CN111082034B - Preparation of tin/tin phosphide/carbon composites as negative electrodes for alkali metal ion batteries - Google Patents

Abstract

The invention discloses a preparation method of a tin/tin phosphide/carbon composite material of an alkali metal ion battery cathode; the method mainly comprises the following steps: firstly, crosslinking sodium alginate and tetravalent tin ions, using sodium chloride as an inhibitor, then freeze-drying a crosslinking product, carbonizing the product in an inert atmosphere, and then phosphorizing the product by using sodium hypophosphite to obtain the tin/tin phosphide/carbon composite material. According to the invention, nano-sized tin oxide particles are generated by a sodium alginate crosslinking method and are wrapped by graphitized carbon, a better pore channel structure is formed in a macromolecule cracking process, and the structure of the tin/tin phosphide/carbon composite material is maintained while the tin/tin phosphide/carbon composite material is obtained by using gaseous phosphorization, so that the prepared composite material has good pore channel and conductivity, can effectively inhibit the expansion of tin, and has good cycle performance and rate capability when being used for an alkali metal ion battery. The method is simple to operate, low in process cost and easy for industrial large-scale production.

Description

Preparation of tin/tin phosphide/carbon composites as negative electrodes for alkali metal ion batteries

technical field

The invention relates to the technical field of preparation of negative electrode materials for alkali metal ion batteries, in particular to the preparation of a tin/tin phosphide/carbon composite material for the negative electrode of alkali metal ion batteries.

Background technique

Lithium ion battery is the most famous alkali metal ion battery, which is a kind of secondary battery, which has the advantages of high energy density, environmental friendliness and good safety. At present, the negative electrode used in lithium-ion batteries is mainly graphite, which is low in cost but small in capacity. With the increase in energy storage requirements, graphite is difficult to meet the current needs. Therefore, it is imminent to develop new anode materials.

Tin-based materials have become a promising anode material for alkali metal ion batteries due to their environmental friendliness and high specific capacity, but their volume expansion rate is large during cycling, which will cause the electrode to pulverize and fall off, which will cause battery performance degradation. degradation. Nanonization and carbon encapsulation is an effective strategy to alleviate this problem. Nanonization refers to reducing the size of a material to the nanometer level, thereby mitigating the effects of its deformation. The carbon coating can not only buffer the volume expansion, but also improve the overall conductivity of the material. However, some of today's nanonization and carbon coating methods are relatively complicated, and the two often cannot be taken into account. For example, Liu Jianhong and others invented a method for preparing carbon-coated manganese oxide (patent number: CN201410666514.0). This method uses acrylonitrile oligomers as raw materials for carbon coating, and requires multiple heating, stirring and drying , and takes a long time. Lu Xiaoxiao et al. invented a method for preparing SnO ₂ /amorphous carbon composite materials by cracking atomized composite precursors online (patent number: CN201810778802.3). This method uses SnO ₂ alcohol sol and glucose mixture as precursors, and undergoes ultrasonic The atomizer is converted into an aerosol and then the carrier gas is introduced into a quartz tube up to 1100-1200°C for cracking. The method is more complicated and the temperature higher than 1000°C makes the particle size of _SnO2 larger.

Contents of the invention

The purpose of the present invention is to overcome the above-mentioned deficiencies in the prior art, and provide a kind of preparation of the tin/tin phosphide/carbon composite material of alkali metal ion battery negative electrode: promptly utilize the characteristic of cross-linking of sodium alginate and tin ion, through seaweed The macromolecule of sodium bicarbonate confines tin ions locally at the nanometer level, and produces nanoscale carbon-coated tin oxide composite materials during the high-temperature reaction process, and uses gaseous phosphating to obtain tin and phosphating while retaining the structure. Tin carbon composite material. Specifically, sodium alginate can cross-link with tin ions to form a uniformly dispersed "egg-box" structure, and carbonize it through the local confinement effect of the structure to obtain a tin oxide/carbon nanocomposite material. The gaseous phosphine can be used to phosphine tin oxide in situ to generate tin and tin phosphide without destroying its structure, and a carbon composite material of tin and tin phosphide can be obtained.

The purpose of the present invention is achieved through the following technical solutions:

The present invention relates to a kind of preparation method of the tin/tin phosphide/carbon composite material that is used for the negative pole of alkali metal ion battery, and described method comprises the following steps:

S1. Under the condition of adding sodium ions as an inhibitor, use sodium alginate and tetravalent tin ions to perform a cross-linking reaction to form a gel;

S2. The gel is freeze-dried and then calcined and carbonized in an inert atmosphere to obtain a tin oxide/carbon composite material;

S3. Phosphating the tin oxide/carbon composite material with sodium hypophosphite under an inert atmosphere, that is, obtaining the tin/tin phosphide/carbon composite material.

In the present invention, step S1 uses the property that sodium alginate can cross-link with polyvalent metal ions to cross-link with tetravalent tin ions to form gel beads. The metal components obtained by crosslinking with sodium alginate have good uniformity, fine particle size and good carbon coating structure.

Step S3, during the phosphating process, sodium hypophosphite is decomposed under heating to form phosphine gas, and the phosphine reduces tin oxide metal tin in situ, and the excess phosphine continues to react with tin to form tin phosphide.

Further, in step S1, sodium alginate is dissolved in water to prepare a sol with a mass concentration of 1-2%, and then the sodium alginate sol is dripped into a tin tetrachloride solution with a concentration of 0.1-0.2 mol/L carry out the crosslinking reaction. If the concentration of metal ions is too low, the cross-linking will be incomplete, and if it is too high, it will cause waste.

Further, in step S1, the cross-linking reaction is carried out under the condition of adding sodium ions as inhibitors. Adding sodium ions (such as sodium chloride) as an inhibitor can make the concentration of metal ions in the gel more uniform.

Further, sodium chloride with tin: sodium molar ratio of 1:1-5 is added as an inhibitor to make the distribution of metal ions inside the gel more uniform during cross-linking; too large a proportion of sodium chloride will affect the gel strength and lead to cross-linking. The linking failed; the crosslinking reaction time was 24h~48h.

Further, in step S1, the G segment in sodium alginate, that is, guluronic acid, undergoes a spontaneous cross-linking reaction with tetravalent tin ions to form a gel, and a uniform "egg box (egg- box)" structure.

Further, in step S2, the freeze-drying is to freeze-dry the gel washed with deionized water at -70-50°C (preferably -60°C) for 1-3 days.

Further, in step S2, the carbonization method specifically includes: under the protection of an inert atmosphere, calcining for 1 to 2 hours at a heating rate of 5 to 10° C. per minute at a temperature of 500° C. to 1200° C. so that the carbonization reaction can fully proceed .

Further, in step S2, after the carbonization is completed, the carbonization is washed with deionized water, and then vacuum-dried for 12-24 hours.

Further, step S3 includes the step of grinding and mixing the tin oxide/carbon composite material with a molar ratio of tin and phosphorus of 1:2 to 1:10 and sodium hypophosphite before phosphating, and the grinding and mixing time is 15 to 30 minutes To ensure that the two are evenly mixed, too little sodium hypophosphite will make the reaction incomplete, and too much will cause waste.

Further, in step S3, the phosphating method is specifically: under an inert atmosphere, using sodium hypophosphite (NaH ₂ PO ₂ ) as a phosphorus source, phosphating at 200-400° C. at a heating rate of 5-10° C. per minute 5 to 30 minutes to ensure that the phosphating reaction is fully completed. This phosphating method can preserve the structure of the tin oxide/carbon composite.

Further, in step S3, after the phosphating is completed, it is washed with deionized water and 0.05 mol/L dilute hydrochloric acid in sequence, and then vacuum-dried for 12-24 hours.

Further, in step S3, the structure of the tin/tin phosphide/carbon composite material is specifically: 3-5nm metal components are evenly distributed in the carbon matrix, and surrounded by multiple layers of graphitized carbon layers. Under the preparation conditions of the present invention, during the carbonization process, sodium alginate is cracked at high temperature to form a carbon material with high carbon content to wrap the tin oxide, the temperature continues to rise, the tin oxide agglomerates and grows up, and the carbon is extruded to wrap it A carbon layer forms around the particles.

Compared with the prior art, the present invention has the following beneficial effects:

1) The present invention uses sodium alginate as a raw material, and obtains a carbon composite material of tin and tin phosphide by crosslinking, carbonizing and rephosphating with tetravalent tin ions; the method is simple to operate, low in process cost, and easy to synthesize Easy; in addition, when sodium alginate and tin ions are cross-linked and carbonized, uniform mesopores will be introduced, and tin can catalyze the graphitization of the carbon layer to a certain extent, thereby improving the conductivity of the material;

2) When the tin/tin phosphide/carbon composite material prepared by the present invention is applied to the negative electrode of alkali metal ion battery, the internal uniform pores can be used as the transmission path of alkali metal ions, and the fine metal component particles make the carbon coating effect better At the same time, the carbon layer can improve the conductivity of the material and inhibit the volume expansion of tin, and phosphorus can form a matrix to further inhibit the volume expansion of tin. Therefore, this material can exhibit good cycle performance and rate performance.

Description of drawings

Other characteristics, objects and advantages of the present invention will become more apparent by reading the detailed description of non-limiting embodiments with reference to the following drawings:

Fig. 1 is the transmission electron micrograph of the tin-based carbon composite material that the embodiment of the present invention 1 gains: Wherein, a, b are the electron micrograph of tin oxide/carbon composite material, c, d are tin/tin phosphide/carbon composite material electronic microscope photo;

Fig. 2 is the X-ray diffraction spectrum of the tin/tin phosphide/carbon composite material that embodiment 1 gains among the present invention;

Fig. 3 is the Raman spectrum of tin/tin phosphide/carbon composite material gained in embodiment 1 in the present invention;

Fig. 4 is the nitrogen adsorption-desorption curve of the tin/tin phosphide/carbon composite material obtained in Example 1 of the present invention;

Fig. 5 is the pore size distribution figure of the tin/tin phosphide/carbon composite material obtained in embodiment 1 of the present invention;

Fig. 6 is the rate performance comparison of tin/tin phosphide/carbon composite material and tin oxide/carbon composite material obtained in Example 1 of the present invention in lithium ion battery negative electrode;

Fig. 7 is the cycle performance comparison of tin/tin phosphide/carbon composite material and tin oxide/carbon composite material obtained in Example 1 of the present invention in lithium-ion battery negative electrode, wherein the current density is 0.1A/g;

Figure 8 is a comparison of the cycle performance of the tin/tin phosphide/carbon composite material and the tin oxide/carbon composite material obtained in Example 1 of the present invention in the negative electrode of lithium-ion batteries, where the current density is 1A/g.

Detailed ways

The present invention will be described in detail below in conjunction with specific embodiments. The following examples will help those skilled in the art to further understand the present invention, but do not limit the present invention in any form. It should be noted that those skilled in the art can make several modifications and improvements without departing from the concept of the present invention. These all belong to the protection scope of the present invention.

Example 1

This embodiment relates to a preparation method of a tin/tin phosphide/carbon composite material, comprising the following steps:

Step 1, cross-linking reaction: 3 g of sodium alginate was dissolved in 197 ml of deionized water to prepare a solution with a mass fraction of 1.5%. Sodium chloride and crystalline tin tetrachloride with a sodium:tin molar ratio of 3:1 were dissolved in 500ml of deionized water to prepare a solution with a tin ion concentration of 0.15mol/L. Sodium alginate was slowly dropped into the aqueous solution of metal ions, stirred and reacted for 24 hours, and waited for the complete completion of the cross-linking reaction. The cross-linked product was rinsed three times with deionized water, then placed in a freeze dryer, and freeze-dried at -60°C for 24 hours.

Step 2, carbonization: transfer the freeze-dried sodium alginate pellets to a tube furnace, raise the temperature to 550°C at a rate of 5°C/min in a nitrogen atmosphere, and keep it warm for 1 hour to obtain a tin oxide/carbon composite Material.

Step 3, phosphating: After cleaning and drying the tin oxide/carbon composite material, mix it with sodium hypophosphite at a tin:phosphorus molar ratio of 1:7, grind it by hand for 15 minutes, place it in a tube furnace, and put it in an inert Under the atmosphere, the temperature was raised to 280°C at a rate of 10°C/min, and kept for 5 minutes; washed with deionized water and 0.05mol/L dilute hydrochloric acid, and then vacuum-dried for 12 hours to obtain a tin/tin phosphide/carbon composite material.

Implementation Effect:

The tin oxide/carbon composite material obtained according to the above method is shown in Figure 1-a (bar=50nm), 1-b (bar=20nm), and it can be seen that tin oxide particles of about 3-5nm are evenly distributed in the carbon matrix . The obtained tin/tin phosphide/carbon composite material is shown in Figure 1-c (bar=20nm), 1-d (bar=5nm), and it can be seen that the tin phosphide of about 3-5nm is evenly distributed in the carbon matrix , some tin melts and grows to form larger particles. The X-ray diffraction pattern of the tin/tin phosphide/carbon composite is shown in Figure 2, showing a mixture of elemental tin and tin phosphide. The Raman ray diagram is shown in Figure 3, which shows the high degree of graphitization of the composite material. The nitrogen absorption-desorption curve and pore size distribution curve of the material are shown in Figure 4 and Figure 5, which show its better pore structure. Take 0.1g of the composite material, add the composite material, conductive carbon black, and binder (the composition is polyvinylidene fluoride PVDF dissolved in NMP in N-methylpyrrolidone NMP, the mass concentration is 0.02g) with a mass ratio of 8:1:1 /ml) was stirred to form a slurry, and the slurry was evenly spread on the copper foil, and after drying, it was cut into circular electrode sheets with a diameter of 11 mm, dried and weighed. In a glove box with an argon atmosphere with a water oxygen content lower than 0.5ppm, metal lithium is used as a counter electrode, a polyolefin porous membrane is used as a diaphragm, and a 1mol/L lithium hexafluorophosphate solution (a solvent with a volume ratio of 1:1:1) Ethylene carbonate, ethyl methyl carbonate, dimethyl carbonate) were used as the electrolyte, and the electrode sheets were assembled into a CR2016 half-cell. Charge-discharge, cyclic voltammetry, and AC impedance tests were performed on the half-cell. Figure 6 is the rate performance graph of the composite material. The specific capacity is 598mAh/g when the current density is 0.1A/g, and the specific capacity is 247mAh/g when the current density is 5A/g. Compared with SnO ₂ /C Composite materials, the rate performance has been improved after phosphating. Figure 7 is the cycle performance diagram of the composite material. When the current density is 0.1A/g, the first Coulombic efficiency is 50%, and the capacity is still 665mAh/g after 100 cycles. Compared with the SnO ₂ /C composite material, phosphorus The cycle performance after thawing has been improved. Figure 8 shows the cycle performance of the composite material at a current density of 1A/g. The first discharge specific smelting is 1767mAh/g, and it continues to rise after a period of capacity decay. It has a specific capacity of 920mAh/g at 500 cycles. Compared with SnO ₂ /C composite material, the capacity is significantly higher.

Example 2

This embodiment relates to a preparation method of a tin/tin phosphide/carbon composite material, comprising the following steps:

Step 1, cross-linking reaction: 2 g of sodium alginate was dissolved in 198 ml of deionized water to prepare a solution with a mass fraction of 1%. Sodium chloride and crystalline tin tetrachloride with a molar ratio of 1:1 were dissolved in 500ml of deionized water to prepare a solution with a tin ion concentration of 0.10mol/L. Sodium alginate was slowly dropped into the metal ion aqueous solution, stirred for 36 hours, and waited for the cross-linking reaction to complete. The cross-linked product was rinsed with deionized water three times, then placed in a freeze dryer, and freeze-dried at -50°C for 24 hours.

Step 2, carbonization: transfer the freeze-dried sodium alginate pellets to a tube furnace, raise the temperature to 500°C at a rate of 5°C/min in a nitrogen atmosphere, and keep it warm for 1 hour to obtain a tin oxide/carbon composite Material.

Step 3, phosphating: After cleaning and drying the tin oxide/carbon composite material, mix it with sodium hypophosphite at a tin:phosphorus molar ratio of 1:2, grind it by hand for 15 minutes, place it in a tube furnace, and place it in an inert Under the atmosphere, the temperature was raised to 200°C at a rate of 5°C/min, and kept for 15 minutes. Use the dilute hydrochloric acid cleaning of deionized water and 0.05mol/L, then vacuum dry 12 hours, obtain tin/tin phosphide/carbon composite material.

Implementation effect: the material prepared according to the above method retains the porous characteristics and nanometer size characteristics. Take 0.1g of the composite material, add the composite material, conductive carbon black, and binder (the composition is polyvinylidene fluoride PVDF dissolved in NMP in N-methylpyrrolidone NMP, the mass concentration is 0.02g) with a mass ratio of 8:1:1 /ml) was stirred to form a slurry, and the slurry was evenly spread on the copper foil, and after drying, it was cut into circular electrode sheets with a diameter of 11 mm, dried and weighed. In a glove box with an argon atmosphere with a water oxygen content lower than 0.5ppm, with metal sodium as the counter electrode, glass fiber as the diaphragm, and 1mol/L sodium perchlorate solution (solvent is carbonic acid with a volume ratio of 1:1) Vinyl ester and propylene carbonate) as the electrolyte, and the electrode sheets were assembled into a CR2032 half-cell. Charge-discharge, cyclic voltammetry, and AC impedance tests were performed on the half-cell. The composite material exhibits good electrochemical performance.

Example 3

This embodiment relates to a preparation method of a tin/tin phosphide/carbon composite material, comprising the following steps:

Step 1, cross-linking reaction: 3 g of sodium alginate was dissolved in 147 ml of deionized water to prepare a solution with a mass fraction of 2%. Sodium chloride and crystalline tin tetrachloride with a molar ratio of 5:1 were dissolved in 500ml of deionized water to prepare a solution with a tin ion concentration of 0.2mol/L. Sodium alginate was slowly dropped into the aqueous solution of metal ions, stirred and reacted for 48 hours, and waited for the complete completion of the cross-linking reaction. The cross-linked product was rinsed three times with deionized water, then placed in a freeze dryer, and freeze-dried at -70°C for 72 hours.

Step 2, carbonization: transfer the freeze-dried sodium alginate pellets to a tube furnace, raise the temperature to 1200°C at a rate of 10°C/min in a nitrogen atmosphere, and keep it warm for 1 hour to obtain a tin oxide/carbon composite Material.

Step 3, phosphating: After cleaning and drying the tin oxide/carbon composite material, mix it with sodium hypophosphite at a tin:phosphorus molar ratio of 1:10, grind it by hand for 30 minutes, place it in a tube furnace, and place it in an inert Under the atmosphere, the temperature was raised to 400°C at a rate of 10°C/min, and kept for 30 minutes. Use the dilute hydrochloric acid cleaning of deionized water and 0.05mol/L, then vacuum dry 12 hours, obtain tin/tin phosphide/carbon composite material.

Implementation effect: the material prepared according to the above method retains the porous characteristics and nanometer size characteristics. Take 0.1g of the composite material, add the composite material, conductive carbon black, and binder (the composition is polyvinylidene fluoride PVDF dissolved in NMP in N-methylpyrrolidone NMP, the mass concentration is 0.02g) with a mass ratio of 8:1:1 /ml) was stirred to form a slurry, and the slurry was evenly spread on the copper foil, and after drying, it was cut into circular electrode sheets with a diameter of 11 mm, dried and weighed. In a glove box with an argon atmosphere with a water oxygen content lower than 0.5ppm, metal potassium is used as the counter electrode, glass fiber is used as the diaphragm, and 1mol/L potassium hexafluorosilicate solution (solvent volume ratio 1:1) Ethylene carbonate and propylene carbonate) were used as the electrolyte, and the electrode sheets were assembled into a CR2032 half-cell. Charge-discharge, cyclic voltammetry, and AC impedance tests were performed on the half-cell. The composite material exhibits good electrochemical performance.

Specific embodiments of the present invention have been described above. It should be understood that the present invention is not limited to the specific embodiments described above, and those skilled in the art may make various changes or modifications within the scope of the claims, which do not affect the essence of the present invention.

Claims (7)

1. a preparation method for the tin/tin phosphide/carbon composite material of alkali metal ion battery negative pole, is characterized in that, described method comprises the steps: S1, using sodium alginate and tetravalent tin ions to perform a cross-linking reaction to generate a gel; S2. The gel is freeze-dried and then calcined and carbonized in an inert atmosphere to obtain a tin oxide/carbon composite material; S3. Using sodium hypophosphite to phosphate the tin oxide/carbon composite material under an inert atmosphere to obtain the tin/tin phosphide/carbon composite material; In step S1, the cross-linking reaction is carried out under the condition of adding sodium ions as inhibitors; In step S1, sodium chloride with a tin:sodium molar ratio of 1:1 to 5 is added as an inhibitor; the crosslinking reaction time is 24h to 48h; In step S3, the phosphating method is specifically: under an inert atmosphere, using sodium hypophosphite as a phosphorus source, and phosphating at 200-400° C. for 5-30 minutes at a heating rate of 5-10° C. per minute; In step S3, the structure of the tin/tin phosphide/carbon composite material is specifically: 3-5nm metal components are evenly distributed in the carbon matrix, and surrounded by multiple layers of graphitized carbon layers. 2. the preparation method of the tin/tin phosphide/carbon composite material that is used for alkali metal ion battery negative pole according to claim 1, is characterized in that, in step S1, sodium alginate is dissolved in water, is mixed with mass concentration 1-2% sol, and then drop the sodium alginate sol into the tin tetrachloride solution with a concentration of 0.1-0.2mol/L to carry out the cross-linking reaction. 3. the preparation method of the tin/tin phosphide/carbon composite material that is used for alkali metal ion battery negative pole according to claim 1, is characterized in that, in step S1, the G segment in sodium alginate is gulose Aldehydic acid and tetravalent tin ions undergo a spontaneous cross-linking reaction to form a gel, forming a uniform "egg-box" structure in sodium alginate. 4. the preparation method of the tin/tin phosphide/carbon composite material that is used for alkali metal ion battery negative electrode according to claim 1, is characterized in that, in step S2, described freeze-drying is after cleaning with deionized water The gel was freeze-dried at -70～-50°C for 1-3 days. 5. the preparation method of the tin/tin phosphide/carbon composite material that is used for alkali metal ion battery negative electrode according to claim 1, is characterized in that, in step S2, described carbonization method is specifically: under the protection of inert atmosphere Calcining for 1-2 hours under the condition of 500-1200° C. at a heating rate of 5-10° C. per minute. 6. the preparation method of the tin/tin phosphide/carbon composite material that is used for alkali metal ion battery negative pole according to claim 1, is characterized in that, step S3 comprises before phosphating that the mol ratio of tin and phosphorus is 1: 2-1:10 tin oxide/carbon composite material and sodium hypophosphite are ground and mixed, and the grinding and mixing time is 15-30 minutes. 7. the preparation method of the tin/tin phosphide/carbon composite material that is used for alkali metal ion battery negative electrode according to claim 1, is characterized in that, in step S3, uses deionized water and 0.05mol successively after phosphating is finished /L of dilute hydrochloric acid, and then vacuum-dried for 12 to 24 hours.

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