High-capacity silicon-based composite lithium battery negative electrode material and preparation method thereof
Technical Field
The invention belongs to the field of lithium ion battery materials, and particularly relates to a high-capacity silicon-based composite lithium battery negative electrode material and a preparation method thereof.
Background
The lithium ion battery is a high and new technology product, is a novel high-capacity long-life environment-friendly battery at the same time, is composed of a positive electrode plate, a negative electrode plate and a solid electrolyte, has excellent performance, and is mainly used in various fields such as electric bicycles, electric automobiles, electric tools of electric motorcycles, solar photovoltaic and wind power generation energy storage systems, intelligent power grid energy storage systems, mobile communication base stations, electric power, chemical engineering, hospital standby UPS, EPS power supplies, security and protection illumination, portable mobile power supplies, notebook computers, electric toys, mine safety equipment, digital products and the like. Compared with nickel-cadmium and nickel-hydrogen batteries, the lithium ion battery has the advantages of high voltage, large specific energy, long cycle life, good safety performance, small self-discharge, no memory effect, rapid charge and discharge, wide working temperature range and the like.
At present, a graphite material is mainly used as a negative electrode material of a commercial lithium ion battery, the reversible specific capacity of the carbon material reaches 360mAh/g, but the theoretical specific capacity is only 372mAh/g, and the development of a future mobile power supply is difficult to meet. In order to further improve the energy density of the lithium ion battery, a novel high-specific-capacity negative electrode material becomes a hotspot of related researches. Silicon can form binary alloy with lithium, and has the advantages of rich storage capacity, high theoretical specific capacity, low intercalation and deintercalation lithium potential, low price and the like, thereby becoming a key point and a hotspot of the research of lithium ion batteries.
With the progress of research, it is found that silicon materials have the advantages of high capacity and low lithium extraction potential, but silicon has fatal defects as a negative electrode material of a lithium battery, and lithium ions are extracted from the positive electrode material and are inserted into crystal lattices in the silicon crystal during charging, so that the silicon crystal greatly expands. The volume change rate of the material reaches up to 300 percent, so that the material is pulverized in the charging and discharging process, the electrode structure is damaged, and the cycle performance is greatly reduced. Therefore, the existing solution is to make silicon nanocrystallized and effectively compound with carbon to buffer the volume change of silicon particles in the charging and discharging process, improve the conductivity of silicon and avoid the agglomeration phenomenon of silicon in the charging and discharging process. In the industrial development process, the cost for carrying out the nanocrystallization of the silicon is high, the final particle nano-scale of the silicon is limited, and the problem of volume expansion of the silicon in the charging and discharging process cannot be fundamentally solved. Therefore, the preparation of the silicon-carbon composite material with excellent performance by using other innovative silicon-carbon materials becomes an urgent task for developing high-capacity power batteries.
Disclosure of Invention
In view of the above, the present invention provides a high-capacity silicon-based composite lithium battery negative electrode material and a preparation method thereof, aiming to overcome the defects in the prior art.
In order to achieve the purpose, the technical scheme of the invention is realized as follows:
the utility model provides a silicon-based composite lithium electricity negative electrode material of high capacity, silicon-based composite lithium electricity negative electrode material obtains for passing through mechanical sanding's mode cladding with tin-based material behind silicon-based material surface.
Due to the ductility and the conductivity of the tin-based material, after mechanical sanding, the obtained mixture of the silicon-based material and the tin powder is in a nanometer level, and meanwhile, the tin-based material can be coated on the surface of the silicon-based material, so that the specific capacity of the cathode material is improved.
Preferably, the particle size of the negative electrode material after mechanical sanding is 10-20 nm.
Preferably, the surface of the tin-based material is further coated with an amorphous carbon coating layer, and the carbon content in the negative electrode material is 5% -10%.
The invention also provides a preparation method of the anode material, which comprises the following steps: fully mixing the silicon-based material and the tin powder, then mechanically sanding to obtain a mixture of the nanoscale silicon-based material and the tin powder, mixing the mixture with a carbon source, and calcining at high temperature to finally obtain the silicon-based composite lithium battery negative electrode material.
Preferably, the mass ratio of the silicon-based material to the tin powder is 1: 2-2: 1.
Preferably, the silicon-based material is silicon monoxide or silicon powder.
Preferably, the carbon source is one or a mixture of several of resin, pitch and coal tar.
Preferably, the carbon content in the finally obtained silicon-based composite lithium battery negative electrode material is 5% -10%.
Preferably, the mechanical sanding time is 10-30 h, and the particle size of the mixture is 10-20 nm.
Preferably, the calcination method is: and under the environment of inert atmosphere, heating to 480-800 ℃ at the speed of 5 ℃/min, and carrying out heat preservation calcination for 2-8 h after reaching the calcination temperature.
Compared with the prior art, the invention has the following advantages:
the preparation method of the negative electrode material is simple to operate, the required conditions are easy to achieve, the specific capacity of the lithium ion battery can be obviously improved, the cycle performance is improved, and the experimental result shows that: the specific capacity of the cathode material prepared by the invention can reach 1000mAh/g at most, and the capacity is not obviously attenuated after the cathode material is circulated for 50 weeks.
Drawings
Fig. 1 is an SEM photograph of the anode material obtained in example 1 of the present invention;
fig. 2 is an SEM photograph of the anode material obtained in example 2 of the present invention;
fig. 3 is an SEM photograph of the anode material obtained in example 3 of the present invention;
fig. 4 is an SEM photograph of the anode material obtained in comparative example 1 of the present invention;
fig. 5 is an SEM photograph of the anode material obtained in comparative example 2 of the present invention;
FIG. 6 is a graph comparing electrochemical performances of five materials obtained in examples 1 to 3 of the present invention and comparative examples 1 to 2.
Detailed Description
Unless defined otherwise, technical terms used in the following examples have the same meanings as commonly understood by one of ordinary skill in the art to which the present invention belongs. The test reagents used in the following examples, unless otherwise specified, are all conventional biochemical reagents; the experimental methods are conventional methods unless otherwise specified.
The invention will be described in detail with reference to the following examples.
Example 1
Weighing 30g of silicon monoxide and 60g of tin powder, uniformly mixing, placing in a sand mill, sanding for 10 hours at a speed of 500r/min in an argon atmosphere until the particle size is 10-20 nm, and obtaining a product c; and (3) uniformly mixing the product c with a proper amount of phenolic resin (according to the residual carbon content, ensuring that the carbon content in the finally prepared material is 5%), calcining in a tubular furnace under the argon atmosphere at the heating rate of 5 ℃/min, heating to 550 ℃, preserving heat for 4h, and naturally cooling to obtain the silicon-based composite lithium battery negative electrode material.
An SEM photograph of the negative electrode material obtained in example 1 is shown in fig. 1, an electrochemical performance chart is shown in fig. 6, and the specific capacity is 520 mAh/g. After sanding, nano-scale silicon monoxide or silicon and tin powder are uniformly mixed and carbonized with phenolic resin to form a stable silicon-carbon composite structure.
Example 2
Weighing 60g of silicon monoxide and 45g of tin powder, uniformly mixing, placing in a sand mill, sanding for 15 hours at a speed of 500r/min in an argon atmosphere until the particle size is 10-20 nm, and obtaining a product c; and (3) uniformly mixing the product c with a proper amount of phenolic resin (according to the residual carbon content, ensuring that the carbon content in the finally prepared material is 5%), calcining in a tubular furnace under the argon atmosphere at the heating rate of 5 ℃/min, heating to 480 ℃, preserving heat for 2 hours, and naturally cooling to obtain the silicon-based composite lithium battery negative electrode material.
An SEM photograph of the negative electrode material obtained in example 2 is shown in fig. 2, an electrochemical performance chart is shown in fig. 6, and the specific capacity is 800 mAh/g. After sanding, nano-scale silicon monoxide or silicon and tin powder are uniformly mixed and carbonized with phenolic resin to form a stable silicon-carbon composite structure.
Example 3
Weighing 60g of silicon monoxide and 30g of tin powder, uniformly mixing, placing in a sand mill, sanding for 30 hours at a speed of 500r/min in an argon atmosphere until the particle size is 10-20 nm, and obtaining a product c; and (3) uniformly mixing the product c with a proper amount of phenolic resin (according to the residual carbon content, ensuring that the carbon content in the finally prepared material is 5%), calcining in a tubular furnace under the argon atmosphere at the heating rate of 5 ℃/min, heating to 800 ℃, preserving heat for 8 hours, and naturally cooling to obtain the silicon-based composite lithium battery negative electrode material.
An SEM photograph of the negative electrode material obtained in example 3 is shown in fig. 3, an electrochemical performance chart is shown in fig. 6, and the specific capacity is 1000 mAh/g. After sanding, nano-scale silicon monoxide or silicon and tin powder are uniformly mixed and carbonized with phenolic resin to form a stable silicon-carbon composite structure.
Comparative example 1
Weighing 60g of silicon monoxide and 30g of tin powder, and putting into a mixer to mix for 40min to obtain a product; and (3) uniformly mixing the product with a proper amount of phenolic resin (according to the residual carbon content, ensuring that the carbon content in the finally prepared material is 5%), calcining in a tubular furnace under the argon atmosphere at the heating rate of 5 ℃/min, heating to 800 ℃, then preserving heat for 8h, and naturally cooling to obtain the silicon-based composite lithium battery negative electrode material.
The SEM photograph of the negative electrode material obtained in comparative example 1 is shown in fig. 4, the electrochemical performance diagram is shown in fig. 6, and the specific capacity is 280 mAh/g. The non-sanded SiO/Si powder and Sn powder particles are too large, and it can be seen that the electrochemical performance of the composite is poor.
Comparative example 2
Weighing 60g of silicon monoxide and 150g of tin powder, uniformly mixing, placing in a sand mill, sanding for 25 hours at a speed of 500r/min in an argon atmosphere until the particle size is 10-20 nm, and obtaining a product; and (3) uniformly mixing the product with a proper amount of phenolic resin (according to the residual carbon content, ensuring that the carbon content in the finally prepared material is 5%), calcining in a tubular furnace under the argon atmosphere at the heating rate of 5 ℃/min, heating to 600 ℃, preserving heat for 6h, and naturally cooling to obtain the silicon-based composite lithium battery negative electrode material.
The SEM photograph of the anode material obtained in comparative example 2 is shown in fig. 5, illustrating that: after sanding, the nano-scale silicon monoxide and tin powder are uniformly mixed and distributed on the distribution resin, the added amount of the tin powder is too much, the added amount of the silicon monoxide is too little, the aggregation of cracked carbon is obvious, the effect of the silicon monoxide is not obvious, the performance effect of the battery is poor, and the electrochemical performance diagram of the comparative example 2 is shown in figure 6, so that the electrochemical performance of the composite material is general, and the specific capacity is 450 mAh/g.
The above description is only for the purpose of illustrating the preferred embodiments of the present invention and should not be taken as limiting the invention, so that any modifications, equivalents, improvements and the like, which are within the spirit and principle of the present invention, should be included in the scope of the present invention.