JP2887632B2 - Non-aqueous electrolyte secondary battery - 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 non-aqueous electrolyte having lithium ion conductivity as a negative electrode active material using a material capable of inserting and extracting lithium. The present invention relates to a novel negative electrode active material that provides a new secondary battery having a high energy density, excellent charge / discharge characteristics, and a long cycle life.

[0002]

2. Description of the Related Art Nonaqueous electrolyte batteries using lithium as a negative electrode active material have advantages such as high voltage, high energy density, low self-discharge, and excellent long-term reliability. It is already widely used as a power source for applications. However, with the recent remarkable development of portable electronic devices and communication devices,
With the emergence of a wide variety of devices that require a large current output from batteries as power sources, there is a strong demand for rechargeable and high-density secondary batteries that can be recharged and discharged from the viewpoint of economy and reduction in size and weight of the devices. ing. For this reason, research and development to promote the non-aqueous electrolyte battery having a high energy density into a secondary battery has been actively carried out, and some of them have been put to practical use. However, energy density, charge / discharge cycle life, reliability, etc. are still insufficient. It is enough.

Conventionally, as a positive electrode active material constituting a positive electrode of this type of secondary battery, the following three types are used depending on the form of charge / discharge reaction.
Species types have been found. The first type is a metal chalcogenide such as TiS ₂ , MoS ₂ , NbSe ₃ , MnO ₂ , MoO ₃ , V ₂ O ₅ , Li _x CoO ₂ , L
_{i X NiO 2, Li x Mn} 2 O 4 or the like as a so metal oxides, only crystals of the interlayer and the grating position or the interstitial gap lithium-ion (cation) of intercalation and deintercalation reactions and the like Type that comes in and out. Second
The type is a type in which mainly anions alone are stably introduced and removed by doping and undoping reactions, such as conductive polymers such as polyaniline, polypyrrole, and polyparaphenylene. The third type is a type (intercalation, deintercalation or doping, undoping, 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 constituting the negative electrode of this type of battery, when metallic lithium is used alone, the electrode potential is the lowest, so that it is combined with a positive electrode using the above positive electrode active material. Although the battery has the highest output voltage and the highest energy density, it is preferable. However, dendrites and passive compounds are generated on the negative electrode during charging and discharging, and there is a problem that the deterioration due to charging and discharging is large and the cycle life is short. In order to solve this problem, (1) lithium and Al, Zn, Sn, Pb, Bi, Cd
(2) WO ₂ , MoO ₂ , Fe
Inorganic compounds such as ₂ O ₃ , TiS ₂ , graphite, carbonaceous materials obtained by firing organic materials, etc. Intercalation compounds or insertion compounds in which lithium ions are occluded in the crystal structure, and (3) lithium ion-doped polyacene It has been proposed to use a substance capable of storing and releasing lithium ions, such as conductive polymers such as polyacetylene and polyacetylene.

[0005]

However, in general, a negative electrode using a material capable of inserting and extracting lithium ions other than lithium metal as described above and a positive electrode active material as described above are used as the negative electrode active material. When a battery is configured by combining the positive electrode and the positive electrode, the operating voltage of the battery is higher than that of the negative electrode active material because the electrode potential of these negative electrode active materials is more noble than the electrode potential of metallic lithium. There is the disadvantage that it is much lower. For example, lithium and A
l, Zn, Pb, Sn, Bi, 0.2~0.8V in the case of using an alloy of Cd, etc., carbon - 0 to 1 V in a lithium intercalation compound, a lithium ion insertion compound such as MoO ₂ and WO ₂ 0 The operating voltage is reduced by 0.5 to 1.5 V.

In addition, since elements other than lithium also serve as negative electrode components, the capacity and energy density per volume and weight are significantly reduced. Further, when the alloy of lithium and another metal of the above (1) is used, the efficiency of use of lithium during charge and discharge is low, and cracks occur in the electrodes due to repetition of charge and discharge, causing cracks 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 insertion compound of (2), deterioration such as collapse of a crystal structure or generation of an irreversible substance due to overcharging / discharging occurs, and a high electrode potential ( There is a drawback that the output potential of a battery using this is low because there are many precious materials, and in the case of the conductive polymer of (3), the charge / discharge capacity, particularly the charge / discharge capacity per volume is small. There's a problem.

Therefore, in order to obtain a secondary battery having a high voltage, a high energy density, excellent charge / discharge characteristics, and a long cycle life, an electrode potential with respect to lithium is low (low) and lithium ions during charge / discharge are required. It is necessary to use a negative electrode active material which is free from deterioration such as collapse of the crystal structure or generation of an irreversible substance due to occlusion and release, and has a large amount capable of reversibly storing and releasing lithium ions, that is, an effective charge / discharge capacity.

[0008]

In order to solve the above-mentioned problems, the present invention provides a negative electrode active material for a battery of this type, which comprises tin represented by the composition formula Li _x SnO (where 0 ≦ X). Another object of the present invention is to use a novel lithium ion occluding and releasing substance composed of a composite oxide of Sn and lithium. That is, it is an oxide in which the composition ratio of tin Sn and oxygen is about 1: 1 and contains lithium in its crystalline structure or amorphous structure, and lithium ions are formed by electrochemical reaction in a non-aqueous electrolyte. A composite oxide capable of occluding and releasing is used.
As described above, the standard composition ratio of tin Sn and oxygen O is 1: 1 as described above, but a non-stoichiometric compound due to tin Sn or oxygen O deficiency often occurs during synthesis, and the range of the deficiency is ± Up to 25%. Such nonstoichiometric compositions are also included in the present invention. Further, the content x of lithium may be in a range where the composite oxide is stably present, and 0 ≦ x ≦
A range of 2 is particularly preferred.

Preferred methods for producing the composite oxide used as the negative electrode active material of the battery of the present invention include, but are not limited to, the following two methods. The first method is a method in which each of tin Sn and lithium alone or a compound thereof is mixed at a predetermined molar ratio, and the mixture is heated in an inert atmosphere or in a vacuum or in an atmosphere in which the amount of oxygen is controlled to synthesize. It is. The respective compounds of tin Sn and lithium as starting materials include oxides, hydroxides, salts such as carbonates and nitrates or organic compounds, etc., heated in an inert atmosphere or in a vacuum to oxidize. Particularly preferred are compounds that produce a product. The heating temperature varies depending on the starting materials and the heating atmosphere, but synthesis is possible at 400 ° C. or higher, preferably 600 ° C. or higher, more preferably 700 ° C. or higher.

The composite oxide of tin Sn and lithium obtained in this way can be used as a negative electrode active material as it is or after necessary processing such as pulverization and sizing or granulation. In the same manner as in the second method described below, depending on the electrochemical reaction between the lithium-containing composite oxide and the metal lithium or the lithium-containing substance, the composite oxide can be further occluded with lithium ions, Alternatively, conversely, a compound having a lithium content increased or decreased by releasing lithium ions from the composite oxide may be used as the active material.

In the second method, a composite oxide of tin Sn and lithium is formed by absorbing lithium ions in the tin monoxide SnO based on an electrochemical reaction between tin monoxide SnO and lithium or a substance containing lithium. Is a way to get Examples of the substance containing lithium for use in this electrochemical reaction include, for example, substances capable of inserting and extracting lithium ions such as those used for the positive electrode active material or the negative electrode active material mentioned in the section of the prior art. Can be used.

[0012] Such occlusion of lithium ions by the electrochemical reaction to tin monoxide SnO can be performed in the battery after the battery is assembled, or in or outside the battery during the battery manufacturing process. It can be performed, specifically, as follows. That is, (1) a material obtained by forming the tin monoxide SnO or a mixture thereof with a conductive agent and a binder into a predetermined shape as one electrode (working electrode), and using metallic lithium or a substance containing lithium. The other electrode (counter electrode) is in contact with a non-aqueous electrolyte having lithium ion conductivity to make the two electrodes face each other to form an electrochemical cell, and to apply or discharge an appropriate current in the direction in which the working electrode performs a cathode reaction. A method of electrochemically inserting lithium ions into the tin monoxide SnO. A non-aqueous electrolyte secondary battery is formed by using the obtained working electrode as a negative electrode as it is or as an active material constituting the negative electrode. (2) The tin monoxide or a mixture thereof with a conductive agent, a binder and the like is formed into a predetermined shape, and lithium or an alloy of lithium or the like is pressed or brought into contact with the tin monoxide to form a laminated electrode as a negative electrode. Install in non-aqueous electrolyte secondary batteries. A method in which the laminated electrode contacts the electrolyte in the battery to form a kind of local battery, self-discharges, and electrochemically occludes lithium in the tin monoxide SnO. (3) A non-aqueous electrolyte secondary battery using the tin monoxide SnO as a negative electrode active material and a material containing lithium and capable of inserting and extracting lithium ions as a positive electrode active material.
A method in which lithium ions released from a positive electrode by charging during use as a battery are occluded in the tin monoxide.

The composite oxide Li _x SnO of tin Sn and lithium thus obtained is used as the negative electrode active material. In particular, the negative electrode using the composite oxide Li _x SnO as an active material according to the present invention has an electrode potential of 1 V with respect to metallic lithium.
Since the charge / discharge capacity of the following lower regions is large and the deterioration due to overcharge and overdischarge is small, this is used as a negative electrode, and the above-mentioned V ₂ O ₅ , Li _x CoO ₂ , Li _x NiO ₂ , and Li _x Mn are used. _Two
When combined with a positive electrode using an active material having a high potential of 3 V or 4 V or higher with respect to lithium metal such as a metal oxide such as O _4, it has a high voltage, high energy density, and excellent large current charge / discharge characteristics. It is particularly preferable because a secondary battery with small deterioration due to charge overdischarge can be obtained.

On the other hand, as the electrolyte, γ-butyrolactone, propylene carbonate, ethylene carbonate,
LiClO ₄ , LiPF ₆ , LiB as a supporting electrolyte in a single or mixed organic solvent such as butylene carbonate, dimethyl carbonate, diethyl carbonate, methylformate, 1,2-dimethoxyethane, tetrahydrofuran, dioxolan, dimethylformamide, etc.
An organic electrolytic solution 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 , LiI, etc., as long as it is a lithium ion conductive non-aqueous electrolyte such as an inorganic solid electrolyte.

[0015]

The composite oxide L of tin Sn and lithium according to the present invention
a i _x SnO an active material negative electrode, a nonaqueous stably repeated lithium storage and release in the electrolyte At a range of electrode potential of at least 0~3V to metallic lithium (intercalation, deintercalation or doped , Undoping, etc.) and 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, it has a high-capacity region in which lithium ions can be stably inserted and released and charged and discharged repeatedly in a base potential region of 0 to 1.0 V with respect to the lithium reference electrode. Further, as compared with carbonaceous materials such as graphite which have been conventionally used as electrodes of this type of battery, the amount of lithium ions that can be inserted and released reversibly, that is, the charge / discharge capacity is extremely large, and the charge / discharge polarization is small. Charging / discharging with current is possible, and an extremely stable battery having a long cycle life can be obtained.

The reason why such excellent charge / discharge characteristics are obtained is not necessarily clear, but is presumed as follows. That is, the composite oxide Li _x SnO of tin Sn and lithium, which is a novel active material according to the present invention, has high mobility of lithium ions in this structure and has very many sites capable of occluding lithium ions. Therefore, it is presumed that the storage and release of lithium ions are easy.

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 evaluating the performance of an electrode active material of a nonaqueous electrolyte secondary battery according to the present invention. In the figure, reference numeral 1 denotes a counter electrode case also serving as a counter electrode terminal, which is formed by drawing a stainless steel plate having one outer surface Ni-plated. 2
Is a counter electrode current collector made of a stainless steel net, which is spot-welded to the counter electrode case 1. The counter electrode 3 is obtained by punching an aluminum plate having a predetermined thickness to a diameter of 15 mm, fixing the aluminum plate to the counter electrode current collector 2, and punching a lithium foil having a predetermined thickness to a diameter of 14 mm. Reference numeral 7 denotes a working electrode case made of stainless steel with one outer surface Ni-plated, and also serves as a working electrode terminal. Reference numeral 5 denotes a working electrode formed by using an active material according to the present invention described later or a comparative active material according to a conventional method, and is operated by a working electrode current collector 6 made of a conductive adhesive using carbon as a conductive filler. Glued to the pole case. Reference numeral 4 denotes a separator made of a porous film of polypropylene, which is impregnated with an electrolytic solution. Reference numeral 8 denotes 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 to make the opening edge of the working electrode case inward. The battery contents are sealed and sealed by being bent and crimped. The electrolyte used was one in which lithium perchlorate LiClO ₄ was dissolved at 1 mol / l in a mixed solvent of propylene carbonate, ethylene carbonate, and 1,2-dimethoxyethane in a volume ratio of 1: 1: 2. The size of the battery was 20 mm in outer diameter and 1.6 mm in thickness.

The working electrode 5 was manufactured as follows. An active material 1 according to the present invention is obtained by pulverizing and sizing commercially available tin monoxide SnO to a particle size of 53 μm or less using an automatic mortar, and using graphite as a conductive agent and a cross-linkable acrylic resin or the like as a binder. The working electrode mixture was mixed at a weight ratio of 65:20:15 to obtain a working electrode mixture.
After pressure-molding into a pellet having a diameter of 15 mm and a thickness of 0.3 mm at m ² , the pellet was dried by heating under reduced pressure at 200 ° C. for 10 hours to obtain a working electrode.

For the sake of comparison, the above-mentioned book was used except that the same graphite as that used for the conductive agent was used as the active material (abbreviated as active material 2) instead of the above-mentioned active material 1 according to the present invention. A similar electrode (comparative working electrode) was prepared in the same manner as the working electrode of the invention. The battery manufactured in this manner was aged at room temperature for one week, and then subjected to a charge / discharge test described later. Due to this aging, the lithium-aluminum laminated electrode of the counter electrode is sufficiently alloyed by touching the non-aqueous electrolyte in the battery, and substantially all of the lithium foil becomes a Li-Al alloy. As compared with the case where metallic lithium was used alone, the value became about 0.4 V lower and stabilized.

The batteries manufactured in this manner are hereinafter abbreviated as batteries 1 and 2 corresponding to the active materials 1 and 2 of the working electrodes used. These batteries 1 and 2 were charged at a constant current of 1 mA (the direction of the current in which the lithium ions were occluded in the working electrode from the electrolyte in the direction of the battery reaction), and the final voltage-0.
4 V, end voltage of discharge (current direction in which a lithium ion is released from the working electrode into the electrolyte in a battery reaction) 2.5 V
FIG. 2 shows the discharge characteristics in the third cycle and FIG. 3 shows the charge characteristics when the charge / discharge cycle was performed under the conditions described above. FIG. 4 shows the cycle characteristics. The charge / discharge cycle started from charging. As is clear from FIGS. 2 to 4, the battery 1 according to the present invention has a remarkably large charge / discharge capacity and a reversible charge / discharge region significantly expanded as compared with the comparative battery 2. In addition, a decrease in discharge capacity (cycle deterioration) due to repeated charging and discharging is small. Furthermore, the difference in operating voltage between charging and discharging is significantly reduced over the entire charging / discharging region, indicating that the polarization (internal resistance) of the battery is extremely small and that large-current charging / discharging is easy.

That is, lithium ions are released from the Li-Al alloy of the counter electrode into the electrolyte by charging, and the lithium ions move in the electrolyte and react with the active material 1 of the working electrode by an electrode. Lithium ions are electrochemically occluded to produce lithium-containing composite oxide Li _x SnO. Next, at the time of discharge, lithium ions are released from the composite oxide into the electrolyte, move in the electrolyte, and are absorbed in the Li-Al alloy at the counter electrode, whereby stable charge and discharge can be performed repeatedly. Here, after the active material 1 generates the composite oxide Li _x SnO containing lithium by the first charge, in the subsequent discharge-charge cycle,
Lithium-containing composite oxide Li except during full discharge
_{x '} SnO is formed.

[0023]

As described in detail above, the present invention uses a novel active material composed of a composite oxide Li _x SnO of tin Sn and lithium as a negative electrode active material of a non-aqueous electrolyte secondary battery. The charge / discharge capacity is remarkably large, that is, the charge / discharge capacity is extremely large, and the charge / discharge polarization is small. Long batteries can be obtained. Particularly, the active material according to the present invention is used as a negative electrode active material, and V ₂ O ₅ , Li _x CoO ₂ , Li _x NiO ₂ ,
When combined with a positive electrode using a high-potential active material having an electrode potential of 3 V or 4 V or more for metal lithium such as a metal oxide such as Li _x Mn ₂ O ₄ , a high-voltage and high-energy-density battery is manufactured. It has an excellent effect that can be obtained.

[Brief description of the 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 a battery according to the present invention and a conventional battery.

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

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

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Counter electrode case 2 Counter electrode current collector 3 Counter electrode 4 Separator 5 Working electrode 6 Working electrode current collector 7 Working electrode case 8 Gasket

──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Seiji Yahagi 6-31-1, Kameido, Koto-ku, Tokyo Seiko Electronic Industry Co., Ltd. No. 1 Inside Seiko Electronic Components Co., Ltd. (72) Inventor Hideki Ishikawa 5-30-1, Nishitaga, Taishiro-ku, Sendai City, Miyagi Prefecture Inside Seiko Electronic Components Co., Ltd. (58) Field surveyed (Int. Cl. ⁶ , DB name) H01M 4/48 H01M 4/02 H01M 4/58 H01M 10/40

Claims (4)

(57) [Claims] 1. A negative electrode active material comprising at least a negative electrode, a positive electrode, and a lithium ion conductive non-aqueous electrolyte, wherein the negative electrode active material is SnO.
A non-aqueous electrolyte secondary battery, comprising: 2. The ratio of Sn: O in said SnO is 1: 0.7.
5 to 1: 1.25
Item 2. The non-aqueous electrolyte secondary battery according to Item 1. 3. A negative electrode, a positive electrode and a lithium ion conductive non-conductive material.
And at least a negative electrode active material comprising Li _x S
Non-aqueous electrolyte characterized by nO and 0 <x
Rechargeable battery. 4. The method according to claim 1, wherein _x The ratio of Sn: O of SnO is 1:
Characterized by the range of 0.75 to 1: 1.25
The non-aqueous electrolyte secondary battery according to claim 1.