JP5386666B2 - Negative electrode material for lithium secondary battery, method for producing the same, and lithium secondary battery - Google Patents

Description

  The present invention relates to a negative electrode material for a lithium secondary battery, a method for producing a negative electrode material for a lithium secondary battery, and a lithium secondary battery.

  Lithium secondary batteries are lightweight and have high energy density, and in recent years, they are expected to be used as power sources for power sources of portable small electronic devices, such as hybrid cars and electric vehicles. Initially, lithium metal was used as the negative electrode material for lithium secondary batteries, but during charging, lithium ions precipitated and grew in the form of dendrites (dendrites) on the negative electrode surface. For this reason, carbon materials that do not cause such dendritic precipitation have been proposed.

  The graphite material has excellent lithium ion doping / undoping properties (desorption / insertion properties), so the charging / discharging efficiency is high, and the potential during charging / discharging is almost equal to that of metallic lithium, resulting in a high-voltage battery. There are advantages such as.

  However, a graphite material with a high degree of graphitization and a highly developed hexagonal network structure is liable to damage the battery output, for example, because it reacts with the electrolyte and decreases the charge / discharge efficiency. For example, when a propylene carbonate-based (hereinafter also abbreviated as PC-based) electrolytic solution having a melting point as low as −50 ° C. is used, it has a characteristic of being easily decomposed. This is because the lithium ions solvated with an electrolyte such as a PC-based electrolyte intercalate (co-intercalate) between the crystal planes (graphite layer) of a carbon material having a high degree of graphitization. This is due to the phenomenon of peeling or decomposing.

  On the other hand, an amorphous carbon material with a low degree of graphitization has low reactivity with the PC electrolyte, but the battery capacity becomes extremely low because there are few sites doped with lithium ions.

Under such circumstances, the present applicant has proposed a negative electrode material for a lithium secondary battery that is stable even in a PC-based electrolyte, has a high lithium ion doping / undoping rate, has a high battery capacity, and can be filled with high density. (See Patent Document 1).
However, due to the demand for higher performance of lithium secondary batteries, the anode for lithium secondary batteries is more stable in PC-based electrolyte and has better lithium ion doping / undoping speed, battery capacity, and battery efficiency. Materials are being sought.
Japanese Patent Laying-Open No. 2005-243410

  Under such circumstances, the present invention provides a negative electrode material for a lithium secondary battery that is stable in a PC-based electrolyte and that is superior in lithium ion doping / undoping rate, battery capacity, and battery efficiency. In addition, an object of the present invention is to provide a method for producing a negative electrode material for a lithium secondary battery and a lithium secondary battery.

  In order to achieve the above object, the present inventor has intensively studied. As a result, a plurality of concave portions having polygonal openings are formed on the surface by continuously extending a plurality of ridge-line pleats, and a disc centrifuging is provided. Negative electrode material for lithium secondary battery comprising Stokes mode particle diameter Dst measured by apparatus of 500 nm or more, and ratio La / Dst of crystallite size La measured by X-ray diffractometry with respect to Dst is 0.04 or more Thus, the inventors have found that the above-described problems can be solved, and have completed the present invention based on this finding.

That is, the present invention
(1) A plurality of concave portions having polygonal openings are provided on the surface by continuously extending a plurality of ridge-line pleats,
Stokes mode particle diameter Dst measured by a disc centrifuging device is 500 nm or more,
A negative electrode material for a lithium secondary battery, comprising a carbon microsphere having a ratio La / Dst of a crystallite size La measured by an X-ray diffraction method with respect to Dst of 0.04 or more,
(2) The negative electrode material for a lithium secondary battery according to (1) above, wherein at least a part of the corners constituting the polygonal opening is constituted by three ridge-line pleats,
(3) The negative electrode material for a lithium secondary battery according to the above (1) or (2), wherein the maximum depth of the recess is 10 to 200 nm,
(4) A method for producing a negative electrode material for a lithium secondary battery according to any one of (1) to (3) above,
A primary carbon sphere deposition step of thermally decomposing primary raw material hydrocarbon gas to deposit primary carbon spheres;
A composite carbon sphere deposition step of precipitating composite carbon spheres by pyrolyzing the primary carbon spheres and the secondary raw material hydrocarbon gas in contact with each other;
A method for producing a negative electrode material for a lithium secondary battery, comprising: a carbon microsphere generation step of obtaining carbon microspheres by heat-treating the composite carbon spheres at a temperature of 2000 ° C. or more,
(5) The primary carbon sphere deposition step is performed under the conditions of a primary raw material hydrocarbon gas concentration of 30 to 100 vol%, a primary raw material hydrocarbon gas supply linear velocity of 0.02 to 4.0 m / sec, and an ambient temperature of 900 to 1200 ° C. Carried out below,
The negative electrode material for a lithium secondary battery according to (4), wherein the composite carbon sphere deposition step is performed such that the atmospheric temperature is 900 to 1200 ° C and the residence time of the secondary raw material hydrocarbon gas is 1 to 20 seconds. A production method and (6) a lithium secondary battery comprising a negative electrode comprising the negative electrode material for a lithium secondary battery according to any one of (1) to (3).

  According to the present invention, a negative electrode material for a lithium secondary battery has a specific surface shape, a Stokes mode particle diameter Dst measured by a disc centrifuging apparatus of 500 nm or more, and a crystallite measured by an X-ray diffraction method with respect to Dst By comprising carbon microspheres with a ratio La / Dst of size La of 0.04 or more, it is stable in a PC-based electrolyte and is excellent in lithium ion doping / undoping speed, battery capacity, and battery efficiency. In addition, a negative electrode material for a lithium secondary battery can be provided. Moreover, according to this invention, the method and lithium secondary battery which manufacture the negative electrode material for lithium secondary batteries which has the said outstanding characteristic can be provided.

  The negative electrode material for a lithium secondary battery of the present invention has a plurality of concave portions having polygonal openings by continuously extending a plurality of ridge-line pleats, and the Stokes measured by a disc centrifuging device. It is characterized by comprising carbon microspheres having a mode particle diameter Dst of 500 nm or more and a ratio La / Dst of crystallite size La measured by X-ray diffraction with respect to Dst of 0.04 or more.

  As illustrated in FIG. 1, the surface of the carbon microsphere constituting the negative electrode material for a lithium secondary battery according to the present invention has a concave portion having a polygonal opening by continuously extending a plurality of ridge-line pleats. Are provided.

  Each ridge-like pleat has a length of about 10 to 500 nm, more preferably has a length of about 50 to 400 nm, and more preferably has a length of about 100 to 150 nm. It is.

  As shown in FIG. 1, a polygonal opening is formed by a plurality of intersections of the ridgeline pleats. Although the shape of an opening part is not specifically limited, For example, triangle shape, quadrangle shape, pentagon shape, hexagon shape, heptagon shape etc. can be mentioned.

  It is appropriate that at least a part of the corners constituting the polygonal opening is constituted by three ridge lines, and 50 to 50 of the corners constituting the polygonal opening. It is more appropriate that 100% is constituted by three ridge-line pleats, and all corners constituting the polygonal opening are constituted by three ridge-line folds. It is more appropriate that it is.

  Moreover, it is preferable that the maximum depth of the said recessed part is 10-200 nm, It is more preferable that it is 10-150 nm, It is more preferable that it is 10-100 nm.

  The opening diameter is preferably 50 to 600 nm, more preferably 50 to 500 nm, and still more preferably 150 to 400 nm. In the present specification, the opening diameter means the maximum diameter of the opening.

  The length of the ridge-shaped pleat, the shape of the opening, the maximum depth of the recess, the diameter of the opening, and the like can be confirmed with a scanning electron microscope (SEM).

  The surface base portion of the carbon microspheres constituting the negative electrode material for a lithium secondary battery of the present invention is suitably composed of 1 to 3000 continuous parallel graphite layers when observed with a cross-sectional transmission electron microscope. And more preferably 700 to 1800 continuous parallel graphite layers, and still more preferably 800 to 1400 continuous parallel graphite layers.

  The carbon microsphere constituting the negative electrode material for a lithium secondary battery of the present invention has a concave portion composed of the plurality of ridge-line pleat portions on the surface thereof, and the concave portion constituted by the ridge-line pleat portions is made of graphite. It is thought to be caused by crystal lattice distortion. And, since this concave portion formed on the surface of the carbon microsphere is capable of inputting and outputting lithium ions, it is considered that the input and output sites of lithium ions are increased, and the charge and discharge efficiency is improved. It is considered that the resistance to the PC-based electrolyte (stability in the PC-based electrolyte) can be improved by forming the concave portion by the lattice strain of the graphite crystal.

  The carbon microspheres constituting the negative electrode material for a lithium secondary battery of the present invention have a Stokes mode particle diameter Dst measured by a disc centrifuging apparatus of 500 nm or more, and the Dst is preferably 500 to 1200 nm. More preferably, the thickness is 600 to 900 nm.

In the present invention, the Stokes mode particle diameter Dst is measured by the following method using a disc centrifuging apparatus.
The dried carbon microspheres are mixed with a 20% by volume ethanol aqueous solution containing a small amount of a surfactant to prepare a dispersion having a carbon concentration of 0.1 kg / m ^3. To do. This measurement sample was placed in a disc centrifuging apparatus (manufactured by JoysLabel, UK) set at a rotational speed of 8 to 166 s ^−1, and after adding 0.015 dm ^{3 of} spin solution (2 wt% glycerin aqueous solution, 25 ° C.), 0 .001 dm ³ buffer solution (20 vol% ethanol aqueous solution, 25 ° C.) is injected. Next, after adding 0.0005 dm ³ of carbon dispersion liquid at a temperature of 25 ° C. with a syringe, centrifugal sedimentation was started, and at the same time, the recorder was operated to show a distribution curve (horizontal axis; carbon dispersion liquid into the syringe). Elapsed time since addition in step ordinate, vertical axis; absorbance at a specific point changed with centrifugal sedimentation of the carbon sample). Then, each time T is read from this distribution curve and substituted into the following equation to calculate the Stokes equivalent diameter corresponding to each time.

(In Equation ¹ , η is the viscosity of the spin liquid (0.935 × 10 ⁻³ Pa · S), N is the disk rotation speed (8 to 166 s ⁻¹ ), and r ₁ is the radius of the dispersion injection point (0 .0456m), _{r 2} is the radius to the absorbance measuring point (0.0482m), ρ _CB is the density of carbon ^{(kg / m 3), ρ} 1 is the density of the spin fluid (1.00178kg / ^{m 3).} )

The maximum Stokes equivalent diameter in the Stokes equivalent diameter and absorbance distribution curve (FIG. 2) thus obtained is defined as the Stokes mode particle diameter Dst (nm).
The Stokes mode particle diameter Dst is an index indicating the size of the aggregate structure in which primary carbon spheres are aggregated. When this value is large, the number of aggregated primary carbon spheres is large and the aggregate diameter is large. .

  As will be described later, the carbon microspheres constituting the negative electrode material for a lithium secondary battery of the present invention are considered to have a structure formed by agglomeration of primary particle carbon spheres. By making the particle size, the specific surface area can be reduced and the coulomb efficiency can be improved. In general, carbon microspheres with larger particle sizes have reduced input / output characteristics of lithium ions due to a decrease in the end face, and crystal distortion is reduced and resistance to PC electrolytes is reduced. Since the carbon microspheres constituting the negative electrode material for lithium secondary batteries of the present invention have a specific surface structure, even when the Stokes mode particle diameter Dst is as large as 500 nm or more, the Coulomb efficiency is improved. While improving, the input / output characteristics of lithium ions and the resistance to the PC electrolyte can also be improved.

  The carbon microspheres constituting the negative electrode material for a lithium secondary battery of the present invention have a ratio La / Dst of the crystallite size La measured by the X-ray diffraction method with respect to the Stokes mode particle diameter Dst of 0.04 or more. is there.

In this specification, the crystallite size La measured by the X-ray diffraction method is obtained by measuring a wide-angle X-ray diffraction curve by a reflective diffractometer method using a CuKα ray monochromatized by a graphite monochromator, Can be sought.
The ratio La / Dst of the crystallite size La to the Stokes mode particle diameter Dst is preferably 0.04 to 0.09.

  The ratio La / Dst of the crystallite size La to the Stokes mode particle diameter Dst represents the size of the crystallite per unit diameter of the carbon microsphere particles constituting the negative electrode material for lithium secondary electrons. It means that the crystallite has developed.

  When the ratio La / Dst of the crystallite size La to the Stokes mode particle diameter Dst is 0.04 or more, doping / undoping (de-insertion) of lithium ions in the negative electrode material can be improved.

  In addition to the above characteristics, the carbon microspheres constituting the negative electrode material for a lithium secondary battery of the present invention preferably have a crystallite lattice spacing (d002) of 0.350 nm or less as measured by an X-ray diffraction method. That is, it is preferable that the degree of graphite crystallinity is high. When the crystallite lattice spacing (d002) exceeds 0.350 nm, the crystallinity of graphite is low, so the number of sites doped with lithium ions decreases, and the battery capacity decreases.

  Next, the manufacturing method of the negative electrode material for lithium secondary electrons of this invention is demonstrated.

  The method for producing a negative electrode material for a lithium secondary battery according to the present invention relates to a method for producing the negative electrode material for a lithium secondary battery according to the present invention, and thermally decomposes a primary raw material hydrocarbon gas to deposit primary carbon spheres. A primary carbon sphere deposition step, a composite carbon sphere deposition step of depositing composite carbon spheres by thermally decomposing the primary carbon spheres in contact with the secondary raw material hydrocarbon gas, And a carbon microsphere generation step of obtaining carbon microspheres by heat treatment at a temperature of at least ° C.

  Hereinafter, the manufacturing method of the negative electrode material for lithium secondary electrons of the present invention will be described with reference to the drawings as appropriate.

  FIG. 3 is a view showing an example of an apparatus for producing carbon microspheres constituting the negative electrode material for lithium secondary electrons of the present invention.

  In FIG. 3, 11 is a gas cylinder filled with raw material hydrocarbon gas, 12 is a gas cylinder filled with carrier gas, and 13 is a flow meter. Reference numeral 14 denotes a primary raw material tank that stores the primary raw material hydrocarbon gas, for example, in a liquid state. Reference numeral 15 denotes a preheating device for the liquid hydrocarbon raw material, which assists vaporization of the liquid raw material gas by preheating. ing.

In the method of the present invention, the primary raw material hydrocarbon gas includes methane gas (natural gas, city gas, LNG (liquefied natural gas), etc.), ethane gas, propane / butane gas (LPG (liquefied petroleum gas), etc.), ethylene gas, propylene Gas, unsaturated aliphatic hydrocarbon gas such as butadiene gas, monocyclic aromatic hydrocarbon gas such as benzene gas, toluene gas and xylene gas, polycyclic aromatic hydrocarbon gas such as naphthalene gas and anthracene gas, or Mention may be made of these mixtures. In the case of liquid or solid at normal temperature, when hydrocarbon is used as the primary raw material hydrocarbon gas, it can be used by heating to a temperature equal to or higher than its boiling point to vaporize it.
Examples of the carrier gas include an inert gas such as nitrogen gas, argon gas, helium gas, neon gas, xenon gas, and krypton gas, and air, and it is preferable not to use hydrogen gas.

  Then, the primary raw material hydrocarbon gas is supplied from the gas cylinder 11 or the primary raw material tank 14 shown in FIG. 3 into the heating furnace 17 alone or together with the carrier gas from the gas cylinder 12 or the like.

  The heating furnace 17 is for pyrolyzing a hydrocarbon gas as a raw material and converting it into carbon microspheres. A primary carbon sphere precipitation part and a middle stream part (heating furnace) are provided in an upstream part (lower stage part of the heating furnace 17). 17 has a composite carbon sphere precipitation part in the middle part) and a carbon microsphere production part in the downstream part (upper part of the heating furnace 17), and the heating temperature can be controlled in each part. The heating furnace 17 is made of, for example, an opaque quartz tube having an inner diameter of 145 mm and a length of 1500 mm. In order to control the flow rate of the mixed gas, it is preferable to insert a mullite tube having a different reaction tube diameter in the heating furnace 17. The flow rate may be controlled by arbitrarily changing the flow rate of the primary raw material hydrocarbon gas or the flow rate of the carrier gas using the flow meter 13. Moreover, it is preferable that the inside of the heating furnace 17 is deoxygenated in advance by the vacuum pump 23 or the like.

  As shown in FIG. 3, it is preferable that a heat generation source 18 for external heat heating is installed outside the heating furnace 17 to supply desired heat into the heating furnace 17. As the external heating method, a high-frequency induction heating method, an electrothermal heating method, or a method of circulating a combustion gas can be applied.

  In the method of the present invention, the primary raw material hydrocarbon gas has a primary raw material hydrocarbon gas concentration of 30 to 100 vol%, a primary raw material hydrocarbon gas supply line speed of 0.02 to 4.0 m / sec, and an ambient temperature of 900. It is preferable that the primary carbon spheres are deposited by heating and thermal decomposition so that the temperature becomes ˜1200 ° C.

  At this time, as shown in FIG. 3, it is preferable to introduce the primary raw material hydrocarbon gas into the primary carbon sphere depositing portion, which is the upstream portion of the heating furnace 17, and to thermally decompose to deposit the primary carbon spheres. The primary raw material hydrocarbon gas concentration is preferably 50 to 100 vol%, more preferably 70 to 100%. The supply linear velocity of the primary raw material hydrocarbon gas is preferably 0.02 to 2.0 m / sec, and more preferably 0.02 to 1.0 m / sec. Moreover, it is preferable that the atmospheric temperature which thermally decomposes primary raw material hydrocarbon gas is 950-1100 degreeC, and it is more preferable that it is 1000-1100 degreeC.

  When the concentration of the primary raw material hydrocarbon gas is less than 30 vol%, the primary raw material hydrocarbon gas is insufficient, and the precipitated carbon spheres are easily atomized. Moreover, when the primary raw material hydrocarbon gas supply linear velocity is less than 0.02 m / sec, the adhesion of the intermediate product to the reaction tube wall becomes prominent and the passage is likely to be blocked, and when it exceeds 4.0 m / sec. A sufficient residence time of the primary raw material gas cannot be obtained, and as a result, the amount of intermediate products in the pyrolyzate increases, and the particle size distribution of the primary carbon spheres obtained by non-uniform gas flow also becomes broad. Furthermore, when the atmospheric temperature for pyrolyzing the primary raw material hydrocarbon gas is lower than 900 ° C., the primary carbon spheres cannot be obtained because the thermal decomposition reaction of the primary raw material hydrocarbon gas does not proceed sufficiently. Since the progress of the decomposition reaction is too fast, it becomes easy to atomize.

  Next, composite carbon spheres are deposited by thermal decomposition in a state where the obtained primary carbon spheres and the secondary raw material hydrocarbon gas are in contact with each other.

At this time, it is preferable to carry out by controlling the atmospheric temperature to be 900 to 1200 ° C. and the residence time of the secondary raw material hydrocarbon gas to be 1 to 20 seconds. The atmospheric temperature for thermally decomposing the secondary raw material hydrocarbon gas is more preferably 950 to 1100 ° C, and more preferably 1000 to 1100 ° C. The residence time of the secondary raw material hydrocarbon gas is preferably 1.0 to 8.0 seconds, and more preferably 2.0 to 5.0 seconds.
If the ambient temperature is lower than 900 ° C, the thermal decomposition of the secondary raw material hydrocarbon gas does not proceed sufficiently, so that the composite carbon spheres cannot be precipitated, and if the temperature exceeds 1200 ° C, the thermal decomposition reaction proceeds rapidly. The carbon spheres are easily atomized.

  Examples of the secondary raw material hydrocarbon gas include those similar to the primary raw material hydrocarbon gas described above, and the secondary raw material hydrocarbon gas can be supplied together with the carrier gas. The supply concentration and the like are the same as in the case of supplying the primary raw material hydrocarbon gas.

  As shown in FIG. 3, the secondary raw material hydrocarbon gas is supplied from the secondary raw material gas inlet 19 provided in the heating furnace 17 to the composite carbon sphere precipitation part, which is the middle part of the reaction furnace 17, and upstream. It is preferable that the composite carbon spheres are deposited by contacting with the primary carbon spheres generated in the part and pyrolyzing. At this time, the temperature in the heating furnace 17 is detected by a thermocouple or a radiation thermometer and controlled to a predetermined temperature by the temperature detector 20, or the supply rate of the secondary raw material hydrocarbon gas into the heating furnace 17 is changed. Therefore, it is preferable to adjust the residence time of the secondary raw material hydrocarbon gas. By controlling the generation conditions of the composite carbon sphere, the Stokes mode particle diameter Dst of the obtained carbon microsphere can be controlled.

  The composite carbon sphere obtained by bringing the primary carbon sphere and the secondary raw material hydrocarbon gas into contact with each other and pyrolyzing can be subjected to a heat treatment at a temperature of 2000 ° C. or more to obtain carbon microspheres. The heat treatment temperature is preferably 2000 to 3000 ° C, and more preferably 2500 to 3000 ° C. When the heat treatment temperature is lower than 2000 ° C., the concave shape of the carbon sphere surface does not proceed sufficiently and the desired effect cannot be obtained.

  As shown in FIG. 3, carbon microspheres can be obtained by heating to 2000 ° C. or higher in the heating zone provided in the downstream portion of the heating furnace 17. The crystallite size La can be controlled by controlling the heat treatment temperature. That is, when the heat treatment temperature is raised, the state change from the amorphous state to the graphite crystallization state easily proceeds, the La value as the crystallite size increases, and La / Dst can be controlled.

  The carbon microspheres obtained in the heating furnace 17 are cooled by the cooling pipe 21 together with the other cracked gas, and then separated and collected in the collection chamber 24. The other cracked gas passes through the water tank 25 and is combusted by the combustion device 26. After being completely burned in, it is discharged out of the system.

  As described above, in the method of the present invention, giant particles having a Stokes mode particle diameter Dst of 500 nm or more can be obtained by bringing primary carbon spheres into contact with each other and colliding with each other. Stability in the PC electrolyte can be imparted to the carbon microspheres. Moreover, the composite carbon sphere formed by contacting and colliding with the primary particles is heat-treated at a high temperature of 2000 ° C. or higher, thereby improving the graphitization degree and improving the charge / discharge efficiency of the lithium battery.

  Next, the lithium secondary battery of the present invention will be described.

  The lithium secondary battery of the present invention has a negative electrode made of the negative electrode material for a lithium secondary battery of the present invention.

  The lithium secondary battery of this invention has a positive electrode and electrolyte solution normally with the said negative electrode material.

  The positive electrode is usually formed by forming an active material layer containing a positive electrode active material, a conductive agent and a binder for forming an electrode plate on a positive electrode current collector, and the active material layer includes a positive electrode active material and a conductive agent. And the slurry containing the binder for electrode plate shaping | molding can be prepared, and this can be produced by apply | coating and drying on a collector.

  Examples of the positive electrode active material include lithium transition metal composite oxide materials such as lithium cobalt oxide, lithium nickel oxide, and lithium manganese oxide, transition metal oxide materials such as manganese dioxide, and carbon such as fluorinated graphite. Materials that can occlude and release lithium, such as quality materials, can be used.

The electrolyte solution is preferably a non-aqueous electrolyte solution in which a solute is dissolved in a non-aqueous solvent, and examples of the solute constituting the non-aqueous electrolyte solution include alkali metal salts and quaternary ammonium salts. For example, LiClO ₄ , LiPF ₆ , LiBF ₄ , LiCF ₃ SO ₃ , LiN (CF ₃ SO ₂ ) ₂ , LiN (CF ₃ CF ₂ SO ₂ ) ₂ , LiN (CF ₃ SO ₂ ) (C ₄ F ₉ One or more kinds selected from SO ₂ ) and LiC (CF ₃ SO ₂ ) ₃ can be mentioned. Examples of the non-aqueous solvent constituting the non-aqueous electrolyte include cyclic carbonates such as ethylene carbonate, propylene carbonate, and butylene carbonate, cyclic ester compounds such as γ-butyrolactone, diethyl carbonate, ethyl methyl carbonate, dimethyl carbonate, and the like. One or more selected from the chain carbonates can be mentioned.

  The content of the solute in the electrolytic solution is preferably 0.2 mol / L or more, particularly preferably 0.5 mol / L or more, more preferably 2 mol / L or less, and particularly preferably 1.5 mol / L or less.

  Further, a separator is usually provided between the positive electrode and the negative electrode so that the positive electrode and the negative electrode are not in physical contact. The separator preferably has high ion permeability and low electrical resistance. The material and shape of the separator are not particularly limited, but those that are stable with respect to the electrolyte and excellent in liquid retention are preferable. Specifically, a porous sheet or a non-woven fabric made of a polyolefin such as polyethylene or polypropylene is used.

  The shape of the lithium secondary battery of the present invention is not particularly limited. For example, a cylindrical shape in which a sheet electrode and a separator are spiraled, a cylinder shape having an inside-out structure in which a pellet electrode and a separator are combined, a pellet electrode and a separator are stacked. A coin shape etc. can be mentioned.

  Hereinafter, examples of the present invention will be described in detail in comparison with comparative examples.

Example 1 Production Example of Negative Electrode Material for Lithium Secondary Battery A negative electrode material for a lithium secondary battery was produced using a thermal decomposition apparatus having the apparatus configuration shown in FIG.

(Primary carbon sphere deposition process)
First, propane gas, which is a primary raw material hydrocarbon gas, is supplied from the gas cylinder 11 to the upstream portion (primary carbon sphere deposition portion) of the heating furnace 17 at a primary raw material hydrocarbon gas concentration of 100 vol% and a gas supply rate of 0.05 m / sec. did.
The heating furnace 17 is made of an opaque quartz tube having an inner diameter of 145 mm and a length of 1500 mm, and is formed by inserting a mullite tube having a different reaction tube diameter inside, and deoxidizing the inside with a vacuum pump 23 in advance. It is.
As shown in FIG. 3, the primary raw material hydrocarbon gas (propane gas) supplied to the upstream portion (primary carbon sphere precipitation portion) of the heating furnace 17 by the heat generation source 18 for external heating provided outside the heating furnace 17. ) Was heated in a temperature atmosphere of 1200 ° C. and pyrolyzed to precipitate primary carbon spheres.

(Composite carbon sphere deposition process)
Next, propane gas, which is a secondary raw material gas, is supplied to the middle portion (composite carbon sphere precipitation portion) of the heating furnace 17 through a secondary raw material gas inlet 19, a secondary raw material gas concentration of 100 vol%, and a residence time in the furnace. The composite carbon sphere was obtained by supplying for 10 seconds and bringing it into contact with and colliding with the primary carbon sphere in a temperature atmosphere of 1000 ° C.

(Carbon microsphere generation process)
The obtained composite carbon sphere was heated at 2800 ° C. in the downstream part (carbon microsphere generating part) of the heating furnace 17 to obtain a desired carbon microsphere.

  The carbon microspheres obtained in the heating path 17 were cooled together with other decomposition gases in the cooling pipe 21, and then separated and collected in the collection chamber 24, whereby a negative electrode material for a lithium secondary battery was obtained.

  An SEM photograph of the obtained carbon fine particles is shown in FIG. As shown in FIG. 4, the obtained carbon fine particles were formed by forming concave portions having polygonal openings by extending a plurality of ridge-line pleats on the surface. The maximum depth of the recess was 100 nm, and the opening diameter was 400 nm.

  The Stokes mode particle diameter Dst and crystallite size La of the carbon microspheres were measured by the following methods. The results are shown in Table 2 together with the crystallite lattice spacing (d002) measured by the X-ray diffraction method.

(Measuring method of Stokes mode particle diameter Dst)
The obtained carbon microspheres were dried and then mixed with a 20 volume% ethanol aqueous solution containing a small amount of a surfactant to prepare a dispersion having a carbon concentration of 0.1 kg / m ^3. Disperse to obtain a measurement sample. This measurement sample was placed in a disc centrifuging apparatus (manufactured by Joyes Robert, UK) set at a rotational speed of 100 s ^−1, and after adding 0.015 dm ^{3 of} a spin solution (2 wt% glycerin aqueous solution, 25 ° C.), 0.001 dm ³ Buffer solution (20% by volume ethanol aqueous solution, 25 ° C.) was injected. Next, after adding 0.0005 dm ³ of carbon dispersion liquid at a temperature of 25 ° C. with a syringe, centrifugal sedimentation was started, and at the same time, a distribution curve (horizontal axis; carbon dispersion liquid after being added with a syringe) Elapsed time, vertical axis; absorbance at a specific point changed with centrifugal sedimentation of the carbon sample), and taking each time T from this distribution curve, substituting into the following equation, Stokes equivalent diameter corresponding to each time Calculated.

(Where, η is the viscosity of the spin liquid (0.935 × 10 ⁻³ Pa · S), N is the disk rotation speed (100 s ⁻¹ ), and r ₁ is the radius of the dispersion injection point (0.0456 m). ), _{r 2} is the radius to the absorbance measuring point (0.0482m), ρ _CB carbon densities ^{(kg / m 3), ρ} 1 is the density of the spin fluid (1.00178kg / ^{m 3).)}

  The Stokes equivalent particle diameter Dst (nm) was defined as the Stokes equivalent diameter of the maximum frequency in the distribution curve of the Stokes equivalent diameter and absorbance thus obtained.

(Measurement method of crystallite size La)
The obtained carbon microspheres were obtained by the Gakushin method by measuring a wide-angle X-ray diffraction curve by a reflective diffractometer method using CuKα rays monochromatized by a graphite monochromator by the X-ray diffraction method.

(Examples 2 to 5) Example of production of negative electrode material for lithium secondary battery Atmospheric temperature in primary carbon sphere deposition step, primary raw material hydrocarbon gas supply rate and primary raw material hydrocarbon gas concentration, and atmosphere in composite carbon precipitation step Carbon microspheres were produced in the same manner as in Example 1 except that the temperature and residence time and the heat treatment temperature in the carbon microsphere production step were changed as shown in Table 1, and used as a negative electrode material for a lithium secondary battery. . In Example 4, nitrogen gas was used as a carrier gas in the primary carbon sphere deposition step.

  When the obtained carbon fine particle was confirmed with the SEM photograph, it has confirmed that the recessed part which has a polygonal opening part was formed when the some ridgeline-shaped pleat part expand | extends on the surface. An SEM photograph of the carbon microparticles obtained in Example 4 is shown in FIG.

  The Stokes mode particle diameter Dst and crystallite size La of each carbon microsphere were measured by the same method as in Example 1. The results are shown in Table 2 together with the crystallite lattice spacing (d002) measured by the X-ray diffraction method.

(Comparative Example 1) Comparative Production Example of Negative Electrode Material for Lithium Secondary Battery Using the apparatus shown in FIG. 3, the atmosphere in the primary carbon sphere deposition step using propane gas as the primary raw material hydrocarbon gas and nitrogen gas as the carrier gas A primary carbon microsphere was produced by pyrolysis for 2 hours at a temperature of 1250 ° C., a raw material gas concentration of 30 vol%, and a linear velocity of propane gas passing through the furnace of 0.12 m / sec. Carbon microspheres were produced in the same manner as in Example 1 except that the oxygen precipitation step was not performed.

  The Stokes mode particle diameter Dst and crystallite size La of the carbon microspheres of the obtained carbon microspheres were measured by the same method as in Example 1. The results are shown in Table 2 together with the crystallite lattice spacing (d002) measured by the X-ray diffraction method.

Comparative Example 2 Comparative Production Example of Negative Electrode Material for Lithium Secondary Battery Using a powder obtained by adjusting the particle size of commercially available natural graphite (manufactured by Chuetsu Graphite Industry Co., Ltd., BF10A), Stokes mode particle diameter Dst and crystallite size La are The measurement was performed in the same manner as in Example 1. The results are shown in Table 2 together with the crystallite lattice spacing (d002) measured by the X-ray diffraction method.

(Comparative example 3) Comparative production example of negative electrode material for lithium secondary battery The atmospheric temperature in the primary carbon sphere deposition step, the atmospheric temperature and residence time in the composite carbon deposition step were changed as shown in Table 1, and the carbon microsphere production step Carbon microspheres were produced in the same manner as in Example 1 except that the heat treatment temperature in was changed to 1900 ° C., which is outside the range of the method of the present invention, and used as a negative electrode material for a lithium secondary battery.

  The Stokes mode particle diameter Dst and crystallite size La of the produced carbon microspheres were measured in the same manner as in Example 1. The results are shown in Table 2 together with the crystallite lattice spacing (d002) measured by the X-ray diffraction method.

(Comparative Example 4) Comparative Production Example of Negative Electrode Material for Lithium Secondary Battery Commercially available carbon black (manufactured by Tokai Carbon Co., Ltd., Seast TA) was heated at 2600 ° C., and the particle size adjusted powder was used for Stokes mode particle diameter Dst. The crystallite size La was measured by the same method as in Example 1. The results are shown in Table 2 together with the crystallite lattice spacing (d002) measured by the X-ray diffraction method.

(Examples 6 to 10) Production Examples of Lithium Secondary Batteries (1) Production of Negative Electrode Polycarbons dissolved in N-methyl-2-pyrrolidone were prepared for each carbon microsphere obtained in Examples 1 to 5. 10% by weight of vinylidene chloride (PVDF) was added as a solid content and kneaded to prepare a carbon paste. This paste was applied to a rolled copper foil having a thickness of 18 μm, dried, and then pressed with a roll press. A sheet cut into a circle having a diameter of about 16 mm was used as the negative electrode.
(2) Preparation of positive electrode Lithium cobaltate (LiCoO ₂ ) was used as a positive electrode material, and 5% by weight of polyvinylidene fluoride powder and 5% by weight of a conductive agent (Ketjen Black EC) were added to lithium cobaltate (LiCoO ₂ ) powder. , N-methylpyrrolidone was used to prepare a slurry, which was uniformly coated on an aluminum foil and dried to prepare an electrode sheet. What was cut out into a circle having a diameter of about 16 mm from this sheet was used as a positive electrode.
(3) Production of battery Using the negative electrode and the positive electrode described above, a solution obtained by dissolving LiPF6 at a concentration of 1 mol / liter in a mixed solvent of ethylene carbonate and dimethyl carbonate (volume ratio 1: 1 mixture) as an electrolytic solution was used. A simple coin-shaped battery was prepared using a polypropylene nonwoven fabric as a separator.
(4) Evaluation of initial efficiency, reversible capacity, and rate characteristics Using each negative electrode produced in the same manner as in (1) above, a mixture of ethylene carbonate and dimethyl carbonate in a ratio of 1: 1 was used as an electrolyte solvent, and lithium metal A lithium ion secondary battery was prepared using as a positive electrode, a charge / discharge cycle test was performed, and initial efficiency, discharge capacity, and rate characteristics were measured by the following methods. The results are shown in Table 2.
<Initial efficiency>
The lithium reference electrode was charged at a constant current of up to 0.002 V, then discharged at a constant current of up to 1.2 V, the initial charge electricity amount and the discharge electricity amount were measured, and the following formula was obtained.
Initial efficiency (%) = (initial discharge electricity amount / initial charge electricity amount) × 100
<Discharge capacity>
Charging / discharging was repeated under the same conditions, and the reversible capacity was calculated as the reversible capacity (mAh / g) = the discharged electric quantity at the third cycle from the amount of electricity that could be discharged at the third cycle.
<Rate characteristics>
With a discharge capacity of 100 mAh / g as the lower limit, the rate characteristic (min) was evaluated with the minimum charge / discharge cycle time that can maintain the charge / discharge capacity as the secondary battery.
(5) Resistance to Propylene Carbonate Electrolyte Using each negative electrode produced in the same manner as in (1) above, a lithium ion secondary battery is produced using a propylene carbonate electrolyte as an electrolyte and metallic lithium as a positive electrode. The resistance to the propylene carbonate electrolyte was measured by the following method. The results are shown in Table 2.
<Production of tripolar test cell>
Polyvinylidene fluoride (PVDF) dissolved in N-methyl-2-pyrrolidone is added to carbon microspheres in a solid content of 20% by weight and kneaded to prepare a carbon paste. This carbon paste is rolled copper foil having a thickness of 18 μm. After being applied to and dried, it was pressed with a roll press. From this sheet, a three-electrode test cell having a diameter of about 16 mm was cut into a negative electrode, and metallic lithium was used as a positive electrode and a reference electrode, and 1M LiClO ₄ / propylene carbonate was used as an electrolyte.

The durability against propylene carbonate electrolyte was measured by measuring cyclic voltammograms with this tripolar test cell and evaluating whether a stable charge / discharge cycle can be obtained. The results are shown in Table 2.
In Table 2, the results obtained in Examples 6 to 10 are described in the columns of Examples 1 to 5 so as to correspond to the carbon microspheres used in each Example. .

(Comparative Example 5 to Comparative Example 8) Production Example of Comparative Lithium Secondary Battery Using the same materials as those used in Comparative Examples 1 to 4, batteries were produced in the same manner as in Examples 4 to 6. Then, initial efficiency, reversible capacity, rate characteristics, and resistance to propylene carbonate electrolyte were evaluated. The results are shown in Table 2.
In Table 2, the results obtained in Comparative Examples 5 to 8 are described in the columns of Comparative Examples 1 to 4 so as to correspond to the carbon microspheres used in each Comparative Example. Yes.

* A case where a stable charge / discharge cycle was obtained was evaluated as “◯”, and a case where the charge / discharge cycle was not stable and peeling of the graphite layer was observed was evaluated as “x”.

  By comparing the results of Examples 1 to 10 and Comparative Examples 1 to 8, in the present invention, as a negative electrode material for a lithium secondary battery, a plurality of ridge-line pleats are continuously extended. It has a specific surface shape that a plurality of concave portions having polygonal openings are provided on the surface, and the Stokes mode particle diameter Dst measured by a disc centrifuging apparatus is 500 nm or more, and measured by an X-ray diffraction method for Dst. By being composed of carbon microspheres having a crystallite size La ratio La / Dst of 0.04 or more, it is stable in a PC-based electrolyte, and discharge efficiency, battery capacity, lithium ion doping / undoping speed It can be seen that an excellent lithium secondary battery can be provided.

It is a figure which shows one example of the carbon microsphere which comprises the negative electrode material for lithium secondary batteries of this invention. It is a figure which shows the Stokes equivalent diameter and the distribution curve of a light absorbency. It is the figure which illustrated the whole structure of the apparatus for enforcing the manufacturing method of the carbon microsphere which comprises the negative electrode material for lithium secondary batteries of this invention. It is a SEM photograph of the carbon microsphere obtained in the example of the present invention. It is a SEM photograph of the carbon microsphere obtained in the example of the present invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 11 Raw material gas cylinder 12 Carrier gas cylinder 13 Flowmeter 14 Raw material tank 16 Pressure gauge 17 Heating furnace 15, 18 Heater 20 Temperature controller 21 Cooling pipe 22 Valve 24 Collection chamber 23 Vacuum pump 25 Water tank 26 Combustion device

Claims (6)

A plurality of concave portions having polygonal openings are provided on the surface by continuously extending a plurality of ridgeline pleats,
Stokes mode particle diameter Dst measured by a disc centrifuging device is 500 nm or more,
A negative electrode material for a lithium secondary battery, comprising carbon microspheres having a ratio La / Dst of a crystallite size La measured by an X-ray diffraction method for Dst of 0.04 or more.   2. The negative electrode material for a lithium secondary battery according to claim 1, wherein at least a part of the corners constituting the polygonal opening is constituted by three ridge lines.   The negative electrode material for a lithium secondary battery according to claim 1 or 2, wherein a maximum depth of the concave portion is 10 to 200 nm. It is a manufacturing method of the negative electrode material for lithium secondary batteries in any one of Claims 1-3,
A primary carbon sphere deposition step of thermally decomposing primary raw material hydrocarbon gas to deposit primary carbon spheres;
A composite carbon sphere deposition step of precipitating composite carbon spheres by pyrolyzing the primary carbon spheres and the secondary raw material hydrocarbon gas in contact with each other;
A method of producing a negative electrode material for a lithium secondary battery, comprising: a carbon microsphere generation step of obtaining carbon microspheres by heat-treating the composite carbon spheres at a temperature of 2000 ° C. or higher. The primary carbon sphere deposition step is performed under the conditions of a gas concentration of primary raw material hydrocarbon of 30 to 100 vol%, a primary raw material hydrocarbon gas supply linear velocity of 0.02 to 4.0 m / sec, and an ambient temperature of 900 to 1200 ° C. And
5. The production of a negative electrode material for a lithium secondary battery according to claim 4, wherein the composite carbon sphere deposition step is performed such that the atmospheric temperature is 900 to 1200 ° C. and the residence time of the secondary raw material hydrocarbon gas is 1 to 20 seconds. Method.   A lithium secondary battery comprising a negative electrode comprising the negative electrode material for a lithium secondary battery according to any one of claims 1 to 3.