JP6136359B2 - Spherical carbon / tin compound composite particles and negative electrode material for Li ion secondary battery - Google Patents

Description

  The present invention relates to spherical carbon / tin compound composite particles and a negative electrode material for a Li ion secondary battery using the same.

  Sn and its oxide are known to electrochemically alloy with Li. Therefore, application of Sn and its oxide to a negative electrode material of a Li ion secondary battery is being studied. However, Sn and its oxide are accompanied by a change in volume during the insertion and release of Li ions. Therefore, there is a problem that if the insertion and release of Li ions are repeated, the particles are eventually pulverized and the particles fall off from the negative electrode.

In order to solve this problem, various proposals have heretofore been made.
For example, Patent Document 1 discloses that
(1) A dispersion liquid containing SnCl ₂ · 2H ₂ O, ketjen black and NaOH is put into a reaction vessel composed of a concentric cylinder of an outer cylinder and an inner cylinder,
(2) The inner cylinder is turned at a high speed for a predetermined time,
(3) A method of filtering and recovering ketjen black after the inner cylinder stops turning is disclosed.
In the same document,
(A) By this method, a negative electrode active material in which SnO ₂ is supported on nano-sized hollow ketjen black is obtained, and
(B) It is described that the obtained negative electrode active material exhibits good cycle characteristics.

Non-Patent Document 1 discloses a composite in which SnO ₂ fine particles are precipitated on mesoporous carbon having an irregular outer shape.
This document describes that by depositing SnO ₂ fine particles on amorphous mesoporous carbon, the volume expansion associated with the alloying reaction of Sn and Li is reduced, and the recycling characteristics are improved.

In the negative electrode active material described in Patent Document 1, in order to sufficiently improve the cycle characteristics, it is necessary to enclose most of SnO ₂ in the pores of ketjen black. However, in order to encapsulate most of SnO _{2 in} the pores in the method described in Patent Document 1, a large amount of ketjen black is required, and the amount of SnO ₂ contained in the whole negative electrode active material is improved. Is difficult. In particular, ketjen black is bulky and it is difficult to improve the amount of SnO ₂ per volume.

Since the composite described in Non-Patent Document 1 is indefinite, gaps are easily formed when the composite is accumulated, and the amount of SnO ₂ supported per unit volume is insufficient. Even if it is indefinite, the mesopores are oriented in the major axis direction of the mesoporous carbon, so the mesopores are oriented in parallel on the current collector in the electrode. As a result, the cycle characteristics deteriorate and there is room for improvement.

JP 2011-253620 A

Int.J.Electrochem.Sci., 6 (2011) 3580-3593

The problem to be solved by the present invention is to provide spherical carbon / tin compound composite particles excellent in recycling characteristics, and a negative electrode material for a Li ion secondary battery using the same.
Another problem to be solved by the present invention is to provide spherical carbon / tin compound composite particles having a large electric capacity per volume, and a negative electrode material for a Li ion secondary battery using the same.

In order to solve the above problems, the globular carbon / tin compound composite particles according to the present invention are summarized as having the following configuration.
(1) The spherical carbon / tin compound composite particles are:
A spherical carbon porous body;
It consists of a composite comprising Sn and / or microcrystals made of an oxide of Sn filled in the pores of the spherical carbon porous body.
(2) The spherical carbon / tin compound composite particles are used as a negative electrode material for a Li ion secondary battery.

  Moreover, the negative electrode material of the Li ion secondary battery according to the present invention comprises an array of spherical carbon / tin compound composite particles according to the present invention.

The composite particles according to the present invention have a structure in which nano-sized microcrystals made of a tin-based compound such as SnO ₂ are dispersed in the pores of a spherical carbon porous body. Since the pore walls reinforce the tin-based compound and the composite particles have certain voids, the volume expansion can be relaxed and absorbed. Moreover, even if the tin-based compound is pulverized, the pore walls prevent the tin-based compound from being detached from the spherical carbon porous body. Therefore, the recycling characteristics are improved.

In particular, when the spherical carbon porous body has carbon nanorods arranged in a spherical symmetry, the volume expansion of the tin-based compound becomes isotropic, and the recycling characteristics are further improved.
Furthermore, the spherical carbon porous body is easily filled in the electrode material. Therefore, when the composite particles according to the present invention are used as the negative electrode material, the electric capacity per volume is improved.

It is a TEM photograph of a spherical carbon / SnO ₂ composite. It is a cyclic voltammetry curve of a spherical carbon / SnO ₂ composite (Example 2). Spherocarbon / SnO ₂ composite, and XRD pattern before and after the charge-discharge test of the negative electrode material (Example 2) containing the same. It is a figure which shows the charging / discharging cycle characteristic of the sample obtained in Examples 1-3 and Comparative Examples 1-2.

Hereinafter, an embodiment of the present invention will be described in detail.
[1. Spherical carbon / tin compound composite particles]
The spherical carbon / tin compound composite particles according to the present invention have the following configuration.
(1) The spherical carbon / tin compound composite particles are:
A spherical carbon porous body;
It consists of a composite comprising Sn and / or microcrystals made of an oxide of Sn filled in the pores of the spherical carbon porous body.
(2) The spherical carbon / tin compound composite particles are used as a negative electrode material for a Li ion secondary battery.

[1.1. Spherical carbon porous body]
The spherical carbon porous body serves as a support for Sn and / or Sn oxides (hereinafter collectively referred to as “tin-based compounds”), and has a large number of pores therein. . The tin-based compound is filled in the pores of the spherical carbon porous body.

In the present invention, “spherical” means that when a plurality of (preferably 20 or more) particles produced under the same conditions are observed with a microscope, the average value of sphericity of each particle is 13% or less. It means that. The “sphericity” is an index representing the degree of deviation of the outer shape of each particle from the perfect circle, and the circumscribed circle and the particle with respect to the radius (r ₀ ) of the smallest circumscribed circle in contact with the particle surface. This is a value represented by the ratio (= Δr _max × 100 / r ₀ (%)) of the maximum value (Δr _max ) of the distance in the radial direction from each point on the surface. When the method described later is used, spherical particles having a sphericity of 7% or less or 3% or less can be obtained.

The spherical carbon porous body is not necessarily “monodispersed” and may have a large variation in diameter. However, when the variation in the diameter of the spherical carbon porous body is reduced, an array in which the composite particles are regularly arranged can be obtained. For this purpose, the monodispersity of the spherical carbon porous body is preferably 10% or less. The monodispersity is more preferably 5% or less.
Here, the “monodispersity” refers to a value represented by the formula (1).
Monodispersity = (standard deviation of particle diameter) × 100 / (average value of particle diameter) (1)

The pore structure of the spherical carbon porous body varies depending on the manufacturing method. The pore structure of the spherical carbon porous body is not particularly limited, and various structures can be selected according to the purpose.
In particular, the spherical carbon porous body is preferably one in which carbon nanorods having a diameter of 10 nm or less are arranged in a spherical symmetry. The spherical carbon porous body in which the carbon nanorods are arranged in a spherical symmetry has isotropic particles, so that the volume change of the tin-based compound filled in the pores is also isotropic. As a result, the recycling characteristics are further improved.

The diameter and pore diameter of the spherical carbon porous body are not particularly limited, and optimum values can be selected according to the purpose.
When the manufacturing conditions are optimized, the pore diameter of the spherical carbon porous body can be controlled in the range of 1 nm to 20 nm.
Further, when the manufacturing conditions are optimized, the diameter of the spherical carbon porous body can be controlled in the range of 0.05 μm to 2.0 μm.

[1.2. Microcrystal]
The fine pores of the spherical carbon porous body are filled with microcrystals made of a tin-based compound.
Specifically, as tin-based compounds,
(1) Sn,
(2) There are tin oxides such as SnO ₂ and SnO.
A microcrystal may consist of any one of these, or may be a mixture of two or more.
In particular, SnO ₂ is suitable as a material constituting microcrystals because it has excellent Li ion storage / release characteristics.

  The microcrystals are deposited between the carbon nanorods, and the crystallite size is about 2 nm when deposited from an aqueous solution under normal conditions. Since the microcrystal grows by expanding between the carbon nanorods, the microcrystal may enter even if the gap between the carbon nanorods (that is, the pores of the spherical carbon porous body) is slightly small. Moreover, when the heat treatment after precipitation is performed, the microcrystal grows, and the size of the crystallite increases to 5 to 20 nm depending on conditions. The size of the microcrystal can be controlled within the range.

The filling amount of the microcrystals into the pores is not particularly limited and can be arbitrarily selected according to the purpose. In general, the greater the filling amount of microcrystals, the greater the electrical capacity per volume.
When the manufacturing conditions are optimized, the filling amount of the microcrystals can be controlled in the range of 20 to 80 wt%.

[1.3. Application]
The spherical carbon / tin compound composite particles according to the present invention are used as a negative electrode material for a Li ion secondary battery.
When the tin-based compound is filled in the pores of the spherical carbon porous body, the volume change of the tin-based compound accompanying the insertion / release of Li ions can be reduced or absorbed. In addition, when the spherical carbon porous body has a spherically symmetric pore structure, the composite particles themselves are isotropic, so that the recycling characteristics are further improved.

[2. Negative electrode material for Li-ion secondary battery]
The negative electrode material of the Li ion secondary battery according to the present invention comprises an array of spherical carbon / tin compound composite particles according to the present invention.
Since the composite particles according to the present invention are spherical, the filling properties are high. Therefore, the negative electrode material composed of such an array of composite particles has a larger electric capacity per unit volume than the negative electrode material composed of an array of amorphous composite particles. In particular, when the composite particles are monodispersed, the composite particles can be regularly arranged. Therefore, when monodispersed composite particles are used, the electric capacity per volume of the negative electrode material is further improved.

  The array may be one in which the composite particles are irregularly arranged, or one in which the composite particles are regularly arranged. In order to regularly arrange the composite particles, the monodispersity of the composite particles is preferably 10% or less, and more preferably 5% or less. In addition, the array may be composed only of composite particles, or may further include other phases.

Other phases include, for example:
(1) Ketjen black to improve conductivity,
(2) polyvinylidene fluoride for strongly bonding the particles,
and so on.

[3. Method for producing spherical carbon / tin compound composite particles]
The spherical carbon / tin compound composite particles according to the present invention are:
(1) producing a spherical mesoporous material;
(2) Precipitating carbon in the mesopores of the spherical mesoporous material to form a spherical mesoporous material / carbon composite,
(3) removing the spherical mesoporous material from the spherical mesoporous material / carbon composite to form a spherical carbon porous material;
(4) It can be produced by precipitating a tin-based compound in the mesopores of the spherical carbon porous body.

[3.1. Spherical mesoporous material production process]
The spherical mesoporous material production process is a process of producing a spherical mesoporous material containing silica.
Spherical mesoporous material may be those of silica alone, or silica as the main component, may include an oxide of a metal element M ₁ other than silica. The metal element M ₁ is not particularly limited, those capable of producing a divalent or more metal alkoxides are preferred. When the metal element M ₁ is capable of producing a bivalent or higher valent metal alkoxide, spherical particles containing an oxide of the metal element M ₁ can be easily produced. As the metal element _{M 1,} specifically, some Al, Ti, Mg, Zr and the like.

The spherical mesoporous material containing silica is
(1) A raw material containing a silica raw material and a surfactant is mixed in a solvent to produce precursor particles containing a surfactant,
(2) removing the surfactant from the precursor particles;
Can be obtained.
In this case, you may further perform the process which expands the pore diameter of a spherical mesoporous body.

[3.1.1. Silica raw material]
Silica raw materials include
(1) Tetraalkoxysilane (silane compound) such as tetramethoxysilane, tetraethoxysilane, tetraisopropoxysilane, tetrabutoxysilane, dimethoxydiethoxysilane,
(2) Trimethoxysilanol, triethoxysilanol, trimethoxymethylsilane, trimethoxyvinylsilane, triethoxyvinylsilane, triethoxy-3-glycidoxypropylsilane, 3-mercaptopropyltrimethoxysilane, 3-chloropropyltrimethoxysilane, 3- (2-aminoethyl) aminopropyltrimethoxysilane, phenyltrimethoxysilane, phenyltriethoxysilane, γ- (methacryloxypropyl) trimethoxysilane, β- (3,4-epoxycyclohexyl) ethyltrimethoxysilane, etc. Trialkoxysilane (silane compound),
(3) dialkoxysilanes (silane compounds) such as dimethoxydimethylsilane, diethoxydimethylsilane, diethoxy-3-glycidoxypropylmethylsilane, dimethoxydiphenylsilane, dimethoxymethylphenylsilane,
(4) Sodium metasilicate (Na ₂ SiO ₃ ), sodium orthosilicate (Na ₄ SiO ₄ ), sodium disilicate (Na ₂ Si ₂ O ₅ ), sodium tetrasilicate (Na ₂ Si ₄ O ₉ ), water Sodium silicate such as glass (Na ₂ O · nSiO ₂ , n = 2 to 4),
(5) Kanemite (NaHSi ₂ O ₅ .3H ₂ O), sodium disilicate crystals (α, β, γ, δ-Na ₂ Si ₂ O ₅ ), macatite (Na ₂ Si ₄ O ₉ ), eyelite ( _{Na 2 Si 8 O 17 · xH} 2 O), magadiite _{(Na 2 Si 14 O 17 ·} xH 2 O), kenyaite _{(Na 2 Si 20 O 41 ·} xH 2 O) layered silicates, such as,
(6) Precipitating silica such as Ultrasil (Ultrasil), Cab-O-Sil (Cabot), HiSil (Pittsburgh Plate Glass), fumed silica such as colloidal silica, Aerosil (Degussa-Huls),
Etc. can be used.

Further, hydroxyalkoxysilane can also be used as the silica raw material. The term “hydroxyalkoxysilane” refers to a hydroxy group (—OH) attached to the carbon atom of the alkoxy group of alkoxysilane. As the hydroxyalkoxysilane, tetrakis (hydroxyalkoxy) silane having four hydroxyalkoxy groups and tris (hydroxyalkoxy) silane having three hydroxyalkoxy groups can be used.
The type of hydroxyalkoxy group and the number of hydroxy groups are not particularly limited, but in the hydroxyalkoxy group such as 2-hydroxyethoxy group, 3-hydroxypropoxy group, 2-hydroxypropoxy group, 2,3-dihydroxyproxy group, etc. Those having a relatively small number of carbon atoms (having about 1 to 3 carbon atoms) are advantageous from the viewpoint of reactivity.

Examples of tetrakis (hydroxyalkoxy) silane include tetrakis (2-hydroxyethoxy) silane, tetrakis (3-hydroxypropoxy) silane, tetrakis (2-hydroxyproxy) silane, tetrakis (2,3-dihydroxypropoxy) silane, and the like. .
As tris (hydroxyalkoxy) silane, methyltris (2-hydroxyethoxy) silane, ethyltris (2-hydroxyethoxy) silane, phenyltris (2-hydroxyethoxy) silane, 3-mercaptopropyltris (2-hydroxyethoxy) silane, Examples include 3-aminopropyltris (2-hydroxyethoxy) silane and 3-chloropropyltris (2-hydroxyethoxy) silane.
These hydroxyalkoxysilanes can be synthesized by reacting an alkoxysilane with a polyhydric alcohol such as ethylene glycol or glycerin (see, for example, Doris Brandhuber et al., Chem. Mater. 2005, 17, 4262). .

Among these, tetraalkoxysilane and tetrakis (hydroxyalkoxy) silane are suitable as silica raw materials because the number of silanol bonds generated by hydrolysis increases and a strong skeleton can be formed.
In addition, these silica raw materials may be used alone or in combination of two or more. However, when two or more kinds of silica raw materials are used, the reaction conditions during the production of the precursor particles may be complicated. In such a case, the silica raw material is preferably used alone.

When the precursor particles contain an oxide of a metal element M ₁ other than silica, a raw material containing a metal element M ₁ in addition to the silica raw material is used.
The raw material containing a metal element M ₁ is,
(1) Al-containing alkoxides such as aluminum butoxide (Al (OC ₄ H ₉ ) ₃ ), aluminum ethoxide (Al (OC ₂ H ₅ ) ₃ ), aluminum isopropoxide (Al (OC ₃ H ₇ ) ₃ ) And salts such as sodium aluminate and aluminum chloride,
(2) Ti such as titanium isopropoxide (Ti (Oi-C ₃ H ₇ ) ₄ ), titanium butoxide (Ti (OC ₄ H ₉ ) ₄ ), titanium ethoxide (Ti (OC ₂ H ₅ ) ₄ ), etc. Containing alkoxide,
(3) Mg-containing alkoxide such as magnesium methoxide (Mg (OCH ₃ ) ₂ ), magnesium ethoxide (Mg (OC ₂ H ₅ ) ₂ ),
(4) Zr of zirconium isopropoxide (Zr (Oi-C ₃ H ₇ ) ₄ ), zirconium butoxide (Zr (OC ₄ H ₉ ) ₄ ), zirconium ethoxide (Zr (OC ₂ H ₅ ) ₄ ), etc. Containing alkoxide,
Etc. can be used.

[3.1.2. Surfactant]
The surfactant serves as a template for forming mesopores in the particles. The type of the surfactant is not particularly limited, and various surfactants can be used. The pore structure in the particles can be controlled according to the type of surfactant used, the amount added, and the like.

The surfactant is particularly preferably an alkyl quaternary ammonium salt. The alkyl quaternary ammonium salt refers to one represented by the following formula (a).
_{CH 3 - (CH 2) n} -N + (R 1) (R 2) (R 3) X - ··· (a)
(A) In the _{formula, R 1, R 2, R} 3 each represent an alkyl group having 1 to 3 carbon atoms. R ₁ , R ₂ and R ₃ may be the same as or different from each other. In order to facilitate aggregation (formation of micelles) between alkyl quaternary ammonium salts, it is preferable that R ₁ , R ₂ , and R ₃ are all the same. Further, at least one of R ₁ , R ₂ , and R ₃ is preferably a methyl group, and all are preferably methyl groups.
(A) In formula, X represents a halogen atom. Although the kind of halogen atom is not particularly limited, X is preferably Cl or Br in view of availability.
(A) In formula, n represents the integer of 7-21. Generally, the smaller n is, the smaller the mesopore central pore diameter is obtained. On the other hand, as n increases, the central pore diameter increases, but if n increases too much, the hydrophobic interaction of the alkyl quaternary ammonium salt becomes excessive. As a result, a layered compound is generated and a spherical porous body cannot be obtained. n is preferably 9 to 17, and more preferably 13 to 17.

Among those represented by the formula (a), alkyltrimethylammonium halide is preferable. Examples of the alkyltrimethylammonium halide include hexadecyltrimethylammonium halide, octadecyltrimethylammonium halide, nonyltrimethylammonium halide, decyltrimethylammonium halide, undecyltrimethylammonium halide, dodecyltrimethylammonium halide, and the like.
Among these, alkyltrimethylammonium bromide or alkyltrimethylammonium chloride is particularly preferable.

  When synthesizing silica particles, one type of alkyl quaternary ammonium salt may be used, or two or more types may be used. However, since the alkyl quaternary ammonium salt serves as a template for forming mesopores in the silica particles, the type greatly affects the shape of the mesopores. In order to synthesize silica particles having more uniform mesopores, it is preferable to use one kind of alkyl quaternary ammonium salt.

[3.1.3. solvent]
As the solvent, an organic solvent such as water or alcohol, a mixed solvent of water and an organic solvent, or the like is used. The alcohol may be any of monovalent alcohols such as methanol, ethanol, and propanol, divalent alcohols such as ethylene glycol, and trivalent alcohols such as glycerin.
When a mixed solvent of water and an organic solvent is used, the content of the organic solvent in the mixed solvent can be arbitrarily selected according to the purpose. In general, when an appropriate amount of an organic solvent is added to the solvent, control of the particle size and particle size distribution is facilitated.

[3.1.4. Mixing ratio]
In general, when the concentration of a raw material containing a silica raw material and a metal element M ₁ added as necessary (hereinafter simply referred to as “silica source”) is too low, silica particles cannot be obtained in a high yield. Moreover, it becomes difficult to control the particle size and particle size distribution, and the uniformity of the particle size decreases. Therefore, the concentration of the silica source is preferably 0.005 mol / L or more. The concentration of the silica source is more preferably 0.008 mol / L or more.
On the other hand, if the concentration of the silica source is too high, the surfactant functioning as a template for forming mesopores is relatively insufficient, and regularly arranged mesopores cannot be obtained. Accordingly, the concentration of the silica source is preferably 0.03 mol / L or less. The concentration of the silica source is more preferably 0.015 mol / L or less.

Generally, when the concentration of the surfactant is too low, a template for forming mesopores is insufficient, and regularly arranged mesopores cannot be obtained. Therefore, the concentration of the surfactant is preferably 0.003 mol / L or more. The concentration of the surfactant is more preferably 0.01 mol / L or more.
On the other hand, if the surfactant concentration is too high, silica particles cannot be obtained in high yield. Therefore, the concentration of the surfactant is preferably 0.03 mol / L or less. The concentration of the surfactant is more preferably 0.02 mol / L or less.

[3.1.5. Reaction conditions]
When a silane compound such as alkoxysilane or hydroxyalkoxysilane is used as the silica material, this is used as it is as a starting material.
On the other hand, when a compound other than a silane compound is used as the silica raw material, a basic material such as sodium hydroxide is added in advance to the silica raw material in water (or an alcohol aqueous solution to which an alcohol is added if necessary). Add. The addition amount of the basic substance is preferably about equimolar to the silicon atom in the silica raw material. When a basic substance is added to a solution containing a silica raw material other than the silane compound, a part of the Si— (O—Si) ₄ bond already formed in the silica raw material is cut, and a uniform solution is obtained. The amount of basic substance contained in the solution affects the yield and porosity of the silica particles. Therefore, after a uniform solution is obtained, a dilute acid solution is added to the solution, and excess base present in the solution is added. Neutralize sex substances. The addition amount of the dilute acid solution is preferably an amount corresponding to 1/2 to 3/4 times mol of silicon atoms in the silica raw material.

  A silica source is added to a solvent containing a predetermined amount of a surfactant to perform hydrolysis and polycondensation. Thereby, surfactant functions as a template and the precursor particle | grains containing a silica and surfactant are obtained.

  As the reaction conditions, optimum conditions are selected according to the type of silica raw material, the particle size of the precursor particles, and the like. In general, the reaction temperature is preferably -20 to 100 ° C. The reaction temperature is more preferably 0 to 80 ° C, more preferably 10 to 40 ° C.

[3.1.6. Diameter expansion processing]
The synthesized spherical mesoporous material can also be used as a template for producing a spherical carbon porous material by removing a surfactant described later. However, generally, the spherical mesoporous material immediately after synthesis has a relatively small pore diameter. In the case of synthesizing a spherical carbon porous body using a spherical mesoporous body, the smaller the pore diameter of the spherical mesoporous body, the thinner the carbon nanorods in the spherical carbon porous body, and the strength of the carbon nanorods decreases. For this reason, when the carbon nanorods are deformed when the template is removed and the gaps between the nanorods are reduced, it may be difficult to introduce the tin-based compound into the pores.

Therefore, in such a case, it is preferable to perform a process for expanding the pore diameter of the spherical mesoporous material (diameter expansion process).
Specifically, the diameter expansion treatment is performed by hydrothermally treating the synthesized spherical mesoporous material (one having the surfactant not removed) in a solution containing the diameter expansion agent. By this treatment, the pore diameter of the spherical mesoporous material can be expanded.

Such a diameter expanding agent is composed of an alkylammonium halide represented by the following general formula (b), a chain hydrocarbon, a cyclic hydrocarbon, a chain aliphatic amine, a chain aliphatic alcohol, and a heterocyclic compound. At least one selected from the group is used.
CH ₃ − (CH ₃ ) _z −N ⁺ (R ₁ ) (R ₂ ) (R ₃ ) X ⁻ (b)
(B) wherein, R _1, R _2, and R ₃ represents an alkyl group of good 1 to 3 carbon atoms the same or different. X represents a halogen atom. z is an integer of 17 to 25 and represents an integer larger than the value of n in the formula (a) of the alkylammonium halide selected as the surfactant used in the synthesis of the spherical mesoporous material. R _1, R ₂ and R _3, as well as for the X, it is of the R _1, R ₂ and R _3, and X as defined in the above general formula (a).

When the alkylammonium halide represented by the general formula (b) is used as the diameter expanding agent, the alkylammonium halide is introduced into the silica by substitution reaction with the surfactant in the pores of the spherical mesoporous material. The hole diameter increases.
Z in General formula (b) shows the integer of 17-25, it is more preferable that it is an integer of 20-25, and it is more preferable that it is an integer of 22-24. With alkylammonium halides having z of 16 or less, it is difficult to sufficiently expand the pore diameter of the spherical mesoporous material. On the other hand, when the alkylammonium halide having z of 26 or more, the alkyl chain becomes too large, and it becomes difficult to introduce into the silica by substitution reaction with the surfactant used in the synthesis.

When chain hydrocarbons, cyclic hydrocarbons, chain aliphatic amines, chain aliphatic alcohols, and heterocyclic compounds are used as the expansion agent, the expansion agent is removed from the solvent, and the more hydrophobic spherical mesoporous material. By being introduced into the pores of the body, the pore diameter of the spherical mesoporous material is expanded.
The chain hydrocarbon is not particularly limited as long as it is a chain hydrocarbon, but is preferably a chain hydrocarbon having 6 to 26 carbon atoms (more preferably 6 to 12). If the number of carbon atoms of the chain hydrocarbon is less than the lower limit, the hydrophobicity tends to be small, and it tends to be difficult to be introduced into the pores of the spherical mesoporous material. On the other hand, if the upper limit is exceeded, the solubility tends to decrease.

  Examples of such chain hydrocarbons include hexane, methylpentane, dimethylbutane, heptane, methylhexane, dimethylpentane, trimethylbutane, octane, methylheptane, dimethylhexane, trimethylpentane, isopropylpentane, nonane, methyloctane, Examples include ethyl heptane, decane, undecane, dodecane, tetradecane, and hexadecane. From the viewpoint of hydrophobicity and solubility, hexane, heptane, octane, nonane, decane, undecane, and dodecane are preferable.

  The cyclic hydrocarbon is not particularly limited as long as it contains a cyclic hydrocarbon in its skeleton, and has 1 to 3 rings and 6 to 20 carbon atoms (more preferably, 6 to 16 carbon atoms). ) Is preferred. When the number of carbon atoms of the cyclic hydrocarbon is less than the lower limit, the hydrophobicity tends to be small, and it tends to be difficult to introduce into the pores of the spherical mesoporous material. On the other hand, if the upper limit is exceeded, the solubility decreases, and the pore diameter tends not to be increased. Further, when the number of cyclic hydrocarbon rings exceeds 3, the solubility is lowered, and therefore the pore diameter tends not to be increased.

  Further, as such cyclic hydrocarbons, for example, cyclohexane, cyclohexene, cyclohexadiene, benzene, methylbenzene, dimethylbenzene, trimethylbenzene, ethylbenzene, diethylbenzene, triethylbenzene, vinylbenzene, divinylbenzene, isopropylbenzene, diisopropylbenzene, Examples include triisopropylbenzene, indene, naphthalene, tetralin, azulene, biphenylene, acenaphthylene, fluorene, phenanthrene, anthracene and the like. From the viewpoint of hydrophobicity and solubility, cyclohexane, benzene, trimethylbenzene, triethylbenzene, triisopropylbenzene, and naphthalene are preferable.

  The chain aliphatic amine is not particularly limited as long as it is a chain aliphatic amine, but is preferably a chain aliphatic amine having 6 to 26 carbon atoms (more preferably 6 to 20). When the number of carbon atoms of the chain aliphatic amine is less than the lower limit, the hydrophobicity tends to be small and it tends to be difficult to be introduced into the pores of the spherical mesoporous material. On the other hand, when the upper limit is exceeded, the solubility tends to decrease.

  Examples of such chain aliphatic amines include hexylamine, methylpentylamine, dimethylbutylamine, heptylamine, methylhexylamine, dimethylpentylamine, trimethylbutylamine, octylamine, methylheptylamine, dimethylhexylamine, Trimethylpentylamine, isopropylpentylamine, nonylamine, methyloctylamine, ethylheptylamine, decylamine, undecylamine, dodecylamine, tetradecylamine, hexadecylamine, N, N'-dimethyl-n-hexylamine, N, N '-Dimethyl-n-octylamine, N, N'-dimethyl-n-decylamine, N, N'-dimethyl-n-dodecylamine, N, N'-dimethyl-n-tetradecylamine, N, N'- Dimethyl n-palmitylamine is mentioned. From the viewpoint of hydrophobicity and solubility, N, N′-dimethyl-n-decylamine, N, N′-dimethyl-n-dodecylamine, N, N′-dimethyl-n-tetradecylamine, N, N′- Dimethyl-n-palmitylamine is preferred.

The chain aliphatic alcohol may be a chain aliphatic alcohol and is not particularly limited, but a chain aliphatic alcohol having 6 to 26 carbon atoms (more preferably 6 to 20) is preferable. If the number of carbon atoms of the chain aliphatic alcohol is less than the lower limit, the hydrophobicity tends to be small, and it tends to be difficult to be introduced into the pores of the spherical mesoporous material. On the other hand, if the upper limit is exceeded, the solubility tends to decrease.
Examples of such chain aliphatic alcohols include hexanol, methylpentanol, dimethylbutanol, heptanol, methylhexanol, dimethylpentanol, trimethylbutanol, octanol, methylheptanol, dimethylhexanol, trimethylpentanol, and isopropylpentanol. Nonanol, methyl octanol, ethyl heptanol, decyl alcohol, undecyl alcohol, dodecyl alcohol, tetradecyl alcohol, hexadecyl alcohol. From the viewpoint of hydrophobicity and solubility, hexanol, octanol and decanol are preferred.

Further, the heterocyclic compound is not particularly limited as long as it contains a heterocyclic ring in its skeleton, but it has 1 to 3 rings and 4 to 18 carbon atoms (more preferably 5 to 12). A heterocyclic compound in which the heteroatom is at least one atom selected from the group consisting of nitrogen, oxygen and sulfur is preferred. When the number of carbon atoms of the heterocyclic compound is less than the lower limit, the hydrophobicity tends to be small, and it tends to be difficult to be introduced into the pores of the spherical mesoporous material. On the other hand, if the upper limit is exceeded, the solubility decreases, and the pore diameter tends not to increase. Further, when the number of rings of the heterocyclic compound exceeds 3, the solubility is lowered, so that the pore diameter tends not to be increased.
Examples of such heterocyclic compounds include pyrrole, thiophene, furan, pyridine, pyrazine, pyrimidine, pyridazine, indole, quinoline, phthalazine, naphthyridine, quinoxaline, quinazoline, carbazole, phenanthridine, acridine, phenanthroline, phenazine, and the like. Can be mentioned. From the viewpoint of hydrophobicity and solubility, pyridine, quinoline, acridine, and phenanthroline are preferable.

As the solvent, a mixed solvent of water and alcohol is used. As such an alcohol, any of monohydric alcohols such as methanol, ethanol and propanol, divalent alcohols such as ethylene glycol, and trivalent alcohols such as glycerin may be used.
The content of alcohol in the solvent needs to be 40 to 90% by volume, and the content of alcohol is preferably 50 to 85% by volume, and more preferably 55 to 75% by volume. When the content of the alcohol in the solvent exceeds 90% by volume, a substitution reaction between the surfactant in the pores and the alkylammonium halide, a chain hydrocarbon, a cyclic hydrocarbon or a chain in the pores Introduction of aliphatic amines, chain aliphatic alcohols and heterocyclic compounds will not proceed sufficiently. On the other hand, when the alcohol content in the solvent is less than 40% by volume, the proportion of water increases, so that an alkyl ammonium halide having a long alkyl chain, a chain hydrocarbon, a cyclic hydrocarbon, a chain aliphatic amine, The chain aliphatic alcohol and heterocyclic compound are not sufficiently dissolved in the solvent. Furthermore, the shape of the silica porous body obtained by promoting the reconstruction of the silica network is changed by high-temperature water, or the silica network of the porous precursor particles is collapsed.

  Further, the concentration of the expanding agent in the solvent is 0.05 to 10 mol / L (preferably 0.05 to 5 mol / L, more preferably 0.1 to 1 mol / L based on the total volume of the solution). ) Is necessary. In addition, the upper limit value of the concentration of the diameter expanding agent in such a solvent is more preferably 0.2 mol / L or less, particularly 0.18 mol / L or less, based on the total volume of the solution. preferable. When the concentration of the expanding agent is less than 0.05 mol / L, a substitution reaction between the surfactant in the pores and the alkylammonium halide, a chain hydrocarbon, a cyclic hydrocarbon, or a chain aliphatic into the pores The introduction of amines, chain aliphatic alcohols and heterocyclic compounds does not proceed sufficiently, the particle size of the resulting particles and the regularity of the pore structure are lowered, and the pore size cannot be sufficiently expanded. On the other hand, when the concentration of the diameter expanding agent exceeds 10 mol / L, it is difficult to control the particle size and the particle size distribution, and the uniformity of the particle size of the obtained particles is lowered.

  The diameter expansion treatment needs to be performed under a temperature condition of 60 to 150 ° C, and is preferably performed under a temperature condition of 70 to 120 ° C. Further, the upper limit value of such a temperature condition is more preferably 100 ° C. (more preferably 90 ° C., particularly preferably 80 ° C.) or less. When the temperature is less than 60 ° C., the substitution reaction between the surfactant contained in the spherical mesoporous material and the alkylammonium halide used as the diameter expanding agent, the chain hydrocarbon or cyclic hydrocarbon in the pores The introduction of chain aliphatic amines, chain aliphatic alcohols and heterocyclic compounds does not proceed sufficiently. On the other hand, when it exceeds 150 ° C., it becomes difficult to control the particle size and particle size distribution.

[3.1.7. Removal of surfactant]
After drying, the surfactant (and the expanding agent added as necessary) is removed from the precursor particles to obtain a spherical mesoporous material. As a method for removing the surfactant,
(1) A firing method in which the precursor particles are fired at 300 to 1000 ° C. (preferably 300 to 600 ° C.) for 30 minutes or longer (preferably 1 hour or longer) in the air or under an inert atmosphere.
(2) The precursor particles are immersed in a good solvent for a surfactant (for example, methanol containing a small amount of hydrochloric acid), stirred while heating at a predetermined temperature (for example, 50 to 70 ° C.), and the interface in the thin film An ion exchange method to extract the active agent,
and so on.

[3.2. Carbon deposition process]
The carbon deposition step is a step of depositing carbon in the mesopores of the spherical mesoporous material. There are the following methods for depositing carbon in the mesopores.

[3.2.1. First method]
The first method for precipitating carbon is a method in which a carbon precursor is introduced into mesopores, and the carbon precursor is polymerized and carbonized.
The “carbon precursor” serves as a carbon source, and any carbon precursor can be used as long as it can generate carbon by thermal decomposition. As such a carbon precursor, specifically,
(1) A liquid polymer precursor at room temperature and thermally polymerizable (for example, furfuryl alcohol, aniline, etc.),
(2) A mixture of an aqueous carbohydrate solution and an acid (for example, monosaccharides such as sucrose (sucrose), xylose (wood sugar), glucose (glucose)), disaccharides, polysaccharides, sulfuric acid, hydrochloric acid, nitric acid, phosphorus Mixtures with acids such as acids),
(3) a mixture of two-component curable polymer precursors (for example, phenol and formalin),
and so on.
Among these, since the polymer precursor can be impregnated in the mesopores without being diluted with a solvent, a relatively large amount of carbon can be generated in the mesopores with a relatively small number of impregnations. Can do. Further, there is an advantage that a polymerization initiator is unnecessary and handling is easy.

When the liquid or solution carbon precursor is used, the amount of adsorption of the liquid or solution per one time is better, and the amount in which the entire mesopores are filled with the liquid or solution is preferable.
When a mixture of an aqueous carbohydrate solution and an acid is used as the carbon precursor, the amount of the acid is preferably set to a minimum amount that can polymerize the organic matter.
Further, when a mixture of a two-component curable polymer precursor is used as the carbon precursor, an optimal ratio is selected according to the type of the polymer precursor.

After introducing the carbon precursor into the mesopores, the precursor is polymerized.
For example, when the carbon precursor is a polymer precursor, a mixture of an aqueous solution of a carbohydrate and an acid, or a mixture of a two-part curable polymer precursor, the polymerization of the carbon precursor is performed by the spherical mesoporous material on which the carbon precursor is adsorbed. This is done by heating the body at a predetermined temperature for a predetermined time. The optimum polymerization temperature and polymerization time vary depending on the type of carbon precursor, but usually the polymerization temperature is 50 ° C. to 400 ° C., and the polymerization time is 5 minutes to 24 hours.

Further, the polymerized carbon precursor is carbonized in the mesopores.
Carbonization of the carbon precursor is performed by heating the spherical mesoporous material to a predetermined temperature in a non-oxidizing atmosphere (for example, in an inert atmosphere or in a vacuum). Specifically, the heating temperature is preferably 500 ° C. or higher and 1200 ° C. or lower. When the heating temperature is less than 500 ° C., carbonization of the carbon precursor becomes insufficient. On the other hand, when the heating temperature exceeds 1200 ° C, silica and carbon react with each other, which is not preferable. As the heating time, an optimum time is selected according to the heating temperature.

Note that the amount of carbon generated in the mesopores only needs to be greater than or equal to the amount by which the carbon particles can maintain the shape when the spherical mesoporous material is removed. Therefore, when the amount of carbon produced by one filling, polymerization and carbonization is relatively small, it is preferable to repeat these steps a plurality of times. In this case, the conditions of the repeated steps may be the same or different.
When each of the filling, polymerization, and carbonization steps is repeated a plurality of times, each carbonization step is carbonized at a relatively low temperature, and after the final carbonization treatment is completed, carbonization is performed again at a higher temperature. Processing may be performed. When the final carbonization treatment is performed at a higher temperature than the previous carbonization treatment, the carbon introduced into the pores in a plurality of times is easily integrated.

[3.2.2. Second method]
The second method of depositing carbon is a method of depositing carbon directly in the mesopores. That is, the second method is a method of depositing carbon in at least the mesopores of the spherical mesoporous material by using a vapor deposition method.
Specifically, a polymerizable gas having an unsaturated bond (for example, acetylene, propylene, etc.) is used as a carbon source, and this is diluted with an inert gas (N ₂ , argon, helium, etc.) to produce a spherical meso It is poured into a flow-through reaction tube provided with a porous body and heated at a predetermined temperature for a predetermined time (so-called “thermal CVD method”). Thereby, polymerization and carbonization occur simultaneously with the adsorption of the carbon source into the mesopores. In a similar manner, a liquid carbon source can be bubbled with an inert gas to deposit carbon in the mesopores in one step. As the heating temperature, an optimum temperature is selected according to the type of gas.

  In the second method, carbon deposition occurs from the surface side of the spherical mesoporous material. Therefore, when the deposition time is relatively short, carbon is deposited only in the mesopores near the surface of the spherical mesoporous material, so that hollow carbon particles can be obtained. On the other hand, when the deposition time is relatively long, carbon is deposited to the center of the mesopores, so that solid carbon particles can be obtained.

[3.3. Spherical mesoporous material removal process]
The spherical mesoporous material removing step is a step of removing the spherical mesoporous material from at least the spherical mesoporous material / carbon composite in which carbon is generated in the mesopores. Thereby, a spherical carbon porous body is obtained.
As a method for removing the spherical mesoporous material, specifically,
(1) A method of heating the composite in an aqueous alkali solution such as sodium hydroxide,
(2) A method of etching the composite with an aqueous hydrofluoric acid solution,
and so on.

[3.4. Tin compound precipitation process]
The tin-based compound deposition step is a step of depositing a tin-based compound in the mesopores of the spherical carbon porous body obtained by the above-described method.
Specifically, the precipitation of the tin-based compound into the pores includes, in addition to the method of adsorbing and precipitating Sn vapor into the pores, introducing a precursor of the tin-based compound into the pores, This can be done by converting to a tin-based compound.

Specifically, as a precursor of a tin compound,
(1) chlorides such as SnCl ₄ and SnCl ₂ ;
(2) an organic complex such as tin acetylacetonate (Sn (CH ₃ COCHCOCH ₃ ) ₂ ),
However, it is not limited to these.

  When the precursor is a liquid, it may be adsorbed as it is in the pores of the spherical carbon porous body. Alternatively, the precursor may be dissolved in an appropriate solvent, and this solution may be adsorbed in the pores of the spherical carbon porous body. When the precursor is dissolved in the solvent, the type of the solvent and the concentration of the precursor are not particularly limited, and an optimal one is selected according to the purpose.

After adsorbing the precursor, the precursor is converted to an oxide. The conversion method is not particularly limited, and an optimal method is selected according to the type of the precursor.
For example, when chloride is used as the precursor, the spherical carbon porous body is dispersed in a solution in which chloride is dissolved and stirred in air. When the stirring is continued, the chloride is eventually adsorbed in the pores of the carbon porous body, and the chloride in the pores gradually becomes an oxide due to dissolved oxygen.
For example, when using an organic complex as a precursor, an organic complex or a solution in which the organic complex is dissolved is added to the spherical carbon porous body, and the organic complex or a solution thereof is impregnated in the pores. When this is heated to a predetermined temperature, thermal decomposition of the organic complex occurs and oxides are generated in the pores.
In addition, when a sufficient amount of a tin-based compound cannot be formed in the pores by one time adsorption of the precursor and conversion to the oxide, the adsorption and conversion may be repeated a plurality of times.

Moreover, the oxide precipitated in the pores is reduced as necessary. Thereby, the valence of Sn can be reduced, or a part or all of Sn can be reduced to metal.
As a reduction method, for example,
(A) A method of heating to 700 ° C. or higher in a nitrogen atmosphere,
(B) A method of heating to 250 ° C. or higher in the presence of H ₂ gas,
(C) A method of heating to 200 ° C. or higher in the presence of CO gas,
and so on.

[4. Method for producing negative electrode material for Li secondary battery]
As a method for producing an array in which spherical carbon / tin compound composite particles are irregularly arranged, for example,
(1) A method of press molding composite particles,
(2) A method of applying a dispersion liquid in which composite particles are dispersed in a volatile solvent and drying it rapidly,
(3) A method of applying a slurry solution prepared by adding composite particles, a solvent and a thickener and removing the solvent and the thickener by evaporation or thermal decomposition,
However, it is not limited to these.

As a method for producing an array in which composite particles are regularly arranged, for example,
(1) A method of immersing electrodes in a dispersion liquid in which composite particles are dispersed and applying a DC electric field between the electrodes (arrangement method using electrophoresis),
(2) A method of injecting a dispersion liquid in which composite particles are dispersed between substrates having a constant interval, and self-assembling the composite particles in a regularly arranged state,
(3) A method in which a dispersion liquid in which composite particles are dispersed is applied to the substrate surface using dip coating, spin coating or the like,
(4) In the above (1) to (3), the composite particles are previously coated with a polymer having a positive or negative charge to facilitate alignment,
(5) A polymer monomer (for example, acrylamide), a cross-linking agent (for example, methylene bisacrylamide), and a photopolymerization initiator (for example, camphorquinone) are added in advance to the composite particle dispersion. A method in which particles are regularly arranged in a liquid and then gelled by light irradiation;
and so on.

[5. Action]
The composite particles according to the present invention have a structure in which nano-sized microcrystals made of a tin-based compound such as SnO ₂ are dispersed in the pores of a spherical carbon porous body. Since the pore walls reinforce the tin-based compound and the composite particles have certain voids, the volume expansion can be relaxed and absorbed. Moreover, even if the tin-based compound is pulverized, the pore walls prevent the tin-based compound from being detached from the spherical carbon porous body. Therefore, the recycling characteristics are improved.

In particular, when the spherical carbon porous body has carbon nanorods arranged in a spherical symmetry, the volume expansion of the tin-based compound becomes isotropic, and the recycling characteristics are further improved.
Furthermore, the spherical carbon porous body is easily filled in the electrode material. Therefore, when the composite particles according to the present invention are used as the negative electrode material, the electric capacity per volume is improved.

(Examples 1-3, Comparative Examples 1-2)
[1. Preparation of composite particles]
[1.1. Synthesis Example 1]
[1.1.1. Preparation of monodispersed spherical mesoporous silica]
38.3 g of octadecyltrimethylammonium chloride (C ₁₈ TMACl) was dissolved in a mixed solvent of purified water: 3806 g, methanol (MeOH): 2020 g, and ethanol (EtOH): 2020 g, and the mixture was kept at 25 ° C. and stirred. Further, tetramethoxysilane (TMOS) diluted with 1M NaOH: 34.2 g, MeOH: 60 g, and EtOH: 60 g: 26.4 g was added. After stirring for about 8 hours and allowing to stand overnight, filtration and redispersion in purified water were repeated twice. Then, it dried at 45 degreeC and obtained white powder: 19.25g. Further, this white powder was baked in the atmosphere at 550 ° C. for 6 hours to obtain monodispersed spherical mesoporous silica particles (MMSS) having a particle diameter of 0.58 μm.

[1.1.2. Production of spherical carbon porous body]
MMSS: 0.5 g was placed in a PFA container (capacity: 15 mL), and furfuryl alcohol (FA) was added to the pore volume to infiltrate into the silica pores. This was heat-treated at 150 ° C. for 24 hours to polymerize FA. Furthermore, this was heat-treated in a nitrogen atmosphere at 500 ° C. for 6 hours to promote carbonization of FA. After repeating this twice, heat treatment was performed at 900 ° C. for 6 hours in a nitrogen atmosphere to obtain an MMSS / carbon composite.
This composite was immersed in a 12% HF solution for 12 hours to dissolve the silica component. After dissolution, filtration and washing were repeated and further dried at 45 ° C. to obtain a spherical carbon porous body.

[1.1.3. Preparation of spherical carbon / SnO ₂ composite particles]
Next, 0.1 g of the spherical carbon porous body was dispersed in a mixed solution of water: 250 g, concentrated hydrochloric acid (35 wt.%): 4 mL, SnCl ₂ : 50 g in a 500 mL beaker. While maintaining this dispersion at 25 ° C., ultrasonic waves were applied for 30 minutes with an ultrasonic cleaner. Further, the dispersion was stirred in the air for 4 hours, and then filtration and redispersion in purified water were repeated twice. Then dried at 45 ° C., to obtain spherical carbon / SnO ₂ composite.

[1.2. Synthesis Example 2]
Spherical carbon / SnO ₂ composite particles were obtained in the same manner as in Synthesis Example 1. Next, the spherical carbon / SnO ₂ composite particles were treated in nitrogen at 350 ° C. for 6 hours to obtain a crystallized spherical carbon / SnO ₂ composite.

[1.3. Synthesis Example 3: Amorphous Carbon / SnO ₂ Composite Particles]
Except for using the amorphous mesoporous silica (SBA-15) in place of MMSS, in the same manner as in Synthesis Example 1 to obtain the amorphous carbon / SnO ₂ composite particles.

[2. Production of negative electrode material and evaluation half-cell]
[2.1. Example 1]
Spherical carbon / SnO ₂ composite obtained in Synthesis Example 1: 0.475 g, Ketjen black: 0.025 g, polyvinylidene fluoride (PVDF): 0.1 g, N-methyl-2-pyrrolidone (NMP): 1 g Was mixed and then developed on the Cu foil. After performing vacuum drying at 120 ° C. for 8 hours, pressurization with a roll press and punching into a circle were performed to obtain a negative electrode material.
Using this as a negative electrode, a half-cell was prepared using a lithium metal as a counter electrode, a porous polypropylene film as a separator, and an ethylene carbot (EC) / dimethyl carbonate (DEC) solution containing 1M LiPF ₆ as an electrolyte.

[2.2. Example 2]
A half cell for evaluation was produced in the same manner as in Example 1 except that the spherical carbon / SnO ₂ composite obtained in Synthesis Example 2 was used.
[2.3. Comparative Example 1]
An evaluation half-cell was produced in the same manner as in Example 1 except that the amorphous carbon / SnO ₂ composite obtained in Synthesis Example 3 was used.

[2.4. Example 3]
[2.4.1. Production of ordered array]
The spherical carbon / SnO ₂ composite obtained in Synthesis Example 1 was mixed with ion-exchanged water at a concentration of 10 wt% and dispersed with ultrasonic waves for 5 hours. The dispersion was poured into a cell in which _two SiO ₂ glass substrates hydrophilized by ozone plasma treatment were held at intervals of 10 μm and left at room temperature for 24 hours. After standing, one glass substrate was carefully peeled off. After drying, it was fired in air at 400 ° C. for 1 hour. The resulting array showed a structural color.

[2.4.2. Production of half-cell]
A PVDF: 10 wt% NMP solution was infiltrated into the array on the SiO ₂ glass substrate, and a Cu foil was placed thereon and pressed. Thereafter, the array was peeled from the SiO ₂ glass substrate and transferred onto the Cu foil. Further, vacuum drying was performed at 120 ° C. for 8 hours, and then punched into a circle to obtain a negative electrode material.
Using the negative electrode material, an evaluation half-cell was produced in the same manner as in Example 1.

[2.5. Comparative Example 2]
A half cell for evaluation was produced in the same manner as in Example 1 except that tin oxide nanoparticles were used instead of the spherical carbon / SnO ₂ composite.

[3. Test method]
[3.1. TEM observation]
The synthesized spherical carbon / SnO ₂ composite was observed by TEM.
[3.2. Cyclic voltammetry]
Prior to the charge / discharge test, the electrode potential was linearly swept in the range of 0.05 to 2 V at a rate of 0.05 mV / min, and cyclic voltammetry (CV) characteristics were measured.

[3.3. Charge / Discharge Test and XRD]
A charge / discharge cycle test was conducted in a potential range of 0.05 to 3 V under a constant current condition of a current density of 100 mA / g.
Further, XRD measurement was performed on the spherical carbon / SnO ₂ composite and the negative electrode material before and after the charge / discharge test.

[4. result]
[4.1. TEM observation]
FIG. 1 shows a TEM photograph of a spherical carbon / SnO ₂ composite. From FIG.
(1) The spherical carbon porous body is composed of carbon nanorods having a diameter of about 2 nm arranged in a spherical symmetry, and
(2) It can be seen that SnO ₂ is filled in the pores of the spherical carbon porous body.

[4.2. Cyclic voltammetry]
FIG. 2 shows a cyclic voltammetry curve of the spherical carbon / SnO ₂ composite (Example 2). Peaks associated with formation of a SEI (Solid Electrolyte Interphase) layer, a conversion reaction, and an alloying reaction were observed.

[4.3. Charge / Discharge Test and XRD]
FIG. 3 shows XRD patterns before and after the charge / discharge test of the spherical carbon / SnO ₂ composite and the negative electrode material (Example 2) containing the same. By the XRD measurement of the sample at 1.0 V and 3.0 V before the evaluation, the SnO ₂ peak observed before the evaluation disappeared, the Sn peak was observed at 1.0 V, and at 3.0 V, Neither peak was observed. From the above, it was confirmed that the alloying reaction represented by the formula (1) and the conversion reaction represented by the formula (2) occurred.
^{Sn + 4.4e - + 4.4Li + ⇔} Li 4.4 Sn ··· (1)
^{_{SnO 2 + 4e - + 4Li +}} ⇔ Sn + 2Li 2 O ··· (2)

In FIG. 4, the charging / discharging cycle characteristic of the sample obtained in Examples 1-3 and Comparative Examples 1-2 is shown. FIG. 4 shows the following.
(1) The initial charge capacity of the spherical carbon / SnO ₂ composite was 1.13 Ah / g in Example 1, 1.04 Ah / g in Example 2, 1.08 Ah / g in Example 3, and both Higher than the comparative example. Moreover, the charge capacity of each Example is larger than the theoretical equivalent 786 mAh / g of the alloying reaction of SnO ₂ . In addition to the alloying reaction, a part of the conversion reaction seems to occur reversibly.
(2) Even in the charge capacity at the 40th cycle, all the examples maintained 90% or more of the initial charge capacity. In particular, the array of Example 3 maintained a maintenance ratio (ratio to the initial capacity) of 98.4%, and was found to have excellent cycle characteristics.

  Although the embodiments of the present invention have been described in detail above, the present invention is not limited to the above embodiments, and various modifications can be made without departing from the scope of the present invention.

  The spherical carbon / tin compound composite according to the present invention can be used as a negative electrode material for a Li secondary battery.

Claims (3)

A spherical carbon / tin compound composite particle having the following configuration.
(1) The spherical carbon / tin compound composite particles are:
A spherical carbon porous body;
It consists of a composite comprising Sn and / or microcrystals made of an oxide of Sn filled in the pores of the spherical carbon porous body.
(2) The spherical carbon / tin compound composite particles are used as a negative electrode material for a Li ion secondary battery.
(3) The spherical carbon porous body is composed of carbon nanorods having a diameter of 10 nm or less arranged in a spherical symmetry,
The crystallites, consisting of SnO _2.   2. The spherical carbon / tin compound composite particle according to claim 1, wherein the spherical carbon porous body has a monodispersity represented by the following formula (1) of 10% or less.
  Monodispersity = (standard deviation of particle diameter) × 100 / (average value of particle diameter) (1)   A negative electrode material for a Li ion secondary battery comprising the array of spherical carbon / tin compound composite particles according to claim 1.

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