JP2015032447A - Negative electrode material and lithium secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide: a negative electrode material obtained by mixing carbon conventionally used as a negative electrode material and scale-like fine powder that achieves further improvement in performance of carbon as a negative electrode material and has properties capable of occluding/eliminating silicon; and a lithium secondary battery using the negative electrode material.SOLUTION: A negative electrode material can be obtained by mixing carbon and scale-like fine powder obtained by finely crushing one of a thin film (A) or a thin film (B). The thin film (A) is formed of (a) a layer of one of simple substances of a metal simple substance, an alloy or a metal compound which can reversibly occlude/eliminate lithium, or a lamination layer of a plurality thereof. The thin film (B) is formed by using both layers to be laminated in two layers or more in total, both layers including (a) a layer of one of simple substances of a metal simple substance, an alloy or a metal compound which can reversibly occlude/eliminate lithium and (b) a layer of one of simple substances of a metal simple substance or an alloy which cannot reversibly occlude/eliminate lithium.

Description

  The present invention relates to a negative electrode material and a lithium secondary battery using the negative electrode material. Specifically, carbon used for a negative electrode of a lithium secondary battery can make the life of the lithium secondary battery longer. The present invention relates to a negative electrode material to which scaly fine powder is added, and a lithium secondary battery using the negative electrode material.

  Since the lithium secondary battery was developed and announced for commercial use, it quickly became the mainstream of secondary batteries. This is because the standard voltage of the lithium secondary battery is 3.7 V, that is, it has an advantage that it is about 3 times that of the nickel cadmium battery and about 2 times that of the lead acid battery. Furthermore, it has a high energy density compared to other secondary batteries, low internal resistance, little decrease in battery capacity due to charging / discharging, that is, charging / discharging cycle characteristics are higher than other systems, that is, battery life is long, The fact that it has the advantage of being widely distributed is also a factor.

  Nowadays, a higher capacity is required for this lithium secondary battery. If the capacity is increased, the battery life of smartphones and other devices that use the battery will be longer, or it can contribute to the thinning of the battery. Therefore, it is required to have a high capacity.

And the big factor which determines the characteristic of such a battery is selection of negative electrode material.
Currently, carbon materials such as graphite are mainly used as the negative electrode material. Incidentally, the theoretical capacity of graphite is 372 mAh / g.

  Since the lithium secondary battery using carbon as a negative electrode has been commercialized, the energy density of the lithium secondary battery has improved more than twice. Currently, so-called mobile phones and laptop computers using lithium secondary batteries are used. While mobile devices are becoming more sophisticated, there is a problem that improving the energy density of conventional lithium secondary batteries using carbon as a negative electrode has almost reached its limit. That is, when carbon is used as the negative electrode, while the cycle characteristics are good, there arises a problem that it cannot be increased until the charge / discharge capacity is required.

  Therefore, instead of carbon materials, studies have been made to use metals or alloys that alloy with lithium, such as aluminum, zinc, magnesium, tin, lead, and silicon. Among them, silicon is extremely large with a theoretical capacity of 4200 mAh / g, and is expected as a high-capacity negative electrode that changes to carbon.

  As a specific application example of silicon, for example, a copper plate is used as a current collector, and a thin film amorphous silicon or microcrystalline silicon is laminated on the surface of the copper plate by a chemical vapor deposition method (CVD method) or the like. Technology has been developed.

  However, when silicon is used for the negative electrode, as the silicon negative electrode repeatedly expands and contracts as lithium is absorbed and desorbed, the cycle characteristics can be reduced by making the particles finer by cracking of the silicon particles or peeling from the copper plate used as the current collector. There was a problem of being bad.

  In other words, if such a phenomenon is repeated, the negative electrode may eventually be deformed, resulting in a decrease in the energy density of the battery, and the silicon that is laminated on the copper plate by repeating expansion and contraction. It is conceivable that the thin film will eventually be detached from the copper plate, resulting in deterioration of the cycle characteristics of the battery. That is, when silicon is used for the negative electrode, the cycle characteristics cannot be said to be preferable, and it cannot be said that the cycle characteristics are better than that of carbon.

  Therefore, for example, it is possible to use carbon and silicon alloyed, but in this case, they are not necessarily uniformly alloyed as desired, and the work of alloying is complicated. There was a problem.

  Thus, for example, in the invention described in Patent Document 1, the amount of occlusion of lithium is suppressed by using a thin film in which copper is dissolved in silicon as the negative electrode material layer, and as a result, the expansion of the negative electrode material when lithium is occluded / desorbed. In other words, a material that suppresses deterioration of the negative electrode material due to expansion and contraction of the silicon negative electrode having a thin silicon film and has good cycle characteristics is disclosed.

  In Patent Document 2, the surface of particles having a structure in which silicon microcrystals are dispersed in a silicon-based compound is coated with carbon, so that deterioration of the negative electrode material due to expansion and contraction of silicon is suppressed, and a large capacity is charged. A discharge capacity is disclosed.

JP 2002-289177 A JP 2004-47404 A

  However, in the invention described in Patent Document 1, a thin film in which silicon is dissolved in copper is laminated on the surface of the current collector. Although the effect may be avoided, it is based on the premise that silicon does not actively occlude lithium and presents a problem that the energy density cannot be maintained high. In addition, it is necessary to work to dissolve silicon in copper before laminating a thin film on the surface of the current collector, and an extra step is imposed in actual negative electrode production, which is not preferable. Moreover, even if silicon is dissolved in copper, it is not certain whether or not they are ideally evenly distributed and present, that is, the effect that was initially expected to be unevenly distributed between silicon and copper in the thin film. There was also a problem that it could not be obtained.

  On the other hand, when considering from the viewpoint of energy density, when a silicon negative electrode obtained by thinning silicon is used as a negative electrode of a practical lithium secondary battery, a film thickness of about 5 μm is required for the silicon thin film. However, when the film thickness is increased, the cycle characteristics of the silicon negative electrode are drastically deteriorated. As a result, it is very difficult to put a lithium secondary battery using a silicon thin film into practical use. In the invention described in Patent Document 1, although it is disclosed that the amount of occlusion of lithium is suppressed by using a thin film in which copper is solid-dissolved in silicon and the expansion of the negative electrode material is suppressed, In other words, the high energy density of silicon could not be used effectively, which was still a problem.

  In Patent Document 2, an advanced technique of coating the surface of silicon particles with carbon is required, and if the surface cannot be uniformly coated, there is a problem that the reaction of silicon particles becomes non-uniform and the electrical characteristics are affected.

  Therefore, the present invention has been made in view of such problems, and the object thereof is silicon that can further improve the performance of carbon as a negative electrode material in order to obtain a lithium secondary battery having excellent cycle characteristics. Is to provide a negative electrode material obtained by mixing a scaly fine powder having a property of occluding and desorbing carbon, and carbon that has been conventionally used as a negative electrode material, and a lithium secondary battery using the negative electrode material. .

  In order to solve the above problems, the negative electrode material according to claim 1 of the present invention is any one of (A) (a) simple metal, alloy, or metal compound capable of reversibly occluding and desorbing lithium. (B) (a) a single metal layer, an alloy, or a metal compound capable of reversibly occluding and desorbing lithium; and (b) ) Any one of the thin films formed by laminating a total of two or more layers using both a single metal layer or a single alloy layer that does not allow lithium to be reversibly occluded / desorbed. It is obtained by mixing flaky fine powder obtained by finely pulverizing a thin film and carbon.

  The negative electrode material according to claim 2 of the present invention enables (A) (a) lithium to be reversibly occluded / desorbed from the surface of the release layer of the polymer resin film formed by laminating a release layer made of resin. A thin film made of a single metal layer, an alloy, or a metal compound, or a laminate of a plurality of single metals, or (B) (A) a simple metal, alloy, or metal compound that can reversibly store and desorb lithium. The total number of layers is two or more, using both the layer of any one of the above, and (b) the layer of any of the metal alone or the alloy that does not allow lithium to be reversibly occluded / desorbed. It is possible to dissolve the resin, and a laminate manufacturing process for obtaining a laminate by laminating any one of the thin films thus laminated on the surface of the release layer by vacuum vapor deposition or sputtering. The product while using a solvent Performing a thin film layer peeling step for peeling the thin film from the body, a fine grinding step for finely grinding the thin film present in the solvent, and a solvent removing step for removing the solvent after the fine grinding step. It is obtained by mixing flaky fine powder obtained by the above and carbon.

  Invention of Claim 3 of this invention is negative electrode material of Claim 1 or Claim 2, Comprising: From the edge in the substantially planar view of the said scaly fine powder of the said scaly fine powder. The average major axis, which is the average value of the entire scale-like fine powder of the longest length among the end lengths, is 0.1 μm or more and 100 μm or less, and is substantially in a side view of the one scale-like fine powder. The average thickness, which is the average value of the entire scale-like fine powder, is 0.01 μm or more and 5 μm or less.

  Invention of Claim 4 of this invention is negative electrode material of any one of Claim 1 thru | or 3, Comprising: The ratio of the said average major axis of the said scaly fine powder and the said average thickness, That is, the aspect ratio represented by the average major axis / average thickness is 5 or more.

The invention according to claim 5 of the present invention is the negative electrode material according to any one of claims 1 to 4, wherein the thin film is (a) a substance capable of inserting and extracting lithium. It is a thin film of a single layer or a plurality of layers using any one of the groups shown in the following (1) to (3).
(1) Metal simple substance: silicon, tin, germanium, aluminum, indium, magnesium, calcium, lead, arsenic, antimony, bismuth, silver, gold, zinc, cadmium (2) Alloy: tin-copper alloy (Cu5Sn5), silicon- Magnesium alloy (Mg2Si), iron-tin alloy (Sn2Fe), tin-nickel alloy (NixSn), tin-cobalt alloy (CoxSn), silicon-nickel alloy (NiSi), silicon-iron alloy (FeSi), nickel-magnesium alloy (MgxNi), antimony-tin alloy (SnSb), antimony-indium alloy (InSb), silver-tin-antimony alloy (AgSnSb),
(3) Metal compound: Oxide or sulfide mainly composed of a simple metal shown in (1), or transition metal oxide or sulfide

The invention according to claim 6 of the present invention is the negative electrode material according to any one of claims 2 to 5, wherein the thin film is (i) a substance that does not allow lithium to be occluded / desorbed. Any one of the following groups (4) to (5) is used.
(4) Metal simple substance: Titanium, manganese, iron, nickel, chromium, copper, zirconium, molybdenum, tantalum, tungsten (5) Alloy: Alloy mainly composed of metal simple substance shown in (4)

  Invention of Claim 7 of this-application invention is negative electrode material of any one of Claim 1 thru | or 6, Comprising: The mixing ratio of the said scaly fine powder and the said carbon is the said, The scaly fine powder is characterized by being less than 40% of the whole by weight.

  Invention of Claim 8 of this-application invention is negative electrode material of any one of Claim 1 thru | or 6, Comprising: The mixing ratio of the said scaly fine powder and the said carbon is the said, The scaly fine powder is characterized by being 40% or more and 60% or less of the whole by weight.

  Invention of Claim 9 of this invention is negative electrode material of any one of Claim 1 thru | or 6, Comprising: The mixing ratio of the said scaly fine powder and the said carbon is the said, Carbon is less than 40% of the total weight ratio.

  An invention relating to a lithium secondary battery according to claim 10 of the present invention is characterized by using the negative electrode material according to any one of claims 1 to 9.

  As described above, the negative electrode material according to the present invention can be obtained by adding scaly fine powder that can reversibly absorb and desorb lithium to carbon that has been conventionally used as a negative electrode material for lithium secondary batteries. The cycle characteristics of the lithium secondary battery can be improved. In addition, when silicon or a silicon-based material is used for the negative electrode material in an attempt to expand the charge capacity rather than carbon, the negative electrode material has a too large volume expansion coefficient, that is, the negative electrode material has a volume change that is too severe. Although there was a problem of breakage of the lithium secondary battery, if it is a negative electrode material according to the present invention, carbon that has been used conventionally may be mainly used, so it can be said that safety has been established, so it is easy Can be solved.

  Embodiments of the present invention will be described below. The embodiment shown here is merely an example, and is not necessarily limited to this embodiment.

(Embodiment 1)
A negative electrode material according to the present invention will be described as a first embodiment. In the following description, it is assumed that the negative electrode material is used for a lithium secondary battery.

The negative electrode material according to the present embodiment has the following configuration. That is,
(A) (A) It is obtained by mixing a thin film made of a single metal, an alloy, or a metal compound that can occlude and desorb lithium reversibly, or a stack of multiple metals and carbon. It will be.

  Hereinafter, the description will be made sequentially. In the present invention, the individual shapes of the scaly fine powder are characterized in that they are scaly by simply pulverizing the thin film. That is, it can be said that it is a fine powder with a flat and flat surface that looks like a fish scale when literally enlarged.

First, the scaly fine powder will be described.
In the present embodiment, the scaly fine powder is obtained by finely pulverizing a thin film made of any one of a single metal, an alloy, and a metal compound. Even if selected, the substance is a substance capable of occluding and desorbing lithium. There are various kinds of such substances, and examples include the following.

That is,
(1) Examples of simple metals include silicon, tin, germanium, aluminum, indium, magnesium, calcium, lead, arsenic, antimony, bismuth, silver, gold, zinc, cadmium, etc.
(2) As alloys, tin-copper alloy (Cu5Sn5), silicon-magnesium alloy (Mg2Si), iron-tin alloy (Sn2Fe), tin-nickel alloy (NixSn), tin-cobalt alloy (CoxSn), silicon-nickel Alloy (NiSi), silicon-iron alloy (FeSi), nickel-magnesium alloy (MgxNi), antimony-tin alloy (SnSb), antimony-indium alloy (InSb), silver-tin-antimony alloy (AgSnSb), etc. ,
Further, (3) a metal compound, which is an oxide or sulfide mainly composed of a single metal shown in (1), or a transition metal oxide or sulfide, etc.
Is mentioned.

  In the following description of the present embodiment, it is assumed that a silicon thin film made of silicon alone is finely pulverized. The shape of the thin film fine powder obtained by finely pulverizing the silicon thin film is basically scaly as described above.

Here, the average thickness and the average major axis of the scale-like fine powder will be described.
The fine powder according to the present embodiment literally has a scaly appearance. In other words, each is in the form of a very fine powder, but almost all of them have a scaly appearance when observed individually. This is because it is obtained by finely pulverizing the thin film, and naturally, the crushed individual substances are flat.

  Further observation of the individual scaly powders reveals that the length from end to end is quite different from one end to another in a substantially plan view. The average value in the maximum length of the scaly fine powder, that is, the average major axis that is the average value of the length from end to end, and considering the range of suitable values in the present embodiment, In such a scaly fine powder, it is preferably 0.1 μm or more and 100 μm or less. More preferably, they are 0.1 micrometer or more and 50 micrometers or less, More preferably, they are 0.1 micrometer or more and 10 micrometers or less.

  Also, the thickness of the scale-like metal fine powder in a side view is naturally different in thickness, and even if it is a single metal fine powder, if it is enlarged and observed, it has a completely uniform thickness. However, the average thickness obtained by averaging the individual thicknesses is preferably 0.01 μm or more and 5 μm or less in the present embodiment. More preferably, it is 0.01 μm or more and 3 μm or less.

  And if it is set as the flaky fine powder in which the aspect ratio of the flaky fine powder, that is, the average major axis / average thickness is 5 or more, more preferably 10 or more, the shape of the flaky fine powder is preferable in the present embodiment. It means having a flat shape.

  The reason why the numerical ranges of the average major axis, the average thickness, and the aspect ratio are preferably as described above will be separately described later.

  As described above, in this embodiment, by determining the numerical range regarding the average major axis, average thickness, and aspect ratio of the scaly fine powder in this way, it is not too small, and is not too large as necessary. It is a scaly fine powder.

  The average major axis and the average thickness of the metal fine powder described above were determined by the following method. It should be noted that the present invention is not limited to this embodiment, and all the same is true in the present invention.

  First, the average major axis was measured using a laser diffraction / scattering particle size distribution analyzer, and the 50% average particle diameter (median diameter) obtained as a result was taken as the average major axis.

  The average thickness is the same as the thickness of the scaly fine powder as it is in the laminating method used when producing the scaly fine powder according to this embodiment described later. As a thickness measurement, a plurality of laminated portions were measured by a fluorescent X-ray analyzer, and a value obtained as an average value was taken as an average thickness.

The scaly fine powder described above is obtained, for example, as follows.
First, a release layer made of a resin is laminated on the surface of a polymer resin film that is a base film. At this time, it should be noted that the release layer is not necessarily provided depending on the substrate film to be selected.

  Next, the above-described layer (silicon in this embodiment) of any one of a metal simple substance, an alloy, or a metal compound capable of reversibly occluding and desorbing lithium as a thin film layer is used as a thin film layer, or A laminate manufacturing process is performed in which a laminate is obtained by laminating the surface of the release layer by a so-called dry coating method such as sputtering.

  Next, the thin film layer peeling process which peels a thin film from a laminated body is performed with respect to the obtained laminated body, using the solvent which can dissolve resin which forms the peeling layer mentioned above.

  Then, a fine pulverization step for finely pulverizing the thin film present in the solvent is performed, and then a solvent removal step for removing the solvent is performed to obtain the scaly fine powder according to the present embodiment.

This procedure will be described.
As the base film, a conventionally known polymer resin film may be used. For example, a polyethylene terephthalate (PET) film, a polypropylene film, a polyamide film, and the like can be considered. Here, a PET film having a thickness of 25 μm is used. . By the way, if it is a PET film, its handling and the like are well known and used because it is easy. Further, the thickness of the PET film is not particularly limited, but a thickness of about 12 μm or more and 100 μm or less is preferable from the viewpoint of operability described below.

  In this embodiment, the base film is not limited to a PET film. For example, if a polymer resin film resistant to a solvent capable of dissolving a release layer described later is used as the base film. For example, since the base film is not dissolved or damaged by the solvent even after the thin film layer peeling step described later, it can be used again as a base film, that is, a reusable base material. It should be noted that it can be used as a film and can be made suitable.

  A release layer is laminated on the surface of the PET film. This release layer must be easily dissolved by a specific solvent in the thin film layer peeling step described later. The thickness of the release layer is not particularly limited as long as it is a level that can be dissolved in a specific solvent as described later. It is not limited. In the present embodiment, it is considered that a release layer that is soluble in an organic solvent such as butyl acetate or water, such as cellulose acetate butyrate (CAB), is suitable. Then, CAB shall be used. This CAB is laminated on the surface of the PET film by a so-called known wet coating method such as a gravure coating method. More specifically, a PET film on which CAB is laminated is obtained by laminating CAB on the PET film by a gravure coating method while conveying the PET film by roll-to-roll.

  The thickness of the release layer by CAB may be set as appropriate. In short, it is not so thin that it does not function sufficiently as a release layer, and is too thick so that it does not adversely affect the thin film layer peeling process described later. It may be set as such a thickness.

  If a film obtained by laminating a release layer made of CAB on the surface of the PET film can be prepared, then a laminate manufacturing process for laminating silicon on the surface of the release layer is performed.

  Here, as a method of laminating silicon, any of a group of conventionally known dry coating methods may be used, but in this embodiment, a vacuum deposition method generally used is used.

  When laminating silicon, the thickness of the silicon thin film layer may be 0.01 μm or more and 5 μm or less, and more preferably 0.01 μm or more and 3 μm or less. This is because, as will be described later, the scaly fine powder according to this example is made from a silicon thin film layer that is laminated in this laminate manufacturing process. That is, the silicon thin film layer is peeled off from the substrate film and finely pulverized until it becomes a fine powder, whereby a scaly fine powder is obtained. The thickness of the obtained scaly fine powder is 0.00. Since it is desired that the thickness is 01 μm or more and 5 μm or less, more preferably 0.01 μm or more and 3 μm or less, the thickness at the time of first stacking may be set within the above range.

  Next, the thin film layer peeling process which peels a thin film from a laminated body is performed with respect to the obtained laminated body, using the solvent which can dissolve resin which forms the peeling layer mentioned above. In the present embodiment, an organic solvent is used as the solvent, but this may be selected according to the resin forming the release layer, and water may be used as the solvent, for example. In any case, what is necessary is just to select the thing according to the peeling layer used. By passing through this step, a solution in which the thin film peeled in the solvent is obtained.

  Next, a fine pulverization step for finely pulverizing the thin film present in the solvent is performed. The pulverization method in the fine pulverization step is not particularly limited or a special method is selected in the present embodiment, and as a result, the pulverization method only needs to be able to satisfy the numerical conditions such as the size of the flaky fine powder described above. .

Finally, a solvent removal step for removing the solvent is performed.
At this stage, the flaky fine powder is present in the solvent, but in order to obtain the flaky fine powder itself, it is necessary to remove the solvent once. For example, a method is conceivable in which the solvent is first evaporated using a high-temperature bath, then transferred to a vacuum dryer and dried for about 1 hour to completely evaporate the solvent. In this way, it may be possible to remove the solvent by heating and vacuum drying, or it may be possible to remove the solvent by filtering the dispersion, but in any case, there are no particular restrictions on the method for removing the solvent. Not.

  Through the above steps, a scaly fine powder is obtained in the present embodiment. And the obtained scaly fine powder and carbon are mixed. In addition, it mixes with the scaly fine powder and carbon obtained by this Embodiment, and obtaining a negative electrode material for lithium secondary batteries using it is mentioned later.

(Embodiment 2)
The scaly fine powder according to the first embodiment described above is assumed to be a single layer made of silicon alone. Next, a case different from this will be described.

  When the scale-like fine powder obtained by the invention of the present application is formed as a lithium secondary battery electrode with carbon by using the inventors' research, the fine powder obtained by a thin film that is a single layer of silicon alone as the scale-like fine powder In addition to this, it was found that the thin film was prepared by laminating two or more different types of materials that can reversibly absorb and desorb lithium. It was found that finely pulverized fine powder can obtain the same effects as those of the first embodiment.

  Therefore, this case will be described as a second embodiment. Note that the description of the same basic components as those of the first embodiment described above is omitted.

  In the first embodiment, a single layer of silicon is laminated on the surface of the release layer having a structure of base film (PET film) / release layer, and finally, a fine powder is obtained using this. As described above, in the present embodiment, the layer formed on the surface of the release layer is not a single layer but a plurality of layers of two or more layers.

  In the case of this embodiment, the material to be selected is a material capable of occluding and desorbing lithium in any layer, and these are as described in the first embodiment.

  For example, a thin film having a configuration of “silicon / tin” may be laminated on the surface of the release layer side having a configuration of “PET film / release layer”, and may also be “silicon / tin-copper alloy”. It may be “tin / silicon” or “tin-copper alloy / silicon”. Further, the number of layers may be three, such as “silicon / tin / silicon”, or a plurality of layers may be stacked in the same manner.

  The method of laminating these on the release layer side of the PET film / release layer may be by a conventionally known so-called dry coating method, and is not particularly limited. Here, the laminated thin film will be further described as having a structure of “silicon / tin”.

  However, it is preferable that the average thickness of the layer formed of the silicon / tin thin film is 0.01 μm or more and 5 μm, more preferably 0.01 μm or more and 3 μm or less, as in the first embodiment. Similarly, the average major axis of the thin film fine powder obtained by finely pulverizing the thin film layer is also 0.1 μm or more and 100 μm or less, more preferably 0.1 μm or more and 50 μm or less, and further preferably 0.1 μm or more and 30 μm or less. The aspect ratio is also 5 or more, more preferably 10 or more. That is, even if the layer configuration is changed, the same effect cannot be obtained unless the overall thickness is the same as in the first embodiment. Thus, for example, a combination of “silicon / tin”, in which the thickness of the silicon layer is 2 μm and the thickness of the tin layer laminated thereon is 1 μm, or the silicon layer is 0.1 μm. A combination of a tin layer of 2.5 μm may be used.

  And the scaly fine powder concerning this Embodiment is obtained by implementing the process similar to 1st Embodiment. How to use the obtained scaly fine powder will be described later.

(Embodiment 3)
Further, a scaly fine powder having a configuration different from that of the first embodiment and the second embodiment will be described.

  In the first embodiment, the scaly fine powder is a single layer using only one kind of substance capable of reversibly occluding and desorbing lithium, such as silicon. In the second embodiment, for example, silicon / It was obtained by finely pulverizing each of a plurality of layers in which two or more substances capable of reversibly occluding and desorbing lithium, such as tin, were used. Even if it is obtained by pulverizing a thin film formed by laminating a substance that cannot reversibly store and desorb lithium, simultaneously with a substance that can reversibly store and desorb lithium, the same effect can be obtained. I found out. In this embodiment, this case will be described. Even in this embodiment, the description of the same parts as those in the first and second embodiments is omitted.

  In the first and second embodiments, the base material film (PET film) / peeling layer is configured such that silicon is laminated as a single layer on the peeling layer side surface, and two or more types of lithium are further added. In the present embodiment, a case where a plurality of reversibly occluding and desorbing substances are stacked has been described. In this embodiment, (a) a substance capable of reversibly occluding and desorbing lithium and (b) lithium. A scale-like fine powder dispersion is obtained using a thin film in which a substance that cannot be reversibly occluded and desorbed simultaneously.

  Here, (a) the substance capable of reversibly occluding and desorbing lithium is as described above.

(B) As a substance that does not reversibly absorb and desorb lithium,
(4) Metal simple substance: Titanium, manganese, iron, nickel, chromium, copper, zirconium, molybdenum, tantalum, tungsten (5) Alloy: It is considered to use an alloy mainly composed of a metal simple substance shown in (4).

  Hereinafter, if (a) a substance capable of reversibly occluding and desorbing lithium is ◯, and (b) a substance not reversibly occluding and desorbing lithium is x, the thin film in the present embodiment May be “O / X”, “O / X / O”, “X / O / X”, or “O / O / X”. (Adjacent circles are different) and may be “× / × / ◯”. (The adjacent Xs are different.) In short, the thin film in this embodiment is composed of a plurality of layers, and at least one (a) lithium is occluded reversibly in the plurality of layers. It is characterized by satisfying the condition that a substance that can be desorbed and a substance that cannot reversibly occlude and desorb one or more (a) lithiums are used simultaneously. In this embodiment, “silicon / nickel / silicon” (“◯ / × / ◯”) is assumed.

  A method for sequentially laminating these substances on the release layer side of the PET film / release layer may be based on a conventionally known so-called dry coating method, and is not particularly limited.

  Also in the present embodiment, as described in the second embodiment, the average thickness of the thin film layer composed of a plurality of layers of silicon / nickel / silicon is 0 as in the first embodiment. The thickness is preferably 0.01 μm or more and 5 μm, more preferably 0.01 μm or more and 3 μm or less. This is also the same, but the thickness of each layer may be the above-mentioned total thickness, that is, 0.01 μm or more and 5 μm or less, more preferably 0.01 μm or more and 3 μm or less. The thickness of each layer may be the same 0.3 μm, the thickness of the silicon layers at both ends may be 0.5 μm, the thickness of the nickel layer may be uneven, such as 0.3 μm.

  Similarly, the average major axis of the flaky fine powder obtained by finely pulverizing the thin film layer is similarly 0.1 μm or more and 100 μm or less, more preferably 0.1 μm or more and 50 μm or less, and further preferably 0.1 μm or more and 30 μm or less. The aspect ratio is also preferably 5 or more, more preferably sub-10 or more.

  Then, by performing the same steps as in the first embodiment, a scaly fine powder having a configuration of “silicon / nickel / silicon” is obtained. How to use the obtained scaly fine powder will be described later.

(Embodiment 4)
As described above, the flaky fine powder according to the present invention has been described by dividing it into three cases. In the present invention, the flaky fine powder thus obtained and carbon are mixed to obtain a paste, which is used as a copper plate surface. To obtain a negative electrode material for a lithium secondary battery. Therefore, in the present embodiment, this negative electrode material will be described. In the present embodiment, the same applies to any scale-like fine powder. The explanation will be continued assuming a scaly fine powder (hereinafter referred to as Si fine powder) obtained using a thin film of silicon alone, and assuming that the carbon is graphite.

First, the paste will be explained.
This paste is obtained by mixing Si fine powder and carbon together through a binder, and is obtained as an example as follows.

  First, each is weighed so that the weight ratio of Si fine powder to carbon is 15 to 75, and they are mixed as appropriate. About 10 to 20 minutes is preferable. On the other hand, what was made into the aqueous solution so that carboxymethylcellulose may become 5 wt% as a binder is prepared. Here, the carboxymethylcellulose aqueous solution is weighed so that the weight ratio of carboxymethylcellulose and Si fine powder + carbon is 10:75. And a paste is obtained by mixing a binder and the mixture obtained by the above-mentioned mixing. In addition, a mortar may be used for mixing, and it can be said that mixing with a kneader is suitable for achieving uniformity. In addition, the weight ratio described here is a ratio that seems to be suitable as a result of various attempts by the inventors.

  A paste obtained by fixing the obtained paste to a copper plate by a conventionally known method is used as a negative electrode. Since the paste contains Si fine powder and carbon, when charging / discharging the lithium secondary battery, a circuit is formed that conducts electrons absorbed and desorbed from the Si fine powder to the copper plate and supplies current to an external load. Will come to be. Further, in order to bind carbon and Si fine powder to each other, a binder is also mixed together, but the binder also has an object of bonding a copper plate and a paste. Furthermore, for the phenomenon that the copper plate and Si fine powder generated during the process of charging and discharging the lithium secondary battery expand and contract, the mutual bonding of the Si fine powder and the adhesion between the current collector plate and the Si fine powder layer are still It also has the purpose of maintaining and improving the manufacturing process when making the Si fine powder into a paste, that is, preventing each element from being separated from where it is working while it is in powder form. .

  As a binder that achieves such a purpose, polyvinylidene fluoride, carboxymethylcellulose or an alkali metal salt thereof, polyacrylic acid and an alkali metal salt thereof, or a mixture thereof may be used. As described above, carboxymethyl cellulose is used in the form. And using this, Si fine powder and carbon are mixed and the paste which has viscosity is obtained.

  On the other hand, the copper plate as the current collector is sufficiently dried in advance. And the obtained paste is apply | coated to the dried copper plate surface by methods, such as a doctor blade method, Then, this is fixed by performing vacuum drying for a fixed time in a high temperature environment, and a negative electrode is obtained.

  When the obtained negative electrode material is used as the negative electrode of a lithium secondary battery, the cycle characteristics of the lithium secondary battery can be improved as compared with the case where a negative electrode made of a conventional carbon simple substance is used.

The electrode according to this embodiment will be further described in comparison with a conventional example.
In the conventional negative electrode, since carbon is used alone, the cycle characteristic is preferable, but the energy density is low. In order to cope with this problem, it has been proposed to use silicon or a silicon-based alloy as a high-capacity negative electrode. However, since the volume change of silicon is severe, the above-mentioned problems, particularly many times, have been satisfied. There is a problem that the negative electrode made of silicon is easily damaged as a result of being unable to withstand expansion and contraction due to repeated discharge, and thus the cycle characteristics of the lithium secondary battery are deteriorated.

  However, in the case of the negative electrode material according to the present embodiment, since a flaky fine powder made of silicon is first manufactured and then obtained by mixing this with carbon, such a negative electrode material is difficult to break. ing.

  That is, even if the individual Si fine powder repeatedly expands and contracts violently in the individual Si fine powder, when the negative electrode material composed of this and the carbon is observed as a whole, the expansion and contraction of the individual Si fine powder inside Are all absorbed. More specifically, the use of Si fine powder enables lithium atoms alloyed from the surface of the negative electrode material to diffuse quickly into the negative electrode, so that the concentration difference between the outside and inside of the negative electrode in the conventional negative electrode material described above As a result, even if the expansion and contraction are repeated, no large stress is generated inside the negative electrode material, that is, the negative electrode material is not crushed or pulverized by the stress.

  If it is a negative electrode material by this invention, it can be set as the new negative electrode material which has sufficient tolerance also with respect to the expansion-contraction of the negative electrode material which will arise by repeating charging / discharging of a lithium secondary battery in this way. It is. That is, the lithium secondary battery can be used over and over again, that is, the life can be extended.

  However, it should be noted that it is not necessary to make the Si fine powder as fine as possible. This is because when the volume of a single negative electrode is set to “1”, when a Si fine powder is used as the negative electrode instead, an unnecessary space may be generated depending on how the Si fine powders are stacked. That is, if the fine powder is filled in the desired specific volume, and as a result, the filling can be completed completely without generating a useless space in the desired specific volume, the filling rate becomes 100%. This is not the case, and a useless space is inevitably produced. And if it is used as a negative electrode of a lithium secondary battery, this filling rate needs to be 40% or more. However, if the average major axis of the Si fine powder is made larger than a certain value, a large number of the above-mentioned useless spaces are generated. As a result, it becomes difficult to reach the required filling rate. Further, if the average major axis of the Si fine powder itself becomes larger than a certain value, it is when the paste containing this is applied, and no matter how flat the coated surface is, for example, the end of the Si fine powder. They may overlap each other, resulting in irregularities that cannot be ignored. In other words, the surface of the electrode may cause unacceptable irregularities. Further, if the average major axis of the Si fine powder becomes smaller than necessary, it becomes difficult to raise the filling rate to a necessary level due to the force acting between the Si fine powders.

  Further, while taking into account the concept of the average major axis in the present invention, the surface of the electrode of the lithium ion secondary battery must be as uniform as possible, that is, in the present invention, it is laminated on the surface of the copper plate by coating or the like. It is desirable that the surface after applying the paste should be as flat as possible. Moreover, the thickness is desirably 1 μm or more and 30 μm or less. If it is 1 μm or less, the effect as a negative electrode material cannot be exhibited in the first place, and if it exceeds 30 μm, lithium occlusion / desorption does not occur effectively.

  Therefore, when the average thickness of the Si fine particles becomes thicker than a certain value, the Si fine powders overlap each other due to the thickness of the Si fine powders contained in the paste even if the paste is applied flatly. Unevenness may occur on the surface. Therefore, in the present invention, the average major axis is set to 100 μm or less. In other words, if this value is exceeded, the paste cannot be laminated substantially uniformly. On the other hand, if Si fine powder having an average major axis of less than 0.1 μm is used, the above-mentioned filling rate cannot be achieved. As a result, the battery capacity per volume cannot be improved. End up.

  In addition, when the thickness of the Si fine powder exceeds a certain thickness, as described above, it has been found that the same phenomenon as described in the case where the conventional simple substance is used as the negative electrode occurs in each Si fine powder. . In other words, even though it is a Si fine powder that occludes lithium, it expands more rapidly than the limit, and then rapidly shrinks when lithium is desorbed. As a result, the fine Si powder itself is further pulverized and loses its function. It has been found that this will occur. Further, if the thickness is less than a certain thickness, the function of absorbing and desorbing lithium cannot be exhibited in the first place, and there arises a problem that it becomes very difficult to handle a too thin Si fine powder.

  The average thickness in the present invention will be further described. As a result of various studies by the inventors, when the average thickness exceeds 3 μm, fine pulverization of the Si fine powder itself was observed. Therefore, in the present invention, the upper limit was set to 3 μm. The lower limit of the thickness at which the Si fine powder itself can be easily handled was 0.01 μm as a result of various studies by the inventors.

  Further, although the average major axis and the average thickness were as described above, it was found that the aspect ratio governing the shape of the Si fine powder was preferably 5 or more, as a result of various examinations by the inventors. .

  Therefore, in the present invention, the average major axis of the Si fine powder is 0.1 μm or more and 100 μm or less, more preferably 0.1 μm or more and 50 μm or less, further preferably 0.1 μm or more and 30 μm or less, and the average thickness is 0. It is preferable that the thickness is 0.01 μm or more and 5 μm or less, more preferably 0.01 μm or more and 3 μm or less, and the aspect ratio is 5 or more.

  As described above, the scale-like fine powder described in the first embodiment is used. However, since the same as that described in the second embodiment is used, the description thereof is omitted.

  Furthermore, although it is stated that the same is true even when the scaly fine powder described in the third embodiment is used, this will be further briefly described below.

  The fine powder according to the third embodiment is obtained by simultaneously laminating (A) a substance capable of reversibly occluding and desorbing lithium and (B) a substance not capable of reversibly occluding and desorbing lithium. It has the structure which consists of. This is because if a fine powder using only a substance capable of reversibly occluding and desorbing lithium is used, it may become difficult to control the speed at which lithium can be occluded and desorbed. Therefore, as a result, it may be possible that the life of the lithium secondary battery cannot be made so long. Therefore, in order to prevent such a phenomenon from occurring, (A) and (B) are formed into fine powders laminated simultaneously.

  That is, in the case of a negative electrode made of silicon used in a conventional lithium secondary battery, in order to control the occlusion of lithium, silicon that can occlude lithium on the surface of the current collector and a substance that does not occlude (for example, nickel) However, in this case, it is necessary to repeatedly perform the lamination process, and there are problems that many steps are required for manufacturing the negative electrode, which takes time. Further, even if the layers are alternately laminated, the negative electrode is repeatedly expanded and contracted particularly due to the charging / discharging of the lithium secondary battery, so that the negative electrode is eventually damaged. However, in the case of what has been described in the third embodiment, each fine powder from the beginning (A) a substance capable of reversibly occluding and desorbing lithium and (B) reversibly occluding and desorbing lithium By observing the entire paste including the substance that is not possible at the same time, it is possible to obtain a material that makes it easy to control the ability of the entire paste to occlude and desorb lithium.

  Naturally, for the same reason as described above, this negative electrode material can be made into a negative electrode material capable of following intense expansion and contraction, so that the lithium secondary battery can be repeatedly used. This can extend the life.

  By the way, in the lithium secondary battery using the negative electrode described here, a lithium transition metal oxide such as lithium cobaltate is used as the positive electrode as in the conventional case, and the following is used as the electrolyte. It should be noted that it can be cited as suitable.

  If it is a negative electrode material concerning this invention, the lithium secondary battery which has a high capacity | capacitance and favorable cycling characteristics can be obtained by using this as a negative electrode of a lithium secondary battery.

Claims (10)

(A) (a) A thin film made of a single metal layer, an alloy, or a metal compound capable of reversibly occluding and desorbing lithium, or a stack of a plurality of single metals,
Or (B) (A) a layer made of any one of a simple substance, an alloy, or a metal compound capable of reversibly occluding and desorbing lithium, and (b) a metal not reversibly occluding and desorbing lithium. A layer of either a simple substance or an alloy,
A thin film formed by laminating so as to have a total of two or more layers using both layers
Scaly fine powder obtained by finely pulverizing any of the thin films;
Carbon,
A negative electrode material for use in a lithium secondary battery electrode, wherein the negative electrode material is obtained by mixing.
For the release layer surface of the polymer resin film formed by laminating the release layer with resin,
(A) (a) A thin film made of a single metal layer, an alloy, or a metal compound capable of reversibly occluding and desorbing lithium, or a stack of a plurality of single metals,
Or (B) (A) a layer made of any one of a simple substance, an alloy, or a metal compound capable of reversibly occluding and desorbing lithium, and (b) a metal not reversibly occluding and desorbing lithium. A layer of either a simple substance or an alloy,
A thin film formed by laminating so as to have a total of two or more layers using both layers
A laminate manufacturing process for obtaining a laminate by laminating any one of the above thin films on the surface of the release layer by vacuum deposition or sputtering,
A thin film layer peeling step of peeling the thin film from the laminate while using a solvent capable of dissolving the resin;
A fine grinding step for finely grinding the thin film present in the solvent;
A solvent removal step for removing the solvent after the fine grinding step;
Scaly fine powder obtained by executing
Carbon,
A negative electrode material for use in a lithium secondary battery electrode, wherein the negative electrode material is obtained by mixing.
The negative electrode material according to claim 1 or 2,
Of the scaly fine powder,
The average major axis, which is the average value of the entire scale-like fine powder having the longest length among the lengths from one end to the other in a plan view of one scale-like fine powder, is 0.1 μm or more and 100 μm or less. Yes,
An average thickness which is an average value of the entire value of the scaly fine powder in a substantially side view of the one scaly fine powder is 0.01 μm or more and 5 μm or less;
A negative electrode material characterized by
The negative electrode material according to any one of claims 1 to 3,
The ratio between the average major axis and the average thickness of the scaly fine powder, that is, the aspect ratio represented by the average major axis / average thickness is 5 or more,
A negative electrode material characterized by
The negative electrode material according to any one of claims 1 to 4, wherein
The thin film is
(A) A thin film composed of a single layer or a plurality of layers using any one of the following groups (1) to (3) as a substance capable of inserting and extracting lithium,
A negative electrode material characterized by
(1) Metal simple substance: silicon, tin, germanium, aluminum, indium, magnesium, calcium, lead, arsenic, antimony, bismuth, silver, gold, zinc, cadmium (2) Alloy: tin-copper alloy (Cu5Sn5), silicon- Magnesium alloy (Mg2Si), iron-tin alloy (Sn2Fe), tin-nickel alloy (NixSn), tin-cobalt alloy (CoxSn), silicon-nickel alloy (NiSi), silicon-iron alloy (FeSi), nickel-magnesium alloy (MgxNi), antimony-tin alloy (SnSb), antimony-indium alloy (InSb), silver-tin-antimony alloy (AgSnSb),
(3) Metal compound: Oxide or sulfide mainly composed of a simple metal shown in (1), or transition metal oxide or sulfide The negative electrode material according to any one of claims 2 to 5,
The thin film is
(B) Using any of the following groups (4) to (5) as a substance that does not allow lithium to be absorbed and desorbed;
A negative electrode material characterized by
(4) Metal simple substance: Titanium, manganese, iron, nickel, chromium, copper, zirconium, molybdenum, tantalum, tungsten (5) Alloy: Alloy mainly composed of metal simple substance shown in (4)
The negative electrode material according to any one of claims 1 to 6,
The mixing ratio of the flaky fine powder and the carbon is
The scaly fine powder is less than 40% of the total by weight,
A negative electrode material characterized by The negative electrode material according to any one of claims 1 to 6,
The mixing ratio of the flaky fine powder and the carbon is
The scaly fine powder is 40% or more and 60% or less of the whole by weight ratio,
A negative electrode material characterized by The negative electrode material according to any one of claims 1 to 6,
The mixing ratio of the flaky fine powder and the carbon is
The carbon is less than 40% by weight,
A negative electrode material characterized by
Using the negative electrode material according to any one of claims 1 to 9,
A lithium secondary battery.