JP5132613B2 - Lithium battery - Google Patents

Description

  The present invention relates to a lithium battery.

  Lithium ion batteries are widely used as power sources for mobile phones and notebook computers, taking advantage of their high energy density.

  These lithium ion batteries have a cylindrical type and a rectangular type, and both of them were inserted into a battery case with a pole group in which a positive electrode and a negative electrode were wound through a separator, and an organic electrolyte was injected and sealed. It has a structure.

This organic electrolytic solution is a mixture of propylene carbonate (PC), dimethyl ethane (DME), diethyl carbonate (DME), ethylene carbonate (EC) or the like as a solvent, and LiClO ₄ , LiPF as a lithium salt. ₆ , LiBF _{4 and the} like are dissolved.

  In recent years, with the demand for thin, lightweight, and compact electronic application devices typified by portable information terminal devices such as video photographing devices, notebook computers, and mobile phones, a pair of positive and negative has been replaced with the organic electrolyte as described above. Attention has been focused on polymer electrolyte batteries in which a polymer electrolyte and an organic electrolyte are mixed between the electrodes.

  However, since these lithium ion batteries and polymer batteries contain an organic electrolyte, they may cause problems such as leakage and smoke generation.

  In order to solve such problems, lithium batteries using an inorganic solid electrolyte as an electrolyte have been actively developed.

  In the lithium battery using such an inorganic solid electrolyte, a lithium battery using a lithium ion conductive inorganic solid electrolyte made of sulfide glass can be mentioned. This inorganic solid electrolyte has a lithium ion conductivity comparable to that of an organic electrolyte. However, sulfide-based glass is highly reactive and has a problem that it easily reacts with moisture and air.

On the other hand, among oxide-based solid electrolytes, lithium ion conductive crystalline solid electrolytes having a crystal structure similar to that of sodium ion conductive solid electrolytes (NASICON-based materials) have recently been 1 × 10 ^−3. Solid electrolytes having lithium ion conductivity of ˜1 × 10 ⁻⁴ S · cm ⁻¹ have been proposed.

For example, in Japanese Patent Laid-Open No. 5-299101, Li _{1+ (4-n) x} M _x Ti _2-x (PO ₄ ) ₃ (M is a monovalent or divalent cation, and n = when M is monovalent) 1 and 1 × 10 ⁻³ to 1 × 10 ⁻⁴ S · cm ⁻ by sintering a granular electrolyte represented by n = 2, x is 0.1 to 0.5 when M is divalent. A lithium ion conductivity of ¹ can be obtained.

In JP-A-10-97811, P ₂ O ₅ , SiO ₂ , TiO ₂ , Al ₂ O ₃ , Li ₂ O and the like having a predetermined composition ratio are melted and molded, and then Li _{1 + x + y} Al _x by heat treatment. by precipitating _{Ti 2-y P 3-y} O 12 (0 ≦ x ≦ 0.4,0 <y ≦ 0.6), 1.0 × 10 - 3 ~2.0 × 10 -3 S · A solid electrolyte having a lithium ion conductivity of cm ⁻¹ is proposed.

Japanese Patent Laid-Open No. 6-1111831 discloses a solid electrolyte in which a positive electrode made of MnO ₂ or a composite oxide of an alkali metal and manganese and a solid electrolyte are integrally formed, and the solid electrolyte is MnO ₂ or an alkali metal and manganese. The lithium oxide is reacted with the composite oxide to form a Li ₂ MnO ₃ layer on the surface of the positive electrode, thereby increasing the contact area of the interface between the positive electrode and the solid electrolyte, thereby reducing the internal resistance of the battery, It has been proposed to improve the charge / discharge characteristics.

  In Japanese Patent Laid-Open No. 8-138724, solid electrolyte powder is added by a solid electrolyte layer or a positive electrode made of a mixture of positive electrode active material powder and solid electrolyte powder and a negative electrode made of a mixture of negative electrode active material powder and solid electrolyte powder. After sandwiching the solid electrolyte layer obtained by pressure forming, pressurization is performed at a temperature not lower than the softening point of the solid electrolyte and not higher than the glass transition point, so that a solid electrolyte layer having low grain boundary resistance is obtained by surface contact. Propose that.

JP-A-6-1111831 JP-A-8-138724

  Conventionally, in the case of a battery using a solid electrolyte, the bonding between the electrode and the solid electrolyte is often formed only by pressure welding, the contact area between the electrode and the solid electrolyte is small, the bonding strength is weak, and the resistance at these interfaces is low. As the battery becomes larger, the internal resistance of the battery increases, and the charge / discharge characteristics are inferior.

  In particular, as the charge / discharge current increases, the voltage drop due to the internal resistance of the battery increases, and there is a problem that the current density is limited.

  Moreover, since many crystalline solid electrolytes have anisotropy in the ion conduction path, the grain boundary resistance in the solid electrolyte becomes a problem. Therefore, a crystalline solid electrolyte often uses a sintered body, and Japanese Patent Laid-Open No. 5-299101 proposes to improve this problem.

  However, this problem of the ion conduction path also applies to the interface between the electrode and the solid electrolyte, and there remains a problem that the resistance of the interface is increased by contact only by pressure welding.

Japanese Patent Laid-Open No. 6-1111831 is a proposal for improving the interfacial resistance between an electrode and a solid electrolyte. In this method, MnO ₂ is formed by sputtering, or Li ₂ MnO ₃ is formed by the aforementioned MnO ₂ . There is a problem that the process is complicated such as reacting with LiOH.

  In JP-A-8-138724, pressure molding is performed at a temperature not lower than the softening point of the solid electrolyte and not higher than the glass transition point. In this case, the grain boundary in the solid electrolyte is reduced, and lithium as the solid electrolyte is reduced. Although the ionic conductivity is improved, there is a problem that in the heat treatment step, a reaction layer is formed at the interface between the electrode and the solid electrolyte, and the reaction layer inhibits lithium ion conduction.

  The present invention has been made in view of the conventional problems as described above, and the conventional problem that the bonding strength between the electrode and the solid electrolyte is weak, the internal resistance as a battery is increased, and the charge / discharge characteristics are inferior. It aims at providing the solid electrolyte battery which eliminated the.

To achieve the above object, the present invention comprises an electrode containing at least an active material and divorced compound, a solid body electrolyte is bonded with the electrode, the silicon compound, the main skeleton of siloxane bond The solid electrolyte is composed mainly of lithium ion conductive crystallized glass, and the solid electrolyte and the active material are bonded via the silicon compound. A lithium battery is provided.

Further, the silicon compound, Ru der those formed by heat-treating the silane compound.

  In addition, a conductive auxiliary agent may be added to the silicon compound.

Further, the solid electrolyte may be met sintered material mainly composed of lithium ion conductive glass-ceramics.

  A lithium battery having a relatively low internal resistance and relatively excellent charge / discharge characteristics can be obtained.

It is sectional drawing which shows one Embodiment of the lithium battery concerning this 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 claim 1. 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 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.

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

  Examples of the active material of the electrode 2 (2a, 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, and lithium titanium. There are composite oxides, titanium oxides, niobium oxides, vanadium oxides, tungsten oxides and the like and their inducers.

Furthermore, in the lithium battery using the solid electrolyte 3, since a separator and an organic electrolyte solution are not used, there is a limitation that allows expansion and contraction of the electrode accompanying charge / discharge. Therefore, as the active material used for the electrode 2 (2a, 2b), 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 , or Li ₄ Mn ₅ O ₁₂ is preferably selected.
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.

  A compound having a siloxane bond (Si—O) as a main skeleton is interposed in the voids of the active material powder. Examples of the compound that forms a siloxane bond include a silane compound. In the silane compound, tetramethoxysilane, methyltrimethoxysilane, dimethyldimethoxysilane, phenyltrimethoxysilane, diphenyldimethoxysilane, tetraethoxysilane, methyltriethoxysilane, dimethyldiethoxysilane, phenyltriethoxysilane, diphenyldiethoxysilane, Examples include hexyltrimethoxysilane.

The joining of the electrode 2 and the solid electrolyte 3 is not performed by pressure bonding or a reaction layer, but is formed by a compound having a skeleton bond as a main skeleton interposed in the voids of the active material powder.
This siloxane bond is formed by heat treatment, and at the same time forms a bond between the active material powder and the electrode and the solid electrolyte.

  When a siloxane bond is formed, it is not necessary to raise the temperature excessively, the reaction between the electrode 2 and the solid electrolyte 3 can be suppressed, and the compound having a siloxane bond as the main skeleton can also suppress the reaction with the electrode active material. .

  Further, a compound having a siloxane bond as a main skeleton intervening in the voids of the electrode active material can form a strong bond with the lithium ion conductive crystallized glass and can strengthen the bonding between the electrode 2 and the solid electrolyte 3. . Therefore, the internal resistance of the battery can be reduced by increasing the contact area of the interface.

The solid electrolyte 3 is roughly classified into a sulfide type and an oxide type. The sulfide-based solid electrolyte has a lithium ion conductivity at room temperature of 1 × 10 ⁻³ S · cm ^−1, which is comparable to that of an organic electrolyte, but has a problem of hygroscopicity. . Therefore, it is desirable to use an oxide system for the solid electrolyte 3. Among them, the amorphous solid electrolyte has a lithium ion conductivity of about 1 × 10 ⁻⁶ S · cm ⁻¹ at room temperature, and it is difficult to satisfy the characteristics sufficiently. On the other hand, a crystalline solid electrolyte has a lithium ion conductivity of about 1 × 10 ⁻³ S · cm ⁻¹ to 1 × 10 ⁻⁴ S · cm ⁻¹ at room temperature. Therefore, the solid electrolyte 3 to be used is more preferably a crystalline solid electrolyte, and in particular has lithium ion conductivity including lithium (Li), titanium (Ti), phosphorus (P) and oxygen (O) elements. A crystalline solid electrolyte is desirable, 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), Li _{1 + x + y} M _x Ti _2-x Si _y P _3-y O ₁₂ (here M is Al, Ga, 0 ≦ x ≦ 0.4, 0 <y ≦ 0.6), Li _{1+ (4-n)} M _x Ti _2-x (PO ₄ ) ₃ (M is monovalent or 2 Valent cation), and the like.

An electron conduction aid is added to the electrode 2 (2a, 2b). Examples of the electron conduction assistant include SnO ₂ , In ₂ O ₃ , TiO _2-x , ZnO, Fe ₃ O ₄ , ReO ₃ , MoO ₂ , RuO ₂ , VO, WO ₂ as an oxide, and carbon as a carbon material. Black, graphite, etc. are mentioned, but in order to obtain a stable low resistivity, one or more of RuO ₂ , SnO ₂ doped with Sb ₂ O ₃ , or In ₂ O ₃ doped with SnO ₂ It is desirable to include. Moreover, when using an oxide, it is desirable that the addition amount as an electron conduction support agent is 10-50 wt% with respect to an active material. When the amount of the electron conduction assistant is less than these addition amounts, the electron conductivity is not sufficiently imparted. When the amount is more than these addition amounts, the electron conduction can be ensured, but the electron conduction aid is between the electrode active materials. It is not preferable because it may interfere with lithium ion conduction.

As a production method of the electrode 2 (2a, 2b), a positive electrode and a negative electrode active material powder and, if necessary, an electron conduction assistant powder are mixed in advance and dispersed in a silane compound, and then the conditions of 80 to 150 ° C. Is dried to obtain a mixed powder obtained by evaporating the methyl group or ethyl group in the silane as alcohol. The obtained mixed powder adjusts a slurry together with water or a solvent and a molding aid, and heats the one cut after the slurry is applied on a base film and dried. Alternatively, the obtained mixed powder is directly or granulated, put into a mold, subjected to pressure molding with a press, and then heat-treated.
Alternatively, after the granulated mixed powder is pressure-formed with a roll press machine and processed into a sheet shape, the sheet is cut and heat-treated.

  As the molding aid that can be used here, a general organic binder for granulating ceramics can be used.

  Moreover, 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.

  The solid electrolyte 3 is produced by the same method as that for the electrodes 2 (2a, 2b). Although the temperature of the heat treatment of the solid electrolyte depends on the composition and the particle size of the powder, it is preferably about 800 ° C. to 1200 ° C.

  In addition, the electrode 2 (2a, 2b) and the solid electrolyte 3 are not only heat-treated alone, but also processed after being laminated in a state where the sintered solid electrolyte 3 is sandwiched between the positive electrode 2a and the negative electrode 2b in the formed form. It doesn't matter.

  Examples of the heat treatment method for producing the positive electrode 2a-solid electrolyte 3-negative electrode 2b include heat treatment under normal pressure and heat treatment with pressurization. In particular, the heat treatment by pressurization improves the filling rate of the electrode active material and increases the contact area of the particles, so that a wider lithium ion conduction path can be secured and the internal resistance of the battery can be reduced.

  Here, 300 to 650 ° C. is appropriate as the heat treatment temperature, and 3 to 30 MPa is appropriate when pressurization is performed.

  The solid electrolyte 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.

[Example 1] Lithium hydroxide and manganese dioxide were mixed so that the molar ratio of Li and Mn was 1.1: 1.9, and this mixture was heated and fired at 650 ° C. for 15 hours in the atmosphere. Manganese composite oxide (Li _1.1 Mn _1.9 O ₄ ) was synthesized and used 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. for 15 hours in the atmosphere to thereby obtain a lithium manganese composite oxide (Li ₄ Mn ₅ O ₁₂ ) was synthesized and used as a negative electrode active material.

The obtained active material was dispersed in tetramethoxysilane together with RuO _{2 serving} as an electron conduction aid and dried at a temperature of 120 ° C. for about 3 hours to obtain a mixed powder. The mixing ratio of the active material powder, RuO ₂ and tetramethoxysilane at this time was 1: 1: 2 by weight.

  The obtained mixed powder was dispersed in a solvent in which a molding aid was dissolved to prepare a slurry. Next, this slurry was formed into a green tape shape by a doctor blade method, and this green tape was further cut into a size of 25 mm × 25 mm to obtain a formed electrode. The thickness at this time was about 60 μm.

As the solid electrolyte 3, a crystalline solid electrolyte whose main crystal phase is represented by Li _{1 + x + y} Al _x Ti _2−x Si _y P _3−y O ₁₂ was used. A powdered solid electrolyte was dispersed in a solvent in which a molding aid was dissolved to prepare a slurry. This slurry was formed into a green tape shape by a doctor blade method to obtain a solid electrolyte product. The thickness at this time was about 60 μm. Furthermore, this green tape was cut into a size of 35 mm × 35 mm and fired at a temperature of 1250 ° C. for 2 hours to obtain a sintered body of the solid electrolyte 3. The thickness of the sintered body at this time was about 46 μm, and the size was 29 mm × 29 mm.

  Subsequently, the positive electrode and negative electrode produced in the above-described manner were laminated so as to sandwich the solid electrolyte sintered body and subjected to pressure heat treatment to obtain a laminate of positive electrode 2a-solid electrolyte 3-negative electrode 2b. The pressure heat treatment was carried out at a temperature of 350 ° C. for 3 hours, followed by debinding for 3 hours at a temperature of 600 ° C. for 20 minutes and a pressure load of 50 MPa. The thickness of the laminated body at this time was about 130 μm, and shrinkage only in the thickness direction was confirmed.

  The positive electrode current collector 4 was joined to the positive electrode 2a of the laminated body, and the negative electrode current collector 5 was similarly joined to the negative electrode 2b to be attached to the aluminum laminate of the package 1. Two aluminum laminates cut to a size of 35 mm × 35 mm were prepared, and the outer periphery of the aluminum laminate was thermocompression bonded with the laminate to which the current collector was bonded, so that the 35 mm × 1 mm shown in FIG. A 35 mm square solid electrolyte battery was assembled.

  [Comparative Example 1] The positive electrode active material and the negative electrode active material were synthesized in the same manner as in Example 1.

  The electrode was formed by the following procedure. The positive electrode and negative electrode active materials obtained above and carbon black were each dispersed in N-methyl-2-pyrrolidone in which polyvinylidene fluoride was dissolved to prepare a slurry. At this time, the mixing ratio of the electrode active material, carbon black, and polyvinylidene fluoride was 85: 12: 7 by weight.

  The obtained slurry was applied onto an aluminum foil by a doctor blade method, and N-methyl-2-pyrrolidone was removed to obtain positive and negative electrodes. Furthermore, roll pressurization was performed for the purpose of improving the powder filling rate of the obtained electrode active material, and the obtained electrode sheet was cut into a size of 25 mm × 25 mm to obtain an electrode. Each of the obtained electrodes had a thickness of 40 μm.

  Similarly to the electrode, the solid electrolyte was dispersed in N-methyl-2-pyrrolidone in which polyvinylidene fluoride was dissolved to prepare a slurry. At this time, the mixing ratio of the solid electrolyte and polyvinylidene fluoride was 93: 7 by weight.

  The obtained slurry was applied onto the positive electrode obtained previously, and N-methyl-2-pyrrolidone was removed to obtain a positive electrode-solid electrolyte laminate. Furthermore, the negative electrode obtained previously was stacked on the solid electrolyte side of the laminate, and pressurized at a temperature of 160 ° C. for the purpose of improving adhesion. The pressure load at this time was 80 MPa. The thickness of the positive electrode-solid electrolyte-negative electrode laminate obtained was 105 μm excluding the thickness of the aluminum foil serving as the current collector.

  A rectangular solid electrolyte battery was assembled in the same manner as in Example 1 using the obtained laminate.

  [Comparative Example 2] The synthesis of the positive electrode active material and the negative electrode active material was carried out in the same manner as in Example 1.

The electrode was formed by the following procedure. Low melting point glass (glass transition point of about 480 ° C.) represented by the composition of B ₂ O ₃ —SiO ₂ —Li ₂ O—ZnO ₂ —Al ₂ O ₃ as the previously obtained positive and negative electrode active materials and firing aid A slurry was prepared by dispersing the powder and further RuO ₂ as an electron conducting agent in a solvent in which a molding aid was dissolved. At this time, the mixing ratio of the electrode active material, the low melting point glass, and the RuO ₂ was 60:10:30 by weight. This slurry was formed into a green tape shape by a doctor blade method.

  The thickness at this time was about 65 μm. Further, this green tape was cut into a size of 35 mm × 35 mm to obtain a positive electrode and a negative electrode.

  The sintered body of the solid electrolyte was produced in the same manner as in Example 1. Next, the positive electrode and the negative electrode obtained in the above were stacked in the form of sandwiching the sintered body of the solid electrolyte and subjected to heat treatment to obtain a positive electrode 2a-solid electrolyte 3-negative electrode 2b laminate. The heat treatment was carried out at a temperature of 350 ° C. for 3 hours and then at a temperature of 580 ° C. for 30 minutes to obtain a positive electrode-solid electrolyte-negative electrode laminate. The thickness of the laminated body at this time was about 125 μm.

  A rectangular solid electrolyte battery was assembled in the same manner as in Example 1 using the obtained laminate.

(Evaluation) thus using the obtained rectangular solid electrolyte battery, the charge and discharge device, 100 .mu.A / cm ² as the charging condition, 200 .mu.A / cm ^2, 1 in the current 500 .mu.A / cm ² to the square solid electrolyte battery of the foregoing Charge up to 5V, stop charging and hold for 5 minutes after the voltage reaches 1.5V, then discharge to 0.5V with the same current as when charging, then charge up to 1.5V again Then, after reaching this voltage, a charge / discharge cycle evaluation was performed in which charging was stopped and held for 5 minutes.

  The results are shown in Table 1. In addition, the number in a table | surface shows the discharge capacity with respect to each discharge current, and a unit is mAh.

  From the above, it can be seen that the lithium battery of the present invention is excellent in charge / discharge characteristics. In particular, even when the discharge current is increased, the decrease in the discharge capacity is remarkable.

  This is considered to be because the electrode and the solid electrolyte can be joined by interposing a compound having a siloxane bond as the main skeleton in the gap between the positive electrode and the negative electrode active material, and the interface resistance is further reduced. Furthermore, according to the present invention, since a siloxane bond is formed in the process of heat treatment, the reaction with the electrode active material is unlikely to occur, and the electrode active material powder is bonded and the electrode and the solid electrolyte are bonded while maintaining the original characteristics of the electrode active material. It is thought that bonding is performed.

DESCRIPTION OF SYMBOLS 1 ... Package 2 ... A pair of electrode 2a ... Positive electrode 2b ... Negative electrode 3 ... Solid electrolyte layer 4 ... Positive electrode collector 5 ... Negative electrode collector

Claims (3)

An electrode containing at least an active material and a silicon compound;
A solid electrolyte joined to the electrode,
The silicon compound is an inorganic compound having a siloxane bond as a main skeleton formed by heat-treating a silane compound ,
The solid electrolyte is mainly composed of lithium ion conductive crystallized glass,
The lithium battery, wherein the solid electrolyte and the active material are bonded via the silicon compound. The lithium battery according to claim 1, wherein a conductive auxiliary agent is added to the silicon compound. The solid electrolyte is a lithium battery according to claim 1 or 2, characterized in that a sintered body composed mainly of the lithium ion conductive glass-ceramics.