A hard carbon-coated nano-silicon oxide composite anode material and its preparation method

Abstract

The present invention relates to the technical field of lithium-ion battery electrode materials, and provides a hard carbon-coated nano-silicon oxide composite anode material and a preparation method thereof. The composite anode material has a core-shell structure, wherein the core of the core-shell structure comprises a nano-silicon / metal oxide composite, and the shell comprises hard carbon; the mass of the shell in the composite anode material is 10-50% of the mass of the composite anode material. Through the above technical solution, the problem of poor cycle performance of the battery when a silicon-carbon and hard-carbon composite material is used as the battery anode in the prior art is solved.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium-ion battery electrode materials, and specifically, to a hard carbon-coated nano silicon oxide composite anode material and a preparation method thereof. Background Art

[0002] Silicon-carbon materials have become the preferred anode materials for high-energy density batteries due to their high energy density (1200 - 2000 mAh / g) and wide material sources. However, their large volume expansion (300%) and poor low-temperature performance limit their wide application. Hard carbon materials, on the other hand, are applied in high-rate battery fields such as 48V / HEV due to their zero expansion, excellent low-temperature performance, and excellent cycling performance. However, their specific capacity (300 mAh / g) and tap density (1.0 g / cm 3 ) are relatively low, and they can only be used in specific fields. If silicon-carbon materials are compounded with hard carbon, not only can the expansion be reduced and the low temperature be improved, but also the energy density can be increased. For example, Patent Application No. 202210704738.0 discloses a hard carbon-stabilized lithium silicon alloy anode and battery, which mainly introduces hard carbon into the LiSi alloy anode to form a uniform and almost stress-free continuous body. The three-dimensional lithium-conducting and conductive network woven by the lithium-rich phases Li15Si4 and LiC6 can effectively increase the active area of the electrode, optimize the kinetic performance of the electrode, and improve the long-cycle performance of the battery. However, the anode material prepared by this scheme has the disadvantages of poor power performance and poor bonding force between materials, and the material is prone to pulverization after long cycling, reducing the cycling performance. Summary of the Invention

[0003] The present invention provides a hard carbon-coated nano silicon oxide composite anode material and a preparation method thereof, which solve the problem of poor cycling performance of the silicon-carbon and hard-carbon composite material as the battery anode in the related art.

[0004] The technical solution of the present invention is as follows:

[0005] A hard carbon-coated nano silicon oxide composite anode material, the composite anode material has a core-shell structure, the core of the core-shell structure includes a nano silicon / metal oxide composite, and the shell includes hard carbon; the mass of the shell in the composite anode material is 10 - 50% of the mass of the composite anode material.

[0006] A preparation method of a hard carbon-coated nano silicon oxide composite anode material, comprising the following steps:

[0007] S1. Mix nano silicon and metal salts and then carbonize them to obtain a nano silicon / metal oxide composite material;

[0008] S2. Add a hard carbon precursor and the nano silicon / metal oxide composite material to an organic solvent and mix them to obtain a mixture;

[0009] S3. After introducing an oxidizing gas, carbonization is carried out to obtain a hard carbon-coated nano-silicon oxide composite anode material.

[0010] As a further technical solution, the metal salt in S1 includes one of aluminum tris(2-methylpropyl), triisobutylaluminum, aluminum borate oxide, titanium trichloride triisopropoxide, titanium carbonyl, ammonium ferric citrate, and zirconium dioxydihydroxydicarbonate.

[0011] As a further technical solution, the mass ratio of nano-silicon to metal salt in S1 is 100:1 - 10.

[0012] As a further technical solution, the mass ratio of the nano-silicon / metal oxide composite material, hard carbon precursor, and organic solvent in S2 is 100:50 - 100:500 - 2000.

[0013] As a further technical solution, the organic solvent in S2 includes one of methanol, ethanol, ethylene glycol, n-butanol, N-methylpyrrolidone, dimethylformamide, diethylformamide, dimethyl sulfoxide, and tetrahydrofuran; the hard carbon precursor includes one of glucose, sucrose, lignin, starch, and cellulose.

[0014] As a further technical solution, the oxidizing gas in S3 includes one of fluorine gas and chlorine gas.

[0015] As a further technical solution, the gas flow rate of the oxidizing gas in S3 is 1 - 10 mL / min, and the introduction time is 30 - 120 min.

[0016] As a further technical solution, after introducing the oxidizing gas in S3, filtration is carried out, and then carbonization is carried out to obtain a hard carbon-coated nano-silicon oxide composite anode material.

[0017] As a further technical solution, the carbonization temperature in S3 is 600 - 1000 °C, and the time is 1 - 6 h.

[0018] The working principle and beneficial effects of the present invention are as follows:

[0019] 1. In the present invention, nano-silicon and metal oxide are mixed, which can reduce the electron impedance of nano-silicon, thereby improving the rate performance. At the same time, hard carbon is coated on the outer layer. On the one hand, the characteristics of low self-expansion and excellent low-temperature performance of the hard carbon material are utilized to improve the low-temperature performance and expansion of the silicon-carbon material. On the other hand, by introducing fluorine gas or chlorine gas into the hard carbon material on the outer layer, C-F or C-Cl chemical bonds are formed on the surface, improving the structural stability and defect degree of the material, and improving the high-temperature storage performance and cycling performance.

[0020] 2. The metal and amorphous carbon obtained by carbonizing the metal salt in the present invention can improve the electronic conductivity of the material, and the characteristics of high isotropy and stable structure obtained by polymerization and carbonization can enhance the rate performance and cycling performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] The present invention will be further described in detail below with reference to the drawings and specific embodiments.

[0022] Figure 1 SEM image of the hard carbon-coated nano-silicon oxide composite anode material prepared in Example 1. SPECIFIC EMBODIMENTS

[0023] The technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts fall within the scope of protection of the present invention.

[0024] Example 1

[0025] A method for preparing a hard carbon-coated nano-silicon oxide composite anode material, comprising the following steps:

[0026] S1. Add 100 g of nano-silicon to 100 g of a methanol solution of tri(2-methylpropyl)aluminum with a concentration of 5 wt% to obtain a suspension. After spray-drying the suspension, carbonize it at 950 °C for 3 h to obtain a nano-silicon / aluminum oxide composite material;

[0027] S2. Add 80 g of glucose to 1000 g of methanol, dissolve and disperse it evenly, then add 100 g of the nano-silicon / aluminum oxide composite material prepared above and disperse it evenly again to obtain a mixture;

[0028] S3. Introduce fluorine gas at a gas flow rate of 5 mL / min. After introducing it for 60 min, stop introducing the gas, filter and transfer it to a tube furnace, carbonize it at 800 °C for 3 h, and pulverize it to obtain a hard carbon-coated nano-silicon oxide composite anode material.

[0029] Example 2

[0030] A method for preparing a hard carbon-coated nano-silicon oxide composite anode material, comprising the following steps:

[0031] S1. Add 100 g of nano-silicon to 100 g of a dimethylformamide solution of triisobutylaluminum with a concentration of 1 wt% to obtain a suspension. After spray-drying the suspension, carbonize it at 700 °C for 6 h to obtain a nano-silicon / aluminum oxide composite material;

[0032] S2. After adding 50 g of lignin to 500 g of dimethylformamide and dissolving and dispersing it evenly, 100 g of the above-prepared nano-silicon / aluminum oxide composite material is added and dispersed evenly again to obtain a mixture;

[0033] S3. Chlorine gas is introduced at a gas flow rate of 1 mL / min. After introducing for 120 min, the gas introduction is stopped, filtered and transferred to a tubular furnace, carbonized at 600 °C for 6 h, and pulverized to obtain a hard carbon-coated nano-silicon oxide composite anode material.

[0034] Example 3

[0035] A preparation method of a hard carbon-coated nano-silicon oxide composite anode material, comprising the following steps:

[0036] S1. 100 g of nano-silicon and 100 g of a n-butanol solution of 10 wt% triisopropoxytitanium chloride are used to obtain a suspension. After spray-drying the suspension, it is carbonized at 1100 °C for 1 h to obtain a nano-silicon / aluminum oxide composite material;

[0037] S2. After adding 100 g of cellulose to 2000 g of n-butanol solvent and dissolving and dispersing it evenly, 100 g of the above-prepared nano-silicon / aluminum oxide composite material is added and dispersed evenly again to obtain a mixture;

[0038] S3. Chlorine gas is introduced at a gas flow rate of 10 mL / min. After introducing for 30 min, the gas introduction is stopped, filtered and transferred to a tubular furnace, carbonized at 1000 °C for 1 h, and pulverized to obtain a hard carbon-coated nano-silicon oxide composite anode material.

[0039] Example 4

[0040] Compared with Example 1, the difference in Example 4 is that the addition amount of the methanol solution of tri(2-methylpropyl)aluminum is 300 g.

[0041] Comparative Example 1

[0042] 100 g of nano-silicon and 80 g of glucose are added to 1000 g of methanol organic solvent and dissolved and dispersed evenly. After spray-drying, it is carbonized at 800 °C for 3 h under an argon atmosphere to obtain a silicon-carbon composite material.

[0043] Comparative Example 2

[0044] A preparation method of a hard carbon-coated nano-silicon oxide composite anode material, comprising the following steps:

[0045] S1. 100 g of nano-silicon and 100 g of a methanol solution of 5 wt% tri(2-methylpropyl)aluminum are used to obtain a suspension. After spray-drying the suspension, it is carbonized at 950 °C for 3 h to obtain a nano-silicon / aluminum oxide composite material;

[0046] S2. After adding 80 g of glucose to 1000 g of methanol and dissolving and dispersing it evenly, add 100 g of the above-prepared nano-silicon / aluminum oxide composite material and disperse it evenly again to obtain a mixture.

[0047] S3. Transfer the mixture to a tubular furnace, introduce a mixed gas, and carbonize it at 800 °C for 3 h. The introduction of the mixed gas is carried out simultaneously with carbonization. The gas flow rate of the mixed gas is 5 mL / min, and it is introduced for 60 min. After carbonization, it is pulverized to obtain a hard carbon-coated nano-silicon oxide composite anode material; the mixed gas is argon and fluorine, and the volume ratio of argon to fluorine is 3:1.

[0048] Comparative Example 3

[0049] Add 100 g of nano-silicon and 80 g of glucose to 1000 g of methanol and dissolve and disperse them evenly. After spray drying, introduce fluorine gas, and carbonize it at 800 °C for 3 h to obtain a silicon-carbon composite material; the gas flow rate of fluorine gas is 5 mL / min, and it is introduced for 60 min.

[0050] Test Example

[0051] (1) SEM test

[0052] The hard carbon-coated nano-silicon oxide composite anode material prepared in Example 1 was subjected to SEM test, and the test results are as Figure 1 shown. It can be seen from Figure 1 that the hard carbon-coated nano-silicon oxide composite anode material prepared in Example 1 is in the shape of particles and has slight adhesion, and the particle size is between 5 - 10 μm.

[0053] (2) Physical and chemical tests

[0054] The hard carbon-coated nano-silicon oxide composite anode materials prepared in Examples 1 - 4 and Comparative Examples 1 - 3 were used to test the specific surface area, powder conductivity, and tapped density of the materials according to the method in GB / T 38823-2020 "Silicon Carbon". The results are shown in Table 1.

[0055] (3) Physical and chemical tests

[0056] Take the composite materials prepared in Examples 1 - 4 and Comparative Examples 1 - 3 as the anode materials and test them according to the following method: Add a binder, a conductive agent, and a solvent to the anode material, stir to make a slurry, coat it on a copper foil, and obtain an anode sheet after drying and rolling; the binder used is PVDF, the conductive agent is conductive carbon black (SP), the solvent is N-methylpyrrolidone (NMP), and the dosage ratio of the anode material, SP, PVDF, and NMP is 95 g: 1 g: 4 g: 220 mL.

[0057] The electrolyte used is LiPF6 with a concentration of 1.3 mol / L, and the solvent is a mixture of ethylene carbonate (EC) and diethyl carbonate (DEC) with a volume ratio of 1:1. The counter electrode is a lithium metal sheet, and the separator is a polypropylene (PP) membrane. The coin cell is assembled in a glove box filled with argon gas.

[0058] The charge-discharge performance was tested on a Wuhan Blue Electric CT2001A battery tester. The charge-discharge voltage range was 0.005 V - 2.0 V, and the charge-discharge rate was 0.1 C. The rate performance (2C / 0.1C) was also tested. The test results are shown in Table 1.

[0059] Table 1 Test Results

[0060]

[0061]

[0062] As can be seen from Table 1, the specific capacity and the first efficiency of the hard carbon-coated nano-silicon oxide composite anode materials prepared in Examples 1 - 3 are significantly better than those in Comparative Example 1 and Comparative Example 3. The reason may be that the nano-silicon and metal oxides prepared in Examples 1 - 3 can be fully and uniformly mixed, which can reduce the electron impedance of nano-silicon, improve the rate performance, and enhance the specific capacity of the material. Compared with Example 1, the amount of metal salt added in Example 4 was changed, and as a result, the specific capacity and the first efficiency of the composite material prepared in Example 4 are lower than those in Example 1. Compared with Example 1, in Comparative Example 2, fluorination and carbonization were carried out simultaneously, and as a result, the electrochemical performance of the composite material prepared in Comparative Example 2 is lower than that in Example 1, indicating that the composite material prepared by carbonization after introducing fluorine has better electrochemical performance.

[0063] (4) Soft-pack battery test

[0064] The composite materials prepared in Examples 1 - 4 and Comparative Examples 1 - 3 were mixed with artificial graphite at a mass ratio of 1:9 as the anode material to prepare an anode sheet. A ternary material (Li(Ni 0.6 Co 0.2 Mn 0.2 )O2) was used as the cathode material to prepare a cathode sheet. The electrolyte was a LiPF6 solution, where the concentration of the electrolyte LiPF6 was 1.3 mol / L, and the solvent was a mixture of ethylene carbonate (EC) and diethyl carbonate (DEC) with a volume ratio of 1:1. A 5 Ah soft-pack battery was prepared using a Celgard 2400 membrane as the separator.

[0065] 1) Liquid absorption capacity and liquid retention rate test

[0066] Use a 1 mL burette, draw V mL of the electrolyte solution, drop one drop on the surface of the above-mentioned negative electrode sheet, and start timing until the electrolyte solution is completely absorbed. Record the time t, and calculate the liquid absorption rate of the electrode sheet as V / t. The test results are shown in Table 2.

[0067] Calculate the theoretical liquid absorption amount m1 of the negative electrode sheet according to the electrode sheet parameters, weigh the weight m2 of the negative electrode sheet, then immerse the negative electrode sheet in the electrolyte solution for 24 h, weigh the weight of the negative electrode sheet as m3, calculate the liquid absorption amount of the negative electrode sheet as m3 - m2, and calculate according to the following formula: Liquid retention rate = (m3 - m2) * 100% / m1. The test results are shown in Table 2.

[0068] Table 2 Test results of liquid absorption capacity and liquid retention rate

[0069]

[0070]

[0071] As can be seen from Table 2, the liquid absorption and retention capacities of the hard carbon-coated nano-silicon oxide composite negative electrode materials prepared in Examples 1 - 3 are significantly higher than those in Comparative Example 1 and Comparative Example 3. This is mainly because the hard carbon-coated nano-silicon oxide composite negative electrode materials prepared in Examples 1 - 3 have a high specific surface area, and their carbonization can form a porous structure, thereby improving the liquid absorption and retention capacities of the materials. The liquid absorption rates and liquid retention rates of the composite materials prepared in Example 4 and Comparative Example 2 are lower than those in Example 1.

[0072] 2) Cycle performance test

[0073] Test the cycle performance of Examples 1 - 4 and Comparative Examples 1 - 3:

[0074] Test the cycle performance of the battery at a charge-discharge rate of 1C / 1C and a voltage range of 2.8V - 4.2V at a temperature of 25 ± 3°C. The test results are shown in Table 3.

[0075] Perform constant current + constant voltage charging at a 2C rate, and calculate the constant current ratio of the material, that is, the charge of constant current charging / (the charge of constant current + constant voltage charging). The test results are shown in Table 3.

[0076] Table 3 Test results of cycle performance

[0077] Capacity retention rate (%) after 500 cycles 2C constant current ratio Example 1 91.64 93.1％ Example 2 90.77 92.8％ Example 3 92.39 93.9％ Example 4 91.98 91.9％ Comparative Example 1 85.21 85.6％ Comparative Example 2 84.23 86.5％ Comparative Example 3 85.01 84.9％

[0078] As can be seen from Table 3, the cycle performance and rate performance of the batteries prepared from the hard carbon-coated nano-silicon oxide composite anode materials prepared in Examples 1-3 are significantly better than those of Comparative Example 1. This may be because fluorine gas is introduced into the hard carbon material, and C-F chemical bonds are formed on the surface, which can improve the structural stability of the material and its cycle performance. Although fluorine gas is introduced in Comparative Example 2 and Comparative Example 3, the cycle performance of the composite materials prepared in Comparative Example 2 with fluorine gas introduction and carbonization carried out simultaneously and in Comparative Example 3 with all raw materials directly mixed is lower than that of Example 1, indicating that the composite materials prepared by the preparation method of the present invention have good cycle performance.

[0079] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A hard carbon-coated nano-silicon oxide composite anode material, characterized in that, The composite anode material has a core-shell structure. The core of the core-shell structure includes a nano-silicon / metal oxide composite, and the shell includes hard carbon. The mass of the shell in the composite anode material is 10-50% of the mass of the composite anode material. The preparation method of the hard carbon-coated nano-silicon oxide composite anode material includes the following steps: S1. Mix nano-silicon and metal salt and then carbonize to obtain a nano-silicon / metal oxide composite material. S2. Add a hard carbon precursor and the nano-silicon / metal oxide composite material to an organic solvent and mix to obtain a mixture. S3. After introducing an oxidizing gas, carbonize to obtain a hard carbon-coated nano-silicon oxide composite anode material. The oxidizing gas in S3 is one of fluorine gas and chlorine gas. The carbonization temperature in S3 is 600-1000 °C, and the time is 1-6 h. The mass ratio of nano-silicon to metal salt in S1 is 100:1-10. The mass ratio of the nano-silicon / metal oxide composite material, hard carbon precursor and organic solvent in S2 is 100:50-100:500-2000. The metal salt in S1 includes one of tri(2-methylpropyl)aluminum, titanium isopropoxide chloride, titanium carbonyl, and ammonium ferric citrate.

2. The hard carbon-coated nano-silicon oxide composite anode material according to claim 1, characterized in that The organic solvent in S2 includes one of methanol, ethanol, ethylene glycol, n-butanol, N-methylpyrrolidone, dimethylformamide, diethylformamide, dimethyl sulfoxide, and tetrahydrofuran. The hard carbon precursor includes one of glucose, sucrose, lignin, starch, and cellulose.

3. The hard carbon-coated nano-silicon oxide composite anode material according to claim 1, characterized in that, The gas flow rate of the oxidizing gas in S3 is 1-10 mL / min, and the introduction time is 30-120 min.

4. A hard carbon-coated nano-silicon oxide composite anode material according to claim 1, characterized in that, After introducing the oxidizing gas in S3, filter and then carbonize to obtain a hard carbon-coated nano-silicon oxide composite anode material.

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