JP2003272621A - Negative electrode material for lithium secondary battery and negative electrode sheet manufactured from it - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a negative electrode material for a lithium secondary battery and a negative electrode sheet with a high charge acceptance and with little swelling of an electrode. <P>SOLUTION: Of the powder-like negative electrode material with a structure in which a carbonaceous matter with inferior crystallinity than a graphite-system carbonaceous matter is coated on a graphite system carbonaceous matter, a resistance (R) of the negative electrode for the lithium secondary battery made of the negative material and a binder is to be not more than 6.5 ohm, and a double-layer capacity (Cdl) at a negative electrode/electrolyte solution interface is to be within the range of 7.0×10<SP>-4</SP>F or more or less than 10×10<SP>-4</SP>F. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a negative electrode material for a lithium secondary battery and a negative electrode sheet produced from the same. More specifically, the present invention relates to a negative electrode material for a lithium secondary battery, which has a high charge acceptability and a small electrode swelling, and a negative electrode sheet produced from the same.

[0002]

2. Description of the Related Art In recent years, with the miniaturization of electronic devices, there has been a demand for higher capacity secondary batteries. Therefore, a lithium secondary battery (or a lithium ion secondary battery) having a higher energy density than the nickel-cadmium secondary battery and the nickel-hydrogen secondary battery has been receiving attention.

Attempts were initially made to use lithium metal as the negative electrode material, but dendrite-like lithium was deposited during repeated charging and discharging, penetrated through the separator to the positive electrode, and short-circuited and ignited. It turned out to be an accident. Therefore, at present, attention is paid to the use of a carbon material as a negative electrode material, which allows a non-aqueous solvent to move in and out between layers during a charge / discharge process and prevent the precipitation of lithium metal.

An example of this carbon material is Japanese Patent Laid-Open No. 57-20.
In 8079, it is proposed to use a graphite material. In particular, when graphite having good crystallinity is used as a carbon negative electrode material for a lithium secondary battery, a capacity close to 372 mAh / g, which is the theoretical capacity of graphite for occluding lithium, is obtained.
It is known that it is preferable as a material. On the other hand, it is known that when a so-called amorphous carbon material, which has lower crystallinity than the graphite material, is used, a higher capacity per weight can be obtained than the graphite material, but these materials have a high potential for Li. However, there is a drawback that it is difficult to obtain a potential difference from the positive electrode. Further, since the true density is smaller than that of graphite, there is a drawback that the capacity per volume is low. Further, since the particles are generally hard, there is a problem that the electrode formability is poor and therefore it is difficult to improve the electrode density.

As one form of the lithium secondary battery,
It has been reported that the rectangular shape of the case causes the case to swell due to the swelling of the electrodes that occurs during charging and discharging. If the battery volume is designed in consideration of this swelling from the beginning, the thickness of the housing is inevitably made thin, resulting in a decrease in battery capacity.

[0006]

An object of the present invention is to compare the potential change during lithium charging / discharging to the Li potential and to obtain a potential hysteresis due to charging / discharging, as compared with the case of using an amorphous carbon material. Since it is a negative electrode material that is easy to take a difference from the positive electrode potential, it has a high capacity, high charge acceptability for Li, and little electrode swelling, making it a suitable lithium battery for prismatic batteries. It is to provide a negative electrode material for a secondary battery.

[0007]

As a result of intensive studies to solve the above problems, the present inventors have found that a specific carbonaceous material solves the above problems and arrived at the present invention. That is, the gist of the present invention is a powdery negative electrode material having a structure in which a carbonaceous material of which crystallinity is inferior to the graphite-based carbonaceous material is adhered to the graphite-based carbonaceous material, the negative-electrode material and a binder. Resistance (R) of negative electrode for lithium secondary battery prepared from
But, 6.5Ohm hereinafter, anode / electrolyte double layer capacity of the interface (Cdl) has, 7.0x10 ^-4 F or higher, 10x10 ^-4 F
It exists in the negative electrode material for lithium secondary batteries characterized by being in the range below.

Another aspect of the present invention is a powdery negative electrode material having a structure in which a carbonaceous material having a crystallinity lower than that of the graphite-based carbonaceous material is adhered to the graphite-based carbonaceous material. The resistance (R) of the negative electrode for a lithium secondary battery, which was prepared from the above and a binder, was 6.5 ohm or less, and the double layer capacity (Cdl) at the negative electrode / electrolyte interface was 7.0 × 10 ⁻⁴ F or more, 10
A negative electrode sheet for a lithium secondary battery, which is characterized in that it is formed into a sheet by adding a binder to a material in the range of less than x10 ^-4 F.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described in detail below. The negative electrode material for a lithium secondary battery of the present invention is a powdery negative electrode material having a structure in which a carbonaceous material having a crystallinity lower than that of the graphite-based carbonaceous material is adhered to the graphite-based carbonaceous material, which has specific physical properties. Is to have.

The term "deposition" as used herein means that a coating phase made of another material is formed on at least a part of the surface of the core material made of a certain material. On the other hand, it does not matter whether it is due to the adhesion of the material supplied from the outside or the deterioration of the material of the surface portion of the core material. [Graphite-based carbonaceous material] The graphite-based carbonaceous material used as the core material in the present invention refers to a highly crystalline graphite-based carbonaceous material, preferably the interplanar spacing (d002) of the (002) plane by X-ray wide angle diffraction method. A graphite-based carbonaceous material having a value of less than 3.37Å is used.

Specific examples of the graphite-based carbonaceous material include natural graphite, artificial graphite, mechanically crushed products thereof, reheated products, reheated products of expanded graphite, and highly purified products of these graphites. Powder is preferred. Specific examples of the artificial graphite, coal tar pitch, coal-based heavy oil,
Atmospheric residual oil, heavy petroleum oil, aromatic hydrocarbons, nitrogen-containing cyclic compounds, sulfur-containing cyclic compounds, polyphenylene, polyvinyl chloride, polyvinyl alcohol, polyacrylonitrile, polyvinyl butyral, various natural polymers, polyphenylene sulfide, polyphenylene Suitable crushing means is obtained by graphitizing one or more kinds of organic substances selected from oxides, furfuryl alcohol resins, phenol-formaldehyde resins, imide resins, etc. at a firing temperature of usually 2500 ° C. or higher and 3200 ° C. or lower. It is preferable that the powder is powdered.

[Carbonaceous material having crystallinity inferior to that of graphite-based carbonaceous material] As a "carbonaceous material having crystallinity inferior to that of graphite-based carbonaceous material" for forming a coating phase on the surface of the core material made of the above-mentioned graphite-based carbonaceous material Can use various carbonaceous materials that are inferior in crystallinity to the graphite-based carbonaceous material of the core material. Normally, the interplanar spacing (d002) of the (002) plane by the X-ray wide angle diffraction method is 3.37Å or more. Various carbonaceous materials with low crystallinity are used.

The formation of the coating phase composed of the above-mentioned "carbonaceous material having a crystallinity inferior to that of the graphite-based carbonaceous material" is caused by the alteration of the surface portion of the core material made of the graphite-based carbonaceous material This can be achieved in various forms such as adhesion of a material composed of an inferior carbonaceous material, adhesion of various materials supplied from the outside of the core material, and conversion into a carbonaceous material having inferior crystallinity. The details will be described in the next section.

[Negative Electrode Material for Lithium Secondary Battery] The negative electrode material for a lithium secondary battery of the present invention has a structure in which a carbonaceous material having a crystallinity lower than that of the graphite-based carbonaceous material is adhered, that is, graphite. A powdery negative electrode material having a structure in which a coating phase made of a carbonaceous material having crystallinity lower than that of the graphite-based carbonaceous material is formed on at least a part of the surface of a core material made of a carbonaceous material.

The ratio of the graphite-based carbonaceous material and the carbonaceous material having inferior crystallinity to the graphite-based carbonaceous material in the above-mentioned lithium secondary battery negative electrode material is usually 99/1 to 5 by weight.
It is 0/50, preferably 98/2 to 95/5, and more preferably 98/2 to 96/4. If the amount of carbonaceous material having poor crystallinity is too small, the effect of coating is small, and if it is too large, the capacity of the negative electrode is reduced.

As described above, a method of depositing a carbonaceous material having a crystallinity less than that on the graphite-based carbonaceous material, that is, a method of forming a coating phase made of a carbonaceous material having a lesser crystallinity on the surface of the graphite-based carbonaceous material. , Are various, but typical methods are as follows. A method of mechanically or chemically treating a graphite-based carbonaceous material to transform the surface of the graphite-based carbonaceous material into a carbonaceous material having poorer crystallinity.

[0017] Soil-like graphite or scaly graphite having low crystallinity such that the interplanar spacing (d002) of the (002) plane by X-ray wide-angle diffraction is 3.37 Å or more, a crushed product of these, preferably laser diffraction Obtained average particle size d50 is 5 μm
Or less, more preferably 1 μm or less, and most preferably 0.
A finely pulverized powder having a particle size of 5 μm or less is used on the surface of the graphite-based carbonaceous material, if necessary, by using an appropriate powder binder,
How to bind.

After the firing, an organic substance having a property of being capable of storing and releasing lithium ions and having a property of being transformed into a carbonaceous substance having poor crystallinity is attached to the surface of the graphite-based carbonaceous substance, and this is fired to have poor crystallinity. A method of converting into a carbonaceous material. Among the above methods, the above method (hereinafter referred to as firing method)
However, it is a simple and excellent method.

Specific examples of the organic substance used in the above-mentioned calcination method include carbonaceous organic substances such as coal tar pitch from soft pitch to hard pitch where carbonization proceeds in a liquid phase and dry distillation liquefied oil. Heavy oil such as coal-based heavy oil, straight-run heavy oil such as atmospheric residual oil and vacuum residual oil, and petroleum heavy oil such as crude oil and cracked heavy oil such as ethylene tar produced as a by-product during thermal decomposition of naphtha. Alternatively, the above may be solidified through a means such as distillation, solvent extraction or the like at a temperature below which carbonization proceeds. Furthermore, aromatic hydrocarbons such as acenaphthylene, decacyclene, and anthracene, nitrogen-containing cyclic compounds such as phenazine and acridine, sulfur-containing cyclic compounds such as thiophene, and polycyclic alicyclic compounds such as adamantane that require a pressure of 30 MPa or more. Is mentioned. In addition, there are thermoplastic polymers such as polyphenylene such as biphenyl and terphenyl, which undergoes a liquid phase in the process of carbonization, polyvinyl chloride such as polyvinyl chloride, polyvinyl acetate, polyvinyl butyral, and polyvinyl alcohol. Further, it is also possible to add an appropriate amount of acids such as phosphoric acid, boric acid and hydrochloric acid, and alkalis such as sodium hydroxide to the above various organic substances. Furthermore, these things
Oxygen, sulfur at 600 ° C, preferably 300-400 ° C,
It may be appropriately crosslinked with an element selected from nitrogen or boron.

In the firing method, the graphite-based carbonaceous material and the organic substance are mixed and fired. The firing temperature is usually 500 to 2200 ° C., preferably 650 to 8
50 degreeC, More preferably, it is 700-800 degreeC. If the firing temperature is too low, the conductivity will be poor and the charge acceptance will be poor. On the contrary, if it is too high, the electrode swells more. The thickness of the powder packed in the container during firing is usually 1 to 50 cm, preferably 5 to 20 cm, and the pressure during firing is usually 0.100 to 0.400 MPa, preferably 0.101.
˜0.200 MPa.

After the above firing, appropriate crushing or crushing is carried out to obtain a particle size of usually 4 to 40 μm, preferably 10 to 3
The negative electrode material for a lithium secondary battery of the present invention can be obtained by adjusting the thickness to 2 μm, more preferably 15 to 30 μm. The negative electrode material for a lithium secondary battery of the present invention is prepared by preparing a negative electrode for a lithium secondary battery from this and a binder according to the method described in [Evaluation Method of Electrode Material] below.
The resistance (R) of the negative electrode portion obtained by assembling a 032 coin cell and performing complex impedance measurement is
6.5 ohm or less, and the double layer capacity (Cdl) at the interface between the negative electrode and the electrolytic solution is 7.0 × 10 ⁻⁴ F or more and 10 × 10.
Must be below ^-4 F. The acquisition of the preferable properties as described above can be achieved by adjusting the firing temperature within the above-mentioned firing temperature range.

Further, the BET surface area was measured using N ₂ gas for the negative electrode material for lithium secondary batteries and the negative electrode for lithium secondary batteries prepared from the negative electrode material and the binder, and the obtained results were obtained. Calculated from the value by the following formula (1),
The surface coverage Γ (%) of the active material with the binder is 20 to 55.
It is preferably in the range of%.

[0023]

## EQU00002 ## Surface coverage .GAMMA. = (Powder SA-negative electrode SA) / powder SAx100 (1) Powder SA: BET surface area of negative electrode material for lithium secondary battery Negative electrode SA: BET surface area of negative electrode for lithium secondary battery Further, the BET surface area of the negative electrode material for lithium secondary batteries by N ₂ gas is preferably 2.4 to ⁴ m ² / g.

The results of Raman spectrum analysis of the negative electrode material for lithium secondary batteries using an argon ion laser beam having a wavelength of 5145Å show that 1570 to 1
The intensity of the peak existing in the range of 620 cm ⁻¹ is I _A , 1
When the intensity of the peak existing in the range of 350 to 1370 cm ⁻¹ is I _B , the ratio R value (= I _B / I _A ) of more than 0.4 is a film of a low resistance negative electrode interface. Are preferred because they are easy to form.

[Negative Electrode for Lithium Secondary Battery] Next, a method for producing a negative electrode sheet for a lithium secondary battery or a negative electrode for a lithium secondary battery using the negative electrode material for a lithium secondary battery of the present invention will be described. The method for producing the negative electrode is not particularly limited as long as it contains the negative electrode material for a lithium secondary battery of the present invention as a component of the negative electrode, and various conventionally known methods can be adopted. For example, by adding a binder, a solvent and the like to a negative electrode material for a lithium secondary battery to form a slurry, and coating and drying the slurry on a metal current collector substrate such as a copper foil to form a negative electrode sheet. The negative electrode. Nickel foil or stainless steel foil may be used instead of the copper foil. Further, the negative electrode material can be directly molded into a negative electrode sheet shape by a method such as roll molding or compression molding.

Examples of the binder include solvent-stable resin polymers such as polyethylene, polypropylene, polyethylene terephthalate, aromatic polyamide and cellulose, styrene-butadiene rubber, isoprene rubber,
Rubber-like polymers such as butadiene rubber and ethylene / propylene rubber, styrene / butadiene / styrene block copolymers, hydrogenated products thereof, styrene / ethylene / butadiene / styrene copolymers, styrene / isoprene / styrene block copolymers, Soft resins such as thermoplastic elastomeric polymers such as hydrogenated products, syndiotactic-1,2-polybutadiene, ethylene / vinyl acetate copolymers, propylene / α-olefin (C2-12) copolymers, etc. Polymers, methyl cellulose, carboxymethyl cellulose, polyvinyl alcohol, polyvinyl butyral, formalized products of these polymers, and the like can be used. A suitable amount of a fluorine-based binder such as polyvinylidene fluoride or polytetrafluoroethylene may be added to this. An organic polymer composition having an ionic conductivity of alkali metal ions, especially lithium ions may be further mixed, but care must be taken so as not to impair the shapeability of the electrode.

The form of mixing the negative electrode material for a lithium secondary battery and the above-mentioned binder when producing the negative electrode for a lithium secondary battery is not particularly limited, and various forms can be adopted. That is, a form in which both particles are mixed, a form in which a fibrous binder is mixed with particles of a carbonaceous material so as to be entangled with each other, or a form in which a layer of the binder is attached to the surface of the particles of the carbonaceous material can be mentioned. The mixing ratio of the carbonaceous material and the binder is usually 0.1 to 30% by weight, preferably 0.5 to 30% by weight based on the carbonaceous material.
It is 10% by weight, more preferably 0.5 to 5% by weight.
When the amount of the binder is too large, the internal resistance of the electrode becomes large, and when it is too small, the binding property between the current collector and the carbonaceous powder is poor.

A suitable conductive agent may be added when the negative electrode is produced. Examples of the conductive agent include carbon black such as acetylene black, furnace black, and Ketjen black, and metal powder such as nickel and copper having an average particle diameter of 1 μm or less. As described above, by mixing the negative electrode material for a lithium secondary battery and a suitable powder binder and adjusting the amount thereof, an electrode having a surface area preferable for Li insertion can be manufactured. Further, since it is possible to form a coating film on the negative electrode interface having a low resistance, it is possible to positively affect the charge acceptability of Li. Further, since the coating can be made uniform, the electrode swelling due to the surface coating is small. Therefore, the lithium secondary battery negative electrode material of the present invention, for example,
It is suitable as a negative electrode material for prismatic batteries.

Furthermore, the negative electrode material for a lithium secondary battery of the present invention uses a graphite-based carbonaceous material as its constituent element, and therefore has a large reversible capacity during cycling and has a high potential with respect to Li like amorphous carbon. Since it is easy to secure the cell voltage when assembled in a battery together with the positive electrode, it is also useful for increasing the capacity. [Electrolytic Solution] When the negative electrode for a lithium secondary battery produced from the negative electrode material for a lithium secondary battery of the present invention and a binder is used as a battery, the electrolytic solution is composed of an organic solvent and an electrolyte.

Examples of the organic solvent include cyclic carbonates such as ethylene carbonate, chain carbonates such as diethyl carbonate, dimethyl carbonate and ethylmethyl carbonate, 1,2-dimethoxyethane, tetrahydrofuran, 2-methyltetrahydrofuran,
Examples include ethers such as 1,3-dioxolane, sulfolane and the like. In these organic solvents, vinylene carbonate, vinyl ethylene carbonate, methylphenyl carbonate, ethylene sulfide, propylene sulfide, 1,3-propane sultone, 1,4-butane sultone, or acid anhydrides such as maleic anhydride and succinic anhydride. A so-called film forming agent selected from the above may be added. The addition amount of the film forming agent is usually 10% by weight or less, preferably 8% by weight or less, more preferably 5% by weight or less, and further preferably 2% by weight or less. If the amount of the film-forming agent added is too large, it may adversely affect other battery characteristics such as an increase in initial irreversible capacity, deterioration of low temperature characteristics and rate characteristics.

Examples of the electrolyte include LiCl
O ₄ , LiPF ₆ , LiBF ₄ , LiCF ₃ SO ₃ , LiA
Examples thereof include salts of sF ₆ , LiCl, LiBr, Li trifluoromethanesulfonimide, and the like. The concentration of the electrolyte is about 0.5 to 2.0 M in the organic solvent. A gel-like, rubber-like, or solid sheet-like material may be used by further incorporating these electrolytic solutions into an organic polymer compound. In such a case, the above composition will be discussed with the composition of only the organic solvent excluding the amount of the organic polymer compound serving as the aggregate. Specific examples of the organic polymer compound, polyethylene oxide, polyether polymer compounds such as polypropylene oxide, cross-linked polymers of these polyether polymer compounds, polyvinyl alcohol, polyvinyl butyral,
Examples thereof include insolubilized products, polyepichlorohydrin, polyphosphazene, polysiloxane, polyvinylpyrrolidone, polyvinylidene carbonate and polyacrylonitrile. Further, polymer copolymers such as poly (ω-methoxy oligooxyethylene methacrylate) and poly (ω-methoxy oligooxyethylene methacrylate-co-methyl methacrylate) can also be used.

It is also possible to use a polymer solid electrolyte which is a conductor of an alkali metal cation such as lithium ion. Examples thereof include those obtained by dissolving a Li salt in the above polyether polymer compound, Examples thereof include polymers in which the ether terminal hydroxyl group is substituted with an alkoxide. [Positive Electrode for Lithium Secondary Battery] The material of the positive electrode body for constituting the lithium secondary battery is not particularly limited, but LiCoO 2 is a standard material for use in combination with the negative electrode for the lithium secondary battery. ₂ is mixed with a conductive material such as acetylene black, polyvinylidene fluoride, etc., coated on an aluminum foil, dried, and pressed. In addition, in general, it is preferably composed of a metal chalcogen compound capable of inserting and extracting an alkali metal cation such as lithium ion during charge and discharge. Such metal chalcogen compounds include vanadium oxide, vanadium sulfide, molybdenum oxide, molybdenum sulfide, manganese oxide, chromium oxide, titanium oxide, titanium sulfide, and these. Complex oxides, complex sulfides, and the like. Preferably,
_{Cr 3 O 8, V 2 O} 5, V 5 O 13, VO 2, Cr 2 O 5, MnO
₂ , TiO ₂ , MoV ₂ O ₈ , TiS ₂ , V ₂ S ₅ , Cr _0.25
V _0.75 S ₂ , Cr _0.5 V _0.5 S _{2 and the} like. In addition, LiMY
₂ (M is a transition metal such as Co and Ni, Y is a chalcogen element such as O and S), LiM ₂ Y ₄ (M is Mn, Y is O), W
O _{3 and} other oxides, CuS, Fe _0.25 V _0.75 S ₂ , Na _0.1
Sulfides such as CrS ₂ and phosphorus such as NiPS ₃ and FePS ₃
Sulfur compounds, selenium compounds such as VSe ₂ and NbSe ₃ can also be used.

The above compound is mixed with a binder, coated on a current collector, and dried to form a positive electrode plate in the same manner as in the method for producing the negative electrode. [Lithium secondary battery] A lithium secondary battery is prepared by combining the negative electrode plate, the positive electrode plate and the electrolytic solution produced as described above with other battery components such as a separator, a gasket, a current collector, a sealing plate and a cell case. Configure the battery. Batteries that can be manufactured are not particularly limited, such as a cylinder type, a prismatic type, and a coin type, but basically, a current collector and a negative electrode material are placed on a cell floor plate, and an electrolytic solution and a separator are placed thereon. Further, the negative electrode and the positive electrode are opposed to each other, and they are caulked together with the gasket and the sealing plate to form a secondary battery.

The separator holding the electrolytic solution is generally a material having excellent liquid retaining properties, and is impregnated with the electrolytic solution using, for example, a nonwoven fabric of polyolefin resin or a porous film.

[0035]

EXAMPLES Specific examples of the present invention will now be described in more detail with reference to Examples, but the present invention is not limited to these Examples. [Evaluation Method of Electrode Material ] In the firing method for the content of carbonaceous material having poor crystallinity in the negative electrode material, the carbonaceous material produced by adhering an organic substance to the surface of the graphite-based carbonaceous material and firing it is crystalline. Since an inferior carbonaceous material is constituted, the amount of carbonaceous material having inferior crystallinity was quantified by the increase in weight due to this firing operation, that is, the residual carbon ratio.

Raman spectrum measurement NR-1800 manufactured by JASCO Corporation, wavelength 5145
The Å argon ion laser beam was irradiated at an intensity of 30 mW. Here the peaks present in the range of 1570～1620Cm ^-1 strength and, 1350 ^-1
The intensity of the peak existing in the range was measured, and the Raman R value obtained from them was determined.

Surface Coverage of Active Material with Binder For the negative electrode material and the negative electrode, BET1 using N ₂ gas was used.
The BET surface area was measured by the dot method. The surface area of the electrode was that before the electrode density was adjusted. From the value of the obtained BET surface area, the surface coverage Γ (%) of the active material with the binder was calculated by the following formula (1).

[0038]

## EQU00003 ## Surface coverage .GAMMA. = (Powder SA-negative electrode SA) / powder SAx100 (1) Powder SA: BET surface area of negative electrode material for lithium secondary battery Negative electrode SA: BET surface area of negative electrode for lithium secondary battery Preparation of sample for electrochemical evaluation To 10 g of the negative electrode material powder, 1% by weight of carboxymethyl cellulose and 1% by weight of styrene-butadiene rubber as a powder binder were added, and the mixture was mixed for 3 minutes with a Keyence hybrid mixer. Stir to obtain a slurry. This slurry was applied on a copper foil and pre-dried at 110 ° C.
10 ± 0.1 mg / cm ² of the negative electrode material powder was made to adhere to the current collector. After drying, the electrode density is 1.5 ± 0.0
The negative electrode sheet was adjusted to ³ g / cm ³ . Further 150
It was vacuum dried at 0 ° C. to obtain a negative electrode.

An electrolytic solution containing ethylene carbonate and ethyl methyl carbonate (1: 1) in which LiPF ₆ was dissolved as a solute to 1 mol / L was used, and Li was added through a separator (made of a porous polyethylene film).
A 2032 coin type cell having CoO ₂ as a counter electrode was assembled. Complex Impedance Measurement After the 2032 coin cell was paused for 24 hours before measurement, it was charged at a current value of 0.6 mA / cm ² until the potential difference between electrodes reached 4.2 V, and the potential difference between electrodes was 3%. It discharged until it became 0.0V. After carrying out this charging and discharging 6 times at room temperature, 10 ^-2 to 10 ⁵ H was obtained at the 7th 4.2V charging.
Complex impedance measurement was performed in the z frequency band, and the resistance (R) of the negative electrode portion and the double layer capacitance (C
dl) was measured. At this time, in order to avoid the influence of the factors of the positive electrode and the low frequency part, a part of the arc appearing as the film resistance component of the negative electrode was extrapolated to obtain the numerical values of the above parameters. Each numerical value was an average value of the results of three coin type cells.

Electrode swelling A 2016 coin type cell was assembled by using the same as above for the negative electrode, the electrolytic solution and the separator, and using lithium metal for the counter electrode.
The battery was disassembled after the fifth charge and discharge similar to the above, the negative electrode was taken out, and the electrode thickness was measured with a micrometer (manufactured by Mitutoyo). The expansion coefficient of the electrode was calculated by the following formula (2) from the difference between the electrode thickness before charge and discharge and after the fifth discharge, and the electrode swelling was obtained. The discharge was performed at a current density of 0.33 mA / cm ² until the potential difference between the electrodes reached 1.5V.

[0041]

## EQU00004 ## Expansion coefficient of electrode (%) = (electrode thickness after fifth discharge-electrode thickness before charge / discharge) / electrode thickness before charge / discharge × 100 (2) Charge-accepting electrode Coin-shaped cell as in the case of electrode swelling the assembly was charged at a current density of 0.16 mA / cm ² until the interelectrode potential difference becomes to 0V, and was discharged at a current density of 0.33 mA / cm ² until the interelectrode potential difference becomes 1.5V. After repeating this charging / discharging process twice, the battery was charged to 0 V at 1.6 mA / cm ² and the charging capacity was measured. The result was evaluated by the average value of the results of four coin cells. From this, the Li charge acceptability at high current density can be estimated. In the present measurement was half-cell evaluation as the counter electrode of lithium, LiCoO ₂
Similar effects can be expected when the above positive electrode material is used.

Example 1 Natural graphite particles 1 having an average particle size of 25 μm obtained by mechanical grinding
5 parts by weight and 1 part by weight of petroleum-based pitch in air at 70 ° C.
Using a mixer, mixed uniformly. The obtained mixture was packed in a container having an open top with a thickness of 10 cm, and heat-treated at 600 ° C. for 1 hour in an inert atmosphere in a batch heating furnace. After cooling, the obtained fired mixture was repacked to a thickness of 20 cm and further heat-treated at 800 ° C. for 1 hour in an inert atmosphere adjusted to a pressure of 0.103 MPa. After cooling, the obtained fired body was crushed and sieved, and the central particle diameter d50 was 25.
A sample powder of μm was used. The content of carbonaceous material, which has a crystallinity inferior to that of graphite, calculated from the residual carbon ratio is 10
When it was 0% by weight, it was 1.2% by weight. The R value calculated from the results of Raman spectroscopy was 0.35.
The BET surface area of this powder was 3.7 m ² / g, and the surface coverage Γ was 33%. The resistance of the negative electrode obtained from the electrochemical evaluation was 4.9 ohm, and the double-layer capacity at the negative electrode / electrolyte interface was 9.6 × 10 ⁻⁴ F. The charge acceptability was 125 mAh / g, and the electrode swelling was 13%.

Example 2 3 parts by weight of graphite as a raw material and 3 parts by weight of petroleum-based pitch, respectively.
Mix as in Example 1 except changing to 1 part by weight,
It heat-processed at 600 degreeC for 1 hour. After cooling, the resulting mixture fired body was repacked to a thickness of 20 cm, and the pressure was 0.153 MP.
It was further heat-treated at 700 ° C. for 1 hour in an inert atmosphere adjusted to a. After cooling, the obtained fired body was crushed and sieved to obtain a sample powder having a median particle diameter d50 of 25 μm.
The content of the carbonaceous material having a crystallinity inferior to that of graphite calculated from the residual carbon ratio was 6.3% by weight when the entire powder was taken as 100% by weight. The R value calculated from the results of Raman spectroscopy was 0.57. The BET surface area of this powder is
It was 2.9 m ² / g, and the surface coverage Γ was 21%. The resistance of the negative electrode obtained from the electrochemical evaluation was 5.9 o.
hm and the double layer capacity at the negative electrode / electrolyte interface is 8.2 ×
It was 10 ^-4 F. In addition, the charge acceptance is 111 mAh /
The electrode swelling was 15%.

Example 3 5 parts by weight of the raw material graphite and 5 parts by weight of petroleum pitch, respectively.
Mixing and heat treatment were performed in the same manner as in Example 2 except that the amount was changed to 1 part by weight. After cooling, the obtained fired body was crushed and sieved to obtain a sample powder having a median particle diameter d50 of 25 μm. The content of the carbonaceous material having a crystallinity inferior to that of graphite calculated from the residual carbon ratio is 4.
It was 4% by weight. The R value calculated from the results of Raman spectroscopy was 0.52. The BET surface area of this powder was 2.9 m ² / g, and the surface coverage Γ was 31%. The negative electrode resistance obtained from the electrochemical evaluation was 5.4.
ohm and the double layer capacity at the negative electrode / electrolyte interface is 9.1.
It was × 10 ^-4 F. Charge acceptability is 115 mAh
/ G, and the electrode swelling was 13%.

Comparative Example 1 3 parts by weight of graphite as a raw material and 3 parts by weight of petroleum pitch, respectively.
1 part by weight and uniformly mixed at 70 ° C. in the air using a mixer. The obtained mixture was packed in a container having an open top with a thickness of 40 cm, and heat-treated at 600 ° C. for 1 hour in an inert atmosphere in a batch heating furnace. After cooling, the obtained mixture fired body was further heat-treated at 1300 ° C. for 1 hour in an inert atmosphere adjusted to a pressure of 0.103 MPa. After cooling, the obtained fired product was crushed and sieved to obtain a median particle diameter d5.
0 was 25 μm sample powder. The content of the carbonaceous material, which was inferior in crystallinity to graphite and was calculated from the residual coal rate, was 6.0% by weight when the entire powder was 100% by weight. The R value calculated from the results of Raman spectroscopy was 0.35. The BET surface area of this powder was 2.3 m ² / g, and the surface coverage Γ was 18%. Resistance of the negative electrode obtained from the electrochemical evaluation is 6.8Ohm, the double layer capacity of the anode / electrolyte interface 7.1 × 10 ^- was ⁴ F.
The charge acceptability was 83 mAh / g, and the electrode swelling was 19%.

Comparative Example 2 The ratio of the raw material graphite to the petroleum pitch was 1 part by weight,
The amount was 2.3 parts by weight, and uniform mixing was performed in the air at 80 ° C. using a mixer. The obtained mixture was packed in a container having an open top with a thickness of 40 cm, and heat-treated at 600 ° C. for 1 hour in an inert atmosphere in a batch heating furnace. After cooling, the obtained mixture was further heat-treated at 1200 ° C. for 1 hour in an inert atmosphere adjusted to a pressure of 0.103 MPa. The R value was 0.71. The BET surface area of this powder is 1.5m
² / g, and the surface coverage Γ was 57%. The film resistance obtained from the electrochemical evaluation is 5.0 ohm,
The double layer capacity at the negative electrode / electrolyte interface was 1.1 × 10 ⁻³ F. The charge acceptability was 55 mAh / g, and the electrode swelling was 25%.

[0047]

EFFECTS OF THE INVENTION According to the present invention, a negative electrode material and a negative electrode sheet for a lithium secondary battery, which have high charge acceptance and less swelling of electrodes, can be obtained.

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Tomiyuki Kamata             3-3-1 Chuo 8-chome, Ami Town, Inashiki District, Ibaraki Prefecture             Within Mitsubishi Chemical Corporation (72) Inventor Kengo Okani             1 Kyushu Town, Sakaide City, Kagawa Prefecture Mitsubishi Chemical Corporation             Inside the company (72) Inventor Shoji Ishihara             3-3-1 Chuo 8-chome, Ami Town, Inashiki District, Ibaraki Prefecture             Within Mitsubishi Chemical Corporation F-term (reference) 4G146 AA01 AA02 AA19 AB01 AD24                       AD25 BA02 BA12 BA13 BA18                       BA21 BA22 BA24 BC02 BC33A                       BC34A BC34B                 5H029 AJ02 AJ03 AK02 AK03 AK05                       AL06 AL07 AL18 AM03 AM04                       AM05 AM07 AM16 CJ08 CJ22                       DJ16 HJ07 HJ13 HJ19 HJ20                 5H050 AA02 AA08 BA17 CA02 CA05                       CA08 CA11 CB07 CB08 FA17                       FA18 GA10 GA22 HA07 HA19

Claims (4)

[Claims] 1. A graphite-based carbonaceous material comprising:
Powder form with a structure in which a carbonaceous material with poor crystallinity is deposited
Which is a negative electrode material and is prepared from the negative electrode material and a binder.
The negative electrode resistance (R) for the rechargeable lithium secondary battery was 6.5 o.
hm or less, negative electrode / electrolyte interface double layer capacity (Cdl)
But 7.0x10^-FourF or higher, 10x10 ^-FourRange less than F
A negative electrode material for a lithium secondary battery, characterized in that 2. A value obtained by measuring the BET surface area using N ₂ gas for a negative electrode material for a lithium secondary battery and a negative electrode for a lithium secondary battery prepared from the negative electrode material and a binder. The negative electrode material for a lithium secondary battery according to claim 1, wherein the surface coverage Γ (%) of the active material with the binder calculated from the following formula (1) is in the range of 20 to 55%. ## EQU00001 ## Surface coverage .GAMMA. = (Powder SA-negative electrode SA) / powder SAx100 (1) Powder SA: BET surface area of negative electrode material for lithium secondary battery Negative electrode SA: BET surface area of negative electrode for lithium secondary battery 3. The negative electrode material for a lithium secondary battery according to claim 1, wherein the negative electrode material for a lithium secondary battery has a BET surface area by N ₂ gas of 2.4 to ⁴ m ² / g. 4. A graphite-based carbonaceous material comprising:
Powder form with a structure in which a carbonaceous material with poor crystallinity is deposited
Which is a negative electrode material and is prepared from the negative electrode material and a binder.
The negative electrode resistance (R) for the rechargeable lithium secondary battery was 6.5 o.
hm or less, negative electrode / electrolyte interface double layer capacity (Cdl)
But 7.0x10^-FourF or higher, 10x10 ^-FourRange less than F
It is formed into a sheet by adding a binder to the one in
A negative electrode sheet for a lithium secondary battery, which is characterized in that