JP2012069412A - Secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a secondary battery capable of suppressing deterioration in energy density.SOLUTION: A secondary battery of the present invention includes: a positive electrode 2 containing a sulfur electrode active material and a conductive material; a negative electrode 3 arranged to face the positive electrode 2 at an interval therebetween; and a separator 4 interposed between the negative electrode 3 and the positive electrode 2. The separator 4 has a margin 7 located at a periphery of a projection plane of the positive electrode 2 when the positive electrode 2 is projected in the opposite direction of the positive electrode 2 and the negative electrode 3. The lower limit of a width orthogonal to the circumferential direction of the margin 7 is 0.5 mm or more, and the upper limit of the width is equivalent to the maximum width of a margin formed when the center of gravity of the positive electrode 2 and the center of gravity of the separator 4 are matched in the opposite direction of the positive electrode 2 and the negative electrode 3, while the positive electrode 2 and the separator 4 have a similar figure, and the area of the separator 4 is 2.56 times relative to the area of the positive electrode 2.

Description

  The present invention relates to a secondary battery, and more particularly to a lithium-sulfur secondary battery.

  In recent years, with the development of electric vehicles such as electric vehicles and hybrid vehicles, and portable electronic devices such as personal computers and mobile phones, various secondary batteries to be mounted on these have been proposed.

  Among such various secondary batteries, lithium-sulfur batteries using a material containing sulfur element as composite particles are attracting attention because high energy density can be expected.

  As such a lithium-sulfur battery, for example, a lithium-sulfur battery including a positive electrode containing a sulfur element, a negative electrode made of lithium metal, a separator between the positive electrode and the negative electrode, and an electrolyte solution containing a lithium salt is used. It has been proposed (see, for example, Patent Document 1).

  And the separator of such a lithium-sulfur battery is normally formed larger than the positive electrode in order to prevent the short circuit with a positive electrode and a negative electrode.

JP 2005-71999 A

  However, in such a lithium-sulfur battery, sulfur ions are eluted from the positive electrode into the electrolyte during the charge / discharge cycle. For this reason, if a separator larger than necessary is used, sulfur ions diffuse, which causes a problem that the energy density of the lithium-sulfur battery is lowered.

  Then, this invention is providing the secondary battery which can suppress the fall of an energy density even if it repeats a charging / discharging cycle.

  In order to achieve the above object, a secondary battery of the present invention includes a positive electrode containing a sulfur-based electrode active material and a conductive material, a negative electrode disposed opposite to the positive electrode at an interval, and A separator including a separator interposed between a negative electrode and the positive electrode, wherein the separator projects the positive electrode in a direction opposite to the positive electrode and the negative electrode when projected on the projection surface of the positive electrode. The lower limit value of the width perpendicular to the circumferential direction of the margin portion is 0.5 mm or more, and the upper limit value of the width is similar to the positive electrode and the separator. Yes, the area of the separator is 2.56 times the area of the positive electrode, and the center of gravity of the positive electrode and the center of gravity of the separator are made to coincide with the opposing direction of the positive electrode and the negative electrode. The margin part to be It is characterized in that corresponding to the width.

  In the secondary battery of the present invention, since the separator has a margin part having a specific size with respect to the positive electrode, diffusion of sulfur ions is suppressed. Therefore, even if the charge / discharge cycle is repeated, a decrease in the electric capacity of the positive electrode can be suppressed, and a decrease in energy density can be suppressed.

It is a schematic block diagram of the lithium-sulfur battery which shows one Embodiment of the secondary battery of this invention. It is a schematic explanatory drawing for demonstrating the upper limit of the width | variety orthogonal to the circumferential direction of a margin part in case a positive electrode is circular shape. It is a schematic explanatory drawing for demonstrating the upper limit of the width | variety orthogonal to the circumferential direction of a margin part in case a positive electrode is a square. It is a schematic explanatory drawing for demonstrating the maximum width orthogonal to the circumferential direction of a margin part in case a positive electrode is rectangular shape. It is a charging / discharging curve which shows the change of the capacity density in the charging / discharging cycle of an Example and a comparative example. It is a charging / discharging curve which shows the change of the energy density in the charging / discharging cycle of an Example and a comparative example.

  FIG. 1 is a schematic configuration diagram of a lithium-sulfur battery showing an embodiment of the secondary battery of the present invention.

  In FIG. 1, a lithium-sulfur battery 1 includes a positive electrode 2, a negative electrode 3 disposed opposite to the positive electrode 2 with a space therebetween, a separator 4 interposed between the positive electrode 2 and the negative electrode 3, and a positive electrode 2. And a gasket 6 that accommodates the negative electrode 3 and the separator 4, and an electrolytic solution 5 (indicated by hatching in FIG. 1) impregnated in the positive electrode 2 and the separator 4. The lithium-sulfur battery 1 is a battery cell (coin cell) employed on a lab scale. Industrially, a lithium-sulfur battery 1 appropriately scaled up by a known technique is employed. .

  The positive electrode 2 contains a sulfur-based electrode active material and a conductive material.

  Examples of the sulfur-based electrode active material include sulfur and sulfur compounds.

  Examples of sulfur include α-sulfur (orthorhombic), β-sulfur (monoclinic), γ-sulfur (monoclinic), and amorphous sulfur depending on the crystal form.

  Moreover, as purity of sulfur, it is 99% or more, for example, Preferably, it is 99.999% or more.

  The melting point of sulfur varies depending on the crystal form of sulfur, but is 118 to 120 ° C., for example.

  Moreover, although the boiling point of sulfur changes with crystal forms of sulfur, for example, a boiling point is 200-445 degreeC.

  Examples of the sulfur compound include alkali metal polysulfide (MnSm: m ≧ 1, n ≧ 1, M = Li, Na, K), alkaline earth metal polysulfide (MnSm: m ≧ 1, n ≧ 1, M = Mg, Ca), an organometallic compound, a carbon-sulfur polymer, and the like can be given, and an alkali metal polysulfide and an alkaline earth metal polysulfide are preferable.

  These sulfur-based electrode active materials may be used alone or in combination.

  Of these sulfur-based electrode active materials, sulfur is preferable.

  Examples of the conductive material include carbon particles such as ketjen black, denka black, acetylene black, thermal black, and channel black, such as carbon fiber, such as graphite, such as activated carbon, such as metal, such as oxyhydroxide. Examples thereof include metal compounds such as cobalt, for example, carbon / metal composites.

  These conductive materials may be used alone or in combination.

  Of these conductive materials, carbon particles are preferable, and ketjen black is more preferable. When carbon particles are used for the conductive material, a complex of sulfur and the conductive material can be densely formed.

  Further, the secondary average particle diameter (volume basis) of the conductive material varies depending on the type of the conductive material, but the median diameter (d50) measured by the dynamic light scattering method is, for example, 10 to 50 μm, preferably 15 to 20 μm.

  Moreover, although melting | fusing point of an electroconductive material changes with kinds of electroconductive material, it is 3000 degreeC or more, for example.

  Next, a method for manufacturing the positive electrode 2 will be described.

  In order to produce the positive electrode 2, first, composite particles are produced by mixing a sulfur-based electrode active material and a conductive material while heating.

  In order to mix the sulfur-based electrode active material and the conductive material, the sulfur-based electrode active material and the conductive material are put into a container of a mixer and mixed while heating at a predetermined heating temperature.

  The blending ratio of the conductive material is, for example, 10 to 50 parts by mass, preferably 20 to 40 parts by mass with respect to 100 parts by mass of the solid content of the electrode material (described later).

  Moreover, the compounding ratio of a sulfur type electrode active material is 40-80 mass parts with respect to 100 mass parts of solid content of an electrode material (after-mentioned), Preferably, it is 50-70 mass parts.

  When the mixing ratio of the sulfur-based electrode active material exceeds the above range, the conductivity of the obtained electrode may be reduced, and when it is less than the above range, the energy density of the obtained secondary battery may be reduced. .

  Examples of the mixer include a ball mill such as a planetary rotating ball mill, a rolling ball mill, and a vibrating ball mill, a vertical roller mill such as a ring roller mill, a high speed rotating mill such as a hammer mill and a cage mill, and an air current such as a jet mill. A well-known mixing and grinding machine such as an expression mill may be used.

  Among these mixers, a ball mill is preferable, and a planetary rotating ball mill is more preferable.

  Examples of the mixing method in the mixer include dry mixing and wet mixing.

  Among these mixing methods, preferably, dry mixing in which only a sulfur-based electrode active material and a conductive material are mixed without using a solvent can be mentioned.

  Moreover, the heating temperature at the time of mixing is more than melting | fusing point of sulfur and less than a boiling point, for example, 118-445 degreeC, Preferably, it is 118-200 degreeC, More preferably, it is 120-160 degreeC.

  In addition, as a method of heating the sulfur-based electrode active material and the conductive material, for example, (1) a method of heating the container by heating the atmosphere around the mixer container with a heater and transmitting the heat of the heated container , (2) a method of heating the container by blowing hot air on the mixer container and transmitting the heat of the heated container, and (3) a method of transmitting the heat by heating the mixer container itself. It is done.

  Among these heating methods, the method (1) of heating the atmosphere around the mixer container with a heater is preferable.

  The mixing time is, for example, 0.5 to 5 hours, preferably 1 to 3 hours.

  As described above, these composite particles can be obtained by mixing the sulfur-based electrode active material and the conductive material.

  The average particle diameter of the obtained composite particles is measured by, for example, microscopy (specifically, observation by an electron microscope (SEM, TEM, etc.)), and the average particle diameter of primary particles is, for example, 30 to 100 nm, Preferably, it is 30-50 nm, and the average particle diameter of secondary particles is 0.3-10 micrometers, for example, Preferably, it is 0.3-3 micrometers.

  Next, for example, a solvent is added to the composite particles and stirred, for example, for 10 to 120 minutes.

  Examples of the solvent include protic polar solvents such as water, methanol, ethanol, isopropanol, and butanol, and aprotic polar solvents such as acetonitrile, dimethylformamide (DMF), and N-methyl-2-pyrrolidone (NMP). Can be mentioned.

  These solvents may be used alone or in combination.

  Among these solvents, a protic polar solvent is preferable, and water is more preferable.

  Next, for example, a binder is added and stirred, for example, for 30 to 120 minutes.

  Examples of the binder include polytetrafluoroethylene (PTFE), polyvinyl acetate, polyethylene oxide, polyvinyl ether, polyvinylidene fluoride (PVdF), a fluoroolefin copolymer crosslinked polymer, a fluoroolefin vinyl ether copolymer crosslinked polymer, polyvinylpyrrolidone, Examples thereof include polyvinyl alcohol and polyacrylic acid.

  These binders may be used alone or in combination.

  Of these binders, PTFE is preferable, and PTFE dispersion is more preferable.

  Moreover, the mixture ratio of a binder is 4-20 mass parts with respect to 100 mass parts of solid content of an electrode material (after-mentioned), Preferably, it is 4-10 mass parts.

  In the production of the electrode material (described later), an additive such as a thickener can be added as necessary to adjust the viscosity of the mixture.

  As a thickener, a well-known thickener is mentioned, for example, Preferably, carboxymethylcellulose is mentioned.

  The timing at which such a thickener is added may be before the solvent is added, when the solvent is added, or when the binder is added, but is preferably before the solvent is added.

  The blending ratio of the thickener is, for example, 1 to 10 parts by mass, preferably 1 to 5 parts by mass in terms of solid content with respect to 100 parts by mass of the solid content of the electrode material (described later).

  Then, after stirring the mixture of composite particles, solvent, binder and additives added as necessary, the resulting slurry of the mixture is applied as an electrode material to the surface of the current collector and dried to form an electrode sheet. obtain.

  Examples of the current collector include metal foils such as aluminum foil (eg, etched aluminum foil), copper foil, stainless steel foil, and nickel foil.

  Among these current collectors, preferably, an aluminum foil subjected to etching treatment is used.

  Next, for example, the electrode sheet is punched into a predetermined shape (for example, a rectangular shape or a circular shape). Thereby, the positive electrode 2 containing the composite particles is obtained.

  The thickness of the positive electrode 2 obtained by such a method varies depending on the scale of the lithium-sulfur battery 1. For example, in the lab scale, the thickness is 30 to 150 μm and the thickness excluding the current collector is 10. ~ 140 μm.

  Moreover, although the magnitude | size of the positive electrode 2 changes with scales of the lithium-sulfur battery 1, for example, in a lab scale, for example, in the case of a rectangular shape, the length in the longitudinal direction is, for example, 10 to 200 mm, preferably 10 to 100 mm, the length orthogonal to the longitudinal direction (width direction) is, for example, 10 to 200 mm, preferably 10 to 100 mm. In the case of a circular shape, the diameter is, for example, 5 to 30 mm. The thickness is preferably 5 to 20 mm.

  The negative electrode 3 is formed, for example, by punching lithium foil into a predetermined shape (for example, a rectangular shape or a circular shape).

  The thickness of the negative electrode 3 varies depending on the scale of the lithium-sulfur battery 1. For example, in the lab scale, the thickness is 30 to 200 μm, preferably 50 to 200 μm.

  Moreover, although the magnitude | size of the negative electrode 3 changes with scales of the lithium-sulfur battery 1, for example, in a lab scale, for example, in the case of a rectangular shape, the length in the longitudinal direction is, for example, 10 to 200 mm, preferably 10 to 100 mm, the length orthogonal to the longitudinal direction (width direction) is, for example, 10 to 200 mm, preferably 10 to 100 mm. In the case of a circular shape, the diameter is, for example, 5 to 30 mm. The thickness is preferably 5 to 20 mm.

  Examples of the separator 4 include separators made of inorganic fibers such as glass fibers, ceramic fibers, and whiskers, natural fibers such as cellulose, and organic fibers such as polyolefin and polyester.

  Among these separators, a separator made of ceramic fibers is preferable.

  Specifically, the thickness of the separator 4 varies depending on the scale of the lithium-sulfur battery 1, but is 100 to 1000 μm, preferably 200 to 500 μm, for example, on a lab scale.

  Moreover, although the magnitude | size of the separator 4 changes with scales of the lithium-sulfur battery 1, for example, in a lab scale, for example, in the case of a rectangular shape, the longitudinal length is, for example, 5 to 240 mm, preferably The length (direction in the width direction) perpendicular to the longitudinal direction is 10 to 100 mm, for example, 5 to 240 mm, preferably 10 to 100 mm. In the case of a circular shape, the diameter is 6 to 36 mm, for example. The thickness is preferably 6 to 24 mm.

  Further, the size (area) of the separator 4 varies depending on the size (area) of the positive electrode 2, but is set larger than the size (area) of the positive electrode, for example. For example, it is 1.10 to 2.56 times, preferably 1.21 to 1.44 times the size (area) of the positive electrode 2.

  The separator 4 is preferably similar to the positive electrode 2.

  The electrolytic solution 5 is made of an organic solvent containing lithium ions, and is prepared, for example, by dissolving a lithium salt in the organic solvent.

Examples of the lithium salt include LiClO ₄ , LiCF ₃ SO ₃ , LiC (SO ₂ CF ₃ ) ₃ , LiC ₄ F ₉ SO ₃ , LiC ₈ F ₁₇ SO ₃ , LiB [C ₆ H ₃ (CF ₃ ) ₂ − 3, 5] ₄ , LiB (C ₆ F ₅ ) ₄ , LiB [C ₆ H ₄ (CF ₃ ) -4] ₄ , LiBF ₄ , LiPF ₆ and other lithium salts such as lithium bistrifluoromethanesulfonylimide, lithium Examples thereof include lithium salts containing sulfur such as bisperfluoroethanesulfonylimide and lithium tristrifluoromethanesulfonylmethide. In the above formula, [C ₆ H ₃ (CF ₃ ) ₂ -3, 5] is the 3rd and 5th positions of the phenyl group, and [C ₆ H ₄ (CF ₃ ) -4] is the 4th position of the phenyl group. Each of which is substituted with —CF ₃ .

  These lithium salts may be used alone or in combination.

  Of these lithium salts, lithium bistrifluoromethanesulfonylimide is preferable.

  Examples of the organic solvent include propylene carbonate, propylene carbonate derivatives, ethylene carbonate, ethylene carbonate derivatives, butylene carbonate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate and the like, for example, 1,2-dimethoxyethane, 1,3 -Ethers such as dioxolane, tetrahydrofuran and tetrahydrofuran derivatives, and carboxylic anhydrides such as maleic anhydride, succinic anhydride and phthalic anhydride.

  These organic solvents may be used alone or in combination.

  Of these organic solvents, 1,2-dimethoxyethane and 1,3-dioxolane are preferable, and a mixed solvent of 1,2-dimethoxyethane and 1,3-dioxolane is more preferable. .

  Moreover, the density | concentration of the lithium salt of the electrolyte solution 5 is 0.5-5 mol / L, for example, Preferably, it is 1.5-2.5 mol / L.

  Next, production of the lithium-sulfur battery 1 will be described.

  In order to produce the lithium-sulfur battery 1, for example, first, the positive electrode 2 and the separator 4 are impregnated with the electrolytic solution 5. Then, after laminating the positive electrode 2 on one side of the separator 4 and the negative electrode 3 on the other side so that the centers of gravity (separator 4, positive electrode 2 and negative electrode 3) coincide with the laminating direction, they are accommodated in the gasket 6. To do.

  The impregnation time is, for example, 1 to 30 minutes, preferably 5 to 20 minutes.

  The laminated separator 4 has a margin portion 7 positioned around the projection surface of the positive electrode 2 when the positive electrode 2 is projected in the facing direction of the positive electrode 2 and the negative electrode 3.

  The lower limit of the width perpendicular to the circumferential direction of the margin portion 7 (hereinafter referred to as “width of the margin portion 7”) is 0.5 mm or more, preferably 1 mm or more. Further, the upper limit is that the positive electrode 2 and the separator 4 are similar in shape, the area of the separator 4 is 2.56 times the area of the positive electrode 2, and the center of gravity of the positive electrode 2 and the center of gravity of the separator 4 are This corresponds to the maximum width of the margin portion 7 formed when the positive electrode 2 and the negative electrode 3 coincide with each other in the facing direction.

  Next, the upper limit value of the width of the margin portion 7 will be described more specifically with reference to FIGS.

FIG. 2 shows an upper limit value of the width of the margin portion 7 when the positive electrode 2 has a circular shape with a diameter of 10 mm. In order to define the upper limit value of the width of the margin portion 7, first, since the positive electrode 2 has a circular shape with an area of 25πmm ² , the separator 4 has a circle with an area of 64πmm ² that is 2.56 times the area of the positive electrode 2. Assume a shape. That is, the separator 4 has a circular shape with a diameter of 16 mm. When the center of gravity of the positive electrode 2 and the center of gravity of the separator 4 are made to coincide with the opposing direction of the positive electrode 2 and the negative electrode 3, the width of the margin part 7 to be formed becomes the upper limit value of the width of the margin part 7. Equivalent to.

  That is, when the positive electrode 2 has a circular shape with a diameter of 10 mm, the upper limit value of the width of the margin portion 7 is 3 mm, and the allowable range of the width of the margin portion 7 is 0.5 mm to 3 mm. In FIG. 2, the range of the width of the margin portion 7 allowed in such a case is shown as a hatched area.

FIG. 3 shows an upper limit value of the width of the margin portion 7 in the case where the positive electrode 2 is a square having a side length of 25 mm. In order to define the upper limit value of the width of the margin portion 7, first, since the positive electrode 2 is a square having an area of 625 mm ² , the separator 4 is a square having an area of 1600 mm ² that is 2.56 times the area of the positive electrode 2. Assume a case. That is, the separator 4 is a square having a side length of 40 mm. When the center of gravity of the positive electrode 2 and the center of gravity of the separator 4 are made to coincide with the opposing direction of the positive electrode 2 and the negative electrode 3, the width of the margin part 7 to be formed becomes the upper limit value of the width of the margin part 7. Equivalent to.

  That is, when the positive electrode 2 is a square having a side length of 25 mm, the upper limit value of the width of the margin portion 7 is 7.5 mm, and the allowable width range of the margin portion 7 is 0.5 mm to 7 mm. .5 mm. FIG. 3 shows the range of the width of the margin portion 7 allowed in such a case as a hatched area.

FIG. 4 shows an upper limit value of the width of the margin portion 7 in the case where the positive electrode 2 has a rectangular shape with a length of 20 mm in the longitudinal direction and a length of 10 mm in the direction orthogonal to the longitudinal direction (width direction). In order to define the upper limit value of the width of the margin portion 7, first, since the positive electrode 2 has a rectangular shape with an area of 200 mm ² , the separator 4 is similar to the positive electrode 2, and the area is 2 of the area of the positive electrode 2. Assume a rectangular shape with an area of 512 mm ² which is .56 times. That is, the separator 4 has a rectangular shape with a length in the longitudinal direction of 32 mm and a length (direction in the width direction) orthogonal to the longitudinal direction of 16 mm. And when the gravity center of the positive electrode 2 and the gravity center of the separator 4 are made to correspond to the opposing direction of the positive electrode 2 and the negative electrode 3, the width | variety of the margin part 7 formed is 3 mm or 6 mm. Among these, the upper limit value of the width of the margin portion 7 corresponds to the maximum width of the margin portion 7 and is 6 mm.

  That is, when the positive electrode 2 has a rectangular shape with a length of 20 mm in the longitudinal direction and a length of 10 mm in the direction orthogonal to the longitudinal direction (width direction), the allowable range of the width of the margin portion 7 is 0.5 mm to 6 mm. is there. In FIG. 4, the range of the width of the margin portion 7 allowed in such a case is shown as a hatched area.

  As described above, when the separator 4 has the margin portion 7 and the range of the width of the margin portion 7 is defined as described above, the positive electrode 2 and the negative electrode 3 can be prevented from being short-circuited. Diffusion of sulfur ions eluted into the electrolytic solution 5 can be suppressed.

  Therefore, even if it repeats a charging / discharging cycle, the fall of the energy density of a secondary battery can be suppressed.

EXAMPLES Next, although an Example and a comparative example are given and this invention is demonstrated in more detail, this invention is not limited by these Examples and comparative examples.
Example 1
1. Preparation of electrode active material 60 parts by mass of sulfur (manufactured by Strem Chemicals, purity: 99.999%), 30 parts by mass of conductive material (Ketjen Black, manufactured by Lion, average particle diameter (median diameter): 17 μm) Was charged in a container of a ball mill (heated planetary rotating ball mill, manufactured by Ito Seisakusho) and mixed at 200 rpm for 2 hours while heating at 120 ° C. As a result, composite particles containing sulfur and a conductive material were produced.
2. Preparation of positive electrode In a ball mill container, add 2 parts by mass of a 1% aqueous solution of a thickener (carboxymethylcellulose, manufactured by Daicel Chemical Industries) to the prepared composite particles, and mix at room temperature for 1 hour. did. Water was then added and mixed for 10 minutes at room temperature.

  Thereafter, 8 parts by mass of a binder (PTFE dispersion) was added in terms of solid content, and the mixture was stirred at room temperature for 45 minutes to prepare a slurry of the mixture.

  Next, the prepared slurry was applied to the surface of an etched aluminum foil (current collector), and dried at room temperature overnight to produce an electrode sheet (thickness 120 μm).

Next, the dried electrode sheet was punched into a circular shape having a diameter of 10 mm. The positive electrode was produced by the above operation.
3. Production of Negative Electrode A negative electrode was produced by punching out lithium foil (thickness 150 μm) into a circular shape having a diameter of 10 mm.
4). Production of Separator A separator was produced by punching a ceramic filter (GB-100R, manufactured by ADVANTEC) into a circular shape having a diameter of 11 mm.
5. Preparation of electrolyte solution By dissolving lithium bistrifluoromethanesulfonylimide in a mixed solvent of 1,2-dimethoxyethane and 1,3-dioxolane (volume ratio 9: 1) so as to have a concentration of 2 mol / L, An electrolyte solution was prepared.
6). Assembling of test coin cell The positive electrode and the separator were impregnated with 0.5 to 1.0 mL of an electrolytic solution for 10 minutes.

Then, a positive electrode was placed on one side of the separator, a negative electrode was placed on the other side, and the center of gravity was aligned with the stacking direction to produce a test coin cell. In addition, the separator laminated | stacked in this way had the margin part located around the projection surface of a positive electrode, when a positive electrode was projected in the opposing direction of a positive electrode and a negative electrode. The width of the margin part was 0.5 mm.
Example 2
In the production of the separator, a test coin cell was produced in the same manner as in Example 1 except that the ceramic filter was punched into a circular shape having a diameter of 12 mm. The width of the margin part of the separator was 1 mm.
Example 3
In the production of the separator, a test coin cell was produced in the same manner as in Example 1 except that the ceramic filter was punched into a circular shape having a diameter of 13 mm. The width of the margin part of the separator was 1.5 mm.
Example 4
In the production of the separator, a test coin cell was produced in the same manner as in Example 1 except that the ceramic filter was punched into a circular shape having a diameter of 14 mm. The width of the separator margin was 2 mm.
Example 5
In the production of the separator, a test coin cell was produced in the same manner as in Example 1 except that the ceramic filter was punched into a circular shape having a diameter of 16 mm. The width of the margin part of the separator was 3 mm.
Comparative Example 1
In the production of the separator, a test coin cell was produced in the same manner as in Example 1 except that the ceramic filter was punched into a circular shape having a diameter of 18 mm. The width of the margin part of the separator was 4 mm.
Comparative Example 2
In the production of the separator, a test coin cell was produced in the same manner as in Example 1 except that the ceramic filter was punched into a circular shape having a diameter of 22 mm. The width of the margin part of the separator was 6 mm.
Comparative Example 3
In the production of the separator, a test coin cell was produced in the same manner as in Example 1 except that the ceramic filter was punched into a circular shape having a diameter of 25 mm. The width of the margin part of the separator was 7.5 mm.
7). Charging / discharging test With respect to the test coin cell assembled in each example and each comparative example, charging / discharging test was performed in a potential range of 1.5 to 2.7 V per cycle (current density: 0.6 mA / cm ² ). Carried out.

  In FIG. 5, the charging / discharging curve which shows the change of the capacity density in the charging / discharging cycle of an Example and a comparative example is shown. The unit indicated by “mAh / g (sulfur)” on the vertical axis in FIG. 5 indicates the capacity (mAh) per gram of the sulfur-based electrode active material contained in the positive electrode.

  In FIG. 6, the charging / discharging curve which shows the change of the energy density in the charging / discharging cycle of an Example and a comparative example is shown. The unit indicated by “Wh / kg (electrode)” on the vertical axis in FIG. 6 represents energy (Wh) per kg of electrode (positive electrode).

1 Lithium-sulfur battery 2 Positive electrode 3 Negative electrode 4 Separator 7 Margin

Claims (1)

A positive electrode containing a sulfur-based electrode active material and a conductive material;
A negative electrode disposed opposite to the positive electrode at an interval;
A secondary battery comprising a separator interposed between the negative electrode and the positive electrode,
The separator has a margin portion located around the projection surface of the positive electrode when the positive electrode is projected in the facing direction of the positive electrode and the negative electrode;
The lower limit value of the width orthogonal to the circumferential direction of the margin portion is 0.5 mm or more,
The upper limit of the width is
The positive electrode and the separator are similar in shape,
The area of the separator is 2.56 times the area of the positive electrode,
The secondary battery is characterized in that it corresponds to the maximum width of the margin portion formed when the center of gravity of the positive electrode and the center of gravity of the separator coincide with each other in the opposing direction of the positive electrode and the negative electrode. .

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