CN204257756U - A kind of very thin si membrane - Google Patents

Abstract

The utility model provides a kind of very thin si membrane, and this very thin si membrane comprises conductive basal layer, silicon film and passivation layer from bottom to top successively.The silicon film thickness uniform, controllable of this very thin si membrane, passivation layer thickness is suitable for, there is excellent chemical property, for the electrode of lithium secondary battery, the electrochemical reaction of electrode material surface can be changed, accelerate the embedding of lithium ion in charge and discharge process and deintercalation process, thus increase substantially the performance of lithium secondary battery.

Description

An ultra-thin silicon membrane

technical field

The utility model relates to the technical field of electrochemical materials, in particular to an ultra-thin silicon film.

Background technique

Lithium secondary batteries are widely used in daily life as portable energy sources such as mobile phones and cameras. In order to solve the fossil energy crisis and alleviate environmental problems caused by automobile exhaust, lithium batteries will be more widely used in electric vehicles, electric vehicles and other fields. However, the low energy density and power density of existing batteries inhibit the further development of electric vehicles and electric vehicles. Therefore, the research and development of new energy storage systems with higher energy density is of great significance.

At present, lithium batteries mainly use carbon electrodes as negative electrodes. The theoretical capacity of graphite is 372mAh/g, while the theoretical capacity of silicon materials as negative electrodes is about 4200mAh/g, which can reach more than ten times the theoretical capacity of carbon negative electrodes, thus having a higher Development prospect and research value. However, in the process of charging and discharging with silicon as the electrode material, the expansion and contraction rate of the silicon negative electrode is relatively large (>300%), which leads to the deterioration of the secondary battery characteristics such as the cycle performance of the battery, thereby affecting the use of the battery, and further research is required. Research.

At present, the performance improvement of silicon materials is mainly carried out through the design of new structures and the surface modification of materials. The design of new structures mainly refers to the use of nanostructures to reduce the impact of volume expansion and contraction, such as nanorods, nanotubes or nanometers. Particles, etc., such as patent CN 102709536A discloses a silicon-carbon composite material and its preparation method, the silicon-carbon composite material is a silicon-carbon composite material coated with nano-scale silicon in a network structure, wherein the nano-scale silicon The average diameter of the material is 50-500nm; and the modification of the material is mainly through surface modification or doping, etc., such as CN 102054966A discloses a multilayer film negative pole piece and its preparation method, including metal substrates and metal substrates. At least one layer of amorphous carbon film and one layer of doped silicon film, the doped silicon film is coated with a layer of polymer coating, and the element of doped silicon film is aluminum copper iron tin boron. These methods have improved the secondary battery performance of the silicon negative electrode from different angles, but still cannot meet the needs of commercialization.

The preparation of silicon film by magnetron sputtering has the characteristics of simple method, controllable thickness and uniform structure, which has certain advantages compared with the above methods. In addition, existing studies have shown that coating a passivation layer on the surface of the silicon film can simulate the role of the SEI film in the charge and discharge process, change the chemical reaction on the electrode surface, and remove the hydrogen fluoride generated by the decomposition of the electrolyte, thereby protecting the silicon negative electrode. However, the thickness of the coated passivation layer should not be too thin or too thick, and should be controlled within an ideal range. Taking the Al ₂ O ₃ coating layer as an example, coating the surface of the silicon negative electrode with Al ₂ O ₃ can accelerate the exchange rate of lithium ions on the electrode surface, thereby improving the large-rate performance of the negative electrode. In addition, the Al ₂ O ₃ coating layer can Simulate the protective effect of the SEI film on the silicon anode and improve the cycle stability of the silicon anode; however, the reaction of Al ₂ O ₃ with Li ⁺ will generate LiAiO ₂ or Li _x Al ₂ O ₃ , and the conductivity of LiAiO ₂ is much lower than The conductivity of the electrolyte. Therefore, depositing a layer of Al ₂ O ₃ too thick on the surface of the silicon film will increase the transport rate of ions or electrons and thus increase the polarization. Therefore, further research is necessary to prepare a silicon film with excellent electrochemical performance that can be used in lithium secondary batteries.

Utility model content

The purpose of the utility model is to provide an ultra-thin silicon film, which can change the electrochemical reaction on the surface of the electrode material, accelerate the intercalation and de-intercalation process of lithium ions in the charging and discharging process, thereby greatly improving the performance of the secondary battery.

For this purpose, the utility model adopts the following technical solutions:

The ultra-thin silicon film of the present invention is defined as having a thickness of 10 μm-100 μm.

An ultra-thin silicon film includes a conductive base layer, a silicon film layer and a passivation layer from bottom to top.

The shapes of the conductive base layer, the silicon film layer and the passivation layer are the same.

The thickness of the silicon film layer is 10nm-1000nm, such as 50nm, 100nm, 200nm, 300nm, 400nm, 500nm, 600nm, 800nm or 900nm.

The conductive base layer is a copper layer, a nickel layer, an iron layer, a copper-nickel layer, a copper-iron layer, a nickel-iron layer or a copper-nickel-iron layer.

The thickness of the conductive base layer is 10 μm-100 μm, such as 20 μm, 30 μm, 40 μm, 50 μm, 60 μm, 80 μm or 90 μm.

The passivation layer is an Al ₂ O ₃ layer, a TiO ₂ layer, a ZnO layer, a MgO layer or a SnO ₂ layer.

The thickness of the passivation layer is 0.1nm-5nm, such as 0.5nm, 1.0nm, 2.0nm, 3.0nm, 3.5nm, 4.0nm or 4.5nm.

When the ultra-thin silicon film provided by the utility model is used in a lithium secondary battery, the passivation layer coated on the surface of the silicon film layer can simulate the effect of the SEI film in the charging and discharging process, change the chemical reaction on the electrode surface, and eliminate the decomposition of the electrolyte. Hydrogen fluoride, thereby protecting the silicon negative electrode.

The lithium secondary battery can be coin type, cylinder type, square type or button type battery.

Compared with the prior art, the beneficial effects of the utility model are:

1. The thickness of the silicon film layer of the ultra-thin silicon film provided by the utility model is uniform and controllable, and the thickness of the passivation layer on the surface of the silicon film layer is suitable, which can simulate the effect of the SEI film, thereby changing the electrochemical reaction on the surface of the electrode material and accelerating the lithium Intercalation and deintercalation of ions during charge and discharge;

2. The ultra-thin silicon film provided by the utility model is used for lithium secondary battery electrodes, has excellent electrochemical performance, and can greatly improve the performance of lithium secondary batteries.

Description of drawings

Fig. 1 is a schematic cross-sectional view of the ultra-thin silicon film provided by the present invention.

Fig. 2 is a process flow chart for preparing an ultra-thin silicon film provided by the utility model.

FIG. 3 is a first-week charge-discharge curve diagram of the battery prepared in Example 1. FIG.

FIG. 4 is a graph of the cycle life of the battery prepared in Example 1.

FIG. 5 is a first-week charge-discharge curve diagram of the battery prepared in Comparative Example 1. FIG.

FIG. 6 is a graph of the cycle life of the battery prepared in Comparative Example 1. FIG.

Wherein, 11, a passivation layer; 12, a silicon film layer; 13, a conductive base layer.

Detailed ways

The technical scheme of the utility model will be further described below in conjunction with the accompanying drawings and through specific embodiments.

As shown in Figure 1, it is the schematic cross-sectional view of the ultra-thin silicon film provided by the utility model, the ultra-thin silicon film provided by the utility model comprises a conductive base layer 13, a silicon film layer 12 and a passivation layer 11 successively from bottom to top, so that The conductive base layer 13 has a thickness of 10-100 um, the silicon film layer 12 has a thickness of 10-1000 nm, and the passivation layer 11 has a thickness of 0.1-5 nm.

As shown in Fig. 2, it is a process flow chart for preparing an ultra-thin silicon film provided by the utility model. The preparation method of described ultra-thin silicon film is:

1) Select the conductive base layer;

2) Preparing a silicon film layer: using magnetron sputtering to prepare a silicon film layer on the conductive base layer;

3) Preparing a passivation layer: using an atomic layer deposition method, a passivation layer is coated on the surface of the silicon film layer.

The method for preparing the ultra-thin silicon film provided by the present invention adopts magnetron sputtering, especially radio frequency sputtering (RFMagnetron Sputtering, RFMS) to prepare a silicon film layer, and the thickness of the obtained silicon film layer is uniform and controllable. The passivation layer is prepared by atomic layer deposition (ALD) method, and the thickness of the obtained passivation layer is appropriate.

Example 1

Preparation of ultrathin silicon membrane:

Select a piece of copper foil with a size of 10cm*10cm and a thickness of 20μm, wipe and dry it with absolute ethanol as a conductive base layer; use 10% HF solution for HF-treated silicon wafers (purity is above 99.99%) As a target material, argon gas was used as a protective gas pressure to control the pressure at 0.5-1 Pa, and a silicon film layer with a thickness of 0.5 μm was obtained by sputtering for 50 min at a sputtering power of 100 W. Then, atomic layer deposition method is used to deposit oxide on the surface of the obtained silicon film layer. The specific parameters are the temperature of 250 ° C, the pulse gas is water vapor and trimethylaluminum mixed gas, the pressure is controlled at 0.5 Pa, and the deposition time is 10 minutes. An aluminum oxide passivation layer with a thickness of 1 nm was obtained on the surface of the film layer.

Manufacture of lithium secondary batteries:

The ultra-thin silicon film prepared by the above magnetron sputtering method was cut into a pole piece as the positive electrode, 1M LiPF ₆ -EC/DMC (volume ratio 1:1) was used as the electrolyte, a Cd2400 separator, and a lithium sheet was used as the negative electrode to assemble a 2025 Button batteries.

The prepared battery was charged and discharged in the voltage range of 0.01-2V, and the test results are shown in Fig. 3 and Fig. 4 . The discharge specific capacity of the battery in the first week is 3261mAh/g, the charge specific capacity in the first week is 2939mAh/g, and the capacity remains at about 2800mAh/g after 5 cycles.

Comparative example 1

Preparation of ultrathin silicon membrane:

Select a piece of copper foil with a size of 10cm*10cm and a thickness of 20μm, wipe and dry it with absolute ethanol as a conductive base layer; use 10% HF solution for HF-treated silicon wafers (purity is above 99.99%) As a target material, argon gas was used as a protective gas pressure to control the pressure at 0.5-1 Pa, and a silicon film layer with a thickness of 0.5 μm was obtained by sputtering for 50 min at a sputtering power of 100 W.

Manufacture of lithium secondary batteries:

The ultra-thin silicon film prepared by the above magnetron sputtering method was cut into a pole piece as the positive electrode, 1M LiPF ₆ -EC/DMC (1:1 in volume ratio) was used as the electrolyte, a Cd2400 diaphragm, and a lithium sheet was used as the negative electrode to assemble a 2025 Button batteries.

Charge and discharge tests were carried out on the prepared battery in the voltage range of 0.01-2V, and the test results are shown in Fig. 5 and Fig. 6 . The discharge specific capacity of the battery in the first week is 3287mAh/g, and the charge specific capacity in the first week is 2723mAh/g. After 5 cycles, the capacity is about 2000mAh/g, and the capacity decays quickly. Compared with Example 1, it can be seen that after depositing aluminum oxide on the surface of the silicon film layer, the performance of the negative electrode of the composite material has been greatly improved, and the cycle stability has been significantly improved, indicating that a layer of passivation layer is coated on the surface of the silicon film layer. The charging and discharging performance has been significantly improved.

Example 2

Preparation of ultrathin silicon membrane:

Select a piece of nickel foil with a size of 10cm*10cm and a thickness of 10μm, wipe and dry it with absolute ethanol as a conductive base layer; use 10% HF solution for HF-treated silicon wafers (purity is above 99.99%) As a target material, argon gas was used as a protective gas pressure to control the pressure at 0.5-1 Pa, and a silicon film layer with a thickness of 10 nm was obtained by sputtering for 0.5 min at a sputtering power of 200 W. Then, atomic layer deposition method is used to deposit oxide on the surface of the obtained silicon film layer. The specific parameters are the temperature of 50°C, the pulse gas is a mixture of water vapor and magnesium chloride, the pressure is controlled at 0.9Pa, and the deposition time is 1min. A magnesium oxide passivation layer with a thickness of 0.1 nm was obtained.

Manufacture of Lithium Secondary Batteries:

The positive pole piece is made of commercial lithium iron phosphate: weigh 0.5g of polyvinylidene fluoride, dissolve it in 1.5g of N-methylpyrrolidone (NMP), add 0.5g of conductive carbon black, stir well, and then add 4g of commercial Thinned lithium iron phosphate cathode material, fully stirred and mixed, coated the mixed slurry on a smooth and clean copper foil, dried at 120°C, and punched into a circular pole piece with a diameter of 14mm as the positive electrode by a punching machine.

The above-mentioned pole piece is used as the positive electrode, 1M LiPF ₆ -EC/DMC (volume ratio is 1:1) is used as the electrolyte, the Cd2400 separator is used, and the negative electrode is made of an ultra-thin silicon film made by magnetron sputtering, assembled into a 2025 button cell .

Example 3

Preparation of ultrathin silicon membrane:

Select a piece of iron foil with a size of 10cm*10cm and a thickness of 100μm, wipe and dry it with absolute ethanol as a conductive base layer; use 10% HF solution for HF-treated silicon wafers (purity is above 99.99%) As the target material, argon gas was used as the protective pressure to control the pressure at 0.5-1 Pa, and a silicon film layer with a thickness of 1 μm was obtained by sputtering for 200 min at a sputtering power of 50 W. Then, atomic layer deposition method was used to deposit oxide on the surface of the obtained silicon film layer. The specific parameters were temperature 250°C, pulse gas selection of water vapor and Ti(OC ₂ H ₅ ) ₄ mixed gas, pressure control at 0.5 Pa, and deposition for 50 min. A titanium dioxide passivation layer with a thickness of 5 nm can be obtained on the surface of the silicon film layer.

Manufacture of Lithium Secondary Batteries:

The positive pole piece is made of commercial lithium iron phosphate: weigh 0.5g of polyvinylidene fluoride, dissolve it in 1.5g of N-methylpyrrolidone (NMP), add 0.5g of conductive carbon black, stir well, and then add 4g of commercial Thinned lithium iron phosphate cathode material, fully stirred and mixed, coated the mixed slurry on a smooth and clean copper foil, dried at 120°C, and punched into a circular pole piece with a diameter of 14mm as the positive electrode by a punching machine.

The above-mentioned pole piece is used as the positive electrode, 1M LiPF ₆ -EC/DMC (volume ratio is 1:1) is used as the electrolyte, the Cd2400 separator is used, and the negative electrode is made of an ultra-thin silicon film made by magnetron sputtering, assembled into a 2025 button cell .

Example 4

Preparation of ultrathin silicon membrane:

Select a piece of nickel foil with a size of 10cm*10cm and a thickness of 50μm, wipe and dry it with absolute ethanol as a conductive base layer; use 10% HF solution for HF-treated silicon wafers (purity is above 99.99%) As a target material, argon gas was used as a protective gas pressure to control the pressure at 0.5-1 Pa, and a silicon film layer with a thickness of 0.1 μm was obtained by sputtering for 10 min at a sputtering power of 120 W. Then, atomic layer deposition method is used to deposit oxide on the surface of the obtained silicon film layer. The specific parameters are temperature 100°C, pulse gas is a mixture of water vapor and zinc chloride, the pressure is controlled at 0.9Pa, and the deposition time is 30min. A passivation layer of zinc oxide with a thickness of 3 nm was obtained on the surface of the layer.

Manufacture of Lithium Secondary Batteries:

The positive pole piece is made of commercial lithium iron phosphate: weigh 0.5g of polyvinylidene fluoride, dissolve it in 1.5g of N-methylpyrrolidone (NMP), add 0.5g of conductive carbon black, stir well, and then add 4g of commercial Thinned lithium iron phosphate cathode material, fully stirred and mixed, coated the mixed slurry on a smooth and clean copper foil, dried at 120°C, and punched into a circular pole piece with a diameter of 14mm as the positive electrode by a punching machine.

The above pole piece is used as the positive electrode, 1M LiPF6-EC/DMC (1:1 volume ratio) is used as the electrolyte, the Cd2400 separator is used, and the negative electrode is made of an ultra-thin silicon film made by magnetron sputtering, and assembled into a 2025 button battery.

Example 5

Preparation of ultrathin silicon membrane:

Select a piece of nickel foil with a size of 10cm*10cm and a thickness of 20μm, wipe and dry it with absolute ethanol as a conductive base layer; use 10% HF solution for HF-treated silicon wafers (purity is more than 99.99%) As a target material, argon gas was used as a protective gas pressure to control the pressure at 0.5-1 Pa, and a silicon film layer with a thickness of 0.5 μm was obtained by sputtering for 50 min at a sputtering power of 100 W. Then, atomic layer deposition method is used to deposit oxide on the surface of the obtained silicon film layer. The specific parameters are the temperature of 250°C, the pulse gas is a mixture of water vapor and tin chloride, the pressure is controlled at 0.5Pa, and the deposition time is 50min. A tin oxide passivation layer with a thickness of 5 nm was obtained on the surface of the layer.

Manufacture of Lithium Secondary Batteries:

The positive pole piece is made of commercial lithium iron phosphate: weigh 0.5g of polyvinylidene fluoride, dissolve it in 1.5g of N-methylpyrrolidone (NMP), add 0.5g of conductive carbon black, stir well, and then add 4g of commercial Thinned lithium iron phosphate cathode material, fully stirred and mixed, coated the mixed slurry on a smooth and clean copper foil, dried at 120°C, and punched into a circular pole piece with a diameter of 14mm as the positive electrode by a punching machine.

The above-mentioned pole piece is used as the positive electrode, 1M LiPF ₆ -EC/DMC (volume ratio is 1:1) is used as the electrolyte, the Cd2400 separator is used, and the negative electrode is made of an ultra-thin silicon film made by magnetron sputtering, assembled into a 2025 button cell .

The applicant declares that the above description is only a specific embodiment of the present utility model, but the protection scope of the present utility model is not limited thereto, and those skilled in the art should understand that any skilled person in the technical field shall Within the technical scope disclosed in the new model, easily conceivable changes or replacements all fall within the scope of protection and disclosure of the present utility model.

Claims (6)

1. An ultra-thin silicon film, characterized in that the ultra-thin silicon film comprises a conductive base layer, a silicon film layer and a passivation layer from bottom to top. 2. The ultra-thin silicon film according to claim 1, characterized in that the thickness of the silicon film layer is 10nm-1000nm. 3. The ultra-thin silicon film according to claim 1 or 2, wherein the conductive base layer is a copper layer, a nickel layer, an iron layer, a copper-nickel layer, a copper-iron layer, a nickel-iron layer or a copper-nickel-iron layer layer. 4. The ultra-thin silicon film according to claim 1 or 2, characterized in that the thickness of the conductive base layer is 10 μm-100 μm. 5. The ultra-thin silicon film according to claim 1 or 2, characterized in that the passivation layer is an Al ₂ O ₃ layer, a TiO ₂ layer, a ZnO layer, a MgO layer or a SnO ₂ layer. 6. The ultra-thin silicon film according to claim 1 or 2, characterized in that the thickness of the passivation layer is 0.1 nm-5 nm.