Patent ID: 12206094

DETAILED DESCRIPTION

The concepts and technical effects of the present disclosure are clearly and completely described below in conjunction with examples, so as to allow the objectives, features and effects of the present disclosure to be fully understood. Apparently, the described examples are merely some rather than all of the examples of the present disclosure. All other examples obtained by those skilled in the art based on the examples of the present disclosure without creative efforts should fall within the protection scope of the present disclosure.

Example 1

In this example, a silicon-carbon composite was prepared through the following specific steps:S1. Housings of scrapped LIBs were removed, positive and negative electrode sheets were separated, and about 500 g of negative electrode sheets were collected for later treatment; and recovered negative electrode sheets were crushed for 15 min at a rotational speed of 34,000 r/min, and then sieved through a 300-mesh sieve such that copper foil and a graphite anode powder were separated to obtain about 380 g of graphite anode powder.S2. The 380 g of graphite anode powder was added to a 5 mol/L sulfuric acid solution, and a resulting mixture was stirred for 6 h and then subjected to SLS to remove residual metal ions; a resulting solid precipitate was repeatedly washed with deionized water and absolute ethanol until a resulting filtrate was neutral (pH=7), and then dried at 60° C. for 12 h to obtain about 300 g of a graphite material; the obtained graphite material was thoroughly mixed with 0.5% (0.5% of a mass of the graphite material) of coke, and a resulting mixture was placed in a furnace; nitrogen was first introduced into the furnace to replace air in the furnace, then a furnace temperature was increased, and when the temperature reached 300° C., chlorine was introduced instead of nitrogen; and heat treatment was conducted at 900° C. for 5 h in a chlorine atmosphere to obtain 240 g of a purified graphite material.S3. SCA kh570 (γ-methacryloxypropyltrimethoxysilane, manufacturer: Nanjing Reagent) was hydrolyzed with an aqueous acetic acid solution at pH=4; 100 g of a silicon powder was taken and added to a 200 ml beaker, and hydrolyzed kh570 was added at an amount 1.2% of the mass of the silicon powder; and a resulting mixture was subjected to ultrasonic dispersion for 5 min and then to a reaction at 80° C. for 10 h in an oven to obtain a modified silicon powder.S4. The graphite material obtained in S2 was added to 35 g of the modified silicon powder obtained in S3 to obtain a mixed material; 35 g of PI was dissolved in 350 ml of DMF to obtain a transparent and colorless solution without residue; and the mixed material was added to the transparent and colorless solution, and a resulting mixture was subjected to high-speed dispersion for 5 h and then to vacuum distillation to remove DMF to obtain a powder.S5. The powder obtained in S4 was sieved through a 300-mesh sieve, heated to 600° C. in a nitrogen atmosphere to undergo carbonization for 6 h, then naturally cooled to room temperature, and taken out to obtain the silicon-carbon composite anode material.

Example 2

In this example, a silicon-carbon composite was prepared through the following specific steps:S1. Housings of scrapped LIB s were removed, positive and negative electrode sheets were separated, and about 500 g of negative electrode sheets were collected for later treatment; and recovered negative electrode sheets were crushed for 15 min at a rotational speed of 34,000 r/min, and then sieved through a 300-mesh sieve such that copper foil and a graphite anode powder were separated to obtain about 380 g of graphite anode powder.S2. The 380 g of graphite anode powder was added to a 5 mol/L sulfuric acid solution, and a resulting mixture was stirred for 4 h and then subjected to SLS to remove residual metal ions; a resulting solid precipitate was repeatedly washed with deionized water and absolute ethanol until a resulting filtrate was neutral (pH=7), and then dried at 70° C. for 10 h to obtain about 300 g of a graphite material; the obtained graphite material was thoroughly mixed with 1% (1% of a mass of the graphite material) of coke, and a resulting mixture was placed in a furnace; nitrogen was first introduced into the furnace to replace air in the furnace, then a furnace temperature was increased, and when the temperature reached 300° C., chlorine was introduced instead of nitrogen; and heat treatment was conducted at 1,100° C. for 3 h in a chlorine atmosphere to obtain 236.4 g of a purified graphite material.S3. SCA kh560 (γ-glycidoxypropyltrimethoxysilane) was hydrolyzed with an aqueous acetic acid solution at pH=4; 100 g of a silicon powder was taken and added to a 200 ml beaker, and hydrolyzed kh560 was added at an amount 1.6% of the mass of the silicon powder; and a resulting mixture was subjected to ultrasonic dispersion for 8 min and then to a reaction at 90° C. for 10 h in an oven to obtain a modified silicon powder.S4. The graphite material obtained in S2 was added to 30 g of the modified silicon powder obtained in S3 to obtain a mixed material; 30 g of PI was dissolved in 350 ml of DMF to obtain a transparent and colorless solution without residue; and the mixed material was added to the transparent and colorless solution, and a resulting mixture was subjected to high-speed dispersion for 5 h and then to vacuum distillation to remove DMF to obtain a powder.S5. The powder obtained in S4 was sieved through a 300-mesh sieve, heated to 800° C. in a nitrogen atmosphere to undergo carbonization for 4 h, then naturally cooled to room Temperature, and Taken Out to Obtain the Silicon-Carbon Composite Anode Material.

Comparative Example 1

In this comparative example, a silicon-carbon composite was prepared, and a preparation process was different from Example 1 mainly in that the pickling step was omitted. The preparation process specifically included the following steps:S1. Housings of scrapped LIBs were removed, positive and negative electrode sheets were separated, and about 500 g of negative electrode sheets were collected for later treatment; and recovered negative electrode sheets were crushed for 15 min at a rotational speed of 34,000 r/min, and then sieved through a 300-mesh sieve such that copper foil and a graphite anode powder were separated to obtain about 380 g of graphite anode powder.S2. The 380 g of graphite anode powder was thoroughly mixed with 0.5% (0.5% of a mass of the graphite material) of coke, and a resulting mixture was placed in a furnace; nitrogen was first introduced into the furnace to replace air in the furnace, then a furnace temperature was increased, and when the temperature reached 300° C., chlorine was introduced instead of nitrogen; and heat treatment was conducted at 900° C. for 5 h in a chlorine atmosphere to obtain a purified graphite material.S3. SCA kh570 (γ-methacryloxypropyltrimethoxysilane, manufacturer: Nanjing Reagent) was hydrolyzed with an aqueous acetic acid solution at pH=4; 100 g of a silicon powder was taken and added to a 200 ml beaker, and hydrolyzed kh570 was added at an amount 1.2% of the mass of the silicon powder; and a resulting mixture was subjected to ultrasonic dispersion for 5 min and then to a reaction at 80° C. for 10 h in an oven to obtain a modified silicon powder.S4. The graphite material obtained in S2 was added to 35 g of the modified silicon powder obtained in S3 to obtain a mixed material; 35 g of PI was dissolved in 350 ml of DMF to obtain a transparent and colorless solution without residue; and the mixed material was added to the transparent and colorless solution, and a resulting mixture was subjected to high-speed dispersion for 5 h and then to vacuum distillation to remove DMF to obtain a powder.S5. The powder obtained in S4 was sieved through a 300-mesh sieve, heated to 600° C. in a nitrogen atmosphere to undergo carbonization for 6 h, then naturally cooled to room temperature, and taken out to obtain the silicon-carbon composite anode material.

COMPARATIVE EXAMPLE 2

In this comparative example, a silicon-carbon composite was prepared, and a preparation process was different from Example 2 mainly in that commercial graphite was used instead of the recovered graphite material. The preparation process specifically included the following steps:S1. SCA kh560 was hydrolyzed with an aqueous acetic acid solution at pH=4; 100 g of a silicon powder was taken and added to a 200 ml beaker, and hydrolyzed kh560 was added at an amount 1.6% of the mass of the silicon powder; and a resulting mixture was subjected to ultrasonic dispersion for 8 min and then to a reaction at 90° C. for 8 h in an oven to obtain a modified silicon powder.S2. 300 g of a commercial graphite powder was taken and added to 30 g of the modified silicon powder obtained in the above step to obtain a mixed material; 35 g of PI was dissolved in 350 ml of DMF to obtain a transparent and colorless solution without residue; and the mixed material was added to the transparent and colorless solution, and a resulting mixture was subjected to high-speed dispersion for 5 h and then to vacuum distillation to remove DMF to obtain a powder.S3. The powder obtained in S2 was sieved through a 300-mesh sieve, heated to 800° C. in a nitrogen atmosphere and kept at the temperature for 4 h, then naturally cooled to room temperature, and taken out to obtain the silicon-carbon composite anode material.

Test Example

Button batteries were prepared from the silicon-carbon composite anode materials obtained in the examples and comparative examples, and electrical tests were conducted, which were specifically as follows:

Each of the silicon-carbon composite anode materials prepared in Examples 1 and 2 and Comparative Examples 1 and 2, conductive black carbon, and polyvinylidene fluoride (PVDF) were mixed in a mass ratio of 92:2:6, an appropriate amount of N-methylpyrrolidone (NMP) was added, and a resulting mixture was stirred for a specified time to obtain an anode slurry; the slurry was uniformly coated on copper foil and dried at 85° C. for a specified time, and then the electrode sheet was punched; the punched electrode sheet was vacuum-dried at 100° C. for 12 h in a vacuum drying oven; the electrode sheet, diaphragm, lithium sheet, electrolyte, positive and negative cases were assembled in a specified order in a glove box to obtain a CR2430 button battery; and the assembled battery stood for 3 h for test.

The battery was tested under the following conditions: room temperature: 25° C., charging and discharging voltage: 0.01 V to 2.0 V, and current density: 100 mA/g. Test results were shown in Table 1.

TABLE 1Comparison of electrochemical performanceamong the examples and comparative examplesSpecificSpecificcapacitycapacityfor the firstfor the firstCapacitylithiumlithiumInitial chargeretentionintercalationdeintercalationand dischargeafter 50(mAh/g)(mAh/g)efficiency/%cycles/%Example 1706.1569.880.795.9Example 2673.7540.380.295.7Comparative567.6428.075.486.8Example 1Comparative670.2575.980.496.2Example 2

It can be seen from Table 1 that the composites prepared in Examples 1 and 2 had a specific capacity of 670 mAh/g to 750 mAh/g for the initial lithium intercalation, a specific capacity of 520 mAh/g to 600 mAh/g for the initial lithium deintercalation, an initial charge and discharge efficiency of 80% to 81%, and a capacity retention of 95% to 97% after 50 cycles. Compared with Example 1, Comparative Example 1 had no pickling step, and a prepared silicon-carbon anode material had a high impurity content and a low capacity. In Comparative Example 2, because commercial graphite was used as a raw material, the prepared silicon-carbon anode material had a high capacity, a high initial charge and discharge efficiency, and a capacity retention of 96.2% after 50 cycles, which was slightly higher than that of the silicon-carbon composite anode material prepared from recovered graphite in Example 1, without an obvious performance advantage. The silicon-carbon anode material prepared from an anode material recovered from a scrapped LIB negative electrode in the present disclosure had excellent performance. It shows that the method for preparing a silicon-carbon composite anode material using a scrapped LIB negative electrode in the present disclosure has high feasibility.

FIG.1is an SEM image of the silicon-carbon composite prepared in Example 1, and it can be seen from the image that nano-silicon particles are uniformly dispersed in the silicon-carbon composite prepared in Example 1.FIG.2shows cycling performance curves of the silicon-carbon composites prepared in Examples 1 and 2 and Comparative Examples 1 and 2 at a current density of 100 mA/g, and it can be seen from the figure that the silicon-carbon composite prepared in Example 1 has prominent cycling stability, high cycling performance, and a capacity retention of 95.9% after 50 cycles, which shows no significant performance difference from the product prepared from commercial graphite in Comparative Example 2 and has promising application prospects.

The examples of present disclosure are described in detail with reference to the accompanying drawings, but the present disclosure is not limited to the above examples. Within the scope of knowledge possessed by those of ordinary skill in the technical field, various changes can also be made without departing from the purpose of the present disclosure. In addition, the examples in the present disclosure or features in the examples may be combined with each other in a non-conflicting situation.