JP5082221B2 - Negative electrode for secondary battery and secondary battery - Google Patents

Description

The present invention relates to a negative electrode and a secondary battery for a secondary battery using the graphite material.

  In recent years, many portable electronic devices such as a camera-integrated VTR (videotape recorder), a mobile phone, or a portable computer have appeared, and their size and weight have been reduced. Accordingly, the development of batteries, particularly secondary batteries, has been actively promoted as portable power sources for electronic devices. Among these, lithium ion secondary batteries are attracting attention as being capable of realizing a high energy density.

On the other hand, the lithium ion secondary battery has a high voltage, the positive electrode has a very noble oxidation potential, and the negative electrode has a very low reduction potential. There was a problem that the water solvent was decomposed and gas was generated. Therefore, conventionally, it has been studied to introduce a carbon material having a high specific surface area as a gas absorbing material into a battery regardless of whether it is a primary battery or a secondary battery (see, for example, Patent Documents 1 and 2). Moreover, although not as a gas absorption material, mixing and using a some carbon material is also examined (for example, refer patent documents 3-7).
Japanese Patent No. 30670080 JP-A-8-24637 Japanese Patent No. 3216661 JP-A-6-111818 JP 2001-196095 A JP 2002-8655 A Japanese Patent Laid-Open No. 2004-87437

  However, when activated carbon or the like having a high gas absorption capacity is added to the battery, there is a problem that side reactions occur in the battery and battery characteristics such as capacity are deteriorated.

The present invention has been made in view of the above problems, and its object is suppresses the blister is to provide a negative electrode and a secondary battery for a secondary battery cell characteristics can be improved, such as capacity .

A negative electrode for a secondary battery according to the present invention includes a negative electrode active material in which a film made of carboxymethylcellulose ammonium salt is formed on at least a part of a graphite material, and a negative electrode active material layer containing mesocarbon microbeads as another negative electrode active material The graphite material is natural graphite, the average interplanar spacing d002 of the (002) plane of hexagonal crystal determined by X-ray diffraction method is 0.3370 nm or less, and rhombohedral crystal by X-ray diffraction method The ratio of the negative electrode active material on which the film in the negative electrode active material layer was formed and the other negative electrode active material (negative electrode active material on which the film was formed: other negative electrode active material) ) is a mass ratio of 5: 95 to 50: in the range of 50, the negative electrode active material layer, upon dropping propylene carbonate 5μl at 23 ° C., the contact angle is 14 degrees after 0.1 seconds And it has a liquid absorbing property of the bottom.

A secondary battery according to the present invention includes an electrolyte together with a positive electrode and a negative electrode, and the negative electrode is a mesocarbon as another negative electrode active material together with a negative electrode active material in which a film made of carboxymethylcellulose ammonium salt is formed on at least a part of the graphite material A negative electrode active material layer containing microbeads , the graphite material is natural graphite, an average interplanar spacing d002 of (002) planes of hexagonal crystal obtained by X-ray diffraction method is 0.3370 nm or less, and The peak attributed to the (101) plane of rhombohedral crystal was obtained by X-ray diffraction method, and the ratio of the negative electrode active material on which the film in the negative electrode active material layer was formed to the other negative electrode active material (the film was formed negative electrode active material: other anode active material) is a mass ratio of 5: 95 to 50: in the range of 50, the negative electrode active material layer, dropping propylene carbonate 5μl at 23 ° C. When the, and has a liquid absorbing property of the contact angle after 0.1 sec is equal to or less than 14 degrees.

According to the negative electrode for a secondary battery and the secondary battery of the present invention, a negative electrode active material in which a film made of carboxymethylcellulose ammonium salt is formed on at least a part of a graphite material, and mesocarbon microbeads as another negative electrode active material. While containing at a predetermined ratio and having the above-mentioned liquid absorption characteristics, while suppressing side reactions, the capacity can be improved, and gas generated by side reactions and the like can be absorbed to swell. Can be suppressed.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

  FIG. 1 shows a configuration of a secondary battery according to an embodiment of the present invention. This secondary battery uses lithium as an electrode reactant, and includes a wound electrode body 20 to which a positive electrode terminal 11 and a negative electrode terminal 12 are attached inside a film-shaped exterior member 30.

  The positive electrode terminal 11 and the negative electrode terminal 12 are each led out from the inside of the exterior member 30 to the outside, for example, in the same direction. The positive electrode terminal 11 and the negative electrode terminal 12 are made of, for example, a metal material such as aluminum, copper (Cu), nickel (Ni), or stainless steel, and have a thin plate shape or a mesh shape, respectively.

  The exterior member 30 is made of, for example, a rectangular aluminum laminated film in which a nylon film, an aluminum foil, and a polyethylene film are bonded together in this order. The exterior member 30 is disposed, for example, so that the polyethylene film side and the wound electrode body 20 face each other, and the outer edge portions are in close contact with each other by fusion or an adhesive. An adhesive film 31 for preventing the entry of outside air is inserted between the exterior member 30 and the positive electrode terminal 11 and the negative electrode terminal 12. The adhesion film 31 is made of a material having adhesion to the positive electrode terminal 11 and the negative electrode terminal 12, for example, a polyolefin resin such as polyethylene, polypropylene, modified polyethylene, or modified polypropylene.

  The exterior member 30 may be constituted by another aluminum laminate film in which an aluminum foil is sandwiched between other polymer films, a laminate film having another structure, a polymer film such as polypropylene, or a metal. You may make it comprise with a film.

  FIG. 2 shows a cross-sectional structure taken along line II-II of the spirally wound electrode body 20 shown in FIG. The wound electrode body 20 is obtained by laminating a positive electrode 21 and a negative electrode 22 via a separator 23 and an electrolyte 24 and winding them, and the outermost periphery is protected by a protective tape 25.

  The positive electrode 21 includes, for example, a positive electrode current collector 21A having a pair of opposed surfaces, and a positive electrode active material layer 21B provided on both surfaces of the positive electrode current collector 21A. The positive electrode current collector 21A has an exposed portion where the positive electrode active material layer 21B is not provided at one end in the longitudinal direction, and the positive electrode terminal 11 is attached to the exposed portion. The positive electrode current collector 21A is made of, for example, a metal foil such as an aluminum foil, a nickel foil, or a stainless steel foil. The positive electrode active material layer 21B includes, for example, any one or more of positive electrode materials capable of inserting and extracting lithium as a positive electrode active material, and a conductive material and a binder as necessary. May be included.

Examples of the positive electrode material capable of inserting and extracting lithium include lithium such as titanium sulfide (TiS ₂ ), molybdenum sulfide (MoS ₂ ), niobium selenide (NbSe ₂ ), and vanadium oxide (V ₂ O ₅ ). A chalcogenide containing no lithium, a lithium composite oxide containing lithium or a lithium-containing phosphate compound, or a polymer compound such as polyacetylene or polypyrrole.

Among them, a lithium composite oxide containing lithium and a transition metal element or a lithium-containing phosphoric acid compound containing lithium and a transition metal element is preferable because it can obtain a high voltage and a high energy density. A metal element containing at least one of cobalt (Co), nickel, manganese (Mn) and iron (Fe) is preferable. The chemical formula is represented by, for example, Li _x MIO ₂ or Li _y MIIPO ₄ . In the formula, MI and MII represent one or more transition metal elements. The values of x and y vary depending on the charge / discharge state of the battery, and are generally 0.05 ≦ x ≦ 1.10 and 0.05 ≦ y ≦ 1.10.

Specific examples include lithium cobalt composite oxide (Li _x CoO ₂ ), lithium nickel composite oxide (Li _x NiO ₂ ), lithium nickel cobalt composite oxide (Li _x Ni _1-z Co _z O ₂ (z <1). )), Lithium manganese composite oxide (LiMn ₂ O ₄ ) having a spinel structure, lithium iron phosphate compound (Li _y FePO ₄ ), or lithium iron manganese phosphate compound (Li _y Fe _1-v Mn _v PO ₄₎ (V <1)).

  Examples of the conductive material include carbon materials such as graphite, carbon black, and ketjen black, and one or more of them are used in combination. In addition to the carbon material, a metal material or a conductive polymer material may be used as long as it is a conductive material. Examples of the binder include synthetic rubbers such as styrene butadiene rubber, fluorine rubber or ethylene propylene diene rubber, or polymer materials such as polyvinylidene fluoride, and one or more of them are mixed. Used.

  The negative electrode 22 includes, for example, a negative electrode current collector 22A having a pair of opposed surfaces and a negative electrode active material layer 22B provided on both surfaces of the negative electrode current collector 22A. The negative electrode current collector 22A also has an exposed portion where the negative electrode active material layer 22B is not provided at one end in the longitudinal direction, and the negative electrode terminal 12 is attached to the exposed portion. The negative electrode current collector 22A is made of, for example, a metal foil such as a copper foil, a nickel foil, or a stainless steel foil.

  The negative electrode active material layer 22B includes, for example, any one or two or more negative electrode materials capable of inserting and extracting lithium as a negative electrode active material. A binder may be included. As the conductive material and the binder, the same materials as those described for the positive electrode 21 can be used.

  Examples of the anode material capable of inserting and extracting lithium include a carbon material, a material containing a metal element or a metalloid element capable of forming an alloy with lithium as a constituent element, a metal oxide, or a polymer compound. . Examples of the carbon material include graphitizable carbon, non-graphitizable carbon having a (002) plane spacing of 0.37 nm or more, or graphite having a (002) plane spacing of 0.340 nm or less. May be artificial graphite or natural graphite. Examples of a material containing a metal element or metalloid element capable of forming an alloy with lithium as a constituent element include, for example, a simple substance, an alloy, or a compound of a metal element capable of forming an alloy with lithium, or a metal element capable of forming an alloy with lithium. Examples include simple substances, alloys, or compounds of metal elements, or materials having at least a part of one or more of these phases, particularly those containing silicon (Si) or tin (Sn) as a constituent element. preferable. Examples of the metal oxide include iron oxide, ruthenium oxide, and molybdenum oxide. Examples of the polymer compound include polyacetylene and polypyrrole.

  Among these, in this embodiment, the average interplanar spacing d002 of the hexagonal (002) plane obtained by the X-ray diffraction method is 0.3370 nm or less, and the rhombohedral (101) plane is determined by the X-ray diffraction method. The negative electrode active material which formed the film which consists of a high molecular compound in at least one part of the graphite material from which the peak which belongs to is obtained is contained. This is because such a graphite material can obtain a high capacity and can absorb the gas generated in the battery. In addition, by providing a coating made of a polymer compound on at least a part of the graphite material, the active sites such as dangling bonds existing on the surface of the graphite material are blocked, and the decomposition of the electrolytic solution or the capture of lithium ions is suppressed. This is because a decrease in capacity can be suppressed. Examples of the graphite material having such characteristics include natural graphite.

As the polymer compound coating the graphite material, for example, derivatives of starch and C ₆ H ₁₀ O ₅ as a basic structure, C ₆ H ₁₀ O ₅ a viscous polysaccharide having a basic structure, a C ₆ H ₁₀ O ₅ Examples thereof include water-soluble cellulose derivatives, polyuronides, and water-soluble synthetic resins having a basic structure. The coating amount of the polymer compound is preferably in the range of 0.1% by mass to 5% by mass with respect to the graphite material. This is because if the coating amount is small, a sufficient effect cannot be obtained, and if the coating amount is large, the movement of lithium ions is hindered and the conductivity of the electrode is further lowered.

The specific surface area of the negative electrode active material in which a film is formed on the graphite material is preferably 3.5 m ² / g or less. This is because if the specific surface area is too large, decomposition of the electrolytic solution or capture of lithium ions cannot be sufficiently suppressed. Moreover, it is preferable that the specific surface area of the negative electrode active material which formed the film in this graphite material is 1 m < ² > / g or more. This is because if the specific surface area is too small, the reactivity decreases, and the capacity and gas absorption capacity decrease.

  For example, as shown in FIG. 3, the negative electrode active material layer 22B has a contact angle θ of 14 ° C. or less after 0.1 seconds when 5 μl of propylene carbonate droplet P is dropped at 23 ° C. It has a liquid absorption characteristic. This is because the electrolyte solution penetrates quickly and uniformly into the negative electrode active material layer 22B, so that the lithium ion acceptability of the negative electrode active material layer 22B can be improved, and the capacity and gas absorption ability can be improved.

  Note that the permeability of the electrolytic solution with respect to the negative electrode active material layer 22B can be adjusted, for example, by selecting the type of the polymer compound that coats the graphite material. Moreover, you may make it adjust by controlling the distribution state of the space | gap in the negative electrode active material layer 22B. This is because if the voids are uniformly and continuously distributed throughout, the permeability can be increased. In order to distribute the voids uniformly and continuously, for example, in addition to the negative electrode active material coated with the above-described graphite material, it is preferable to mix and use other negative electrode active materials. Since the above-mentioned graphite material is flat and soft, the crystal plane is likely to be aligned in parallel with the current collector direction during press molding. Therefore, with such a negative electrode active material alone, the electrolyte solution penetrates between the negative electrode active material particles. This is because voids are likely to disappear and large voids are easily distributed intermittently. The other negative electrode active material to be mixed is preferably hard artificial graphite having a high circularity such as mesocarbon microbeads and acting as a filler during press molding.

  The separator 23 has a high ion permeability and a predetermined mechanical strength, such as a porous film made of a polyolefin-based synthetic resin such as polypropylene or polyethylene, or a porous film made of an inorganic material such as a ceramic nonwoven fabric. It is comprised by the insulating thin film which has, and may be set as the structure which laminated | stacked these 2 or more types of porous films.

  The electrolyte 24 is constituted by a so-called gel electrolyte in which an electrolytic solution is held in a polymer compound. The electrolyte 24 may be impregnated in the separator 23, or may exist between the separator 23 and the positive electrode 21 and the negative electrode 22.

  The electrolytic solution includes, for example, a solvent and an electrolyte salt dissolved in the solvent. Examples of the solvent include lactone solvents such as γ-butyrolactone, γ-valerolactone, δ-valerolactone, and ε-caprolactone, ethylene carbonate, propylene carbonate, butylene carbonate, vinylene carbonate, dimethyl carbonate, ethyl methyl carbonate, or diethyl carbonate. Carbonate ester solvents such as 1,2-dimethoxyethane, 1-ethoxy-2-methoxyethane, 1,2-diethoxyethane, ether solvents such as tetrahydrofuran or 2-methyltetrahydrofuran, nitrile solvents such as acetonitrile, Nonaqueous solvents such as sulfolane-based solvents, phosphoric acids, phosphate ester solvents, or pyrrolidones are mentioned. Any one type of solvent may be used alone, or two or more types may be mixed and used.

Any electrolyte salt may be used as long as it dissolves in a solvent to generate ions, and one kind may be used alone, or two or more kinds may be used in combination. For example, in the case of a lithium salt, lithium hexafluorophosphate (LiPF ₆ ), lithium tetrafluoroborate (LiBF ₄ ), lithium hexafluoroarsenate (LiAsF ₆ ), lithium perchlorate (LiClO ₄ ), trifluoro Lithium methanesulfonate (LiCF ₃ SO ₃ ), bis (trifluoromethanesulfonyl) imidolithium (LiN (SO ₂ CF ₃ ) ₂ ), tris (trifluoromethanesulfonyl) methyllithium (LiC (SO ₂ CF ₃ ) ₃ ), four Examples thereof include lithium chloroaluminate (LiAlCl ₄ ) and lithium hexafluorosilicate (LiSiF ₆ ).

  Preferred examples of the polymer compound include a polymer of vinylidene fluoride such as polyvinylidene fluoride containing the structural unit shown in Chemical Formula 1 or a copolymer of vinylidene fluoride and hexafluoropropylene. This is because the redox stability is high.

  Examples of the polymer compound include those formed by polymerizing a polymerizable compound. Examples of the polymerizable compound include those containing a vinyl group or a group obtained by substituting a part of hydrogen with a substituent such as a methyl group. Specifically, monofunctional acrylates such as acrylic acid esters, monofunctional methacrylates such as methacrylic acid esters, polyfunctional acrylates such as diacrylic acid esters or triacrylic acid esters, and polyfunctional acrylates such as dimethacrylic acid esters or trimethacrylic acid esters. There are functional methacrylate, acrylonitrile, methacrylonitrile, and the like. Among them, an ester having an acrylate group or a methacrylate group is preferable. This is because the polymerization proceeds easily and the reaction rate of the polymerizable compound is high. Moreover, as a polymeric compound, what does not contain an ether group is preferable. This is because if an ether group is present, lithium ions are coordinated to the ether group, thereby reducing the ionic conductivity. Examples of such a polymer compound include polyacrylic acid ester, polymethacrylic acid ester, polyacrylonitrile, or polymethacrylonitrile containing the structural unit shown in Chemical Formula 2.

（式中、Ｒ１は、Ｃ_j Ｈ_2j-1Ｏ_k を表す。ｊ，ｋは、１≦ｊ≦８，０≦ｋ≦４の範囲内の整数である。）

(In the formula, R1 represents C _j H _2j-1 O _k. J and k are integers in the range of 1 ≦ j ≦ 8, 0 ≦ k ≦ 4.)

  Any one of the polymerizable compounds may be used alone, but it is desirable to mix a monofunctional compound and a polyfunctional compound, or to use a polyfunctional compound singly or in combination of two or more. . This is because such a configuration makes it easy to achieve both the mechanical strength of the polymer compound formed by polymerization and the electrolyte solution retention.

  Furthermore, the thing which has a structure which polymerized at least 1 sort (s) of the high molecular compound from the group which consists of polyvinyl acetal and its derivative (s) is mentioned preferably.

  The polyvinyl acetal includes a structural unit containing an acetal group shown in Chemical Formula 3 (1), a structural unit containing a hydroxyl group shown in Chemical Formula 3 (2), and a structural unit containing an acetyl group shown in Chemical Formula 3 (3) In a repeating unit. Specifically, for example, R2 is hydrogen polyvinyl formal shown in Chemical Formula 3 (1), or R2 is propyl group polyvinyl butyral.

（Ｒ２は水素原子もしくは炭素数１〜３のアルキル基を表す。）

(R2 represents a hydrogen atom or an alkyl group having 1 to 3 carbon atoms.)

  The ratio of the acetal group in the polyvinyl acetal is preferably in the range of 60 mol% to 80 mol%. This is because the solubility with the solvent can be improved within this range, and the stability of the electrolyte can be further increased. Moreover, it is preferable that the weight average molecular weight of polyvinyl acetal exists in the range of 10,000 or more and 500,000 or less. This is because if the molecular weight is too low, the polymerization reaction does not proceed easily, and if it is too high, the viscosity of the electrolytic solution increases.

  The polymer compound may be a polymer obtained by polymerizing only polyvinyl acetal or one of its derivatives, or a polymer obtained by polymerizing two or more of them, and a copolymer with monomers other than polyvinyl acetal and its derivatives. But you can. Moreover, what was polymerized with the crosslinking agent may be used.

  The electrolyte 24 may be used as it is as a liquid electrolyte without holding the electrolytic solution in the polymer compound. In this case, the electrolytic solution is impregnated in the separator 23.

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

  First, for example, the positive electrode active material layer 21B is formed on the positive electrode current collector 21A to produce the positive electrode 21. The positive electrode active material layer 21B is prepared, for example, by mixing a positive electrode active material powder, a conductive material, and a binder to prepare a positive electrode mixture, and then using the positive electrode mixture in a solvent such as N-methyl-2-pyrrolidone. The positive electrode mixture slurry is dispersed to form a positive electrode mixture slurry, and the positive electrode mixture slurry is applied to the positive electrode current collector 21A, dried, and compression molded. Further, for example, in the same manner as the positive electrode 21, the negative electrode active material layer 22 </ b> B is formed on the negative electrode current collector 22 </ b> A to produce the negative electrode 22.

  Next, the positive electrode terminal 11 is attached to the positive electrode current collector 21A, and the negative electrode terminal 12 is attached to the negative electrode current collector 22A. Subsequently, the positive electrode 21 and the negative electrode 22 are laminated via the separator 23, wound in the longitudinal direction, and a protective tape is adhered to the outermost peripheral portion, thereby producing a wound body that is a precursor of the wound electrode body 20. . After that, the wound body is sandwiched between the exterior members 30, and the outer peripheral edge of the exterior member 30 is heat-sealed except for one side, and an electrolyte composition containing an electrolyte and a monomer that is a raw material for the polymer compound is obtained. inject. Next, after the remaining one side of the exterior member 30 is heat-sealed and sealed, the monomer is polymerized to form the electrolyte 24. Thereby, the secondary battery shown in FIGS. 1 and 2 is obtained.

  Further, instead of injecting the electrolyte composition into the exterior member 30 and polymerizing the monomer to form the electrolyte 24, the positive electrode 21 and the negative electrode 22 are produced, and then the electrolytic solution and the polymer compound are formed thereon. The electrolyte 24 may be formed, wound around the separator 23, and sealed in the exterior member 30.

  Further, when an electrolytic solution is used as the electrolyte 24, the wound body is produced as described above and sandwiched between the exterior members 30, and then the electrolytic solution is injected to seal the exterior member 30.

  In the secondary battery, when charged, for example, lithium ions are extracted from the positive electrode 21 and inserted in the negative electrode 22 through the electrolyte 24. On the other hand, when discharging is performed, for example, lithium ions are extracted from the negative electrode 22 and inserted in the positive electrode 21 through the electrolyte 24. At this time, since the negative electrode active material layer 22B contains the negative electrode active material coated with the above-described graphite material, a high capacity is obtained, side reactions are suppressed, and the generated gas is also absorbed. Furthermore, since the negative electrode active material layer 22B has the liquid absorption characteristics as described above, the lithium ion acceptability of the negative electrode active material layer 22B is improved, and the capacity and gas absorption ability are further improved.

  As described above, according to the present embodiment, the negative electrode active material layer 22B contains the negative electrode active material coated with the graphite material and has the above-described liquid absorption characteristics. In addition, the gas generated by a side reaction or the like can be absorbed, and swelling can be suppressed.

  Further, specific embodiments of the present invention will be described in detail.

( Experimental Examples 1-1 to 1-4)
A secondary battery using the film-shaped exterior member shown in FIGS.

First, 0.5 mol of lithium carbonate and 1 mol of cobalt carbonate were mixed, and this mixture was fired in air at 900 ° C. for 5 hours to synthesize a lithium cobalt composite oxide (LiCoO ₂ ) as a positive electrode active material. Subsequently, 85% by mass of this lithium cobalt composite oxide powder, 5% by mass of artificial graphite as a conductive material, and 10% by mass of polyvinylidene fluoride as a binder were prepared, and then a positive electrode mixture was prepared. A positive electrode mixture slurry was prepared by dispersing in N-methyl-2-pyrrolidone. Subsequently, this positive electrode mixture slurry was applied to both surfaces of a positive electrode current collector 21A made of an aluminum foil having a thickness of 20 μm and dried, and then compression molded to form a positive electrode active material layer 21B, whereby the positive electrode 21 was produced. After that, the positive electrode terminal 11 was attached to the positive electrode 21.

Further, a negative electrode active material in which a polymer compound film was formed on at least a part of natural graphite was produced. Specifically, it was prepared by dissolving a polymer compound in water, adding and mixing natural graphite particles therein, and then precipitating, drying and pulverizing the precipitate. A polymer compound with a carboxymethylcellulose ammonium salt in Examples 1-1, using sodium carboxymethylcellulose in Examples 1-2, using propylene glycol alginate in Examples 1-3 and 1-4. When the obtained negative electrode active material was observed with a scanning electron microscope (SEM), it was confirmed that a polymer compound adhered or coated on at least a part of the natural graphite particles. Further, when qualitative analysis was performed on the used natural graphite by X-ray diffraction, the average interplanar spacing d002 of the hexagonal (002) plane was 0.3370 nm or less and the rhombohedral (101) plane was found. An attributed peak was obtained.

Further, in Experimental Examples 1-1 to 1-4, the specific surface area of the negative electrode active material was changed by changing the polymer compound covering the natural graphite. When the specific surface area of each of the obtained negative electrode active materials was measured, Experimental Example 1-1 was 3.6 m ² / g, Experimental Examples 1-2 and 1-3 were 3.5 m ² / g, and Experimental Example 1-4. Was 3.2 m ² / g. The specific surface area was estimated by the BET (Brunauer Emmett Teller) one-point method using nitrogen and nitrogen helium mixed gas as a carrier and reference.

Using these prepared negative electrode active materials, 95% by mass of this negative electrode active material powder and 5% by mass of polyvinylidene fluoride as a binder were mixed to prepare a negative electrode mixture, and then N-methyl as a solvent. A negative electrode mixture slurry was prepared by dispersing in -2-pyrrolidone. Next, this negative electrode mixture slurry was applied to both surfaces of a negative electrode current collector 22A made of a copper foil having a thickness of 15 μm and dried, and then compression molded to form a negative electrode active material layer 22B, whereby a negative electrode 22 was produced. About the produced negative electrodes 22 of Experimental Examples 1-1 to 1-4, 5 μl of propylene carbonate was dropped onto the negative electrode active material layer 22B at 23 ° C., and the contact angle θ of the propylene carbonate droplets P after 0.1 seconds was measured. As a result, Experimental Example 1-1 was 14 degrees, Experimental Examples 1-2 and 1-3 were 12 degrees, and Experimental Example 1-4 was 10 degrees.

  Subsequently, after attaching the negative electrode terminal 12 to the negative electrode 22, the prepared positive electrode 21 and negative electrode 22 are closely attached via a separator 23 made of a microporous polyethylene film having a thickness of 25 μm, and wound in the longitudinal direction. Was made. After that, the produced wound body was loaded between the exterior members 30, and the outer peripheral edge of the exterior member 30 was heat-sealed except for one side. The exterior member 30 was a moisture-proof aluminum laminate film in which a 25 μm thick nylon film, a 40 μm thick aluminum foil, and a 30 μm thick polypropylene film were laminated in order from the outermost layer.

  Next, an exterior member is prepared by dissolving an electrolytic solution in which lithium hexafluorophosphate is dissolved at a concentration of 1 mol / l in a solvent in which ethylene carbonate and diethyl carbonate are mixed at a mass ratio of ethylene carbonate: diethyl carbonate = 3: 7. The secondary battery was obtained by injecting into the interior of 30 and thermally fusing the remaining one side of the exterior member 30.

Further, as Comparative Example 1-1 with respect to Experimental Examples 1-1 to 1-4, instead of using a negative electrode active material coated with natural graphite, it was used as a negative electrode active material without forming a film on natural graphite. Otherwise, secondary batteries were fabricated in the same manner as in Experimental Examples 1-1 to 1-4. As Comparative Example 1-2, except that it was directly used as a negative electrode active material without forming a film on mesocarbon microbeads, which are artificial graphite, secondary conditions were the same as in Experimental Examples 1-1 to 1-4. A battery was produced. As Comparative Examples 1-3 to 1-7, secondary batteries were fabricated in the same manner as in Experimental Examples 1-1 to 1-4 except that the type of the polymer compound to be coated was changed.

For Comparative Examples 1-1 to 1-7, the specific surface area of the negative electrode active material and the liquid absorption characteristics of the negative electrode active material layer 22B were measured in the same manner as in Experimental Examples 1-1 to 1-4. The specific surface area of the negative electrode active material of Comparative Example 1-1 is 4.2 m ² / g, Comparative Example 1-2 0.6 m ² / g, Comparative Example 1-3 and 1-4 are 3.8 m ² / g Comparative Examples 1-5 and 1-6 were 3.7 m ² / g, and Comparative Example 1-7 was 3.6 m ² / g. The contact angle θ of the propylene carbonate droplet P after 0.1 seconds was 18 degrees in Comparative Example 1-1, 16 degrees in Comparative Example 1-2, 17 degrees in Comparative Examples 1-3 and 1-4, and Comparative Example 1 −5 was 16 degrees, and Comparative Examples 1-6 and 1-7 were 15 degrees. Further, when the artificial graphite used in Comparative Example 1-2 was subjected to qualitative analysis by X-ray diffraction, the average interplanar spacing d002 of the hexagonal (002) plane was 0.3370 nm or less, and rhombohedral crystals The two requirements for obtaining a peak attributed to the (101) plane were not satisfied.

About the produced secondary battery of Experimental example 1-1 to 1-4 and Comparative example 1-1 to 1-7, it charged / discharged at 23 degreeC, and calculated | required the rated capacity and the discharge capacity maintenance factor of the 300th cycle. Charging was performed at a constant current and constant voltage of 100 mA for 15 hours up to an upper limit of 4.2 V, and discharging was performed at a constant current of 100 mA up to a final voltage of 2.5 V. The rated capacity was the discharge capacity at the first cycle, and the discharge capacity at the 300th cycle was determined by the ratio of the discharge capacity at the 300th cycle to the rated capacity, (discharge capacity at the 300th cycle / rated capacity) × 100.

  In addition, for each secondary battery that was charged and discharged for the first time under the above-described conditions separately, after measuring the thickness of the battery, it was charged again to 4.31 V for 3 hours and stored in a thermostatic bath at 60 ° C. for 1 month. The thickness of the battery after storage was measured. A value obtained by subtracting the battery thickness before storage from the battery thickness after storage was determined as the swelling after storage. The obtained results are shown in Table 1.

As shown in Table 1, according to Experimental Examples 1-1 to 1-4, compared with Comparative Example 1-1 in which a film was not formed on natural graphite, the discharge capacity retention rate was significantly improved and swollen. The amount has been greatly reduced, and the rated capacity has been improved. In addition, compared with Comparative Example 1-2 using artificial graphite, the discharge capacity retention rate was significantly improved, the amount of swelling was significantly reduced, and the rated capacity was also improved. Furthermore, even compared with Comparative Examples 1-3 to 1-7 using coated natural graphite, the discharge capacity retention rate and the rated capacity were improved, and the amount of swelling was the same or smaller.

  That is, the negative electrode active in which the average interplanar spacing d002 of the hexagonal (002) plane is 0.3370 nm or less and the graphite material in which a peak attributed to the (101) plane of rhombohedral crystal is obtained is coated with a polymer compound. When a material is used and when 5 μl of propylene carbonate is dropped onto the negative electrode active material layer 22B at 23 ° C., the contact angle after 0.1 seconds is 14 degrees or less, the capacity and cycle characteristics are improved. It was found that swelling could be suppressed.

( Experimental examples 2-1 and 2-2)
A secondary battery was fabricated in the same manner as in Experimental Example 1-4, except that mesocarbon microbeads, which are artificial graphite, were mixed and used in addition to natural graphite coated with the polymer compound. The mixing ratio of the coated natural graphite and mesocarbon microbeads was 5% by mass for coated natural graphite, 95% by mass for mesocarbon microbeads in Experimental Example 2-1, and the coated natural graphite in Experimental Example 2-2. Was 50 mass%, and mesocarbon microbeads were 50 mass%. The specific surface area of the mesocarbon microbeads used in Experimental Examples 2-1 and 2-2 is 0.6 m ² / g. For the negative electrodes 22 of Experimental Examples 2-1 and 2-2, 5 μl of propylene carbonate was dropped on the negative electrode active material layer 22B at 23 ° C., and the contact angle θ of the propylene carbonate droplet P after 0.1 seconds was measured. . As a result, both Experimental Example 2-1 and Experimental Example 2-2 were 10 degrees.

For the fabricated secondary batteries of Experimental Examples 2-1 and 2-2, the rated capacity, the discharge capacity maintenance ratio at the 300th cycle, and the swelling amount after storage were examined in the same manner as in Experimental Example 1-4. The obtained results are shown in Table 2 together with the results of Experimental Example 1-4.

As shown in Table 2, for the experimental examples 2-1 and 2-2 were mixed with other anode active material, in the same manner as in Experimental Example 1-4, to improve the discharge capacity retention ratio, swelling amount becomes small The rated capacity has also been improved. That is, it was found that if the negative electrode active material coated with the above-described graphite material is used, the same effect can be obtained even if other negative electrode active materials are mixed.

( Experimental examples 3-1 to 3-6)
A secondary battery was fabricated in the same manner as in Experimental Example 2-2 except that instead of the electrolytic solution, a gel electrolyte 24 in which the electrolytic solution was held in a polymer compound was used. At that time, in Experimental Example 3-1, a copolymer of vinylidene fluoride and hexafluoropropylene and an electrolytic solution are dissolved in a mixed solvent and applied to the positive electrode 21 and the negative electrode 22 to volatilize the mixed solvent. Thus, the electrolyte 24 was formed. As the electrolytic solution, a solution obtained by dissolving lithium hexafluorophosphate at a concentration of 1 mol / l in a solvent in which 60% by mass of ethylene carbonate and 40% by mass of propylene carbonate were mixed was used.

In Experimental Example 3-2, a polymerizable compound having three structural parts a, b, and c shown in Chemical Formula 4 at a molar ratio of a: b: c = 2: 3: 5 was used, and an electrolytic solution was used. And the electrolyte 24 was formed by polymerizing the polymerizable compound. The composition of the electrolytic solution is the same as in Experimental Example 2-2.

In Experimental Example 3-3, trimethylolpropane triacrylate shown in Chemical Formula 5 and neopentylglycol diacrylate shown in Chemical Formula 6 were used at a mass ratio of 3: 7 as a polymerizable compound, and mixed with the electrolytic solution. And after inject | pouring in the inside of the exterior member 30, the electrolyte 24 was formed by polymerizing a polymeric compound. The composition of the electrolytic solution is the same as in Experimental Example 2-2.

In Experimental Example 3-4, the compound shown in Chemical Formula 7 was used as the polymerizable compound, mixed with the electrolytic solution, injected into the exterior member 30, and then the polymerizable compound was polymerized to form the electrolyte 24. . The composition of the electrolytic solution is the same as in Experimental Example 2-2.

In Experimental Example 3-5, polyvinylidene fluoride was applied to the surface of the separator 23, a wound body was prepared and housed in the exterior member 30, and then the electrolyte 24 was formed by injecting an electrolytic solution. The composition of the electrolytic solution is the same as in Experimental Example 2-2.

In Experimental Example 3-6, after the polyvinyl formal and the electrolytic solution were mixed and injected into the exterior member 30, the electrolyte 24 was formed by polymerizing the polyvinyl formal. The composition of the electrolytic solution is the same as in Experimental Example 2-2.

As Comparative Examples 3-1 to 3-6 with respect to Experimental Examples 3-1 to 3-6, except that natural graphite without a film was used as the negative electrode active material, the other was Experimental Examples 3-1 to 3- In the same manner as in Example 6, a secondary battery was produced.

For Experimental Examples 3-1 to 3-6 and Comparative Examples 3-1 to 3-6, the liquid absorption characteristics of the negative electrode active material layer 22B, the rated capacity, and the 300th cycle were the same as in Experimental Example 2-2. The discharge capacity retention ratio and the swelling amount after storage were examined. The obtained results are shown in Table 3.

As shown in Table 3, according to Experimental Examples 3-1 to 3-6, compared with Comparative Examples 3-1 to 3-6, the discharge capacity retention rate is significantly improved, and the amount of swelling is also greatly reduced. The rated capacity has also been improved. That is, even when the so-called gel electrolyte 24 is used, the same effect can be obtained by using the above-described negative electrode active material coated with the graphite material and making the negative electrode active material layer 22B have the above-described liquid absorption characteristics. I found out that

  Although the present invention has been described with reference to the embodiments and examples, the present invention is not limited to the embodiments and examples, and various modifications can be made. For example, in the embodiments and examples described above, the case where an electrolytic solution is used as the electrolyte and the case where a gel electrolyte in which the electrolytic solution is held in a polymer compound are used have been described. However, other electrolytes may be used. . Examples of other electrolytes include ion conductive inorganic compounds such as organic solid electrolytes, ion conductive ceramics, ion conductive glasses, or ionic crystals in which electrolyte salts are dissolved or dispersed in polymer compounds having ion conductivity. Inorganic solid electrolytes to be included, or a mixture of these with an electrolyte solution.

  Moreover, although the said embodiment and Example demonstrated the case where the winding electrode body which wound the positive electrode 21 and the negative electrode 22 was provided in the exterior member 30, the positive electrode 21 and the negative electrode 22 were laminated | stacked by 1 layer or multiple layers. You may make it provide what was done.

  Further, in the above embodiments and examples, a battery using lithium as an electrode reactant has been described. However, another alkali metal such as sodium (Na) or potassium (K), or an alkali such as magnesium or calcium (Ca) is used. The present invention can also be applied to the case of using an earth metal or another light metal such as aluminum. In addition, the present invention is not limited to the secondary battery, and can be similarly applied to other batteries such as a primary battery.

It is a disassembled perspective view showing the structure of the secondary battery which concerns on one embodiment of this invention. It is sectional drawing along the II-II line of the winding electrode body shown in FIG. It is a figure for demonstrating the contact angle of a propylene carbonate droplet.

Explanation of symbols

DESCRIPTION OF SYMBOLS 11 ... Positive electrode terminal, 12 ... Negative electrode terminal, 20 ... Winding electrode body, 21 ... Positive electrode, 21A ... Positive electrode collector, 21B ... Positive electrode active material layer, 22 ... Negative electrode, 22A ... Negative electrode collector, 22B ... Negative electrode active Material layer, 23 ... separator, 24 ... electrolyte, 25 ... protective tape, 30 ... exterior member, 31 ... adhesion film.

Claims (8)

Along with the negative electrode active material in which a film made of carboxymethylcellulose ammonium salt is formed on at least a part of the graphite material, the negative electrode active material layer containing mesocarbon microbeads as another negative electrode active material ,
The graphite material is natural graphite, the average interplanar spacing d002 of the hexagonal (002) plane determined by the X-ray diffraction method is 0.3370 nm or less, and rhombohedral (101 ) The peak attributed to the surface is obtained,
The ratio of the negative electrode active material on which the film is formed and the other negative electrode active material in the negative electrode active material layer (negative electrode active material on which the film is formed: other negative electrode active material) is 5:95 by mass ratio. In the range of ~ 50: 50,
The negative electrode active material layer is a negative electrode for a secondary battery having a liquid absorption characteristic that a contact angle after 0.1 seconds is 14 degrees or less when 5 μl of propylene carbonate is dropped at 23 ° C. ^{2. The} negative electrode for a secondary battery according to claim 1, wherein the negative electrode active material on which the coating film is formed has a specific surface area of 3.5 m ² / g or less. With electrolyte together with positive and negative electrodes,
The negative electrode has a negative electrode active material layer containing mesocarbon microbeads as another negative electrode active material, together with a negative electrode active material in which a film made of carboxymethylcellulose ammonium salt is formed on at least a part of the graphite material,
The graphite material is natural graphite, the average interplanar spacing d002 of the hexagonal (002) plane determined by the X-ray diffraction method is 0.3370 nm or less, and rhombohedral (101 ) The peak attributed to the surface is obtained,
The ratio of the negative electrode active material on which the film is formed and the other negative electrode active material in the negative electrode active material layer (negative electrode active material on which the film is formed: other negative electrode active material) is 5:95 by mass ratio. In the range of ~ 50: 50,
The negative electrode active material layer is a secondary battery having a liquid absorption characteristic that when 5 μl of propylene carbonate is dropped at 23 ° C., the contact angle after 0.1 seconds becomes 14 degrees or less. The secondary battery according to claim 3 , wherein the negative electrode active material on which the film is formed has a specific surface area of 3.5 m ² / g or less. The secondary battery according to claim 3 , wherein the positive electrode, the negative electrode, and the electrolyte are housed inside a film-shaped exterior member. The secondary battery according to claim 3 , wherein the electrolyte includes an electrolytic solution and a polymer containing vinylidene fluoride as a component. The secondary battery according to claim 3 , wherein the electrolyte includes an electrolytic solution and a polymer having a structure in which a polymerizable compound having an acrylate group or a methacrylate group is polymerized. The secondary battery according to claim 3 , wherein the electrolyte includes an electrolytic solution and a polymer having a structure obtained by polymerizing at least one selected from the group consisting of polyvinyl acetal and derivatives thereof.

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