CARBON-COATED LITHIUM-RICH OXIDE COMPOSITE MATERIAL AND PREPARATION METHOD THEREOF

Abstract

The present disclosure relates to the technical field of positive electrode lithium-supplementing additives of the lithium battery, and discloses a carbon-coated lithium-rich oxide composite material and a preparation method thereof. The method comprises the following steps: (1) mixing an iron source or a cobalt source with a lithium source, and sintering to obtain a lithium-rich oxide Li.sub.5FeO.sub.4 or Li.sub.6CoO.sub.4; wherein, a molar ratio of the lithium source to the iron source is 5-25:1, and a molar ratio of the lithium source to the cobalt source is 6-30:1; (2) crushing the lithium-rich oxide obtained in the step (1); and (3) mixing the lithium-rich oxide crushed in the step (2) with a carbon source, and sintering to obtain the carbon-coated lithium-rich oxide composite material. The carbon-coated lithium-rich oxide composite material prepared by the method of the present disclosure overcomes the insufficient conductivity of lithium-rich materials, and has good electrochemical properties, which is capable of effectively compensating for active lithium lost during the initial charge-discharge process of the lithium battery.

Claims

1. A method for preparing a carbon-coated lithium-rich oxide composite material, wherein, comprising the following steps: (1) mixing an iron source or a cobalt source with a lithium source, and sintering to obtain a lithium-rich oxide Li.sub.5FeO.sub.4 or Li.sub.6CoO.sub.4; wherein, a molar ratio of the lithium source to the iron source is 5-25:1, and a molar ratio of the lithium source to the cobalt source is 6-30:1; (2) crushing the lithium-rich oxide obtained in the step (1); and (3) mixing the lithium-rich oxide crushed in the step (2) with a carbon source, and sintering to obtain the carbon-coated lithium-rich oxide composite material.

2. The method according to claim 1, wherein, in the step (1), the iron source is one or more of iron(III) oxide, iron(II,III) oxide, ferric oxyhydroxide, ferric nitrate and ferric citrate.

3. The method according to claim 1, wherein, in the step (1), the cobalt source is one or more of cobalt(II) oxide, cobalt(II,III) oxide, cobalt carbonate, cobalt sulfate, cobalt chloride and cobalt nitrate.

4. The method according to claim 1, wherein, in the step (1), the lithium source is one or more of lithium carbonate, lithium hydroxide monohydrate, lithium hydroxide anhydrous and lithium oxide.

5. The method according to claim 1, wherein, in the step (1), the sintering process comprises putting the mixture of the iron source or the cobalt source and the lithium source in a sintering furnace, and heating to a first sintering temperature at a first preset heating rate for first sintering at an inert gas atmosphere; wherein, preferably, the first preset heating rate is 1-10° C./min; preferably, the first sintering temperature is 500-1000° C., and the first sintering time is 3-60 h.

6. The method according to claim 1, wherein, in the step (2), an average particle size of the lithium-rich oxide crushed is 2-50 μm.

7. The method according to claim 1, wherein, in the step (3), the carbon source is one or more of conductive carbon black, Ketjen black, carbon nanotube, acetylene black, vapor-grown carbon fiber, graphene and biomass carbon.

8. The method according to claim 1, wherein, in the step (3), based on the total weight of the lithium-rich oxide and the carbon source, the carbon source is 0.5-10 wt %.

9. The method according to claim 1, wherein, in the step (3), the sintering process comprises mixing the lithium-rich oxide crushed with the carbon source uniformly, and then heating to a second sintering temperature at a second preset heating rate for second sintering at the inert gas atmosphere; wherein, preferably, the second preset heating rate is 1-10° C./min; preferably, the second sintering temperature is 200-600° C., and the second sintering time is 2-20 h.

10. A carbon-coated lithium-rich oxide composite material prepared by the method according to claim 1, wherein, the carbon-coated lithium-rich oxide composite material comprises a carbon layer and a lithium-rich oxide coated by the carbon layer; wherein, the lithium-rich oxide is Li.sub.5FeO.sub.4 or Li.sub.6CoO.sub.4.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0025] FIG. 1 is a scanning electron microscope image of a carbon-coated Li.sub.5FeO.sub.4 composite material prepared in Example 1 of the present disclosure;

[0026] FIG. 2 is a scanning electron microscope image of a carbon-coated Li.sub.6CoO.sub.4 composite material prepared in Example 4 of the present disclosure;

[0027] FIG. 3 is a charge-discharge curve of the carbon-coated Li.sub.5FeO.sub.4 composite material prepared in Example 1 of the present disclosure; and

[0028] FIG. 4 is a charge-discharge curve of the carbon-coated Li.sub.6CoO.sub.4 composite material prepared in Example 4 of the present disclosure.

DETAILED DESCRIPTION OF THE EMBODIMENTS

[0029] The specific examples of the present disclosure will be described in detail below with reference to the accompanying drawings. It shall be understood that the specific examples described herein are illustrative only and not intended to limit the present disclosure.

[0030] The endpoints of the ranges and any values disclosed herein are not limited to the precise range or value, which are to be understood to include values approximating these ranges or values. In terms of the numerical ranges, one or more new numerical ranges may be acquired by combining endpoint values of each range, or by combining the endpoint value of each range and an individual point value, or by combining the individual point values, and these numerical ranges shall be considered as specifically disclosed herein.

[0031] One aspect of the present disclosure provides the method for preparing the carbon-coated lithium-rich oxide composite material, including the following steps:

[0032] (1) The iron source or the cobalt source is mixed with the lithium source to sinter, to obtain the lithium-rich oxide Li.sub.5FeO.sub.4 or Li.sub.6CoO.sub.4. The molar ratio of the lithium source to the iron source is 5-25:1, and the molar ratio of the lithium source to the cobalt source is 6-30:1.

[0033] (2) The lithium-rich oxide obtained in the step (1) is crushed.

[0034] (3) The lithium-rich oxide crushed in the step (2) is mixed with the carbon source to sinter, to obtain the carbon-coated lithium-rich oxide composite material.

[0035] The lithium-rich oxide in the carbon-coated lithium-rich oxide composite material prepared by the method of the present disclosure has good crystallinity, no impure phase, and good electrochemical properties. The carbon-coated layer is capable of improving the stability and conductivity of the lithium-rich oxide, which is beneficial to its performance.

[0036] In the method of the present disclosure, in the step (1), the iron source may be the conventional option in the art. Specifically, the iron source is one or more of iron(III) oxide, iron(II,III) oxide, ferric oxyhydroxide, ferric nitrate and ferric citrate. Preferably, the iron source is iron(III) oxide.

[0037] In the method of the present disclosure, in the step (1), the cobalt source may be the conventional option in the art. Specifically, the cobalt source is one or more of cobalt(II) oxide, cobalt(II,III) oxide, cobalt carbonate, cobalt sulfate, cobalt chloride and cobalt nitrate. Preferably, the cobalt source is cobalt(II) oxide.

[0038] In the method of the present disclosure, in the step (1), the lithium source may be the conventional option in the art. Specifically, the lithium source is one or more of lithium carbonate, lithium hydroxide monohydrate, lithium hydroxide anhydrous and lithium oxide. Preferably, the lithium source is lithium oxide.

[0039] To ensure that the mixture of the iron source or the cobalt source and the lithium source is sintered into the lithium-rich oxide with high crystallinity, the molar ratio of the lithium source to the iron source or the cobalt source is required to be controlled within an appropriate range.

[0040] In the specific example, the molar ratio of the lithium source to the iron source may be 5:1, 7:1, 9:1, 11:1, 13:1, 15:1, 17:1, 19:1, 21:1, 23:1, 25:1, and any value in the range formed by any two of the above-mentioned point values. In the preferred example, the molar ratio of the lithium source to the iron source is 5.5:1.

[0041] In the specific example, the molar ratio of the lithium source to the cobalt source may be 6: 1, 8:1, 10:1, 12:1, 14:1, 16:1, 18:1, 20:1, 22:1, 24:1, 26:1, 28:1, 30:1, and any value in the range formed by any two of the above-mentioned point values. In the preferred example, the molar ratio of the lithium source to the cobalt source is 6.6:1.

[0042] In the method of the present disclosure, in the step (1), the sintering process includes putting the mixture of the iron source or the cobalt source and the lithium source in the sintering furnace, and heating to the first sintering temperature at the first preset heating rate for the first sintering at the inert gas atmosphere.

[0043] In the sintering process of the step (1), the sintering furnace may be the conventional option in the art. Preferably, the sintering furnace is oven-type furnace.

[0044] In the sintering process of the step (1), the first preset heating rate is 1-10° C./min. Specifically, the first preset heating rate may be 1° C./min, 2° C./min, 3° C./min, 4° C./min, 5° C./min, 6° C./min, 7° C./min, 8° C./min, 9° C./min or 10° C./min. Preferably, the first preset heating rate is 2° C./mm.

[0045] In the sintering process of the step (1), the first sintering temperature is 500-1000° C. Specifically, the first sintering temperature may be 500° C., 550° C., 600° C., 700° C., 750° C., 800° C., 850° C., 900° C., 950° C. or 1000° C.

[0046] When the lithium-rich oxide obtained by sintering is Li.sub.5FeO.sub.4, the first sintering temperature is preferably 850° C.

[0047] When the lithium-rich oxide obtained by sintering is Li.sub.5CoO.sub.4, the first sintering temperature is preferably 700° C.

[0048] In the sintering process of the step (1), the first sintering time is 3-60 h. Specifically, the first sintering time may be 3 h, 5 h, 8 h, 10 h, 13 h, 16 h, 20 h, 23 h, 25 h, 30 h, 35 h, 40 h, 43 h, 48 h, 52 h, 55 h, 57 h, 60 h, and any value in the range formed by any two of the above-mentioned point values.

[0049] When the lithium-rich oxide obtained by sintering is Li.sub.5FeO.sub.4, the first sintering time is preferably 10-40 h, and more preferably 12-30 h.

[0050] When the lithium-rich oxide obtained by sintering is Li.sub.5CoO.sub.4, the first sintering time is preferably 5-30 h, and more preferably 6-24 h.

[0051] In the method of the present disclosure, in the step (2), the average particle size of the lithium-rich oxide crushed is 2-50 μm. Specifically, the average particle size of the lithium-rich oxide crushed may be 2 μm, 5 μm, 10 μm, 15 μm, 20 μm, 25 μm, 30 μm, 35 μm, 40 μm, 45 μm, 50 μm, and any value in the range formed by any two of the above-mentioned point values. Preferably, in the step (2), the average particle size of the lithium-rich oxide crushed is 25 μm.

[0052] In the method of the present disclosure, in the step (3), the carbon source may be a conductive carbon material conventionally used in the art. Specifically, the carbon source may be one or more of conductive carbon black, Ketjen black, carbon nanotube, acetylene black, vapor-grown carbon fiber, graphene and biomass carbon. The carbon source is preferably conductive carbon black, and more preferably conductive carbon black Super P.

[0053] In the method of the present disclosure, in the step (3), based on the total weight of the lithium-rich oxide and the carbon source, the carbon source is 0.5-10 wt %. Specifically, the carbon source may be 0.5 wt %, 1 wt %, 2 wt %, 4 wt %, 6 wt %, 8 wt %, 10 wt %, and any value in the range formed by any two of the above-mentioned point values. Preferably, in the step (3), based on the total weight of the lithium-rich oxide and the carbon source, the carbon source is 1 wt %

[0054] In the method of the present disclosure, in the step (3), the sintering process includes mixing the lithium-rich oxide crushed with the carbon source uniformly, and then heating to the second sintering temperature at the second preset heating rate for the second sintering at the inert gas atmosphere.

[0055] In the sintering process of the step (3), the sintering furnace may be the conventional option in the art. Preferably, the sintering furnace is oven-type furnace.

[0056] In the sintering process of the step (3), the second preset heating rate is 1-10° C./min. Specifically, the second preset heating rate may be 1° C./min, 2° C./min, 3° C./min, 4° C./min, 5° C./min, 6° C./min, 7° C./min, 8° C./min, 9° C./min or 10° C./min. Preferably, the second preset heating rate is 5° C./min.

[0057] In the sintering process of the step (3), the second sintering temperature is 200-600° C. Specifically, the second sintering temperature may be 200° C., 300° C., 400° C., 500° C., 600° C., and any value in the range formed by any two of the above-mentioned point values. Preferably, the second sintering temperature is 450° C.

[0058] In the sintering process of the step (3), the second sintering time is 2-20 h. Specifically, the second sintering time may be 2 h, 5 h, 8 h, 10 h, 13 h, 15 h, 17 h, 20 h, and any value in the range formed by any two of the above-mentioned point values. Preferably, the second sintering time is 4-10 h.

[0059] Another aspect of the present disclosure provides the carbon-coated lithium-rich oxide composite material prepared by the above-mentioned method. The carbon-coated lithium-rich oxide composite material includes a carbon layer and a lithium-rich oxide coated by the carbon layer. The lithium-rich oxide is anti-fluorite structures Li.sub.5FeO.sub.4 or Li.sub.6CoO.sub.4. The carbon-coated lithium-rich oxide composite material may be used as the additives to provide the irreversible lithium consumed in the initial charge-discharge process of the positive electrode material.

[0060] The present disclosure will be described in detail by the following examples which are not intended to limit the protection scope of the present disclosure.

[0061] Examples 1-3 of the present disclosure are used to illustrate the preparation process of the carbon-coated Li.sub.5FeO.sub.4 composite material. Examples 4-6 of the present disclosure are used to illustrate the preparation process of the carbon-coated Li.sub.6CoO.sub.4 composite material.

EXAMPLE 1

[0062] 206.2 g of Li.sub.2O and 200 g of Fe.sub.2O.sub.3 are mixed uniformly to obtain the mixture, and then the mixture is put into the oven-type furnace to heat up to 850° C. at the heating rate of 2° C./min and sinter for 24 h at the inert gas atmosphere. Li.sub.5FeO.sub.4 obtained by sintering is crushed until the average particle size is 35 μm, and then evenly mixed with the conductive carbon black Super P to obtain the mixture. The mixture is put into the oven-type furnace to heat up to 450° C. at the heating rate of 5° C./min and insulate for 7 h at the inert gas atmosphere, to obtain the carbon-coated Li.sub.5FeO.sub.4 composite material (the scanning electron microscope image and the charge-discharge curve are shown as FIG. 1 and FIG. 3). The conductive carbon black Super P accounts for 3 wt % of the total weight of the composite material.

EXAMPLE 2

[0063] 283.8 g of Li.sub.2OH.H.sub.2O and 100 g of Fe.sub.2O.sub.3 are mixed uniformly to obtain the mixture, and then the mixture is put into the oven-type furnace to heat up to 950° C. at the heating rate of 5° C./min and sinter for 36 h at the inert gas atmosphere. Li.sub.5FeO.sub.4 obtained by sintering is crushed until the average particle size is 15 μm, and then evenly mixed with the Ketjen black to obtain the mixture. The mixture is put into the oven-type furnace to heat up to 600° C. at the heating rate of 10° C./min and insulate for 18 h at the inert gas atmosphere, to obtain the carbon-coated Li.sub.5FeO.sub.4 composite material. The Ketjen black accounts for 2 wt % of the total weight of the composite material.

EXAMPLE 3

[0064] 109.1 g of Li.sub.2O and 100 g of Fe.sub.2O.sub.3 are mixed uniformly to obtain the mixture, and then the mixture is put into the oven-type furnace to heat up to 750° C. at the heating rate of 8° C./min and sinter for 40 h at the inert gas atmosphere. Li.sub.5FeO.sub.4 obtained by sintering is crushed until the average particle size is 50 pm, and then evenly mixed with the conductive carbon black Super P to obtain the mixture. The mixture is put into the oven-type furnace to heat up to 300° C. at the heating rate of 2° C./min and insulate for 4 h at the inert gas atmosphere, to obtain the carbon-coated Li.sub.5FeO.sub.4 composite material. The conductive carbon black Super P accounts for 5 wt % of the total weight of the composite material.

COMPARATIVE EXAMPLE 1

[0065] The Li.sub.5FeO.sub.4 material is prepared according to the method of Example 1, and the difference is that Li.sub.5FeO.sub.4 crushed is not carbon-coated.

EXAMPLE 4

[0066] 130.67 g of Li.sub.2O and 100 g of CoO are mixed uniformly to obtain the mixture, and then the mixture is put into the oven-type furnace to heat up to 700° C. at the heating rate of 2° C./min and sinter for 18 h at the inert gas atmosphere. Li.sub.6CoO.sub.4 obtained by sintering is crushed until the average particle size is 10 Ξm, and then evenly mixed with the conductive carbon black Super P to obtain the mixture. The mixture is put into the oven-type furnace to heat up to 450° C. at the heating rate of 8° C./min and insulate for 10 h at the inert gas atmosphere, to obtain the carbon-coated Li.sub.6CoO.sub.4 composite material (the scanning electron microscope image and the charge-discharge curve are shown as FIG. 2 and FIG. 4). The conductive carbon black Super P accounts for 3 wt % of the total weight of the composite material.

EXAMPLE 5

[0067] 87.3 g of Li.sub.2O and 100 g of CoCO.sub.3 are mixed uniformly to obtain the mixture, and then the mixture is put into the oven-type furnace to heat up to 800° C. at the heating rate of 6° C./min and sinter for 12 h at the inert gas atmosphere. Li.sub.6CoO.sub.4 obtained by sintering is crushed until the average particle size is 30 μm, and then evenly mixed with the carbon nanotube to obtain the mixture. The mixture is put into the oven-type furnace to heat up to 350° C. at the heating rate of 4° C./min and insulate for 5 h at the inert gas atmosphere, to obtain the carbon-coated Li.sub.6CoO.sub.4 composite material. The carbon nanotube accounts for 1 wt % of the total weight of the composite material.

EXAMPLE 6

[0068] 205.64 g of LiOH and 100 g of CoO are mixed uniformly to obtain the mixture, and then the mixture is put into the oven-type furnace to heat up to 750° C. at the heating rate of 9° C./min and sinter for 15 h at the inert gas atmosphere. Li.sub.6CoO.sub.4 obtained by sintering is crushed until the average particle size is 5 μm, and then evenly mixed with the conductive carbon black KS-6 to obtain the mixture. The mixture is put into the oven-type furnace to heat up to 300° C. at the heating rate of 7° C./min and insulate for 15 h at the inert gas atmosphere, to obtain the carbon-coated Li.sub.6CoO.sub.4 composite material. The conductive carbon black KS-6 accounts for 2 wt % of the total weight of the composite material.

COMPARATIVE EXAMPLE 1

[0069] The Li.sub.6CoO.sub.4 material is prepared according to the method of Example 4, and the difference is that Li.sub.6CoO.sub.4 crushed is not carbon-coated.

[0070] Testing Example

[0071] The materials prepared in Examples 1-6 and Comparative Examples 1-2 are prepared into the lithium-ion battery to test. The testing steps are as follows: The carbon-coated Li.sub.5FeO.sub.4, Super P and PVDF are dispersed in NMP at the mass ratio of 90:5:5, and the solid content is controlled to be about 40%. Then, the mixture obtained is coated on the aluminum foil after being evenly dispersed by the defoamer, and dried in vacuum to prepare the positive electrode sheet. The positive electrode sheet is assembled into the coin battery 2025 in the glove box, and the electrolyte is 1.2 mol/L LiPF.sub.6 in EC:EMC at the volume ratio of 3:7. The separator is Celgard polypropylene film, and the lithium sheet is used as the counter electrode. The capacity of the assembled half battery is tested by Neware tester. The charge cut-off voltage is 4.7 V, the discharge cut-off voltage is 2.0 V, and the charge-discharge rate is 0.05 C. The test results are shown in Table 1 and Table 2.

[0072] Table 1 Test results of the carbon-coated Li.sub.5FeO.sub.4 composite material

TABLE-US-00001 Serial No. First charge specific of Example capacity (mAh/g) Example 1 672.73 Example 2 605.48 Example 3 622.95 Comparative 551.32 Example 1

[0073] It can be seen from the data in Table 1 that the carbon-coated Li.sub.5FeO.sub.4 composite materials prepared in Examples 1-3 have a significantly higher first charge specific capacity, indicating that the carbon-coated lithium-rich oxide composite material prepared by the method of the present disclosure has significantly improved electrochemical properties.

[0074] Table 2 Test results of the carbon-coated Li.sub.6CoO.sub.4 composite material

TABLE-US-00002 Serial No. First charge specific of Example capacity (mAh/g) Example 4 851.15 Example 5 799.77 Example 6 847.82 Comparative 769.92 Example 2

[0075] It can be seen from the data in Table 2 that the carbon-coated Li.sub.6CoO.sub.4 composite materials prepared in Examples 4-6 have a significantly higher first charge specific capacity, indicating that the carbon-coated lithium-rich oxide composite material prepared by the method of the present disclosure has significantly improved electrochemical properties.

[0076] The preferred examples of the present disclosure have been described above in detail. However, the present disclosure is not limited thereto. Within the scope of the technical concept of the present disclosure, various simple modifications, including combining various technical features in any other suitable manner, may be made to the technical solutions of the present disclosure, which shall be regarded as the content disclosed in the present disclosure and fall within the protection scope of the present disclosure.