JP2017188329A - Negative electrode material for lithium ion battery, lithium ion battery, method for manufacturing negative electrode material for lithium ion battery, and apparatus for manufacturing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a higher performance negative electrode material for a lithium ion battery in which the usefulness of silicon fine particles is remarkably enhanced. Kind Code: A1 Silicon fine particles having a volume distribution with a mode diameter and a median diameter of 30 nm or less, and/or aggregates or aggregates of the silicon fine particles, which are folded in at least a multi-layer petal shape or a scaly shape. A negative electrode material for a lithium ion battery, which contains the aggregate or the aggregate, and graphite surrounds at least a part of the silicon fine particles and/or the aggregate or the aggregate. [Selection diagram] None

Description

  The present invention relates to a negative electrode material for a lithium ion battery, a lithium ion battery, a method for producing a negative electrode material for a lithium ion battery, and a production apparatus therefor.

Conventionally adopted lithium-ion batteries use a negative electrode active material (hereinafter also referred to as “negative electrode material”) graphite (natural graphite, artificial graphite, etc.) and a negative electrode material as a binder on the negative electrode side. It has a negative electrode with a mixed material layer. Further, the positive electrode side is formed by binding a positive electrode material and a positive electrode active material lithium (Li) oxide powder (LiCoO ₂ , LiNiO ₂ , LiMnO _2, etc.) and conductive graphite (mainly carbon black, etc.) to a binder (PVDF : Polyvinylidene fluoride, etc.) and a positive electrode provided with a mixture layer formed by coating. The cell container of the lithium ion battery is filled with an electrolytic solution, and a separator (mainly a polyolefin-based porous material or a porous polypropylene sheet) is provided between the negative electrode material and the positive electrode material. It has been.

  The above-described separator is provided so as to allow the electrolyte solution to pass therethrough and cause lithium ions to move, and to separate the electrodes from each other so that an electrical short circuit does not occur.

  Charging and discharging of a lithium ion battery is performed by moving lithium ions between a negative electrode material and a positive electrode material in an electrolytic solution. Lithium ions move to the negative electrode side during charging, and lithium ions move to the positive electrode side during discharging. Charging is performed through an externally connected power source, and discharging is performed through an externally connected resistor (load).

  By the way, in the field of lithium ion batteries, in recent years, a technique has been disclosed in which silicon particles are used as a negative electrode active material instead of the above graphite. For example, as an example of silicon particles, a powder having a diameter of about 38 microns (μm) or less formed by pulverizing single crystal silicon with a mortar and classifying it with a mesh is heated at 30 ° C./min in an argon atmosphere. Some have been heated to a temperature of 150 ° C. (reached temperature) (see Patent Document 1). As another example, by supplying liquid silicon tetrachloride in high-temperature and high-concentration zinc gas and reacting at a high temperature of 1050 ° C. or higher, silicon tetrachloride is reduced to form silicon particles, Fine silicon is crystallized and agglomerated at 1000 ° C. or less, particularly 500 to 800 ° C., and the particle size of the formed silicon particles is adjusted and collected in an aqueous zinc chloride solution. It has been disclosed that high-purity silicon particles having a particle diameter of about 1 to 100 μm are obtained by this work and that it is used (see Patent Document 2).

JP 2005-032733 A JP 2012-101998 A International Publication No. WO2015 / 189926 Pamphlet International Publication No. WO2013 / 027686 Pamphlet

  However, in the prior art, when silicon particles are used as the negative electrode material, the electric capacity in charge / discharge can be increased, but on the other hand, lithium is occluded / released into the silicon particles, and the silicon particles change in volume. Or will be destroyed. As a result, there is a problem that the charge / discharge cycle characteristics cannot be maintained.

  For example, in the case of the silicon particles disclosed in the above-mentioned Patent Documents 1 and 2, since it is necessary to perform a high-temperature synthesis and collection process, the manufacturing process until obtaining silicon particles as a negative electrode material becomes extremely complicated. As a result, it is unavoidable that productivity is lowered and manufacturing costs are increased. Further, the technique disclosed in Patent Document 3 is effective in that a part of silicon particles is considered not to be electrically isolated by, for example, expansion and contraction, but there is still room for improvement. Yes. That is, development of lithium ion batteries using silicon particles is still in progress.

  In order to find a higher-performance negative electrode material that can be adapted to the mechanism of a lithium ion battery, without limiting the material used as the negative electrode material only to silicon particles, in light of the above technical problem, Repeated research and analysis.

  As a result, the inventors of the present invention take, in a unique manner, certain characteristic silicon fine particles into an internal space formed using graphite, and surround and internalize them, so to integrate or merge. (Hereinafter, also referred to as “compositing”), the inventors have obtained the knowledge that it is possible to realize a higher performance negative electrode material that significantly increases the usefulness of the characteristic silicon fine particles. The present invention was created based on the above viewpoint.

  The present invention solves at least a part of various problems related to charge / discharge cycle characteristics, etc., which a negative electrode material using conventional silicon particles has, and a lithium ion battery that is also expected to reduce carbon dioxide gas. This greatly contributes to the realization of a negative electrode material for a higher performance lithium ion battery and a method for producing the same.

  The negative electrode material of one lithium ion battery of the present invention is silicon fine particles having a volume distribution with a mode diameter and a median diameter of 30 nm or less and / or an aggregate or aggregate of the silicon fine particles, and at least a multilayer petal The aggregates or the aggregates in a state of being folded in the shape of a scale or scaly, and graphite surrounds at least a part of the silicon fine particles and / or the aggregates or the aggregates.

  The negative electrode material described above is a composite in which at least a part of an aggregate or aggregate of silicon fine particles and / or a multi-layered petal-like or scaly state of silicon fine particles is surrounded by graphite. Contains. In addition, the silicon fine particles and / or the aggregates or aggregates are very fine aggregates or aggregates having a volume distribution with a mode diameter and a median diameter of 30 nm or less. Therefore, although the detailed mechanism is not yet clear, the silicon fine particles and / or the aggregates or the aggregates are combined with the specificity of the multi-layered petal-like or scale-like shape included in the aggregates or the aggregates. When the object is surrounded by graphite, the degree of freedom of the silicon fine particles and / or the aggregates or aggregates is suppressed to some extent, the graphite and the silicon fine particles and / or the graphite and the aggregates or It leads to improving cooperation with the aggregate. As a result, by adopting this negative electrode material, it is possible to realize a lithium ion battery with little change in charge / discharge capacity even when charge / discharge is repeated, in other words, a good charge / discharge cycle characteristic. Alternatively, an increase in charge / discharge capacity can be realized.

  The apparatus for producing a negative electrode material for a lithium ion battery according to the present invention includes a fine silicon particle having a volume distribution with a mode diameter and a median diameter of 30 nm or less and / or the fine silicon particle by grinding crystalline silicon. Agglomerates or aggregates of at least a multilayer petal-like or scaly folded state of the agglomerates or aggregates, and graphite, the silicon fine particles and / or the agglomerates A composite containing the above graphite and the silicon fine particles, or a composite containing the graphite and the aggregate or the aggregate by enclosing at least a part of the aggregate or the aggregate A forming part.

  According to the negative electrode material manufacturing apparatus of the lithium ion battery, the pulverization unit makes very fine silicon fine particles and / or aggregates of the silicon fine particles having a volume distribution with a mode diameter and a median diameter of 30 nm or less, or Form an aggregate. Here, the aggregates or aggregates in a state of being folded at least in a multi-layered petal shape or scale shape are formed. In addition, the manufacturing apparatus includes at least a part of the silicon fine particles and / or the aggregate or the aggregate so that the graphite surrounds the composite, and the graphite and the silicon fine particles. It further includes a complex forming part that forms a complex including the aggregate or the aggregate. Therefore, although the detailed mechanism is not yet clear, the silicon fine particles and / or the aggregates or the aggregates are combined with the specificity of the multi-layered petal-like or scale-like shape included in the aggregates or the aggregates. When the object is surrounded by graphite, the degree of freedom of the silicon fine particles and / or the aggregates or aggregates is suppressed to some extent, the graphite and the silicon fine particles and / or the graphite and the aggregates or It leads to improving cooperation with the aggregate. As a result, according to this manufacturing apparatus, even if charging / discharging is repeated, the change in charge / discharge capacity is small, in other words, the negative electrode material of the lithium ion battery having good charge / discharge cycle characteristics, or the charge / discharge capacity can be increased. This can contribute to the production of negative electrode materials for lithium ion batteries.

  The method for producing a negative electrode material for a lithium ion battery according to the present invention includes: fine silicon particles having a volume distribution having a mode diameter and a median diameter of 30 nm or less and / or the fine silicon particles by grinding crystalline silicon A pulverization step for forming the aggregate or aggregate in a state of being folded into at least a multi-layer petal shape or a scale shape, and graphite is the silicon fine particles and / or the aggregate Forming a composite containing the graphite and the silicon fine particles, or forming a composite containing the graphite and the aggregate or the aggregate by enclosing at least a part of the product or the aggregate And a process.

  According to this method for producing a negative electrode material for a lithium ion battery, very fine silicon fine particles having a volume distribution with a mode diameter and a median diameter of 30 nm or less and / or aggregates of the silicon fine particles or Form an aggregate. Here, the aggregates or aggregates in a state of being folded at least in a multi-layered petal shape or scale shape are formed. In addition, this production method includes at least a part of the silicon fine particles and / or the aggregates or the aggregates so that the graphite surrounds the composite, the graphite and the silicon fine particles, or the graphite. The method further includes a complex forming step of forming a complex containing the aggregate or the aggregate. Therefore, although the detailed mechanism is not yet clear, the silicon fine particles and / or the aggregates or the aggregates are combined with the specificity of the multi-layered petal-like or scale-like shape included in the aggregates or the aggregates. When the object is surrounded by graphite, the degree of freedom of the silicon fine particles and / or the aggregates or aggregates is suppressed to some extent, the graphite and the silicon fine particles and / or the graphite and the aggregates or It leads to improving cooperation with the aggregate. As a result, according to this manufacturing apparatus, even if charging / discharging is repeated, the change in charge / discharge capacity is small, in other words, the negative electrode material of the lithium ion battery having good charge / discharge cycle characteristics, or the charge / discharge capacity can be increased. This can contribute to the production of negative electrode materials for lithium ion batteries.

  Incidentally, the crystalline silicon in each of the above-described inventions includes not only single crystal silicon but also polycrystalline silicon. In addition, metallic silicon can be selected as the crystalline silicon in each of the above-described inventions. It is to be noted that the crystalline silicon of each of the above-described inventions is, for example, silicon chips, silicon cutting scraps or polishing scraps that are normally discarded in the silicon cutting process in the production process of silicon wafers. This is a very suitable aspect from various viewpoints such as reduction of environmental load, reduction of environmental load, and reuse of resources.

  Therefore, from the viewpoint of reduction of manufacturing cost, ease of procurement of raw materials, reduction of environmental burden, and / or utilization of resources, etc., it contains crystalline silicon chips or cutting waste, and graphite has The negative electrode material of the lithium ion battery that surrounds at least a part of the chips or the cutting waste is another aspect that can be adopted. Moreover, a lithium ion battery provided with the composite_body | complex formation part which forms the composite_body | complex containing this graphite and this chip or this cutting waste by surrounding at least one part of the chip or cutting waste of crystalline silicon by graphite. The negative electrode material manufacturing apparatus is another embodiment that can be adopted. In addition, the lithium includes a complex forming step in which the graphite surrounds at least a part of the crystalline silicon chips or cutting chips to form a composite including the graphite and the chips or cutting chips. The manufacturing method of the negative electrode material of the battery is another aspect that can be adopted.

  Furthermore, in each of the above-described inventions, the above-mentioned aggregate or aggregate in a state of being folded into a multi-layered petal shape or a scale shape is more accurate or easier to store and release lithium ions more easily. In order to achieve this, it is possible to employ a negative electrode material for a lithium ion battery in which at least a part of the surface of the above-described aggregate, the above-described aggregate, the above-described chips, or the above-described cutting waste is covered with carbon This is a preferred embodiment. From the viewpoint of easy storage or release of lithium ions, carbon is formed to cover at least a part of the surface of the above-mentioned aggregate, the above-mentioned aggregate, or the above-mentioned chips or the above-mentioned cutting waste. It is another preferable aspect to employ a negative electrode material manufacturing apparatus for a lithium ion battery that includes a coating forming section. Similarly, a method for producing a negative electrode material for a lithium ion battery comprising a coating forming step of forming carbon covering at least a part of the surface of the above-mentioned aggregate, the above-mentioned aggregate, or the above-mentioned chips or the above-mentioned cutting waste Employing is another preferred embodiment.

  In each of the above-described inventions, graphite, or more positively, the so-called “layer” of graphite (for example, graphene or graphene sheet) is an aggregate having the above-mentioned very fine and unique shape, or Surrounds the collective. However, the graphite does not necessarily completely surround the silicon fine particles and / or the aggregates or aggregates. Therefore, it can be said that the above-mentioned composite is surrounded by graphite rather than the aggregate or aggregate contained in graphite.

  According to the negative electrode material of one lithium ion battery of the present invention, it is possible to realize a lithium ion battery having a small change in charge / discharge capacity even when charge / discharge is repeated, in other words, a good charge / discharge cycle characteristic. Alternatively, an increase in charge / discharge capacity can be realized. Moreover, according to the negative electrode material manufacturing apparatus for one lithium ion battery of the present invention, the change in charge / discharge capacity is small even when charge / discharge is repeated, in other words, the negative electrode of the lithium ion battery having good charge / discharge cycle characteristics. This can contribute to the production of a negative electrode material for a lithium ion battery that can increase the material or charge / discharge capacity. In addition, according to the method for producing a negative electrode material for one lithium ion battery of the present invention, the change in charge / discharge capacity is small even when charge / discharge is repeated, in other words, a lithium ion battery having good charge / discharge cycle characteristics. This can contribute to the production of a negative electrode material or a negative electrode material for a lithium ion battery that can increase the charge / discharge capacity.

It is a flowchart which shows the manufacturing process of the negative electrode material of the lithium ion battery of 1st Embodiment. It is a schematic diagram which shows the manufacturing apparatus and manufacturing process of the negative electrode material of the lithium ion battery of 1st Embodiment. It is a figure which shows the TEM (transmission electron microscope) image of an example of the silicon | silicone fine particle which passed through the coating formation process (S4) of 1st Embodiment, and / or its aggregate or aggregate. It is a SEM image of an example of the silicon fine particle of 1st Embodiment, and / or its aggregate or aggregate. It is a SEM image of an example of the enlarged silicon fine particle and / or its aggregate or aggregate in a 1st embodiment. FIG. 4A is an SEM image of another example of an aggregate or aggregate of silicon fine particles and (b) a partly enlarged view of (a) in the first embodiment. It is a figure which shows the TEM image of the silicon | silicone fine particle of 1st Embodiment. It is a graph which shows the crystallite diameter distribution in (a) number distribution and the (b) crystallite diameter distribution in volume distribution with respect to crystallite diameters, such as a silicon | silicone fine particle of 1st Embodiment. It is a graph which shows the result ((a) wide range, (b) limited range) of the X-ray-diffraction measurement of the silicon | silicone fine particle of 1st Embodiment, and / or its aggregate or aggregate. It is a schematic block diagram of the lithium ion battery of 2nd Embodiment. It is a schematic diagram which shows the manufacturing apparatus and manufacturing process of the negative electrode material of the lithium ion battery of other embodiment.

  Embodiments of the present invention will be described in detail with reference to the accompanying drawings. In this description, common parts are denoted by common reference symbols throughout the drawings unless otherwise specified. In the drawings, each element of each embodiment is not necessarily shown in a scale ratio. Moreover, in order to make each drawing easy to see, some reference numerals may be omitted.

<First Embodiment>
FIG. 1 is a flow diagram showing a manufacturing process of a negative electrode material of the lithium ion battery of this embodiment. FIG. 2 is a schematic diagram showing a negative electrode material manufacturing apparatus and manufacturing process of the lithium ion battery of this embodiment.

A method for producing a negative electrode material for a lithium ion battery according to the present embodiment and a method for producing a lithium ion battery including the negative electrode material include silicon cutting in the production process of a silicon wafer used for a semiconductor product such as a solar cell. Various processes using silicon chips or silicon cutting scraps or polishing scraps (hereinafter also referred to as “silicon chips or the like” or “chips or the like”) as waste materials in Is provided. Further, the chips and the like include fine scraps obtained by pulverizing a silicon wafer to be discarded by a known pulverizer. As shown in FIG. 1, the manufacturing method of the lithium ion battery of the present embodiment includes the following steps (1), (2), (5), and (6), or the following (1), (2 ), (4), (5), and (6). Moreover, the manufacturing method of the lithium ion battery of this embodiment can further include the following step (3) as another aspect that can be adopted.
(1) Cleaning step (S1)
(2) Grinding step (S2)
(3) Oxide film removal step (S3)
(4) Coating formation process (S4)
(5) Complex formation step (S5)
(6) Negative electrode forming step (S6)

  As shown in FIG. 2, the negative electrode material (or negative electrode) manufacturing apparatus 100 of the lithium ion battery of this embodiment mainly includes a cleaning machine (cleaning and preliminary pulverizer) 10, a pulverizer 20, and a dryer (illustrated). No), coating formation for forming carbon covering at least a part of the surface of the rotary evaporator 40, silicon fine particles and / or aggregates or aggregates thereof (hereinafter also expressed as “silicon fine particles etc.”) Part 60, composite forming part 70 for forming a composite containing graphite and silicon fine particles, etc. by surrounding graphite with at least some of the silicon fine particles, and part of the negative electrode forming step of the lithium ion battery The mixing part 80 which bears is provided. Of the above-described components, the negative electrode material (or negative electrode) manufacturing apparatus 100 of the lithium ion battery that does not include the coating forming unit 60 is another aspect that can be employed.

  Moreover, the manufacturing apparatus 100 of the negative electrode material (or negative electrode) of the lithium ion battery of this embodiment can be provided with the oxide film removal tank 50 and the centrifuge 58 as another aspect which can be employ | adopted. Note that only the pulverizer 20 described above, or the washing machine 10 and the pulverizer 20 are referred to as a pulverization unit in the present embodiment.

(1) Cleaning step (S1)
In the cleaning step (S1) of the present embodiment, for example, it is formed in the cutting process of single crystal or polycrystalline silicon, that is, a crystalline silicon lump or ingot (n-type crystalline silicon lump or ingot). Silicon chips and the like are cleaned. Typical silicon chips and the like are chips and the like in which a silicon ingot is cut out by a known wire or the like (typically, a fixed abrasive wire). Therefore, in the present embodiment, since silicon fine particles and the like that constitute the negative electrode material of a lithium ion battery are formed using silicon chips and the like, which have been conventionally regarded as waste materials, as a starting material, the manufacturing cost is reduced. It is excellent in terms of easy procurement of raw materials, reduction of environmental burden, and / or resource utilization.

  The cleaning step (S1) of the present embodiment is mainly for the purpose of removing organic substances adhering in the formation process of the above-described silicon chips, typically organic substances such as coolants and additives used in the cutting process. And In this embodiment, as shown in FIG. 2, first, after the chips 1 to be cleaned are weighed, the chips 1, the predetermined first liquid, and the ball 11 have a bottomed cylindrical shape. It is introduced into the pot 13a. After sealing the inside of the pot 13a using the lid 13b, the two cylindrical rotating bodies 15 included in the ball mill which is the cleaning machine (cleaning and preliminary pulverizing machine) 10 are rotated, thereby rotating the rotary body 15 on the rotary body 15. The pot 13a is rotated. As a result, in the pot 13a, the chips 1 to be cleaned are dispersed in the first liquid, whereby the chips 1 are cleaned and preliminarily pulverized.

  Here, the ball mill machine of this embodiment uses the steel balls, porcelain balls, cobblestones and the like contained in the pots 13a and the lid 13b as balls 11 (grinding media), and rotates the pot 13a and the lid 13b. It is a crusher that gives a physical impact force. A suitable example of the first liquid is acetone. Moreover, in one more specific aspect, for example, 300 milliliters (mL) of acetone is added to 100 grams (g) of silicon chips and the like, and a ball mill machine (in this embodiment, manufactured by MASUDA, The silicon chips and the like were dispersed in acetone by stirring in a pot 13a and a lid 13b placed on a rotating body 15 of Universal BALL MILL) for about 1 hour. Ball types of the ball mill machine were alumina balls having a particle diameter of φ10 millimeters (mm) and alumina balls having a particle diameter of φ20 mm. In the cleaning step (S1) of the present embodiment, the dispersion process is performed by pre-grinding and stirring silicon chips and the like in the first liquid in the ball mill. Accordingly, since the cleaning efficiency is remarkably improved as compared with the treatment of simply immersing in the first liquid, silicon particles suitable for improving the negative electrode characteristics of the lithium ion battery, particularly for improving the charge / discharge cycle characteristics, are used. Can be obtained.

  After the cleaning step (S1), the lid 13b is opened to discharge the silicon particles together with the first liquid, and then the first liquid is removed by suction filtration with a known vacuum filtration means to become a waste liquid. On the other hand, the remaining silicon particles are dried in a known dryer. If necessary, the silicon particles obtained after the drying treatment are again preliminarily crushed and washed in the washing machine (washing / preliminary pulverizer) 10 in the same process. In addition, the example of the other washing | cleaning method which can be employ | adopted in washing | cleaning process (S1) is the washing | cleaning using the RCA washing | cleaning method, or the washing | cleaning using water (a pure water is included).

(2) Grinding step (S2)
Thereafter, in the pulverization step (S2), a predetermined second liquid is added to the washed silicon particles, and the silicon particles are pulverized in the bead mill. Therefore, in this embodiment, the silicon particles that have undergone the cleaning step (S1) are further finely pulverized by the bead mill used after the above-described ball mill, in other words, after the above-described ball mill. Become.

  A suitable example of the second liquid of this embodiment is IPA (isopropyl alcohol). As a pretreatment of the pulverization step, the silicon particles obtained in the second liquid and the washing step (S1) are placed in the pot 13a so that the second liquid is 95% of the silicon particles and 95% of the second liquid. After storing, a preliminary pulverization process is performed by rotating the pot 13a and the lid 13b of the cleaning machine (cleaning and preliminary pulverizer) 10. After relatively coarse particles are removed by passing the slurry containing silicon particles that have been subjected to pre-grinding treatment through a mesh having an opening of 180 microns, the obtained slurry containing silicon particles is used as a bead mill (this embodiment). Is further pulverized using a star mill LMZ015 manufactured by Ashizawa Fineting. More specifically, a slurry containing silicon chips from which silicon chips having a particle diameter of 180 microns or more have been removed is introduced into the inlet 21 of the pulverizer 20, and the pulverizer 20 is performing a fine pulverization process or After the treatment, it is guided to the filter 25 on the discharge port 24 side. Further, when the pulverization is insufficient by this process, the slurry is returned to the inlet 21 side of the pulverizer 20 using the pump 28 and circulated so that the pulverization process can be performed again. Processing can also be performed. A specific example of the bead type of the bead mill is zirconia beads having a particle diameter of φ0.5 mm. After recovering the slurry containing finely pulverized silicon particles, the second liquid is removed using a rotary evaporator 40 that automatically performs vacuum distillation, so that the finely pulverized silicon fine particles as a result are obtained. can get.

  In this embodiment, silicon fine particles and the like can be obtained by introducing about 450 g of zirconia beads having a particle diameter of φ0.5 mm and performing a fine pulverization treatment at 2900 rpm for 4 hours. Further, in the pulverization step (S2), it is also possible to perform the pulverization treatment by any one of the pulverizers other than those described above, or a combination of two or more of the pulverizers composed of a ball mill, a bead mill, a jet mill, and a shock wave pulverizer. Another aspect that can be achieved. In addition, as a pulverizer used in the pulverization step (S2), not only an automatic pulverizer but also a manual pulverizer may be employed. However, from the viewpoint of forming agglomerates or aggregates of silicon fine particles in a state of being highly accurate and folded into a multi-layered petal shape or scale shape, which will be described later, a pulverization step (S2) consisting of a treatment by a bead mill, or It is preferable to employ a pulverization step (S2) including processing by a bead mill.

  Further, by using a known reiki machine (as a typical reiki machine, manufactured by Ishikawa Factory Co., Ltd., model 20D type), the silicon fine particles obtained by the above-described crushing step (S2) are further crushed. Is another preferred embodiment that can be employed. Since this disintegration treatment improves the dispersibility when forming the negative electrode of the lithium ion battery, it is possible to highly reliably prevent or suppress destruction of the negative electrode due to insertion and extraction of lithium. .

(3) Oxide film removal step (S3)
In the present embodiment, an oxide film removing step (S3) is performed as a preferred embodiment. However, even if this oxide film removal step (S3) is not performed, at least a part of the effects of the present embodiment can be achieved.

  In the oxide film removing step (S3) of the present embodiment, a process of bringing the silicon fine particles 2 obtained by the pulverizing step (S2) into contact with hydrofluoric acid or ammonium fluoride aqueous solution is performed. The silicon fine particles 2 and the like obtained by the pulverization step (S2) are dispersed by being immersed in hydrofluoric acid or ammonium fluoride aqueous solution. Specifically, in the oxide film removal tank 50, the surface of the silicon fine particles 2 is oxidized by dispersing the silicon fine particles 2 in the hydrofluoric acid or ammonium fluoride aqueous solution 55 using the stirrer 57. Objects (mainly silicon oxide) are removed.

  Thereafter, the silicon fine particles or the like from which part or all of the surface oxide has been removed are separated from the hydrofluoric acid aqueous solution by the centrifuge 58. Thereafter, silicon fine particles and the like are immersed in a third liquid such as an ethanol solution. By removing the third liquid, it is possible to obtain silicon fine particles or the like from which part or all of the oxide (or oxide film) on the surface that was originally formed is removed. In addition, when the removal process of the oxide which may exist on the surface of silicon | silicone fine particle 2 etc. is not performed, silicon | silicone fine particle etc. are the coating formation process (S4) mentioned later, composite formation process (S5), and negative electrode formation. Processing by the step (S6) is performed.

  In the oxide film removing step (S3) of the present embodiment, hydrofluoric acid is brought into contact with the silicon fine particles and the like by immersing the silicon fine particles and the like in hydrofluoric acid or an aqueous ammonium fluoride solution. In addition, a step of bringing hydrofluoric acid or ammonium fluoride aqueous solution into contact with silicon fine particles or the like by other methods may be employed. For example, spraying a hydrofluoric acid aqueous solution onto silicon fine particles or the like as in a so-called shower is another aspect that can be adopted.

(4) Coating formation process (S4)
In this embodiment, a coating formation process (S4) is performed as a suitable aspect. However, even if this coating forming step (S4) is not performed, at least a part of the effects of the present embodiment can be achieved. Therefore, as described above, after the pulverization step (S2) or after the oxide film removal step (S3), without performing the coating formation step (S4), the following (5) complex formation step (S5) It is another aspect that can be adopted.

  In the present embodiment, a coating forming step is performed in which a part or the whole of the surface of silicon fine particles or the like that has passed or not passed through the oxide film removing step (S3) is covered with a carbon film. Accordingly, since the silicon fine particles and the like that have undergone the coating formation step (S4) of the present embodiment are covered with carbon at least partly on the surface, the thickness is smaller than the silicon fine particles that are not covered with carbon. Will increase. In addition, when the carbon of this embodiment is provided with conductivity, a negative electrode material having conductivity can be formed. Further, for example, by covering silicon fine particles with carbon having a film thickness of several nm to several μm, not only a thin negative electrode but also a relatively thick negative electrode can be easily formed. FIG. 3 is a TEM of an example of silicon fine particles and the like (partially enlarged view) and / or aggregates or aggregates (partially enlarged view) that have undergone the coating formation step (S4) of the present embodiment. It is a (transmission electron microscope) image. The crystalline silicon shown in FIG. 3 mainly has a crystal plane orientation (111) (also simply referred to as “Si (111)” or “(111)”. The same applies to other plane orientations). Observed.

  In addition, for example, the internal stress of the negative electrode as a whole can be reduced by covering silicon fine particles and the like with carbon, and more microscopically, the internal stress of individual silicon fine particles can be reduced. As a result, the production of the lithium ion battery can be made easier, and it can contribute to the improvement of the performance (for example, charge / discharge cycle characteristics) of the lithium ion battery.

  Further, by forming a negative electrode material of a lithium ion battery using silicon fine particles or the like at least a part of which is covered with carbon, a charge capacity value and a capacity compared with silicon fine particles or the like not covered with carbon It is also possible to increase the discharge capacity value. For example, according to the study of the present inventors, in the case of silicon fine particles not covered with carbon, for example, when the thickness of the negative electrode material is about 30 μm, the charge capacity value and the discharge capacity value are 500 ( mAh / g). However, the charge capacity value and the discharge capacity value are increased more than twice (typically about 3 to about 5 times) by using silicon fine particles or the like whose surface is at least partially covered with carbon. Can be made.

  By the way, in the coating forming step (S4) of the present embodiment, means for coating a part or all of the surface of the silicon fine particles or the like (in other words, at least a part on the surface) with the carbon film is particularly limited. Not. For example, a method of covering at least a part of the surface of the silicon fine particles 2 or the like with carbon by a thermal CVD method which is an example of a chemical vapor deposition method can be employed. Specifically, at least part of the surface of the silicon fine particles 2 is heated by heating the silicon fine particles 2 in an atmosphere containing an organic gas and / or vapor thereof at about 600 ° C. or more and about 1200 ° C. or less. Can be covered by a carbon film. Therefore, the thermal CVD apparatus which is an example of the chemical vapor deposition apparatus is an aspect of the coating forming unit 60 that can be employed in the coating forming step (S4) of the present embodiment. Examples of materials (or raw materials) that can be employed in the thermal CVD method include one or more selected from the group of methane, ethane, acetylene, ethylene, propane, butane, butene, pentane, isobutane, and hexane. It is a hydrocarbon and / or one or more known aromatic hydrocarbons. In addition, the point which can thermally decompose acetylene at about 400 degreeC by employ | adopting copper or a copper alloy as a catalyst can contribute to the reduction in processing temperature.

  As described above, typically, hydrocarbon gas is pyrolyzed and carbonized on or near the heated silicon fine particles 2 so that at least a part of the surface of the silicon fine particles 2 is obtained. Covering with the carbon film realizes an example of a suitable carbon film in the present embodiment, and can be said to be a technique excellent in productivity and industrial efficiency. Note that a low-pressure thermal CVD method or a plasma CVD method, which is another example of the chemical vapor deposition method, can also be appropriately employed.

  Another example of the method of covering at least part of the surface of the silicon fine particles 2 etc. with a carbon film is as follows. First, a known organic compound (such as chlorinated polyethylene elastomer) or a mixture of the organic compound and graphite powder is mixed in the coating forming unit 60 at least in the cleaning step (S1) and the pulverization step ( It adheres or adsorbs to the silicon fine particles 2 treated in S2). Thereafter, the organic compound is heated to a temperature at which the organic compound is thermally decomposed to carbonize the organic compound, whereby at least a part of the surface is covered with carbon (typically, graphene, graphite, and / or amorphous carbon). The broken silicon fine particles 2 can be formed. In addition, it is also possible to perform the step of firing the silicon fine particles 2 and the like 2 once formed in a nitrogen atmosphere or a hydrogen atmosphere, for example, at 400 ° C. to 1200 ° C. in addition and / or in advance. It is an aspect of the modification of a form. From the viewpoint of accurately preventing, suppressing, or removing the formation of an oxide film on the surface of the silicon fine particles 2 and the like, it is preferable to heat the silicon fine particles 2 and the like in a hydrogen atmosphere.

  Moreover, it is another aspect which can employ | adopt forming the silicon | silicone fine particle 2 etc. with which at least one part on the surface was covered with carbon using another well-known means. For example, a carbon film formed by a known carbon black production method (furnace method or channel method) can be used. The furnace method is a method in which droplets are cooled with water after partial combustion of creosote oil is performed in a predetermined chamber in which creosote oil obtained by distillation of coal tar is turbulently diffused. The channel method is a method of depositing carbon by, for example, causing a flame formed by burning natural gas to collide with a cooling surface of channel steel. However, since a petroleum-derived sulfur component is contained, it is more preferable to employ the above-described thermal CVD method, which is a method in which such an impurity component is hardly mixed. Further, when each of the above-described methods is employed, for example, by applying a known mechanical structure to kinetic energy as appropriate for silicon fine particles, etc., silicon fine particles 2 and / or aggregates thereof or the like Employing a method of coating at least a part of the surface of the aggregate with a carbon film makes it more uniform on the surface of the silicon fine particles 2 and / or aggregates or aggregates thereof (for example, This is a preferred embodiment because a carbon film can be formed with good uniformity in thickness and / or density. More specifically, while rotating the chamber or tube containing the silicon fine particles 2 and / or applying ultrasonic vibrations to the silicon fine particles 2 and / or aggregates or aggregates thereof, Adopting a method of coating at least a part of the surface of the silicon fine particles 2 and / or aggregates or aggregates thereof with a carbon film means that the silicon fine particles 2 and / or aggregates or aggregates thereof are covered. Since a carbon film can be more uniformly formed on the surface of an object, this is a preferred embodiment.

  In the first embodiment in the case where the coating forming step (S4) is performed, carbon (C) when silicon (Si) is set to 1 for the negative electrode material or the silicon fine particles 2 serving as a part of the negative electrode. The weight ratio of carbon (C) when silicon (Si) is set to 1 is stable and charged if the weight ratio of carbon (C) is 0.05 or more and less than 0.37. A lithium ion battery having a high capacity value and high discharge capacity value can be obtained.

  Further, as a result of further detailed analysis by the present inventor, carbon (C) when the weight ratio of carbon (C) when silicon (Si) is set to 1 is 0.1 by a TEM (transmission electron microscope) image. The film thickness of the portion where C) adhered to silicon (Si) was about 2 nm to about 3 nm. Further, when the weight ratio of carbon (C) when silicon (Si) is 1 is 0.16, the film thickness of the portion where carbon (C) is attached to silicon (Si) is about 5 nm to About 10 nm. Further, when the weight ratio of carbon (C) when silicon (Si) is 1 is 0.21, the film thickness of the portion where carbon (C) is attached to silicon (Si) is also about 5 nm to About 10 nm. In addition, when the weight ratio of carbon (C) when silicon (Si) is 1 is 0.37, the film thickness of the portion where carbon (C) is attached to silicon (Si) is about 50 nm. ~ 90 nm. Therefore, if the film thickness of carbon (C) attached to silicon (Si) is 1 nm or more and less than 50 nm, in particular, if the film thickness is 2 nm or more and 10 nm or less, the film is stable and has a charge capacity. A lithium ion battery having a high value and a high discharge capacity value can be obtained.

  Further, at least a part of the surface of the silicon fine particles and / or aggregates or aggregates thereof is not covered with carbon (that is, not subjected to the coating formation step (S4)), and the charge capacity value and discharge of the lithium ion battery The one that has undergone the coating formation step (S4) than the capacity value can have a charge capacity value and a discharge capacity value that are twice or more (typically about three times) higher.

(5) Complex formation step (S5)
As described above, after the crushing step (S2) or after the oxide film removing step (S3), the composite formation step (S5) is performed through the coating formation step (S4) or without the coating formation step (S4). ) Is performed. The composite formation step (S5) of the present embodiment is a step of forming a composite including graphite and silicon fine particles 2 by surrounding graphite with at least some of the silicon fine particles 2 and the like.

  Specifically, first, silicon fine particles 2 and graphite (typically flaky graphite or expanded graphite) are introduced into the composite forming part 70. The flaky graphite or expanded graphite of this embodiment can be formed by a method disclosed in a known method.

  In the present embodiment, since the pulverization step (S2) is performed, very fine aggregates or aggregates of silicon fine particles having a volume distribution with a mode diameter and a median diameter of 30 nm or less (silicon fine particles). Particles 2) are formed. In addition, the agglomerates or aggregates are agglomerates or aggregates of silicon fine particles that are folded in a multi-layered petal shape or scale shape. Since such very fine silicon fine particles 2 are employed, silicon fine particles 2 and graphite are mixed, and silicon fine particles 2 are taken into the internal space formed using graphite, A bead mill similar to the bead mill used in the pulverizer 20 can be adopted as an example of the composite forming unit 70 in the case of surrounding and internalizing it, that is, integrating or merging. Another example of the complex forming unit 70 is a group of devices that use a known dry process or a known wet process and a pulverizer represented by a high-speed rotational impact pulverizer. However, from the viewpoint of reducing the number of substantial steps, when the silicon fine particles 2 and graphite are combined with graphite, the composite forming unit 70 includes only the above-described bead mill machine or a composite including at least the bead mill machine. It is preferable to employ a processing apparatus or a composite processing apparatus including a high-speed rotational impact pulverizer.

  In particular, because of the specific shape of the scaly silicon fine particles and / or aggregates or aggregates thereof, silicon fine particles 2 are taken in between layers having an appropriate distance of graphite (particularly expanded graphite). It is advantageous for the combination of graphite and silicon fine particles 2 when graphite and silicon fine particles 2 etc. are introduced into the composite forming part 70 in order to easily be surrounded and / or to be surrounded by the graphite. is there. In addition, the adoption of the scaly silicon fine particles and / or the aggregates or aggregates thereof having undergone the coating formation step (S4) means that silicon between layers having an appropriate distance of graphite (particularly expanded graphite) is used. It is preferable because the fine particles 2 can be easily taken in with higher accuracy and / or the silicon fine particles 2 can be easily surrounded by the graphite. In addition, as described above, from the viewpoint of having a higher charge capacity value and discharge capacity value, the scaly silicon fine particles and / or aggregates or aggregates thereof are subjected to the coating formation step (S4). This is a preferred embodiment.

  By performing the composite formation step (S5), the above-described very fine silicon fine particles 2 having aggregates or aggregates folded in a multi-layered petal shape or scale shape are surrounded by graphite. A broken state can be formed. In this embodiment, it is not always necessary to go through a process (typically, “spheroidization”) in which the edge portion of the graphite is folded so that the silicon fine particles 2 and the like are taken in by the sheet-like graphite. It is also an aspect that can be adopted in which a state in which the silicon fine particles 2 are surrounded by graphite after such a process is formed.

(6) Negative electrode forming step (S6)
The negative electrode material (or negative electrode) manufacturing apparatus 100 of the lithium ion battery of the present embodiment has been processed by the coating formation step (S4) after the pulverization step (S2) or after the oxide film removal step (S3). As a negative electrode material that has not been processed, a material in which at least a part of silicon fine particles and the like is surrounded by graphite and a member (for example, copper foil) that constitutes a part of the negative electrode are bound (for example, ammonium carboxyl) A mixing unit 80 for mixing using methylcellulose (CMC) and styrene-butadiene rubber (SBR), or ammonium carboxylmethylcellulose (CMC) and polyvinyl alcohol (PVA)) is provided. A negative electrode is formed using the mixture layer formed by the mixing unit 80.

<Other processes>
In addition, the silicon fine particles obtained by the following steps (A) to (D) are classified, for example, in order to reduce variations in the number distribution and / or volume distribution of crystallite diameters of the respective silicon fine particles. Can be done.
(A) Washing step (S1), crushing step (S2), and complex forming step (S5)
(B) Cleaning step (S1), crushing step (S2), oxide film removing step (S3), and complex forming step (S5)
(C) Cleaning step (S1), crushing step (S2), coating formation step (S4), and complex formation step (S5)
(D) Cleaning step (S1), crushing step (S2), oxide film removal step (S3), coating formation step (S4), and complex formation step (S5)

<Analytical result of silicon fine particles and the like obtained in the first embodiment>
1. Analysis of silicon fine particles by SEM and TEM images

  FIG. 4A is an SEM (scanning electron microscope) image of an example of silicon fine particles and / or aggregates or aggregates thereof after the crushing step (S2) of the first embodiment. Moreover, FIG. 4B is a figure which shows the SEM image of an example of the expanded silicon | silicone fine particle and / or its aggregate or aggregate after the grinding | pulverization process (S2) of 1st Embodiment. 4C is a diagram showing an SEM image of another example of an aggregate or aggregate of silicon fine particles and (b) a partially enlarged view of (a) in the first embodiment. is there. In addition, FIG. 5 is a diagram showing a transmission electron microscope (TEM) image of the silicon fine particles of the first embodiment.

  As shown in FIG. 4A, not only individual silicon fine particles but also silicon fine particles shown in Y1 and Y2 and / or aggregates or aggregates thereof were confirmed. Interestingly, when analyzed in more detail, as shown in FIG. 4B and the Z portion of FIGS. 4C (a) and 4 (b), silicon fine particles or aggregates thereof are, so to speak, thin-layered silicon fine particles. It was confirmed that it was an aggregate or aggregate in a state of being folded into a multi-layer petal shape or a scale shape. In more detail, for example, the range of the length (major axis) when the width (minor axis) of one or a group of scale-like silicon fine particles is 1, is 3.3 to 12.9. there were.

  Further, another interesting finding was obtained from the TEM image shown in FIG. 5 focusing on individual silicon fine particles. Specifically, it was confirmed that the individual silicon fine particles and the like indicated by the region surrounded by the white line in FIG. 5 are crystalline, that is, single crystal silicon. In addition, it was confirmed that at least a part of the silicon fine particles and the like were amorphous polygonal crystallites having a size of about 2 nm to about 10 nm in a cross-sectional view. In FIG. 5, the crystal plane orientation is shown in each region surrounded by a white line.

2. 6. Analysis of crystallite size distribution of silicon fine particles and the like by X-ray diffraction method FIG. 6 shows crystallites in (a) number distribution with respect to the crystallite size in the Si (111) direction of silicon fine particles and the like of the first embodiment. It is a graph which shows a diameter distribution and the crystallite diameter distribution in (b) volume distribution. FIG. 6 shows the results obtained by analyzing the crystallite size distribution of silicon fine particles and the like after the pulverization step (S2) using the X-ray diffraction method. In each of FIGS. 6A and 6B, the horizontal axis represents the crystallite diameter (nm), and the vertical axis represents the frequency.

  From the results of FIG. 6A and FIG. 6B, in the number distribution, the mode diameter was 1.6 nm, and the median diameter (50% crystallite diameter) was 2.6 nm. In the volume distribution, the mode diameter was 6.3 nm and the median diameter was 9.9 nm. Accordingly, it was confirmed that the number distribution was 5 nm or less regardless of the mode diameter or the median diameter, and more specifically, a value of 3 nm or less was realized. It is worthy to note that the volume distribution was confirmed to be at least 50 nm, particularly 30 nm or less, and more narrowly 20 nm or less, regardless of mode diameter or median diameter. Further, in FIG. 6, it was confirmed that an extremely small value of 10 nm or less was realized.

  From the results of FIG. 6 (a) and FIG. 6 (b), the silicon fine particles obtained after the pulverization step (S2) using the bead mill method have an average crystallite diameter of about 20 nm or less, more specifically, It was confirmed that the thickness was about 9.8 nm, realizing 10 nm or less. The crystallite size distribution of the silicon fine particles after the oxide film removing step (S3) is almost the same as that in FIG.

  Therefore, if the results of FIG. 6 and the results of FIG. 4 are combined and analyzed, aggregates or aggregates such as silicon fine particles after at least the pulverization step (S2) or the oxide film removal step (S3) will be obtained. In other words, it can be said that the so-called thin-layered silicon fine particles having a major axis of about 100 nm or less are folded in a multi-layered petal shape or a scale shape. Further, as can be seen from FIGS. 5 and 6, silicon fine particles and the like are mainly composed of crystallites having a major axis of 10 nm or less.

  Moreover, it turns out that the silicon | silicone fine particle etc. of this embodiment contain the silicon | silicone fine particle etc. of a crystallite diameter of 1 nm or less as shown in FIG. Interestingly, it was also confirmed that the average crystallite diameter in the volume distribution of the silicon fine particles and the like of this embodiment is about 10 nm. This numerical value can be said to be a very small value. Further, as described above, by further investigation, it was confirmed that the apparent volume diameter of the silicon fine particles and the like was in the range of about 100 nm or less. In particular, by including a large number of ultrafine silicon particles having a crystallite diameter of 5 nm or less in the major axis, the charge / discharge cycle characteristics derived from silicon fine particles used as a negative electrode material of a lithium ion battery, which will be described later, are improved with higher accuracy. It is something to be made. In addition, since at least a part of the surface is covered with carbon in the ultrafine silicon particles described above, higher charge capacity value and discharge capacity value, and excellent charge / discharge cycle characteristics can be realized.

3. Analysis of plane orientation of crystallites such as silicon fine particles by X-ray diffraction method FIG. 7A shows the silicon fine particles and / or aggregates or aggregates thereof before the pulverization step (S2) of the first embodiment. It is the result of analyzing the X-ray diffraction measurement result (P) and the X-ray diffraction measurement result (Q) of the silicon fine particles and / or their aggregates or aggregates after the grinding step (S2) in a wide angle range. . FIG. 7B is an enlarged view of a part of the result (P) of FIG. 7A, and silicon fine particles and / or their aggregation after the pulverization step (S2) of the first embodiment. It is the result (R) which analyzed the result of the X-ray-diffraction measurement of the thing or the aggregate | assembly in the limited angle range. Note that the peak intensities of the C (002) plane and C (003) plane shown in FIG. 7B are about 1 wt% to about 3 wt% of graphite fine particles or silicon fine particles. This indicates that it is contained in an aggregate or aggregate. As an example, the size of the fine graphite particles on the C (002) plane is about 50 nm or less, more specifically about 35 nm, and the size of the fine graphite particles on the C (003) plane is about 100 nm. Hereinafter, more specifically, it was about 75 nm.

  As shown in FIGS. 7A and 7B, compared to the diffraction peak attributed to the Si crystal plane (111) near 2θ = 28.4 ° before the pulverization step (S2) of the first embodiment. It was confirmed that the half value width of the diffraction peak attributed to Si (111) after the pulverization step (S2) is large. In addition, the average crystallite diameter calculated using the Scherrer equation from the half width of the Si (111) peak after the pulverization step (S2) was 9.8 nm. Also, very interestingly, the intensity of the diffraction peak attributed to Si (111) near 2θ = 28.4 ° after the crushing step (S2) is the intensity of other diffraction peaks (for example, Si (220) or Si (311) peak intensity) was found to be larger. In addition, as shown in FIG. 5, the arrangement interval of Si (111) in the crystal lattice of the silicon fine particles after the pulverization step (S2) is 0.31 nm (3.1 cm).

  Based on the above analysis results, for the silicon fine particles and the like after the pulverization step (S2) of the present embodiment, crystalline silicon fine particles having a plane orientation of (111) are mainly multi-layer petals or It can be said that it is an aggregate or aggregate in a state of multiple folds in a scale shape.

Then, lithium fine particles and / or aggregates or aggregates thereof after the pulverization step (S2) or the oxide film removal step (S3) of this embodiment are used as a part of the negative electrode material of the lithium ion battery. When lithium ions (Li ⁺ ) ionized from the positive electrode material of an ion battery reach the negative electrode, the aggregates or aggregates of the lithium ions (Li ⁺ ) are multiply folded in a multi-layered petal shape or scale shape It is possible to achieve a unique effect that it is easy to enter and exit the heel gap.

  In addition, in the present embodiment, graphite surrounds at least a part of the agglomerates or aggregates of the silicon fine particles in a state of being folded in the above-described multi-layer petal shape or scale shape. Therefore, the presence of the aggregate or aggregate in a state of being folded into a multi-layer petal shape or a scale shape makes it possible to obtain a negative electrode material or a negative electrode in which lithium ions are easily stored and released. In addition, coupled with the specificity of the multi-layered petal-like or scaly shape of the aggregate or aggregate, they are surrounded by graphite, thereby suppressing the degree of freedom of the aggregate or aggregate to some extent. This leads to an increase in cooperation between graphite and the aggregates or aggregates, so that a high degree of stability of the lithium ion migration state can be achieved. As a result, by adopting this negative electrode material, it is possible to realize a lithium ion battery with little change in charge / discharge capacity even when charge / discharge is repeated, in other words, a good charge / discharge cycle characteristic. Alternatively, an increase in charge / discharge capacity can be realized.

<Modification of First Embodiment>
Of the first embodiment, silicon chips or the like (more specifically, crystalline silicon chips or cutting chips) obtained as a result of performing only the cleaning step (S1) are pulverized (S2). Performing the process of forming the complex by the complex forming step (S5) using the complex forming unit 70 as an example without performing () is one of the modifications that can be adopted. As in the first embodiment, the oxide film removal step (S3) can be performed after the cleaning step (S1). Moreover, similarly to 1st Embodiment, the coating formation part (S4), ie, the coating formation part 60 which forms the carbon which covers at least one part on the surface of the above-mentioned chip or the above-mentioned cutting waste, as an example. The used coating formation step can be performed after the cleaning step (S1) or after the cleaning step (S1) and the oxide film removing step (S3).

  In this modified example, as described above, the graphite surrounds at least a part of silicon chips and the like obtained only by the cleaning step (S1). In this modification, the silicon chips and graphite (typically flaky graphite or expanded graphite) are contained in the composite forming unit 70 used in the first embodiment. be introduced. After that, by performing the same process as the composite formation step (S5) of the first embodiment, a composite in which at least a part of silicon chips or the like is surrounded by graphite is formed.

  Even when this modification is employed, the same or at least part of the effect of the first embodiment can be achieved.

<Second Embodiment>
In the lithium ion battery of this embodiment, a silicon chip or the like of the following aspects (1) to (3) or a silicon fine particle surrounded by graphite is used as a negative electrode material. The configuration other than the negative electrode material is the same as the configuration of a conventional CR2032-type coin cell lithium ion battery.
(1) Graphite surrounds at least a part of silicon fine particles and / or aggregates or aggregates of silicon fine particles in a state of being folded into a multi-layer petal shape or a scale shape.
(2) In (1), at least a part of the surface of the silicon fine particles and / or the aggregates or aggregates is covered with carbon.
(3) At least a part of the crystalline silicon chips or chips are surrounded by graphite.

  FIG. 8 is a schematic configuration diagram of the lithium ion battery 500 of the present embodiment. The lithium ion battery 500 of this embodiment includes a negative electrode 512 that is electrically connected to the negative electrode material and the negative electrode material 514 and a positive electrode that is electrically connected to the positive electrode material and the positive electrode material 518 in the CR5102-type coin cell container 510. 516, a separator 520 that electronically insulates the negative electrode material and negative electrode material 514 from the positive electrode material and positive electrode material 518, and an electrolyte solution 530. Further, the lithium ion battery 500 of the present embodiment has an external circuit including a power source 540 and a resistor 550 connected to the negative electrode 512 and the positive electrode 516 in order to realize charging and discharging.

  Moreover, the manufacturing method of the lithium ion battery 500 of this embodiment is as follows.

  Regarding the manufacturing method of the negative electrode, first, the silicon fine particles produced in the first embodiment, in which at least a part of the silicon fine particles and the like are surrounded by graphite, or at least a part of the surface is covered with carbon About 0.3 g of a material surrounded by graphite (hereinafter collectively referred to as “negative electrode active material”), 1 wt% CMC binder aqueous solution, SBR binder aqueous dispersion (manufactured by JSR Corporation, TRD2001) In a solution of about 10 mL (milliliter).

  In this embodiment, the dry weight ratio is 67: 11: 13: 9 or 50: 25: 20: 5 in the order of silicon fine particles, carbon black, CMC binder aqueous solution, and SBR binder aqueous dispersion. Blend as follows. Moreover, in one modification of this embodiment, it mix | blends so that it may become 50: 25: 20: 5 in order of dry weight ratio, such as a silicon fine particle, carbon black, CMC binder aqueous solution, and PVA binder aqueous dispersion. To do.

  Next, the slurry prepared by mixing using an agate mortar is 15 μm thick and has a thickness of about 30 μm to about 200 μm after drying on one side of a copper foil of about 9 cm (length) × 10 cm (width). After the coating, a drying process is performed on the hot plate in the air at 80 ° C. for about 1 hour. Thereafter, the working electrode is formed by punching the above-described copper foil together with the dry slurry into a circle having a diameter corresponding to the battery standard CR2032 type coin cell of 11.3 mm. After measuring the weight of the working electrode, the material dried again by vacuum heating at 120 ° C. for 6 hours in the glow box is pasted on the inner surface of the negative electrode 512 made of copper foil, whereby A negative electrode is produced.

  Next, as a positive electrode, a positive electrode 516 was formed by punching a lithium substrate into a circle having a diameter of 13 mm in order to evaluate the characteristics of the negative electrode material using a lithium ion battery having a half cell structure. As the positive electrode of the lithium ion battery, a known positive electrode can be used instead of the positive electrode 516 described above.

Further, the separator 520 of the present embodiment is a porous polyprolene sheet. In addition, the electrolytic solution 530 of the present embodiment is prepared by adding 1 mol of lithium hexafluorophosphate (1 L) in a solvent (1 L) of ethylene carbonate (EC) / diethyl carbonate (DEC) mixed at a volume ratio of 1/1. An electrolytic solution in which LiPF ₆ ) is dissolved, or a solution obtained by adding fluoroethylene carbonate (FEC) to the electrolytic solution, and injecting an amount within an amount that satisfies the internal volume (about 1 mL) of the CR2032 type coin cell. is there.

  The positive electrode material and positive electrode material 518, the positive electrode 516, the negative electrode material and negative electrode material 514, the negative electrode 512, the separator 520, and the electrolyte solution 530 are placed in the container 510 of the CR2032-type coin cell. Thereafter, the constituent materials of the separator 520 and the electrolytic solution 530 are sealed in the container 510 in a state where the positive electrode 516 and the negative electrode 512 of the outer frame of the coin cell are insulated in a glove box in an argon atmosphere. Thus, a lithium ion battery 500 of a CR2032-type coin cell was prototyped.

  Examples of the electrolytic solvent constituting the electrolytic solution 530 in this embodiment are ethylene carbonate (EC), propylene carbonate (PC) (polyprolene sheet) cyclic carbonate, dimethyl carbonate (DMC), and diethyl carbonate (DEC). ) And the like. Further, a supporting salt such as lithium hexafluorophosphate (LiPF) or lithium tetrafluoroborate (LiBF) can be used by dissolving in the above-mentioned electrolytic solvent.

  By adopting the above-described structure, coupled with the presence of the above-mentioned silicon fine particles, or the specificity of the multi-layered petal-like or scale-like shape of the aggregate or aggregate, these are surrounded by graphite. By suppressing the degree of freedom of the silicon fine particles and / or the aggregates or aggregates to a certain extent, the cooperation between graphite and the silicon fine particles and / or graphite and the aggregates or the aggregates can be reduced. It leads to increase. As a result, by adopting this negative electrode material, it is possible to realize a lithium ion battery with little change in charge / discharge capacity even when charge / discharge is repeated, in other words, a good charge / discharge cycle characteristic. Alternatively, an increase in charge / discharge capacity can be realized.

<Other embodiment (1)>
By the way, in each of the above-described embodiments, as a starting material, a single-crystal or polycrystalline silicon lump or silicon chips formed in the cutting process of an ingot is exemplified, but other forms of silicon It is another aspect in which chips and the like are used as a starting material. Specifically, silicon chips and the like are not necessarily formed in the cutting process of silicon ingots in the production process of semiconductor products. It is also possible to cut them randomly or randomly. Further, so-called silicon waste materials such as silicon chips and silicon polishing scraps that are normally discarded can be used as starting materials such as silicon fine particles in each of the embodiments described above. Fine debris obtained by crushing debris, waste wafers and the like may also be included. Furthermore, silicon fine particles using a material such as metallic silicon chips or metallic silicon polishing scraps, or other metallic silicon particles as a starting material may be employed.

<Other embodiment (2)>
Further, the impurity concentration of the n-type crystalline silicon in each of the above embodiments is not particularly limited. Further, not only n-type but also p-type crystalline silicon can be employed. Furthermore, crystalline silicon which is a genuine semiconductor can also be employed as the crystalline silicon in each of the embodiments described above. Note that since movement of electrons in the negative electrode material of the lithium ion battery is emphasized, it is more preferable to use crystalline silicon containing an n-type impurity. Further, the graphite fine particles of about 1 wt% to about 3 wt% indicated by the peak intensities of the C (002) plane and the C (003) plane shown in FIG. 7B are silicon fine particles or the like. Therefore, it is added that a part or all of these graphites can contribute to the improvement of the conductivity of the negative electrode material.

<Other embodiment (3)>
Further, the silicon fine particles and the like of each of the above-described embodiments and the lithium ion battery including the same are not limited to application to the coin cell type structure introduced in the second embodiment. Therefore, the present invention can be applied to various devices or apparatuses including or using a lithium ion battery having a larger electric capacity than a coin cell type structure.

<Other embodiment (4)>
Moreover, as an alternative device of the negative electrode material (or negative electrode) manufacturing apparatus 100 of the lithium ion battery shown in FIG. 2 in the first embodiment, the negative electrode material (or negative electrode) of the lithium ion battery shown in FIG. The manufacturing apparatus 200 may be employed. Specifically, from the viewpoint of simplification of equipment and / or reduction of manufacturing cost, in the negative electrode material (or negative electrode) manufacturing apparatus 200 of a lithium ion battery, silicon chips formed in the cutting process of silicon, etc. This is a mode in which the washer 10 for washing is also used as the grinder 20 for forming the silicon fine particles 2 by crushing the washed silicon chips and the like. Therefore, in the apparatus / method shown in FIG. 9, for example, beads having a relatively large diameter are used in the cleaning process, and beads having a relatively small diameter are used in the pulverization process, so that the negative electrode material of the lithium ion battery is used. Silicon fine particles 2 are obtained. However, in order to obtain the silicon fine particles 2 described in the first embodiment with higher accuracy, the silicon fine particles are processed by a bead mill machine after processing using a ball mill machine as in the first embodiment. Etc. 2 is preferably formed.

<Other embodiment (5)>
In addition, according to the analysis of the inventors of the present application, the amount of fluoroethylene carbonate (FEC) added to the electrolyte solution 530 in the second embodiment depends on the charge capacity value, the discharge capacity value, and the charge / discharge cycle characteristics. It became clear that it could have an impact. This is to form a good (eg, low resistance and / or thin) solid electrolyte interface (SEI) on the surface of the negative electrode material.

  The disclosure of each of the above-described embodiments is described for explaining the embodiments, and is not described for limiting the present invention. In addition, modifications within the scope of the present invention including other combinations of the embodiments are also included in the claims.

  The negative electrode material of the lithium ion battery and the lithium ion battery including the same of the present invention include, for example, various power generation or power storage devices (including small household power storage devices and large power storage systems), smartphones, portable information terminals, and portable electronics. Equipment (cell phones, portable music players, notebook computers, digital cameras / videos), electric vehicles, hybrid electric vehicles (HEV) or plug-in hybrid electric vehicles (PHEV), motorcycles powered by motors, motors The present invention can be applied to various devices or apparatuses including a motor tricycle as a power source, other transport machines or vehicles.

1 Chips, etc. 2 Silicon fine particles, etc. 10 Washing machine (cleaning and preliminary grinding machine)
11 Ball 13a Pot 13b Lid 15 Rotating body 20 Crusher 21 Inlet 22 Processing chamber 24 Discharge 25 Filter 40 Rotary evaporator 50 Oxide film removal tank 55 Hydrofluoric acid or ammonium fluoride aqueous solution 57 Stirrer 58 Centrifugal separator 60 Coating Formation unit 70 Complex formation unit 80 Mixing unit 100 Negative electrode material (or negative electrode) manufacturing apparatus for lithium ion battery 500 Lithium ion battery 510 Container 512 Negative electrode 514 Negative electrode material and negative electrode material 516 Positive electrode 518 Positive electrode material and positive electrode material 520 Separator 530 Electrolytic solution 540 Power supply 550 Resistance

Claims (23)

Silicon fine particles having a volume distribution with a mode diameter and a median diameter of 30 nm or less and / or an aggregate or aggregate of the silicon fine particles, wherein the aggregate is in a state of being folded at least in a multi-layer petal shape or a scale shape Or comprising the aggregate, and the graphite surrounds at least a part of the silicon fine particles and / or the aggregate or the aggregate,
A negative electrode material for lithium ion batteries. At least a part of the surface of the silicon fine particles and / or the aggregates or the aggregates is covered with carbon;
The negative electrode material of the lithium ion battery according to claim 1. 3. The negative electrode material for a lithium ion battery according to claim 1, wherein the mode diameter and the median diameter include the silicon fine particles and / or the aggregates or the aggregates having a volume distribution of 20 nm or less. According to the X-ray diffraction measurement of the silicon fine particles and / or the aggregates or the aggregates, the intensity of diffraction peaks attributed to Si (111) near 2θ = 28.4 ° is higher than the intensity of other diffraction peaks. large,
The negative electrode material for a lithium ion battery according to any one of claims 1 to 3. The graphite is expanded graphite;
The negative electrode material for a lithium ion battery according to any one of claims 1 to 4. Including crystalline silicon chips or chips, and graphite surrounds at least a portion of the chips or chips;
A negative electrode material for lithium ion batteries. At least a part of the surface of the chip or the cutting waste was covered with carbon,
The negative electrode material of the lithium ion battery according to claim 6. A negative electrode material for a lithium ion battery according to any one of claims 1 to 7,
Lithium ion battery.   An apparatus comprising the lithium ion battery according to claim 8. By crushing crystalline silicon, silicon fine particles having a volume distribution with a mode diameter and a median diameter of 30 nm or less and / or an aggregate or aggregate of the silicon fine particles, at least in a multi-layer petal shape or scale shape A pulverized portion that forms the aggregate or the aggregate in a state of being folded on,
The graphite contains the graphite and the silicon fine particles by surrounding at least a part of the silicon fine particles and / or the aggregates or the aggregates, or the graphite and the aggregates or the aggregates. A complex forming part that forms a complex including:
An apparatus for producing a negative electrode material for a lithium ion battery. A coating forming part that forms carbon that covers at least a part of the surface of the silicon fine particles and / or the aggregates or the aggregates;
The manufacturing apparatus of the negative electrode material of the lithium ion battery of Claim 10. The crystalline silicon is chips or cutting scraps cut by a fixed abrasive wire.
The manufacturing apparatus of the negative electrode material of the lithium ion battery of Claim 10 or Claim 11. The pulverization unit includes a ball mill and a bead mill used after the ball mill.
The manufacturing apparatus of the negative electrode material of the lithium ion battery of any one of Claims 10 thru | or 12. Graphite forms a composite containing the graphite and the chips or the cutting scraps by surrounding at least a part of the crystalline silicon chips or cutting scraps, and a composite forming section,
An apparatus for producing a negative electrode material for a lithium ion battery. The complex forming unit includes a bead mill.
The manufacturing apparatus of the negative electrode material of the lithium ion battery of Claim 14. A coating forming part that forms carbon covering at least a part of the surface of the chip or the cutting waste;
The manufacturing apparatus of the negative electrode material of the lithium ion battery of Claim 14 or Claim 15. By crushing crystalline silicon, silicon fine particles having a volume distribution with a mode diameter and a median diameter of 30 nm or less and / or an aggregate or aggregate of the silicon fine particles, at least in a multi-layer petal shape or scale shape Crushing step to form the aggregate or aggregate in a state of being folded on,
The graphite contains the graphite and the silicon fine particles by surrounding at least a part of the silicon fine particles and / or the aggregates or the aggregates, or the graphite and the aggregates or the aggregates. Forming a complex comprising: a complex forming step;
A method for producing a negative electrode material for a lithium ion battery. A coating forming step of forming carbon covering at least part of the surface of the silicon fine particles and / or the aggregates or the aggregates;
The manufacturing method of the negative electrode material of the lithium ion battery of Claim 17. The crystalline silicon is chips or cutting scraps cut by a fixed abrasive wire.
The manufacturing method of the negative electrode material of the lithium ion battery of Claim 17 or Claim 18. In the pulverizing step, the crystalline silicon is pulverized by a bead mill after being pulverized by a ball mill, thereby forming the aggregate or the aggregate.
The method for producing a negative electrode material for a lithium ion battery according to any one of claims 17 to 19. Including a composite forming step in which graphite forms a composite containing the graphite and the chips or the cutting waste by surrounding at least a part of the crystalline silicon chips or the cutting waste.
A method for producing a negative electrode material for a lithium ion battery. In the complex formation step, the complex is formed by a bead mill.
The manufacturing method of the negative electrode material of the lithium ion battery of Claim 21. A coating forming step of forming carbon covering at least part of the surface of the chip or the cutting waste,
The manufacturing method of the negative electrode material of the lithium ion battery of Claim 21 or Claim 22.