CN112072096A - Preparation method of nano-silicon lithium-ion battery anode material - Google Patents

Abstract

The invention discloses a preparation method of a nano-silicon lithium-ion battery negative electrode material. The method adopts the method of rapid alloy solidification. First, pure aluminum and pure silicon are mixed and smelted to form an aluminum-silicon alloy ingot, then the aluminum-silicon alloy ingot is removed from the oxide layer, and then suction-casting is performed, and then the alloy material is stirred and corroded with acid to remove the alloying, Silicon nanoparticles are obtained, and then the silicon nanoparticle powder, the conductive agent and the binder are stirred and mixed uniformly to obtain electrode slurry, and finally the electrode slurry is uniformly coated on the current collector, dried, rolled and cut to obtain electrode pads. The preparation process of the invention is simple and easy to repeat. The prepared nano-silicon is used as a negative electrode material of a lithium ion battery, and the first-week discharge specific capacity can reach 3699 mAh/g, and the first Coulomb efficiency can reach 83.7%, which is suitable for large-scale industrial production.

Description

Preparation method of nano-silicon lithium-ion battery anode material

technical field

The invention belongs to the technical field of lithium ion batteries, and relates to a preparation method of a negative electrode material for nano-silicon lithium ion batteries.

Background technique

Lithium-ion batteries have the advantages of high specific energy, green environmental protection, long cycle life, and small self-discharge. Although the energy density is increasing at a rate of 7% to 10% per year, it is still far below the energy demand of electric vehicles. At present, the practical anode materials of lithium-ion batteries are still mainly carbon materials such as graphitized carbon and amorphous carbon, but their maximum theoretical specific capacity is only 372mAh/g. Silicon-based anode materials can form alloys with high lithium content after lithium intercalation. Among them, Li ₂₂ Si ₅ has a theoretical capacity of up to 4200mAh/g, and the reserves of silicon are extremely rich and greener. It is the most likely to replace commercial graphite. One of the negative electrode materials. However, during the intercalation process of lithium, it will cause the expansion (100-300%) of the silicon-based negative electrode material, which will destroy the stability of the electrode material structurally, resulting in the collapse of the electrode structure and the peeling of the electrode material; The solid electrolyte interphase (SEI) affects the lithium capture in active silicon materials, resulting in an irreversible rapid battery capacity decay and low initial Coulombic efficiency. In addition, the slow lithium diffusion kinetics in silicon (diffusion coefficients of 10 ^-14 to 10 ^-13 cm ² /s) and the low intrinsic conductivity of silicon (10 ^-5 to 10 ^-3 S/cm) also significantly affect silicon. Electrode rate capability and full capacity utilization.

Nanoscale morphology of silicon can solve the problem of expansion/contraction stress of silicon during lithiation/delithiation. The nanoscale size allows for rapid pressure relief, so nanosilicon is less prone to fracture than bulk particles. Nano-silicon-based anode materials have unique advantages such as surface effect and size effect, which can greatly improve the cycle performance of silicon-based anode materials. The existing preparation methods of nano-silicon particles include chemical and physical methods. Chemical methods mainly include chemical vapor deposition method, plasma reaction synthesis method, molten salt electrolysis method, metal induced chemical corrosion method, magnesium thermal reduction method, etc., which are to convert silicide precursors such as gaseous _SiH4 or solid _SiO2 into pure silicon. The process of (Zhou Shu. Preparation of silicon and boron nanoparticles by cold plasma [D]. Hangzhou: Zhejiang University, 2013.; LIU Nian, HUO Kaifu, MCDOWELL MT, et al. Ricehusks as a sustainable source of nanostructured silicon for high performance Li -ion battery anodes [J]. Scientific Reports, 2013, 3(5):1919.). Chemical methods can obtain nano-silicon particles with smaller size and more uniform distribution, but there are many disadvantages in the preparation process, such as harsh reaction conditions, complex process routes, poor controllability, high cost, and low yield. Chemical methods are used to prepare different sizes of silicon particles. of nano-silicon particles is very difficult. Physical methods include ball milling, laser ablation, spark discharge, etc., all of which are top-down preparation methods based on solid pure silicon raw materials (Zhao Mingcai, Cao Xiangwei, Sun Hongkai, etc. The combination of spark discharge and high-energy ball milling to efficiently prepare nano-silicon Particles[J]. Electrical Machining and Die, 2017(4):15-19; VONS VA, DESMET LC PM, MUNAO D, et al.Silicon nanoparticles produced by spark discharge[J]. Journal of Nanoparticle Research, 2011, 13( 10): 4867-4879.). These preparation methods are not only complicated in preparation process, high equipment requirements, difficult to mass-produce, but also expensive, making it difficult to realize industrialization of silicon-based composite material systems, and the first Coulomb efficiency of prepared pure silicon is mostly lower than 60%.

Aluminum-silicon alloys are widely used industrial aluminum alloys, accounting for more than 90% of aluminum alloys, and can be used in the automotive industry, aviation industry, and weaponry and other fields. The Al-Si binary alloy has a simple binary eutectic phase diagram. There are only two phases, α-Al and p-Si, at room temperature, and the two phases are not mutually soluble. The content of Si at the eutectic point is about 12.6% (mass fraction). In the eutectic Al-Si alloy, the primary silicon exists in the form of coarse needle-like crystals, and the eutectic silicon exists in the form of smaller lamellae, but the size of both phases is in the micrometer level. After adding a modifier for refinement, the primary crystal silicon phase can be refined, but the refinement effect of the eutectic silicon phase is not obvious.

SUMMARY OF THE INVENTION

The purpose of the present invention is to provide a preparation method of a nano-silicon lithium-ion battery negative electrode material which improves the specific capacity and the first coulombic efficiency of the lithium-ion battery.

The technical scheme that realizes the object of the present invention is as follows:

The preparation method of the negative electrode material of nano-silicon lithium ion battery comprises the following steps:

Step 1, taking pure aluminum and pure silicon, placing them in a vacuum melting furnace, and mixing and melting them into an aluminum-silicon alloy ingot with a Si content of 11.0-16.0 wt.%;

Step 2, removing the oxide layer from the aluminum-silicon alloy ingot, then suction-casting and forming, and controlling the diameter of the suction-casting copper mold to be 1.5-5.0 mm to obtain an alloy material;

Step 3, stirring and corroding the alloy material with acid, removing the alloying, washing with water, centrifuging and drying to obtain silicon nanoparticles.

The present invention also provides a method for preparing a negative electrode material for a nano-silicon lithium-ion battery, comprising the following steps:

Step 1, taking pure aluminum and pure silicon and placing them in a vacuum smelting furnace, and mixing and smelting them into an aluminum-silicon alloy ingot with a Si content of 11.0-16.0 wt%;

Step 2, removing the oxide layer from the aluminum-silicon alloy ingot, then suction-casting and forming, and controlling the diameter of the suction-casting copper mold to be 1.5-5.0 mm to obtain an alloy material;

Step 3, stirring and corroding the alloy material with acid to remove alloying, washing with water, centrifuging and drying to obtain silicon nanoparticles;

Step 4, stirring and mixing the silicon nanoparticle powder with the conductive agent and the binder uniformly to obtain electrode slurry;

Step 5, the electrode slurry is uniformly coated on the current collector, and the electrode sheet is obtained after drying, rolling and cutting.

Preferably, the silicon content in the aluminum-silicon alloy is 12.0-16.0 wt %, more preferably 13.0-15.0 wt %.

Preferably, the hole diameter of the suction casting copper mold is 2.0-3.0 mm.

Preferably, the mass ratio of the silicon nanoparticles: conductive agent (super P): binder is 1:1:1.

Further, the present invention provides the nano-silicon lithium-ion battery negative electrode material prepared by the above preparation method.

Further, in the lithium ion battery assembled with the nano-silicon lithium ion battery negative electrode material prepared by the above preparation method, the electrolyte is 1M LiPF ₆ /EC:DMC:DEC=1:1:1 (V/V/V).

Compared with the prior art, the present invention has the following advantages:

(1) The present invention adopts the method of smelting suction casting and then dealloying for the first time, and uses the rapid solidification technology of the alloy melt to refine the size of the silicon phase in the eutectic structure of the aluminum-silicon alloy, so that the size can reach the nanometer level. , and further through the dealloying technology, it is used to prepare the silicon anode material, and the size of the prepared silicon material can reach nano-scale and the particles are relatively uniform;

(2) The present invention regulates the size of the prepared nano-silicon particles by regulating the alloy composition ratio and the pore size of the suction casting mold;

(3) The nano-silicon prepared by the invention is used as the negative electrode material of lithium ion battery, and the first-week discharge specific capacity can reach 3699mAh/g, the first coulombic efficiency can reach 83.7%, the preparation process is simple, easy to repeat, and suitable for large-scale industrial production.

Description of drawings

Figure 1 is a scanning electron microscope (SEM) photograph of an aluminum-silicon alloy round rod with a diameter of 2.5mm prepared by the present invention with different Si contents, (a) 2.0wt% Si; (b) 11.7wt% Si; (c) 12.6wt% Si ; (d) 15.0 wt % Si; (e) 16.0 wt % Si; (f) 20.0 wt % Si; (g) 50.0 wt % Si.

Fig. 2 is the scanning electron microscope image of aluminum-silicon alloy round rods with different diameters and composition of 14.0wt% Si prepared by the present invention, (a) D=1.5mm; (b) D=2.0mm; (c) D=2.5mm; (d) D=3.0 mm; (e) D=5.0 mm.

3 is a scanning electron microscope image and a silicon particle size distribution diagram of the unmilled nano-silicon (a, c) in Comparative Example 2 and the milled nano-silicon (b, d) in Example 1.

FIG. 4 is an X-ray diffraction pattern (XRD) of the nano-silicon prepared in the example.

Figure 5 shows the charge-discharge curves and cycle-discharge ratios of lithium-ion batteries assembled with nano-silicon prepared in Example 2 (c, d) and Example 1 (e, f) as negative electrode materials in Comparative Example 1 (a, b) Capacity and coulombic efficiency graphs.

FIG. 6 is a charge-discharge curve diagram, a cycle-discharge specific capacity and a Coulomb efficiency diagram of a lithium-ion battery assembled with nano-silicon prepared in Comparative Example 2 as a negative electrode material.

Detailed ways

The present invention will be further described below with reference to the embodiments and accompanying drawings.

The preparation method of nano-silicon lithium-ion battery negative electrode material specifically includes the following steps:

Step 1, Smelting:

In proportion to pure aluminum, pure silicon and titanium ingots under the vacuum degree of less than 2×10 ^-3 Pa, pass argon gas, smelt pure titanium ingots for 2 to 5 times to remove oxygen, and control the arc current at 60 to 200A, smelting aluminum The silicon alloy is processed 3 to 5 times until the alloy is uniform, and the arc current is controlled at 60 to 200A to obtain an aluminum-silicon alloy.

Step 2, suction casting:

The polished aluminum-silicon alloy and titanium ingots are poured into argon at a vacuum degree lower than 2×10 ^-3 Pa, and the pure titanium ingots are smelted for 2 to 5 times to remove oxygen. The arc current is controlled at 60 to 200A, and the aluminum For silicon alloy, the arc current is controlled at 60-200A, and the completely molten state is maintained for 2-10s, and the rod-shaped aluminum-silicon alloy is obtained by suction casting.

Step 3, Dealloying:

The obtained aluminum-silicon alloy is cut into several parts and placed in a 0.5-5.0 mol/L HCl solution, stirred and corroded for 6-24 hours, and washed with water for 3-5 times after centrifugation to remove the residual acid solution; the solution is placed in a 0.5-5.0 mol/L HF ethanol solution, stir and corrode for 2 to 24 hours to remove excess SiO ₂ , and rinse with water for 3 to 5 times to remove residual acid solution after centrifugation; Dry until completely dry silicon nanoparticle powder is obtained.

Step 4, Preparation of Electrode Slurry:

Mix the nano-silicon powder and the conductive agent (super P) in a mortar and grind for 15-35 minutes; place the powder and the binder in a glass bottle, add water, and stir for 6-24 hours to obtain electrode slurry.

Step 5, preparation of electrode sheet:

Coat the slurry on the copper foil, place the copper foil in a vacuum drying oven for 12 to 24 hours, at a temperature of 60 to 80° C., dry and roll, and cut into circular electrode sheets.

Example 1

According to the silicon mass fraction of 11.7%, take 1.38g of pure silicon and 10.40g of pure aluminum, put them in a vacuum melting furnace, and control the vacuum degree in the furnace to be lower than 10 ^-3 Pa. Invert and smelt the titanium ingot 3 times and then smelt the alloy 5 times. The aluminum-silicon alloy ingot is formed, and it is taken out after cooling, and the arc current is 110A.

After grinding to remove the oxide scale on the surface, place it in a vacuum melting furnace. The vacuum degree in the furnace is controlled to be lower than 10 ^-3 Pa. After smelting the titanium ingot 3 times, the aluminum-silicon alloy is smelted and kept in a completely molten state for 5s. The arc was extinguished, and the rod was sucked and cast into a round bar with a diameter of 2.5mm. After cooling, the alloy material was taken out, and the arc current was 110A.

The round bar wire was cut into several sections, placed in a 2.5mol/L HCl(AR) solution after ultrasonic cleaning, and corroded by magnetic stirring for 8h at room temperature. In the alcohol solution, magnetic stirring was etched for 2 hours at room temperature, and after centrifugation, it was washed three times with deionized water and then placed in an oven, and dried at 80 °C for 24 hours to obtain dry nano-silica powder.

The obtained silicon powder and conductive agent (super P carbon black) were ground in a mortar for 20 minutes, poured into a glass bottle, added with a binder (SBR:CMC=1:1) and an appropriate amount of deionized water, and the magnetic force was applied at room temperature. After stirring for 10h, electrode slurry was obtained, and the rotating speed was 2000r/min.

The slurry was uniformly coated on a copper foil with a thickness of 20 μm, and the coating thickness was 50 μm, and then placed in a vacuum oven at 80 °C for 24 hours, rolled and punched into a circular electrode sheet with a diameter of 12 mm.

Among them, the active material (that is, the silicon nano-powder prepared by the present invention), conductive agent (super P carbon black), sodium carboxymethyl cellulose (CMC), and styrene-butadiene rubber (SBR) are in a mass ratio of 2:2:1 :1. A button-type battery was made with a lithium sheet as the counter electrode, and the electrolyte was a commonly used lithium-ion battery electrolyte: 1M LiPF ₆ /EC:DMC:DEC=1:1:1 (V/V/V).

The lithium-ion battery prepared in this example was subjected to a charge-discharge test, with constant current charge and discharge at a current density of 200mAg ^-1 , and the cut-off potentials were 0.01V and 1.5V, respectively. The discharge specific capacity in the first week is 3699mAh/g, and the first cycle efficiency is 83.72%. The charge-discharge curve is shown in Figure 5.

Figure 1 is a scanning electron microscope (SEM) photograph of an aluminum-silicon alloy round rod with a diameter of 2.5mm prepared by the present invention with different Si contents, (a) 2.0wt% Si; (b) 11.7wt% Si; (c) 12.6wt% Si ; (d) 15.0 wt % Si; (e) 16.0 wt % Si; (f) 20.0 wt % Si; (g) 50.0 wt % Si. Fig. 1(b) is the scanning electron microscope image of the sample prepared in this example. It can be seen from the figure that the sample is composed of the first precipitation aluminum phase and the aluminum-silicon eutectic structure, and the silicon in the eutectic structure is uniform and elongated. 3(b, d), it can be seen that the particle size is between 70 and 100 nm, and it is relatively uniform. It can be seen from Fig. 5(e, f) that the prepared nano-silicon powder has higher coulombic efficiency in the first week.

Example 2

This example is basically the same as Example 1, the only difference is that the electrolyte is a commonly used lithium-ion battery electrolyte: 1M LiPF ₆ /EC:DMC=1:1 (V/V).

The lithium-ion battery prepared in this example was subjected to a charge-discharge test, with constant current charge and discharge at a current density of 200mAg ^-1 , and the cut-off potentials were 0.01V and 1.5V, respectively. Its first-week discharge specific capacity is 2977.5mAh/g, and its first cycle efficiency is 82.57%. The charge-discharge curves are shown in Figure 5(c, d).

Comparative Example 1

This comparative example is basically the same as Example 1, the only difference is that the electrolyte is a common electrolyte for lithium ion batteries: 1M LiPF ₆ /EC:DEC=1:1 (V/V).

The lithium ion battery prepared in this comparative example was tested for charge and discharge, and the battery was charged and discharged at constant current at a current density of 200mAg ^-1 , and the cut-off potentials were 0.01V and 1.5V, respectively. Its first-week discharge specific capacity is 1103.5mAh/g, and its first cycle efficiency is 52.27%. The charge-discharge curves are shown in Figure 5(a,b). The coulombic efficiency in the first week is low, indicating that the prepared nano-silicon powder is not suitable for 1M LiPF ₆ /EC:DEC=1:1(V/V) electrolyte.

Comparative Example 2

This comparative example is basically the same as Example 1, except that the mass fraction of silicon is 20.0%, and the electrolyte is a common lithium-ion battery electrolyte: 1M LiPF ₆ /EC:DEC=1:1 (V/V).

Figure 1(f) is the SEM image of the sample prepared in this example. It is a hypereutectic structure. It can be seen that micron-sized coarse crystalline silicon has appeared. Combined with the SEM images of the sample powder in Figure 3(a, c), it can be seen that the eutectic structure is in the eutectic structure. The silicon particle size is approximately 100-200 nm.

The lithium ion battery prepared in this comparative example was tested for charge and discharge, and the battery was charged and discharged at constant current at a current density of 200mAg ^-1 , and the cut-off potentials were 0.01V and 1.5V, respectively. The discharge specific capacity in the first week is 3938.3mAh/g, and the first cycle efficiency is 55.22%. The charge-discharge curve is shown in Figure 6. Combined with its topography, it can be seen that the micron-scale coarse crystalline silicon and the inappropriate electrolyte (1MLiPF ₆ /EC:DEC=1:1(V/V)) are the reasons for its low coulombic efficiency in the first week.

Comparative Example 3

This comparative example is basically the same as Example 1, except that the mass fraction of silicon is 2.0 wt%. The SEM image of the prepared Al-Si alloy is shown in Figure 1(a). It can be seen from the figure that the number of nano-silicon particles is too small, which is not conducive to practical application.

Comparative Example 4

This comparative example is basically the same as Example 1, except that the mass fraction of silicon is 50.0 wt%. The SEM image of the prepared Al-Si alloy is shown in Figure 1(g). It can be seen from the figure that a large number of micron-sized coarse-crystalline silicon particles appear, with a size larger than 10 μm, which makes its electrochemical performance as a negative electrode material affected. Serious impact.

Claims (10)

1. The preparation method of the nano silicon lithium ion battery cathode material is characterized by comprising the following steps of:

step 1, putting pure aluminum and pure silicon into a vacuum smelting furnace, and mixing and smelting the pure aluminum and the pure silicon into an aluminum-silicon alloy spindle with the Si content of 11.0-16.0 wt%;

step 2, removing an oxide layer from an aluminum-silicon alloy spindle, performing suction casting molding, and controlling the aperture of a suction casting copper mold to be 1.5-5.0 mm to obtain an alloy material;

and 3, stirring and corroding the alloy material with acid, removing alloying, washing with water, centrifuging, and drying to obtain the silicon nano particles.

2. The preparation method of the nano silicon lithium ion battery cathode material is characterized by comprising the following steps of:

step 1, putting pure aluminum and pure silicon into a vacuum smelting furnace, and mixing and smelting the pure aluminum and the pure silicon into an aluminum-silicon alloy spindle with the Si content of 11.0-16.0 wt%;

step 2, removing an oxide layer from an aluminum-silicon alloy spindle, performing suction casting molding, and controlling the aperture of a suction casting copper mold to be 1.5-5.0 mm to obtain an alloy material;

step 3, stirring and corroding the alloy material with acid to remove alloying, washing with water, centrifuging, and drying to obtain silicon nanoparticles;

step 4, uniformly stirring and mixing the silicon nanoparticle powder, a conductive agent and a binder to obtain electrode slurry;

and 5, uniformly coating the electrode slurry on a current collector, drying, rolling and cutting into pieces to obtain the electrode slice.

3. The production method according to claim 1 or 2, wherein the aluminum-silicon alloy contains silicon in an amount of 12.0 to 16.0 wt%.

4. The production method according to claim 1 or 2, wherein the content of silicon in the aluminum-silicon alloy is 13.0 to 15.0 wt%.

5. The preparation method according to claim 1 or 2, wherein the pore diameter of the suction casting copper mold is 2.0-3.0 mm.

6. The preparation method according to claim 1 or 2, characterized in that the specific steps of step 1 are: proportionally mixing pure Al-Si ingot with Ti ingot at a temperature lower than 2X 10^-3Introducing argon gas under the Pa vacuum degree, smelting a pure titanium ingot for 2-5 times to remove oxygen, controlling the arc current to be 60-200A, smelting the aluminum-silicon alloy for 3-5 times until the alloy is uniform, and controlling the arc current to be 60-200A to obtain the aluminum-silicon alloy; the specific steps of the step 2 are as follows: the aluminum-silicon alloy and the titanium ingot after being polished are lower than 2 multiplied by 10^-3And introducing argon gas under the Pa vacuum degree, smelting a pure titanium ingot for 2-5 times to remove oxygen, controlling the arc current to be 60-200A, smelting the aluminum-silicon alloy, controlling the arc current to be 60-200A, keeping the complete melting state for 2-10 s, and performing suction casting to obtain the rod-shaped aluminum-silicon alloy.

7. The preparation method according to claim 1 or 2, wherein the specific steps of step 3 are: cutting the aluminum-silicon alloy, placing the cut aluminum-silicon alloy in 0.5-5.0 mol/L HCl solution, stirring and corroding for 6-24 h, centrifuging, and cleaning with water for 3-5 times to remove residual acid solution; putting the solution into 0.5-5.0 mol/L HF ethanol solution, stirring and corroding for 2-24 h, and removing redundant SiO₂After centrifugation, washing with water for 3-5 times to remove residual acid solution; and drying the solution at 60-80 ℃ to obtain the silicon nanoparticles.

8. The preparation method of claim 2, wherein the mass ratio of the silicon nanoparticles to the conductive agent to the binder is 1:1: 1.

9. The negative electrode material of the nano silicon lithium ion battery prepared by the preparation method of any one of claims 2 to 8.

10. The lithium ion battery assembled by the negative electrode material of the nano-silicon lithium ion battery as claimed in claim 9, wherein the electrolyte is 1M LiPF₆/EC:DMC:DEC＝1:1:1(V/V/V)。

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