JP2013008654A - Method for manufacturing negative electrode active material for nonaqueous electrolyte secondary battery, negative electrode active material for nonaqueous electrolyte secondary battery, lithium ion secondary battery, and electrochemical capacitor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for manufacturing a negative electrode active material for a nonaqueous electrolyte secondary battery which allows the continuous mass production of a negative electrode active material of a nonaqueous electrolyte secondary battery having a high capacity and a high-level cycle performance, and to provide a negative electrode active material for a nonaqueous electrolyte secondary battery, a lithium ion secondary battery, and an electrochemical capacitor.SOLUTION: In the method for manufacturing a negative electrode active material for a nonaqueous electrolyte secondary battery such that the surface of a material capable of occluding and releasing lithium ions is covered with a graphite coating, the step of covering the surface of the material with graphite coating is performed in a continuous furnace.

Description

  The present invention relates to a method for producing a negative electrode active material for a non-aqueous electrolyte secondary battery having high charge / discharge capacity and good cycle characteristics when used as a negative electrode active material for a lithium ion secondary battery.

In recent years, with the remarkable development of portable electronic devices, communication devices, etc., secondary batteries with high energy density are strongly demanded from the viewpoints of economy and downsizing and weight reduction of devices.
Conventionally, as a measure for increasing the capacity of this type of secondary battery, for example, a method of using an oxide such as V, Si, B, Zr, Sn, or a composite oxide thereof as a negative electrode material (for example, Patent Document 1, Patent 2), a method in which a melted and quenched metal oxide is applied as a negative electrode material (for example, see Patent Document 3), a method in which silicon oxide is used as a negative electrode material (for example, see Patent Document 4), and Si ₂ N as a negative electrode material. _A method using ₂ O and Ge ₂ N ₂ O (see, for example, Patent Document 5) is known. Further, for the purpose of imparting conductivity to the negative electrode material, a method of carbonizing SiO with graphite and then carbonizing (see, for example, Patent Document 6), a method of coating a carbon layer on the surface of silicon particles by chemical vapor deposition ( For example, refer to Patent Document 7), and a method of coating a carbon layer on the surface of silicon oxide particles by chemical vapor deposition (for example, refer to Patent Document 8).

  However, in the above conventional method, although the charge / discharge capacity is increased and the energy density is increased, the cycleability is insufficient or the required characteristics of the market are still insufficient, which is not always satisfactory. Further improvement in energy density has been desired.

  In particular, Patent Document 4 uses silicon oxide as a negative electrode active material for a lithium ion secondary battery to obtain a high-capacity electrode, but as far as the inventors see, the irreversible capacity at the time of initial charge / discharge is still large, Moreover, since the cycle performance has not reached the practical level, there is room for improvement.

  In addition, regarding the technique for imparting conductivity to the negative electrode active material, Patent Document 6 has a problem that a uniform carbon film is not formed because of solid-solid fusion, and the conductivity is insufficient. . Further, although the method of Patent Document 7 can form a uniform carbon film, since Si is used as the negative electrode active material, the expansion / contraction at the time of adsorption / desorption of lithium ions is too large, resulting in practical use. In order to prevent this, it is necessary to limit the amount of charge in order to prevent this. In the method of Patent Document 8, although the improvement in cycleability is confirmed, the number of cycles of charge and discharge is increased due to insufficient deposition of fine silicon crystals, the carbon coating structure and the base material. There is a phenomenon that the capacity gradually decreases and rapidly decreases after a certain number of times, which is still insufficient for a secondary battery. In Patent Document 9, a carbon film is chemically vapor-deposited on silicon oxide represented by the general formula SiOx to improve capacity and cycle characteristics.

  The negative electrode active material provided with conductivity by forming the carbon film (graphite film) as described above can obtain a high-capacity electrode, but is coated with a good carbon film that can sufficiently improve battery characteristics. A method for mass-producing the negative electrode active material (negative electrode material) has not been established.

JP-A-5-174818 JP-A-6-60867 JP 10-294112 A Japanese Patent No. 2999741 JP-A-11-102705 JP 2000-243396 A JP 2000-215887 A JP 2002-42806 A Japanese Patent No. 4171897

  The present invention has been made in view of the above problems, and an object of the present invention is to provide a production method capable of mass-producing a negative electrode active material for a non-aqueous electrolyte secondary battery having a high capacity and high cycleability. And

  In order to achieve the above object, the present invention provides a method for producing a negative electrode active material for a non-aqueous electrolyte secondary battery in which the surface of a material capable of occluding and releasing lithium ions is coated with a graphite coating, Provided is a method for producing a negative electrode active material for a non-aqueous electrolyte secondary battery, wherein the step of coating the surface with a graphite film is performed in a continuous furnace.

  Thus, by performing graphite coating in a continuous furnace, a uniform and good graphite film can be continuously coated on the material surface. For this reason, conductivity is improved, negative electrode active materials satisfying the characteristic level required by the market can be mass-produced, and costs can be reduced.

At this time, in the step of coating the surface of the material with a graphite coating, as the continuous furnace, a rotary kiln is used that coats the surface with a graphite coating while mixing and stirring the material inside by rotating a furnace core tube. Can do.
By coating using such a rotary kiln, the surface of the material can be efficiently coated with a graphite coating, and a negative electrode active material with little variation in characteristics can be produced with high productivity.

At this time, it is preferable to use carbon as the material of the powder contact portion of the furnace core tube.
Thus, if the material of the contact part is made of carbon, the material can be prevented from adhering to the inner wall of the furnace core tube and can be stably coated with the graphite coating for a long time.

At this time, it is preferable to periodically vibrate the furnace core tube with an air knocker.
Thus, it can suppress effectively that material adheres to the inner wall of a furnace core pipe by vibrating with an air knocker.

In addition, in the step of coating the surface of the material with a graphite film, as the continuous furnace, a roller hearth that covers the surface of the material with a graphite film while transporting the mortar charged with the material on a rotating roller It is preferable to use a kiln.
By coating using such a roller hearth kiln, the graphite surface can be efficiently coated on the surface of the material, and a negative electrode active material having almost no variation in characteristics can be produced with high productivity.

At this time, in the step of coating the surface of the material with a graphite coating, it is preferable to coat the surface of the material with a graphite coating by chemical vapor deposition at 800 to 1300 ° C. in an organic gas and / or vapor.
According to such chemical vapor deposition, the entire surface of the material can be efficiently and uniformly coated with graphite.

At this time, the material capable of inserting and extracting lithium ions is represented by silicon, a particle having a composite structure in which silicon fine particles are dispersed in a silicon compound, and a general formula SiO _x (0.5 ≦ x <1.6). It is preferable to use one of silicon oxides or a mixture of two or more thereof.
If it is such a material, the negative electrode active material which can improve the charging / discharging capacity of a battery effectively can be manufactured.

The present invention also provides a negative electrode active material for a nonaqueous electrolyte secondary battery, which is produced by the method for producing a negative electrode active material for a nonaqueous electrolyte secondary battery of the present invention.
Thus, if it was manufactured by the manufacturing method of this invention, the battery which has a high charging / discharging capacity | capacitance and favorable cycling characteristics can be produced, and it becomes an inexpensive negative electrode active material for nonaqueous electrolyte secondary batteries.

The present invention also provides a lithium ion secondary battery or an electrochemical capacitor using the negative electrode active material for a nonaqueous electrolyte secondary battery of the present invention.
Thus, if it uses the negative electrode active material for nonaqueous electrolyte secondary batteries of this invention, it will become a low quality, high quality lithium ion secondary battery or an electrochemical capacitor.

  As described above, according to the present invention, it is possible to continuously produce a negative electrode active material having improved conductivity and satisfying the characteristic level required by the market at a low cost.

It is the schematic of the roller hearth kiln which can be used with the manufacturing method of this invention. It is a figure which shows the preset temperature and actual temperature according to zone of roller hearth kiln. It is the schematic of the rotary kiln which can be used with the manufacturing method of this invention. It is sectional drawing of the furnace core pipe of a rotary kiln which can be used with the manufacturing method of this invention.

As a result of various studies to achieve the purpose of improving the capacity and cycle characteristics of the secondary battery, the present inventors have determined the surface of the material capable of occluding and releasing lithium ions, for example, organic gas and / or vapor. At the same time, it was confirmed that a significant improvement in battery characteristics was observed by coating with a graphite film by the chemical vapor deposition method in the inside, and at the same time, it was found that mass production was not practical in a batch furnace or the like conventionally used.
Therefore, as a result of detailed examination of the possibility of continuous production, the present inventors have used a continuous furnace, and in particular, a roller hearth kiln with a method of carrying a mortar filled with material powder on a rotating roller. In addition, by using a rotary kiln that rotates the furnace core tube, it has been found that continuous production is possible while satisfying the characteristic level required by the market, and the present invention has been completed.

  Here, a continuous furnace is a furnace in which supply of raw materials and discharge of products are performed continuously, for example, a fluidized bed furnace, a pusher furnace, a tunnel furnace, a rotary kiln, a conveyor furnace, a roller. For example, Herskirin.

Hereinafter, the present invention will be described in more detail.
The present invention is a method for producing a negative electrode active material for a non-aqueous electrolyte secondary battery in which the surface of a material capable of occluding and releasing lithium ions is coated with a graphite film.

First, as a material that can occlude and release lithium ions as a raw material of a negative electrode active material produced by the production method of the present invention, Si (metal silicon), composite dispersion of silicon (Si) and silicon dioxide (SiO ₂ ) Body, SiO _x (0.5 ≦ x <1.6, especially 1.0 ≦ x <1.3, 0.8 ≦ x <1.3 when a rotary kiln is used as a continuous furnace in the coating process of the graphite film. In addition to silicon oxide such as silicon oxide, particles having a fine structure (composite structure) in which silicon fine particles are dispersed in a silicon compound, silicon lower oxide (so-called silicon oxide), etc. _a (wherein, M is at least one selected from Ge, Sn, Pb, Bi, Sb, Zn, In, and Mg, and is a positive number of a = 0.1 to 4). Or a metal oxide not containing LiM _b O _c (wherein M is at least one selected from Ge, Sn, Pb, Bi, Sb, Zn, In, Mg, Si, b = a positive number of 0.1 to 4, c = 0.1 8 which is a positive number.) represented by (may be one containing silicon) and lithium composite oxides, _{specifically, GeO, GeO 2, SnO,} SnO 2, Sn 2 O ₃ , Bi ₂ O ₃ , Bi ₂ O ₅ , Sb ₂ O ₃ , Sb ₂ O ₄ , Sb ₂ O ₅ , ZnO, In ₂ O, InO, In ₂ O ₃ , MgO, Li ₂ SiO ₃ , Li ₄ SiO ₄ , Li ₂ Si ₃ O ₇ , Li ₂ Si ₂ O ₅ , Li ₈ SiO ₆ , Li ₆ Si ₂ O ₇ , Li ₄ Ge ₉ O ₇ , Li ₄ Ge ₉ O ₂ , Li ₅ Ge ₈ O ₁₉ , Li ₄ Ge ₅ O ₁₂ , Li ₅ Ge ₂ O ₇ , Li ₄ GeO _{4 , Li 2 Ge 7 O 15,} Li 2 GeO 3, Li 2 Ge 4 O 9, Li 2 SnO 3, Li 8 SnO 6, Li 2 PbO 3, Li 7 SbO 5, LiSbO 3, Li 3 SbO 4, Li 3 BiO ₅ , Li ₆ BiO ₆ , LiBiO ₂ , Li ₄ Bi ₆ O ₁₁ , Li ₆ ZnO ₄ , Li ₄ ZnO ₃ , Li ₂ ZnO ₂ , LiInO ₂ , Li ₃ InO ₃ , or non-stoichiometric compounds thereof Is mentioned.
In particular, when using either Si having a large theoretical charge / discharge capacity, particles having a composite structure in which silicon fine particles are dispersed in a silicon-based compound, silicon oxide, or a mixture of two or more of these, the charge / discharge capacity is reduced. The production method of the present invention is more effective.

In this case, the physical properties of Si particles or particles having a composite structure in which silicon fine particles are dispersed in a silicon-based compound are not particularly limited, but the average particle diameter may be 0.01 to 50 μm. 0.1 to 20 μm is preferable, and 0.5 to 15 μm is more preferable.
When the average particle size is smaller than 0.01 μm, the purity decreases due to the effect of surface oxidation, and when used as a negative electrode active material of a lithium ion secondary battery, the charge / discharge capacity decreases, the bulk density decreases, and the unit volume The charge / discharge capacity per unit may decrease. Conversely, if it is larger than 50 μm, there is a possibility that the slurry cannot be applied well at the time of electrode preparation.
In addition, an average particle diameter can be represented by the volume average particle diameter in the particle size distribution measurement by a laser beam diffraction method.

  In addition, in particles having a composite structure in which silicon fine particles are dispersed in a silicon-based compound, the silicon-based compound is preferably inactive, and silicon dioxide is preferable in terms of ease of manufacture. Moreover, it is preferable that this particle | grain has the following property.

i. In X-ray diffraction (Cu-Kα) using copper as the counter-cathode, a diffraction peak attributed to Si (111) centered around 2θ = 28.4 ° is observed, and based on the broadening of the diffraction line The particle size of silicon fine particles (crystals) determined by the Scherrer equation is preferably 1 to 500 nm, more preferably 2 to 200 nm, and still more preferably 2 to 20 nm. If the size of the silicon fine particles is smaller than 1 nm, the charge / discharge capacity may be reduced. Conversely, if the silicon fine particle is larger than 500 nm, the expansion / contraction during charge / discharge increases, and the cycle performance may decrease. The size of the silicon fine particles can also be measured by a transmission electron micrograph.

ii. In solid state NMR ( ²⁹ Si-DDMAS) measurement, there is a broad silicon dioxide peak whose spectrum is centered around −110 ppm, and a peak characteristic of Si diamond crystal is present near −84 ppm. This spectrum is completely different from ordinary silicon oxide (SiO _x : x = 1.0 + α), and the structure itself is clearly different. Further, it is confirmed by transmission electron microscope that silicon crystals are dispersed in amorphous silicon dioxide.
The amount of silicon fine particles (Si) dispersed in the silicon / silicon dioxide dispersion (Si / SiO ₂ ) is preferably 2 to 36% by mass, more preferably 10 to 30% by mass. If the amount of dispersed silicon is less than 2% by mass, the charge / discharge capacity may be reduced, and conversely if it exceeds 36% by mass, the cycle performance may be reduced.

The particles having a composite structure in which the silicon fine particles are dispersed in a silicon-based compound (silicon composite powder) are particles having a structure in which silicon microcrystals are dispersed in the silicon-based compound. If it has 0.01-50 micrometers, the manufacturing method will not be specifically limited, The following method can be employ | adopted suitably.
For example, a method of disproportionating a silicon oxide powder represented by the general formula SiO _x (0.5 ≦ x <1.6) by subjecting it to a heat treatment in a temperature range of 900 to 1400 ° C. in an inert gas atmosphere. It can be suitably employed.

In this case, silicon oxide is a general term for amorphous silicon oxide obtained by cooling and precipitating silicon monoxide gas generated by heating a mixture of silicon dioxide and metal silicon. . The silicon oxide powder is represented by the general formula SiO _x , and the average particle size is 0.01 μm or more, more preferably 0.1 μm or more, still more preferably 0.5 μm or more, and the upper limit is 20 μm or less, more preferably 15 μm or less. . The BET specific surface area is 0.1 m ² / g or more, more preferably 0.2 m ² / g or more, and the upper limit is 30 m ² / g or less, more preferably 20 m ² / g or less. The range of x is desirably 0.5 ≦ x <1.6, more preferably 0.8 ≦ x <1.3, and still more preferably 0.8 ≦ x ≦ 1.0.
When the average particle diameter and BET specific surface area of the silicon oxide powder are outside the above ranges, it is difficult to obtain a silicon composite powder having a desired average particle diameter and BET specific surface area. In addition, the production of SiO _x powder having a value of _x smaller than 0.5 is difficult in cycle characteristics, and those having a value of x of 1.6 or more are not suitable when heat treatment is performed and a disproportionation reaction is performed. When the proportion of active SiO ₂ is large and the lithium ion secondary battery is used, the charge / discharge capacity may be reduced.

Also, in disproportionation of silicon oxide, if the heat treatment temperature is lower than 900 ° C., disproportionation does not proceed at all or it takes an extremely long time to form fine silicon cells (silicon microcrystals), which is efficient. Not. On the other hand, when the temperature is higher than 1400 ° C., the structure of the silicon dioxide portion is advanced and the traffic of lithium ions is hindered, so that the function as a lithium ion secondary battery may be deteriorated. A more preferable heat treatment temperature is 1000 to 1300 ° C, particularly 1000 to 1200 ° C.
The treatment time (disproportionation time) can be appropriately selected in the range of 10 minutes to 20 hours, particularly 30 minutes to 12 hours, depending on the disproportionation treatment temperature. For example, at a treatment temperature of 1100 ° C. Can obtain a silicon composite powder (disproportionate) having desired physical properties in about 5 hours.

The above disproportionation treatment can be performed in an inert gas atmosphere using a reaction apparatus having a heating mechanism. The reaction apparatus is not particularly limited, and is a furnace capable of processing by a continuous process or a batch process. Specifically, a fluidized bed reaction furnace, a rotary furnace, a vertical moving bed reaction furnace, a tunnel furnace, a batch furnace, a rotary kiln and the like can be appropriately selected according to the purpose. In this case, as the (treatment) gas, an inert gas alone or a mixed gas thereof such as Ar, He, H ₂ , and N ₂ can be used.

And in the manufacturing method of the negative electrode active material for nonaqueous electrolyte secondary batteries in this invention, the surface of the material which can occlude and discharge | release said lithium ion is coat | covered with a graphite film in a continuous furnace, The chemical vapor deposition method (CVD method) or the like is preferably used.
If it is such a continuous furnace, a uniform graphite film can be formed with a desired coating amount to the same extent as a conventionally used batch furnace, etc., and a high-quality negative electrode active material is continuously produced, Mass production is possible. Therefore, a negative electrode active material that can improve battery characteristics can be manufactured at low cost.

Although it does not specifically limit as a continuous furnace which can be used in this invention, It is preferable to use the roller hearth kiln of the system which mounts and conveys the mortar filled with raw material powder (material) on the roller which rotates.
If it is a roller hearth kiln, it is suitable for coating the surface of a material that can occlude and release lithium ions, especially by chemical vapor deposition, with a graphite coating, and an anode active material that can achieve improved battery capacity and cycle characteristics. It can be manufactured without variation.

  FIG. 1 is a schematic sectional view of a roller hearth kiln. The roller hearth kiln 10 used in the present invention was supplied with, for example, a heater 11 for heating the material, a mortar 14 for charging the material, a rotating ceramic roller 15, and a gas inlet 13 for supplying gas into the furnace. And a gas outlet 12 for discharging the gas out of the furnace. The furnace main body is composed of, for example, eight chambers, and controls the output of the heater 11 so that the temperature of each chamber becomes a predetermined set temperature when the pot 14 loaded with materials is conveyed by the rollers 15. Thus, the surface of the material can be coated with the graphite film while supplying a gas as a raw material for the graphite film from the gas inlet 13.

Moreover, as a continuous furnace which can be used in the present invention, it is also preferable to use a rotary kiln whose surface is covered with a graphite film while mixing and stirring the internal materials by rotating the furnace core tube.
The rotary kiln is also particularly suitable for coating the surface of a material with a graphite coating by chemical vapor deposition, and a negative electrode active material capable of achieving improvement in battery capacity and cycle characteristics can be reliably produced without variation.

FIG. 3 is a schematic view of a rotary kiln. The rotary kiln 6 used in the present invention includes a furnace core tube 1, a heater 2 that heats the furnace core tube 1 from the outside, a feeder 3 that continuously supplies the material, and a processed product (a material coated with a graphite coating). ) And an air knocker 5 provided on the outer wall of the furnace core tube 1. In the present invention, using such a rotary kiln 6, the output of the heater 2 is controlled so that the temperature becomes a predetermined set temperature, and a gas as a raw material for the graphite coating is supplied from the gas inlet, while the graphite is applied to the material surface. A coating can be applied.
FIG. 4 is a cross-sectional view of the furnace core tube 1 of the rotary kiln 6. It is preferable that the furnace core tube 1 used in the present invention has a double structure in which the outer side is a metal and the inner contact part is carbon. When the graphite coating is deposited, the particles may aggregate and adhere to the inner wall of the furnace core tube. To suppress this, it is preferable that the material of the inner wall (the powder contact portion) is carbon. Carbon is a CIP material, extruded material, molding material, a composite material of carbon fiber (CF) and resin (mainly thermosetting resin such as epoxy) called carbon composite, and carbon fiber called C / C composite. An advanced composite material of carbon and graphite matrix can be used, and is not particularly limited. In order to further reduce the adhesion, it is effective to install an air knocker 5 or the like on the outer wall of the furnace core tube 1 to periodically vibrate the furnace core tube 1. In this respect, the outer wall should be made of metal. preferable. This material is not particularly limited, and may be appropriately selected from stainless steel, Inconel, Hastelloy, heat-resistant cast steel, etc., depending on use conditions such as temperature. Further, if the outer wall is made of a ceramic such as alumina or SiC, there is a risk of cracking due to impact. By using the rotary kiln having the specific material and structure as described above, the graphite film can be stably coated for a long time.

The treatment temperature at this time is preferably 800 to 1300 ° C, more preferably 900 to 1200 ° C. Moreover, when using a rotary kiln, the process temperature of 900-1000 degreeC is especially preferable.
When the processing temperature is 800 ° C. or higher, the graphite coating is efficiently performed and the processing time can be shortened, so that productivity is good. Further, when the temperature is higher than 1300 ° C., particles may be fused and aggregated by chemical vapor deposition, and when the conductive film is not formed on the aggregated surface, it is used as a negative electrode active material of a lithium ion secondary battery. , There is a risk that the cycle performance is reduced. In addition, when the material is a silicon composite powder, crystallization of silicon fine particles in the composite powder proceeds, and when used as a negative electrode active material of a lithium ion secondary battery, there is a possibility that expansion during charging may increase. . Here, the processing temperature is the maximum set temperature in the apparatus. In the case of a continuous roller hearth kiln or rotary kiln, the temperature at the center of the furnace often corresponds.

  The treatment time is appropriately selected depending on the target graphite coating amount, treatment temperature, gas (organic gas) concentration (flow rate), introduction amount, and the like. Usually, the residence time in the maximum temperature range is 1 to 10 hours. In particular, 2 to 7 hours are economically efficient. Moreover, when using a rotary kiln, 1-4 hours are especially preferable economically.

As the organic material used as a raw material for generating the organic gas supplied to the furnace in the present invention, a material that can be pyrolyzed at the above heat treatment temperature to generate carbon (graphite) is selected particularly in a non-acidic atmosphere.
For example, hydrocarbons such as methane, ethane, ethylene, acetylene, propane, butane, butene, pentane, isobutane, hexane, etc., alone or as a mixture, benzene, toluene, xylene, styrene, ethylbenzene, diphenylmethane, naphthalene, phenol, cresol, nitrobenzene, And monocyclic to tricyclic aromatic hydrocarbons such as chlorobenzene, indene, coumarone, pyridine, anthracene, phenanthrene, or a mixture thereof. Further, gas light oil, creosote oil, anthracene oil, and naphtha cracked tar oil obtained in the tar distillation step can be used alone or as a mixture.

Next, physical properties of the conductive powder (negative electrode active material) coated with graphite in a continuous furnace in the production method of the present invention will be described.
The graphite coating amount is not particularly limited, but is 0.3 to 40% by mass, preferably 0.5 to 30% by mass, and more preferably 2 to 20% by mass. When the graphite coating amount is less than 0.3% by mass, sufficient conductivity cannot be maintained, and as a result, the cycle performance may be lowered when used in a non-aqueous electrolyte secondary battery. On the contrary, not only the improvement of the effect is not seen even if the graphite coating amount exceeds 40% by mass, but the proportion of graphite in the negative electrode material increases, and the charge / discharge capacity decreases when used in a non-aqueous electrolyte secondary battery. There are things to do.

Using the negative electrode active material of the non-aqueous electrolyte secondary battery obtained in the present invention, a high-quality and low-cost lithium ion secondary battery or electrochemical capacitor can be produced.
For example, a lithium ion secondary battery is characterized in that the negative electrode active material is used, and other materials used for the negative electrode, materials such as a positive electrode, an electrolyte, a separator, and a battery shape are not limited. For example, as the positive electrode active material, oxides of transition metals such as LiCoO ₂ , LiNiO ₂ , LiMn ₂ O ₄ , V ₂ O ₅ , MnO ₂ , TiS ₂ , and MoS ₂ , chalcogen compounds, and the like are used. As the electrolyte, for example, a non-aqueous solution containing a lithium salt such as lithium perchlorate is used, and as the non-aqueous solvent, propylene carbonate, ethylene carbonate, dimethoxyethane, γ-butyrolactone, 2-methyltetrahydrofuran or the like alone or in two types The above is used in combination. Various other non-aqueous electrolytes and solid electrolytes can also be used.

  In addition, when producing a negative electrode using the negative electrode active material for nonaqueous electrolyte secondary batteries manufactured by this invention, electrically conductive agents, such as graphite, can be added to a negative electrode active material. Also in this case, the kind of the conductive agent is not particularly limited, and any electronic conductive material that does not cause decomposition or alteration in the constituted battery may be used. Specifically, Al, Ti, Fe, Ni, Cu, Metal powder such as Zn, Ag, Sn, Si, metal fiber or natural graphite, artificial graphite, various coke powders, mesophase carbon, vapor grown carbon fiber, pitch carbon fiber, PAN carbon fiber, various resin fired bodies Such graphite can be used.

EXAMPLES Hereinafter, although an Example and a comparative example are shown and this invention is demonstrated more concretely, this invention is not limited to these.
Example 1
40 g of silicon oxide powder represented by the general formula SiO _x (x = 1.02) having an average particle diameter of 8 μm was charged into an alumina sagger having an inner dimension of 100 mm × 100 mm and a height of 20 mm. The thickness of the charged powder layer was about 5 mm.

This was passed through the furnace with two bowls arranged in two rows and one row in a roller hearth kiln (manufactured by Noritake Company Limited) having a furnace length of 1.8 m as shown in FIG. Of the 8 zones (rooms), 4 zones (3-6 rooms) are set to the highest 1100 ° C, and the previous zone (2 rooms) is set to 850 ° C so that the material is held at 1100 ° C for 5 hours. It was conveyed at 3 mm / min. FIG. 2 shows the set temperature and actual temperature for each zone in the furnace.
As the gas, methane diluted to 2% by volume with nitrogen was introduced at 140 L / min from the gas inlet at the bottom of the furnace. The mortar was collected from the furnace outlet to obtain about 43 g of black powder per mortar. The obtained black powder was a conductive powder having an average particle size = 8.2 μm and a graphite coating amount of 6.8% by mass.

Battery Evaluation Next, battery evaluation using the obtained conductive powder as a negative electrode active material was performed by the following method.
First, 10% by mass of polyimide is added to the obtained conductive powder, and further N-methylpyrrolidone is added to form a slurry. This slurry is applied to a copper foil having a thickness of 20 μm, dried at 80 ° C. for 1 hour, and then a roller press. The electrode was pressure-molded by the following, and this electrode was vacuum-dried at 350 ° C. for 1 hour, and then punched out to 2 cm ² to obtain a negative electrode.

  Here, in order to evaluate the charge / discharge characteristics of the obtained negative electrode, a lithium foil was used as a counter electrode, and lithium hexafluoride was mixed with 1/1 (volume ratio) of ethylene carbonate and diethyl carbonate as a non-aqueous electrolyte. A lithium ion secondary battery for evaluation using a non-aqueous electrolyte solution dissolved at a concentration of 1 mol / L and a polyethylene microporous film having a thickness of 30 μm as a separator was prepared.

The prepared lithium ion secondary battery was allowed to stand overnight at room temperature, and then charged with a secondary battery charge / discharge tester (manufactured by Nagano Co., Ltd.) until the test cell voltage reached 0 V at 0.5 mA / cm ² . Charging was performed at a constant current, and after reaching 0V, charging was performed by decreasing the current so as to keep the cell voltage at 0V. Then, the charging was terminated when the current value fell below 40 μA / cm ² . Discharging was performed at a constant current of 0.5 mA / cm ² , discharging was terminated when the cell voltage exceeded 2.0 V, and the discharge capacity was determined.

  The above charge / discharge test was repeated, and a charge / discharge test after 50 cycles of the lithium ion secondary battery for evaluation was performed. As a result, the initial charge capacity is 2036 mAh / g, the initial discharge capacity is 1649 mAh / g, the initial charge and discharge efficiency is 81.0%, the 50th cycle discharge capacity is 1517 mAh / g, and the cycle retention rate after 50 cycles is 92%. And it was confirmed that it is a lithium ion secondary battery excellent in first-time charge / discharge efficiency and cycle property.

(Example 2)
40 g of silicon oxide powder similar to that in Example 1 was charged in the same alumina sagger as in Example 1. Fifty of these were prepared and passed through the same roller hearth kiln as in Example 1 in two rows. The temperature setting of the zone, the conveyance speed, and the gas conditions were also set in the same manner as in Example 1, and the conditions were satisfied when the sagger that first entered the furnace came out of the outlet. At this time, the total number of mortars simultaneously present in the furnace is 30 in 2 rows and 15 rows. After the conditions were established, the first mortar entered from the furnace inlet was recovered from the furnace outlet, and then the powder was taken out from the mortar of 10 rows (× 2 rows = 20 pieces) and the mass was measured. It was within the range of 42.4 g. Table 1 shows the graphite coverage of the obtained black powder. As shown in Table 1, the conductive powder had little variation between the mortars.

This conductive powder was extracted for two mortars, a test battery was produced in the same manner as in Example 1, and the same battery evaluation was performed.
As a result, the 2nd row-1st column (Example 2-1) is the initial charge capacity 2040 mAh / g, the initial discharge capacity 1651 mAh / g, the initial charge / discharge efficiency 80.9%, the 50th cycle discharge capacity 1486 mAh / g, The cycle retention after 50 cycles is 90%, and the other 8th row-2nd column (Example 2-2) is the initial charge capacity 2039 mAh / g, the initial discharge capacity 1652 mAh / g, and the initial charge / discharge efficiency 81.0. %, The discharge capacity at the 50th cycle was 1487 mAh / g, and the cycle retention after 50 cycles was 90%.

(Comparative Example 1)
40 g of silicon oxide powder similar to that in Example 1 was placed in the same mortar and charged into a batch type heating furnace. Then, it heated up and hold | maintained to 1100 degreeC with the temperature increase rate of 300 degrees C / hr, reducing pressure to 100 Pa or less with an oil rotary vacuum pump. Next, CH ₄ gas was introduced at 0.1 NL / min, and a graphite coating treatment was performed for 5 hours. The degree of vacuum at this time was 1000 Pa. After the treatment, the temperature was lowered to obtain 42.3 g of black powder. The obtained black powder was a conductive powder having an average particle size = 8.2 μm and a graphite coating amount of 5.3 mass%.

  Using this conductive powder, a test battery was prepared in the same manner as in Example 1, and the same battery evaluation was performed. As a result, the initial charge / discharge capacity was 2037 mAh / g, the initial discharge capacity was 1645 mAh / g, and the initial charge / discharge efficiency was 80. The discharge capacity at the 50th cycle was 1481 mAh / g, and the cycle retention after the 50th cycle was 90%.

  Table 2 shows the battery evaluation results of Examples 1 and 2 and Comparative Example 1. The conductive powder obtained in Examples 1 and 2 was equivalent in performance to the conductive powder produced in the batch type furnace of Comparative Example 1 in terms of battery evaluation. From the above, it was confirmed that a continuous furnace (roller hearth kiln) can be used as a method of continuously covering the surface of a material capable of inserting and extracting lithium ions with a graphite film. Moreover, since it is a continuous furnace, it can process continuously and productivity improves significantly compared with a batch furnace.

(Example 3)
The silicon oxide powder represented by the general formula SiO _x (x = 0.96) having an average particle diameter of 8 μm is placed on a rotary kiln having a furnace core tube inner diameter of 200 mm and a furnace core tube length of 3 m as shown in FIG. Used and supplied at 1 kg / hour. The material of the furnace core tube was a double tube structure of outside: heat-resistant cast steel and inside: carbon as shown in FIG. The heater was set at 1020 ° C. At this time, the center part of the furnace core tube was 1000 ° C. The furnace core tube was adjusted to an inclination of 1 ° so that the raw material supply unit side was higher. The rotation speed of the furnace core tube was set to 0.4 rotation / min.
In addition, as shown in FIG. 3, three air knockers 5 were installed and set to operate at intervals of once / 30 seconds, with a shift of 10 seconds.
As the gas, methane diluted to 15% by volume with nitrogen was introduced from the gas inlet at 30 L / min. Since the discharge amount per hour became stable after 5 hours from the start of the supply of raw materials, the product for 2 hours was recovered from that point. The resulting black powder was a conductive powder having an average particle size = 8.2 μm and a graphite coverage of 5.8% by mass.

Battery Evaluation Next, battery evaluation using the obtained conductive powder as a negative electrode active material was performed by the following method.
First, 10% by mass of polyimide is added to the obtained conductive powder, and further N-methylpyrrolidone is added to form a slurry. This slurry is applied to a copper foil having a thickness of 20 μm, dried at 80 ° C. for 1 hour, and then a roller press. The electrode was pressure-molded by the following, and this electrode was vacuum-dried at 350 ° C. for 1 hour, and then punched out to 2 cm ² to obtain a negative electrode.

  Here, in order to evaluate the charge / discharge characteristics of the obtained negative electrode, a lithium foil was used as a counter electrode, and lithium hexafluoride was mixed with 1/1 (volume ratio) of ethylene carbonate and diethyl carbonate as a non-aqueous electrolyte. A lithium ion secondary battery for evaluation using a non-aqueous electrolyte solution dissolved at a concentration of 1 mol / L and a polyethylene microporous film having a thickness of 30 μm as a separator was prepared.

The prepared lithium ion secondary battery was allowed to stand overnight at room temperature, and then charged with a secondary battery charge / discharge tester (manufactured by Nagano Co., Ltd.) until the test cell voltage reached 0 V at 0.5 mA / cm ² . Charging was performed at a constant current, and after reaching 0V, charging was performed by decreasing the current so as to keep the cell voltage at 0V. Then, the charging was terminated when the current value fell below 40 μA / cm ² . Discharging was performed at a constant current of 0.5 mA / cm ² , discharging was terminated when the cell voltage exceeded 2.0 V, and the discharge capacity was determined.

  The above charge / discharge test was repeated, and a charge / discharge test after 50 cycles of the lithium ion secondary battery for evaluation was performed. As a result, the initial charge capacity is 2036 mAh / g, the initial discharge capacity is 1649 mAh / g, the initial charge / discharge efficiency is 81.0%, the capacity retention is 50% after 50 cycles, and the initial charge / discharge efficiency and cycle performance are high. It was confirmed that this was an excellent lithium ion secondary battery.

Example 4
The same raw material as in Example 3 was used, and the same rotary kiln as in Example 3 was supplied at 2 kg / hour using a screw feeder. As the gas, methane diluted to 30% by volume with nitrogen was introduced from the gas inlet at 30 L / min. Other conditions were the same as in Example 3. Since the discharge amount per hour became stable after 5 hours from the start of the supply of raw materials, the product for 2 hours was recovered from that point. The obtained black powder was a conductive powder having an average particle size = 8.1 μm and a graphite coating amount of 5.3 mass%.

(Example 5)
The raw material and the apparatus were the same as in Example 3, and the operating conditions were the same as in Example 3. However, the operation was performed without operating the air knocker.
The discharge became stable after 5 hours from the start of raw material supply due to sticking to the inner wall of the furnace core tube, but the discharge per hour started to decrease after about 8 hours, and finally it was discharged due to clogging I had to stop driving because it was gone.
The sample collected when the discharge was stable was a black powder, which was a conductive powder having an average particle diameter = 8.1 μm and a graphite coating amount of 5.7% by mass.

(Comparative Example 2)
40 g of silicon oxide powder similar to that in Example 3 was placed in a carbon tray so as to have a layer thickness of 10 mm, and charged in a batch type heating furnace. Then, it heated up and hold | maintained to 1000 degreeC with the temperature increase rate of 300 degrees C / hr, reducing pressure to 100 Pa or less with an oil rotary vacuum pump. Next, methane gas was introduced at a rate of 0.1 NL / min, and a graphite coating treatment was performed for 15 hours. In addition, the pressure reduction degree at this time was 1000 Pa. After the treatment, the temperature was lowered to obtain 42 g of black powder. The obtained black powder was a conductive powder having an average particle size = 8.2 μm and a graphite coating amount of 5.1% by mass.

  Using this conductive powder, a test battery was prepared in the same manner as in Example 3, and the same battery evaluation was performed. As a result, the initial charge capacity was 2037 mAh / g, the initial discharge capacity was 1645 mAh / g, and the initial charge / discharge efficiency was 80. The capacity retention after 8% and 50 cycles was 90%.

(Comparative Example 3)
40 g of silicon oxide powder similar to that in Example 3 was placed in a carbon tray so as to have a layer thickness of 10 mm, and charged in a batch type heating furnace. The temperature was raised to 1000 ° C. and held at a temperature raising rate of 300 ° C./hr with normal pressure. Next, what diluted methane to 20 volume% with nitrogen was flowed in at 1 NL / min, and the graphite coating process was performed for 5 hours. After the treatment, the temperature was lowered to obtain 42.1 g of black powder. The obtained black powder was a conductive powder having an average particle size = 8.3 μm and a graphite coating amount of 5.0% by mass.

  Using this conductive powder, a test battery was prepared in the same manner as in Example 3, and the same battery evaluation was performed. As a result, the initial charge capacity 1854 mAh / g, the initial discharge capacity 1481 mAh / g, and the initial charge / discharge efficiency 79. The capacity retention was 85% after 9% and 50 cycles, the capacity was lower than in Example 3-5, and the cycle characteristics were also poor.

The battery evaluation results of Example 3-5 and Comparative Examples 2 and 3 are shown in Table 3. The conductive powder obtained in Example 3-5 all had the same performance in terms of battery evaluation as that of the conductive powder produced in the batch furnace of Comparative Example 2 under reduced pressure. As in Comparative Example 3, it was confirmed that the performance deteriorated even when produced in a batch furnace at normal pressure, but in Example 3, performance equivalent to that of the batch-type decompression treatment was obtained even at normal pressure.
Further, “C usage rate” in Table 3 is a numerical value obtained by calculating how much of the C (carbon) content contained in the aerated gas was used for coating. Compared with the batch type in which the powder is allowed to stand on the tray, the rotary kiln that is in contact with the processing gas while being stirred has a very high usage rate and can be confirmed to be economical.

  From the above, it has been confirmed that a continuous furnace (rotary kiln) can be used as a method of continuously covering the surface of a material capable of inserting and extracting lithium ions with a graphite coating. Since it is a continuous furnace, it can be continuously processed, and the productivity is significantly improved as compared with a batch furnace. The C conversion rate in the processing gas is also increased because it efficiently contacts the processing gas while stirring. In addition, the material of the powder contact part of the furnace core tube is made of carbon, and the furnace core tube is vibrated periodically with an air knocker to prevent powder from growing on the inner wall of the furnace core tube, enabling stable operation for a long time. It becomes.

  The present invention is not limited to the above embodiment. The above-described embodiment is an exemplification, and the present invention has substantially the same configuration as the technical idea described in the claims of the present invention, and any device that exhibits the same function and effect is the present invention. It is included in the technical scope of the invention.

1 ... Furnace core tube, 2 ... Heater, 3 ... Feeder, 4 ... Recovery container,
5 ... Air knocker, 6 ... Rotary kiln,
10 ... roller hearth kiln, 11 ... heater, 12 ... gas outlet,
13 ... gas inlet, 14 ... basket, 15 ... roller.

Claims (10)

A method for producing a negative electrode active material for a non-aqueous electrolyte secondary battery in which the surface of a material capable of inserting and extracting lithium ions is coated with a graphite film,
A method for producing a negative electrode active material for a non-aqueous electrolyte secondary battery, wherein the step of coating the surface of the material with a graphite coating is performed in a continuous furnace.   In the step of coating the surface of the material with a graphite coating, as the continuous furnace, a rotary kiln is used that coats the surface with a graphite coating while mixing and stirring the material inside by rotating a furnace core tube. The manufacturing method of the negative electrode active material for nonaqueous electrolyte secondary batteries of Claim 1.   The method for producing a negative electrode active material for a non-aqueous electrolyte secondary battery according to claim 2, wherein carbon is used as a material of the powder contact portion of the furnace core tube.   The method for producing a negative electrode active material for a nonaqueous electrolyte secondary battery according to claim 2 or 3, wherein the furnace core tube is periodically vibrated with an air knocker.   In the step of coating the surface of the material with a graphite film, as the continuous furnace, a roller hearth skin that coats the surface of the material with a graphite film while carrying a mortar charged with the material on a rotating roller. The method for producing a negative electrode active material for a nonaqueous electrolyte secondary battery according to claim 1, wherein the negative electrode active material is used.   2. The process of coating the surface of the material with a graphite film, wherein the surface of the material is coated with a graphite film by chemical vapor deposition at 800 to 1300 ° C. in an organic gas and / or vapor. 5. The method for producing a negative electrode active material for a non-aqueous electrolyte secondary battery according to claim 5. The material capable of occluding and releasing lithium ions is composed of silicon, particles having a composite structure in which silicon fine particles are dispersed in a silicon-based compound, and an oxidation represented by the general formula SiO _x (0.5 ≦ x <1.6). The method for producing a negative electrode active material for a nonaqueous electrolyte secondary battery according to any one of claims 1 to 6, wherein any one of silicon or a mixture of two or more thereof is used.   A negative electrode active material for a nonaqueous electrolyte secondary battery, which is produced by the method for producing a negative electrode active material for a nonaqueous electrolyte secondary battery according to any one of claims 1 to 7.   A lithium ion secondary battery using the negative electrode active material for a non-aqueous electrolyte secondary battery according to claim 8. An electrochemical capacitor using the negative electrode active material for a non-aqueous electrolyte secondary battery according to claim 8.

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