JP2021047980A - Negative electrode material for lithium ion secondary battery and method for producing the same, electrode structure, and secondary battery - Google Patents

Abstract

To provide: an active material including silicon as a primary component, in which the formation of a silicon oxide is suppressed; an electrode structure with a high capacity and a long life; and a power storage device.SOLUTION: There are provided: an electrode structure comprising a negative electrode active material for a secondary battery capable of electrochemically occluding and releasing lithium ions, which is a particle including amorphous or nanocrystal silicon dispersed in a lithium ion conductor made of an inorganic material, the content of silicon in the particle being 20-60 mass%; and a lithium ion secondary battery in which the electrode structure is used as a negative electrode.SELECTED DRAWING: Figure 1

Description

The present invention relates to an electrode material for a negative electrode capable of accumulating and releasing lithium ions, which contains silicon as a main component, a method for producing the same, an electrode structure made of the material, and a lithium ion secondary battery having the electrode structure.

In recent years, it has been pointed out that the global climate change may be caused by the greenhouse effect, which is mainly due to the increase in the amount of carbon dioxide gas in the atmosphere. It has been pointed out that air pollution containing carbon dioxide, nitrogen oxides, hydrocarbons, etc. emitted from automobiles used as a means of transportation also has an impact on health. Due to the soaring energy of crude oil and environmental conservation, we have recently managed the network of power from hybrid vehicles, electric vehicles, and power generation facilities that combine an electric motor and engine that are operated by electricity stored in a power storage device, which is highly energy efficient. There are great expectations for smart grids, which are systems that optimize the balance of electricity demand. Also, in the field of information and communication, information terminals such as smartphones can easily send and receive information, so that they are rapidly permeating society. Under these circumstances, in order to improve the performance of smartphones, hybrid vehicles, electric vehicles, smart grids, etc. and reduce production costs, we have developed a secondary battery storage device that has high output density, high energy density, and long life. Is expected.

Among the above-mentioned energy storage devices currently commercialized, the one having the highest energy density is a lithium ion secondary battery (in a broad sense) using carbon such as graphite for the negative electrode and a compound of lithium and a transition metal for the positive electrode. In that sense, it is called a lithium secondary battery).

However, in this lithium ion secondary battery, since the negative electrode is composed of a carbon material, theoretically, only a maximum of 1/6 lithium atom per carbon atom can be intercalated. Therefore, it is difficult to further increase the capacity, and a new electrode material for increasing the capacity is desired. In addition, the above-mentioned lithium ion secondary battery is expected as a power source for hybrid vehicles and electric vehicles because of its high energy density, but the internal resistance of the battery is large for rapid discharge, and a sufficient amount of electricity cannot be released, that is, output. There is also the problem that the density is low. Therefore, there is a demand for the development of a power storage device having a high output density and a high energy density. To meet these demands, silicon and its alloys, which can store and release more lithium ions than graphite, are being studied. Silicon can store more lithium ions electrochemically, but it expands in volume by about four times, and by repeating expansion and contraction by charging and discharging, it becomes finely divided, and the impedance of the electrode increases and the performance deteriorates. Invite. Furthermore, unstable SEI (Solid Electrolyte Interface) is formed during charging, the thickness of the SEI layer increases with the number of charges and discharges, and the impedance of the electrodes increases, so batteries with a long charge / discharge cycle life are still in practical use. Not.

In order to improve the cycle life of the silicon electrode, Patent Document 1 proposes silicon particles coated with titanium oxide or zirconium oxide by the sol-gel method. Further, Patent Document 2 proposes a negative electrode material in which the surface is coated with an oxide of Mg, Al, Ti, Si and silicon nanoparticles are dispersed in silicon oxide.
However, in the case of 3 μm silicon particles coated with a coating layer of titanium oxide of 150 nm shown in Examples in Patent Document 1, volume expansion occurs due to lithium insertion into the silicon particles during charging, which occurs during expansion. The stress causes micronization, and the charge / discharge cycle life cannot be extended to the practical range. Further, in Patent Document 2, although the charge / discharge cycle life can be extended, the metal oxide of the surface coating layer and the silicon oxide of the negative electrode material and lithium cause an irreversible reaction during charging, and the initial charge / discharge efficiency is extremely lowered. There is a problem.

Patent Document 3 describes a composite of silicon or tin and an alloy thereof, and a metal oxide or a semi-metal oxide having a smaller gypsum free energy than the oxide of silicon oxide and tin, and the metal oxide in the composite. Alternatively, a material having a mass ratio of semi-metal oxide of 1/99 to 3/7 has been proposed. Further, Patent Document 4 discloses a method of coating the surface of silicon nanoparticles with an oxide containing at least an element of a metal selected from Li and Al, Zr, Mg, and La.
When the materials proposed in both Patent Document 3 and Patent Document 4 are used as the negative electrode material of a secondary battery that electrochemically occludes and releases lithium ions, an electrolytic solution on the surface of silicon or tin and their alloys. Although the decomposition of such substances is suppressed and the charge / discharge cycle life is improved, the volume expansion during charging is still large, the proposed effect cannot be maintained for a long time, and the charge / discharge cycle life cannot be sufficiently improved.

Non-Patent Document 1 shows that a long life can be achieved by producing double-walled silicon nanotubes coated with silicon oxide by an electrospinning method. However, even in Non-Patent Document 1, there is a problem that the initial charge / discharge efficiency is low because there is lithium that irreversibly reacts with silicon oxide by the initial charge. In addition, the manufacturing cost in the manufacturing process is high, and mass production is difficult.
Non-Patent Document 2 proposes an alumina-coated silicon nanowire by the atomic layer deposition method as an electrode active material having a long cycle life. However, the production of the silicon nanotubes requires many steps and cannot be said to be a method suitable for mass production, and the production of the silicon nanowires is also unsuitable for mass production, so that the silicon nanotubes and silicon nanowires are provided at low cost. It was difficult to do. In addition, the alumina coating by the atomic layer deposition method was also unsuitable for mass production.

Japanese Unexamined Patent Publication No. 2006-190642 Japanese Unexamined Patent Publication No. 2011-96455 US Published Patent 2017/0200943A1 Japanese Unexamined Patent Publication No. 2016-021332

Nature Nanotechnology, 7, 310-315 (2012) The Journal of Materials Chemistry, 22, 24618-24626 (2012)

Silicon is a material that can electrochemically store and release a large amount of lithium, but storing lithium ions is accompanied by large volume expansion. In addition, it expands to a maximum of about four times the volume by storing lithium ions, and contracts by releasing lithium ions, but by repeating expansion and contraction, silicon particles (silicon particles including silicon alloy particles) Here, collectively referred to as silicon particles), when they are large, they collapse and become finely divided. Even when finely divided silicon particles are used and they do not become fine particles during storage of lithium ions, at least in the electrode formed from the silicon particles and the binder, due to the expansion and contraction of the silicon particles, (i) the silicon particles and the silicon particles The binder that adheres to the particles is stretched or cut. (Ii) A new active surface of silicon particles appears due to the expansion and contraction of the volume during charging and discharging, and the insulator layer grows due to a side reaction such as an electrolytic solution. The impedance of the electrode increases. When an electrolytic solution in which a lithium salt is dissolved in a solvent is used as the electrolyte, various compounds are contained in the solid-liquid interface between the silicon particles and the electrolytic solution in the decomposition of the electrolytic solution and the reaction between the decomposition products and lithium ions. , What is called an SEI (Solid Electrolyte Interface) layer is formed, and by repeating charging and discharging, the film thickness of the SEI layer increases, the impedance of the electrode increases, and the charging and discharging performance deteriorates. It is considered that the electrolytic solution decomposition reaction, which is the basis of the SEI layer formation, occurs remarkably in the active silicon dangling bond on the surface of the silicon particles.

In a lithium ion secondary battery using the electrode using the silicon particles as the negative electrode, the impedance increases and the charge / discharge amount decreases as the charging / discharging is repeated.
In addition, a silicon oxide layer is usually formed on the surface of the silicon particles. The silicon oxide causes an irreversible reaction with lithium during the lithium insertion reaction during charging, and if the silicon oxide layer is thick, the initial charge / discharge efficiency is greatly reduced, which makes battery design difficult.

As described above, the lithium ion secondary battery using silicon particles as the negative electrode material can achieve a high capacity, but has a short charge / discharge cycle life, and the following problems have not been solved and have not been put into practical use.
(1) Suppression of expansion of individual silicon particles
(2) Reduction of silicon oxide layer on the surface of silicon particles
(3) Suppression of decomposition of electrolytic solution and suppression of increase in film thickness of SEI layer

In order to solve the above-mentioned problems, the present inventor has made extensive studies and found a method for solving the above-mentioned problems.
When a lithium insertion reaction occurs in silicon particles during charging, it is considered that lithium invades and alloys from the surface of silicon due to the reduction reaction of lithium ions, lithium diffuses inside, and alloying and volume expansion occur. .. Of the large silicon particles and the small silicon particles, the electric field applied to the surface of the silicon particles during charging is non-uniform in the large silicon particles, so that lithium precipitation tends to be non-uniform, causing non-uniform and large volume expansion. In addition, since the distance that lithium diffuses in the silicon particles is long, the stress generated when lithium and silicon are alloyed and volume-expanded is large, and the particles tend to collapse and become finely divided. Since the alloying reaction occurs more uniformly with small silicon particles, even when the total weights of the large particles and the small particles are equal, the volume expansion of the small particles is smaller and the particles are less likely to be micronized.

Therefore, in order to suppress the volume expansion due to the lithium insertion reaction during charging of the electrode composed of silicon particles as much as possible, it is better to make the silicon particles smaller, but as the particle size becomes smaller, the specific surface area also increases and oxygen When used as the negative electrode of a lithium-ion secondary battery, the initial charge / discharge efficiency drops extremely due to the fact that it easily reacts with and forms silicon oxide, and the ratio of silicon oxide in the silicon particles increases. To do.
Further, when the active surface of the silicon particles comes into direct contact with the electrolytic solution, the decomposition reaction of the electrolytic solution is promoted by the redox reaction during storage or charging, and the SEI layer grows on the silicon surface.

The present inventor solves the above problems (1), (2), and (3) by the following methods, suppresses the production of silicon oxide, and realizes fine particles of silicon particles that can improve the initial charge / discharge efficiency. I found a way to do it.
We have devised active material particles for the negative electrode of a lithium-ion battery in which nanocrystals or amorphous silicon with a small crystallite size are dispersed in a lithium-ion conductor, which is an inorganic material. Further, in order to suppress the volume expansion of the active material particles during charging, the silicon content in the active material particles was limited to 20 to 60% by mass. Then, by making the crystal size of silicon and its crystallite size smaller, the amount of volume that occludes and expands lithium during charging is reduced. In the above method, by forming a thick lithium ion conductor around the silicon particles, it is possible to prevent the formation of the SEI layer by a side reaction on the surface of the silicon particles by making them non-contact with the electrolytic solution. Since the lithium ion conductor surrounding the silicon particles is thick, the active surface of the silicon particles is not exposed to the electrolytic solution due to volume expansion and contraction due to charge and discharge, which suppresses the growth of a new SEI layer. Will be done. Further, by limiting the silicon element content in the active material particles, the volume expansion of the active material particles during charging can also be limited, and the design of the battery can be facilitated.
The silicon particles include silicon or a silicon alloy. The silicon alloy is preferably an alloy of at least a silicon element and a transition metal element, and more preferably an alloy containing a tin element. The silicon alloy is more preferable because it can use an ingot as a raw material, can be manufactured at a lower cost, and has an advantage that the crystallite size can be reduced.

The active material for a negative electrode of the present invention is particles in which amorphous or nanocrystalline silicon is dispersed in a lithium ion conductor of an inorganic material, and the mass ratio of silicon elements in the particles is 20 to 60% by mass. It is characterized by being. By using the above active material, which limits the silicon content (excluding silicon oxide) to 20 to 60% by mass, for the negative electrode of a lithium ion secondary battery, volume expansion caused by occluding lithium during charging can be achieved. It becomes easier to limit. When the amount of silicon in the active material is less than 20% by mass, it is not possible to obtain an advantageous capacity density as compared with the existing negative electrode active material graphite. Further, when the amount of silicon exceeds 60% by mass, a higher capacity density can be obtained, but the repeated charge / discharge life is shortened. The mass ratio of silicon is more preferably 20 to 50% by mass in order to maintain a high capacity and reduce the coefficient of thermal expansion. Further, it is more preferable that the silicon alloy particles are dispersed in the lithium ion conductor of the inorganic material, and the silicon alloy contains amorphous or nanocrystalline silicon.

As the lithium ion conductor of the inorganic material,
A _{Li x M y A z = Li} x (M1 a M2 b M3 c M4 d M5 e M6 f M7 g) compounds which can be represented as _{(A1 h A2 i A3 j)} , in said compound,
M is a metal element and is a group 1 element (M1), a group 2 element (M2), a group 3 element (M3), a group 4 element (M4), and a group 5 element (M5) in the periodic table of elements. , One or more types of elements selected from Group 13 elements (M6) and Group 14 elements (M7).
A is a non-metallic element consisting of one or more elements selected from Group 15 elements (A1), Group 16 elements (A2), and Group 17 elements (A3).
x> 0, y> 0, z> 0, a ≧ 0, b ≧ 0, c ≧ 0, d ≧ 0, e ≧ 0, f ≧ 0, g ≧ 0, h ≧ 0, i ≧ 0, It is preferable that the compound has j ≧ 0, (a + b + c + d + e + f + g)> 0, (h + i + j)> 0.

Furthermore, in the above lithium ion conductor Li _x (M1 _a M2 _b M3 _c M4 _d M5 _e M6 _f M7 _g ) (A1 _h A2 _i A3 _j ),
One or more elements selected from Na and K as the Group 1 element (M1), and one or more elements selected from Mg, Ca, Sr, Ba as the Group 2 element (M2), the third One or more elements selected from Sc, Y, and La as Group 4 elements (M3), one or more elements selected from Ti, Zr, and Hf as Group 4 elements (M4), Group 5 elements One or more elements selected from V, Nb, Ta as (M5), one or more elements selected from B, Al, Ga, In as Group 13 elements (M6), Group 14 elements One or more elements selected from Si, Ge, Sn as (M7), one or more elements selected from N, P, Bi as Group 15 elements (A1), Group 16 elements (A2) ) Is preferably one or more elements selected from O and S, and Group 17 element (A3) is preferably one or more elements selected from F, Cl, Br and I. In order for the ionic conductor to obtain high ionic conductivity, it is more preferable that the combined element of the metallic element and the non-metallic element is composed of three or more kinds of elements. In order for the ionic conductor to have higher ionic conductivity, it is preferable to contain element P as a group 15 element (A1).
The Group 16 element (A2) is more preferably an O element. The oxide in which the group 16 element (A2) is an O element has a higher hardness than the sulfide in which the group 16 element (A2) is an S element, and produces the negative electrode active material for the power storage device of the present invention. Mechanical milling (mechanical milling) at high acceleration in the process facilitates amorphization of silicon or silicon alloys.

Further, in the present invention, the active material particles formed by dispersing silicon particles in the inorganic lithium ion conductor are selected from the group consisting of graphite, amorphous carbon, carbon nanofibers, carbon nanotubes, and graphene. It is preferably composited with more than one type of carbon material. By combining with a carbon material, electron conductivity can be improved.

Further, in the present invention, as a method for producing the active material particles, silicon or a silicon alloy and a raw material of a lithium ion conductor or a lithium ion conductor are mixed and synthesized by a mechanical alloying method of mechanical grinding at high acceleration. It is characterized by having a process. The advantages of the above manufacturing method are that the manufacturing cost is lower than that of SiO and Si-C (composite of silicon and graphite), and the crystallite size of silicon particles dispersed in the lithium ion conductor can be reduced. By reducing the crystallite size, it is possible to reduce the volume expansion of silicon particles due to occlusion of lithium during charging, and it becomes possible to provide a negative electrode for a lithium ion battery having a high capacity and a long charge / discharge cycle life.
In the production method of the present invention, it is also preferable to have a step of performing a heat treatment at a temperature of 300 to 1250 ° C. after the mechanical pulverization treatment. This makes it possible to improve the lithium ion conductivity in the produced active material.

Further, the present invention is characterized in that an electrode layer composed of the negative electrode active material of the present invention and at least a binder selected from a polymer or a low melting point glass is formed on a current collector. It is an electrode structure for the negative electrode of a secondary battery.

Further, the present invention is characterized in that the polar structure is used as a negative electrode and is composed of at least a lithium ion conductor and a positive electrode composed of a lithium transition metal compound capable of inserting and removing lithium ions. Next battery. In the above secondary battery, when the lithium ion conductor provided between the negative electrode and the positive electrode is an electrolytic solution, the electrolytic solution and the silicon particles do not come into direct contact with each other, so that the growth of the SEI layer due to repeated charging and discharging is suppressed. When a solid electrolyte is used for the lithium ion conductor between the negative electrode and the positive electrode, since the lithium ion conductor is contained in the negative electrode active material, it is not necessary to newly contain the solid electrolyte in the negative electrode. There is no decrease in battery capacity density.

In the lithium ion secondary battery using the negative electrode active material of the silicon particles of the present invention, the content of silicon oxide that lowers the charge / discharge efficiency is small, the amount of electricity that can be stored is large, and the resistance is high even if the charge / discharge cycle is repeated. It is difficult to form the SEI layer of the above, and a high capacity can be maintained.

Further, in the lithium ion secondary battery using the electrode structure of the present invention as the negative electrode, the maximum amount of lithium inserted into silicon during charging is limited, so that the stress due to expansion due to the insertion reaction is alleviated and charged. High performance can be maintained even after repeated discharges.

Further, in the lithium ion secondary battery of the present invention, when an electrolytic solution is used for the lithium ion conductor between the negative electrode and the positive electrode, decomposition of the electrolytic solution is suppressed by repeated charging and discharging, and an increase in battery impedance is suppressed. Therefore, the decrease in battery performance is small. In a secondary battery in which a solid electrolyte is used between the negative electrode and the positive electrode to completely solidify the battery, the capacitance density of the negative electrode can be maintained high.

Further, since the method for producing the negative electrode active material of the present invention has a simple process, the negative electrode active material can be produced at low cost.

Therefore, according to the present invention, it is possible to achieve a secondary battery having high energy density, high output density, and longer charge / discharge cycle life performance.

It is schematic cross-sectional block diagram of the active material particle for the negative electrode of the lithium ion secondary battery of this invention. It is a schematic cross-sectional block diagram of the active material particle for the negative electrode of the lithium ion secondary battery in which the carbon material of this invention is composited.

Hereinafter, the present invention will be described in detail.

[Negative electrode active material for lithium ion secondary batteries]
The active material for the negative electrode of the lithium ion secondary battery of the present invention is particles in which amorphous or nanocrystalline silicon is dispersed in a lithium ion conductor, which is an inorganic material, and the silicon in the particles is 20 to 60. It is characterized by having a mass%. In FIG. 1, the negative electrode active material particles 3 of the present invention are formed by dispersing amorphous or nanocrystalline silicon 1 in a lithium ion conductor 2 of an inorganic material. Further, as shown in FIG. 2, the negative electrode active material particles 5 of the present invention may be composited with the carbon material 4.
The crystallite size of silicon in the active material for the negative electrode is preferably 50 nm or less, more preferably 20 nm or less. The smaller the crystallite size of silicon, the more uniform the Li insertion and the less volume expansion. The crystallite size is calculated by the half-value width of the peak of X-ray diffraction and the Scherrer equation. The crystal size can also be observed from the transmission electron microscope image.

Wherein the lithium ion conductor is _{Li x M y A z = Li} x (M1 a M2 b M3 c M4 d M5 e M6 f M7 g) compounds which can be represented as _{(A1 h A2 i A3 j)} , in the compound ,
M is a metal element and is a group 1 element (M1), a group 2 element (M2), a group 3 element (M3), a group 4 element (M4), and a group 5 element (M5) in the periodic table of elements. , One or more types of elements selected from Group 13 elements (M6) and Group 14 elements (M7).
A is a non-metallic element consisting of one or more elements selected from Group 15 elements (A1), Group 16 elements (A2), and Group 17 elements (A3).
x> 0, y> 0, z> 0, a ≧ 0, b ≧ 0, c ≧ 0, d ≧ 0, e ≧ 0, f ≧ 0, g ≧ 0, h ≧ 0, i ≧ 0, It is characterized in that j ≧ 0, (a + b + c + d + e + f + g)> 0, (h + i + j)> 0.
One or more elements selected from Na and K as the Group 1 element (M1), and one or more elements selected from Mg, Ca, Sr, Ba as the Group 2 element (M2), the third One or more elements selected from Sc, Y, and La as Group 4 elements (M3), one or more elements selected from Ti, Zr, and Hf as Group 4 elements (M4), Group 5 elements One or more elements selected from V, Nb, Ta as (M5), one or more elements selected from B, Al, Ga, In as Group 13 elements (M6), Group 14 elements One or more elements selected from Si, Ge, Sn as (M7), one or more elements selected from N, P, Bi as Group 15 elements (A1), Group 16 elements (A2) ) Is preferably one or more elements selected from O and S, and Group 17 element (A3) is preferably one or more elements selected from F, Cl, Br and I.
In order to obtain high ionic conductivity, it is more preferable that the combined element of the metallic element and the non-metallic element is composed of three or more kinds of elements. In order for the ionic conductor to have higher ionic conductivity, it is preferable to contain element P as a group 15 element (A1).
The Group 16 element (A2) is more preferably an O element. The oxide in which the group 16 element (A2) is an O element has a higher hardness than the sulfide in which the group 16 element (A2) is an S element. Mechanical milling (mechanical milling) at high acceleration in the manufacturing process facilitates amorphization of silicon or silicon alloys.

(Lithium-ion conductor constituting the negative electrode active material)
Examples of the lithium ion conductor of the inorganic material include Li ₇ La ₃ Zr ₂ O ₁₂ series, Li _{10 GeP 2} O ₁₂ series, Li ₃ BO _{3 -Li 2} SO ₄ series, and algyrodite (Li ₆ PS ₅ Cl) series. Various inorganic solid electrolytes such as _{Li 2} SP ₂ S ₅ series of glass ceramics can be used. Examples of the above inorganic solid electrolytes are Li _0.34 La _0.51 TiO _2.94 , Li _1.07 Ti _1.46 Al _0.69 P ₃ O ₁₂ , Li _1.5 Ti _1.5 Al _0.5 P ₃ O ₁₂ , Li _1.5 Ti _1.7 Al _0.3 Si _0.2 P _2.8 O ₁₂ , Li _1.5 Al _0.5 Ge _1.5 P ₃ O ₁₂ , Li ₇ La ₃ Zr ₂ O ₁₂ , Li ₃ YCl ₆ , Li ₃ YBr ₆ , Li _9.54 Si _1.74 P _1.44 S _11.7 Cl _0.3 , Li ₁₀ GeP ₂ S ₁₂ , 57Li such as _{2 S-38SiS 2 -5Li 4 SiO} 4, 75Li 2 S-25P 2 S 5 , and the like.

[Manufacturing method of negative electrode active material for lithium ion secondary battery]
The method for producing a negative electrode active material for a lithium ion secondary battery of the present invention is a mechanical alloying method in which silicon or a silicon alloy is mixed with a lithium ion conductor or a raw material of a lithium ion conductor and mechanically pulverized at a high acceleration. It is characterized by having a step of synthesizing. As the high-acceleration mechanical crushing device, a vibration mill, an attritor, a planetary ball mill, or other device using a similar technique is used. In these devices, high acceleration is applied to the pulverized media and the raw material, and pulverization, compounding, and amorphization proceed due to collision.
As the silicon material used as the raw material, metallic silicon or a silicon alloy is preferable because of its low price. In particular, a silicon alloy is more preferable because the raw material for forming the alloy is inexpensive and amorphization is easier than that of silicon alone.
The silicon alloy is an alloy composed of at least a silicon element and a transition metal element (elements existing between Group 3 and Group 11 elements in the periodic table), and is preferably composited with a carbon material. .. Further, it is more preferable that the silicon alloy contains a tin element.

As a specific example, the negative electrode active material for a lithium ion secondary battery of the present invention is produced from a silicon alloy by the following procedure.
(1) Metallic silicon, transition metal, etc. are used as raw materials, melted by a liquid quenching and solidifying device or an atomizing device, and rapidly cooled and solidified to produce an alloy.
(2) The alloy powder obtained in (1) and the lithium ion conductor of the inorganic material are mixed, a carbon material is added as appropriate, and fine pulverization, compounding, and amorphization are performed with a high-acceleration mechanical pulverizer. Do.
(3) The composite of the silicon alloy and the lithium ion conductor obtained in (2) is heat-treated at a temperature of 300 to 1250 ° C. to obtain the desired negative electrode active material.
Or
(1) Using metallic silicon, transition metal, etc. as raw materials, an alloy is produced by melting and quenching and solidifying with a liquid quenching and solidifying device or an atomizing device.
(2) A carbon material is appropriately added to the alloy powder obtained in (1), and fine pulverization, compounding, and amorphization are performed with a high-acceleration mechanical pulverizer.
(3) The amorphized alloy powder obtained in (2) and the lithium ion conductor of the inorganic material are mixed, a carbon material is added as appropriate, and finely pulverized, composited, and non-composited with a high-acceleration mechanical pulverizer. Crystallize.
(4) The composite of the silicon alloy and the lithium ion conductor obtained in (3) is heat-treated at a temperature of 300 to 1250 ° C. to obtain the desired negative electrode active material.

Examples of the apparatus for producing the above silicon alloy include a single roll liquid quenching and solidifying apparatus, a water atomizing apparatus, and the like, and an inexpensive metal ingot or lump metal can be used as a raw material, so that the production cost is low.
The carbon material added in the above manufacturing process suppresses the adhesion of pulverized products to the surface of the pulverized media and the inner wall of the container during pulverization, and also plays a role of compounding and enhancing electron conduction. The carbon material is preferably one or more types of carbon materials selected from the group consisting of graphite, amorphous carbon, carbon nanofibers, carbon nanotubes, and graphene.

[Electrode structure]
The electrode structure for the negative electrode of the lithium ion secondary battery of the present invention is characterized in that at least an electrode layer composed of the negative electrode active material and the binder of the present invention is formed on the current collector. In addition to the negative electrode active material and the binder of the present invention, the electrode layer contains one or more types of carbon materials selected from the group consisting of graphite, amorphous carbon, carbon nanofibers, carbon nanotubes, and graphene. May be good.
By adjusting the content of the negative electrode active material and graphite of the present invention in the electrode structure, the capacity of the battery can be adjusted when it is incorporated as a negative electrode in a lithium ion secondary battery.

(binder)
Specific binders used for forming the electrode layer of the electrode structure of the present invention include sodium alginate, sodium carboxymethyl cellulose, carboxymethyl cellulose, sodium carboxymethyl cellulose, sodium polyacrylate, polyacrylic acid, polyvinyl alcohol, chitin, chitosan, and the like. Examples thereof include polyamic acid (polyimide precursor), polyimide, polyamideimide, epoxy resin, styrene-butadiene copolymer-carboxymethyl cellulose, polyfluorinidene, and the like.

(Current collector)
The material of the current collector of the electrode structure of the present invention needs to be stable without being dissolved in the charge / discharge reaction of the power storage device, and specific examples thereof include copper, stainless steel, titanium, and nickel. .. The shape of the current collector is plate-shaped, but this "plate-like" is not specified in the practical range, and is called "foil" with a thickness of about 5 μm to 100 μm. Also includes morphology. Further, plate-shaped members such as mesh-shaped, sponge-shaped, and fibrous members, punching metal, metal foil having a three-dimensional uneven pattern formed on both front and back surfaces, expanded metal, and the like can also be adopted.

[Lithium-ion secondary battery]
The lithium ion secondary battery of the present invention is a power storage device that utilizes a reduction oxidation reaction of lithium ions, and at least a positive electrode composed of a lithium ion conductor and a lithium transition metal compound with the electrode structure of the present invention as a negative electrode. However, they are sequentially laminated and configured. Specific cell shapes of the battery include, for example, a flat shape, a cylindrical shape, a rectangular parallelepiped shape, and a sheet shape. Further, as the cell structure, for example, there are a single layer type, a multi-layer type, a spiral type and the like.

(Positive electrode)
In the positive electrode, a positive electrode active material layer composed of a lithium-transition metal compound serving as a positive electrode active material, a binder, and a conductive auxiliary material such as carbon black is formed on the positive electrode current collector.
As the lithium-transition metal compound, a lithium-transition metal oxide or a lithium-transition metal phosphoric acid compound is used. As the transition metal element contained in the positive electrode active material, Ni. Co, Mn, Fe, Cr, V and the like are more preferably used as the main elements. Further, the surface of the positive electrode active material is a lithium transition metal compound fine particle whose surface layer is coated with a composite metal oxide composed of at least one metal element selected from Al, Zr, Mg, Ca and La and Li. It is preferably composed of.
As the binder, a fluororesin such as polyvinylidene fluoride, polyacrylate, polyamic acid (polyimide precursor), polyimide, polyamideimide, epoxy resin, styrene-butadiene copolymer-carboxymethyl cellulose can be used.

As the material of the current collector, a material having high electrical conductivity and being inert to the battery reaction is desirable. Preferred materials include those made of one or more metallic materials selected from aluminum, nickel, iron, stainless steel and titanium. As a more preferable material, aluminum, which is inexpensive and has low electrical resistance, is used. The shape of the current collector is plate-shaped, but this "plate-like" is not specified in the practical range, and is called "foil" with a thickness of about 5 μm to 100 μm. Also includes morphology. Further, it is also possible to adopt a plate-like member, for example, a mesh-like, sponge-like, fibrous member, punching metal, a metal foil having a three-dimensional uneven pattern formed on both the front and back surfaces, an expanded metal, and the like.

(Lithium ion conductor)
The ionic conductor includes a separator holding an electrolyte solution (an electrolyte solution prepared by dissolving an electrolyte in a solvent), a solid electrolyte, a solid electrolyte obtained by gelling the electrolyte solution with a polymer gel, and a polymer gel. Lithium ion conductors such as solid electrolyte complexes and ionic liquids can be used.
A resin film having a micropore structure or a non-woven fabric structure is used as the separator for preventing an electrical short circuit between the negative electrode and the positive electrode, and the resin material is preferably polyolefin such as polyethylene or polypropylene, polyimide, polyamideimide, or cellulose. .. The surface of the microporous resin film may be coated with a metal oxide particle-containing layer such as alumina, zirconia, or titania that allows lithium ions to pass through in order to enhance heat resistance.

As the electrolyte, for example, lithium ion (Li ⁺⁾ and Lewis acid ion _{^{(BF 4 -, PF 6 -}} , AsF 6 -, ClO 4 -, CF 3 SO 3 -, BPh 4 - (Ph: phenyl group)) Examples thereof include salts composed of, lithium-bis (fluorosulfonyl) imide and mixed salts thereof, and ionic liquids.
It is desirable that the salt be sufficiently dehydrated and deoxidized by heating it under reduced pressure. Further, an electrolyte prepared by dissolving the above lithium salt in an ionic liquid can also be used. Examples of the solvent for the electrolyte include acetonitrile, benzonitrile, propylene carbonate, ethylene carbonate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, dimethylformamide, tetrahydrofuran, nitrobenzene, dichloroethane, diethoxyethane, 1,2-dimethoxyethane, and the like. Chlorobenzene, γ-butyrolactone, dioxolane, sulfolane, nitromethane, dimethylsulfide, dimethylsulfoxide, 3-methyl-2-oxidezolidinone, 2-methyltetrahydrofuran, 3-propylsidenone, sulfur dioxide, or a mixture thereof can be used. .. A solvent having a structure in which the hydrogen element of the solvent is replaced with a fluorine element can also be used.
The solvent may be dehydrated with activated alumina, molecular sieve, phosphorus pentoxide, calcium chloride, etc., or depending on the solvent, it may be distilled in the presence of an alkali metal in an inert gas to remove impurities and dehydrate. Good.
Further, in order to suppress the reaction between the electrode and the electrolytic solution, it is preferable to add an organic fluorine compound such as fluoroethylene carbonate or difluoroethylene carbonate, or a compound such as vinylene carbonate, which forms a stable SEI layer on the electrode surface.

The solid electrolytes include Li ₇ La ₃ Zr ₂ O ₁₂ series, Li ₁₀ GeP ₂ O ₁₂ series, Li ₃ BO _{3 -Li 2} SO ₄ series, Algirodite (Li ₆ PS ₅ Cl) series, and glass ceramics Li ₂ SP. Various inorganic solid electrolytes such as ₂ S _{5 series can be used.} Examples of the above inorganic solid electrolytes are Li _0.34 La _0.51 TiO _2.94 , Li _1.07 Ti _1.46 Al _0.69 P ₃ O ₁₂ , Li _1.5 Ti _1.5 Al _0.5 P ₃ O ₁₂ , Li _1.5 Ti _1.7 Al _0.3 Si _0.2 P _2.8 O ₁₂ , Li _1.5 Al _0.5 Ge _1.5 P ₃ O ₁₂ , Li ₇ La ₃ Zr ₂ O ₁₂ , Li ₃ YCl ₆ , Li ₃ YBr ₆ , Li _9.54 Si _1.74 P _1.44 S _11.7 Cl _0.3 , Li ₁₀ GeP ₂ S ₁₂ , 57Li such as _{2 S-38SiS 2 -5Li 4 SiO} 4, 75Li 2 S-25P 2 S 5 , and the like.
As the solidified electrolyte, it is preferable that the electrolytic solution is gelled with a gelling agent and solidified. As the gelling agent, it is desirable to use a polymer that absorbs the solvent of the electrolytic solution and swells, or a porous material having a large amount of liquid absorption such as silica gel. As the polymer, polyethylene oxide, polyacrylonitrile, polymethylmethacrylate, vinylidene fluoride-hexafluoropropylene copolymer, polyethylene glycol and the like are used. Further, the polymer having a crosslinked structure is more preferable.

Hereinafter, the present invention will be described in more detail with reference to Examples.

[Preparation of negative electrode active material for power storage devices whose main component is silicon]
Example M1
(Manufacturing of silicon alloy)
Metallic silicon, metallic tin, and metallic copper were mixed in a mass ratio of 65: 30: 5 to form flaky Si-Sn-Cu alloy powder using a single-roll liquid quenching and solidifying device. Then, the obtained Si-Sn-Cu alloy and graphite powder were mixed at a mass ratio of 95: 5, and pulverized for 10 hours in a vibrating mill of a zirconia ball and a pot to amorphize Si-Sn. -Cu alloy / C (carbon) composite powder was prepared.
(Preparation of active material for negative electrode)
Amorphous Si-Sn-Cu alloy / C composite powder obtained by the above method and Li _1.5 Ti _1.7 Al _0.3 Si _0.2 P _2.8 O ₁₂ powder of inorganic lithium ion conductor were mixed at a mass ratio of 50:50. The mixture was mixed and mechanically milled for 4 hours at a gravitational acceleration of 150 G in a zirconia pot and a zirconia ball planetary ball mill. Then, it was heat-treated at 900 ° C. for 1 hour in an argon atmosphere to obtain an active material for the negative electrode of a lithium ion secondary battery.
As a result of analyzing the obtained active material by X-ray diffraction and transmission electron microscope observation, the crystallite size calculated from the Scherrer equation is 11 nm, and the size of the silicon crystal observed from the transmission electron microscope is 10 to 20 nm. Met.

Example M2
Metallic silicon powder with an average particle size of 5 μm, Li _1.5 Ti _1.7 Al _0.3 Si _0.2 P _2.8 O ₁₂ powder of inorganic lithium ion conductor, and single-walled carbon nanotubes are mixed at a mass ratio of 60:39: 1, and zirconia pot and zirconia are mixed. Mechanical milling was performed for 4 hours at a gravity acceleration of 150 G on a ball planetary ball mill. Then, it was heat-treated at 1100 ° C. for 2 hours in an argon atmosphere.

Example M3
In Example M2, the metal silicon powder, the inorganic lithium ion conductor Li _1.5 Ti _1.7 Al _0.3 Si _0.2 P _2.8 O ₁₂ powder, and the single-phase carbon nanotubes were changed to a mass ratio of 50:49: 1, and Example M2 was used. It was produced in the same manner.

Example M4
In Example M2, the metal silicon powder, the inorganic lithium ion conductor Li _1.5 Ti _1.7 Al _0.3 Si _0.2 P _2.8 O ₁₂ powder, and the single-phase carbon nanotubes were changed to a mass ratio of 40:59: 1, and Example M2 was used. It was produced in the same manner.

Example M5
In Example M2, the metal silicon powder, the inorganic lithium ion conductor Li _1.5 Ti _1.7 Al _0.3 Si _0.2 P _2.8 O ₁₂ powder, and the single-phase carbon nanotubes were changed to a mass ratio of 20:79: 1, and Example M2 was used. It was produced in the same manner.

Example M6
Lithium sulfide Li ₂ S, diphosphorus diphosphorus P ₂ S ₅ and lithium nitride Li ₃ N are mixed in a mass ratio of 55:30:15 and gravitationally accelerated at 150 G in a zirconia pot and a zirconia ball planetary ball mill. _{Amorphous 55Li 2} S-30P ₂ S ₅ -15Li ₃ N was prepared by time mechanical milling treatment.
After that, the amorphized alloy Si-Sn-Cu / C powder prepared in Example M1 and 55Li ₂ S-30P ₂ S ₅ -15Li ₃ N were mixed by mass ratio with Si-Sn-Cu / C: 55Li ₂ S. After mixing so that -30P ₂ S ₅ -15Li ₃ N = 55: 45, mechanical milling treatment is performed for 2 hours at a gravitational acceleration of 150 G in a planetary ball mill, and further heat treatment is performed at 330 ° C for 1 hour in an argon gas atmosphere. Was applied to obtain an active material.

Comparative example M1
In Example M2, the metal silicon powder, the inorganic lithium ion conductor Li _1.5 Ti _1.7 Al _0.3 Si _0.2 P _2.8 O ₁₂ powder, and the single-phase carbon nanotubes were changed to a mass ratio of 65:34: 1, and Example M2 was used. It was produced in the same manner.

Comparative example M2
In Example M2, the powder of metallic silicon powder and the inorganic lithium ion conductor Li _1.5 Ti _1.7 Al _0.3 Si _0.2 P _2.8 O ₁₂ and the single-phase carbon nanotubes were changed to a mass ratio of 15:84: 1, and Example M2 was used. It was produced in the same manner.

[Preparation of electrode structure]
Example A1
60% by mass of the silicon-based active material obtained in Example M1 and 25% by mass of graphite powder,
5% by mass of acetylene black, a conductive aid, and 8% by mass (solid content of 10 mass% aqueous solution) of polyvinyl alcohol (PVA) and 2% by mass (solid content of 2 mass% aqueous solution) as a binder. The mixture was mixed with sodium carboxymethyl cellulose (CMC), ion-exchanged water was added, and the mixture was kneaded with a bead mill to prepare a slurry. Next, the prepared slurry was applied onto a copper foil with a coater, dried at 110 ° C., the electrode layer density was adjusted with a roll press machine, and then heat-treated at 150 ° C. under reduced pressure to prepare an electrode structure. Next, after cutting the electrode structure to a predetermined size, nickel leads were welded to the copper foil tabs of the current collector with a spot welder, and the lead terminals were taken out to prepare an electrode structure.

Example A2
Examples A1 except that the materials of the conductive auxiliary agent and the binder in Example A1 are the same in mass% and 40% by mass of the silicon-based active material obtained in Example M2 and 45% by mass of graphite powder are mixed. The electrode structure was prepared in the same manner as in the above.

Example A3
The materials of the conductive auxiliary agent and the binder in Example A1 are the same in mass%, and Example A1 except that 50% by mass of the silicon-based active material obtained in Example M3 and 35% by mass of graphite powder are mixed. The electrode structure was prepared in the same manner as in the above.

Example A4
Examples A1 except that the materials of the conductive auxiliary agent and the binder in Example A1 are the same in mass% and 20% by mass of the silicon-based active material obtained in Example M3 and 65% by mass of graphite powder are mixed. The electrode structure was prepared in the same manner as in the above.

Example A5
The materials of the conductive auxiliary agent and the binder in Example A1 are the same in mass%, and the silicon-based active material obtained in Example M4 is mixed with 35% by mass and the graphite powder is 50% by mass. The electrode structure was prepared in the same manner as in the above.

Example A6
The materials of the conductive auxiliary agent and the binder in Example A1 are the same in mass%, and the silicon-based active material obtained in Example M5 is mixed with 50% by mass and the graphite powder is 35% by mass. An electrode structure was prepared in the same manner as in A1.

Example A7
Active material powder of composite of amorphized alloy Si-Sn-Cu / C powder and solid electrolyte 55Li ₂ S-30P ₂ S ₅ -15Li ₃ N prepared in Example M6, polyfluorinated bilinidene (PVdF) as a binder ), The solid content of the 5 mass% butyl acetate solution, and the single-phase carbon nanotube (SWCN) as the conductive auxiliary agent are mixed so that the mass ratio is 97: 2: 1, and butyl acetate is added as appropriate. A slurry was prepared by kneading with a self-revolving mixer. Then, the slurry is coated on the copper foil as a current collector, dried at 110 ° C. for 1 hour, the thickness is adjusted with a roll press, and further dried at 150 ° C. under reduced pressure to form the electrode active material layer. The formed electrode structure was obtained. The obtained electrode structure was punched to a predetermined size, and nickel leads were welded to a copper foil current collector tab by ultrasonic welding to prepare an electrode structure.

Comparative example A1
Amorphous Si-Sn-Cu alloy / C (carbon) composite powder obtained in Example M1 30% by mass of silicon-based active material and inorganic lithium ion conductor Li _1.5 Ti _1.7 Al _0.3 Si _0.2 P _2.8 O _{30% by mass of 12} powders, 25% by mass of graphite powder, 5% by mass of acetylene black as a conductive aid, and 8% by mass (solid content of 10 mass% aqueous solution) of polyvinyl alcohol (PVA) as a binder. ) And 2% by mass (solid content of 2 mass% aqueous solution) of sodium carboxymethyl cellulose (CMC) were mixed, ion-exchanged water was added, and the mixture was kneaded with a bead mill to prepare a slurry. Next, the prepared slurry was applied onto a copper foil with a coater, dried at 110 ° C., the electrode layer density was adjusted with a roll press machine, and then heat-treated at 150 ° C. under reduced pressure to prepare an electrode structure. Next, after cutting the electrode structure to a predetermined size, nickel leads were welded to the copper foil tabs of the current collector with a spot welder, and the lead terminals were taken out to prepare an electrode structure.

Comparative example A2
In Comparative Example A1, the materials of the conductive auxiliary agent and the binder were made the same in mass%, and 50% by mass of the silicon-based active material obtained in Comparative Example M1 and 35% by mass of the graphite powder were mixed. An electrode structure was prepared in the same manner as in Example A1.

Comparative example A3
In Comparative Example A1, the materials of the conductive auxiliary agent and the binder are the same in mass%, and 25 mass% of metallic silicon powder having an average particle size of 5 μm and Li _1.5 Ti _1.7 Al _0.3 Si _0.2 P of the inorganic lithium ion conductor are used. _{An electrode structure was prepared in the same manner as in Comparative Example A1 except that 24.5% by mass of 2.8} O ₁₂ powder, 0.5% by mass of single-walled carbon nanotubes, and 35% by mass of graphite powder were mixed.

Comparative example A4
In Comparative Example A1, the materials of the conductive auxiliary agent and the binder are the same in mass%, and 20% by mass of SiO powder having a capacity density of 1100 mAh / g and 65% by mass of graphite powder are mixed as a silicon-based active material. An electrode structure was prepared in the same manner as in Comparative Example A1 except for the above.

Comparative example A5
In Comparative Example A1, the materials of the conductive auxiliary agent and the binder are the same in mass%, and as a silicon-based active material, a composite (Si-C) powder of silicon nanoparticles and graphite having a capacitance density of 1100 mAh / g is used. An electrode structure was prepared in the same manner as in Comparative Example A1 except that 35% by mass and 50% by mass of graphite powder were mixed.

Comparative example A6
In Comparative Example A1, the materials of the conductive auxiliary agent and the binder were made the same in mass%, and the silicon-based active material obtained in Comparative Example M2 was mixed with 85% by mass in the same manner as in Comparative Example A1. An electrode structure was prepared.

Comparative example A7
Lithium sulfide Li ₂ S, diphosphorus diphosphorus P ₂ S ₅ and lithium nitride Li ₃ N are mixed in a mass ratio of 55:30:15 and gravitationally accelerated at 150 G in a zirconia pot and a zirconia ball planetary ball mill. _{Amorphous 55Li 2} S-30P ₂ S ₅ -15Li ₃ N was prepared by time mechanical milling treatment. Then, it was heat-treated at 330 ° C. for 1 hour in an argon atmosphere to obtain a _{solid electrolyte 55Li 2} S-30P ₂ S ₅ -15Li _{3 N.}
Then, the amorphized alloy Si-Sn-Cu / C powder prepared in Example M1, the solid electrolyte 55Li ₂ S-30P ₂ S ₅ -15Li ₃ N, and 5% by mass of polyvinylidene fluoride (PVdF) as a binder. Solids of butyl acetate solution, single-walled carbon nanotubes (SWCN) as conductive aids,
After mixing so that the mass ratio was 53.35: 43.65; 2: 1 in this order, butyl acetate was appropriately added and kneaded with a revolution mixer to prepare a slurry. Then, the slurry is coated on the copper foil as a current collector, dried at 110 ° C. for 1 hour, the thickness is adjusted with a roll press, and further dried at 150 ° C. under reduced pressure to form the electrode active material layer. The formed electrode structure was obtained. The obtained electrode structure was punched to a predetermined size, and nickel leads were welded to a copper foil current collector tab by ultrasonic welding to prepare an electrode structure.

[Evaluation of electrochemical lithium insertion amount of electrode structure]
The evaluation of the amount of electrochemical lithium inserted as a single pole in the electrode structure for the negative electrode of the power storage device was carried out by the following procedure.
Using the electrodes of Examples A1 to A6 and Comparative Examples A1 to A6 as working electrodes, a cell (half cell) in which metallic lithium was combined as the counter electrode was prepared, and the amount of electrochemical lithium inserted was evaluated.
The lithium electrode was produced by crimping a metallic lithium foil to an expanded metal of a nickel foil and punching it to a predetermined size. A pouch cell was used as the evaluation cell. The evaluation cell of the pouch cell was prepared by the following procedure. All pouch cells (laminate type cells) were prepared in a dry atmosphere with a dew point of -60 ° C or lower and a controlled moisture content. An electrode group of working electrode / separator / lithium electrode is inserted into an electric tank made of a polyethylene / aluminum foil / nylon structure aluminum laminate film into a pocket shape, an electrolytic solution is injected, electrode leads are taken out, and heat-sealed for evaluation. Cell was prepared. The outside of the aluminum laminated film is a nylon film, and the inside is a polyethylene film. A polyethylene film having a micropore structure was used as the separator.
In the electrolytic solution, 1 M (mol / liter) of _{lithium hexafluorophosphate (LiPF 6} ) was dissolved in a solvent in which ethylene carbonate and diethyl carbonate from which water was sufficiently removed were mixed at a volume ratio of 3: 7. Then, 5% by volume of fluoroethylene carbonate (FEC) was added to prepare the mixture.

Charging and discharging was performed with a constant current of about 0.2C (1C: current for charging and discharging the capacity of the battery in 1 hour), discharged until the cell voltage became 0.01V, and charged to 1.50V for evaluation. The amount of discharged electricity was defined as the amount of electricity used for inserting lithium, and the amount of charged electricity was defined as the amount of electricity used for releasing lithium.
In the performance evaluation, the Coulomb efficiency of the first Li release amount (electric amount) with respect to the first Li insertion amount (electric amount) and the 100th Li release amount (mAh / g) were evaluated. Each amount of electricity (mAh / g) was converted per weight of the electrode layer. The evaluation results were as follows.

(Results of comparative evaluation of the performance of the electrodes of Examples A1 to A6 and Comparative Examples A1 to A6)
When the performances of Example A1 and Comparative Example A1 and Example A3 and Comparative Example A3 were compared, the first charge / discharge electrode capacitance per electrode layer of Example A1 and Comparative Example A1 was about 900 mAh / g. Although it was about 800 mAh / g in Example A3 and Comparative Example A3, it was confirmed that the Coulomb efficiency at the first charge / discharge and the Li release amount (mAh / g) at the 100th time were higher in the Example. It should be noted that Comparative Examples A1 and A3 are electrodes produced by simply mixing a silicon-based active material and a solid electrolyte, and it was found that the performance is improved by the active material manufacturing method of the present invention.
The performances of Example A2 and Comparative Example A2 and Example A6 and Comparative Example A6 were compared. In Example A2 and Comparative Example A2, the mass% of silicon in the composite of silicon and Li ion conductor was 60% in Example A2 and 65% in Comparative Example A2, per electrode layer of the first charge and discharge. The electrode capacitance was about 1000 mAh / g in both cases, but the electrode capacitance at the 100th time was higher in Example A2 than in Comparative Example A2. The increase in cell thickness after 100 charges and discharges was larger in Comparative Example A2. In Example A6 and Comparative Example A6, the mass% of silicon in the composite of silicon and Li ion conductor was 20% in Example A6 and 15% in Comparative Example A6, and the first electrode capacitance was Example. It was 470 mAh / g for A6 and 420 mAh / g for Comparative Example A6, and the electrode of Comparative Example A6 did not show a significant advantage over the capacitance of the graphite electrode.
The performances of Example A4 and Comparative Example A4 and Example A5 and Comparative Example A5 were compared. As the silicon-based active material in the electrode, SiO is used in the electrode of Comparative Example A4, and Si-C (composite of silicon nanoparticles and graphite) is used in the electrode of Comparative Example A4. The electrode capacities of Example A4 and Comparative Example A4 at the first charge and discharge were 580 mAh / g and 555 mAh / g, respectively, and the Coulomb efficiency was 86% and 74%, respectively, and the capacity retention rate at the 100th time was about the same. .. In Example A5 and Comparative Example A5, the electrode capacitances at the first charge and discharge were 650 mAh / g and 575 mAh / g, respectively, the coulombic efficiency was 85% and 88%, respectively, and the capacitance retention rate at the 100th time was that of Example A5. The number of electrodes exceeded that of Comparative Example A5.
From the above evaluation results, it was found that the electrode performance using the silicon-based active material of the present invention is excellent, and an electrode having high electrode capacitance, high Coulomb efficiency, and capacitance retention rate can be produced.

[Manufacturing of power storage device]
A lithium-ion secondary battery full cell in which a positive electrode was combined with the prepared electrode as a counter electrode was manufactured, and the charge / discharge performance was evaluated. The charge / discharge characteristics of the battery were evaluated under the charge / discharge conditions of charging with a 0.2 C constant current-constant voltage charge with an upper limit voltage of 4.3 V and discharging to 2.5 V with a 0.2 C constant current.

Example F1
(Preparation of positive electrode)
Positive electrode material _{Li Ni 0.8} Co _0.1 Mn _0.1 O ₂ is immersed in an ethyl alcohol solution of lithium citrate and aluminum nitrate, dried, and then heat-treated at 300 ° C in a nitrogen atmosphere to form a composite oxide of lithium and aluminum Li _x Al _y O. _{A Li Ni 0.8} Co _0.1 Mn _0.1 O ₂ powder surface-coated with _{2 was prepared.}
Li _{Ni 0.8} Co _0.1 Mn _0.1 O ₂ powder surface coated with _{Li x} Al _y O ₂ , acetylene black, polyfluoridene (PVdF) 12% by mass N-methyl-2-pyrrolidone (NMP) solution mass ratio The mixture was mixed so that the ratio was 97: 1: 2, NMP was added, and the mixture was kneaded to prepare a slurry for forming an electrode active material layer. Next, the obtained slurry was applied onto an aluminum foil using a coater, dried at 110 ° C. for 1 hour, adjusted in thickness with a roll press, and further dried at 150 ° C. under reduced pressure. An electrode structure on which an electrode active material layer was formed was obtained. The obtained electrode structure was punched to a predetermined size, and an aluminum lead was welded to an aluminum current collector tab by ultrasonic welding to prepare an electrode for a positive electrode.

(Preparation of electrolyte)
Fluoroethylene carbonate is obtained by dissolving 1 M (mol / liter) of _{lithium hexafluorophosphate (LiPF 6} ) in a solvent in which ethylene carbonate and diethyl carbonate from which water has been sufficiently removed are mixed at a volume ratio of 3: 7. (FEC) was added in an amount of 5% by mass to prepare an electrolytic solution.

(Lithium-ion secondary battery fabrication and performance evaluation)
Using the electrode structure of Example A1 as the negative electrode, a pouch cell was prepared by the following procedure. All pouch cells (laminate type cells) were prepared in a dry atmosphere with a dew point of -60 ° C or lower and a controlled moisture content. Insert the negative electrode / separator / positive electrode group into a pocket-shaped battery case made of polyethylene / aluminum foil / nylon structure aluminum laminate film, inject the electrolytic solution, take out the electrode leads, heat seal and lithium ion II. A cell for evaluation as a next battery was prepared.

Example F2
(Preparation of positive electrode)
Positive electrode material _{Li Ni 0.8} Co _0.1 Mn _0.1 O ₂ is immersed in an ethyl alcohol solution of lithium citrate and aluminum nitrate, dried, and then heat-treated at 300 ° C in a nitrogen atmosphere to form a composite oxide of lithium and aluminum Li _x Al _y O. _{A Li Ni 0.8} Co _0.1 Mn _0.1 O ₂ powder surface-coated with _{2 was prepared.
85% by mass of LiNi 0.8} Co _0.1 Mn _0.1 O ₂ powder surface-coated as the positive electrode active material, and 12% by mass of _{the solid electrolyte 55Li 2} S-30P ₂ S ₅ -15Li ₃ N formed by the same method as in Example M6. , 2% by mass as the solid content of polyvinylidene fluoride PVdF (5% by mass butyl acetate solution) as a binder, 1% by mass of a single-phase carbon nanotube SWCN as a conductive auxiliary agent, add butyl acetate as appropriate, and add zirconia beads. And kneaded with a wet bead mill to prepare a slurry. Then, the slurry is coated on the aluminum foil as a current collector, dried at 110 ° C for 1 hour, pressed with a roll press to adjust the thickness, and further dried at 150 ° C under reduced pressure to dry the electrode active material. An electrode structure having a layer formed was obtained. The obtained electrode structure was punched to a predetermined size, and an aluminum lead was welded to an aluminum current collector tab by ultrasonic welding to prepare an electrode for a positive electrode.

(Preparation of solid electrolyte layer)
_{The solid content of the solid electrolyte 55Li 2} S-30P ₂ S ₅ -15Li ₃ N vs. butyl rubber (isobutylene-isoprene copolymer) hexane solution formed by the same method as in Example M6 is 96: 4 in mass ratio. And kneaded in a wet bead mill using zirconia beads to form a slurry. Then, the slurry was coated on the fluororesin film, dried at 100 ° C., sandwiched between the fluororesin films, and pressure-treated with a roll press machine to form a solid electrolyte film. (Use by peeling from the fluororesin film when incorporating it into a lithium-ion secondary battery.)

(Lithium-ion secondary battery fabrication and performance evaluation)
Using the electrode structure obtained in Example A7 as a negative electrode, the solid electrolyte film was laminated on the electrode structure, and the positive electrode was further laminated on the electrolyte film, and the mixture was pressurized and cooled by a roll press machine at 150 ° C. A cell was prepared, and an aluminum laminate film having a polyethylene / aluminum foil / nylon structure was inserted into a pocket-shaped electric tank and sealed under reduced pressure. Further, the cell surface was pressed from the laminated film with a restraining jig to obtain an evaluation cell as a lithium ion secondary battery.

Comparative example F1
In Example F1, an evaluation cell was prepared in the same manner as in Example F1 except that the electrode structure of Comparative Example A1 was used as the negative electrode.

Comparative example F2
In Example F2, an evaluation cell was prepared in the same manner as in Example F2 except that the electrode structure of Comparative Example A7 was used as the negative electrode.

[Performance evaluation of power storage device]
The charge / discharge amount, charge / discharge efficiency, and charge / discharge repetition life of the power storage device of Example F1 and Comparative Example F1 all reflect the electrode performance in the previous half cell, and the performance of Example F1 is that of Comparative Example F1. It exceeded the performance.
The performance of Example F2 exceeded that of Comparative Example F2 in all of the charge / discharge amount, charge / discharge efficiency, and charge / discharge repetition life of the power storage device of Example F2 and Comparative Example F2. It is presumed that the interface formation between the silicon alloy and the lithium ion conductor, which is a solid electrolyte, affects the performance as a power storage device.

From the above evaluation results, it was found that the performance of the electrode of the electrode structure using the active material of the present invention and the power storage device of the present invention is high when the charge / discharge amount and the repetitive characteristics of charge / discharge are comprehensively considered.

As described above, according to the present invention, a power storage device having a high output density and a high energy density and a long repeat life, an electrode structure for the negative electrode of the power storage device, and an activity used for the electrode structure for the negative electrode. A substance (negative electrode material) can be provided.

1 Amorphous or nanocrystalline silicon
2 Lithium-ion conductor of inorganic material
3 Negative electrode active material particles
4 carbon material
5 Negative electrode active material particles with composite carbon material

Claims (10)

Electrochemically lithium particles in which amorphous or nanocrystalline silicon is dispersed in a lithium ion conductor of an inorganic material, wherein the silicon element in the particles is 20 to 60% by mass. Active material for the negative electrode of a secondary battery (lithium ion secondary battery) that can occlude and release ions. A compound of lithium ion conductor according to claim 1, wherein the _{Li x M y A z = Li} x (M1 a M2 b M3 c M4 d M5 e M6 f M7 g) (A1 h A2 i A3 j) and can be expressed, In the compound
M is a metal element and is a group 1 element (M1), a group 2 element (M2), a group 3 element (M3), a group 4 element (M4), and a group 5 element (M5) in the periodic table of elements. , One or more types of elements selected from Group 13 elements (M6) and Group 14 elements (M7).
A is a non-metallic element consisting of one or more elements selected from Group 15 elements (A1), Group 16 elements (A2), and Group 17 elements (A3).
x> 0, y> 0, z> 0,
a ≧ 0, b ≧ 0, c ≧ 0, d ≧ 0, e ≧ 0, f ≧ 0, g ≧ 0, h ≧ 0, i ≧ 0, j ≧ 0, (a + b + c + d + e The activity for the negative electrode of a secondary battery (lithium ion secondary battery) capable of occluding and releasing lithium ions electrochemically, which is characterized by + f + g)> 0 and (h + i + j)> 0. material. In the compounds Li _x M _y A _z of claim 2, wherein, in the previous year metal element M,
Group 1 elements (M1) include one or more elements selected from Na and K.
As a group 2 element (M2), one or more kinds of elements selected from Mg, Ca, Sr, Ba,
Group 3 elements (M3) include one or more elements selected from Sc, Y, and La.
Group 4 elements (M4) include one or more elements selected from Ti, Zr, and Hf.
Group 5 elements (M5) include one or more elements selected from V, Nb, and Ta.
As a Group 13 element (M6), one or more elements selected from B, Al, Ga, In,
As a Group 14 element (M7), one or more elements selected from Si, Ge, Sn,
Of the non-metal element A
Group 15 element (A1) is one or more elements selected from N, P, Bi,
As a group 16 element (A2), one or more kinds of elements selected from O and S,
Group 17 elements (A3) include one or more elements selected from F, Cl, Br, and I.
An active material for the negative electrode of a secondary battery (lithium ion secondary battery) capable of electrochemically inserting and removing lithium ions. The active material particles according to claim 1 are composited with one or more types of carbon materials selected from the group consisting of graphite, amorphous carbon, carbon nanofibers, carbon nanotubes, and graphene. An active material for the negative electrode of a secondary battery (lithium ion secondary battery) in which lithium ions can be inserted and removed electrochemically. The active material particles according to claim 1 are composited with one or more types of carbon materials selected from the group consisting of graphite, amorphous carbon, carbon nanofibers, carbon nanotubes, and graphene. An active material for the negative electrode of a secondary battery (lithium ion secondary battery) in which lithium ions can be inserted and removed electrochemically. The active material particles according to claim 1 are electrochemically lithium particles in which silicon alloy particles containing amorphous or nanocrystalline silicon are dispersed in a lithium ion conductor of the inorganic material. Active material for the negative electrode of a secondary battery (lithium ion secondary battery) that can insert and remove ions. The method for producing an active material particle according to claim 1 includes a step of mixing a silicon or a silicon alloy with a lithium ion conductor or a raw material of the lithium ion conductor and synthesizing the mixture by a mechanical arranging method of mechanical pulverization. A method for producing a negative electrode active material for a secondary battery (lithium ion secondary battery), which is characterized by an electrochemical insertion and removal of lithium ions. In the production method according to claim 6, a step of mixing and compounding one or more kinds of carbon materials selected from the group consisting of graphite, amorphous carbon, carbon nanofibers, carbon nanotubes, and graphene at the time of mechanical grinding is performed. A method for producing a negative electrode active material for a secondary battery (lithium ion secondary battery), which is electrochemically capable of inserting and removing lithium ions. The manufacturing method according to claim 6, wherein the secondary battery (lithium ion) capable of electrochemically inserting and removing lithium ions includes a step of performing a heat treatment at a temperature of 300 to 1250 ° C. after the mechanical crushing. A method for manufacturing a negative electrode active material for a secondary battery). Electrochemically, the electrode structure according to claim 8 is used as a negative electrode, and is composed of at least a lithium ion conductor and a positive electrode made of a lithium transition metal compound capable of desorbing and inserting lithium ions. A secondary battery (lithium ion secondary battery) that allows insertion and removal of lithium ions.

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