WO2015181941A1

WO2015181941A1 - Negative electrode active material for lithium ion secondary batteries, and lithium ion secondary battery

Info

Publication number: WO2015181941A1
Application number: PCT/JP2014/064367
Authority: WO
Inventors: 岡井　誠
Original assignee: 株式会社日立製作所
Priority date: 2014-05-30
Filing date: 2014-05-30
Publication date: 2015-12-03

Abstract

Achieved is a negative electrode active material for lithium ion secondary batteries, which is used in a lithium ion secondary battery that has a high electrical capacity per unit volume. A negative electrode active material for lithium ion secondary batteries, which comprises a base, silicon nanoparticles formed on the surface of the base and silicon nanowires formed on the surface of the base. The surface of the base is configured of a carbon layer; the silicon nanoparticles are bonded to the base through the carbon layer; and the silicon nanowires are bonded to the base through the carbon layer.

Description

Negative electrode active material for lithium ion secondary battery and lithium ion secondary battery

The present invention relates to a negative electrode active material for a lithium ion secondary battery and a lithium ion secondary battery.

Graphite-based carbon materials are widely used as negative electrode active materials of lithium ion secondary batteries. The stoichiometric composition when lithium is charged into graphite is LiC ₆ , and its theoretical capacity can be calculated to be 372 mAh / g.

On the other hand, when the silicon is filled with lithium ions, the stoichiometric composition is Li ₁₅ Si ₄ or Li ₂₂ Si ₅ , and its theoretical capacity can be calculated to be 3577 mAh / g or 4197 mAh / g. Thus, silicon is an attractive material that can store 9.6 times or 11.3 times more lithium than graphite. However, when the silicon particles are filled with lithium ions, the volume expands to about 3.1 times or about 4.1 times, so that the silicon particles are mechanically broken while repeating the lithium ion charging and discharging. The destruction of the silicon particles electrically isolates the broken fine silicon particles, and the formation of a new electrochemical covering layer on the fracture surface increases the irreversible capacity and significantly reduces the charge-discharge cycle characteristics.

By forming silicon particles as nanowires as a negative electrode active material of a lithium ion secondary battery, mechanical destruction associated with charging and discharging of lithium ions can be prevented. As a prior art, Patent Document 1 describes an example in which a silicon nanowire is attached to the surface of a carbon substrate.

Japanese Patent Application Publication No. 2012-527735

In Patent Document 1, although silicon nanowires are used as a main negative electrode active material, when the weight ratio of silicon nanowires is increased to increase electric capacity because of the low bulk density of silicon nanowires, electricity per unit volume can be obtained. There was a problem that capacity decreased.

An object of the present invention is to provide a negative electrode active material for a lithium ion secondary battery used in a lithium ion secondary battery having a large electric capacity per unit volume.

The features of the present invention for solving the above problems are, for example, as follows.

A substrate, silicon nanoparticles formed on the surface of the substrate, and silicon nanowires formed on the surface of the substrate, wherein the surface of the substrate is composed of a carbon layer, and the silicon nanoparticles are The negative electrode active material for lithium ion secondary batteries which has joined to the base material through the carbon layer, and the silicon nanowire has joined to the base material through the carbon layer.

ADVANTAGE OF THE INVENTION It is possible to implement | achieve the negative electrode active material for lithium ion secondary batteries used for a lithium ion secondary battery with large electric capacity per unit volume by this invention. Problems, configurations, and effects other than those described above will be apparent from the description of the embodiments below.

It is the figure which represented the negative electrode active material based on one Embodiment of this invention typically. It is the figure which represented typically the form of the silicon nanowire based on one Embodiment of this invention. It is the figure which represented typically the form of the silicon nanowire based on one Embodiment of this invention. It is the figure which represented typically the form of the silicon nanoparticle based on one Embodiment of this invention. It is the figure which represented typically the form of the silicon nanoparticle based on one Embodiment of this invention. It is a calculation result regarding the relationship between electrical capacity and silicon weight ratio based on one Embodiment of this invention. It is the result of computing the relation between the radius of the carbon substrate and the silicon weight ratio according to one embodiment of the present invention. It is the result of calculating the relationship between the density of a negative electrode active material, and a silicon weight ratio according to an embodiment of the present invention. It is a schematic diagram of the preparation apparatuses of a negative electrode active material based on one Embodiment of this invention. It is a scanning electron micrograph of the negative electrode active material concerning one Example of this invention. It is a scanning electron micrograph of the negative electrode active material concerning one Example of this invention. 1 is an internal structure of a lithium ion secondary battery according to an embodiment of the present invention.

Hereinafter, embodiments of the present invention will be described using the drawings and the like. The following description shows specific examples of the content of the present invention, and the present invention is not limited to these descriptions, and various modifications by those skilled in the art can be made within the scope of the technical idea disclosed herein. Changes and modifications are possible. Further, in the present specification, a numerical range indicated using “to” indicates a range including numerical values described before and after “to” as the minimum value and the maximum value, respectively.

A first embodiment of the present invention will be described with reference to FIG. FIG. 1 is a view schematically showing a negative electrode active material for a lithium ion secondary battery according to an embodiment of the present invention.

The lithium ion secondary battery negative electrode active material 1000 has a structure in which silicon nanoparticles 102 and silicon nanowires 103 are simultaneously bonded to the surface of a base material 101. The base material 101 may be any carbon material such as natural graphite, various types of artificial graphite, graphite whose surface is coated with amorphous carbon, carbon black, carbon nanotubes, and the like. It is also possible to cover the surface of the silicon nanoparticles 102 and / or the silicon nanowires 103 with a carbon-based (or containing) carbon coating layer.

Further, instead of a carbon base material as the base material 101, a metal such as silicon or metal capable of inserting and extracting lithium or a compound containing them is used as a base material body, and the surface of the base material body is mainly composed of carbon. It is also possible to use a substrate covered with a carbon coating layer. Even when a carbon material is used as the base material 101, the base material that can occlude and release lithium is a main body, and the surface of the base body is covered with a carbon coating layer containing carbon as a main component. The surface is composed of a carbon layer.

The form of the silicon nanowire 103 is described with reference to FIG. The silicon nanowire 103 is bonded to the surface of the substrate 101 via one end thereof. In other words, the silicon nanowires 103 are bonded to the base material 101 via the carbon layer on the surface of the base material 101. As described later, since the silicon nanowires 103 are formed on the surface of the base material 101 by vapor deposition, the silicon nanowires 103, the carbon atoms on the surface of the base material 101, and the silicon atoms in the silicon nanowires 103 are chemically bonded. It is considered to be very strongly bonded to the surface of the substrate 101.

The diameter of the cross section of the silicon nanowire 103 is preferably 1 to 100 nm, more preferably 1 to 30 nm. If the diameter is smaller than 1 nm, the bonding strength with the substrate 101 is weak, and the possibility of peeling from the substrate 101 is high. Also, if the diameter is larger than 100 nm, it is likely to be broken due to mechanical strain associated with lithium ion loading and release. The diameter is preferably 30 nm or less in order not to destroy mechanical strain caused by high-speed charge and discharge.

As shown in FIG. 3, it is also possible to form a carbon covering layer 303 on the surface of the silicon nanowire 103. In particular, in the case where the carbon covering layer 303 has a nanographene structure, it has an electrical conductivity of 1000 S / m or more, and the silicon nanowire 103 can be provided with the electrical conductivity. This makes it possible to improve particularly the charge and discharge characteristics at high speed. Also, even if the silicon nanowires 103 break for any reason and come off the substrate 101, it is possible to prevent electrical isolation and to significantly improve the life characteristics.

The thickness of the carbon coating layer 303 is preferably 0.5 to 100 nm. If it is larger than 0.5 nm, it is technically difficult to uniformly cover the surface of the silicon nanoparticles 102. In addition, when it is larger than 100 nm, the carbon covering layer 303 is likely to be peeled off from the surface of the silicon nanowire 103.

Next, the form of the silicon nanoparticles 102 will be described with reference to FIG. The silicon nanoparticles 102 are bonded to the surface of the substrate 101 through flat portions having a curvature smaller than the average curvature thereof. In other words, the silicon nanoparticles 102 are bonded to the substrate 101 via the carbon layer on the surface of the substrate 101. As described later, since the silicon nanoparticles 102 are formed on the surface of the substrate 101 by vapor deposition, the silicon nanoparticles 102 consist of carbon atoms on the surface of the substrate 101 and silicon atoms in the silicon nanoparticles 102. It is considered to be very strongly bonded to the surface of the substrate 101 by chemical bonding.

The diameter of the silicon nanoparticles 102 needs to be 1 to 100 nm, more preferably 1 to 30 nm. If the diameter is smaller than 1 nm, the bonding strength with the substrate 101 is weak, and the possibility of peeling from the substrate 101 is high. Also, if the diameter is larger than 100 nm, it is likely to be broken due to mechanical strain associated with lithium ion loading and release. The diameter is preferably 30 nm or less in order not to destroy mechanical strain caused by high-speed charge and discharge.

As shown in FIG. 5, it is also possible to form a carbon coating layer 303 on the surface of the silicon nanoparticle 102. In particular, in the case where the carbon coating layer 303 has a nanographene structure, it has an electrical conductivity of 1000 S / m or more, and the silicon nanoparticles 102 can be imparted with the electrical conductivity. This makes it possible to improve particularly the charge and discharge characteristics at high speed. Also, even if the silicon nanoparticles 102 are detached from the substrate 101 for any reason, it is possible to prevent electrical isolation and to significantly improve the life characteristics.

The thickness of the carbon coating layer 303 is preferably 0.5 to 100 nm. If it is smaller than 0.5 nm, it is technically difficult to uniformly cover the surface of the silicon nanoparticles 102. In addition, when the diameter is larger than 100 nm, the carbon covering layer 303 is likely to be peeled off from the surface of the silicon nanoparticle 102.

FIG. 6 shows silicon with respect to the entire weight of the negative electrode active material 1000 for a lithium ion secondary battery in which the silicon nanowires 103 and the silicon nanoparticles 102 are bonded to the surface of a carbon substrate when a carbon substrate is used as the substrate 101. The dependency of the negative electrode capacitance on the weight ratio Si / (Si + C) of For carbon, assuming that the stoichiometric composition when charged with lithium ions is LiC ₆ , its electric capacity was 372 mAh / g. In addition, for silicon, assuming that the stoichiometric composition at the time of charging with lithium ions is Li ₁₅ Si ₄ and assuming that the electric capacity is 3577 mAh / g, it is assumed that Li ₂₂ Si ₅ , It calculated about the case where the electric capacity was 4197 mAh / g.

From the balance with the positive electrode electric capacity, if 1000 mAh / g or more can be realized as the negative electrode electric capacity, it is considered that the performance is sufficient for the time being. From the calculation results of FIG. 6, in order to realize 1000 mAh / g or more as the negative electrode electric capacity, the weight ratio is 20% or more, particularly 40% or more, and further 80% to the lithium ion secondary battery negative electrode active material. It is desirable to contain% or more of silicon.

In the above, the case where a carbon material was used as a base material was calculated as an example, but when a base material having a base body other than carbon is used, similar calculation is performed using the specific electric capacity of the base material. It can be done.

In order to increase the silicon weight ratio in the negative electrode active material using only the silicon nanoparticles 102, it is necessary to reduce the size of the base material 101 and increase the surface area of the base material 101. The silicon weight ratio dependency of the radius of the carbon substrate is calculated on the assumption that the silicon nanoparticles 102 are closely packed on the carbon substrate when the carbon substrate is used as the substrate 101.

In this calculation, it is assumed that the carbon substrate is spherical and silicon nanoparticles are hemispherical. Moreover, in this calculation, MKSA unit system was used, and the physical quantity which used the other unit was shown in the square bracket about the physical quantity. Assuming that the weight of silicon bonded to the carbon substrate weight 1 is x, the weight ratio R of silicon can be expressed by equation (1).

When the equation (1) is transformed, x is expressed by the equation (2).

In the case of silicon weight x, the number N of silicon nanoparticles can be expressed by equation (3).

Here, r _np [nm] is the radius of the silicon nanoparticle, and D _np is the true density of the silicon nanoparticle. The total area C of the bonding surface of the silicon nanoparticles on the surface of the carbon substrate is expressed by equation (4).

Assuming that the specific surface area of the carbon substrate is S [m ² / g] and that silicon nanoparticles are closely packed and bonded to the surface of the carbon substrate, the relationship between S [m ² / g] and C is It can be expressed by the equation (5).

Substituting the equation (4) and further the equation (3) into the equation (5), the equation (6) is obtained.

Assuming that the radius of the carbon base material is r _s [nm] and the true density is D _s , S [m ² / g] is expressed by equation (7), which is rearranged by equation (8).

In order to match equation (8) with experimental values, a correction coefficient f is introduced to obtain equation (9).

Further, equation (10) is obtained using equations (9) and (6).

Using the equation (10), the silicon weight ratio dependence of r _s [nm] of the radius of the carbon substrate was calculated using the radius of silicon nanoparticles as a parameter. Here, as D _np , D _s , f, D _np = 2.33 × 10 ³ [kg / m ³ ], D _s = 2.2 × 10 ³ [kg / m ³ ], f = 25.6 Using.

The calculation results are shown in FIG. The ordinate represents the radius of the carbon substrate when the carbon substrate is used as the substrate 101, and the abscissa represents the silicon weight ratio. The radius of the silicon nanoparticles bound to the surface of the carbon substrate was calculated in three ways of 7.5 nm, 15.0 nm and 30.0 nm. The radius of a typical silicon nanoparticle 102 is 15.0 nm, in which case the radius of the carbon substrate needs to be 3.0 μm or less in order to achieve a silicon weight ratio of 20% or more. In this calculation, it is assumed that the silicon nanoparticles 102 are closely packed and bonded to the surface of the carbon substrate, and in fact, it needs to be less than half thereof. However, it is technically difficult to reduce the radius of the carbon substrate to 1.0 μm or less, and even if it can be realized, the production cost is likely to increase significantly. In addition, increasing the radius of the silicon nanoparticles 102 alleviates the requirement for reducing the radius of the carbon substrate. However, the radius of the silicon nanoparticles 102 needs to be 50.0 nm or less, more preferably 15.0 nm or less, in order to prevent mechanical destruction associated with lithium ion loading and release.

As described above, there is a practical limit to increasing the silicon weight ratio by the method of bonding the silicon nanoparticles 102 to the carbon substrate surface.

On the other hand, when only the silicon nanowires 103 are used to increase the silicon weight ratio in the negative electrode active material, there is a problem that the bulk density decreases. As the bulk density decreases, the power per unit capacity or power decreases. The silicon weight ratio dependency of relative bulk density is calculated, assuming a structure in which silicon nanowires 103 are bonded on a carbon substrate when a carbon substrate is used as the substrate 101.

In this calculation, MKSA unit system is used, and the physical quantities using other units are shown in square brackets. Assuming that the weight of silicon bonded to the carbon substrate weight 1 is x, the weight ratio R of silicon can be expressed by equation (11).

When the equation (1) is transformed, x is expressed by the equation (12).

The bulk density T _s of the carbon substrate can be expressed by equation (13).

Here, D _s represents the true density of the carbon substrate, and V _s represents the porosity of the carbon substrate. Assuming that the porosity V _s of the carbon substrate does not change even when the silicon nanowires 103 are bonded to the surface of the carbon substrate, the overall bulk density T _tot is expressed by Equation (14).

Here, D _nw indicates the true density of silicon nanowires, and V _nw indicates the porosity of the silicon nanowires 103. From the equations (14) and (13), the relative bulk density T _tot / T _s can be expressed by the equation (15). Here, as D _np , D _s and V _s , D _np = 2.33 × 10 ³ [kg / m ³ ], D _s = 2.2 × 10 ³ [kg / m ³ ], V _s = 0. 30 was used.

The calculation results are shown in FIG. The vertical axis is relative bulk density, and the horizontal axis is silicon weight ratio. The porosity of the silicon nanowire 103 was calculated for three ways of 0.6, 0.7, and 0.8. The actual measured value of the porosity of a typical silicon nanowire 103 is 0.7, in which case the relative bulk density is reduced to 80% or less in order to make the silicon weight ratio 20% or more. The relative bulk density reduction tolerance depends on the battery design, but there is a practical limit to increasing the silicon weight ratio in the method of bonding the silicon nanowires 103 to the carbon substrate surface.

In contrast to the above, as in the embodiment of the present invention, the base material 101, the silicon nanoparticles 102 formed on the surface of the base material 101, and the silicon nanowires 103 formed on the surface of the base material 101 The surface of the substrate 101 is formed of a carbon layer, the silicon nanoparticles 102 are bonded to the substrate 101 via the carbon layer, and the silicon nanowires 103 are on the substrate via the carbon layer. By bonding to 101, the weight of silicon can be increased and the volume can be suppressed low, so a negative electrode active material for a lithium ion secondary battery used in a lithium ion secondary battery having a large electric capacity per unit volume Can be realized.

Next, a method of manufacturing the silicon nanoparticles 102 and the silicon nanowires 103 will be described. FIG. 9 is a schematic view of a thermal vapor deposition apparatus for forming carbon-coated silicon nanoparticles 102 and carbon-coated silicon nanowires 103 on the surface of a substrate.

As a silicon raw material, liquid silicon tetrachloride was introduced into the reactor by bubbling with hydrogen gas. The vapor pressure of silicon tetrachloride at 20 ° C. is 30 kPa, and when bubbling is introduced, the amount of silicon tetrachloride introduced is 34%. Therefore, in order to introduce less amount of silicon tetrachloride, it is necessary to cool the silicon tetrachloride or to provide a separate line of hydrogen gas. In FIG. 9, a separate hydrogen line not bubbling was provided, joined with the bubbling line, and introduced into the reactor. The procedure for growing the carbon-coated silicon nanoparticles 102 and the carbon-coated silicon nanowires 103 is as follows.

Place the substrate in the sample boat and place it near the center of the reactor. The reactor is made of quartz and has a diameter of 5 cm and a length of 40 cm. With the hydrogen line flowing at the flow rate of 200 mL / min flowing in the upper hydrogen line in FIG. 9 and the bubbling hydrogen line below closed, the growth furnace is heated from room temperature to 1000 ° C. at a rate of 10 ° C./min. did.

Next, when reaching 1000 ° C., the flow rate of the upper hydrogen line was changed to 160 mL / min, and the flow rate of the hydrogen line of the lower bubbling hydrogen line was set to 40 mL / min. Under this condition, 6.8% of silicon tetrachloride can be introduced. After growing at 1000 ° C. for 3 hours, the lower bubbling hydrogen line was closed, and the flow rate of the upper hydrogen line was changed to 200 mL / min and held at 1000 ° C. for 30 minutes. Thereby, it is possible to simultaneously produce the silicon nanoparticles 102 and the silicon nanowires 103 with a diameter of 30 nm on the surface of the base material 101.

Thereafter, both hydrogen lines were closed, argon gas was flowed at a flow rate of 200 mL / min, the temperature was decreased at a rate of 10 ° C./min, and the temperature was decreased to 800 ° C. When the temperature reached 800 ° C., propylene gas was introduced at a flow rate of 10 mL / min, and at the same time, the flow rate of argon gas was set to 190 mL / min, and a carbon coated layer 303 was grown for 1 hour.

After that, the propylene gas line was closed, argon gas was flowed at a flow rate of 200 mL / min, and was kept for 30 minutes, and then naturally cooled. Thereby, it is possible to produce the carbon coating layer 303 (film thickness of 10 nm) which has a nanographene multilayer structure on the surface of the silicon nanoparticle 102 and the silicon nanowire 103. Thus, formation of a natural oxide film on the surface of the silicon nanoparticle 102 and the silicon nanowire 103 is performed by continuously performing the preparation of the silicon nanoparticle 102 and the silicon nanowire 103 and the subsequent formation of the carbon covering layer 303. To eliminate the need for a native oxide reduction and removal process.

The scanning electron micrograph of the sample in which the silicon nanoparticles 102 and the silicon nanowires 103 were formed on the surface of the base material 101 made of graphite by the above method is shown in FIG. As described above, when the growth time of the silicon nanoparticles 102 and the silicon nanowires 103 is 3 hours, a large amount of the silicon nanowires 103 is produced on the surface of the base material 101 made of carbon, so the silicon nanoparticles 102 are hidden and not visible . Therefore, a sample whose growth time was stopped at 30 minutes was prepared and observed with a scanning electron microscope. FIG. 11 shows a scanning electron micrograph of a sample with a growth time of 30 minutes. It can be seen that the silicon nanoparticles 102 and the silicon nanowires 103 are mixed.

The weight ratio of all silicon, the weight ratio of silicon nanoparticles 102, and the weight ratio of silicon nanowires 103 are shown in Table 1 for samples in which the silicon nanoparticles 102 and the silicon nanowires 103 were formed on the base material 101 that is carbon.

The growth time of the sample 1 is 1 hour for the silicon nanoparticles 102 and the silicon nanowires 103, 2 hours for the sample 2, and 3 hours for the sample 3. It can be seen that the weight ratio of all the silicons increases and the ratio of the silicon nanowires 103 to all the silicons increases as the growth time becomes longer. The weight ratio of total silicon was determined by heat treating the sample in air at 1200 ° C. for 2 hours, assuming that all the residue is silicon oxide. The weight ratio of the silicon nanowire 103 is as follows: the sample is put in pure water and sonicated for 1 hour, then the filtrate filtered with a 5 μm filter is dried and then heat treated in air at 1200 ° C. for 2 hours It asked assuming that it was silicon. In the filtrate, since the silicon-nan wire 103 detached by ultrasonication is separated, it is possible to measure the weight ratio of the silicon nanowires 103 by the above method. The weight ratio of the silicon nanoparticles 102 was determined on the assumption that the sample remaining on the filter was heat treated in air at 1200 ° C. for 2 hours, and all the residue was silicon oxide.

In FIG. 9, in order to prevent the surface oxidation of the silicon nanoparticles 102 and the silicon nanowires 103, the production of the silicon nanoparticles 102 and the silicon nanowires 103 and the subsequent production of the carbon covering layer 303 were continuously performed. After the silicon nanoparticles 102 and the silicon nanowires 103 are grown, they are once taken out into the air and then heat-treated in a reducing atmosphere to remove the native oxide film on the surfaces of the silicon nanoparticles 102 and the silicon nanowires 103, and subsequently the carbon covering layer. It is also possible to make 303. Productivity is improved by performing the growth of the silicon nanoparticles 102 and the silicon nanowires 103 and the preparation of the carbon coating layer 303 in separate reactors. In addition, it is possible to change the weight ratio of the silicon nanoparticles 102 and the silicon nanowires 103 by changing the temperature at the time of growth of the silicon nanoparticles 102 and the silicon nanowires 103, the introduced amount of silicon tetrachloride, and the growth time. In addition, by changing the growth time of the carbon covering layer 303, it is possible to control the film thickness of the carbon covering layer 303. In addition to propylene gas, various hydrocarbon gases such as acetylene gas, propane gas, and methane gas can be used for producing the carbon coating layer 303.

FIG. 12 is an internal structure of a lithium ion secondary battery according to an embodiment of the present invention. In FIG. 12, 1201 is a positive electrode, 1202 is a separator, 1203 is a negative electrode, 1204 is a battery can, 1205 is a positive current collection tab, 1206 is a negative current collection tab, 1207 is an inner lid, 1208 is an internal pressure release valve, 1209 is a gasket, 1210 is a positive temperature coefficient (PTC) resistive element, 1211 is a battery cover. The battery lid 1211 is an integrated component including an inner lid 1207, an internal pressure release valve 1208, a gasket 1209, and a positive temperature coefficient resistance element 1210.

For example, the positive electrode 1201 can be manufactured by the following procedure. LiMn ₂ O ₄ is used as the positive electrode active material. To 85.0 wt% of the positive electrode active material, 7.0 wt% and 2.0 wt% of a graphite powder and acetylene black are added as a conductive material, respectively. Further, a solution dissolved in 6.0 wt% of polyvinylidene fluoride (hereinafter abbreviated as PVDF) and 1-methyl-2-pyrrolidone (hereinafter abbreviated as NMP) as a binder is added and mixed by a planetary mixer. Further, the bubbles in the slurry are removed under vacuum to prepare a homogeneous positive electrode mixture slurry. This slurry is uniformly and evenly applied on both sides of a 20 μm thick aluminum foil using a coater. After application, it is compression molded by a roll press so that the electrode density is 2.55 g / cm ³ . This is cut with a cutting machine to produce a positive electrode 1201 having a thickness of 100 μm, a length of 900 mm, and a width of 54 mm.

For example, the negative electrode 1203 can be manufactured by the following procedure. As the negative electrode active material, the negative electrode active material for lithium ion secondary batteries in the present invention can be used. To 95.0 wt% of the negative electrode active material, a solution of 5.0 wt% of PVDF dissolved in NMP as a binder is added. It is mixed with a planetary mixer, and bubbles in the slurry are removed under vacuum to prepare a homogeneous negative electrode mixture slurry. This slurry is uniformly and uniformly applied on both sides of a 10 μm-thick rolled copper foil with a coating machine. After application, the electrode is compression molded by a roll press to an electrode density of 1.3 g / cm ³ . This is cut with a cutting machine to produce a negative electrode 1203 having a thickness of 110 μm, a length of 950 mm, and a width of 56 mm.

The positive electrode current collecting tab 1205 and the negative electrode current collecting tab 1206 are ultrasonically welded to the positive electrode 1201 and the uncoated part (current collector plate exposed surface) of the negative electrode 1203 which can be manufactured as described above. The positive electrode current collection tab 1205 may be an aluminum lead piece, and the negative electrode current collection tab 1206 may be a nickel lead piece.

Thereafter, a separator 1202 made of a porous polyethylene film with a thickness of 30 μm is inserted into the positive electrode 1201 and the negative electrode 1203, and the positive electrode 1201, the separator 1202, and the negative electrode 1203 are wound. The wound body is housed in a battery can 1204, and the negative electrode current collecting tab 1206 is connected to the can bottom of the battery can 1204 by a resistance welder. The positive electrode current collection tab 1205 is connected to the bottom surface of the inner lid 1207 by ultrasonic welding.

Before attaching the upper battery lid 1211 to the battery can 1204, a non-aqueous electrolyte is injected. The solvent of the electrolytic solution is, for example, composed of ethylene carbonate (EC), dimethyl carbonate (DMC) and diethyl carbonate (DEC), and there is a volume ratio of 1: 1: 1 or the like. The electrolyte is LiPF ₆ at a concentration of 1 mol / L (about 0.8 mol / kg). Such an electrolytic solution is dropped from above the wound body, and the battery lid 1211 is crimped and sealed in the battery can 1204, so that a lithium ion secondary battery can be obtained.

101 substrate 102 silicon nanoparticle 103 silicon nanowire 303 carbon coating layer 1000 for lithium ion secondary battery negative electrode active material 1201 positive electrode 1202 separator 1203 negative electrode 1204 battery can 1205 positive electrode current collecting tab 1206 negative electrode current collecting tab 1207 inner lid 1208 pressure release valve 1209 gasket,
1210 Positive temperature coefficient resistance element 1211 Battery cover

Claims

A substrate,
Silicon nanoparticles formed on the surface of the substrate;
Silicon nanowires formed on the surface of the substrate;
The surface of the substrate is composed of a carbon layer,
The silicon nanoparticles are bonded to the base via the carbon layer,
The negative electrode active material for lithium ion secondary batteries in which the said silicon nanowire is joined to the said base material through the said carbon layer.
In claim 1,
The substrate has a substrate body,
The carbon layer is formed on the surface of the base body,
A negative electrode active material for a lithium ion secondary battery, wherein a compound containing a material capable of absorbing and desorbing lithium ions is used as the base body.
In any one of claims 1 to 2,
The negative electrode active material for a lithium ion secondary battery, wherein the diameter of the silicon nanoparticles is 1 to 100 nm.
In any one of claims 1 to 3,
The negative electrode active material for a lithium ion secondary battery, wherein the diameter of the cross section of the silicon nanowire is 1 to 100 nm.
In any one of claims 1 to 4,
The negative electrode active material for lithium ion secondary batteries by which the surface of the said silicon nanoparticle or the said silicon nanowire is covered by the carbon film layer.
In claim 5,
The negative electrode active material for lithium ion secondary batteries in which the said carbon coating layer has a nano graphene structure.
In any one of claims 5 to 6,
A negative electrode active material for a lithium ion secondary battery, wherein the film thickness of the carbon coating layer is 0.5 nm to 100 nm.
In any one of claims 1 to 7,
The negative electrode active material for lithium ion secondary batteries whose sum total weight of the said silicon nanoparticle and the said silicon nanowire is 20 wt% or more with respect to the said negative electrode active material for lithium ion secondary batteries in weight ratio.
A lithium ion secondary battery comprising the lithium ion secondary battery negative electrode active material according to any one of claims 1 to 8.