COMPOUND, PREPARATION METHOD THEREFORE, AND USE IN LITHIUM ION SECONDARY BATTERY

Abstract

Disclosed in the present application is a compound, comprising nano silicon, a lithium-containing compound and a carbon coating, or comprising nano silicon, silicon oxide, a lithium-containing compound, and a carbon coating. The method comprises: (1) solid-phase mixing of carbon coated silicon oxide with a lithium source; and (2) preforming heat-treatment of the pre-lithium precursor obtained in step (1) in a vacuum or non-oxidising atmosphere to obtain a compound. The method is simple, and has low equipment requirements and low costs; the obtained compound has a stable structure and the structure and properties do not deteriorate during long-term storage, a battery made of cathode material containing said compound exhibits high delithiation capacity, high initial coulombic efficiency, and good recycling properties, the charging capacity is over 1920 mAh/g, the discharging capacity is over 1768 mAh/g, and the initial capacity is over 90.2%.

Claims

1-13. (canceled)

14. A composite, which is a SiOCLi composite comprising nano-silicon, a lithium-containing compound and a carbon coating.

15. The composite according to claim 14, wherein the composite further comprises a silicon oxide.

16. The composite according to claim 14, wherein the nano-silicon is grown from in-situ reduction of a carbon-coated silicon oxide, and the carbon-coated silicon oxide comprises a silicon oxide and a carbon coating coated on the surface of the silicon oxide.

17. The composite according to claim 14, wherein when the composite comprises nano-silicon, a lithium-containing compound and a carbon coating, the composite has such a structure that: the nano-silicon is dispersed in the lithium-containing compound served as a matrix in a sea-island form to form fusion particles, with the carbon coating coated on the surface of the fusion particles.

18. The composite according to claim 15, wherein when the composite comprises nano-silicon, a silicon oxide, a lithium-containing compound and a carbon coating, the composite has such a structure that: nano-silicon is dispersed in the lithium-containing compound to form fusion particles, and the fusion particles are dispersed in the silicon oxide served as a matrix in a sea-island form to form composite particles, with the carbon coating coated on the surface of the composite particles.

19. The composite according to claim 14, wherein the lithium-containing compound comprises any one selected from the group consisting of LiSi compounds, LiO compounds, silicon-oxygen-lithium compounds, and a mixture of at least two selected therefrom.

20. The composite according to claim 19, wherein the silicon-oxygen-lithium compound comprises any one selected from the group consisting of Li.sub.2SiO.sub.3, Li.sub.4SiO.sub.4, Li.sub.2Si.sub.2O.sub.5, Li.sub.2Si.sub.3O.sub.7, and a mixture of at least two selected therefrom.

21. The composite according to claim 14, wherein the carbon coating comprises a carbon matrix and carbon nanotubes and/or graphene sheets embedded in the carbon matrix, and the carbon matrix is obtained by cracking an organic carbon source via carbonization treatment.

22. The composite according to claim 14, wherein based on 100 wt % of the total mass of the composite, the carbon coating has a mass percent of 0.1-50 wt %.

23. A preparation method of the composite according to claim 14, comprising the following steps: (1) blending a carbon-coated silicon oxide and a lithium source by solid-phase mixing mode to implement primary treatment to form a pre-lithium precursor; and (2) heat-treating the pre-lithium precursor in vacuum or a non-oxidizing atmosphere to implement structural adjustment and secondary treatment to form the composite.

24. The method according to claim 23, further comprising step (3) of subjecting the composite to surface treatment after the heat treatment of step (2) to obtain a surface-treated composite.

25. The method according to claim 23, wherein the lithium source in step (1) is any one selected from the group consisting of lithium-containing compound with strong alkalinity, lithium-containing compound with reducibility, elemental lithium, and a combination of at least two selected therefrom.

26. The method according to claim 23, wherein the carbon-coated silicon oxide in step (1) comprises a silicon oxide and a carbon coating coated on the surface of the silicon oxide.

27. The method according to claim 26, wherein the carbon coating comprises a carbon matrix and carbon nanotubes and/or graphene sheets embedded in the carbon matrix, and the carbon matrix is obtained by cracking an organic carbon source via carbonization treatment.

28. The method according to claim 27, wherein the temperature of the carbonization treatment is 500-1300 C.; the time for the carbonization treatment is 1-10 h.

29. The method according to claim 23, wherein in the carbon-coated silicon oxide in step (1), the mass ratio of the silicon oxide to the carbon coating is 100:(2-15); the mass ratio of the carbon-coated silicon oxide to the lithium source in step (1) is 1:(0.01-0.3).

30. The method according to claim 23, wherein the solid-phase mixing mode in step (1) comprises any one selected from the group consisting of ball milling, VC mixing, fusion, mixing, kneading, dispersion, and a combination of at least two selected therefrom; the time for the blending in step (1) is 2-12 h.

31. The method according to claim 23, wherein the non-oxidizing atmosphere in step (2) comprises any one selected from the group consisting of hydrogen atmosphere, nitrogen atmosphere, helium atmosphere, neon atmosphere, argon atmosphere, krypton atmosphere, xenon atmosphere, and a combination of at least two selected therefrom; the temperature of the heat-treating in step (2) is 160-1000 C.; the time for the heat-treating in step (2) is 2-12 h.

32. The method according to claim 23, wherein the manner of the surface treatment in step (3) comprises any one selected from the group consisting of impurity removal, cladding, surface functional group alteration, coating, film plating, spraying, and a combination of at least two selected therefrom.

33. A lithium-ion secondary battery comprising the composite according to claim 14.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0077] FIG. 1 is a schematic structural view of a composite comprising nano-silicon, a lithium-containing compound and a carbon coating, wherein reference number 1 represents a carbon coating, reference number 2 represents a lithium-containing compound, and reference number 3 represents nano-silicon;

[0078] FIG. 2 is a schematic structural view of a composite comprising nano-silicon, a silicon oxide, a lithium-containing compound and a carbon coating, wherein reference number 1 represents a carbon coating, reference number 2 represents a lithium-containing compound, reference number 3 represents nano-silicon, and reference number 4 represents a silicon oxide;

[0079] FIG. 3 is a SEM image of the composite obtained in Example 1 of the present disclosure.

DETAILED DESCRIPTION

[0080] The technical solutions of the present disclosure will be further described below in conjunction with the accompanying drawings and specific embodiments.

EXAMPLE 1

[0081] 50 g of SiO.sub.x (x=0.95) with carbon coating on the surface and 12.5 g of lithium source LiNH.sub.2 were high-speed dispersed until homogeneously mixed; then the mixture was heat treated at 500 C. for 2 h in an argon atmosphere, naturally cooled to room temperature to take out a composite. Then impurity removal was performed by means of impregnation, and the composite was dried to obtain a surface-treated composite.

[0082] FIG. 3 is a SEM image of the composite obtained in the present example. It can be seen from the figure that dark regions formed by a nano-silicon inlaid lithium-containing compound were uniformly distributed in the particle, which formed a sea-island structure in which the lithium-containing compound inlaid with nano-silicon was served as islands, and silicon oxide was served as the sea.

EXAMPLE 2

[0083] 500 g of SiO.sub.x (x=0.95) with carbon coating on the surface and 125 g of lithium source Li.sub.2CO.sub.3 were high-speed dispersed until homogeneously mixed; then the mixture was heat treated at 500 C. for 2 h in an argon atmosphere, naturally cooled to room temperature to take out a composite. Then impurity removal was performed by means of impregnation, and the composite was dried to obtain a surface-treated composite.

EXAMPLE 3

[0084] 50 g of SiO.sub.x (x=0.95) with carbon coating on the surface and 10.8 g of lithium metal powder as a lithium source were mixed in a vacuum state for 3 h; then the mixture was heat treated at 500 C. for 2 h in an argon atmosphere, naturally cooled to room temperature to take out a composite. Then impurity removal was performed by means of impregnation, and the composite was dried to obtain a surface-treated composite.

EXAMPLE 4

[0085] 500 g of SiO.sub.x (x=0.95) with carbon coating on the surface and 108 g of lithium oxide powder as a lithium source were mixed in a vacuum state for 3 h; then the mixture was heat treated at 500 C. for 2 h in an argon atmosphere, naturally cooled to room temperature to take out a composite. Then impurity removal was performed by means of impregnation, and the composite was dried to obtain a surface-treated composite.

EXAMPLE 5

[0086] 500 g of SiO.sub.x (x=0.5) with carbon coating on the surface and 108 g of lithium metal powder as a lithium source were ball milled for 8 h; then the mixture was heat treated at 800 C. for 1.5 h in an argon atmosphere, naturally cooled to room temperature to take out a composite. Then impurity removal was performed by means of impregnation, and the composite was dried to obtain a surface-treated composite.

EXAMPLE 6

[0087] 100 g of SiO.sub.x (x=1.5) with carbon coating on the surface and 30 g of lithium source LiNH.sub.2 were high-speed dispersed until homogeneously mixed; then the mixture was heat treated at 300 C. for 6 h in a nitrogen atmosphere, naturally cooled to room temperature to take out a composite. Then impurity removal was performed by means of impregnation, and the composite was dried to obtain a surface-treated composite.

EXAMPLE 7

[0088] 200 g of SiO (x=0.7) with carbon coating on the surface and 45 g of lithium source Li.sub.2CO.sub.3 were VC mixed for 2 h; then the mixture was heat treated at 900 C. for 2 h in an argon atmosphere, naturally cooled to room temperature to take out a composite. Then a layer of polymer film was sprayed on the surface of the composite, filtered and dried to obtain a surface-treated composite.

COMPARISON EXAMPLE 1

[0089] 50 g of SiO was mixed with 6.3 g of citric acid homogeneously, and then the mixture was fired in a nitrogen atmosphere box-type furnace at a firing temperature of 800 C. After 2 h of heat preservation, a SiO raw material having a carbon coating layer was obtained by naturally cooling to room temperature.

[0090] Electrochemical Performance Test

[0091] The anode materials for lithium ion batteries prepared in Examples 1-7 and the Comparative Example were used as active materials respectively, and PI was used as a binder. After conductive carbon black was added, a slurry was obtained by stirring and then coated on a copper foil, and finally anode plates were obtained by oven drying and rolling, wherein active material : conductive agent : binder=85:15:10. Lithium metal sheet was used as the counter electrode, PP/PE was used as the diaphragm, LiPF.sub.6/EC+DEC+DMC (the volume ratio of EC, DEC and DMC is 1:1:1) was used as the electrolyte, and simulated batteries were assembled in a glove box filled with argon. The electrochemical performances of the batteries were tested with a LAND or Xinwei 5V/10 mA battery tester, in which the charge-discharge voltage was set as 1.5V and the charge-discharge rate was set as 0.1C, and the test results were shown in Table 1.

TABLE-US-00001 TABLE 1 Charge Discharge Specific surface capacity capacity Initial area (m.sup.2/g) (mAh/g) (mAh/g) efficiency (%) Comparison 2.7 1892 1400 74 Example 1 Example 1 1.8 2042 1850 90.6 Example 2 2.3 2006 1810 90.2 Example 3 1.9 2044 1860 91.0 Example 4 2.0 2026 1840 90.8 Example 5 1.6 2001 1842 92.1 Example 6 2.6 2080 1868 89.8 Example 7 2.0 1920 1768 92.1

[0092] As can be seen from the comparison of Examples 1-7 and Comparative Example 1, the lithium-ion secondary batteries made of the anode materials containing the composite of the present disclosure exhibit high delithiation capacity, high initial coulombic efficiency and excellent cycling performance, which has a charge capacity of 1920 mAh/g or more, a discharge capacity of 1768 mAh/g or more and an initial efficiency of 90.2% or more, and the electrochemical performances are significantly superior to those of the battery made of a conventional carbon-coated SiO anode material.

[0093] The Applicant claims that the detailed methods of the present disclosure is described by the above-described embodiments, but the present invention is not limited to the detailed methods described above, that is, it does not mean that the present invention must be implemented by the above detailed methods. It is to be understood by those skilled in the art that any modifications of the present disclosure, equivalent substitution of the various materials of the present disclosure, and the addition of auxiliary components, the selection of the specific manner and the like, are all within the protection scope and disclosure scope of the present invention.