JP5365215B2 - Secondary battery - Google Patents

Description

  The present invention relates to a secondary battery including a wound body in which a positive electrode and a negative electrode are stacked via a separator.

  In recent years, portable electronic devices typified by mobile phones and notebook personal computers have been energetically reduced in size and weight, and as part of this, the energy density of batteries, especially secondary batteries, as their driving power source has been increased. Improvement is strongly desired. As a secondary battery capable of obtaining a high energy density, a lithium ion secondary battery using a material capable of inserting and extracting lithium (Li) such as a carbon material in a negative electrode has been commercialized, and its market is It is expanding.

  In the lithium ion secondary battery, for example, a wound body (battery element) in which a positive electrode and a negative electrode are stacked via a separator is accommodated in an outer can. As the separator, a porous film made of synthetic resin made of polytetrafluoroethylene, polypropylene, polyethylene or the like, or a porous film made of ceramic is used. The separator prevents a short circuit of current due to contact between both electrodes, while holding an electrolyte allows lithium ions to pass therethrough and allows a battery reaction between both electrodes.

  As a negative electrode active material used for a lithium ion secondary battery, a carbon material such as non-graphitizable carbon or graphite having a relatively high capacity and good cycle characteristics is widely used.

On the other hand, as a high-capacity negative electrode that surpasses carbon materials, research is being conducted on alloy materials that apply the fact that a certain metal is electrochemically alloyed with lithium and is reversibly generated and decomposed. Furthermore, as a method for improving the cycle characteristics, it is studied to alloy tin and silicon (Si) to suppress their expansion. For example, it has been proposed to alloy a transition metal such as iron with tin (see Patent Documents 1 to 3 and Non-Patent Documents 1 to 3). In addition, Mg ₂ Si and the like have been proposed (see Non-Patent Document 4).

As another secondary battery capable of obtaining a high energy density, there is a lithium metal secondary battery using lithium metal for the negative electrode and utilizing only precipitation and dissolution reactions of lithium metal for the negative electrode reaction. Lithium metal secondary batteries have a large theoretical electrochemical equivalent of 2054 mAh / cm ^{3 of} lithium metal, which is equivalent to 2.5 times that of graphite used in lithium ion secondary batteries, so it is higher than lithium ion secondary batteries. The energy density is expected to be obtained. Until now, research and development relating to the practical application of lithium metal secondary batteries have been made by many researchers and the like (see, for example, Non-Patent Document 5).

Japanese Patent Laid-Open No. 2004-22306 JP 2004-63400 A JP 2005-78999 A

“Journal of the Electrochemical Society”, 1999, No. 146, p405 “Journal of the Electrochemical Society”, 1999, No. 146, p414 “Journal of the Electrochemical Society”, 1999, No. 146, p423 “Journal of the Electrochemical Society”, 1999, No. 146, p4401 Edited by Jean-Paul Gabano, "Lithium Batteries", London, New York, Academic Press, 1983

  However, when an alloy material as described above is used as the negative electrode active material, the pressure distribution of the battery element tends to be non-uniform due to expansion associated with charge / discharge. As a result, when the capacity is extremely increased, the current collector made of the metal foil is more likely to crack in the curved portion of the wound body.

  The present invention has been made in view of such problems, and an object of the present invention is to provide a secondary battery that is more reliable while ensuring a sufficient capacity.

A first secondary battery of the present invention has a laminated structure of a positive electrode, a separator and a negative electrode, and has a flat cross section including a pair of opposed flat portions and a pair of opposed curved portions. A body and an outer can that accommodates the wound body. Here, the separator has a base material made of porous resin and a resin layer provided on both surfaces of the base material, and the air permeability of the separator in the curved portion is in a flat portion continuous with the curved portion. The air permeability of the separator is higher. On one side of the pair of curved portions, the resin layer located on the wound outer surface side of the substrate has a greater thickness than the resin layer located on the wound inner surface side of the substrate, and on the other of the pair of curved portions, The resin layer located on the wound inner surface side of the substrate has a greater thickness than the resin layer located on the wound outer surface side of the substrate.
The second secondary battery of the present invention has a laminated structure of a positive electrode, a separator and a negative electrode, and has a flat cross section including a pair of opposed flat portions and a pair of opposed curved portions. A body and an outer can that houses the wound body. Here, the separator has a base material made of a porous resin, and resin layers provided on both surfaces of the base material, and the thickness of the separator resin layer in the curved portion is that of the separator resin layer in the flat portion. It is larger than the thickness, and the air permeability of the separator in the curved portion is higher than the air permeability of the separator in the flat portion continuous with the curved portion. On one side of the pair of curved portions, the resin layer located on the wound outer surface side of the substrate has a greater thickness than the resin layer located on the wound inner surface side of the substrate, and on the other of the pair of curved portions, A secondary battery in which the resin layer located on the wound inner surface side of the substrate has a greater thickness than the resin layer located on the wound outer surface side of the substrate.

According to the secondary battery of the present invention, since the air permeability of the separator in the curved portion is relatively high, the battery reaction in the curved portion of the wound body is suppressed. For this reason, the stress inside the wound body due to expansion and contraction associated with charge / discharge is relieved, and cracks such as a positive electrode current collector in a curved portion of the wound body are less likely to occur.
Further, on one side of the pair of curved portions, the resin layer located on the wound outer surface side of the substrate has a larger thickness than the resin layer located on the wound inner surface side of the substrate, and the other of the pair of curved portions Then, since the resin layer located on the wound inner surface side of the substrate has a larger thickness than the resin layer located on the wound outer surface side of the substrate, the expansion and contraction accompanying charging / discharging at the curved portion And the volume energy density fall accompanying the increase in the radial dimension of the wound body due to the thickness of the resin layer can be suppressed in a well-balanced manner.

  According to the secondary battery of the present invention, the separator has a higher air permeability in the curved portion than in the flat portion, and the battery reaction in the curved portion is suppressed. For example, a high capacity containing tin or silicon Even when a negative electrode active material that can be obtained is employed, damage to the positive electrode and the like due to repeated charge and discharge can be prevented, and high reliability can be ensured.

It is sectional drawing showing the secondary battery as one embodiment of this invention. It is sectional drawing showing the structure along the II-II line of the secondary battery shown in FIG. It is the top view and sectional drawing which expand | deploy and represent the separator shown in FIG. It is sectional drawing which expand | deploys and represents the separator as a modification.

  Hereinafter, modes for carrying out the present invention (hereinafter referred to as embodiments) will be described in detail with reference to the drawings.

  1 and 2 show a cross-sectional structure of a secondary battery as an embodiment of the present invention. The cross section shown in FIG. 1 and the cross section shown in FIG. 2 are in a positional relationship orthogonal to each other. That is, FIG. 2 is a cross-sectional view in the arrow direction along the line II-II shown in FIG.

  This secondary battery is, for example, a lithium ion secondary battery in which the capacity of the negative electrode 22 is expressed based on insertion and extraction of lithium as an electrode reactant.

  The outer can 11 is, for example, a square outer member. As shown in FIG. 1, the rectangular exterior member has a rectangular or substantially rectangular cross section in the longitudinal direction (including a curve in part), and is a rectangular prismatic battery. In addition to this, an oval prismatic battery is also configured. That is, the square-shaped exterior member is a bottomed rectangular type or bottomed oval shaped vessel-like member having a rectangular shape or a substantially rectangular shape (oval shape) obtained by connecting arcs with straight lines. FIG. 1 shows the case where the outer can 11 has a rectangular cross-sectional shape. The battery structure including the outer layer can 11 is called a so-called square shape.

  The outer can 11 is made of, for example, iron (Fe) plated with nickel (Ni), and also has a function as a negative electrode terminal. The outer can 11 has a structure in which one end is closed and the other end is opened, and the inside is sealed by attaching an insulating plate 12 and a battery lid 13 to the open end. The insulating plate 12 is made of polypropylene or the like, and is disposed on the battery element 20 perpendicular to the winding peripheral surface. The battery cover 13 is made of, for example, the same material as that of the outer can 11 and has a function as a negative electrode terminal together with the outer can 11. A terminal plate 14 serving as a positive electrode terminal is disposed outside the battery lid 13. A through hole is provided near the center of the battery lid 13, and a positive electrode pin 15 electrically connected to the terminal plate 14 is inserted into the through hole. The terminal plate 14 and the battery lid 13 are electrically insulated by an insulating case 16, and the positive electrode pin 15 and the battery lid 13 are electrically insulated by a gasket 17. The insulating case 16 is made of, for example, polybutylene terephthalate. The gasket 17 is made of, for example, an insulating material, and asphalt is applied to the surface.

  A cleavage valve 18 and an injection hole 19 are provided near the periphery of the battery lid 13. The cleaving valve 18 is electrically connected to the battery lid 13 and is cleaved when the internal pressure of the battery exceeds a certain level due to an internal short circuit or external heating, thereby suppressing an increase in the internal pressure. . The injection hole 19 is closed by a sealing member 19A made of, for example, a stainless steel ball.

  The battery element 20 is a wound body in which a positive electrode 21 and a negative electrode 22 are stacked with a separator 23 therebetween. The battery element 20 is wound along a winding direction R indicated by an arrow in FIG. 1 from the winding center side toward the winding outer peripheral side, and includes a pair of flat portions 20S and a pair of curved portions 20R that face each other. In this way, the outer can 11 is formed into a flat shape according to the shape of the can 11. The separator 23 is located on the outermost periphery of the battery element 20, and the positive electrode 21 is located immediately inside thereof. A positive electrode lead 24 made of a metal material such as aluminum is attached to an end portion (for example, an inner terminal portion) of the positive electrode 21, and an end portion (for example, an outer terminal portion) of the negative electrode 22 is made of a metal material such as nickel. A configured negative electrode lead 25 is attached. The positive electrode lead 24 is welded to one end of the positive electrode pin 15 and electrically connected to the terminal plate 14, and the negative electrode lead 25 is welded and electrically connected to the outer can 11. In FIG. 2, the laminated structure of the positive electrode 21 and the negative electrode 22 is shown in a simplified manner. Further, the number of windings of the battery element 20 is not limited to that shown in FIGS. 1 and 2 and can be arbitrarily set.

  The positive electrode 21 is, for example, one in which a positive electrode active material layer 21B is provided on both surfaces of a positive electrode current collector 21A. However, the positive electrode active material layer 21B may be provided only on one surface of the positive electrode current collector 21A.

  The positive electrode current collector 21A has, for example, a thickness of about 5 μm to 50 μm and is made of a metal foil such as an aluminum foil, a nickel foil, or a stainless steel foil.

The positive electrode active material layer 21B contains one or more positive electrode materials capable of occluding and releasing lithium, which is an electrode reactant, as a positive electrode active material, and a conductive agent and a binder as necessary. Other materials such as may be included.

As a positive electrode material capable of inserting and extracting lithium, for example, a lithium-containing compound is preferable. This is because a high energy density can be obtained. Examples of the lithium-containing compound include a composite oxide containing lithium and a transition metal element, and a phosphate compound containing lithium and a transition metal element. Especially, what contains at least 1 sort (s) of the group which consists of cobalt, nickel, manganese, and iron as a transition metal element is preferable. This is because a higher voltage can be obtained. The chemical formula is represented by, for example, Li _x M1O ₂ or Li _y M2PO ₄ . In the formula, M1 and M2 represent one or more transition metal elements. The values of x and y vary depending on the charge / discharge state, and are generally 0.05 ≦ x ≦ 1.10 and 0.05 ≦ y ≦ 1.10.

Examples of the composite oxide containing lithium and a transition metal element include lithium cobalt composite oxide (Li _x CoO ₂ ), lithium nickel composite oxide (Li _x NiO ₂ ), and lithium nickel cobalt composite oxide (Li _x Ni). _1-z Co _z O ₂ (z <1)), lithium nickel cobalt manganese composite oxide (Li _x Ni _(1-vw) Co _v Mn _w O ₂ (v + w <1)), or lithium having a spinel structure Manganese composite oxide (LiMn ₂ O ₄ ) and the like can be mentioned. Among these, a complex oxide containing cobalt is preferable. This is because a high capacity can be obtained and excellent cycle characteristics can be obtained. Examples of the phosphate compound containing lithium and a transition metal element include a lithium iron phosphate compound (LiFePO ₄ ) or a lithium iron manganese phosphate compound (LiFe _1-u Mn _u PO ₄ (u <1)). Is mentioned.

  In addition, examples of the positive electrode material capable of inserting and extracting lithium include oxides such as titanium oxide, vanadium oxide and manganese dioxide, disulfides such as titanium disulfide and molybdenum sulfide, and niobium selenide. And chalcogenides such as sulfur, polyaniline and polythiophene, and other conductive polymers.

  Of course, the positive electrode material capable of inserting and extracting lithium may be other than the above. Further, two or more kinds of the series of positive electrode materials described above may be mixed in any combination.

  Examples of the binder include synthetic rubbers such as styrene butadiene rubber, fluorine rubber or ethylene propylene diene, and polymer materials such as polyvinylidene fluoride. These may be single and multiple types may be mixed.

  Examples of the conductive agent include carbon materials such as graphite, carbon black, acetylene black, and ketjen black. These may be single and multiple types may be mixed. Note that the conductive agent may be a metal material or a conductive polymer as long as it is a conductive material.

  The negative electrode 22 is one in which a negative electrode active material layer 22B is selectively provided on both surfaces of a strip-shaped negative electrode current collector 22A. The negative electrode lead 25 is bonded to a region where the negative electrode current collector 22A is exposed, for example, on the outer periphery of the winding. Note that the region where the negative electrode current collector 22A is exposed does not need to coincide on both surfaces, and there may be a region where the negative electrode active material layer 22B is provided on only one surface.

  The negative electrode current collector 22A is made of, for example, a metal foil such as a copper foil, a nickel foil, or a stainless steel foil. The thickness of the negative electrode current collector 22A is, for example, 5 μm to 50 μm.

  The negative electrode active material layer 22B includes one or more negative electrode materials capable of occluding and releasing lithium, which is an electrode reactant, as a negative electrode active material. A binder, a conductive agent, and the like of the same type as those used for the material layer 21B may be included.

  Examples of the negative electrode material capable of inserting and extracting lithium include materials capable of inserting and extracting lithium and having at least one of a metal element and a metalloid element as a constituent element. . This is because a high energy density can be obtained. The negative electrode material may be a single element, alloy or compound of a metal element or metalloid element, or may have at least a part of one or more phases thereof. In addition, the alloy in the present invention includes an alloy containing one or more metal elements and one or more metalloid elements in addition to an alloy composed of two or more metal elements. Of course, the above-described alloy may contain a nonmetallic element. This structure includes a solid solution, a eutectic (eutectic mixture), an intermetallic compound, or one in which two or more of them coexist.

  Examples of the metal element and metalloid element constituting the negative electrode material include metal elements and metalloid elements capable of forming an alloy with lithium. Specifically, magnesium, boron (B), aluminum, gallium (Ga), indium (In), silicon, germanium (Ge), tin (Sn), lead (Pb), bismuth (Bi), cadmium (Cd) Silver (Ag), zinc, hafnium (Hf), zirconium (Zr), yttrium (Y), palladium (Pd), or platinum (Pt). Among these, at least one of silicon and tin is particularly preferable. This is because a high energy density can be obtained because the ability to occlude and release lithium is large.

  Examples of the negative electrode material containing at least one of silicon and tin include, for example, a simple substance, an alloy, or a compound of silicon, a simple substance, an alloy, or a compound of tin, or one or two or more phases thereof. The material which has in part is mentioned. These may be used alone or in combination of two or more.

  Examples of the silicon alloy include, as the second constituent element other than silicon, tin, nickel, copper, iron, cobalt (Co), manganese (Mn), zinc, indium, silver, titanium (Ti), germanium, and bismuth. And at least one selected from the group consisting of antimony (Sb) and chromium (Cr). As an alloy of tin, for example, as a second constituent element other than tin, among the group consisting of silicon, nickel, copper, iron, cobalt, manganese, zinc, indium, silver, titanium, germanium, bismuth, antimony and chromium The thing containing at least 1 sort (s) is mentioned.

  Examples of the silicon compound or tin compound include those containing oxygen (O) or carbon (C), and may contain the above-described second constituent element in addition to silicon or tin.

  As a specific example of a material having at least one of a metal element and a metalloid element, a material containing tin as a first constituent element and further containing second and third constituent elements is preferable. The second constituent element is cobalt, iron, magnesium, titanium, vanadium (V), chromium, manganese, nickel, copper, zinc, gallium, zirconium, niobium (Nb), molybdenum (Mo), silver, indium, cerium ( Ce), hafnium, tantalum (Ta), tungsten (W), bismuth and silicon. The third constituent element is at least one selected from the group consisting of boron, carbon, aluminum, and phosphorus (P). This is because excellent cycle characteristics can be obtained by including these second and third elements.

  Among these, tin, cobalt, and carbon are included as constituent elements, the carbon content is in the range of 9.9 mass% to 29.7 mass%, and the ratio of cobalt to the total of tin and cobalt (Co / (Sn + Co CoSnC-containing material in which)) is in the range of 20% by mass to 40% by mass is preferable. This is because in such a composition range, a high energy density is obtained and the cycle characteristics are improved.

  This SnCoC-containing material may further contain other constituent elements as necessary. As other constituent elements, for example, silicon, iron, nickel, chromium, indium, niobium, germanium, titanium, molybdenum, aluminum, phosphorus, gallium, bismuth, and the like are preferable, and two or more of them may be included. Good. This is because a higher effect can be obtained.

  The SnCoC-containing material has a phase containing tin, cobalt, and carbon, and the phase is preferably a low crystalline or amorphous phase. This phase is a reaction phase capable of reacting with lithium, whereby excellent cycle characteristics can be obtained. The half-value width of the diffraction peak obtained by X-ray diffraction of this phase is 1.0 ° or more at a diffraction angle 2θ when CuKα ray is used as the specific X-ray and the drawing speed is 1 ° / min. Is preferred. This is because lithium is more smoothly inserted and extracted, and the reactivity with the electrolytic solution is reduced when the negative electrode is used in an electrochemical device such as a secondary battery equipped with the electrolytic solution.

  Whether or not the diffraction peak obtained by X-ray diffraction corresponds to a reaction phase capable of reacting with lithium can be easily determined by comparing X-ray diffraction charts before and after electrochemical reaction with lithium. can do. For example, if the position of the diffraction peak changes before and after the electrochemical reaction with lithium, it corresponds to a reaction phase capable of reacting with lithium. In this case, for example, a diffraction peak of a low crystalline or amorphous reaction phase is observed between 2θ = 20 ° and 50 °. This low crystalline or amorphous reaction phase contains, for example, each of the above-described constituent elements, and is considered to be mainly low-crystallized or amorphous due to carbon.

  In addition to the low crystalline or amorphous phase, the SnCoC-containing material may have a phase containing a simple substance or a part of each constituent element.

  In particular, in the SnCoC-containing material, it is preferable that at least a part of carbon as a constituent element is bonded to a metal element or a metalloid element as another constituent element. This is because aggregation or crystallization of tin or the like is suppressed.

  As a measuring method for examining the bonding state of elements, for example, X-ray photoelectron spectroscopy (XPS) can be cited. This XPS irradiates the sample surface with soft X-rays (Al-Kα ray or Mg-Kα ray is used in a commercial apparatus), and measures the kinetic energy of photoelectrons jumping out of the sample surface. To elemental composition in the region of several nanometers and the bonding state of the elements.

  The binding energy of the core orbital electrons of the element changes in a first approximation in correlation with the charge density on the element. For example, when the charge density of the carbon element decreases due to an interaction with an element present in the vicinity, the outer electrons such as 2p electrons decrease, so the 1s electron of the carbon element exerts a strong binding force from the shell. Will receive. That is, the binding energy increases as the charge density of the element decreases. In XPS, when the binding energy increases, the peak shifts to a high energy region.

  In XPS, if the peak of carbon 1s orbital (C1s) is graphite, it appears at 284.5 eV in an energy calibrated apparatus so that the peak of 4f orbital (Au4f) of gold atom is obtained at 84.0 eV. . Moreover, if it is surface contamination carbon, it will appear at 284.8 eV. On the other hand, when the charge density of the carbon element is high, for example, when it is bonded to an element more positive than carbon, the C1s peak appears in a region lower than 284.5 eV. That is, when at least a part of carbon contained in the SnCoC-containing material is bonded to a metal element or a metalloid element that is another constituent element, the peak of the synthetic wave of C1s obtained for the SnCoC-containing material is 284. Appears in a region lower than 5 eV.

  When performing XPS measurement, it is preferable that the surface is lightly sputtered with an argon ion gun attached to the XPS apparatus when the surface is covered with surface-contaminated carbon. In addition, when a negative electrode having a SnCoC-containing material to be measured is present in an electrochemical device such as a secondary battery provided with an electrolytic solution, the electrochemical device is disassembled and the negative electrode is taken out, and then dimethyl carbonate, etc. It is good to wash with a volatile solvent. This is for removing the low-volatile solvent and the electrolyte salt present on the negative electrode surface. These samplings are preferably performed under an inert atmosphere.

  In XPS measurement, for example, the peak of C1s is used to correct the energy axis of the spectrum. Usually, since surface-contaminated carbon exists on the surface of the substance, the C1s peak of the surface-contaminated carbon is set to 284.8 eV, and this is used as an energy standard. In XPS measurement, the waveform of the peak of C1s is obtained as a form including the surface contamination carbon peak and the carbon peak in the SnCoC-containing material. For example, by analyzing using commercially available software, The surface contamination carbon peak is separated from the carbon peak in the SnCoC-containing material. In the waveform analysis, the position of the main peak existing on the lowest bound energy side is used as the energy reference (284.8 eV).

  This SnCoC-containing material can be formed by, for example, a method in which a mixture obtained by mixing raw materials of each constituent element is melted in an electric furnace, a high-frequency induction furnace, an arc melting furnace or the like and then solidified. Also, various atomizing methods such as gas atomization or water atomization, methods using various mechanochemical reactions such as various roll methods, mechanical alloying methods, and mechanical milling methods may be used. Among these, a method using a mechanochemical reaction is preferable. This is because the SnCoC-containing material has a low crystalline or amorphous structure. In the method using the mechanochemical reaction, for example, a manufacturing apparatus such as a planetary ball mill or an attritor can be used.

  The raw material may be a mixture of individual constituent elements, but it is preferable to use an alloy for some of the constituent elements other than carbon. This is because, by adding carbon to such an alloy and synthesizing it by a method using a mechanical alloying method, a low crystalline or amorphous structure is obtained, and the reaction time is shortened. The raw material may be in the form of powder or a block.

  In addition to this SnCoC-containing material, an SnCoFeC-containing material having tin, cobalt, iron and carbon as constituent elements is also preferable. The composition of the SnCoFeC-containing material can be arbitrarily set. For example, as the composition when the iron content is set to be small, the carbon content is 9.9 mass% or more and 29.7 mass% or less, and the iron content is 0.3 mass% or more and 5.9 weight% %, And the ratio of cobalt to the total of tin and cobalt (Co / (Sn + Co)) is preferably 20% by mass or more and 40% by mass or less. In addition, for example, as a composition when the content of iron is set to be large, the content of carbon is 11.9 mass% or more and 29.7 mass% or less, and cobalt and iron with respect to the total of tin, cobalt, and iron The total ratio of (Co + Fe) / (Sn + Co + Fe)) is 26.4 mass% to 48.5 mass%, and the ratio of cobalt to the total of cobalt and iron (Co / (Co + Fe)) is 9.9 mass% It is preferable that it is 79.5 mass% or more. This is because a high energy density can be obtained in such a composition range. The crystallinity of the SnCoFeC-containing material, the method for measuring the bonding state of elements, the formation method, and the like are the same as those of the above-described SnCoC-containing material.

  As a negative electrode material capable of inserting and extracting lithium, a simple substance, an alloy or a compound of silicon, a simple substance, an alloy or a compound of tin, or a material having one or more phases thereof at least in part. The used negative electrode active material layer 22B is formed by using, for example, a gas phase method, a liquid phase method, a thermal spraying method, a coating method or a firing method, or two or more of these methods. In this case, the anode current collector 22A and the anode active material layer 22B2 are preferably alloyed at least at a part of the interface. Specifically, the constituent element of the negative electrode current collector 22A may be diffused into the negative electrode active material layer 22B at the interface between them, or the constituent element of the negative electrode active material layer 22B is diffused into the negative electrode current collector 22A. These constituent elements may be diffused with each other. This is because breakage due to expansion and contraction of the negative electrode active material layer 22B during charging and discharging is suppressed, and electron conductivity between the negative electrode current collector 22A and the negative electrode active material layer 22B is improved.

  As the vapor phase method, for example, physical deposition method or chemical deposition method, specifically, vacuum deposition method, sputtering method, ion plating method, laser ablation method, thermal chemical vapor deposition (CVD) Or plasma chemical vapor deposition. As the liquid phase method, a known method such as electrolytic plating or electroless plating can be used. The application method is, for example, a method in which a particulate negative electrode active material is mixed with a binder and then dispersed in a solvent and applied. The baking method is, for example, a method in which a heat treatment is performed at a temperature higher than the melting point of a binder or the like after being applied by a coating method. A known method can also be used for the firing method, for example, an atmospheric firing method, a reactive firing method, or a hot press firing method.

  In addition to the above, examples of the anode material capable of inserting and extracting lithium include a carbon material. Examples of the carbon material include graphitizable carbon, non-graphitizable carbon having a (002) plane spacing of 0.37 nm or more, and graphite having a (002) plane spacing of 0.34 nm or less. It is. More specifically, there are pyrolytic carbons, cokes, glassy carbon fibers, organic polymer compound fired bodies, activated carbon or carbon blacks. The cokes include pitch coke, needle coke, petroleum coke and the like. The organic polymer compound fired body is obtained by firing and carbonizing a phenol resin, a furan resin, or the like at an appropriate temperature. Since carbon materials undergo very little change in crystal structure due to insertion and extraction of electrode reactants, for example, when used together with other negative electrode materials, high energy density can be obtained, and the negative electrode can be used for secondary batteries, etc. When used in an electrochemical device, excellent cycle characteristics can be obtained, and it also functions as a conductive agent, which is preferable. The shape of the carbon material may be any of fibrous, spherical, granular or scale-like.

  Furthermore, examples of the negative electrode material capable of inserting and extracting lithium include metal oxides and polymer compounds capable of inserting and extracting lithium. Examples of the metal oxide include iron oxide, ruthenium oxide, and molybdenum oxide. Examples of the polymer compound include polyacetylene, polyaniline, and polypyrrole.

  Of course, the negative electrode material capable of inserting and extracting lithium may be other than the above. Further, two or more kinds of the above series of negative electrode materials may be mixed in any combination.

  In this secondary battery, the charge capacity of the negative electrode active material is larger than the charge capacity of the positive electrode active material by adjusting the amount between the positive electrode active material and the negative electrode active material. This prevents lithium metal from being deposited on the negative electrode 22 even during full charge.

  The separator 23 separates the positive electrode 21 and the negative electrode 22 and allows ions of the electrode reactant to pass through while preventing a short circuit of current due to contact between the two electrodes. In FIG. 3, the separator 23 is shown expanded. 3A is a plan view, and FIG. 3B is a cross-sectional view taken along line IIIB-IIIB in FIG. 3A. As shown in FIG. 3, the separator 23 has a base material 231 and a polymer compound layer 232 (232A, 232B) applied on the surface thereof. The base material 231 is mechanically reinforced by the polymer compound layer 232 and is bonded to the positive electrode 21 and the negative electrode 22 through the polymer compound layer 232.

  As shown in FIGS. 3A and 3B, in the polymer compound layers 232A and 232B, the portion 23R corresponding to the curved portion 20R has a thickness of about 5 μm, for example, than the portion 23S corresponding to the flat portion 20S. It is getting bigger. As a result, the air permeability of the separator 23 in the curved portion 20R is higher than the air permeability of the separator 23 in the flat portion 20S continuous with the curved portion 20R. That is, when the separator 23 of the curved portion 20R and the separator 23 of the flat portion 20S adjacent in the winding direction R of the battery element 20 are compared, the separator 23 of the curved portion 20R has higher air permeability. For example, the separator 23 positioned at the outermost curved portion 20 </ b> R of the battery element 20 has a higher air permeability than the separator 23 positioned at the outermost flat portion 20 </ b> S of the battery element 20. Similarly, the separator 23 positioned on the innermost peripheral curved portion 20 </ b> R of the battery element 20 has a higher air permeability than the separator 23 positioned on the innermost flat portion 20 </ b> S of the battery element 20. The same relationship as described above with respect to the air permeability of the separator 23 is also maintained in the circumferential portion of the battery element 20 other than the outermost periphery and the innermost periphery.

The air permeability of the separator 23 is, for example, 200 seconds / 100 cm ³ or more and 800 seconds / 100 cm ³ or less in the flat portion 20S. On the other hand, the air permeability of the separator 23 in the curved portion 20R is preferably 800 seconds / 100 cm ³ or more, and particularly preferably 1500 seconds / 100 cm ³ or more. Note that the air permeability of the separator 23 is measured by a method defined in JIS K7126.

  The base material 231 is required to be electrically stable and chemically stable with respect to the positive electrode active material, the negative electrode active material, the solvent of the electrolytic solution, and the like. For this reason, the base material 231 is composed of, for example, a porous film made of a synthetic resin such as polytetrafluoroethylene, polypropylene, or polyethylene, or a porous film made of ceramic. Note that two or more of these porous films may be laminated.

  The polymer compound layers 232A and 232B include an electrolytic solution in which an electrolyte salt is dissolved in a solvent, and a polymer compound that holds the electrolytic solution. Here, the term “holds” the electrolytic solution by the polymer compound is a concept that includes not only the state in which the polymer compound is swollen in the electrolyte solution but also the state in which the electrolyte solution and the polymer compound are mixed without interaction. It is. That is, the polymer compound layers 232A and 232B may be a so-called gel electrolyte in which a polymer compound is swollen in an electrolyte solution, or the electrolyte solution exists without causing an interaction in a void of a rigid polymer compound. It may be an electrolyte in the state. The electrolytic solution may be impregnated in the positive electrode 21, the negative electrode 22, or the separator 23.

  As the solvent contained in the electrolytic solution, various high dielectric constant solvents and low viscosity solvents can be used. For example, as a high dielectric constant solvent, in addition to ethylene carbonate, propylene carbonate, butylene carbonate, vinylene carbonate, 4-fluoro-1,3-dioxolan-2-one (fluoroethylene carbonate), 4-chloro-1,3-dioxolane Cyclic carbonates such as 2-one (chloroethylene carbonate) and trifluoromethylethylene carbonate are preferably used. As the high dielectric constant solvent, a lactone such as γ-butyrolactone, γ-valerolactone, δ-valerolactone or ε-caprolactone, N-methylpyrrolidone, or the like, instead of or in combination with the above cyclic carbonate Lactam, cyclic carbamates such as N-methyloxazolidinone, and sulfone compounds such as tetramethylene sulfone can also be used. On the other hand, as low-viscosity solvents, in addition to diethyl carbonate, chain carbonates such as dimethyl carbonate, ethyl methyl carbonate and methyl propyl carbonate, methyl acetate, ethyl acetate, methyl propionate, ethyl propionate, methyl butyrate, methyl isobutyrate, Chain carboxylic acid esters such as methyl trimethylacetate and ethyl trimethylacetate, chain amides such as N, N-dimethylacetamide, chain carbamic acid such as methyl N, N-diethylcarbamate and ethyl N, N-diethylcarbamate Esters and ethers such as 1,2-dimethoxyethane, tetrahydrofuran, tetrahydropyran and 1,3-dioxolane can be used.

  In addition, as a solvent, 1 type in the above-mentioned high-dielectric-constant solvent and low-viscosity solvent can be used individually, or 2 or more types can be arbitrarily mixed, but 20-50 mass% cyclic carbonate can be used. And a low-viscosity solvent of 50 to 80% by mass are preferable, and a low-viscosity solvent including a chain carbonate having a boiling point of 130 ° C. or less is particularly preferable. By using such a solvent, the polymer compound can be swelled satisfactorily with a small amount of electrolytic solution, and it is possible to achieve both suppression of battery swelling and prevention of leakage and high ion conductivity. Here, if the content of the low-viscosity solvent occupying the electrolytic solution is too high, the dielectric constant will be lowered, and if the content of the low-viscosity solvent is too low, the viscosity will be lowered. Ionic conductivity may not be obtained, and good battery characteristics may not be obtained.

Any electrolyte salt may be used as long as it dissolves in a solvent to generate ions, and one kind may be used alone, or two or more kinds may be mixed and used. For example, if the lithium salt, lithium hexafluorophosphate (LiPF _6), lithium tetrafluoroborate (LiBF _4), lithium hexafluoroarsenate (LiAsF _6), lithium hexafluoro antimonate (LiSbF ₆₎ Inorganic lithium salts such as lithium perchlorate (LiClO ₄ ) and lithium tetrachloride aluminum oxide (LiAlCl ₄ ), lithium trifluoromethanesulfonate (LiCF ₃ SO ₃ ), lithium bis (trifluoromethanesulfone) imide (LiN (CF ₃ SO _2
2 ), perfluoroalkanes such as lithium bis (pentafluoromethanesulfone) imide (LiN (C ₂ F ₅ SO ₂ ) ₂ ) and lithium tris (trifluoromethanesulfone) methide (LiC (CF ₃ SO ₂ ) ₃ ) Lithium salts of sulfonic acid derivatives can be used. Of these, lithium hexafluorophosphate and lithium tetrafluoroborate are preferable from the viewpoint of oxidation stability.

Incidentally, the concentration of such electrolyte salt is preferably at 0.1mol or more 3.0mol or less with respect to solvent 1 dm ^3, in particular, 0.5 mol or more 2.0mol or less with respect to solvent 1 dm ³ Is preferred. This is because higher ion conductivity can be obtained in such a range.

  The polymer compound constituting the polymer compound layers 232A and 232B is not particularly limited as long as it retains the electrolytic solution and exhibits ionic conductivity, but the acrylonitrile copolymer is 50% or more (particularly 80%). % Acrylonitrile polymer, aromatic polyamide, acrylonitrile / butadiene copolymer, acrylic polymer made of homopolymer or copolymer of acrylate or methacrylate, acrylamide polymer, vinylidene fluoride, etc. , Celluloses such as polysulfone, polyallylsulfone, and carboxymethylcellulose. In particular, a polymer having a copolymerization amount of 50% or more of acrylonitrile has a CN group in its side chain, and thus can form a gel electrolyte having a high dielectric constant and high ion conductivity. Acrylic nitriles and vinyl carboxylic acids such as acrylic acid, methacrylic acid, itaconic acid, acrylamide, methacryl sulfonic acid, hydroxyalkylene glycol (meth) are used to improve the electrolyte support for these polymers and the ionic conductivity of the electrolyte. A copolymer obtained by copolymerizing acrylate, alkoxyalkylene glycol (meth) acrylate, vinyl chloride, vinylidene chloride, vinyl acetate, various (meth) acrylates or the like at a ratio of preferably 50% or less, particularly preferably 20% or less can also be used. . Moreover, since aromatic polyamide is a high heat resistant polymer, it is suitable when high heat resistance is required.

In addition to the above, examples of the polymer compound constituting the polymer compound layers 232A and 232B include a polymer having a crosslinked structure obtained by copolymerizing butadiene or the like. Furthermore, polymers containing vinylidene fluoride as a constituent component, that is, homopolymers, copolymers, and multi-component copolymers can also be used as the polymer compound. Specifically, polyvinylidene fluoride (PVdF), polyvinylidene fluoride-hexafluoropropylene copolymer (PVdF-HFP), and polyvinylidene fluoride-hexafluoropropylene-chlorotrifluoroethylene copolymer (PVdF-HEP-CTFE). ). In particular, from the viewpoint of redox stability, a fluorine-based polymer compound such as polyvinylidene fluoride or a copolymer of vinylidene fluoride and hexafluoropropylene is desirable. The polymer compound layers 232A and 232B further contain metal oxide particles such as aluminum oxide (Al ₂ O ₃ ), titanium oxide (TiO ₂ ), or silicon oxide (SiO ₂ ) for the purpose of improving safety. It may be.

  In the secondary battery, when charged, for example, lithium ions are extracted from the positive electrode 21 and inserted in the negative electrode 22 through the electrolytic solution impregnated in the separator 23. When the discharge is performed, for example, lithium ions are released from the negative electrode 22 and inserted into the positive electrode 21 through the electrolytic solution impregnated in the separator 23.

  For example, the secondary battery can be manufactured as follows.

  First, a positive electrode active material, a conductive agent, and a binder are mixed to prepare a positive electrode mixture, and the positive electrode mixture is dispersed in a solvent such as N-methyl-2-pyrrolidone to obtain a paste-like positive electrode mixture. A slurry is obtained. Subsequently, the positive electrode mixture slurry is uniformly applied to the positive electrode current collector 21A using a doctor blade or a bar coater, and the solvent is dried. Then, the positive electrode active material layer 21B is formed by compression molding using a roll press or the like. Then, the positive electrode 21 is produced.

  Next, a negative electrode active material and a binder are mixed to prepare a negative electrode mixture, and the negative electrode mixture is dispersed in a solvent such as N-methyl-2-pyrrolidone to obtain a paste-like negative electrode mixture slurry. . Subsequently, the negative electrode mixture slurry is uniformly applied to the negative electrode current collector 22A using a doctor blade or a bar coater, and the solvent is dried. Then, the negative electrode active material layer 22B is formed by compression molding using a roll press. Then, the negative electrode 22 is produced. The roll press machine may be used by heating. Moreover, you may compression-mold several times until it becomes the target physical-property value. Furthermore, you may use press machines other than a roll press machine. Alternatively, the negative electrode 22 may be manufactured by providing the negative electrode active material layer 22 </ b> B on the negative electrode current collector 22 </ b> A by other methods such as a gas phase method.

  Subsequently, the positive electrode lead 24 is attached to the positive electrode current collector 21A by welding or the like, and the negative electrode lead 25 is attached to the negative electrode current collector 22A by welding or the like.

  On the other hand, the polymer compound layer 232 is formed on both surfaces of the base material 231. Specifically, first, a polymer solution in which a polymer compound such as polyvinylidene fluoride or carboxymethylcellulose is dissolved in a solvent such as N-methyl-2-pyrrolidone or water is applied to both surfaces of the substrate 231. Next, the polymer solution layer 232 is formed by drying the applied polymer solution and removing the solvent. Here, for example, a pot having a shutter is placed on a base material 231 that travels in the longitudinal direction of the device, and the shutter is opened while supplying the polymer solution to the pot, and a predetermined amount of the polymer solution is used as a base. It is made to adhere on the material 231. At this time, the coating amount of the polymer solution in the longitudinal direction of the base material 231 is changed by adjusting the opening amount of the shutter of the pot, and the thickness of the polymer compound layer 232 finally obtained is a portion that is smaller than the portion 23S. It is made to become large in 23R (refer FIG. 3). In addition, the space | interval of adjacent part 23R will spread gradually according to the winding amount, so that it goes to the winding outer peripheral side from the winding center side of the battery element 20. For this reason, the opening / closing operation of the shutter of the pot is performed according to the change in the interval.

  Next, the positive electrode 21, the separator 23, the negative electrode 22, and the separator 23 are laminated in this order, and after being wound a plurality of times in the winding direction R shown in FIG. 1, the battery element 20 having a flat shape is formed. Is made.

  Subsequently, the battery element 20 produced as described above is accommodated in the outer can 11. After that, the insulating plate 12 is disposed on the battery element 20, the negative electrode lead 25 is welded to the outer can 11, and the positive electrode lead 24 is welded to the lower end of the positive electrode pin 15, so that the open end of the outer can 11 is The battery lid 13 is fixed by laser welding. Finally, the electrolytic solution is injected into the outer can 11 from the electrolytic solution injection hole 19 and impregnated in the separator 23, and the electrolytic solution injection hole 19 is closed with the sealing member 19A. Thereby, the secondary battery shown in FIGS. 1 and 2 is completed.

  Thus, in the secondary battery of the present embodiment, the air permeability of the separator 23 in the curved portion 20R of the battery element 20 is set higher than the air permeability of the separator 23 in the flat portion 20S. The ionic conductivity at the curved portion 20R of the element 20 is lowered, and the battery reaction is suppressed. For this reason, the stress inside the battery element 20 due to expansion / contraction due to charging / discharging is relieved, and cracks such as the positive electrode current collector 21A hardly occur in the curved portion 20R that is particularly susceptible to stress. As a result, even when a negative electrode active material containing tin or silicon capable of obtaining a high capacity is employed, damage to the positive electrode 21 and the like due to repeated charge and discharge can be prevented, and high reliability as a battery is ensured. be able to.

  Further, according to the secondary battery of the present embodiment, since the base material 231 of the separator 23 is bonded to the positive electrode 21 and the negative electrode 22 through the polymer compound layer 232, the separator 23, the positive electrode 21, and the negative electrode 22 The relative position can be held with high accuracy. Therefore, a short circuit inside the battery element 20 can be reliably prevented. Furthermore, since the separator 23 is sufficiently adhered to the positive electrode 21 and the negative electrode 22, the electrolyte retention performance in the separator 23 is enhanced, and good battery characteristics (for example, cycle characteristics) can be ensured.

(Modification)
Next, a separator 23A as a modification of the secondary battery of the present embodiment will be described. FIG. 4 illustrates a cross-sectional configuration of a separator 23A as a modification, and corresponds to FIG. 3B of the above embodiment.

  In the above embodiment, both of the polymer compound layers 232A and 232B applied to the surface of the base material 231 have a thickness larger than that of the portion 23S corresponding to the flat portion 20S in each of the portions 23R corresponding to the curved portion 20R. Configured to have. On the other hand, in this modified example, only one of the polymer compound layers 232A and 232B is configured to have a thickness larger than the portion 23S in each portion 23R. That is, the portions 23R1 in which the polymer compound layer 232A has a relatively large thickness and the portions 23R2 in which the polymer compound layer 232B has a relatively large thickness are alternately arranged in the winding direction R. Therefore, in one of the pair of curved portions 20 </ b> R in the secondary battery, the polymer compound layer 232 </ b> A positioned on the wound inner surface side of the substrate 231, for example, is positioned on the wound outer surface side of the substrate 231. It has a greater thickness than layer 232A. On the other hand, in the other curved portion 20R, the polymer compound layer 232B located on the winding outer surface side of the substrate 231 has a larger thickness than the polymer compound layer 232A located on the winding inner surface side of the substrate 231. .

  In this modification, the same effect as the secondary battery of the above embodiment can be obtained by such a configuration. Furthermore, when compared with the secondary battery of the above embodiment, the volume associated with the expansion and contraction accompanying charging / discharging at the curved portion 20R and the increase in the radial dimension of the battery element 20 due to the thickness of the polymer compound layer 232. It is possible to suppress a decrease in energy density with a good balance. That is, compared with the said embodiment, it is advantageous in the point of coexistence with moderate relaxation of the stress resulting from the expansion / contraction accompanying charging / discharging, and a capacity improvement.

  Specific examples of the present invention will be described in detail.

(Experimental Examples 1-1 to 1-7)
In this experimental example, the square secondary battery shown in FIGS. 1 and 2 was manufactured by the following procedure. Here, the separator 23 having the structure shown in FIG. 3 is employed.

First, the positive electrode 21 was produced. Specifically, lithium carbonate (Li ₂ CO ₃ ) and cobalt carbonate (CoCO ₃ ) are mixed at a molar ratio of 0.5: 1, and then calcined in air at 900 ° C. for 5 hours. A cobalt composite oxide (LiCoO ₂ ) was obtained. Subsequently, 91 parts by mass of a lithium-cobalt composite oxide as a positive electrode active material, 6 parts by mass of graphite as a conductive agent, and 3 parts by mass of polyvinylidene fluoride as a binder were mixed to prepare a positive electrode mixture. This positive electrode mixture was dispersed in N-methyl-2-pyrrolidone to obtain a paste-like positive electrode mixture slurry. Thereafter, the above positive electrode mixture slurry is uniformly applied to both surfaces of the positive electrode current collector 21A made of a strip-shaped aluminum foil (thickness = 20 μm), dried, and then compression-molded with a roll press machine. A positive electrode active material layer 21B was formed. Finally, the positive electrode lead 24 made of aluminum was welded and attached to one end of the positive electrode current collector 21A.

  Next, the negative electrode 22 was produced as follows. Specifically, first, a negative electrode current collector 22A (surface roughness Rz = 3.5 μm) made of an electrolytic copper foil was prepared and placed in a chamber of a vapor deposition apparatus. Next, after the chamber was evacuated, silicon as the negative electrode active material was deposited on both surfaces of the negative electrode current collector 22A by electron beam evaporation to form a negative electrode active material layer 22B having an average thickness of 7 μm. At this time, single-crystal silicon having a purity of 99% was used as the evaporation source, and the deposition rate was 150 nm / second. Finally, a nickel negative electrode lead 25 was attached to one end of the negative electrode current collector 22A.

  Subsequently, a base material 231 made of a 20 μm-thick microporous polyethylene film (manufactured by Tonen Chemical) was prepared, and a polymer solution in which aramid (aromatic polyamide) was dissolved in N-methyl-2-pyrrolidone was used as the base material 231. After being coated on both surfaces by roller coating, the separator 23 having the polymer compound layers 232A and 232B formed on the substrate 231 was obtained by washing with pure water and drying. Here, by adjusting the discharge amount of the polymer solution from the head in the coating apparatus, the polymer compound layers 232A and 232B alternately have relatively thick portions 23R and relatively thin portions 23S. To have. At this time, by changing the thickness (average thickness) of the portions 23R and 23S for each experimental example, the air permeability of the portion 23R is made larger than the air permeability of the portion 23S (Table 1 described later). reference). The portion 23R was formed at a position corresponding to the curved portion 20R, and the portion 23S was formed at a position corresponding to the flat portion 20S. The width in the winding direction of the portion 23R was 7 mm. The air permeability was measured by the method defined in JIS K7126.

  Furthermore, after the positive electrode 21, the separator 23, the negative electrode 22, and the separator 23 are sequentially laminated to form a laminated body, the laminated body is wound 20 times in a spiral shape and further formed into a flat shape. A battery element 20 was produced.

Next, after the battery element 20 is accommodated in the outer can 11, the insulating plate 12 is disposed on the battery element 20, the negative electrode lead 25 is welded to the outer can 11, and the positive electrode lead 24 is connected to the positive electrode pin 15. The battery lid 13 was fixed to the open end of the outer can 11 by laser welding. After that, an electrolytic solution was injected into the outer can 11 from the injection hole 19. As the electrolytic solution, a solution obtained by dissolving LiPF ₆ as an electrolyte salt at a concentration of 1 mol / dm ³ in a solvent in which 30% by volume of ethylene carbonate (EC) and 70% by volume of diethyl carbonate (DEC) were mixed was used. Finally, the injection hole 19 was closed with a sealing member 19A to obtain a square secondary battery. The battery capacity was set to 800 mAh. In addition, the capacity utilization factor of the negative electrode active material was designed to be 60%. The capacity utilization factor of the negative electrode active material here means the ratio of the positive electrode capacity to the negative electrode capacity (that is, positive electrode capacity / negative electrode capacity).

(Experimental example 2-1)
In this experimental example, the polymer compound layers 232 </ b> A and 232 </ b> B are not formed on both surfaces of the substrate 231, and the substrate 231 is used as it is as the separator 23. Except for this point, square secondary batteries were fabricated in the same manner as in Experimental Examples 1-1 to 1-7.

(Experimental example 2-2)
In this experimental example, when the separator 23 was manufactured, the thicknesses of the polymer compound layers 232A and 232B formed on both surfaces of the substrate 231 were made substantially constant. Except for this point, square secondary batteries were fabricated in the same manner as in Experimental Examples 1-1 to 1-7.

(Experimental example 2-3, 2-4)
In this experimental example, when the separator 23 was manufactured, the polymer compound layers 232A and 232B were formed so that the thickness of the portion 23S was larger than the thickness of the portion 23R. Except for this point, square secondary batteries were fabricated in the same manner as in Experimental Examples 1-1 to 1-7.

  For each of the secondary batteries of Experimental Examples 1-1 to 1-7 and 2-1 to 2-4 manufactured as described above, the first and second discharge capacity retention rates were examined as cycle characteristics in the following manner. However, the results shown in Table 1 were obtained. Here, a plurality of samples were prepared for each experimental example, and the first and second discharge capacity retention rates were measured for different samples.

(Measurement of the first discharge capacity maintenance rate)
In examining the cycle characteristics, the first discharge capacity retention rate was determined by performing a cycle test in the following procedure in an atmosphere at 25 ° C. Here, a series of charge / discharge processes of the first charge process, the first discharge process, the second charge process, and the second discharge process described below is defined as one cycle, and the charge / discharge process is repeated up to 100 cycles. It was. Specifically, in the first charging process, constant current charging is performed until the battery voltage reaches 4.25 V at a constant current density of 0.6 mA / cm ² , and the current value is continuously maintained at a constant voltage of 4.25 V. The battery was charged at a constant voltage until it reached 40 mA. In the first discharge treatment, constant current discharge was performed at a constant current density of 0.6 mA / cm ² until the battery voltage reached 2.5V. In the second charging process, constant current charging is performed until the battery voltage reaches 4.2 V at a constant current density of 3 mA / cm ² , and then constant voltage is maintained until the current value reaches 50 mA at a constant voltage of 4.2 V. Charged. In the second discharge treatment, constant current discharge was performed at a constant current density of 3 mA / cm ² until the battery voltage reached 2.7V. Further, the ratio of the discharge capacity at the 100th cycle to the discharge capacity at the first cycle, that is, (discharge capacity at the 100th cycle / discharge capacity at the first cycle) × 100 (%) is calculated as the first discharge capacity maintenance ratio. did.

(Measurement of second discharge capacity maintenance rate)
In examining the cycle characteristics, the second discharge capacity was maintained in the same manner as the measurement of the first discharge capacity maintenance rate, except that the current density during the first discharge treatment was set to 1.8 mA / cm ^2. The rate (load characteristics) was determined.

(Confirmation of damage to the positive electrode current collector)
The sample of each experimental example used for the measurement of the first discharge capacity retention rate was disassembled, and the number of cracks and breakage locations in the positive electrode current collector 21A was confirmed. The results are also shown in Table 1. In Table 1, the case where no cracks and breakage occurred was indicated as ◎, the case where one or two cracks were observed was indicated as ◯, and the case where cracks or fractures were observed in three or more locations was indicated as ×. Is displayed.

  Note that the procedure and conditions for examining the cycle characteristics described above, and the procedure and conditions for confirming damage to the positive electrode current collector are the same for the evaluation of the same characteristics for the series of experimental examples below unless otherwise specified. is there.

  As shown in Table 1, in Experimental Examples 1-1 to 1-7, cracking of the positive electrode current collector is less likely to occur than in Experimental Examples 2-1 to 2-4, and good cycle characteristics are obtained. It was confirmed that This is because, in Experimental Examples 1-1 to 1-7, the portion 23R of the separator 23 located in the curved portion 20R has a higher air permeability than the portion 23S of the separator 23 located in the flat portion 20S. This is considered to be due to the result that the stress accompanying charging / discharging at the curved portion 20R was relaxed. On the other hand, in Experimental Examples 2-1 to 2-4, the battery reaction at the curved portion 20R is active, and it is considered that the second discharge capacity maintenance ratio is reduced due to the damage of the positive electrode current collector. In Experimental Examples 1-4 and 1-5, higher numerical values were obtained in the second discharge capacity retention ratio than in Experimental Examples 1-1 to 1-3. This is because in Examples 1-1 to 1-3, the resistance increased due to the occurrence of slight cracks in the positive electrode current collector, while in Examples 1-4 and 1-5, the air permeability in the portion 23R was increased. This is because cracks did not occur at all in the positive electrode current collector because the degree was greatly increased. Further, in Experimental Examples 1-6 and 1-7, since the absolute value of the air permeability in the portion 23R is smaller than in Experimental Examples 1-4 and 1-5, a slight crack is generated in the positive electrode current collector, The numerical value of the 2nd discharge capacity maintenance factor became small compared with experiment examples 1-4 and 1-5.

(Experimental example 3-1)
In this experimental example, when the separator 23 is manufactured, the polymer compound layers 232A and 232B are formed on the substrate 231 so as to have a substantially constant thickness, and a portion 23R (7 mm width) of the separator 23 corresponding to the curved portion 20R. ) Was rolled with a press to increase its air permeability. Except for this point, square secondary batteries were fabricated in the same manner as in Experimental Examples 1-1 to 1-7.

(Experimental example 4-1)
In this experimental example, a square secondary battery was manufactured in the same manner as in Experimental Examples 1-1 to 1-7 except that the separator 23 was manufactured as follows. Specifically, after the polymer compound layers 232A and 232B are formed on the substrate 231 so as to have a substantially constant thickness, the polymer compound other than the portion 23R (7 mm width) of the separator 23 corresponding to the curved portion 20R. The layers 232A and 232B were washed with water. In other words, the masking tape is applied to the polymer compound layers 232A and 232B of the portion 23R of the separator 23 so as to cover the polymer compound layers 232A and 232B so as not to come into contact with water at the time of cleaning, so did. As a result, the air permeability of the portion 23R of the separator 23 could be increased.

  For each of the secondary batteries of Experimental Examples 3-1 and 4-1 produced as described above, the first and second discharge capacity retention rates and the positive electrode collectors were measured in the same manner as in Experimental Examples 1-1 to 1-7. When the damage of the electric body was examined, the results shown in Table 2 were obtained.

  As shown in Table 2, also in Experimental Examples 3-1 and 4-1, the portion 23R has a higher air permeability than the portion 23S, so that the positive electrode current collector is hardly cracked, and the like. It was confirmed that good cycle characteristics were obtained.

(Experimental Examples 5-1 to 5-7)
The polymer solution to be applied to the base material 231 is other than that in which each resin shown in Table 3 is dissolved in N-methyl-2-pyrrolidone instead of aramid (aromatic polyamide). Were fabricated in the same manner as in Experimental Examples 1-1 to 1-7. Specifically, Polyimide in Experimental Example 5-1, Polyamide in Experimental Example 5-2, Polyamideimide in Experimental Example 5-3, Polyethersulfone in Experimental Example 5-4, Polyetherimide in Experimental Example 5-5 Were used respectively. In Experimental Example 5-6, Al ₂ O ₃ particles (average particle size: 0.3 μm) were added so that the mass ratio of aramid (aromatic polyamide) and Al ₂ O ₃ particles was 20:80. Was dissolved in N-methyl-2-pyrrolidone and used. Further, in Experimental Example 5-7, SiO ₂ particles (average particle size: 0.3 μm) were added so that the mass ratio of aramid (aromatic polyamide) and Al ₂ O ₃ particles was 20:80. Was dissolved in N-methyl-2-pyrrolidone and used.

  For each of the secondary batteries of Experimental Examples 5-1 to 5-7 manufactured as described above, the first and second discharge capacity retention rates and the positive electrode collectors were measured in the same manner as in Experimental Examples 1-1 to 1-7. When the damage of the electric body was examined, the results shown in Table 3 were obtained.

  As shown in Table 3, also in Experimental Examples 5-1 to 5-7, the portion 23R has a higher air permeability than the portion 23S, so that a crack or the like of the positive electrode current collector hardly occurs, and It was confirmed that good cycle characteristics were obtained.

  From the results of the above experimental examples, according to the secondary battery of the present invention, the separator 23 has a higher air permeability in the curved portion 20R than in the flat portion 20S, regardless of the resin type or the manufacturing method of the polymer compound layer 342. It has been found that the cycle characteristics and reliability are excellent.

  Although the present invention has been described with reference to the embodiments and examples, the present invention is not limited to the above embodiments and examples, and various modifications can be made. For example, in the above-described embodiments and examples, the polymer compound layer is provided on both sides of the separator, but the polymer compound layer may be provided only on one side.

  In the above embodiments and examples, the case where lithium is used as the electrode reactant has been described, but other group 1 elements in the long-period periodic table such as sodium (Na) or potassium (K), or magnesium Alternatively, the present invention can be applied to the case where a Group 2 element in a long-period periodic table such as calcium (Ca), another light metal such as aluminum, lithium, or an alloy thereof is used, and similar effects are obtained. Can be obtained. At that time, a negative electrode active material, a positive electrode active material, a solvent, or the like that can occlude and release the electrode reactant is selected according to the electrode reactant.

  DESCRIPTION OF SYMBOLS 11 ... Exterior can, 12 ... Insulating plate, 13 ... Battery cover, 14 ... Terminal board, 15 ... Positive electrode pin, 16 ... Insulating case, 17 ... Gasket, 18 ... Cleavage valve, 19 ... Injection hole, 19A ... Sealing member, DESCRIPTION OF SYMBOLS 20 ... Battery element, 20R ... Curve part, 20S ... Flat part, 21 ... Positive electrode, 21A ... Positive electrode collector, 21B ... Positive electrode active material layer, 22 ... Negative electrode, 22A ... Negative electrode collector, 22B ... Negative electrode active material layer 23, 23A ... separator, 231 ... substrate, 232A, 232B ... polymer compound layer, 23R, 23S ... part, 24 ... positive electrode lead, 25 ... negative electrode lead.

Claims (11)

A wound body having a laminated structure of a positive electrode, a separator, and a negative electrode, and having a flat cross section including a pair of opposed flat portions and a pair of opposed curved portions;
An outer can that accommodates the wound body,
The separator has a base material made of a porous resin, and a resin layer provided on both surfaces of the base material,
The air permeability of the separator in the curved portion is higher than the air permeability of the separator in the flat portion continuous with the curved portion,
On one of the pair of curved portions, the resin layer located on the winding outer surface side of the base material has a larger thickness than the resin layer located on the winding inner surface side of the base material,
The secondary battery in which the resin layer located on the wound inner surface side of the substrate has a larger thickness than the resin layer located on the wound outer surface side of the substrate on the other of the pair of curved portions. A wound body having a laminated structure of a positive electrode, a separator, and a negative electrode, and having a flat cross section including a pair of opposed flat portions and a pair of opposed curved portions;
An outer can that accommodates the wound body,
The separator has a base material made of a porous resin, and a resin layer provided on both surfaces of the base material,
The thickness of the resin layer of the separator in the curved portion is larger than the thickness of the resin layer of the separator in the flat portion,
The air permeability of the separator in the curved portion is higher than the air permeability of the separator in the flat portion continuous with the curved portion,
On one of the pair of curved portions, the resin layer located on the winding outer surface side of the base material has a larger thickness than the resin layer located on the winding inner surface side of the base material,
The secondary battery in which the resin layer located on the wound inner surface side of the substrate has a larger thickness than the resin layer located on the wound outer surface side of the substrate on the other of the pair of curved portions. The resin layer is obtained by applying a polymer solution on both surfaces of the base material using a coating device and drying it, and by adjusting the discharge amount of the polymer solution from the coating device. The secondary battery according to claim 1, wherein the secondary battery has a first portion and a second portion having different thicknesses . The resin layer of the separator is made of a material containing at least one of polyvinylidene fluoride, polytetrafluoroethylene, polyimide, polyamide, polyamideimide, polyethersulfone, polyetherimide, and aramid. The secondary battery according to any one of 3. The base material of the separator is composed of a single layer film of a resin mainly containing at least one of polypropylene and polyethylene, or a multilayer film in which a plurality of such single layer films are laminated. A secondary battery according to item. The air permeability of the separator in the curved portion, the secondary battery according to any one of claims 1 to 5 is 800 sec / 100 cm ³ or more. The secondary battery according to claim 6, wherein the air permeability of the separator in the curved portion is 1500 seconds / 100 cm ³ or more. The secondary battery according to any one of claims 1 to 7, wherein the negative electrode includes at least one of silicon (Si), germanium (Ge), and tin (Sn) as an active material. 9. The positive electrode according to claim 1, wherein the positive electrode includes, as an active material, a composite oxide containing lithium and a transition metal element, or a phosphate compound containing lithium and a transition metal element. Next battery. The complex oxide includes lithium cobalt complex oxide (Li _x CoO ₂ ), lithium nickel complex oxide (Li _x NiO ₂ ), lithium nickel cobalt complex oxide (Li _x Ni _1-z Co _z O ₂ (z < 1)), lithium-nickel-cobalt-manganese composite oxide _{(Li x Ni (1-vw} ) Co v Mn w O 2 (v + w <1)) or lithium manganese composite oxide having a spinel structure (LiMn ₂ O ₄₎ Yes,
The secondary battery according to claim 9, wherein the phosphate compound is a lithium iron phosphate compound (LiFePO ₄ ) or a lithium iron manganese phosphate compound (LiFe _1-u Mn _u PO ₄ (u <1)). The positive electrode includes, as an active material, titanium oxide, vanadium oxide, manganese dioxide, titanium disulfide, molybdenum sulfide, niobium selenide, sulfur, polyaniline, and polythiophene. Secondary battery.

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