JP2015230824A - Electrode structure and lithium secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To further suppress the increase in internal resistance of a lithium secondary battery.SOLUTION: A lithium secondary battery of the present invention comprises: a positive electrode sheet 15 including a collector 13C and a positive electrode mixture layer 14 formed on the collector; a negative electrode sheet 18 including a collector 16C and a negative electrode mixture layer 17 formed on a surface of the collector; a separator 26 provided between the positive electrode sheet 15 and the negative electrode sheet 18; and a nonaqueous electrolyte 20 filled in between the positive electrode sheet 15 and the negative electrode sheet 18. In the lithium secondary battery, the negative electrode sheet 18 enwrapped by the separator 26, and the positive electrode sheet 15 is put on the negative electrode sheet thus enwrapped; in this state, the positive and negative electrode sheets and separator are wound and encased in a cylindrical case 21. The negative electrode sheet 18 has a structure arranged so that the separator 26 includes a negative electrode active material, and the separator 26 is sealed to make more difficult for the nonaqueous electrolyte 20 to escape.

Description

  The present invention relates to an electrode structure and a lithium secondary battery.

  Conventionally, as an electrode structure, a bag-packed electrode produced by pressing and heating a portion where a separator layer made of a resin material is overlapped with a heat-resistant layer between a pair of welding tips has been proposed. (For example, refer to Patent Document 1). In this electrode structure, the heat-resistant layer is broken by the welding tip, and by heating this, the separator layer resin is melted and joined from the broken portion.

JP 2013-143336 A

  However, in the electrode structure of Patent Document 1 described above, a bag-packed structure is used for positioning the electrodes, and for example, it has not been studied to further improve the charge / discharge characteristics. For example, in a lithium secondary battery, it has been required to further improve charge / discharge characteristics, such as suppressing an increase in internal resistance of the battery caused by charge / discharge.

  This invention is made | formed in view of such a subject, and it aims at providing the electrode structure and lithium secondary battery which can suppress the increase in internal resistance more.

  As a result of diligent research to achieve the above-described object, the present inventors have suppressed the increase in internal resistance when the electrode sheet is sealed with a separator so that the non-aqueous electrolyte does not leak out. The present invention has been completed.

That is, the electrode structure of the present invention is
Used for secondary batteries with non-aqueous electrolyte,
A positive electrode sheet comprising a positive electrode active material and a current collector;
A negative electrode sheet comprising a negative electrode active material and a current collector;
An electrode structure in which a separator interposed between the positive electrode sheet and the negative electrode sheet is laminated,
In the negative electrode sheet, the separator is sealed so that the negative electrode active material is contained by the separator and the non-aqueous electrolyte is difficult to be discharged.

The lithium secondary battery of the present invention is
The above-described electrode structure having the positive electrode active material and the negative electrode active material that occlude and release lithium; and
A non-aqueous electrolyte that is interposed between the positive electrode and the negative electrode and conducts lithium ions.

  The electrode structure and lithium secondary battery of the present invention can further suppress an increase in internal resistance. The reason why such an effect can be obtained is presumed that, for example, the non-aqueous electrolyte is sealed inside the electrode structure by the separator, and the movement of the electrolyte from the electrode structure is further suppressed. .

The schematic diagram which shows an example of the lithium secondary battery 10 of this invention. FIG. 3 is a cross-sectional view showing an example of an electrode structure 11. An explanatory view showing an example of sealing by separator 26. FIG. An explanatory view showing an example of continuous sealing by separator 26. FIG. Sectional drawing which shows an example of the electrode structure 11B. A sectional view showing an example of electrode structure 11C. The pore distribution curve of a positive electrode active material layer and a negative electrode active material layer.

  Next, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a schematic diagram showing an example of a lithium secondary battery 10 of the present invention. FIG. 2 is a cross-sectional view illustrating an example of the electrode structure 11. As shown in FIGS. 1 and 2, the lithium secondary battery 10 of this embodiment includes, for example, a positive electrode sheet 15 in which a positive electrode mixture layer 14 is formed on a current collector 13 and a negative electrode mixture on the surface of the current collector 16. The negative electrode sheet 18 in which the layer 17 is formed, the separator 26 provided between the positive electrode sheet 15 and the negative electrode sheet 18, and the nonaqueous electrolytic solution 20 that fills between the positive electrode sheet 15 and the negative electrode sheet 18 are provided. . In this lithium secondary battery 10, the negative electrode sheet 18 is wrapped with a separator 26, wound in a state of being laminated with the positive electrode sheet 15, inserted into the cylindrical case 21, the positive electrode terminal 22 is connected to the positive electrode sheet 15, and the negative electrode A negative electrode terminal 23 is connected to the sheet 18.

  The lithium secondary battery 10 includes a positive electrode sheet 15 including a positive electrode mixture layer 14 containing a positive electrode active material and a current collector 13, a negative electrode mixture layer 17 containing a negative electrode active material, and a current collector 16. The electrode structure 11 includes a sheet 18 and a separator 26 interposed between the positive electrode sheet 15 and the negative electrode sheet 18. In this electrode structure 11, the negative electrode sheet 18 has a structure in which the negative electrode active material is included by the separator 26 and the separator 26 is sealed so that the nonaqueous electrolytic solution 20 is not easily discharged. By so doing, it is possible to further suppress an increase in internal resistance in the lithium secondary battery 10. This is particularly effective in a battery that charges and discharges at a high current rate. The reason why this effect is obtained is considered to be because the movement of the nonaqueous electrolytic solution 20 is further suppressed, for example. In the electrode structure 11, as shown in FIG. 2, the separator 26 is a bag-like separator in which one end of the separator 26 is folded and the overlapping ends are welded together by a binding portion 27. In the accommodated state, the end of the separator 26 that overlaps the current collector 16 of the negative electrode sheet 18 may be welded to the current collector 16 and sealed. In this electrode structure 11, the negative electrode sheet 18 has a non-formation region 28 in which the negative electrode mixture layer 17 is not formed in a part of the current collector 16, and the non-formation region 28 is exposed to the outside. The end of 26 is welded to the current collector 16. The negative electrode terminal 23 is connected to the non-formed region 28. In this electrode structure 11, the separator 26 is sealed over the entire end portion, and the negative electrode mixture layer 17 is completely covered with the separator 26 without any opening portion. Here, “sealing over the entire area of the end portion” is sufficient if the entire area of the end portion is sealed, and in addition to the case where the entire area of the end portion is continuously sealed, This includes the case where the entire region is sealed in a discontinuous state. For example, the nonaqueous electrolytic solution 20 may be made difficult to come out of the electrode structure 11, and a portion having a length of 80% or more of the end portion, more preferably 90% or more is sealed, There may be a portion that is partially interrupted.

As shown in FIG. 2, a positive electrode mixture layer 14 containing a positive electrode active material is formed on both surfaces of the positive electrode sheet 15. The positive electrode mixture layer 14 may be formed on one side of the positive electrode sheet 15 depending on the structure to be employed. The positive electrode sheet 15 of the lithium secondary battery 10 is obtained by mixing, for example, a positive electrode active material, a conductive material, and a binder, and adding a suitable solvent to form a paste-like positive electrode mixture. And may be formed by compression to increase the electrode density as necessary. As the positive electrode active material, a sulfide containing a transition metal element, an oxide containing lithium and a transition metal element, or the like can be used. Specifically, transition metal sulfides such as TiS ₂ , TiS ₃ , MoS ₃ , and FeS _2, and the basic composition formula are Li _(1-x) MnO ₂ (0 <x <1, etc., the same shall apply hereinafter) and Li _{(1 -x)} Lithium-manganese composite oxides such as Mn ₂ O _4, lithium cobalt composite oxides whose basic composition formula is Li _(1-x) CoO _2, etc., basic composition formulas such as Li _(1-x) NiO ₂ lithium nickel composite oxide, the basic compositional formula _{Li (1-x) Ni a} Co b Mn c O 2 ( where 0 <a <1,0 <b < 1,0 <c <1, a + b + c = 1 Lithium nickel cobalt manganese composite oxide such as LiV ₂ O ₃ as a basic composition formula, transition metal oxide such as V ₂ O ₅ as a basic composition formula, etc. it can. Of these, lithium transition metal composite oxides such as LiCoO ₂ , LiNiO ₂ , LiMnO ₂ , LiNi _1/3 Co _1/3 Mn _1/3 O _{2 and the} like are preferable. The “basic composition formula” means that the composition of each element may be different or may contain other elements. The conductive material is not particularly limited as long as it is an electron conductive material that does not adversely affect the battery performance of the positive electrode. For example, graphite such as natural graphite (scale-like graphite, scale-like graphite) or artificial graphite, acetylene black, carbon black, What mixed 1 type (s) or 2 or more types, such as ketjen black, carbon whisker, needle coke, carbon fiber, metal (copper, nickel, aluminum, silver, gold, etc.) can be used. Among these, as the conductive material, carbon black and acetylene black are preferable from the viewpoints of electron conductivity and coatability. The binder serves to bind the active material particles and the conductive material particles. For example, polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), fluorine-containing resin such as fluorine rubber, or polypropylene, Thermoplastic resins such as polyethylene, ethylene propylene diene monomer (EPDM) rubber, sulfonated EPDM rubber, natural butyl rubber (NBR) and the like can be used alone or as a mixture of two or more. In addition, an aqueous dispersion of cellulose or styrene butadiene rubber (SBR), which is an aqueous binder, can also be used. Examples of the solvent for dispersing the positive electrode active material, the conductive material, and the binder include N-methylpyrrolidone, dimethylformamide, dimethylacetamide, methyl ethyl ketone, cyclohexanone, methyl acetate, methyl acrylate, diethylenetriamine, and N, N-dimethylaminopropylamine. Organic solvents such as ethylene oxide and tetrahydrofuran can be used. Moreover, a dispersing agent, a thickener, etc. may be added to water, and an active material may be slurried with latex, such as SBR. As the thickener, for example, polysaccharides such as carboxymethyl cellulose and methyl cellulose can be used alone or as a mixture of two or more. Examples of the application method include roller coating such as applicator roll, screen coating, doctor blade method, spin coating, bar coater, and the like, and any of these can be used to obtain an arbitrary thickness and shape. As the current collector 13, in addition to aluminum, titanium, stainless steel, nickel, iron, calcined carbon, conductive polymer, conductive glass, etc., aluminum and copper are used for the purpose of improving adhesiveness, conductivity and oxidation resistance. A surface treated with carbon, nickel, titanium, silver or the like can be used. For these, the surface can be oxidized. Examples of the shape of the current collector 13 include a foil shape, a film shape, a sheet shape, a net shape, a punched or expanded shape, a lath body, a porous body, a foamed body, and a formed body of fiber groups. The current collector 13 has a thickness of 1 to 500 μm, for example.

  A negative electrode mixture layer 17 containing a negative electrode active material is formed on both surfaces of the negative electrode sheet 18. The negative electrode mixture layer 17 may be formed on one surface of the negative electrode sheet 18 depending on the structure to be employed. For example, the negative electrode sheet 18 is prepared by mixing a negative electrode active material, a conductive material, and a binder, and adding a suitable solvent to form a paste-like negative electrode mixture on the surface of the current collector 16. Depending on the case, the electrode may be compressed to increase the electrode density. Examples of the negative electrode active material include a carbonaceous material capable of inserting and extracting lithium ions, a composite oxide containing a plurality of elements, and a conductive polymer. Examples of the carbonaceous material include cokes, glassy carbons, graphites, non-graphitizable carbons, pyrolytic carbons, and carbon fibers. Of these, graphites such as artificial graphite and natural graphite have an operating potential close to that of metallic lithium, can be charged and discharged at a high operating voltage, and suppresses self-discharge when a lithium salt is used as a supporting salt. In addition, the irreversible capacity during charging can be reduced, which is preferable. Examples of the composite oxide include lithium titanium composite oxide and lithium vanadium composite oxide. Among these, as the negative electrode active material, a carbonaceous material is preferable from the viewpoint of safety. In addition, as the conductive material, the binder, the solvent, and the like used for the negative electrode sheet 18, those exemplified for the positive electrode sheet 15 can be used. The current collector 16 of the negative electrode sheet 18 includes copper, nickel, stainless steel, titanium, aluminum, calcined carbon, conductive polymer, conductive glass, Al-Cd alloy, and the like, as well as adhesion, conductivity, and reduction resistance. For the purpose of improving the properties, for example, a surface of copper or the like treated with carbon, nickel, titanium, silver or the like can be used. For these, the surface can be oxidized. The shape of the current collector 16 can be the same as that of the positive electrode.

  As the nonaqueous electrolytic solution 20 of the lithium secondary battery 10, a nonaqueous electrolytic solution in which a supporting salt is dissolved in a solvent can be used. Examples of the solvent include carbonates, esters, ethers, nitriles, furans, sulfolanes and dioxolanes, and these can be used alone or in combination. Specifically, as carbonates, cyclic carbonates such as ethylene carbonate, propylene carbonate, vinylene carbonate, butylene carbonate, chloroethylene carbonate, dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, ethyl-n-butyl carbonate, methyl-t -Chain carbonates such as butyl carbonate, di-i-propyl carbonate, t-butyl-i-propyl carbonate, cyclic esters such as γ-butyllactone and γ-valerolactone, methyl formate, methyl acetate, ethyl acetate, Chain esters such as methyl butyrate, ethers such as dimethoxyethane, ethoxymethoxyethane, and diethoxyethane; nitriles such as acetonitrile and benzonitrile; Examples include furans such as lan, methyltetrahydrofuran, sulfolanes such as sulfolane and tetramethylsulfolane, and dioxolanes such as 1,3-dioxolane and methyldioxolane. Among these, the combination of cyclic carbonates and chain carbonates is preferable. According to this combination, not only the cycle characteristics representing the battery characteristics in repeated charge and discharge are excellent, but also the viscosity of the electrolyte, the electric capacity of the obtained battery, the battery output, etc. should be balanced. it can. The cyclic carbonates are considered to have a relatively high relative dielectric constant and increase the dielectric constant of the electrolytic solution, and the chain carbonates are considered to suppress the viscosity of the electrolytic solution.

Examples of the supporting salt include LiPF ₆ , LiBF ₄ , LiAsF ₆ , LiCF ₃ SO ₃ , LiN (CF ₃ SO ₂ ) ₂ , LiC (CF ₃ SO ₂ ) ₃ , LiSbF ₆ , LiSiF ₆ , LiAlF ₄ , LiSCN, LiClO. ₄ , LiCl, LiF, LiBr, LiI, LiAlCl _{4 and the} like. Among these, from the group consisting of inorganic salts such as LiPF ₆ , LiBF ₄ , LiAsF ₆ , LiClO ₄ , and organic salts such as LiCF ₃ SO ₃ , LiN (CF ₃ SO ₂ ) ₂ , LiC (CF ₃ SO ₂ ) _3. It is preferable from the viewpoint of electrical characteristics to use a combination of one or two or more selected salts. The supporting salt preferably has a concentration in the non-aqueous electrolyte of 0.1 mol / L or more and 5 mol / L or less, and more preferably 0.5 mol / L or more and 2 mol / L or less. When the concentration for dissolving the supporting salt is 0.1 mol / L or more, a sufficient current density can be obtained, and when it is 5 mol / L or less, the electrolytic solution can be made more stable. Moreover, you may add flame retardants, such as a phosphorus type and a halogen type, to this non-aqueous electrolyte.

  The lithium secondary battery 10 includes a separator 26 between the positive electrode sheet 15 and the negative electrode sheet 18. As described above, the separator 26 is formed so as to cover the negative electrode mixture layer 17. The separator 26 is not particularly limited as long as it is a composition that can withstand the use range of the lithium secondary battery 10. For example, a polymer nonwoven fabric such as a polypropylene nonwoven fabric or a polyphenylene sulfide nonwoven fabric, or an olefin resin such as polyethylene or polypropylene is used. A thin microporous membrane can be mentioned. Alternatively, a cellulose separator may be used. These may be used alone or in combination.

  Next, a method for producing the electrode structure 11 including the negative electrode mixture layer 17 with the separator 26 will be described. 3A and 3B are explanatory views showing an example of sealing of the negative electrode sheet 18 by the separator 26, FIG. 3A is an explanatory view of the bag-shaped separator, and FIG. 3B is an explanatory view of sealing by the bag-shaped separator. FIG. 3 (c) is an explanatory view of the folding separator, and FIG. 3 (d) is an explanatory view of sealing with the folding separator. Here, a method for producing the negative electrode sheet 18 will be mainly described. First, a negative electrode mixture paste in which a negative electrode active material, a conductive material, and the like are mixed is prepared, the negative electrode mixture paste is applied to the surface of the current collector 16, and the negative electrode mixture layer 17 is placed on the current collector 16. Then, the negative electrode sheet 18 is produced (FIG. 3A). At this time, the negative electrode mixture layer 17 is formed on the current collector 16 so that the band-shaped non-formation region 28 is formed. Next, a bag-like separator 26 having both ends welded at the binding part 27 is prepared. The bag-shaped separator has an opening larger than the width of the negative electrode sheet 18, and the negative electrode sheet 18 can be inserted through the opening. Subsequently, the negative electrode sheet 18 is accommodated in the bag-shaped separator 26 from the opening so that a part of the non-formation region 28 of the current collector 16 is exposed, and the opening end of the bag-shaped separator 26 is accommodated. The end is heated and pressed to weld this end to the current collector 16 (FIG. 3B). In this way, the negative electrode mixture layer 17 is covered and accommodated by the separator 26, and the end overlapping the current collector 16 is welded to the current collector 16 to be sealed. Alternatively, instead of the bag-like separator 26, a folded one separator 26 may be used. First, the negative electrode sheet 18 on which the negative electrode mixture layer 17 is formed is prepared, and one separator 26 is folded back (FIG. 3C). Next, the negative electrode sheet 18 is accommodated in the folded separator 26 so that the negative electrode mixture layer 17 is covered with the separator 26 and a part of the non-formation region 28 of the current collector 16 is exposed. Subsequently, both ends of the separator 26 and the end overlapping the current collector 16 are heated and pressed, and the end is welded to the current collector 16 (FIG. 3D). In this way, it is possible to produce the negative electrode sheet 18 in which the negative electrode mixture layer 17 is covered with the separator 26 and accommodated, and the end overlapping the current collector 16 is welded to the current collector 16 and sealed. .

  Alternatively, the method for producing the negative electrode sheet 18 of the electrode structure 11 may be one in which the separator 26 is sealed and wound. 4A and 4B are explanatory diagrams showing an example of continuous sealing by the separator 26. FIG. 4A is a plan view of the manufacturing apparatus 30 viewed from above, and FIG. 4B is an A-line in FIG. 4A. It is A sectional drawing. In FIG. 4A, the positive electrode sheet 15 is omitted. The manufacturing apparatus 30 wraps the positive electrode sheet 15 on the laminated body after pressing and heating the laminated chip obtained by pressing and heating the laminated body in which the separator 26, the negative electrode sheet 18, and the separator 26 are laminated. And a winding roller 34. As shown in FIG. 4, the laminate 26 in which the separator 26 and the negative electrode mixture layer 17 formed on both surfaces of the current collector 16 are sandwiched between the separator 26 and the separator 26 is wound while being wound by the winding roller 34. And heated from above and below by the welding tip 32. At this time, the end portion of the separator 26 that overlaps the current collector 16 and the end portion that overlaps the separators 26 are pressed and heated with the non-formed region 28 exposed to the outside. In this way, it is possible to produce the negative electrode sheet 18 in which the negative electrode mixture layer 17 is covered with the separator 26 and accommodated, and the end overlapping the current collector 16 is welded to the current collector 16 and sealed. .

  In the lithium secondary battery 10 of the present embodiment described in detail above, the negative electrode mixture layer 17 is covered and accommodated by the separator 26, and an end portion overlapping the current collector 16 is welded to the current collector 16 and sealed. The electrode structure 11 is provided. That is, the lithium secondary battery 10 includes the electrode structure 11 in which the negative electrode active material is contained by the separator 26 and the separator is sealed so that the non-aqueous electrolyte is difficult to be discharged. And in this lithium secondary battery 10, the increase in internal resistance can be suppressed more. This is because, for example, in the electrode structure 11, when the negative electrode sheet 18 included in the separator 26 is impregnated with the nonaqueous electrolytic solution 20, the nonaqueous electrolytic solution 20 is sealed inside the separator 26. This is considered to be because the movement from the negative electrode sheet 18 contained in the separator 26 is further suppressed.

  It should be noted that the present invention is not limited to the above-described embodiment, and it goes without saying that the present invention can be implemented in various modes as long as it belongs to the technical scope of the present invention.

  For example, in the above-described embodiment, the electrode structure 11 is described as including only the negative electrode mixture layer 17 in the separator 26. However, the present invention is not particularly limited thereto. For example, as illustrated in FIG. The electrode structure 11 </ b> B included in 24 may be used. FIG. 5 is a cross-sectional view showing an example of the electrode structure 11B. In this electrode structure 11 </ b> B, the separator 24 is a bag-like separator in which one separator 26 is folded and the overlapping end portions are welded together by the binding portion 25, and the positive electrode sheet 15 is accommodated in the state where the positive electrode sheet 15 is accommodated. The end of the separator 24 that overlaps the current collector 13 of the sheet 15 may be welded to the current collector 13 and sealed. In the electrode structure 11B, the positive electrode sheet 15 has a non-formation region 29 in which the positive electrode mixture layer 14 is not formed in a part of the current collector 13, and the separator 13 is exposed in a state where the non-formation region 29 is exposed to the outside. The ends of 24 may be welded to the current collector 13. The positive electrode terminal 22 is connected to the non-formation region 29. In this electrode structure 11B, the separator 24 is sealed over the entire end portion, and the positive electrode mixture layer 14 is completely covered with the separator 24 in a state where there is no opening portion. By so doing, the movement of the non-aqueous electrolyte solution 20 is further suppressed in the positive electrode sheet 15, so that an increase in internal resistance can be further suppressed. Here, the manufacturing method of the electrode structure 11 </ b> B including the positive electrode mixture layer 14 with the separator 24 can adopt the same contents as the electrode structure 11 described above. For example, when producing the electrode structure 11B including the positive electrode mixture layer 14 in the separator 24, a bag-like separator may be used, a folded separator may be used, and the separator is sealed. It is good also as a thing to wind. The positive electrode mixture layer 14 and the negative electrode mixture layer 17 have different pore distributions, and the negative electrode mixture layer 17 has a larger average pore diameter (see FIG. 7 described later), so that the positive electrode sheet 15 and the negative electrode sheet As a priority order with respect to 18, it is preferable to seal the negative electrode sheet 18 with the separator 26.

  In the above-described embodiment, the foil-shaped current collector 16 has been described. However, a mesh-shaped current collector 16 may be used. FIG. 6 is a cross-sectional view showing an example of the electrode structure 11C. As shown in FIG. 6, the electrode structure 11C includes a mesh current collector 13C and a mesh current collector 16C. By so doing, the non-aqueous electrolyte 20 is likely to move in the surface direction of the electrode, so that the time required for impregnating the non-aqueous electrolyte 20 into the electrode can be further shortened.

  In the above-described embodiment, the two separators 26 are overlapped when continuously sealed as shown in FIG. 4. However, the present invention is not particularly limited to this, and the bag-like separator shown in FIG. 3 may be used. Alternatively, a folded separator may be used. In addition, as illustrated in FIG. 4, it has been described that the non-formation region 28 of the current collector 16 is exposed to the outside during continuous sealing. The separator 26 may be sealed with. Even in this case, an increase in internal resistance can be further suppressed.

  In the above-described embodiment, the electrode structure 11 is described by laminating and winding the positive electrode sheet 15, the negative electrode sheet 18, and the separator 26. However, the electrode structure 11 is not particularly limited, and may be, for example, an electrode structure that is not wound. . In the embodiment described above, the shape of the lithium secondary battery is a cylindrical shape, but is not particularly limited thereto, and examples thereof include a coin shape, a button shape, a sheet shape, a stacked shape, a flat shape, and a square shape. . Moreover, you may apply to the large sized thing etc. which are used for an electric vehicle etc.

  In the above-described embodiment, the lithium secondary battery 10 including the electrode structure 11 has been described. However, the electrode structure 11 used in the lithium secondary battery may be used. Even if it does in this way, if it is used for a lithium secondary battery, the same effect as a lithium secondary battery can be acquired.

  Hereinafter, an example in which the lithium secondary battery of the present invention was specifically manufactured will be described as an example.

[Example]
When the entire positive electrode mixture was 100% by mass, 91.0% by mass of LiNi _1/3 Co _1/3 Mn _1/3 O ₂ was used as the positive electrode active material. 6% by mass of carbon black was used as the conductive material, and 3% by mass of polyvinylidene fluoride (PVdF) was used as the binder. A positive electrode active material and PVdF were added to N-methyl-2-pyrrolidone (NMP) as a solvent and mixed, and then carbon black was further added and kneaded to obtain a positive electrode mixture paste. The positive electrode mixture was applied to both surfaces of a 15 μm thick aluminum foil as a positive electrode current collector. The dried positive electrode current collector was rolled with a rolling press to obtain a positive electrode sheet. Further, natural graphite powder as a negative electrode active material and styrene butadiene rubber (SBR) and carboxymethyl cellulose (CMC) as a binder are used as a solvent so that the mass ratio thereof becomes 98: 1: 1. A negative electrode mixture paste was prepared by kneading with water. This negative electrode mixture paste was applied to both surfaces of a 10 μm thick copper foil as a negative electrode current collector. The negative electrode current collector after application was dried, and the dried negative electrode current collector was rolled with a rolling press to obtain a negative electrode sheet. As a non-aqueous electrolyte, a solvent in which ethylene carbonate (EC), ethyl methyl carbonate (EMC), and dimethyl carbonate (DMC) are mixed at a volume ratio of 3: 4: 3, LiPF ₆ as a supporting salt is 1 What was contained so that it might become 0.0 mol / L was used. The negative electrode sheet was accommodated in a bag-like polyethylene separator, and the opening end of the separator was pressed and heated on the current collector for welding. The negative electrode sheet accommodated in the separator and the positive electrode sheet were laminated, and the laminate was wound and accommodated in a cylindrical battery container together with the non-aqueous electrolyte. Then, the opening part of this battery container was sealed airtight, and the lithium secondary battery provided with the electrode structure of the structure shown to FIG.

(Charge / discharge measurement)
The manufactured battery was charged and discharged for 5 cycles with an upper limit of 4.1 V and a lower limit of 3.0 V at a current of 1.5 C. After adjusting the battery to a charged state of 60% of the battery capacity (SOC = 60%), a current of 0.2 A, 0.5 A, 1 A, 1.5 A, 3 A was passed at a measurement temperature of 25 ° C., and 10 seconds later The battery voltage of was measured. The applied current and voltage were linearly approximated, and the IV resistance, that is, the internal resistance of the battery was obtained from the slope.

(Measurement results and discussion)
With respect to the positive electrode active material layer of the positive electrode sheet and the negative electrode active material layer of the negative electrode sheet, the pore distribution was measured using a nitrogen adsorption / desorption measuring machine. FIG. 7 is a pore distribution curve of the positive electrode active material layer and the negative electrode active material layer. As shown in FIG. 7, the negative electrode pore distribution tended to be larger than that of the positive electrode. Therefore, it was expected that at least if the negative electrode composite material layer of the negative electrode sheet is wrapped with a separator, the movement of the non-aqueous electrolyte can be further suppressed and the increase in internal resistance can be further suppressed. Moreover, when the produced lithium secondary battery was charged and discharged at a high rate, it was found that the increase in the internal resistance of the battery could be further suppressed as compared with a battery in which the negative electrode mixture layer was not wrapped with a separator. The reason for this could be determined to be that the non-aqueous electrolyte was difficult to move from the inside of the electrode structure.

  The present invention can be used in the technical field related to the manufacture of secondary batteries.

10 lithium secondary battery, 11, 11B, 11C electrode structure, 13, 13C current collector, 14 positive electrode mixture layer, 15 positive electrode sheet, 16, 16C current collector, 17 negative electrode mixture layer, 18 negative electrode sheet, 20 Non-aqueous electrolyte, 21 cylindrical case, 22 positive terminal, 23 negative terminal, 24 separator, 25 binding part, 26 separator, 27 binding part, 28 non-forming area, 29 non-forming area, 30 manufacturing device, 32 welding tip 34 Roller.

Claims (9)

Used for secondary batteries with non-aqueous electrolyte,
A positive electrode sheet comprising a positive electrode active material and a current collector;
A negative electrode sheet comprising a negative electrode active material and a current collector;
An electrode structure in which a separator interposed between the positive electrode sheet and the negative electrode sheet is laminated,
In the negative electrode sheet, the separator is sealed so that the negative electrode active material is contained by the separator and the non-aqueous electrolyte is difficult to come out.
Electrode structure.   The separator is a bag-like separator in which the end portions of the separator that overlap each other after being folded are welded, the negative electrode sheet is accommodated, and the end portion that overlaps the current collector of the negative electrode sheet is the current collector The electrode structure according to claim 1, wherein the electrode structure is welded and sealed.   The electrode structure according to claim 1, wherein the negative electrode sheet is wound and sealed while welding the separator while being sandwiched between the separators.   The electrode structure according to any one of claims 1 to 3, wherein the positive electrode sheet includes the positive electrode active material and the separator is sealed so that the non-aqueous electrolyte is difficult to come out. .   The separator is a bag-like separator in which the end portions of the separator that overlap each other after being folded are welded, the positive electrode sheet is accommodated, and the end portion that overlaps the current collector of the positive electrode sheet is the current collector The electrode structure according to claim 4, wherein the electrode structure is sealed by welding.   The electrode structure according to claim 4 or 5, wherein the positive electrode sheet is wound and sealed while welding the separator while being sandwiched between the separators.   The said separator is an electrode structure of any one of Claims 1-6 sealed over the whole region of an edge part.   The electrode structure according to claim 1, wherein the positive electrode sheet, the negative electrode sheet, and the separator are wound in a stacked state. The electrode structure according to any one of claims 1 to 8, comprising the positive electrode active material that absorbs and releases lithium and the negative electrode active material;
A lithium secondary battery comprising: a nonaqueous electrolytic solution that is interposed between the positive electrode sheet and the negative electrode sheet and conducts lithium ions.

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