JP2014239022A - Power storage device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To solve the problem in which, although an expensive resin separator is not necessary when an electrode surface has insulation properties, there is a risk in which a collector exposed to an electrode end is brought in contact with a counter electrode and a power storage device may cause an internal short circuit.SOLUTION: In the power storage device, either of a positive electrode and a negative electrode is an insulating electrode whose electrode surface has insulating properties, two sheets adjacent to the insulating electrode have electrode ends that is hardened by resin to be of an envelope shape, and a counter electrode is accommodated in the electrode of the envelope shape.

Description

    The present invention relates to a power storage device, and particularly to a power storage element of a power storage device.

    Lithium-ion batteries, which have been widely used as power sources for electronic devices such as mobile phones and notebook computers, have recently become large-scale power storage devices for electric vehicles and power storage (hereinafter collectively referred to as secondary batteries and capacitors). It is expected to be used for a power storage device), and improvement of output density (W / L), reduction of price and improvement of safety of lithium ion batteries are important issues.

    The active material greatly affects the price and safety of the power storage device. An “active material” in a power storage device is a substance that directly contributes to a power storage reaction, and can be classified into a material that undergoes a chemical change reversibly based on an electrochemical redox reaction and a material that does not undergo a chemical change. In general, an active material based on a chemical change (electrochemical change) follows Faraday's law of electrolysis, and therefore has a larger electrochemical capacity (mAh / g) than an active material not based on a chemical change.

    A power storage device that uses an active material based on an electrochemical chemical change for both the positive electrode and the negative electrode is a “secondary battery (or simply a battery)”. On the other hand, power storage devices that use active materials that are not based on chemical changes are called “capacitors”, but power storage devices that use active materials based on chemical changes only on one side of the negative electrode are also generally classified as “capacitors”. Is done.

A capacitor is noted as a power storage device that surpasses a secondary battery in terms of output density (W / L) and cycle characteristics, but its energy density (Wh / L) is small. Therefore, in order to increase the energy density (= storage capacity) of the capacitor, a hybrid capacitor using an active material (for example, TiO ₂ —B, Li ₄ Ti ₅ O _12, etc.) based on a chemical change as a negative electrode has been proposed ( Non-patent documents 1 and 2). However, even if only the negative electrode active material capacity is increased, it is difficult to reach the energy density required for electric vehicles, power storage, and the like, and such a large power storage device must be expected for a secondary battery.

The lithium ion battery is a secondary battery system in which lithium ions (Li ⁺ ) present in the active material of the positive electrode move to the negative electrode by charging and return to the positive electrode again by discharging. Such a secondary battery system has already been proposed before 1980. In a charged state, a specific ion is biased to a negative electrode (or positive electrode), and in a discharged state, it is biased to a positive electrode (or negative electrode). "It was called" but has not been put into practical use for a long time. "

The inventors of this application succeeded in commercializing this rocking chair battery for the first time in the world using LiCoO ₂ for the positive electrode and carbon for the negative electrode, and named it “Lithium ion battery”. A press release was made in February 1990. In March of the same year, at the third secondary battery seminar held in Florida, the present inventor first introduced the excellent performance of lithium ion batteries to the world (see Non-Patent Documents 3 to 4). Nowadays, all rocking chair batteries using various positive and negative electrode materials are called lithium ion batteries.

In order to reduce the price of a lithium ion battery (rocking chair battery), a low-price type has been put into practical use by replacing the positive electrode active material with an inexpensive material such as LiMn ₂ O ₄ or LiFePO ₄ from LiCoO ₂ . Moreover, regarding the improvement of safety, proposals have been made to replace the negative electrode active material from carbon to a ceramic material (for example, TiO ₂ —B, Li ₄ Ti ₅ O _12, etc.) (see Non-Patent Documents 5 to 11).

    In addition to the active material, there are separators that relate to improvements in output density (W / L) of power storage devices, price reduction, and safety improvement. In the power storage device, the positive electrode and the negative electrode facing each other must be conducted by ion conduction and not conducted by electron conduction. Therefore, generally, a sheet-like “separator” is interposed between the positive electrode and the negative electrode facing each other. Lithium-ion batteries use a special porous membrane with a “separator function” made of polyethylene (PE) or polypropylene (PP) as the separator, but such resin separators are expensive and the use of separators The amount greatly affects the battery price. The “separator function” is a function that cuts off electronic conduction while securing a conduction path for ion conduction between the positive electrode and the negative electrode.

    In order to increase the output density (W / L) of a lithium ion battery, it is effective to increase the electrode area. However, the amount of separator used increases in proportion to the electrode area, and the battery price is high. Become.

    In lithium-ion batteries (rocking chair batteries), a system with a low operating voltage may be said to be relatively safe, but a battery with a low operating voltage is relatively used as a separator per storage capacity (Wh). Will increase the battery price.

For example, a lithium ion battery using the above-described Li ₄ Ti ₅ O ₁₂ as a negative electrode active material has been attracting attention as being expected to have high safety (see Non-Patent Documents 5 to 9), but the operating voltage is carbon. Since it is about 2/3 of the material battery, the amount of separator used per Wh increases 1.5 times. Therefore, if Li ₄ Ti ₅ O ₁₂ is used as the negative electrode active material, the battery price increases even if the safety of the lithium ion battery is improved.

    Furthermore, in order to ensure the safety of the lithium ion battery, the low heat resistance of the resin separator is a major obstacle. Lithium-ion batteries must avoid internal shorts, external shorts, overcharging, etc., which can lead to sudden heat generation of the battery, but only internal shorts that occur inside the battery cannot be controlled from the outside. .

    In fact, lithium ion battery smoke and fire accidents are likely due to an internal short circuit. In lithium-ion batteries that use current resin separators, even if the positive and negative electrodes are slightly short-circuited by minute conductive foreign matter, the resin separator partially heat-shrinks due to a partial increase in temperature at the short-circuited location. Then, there is a possibility that the internal short circuit becomes serious and the battery runs out of heat, resulting in a fire accident or the like.

    Therefore, a method has been proposed in which a non-electron conductive (electron insulating) ceramic layer is formed on the electrode surface to increase the heat resistance of the separator function (see Non-Patent Document 12). The ceramic layer formed on the electrode surface has high heat resistance and can be formed at low cost by applying a ceramic slurry to the electrode surface. Therefore, there is a possibility that the cost of the separator function can be reduced and the heat resistance can be improved at the same time.

    Usually, an electrode of a power storage device has an active material layer formed of an active material formed on a current collector. If the active material is electronically conductive, the electrode surface becomes electronically conductive, Even if it is non-electron conductive, the active material layer is usually formed by mixing a conductive additive, so that the electrode surface is still electronically conductive. Therefore, it is necessary to interpose a “separator” between the positive electrode and the negative electrode facing each other.

    However, if one electrode surface of the positive electrode or the negative electrode is electronically insulative, even if the positive electrode and the negative electrode facing each other are in direct contact, the electronic conduction between the positive electrode and the negative electrode is interrupted, and the electrolyte solution is connected to the positive electrode and the negative electrode. Is impregnated, the ionic conduction between the positive electrode and the negative electrode is ensured. Therefore, a separator function is provided without interposing a “separator” between the positive electrode and the negative electrode facing each other.

    In order to make the electrode surface electronically insulating, an electronically insulating ceramic layer may be formed on the surface of the electron conductive electrode. Further, if the active material is non-electron conductive, the electrode surface becomes electronically insulating if the active material layer is formed without mixing the conduction aid. Therefore, if the surface of one of the positive electrode and the negative electrode is made electronically insulating even in the lithium ion battery, a resin separator is unnecessary, and the improvement of the safety and the price reduction of the lithium ion battery can be realized at the same time.

In general, a material having an electric conductivity of less than 10 ⁻¹⁰ S / cm is called an insulator, and “electron insulating” or “non-electron conductive” in this specification means an electron conductivity of 10 ^It means less than ⁻¹⁰ S / cm, and an electron conductivity of 10 ⁻¹⁰ S / cm or more is usually classified as a semiconductor (electron conductivity is about 10 ³ to 10 ⁻¹⁰ S / cm). Including, it is referred to as “electron conductivity” in this specification.

Masayuki Abe, others, Proceedings of the 53rd Battery Discussion Meeting, 288 (2012) Yoshiyuki Otsuki, others, Proceedings of the 53rd Battery Discussion Meeting, 292 (2012) Nagaura, JEC Battery Newsletter No. 2 (Mar.-Apr.) 1990 Nagaura, Progress in Batteries & Solar Cells, Vol. 9, P.I. 209, 1990, Norio Takami, others, Toshiba Review Vol. 63 No. 12 (2008) Yoshinori Tachida, et al., Proceedings of the 53rd Battery Discussion Meeting, 238 (2012) Kenta Shibukawa and others, Proceedings of the 53rd Battery Discussion Meeting, 240 (2012) Ryuta Ito, et al., Proceedings of the 53rd Battery Conference, 241 (2012) Yoshihiro Kadoma and others, Proceedings of the 53rd Battery Conference 242 (2012) Yoshiyuki Nakano, et al., Proceedings of the 53rd Battery Discussion Meeting, p. 245 (2012) Yasuyuki Furuya, et al., Proceedings of the 53rd Battery Discussion Meeting, p. 246 (2012) Yujiro Toyoda, et al., Proceedings of the 53rd Battery Conference, 2 (2012)

    In a power storage device in which a positive electrode and a negative electrode face each other, when the power storage element is configured as an electrode stack in which three or more electrodes are stacked, the electrode constituting the power storage element usually collects an active material layer. It is formed by continuously forming on the electric body and punching to the required electrode dimensions. In this case, even if the electrode surface is an electronic insulating electrode, the conductive current collector is exposed at the electrode end.

    However, if the electrode laminate is configured by interposing a sheet-like separator between the electrodes, the current collector exposed at the electrode end contacts the counter electrode if the sheet-like separator is made larger than the electrode dimensions. Thus, there is almost no case where the power storage device is internally short-circuited.

    However, in an electrode laminate in which a positive electrode and a negative electrode are laminated without a sheet separator, even if the electrode surface is an electronic insulating electrode, the current collector exposed at the electrode end is in contact with the counter electrode. There is a risk that the power storage device will short-circuit inside.

    Therefore, even in a battery using an electrode whose surface is electronically insulating, a sheet-like separator must be used together in order to avoid an internal short circuit. Even if the electrode surface uses an electronic insulating electrode, the combined use with the sheet-like separator does not lead to cost reduction of the separator function.

    The present invention has been made in view of the above problems, and its object is to expose the electrode surface at the electrode end without using a sheet-like separator in a power storage device using an electronically insulating electrode. An object of the present invention is to provide an electrode laminate in which a current collector is not in contact with a counter electrode.

    In the power storage device in which the power storage element is configured as an electrode laminate in which three or more electrodes are stacked, at least one of the positive electrode and the negative electrode constituting the electrode stack is an electrode whose surface is electronically insulating, In the electrode laminate, the two adjacent electrodes are in an envelope shape with the electrode ends being hardened with a resin, and the counter electrode is contained in the envelope-shaped electrode. It is characterized by. Hereinafter, an electrode whose surface is electronically insulating is also referred to as an “insulating electrode”.

    In the power storage device according to the present invention, the power storage element is configured as an electrode laminated body in which three or more electrodes are stacked, and in such an electrode laminated body, an electrode (positive electrode or negative electrode) whose electrode surface is electronically insulating is adjacent thereto. The two sheets are made into an envelope shape with the electrode ends hardened with resin. Since the inside of the envelope-shaped electrode is surrounded by an electronic insulating electrode surface and resin, it is completely electronic insulating. On the other hand, since the counter electrode (negative electrode or positive electrode) is housed in the envelope-shaped electrode, even if the electrode surface and the electrode end surface of the counter electrode are electronically conductive, the positive electrode and the negative electrode are not electrically connected. . Therefore, according to the present invention, the sheet-like separator is unnecessary, and the improvement of the safety and the price reduction of the lithium ion battery can be realized at the same time.

    Problems other than those described above and solutions and effects thereof will be described in more detail with reference to the following embodiments.

    It is a front view of the electrode laminated body which concerns on implementation of this invention.     It is sectional drawing of the electrode laminated body which concerns on implementation of this invention.     It is sectional drawing of the electrode laminated body which concerns on implementation of this invention.     It is a perspective view before sealing of the electrical storage apparatus which concerns on implementation of this invention.     It is sectional drawing of the multilayer electrode laminated body which concerns on implementation of this invention.     It is sectional drawing of the multilayer electrode laminated body which concerns on implementation of this invention.     It is sectional drawing before electrolyte solution impregnation of the electrical storage apparatus which concerns on implementation of this invention.     It is sectional drawing after electrolyte solution impregnation of the electrical storage apparatus which concerns on implementation of this invention.     It is a front view of the electrode pair which concerns on implementation of this invention.     It is a perspective view of the electrical storage apparatus which concerns on implementation of this invention.     It is sectional drawing of the conventional electrode laminated body.

    Hereinafter, embodiments of the present invention will be described in more detail with reference to the drawings.

    In an embodiment of the present invention, at least one of the positive electrode and the negative electrode is an electrode whose surface is electronically insulating (insulating electrode). Hereinafter, an embodiment in which the electrode surface of the negative electrode is electronically insulating and the electrode surface of the positive electrode is electronically conductive will be described in detail.

    FIG. 1 is a front view of an electrode laminate 10 (hereinafter also referred to as a power storage element 10) according to a basic embodiment of the present invention. 2 and 3 are cross-sectional views of the electrode laminate 10 shown in FIG. 1, FIG. 2 is a cross-sectional view taken along the line CC ′ shown in FIG. 1, and FIG. 3 is a cross-sectional view taken along the line DD ′ shown in FIG. Show. FIG. 4 is a perspective view of the power storage device according to the embodiment of the present invention when the electrolyte is injected.

    FIG. 1 shows an electrode laminate 10 according to one basic embodiment of the present invention. As shown in FIGS. 2 and 3, a single positive electrode 31 and two negative electrodes 32. It consists of As shown in FIG. 2, the positive electrode 31 is formed such that the active material layer 2 (hereinafter also referred to as the positive electrode active material layer 2) is in close contact with the current collector 4 (hereinafter also referred to as the positive electrode current collector 4). It is an electrode, and the electrode surface of the positive electrode 31 is electronically conductive. On the other hand, the negative electrode 32 is an electrode in which the active material layer 1 (hereinafter also referred to as negative electrode active material layer 1) is formed in close contact with the current collector 3 (hereinafter also referred to as negative electrode current collector 3). The electrode surface of 32 is electronically insulating.

    As shown in FIG. 2 and FIG. 3, the two negative electrodes 32 whose electrode surfaces are electronically insulative are formed in an envelope shape in which the left and right and lower electrode ends are solidified with a resin 35. The negative electrode 32 is characterized in that a positive electrode 31 serving as a counter electrode is accommodated. Since the inside of the envelope-shaped negative electrode 32 is surrounded by the electronic insulating electrode surface and the electronic insulating resin 35, the positive electrode 31 and the negative electrode 32 are not connected even if the electrode surface or the electrode end surface of the positive electrode 31 is electronically conductive. There is no electronic conduction.

    As shown in FIGS. 1 and 2, the upper electrode end of the negative electrode 32 is not hardened with the resin 35, and the envelope-like structure formed of the negative electrode 32 is in an open state. Thus, if the electrode end of the negative electrode 32 is not partially hardened with a resin and is opened, an electrolyte solution impregnation path to the electrode laminate 10 can be secured.

    In the electrode laminate 10, as shown in FIGS. 1, 2, and 3, the electrode end of the negative electrode 32 is positioned outside the electrode end of the positive electrode 31 by a dimension A. There is almost no possibility that the exposed current collector contacts the positive electrode 31.

    The electrode tab attachment portions 33 provided on the negative electrode 32 are all welded to the negative electrode tab 6, and the electrode tab attachment portions 34 provided on the positive electrode 31 are also welded to the positive electrode tab 7. Thereafter, as shown in FIG. 4, the storage element 10 is sandwiched between aluminum and polypropylene laminate sheets 11 and 12, and the end 112 a of the laminate sheet is heat-sealed. As shown in FIG. 4, the upper part of the laminate sheet is left unfused, but the electrode stack 10 contained in the laminate sheet has the electrode end of the negative electrode 32 not solidified with resin positioned below. .

    In the state shown in FIG. 4, the storage element 10 wrapped with a laminate sheet is sufficiently dried with a vacuum dryer, and then injected with an electrolyte from an unfused laminate sheet opening, and the electrolyte is poured by a vacuum impregnation method. When the power storage element 10 is impregnated, and then the laminate sheet opening is heat-sealed and sealed, the power storage device according to this embodiment is completed.

    The above has described a basic embodiment of the present invention in which the electrode stack 10 is composed of two negative electrodes 32 and one positive electrode 31, but the present invention basically has n + 1 electrode stacks 10. It is possible to implement with an insulating electrode of n and n counter electrodes (n is an integer of 1 or more).

    For example, in the case of n = 6, the electrode laminate 10 includes seven negative electrodes 32 and six positive electrodes 31, as shown in cross-sectional views in FIGS. Even in this case, the electrode surfaces of the seven negative electrodes 32 having an electronic insulating property are such that any adjacent negative electrode 32 has its electrode end hardened with resin 35 to form an envelope-like structure. It is characterized in that one positive electrode 31 serving as a counter electrode is housed therein. The inside of the envelope-like structure is completely electronically insulating because it is surrounded by the electronically insulating electrode surface and the resin 35, and any positive electrode 31 contained therein is electrically connected to the negative electrode 32. Absent.

    5 and FIG. 6, the positive electrode 31 is slightly smaller (by 2A) than the negative electrode 32, and as shown in FIG. Are arranged inside the single negative electrode 32 by shifting the electrode end by the dimension A, and bonded and fixed at one place (or several places) by the adhesive 8 (or adhesive 8). In the pair of the positive electrode 31 and the negative electrode 32 that are joined, the relationship that the positive electrode 31 is located inside the electrode end of the negative electrode 32 by a certain dimension A is reliably maintained.

    If the pair of electrodes 20 in such a bonded state is laminated with only the electrode ends of the negative electrode 32 positioned outside, the positive electrode 31 is automatically positioned inside the electrode end of the negative electrode 32 by a certain dimension A. Laminated. If the electrode ends of the negative electrode 32 aligned on the outside are solidified with the resin 35, the electrode laminate 10 shown in FIGS. 5 and 6 can be easily assembled. Also in this case, as shown in FIG. 5, if the electrode end of the negative electrode 32 (the upper electrode end in FIG. 5) is not hardened with resin and left open, the electrolyte solution to the electrode laminate 10 is not sealed. An impregnation path can be secured.

    As in the electrode laminate 10 shown in FIGS. 5 and 6, even in the case of an electrode laminate in which the number of electrodes is increased, the tab attachment portions of all the electrodes are attached to the positive electrode tab and the negative electrode tab, respectively. The end of the laminate sheet is heat-sealed between the polypropylene laminate sheets. At this time, the electrode laminate 10 is placed in a laminate sheet with the electrode end not secured by the resin, which is secured as an electrolyte solution impregnation path, and the upper end of the laminate sheet is left unfused.

    Since the electricity storage element 10 wrapped with the laminate sheet is not hermetically sealed, it can finally be sufficiently dried in a vacuum dryer at this stage. When the fully dried power storage element 10 is impregnated with an electrolytic solution and sealed, the power storage device 100 according to this embodiment shown in FIG. 9 is completed. The laminate sheet heat-sealed portion 112b shown in the figure is the end of the laminate sheet that has been finally heat-sealed for sealing.

    In addition, since the plastic tape 9 is preliminarily bonded to the electrode tabs 6 and 7 attached to the electricity storage element 10 by thermocompression bonding, the plastic tape 9 is integrated with the heat-bonding portion 112a of the laminate sheet and heat-sealed. Then, the negative electrode tab 6 and the positive electrode tab 7 are taken out to become a negative electrode external terminal 13 and a positive electrode external terminal 14.

    The impregnation of the electrolytic solution into the electric storage element is usually performed by a vacuum impregnation method. However, in the vacuum impregnation method, the electric storage element is once under vacuum, the air in the electric storage element is extracted, and the air is replaced with air when the pressure is returned to normal pressure. It is impregnated with an electrolytic solution. However, in the conventional impregnation of the electrolytic solution into the electric storage element by the vacuum impregnation method, when the pressure is returned to normal pressure, the air is also returned to the electric storage element together with the air again. It was necessary to repeat it.

    In the present embodiment, the electrode laminate 10 is housed in the laminate sheet with the electrode end not solidified with resin as the electrolyte solution impregnation path, so that the laminate sheet is not sealed as shown in FIG. 7A. If a required amount of the electrolytic solution 15 is injected into the bag-shaped laminate sheet from the portion, there is no other way than the electrode end 41b not solidified by the resin. Therefore, under vacuum, the air contained in the storage element 10 is sucked out from the lower portion 41b of the electrode laminate 10 to the outside. Next, when the pressure is returned to normal pressure, the air excluded from the electrode laminate 10 is resin. It cannot return to the electrode laminated body 10 from the electrode end 41a solidified. Therefore, the electrolyte solution is efficiently impregnated inside the electrode laminate 10 only from the electrode end 41b not solidified with resin, instead of the air excluded from the electrode laminate 10.

    In the power storage device 100 according to this embodiment shown in FIG. 9, the positive electrode 31 and the negative electrode 32 face each other without a sheet-like separator therebetween, but naturally contact each other, but the electrode surface of the negative electrode 32 is electronically insulating. Therefore, the electronic conduction between the positive electrode 31 and the negative electrode 32 is cut off. Further, since the positive electrode 31 and the negative electrode 32 each have a hole, and the hole and the electrode contact surface are filled with the electrolytic solution, the positive electrode 31 and the negative electrode 32 are electrically connected by ion conduction. That is, the positive electrode 31 and the negative electrode 32 facing each other have a separator function.

    Moreover, in the electrical storage apparatus 100 which concerns on this embodiment, the livestock element 10 is comprised as an electrode laminated body which has located the electrode end of the negative electrode 32 which is an insulating electrode outside the electrode end of the positive electrode 31 which opposes. Therefore, the current collector exposed from the electrode end of the insulating electrode (negative electrode 32) does not come into contact with the positive electrode 31, and therefore does not cause an internal short circuit of the power storage device.

    Although the above description has described one embodiment in which the electrode surface of the negative electrode is electronically insulating and the electrode surface of the positive electrode is electronically conductive, the present invention is an embodiment in which the electrode surface of the positive electrode is electronically insulating. There can also be a form. The above description can describe an embodiment in which the electrode surface of the positive electrode is substantially insulative by replacing the negative electrode in the description with the positive electrode and replacing the positive electrode with the negative electrode.

    Incidentally, the electrode structure of the conventional power storage element is shown in FIG. 10, but in the conventional electrode laminate 10, a sheet-like separator 5 larger than the electrode size is interposed between the electrodes, so that it is exposed at the electrode end. Neither the negative electrode current collector 3 nor the positive electrode current collector 4 is blocked by the separator 5 and comes into contact with the counter electrode. However, even in a battery using an insulating electrode, in the electrode structure in which the sheet-like separator 5 is used in combination, even if the heat resistance of the separator function can be improved, the cost of the separator function is increased.

    According to the present invention, since an expensive resin separator is not used, an inexpensive and highly safe secondary battery can be provided as a large power storage device such as an electric vehicle or an electric power storage, and thus its industrial value is great. It is.

    Hereinafter, the present invention will be described in more detail with reference to examples.

In this example, a lithium ion battery using spinel-based lithium manganese oxide (LiMn ₂ O ₄ ) as a positive electrode active material and spinel-based lithium titanium oxide (Li ₄ Ti ₅ O ₁₂ ) as a negative electrode active material is used. The electrode structure shown in FIGS. 5 and 6 is applied using 16 sheets and 16 negative electrodes.

In this embodiment, the positive electrode is composed of a positive electrode active material layer by mixing a conductive additive with an active material (LiMn ₂ O ₄ ), so that the electrode surface of the positive electrode is electronically conductive. On the other hand, since the negative electrode constitutes the negative electrode active material layer without mixing the conductive material in the active material (Li ₄ Ti ₅ O ₁₂ ), the electrode surface of the negative electrode is non-electron conductive (electronic insulating). _{Incidentally,} Li ₄ Ti _{5 O 12} is a non-electron-conductive an electronic conductivity of about ^10- 13 S / cm.

First, Li ₄ Ti ₅ O ₁₂ is a container of alumina in which lithium hydroxide (LiOH) and titanium dioxide (TiO ₂ ) are mixed well in a molar ratio of 4: 5, pressed into a pellet, and nickel foil is spread. And synthesized by firing at 800 ° C. in a helium atmosphere. The particle size of the synthesized Li ₄ Ti ₅ O ₁₂ was adjusted such that 90% was 2.57 μm or less, 50% was 1.00 μm or less, and 0.64 μm or less was 10%.

A slurry is prepared by wet-mixing 94 parts by weight of the adjusted Li ₄ Ti ₅ O ₁₂ with a solvent in which 6 parts by weight of PVDF (polyvinylidene fluoride) as a binder is dissolved. This slurry was uniformly applied with a coating width of 100 mm and dried on one side of an aluminum foil having a width of 200 mm and a thickness of 0.02 mm, leaving uncoated portions of 50 mm on both ends, and then the same on the other side. After coating with a coating width and drying, a roller press is pressed to a thickness of 0.08 to 0.09 mm to produce a strip-shaped negative electrode in which the negative electrode active material layer is in close contact with the current collector. did.

    In such a strip-shaped negative electrode, the uncoated portion of the current collector is left as an electrode tab mounting portion 33 with a size of 6 × 20 mm, and the final negative electrode is cut into a size of 93 × 93 mm in the coated area of the negative electrode active material layer 32.

LiMn ₂ O ₄ used as the positive electrode active material was prepared by firing a mixture of manganese dioxide and lithium carbonate in air at 850 ° C. and then using a conventional synthesis method. However, the LiMn ₂ O ₄ synthesized here agrees well with the diffraction pattern of spinel type LiMn ₂ O _{4 in} X-ray diffraction. Li _1.05 Mn ₁₉₅ O ₄ substituted with lithium is considered. The particle size of LiMn ₂ O ₄ was adjusted so that 90% was 17.84 μm or less, 50% was 4.40 μm or less, and 0.97 μm or less was 10%.

A slurry obtained by wet mixing with 89 parts by weight of the prepared LiMn ₂ O ₄ with N-methyl-2-pyrrolidone as a solvent together with 2 parts by weight of acetylene black and 3 parts by weight of graphite as a conductive aid and 6 parts by weight of PVDF as a binder. And Applying and drying uniformly with a coating width of 100 mm, leaving an uncoated portion of the aluminum foil of 50 mm on both ends on one side of an aluminum foil having a thickness of 0.020 mm and a width of 200 mm using the slurry as a current collector, Apply to the other side with the same coating width and dry. Then, it pressed with thickness 0.06-0.07mm with the roller press machine, and produced the strip | belt-shaped positive electrode by which a positive electrode active material layer closely_contact | adheres to a collector.

    In such a strip-like positive electrode, the uncoated portion of the current collector is left as an electrode tab attachment portion 34 with a size of 10 × 20 mm, and the final positive electrode is cut into a size of 85 × 85 mm in the coated area of the positive electrode active material layer. 31.

    As shown in FIG. 8, the positive electrode 31 and the negative electrode 32 form an electrode pair 20 by bonding and fixing one positive electrode and one negative electrode. Specifically, one of the positive electrodes 31 in which the epoxy adhesive 8 is applied to both surfaces of the positive electrode tab attachment portion 34 is overlapped on the inner side of one negative electrode 32, and the electrode tab attachment portion 34 of the positive electrode 31 is connected to the negative electrode 32. Adhere and fix to the electrode end of

    Next, 15 pairs of electrode pairs 20 are stacked with the negative electrode ends aligned, and finally, the other negative electrode is stacked to stack 16 negative electrodes 32 and 15 positive electrodes 31, and the negative electrode 32 electrode ends are stacked. The electrode laminate 10 is assembled by hardening with an epoxy resin 35. By stacking 15 electrode pairs in this manner, an integrated electrode stack 10 similar to the electrode structure shown in FIGS. 5 and 6 is assembled, although the number of stacked electrodes is different. In this case, as shown in FIG. 5, the electrode end of the negative electrode 32 (the upper electrode end in FIG. 5) is left open without being hardened with epoxy resin. A liquid impregnation route is secured.

    The electrode element 10 is completed by welding the positive electrode tab attachment portion provided on the positive electrode and the negative electrode tab attachment portion provided on the negative electrode to the positive electrode tab and the negative electrode tab, respectively.

As shown in FIG. 7A, the storage element 10 is placed in a laminate sheet with the electrode end 41b not solidified with an epoxy resin positioned below, and 1 mol / L LiPF ₆ is placed in the laminate sheet bag. A mixed solution of dissolved ethylene carbonate (EC) and diethyl carbonate (DEC) is injected as an electrolyte. As shown in FIG. 7A, the injected electrolytic solution 15 is not immediately impregnated in the electric storage element 10, but most of the electrolytic solution 15 is removed from the electrode end 41b that is not hardened with an epoxy resin according to the vacuum impregnation method. The storage element can be impregnated.

    Thereafter, as shown in FIG. 7B, the unsealed portion of the laminate sheet was heat-sealed and sealed under vacuum to produce a lithium ion battery according to this example with the battery structure shown in FIG. The finished lithium-ion battery is aged for 24 hours, the first charge is 50 mA, the upper limit of the charge voltage is set to 3.0 V, the charge is charged for 24 hours, and the battery is discharged at a constant current of 0.2 A As a result, an average discharge voltage was about 2.5 V, and a discharge capacity of about 800 mAh was obtained.

    The energy capacity of this battery is about 2.0 Wh, but the theoretical material cost calculated by simply multiplying the amount of each material used by the material unit price (material price available on a mass production basis) is 40.6 yen / It becomes a cell and is 20.3 yen / Wh.

Embodiments of the present invention that do not require a sheet separator are extremely effective in reducing the cost of lithium ion batteries. By the way, if a resin separator is interposed between 15 positive electrodes and 16 negative electrodes, the separator requires 0.52 m ² , and the price of a commercially available resin separator (material price available on a mass production basis) ) Is 200 yen / m ² , the theoretical material costs are 144.6 yen / cell and 72.3 yen / Wh, respectively.

Since the negative electrode in the present example constitutes the negative electrode active material layer without mixing the conductive assistant in the negative electrode active material (Li ₄ Ti ₅ O ₁₂ ) that is electronically insulating, the electrode surface is electronically insulating, It is easy to see that the positive electrode is not electrically connected to the opposing positive electrode without using a separator. However, it can be understood as follows why the negative electrode active material (Li ₄ Ti ₅ O ₁₂ ) can be charged even though the negative electrode active material layer itself is electronically insulating.

That is, even when the negative electrode active material layer is electronically insulating, the Li ₄ Ti ₅ O ₁₂ particles that are in close contact with the current collector can receive electrons from the current collector during charging. Are sequentially charged from the particles to be changed, and the electron insulating Li ₄ Ti ₅ O ₁₂ is changed to electron conductive Li ₇ Ti ₅ O ₁₂ .

In the first crystals of Li ₄ Ti ₅ O ₁₂ , all titanium is tetravalent (Ti ⁴⁺ ), but electrons are supplied through the current collector by charging, and Li ⁺ is supplied from the electrolyte to Li If it is changed to ₇ Ti ₅ O ₁₂ , Ti ⁴⁺ and Ti ³⁺ coexist in the crystal, so that Ti ⁴⁺ and Ti ³⁺ in the crystal can exchange electrons freely and become electron conductive.

Accordingly, the particles of Li ₄ Ti ₅ O _{12 in} the negative electrode active material layer are not directly adhered to the current collector, but the current collector and the electron are also connected via the Li ₇ Ti ₅ O ₁₂ particles changed to electron conductivity. Since it conducts by conduction, it is charged sequentially.

In this example, the amount of Li ₄ Ti ₅ O ₁₂ in the negative electrode active material layer is substantially chargeable capacity and is designed to exceed the amount of LiMn ₂ O ₄ in the positive electrode active material layer by about 1.3 times. When the LiMn ₂ O ₄ that can participate in the reaction is completely charged, the charging ends.

At the end of charging, approximately 30% of Li ₄ Ti ₅ O ₁₂ remains uncharged and remains in the vicinity of the boundary with the active electrode layer farthest from the current collector. In particular, even after charging is completed, a non-electron conductive active material layer in an uncharged state is always present on the electrode surface of the negative electrode and functions as a separator. Therefore, a sheet-like separator is interposed between the positive electrode and negative electrode active material layers. There is no need to intervene.

    In this embodiment, a conductive current collector is exposed at the electrode end of the negative electrode, which is an insulating electrode. However, since the electrode end of the negative electrode is hardened with resin, the electrode end of the negative electrode is opposed. Since the storage element is configured to be located outside the electrode end of the positive electrode, the current collector exposed from the electrode end of the negative electrode does not contact the positive electrode.

    In the above embodiment, the electrode end of the negative electrode located outside in the electrode laminate is hardened with an epoxy resin, but the resin for the purpose is not limited to this.

In the embodiment of the present invention, at least one of the positive electrode and the negative electrode is an electrode whose surface is electronically insulating (insulating electrode), and in the above example, an electronically insulating negative electrode active material (Li ₄ Ti ₅ O ₁₂ ). Although one embodiment has been shown in which the negative electrode active material layer is formed without mixing the conductive additive to make the electrode surface of the negative electrode non-electron conductive (electronic insulating), other methods, for example, the electrode surface Of course, it is possible to make the surface of either the positive electrode or the negative electrode non-electroconductive (electronic insulating) by a method such as forming an insulating ceramic layer.

    In general, in a power storage device using an organic electrolyte, the separator used is a special porous film and is expensive. In particular, in a power storage device in which the output electrode density is increased by increasing the opposing electrode area, the amount of separator used increases in proportion to the electrode opposing area, and therefore the separator price greatly increases the material cost. According to the present invention, since a separator is not required, a power storage device with high safety and high output density can be provided at low cost.

    Although one embodiment of the present invention has been described above, the above embodiment shows one example of application of the present invention, and the technical scope of the present invention is limited to the specific configuration of the above embodiment. is not. Various modifications can be made without departing from the scope of the present invention.

DESCRIPTION OF SYMBOLS 1 Negative electrode active material layer 2 Positive electrode active material layer 3 Negative electrode collector 4 Positive electrode collector 5 Sheet-like separator 6 Negative electrode tab 7 Positive electrode tab 8 Adhesive 9 Plastic tape 10 Power storage element 11, 12 Laminate sheet 13 Negative electrode external terminal 14 Positive electrode External terminal 15 Electrolytic solution 20 Electrode pair 31 Positive electrode 32 Negative electrode 33 Attaching portion 34 of negative electrode tab 35 Attaching portion 35 of positive electrode tab Resin 41 Side surface of electrode laminate

Claims (4)

    In the power storage device in which the power storage element is configured as an electrode laminate in which three or more electrodes are stacked, at least one of the positive electrode and the negative electrode constituting the electrode laminate is an electrode having a non-electron conductive surface. In the electrode laminate, the two adjacent electrodes are in the form of an envelope with the electrode ends being hardened with resin, and the electrode serving as the counter electrode is contained in the envelope-shaped electrode. A power storage device.     2. The power storage device according to claim 1, wherein the electrode surface has a non-electron conductive electrode, and the electrode end is positioned outside the electrode end of the counter electrode to constitute the electrode stack.     2. The power storage device according to claim 1, wherein the envelope-shaped electrode is left in an opened state, leaving an electrode end that is not partially hardened with a resin, and an electrolyte impregnation path for the electrode laminate is secured. .     4. The power storage device in which the power storage element is configured as an electrode laminate in which rectangular electrodes are stacked, wherein three side surfaces of four side surfaces of the electrode stack are solidified with resin. The power storage device described.

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