JP3390195B2 - Non-aqueous electrolyte secondary battery and method of manufacturing the same - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a non-aqueous electrolyte secondary battery using a lithium ion conductive non-aqueous electrolyte as a negative electrode active material, which is capable of inserting and extracting lithium, and particularly to a high voltage, The present invention relates to a novel negative electrode active material that provides a new secondary battery having high energy density, excellent charge / discharge characteristics, and long cycle life.

[0002]

Non-aqueous electrolyte batteries using lithium as a negative electrode active material have advantages of high voltage, high energy density, small self-discharge and excellent long-term reliability. It has already been widely used as a power source for industrial use. However, with the remarkable development of portable electronic devices and communication devices in recent years,
A wide variety of devices that require a large current output for batteries as power sources have appeared, and rechargeable / dischargeable secondary batteries with high energy density have been strongly demanded from the viewpoint of economy and reduction in size and weight of devices. ing. Therefore, research and development for promoting the non-aqueous electrolyte battery having a high energy density into a secondary battery have been actively carried out and partially put into practical use, but energy density, charge / discharge cycle life, reliability, etc. are still unsatisfactory. It is enough.

Conventionally, as the positive electrode active material used for the positive electrode of this type of secondary battery, the following three types have been found depending on the form of charge / discharge reaction. The first type is
Metal chalcogenides such as TiS ₂ , MoS ₂ and NbSe ₃ , and MnO ₂ , MoO ₃ , V ₂ O ₅ , Li _X CoO ₂ and Li _X.
Like metal oxides such as NiO ₂ and Li _x Mn ₂ O _4, etc., only lithium ions (cations) enter and leave due to intercalation, deintercalation reactions, etc. between crystal layers or between lattice positions or gaps. Type to do.

The second type is a type such as a conductive polymer such as polyaniline, polypyrrole, polyparaphenylene, etc. in which mainly anions are stably doped and come in and out by a dedoping reaction. The third type is a type (intercalation, deintercalation or doping, dedoping, etc.) in which both lithium cations and anions can enter and exit, such as graphite intercalation compounds and conductive polymers such as polyacene. .

On the other hand, as the negative electrode active material used for the negative electrode of this type of battery, when metal lithium is used alone, the electrode potential is the most base, so that it was combined with the positive electrode using the positive electrode active material as described above. The highest output voltage as a battery,
Although the energy density is high and preferable, there is a problem that dendrites and passivation compounds are generated on the negative electrode with charge and discharge, the deterioration due to charge and discharge is large, and the cycle life is short. In order to solve this problem, as a negative electrode active material (1)
Alloys of lithium with other metals such as Al, Zn, Sn, Pb, Bi, Cd, (2) WO ₂ , MoO ₂ , Fe ₂ O ₃ , Ti
Inorganic compounds such as S ₂ and graphite, intercalation compounds or insertion compounds in which lithium ions are occluded in the skeleton structure of carbonaceous materials obtained by firing organic substances, (3) lithium ion-doped polyacene and polyacetylene, etc. It has been proposed to use a substance capable of inserting and extracting lithium ions such as a conductive polymer.

[0006]

However, generally, a negative electrode using a material capable of inserting and extracting lithium ions other than metallic lithium as described above as a negative electrode active material, and a positive electrode active material as described above are used. When a battery is constructed by combining the positive electrode and the negative electrode active material, the electrode potential of these negative electrode active materials is nobler than the electrode potential of metallic lithium. It has the drawback of being significantly lower. For example, lithium and A
0.2 to 0.8 V when using an alloy such as 1, Zn, Pb, Sn, Bi, Cd, 0 to 1 V for a carbon-lithium intercalation compound, and 0 for a lithium ion insertion compound such as MoO ₂ or WO _2. The operating voltage is reduced by 0.5 to 1.5V.

Further, since elements other than lithium also serve as negative electrode constituents, the capacity and energy density per volume and weight are significantly reduced. Furthermore, when the alloy of (1) above with lithium and another metal is used, the utilization efficiency of lithium during charging and discharging is low, and cracks occur in the electrode due to repeated charging and discharging, and the like. Therefore, there is a problem that the cycle life is short, and in the case of the lithium intercalation compound or the intercalation compound of (2), there is deterioration such as collapse of the crystal structure or generation of an irreversible substance due to overcharge and discharge, and a high electrode potential ( Since there are many (noble) batteries, there is a drawback that the output voltage of a battery using this is low, and in the case of the conductive polymer of (3), the charge / discharge capacity, especially the charge / discharge capacity per volume is small. There's a problem.

Among the above-mentioned negative electrode active materials, tungsten dioxide WO ₂ having a rutile type crystal structure is the same as the positive electrode active material capable of inserting and extracting lithium (1) Formula WO ² + xLi ⁺ + xe ⁻ ← → Li _x WO ₂ (1) The battery reaction shown in (1) is performed, the electrode potential has a relatively base potential of 0.5 to 1.0 V with respect to metallic lithium, and 1 equivalent of WO ₂ depends on charge and discharge. 1 equivalent of lithium ion (corresponding to x = 1) can be intercalated and deintercalated per unit, and a theoretical capacity density of 1500 mAh / cm ₃ or more is expected, and the negative electrode active material of this type of secondary battery It is a particularly promising substance.

However, even in the case of this lithium ion insertion compound WO ₂ , when 0.5 equivalent or more of lithium ion is intercalated per 1 equivalent of WO ₂ , a phase transition occurs to cause a structural change. Range that can be reversibly charged / discharged at a specific charge / discharge voltage and current density, that is, the effective charge / discharge capacity is small and 50% or less of the above theoretical capacity,
Moreover, there is a problem that the larger the current, the smaller the current. or,
If overcharge of 50% or more of the theoretical capacity is performed, there is a problem that the charge / discharge capacity is significantly reduced. Furthermore, since the change in the operating voltage due to the polarization during discharge is large, there is a problem that the output voltage of the battery using the same is greatly reduced. In addition, this WO
For batteries using ₂ , see JJ Aubornand YL Barberi
o, J.Electrochem.Soc., 134,638 ('87); DWMurphy, FJD
i Salvo, JNCarides, and JVWaszczak, Mater.Res.Bul
L., 13, 1395 ('78) and the like.

Therefore, at high voltage and high energy density,
In addition, in order to obtain a secondary battery with excellent charge / discharge characteristics and a long cycle life, the electrode potential with respect to lithium is low (base), and the collapse of the crystal structure or the irreversible substance due to the absorption / desorption of lithium ions during charge / discharge. There is a need for a negative electrode active material that has a large amount of lithium ions that can be occluded and released reversibly without deterioration such as generation, that is, a large effective charge / discharge capacity.

[0011]

In order to solve the above problems, the present invention provides a negative electrode active material for a battery of this type,
It proposes to use a product obtained by heat treating tungsten dioxide WO ₂ in a non-oxidizing atmosphere.

That is, tungsten dioxide WO ₂ is reduced in an atmosphere of an inert gas such as argon, neon, helium, krypton, xenon or nitrogen, in vacuum, in a reduced pressure atmosphere or in a weak atmosphere such as carbon dioxide CO ₂ or a gas containing dilute hydrogen. The negative electrode active material is used after being heat-treated in a non-oxidizing atmosphere in which tungsten dioxide WO ₂ is not oxidized to form tungsten trioxide WO ₃ by heating, such as in an oxidizing gas atmosphere. Although the heat treatment temperature varies depending on the starting material and the heat treatment atmosphere, it is preferably 300 to 750 ° C., preferably 4
00-750 ° C, more preferably 500-750 ° C
Temperature is good. The reason is that if the temperature is lower than 300 ° C., there is almost no effect on improving the charge / discharge performance, and if the temperature is 750 ° C. or higher, the sublimation temperature is close to 800 ° C., so that the structural change is large and conversely the charge / discharge performance deteriorates.

Tungsten dioxide thus obtained
WO₂ The heat treatment product of
Negative electrode active material after processing such as sizing and granulation with
Can be used as On the other hand, as the positive electrode active material,
As mentioned above, TiS₂, MoS₂, NbSe₃Etc. Metal cal
Cogenide and MnO₂, MoO₃, V₂O_Five, Li_XCo
O₂, Li_XNiO₂, Li_xMn₂O_Four Metal oxides such as
Polyaniline, polypyrrole, polyparaphenylene poly
Conductive polymer such as acene, and graphite intercalation compound
Can store and release lithium ions and / or anions, etc.
Various effective substances can be used. In particular, the present invention
Dependent tungsten dioxide WO₂The heat-treated product of
The negative electrode used as a substance has a low electrode potential with respect to metallic lithium.
The charge / discharge capacity of the base area (less than 2V)
Since it has the advantage of being large, the above-mentioned metal oxides, etc.
The electrode potential for metallic lithium such as
Preferably V₂O_Five, MnO ₂, Li_XCoO₂, Li_xNi
O₂And Li_xMn₂O_Four3.5V or 4V or more like etc.
Combined with positive electrode using (noble) active material with high potential above
High voltage, high energy density and charge by combining
A secondary battery with excellent electrical characteristics can be obtained, so it is particularly preferable.
Yes.

As the electrolyte, γ-butyrolactone, propylene carbonate, ethylene carbonate,
LiClO ₄ , LiPF ₆ , LiB as a supporting electrolyte in an organic solvent such as butylene carbonate, dimethyl carbonate, diethyl carbonate, methyl formate, 1,2-dimethoxyethane, tetrahydrofuran, dioxolane and dimethylformamide, alone or in a mixed solvent.
An organic electrolyte in which a lithium ion dissociable salt such as F ₄ or LiCF ₃ SO ₃ is dissolved, a polymer solid electrolyte in which the lithium salt is dissolved in a polymer such as polyethylene oxide or a crosslinked polyphosphazene, or Li ₃ N , Lithium ion conductive non-aqueous electrolytes such as inorganic solid electrolytes such as LiI.

[0015]

The negative electrode using the heat-treated product of tungsten dioxide WO _{2 in} the non-oxidizing atmosphere according to the present invention as the negative electrode active material has at least 0 relative to the lithium reference electrode (metal lithium) in the non-aqueous electrolyte. Lithium ions can be occluded and released stably and repeatedly in the range of electrode potential of 3V,
It can be used as a negative electrode of a secondary battery that can be repeatedly charged and discharged by such an electrode reaction. In particular, in a base potential region of 0 to 2 V with respect to the lithium reference electrode (metal lithium), it has a high-capacity charge / discharge region capable of stably absorbing and desorbing lithium ions and repeatedly charging and discharging. In addition, the amount of lithium ions that can be reversibly occluded and released, that is, the effective charge / discharge capacity is remarkably large, as compared with tungsten dioxide WO ₂ that has not been heat-treated in a non-oxidizing atmosphere that has been conventionally used as the negative electrode active material of this type of battery. In addition, since the polarization of charge and discharge is small, it is possible to charge and discharge with a large current, and almost no deterioration such as generation of irreversible substances due to overcharge and overdischarge is observed, and the secondary battery is extremely stable and has a long cycle life. Can be obtained.

The reason why such excellent charge and discharge characteristics are obtained is not always clear, but it is presumed as follows. That is, the heat treatment product of tungsten dioxide WO ₂ which is a novel negative electrode active material according to the present invention changes the surface state and the internal structure by heat treatment in a non-oxidizing atmosphere, and the lithium ion in this structure It is presumed that since the mobility is high and the number of sites that can store lithium ions is very large, it is easy to store and release lithium ions, and phase change is unlikely to occur.

Hereinafter, the present invention will be described in more detail with reference to examples.

[0018]

【Example】

(Example 1) FIG. 1 is a sectional view of a coin-type battery showing an example of a test cell used for performance evaluation of a negative electrode active material of a non-aqueous electrolyte secondary battery according to the present invention. In the figure, reference numeral 1 is a counter electrode case which also serves as a counter electrode terminal, which is obtained by drawing a stainless steel plate having Ni plated on one outer surface. Two
Is a counter electrode current collector made of a stainless steel net, and is spot-welded to the counter electrode case 1. The counter electrode 3 is formed by punching out an aluminum plate having a predetermined thickness to a diameter of 15 mm, fixing it to the counter electrode current collector 2, and pressing a lithium foil having a predetermined thickness punched out to have a diameter of 14 mm on it. Reference numeral 7 denotes a working electrode case made of stainless steel whose outer surface is plated with Ni, and also serves as a working electrode terminal. Reference numeral 5 denotes a working electrode composed of a negative electrode active material according to the present invention or a comparative active material according to a conventional method, which is formed by pressure molding together with a working electrode current collector 6 made of a stainless steel net. ing. 4 is a separator made of a polypropylene porous film, which is impregnated with an electrolytic solution. Numeral 8 is a gasket mainly composed of polypropylene, which is interposed between the counter electrode case 1 and the working electrode case 7 to maintain the electrical insulation between the counter electrode and the working electrode, and at the same time the working electrode case opening edge is inward. By folding and crimping, the battery contents are hermetically sealed. The electrolyte used was prepared by dissolving 1 mol / l of lithium perchlorate LiClO ₄ in a mixed solvent of propylene carbonate and 1,2-dimethoxyethane in a volume ratio of 1: 1. The battery had an outer diameter of 20 mm and a thickness of 1.6 mm.

The working electrode 5 was manufactured as follows. Commercially available
Tungsten dioxide WO with a purity of 99.9%₂ The nitrogen gas
Heat treatment at 700 ° C for 12 hours in airflow, and after cooling,
The particles were crushed and sized to a particle size of 53 μm or less. Obtained in this way
The obtained product is used as the active material a according to the present invention, and a conductive agent
And graphite as a binder, cross-linked acrylic acid resin
Mixing fats etc. at a weight ratio of 30: 65: 5
Agent, and then apply this working mixture to a stainless steel net.
2 ton / cm with working electrode current collector 6 consisting of ² In diameter
After pressure molding into a pellet with a thickness of 15 mm and a thickness of 0.5 mm,
What was dried under reduced pressure at 200 ° C for 12 hours was used as the working electrode.
It was

Also, for comparison, instead of the above-mentioned active material a according to the present invention, the above-mentioned commercially available tungsten dioxide WO
_The same electrode as in the case of the working electrode of the present invention except that 2 was used as the active material b as it was, and the same graphite as that used for the conductive agent was used as the active material of the working electrode. (Comparative working electrode) was prepared.

The battery thus produced has a temperature of 1
After being left to stand for a week, it was subjected to the charge / discharge test described below. By this aging, the lithium-aluminum laminated electrode of the counter electrode is sufficiently alloyed by touching the non-aqueous electrolyte in the battery, and the lithium foil is substantially all Li-Al alloy. 0.4V compared with the case where metallic lithium is used alone as
It became a lowered value and became stable.

The batteries thus produced will be described below in correspondence with the active materials a, b and c of the working electrodes used.
These are abbreviated as batteries A, B and C, respectively. These batteries A, B, and C were charged with a constant current of 0.4 mA, the final voltage of charging (the current direction in which the battery reaction in which lithium ions were occluded in the working electrode from the electrolyte was −0.4 V), and the discharge (working electrode). 2 shows the discharge characteristics at the third cycle and the charge characteristics are shown in FIG. It was shown to. The cycle characteristics are shown in FIG.

The charging / discharging cycle started from charging. As is apparent from FIGS. 2 and 3, the battery A according to the present invention has a significantly larger charge / discharge capacity than the comparative batteries B and C, and the reversible charge / discharge region is significantly expanded.
Further, it can be seen that the difference in operating voltage between charging and discharging is extremely small over the entire charging / discharging region, the polarization (internal resistance) of the battery is extremely small, and large current charging / discharging is easy. Furthermore, it can be seen from FIG. 4 that the decrease in discharge capacity (cycle deterioration) due to repeated charging and discharging is extremely small. That is,
Lithium ions are released from the Li-Al alloy of the counter electrode into the electrolyte due to charging, and the lithium ions move in the electrolyte to cause an electrode reaction with the active material a composed of the heat-treated product of tungsten dioxide WO ₂ of the present invention. The lithium ions are electrochemically occluded in the active material a. Next, during discharge, lithium ions are released from the heat-treated product into the electrolyte, move in the electrolyte, and are occluded in the Li-Al alloy of the counter electrode, so that stable charge and discharge can be performed repeatedly.

Example 2 In this example, the heat treatment of tungsten dioxide WO ₂ used as the negative electrode active material was carried out at various temperatures for comparison. A similar battery was produced in the same manner as in Example 1 except for the active material forming the working electrode 5.

The active material used for the working electrode of this example was prepared as follows. Commercially available tungsten dioxide WO ₂ having a purity of 99.9% was heat-treated at a predetermined temperature for 12 hours in a nitrogen gas stream, cooled, and then pulverized and sized to a particle size of 53 μm or less.
The product thus obtained was used as the active material according to the present invention. In this embodiment, the heat treatment temperature is 300 ° C. (a
1), 400 ° C (a2), 500 ° C (a3), 600 ° C
Six types of (a4), 700 ° C. (a5), and 750 ° C. (a6) were prepared. For comparison, the same active materials b and c as those used in Example 1 were used as active materials.

The batteries thus produced were used as active materials a1, a2, a3, a4, a in the following working electrodes.
5, a6, b and c corresponding to batteries A1, A2, A3,
Abbreviated as A4, A5, A6, B and C. Batteries A1, A2, A3, A4, A5, A6, B thus obtained
For C and C, the same charge / discharge cycle test as in Example 1 was performed. The discharge capacity (cycle characteristics) for each cycle at this time is shown in FIG. As is apparent from FIG. 5, the batteries A1, A2, A3, A4 and A5 according to the present invention are comparative batteries B.
It can be seen that the discharge capacity is significantly larger than that of C and C, and the reversible region of charge and discharge is significantly expanded. Further, the decrease in discharge capacity (cycle deterioration) due to repeated charging and discharging is extremely small. Further, the batteries A1, A2, A3, A4 of the present embodiment,
Oite to A5 also has become remarkably small difference between operating voltages of charge and discharge over a ZenTakashi discharge region as well as the battery A according to the present invention of Example 1, the polarization of the battery (internal resistance) is remarkably The result was small and easy to charge and discharge with a large current.

The reason for having such excellent charge and discharge characteristics is not always clear, but it is presumed as follows. That is, as described above, in the heat treatment product of tungsten dioxide which is the active material of the working electrode of the batteries A1 to A6 according to the present invention, the surface state and the internal structure are changed by the heat treatment in the non-oxidizing atmosphere. Therefore, it is presumed that the mobility of lithium ions in this structure is high, and the structural change accompanying the occlusion / release of lithium ions is small and stable, so that the occlusion / release of lithium ions is easy.

Further, in the examples, only the case of the lithium-aluminum alloy was shown as the counter electrode, but the present invention is not limited to the examples, and as described above, TiS ₂ , Mo.
Metal chalcogenides such as S ₂ and NbSe ₃ , MnO ₂ and M
oO ₃ , V ₂ O ₅ , Li _X CoO ₂ , Li _X NiO ₂ , Li _x M
A substance capable of occluding and releasing a lithium cation and / or anion such as a metal oxide such as n ₂ O ₄ , a conductive polymer such as polyaniline, polypyrrole, polyparaphenylene, and polyacene, a graphite intercalation compound, etc. is used as an active material. It goes without saying that the positive electrode can be used as a counter electrode in combination with the negative electrode using the negative electrode active material according to the present invention.

[0029]

As described in detail above, according to the present invention, tungsten dioxide W is used as the negative electrode active material of the non-aqueous electrolyte secondary battery.
A novel active material composed of a product obtained by heat-treating O ₂ in a non-oxidizing atmosphere is used, and the negative electrode active material has a lithium reference electrode (compared to conventional non-heat-treated tungsten dioxide WO ₂ ). In a base potential range of 0 to 2 V relative to metallic lithium), the amount that can reversibly store and release lithium ions by charging and discharging, that is, the charging and discharging capacity is extremely large, and the polarization of charging and discharging is small, so high voltage It is possible to obtain a secondary battery having high energy density and excellent charge / discharge characteristics at a large current. In addition, there is almost no deterioration such as a decrease in discharge capacity due to repeated charging and discharging, and an extremely stable secondary battery having a long cycle life can be obtained.

[Brief description of drawings]

FIG. 1 is an explanatory diagram showing an example of the structure of a battery implemented in the present invention.

FIG. 2 is an explanatory diagram showing a comparison of the discharge characteristics at the third cycle between the battery according to the present invention and the conventional battery.

FIG. 3 is an explanatory diagram showing a comparison of the charging characteristics in the third cycle between the battery according to the present invention and the conventional battery.

FIG. 4 is an explanatory diagram showing a comparison of cycle characteristics of a battery according to the present invention and a conventional battery.

FIG. 5 is an explanatory diagram showing the effect of the heat treatment temperature of tungsten dioxide WO2 on the cycle characteristics.

[Explanation of symbols]

1 counter case 2 Counter electrode current collector 3 opposite poles 4 separator 5 Working pole 6 Working electrode current collector 7 Working pole case 8 gasket

─────────────────────────────────────────────────── ─── Continued Front Page (72) Kensuke Tahara, Kensuke Tahara 5-30-1 Nishitaga, Taihaku-ku, Sendai-shi, Miyagi Seiko Electronic Components Co., Ltd. (72) Hideki Ishikawa 5-30, Nishitaga, Taihaku-ku, Sendai-shi, Miyagi No. 1 in Seiko Electronic Components Co., Ltd. (56) Reference US Patent 3410731 (US, A) J. Electrochem. So c. , 1987, Vol. 134, No. 3, pp. 638-641 (58) Fields investigated (Int.Cl. ⁷ , DB name) H01M 4/36-4/62 H01M 4/02 H01M 10/40

Claims (3)

(57) [Claims] 1. A non-aqueous electrolyte secondary battery comprising a negative electrode , a positive electrode, and a lithium ion conductive non-aqueous electrolyte , wherein the negative electrode active material of the negative electrode is tungsten dioxide WO2 in a non-oxidizing atmosphere. A non-aqueous electrolyte secondary battery, which is formed by heat treatment at a temperature of 400 to 700 ° C. 2. A method for producing a non-aqueous electrolyte secondary battery comprising a negative electrode , a positive electrode, and a lithium ion conductive non-aqueous electrolyte solution , wherein the negative electrode active material of the negative electrode is tungsten dioxide WO2.
A method of manufacturing a non-aqueous electrolyte secondary battery, comprising a step of forming by heat treatment at a temperature of 400 to 700 ° C. in a non-oxidizing atmosphere . 3. The negative electrode active material is cooled after the heat treatment.
It is characterized by having a step of
The method for manufacturing a non-aqueous electrolyte secondary battery according to claim 2.