JP5827261B2 - Silicon-containing particles, negative electrode material for nonaqueous electrolyte secondary battery, and nonaqueous electrolyte secondary battery - Google Patents

Description

  The present invention relates to silicon-containing particles, a negative electrode material for a non-aqueous electrolyte secondary battery using the same, and a non-aqueous electrolyte secondary battery.

  In recent years, with the remarkable development of portable electronic devices, communication devices, etc., there is a strong demand for non-aqueous electrolyte secondary batteries with high energy density from the viewpoints of economy and downsizing and weight reduction of devices. On the other hand, in automobile applications, hybrid cars and electric cars have been actively developed for the purpose of improving fuel consumption and suppressing emission of global warming gas.

    Since silicon exhibits a theoretical capacity of 4200 mAh / g, which is much higher than the theoretical capacity of 372 mAh / g of carbon materials currently in practical use, it is the most promising material for reducing the size and increasing the capacity of batteries.

  On the other hand, the volume change of particles accompanying charging / discharging is much larger than that of carbon material in silicon, and by repeating charging / discharging, silicon particles become finer and peeling / dropping from the conductive material or current collector proceeds. As a result, there is a problem that good cycle characteristics cannot be obtained, and improvement is demanded.

  As means for solving the above-mentioned problems, for example, a technique of compounding silicon particles and graphite as shown in Patent Documents 1 and 2 with a carbonaceous material and performing carbonization by firing, or silicon as shown in Patent Document 3 A method of mixing and sintering an alloy with a ceramic such as alumina, silica, titania, silicon carbide, or silicon nitride has been proposed.

JP 2011-119207 A JP2012-124113A Japanese Patent No. 4967839

  However, as a result of intensive studies by the present inventor, these methods cannot suppress the expansion of silicon particles or silicon alloy particles, and the problem that the capacity of the battery decreases as the charge / discharge cycle elapses still remains. It was left.

  The present invention has been made in view of the above problems, and when used as a negative electrode active material for a non-aqueous electrolyte secondary battery, it has a higher capacity than graphite and has excellent cycle characteristics. Another object of the present invention is to provide silicon-containing particles used for the negative electrode active material of a non-aqueous electrolyte secondary battery that can be a non-aqueous electrolyte secondary battery.

  In order to achieve the above object, the present invention provides a silicon-containing particle used in a negative electrode active material of a non-aqueous electrolyte secondary battery, wherein the silicon-containing particle is obtained by thermally curing at least a part of the surface of the silicon particle. The silicon is coated with a thermosetting resin, the thickness of the thermosetting resin is 5 nm or more and 500 nm or less, and the crystal particle diameter of the silicon particles is 1 nm or more and 300 nm or less. Provide contained particles.

  If such a silicon-containing particle is used as a negative electrode active material for a non-aqueous electrolyte secondary battery, the volume expansion associated with charging / discharging of the silicon particles as a base material is relatively small, and the thermosetting coating the surface The volume expansion of the silicon-containing particles can be further suppressed by the functional resin, which enables not only the organic solvent-based binder having a strong binding force but also SBR (styrene-butadiene rubber), polyacrylic acid, etc. having a relatively weak binding force. Even if a negative electrode active material mixture is prepared using an aqueous binder (water-soluble binder) as a binder and applied to a current collector to produce a negative electrode, a non-aqueous electrolyte secondary battery with good cycle characteristics is obtained. In addition, even when mixed with a graphite-based negative electrode material, good cycle characteristics can be obtained.

  Furthermore, even when the silicon particles are refined (ie, split) due to volume expansion, the surface of the silicon particles is covered with a thermosetting resin, so that the active silicon surface newly generated by the refinement can be electrolyzed. Since excessive reaction with the liquid can be suppressed, a non-aqueous electrolyte secondary battery with stable cycle characteristics can be provided.

The true density of the silicon particles is preferably 2.260 g / cm ³ or more and 3.500 g / cm ³ or less.
By setting the true density to 2.260 g / cm ³ or more, silicon particles having a small volume change accompanying charge / discharge and good cycle characteristics can be obtained. In addition, by setting the true density to 3.500 g / cm ³ or less, it is possible to prevent the electric capacity per weight from greatly decreasing.

At this time, the silicon particles, as additive elements, boron, aluminum, phosphorus, titanium, vanadium, chromium, manganese, iron, cobalt, nickel, copper, zinc, arsenic, germanium, tin, antimony, indium, tantalum, tungsten, It is preferable that one or more elements selected from gallium are added .
If one or more elements selected from such element groups are added as additive elements , the volume resistivity can be lowered, so that the non-aqueous electrolyte with excellent electron conductivity can be reduced. The negative electrode of a secondary battery can be formed.

Furthermore, the silicon-containing particles described above can be used as a negative electrode material for a nonaqueous electrolyte secondary battery as a negative electrode active material for a nonaqueous electrolyte secondary battery.
Thus, by using the above-mentioned silicon-containing particles as a negative electrode active material for a non-aqueous electrolyte secondary battery in a negative electrode material for a non-aqueous electrolyte secondary battery, a high-capacity and long-life non-aqueous electrolyte secondary battery can be obtained. Can be provided.

Moreover, the negative electrode material of the nonaqueous electrolyte secondary battery may further include a water-soluble binder as a binder.
As described above, in the present invention, the negative electrode material of the non-aqueous electrolyte secondary battery can use a water-soluble binder having a relatively weak fixing power as a binder, and has a high capacity and long life non-aqueous electrolyte secondary battery. Battery can be provided.

Moreover, the negative electrode material of the nonaqueous electrolyte secondary battery may further include graphite as a conductive agent.
Thus, the electrical conductivity of the negative electrode material of a nonaqueous electrolyte secondary battery can be maintained by further including graphite as a conductive agent.

Here, the nonaqueous electrolyte secondary battery includes a negative electrode molded body made of the negative electrode material of the nonaqueous electrolyte secondary battery described above, a positive electrode molded body, the negative electrode molded body, and a separator that separates the positive electrode molded body. The nonaqueous electrolyte is preferably included.
Thus, the nonaqueous electrolyte secondary battery includes the negative electrode molded body made of the negative electrode material of the nonaqueous electrolyte secondary battery described above, whereby a nonaqueous electrolyte secondary battery having a high capacity and a long life can be obtained.

In the above non-aqueous electrolyte secondary battery, the non-aqueous electrolyte preferably contains lithium ions.
The negative electrode molded body made of the negative electrode material of the non-aqueous electrolyte secondary battery described above has a higher capacity than a negative electrode molded body made of a negative electrode material of a non-aqueous electrolyte secondary battery containing a conventional graphite material as an active material, and the like. Since the irreversible capacity is small, the volume change accompanying charge / discharge is controlled to be small, and the cycle characteristics are excellent, the nonaqueous electrolyte can be suitably used for a lithium ion secondary battery containing lithium ions.

  As described above, by using the silicon-containing particles of the present invention for the negative electrode active material of a non-aqueous electrolyte secondary battery, a high-capacity and long-life non-aqueous electrolyte secondary battery can be provided.

Hereinafter, the present invention will be described more specifically.
As described above, various methods have been proposed in order to use silicon as an active material. However, in these methods, expansion of silicon particles or silicon alloy particles cannot be suppressed, and a charge / discharge cycle is performed. The problem that the capacity of the battery decreased as time passed remained.

Therefore, the present inventor conducted extensive studies on a silicon-based active material in which the battery capacity per unit mass of the active material exceeds the theoretical capacity of 372 mAh / g of the carbon material while maintaining cycle stability.
As a result, as the silicon-containing particles used in the negative electrode active material of the nonaqueous electrolyte secondary battery, at least a part of the surface of the silicon particles is coated with a thermosetting resin that is thermoset, and the thermosetting resin By using silicon-containing particles having a thickness of 5 nm or more and 500 nm or less and a crystal particle diameter of silicon particles of 1 nm or more and 300 nm or less, a battery capacity higher than that of the carbon-based active material is exhibited, and a substrate is obtained. It has been found that the thermosetting resin on the particle surface can suppress the volume change associated with charging / discharging of the silicon particles and the cycle characteristics can be improved, and the present invention has been made.

  As a method of coating the surface of silicon particles, which are the base material of the silicon-containing particles of the present invention, with a thermosetting resin, a solution of a thermosetting resin or a precursor thereof and silicon particles are mixed, and heated or reduced pressure conditions. A method of removing the solvent under such as below. The method for removing the solvent is not particularly limited, but it is more advantageous to use a spray drying method or a stirring drying method because the particle surface can be coated more uniformly.

The above-mentioned thermosetting resin is used without particular limitation, for example, phenol resin, urea resin, melamine resin, furan resin, xylene resin, epoxy resin, unsaturated polyester resin, thermosetting polyimide, thermosetting polyamideimide, etc. However, it is preferable to use polyimide or polyamideimide from the viewpoint of the strength, heat resistance, and solvent resistance of the resin.
In addition, these thermosetting resins preferably have a hydroxyl group, a carboxyl group, an amino group, or a sulfonyl group introduced as a functional group. By using a thermosetting resin having these functional groups, it is possible to smoothly insert or desorb lithium ions during charging and discharging.

  Further, a conductive material may be mixed with the thermosetting resin. The conductive material is not particularly limited as long as it is widely used as a conductive material for non-aqueous electrolyte secondary batteries, such as carbon black such as acetylene black and ketjen black, and carbon nanofibers. One type or a mixture of two or more types can be used. Thereby, the electrical resistance of the silicon-containing particles obtained by the present invention can be lowered.

The thermosetting of the thermosetting resin covering the surface of the silicon particles is preferably performed at a temperature of 150 ° C. or more and 600 ° C. or less in an inert atmosphere under normal pressure or reduced pressure, and is preferably performed at a temperature of 400 ° C. or less. More preferred.
If the thermosetting temperature is 150 ° C. or higher, the curing of the thermosetting resin by heating proceeds sufficiently, and if the thermosetting temperature is 600 ° C. or lower, the thermosetting resin will not carbonize. In any case, the effect of suppressing the volume expansion of the particles accompanying charge / discharge is sufficiently exhibited.

The thermosetting resin covering the surface of the silicon particles has a thickness of 5 nm or more and 500 nm or less after thermosetting.
When the thickness is smaller than 5 nm, the effect of suppressing the volume expansion of the silicon particles serving as the base material associated with charge / discharge is reduced, and it does not contribute to the improvement of the cycle characteristics.
On the other hand, when the thickness is larger than 500 nm, the proportion of the thermosetting resin in the obtained silicon-containing particles becomes too large, and the battery capacity is lowered.

  The silicon-containing particles of the present invention have a Scherrer as the crystal particle diameter of the silicon particles that are the substrate, from the full width at half maximum of the diffraction line attributed to Si (111) near 2θ = 28.4 ° in the analysis of the X-ray diffraction pattern. The value obtained by the method (Scherrer method) is 1 nm or more and 300 nm or less.

With such silicon-containing particles, when used as a negative electrode active material for a secondary battery using a non-aqueous electrolyte, the volume change during charging and discharging is suppressed, and the stress at the crystal grain boundary is relieved, High initial efficiency (ratio of discharge capacity to initial charge capacity) and high battery capacity of the silicon-based active material are maintained.
In general, even when mixed with graphite-based materials having a small volume expansion, only silicon-containing particles do not cause large volume expansion, so that the separation between the graphite material and the silicon-containing particles is small and the cycle characteristics are excellent. A water electrolyte secondary battery is obtained.

Below, the measurement conditions of X-ray crystal diffraction are illustrated.
As an X-ray diffractometer, D8 ADVANCE manufactured by BRUKER AXS can be used. X-ray source is Cu Kα ray, using Ni filter, output 40kv / 40mA, slit width 0.3 °, step width 0.0164 °, measurement up to 10-90 ° with counting time of 1 second per step To do. The data processing after the measurement is performed by removing the Kα2 line at an intensity ratio of 0.5 and performing smoothing processing. By observing the range of 10-60 ° in detail by this measurement, a diffraction line of 28.4 ° attributed to Si (111) having a diamond structure and a diffraction line of 47.2 ° belonging to Si (220). , Three signals of a diffraction line of 56.0 ° attributed to Si (311) are observed as sharp signals with high intensity.

  The silicon particles, which are the base of the silicon-containing particles of the present invention, are analyzed by the Scherrer method (Scherrer method) from the full width at half maximum of the 28.4 ° diffraction line attributed to Si (111), and the crystal particle diameter is calculated. Sorted by things. The crystal particle diameter of the silicon particles that are the substrate of the silicon-containing particles of the present invention is 1 nm or more and 300 nm or less, and preferably 200 nm or less.

It is preferable that the true density value of silicon particles as a substrate of the silicon-containing particles of the present invention measured by a dry densimeter is higher than 2.260 g / cm ^{3 and} lower than 3.500 g / cm ³ .
By setting the true density to 2.260 g / cm ³ or more, silicon particles having a small volume change accompanying charge / discharge and good cycle characteristics can be obtained. In addition, by setting the true density to 3.500 g / cm ³ or less, it is possible to prevent the electric capacity per weight from greatly decreasing.

The measurement conditions of a dry densimeter when measuring the true density of silicon particles are exemplified below.
As a dry density meter, Accupic II 1340 manufactured by Shimadzu Corporation can be used. The purge gas is helium gas, and measurement is performed after purging 200 times in a sample holder set at 23 ° C.

The true density of the silicon particles that are the substrate of the silicon-containing particles of the present invention can also be achieved, for example, by adding an element different from silicon.
The element to be added is one selected from boron, aluminum, phosphorus, titanium, vanadium, chromium, manganese, iron, cobalt, nickel, copper, zinc, arsenic, germanium, tin, antimony, indium, tantalum, tungsten, and gallium. Or it is especially preferable to set it as 2 or more types of elements.
The addition amount of such an element different from silicon is added as necessary, and may be approximately 50% by mass or less, preferably 0.001 to 30% by mass, and further 0.01 to 10% by mass. More preferably.
When the content is 0.01% by mass or more, the volume resistivity is surely lowered. On the other hand, when the content is 10% by mass or less, segregation of the additive element hardly occurs, and an increase in volume expansion can be prevented.

  Examples of methods for adding an element different from silicon to silicon particles include vacuum deposition, melt quenching, sputtering, mechanochemical methods, and the like, and these methods can be used without any particular limitation. From the viewpoint of cost, vacuum deposition is preferred.

  The silicon particles as the base of the silicon-containing particles used as the negative electrode active material of the non-aqueous electrolyte secondary battery obtained as described above have an amorphous grain boundary and a crystalline grain boundary. Due to the stress relaxation effect of the grain boundary, particle collapse in the charge / discharge cycle is reduced. Therefore, by using it as a substrate of silicon-containing particles used as the negative electrode active material of a non-aqueous electrolyte secondary battery, it can withstand the stress of volume expansion change due to charge and discharge, and exhibits high-capacity and long-life battery characteristics.

The powder particle diameter (hereinafter referred to as particle diameter) of silicon particles, which are the base of silicon-containing particles used in the negative electrode active material of the nonaqueous electrolyte secondary battery of the present invention, is a volume average measured by a laser diffraction scattering type particle size distribution measurement method. The value D ₅₀ (that is, the particle diameter or median diameter when the cumulative volume becomes 50%) is preferably 1 μm or more and 20 μm or less.
By the D ₅₀ or more 1 [mu] m, and reduced bulk density, charge and discharge capacity per unit volume can be as much as possible reduced risk of decrease.
Further, by making the D ₅₀ and 20μm or less, it is possible to minimize the risk of causing a short circuit through the negative electrode film, that no formation of the electrode becomes difficult, peeling from the current collector This possibility can be made sufficiently low.

Nikkiso Co., Ltd. Microtrac MT3000 can be used as a laser diffraction scattering type particle size distribution measuring device used for measuring the particle size of silicon particles. The dispersion medium with water, the average value was measured twice is calculated as D _50.

  In order to make the silicon particles that are the base of the silicon-containing particles of the present invention have the above-mentioned particle diameter, they can be pulverized and classified by a known method as described below.

As a pulverizer to be used, for example, a ball mill, a media agitating mill, or a roller compression machine that moves a pulverizing medium such as a ball or a bead and pulverizes a material to be crushed using an impact force, a frictional force, or a compressive force due to the kinetic energy A roller mill that performs pulverization using force, and a rotor that is fixedly equipped with a jet mill, hammer, blade, pin, etc. that pulverizes the crushed material against the lining material or collides with each other at high speed and performs pulverization by the impact force of the impact A hammer mill, a pin mill, a disk mill, a colloid mill using a shearing force, a high-pressure wet facing collision disperser “Ultimizer”, or the like can be used.
The pulverization can be used for both wet and dry processes.

In order to adjust the particle size distribution, dry classification, wet classification or sieving classification is performed after pulverization.
In the dry classification, an air stream is mainly used, and dispersion, separation (separation of fine particles and coarse particles), collection (separation of solid and gas), and discharge are performed sequentially or simultaneously. Pre-treatment (adjustment of moisture, dispersibility, humidity, etc.) before classification so as not to reduce the classification efficiency due to interference between particles, particle shape, air flow turbulence, velocity distribution, static electricity, etc. Or by adjusting the water content and oxygen concentration of the airflow used.
Further, in a dry type in which a classifier is integrated, pulverization and classification are performed at a time, and a desired particle size distribution can be obtained.

  The compounding quantity in the negative electrode material of the silicon-containing particle | grains of this invention can be 3-97 mass% with respect to the whole negative electrode material. Moreover, the compounding quantity of the binder in the said negative electrode material has a good ratio of 1-20 mass% (more desirably 3-10 mass%) with respect to the whole negative electrode material. By setting the blending amount of the binder within the above range, the risk of separation of the negative electrode active material can be reduced as much as possible, the porosity is reduced, the insulating film is thickened, and Li ions move. The risk of obstructing can be reduced as much as possible.

When a negative electrode material is produced using silicon-containing particles for the negative electrode active material of the non-aqueous electrolyte secondary battery as an active material and a binder, the conductive material is diluted with an active material such as graphite. In addition, the effect of relaxing the volume expansion can be further obtained.
In that case, the battery capacity of the negative electrode material is reduced depending on the dilution ratio, but it is possible to increase the capacity compared to the conventional graphite material, and the cycle characteristics are improved as compared with the case of the silicon-containing particles alone. .

  In this case, the type of graphite material is not particularly limited. Specifically, natural graphite, artificial graphite, various coke powders, mesophase carbon, vapor grown carbon fiber, pitch-based carbon fiber, PAN-based carbon fiber, various types Graphite such as a resin fired body can be used.

When the graphite material is used, the addition amount is 2 to 96% by mass with respect to the whole negative electrode material, and even if it is 60 to 95% by mass, the capacity is higher than that of the conventional graphite material.
By making the addition amount and blending amount of this conductive agent within the above ranges, it is possible to reliably suppress the negative electrode material from having poor conductivity and increasing the initial resistance.

The negative electrode material for a nonaqueous electrolyte secondary battery of the present invention obtained as described above can be used as a negative electrode, for example, as follows.
That is, a negative electrode material composed of the negative electrode active material, graphite material, binder, and other additives is kneaded with a solvent suitable for dissolving and dispersing the binder such as N-methylpyrrolidone or water. The mixture is made into a paste, and this mixture is applied in a sheet form on the current collector.
In this case, as the current collector, any material that is usually used as a negative electrode current collector, such as a copper foil or a nickel foil, can be used without any particular limitation on thickness and surface treatment.
In addition, the shaping | molding method which shape | molds said mixture into a sheet form is not specifically limited, A well-known method can be used.
A negative electrode including such a negative electrode material for a non-aqueous electrolyte secondary battery is used for the negative electrode active material for a non-aqueous electrolyte secondary battery of the present invention in which the volume change during charge / discharge is significantly smaller than that of conventional silicon-containing particles. It is mainly composed of a negative electrode active material composed of silicon-containing particles, and the change in film thickness before and after charging does not exceed 3 times (particularly 2.5 times).

By using the molded negative electrode using the negative electrode thus obtained, a non-aqueous electrolyte secondary battery, particularly a lithium ion secondary battery can be manufactured.
In this case, the non-aqueous electrolyte secondary battery is characterized in that the negative electrode molded body is used, and other positive electrodes (molded bodies), separators, electrolytes, non-aqueous electrolyte materials, and battery shapes are particularly limited. Not.

For example, examples of the positive electrode active material include oxides or sulfides capable of inserting and extracting lithium ions, and any one or two or more of these are used.
Specifically, TiS ₂ , MoS ₂ , NbS ₂ , ZrS ₂ , VS ₂ or V ₂ O ₅ , MoO ₃ and Mg (V ₃ O ₈ ) ₂ -free metal sulfide or oxide containing no lithium, or Examples thereof include lithium and lithium composite oxides containing lithium, and also include composite metals such as NbSe _{2 and} iron olivate. Among these, in order to increase the energy density, a lithium composite oxide mainly composed of Li _p MetO ₂ is desirable. “Met” is preferably at least one of cobalt, nickel, iron, and manganese, and p is usually a value in the range of 0.05 ≦ p ≦ 1.10. Specific examples of the lithium composite _{oxide, LiCoO 2, LiNiO 2, LiFeO} 2, Li q Ni r Co 1-r O 2 ( where, the values of q and r is a charge-discharge state of the battery with a layer structure Usually, 0 <q <1, 0.7 <r ≦ 1), spinel-structured LiMn ₂ O ₄ and orthorhombic LiMnO ₂ are mentioned.
Furthermore, LiMet _s Mn _1-s O ₄ (0 <s <1) is also used as a substituted spinel manganese compound as a high-voltage compatible type, where Met is titanium, chromium, iron, cobalt, nickel, copper and zinc. Etc.

  The lithium composite oxide is obtained by, for example, grinding lithium carbonate, nitrate, oxide or hydroxide, and transition metal carbonate, nitrate, oxide or hydroxide according to a desired composition. It can prepare by mixing and baking at the temperature within the range of 600-1000 degreeC in oxygen atmosphere.

  Furthermore, an organic substance can also be used as the positive electrode active material. Illustrative examples include polyacetylene, polypyrrole, polyparaphenylene, polyaniline, polythiophene, polyacene, polysulfide compounds and the like.

  The above positive electrode active material is kneaded together with the conductive agent and binder used for the negative electrode mixture and applied to the current collector, and can be formed into a positive electrode molded body by a known method.

  In addition, the separator used between the positive electrode and the negative electrode is not particularly limited as long as it is stable with respect to the electrolytic solution and has excellent liquid retention, but in general, polyolefins such as polyethylene and polypropylene, and copolymers thereof. Examples thereof include a porous sheet such as a polymer and an aramid resin, or a nonwoven fabric. These may be used as a single layer or multiple layers, and ceramics such as metal oxide may be laminated on the surface. Moreover, porous glass, ceramics, etc. are also used.

The solvent for the non-aqueous electrolyte secondary battery used in the present invention is not particularly limited as long as it can be used as a non-aqueous electrolyte.
Generally, aprotic high dielectric constant solvents such as ethylene carbonate, propylene carbonate, butylene carbonate, γ-butyrolactone, dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, methyl propyl carbonate, dipropyl carbonate, diethyl ether, tetrahydrofuran, 1,2, -Aprotic low viscosity such as acetate ester or propionate ester such as dimethoxyethane, 1,2-diethoxyethane, 1,3-dioxolane, sulfolane, methylsulfolane, acetonitrile, propionitrile, anisole, methyl acetate A solvent is mentioned. It is desirable to use these aprotic high dielectric constant solvents and aprotic low viscosity solvents in combination at an appropriate mixing ratio.
Furthermore, ionic liquids using imidazolium, ammonium, and pyridinium type cations can be used. The counter anion is not particularly limited, and examples thereof include BF ₄ ⁻ , PF ₆ ⁻ , (CF ₃ SO ₂ ) ₂ N ^{− and the} like. The ionic liquid can be used by mixing with the non-aqueous electrolyte solvent described above.

  When a solid electrolyte or a gel electrolyte is used, it is possible to contain a silicone gel, a silicone polyether gel, an acrylic gel, a silicone acrylic gel, an acrylonitrile gel, poly (vinylidene fluoride), or the like as a polymer material. These may be polymerized in advance or may be polymerized after injection. These can be used alone or as a mixture.

Moreover, as an electrolyte salt, a light metal salt is mentioned, for example.
Examples of the light metal salt include alkali metal salts such as lithium salt, sodium salt, or potassium salt, alkaline earth metal salts such as magnesium salt or calcium salt, or aluminum salt, and one or more kinds depending on the purpose. Is selected.
For example, in the case of a lithium salt, LiBF ₄ , LiClO ₄ , LiPF ₆ , LiAsF ₆ , CF ₃ SO ₃ Li, (CF ₃ SO ₂ ) ₂ NLi, C ₄ F ₉ SO ₃ Li, CF ₃ CO ₂ Li, ( CF ₃ CO ₂ ) ₂ NLi, C ₆ F ₅ SO ₃ Li, C ₈ F ₁₇ SO ₃ Li, (C ₂ F ₅ SO ₂ ) ₂ NLi, (C ₄ F ₉ SO ₂ ) (CF ₃ SO ₂ ) NLi , (FSO ₂ C ₆ F ₄ ) (CF ₃ SO ₂ ) NLi, ((CF ₃ ) ₂ CHOSO ₂ ) ₂ NLi, (CF ₃ SO ₂ ) ₃ CLi, (3,5- (CF ₃ ) ₂ C ₆ F ₃ ) ₄ BLi, LiCF ₃ , LiAlCl _4, or C ₄ BO ₈ Li may be used, and any one or two or more of these may be used in combination.

  The concentration of the electrolyte salt in the nonaqueous electrolytic solution is preferably 0.5 to 2.0 mol / L from the viewpoint of electrical conductivity. The conductivity of the electrolyte at 25 ° C. is preferably 0.01 S / cm or more, and is adjusted according to the type or concentration of the electrolyte salt.

Furthermore, various additives may be added to the nonaqueous electrolytic solution as necessary.
For example, vinylene carbonate, methyl vinylene carbonate, ethyl vinylene carbonate, 4-vinyl ethylene carbonate for the purpose of improving cycle life, biphenyl, alkyl biphenyl, cyclohexyl benzene, t-butyl benzene, diphenyl ether for the purpose of preventing overcharge. Benzofuran and the like, various carbonate compounds for the purpose of deoxidation and dehydration, various carboxylic acid anhydrides, various nitrogen-containing compounds and sulfur-containing compounds.

  And the shape of a nonaqueous electrolyte secondary battery is arbitrary, and there is no restriction | limiting in particular. In general, a coin type battery in which an electrode punched into a coin shape and a separator are stacked, and a square type or cylindrical type battery in which an electrode sheet and a separator are wound in a spiral shape are included.

  EXAMPLES Hereinafter, although an Example and a comparative example are shown and this invention is demonstrated more concretely, this invention is not limited to these.

(Preparation of silicon particles 1)
A multi-point copper crucible having a carbon hearth liner with a thickness of 5 mm was placed inside a vacuum chamber having an exhaust device composed of an oil diffusion pump, a mechanical booster pump and an oil rotary vacuum pump, and 200 g of metal silicon lump was charged. The inside of the chamber was depressurized. The ultimate pressure after 2 hours was 2 × 10 ⁻⁴ Pa.
Next, the melting of the metal silicon mass was completed while gradually increasing the output with a deflection electron gun installed in the chamber, and then the deposition was continued for 2 hours at an output of 10 kW and an output density of 1.2 kW / cm ² . During vapor deposition, the temperature of the vapor deposition substrate made of stainless steel was controlled at 600 ° C. The chamber was opened to obtain 100 g of deposited silicon lump.

  A rotary kiln having an alumina furnace core tube in which the deposited silicon mass produced as described above is pulverized and classified using a roll crusher mill and a jet mill, and the obtained silicon powder is held at 700 ° C. under an Ar stream. The silicon particles 1 were obtained by performing a heat treatment for 3 hours.

(Preparation of silicon particles 2)
Silicon particles 2 were produced in the same manner as silicon particles 1. However, the heat treatment temperature was 200 ° C.

(Preparation of silicon particles 3)
Silicon for chemicals (manufactured by SIMCOA) was pulverized and classified using a roll crusher mill and a jet mill to obtain silicon particles 3.

(Preparation of silicon particles 4)
Silicon particles 4 were produced in the same manner as silicon particles 1. However, the heat treatment temperature was 1100 ° C.

The cumulative volume 50% diameter D ₅₀ , crystal particle diameter, and true density of the silicon particles 1 to 4 are summarized in Table 1.

As shown in Table 1, silicon particles 1 and silicon particles 4 have a crystal particle diameter of 1 nm to 300 nm and a true density of 2.260 to 3.500 g / cm ³ , whereas silicon particles No. 2 has a true density smaller than 2.260 g / cm ³ , and the silicon particles 3 have a crystal grain diameter larger than 300 nm.

(Production of silicon-containing particles)
Example 1
10 g of silicon particles 1 and 0.05 g of polyimide precursor NMP solution (solid content 30.7% by mass) are added to 100 g of N-methyl-2-pyrrolidone (NMP), respectively, and stirred for 30 minutes using a magnetic stirrer. It was.
The obtained slurry was spray-dried using a spray dryer (Nihon Büch B-290) with a drying temperature set to 200 ° C., and the obtained powder was held at 400 ° C. under an Ar stream. Silicon-containing particles were obtained by performing thermosetting for 3 hours in a rotary kiln having an alumina furnace core tube.
When the cross section of the obtained silicon-containing particles was observed with a TEM and the average value of the thickness of the resin layer on the surface of the silicon-containing particles was calculated, it was 7 nm.

(Example 2)
10 g of silicon particles 1 and 7 g of a polyimide precursor NMP solution (solid content: 30.7 mass%) were added to 100 g of NMP, respectively, and stirred for 30 minutes using a magnetic stirrer.
The slurry obtained was spray-dried using a spray dryer with a drying temperature set at 150 ° C., and then the resulting powder was rotary kiln having an alumina furnace core tube held at 400 ° C. under an Ar stream. The silicon-containing particles were obtained by performing thermosetting for 3 hours.
The cross section of the obtained silicon-containing particles was observed with a TEM, and the average value of the thickness of the resin layer on the surface of the silicon-containing particles was calculated to be 472 nm.

(Example 3)
10 g of silicon particles 1 in 100 g of NMP, 7 g of NMP solution of polyimide precursor (solid content 30.7% by mass), 0.12 g of NMP dispersion (solid content 17.5%) of acetylene black were added, respectively, and magnetic. Stirring was performed for 30 minutes using a stirrer.
The slurry obtained was spray-dried using a spray dryer with a drying temperature set at 150 ° C., and then the resulting powder was rotary kiln having an alumina furnace core tube held at 400 ° C. under an Ar stream. The silicon-containing particles were obtained by performing thermosetting for 3 hours.
It was 487 nm when the cross section of the obtained silicon containing particle was observed by TEM and the average value of the thickness of the resin layer of the silicon containing particle surface was computed.

Example 4
10 g of silicon particles 1 in 100 g of NMP, 9 g of NMP solution of polyamideimide precursor (solid content 29.8% by mass), and 0.12 g of NMP dispersion (solid content 17.5%) of acetylene black were added respectively. Stirring was performed for 30 minutes using a tic stirrer.
The slurry obtained was spray-dried using a spray dryer with a drying temperature set at 150 ° C., and then the resulting powder was rotary kiln having an alumina furnace core tube held at 400 ° C. under an Ar stream. The silicon-containing particles were obtained by performing thermosetting for 3 hours.
It was 452 nm when the cross section of the obtained silicon containing particle was observed by TEM and the average value of the thickness of the resin layer of the silicon containing particle surface was computed.

(Example 5)
10 g of silicon particles 1 in 100 g of acetone, 0.3 g of an acetone solution of resol resin (solid content 30.0% by mass), 0.12 g of acetone dispersion of acetylene black (solid content 17.5%) were added, Stirring was performed for 30 minutes using a magnetic stirrer.
The resulting slurry was spray dried using a spray dryer whose drying temperature was set to 80 ° C., and then the obtained powder was rotary kiln having an alumina furnace core tube held at 170 ° C. under an Ar stream. The silicon-containing particles were obtained by performing thermosetting for 3 hours.
When the cross section of the obtained silicon-containing particles was observed with a TEM and the average value of the thickness of the resin layer on the surface of the silicon-containing particles was calculated, it was 15 nm.

(Example 6)
10 g of silicon particles 4 and 0.05 g of a polyimide precursor NMP solution (solid content: 30.7% by mass) were added to 100 g of NMP, respectively, and stirred for 30 minutes using a magnetic stirrer.
The slurry obtained was spray-dried using a spray dryer with a drying temperature set at 150 ° C., and then the resulting powder was rotary kiln having an alumina furnace core tube held at 400 ° C. under an Ar stream. The silicon-containing particles were obtained by performing thermosetting for 3 hours.
When the cross section of the obtained silicon-containing particles was observed with a TEM and the average value of the thickness of the resin layer on the surface of the silicon-containing particles was calculated, it was 6 nm.

(Example 7)
10 g of silicon particles 4 and 0.05 g of a polyimide precursor NMP solution (solid content: 30.7% by mass) were added to 100 g of NMP, respectively, and stirred for 30 minutes using a magnetic stirrer.
The slurry obtained was spray-dried using a spray dryer with a drying temperature set at 150 ° C., and then the resulting powder was rotary kiln having an alumina furnace core tube held at 400 ° C. under an Ar stream. The silicon-containing particles were obtained by performing thermosetting for 3 hours.
It was 487 nm when TE observation of the cross section of the obtained silicon-containing particle | grain and the average value of the thickness of the resin layer of the silicon-containing particle | grain surface was computed.

(Comparative Example 1)
The silicon particles 1 were not coated with a thermosetting resin, and were subjected to heat treatment for 3 hours in a rotary kiln having an alumina core tube maintained at 400 ° C. under an Ar stream.

(Comparative Example 2)
10 g of silicon particles 1 and 0.02 g of an NMP solution of a polyimide precursor (solid content: 8.7% by mass) were added to 100 g of NMP, respectively, and stirred for 30 minutes using a magnetic stirrer.
The slurry obtained was spray-dried using a spray dryer with a drying temperature set at 150 ° C., and then the resulting powder was rotary kiln having an alumina furnace core tube held at 400 ° C. under an Ar stream. The silicon-containing particles were obtained by performing thermosetting for 3 hours.
The cross section of the obtained silicon-containing particles was observed with a TEM, and the average value of the thickness of the resin layer on the surface of the silicon-containing particles was calculated to be 2 nm.

(Comparative Example 3)
10 g of silicon particles 1 and 28 g of an NMP solution of polyimide precursor (solid content: 8.7% by mass) were added to 100 g of NMP, respectively, and stirred for 30 minutes using a magnetic stirrer.
The slurry obtained was spray-dried using a spray dryer with a drying temperature set at 150 ° C., and then the resulting powder was rotary kiln having an alumina furnace core tube held at 400 ° C. under an Ar stream. The silicon-containing particles were obtained by performing thermosetting for 3 hours.
It was 541 nm when the cross section of the obtained silicon containing particle was observed by TEM and the average value of the thickness of the resin layer of the silicon containing particle surface was computed.

(Example 8)
Silicon-containing particles were produced in the same manner as in Example 1. However, silicon particles 2 were used as silicon particles. When the cross section of the obtained silicon-containing particles was observed with a TEM and the average value of the thickness of the resin layer on the surface of the silicon-containing particles was calculated, it was 6 nm.

(Comparative Example 4)
Silicon-containing particles were produced in the same manner as in Example 1. However, silicon particles 3 were used as silicon particles. The cross section of the obtained silicon-containing particles was observed with a TEM and the average value of the thickness of the resin layer on the surface of the silicon-containing particles was calculated to be 10 nm.

  Table 2 summarizes the types and thicknesses of the base silicon particles and the thermosetting resin of the silicon-containing particles of Examples 1-8 and Comparative Examples 1-4.

<Evaluation of battery characteristics>
The silicon-containing particles of Example 1-8 and Comparative Example 1-4 were evaluated for battery characteristics in order to confirm their usefulness as a negative electrode active material.
15% by mass of the silicon-containing particles of Examples 1-8 and Comparative Example 1-4 as the negative electrode active material, 79.5% of artificial graphite (average particle diameter D ₅₀ = 10 μm) as the conductive agent, CMC (carboxymethylcellulose) ) 1.5% by mass of powder was mixed. To this, an aqueous dispersion of acetylene black (solid content 17.5%) was 2.5% by mass in terms of solid content and an aqueous dispersion of SBR (styrene-butadiene rubber) (solid content 40%) was 1 in terms of solid content. 0.5% by mass was added and diluted with ion-exchanged water to obtain a slurry.

This slurry was applied to a copper foil having a thickness of 12 μm using a 150 μm doctor blade, and after preliminary drying, the electrode was pressure-formed by a roller press at 60 ° C., dried at 160 ° C. for 2 hours, and then punched to 2 cm ² . A negative electrode molded body was obtained.

The negative electrode molded body obtained as described above was prepared using a lithium foil as a counter electrode, and lithium bis (trifluoromethanesulfonyl) imide as a nonaqueous electrolyte in a 1/1 (volume ratio) mixture of ethylene carbonate and diethyl carbonate. Four lithium ion secondary batteries for evaluation each using a non-aqueous electrolyte solution dissolved at a concentration of 1 mol / L and a polyethylene microporous film having a thickness of 30 μm as a separator were prepared.
Then, the produced lithium ion secondary battery was aged overnight at room temperature, two of them were disassembled, the thickness of the negative electrode was measured, and the electrode density based on the initial weight in the electrolyte solution swollen state was calculated. Note that the amount of increase in lithium due to the electrolyte and charging was not included.

  In addition, using a secondary battery charge / discharge test device (manufactured by Nagano Co., Ltd.), charge two with a constant current of 0.15c until the voltage of the test cell reaches 0V. Charging was performed by decreasing the current so as to keep the voltage at 0V. And charging was complete | finished when the electric current value fell below 0.02c, and charge capacity was computed. Note that c is a current value for charging the theoretical capacity of the negative electrode in one hour.

  After the completion of charging, these evaluation lithium ion secondary batteries were disassembled, and the thickness of the negative electrode was measured. Similarly, the electrode density was calculated from the measured thickness, and the charge capacity per volume during charging was determined. The results are shown in Table 2.

<Evaluation of cycle characteristics>
In order to evaluate the cycle characteristics of the obtained molded negative electrode, a molded negative electrode prepared from the negative electrode active materials of Example 1-8 and Comparative Example 1-4 was prepared. A positive electrode molded body was produced using a single layer sheet (trade name: PIOCSEL C-100, manufactured by Pionics Corporation) using LiCoO ₂ as a positive electrode material and a positive electrode active material and an aluminum foil as a current collector. For the non-aqueous electrolyte, a non-aqueous electrolyte solution in which lithium hexafluorophosphate was dissolved in a 1/1 (volume ratio) mixture of ethylene carbonate and diethyl carbonate at a concentration of 1 mol / L was used, and a polyethylene having a thickness of 30 μm was used as the separator. A coin-type lithium ion secondary battery using the manufactured microporous film was produced.

After the four types of coin-type lithium ion secondary batteries produced were left at room temperature overnight, using a secondary battery charge / discharge tester (manufactured by Nagano Co., Ltd.) until the voltage of the test cell reached 4.2V Charging was performed at a constant current of 1.2 mA (0.25 c based on the positive electrode), and after reaching 4.2 V, charging was performed by decreasing the current so as to keep the cell voltage at 4.2 V. The charging was terminated when the current value was less than 0.3 mA.
The discharge was performed at a constant current of 0.6 mA, and when the cell voltage reached 3.3 V, the discharge was terminated and the discharge capacity was determined.

  Table 3 shows values (capacity retention ratio) obtained by dividing the above-described charging / discharging for 200 cycles and dividing the initial discharge capacity and the discharge capacity after 100 cycles and 200 cycles by the initial discharge capacity.

As shown in Table 3, with respect to the charge capacity, in all of Examples 1-8 and Comparative Examples 1-4, a negative electrode material having a higher charge capacity than that of graphite (372 mAh / g) was formed. It was confirmed that Next, when Example 1 and Comparative Example 4 are compared, Example 1 using silicon particles 1 having a crystal particle diameter of 1 nm to 300 nm is compared with Comparative Example 4 in which the crystal particle diameter does not satisfy the above range. The volume expansion rate was low and the capacity retention rate was high, confirming the superiority. Further, Example 1 using silicon particles 1 having a true density of 2.260 g / cm ³ or more and 3.500 g / cm ³ or less is similar to Example 8 using silicon particles 2 whose true density does not satisfy the above range. It can be seen that the capacity retention rate is higher than that. Further, when Example 1-8 is compared with Comparative Example 1-3, Example 1-8 in which the thickness of the thermosetting resin covering the surface of the silicon particles is 5 nm or more and 500 nm or less is a comparison that does not satisfy the above range. Compared with Example 1-3, the charge capacity or capacity maintenance rate was high, and superiority was confirmed. Further, Comparative Example 1 in which the surface of the silicon particles is not coated with the thermosetting resin has a higher volume expansion rate and a lower capacity retention rate than those of Examples 1-8 and Comparative Example 2-4. It has been confirmed that the coating by is effective in lowering the volume expansion rate and improving the capacity retention rate.

  The present invention is not limited to the above embodiment. The above-described embodiment is an exemplification, and the present invention has substantially the same configuration as the technical idea described in the claims of the present invention, and any device that exhibits the same function and effect is the present invention. It is included in the technical scope of the invention.

Claims (8)

Silicon-containing particles used in the negative electrode active material of a non-aqueous electrolyte secondary battery,
The silicon-containing particles are coated with a thermosetting resin in which at least a part of the surface of the silicon particles is thermoset,
The thickness of the thermosetting resin is 5 nm or more and 500 nm or less,
Silicon-containing particles, wherein the silicon particles have a crystal particle diameter of 1 nm or more and 300 nm or less. 2. The silicon-containing particle according to claim 1, wherein a true density of the silicon particle is 2.260 g / cm ³ or more and 3.500 g / cm ³ or less. The silicon particles are selected from boron, aluminum, phosphorus, titanium, vanadium, chromium, manganese, iron, cobalt, nickel, copper, zinc, arsenic, germanium, tin, antimony, indium, tantalum, tungsten, and gallium as additive elements. The silicon-containing particles according to claim 1 or 2, wherein one or two or more elements to be added are added .   A negative electrode material for a non-aqueous electrolyte secondary battery comprising the silicon-containing particles according to any one of claims 1 to 3 as a negative electrode active material for a non-aqueous electrolyte secondary battery.   The negative electrode material of the nonaqueous electrolyte secondary battery according to claim 4, wherein the negative electrode material of the nonaqueous electrolyte secondary battery further includes a water-soluble binder as a binder.   The negative electrode material for a nonaqueous electrolyte secondary battery according to claim 4 or 5, wherein the negative electrode material for the nonaqueous electrolyte secondary battery further contains graphite as a conductive agent. A negative electrode molded body comprising the negative electrode material for a nonaqueous electrolyte secondary battery according to any one of claims 4 to 6,
A positive electrode molded body,
A separator for separating the molded negative electrode and the molded positive electrode;
A non-aqueous electrolyte,
A non-aqueous electrolyte secondary battery comprising:   The nonaqueous electrolyte secondary battery according to claim 7, wherein the nonaqueous electrolyte contains lithium ions.