JP2010080376A - Electrochemical device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide means which controls occurrence of short circuit in an electrochemical device such as a lithium ion secondary battery provided with an electrode containing needle-like active particles like whiskers. <P>SOLUTION: The electrochemical device includes a laminated body provided with a positive electrode, a separator, and a negative electrode stacked in this order. At least one of the positive electrode and the negative electrode includes a collector and an active material layer which is joined to a surface of the collector and includes needle-like active material particles. The active material layer is further filled with a solid electrolyte. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an electrochemical device. In particular, the present invention relates to improvements for improving the reliability of electrochemical devices.

  In recent years, in order to cope with air pollution and global warming, reduction of the amount of carbon dioxide has been strongly desired. In the automobile industry, there is a great expectation for reducing carbon dioxide emissions by introducing electric vehicles (EV) and hybrid electric vehicles (HEV), and the development of secondary batteries for motor drive that holds the key to commercialization of these is thriving. Has been done.

  As a secondary battery for driving a motor, a lithium ion secondary battery having the highest theoretical energy among all the batteries is attracting attention, and is currently being developed rapidly. Generally, a lithium ion secondary battery includes a positive electrode in which a positive electrode active material or the like is applied to both surfaces of a positive electrode current collector using a binder, and a negative electrode in which a negative electrode active material or the like is applied to both surfaces of a negative electrode current collector using a binder. However, it has the structure which is connected through the electrolyte layer which consists of a separator holding electrolyte (lithium salt), and is accommodated in a battery case.

  By the way, although it is not related to a lithium ion secondary battery, a technique using nano-sized whiskers as an electrode material of a redox capacitor has been proposed (see, for example, Patent Document 1). Here, according to JIS H 0400, “whisker” is defined as “a single crystal fine metal fiber growth product”. From the same idea, it is conceivable to use a whisker-like material as an active material of a lithium ion secondary battery. However, if a battery is simply formed using a whisker-like active material without any treatment, the following problems occur due to the shape of the active material. That is, the separator of a lithium ion secondary battery is generally made of a single resin microporous film. The average pore diameter of the pores of such a separator is usually about 0.1 to 15 μm as disclosed in Patent Document 2, for example. When the above-mentioned whisker-like active material is used in combination with a separator made of a microporous film having pores of this size, whiskers enter the pores of the separator and pass through the separator and short-circuit between the positive and negative electrodes May occur.

Patent Document 3 discloses a technique in which a needle-like active material is embedded in a polymer in advance for the purpose of preventing the occurrence of a short circuit. However, depending on such means, there is a problem that even if the occurrence of a short circuit is suppressed, the cycle durability of the battery is lowered.
JP 2005-252217 A JP 2005-268096 A JP-A-8-505227

  Accordingly, the present invention provides an electrochemical device such as a lithium ion secondary battery in which needle-like active material particles such as whiskers are present on an electrode, while generating a short circuit while minimizing a decrease in battery cycle durability. It aims at providing the means which can suppress.

  The present inventors have intensively studied to solve the above problems. In the process, an attempt was made to join acicular active material particles (whiskers, etc.) used as an active material to the surface of a current collector in an electrode of an electrochemical device such as a lithium ion secondary battery. And on that, it discovered that the said subject could be solved by filling the active material layer containing the said particle | grain with a solid electrolyte, and came to complete this invention.

  That is, the electrochemical device of the present invention has a laminate in which a positive electrode, an electrolyte layer, and a negative electrode are laminated in this order. At least one of the positive electrode and the negative electrode includes a current collector and an active material layer including needle-like active material particles bonded to the surface of the current collector. Furthermore, the active material layer is characterized in that it is filled with a solid electrolyte.

  According to the present invention, in an electrochemical device such as a lithium ion secondary battery, when the solid electrolyte prevents the needle-like active material particles from protruding, the needle-like active material particles such as whiskers are present on the electrode. Even so, the occurrence of a short circuit can be suppressed. Further, contact between the current collector and the active material particles is ensured, and a decrease in cycle durability is also suppressed.

  Hereinafter, embodiments of the present invention will be described. However, the technical scope of the present invention should be determined based on the description of the scope of claims, and is not limited to the following embodiments.

  Hereinafter, the present invention will be described in detail with reference to the drawings, taking a nonaqueous electrolyte lithium ion secondary battery as an example. In the present specification, the drawings are exaggerated for convenience of explanation. Therefore, the technical scope of the present invention is not limited to the form shown in the drawings, and embodiments other than the drawings can be adopted.

  FIG. 1 is a schematic cross-sectional view schematically showing the overall structure of a lithium ion secondary battery according to an embodiment of the present invention.

  The lithium ion secondary battery 10 of this embodiment shown in FIG. 1 has a structure in which a substantially rectangular battery element 21 in which a charge / discharge reaction actually proceeds is sealed inside a laminate sheet 29 that is an exterior.

  As shown in FIG. 1, the battery element 21 of the lithium ion secondary battery 10 of the present embodiment includes a plurality of single battery layers 19. The unit cell layer 19 includes an electrolyte layer 17, a positive electrode active material layer 13 formed on one surface of the electrolyte layer 17, and a negative electrode active material layer 15 formed on the other surface of the electrolyte layer 17. The A positive electrode current collector 33 is disposed between the positive electrode active material layers 13, and a negative electrode current collector 35 is disposed between the negative electrode active material layers 15. That is, the battery element 21 includes a plurality of single battery layers 19 and a plurality of current collectors (a positive electrode current collector 33 and a negative electrode current collector 35).

  Further, the positive electrode current collector 33 and the negative electrode current collector 35 are electrically connected to the positive electrode tab 25 and the negative electrode tab 27, respectively. The battery element 21 is sealed with a laminate sheet 29 as an exterior so that the positive electrode tab 25 and the negative electrode tab 27 are led out to the outside.

  In the lithium ion secondary battery 10 shown in FIG. 1, the negative electrode active material layer 15 is slightly smaller than the positive electrode active material layer 13, but is not limited to such a form. A negative electrode active material layer 15 that is the same as or slightly larger than the positive electrode active material layer 13 may also be used.

  Hereinafter, although the member which comprises the lithium ion secondary battery 10 of this embodiment is demonstrated easily, it is not restrict | limited only to the following form, A conventionally well-known form can be employ | adopted similarly.

[Current collector]
The current collectors (33, 35) are made of a conductive material. In addition to the same current collecting function as in a normal lithium ion secondary battery, this current collector (33, 35) can also be used as a metal substrate to which needle-like active material particles contained in an active material layer to be described later are joined. Function.

  There is no restriction | limiting in particular in the material which comprises an electrical power collector (33, 35). For example, silicon (Si), manganese (Mn), aluminum (Al), chromium (Cr), indium (In), silver (Ag), gallium (Ga), tin (Sn), copper (Cu), scandium (Sc) ) Or germanium (Ge), zinc (Zn), and any combination thereof. These are metals having a high vapor pressure. By evaporating these metals and precipitating them on the surface of the metal substrate, acicular active material particles (hereinafter also referred to as “whiskers”) contained in the active material layer described later are formed. Can be formed. Further, as will be described later, when oxygen is present in the atmosphere during the precipitation, oxide whiskers can be formed.

  Furthermore, a metal substrate that does not contain the above-described material that can form whiskers by itself may be used. Examples of such materials include iron (Fe), cobalt (Co), nickel (Ni), platinum (Pt), palladium (Pd), rhodium (Rh), titanium (Ti), molybdenum (Mo), and tungsten. (W).

  Further, the size of the current collector is determined according to the intended use of the battery. For example, if it is used for a large battery that requires a high energy density, a current collector having a large area is used.

  There is no particular limitation on the thickness of the current collector (33, 35). The thickness of the current collector is usually about 1 to 100 μm.

  As shown in FIG. 1, in the battery having a power generation element formed by laminating a plurality of single battery layers, the electrode located in the outermost layer does not participate in the battery reaction, so in the current collector located in the outermost layer, The active material layer only needs to exist inside the power generation element.

[Active material layer]
In the present embodiment, one of the features is that the active material layer includes acicular active material particles. In the present specification, “needle-like active material particles” mean active material particles having an aspect ratio (c = a / b) of 5 or more of the particle major axis (a) of the active material particles to the particle minor axis (b). To do. The acicular active material particles are also referred to as nanowires or nanorods. Such active material particles have a large specific surface area. Therefore, there is an advantage that the output characteristics of the battery can be improved by adopting such an active material. On the other hand, when the aspect ratio becomes too large, the number of particles that may penetrate through the separator also decreases as the number of active material particles contained in the active material layer decreases. From such a viewpoint, the aspect ratio (c) described above is preferably 10 to 100,000, more preferably 20 to 10,000, in order to further exert the effects of the present invention. However, it goes without saying that these ranges may be excluded.

The constituent material of the acicular active material particles contained in the positive electrode active material layer 13 is not particularly limited, and a conventionally known material can be similarly used as the positive electrode active material of the lithium ion secondary battery. Examples of the positive electrode active material include lithium-transition metal composite oxides such as LiMn ₂ O ₄ and LiNiO ₂ , lithium-transition metal phosphate compounds, and lithium-transition metal sulfate compounds. By using such a material, the energy density of the battery can be improved, and a battery having an excellent balance between output characteristics and capacity characteristics can be provided. In some cases, two or more positive electrode active materials may be used in combination. Of course, other positive electrode active materials may be used (see below).

  The constituent material of the acicular active material particles contained in the negative electrode active material layer 15 is not particularly limited, and a conventionally known material can be used as the negative electrode active material of the lithium ion secondary battery. Examples of the negative electrode active material include metal oxides such as tin oxide, zinc oxide, indium oxide, tungsten oxide, and vanadium oxide, carbon materials such as graphite, soft carbon, and hard carbon, lithium-transition metal compounds as described above, Examples thereof include metal materials and lithium-metal alloy materials. In some cases, two or more negative electrode active materials may be used in combination. Of course, negative electrode active materials other than those described above may be used (see below).

  In the present embodiment, acicular active material particles (hereinafter also simply referred to as “whiskers”) included in the active material layer have a form formed and bonded to the surface of a metal substrate as a current collector.

  The whisker can be formed by evaporating the metal component constituting the metal base as the current collector described above and depositing it on the surface of the metal base. Further, when oxygen is present in the atmosphere during precipitation, oxide whiskers can be formed.

  Here, as a form of the whisker formed on the surface of the metal base described above, a configuration having a spherical head at the tip of the trunk or a configuration of only the trunk is exemplified. However, in addition to these, a branched shape, a molding shape, a hairball shape, or the like may be used. In addition, if the function of the metal substrate as a current collector and other manufacturing processes are not hindered by the formation of the whisker, the whisker is basically formed at any part of the surface of the metal substrate as the current collector. sell.

  As the constituent material of the whisker, for example, a material mainly composed of the metal element or its oxide contained in the above-described metal substrate is exemplified. According to such a form, the whisker is continuously formed from the metal substrate. In addition, since the whisker forming component is the same as the constituent material of the surface portion of the metal substrate, the adhesion strength between the metal substrate and the whisker can be increased, and the durability can be improved. In the present specification, the “main component” means about 50 to 100% by mass.

  On the other hand, a whisker forming layer (for example, a tin plating layer) containing the element that is the main component of the whisker described above may be disposed on the surface of the metal substrate. According to such a form, whisker can be formed even when the whisker forming component is not included in the metal substrate. Further, as described above, since the whisker forming component is the same as the constituent material of the surface portion of the metal substrate, the adhesion strength between the metal substrate and the whisker can be increased, and the durability can be improved. In addition, as long as the whisker as the acicular active material particles is continuously formed from the metal substrate as the current collector, the present embodiment in which the whisker forming layer is disposed between the whiskers is also included in the technical scope of the present invention. Can be included.

  Here, as the element that is the main component of the whisker, for example, tin, zinc, indium, tungsten, vanadium, silicon, manganese, aluminum, chromium, silver, gallium, copper, scandium, or germanium, and any combination thereof Such a thing is mentioned.

  There is no restriction | limiting in particular about the size of the whisker as an acicular active material particle. However, the length of the whisker described above (corresponding to the particle long diameter (a)) is preferably 0.1 to 1000 μm, more preferably 1 to 500 μm, and further preferably 5 to 200 μm. Moreover, the particle | grain short diameter (b) of the said acicular active material particle becomes like this. Preferably it is 10 nm-10 micrometers, More preferably, it is 20 nm-2 micrometers, More preferably, it is 30-500 nm. In this specification, the size of the acicular active material particles (whiskers) is observed in several to several tens of fields using an observation means such as a scanning electron microscope (SEM) or a transmission electron microscope (TEM). The value calculated as the average value of the measured values in the active material particles is adopted.

  Thus, there is no restriction | limiting in particular about the method of forming a whisker in the surface of a metal base | substrate, A conventionally well-known knowledge can be referred suitably. For example, whiskers can be formed on the surface of the metal substrate by heat-treating the metal substrate or a precursor thereof under reduced pressure or in an inert gas atmosphere. At this time, when heat treatment is performed in the presence of a small amount of oxygen, whiskers made of the oxides of the elements described above are formed. Note that “metal substrate or its precursor” is described in consideration of the case where the composition of the metal substrate changes due to heat treatment. Here, the “trace amount of oxygen” is usually an oxygen amount of 1 to 1000 volume ppm, although it varies depending on the element used as the whisker raw material and its content. Moreover, heat processing can be normally performed in 700-1100 degreeC.

  Further, when the whisker is formed on the surface of the metal substrate, preferably, a whisker forming layer containing an element that is a main component of the oxide whisker is disposed on the surface of the metal substrate or a precursor thereof, and the whisker forming layer Oxide whiskers are preferably formed on the surface (see Examples described later). According to such a form, even if the metal base does not contain a whisker forming material, the whisker can be formed at any part of the metal base by disposing the whisker forming layer on the surface of the metal base. .

  In a preferred embodiment, whiskers made of the above-described metal element oxide (for example, tin oxide, zinc oxide, indium oxide, tungsten oxide, vanadium oxide, etc.) are similarly formed on the surface of the above-described metal substrate, and the negative electrode Used for. In particular, tin oxide can be preferably used. Such a metal oxide has a large capacity as an active material. For this reason, when these materials are used as the negative electrode active material, the energy density of the battery can be improved. At this time, the whisker corresponds to the acicular negative electrode active material particles, and the metal substrate corresponds to the negative electrode current collector.

  In the lithium ion secondary battery 10 of the present embodiment, the active material layers (13, 15) are filled with a solid electrolyte.

The solid electrolyte is not particularly limited as long as it is an electrolyte containing a solid component capable of conducting lithium ions. Examples of solid electrolytes include polymer electrolytes and various ceramics (for example, lithium-containing sulfide glass, LISICON (Li ₁₄ Zn (GeO ₄ ) ₄ ), Thio-LISICON, etc.) and the like.

  Especially, a polymer electrolyte is classified into the polymer gel electrolyte containing electrolyte solution, and the polymer solid electrolyte which does not contain electrolyte solution. The polymer electrolyte can be preferably used in that it has high ion conductivity and is easy to form.

  The polymer gel electrolyte has a configuration in which a liquid electrolyte is injected into a matrix polymer having lithium ion conductivity. By having such a configuration, the polymer gel electrolyte is preferable because it can achieve ion conductivity equivalent to that of a normal liquid electrolyte and can improve the output characteristics of the battery.

Examples of the matrix polymer having lithium ion conductivity include polyethylene oxide (PEO), polypropylene oxide (PPO), and copolymers thereof. In such a matrix polymer, an electrolyte salt such as a lithium salt can be well dissolved. Here, the liquid electrolyte contained in the gel electrolyte has a form in which a lithium salt as a supporting salt is dissolved in an organic solvent as a plasticizer. Examples of the organic solvent used as the plasticizer include carbonates such as ethylene carbonate (EC) and propylene carbonate (PC). Examples of the supporting salt (lithium salt) include LiN (SO ₂ C ₂ F ₅ ) ₂ , LiN (SO ₂ CF ₃ ) ₂ , LiPF ₆ , LiBF ₄ , LiClO ₄ , LiAsF ₆ , LiSO ₃ CF _{3 and the} like. It is done. When the polymer gel electrolyte is filled in the active material layer, the polymer gel electrolyte is preferably 3 to 20% by mass, more preferably 4 to 15% by mass of the matrix polymer based on the total amount of 100% by mass. %, More preferably 5 to 10% by mass. By setting it as such a form, generation | occurrence | production of a short circuit can be prevented, maintaining the output of a battery at a high value.

  On the other hand, the polymer solid electrolyte has a structure in which a supporting salt (lithium salt) is dissolved in the above matrix polymer, and does not include an organic solvent that is a plasticizer. Therefore, when a polymer solid electrolyte is employed as the solid electrolyte, there is no risk of liquid leakage from the battery, and the battery reliability can be improved.

  A matrix polymer of a polymer gel electrolyte or a polymer solid electrolyte can exhibit excellent mechanical strength by forming a crosslinked structure. In order to form a crosslinked structure, thermal polymerization, ultraviolet polymerization, radiation polymerization, electron beam polymerization, etc. are performed on a polymerizable polymer (for example, PEO or PPO) for forming a polymer electrolyte, using an appropriate polymerization initiator. A polymerization treatment may be performed.

  In manufacturing the lithium ion secondary battery of the present embodiment, first, a metal substrate having whiskers formed on the surface as described above is prepared. On the other hand, an electrolyte layer forming composition containing a solid electrolyte is prepared. When it is desired to fill the active material layer with the polymer solid electrolyte, the electrolyte layer forming composition may be prepared by mixing a matrix polymer and, if necessary, a polymerization initiator or a volatile solvent. In addition, when it is desired to fill the active material layer with the polymer gel electrolyte, in addition to this, the above-described composition for forming an electrolyte layer containing the liquid electrolyte may be prepared. Then, the prepared electrolyte layer forming composition is applied to the side of the metal substrate where the whiskers are formed, and polymerized (such as heat treatment or light irradiation treatment) as necessary, to thereby obtain a polymer solid electrolyte or polymer. An active material layer filled with a gel electrolyte can be formed.

  The active material layer may further contain an additive as necessary. Examples of the additive that can be contained in the active material layer include a binder and a conductive additive. Examples of the binder include polyvinylidene fluoride (PVdF) and a synthetic rubber binder. A conductive support agent means the additive mix | blended in order to improve the electroconductivity of an active material layer. Examples of the conductive assistant include carbon materials such as carbon black such as acetylene black, graphite, and vapor grown carbon fiber. When the active material layer contains a conductive additive, an electronic network inside the active material layer is effectively formed, which can contribute to improvement of the output characteristics of the battery. However, in the present invention, when the active material layer includes acicular active material particles (whiskers), the conductivity of the active material layer is relatively ensured by the acicular shape of the whiskers. Therefore, the present invention also has an advantage that conductivity can be ensured without adding a conductive additive to the active material layer.

  The compounding ratio of the components contained in the active material layer is not particularly limited. The blending ratio can be adjusted by appropriately referring to known knowledge about lithium ion secondary batteries.

  The thickness of each active material layer (13, 15) is not particularly limited, and conventionally known knowledge about lithium ion secondary batteries can be appropriately referred to. As an example, the thickness of each active material layer (13, 15) is about 2 to 100 μm.

[Electrolyte layer]
The electrolyte layer 17 functions as a partition for preventing a short circuit between the positive electrode active material layer 13 and the negative electrode active material layer 15. Conventionally, in a battery using acicular active material particles (whiskers) as an active material, there is a problem in that a short circuit occurs in a single cell layer and a battery voltage decreases because the whisker penetrates a separator constituting the electrolyte layer. It was happening. On the other hand, according to the present invention, since the active material layer is filled with the solid electrolyte, whisker protrusion from the active material layer is suppressed, and a short circuit in the single cell layer, which has been a problem in the past, is suppressed. sell.

  In the lithium ion secondary battery of the present embodiment, the electrolyte layer 17 includes an electrolyte. The electrolyte layer 17 may be composed of the above-described solid electrolyte (polymer gel electrolyte or polymer solid electrolyte), or may be composed of an electrolyte other than the solid electrolyte (that is, a liquid electrolyte). When the electrolyte layer 17 contains a solid electrolyte, there is an advantage that handling becomes easy and the risk of liquid leakage from the battery can be reduced. This advantage is particularly remarkable when the electrolyte layer 17 is composed of a solid polymer electrolyte. On the other hand, from another viewpoint, when the electrolyte layer 17 contains a liquid electrolyte (that is, the electrolyte layer is composed of a polymer gel electrolyte or a liquid electrolyte), lithium ion conductivity in the electrolyte layer can be improved. As a result, the output characteristics of the battery can be improved, which is preferable.

  When the electrolyte layer 17 includes a liquid electrolyte, a separator can be used as the base of the electrolyte layer 17. As the separator, a conventionally known separator can be used as it is. However, it is of course possible to use a separator that has been devised to prevent short-circuiting due to the above whiskers.

  There is no restriction | limiting in particular about the material of a separator, A conventionally well-known knowledge can be referred suitably. As a preferable form, the form which comprises a separator from resin is mentioned. According to such a form, it is excellent in the handling property of a separator resulting from the softness | flexibility of resin. Examples of the resin that can constitute the separator include olefin-based polyethylene, polypropylene, fluorine-based polytetrafluoroethylene, polyvinylidene fluoride, polyimide, polyamide, polyamideimide, and cellulose. Of course, other materials may be used.

  There is no particular limitation on the thickness of the separator. As an example, the thickness of the separator is about 5 to 100 μm.

[tab]
In the lithium ion secondary battery 10, a laminate sheet 29 in which the tabs (the positive electrode tab 25 and the negative electrode tab 27) electrically connected to the current collectors (33, 35) are the exterior for the purpose of taking out current outside the battery. It is taken out outside. Specifically, the positive electrode tab 25 electrically connected to the positive electrode current collector 33 and the negative electrode tab 27 electrically connected to the negative electrode current collector 35 are taken out of the exterior.

  The material constituting the tabs (the positive electrode tab 25 and the negative electrode tab 27) is not particularly limited, and a known material conventionally used as a tab for a lithium ion secondary battery can be used. Examples of the constituent material of the tab include aluminum, copper, titanium, nickel, stainless steel (SUS), and alloys thereof. Note that the same material may be used for the positive electrode tab 25 and the negative electrode tab 27, or different materials may be used. Further, as in the present embodiment, separately prepared tabs (25, 27) may be connected to the current collectors (33, 35), or the current collectors may be extended to form tabs.

[Positive electrode and negative electrode lead]
If necessary, a positive terminal lead and a negative terminal lead may be used. For example, when a positive electrode tab and a negative electrode tab that are output electrode terminals are directly taken out from each current collector, the positive electrode terminal lead and the negative electrode terminal lead may not be used.

  As the positive electrode terminal lead and the negative electrode terminal lead, a terminal lead used in a conventionally known lithium ion battery can be used. It should be noted that the portion taken out from the laminate sheet 29 has a heat insulating property so as not to affect a product (for example, an automobile part, particularly an electronic device, etc.) by contacting with peripheral devices or wiring and causing leakage. It is preferable to coat with a heat shrinkable tube or the like.

[Exterior]
In the lithium ion secondary battery 10, the battery element 21 is preferably housed in an exterior such as a laminate sheet 29 in order to prevent external impact and environmental degradation during use. The exterior is not particularly limited, and a conventionally known exterior can be used. A polymer-metal composite laminate sheet or the like excellent in thermal conductivity can be preferably used in that heat can be efficiently transferred from a heat source of an automobile and the inside of the battery can be rapidly heated to the battery operating temperature.

  In addition, there is no restriction | limiting in particular about the manufacturing method of the lithium ion secondary battery 10 of embodiment of this invention mentioned above, It can manufacture with reference to conventionally well-known knowledge in the manufacturing field of a battery.

  Moreover, when the electrochemical device of the present invention is a lithium ion secondary battery, the battery may be a bipolar battery.

  FIG. 2 is a schematic cross-sectional view schematically showing the entire structure of a bipolar battery according to an embodiment of the present invention, but the technical scope of the present invention is not limited to such a form.

  As shown in FIG. 2, in the battery element 21 of the bipolar battery 10 ′ of this embodiment, the positive electrode active material layer 13 is formed on one surface of the current collector 11 and the negative electrode active material layer 15 is formed on the other surface. A plurality of bipolar electrodes. Each bipolar electrode is laminated via an electrolyte layer 17 to form a battery element 21. At this time, each bipolar type is formed such that the positive electrode active material layer 13 of one bipolar electrode and the negative electrode active material layer 15 of another bipolar electrode adjacent to the one bipolar electrode face each other through the electrolyte layer 17. An electrode and an electrolyte layer 17 are laminated.

  The adjacent positive electrode active material layer 13, electrolyte layer 17, and negative electrode active material layer 15 constitute one unit cell layer 19. Accordingly, it can be said that the bipolar battery 10 ′ has a configuration in which the unit cell layers 19 are electrically connected in series via the surface. Therefore, a high output can be obtained as compared with the parallel connection type battery shown in FIG. The current collector (outermost layer current collector) (11a, 11b) located in the outermost layer of the battery element 21 has a positive electrode active material layer 13 (positive electrode side outermost layer current collector 11a) or a negative electrode only on one side. One of the active material layers 15 (negative electrode side outermost layer current collector 11b) is formed.

  Further, in the bipolar battery 10 ′ shown in FIG. 2, the positive electrode outermost layer current collector 11 a is extended to form a positive electrode tab 25, which is led out from a laminate sheet 29 that is an exterior. On the other hand, the negative electrode side outermost layer current collector 11 b is extended to form a negative electrode tab 27, which is similarly derived from the laminate sheet 29.

[Insulation layer]
In the bipolar battery 10 ′, an insulating layer 31 is usually provided around each single battery layer 19. The insulating layer 31 prevents the adjacent current collectors 11 in the battery from coming into contact with each other or a short circuit caused by a slight irregularity at the end of the unit cell layer 19 in the battery element 21. Is provided. By installing such an insulating layer 31, long-term reliability and safety are ensured, and a high-quality bipolar battery 10 ′ can be provided.

  The insulating layer 31 may be made of a material having insulating properties, sealing properties against falling off of the solid electrolyte, sealing properties against moisture permeation from the outside (sealing properties), heat resistance at the battery operating temperature, and the like. For example, urethane resin, epoxy resin, polyethylene resin, polypropylene resin, polyimide resin, rubber or the like can be used. Among these, polyethylene resin and polypropylene resin are preferably used as the constituent material of the insulating layer 31 from the viewpoints of corrosion resistance, chemical resistance, ease of production (film forming property), economy, and the like.

(Storage module; battery pack)
A plurality of the lithium ion secondary batteries (10, 10 ′) described above may be electrically connected to form an assembled battery that is a power storage module.

  FIG. 3 is a perspective view showing an assembled battery according to an embodiment of the present invention.

  As shown in FIG. 3, the assembled battery 40 is configured by connecting a plurality of the lithium ion secondary batteries (10, 10 '). Each lithium ion secondary battery is connected by connecting the positive electrode tab and the negative electrode tab of each lithium ion secondary battery using a bus bar. On one side surface of the assembled battery 40, electrode terminals (42, 43) are provided as electrodes of the entire assembled battery 40.

  The connection method in particular when connecting the some lithium ion secondary battery which comprises an assembled battery is not restrict | limited, A conventionally well-known method can be employ | adopted suitably. For example, a technique using welding such as ultrasonic welding or spot welding, or a technique of fixing using rivets, caulking, or the like can be employed. According to such a connection method, the long-term reliability of the assembled battery can be improved.

  According to the assembled battery of the present invention, an assembled battery having excellent long-term reliability can be provided by using the lithium ion secondary battery as an assembled battery.

  In addition, connection of all the batteries which comprise an assembled battery may be connected in parallel, all may be connected in series, Furthermore, you may combine series connection and parallel connection.

[vehicle]
The battery and the assembled battery (storage module) described above can be mounted on a vehicle. A battery mounted on a vehicle can be used as a power source for driving a motor of the vehicle, for example.

  As a vehicle using a battery or a battery pack as a motor power source, for example, a complete electric vehicle that does not use gasoline, a hybrid vehicle such as a series hybrid vehicle or a parallel hybrid vehicle, and a vehicle whose wheels are driven by a motor, such as a fuel cell vehicle Is mentioned. In some cases, it may be employed as a power source for other transport equipment such as a motorcycle and a train.

  For reference, FIG. 4 shows a schematic diagram of an automobile 50 on which the assembled battery 40 is mounted. The assembled battery 40 mounted on the automobile 50 has the characteristics as described above. For this reason, mounting the assembled battery 40 on the automobile 50 can improve the long-term reliability of the automobile 50.

  As described above, the electrochemical device of the present invention has been described in detail by taking a lithium ion secondary battery as an example, but the present invention can also be applied to other electrochemical devices. For example, the present invention can be applied to capacitors such as electric double layer capacitors and redox capacitors. In addition, the present invention can also be applied to a fuel cell by supporting a catalyst component such as platinum on the surface of the above-mentioned acicular active material particles and using this as a conductive catalyst layer filled with a solid electrolyte. is there. In such a fuel cell, the output characteristics can be improved and the risk of a short circuit can be reduced.

  The effects of the present invention will be described using the following examples and comparative examples. However, the technical scope of the present invention is not limited to only the forms shown in the following examples.

<Example 1>
By the following method, an electrode in which whiskers as acicular active material particles were formed on the surface of a metal substrate as a current collector was produced.

First, lithium manganate (LiMn ₂ O ₄ ) (particle size: 1 μm, 85% by mass) as a positive electrode active material, acetylene black (10% by mass) as a conductive additive, and polyvinylidene fluoride (PVdF) as a binder ( 5 mass%) was mixed, and then an appropriate amount of N-methyl-2-pyrrolidone (NMP) which is a slurry viscosity adjusting solvent was added to prepare a positive electrode active material slurry.

  In addition, an aluminum foil (thickness: 20 μm) was prepared as a positive electrode current collector. The positive electrode active material slurry prepared above was applied to one surface of the prepared current collector by a doctor blade method to form a coating film. Next, this coating film was dried to form a positive electrode active material layer (thickness: 30 μm). Thereafter, the obtained laminate was punched out with a diameter of 15 mm to obtain a positive electrode precursor.

  On the other hand, a nickel substrate (thickness: 100 μm) was prepared as a metal substrate as a current collector. Next, a tin plating process was performed on one surface of the nickel substrate to form a tin plating layer (thickness: 20 μm). Thereafter, the tin-plated nickel substrate was heated to 800 ° C. in a 100% argon atmosphere, and maintained for 1 hour in a 100 volume ppm oxygen atmosphere after the temperature rising, and tin oxide needle crystals ( Whisker). The photograph (magnification: 1000 times) which observed the obtained whisker using the scanning electron microscope (SEM) is shown in FIG. The whisker-formed substrate thus obtained was punched out with a diameter of 16 mm to obtain a negative electrode precursor. The aspect ratio of whiskers formed on the substrate was about 2000.

Next, as an electrolytic solution, a solution was prepared by dissolving LiBF ₄ which is a lithium salt in an equal volume mixed solution of ethylene carbonate (EC) and propylene carbonate (PC) at a concentration of 1 mol / L. The electrolyte solution (97% by mass) was added to a polyethylene oxide macromonomer (3% by mass) as an ion conductive polymer and azobisisobutyronitrile (AIBN) (0.05% by mass) as a thermal polymerization initiator. ) Was added and mixed to prepare an electrolyte layer forming composition.

  Then, the prepared composition for forming an electrolyte layer is applied to the surface of each of the active material layers of the positive electrode precursor and the negative electrode precursor prepared above, and heat-treated at 80 ° C. for 1 hour in a vacuum. Ethylene oxide macromonomer was cross-linked to produce a polymer gel electrolyte. Thereby, the positive electrode and the negative electrode were completed.

  Separately, a uniaxially stretched polypropylene microporous membrane (thickness: 24 μm, porosity: 60%, flexion degree: 1.7) was prepared as a separator.

  The positive electrode, separator, and negative electrode prepared above were laminated in this order so that the positive electrode active material layer and the negative electrode active material layer (side on which the whiskers were formed) faced, and the electrolyte solution prepared above was added to the obtained laminate. The battery element was produced by pouring. The obtained battery element was sealed in a 2032 type coin cell to complete the battery of this example.

<Example 2>
A battery was produced in the same manner as in Example 1 except that the blending amount in the composition for forming an electrolyte layer was an electrolytic solution (95% by mass) and a polyethylene oxide macromonomer (5% by mass).

<Example 3>
A battery was produced in the same manner as in Example 1 except that the blending amount in the composition for forming an electrolyte layer was an electrolytic solution (90% by mass) and a polyethylene oxide macromonomer (10% by mass).

<Example 4>
A battery was produced in the same manner as in Example 1 except that the blending amount in the composition for forming an electrolyte layer was an electrolytic solution (80% by mass) and a polyethylene oxide macromonomer (20% by mass).

<Example 5>
A battery was produced in the same manner as in Example 1 except that the blending amount in the composition for forming an electrolyte layer was an electrolytic solution (70% by mass) and a polyethylene oxide macromonomer (30% by mass).

<Comparative Example 1>
The implementation described above, except that the tin oxide needle-like crystals (whiskers) grown on the substrate were once peeled off from the substrate using a spatula and then subjected to the operation after application of the electrolyte layer forming composition. A battery was produced in the same manner as in Example 1.

<Comparative example 2>
The implementation described above, except that the tin oxide needle-like crystals (whiskers) grown on the substrate were once peeled off from the substrate using a spatula and then subjected to the operation after application of the electrolyte layer forming composition. A battery was produced in the same manner as in Example 5.

<Comparative Example 3>
A battery was produced in the same manner as in Example 1 except that the above-described electrolyte solution was used instead of the electrolyte layer forming composition.

<Evaluation>
Ten batteries were manufactured for each of the above-described examples and comparative examples. And each battery was left to stand for 4 days in the state hold | maintained at 4V, and the voltage drop in that case was measured. The results are shown in Table 1 below. In Table 1, for each of the examples / comparative examples, the voltage drop values of 10 batteries are classified by dividing the range.

  Further, after measuring the voltage drop as described above, the resistance value of the battery was measured. Thereafter, a charge / discharge test of 20 cycles was further performed, and the maintenance rate (capacity maintenance rate) of the battery capacity after 20 cycles with respect to the battery capacity before the test was calculated. These results are shown in Table 2 below.

  As shown in Table 1, according to the lithium ion secondary battery which is one type of the electrochemical device according to the present invention, even when whisker-shaped needle-shaped active material particles are used as the negative electrode active material, the battery It shows that the voltage drop (that is, the deterioration of the output characteristics) can be suppressed. In the battery according to the present invention, the acicular active material particles are bonded to a substrate as a current collector, and the active material layer is filled with a solid electrolyte to suppress the protrusion of the acicular active material particles from the active material layer. ing. By doing so, it is considered that the penetration of the separator by the whisker is suppressed and the minute short circuit inside the single cell layer is prevented, and as a result, the battery voltage is prevented from being lowered.

  On the other hand, in the batteries of Comparative Examples 1 and 2, the decrease in battery voltage was comparable to that of the battery of the present invention. However, in the battery of Comparative Example 3, a significant decrease in battery voltage was observed. This is presumably because the whisker could not prevent the separator from penetrating due to the fact that the active material layer did not contain a solid electrolyte, and an internal short circuit occurred in the single cell layer.

  In addition, the results shown in Table 2 indicate that the cycle durability at the end of 20 cycles can be maintained at a relatively high value according to the lithium ion secondary battery which is one type of electrochemical device according to the present invention. It is. It is also shown that the resistance value of the battery can be suppressed to a relatively low value.

  On the other hand, in the battery of Comparative Example 3, results similar to those of the battery according to the present invention were observed in both capacity retention ratio and battery resistance value. However, in the batteries of Comparative Examples 1 and 2, the result that the capacity maintenance rate was extremely low was observed, indicating that the cycle durability was poor. This is considered to be because the interface between the current collector and the active material was peeled off due to the expansion and contraction of the active material due to charge and discharge.

  In summary, according to the lithium ion secondary battery according to an embodiment of the present invention, even when a needle-like active material is used, occurrence of a short circuit is suppressed while minimizing a decrease in cycle durability. It is shown that it can be effectively prevented.

1 is a schematic cross-sectional view schematically showing the entire structure of a lithium ion secondary battery according to an embodiment of the present invention. 1 is a schematic cross-sectional view schematically showing the overall structure of a bipolar battery according to an embodiment of the present invention. It is a perspective view which shows the assembled battery which is one Embodiment of this invention. It is the schematic of the motor vehicle carrying the assembled battery shown in FIG. It is the photograph (magnification: 1000 times) which observed the whisker obtained in Example 1 using the scanning electron microscope (SEM).

Explanation of symbols

10 Lithium ion secondary battery,
10 'bipolar lithium ion secondary battery,
11 Current collector,
11a, 11b outermost layer current collector,
13 positive electrode active material layer,
15 negative electrode active material layer,
17 electrolyte layer,
19 cell layer,
21 battery elements,
25 positive electrode tab,
27 negative electrode tab,
29 Laminate sheet,
31 insulating layer,
33 positive electrode current collector,
35 negative electrode current collector,
40 battery packs,
42, 43 electrode terminals,
50 cars.

Claims (15)

An electrochemical device having a laminate in which a positive electrode, an electrolyte layer, and a negative electrode are laminated in this order,
At least one of the positive electrode or the negative electrode has a current collector and an active material layer containing acicular active material particles bonded to the surface of the current collector, and a solid electrolyte is formed in the active material layer. An electrochemical device characterized by being filled.   2. The electrochemical device according to claim 1, wherein an aspect ratio (c = a / b) of a particle major axis (a) to a particle minor axis (b) of the acicular active material particles is 10 to 100,000.   The electrochemical device according to claim 1, wherein the solid electrolyte includes a polymer electrolyte.   The electrochemical device according to claim 3, wherein the solid electrolyte is a polymer gel electrolyte.   The electrochemical device according to claim 4, wherein the polymer gel electrolyte contains 3 to 20% by mass of a matrix polymer based on a total amount of 100% by mass.   The electrochemical device according to claim 1, wherein the electrolyte layer includes a solid electrolyte.   The electrochemical device according to claim 1, wherein the electrolyte layer includes a liquid electrolyte.   Acicular active material particles in which the active material layer of the positive electrode is made of a material selected from the group consisting of a lithium-transition metal composite oxide, a lithium-transition metal phosphate compound, and a lithium-transition metal sulfate compound. The electrochemical device according to claim 1, comprising:   The electrochemical device according to any one of claims 1 to 8, wherein the active material layer of the negative electrode includes acicular active material particles composed of a metal oxide.   The electrochemical device according to claim 9, wherein the metal oxide is one or more metal oxides selected from the group consisting of tin oxide, zinc oxide, indium oxide, tungsten oxide, and vanadium oxide. .   The electrochemical device according to any one of claims 1 to 10, which is a nonaqueous electrolyte secondary battery.   The electrochemical device according to claim 11, which is a lithium ion secondary battery.   The electrochemical device according to any one of claims 1 to 10, which is a capacitor.   The electrical storage module using the electrochemical device of any one of Claims 1-13.   The vehicle carrying the electrochemical device of any one of Claims 1-13, or the electrical storage module of Claim 14.