CARBONACEOUS MATERIAL, METHOD FOR PRODUCING SAME, AND ELECTROCHEMICAL DEVICE

Abstract

The present invention relates to a carbonaceous material having a pore volume determined by performing Grand Canonical Monte Carlo simulation on an adsorption-desorption isotherm of carbon dioxide of 0.05 cm.sup.3/g or more and 0.20 cm.sup.3/g or less, and a ratio of desorption amount to adsorption amount (desorption amount/adsorption amount) at a relative pressure of 0.01 in the adsorption-desorption isotherm of 1.05 or more.

Claims

1. A carbonaceous material, which has a pore volume determined by performing Grand Canonical Monte Carlo simulation on an adsorption-desorption isotherm of carbon dioxide of 0.05 cm.sup.3/g or more and 0.20 cm.sup.3/g or less, and a ratio of desorption amount to adsorption amount at a relative pressure of 0.01 in the adsorption-desorption isotherm of 1.05 or more.

2. The carbonaceous material according to claim 1, having an oxygen element content of 0.5% by mass or more.

3. The carbonaceous material according to claim 1, having a BET specific surface area measured in accordance with a nitrogen adsorption method of 1 m.sup.2/g or more and 20 m.sup.2/g or less.

4. The carbonaceous material according to claim 1, having a mesopore volume measured in accordance with a BJH method of 3.7 mm.sup.3/g or more and 41 mm.sup.3/g or less.

5. The carbonaceous material according to claim 4, having an average particle size (D50) of 1.3 μm or more and 9.5 μm or less.

6. The carbonaceous material according to claim 4, having a BET specific surface area measured in accordance with a nitrogen adsorption method of 3 m.sup.2/g or more and 60 m.sup.2/g or less.

7. The carbonaceous material according to claim 1, having an average interplanar spacing d002 of the (002) plane calculated in accordance with a Bragg equation by means of a wide-angle X-ray diffraction method of 0.36 nm or more and 0.42 nm or less.

8. The carbonaceous material according to claim 1, for an electrochemical device.

9. The carbonaceous material according to claim 8, which is used with a pre-doping of a metal ion.

10. An electrochemical device, comprising the carbonaceous material according to claim 1.

11. A method of producing the carbonaceous material according to claim 1, the method comprising heating a carbon precursor having a BET specific surface area measured in accordance with a nitrogen adsorption method of 500 m.sup.2/g or less to 900° C. at a heating rate of 60° C./minute or less in a temperature range of from 600° C. to 900° C., thereby obtaining a heat treated carbon precursor.

12. The method according to claim 11, wherein the heating is performed in the presence of a volatile organic substance.

13. A method of producing the carbonaceous material according to claim 1, the method comprising performing a heat treatment of a carbon precursor having a BET specific surface area measured in accordance with a nitrogen adsorption method of 500 m.sup.2/g or less at a temperature of 600° C. or higher and lower than 900° C. for more than 5 minutes in the presence of a volatile substance derived from a volatile organic substance, thereby obtaining a heat treated carbon precursor.

14. The method according to claim 11, further comprising subsequently performing a heat treatment at 900° C. or higher and 1180° C. or lower.

15. The method according to claim 11, further comprising pulverizing the carbon precursor and/or the heat treated carbon precursor.

16. The method according to claim 13, further comprising subsequently performing a second heat treatment at 900° C. or higher and 1180° C. or lower.

17. The method according to claim 13, further comprising pulverizing the carbon precursor and/or the heat treated carbon precursor.

Description

EXAMPLES

<Measurement of Adsorption-Desorption Isotherm of Carbon Dioxide>

[0128] For each carbonaceous material, using a gas adsorption measurement device (AUTOSORB-iQ MP-XR, manufactured by Quantachrome), adsorption-desorption isotherms were obtained by measuring the adsorption and desorption of carbon dioxide at 273 K at relative pressures (p/p.sub.o) from 0.00075 to 0.030.

(Pore Volume)

[0129] The adsorption-desorption isotherms obtained above were analyzed by Grand Canonical Monte Carlo method using “CO.sub.2 at 273K on carbon” as a calculation model and a pore volume of pores having a diameter of 0.35 to 1.47 nm was determined. s

[0130] (Adsorption Amount and Desorption Amount of Carbon Dioxide)

[0131] From the adsorption-desorption isotherms obtained above, desorption amount/adsorption amount was obtained from the ratio of the desorption amount to the adsorption amount at a relative pressure of 0.01.

<Oxygen Element Content>

[0132] Oxygen element content was measured by using “oxygen/nitrogen/hydrogen analyzer EMGA-930” manufactured by HORIBA, Ltd.

[0133] The detection method of the analyzer is: oxygen: inert gas fusion-non-dispersive infrared absorption method (NDIR), and calibrated with a Ni capsule, TiH.sub.2 (H standard sample), and SS-3 (oxygen standard sample). 20 mg of a sample having the moisture content measured at 250° C. for about 10 minutes for a pretreatment was put into a Ni capsule and measured after 30 seconds of degasification in the elemental analyzer. The test was performed by analyzing three specimens, and an average value was used as an analysis value.

<Mesopore Volume>

[0134] Using BELSORP-mini manufactured by Bell Japan Inc., the carbonaceous material obtained in Examples and Comparative Examples was filled in a sample tube and the heat treatment at 300° C. was performed for 5 hours under reduced pressure. Then, nitrogen adsorption isotherm of the carbonaceous material at 77K was measured. The Barrett-Joyner-Halenda (BJH) method was applied to the obtained adsorption isotherm, and the mesopore volume was defined as the range of pore diameters from 2.5 nm to 33 nm. s

[0135] <Average Particle Size (D.sub.50)>

[0136] The average particle size D.sub.50 (particle size distribution) of the carbon precursor used in Examples and Comparative Examples and carbonaceous material obtained in Examples and Comparative Examples was measured in accordance with following laser scattering method. The sample of the carbon precursor and carbonaceous material of Examples and Comparative Examples to be described later was put into an aqueous solution comprising 0.3% by mass surfactant (“Toriton X 100” manufactured by Wako Pure Chemical Industries), treated by an ultrasonic cleaner for 10 minutes or more, and dispersed in the aqueous solution. The particle size distribution was measured by using this dispersion. The particle size distribution measurement was performed by using a particle size/particle size distribution measuring device (“Microtrac MT3000” manufactured by Nikkiso Co., Ltd.) with a solvent refractive index of 1.33 and particle permeability as absorption. The particle size at which the cumulative volume reached 50% was defined as the average particle size D.sub.50.

<BET Specific Surface Area by Nitrogen Adsorption Method>

[0137] The specific surface area of the carbonaceous material and carbon precursor is determined by the BET method (3 points BET method by nitrogen adsorption) (BET specific surface area). An approximate equation derived from a BET equation is described below.

p/[v(p.sub.0−p)]=(1/v.sub.mc)+[(c−1)/v.sub.mc](p/p.sub.0)   [Math. 3]

[0138] By using the approximate equation, v.sub.m is obtained by the three-point method by nitrogen adsorption at liquid nitrogen temperature, and the specific surface area of the sample was calculated by the following formula.

[00003]$\begin{array}{cc}\mathrm{Specific}\mathrm{surface}\mathrm{area}=\left(\frac{v_{m}Na}{22400}\right)\times {10}^{-18}& \left[\mathrm{Math}.4\right]\end{array}$

[0139] In the formula, v.sub.m is the adsorption amount (cm.sup.3/g) required for forming a monomolecular layer on the sample surface, v is the actually measured adsorption amount (cm.sup.3/g), p.sub.0 is the saturated vapor pressure, p is the absolute pressure, c is the constant (reflecting the adsorption heat), N is the Avogadro's number 6.022×10.sup.23, and a (nm.sup.2) is the area occupied by adsorbate molecules on the sample surface (molecular occupied cross-sectional area).

[0140] Specifically, the adsorption amount of nitrogen to the sample at the liquid nitrogen temperature was measured by using “BELL Sorb Mini” manufactured by Bell Japan Inc. as follows. The sample was filled in a sample tube and the sample tube was cooled to −196° C., the pressure was once reduced, and nitrogen (purity: 99.999%) was then adsorbed to the sample at a desired relative pressure. An adsorbed gas amount v was defined as an amount of nitrogen adsorbed to the sample when the equilibrium pressure was reached at each desired relative pressure.

<Interplanar Spacing d.sub.002 of (002) Plane>

[0141] Using “MiniFlex II” manufactured by Rigaku Corporation, the carbonaceous material was loaded to a sample holder, and an X-ray diffraction pattern was obtained using a CuKa ray monochromatized through an Ni filter as a radiation source. A peak position of the diffraction pattern was determined by a centroid method (a method of determining the centroid position of a diffraction line to determine a peak position at a corresponding value of 2θ) and then corrected using a diffraction peak of the (111) plane of high-purity silicon powder for a standard substance. The wavelength λ of the CuKa ray was set at 0.15418 nm, and d.sub.002 was calculated by the following Bragg equation.

[00004]$\begin{array}{cc}{d}_{002}=\frac{\lambda }{2.Math.\sin \theta }\left(\mathrm{Bragg}\mathrm{equation}\right)& \left[\mathrm{Math}.5\right]\end{array}$

<Measurement of Residual Carbon Ratio>

[0142] The residual carbon ratio was measured by quantifying the amount of carbon in the ignition residue after the ignition of the sample in an inert gas. The ignition was performed by putting about 1 g of the volatile organic substance (this exact mass is defined as W.sub.1 (g)) in a crucible, and heating the crucible in an electric furnace from normal temperature to 800° C. at a heating rate of 10° C./minute while flowing 20 liters of nitrogen per minute, and then igniting at 800° C. for 1 hour. The residue at this time was defined as the ignition residue, and the mass thereof was defined as W2 (g).

[0143] Then, the ignition residue was subjected to an elemental analysis according to the method specified in JIS M8819, and the carbon mass ratio P.sub.1 (% by mass) was measured. The residual carbon ratio P.sub.2 (% by mass) was calculated by the following formula.

[00005]$\begin{array}{cc}{P}_2=P_1\times \frac{W_2}{W_1}& \left[\mathrm{Math}.6\right]\end{array}$

<Preparation of Carbon Precursor>

[0144] 100 g of coconut shell char A (comprising 98% by mass of particles with a particle size of 0.850 to 2.360 mm) obtained by crushing coconut shells and carbonizing at 500° C. was treated at 950° C. for 80 minutes with supplying nitrogen gas comprising 1% by volume of hydrogen chloride gas at a flow rate of 10 L/minute. Then, only the supply of hydrogen chloride gas was stopped, and the further heat treatment was performed at 950° C. for 30 minutes. After that, the char was coarsely pulverized with a fine mill SF5 (manufactured by Nippon Coke Co., Ltd.) to an average particle size of 10 μm, and then pulverized with a compact jet mill (“Cojet System α-mkIII” manufactured by Seishin Enterprise Co., Ltd.). Further, the char was classified using Labo Classile N-01 (manufactured by Seishin Enterprise Co., Ltd.) to obtain a carbon precursor A with a specific surface area of 410 m.sup.2/g and an average particle size of 5.1 μm, and carbon precursor B with a specific surface area of 400 m.sup.2/g and an average particle size of 9.7 μm, respectively.

[0145] The obtained carbon precursor A with an average particle size of 5.1 μm was further pulverized with the fine mill SF5 (manufactured by Nippon Coke Co., Ltd.) to obtain carbon precursors with an average particle size of 1.3 μm, 2.2 μm, 2.6 μm, and 3.1 μm (each of them was defined as carbon precursor C, D, E, and F, respectively).

1. Experimental Example Regarding Carbonaceous Material of Embodiment I

Example 1

[0146] 0.9 g of polystyrene (manufactured by Sekisui Kasei Co., Ltd., average particle size: 400 μm, residual carbon ratio: 1.2% by mass) was mixed with 9.1 g of carbon precursor B. 10 g of this mixture was placed in a graphite sagger so that the thickness of the sample layer was about 3 mm. The sagger was placed in a high-speed heating furnace manufactured by Motoyama Co., Ltd., and heated under a nitrogen flow rate of 5 L per minute. The heating rate from 600° C. to 900° C. was 5° C. per minute (heating time: 60 minutes), and the heating rate in other temperature ranges was 60° C. per minute. After the temperature was raised to 900° C., the temperature was maintained at 900° C. for 60 minutes and then the sample was naturally cooled. After confirming that the temperature in the furnace had dropped to 200° C. or less, the carbonaceous material was taken out from the furnace.

Example 2

[0147] A carbonaceous material was obtained in the same manner as in Example 1 except that the heating rate from 600° C. to 900° C. was 10° C. per minute (heating time: 30 minutes) and after the temperature was raised to 900° C., the temperature was maintained at 900° C. for 20 minutes.

Example 3

[0148] A carbonaceous material was obtained in the same manner as in Example 1 except that the heating rate from 600° C. to 900° C. was 20° C. per minute (heating time: 15 minutes), then the temperature was raised to 1000° C. at the heating rate of 60° C. per minute, and the temperature was maintained at 1000° C. for 20 minutes.

Example 4

[0149] A carbonaceous material was obtained in the same manner as in Example 1 except that the heating rate from 600° C. to 900° C. was 20° C. per minute (heating time: 15 minutes), then the temperature was raised to 1100° C. at the heating rate of 60° C. per minute, and the temperature was maintained at 1100° C. for 20 minutes.

Example 5

[0150] A carbonaceous material was obtained in the same manner as in Example 1 except that the heating rate from 600° C. to 900° C. was 5° C. per minute (heating time: 60 minutes), then the temperature was raised to 1175° C. at the heating rate of 60° C. per minute, and the temperature was maintained at 1175° C. for 20 minutes.

Example 6

[0151] 6.4 g of carbon precursor B was placed in a graphite sagger so that the thickness of the sample layer was about 3 mm. The sagger was placed in a tubular furnace manufactured by Motoyama Co., Ltd., and heated to 600° C. at the heating rate of 60° C. per minute under a nitrogen flow rate of 5 L per minute. After reaching 600° C., toluene was introduced into the furnace using a syringe pump so that the toluene concentration in the nitrogen gas was 1.5% by volume, and the temperature was raised to 900° C. at the heating rate of 5° C. per minute (heating time: 60 minutes). Then, the temperature was maintained at 900° C. for 60 minutes, and the sample was naturally cooled. After confirming that the temperature in the furnace had dropped to 200° C. or less, the carbonaceous material was taken out from the furnace.

Comparative Example 1

[0152] 0.6 g of polystyrene (manufactured by Sekisui Kasei Co., Ltd., average particle size: 400 μm, residual carbon ratio: 1.2% by mass) was mixed with 6.4 g of carbon precursor B. 7 g of this mixture was placed in a graphite sagger so that the thickness of the sample layer was about 3 mm. The sagger was placed in a tubular furnace manufactured by Motoyama Co., Ltd. which was preheated to 900° C. under a nitrogen flow rate of 5 L per minute. When the temperature inside the furnace was measured, the temperature inside the furnace dropped when the sample was put in, however the temperature rose from 600° C. to 900° C. in 1 minute. After that, the temperature was maintained at 900° C. for 20 minutes, and the sample was naturally cooled. After confirming that the temperature in the furnace had dropped to 200° C. or less, the carbonaceous material was taken out from the furnace.

Comparative Example 2

[0153] 9.1 g of carbon precursor B was placed in a graphite sagger so that the thickness of the sample layer was about 3 mm. The sagger was placed in a high-speed heating furnace manufactured by Motoyama Co., Ltd., and heated under a nitrogen flow rate of 5 L per minute. The heating rate from 600° C. to 900° C. was 10° C. per minute (heating time: 30 minutes), and the heating rate in other temperature ranges was 60° C. per minute. After the temperature was raised to 900° C., the temperature was maintained at 900° C. for 20 minutes and then the sample was naturally cooled. After confirming that the temperature in the furnace had dropped to 200° C. or less, the carbonaceous material was taken out from the furnace.

Comparative Example 3

[0154] 0.9 g of polystyrene (manufactured by Sekisui Kasei Co., Ltd., average particle size: 400 μm, residual carbon ratio: 1.2% by mass) was mixed with 9.1 g of carbon precursor B. 10 g of this mixture was placed in a high-speed heating furnace manufactured by Motoyama Co., Ltd., and heated to 1270° C. at the heating rate of 60° C. per minute under a nitrogen flow rate of 5 L per minute. The temperature was maintained at 1270° C. for 11 minutes and then the sample was naturally cooled. After confirming that the temperature in the furnace had dropped to 200° C. or less, the carbonaceous material was taken out from the furnace.

Comparative Example 4

[0155] 0.9 g of polystyrene (manufactured by Sekisui Kasei Co., Ltd., average particle size: 400 μm, residual carbon ratio: 1.2% by mass) was mixed with 9.1 g of carbon precursor B. 10 g of this mixture was placed in a high-speed heating furnace manufactured by Motoyama Co., Ltd., and heated to 1290° C. at the heating rate of 60° C. per minute under a nitrogen flow rate of 5 L per minute. The temperature was maintained at 1290° C. for 11 minutes and then the sample was naturally cooled. After confirming that the temperature in the furnace had dropped to 200° C. or less, the carbonaceous material was taken out from the furnace.

[0156] The conditions of the heating step and/or heat treatment step and the physical properties of the obtained carbonaceous material were shown in Tables 1 and 2 show, respectively.

TABLE-US-00001 TABLE 1 heating step and/or additional heat heat treatment step treatment step volatile heating temper- organic rate (° C./ time ature time substance minute) (minute) (° C.) (minute) Example 1 polystyrene 5 60 900 60 Example 2 polystyrene 10 30 900 20 Example 3 polystyrene 20 15 1000 20 Example 4 polystyrene 20 15 1100 20 Example 5 polystyrene 5 60 1175 20 Example 6 1.5 vol. % 5 60 900 60 toluene Comparative polystyrene 300 1 900 20 example 1 Comparative — 10 30 900 20 example 2 Comparative polystyrene 60 5 1270 11 example 3 Comparative polystyrene 60 5 1290 11 example 4

TABLE-US-00002 TABLE 2 BET CO.sub.2 CO.sub.2 desorption oxygen specific pore desorption adsorption amount/ content surface volume amount amount adsorption (% by area d.sub.002 (cm.sup.3/g) (cm.sup.3/g) (cm.sup.3/g) amount mass) (m.sup.2/g) (nm) Example 1 0.177 46.1 38.4 1.20 1.0 4 0.39 Example 2 0.186 49.8 42.3 1.18 1.2 5 0.39 Example 3 0.175 47.8 32.0 1.49 1.1 5 0.39 Example 4 0.151 46.1 19.4 2.38 1.2 4 0.39 Example 5 0.072 24.7 5.9 4.19 0.6 4 0.39 Example 6 0.162 44.0 33.0 1.33 1.0 3 0.39 Comparative 0.203 54.2 52.3 1.04 1.1 16 0.39 example 1 Comparative 0.208 55.4 53.0 1.05 1.3 447 0.39 example 2 Comparative 0.039 6.5 2.0 3.25 0.1 5 0.39 example 3 Comparative 0.030 5.0 1.5 3.33 0.1 6 0.39 example 4

<Battery Evaluation>

(Preparation of Carbon Electrode)

[0157] 96.2 parts by mass of the carbonaceous material, 2 parts by mass of conductive carbon black (“Super-P (registered trademark)” manufactured by TIMCAL), 1 part by mass of CMC, predetermined amounts of SBR and water were mixed to obtain a slurry. The obtained slurry was applied to a copper foil, dried and pressed to obtain an electrode with a thickness of 60 to 80 μm. The density of the obtained electrode was 0.95 g/cm.sup.3. This electrode was punched into a disk shape with a diameter of 14 mm to obtain a carbon electrode plate.

(Preparation of Negative Electrode Half Cell)

[0158] The obtained carbon electrode was punched into a disk shape with a diameter of 14 mm to obtain a working electrode, and metallic lithium was used as a counter electrode. As a solvent, ethylene carbonate, dimethyl carbonate and ethyl methyl carbonate were mixed at a volume ratio of 1:1:1 and used. LiPF.sub.6 was dissolved in this solvent to a concentration of 1 mol/L and used as an electrolyte. A polypropylene film was used as a separator. A coin cell was produced in a glove box under an argon atmosphere.

(Measurement of Discharge Capacity and Initial Efficiency)

[0159] A charge/discharge test was performed on the negative electrode half-cell having the above configuration using a charge/discharge tester (“TOSCAT” manufactured by Toyo System Co., Ltd.). Lithium doping was performed to 1 mV relative to the lithium potential at a rate of 70 mA/g with respect to the mass of the active material. A constant voltage of 1 mV relative to the lithium potential was further applied for 8 hours, and the doping was terminated thereafter. The capacity at this point was defined as the charge capacity (mAh/g). Subsequently, de-doping was performed to 1.5 V relative to the lithium potential at a rate of 70 mA/g with respect to the mass of the active material, and the discharged capacity at this point was defined as the discharge capacity (mAh/g). The percentage of the value obtained by dividing the discharge capacity (mAh/g) by the charge capacity (mAh/g) was defined as the charge-discharge efficiency (initial efficiency) (%), and was used as an indicator of the utilization efficiency of lithium ions in the battery. The results were shown in Table 3.

(Preparation of Positive Electrode)

[0160] As a positive electrode active material, 90 parts by mass of lithium iron phosphate (LiFePO.sub.4), 5 parts by mass of PVDF (polyvinylidene fluoride), 5 parts by mass of acetylene black and NMP (N-methylpyrrolidone) were mixed to obtain a slurry. The obtained slurry was applied to an aluminum foil, dried and then pressed to obtain an electrode with a thickness of 80 to 140 μm. The density of the obtained electrode was 1.8 g/cm.sup.3. This electrode was punched into a disk shape with a diameter of 14 mm to obtain a positive electrode plate.

(Preparation of Positive Electrode Half Cell)

[0161] Metallic lithium was used as a counter electrode and a reference electrode for the obtained positive electrode. As a solvent, ethylene carbonate and methyl ethyl carbonate were mixed at a volume ratio of 3:7 and used. LiPF.sub.6 was dissolved in this solvent to a concentration of 1 mol/L and used as an electrolyte. A glass fiber nonwoven fabric was used for a separator. A coin cell was produced in a glove box under an argon atmosphere.

[0162] A charge/discharge test was performed on the positive electrode half-cell having the above configuration using a charge/discharge tester (“TOSCAT” manufactured by Toyo System Co., Ltd.). Lithium de-doping from the positive electrode was performed to 4.0 V relative to the lithium potential at a rate of 15 mA/g with respect to the mass of the active material. The capacity at this time was defined as the charge capacity. Next, lithium doping to the positive electrode was performed to 2.0 V relative to the lithium potential at a rate of 15 mA/g with respect to the mass of the active material. The capacity at this time was defined as the discharge capacity. The resulting charge capacity was 153 mAh/g, the discharge capacity was 141 mAh/g, and the charge-discharge efficiency (initial charge-discharge efficiency) calculated as a percentage of discharge capacity/charge capacity was 92%.

(Preparation of Coin Cell (Full Cell))

[0163] The obtained carbon electrode was punched into a disk shape with a diameter of 15 mm and used as a negative electrode. The electrode mixture coated surfaces of the negative electrode and positive electrode were opposed to each other via a separator made of glass fiber nonwoven fabric interposed therebetween so that the positive electrode (14 mm in diameter) did not protrude from the negative electrode plane. At this time, the ratio of the negative electrode charge capacity (mAh) to the positive electrode charge capacity (mAh) per facing area (negative electrode capacity/positive electrode capacity) was adjusted to 1.05. As a solvent, ethylene carbonate and methyl ethyl carbonate were mixed and used at a volume ratio of 3:7. LiPF.sub.6 was dissolved in this solvent to a concentration of 1 mol/L and used as an electrolyte. A coin cell was produced in a glove box under an argon atmosphere.

(Charge and Discharge Test (Cycle Durability Test))

[0164] A charge/discharge test was performed on the coin cell (full cell) having the above configuration using a charge/discharge tester (“TOSCAT” manufactured by Toyo System Co., Ltd.). The charge was performed to 4.0 V relative to the lithium potential at a rate of 70 mA/g with respect to the mass of the negative electrode active material. The discharge was then performed to 2.0 V relative to the lithium potential at a rate of 70 mA/g with respect to the mass of the negative electrode active material. This cycle was repeated 3 times.

[0165] After that, the charge was performed to 4.0 V relative to the lithium potential at a rate of 500 mA/g with respect to the mass of the negative electrode active material, and the capacity at this time was defined as the charge capacity. Then, the discharge was performed to 2.0 V relative to the lithium potential at a rate of 500 mA/g with respect to the mass of the negative electrode active material, and the capacity at this time was defined as the discharge capacity. This cycle was repeated 500 times. The percentage obtained by dividing the discharge capacity at the 500th cycle by the discharge capacity at the 1st cycle was defined as a 500 cycles retention rate. The results are shown in Table 3.

TABLE-US-00003 TABLE 3 initial discharge efficiency capacity 500 cycles (%) (mAh/g) retention rate (%) Example 1 79 535 80 Example 2 79 532 77 Example 3 79 525 81 Example 4 81 484 89 Example 5 85 443 90 Example 6 80 533 82 Comparative example 1 70 498 59 Comparative example 2 64 387 43 Comparative example 3 90 387 84 Comparative example 4 89 416 85

[0166] It can be understood that the lithium ion secondary battery comprising the negative electrode comprising the carbonaceous material obtained in Examples 1 to 6 has high initial efficiency and high discharge capacity. In addition, it can be understood that the discharge capacity retention rate after 500 cycles is also high. Meanwhile, at least one of the discharge capacity and 500 cycles retention rate of the lithium ion secondary battery comprising the negative electrode comprising the carbonaceous material obtained in Comparative Examples 1 to 4 was insufficient.

2. Experimental Example Regarding Carbonaceous Material of Embodiment II

Example 7

[0167] 0.9 g of polystyrene (manufactured by Sekisui Kasei Co., Ltd., average particle size: 400 μm, residual carbon ratio: 1.2% by mass) was mixed with 9.1 g of carbon precursor B with an average particle size of 9.7 μm. 10 g of this mixture was placed in a graphite sagger so that the thickness of the sample layer was about 3 mm. The sagger was placed in a high-speed heating furnace manufactured by Motoyama Co., Ltd., and heated under a nitrogen flow rate of 5 L per minute. The heating rate from 600° C. to 900° C. was 5° C. per minute (heating time: 60 minutes), and the heating rate in other temperature ranges was 60° C. per minute. After the temperature was raised to 900° C., the temperature was maintained at 900° C. for 20 minutes and then the sample was naturally cooled. After confirming that the temperature in the furnace had dropped to 200° C. or less, the carbonaceous material was taken out from the furnace and the carbonaceous material with an average particle size of 9.6 μm was obtained.

[0168] The carbon precursor D with an average particle size of 2.2 μm was treated in the same manner as the carbon precursor B with an average particle size of 9.7 μm to obtain a carbonaceous material with an average particle size of 2.1 μm.

[0169] Next, the carbonaceous material with an average particle size of 2.1 μm and carbonaceous material with an average particle size of 9.7 μm were mixed at a mass ratio of 1:1 to obtain a carbonaceous material with an average particle size of 4.5 μm.

Example 8

[0170] A carbonaceous material was obtained in the same manner as in Example 7 except that the heating rate from 600° C. to 900° C. was 20° C. per minute (heating time: 15 minutes) and after the temperature was raised to 1000° C., the temperature was maintained at 1000° C. for 20 minutes.

Example 9

[0171] 0.9 g of polystyrene (manufactured by Sekisui Kasei Co., Ltd., average particle size: 400 μm, residual carbon ratio: 1.2% by mass) was mixed with 9.1 g of the carbon precursor D with an average particle size of 2.2 μm. 10 g of this mixture was placed in a graphite sagger so that the thickness of the sample layer was about 3 mm. The sagger was placed in a high-speed heating furnace manufactured by Motoyama Co., Ltd., and heated under a nitrogen flow rate of 5 L per minute. The heating rate from 600° C. to 900° C. was 20° C. per minute (heating time: 15 minutes), and the heating rate in other temperature ranges was 60° C. per minute. After the temperature was raised to 1100° C., the temperature was maintained at 1100° C. for 20 minutes and then the sample was naturally cooled. After confirming that the temperature in the furnace had dropped to 200° C. or less, the carbonaceous material was taken out from the furnace and the carbonaceous material with an average particle size of 2.1 μm was obtained.

Example 10

[0172] A carbonaceous material with an average particle size of 2.5 μm was obtained in the same manner as in Example 9 except that the carbon precursor E with an average particle size of 2.6 μm was used.

Example 11

[0173] A carbonaceous material with an average particle size of 3.0 μm was obtained in the same manner as in Example 9 except that the carbon precursor F with an average particle size of 3.1 μm was used.

Example 12

[0174] The carbonaceous material with an average particle size of 3.0 μm obtained in Example 11 and the carbonaceous material with an average particle size of 9.6 μm obtained by treating the carbon precursor B with an average particle size of 9.7 μm in the same manner as in Example 9 were mixed at a mass ratio of 1:1. The average particle size of the obtained carbonaceous material was 4.8 μm.

Example 13

[0175] The carbonaceous material with an average particle size of 2.1 μm obtained in Example 9 and the carbonaceous material with an average particle size of 9.6 μm obtained by treating the carbon precursor B with an average particle size of 9.7 μm in the same manner as in Example 9 were mixed at a mass ratio of 1:1. The average particle size of the obtained carbonaceous material was 4.5 μm.

Example 14

[0176] A carbonaceous material was obtained in the same manner as in Example 7 except that the heating rate from 600° C. to 900° C. was 20° C. per minute (heating time: 15 minutes), and after the temperature was raised to 1175° C., the temperature was maintained at 1175° C. for 20 minutes.

Example 15

[0177] 9.1 g of carbon precursor A with an average particle size of 5.1 μm was placed in a graphite sagger so that the thickness of the sample layer was about 3 mm. The sagger was placed in a high-speed heating furnace manufactured by Motoyama Co., Ltd., and heated under a nitrogen flow rate of 5 L per minute. The heating rate from 600° C. to 900° C. was 60° C. per minute (heating time: 5 minutes), and the heating rate in other temperature ranges was also 60° C. per minute. After the temperature was raised to 1150° C., the temperature was maintained at 1150° C. for 20 minutes and then the sample was naturally cooled. After confirming that the temperature in the furnace had dropped to 200° C. or less, the carbonaceous material was taken out from the furnace and the carbonaceous material with an average particle size of 5.0 μm was obtained.

Comparative Example 5

[0178] A carbonaceous material was obtained in the same manner as in Example 7 except that the heating rate from 600° C. to 900° C. was 300° C. per minute (heating time: 1 minute).

Comparative Example 6

[0179] A carbonaceous material was obtained in the same manner as in Example 7 except that the heating rate from 600° C. to 900° C. was 60° C. per minute (heating time: 5 minutes) and after the temperature was raised to 1270° C., the temperature was maintained at 1270° C. for 20 minutes.

Comparative Example 7

[0180] A carbonaceous material was obtained in the same manner as in Example 15 except that the heating rate from 600° C. to 900° C. was 60° C. per minute (heating time: 5 minutes) and after the temperature was raised to 1100° C., the temperature was maintained at 1100° C. for 20 minutes.

Comparative Example 8

[0181] A carbonaceous material was obtained in the same manner as in Example 15 except that the heating rate from 600° C. to 900° C. was 60° C. per minute (heating time: 5 minutes) and after the temperature was raised to 1050° C., the temperature was maintained at 1050° C. for 360 minutes.

[0182] Regarding the carbonaceous material obtained in Examples and Comparative Examples, the pore volume, mesopore volume, adsorption and desorption amount of carbon dioxide, and ratio of adsorption amount to desorption amount (adsorption amount/desorption amount), average particle size (D.sub.50), specific surface area and interplanar spacing d.sub.002 are shown in Table 4.

TABLE-US-00004 TABLE 4 pore mesopore CO.sub.2 CO.sub.2 BET specific volume volume desorption adsorption desorption/ D.sub.50 surface area d.sub.002 (cm.sup.3/g) (mm.sup.3/g) (cm.sup.3/g) (cm.sup.3/g) adsorption (μm) (m.sup.2/g) (nm) Example 7 0.192 14.5 50.2 43.5 1.15 4.5 22 0.39 Example 8 0.178 10.8 48.8 35.6 1.37 4.5 22 0.39 Example 9 0.163 22.5 48.2 21.0 2.30 2.1 40 0.39 Example 10 0.160 14.1 47.6 20.5 2.32 2.5 22 0.39 Example 11 0.156 10.9 46.3 20.1 2.30 3.0 12 0.39 Example 12 0.153 7.7 46.3 19.7 2.35 4.8 8 0.39 Example 13 0.157 13.1 47.2 19.8 2.38 4.5 15 0.39 Example 14 0.072 10.3 24.9 6.2 4.02 4.5 21 0.39 Example 15 0.133 3.9 32.6 30.7 1.06 5.0 29 0.39 Comparative 0.204 20.0 55.0 53.0 1.04 4.5 26 0.39 example 5 Comparative 0.040 10.2 6.7 3.1 2.16 4.5 20 0.39 example 6 Comparative 0.189 13.2 45.2 44.8 1.01 5.0 58 0.39 example 7 Comparative 0.194 14.5 47.0 45.0 1.04 5.0 47 0.39 example 8

[0183] Using the carbonaceous material of Examples 7 to 15 and Comparative Examples 5 to 8, battery evaluation (discharge capacity, initial efficiency, and cycle durability) was performed in the same manner as in the experimental example regarding the carbonaceous material of Embodiment I. In addition to the battery evaluation, input characteristics were measured by the following method. The results are shown in Table 5.

(Measurement of Input Characteristics)

[0184] After measuring the discharge capacity and initial efficiency, the negative electrode half-cell was subjected to a charge/discharge test using a charge/discharge tester (“TOSCAT” manufactured by Toyo System Co., Ltd.) to evaluate the input characteristics. Doping was performed in a constant temperature bath at 25° C. to 0 mV relative to the lithium potential at a rate of 500 mA/g with respect to the mass of the negative electrode active material. Next, de-doping was performed to 1.5 V relative to the lithium potential at a rate of 100 mA/g with respect to the mass of the active material, and the discharge capacity at this time was defined as the discharged capacity at 25° C. 1 C (mAh/g).

[0185] Next, doping was performed in a constant temperature bath at −20° C. to 0 mV relative to the lithium potential at a rate of 100 mA/g with respect to the mass of the negative electrode active material. Next, de-doping was performed to 1.5 V relative to the lithium potential at a rate of 100 mA/g with respect to the mass of the active material, and the discharged capacity at this time was defined as the discharged capacity at −20° C. 0.2 C (mAh/g).

[0186] Subsequently, doping was performed in a constant temperature bath at −20° C. to 0 mV relative to the lithium potential at a rate of 500 mA/g with respect to the mass of the negative electrode active material. Next, de-doping was performed to 1.5 V relative to the lithium potential at a rate of 100 mA/g with respect to the mass of the active material, and the discharged capacity at this time was defined as the discharged capacity at −20° C. 10 (mAh/g).

[0187] −20° C. 10/25° C. 1 C and −20° C. 1 C/−20° C. 0.2 C were used as indices of input characteristics and of pre-doping. The value of −20° C. 10/25° C. 1 C measured according to this example is preferably 30% or more, more preferably 40% or more, and still more preferably 45% or more. The value of −20° C. 1 C/−20° C. 0.2 C is preferably 50% or more, more preferably 70% or more, and still more preferably 75% or more.

TABLE-US-00005 TABLE 5 discharge discharge discharge discharge initial 500 cycles capacity at capacity at capacity at −20° C. 1 C/ −20° C. 1 C/ capacity efficiency retention 25° C. 1 C −20° C. 0.2 C −20° C. 1 C 25° C. 1 C −20° C. 0.2 C (mAh/g) (%) rate (%) (mAh/g) (mAh/g) (mAh/g) (%) (%) Example 7 525 75 77 217 110 82 38 75 Example 8 478 80 78 214 108 83 39 77 Example 9 468 77 74 194 112 87 45 78 Example 10 477 78 77 211 121 95 45 79 Example 11 481 79 82 163 110 84 52 76 Example 12 488 81 86 158 92 67 42 73 Example 13 472 78 83 201 104 80 40 77 Example 14 433 82 88 160 98 73 46 74 Example 15 488 82 72 155 86 64 41 74 Comparative 489 68 42 189 102 72 38 71 example 5 Comparative 377 88 82 154 92 63 41 68 example 6 Comparative 498 73 57 163 105 74 45 70 example 7 Comparative 507 70 58 172 105 73 42 70 example 8

[0188] It can be understood that non-aqueous electrolyte secondary batteries comprising the negative electrode comprising the carbonaceous materials obtained in Examples 7 to 15 can be pre-doped at high speed, and simultaneously satisfy high capacity, high initial efficiency and high cycle durability. Meanwhile, the carbonaceous materials obtained in Comparative Examples 5, 7 and 8 have low initial efficiency and cycle retention rate, and the carbonaceous material obtained in Comparative Example 6 has low discharge capacity.

INDUSTRIAL APPLICABILITY

[0189] The carbonaceous material of the present invention can be used in the production of electrochemical devices, and such electrochemical devices can have the properties of high capacity and high cycle durability.