JP4845245B2 - Lithium battery - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a lithium battery.
[0002]
[Background Art and Problems to be Solved by the Invention]
Lithium ion batteries are widely used in mobile phones and notebook computers, taking advantage of their high energy density, low self-discharge, and compatibility with long-term storage. In these lithium ion batteries, lithium cobaltate (LiCoO ₂ ) and lithium manganate (LiMn ₂ O ₄ ) are generally used as the positive electrode active material, and carbon materials such as coke and carbon fiber are used as the negative electrode active material. It has been.
[0003]
In general, a lithium ion battery includes an aluminum foil or a negative electrode active material, a conductive agent such as acetylene black or graphite, and a binder such as polyvinylidene fluoride (PVdF) or polytetrafluoroethylene (PTFE). A structure that is coated on copper foil, spirally wound through a separator made of polypropylene, polyethylene, or a combination thereof, inserted into a battery case, and sealed by injecting an organic electrolyte. It has become.
[0004]
The components of these organic electrolytes are an aprotic solvent and an electrolyte salt. Examples of the aprotic solvent include propylene carbonate (PC), dimethoxyethane (DME), ethylene carbonate (EC), dimethyl carbonate (DMC), and diethyl. Carbonate (DEC) is used alone or in a mixed state, and LiClO ₄ , LiAsF ₆ , LiBF ₄ , LiPF ₆ , LiCF ₃ SO ₃ , Li (CF ₃ SO ₂ ) ₂ N, etc. are used as the electrolyte salt. Yes.
[0005]
In recent years, polymer electrolytes have been used in place of organic electrolytes as described above in response to demands for thin and small electronic devices such as portable information communication terminals such as mobile phones and laptop computers. Lithium batteries that have been attracting attention.
[0006]
The polymer electrolyte is a mixture of a polymer having a donor-type polar group, such as polyethylene oxide (PEO) and polypropylene oxide (PPO), and an electrolyte salt, and the energy density can be reduced by making the electrolyte layer thinner. Improvement is expected. Alternatively, there is no concern about leakage or corrosion, and since no volatile aprotic solvent is used, the battery characteristics and safety can be improved, such as low risk of explosion and ignition.
[0007]
However, the above-mentioned polymer electrolyte has a problem that the ionic conductivity is lower than that of the organic electrolyte, and the gel electrolyte obtained by mixing the organic electrolyte with the polymer electrolyte has an ionic conductivity comparable to the organic electrolyte. Therefore, development is actively conducted.
[0008]
When such a gel electrolyte is used, it is difficult to ideally maintain the electrical contact between the solid electrolyte layer and the electrode layer. For example, in JP-A-7-326383, an electrolyte salt and a solvent are used as a polymer compound. The monomer composition is mixed and polymerized to form a positive electrode active material layer, and a portion of the monomer composition is impregnated into the positive electrode active material layer, and the positive electrode active material layer is impregnated with the monomer composition and the positive electrode active material. The positive electrode active material layer and the polymer solid electrolyte can be sufficiently adhered by polymerizing the monomer composition laminated on the surface of the material and closely adhering to the positive electrode active material layer to produce a polymer solid electrolyte in a laminated state. Proposed.
[0009]
JP-A-8-111233 discloses a resistance at the interface between a positive electrode and a solid electrolyte in which both ends or one end of a main chain of polyether, polythioether, or polyacrylate are chemically bonded to the surface of the positive electrode oxide, and a positive electrode active material. It has been proposed to reduce the interfacial resistance between particles.
[0010]
In JP-A-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 then the polymerization is completed, whereby the electrolyte and the electrode are separated. It has been proposed to prevent the formation of an interface between them and to prevent separation between the solid electrolyte and the electrode.
[0011]
In JP-A-3-37971, an inorganic solid electrolyte such as LiI, Li-β-Al ₂ O ₃ , Li ₃ N, LiI-Al ₂ O ₃ is dispersed in an organic polymer solid electrolyte, and ion conduction is performed. A highly reliable thin battery with improved flexibility and withstand voltage has been proposed.
[0012]
In JP-A-9-50816, a metal carbonate such as Li ₂ CO ₃ , CoCO ₃ , NiCO ₃ , and MgCO ₃ is dispersed in a polymer electrolyte in which a solute and an electrolyte salt are mixed. A composite solid electrolyte having excellent chemical properties and workability and high chemical stability at the interface with the negative electrode has been proposed.
[0013]
However, these methods still have a problem that the lithium ion conductivity of the electrolyte is low and the current density becomes small, and it is necessary to contain a large amount of an organic solvent and a lithium salt, which are main lithium ion conductors.
[0014]
Furthermore, development of a solid electrolyte battery using an inorganic compound as the solid electrolyte is also underway. For example, in JP-A-8-148180, a compound comprising a transition metal oxide and a transition metal sulfide as a positive electrode active material as a positive electrode, a lithium ion conductive glass solid electrolyte containing Li ₂ S, and a metal alloyed with lithium It has been proposed that an all-solid-state lithium battery having a negative electrode does not generate dendrites in the negative electrode or drop off the active material, and has an excellent charge / discharge cycle life. However, this proposal has problems such as high reactivity with moisture because the positive electrode and the solid electrolyte contain sulfide compounds.
[0015]
Japanese Patent Application Laid-Open No. 5-299101 discloses that a sintered body of Li _{1+ (4-n)} M _x Ti _2-x (PO ₄ ) ₃ excellent in lithium ion conductivity is used as a solid electrolyte. We have proposed lithium batteries with excellent rate discharge characteristics. However, even in such an all solid lithium battery using an oxide inorganic solid electrolyte, there are problems such as inferior energy density and discharge current density as compared with a secondary battery using a conventional nonaqueous solvent as an electrolyte. Have not been put to practical use.
[0016]
Even if the lithium ion conductivity of the inorganic solid electrolyte is improved, the interfacial resistance between the particles and the electrode and the interfacial resistance between the electrodes and the solid electrolyte can be considered as the reasons why the characteristics as a battery are not improved. Even if each material has sufficient characteristics, sufficient characteristics cannot be obtained due to high interface resistance.
[0017]
The present invention has been made in view of such problems of the prior art, and the electrolyte has a low lithium ion conductivity and a low current density. For example, it is necessary to include an organic solvent or a lithium salt which is a lithium ion conductor. An object of the present invention is to provide a lithium battery that solves the conventional problem of the existence of a battery.
[0018]
[Means for Solving the Problems]
In order to achieve the above object, the lithium battery of the invention according to claim 1 is a lithium battery in which a solid electrolyte layer containing lithium is interposed between a pair of electrodes, and the solid electrolyte layer has lithium ion conductivity. an oxide-based crystallized glass having sex, the electrode and the solid electrolyte layer, a lithium battery, wherein the aprotic solvent containing no electrolytic salt including it.
[0019]
In the lithium battery, it is preferable that the electrode includes an electrode active material and a solid electrolyte, and the solid electrolyte layer is made of the same material as the solid electrolyte.
[0020]
In the lithium battery, it is preferable that the solid electrolyte layer is made of an oxide-based crystallized glass having lithium ion conductivity.
[0021]
In the lithium battery, the aprotic solvent is preferably composed of one or more of propylene carbonate, ethylene carbonate, 1,2-dimethoxyethane, dimethyl carbonate, and diethyl carbonate.
[0022]
In the 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 at least one selected from the group consisting of Li ₄ Mn ₅ O ₁₂ is desirable.
[0023]
Conventional organic electrolytes provide electrolytes with lithium ion conductivity by dissolving an electrolyte salt in an aprotic solvent. In the present invention, an aprotic solvent not containing an electrolyte salt is included. It is considered that the battery characteristics are improved only by this, and the lithium ions are moved by an unprecedented conduction mechanism.
[0024]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the lithium battery of the present invention will be described.
FIG. 1 is a cross-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.
[0025]
The package 1 is not limited to a material as long as airtightness can be maintained. For example, a laminate material made of aluminum, a metal such as nickel or aluminum, or a shrink case can be used.
[0026]
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. For example, a metal foil such as aluminum (Al), nickel (Ni), or copper (Cu) can be used. .
[0027]
The positive electrode 2a is made of a powder of a positive electrode active material, and a solid electrolyte powder of the same material as that of the solid electrolyte layer is mixed as necessary. 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 necessary. When mixing the positive electrode or negative electrode active material and the solid electrolyte powder, an improvement in lithium ion conductivity in the electrode is expected, but if the amount of the solid electrolyte powder is excessive, the positive electrode or the positive electrode contributing to the charge / discharge reaction of the battery The amount per volume or weight of the negative electrode active material decreases, and the energy density of the 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 and a binder are added to the positive electrode 2a and the negative electrode 2b as necessary.
[0028]
Examples of the electrode active material used for the positive electrode 2a and the negative electrode 2b include lithium manganese composite oxide, manganese dioxide, lithium nickel composite oxide, lithium cobalt composite oxide, lithium nickel cobalt composite oxide, lithium vanadium composite oxide, Lithium titanium composite oxide, titanium oxide, niobium oxide, vanadium oxide, tungsten oxide, and the like and their inducers can be used. Among the above transition metal oxides, 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), the group consisting of Li ₄ Ti ₅ O ₁₂ or Li ₄ Mn ₅ O ₁₂ is a spinel-based active material in which the crystal system in which the volume change of the active material during charge / discharge is small is good. This shows a good cycle characteristic. Here, there is no clear distinction between the positive electrode active material and the negative electrode active material, and the charge / discharge potentials of two types of compounds are compared with each other indicating a noble potential and the one indicating a base potential as a negative electrode. The battery of arbitrary voltage can be comprised by using.
[0029]
The solid electrolyte powder used in the solid electrolyte layer 3, as 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, 40Li 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 an oxide system such as 65LiNbO ₂ -35SiO ₂ amorphous solid electrolyte and _{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), and Li _{1 + x + y} Al _x Ti _2−x Si _y P _3−y O ₁₂ and other oxide crystallized glass. The solid electrolyte powder is desirably oxide-based crystallized glass from the viewpoint of ionic conductivity.
[0030]
Examples of the conductive agent include acetylene black, graphite, ketjen black, RuO ₂ , SnO ₂ doped with Sb ₂ O ₃ , or In ₂ O ₃ doped with SnO ₂ .
[0031]
Examples of the binder include polyvinylidene fluoride (PVdF), polytetrafluoroethylene (PTFE), polyolefins, and polyimide.
[0032]
As a method for forming the positive electrode 2a, the negative electrode 2b, and the solid electrolyte 3, each powder is dispersed in the binder dispersed in a solvent to form a slurry, and then this slurry is applied onto a substrate film and dried. At this time, the positive electrode 2a, the negative electrode 2b, and the solid electrolyte 3 are each formed and cut, and then laminated by thermocompression bonding or the like, or the positive electrode 2a or the negative electrode 2b is formed and then dried, and the solid electrolyte 3 is formed thereon. And then drying and further forming the negative electrode 2b or the positive electrode 2a thereon. In addition, there is a method in which powder is put into a mold and pressure-molded with a press, or a granulated powder is pressure-molded with a roll press and molded into a sheet.
[0033]
Here, as a base film, metal foils, such as resin films, such as a polyethylene terephthalate, a polypropylene, polyethylene, tetrafluoroethylene, aluminum, stainless steel, copper, can be used, for example.
[0034]
As the aprotic solvent to be included in the positive electrode 2a-solid electrolyte 3-negative electrode 2b, propylene carbonate (PC), ethylene carbonate (EC), 1,2-dimethoxyethane (DME) can be used in consideration of the boiling point and viscosity of the solvent. ), Dimethyl carbonate (DMC), and diethyl carbonate (DEC).
[0035]
Examples of the method of including the aprotic solvent in the laminate of the positive electrode 2a-solid electrolyte 3-negative electrode 2b include a method of dipping the laminate into an aprotic solvent, a method of impregnating the aprotic solvent directly into the laminate, etc. Is mentioned. The amount of the aprotic solvent to be included in the laminate is not particularly limited, but is preferably 0.1 cc or more per 1 cm ² because it is necessary to wet the powder forming the laminate moderately.
[0036]
In an all-solid battery that does not contain an aprotic solvent, lithium ions rely only on bulk movement, but in the lithium battery of the present invention, ions are present at the interface between the particles and the aprotic solvent that wets the particle surface. Is presumed to have moved.
[0037]
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 shape, a square shape, a button shape, a coin shape, a flat shape, or the like.
[0038]
【Example】
[Example 1]
Lithium hydroxide and manganese dioxide are mixed so that the molar ratio of Li and Mn is 1: 2, and this mixture is heated and fired at 900 ° C. in the atmosphere for 15 hours to obtain a lithium manganese composite oxide (LiMn ₂ O ₄ ) Was synthesized as a positive electrode active material. Next, lithium hydroxide and manganese dioxide are mixed so that the molar ratio of Li and Mn is 4: 5, and this mixture is heated and fired at 600 ° C. in the atmosphere for 15 hours to obtain a lithium manganese composite oxide (Li ₄ Mn ₅ O ₁₂ ) was synthesized and used as a negative electrode active material.
[0039]
This LiMn ₂ O ₄ was mixed with Li _{1 + x + y} Al _x Ti _{2 -x} Si _y P _{3 -yO 12} as a solid electrolyte powder in a volume ratio of 8: 2, and this mixed powder Acetylene black and polyvinylidene fluoride (PVdF) were mixed at a weight ratio of 82: 8: 10. Polyvinylidene fluoride (PVdF) used was previously dissolved in N-methylpyrrolidone. Further, 12 g of polyvinylidene fluoride (PVdF) was added to this mixture and mixed to make a slurry. After applying this slurry onto aluminum (Al) by a doctor blade method, polyvinylidene fluoride (PVdF) was dried and formed into a sheet.
[0040]
Further, the solid electrolyte紛末 _{Li 1 + x + y Al x} Ti 2-x Si y P 3-y O 12 polyvinylidene fluoride (PVdF) in a weight ratio of 9 were mixed so that the ratio of 1. Polyvinylidene fluoride (PVdF) was previously dissolved in N-methylpyrrolidone (NMP) as described above. Further, about 15 g of N-methylpyrrolidone (NMP) was added to this mixture and mixed to make a slurry. This slurry was applied onto the above positive electrode by the doctor blade method, laminated, and dried to obtain a laminate of the positive electrode 2a and the solid electrolyte 3.
[0041]
Further, Li ₄ Mn ₅ O ₁₂ is slurried in the same manner as LiMn ₂ O ₄ as the positive electrode active material, applied to the solid electrolyte side of the laminate, laminated and dried, so that the positive electrode 2a-solid electrolyte 3 is obtained. -The laminated body of the negative electrode 2b was obtained. The thickness of the obtained laminate was about 200 μm.
[0042]
The obtained laminate is impregnated with propylene carbonate (PC) to join the positive electrode current collector 4 to the positive electrode 2a of the laminate, and similarly, the negative electrode current collector 5 is joined to the negative electrode 2b. Mounted on aluminum laminate. Two aluminum laminates cut to a size of 35 mm × 35 mm were prepared, the laminate to which the current collector was bonded was sandwiched, and the outer peripheral portion of the aluminum laminate was thermocompression bonded, whereby the 35 mm shown in FIG. A × 35 mm square lithium battery was assembled.
[0043]
[Example 2]
The method for synthesizing the positive electrode active material and the negative electrode active material and the method for forming the positive electrode 2a-solid electrolyte 3-negative electrode 2b were 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 μm. The obtained laminate was impregnated with a mixed solvent of propylene carbonate (PC) and 1,2-dimethoxyethane (DME) (PC: DME = 1: 1 volume ratio). Type lithium battery was assembled.
[0044]
[Comparative Example 1]
The following comparative experiment was conducted for the purpose of confirming the characteristics of a conventional lithium ion battery.
[0045]
The synthesis method of the positive electrode active material and the negative electrode active material was performed in the same manner as in the examples. Further, the solid electrolyte powder was not mixed in the positive electrode and the negative electrode, but an electrode active material, acetylene black, and polyvinylidene fluoride (PVdF) were used, and the mixing ratio was 82: 8: 10 by weight. The positive electrode and negative electrode were produced in the same manner as in the examples. The obtained positive electrode and negative electrode had a thickness of about 30 μm and a coating weight of about 0.048 g.
[0046]
A mixed solvent (PC: DME = 1: 1 volume ratio) of propylene carbonate (PC) and dimethoxyethane (DME) in which LiClO ₄ was dissolved in the resulting positive electrode and negative electrode to a concentration of 1 M / l was used as an electrolyte solution. . 3 cc was dropped and impregnated. Further, a polypropylene non-woven fabric was selected as the separator, and this was impregnated with the same mixed solvent as described above.
[0047]
The positive electrode and the negative electrode impregnated with the electrolytic solution were superposed through a separator to form a positive electrode-electrolyte layer-negative electrode laminate.
[0048]
Thereafter, a rectangular lithium battery was assembled in the same manner as in Example 1.
[0049]
[Comparative Example 2]
The method for synthesizing the positive electrode active material and the negative electrode active material and the method for forming the positive electrode-solid electrolyte-negative electrode were performed in the same manner as in Example 1. The thickness of the obtained positive electrode-solid electrolyte-negative electrode was about 180 μm. Furthermore, roll pressurization was performed for the purpose of improving the filling rate of the laminate and improving 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 evaluation prismatic lithium battery thus obtained, a redox reaction was confirmed with a potentiostat. FIG. 2 shows the results of the redox reaction according to Example 1, FIG. 3 shows the results of the redox reaction according to Example 2, FIG. 4 shows the results of the redox reaction according to Comparative Example 1, and FIG. The result of the oxidation-reduction reaction concerning the comparative example 2 is shown. The measurement conditions were a voltage sweep rate of 10 ^-1 mV / sec, a voltage range of 0 to 1.5 V in Example 1, Example 2 and Comparative Example 1, and 0 to 5 V in Comparative Example 2. did.
[0050]
As a result, in Example 1 and Example 2, it was confirmed that a current associated with redox was obtained and a current value almost equivalent to that of Comparative Example 1 using an organic electrolyte containing an electrolyte salt was obtained. It was done. Furthermore, the decrease in current value is smaller than that of Comparative Example 1, and the lithium battery according to the present invention may have excellent cycle characteristics. In addition, it can be seen that even when compared with the all-solid-state battery of Comparative Example 2, it is markedly superior.
[0051]
The lithium ion conduction mechanism in the lithium battery of the present invention is presumed to be caused by the lithium ion conduction mechanism at the interface between the particle surface and the non-propylene solvent.
[0052]
【The invention's effect】
As described above, according to the lithium battery according to claim 1, since the electrode and the solid electrolyte layer contain the aprotic solvent, the lithium battery is equivalent to the lithium ion battery using the organic electrolyte solution in which the electrolyte salt is dissolved. In addition to the conventional lithium ion conduction mechanism and the absence of electrolyte salt, the electrolyte salt is not decomposed by overvoltage, and a highly reliable lithium battery is obtained.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view showing an embodiment of a lithium battery according to the present invention.
FIG. 2 is a graph showing an oxidation-reduction reaction according to Example 1 of the present invention.
FIG. 3 is a graph showing an oxidation-reduction reaction according to Example 2 of the present invention.
4 is a graph showing an oxidation-reduction reaction according to Comparative Example 1. FIG.
5 is a graph showing an oxidation-reduction reaction according to Comparative Example 2. FIG.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Package, 2 ... Pair of electrodes, 2a ... Positive electrode, 2b ... Negative electrode, 3 ... Solid electrolyte layer, 4 ... Current collector for positive electrode, 5 .... Negative electrode current collector

Claims (4)

A lithium battery in which a solid electrolyte layer containing lithium is interposed between a pair of electrodes,
The solid electrolyte layer is made of an oxide-based crystallized glass having lithium ion conductivity,
Lithium batteries the electrode and the solid electrolyte layer, characterized in including that the aprotic solvent containing no electrolytic salt. 2. The lithium battery according to claim 1, wherein the electrode includes an electrode active material and a solid electrolyte, and the solid electrolyte layer is made of the same material as the solid electrolyte. The said aprotic solvent consists of any 1 type or several types in the propylene carbonate, ethylene carbonate, 1, 2- dimethoxyethane, dimethyl carbonate, and diethyl carbonate, The Claim 1 or Claim 2 characterized by the above-mentioned. Lithium battery. The electrode active material 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. The lithium battery according to claim 1, comprising at least one selected from the group consisting of 6), Li ₄ Ti ₅ O ₁₂ , and Li ₄ Mn ₅ O ₁₂ .

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