JP2001283913A - Lithium battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent decrease in electric current density due to low conductivity of lithium ions in the electrolyte, and for example, to eliminate the need for containing organic solvent or lithium salt, which is a lithium ion conductor in an electrolyte. SOLUTION: This lithium battery holding solid electrolyte layer lies between a pair of electrodes. The electrode and the solid electrolyte layer contain a compound made of siloxane bond and a non-protonic solvent as a main structure.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to a lithium battery.

[0002]

2. Description of the Related Art A lithium battery has a high energy density, low self-discharge,
It is widely used in mobile phones and notebook computers, taking advantage of its properties such as long-term storage. These lithium batteries use lithium cobalt oxide (L) as a positive electrode active material.
iCoO ₂ ) and lithium manganate (LiMn ₂ O ₄ ) are generally used, and a carbon material such as coke and carbon fiber is used as a negative electrode active material.

In general, a lithium battery is made of aluminum together with the above-mentioned positive electrode active material or negative electrode active material, a conductive agent such as acetylene black or graphite, and a binder such as polyvinylidene fluoride (PVdF) or polytetrafluoroethylene (PTFE). It is applied to a foil or copper foil, spirally wound through a separator made of polypropylene or polyethylene or a combination thereof and inserted into a battery case, and further sealed by injecting an organic electrolytic solution. It has a structure.

The components of these organic electrolytes are an aprotic solvent and an electrolyte salt, and the aprotic solvents include propylene carbonate (PC), dimethoxyethane (DME), ethylene carbonate (EC), and dimethyl carbonate (DMC). ), Diethyl carbonate (DE
C) is used alone or in a mixed state, and as electrolyte salts, LiClO ₄ , LiAsF ₆ , LiBF ₄ , L
iPF ₆ , LiCF ₃ SO ₃ , Li (CF ₃ SO ₂ ) ₂ N and the like are used.

[0005] In recent years, with the demand for thinner and smaller electronic equipment such as portable information communication terminals such as mobile phones and notebook personal computers, polymer electrolytes have been used in place of the above-mentioned organic electrolytes. Attention has been paid to lithium batteries using an electrolyte.

[0006] The polymer electrolyte is a mixture of a polymer having a donor type polar group represented by polyethylene oxide (PEO) and polypropylene oxide (PPO) and an electrolyte salt, and can form a thin electrolyte layer. It is expected that the energy density will be improved. Alternatively, since there is no risk of liquid leakage and corrosion and no volatile aprotic solvent is used, there is little risk of explosion or ignition, so that battery characteristics and safety can be improved.

However, the aforementioned polymer electrolyte is
There is a problem that the ionic conductivity is lower than that of the organic electrolyte, and the gel electrolyte in which the organic electrolyte is mixed with the polymer electrolyte has an ion conductivity comparable to that of the organic electrolyte. It is being actively performed.

[0008] When such a gel electrolyte is used, it is difficult to keep the electrical contact between the solid electrolyte layer and the electrode layer ideally. For example, Japanese Patent Application Laid-Open No. A monomer composition obtained by polymerizing a monomer composition by mixing a salt and a solvent is laminated on the positive electrode active material layer, a part of the monomer composition is impregnated in the positive electrode active material layer, and the positive electrode active material layer is impregnated. The positive electrode active material layer and the polymer solid electrolyte are sufficiently adhered to each other by polymerizing the monomer composition laminated on the surface of the positive electrode active material and forming a polymer solid electrolyte in close contact with the positive electrode active material layer. It has been proposed to do so.

In Japanese Patent Application Laid-Open No. HEI 8-111233, the resistance of the interface between the positive electrode and the solid electrolyte in which both ends or one end of the main chain of polyether, polythioether or polyacrylate are chemically bonded to the surface of the positive electrode oxide, and It has been proposed to reduce the interface resistance between the positive electrode active material particles.

In Japanese Patent Application Laid-Open No. Hei 8-315855, a mixture of an organic compound having a polymerizable functional group, an organic solvent, and a lithium salt is sandwiched between both electrodes, and thereafter, the polymerization is completed. Proposals have been made to prevent the generation of an interface between the electrode and the electrode and to prevent separation of the solid electrolyte and the electrode.

In Japanese Patent Application Laid-Open No. 9-50816,
Li ₂ in the polymer electrolyte mixed with solute and electrolyte salt
_{CO 3, CoCO 3, NiCO 3} , by dispersing the metal carbonate such as MgCO _3, is excellent in mechanical properties and workability, and high chemical stability composite solid electrolyte have been proposed in the interface with the anode I have.

However, these methods still have a problem that the lithium ion conductivity of the electrolyte is low and the current density is low, and it is necessary to contain a large amount of the main lithium ion conductor, that is, the organic solvent and the lithium salt. Further, when a lithium salt is contained in the organic solvent, there is a problem that the withstand voltage against an electrochemical reaction is reduced, and there is a problem that the organic solvent is unstable against overvoltage.

Further, the development of a solid electrolyte battery using an inorganic compound for the solid electrolyte is also in progress. A negative electrode in an all-solid lithium battery in which a compound comprising a transition metal oxide and a transition metal sulfide is used as a positive electrode as a positive electrode, a lithium ion conductive glass solid electrolyte containing Li ₂ S and a metal alloying with lithium are used as a negative electrode It has been proposed that dendrites do not occur and active materials do not fall off, and the charge / discharge cycle life is excellent. However, this proposal,
Since the positive electrode and the solid electrolyte contain sulfide compounds,
There are problems such as high reactivity with moisture.

Among oxide-based lithium ion conductors, there is a crystalline glass having a crystal structure similar to that of the NASICON-based lithium ion conductor. By using a sintered product of this as a solid electrolyte, high-rate discharge characteristics are excellent. A lithium battery is proposed. However, even in the case of an all-solid lithium battery using an oxide inorganic solid electrolyte as described above, there are problems such as inferior energy density and discharge current density as compared with a conventional secondary battery using a non-aqueous solvent as an electrolyte. And it has not been put to practical use.

Even if the lithium ion conductivity of the inorganic solid electrolyte is improved, the characteristics of the battery are not improved because of the interface resistance between particles and the interface resistance between the electrode and the solid electrolyte. Even if each material has sufficient characteristics, sufficient characteristics cannot be obtained due to high interface resistance.

The present invention has been made in view of such problems of the prior art, and has a low lithium ion conductivity of an electrolyte and a low current density. For example, an organic solvent or a lithium salt which is a lithium ion conductor is used. An object of the present invention is to provide a lithium battery that has solved the conventional problem that it needs to be included.

[0017]

According to a first aspect of the present invention, there is provided a lithium battery having a solid electrolyte layer sandwiched between a pair of electrodes. The solid electrolyte layer contains a compound having a siloxane bond as a main skeleton and an aprotic solvent.

In the above-mentioned lithium battery, it is preferable that the electrode is made of an electrode active material and a solid electrolyte, and the solid electrolyte layer is made of the same material as the solid electrolyte.

In the above lithium battery, it is preferable that the solid electrolyte layer is an oxide crystallized glass having lithium ion conductivity.

In the above-mentioned lithium battery, it is preferable that the aprotic solvent is composed of one or more of γ-butyrolactone, propylene carbonate, and ethylene carbonate.

In the above lithium battery, the active material of the electrode is Li _{1 + x} Mn _2-x O ₄ (0 ≦ x ≦ 0.2), LiMn _2-y
Me _y O ₄ (Me = Ni, Cr, Cu, Zn, 0 <y ≦
0.6), Li ₄ Ti ₅ O ₁₂ , and Li ₄ Mn ₅ O ₁₂ .

A conventional organic electrolyte solution is to impart lithium ion conductivity to an electrolyte by dissolving an electrolyte salt in an aprotic solvent. In the present invention, a compound having a siloxane bond as a main skeleton is used. The battery characteristics are improved only by including the aprotic solvent not containing the electrolyte salt, and it is considered that lithium ions are moved by an unconventional conduction mechanism. Further, since the aprotic solvent is present in the compound having a siloxane bond as a main skeleton, the problem of liquid leakage is reduced.

[0023]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments of the lithium battery of the present invention will be described.

FIG. 1 is a sectional view showing a configuration example of a lithium battery according to the present invention. In FIG. 1, 1 is a package, 2 is a pair of electrodes, 2a is a positive electrode, 2b is a negative electrode, 3 is a solid electrolyte layer, 4 is a positive electrode current collector, and 5 is a negative electrode current collector.

The material of the package 1 is not limited as long as it can maintain airtightness. For example, an aluminum laminate, a metal such as nickel or aluminum, or a shrink case can be used.

The positive electrode current collector 4 or the negative electrode current collector 5 is provided for collecting the current of the positive electrode 2a or the negative electrode 2b, and uses a metal foil such as aluminum (Al), nickel (Ni), copper (Cu). be able to.

The positive electrode 2a is made of a powder of a positive electrode active material, and if necessary, a solid electrolyte powder of the same material as the solid electrolyte layer is mixed. The negative electrode 2b is made of a negative electrode active material powder, and a solid electrolyte powder of the same material as the solid electrolyte layer is mixed as needed. When the positive or negative electrode active material and the solid electrolyte powder are mixed, the lithium ion conductivity in the electrode is expected to be improved.However, when the mixing amount of the solid electrolyte powder is excessive, the positive electrode or the positive electrode that contributes to the charge / discharge reaction of the battery is improved. The amount per volume or weight of the negative electrode active material decreases, and the energy density as a battery decreases. Therefore, the amount of the positive electrode or negative electrode active material in the electrode is desirably 40% by weight or more. Further, a conductive agent is added to the positive electrode 2a and the negative electrode 2b as needed.

As the electrode active material used for the positive electrode 2a and the negative electrode 2b, for example, lithium manganese composite oxide, manganese dioxide, lithium nickel composite oxide, lithium cobalt composite oxide, lithium nickel cobalt composite oxide, lithium vanadium composite oxide Oxides, lithium titanium composite oxides, titanium oxide, niobium oxide, vanadium oxide, tungsten oxide, and the like and derivatives thereof can be used. Among the above transition metal oxides, particularly L
i _{1 + x} Mn _2-x O ₄ (0 ≦ x ≦ 0.2), LiMn _{2 -y} Me
_y O ₄ (Me = Ni, Cr, Cu, Zn, 0 <y ≦ 0.6
), Li ₄ Ti ₅ O ₁₂ , or Li ₄ Mn ₅ O ₁₂ , a crystalline system in which the volume change of the active material during charging / discharging is small is a spinel-based active material and shows good cycle characteristics. It is. Here, there is no clear distinction between the positive electrode active material and the negative electrode active material, and those showing a noble potential by comparing the charge and discharge potentials of the two compounds are shown as the positive electrode, and those showing the noble potential are shown as the negative electrode. It can be used to form a battery of any voltage.

Solid electrolyte powder used for the solid electrolyte layer 3,
The solid electrolyte powder to be mixed with the positive electrode 2a or the negative electrode _{2b, 30LiI-41Li 2 O-} 29P 2 O 5, 40
_{Li 2 O-35B 2 O 5} -25LiNbO 3, 25Li 2 O
_{-25Al 2 O 3 -50SiO 2, 40Li} 2 O-6Y 2 O 3
-54SiO ₂ or 65LiNbO ₂ -35SiO
₂ or an oxide-based amorphous solid electrolyte such as Li _{1 + x} M _x Ti _2-x
(PO ₄ ) ₃ (where M is Al, Sc, Y, La), Li
_{1 + x} Ti _2-x (PO ₄ ) ₃ , Li _0.5-3x R _{0.5 + x} TiO ₃ (where R is La, Pr, Nd, Sm), Li _{1 + x + y} Al _x T
An oxide-based crystallized glass such as i _2-x Si _y P _{3 -y} O ₁₂ can be used. The solid electrolyte powder is preferably an oxide crystallized glass from the viewpoint of ionic conductivity.

Examples of the conductive agent include acetylene black, graphite, Ketjen black, RuO ₂ , SnO ₂ doped with Sb ₂ O _3, and SnO ₂ doped In ₂ O ₃ .

Examples of the compound forming a siloxane bond include a silane compound. In the silane compound, tetramethoxysilane, methyltrimethoxysilane, dimethyldimethoxysilane, phenyltrimethoxysilane,
Diphenyldimethoxysilane, tetraethoxysilane,
Examples include methyltriethoxysilane, dimethyldiethoxysilane, phenyltriethoxysilane, diphenyldiethoxysilane, hexyltrimethoxysilane, polymethoxysiloxane, polyethoxysiloxane, and polybutoxysiloxane.

Electrode 2 (2a, 2b) and solid electrolyte 3
The following method can be mentioned as a method for producing the same. The positive electrode, the negative electrode active material powder, the solid electrolyte powder and, if necessary, the electron conduction aid powder are mixed in advance and dispersed in a mixture of the silane compound and the aprotic solvent. If necessary, a solvent such as isopropyl alcohol is added to form a slurry and adjust the viscosity of the slurry. At this time, it is not necessary to mix the electron conduction aid powder with the solid electrolyte powder.

In order to cure the silane compound, a curing catalyst may be used. This curing catalyst is
It may be added before dispersing the powder, or may be added after dispersing the powder.

The slurry thus obtained is applied on the positive electrode current collector 4 or the negative electrode current collector 5 by a doctor blade method or a roll coater method, and then the silane compound is cured. When a curing catalyst is used, the curing condition is appropriately from room temperature to about 150 ° C., and the higher the curing temperature, the shorter the holding time. However, the curing temperature and time are not particularly limited. When a curing catalyst is not used, it is desirable to heat at a temperature of 150 ° C. or higher, but in this case, a temperature higher than the boiling point of the aprotic solvent is not preferable.

Here, the electrode 2 may be mixed with a solid electrolyte having the same composition as the solid electrolyte 3 if necessary.

The positive electrode 2a, the negative electrode 2b, the solid electrolyte 3
The method of laminating the positive electrode 2a, the solid electrolyte 3 and the negative electrode 2b in this order, followed by heating and curing at once, the positive electrode 2a,
The negative electrode 2b may be separately molded, heated and cured, then the solid electrolyte 3 may be molded on one of the electrodes, and the other electrode may be laminated and cured. Further, when pressure is applied during heating and curing, the filling rate of the powder is improved, and the bonding between the electrode 2 and the solid electrolyte 3 is preferably further strengthened.

In an all-solid battery that does not contain an aprotic solvent, lithium ions rely only on transport in bulk. However, in the lithium battery of the present invention, a siloxane bond that wets the particles and the particle surface has a main skeleton. It is presumed that ions move at the interface with the aprotic solvent contained in the compound.

The lithium battery to which the present invention is applied may be a primary battery or a secondary battery. The battery shape is not limited to a cylindrical type, a square type, a button type, a coin type, a flat type and the like.

[0039]

EXAMPLES Example 1 Lithium hydroxide and manganese dioxide were mixed so that the molar ratio of Li and Mn was 1: 2.
This mixture was heated and baked at 900 ° C. in the air for 15 hours to obtain a lithium manganese composite oxide (LiMn _2).
O ₄ ) was synthesized and used as a positive electrode active material. Next, lithium hydroxide and manganese dioxide are mixed such that the molar ratio of Li and Mn is 4: 5.
By heating and baking at 0 ° C. for 15 hours, a lithium manganese composite oxide (Li ₄ Mn ₅ O ₁₂ ) was synthesized and used as a negative electrode active material.

This LiMn ₂ O ₄ was mixed with Li _{1 + x + y} Al _x Ti _2-x Si _y P _{3- y} O ₁₂ as a solid electrolyte powder in a volume ratio of 8: 2. Acetylene black was mixed with this mixed powder in a weight ratio of 90:10.

The siloxane compound was prepared according to the following procedure. Siloxane compound (siloxane compound concentration: about 20
wt%, solvent: about 80 wt%) and a maleic acid-based curing catalyst were mixed and stirred at room temperature to prepare a mixed solution. At this time, the mixing ratio of the curing catalyst was 120 g with respect to 100 g of the siloxane compound. In order to stabilize the mixture, the mixture was allowed to stand at room temperature for 12 hours (hereinafter, this is referred to as an adjusted mixture).

5 g of propylene carbonate was mixed with 100 g of this adjusted mixed solution, and the mixture was thoroughly stirred. The mixed powder of LiMn ₂ O ₄ and acetylene black was mixed to form a slurry. The slurry was applied on aluminum (Al) by a doctor blade method, and then heat-treated at a temperature of 150 ° C. for 1 hour to form a siloxane bond and obtain an electrode.

Further, the solid electrolyte powder Li _{1 + x + y} Al _x Ti
_{2-x Si y P 3-} y O 12 is mixed with a liquid obtained by mixing propylene carbonate to adjust mixture in the same manner as described above was slurried. This slurry was applied and laminated on the above-mentioned positive electrode by a doctor blade method, and heat-treated at a temperature of 150 ° C. for 1 hour to obtain a laminated body of the positive electrode 2 a and the solid electrolyte 3.

Further, Li ₄ Mn ₅ O ₁₂ is slurried in the same manner as LiMn ₂ O ₄ as a positive electrode active material, applied and laminated on the solid electrolyte side of the laminate, and heat-treated.
A laminate of the positive electrode 2a, the solid electrolyte 3, and the negative electrode 2b was obtained. The thickness of the obtained laminate was about 200 μm.

The positive electrode current collector 4 was applied to the positive electrode 2a of the obtained laminate.
And the negative electrode current collector 5 was similarly bonded to the negative electrode 2 b and mounted on the aluminum laminate of the package 1. Aluminum laminate is 35mm x 35mm
Two pieces cut to the size shown in FIG. 1 were prepared, and the laminated body to which the current collector was joined was sandwiched, and the outer periphery of the aluminum laminate was thermocompressed to obtain a 35 mm × 35 mm shown in FIG.
Was assembled.

Example 2 A method for synthesizing a positive electrode active material and a negative electrode active material, except that γ-butyrolactone was used instead of propylene carbonate, the positive electrode 2a and the solid electrolyte 3
-The forming method of the negative electrode 2b was performed in the same manner as in Example 1. The thickness of the obtained positive electrode 2a-solid electrolyte 3-negative electrode 2b was about 220 [mu] m. Hereinafter, a prismatic lithium battery was assembled in the same manner as in the example.

Comparative Example 1 The method for synthesizing the positive electrode active material and the negative electrode active material was the same as in Example 1. The positive electrode
The method for forming the solid electrolyte-negative electrode was performed in the same manner as in Example 1, except that PVdF was used as a binder and N-methyl-2-pyrrolidone was used as a solvent.

The thickness of the obtained cathode-solid electrolyte-negative electrode was about 180 μm. Further, roll pressing was performed for the purpose of improving the filling rate of the laminate and the contact area of the powder. The obtained laminate was not impregnated with an aprotic solvent, and a prismatic lithium battery was assembled in the same manner as in the example. (Evaluation) Using the thus obtained rectangular solid electrolyte battery, a charging / discharging device was used as a charging condition of 50 μA / cm.
^2, 100 .mu.A / cm ^2, was charged to 1.5V in current square solid electrolyte battery of the aforementioned 300 .mu.A / cm ^2, after the voltage reaches the 1.5V, and held for 5 minutes to stop the charging, After that, the battery was discharged to the voltage of 0.5 V at the same current as that at the time of charging, then charged again to 1.5 V, and after reaching this voltage, the charging was stopped and the charge / discharge cycle was evaluated for 5 minutes.

Table 1 shows the results. The numbers in the table indicate the discharge capacity for each discharge current, and the unit is mAh.

[0050]

[Table 1]

Table 1 shows that the lithium battery of the present invention has excellent charge / discharge characteristics. In particular, it is remarkable that the decrease in the discharge capacity is small even when the discharge current increases.
This is because, by interposing a compound having a siloxane bond as the main skeleton and an aprotic solvent in the gap between the active material and the solid electrolyte, the bond between the particles and the bond between the electrode and the solid electrolyte are strengthened, and together with the inside of the bulk. It is assumed that the interface between the particle surface and the aprotic solvent also serves as a lithium ion conduction path.

Further, it was found that the lithium battery of the present invention was stable against overvoltage, and did not affect the cycle characteristics even when the charge / discharge voltage was intentionally increased.
This is probably because the aprotic solvent does not contain a lithium salt.

Further, it is considered that the aprotic solvent contained in the lithium battery of the present invention is present in a compound having a siloxane bond as a main skeleton, and almost no liquid leakage is confirmed and the reliability is high. Was also confirmed.

[0054]

As described above, according to the lithium battery of the present invention, since the electrode and the solid electrolyte layer contain a compound having a siloxane bond as a main skeleton and an aprotic solvent, the electrolyte salt is dissolved. Electrochemical characteristics equivalent to those of a lithium battery using a modified organic electrolyte solution are obtained, and an unconventional lithium ion conduction mechanism is exhibited. A highly reliable lithium battery is obtained.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view showing one embodiment of a lithium battery according to the present invention.

[Explanation of symbols]

1: package, 2: pair of electrodes, 2a: positive electrode, 2b:
Negative electrode, 3: solid electrolyte layer, 4: positive electrode current collector, 5: negative electrode current collector

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) H01M 4/58 H01M 6/18 E 6/18 C08K 5/15 F-term (Reference) 4J002 CP031 DA037 DE057 DE097 DE147 DH017 DJ017 DK007 EB017 EL066 EL106 FD117 FD206 GQ00 5H024 AA01 AA02 BB07 CC02 CC03 CC04 DD14 EE02 EE06 EE09 FF15 FF22 5H029 AJ07 AK02 AK03 AK05 AL02 AL03 AL04 AM03 AM05 AM11 AM12 BJ02 BJ03 A04 DJ04 CA09 CA11 CB02 CB03 CB05 DA02 DA03 DA09 DA13 EA13 EA23 HA02

Claims (5)

[Claims] 1. A lithium battery having a solid electrolyte layer sandwiched between a pair of electrodes, wherein the electrodes and the solid electrolyte layer comprise a compound having a siloxane bond (Si—O) as a main skeleton and an aprotic solvent. A lithium battery, comprising: 2. The lithium battery according to claim 1, wherein the electrode comprises an electrode active material and a solid electrolyte, and the solid electrolyte layer comprises the same material as the solid electrolyte. 3. The lithium battery according to claim 1, wherein the solid electrolyte layer is made of an oxide crystallized glass having lithium ion conductivity. 4. The lithium according to claim 1, wherein the aprotic solvent comprises one or more of γ-butyrolactone, propylene carbonate, and ethylene carbonate. battery. 5. The electrode according to claim 1, wherein the active material is Li _{1 + x} Mn _2-x O _4.
(0 ≦ x ≦ 0.2), LiMn _2-y Me _y O ₄ (Me = N
i, Cr, Cu, Zn, 0 <y ≦ 0.6), Li ₄ Ti ₅
O _12, and Li ₄ Mn claim 1, characterized in that it consists of any one or more of ₅ O _12, claim 2, lithium battery according to claim 3 or claim 4.