JP2002260658A - Carbonaceous material and lithium secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a carbonaceous material having high charge and discharge capacity and superior cycle characteristics, at the same time. SOLUTION: Composite particles 3, each of which contains at least silicon and carbon and has a smaller particle diameter than that of a graphite particle 2, are dispersedly disposed around the graphite particle 2 in which a spacing d002 of a (002) plane obtained by wide-angle X-ray diffraction is less than 0.337 nm, and the graphite particle 2 and the composite particles 3 are coated by an amorphous carbon film 4. In this composite particle 3, a conductive carbon material is disposed around a Si grain comprising crystalline silicon, and the Si grains and the conductive carbon material are coated by a hard carbon film. Si grains are of a SiO2 phase, SiC phase and SiB4 phase deposited in the crystalline Si phase. The carbonaceous material 1 having this characteristic is adopted.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention relates to a carbonaceous material for a lithium secondary battery and a lithium secondary battery.

[0002]

2. Description of the Related Art In order to meet the needs of portable electronic devices that are becoming smaller, lighter and have higher performance, it is urgent to increase the capacity of lithium secondary batteries. By the way, graphite, which is one of the negative electrode active materials of the lithium secondary battery, is 372 mAh /
In order to obtain a negative electrode active material having a theoretical electric capacity of g but higher capacity, it is necessary to promote the development of an amorphous carbon material or a new material replacing the carbon material. As a new material replacing graphite, silicon and its compounds have been studied. Silicon and its compounds
It is known that silicon itself forms an alloy with lithium, and a larger electric capacity can be obtained than graphite. Therefore, recently, as a negative electrode material of a lithium secondary battery, (1) a material obtained by simply mixing a silicon compound powder with graphite, or (2) a fine powdered silicon compound or the like on the graphite surface using a silane coupling agent or the like. A chemically fixed material, and (3) a material in which a graphite-based carbon material and a metal material such as Si are bonded or covered with an amorphous carbon material have been proposed.

[0003]

However, in the above-mentioned material (1), since the graphite and the silicon compound are not always in intimate contact with each other, when the graphite expands and contracts due to the progress of the charge / discharge cycle, the silicon compound becomes graphite. And the silicon compound itself has low electron conductivity, so that the silicon compound is not sufficiently used as a negative electrode active material, and there is a problem that the cycle characteristics of the lithium secondary battery are reduced.

In the material (2), the charge / discharge cycle is maintained in a state where the silicon compound adheres to the graphite in the initial stage of the charge / discharge cycle. Therefore, the silicon compound functions as a negative electrode active material similarly to the graphite. As the cycle proceeds, the silicon compound itself expands with the formation of an alloy with lithium, thereby breaking the bond by the silane coupling agent and releasing the silicon compound from the graphite, and the silicon compound is sufficiently used as a negative electrode active material. And the cycle characteristics of the lithium secondary battery deteriorate. In addition, there is a problem that the silane coupling treatment performed during the production of the negative electrode material may not be performed homogeneously, and a stable quality of the negative electrode material has not been easily obtained.

Further, the material (3) causes the same problem as the material (2). That is, as the charge / discharge cycle progresses, the expansion of the metallic material itself due to the formation of an alloy with lithium breaks the bond formed by the amorphous carbonaceous material and releases the metallic material from the graphite-based carbonaceous material. There has been a problem that the lithium secondary battery is not sufficiently used as a substance, and the cycle characteristics of the lithium secondary battery deteriorate.

The present invention has been made in view of the above circumstances, and provides a carbonaceous material having high charge / discharge capacity and excellent cycle characteristics, and a lithium secondary battery having the carbonaceous material. The purpose is to provide.

[0007]

In order to achieve the above object, the present invention employs the following constitution. The carbonaceous material of the present invention has a (002) plane spacing d00 by X-ray wide-angle diffraction.
2, composite particles containing at least silicon and carbon and having a smaller particle size than the graphite particles are dispersedly arranged around the graphite particles having a particle diameter of less than 0.337 nm, and the graphite particles and the composite particles have a particle size of 0.3. Covered with an amorphous carbon film having a plane distance d002 of 37 nm or more,
The composite particles are formed by disposing a conductive carbon material around Si fine particles made of crystalline silicon, and coating the Si fine particles and the conductive carbon material with a hard carbon film. SiO ₂ phase in Si phase,
It is characterized in that the SiC phase and the SiB ₄ phase are precipitated.

In the present invention, the meaning of “around” indicates the positional relationship of the composite particles with respect to the graphite particles, and means “on or near the surface” of the graphite particles. The meaning of "around" also indicates the positional relationship of the conductive carbon material with respect to the Si fine particles, and means "on or near the surface" of the Si fine particles. Further, the meaning of “dispersed and arranged” means a state in which a plurality of composite particles are bonded to or slightly separated from the surface of the graphite particles in a state of being mutually dispersed without aggregation. The meaning of “coating” means a state in which the particles to be coated are bonded to each other by completely covering the particles to be coated. In this case, the particles to be coated need not necessarily be in direct contact. Specifically, to cover the graphite particles and the composite particles with the amorphous carbon film means that the graphite particles and the composite particles are completely covered with the amorphous carbon film to bond the graphite particles and the composite particles, Means that the composite particles are embedded in the carbonaceous carbon film and brought close to the graphite particle surface. Similarly, covering the Si fine particles and the conductive carbon material with the hard carbon film means that the Si fine particles and the conductive carbon material are completely covered with the hard carbon film, and the Si fine particles and the conductive carbon material are bonded. This means that a conductive carbon material was buried in the film and brought close to the surface of the Si fine particles. Further, the meaning of “precipitation” is a term for explaining the state of a crystal phase, and means a state in which a precipitation phase having a composition different from that of the parent phase is formed in the parent phase. That is, ie, SiO ₂ phase, S
iC phase and SiB ₄ phase does not mean a state contained in inseparable in the Si phase, Si phase, SiO ₂ phase, Si
This does not mean that the C phase and the SiB ₄ phase are physically separated from each other.

In such a carbonaceous material, since the graphite particles and the Si fine particles occlude Li, the charge / discharge capacity is improved as compared with the case of the graphite particles alone. By arranging a conductive carbon material around Si fine particles having high specific resistance to graphite particles, the conductivity of Si fine particles is apparently improved. Further, by coating Si fine particles with a hard carbon film, Li
Volumetric expansion and contraction of the Si fine particles due to occlusion and release of the particles are mechanically suppressed. Furthermore, by covering the graphite particles and the composite particles with the amorphous carbon film, the decomposition of the electrolytic solution is suppressed without the graphite particles directly touching the electrolyte, and the composite particles do not fall off from the graphite particles. Further, it is possible to prevent the Si fine particles from being pulverized due to volume expansion due to charging.

Further, a SiO ₂ phase and a Si
The precipitation of the C phase and the SiB ₄ phase results in the relative S
The content of the i-phase is reduced, and at the same time, the Si phase is distorted to lower the crystallinity, thereby suppressing excessive Li occlusion. As a result, the expansion and expansion of Si fine particles due to occlusion and release of Li
Shrinkage is moderately suppressed. SiO ₂ phase, SiC phase and S
Since the iB ₄ phase does not react with Li, it has no capacity of its own, but promotes diffusion of Li ions and suppresses pulverization due to volume expansion of Si fine particles. Further, Si
Since all of the O ₂ phase, the SiC phase and the SiB ₄ phase are included, the above function can be obtained more effectively. From the above, in the carbonaceous material of the present invention, while increasing the charge / discharge capacity, suppressing the pulverization of the Si fine particles due to the volume expansion of the Si fine particles and the dropout of the composite particles, and the volume expansion due to charging, It is possible to prevent the deterioration of the cycle characteristics. In particular, the dissociation of the Si fine particles from the graphite particles due to the volume expansion can be prevented, and the decrease in cycle efficiency can be more effectively prevented. In addition, by increasing the diffusion rate of Li ions, it is possible to quickly absorb and release Li ions even in an electrode filled with an active material at a high density, and to improve charge / discharge efficiency.

Further, the carbonaceous material of the present invention comprises
A raw material, wherein the Si phase is analyzed by X-ray wide-angle diffraction.
Let the diffraction intensity of the (111) plane be P_SiAnd the SiO_TwoPhase
Let the diffraction intensity of the (111) plane be P_SiO2And the SiC phase
Let the diffraction intensity of the (111) plane be P_{Si C}And the SiB_FourPhase
Let the diffraction intensity of the (104) plane be P_SiBAnd P_SiO2/ P
_SiIs 0.005 or more and 0.1 or less, and P_SiC/ P_SiBut
0.005 or more and 0.1 or less, and P_SiB/ P_SiO2But
0.1 or more and 5.0 or less, and P_SiB/ P_SiCIs 0.1
It is characterized in that it is 5.0 or less.

In such a carbonaceous material, since the diffraction intensity ratio of each phase is within the above range, the content of the Si phase does not extremely decrease and the Li occlusion amount does not decrease. Further, by optimizing the contents of the SiO ₂ phase, the SiC phase and the SiB ₄ phase, the volume expansion and contraction of the Si fine particles are suppressed. Accordingly, the charge / discharge capacity of the carbonaceous material is increased, and further, dissociation from the graphite particles due to the volume expansion of the Si particles and pulverization of the Si particles due to the volume expansion due to charging are prevented, thereby preventing a decrease in cycle efficiency. Becomes possible.

Further, the carbonaceous material of the present invention is the above-mentioned carbonaceous material, wherein the graphite particles have a particle size of 2 μm or more and 7 μm or more.
0 μm or less, and the particle size of the composite particles is 50 n
m and 2 μm or less, and the film thickness of the amorphous carbon film is 50 nm or more and 5 μm or less.

If the particle size of the graphite particles is less than 2 μm, the particle size of the graphite particles becomes relatively smaller than the particle size of the composite particles,
It is not preferable because it becomes difficult to uniformly attach the composite particles to the surface of the graphite particles, and when the particle size exceeds 70 μm, the adhesion to the current collector is reduced, and the voids in the electrode are also preferably increased. Absent. Further, the particle size of the composite particles should be more than 50 nm and not more than 2 μm, preferably 50 nm.
Is set to 500 nm or less because the composite particles need to be 2 μm or less, which is the minimum particle size of the graphite particles, in order to disperse and arrange the composite particles on the surface of the graphite particles. If the diameter is 500 nm or less, the volume change of the composite particles due to expansion and contraction can be reduced. On the other hand, if the particle size is 50 nm or less, the crystal structure of the Si fine particles contained in the composite particles becomes more disordered, and the amount of Li occluded is undesirably reduced. Further, if the thickness of the amorphous carbon film is less than 50 nm, the graphite particles may not be completely covered with the amorphous carbon film, so that it is impossible to prevent the composite particles from falling off from the graphite particles and to prevent decomposition of the electrolytic solution. It is not preferable because it may not be possible,
If the film thickness exceeds 5 μm, the irreversible capacity due to the amorphous carbon is increased, and lithium ions do not reach the graphite particles.

Further, the carbonaceous material of the present invention is the carbonaceous material described above, wherein the particle size of the Si fine particles is in a range of 10 nm or more and less than 2 μm, and the specific resistance of the conductive carbon material is 10 ^{−. 4} Ω · m or less, and the hard carbon film has a bending strength of 500 kg / cm ² or more and a film thickness of 1
The thickness is not less than 0 nm and not more than 1 μm.

The reason why the particle size of the Si fine particles is set to 10 nm or more is to prevent disorder of the crystal structure of the Si fine particles and to improve the amount of Li occlusion. The particle size is 2 μm, the minimum particle size of graphite particles.
This is to make it smaller. Further, the specific resistance of the conductive carbon material is set to 10 ⁻⁴ Ω · m or less in order to impart sufficient conductivity to the Si fine particles. Further, the bending strength of the hard carbon film is set to 500 kg / cm ² or more because of the occlusion of Li,
This is for reducing the volume change by mechanically suppressing the expansion and contraction of the Si fine particles due to the release.
The reason for setting the thickness to 0 nm or more and 1 μm or less is that if the film thickness is less than 10 nm, the binding force between the conductive carbon material and the Si fine particles is reduced and the effect of suppressing the volume expansion of the composite particles is lost. This is because if the film thickness exceeds 1 μm, lithium ions do not reach the Si fine particles and the charge / discharge capacity decreases, which is not preferable.

The carbonaceous material for a lithium secondary battery according to the present invention is the carbonaceous material described above, wherein the content of the composite particles is 1% by weight or more and 25% by weight or less. I do.

If the content of the composite particles is less than 1% by weight, it is not preferable because a sufficient discharge capacity cannot be obtained as compared with the case where only the carbon material is used as the active material. On the other hand, if the content exceeds 25% by weight, the contribution of the carbon material portion decreases, and the voltage increases from the initial discharge to near the reaction potential of Si, which is not preferable. And the volume expansion and contraction due to the Si fine particles are liable to occur, and the cycle characteristics deteriorate, which is not preferable.

Next, a lithium secondary battery according to the present invention includes the carbonaceous material described above. Such a lithium secondary battery has, for example, at least a positive electrode, an electrolyte, and a negative electrode having the above-described negative electrode material, and has various shapes such as a cylindrical shape, a square shape, a coin shape, and a sheet shape. It should be noted that the lithium secondary battery of the present invention is not limited to the above-described embodiment, but may be formed in another embodiment. According to such a lithium secondary battery, a lithium secondary battery having high energy density and excellent cycle characteristics can be configured.

Next, the method for producing a carbonaceous material according to the present invention comprises:
Si fine particles made of crystalline silicon _TwoO_ThreeCharcoal with powder
Bake at 1300 ° C or higher and 1400 ° C or lower in a crucible
As a result, SiO_TwoPhase, SiC phase
And SiB_FourA step of precipitating a phase;
Attach the conductive carbon material and cover the Si fine particles.
Forming a molecular material film to form a composite particle precursor,
The polymer film is hardened by firing the composite particle precursor.
Obtaining composite particles as a porous carbon film;
Attach Si fine particles and cover the graphite particles
A carbonaceous material precursor to form a carbonaceous material precursor;
By baking the raw material precursor, the polymer film is formed.
Obtaining a carbonaceous material as an amorphous carbon film.
Characterized by

[0021]

Embodiments of the present invention will be described below with reference to the drawings. 1 to 4 show schematic cross-sectional views of a carbonaceous material for a lithium secondary battery of the present invention. In this carbonaceous material, composite particles are dispersedly arranged around graphite particles, and the graphite particles and the composite particles are covered with an amorphous carbon film.

Here, "around" indicates the positional relationship of the composite particles with respect to the graphite particles, and means "on or near the surface" of the graphite particles. That is, this includes the state in which the composite particles are bonded to the surface of the graphite particles, and the case where the composite particles are separated from the surface of the graphite particles and located around the graphite particles. Further, “dispersed and arranged” means a state where a plurality of composite particles are bonded to or slightly separated from the surface of graphite particles in a state of being mutually dispersed.
The composite particles may be in contact with each other to the extent that they do not aggregate. Further, “coating” means a state in which the particles to be coated are bonded to each other by completely covering the particles to be coated. In this case, the particles to be coated need not necessarily be in direct contact. Specifically, to cover the graphite particles and the composite particles with the amorphous carbon film means that the graphite particles and the composite particles are completely covered with the amorphous carbon film to bond the graphite particles and the composite particles, Means that the composite particles are embedded in the carbonaceous carbon film and brought close to the graphite particle surface. Accordingly, the carbonaceous material of the present invention includes various forms as described below.

For example, the carbonaceous material 1 shown in FIG. 1 is bonded to the surface of graphite particles 2 in a state where a plurality of composite particles 3 are dispersed in each other, and the amorphous carbon film 4 is formed of particles of the composite particles 3. It is constituted by coating the graphite particles 2 and the composite particles 3 with a uniform film thickness smaller than the diameter.

The carbonaceous material 1 shown in FIG. 2 is bonded to a surface of a plurality of graphite particles 2 in a state in which a plurality of composite particles 3 are mutually dispersed, and an amorphous carbon film 4 is formed of the composite particles 3. Graphite particles 2 and composite particles 3 having a uniform film thickness larger than the particle size of
Are formed so as to cover the plurality of graphite particles 2 by the amorphous carbon film 4. FIG. 2 shows a state in which two or three graphite particles 2 are bonded by an amorphous carbon film 4,
The present invention is not limited to this, and four or more graphite particles 2 may be bonded by the amorphous carbon film 4.

Further, the carbonaceous material 1 shown in FIG. 3 is bonded to the surface of the graphite particles 2 in a state in which a plurality of composite particles 3 are mutually dispersed, and the amorphous carbon film 4 is formed by the graphite particles 2 and the composite particles. 3 ...
Is formed. The thickness of the amorphous carbon film 4 shown in FIG.
The portion covering only the composite particles 3 is set to be larger than the particle size of the composite particles 3, and the portion covering the composite particles 3 is set to be smaller than the particle size of the composite particles 3.

Further, the carbonaceous material 1 shown in FIG. 4 is bonded to the surface of the graphite particles 2 in a state in which a plurality of composite particles 3 are mutually dispersed, and the amorphous carbon film 4 is formed by the graphite particles 2 and the composite particles. 3 ...
Is formed. The thickness of the amorphous carbon film 4 shown in FIG.
The portion covering only the composite particles 3 is set to be larger than the particle size of the composite particles 3. The portion covering the composite particles 3 is set to be smaller than the particle size of the composite particles 3. The particles 3 are formed on a smooth surface without irregularities without reflecting the shape of the particles 3.

The carbonaceous material of the present invention is not limited to those shown in FIGS. 1 to 4 and may be any material as long as the above terms are satisfied.

The graphite particles 1 contained in the carbonaceous material have a (002) plane spacing d002 of 0.33 by X-ray wide-angle diffraction.
It is preferable to use one having a thickness of 5 nm to less than 0.337 nm, more preferably 0.335 nm to 0.34 nm. If the plane distance d002 is 0.337 nm or more, the crystallinity of the graphite particles is reduced, the initial irreversible capacity is significantly increased, and the electron conductivity is undesirably reduced. The particle size of the graphite particles 2 is 2 μm or more and 70 μm or more.
The range of not more than μm is preferred. The particle size of the graphite particles 2 is 2 μm
Is smaller than the particle size of the composite particles 3, it is difficult to uniformly adhere the composite particles 3 to the surface of the graphite particles 2. If the diameter exceeds 70 μm, the adhesion to the current collector decreases, and the voids in the electrode also increase, which is not preferable.

Next, as shown in FIGS. 1 to 4, the amorphous carbon film 4 covers the graphite particles 2 and the composite particles 3 and adheres the composite particles 3 to the surface of the graphite particles 2. . The amorphous carbon film 4 also has the function of bonding the graphite particles 2 to each other as shown in FIG. The amorphous carbon film 4 heat-treats at least one of a thermoplastic resin, a thermosetting resin, a vinyl resin, a cellulose resin, a phenol resin, a coal pitch material, a petroleum pitch material, a tar material, and the like. This is an amorphous material having relatively less graphitization, having an interplanar spacing d002 of 0.37 nm or more. Since the amorphous carbon film 4 is amorphous, the organic electrolyte does not decompose even if it touches the amorphous carbon film 4, and the charge / discharge efficiency of the carbonaceous material 1 can be increased. The plane spacing d002 of the amorphous carbon film 4 is 0.37 nm
If it is less than 10%, the crystallinity of the amorphous carbon film 4 is improved, and the amorphous carbon film 4 approaches a graphite structure, which may undesirably decompose the organic electrolyte.

The composite particles 3 are formed by the amorphous carbon film 4.
Are arranged on the surface of the graphite particles 2 to prevent the composite particles 3 having a relatively high specific resistance from being separated from the graphite particles 2 and to generate the composite particles 3 that do not contribute to the charge / discharge reaction. Can be prevented. The amorphous carbon film 4 is obtained by throwing it into a solvent in which the above-mentioned polymer material is dissolved, depositing the polymer material on the surface of the graphite particles 2, and further baking it. Since the entire particles 2 can be completely covered, and the density is relatively low and lithium ions are easily transmitted, the reaction between the graphite particles 2 and the composite particles 3 and the lithium ions is not hindered. Amorphous carbon film 4
Is preferably in the range from 50 nm to 5 μm. If the film thickness is less than 50 nm, the graphite particles 2 are not completely covered, and the composite particles 3 may fall off from the graphite particles 2, which is not preferable. If the film thickness exceeds 5 μm, it is caused by amorphous carbon. This is not preferable because the irreversible capacity increases.

Next, the composite particles 3 are, as shown in FIG.
The conductive carbon materials 6 are arranged around the Si fine particles 5 and the hard carbon film 7 covers the Si fine particles 5 and the conductive carbon materials 6. The Si fine particles 3 are formed by depositing a SiO ₂ phase, a SiC phase and a SiB ₄ phase in a crystalline Si phase. Here, “around” indicates the positional relationship of the conductive carbon material 6 to the Si fine particles 5 and means “on or near the surface” of the Si fine particles 5. That is, the conductive carbon material 6 ...
Are in contact with the surface of the Si fine particles 5 and the conductive carbon material 6 is located around the Si fine particles 5 apart from the surface of the Si fine particles 5. Further, covering the Si fine particles 5 and the conductive carbon materials 6 with the hard carbon film 7 means that:
The Si fine particles 5 and the conductive carbon materials 6 are completely covered with the hard carbon film 7 to bond the Si fine particles 5 with the conductive carbon materials 6. The conductive carbon materials 6 are embedded in the hard carbon film 7. And that it is brought close to the surface of the Si fine particles 5.

Further, "precipitation" is a term for explaining the state of a crystal phase, and means a state in which a precipitation phase having a composition different from that of the parent phase is formed in the parent phase. That is, in the Si phase, SiO ₂
It means a state in which the SiC phase, the SiC phase and the SiB ₄ phase are inseparably contained, and does not mean a state where the Si phase, the SiO ₂ phase, the SiC phase and the SiB ₄ phase are physically separated from each other.

The particle size of the composite particles 3 exceeds 50 nm and is 2
μm or less, and preferably more than 50 nm and 500 n
m is more preferable. The particle size of the composite particles 3 is 2 μm
m or less because the particle size of the composite particles 3 must be 2 μm or less, which is the minimum particle size of the graphite particles 2, in order to disperse and arrange the composite particles 3 on the surface of the graphite particles 2. In addition, if the particle diameter is set to 500 nm or less, the volume change due to expansion and contraction of the Si fine particles 5 caused by insertion and extraction of lithium can be reduced. Also, the lower limit of the particle size is 50
The reason for exceeding 500 nm is that if it is 50 nm or less, the disorder of the crystal structure of the Si fine particles 5 contained in the composite particles 3 increases, and the amount of Li occluded may decrease and the charge / discharge capacity may decrease. is there.

The Si fine particles 5 contain crystalline silicon (Si phase) as a main component, and are further formed by depositing an SiO ₂ phase, a SiC phase and a SiB ₄ phase, and have a particle size of 10 nm or more and 2 μm or more.
Less than the range. Silicon is an element that forms an alloy with lithium, and an alloy is formed by the action of lithium ions on a Si phase made of silicon. In particular, lithium ions penetrate into the surface of the Si fine particles 5 or the voids inside the Si fine particles 5 to form an alloy, whereby the Si fine particles 5 themselves expand.

The Si fine particles 5 contain an SiO ₂ phase,
It contains a SiC phase and a SiB ₄ phase, and these phases do not react with lithium and thus have no capacity per se, but have an effect of promoting diffusion of lithium ions. Therefore, when the SiO ₂ phase, the SiC phase, and the SiB ₄ phase are included in the Si phase, the diffusion rate of lithium ions in the Si phase is improved, and, for example, even in an electrode in which the carbonaceous material is densely filled, quickness is achieved. Li ions can be stored and released, and the charge and discharge efficiency can be improved.

Further, an SiO ₂ phase, SiC
When the phase and the SiB ₄ phase are contained, the content of the Si phase is relatively reduced, and the Si phase is strained to lower the crystallinity. As a result, the occlusion amount of lithium ions slightly decreases, but at the same time, the expansion and contraction of the Si fine particles due to occlusion and release of lithium are appropriately suppressed. This suppresses pulverization due to volume expansion of the Si fine particles,
Drops of composite particles due to volume expansion of the particles are reduced,
The cycle characteristics can be prevented from deteriorating.

[0037] Specifically, the diffraction intensity of the (111) plane of the Si phase by X-ray wide angle diffraction and P _Si, the SiO ₂ phase (1
11) The diffraction intensity of the plane is defined as P _SiO2, and the (11)
A diffraction intensity 1) plane and P _SiC, of SiB ₄ phase (104)
_Assuming that the diffraction intensity of the surface is P _SiB , P _SiO2 / P _Si is _0.1 .
005 or more and 0.1 or less, and P _SiC / P _Si is 0.00
5 or more and 0.1 or less, and P _SiB / P _SiO2 is 0.1 or more
5.0 or less, and P _{Si B} / P _SiC is 0.1 or more 5.0
The following is preferred. 0.005 for P _SiO2 / P _Si
If it is less than 10%, the content of the SiO ₂ phase is reduced, so that the expansion and contraction of the Si fine particles 5 cannot be suppressed, and the diffusion rate of lithium ions is undesirably reduced. If the _{ratio of} P _SiO2 / P _Si exceeds 0.1, the content of the Si phase in the Si fine particles 5 decreases, and the charge / discharge capacity decreases, which is not preferable. Also, P _SiC / P _Si is 0.005
Also, the content of the SiC phase decreases, the expansion and shrinkage of the Si fine particles 5 cannot be suppressed, and the diffusion rate of lithium ions decreases.
If P _SiC / P _Si exceeds 0.1, Si in Si fine particles 5
It is not preferable because the content of the phase is reduced and the charge / discharge capacity is reduced.

Further, if the _ratio of P _SiB / P _SiO2 is less than 0.1, the effect of suppressing the expansion and contraction of the Si fine particles 5 is hardly obtained, which is not preferable. On the other hand, if P _SiB / P _SiO2 exceeds 5.0, the effect of the SiO ₂ phase to promote the diffusion of lithium ions is hindered, and the crystal structure of the Si phase becomes too large to decrease the discharge capacity. Therefore, it is not preferable. Furthermore, if P _SiB / P _SiC is less than 0.1, the effect of suppressing the expansion and contraction of the Si fine particles 5 is hardly obtained, which is not preferable. Also, P _SiB / P
_{If SiC} exceeds 5.0, the SiC phase hinders the effect of accelerating the diffusion of lithium ions, and the crystal structure of the Si phase becomes too large in strain, which is not preferable because the discharge capacity is reduced. The SiO ₂ phase and the SiC phase have a particularly high effect of promoting the diffusion of lithium ions, and the SiB ₄ phase has a particularly strong effect of suppressing the expansion and contraction of the Si fine particles 5. An electrode material exhibiting high efficiency and a high capacity retention ratio can be obtained by not being able to sufficiently exert the effect and having all phases coexist.
Therefore, in the present invention, the SiO ₂ phase, SiC phase and S
It is preferred to include all of the iB ₄ phases.

The reason why the particle size of the Si fine particles 5 is set to 10 nm or more is to prevent the crystal structure of the Si fine particles 5 from being disordered and to reduce the L size.
The reason why the particle size is set to be smaller than 2 μm is to improve the occlusion amount because the particle size of the composite particles 3 needs to be smaller than 2 μm, which is the minimum particle size of the graphite particles 2.

Next, the conductive carbon materials 6 are arranged on or near the surface of the Si fine particles 5. In FIG. 5, the conductive carbon materials 6 are arranged around the Si fine particles 5. However, the shape of the conductive carbon material 6 is not limited to a particle shape, and may be various forms such as a film shape, a layer shape, and a fiber shape.
The conductive carbon materials 6 are located on the surface of the semiconductor Si fine particles 5 and impart apparent conductivity to the Si fine particles 5. The specific resistance of the conductive carbon materials 6 is preferably in the range of 10 ⁻⁴ Ω · m or less. When the specific resistance exceeds 10 ^-4 Ω · m,
Since the apparent conductivity of the Si fine particles 5 is reduced, the charge / discharge reaction of lithium ions with respect to the Si fine particles 5 does not proceed smoothly, and the charge / discharge capacity of the carbonaceous material cannot be improved, which is not preferable. As the conductive carbon material 6,
For example, carbon black, Ketjen black, vapor grown carbon fiber (VGCF) and the like can be exemplified.

The hard carbon film 7 covers the Si fine particles 5 and the conductive carbon materials 6. The conductive carbon materials 6 are arranged on the surface of the Si fine particles 5. This hard carbon film 7
Is obtained by sintering polyvinyl alcohol, a phenol resin or the like, and has a bending strength of 500 kg / cm ² or more and a film thickness of 10 nm or more and 1 μm or less.

The hard carbon film 7 is used to prevent the release of the composite particles 3 from the graphite particles 2 caused by the expansion and contraction of the Si fine particles 5 caused by the charge / discharge reaction of lithium ions. Mechanically suppresses expansion and contraction.
Therefore, it is preferable that the bending strength of the hard carbon film 7 be 500 kg / cm ² or more. Flexural strength of 500kg / cm
^If it is less than ² , the expansion and contraction of the Si fine particles 5 cannot be mechanically suppressed, and the composite particles 3 may be separated from the graphite particles 2, which is not preferable. If the thickness of the hard carbon film 7 is less than 10 nm, the binding force between the conductive carbon materials 6 and the Si fine particles 5 decreases, and the effect of suppressing the volume expansion of the composite particles 3 decreases. . Further, when the film thickness exceeds 1 μm, the negative reversible capacity increases due to amorphous carbon, which is not preferable.

The content of the composite particles 3 in the carbonaceous material of the present invention is preferably 1% by weight or more and 25% by weight or less. The content of the composite particles 3 is 1% by weight.
If it is less than this, it is not preferable because a sufficient discharge capacity cannot be obtained as compared with the case where only the carbon material is used as the active material.
On the other hand, if the content exceeds 25% by weight, the contribution of the carbon material portion is reduced, the reaction potential of Si is reached from the beginning of discharge, and the average voltage of the battery is lowered. It is not preferable because it narrows and re-aggregates, volume expansion and contraction by the Si fine particles 5 easily occur, and the cycle characteristics deteriorate.

When the carbonaceous material 1 reacts with lithium ions, the lithium ions are mainly absorbed by the graphite particles 2 and combined with the Si fine particles 5 to form an alloy. A conductive carbon material 6 is provided on the surface of the Si fine particles 5.
Is attached and the conductivity is apparently high, and Si
The lithium ions are easily alloyed with the fine particles 5. At this time, the volumes of the graphite particles 2 and the Si fine particles 5 expand, but since the Si fine particles 5 are covered with the hard carbon film 76, the volume expansion is mechanically suppressed,
The composite particles 3 including the fine particles 5 do not dissociate from the graphite particles 2. The Si fine particles 5 have Si phase and Si
Since the O ₂ phase, the SiC phase, and the SiB ₄ phase are included, the amount of lithium ions absorbed is suppressed, and the volume expansion of the Si fine particles 5 is appropriately suppressed. 3 do not dissociate from the graphite particles 2. Therefore, the Si fine particles 5 can always contribute to the charge / discharge reaction, and the charge / discharge capacity of the carbonaceous material 1 does not decrease even if the charge / discharge cycle proceeds.

Further, by covering the graphite particles 2 and the composite particles 3 with the amorphous carbon film 4, the graphite particles 2 do not come into direct contact with the organic electrolyte, and the decomposition of the organic electrolyte is suppressed. Further, the composite particles 3 do not fall off from the graphite particles 2, and further, the pulverization of the Si fine particles 5 due to volume expansion due to charging is prevented.

Therefore, according to the carbonaceous material 1 described above, the charge / discharge capacity is increased, and the volume expansion of the Si fine particles 5, the dropout of the composite particles 3, and the volume expansion of the Si fine particles 5 due to the charge are caused. Can be suppressed, and a decrease in cycle characteristics can be prevented.

The above carbonaceous material can be produced, for example, as follows. The production of this carbonaceous material
It comprises a step of producing composite particles and a step of mixing graphite particles with the obtained composite particles and coating them with an amorphous carbon film. First, in the step of producing the composite particles, Si fine particles composed of only the Si phase and a boron compound such as boron or boron oxide as a boron source are prepared, and the Si fine particles boron or the boron compound are charged into a carbon crucible to be unreacted. 120-3 at about 1300-1400 ° C in an active atmosphere
Heat for 00 minutes. By this heating, carbon which is a constituent material of the crucible reacts with the Si phase, and SiC is contained in Si fine particles.
A phase is precipitated, and the boron contained in the boron source reacts with the Si phase to precipitate a SiB ₄ phase in the Si fine particles.
The slightly mixed oxygen reacts with the Si phase to precipitate a SiO ₂ phase in the Si fine particles. However, the heating temperature is 1300 ° C
And / or heating time is less than 120 minutes, S
Since the iC phase, SiO ₂ phase and SiB ₄ phase are not sufficiently precipitated, it is not preferable. If the heating temperature exceeds 1400 ° C., the Si
Is unfavorable because it melts. If the heating time exceeds 300 minutes, the amounts of the SiC phase, SiO ₂ phase and SiB ₄ phase deposited are undesirably excessive.

The mixing ratio between the Si fine particles and a boron source such as boron or a boron compound is preferably 10: 1. If the amount of boron is small relative to the Si fine particles, SiB
_{If the} amount of boron is excessive, the amount of precipitation of the _four phases is not preferable. If the amount of boron is excessive, the crystal structure of the Si phase is excessively distorted, and the discharge capacity is undesirably reduced.

Next, the heated Si fine particles and the conductive carbon material are mixed by dry mixing or wet mixing. In the case of wet mixing, it is preferable to use a dispersion medium such as isopropyl alcohol, acetone, and water.

Next, the polymer material is dissolved in a suitable solvent,
After mixing a mixture of Si fine particles and a conductive carbon material into this solution, the solvent is removed. By removing the solvent, S
A composite particle precursor in which the i-fine particles and the conductive carbon material are coated with a polymer film is formed. Note that as the above polymer material, it is preferable to use at least one of a thermoplastic resin, a thermosetting resin, a vinyl resin, a cellulose resin, and a phenol resin, and particularly preferably a phenol resin. Coal pitch materials, petroleum pitch materials,
A tar-based material or the like may be used.

Next, by heating the composite particle precursor, the polymer film is carbonized to form a hard carbon film. The heat treatment is preferably performed in a vacuum atmosphere or an inert gas atmosphere, and the heat treatment temperature is 800 ° C. or more and 1200 ° C.
The following range is preferable, and the heat treatment time is preferably 120 minutes or more. When the heat treatment is performed in a vacuum atmosphere or an inert gas atmosphere, oxidation of the polymer film is prevented, and a good hard carbon film can be formed. If the heat treatment temperature is less than 800 ° C., carbonization is not completely performed, the specific resistance of the hard carbon film is high, and insertion and removal of lithium ions are difficult to be performed, which is not preferable. If the heat treatment temperature exceeds 1200 ° C., Si
While the fine particles are carbonized, excessive SiC is generated,
Graphitization of the carbon film proceeds, and the strength of the film decreases, which is not preferable. Similarly, if the heat treatment time is less than 120 minutes, a uniform hard carbon film cannot be formed, which is not preferable. Thus, composite particles are obtained.

In the next step, graphite particles are mixed with the obtained composite particles by dry mixing or wet mixing. In the case of wet mixing, it is preferable to use a dispersion medium such as ethanol.

Next, another polymer material is dissolved in an appropriate solvent, a mixture of the composite particles and the graphite particles is mixed with the solution, and the solvent is removed. By removing the solvent, a carbonaceous material precursor in which the composite particles and the graphite particles are coated with the polymer film is formed. In addition, it is preferable to use at least one of the above polymer materials such as a thermoplastic resin, a thermosetting resin, a vinyl resin, a cellulose resin, and a phenol resin, and particularly to use a phenol resin. Is preferred. Further, a coal-based pitch material, a petroleum-based pitch material, a tar-based material, or the like may be used.

Next, by heat-treating the carbonaceous material precursor, the polymer film is carbonized to form an amorphous carbon film. The heat treatment is preferably performed in a vacuum atmosphere or an inert gas atmosphere.
The temperature is preferably in the range of not higher than 00 ° C., and the heat treatment is preferably performed for 120 minutes or more. When the heat treatment is performed in a vacuum atmosphere or an inert gas atmosphere, oxidation of the polymer film is prevented, and a favorable amorphous carbon film can be formed. The heat treatment temperature is 80
If the temperature is lower than 0 ° C., the carbonization is not completely performed due to the low temperature,
The amorphous carbon film has high specific resistance,
It is not preferable because delamination is difficult to be performed, and the heat treatment temperature is 1
If the temperature is higher than 200 ° C., the Si fine particles are carbonized, SiC is excessively generated, and the graphitization of the polymer film proceeds, so that the strength of the amorphous carbon film is undesirably reduced. Similarly, if the heat treatment time is less than 120 minutes, a uniform hard carbon film cannot be formed, which is not preferable. Thus, the carbonaceous material according to the present invention is obtained.

The negative electrode having the above carbonaceous material, the positive electrode capable of inserting and extracting lithium, and the organic electrolyte form:
A lithium secondary battery can be configured. As the positive electrode, for example, LiMn ₂ O ₄ , LiCoO ₂ , LiNi
Examples include a positive electrode material capable of inserting and extracting lithium, such as O ₂ , LiFeO ₂ , V ₂ O ₅ , TiS, and MoS, and a material including a positive electrode material such as an organic disulfide compound or an organic polysulfide compound. As a specific example of the positive electrode or the negative electrode, the above-described positive electrode material or carbonaceous material, a binder and further mixed with a conductive auxiliary as necessary, and applying these to a current collector made of a metal foil or a metal net. A sheet-shaped member can be exemplified.

Examples of the organic electrolyte include an organic electrolyte in which a lithium salt is dissolved in an aprotic solvent. Examples of aprotic solvents include propylene carbonate, ethylene carbonate, butylene carbonate, benzonitrile, acetonitrile, tetrahydrofuran, 2-methyltetrahydrofuran, γ-butyrolactone, dioxolan, 4-methyldioxolan, N, N
-Dimethylformamide, dimethylacetamide, dimethylsulfoxide, dioxane, 1,2-dimethoxyethane, sulfolane, dichloroethane, chlorobenzene,
Non-protic solvents such as nitrobenzene, dimethyl carbonate, methyl ethyl carbonate, diethyl carbonate, methyl propyl carbonate, methyl isopropyl carbonate, ethyl butyl carbonate, dipropyl carbonate, diisopropyl carbonate, dibutyl carbonate, diethylene glycol, dimethyl ether, and among these solvents Illustrative of the mixed solvent is a mixture of two or more of, especially propylene carbonate,
It is preferable to include at least one of ethylene carbonate and butylene carbonate and to include at least one of dimethyl carbonate, methyl ethyl carbonate, and diethyl carbonate.

As the lithium salt, LiPF ₆ ,
_{LiBF 4, LiSbF 6, LiAsF 6} , LiClO 4,
LiCF ₃ SO ₃ , Li (CF ₃ SO ₂ ) ₂ N, LiC ₄ F ₉
SO ₃ , LiSbF ₆ , LiAlO ₄ , LiAlCl ₄ , Li
One or more lithium salts of N (C _x F _{2x + 1} SO ₂ ) (C _y F _{2 y10 1} SO ₂ ) (where x and y are natural numbers), LiCl, LiI, etc. are mixed. In particular, those containing any one of LiPF ₆ and LiBF ₄ are preferable. In addition, other known organic electrolytes for lithium secondary batteries can also be used.

As another example of the organic electrolyte, PEO,
A so-called polymer electrolyte may be used, such as a mixture of any of the above-described lithium salts in a polymer such as PVA, or a polymer obtained by impregnating a polymer having high swellability with an organic electrolyte. Further, the lithium secondary battery of the present invention has a positive electrode,
The invention is not limited to the negative electrode and the electrolyte, but may include other members as necessary. For example, a separator for separating the positive electrode from the negative electrode may be provided.

According to the above-mentioned lithium secondary battery, since the above-mentioned carbonaceous material 1 is provided, a lithium secondary battery having a high energy density and excellent cycle characteristics can be constituted.

[0060]

EXAMPLES [Production of carbonaceous material of Examples] Average particle size 2μ
10 g of Si powder and 1.4-2.8 g of boron oxide or 1 g of boron were placed in a carbon crucible having an internal volume of 200 ml, and heated at 1400 ° C. for 240 minutes in an argon gas atmosphere. The Si particles harden after aggregation by this heat treatment, and become larger particles than before heating. This was pulverized by a ball mill or the like until the particle size became 300 nm. Next, 2 parts by weight of carbon black was mixed with 1 part by weight of the pulverized Si fine particles. Carbon black has a specific resistance of 1
0 ^-4 Ω · m. Next, a solution prepared by dissolving 10 parts by weight of a phenol resin in isopropyl alcohol was prepared. The mixture of the Si fine particles and carbon black was mixed with the solution, and the mixture was sufficiently stirred, and then the solvent was removed. In this way, a composite particle precursor in which carbon black and a phenol resin film were adhered to the surface of the Si fine particles was formed. Next, this composite particle precursor was heat-treated at 1000 ° C. for 180 minutes in an argon atmosphere to carbonize the polyvinyl alcohol resin film to form a 0.05 μm thick hard carbon film. When the polyvinyl alcohol resin is carbonized alone under the same conditions as above, the bending strength of the obtained carbide is about 800 kg / cm ^2, so the bending strength of the hard carbon film is estimated to be about the same. Is done. Thus, composite particles were obtained.

Next, 95% of natural graphite having an average particle size of 15 μm was used.
To the parts by weight, 5 parts by weight of the composite particles were added, and isopropyl alcohol was further added, followed by wet mixing. The spacing d002 of the (002) plane of the natural graphite by X-ray wide-angle diffraction was 0.3355 nm. Next, after adding and mixing an isopropyl alcohol solution containing 10 parts by weight of a phenol resin to the mixture of the natural graphite and the composite particles,
The isopropyl alcohol was evaporated. In this way, a carbonaceous material precursor formed by attaching the composite particles and the polyvinyl alcohol resin film to the surface of natural graphite was formed.

Next, this carbonaceous material precursor was calcined in a vacuum atmosphere at 1000 ° C. (1273 K) to carbonize the phenol resin to form a 0.05 μm thick amorphous carbon film. When the phenol resin is carbonized alone under the same conditions as described above, (00)
2) Since the plane distance d002 between the planes is about 0.39 nm, it is estimated that the plane distance d002 of the amorphous carbon film is also about the same. Thus, the carbonaceous materials of Examples 1 to 4 were obtained.

[Production of Carbon Material of Comparative Example] 10 g of Si powder having an average particle size of 2.0 μm and 2.8 g of boron oxide or 1 g of boron were placed in a crucible made of zirconium having an internal volume of 100 ml and placed in an argon gas atmosphere. 1 at 1400 ° C
Except for heating for 80 minutes, carbonaceous materials of Comparative Examples 1 and 2 were obtained in the same manner as in Examples 1 to 4. The heated Si fine particles prepared in Example 2 were pulverized again by a ball mill or the like until the average particle size became 2 μm, and the carbonaceous material of Comparative Example 3 was obtained in the same manner as in Examples 1 to 4. Was. Further, Comparative Example 4 was made of a carbonaceous material composed of only natural graphite.

[Preparation of Test Cell for Charge / Discharge Test]
Examples 1 to 4 and Comparative Examples 1 to 4
Mix vinylidene fluoride and add N-methylpyrrolidone
Was added to obtain a slurry liquid. This slurry liquid is
-Apply to 14μm thick copper foil by blade method and vacuum
After drying in an atmosphere at 120 ° C. for 24 hours, N-methylpi
Loridone was volatilized. Thus, the thickness of 100 μm
m of the negative electrode mixture was laminated on a copper foil. Note that, in the negative electrode mixture,
The content of polyvinylidene fluoride was 8% by weight.
The density of the mixture is 1.5 g / cm ^ThreeThat was all. And
A copper foil with a negative electrode mixture laminated is punched into a circle with a diameter of 13 mm.
Pull out the negative electrodes of Examples 1 to 4 and Comparative Examples 1 to 4.
Was.

Negative Electrodes of Examples 1-4 and Comparative Examples 1-4
Is the working electrode, and a metal lithium foil punched in a circular shape is the counter electrode.
Between the working electrode and the counter electrode.
Insert a separator made of
Carbonate (DMC), diethyl carbonate (D
EC) and ethylene carbonate (EC)
LiPF6 has a concentration of 1 (mol / L) as a solute.
Using a solution that has been melted, a coin-shaped test cell
Created. Then, the charge / discharge current density was set to 0.2 C,
The terminal voltage is 0 V (Li / Li) ⁺), The discharge end voltage
1.5V (Li / Li⁺) As a charge / discharge test
Was. Table 1 shows one cycle of Examples 1 to 4 and Comparative Examples 1 and 2.
2 shows the discharge capacity and the charge / discharge efficiency at the grid line. Also, the table
FIG. 2 shows the discharge at the 20th cycle of Example 2 and Comparative Examples 3 and 4.
Capacity ratio between electric capacity and first cycle discharge capacity (20th / 1st)
Is shown. However, the measurement of the capacity ratio was performed by 1C discharge.

[0066]

[Table 1]

[Table 2] Samples Si fine particles after heat pulverization Volume ratio (20th / 1st) Example 2 0.3 μm 88.0% Comparative example 3 2.0 μm 81.2% Comparative example 4-84.4%

As shown in Table 1, it can be seen that the discharge capacity in the first cycle of Comparative Examples 1 and 2 is almost equal to or higher than Examples 1 to 4. This is the first embodiment
In the cases of Nos. To 4, the SiC phase was precipitated in the Si phase of the Si fine particles by heating the Si fine particles in the carbon crucible,
It is considered that the content of the Si phase forming an alloy with lithium was relatively reduced. On the other hand, in Comparative Examples 1 and 2, since a crucible made of zirconium was used, Si fine particles of Si were used.
It is considered that the SiC phase did not precipitate in the phase, and therefore the content of the Si phase was relatively higher than in Examples 1 to 4.

Further, when comparing Examples 1 to 3 and Example 4 in terms of discharge capacity, Example 4 shows a high discharge capacity. This is because, in the case of Examples 1 to 3, Si fine particles and B ₂ O ₃
And heated, the oxygen atoms of B ₂ O ₃ become S
This is probably because i was oxidized and a relatively large amount of SiO ₂ phase precipitated in addition to the SiB ₄ phase, so that the content of the Si phase was relatively reduced. On the other hand, in Example 4, since the Si fine particles and B were mixed and heated, the amount of oxygen was smaller than in Examples 1 to 3, and the SiO ₂ phase was slightly precipitated due to minute residual oxygen and the like in the atmosphere. However, the amount was smaller than in Examples 1 to 3, and it is considered that the content of the Si phase was relatively higher than in Examples 1 to 3.

Further, in Examples 1 to ₃ , the discharge capacity decreased as the added amount of B ₂ O ₃ increased. This is considered to be due to the fact that as the amount of B ₂ O ₃ added increased, more SiB ₄ phase was precipitated, and the content of Si phase relatively decreased.

Next, as for the charging / discharging efficiency, Table 1 shows that the charging / discharging efficiencies of Examples 1 to 4 are higher than those of Comparative Examples 1 and 2. This is because SiC
Phase, SiO ₂ phase and SiB ₄ phase are precipitated, and the content of the Si phase forming an alloy with lithium is relatively reduced.
It is considered that the expansion and contraction of the Si fine particles themselves were appropriately suppressed, whereby the release of the composite particles from the graphite was reduced, and the charge / discharge efficiency was improved. In addition, SiC phase, S
It is considered that the crystallinity of the Si phase is reduced due to the precipitation of the iO ₂ phase and the SiB ₄ phase, and the diffusion rate of lithium in the Si phase is improved.

FIG. 6 shows an X-ray diffraction pattern of Si fine particles of the carbonaceous material of Example 2. As is clear from FIG. 6, diffraction peaks derived from the SiC phase, the SiO ₂ phase and the SiB ₄ phase are observed in addition to the Si phase. (11)
1) The diffraction intensity of the plane is defined as P _Si, and (111) of the SiO ₂ phase
When the diffraction intensity of the surface and P _SiO2, the diffraction intensity of the SiC phase (111) plane and P _SiC, the diffraction intensity of SiB ₄ phase (104) plane was P _SiB, from Fig 6, P _SiO2 / P _Si =
0.034, and P _SiC / P _Si = 0.044,
P _SiB / P _SiO2 = 1.50, and P _SiB / P _SiC = 1.
It turns out that it is 16.

Next, as apparent from Table 2, Example 2
It can be seen that the capacity ratio of the comparative example is much higher than that of the comparative example 4. This is because the SiC phase, the SiO ₂ phase and the SiB ₄ phase precipitate in the Si fine particles to form an alloy with lithium, similarly to the reason that the charge and discharge efficiency in the first cycle is improved.
It is considered that since the phase content was relatively reduced, the expansion and contraction of the Si fine particles themselves were moderately suppressed, whereby the release of the composite particles from the graphite was reduced, and the cycle characteristics were improved. In addition, it is considered that the crystallinity of the Si phase is reduced due to the precipitation of the SiC phase, the SiO ₂ phase, and the SiB ₄ phase, and the diffusion rate of lithium in the Si phase is improved. Also,
The results of Comparative Example 3 show that when the Si fine particles after heating and firing are large, the curing that suppresses the expansion and contraction of the Si fine particles is weakened.

[0074]

As described in detail above, the present invention
According to the carbonaceous material, graphite particles and Si fine particles convert Li.
Because of the occlusion, the charge / discharge capacity is higher than when graphite particles are used alone.
improves. Si fine particles with high specific resistance to graphite particles
By placing a conductive carbon material around the
Improve conductivity apparently. Further harden Si fine particles
By covering with carbon film, it accompanies the occlusion and release of Li
Volume expansion and contraction of the Si fine particles are mechanically suppressed. Change
In addition, cover graphite particles and composite particles with an amorphous carbon film.
Electrolysis without graphite particles directly touching the electrolyte
Liquid decomposition is suppressed and composite particles are converted from graphite particles.
It does not fall off and is also caused by volume expansion due to charging.
To prevent the Si fine particles from being pulverized. Furthermore, the crystalline Si phase
SiO inside _TwoPhase, SiC phase and SiB_FourPhase precipitation
Thereby, while the content of the Si phase is relatively reduced,
Strain is given to the Si phase to lower the crystallinity and excessive Li absorption
Storage is suppressed. Due to the absorption and release of Li
The expansion and contraction of the Si fine particles are appropriately suppressed. SiO_Two
Phase, SiC phase and SiB_FourThe phase does not react with Li
Although it has no capacity, it promotes diffusion of Li ions.
And minimizing pulverization due to volume expansion of Si fine particles
Is done. Furthermore, SiO_TwoPhase, SiC phase and SiB_FourAll of the phases
The above functions can be obtained more effectively because
Wear. From the above, in the carbonaceous material of the present invention, charging and discharging
While increasing the capacity, the volume expansion and
S caused by dropout of composite particles and volume expansion due to charging
Suppresses the micronization of i-particles and prevents deterioration of cycle characteristics
Can be stopped.

Further, according to the lithium secondary battery of the present invention, since the carbonaceous material according to the present invention is provided as a negative electrode, energy density and cycle characteristics can be improved.

[Brief description of the drawings]

FIG. 1 is a schematic sectional view showing an example of a carbonaceous material according to an embodiment of the present invention.

FIG. 2 is a schematic cross-sectional view showing another example of the carbonaceous material according to the embodiment of the present invention.

FIG. 3 is a schematic sectional view showing still another example of the carbonaceous material according to the embodiment of the present invention.

FIG. 4 is a schematic sectional view showing another example of the carbonaceous material according to the embodiment of the present invention.

FIG. 5 is a schematic cross-sectional view showing an example of composite particles contained in a carbonaceous material according to an embodiment of the present invention.

FIG. 6 is a diagram showing an X-ray diffraction pattern of Si fine particles after heating.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Carbonaceous material 2 Graphite particle 3 Composite particle 4 Amorphous carbon film 5 Si fine particle 6 Conductive carbon material 7 Hard carbon film

 ────────────────────────────────────────────────── ─── Continuing on the front page (72) Inventor Shen Ryunyun 508 Sanctuary Cave, Cheonan-si, Republic of Korea F-term in Samsung DIA Corporation (reference) 4G046 EA03 EA05 EB02 EB04 EB06 EC02 EC06 5H029 AJ05 AK03 AL01 AL06 AL07 AM00 AM03 AM04 AM06 AM16 CJ02 HJ05 5H050 AA07 BA17 CA07 CA08 CA09 CB01 CB07 CB08 DA03 FA17 FA18 GA02 HA13

Claims (7)

[Claims] 1. Around a graphite particle having a (002) plane spacing d002 of less than 0.337 nm according to X-ray wide-angle diffraction, composite particles containing at least silicon and carbon and having a smaller particle size than the graphite particle are provided. Distributed and arranged
And the graphite particles and the composite particles are coated with an amorphous carbon film having an interplanar spacing d002 of 0.37 nm or more, and the composite particles have a conductive carbon material around Si fine particles made of crystalline silicon. The Si fine particles and the conductive carbon material are covered with a hard carbon film while being disposed, and the Si fine particles are composed of SiO ₂ phase, Si
A carbonaceous material, wherein a C phase and a SiB ₄ phase are precipitated. 2. The method according to claim 1, wherein (11)
1) The diffraction intensity of the plane and P _Si, the SiO ₂ phase (11
1) The diffraction intensity of the plane is defined as P _SiO2, and (11)
1) The diffraction intensity of the plane and P _SiC, the SiB ₄ phase (10
4) _Assuming that the diffraction intensity of the plane is P _SiB , P _SiO2 / P _Si is 0.005 or more and 0.1 or less;
_SiC / P _Si is 0.005 or more and 0.1 or less, and P _SiB /
P _SiO2 is 0.1 or more and 5.0 or less, and P _SiB / P _SiC
The carbonaceous material according to claim 1, wherein is not less than 0.1 and not more than 5.0. 3. The graphite particles have a particle size of 2 μm or more and 70 μm or more.
m, the particle size of the composite particles is more than 50 nm and 2 μm or less, and the film thickness of the amorphous carbon film is 50 nm or more and 5 μm or less. The carbonaceous material according to claim 1 or 2. 4. The method according to claim 1, wherein said Si fine particles have a particle size of at least 10 nm.
μm, and the specific resistance of the conductive carbon material is 1
^0-4 Ω · m or less, and the bending strength of the hard carbon film is 500 kg / cm ² or more and the film thickness is 10 n
The carbonaceous material according to any one of claims 1 to 3, wherein the carbonaceous material has a length of not less than m and not more than 1 µm. 5. The method according to claim 1, wherein the content of the composite particles is 1% by weight or more.
The carbonaceous material according to any one of claims 1 to 4, wherein the content is 5% by weight or less. 6. A lithium secondary battery comprising the carbonaceous material according to any one of claims 1 to 5. 7. Si fine particles composed of crystalline silicon are mixed with B ₂ O ₃
1300 ° C or more and 1400 ° C in a carbon crucible with powder
By sintering below, SiO ₂ is contained in the crystalline Si phase.
Phases, and a step of precipitating the SiC phase and SiB ₄ phases, as well as adhering the conductive carbon material in the Si fine particles, to form a polymeric material coating covering the Si fine composite particle precursor, further said composite particles A step of obtaining composite particles using the polymer film as a hard carbon film by firing the precursor; and forming a polymer material film covering the graphite particles while attaching the Si fine particles to the graphite particles. Obtaining a carbonaceous material using the polymer film as an amorphous carbon film by firing the carbonaceous material precursor as a precursor.