JP6376054B2 - Silicon material, manufacturing method thereof, and secondary battery including silicon material - Google Patents

Description

  The present invention relates to a silicon material, a manufacturing method thereof, and a secondary battery including the silicon material.

  Silicon is known to be used as a component of semiconductors, solar cells, secondary batteries, etc. Therefore, research on silicon is actively conducted.

For example, Patent Document 1 describes that CaSi ₂ was treated with concentrated hydrochloric acid to produce a layered polysilane, and that the layered polysilane can function as an active material of a secondary battery.

Patent Document 2 discloses that a layered silicon compound mainly composed of layered polysilane obtained by reacting CaSi ₂ and an acid to remove Ca, and heating the layered silicon compound at 300 ° C. or higher to generate hydrogen. It describes that a detached silicon material was manufactured and a lithium ion secondary battery comprising the silicon material as an active material.

JP 2011-90806 A International Publication No. 2014/080608

  Incidentally, the layered silicon compound mainly composed of layered polysilane described in the above-mentioned patent document contains a large amount of components such as chlorine derived from an anion of an acid, even though it has undergone a cleaning process. Here, the component derived from the acid anion may impair the function of the layered polysilane itself. Further, even in a silicon material obtained by heating a layered silicon compound containing layered polysilane as a main component to release hydrogen, components derived from the acid anion described above remain. And the component derived from the anion of an acid may impair the function which silicon material itself has.

  This invention is made | formed in view of this situation, and it aims at providing the manufacturing method of the silicon material which can reduce content of the component derived from the anion of an acid.

  This inventor repeated trial and error, and examined the manufacturing method of the silicon material which can reduce content of the component derived from the anion of an acid. As a result, the present inventor has found a method for producing a silicon material capable of reducing the content of components derived from an anion of an acid, and the silicon material produced by the production method functions as an active material for a secondary battery. This was confirmed and the present invention was completed.

That is, in the method for producing a silicon material of the present invention, a) a step of producing a layered silicon compound by reacting CaSi ₂ with an acid in the presence of alcohol, and b) a step of heating the layered silicon compound at 300 ° C. or higher. It is characterized by including.

  The method for producing a silicon material of the present invention can suitably reduce the content of components derived from acid anions in the silicon material.

2 is an enlarged powder X-ray diffraction chart of the layered silicon compound of Example 1. 3 is an enlarged powder X-ray diffraction chart of a layered silicon compound of Comparative Example 1.

  The best mode for carrying out the present invention will be described below.

In the method for producing a layered silicon compound containing layered polysilane as a main component in which CaSi ₂ is reacted with an acid, the reaction proceeds by replacing Ca with hydrogen. The reaction can be represented by the following reaction formula when hydrochloric acid is used as the acid.
3CaSi ₂ + 6HCl → Si ₆ H ₆ + 3CaCl ₂

That is, theoretically, the reaction proceeds if an acid capable of supplying 2 moles of protons to 1 mole of CaSi ₂ is present in the reaction system.

However, for example, when concentrated hydrochloric acid is selected as the acid and an amount corresponding to 2 mol of HCl is used with respect to 1 mol of CaSi ₂ , the amount of the reaction solution is too small to sufficiently stir. It cannot be said that polysilane can be produced with good reproducibility.

  In order to improve such a situation, the conventional production method has used concentrated hydrochloric acid not only as an acid but also as a solvent for sufficiently stirring the reaction solution.

  In contrast to the conventional production method, alcohol is used instead of concentrated hydrochloric acid as a solvent in the step a) in the production method of the silicon material of the present invention.

First, a) process is demonstrated. The step a) is a step for producing a layered silicon compound by reacting CaSi ₂ with an acid in the presence of alcohol.

  The alcohol is preferably in a liquid state at normal temperature (25 ° C.), and is preferably miscible with the acid used in step a). The alcohol may be a monohydric alcohol having one hydroxyl group in the molecule or a polyhydric alcohol having a plurality of hydroxyl groups. One kind of alcohol may be used, or a plurality of kinds may be used in combination.

  As carbon number of the hydrocarbon group of alcohol, the inside of the range of 1-6 is preferable, the inside of the range of 1-4 is more preferable, and the inside of the range of 1-2 is further more preferable. The hydrocarbon group of the alcohol is preferably a saturated hydrocarbon group.

  Specific examples of alcohol include methanol, ethanol, n-propanol, 2-propanol, n-butanol, iso-butanol, sec-butanol, 1-pentanol, 2-pentanol, 3-pentanol, 2-methyl-1 -Monohydric alcohols such as butanol, 3-methyl-1-butanol, 2-methyl-2-butanol, 3-methyl-2-butanol, 1-hexanol, 2-hexanol, 3-hexanol, ethylene glycol, propylene glycol, 1,2-butanediol, 1,3-butanediol, 1,4-butanediol, 2,3-butanediol, 1,2-pentanediol, 1,3-pentanediol, 1,4-pentanediol, 1 , 5-pentanediol, 2,3-pentanediol, 1,2-hexane Dihydric alcohols such as ol, glycerol, 1,2,3-butanetriol, mention may be made of trihydric alcohols such as 1,2,4-butanetriol.

  From the viewpoint of the stability of the layered silicon compound obtained in the step a), methanol is most preferable as the alcohol.

CaSi ₂ generally has a structure in which a Ca layer and a Si layer are laminated. CaSi ₂ may be synthesized by a known production method, or a commercially available one may be adopted. The CaSi ₂ used in the step a) is preferably pulverized in advance.

In the step a), the mass ratio of alcohol to CaSi ₂ is preferably in the range of 0.5: 1 to 30: 1, more preferably in the range of 0.5: 1 to 15: 1, and 1: 1 to 5 A range of 1 is more preferable. If the amount of alcohol is too small, the stirring in step a) may be insufficient, and conversely, if the amount of alcohol is too large, the acid concentration will be too diluted, so that the reaction in step a) is sufficient. There is a risk of not progressing.

  Acids include hydrogen fluoride, hydrogen chloride, hydrogen bromide, hydrogen iodide, sulfuric acid, nitric acid, phosphoric acid, formic acid, acetic acid, methanesulfonic acid, tetrafluoroboric acid, hexafluorophosphoric acid, hexafluoroarsenic acid, fluoro Examples include antimonic acid, hexafluorosilicic acid, hexafluorogermanic acid, hexafluorotin (IV) acid, trifluoroacetic acid, hexafluorotitanic acid, hexafluorozirconic acid, trifluoromethanesulfonic acid, and fluorosulfonic acid. These acids may be used alone or in combination.

  The acid is preferably an inorganic acid, and particularly preferred inorganic acids include hydrogen fluoride, hydrogen chloride, hydrogen bromide, hydrogen iodide, tetrafluoroboric acid, and hexafluorophosphoric acid.

  The acid is preferably used as an aqueous solution from the viewpoint of the stirring state of the reaction solution and the convenience and safety of work.

acid used in step a), it may be used in an amount capable of providing 2 or more equivalents of protons relative CaSi _2. When the amount of CaSi ₂ and acid used is shown in molar ratio, it is preferably 1: 2 or more, more preferably in the range of 1: 2 to 1: 6, and still more preferably in the range of 1: 2 to 1: 4. If the amount of acid used is too small, the reaction may not proceed sufficiently. Moreover, when there is too much usage-amount of an acid, there exists a possibility that many components derived from the anion of an acid may be contained in a layered silicon compound.

  The reaction conditions in the step a) are preferably reduced pressure conditions such as vacuum or an inert gas atmosphere, and the reaction time and reaction temperature are not particularly limited, but the reaction temperature is usually in the range of −10 ° C. to 50 ° C. It is. The reaction time of a) process should just be set suitably, For example, 1 to 30 hours, 3 to 20 hours, and 10 to 20 hours can be illustrated.

From the viewpoint of reaction control, step a) is performed by a method in which an aqueous acid solution is dropped into a suspension obtained by suspending CaSi ₂ in an alcohol or a mixed solvent of alcohol and water to obtain a reaction solution. Is preferred. Examples of the mass ratio of alcohol to water in the mixed solvent of alcohol and water include 10: 1 to 1: 1 and 9: 1 to 3: 1.

  a) The concentration of the acid in the reaction solution in the step is preferably 3 to 30% by mass, more preferably 5 to 25% by mass, further preferably 10 to 25% by mass, and most preferably 15 to 25% by mass.

In the step a), the reaction formula when hydrochloric acid is used as the acid is as follows as described above.
3CaSi ₂ + 6HCl → Si ₆ H ₆ + 3CaCl ₂

Si ₆ H ₆ corresponds to an ideal layered silicon compound. It can be considered that this reaction forms Si—H bonds while Ca in the layered CaSi ₂ is substituted with 2H. The layered silicon compound has a layer shape because the basic skeleton of the Si layer in the raw material CaSi ₂ is maintained.

As described above, in the step a), the acid is preferably used as an aqueous solution. Here, since Si ₆ H ₆ can react with water, the layered silicon compound is rarely obtained only with a compound of Si ₆ H ₆ , and usually contains an element derived from an anion of oxygen or acid.

  In order to isolate the layered silicon compound obtained in the step a), a filtration step, a washing step, and a drying step may be appropriately performed. Since some layered silicon compounds generate heat in the air, it is preferable to carry out these steps in an inert gas atmosphere such as argon.

  Next, step b) will be described. Step b) is a step of heating the layered silicon compound at 300 ° C. or higher. Hereinafter, the silicon material manufactured through the steps a) and b) may be referred to as the silicon material of the present invention.

From a chemical point of view, step b) is a step of synthesizing a silicon material by removing hydrogen from the layered silicon compound by heating. b) The process is represented by an ideal reaction formula as follows.
Si ₆ H ₆ → 6Si + 3H ₂ ↑

  However, since the layered silicon compound actually used in step b) contains an element derived from an anion of oxygen or acid, and also contains inevitable impurities, the silicon material actually obtained also contains an element derived from an anion of oxygen or acid. In addition, it also contains inevitable impurities.

  The step b) is preferably performed in a non-oxidizing atmosphere having a lower oxygen content than that in normal air. Examples of the non-oxidizing atmosphere include a reduced pressure atmosphere including a vacuum and an inert gas atmosphere. The heating temperature is preferably in the range of 350 ° C to 1200 ° C, more preferably in the range of 400 ° C to 1200 ° C. If the heating temperature is too low, hydrogen may not be released sufficiently. On the other hand, if the heating temperature is too high, energy is wasted. What is necessary is just to set a heating time suitably according to heating temperature, and it is also preferable to determine a heating time, measuring the quantity of hydrogen etc. which escapes out of a reaction system. By appropriately selecting the heating temperature and the heating time, the ratio of amorphous silicon and silicon crystallites contained in the silicon material to be manufactured, and the size of the silicon crystallites can also be adjusted, and further manufactured. The shape and size of a nano-level layer containing amorphous silicon and silicon crystallites contained in the silicon material can also be prepared.

  The size of the silicon crystallite is preferably nano-sized. Specifically, the silicon crystallite size is preferably in the range of 0.5 nm to 300 nm, more preferably in the range of 1 nm to 100 nm, still more preferably in the range of 1 nm to 50 nm, and particularly in the range of 1 nm to 10 nm. preferable. Note that the silicon crystallite size is calculated from the Scherrer equation using X-ray diffraction measurement (XRD measurement) on the silicon material and using the half-value width of the diffraction peak of the Si (111) plane of the obtained XRD chart. The

  By the step b), a silicon material having a structure in which a plurality of plate-like silicon bodies are laminated in the thickness direction can be obtained. This structure can be confirmed by observation with a scanning electron microscope or the like. In consideration of using the silicon material of the present invention as an active material of a lithium ion secondary battery, the plate-like silicon body has a thickness of 10 nm to 100 nm for efficient insertion and desorption reaction of lithium ions. Those within the range are preferable, and those within the range of 20 nm to 50 nm are more preferable. The length of the plate-like silicon body in the major axis direction is preferably in the range of 0.1 μm to 50 μm. The plate-like silicon body preferably has a (length in the major axis direction) / (thickness) range of 2 to 1000.

  The silicon material of the present invention may be pulverized and classified into particles having a certain particle size distribution. As a preferable particle size distribution of the silicon material of the present invention, D50 can be exemplified within a range of 1 to 30 μm when measured with a general laser diffraction type particle size distribution measuring apparatus.

  The silicon material of the present invention preferably contains oxygen at 20% by mass or less, more preferably contains at 17% by mass or less, more preferably contains at 14% by mass or less, particularly preferably contains at 13% by mass or less. preferable. Examples of the lower limit of the oxygen content include 5% by mass and 10% by mass.

  The silicon material of the present invention preferably contains 0.001 to 5% by mass of the element derived from the anion of the acid used in step a), more preferably contains 0.01 to 3% by mass. More preferably, it is contained at ˜1% by mass.

  As a suitable silicon material of the present invention, for example, a material containing 0.001 to 5% by mass of an element derived from an acid anion and 14% by mass or less of oxygen can be cited.

  The silicon material of the present invention can be used as a negative electrode active material for a secondary battery such as a lithium ion secondary battery. In that case, the silicon material of the present invention is preferably coated with carbon.

  Hereinafter, a secondary battery comprising the silicon material of the present invention as a negative electrode active material will be described by taking a lithium ion secondary battery as an example. The lithium ion secondary battery comprising the silicon material of the present invention as the negative electrode active material is hereinafter referred to as the lithium ion secondary battery of the present invention. Specifically, the lithium ion secondary battery of the present invention includes a positive electrode, a negative electrode including the silicon material of the present invention as a negative electrode active material, an electrolytic solution, and, if necessary, a separator.

  The positive electrode has a current collector and a positive electrode active material layer bound to the surface of the current collector.

  The current collector refers to a chemically inert electronic conductor that keeps a current flowing through an electrode during discharge or charging of a lithium ion secondary battery. As the current collector, at least one selected from silver, copper, gold, aluminum, tungsten, cobalt, zinc, nickel, iron, platinum, tin, indium, titanium, ruthenium, tantalum, chromium, molybdenum, and stainless steel, etc. Metal materials can be exemplified. The current collector may be covered with a known protective layer. What collected the surface of the electrical power collector by the well-known method may be used as an electrical power collector.

  The current collector can take the form of a foil, a sheet, a film, a linear shape, a rod shape, a mesh, or the like. Therefore, for example, a metal foil such as a copper foil, a nickel foil, an aluminum foil, and a stainless steel foil can be suitably used as the current collector. When the current collector is in the form of foil, sheet or film, the thickness is preferably in the range of 1 μm to 100 μm.

  The positive electrode active material layer includes a positive electrode active material and, if necessary, a conductive additive and / or a binder.

As the positive electrode active material, the layered compound Li _a Ni _b Co _c Mn _{d De} O _f (0.2 ≦ a ≦ 2, b + c + d + e = 1, 0 ≦ e <1, D is Li, Fe, Cr, Cu, At least one element selected from Zn, Ca, Mg, S, Si, Na, K, Al, Zr, Ti, P, Ga, Ge, V, Mo, Nb, W, La, 1.7 ≦ f ≦ 3 ), Li ₂ MnO ₃ . Further, as a positive electrode active material, a solid solution composed of a spinel such as LiMn ₂ O ₄ and a mixture of a spinel and a layered compound, LiMPO ₄ , LiMVO ₄ or Li ₂ MSiO ₄ (wherein M is Co, Ni, Mn, And a polyanionic compound represented by (selected from at least one of Fe). Furthermore, as the positive electrode active material, tavorite compound (the M a transition metal) LiMPO ₄ F, such as LiFePO ₄ F represented by, Limbo ₃ such LiFeBO ₃ (M is a transition metal) include borate-based compound represented by be able to. Any metal oxide used as the positive electrode active material may have the above composition formula as a basic composition, and a metal element contained in the basic composition may be substituted with another metal element. Further, as a positive electrode active material, a positive electrode active material that does not contain lithium ions that contribute to charge / discharge, for example, sulfur alone, a compound in which sulfur and carbon are combined, a metal sulfide such as TiS ₂ , V ₂ O ₅ , MnO ₂ and other oxides, polyaniline and anthraquinone, compounds containing these aromatics in the chemical structure, conjugated materials such as conjugated diacetate-based organic substances, and other known materials can also be used. Further, a compound having a stable radical such as nitroxide, nitronyl nitroxide, galvinoxyl, phenoxyl, etc. may be adopted as the positive electrode active material. When using a positive electrode active material that does not contain lithium, it is necessary to add ions to the positive electrode and / or the negative electrode in advance by a known method. Here, in order to add the ion, a metal or a compound containing the ion may be used.

  The conductive assistant is added to increase the conductivity of the electrode. Therefore, the conductive auxiliary agent may be added arbitrarily when the electrode conductivity is insufficient, and may not be added when the electrode conductivity is sufficiently excellent. The conductive auxiliary agent may be any chemically inert electronic high conductor, such as carbon black, graphite, acetylene black, ketjen black (registered trademark), vapor grown carbon fiber (Vapor Grown Carbon). Fiber: VGCF) and various metal particles are exemplified. These conductive assistants can be added to the active material layer alone or in combination of two or more.

  The blending ratio of the conductive additive in the active material layer is preferably a mass ratio of active material: conductive additive = 1: 0.005 to 1: 0.5, and 1: 0.01 to 1: 0. .2 is more preferable, and 1: 0.03 to 1: 0.1 is even more preferable. This is because if the amount of the conductive auxiliary is too small, an efficient conductive path cannot be formed, and if the amount of the conductive auxiliary is too large, the moldability of the active material layer is deteriorated and the energy density of the electrode is lowered.

  The binder plays a role of securing an active material or a conductive auxiliary agent to the surface of the current collector and maintaining a conductive network in the electrode. Examples of the binder include fluorine-containing resins such as polyvinylidene fluoride, polytetrafluoroethylene, and fluororubber, thermoplastic resins such as polypropylene and polyethylene, imide resins such as polyimide and polyamideimide, alkoxysilyl group-containing resins, poly ( Examples thereof include acrylic resins such as (meth) acrylic acid, styrene-butadiene rubber (SBR), and carboxymethyl cellulose. These binders may be used singly or in plural.

  The blending ratio of the binder in the active material layer is preferably a mass ratio of active material: binder = 1: 0.001 to 1: 0.3, and 1: 0.005 to 1: 0. .2 is more preferable, and 1: 0.01 to 1: 0.15 is still more preferable. This is because when the amount of the binder is too small, the moldability of the electrode is lowered, and when the amount of the binder is too large, the energy density of the electrode is lowered.

  The negative electrode has a current collector and a negative electrode active material layer bound to the surface of the current collector. What is necessary is just to employ | adopt suitably what was demonstrated with the positive electrode about a collector. The negative electrode active material layer includes a negative electrode active material and, if necessary, a conductive additive and / or a binder.

  The negative electrode active material only needs to contain the silicon material of the present invention, and only the silicon material of the present invention may be employed, or the silicon material of the present invention and a known negative electrode active material may be used in combination. .

  About the conductive support agent and binder used for a negative electrode, what was demonstrated in the positive electrode should just be employ | adopted suitably suitably with the same mixture ratio.

  In order to form an active material layer on the surface of the current collector, a current collecting method such as a roll coating method, a die coating method, a dip coating method, a doctor blade method, a spray coating method, or a curtain coating method can be used. An active material may be applied to the surface of the body. Specifically, an active material, a solvent, and, if necessary, a binder and / or a conductive aid are mixed to prepare a slurry. Examples of the solvent include N-methyl-2-pyrrolidone, methanol, methyl isobutyl ketone, and water. The slurry is applied to the surface of the current collector and then dried. In order to increase the electrode density, the dried product may be compressed.

  The electrolytic solution includes a nonaqueous solvent and an electrolyte dissolved in the nonaqueous solvent.

  As the non-aqueous solvent, cyclic esters, chain esters, ethers and the like can be used. Examples of cyclic esters include ethylene carbonate, propylene carbonate, butylene carbonate, gamma butyrolactone, vinylene carbonate, 2-methyl-gamma butyrolactone, acetyl-gamma butyrolactone, and gamma valerolactone. Examples of chain esters include dimethyl carbonate, diethyl carbonate, dibutyl carbonate, dipropyl carbonate, ethyl methyl carbonate, propionic acid alkyl ester, malonic acid dialkyl ester, and acetic acid alkyl ester. Examples of ethers include tetrahydrofuran, 2-methyltetrahydrofuran, 1,4-dioxane, 1,2-dimethoxyethane, 1,2-diethoxyethane, and 1,2-dibutoxyethane. As the non-aqueous solvent, a compound in which part or all of hydrogen in the chemical structure of the specific solvent is substituted with fluorine may be employed.

Examples of the electrolyte include lithium salts such as LiClO ₄ , LiAsF ₆ , LiPF ₆ , LiBF ₄ , LiCF ₃ SO ₃ , and LiN (CF ₃ SO ₂ ) ₂ .

As an electrolytic solution, 0.5 mol / L to 1.7 mol of a lithium salt such as LiClO ₄ , LiPF ₆ , LiBF ₄ , LiCF ₃ SO _{3 in} a nonaqueous solvent such as ethylene carbonate, dimethyl carbonate, propylene carbonate, and diethyl carbonate. A solution dissolved at a concentration of about / L can be exemplified.

  The separator separates the positive electrode and the negative electrode and allows lithium ions to pass while preventing a short circuit due to contact between the two electrodes. As separators, natural resins such as polytetrafluoroethylene, polypropylene, polyethylene, polyimide, polyamide, polyaramid (Aromatic polymer), polyester, polyacrylonitrile and other polysaccharides, cellulose, amylose and other polysaccharides, fibroin, keratin, lignin and suberin Examples thereof include porous bodies, nonwoven fabrics, and woven fabrics using one or more electrically insulating materials such as polymers and ceramics. The separator may have a multilayer structure.

  Next, the manufacturing method of the lithium ion secondary battery of this invention using a positive electrode, a negative electrode, and electrolyte solution is demonstrated.

  A separator is sandwiched between the positive electrode and the negative electrode as necessary to form an electrode body. The electrode body may be either a stacked type in which the positive electrode, the separator and the negative electrode are stacked, or a wound type in which the positive electrode, the separator and the negative electrode are sandwiched. After connecting the current collector of the positive electrode and the current collector of the negative electrode to the positive electrode terminal and the negative electrode terminal that communicate with the outside using a lead for current collection, etc., an electrolyte is added to the electrode body and a lithium ion secondary Use batteries. Moreover, the lithium ion secondary battery of this invention should just be charged / discharged in the voltage range suitable for the kind of active material contained in an electrode.

  The shape of the lithium ion secondary battery of the present invention is not particularly limited, and various shapes such as a cylindrical shape, a square shape, a coin shape, and a laminate shape can be adopted.

  The lithium ion secondary battery of the present invention may be mounted on a vehicle. The vehicle may be a vehicle that uses electric energy from a lithium ion secondary battery for all or a part of its power source, and may be, for example, an electric vehicle or a hybrid vehicle. When a lithium ion secondary battery is mounted on a vehicle, a plurality of lithium ion secondary batteries may be connected in series to form an assembled battery. Examples of devices equipped with lithium ion secondary batteries include various home appliances driven by batteries such as personal computers and portable communication devices, office devices, and industrial devices in addition to vehicles. Furthermore, the lithium ion secondary battery of the present invention includes wind power generation, solar power generation, hydroelectric power generation and other power system power storage devices and power smoothing devices, power supplies for ships and / or auxiliary power supply sources, aircraft, Power supply for spacecraft and / or auxiliary equipment, auxiliary power supply for vehicles that do not use electricity as a power source, power supply for mobile home robots, power supply for system backup, power supply for uninterruptible power supply, You may use for the electrical storage apparatus which stores temporarily the electric power required for charge in the charging station for electric vehicles.

  As mentioned above, although embodiment of this invention was described, this invention is not limited to the said embodiment. The present invention can be implemented in various forms without departing from the gist of the present invention, with modifications and improvements that can be made by those skilled in the art.

  Hereinafter, the present invention will be described more specifically with reference to examples and comparative examples. In addition, this invention is not limited by these Examples.

Example 1
a) Step 50 g of CaSi ₂ (Ca content 32 wt%) was added to 75 g of methanol at 0 ° C. under an argon atmosphere, and the mixture was stirred to obtain a suspension. Under the same conditions, 85.5 g of a 35% by weight HCl aqueous solution was dropped into the suspension to initiate the reaction. After dropping HCl aqueous solution and confirming that foaming disappeared from the reaction solution, the mixture was further stirred for 20 hours under the same conditions. The concentration of HCl with respect to the solvent of the reaction solution was 19% by mass, and the molar ratio of CaSi ₂ and HCl was 1: 2. Thereafter, the reaction solution was heated to room temperature and filtered. The residue was washed with 300 mL of distilled water three times, then with 300 mL of ethanol, and dried under reduced pressure to obtain a layered silicon compound. This was used as the layered silicon compound of Example 1.

b) Step The layered silicon compound of Example 1 was heated at 900 ° C. for 1 hour in an argon atmosphere containing O ₂ in an amount of 1% by volume or less to obtain a silicon material. This was used as the silicon material of Example 1.

  The lithium ion secondary battery of Example 1 was manufactured as follows.

  45 parts by mass of the silicon material of Example 1 as a negative electrode active material, 40 parts by mass of natural graphite as a negative electrode active material, 5 parts by mass of acetylene black as a conductive additive, 10 parts by mass of polyamideimide as a binder, and N-methyl- as a solvent 2-Pyrrolidone was mixed to prepare a slurry. The slurry was applied to the surface of an electrolytic copper foil having a thickness of about 20 μm as a current collector using a doctor blade and dried to form a negative electrode active material layer on the copper foil. Thereafter, the current collector and the negative electrode active material layer were firmly and closely joined by a roll press. This was dried under reduced pressure at 200 ° C. for 2 hours to obtain a negative electrode having a negative electrode active material layer thickness of 23 μm.

  A lithium ion secondary battery (half cell) was produced using the negative electrode produced by the above procedure as an evaluation electrode. The counter electrode was a metal lithium foil having a thickness of 500 μm.

The counter electrode was cut to φ14 mm and the evaluation electrode was cut to φ11 mm, and a separator (Hoechst Celanese glass filter and Celgard “Celgard 2400”) was interposed between the two electrodes to form an electrode body. This electrode body was accommodated in a battery case (CR2032-type coin battery member, manufactured by Hosen Co., Ltd.). Into the battery case, a nonaqueous electrolyte solution in which LiPF ₆ was dissolved at a concentration of 1M was poured into a mixed solvent in which ethylene carbonate and diethyl carbonate were mixed at a volume ratio of 1: 1, the battery case was sealed, and A lithium ion secondary battery was obtained.

(Example 2)
a) In the step, Example 1 except that 0.9 g of ethanol was used instead of 75 g of methanol, 1 g of CaSi ₂ (Ca content 32 wt%) and 1.7 g of an aqueous HCl solution having a concentration of 35 wt% were used. In the same manner, the layered silicon compound, silicon material and lithium ion secondary battery of Example 2 were produced. The concentration of HCl in the solvent of the reaction solution a) step is 23 wt%, and the molar ratio of CaSi ₂ and HCl was 1: 2.

(Example 3)
a) In the step, 3 g of a mixed solvent of 9 parts by mass of ethanol and 1 part by mass of water was used instead of 75 g of methanol, ₂ g of CaSi ₂ (Ca content 32 wt%), and 3.4 g of HCl aqueous solution having a concentration of 35 wt%. A layered silicon compound, a silicon material, and a lithium ion secondary battery of Example 3 were produced in the same manner as in Example 1 except that they were used. The concentration of HCl in the solvent of the reaction solution a) step is 19 wt%, and the molar ratio of CaSi ₂ and HCl was 1: 2.

Example 4
a) In the step, 1.8 g of a mixed solvent of 2 parts by mass of ethanol and 1 part by mass of water is used instead of 75 g of methanol, ₂ g of CaSi ₂ (Ca content 32 wt%) and 3% by weight HCl aqueous solution having a concentration of 35 wt% A layered silicon compound, a silicon material, and a lithium ion secondary battery of Example 4 were produced in the same manner as in Example 1 except that .4 g was used. The concentration of HCl in the solvent of the reaction solution a) step is 23 wt%, and the molar ratio of CaSi ₂ and HCl was 1: 2.

(Example 5)
a) In the step, 21.8 g of ethanol at 25 ° C. was used instead of 75 g of methanol at 0 ° C., 1 g of CaSi ₂ (Ca content 32 wt%), and 4.8 g of HCl aqueous solution having a concentration of 35 wt% were used. The layered silicon compound, silicon material, and lithium ion secondary battery of Example 5 were produced in the same manner as in Example 1 except that the total stirring time was 3 hours. The concentration of HCl in the solvent of the reaction solution a) step is 6 wt%, and the molar ratio of CaSi ₂ and HCl was 1: 6.

(Comparative Example 1)
Under an argon atmosphere, 50 g of CaSi ₂ (Ca content 32 wt%) was added to 507 g of an aqueous HCl solution having a concentration of 35 wt% at 0 ° C. and stirred. After confirming that foaming disappeared from the reaction solution, the mixture was further stirred for 3 hours under the same conditions. Thereafter, the reaction solution was heated to room temperature and filtered. Thereafter, the layered silicon compound, silicon material, and lithium ion secondary battery of Comparative Example 1 were produced in the same manner as in Example 1. The molar ratio of CaSi ₂ and HCl was 1:12.

(Comparative Example 2)
a) In Example 1, except that 1.8 g of water was used instead of 75 g of methanol, ₂ g of CaSi ₂ (Ca content 32 wt%) and 3.4 g of an aqueous HCl solution having a concentration of 35 wt% were used. In the same manner, the layered silicon compound, silicon material, and lithium ion secondary battery of Comparative Example 2 were produced. The concentration of HCl in the solvent of the reaction solution a) step is 23 wt%, and the molar ratio of CaSi ₂ and HCl was 1: 2.

(Comparative Example 3)
a) Layered silicon compound of Comparative Example 3 in the same manner as in Example 5 except that 20 g of water was used instead of 21.8 g of ethanol and 2.5 g of 35% by weight HCl aqueous solution was used in step a). A silicon material and a lithium ion secondary battery were manufactured. The concentration of HCl in the solvent of the reaction solution a) step is 4 wt%, and the molar ratio of CaSi ₂ and HCl was 1: 3.

  Table 1 shows a list of examples and comparative examples.

(Evaluation example 1)
For each silicon material, the amount of chlorine which is an element derived from an anion of an acid was analyzed by fluorescent X-ray elemental analysis. Further, the oxygen amount of each silicon material was analyzed using an oxygen / nitrogen / hydrogen analyzer EMGA (Horiba, Ltd.). Table 2 shows the analysis results for each silicon material.

  From the results in Table 2, the silicon materials of Examples 1 to 5 have significantly reduced the chlorine content, which is an element derived from an acid anion, as compared with the silicon material of Comparative Example 1 obtained by the conventional production method. I understand that. Compared with the silicon material of Comparative Example 1 obtained by the conventional manufacturing method, the silicon materials of Comparative Example 2 and Comparative Example 3 significantly decreased the chlorine content but increased the oxygen content significantly.

(Evaluation example 2)
The layered silicon compounds of Examples 1-4 and Comparative Examples 1-2 were observed in the air. Moreover, about the layered silicon compound of Examples 1-4 and Comparative Examples 1-2, the diffraction pattern was measured using the powder X-ray-diffraction apparatus. The silicon layer interval d is calculated by using 2θ = 9 to 13 ° peak θ indicating the diffraction of the silicon layer interval in the diffraction pattern of each layered silicon compound, the measurement condition, and the Bragg condition: 2dsin θ = nλ. did. The results are shown in Table 3. An enlarged powder X-ray diffraction chart of the layered silicon compound of Example 1 is shown in FIG. 1, and an enlarged powder X-ray diffraction chart of the layered silicon compound of Comparative Example 1 is shown in FIG.

  From the results of Table 3, it can be said that heat generation in the air of the layered silicon compound is observed when the distance d between the silicon layers in the layered silicon compound is 9.0 mm or more. If the distance d between the silicon layers in the layered silicon compound is increased, it is presumed that oxygen in the air is easily inserted into the distance between the silicon layers, and an oxidation reaction is likely to occur.

The difference between the results of Example 1 and Example 2 is that, in the layered silicon compound of Example 1, Si—OCH ₃ in which Si—H and methanol reacted was formed, and in the layered silicon compound of Example 2, Si—H It is presumed that Si—OCH ₂ CH ₃ is produced by the reaction of ethanol with ethanol, and the bulk difference between OCH ₃ and OCH ₂ CH ₃ is considered to be reflected in the distance between the silicon layers. Considering the stability of the layered silicon compound in the air, methanol is most preferable as the alcohol used in the step a).

The difference between the results of Example 3 and Example 4 is that although Si—OCH ₂ CH ₃ in which Si—H and ethanol react with each other in the layered silicon compound of both Examples is generated, Example 4 is more ethanol. Since the amount is small and the amount of water is large, it is considered that in the layered silicon compound of Example 4, a larger amount of Si—OH produced by the reaction of Si—H and water was generated. Considering the stability of the layered silicon compound in the air, it can be said that it is preferable to mix water in advance with the alcohol used in the step a).

(Evaluation example 3)
About the lithium ion secondary battery of Examples 1-5 and the lithium ion secondary battery of Comparative Examples 1-3, it charges until the voltage with respect to the counter electrode of an evaluation electrode will be 0.01V at temperature 25 degreeC and current 0.2mA. Then, discharging was performed at a temperature of 25 ° C. and a current of 0.2 mA until the voltage with respect to the counter electrode of the evaluation electrode became 1V. The (discharge capacity / charge capacity) × 100 at this time was calculated as the initial efficiency (%). In Evaluation Example 3, occlusion of Li in the evaluation electrode is called charging, and discharging Li from the evaluation electrode is called discharging.

  The results are shown in Table 4.

  It turns out that the lithium ion secondary battery of Examples 1-3 showed the outstanding initial stage charge capacity and initial stage efficiency. Moreover, the comparison of the result of the lithium ion secondary battery of Example 4 and the lithium ion secondary battery of Comparative Example 2 and the result of the lithium ion secondary battery of Example 5 and the lithium ion secondary battery of Comparative Example 3 From the comparison, it is understood that the initial charge capacity of the lithium ion secondary battery is improved by adopting the silicon material using alcohol in the step a). It was confirmed that the silicon material of the present invention suitably functions as an active material.

Claims (8)

a) a step of producing a layered silicon compound by reacting CaSi ₂ with an acid in the presence of alcohol;
b) heating the layered silicon compound at 300 ° C. or higher;
A method for producing a silicon material, comprising:
(However, the following manufacturing methods are excluded.
A layered polysilane having a layered structure in which at least one of a hydroxyl group and a hydrogen group is bonded to a silicon skeleton having a structure in which a plurality of six-membered rings composed of silicon atoms are connected to each other is mixed in an organic solvent. And a first step of obtaining a layered compound in which the alkoxysilane has infiltrated between the layers of the layered polysilane,
An aqueous solution of an alkali compound containing at least one metal selected from alkali metals and alkaline earth metals is mixed with the layered compound to hydrolyze the alkoxysilane between the layers of the layered polysilane and form a silicate of the metal. A second step of obtaining a composite precursor,
A silicon composite comprising: a third step of heating the composite precursor in a non-oxidizing atmosphere to decompose the layered polysilane to form amorphous silicon particles having a particle diameter of 0.5 nm to 20 nm. Manufacturing method. )   The method for producing a silicon material according to claim 1, wherein the hydrocarbon group of the alcohol has 1 to 6 carbon atoms. a) a step of producing a layered silicon compound by reacting CaSi ₂ with an acid in the presence of methanol ;
b) heating the layered silicon compound at 300 ° C. or higher;
A method for producing a silicon material, comprising: The method for producing a silicon material according to any one of claims 1 to 3, wherein the molar ratio of CaSi ₂ to the acid is 1: 2 to 1: 6.   The method for producing a silicon material according to any one of claims 1 to 4, wherein the acid concentration relative to the solvent in the reaction solution in step a) is 3 to 30% by mass.   A silicon material comprising an element derived from an anion of an acid in an amount of 0.001 to 5% by mass and oxygen in an amount of 14% by mass or less. The process of manufacturing a silicon material with the manufacturing method of any one of Claims 1-5,
Producing a negative electrode using the silicon material as a negative electrode active material;
The manufacturing method of the secondary battery which comprises a silicon material for a negative electrode as a negative electrode active material containing . A secondary battery comprising the silicon material according to claim 6 as a negative electrode active material in a negative electrode .

Images