JP2000173612A - Nonaqueous electrolyte secondary battery and negative electrode material thereof - Google Patents

Nonaqueous electrolyte secondary battery and negative electrode material thereof

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JP2000173612A
JP2000173612A JP10342907A JP34290798A JP2000173612A JP 2000173612 A JP2000173612 A JP 2000173612A JP 10342907 A JP10342907 A JP 10342907A JP 34290798 A JP34290798 A JP 34290798A JP 2000173612 A JP2000173612 A JP 2000173612A
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negative electrode
particles
electrode material
fibrous carbon
si
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JP4218098B2 (en
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Takayuki Nakamoto
Yoshiaki Nitta
Harunari Shimamura
貴之 中本
治成 島村
芳明 新田
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Matsushita Electric Ind Co Ltd
松下電器産業株式会社
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    • YGENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02EREDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E60/00Enabling technologies or technologies with a potential or indirect contribution to GHG emissions mitigation
    • Y02E60/10Energy storage
    • Y02E60/12Battery technologies with an indirect contribution to GHG emissions mitigation
    • Y02E60/122Lithium-ion batteries

Abstract

PROBLEM TO BE SOLVED: To attain high capacity, and to improve reduction in discharge capacity with a cycle through the formation of a negative electrode by fixing and electrically jointing composite particles by covering a particle of only an Si phase or an Si phase particle with a solid solution, including Si by a carbonaceous material which includes fibered carbon. SOLUTION: A negative electrode material molded pole 5 is integrally molded on a current collector 3 arranged at the inside bottom of a cell case 1, a metallic lithium positive electrode 4 is arranged/sealed on it via a porous separator 6, and a nonaqueous electrolyte by means of dissolving lithium salt in an organic solvent is injected to obtain a nonaqueous electrolyte secondary battery. The negative electrode material is formed by fixing a particle, including Si by a carbonaceous material of 5 to 80 wt.%, the particle including Si is composed of composite particles, by covering one or more Si phase particles with a solid solution or an intermetallic compound, including Si or a particle of only an Si phase, the carbonaceous material is fixed in less than 10 to 100% of the surface are of the particle, and fibered carbon having d002 of 3.35 to 3.70 Å, a length of 1 to 20 μm and a diameter not more than 0.5 μm is desirably included by 1 to 20% with respect to the entire negative electrode material.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an improvement in capacity and cycle characteristics of a non-aqueous electrolyte secondary battery, particularly when Si is used as its negative electrode material.

[0002]

2. Description of the Related Art In recent years, lithium ion secondary batteries which have greatly contributed to the development of mobile communication devices and portable electronic devices are:
High electromotive force and high energy density. If lithium metal, which is the active material, is used as the negative electrode material, the energy density is the best, but the dendrite precipitates during charging, breaks through the separator, reaches the positive electrode side, and may cause an internal short circuit. there were.

[0003] The precipitated dendrite has a high specific activity due to its large specific surface area, and reacts with the solvent in the electrolytic solution on the surface thereof to form a solid electrolyte interface film lacking electron conductivity. For this reason, the internal resistance of the battery is increased, and particles isolated from the electron conduction network are present, and these are factors that lower the charge / discharge efficiency. For these reasons, batteries using lithium metal as the negative electrode material have drawbacks in that safety and cycle life are shortened.

At present, a carbonaceous material capable of occluding and releasing lithium ions is used as a negative electrode material instead of lithium metal, and has been put to practical use. However, when graphite is used as the carbonaceous material, its theoretical capacity is 372 mAh / g, which is only about one-tenth of the theoretical capacity of Li metal alone, which is not a satisfactory level in terms of high capacity.

As a negative electrode active material capable of increasing the capacity,
Examples include Si, Sn, and Al. In particular, the theoretical capacity of charge and discharge of Si is as large as 4200 mAh / g (9800 mAh / cm 3 : specific gravity 2.33). In fact, for the electrochemical evaluation of Si, for example, using a sample electrode mixed with AB (acetylene black) as a conductive agent and PTFE (polytetrafluoroethylene) as a binder, metallic lithium in an organic electrolyte containing a lithium salt was used. , A reversible capacity of 3000 mAh / g or more is obtained at the beginning of the cycle, and it is known that the test cell has a high capacity density.

As a material having a higher capacity than a carbonaceous material, a non-ferrous metal silicide comprising a transition element is disclosed in JP-A-7-240201.
Japanese Patent Application Publication No. JP-A-2003-115122 proposes a fluorite-type structure silicide.

[0007]

However, although there are various candidates for materials having higher capacities than the carbonaceous materials as described above, each has the following problems.

The negative electrode material composed of a single phase of Si becomes particles in which phases having different Li concentrations coexist as particles as a whole when absorbing and releasing Li, that is, particles composed of a heterogeneous phase, and the volume of these phases is as described above. As a result, a large stress strain is generated at the boundary between different phases, cracks are generated, and the refinement of the whole particle proceeds. As a result, fine particles that cannot be brought into contact with the conductive agent are generated, and the number of particles that cannot participate in the electrochemical reaction is increased.

When the Si particles expand significantly due to electrochemical absorption of Li, the surrounding conductive agent, acetylene black, can absorb the expansion, but the Si particles absorb electrochemical Li. When it shrinks greatly due to, the surrounding conductive agent that has absorbed the expansion has a weak restoring force against displacement equivalent to the shrinkage amount of the Si particles, so it is difficult to maintain a contact state with the Si particles, It becomes difficult to obtain contact with the conductive agent. As a result, particles that cannot participate in the electrochemical reaction increase.

[0010] For these reasons, the negative electrode material composed of a single phase of Si has a problem that a practically satisfactory cycle life characteristic cannot be obtained.

On the other hand, unlike the Si single phase, a non-ferrous metal silicide comprising a transition element and a fluorite-type structure silicide are disclosed in Japanese Unexamined Patent Publication No. 7-240201, respectively, as negative electrode materials having practically satisfactory cycle life characteristics. Gazette, JP-A-9-6
3651 publication. In these materials, the electrochemical absorption and release of Li at the time of charge and discharge occur at interstitial positions, so the skeleton of the original crystal phase does not break down, and the phase of the whole particle does not change according to the Li concentration It is an intermetallic compound composed of phases.

The volume change of the original crystal phase due to the occlusion and release of Li causes only expansion and contraction within two times, so that almost no stress strain is generated at the boundary of the different phases, compared with the negative electrode material composed of a single phase of Si. However, the above-mentioned silicide active material particles are hardly made fine. In this respect, the cycle life characteristics of the silicide are much better than those of the negative electrode material composed of the Si single phase.

However, since the silicide active material particles also expand and contract slightly, although not more than twice, when the active material particles contract due to electrochemical release of Li, the volume change is reduced.
It is much less than the negative electrode material composed of Si single phase, but for the same reason as in the case of Si single phase, it is difficult to maintain the contact state with the conductive agent, and the contact between the active material particles and the conductive agent becomes poor. Particles that slightly decrease are generated as charge and discharge are repeated. As a result, the number of particles that cannot participate in the electrochemical reaction increases, and the cycle life characteristics deteriorate.

Moreover, the theoretical capacity of these silicide materials is less than half that of a single-phase Si, and although the capacity is higher than that of a carbonaceous material in order to increase the capacity, a negative electrode material composed of a single-phase Si is desired. The capacity cannot be increased as much.

According to the present invention, a composite particle in which Si phase particles are at least partially covered with a solid solution containing Si or an intermetallic compound phase, or particles composed only of a Si phase is used as a negative electrode material for a non-aqueous electrolyte secondary battery. When used, even when the negative electrode material repeatedly expands and contracts due to electrochemical occlusion and release of Li, the contact state between the negative electrode material particles and the conductive agent is maintained well, and the charge / discharge cycle life characteristics are improved. It is an object to provide a negative electrode material that can be improved.

The present invention relates to a composite material comprising Si phase particles at least partially covered with a solid solution containing Si or an intermetallic compound phase, or a particle comprising only a Si phase. When used, fibrous carbon is fixedly arranged on a part of or the entire surface of the composite particles, or particles composed only of Si phase, and the space between these particles is electrically controlled by the fibrous carbon. Are bonded together. Thereby, even if the particles repeatedly expand and contract with electrochemical occlusion and release of Li, the contact state between each of the particles and the conductive agent is favorably maintained, and the charge / discharge cycle life characteristics can be improved. it can.

The carbonaceous material other than the fibrous carbon may be contained. In this case, the amount of the carbonaceous material containing the fibrous carbon is 5% by weight or more and 80% by weight or less based on the whole negative electrode material. This is achieved by immobilizing at least 10% and less than 100% of the total surface area of the composite particles or the particles composed only of the Si phase with carbonaceous material including fibrous carbon.

Specifically, the fibrous carbon according to the present invention is in the range of 1% by weight or more and 20% by weight or less based on the whole negative electrode material, d 002 is 3.35 ° to 3.70 °, and the length is 1%.
μm or more, 20 μm or less, diameter 0.1 μm or more, 0.5 μm
This has been achieved by the following flexible thin thread shape.

In the case of composite particles in which Si phase particles are at least partially coated with a phase of a solid solution containing Si or an intermetallic compound, the surface of the Si phase particles is coated with a silicide which is unlikely to be miniaturized, whereby the coating layer is formed. The silicide can restrain a change in the crystal structure of the Si phase particle, that is, a large change in volume caused by electrochemical occlusion and release of Li, and can suppress the miniaturization of the Si phase particle.

As a result, a highly efficient electrochemical reaction system can be realized, and a high-capacity negative electrode material with less capacity deterioration during the progress of charge / discharge cycles can be obtained. However, the expansion and contraction associated with the charge and discharge that occur as a whole particle cannot be completely eliminated, and the surrounding conductive agent, acetylene black, in contact with it can absorb the expansion, but the particles cannot be electrochemically treated. When shrinking with the release of Li, the surrounding conductive agent that absorbed the expansion has a weak restoring force against displacement equivalent to the amount of shrinkage of the particles, making it difficult to maintain contact with the particles,
It becomes difficult to obtain contact between the particles and the conductive agent.

Therefore, the conductive agent not only has a high electric conductivity and a high liquid retention property, but also has a function of absorbing the expansion of the particles and maintaining the contact even if the particles shrink. It is important to have Examples of the conductive agent include carbon black, artificial graphite, graphitizable carbon, and non-graphitizable carbon. Various studies have shown that fibrous carbon having the above properties is preferable.

The fibrous carbon is thinner and more flexible in shape than conventional acetylene black or artificial graphite, so that the number of contact points with particles can be increased. In particular, when the particles have a shape close to a sphere, contact between the particles and the carbon material is limited to point contact when the carbon material is, for example, scaly. However, in the case of fibrous carbon, it is possible for the fibers to be in close contact with each other around the sphere, thereby increasing the number of contact points between the active material particles and the conductive agent. As a result of intensive studies by the present inventors, this can be confirmed by observation using a scanning electron microscope (SEM) or the like.

Further, fibrous carbon has a greater restoring force against macroscopic displacement than conventional acetylene black or artificial graphite. This is a result of extensive studies by the present inventors, and in a powder pressurized container having a constant diameter, after pressurizing at a constant pressure (1000 kg / cm 2 ), and measuring the return amount when the pressure is released, As shown in Table 1, the content of the fibrous carbon can be confirmed by having a restoration rate of about 2 to 40 times that of acetylene black or flaky artificial graphite.

[0024]

[Table 1]

* Restoration rate = (powder height after pressing / powder height before pressing) × 100%

When the particles are immobilized with fibrous carbon, the number of contact points with the particles can be increased as described above, and the restoring force against macroscopic displacement is large. When the particles shrink with the release of the particles, the frequency at which the particles and the fibrous carbon maintain a contact state is much higher than in the past, and the particles can be kept in good contact with the conductive agent. As a result, the number of electrochemically isolated particles does not increase, and a practically satisfactory cycle life characteristic can be exhibited.

[0027] The fibrous carbon used in the present invention is not required to have an elastic force capable of plastically deforming its shape.
As in the case of conventional carbon materials such as acetylene black, brittle whisker-like fibrous carbon is not preferable because the number of contact points with the particles is small and the restoring force against macroscopic displacement is small.

The fibrous carbon used in the present invention includes PAN
There are carbon fibers, pitch-based carbon fibers, vapor-grown carbon fibers, and the like, and any of them may be used. Vapor-grown carbon fibers are particularly preferable because they have higher graphitization properties and good electron conductivity as compared with PAN-based carbon fibers and pitch-based carbon fibers.

The fibrous carbon is a fibrous material substantially composed of only carbon produced by thermal decomposition of an organic substance. Particularly preferred vapor-grown carbon fiber is to pyrolyze gaseous hydrocarbons at high temperature to produce carbon fiber,
Heat-treated at a temperature of at least ℃.

The fibrous carbon has physical properties of good electron conductivity since d 002 is 3.35 ° to 3.70 °, and has a length of 1 μm or more and 20 μm or less, a diameter of 0.1 μm or more,
Since it is 0.5 μm or less, it has physical properties that it is hard to aggregate and has good dispersion. This makes it possible to satisfactorily electrically connect the particles, and to construct an electron conduction network for applying an electrochemical reaction to all the particles.

The carbonaceous material containing fibrous carbon is preferably in contact with 10% or more and less than 100% of the total surface area of the particles. As a result of extensive studies by the present inventors, observation and confirmation can be made using a scanning electron microscope (SEM), precision analysis using an electronic probe (EPMA), and the like. When the contact area is less than 10%, the contact frequency is too low, and the effect of the present invention utilizing the increase in the contact points and the large restoring force by using fibrous carbon as the conductive agent is difficult to appear, which is preferable. Absent. The state in which the contact area is 100% is a state in which the entire surface of the particle is completely covered, but it is impossible to make this state using carbonaceous material including fibrous carbon.

As a method of fixing the particle surface with carbonaceous material containing fibrous carbon, a method using a binder, or fusion of the particle surfaces by heat generated by friction between powders using compressive shear stress are used. Any method may be used, such as a so-called mechanochemical method of forming the wobbled powder into a composite, or a method of performing surface adsorption using frictional charging generated when powders dispersed in a gas phase come into contact with each other.

The carbon other than fibrous carbon is at least one of carbon black, artificial graphite, graphitizable carbon such as mesophase carbon microspheres, and non-graphitizable carbon.
More than kind.

The content of carbonaceous material including fibrous carbon is preferably in the range of 5% by weight or more and 80% by weight or less based on the whole negative electrode material. If the carbonaceous content is less than 5% by weight, the volume of the carbonaceous material is too small relative to the particle volume, so that sufficient electron conductivity cannot be provided between the particles, and the internal resistance of the battery increases, Particles isolated from the network are present, and these are factors that lower the charging / discharging efficiency, so that practically satisfactory cycle life characteristics cannot be obtained. The carbonaceous content is 80% by weight.
If the number exceeds the range, the volume per unit volume of the carbonaceous material is too large with respect to the volume of the particles, so that the capacity per volume cannot be increased.

Since fibrous carbon can electrochemically store and release Li ions between its layers, it can contribute to the capacity of the negative electrode in addition to the electron conductivity. According to the measurement, d 002 is 3.35Å or more, 3.70Å
The following is preferred. Fibrous carbon having d 002 of less than 3.35 ° is difficult to produce, and if it exceeds 3.70 °, the electronic conductivity is reduced, and is not suitable as a conductive agent. The length of the fibrous carbon is preferably 1 μm or more and 20 μm or less.

The reason is that if the length of the fibrous carbon is as short as less than 1 μm, the electrical connection between the particles is not good, and an electron conduction network is established for giving an electrochemical reaction to all the particles. And the charge / discharge capacity is reduced. When the length of the fibrous carbon exceeds 20 μm, the fibrous carbon is entangled and aggregated, so that the dispersibility of the fibrous carbon with respect to the particles is not good, and the number of contact points between the particles and the fibrous carbon is reduced. . Therefore, particles that cannot participate in the electrochemical reaction are formed, and the charge / discharge capacity is reduced.

The diameter of the fibrous carbon is preferably 0.1 μm or more and 0.5 μm or less. If the diameter of the fibrous carbon is smaller than 0.1 μm, production is difficult. Also, the diameter of fibrous carbon is 0.5
If it exceeds μm, the ratio of fine thread-like fibrous carbon decreases, and the surface including the diametric direction is more likely to contact the particles than the surface including the length direction, but the surface including the diametric direction has less flexibility. Therefore, the effect of increasing the number of contact points according to the present invention is not preferable because it is almost flat. The length and diameter of the fibrous carbon can be observed and confirmed using a scanning electron microscope (SEM) or the like.

The content of the fibrous carbon in the carbonaceous material containing the fibrous carbon for fixing the surface of the particles is preferably 1% by weight or more and 20% by weight or less based on the whole negative electrode material.
When the content of the fibrous carbon is less than 1% by weight based on the whole negative electrode material, the volume of the fibrous carbon with respect to the volume of the particles is too small, so that the number of contact points between the particles and the fibrous carbon is small, The effect of the present invention utilizing the increase in contact points and the large restoring force by using carbonaceous carbon as the conductive agent is not preferable, and is not preferable. When the content of fibrous carbon is more than 20% by weight based on the whole negative electrode material, the bulk density of the particles is 3 to 10 times larger than the bulk density of fibrous carbon, so that the capacity per volume is increased. Can not.

The Si particles or the composite particles in which one or more Si phase particles are at least partially coated with a solid solution containing Si or an intermetallic compound phase have an average particle diameter of at least 0.1 μm, It is 50 μm or less, and the ratio occupied by the Si phase particles in the composite particles is 5% by weight or more and 99% by weight or less.
The composite particles may include one Si phase particle or a plurality of Si phase particles. The average particle size of the Si phase particles in the composite particles is preferably 0.01 μm or more and 40 μm or less. The `` solid solution or intermetallic compound containing Si '' covering the Si phase particles is made of Si and a group 2 element, a transition element, a group 12, a group 13 element, and a group 14 element excluding carbon of the periodic table. It can be composed of at least one selected element.

As the negative electrode material in the nonaqueous electrolyte secondary battery of the present invention, Si particles or one or more Si particles
Part of the particles where the phase particles are at least partially coated with a solid solution or intermetallic compound phase containing Si, or the entire surface,
Anode material fixed with only 1% by weight or more and 20% by weight or less of fibrous carbon based on the entire anode material, or Si particles, or a solid solution containing 1 or 2 or more Si phase particles containing Si Part or the whole surface of the particles at least partially coated with the compound phase has a content of 1% by weight or more and 20% by weight or less of the fibrous carbon and the total carbonaceous material including the same in the entire negative electrode material. 5% by weight based on the total weight of the negative electrode material
As described above, any of the negative electrode materials immobilized with carbonaceous materials other than fibrous carbon such that the amount is 80% by weight or less may be used.

As the positive electrode material in the non-aqueous electrolyte secondary battery of the present invention, a transition metal compound containing lithium can be used. Examples are LiM 1-x M ' x O 2 or LiM 2y M'
y O 4 (where 0 ≦ X, Y ≦ 1, M and M ′ are each Ba, Co, Ni, Mn, C
r, Ti, V, Fe, Zn, Al, In, Sn, Sc, Y). However, transition metal chalcogenides,
It is also possible to use other positive electrode materials such as vanadium oxide and its Li compound, niobium oxide and its Li compound, conjugated polymers using organic conductive substances, Chevrel phase compounds, activated carbon, and activated carbon fibers. .

The electrolyte of a lithium ion secondary battery is generally
Is a non-aqueous electrolyte in which a lithium salt is dissolved in an organic solvent.
You. As the lithium salt, for example, LiClOFour, LiBFFour, LiP
F6, LiAsF6, LiB (C6HFive), LiCFThreeSOThree, LiCHThreeSOThree, Li (CFThreeS
OTwo)TwoN, LiCFourF9SOThree, Li (CFTwoSO Two)Two, LiCl, LiBr, LiI etc.
For example, one or more kinds can be used.
You.

As the organic solvent, carbonates such as propylene carbonate, ethylene carbonate, ethyl methyl carbonate, dimethyl carbonate and diethyl carbonate are preferred. However, other various organic solvents including carboxylic acid esters and ethers can also be used.

The separator plays a role as an insulator provided between the positive electrode and the negative electrode, and also greatly contributes to retention of the electrolyte. Usually, a porous body such as polypropylene, polyethylene or a mixed cloth of both, or a glass filter is generally used.

[0045]

Embodiments of the present invention will be described below with reference to the drawings.

The negative electrode material used for the nonaqueous electrolyte secondary battery and the negative electrode test used for evaluating the negative electrode will be described. Shown in Figure 1
A coin-shaped test cell having an R2016 size (diameter of 20.0 mm, total height of 1.6 mm) was prepared, and electrochemical characteristics such as charge / discharge capacity of the negative electrode material were measured and evaluated.

In FIG. 1, the space between the cell case 1 made of stainless steel plate and the cover 2 is sealed in a liquid-tight and air-tight manner via a polypropylene gasket 7.

The negative electrode material forming pole 5 is integrally formed with the current collector 3 made of stainless steel expanded metal welded to the inner bottom surface of the cell case 1. A disc-shaped metal lithium electrode 4 is crimped on the inner surface of the cover 2.

The negative electrode material molded electrode 5 and the metallic lithium electrode 4 are separated by a separator 6 made of a microporous polypropylene film, and the gap, the negative electrode material molded electrode 5 and the separator 6 are impregnated with an organic electrolyte. I have.

In the present invention, a Ni-52 wt% Si alloy was used for particles in which one or more Si phase particles were at least partially covered with a solid solution containing Si or an intermetallic compound phase. When the cross section of this composite particle was examined by SEM, it was found that the parent phase was a NiSi 2 phase and the structure in which the Si phase particle was present.

The negative electrode material molding electrode 5 integrally molds a predetermined amount of a mixture obtained by mixing 5% by weight of polyvinylidene fluoride as a binder with 95% by weight of the negative electrode material powder in the present invention on the current collector 3. did. After the negative electrode material molded electrode 5 molded in the cell case 1 is sufficiently dried under reduced pressure at 80 ° C., a test cell is assembled.

As the organic electrolyte, ethylene carbonate is used.
1 mol / l of solute lithium hexafluorophosphate as an electrolyte in an equal volume mixed solvent of (EC) and diethyl carbonate (DEC)
The dissolved one was used.

The test cell has a structure in which a manganese dioxide positive electrode of a general coin-type lithium primary battery such as a CR2016 type manganese dioxide lithium battery is replaced with a test electrode of a negative electrode material.

The charge and discharge of the test cell are performed at a constant current of 0.5 mA / cm 2 for both charging and discharging, first charging to 0 V, and then discharging to 3 V. Charge and discharge were repeated under such conditions.

[0055] area of the discharge capacity calculated in the combined volume both the carbonaceous particles or composite particles and a conductive agent consisting of Si phase only, the unit of mAh / cm 3 (the quantity of electricity of the negative plate in each example And the unit divided by the volume calculated from the thickness of the negative electrode material layer).

In each embodiment, the cycle life (%) is (3
(00th cycle discharge capacity / 1 cycle discharge capacity) x 100
Indicated by

Example 1 The effect of carbonaceous material containing fibrous carbon, which fixes the particle surface, on discharge capacity and cycle life characteristics was examined as compared with carbonaceous material containing no fibrous carbon. The fibrous carbon used had a d 002 value of about 3.40 °, a length of about 10 μm, and a diameter of about 0.25 μm.

[0058]

[Table 2]

In Table 2, the negative electrode material was negative electrode active material particles.
The composition is such that 10% by weight of a carbon material and 5% by weight of polyvinylidene fluoride as a binder are mixed with 85% by weight. According to Table 2, the active material particles containing Si according to the present invention have a higher capacity with respect to the discharge in the initial cycle than the conventional artificial graphite alone of Comparative Example 5.

In particular, in the case of particles in which one or more Si phase particles are at least partially coated with a solid solution containing Si or an intermetallic compound phase (Ni-52 wt% Si), the cycle life is as high as that of any conductive material. Even with the use of carbon material, it is better than conventional artificial graphite alone, and a highly efficient electrochemical reaction system can be realized. A negative electrode material has been obtained.

Further, when the carbon material for fixing the surface of the active material particles containing Si according to the present invention contains fibrous carbon,
As can be seen from the samples Nos. 1 and 2, the cycle life was better than those of the comparative examples 1 to 4. In particular, in the case of a negative electrode material composed of a single phase of Si, the cycle life was significantly improved as compared with Comparative Examples 2 and 4, though not as sufficient as that of the graphite type. This shows the effect of the present invention in which the use of fibrous carbon as the conductive agent increases the number of contact points and utilizes a large restoring force.

Next, in order to confirm the effect of the fibrous carbon electrically connecting the particles, when producing a negative electrode material having the structure of Sample No. 1, a molded electrode sufficiently kneaded,
A molded electrode with almost no kneading was tested. As a result, the molded electrode that was sufficiently kneaded was the result of sample No. 1, but the molded electrode that was almost not kneaded was because the fibrous carbon could not electrically connect the particles,
The discharge capacity in the initial cycle was as small as 420 mAh / cm 3, and it was not possible to construct an electron conduction network for giving an electrochemical reaction to all particles. This shows that it is essential that the fibrous carbon electrically connects the particles. In addition, as fibrous carbon, d
002 value is about 3.40Å, length is about 10μm, diameter is 0.25μm
Although using such a degree, a d 002 value 3.35A~3.70A is 20μm or less is 1μm or more in length, 0.1 [mu] m in diameter
As described above, even in the case where the thickness was 0.5 μm or less, the same result as in the present example was obtained.

Example 2 The influence of the frequency of contact between the particles or composite particles consisting of only the Si phase used in Example 1 and carbonaceous material containing fibrous carbon on the discharge capacity and cycle life characteristics was examined. . In a sufficiently kneaded negative electrode, the contact frequency is proportional to the carbonaceous content of the negative electrode material, including fibrous carbon. The fibrous carbon used had a d 002 value of about 3.40 °, a length of about 10 μm, and a diameter of about 0.25 μm. The negative electrode material was 95% by weight of the particles and the carbon material in total, and polyvinylidene fluoride 5 as a binder.
% By weight.

[0064]

[Table 3]

In Comparative Examples 6 and 7, in which 5% of the surface area of the particles were in contact, the initial discharge capacity was smaller than in Samples No. 3 to No. 6, which had a contact frequency of 10% or more and less than 100%. Moreover, the cycle life is considerably poor. From this, the frequency of contact
If the content is less than 10%, that is, if the content of carbonaceous matter is less than 5% by weight, sufficient electron conductivity cannot be provided between the particles, and particles isolated from the network of the electron conduction will be present. It can be seen that this is a factor that lowers the charge / discharge efficiency, and a practically satisfactory cycle life characteristic cannot be obtained.

Further, as in Comparative Examples 8 and 9, when the carbonaceous content exceeds 80% by weight, in the case of Ni-52wt% Si, the cycle life of the carbonaceous material is small, and the present invention and the present invention are not affected. The cycle life is slightly shorter than that. In the case of Si, Ni-52wt% Si
On the contrary, the magnitude of the cycle life of the carbonaceous material has an influence, and the cycle life characteristics as a whole are slightly larger than those of the present invention.

However, in both Comparative Examples 8 and 9, it is found that the volume per volume cannot be increased because the volume of the carbonaceous material is too large relative to the volume of the particles. As fibrous carbon, d 002 value is about 3.40Å, length is about 10μm, and diameter is
Although the thing of about 0.25 μm was used, the d 002 value was 3.35Å to 3.
The same result as in the present example was obtained when the length was 70 °, the length was 1 μm or more and 20 μm or less, and the diameter was 0.1 μm or more and 0.5 μm or less.

Example 3 Next, the effects of changes in physical properties (d002 value, length, diameter) of the fibrous carbon used in the present invention on the discharge capacity and cycle life characteristics were examined.
The negative electrode material was 5% by weight of fibrous carbon, 5% by weight of artificial graphite, and 5% by weight of polyvinylidene fluoride as a binder with respect to 85% by weight of the particles or composite particles composed of only the Si phase used in Example 1.
% By weight. First, d
Table 4 shows the results of evaluating the 002 value.

[0069]

[Table 4]

As shown in Table 4, when the d 002 value exceeds 3.70 °, the electron conductivity of the fibrous carbon decreases, so that sufficient electron conductivity cannot be provided between the particles and the carbon is isolated from the electron conduction network. No matter what the size and length of the fibrous carbon are used, the initial discharge capacity is smaller than that of the present invention as in Comparative Examples 10 and 11, The cycle life has also deteriorated considerably.
Therefore, it was found that it is preferable to use fibrous carbon having a d 002 value of 3.35 ° to 3.70 °.

Next, the change in the length and diameter of the fibrous carbon is
The effects on discharge capacity and cycle life characteristics were studied. The d 002 value of the fibrous carbon used is about 3.40 °. The results are shown in (Table 5).

[0072]

[Table 5]

According to Table 5, when the length of the fibrous carbon is as short as less than 1 μm, the electrical connection between the particles is not good, and the electron conduction network for imparting an electrochemical reaction to all the particles is not provided. Particles that could not be constructed and did not participate in the electrochemical reaction were formed, and the discharge capacity in the initial cycle was considerably reduced as in Comparative Examples 16 to 21. Further, when the length of the fibrous carbon exceeds 20 μm, since the fibrous carbon is entangled and aggregated, the dispersibility of the fibrous carbon with respect to the particles is not good, and the contact point between the particles and the fibrous carbon is reduced. As a result, particles that could not participate in the electrochemical reaction were formed, and the discharge capacity in the initial cycle was considerably reduced as in Comparative Examples 22 to 27. Also, the diameter of fibrous carbon is 0.
When it exceeds 5 μm, the ratio of the fine thread-like fibrous carbon decreases, and the surface including the diametric direction is more likely to come into contact with the particles than the surface including the length direction, but the surface including the diametric direction has flexibility. Since there is not much, and the state is close to a plane, the effect of increasing the number of contact points of the present invention is hardly exhibited, and both the initial discharge capacity and the cycle life are slightly reduced as in Comparative Examples 12 to 15. Although 5% by weight of fibrous carbon and 5% by weight of artificial graphite were used, the content of carbonaceous material including fibrous carbon in the whole negative electrode material was in the range of 5% by weight or more and 80% by weight or less. Content of fibrous carbon in the anode material
Even in the range of 1% by weight or more and 20% by weight or less, the same result as in the present example was obtained.

Example 4 The effect of the content of fibrous carbon in carbonaceous material containing fibrous carbon on discharge capacity and cycle life characteristics was examined. As fibrous carbon, d
002 value is about 3.40Å, length is about 10μm, diameter is 0.25μm
Something was used. The negative electrode material was used in Example 1.
With respect to 45% by weight of particles or composite particles composed only of Si phase,
The structure is such that 50% by weight of a carbonaceous material containing fibrous carbon and 5% by weight of polyvinylidene fluoride as a binder are mixed.

[0075]

[Table 6]

According to Table 6, the content of fibrous carbon in the carbonaceous material was 1% by weight or more and 20% by weight with respect to the whole negative electrode material.
In the examples of the present invention in the following ranges, the cycle life of Ni-52wt% Si particles shows 92% or more, and the cycle life of Si particles shows 21% or more. It became good.

The content of the fibrous carbon was 1 to the negative electrode material.
In the case of less than 10% by weight, Ni-52wt% Si particles as in Comparative Example 28 increase the number of contact points due to the fibrous carbon and utilize the large restoring force, but the effect of the present invention is less likely to be exerted. Since the volume change of the crystal phase of the group accompanying the expansion and contraction occurs only within 2 times, the cycle life was slightly deteriorated as compared with the examples of the present invention.

On the other hand, in Si, the volume change accompanying the occlusion and release of Li is larger expansion and contraction than that of the Ni-52 wt% Si particles. Therefore, the volume of the fibrous carbon with respect to the volume of the particles is too small. In the case where the effect of the present invention utilizing the increase of the contact points and the large restoring force is hardly exhibited by using the method, the charge / discharge capacity was significantly reduced as compared with the example of the present invention as in Comparative Example 29. In Comparative Examples 30 and 31, the cycle life was good, but the volume per unit volume of carbonaceous material was too large with respect to the volume of the particles, and the capacity per volume could not be increased. The discharge capacity was small.

Although the carbonaceous material containing fibrous carbon was used in an amount of 50% by weight, the same result as in the present example was obtained when the amount was in the range of 5% by weight to 80% by weight. Also, in the negative electrode material fixed with only fibrous carbon, the same tendency as that of the inventive examples and comparative examples in Table 6 was obtained. Further, in this embodiment, the case where particles composed only of the Si phase or particles coated with the Si phase particles are used is shown, but the same effect is obtained when Zn is used in addition to Si.

[0080]

According to the present invention, Si particles, or one or more Si particles
Phase particles are particles that are at least partially coated with a solid solution or intermetallic compound phase containing Si, and some or all of the particles are fixed with carbonaceous material containing fibrous carbon, and Since the particles are electrically connected to each other by the fibrous carbon, even if the particles repeatedly expand and contract with electrochemical occlusion and release of Li, the contact state between the particles and the conductive agent is maintained. And a negative electrode material for a non-aqueous electrolyte secondary battery having improved charge-discharge cycle life characteristics and a non-aqueous electrolyte secondary battery provided with the negative electrode.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view of a test cell for evaluating a negative electrode for a non-aqueous electrolyte secondary battery of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Battery case 2 Cover 3 Current collector 4 Metal lithium electrode 5 Negative electrode material molding electrode 6 Separator 7 Gasket

Continued on the front page (72) Inventor Yoshiaki Nitta 1006 Kazuma Kadoma, Kazuma-shi, Osaka Matsushita Electric Industrial Co., Ltd.F-term (reference) AA03 AS10 BB11 EE06 HH01 HH03 HH05 5H029 AJ05 AK03 AL01 AL11 AM03 AM04 AM05 AM07 BJ03 BJ16 DJ12 DJ15 DJ16 EJ04 HJ01 HJ05 HJ07 HJ12

Claims (8)

    [Claims]
  1. Claims 1. There is a composite particle in which a Si phase particle is at least partially covered with a solid solution containing Si or an intermetallic compound phase, or a particle composed only of a Si phase, and a part or the entire surface of the particle. Is a negative electrode material for a non-aqueous electrolyte secondary battery, in which fibrous carbon is fixedly arranged, and these particles are electrically joined by the fibrous carbon.
  2. 2. The negative electrode material for a non-aqueous electrolyte secondary battery according to claim 1, wherein one or more Si phase particles are present in the composite particles.
  3. (3) at least 10% of the total surface area of the particles containing Si,
    The negative electrode material for a non-aqueous electrolyte secondary battery according to claim 1, wherein less than 0% is fixed with carbonaceous material containing fibrous carbon.
  4. 4. The fibrous carbon has d 002 of 3.35Å3.703.7.
    , The length is 1 μm or more, 20 μm or less, and the diameter is 0.1
    The negative electrode material for a non-aqueous electrolyte secondary battery according to claim 1, wherein the negative electrode material is in the form of a fiber having a size of not less than μm and not more than 0.5 μm.
  5. 5. The negative electrode material for a non-aqueous electrolyte secondary battery according to claim 1, further comprising a carbonaceous material other than fibrous carbon.
  6. 6. The negative electrode for a non-aqueous electrolyte secondary battery according to claim 5, wherein the amount of carbonaceous material containing fibrous carbon is in a range of 5% by weight or more and 80% by weight or less based on the whole negative electrode material. material.
  7. 7. The nonaqueous electrolyte secondary battery according to claim 5, wherein the amount of fibrous carbon in the carbonaceous material containing fibrous carbon is in a range of 1% by weight or more and 20% by weight or less based on the whole negative electrode material. For negative electrode material.
  8. 8. A positive electrode capable of reversible electrochemical reaction of lithium ions, a non-aqueous electrolyte in which a lithium salt is dissolved in an organic solvent, and a negative electrode material according to claim 1. Non-aqueous electrolyte secondary battery comprising a negative electrode.
JP34290798A 1998-12-02 1998-12-02 Nonaqueous electrolyte secondary battery and negative electrode material thereof Expired - Lifetime JP4218098B2 (en)

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