobalt-free and nickel-free positive electrode material prepared in this example had an irregular single crystal structure. FIG. 3 is an XRD characterization graph, showing that the material included lamellar Li.sub.2MnO.sub.3.

Example 2

[0051] A preparation method for a cobalt-free and nickel-free positive electrode material included the following steps: [0052] (I) Lithium hydroxide, sodium acetate, and manganese oxide were mixed with a molar ratio of lithium, sodium, and manganese of 0.25:1:0.75, and heated at 500? C. for 12 h in an air atmosphere with an air flow rate of 5 L/min to obtain a cobalt-free and nickel-free matrix material, a general formula of which was NaLi.sub.0.25Mn.sub.0.75O.sub.2, [0053] (II) The cobalt-free and nickel-free matrix material prepared in step (I), lithium hydroxide, and Mn.sub.3O.sub.4 were mixed to obtain a mixture in which a molar ratio of lithium to manganese was 0.9:1, a melting reaction was performed at 400? C. for 8 h, water was added in a mass twice that of the material after reaction to the material, and the material was stirred and washed for 10 min and then dried; and [0054] (III) The dried cobalt-free and nickel-free positive electrode material was mixed with AlPO.sub.4, and primary calcination was performed at 800? C. in the air atmosphere for 5 h to coat AlPO.sub.4 with a coating amount of 1000 ppm; and the material was mixed with TiO.sub.2, a secondary calcination was performed at 700? C. in the air atmosphere for 5.5 h to coat TiO.sub.2 with a coating amount of 1000 ppm to obtain the cobalt-free and nickel-free positive electrode material.

[0055] A chemical formula of the cobalt-free and nickel-free positive electrode material prepared in this example was Li.sub.0.8Mn.sub.0.89O.sub.2, where a molar ratio of lamellar Li.sub.2MnO.sub.3 was 50%.

Example 3

[0056] A preparation method for a cobalt-free and nickel-free positive electrode material included the following steps: [0057] (I) Lithium chloride, sodium chloride, and manganese dioxide were mixed with a molar ratio of lithium, sodium, and manganese of 0.25:1:0.75, and heated at 800? C. for 8 h in an air atmosphere with an air flow rate of 10 L/min to obtain a cobalt-free and nickel-free matrix material, a general formula of which was NaLi.sub.0.25Mn.sub.0.75O.sub.2, [0058] (II) The cobalt-free and nickel-free matrix material prepared in step (I), lithium chloride, and MnO 3 were mixed to obtain a mixture in which a molar ratio of lithium to manganese was 1.5:1, a melting reaction was performed at 800? C. for 4 h, water was added in a mass twice that of the material after reaction to the material, and the material was stirred and washed for 10 min and then dried; and [0059] (III) The dried cobalt-free and nickel-free positive electrode material was mixed with AlPO.sub.4, and primary calcination was performed at 300? C. in an oxygen atmosphere for 8 h to coat AlPO.sub.4 with a coating amount of 3000 ppm; and the material was mixed with TiO.sub.2, a secondary calcination was performed at 300? C. in the oxygen atmosphere for 8 h to coat TiO.sub.2 with a coating amount of 3000 ppm to obtain the cobalt-free and nickel-free positive electrode material.

[0060] A chemical formula of the cobalt-free and nickel-free positive electrode material prepared in this example was Li.sub.1.05Mn.sub.0.7O.sub.2, where a molar ratio of lamellar Li.sub.2MnO.sub.3 was 87.5%.

Example 4

[0061] A preparation method for a cobalt-free and nickel-free positive electrode material included the following steps: [0062] (I) Lithium fluoride, sodium bicarbonate, and manganese acetate were mixed with a molar ratio of lithium, sodium, and manganese of 0.25:1:0.75, and heated at 650? C. for 9 h in an air atmosphere with an air flow rate of 7 L/min to obtain a cobalt-free and nickel-free matrix material, a general formula of which was NaLi.sub.0.25Mn.sub.0.75O.sub.2, [0063] (II) The cobalt-free and nickel-free matrix material prepared in step (I), lithium fluoride, and MnO were mixed to obtain a mixture in which a molar ratio of lithium to manganese was 1:1, a melting reaction was performed at 700? C. for 5 h, water was added in a mass twice that of the material after reaction to the material, and the material was stirred and washed for 10 min and then dried; and [0064] (III) The dried cobalt-free and nickel-free positive electrode material was mixed with AlPO.sub.4, and primary calcination was performed at 700? C. in the air atmosphere for 7 h to coat AlPO.sub.4 with a coating amount of 5000 ppm; and the material was mixed with TiO.sub.2, a secondary calcination was performed at 800? C. in an oxygen atmosphere for 5 h to coat TiO.sub.2 with a coating amount of 5000 ppm to obtain the cobalt-free and nickel-free positive electrode material.

[0065] A chemical formula of the cobalt-free and nickel-free positive electrode material prepared in this example was Li.sub.0.8Mn.sub.0.8O.sub.2, where a molar ratio of lamellar Li.sub.2MnO.sub.3 was 55%.

Example 5

[0066] A preparation method for a cobalt-free and nickel-free positive electrode material included the following steps: [0067] (I) Lithium fluoride, sodium bicarbonate, and manganese acetate were mixed with a molar ratio of lithium, sodium, and manganese of 0.25:1:0.75, and heated at 600? C. for 9 h in an air atmosphere with an air flow rate of 9 L/min to obtain a cobalt-free and nickel-free matrix material, a general formula of which was NaLi.sub.0.25Mn.sub.0.75O.sub.2, [0068] (II) The cobalt-free and nickel-free matrix material prepared in step (I), lithium carbonate, and MnO were mixed to obtain a mixture in which a molar ratio of lithium to manganese was 1.3:1, a melting reaction was performed at 500? C. for 7 h, water was added in a mass twice that of the material after reaction to the material, and the material was stirred and washed for 10 min and then dried; and [0069] (III) The dried cobalt-free and nickel-free positive electrode material was mixed with AlPO.sub.4, and primary calcination was performed at 400? C. in an oxygen atmosphere for 7.5 h to coat AlPO.sub.4 with a coating amount of 1500 ppm; and the material was mixed with TiO.sub.2, a secondary calcination was performed at 400? C. in the oxygen atmosphere for 7.5 h to coat TiO.sub.2 with a coating amount of 2000 ppm to obtain the cobalt-free and nickel-free positive electrode material.

[0070] A chemical formula of the cobalt-free and nickel-free positive electrode material prepared in this example was Li.sub.0.98Mn.sub.0.75O.sub.2, where a molar ratio of lamellar Li.sub.2MnO.sub.3 was 78%.

Example 6

[0071] Different from Example 1, the molar ratio of lithium to manganese in step (II) was changed to 0.6:1. A chemical formula of the prepared cobalt-free and nickel-free positive electrode material was Li.sub.0.5Mn.sub.0.83O.sub.2, where lamellar Li.sub.2MnO.sub.3 was not included.

Example 7

[0072] Different from Example 1, the molar ratio of lithium to manganese in step (II) was changed to 1.7:1. A chemical formula of the prepared cobalt-free and nickel-free positive electrode material was Li.sub.1.2 Mn.sub.0.7O.sub.2, where a molar ratio of lamellar Li.sub.2MnO.sub.3 was 94%.

Example 8

[0073] Different from Example 1, step (III) was not performed, that is, AlPO.sub.4 coating and TiO.sub.2 coating were not performed.

Example 9

[0074] Different from Example 1, AlPO.sub.4 coating was not performed in step (III).

Example 10

[0075] Different from Example 1, TiO.sub.2 coating was not performed in step (III).

Example 11

[0076] Different from Example 1, the coating amount of AlPO.sub.4 was changed to 300 ppm and the coating amount of TiO.sub.2 was changed to 300 ppm in step (III).

Example 12

[0077] Different from Example 1, the coating amount of AlPO.sub.4 was changed to 6000 ppm and the coating amount of TiO.sub.2 was changed to 6000 ppm in step (III).

Comparative Example 1

[0078] Different from Example 1, MnO was not added in step (II). In the prepared cobalt-free and nickel-free positive electrode material, a molar ratio of lamellar Li.sub.2MnO.sub.3 was 20%.

Comparative Example 2

[0079] Different from Example 1, MnO was replaced with MnO 2 in step (II). In the prepared cobalt-free and nickel-free positive electrode material, a molar ratio of lamellar Li.sub.2MnO.sub.3 was 25%.

[0080] The cobalt-free and nickel-free positive electrode material prepared in the examples and comparative examples provided in the present disclosure was assembled into a battery: an appropriate amount of material was coated with slurry uniformly, where the cobalt-free and nickel-free positive electrode material: Sp: PVDF gel=92:4:4, and the solid content of the PVDF gel was 6.05%; and the prepared electrode plate was assembled with a CR2032 shell to form a button battery, where Sp represented conductive carbon black, PVDF represented polyvinylidene fluoride, and CR2032 shell represented a cylindrical shell having a diameter of 20 mm and a height of 3.2 mm.

[0081] The obtained button battery was tested for cycle performance at a voltage of 2-4.6 V. The test results were shown in Table 1. FIG. 4 shows charging and discharging curves of the battery assembled using the cobalt-free and nickel-free positive electrode material in Comparative Example 1 in 1.sup.st and 2.sup.nd weeks, and FIG. 5 shows charging and discharging curves of the battery assembled using the cobalt-free and nickel-free positive electrode material in Example 1 in 1.sup.st, 2.sup.nd, and 51.sup.st weeks.

TABLE-US-00001 TABLE 1 20-week 50-week A1PO.sub.4 TiO.sub.2 0.1 C 0.1 C 1 C capacity capacity coating coating charging discharging Initial discharging retention retention amount amount capacity capacity efficiency capacity rate rate Number (ppm) (ppm) (mAh/g) (mAh/g) (%) (mAh/g) (%) (%) Example 1 500 500 250.1 244.1 97.6 205.8 88.5 85.6 Example 2 1000 1000 258.4 254.4 98.5 204.8 90.2 84.2 Example 3 3000 3000 259.9 255.7 98.4 206.1 98.7 90.2 Example 4 5000 5000 253.4 246.2 97.2 203.4 91.5 85.6 Example 5 1500 2000 259.5 251.6 97.0 204.1 94.2 85.9 Example 6 500 500 240.2 231.1 96.2 188.2 75.4 50.6 Example 7 500 500 234.5 195.8 83.5 165.7 75.3 52.5 Example 8 0 0 259.0 254.4 98.2 205.6 75.2 40.2 Example 9 0 500 254.4 251.1 98.7 201.1 78.4 68.9 Example 10 500 0 255.1 252.1 98.8 204.1 68.7 61.2 Example 11 300 300 240.3 221.2 92.0 189.2 85.6 65.4 Example 12 6000 6000 246.6 231.5 93.9 193.6 90.4 84.6 Comparative 500 500 264.9 231.5 87.4 101.4 60.2 45.2 Example 1 Comparative 500 500 263.8 231.8 88.0 104.4 61.3 46.6 Example 2

[0082] It can be seen by comparing Example 1 with Examples 6 and 7 that, by controlling the addition amount of the divalent manganese compound, after the cobalt-free and nickel-free matrix material, the divalent manganese compound, and the lithium source were mixed, the molar ratio of lithium to manganese was (0.8-1.5):1, which effectively inhibited the formation of lamellar LiMnO.sub.2, thereby improving the cycle performance of the battery; if the molar ratio of lithium to manganese was less than 0.8:1, excessive lithium-deficient materials, such as spinel structures, will be formed, resulting in low capacity; and if the molar ratio of lithium to manganese was more than 1.5:1, cost waste will be caused, and the total alkali content of the material was too high to affect the performance of the material.

[0083] It can be seen by comparing Example 1 with Examples 8, 9, and 10 that, through double-layer coating with TiO.sub.2 as an outer coating, TiO.sub.2 bound to Li diffused from the active material in the coating process to generate Li.sub.2TiO.sub.3, which was a lithium ion conductor; the Li.sub.2TiO.sub.3 generated on the surface can improve the diffusion rate of ions; and AlPO.sub.4 served as an inner coating, Al.sup.3+ diffused into oxide lattices in the cycling process to stabilize the structure, and PO.sub.4.sup.3? interacted with Li.sup.+ to generate a good lithium ion conductor Li.sub.3PO.sub.4.

[0084] It can be seen by comparing Example 1 with Examples 11 and 12 that the coating amount of the AlPO.sub.4 was controlled to 500-5000 ppm; if the coating amount was less than 500 ppm, problems of uneven material coating and thin coating were caused, and the effect of isolation from an electrolytic solution was poor, which increased side reactions, so that the electrical performance of the battery was poor; and if the coating amount is more than 5000 ppm, the coating of the material was too thick, which hindered the intercalation and deintercalation of Lit, thereby affecting the capacity and rate performance of the material.

[0085] It can be seen by comparing Example 1 with Comparative Examples 1 and 2 that, in combination with FIG. 4 and FIG. 5, there were two capacity plateaus at 3.5-4.5 V, showing the presence of a LiMnO.sub.2 phase in the material; in the cycling process, the lamellar LiMnO.sub.3 and spinel LiMn.sub.2O.sub.4 caused capacity loss, and the disproportionation reaction of Mn.sup.3+ and the Jahn-Teller effect in the LiMn.sub.2O.sub.4 cycle will lead to severe deterioration of material cycle, so the cycle performance in Comparative Example 1 was poor, and the retention rate was only 60.2% after 20 cycles; and by adding the divalent manganese compound in the preparation process, the generation of the lamellar LiMnO.sub.3 and spinel LiMn.sub.2O.sub.4 was effectively inhibited, and the generation of lamellar Li.sub.2MnO.sub.3 was promoted to effectively improve the cycle performance of the cobalt-free and nickel-free material.