CN112652740B

CN112652740B - Electrode material composition and preparation method and application thereof

Info

Publication number: CN112652740B
Application number: CN201910958937.2A
Authority: CN
Inventors: 彭茜; 林伟国; 涂志强; 余伟发; 荣峻峰; 杜泽学
Original assignee: Sinopec Research Institute of Petroleum Processing; China Petroleum and Chemical Corp
Current assignee: Sinopec Research Institute of Petroleum Processing; China Petroleum and Chemical Corp
Priority date: 2019-10-10
Filing date: 2019-10-10
Publication date: 2022-10-21
Anticipated expiration: 2039-10-10
Also published as: CN112652740A

Abstract

The invention provides an electrode material composition and a preparation method and application thereof, the electrode material composition comprises a silicon-carbon composite material with the content not less than 80wt% and nano-silver with the content not more than 5wt%, wherein the silicon-carbon composite material is a three-level coated silicon-carbon composite material and is obtained through the following steps: crushing and dealloying the silicon-based alloy to obtain micron silicon powder; dispersing micron silicon powder in a solution containing a first carbon source, and crushing to obtain primary coated nano silicon slurry; mixing the nano silicon slurry with a second carbon source, uniformly stirring, drying and roasting to obtain a secondary coated precursor; and carrying out chemical vapor deposition on the precursor in a third carbon source atmosphere to obtain the three-stage coated silicon-carbon composite material. By compounding the nano silver and the silicon-carbon composite material with the three-layer carbon coating layer, the charging and discharging specific capacity of the battery is effectively improved, the utilization rate of the battery is improved, the cycling stability of the electrode material is improved to a certain extent, and the electrode material has good comprehensive performance.

Description

Electrode material composition and preparation method and application thereof

Technical Field

The invention relates to the technical field of electrode materials, in particular to an electrode material composition and a preparation method and application thereof.

Background

Currently, various carbon materials such as natural graphite, artificial graphite, soft carbon, hard carbon, and the like are used for commercial lithium ion battery electrodes. The carbon material has good cycle performance, conductive performance and coulombic efficiency, but is limited by the theoretical specific capacity (372 m Ah/g) of the carbon material, so that the requirement of the market on high-capacity battery materials cannot be met. Silicon-based lithium ion battery materials are among the most promising high-capacity electrode materials due to their high theoretical capacity (4200 mAh/g) and relatively modest de-intercalation potential (< 0.5V). However, except for the fact that the silicon is easy to be pulverized due to too large volume expansion in charge-discharge cycles, the silicon has conductivity (intrinsic conductivity of only 6.7 multiplied by 10) as a semiconductor material ^－4 S/cm) is far less than the carbon material having excellent conductivity (intrinsic conductivity of graphite is about 1.0 × 10) ³ S/cm). The silicon-carbon composite material has both high lithium storage capacity and good cycle performance, and is considered to be one of the most promising high-capacity electrode materials for power batteries in the next 5-10 years.

The active or inactive substance with good conductivity and small volume change is added as a buffer matrix, so that the problem of volume expansion of the silicon active substance can be reduced, and the long-term stability of the battery is further improved. Silver is a metal conductive material, is the best conductive material in nature, and has the conductivity as high as 63 multiplied by 10 ⁶ S/cm is very suitable for improving the conductivity of the silicon-carbon composite material and reducing the internal resistance of the battery, and the silver has good ductility and can relieve the expansion and pulverization of silicon in charge-discharge cycles, so that the multiplying power, the cycle life and the charge-discharge specific capacity of the lithium ion battery are optimized. At present, the method for preparing nano silver comprises a gas phase method, a solid phase method and a liquid phase method. The liquid phase chemical reduction method is often adopted in industry to prepare the metal silver nano particles, and the process is simple and the parameters are easy to control.

In the existing literature, research on improving the performance of a battery material by adopting a composite nano silver method has been reported, for example, patent CN102544438 discloses a method for manufacturing a nano silver powder-doped lithium titanate electrode, the nano silver powder of the method is modified by the lithium titanate electrode instead of a silicon-carbon electrode, the addition amount of the nano silver powder is large, and the description of the particle size and the morphology of the nano silver powder is lacked; CN101262062A discloses a lithium ion electrode material composition and a preparation method of a battery, wherein the method mentions that nano silver powder can be used as a conductive agent, but the influence of the nano silver on a silicon-carbon negative electrode material is not specifically researched; CN108336311A discloses a preparation method of a silver particle doped silicon-carbon negative electrode material, which comprises grinding silicon powder, performing carbon coating, and doping silver particles on the surface of the coating layer through the reduction property of dopamine.

It is noted that the information disclosed in the foregoing background section is only for enhancement of background understanding of the invention and therefore it may contain information that does not constitute prior art that is already known to a person of ordinary skill in the art.

Disclosure of Invention

The invention aims to overcome at least one defect in the prior art and provides an electrode material composition and a preparation method and application thereof.

In order to achieve the purpose, the invention adopts the following technical scheme:

one aspect of the present invention provides an electrode material composition comprising a silicon carbon composite material in an amount of not less than 80wt% and nano silver in an amount of not more than 5wt%, preferably, not more than 2wt%. The silicon-carbon composite material is a three-level coated silicon-carbon composite material and is obtained through the following steps: crushing and dealloying the silicon-based alloy to obtain micron silicon powder; dispersing micron silicon powder in a solution containing a first carbon source, and crushing to obtain primary coated nano silicon slurry; mixing the nano silicon slurry with a second carbon source, uniformly stirring, drying and roasting to obtain a secondary coated precursor; and carrying out chemical vapor deposition on the precursor in a third carbon source atmosphere to obtain the three-stage coated silicon-carbon composite material.

According to one embodiment of the present invention, the silicon content of the silicon-carbon composite material is 10wt% to 30wt%, and the carbon content is 70wt% to 90wt%.

According to one embodiment of the present invention, the silicon-carbon composite material comprises silicon-carbon microspheres having three carbon coating layers and a silicon core, and the particle size of the silicon-carbon microspheres is 10 μm to 35 μm.

According to one embodiment of the invention, the silicon-based alloy is a silicon-aluminum alloy, a silicon-iron alloy or a silicon-copper alloy, and the silicon content in the silicon-based alloy is 40wt% to 80wt%.

According to one embodiment of the invention, the first carbon source is selected from one or more of citric acid, glucose and polyvinylpyrrolidone, the second carbon source is a mixture of graphite and pitch, and the third carbon source is selected from one or more of acetylene, methane, ethanol, ethylene.

According to one embodiment of the present invention, the nano silver has a particle size of 20nm to 60nm.

According to one embodiment of the present invention, the electrode material composition further includes a binder and a conductive additive, wherein the binder is present in an amount of 1wt% to 10wt% of the electrode material composition, and the conductive additive is present in an amount of 0.1wt% to 5wt% of the electrode material composition.

According to one embodiment of the present invention, the binder is selected from one or more of styrene-butadiene rubber, polyacrylate, polyvinylidene fluoride and polytetrafluoroethylene, and the conductive additive is selected from one or more of conductive graphite, acetylene black and carbon nanotubes.

A second aspect of the present invention provides a method for preparing an electrode material composition, comprising the steps of:

mixing silver nitrate and a part of protective agent according to the mass ratio of (0.05-0.5) to 1, adding the mixture into water to prepare silver nitrate solution; mixing a reducing agent and the other part of protective agent according to the mass ratio of (0.05-0.5) to 1, and adding the mixture into water to prepare a reducing base solution; dripping silver nitrate solution into the reduction base solution for reaction to obtain nano silver; mixing the nano silver and the silicon-carbon composite material, and uniformly stirring to obtain an electrode material composition; wherein the protective agent is selected from one or more of polyvinylpyrrolidone and polyvinyl alcohol.

According to one embodiment of the invention, the reducing agent is selected from one or more of ascorbic acid, glucose, ammonium formate and sodium borohydride; the molar ratio of the reducing agent to the silver nitrate is 1:4 to 4:1.

according to one embodiment of the invention, the concentration of the silver nitrate solution is 35 g/L-60 g/L, and the concentration of the reduction base solution is 40 g/L-100 g/L.

According to an embodiment of the present invention, the method further comprises adding an auxiliary reducing solution to the reducing base solution to allow the reaction to proceed at a pH of 8 to 10.5, wherein the auxiliary reducing solution is one or more selected from the group consisting of a sodium hydroxide solution and an aqueous ammonia solution.

According to one embodiment of the invention, the dropping rate is 0.5mL/min to 4mL/min, the reaction temperature is 20 ℃ to 50 ℃, and the stirring rate in the reaction is 200r/min to 1000r/min.

According to one embodiment of the invention, the nano silver and silicon carbon composite material is firstly stirred for 5min to 30min at the speed of 50r/min to 350r/min and then stirred for 1h to 5h at the speed of 350r/min to 2000 r/min.

The third aspect of the invention provides the application of the electrode material composition as an electrode plate of a lithium ion battery.

According to the technical scheme, the electrode material composition and the preparation method thereof have the advantages and positive effects that:

according to the electrode material composition provided by the invention, the nano silver and the novel silicon-carbon composite material with the three-layer carbon coating layer are compounded, so that the charging and discharging specific capacity and the battery utilization rate of the material are integrally improved when the material is used for a battery. According to the preparation method of the electrode material composition, the specific protective agent is adopted in the preparation process of the nano silver, so that the obtained nano silver is not easy to agglomerate and has better dispersibility. Meanwhile, the prepared nano silver particles are particularly suitable for the micron-sized silicon-carbon composite microspheres with three carbon coating layers, the gaps of the micron-sized silicon-carbon material are fully utilized, the conductivity is improved, the volume effect problem of the silicon material can be relieved, and the cycling stability of the battery is improved.

Drawings

The accompanying drawings, which are included to provide a further understanding of the invention and are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and together with the description serve to explain the principles of the invention and not to limit the invention.

FIG. 1 is a scanning electron microscope image of primary coated nano-silicon obtained in step (2) of preparation example 1;

FIGS. 2a and 2b are scanning electron micrographs at different magnifications of the silicon-carbon composite material of preparation example 1, respectively;

FIG. 3 is an XRD spectrum of a silicon carbon composite material of preparation example 1;

FIG. 4 shows the SEM topography of the nano-silver obtained in example 1;

FIG. 5 shows the EDX spectrum of the nano-silver obtained in example 1;

FIG. 6 shows an SEM topography of the electrode sheet obtained in example 2;

fig. 7 shows an EDX energy spectrum of the electrode sheet obtained in example 2;

fig. 8 shows first-cycle charge and discharge graphs after the electrode tabs obtained in examples 1 and 2, and comparative examples 1 and 2, respectively, were mounted in a battery.

Detailed Description

The following presents various embodiments, or examples, in order to enable one of ordinary skill in the art to practice the invention with reference to the description herein. These are, of course, merely examples and are not intended to limit the invention. The endpoints of the ranges and any values disclosed in the present application are not limited to the precise range or value and should be understood to encompass values close to these ranges or values. For ranges of values, between the endpoints of each of the ranges and the individual points, and between the individual points may be combined with each other to yield one or more new ranges of values, which ranges of values should be considered as specifically disclosed herein.

One aspect of the invention provides an electrode material composition, which comprises a silicon-carbon composite material with the content of not less than 80wt% and nano-silver with the content of not more than 5wt%, wherein the silicon-carbon composite material is a three-level coated silicon-carbon composite material and is obtained through the following steps: crushing and dealloying the silicon-based alloy to obtain micron silicon powder; dispersing the micron silicon powder in a solution containing a first carbon source, and crushing to obtain first-class coated nano silicon slurry; mixing the nano silicon slurry with a second carbon source, uniformly stirring, drying and roasting to obtain a secondary coated precursor; and carrying out chemical vapor deposition on the precursor in a third carbon source atmosphere to obtain the three-stage coated silicon-carbon composite material.

According to the invention, nano silver is used as a metal conductive material, and although the nano silver is reported to be compounded into an electrode material to improve the conductivity, the nano silver has no ideal effect on performance improvement. This is probably because, firstly, due to the limitations of the preparation method and the nature of the nano-silver itself, it is easy to agglomerate, and the dispersibility is not good in practical application, so that it is difficult to stably exist in the material to achieve the ideal effect; secondly, the structure of the active material compounded with the nano silver also has the effect of improving the overall performance. The inventor of the invention finds that stable nano silver particles with proper particle size and morphology characteristics are synthesized by adopting a specific method, and are dispersed into a micron-sized silicon-carbon composite microsphere material, so that the internal resistance of a silicon-carbon electrode plate can be reduced, the electrochemical properties of the battery such as charge-discharge specific capacity, conductivity, rate capability and the like can be effectively improved, and the utilization rate of the battery can be improved.

In some embodiments, the particle size of the nano silver is 20nm to 60nm, the silicon content of the silicon-carbon composite material can reach 10wt% to 30wt%, and the carbon content is 70wt% to 90wt%. The tap density of the silicon-carbon composite material is 0.8g cm ^-3 ～0.9g cm ^-3 The silicon-carbon microsphere comprises silicon-carbon microsphere particles with three carbon coating layers, the median particle size is 10-35 mu m, and the nano silver can be just filled into gaps among the micron-sized silicon-carbon microspheres, so that electrons generated in the charging and discharging process can be rapidly transferred out, and the silicon-carbon microsphere particles have good ductility,the problem of volume effect of the silicon material is alleviated, and the charge and discharge capacity of the battery material is further excavated, so that the purposes of improving the conductivity and optimizing the performance of the battery are achieved.

In some embodiments, the electrode material composition further comprises a binder and a conductive additive, wherein the binder accounts for 1wt% to 10wt% of the electrode material composition, and the conductive additive accounts for 0.1wt% to 5wt% of the electrode material composition. The binder includes, but is not limited to, styrene butadiene rubber, polyacrylate, polyvinylidene fluoride, polytetrafluoroethylene, etc., the conductive additive includes, but is not limited to, conductive graphite, acetylene black, carbon nanotubes, etc., and in addition, a thickening agent, such as carboxymethyl cellulose, etc., may also be added to adjust the material properties according to actual needs, to which the invention is not limited.

As mentioned above, the silicon carbon composite material of the present invention also has good properties by itself. The inventor of the invention finds that the silicon-carbon composite material obtained by using silicon-based alloy as a raw material to perform dealloying and nanocrystallization on prepared nano silicon and then compounding the nano silicon with a carbon material can effectively relieve the problem of silicon volume expansion. Furthermore, the invention further improves the structural reliability of the whole material by constructing a three-level buffering carbon coating structure on the obtained nano silicon on the basis, so that the material can still keep the structure intact in long-term cyclic use, and cannot collapse due to the expansion of silicon, thereby ensuring the cyclic stability of the material. Wherein, the primary coating is in-situ coating in the process of further crushing the micron silicon powder; the secondary coating is further mixed and stirred with a solution containing a carbon source and roasted at high temperature on the basis of in-situ coating, so that a carbon coating layer on the silicon surface is more compact, and the tap density and the reliability of the material are further improved; and finally, performing three-stage coating by a chemical vapor deposition method to ensure that the carbon layer on the surface of the material is more uniform and compact. The three-level coated silicon-carbon composite material obtained by the method effectively improves the long-cycle stability, and the capacity retention rate can reach over 90 percent after 100 cycles. More importantly, the method can still ensure the performances of high capacity, first coulombic efficiency and the like of the battery, and simultaneously the tap density can also be kept at a higher level, so that the method has good comprehensive performance.

The preparation method of the silicon-carbon composite material of the present invention is further described as follows:

in some embodiments, the aforementioned silicon-based alloy is a silicon-aluminum alloy, a silicon-iron alloy, or a silicon-copper alloy, preferably a silicon-aluminum alloy or a silicon-iron alloy, and more preferably a silicon-aluminum alloy. Wherein the silicon content in the silicon-based alloy is 40wt% to 80wt%, optionally 50wt% to 80wt%.

In some embodiments, the silicon-based alloy is preferably comminuted by ball milling, wherein a shielding gas, such as one or more of nitrogen or argon, is added during the ball milling process. The rotation speed of the ball mill can be 200 rpm-500 rpm, the ball milling time is 12 h-24 h, and the ball mass ratio is 10. Under this condition, the silicon-based alloy can be more favorably pulverized.

And finally, performing acid etching on the silicon-based alloy chips subjected to ball milling to remove alloying, thereby obtaining the micron silicon powder. Wherein the acid selected in the acid etching process can react with the active metal in the silicon-based alloy but can not react with silicon. The acid can be hydrochloric acid, alkene sulfuric acid (concentration less than 3mol L) ^-1 ) Or alkene nitric acid. When the acid is hydrochloric acid, it may be concentrated hydrochloric acid, with a concentration of about 28mol/L, but will react violently, giving off a large amount of hydrogen and heat; or dilute hydrochloric acid with the concentration of 1mol L ^-1 ～3mol L ^-1 . When the silicon-based alloy is a silicon-aluminum alloy or a silicon-iron alloy, preferably, the acid etching is performed using hydrochloric acid.

Compared with nano silicon prepared by other methods, the nano silicon prepared by dealloying the silicon-based alloy as the raw material has fewer impurities and low cost. In addition, the micron silicon powder obtained after the alloying removal by acid etching has a certain pore structure and is easier to crush, so that the subsequent silicon nanocrystallization is facilitated.

In some embodiments, the micro silicon powder obtained after dealloying is dispersed in a solution containing a first carbon source and then subjected to a crushing treatment to obtain a primary coated nano silicon slurry. Specifically, the first carbon source is an organic carbon source, preferably one or more of citric acid, glucose and polyvinylpyrrolidone (PVP), and preferably, sodium carboxymethylcellulose (CMC) may also be added as a binder, so that the organic carbon source is better coated on the silicon surface. The first carbon source accounts for 50-120 wt% of the content of the micron silicon powder.

In some embodiments, the solvent in the solution containing the first carbon source is selected from one or more of ethanol, isopropanol, and n-heptane. In some embodiments, the nano silicon slurry is obtained by grinding and pulverizing. In-situ coating of silicon is performed in the sanding process, and the carbon layer is favorably reduced from being oxidized by air through the isolation of an organic solvent, so that a better carbon coating layer is obtained.

In some embodiments, the sanding speed is 1800 rpm-2500 rpm, the sanding time is 240 min-720 min, and the solid content of the sanding process is maintained at 5wt% -15 wt%. Under the condition, the micron silicon powder can be further and better ground and crushed, and the average particle size of the nano silicon obtained by the treatment of the method is 2 nm-150 nm. In addition, in some embodiments, the sanding process described above is purged with argon or nitrogen as a shielding gas to prevent oxidation of the carbon layer during sanding.

According to the invention, the primary coated nano silicon slurry obtained by the method is subjected to secondary coating. Specifically, the nano silicon slurry and a second carbon source are mixed, uniformly stirred, dried and roasted to obtain a secondary coated precursor.

In some embodiments, the second carbon source is a mixture of graphite and pitch, wherein the graphite can be spheroidal graphite, flake graphite, and the like, preferably spheroidal graphite, and the spheroidal graphite has a tap density of 0.8g cm ^-3 ～1.1g cm ^-3 The median particle size is 10-25 μm; the softening point of the asphalt is 200-300 ℃, and the average grain diameter of the asphalt is 1-5 mu m. By adopting graphite and asphalt to be mixed as a second carbon source for coating, on one hand, the adhesiveness of asphalt after pyrolysis and carbonization in the high-temperature process can be utilized, and the carbon layer can be better coated on the molecular level, and on the other hand, the good conductivity of graphite is combined, so that the overall conductivity of the silicon-carbon composite material is improved, and the tap density is also favorably improved.

In some embodiments, the pitch to graphite mass ratio is 1 (3-5), which primarily serves as a cladding and binding function in the composite material due to the small contribution of pitch to the contrast capacity. The specific capacity of the finally obtained composite material is greatly reduced due to excessive addition of the asphalt; the asphalt addition is too small, and the coating and bonding effects are poor. Therefore, the mass ratio is preferably as described above.

In some embodiments, the solid content of the nano-silicon slurry mixed with the second carbon source is 10wt% to 15wt%, wherein the solid content refers to the mass percentage of the asphalt, the graphite and the primary coated nano-silicon in the mixed slurry.

In some embodiments, the mass ratio of nanosilicon to graphite is 1. Specifically, since the volume of liquid and the mass of solid added during sanding are determined, the solid content of nano silicon in the slurry after sanding can be calculated (only the mass of micro silicon is calculated, and carbon sources used for carbon coating are not included). The actual mass of nano silicon in the slurry (nano silicon changed after the micro silicon is sanded, and no carbon source is contained) is calculated by measuring the volume of the slurry in the following compounding process. The mass ratio of the nano silicon to the graphite is controlled by controlling the volume of the measured liquid and the mass of the added graphite.

In some embodiments, firing is performed under a non-oxidizing atmosphere, e.g., under an argon or nitrogen atmosphere, at a temperature of 700 ℃ to 900 ℃. Preferably, the calcination comprises at 3 ℃ min ^-1 ～5℃·min ^-1 Heating to 250-350 deg.C at a heating rate, pre-carbonizing, maintaining for 1-3 h to melt asphalt, and cooling at 5 deg.C/min ^-1 ～10℃·min ^-1 The temperature is raised to 700-900 ℃ at the heating rate, the temperature is kept for 2-4 h, and then the silicon-carbon composite material is naturally cooled to room temperature, thus obtaining the secondary coated silicon-carbon composite material precursor.

According to the invention, the obtained secondary coated silicon-carbon composite material precursor is subjected to chemical vapor deposition in a third carbon source atmosphere to obtain a tertiary coated silicon-carbon composite material.

In some embodiments, the third carbon source is selected from one or more of acetylene, methane, ethanol, ethylene, preferably acetylene. Acetylene is used as a vapor deposition carbon source, which is more beneficial to forming a graphitized carbon layer and improving the electrical property of the material. In some embodiments, the third carbon source has a flow rate of 100sccm to 200sccm. The deposition temperature of the chemical vapor deposition is 700-900 ℃, and the deposition time is 10-30 min. Under the conditions, a uniform and compact graphitized carbon layer is further formed on the precursor, and the three-stage coated silicon-carbon composite material is obtained.

According to the preparation method of the silicon-carbon composite material, the cost of raw materials is low, the process is simple, and the large-scale production is easy. The obtained silicon-carbon composite material effectively improves the long cycle stability while ensuring the high capacity and the first coulombic efficiency of the battery by constructing the multi-layer buffer coating layer, and simultaneously the tap density can be kept at a higher level, so that the silicon-carbon composite material has good comprehensive performance, is applied to an electrode material of a lithium ion battery, and has good industrial prospect.

The second aspect of the present invention provides a method for preparing an electrode material composition, comprising the steps of:

firstly, silver nitrate solution and reduction base solution are respectively prepared, and protective agents are added into the silver nitrate solution and the reduction base solution. Specifically, silver nitrate and a part of protective agent are mixed and added into water according to the mass ratio of (0.05-0.5) to 1 to prepare a silver nitrate solution; the reducing agent and the same protective agent are mixed and added into water according to the mass ratio of (0.05-0.5) to 1 to prepare the reducing base solution. By adding a certain proportion of protective agent into the silver nitrate and the reduction base solution, the prepared nano silver particles are not easy to agglomerate and have better dispersibility.

In some embodiments, the foregoing protective agent is selected from one or more of polyvinylpyrrolidone and polyvinyl alcohol. The reducing agent is selected from one or more of ascorbic acid, glucose, ammonium formate and sodium borohydride; the molar ratio of the reducing agent to the silver nitrate is 1. The concentration of the silver nitrate solution is 35 g/L-60 g/L, and the concentration of the reduction base solution is 40 g/L-100 g/L.

Then, dropwise adding a silver nitrate solution into the reduction base solution for reaction to obtain nano silver; specifically, the silver nitrate solution is firstly added into the reduction base solution at a dropping rate of 0.5mL/min to 4mL/min, and after all the silver nitrate solution is added, the solution is continuously kept to react for a period of time, for example, the reaction time is about 5 minutes. The temperature is kept between 20 and 50 ℃ in the reaction process, and the stirring speed in the reaction is between 200 and 1000r/min. After the reaction is finished, carrying out solid-liquid separation, washing and drying, for example, carrying out vacuum filtration liquid-solid separation, and washing the precipitate for three times respectively by using deionized water and ethanol; drying the precipitate in a vacuum drying oven at 40 ℃ for 8-10h, grinding and sieving to obtain the nano silver particles with the required particle size.

In some embodiments, the method further comprises adding an auxiliary reducing solution to the reduction base solution during the reaction so that the reaction is carried out at a pH value of 8-10.5, wherein the auxiliary reducing solution is selected from one or more of sodium hydroxide solution and ammonia solution. Taking preparation of the alkene ammonia water as an example, 2ml of 28% concentrated ammonia water is diluted by 7 times with 6ml of deionized water to prepare a 4% diluted ammonia water solution for later use, and when a silver nitrate solution is dripped into the reduction base solution, the pH value of the reduction base solution can be adjusted by using the alkene ammonia water solution while dripping.

Next, the obtained nano silver is mixed with the prepared silicon-carbon composite material coated with three layers of carbon, and further, the auxiliary conductive additive, the binder, the thickener, and the like may be added and mixed together. After mixing, stirring was carried out. In some embodiments, the electrode material composition of the invention can be obtained by firstly stirring at a speed of 50r/min to 350r/min for 5min to 30min, then stirring at a speed of 350r/min to 2000r/min for 1h to 5h, wherein when the thickening agent does not fully wrap the silicon carbon particles, the initial rotation speed is too high, which easily destroys the colloid stability of the thickening agent, so that the slurry is not easy to form a film, and after the silicon carbon composition and the thickening agent are uniformly mixed, the rotation speed is further increased, and the obtained slurry is more stable and uniform. The composition can be used as an electrode plate to assemble a lithium ion battery through further steps of film coating, tabletting and the like.

In conclusion, the electrode material composition obtained by the method is compounded by adopting the nano silver and the silicon-carbon composite material with the three-layer carbon coating layer, so that the charge-discharge specific capacity and the battery utilization rate of the material are integrally improved when the material is used for a battery. According to the preparation method of the electrode material composition, the specific protective agent is adopted in the preparation process of the nano silver, so that the obtained nano silver is not easy to agglomerate and has better dispersibility. Meanwhile, the prepared nano silver particles are particularly suitable for the micron-sized silicon-carbon composite microspheres with three carbon coating layers, the gaps of the micron-sized silicon-carbon material are fully utilized, the conductivity is improved, the volume effect problem of the silicon material can be relieved, the cycling stability of the battery is improved, and the nano silver particle has a good industrial application prospect.

The invention will be further illustrated by the following examples, but is not to be construed as being limited thereto. Unless otherwise specified, all reagents used in the invention are analytically pure.

The scanning electron microscope adopted by the invention is a German Zeiss scanning electron microscope (Zeiss Supra 55), and is provided with an EDAX energy spectrum analyzer.

The test conditions were: fixing the powder sample on a sample table through conductive adhesive, wherein the accelerating voltage is 20kV, and the magnification is 1000-20000.

The X-ray diffraction (XRD) adopted by the invention is a Japan Shimadzu X-ray diffractometer (XRD-6000), and the test conditions are as follows: the Cu target is subjected to Kalpha rays (the wavelength is lambda =0.154 nm), the tube voltage is 40KV, the tube current is 200mA, and the scanning speed is 10 degrees (2 theta)/min when the 2 theta scanning range is 20-80 degrees.

Preparation example 1

This preparation example is used to illustrate the preparation method of the silicon-carbon composite material used in the present invention.

(1) Putting 50g of Al-Si alloy block (with Si content of 60 wt%) into a ball milling tank, putting a stainless steel grinding ball according to the ball-material mass ratio of 15 to 1, introducing nitrogen as a protective gas, and then carrying out ball milling for 24 hours at a rotating speed of 200rpm to obtain Al-Si alloy powder. Adding Al-Si alloy powder to the mixture with the concentration of 1mol L ^-1 Etching in hydrochloric acid, filtering, washing, and drying at 50 ℃ in vacuum to obtain micron silicon powder;

(2) Dissolving 100g of citric acid in 2L of isopropanol, adding 100g of the micron silicon powder prepared in the step (2), ultrasonically mixing uniformly, pouring into a sand mill dispersion tank, sanding at 2300rpm for 8 hours under the protection of nitrogen, and taking out to obtain citric acid coated nano silicon slurry;

(3) Putting 14g of spherical graphite and 4g of asphalt into 150mL of the slurry prepared in the step (2), uniformly stirring and mixing, drying, and finally heating at 3 ℃ for min in an argon atmosphere ^-1 Heating to 300 deg.C, maintaining for 2 hr to melt asphalt, and heating at 5 deg.C for 5min ^-1 Heating to 800 ℃, preserving heat for 3h, and naturally cooling to room temperature to obtain a silicon-carbon composite material precursor;

(4) Taking 1g of the silicon-carbon composite material precursor prepared in the step (3) under the nitrogen atmosphere for 10 ℃ min ^-1 And raising the temperature to 800 ℃, then changing acetylene gas to deposit for 20min at the flow of 150sccm, then changing nitrogen gas to naturally cool to room temperature, and obtaining the silicon-carbon composite material. Wherein, the mass proportion of the nano silicon in the composite material is 25 percent, and the mass proportion of the carbon in the composite material is 75 percent.

Material characterization:

the silicon-aluminum alloy raw material is silver and has the length of about 1-5cm. Fig. 1 is a scanning electron microscope image of the primarily coated nano-silicon obtained in step (2) of preparation example 1, and as shown in fig. 1, a sheet structure of about 80nm can be observed. FIGS. 2a and 2b are scanning electron micrographs at different magnifications of the silicon-carbon composite material obtained in preparation example 1, respectively, as shown in FIGS. 2a and 2b, which are of a spheroidal structure with particle sizes mainly concentrated between 10-20 μm.

Fig. 3 is an XPS spectrum of the silicon-carbon composite material of preparation example 1, which shows that the silicon-carbon composite material corresponds to characteristic peaks of silicon at positions of 28.55 °, 47.44 °, and 56.12 ° 2 θ, and is characteristic peaks of graphite at positions of 26.38 °, 42.22 °, 44.39 °, 54.54 °, 59.69 °, and 77.24 ° 2 θ, as shown in fig. 3. It can be seen that the silicon-carbon composite material of the present invention is prepared by the foregoing method.

Example 1

This example is intended to illustrate the preparation method of the electrode material composition of the present invention and the preparation of an electrode sheet using the electrode material composition.

(1) 2g of silver nitrate and 0.2g of polyvinylpyrrolidone (PVP) are weighed and dissolved in 25ml of deionized water to prepare 80g/L of silver nitrate solution.

(2) 1.1g of ascorbic acid and 0.2g of polyvinylpyrrolidone (PVP) are weighed and dissolved in 25ml of deionized water to prepare 40g/L ascorbic acid reduction base solution containing a dispersing agent. The molar ratio of ascorbic acid to silver nitrate is approximately 1.

(3) 2ml of 28 percent strong ammonia water is diluted by 7 times by 6ml of deionized water to prepare 4 percent weak ammonia water solution for later use.

(4) Dropwise adding the silver nitrate solution prepared in the step (1) into the reduction base solution prepared in the step (2) at a constant speed, finishing the dropwise adding within about 10min and 30s, and adjusting the pH of the reduction base solution to be within the range of 8 +/-0.5 by using the diluted ammonia water solution prepared in the step (3) while dropwise adding; after the addition of the silver nitrate solution, the reaction solution was kept for another 5 minutes.

(5) Carrying out vacuum filtration on the solution obtained in the step (4) for liquid-solid separation, and cleaning precipitates for three times by using deionized water and ethanol respectively; drying the precipitate in a vacuum drying oven at 40 deg.C for 8-10h, grinding, and sieving with 325 mesh sieve to obtain nanometer silver particles with average particle diameter of 37 nm. Wherein, fig. 4 shows an SEM topography of the nano silver, and fig. 5 shows an energy spectrum of the nano silver particle.

(6) Mixing the silicon-carbon composite material obtained in the preparation example 1, the nano silver obtained in the step (5), the carboxymethyl cellulose and the styrene-butadiene rubber in a proportion of 92:1:4:3, stirring the mixture at a low speed of 150r/min for 15min, and then stirring the mixture at a high speed of 1500r/min for 3h.

(7) And (4) respectively coating the electrode material composition obtained in the step (6) with a film thickness of 100 mu m, and drying the film at 70 ℃ in vacuum for 5h. The dried film was tabletted and transferred to a glove box of the UN-Lab type (O) ₂ ＜1ppm、H ₂ O is less than 1 ppm) to form the button cell. The negative electrode adopts a lithium sheet (purity)>99.9%), the positive electrode is the prepared silicon-carbon pole piece, the electrolyte adopts 1.0mol/L lithium hexafluorophosphate non-aqueous electrolyte, the solvent is a mixed solution of EC + DMC + DEC (volume ratio 1.

Example 2

An electrode material composition was prepared by the method of example 1, except that acetylene black was further added to the mixture in step (6), that is, the silicon-carbon composite material of example 1, the nano silver obtained in step (5), the acetylene black, the carboxymethyl cellulose, and the styrene-butadiene rubber were mixed in a ratio of 92:1:1:4:2, and stirring to obtain the electrode material composition and the electrode sheet. Fig. 6 shows the SEM topography of the electrode sheet obtained in example 2, and fig. 7 shows the SEM energy spectrum of the electrode sheet obtained in example 2.

Comparative example 1

An electrode material composition and an electrode sheet were prepared by the method of example 1, except that nano silver was not added, that is, a silicon carbon active material, acetylene black, carboxymethyl cellulose, and styrene butadiene rubber were mixed in a ratio of 92:2:4:2, stirring the mixture at a low speed of 150r/min for 30min, and then stirring the mixture at a high speed of 1500r/min for 3h.

Comparative example 2

An electrode material composition was prepared by the method of example 1, except that a protective agent was not added in step (1) and step (2).

Test example

And (3) carrying out an electrical property test on the silicon-carbon button cell prepared from the electrode material composition under the test conditions of constant current charging and discharging and the test current of 100 muA. The electrical property results are shown in table 1 below.

TABLE 1

As can be seen from the above table 1, the invention can improve the conductivity of the electrode plate, reduce the internal resistance of the battery, improve the charge-discharge specific capacity of the battery to a certain extent and improve the utilization rate of the battery by adding a very small amount of nano silver powder.

Fig. 8 shows first-cycle charge-discharge graphs after the electrode tabs obtained in examples 1 and 2, and comparative examples 1 and 2, respectively, were mounted in a battery. As can be seen from fig. 8, the first cycle charge/discharge capacity of the battery containing silver nanoparticles was improved. In addition, the electrode plate obtained by adopting the silicon-carbon composite material has an effect obviously superior to that of electrode plates prepared by other materials. As can be seen from the comparative example 2, the nano silver prepared without the protective agent has the advantages that the charging specific capacity of the electrode plate prepared by using the nano silver is improved, but the first coulombic efficiency of the electrode plate is obviously reduced, and the dispersibility of the nano silver plays an important role in improving the material performance.

According to the invention, stable nano silver particles with proper particle size and morphology characteristics are synthesized by a specific method and dispersed into the micron-sized silicon-carbon composite microsphere material, so that the internal resistance of a silicon-carbon electrode plate can be reduced, the electrochemical performances of the battery such as charge-discharge specific capacity, conductivity, rate capability and the like are effectively improved, and the utilization rate of the battery is improved. In addition, the special silicon-carbon microsphere particles with three carbon coating layers adopted by the invention are used as electrode active substances, have good electrochemical performance, can be just filled into gaps among the micron-sized silicon-carbon microspheres by utilizing the size of nano silver, so that electrons generated in the charging and discharging process are quickly transferred out, the problem of volume effect of a silicon material is alleviated through good ductility of the silicon material, and the charging and discharging capacity of the battery material is further excavated, thereby achieving the purposes of improving the conductivity and optimizing the battery performance.

It should be noted by those skilled in the art that the described embodiments of the present invention are merely exemplary and that various other substitutions, alterations, and modifications may be made within the scope of the present invention. Accordingly, the present invention is not limited to the above-described embodiments, but is only limited by the claims.

Claims

1. The electrode material composition is characterized by comprising a silicon-carbon composite material with the content not less than 80wt% and nano silver with the content not more than 5wt%, wherein the silicon-carbon composite material is a three-level coated silicon-carbon composite material and is obtained through the following steps:

crushing and dealloying the silicon-based alloy to obtain micron silicon powder;

dispersing the micron silicon powder in a solution containing a first carbon source, and crushing to obtain primary coated nano silicon slurry;

mixing the nano silicon slurry with a second carbon source, uniformly stirring, drying and roasting to obtain a secondary coated precursor;

performing chemical vapor deposition on the precursor in a third carbon source atmosphere to obtain the three-level coated silicon-carbon composite material;

the nano silver is obtained through the following steps:

mixing silver nitrate and a part of protective agent according to the mass ratio of (0.05-0.5) to 1, adding the mixture into water to prepare silver nitrate solution;

mixing a reducing agent and the other part of protective agent according to the mass ratio of (0.05-0.5) to 1, and adding the mixture into water to prepare a reducing base solution;

dropwise adding the silver nitrate solution into the reduction base solution for reaction to obtain the nano silver;

wherein the first carbon source is one or more selected from citric acid, glucose and polyvinylpyrrolidone, the second carbon source is a mixture of graphite and asphalt, the protective agent is one or more selected from polyvinylpyrrolidone and polyvinyl alcohol, and the reducing agent is one or more selected from ascorbic acid, glucose, ammonium formate and sodium borohydride.

2. The electrode material composition as claimed in claim 1, wherein the silicon-carbon composite has a silicon content of 10wt% to 30wt% and a carbon content of 70wt% to 90wt%.

3. The electrode material composition as claimed in claim 1, wherein the silicon-carbon composite material comprises silicon-carbon microspheres having three carbon coating layers and a silicon core, and the particle size of the silicon-carbon microspheres is 10 μm to 35 μm.

4. The electrode material composition as claimed in claim 1, wherein the silicon-based alloy is a silicon-aluminum alloy, a silicon-iron alloy or a silicon-copper alloy, and the silicon content in the silicon-based alloy is 40-80 wt%.

5. The electrode material composition of claim 1, wherein the third carbon source is selected from one or more of acetylene, methane, ethanol, and ethylene.

6. The electrode material composition according to claim 1, wherein the nano silver has a particle size of 20nm to 60nm.

7. The electrode material composition as claimed in claim 1, further comprising a binder and a conductive additive, wherein the binder is present in an amount of 1 to 10wt% and the conductive additive is present in an amount of 0.1 to 5wt% based on the electrode material composition.

8. The electrode material composition as claimed in claim 7, wherein the binder is selected from one or more of styrene-butadiene rubber, polyacrylate, polyvinylidene fluoride and polytetrafluoroethylene, and the conductive additive is selected from one or more of conductive graphite, acetylene black and carbon nanotubes.

9. A method for producing the electrode material composition according to any one of claims 1 to 8, characterized by comprising the steps of:

and mixing the nano silver and the silicon-carbon composite material, and uniformly stirring to obtain the electrode material composition.

10. The method according to claim 9, wherein the molar ratio of the reducing agent to the silver nitrate is 1:4 to 4:1.

11. the method according to claim 9, wherein the silver nitrate solution has a concentration of 35 to 60g/L, and the reducing base solution has a concentration of 40 to 100g/L.

12. The preparation method according to claim 9, further comprising adding an auxiliary reducing solution to the reducing bottom solution to perform the reaction at a pH of 8 to 10.5, wherein the auxiliary reducing solution is selected from one or more of a sodium hydroxide solution and an aqueous ammonia solution.

13. The preparation method according to claim 9, wherein the dropping rate is 0.5mL/min to 4mL/min, the reaction temperature is 20 ℃ to 50 ℃, and the stirring rate in the reaction is 200r/min to 1000r/min.

14. The preparation method of claim 9, wherein the nano silver and the silicon-carbon composite material are firstly stirred at a speed of 50r/min to 350r/min for 5min to 30min and then stirred at a speed of 350r/min to 2000r/min for 1h to 5h.

15. Use of the electrode material composition according to any one of claims 1 to 8 as an electrode sheet for a lithium ion battery.