JP2010250968A - Lithium ion secondary battery - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To restrain deterioration of battery performance such as charge and discharge cycle characteristics, output characteristics, and rate characteristics, and generation of deformation and swelling of a battery in the lithium ion secondary battery using an alloy system negative electrode active material. <P>SOLUTION: In the lithium ion secondary battery 1 including a positive electrode 11, a negative electrode 12, a separator 14, a positive electrode lead 15, a negative electrode lead 16, a gasket 17, and an outer package case 18, a polymer layer 13 is formed on the surface of a negative electrode active material layer 12b of the negative electrode 12. The polymer layer 13 includes first polymer and inorganic oxide particles. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a lithium ion secondary battery. More specifically, the present invention relates to an improvement in a negative electrode containing an alloy-based negative electrode active material.

  Lithium ion secondary batteries have a high capacity and high energy density, and are easy to reduce in size and weight, so that they are widely used as power sources for portable small electronic devices, for example. Examples of portable small electronic devices include a mobile phone, a personal digital assistant (PDA), a notebook personal computer, a video camera, and a portable game machine. A typical lithium ion secondary battery includes a positive electrode containing a lithium cobalt composite oxide as a positive electrode active material, a negative electrode containing a carbon material as a negative electrode active material, and a polyolefin porous membrane (separator).

  An alloy-based negative electrode active material is known as a negative electrode active material for lithium ion secondary batteries. The alloy-based negative electrode active material reversibly occludes and releases lithium ions under a negative electrode potential. The alloy-based negative electrode active material occludes lithium ions by alloying with lithium. Examples of the alloy-based negative electrode active material include silicon, tin, oxides thereof, compounds and alloys containing these, and the like. The alloy-based negative electrode active material has a high discharge capacity. For example, the theoretical discharge capacity of silicon is about 4199 mAh / g, which is about 11 times the theoretical discharge capacity of graphite conventionally used as a negative electrode active material. Therefore, the alloy-based negative electrode active material is effective for increasing the capacity of the lithium ion secondary battery.

  A lithium ion secondary battery using an alloy-based negative electrode active material has excellent battery performance in the initial stage of use. However, in the battery, when the number of times of charging / discharging increases, the nonaqueous electrolyte decreases, the charge / discharge cycle characteristics and discharge capacity rapidly decrease, and the battery tends to deform. One of the causes is presumed to be a volume change of the alloy-based negative electrode active material. That is, the alloy-based negative electrode active material has a large volume change (expansion and contraction) due to insertion and extraction of lithium ions, and generates a relatively large stress during the volume change. Therefore, various proposals have been made to improve battery performance of lithium ion secondary batteries using alloy-based negative electrode active materials.

  A negative electrode for a lithium ion secondary battery including a negative electrode current collector, a negative electrode active material layer, and a polymer layer has been proposed (see, for example, Patent Document 1). The negative electrode active material layer contains lithium alloy particles and a binder. Examples of the lithium alloy include alloy-based negative electrode active materials such as an alloy of lithium and tin and an alloy of lithium and silicon. The polymer layer is formed on the surface of the negative electrode active material layer, and contains a polymer support and a crosslinkable monomer. Furthermore, the crosslinkable monomer is not only contained in the polymer layer, but is filled in the voids in the negative electrode active material layer in the form of a crosslinked product.

  As the crosslinkable monomer, an organic compound that can conduct ions but has low electrical conductivity is used. Specifically, hexyl acrylate, butyl acrylate, trimethylolpropane triacrylate, butanediol methacrylate, ethylene glycol dimethacrylate, tritetraethylene glycol diacrylate, poly (ethylene glycol) diacrylate, polyethylene glycol dimethacrylate, diglycidyl ester, Examples include acrylamide and divinylbenzene. Examples of the polymer support include polymethyl methacrylate, polyacrylic acid, polymethacrylic acid, polyethyl methacrylate, and propylene carbonate methacrylate.

  In the technique of Patent Document 1, an attempt is made to relieve stress generated with the volume change of the alloy-based negative electrode active material by the polymer layer. However, even in the lithium ion secondary battery including the negative electrode of Patent Document 1, it is not possible to sufficiently suppress non-aqueous electrolyte reduction, rapid charge / discharge cycle characteristics reduction, battery deformation, and the like. That is, even if a layer made of a single polymer is formed on the surface of the active material layer containing the alloy-based negative electrode active material, it is difficult to significantly improve the battery performance.

  According to FIG. 2 and FIG. 4 of Patent Document 1, the discharge capacity of the battery in the initial stage of use is maintained at a high rate of about 80 to 95% even after repeated charging and discharging due to the formation of the polymer layer. However, the number of charge / discharge cycles in FIGS. 2 and 4 is only 30 or 40 times. Usually, there is no lithium ion secondary battery in which the discharge capacity is rapidly reduced when the charge / discharge cycle is repeated 30 or 40 times.

  Further, there has been proposed a negative electrode for a lithium ion secondary battery that includes a negative electrode current collector, a negative electrode active material layer, and an oxide film, and the oxide film is formed on the surface of the negative electrode active material layer (for example, Patent Document 2). reference). The negative electrode active material layer contains an alloy-based negative electrode active material. The oxide film contains an oxide of a metal selected from silicon, germanium, and tin, and is formed by a liquid phase method. Patent Document 2 describes that since the oxide film is formed by a liquid phase method, the surface of the alloy-based negative electrode active material particles inside the negative electrode active material layer can also be covered.

  However, the oxide film of Patent Document 2 cannot sufficiently absorb the volume change of the alloy-based negative electrode active material accompanying charge / discharge. Also in the lithium ion secondary battery including the negative electrode of Patent Document 2, the life of the electrode is shortened and the battery is easily deformed. Also, battery performance such as charge / discharge cycle characteristics is likely to deteriorate.

JP-A-2005-197258 JP 2008-004534 A

  The object of the present invention is a lithium ion secondary battery using an alloy-based negative electrode active material, which has excellent battery performance such as charge / discharge cycle characteristics and output characteristics, has a long service life, and increases the number of charge / discharge cycles. It is an object of the present invention to provide a lithium ion secondary battery that has very little deterioration in battery characteristics and is highly safe against internal short circuits.

  In order to solve the above-mentioned problems, the present inventors first studied various causes of the battery performance of a lithium ion secondary battery using an alloy-based negative electrode active material rapidly decreasing. And it discovered that the alloy type negative electrode active material and the non-aqueous electrolyte reacted, and the film which does not contribute to the charging / discharging reaction in a battery was formed on the surface of an alloy type negative electrode active material. Furthermore, it discovered that non-aqueous electrolyte was consumed by reaction with an alloy type negative electrode active material and non-aqueous electrolyte. However, these causes alone do not lead to a rapid decrease, although the battery performance is reduced to some extent.

  The inventors have further studied. As a result, in the active material layer containing the alloy-based negative electrode active material, when the number of charge / discharge increases, cracks are generated on the surface and inside of the alloy-based negative electrode active material due to the volume change of the alloy-based negative electrode active material. I found out. When a new crack occurs, a new surface (hereinafter referred to as “new surface”) that has not been directly touched by the non-aqueous electrolyte appears. A new surface may be newly generated each time the charge / discharge cycle is repeated. The present inventors believe that this new surface causes a rapid decrease in battery performance.

When the new surface and the non-aqueous electrolyte are brought into contact with each other rapidly, a side reaction other than the charge / discharge reaction occurs and a byproduct is deposited, thereby forming a film that does not contribute to the charge / discharge reaction. This coating causes abnormal expansion with repeated charging / discharging, leading to shortened electrode life and battery deformation. In addition, when the nonaqueous electrolyte is consumed by a side reaction, the nonaqueous electrolytic mass in the battery is insufficient, and battery performance such as charge / discharge cycle characteristics is rapidly deteriorated.
Moreover, the present inventors considered the reason why the technique of Patent Document 1 cannot obtain a sufficient effect in the research process for solving the above-described problems. As a result, the following knowledge was obtained.

  The polymer layer of Patent Document 1 is considered to have poor flexibility and insufficient adhesion to the negative electrode active material layer due to the types of crosslinkable monomer and polymer support. Furthermore, although the polymer layer of Patent Document 1 includes a polymer support, it is still a single polymer layer. For this reason, adhesiveness with a negative electrode active material layer further falls by the volume change of the alloy type negative electrode active material accompanying charging / discharging. Therefore, the polymer layer of Patent Document 1 cannot sufficiently suppress the contact between the surface of the negative electrode active material layer and the new surface formed in the layer and the nonaqueous electrolyte.

In addition, the present inventors paid attention to the following points 1) to 3).
1) The alloy-based negative electrode active material has a much larger capacity than conventional carbon materials such as graphite.
2) A negative electrode active material layer can be formed by depositing an alloy-based negative electrode active material on the current collector surface by a vapor phase method.

3) Even if a negative electrode active material layer containing an alloy-based negative electrode active material is formed into a thin film by a vapor phase method, its capacity does not decrease, and the output characteristics of the battery are not adversely affected.
The present inventors have further studied based on the knowledge about the mechanism that the battery performance is drastically lowered in the lithium ion secondary battery containing the alloy-based negative electrode active material, the knowledge on Patent Document 1, and the viewpoints of the above 1) to 3). Piled up. As a result, it was found that the surface of the thin film negative electrode active material layer having a thickness of about 1 μm to several tens of μm formed by a vapor phase method has an appropriate surface roughness.

  From these research results, the present inventors have come up with a configuration in which a polymer layer is formed on the surface of a negative electrode active material layer formed by a gas phase method, and the polymer layer contains inorganic oxide particles. . In this configuration, the surface of the negative electrode active material layer has an appropriate surface roughness. Moreover, the adhesive force with respect to the negative electrode active material layer surface of a polymer layer improves because a polymer layer contains an inorganic oxide particle. For this reason, it became clear that the adhesion between the negative electrode active material layer and the polymer layer was unexpectedly high, and even when the volume change of the alloy-based negative electrode active material occurred, peeling of the polymer layer was suppressed. In addition, since the adhesion between the negative electrode active material layer and the polymer layer is high, it has been clarified that the polymer layer can suppress contact between the new surface and the nonaqueous electrolyte.

Further, it has been clarified that the polymer layer can sufficiently follow the volume expansion of the alloy-based negative electrode active material, and peeling of the polymer layer from the negative electrode active material surface is further suppressed. As a result, it was found that battery performance such as electrode life shortening, battery deformation, charge / discharge cycle characteristics, output characteristics, and discharge capacity is unlikely to suddenly decrease. Furthermore, it has been found that even when the inside of the battery becomes heated due to internal short circuit, overcharge, etc., further progress of heat generation can be suppressed and the safety of the battery can be improved.
The present inventors have completed the present invention based on these findings.

  That is, the present invention includes a positive electrode, a negative electrode, a polymer layer, and a lithium ion permeable insulating layer, and the positive electrode includes a positive electrode active material layer containing a positive electrode active material capable of occluding and releasing lithium, and a positive electrode current collector. Includes a negative electrode active material layer and a negative electrode current collector formed by a vapor phase method and containing an alloy-based negative electrode active material, the polymer layer being formed on the surface of the negative electrode active material layer, the first polymer and the first inorganic oxide And a lithium ion permeable insulating layer according to a lithium ion secondary battery disposed so as to be interposed between a positive electrode and a negative electrode.

In a preferred embodiment of the present invention, the lithium ion permeable insulating layer is a separator or a porous layer, and further contains a lithium ion conductive nonaqueous electrolyte.
In another preferred embodiment of the present invention, the lithium ion permeable insulating layer is a lithium ion conductive solid electrolyte layer.

The content of the first inorganic oxide particles in the polymer layer is preferably 25 to 75% by weight of the total amount of the polymer layer.
The first inorganic oxide particles contained in the polymer layer are preferably one or more selected from the group consisting of alumina, magnesia, silica, zirconia and titania.
The first polymer contained in the polymer layer is preferably a fluororesin.
The thickness of the polymer layer is preferably 0.05 to 25 μm.

When the lithium ion permeable insulating layer is a porous layer, the porous layer contains the second polymer and the second inorganic oxide particles, and the content of the second inorganic oxide particles is 25 to 99 of the total amount of the porous layer. 0.5% by weight is preferred.
The negative electrode active material layer is an aggregate of a plurality of columnar bodies, and the columnar bodies preferably contain an alloy-based negative electrode active material, extend outward from the surface of the negative electrode current collector and are separated from each other.
The particle diameter of the first inorganic oxide particles is preferably smaller than the distance between the axes of one columnar body and a columnar body adjacent thereto.

  The polymer layer is a laminate of a plurality of polymer layers, each of the plurality of polymer layers contains a first polymer and a first inorganic oxide particle, and the content of the first inorganic oxide particles in the plurality of polymer layers is It is more preferable that the number increases stepwise in the direction from the negative electrode active material layer to the lithium ion permeable insulating layer.

  The plurality of polymer layers are a first layer and a second layer, the first layer is formed on the surface of the negative electrode active material layer, contains the first polymer and the first inorganic oxide particles, and the second layer is the first layer. Formed on the surface of the layer, containing the first polymer and the first inorganic oxide particles, and the content of the first inorganic oxide particles in the first layer is the content of the first inorganic oxide particles in the second layer Preferably less than the amount.

  The alloy-based negative electrode active material is preferably one or more selected from an alloy-based negative electrode active material containing silicon and an alloy-based negative electrode active material containing tin.

  The lithium ion secondary battery of this invention is excellent in battery performance, such as a charge / discharge cycle characteristic and an output characteristic, by containing an alloy type negative electrode active material. Moreover, although the lithium ion secondary battery of this invention contains an alloy type negative electrode active material, the fall of the said battery characteristic is suppressed notably and its useful life is long.

  Furthermore, the lithium ion secondary battery of the present invention has high safety when an internal short circuit occurs or during overcharge. Specifically, heat generation due to internal short circuit, overcharge, etc. is suppressed. Therefore, the lithium ion secondary battery of the present invention can be suitably used as a power source for various portable small electronic devices currently on the market. Furthermore, it can also be suitably used as a power source for electronic devices whose power consumption has further increased due to the increase in functionality.

It is a longitudinal cross-sectional view which shows typically the structure of the lithium ion secondary battery which is one of the embodiment of this invention. It is a perspective view which shows typically the structure of a negative electrode electrical power collector. It is a longitudinal cross-sectional view which shows typically the structure of the negative electrode of another form containing the negative electrode collector shown in FIG. It is a longitudinal cross-sectional view which shows typically the structure of the columnar body contained in the negative electrode active material layer of the negative electrode shown in FIG. It is sectional drawing which shows typically the structure of the principal part of the negative electrode of another form. It is sectional drawing which shows typically the structure of the principal part of the negative electrode of another form. It is a side view which shows typically the structure of an electron beam vapor deposition apparatus.

  The lithium ion secondary battery of the present invention includes a positive electrode, a negative electrode, a polymer layer, an ion-permeable insulating layer, and a nonaqueous electrolyte. The negative electrode includes a negative electrode current collector and a negative electrode active material layer, and the negative electrode active material layer is formed by a vapor phase method and contains an alloy-based negative electrode active material. The polymer layer is formed on the surface of the negative electrode active material layer and contains a polymer and inorganic oxide particles. That is, the lithium ion secondary battery of the present invention is characterized by a combination of a specific negative electrode and a polymer layer. Other configurations, that is, the positive electrode, the ion-permeable insulating layer, and the nonaqueous electrolyte are the same as those of the conventional lithium ion secondary battery.

  FIG. 1 is a longitudinal sectional view schematically showing a configuration of a lithium ion secondary battery 1 which is one embodiment of the present invention. The lithium ion secondary battery 1 includes a positive electrode 11, a negative electrode 12, a polymer layer 13, a separator 14, a positive electrode lead 15, a negative electrode lead 16, a gasket 17, an outer case 18, and a non-aqueous electrolyte (not shown). The lithium ion secondary battery 1 is a flat battery including a stacked electrode group in which a separator 14 is interposed between a positive electrode 11 and a negative electrode 12.

The positive electrode 11 includes a positive electrode current collector 11a and a positive electrode active material layer 11b.
A conductive substrate is used for the positive electrode current collector 11a. The material of the conductive substrate is a metal material such as stainless steel, titanium, aluminum, aluminum alloy, or a conductive resin. In addition, the conductive substrate includes a porous conductive substrate and a non-porous conductive substrate. Examples of porous conductive substrates include mesh bodies, net bodies, punching sheets, lath bodies, porous bodies, foams, and nonwoven fabrics. Non-porous conductive substrates include foils, sheets and films. The thickness of the conductive substrate is usually 1 to 500 μm, preferably 1 to 50 μm.

The positive electrode active material layer 11b is provided on one or both surfaces in the thickness direction of the positive electrode current collector 11a and contains a positive electrode active material. Furthermore, the positive electrode active material layer 11b may contain a conductive agent, a binder, and the like together with the positive electrode active material.
The positive electrode active material is not particularly limited as long as it is a material that can occlude and release lithium ions. For example, lithium-containing composite metal oxides, olivine-type lithium phosphate, and the like can be preferably used.

  The lithium-containing composite metal oxide is a metal oxide containing lithium and a transition metal or a metal oxide in which a part of the transition metal in the metal oxide is substituted with a different element. Here, examples of the different element include Na, Mg, Sc, Y, Mn, Fe, Co, Ni, Cu, Zn, Al, Cr, Pb, Sb, and B. Among these, Mn, Al, Co, Ni, Mg, etc. are preferable. One kind or two or more kinds of different elements may be used.

Specific examples of the lithium-containing composite metal oxide, for _{example, Li l CoO 2, Li l} NiO 2, Li l MnO 2, Li l Co m Ni 1-m O 2, Li l Co m M 1-m O n , Li _l Ni _1-m M _m O _n , Li _l Mn ₂ O ₄ , Li _l Mn _2−m M _n O ₄ (wherein M is Na, Mg, Sc, Y, Mn, Fe, Co And at least one element selected from the group consisting of Ni, Cu, Zn, Al, Cr, Pb, Sb and B. 0 <l ≦ 1.2, 0 ≦ m ≦ 0.9, 2.0 ≦ n ≦ 2.3).

Here, the value of l indicating the molar ratio of lithium is a value immediately after the production of the positive electrode active material, and is increased or decreased by charging and discharging. Among these, (wherein, M, l, m and n are the same. Above) the composition formula _{Li l Co m M 1-m} O n lithium-containing composite metal oxide represented by are preferred. Specific examples of the olivine-type lithium phosphate include LiXPO ₄ and Li ₂ XPO ₄ F (wherein X is at least one selected from the group consisting of Co, Ni, Mn and Fe). Can be mentioned. A positive electrode active material can be used individually by 1 type or in combination of 2 or more types.

  Examples of the conductive agent include graphites such as natural graphite and artificial graphite, carbon blacks such as acetylene black, ketjen black, channel black, furnace black, lamp black and thermal black, and conductive properties such as carbon fiber and metal fiber. Examples include fibers, metal powders such as aluminum, conductive whiskers such as zinc oxide whisker and potassium titanate whisker, conductive metal oxides such as titanium oxide, organic conductive materials such as phenylene derivatives, and carbon fluoride. It is done. A conductive agent can be used individually by 1 type or in combination of 2 or more types.

  Examples of the binder include polyvinylidene fluoride (PVDF), polytetrafluoroethylene, polyethylene, polypropylene, aramid resin, polyamide, polyimide, polyamideimide, polyacrylonitrile, polyacrylic acid, polymethyl acrylate, and polyethyl acrylate. , Polyhexyl acrylate, polymethacrylic acid, polymethyl methacrylate, polyethyl methacrylate, polyhexyl methacrylate, polyvinyl acetate, polyvinyl pyrrolidone, polyether, polyethersulfone, polyhexafluoropropylene, styrene butadiene rubber, modified Examples include acrylic rubber and carboxymethyl cellulose.

  A copolymer containing two or more types of monomer compounds can be used as a binder. Examples of the monomer compound include tetrafluoroethylene (TFE), hexafluoropropylene (HFP), perfluoroalkyl vinyl ether, vinylidene fluoride, chlorotrifluoroethylene, ethylene, propylene, pentafluoropropylene, fluoromethyl vinyl ether, acrylic acid, Examples include hexadiene. A binder can be used individually by 1 type or in combination of 2 or more types.

  The positive electrode active material layer 11b can be formed, for example, by applying a positive electrode mixture slurry to the surface of the positive electrode current collector 11a, drying and rolling. The positive electrode mixture slurry can be prepared by dissolving or dispersing a positive electrode active material and, if necessary, a conductive agent and a binder in an organic solvent. As the organic solvent, for example, dimethylformamide, dimethylacetamide, methylformamide, N-methyl-2-pyrrolidone (NMP), dimethylamine, acetone, cyclohexanone and the like can be used.

The negative electrode 12 includes a negative electrode current collector 12a and a negative electrode active material layer 12b.
A conductive substrate can be used for the negative electrode current collector 12a. The material of the conductive substrate is, for example, a metal material such as stainless steel, nickel, copper, or a copper alloy, or a conductive resin. In addition, the conductive substrate includes a porous conductive substrate and a non-porous conductive substrate. Examples of porous conductive substrates include mesh bodies, net bodies, punching sheets, lath bodies, porous bodies, foams, and nonwoven fabrics. Non-porous conductive substrates include foils, sheets and films. The thickness of the conductive substrate is usually 1 to 500 μm, preferably 1 to 50 μm.

  The negative electrode active material layer 12b contains an alloy-based negative electrode active material and is formed into a thin film by a vapor phase method on one surface or both surfaces in the thickness direction of the negative electrode current collector 12a. The negative electrode active material layer 12b may contain a known negative electrode active material other than the alloy negative electrode active material, additives, and the like, as long as the characteristics thereof are not impaired, together with the alloy negative electrode active material. The negative electrode active material layer 12b is more preferably an amorphous or low crystalline thin film containing an alloy-based negative electrode active material. The negative electrode active material layer 12b formed by the vapor phase method is usually made of an alloy-based negative electrode active material and does not contain a binder.

  Since the negative electrode active material layer 12b is formed by a vapor phase method, the surface of the negative electrode active material layer 12b has an appropriate surface roughness. Thereby, adhesion between the negative electrode active material layer 12b and the polymer layer 13 is maintained. And even if the alloy type negative electrode active material contained in the negative electrode active material layer 12b repeats a volume change, peeling of the polymer layer 13 from the negative electrode active material layer 12b is suppressed. As a result, the effect of suppressing direct contact between the new surface of the polymer layer 13 and the nonaqueous electrolyte is exhibited over a long period of time.

  The thickness of the negative electrode active material layer 12b is usually 1 to several tens of μm, preferably 1 to 20 μm. The effect of adjusting the thickness of the negative electrode active material layer 12b to the above range is as follows. Even if cracks occur in the alloy-based negative electrode active material particles inside the negative electrode active material layer 12b and a new surface is generated, it is estimated that most of the new surface is likely to appear on or near the surface of the negative electrode active material layer 12b. . As a result, the new surface is easily protected by the polymer layer 13, and rapid contact between the new surface and the nonaqueous electrolyte is suppressed.

  As a result, side reactions between the new surface and the non-aqueous electrolyte are suppressed, and the amount of by-products that cause a reduction in the life of the negative electrode 12, deformation of the battery 1, deterioration in battery performance of the battery 1, and the like is significantly reduced. As a result, the advantages (high capacity) of the alloy-based negative electrode active material are sufficiently exhibited, and the lithium ion secondary battery 1 having high capacity and high output, excellent charge / discharge cycle characteristics, and a long service life can be obtained.

  The alloy-based negative electrode active material is a material that is alloyed with lithium during charging and occludes lithium and releases lithium during discharging under a negative electrode potential. Although it does not restrict | limit especially as an alloy type negative electrode active material, The alloy type negative electrode active material containing silicon and the alloy type negative electrode active material containing tin are preferable. Examples of the alloy-based negative electrode active material containing silicon include silicon, silicon oxide, silicon carbide, silicon nitride, silicon-containing alloys, silicon compounds, and solid solutions thereof.

Examples of the silicon oxide include silicon oxide represented by the composition formula: SiO _a (0.05 <a <1.95). Examples of silicon carbide include silicon carbide represented by the composition formula: SiC _b (0 <b <1). Examples of the silicon nitride include silicon nitride represented by the composition formula: SiN _c (0 <c <4/3). Examples of the silicon-containing alloy include an alloy of silicon and an element other than silicon. Examples of elements other than silicon include Fe, Co, Sb, Bi, Pb, Ni, Cu, Zn, Ge, In, Sn, and Ti. Elements other than silicon can be used alone or in combination of two or more.

  The silicon compound is a compound in which part of silicon contained in silicon, silicon oxide, silicon carbide, silicon nitride, or silicon-containing alloy is substituted with one or more elements. Examples of this element include B, Mg, Ni, Ti, Mo, Co, Ca, Cr, Cu, Fe, Mn, Nb, Ta, V, W, Zn, C, N, and Sn. Of the alloy-based negative electrode active materials containing silicon, silicon and silicon oxide are preferable.

Examples of the alloy-based negative electrode active material containing tin include tin, tin oxide, tin nitride, a tin-containing alloy, a tin compound, and a solid solution thereof. Examples of the tin oxide include tin oxide represented by the composition formula: SnO _d (0 <d <2), tin dioxide (SnO ₂ ), and the like. Examples of the tin-containing alloy include Ni—Sn alloy, Mg—Sn alloy, Fe—Sn alloy, Cu—Sn alloy, Ti—Sn alloy and the like. Examples of the tin compound include SnSiO ₃ , Ni ₂ Sn ₄ , and Mg ₂ Sn. Among alloy-based negative electrode active materials containing tin, tin oxides, tin-containing alloys, tin compounds, and the like are preferable.

  Among alloy-based negative electrode active materials, silicon, silicon oxide, tin, tin oxide and the like are preferable, and silicon, silicon oxide and the like are particularly preferable. An alloy type negative electrode active material can be used individually by 1 type or in combination of 2 or more types.

  The negative electrode active material layer 12b is formed in a thin film on the surface of the negative electrode current collector 12a according to a vapor phase method. Examples of the vapor phase method include a vacuum deposition method, a sputtering method, an ion plating method, a laser ablation method, a chemical vapor deposition (CVD) method, a plasma chemical vapor deposition method, and a thermal spray method. Among these, the vacuum evaporation method is preferable.

  In addition, before forming the polymer layer 13 on the surface of the negative electrode active material layer 12b, an amount of lithium corresponding to the irreversible capacity may be deposited on the negative electrode active material layer 12b. The irreversible capacity is the amount of lithium that is stored in the negative electrode active material layer 12b at the time of initial charge / discharge and is not subsequently released from the negative electrode active material layer 12b.

  The polymer layer 13 is formed so as to be in close contact with the surface of the negative electrode active material layer 12 b and is interposed between the negative electrode active material layer 12 b and the separator 14. Moreover, in the polymer layer 13, the 1st inorganic oxide particle is disperse | distributing in the 1st polymer which is a matrix. Thereby, the effect that the adhesiveness with respect to the negative electrode active material layer 12b is high is acquired. In addition, while following the volume change of the alloy-based negative electrode active material due to the flexibility of the first polymer that is the matrix, deformation or the like is difficult to occur due to the reinforcing effect of the first inorganic oxide particles. For this reason, adhesion between the negative electrode active material layer 12 b and the polymer layer 13 is maintained throughout the usable period of the battery 1.

  As a result, even if a crack occurs in the negative electrode active material layer 12b with charge / discharge and a new surface is generated, the polymer layer 13 suppresses the new surface from coming into contact with the nonaqueous electrolyte. That is, the side reaction between the new surface and the non-aqueous electrolyte is suppressed, and a rapid decrease in battery performance hardly occurs. Furthermore, the consumption of the nonaqueous electrolyte more than necessary is suppressed. Further, since the polymer layer 13 absorbs the volume expansion of the alloy-based negative electrode active material and is not easily deformed, the battery 1 is hardly deformed. In addition, since the polymer layer 13 contains the first inorganic oxide particles, even if heat generation occurs due to internal short circuit or overcharge in the battery 1, the excessive heat generation is suppressed, and the battery 1 is safe. Improves.

  The polymer layer 13 exhibits lithium ion conductivity or lithium ion permeability by being formed according to a method described later. Therefore, the polymer layer 13 does not hinder the battery reaction in the lithium ion secondary battery 1 and does not deteriorate the output characteristics, rate characteristics, etc. of the battery 1.

  The polymer layer 13 may be a laminate of a plurality of polymer layers having different contents of the first inorganic oxide particles. The number of laminated polymer layers having different contents of the first inorganic oxide particles is preferably 2 to 5, and more preferably 2 to 3. In this case, a configuration in which the content of the first inorganic oxide particles is increased stepwise from the negative electrode 12 toward the separator 14 is preferable. In this configuration, the content of the first inorganic oxide particles in the polymer layer formed on the surface of the negative electrode active material layer 12b is the smallest, and the content of the first inorganic oxide particles in the polymer layer in contact with or closest to the separator 14 is included. The amount is the largest.

  Specifically, a configuration in which the polymer layer 13 includes a first layer and a second layer is exemplified. The first layer is formed so as to be in close contact with the surface of the negative electrode active material layer 12b, and contains a first polymer and first inorganic oxide particles. The second layer is formed so as to be in close contact with the surface of the first layer (the surface opposite to the surface in contact with the negative electrode active material layer 12b of the first layer), and contains the first polymer and the first inorganic oxide particles. To do. The first polymer and the first inorganic oxide particles contained in the first layer and the second layer may be the same or different, respectively. However, considering the adhesion between the first layer and the second layer, it is preferable to use the same first polymer. Further, the content of the first inorganic oxide particles in the first layer is less than the content of the first inorganic oxide particles in the second layer.

  According to this configuration, since the first layer has a relatively small content of the first inorganic oxide particles as compared with the second layer, the first layer is excellent in adhesion and flexibility to the surface of the negative electrode active material layer 12b. For this reason, it follows easily the volume change of an alloy type negative electrode active material, and the adhesive state with the surface of the negative electrode active material layer 12b is hold | maintained, relieving the stress which generate | occur | produces with the volume change. On the other hand, the second layer has a relatively high mechanical strength while maintaining a certain degree of adhesion and flexibility since the content of the first inorganic oxide particles is relatively large compared to the first layer. ing. Therefore, the second layer contributes to maintaining the shape of the first layer while being in close contact with the first layer.

  That is, in the polymer layer 13 that is a laminate of the first layer and the second layer, the stress generated from the alloy-based negative electrode active material is relieved while maintaining the close contact state with the surface of the negative electrode active material layer 12b by the first layer. To do. Further, the shape of the polymer layer 13 is maintained by the second layer to suppress deformation. As a result, deterioration of charge / discharge cycle characteristics and output characteristics of the battery 1, deformation and swelling of the battery 1 are suppressed, and the advantages (energy density and output height) of using the alloy-based negative electrode active material are maximized. It is.

  The thickness of the polymer layer 13 is not particularly limited, but is preferably 0.05 to 25 μm. If the thickness of the polymer layer 13 is less than 0.05 μm, the followability of the polymer layer 13 to the volume change of the alloy-based negative electrode active material and the adhesion between the polymer layer 13 and the surface of the negative electrode active material layer 12b may be reduced. As a result, there is a possibility that the polymer layer 13 cannot sufficiently suppress the rapid contact between the new surface of the negative electrode active material layer 12b and the nonaqueous electrolyte. On the other hand, when the thickness of the polymer layer 13 exceeds 25 μm, the ion conductivity or ion permeability of the polymer layer 13 is lowered, and the output characteristics, charge / discharge cycle characteristics, storage characteristics, etc. of the battery 1 may be lowered. Further, the mechanical strength of the polymer layer 13 becomes too high, and the followability to the volume change of the alloy-based negative electrode active material may be reduced.

  Examples of the first polymer contained in the polymer layer 13 include a fluororesin, polyacrylonitrile, polyethylene oxide, and polypropylene oxide. A polymer can be used individually by 1 type or in combination of 2 or more types. Among these, considering the adhesion between the negative electrode active material layer 12b and the polymer layer 13, a fluororesin is preferable.

Examples of the fluororesin include polyvinylidene fluoride (PVDF), a copolymer of vinylidene fluoride (VDF) and an olefin monomer, and polytetrafluoroethylene. Examples of the olefin monomer include tetrafluoroethylene (TFE), hexafluoropropylene (HFP), and ethylene.
When the polymer layer 13 is a single phase, among the fluororesins, PVDF, a copolymer of VDF and TFE, a copolymer of VDF and HFP, a copolymer of VDF, TFE, and HFP are preferable.

  Further, when the polymer layer 13 includes the first layer and the second layer as described above, as the first polymer of the first layer, VDF and TFE are used to suppress swelling of the first polymer due to the nonaqueous electrolyte. And a copolymer of VDF, TFE and HFP are preferred. Of the copolymers of VDF, TFE, and HFP, a copolymer having a TEF amount larger than the HFP amount is preferable. Moreover, as a polymer of a 2nd layer, in order to enlarge lithium ion conductivity, the copolymer of VDF and HFP, the copolymer of VDF, TFE, and HFP etc. are preferable. Of the copolymers of VDF, TFE, and HFP, a copolymer having an HFP amount larger than an TEF amount is preferable.

  The first inorganic oxide particles contained in the polymer layer 13 are not particularly limited as long as they are inert to the charge / discharge reaction inside the battery 1, but alumina, magnesia, silica, zirconia, titania and the like are preferable. Alumina is particularly preferred. The 1st inorganic oxide particle can be used individually by 1 type or in combination of 2 or more types. The content of the inorganic oxide particles in the polymer layer 13 is preferably 25 to 75% by weight of the total amount of the polymer layer 13, more preferably 48 to 73% by weight of the total amount of the polymer layer 13, and the remainder is the first polymer.

  If the content of the first inorganic oxide particles is less than 25% by weight, the adhesion of the polymer layer 13 to the surface of the negative electrode active material layer 12b may be insufficient. In addition, the effect of suppressing the progress of heat generation due to internal short circuit or overcharge may be reduced. Moreover, when content of 1st inorganic oxide particle exceeds 75 weight%, the softness | flexibility of the polymer layer 13 will fall and there exists a possibility that the followability of the polymer layer 13 with respect to the volume change of an alloy type negative electrode active material may fall. . As a result, the adhesion of the polymer layer 13 to the surface of the negative electrode active material layer 12b may be insufficient.

  When the polymer layer 13 includes the first layer and the second layer as described above, the content of the first inorganic oxide particles in the first layer is preferably 0.01 to 96% by weight, more preferably 0. 0.01 to 48% by weight. The content of the first inorganic oxide particles in the second layer is preferably 50 to 96% by weight, more preferably 50 to 73% by weight. Note that a layer made of only the first polymer may be interposed between the first layer of the polymer layer 13 and the negative electrode active material layer 12b.

The polymer layer 13 may contain a supporting salt in addition to the first polymer and the first inorganic oxide particles. The supporting salt is preferably a supporting salt containing lithium ions. Such supporting salts are commonly used in the field of lithium ion secondary batteries. Specific examples of the supporting salt include, for example, LiClO ₄ , LiBF ₄ , LiPF ₆ , LiAlCl ₄ , LiSbF ₆ , LiSCN, LiCF ₃ SO ₃ , LiCF ₃ CO ₂ , LiAsF ₆ , LiB ₁₀ Cl ₁₀ , lower aliphatic carboxylic acid Examples thereof include lithium, LiCl, LiBr, LiI, LiBCl ₄ , borate salts, and imide salts. The supporting salt can be used alone or in combination of two or more.

  The polymer layer 13 can be formed, for example, by applying a polymer layer coating liquid on the surface of the negative electrode active material layer 12b and drying. The polymer layer coating solution contains the first polymer, the first inorganic oxide particles and the organic solvent, and may further contain a supporting salt. The polymer layer coating liquid can be prepared, for example, by dissolving or dispersing the first polymer and the first inorganic oxide particles and, if necessary, the supporting salt in an organic solvent. Examples of organic solvents that can be used include dimethylformamide, dimethylacetamide, methylformamide, N-methyl-2-pyrrolidone (NMP), dimethylamine, acetone, and cyclohexanone.

  The polymer layer coating solution can be applied to the surface of the negative electrode active material layer 12b by a known method. Specific examples thereof include dipping, screen printing, die coater, comma coater, roll coater, bar coater, gravure coater curtain coater, spray coater, air knife coater, reverse coater, dip squeeze coater and the like. Among these, the dipping method is preferable. In addition, the thickness of the polymer layer 13 can be appropriately adjusted by changing, for example, the amount of the polymer layer coating liquid applied to the surface of the negative electrode active material layer 12b, the viscosity of the polymer layer coating liquid, and the like. The viscosity of the polymer layer coating liquid can be easily adjusted by changing, for example, the type and content of the first polymer, the content of the first inorganic oxide particles, the amount of organic solvent used, and the like.

  The separator 14 is an ion permeable insulating layer. The separator 14 is disposed between the positive electrode 11 and the negative electrode 12. The separator 14 has at least a part of the surface thereof in contact with the surface of the polymer layer 13 or close to the polymer layer 13 on the negative electrode 12 side. As the separator 14, a sheet or film having a predetermined ion permeability, mechanical strength, insulation, and the like can be used. Specific examples of the separator 14 include a porous sheet or a porous film such as a microporous film, a woven fabric, and a non-woven fabric. The microporous film may be either a single layer film or a multilayer film (composite film). Further, two or more layers of microporous membrane, woven fabric, non-woven fabric, etc. may be laminated.

  Various resin materials can be used as the material of the separator 14, but polyolefins such as polyethylene and polypropylene are preferable in view of durability, shutdown function, battery safety, and the like. The shutdown function is a function that blocks the through-hole when the battery is abnormally heated, thereby suppressing ion permeation and blocking the battery reaction. The thickness of the separator 14 is generally 10 to 300 μm, preferably 10 to 40 μm. Moreover, the porosity of the separator 14 is preferably 30 to 70%, more preferably 35 to 60%.

The separator 14 is impregnated with a non-aqueous electrolyte (liquid non-aqueous electrolyte) having lithium ion conductivity.
The liquid non-aqueous electrolyte contains a solute (supporting salt) and a non-aqueous solvent, and further contains various additives as necessary. Solutes usually dissolve in non-aqueous solvents. For example, the separator is impregnated with the liquid non-aqueous electrolyte.

As the solute, those commonly used in this field can be used. For example, LiClO ₄ , LiBF ₄ , LiPF ₆ , LiAlCl ₄ , LiSbF ₆ , LiSCN, LiCF ₃ SO ₃ , LiCF ₃ CO ₂ , LiAsF ₆ , LiB ₁₀ Cl ₁₀ , lower aliphatic lithium carboxylates, LiCl, LiBr, LiI, LiBCl ₄ , borates, imide salts and the like.

Examples of borates include lithium bis (1,2-benzenediolate (2-)-O, O ') borate, bis (2,3-naphthalenedioleate (2-)-O, O') boric acid. Lithium, bis (2,2′-biphenyldiolate (2-)-O, O ′) lithium borate, bis (5-fluoro-2-olate-1-benzenesulfonic acid-O, O ′) lithium borate and so on. Examples of the imide salts include LiN (SO ₂ CF ₃ ) ₂ , LiN (SO ₂ CF ₃ ) (SO ₂ C ₄ F ₉ ), LiN (SO ₂ C ₂ F ₅ ) ₂ and the like. Solutes can be used alone or in combination of two or more. The amount of solute dissolved in 1 liter of non-aqueous solvent is preferably 0.5 to 2 mol.

  Examples of the non-aqueous solvent include a cyclic carbonate, a chain carbonate, and a cyclic carboxylic acid ester. Examples of the cyclic carbonate include propylene carbonate (PC) and ethylene carbonate (EC). Examples of the chain carbonate include diethyl carbonate (DEC), ethyl methyl carbonate (EMC), and dimethyl carbonate (DMC). Examples of cyclic carboxylic acid esters include γ-butyrolactone (GBL) and γ-valerolactone (GVL). A non-aqueous solvent can be used individually by 1 type or in combination of 2 or more types.

  Further, instead of the liquid non-aqueous electrolyte, a gel-like non-aqueous electrolyte may be used. The gel-like non-aqueous electrolyte includes a liquid non-aqueous electrolyte and a polymer material that gels and holds the liquid non-aqueous electrolyte. As the polymer material, those commonly used in this field can be used, and examples thereof include polyvinylidene fluoride (PVDF), polyacrylonitrile, polyethylene oxide, polyvinyl chloride, and polyacrylate.

  In the present embodiment, the separator 14 is used, but the present invention is not limited thereto, and a porous layer may be used. The porous layer contains second inorganic oxide particles and a second polymer (binder). For the second inorganic oxide particles, alumina, titania, silica, magnesia, calcia, zirconia, or the like can be used. As the second polymer, the same binder as that contained in the positive electrode active material layer 11b can be used. The content of the second inorganic oxide particles in the porous layer is preferably 25 to 99.5% by weight of the total amount of the porous layer, more preferably 25 to 90% by weight, particularly preferably 25 to 75% by weight, The balance is the second polymer.

  The porous layer can be formed in the same manner as the positive electrode active material layer 11b. For example, a slurry is prepared by dissolving or dispersing the second polymer and the second inorganic oxide particles in an organic solvent. A porous layer can be formed by applying this slurry to the surface of the positive electrode active material layer 11b and / or the polymer layer 13 and drying it. Here, as an organic solvent, the same thing as the organic solvent used for preparation of positive mix slurry can be used. The thickness of the porous layer is preferably 1 to 10 μm.

In the present embodiment, the separator 14 and the nonaqueous electrolyte are used, but the present invention is not limited to this, and a solid electrolyte layer may be used. The solid electrolyte layer contains a solid electrolyte. Solid electrolytes include inorganic solid electrolytes and organic solid electrolytes. When an organic solid electrolyte, particularly a polymer non-aqueous electrolyte, is used, a flexible thin battery can be obtained.
Examples of inorganic solid electrolytes include sulfide-based inorganic solid electrolytes, oxide-based inorganic solid electrolytes, and other lithium-based inorganic solid electrolytes.

The sulfide-based inorganic solid electrolyte includes (Li ₃ PO ₄ ) _x- (Li ₂ S) _y- (SiS ₂ ) _z glass, (Li ₂ S) _x- (SiS ₂ ) _y , (Li ₂ S) _{x - (P 2 S 5) y} , Li 2 S-P 2 S 5, and the like thio-LISICON. Examples of the oxide-based inorganic solid electrolyte include NASICON types such as LiTi ₂ (PO ₄ ) ₃ , LiZr ₂ (PO ₄ ) ₃ , LiGe ₂ (PO ₄ ) ₃ , (La _{0.5 + x} Li _0.5-3x ) TiO _3, etc. Perovskite type. Other lithium-based inorganic solid electrolytes include LiPON, LiNbO ₃ , LiTaO ₃ , Li ₃ PO ₄ , LiPO _4−x N _x (x is 0 <x ≦ 1), LiN, LiI, and LISICON.

  Known organic solid electrolytes can be used, and examples thereof include ion conductive polymers and polymer non-aqueous electrolytes. Examples of the ion conductive polymers include polyethers having a low glass transition temperature (Tg), amorphous vinylidene fluoride copolymers, blends of different polymers, and the like. Furthermore, as the organic solid electrolyte, a polymer containing an electron donating element in the skeleton and a polymer non-aqueous electrolyte containing a lithium salt can be used.

  As the polymer containing an electron donating element in the skeleton, a polymer containing electron donating oxygen in one or both of the main chain and the side chain is preferable. The electron donating oxygen is ether oxygen, ester oxygen or the like. Specific examples of the polymer include, for example, polyethylene oxide, polypropylene oxide, a copolymer of ethylene oxide and propylene oxide, a polymer containing an ethylene oxide unit and a monomer unit copolymerizable with the unit, a propylene oxide unit and the propylene oxide unit. Examples thereof include a polymer containing a monomer unit copolymerizable with the unit, and polycarbonate. Moreover, as lithium salt, the same thing as the lithium salt (supporting salt) illustrated by the item of the nonaqueous electrolyte can be used.

Here, the description returns to the lithium ion secondary battery 1.
One end of the positive electrode lead 15 is connected to the positive electrode current collector 11 a and the other end is led out from the opening 18 a of the outer case 18 to the outside of the lithium ion secondary battery 1. One end of the negative electrode lead 16 is connected to the negative electrode current collector 12 a, and the other end is led out from the opening 18 b of the outer case 18 to the outside of the lithium ion secondary battery 1. For the positive electrode lead 15, for example, an aluminum lead can be used. For the negative electrode lead 16, for example, a nickel lead can be used.

  Further, the openings 18 a and 18 b of the outer case 18 are sealed with a gasket 17. As the gasket 17, for example, those made of various resin materials can be used. As the outer case 18, any one commonly used in the technical field of lithium ion secondary batteries such as a metal material and a laminate film can be used. When the outer case 18 is formed of a material containing a resin such as a laminate film, the openings 18a and 18b of the outer case 18 may be directly sealed by welding or the like without using the gasket 17. .

  The lithium ion secondary battery 1 can be manufactured as follows, for example. First, one end of the positive electrode lead 15 is connected to the surface of the positive electrode current collector 11a of the positive electrode 11 opposite to the surface on which the positive electrode active material layer 11b is formed. Similarly, one end of the negative electrode lead 16 is connected to the surface of the negative electrode current collector 12a of the negative electrode 12 opposite to the surface on which the negative electrode active material layer 12b is formed. Next, the positive electrode 11 and the negative electrode 12 are laminated via the separator 14 to produce an electrode group. At this time, the positive electrode 11 and the negative electrode 12 are disposed so that the positive electrode active material layer 11b and the negative electrode active material layer 12b face each other.

  This electrode group is inserted into the outer case 18 together with the nonaqueous electrolyte, and the other ends of the positive electrode lead 15 and the negative electrode lead 16 are led out of the outer case 18. Next, the openings 18 a and 18 b are welded through the gaskets 17 while vacuuming the inside of the outer case 18. Thereby, the lithium ion secondary battery 1 is obtained.

  In the present embodiment, the negative electrode active material layer is formed in a thin film shape, but is not limited thereto, and may be an aggregate of a plurality of columnar bodies, for example. The columnar body contains an alloy-based negative electrode active material, and the adjacent columnar bodies are spaced apart from each other and are formed to extend toward the outside of the negative electrode current collector. In the case where the negative electrode active material layer is formed as an aggregate of a plurality of columnar bodies, the anchor effect as the whole negative electrode active material layer is significantly improved by the gaps formed between the columnar bodies. As a result, the adhesion between the negative electrode active material layer and the polymer layer is further enhanced. In the case of forming a negative electrode active material layer that is an aggregate of columnar bodies, it is preferable to provide a plurality of convex portions on the surface of the negative electrode current collector and form the columnar bodies on the convex portions.

That is, in the present invention, it is possible to use another form of negative electrode including a negative electrode current collector having a plurality of convex portions on the surface and a negative electrode active material layer that is an aggregate of a plurality of columnar bodies. FIG. 2 is a perspective view schematically showing the configuration of the negative electrode current collector 21. FIG. 3 is a longitudinal sectional view schematically showing a configuration of another form of negative electrode 20 including the negative electrode current collector 21 shown in FIG. 2. FIG. 4 is a longitudinal sectional view schematically showing the configuration of the columnar body 24 included in the negative electrode active material layer 23 of the negative electrode 20 shown in FIG. FIG. 7 is a side view schematically showing a configuration of an electron beam evaporation apparatus 30 for forming the negative electrode active material layer 23.
The negative electrode 20 includes a negative electrode current collector 21 and a negative electrode active material layer 23.

As shown in FIG. 2, the negative electrode current collector 21 is provided with a plurality of convex portions 22 on one surface 21 a in the thickness direction. The other configuration is the same as that of the negative electrode current collector 12a. In the present embodiment, the convex portion 22 is formed on one surface 21 a in the thickness direction of the negative electrode current collector 21. However, the present invention is not limited to this, and both surfaces in the thickness direction of the negative electrode current collector 21 are formed. The convex portion 22 may be formed.
The convex portion 22 is a protrusion that extends from the surface 21 a in the thickness direction of the negative electrode current collector 21 toward the outside of the negative electrode current collector 21. The convex portions 22 are separated from each other. There is a gap between one convex portion 22 and the adjacent convex portion 22.

  The height of the convex portion 22 is not particularly limited, but the average height is preferably about 3 to 20 μm. In the present specification, the height of the convex portion 22 is defined in the cross section of the convex portion 22 in the thickness direction of the negative electrode current collector 21. Note that the cross section of the convex portion 22 is a cross section including the most distal point in the direction in which the convex portion 22 extends. In such a cross section of the convex portion 22, the height of the convex portion 22 is the length of a perpendicular line dropped from the most distal point in the extending direction of the convex portion 22 to the surface 21 a. The average height of the protrusions 22 is obtained by, for example, observing a cross section in the thickness direction of the negative electrode current collector 21 with a scanning electron microscope (SEM) and measuring the height of 100 protrusions 22. It is obtained as an average value.

Moreover, although the cross-sectional diameter of the convex part 22 is not specifically limited, For example, it is 1-50 micrometers. The cross-sectional diameter of the convex portion 22 is the length of the convex portion 22 in the direction parallel to the surface 21 a in the cross section of the convex portion 22 for obtaining the height of the convex portion 22. Similarly to the height of the convex portion 22, the cross-sectional diameter of the convex portion 22 is also obtained as an average value of measured values by measuring the length of 100 convex portions 22.
Note that the plurality of convex portions 22 do not have to be formed with the same height or the same cross-sectional diameter.

  The shape of the convex part 22 is circular in this embodiment. The shape of the convex portion 22 is the shape of the convex portion 22 when the surface 21a of the negative electrode current collector 21 is made to coincide with a horizontal plane and viewed from above in the vertical direction. The shape of the convex portion 22 is not limited to a circle, and may be, for example, a polygon, an ellipse, a parallelogram, a trapezoid, or a rhombus.

  The convex portion 22 has a substantially flat top portion at the tip portion in the extending direction. Since the convex portion 22 has a flat top at the tip portion, the bonding property between the convex portion 22 and the columnar body 24 is improved. In the present embodiment, the tip portion of the convex portion 22 is substantially planar, but is not limited thereto, and may be a dome shape, a shape with a sharp tip, or the like.

The number of the protrusions 22 and the spacing between the protrusions 22 are not particularly limited, depending on the size of the protrusions 22 (height, cross-sectional diameter, etc.), the size of the columnar body 24 provided on the surface of the protrusions 22, and the like. Are appropriately selected. If an example of the number of the convex parts 22 is shown, it is about 10,000 to 10 million pieces / cm ² . Moreover, it is preferable to form the convex portions 22 so that the distance between the axes of the adjacent convex portions 22 is about 2 to 100 μm. The convex portions 22 can be formed on the surface 21a in a regular or irregular arrangement. The regular arrangement includes a lattice arrangement, a staggered arrangement, a close-packed arrangement, and the like.

  When the shape of the convex portion 22 is circular, the axis of the convex portion 22 is an imaginary line that extends in the direction perpendicular to the surface of the negative electrode current collector 21 through the center of the circle. When the shape of the convex portion 22 is a polygon, a parallelogram, a trapezoid, a rhombus, etc., the axis of the convex portion 22 passes through the intersection of diagonal lines and extends in a direction perpendicular to the surface of the negative electrode current collector 21 It is. When the shape of the convex portion 22 is an ellipse, the axis of the convex portion 22 is an imaginary line that passes through the intersection of the major axis and the minor axis and extends in a direction perpendicular to the surface of the negative electrode current collector 21.

  The protrusion 22 may form a protrusion (not shown) on the surface thereof. Thereby, for example, the bondability between the convex portion 22 and the columnar body 24 is further improved. As a result, peeling from the convex portion 22 of the columnar body 24, peeling propagation, and the like are more reliably prevented. The protrusion is provided so as to protrude from the surface of the protrusion 22 to the outside of the protrusion 22.

  A plurality of protrusions having a smaller dimension than the protrusion 22 may be formed. Further, the protrusion may be formed on the side surface of the convex portion 22 so as to extend in the circumferential direction and / or the growth direction of the convex portion 22. Moreover, when the convex part 22 has a planar top part in the front-end | tip part, 1 or several protrusion smaller than the convex part 22 may be formed in a top part, and also 1 or several protrusion extended in one direction May be formed on the top.

  The negative electrode current collector 21 can be manufactured using, for example, a technique for forming irregularities on a metal sheet. Specifically, for example, a method using a roller having a concave portion formed on the surface (hereinafter referred to as “roller processing method”) and the like can be mentioned. For example, a metal foil, a metal film, a metal plate, or the like can be used for the metal sheet. The material of the metal sheet is, for example, a metal material such as stainless steel, nickel, copper, or copper alloy.

  The metal sheet may be subjected to a surface roughening treatment before the convex portions are formed. Examples of the roughening treatment method include plating, etching, and sand blasting. When the convex portion is formed by the roller processing method, the surface roughness obtained by the roughening treatment is maintained on the convex portion surface as it is.

  According to the roller processing method, the metal sheet may be pressed using a roller having a concave portion formed on the surface (hereinafter referred to as “convex roller”). As described above, a plurality of concave portions are regularly formed on the surface of the convex portion roller. Thereby, the convex part 22 substantially corresponding to the size and shape of the internal space of the concave part and the number and arrangement of the concave parts is formed, and the negative electrode current collector 21 is obtained. The surface of the negative electrode current collector 21 may be roughened. The various surface roughening methods described above can be used for the surface roughening treatment.

  More specifically, when the two convex rollers are pressed against each other so that their axes are parallel to each other, and the metal sheet is passed through the pressure nip portion and pressed, the convex portions are formed on both surfaces in the thickness direction. A negative electrode current collector 21 having 22 formed thereon is obtained. In addition, when the convex roller and the roller having a smooth surface are pressed against each other so that their respective axes are parallel, and the metal sheet is passed through the press nip portion and pressed, the convex roller is projected on one surface in the thickness direction. The negative electrode current collector 21 in which the part 22 is formed is obtained. The pressure contact pressure of the roller is appropriately selected according to the material of the metal sheet, the thickness, the shape and size of the convex portion 22, the set value of the thickness of the negative electrode current collector 21 obtained after pressure molding, and the like.

  The convex roller can be produced, for example, by forming a concave portion by laser processing at a predetermined position on the surface of the ceramic roller. A ceramic roller including a core roller and a sprayed layer can be used. As the core roller, an iron roller, a stainless steel roller, or the like can be used. The sprayed layer is formed by uniformly spraying a ceramic material such as chromium oxide on the surface of the core roller. A recess is formed in the sprayed layer.

Instead of the ceramic roller, a roller including a core roller and a cemented carbide layer can be used. The core roller is the same as described above. The cemented carbide layer is formed on the surface of the core roller and includes a cemented carbide such as tungsten carbide. The cemented carbide layer can be formed by shrink fitting or cold fitting a cemented carbide alloy formed on the core roller.
Moreover, a hard iron-type roller can be used instead of a ceramic roller. As the hard iron-based roller, a roller having at least a concave surface formed of high-speed steel, forged steel, or the like can be used.

  The negative electrode active material layer 23 is an aggregate of a plurality of columnar bodies 24, for example, as shown in FIG. The columnar body 24 extends from the surface of the convex portion 22 toward the outside of the negative electrode current collector 21. The columnar body 24 extends at an angle with respect to the direction perpendicular to the surface 21a of the negative electrode current collector 21 or the perpendicular direction. Further, the columnar bodies 24 are spaced apart from each other with a gap between adjacent columnar bodies 24. The voids relieve stress due to expansion and contraction of the columnar body 24 during charging and discharging. As a result, the columnar body 24 is difficult to peel off from the convex portion 22, and the negative electrode current collector 21 and thus the negative electrode 20 are hardly deformed.

  As shown in FIG. 4, the columnar body 24 is preferably formed as a laminate of eight columnar chunks 24a, 24b, 24c, 24d, 24e, 24f, 24g, and 24h. More specifically, the columnar body 24 is formed as follows. First, the columnar chunk 24a is formed so as to cover the top of the convex portion 22 and a part of the side surface following the top. Next, the columnar chunk 24b is formed so as to cover the remaining side surface of the convex portion 22 and a part of the top surface of the columnar chunk 24a. That is, in FIG. 4, the columnar block 24 a is formed at one end including the top of the convex portion 22. On the other hand, the columnar chunk 24 b partially overlaps the columnar chunk 24 a, but the portion not overlapping the columnar chunk 24 a is formed at the other end of the convex portion 22.

  Further, the columnar chunk 24c is formed so as to cover the rest of the top surface of the columnar chunk 24a and a part of the top surface of the columnar chunk 24b. That is, the columnar chunk 24c is formed mainly in contact with the columnar chunk 24a. Further, the columnar chunk 24d is formed so as to mainly contact the columnar chunk 24b. Similarly, the columnar bodies 24 are formed by alternately stacking the columnar chunks 24e, 24f, 24g, and 24h. Note that the number of stacked columnar lumps is not limited to eight, and can be any number of two or more.

The columnar body 24 can be formed by, for example, an electron beam evaporation apparatus 30 shown in FIG. In FIG. 7, each member inside the vapor deposition apparatus 30 is also shown by a solid line. The vapor deposition apparatus 30 includes a chamber 31, a first pipe 32, a fixing base 33, a nozzle 34, a target 35, an electron beam generator (not shown), a power source 36, and a second pipe (not shown).
The chamber 31 is a pressure-resistant container, and accommodates the first pipe 32, the fixing base 33, the nozzle 34 and the target 35 therein.

  The first pipe 32 has one end connected to the nozzle 34 and the other end extending outward from the chamber 31 and is connected to a source gas cylinder or source gas manufacturing apparatus (not shown) via a mass flow controller (not shown). Oxygen, nitrogen, etc. can be used for the source gas. The first pipe 32 supplies the raw material gas to the nozzle 34.

  The fixing base 33 is a plate-like member that is rotatably supported, and the negative electrode current collector 21 can be fixed to one surface in the thickness direction. The rotation of the fixing base 33 is performed between the position indicated by the solid line and the position indicated by the alternate long and short dash line in FIG. At the position indicated by the solid line, the angle formed by the current collector fixing surface of the fixing base 33 and the horizontal line is α °. At the position indicated by the alternate long and short dash line, the angle formed by the current collector fixing surface of the fixing base 33 and the horizontal line is (180−α) °. The angle α ° can be appropriately selected according to the dimensions of the columnar body 24 to be formed.

  The nozzle 34 is provided between the fixed base 33 and the target 35 and is connected to one end of the first pipe 32. The nozzle 34 supplies a source gas into the chamber 31. The target 35 accommodates an alloy-based negative electrode active material or its raw material. The electron beam generator irradiates the alloy-based negative electrode active material accommodated in the target 35 or its raw material with an electron beam and heats it to generate these vapors.

  The power source 36 is provided outside the chamber 31 and applies a voltage to the electron beam generator. The second pipe introduces a gas that becomes the atmosphere in the chamber 31. An electron beam vapor deposition apparatus having the same configuration as the vapor deposition apparatus 30 is commercially available from ULVAC, Inc., for example.

  According to the electron beam evaporation apparatus 30, first, the negative electrode current collector 21 is fixed to the fixing base 33, and oxygen gas is introduced into the chamber 31. In this state, the target 35 is irradiated with an electron beam to heat the alloy-based negative electrode active material or its raw material to generate its vapor. In the present embodiment, silicon is used as the alloy-based negative electrode active material that becomes the target 35. The generated steam rises upward in the vertical direction, and when it passes through the nozzle 34, it is mixed with the raw material gas, and then rises and is supplied to the surface of the negative electrode current collector 21 fixed to the fixed base 33. A layer containing silicon and oxygen is formed on the surface of the protrusions 22 that are not.

  At this time, the columnar block 24a shown in FIG. 4 is formed on the surface of the convex portion by arranging the fixing base 33 at the position of the solid line. Next, the fixed base 33 is rotated to the position indicated by the alternate long and short dash line to form the columnar block 24b shown in FIG. By alternately rotating the position of the fixing base 33 in this way, a plurality of columnar bodies 24 that are a laminate of the eight columnar chunks 24a, 24b, 24c, 24d, 24e, 24f, 24g, and 24h shown in FIG. The negative electrode active material layer 23 is obtained at the same time on the surface of the protrusions 22.

When the negative electrode active material is a silicon oxide represented by, for example, SiO _a (0.05 <a <1.95), the columnar body 24 is formed so that a concentration gradient of oxygen is formed in the thickness direction of the columnar body 24. It may be formed. Specifically, the oxygen content may be increased at a portion close to the current collector 21, and the oxygen content may be reduced as the distance from the current collector 21 increases. Thereby, the bondability between the convex portion 22 and the columnar body 24 can be further improved.

  In the case where the source gas is not supplied from the nozzle 34, the columnar body 24 mainly composed of silicon or tin is formed. Further, the negative electrode active material layer 12b can be formed by using the negative electrode current collector 12a instead of the negative electrode current collector 21 and fixing the fixing base 33 in the horizontal direction without rotating.

  Although FIG. 1 shows a specific example of the laminated lithium ion secondary battery 1, the present invention is not limited to this, and a wound electrode group wound with a separator interposed between a positive electrode and a negative electrode is used as an outer case or It can also be assembled in the form of a wound lithium ion secondary battery housed in a battery can. That is, the lithium ion secondary battery of the present invention has various forms such as a flat battery including a stacked electrode group, a cylindrical battery including a wound electrode group, and a square battery including a wound electrode group. Can be taken.

  FIG. 5 is a cross-sectional view schematically showing a configuration of a main part of a negative electrode 25 which is another embodiment of the present invention. In FIG. 5, for the sake of convenience, it is assumed that the negative electrode current collector 21 side is the bottom and the polymer layer 28 side is the top. The negative electrode 25 is similar to the negative electrode 20, and corresponding portions are denoted by the same reference numerals and description thereof is omitted. The negative electrode 25 includes a negative electrode current collector 21, a negative electrode active material layer 26, and a polymer layer 28. The negative electrode 25 has two major characteristics, and the other configuration is the same as that of the negative electrode 20.

  One feature is that the negative electrode active material layer 26 is formed as an aggregate of spindle-shaped columns 27. The columnar body 27 contains an alloy-based negative electrode active material. This configuration provides the following advantages. That is, on the surface of the negative electrode active material layer 26, portions where the columnar bodies 27 are present and portions where the columnar bodies 27 are not present alternately appear. This is an apparent unevenness. Further, the gap between the columnar bodies 27 becomes an apparent crack. The unevenness and cracks show a remarkable anchor effect, and the adhesion between the negative electrode active material layer 26 and the polymer layer 28 is further improved.

  Moreover, it is preferable that the distance between axes of one columnar body 27 and the other columnar body 27 adjacent to it is 10-50 micrometers. Thereby, the polymer layer coating liquid smoothly flows into the gaps between the columnar bodies 27, and the polymer layer 28 can be easily formed between the columnar bodies 27. The axis of the columnar body 27 is a line that connects the center of the contact surface with the surface of the convex portion 22 of the columnar body 27 and the most distal portion of the columnar body 27. The center of the contact surface is the center of the smallest circle that can contain the contact surface. Since the plurality of columnar bodies 27 grow in substantially the same direction, their axes are substantially parallel.

  Further, when the columnar body 27 is formed in a spindle shape, a relatively large gap is formed around the columnar body 27. The voids relieve internal stress generated when the adjacent columnar bodies come into contact with each other due to the expansion of the alloy-based negative electrode active material contained in the columnar bodies 27. For this reason, in the columnar body 27, cracks are not easily formed even if charge and discharge are repeated. Therefore, generation of by-products due to contact between the new surface and the non-aqueous electrolyte, wasteful consumption of the non-aqueous electrolyte, and the like are suppressed, and various battery performances are unlikely to deteriorate.

  If the distance between the axes of the columnar bodies 27 is less than 10 μm, the polymer layer coating liquid may not easily flow into the gaps between the columnar bodies 27. Further, there is a possibility that the volume expansion of the alloy-based negative electrode active material contained in the columnar body 27 cannot be sufficiently absorbed. When the distance between the axes exceeds 50 μm, the number of the columnar bodies 27 becomes too small, and the capacity of the negative electrode 25 may be reduced. The spindle-shaped columnar body 27 can be produced by adjusting the rotation angle of the turntable 33 in the electron beam evaporation apparatus 30 shown in FIG.

  Another feature is that the polymer layer 28 enters not only the surface of the negative electrode active material layer 26 but also the gap between one columnar body 27 and another columnar body 27 adjacent thereto. The polymer layer 28 that has entered the space between the columnar bodies 27 exists only in the upper part between the columnar bodies 27 and does not reach the surface 21 a of the negative electrode current collector 21. When the polymer layer 28 enters the upper part of the space between the columnar bodies 27, the anchor effect of an apparent crack (the space between the columnar bodies 27) is sufficiently exhibited. As a result, the adhesion between the negative electrode active material layer 26 and the polymer layer 28 is further improved. Furthermore, the battery charge / discharge cycle characteristics, output characteristics, and the like are significantly reduced.

  Similar to the polymer layer 13, the polymer layer 28 contains the first polymer and the first inorganic oxide particles. The particle diameter of the first inorganic oxide particles contained in the polymer layer 28 is preferably smaller than the distance between the axes of the columnar bodies 27. As a result, the polymer layer coating liquid easily enters the gaps between the columnar bodies 27, and the adhesion between the columnar bodies 27 and the polymer layer 28 is further improved. The degree to which the polymer layer coating liquid enters the gaps between the columnar bodies 27 can be easily adjusted, for example, by changing the viscosity of the coating liquid. When the viscosity of the coating liquid is high, the degree to which the coating liquid enters decreases. On the other hand, when the viscosity of the coating liquid is low, the degree of penetration of the coating liquid increases.

  FIG. 6 is a cross-sectional view schematically showing a configuration of a main part of a negative electrode 29 which is another embodiment of the present invention. The negative electrode 29 is similar to the negative electrode 25, and corresponding portions are denoted by the same reference numerals and description thereof is omitted. The negative electrode 29 is characterized in that the polymer layer 28 a enters the gap between one columnar body 27 and a columnar body 27 adjacent thereto, and reaches the surface 21 a of the negative electrode current collector 20. That is, the gaps between one columnar body 27 and the columnar body 27 adjacent to the columnar body 27 are all filled with the polymer layer 28a. The polymer layer 28a contains the first polymer, the first inorganic oxide particles, and the lithium ion conductive support salt, and has lithium ion conductivity.

  With this configuration, first, the same effect as that of the negative electrode 25 can be obtained. Furthermore, since the polymer layer 28a is formed in the entire space between the columnar bodies 27, the anchor effect of the negative electrode active material layer 26 is further enhanced. As a result, the adhesion between the surface of the negative electrode active material layer 26 and the polymer layer 28a is further improved. Moreover, it can suppress reliably that the columnar body 27 peels from the convex part 22 by expansion | swelling and shrinkage | contraction of an alloy type negative electrode active material.

  Furthermore, a polymer layer may be formed on the surface of the columnar body 27. At this time, you may comprise so that a space | gap may exist between the polymer layer formed in the surface of one columnar body 27, and the polymer layer formed in the surface of the other adjacent columnar body 27. FIG. Since the polymer layer has flexibility, it can follow the volume change of the alloy-based negative electrode active material contained in the columnar body 27. Therefore, by adopting this configuration, it is possible to achieve both a high level of suppression of rapid contact between the new surface and the non-aqueous electrolyte and relaxation of stress generated by the volume change of the alloy-based negative electrode active material.

Hereinafter, the present invention will be specifically described with reference to Examples, Comparative Examples, and Test Examples.
Example 1
(1) Preparation NiSO ₄ aqueous solution of the positive electrode active material, Ni: Co = 8.5: to prepare an aqueous solution of metal ion concentration 2 mol / L so as to 1.5 (molar ratio) was added cobalt sulfate. While stirring, a 2 mol / L sodium hydroxide solution is gradually added dropwise to the aqueous solution to neutralize, thereby coprecipitation of a binary precipitate having a composition represented by Ni _0.85 Co _0.15 (OH) _2. Was generated by This precipitate was separated by filtration, washed with water, and dried at 80 ° C. to obtain a composite hydroxide.

This composite hydroxide was heated in the atmosphere at 900 ° C. for 10 hours for heat treatment to obtain a composite oxide having a composition represented by Ni _0.85 Co _0.15 O. Here, lithium hydroxide monohydrate is added so that the sum of the number of atoms of Ni and Co and the number of atoms of Li are equal, and heat treatment is performed at 800 ° C. for 10 hours in air. Thus, a lithium nickel-containing composite metal oxide having a composition represented by LiNi _0.85 Co _0.15 O ₂ was obtained. In this way, a positive electrode active material having a secondary particle volume average particle size of 10 μm was obtained.

(2) Production of Positive Electrode 93 g of the positive electrode active material obtained above, 3 g of acetylene black (conductive agent), 4 g of polyvinylidene fluoride powder (binder) and 50 ml of N-methyl-2-pyrrolidone (NMP) are sufficient. To prepare a positive electrode mixture paste. This positive electrode mixture paste was applied to one side of an aluminum foil (positive electrode current collector) having a thickness of 15 μm, dried, and rolled to form a positive electrode active material layer having a thickness of 130 μm.

(3) Production of negative electrode On the surface of a forged steel roller having a diameter of 50 mm, a hole which is a circular concave portion having a diameter of 20 μm and a depth of 8 μm was formed by laser processing to produce a convex roller. The holes were in a close-packed arrangement with an axial distance of 20 μm between adjacent holes. Two convex rollers were produced. The two convex rollers obtained above were pressed so that their axes were parallel to form a pressure nip.

  An alloy copper foil (trade name: HCL-02Z, thickness: 20 μm, manufactured by Hitachi Cable Co., Ltd.) containing zirconia at a ratio of 0.03% by weight with respect to the total amount is applied to the above-mentioned pressure nip portion with a linear pressure of 2. It was made to pass through at 0 kgf / cm, and both sides of the alloy copper foil were pressure-molded to produce a negative electrode current collector used in the present invention. When a cross section in the thickness direction of the obtained negative electrode current collector was observed with a scanning electron microscope, a plurality of convex portions were formed on both surfaces of the negative electrode current collector. The average height of the protrusions was about 8 μm. This negative electrode current collector was cut into a size of 35 mm × 185 mm.

  Columnar bodies were formed on the convex surface of the negative electrode current collector using a commercially available vapor deposition apparatus (manufactured by ULVAC, Inc.) having the same structure as the electron beam vapor deposition apparatus 30 shown in FIG. The conditions for vapor deposition are as follows. Note that the fixed base on which the negative electrode current collector having a size of 35 mm × 185 mm is fixed has a position at an angle α = 60 ° (a position of a solid line shown in FIG. 7) and a position at an angle (180−α) = 120 ° (FIG. 7). And the position of the alternate long and short dash line). Thereby, a plurality of columnar bodies in which eight layers of columnar chunks as shown in FIG. 4 were laminated were formed, and a negative electrode active material layer was produced. Each columnar body grew in the direction in which the convex portion extends from the top portion of the convex portion and the side surface near the top portion.

Negative electrode active material (evaporation source): silicon, purity 99.9999%, oxygen released from nozzle manufactured by Kojundo Chemical Laboratory Co., Ltd .: purity 99.7%, oxygen released from nozzle manufactured by Nippon Oxygen Co., Ltd. Flow rate: 80sccm
Angle α: 60 °
Electron beam acceleration voltage: -8 kV
Emission: 500mA
Deposition time: 3 minutes

The formed negative electrode active material layer had a thickness T of 16 μm. The thickness of the negative electrode active material layer was determined as follows. The cross section in the thickness direction of the negative electrode was observed with a scanning electron microscope, and the length from the top of the convex portion to the top of the columnar body was determined for 10 columnar bodies formed on the surface of the convex portion. The average value of the ten measured values obtained was taken as the thickness of the negative electrode active material layer. Further, when the amount of oxygen contained in the columnar body was quantified by a combustion method, it was found that the composition of the compound constituting the columnar body was SiO _0.5 .

  Next, lithium metal was deposited on the surface of the negative electrode active material layer. By depositing lithium metal, lithium corresponding to the irreversible capacity stored in the negative electrode active material layer at the time of the first charge / discharge was supplemented. Lithium metal was deposited using a resistance heating vapor deposition apparatus (manufactured by ULVAC, Inc.) in an argon atmosphere. Lithium metal is loaded into a tantalum boat in a resistance heating vapor deposition apparatus, the negative electrode is fixed so that the negative electrode active material layer faces the tantalum boat, and a 50 A current is passed through the tantalum boat in an argon atmosphere. Deposition was performed for 10 minutes.

(4) Formation of polymer layer LiPF ₆ was dissolved at a concentration of 1.0 mol / L in a mixed solvent containing ethylene carbonate (EC) and propylene carbonate (PC) in a volume ratio of 1: 1 to prepare a coating solution. A non-aqueous electrolyte was prepared. To this non-aqueous electrolyte, VDF, HFP and TFE were added at a weight ratio of 6.4: 3.25: 0.35, and the mixture was heated to 80 ° C. for copolymerization, and the weight of VDF, HFP and TFE was increased. A 15% by weight solution (hereinafter referred to as “first layer solution”) of the union (first polymer) was prepared. In 100 parts by weight of the obtained first layer solution, 25 parts by weight of alumina (first inorganic oxide particles) was uniformly dispersed to prepare a first layer coating solution.

  VDF and HFP are added in a weight ratio of 8.8: 1.2 to a non-aqueous electrolyte for preparing a coating liquid having the same composition as described above, and the mixture is heated to 80 ° C. for copolymerization. A 15% by weight solution of the copolymer (first polymer) (hereinafter “second layer solution”) was prepared. A second layer coating solution was prepared by uniformly dispersing 50 parts by weight of alumina (first inorganic oxide particles) in 100 parts by weight of the second layer solution.

  The negative electrode plate obtained above was immersed in the first layer coating solution for 1 minute, and the negative electrode plate was impregnated with the first layer coating solution. The impregnated negative electrode plate was introduced into a vacuum dryer and vacuum dried at 80 ° C. for 10 minutes. A first layer having a thickness of about 0.1 μm was formed on the negative electrode plate surface by the first layer coating liquid. The negative electrode plate on which the first layer was formed was immersed in the second layer coating solution for 1 minute, and the second layer coating solution was applied to the surface of the first layer of the negative electrode plate. The negative electrode plate after application was placed on a glass plate and vacuum-dried at 80 ° C. for 10 minutes to form a second layer on the surface of the first layer.

  The content of alumina (first inorganic oxide particles) in the first layer is 37.5% by weight of the total amount of the first layer, and the remainder of the first layer is a copolymer of VDF, HFP, and TFE (first Polymer). The content of alumina (first inorganic oxide particles) in the second layer is about 23% by weight of the total amount of the second layer, and the remainder of the second layer is a copolymer (first polymer) of VDF and HEP. there were. Thus, a polymer layer composed of the first layer and the second layer was formed on the surface of the negative electrode active material layer of the negative electrode plate.

(5) Production of a wound battery A polyethylene microporous membrane (separator, trade name: hypopore, thickness) between the positive electrode plate obtained above and the negative electrode plate on which the first and second polymer layers are formed. 20 μm, manufactured by Asahi Kasei Co., Ltd.) and wound to prepare an electrode group. At this time, it arrange | positioned so that a positive electrode active material layer and a negative electrode active material layer may oppose through a separator, and a separator and negative electrode active material layer may oppose through a polymer layer. Next, one end of the aluminum positive electrode lead was welded to the positive electrode current collector of the positive electrode plate, and one end of the nickel negative electrode lead was welded to the negative electrode current collector of the negative electrode plate.

This electrode group was inserted into an outer case made of an aluminum laminate sheet together with a nonaqueous electrolyte. For the non-aqueous electrolyte, a mixed solvent containing ethylene carbonate (EC), tilmethyl carbonate (EMC) and diethyl carbonate (DEC) at a volume ratio of 2: 3: 5, and LiPF ₆ at a concentration of 1.4 mol / L. The non-aqueous electrolyte dissolved in was used. Next, the positive electrode lead and the negative electrode lead are led out from the opening of the outer case to the outside of the outer case, and the opening of the outer case is welded while vacuuming the inside of the outer case, so that the lithium ion secondary battery of the present invention Was made.

(Example 2)
A single-phase polymer layer was formed on the negative electrode surface in the same manner as in Example 1 except that PVDF was used instead of the copolymer of VDF, HFP, and TFE in the first polymer solution A. A lithium ion secondary battery was produced.

(Comparative Example 1)
A lithium ion secondary battery was produced in the same manner as in Example 2 except that alumina was not added.

(Comparative Example 2)
A lithium ion secondary battery was produced in the same manner as in Example 1 except that the polymer layer was not formed.

(Test Example 1)
The following evaluation tests were performed on the lithium ion secondary batteries obtained in Examples 1 to 3 and Comparative Example 1.

[Battery capacity evaluation test]
About the lithium ion secondary battery of Examples 1-2 and the comparative example 1, the charging / discharging cycle was performed twice on the following conditions, and the discharge capacity was calculated | required. The results are shown in Table 1.
Constant current charging: 370 mA (1.0 C), final voltage 4.15 V.
Constant voltage charging: End current 18.5 mA (0.05 C), rest time 20 minutes.
Constant current discharge: current 74 mA (0.2 C), end voltage 2 V, rest time 20 minutes.

[Charge / discharge cycle characteristics test]
Each battery was charged at a constant current up to 4.15 V at 370 mA (1.0 C) in a 25 ° C. environment, then charged at a constant voltage to a termination current of 18.5 mA (0.05 C), and 2 V at 74 mA (0.2 C). Discharged up to a constant current. The discharge capacity at this time was defined as the initial discharge capacity. Then, the current value at the time of discharge was set to 370 mA (1 C), and the charge / discharge cycle was repeated. After 100 cycles, constant current discharge was performed at 74 mA (0.2 C) to obtain a discharge capacity after 100 cycles. Then, the percentage of the discharge capacity after 100 cycles with respect to the initial discharge capacity (cycle capacity maintenance rate,%) was determined. The results are shown in Table 1.

[Battery measurement]
In the first cycle of the charge / discharge cycle characteristic test, the thickness of the electrode group during charging was measured. Moreover, the thickness at the time of charge of an electrode group was measured in the 200th cycle of a charge / discharge cycle characteristic test. The difference between the thickness at the time of charging the electrode group at the 200th cycle and the thickness at the time of charging the electrode group at the first cycle was defined as the swelling of the battery. The results are shown in Table 1.

[Nail penetration test]
The battery after the capacity measurement was charged under the same conditions as the capacity measurement. A battery with an open circuit voltage of about 4.1 V was passed through a battery with an iron nail (diameter: 1.0 mm) at a speed of 1 mm / second in a temperature bath at 60 ° C. The battery voltage at that time was monitored, and the battery voltage one second after the battery started short-circuiting by the nail is shown in Table 1.

  From Table 1, it can be seen that the batteries of the present invention of Examples 1 and 2, especially of Example 1, have little deterioration in charge / discharge cycle characteristics and the swelling of the battery is suppressed. This is because, by forming a polymer layer on the surface of the negative electrode active material layer, even if a crack occurs in the alloy-based negative electrode active material and a new surface is generated, the polymer layer suppresses contact between the new surface and the nonaqueous electrolyte. This is presumed.

  Moreover, it can be seen from the comparison between Example 1 and Example 2 that when the polymer layer is formed of a plurality of layers instead of a single phase, the deterioration of the charge / discharge cycle characteristics is remarkably suppressed. Moreover, in the battery of this invention, it can also be estimated that the progress of heat generation is suppressed when an internal short circuit occurs.

  The lithium ion secondary battery of the present invention can be used in the same applications as conventional lithium ion secondary batteries, and in particular, personal computers, mobile phones, mobile devices, personal digital assistants (PDAs), portable game devices, and video cameras. It is useful as a power source for portable electronic devices such as In addition, it is expected to be used as a secondary battery for assisting an electric motor, a power tool, a cleaner, a power source for driving a robot, a power source for a plug-in HEV, etc. in a hybrid electric vehicle, a fuel cell vehicle and the like.

DESCRIPTION OF SYMBOLS 1 Lithium ion secondary battery 11 Positive electrode 11a Positive electrode collector 11b Positive electrode active material layer 12, 20, 25 Negative electrode 12a, 21 Negative electrode collector 12b, 23, 26 Negative electrode active material layer 13, 28, 28a Polymer layer 14 Separator 15 Positive electrode lead 16 Negative electrode lead 17 Gasket 18 Exterior case 22 Convex part 24, 27 Columnar body 30 Electron beam vapor deposition apparatus 40 Vapor deposition apparatus

Claims (13)

Including a positive electrode, a negative electrode, a polymer layer and a lithium ion permeable insulating layer;
The positive electrode includes a positive electrode active material layer containing a positive electrode active material capable of inserting and extracting lithium and a positive electrode current collector,
The negative electrode includes a negative electrode active material layer formed by a vapor phase method and containing an alloy-based negative electrode active material and a negative electrode current collector,
The polymer layer is formed on a surface of the negative electrode active material layer, contains a first polymer and first inorganic oxide particles, and the lithium ion permeable insulating layer is interposed between the positive electrode and the negative electrode Lithium ion secondary battery arranged to do.   The lithium ion secondary battery according to claim 1, wherein the lithium ion permeable insulating layer is a separator or a porous layer, and further includes a lithium ion conductive nonaqueous electrolyte.   The lithium ion secondary battery according to claim 1, wherein the lithium ion permeable insulating layer is a lithium ion conductive solid electrolyte layer.   4. The lithium ion secondary battery according to claim 1, wherein the content of the first inorganic oxide particles in the polymer layer is 25 to 75% by weight of the total amount of the polymer layer.   The lithium ion secondary battery according to any one of claims 1 to 4, wherein the first inorganic oxide particles are at least one selected from the group consisting of alumina, magnesia, silica, zirconia, and titania.   The lithium ion secondary battery according to any one of claims 1 to 5, wherein the first polymer is a fluororesin.   The lithium ion secondary battery according to any one of claims 1 to 6, wherein the polymer layer has a thickness of 0.05 to 25 µm.   The porous layer includes a second polymer and second inorganic oxide particles, and the content of the second inorganic oxide particles is 25 to 99.5% by weight of the total amount of the porous layer. The lithium ion secondary battery as described.   The negative electrode active material layer is an aggregate of a plurality of columnar bodies, the columnar bodies contain an alloy-based negative electrode active material, extend outward from the surface of the negative electrode current collector and are separated from each other. The lithium ion secondary battery according to any one of 8.   The lithium ion secondary battery according to claim 9, wherein a particle diameter of the first inorganic oxide particles is smaller than a distance between the axes of one columnar body and the columnar body adjacent thereto.   The polymer layer is a laminate of a plurality of polymer layers, and each of the plurality of polymer layers contains the first polymer and the first inorganic oxide particles, and the first inorganic oxide particles in the plurality of polymer layers. The lithium ion secondary battery according to any one of claims 1 to 10, wherein the content of is gradually increased in a direction from the negative electrode active material layer toward the lithium ion permeable insulating layer. The plurality of polymer layers are a first layer and a second layer;
The first layer is formed on the surface of the negative electrode active material layer, and contains the first polymer and the first inorganic oxide particles.
The second layer is formed on the surface of the first layer, contains the first polymer and the first inorganic oxide particles, and the content of the first inorganic oxide particles in the first layer is The lithium ion secondary battery according to claim 11, wherein the content is less than the content of the first inorganic oxide particles in the second layer.   The lithium according to any one of claims 1 to 12, wherein the alloy-based negative electrode active material is one or more selected from an alloy-based negative electrode active material containing silicon and an alloy-based negative electrode active material containing tin. Ion secondary battery.

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