Disclosure of Invention
The invention aims to overcome the defects and provide the phosphorus-silver-silicon co-doped hard carbon composite material with ion conductivity and first efficiency and improved cycle performance.
The invention further aims at providing a preparation method of the phosphorus-silver-silicon co-doped hard carbon composite material.
The phosphorus-silver-silicon co-doped hard carbon composite material has a core-shell structure, wherein the core is silver, phosphorus and silicon doped hard carbon, the shell is composed of amorphous carbon and lithium salt compound, and the shell accounts for 1-10wt% calculated by 100% of the composite material by mass.
The invention discloses a preparation method of a phosphorus-silver-silicon co-doped hard carbon composite material, which comprises the following steps:
step S1: silver powder is prepared according to the mass ratio: red phosphorus: nano silicon = 1-5:10:1-5, adding micrometer silicon into a high-energy ball mill, grinding for 12-72 hours to obtain nanometer silicon with the particle size of 100-200nm, continuously adding red phosphorus, grinding silver powder into the ball mill for 12-72 hours, and vacuum drying at 80 ℃ for 24 hours to obtain a silver/phosphorus/silicon composite material;
step S2, resin according to mass ratio: organic solvent: silver/phosphorus/silicon composite = 100:500-1500:1-10, dissolving resin in an organic solvent, adding a silver/phosphorus/silicon composite material, performing ultrasonic dispersion (the ultrasonic frequency is 25KHz, the dispersion speed is 5000r/min, the dispersion time is 60 min), obtaining a precursor material through spray drying (the air inlet temperature is 200 ℃, the flow is 60mL/min, and the air outlet temperature is 80 ℃), transferring the precursor material into a tube furnace, and carbonizing for 1-6h at the temperature of 600-1000 ℃ under inert atmosphere to obtain the amorphous carbon coated silver/phosphorus/silicon composite material;
step S3, coating the silver/phosphorus/silicon composite material according to the mass ratio of amorphous carbon: binder = 100:1-10, mixing and pressing the amorphous carbon coated silver/phosphorus/silicon composite material with a binder to form a block structure, taking a saturated calomel electrode as a working electrode, simultaneously preparing 0.1mol/L of lithium difluorodioxalate phosphate ethylene carbonate, depositing lithium salt on the surface of the working electrode by an electrochemical deposition method, washing 1-5 times by adopting 1mol/L of hydrochloric acid after the deposition time is 10-120min, drying in vacuum at 80 ℃ for 24h, and carbonizing at 700-1000 ℃ for 1-6h to obtain the phosphorus-silver-silicon co-doped hard carbon composite material.
The preparation method of the phosphorus-silver-silicon co-doped hard carbon composite material comprises the following steps: the resin in the step S2 is one of phenolic resin, furfural resin or epoxy resin; the organic solvent is one of chloroform, toluene, acetone or xylene.
The preparation method of the phosphorus-silver-silicon co-doped hard carbon composite material comprises the following steps: the binder in the step S2 is one of polyvinyl alcohol, polyacrylic acid, polytetrafluoroethylene, polyvinylidene fluoride or sodium carboxymethyl cellulose.
The preparation method of the phosphorus-silver-silicon co-doped hard carbon composite material comprises the following steps: the electrochemical deposition method in the step S3 is one of a cyclic voltammetry, a constant voltage method, a constant current method or a pulse method; the cyclic voltammetry parameter is-2V, 0.5-5mV/S, and the constant voltage parameter is 2V; constant current method of 1-10mA/cm2 。
Compared with the prior art, the invention has obvious beneficial effects, and the technical scheme can be adopted as follows: according to the invention, the silver powder is doped in red phosphorus to improve electronic conductivity, the silicon powder improves energy density, and meanwhile, the advantages of the red phosphorus material such as high energy density, high first efficiency, low cost and the like are brought into play to prepare the composite, and the surface of the composite is coated with the hard carbon precursor to improve the energy density and power performance of the hard carbon material. Lithium salt is deposited on the surface of the hard carbon precursor material by an electrochemical deposition method, so that the ionic conductivity and the first efficiency of the material are improved, and the cycle performance is improved. And the preparation process is simple, the cost is low, and the method is suitable for industrial production.
Detailed Description
Example 1:
a preparation method of a phosphorus-silver-silicon co-doped hard carbon composite material comprises the following steps:
step S1: adding 3g of micrometer silicon into a high-energy ball mill, grinding for 48 hours to obtain nanometer silicon with the particle size of 150nm, adding 10g of red phosphorus, 3g of silver powder and 500g of ethanol, grinding for 48 hours in the ball mill, and vacuum drying for 24 hours at 80 ℃ to obtain a silver/phosphorus/silicon composite material;
step S2, dissolving 100g of phenolic resin in 1000g of chloroform, adding 5g of silver/phosphorus/silicon composite material, performing ultrasonic dispersion (the ultrasonic frequency is 25KHz, the dispersion speed is 5000r/min, the dispersion time is 60 min), obtaining a precursor material through spray drying (the air inlet temperature is 200 ℃, the flow is 60mL/min, and the air outlet temperature is 80 ℃), transferring the precursor material into a tubular furnace, and carbonizing for 3 hours at the temperature of 800 ℃ under the inert atmosphere of argon to obtain the amorphous carbon coated silver/phosphorus/silicon composite material;
and S3, mixing and pressing 100g of amorphous carbon coated silver/phosphorus/silicon composite material and 5g of polyvinyl alcohol to form a block structure, taking a saturated calomel electrode as a working electrode, simultaneously preparing 0.1mol/L of ethylene carbonate of lithium difluorodioxalate phosphate, depositing lithium salt on the surface of the working electrode by cyclic voltammetry at the voltage range of-2V-2V and the scanning speed of 1mV/S, washing 3 times by adopting 1mol/L of hydrochloric acid for 60min, drying in vacuum at 80 ℃ for 24h, and carbonizing at 800 ℃ for 3h to obtain the phosphorus-silver-silicon co-doped hard carbon composite material.
Example 2
A preparation method of a phosphorus-silver-silicon co-doped hard carbon composite material comprises the following steps:
step S1: adding 1g of micrometer silicon into a high-energy ball mill, grinding for 12 hours to obtain nanometer silicon with the particle size of 100nm, adding 10g of red phosphorus, 1g of silver powder and 500g of ethanol, grinding for 12 hours in the ball mill, and vacuum drying for 24 hours at 80 ℃ to obtain a silver/phosphorus/silicon composite material;
step S2, 100g of phenolic resin is dissolved in 500g of toluene organic solvent, 1g of silver/phosphorus/silicon composite material is added and ultrasonic dispersion is carried out (the ultrasonic frequency is 25KHz, the dispersion speed is 5000r/min, the dispersion time is 60 min), a precursor material is obtained through spray drying (the air inlet temperature is 200 ℃, the flow is 60mL/min, and the air outlet temperature is 80 ℃), the precursor material is transferred into a tube furnace, and the precursor material is carbonized for 6 hours at 600 ℃ under the inert atmosphere of argon, so that the amorphous carbon coated silver/phosphorus/silicon composite material is obtained;
and step S3, mixing and pressing 100g of amorphous carbon coated silver/phosphorus/silicon composite material and 1g of polyacrylic acid binder to form a block structure, taking a saturated calomel electrode as a working electrode, simultaneously preparing 0.1mol/L of lithium difluorophosphate ethylene carbonate, depositing lithium salt on the surface of the working electrode by an electrochemical deposition method for 10min, washing 1 time by adopting 1mol/L of hydrochloric acid, drying in vacuum at 80 ℃ for 24h, and carbonizing at 700 ℃ for 6h to obtain the phosphorus-silver-silicon co-doped hard carbon composite material.
Example 3
A preparation method of a phosphorus-silver-silicon co-doped hard carbon composite material comprises the following steps:
step S1: adding 5g of micrometer silicon into a high-energy ball mill, grinding for 72 hours to obtain nanometer silicon with the particle size of 200nm, adding 10g of red phosphorus, 5g of silver powder and 500g of ethanol, grinding for 72 hours in the ball mill, and drying at 80 ℃ in vacuum for 24 hours to obtain a silver/phosphorus/silicon composite material;
step S2, dissolving 100g of furfural resin in 1500g of xylene organic solvent, adding 10g of silver/phosphorus/silicon composite material, performing ultrasonic dispersion (the ultrasonic frequency is 25KHz, the dispersion speed is 5000r/min, the dispersion time is 60 min), obtaining a precursor material through spray drying (the air inlet temperature is 200 ℃, the flow is 60mL/min, and the air outlet temperature is 80 ℃), transferring the precursor material into a tubular furnace, and carbonizing for 1h at the temperature of 1000 ℃ under an argon inert atmosphere to obtain the amorphous carbon coated silver/phosphorus/silicon composite material;
and step S3, mixing and pressing 100g of amorphous carbon coated silver/phosphorus/silicon composite material and 10g of polyvinylidene fluoride to form a block structure, taking a saturated calomel electrode as a working electrode, simultaneously preparing 0.1mol/L of lithium difluorophosphate carbonate as a counter electrode, depositing lithium salt on the surface of the working electrode by a constant voltage method (voltage is 2V), depositing for 120min, washing 5 times by 1mol/L of hydrochloric acid, drying in vacuum at 80 ℃ for 24h, and carbonizing at 1000 ℃ for 1h to obtain the phosphorus-silver-silicon co-doped hard carbon composite material.
Comparative example 1:
a method of preparing a composite material comprising the steps of:
except for the difference from example 1, red phosphorus was not added, and silver powder was otherwise the same as in example 1.
Comparative example 2:
a preparation method of a phosphorus-silver-silicon co-doped hard carbon composite material comprises the following steps:
the amorphous carbon coated silver/phosphorus/silicon composite material prepared in the step S2 in the example 1 is adopted and transferred into a tube furnace, and carbonized for 3 hours at 800 ℃ to obtain the phosphorus-silver-silicon co-doped hard carbon composite material.
Experimental example:
performance testing of the materials prepared in examples 1-3 and comparative examples 1-2 above:
(1) SEM test
SEM test was conducted on the phosphorus-silver-silicon co-doped hard carbon composite material prepared in example 1, and the test results are shown in FIG. 1. As can be seen from fig. 1, the hard carbon composite material prepared in example 1 has a spherical structure, and has a uniform size distribution and a particle size of 1-5 μm.
(2) Physical and chemical properties and button cell testing
The phosphorus-silver-silicon co-doped hard carbon composite materials prepared in examples 1-3 and comparative examples 1-2 were tested for particle size, tap density, specific surface area, interlayer spacing, trace element content (phosphorus-silver-silicon), powder resistivity, and powder OI values. The trace element content is tested by EDS, the interlayer spacing is tested by XRD, and other test projects are tested according to the method of national standard GBT-24533-2019 lithium ion battery graphite cathode material. The test results are shown in Table 1.
TABLE 1
The phosphorus-silver-silicon co-doped hard carbon composite materials in the examples 1-3 and the comparative examples 1-2 are used as the anode materials of the lithium ion batteries to be assembled into button batteries, and the specific preparation method of the anode materials is as follows: adding binder, conductive agent and solvent into the composite material, stirring to slurry, coating on copper foil, oven drying, and rolling. The adhesive is LA132 adhesive, the conductive agent SP, the solvent is secondary distilled water, and the composite material is prepared from the following components: SP: LA132: secondary distilled water = 90g:3g:7g:220mL, preparing a negative electrode plate; a metal lithium sheet is used as a counter electrode; the electrolyte adopts LiPF6 EC+DEC, liPF in electrolyte6 The electrolyte is a mixture of EC and DEC with the volume ratio of 1:1, and the concentration of the electrolyte is 1.3mol/L; the diaphragm adopts a polyethylene PE film. The button cell assembly was performed in an argon filled glove box. Electrochemical performance was performed on a wuhan blue electric CT2001A type battery tester with a charge-discharge voltage ranging from 0.00V to 2.0V and a charge-discharge rate of 0.1C, and the button cell was tested for first discharge capacity and first efficiency, while the rate performance (2C, 0.1C) and cycle performance (0.2C/0.2C, 200 times) were tested. The test results are shown in Table 2.
TABLE 2
As can be seen from table 1 and table 2, the material prepared by the embodiment of the invention has high specific capacity and first efficiency, and is characterized in that the hard carbon material is filled with phosphorus, silver and silicon to improve the electronic conductivity and the multiplying power; meanwhile, the silver material has the characteristic of high tap density, the tap density of the material is improved, silver has a catalytic effect, a hard carbon material with high interlayer spacing can be generated in the carbonization process of the material, and the rate capability is improved; while silicon has a high specific capacity boost energy density.
(3) Soft package battery test:
the phosphorus-silver-silicon co-doped hard carbon composite materials in examples 1-3 and comparative examples 1-2 were subjected to slurry mixing and coating to prepare a negative electrode sheet, and a ternary material (LiNi1/3 Co1/3 Mn1/3 O2 ) As positive electrode, with LiPF6 (the solvent is EC+DEC, the volume ratio is 1:1, the electrolyte concentration is 1.3 mol/L) is taken as electrolyte, and a Celgard2400 membrane is taken as a diaphragm, so that the 2Ah soft-package battery is prepared.
The rate performance of the soft package battery is tested, the charging and discharging voltage ranges from 2.5V to 4.2V, the temperature is 25+/-3.0 ℃, the charging is carried out at 1.0C, 3.0C, 5.0C and 10.0C, and the discharging is carried out at 1.0C. The results are shown in Table 3.
TABLE 3 Table 3
As can be seen from table 3, the rate charging performance of the soft pack batteries prepared from the materials of examples 1 to 3 is significantly better than that of comparative examples 1 to 2, i.e., the charging time is shorter, because of the analysis: lithium ions are required to migrate in the battery charging process, and silver with high electronic conductivity is doped in the hard carbon of the negative electrode material in the embodiment to reduce impedance, and meanwhile, the large interlayer spacing of the material in the embodiment improves the rate capability and constant current ratio.
(4) And (3) testing the cycle performance:
the cycle performance test conditions were: the charge and discharge current is 3C/3C, the voltage range is 2.5-4.2V, and the cycle times are 500. The test results are shown in Table 4.
TABLE 4 Table 4
It can be seen from Table 4 that the cycle performance of the lithium ion batteries prepared using the composite materials obtained in examples 1 to 3 was significantly better than that of the comparative example. The reason is that the composite material is doped with silver and filled in the hard carbon pores, so that the side reaction of the material and the electrolyte is reduced, the first efficiency of the material and the compatibility of the material and the electrolyte can be improved, and the cycle performance is improved. Meanwhile, the doped silver has the characteristic of low electronic impedance, so that side reaction in the charge and discharge process is reduced, the cycle performance is improved, and lithium is doped in the material to provide sufficient lithium ions, so that the cycle performance is improved.
The foregoing disclosure is illustrative of the present invention and is not to be construed as limiting the scope of the invention, which is defined by the appended claims.