JPH05144474A - Nonaqueous electrolyte secondary battery and active material manufacturing method - Google Patents

Abstract

PURPOSE:To provide a nonaqueous electrolyte secondary battery which presents excellent charging/discharging characteristics and is equipped with a long cyclic lifetime. CONSTITUTION:A nonaqueous electrolyte secondary battery includes at least a neg. electrode, a pos. electrode, and a nonaqueous electrolyte having Li ion electroconductivity, and therein the active material of at least either of the neg. and pos. electrodes consists in an organic silicon compound having direct bond of silicon and carbon subjected to a heat treatment, or the resultant from heat treatment to which lithium is stored. This gives a large charging/ discharging capacity, high energy density, and less polarization (internal resistance) at the time of charging and discharging, so that it is easy to make charging and discharging with a large current, ensures lesser deterioration due to overcharge/overdischarge, and prolongs the cyclic lifetime.

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 in which lithium or a substance capable of inserting and extracting lithium is used as a negative electrode active material and / or a positive electrode active material and a lithium ion conductive non-aqueous electrolyte is used. It is capable of repeated charge and discharge, has a high capacity and excellent overcharge and overdischarge characteristics,
The present invention relates to a novel negative electrode active material and positive electrode active material.

[0002]

2. Description of the Related Art Non-aqueous electrolyte batteries using lithium as a negative electrode active material have advantages of high voltage, high energy density, low self-discharge and excellent long-term reliability. It has already been widely used as a power source for business. However,
With the recent remarkable development of portable electronic devices, communication devices, etc., a large number of devices that require a large current output for a battery as a power source have appeared, and from the viewpoints of economy and reduction in size and weight of devices, the There is a strong demand for a secondary battery that can be charged and discharged and that has a high energy density. For this reason, 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 constituting 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 a metal chalcogenide such as TiS ₂ , MoS ₂ , NbSe ₃ or MnO ₂ , MoO ₃ , V ₂ O ₅ , Li _X Co.
Like metal oxides such as O ₂ , Li _X NiO ₂ , Li _X Mn ₂ O _4, etc., only lithium ions (cations) are intercalated or deintercalated between crystal layers or between lattice positions or gaps. Type that goes in and out depending on the reaction. The second type is polyaniline, polypyrrole,
A type in which only anions are stably doped and desorbed by the dedoping reaction, such as conductive polymers such as polyparaphenylene. 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 constituting the negative electrode of this type of battery, when metal lithium is used alone, the electrode potential is the most base, and therefore it is combined with the positive electrode using the positive electrode active material as described above. The battery has the highest output voltage and the high energy density, which is preferable, but there is a problem that dendrites and passivation compounds are generated on the negative electrode during charging and discharging, the deterioration due to charging and discharging is large, and the cycle life is short. In order to solve this problem, as a negative electrode active material, (1) lithium and Al, Zn, Sn, Pb, Bi, Cd
Alloys with other metals such as (2) WO ₂ , MoO ₂ , Fe
An intercalation compound or an intercalation compound in which lithium ions are occluded in the crystal structure of an inorganic compound such as ₂ O ₃ or TiS ₂ or graphite, a carbonaceous material obtained by firing an organic substance, or the like, and (3) lithium ion-doped polyacene It has been proposed to use a substance capable of inserting and extracting lithium ions, such as a conductive polymer such as or polyacetylene.

[0004]

However, generally, a negative electrode using a substance 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 it with a positive electrode, the electrode potential of these substances is nobler than the electrode potential of metallic lithium, so the operating voltage of the battery is considerably higher than that when metallic lithium is used alone as the negative electrode active material. It has the drawback of decreasing. For example, lithium and Al,
0.2 to 0.8 V when an alloy such as Zn, Pb, Sn, Bi, Cd is used, and 0 when a carbon-lithium intercalation compound is used.
To 1V, the lithium ion insertion compound such as MoO ₂ and WO ₂ 0.5 to 1.5 operating voltage is reduced.

Furthermore, since elements other than lithium also serve as negative electrode constituents, the capacity and energy density per volume and weight are significantly reduced. Therefore, in order to obtain a secondary battery with excellent charge / discharge characteristics, long cycle life, high voltage, and high energy density, the electrode potential for lithium is low (base) and reversibly occludes lithium ions. A negative electrode active material that can release a large amount is required.

On the other hand, of the above-mentioned positive electrode active materials, the first type generally has a large energy density, but has a drawback that if it is overcharged or overdischarged, it is greatly deteriorated due to crystal collapse or generation of irreversible substances. .. On the contrary, the second and third types have a drawback that the capacity and energy density are small. Therefore, in order to obtain a secondary battery with excellent overcharge characteristics and overdischarge characteristics, high capacity, and high energy density, there is no crystal collapse or irreversible substance generation due to overcharge overdischarge, and reversible There is a need for a positive electrode active material that can store and release lithium ions in a larger amount.

[0007]

In order to solve the above-mentioned problems, the present invention provides a direct bond of silicon Si and carbon C as an active material of at least one of the negative electrode and the positive electrode of this type of battery. The present invention proposes to use a novel lithium ion occluding / releasing substance comprising a heat-treated product of an organosilicon compound having the above or a heat-treated product obtained by occluding lithium.

The heat-treated product of the organosilicon compound used as the active material of the negative electrode and / or the positive electrode of the battery of the present invention can be manufactured as follows. The organosilicon compound used as a starting material may be a compound having a direct bond between silicon and carbon in a form in which a part of carbon in the organic compound is replaced by silicon, but it also has a direct bond between silicon and oxygen. Compounds are more preferred. Specifically, silane derivatives _{(RmSinH 2 n + 2 -m)} , cyclohexylene derivatives, halogenated silane derivative (RnSiX ₄ -n), silanol derivative (RNS
i (OH) ₂ ) and an alkoxysilane derivative (RnSi (O
R ') _4- n), siloxane derivatives and the like, and polymers thereof. However, as the substituents R and R ', all hydrocarbon groups such as an alkyl group such as a methyl group and an ethyl group, a phenyl group, a tolyl group, an xylyl group, an aryl group such as a naphthyl group, and an alicyclic hydrocarbon group, Any organic group such as a fluoroalkyl group such as a trifluoropropyl group and an organic group derived from a heterocyclic compound can be used, and X is a halogen atom such as chlorine, fluorine, bromine or iodine, m and n.
Is an integer.

100 to 30 of these organosilicon compounds
The product obtained by heat treatment at a temperature of 00 ° C is used. Limit with the heating temperature and atmosphere, the organosilicon compound is carbon are completely thermally decomposed or oxidized all dissipated as hydrocarbon gas or CO2 gas or the like by the heat treatment, only silicon oxide (SiO ₂ or the like) is heat-treated It is limited to a range where it does not form as a residue, that is, a range where silicon and carbon are the main constituents, and preferably oxygen is further contained, and those atoms are directly bonded to form a compound having a network structure or a three-dimensional structure. Therefore, in an inert atmosphere or in a vacuum, the temperature is 100 to 3000 ° C, more preferably 300 to 2 ° C.
1 at 500 ° C in the air or in an atmosphere containing oxygen
00-900 ° C, more preferably 200-700 ° C
Is preferred. By such heat treatment, the organosilicon compound undergoes polymerization, in-situ polymerization, cross-linking and / or thermal decomposition, and has a network structure in which silicon and carbon or silicon, carbon and oxygen are the main components and their atoms are directly bonded to each other, or 3 A compound having a three-dimensional network structure is produced. Among the above-mentioned organosilicon compounds, silicone (polyorganosiloxane), which is a polymer of an organosiloxane having a side chain of an organic group bonded to silicon, has a skeleton of a direct bond between silicon and carbon and between silicon and oxygen. It is a stable polymer compound and is particularly preferable as a starting material for the present invention.

The storage of lithium in this heat-treated product is
It can be done as follows. That is, (1) a method in which the heat-treated product and lithium metal are used as both electrodes in contact with a lithium ion conductive non-aqueous electrolyte so as to be opposed to each other and discharged or energized at an appropriate current to electrochemically occlude lithium ions. (2) The heat-treated product or a mixture of the heat-treated product and a conductive agent and a binder is molded into a predetermined shape, and lithium is pressure-bonded to form a laminated electrode, which is incorporated into a battery as an electrode. A method in which this laminated electrode contacts the electrolyte in the battery to self-discharge and electrochemically occlude lithium. (3) A battery is constructed using the heat-treated product as an active material for one electrode and an active material containing lithium for the other electrode. A method in which lithium is occluded in the heat-treated product by performing charging and discharging during use as a battery.

The heat-treated product thus obtained or the heat-treated product obtained by occluding lithium is used as the active material of the negative electrode and / or the positive electrode. A heat-treated product of an organosilicon compound according to the present invention or an electrode having an active material obtained by occluding lithium in the heat-treated product can be used as a positive / negative active material to form a secondary battery,
Further, by using this as either the positive electrode or the negative electrode, the above-mentioned various negative electrode active materials capable of inserting and extracting lithium or lithium ions or the electrode using the positive electrode active material is combined as the other electrode. It can also be used. In particular, a heat-treated product of the organosilicon compound of the present invention or an electrode using the heat-treated product obtained by occluding lithium as an active material has a large charge / discharge capacity in a base region where the electrode potential with respect to metallic lithium is 1 V or less. By using this as a negative electrode and combining it with a positive electrode using an active material having a high potential of 2 V or more for metallic lithium such as the above-mentioned metal oxides and metal chalcogenides, a high voltage and a high energy density and a high voltage are obtained. Excellent current charge / discharge characteristics,
It is particularly preferable because a secondary battery with little deterioration due to overcharge and overdischarge can be obtained.

On the other hand, as the electrolyte, γ-butyrolactone, propylene carbonate, ethylene carbonate,
Butylene carbonate, 1,2-dimethoxyethane, tetrahydrofuran, _{dioxolane, LiClO 4, LiPF 6, LiBF} 4 as a supporting electrolyte alone or organic solvents such as dimethylformamide, LiCF ₃ SO
An organic electrolyte solution in which a lithium ion dissociable salt such as ₃ is dissolved,
A lithium ion conductive non-aqueous electrolyte such as a polymer solid electrolyte in which the lithium salt is dissolved in a polymer such as polyethylene oxide or a crosslinked polyphosphazene or an inorganic solid electrolyte such as Li ₃ N or LiI may be used. ..

[0013]

A heat-treated product of the organosilicon compound of the present invention or an electrode using the heat-treated product obtained by occluding lithium as an active material has an electrode potential of at least 0 to 3 V with respect to metallic lithium in a non-aqueous electrolyte. It is possible to stably occlude and release lithium (intercalation, deintercalation or doping, dedoping, etc.) repeatedly within a range, and the negative electrode and / or positive electrode of a secondary battery capable of being repeatedly charged and discharged by such an electrode reaction. Can be used as In particular, in a base potential region of 0 to 1 V with respect to the lithium reference electrode, it has a high capacity region in which lithium ions can be occluded and released stably and can be repeatedly charged and discharged. Further, as compared with carbonaceous materials such as graphite that have been conventionally used as electrodes of this type of battery, the amount capable of reversibly occluding and releasing lithium ions, that is, the charging / discharging capacity is extremely large, and the polarization of charging / discharging is small. The battery can be charged and discharged with an electric current, and further, degradation such as decomposition and crystal collapse due to overcharge and overdischarge is hardly seen, and a very stable battery having 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, a heat-treated product of an organosilicon compound which is a novel active material according to the present invention is mainly composed of silicon and carbon or silicon, carbon and oxygen, and their atoms are directly bonded to each other to form a network structure or a three-dimensional network structure. It is presumed that the lithium ions are formed, the mobility of lithium ions in this structure is high, and the number of sites that can store lithium ions is very large, so that it is easy to store and release lithium ions.

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

[0016]

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 an electrode active material of a non-aqueous electrolyte secondary battery according to the present invention. In the figure, reference numeral 1 denotes 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. Reference numeral 2 denotes 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 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 stainless steel working electrode case having one outer surface plated with Ni, which also serves as a working electrode terminal. Reference numeral 5 denotes a working electrode composed of an active material according to the present invention described below or a comparative active material according to a conventional method, which is integrally molded with a working electrode current collector 6 made of a stainless steel net under pressure. There is. 4 is a separator made of a polypropylene porous film, which is impregnated with an electrolytic solution. Reference 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 is a 1: 1 volume ratio of propylene carbonate and 1,2-dimethoxyethane.
1 mol / l of lithium perchlorate LiClO4 as a mixed solvent
What was melt | dissolved was used. Battery size is 20m outside diameter
m and the thickness was 1.6 mm.

The working electrode 5 was manufactured as follows. A solution (silicone varnish TSR117 manufactured by Toshiba Silicone Co., Ltd.) obtained by diluting polymethylphenylsiloxane, which is an organosilicon compound polymer having an organic group such as a methyl group and a phenyl group bonded to a silicon atom, with an atmosphere of 5 at 100 ° C. in the atmosphere. Heat dried for hours. Next, this dried product was heat-treated in a nitrogen gas stream at 700 ° C. for 8 hours, cooled and then cooled to a particle size of
The particles were pulverized and sized to a size of less than μm. The obtained heat-treated product was used as the active material a according to the present invention, and graphite was used as a conductive agent, and a cross-linked acrylic acid resin was used as a binder in a weight ratio of 3
The working electrode mixture is mixed at a ratio of 0: 65: 5, and then this working electrode mixture is used together with the working electrode current collector 6 made of a stainless steel net at 2 ton / cm 2 and the diameter is 15 mm and the thickness is 0.5 mm. After pressure forming into pellets,
What was dried under reduced pressure for 0 hours was used as a working electrode.

For comparison, instead of the active material a according to the present invention, silicon dioxide SiO2 (active material b) which is an oxide of only silicon without carbon and silicon without carbon is used instead. A similar electrode (comparative working electrode) was prepared in the same manner as in the case of the working electrode of the present invention, except that the same graphite (active material c) as that used for the above-mentioned conductive agent was used as the active material.

The battery thus manufactured was aged for 1 week at room temperature and then 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. As compared with the case where metallic lithium is used alone, it is about 0.4
The value decreased by V 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.
The batteries A, B, and C are abbreviated. These batteries A, B and C
At a constant current of 0.4 mA, the end voltage of charging (current direction in which battery reaction in which lithium ions are occluded in the working electrode) −
FIG. 2 shows the charge characteristics of the third cycle when a charge / discharge cycle was performed under the conditions of 0.4 V and a final voltage of 2.5 V of discharge (current direction in which battery reaction in which lithium ions are released from the working electrode). The discharge characteristics are shown in FIG. The cycle characteristics are shown in FIG. The charging / discharging cycle started from charging. As is clear from FIGS. 2 to 4, it can be seen that the battery A according to the present invention has a significantly larger charge / discharge capacity and a reversible charge / discharge region is significantly expanded as compared with the comparative batteries B and C. Further, the decrease in discharge capacity (cycle deterioration) due to repeated charging and discharging is extremely small. 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. As described above, in the heat-treated product of the organic silicon compound which is the active material of the working electrode of the battery A according to the present invention, the network structure in which silicon and carbon coexist and those atoms are directly bonded to each other is used. It is presumed that the mobility of lithium ions is high due to having a three-dimensional network structure and there are many sites that can store lithium ions.

Example 2 A dried product of the same polymethylphenylsiloxane as that used in Example 1 was used in air at 200
After heat-treatment at ° C for 5 hours, the active material d was prepared by pulverizing and sizing to a particle size of 53 µm or less. A similar battery D was produced in the same manner as in Example 1 except that the heat-treated organosilicon compound thus obtained was used as the active material of the working electrode.

The battery D thus obtained was subjected to the same charge / discharge cycle test as in Example 1. The results at this time are also shown in FIGS. As is apparent from the figure, the battery D of this example has excellent charge / discharge characteristics as the battery A of the first example according to the present invention. Further, the active materials a and d of the batteries A and D according to the present invention are 1.0 to 2.
5V (corresponding to about 1.4 to 2.9V with respect to metallic lithium), as well as or above the noble potential region,
0.4 to + 0.6V (about 0 to 1V against metallic lithium)
(Corresponding to (1)), the charge and discharge capacities in the base potential region are large, and thus it is found that not only it is used as the positive electrode active material of the non-aqueous electrolyte secondary battery, but also as the negative electrode active material. In particular, the active material d of Example 2 has a larger charge / discharge capacity in a base potential region and a base potential, and is particularly excellent as a negative electrode active material.

In the embodiment, lithium is used as the counter electrode.
Although only the case of the aluminum alloy is shown, the present invention
The invention is not limited to the examples, and as described above, metallic lithium, lithium
Alloys of titanium with other metals such as Zn, Sn, Pb, Bi,
Carbon and MoO₂, WO₂, Fe ₂O₃Lithium insertion compounds such as
Materials, polyacetylene, polypyrrole, polyacene, etc.
Lithium such as conductive polymer that can be doped with thion ion
Negative electrode that uses a substance capable of occluding and releasing titanium oxide as the active material, and TiS
₂, MoS₂, NbSe₃Metal chalcogenides such as Mn
O₂, MoO₃, V₂O_Five, Li_XCoO₂, Li_X Ni
O₂, Li_XMn₂O_FourMetal oxides such as polyaniline,
Conductivity of lipyrole, polyparaphenylene, polyacene, etc.
Lithium such as conductive polymers, graphite intercalation compounds, etc.
Substances capable of occluding and releasing cations and / or anions
A positive electrode using as an active material a counter electrode and an electrode according to the present invention
It goes without saying that they can be used together.

[0024]

INDUSTRIAL APPLICABILITY As described above in detail, the present invention provides a heat-treated product of an organic silicon compound having a direct bond between silicon and carbon as an active material of at least one of the negative electrode and the positive electrode of a non-aqueous electrolyte secondary battery. Alternatively, the heat-treated product uses a novel active material composed of lithium occluded, and the amount capable of reversibly occluding and releasing lithium ions by charging / discharging, that is, the charging / discharging capacity is extremely large, and the polarization of charging / discharging is Since it is small, it can be charged and discharged with a large current, and degradation such as decomposition and crystal collapse due to overcharge and overdischarge is hardly seen,
An extremely stable battery with a long cycle life can be obtained. Further, in particular, when the active material according to the present invention is used as a negative electrode active material, there are excellent effects such that a battery having high voltage and high energy density 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 charging characteristics in 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 discharge characteristics at 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.

[Explanation 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

Claims (2)

[Claims] 1. A non-aqueous electrolyte secondary battery comprising at least a negative electrode, a positive electrode, and a lithium ion conductive non-aqueous electrolyte, wherein silicon Si and carbon C are directly bonded as an active material of at least one of the negative electrode and the positive electrode. A non-aqueous electrolyte secondary battery characterized by using a heat-treated product of an organosilicon compound having: or a heat-treated product obtained by occluding lithium. 2. The method for producing a negative electrode active material and / or a positive electrode active material for a non-aqueous electrolyte secondary battery according to claim 1, wherein silicone (polyorganosiloxane) is used as the organosilicon compound.