Preparation method of gradient-doped metal oxide spinel coated hard carbon composite material and application of gradient-doped metal oxide spinel coated hard carbon composite material in lithium ion battery

Abstract

The invention belongs to the technical field of lithium ion battery negative electrode materials, and particularly relates to a spinel type metal oxide coated hard carbon composite material based on a lattice matching mechanism, and a gradient doping preparation method of the spinel type metal oxide coated hard carbon composite material can overcome the defects that a hard carbon material is low in initial coulombic efficiency (about 50%), low in lithium ion transmission rate and poor in rate capability. According to the invention, magnesium salt, aluminum salt, copper salt and other metal salts are mixed with hard carbon, a precipitant is added, and a hydrothermal method is combined with a calcination process to obtain the core-shell structure composite material with hard carbon coated with a spinel structure. The technology has the following three obvious advantages: (1) lattice adaptive design of the spar type metal oxide and the hard carbon, (2) molybdenum-copper gradient doping repair of the SEI film, and (3) stable circulation of more than 5000 times at the capacity of 350mAh / g.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of lithium ion battery negative electrode materials, and particularly relates to a doped spinel metal oxide coated hard carbon composite material based on a lattice matching mechanism, a gradient doping preparation method of the material, and application of the material as a high initial efficiency and high rate lithium ion battery negative electrode. TECHNICAL BACKGROUND

[0002] The bottlenecks of the prior art include that the interface between the coating layer and the hard carbon is weakly combined: the lattice mismatch degree of the traditional metal oxide coating (such as ZnO and TiO2) and the hard carbon is greater than 8%, which causes interface stress accumulation and peeling of the coating layer in the cycle.

[0003] The metal oxide has poor intrinsic conductivity: Fe3O4 and Co3O4 have high theoretical capacity, but the electronic conductivity is less than 10 -5 S / cm, and a conductive agent (such as CNT) needs to be compounded, which increases the cost.

[0004] The coating uniformity is insufficient: chemical deposition method is easy to cause metal oxide aggregation, forming local "islands", and blocking ion diffusion channels.

[0005] Limitations of sulfide coating: although the multi-layer coating structure (such as ZrO2 / ZrS2) improves the interface stability, the sulfurization process produces H2S pollution.

[0006] Innovative findings of the application

[0007] Innovative breakthrough based on lattice matching-doping synergy: interface bonding innovation: the spinel structure metal oxide (lattice constant ) is selected to form a coherent interface with the (002) crystal face spacing of the hard carbon, the lattice mismatch degree is less than or equal to 4%, atomic level bonding is achieved, and the stability of the lithium ion battery negative electrode is improved.

[0008] Dynamic catalytic mechanism: gradient doping in the spinel structure metal oxide, the redox pair of the multivalent metal can catalyze the repair of the SEI film, large size ions widen the lithium ion diffusion channel, and the first cycle coulombic efficiency and the rate performance are optimized.

[0009] Nuclear shell lithium storage synergy: the hard carbon core provides capacity (≈230 mAh / g), the spinel structure metal oxide shell contributes capacity (≈120 mAh / g), and high efficiency lithium storage in the full potential range is achieved. SUMMARY

[0010] Therefore, one of the purposes of the present application is to provide a gradient-doped metal oxide spinel coated hard carbon composite material, the second purpose is to provide a preparation method of the gradient-doped metal oxide spinel coated hard carbon composite material, and the third purpose is the application of the gradient-doped metal oxide spinel coated hard carbon composite material in a lithium battery negative electrode.

[0011] To achieve the above purposes, the present application provides the following technical solutions:

[0012] The present application provides a gradient-doped metal oxide spinel coated hard carbon composite material. The spinel coated hard carbon is one or more of biomass hard carbon, pitch hard carbon and coal hard carbon, and the metal oxide spinel contains two or more of magnesium, aluminum, cobalt, iron, molybdenum and copper. The composite material is prepared by a hydrothermal method and a calcination process, the mixing ratio of metal salt and hard carbon is accurate, the precipitant is selected and optimized, the spinel structure is uniformly coated, and the electrochemical performance is significantly improved.

[0013] The further specific preparation steps are as follows:

[0014] (1) One of biomass, pitch and coal is ground and crushed, the obtained powder is pre-carbonized and conventionally carbonized to obtain corresponding hard carbon powder.

[0015] (2) Two or more of magnesium, aluminum, cobalt, iron, molybdenum and copper precursor metal salts and hard carbon are mixed, and a precipitant is added to perform a hydrothermal reaction to obtain a suspension.

[0016] (3) The suspension is centrifuged and dried, and the obtained powder is oxidized and calcined to obtain the black powder, which is the gradient-doped metal oxide spinel coated hard carbon composite material.

[0017] The pre-carbonization in step (1) is to heat to 600℃ at a speed of 5℃ / min and keep for 2h, and the carbonization is to heat to 1000℃ at a speed of 5℃ / min based on 600℃ and keep for 5h.

[0018] The hydrothermal reaction in step (2) is performed in a stainless steel reaction kettle, and the temperature is raised to 180℃ at a speed of 5℃ / min and kept for 12h.

[0019] The centrifugal speed in step (3) is 8000rpm / min, and the drying condition is 65℃ drying for 5h.

[0020] The calcination atmosphere in step (3) is air, the temperature is raised to 500℃ at a speed of 5℃ / min, and the calcination is performed for 5h.

[0021] The content of the metal oxide spinel in the prepared powder in step (3) is (10-15wt%).

[0022] Further, the application relates to application of the gradient-doped metal oxide spinel-coated hard carbon composite material as a negative electrode of a lithium ion battery.

[0023] The application has the following beneficial effects:

[0024] The metal salt and the hard carbon are mixed in a precise ratio, and the precipitant is selected and optimized, so that the spinel structure is uniformly coated, and the electrochemical performance is significantly improved.

[0025] Interface bonding innovation: the spinel structure metal oxide (lattice constant ) and the hard carbon (002) crystal face spacing form a coherent interface, the lattice mismatch degree is less than or equal to 4%, atomic level bonding is realized, and the stability of the lithium ion battery negative electrode is improved.

[0026] Dynamic catalytic mechanism: the spinel structure metal oxide is gradient-doped, the redox pair of the multivalent metal can catalyze the repair of the SEI film, the large-size ion widens the lithium ion diffusion channel, and the first cycle coulombic efficiency and the rate performance are collectively optimized.

[0027] Nuclear-shell lithium storage synergy: the hard carbon core provides a platform capacity (≈280 mAh / g), and the spinel structure metal oxide shell contributes a capacity (≈120 mAh / g), and high-efficiency lithium storage in the full potential range is realized. BRIEF DESCRIPTION OF DRAWINGS

[0028] In order to make the purpose, innovation advantage and technical scheme of the application clearer, the application will be described in detail below in combination with the drawings, in which:

[0029] Figure 1 is the XRD pattern of the material of the comparative example 1 and the example 1;

[0030] Figure 2 is the first charge-discharge comparison diagram of the material of the comparative example 1 and the example 1;

[0031] Figure 3 is the capacity cycle comparison diagram of the material of the comparative example 1 and the example 1.

[0032] Figure 4 is the rate performance diagram of the material of the comparative example 1 and the example 1. DETAILED DESCRIPTION

[0033] The embodiments of the application will be described below through specific examples. Although the drawings show some examples of the application, it should be understood that the application can also be implemented and applied in different embodiments. It should be understood that the embodiments and the drawings are only used as examples, and are not used for the protection scope of the embodiments.

[0034] Example 1

[0035] The embodiment discloses a preparation method of a gradient-doped spinel-structured metal oxide MgAl2O4-coated hard carbon composite material, and the specific steps are as follows:

[0036] Step 1, grind and crush the macadamia nut shell, and then heat the obtained powder to 600 ℃ at a speed of 5 ℃ / min and keep the temperature for 2 h, and then heat to 1000 ℃ at a speed of 5 ℃ / min on the basis of 600 ℃ and keep the temperature for 5 h. The corresponding biomass hard carbon powder is obtained.

[0037] Step 2, mix magnesium nitrate, aluminum nitrate, ammonium molybdate, copper sulfate, urea and hard carbon according to a weight ratio of (6:12:2:2:2):80, and add 200 ml of water, ultrasonic mix, and then transfer into a 250 ml stainless steel reaction kettle, put the stainless steel reaction kettle into an electric oven, heat to 180 ℃ at a speed of 5 ℃ / min, keep the temperature for 12 h for hydrothermal reaction, and then naturally cool down, open the inner lining of the reaction kettle to obtain a suspension.

[0038] Step 3, centrifugal precipitation is carried out on the suspension at a speed of 8000 rpm / min, and the precipitate is dried at 65 ℃ for 5 h to obtain a powder.

[0039] Step 4, oxidation calcination is carried out on the dried precipitate in a tube furnace, the calcination atmosphere is air, the temperature is raised to 500 ℃ at a speed of 5 ℃ / min, and the calcination is carried out for 5 h. The obtained black powder is the gradient-doped metal oxide spinel-coated hard carbon composite material.

[0040] Comparative Example 1

[0041] The source of the pure hard carbon is Kureha hard carbon.

[0042] X-ray diffraction analysis is carried out on the materials of Example 1 and Comparative Example 1, and the obtained X-ray diffraction patterns are shown in Figures 1 and 2. Figure 1 .

[0043] Example 2, preparation of an electrode sheet, and the specific operation steps are as follows:

[0044] Hard carbon, polyvinylidene fluoride and Super P are mixed with a solvent (N-methyl pyrrolidone) according to a mass ratio of 8:1:1, and magnetic stirring is carried out at room temperature for 8 hours. The obtained slurry is coated on a copper foil to form a thin film with a thickness of 75 μm, and then dried at a temperature of 80 ℃ for 10 hours. A diameter of 12 mm is used as an anode of a CR2025 type button cell, a Celgard 2325 is used as a diaphragm, and a DME:PC:EC=1:1:1 volume ratio mixed solution in which 1M LiClO4 is dissolved is used as an electrolyte. A lithium metal wafer is used as a counter electrode. The whole button cell assembly process is completed in an argon glove box, and after standing for 6 hours, a measurement system is used to carry out constant current charge and discharge test under a constant temperature condition of 25 ℃.

[0045] Example 3, performance test

[0046] The materials of Example 1 and Comparative Example 1 were respectively cycled one circle as the negative electrode sheet of the button cell at a current density of 35.8 mA / g, and the charge-discharge curves obtained are shown in FIG. 2. As can be seen from FIG. 2, the first coulombic efficiency of Example 1 is improved from 51.8% to 90.1% compared with Comparative Example 1. Figure 2

[0047] The materials of Example 1 and Comparative Example 1 were respectively cycled 5000 circles as the negative electrode sheet of the button cell at a current density of 385 mA / g, and the capacity curves after cycling are shown in FIG. 3. As can be seen from FIG. 3, the capacity retention rate of Example 1 is improved from 45.3% to 93.8% compared with Comparative Example 1. Figure 3

[0048] The current density of the button cell running with the materials of Example 1 and Comparative Example 1 as the negative electrode sheet was respectively increased from 192.5 mA / g to 3850 mA / g, and the rate performance curves are shown in FIG. 4. As can be seen from FIG. 4, the rate performance of Example 1 is greatly improved compared with Comparative Example 1. Figure 4

[0049] Comparing the above data, it can be found that the composite material of gradient-doped metal oxide spinel coated hard carbon has more excellent electrochemical performance than the pure hard carbon material. Especially in the first circle coulombic efficiency and cycle stability. The coating of metal oxide improves the stability; the redox of multi-valence metal repairs the SEI film, widens the transmission channel of lithium ions, improves the first circle coulombic efficiency and rate performance; the core-shell structure together improves the lithium storage capacity of the composite material.​​​

Claims

1. A composite of a spinel-coated hard carbon of a gradient-doped metal oxide, characterized by: The spinel-coated hard carbon is one or more of biomass hard carbon, pitch hard carbon, and coal hard carbon, and the spinel structure metal oxide contains two or more of magnesium, aluminum, cobalt, iron, molybdenum, and copper. The composite material is prepared by a hydrothermal method and a calcination process, the mixing ratio of the metal salt and the hard carbon is accurate, the precipitant is selected and optimized, the spinel structure is uniformly coated, and the electrochemical performance is significantly improved.

2. The method of making the gradient doped metal oxide spinel-coated hard carbon composite of claim 1 characterized in that The preparation steps are as follows: (1) Biomass, pitch, and coal are ground and crushed, and the obtained powder is pre-carbonized and conventionally carbonized to obtain corresponding hard carbon powder. (2) Two or more of the precursor metal salts of magnesium, aluminum, cobalt, iron, molybdenum, and copper are mixed with the hard carbon, and a precipitant is added for hydrothermal reaction to obtain a suspension. (3) The suspension is centrifuged and dried, and the obtained powder is oxidized and calcined to obtain black powder, which is the gradient-doped metal oxide spinel-coated hard carbon composite material of claim 1.

3. The method for preparing the hard carbon composite material coated with gradient-doped metal oxide spinel according to claim 2, characterized in that, The content of the metal oxide spinel in the prepared powder is (10-15wt%).

4. The method of claim 2, wherein the gradient doped metal oxide spinel coated hard carbon composite is prepared by the steps of: a) mixing a metal oxide precursor, a hard carbon, and a dopant to form a mixture; b) heating the mixture to form a gradient doped metal oxide spinel coated hard carbon composite; and c) cooling the gradient doped metal oxide spinel coated hard carbon composite. The pre-carbonization in step (1) is to heat to 600℃ at a rate of 5℃ / min and keep for 2h, and the carbonization is to heat to 1000℃ at a rate of 5℃ / min based on 600℃ and keep for 5h.

5. The method for preparing the gradient-doped metal oxide spinel-coated hard carbon composite material according to claim 2, characterized in that, The hydrothermal reaction in step (2) is carried out in a stainless steel reaction kettle, and the temperature is raised to 180℃ at a rate of 5℃ / min and kept for 12h.

6. The method of claim 2, wherein the gradient doped metal oxide spinel coated hard carbon composite is prepared by the steps of: a) mixing a metal oxide precursor, a hard carbon, and a dopant to form a mixture; b) heating the mixture to form a gradient doped metal oxide spinel coated hard carbon composite; and c) cooling the gradient doped metal oxide spinel coated hard carbon composite. The centrifugal speed in step (3) is 8000rpm / min, and the drying condition is 65℃ for 5h.

7. The method of claim 2, wherein the gradient doped metal oxide spinel coated hard carbon composite is prepared by the steps of: a) mixing a metal oxide precursor, a hard carbon, and a dopant to form a mixture; b) heating the mixture to form a gradient doped metal oxide spinel coated hard carbon composite; and c) cooling the gradient doped metal oxide spinel coated hard carbon composite. The calcination atmosphere in step (3) is air, the temperature is raised to 500℃ at a rate of 5℃ / min, and the calcination is carried out for 5h.

8. The gradient-doped metal oxide spinel-coated hard carbon composite material of claim 1 is used as a negative electrode of a lithium battery.

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