JP2002063892A - Nonaqueous secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a secondary battery of high energy density through the use of a negative electrode material manufactured from low-cost material, enabling manufacturing cost reduction and enabling doping of a large amount of lithium. SOLUTION: The nonaqueous secondary battery is provided with a positive electrode, a negative electrode, and nonaqueous electrolyte solution; (1) the positive electrode is made of a material which can electrochemically absorb and store as well as discharge lithium; (2) the negative electrode (a) is obtained by thermal reaction of a raw material with pitch as a main component; (b) has a hydrogen/carbon atomic ratio of 0.35 to 0.05, (c) being made of a material with polycyclic aromatic hydrocarbons with a specific surface area of 50 m2/g or lower by BET method which is pre-doped with lithium.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a secondary battery using a non-aqueous electrolyte, and more particularly to a non-aqueous electrolyte secondary battery using a novel negative electrode material predoped with lithium.
According to the present invention, the performance of a lithium secondary battery can be significantly improved.

[0002]

2. Description of the Related Art In recent years, in connection with a power supply for a small portable device represented by a mobile phone, a late-night power storage system, a distributed power storage system for homes based on solar power generation, a power storage system for an electric vehicle, and the like, Various types of high energy density batteries are being vigorously developed. In particular, lithium-ion batteries have a volume energy density exceeding 350 Wh / l, and are superior in safety, reliability such as cycle characteristics, etc., compared to lithium secondary batteries using metallic lithium as the negative electrode. The market for power supplies for small portable devices is expanding exponentially.

[0003] Lithium ion batteries use LiCo as a positive electrode.
Lithium-containing transition metal oxides such as O ₂ and LiMn ₂ O ₄ are used, and a carbon-based material such as graphite is used as a negative electrode. At present, the capacity of lithium-ion batteries is being further increased.However, the capacity improvement by improving the cathode oxide and anode carbon-based material has almost reached its limit, and energy densities exceeding 450 Wh / l have been reached. It is difficult to achieve. In addition, in order to meet the needs for large-scale projections expected in the future, it is strongly desired to reduce material costs.

[0004] In particular, in order to increase the energy density and increase the size of the battery, securing safety is the most important issue, and from this viewpoint, further improvement in the characteristics of the electrode material is desired.

As the negative electrode material, various graphite materials,
Carbon-based materials and polycyclic aromatic conjugated materials (generally,
Low-temperature-treated carbon materials or polyacene-based materials) have been developed. In particular, the polycyclic aromatic conjugated structural material obtained by heat-treating various raw materials at a relatively low temperature of about 550 to 1000 ° C. has a theoretical capacity of graphite.
As a material exceeding C ₆ Li (372 mAh / g), it has received special attention.

As a raw material of various polycyclic aromatic conjugated structural substances that are currently being developed, phenol resins, polyparaphenylene, polyphenylene sulfide, mesocarbon microbeads, pitch fibers, coke, and the like are used. A capacity exceeding 400 mAh / g has been obtained for all polycyclic aromatic conjugated substances ("Latest technology for polymer batteries", published by CMC Corporation (1998)
p22-p30).

[0007] Among these polycyclic aromatic conjugated structural materials, those using a synthetic resin such as a phenol resin as a starting material have a relatively high capacity. For example, Synth. M
At., 73 (1995), p273-277, a polyacene-based organic semiconductor using a phenol resin as a raw material is reported. According to this report, 1100 mAh / g lithium can be doped, and 850 mAh / g lithium can be undoped. In addition, this material has a small exothermic peak due to the reaction with the electrolytic solution at around 150 ° C., and is a highly safe material (Proceedings of the 8th Battery Symposium (1997) pp.213-214). However, such a material using a synthetic resin as a starting material has a high raw material cost, and therefore requires a significant cost reduction in order to be practically used as a negative electrode material.

On the other hand, pitch or coke is inexpensive and mass-produced, and is promising as a raw material for a negative electrode material for a large lithium secondary battery. However, the capacity and initial efficiency of the polycyclic aromatic conjugated structural material using the material as a raw material are still insufficient, and further higher capacity and higher efficiency are desired. For example, 8th Internatio
nal Meeting on Lithium Batteries, Extend Abstracts
(1996) p174-175 discloses a polycyclic aromatic conjugated structural material obtained by thermally reacting a petroleum pitch raw material at 700 ° C.
Its capacity is 600mAh / g, and its efficiency is low at less than 60%.

Electrochemica Acta, vol. 38 No. 9 (19
93) According to p1179-1191, petroleum pitch is set to 550 ° C or 900 ° C.
A polycyclic aromatic conjugated structure material has been obtained by a thermal reaction at a temperature of ° C, but this material has not achieved a capacity exceeding C ₆ Li (372 mAh / g).

According to the method described in JP-A-8-115723, a polycyclic aromatic conjugated structural material having an H / C = 0.12 is obtained by thermally reacting an infusible petroleum pitch raw material at 800 ° C. However, its lithium doping capacity is 951 mAh / g, and its undoping amount is 546 mAh / g (discharge efficiency 57.4%), which is low in both capacity and efficiency.

Further, J. Electrochem. Soc. Vol. 142
No. 4 (1995) p1041-1046 discloses a polycyclic aromatic conjugated structural material obtained by thermally reacting mesocarbon microbeads at 700 ° C. According to this material, a lithium doping capacity of 750 mAh / g is obtained, but the initial efficiency is as low as 62%.

Further, there has been an attempt to heat-treat the mesophase pitch-based carbon fiber precursor at 800 to 1000 ° C., but from the viewpoint of performance as well as cost, it is not practical to use the pitch secondary molding material as a raw material. Not a target.

As is apparent from the above description, a negative electrode material for a lithium secondary battery having a low production cost, a high capacity and a high efficiency has not been found yet. And since no major progress has been seen in the development of cathode materials, ultra-high energy density secondary batteries that surpass current lithium-ion batteries
Not completed.

[0014]

SUMMARY OF THE INVENTION Accordingly, the present invention provides a high energy storage device using an anode material which can be manufactured using inexpensive raw materials which can reduce the manufacturing cost and which can dope a large amount of lithium. The main purpose is to obtain a density secondary battery.

[0015]

Means for Solving the Problems The inventors of the present invention have conducted research while paying attention to the current state of the technology as described above, and as a result, have pre-doped lithium into a negative electrode material having a specific structure using pitch as a raw material. As a result, they have found that the energy density of a non-aqueous secondary battery can be dramatically improved even when a conventional positive electrode material is used. That is, the present invention provides the following non-aqueous secondary battery. 1. In a non-aqueous secondary battery including a positive electrode, a negative electrode, and a non-aqueous electrolyte,
(1) the positive electrode is made of a material capable of electrochemically storing and releasing lithium; (2) the negative electrode is obtained by thermally reacting (a) a raw material mainly containing pitch; (b) hydrogen / C is an atomic ratio of 0.35 to 0.05, and (c) is made of a material obtained by pre-doping lithium into a polycyclic aromatic hydrocarbon having a specific surface area of 50 m ² / g or less by a BET method. Water-based secondary battery. 2. In the non-aqueous secondary battery according to the above item 1, the amount of lithium that can be released from the positive electrode is Cp (mAh), and the amount of pre-doping of lithium into the negative electrode is Cn (mAh).
Wherein, when the weight of the polycyclic aromatic hydrocarbon in the negative electrode is W (g), 50 <Cn / W and 800 <(Cn + Cp) / W, the nonaqueous secondary battery being characterized in that . 3. Item 3. The non-aqueous secondary battery according to Item 2, wherein 400 <Cp / W. 4. 4. The non-aqueous secondary battery according to any one of items 1 to 3, wherein the negative electrode material is a material in which lithium is pre-doped by bringing the negative electrode and metallic lithium into electrochemical contact in the battery. 5. The thickness of the battery exterior is 0.
Item 5. The non-aqueous secondary battery according to any one of Items 1 to 4, wherein the non-aqueous secondary battery is 2 mm or less, and is sealed in a state where the battery internal pressure is equal to or less than the atmospheric pressure.

[0016]

DESCRIPTION OF THE PREFERRED EMBODIMENTS A non-aqueous secondary battery according to the present invention
It comprises a negative electrode, a positive electrode, a separator and a non-aqueous electrolyte as basic elements.

The negative electrode of the non-aqueous secondary battery according to the present invention is a material obtained by pre-doping lithium into a polycyclic aromatic conjugated structural material (hereinafter referred to as “a negative electrode material of the present invention”) obtained by thermally reacting pitch. Consists of

The pitch used as a raw material for producing the negative electrode material of the present invention is not particularly limited as long as a negative electrode material having predetermined physical properties can be obtained, but is roughly classified into a petroleum pitch and a coal pitch. Divided. For example, examples of the petroleum pitch include crude oil distillation residue, fluid catalytic cracking residue (such as decant oil), bottom oil from a thermal cracker, and ethylene tar obtained during naphtha cracking. By subjecting these materials to polycondensation by heat treatment, a negative electrode material is obtained.

As the coal-based pitch, coal tar, which is an oil obtained by dry distillation of coal, is distilled, and a straight pitch, which is a residue from which light components are discharged, is further added with anthracene oil, tar and the like. And the like. Also, mesophase pitch synthesized using these pitches as a raw material can be used as a raw material for producing the negative electrode material of the present invention.

These pitches are currently inexpensive and mass-produced, and are mainly used as coke binders for iron making, impregnating materials for electrodes, raw materials for coke, raw materials for carbon fiber, binders for molded carbon materials, and the like. , Widely used.

The negative electrode material of the present invention is produced by thermally reacting at least one of the above pitches, (1) the hydrogen / carbon atomic ratio is 0.35 to 0.05, and (2) the specific surface area by the BET method. Must be 50 m ² / g or less.

The thermal reaction of the raw material pitch is performed in an inert atmosphere (including vacuum) such as nitrogen or argon. The thermal reaction temperature, heating rate, reaction time, and the like of the raw material pitch are appropriately determined according to the type of the raw material, the target H / C ratio and the specific surface area of the negative electrode material, and the like. The thermal reaction temperature is usually about 550 to 750 ° C, more preferably about 600 to 700 ° C. The heating rate is usually in the range of about 10 to 1000 ° C./hour. The heating rate does not need to be constant, for example, up to 300 ° C.
It is also possible to raise the temperature at a rate of 00 ° C / hour, and at a rate of 50 ° C / hour from 300 to 650 ° C. Reaction time is usually
It is in the range of 1-100 hours.

The thus obtained negative electrode material of the present invention has an atomic ratio of hydrogen / carbon (hereinafter referred to as "H / C") of usually 0.35 to 0.35.
It is about 0.05, preferably about 0.30 to 0.10, and more preferably about 0.30 to 0.15. When the H / C value is too high, the polycyclic aromatic conjugated structure in the product is not sufficiently developed, so that the capacity and efficiency are reduced. On the other hand, if the H / C value is too low, sufficient carbonization cannot be obtained because carbonization has progressed too much.

The negative electrode material of the present invention may contain impurities such as oxygen, sulfur and nitrogen derived from the raw material pitch in the form of various compounds. If these compounds are present in excess, the properties of the negative electrode material may be impaired, so that the total amount of these impurities is 20% by weight or less.
It is desirable to select the raw materials and set the thermal reaction conditions so as to be (as an element), more preferably 10% by weight or less.

The specific surface area of the negative electrode material of the present invention by the BET method is usually 50 m ² / g or less, more preferably 30 m ² / g or less. If the specific surface area of the negative electrode material is too high, the initial efficiency of doping and undoping of lithium deteriorates,
In addition, the amount of lithium to be pre-doped is increased, which is not preferable for practical use. In the conventionally reported polycyclic aromatic conjugated structural substances, the specific surface area is generally larger than that of carbon-based materials and graphite-based materials, and exceeds 50 m ² / g. In order to increase the efficiency by reducing the specific surface area, a technique for re-surface-treating the carbon-based material and the graphite-based material has also been developed.However, this technique requires complicated operations and significantly increases the cost of the negative electrode material. Disadvantageous in practice.
On the other hand, the negative electrode material of the present invention can have a specific surface area of 50 m ² / g or less by one thermal reaction of the pitch raw material, and is easy to manufacture. In general, the specific surface area of the negative electrode material decreases as the heat treatment reaction temperature increases, and the initial efficiency of lithium doping and undoping increases. However, as the specific surface area decreases, the capacity decreases sharply. . The negative electrode material of the present invention is characterized in that the specific surface area is 50 m ² / g or less in the above-mentioned H / C ratio range.
The lower limit of the specific surface area is not particularly limited, but is about 0.1 m ² / g.

An example of a specific method for obtaining the negative electrode material of the present invention will be described. The negative electrode material of the present invention using pitch as a raw material is subjected to thermal reaction conditions (thermal reaction time, heating rate, atmosphere,
The specific structure can be obtained by controlling the pressure, the rate of removing gas components generated during the reaction to the outside of the reaction system, and the like. In particular, by appropriately selecting the pitch raw material, restrictions due to thermal reaction conditions can be reduced. In general, for pitch-based carbon materials, the pitch is heated at a temperature of about 100 to 400 ° C in air or treated with an oxidizing liquid such as nitric acid or sulfuric acid to make the entire pitch or its surface infusible. After the treatment (crosslinking treatment), it is manufactured by heat treatment in an inert atmosphere. However, in the present invention, the negative electrode material of the present invention can be easily obtained by subjecting the pitch to a thermal reaction in a state where the pitch is not subjected to infusibilizing treatment or surface oxidation treatment.

The softening point of the raw material pitch used in the present invention is preferably about 70 to 400 ° C., more preferably 100 to 400 ° C.
The temperature is about 350 ° C, particularly preferably about 150 to 300 ° C. If the softening point of the raw material pitch is too low, the yield of the negative electrode material decreases, while if it is too high, the specific surface area of the negative electrode material tends to increase.

Using such a pitch as a raw material, at 550 to 750 ° C. in an inert atmosphere such as nitrogen, argon, or vacuum.
By performing a thermal reaction below, the negative electrode material of the present invention is obtained. The yield of the product in this thermal reaction varies depending on the kind of the raw material pitch, etc., but it is desirable to obtain a value of 60% or more.

Since the negative electrode material of the present invention obtained by the thermal reaction has an irregular shape, it is pulverized by a pulverizer such as a ball mill or a jet mill and, if necessary, further classified to obtain a predetermined particle size. And sized. The average particle size of the negative electrode material is determined in consideration of the shape and characteristics of the intended battery, the thickness and density of the electrode, and is preferably 30 μm or less, more preferably 20 μm or less. The average particle size is preferably at least 0.1 μm, more preferably at least 1 μm, in consideration of the operability at the time of manufacturing the electrode.

The capacity (doping amount and undoping amount of lithium) of the obtained negative electrode material of the present invention can be measured as follows. For example, an electrode using the negative electrode material is used as a working electrode, an electrochemical cell using lithium metal as a counter electrode and a reference electrode is assembled, and in a nonaqueous electrolyte described later, a constant voltage of 1 mV with respect to the lithium metal potential is applied. Applied, the current value is sufficiently small (for example, 0.01 mA / cm ² )
After the doping with lithium to the extent possible, the measurement is performed by undoping the lithium metal potential at a sufficiently low rate (for example, 0.25 mA / cm ² ) to 2 V with respect to the lithium metal potential. The negative electrode material of the present invention can be doped with 1000 mAh / g or more of lithium and 65% or more of the lithium can be undoped when measured by the above method.

The negative electrode according to the present invention is made of a material obtained by predoping lithium into the negative electrode material according to the present invention. The method of predoping lithium into the negative electrode material of the present invention is not particularly limited, but it is practical to perform the method after forming the negative electrode material of the present invention into an electrode.

The molding of the electrode using the negative electrode material of the present invention is performed as follows.
While considering the shape and characteristics of the desired non-aqueous secondary battery,
It can be performed by a known method. For example, an electrode can be obtained by mixing and molding a negative electrode material, a binder resin, and a conductive agent as needed. The binder resin is not particularly limited, but specifically,
Examples include fluorine-based resins such as polyvinylidene fluoride (PVdF) and polytetrafluoroethylene; rubber-based materials such as fluororubber and SBR; polyolefins such as polyethylene and polypropylene; and acrylic resins.

The amount of the binder compounded in the negative electrode molding mixture is as follows:
The type of the negative electrode material of the present invention, the particle size, the shape, the thickness of the target electrode, may be appropriately determined according to the strength, etc., although not particularly limited, usually the weight of the negative electrode material of the present invention
It is preferable to set it to about 1 to 30%.

In the present invention, the current collector used for forming the negative electrode on the current collector is not particularly limited, and examples thereof include a copper foil, a stainless steel foil, and a titanium foil. Furthermore, a material on which an electrode can be formed on a metal foil or in a gap between metals, for example, an expanded metal, a mesh, or the like can also be used.

The pre-doping of lithium into the negative electrode material of the present invention is performed electrochemically after forming the negative electrode material of the present invention into an electrode. Specifically, before assembling the battery, an electrochemical system using lithium metal as a counter electrode is assembled, a method of pre-doping in a non-aqueous electrolyte described later, and a method of bonding lithium metal to a negative electrode impregnated with the electrolyte are described. No. To perform pre-doping of lithium after assembling the battery, a lithium source such as lithium metal and a negative electrode are bonded to each other by a method such as laminating, and an electrolyte is injected into the battery. It is possible to pre-dope lithium.

The amount of lithium pre-doped into the negative electrode material of the present invention is defined as Cp (mAh) where the amount of lithium releasable from the positive electrode is Cp (mAh) and the amount of lithium pre-doped into the negative electrode is Cn (mAh).
When the weight of the polycyclic aromatic hydrocarbon in the negative electrode is W (g), it is preferable that the relations of 50 <Cn / W and 800 <(Cn + Cp) / W hold. Here, the “amount of lithium Cp (mAh) that can be released from the positive electrode” is the amount of lithium contained in the positive electrode during battery assembly and released during the charging operation and taken into the negative electrode. For example, LiCoO ₂ , Li
Lithium-containing composite oxides such as NiO ₂ and LiMn ₂ O ₄
It is a typical example of a positive electrode material containing lithium contained in the positive electrode. On the other hand, in oxides containing no lithium, such as MnO ₂ and V ₂ O ₅ , the value of Cp is 0.

If the lithium pre-doping amount Cn / W with respect to the weight of the negative electrode material is 50 or less, a sufficient capacity cannot be obtained when the battery is assembled. The pre-doping amount is more preferably 100 <Cn / W, and further preferably 150 <Cn / W.
Cn / W, and particularly preferably 200 <Cn / W. Also,
Of the lithium in the negative electrode, the amount of lithium that cannot be released up to 2V (vs. Li / Li ⁺ ) (generally irreversible lithium) is Cirr (m
When Ah), it is preferable that Cirr (mAh) +50 <Cn / W <Cirr (mAh) +300.

On the other hand, when (Cn + Cp) / W is 800 or less, the capacity of the negative electrode is low, so that a sufficient capacity cannot be obtained when the battery is assembled. (Cn + Cp) /
W is more preferably 900 or more, particularly preferably 10
00 or more.

In the present invention, the amount of lithium Cp / W that can be released from the positive electrode with respect to the weight of the negative electrode preferably satisfies the relationship of 400 <Cp / W. In this case, as described above, the positive electrode material is a lithium-containing composite oxide such as LiCoO ₂ , LiNiO ₂ , and LiMn ₂ O ₄ . Cp / W value is more preferably 550
And more preferably 700 or more. Cp / W 400
If it is less than 1, the pre-doping amount becomes large, so that a practical problem is likely to occur.

In the present invention, as described above, as one example of a simple pre-doping method, a lithium metal foil is attached to a negative electrode, a battery is assembled, and an electrolyte is injected into the battery to pre-dope lithium. Method. In this case, after completion of lithium pre-doping,
A gap is formed in the lithium metal portion, and the internal resistance tends to increase. In this case, the thickness of the battery
0.2 mm or less, by sealing the battery internal pressure to the state of the atmospheric pressure or less, by pressing the gap created after the completion of lithium pre-doping by the differential pressure between the atmospheric pressure and the battery internal pressure,
It is possible to eliminate it. Further, it is also possible to seal again after the completion of the pre-doping. A well-known aluminum-resin laminate film is typically used as the battery package having a thickness of 0.2 mm or less, and this is also applicable to the present invention.

As the positive electrode active material used in the present invention, any positive electrode material capable of inserting and extracting lithium can be used.
There is no particular limitation, and for example, use of a lithium composite cobalt oxide, a lithium composite nickel oxide, a lithium composite manganese oxide, a mixture thereof, or a system in which one or more different metal elements are added to these composite oxides is used. Can be. It is also possible to use metal oxides such as manganese, vanadium, and iron, disulfide compounds, polyacene substances, activated carbon, and the like.

As the non-aqueous electrolyte used in the present invention, known non-aqueous electrolytes such as a non-aqueous electrolyte containing a lithium salt, a polymer electrolyte, and a polymer gel electrolyte can be used. It is appropriately determined according to the properties of the material, usage conditions such as the charging voltage, and the like. As the non-aqueous electrolyte containing a lithium salt, e.g., LiPF _6, LiBF _4, propylene carbonate lithium salt such as LiClO _4, ethylene carbonate, diethyl carbonate, dimethyl carbonate, methylethyl carbonate, dimethoxyethane, .gamma.-butyrolactone, Those dissolved in one or more organic solvents such as methyl acetate and methyl formate can be used. Also,
The concentration of the electrolytic solution is not particularly limited, but generally about 0.5 to 2 mol / l is practical. Of course, it is preferable to use an electrolyte having a water content of 100 ppm or less. In addition, the "non-aqueous electrolyte" used in this specification
The term means a concept including a non-aqueous electrolyte and an organic electrolyte, and also includes a concept including a gel electrolyte and a solid electrolyte.

The shape, size, etc. of the non-aqueous secondary battery of the present invention are not particularly limited, and may be any shape such as a cylindrical type, a square type, a film battery, a box type, etc., according to each application. What is necessary is just to select the thing of a size.

[0044]

The following examples are provided to further clarify the features of the present invention. Example 1 1) Osaka Gas Co., Ltd. coal-based isotropic pitch (softening point 280)
C.) with a coffee mill to obtain a pitch raw material having a particle size of 1 mm or less. Put 1000 g of the pitch powder in a stainless steel dish, and place it in an electric furnace (effective size of the furnace: 300 mm x 300 mm x 300 m
m) to perform a thermal reaction. The thermal reaction was performed in a nitrogen atmosphere, and the flow rate of nitrogen was 10 l / min. During the thermal reaction, the temperature was raised from room temperature to 634 ° C (furnace temperature) at a rate of 100 ° C / hour, maintained at this temperature for 4 hours, and then cooled to 60 ° C by natural cooling to obtain the reaction product. Was taken out of the electric furnace. The obtained product was an amorphous insoluble and infusible solid without keeping the shape of the raw material. The yield was 801 g, and the yield was 80% by weight.

The obtained product was pulverized by a jet mill and classified to an average particle size of 6 μm to obtain a negative electrode material. Using the negative electrode material, elemental analysis (measurement and use machine: manufactured by PerkinElmer, elemental analyzer "PE2400 series II, CHNS / 0") and specific surface area measurement by BET method (measurement and use machine: manufactured by Yuasa Ionics, " NOVA1200 ”), H / C
= 0.22, and the specific surface area was 18 m ² / g.

Next, 90 parts by weight of the above negative electrode material powder, PV
10 parts by weight of dF and 120 parts by weight of N-methylpyrrolidone (NMP) were mixed to obtain a negative electrode mixture slurry. Thick the slurry 14
An electrode having a thickness of 90 μm was obtained by applying it to one side of a copper foil having a thickness of μm, drying it, and pressing it.

Next, the electrode obtained above was used as a working electrode, lithium metal was used as a counter electrode and a reference electrode, and ethylene carbonate and diethyl carbonate were used as electrolytes.
An electrochemical cell was prepared in an argon dry box using a solution in which LiPF ₆ was dissolved at a concentration of 1 mol / l in a solvent mixed at a 1: 1 weight ratio. The doping of lithium was performed at a rate of 0.25 mA / cm ² until the potential became 1 mV with respect to the lithium potential, and a constant voltage of 1 mV with respect to the lithium potential was applied for 40 hours to complete the doping. Subsequently, dedoping was performed at a rate of 0.25 mA / cm ² to 2 V with respect to the lithium potential.

The doping amount was 1451 mAh / g, the undoping amount was 1109 mAh / g, and the initial efficiency was 76.4%.

2) LiCoO ₂ (Seimi Chemical, part number C-01)
2) 100 parts by weight, 4 parts by weight of acetylene black, 5 parts by weight of PVdF and 80 parts by weight of NMP were mixed to obtain a positive electrode mixture slurry. Next, the slurry was applied to both surfaces of a 20 μm-thick aluminum foil serving as a current collector, dried, and pressed to obtain a positive electrode.

As shown in FIGS. 1 and 2, the positive electrode has an electrode coated portion 1 of 50 × 30 mm ² , and is coated on both sides of a 20 μm thick aluminum foil with a thickness of 140 μm. Further, one end of the electrode is provided with a lug portion of the positive electrode current collector 2 on which the electrode is not applied.

3) The negative electrode material of the present invention obtained in the above 1)
100 parts by weight, 10 parts by weight of acetylene black and PVdF10
Parts by weight were mixed with 200 parts by weight of NMP to obtain a negative electrode mixture slurry. Next, the slurry was applied to both sides of a 14 μm-thick copper foil serving as a current collector, dried, and pressed to obtain a negative electrode.

As shown in FIGS. 3 and 4, the negative electrode has an electrode coating portion 3 of 51 × 31 mm ² , and is coated on both surfaces of a 14 μm thick copper foil with a thickness of 100 μm. Further, a lug portion of the negative electrode current collector 4 on which the electrode is not applied is provided at one end of the electrode.

Further, a single-sided electrode was prepared by applying the same method to only one side, and otherwise applying the same method. The single-sided electrode is arranged on the outside in the electrode laminate of the following item 4).

4) The positive electrode 6 obtained in the above 2) and 3)
The negative electrode and five negative electrodes (two inner electrodes on one side) were alternately laminated via a separator (porous polyethylene: 52 × 32 mm ² made by Tonen Tapils) to form an electrode laminate. At this time, a lithium metal foil having a thickness of 20 μm is adhered to the surface of the negative electrode (total of 12 sheets: 750 mAh), and the negative electrode is pre-doped after the electrolyte injection in the following section 5).

5) The positive and negative electrode lugs of the obtained electrode laminate were welded to tabs (positive electrode: aluminum, negative electrode: nickel), and ethylene carbonate and methyl ethyl carbonate were used as electrolytes in a weight ratio of 3: 7. After impregnating the mixed solvent with a solution of LIPF ₆ dissolved at a concentration of 1 mol / l,
A battery was obtained by vacuum sealing under reduced pressure (0.1 atm) using an aluminum-resin laminate film (aluminum layer: 0.02 mm) having a thickness of 0.11 mm as an exterior body.

6) Next, the battery prepared as described above was charged to 4.2 V with a current of 200 mA, and thereafter, constant-current constant-voltage charging in which a constant voltage of 4.2 V was applied was performed for 8 hours. Subsequently, the battery was discharged to 2.5 V at a constant current of 200 mA. Discharge capacity is 1002mAh, 10
The capacity degradation was slight in the cycle.

On the other hand, the capacity of a commercially available lithium ion battery of the same type using a graphite material for the negative electrode is about 500 to 600 mAh. Therefore, in the lithium ion battery according to the present invention, a capacity improvement of 1.5 times or more as compared with a commercially available battery is seen.

Table 1 below shows Examples 1 to 3 and Comparative Example 1.
2 collectively shows the performance of each battery. Example 2 The amount of lithium to be pre-doped in Example 1 was set to 600 mA.
At the same time, an electrochemical system using lithium metal as a counter electrode was assembled before assembling the battery, and LiPF ₆ was dissolved at a concentration of 1 mol / l in a solvent mixture of ethylene carbonate and methyl ethyl carbonate at a weight ratio of 3: 7. A battery was prototyped in the same manner as in Example 1 except that the solution was pre-doped in the solution. Example 3 The amount of lithium to be pre-doped in Example 1 was 450 m.
Before assembling the battery, an electrochemical system using lithium metal was assembled as a counter electrode, and LiPF ₆ was dissolved at a concentration of 1 mol / l in a solvent mixture of ethylene carbonate and methyl ethyl carbonate at a weight ratio of 3: 7. A battery was prototyped in the same manner as in Example 1 except that the solution was pre-doped in the solution. Comparative Example 1 The amount of lithium to be pre-doped in Example 1 was set to 0 mAh.
A battery was prototyped in the same manner as in Example 1, except that lithium was not attached to the negative electrode. Comparative Example 2 A battery was prototyped in the same manner as in Comparative Example 1, except that the thickness of the positive electrode layer was changed to 170 μm and the thickness of the negative electrode layer was changed to 70 μm.

[0059]

[Table 1]

[0060]

According to the present invention, a battery obtained by using a material pre-doped with lithium as a negative electrode material having a specific structure obtained from an inexpensive pitch as a raw material can be used as a negative electrode. The capacity is greatly improved as compared with a conventional lithium ion battery using graphite or the like. In addition, the negative electrode material of the present invention greatly contributes to ensuring battery safety and reducing costs.

[Brief description of the drawings]

FIG. 1 is a plan view showing a battery cathode obtained in Example 1.

FIG. 2 is a side view of the electrode positive electrode shown in FIG.

FIG. 3 is a plan view showing a battery negative electrode obtained in Example 1.

FIG. 4 is a side view of the electrode negative electrode shown in FIG.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Positive electrode coating part 2 ... Positive electrode collector 3 ... Negative electrode coating part 4 ... Negative electrode collector

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Junko Nagano 4-1-2 Hirano-cho, Chuo-ku, Osaka-shi, Osaka Inside the Kansai New Technology Research Institute Co., Ltd. (72) Shizukuni Yada Hirano-cho, Chuo-ku, Osaka-shi, Osaka 4-chome 1-2 F-term in Kansai New Technology Research Laboratories Co., Ltd. (reference)

Claims (5)

[Claims] 1. A non-aqueous secondary battery comprising a positive electrode, a negative electrode and a non-aqueous electrolyte, (1) the positive electrode is made of a material capable of electrochemically occluding and releasing lithium, and (2) the negative electrode is (a) obtained by thermally reacting a raw material containing pitch as a main component, (b) an atomic ratio of hydrogen / carbon is 0.35 to 0.05, and (c) a specific surface area by a BET method is 50 m ² / g or less. A non-aqueous secondary battery comprising a material obtained by pre-doping a certain polycyclic aromatic hydrocarbon with lithium. 2. The non-aqueous secondary battery according to claim 1, wherein the amount of lithium that can be released from the positive electrode is Cp (mAh);
When the pre-doping amount of lithium on the negative electrode is Cn (mAh) and the weight of the polycyclic aromatic hydrocarbon in the negative electrode is W (g), 50 <Cn / W and 800 <(Cn + Cp) / W is a non-aqueous secondary battery. 3. The non-aqueous secondary battery according to claim 2,
A non-aqueous secondary battery, wherein 400 <Cp / W. 4. The non-aqueous secondary material according to claim 1, wherein the negative electrode material is a material in which lithium is pre-doped by bringing the negative electrode and metallic lithium into electrochemical contact in a battery. battery. 5. The battery outer body has a thickness of 0.2 mm or less,
2. The battery is sealed in a state where the internal pressure of the battery is lower than the atmospheric pressure.
5. The non-aqueous secondary battery according to any one of items 1 to 4.