JP2011258351A - Lithium ion secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve a cycle characteristic of a lithium ion secondary battery which includes a negative electrode containing an alloy active material.SOLUTION: A lithium ion secondary battery includes: a positive electrode 3 which includes a positive electrode active material layer containing a positive electrode active material capable of occluding and discharging lithium ions and a binder, and a positive electrode current collector supporting the positive electrode active material layer; a negative electrode 4 which includes a negative electrode active material layer containing an alloy active material and a negative electrode current collector supporting the negative electrode active material layer; a separator 5 interposed between the positive electrode 3 and the negative electrode 4; and a nonaqueous electrolyte. The binder contained in the positive electrode active material layer contains a readily swellable resin of which a degree of swelling with respect to the nonaqueous electrolyte is 50% or more.

Description

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

  A lithium ion secondary battery using an alloy active material as a negative electrode active material (hereinafter sometimes referred to as an “alloy secondary battery”) is more than a conventional lithium ion secondary battery using graphite as a negative electrode active material. It is known to have a high capacity and energy density. Therefore, the alloy-based secondary battery is expected not only as a power source for electronic devices but also as a main power source or auxiliary power source for transportation equipment, machine tools, and the like. Known alloy-based active materials include silicon-based active materials such as silicon and silicon oxide, and tin-based active materials such as tin and tin oxide.

  Patent Document 1 discloses a positive electrode including a positive electrode active material including a lithium manganese composite oxide and a lithium nickel composite oxide and a binder, a negative electrode capable of inserting and extracting lithium ions, and a positive electrode and a negative electrode. Disclosed is a non-aqueous electrolyte secondary battery comprising an intervening separator and a non-aqueous electrolyte, wherein the binder contained in the positive electrode contains polyvinylidene fluoride and hexafluoropropylene.

  According to Patent Document 1, with the above-described configuration, a decrease in the fluidity of the positive electrode mixture slurry is suppressed, and the productivity and quality of the nonaqueous electrolyte secondary battery are improved.

  Patent Document 2 discloses a positive electrode including a positive electrode active material layer including a positive electrode active material and a binder, a negative electrode including a negative electrode active material layer including a negative electrode active material and a binder, and a positive electrode and a negative electrode. And a separator containing a polymer that holds the non-aqueous electrolyte, and the binder contained in the positive electrode active material layer and / or the negative electrode active material layer has a swelling ratio of 5% by weight with respect to the non-aqueous electrolyte. A polymer electrolyte battery comprising the following first polymer and a second polymer having a swelling ratio of 30% by weight or more with respect to the non-aqueous electrolyte is disclosed.

  According to Patent Document 2, with the above-described configuration, the peeling of the active material layer from the current collector due to repeated charge and discharge and the leakage of the nonaqueous electrolyte solution to the outside of the battery are suppressed, and the deterioration of the battery characteristics is small. We are trying to obtain a highly safe polymer electrolyte battery.

  Patent Document 3 discloses a positive electrode including a positive electrode active material layer including a positive electrode active material and a binder, a negative electrode including a negative electrode active material layer including a negative electrode active material and a binder, and a positive electrode and a negative electrode. And a polymer support interposed between the positive electrode active material layer and / or the negative electrode active material layer and the separator, and the degree of solvent swelling of the polymer constituting the polymer support is high Disclosed is a non-aqueous electrolyte secondary battery characterized by having a degree of solvent swelling of a binder contained in a positive electrode active material layer and / or a negative electrode active material layer in contact with a support.

  According to Patent Document 3, an attempt is made to eliminate leakage of the non-aqueous electrolyte with the above-described configuration.

JP 2002-050405 A JP 2002-203560 A JP 2008-047402 A

  In the alloy-based secondary battery, as the number of times of charging / discharging increases, the cycle characteristics may be significantly reduced. As a result of repeated studies on this cause, the present inventors have obtained the following knowledge.

  In a negative electrode containing an alloy-based active material, many minute voids are formed in the negative-electrode active material layer as the alloy-based active material repeatedly expands and contracts with charge and discharge. When the alloy-based active material contracts due to discharge, the volume of the gap increases, and the nonaqueous electrolytic solution stored in the alloy-based secondary battery is absorbed into the gap by capillary action. As a result, most of the non-aqueous electrolyte is unevenly distributed in the negative electrode, while the positive electrode is locally impregnated with the non-aqueous electrolyte, but most of the positive electrode is in a liquid-drying state.

  For this reason, the charge / discharge reaction concentrates only on the portion of the positive electrode impregnated with the non-aqueous electrolyte (hereinafter referred to as “impregnated portion”). In particular, during discharge, lithium ions released from the negative electrode are occluded only in the impregnated portion, the impregnated portion is overdischarged, and the crystal structure is disturbed in the impregnated portion. Thereby, deterioration of the positive electrode of the positive electrode is promoted. The present inventors considered that this was the cause of the deterioration of the cycle characteristics. And as a result of earnest studies to suppress the non-aqueous electrolyte from being unevenly distributed in the negative electrode containing the alloy-based active material, the present invention has been completed.

  An object of the present invention is to provide a lithium ion secondary battery including a negative electrode containing an alloy-based active material and having excellent cycle characteristics.

  A lithium ion secondary battery of the present invention includes a positive electrode active material layer containing a positive electrode active material capable of occluding and releasing lithium ions and a binder, and a positive electrode provided with a positive electrode current collector supporting the positive electrode active material layer A negative electrode active material layer made of an alloy-based active material, a negative electrode including a negative electrode current collector that supports the negative electrode active material layer, a separator interposed between the positive electrode and the negative electrode, and a non-aqueous electrolyte. The binder contains an easily swellable resin having a degree of swelling with respect to the non-aqueous electrolyte of 50% or more.

  In this way, the positive electrode active material particles are bound using an easily swellable resin having a high nonaqueous electrolyte absorption capability, thereby improving the nonaqueous electrolyte absorption capability of the positive electrode. Thereby, it is possible to suppress the easily swellable resin dispersed in the positive electrode from being impregnated with the nonaqueous electrolytic solution, and the positive electrode from being locally dried up. As a result, a phenomenon in which the positive electrode is in a local overdischarge state due to the concentration of local charge / discharge reactions and the crystal structure is disturbed is very unlikely to occur. For this reason, deterioration of the positive electrode is remarkably suppressed.

  According to the present invention, a lithium ion secondary battery having high capacity and high energy density and excellent cycle characteristics is provided.

It is a longitudinal cross-sectional view which shows typically the structure of the lithium ion secondary battery which is 1st Embodiment of this invention. It is a longitudinal cross-sectional view which shows typically the structure of the negative electrode with which the lithium ion secondary battery shown in FIG. 1 is equipped. It is a longitudinal cross-sectional view which shows typically the structure of the columnar body with which the negative electrode shown in FIG. 2 is equipped. It is side surface perspective drawing which shows the structure of an electron beam type vacuum evaporation system typically. It is a side perspective view which shows typically the structure of the vacuum evaporation system of another form.

  An embodiment of the present invention will be described in detail with reference to the drawings.

  FIG. 1 is a longitudinal sectional view schematically showing a configuration of a lithium ion secondary battery 1 according to the first embodiment of the present invention. In FIG. 1, the positive electrode current collector and the positive electrode active material layer in the positive electrode 3 and the negative electrode current collector 20 and the negative electrode active material layer 22 in the negative electrode 4 are not shown. FIG. 2 is a longitudinal sectional view schematically showing the configuration of the negative electrode 4 provided in the lithium ion secondary battery 1 shown in FIG.

  The lithium ion secondary battery 1 includes a positive electrode 3 containing an easily swellable resin having a degree of swelling of 50% or more with respect to a non-aqueous electrolyte as a binder, and a negative electrode 4 using an alloy-based active material as a negative electrode active material. The wound electrode group 2 (hereinafter simply referred to as “electrode group 2”) obtained by winding with the separator 5 interposed therebetween, and the positive electrode current collector of the positive electrode 3 and the sealing plate 15 are electrically connected. Positive electrode lead 10, negative electrode lead 11 that conducts negative electrode current collector 20 of negative electrode 4 and battery case 14, upper insulating plate 12 and lower insulating plate 13 that are respectively attached to both ends in the longitudinal direction of electrode group 2, bottomed cylinder A battery case 14 that functions as a negative electrode terminal, a sealing plate 15 that functions as a positive electrode terminal, and a battery case 14 that functions as a negative electrode terminal. , Battery case 4 is arranged so as to be interposed between the sealing plate 15, a gasket 16, which insulates them.

  The lithium ion secondary battery 1 is a positive electrode active material containing, as a binder, an easily swellable resin having a degree of swelling with respect to a non-aqueous electrolyte of 50% or more (hereinafter sometimes simply referred to as “an easily swellable resin”). It has the positive electrode 3 provided with a layer, It is characterized by the above-mentioned. Due to this feature, the difference between the ability of the positive electrode 3 to absorb the non-aqueous electrolyte and the ability of the negative electrode 4 to absorb the non-aqueous electrolyte becomes very small, and the non-aqueous electrolyte in the lithium ion secondary battery 1 is reduced. The balance around the liquid can be kept good.

  In particular, even when the ability of the negative electrode 4 to absorb the non-aqueous electrolyte is increased by discharge, the non-aqueous electrolyte is distributed throughout the positive electrode 3 without the non-aqueous electrolyte being unevenly distributed in the negative electrode 4. Thereby, it can suppress that the positive electrode 3 impregnates a non-aqueous electrolyte locally, and a part other than that will be in a liquid dry state. As a result, the charge / discharge reaction does not concentrate only on the portion impregnated with the non-aqueous electrolyte, and the variation in the charge / discharge depth in the positive electrode is significantly reduced. And especially at the time of discharge, the portion impregnated with the non-aqueous electrolyte becomes overdischarged, and the crystal structure is not disturbed, so that the deterioration of the positive electrode can be suppressed.

In the present specification, the degree of swelling of the resin with respect to the non-aqueous electrolyte is measured as follows. First, a resin is dissolved in an organic solvent to prepare a resin solution, this resin solution is applied to a flat glass surface, and the obtained coating film is dried to produce a sheet having a thickness of 1 mm to 3 mm. This sheet is cut into 20 mm × 20 mm and used as a sample. On the other hand, the sample obtained above is immersed in a non-aqueous electrolyte used in the lithium ion secondary battery 1 at 25 ° C. for 24 hours in a sealed container. And the degree of swelling is calculated | required according to a following formula as an increase rate of the mass (Y) of the sample after being immersed in a non-aqueous electrolyte with respect to the mass (X) of the sample before being immersed in a non-aqueous electrolyte.
Swelling degree (%) = {(Y−X) / X} × 100

  Below, the structure of the lithium ion secondary battery 1 of this embodiment is demonstrated concretely. First, the electrode group 2 will be described. As shown in FIG. 1, the electrode group 2 includes a positive electrode 3 containing an easily swellable resin as a binder, a negative electrode 4 using an alloy-based active material as a negative electrode active material, and a separator 5 interposed therebetween. , And a layer structure in which are stacked. In addition, as shown in FIG. 2, the negative electrode 4 includes a negative electrode current collector 20 and a plurality of columnar bodies 23 made of an alloy-based active material supported on the surface of the convex portion 21 of the negative electrode current collector 20. Prepare.

  The positive electrode 3 includes a positive electrode current collector and a positive electrode active material layer formed on both surfaces of the positive electrode current collector, and the positive electrode active material layer has an easily swollen degree of 50% or more with respect to the nonaqueous electrolytic solution. A functional resin is contained as a binder. In this embodiment, the positive electrode active material layer is formed on both surfaces of the positive electrode current collector, but may be formed only on one surface of the positive electrode current collector.

  As the positive electrode current collector, a metal foil made of a metal material such as aluminum, an aluminum alloy, stainless steel, or titanium can be used. Among the metal materials, aluminum and aluminum alloys are preferable. The thickness of the positive electrode current collector is not particularly limited, but is preferably 10 μm to 30 μm. In the present embodiment, the positive electrode current collector has a strip shape.

  The positive electrode active material layer contains a positive electrode active material, an easily swellable resin (binder), and a conductive agent. The positive electrode active material layer can be formed, for example, by applying a positive electrode mixture slurry to the surface of the positive electrode current collector, and drying and rolling the obtained coating film. The positive electrode mixture slurry can be prepared, for example, by mixing a positive electrode active material, an easily swellable resin and a conductive agent, and a solvent.

  The degree of swelling of the easily swellable resin of the present embodiment with respect to the non-aqueous electrolyte (hereinafter simply referred to as “the degree of swelling of the easily swellable resin”) is 50% or more, and more preferably 50% to 200%. .

  When the swelling degree of the easily swellable resin is less than 50%, the absorption capacity of the nonaqueous electrolyte solution of the positive electrode 3 becomes insufficient, and the nonaqueous electrolyte solution cannot be prevented from being unevenly distributed in the negative electrode 4 at the initial stage of charging. There is a risk that the positive electrode 3 will be in a liquid-dry state. On the other hand, when the degree of swelling of the easily swellable resin becomes too large, the mechanical strength of the positive electrode active material layer may decrease due to gelation of the easily swellable resin. As a result, the adhesion between the positive electrode active material layer and the positive electrode current collector and the current collection performance may be reduced.

  As the easily swellable resin, any resin having a degree of swelling of 50% or more can be used without particular limitation, but polyhexafluoropropylene (hereinafter referred to as “PHFP”), co-polymerization of hexafluoropropylene and vinylidene fluoride. Polymer (hereinafter referred to as “HFP-VDF copolymer”), cross-linked polyacrylonitrile-based polymer (hereinafter referred to as “cross-linked PAN-based polymer”) and cross-linked polymethyl methacrylate-based polymer (hereinafter referred to as “cross-linked PMMA”). At least one selected from the group consisting of “based polymers” is preferred. Among these, PHFP and HFP-VDF copolymers that exhibit lithium ion conductivity upon contact with a non-aqueous electrolyte are preferable.

  Since PHFP has a high affinity for the non-aqueous electrolyte of hexafluoropropylene units, it exhibits swelling properties for the non-aqueous electrolyte. PHFP is not particularly limited as long as the degree of swelling is 50% or more, but PHFP having a number average molecular weight in the range of 100,000 to 1,000,000 is preferable. If the number average molecular weight of PHFP is too small, the binding force of PHFP may be reduced, and the positive electrode active material layer may be peeled off from the positive electrode current collector as the number of charge / discharge cycles increases. Thereby, there exists a possibility that the cycling characteristics etc. of the battery 1 may fall. Moreover, there exists a possibility that a swelling degree may be less than 50%. On the other hand, if the number average molecular weight of PHFP is too large, the handleability of PHFP is lowered, and the productivity of the battery 1 may be adversely affected.

  The degree of swelling of the HFP-VDF copolymer can be adjusted by selecting the content ratio of the hexafluoropropylene unit, the number average molecular weight, and the like. The HFP-VDF copolymer is not particularly limited as long as the degree of swelling is 50% or more, but an HFP-VDF copolymer having a hexafluoropropylene unit content of 5 mol% or more and less than 100 mol% is preferable. . If the content ratio of the hexafluoropropylene unit is too small, the swelling degree of the HFP-VDF copolymer may be less than 50%. Further, the number average molecular weight of the HFP-VDF copolymer is not particularly limited, but is preferably in the range of 100,000 to 1,000,000 in consideration of the swelling degree, binding force, handleability and the like of the HFP-VDF copolymer.

  The crosslinked PAN-based polymer exhibits swellability with respect to the non-aqueous electrolyte solution by containing acrylonitrile units having high affinity with the non-aqueous electrolyte solution. In addition, the crosslinked PAN-based polymer is insolubilized in the nonaqueous electrolytic solution by crosslinking a plurality of polyacrylonitrile chains with a crosslinking compound. Although it does not specifically limit as a crosslinkable compound, Dialkyl methacrylates, dialkyl acrylates, etc. are preferable. Such a crosslinkable compound can make the distance between a plurality of polyacrylonitrile chains crosslinked by them relatively long. As a result, a crosslinked PAN-based copolymer having a high level of swelling properties with respect to the non-aqueous electrolyte and insolubility with respect to the non-aqueous electrolyte can be obtained.

  The crosslinked PAN-based polymer is not particularly limited as long as the degree of swelling is 50% or more, but a PAN-based polymer having a degree of swelling of 50% or more and a number average molecular weight in the range of 100,000 to 1,000,000 is preferable. . If the number average molecular weight of the crosslinked PAN-based polymer is too small, the binding force is reduced, and the positive electrode active material layer may be peeled off from the positive electrode current collector as charge and discharge are repeated. If the number average molecular weight of the crosslinked PAN-based polymer is too large, the degree of swelling may be less than 50%. Moreover, the handleability may be reduced.

  The crosslinked PMMA-based polymer exhibits swelling properties with respect to the non-aqueous electrolyte by containing methyl methacrylate units having high affinity for the non-aqueous electrolyte. Moreover, the crosslinked PMMA polymer is insolubilized with respect to the nonaqueous electrolytic solution by crosslinking a plurality of polymethyl methacrylate chains with a crosslinking compound. As the crosslinkable compound, the same crosslinkable compound used for the crosslinked PAN-based polymer can be used. In particular, by using a crosslinkable compound such as dialkyl methacrylates and dialkyl acrylates, a cross-linked PMMA polymer having both high swellability with respect to the non-aqueous electrolyte and insolubility with respect to the non-aqueous electrolyte can be obtained.

  The cross-linked PMMA polymer is not particularly limited as long as the swelling degree is 50% or more, but a PMMA copolymer having a swelling degree of 50% or more and a number average molecular weight in the range of 100,000 to 1,000,000 is used. preferable. If the number average molecular weight of the cross-linked PMMA polymer is too small, the binding force is reduced, and the positive electrode active material layer may be peeled off from the positive electrode current collector with repeated charge and discharge. If the number average molecular weight of the crosslinked PMMA polymer is too large, the degree of swelling may be less than 50%. Moreover, the handleability may be reduced.

  The positive electrode active material layer preferably contains the aforementioned easily swellable resin in a proportion of 0.5 parts by mass to 5 parts by mass with respect to 100 parts by mass of the positive electrode active material, and more preferably, the aforementioned easily swellable resin. The resin is contained at a ratio of 0.5 to 3 parts by mass.

  If the content of the easily swellable resin is too small, the effect of improving the absorption capacity of the non-aqueous electrolyte of the positive electrode 3 may be insufficient. As a result, the liquid circulation property of the non-aqueous electrolyte in the battery 1 is lowered, and the positive electrode 3 may be in a liquid withered state at the beginning of discharge. Thereby, the cycle characteristics and the like of the battery 1 are deteriorated. When the content ratio of the easily swellable resin is too large, the adhesion between the positive electrode active material layer and the positive electrode current collector is reduced, and the positive electrode active material layer is peeled off from the positive electrode current collector as the number of charge / discharge increases. May occur. Thereby, the cycle characteristics and the like of the battery 1 are deteriorated.

  The positive electrode active material layer may be referred to as a non-swellable resin (hereinafter simply referred to as “non-swellable resin”) having a swelling degree of less than 30% with respect to the non-aqueous electrolyte, together with the above-described easily swellable resin as a binder. ) May be contained. Thereby, the adhesiveness between the positive electrode active material layer and the positive electrode current collector, the mechanical strength of the positive electrode active material layer, and the like can be further improved without substantially reducing the absorption capacity of the nonaqueous electrolyte solution of the positive electrode 3. . As a result, peeling from the positive electrode current collector of the positive electrode active material layer due to an increase in the number of times of charge and discharge, local dropout, etc. were suppressed, excellent cycle characteristics, and occurrence of internal short circuits, etc. were significantly suppressed, A highly safe battery 1 is obtained.

  The positive electrode active material layer containing the hardly swellable resin together with the easily swellable resin is, for example, a positive electrode mixture slurry obtained by mixing a positive electrode active material, an easily swellable resin, a hardly swellable resin and a conductive agent with a solvent It can form by apply | coating to the positive electrode collector surface, and drying and rolling the obtained coating film.

  The degree of swelling of the hardly swellable resin of the present embodiment with respect to the non-aqueous electrolyte (hereinafter simply referred to as “the degree of swelling of the hardly swellable resin”) is preferably less than 30%, more preferably 0% to 20%. is there.

  When the swelling degree of the hardly swellable resin is too high, the effect of improving the adhesion between the positive electrode active material layer and the positive electrode current collector, the mechanical strength of the positive electrode active material layer, and the like may be insufficient. In addition, when the swelling degree of the hardly swellable resin is too low, the compatibility between the easily swellable resin and the hardly swellable resin in the positive electrode mixture slurry is reduced, so that the positive electrode active material layer having a non-uniform structure can be obtained. There is a risk of formation. As a result, as the number of times of charging / discharging increases, the positive electrode active material layer may fall off locally, which may cause deterioration of cycle characteristics, internal short circuit, and the like.

  As the hardly swellable resin, any resin having a degree of swelling of less than 30% can be used without particular limitation, but a hardly swellable resin having high binding force and resistance to a non-aqueous electrolyte is preferable. Examples of such a hardly swellable resin include polyvinylidene fluoride, polytetrafluoroethylene, vinylidene fluoride-tetrafluoroethylene copolymer, polyimide, polyamide, and polyamideimide. These hardly swellable resins can be used alone or in combination of two or more.

  The positive electrode active material layer preferably contains the aforementioned hardly swellable resin in a proportion of 0.1 to 5 parts by mass, more preferably the aforementioned hardly swellable material, relative to 100 parts by mass of the positive electrode active material. The resin is contained at a ratio of 0.5 to 3 parts by mass.

  By including the hardly swellable resin in the positive electrode active material layer, in particular, the adhesion between the positive electrode active materials is increased, and the cycle characteristics can be further improved. If the content of the hardly swellable resin is too small, the effect of adding the hardly swellable resin may not be sufficiently exhibited. If the content of the hardly swellable resin is too large, the charge transfer resistance in the positive electrode 3 is increased, and the cycle characteristics may be deteriorated.

  When the easily swellable resin and the hardly swellable resin are used in combination, the use ratio thereof is not particularly limited, but preferably the easily swellable resin is 20 parts by mass to 200 parts by mass with respect to 100 parts by mass of the hardly swellable resin. It is good to use part. If the use ratio of the easily swellable resin is too small, the effect of improving the absorption capacity of the non-aqueous electrolyte of the positive electrode 3 may be insufficient. Moreover, when there is too much usage-amount of easily swellable resin, there exists a possibility that the effect of adding hardly swellable resin may not fully appear.

  Next, components included in the positive electrode active material layer other than the easily swellable resin and the hardly swellable resin will be described. As the positive electrode active material, a positive electrode active material commonly used in the field of lithium ion secondary batteries can be used, among which lithium-containing composite oxides and olivine type lithium salts are preferable.

  The lithium-containing composite oxide is a metal oxide containing lithium and a transition metal element, or a metal oxide in which a part of the transition metal element in the metal oxide is substituted with a different element. Examples of the transition metal element include Sc, Y, Mn, Fe, Co, Ni, Cu, and Cr. Among transition metal elements, Mn, Co, Ni and the like are preferable. Examples of the different elements include Na, Mg, Zn, Al, Pb, Sb, and B. Among the different elements, Mg, Al and the like are preferable. Each of the transition metal element and the different element can be used alone or in combination of two or more.

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

Specific examples of the olivine type lithium salt include, for example, LiXPO ₄ , Li ₂ XPO ₄ F (wherein X represents at least one element selected from the group consisting of Co, Ni, Mn, and Fe). Of olivine type lithium phosphate.

  In each of the above formulas showing the lithium-containing composite oxide and the olivine-type lithium salt, the number of moles of lithium is a value immediately after the production thereof, and increases or decreases due to charge / discharge. A positive electrode active material can be used individually by 1 type, or can be used in combination of 2 or more type.

  Examples of the conductive agent include carbon blacks such as acetylene black and ketjen black, and graphites such as natural graphite and artificial graphite. The content rate of a electrically conductive agent can be suitably changed according to the design etc. of the positive electrode 3 and the lithium ion secondary battery 1, for example.

  As a solvent mixed with the positive electrode active material, the binder, and the conductive agent, organic solvents such as N-methyl-2-pyrrolidone, tetrahydrofuran, dimethylformamide, water, and the like can be used.

  Next, the negative electrode 4 will be described with reference to FIGS. 2 and 3. The negative electrode 4 includes a negative electrode current collector 20 having a plurality of convex portions 21 on both surfaces, and a negative electrode active material layer 22 including a plurality of columnar bodies 23 supported on the surfaces of the convex portions 21.

  The negative electrode current collector 20 is a strip-shaped metal foil made of a metal material such as copper, copper alloy, stainless steel, or nickel, and has a plurality of convex portions 21 on both surfaces 20a. The convex portion 21 is a protrusion extending outward from the surface 20a, and has a flat surface substantially parallel to the surface 20a at the tip portion. The thickness of the portion of the negative electrode current collector 20 where the convex portions 21 are not formed is preferably 5 μm to 30 μm. In addition, although the negative electrode collector 20 of this embodiment has the convex part 21 on both surfaces, you may have the convex part 21 only on one surface.

Examples of the arrangement of the convex portions 21 on the surface 20a include a staggered arrangement, a close-packed arrangement, a lattice arrangement, a grid arrangement, and an irregular arrangement. The number of convex portions 21 is preferably 10,000 pieces / cm ^{2 to} 10 million pieces / cm ² . Moreover, the distance between the axes of the adjacent convex portions 21 is preferably 10 μm to 100 μm. When the shape of the convex portion 21 is a rhombus, polygon, parallelogram, trapezoid, or ellipse, the axis of the convex portion 21 passes through the intersection of diagonal lines or the intersection of the major axis and minor axis and is perpendicular to the surface 20a. Extending in the direction. When the shape of the convex part 21 is circular, the axis of the convex part 21 passes through the center of the circle and extends in a direction perpendicular to the surface 20a.

  The height and width of the convex portion 21 are respectively the length of the perpendicular dropped from the foremost point of the convex portion 21 to the surface 20a and the maximum length of the convex portion 21 in the direction parallel to the surface 20a in the cross section of the negative electrode 4. It is. The height and width of the convex portion 21 are preferably 3 μm to 20 μm and 5 μm to 50 μm, respectively. The height and width of the convex portion 21 are obtained by observing the cross section of the negative electrode 4 with a scanning electron microscope and measuring the height and width of a predetermined number (for example, 100) of the convex portions 21, respectively. It can be calculated as an average value.

Examples of the shape of the convex portion 21 in the orthographic projection from above in the vertical direction of the negative electrode current collector 20 include a rhombus, a triangle to an octagon, a parallelogram, a trapezoid, a circle, and an ellipse. .
The negative electrode current collector 20 is formed, for example, by pressing two convex rollers each having a plurality of concave portions formed on the surface thereof so that the axes thereof are parallel to form a nip portion, and a metal foil is formed in the nip portion. It can be made by passing and pressing.

  The negative electrode active material layer 22 includes a plurality of columnar bodies 23 mainly supported on the surface of the convex portion 21. The columnar body 23 made of an alloy-based active material extends from the surface of the convex portion 21 to the outside of the negative electrode current collector 20. In the present embodiment, one columnar body 23 is formed on one convex portion 21. A gap 24 exists between a pair of columnar bodies 23 adjacent to each other.

  The alloy-based active material expands when occluding lithium ions and generates internal stress, thereby causing the negative electrode active material layer to peel from the negative electrode current collector, deformation of the negative electrode, etc. Reduce. However, by providing the above-described void 24, the stress generated with the volume change of the alloy-based active material is relieved. As a result, separation of the columnar body 23 from the convex portion 21, deformation of the negative electrode current collector 20 and the negative electrode 4, and the like are suppressed. Therefore, by using the negative electrode 4 having such a configuration, it is possible to remarkably suppress the deterioration of the cycle characteristics due to the expansion of the alloy-based active material.

  In the negative electrode active material layer 22, as the number of charging / discharging increases, minute voids are generated inside each columnar body 23, and the voids 24 exist around the columnar bodies 23, so that the negative electrode 4 during discharge is discharged. However, the ability to absorb non-aqueous electrolyte is significantly increased. Even when the negative electrode 4 having such a negative electrode active material layer 22 is used, by using the positive electrode 3 containing a readily swellable resin as a binder, the liquidity of the non-aqueous electrolyte in the battery 1 can be improved. Remarkably improved.

  FIG. 3 is a longitudinal sectional view schematically showing the configuration of the columnar body 23. The plurality of columnar bodies 23 are formed on the surface of each convex portion 21 by a vapor phase method as a stacked body of lumps 23a to 23h shown in FIG. More specifically, the columnar body 23 is formed by alternately stacking the masses 23a, 23c, 23e, and 23g and the masses 23b, 23d, 23f, and 23h. The number of lumps stacked is not limited to eight, and any number of lumps of two or more can be stacked.

  The alloy-based active material constituting the columnar body 23 is a substance that occludes lithium by alloying with lithium and reversibly occludes and releases lithium ions under a negative electrode potential. The alloy-based active material is preferably amorphous or low crystalline. As the alloy-based active material, an alloy-based active material for a lithium ion secondary battery can be used, but a silicon-based active material and a tin-based active material are preferable. An alloy type active material can be used individually by 1 type, or can be used in combination of 2 or more type.

Examples of the silicon-based active material include silicon, silicon compounds, and partial substitutes thereof.
Examples of the silicon compound include silicon oxide represented by the formula SiO _a (0.05 <a <1.95), silicon carbide represented by the formula SiC _b (0 <b <1), and formula SiN _c (0 < a silicon nitride represented by c <4/3), an alloy of silicon and a different element (A), and the like. Examples of the different element (A) include Fe, Co, Sb, Bi, Pb, Ni, Cu, Zn, Ge, In, Sn, and Ti. In addition, the partially substituted body is a compound in which a part of silicon atoms contained in silicon and a silicon compound is substituted with a different element (B). Specific examples of the different element (B) include B, Mg, Ni, Ti, Mo, Co, Ca, Cr, Cu, Fe, Mn, Nb, Ta, V, W, Zn, C, N, and Sn. Can be mentioned. Of these, silicon and silicon oxide are preferred.

Examples of tin-based active materials include tin, tin compounds, tin oxides represented by the formula SnO _d (0 <d <2), tin dioxide (SnO ₂ ), tin nitride, Ni—Sn alloy, and Mg—Sn alloy. , Fe-Sn alloy, Cu-Sn alloy, tin alloy, such as Ti-Sn _{alloy, SnSiO 3, Ni 2 Sn 4} , Mg 2 Sn and tin compounds such like. Among the tin-based active materials, tin oxide, tin alloy, tin compound, and the like are preferable.

  The height and width of the columnar body 23 are respectively the length of the perpendicular dropped from the foremost point of the columnar body 23 to the flat top surface of the projection 21 and the columnar shape in the direction parallel to the surface 20a in the cross section of the negative electrode 4. This is the maximum length of the body 23. The height and width of the columnar body 23 are preferably 5 μm to 50 μm and 5 μm to 60 μm, respectively. The height and width of the columnar body 23 can be obtained in the same manner as the height and width of the convex portion 21. Examples of the three-dimensional shape of the columnar body 23 include a columnar shape, a prismatic shape, and a spindle shape.

  In this embodiment, although the negative electrode 4 provided with the negative electrode collector 20 which has the some convex part 21 on both surfaces, and the negative electrode active material layer 22 which consists of several columnar body 23 was used, it is not limited to this. . For example, a negative electrode in which a thin film (solid film) made of an alloy-based active material is formed on the surface of a negative electrode current collector not having the convex portion 21 by a vapor phase method may be used. Further, a negative electrode in which alloy-based active material particles are bound with a binder on the surface of the negative electrode current collector with or without the convex portion 21 may be used. In this case, as the binder, a negative electrode binder commonly used in the field of lithium ion secondary batteries can be used.

  As the separator 5 disposed between the positive electrode 3 and the negative electrode 4, a porous sheet having pores, a resin fiber nonwoven fabric, a resin fiber woven fabric, or the like can be used. Among these, a porous sheet is preferable, and a porous sheet having a pore diameter of about 0.05 μm to 0.15 μm is more preferable. The thickness of the porous sheet is preferably 5 μm to 30 μm. Examples of the resin material constituting the porous sheet and the resin fiber include polyolefins such as polyethylene and polypropylene, polyamide, and polyamideimide.

The nonaqueous electrolytic solution contains a lithium salt and a nonaqueous solvent. Lithium salts include LiPF ₆ , LiClO ₄ , LiBF ₄ , LiAlCl ₄ , LiSbF ₆ , LiSCN, LiAsF ₆ , LiB ₁₀ Cl ₁₀ , LiCl, LiBr, LiI, LiCO ₂ CF ₃ , LiSO ₃ CF ₃ , Li (SO _{3 CF 3) 2, LiN (SO} 2 CF 3) 2, and lithium imide salt and the like. A lithium salt can be used individually by 1 type, or can be used in combination of 2 or more type. The concentration of the lithium salt in 1 L of the nonaqueous solvent is preferably 0.2 mol to 2 mol.

  Non-aqueous solvents include cyclic carbonates such as ethylene carbonate, propylene carbonate, and butylene carbonate, chain carbonates such as dimethyl carbonate, ethyl methyl carbonate, and diethyl carbonate, 1,2-dimethoxyethane, 1,2-diethoxyethane. Chain ethers such as γ-butyrolactone, cyclic carboxylic acid esters such as γ-valerolactone, and chain esters such as methyl acetate. A non-aqueous solvent can be used individually by 1 type, or can be used in combination of 2 or more type.

  When the lithium ion secondary battery 1 is manufactured, first, both ends of the positive electrode lead 10 and the negative electrode lead 11 are welded to predetermined positions, respectively. And after accommodating the electrode group 2 equipped with the upper insulating plate 12 and the lower insulating plate 13 in the battery case 14, a non-aqueous electrolyte is injected. Next, the gasket 16 and the sealing plate 15 are sequentially attached to the opening of the battery case 14 to seal the battery case 14. Thereby, the lithium ion secondary battery 1 is obtained.

  For example, an aluminum lead or the like can be used as the positive electrode lead 10. As the negative electrode lead 11, for example, a nickel lead, a copper lead, or the like can be used. As the battery case 14 and the sealing plate 15, for example, a metal material such as iron or stainless steel formed into a predetermined shape can be used. As the upper insulating plate 12, the lower insulating plate 13, and the gasket 16, for example, an insulating material such as a resin material or a rubber material formed into a predetermined shape can be used.

  Although the lithium ion secondary battery 1 of this embodiment is a cylindrical battery provided with the wound electrode group 2, it is not limited to this and can take various forms. Examples of the form include a cylindrical battery in which a wound electrode group 2, a battery case containing a non-aqueous electrolyte and the like are sealed with a sealing plate made of an insulating material that supports a positive electrode terminal, and a wound electrode group 2 Alternatively, a prismatic battery in which the stacked electrode group is accommodated in a rectangular battery case, a rectangular battery in which a flat electrode group formed by pressing the wound electrode group 2 into a flat shape is accommodated in the rectangular battery case, and wound. Examples thereof include a laminated film battery in which the type electrode group 2 or the flat electrode group or the laminated electrode group is accommodated in a laminated film battery case, and a coin type battery in which the laminated electrode group is accommodated in a coin type battery case.

Hereinafter, the present invention will be specifically described with reference to Examples and Comparative Examples.
Example 1
(A) Production of positive electrode 85 parts by mass of a positive electrode active material (LiNi _0.85 Co _0.15 Al _0.05 O ₂ ), 10 parts by mass of graphite powder, and a copolymer of vinylidene fluoride and hexafluoropropylene (easily swellable resin, hexafluoropropylene) Content ratio of unit: 5 mol%, swelling degree: 55%, number average molecular weight: 400,000, hereinafter referred to as “VDF-HFP copolymer (1)”), 5 parts by mass, an appropriate amount of N-methyl-2- A positive electrode mixture slurry was prepared by mixing with pyrrolidone.

  The obtained positive electrode mixture slurry was applied to both surfaces of an aluminum foil (positive electrode current collector) having a thickness of 15 μm, and the obtained coating film was dried and rolled to produce a positive electrode having a thickness of 130 μm. The obtained positive electrode was cut into a width that can be inserted into a battery case of a 18650 cylindrical battery (diameter: about 18 mm, height: about 65 mm). In addition, the swelling degree of VDF-HFP copolymer (1) is a swelling degree with respect to the non-aqueous electrolyte obtained by "(c) Preparation of non-aqueous electrolyte" mentioned later. The same applies hereinafter.

(B) Production of negative electrode plate (b-1) Production of negative electrode current collector Two forged steel rollers having a plurality of recesses arranged in a staggered pattern on the surface are pressed so that the respective axes are parallel, A nip was formed. By passing an electrolytic copper foil (made by Furukawa Circuit Foil Co., Ltd.) having a thickness of 35 μm through this nip portion at a linear pressure of 1000 N / cm, a negative electrode current collector 20 having a plurality of convex portions 21 formed on both surfaces. Was made.

  The plurality of convex portions 21 had an average height of 8 μm and were arranged in a staggered pattern. Further, the tip portion of the convex portion 21 was a plane substantially parallel to the surface 20 a of the negative electrode current collector 20. Further, in the orthographic projection view from above in the vertical direction of the negative electrode current collector 20, the shape of the convex portion 21 was substantially rhombus. Further, the distance between the axes of the protrusions 21 was 50 μm in the longitudinal direction of the negative electrode current collector and 50 μm in the width direction.

(B-2) Formation of Negative Electrode Active Material Layer FIG. 4 is a side perspective view schematically showing the configuration of an electron beam vacuum deposition apparatus 30 (hereinafter referred to as “deposition apparatus 30”). A columnar body 23 was formed on the surface of each convex portion 21 (not shown in FIG. 4) of the negative electrode current collector 20 obtained above by using the vapor deposition apparatus 30, thereby manufacturing the negative electrode 4.

  The vapor deposition apparatus 30 includes a feed roller 32 around which the strip-shaped negative electrode current collector 20 is wound in advance, and conveyance rollers 33a, 33b, 33c, 33d, 33e, and 33f that guide the negative electrode current collector 20 to the take-up roller 35; Vapor deposition sources 36a and 36b that contain raw materials for the alloy active material, a take-up roller 35 for winding the negative electrode current collector 20 with the alloy active material deposited on the surface, and a negative electrode current collector for the alloy active material vapor 20, a pair of shielding plates 37 and 38 for regulating the supply area to the surface, an oxygen nozzle (not shown) for supplying oxygen, a chamber 31 for housing these, and a vacuum pump 39 for reducing the pressure in the chamber 31 And an electron beam irradiation device (not shown) for irradiating the raw material of the alloy-based active material accommodated in the vapor deposition sources 36a and 36b with an electron beam to generate a vapor of the raw material of the alloy-based active material. . The shielding plate 37 includes shielding pieces 37a, 37b, and 37c. The shielding plate 38 includes shielding pieces 38a, 38b, and 38c.

  In the vapor deposition apparatus 30, in the conveyance direction of the negative electrode current collector 20, a first vapor deposition region is formed between the shielding pieces 37a and 37b, a second vapor deposition region is formed between the shielding pieces 37b and 37c, and the shielding pieces 38c and 38b. A third vapor deposition region is formed therebetween, and a fourth vapor deposition region is formed between the shielding pieces 38b and 38a.

As the alloy-based active material raw material, scrap silicon (silicon single crystal, purity 99.9999%, manufactured by Shin-Etsu Chemical Co., Ltd.) was used and accommodated in evaporation sources 36a and 36b. After the chamber 31 was evacuated to 5 × 10 ⁻³ Pa by the vacuum pump 38, oxygen was supplied from the oxygen nozzle into the chamber 31 to create an oxygen atmosphere with a pressure of 3.5 Pa. Next, the scrap silicon accommodated in the evaporation sources 36a and 36b was irradiated with an electron beam (acceleration voltage: 10 kV, emission: 500 mA) to generate silicon vapor. In the middle of the rise of silicon vapor, it mixed with oxygen to generate a mixed gas of silicon vapor and oxygen.

  On the other hand, the negative electrode current collector 20 is fed from the feed roller 32 at a feed rate of 2 cm / min, and a mixture of silicon vapor and oxygen is deposited on the surface of the convex portion 21 of the negative electrode current collector 20 running in the first deposition region. A lump 23a shown in FIG. 3 was formed. Next, a lump 23b was formed on the surface of the convex portion 21 and the surface of the lump 23a of the negative electrode current collector 20 running in the second vapor deposition region. Furthermore, in the 3rd and 4th vapor deposition area | region, the masses 23a and 23b were laminated | stacked on the convex part 21 surface of the surface on the opposite side to which the masses 23a and 23b were formed in the 1st and 2nd vapor deposition area | regions.

  Next, the feeding direction of the negative electrode current collector 20 is reversed by reversing the rotation directions of the feed roller 32 and the take-up roller 35, and the lump 23 c is formed on the surfaces of the lumps 23 a and 23 b on both sides of the negative electrode current collector 20. , 23d. Thereafter, one reciprocal deposition is performed in the same manner, and the columnar body 23 which is a laminated body of lumps 23a, 23b, 23c, 23d, 23e, 23f, 23g, and 23h is formed on the surfaces of both convex portions 21 of the negative electrode current collector 20. Formed.

The columnar body 23 was supported by the surface of the convex portion 21 and grew to extend outward from the negative electrode current collector 20. The columnar body 23 had a substantially cylindrical solid shape. The columnar body 23 had an average height of 20 μm and an average width of 40 μm. Moreover, when the amount of oxygen contained in the columnar body 23 was quantified by a combustion method, the composition of the columnar body 23 was SiO _0.25 .

  The negative electrode active material layer composed of the plurality of columnar bodies 23 of the negative electrode 4 obtained above was supplemented with irreversible capacity lithium using a resistance heating vacuum deposition apparatus 40 shown in FIG. The vapor deposition apparatus 40 includes a feeding roller 42 around which the strip-shaped negative electrode 4 is wound in advance, a can 43 in which a cooling device (not shown) is disposed, a winding roller 44 that winds up the negative electrode 4 supplemented with lithium, Conveying rollers 45a and 45b for conveying the negative electrode 4, tantalum evaporation sources 46a and 46b for storing metallic lithium, a shielding plate 47 for restricting supply of lithium vapor to the surface of the negative electrode 4, and a pressure-resistant chamber for storing these 41.

First, the inside of the chamber 51 of the vapor deposition apparatus 40 was replaced with an argon atmosphere, and the degree of vacuum in the chamber 41 was set to 1 × 10 ⁻¹ Pa by a vacuum pump (not shown). Next, a current of 50 A is supplied from a power source (not shown) to the evaporation source 57 to generate lithium vapor, and the negative electrode 4 is fed from the feed roller 42 at a speed of 2 cm / min, and the negative electrode 4 passes through the surface of the can 43. In doing so, lithium for an irreversible capacity was deposited on the surface of the negative electrode active material layer of the negative electrode 4. Lithium was deposited on both negative electrode active material layers of the negative electrode 4. The negative electrode 4 after lithium deposition was cut into a width that could be inserted into a battery case of a 14400 cylindrical battery (diameter: about 14 mm, height: about 40 mm) to produce a negative electrode plate.

(C) a non-aqueous electrolyte solution volume ratio of preparation of ethylene carbonate and ethyl methyl carbonate of 1: in a mixed solvent of 1, LiPF ₆ was dissolved at a concentration of 1.0 mol / L, to prepare a nonaqueous electrolyte.

(D) Battery assembly Between the positive electrode plate obtained above and the negative electrode plate obtained above, a separator having a thickness of 20 μm (trade name: Hypore, polyethylene porous membrane, manufactured by Asahi Kasei Co., Ltd.) ) To interpose a wound electrode group. One end of an aluminum lead was connected to the positive electrode current collector, and one end of the nickel lead was connected to the negative electrode current collector. An upper insulating plate and a lower insulating plate made of polypropylene were respectively attached to the wound electrode group. Next, the wound electrode group is accommodated in a bottomed cylindrical iron battery case, the other end of the aluminum lead is connected to a stainless steel sealing plate, and the other end of the nickel lead is connected to the inner surface of the bottom of the battery case. Connected to.

  Next, a nonaqueous electrolyte was injected into the battery case by a reduced pressure method. A polypropylene gasket was attached to the periphery of the sealing plate that supported the safety valve, and in this state, the sealing plate was attached to the opening of the battery case. The battery case was hermetically sealed by caulking the open end of the battery case toward the sealing plate. Thus, a cylindrical lithium ion secondary battery having an outer diameter of 18 mm and a height of 65 mm was produced. Ten cells of this cylindrical battery were produced.

(Example 2)
(A) In the preparation of the positive electrode, a 10-cell cylindrical lithium ion was used in the same manner as in Example 1 except that the VDF-HFP copolymer (1) was used instead of the VDF-HFP copolymer (1). A secondary battery was produced. In addition, VDF-HFP copolymer (2) was HFP content rate: 12 mol%, swelling degree: 140%, and number average molecular weight: 400,000.

(Example 3)
(A) In the production of the positive electrode, a 10-cell cylindrical lithium ion was used in the same manner as in Example 1 except that the VDF-HFP copolymer (3) was used instead of the VDF-HFP copolymer (1). A secondary battery was produced. In addition, VDF-HFP copolymer (3) was HFP content rate: 7 mol%, swelling degree: 80%, and number average molecular weight: 400,000.

Example 4
(A) In the production of the positive electrode, the same procedure as in Example 1 was conducted except that polyhexafluoropropylene (swelling degree: 200%, number average molecular weight: 450,000) was used instead of the VDF-HFP copolymer (1). Thus, a 10-cell cylindrical lithium ion secondary battery was produced.

(Example 5)
(A) In the production of the positive electrode, the same procedure as in Example 1 was conducted except that crosslinked polyacrylonitrile (swelling degree: 180%, number average molecular weight: 800,000) was used instead of the VDF-HFP copolymer (1). A 10-cell cylindrical lithium ion secondary battery was produced.

(Example 6)
(A) In the production of the positive electrode, the same procedure as in Example 1 was conducted except that crosslinked polymethyl methacrylate (swelling degree: 185%, number average molecular weight: 700,000) was used instead of the VDF-HFP copolymer (1). Thus, a 10-cell cylindrical lithium ion secondary battery was produced.

(Example 7)
A 10-cell cylindrical lithium ion secondary battery was produced in the same manner as in Example 1 except that the positive electrode obtained below was used.

(A) Production of positive electrode 85 parts by mass of positive electrode active material (LiNi _0.85 Co _0.15 Al _0.05 O ₂ ), 10 parts by mass of graphite powder, 3 parts by mass of VDF-HFP copolymer (2) and polyvinylidene fluoride (hardly swellable resin) 2 parts by mass of a swelling ratio: 15%, an average molecular weight: 600,000, hereinafter referred to as “PVDF”) was mixed with an appropriate amount of N-methyl-2-pyrrolidone to prepare a positive electrode mixture slurry. The obtained positive electrode mixture slurry was applied to both surfaces of an aluminum foil (positive electrode current collector) having a thickness of 15 μm, and the obtained coating film was dried and rolled to produce a positive electrode having a thickness of 130 μm. The obtained positive electrode was cut into a width that can be inserted into a battery case of a 18650 cylindrical battery (diameter: about 18 mm, height: about 65 mm).

(Comparative Example 1)
(A) In the production of the positive electrode, the same procedure as in Example 1 was conducted except that polyvinylidene fluoride (swelling degree: 15%, number average molecular weight: 600,000) was used instead of the VDF-HFP copolymer (1). Thus, a 10-cell cylindrical lithium ion secondary battery was produced.

(Comparative Example 2)
(A) In preparation of a positive electrode, it replaced with VDF-HFP copolymer (1), VDF-HFP copolymer (The content rate of a hexafluoropropylene unit: 1 mol%, swelling degree: 23%, number average molecular weight: A 10-cell cylindrical lithium ion secondary battery was produced in the same manner as in Example 1 except for using 400,000).

(Comparative Example 3)
(A) In preparation of a positive electrode, it replaced with VDF-HFP copolymer (1), VDF-HFP copolymer (The content rate of a hexafluoropropylene unit: 3 mol%, swelling degree: 40%, number average molecular weight: A 10-cell cylindrical lithium ion secondary battery was produced in the same manner as in Example 1 except for using 400,000).

[Battery capacity]
The batteries of Examples 1 to 7 and Comparative Examples 1 to 3 are each housed in a constant temperature bath of 20 ° C., and are charged (constant current charging and subsequent constant voltage charging) and discharged (constant current discharging) under the following charging / discharging conditions. The charging / discharging was repeated 3 cycles, and the discharge capacity (0.2 C capacity) for the third time was determined and used as the battery capacity. The results are shown in Table 1.

Constant current charging: 0.7C, end-of-charge voltage of 4.2V.
Constant voltage charging: 4.2 V, charging end current 0.05 C, rest time 20 minutes.
Constant current discharge: 0.2 C, discharge end voltage 2.5 V, rest time 20 minutes.

[Cycle characteristics]
The batteries of Examples 1 to 7 and Comparative Examples 1 to 3 and 10 cells each were housed in a constant temperature bath at 20 ° C., and charged and discharged for one cycle under the same charge and discharge conditions as the battery capacity evaluation. Asked. Then, charge / discharge of 298 cycles was performed on the same charge / discharge conditions as the 1st cycle except changing the electric current value of constant current discharge from 0.2C to 1C. Next, charging / discharging was performed under the same charging / discharging conditions as in the first cycle, and a 300-cycle discharging capacity was obtained. The capacity retention rate (%) was determined as a percentage of the 300 cycle discharge capacity with respect to the 1 cycle discharge capacity. The capacity retention rate (%) was an average value of 10 cells. The results are shown in Table 1.

  Moreover, about the battery of Examples 1-7 and Comparative Examples 1-3, and 10 cells each, the number of the batteries in which a capacity | capacitance maintenance rate is less than 60% was measured. The results are shown in Table 1.

  From Table 1, in the lithium ion secondary battery using an alloy-based active material, the positive electrode active material layer of the positive electrode contains an easily swellable resin having a swelling degree of 50% or more with respect to the non-aqueous electrolyte as a binder. It can be seen that even if the cycle characteristics of the battery are improved and the number of charge / discharge cycles is increased, a rapid decrease in the cycle characteristics is suppressed.

  The lithium ion secondary battery of the present invention can be used for the same applications as conventional lithium ion secondary batteries, and in particular, as a main power source or auxiliary power source for electronic devices, electrical devices, machine tools, transportation devices, power storage devices, etc. Useful. Electronic devices include personal computers, mobile phones, mobile devices, portable information terminals, portable game devices, and the like. Electrical equipment includes vacuum cleaners and video cameras. Machine tools include electric tools and robots. Transportation equipment includes electric vehicles, hybrid electric vehicles, plug-in HEVs, fuel cell vehicles, and the like. Examples of power storage devices include uninterruptible power supplies.

DESCRIPTION OF SYMBOLS 1 Lithium ion secondary battery 2 Winding-type electrode group 3 Positive electrode 4 Negative electrode 5 Separator 10 Positive electrode lead 11 Negative electrode lead 12 Upper insulating plate 13 Lower insulating plate 14 Battery case 15 Sealing plate 16 Gasket 20 Negative electrode collector 21 Protruding part 22 Negative electrode Active material layer 23 Columnar body 24 Void 30 Electron beam vacuum deposition apparatus

Claims (8)

A positive electrode active material layer containing a positive electrode active material capable of occluding and releasing lithium ions and a binder, a positive electrode comprising a positive electrode current collector supporting the positive electrode active material layer, and a negative electrode comprising an alloy-based active material A lithium ion secondary battery comprising an active material layer, a negative electrode including a negative electrode current collector that supports the negative electrode active material layer, a separator interposed between the positive electrode and the negative electrode, and a non-aqueous electrolyte. There,
The lithium ion secondary battery, wherein the binder contains an easily swellable resin having a degree of swelling with respect to the non-aqueous electrolyte of 50% or more.   The lithium ion secondary battery according to claim 1, wherein the negative electrode active material layer includes a plurality of columnar bodies made of the alloy-based active material, which are supported on the surface of the negative electrode current collector.   The lithium ion secondary battery according to claim 1, wherein the alloy-based active material is at least one selected from a silicon-based active material and a tin-based active material.   The easily swellable resin is selected from the group consisting of polyhexafluoropropylene, a copolymer of hexafluoropropylene and vinylidene fluoride, a crosslinked polyacrylonitrile polymer, and a crosslinked polymethyl methacrylate polymer. The lithium ion secondary battery according to any one of claims 1 to 3, wherein the lithium ion secondary battery is at least one kind.   The said positive electrode active material layer contains the said easily swellable resin in the ratio of 0.5 mass part-5 mass parts with respect to 100 mass parts of the said positive electrode active materials. Lithium ion secondary battery.   The lithium ion according to any one of claims 1 to 5, wherein the binder further contains, together with the easily swellable resin, a hardly swellable resin having a degree of swelling with respect to the non-aqueous electrolyte of less than 30%. Secondary battery.   The said difficulty swelling resin is at least 1 sort (s) chosen from the group which consists of a polyvinylidene fluoride, a polytetrafluoroethylene, a vinylidene fluoride-tetrafluoroethylene copolymer, a polyimide, polyamide, and a polyamideimide. Lithium ion secondary battery.   The lithium ion secondary battery according to claim 6 or 7, wherein the positive electrode active material layer contains the hardly-swellable resin in a ratio of 1 part by mass to 5 parts by mass with respect to 100 parts by mass of the positive electrode active material.

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