CN107195893A - Boron-doped silicon-based negative electrode material for lithium ion battery - Google Patents

Abstract

The invention discloses a boron-doped silicon-based negative electrode material for a lithium-ion battery. The boron-doped silicon-based negative electrode material is compounded by a boron-doped nano-silicon material and graphite. The mass of the boron-doped nano-silicon material is The percentage is 3‑100%, with graphite as the balance. In the present invention, diboron trioxide gradually diffuses to the silicon negative electrode material in the process of high-temperature sintering, replaces part of the silicon atoms, forms a substitutional doping, and increases the concentration of vacancy carriers in the nano-silicon material, thereby improving the intrinsic properties of the silicon material. Electronic conductivity, while graphite buffers the volume expansion of the silicon material. The method has the advantages of simple preparation process, convenient operation, easy-to-obtain natural raw materials, low cost, convenient follow-up treatment and easy large-scale production.

Description

A boron-doped silicon-based negative electrode material for lithium-ion batteries

technical field

The invention relates to the technical field of lithium ion batteries, in particular to a boron-doped silicon-based negative electrode material for lithium ion batteries.

Background technique

In recent years, with the continuous expansion of the application of lithium-ion batteries in high-power equipment such as electric tools, electric/hybrid vehicles, and energy storage power stations, traditional graphite negative electrodes (372mAh/g) have been difficult to meet human needs for high-energy-density batteries. Therefore, finding a next-generation lithium-ion battery anode material that can replace graphite has become one of the current research hotspots in lithium-ion batteries. The theoretical specific capacity of silicon material is 4200mAh/g, which is rich in resources, and will not co-intercalate with the electrolyte, and has a higher potential for lithium intercalation, which is safer. However, the silicon electrode material will experience a volume change of up to 300% during the charging and discharging process. Such a high volume expansion and contraction will easily lead to defects such as crushing of the electrode material, and loss of contact with the current collector and the electrode conductive network; at the same time, the volume change will also bring The generation of a new surface requires the formation of a new solid-electrolyte interface (SEI), which leads to a large consumption of electrolyte, which in turn leads to a substantial decrease in battery cycle life. On the other hand, the conductivity and lithium ion diffusion rate of silicon are lower than those of graphite, which will limit the performance of silicon under high current and high power conditions.

At present, the academic community mainly optimizes the structure of materials by means of nanosizing, compounding with inert phases, and creating pores to improve their electrochemical performance. Such as Houd et al. (Chou S, Wang J, Choucair M, et al. Enhanced reversible lithium storage in a nanosize silicon/graphene composite [J]. Electrochemistry Communications, 2010, 12 (2): 303-306.) through a simple liquid phase method A silicon/graphene composite material was prepared with a reversible capacity of 2158mAh/g for the first time. Kim et al. (Jo Y N, Kim Y, Kim J S, et al.Si-graphite composites as anode materials for lithium secondary batteries[J].Journal of PowerSources,2010,195(18):6031-6036.) using mechanical ball milling method The silicon/graphite/amorphous carbon material is prepared, the material has good conductivity, and the first Coulombic efficiency is as high as 86.4%. Liu et al. (Liu N, Lu Z, Zhao J, et al.Apomegranate-inspired nanoscale design for large-volume-change lithium batteryanodes[J].Nat Nanotechnol,2014,9(3):187-192.) adopted polymer A garnet-structured nano-silicon-based composite material is prepared by cracking method. The surface of nano-silicon cluster particles is covered with a layer of resin pyrolytic carbon. This material has a reversible specific capacity of 2350mAh/g for the first time at a current density of 1A/g. However, these methods all use carbon materials or conductive polymers to improve the electronic conductivity of silicon-based materials, but do not improve the intrinsic electronic conductivity of silicon materials.

Contents of the invention

In order to solve the above-mentioned phenomenon that the electron conductivity of the silicon material itself is relatively low, the present invention provides a boron-doped silicon negative electrode material for lithium ion batteries.

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

A boron-doped silicon-based negative electrode material for a lithium-ion battery, the boron-doped silicon-based negative electrode material is compounded by a boron-doped nano-silicon material and graphite, wherein the mass percentage of the boron-doped nano-silicon material is 3 -100%, with graphite as the balance.

In a further solution, the boron-doped nano-silicon material is ground after mixing silicon and boron trioxide uniformly, and then placed in a tube furnace with an inert atmosphere for sintering; finally placed in an alkaline solution for 10-60 minutes Afterwards, the resultant was washed, filtered and dried.

In a further solution, the silicon is one or more of silicon nanoparticles, silicon nanotubes, silicon nanowires, and silicon nanofilms.

In a further solution, the silicon and diboron trioxide are mixed in one or more of liquid phase mixing, mechanical grinding, planetary ball milling, and high-energy ball milling.

In a further scheme, the mass of the diboron trioxide accounts for 1%-10% of the silicon mass.

In a further scheme, the sintering temperature is 800°C-1200°C, the heating rate is 5°C/min-20°C/min, and the sintering time is 1-12h.

In a further scheme, the alkaline solution is one or more of NaOH solution, KOH solution, Ba(OH) ₂ solution, and Ca(OH) ₂ solution.

In a further scheme, the graphite is natural graphite, artificial graphite or mesocarbon microspheres.

In a further solution, the boron-doped silicon-based negative electrode material is formed by mixing boron-doped nano-silicon material with graphite after spray-drying and granulating, or by mixing boron-doped nano-silicon material with graphite and then spraying and granulating .

The boron-doped silicon-based negative electrode material of the present invention is compounded by boron-doped nano-silicon material and graphite material that provides a certain proportion according to capacity requirements and plays a role in buffering expansion.

Compared with the prior art, the present invention has the following advantages:

The existing technology mainly improves the electronic conductivity of silicon-based materials by compounding with conductive carbon, conductive polymers or metals; and the present invention starts from the electronic conductivity of the silicon material itself, and transfers boron atoms to the silicon negative electrode material under high temperature conditions. Gradually diffuse, replace part of the silicon atoms, and form a substitutional doping, thereby increasing the concentration of vacancy carriers in the nano-silicon material, and then improving the intrinsic electronic conductivity of the silicon material. At the same time, according to the capacity requirement, a certain amount of graphite can be compounded to buffer the volume expansion of the material.

The invention adopts a high-temperature sintering method to prepare the boron-doped silicon negative electrode material, the preparation process is simple, the operation is convenient, the raw materials are easy to obtain naturally, the cost is low, and the subsequent processing method is convenient.

The boron-doped silicon material prepared by the invention can not only be applied to the field of lithium-ion battery negative electrodes, but also can be applied to the fields of field effect devices, solar devices, light emitting devices, sensor devices and the like.

Description of drawings

FIG. 1 is a comparison diagram of the electronic conductivity of the boron-doped silicon nanowires prepared in Example 1-2 and the silicon nanowires of the comparative example.

FIG. 2 is an EDS image of boron-doped nano-silicon particles prepared in Example 3. FIG.

FIG. 3 is a charge-discharge curve diagram of nano-silicon and boron-doped nano-silicon particles in Example 3. FIG.

Fig. 4 is the SEM image of the silicon-based negative electrode material prepared in embodiment 4

Figure 5 is the first charge and discharge curve of the silicon-based negative electrode material prepared in Example 4

detailed description

In order to facilitate the understanding of the present invention, the present invention will be described more fully and in detail below in conjunction with examples, but the protection scope of the present invention is not limited to the following specific examples.

Unless otherwise defined, all technical terms used hereinafter have the same meanings as commonly understood by those skilled in the art. The terminology used herein is only for the purpose of describing specific embodiments, and is not intended to limit the protection scope of the present invention.

Unless otherwise specified, the various reagents and raw materials used in the present invention are commercially available products or products that can be prepared by known methods.

Example 1:

Add 1g of boron trioxide and 10g of silicon nanowires into a mortar, grind to make the materials evenly dispersed, put the materials into a porcelain boat, put them into a tube furnace with nitrogen, and heat up at a rate of 5°C/min Sinter at 900°C for 1h. Cool to room temperature, immerse the material in sodium hydroxide solution for 0.5 h, wash with deionized water and dry to obtain a silicon-based negative electrode material (boron-doped silicon nanowire).

The electrochemical performance test of the silicon-based anode material was carried out with two probes using a semiconductor characteristic analysis system, and its conductivity is shown in Table 1 and Figure 1. The electronic conductivity of the boron-doped silicon nanowire material after sintering at 900°C for 1 hour is 5.2×10 ^-4 S/cm, so the silicon-based negative electrode material prepared by the present invention has improved electronic conductivity after boron doping.

Comparative example 1:

Taking the silicon nanowire material as a comparison, the electrochemical performance test of the material is also carried out by using the semiconductor characteristic analysis system. It can be found that the electronic conductivity of the undoped silicon nanowire material is 1.1×10 ^-7 S/cm.

Example 2:

Add 1g of boron trioxide and 10g of silicon nanowires into the mortar, grind the material to disperse evenly, put the material into a porcelain boat, put it into a tube furnace with nitrogen gas, and raise the temperature to 5°C/min. Sinter at 1000°C for 1h. Cool to room temperature, immerse the material in sodium hydroxide solution for 0.5 h, wash with deionized water and dry to obtain a silicon-based negative electrode material (boron-doped silicon nanowire).

The electrochemical properties of the material were tested with two probes using a semiconductor characteristic analysis system, and its electrical conductivity is shown in Table 1 and Figure 1. The electronic conductivity of boron-doped silicon nanowire material after sintering at 1000℃ for 1h is 0.21S/cm. By comparison, it can be found that the electronic conductivity of the material after boron doping is improved, and to a certain extent increases with the increase of temperature.

Table 1 Electronic conductivity of doped and undoped silicon nanowires

Material Conductivity Comparative example 1 1.1×10 ^-7 S/cm Example 1 5.2×10 ^-4 S/cm Example 2 0.21S/cm

Example 3:

Add 1g of diboron trioxide and 10g of nano-silicon particles into the mortar, grind the material to disperse evenly, put the material into a porcelain boat, put it into a tube furnace with nitrogen, and raise the temperature to 1000 at a heating rate of 20°C/min. Sintering at ℃ for 1h. Cool to room temperature, soak the material in sodium hydroxide solution for 0.5 h, wash with deionized water and dry to obtain a silicon-based negative electrode material (boron-doped nano-silicon).

Figure 2 is the EDS energy spectrum, and it can be found that there is obvious boron element in the material.

Nano-silicon: SP: LA133 = 8:1:1 ratio was mixed and coated, and CR2016 button cells were assembled. The electrolyte was EC+DMC solution with 1mol/L LiPF6, and the electrochemical performance was tested.

Figure 3 shows the charge and discharge curves of nano-silicon and boron-doped nano-silicon. It can be seen from Figure 3 that the first-time charge specific capacity of nano-silicon is 1650mAh/g, and the first effect is only 45.8%; boron-doped nano-silicon The first charge specific capacity of silicon is 2244mAh/g, and the first charge is 62.3%. This is because the volume expansion and contraction of nano-silicon in the process of charging and discharging causes the material to lose electrical contact with the surrounding SP, but the electrons of boron-doped nano-silicon The conductivity is relatively high, so the internal resistance of the pole piece is small, and the electrochemical performance is good.

Example 4:

Add 0.1g of diboron trioxide and 10g of nano-silicon particles into the mortar, grind the material to disperse evenly, put the material into a porcelain boat, put it into a tube furnace with nitrogen gas, and raise the temperature to Sinter at 800°C for 12h. Cool to room temperature, soak the material in sodium hydroxide solution for 0.5 h, wash with deionized water and dry to obtain boron-doped nano-silicon material.

3g of boron-doped nano-silicon material was dissolved in absolute ethanol, spray-dried and granulated, and then mixed with 97g of artificial graphite to obtain a silicon-based negative electrode material.

Fig. 4 is an SEM image of the silicon-based negative electrode material prepared in this example, in which the spherical particles are formed by boron-doped nano-silicon and spray granulation.

The above materials: SP: LA133 = 8:1:1 ratio was mixed and coated, and the CR2016 button battery was assembled. The electrolyte was 1mol/L LiPF6 EC+DMC solution, and the electrochemical performance test was carried out. Figure 5 shows the charge and discharge curves of the silicon-based negative electrode material prepared in this example. The first charge specific capacity is 421.8mAh/g, the first discharge specific capacity is 460.1mAh/g, and the first effect reaches 91.7%. This is because the electronic conductivity of boron-doped nano-silicon is relatively high, so the internal resistance of the electrode sheet is small, and the volume of the graphite buffer material expands, so the electrochemical performance is better.

Example 5:

Add 0.5g of diboron trioxide and 10g of nano-silicon particles into the mortar, grind the material to disperse evenly, put the material into a porcelain boat, put it into a tube furnace with nitrogen gas, and raise the temperature to 15°C/min. Sinter at 1200°C for 10h. Cool to room temperature, soak the material in potassium hydroxide solution for 0.8h, wash with deionized water and dry to obtain boron-doped nano-silicon material.

5 g of the obtained boron-doped nano-silicon material was dissolved in absolute ethanol, spray-dried and granulated, and mixed with 95 g of artificial graphite to obtain a silicon-based negative electrode material.

Embodiment 6:

Add 0.5g of diboron trioxide and 10g of silicon nanowires into a mortar, grind to make the materials evenly dispersed, put the materials into a porcelain boat, and put them into a tube furnace with nitrogen gas at a heating rate of 5°C/min-20 °C/min, heat up to 1000 °C and sinter for 1 h. Cool to room temperature, soak the material in calcium hydroxide solution for 1 h, wash with deionized water and dry to obtain boron-doped nano-silicon material. 10 g of the obtained boron-doped nano-silicon material was dissolved in absolute ethanol, mixed with 90 g of natural graphite, spray-dried and granulated to obtain a silicon-based negative electrode material.

Embodiment 7:

Add 1g of boron trioxide and 10g of silicon nano-film into the mortar, grind the material to disperse evenly, put the material into a porcelain boat, put it into a tube furnace with nitrogen, and heat up at a rate of 5°C/min-20°C /min and heat up to 1000°C for sintering for 1h. After cooling to room temperature, the material was immersed in a barium hydroxide solution for 0.5 h, washed with deionized water and dried to obtain a boron-doped nano-silicon material. 60 g of the boron-doped nano-silicon material was dissolved in absolute ethanol, mixed with 40 g of mesocarbon microspheres, spray-dried and granulated to obtain a silicon-based negative electrode material.

In addition, it should be understood that although this specification is described according to implementation modes, not each implementation mode only contains an independent technical solution, and this description in the specification is only for clarity, and those skilled in the art should take the specification as a whole , the technical solutions in each embodiment can also be properly combined to form other implementation methods that can be understood by those skilled in the art.

Claims (9)

1. A boron-doped silicon-based negative electrode material for lithium-ion batteries, characterized in that: the boron-doped silicon-based negative electrode material is compounded by boron-doped nano-silicon material and graphite, wherein boron-doped nano-silicon The mass percentage of the material is 3-100%, and graphite is the balance. 2. A boron-doped silicon-based negative electrode material for a lithium-ion battery according to claim 1, wherein the boron-doped nano-silicon material is ground after silicon and boron trioxide are mixed uniformly, Then place it in a tube furnace with an inert atmosphere for sintering; finally place it in an alkali solution for 10-60 minutes, wash, filter and dry the obtained product. 3. The boron-doped silicon-based negative electrode material for lithium-ion batteries according to claim 2, wherein the silicon is one or more of silicon nanoparticles, silicon nanotubes, silicon nanowires, and silicon nanofilms. Several kinds. 4. The boron-doped silicon-based negative electrode material for lithium ion batteries according to claim 2, characterized in that: the mixing method of the silicon and boron trioxide is liquid phase mixing, mechanical grinding, planetary ball milling, high energy One or several types of ball milling. 5. The boron-doped silicon-based negative electrode material for lithium ion batteries according to claim 2, wherein the mass of the boron trioxide accounts for 1%-10% of the mass of silicon. 6. The boron-doped silicon-based negative electrode material for lithium-ion batteries according to claim 2, characterized in that: the sintering temperature is 800°C-1200°C, and the heating rate is 5°C/min-20°C/min, The sintering time is 1-12h. 7. The boron-doped silicon-based negative electrode material for lithium-ion batteries according to claim 2, characterized in that: the alkaline solution is NaOH solution, KOH solution, Ba(OH) ₂ solution, Ca(OH) ₂ solution one or more of them. 8. The boron-doped silicon-based negative electrode material for lithium ion batteries according to claim 1, wherein the graphite is natural graphite, artificial graphite or mesocarbon microspheres. 9. The boron-doped silicon-based negative electrode material for lithium ion batteries according to claim 1, characterized in that: the boron-doped silicon-based negative electrode material is spray-dried and granulated with boron-doped nano-silicon material and graphite It is made by mixing, or by mixing boron-doped nano-silicon material with graphite and then spraying and granulating.