JP2003031220A - Secondary power source - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a secondary power source with high capacity, high breakdown voltage, and high charge/discharge cycle reliability. SOLUTION: This secondary power source has a positive electrode containing activated carbon, a negative electrode containing a composite carbon material in which graphitization retardant carbon is covered with carbon having grown turbulent layer structure, and an organic electrolyte containing a lithium salt. Preferably, the composite carbon material has the spacing between the [002] faces of 0.354-0.395 nm, the intensity ratio R (R=I1360 /I1580 ) of the peak value (I1360 ) at 1360 cm<-1> to the peak value (I1580 ) at 1580 cm<-1> , in argon ion Raman spectrum, of 0.5-1.8. Mass ratio of the graphitization retardant carbon and the carbon having the grown turbulent layer structure in the composite carbon material in the negative electrode is 100:2 to 100:30.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a secondary power source which has a high withstand voltage and a high discharge capacity and is excellent in reliability in a charge / discharge cycle at a large current.

[0002]

2. Description of the Related Art As electrodes of a conventional electric double layer capacitor, polarizable electrodes mainly composed of activated carbon are used for both positive and negative electrodes. The withstand voltage of the electric double layer capacitor is 1.2 V when an aqueous electrolytic solution is used, and 2.5 to 3.3 V when an organic electrolytic solution is used. Since the energy of the electric double layer capacitor is proportional to the square of the withstand voltage, the organic electrolytic solution having a higher withstand voltage has higher energy than the aqueous electrolytic solution.
However, the energy density of an electric double layer capacitor using an organic electrolyte is 1/1 times that of a secondary battery such as a lead storage battery.
It is 0 or less, and further improvement in energy density is required.

On the other hand, in Japanese Unexamined Patent Publication No. 64-14882, an electrode mainly composed of activated carbon is used as a positive electrode, and the [002] plane spacing by X-ray wide angle diffraction is 0.338-0.
A secondary power supply with an upper limit voltage of 3.0 V has been proposed in which a negative electrode is an electrode in which a lithium material is occluded in a carbon material having a wavelength of 356 nm. In addition, JP-A-8-107048
The publication proposes a battery using a carbon material capable of occluding and desorbing lithium ions in advance as a negative electrode by occluding the lithium ions by a chemical method or an electrochemical method. Japanese Unexamined Patent Publication No. 9-55342 proposes a secondary power source having an upper limit voltage of 4.0 V, which has a negative electrode in which a carbon material capable of absorbing and desorbing lithium ions is supported on a porous current collector that does not form an alloy with lithium. Has been done.

A secondary power source using activated carbon for the positive electrode and a carbon material capable of absorbing and desorbing lithium ions for the negative electrode can operate at a higher voltage than conventional electric double layer capacitors using active carbon for both the positive electrode and the negative electrode. It can have a high capacity. In particular, in this secondary power source, a higher capacity can be obtained by using a base graphite-based carbon material having a potential for inserting and extracting lithium ions in the negative electrode. In addition to the electric double layer capacitor and the secondary power source, there is a lithium ion secondary battery using a lithium-containing compound for the positive electrode and a carbon material for the negative electrode as a high-performance secondary power source. The lithium-ion secondary battery has a higher voltage and a higher capacity than the electric double layer capacitor, but has a problem that the resistance is high and the life due to the rapid charge / discharge cycle is significantly shorter than that of the electric double layer capacitor.

[0005]

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide a secondary power source which can be charged and discharged rapidly, has a high withstand voltage, a high capacity, a high energy density, and is highly reliable in a charge and discharge cycle. To do.

[0006]

The present invention is directed to a positive electrode containing activated carbon, a negative electrode containing a composite carbon material in which non-graphitizable carbon is coated with carbon having a disordered structure, and an organic material containing a lithium salt. An electrolytic solution is provided, and a secondary power source is provided. In the present specification, a negative electrode body is formed by joining and integrating a negative electrode mainly composed of a carbon material capable of inserting and extracting lithium ions and a current collector. The same definition is applied to the positive electrode body. Further, both the secondary battery and the electric double layer capacitor are one kind of the secondary power source, but in the present specification, a positive electrode containing activated carbon and a negative electrode containing a carbon material capable of absorbing and desorbing lithium ions have a specific structure. The secondary power source is simply called the secondary power source.

In the lithium ion secondary battery, the positive electrode is an electrode mainly composed of a transition metal oxide containing lithium, the negative electrode is an electrode mainly composed of a carbon material capable of absorbing and desorbing lithium ions, and the lithium ions are positively charged by charging. Is desorbed from the lithium-containing transition metal oxide, the lithium ion of the negative electrode is occluded and occluded by the desorbable carbon material, the lithium ion is desorbed from the negative electrode by the discharge, and the lithium ion is occluded in the positive electrode. Therefore, the lithium ions in the electrolytic solution do not essentially participate in the charging and discharging of the battery. On the other hand, in the secondary power source of the present invention, anions in the electrolytic solution are adsorbed by the activated carbon of the positive electrode by charging, and lithium ions in the electrolytic solution are occluded by the carbon material capable of absorbing and desorbing the lithium ions of the negative electrode.
Then, the lithium ions are desorbed from the negative electrode by the discharge, and the anions are desorbed from the positive electrode. That is, in the secondary power source of the present invention, the solute of the electrolytic solution is essentially involved in charging and discharging,
The charging / discharging mechanism is different from that of the lithium ion secondary battery. Then, unlike a lithium ion secondary battery, lithium ions do not occlude and desorb in the positive electrode active material itself,
Since there is no deterioration of the positive electrode due to occlusion and desorption of lithium ions, the secondary power supply of the present invention is less deteriorated by charge / discharge cycles and is excellent in long-term reliability.

As carbon materials capable of occluding and desorbing lithium ions of the negative electrode in the secondary power source, generally graphite-based carbon materials (the plane spacing of [002] plane by X-ray wide angle diffraction is 0.337 nm or less) and non-graphite A low crystalline carbon material containing volatile carbon and graphitizable carbon (the interplanar spacing of [002] planes by the X-ray wide angle diffraction method exceeds 0.337 to 0.395n.
m) Graphite-based carbon materials have a particularly low potential for lithium ion absorption and desorption, and show a flat charge-discharge curve.Therefore, the discharge capacity under practical use conditions is lower than that under low-crystalline carbon materials. large. However, when considering the cycle characteristics for rapid charge / discharge, the present inventors found the following correlation. That is,
The cycle characteristics for rapid charging / discharging depend on the interplanar spacing of the [002] plane of the negative electrode carbon material by the X-ray wide-angle diffraction method. It was found that the cycle characteristics for discharge are good. In other words, the cycle characteristics of the carbon negative electrode with the developed disordered layer structure having a large [002] plane spacing are better than those of a graphite-based negative electrode having a small [002] plane spacing.

Further, it is considered that the characteristics of the surface of the carbon material as well as the bulk property of the carbon material largely contribute to the cycle characteristics of the material. The interplanar spacing of the [002] plane mainly reflects the properties of the bulk, while the argon ion Raman spectrum reflects the properties of the carbon material surface. Ratio of the intensity ratio _{R (R = I 1360 / I} 1580) is an amorphous structure of the surface and graphite structure of the peak value in 1360 cm ^-1 peak value in 1580 cm ^-1 in the argon ion Raman spectrum for (I ₁₅₈₀₎ (I ₁₃₆₀₎ It means that the larger R is, the lower the graphitization degree of the surface becomes, and the more the structure has a higher degree of disorder. Generally, the surface is determined by the properties of the bulk, and thus depends on the properties of the bulk.

Generally, in a carbon material having a uniform structure, there is a correlation that the larger the [002] plane spacing, the larger the R of the Raman spectrum, and these are used as independent parameters for the bulk and the surface. It is difficult to evaluate each property of. On the other hand, recently, attempts have been made to modify conventional carbon materials by various methods to bring new performance to the materials. For example, there is core-shell type carbon in which boron-added graphite or a nucleus made of graphite is covered with low crystalline carbon. These novel carbons deviate from the conventional correlation between the interplanar spacing and R. Boron-added carbon has a further graphitization degree of bulk developed by adding boron to the graphite-based material, while the surface structure is conversely a disordered structure. It is a high-quality material. In addition, the core-shell type carbon uses a carbon material with a high degree of graphitization in the bulk,
By coating the surface with a carbon shell with a well-developed turbostratic structure, the surface is modified to an amorphous structure while maintaining the properties of bulk graphite. In the case of these materials, it is possible to independently evaluate the bulk and surface performances of the carbon material by the interplanar spacing and R. As a result of earnest research using this evaluation method, the inventors have found that a material having a large disordered layer structure having a large interplanar spacing as a bulk has a good cycle characteristic for large current charge / discharge and an amorphous material having a high R as a surface characteristic. The present invention has been found out that a material having a structure has a good cycle characteristic.

The negative electrode composite material in the present invention is characterized in that it is a composite carbon material obtained by coating non-graphitizable carbon with carbon having a disordered layer structure. The non-graphitizable carbon, which is a raw material of the core of the composite material, has relatively high interplanar spacing and Coulombic efficiency, and the interplanar spacing of [002] plane by X-ray wide angle diffraction method is more than 0.337 nm to 0.395 nm. is there. By coating the surface of the non-graphitizable carbon particles with carbon having a highly disordered turbostratic structure, a negative electrode material excellent in large-current charge / discharge cycle characteristics was obtained. The interplanar spacing of the [002] plane of the composite carbon material according to the present invention measured by the X-ray wide-angle diffraction method is preferably 0.354 to 0.395 nm based on the non-graphitizable carbon that is the nucleus, and particularly 0.360. ~ 0.390 nm is more preferred. Within this range, the capacity change rate in a charge / discharge cycle at a large current is low without lowering the withstand voltage and the discharge capacity. The non-graphitizable carbon is obtained, for example, by heat-treating a furfuryl resin obtained by heat-treating a furfuryl alcohol resin at 1000 to 1500 ° C., a fired novolak resin obtained by heat-treating a novolac resin at a temperature of 700 ° C. or lower, and heat-treating a phenol resin. Examples include fired products of phenol resin.

As a method for coating the non-graphitizable carbon particles with carbon having a disordered layer structure, the non-graphitizable carbon particles are coated with various resins, tar or pitch in advance. , A method of carbonizing resin, tar or pitch, or flowing an organic gas on the surface of the non-graphitizable carbon particles, and thermally decomposing this gas to form a carbon film having a disordered structure on the surface of the non-graphitizable carbon particles. Chemical vapor deposition method (CVD), or a chemical vapor impregnation method (C) capable of uniformly treating the inside of a non-graphitizable carbon powder lump depending on conditions.
VI) method can be used, but the CVD method and the CVI method are preferable because they can provide more complete and uniform coating. CV
The processing temperature of the D and CVI methods is preferably 700 to 1200 ° C, more preferably 800 to 1100 ° C.

The shape of the powder of the composite carbon material having a non-graphitizable carbon / carbon structure with a developed turbostratic structure after the preparation is particulate, and the particle diameter is preferably 5 to 40 μm. The composite carbon material, when subjected to the carbon surface analysis by Raman spectrum, the peak value at 1580 cm ^-1 (I
Peak value in 1360 cm ^-1 for ₁₅₈₀₎ (I ₁
The intensity ratio R (R = I ₁₃₆₀ / I ₁₅₈₀ ) of ₃₆₀ ) is preferably 0.
It is 5 to 1.8, more preferably 0.6 to 1.5, still more preferably 0.7 to 1.4. The reason for this is that if R is too small, the degree of disorderedness of the surface will be small and the deterioration in the charge / discharge cycle will be large, and if R is too large, the cloning efficiency will be low. Further, when the composite carbon material particles in the present invention are measured by the X-ray wide angle diffraction method, a broad peak showing a low crystalline structure is confirmed,
That is, it can be confirmed that the surface of the non-graphitizable carbon bulk has a structure covered with carbon having a high degree of disorder. In the composite carbon material, the mass ratio of the non-graphitizable carbon and the carbon having a disordered layer structure is preferably 100: 2 to 100: 30, more preferably 100: 5 to 100: 30, and further preferably Is 100: 10 to 100: 20. If the proportion of carbon having a disordered structure is less than 2 parts by mass, the carbon having a disordered structure covered by the non-graphitizable carbon core may not be completely covered.
Even if the amount is more than the mass part, there is no effect in further improving the cycle characteristics.

The negative electrode of the present invention may further contain a carbon material such as carbon black as a conductive agent or vapor grown carbon in addition to the above-mentioned essential composite carbon material, the amount of which is 30% by mass in the carbon material of the negative electrode. The following is preferable.

The activated carbon contained in the positive electrode of the present invention is
The specific surface area is preferably 800 to 3000 m ² / g. The raw material and activation conditions for the activated carbon are not limited, but examples of the raw material include coconut husk, phenol resin, petroleum coke, and the like, and examples of the activation method include a steam activation method and a molten alkali activation method. In particular, activated carbon obtained by activating steam with coconut husk or phenol resin as a raw material is preferable. In order to reduce the resistance of the positive electrode, it is also preferable to include conductive carbon black or graphite as a conductive material in the positive electrode.
It is preferably contained in an amount of -20% by mass. As a method for producing the positive electrode body, for example, a mixture of activated carbon powder and a conductive material is mixed with polytetrafluoroethylene as a binder, and the mixture is kneaded and then molded into a sheet to form a positive electrode. There is a method of fixing using. Further, as a binder, polyvinylidene fluoride, polyamide imide,
It may be obtained by dispersing activated carbon powder and conductive material powder in a varnish in which polyimide or the like is dissolved, applying this liquid on a current collector by a doctor blade method or the like, and drying. The amount of the binder contained in the positive electrode is preferably 1 to 20 mass% from the balance of the strength of the positive electrode body and the characteristics such as capacity.

Like the positive electrode, the negative electrode of the present invention can be obtained by kneading polytetrafluoroethylene as a binder to form a sheet, forming a negative electrode, and adhering it to a current collector using a conductive adhesive. it can. In addition, polyvinylidene fluoride, polyamide imide or polyimide as a binder, a resin or a precursor of the binder is dissolved in an organic solvent to disperse the carbon material in a solution, coated on a current collector, and obtained by drying. There is also a method. Of these methods, the method of coating on the current collector is more preferable. In the method for obtaining the negative electrode body by applying the solution to the current collector, the solvent for dissolving the binder resin or its precursor is not limited, but can easily dissolve the resin constituting the binder or its precursor, N-methyl-2-pyrrolidone (hereinafter referred to as NMP) is preferable because it is easily available. here,
The precursor of polyvinylidene fluoride, the precursor of polyamideimide, or the precursor of polyimide means that they are polymerized by heating to be polyvinylidene fluoride, polyamideimide or polyimide, respectively.

In the present invention, the weight ratio of the carbon material capable of inserting and extracting lithium ions in the negative electrode to the binder is preferably 70:30 to 96: 4. More preferably 7
It is 5:25 to 90:10. When the binder content is more than 30% by mass, the negative electrode capacity becomes small. 4% by mass of binder
If it is less than the above range, the effect as a binder is weakened, and peeling between the negative electrode and the current collector increases.

Lithium contained in the organic electrolyte of the present invention
Umium salt is LiPF₆, LiBF_Four, LiClO_Four, L
iN (SO₂CF₃)₂, CF₃SO₃Li, LiC
(SO ₂CF₃)₃, LiAsF₆And LiSbF₆Or
One or more selected from the group consisting of In electrolyte
The concentration of lithium salt is 0.1-2.5 mol / L,
Is preferably 0.5 to 2 mol / L. In addition, in the present invention
The solvent of the electrolyte solution is propylene carbonate (
Hereinafter abbreviated as PC), ethylene carbonate (hereinafter referred to as EC
Abbreviated), butylene carbonate, dimethyl carbonate
G, ethyl methyl carbonate, diethyl carbonate
, Sulfolane, dimethoxyethane, etc.
Can be used alone or as a mixed solvent of two or more kinds.
It Among them, PC, EC, dimethyl carbonate, ethi
From the group of rumethyl carbonate and diethyl carbonate
At least one selected is preferable. The reason for this is that they are
Gas-chemically stable and has high electrical conductivity when solute is dissolved
This is because

[0019]

EXAMPLES Next, Examples (Examples 1-2) and Comparative Examples (Examples 3-)
The present invention will be described in more detail with reference to 4), but the present invention is not limited thereto. The cells of Examples 1 to 4 were all manufactured and measured in an argon glove box with a dew point of -60 ° C or lower. [Example 1] Average particle size of 10 μm, measured by X-ray wide angle diffraction method [0
[02] The non-graphitizable carbon particles having a surface spacing of 0.380 nm are immersed in a phenol resin solution, deaerated in vacuum, and then filtered, and the temperature is increased from room temperature to 800 ° C. under an argon gas atmosphere.
The carbon material fired for 2 hours was dispersed in a solution of polyvinylidene fluoride dissolved in NMP, applied on a current collector made of copper and dried to form a negative electrode on the current collector. The mass ratio of the carbon material capable of inserting and extracting lithium ions in the negative electrode and polyvinylidene fluoride was 9: 1. This is further pressed by a roll press machine to reduce the area of the negative electrode to 1c.
It was m × 1 cm and had a thickness of 15 μm, and was heat-treated under reduced pressure at 150 ° C. for 10 hours to obtain a negative electrode body. The carbon material had a [002] plane spacing of 0.380 nm and an R of Raman spectrum of 0.90.

Next, 80% by weight of activated carbon having a specific surface area of 2000 m ² / g and 10% by weight of conductive carbon black obtained by a steam activation method using a phenol resin as a raw material,
And, a mixture of 10% by weight of polytetrafluoroethylene as a binder was kneaded by adding ethanol, rolled, and then vacuum dried at 200 ° C. for 2 hours to give a thickness of 150 μm.
m electrode sheet was obtained. 1 cm x 1 from this electrode sheet
cm electrode was obtained and bonded to an aluminum foil using a conductive adhesive having polyamide imide as a binder, and heat-treated at 260 ° C. for 10 hours under reduced pressure to obtain a positive electrode body. The positive electrode body and the negative electrode body were made to face each other with a polypropylene separator interposed therebetween and sandwiched by sandwiching plates to fabricate an element. Using a mixed solvent of PC and ethyl methyl carbonate (mass ratio 1: 1), 1 mL of LiBF ₄ was used.
The device was sufficiently impregnated with a solution dissolved at a concentration of ol / L as an electrolytic solution, and the initial capacity was measured in the range of 4.2V to 2.75V. After that, charge / discharge current 10mA
/ Cm ² , the charge and discharge cycle was performed in the range of 4.0 V to 2.75 V, the capacity after 2000 cycles was measured, and the rate of change of capacity was calculated. The results are shown in Table 1.

[Example 2] X-ray wide-angle diffraction method [002]
Using non-graphitizable carbon particles having a surface spacing of 0.380 nm as a raw material, benzene vapor was introduced at 800 ° C., and C
A secondary power source was obtained in the same manner as in Example 1 except that VD was performed and the obtained carbon material was used as the negative electrode active material, and the same evaluation as in Example 1 was performed. The results are shown in Table 1. The carbon material is [00
The interplanar spacing of the [2] plane was 0.380 nm, and the R according to Raman spectrum was 0.85. [Example 3] A carbon material obtained by introducing benzene vapor at 800 ° C and performing CVD for a predetermined period from graphite-based particles having a spacing of [002] planes of 0.336 nm by X-ray wide-angle diffraction method as a raw material A secondary power source was obtained in the same manner as in Example 1 except that it was used as the negative electrode active material, and evaluated in the same manner as in Example 1. The results are shown in Table 1. The carbon material has a [002] plane spacing of 0.
336 nm, R by Raman spectrum is 0.6
It was 0. [Example 4] A secondary power source was obtained in the same manner as in Example 1 except that non-graphitizable carbon having a [002] plane spacing of 0.373 nm determined by the X-ray wide-angle diffraction method was used as the negative electrode active material. It evaluated similarly to 1. The results are shown in Table 1. The carbon material had a [002] plane spacing of 0.373 nm and an R of Raman spectrum of 0.51.

[0022]

[Table 1]

[0023]

According to the present invention, since the activated carbon positive electrode and the negative electrode containing the composite carbon material in which the non-graphitizable carbon is coated with the carbon having the disordered layer structure are used, the capacity is large and the withstand voltage is high. It is possible to provide a secondary power supply which is highly reliable and has high reliability in rapid charge / discharge cycles.

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor, Keima             1150 Hazawa-machi, Kanagawa-ku, Yokohama-shi, Kanagawa             Asahi Glass Co., Ltd. F-term (reference) 4G046 EA03 EA05 EC05                 5H029 AJ02 AJ03 AJ05 AK08 AL06                       AM02 AM03 AM04 AM05 AM07                       DJ16 DJ17 HJ01 HJ13                 5H050 AA02 AA07 AA08 BA17 CA16                       CB07 FA18 FA19 HA01 HA13

Claims (4)

[Claims] 1. A positive electrode containing activated carbon, a negative electrode containing a composite carbon material in which non-graphitizable carbon is coated with carbon having a turbostratic structure, and an organic electrolyte containing a lithium salt. Characteristic secondary power supply. 2. The composite carbon material has a [002] plane spacing of 0.354 to 0..0 measured by an X-ray wide angle diffraction method.
The secondary power source according to claim 1, which has a wavelength of 395 nm. 3. The composite carbon material is an argon ion llama.
In the spectrum, 1580 cm^-1Peak in
Value (I₁₅₈₀) To 1360 cm^-1Peak value at
(I ₁₃₆₀) Intensity ratio R (R = I₁₃₆₀/ I₁₅₈₀) Is 0.5-
The secondary power source according to claim 1 or 2, which is 1.8. 4. The mass ratio of the non-graphitizable carbon and the carbon having the disordered layer structure developed is 10 in the composite carbon material of the negative electrode.
The secondary power source according to any one of claims 1 to 3, which is 0: 2 to 100: 30.