CN106784766A - A kind of preparation method and application of the porous negative material for lithium ion battery - Google Patents

Abstract

A preparation method for a porous negative electrode material for a lithium-ion battery, the preparation steps are as follows: firstly prepare a Ge-Si-Al alloy ingot, then throw it into strips as a dealloyed precursor, and finally use dealloying technology to make it A bimodal nanoporous silicon-germanium alloy is prepared as a porous negative electrode material for a lithium-ion battery. The application of the prepared lithium ion battery porous negative electrode material is used for assembling half batteries. The advantages of the present invention are: the method utilizes the characteristics of solid solution of germanium and silicon, combined with the dealloying method to prepare bimodal nano-porous germanium-silicon alloy. The volume expansion of the material when charging further enhances the cycle life of the negative electrode material; it has the characteristics of low raw material cost, simple preparation process, and short process cycle. stability.

Description

A kind of preparation method and application of porous negative electrode material for lithium ion battery

technical field

The invention belongs to the technical field of negative electrode materials for lithium ion batteries, and in particular relates to a preparation method and application of porous negative electrode materials for lithium ion batteries.

Background technique

Lithium-ion batteries have received more attention due to their advantages such as large specific energy, high working voltage, good cycle stability, fast charge and discharge, and no environmental pollution. The performance of lithium-ion batteries largely depends on the electrode materials of lithium-ion batteries. Lithium ion anode materials can be divided into three categories according to their mechanism, lithium ion intercalation type anode, conversion mechanism anode and alloy mechanism anode. Among them, the theoretical capacities of traditional embedded negative electrodes such as graphite and lithium titanate are only 372mAh/g and 175mAh/g, respectively. With the development of lithium-ion batteries, traditional negative electrodes such as graphite and lithium carbonate will gradually be replaced by other negative electrode materials with high capacity and high stability.

At present, compared with graphite-based negative electrode materials, germanium and silicon, which are both group IVA elements, are good lithium-ion negative electrode materials, and the capacity of both of them is higher than that of graphite. Used in germanium and silicon alloys, the capacity of silicon (4200mAh/g) is higher than that of germanium (1600mAh/g); and germanium has a lower band gap (0.67eV) than silicon (1.12eV), So germanium conducts electrons better than silicon. Therefore, the study of silicon-germanium alloy anode materials can take advantage of their advantages respectively, which not only improves the battery capacity but also improves the electrical conductivity. However, the SiGe negative electrode material will undergo a large volume expansion (about 400%) during the charging process, causing the active material to pulverize and fall off, thereby destroying the structure of the material, reducing the ability of the material to intercalate lithium, and causing the stability of the battery. The safety cannot meet the application standard. In addition, the formed SEI film is prone to rupture during each cycle of volume expansion and contraction, so that the germanium-silicon alloy directly contacts the electrolyte to form a new SEI film. The SEI film with insulating properties gradually thickens after multiple cycles, which reduces the electrochemical activity of the material and causes capacity loss. Therefore, to improve the service life (cycle stability) and safety of the silicon-germanium negative electrode material, it is necessary to reduce the damage caused by the volume expansion of the silicon-germanium alloy to the performance.

In the prior art, CN106058256A discloses a method for preparing a carbon nanotube composite porous silicon negative electrode material for lithium ion batteries. The invention mainly includes preparation of porous silicon by thermal reduction method, carbon coating and composite carbon nanotubes on porous silicon by chemical vapor deposition method, and removal of iron catalyst by acid treatment. The invention adopts processes such as thermal reduction method and chemical vapor deposition method, so that the material preparation process period is long and the output is low; moreover, the magnesium powder in the experiment process is flammable and explosive, which has potential safety hazards. CN103985836A discloses a method for preparing a germanium negative electrode material on a nickel nano needle cone array. In this invention, a nickel nano-needle array of a certain height is prepared on a nickel substrate by means of aqueous solution electrodeposition, and then germanium anode materials are prepared on the nickel nano-needle array by means of ionic liquid electrodeposition in an anaerobic and anaerobic environment. . The germanium particle size prepared by the method is large, the porosity of the material is not high, and the preparation process is complicated, the preparation period is long, and the yield is low. S. Liu et al. (Nano Energy2015, 13: 651-657) prepared nanoporous germanium by dealloying process, and used it as the negative electrode material of high-performance lithium-ion batteries. Compared with silicon, germanium has a lower capacity, and its The content of germanium in the precursor alloy used is relatively high (28.4 at.%), and the cost is relatively high.

Contents of the invention

The purpose of the present invention is to solve the above-mentioned problems, and provide a preparation method and application of a porous negative electrode material for lithium-ion batteries. Nanoporous germanium-silicon alloy, this material shows high specific capacity and cycle stability as the negative electrode material of lithium-ion batteries.

Technical scheme of the present invention:

A preparation method for a porous negative electrode material for a lithium ion battery, the steps are as follows:

1) Preparation of Ge-Si-Al alloy ingot

Using germanium blocks, silicon grains, and aluminum blocks with a purity of 99.99wt% as raw materials, the raw materials are prepared according to the atomic ratio of the target alloy composition Ge _x Si _x Al _100-2x , where 8≤x≤11, and the raw materials are prepared separately Multiply a correction factor to reduce the composition deviation caused by the burning loss during alloy smelting. The correction coefficients are 1.01 for germanium, 1.02 for silicon, and 1.05 for aluminum. The weighed raw materials are smelted by arc melting. The degree of vacuum is pumped to 9×10 ^-4 Pa, and then high-purity argon gas is introduced to -0.05MPa. The germanium and silicon are smelted into small alloy ingots first, and the aluminum is smelted into ingots separately, and then the two sets of alloy ingots are smelted together, and repeated Melting 4 times to ensure that the material is evenly refined, and the material is cooled with a water-cooled crucible to obtain a refined Ge-Si-Al alloy ingot;

2) Preparation of dealloyed precursor strips

Put the above alloy ingot into a quartz test tube, the diameter of the quartz tube mouth is 1.1mm, the distance between the quartz tube mouth and the copper roller is 2.1mm, the alloy ingot is melted by induction heating, and then the molten alloy is quickly blown out by argon gas, blowing pressure 0.085MPa, the molten liquid alloy is rapidly solidified on a copper roller with a rotating speed of 3580 rpm to form alloy strips, and the width of the obtained strips is 2.3mm, and the thickness is 26μm, which is used as a dealloyed precursor strip;

3) Preparation of bimodal nanoporous germanium silicon alloy

Place the above-prepared dealloyed precursor strips in a sodium hydroxide solution with a concentration of 2.0-2.3M and a temperature of 63-67°C, free to dealloy for 400-420min, and remove the dealloyed product after the reaction Repeatedly wash twice with deionized water to remove residual sodium hydroxide on the surface of the sample, separate the dealloyed product with a centrifuge, then dry the product in a vacuum drying oven at 60°C and -0.1Mpa, and finally the prepared The bimodal nanoporous negative electrode material was stored in a dry oven with a vacuum degree of -0.1Mpa and a temperature of 25°C for future use.

An application of the prepared porous anode material for lithium-ion batteries for assembling half-cells.

The raw materials and equipment used in the preparation method of the above-mentioned porous negative electrode material for lithium-ion batteries are all obtained through known channels, and the operating techniques used are within the grasp of those skilled in the art.

Beneficial effects and outstanding substantive features of the present invention are:

The present invention utilizes the characteristics that germanium and silicon can be completely dissolved, and combines the dealloying method to prepare a bimodal nanoporous germanium-silicon alloy negative electrode material. This material combines the fast electron conduction rate of germanium with the high lithium intercalation ability of silicon. When used as the negative electrode material of lithium-ion batteries, it exhibits high cycle stability and specific capacitance. At the same time, the nanoporous structure of the material has a high porosity and suitable pore spacing, which can buffer the volume expansion of the active material during charging and further enhance the The cycle life of negative electrode materials. And it has the characteristics of low raw material cost, simple preparation process, short process cycle, etc., and overcomes the shortcomings of the prior art such as complicated process, long production cycle, high energy consumption, high material cost, and low output.

Compared with prior art, remarkable progress of the present invention is as follows:

1. The present invention has simple operating conditions, low requirements on environmental conditions (normal temperature and pressure), low requirements on working equipment, short preparation cycle, high output, and low material preparation cost;

2. The porous negative electrode material of the present invention has high capacity and low potential platform, and is suitable for being applied to the negative electrode of lithium-ion batteries;

3. The negative electrode material of the present invention has a bimodal nanoporous structure, which provides enough space for the expansion of the material, reduces the stress generated when the material expands, reduces the degree of pulverization and shedding, and improves the cycle life of the negative electrode material ;

4. The present invention comprehensively utilizes the advantages of silicon and germanium. Compared with pure germanium metal, the capacity of negative electrode material is improved, the cost of raw materials is reduced, and the conductivity of negative electrode material is improved compared with pure silicon material, thereby increasing the circulation of materials. stability.

Description of drawings

FIG. 1 is an XRD pattern of the precursor alloy strip prepared in Example 1.

FIG. 2 is an XRD pattern of the dealloyed product prepared in Example 1.

3 is a scanning electron micrograph of the dealloyed product prepared in Example 1.

Fig. 4 is the charging and discharging curve of the negative electrode material obtained in Example 1 packaged into a lithium-ion battery.

Figure 5 shows the cycle performance and coulombic efficiency of lithium-ion batteries packaged with the anode material obtained in Example 1.

detailed description

The present invention will be further described below in conjunction with the accompanying drawings and embodiments.

Example 1:

A preparation method for a porous negative electrode material for a lithium ion battery, the steps are as follows:

1) Preparation of Ge-Si-Al alloy ingot

Using germanium blocks, silicon grains, and aluminum blocks with a purity of 99.99wt% as raw materials, the materials are prepared according to the atomic ratio of the target alloy composition Ge ₁₀ Si ₁₀ Al ₈₀ , and the amount of raw materials is multiplied by a correction factor to reduce the alloy. Composition deviation caused by burning loss during smelting. According to the results of burning loss detection obtained through a large number of experiments by the inventor, the correction coefficients are 1.01 for germanium, 1.02 for silicon, and 1.05 for aluminum, and the weighed raw materials are smelted by arc melting. After the material is loaded into the furnace, the vacuum is pumped to 9×10 ^-4 Pa, and then the high-purity argon gas is introduced to -0.05MPa. The germanium and silicon are first smelted into a small alloy ingot, and the aluminum is smelted into an ingot separately, and then the two sets of alloy ingots are Smelting together, repeated smelting 4 times to ensure that the material is evenly smelted, and the material is cooled with a water-cooled crucible to obtain a refined Ge-Si-Al alloy ingot.

2) Preparation of dealloyed precursor strips

Put the above alloy ingot into a quartz test tube, the diameter of the quartz tube mouth is 1.1mm, the distance between the quartz tube mouth and the copper roller is 2.1mm, the alloy ingot is melted by induction heating, and then the molten alloy is quickly blown out by argon gas, blowing pressure 0.085MPa, the molten liquid alloy is rapidly solidified on a copper roller with a rotational speed of 3580 rpm to form alloy strips, the width of which is about 2.3mm, and the thickness is about 26μm, which is used as a dealloyed precursor material. The XRD pattern of the precursor alloy strip is shown in Figure 1, and the crystal peaks of Ge, Si, and Al can be clearly seen, indicating that the material is a Ge-Si-Al ternary alloy;

3) Preparation of bimodal nanoporous germanium silicon alloy

Put the above-prepared precursor alloy strips in a sodium hydroxide solution with a concentration of 2.1M and a temperature of 65°C, and dealloy freely for 410 minutes. After the reaction, remove the dealloyed product and wash it twice with deionized water repeatedly , remove the residual sodium hydroxide on the surface of the sample, separate the dealloyed product with a centrifuge, and then dry the product in a vacuum oven at 60°C, then place the final nanoporous negative electrode material in a vacuum of -0.1 Mpa and a temperature of 25 ° C in a dry box for future use.

Figure 2 is the XRD picture of the dealloyed product. Only the peaks of Ge and Si are detected in the spectrum, and part of Ge is dissolved in Si, which makes the diffraction peak broaden, but no peak of Al is detected, indicating that after dealloying, Al Elements are all filtered out. Figure 3 is a scanning electron micrograph of the dealloyed product. It can be clearly seen from the figure that the material is a bimodal porous structure composed of small and uniform pores/ligaments. The diameter of the primary large pores is about 0.5-1.6 μm, and the diameter of the secondary small pores is about 40-60 nm. The finally prepared nanoporous negative electrode material was placed in a drying oven with a vacuum degree of -0.1 MPa and a temperature of 25° C. for future use.

The nanoporous germanium-silicon negative electrode material prepared in this embodiment is used to assemble a half-cell and perform a performance test, the method is:

1) Half-cell assembly: Weigh the nanoporous germanium-silicon negative electrode material prepared by the present invention, conductive carbon black and binder sodium carboxymethyl cellulose with a mass ratio of 7:2:1, and drop them into super Pure water is made into a paste, evenly spread on the copper foil, and used as the negative electrode after drying. 1M LiPF ₆ was used as the electrolyte, the metal lithium sheet was used as the counter electrode, and the porous polypropylene (Celgard) was used as the diaphragm for battery packaging.

2) Battery performance test: The battery assembled in 1) is subjected to a performance test. Fig. 4 is the charging and discharging test curve of the battery prepared in this embodiment. It can be seen from the figure that the first discharge and charging capacities of the battery are 2776.2mAh/g and 2447.3mAh/g respectively, and the coulombic efficiency is 88.15%. Figure 5 shows the battery cycle performance and coulombic efficiency test results. It can be seen from the figure that the battery shows a good capacity performance. After 20 cycles, the charge and discharge capacity is maintained at about 2200mAh/g, and the coulombic efficiency remains above 99.6%.

Example 2:

A preparation method for a porous negative electrode material for a lithium ion battery, the steps are as follows:

1) The preparation of the Ge-Si-Al alloy ingot is basically the same as in Example 1, except that the target alloy composition is Ge ₈ Si ₈ Al ₈₄ ;

2) The preparation of the dealloyed precursor strip is exactly the same as in Example 1;

3) Preparation of bimodal nanoporous germanium silicon alloy

Place the precursor alloy strip prepared above in a sodium hydroxide solution with a concentration of 2.0M and a temperature of 63°C, and dealloy freely for 400 minutes. After the reaction, remove the dealloyed product and wash it twice with deionized water repeatedly , remove the residual sodium hydroxide on the surface of the sample, separate the dealloyed product with a centrifuge, then dry the product in a vacuum oven at 60°C, and place the final bimodal nanoporous negative electrode material in a vacuum of -0.1MPa, keep it in a dry box at 25°C for later use. In the XRD detection of the dealloyed product, only the peaks of Ge and Si were detected, and part of Ge was solid-dissolved in Si, which broadened the diffraction peak, but no peak of Al was detected, indicating that the Al element has been completely filtered out after dealloying . The dealloyed product is a bimodal porous structure mainly composed of small and uniform pores/ligaments, the diameter of the primary large pores is about 0.7-1.8 μm, and the diameter of the secondary small pores is about 50-80 nm. The finally prepared nanoporous negative electrode material was placed in a drying oven with a vacuum degree of -0.1 MPa and a temperature of 25° C. for future use.

The nanoporous germanium-silicon negative electrode material prepared in this embodiment is used to assemble a half-cell and perform a performance test, the method is:

1) Half-cell assembly: Weigh the nanoporous germanium-silicon negative electrode material prepared by the present invention, conductive carbon black and binder sodium carboxymethyl cellulose with a mass ratio of 7:2:1, and drop them into super Pure water is made into a paste, evenly spread on the copper foil, and used as the negative electrode after drying. 1M LiPF ₆ was used as the electrolyte, the metal lithium sheet was used as the counter electrode, and the porous polypropylene (Celgard) was used as the diaphragm for battery packaging.

2) Battery performance test: The battery assembled in 1) is subjected to a performance test. The charge and discharge test curve of the battery shows that the discharge and charge capacity of the battery in the first cycle are 2753.3mAh/g and 2432.7mAh/g respectively, and the Coulombic efficiency is 88.36%. The battery cycle performance and coulombic efficiency test results show good capacity performance. After 20 cycles, the charge and discharge capacity is maintained at about 2200mAh/g, and the coulombic efficiency remains above 99.7%.

Example 3:

A preparation method for a porous negative electrode material for a lithium ion battery, the steps are as follows:

1) The preparation of the Ge-Si-Al alloy ingot is basically the same as in Example 1, except that the target alloy composition is Ge ₁₁ Si ₁₁ Al ₇₈ ;

2) The preparation of the dealloyed precursor strip is exactly the same as in Example 1;

3) Preparation of bimodal nanoporous germanium silicon alloy

Put the above-prepared precursor alloy strips in a sodium hydroxide solution with a concentration of 2.3M and a temperature of 67°C, and dealloy freely for 420 minutes. After the reaction, remove the dealloyed product and wash it twice with deionized water repeatedly , remove the residual sodium hydroxide on the surface of the sample, separate the dealloyed product with a centrifuge, and then dry the product in a vacuum oven at 60°C, then place the final nanoporous negative electrode material in a vacuum of -0.1 MPa, stored in a dry box at 25°C for later use. In the XRD detection of the dealloyed product, only the peaks of Ge and Si were detected, and part of Ge was solid-dissolved in Si, which broadened the diffraction peak, but no peak of Al was detected, indicating that the Al element has been completely filtered out after dealloying . The dealloyed product is a bimodal porous structure mainly composed of fine and uniform pores/ligaments, the diameter of the primary large pores is about 0.4-1.5 μm, and the diameter of the secondary small pores is about 30-60 nm. The finally prepared nanoporous negative electrode material was placed in a drying oven with a vacuum degree of -0.1 MPa and a temperature of 25° C. for future use.

The nanoporous germanium-silicon negative electrode material prepared in this embodiment is used to assemble a half-cell and perform a performance test, the method is:

1) Half-cell assembly: Weigh the nanoporous germanium-silicon negative electrode material prepared by the present invention, conductive carbon black and binder sodium carboxymethyl cellulose with a mass ratio of 7:2:1, drop them into super Pure water is made into a paste, evenly spread on the copper foil, and used as the negative electrode after drying. 1M LiPF ₆ was used as the electrolyte, the metal lithium sheet was used as the counter electrode, and the porous polypropylene (Celgard) was used as the diaphragm for battery packaging.

2) Battery performance test: The battery assembled in 1) is subjected to a performance test. The charge and discharge test curve of the battery shows that the discharge and charge capacity of the battery in the first cycle are 2755.8mAh/g and 2436.9mAh/g respectively, and the Coulombic efficiency is 88.43%. The battery cycle performance and coulombic efficiency test results show good capacity performance. After 20 cycles, the charge and discharge capacity is maintained at around 2200mAh/g, and the coulombic efficiency remains above 99.6%.

Comparative example 1:

The Ge ₅ Si ₅ Al ₉₀ (atomic ratio) alloy was prepared into strips, and other conditions were the same as in Example 1. The results showed that too little germanium and silicon elements could not form a continuous ligament structure after dealloying, and germanium and silicon were obtained. Granular materials mixed with silicon have not obtained nanoporous negative electrode materials. On the one hand, the granular silicon germanium negative electrode material greatly reduces the electron transfer ability of the material, and on the other hand, it will cause serious volume expansion problems during charging, making the battery cycle stable. reduced sex. Therefore, this material is not suitable as an anode material for high-performance lithium-ion batteries.

Comparative example 2:

The Ge ₁₅ Si ₁₅ Al ₇₀ (atomic ratio) alloy was prepared into strips, and other conditions were the same as in Example 1. The results showed that too much germanium and silicon elements made the dealloying reaction insufficient, and could not form a continuous and effective ligament structure. The material The ligament becomes wider, the porosity decreases, and the anode material with bimodal nanoporous structure cannot be obtained, and it cannot provide sufficient space for the volume expansion of the germanium-silicon anode material during charging, which reduces the cycle stability of the battery. Therefore, this material is not suitable as an anode material for high-performance lithium-ion batteries.

Comparative example 3:

The Ge ₁₀ Si ₁₀ Al ₈₀ (atomic ratio) alloy was prepared into strips, and the strips were placed in a sodium hydroxide solution with a concentration of 2.5M and a temperature of 60°C for free dealloying for 450min, and other conditions were the same as in Example 1. The results show that bimodal nanoporous materials cannot be obtained, and sufficient space cannot be provided for the volume expansion of the silicon-germanium negative electrode material during charging, which reduces the cycle stability of the battery. Therefore, this material is not suitable as an anode material for high-performance lithium-ion batteries.

The above examples and comparative examples illustrate that the preparation method of porous negative electrode materials for lithium-ion batteries is to continuously try different proportions of alloys, strictly control the alloy preparation conditions and dealloying process, and finally develop a bimodal nanometer through repeated practice. Negative electrode material with porous structure.

The raw materials and equipment used in the above examples are all obtained through known channels, and the operating techniques used are within the grasp of those skilled in the art.

Claims (2)

1. the preparation method of a kind of porous negative material for lithium ion battery, it is characterised in that step is as follows：

1) preparation of Ge-Si-Al alloy pigs

Germanium block, silicon grain, the aluminium block of 99.99wt% are as raw material with purity, according to subject alloy composition Ge_xSi_xAl_100-2x's Atomic ratio is got the raw materials ready, wherein 8≤x≤11, the standby amount of raw material is multiplied by a correction factor respectively when getting the raw materials ready, to cut down during alloy melting The composition tolerances that cause of scaling loss, the correction factor is respectively germanium 1.01, silicon 1.02, aluminium 1.05, by load weighted raw material Using arc melting method melting, vacuum is evacuated to 9 × 10 after material shove charge^-4Pa, then passes to high-purity argon gas to -0.05MPa, will Germanium and silicon are first smelted into primary alloy ingot, the independent melting ingot of aluminium, then combine ingot meltings together by two, and melt back 4 times is protecting Card material refining is uniform, after material is cooled down with cold-crucible, obtains the Ge-Si-Al alloy pigs refined；

2) preparation of alloy presoma band is taken off

Above-mentioned alloy pig is put into quartz test tube, quartz ampoule nozzle diameter 1.1mm, the quartz ampoule mouth of pipe away from copper roll spacing from 2.1mm, Sensing heating melts alloy pig, is then quickly blown out the alloy of melting using argon gas, and it is 0.085MPa, melting to blow casting pressure Liquid alloy on the copper roller of 3580 revs/min of rotating speed rapid solidification form alloy strip, the width that band is obtained is 2.3mm, thickness is 26 μm, used as de- alloy presoma band；

3) preparation of bimodal nanoporous germanium-silicon alloy

De- alloy presoma band obtained above is placed in the NaOH that concentration is 2.0~2.3M, temperature is 63~67 DEG C In solution, 400~420min of alloy is freely taken off, de- alloy product is pulled out and cleaned repeatedly with deionized water 2 times by reaction after terminating, The NaOH of sample surfaces residual is removed, is separated de- alloy product with centrifuge, then by product in vacuum drying chamber In being dried under 60 DEG C, -0.1Mpa, obtained bimodal nanoporous negative material is finally placed in vacuum for -0.1Mpa, temperature To retain standby in 25 DEG C of drying boxes.

2. the application of the porous negative material for lithium ion battery prepared by a kind of claim 1, it is characterised in that：For Assembling half-cell.