JP2006216276A - Lithium secondary battery and its manufacturing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a lithium secondary battery capable of enhancing energy density and a cycle life. <P>SOLUTION: This lithium secondary battery has a positive electrode, a negative electrode, and a nonaqueous electrolyte, and the nonaqueous electrolyte contains an electrolytic oxidation polymerizable monomer and an electrolytic reduction polymerizable monomer. In this lithium secondary battery having the positive electrode, the negative electrode, and the nonaqueous electrolyte, a voltage is impressed on the nonaqueous electrolyte containing the electrolytic oxidation polymerizable monomer and the electrolytic reduction polymerizable monomer, and a polymer obtained by polymerizing the electrolytic oxidation polymerizable monomer and the electrolytic reduction polymerizable monomer with at least either one of the positive electrode or the negative electrode is thereby formed. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a lithium secondary battery and a method for manufacturing the same, and more particularly, to improve a charge / discharge cycle characteristic of a secondary battery having a high energy density and to reduce an increase in internal impedance and the lithium secondary battery. The present invention relates to a battery manufacturing method.

Recently, since the amount of CO ₂ gas contained in the atmosphere is increasing, the possibility of global warming due to the room temperature effect has been pointed out. Thermal power plants convert thermal energy obtained by burning fossil fuels into electrical energy, but because of the large amount of CO ₂ gas emitted by combustion, new thermal power plants become difficult to construct. It is coming. Therefore, as an effective use of power generated by generators such as thermal power plants, surplus power is stored in secondary batteries installed in ordinary households and used in the daytime when power consumption is high. Level the load. So-called road leveling is being proposed.

In addition, for electric vehicle applications having a feature of not discharging substances related to air pollution including CO ₂ , NO _x , hydrocarbons, etc., development of secondary batteries with high energy density is expected. Furthermore, in the power supply applications of portable devices such as book-type personal computers, word processors, video cameras, and mobile phones, it is an urgent task to develop a compact, lightweight, high-performance secondary battery.

  As such a small, lightweight and high-performance secondary battery, a lithium intercalation compound that deintercalates lithium ions from the interlayer is used as a positive electrode material, and lithium ions are formed from carbon atoms. The development of a rocking chair type “lithium ion battery” using a carbon material typified by graphite, which can be intercalated between the layers of a six-membered ring network plane, as a negative electrode material has been developed and put into practical use. ing.

  However, in this “lithium ion battery”, a negative electrode composed of a carbon material can theoretically intercalate only a maximum of 1/6 lithium atoms per carbon atom. A secondary battery having a high energy density comparable to that of the primary battery cannot be realized. If a negative electrode made of carbon in a “lithium ion battery” is intercalated with a lithium amount greater than the theoretical amount during charging, or if charging is performed under conditions of high current density, lithium metal is dendrited on the surface of the carbon negative electrode. “Lithium ion battery” that grows in a (dendritic) shape and may eventually lead to an internal short circuit between the negative electrode and the positive electrode due to repeated charge and discharge cycles, and a sufficient cycle life can be obtained with a “lithium ion battery” exceeding the theoretical capacity of a graphite negative electrode Not.

  On the other hand, a high-capacity lithium secondary battery using metallic lithium as a negative electrode has attracted attention as a secondary battery exhibiting a high energy density, but has not yet been put into practical use. This is because the cycle life of charge / discharge is extremely short. The main causes of extremely short charge / discharge cycle life are that metal lithium reacts with impurities such as moisture in the electrolyte and an organic solvent to form an insulating film, or the surface of the metal lithium foil is not flat and the electric field is concentrated. It is considered that the lithium metal grows in a dendrite shape due to repeated charge and discharge due to this, causing an internal short circuit between the negative electrode and the positive electrode and reaching the life.

  In addition, when the above-mentioned lithium dendrite grows and the negative electrode and the positive electrode are short-circuited, the energy of the battery is consumed in the short-circuited portion in a short time, so that the battery generates heat or the solvent of the electrolyte solution It may decompose by heat to generate gas and increase the internal pressure in the battery. In any case, the growth of dendrites tends to cause damage to the battery and a decrease in life due to a short circuit.

  In order to suppress the progress of the reaction between metallic lithium and the water or organic solvent in the electrolytic solution, which is a problem of the secondary battery using the above metallic lithium negative electrode, there is a method using a lithium alloy composed of lithium and aluminum for the negative electrode. Proposed. However, in this case, since the lithium alloy is hard, it cannot be spirally wound, so that a spiral cylindrical battery cannot be produced, the cycle life is not sufficiently extended, and energy comparable to a battery using metallic lithium as a negative electrode. The current situation is that a wide range of practical applications has not been achieved because the density cannot be obtained sufficiently.

  In addition, the above-mentioned aluminum, cadmium, indium, tin, antimony, lead, bismuth, and the like are listed as the metal that forms an alloy with lithium at the time of charging. These metals, alloys made of these metals, and these Patent Documents 1 to 7 disclose secondary batteries using a metal-lithium alloy as a negative electrode.

  However, in the secondary batteries described in these patent documents, the shape of the negative electrode is not clearly shown, and the secondary battery (lithium as an active material) is used as a plate-like member including the above alloy material as a general shape of foil. When used as the negative electrode of the secondary battery, the surface area of the electrode material layer contributing to the battery reaction is small, and charging / discharging with a large current is difficult.

  Furthermore, in a secondary battery using the above alloy material as a negative electrode, volume expansion due to alloying with lithium during charging and contraction during discharge occur, and this volume change is large, and the electrode is distorted and cracks. When the charge / discharge cycle is repeated, pulverization occurs, the electrode impedance increases, and the battery cycle life is shortened.

In order to solve the above problems, the present inventors have proposed Patent Documents 8 to 13 as negative electrodes for lithium secondary batteries made of silicon or tin element.
Patent Document 8 uses a negative electrode in which a metal material that is not alloyed with lithium and an electrode layer formed of a metal that is alloyed with lithium such as silicon or tin and a metal that is not alloyed with nickel or copper is used. We have proposed a lithium secondary battery. In Patent Document 9, a negative electrode formed from an alloy powder of an element such as nickel or copper and an element such as tin is used. In Patent Document 10, particles made of silicon or tin having an average particle size of 0.5 to 60 μm are used. A lithium secondary battery using a negative electrode containing 35 wt% or more, having a porosity of 0.10 to 0.86 and a density of 1.00 to 6.56 g / cm ³ is proposed. Patent Document 11 proposes a lithium secondary battery using a negative electrode having silicon or tin having an amorphous phase. Patent Document 12 proposes a lithium secondary battery using a negative electrode made of non-stoichiometric amorphous tin-transition metal alloy particles. Patent Document 13 proposes a lithium secondary battery using a negative electrode made of non-stoichiometric amorphous silicon-transition metal alloy particles.

  However, in the above proposal, the efficiency of the amount of electricity associated with the release of lithium relative to the amount of electricity associated with lithium insertion has not been obtained to the same level as that of the graphite negative electrode, and further improvement in efficiency has been expected. Further, the proposed electrode has a higher resistance than the graphite electrode, and a reduction in resistance has been desired.

When using fine powder made of silicon as the electrode material for lithium secondary batteries or when using an insulating resin as the binder, the impedance of the electrode increases, the cycle life of the battery, and the initial charge / discharge Decreases the efficiency. In order to improve this, Patent Document 14 proposes polymerizing a conductive polymer monomer in a battery. However, the conductive polymer has poor flexibility, and the film formed by polymerization on the electrode surface is peeled off or polymerized into fine particles, so it is difficult to effectively coat the electrode material surface without forming a uniform film. . Depending on the concentration of the conductive polymer in the non-aqueous electrolyte and the current density at the time of electrolytic polymerization, the formed conductive polymer penetrates the separator and causes a short circuit. It is not done.
JP-A-8-64239 Japanese Patent Laid-Open No. 3-62464 JP-A-2-12768 Japanese Patent Laid-Open No. 62-113366 Japanese Patent Application Laid-Open No. Sho 62-15761 JP-A-62-93866 JP-A-54-78434 US Pat. No. 6,051,340 US Pat. No. 5,795,679 US Pat. No. 6,432,585 JP-A-11-283627 Japanese Unexamined Patent Publication No. 2000-311681 Japanese Patent Publication WO00 / 17949 JP 2001-135350 A

  The present invention reduces the internal resistance of the electrode structure and the lithium secondary battery, and further suppresses the increase of the internal resistance when charging and discharging are repeated, and the amount of electricity accompanying lithium insertion in the lithium secondary battery An object of the present invention is to provide a lithium secondary battery capable of improving the efficiency of the amount of electricity associated with lithium release and improving the energy density and cycle life, and a method for producing the same.

  That is, the present invention is a lithium secondary battery having a positive electrode, a negative electrode, and a nonaqueous electrolytic solution, wherein the nonaqueous electrolytic solution contains an electrolytic oxidation polymerization monomer and an electrolytic reduction polymerization monomer. It is a battery.

  Further, the present invention is a lithium secondary battery having a positive electrode, a negative electrode, and a nonaqueous electrolytic solution, and at least by applying a voltage to the nonaqueous electrolytic solution containing an electrolytic oxidation polymerization monomer and an electrolytic reduction polymerization monomer, The lithium secondary battery is characterized in that a polymer obtained by polymerizing the electrolytic oxidation polymerization monomer and the electrolytic reduction polymerization monomer is formed on either the positive electrode or the negative electrode.

  Furthermore, the present invention provides a method for producing a lithium secondary battery having a positive electrode, a negative electrode, and a nonaqueous electrolytic solution, wherein a voltage is applied from the positive electrode and the negative electrode to the nonaqueous electrolytic solution containing an electrolytic oxidation polymerization monomer and an electrolytic reduction polymerization monomer. Thus, a method for producing a lithium secondary battery, comprising a step of forming a polymer composed of the electrolytic oxidation polymerization monomer and the electrolytic reduction polymerization monomer on at least one of the positive electrode and the negative electrode.

  The present invention provides a lithium secondary battery capable of improving the energy density and cycle life by improving the efficiency of the amount of electricity associated with lithium release relative to the amount of electricity associated with lithium insertion in the lithium secondary battery, and a method for manufacturing the same. can do.

Hereinafter, the present invention will be described in detail.
The present invention relates to a non-aqueous electrolyte secondary battery comprising a positive electrode, a negative electrode made of lithium metal, a lithium alloy or a material capable of occluding and releasing lithium, and a non-aqueous electrolyte made of a solvent and a solute. The non-aqueous electrolyte contains both an electrolytic reduction polymerization monomer and an electrolytic oxidation polymerization monomer.

  The content of the electrolytic oxidation polymerization monomer contained in the non-aqueous electrolyte is 0.01 wt% or more and 10 wt% or less, preferably 0.05 to 5.0 wt%. The content of the electrolytic reduction polymerization monomer is 0.01 wt% or more and 10 wt% or less, preferably 0.05 to 5.0 wt%.

  In the present invention, the nonaqueous electrolytic solution contains both an electrolytic reduction polymerization monomer and an electrolytic oxidation polymerization monomer, and a voltage at which the monomer is polymerized is applied between the negative electrode and the positive electrode of the battery. Polymerization is performed on the surface of the electrode or electrode active material by polymerizing in the process of charge and discharge.

  Reduce the internal resistance of the electrode by coating the surface of the electrode material or electrode structure with both electrolytic oxidation polymer and electrolytic reduction polymer, and forming a conductive path on the electrode with the conductive polymer that is electrolytic oxidation polymer. It is possible to suppress the increase in resistance in the electrode when charging and discharging are repeated. Furthermore, the coating film made of a polymer formed on the surfaces of the positive electrode and the negative electrode active material suppresses direct contact between the active material and the electrolytic solution, and prevents reaction between Li and the electrolytic solution and elution of the positive electrode active material. Moreover, current concentration can be prevented from occurring. A conductive polymer obtained by polymerizing an electrolytic oxidation polymerization monomer has poor flexibility, and causes problems such as short circuit through the separator. However, by conducting simultaneous polymerization of electrolytic oxidation polymerization monomer and electrolytic reduction polymerization monomer. A more uniform, conductive and flexible polymer can be formed.

  As a result, it is possible to improve the efficiency of the amount of electricity associated with lithium release relative to the amount of electricity associated with lithium insertion in the lithium secondary battery, and to improve the energy density and cycle life.

  In the negative electrode using an alloy powder containing silicon or tin as an active material and at least one of these as a main constituent element, the present inventors formed both an electrolytic oxidation polymer and an electrolytic reduction polymer. It has been found that a high-capacity lithium secondary battery with little increase in battery internal impedance due to repeated charging and discharging can be provided.

Hereinafter, the battery of this invention and the material of each member which comprises this are demonstrated concretely along the aspect.
[Electrode structure]
FIG. 1 is a conceptual diagram schematically showing a cross section of one embodiment of an electrode structure 103 made of a fine powder of a negative electrode material in a lithium secondary battery of the present invention. FIG. 1A shows an electrode structure 103 in which an electrode material layer 101 made of a negative electrode material fine powder is provided on a current collector 100, and an electropolymerized polymer layer (film) 102 is provided on the surface thereof. In FIG. 1B, an electrode structure 103 provided with an electrode material layer 101 made of a negative electrode material fine powder is composed of a negative electrode active material 104, a conductive auxiliary material 105, and a binder 106. It can be presumed that the surfaces of the negative electrode active material 104 and the conductive auxiliary material 105 constituting these electrode material layers 101 are also covered with the electropolymerized polymer. In the figure, the electrode material layer 101 is provided only on one side of the current collector 100, but it can be provided on both sides of the current collector 100 depending on the form of the battery.

Below, an example of the manufacturing method of the electrode structure 103 of FIG.1 (b) is demonstrated.
The negative electrode active material 104, the conductive auxiliary material 105, and the binder 106 are mixed, and a solvent is added as appropriate to adjust the viscosity to prepare a paste. Next, the paste is applied on the current collector 100 and dried to form the electrode material layer 101. It is formed by adjusting the thickness with a roll press or the like as necessary.

(Current collector 100)
The current collector 100 plays a role of efficiently supplying a current consumed by an electrode reaction during charging or collecting a current generated during discharging. In particular, when the electrode structure 103 is applied to the negative electrode of a secondary battery, the material forming the current collector 100 is preferably a material having high electrical conductivity and inert to battery reaction. Preferable materials include those made of one or more metal materials selected from copper, nickel, iron, stainless steel, titanium, and platinum. As a more preferable material, copper which is inexpensive and has low electric resistance is used. The shape of the current collector is plate-like, but the “plate-like” is not specified in terms of the practical range, and is called a “foil” having a thickness of about 100 μm or less. It includes forms. Further, a plate-like member such as a mesh shape, a sponge shape, or a fiber shape, a punching metal, an expanded metal, or the like may be employed.

(Electrode material layer 101)
The electrode material layer 101 is a layer composed of a negative electrode material fine powder, and is a composite layer of an alloy powder coated with an electrolytic polymerization polymer, a conductive auxiliary material, a polymer material as a binder, and the like.

  The composite layer is formed by appropriately adding a conductive auxiliary material and a binder to the negative electrode material fine powder, mixing, applying, and pressure forming. In order to make it easy to apply, it is also preferable to add a solvent to the mixture to make a paste. As the coating method, for example, a coater coating method or a screen printing method can be applied. In addition, the main material, the conductive auxiliary material and the binder without adding a solvent, or only the negative electrode material and the conductive auxiliary material without being mixed with the binder are pressure-molded on the current collector. It is also possible to form an electrode material layer. Graphite powder is used as the conductive auxiliary material. As the graphite powder, a carbon material such as amorphous carbon such as acetylene black or ketjen black or carbon having a graphite structure can be used. Preferred examples of the shape of the conductive material include a spherical shape, a flake shape, a filament shape, a fiber shape, a spike shape, and a needle shape, and more preferably two or more different shapes selected from these shapes are adopted. By doing so, the packing density at the time of electrode material layer formation can be raised, and the impedance of an electrode can be reduced.

Since the Si element-containing negative electrode material (more specifically, Si fine powder or Si alloy fine powder) has a volume expansion at the time of charging as compared with conventional carbon materials such as graphite, the negative electrode material is mainly used. If the density of the active material layer (electrode material layer) produced on the current collector is too high, the volume expansion during charging causes peeling from the current collector. If the density is too low, the contact resistance between the particles increases and the current collection capacity increases. Is reduced, the range of 0.9 to 2.5 g / cm ³ is preferable, and the range of 1.0 to 1.8 g / cm ³ is more preferable.

  The binder is preferably an organic polymer, and either a water-insoluble polymer or a water-soluble polymer can be used. Specific examples of the water-insoluble polymer include polyolefins such as polyethylene and polypropylene, fluorine resins such as poly (vinylidene fluoride), tetrafluoroethylene polymer, and vinylidene fluoride-hexafluoropropylene copolymer, polyethylene-polyvinyl alcohol copolymer, styrene. -Butadiene rubber, polyamic acid, polyimide, polyamideimide and the like. Specific examples of the water-soluble polymer include polyvinyl alcohol, ethylene-vinyl alcohol copolymer (low ethylene component), polyvinyl butyral, polyvinyl acetal, polyvinyl methyl ether, polyvinyl ethyl ether, polyvinyl isobutyl ether, carboxymethyl cellulose, hydroxyethyl cellulose, hydroxypropyl Examples thereof include cellulose, hydroxymethyl ethyl cellulose, polyethylene glycol and the like.

  The ratio of the binder to the electrode material layer is in the range of 1 to 20 wt% with respect to the electrode material layer in order to exhibit a function as a binder and to retain a larger amount of active material during charging. It is preferable to make it into the range of 5 to 15 wt%.

(Electropolymerized polymer layer 102)
The electropolymerized polymer layer 102 which is the main point of the present invention is made of a polymer obtained by polymerizing an electrolytic oxidation polymerization monomer and an electrolytic reduction polymerization monomer contained in a nonaqueous electrolytic solution by applying a voltage. The electropolymerized polymer layer 102 is formed by polymerizing the monomer added to the non-aqueous electrolyte on the electrode surface after battery assembly. The monomer is intentionally added by applying a voltage before the first charge / discharge. It may be polymerized or formed in the process of charging / discharging the battery.

[Secondary battery]
Next, the secondary battery according to the present invention will be described.
The secondary battery of the present invention includes a negative electrode, an electrolyte, and a positive electrode using the electrode structure having the above-described features, and utilizes a lithium oxidation reaction and a lithium ion reduction reaction. FIG. 2 is a diagram showing a basic configuration of the lithium secondary battery of the present invention. In the secondary battery of FIG. 2, 201 is a negative electrode using the electrode structure of the present invention, 202 is a positive electrode, 203 is an ionic conductor, 204 is a negative electrode terminal, 205 is a positive electrode terminal, and 206 is a battery case (housing). .

  The above secondary battery forms an electrode group with a microporous polymer film sandwiched between the negative electrode and the positive electrode in a dry air or dry inert gas atmosphere where the dew point temperature is well controlled. After that, the battery is inserted into a battery case, each electrode and each electrode terminal are connected, and an electrolyte solution is injected. Then, the battery case is sealed and a battery is assembled.

(Positive electrode 202)
The positive electrode 202 serving as a counter electrode of a lithium secondary battery using the above-described electrode structure of the present invention as a negative electrode is composed of at least a positive electrode material serving as a lithium ion host material, preferably a positive electrode material serving as a lithium ion host material. It consists of a formed layer and a current collector. Further, the layer formed from the positive electrode material is preferably made of a positive electrode material which becomes a lithium ion host material and a binder, and in some cases, a material obtained by adding a conductive auxiliary material thereto.

  Examples of the positive electrode material used as a lithium ion host material for the lithium secondary battery of the present invention include transition metal oxides, transition metal sulfides, transition metal nitrides, lithium-transition metal oxides, lithium-transition metal sulfides, Lithium-transition metal nitrides are preferred, and lithium-containing transition metal oxides, lithium-transition metal sulfides, and lithium-transition metal nitrides are more preferred. Examples of transition metal elements of transition metal oxides, transition metal sulfides, and transition metal nitrides are metal elements having a d-shell or f-shell, such as Sc, Y, lanthanoid, actinoid, Ti, Zr, Hf, V Nb, Ta, Cr, Mo, W, Mn, Tc, Re, Fe, Ru, Os, Co, Rh, Ir, Ni, Pb, Pt, Cu, Ag, and Au are preferably used.

  When the shape of the positive electrode active material is powder, a binder is used, or a positive electrode active material layer is formed on a current collector by sintering or vapor deposition to produce a positive electrode. Further, when the positive electrode active material powder has low conductivity, it is necessary to appropriately mix a conductive auxiliary material as in the formation of the active material layer of the electrode structure. As the conductive auxiliary material and the binder, those used for the electrode structure 103 of the present invention described above can be similarly used.

  The current collector material used for the positive electrode is preferably aluminum, titanium, stainless steel, nickel, or platinum, which is a material that has high electrical conductivity and is inert to battery reaction, and among them, aluminum is inexpensive and has high electrical conductivity. It is more preferable. The shape of the current collector is plate-like, but the “plate-like” is not specified in terms of the practical range, and is called a “foil” having a thickness of about 100 μm or less. It includes forms. Further, a plate-like member such as a mesh shape, a sponge shape, or a fiber shape, a punching metal, an expanded metal, or the like may be employed.

(Ion conductor 203)
As the ion conductor of the lithium secondary battery of the present invention, a lithium ion conductor such as a separator holding an electrolytic solution (an electrolyte solution prepared by dissolving an electrolyte in a solvent) can be used.

The conductivity of the ionic conductor used for the secondary battery of the present invention is preferably 1 × 10 ⁻³ S / cm or more, preferably 5 × 10 ⁻³ S / cm or more, as a value at 25 ° C. More preferred.

Examples of the electrolyte include lithium ions (Li ⁺ ) and Lewis acid ions (BF ₄ ⁻ , PF ₆ ⁻ , AsF ₆ ⁻ , ClO ₄ ⁻ , CF ₃ SO ₃ ⁻ , BPh ₄ ⁻ (Ph: phenyl group)). And mixed salts thereof. It is desirable that the salt be sufficiently dehydrated and deoxygenated by heating under reduced pressure.

  Examples of the electrolyte solvent include acetonitrile, benzonitrile, propylene carbonate, ethylene carbonate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, dimethylformamide, tetrahydrofuran, nitrobenzene, dichloroethane, diethoxyethane, 1,2-dimethoxyethane, Chlorobenzene, γ-butyrolactone, dioxolane, sulfolane, nitromethane, dimethyl sulfide, dimethylsulfoxide, methyl formate, 3-methyl-2-oxazolidinone, 2-methyltetrahydrofuran, 3-propyl sydnone, sulfur dioxide, phosphoryl chloride, thionyl chloride, Sulfuryl chloride or a mixture thereof can be used.

  For example, the solvent may be dehydrated with activated alumina, molecular sieve, phosphorus pentoxide, calcium chloride or the like, or depending on the solvent, distillation may be performed in an inert gas in the presence of an alkali metal to remove impurities and dehydrate. Good.

(Nonaqueous electrolyte)
The present invention is characterized by a nonaqueous electrolytic solution used in a lithium secondary battery, and the nonaqueous electrolytic solution contains an electrolytic oxidation polymerization monomer and an electrolytic reduction polymerization monomer.

As the electrolytic oxidation polymerization monomer, one or more monomers or olegomers selected from the group consisting of pyrrole, aniline, thiophene, and derivatives thereof are used.
As the electrolytic reduction polymerization monomer, one or more monomers selected from the group consisting of acrylonitrile, methacrylic acid ester, styrene, butadiene, methylene malonic acid ester, α-cyanoacrylic acid ester, nitroethylene, vinylene carbonate, or olegomer are used. It is done.

  If the amount of the monomer added to the electrolytic solution is too small, there is no effect, and if it is too large, the ionic conductivity of the electrolytic solution is lowered, and the thickness of the polymer film formed at the time of charging is increased and the resistance of the electrode is increased. In our experiment, when 7.5 wt% of electrolytic oxidation polymerization monomer was added, a short circuit was caused by the conductive polymer. Further, when 5.0 wt% of electrolytic reduction polymerization monomer was added, the discharge amount with respect to the first charge was reduced due to an increase in battery internal resistance. It was confirmed that the electrolytic oxidation polymerization monomer was effective even when 0.2 wt% was added. Therefore, the optimum amount of monomer added to the non-aqueous electrolyte depends on the ionic conductivity of the non-aqueous electrolyte, the resistance / thickness / concaveness of the electrode, the porosity / thickness of the separator, the applied voltage / current density during polymerization, etc. However, the content of the electrolytic oxidation polymerization monomer and the electrolytic reduction polymerization monomer in the electrolytic solution is preferably in the range of 0.01 to 10 wt%. More preferably, it is 0.05-5 wt%.

Furthermore, when more electrolytic reduction polymerization monomer is added than electrolytic oxidation polymerization monomer, a more uniform polymer film is easily formed. Therefore, the electrolytic oxidation polymerization monomer (M _O ) and the electrolytic reduction polymerization monomer (M _R ) contained in the non-aqueous electrolyte ) Ratio (M _R / M _O ) is preferably in the range of 1 <M _R / M _O <50 by weight ratio. More preferably, 5 <M _R / M _O <25.

  Further, the method for producing a lithium secondary battery of the present invention includes applying a voltage from the positive electrode and the negative electrode to the non-aqueous electrolyte containing the electrolytic oxidation polymerization monomer and the electrolytic reduction polymerization monomer, so that at least either the positive electrode or the negative electrode is applied. On the other hand, the method has a step of forming a polymer comprising the electrolytic oxidation polymerization monomer and the electrolytic reduction polymerization monomer.

  In the present invention, by applying a voltage between the positive electrode and the negative electrode, the electrolytic oxidation polymerization monomer and the electrolytic reduction polymerization monomer contained in the non-aqueous electrolyte polymerize by passing electrons on the electrode surface to form a polymer. . On the other hand, a polymerization method may be considered by adding a polymerization initiator, but if a polymerization initiator or the like is added, the polymerization reaction may start not in the electrode surface but in the electrolytic solution, and the pores of the separator are blocked. This is not preferable because of the negative effects.

  In the battery of the present invention, a polymer can be formed by applying a constant voltage of 3 V or more to the battery for a predetermined time. In the case of a 4V class secondary battery, if charging is performed at a constant current density to a charge end voltage of about 4.2V, and then charging is continued for a predetermined time while maintaining the constant voltage at that voltage, A polymer can be easily formed. In addition, since a constant voltage of 3 V or more is applied to the battery for a predetermined time even during discharge, a polymer can be formed.

(separator)
The separator serves to prevent a short circuit between the negative electrode 201 and the positive electrode 202 in the secondary battery. Moreover, it may have a role of holding the electrolytic solution.

  The separator must have pores through which lithium ions can move and be insoluble and stable in the electrolyte. Therefore, as the separator, for example, glass, polyolefin such as polypropylene or polyethylene, non-woven fabric such as fluororesin, or a material having a micropore structure is preferably used. Moreover, the metal oxide film which has a micropore, or the resin film which compounded the metal oxide can also be used.

[Battery shape and structure]
Specific examples of the secondary battery of the present invention include a flat shape, a cylindrical shape, a rectangular parallelepiped shape, and a sheet shape. Examples of the battery structure include a single layer type, a multilayer type, and a spiral type. Among them, the spiral cylindrical battery has a feature that an electrode area can be increased by winding a separator between a negative electrode and a positive electrode, and a large current can flow during charging and discharging. Moreover, a rectangular parallelepiped type or sheet type battery has a feature that a storage space of a device configured by storing a plurality of batteries can be used effectively.

  In the spiral cylindrical secondary battery shown in FIG. 3, a positive electrode 306 having a positive electrode active material (material) layer 305 formed on the positive electrode current collector 304 and a negative electrode active material formed on the negative electrode current collector 301. A negative electrode 303 having a substance (material) layer 302 is opposed to, for example, an ion conductor 307 formed of a separator holding at least an electrolytic solution, and forms a multilayer structure of a cylindrical structure wound in multiple layers. ing. The laminated body having the cylindrical structure is accommodated in a negative electrode can 308 serving as a negative electrode terminal. In addition, a positive electrode cap 309 as a positive electrode terminal is provided on the opening side of the negative electrode can 308, and a gasket 310 is disposed in another part of the negative electrode can. The electrode stack having a cylindrical structure is separated from the positive electrode cap side by an insulating plate 311. The positive electrode 306 is connected to the positive electrode cap 309 via the positive electrode lead 313. The negative electrode 303 is connected to the negative electrode can 308 via the negative electrode lead 312. A safety valve 314 for adjusting the internal pressure inside the battery is provided on the positive electrode cap side. As described above, the ionic conductor 307 includes both the electrolytic oxidation polymerization monomer and the electrolytic reduction polymerization monomer, and the active material layer 305 of the positive electrode 306 and the active material layer 302 of the negative electrode 303 are applied to the active material layer 302 by applying a voltage as described above. The polymerized polymer of the present invention is coated.

Below, an example of the assembly method of the battery shown in FIG. 3 is demonstrated.
(I) The separator 307 is sandwiched between the negative electrode 303 and the formed positive electrode 306, and the negative electrode can 308 is assembled.
(Ii) After injecting the electrolyte added with the monomer, the positive electrode cap 309 and the gasket 310 are assembled.
(Iii) The battery is completed by caulking (ii) above.

It is desirable that the above-described lithium battery material preparation and battery assembly be performed in dry air from which moisture has been sufficiently removed or in a dry inert gas.
The member which comprises the above secondary batteries is demonstrated.

(gasket)
As a material of the gasket 310, for example, a fluororesin, a polyolefin resin, a polyamide resin, a polysulfone resin, and various rubbers can be used. As a battery sealing method, a glass sealing tube, an adhesive, welding, soldering, or the like is used in addition to “caulking” using a gasket as shown in FIG. Further, as the material of the insulating plate 311 in FIG. 3, various organic resin materials and ceramics are used.

(Outside can)
As an outer can of the battery, a negative electrode can 308 of the battery and a positive electrode cap 309 are configured. Stainless steel is suitably used as the material for the outer can. In particular, a titanium clad stainless plate, a copper clad stainless plate, a nickel plated steel plate, etc. are frequently used.

  In FIG. 3, since the negative electrode can 308 serves as a battery housing (case) and a terminal, the above stainless steel is preferable. However, if the positive electrode can or negative electrode can does not serve as the battery housing and terminal, the material of the battery case is not only stainless steel but also metals such as zinc, plastics such as polypropylene, or metal or glass fiber and plastic. Composite materials can be used.

(safety valve)
A lithium secondary battery is provided with a safety valve as a safety measure when the internal pressure of the battery increases. As the safety valve, for example, rubber, a spring, a metal ball, a rupture foil, or the like can be used.

  Hereinafter, the present invention will be described in more detail on the basis of examples. However, the present invention is not limited to the following examples, and can be implemented with appropriate modifications without departing from the scope of the present invention. It is.

Example 1
[Production of electrode structure]
In this example, a lithium secondary battery was prepared using thiophene as the electrolytic oxidation polymerization monomer and vinylene carbonate as the electrolytic reduction polymerization monomer.

(Production of negative electrode)
74% by weight of fine powder of silicon-tin alloy, 10.0% by weight of graphite powder (substantially disk-shaped graphite powder having a diameter of about 5 μm and a thickness of about 1 μm) as a conductive auxiliary material, and graphite powder (substantially spherical) The average particle size is 5 μm) 5.0 wt% and 11.0 wt% polyamic acid as a binder (binder) are mixed, and N-methyl-2pyrrolidone is added and kneaded to prepare a paste. .

  Next, the paste thus prepared is applied onto a 15 μm thick electrolytic copper foil (electrochemically produced copper foil) with a coater, dried, and the thickness is adjusted with a roll press, and the thickness is 25 μm. An electrode structure having an active material layer was prepared.

The electrode structure was cut into a size of 2.5 cm × 2.5 cm, and a copper tab was welded to form a negative electrode.
[Production of positive electrode]
(I) Lithium citrate and cobalt nitrate are mixed at a molar ratio of 1: 3, and an aqueous solution in which citric acid is added and dissolved in ion-exchanged water is sprayed into an air stream at 200 ° C. A precursor of cobalt oxide was prepared.
(Ii) The lithium-cobalt oxide precursor obtained in (i) above was further heat-treated at 850 ° C. in an oxygen stream.
(Iii) After mixing 3% by weight of graphite powder and 5% by weight of polyvinylidene fluoride powder with the lithium-cobalt oxide prepared in (ii) above, N-methyl-2-pyrrolidone was added to prepare a paste.
(Iv) After applying and drying the paste obtained in (iii) above on both sides of the aluminum foil current collector 304 with a thickness of 20 microns, the thickness of the positive electrode active material layer on one side is adjusted to 90 microns with a roll press. did. Further, aluminum leads were connected with an ultrasonic welder and dried under reduced pressure at 150 ° C. to produce a positive electrode.

[Evaluation procedure for lithium insertion / extraction]
Next, 1M (mol / liter) (15.19 g) of a salt of LiPF ₆ was dissolved in 0.1 liter of an organic solvent obtained by mixing ethylene carbonate and diethyl carbonate in a volume ratio of 3: 7, An electrolyte solution was prepared by adding 0.2 wt% (0.24 g) of thiophene and 5.0 wt% (6.13 g) of vinylene carbonate. Then, this electrolytic solution is impregnated into a porous polyethylene film having a thickness of 25 μm, the negative electrode described above is disposed on one surface of the film, and the positive electrode described above is disposed on the other surface. The film was sandwiched between them. Next, in order to obtain flatness, it was sandwiched between glass plates from both sides, and further covered with an aluminum laminate film to produce an evaluation cell.

  The aluminum laminate film was a three-layer film in which the outermost layer was a nylon film, the middle layer was an aluminum foil with a thickness of 20 μm, and the inner layer was a polyethylene film. The lead terminal portion of each electrode was fused and sealed without being laminated.

In order to evaluate the function as the secondary battery, a lithium insertion / extraction cycle test (a charge / discharge cycle test) was performed.
That is, the above-described evaluation cell is connected to the charging / discharging device, the evaluation cell is first charged at a current density of 3.2 mA / cm ² , and when the voltage reaches 4.2 V, the voltage is kept constant. Was charged to 0.16 mA / cm ² . Subsequently, the evaluation cell was discharged at a current density of 3.2 mA / cm ² until the voltage reached 2.5V. The charge electricity amount and the discharge electricity amount at this time were measured, and the charge / discharge efficiency of the battery was evaluated.

Comparative Example 1
A battery was fabricated in the same manner as in Example 1 except that no monomer was added to the electrolytic solution.
Comparative Example 2
A battery was fabricated in the same manner as in Example 1 except that 0.2 wt% of thiophene was added as an electrolytic oxidation polymerization monomer to the electrolytic solution, and no electrolytic reduction polymerization monomer was added.

Comparative Example 3
A battery was fabricated in the same manner as in Example 1 except that 7.5 wt% of thiophene was added as an electrolytic oxidation polymerization monomer to the electrolytic solution, and no electrolytic reduction polymerization monomer was added.

Comparative Example 4
A battery was fabricated in the same manner as in Example 1 except that 5.0 wt% of vinylene carbonate was added as an electrolytic reduction polymerization monomer to the electrolytic solution, and no electrolytic oxidation polymerization monomer was added.

(Performance evaluation result of lithium insertion / extraction of electrode structure)
Table 1 below shows the charge / discharge efficiency in terms of percentage of the amount of desorption relative to the amount of lithium inserted at the first and 50th cycles for the examples and comparative examples.

  From Table 1, since Comparative Example 3 has a large amount of electrolytic oxidation polymerization monomer added to the electrolytic solution, the conductive polymer formed by polymerization penetrated the separator and was short-circuited. In Example 1 and Comparative Example 4 in which the monomer was added in an amount of 5.0 wt% or more to the electrolytic solution, the initial charge / discharge efficiency was lower than that in Comparative Example 1 in which no monomer was added. As described above, if the amount of the monomer added is too large, the ionic conductivity of the electrolytic solution is lowered, and the thickness of the polymer film formed at the time of charging is increased, and the resistance of the electrode is increased. However, looking at the charge / discharge efficiency at the 50th cycle, in Example 1, the deterioration was the highest compared with the comparative example due to the effect of simultaneously adding the electrolytic reduction polymerization monomer and the electrolytic oxidation polymerization monomer to the electrolytic solution.

  Since the effect is sufficiently obtained when the addition amount of the electrolytic oxidation polymerization monomer is 0.2 wt%, it is understood that the electrolytic oxidation polymerization monomer may be added in a smaller amount than the electrolytic reduction polymerization monomer. For these reasons, the amount of monomer added is preferably 0.01 to 10.0 wt%. More preferably, it is 0.05-5.0 wt%. The ratio of the electrolytic oxidation polymerization monomer to the electrolytic reduction polymerization monomer is preferably in the range of 1 <content of electrolytic reduction polymerization monomer / content of electrolytic oxidation polymerization monomer <50.

  FIG. 4 shows the results of the lithium insertion / extraction cycle test of the secondary battery in Example 1 and Comparative Examples 1 and 2, with the horizontal axis representing the cycle number and the vertical axis representing the maximum lithium desorption amount as 100%. It is the graph which showed the amount of lithium desorption of each cycle. As shown in FIG. 4, the battery of the present invention (Example 1), the battery of Comparative Example 1 in which no monomer is added to the non-aqueous electrolyte, and the battery of Comparative Example 2 in which only thiophene is added to the non-aqueous electrolyte are cycled. Is repeated, the battery capacity retention rate of the battery of the present invention is superior. Further, in Example 1, the initial charge / discharge efficiency is lower than in Comparative Example 1 and Comparative Example 2, but the discharge amount increases in the second and third cycles, so the discharge amount in the third cycle is Comparative Example 1. The amount is almost the same as in Comparative Example 2. From the above, it was found that the secondary battery produced in Example 1 has a long cycle life while maintaining a high capacity.

  The lithium secondary battery of the present invention can reduce the resistance in the lithium secondary battery, and has high cycle density and high energy density. Therefore, the lithium secondary battery is used for a digital camera, a digital video camera, a mobile phone, a notebook PC, and the like. be able to.

It is sectional drawing which shows typically an example of the structure of the electrode structure of the secondary battery in this invention. It is a conceptual diagram which shows typically the cross section of one embodiment of the secondary battery (lithium secondary battery) of this invention. It is sectional drawing which shows the structure of a spiral type cylindrical battery. It is a figure which shows the charging / discharging cycling characteristics of the electrode structure of Example 1 and Comparative Examples 1 and 2 of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 100 Current collector 101 Electrode material layer 102 Electropolymerization polymer layer 103 Electrode structure 104 Active material 105 Conductive material 106 Binder 201, 303 Negative electrode 202, 306 Positive electrode 203, 307 Ion conductor 204 Negative electrode terminal 205 Positive electrode terminal 206 Battery case (Battery housing)
301 Negative electrode current collector
302 Negative electrode active material layer 304 Positive electrode current collector 305 Positive electrode active material layer 308 Negative electrode can (negative electrode terminal)
309 Positive electrode cap (positive electrode terminal)
310 Gasket 311 Insulating plate 312 Negative electrode lead 313 Positive electrode lead 314 Safety valve

Claims (8)

  A lithium secondary battery comprising a positive electrode, a negative electrode, and a non-aqueous electrolyte, wherein the non-aqueous electrolyte contains an electrolytic oxidation polymerization monomer and an electrolytic reduction polymerization monomer.   A lithium secondary battery having a positive electrode, a negative electrode, and a non-aqueous electrolyte solution, wherein at least one of the positive electrode and the negative electrode is applied by applying a voltage to the non-aqueous electrolyte solution containing an electrolytic oxidation polymerization monomer and an electrolytic reduction polymerization monomer. A lithium secondary battery characterized in that a polymer formed by polymerizing the electrolytic oxidation polymerization monomer and the electrolytic reduction polymerization monomer is formed on one side.   The content of the electrolytic oxidation polymerization monomer contained in the nonaqueous electrolytic solution is 0.01 wt% or more and 10 wt% or less, and the content of the electrolytic reduction polymerization monomer is 0.01 wt% or more and 10 wt% or less. The lithium secondary battery according to claim 1 or 2. The ratio (M _R / M _O ) between the electrolytic oxidation polymerization monomer (M _O ) and the electrolytic reduction polymerization monomer (M _R ) contained in the non-aqueous electrolyte is in the range of 1 <M _R / M _O <50. The lithium secondary battery according to any one of claims 1 to 3, wherein:   5. The lithium secondary battery according to claim 1, wherein the electrolytic oxidation polymerization monomer is at least one monomer selected from the group consisting of pyrrole, aniline, thiophene, and derivatives thereof, or an olegomer. 6.   The electrolytic reduction polymerization monomer is at least one monomer or olegomer selected from the group consisting of acrylonitrile, methacrylic acid ester, styrene, butadiene, methylenemalonic acid ester, α-cyanoacrylic acid ester, nitroethylene, vinylene carbonate. The lithium secondary battery according to any one of claims 1 to 4, wherein:   The lithium secondary battery according to claim 1, wherein the negative electrode contains at least Si element.   In a method for producing a lithium secondary battery having a positive electrode, a negative electrode, and a non-aqueous electrolyte, at least a positive electrode is obtained by applying a voltage from the positive electrode and the negative electrode to the non-aqueous electrolyte containing an electrolytic oxidation polymerization monomer and an electrolytic reduction polymerization monomer. A method for producing a lithium secondary battery, comprising a step of forming a polymer comprising the electrolytic oxidation polymerization monomer and the electrolytic reduction polymerization monomer on either the negative electrode or the negative electrode.