JP2007234458A - Nonaqueous electrolyte secondary battery - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a nonaqueous electrolyte secondary battery having high charge discharge cycle characteristics and high productivity. <P>SOLUTION: The nonaqueous electrolyte secondary battery is equipped with a positive electrode, a negative electrode having lithium or a lithium alloy, a separator, and a nonaqueous electrolyte, the separator has three layer structure interposing a microporous film between two nonwoven fabrics, and the retaining amount of the nonaqueous electrolyte in the nonwoven fabric facing the negative electrode out of two nonwoven fabrics constituting the separator is made less than that of the nonaqueous electrolyte in the nonwoven fabric facing the positive electrode. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a non-aqueous electrolyte secondary battery, and more particularly to a non-aqueous electrolyte secondary battery having good charge / discharge cycle characteristics and excellent productivity.

  Nonaqueous electrolyte batteries using lithium or a lithium alloy as a negative electrode are widely used as main power sources and memory backup power sources for various electronic devices because of their high energy density.

  Such a battery generally includes a positive electrode, a negative electrode using lithium or a lithium alloy, a separator, and a non-aqueous electrolyte (hereinafter sometimes simply referred to as “electrolyte”) as constituent elements. In general, a microporous film or a nonwoven fabric is used.

  The main role of the separator in the battery is as follows: (1) the action of preventing the short circuit by preventing the contact between the positive electrode and the negative electrode; (2) the function of preventing the movement of fine powder between the positive electrode and the negative electrode and preventing the short circuit; (4) A function of facilitating the injection of the electrolyte into the battery by preliminarily absorbing the electrolyte in the separator during battery production; Is mentioned.

  From the viewpoint of these roles in the separator, the separator made of microporous film is a porous film, so it mainly works to prevent the movement of fine powder and dendrite from the positive and negative electrodes and prevent short circuit. ing. On the other hand, since the separator made of nonwoven fabric is an aggregate of fibers folded in a complicated manner, it mainly has an excellent function of holding the electrolyte.

  By the way, although the microporous film and nonwoven fabric which comprise these separators are generally comprised individually or in the laminated body which laminated | stacked several sheets, when a separator is comprised only with a nonwoven fabric, for example May cause problems in terms of preventing the occurrence of fine powder and dendrites of the positive and negative electrodes and preventing short circuits. On the other hand, for example, as disclosed in Patent Document 1 and Patent Document 2, the separator has a two-layer structure composed of a microporous film and a non-woven fabric. Generation | occurrence | production of a short circuit can be suppressed, and the retainability of electrolyte solution can also be improved by the effect | action of a nonwoven fabric.

JP 2003-187814 A Japanese Patent No. 3167157

  However, in the case of a two-layer separator composed of a microporous film and a non-woven fabric as described above, the microporous film is inferior in electrolytic solution retention compared to the non-woven fabric, so that the discharge of the non-aqueous electrolyte secondary battery In order to ensure characteristics (particularly charge / discharge cycle characteristics), it was necessary to devise a method for supplying an amount of electrolyte necessary for discharge to the electrode (positive electrode or negative electrode) on the side facing the microporous film. .

  In addition, a separator having a two-layer structure composed of a microporous film and a non-woven fabric as described above is easily charged and inferior in handleability, so that the productivity of the nonaqueous electrolyte secondary battery is impaired.

  In addition, in non-aqueous electrolyte secondary batteries equipped with a negative electrode having lithium or lithium alloy, the amount of electrolyte required for discharge differs between the positive electrode side and the negative electrode side, so the amount of electrolyte is set based on the negative electrode side. Then, the amount of the electrolyte on the positive electrode side is insufficient, and on the other hand, if the amount of the electrolyte is set based on the positive electrode side, the electrolyte solution is left on the negative electrode side, so that the electrolyte solution may overflow from the outer can during battery manufacture. From the standpoint of securing the discharge characteristics of the battery, the amount of the electrolyte must be set on the positive electrode side, and therefore a device for preventing overflow of the electrolyte during battery production is necessary. This is an impediment to improving the productivity of electrolyte secondary batteries.

  This invention is made | formed in view of the said situation, The objective is to provide the non-aqueous-electrolyte secondary battery which has favorable charging / discharging cycling characteristics, and was excellent also in productivity.

  The non-aqueous electrolyte secondary battery of the present invention capable of achieving the above object comprises a positive electrode, a negative electrode having lithium or a lithium alloy, a separator, and a non-aqueous electrolyte, and the separator is microporous. The film has a three-layer structure sandwiched between two non-woven fabrics. Among the two non-woven fabrics constituting the separator, the non-woven fabric on the side facing the negative electrode (hereinafter referred to as “negative electrode non-woven fabric”) The amount of non-aqueous electrolyte retained in the non-woven electrolyte on the side facing the positive electrode (hereinafter sometimes referred to as “non-woven fabric on the positive electrode side”) is smaller than the amount retained in the non-aqueous electrolyte. Is.

  In the non-aqueous electrolyte secondary battery of the present invention, a negative electrode having lithium or a lithium alloy is used. On the positive electrode, a positive electrode mixture composed of a positive electrode active material, a conductive additive and a binder is molded. Use (details will be described later). In this case, since the positive electrode becomes porous, the electrolytic solution penetrates into the inside thereof, whereas the negative electrode does not substantially have pores, so that the electrolytic solution does not penetrate into the negative electrode. Therefore, in the battery having the positive and negative electrodes as described above, the amount of the electrolytic solution required for discharging is larger at the positive electrode than at the negative electrode.

  Therefore, when manufacturing a non-aqueous electrolyte secondary battery having positive and negative electrodes as described above, if the amount of electrolyte injected into the battery is set based on the negative electrode, the amount of electrolyte supplied is insufficient at the positive electrode. Thus, the battery characteristics are impaired, and on the other hand, when the amount of the electrolyte solution to be injected into the battery is set based on the positive electrode, the electrolyte solution is left on the negative electrode side, so that the electrolyte solution overflows from the outer can.

  Therefore, in the non-aqueous electrolyte secondary battery of the present invention, a separator having a three-layer structure in which a microporous film is sandwiched between two nonwoven fabrics, and the amount of electrolyte retained in the nonwoven fabric on the side facing the negative electrode ( Hereinafter, it may be referred to as “amount of liquid retained”) smaller than the amount of electrolyte retained in the non-woven fabric on the side facing the positive electrode, so that an appropriate amount of electrolyte can be supplied to the positive and negative electrodes. In addition to ensuring good charge / discharge cycle characteristics, it is possible to easily suppress overflow of the electrolyte during battery manufacture. In addition, since the separator has a structure in which both surfaces of a microporous film that is easily charged are sandwiched between two non-woven fabrics that are difficult to be charged, a decrease in handleability due to charging of the separator is also prevented.

  Thus, in the non-aqueous electrolyte secondary battery of the present invention, by adopting the above configuration, in addition to ensuring good charge / discharge cycle characteristics, suppressing overflow of the electrolyte during battery production and handling of the separator Improvements in productivity have also improved productivity.

  According to the present invention, it is possible to provide a non-aqueous electrolyte secondary battery having good charge / discharge cycle characteristics and excellent productivity.

  As described above, the separator according to the present invention has a three-layer structure in which a microporous film is sandwiched between two nonwoven fabrics. By making the separator into such a three-layer structure, the microporous film present in the center prevents the movement of fine powders of the positive electrode and the negative electrode and the generation of lithium dendrite, and prevents the occurrence of short circuits due to these. Can do. Moreover, since both the outer surfaces of a separator are a nonwoven fabric as above-mentioned, it is hard to produce the charge by static electricity and handling property is favorable.

  Furthermore, in the separator according to the present invention, the liquid retention amount of the nonwoven fabric on the side facing the negative electrode is smaller than the liquid retention amount of the nonwoven fabric on the side facing the positive electrode. By adopting such a configuration, as described above, it is possible to easily suppress overflow of the electrolyte during battery production and increase battery productivity, while supplying an appropriate amount of electrolyte to each of the positive and negative electrodes, In addition to improving battery characteristics, particularly charge / discharge cycle characteristics, it is also possible to suppress the occurrence of liquid leakage.

  Examples of the microporous film for constituting the separator include those made of polyolefin such as polyethylene and polypropylene, and fluorine such as tetrafluoroethylene-perfluoroalkoxyethylene copolymer (PFA) for heat resistance. Resins; Polyphenylene sulfide (PPS); Polyetheretherketone (PEEK); Polybutylene terephthalate (PBT);

  As a hole diameter of a microporous film, it is preferable that it is 1 micrometer or less, for example. If it is a microporous film which has the hole of such a hole diameter, the movement of the fine powder of positive and negative electrodes and generation | occurrence | production of lithium dendrite can be prevented, and generation | occurrence | production of the short circuit resulting from these can be prevented favorably. Moreover, it is preferable that the thickness of a microporous film is 20-100 micrometers, for example, and it is preferable that the porosity is 40-60%, for example.

  In addition, there is no restriction | limiting in particular about the manufacturing method as a microporous film, The thing obtained by various conventionally well-known manufacturing methods can be used, and a commercial item can also be obtained and used.

  Examples of the nonwoven fabric for constituting the separator include those made of polyolefin fibers such as polyethylene and polypropylene, and fluorine resins such as tetrafluoroethylene-perfluoroalkoxyethylene copolymer (PFA) for heat resistance. And polyphenylene sulfide (PPS); polyether ether ketone (PEEK); polybutylene terephthalate (PBT); As a porosity of a nonwoven fabric, it is preferable that it is 70 to 90%, for example.

The porosity of the microporous film constituting the separator and the porosity of the nonwoven fabric can be obtained by the following formula.
P = 100 × (Va−Vb) / Va
In the above formula, P is the porosity of the microporous film or the porosity of the nonwoven fabric, Va is the apparent volume of the microporous film or nonwoven fabric, and Vb is the true volume of the microporous film or nonwoven fabric. Moreover, the true volume Vb of a microporous film or a nonwoven fabric can be calculated | required by following Formula.
Vb = m / s
In the above formula, m is the mass of the microporous film or nonwoven fabric, and s is the specific gravity of the material constituting the microporous film or nonwoven fabric.

  In addition, there is no restriction | limiting in particular about the manufacturing method as a nonwoven fabric, The thing obtained by various conventionally well-known manufacturing methods can be used, and a commercial item can also be obtained and used.

  The two nonwoven fabrics for constituting the separator may be made of the same material or different materials, but the nonwoven fabric on the side facing the negative electrode is the nonwoven fabric on the side facing the positive electrode Rather, the amount of electrolyte retained must be selected to be small.

  In both the nonwoven fabrics which concern on the said separator, a non-aqueous electrolyte is hold | maintained at the space | gap part. Therefore, in the separator, the relationship between the liquid retention amount in the nonwoven fabric on the side facing the negative electrode and the liquid retention amount in the nonwoven fabric on the side facing the positive electrode is, for example, the volume of the void portion of the nonwoven fabric on the side facing the negative electrode It can be estimated from the relationship with the volume of the void portion of the nonwoven fabric on the side facing the positive electrode. That is, the separator may be configured such that the volume of the void portion of the nonwoven fabric on the side facing the negative electrode is smaller than the volume of the void portion of the nonwoven fabric on the side facing the positive electrode.

  The void volume of the nonwoven fabric constituting the separator is expressed by “Va−Vb” using Va: apparent volume of the nonwoven fabric and Vb: true volume of the nonwoven fabric according to the above formula for calculating the porosity of the nonwoven fabric. Can be sought.

  In the separator, for example, of the two nonwoven fabrics constituting the separator, the volume X of the void portion in the nonwoven fabric on the side facing the negative electrode and the volume Y of the void portion in the nonwoven fabric on the side facing the positive electrode It is desirable that the ratio Y / X is 1.5 or more, more preferably 1.8 or more, and 4.5 or less, more preferably 4.0 or less. If the volume of the void portion of the nonwoven fabric on the side facing the positive electrode is too small or too large relative to the nonwoven fabric on the side facing the negative electrode (that is, the value of the volume ratio Y / X of the void portion is too small or too large) The ratio of the liquid retention amount of the nonwoven fabric facing the positive electrode to the liquid retention amount of the nonwoven fabric facing the negative electrode is too small or too large, and the amount of electrolyte supplied to the positive and negative electrodes is It becomes difficult to optimize, and the effect of the present invention may be reduced.

  In the separator according to the present invention, the negative electrode-side non-woven fabric has a smaller amount of electrolyte solution retained than the positive-electrode-side non-woven fabric, and preferably the above-described void portion volume ratio is achieved, for example, by the negative electrode side And changing the thickness of the non-woven fabric and the non-woven fabric on the positive electrode side. That is, it is only necessary to use a non-woven fabric on the negative electrode side that is thinner than the non-woven fabric on the positive electrode side.

  In order to control the ratio of the liquid retention amount of both nonwoven fabrics by adjusting the volume ratio of the voids of both nonwoven fabrics to the above preferred value depending on the difference in thickness between the nonwoven fabric on the negative electrode side and the nonwoven fabric on the positive electrode side, The thickness of the non-woven fabric on the positive electrode side is, for example, 1.5 times or more, more preferably 1.8 times or more, and 4.5 times or less, more preferably 4.0 times or less. Is desirable. If the non-woven fabric on the positive electrode side is too thin with respect to the non-woven fabric on the negative electrode side, the above-described effect due to changing the amount of liquid retained between the non-woven fabric on the negative electrode side and the non-woven fabric on the positive electrode side may be reduced. On the other hand, if the non-woven fabric on the positive electrode side is too thick with respect to the non-woven fabric on the negative electrode side, for example, the amount of the electrolyte solution that must be injected into the battery increases or the thickness of the battery increases.

  The specific thickness of the negative electrode-side non-woven fabric and the positive electrode-side non-woven fabric varies depending on the configuration (mainly size) of the non-aqueous electrolyte secondary battery. In the case of so-called “ML1220” which is one of the secondary batteries, the thickness of the non-woven fabric on the negative electrode side is 80 μm or more, more preferably 90 μm or more, and 200 μm or less, more preferably 180 μm or less. The thickness is preferably 300 μm or more, more preferably 310 μm or more, and 400 μm or less, more preferably 380 μm or less. And it is preferable to satisfy | fill the ratio of the above-mentioned thickness, satisfy | filling such thickness.

  In the separator according to the present invention, the non-woven fabric on the negative electrode side has a smaller amount of electrolyte solution retained than the non-woven fabric on the positive electrode side, and preferably the above-mentioned volume ratio of the voids is achieved to maintain both non-woven fabrics. As a method for controlling the ratio of the liquid amount, in addition to changing the thicknesses of both nonwoven fabrics, a method of making the porosity of the nonwoven fabric on the negative electrode side smaller than the porosity of the nonwoven fabric on the positive electrode side can also be adopted.

  In addition, when adopting a method of changing the liquid retention amount of these nonwoven fabrics by changing the thickness of the nonwoven fabric on the negative electrode side and the nonwoven fabric on the positive electrode side, the nonwoven fabric on the negative electrode side is made thin so that the separator in the battery Since the apparent occupied volume can be reduced, it is also possible to increase the filling amount of the positive and negative electrodes, thereby increasing the capacity.

  In the separator according to the present invention, the microporous film and the two non-woven fabrics may be bonded to each other or simply overlapped. When pasting each other, for example, a method of applying heat to the surface of the microporous film or the nonwoven fabric to such an extent that the porosity and porosity are not so much influenced, and then superposing and heat-sealing can be employed. Also, for example, if the microporous film and two nonwoven fabrics are overlapped and punched to the required size, the microporous film and the two nonwoven fabrics may adhere to each other at the end. Yes, it can also be used as a separator in such a state.

  The negative electrode according to the nonaqueous electrolyte secondary battery of the present invention uses lithium as an active material. Here, using lithium as an active material means that lithium metal, a lithium compound, or lithium ions are involved in the electrode reaction. As a material constituting the negative electrode, lithium metal or a lithium alloy reversibly alloyed with lithium such as lithium-aluminum or lithium-gallium can be used. In the case of a lithium alloy, the lithium content is preferably 1 to 15 atomic%, for example. These negative electrode materials may be used individually by 1 type, and may be used in combination of 2 or more type. The negative electrode material can be used as it is in the form of a foil, for example, or a foil-like material can be used by being pressure-bonded to a metal foil, an expanded metal, a plain weave wire mesh or the like as a current collector.

  In the nonaqueous electrolyte secondary battery of the present invention, there are no particular limitations on the components other than the separator and the negative electrode, and various components adopted in conventionally known nonaqueous electrolyte secondary batteries are applied. be able to.

As the positive electrode, for example, a positive electrode generally used for a non-aqueous electrolyte secondary battery that reversibly occludes and releases lithium ions can be used. Examples of the material capable of reversibly occluding and releasing lithium ions that can be used as the positive electrode active material include LiCoO ₂ (lithium cobaltate), LiNiO ₂ (lithium nickelate), and manganese-containing oxide [LiMn ₂ O ₄ , LiMn ₃ O ₆ , Li ₂ MnO ₃ , LiMnO ₂ (lithium manganate), LiMn ₂ O ₄ (spinel), etc.], V ₂ O ₅ (vanadium pentoxide) and the like.

  For the positive electrode, a conductive additive and a binder are usually used in addition to the positive electrode active material as described above. Examples of the conductive assistant include carbon black, flaky graphite, ketjen black, acetylene black, and fibrous carbon. As the binder, for example, polytetrafluoroethylene, polyvinylidene fluoride, carboxymethyl cellulose, styrene butadiene rubber or the like is used.

  In producing the positive electrode, the positive electrode mixture prepared by mixing the positive electrode active material, the conductive additive and the binder is pressure-molded, or the positive electrode mixture is dispersed in water or an organic solvent to contain the positive electrode mixture. A paste is prepared (in this case, the binder may be previously dissolved or dispersed in water or a solvent and mixed with a positive electrode active material or the like to prepare a positive electrode mixture-containing paste), and the positive electrode mixture The paste is applied to a current collector made of a metal foil, an expanded metal, a plain weave wire net, and the like, dried, and then press-molded. However, the method for manufacturing the positive electrode is not limited to the above-described method, and other methods may be used.

  As described above, the positive electrode produced in this way is a porous body having pores, and it is necessary to sufficiently contain an electrolytic solution therein in order to efficiently discharge. Therefore, the liquid retention amount of the nonwoven fabric on the side facing the positive electrode in the separator is required to be larger than the liquid retention amount of the nonwoven fabric on the side facing the negative electrode which does not substantially have such pores.

  Examples of the electrolytic solution according to the present invention include cyclic carbonates such as propylene carbonate, ethylene carbonate, butylene carbonate, and vinylene carbonate; chain carbonate esters such as dimethyl carbonate, diethyl carbonate, and methyl ethyl carbonate; Selected from ethers such as dimethoxyethane, diglyme (diethylene glycol methyl ether), triglyme (triethylene glycol dimethyl ether), tetraglyme (tetraethylene glycol dimethyl ether), 1,2-dimethoxyethane, 1,2-diethoxymethane, and tetrahydrofuran; A nonaqueous electrolytic solution prepared by dissolving an electrolyte in one kind of solvent or two or more kinds of mixed solvents is used.

The electrolytes dissolved in the electrolytic solution according to the present invention, for _{example, LiBF 4, LiPF 6, LiAsF} 6, LiSbF 6, LiClO 4, LiCF 3 SO 3, LiC 4 F 9 SO 3 LiC n F 2n + 1 SO 3 , such as ( n ≧ 1), LiN (CF ₃ SO ₂ ) ₂ , LiC (CF ₃ SO ₂ ) ₃ , LiCF ₃ CO ₂ , LiB ₁₀ Cl ₁₀ , lower fatty acid carboxylate, LiAlCl ₄ , LiCl, LiBr, LiI, chloroborane Examples include lithium and lithium tetraphenylborate. Each of these electrolytes may be used alone or in combination of two or more. Among the above electrolytes, when a manganese-containing oxide is used as the positive electrode active material, LiC _n F _{2n + 1} SO such as LiClO ₄ , LiPF ₆ , LiCF ₃ SO ₃ , LiC ₄ F ₉ SO ₃ is used because of its coexistence. ₃ (n ≧ 1), lithium imide salts such as LiN (CF ₃ SO ₂ ) ₂ and LiN (C ₂ F ₅ SO ₂ ) ₂ are preferable.

  Although there is no restriction | limiting in particular in the density | concentration of the electrolyte in electrolyte solution, For example, it is preferable that it is 0.2-2 mol / l, and it is more preferable that it is 0.3-1.5 mol / l.

  In the present invention, the electrolytic solution is usually used in a liquid state, but a gelling agent such as a polymer may be further added to the above electrolytic solution to be used as a so-called gel.

  The form of the nonaqueous electrolyte secondary battery of the present invention is not particularly limited. For example, a so-called coin battery or button battery, a flat battery, a cylindrical battery such as a cylindrical battery, a rectangular battery, or the like is used. In addition, various forms employed in conventionally known non-aqueous electrolyte secondary batteries such as a laminated battery having an aluminum laminate film as an exterior body can be used. In the case of a flat battery or a laminated battery, for example, a structure in which a positive electrode and a negative electrode are stacked via a separator, is loaded in the battery outer body, and is further sealed by injecting an electrolyte. Good. On the other hand, in the case of a cylindrical battery, a laminated electrode body in which a positive electrode and a negative electrode are stacked with a separator interposed therebetween, and a wound electrode body obtained by winding the positive electrode and the negative electrode in a spiral shape are loaded into the cylindrical battery exterior body. It is only necessary to have a structure in which an electrolytic solution is injected and sealed.

  The non-aqueous electrolyte secondary battery of the present invention has good charge / discharge cycle characteristics, and by utilizing such characteristics, various applications in which conventionally known non-aqueous electrolyte secondary batteries are used ( It can be suitably used for a main power source and a memory backup power source of various electronic devices.

  Hereinafter, the present invention will be described in detail based on examples. However, the following examples are not intended to limit the present invention, and all modifications made without departing from the spirit of the preceding and following descriptions are included in the technical scope of the present invention.

Example 1
0.75 mol of electrolytic manganese dioxide (average particle size: 30 μm, BET specific surface area: 60 m ² / g) neutralized with NH ₄ OH in a saturated aqueous solution in which 0.25 mol of lithium hydroxide (LiOH) was dissolved in ion-exchanged water. Mole was added, pre-dried at a temperature of 120 ± 10 ° C., and water was removed while stirring on the way. This was dried and ground, and then heated in the atmosphere at a temperature of 350 ± 10 ° C. for 20 hours to synthesize a lithium manganese composite oxide.

  To 100 parts by mass of the lithium manganese composite oxide synthesized as described above, 5 parts by weight of scaly graphite as a conductive assistant and 2 parts by weight of polytetrafluoroethylene dispersion having a concentration of 60% by weight as a binder are blended. Thus, a positive electrode mixture was prepared.

  After press-molding the above positive electrode mixture and a stainless steel plain woven wire net punched into a circle having a diameter of 8.6 mm, it is vacuum-dried at 250 ° C., and has a diameter of 8.6 mm and a thickness of 0.75 mm. A positive electrode was obtained.

As the electrolytic solution, 0.5 mol of LiPF ₆ dissolved in a mixed solvent of propylene carbonate and 1,2-dimethoxyethane at 67:33 (mass ratio) was used, and non-aqueous electrolysis having the structure shown in FIG. A liquid secondary battery (coin-shaped non-aqueous electrolyte secondary battery) was produced.

  The battery shown in FIG. 1 will be described. 1 is a positive electrode can made of stainless steel, and 2 is the above positive electrode. Reference numeral 3 denotes a positive electrode current collector, and the positive electrode current collector 3 is made of a stainless steel plain weave metal net disposed on one side of the positive electrode mixture when the positive electrode 2 is pressed.

  4 is a separator, 5 is a negative electrode made of a lithium-aluminum alloy (lithium content 14 atomic%) having a thickness of 500 μm, 6 is a negative electrode current collector made of a stainless steel net, and 7 is a negative electrode can made of stainless steel. The negative electrode current collector 6 is spot welded to the inner surface of the negative electrode can 7.

  8 is an annular gasket made of polypropylene, and in the battery of FIG. 1, the negative electrode can 7 and the positive electrode can 1 are caulked so that the opening end of the positive electrode can 1 is tightened inward via the annular gasket 8, The peripheral folded portion of the negative electrode can 7 and the open end of the positive electrode can 1 are sealed by being pressed against the annular gasket 8. In addition, an electrolytic solution having the above composition is injected into this battery, and the battery has a diameter of 12.5 mm and a height of 2.0 mm.

  Moreover, although the enlarged view of the part containing the separator 4 which concerns on the battery of FIG. 1 is shown in FIG. 2, the separator 4 is comprised by the nonwoven fabric 4a, 4c and the microporous film 4b. The nonwoven fabric 4a on the negative electrode 5 side is made of polypropylene and has a thickness of 100 μm and a porosity of 89%. The nonwoven fabric 4c on the positive electrode 2 side is made of polypropylene and has a thickness of 380 μm and a porosity of 86%. The microporous film 4b has a thickness of 30 μm and a porosity of 50%. At this time, the volume ratio Y / X of the void portion between the negative electrode-side nonwoven fabric and the positive electrode-side nonwoven fabric was 3.67. In FIGS. 1 and 2, the size of each component is not necessarily expressed accurately.

Example 2
Nonwoven fabric 4a (negative electrode 5 side) made of polypropylene and having a thickness of 170 μm and porosity of 84%; Nonwoven fabric 4c (positive electrode 2 side) made of polypropylene and having a thickness of 280 μm and porosity of 87%; and a thickness of 30 μm A coin-shaped nonaqueous electrolyte secondary battery was produced in the same manner as in Example 1 except that a separator having a three-layer structure composed of a microporous film 4b having a porosity of 50% was used. In the separator used for this battery, the volume ratio Y / X of the gap between the nonwoven fabric on the negative electrode side and the nonwoven fabric on the positive electrode side was 1.71.

Example 3
Nonwoven fabric 4a (negative electrode 5 side) made of polypropylene and having a thickness of 170 μm and porosity of 84%; Nonwoven fabric 4c (positive electrode 2 side) made of polypropylene and having a thickness of 320 μm and porosity of 83%; and a thickness of 30 μm A coin-shaped nonaqueous electrolyte secondary battery was produced in the same manner as in Example 1 except that a separator having a three-layer structure composed of a microporous film 4b having a porosity of 50% was used. In the separator used for this battery, the volume ratio Y / X of the gap between the negative electrode-side nonwoven fabric and the positive electrode-side nonwoven fabric was 1.86.

Example 4
Nonwoven fabric 4a (negative electrode 5 side) made of polypropylene and having a thickness of 100 μm and porosity of 89%; Nonwoven fabric 4c (positive electrode 2 side) made of polypropylene and having a thickness of 400 μm and porosity of 86%; and a thickness of 30 μm A coin-shaped nonaqueous electrolyte secondary battery was produced in the same manner as in Example 1 except that a separator having a three-layer structure composed of a microporous film 4b having a porosity of 50% was used. In the separator used in this battery, the volume ratio Y / X of the gap between the nonwoven fabric on the negative electrode side and the nonwoven fabric on the positive electrode side was 3.87.

Example 5
Nonwoven fabric 4a (negative electrode 5 side) made of polypropylene and having a thickness of 100 μm and porosity of 89%; Nonwoven fabric 4c (positive electrode 2 side) made of polypropylene and having a thickness of 420 μm and porosity of 87%; and a thickness of 30 μm A coin-shaped nonaqueous electrolyte secondary battery was produced in the same manner as in Example 1 except that a separator having a three-layer structure composed of a microporous film 4b having a porosity of 50% was used. In the separator used for this battery, the volume ratio Y / X of the void portion between the negative electrode-side nonwoven fabric and the positive electrode-side nonwoven fabric was 4.11.

Comparative Example 1
As the separator, a coin-shaped non-water is formed in the same manner as in Example 1 except that a separator having a two-layer structure composed of a microporous film and a nonwoven fabric is used and the microporous film side is disposed facing the negative electrode. An electrolyte secondary battery was produced. The microporous film constituting the separator is the same as the microporous film constituting the separator according to Example 1, and the non-woven fabric constituting the separator is the positive electrode constituting the separator according to Example 1. The same non-woven fabric was used.

Comparative Example 2
As a separator, a three-layer structure in which the same thing as the microporous film constituting the separator used in Example 1 is sandwiched between two sheets of the same non-woven fabric on the positive electrode side constituting the separator used in Example 1 A coin-shaped non-aqueous electrolyte secondary battery was produced in the same manner as in Example 1 except that the separator was used.

Comparative Example 3
As a separator, a three-layer structure in which the same thing as the microporous film constituting the separator used in Example 1 is sandwiched between two sheets of the same non-woven fabric on the negative electrode side constituting the separator used in Example 1 A coin-shaped non-aqueous electrolyte secondary battery was produced in the same manner as in Example 1 except that the separator was used.

  About the nonaqueous electrolyte secondary battery of the said Example 1 and Comparative Examples 1-3, while performing the following charging / discharging cycle characteristic evaluation, thickness was measured. The results are shown in Table 1. Charging / discharging cycle characteristics are as follows. For each of the above batteries, charging is performed at 20 ° C. with a charging voltage of 3.25 ± 0.01 V, a current regulating resistance of 390Ω, and 17 hours of charging and 2.7 kΩ of discharging for 12 hours. Evaluation was made based on the number of times that the voltage during discharge could be maintained at 2.0 V or higher.

  As is clear from Table 1, the nonaqueous electrolyte secondary batteries of Examples 1 to 5 have a larger number of charge / discharge cycles than the nonaqueous electrolyte secondary batteries of Comparative Examples 1 to 3, and the charge / discharge is performed. The cycle characteristics were good.

  On the other hand, the non-aqueous electrolyte secondary battery of Comparative Example 1 is difficult to handle the separator at the time of battery production, and is assembled when the electrolyte is absorbed by only one layer of nonwoven fabric. Since the problem that the electrolytic solution overflows sometimes occurs, the problem that the electrolytic solution becomes insufficient during the charge / discharge cycle occurred. Moreover, since the amount of electrolyte supplied to the negative electrode was small, the number of charge / discharge cycles was small. In the non-aqueous electrolyte secondary battery of Comparative Example 2, since the electrolyte solution is excessively absorbed by the nonwoven fabric related to the separator, the electrolyte solution optimal for the discharge reaction of the positive and negative electrodes cannot be disposed, and the number of charge / discharge cycles is reduced. Declined. In addition, while the thickness of the batteries of other examples and comparative examples is 1.8 to 2.0 mm, the battery thickness is much larger than 2.0 mm and becomes too thick to exceed the allowable range. There has occurred. The non-aqueous electrolyte secondary battery of Comparative Example 3 has a problem that the electrolyte is insufficient during the charge / discharge cycle because the separator has insufficient liquid retention performance and the electrolyte overflows during battery assembly. The number of times decreased.

It is a fragmentary longitudinal cross-sectional view which shows roughly an example of the structure of the nonaqueous electrolyte secondary battery of this invention. It is an enlarged view of the principal part of FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Positive electrode can 2 Positive electrode 3 Positive electrode collector 4 Separator 4a, 4c Nonwoven fabric 4b Microporous film 5 Negative electrode 6 Negative electrode collector 7 Negative electrode can 8 Cylindrical gasket

Claims (3)

A non-aqueous electrolyte secondary battery comprising a positive electrode, a negative electrode having lithium or a lithium alloy, a separator and a non-aqueous electrolyte,
The separator has a three-layer structure in which a microporous film is sandwiched between two nonwoven fabrics,
Of the two nonwoven fabrics constituting the separator, the amount of nonaqueous electrolyte retained in the nonwoven fabric facing the negative electrode is less than the amount of nonaqueous electrolyte retained in the nonwoven fabric facing the positive electrode. Non-aqueous electrolyte secondary battery characterized.   Of the two nonwoven fabrics constituting the separator, the ratio Y / X of the volume X of the void portion in the nonwoven fabric facing the negative electrode and the volume Y of the void portion in the nonwoven fabric facing the positive electrode is 1 The nonaqueous electrolyte secondary battery according to claim 1, which is 5 to 4.5. 3. The non-aqueous electrolyte secondary battery according to claim 1, wherein, of the two nonwoven fabrics constituting the separator, the nonwoven fabric on the side facing the negative electrode is thinner than the nonwoven fabric on the side facing the positive electrode.

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