JP2011175905A - All-solid lithium ion secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an all solid state lithium ion secondary battery capable of high speed charge / discharge while maintaining a high capacity.
In an all solid-state lithium ion secondary battery in which a plurality of power generating elements in which a positive electrode, a solid electrolyte, and a negative electrode are sequentially stacked are connected via a current collector, the positive electrode and In at least one electrode 1, 3 of the negative electrode 3, conductors 1 a, 3 a are provided in parallel to the main surfaces of the electrodes 1, 3, and the conductors 1 a, 3 a are electrically connected to the current collector 4. It is connected. The conductors 1a and 3a are connected to the current collector 4 by end surface conductors 1b and 3b formed on the side surfaces of the electrodes 1 and 3, or are connected to the current collector 4 by columnar conductors 7 formed in the electrodes 1 and 3. .
[Selection] Figure 1

Description

  The present invention relates to an all solid-state lithium ion secondary battery in which a plurality of power generating elements in which a positive electrode, a solid electrolyte, and a negative electrode are sequentially stacked are connected in series via a current collector.

  In recent years, secondary batteries have been used not only for mobile phones and notebook computers, but also as batteries for electric vehicles. What is commonly required for these secondary batteries is an increase in capacity that is an indicator of long-term use. Methods for increasing the capacity of the secondary battery include a method using an electrode material having a large capacity, application of a positive electrode material exhibiting a high discharge voltage, solidification of an electrolyte, and the like.

  For example, in Patent Document 1, carbon is used as the negative electrode material, and copper powder having a particle size of 0.01 to 20 μm is added to the negative electrode in order to obtain the conductivity of the negative electrode, thereby improving the electron conductivity of the electrode. ing. Moreover, in patent document 2, the improvement of the electronic conductivity of an electrode is aimed at by using the electrode containing the carbon particle which adhered the metal. On the other hand, in Patent Document 3, the internal resistance of the positive electrode is lowered by using, as a positive electrode material, a material in which a conductive film such as carbon is formed on the surface of particles forming the positive electrode by a film forming technique.

Japanese Patent Laid-Open No. 1996-7895 JP 2001-126768 A JP 2000-58063 A

  High capacity and high-speed charging / discharging are very important in the characteristics of all solid-state lithium ion secondary batteries. In order to perform high-speed charging / discharging, conventionally, for example, as described in Patent Documents 1 and 2 above, it is generally performed to add or adhere a conductive material to an electrode substance to improve the conductivity of the electrode. Since conductivity cannot be obtained only by adding a small amount of conductive material, it is necessary to add a large amount of conductive material so that the conductive materials are in contact with each other in the electrode. As a result, the proportion of the conductive material in the electrode is increased, while the proportion of the active material in the electrode is decreased, and when trying to obtain a predetermined capacity, the total weight and volume of the battery are increased. The battery capacity will be reduced if it is intended to fit within a predetermined dimension.

  In Patent Document 3, the surface of the particles forming the positive electrode is covered with a conductive film such as carbon to increase the electron conductivity in the electrode without significantly reducing the capacity of the particles forming the positive electrode. However, in the electrode, high ion conductivity is important for increasing the capacity along with the movement of electrons. When a solid electrolyte is used, if the surface of the particles forming the positive electrode is covered with a conductive film, the conductivity is increased. The conductive film hinders ion conduction in the positive electrode, resulting in a problem that high capacity cannot be obtained.

  An object of the present invention is to provide an all solid-state lithium ion secondary battery capable of high-speed charge / discharge while maintaining a high capacity.

The all-solid-state lithium ion secondary battery of the present invention is an all-solid-state lithium ion secondary battery in which a plurality of power generating elements in which a positive electrode, a solid electrolyte, and a negative electrode are sequentially stacked are connected in series via a current collector. In the present invention, a conductor is provided in parallel with a main surface of the electrode in at least one of the positive electrode and the negative electrode, and the conductor is electrically connected to the current collector. And

  In such an all solid-state lithium secondary battery, a conductor is provided in at least one of the positive electrode and the negative electrode in parallel with the main surface of the electrode, and the conductor is electrically connected to the current collector. Therefore, electrons in the electrode flow through the current collector through a conductor provided in parallel with the main surface of the electrode, and high-speed charge / discharge is possible. In addition, since electrons are conducted through the conductor, the electron density in the electrode is lowered, and the mobility of ions (metal cations) in the electrode is not suppressed by the Coulomb force caused by the electrons. In addition, the conductor thickness in the electrode can be reduced by reducing the thickness and line width of the conductor, minimizing the reduction in the proportion of the active material in the electrode, and high energy density. An all-solid-state lithium ion secondary battery having a capacity can be obtained.

  The all solid-state lithium ion secondary battery according to the present invention is such that at least one of the positive electrode and the negative electrode is made of an inorganic oxide, and the conductor is provided in the electrode made of an inorganic oxide. It is characterized by being. Since the electron conductivity is low when the electrode is made of an inorganic oxide, the electron conductivity in the electrode can be remarkably improved by forming a conductor in the electrode.

  Furthermore, in the all-solid-state lithium ion secondary battery of the present invention, the conductor is formed of a conductor pattern, and a columnar conductor is provided in the electrode in the thickness direction of the electrode. A pattern and the current collector are connected to each other. In such an all-solid-state lithium ion secondary battery, electrons in the electrode flow through the conductor and flow to the current collector through the columnar conductor formed in the thickness direction of the electrode, and therefore, between the conductor pattern and the current collector. The distance is short, which can improve the electron conductivity in the electrode.

  Furthermore, in the all solid-state lithium ion secondary battery of the present invention, the conductor comprises a conductor pattern, and an end face conductor is provided on a side surface of the electrode, and the conductor pattern and the current collector are provided on the end face conductor. It is characterized by being connected to the body. In such an all solid-state lithium ion secondary battery, electrons in the electrode flow through the conductor and flow to the current collector through the end surface conductor on the side surface of the electrode, so that the electron conductivity in the electrode can be improved.

  In the all-solid-state lithium ion secondary battery of the present invention, electrons in the electrode flow through the current collector through the conductor provided in parallel with the main surface of the electrode, enabling high-speed charging / discharging and the conductor. As a result, the electron density in the electrode decreases, and accordingly, the ionic conduction in the electrode increases, and the volume occupation of the conductor in the electrode decreases, resulting in a high energy density. An all-solid-state lithium ion secondary battery having a capacity can be obtained.

It is a longitudinal cross-sectional view of a bipolar all-solid-state lithium ion secondary battery. The connection structure of the conductor and collector in a positive electrode is shown, (a) is a longitudinal cross-sectional view of a positive electrode, (b) is a longitudinal cross-sectional view of a positive electrode. The other connection structure of the conductor and collector in a positive electrode is shown, (a) is a longitudinal cross-sectional view of a positive electrode, (b) is a longitudinal cross-sectional view of a positive electrode. It is a longitudinal cross-sectional view which shows the state which accommodated the all-solid-type lithium ion secondary battery in the storage container.

FIG. 1 is a vertical sectional view of a bipolar all solid-state lithium ion secondary battery. As shown in FIG. 1, an all-solid-state lithium ion secondary battery includes a positive electrode 1 made of at least a positive electrode active material, a solid electrolyte 2 and a negative electrode 3 made of at least a negative electrode active material, which are sequentially stacked and joined together. A plurality of generated power generation elements are connected in series via a current collector 4.

  In general, the positive electrode 1 and the negative electrode 3 are connected by a metal current collector 4. However, a power generation element in which the positive electrode 1, the solid electrolyte 2, and the negative electrode 3 having a self-supporting strength are laminated and integrated is manufactured. In addition, an all-solid-state lithium ion secondary battery can be configured by electrically connecting a plurality of power generation elements in series via the current collector 4.

  In the present invention, three layers of conductors 1 a are formed in the positive electrode 1 in parallel with the main surface of the positive electrode 1, and the three layers of conductors 1 a are connected by an end surface conductor 1 b formed on the side surface of the positive electrode 1. The end face conductor 1b is connected to the current collector 9. Similarly, in the negative electrode 3, three layers of conductors 3 a are formed in parallel to the main surface of the negative electrode 3, and the three layers of conductors 3 a are connected by an end surface conductor 3 b formed on the side surface of the negative electrode 3. The end face conductor 3b is connected to the current collector 9. As materials for the conductors 1a and 3a and the end face conductors 1b and 3b, Cu, Ag-Pd, Ag, W, or the like can be used. Different materials can be used for the positive electrode 1 and the negative electrode 3 as the material of the conductors 1a and 3a and the material of the end face conductors 1b and 3b. The conductors 1a and 3a are formed of a conductor pattern formed by applying a conductor paste, and are thin conductor films. The same applies to the cases of FIGS.

  As shown in FIG. 2A, the conductor 1a is formed in parallel with the main surface of the positive electrode 1 in the positive electrode 1 having a rectangular cross section, and is formed into a straight line, and a plurality of linear conductors 1a. Are formed in parallel. One end of these linear conductors 1 a is exposed on the side surface of the positive electrode 1 and is connected to an end surface conductor 1 b provided on the side surface of the positive electrode 1. The interval L between the seven linear conductors 1a is preferably equal to or less than the thickness of the positive electrode 1.

  Similarly, although not shown, the conductor 3a is formed in parallel with the main surface of the negative electrode 3 in the negative electrode 3 having a rectangular cross-sectional shape, and is formed into a straight line, and a plurality of linear conductors 3a are parallel to each other. Is formed. One end of these linear conductors 3 a is exposed on the side surface of the negative electrode 3, and is connected to an end surface conductor 3 b provided on the side surface of the negative electrode 3. The interval L between the plurality of linear conductors 3 a is desirably equal to or less than the thickness of the negative electrode 3.

  The thickness of the positive electrode 1 is desirably 5 μm or more, preferably 30 μm or more, and more preferably 50 μm or more. When the thickness of the positive electrode 1 is small, the electron travel distance is short, and thus the electron conduction in the positive electrode 1 does not affect the battery performance so much. However, when the thickness is larger than 30 μm or more than 50 μm, the electron conduction in the positive electrode 1 Affects the battery performance, so that the present invention can be preferably used.

  Although the thickness of the negative electrode 3 depends on the negative electrode capacity, the thickness is equal to or greater than that of the positive electrode, the thickness of the solid electrolyte 2 is a thickness that can maintain insulation, and a thickness as thin as possible is preferably 100 to 500 nm. Yes.

  In FIGS. 1 and 2, the conductors 1 a and 3 a are connected to the current collector 4 by the end face conductors 1 b and 3 b, but as shown in FIG. 3, they are provided in the positive electrode 1 in the thickness direction of the positive electrode 1. The conductor 1 a and the current collector 4 are connected by the columnar conductor 7. The same applies to the conductor 3a of the negative electrode 3.

In such an all-solid-state lithium ion secondary battery, the electrons in the electrodes 1 and 3 flow through the conductors 1a and 3a and pass through the columnar conductors 7 formed in the thickness direction of the electrodes 1 and 3 to the current collector 4. Since it flows, the distance between the conductors 1a and 3a and the current collector 4 is short, whereby the electron conductivity in the electrodes 1 and 3 can be improved. In FIG. 3, one columnar conductor 7 is connected to one conductor 1a, 3a, but a plurality of columnar conductors 7 can be connected to one conductor 1a, 3a. In this case, the current flows from the current collector 4 also from the columnar conductor 7, and high-speed charge / discharge is possible.

  In FIG. 1, the conductors 1 a and 3 a are formed on the positive electrode 1 and the negative electrode 2, respectively, but the conductor 1 a or the conductor 3 a may be formed on either the positive electrode 1 or the negative electrode 2.

  Moreover, although FIGS. 1-3 demonstrated the case where the conductors 1a and 3a were formed with the conductor pattern formed by apply | coating a conductor paste, in this invention, the conductors 1a and 3a were braided, for example, conducting wire. You may produce with a mesh. In this case, it can be produced by sandwiching a mesh between sheets forming electrodes and firing. Moreover, a mesh can be arrange | positioned so that it may protrude from the side surface of the electrodes 1 and 3, and the protruded part can be connected with a collector.

  As the positive electrode 1, the solid electrolyte 2, the negative electrode 3, the current collector 4, and the like constituting the all solid-state lithium ion secondary battery, those used in general lithium ion secondary batteries can be used. The positive electrode 1, solid electrolyte 2, negative electrode 3, current collector 4, and the like that can be used in the all solid-state lithium ion secondary battery of this embodiment will be described below.

  As the current collector 4, for example, a conductive adhesive made of a thermoplastic resin and a conductive filler can be used. Moreover, the conductor plate generally used can also be used.

  The positive electrode 1 is composed of at least a positive electrode active material, and a lithium-containing transition metal oxide is preferably used as the positive electrode active material. Specific examples include lithium manganese composite oxide, lithium nickel composite oxide, lithium cobalt composite oxide, lithium nickel cobalt manganese composite oxide, phosphoric acid lithium iron composite oxide, and lithium titanium composite oxide.

  The negative electrode 3 is also made of at least a negative electrode active material. As the negative electrode active material, a carbon material, a transition metal oxide, a lithium-containing transition metal oxide, or the like can be used. In addition, when using metal lithium etc. for a negative electrode active material, what is necessary is just to use a conductor only for a positive electrode.

  The solid electrolyte 2 has no fluidity such as a gel electrolyte obtained by gelling an organic electrolyte with a polymer material, a polymer solid electrolyte obtained by dissolving an electrolyte salt in an ion conductive polymer material, and an inorganic solid electrolyte made of an inorganic material. As long as the electrolytes can be immobilized between the positive and negative electrodes, any of them can be applied, for example, an inorganic solid electrolyte can be dispersed and combined in a polymer solid electrolyte. Among them, the inorganic solid electrolyte is excellent in flame retardancy and non-flammability, and therefore, when used alone, a bipolar all solid lithium ion secondary battery with high safety can be provided, which is preferable.

  Examples of the organic solvent used in the organic electrolyte include ethylene carbonate, propylene carbonate, butylene carbonate, dimethyl carbonate, gamma-butyrolactone, sulfolane, 1,2-dimethoxyethane, 1,3-dimethoxypropane, dimethyl ether, tetrahydrofuran, and 2-methyltetrahydrofuran. , One or a mixture of two or more solvents selected from dimethyl carbonate, diethyl carbonate, and methyl ethyl carbonate. Examples of the electrolyte salt include lithium salts such as LiClO4, LiBF4, LiPF6, LiCF3SO3, LiN (CF3SO2) 2, and LiN (C2F5SO2) 2.

  Examples of the polymer material used for the gel electrolyte include a polymer material having no ion conductivity and a polymer material having ion conductivity, such as polyvinylidene fluoride, polyvinyl chloride, polyacrylonitrile, and polymethyl methacrylate. .

  Examples of the polymer material having ion conductivity include a polymer having an ethylene oxide skeleton represented by polyethylene oxide, a polymer having a propylene oxide skeleton represented by propylene oxide, and a mixture or copolymer thereof. It is done. When producing a polymer solid electrolyte, the same electrolyte salt as the above-mentioned organic electrolyte can be dissolved in these ion conductive polymers.

Examples of inorganic solid electrolytes include crystalline solid electrolytes such as Li1.3Al0.3Ti1.7 (PO4) 3, Li3.6Ge0.6V0.4O4, Li0.35La0.55TiO3, 30LiI-41Li2O-29P2O5 and 40Li2O-35B2O3-25LiNbO3 Oxide-based amorphous solid electrolyte such as 45LiI-37Li2S-18P2S5 and sulfide-based amorphous solid electrolyte such as 1Li3PO4-63Li2S-36SiS2, amorphous thin-film solid electrolyte such as Li ₃ PO _4-x N _x Can be mentioned.

  A method for producing an all solid-state lithium ion secondary battery will be described.

First, for example, a predetermined amount of a binder and a dispersing agent together with a solvent are added to a LiMn ₂ O ₄ powder to prepare a slurry. For example, B, Li, or Si oxide may be added to the slurry as a sintering aid. Thereafter, a green sheet having a thickness of 50 μm, for example, is produced by tape forming with a doctor blade or a coater and drying.

  For example, a Cu paste was printed on the obtained green sheet by, for example, screen printing to form a plurality of conductor patterns. Three layers of green sheets on which these conductor patterns are formed are stacked, and finally a green sheet on which no conductor patterns are formed is stacked, pressed and dried, and then fired to form a positive electrode.

A 300 μm solid electrolyte of Li ₃ PO _4-x N _x is formed on the surface of the positive electrode by, for example, RF sputtering.

Similarly, for the negative electrode, a predetermined amount of a binder and a dispersant are added together with a solvent to a Li ₄ Ti ₅ O ₁₂ powder to prepare a slurry. A sintering aid such as an oxide of B, Li, or Si may be further added to the slurry in the same manner as the positive electrode material. Thereafter, a green sheet having a thickness of, for example, 25 μm is produced by tape forming with a doctor blade, a coater, or the like and drying.

  For example, a Cu paste is printed on the obtained green sheet, for example, by screen printing to form a plurality of conductor patterns. Three green sheets on which these conductor patterns are formed are laminated, and finally, green sheets on which no conductor pattern is formed are laminated, pressed and dried, and then fired to form a negative electrode.

A 300 μm solid electrolyte of Li ₃ PO _4-x N _x is also formed on the surface of the negative electrode by RF sputtering, for example.

  Then, the solid electrolyte formed on the positive electrode and the solid electrolyte formed on the negative electrode are heated and brought into contact with each other to produce a power generation element.

  Thereafter, a conductive adhesive such as carbon is applied to both surfaces of a current collector made of, for example, stainless steel, and a plurality of power generation elements are joined using this, and then, a paste for end face conductors on the side surfaces of the positive electrode and the negative electrode Is printed and heated to form an end face conductor connected to the current collector and the conductor, and an all-solid-state lithium ion secondary battery can be manufactured.

A case where the conductor is connected to the current collector via the columnar conductor will be described. For example, a through hole is formed in a green sheet for forming a positive electrode (which becomes a part of the electrode layer), and a conductor (which becomes a part of a columnar conductor) is printed and embedded in the through hole. A positive electrode can be formed by forming a conductor pattern so as to be connected to a conductor, laminating a plurality of layers of such a conductor and a green sheet on which the conductor pattern is formed, and firing the laminated layer. When it is difficult to connect the conductors filled in the through hole, the land conductor pattern was printed on the exposed portion of the green sheet through which the conductor filled in the through hole was exposed. By laminating the green sheets, the conductor of the through hole and the conductor pattern can be easily connected.

  Several methods are possible for producing a positive electrode or a negative electrode. For example, a film made of polyethylene terephthalate having a releasability by producing a slurry containing a positive electrode active material or a negative electrode active material, a conductive agent and a binder (hereinafter referred to as a film) , PET film), drying, peeling, and applying shape processing as necessary to form a positive electrode or a negative electrode, or a positive electrode active material or a slurry comprising a negative electrode active material and a binder in the same manner. A sintered body made of a positive electrode active material or a negative electrode active material can be produced by applying it on the surface, peeling, shaping and firing, and forming a positive electrode or a negative electrode.

  As the solid electrolyte for joining and integrating the positive electrode and the negative electrode, a gel electrolyte that contains a polymer solid electrolyte, an inorganic solid electrolyte, or an organic electrolyte but loses its fluidity by gelation can be used. Various electrolytes can be used alone, in layers, or in composite form.

  The all solid-state lithium ion secondary battery formed in this way is used by being accommodated in a storage container. As the storage container, any of an exterior body and a current collecting terminal used in a laminate type lithium ion battery or a conventional coin battery can be applied. For example, as shown in FIG. 4, a lid member 21 obtained by processing a metal plate having electronic conductivity made of aluminum, zinc, iron, nickel, stainless steel, or the like by a press molding method and the battery case body 22 are insulative packing 23. It can be produced by caulking and sealing. In FIG. 4, the conductors 1a and 3a are not shown. Further, in FIG. 1, the number of power generation elements in which the positive electrode 1, the solid electrolyte 2, and the negative electrode 3 are sequentially stacked, joined, and integrated is three, but the number of stacks varies depending on the application. There is no particular limitation.

DESCRIPTION OF SYMBOLS 1 ... Positive electrode 1a ... Conductor 1b ... End surface conductor 2 ... Solid electrolyte 3 ... Negative electrode 3a ... Conductor 3b ... End surface conductor 4 ... Current collector 7 ... Columnar shape conductor

Claims (4)

  In an all-solid-state lithium ion secondary battery in which a plurality of power generation elements in which a positive electrode, a solid electrolyte, and a negative electrode are sequentially stacked are connected in series via a current collector, at least one of the positive electrode and the negative electrode An all-solid-state lithium ion secondary battery, wherein a conductor is provided in an electrode in parallel with the main surface of the electrode, and the conductor is electrically connected to the current collector.   The all-solid-state type according to claim 1, wherein at least one of the positive electrode and the negative electrode is made of an inorganic oxide, and the conductor is provided in the electrode made of an inorganic oxide. Lithium ion secondary battery.   The conductor comprises a conductor pattern, and a columnar conductor is provided in the electrode in the thickness direction of the electrode, and the conductor pattern and the current collector are connected to the columnar conductor. The all-solid-state lithium ion secondary battery according to claim 1 or 2.   The conductor comprises a conductor pattern, and an end face conductor is provided on a side surface of the electrode, and the conductor pattern and the current collector are connected to the end face conductor. 2. The all solid state lithium ion secondary battery according to 2.

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