JP2012084521A - Porous silicon particle and manufacturing method thereof and lithium ion secondary battery anode and lithium ion secondary battery - Google Patents

Porous silicon particle and manufacturing method thereof and lithium ion secondary battery anode and lithium ion secondary battery Download PDF

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JP2012084521A
JP2012084521A JP2011202789A JP2011202789A JP2012084521A JP 2012084521 A JP2012084521 A JP 2012084521A JP 2011202789 A JP2011202789 A JP 2011202789A JP 2011202789 A JP2011202789 A JP 2011202789A JP 2012084521 A JP2012084521 A JP 2012084521A
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porous silicon
silicon particles
pores
negative electrode
lithium ion
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JP5809897B2 (en
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Koji Hataya
Kazuhiko Kurusu
Kazutomi Miyoshi
Takeshi Nishimura
Toshio Tani
Koichi Yoshida
一富 三好
一彦 久留須
浩一 吉田
耕二 幡谷
健 西村
俊夫 谷
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Furukawa Electric Co Ltd:The
古河電気工業株式会社
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Abstract

A negative electrode material for a lithium ion secondary battery that achieves high capacity and good cycle characteristics is obtained.
Porous silicon particles having continuous pores and having a three-dimensional network structure, the pores penetrating the porous silicon particles, and Cu, Ni, It is a porous silicon particle characterized by having a single element or an alloy of one or more conductive elements of Sn, Zn, Ag, and C. It is preferable that the single element or alloy of the conductive element covers at least a part of the surface in the pores or is filled in at least a part of the pores. Such porous silicon particles are produced by electroless plating, displacement plating, or carbon coating on the porous silicon particles.
[Selection] Figure 2

Description

  The present invention relates to a porous silicon particle useful as a negative electrode material for a lithium ion secondary battery.

  Conventionally, lithium ion secondary batteries using graphite as a negative electrode active material have been put into practical use. In general, the negative electrode of this lithium ion secondary battery is prepared by kneading a negative electrode active material, a conductive aid such as carbon black, and a resin binder to prepare a slurry on a current collector such as a copper foil. It is formed by coating and drying.

  On the other hand, development of a negative electrode for a lithium ion secondary battery using a metal or an alloy having a large theoretical capacity as a negative electrode active material, in particular, silicon or an alloy thereof has been promoted with the aim of increasing the capacity.

  As a method of manufacturing a negative electrode for a lithium ion secondary battery using silicon, metal silicon as an active material is mechanically pulverized to a nanometer size, granulated, and a conductive assistant such as carbon black. There is a method in which a slurry is prepared by kneading together with a resin binder and applied onto a copper foil. There is also a method of directly producing nano-sized particles by a plasma method. The nanometer-sized silicon particles are granulated for the purpose of coating the surface of the particles with a binder and uniformly coating the copper foil. However, since the silicon particles are very small, the volume ratio of silicon in the granulated body frequently occurs below 50%. For this reason, there is a disadvantage that the battery capacity does not increase.

Further, by repeating charge and discharge with a lithium battery, for example, silicon repeatedly expands and contracts by about four times. Since the bonding force between the silicon particles is small and the volume change cannot be prevented, the silicon particles are pulverized and the cycle characteristics are rapidly deteriorated.
For these reasons, a manufacturing method for directly manufacturing a porous body without granulating nanometer-sized silicon has been proposed. Specifically, (1) a method of forming a groove such as a slit by anodizing a silicon substrate, or (2) a method of crystallizing fine silicon in a ribbon-like bulk metal (for example, Patent Document 1) For example). Similarly, a technique (for example, see Patent Document 2) applying a rapid solidification technique and a method for obtaining porous silicon by hydrofluoric acid treatment of silicon particles (for example, see Patent Documents 3 and 4) are known. ing.

Even in these porous bodies, (1) pulverization associated with charge / discharge and (2) deterioration of conductivity exist as problems. In order to clear these problems, composite materials for covering the silicon surface with tin, copper or the like as shown in Patent Documents 5 to 10 have been proposed.
In these prior arts, a fine silicon particle is produced from a silicon lump, and the particle diameter is proposed to be 10 nm to 60 μm. Specifically, a method of plating the surface of a laminate of silicon particles having an average particle size of 0.1 to 5 μm (Patent Document 5), a method of mixing silicon having an average particle size of 0.5 to 60 μm and an electron conduction auxiliary material (Patent Document 6), a method of mixing silicon and carbon having an average particle diameter of 0.1 to 50 μm (Patent Document 7), and a method of manufacturing silicon having a particle diameter of 0.01 to 0.5 μm together with carbon by mechanical alloying ( Patent Document 8), a method of performing chemical vapor deposition of carbon on silicon having an average particle diameter of 0.1 to 5 μm (Patent Document 9), and the like.

JP 2008-135364 A Japanese Patent No. 3827642 US Application Publication No. 2006/0251561 US Application Publication No. 2009/0186267 JP 2009-164014 A Japanese Patent Laid-Open No. 11-242955 JP 2000-215887 A Japanese Patent Laid-Open No. 2002-216751 JP 2004-349056 A

  However, a conventional negative electrode formed by applying and drying a slurry of a negative electrode active material, a conductive additive, and a binder binds the negative electrode active material and the current collector with a binder of a resin having low conductivity. Therefore, it is necessary to minimize the amount of resin used so that the internal resistance does not increase, and the bonding force between the negative electrode active material and the current collector was not strong. Therefore, if the volume expansion of the negative electrode during charge / discharge cannot be suppressed, the negative electrode active material is pulverized or peeled off, the negative electrode cracks are generated, the conductivity between the negative electrode active materials is reduced, and the capacity is reduced. . In addition, if the resin is increased in order to strengthen the binding between the negative electrode active materials or the current collector, the volume ratio of the resin increases and the capacity of the battery decreases. Problems occur.

For these reasons, in order to prevent the pulverization, the negative electrode active material is made nano-sized. However, when the nanoparticles themselves are used to form a slurry, there is a problem that they are not uniformly dispersed in the slurry. Therefore, a method of granulating using these nanoparticles is widely used. However, since the bonding force between the active materials in this granulated product is extremely small, the granulated product collapses with the volume expansion of the active material during charge and discharge. In addition, there is a porous body having voids to be connected, but there is a problem that the charge / discharge efficiency is lowered because the conductive auxiliary agent does not enter the voids of the porous body during slurry production.
Therefore, the conventional negative electrode using silicon has problems that the cycle characteristics are poor and the life of the secondary battery is short. In particular, silicon, which is expected to be put to practical use as a negative electrode material, has a large volume change of about 4 times during storage of lithium ions, so that the negative electrode active material is easily cracked and peeled off, and has charge / discharge cycle characteristics. There was a problem that it was bad, and there was a fault that the life was extremely short compared with the conventional graphite negative electrode.

The technique of Patent Document 2 is applied when producing an amorphous ribbon or fine powder, and solidifies at a cooling rate of 10 4 K / second or more.
In the solidification of a general alloy, dendrites in which secondary dendrite grows while primary dendrite grows are taken.
A special alloy system (Cu-Mg system, Ni-Ti system, etc.) can form an amorphous metal at 10 4 K / second or more, but other systems (for example, Si-Ni system) have a cooling rate. Even when solidified at a rate of 10 4 K / sec or more, an amorphous metal cannot be obtained and a crystalline phase is formed.
The size of the crystal when this crystal phase is formed follows the relationship between the cooling rate (R: K / sec) and the dendrite arm spacing (DAS: μm).
DAS = A × R B (generally A: 40 to 100, B: −0.3 to −0.4)
Therefore, in the case of having a crystal phase, for example, when A: 60 and B: −0.35, DAS becomes 1 μm at R: 10 4 K / sec. The crystal phase is equivalent to this size, and a fine crystal phase of 10 nm or the like cannot be obtained. For these reasons, it is not possible to obtain a porous material composed of a fine crystalline phase with this rapid solidification technique alone with materials such as Si—Ni.

  Further, in order to avoid pulverization of the plated silicon particles, there is a trade-off that if the silicon particles are made smaller, the ratio of the covering material becomes relatively larger and the lithium battery capacity becomes smaller. In addition, there is a method (for example, Patent Document 8) in which volume change is mitigated by a method of mechanical alloying with silicon and a conductive material (carbon or the like), but the porosity is small and it is difficult to enter the electrolyte in the battery. There is also a trade-off, and it has not been put into practical use.

  Further, in order to avoid silicon pulverization, a porous body having connected nano-sized voids has also been proposed (for example, Patent Documents 3 and 4). However, even if a slurry is produced using this porous silicon, there is a problem that the charge / discharge efficiency is lowered because the conductive auxiliary agent does not enter the nano-sized voids, and it has not been put into practical use.

  The present invention has been made in view of the above-mentioned problems, and its object is to provide porous silicon particles suitable for a negative electrode material for a lithium ion secondary battery that achieves high capacity and good cycle characteristics. Is to get.

  The present inventor, by depositing the conductive material in the pores of the porous silicon particles of the three-dimensional network structure having continuous voids, these conductive materials become a conductive path, can improve the conductivity, Furthermore, it discovered that pulverization could be prevented. The present invention has been made based on this finding.

That is, the present invention is as follows.
(1) Porous silicon particles having continuous pores and having a three-dimensional network structure, wherein the pores penetrate the porous silicon particles, and Cu, Ni, Sn are contained in the pores. A porous silicon particle comprising a single element or an alloy of one or more conductive elements of any one of Zn, Ag, Ag, and C.
(2) The porous silicon particles according to (1), wherein the single element or alloy of the conductive element covers at least a part of the surface in the pores.
(3) The porous silicon particles according to (1), wherein the conductive element alone or an alloy is filled in at least a part of the pores.
(4) In the porous silicon particles, As, Ba, C, Ca, Ce, Co, Cr, Cu, Er, Fe, Gd, Hf, Lu, Mg, Mn, Mo, Nb, Nd, Ni, P , Pd, Pr, Pt, Pu, Re, Rh, Ru, Sc, Sm, Sr, Ta, Te, Th, Ti, Tm, U, V, W, Y, Yb, Zr The porous silicon particle according to any one of (1) to (3), which has a silicide with one kind of element.
(5) The average particle diameter of the porous silicon particles is 0.1 μm to 1000 μm, the average porosity of the porous silicon particles is 15 to 93%, and the average pore diameter of the porous silicon particles is The porous silicon particle according to any one of (1) to (4), wherein the porous silicon particle has a ratio of 5 nm to 2 μm and a ratio of an average particle diameter to an average pore diameter of the porous silicon particle is 5 or more .
(6) A negative electrode for a lithium ion secondary battery, wherein the porous silicon particles according to any one of (1) to (5) are used as a negative electrode active material.
(7) having a positive electrode capable of inserting and extracting lithium ions, a negative electrode for a lithium ion secondary battery according to (6), and a separator disposed between the positive electrode and the negative electrode, A lithium ion secondary battery, wherein the positive electrode, the negative electrode, and the separator are disposed in an electrolyte having a property.
(8) Inside the pores of the porous silicon particles having continuous pores and having a three-dimensional network structure, any one or more conductive elements of Cu, Ni, Sn, Zn, Ag, and C are contained. A method for producing porous silicon particles, comprising depositing a simple substance or an alloy.
(9) Electroless plating with at least one of Cu, Ni, Sn, Zn, and Ag is performed on at least a part of the pores of the porous silicon particles to deposit the conductive element (6) The method for producing porous silicon particles according to (8).
(10) The porous silicon particles contain 1 atomic% or more of an element having a deposition potential lower than that of any one or more conductive elements of Cu, Ni, Sn, Zn, and Ag. The porous silicon particle according to (8), wherein the conductive element is deposited in at least a part of the pores of the porous silicon particle by performing substitution plating replacing the conductive element. Production method.
(11) The porous silicon particles are placed on a filter, and the electroless plating or the displacement plating is performed in a flow field having an average flow rate of 0.1 cm / second or more (9) or (10) The manufacturing method of the porous silicon particle as described in any one of Claims 1-3.
(12) The porous silicon particles are heated to 600 ° C. or higher at a temperature increase rate of 100 K / min or more in an atmosphere containing 10% by volume or more of hydrocarbon-based gas, and the carbonization is performed in the pores. The method for producing porous silicon particles according to (8), wherein carbon is deposited in at least a part of the pores of the porous silicon particles by thermally decomposing a hydrogen-based gas.

  According to the present invention, porous silicon particles suitable for a negative electrode material for a lithium ion secondary battery that achieves a high capacity and good cycle characteristics can be obtained.

1 is a schematic cross-sectional view of porous silicon particles 1 according to the present invention. (A), (b) The schematic sectional drawing of the porous silicon particle 1a, 1b which concerns on this invention. (A)-(d) The figure explaining the electroless-plating process which concerns on this invention. (A)-(c) The figure explaining the carbon coating process which concerns on this invention. (A)-(d) The figure explaining the displacement plating process which concerns on this invention. It is a cross-sectional schematic diagram which shows an example of the lithium ion secondary battery which concerns on this invention.

(Porous silicon particles)
Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. FIG. 1 is a diagram showing an example of porous silicon particles 1 according to the present invention. The porous silicon particle 1 has continuous pores 3 and has a three-dimensional network structure. The pores 3 penetrate through the porous silicon particles 1, and Cu, Ni, Sn, It has a single element or an alloy 7 of any one or more conductive elements of Zn, Ag, and C.

  The three-dimensional network structure in the porous silicon particle 1 according to the present invention means a structure in which pores are connected to each other. In FIG. 1, porous silicon particles 1 in which a large number of silicon fine particles 5 are joined and the space between the silicon fine particles 5 are pores 3 are illustrated. As long as the pores penetrate the porous silicon particles in the connected structure, such porous silicon particles can also be used. For example, silicon particles in which tube-like holes are formed can also be used. In FIG. 1 and the like, the silicon fine particles 5 are not in contact with each other, but this is because the porous silicon particles 1 are schematically drawn. Actually, the silicon fine particles 5 are joined to the adjacent silicon fine particles 5 or at the back or in front. The other silicon fine particles 5 are joined to each other, and the silicon fine particles 5 are joined and integrated.

  The porous silicon particles 1 according to the present invention, 1a and 1b, which will be described later, have an average particle size of 0.1 to 1000 μm and an average porosity of 15 to 93 before the single element or alloy of the conductive element is precipitated. %, The average pores are 5 nm to 2 μm, the ratio of the average particle size to the average pores is 5 or more, and the porous silicon particles have a three-dimensional network structure having continuous voids. These porous silicon particles have an average particle diameter or an average column diameter of 0.1 to 1000 μm, preferably 1 to 50 μm, and more preferably 5 to 20 μm. Moreover, an average porosity is 15 to 93%, Preferably it is 30 to 80%. An average void | hole is 5 nm-2 micrometers, Preferably it is 10-500 nm, More preferably, it is 20-200 nm.

  The silicon fine particles 5 have an average particle diameter or an average column diameter of 2 nm to 2 μm, preferably 10 to 500 nm, and more preferably 20 to 300 nm. The crystal structure of each silicon fine particle 5 is preferably a single crystal having crystallinity. The silicon fine particles 5 are preferably solid fine particles containing 80 atomic% or more of silicon in a ratio of elements excluding oxygen.

  The single element or alloy 7 of the conductive element is a single element or alloy of any one or more of the conductive elements of Cu, Ni, Sn, Zn, Ag, and C. In FIG. 1, the particulate conductive element alone or the alloy 7 is precipitated in the pores 3, but the precipitation form is not particularly limited, and the first embodiment and the second embodiment described later are used. As described above, the surface of the hole 3 may be covered or the inside of the hole 3 may be filled.

  Further, in the porous silicon particle 1, As, Ba, C, Ca, Ce, Co, Cr, Cu, Er, Fe, Gd, Hf, Lu, Mg, Mn, Mo, Nb, Nd, Ni, P, At least one selected from the group consisting of Pd, Pr, Pt, Pu, Re, Rh, Ru, Sc, Sm, Sr, Ta, Te, Th, Ti, Tm, U, V, W, Y, Yb, Zr A silicide of a seed element and silicon may be included. Since these elements are more difficult to occlude lithium ions than silicon, this silicide does not easily expand during occlusion of lithium ions, the expansion of the entire porous silicon particles is suppressed, and a longer-life anode active material Can be obtained.

(Effect of porous silicon particles according to the present invention)
Since the porous silicon particle according to the present invention uses silicon, it becomes a high-capacity negative electrode active material when used for the negative electrode of a lithium ion secondary battery.

  Further, since the porous silicon particles according to the present invention have a single element or an alloy of a conductive element, this conductive element becomes a conductive path to silicon inside the porous silicon particle. Furthermore, since the porous silicon particles according to the present invention have continuous pores and have a three-dimensional network structure, the electrolytic solution can contact the silicon inside the porous silicon particles. Therefore, even the silicon inside the porous silicon particles can participate in the charge / discharge reaction, the silicon utilization efficiency is high, and the porous silicon particles according to the present invention become a high-capacity negative electrode active material.

  In addition, since the porous silicon particles according to the present invention have continuous pores and have a three-dimensional network structure, even if the silicon constituting the porous silicon particles expands or contracts, The stress relating to the inside is dispersed to a small extent, and the micronization of the porous silicon particles can be prevented. That is, when the porous silicon particles according to the present invention are used for the negative electrode of a lithium ion secondary battery, a long-life negative electrode active material having excellent cycle characteristics is obtained.

  Further, since the porous silicon particles according to the present invention have a simple substance or an alloy of a conductive element, this conductive element becomes a conductive path to silicon constituting the porous silicon particle, and the conductivity of the porous silicon particle Becomes higher. Furthermore, it is excellent in charge / discharge characteristics at a high rate.

  Further, since the porous silicon particles according to the present invention have a single element or alloy of the conductive element, the single element or alloy of the conductive element inside the pores 3 can suppress pulverization of the porous silicon particles. .

(First Embodiment of Porous Silicon Particles According to the Present Invention)
In the following embodiment, the same number is attached | subjected to the element which fulfill | performs the same aspect, and the duplicate description is avoided.
FIG. 2A is a diagram showing an example of porous silicon particles 1a according to the first embodiment of the present invention. The porous silicon particle 1 a is formed by joining a large number of silicon fine particles 5, and the space between the silicon fine particles 5 is the void 3. The holes 3 are continuous and penetrate the porous silicon particles 1a. The porous silicon particle 1a has a three-dimensional network structure. Further, at least a part of the surface of the hole 3, that is, the surface of the silicon fine particle 5 is covered with a single element or an alloy 7a of one or more conductive elements of Cu, Ni, Sn, Zn, Ag, and C. The

  The thickness of the conductive element or the alloy 7a to be coated is about 0.005 to 1.0 μm.

  The porous silicon particle 1a according to the first embodiment of the present invention is obtained by electroless plating or carbon coating, which will be described later. Further, even in substitution plating described later, if the base element 19 is coated on the surface of the hole 3, the base element 19 is replaced with a conductive element, and the surface of the hole 3 is made of a single element or alloy of the conductive element. It can be coated with 7a.

  According to the porous silicon particles according to the first embodiment, in addition to the effect of the porous silicon particles 1 according to the present invention described above, the simple substance or the alloy 7a of the conductive element has at least a part of the pores 3. Since it coat | covers, the pulverization of the silicon which comprises the porous silicon particle 1a can be prevented. Therefore, the porous silicon particles according to the first embodiment become a long-lived negative electrode active material.

(Second Embodiment of Porous Silicon Particles According to the Present Invention)
FIG.2 (b) is a figure which shows an example of the porous silicon particle 1b which concerns on the 2nd Embodiment of this invention. The porous silicon particle 1 b is formed by joining a large number of silicon fine particles 5, and the space between the silicon fine particles 5 is the void 3. The pores 3 are continuous and penetrate the porous silicon particles 1b. The porous silicon particle 1b has a three-dimensional network structure. Further, at least some of the holes 3 are filled with a single element or an alloy 7b of one or more conductive elements of Cu, Ni, Sn, Zn, Ag, and C.

  The porous silicon particle 1b according to the second embodiment of the present invention is obtained by displacement plating, which will be described later. Also, in electroless plating and carbon coating, which will be described later, the conductive element partially deposits in the porous silicon particles 1b depending on conditions, so that at least some of the pores 3 are filled with the conductive element. Can be made.

  According to the porous silicon particles according to the second embodiment, in addition to the effect of the porous silicon particles 1 according to the present invention described above, the simple substance or the alloy 7b of the conductive element is present in at least a part of the pores 3. Since it is filled, it is possible to prevent pulverization of silicon constituting the porous silicon particles 1b. Therefore, the porous silicon particles according to the second embodiment become a long-lived negative electrode active material.

(Method for producing porous silicon particles according to the present invention)
A method for producing porous silicon particles according to the present invention will be described. One or more of Cu, Ni, Sn, Zn, Ag, and C are formed in the pores of the porous silicon particles having continuous pores penetrating the porous silicon particles and having a three-dimensional network structure. Any method can be used as long as a single element or an alloy of a conductive element can be deposited, but it is preferable to use methods such as electroless plating, displacement plating, and carbon coding as shown in FIGS.

(Production method by electroless plating)
3A to 3D are diagrams showing an electroless plating process according to the present invention. Electroless plating is performed on the porous silicon particles 8 before treatment to deposit a metal conductive element in the pores 3 to obtain porous silicon particles 1a.

First, as shown in FIG. 3A, a pre-treatment porous silicon particle 8 having a three-dimensional network structure is prepared.
In FIG. 3A, the porous silicon particles 8 are formed by joining a large number of silicon fine particles 5, but are not limited to such a shape. In addition, any porous silicon particles can be used as long as the pores of the porous silicon particles are connected to each other and the pores penetrate the porous silicon particles.

As the porous silicon particles 8, particles obtained by treating silicon powder with hydrofluoric acid to make it porous can be used. When the hydrofluoric acid treatment is performed, the crystal grain boundaries are etched with hydrofluoric acid, and the silicon fine particles 5 having high crystallinity are joined. In addition, when etching with hydrofluoric acid, the pore structure develops on the surface, but the pore structure hardly develops inside the particle, so the entire particle is a three-dimensional network structure only by etching with hydrofluoric acid. Hard to become. Therefore, by etching and then pulverizing the particles, it is possible to obtain particles composed only of the surface portion of the particles before pulverization, in which the pore structure has been developed, and to obtain porous silicon particles 8 having a three-dimensional network structure. be able to.
In addition, particles obtained by promoting the aggregation and coalescence of fine particles by an ultra-high temperature plasma method can be used as the porous silicon particles 8.

Next, as shown in FIG. 3B, one or more of Cu, Ni, Sn, Zn, and Ag is electrolessly plated with a plating solution 11.
In order to reliably perform electroless plating inside the porous silicon particles 8, the porous silicon particles 8 are deposited on the filter 9, and the plating solution 11 is 0.1 cm / second or more, preferably 1 cm / second. Electroless plating is performed in a flow field having the above flow velocity.

  FIG.3 (c) is an enlarged view of A area | region in FIG.3 (b). It can be seen that the plating solution 11 flows inside the pores 3 of the porous silicon particles 8 before the treatment. Further, since the porous silicon particles 8 have continuous pores 3 and have a three-dimensional network structure, the plating solution 11 passes through the pores 3 and passes through the inside of the porous silicon particles 8. can do. In particular, since the porous silicon particles 8 are placed on the filter 9 and the plating solution 11 is used as a flow field, the plating solution 11 flows through the pores 3 of the porous silicon particles 8 at a predetermined flow rate. Therefore, a new plating solution 11 is always supplied to the surface of the hole 3 of the porous silicon particle 8, and the surface of the hole 3 can be electrolessly plated.

  On the other hand, without fixing the porous silicon particles 8 on the filter, for example, when the porous silicon particles 8 are put into the stirring plating solution, the porous silicon particles 8 move together with the plating solution in the pores 3. Therefore, the plating solution hardly flows in the actual holes 3, and no new plating solution is supplied into the holes 3. Therefore, the outer surface of the porous silicon particles 8 is plated more than the surface of the pores 3 and the surface of the pores 3 is not easily covered.

  The plating solution 11 for electroless plating is not particularly limited, and a plating solution that is usually used when electrolessly plating any one or more of Cu, Ni, Sn, Zn, and Ag can be used.

  As shown in FIG. 3 (d), porous silicon particles 8 are coated with a conductive element (metal) alone or an alloy 7a by applying electroless plating to the porous silicon particles 8 before treatment. 1a is obtained. The thickness of the conductive element or the alloy 7a to be coated is about 0.005 to 1.0 μm.

(Production method by carbon coating)
4 (a) to 4 (c) are diagrams showing a carbon coating process according to the present invention. The porous silicon particles 8 before treatment are coated with carbon, and carbon is deposited in the pores 3 to obtain porous silicon particles 1a.

  First, as shown in FIG. 4 (a), a pre-treatment porous silicon particle 8 having a three-dimensional network structure is prepared.

  As shown in FIG. 4 (b), the porous silicon particles 8 are placed in the furnace 13, the hydrocarbon-based gas 17 is supplied to the furnace 13, and the atmosphere containing the hydrocarbon-based gas 17 is 10% by volume or more. The surface of the porous silicon particles 8 and the pores 3 are heated by heating with a heater 15 to 600 ° C. or more at a temperature rising rate of 100 K / min or more to thermally decompose the hydrocarbon gas 17 in the pores 3. A coating of carbon having a thickness of 0.005 to 0.5 μm is applied to at least a part of the inside of the substrate. The hydrocarbon-based gas concentration is preferably 20 to 90% by volume, more preferably 30 to 50% by volume. The rate of temperature rise is 100 K / min or more, preferably 200 to 1000 K / min. When a rate of temperature increase of 1000 K / min is applied, a large temperature distribution is generated in the porous silicon particles, and the porous silicon particles collapse, which is not desirable.

  As shown in FIG. 4C, the porous silicon particles 8 are coated with carbon to obtain porous silicon particles 1a in which the periphery of the silicon fine particles 5 is covered with a single element 7c of a conductive element (carbon).

(Production method by displacement plating)
FIGS. 5A to 5D are diagrams showing a displacement plating process according to the present invention. Displacement plating is performed on the porous silicon particles 18 containing a base element, and a conductive element is precipitated in the pores 3 to obtain porous silicon particles 1b.

  First, as shown in FIG. 5A, porous silicon particles 18 containing a base element are prepared. In the porous silicon particles 18, at least some of the pores 3 are filled with the base element 19. Further, the content of the base element 19 is 1 atomic% or more of the porous silicon particles 18, preferably 10 atomic% or more, and more preferably 30 atomic% or more. The upper limit of the content of the base element is practically 40 atomic%.

  The porous silicon particles 18 may be made of a powder of an alloy of silicon and a base element made porous with hydrofluoric acid or the like.

  Further, as the porous silicon particles 18, a material obtained by partially removing the base element 19 from a material in which a large number of silicon fine particles 5 bonded to each other exist in a matrix of the base element 19 can be used.

The element 19 having a low deposition potential is an element having a lower deposition potential than any one or more conductive elements of Cu, Ni, Sn, Zn, and Ag deposited by displacement plating.
For example, when displacement plating is performed in a sulfuric acid bath or nitric acid bath, the deposition potential of each element (left: base <noble: right) is as follows:
Be <Al <Zn <Ga <Cd <In <Tl <Ni <Sn <Pb <Bi <Sb <Cu <Ag <Au
For example, when Ag is deposited, the element on the left side of Cu can be used as the base element 19.
When displacement plating is performed in a cyan bath, the following is performed.
Zn <Cd <Cu <Ag <Au

Next, as shown in FIG. 5B, when porous silicon particles 18 are deposited on the filter 9, any one of Cu, Ni, Sn, Zn, and Ag is used in the plating solution 20. The above is deposited by displacement plating.
In order to perform displacement plating on the inside of the porous silicon particles 18, displacement plating is performed in a flow field where the plating solution 20 has a flow rate of 0.1 cm / second or more, preferably 1 cm / second or more.

  As the plating solution 20, a plating solution usually used for displacement plating of one or more of Cu, Ni, Sn, Zn, and Ag can be used. Usually, nitrates, sulfates, and the like of these elements are used. A solution of a cyanide compound can be used.

  FIG.5 (c) is an enlarged view of the B area | region in FIG.5 (b). It can be seen that the plating solution 20 flows inside the pores 3 of the porous silicon particles 18. Further, since the porous silicon particles 18 have continuous pores 3 and have a three-dimensional network structure, the plating solution 20 passes through the pores 3 and passes through the inside of the porous silicon particles 18. can do.

  As a result, as shown in FIG. 5D, the base element 19 is replaced with a single element of the conductive element (metal) or the alloy 7b, and at least a part of the holes 3 is a single element of the conductive element (metal). Alternatively, porous silicon particles 1b filled with alloy 7b are obtained. The thickness of the single element of the conductive element or the alloy 7b is about 0.005 to 0.5 μm.

  By displacement plating, for example, by substituting Ag for porous silicon particles 18 in which Bi remains as the base element 19, it is possible to avoid silicon pulverization during charge and discharge, and further to the inside of the porous body. A conductive path can be provided. In addition, various characteristics are similar to Pb, and Bi that may be subject to RoHS regulation or the like can be refined and removed at a low cost.

  Note that conductive elements such as Cu, Ni, Sn, Zn, and Ag easily form silicide with silicon. Therefore, when porous silicon particles containing a conductive element are formed, the conductive element forms silicide, and a conductive path. It becomes difficult to become. On the other hand, since the base element is an element that does not easily form silicide, even if porous silicon particles containing the base element are prepared, the base element does not form a compound with silicon and remains in a metal state. To do. Therefore, when forming porous silicon particles, a base element is added, and then the base element is replaced with a conductive element, thereby introducing a conductive element in a metallic state into the porous silicon particle. be able to.

(Granulation)
In addition, when the particle diameter of said porous silicon particle is too large at the time of slurry preparation, it can grind | pulverize to a desired particle diameter with a ball mill etc., and can adjust a particle size simply by granulating.
Moreover, you may include the conductive support agent which consists of at least 1 sort (s) chosen from Cu, Ni, Sn, Zn, Ag, and C at the process of granulating. As the binder, fluororesins such as polyvinylidene fluoride (PVdF) and styrene butadiene rubber (SBR), rubber-based materials, and the like are used. For the granulation process, general dry and wet granulation methods can be used. For example, in the dry process, the mechanical alloying method in which compression and shear force are applied, and the powders collide with each other at high speed in an air stream. There is a hybridization method. Furthermore, a spray dryer method can be used in a wet process. For example, porous silicon particles or porous silicon composite particles are dispersed in a solvent such as normal methylpyrrolidone (NMP) containing a binder such as PVdF and spray-dried so that the suspension has a predetermined size. There is a method of granulation.

(Lithium ion secondary battery)
The lithium ion secondary battery of the present invention includes a positive electrode capable of inserting and extracting lithium ions, a negative electrode for a lithium ion secondary battery in which the porous silicon particles according to the present invention are used as a negative electrode active material, and the positive electrode. A separator disposed between the negative electrode and the negative electrode, wherein the positive electrode, the negative electrode, and the separator are disposed in an electrolyte having lithium ion conductivity. Below, the manufacturing method is also demonstrated in detail about the structure.

(Anode for lithium ion secondary battery)
The negative electrode for a lithium ion secondary battery of the present invention is characterized in that the porous silicon particles according to the present invention are used as a negative electrode active material. Porous silicon particles, which are negative electrode active materials, are arranged on the surface of the current collector in a state of being mixed with a conductive additive, a binder, a thickener, etc., thereby forming a negative electrode for a lithium ion secondary battery. .

  Such a negative electrode for a lithium ion secondary battery, for example, put slurry raw materials such as porous silicon particles, a conductive additive, a binder, a thickener, a solvent, etc. into a mixer, kneaded to form a slurry, It can be manufactured by applying this to a current collector.

  The solid content in the slurry is appropriately adjusted based on 25 to 90% by mass of porous silicon particles, 0 to 70% by mass of a conductive additive, 1 to 30% by mass of a binder, and 0 to 25% by mass of a thickener. be able to.

  As the mixer, a general kneader used for preparing a slurry can be used, and a device called a kneader, a stirrer, a disperser, a mixer, or the like that can prepare a slurry may be used. Moreover, when preparing an aqueous slurry, latex (fine particle rubber dispersion) such as styrene butadiene rubber (SBR) can be used as a binder, and carboxymethylcellulose, methylcellulose, etc. can be used as a thickener. It is suitable to use polysaccharides and the like as one kind or a mixture of two or more kinds. In preparing an organic slurry, polyvinylidene fluoride (PVdF) or the like can be used as a binder, and N-methyl-2-pyrrolidone can be used as a solvent.

  The conductive assistant is a powder made of at least one conductive material selected from the group consisting of Cu, Ni, Sn, Zn, Ag, and C. A single powder of Cu, Ni, Sn, Zn, Ag, and C may be used, or a powder of each alloy may be used. For example, general carbon black such as furnace black and acetylene black can be used. In particular, when silicon is exposed on the surface of the porous silicon particles, the conductivity becomes low. Therefore, it is preferable to add carbon nanohorn as a conductive aid. Here, the carbon nanohorn (CNH) has a structure in which a graphene sheet is rounded into a conical shape, and the actual form is an aggregate of a shape like a radial sea urchin with many CNHs facing the apex to the outside. Exists as. The outer diameter of the CNH sea urchin-like aggregate is about 50 nm to 250 nm. In particular, it is preferable to use CNH having an average particle size of about 80 nm.

  The average particle size of the conductive assistant also refers to the average particle size of the primary particles. Even when the structure shape is highly developed such as acetylene black (AB), the average particle diameter can be defined by the primary particle diameter here, and the average particle diameter can be obtained by image analysis of the SEM photograph.

  Moreover, you may use both a particulate-form conductive support agent and a wire-shaped conductive support agent. The wire-shaped conductive aid is a wire made of a conductive material, and the conductive materials listed in the particulate conductive aid can be used. As the wire-shaped conductive assistant, a linear body having an outer diameter of 300 nm or less, such as carbon fiber, carbon nanotube, copper nanowire, or nickel nanowire, can be used. By using a wire-shaped conductive aid, electrical connection with the negative electrode active material or current collector is easily maintained, and the current collection performance is improved. Cracks are less likely to occur. For example, it is conceivable to use AB or copper powder as the particulate conductive aid, and use vapor grown carbon fiber (VGCF) as the wire shaped conductive aid. In addition, you may use only a wire-shaped conductive support agent, without adding a particulate-form conductive support agent.

  The length of the wire-shaped conductive assistant is preferably 0.1 μm to 2 mm. The outer diameter of the conductive aid is preferably 4 nm to 1000 nm, more preferably 25 nm to 200 nm. If the length of the conductive auxiliary agent is 0.1 μm or more, the length is sufficient to increase the productivity of the conductive auxiliary agent, and if the length is 2 mm or less, application of the slurry is easy. Further, when the outer diameter of the conductive auxiliary agent is larger than 4 nm, the synthesis is easy, and when the outer diameter is thinner than 1000 nm, the slurry is easily kneaded. The measuring method of the outer diameter and length of the conductive material can be performed by image analysis using SEM.

  The binder is a resin binder, and a fluororesin such as polyvinylidene fluoride (PVdF) and styrene butadiene rubber (SBR) or a rubber system, and an organic material such as polyimide (PI) or acrylic is used. Can do.

  For applying the slurry to the current collector, for example, the slurry can be applied to one side of the current collector using a coater. As the coater, a general coating apparatus capable of applying the slurry to the current collector can be used, for example, a coater using a roll coater or a doctor blade, a comma coater, a die coater, or the like.

  The current collector is a foil made of at least one metal selected from the group consisting of copper, nickel, and stainless steel. Each may be used alone or may be an alloy of each. The thickness is preferably about 4 μm to 35 μm, and more preferably about 8 μm to 18 μm.

  The prepared slurry is uniformly applied to the current collector, then dried at about 50 to 150 ° C., and passed through a roll press to adjust the thickness. Thus, a negative electrode for a lithium ion secondary battery can be obtained.

(Positive electrode for lithium ion secondary battery)
As the positive electrode for a lithium ion secondary battery, various positive electrodes capable of inserting and extracting lithium ions can be used. The positive electrode for a lithium ion secondary battery is prepared by mixing a positive electrode active material, a conductive additive, a binder, a solvent, and the like to prepare a positive electrode active material composition on a metal current collector such as an aluminum foil. It can be produced by direct application and drying.

Any positive electrode active material can be used as long as it is generally used. For example, LiCoO 2 , LiMn 2 O 4 , LiMnO 2 , LiNiO 2 , LiCo 1/3 Ni 1/3 Mn 1/3 , Compounds such as LiFePO 4 can be used.

  For example, carbon black is used as the conductive auxiliary agent, and, for example, polyvinylidene fluoride (PVdF) and a water-soluble acrylic binder can be used as the binder, and N-methyl-2-pyrrolidone is used as the solvent. (NMP), water, etc. can be used. At this time, the composition of the positive electrode active material, the conductive additive, the binder, and the solvent can be appropriately adjusted within a range that is normally employed in a lithium ion secondary battery.

(Separator)
Any separator can be used as long as it has a function of insulating electronic conduction between the positive electrode and the negative electrode and is usually used in a lithium ion secondary battery. For example, a microporous polyolefin film can be used.

(Electrolytes)
Various electrolytes and electrolytes having lithium ion conductivity can be used as the electrolyte. For example, an organic electrolyte (non-aqueous electrolyte), an inorganic solid electrolyte, a polymer solid electrolyte, or the like can be used as an electrolyte and an electrolyte in an electrolyte lithium ion secondary battery, a Li polymer battery, or the like.

  Specific examples of the organic electrolyte solvent include carbonates such as ethylene carbonate, propylene carbonate, butylene carbonate, diethyl carbonate, dimethyl carbonate, and methyl ethyl carbonate; diethyl ether, dibutyl ether, ethylene glycol dimethyl ether, ethylene glycol diethyl ether, ethylene glycol di Ethers such as butyl ether and diethylene glycol dimethyl ether; aprotic such as benzonitrile, acetonitrile, tetrahydrofuran, 2-methyltetrahydrofuran, γ-butyrolactone, dioxolane, 4-methyldioxolane, N, N-dimethylformamide, dimethylacetamide, dimethylchlorobenzene, nitrobenzene Solvent, or two or more of these solvents Mixed solvent of thereof.

The electrolyte of the organic electrolyte includes LiPF 6 , LiClO 4 , LiBF 4 , LiAlO 4 , LiAlCl 4 , LiSbF 6 , LiSCN, LiCl, LiCF 3 SO 3 , LiCF 3 CO 3 , LiC 4 F 9 SO 3 , LiN (CF 3 SO 2 ) A mixture of one or more electrolytes made of a lithium salt such as 2 can be used.

  It is desirable to add a compound capable of forming an effective solid electrolyte interface film on the surface of the negative electrode active material as an additive to the organic electrolyte. For example, a substance having an unsaturated bond in the molecule and capable of reductive polymerization during charging, such as vinylene carbonate (VC), is added.

  Moreover, it can replace with said organic electrolyte solution and can use a solid-state lithium ion conductor. For example, a solid polymer electrolyte in which the lithium salt is mixed with a polymer made of polyethylene oxide, polypropylene oxide, polyethyleneimine, or the like, or a polymer gel electrolyte in which a polymer material is impregnated with an electrolytic solution and processed into a gel shape can be used.

Further, lithium nitride, lithium halide, lithium oxyacid salt, Li 4 SiO 4, Li 4 SiO 4 -LiI-LiOH, Li 3 PO 4 -Li 4 SiO 4, Li 2 SiS 3, Li 3 PO 4 -Li Inorganic materials such as 2 S—SiS 2 and phosphorus sulfide compounds may be used as the inorganic solid electrolyte.

(Assembly of lithium ion secondary battery)
In the lithium ion secondary battery of the present invention, a separator is disposed between the positive electrode as described above and the negative electrode for the lithium ion secondary battery of the present invention to form a battery element. After winding or stacking such battery elements into a cylindrical or rectangular battery case, an electrolyte is injected to obtain a lithium ion battery.

  An example (cross-sectional view) of the lithium ion secondary battery of the present invention is shown in FIG. The lithium ion secondary battery 21 includes a positive electrode 23 and a negative electrode 25 which are stacked in the order of separator-negative electrode-separator-positive electrode with a separator 27 interposed therebetween, and wound so that the positive electrode 23 is on the inside. This is inserted into the battery can 37. The positive electrode 23 is connected to the positive electrode terminal 31 via the positive electrode lead 33, and the negative electrode 25 is connected to the battery can 37 via the negative electrode lead 35. Chemical energy generated inside the lithium ion secondary battery 21 is externally output as electric energy. It can be taken out. Next, after filling the battery can 37 with the nonaqueous electrolyte 29 so as to cover the electrode plate group, the upper end (opening portion) of the battery can 37 is composed of a circular lid plate and the positive electrode terminal 31 on the upper portion thereof, The lithium ion secondary battery 21 of the present invention can be manufactured by attaching the sealing body 39 incorporating the safety valve mechanism via an annular insulating gasket.

(Effect of negative electrode for lithium ion secondary battery)
According to the present invention, since the porous silicon particles according to the present invention are used as the negative electrode active material, volume expansion at the time of occlusion of lithium ions is suppressed, pulverization and peeling of the negative electrode active material, generation of cracks in the negative electrode, Provided is a high-capacity, long-life negative electrode in which problems such as a decrease in conductivity between negative electrode active materials are eliminated.

  According to the present invention, Cu, Ni, Sn, Zn, Ag, or a C simple substance or alloy is contained in the pores of the porous silicon particles that are the negative electrode active material, and thus has high conductivity. Since the amount of the conductive auxiliary agent and the amount of the binder can be reduced, the bonding strength between the negative electrode active material and the current collector can be increased, and the internal resistance of the electrode can be reduced. Cycle characteristics can be improved.

(Effect of lithium ion secondary battery)
According to the present invention, a long-life lithium ion secondary battery having a high capacity and good cycle characteristics can be obtained.

  Hereinafter, the present invention will be specifically described using examples and comparative examples.

[Sample 1]
First, as sample 1 in Table 1, silicon and bismuth were dissolved and an ingot was cast. This ingot was mechanically pulverized to obtain a silicon alloy powder. This silicon alloy powder was subjected to an etching treatment using a mixed acid obtained by mixing 20% by mass of hydrogen fluoride water and 25% by mass of nitric acid, followed by filtration. Further, the porous silicon particles were pulverized mechanically, contained Bi, and had a three-dimensional network structure with continuous voids (average particle size: 2.1 μm, average porosity: 49.7%, average pore size: 0) .061 μm). The Bi content in this material was 1.2 atomic%.

  The average particle diameter of the porous silicon particles in Table 1 was 2.1 μm as measured using SEM. The average porosity of the porous silicon particles was about 50% when measured in a 15 mL cell by the mercury intrusion method (JIS R 1655).

  When the composition of the porous silicon particles was examined with an ICP emission spectrometer, Si was the main component, Bi was 1.2 atomic%, and other elements were 0.5 atomic% or less.

[Samples 2-7, AD]
Samples 2 to 7 and A to D were produced in the same manner as in sample 1 by changing the type and ratio of the contained elements and changing the presence or absence of addition of an element that forms silicide.

[Samples 8 to 10, E to G]
Samples 8 to 10 and E to G were obtained by subjecting commercially available silicon powder to the same etching treatment and pulverization treatment as those of Sample 1 to produce porous silicon particles having a three-dimensional network structure having continuous voids.
Table 1 shows the characteristics of each sample.

Sample 5 contains FeSi 2 as a silicide, samples 8 and 9 contain NiSi 2 , and samples D and E contain FeSi 2 .

[Example 1]
The porous silicon particles of Sample 1 were deposited 2 mm on a filter having a mesh size of 1 μm, and a 35 ° C. silver nitrate solution having a pH = 2 was allowed to flow at an average flow rate of 0.18 cm / sec for 10 minutes to perform displacement plating. As a result, an Ag plating layer having a thickness of 5 nm was locally formed inside the voids of silicon.

  The Ag plating layer after the displacement plating was locally observed. This plating thickness is an arithmetic average of those observed by FE-SEM, FE-TEM, or the like. In addition, the site | part which was not observed was not used for calculation of an average value as none. The same applies to the plating thickness and carbon layer thickness of other examples and comparative examples.

  In the plating process, the plating solution was passed through the porous body at an average flow rate of 0.1 cm / second or more. Since this silicon porous body has continuous voids, a pressure of 0.05 MPa is sufficient for the filter. there were.

[Examples 2 to 7]
As in Example 1, Samples 2 to 7 were subjected to displacement plating by appropriately changing the plating element, the flow rate, and the plating time. The solution used for displacement plating of each element is an aqueous solution of copper sulfate, zinc sulfate, tin sulfate, and nickel sulfamate.

[Example 8]
In Example 8, the following general catalyst application treatment was performed on the porous silicon particles of Sample 8.
In the catalyst application treatment, the substrate surface is washed by a conditioner treatment (treatment liquid 1: temperature of about 55 ° C. for 1 minute), followed by a pre-dip treatment (treatment solution 2: temperature of about 20 ° C. for 30 seconds). The catalyst is applied using a catalyst C-10 manufactured by Kogyo Co., Ltd. (temperature of 30 ° C. for 1 minute), and the catalyst is activated using an accelerator (treatment liquid 3: temperature of about 20 ° C. for 1 minute). After that, it was immersed in an oxidizing agent (treatment liquid 4: temperature of about 50 ° C. for 1 minute) to oxidize the remaining tin and to easily deposit a copper film. Washing and drying were performed for each step.
<Composition of treatment liquid>
Treatment liquid 1 2-aminoethanol 2ml / liter
Triethanolamine 1 ml / liter Treatment liquid 2 Hydrochloric acid 200 ml / liter Treatment liquid 3 Hydrochloric acid 50 ml / liter Treatment liquid 4 Sodium chlorite 3 grams / liter

For the electroless plating of copper for forming the base metal layer, an electroless copper plating layer having a thickness of 0.032 μm was formed using the following plating bath composition and plating conditions.
<Electroless copper plating bath composition>
Copper sulfate pentahydrate 28.3 grams / liter Sodium hypophosphite 17.5 grams / liter Sodium citrate 61.3 grams / liter Boric acid 35.2 grams / liter <Plating conditions>
Bath temperature 60-85 ° C
pH 7.7 to 9.2
Plating time 3 minutes

[Examples 9 to 10]
Electroless plating was performed in the same manner as in Example 8.
In addition, the electroless silver plating of Example 10 was performed by a general bath composition.

[Comparative Examples 1 to 7]
Using the porous silicon samples A to G shown in Table 1 above, displacement plating or electroless plating was performed under the conditions of Comparative Examples 1 to 7.

[Comparative Example 8]
Sample 1 shown in Table 1 was used as an active material without plating.

[Examples 11 to 12]
Next, carbon coating was performed under the conditions shown in Table 3 using Samples 8 and 9 in Table 1. For carbon coating, acetylene gas was used as a raw material gas, and carbon coating was performed by changing the concentration of hydrocarbon gas in the ambient gas, the temperature rising rate, and the ultimate temperature.

[Comparative Examples 9-12]
Similarly, carbon coating was performed using the samples E and F in Table 1 under the conditions shown in Table 3.

(Evaluation of battery characteristics when particles are used for the negative electrode)
(I) Preparation of negative electrode slurry 65 parts by mass of the obtained porous silicon particles and 20 parts by mass of acetylene black (manufactured by Denki Kagaku Kogyo Co., Ltd.) were charged into a mixer. Furthermore, 5 mass parts of styrene butadiene rubber (SBR) emulsion (manufactured by Nippon Zeon Co., Ltd.) as a binder, 5 parts by mass in terms of solid content, and sodium carboxymethyl cellulose (Daicel Chemical Industries) as a thickener to adjust the viscosity of the slurry A slurry was prepared by mixing a 1% by mass solution in a proportion of 10 parts by mass in terms of solid content.

(Ii) Production of negative electrode Using the doctor blade of the automatic coating apparatus, the prepared slurry was 25 μm thick on a 10 μm thick electrolytic copper foil for current collector (Furukawa Electric Co., Ltd., NC-WS). After being coated at 70 ° C. and dried at a temperature of 70 ° C., a negative electrode for a lithium ion secondary battery was produced through a thickness adjusting process using a press.

(Iii) Characteristic evaluation A lithium ion battery is configured using a negative electrode for a lithium ion secondary battery, an electrolytic solution composed of a mixed solution of ethylene carbonate and diethyl carbonate containing 1 mol / L LiPF 6 , and a metal Li foil counter electrode. The charge / discharge characteristics were examined. The characteristics were evaluated by measuring the initial discharge capacity and the discharge capacity after 50 cycles of charge / discharge, and calculating the discharge capacity retention rate. The discharge capacity was calculated on the basis of the total mass of silicide and active material Si effective for occlusion / release of lithium. First, in a 25 ° C. environment, charging was performed under constant current and constant voltage conditions until the current value was 0.1 C and the voltage value was 0.02 V, and the charging was stopped when the current value decreased to 0.05 C. Next, discharging was performed under the condition of a current value of 0.1 C until the voltage with respect to the metal Li became 1.5 V, and a 0.1 C initial discharge capacity was measured. 1C is a current value that can be fully charged in one hour. Both charging and discharging were performed in a 25 ° C. environment. Next, the above charge / discharge cycle was repeated 50 cycles at a charge / discharge rate of 0.1C. The ratio of the discharge capacity when charging / discharging was repeated 50 cycles with respect to the initial discharge capacity of 0.1 C was obtained as a percentage, and the discharge capacity retention rate after 50 cycles was determined.

  The evaluation results are summarized in Tables 2 and 3.

  As shown in the table, it was confirmed that the battery life was long in the example because the capacity retention rate after 50 cycles was higher than that in the comparative example and the rate of decrease in discharge capacity due to repeated charge and discharge was small.

  In each example, since the negative electrode active material is a porous silicon particle having a three-dimensional network structure, even if a volume change of expansion / contraction occurs due to alloying / dealloying of Li and Si during charge / discharge. It was found that the discharge capacity retention rate was high without cracking or pulverizing the silicon composite particles.

In Comparative Example 1, the average particle size of the porous silicon particles of Sample A was 0.08 μm, and the particle size was too small.
In Comparative Example 2, the average particle size of the porous silicon particles of Sample B was 1100 μm, and the particle size was too large.
In Comparative Example 3, the porosity of Sample C was too high at 94%.
In Comparative Example 4, since the plating solution flow rate was too slow, plating deposition in the porous silicon particles was small, and the cycle characteristics were poor.

In Comparative Examples 5 and 6, the plating thickness was not sufficient.
In Comparative Example 7, the plating was performed excessively and the plating thickness was too thick.
In Comparative Example 8, since the porous silicon particles were not subjected to displacement plating, the pulverization progressed and the cycle characteristics were poor.

  In Comparative Example 9, the hydrocarbon gas concentration was not sufficient, in Comparative Example 10, the rate of temperature increase was low, and in Comparative Example 11, the heating temperature was low, so the carbon layer thickness was not sufficient. Moreover, in the comparative example 12, since the carbon coating time was short, the thickness of the carbon layer was not sufficient. In Comparative Examples 9 to 12 where the thickness of the carbon layer was not sufficient, the cycle characteristics were poor.

  The preferred embodiments of the present invention have been described above with reference to the accompanying drawings, but the present invention is not limited to such examples. It will be apparent to those skilled in the art that various changes and modifications can be made within the scope of the technical idea disclosed in the present application, and these are naturally within the technical scope of the present invention. Understood.

  The porous silicon particles according to the present invention can be used not only for a negative electrode of a lithium ion battery but also as a negative electrode of a lithium ion capacitor, a solar battery, a light emitting material, and a filter material.

DESCRIPTION OF SYMBOLS 1, 1a, 1b ......... Porous silicon particle 3 ......... Void 5 ......... Silicon fine particle 7a, 7b ......... Conductive element simple substance or alloy 7c ......... Conductive element (carbon) simple substance 8 ……… Porous silicon particles 9 ……… Filter 11 ……… Plating solution 13 ……… Furnace 15 ……… Heater 17 ……… Hydrocarbon-based gas 18 ……… Porous silicon particles 19 ……… Low Element 20 ......... Plating solution 21 ......... Lithium ion secondary battery 23 ......... Positive electrode 25 ......... Negative electrode 27 ......... Separator 29 ......... Non-aqueous electrolyte 31 ......... Positive electrode terminal 33 ......... Positive lead 35 ……… Negative electrode lead 37 ……… Battery can 39 ……… Sealing body

Claims (12)

  1. Porous silicon particles having continuous pores and a three-dimensional network structure,
    The pores penetrate the porous silicon particles;
    A porous silicon particle comprising a single element or an alloy of one or more conductive elements of Cu, Ni, Sn, Zn, Ag, and C in the pores.
  2.   2. The porous silicon particle according to claim 1, wherein the single element or alloy of the conductive element covers at least a part of the surface in the pores.
  3.   2. The porous silicon particle according to claim 1, wherein the single element or alloy of the conductive element is filled in at least a part of the pores.
  4.   In the porous silicon particles, As, Ba, C, Ca, Ce, Co, Cr, Cu, Er, Fe, Gd, Hf, Lu, Mg, Mn, Mo, Nb, Nd, Ni, P, Pd, At least one selected from the group consisting of Pr, Pt, Pu, Re, Rh, Ru, Sc, Sm, Sr, Ta, Te, Th, Ti, Tm, U, V, W, Y, Yb, Zr The porous silicon particle according to any one of claims 1 to 3, further comprising silicide with an element.
  5. The average particle diameter of the porous silicon particles is 0.1 μm to 1000 μm,
    The average porosity of the porous silicon particles is 15 to 93%,
    The average pore diameter of the porous silicon particles is 5 nm to 2 μm,
    The porous silicon particle according to any one of claims 1 to 4, wherein a ratio of an average particle diameter to an average pore diameter of the porous silicon particle is 5 or more.
  6.   A negative electrode for a lithium ion secondary battery, wherein the porous silicon particles according to any one of claims 1 to 5 are used as a negative electrode active material.
  7. A positive electrode capable of inserting and extracting lithium ions;
    A negative electrode for a lithium ion secondary battery according to claim 6,
    Having a separator disposed between the positive electrode and the negative electrode;
    A lithium ion secondary battery, wherein the positive electrode, the negative electrode, and the separator are disposed in an electrolyte having lithium ion conductivity.
  8. A single element or alloy of one or more conductive elements of Cu, Ni, Sn, Zn, Ag, and C inside the pores of the porous silicon particles having continuous pores and having a three-dimensional network structure A method for producing porous silicon particles, wherein
  9.   Performing electroless plating with at least one of Cu, Ni, Sn, Zn, and Ag in at least a part of the pores of the porous silicon particles to deposit the conductive element. The method for producing porous silicon particles according to claim 8, wherein:
  10. The porous silicon particles contain 1 atomic% or more of an element having a lower deposition potential than any one or more conductive elements of Cu, Ni, Sn, Zn, and Ag,
    Perform substitution plating to replace the base element with the conductive element,
    The method for producing porous silicon particles according to claim 8, wherein the conductive element is precipitated in at least a part of the pores of the porous silicon particles.
  11. Placing the porous silicon particles on a filter;
    The method for producing porous silicon particles according to claim 9 or 10, wherein the electroless plating or the displacement plating is performed in a flow field having an average flow rate of 0.1 cm / second or more.
  12.   The porous silicon particles are heated to 600 ° C. or higher at a temperature rising rate of 100 K / min or more in an atmosphere containing 10% by volume or more of hydrocarbon-based gas, and the hydrocarbon-based gas in the pores The method for producing porous silicon particles according to claim 8, wherein carbon is precipitated in at least a part of the pores of the porous silicon particles by thermally decomposing them.
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