JP2006182925A - Core/shell type fine particle and lithium secondary battery including the fine particle - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide core/shell type fine particles capable of composing a lithium secondary battery having a gel-like electrolyte, excellent in battery performances (especially charge/discharge cycle characteristic) and safety, also good in productivity, and the lithium secondary battery comprising the fine particles. <P>SOLUTION: This core/shell type fine particle is composed of a shell part containing a polymer compound dissolvable or gelatinizable in an organic solvent and a core part being a fine particle stable to the organic solvent at a room temperature, where the polymer compound in the shell part is chemically bound with the core part, and the particle diameter in a dry state is ≤15 μm. The lithium secondary battery has the core/shell type fine particles in its insulating layer for insulating the space between a positive electrode and a negative electrode. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a core-shell type fine particle suitable for use in a lithium secondary battery and a lithium secondary battery having the fine particle.

  In recent years, the demand for mobile terminal devices such as mobile phones, notebook personal computers, and personal digital assistants (PDAs) has been rapidly expanding. With the reduction in size and weight and the increase in functionality, there is a demand for further increase in energy density of lithium secondary batteries used as a power source, and the capacity is increasing year by year. In addition, there is an increasing need to ensure the safety and reliability of batteries.

  Under such circumstances, as a means for improving the safety of the battery, a battery using a so-called gel electrolyte in which a polymer is used as a host and the electrolyte is held in the matrix, instead of the conventional liquid electrolyte. (For example, Patent Documents 1 to 4) have been put to practical use.

  However, in batteries using gel electrolyte, there are no problems such as leakage, but in abnormal situations where the internal temperature becomes extremely high, such as overcharge or short circuit, the viscosity of the gel electrolyte decreases and short circuit occurs. Is more likely to be triggered. In this respect, the safety of a battery using a gel electrolyte is not sufficient, and as with a battery having a conventional liquid electrolyte, the holes are closed by heat melting of the constituent materials at high temperatures. At present, safety is ensured by using a polyolefin-based separator having a function capable of increasing resistance (so-called shutdown function).

  In addition, as a method for producing a battery having such a gel electrolyte, (1) a laminated electrode body or a wound electrode similar to a battery having a liquid electrolyte (non-aqueous electrolyte, hereinafter simply referred to as “electrolyte”) Electrolyte containing a substance (monomer, macromer or non-crosslinked polymer and gelling agent, etc.) and a reaction initiator as a raw material of a polymer constituting a gel electrolyte by preparing a body and inserting it into an exterior material (battery case) A method of gelling an electrolyte solution by polymerizing or cross-linking the raw material after being injected into the exterior material; (2) Applying a solution containing a polymer constituting the gel electrolyte to the electrode surface and removing the solvent Then, after the electrode is dried, a laminated electrode body or a wound electrode body is produced and inserted into the outer packaging material, and the electrolyte is injected into the electrolyte to gel the electrolyte in the battery; 3) On the electrode surface A material that is a raw material of the polymer that constitutes the electrolyte and a reaction initiator are applied, and the polymer is formed by a crosslinking reaction with heat or light, and then a laminated electrode body or a wound electrode body is formed using this electrode. And a method of injecting the electrolyte into the exterior material and gelling the electrolyte in the battery is proposed.

  However, in the method (1), since the electrolyte to be injected contains a reaction initiator, the gelation reaction proceeds in a state where the electrolyte is left standing, so that there is a problem in its storage stability. In addition, the reaction initiator remaining in the battery may affect the battery characteristics. Furthermore, when the viscosity of the electrolyte to be injected is low, a gel may be formed in the gap of the electrode, leading to an increase in interfacial resistance. On the other hand, when the viscosity is high, the liquid injection property is deteriorated. Productivity cannot be improved.

  In the method (2), when a polymer solution is applied to the electrodes, the polymer may enter the gaps between the electrodes, leading to an increase in interface resistance, which may cause a decrease in battery characteristics. In order to prevent such an increase in interfacial resistance, a method of applying a polymer by impregnating a block solution in advance in an electrode has also been proposed (Patent Document 5). However, when such a method is used, it is necessary to remove the block liquid under the coating film coated with the polymer, and the drying time is longer than the drying of the normal electrode and polymer coating film. Takes time and productivity is not good. Further, when the drying is insufficient and the solvent or moisture remains on the electrode, there arises a problem that the battery characteristics are adversely affected.

  Furthermore, in the method (3), when the gel electrolyte is produced on the electrode surface or after the production, it is necessary to work in an environment in which water absorption is avoided, so that the handling is troublesome and the productivity is also poor. There is a point.

Japanese Patent No. 29987474 JP 2002-25621 A US Pat. No. 5,453,335 JP 2002-367777 A JP 2002-343438 A

  The present invention has been made in view of the above circumstances, and is a lithium secondary battery having a gel electrolyte, which has excellent battery characteristics (particularly charge / discharge cycle characteristics) and safety, and good productivity. An object of the present invention is to provide core-shell type fine particles capable of constituting a lithium secondary battery and a lithium secondary battery having the fine particles.

  The core-shell type fine particles of the present invention that can achieve the above-mentioned object are a shell part containing a polymer compound that can be dissolved in an organic solvent or become a gel in the organic solvent, and a room temperature relative to the organic solvent. And a core part that is a stable fine particle, the polymer chain of the polymer compound related to the shell part is chemically bonded to the core part, and the particle size in a dry state is 15 μm. It is characterized by the following. The “gel” in the present invention includes, in addition to the usual “gel”, a state similar to an electrolyte called a “gel electrolyte” in the battery industry (a gel in a strict sense). Even if it is not, there is almost no fluidity of the liquid or a state in which the liquid no longer flows. Furthermore, “stable at room temperature with respect to an organic solvent” in the core part means that the shape is maintained even in a useful solvent.

  In the lithium secondary battery of the present invention, (A) the ion permeable insulating layer containing the core-shell type fine particles of the present invention is formed on the surface of the negative electrode, and the ion permeable insulating layer comprises a positive electrode, a negative electrode, Or (B) having a separator formed by combining the porous base material and the core-shell type fine particles of the present invention, and the separator is disposed between the positive electrode and the negative electrode. It is characterized by being;

  In the lithium secondary battery of the present invention, the core-shell type fine particles of the present invention may be present in the positive electrode and / or the negative electrode.

  That is, the core-shell type fine particles of the present invention are interposed between the positive electrode and the negative electrode, and constitute a layer (ion-permeable insulating layer, separator) for insulating between the positive and negative electrodes while allowing the ions involved in the battery reaction to pass therethrough. By being introduced into the battery as a component, the shell portion holds the electrolytic solution and constitutes a so-called gel electrolyte. Therefore, since the gel electrolyte can be introduced into the battery very easily, the productivity of the battery can be improved.

  In addition, even if the polymer compound that is the raw material of the shell part can be dissolved in the electrolyte solution, it does not dissolve in the electrolyte solution because of the chemical bond with the core part. In addition, there is no possibility that the gel penetrates into the gaps of the electrodes, and in addition, there is no need to add a crosslinking agent or the like for the gelation, so that the battery characteristics are not impaired. Furthermore, what has various characteristics can be used for a core part according to the required characteristic of a battery. For example, when high heat-resistant fine particles are used, even when the temperature becomes abnormally high due to overcharge or the like, the core portion exhibits high insulation, so that the insulating layer between the positive and negative electrodes is melted (so-called melt). The occurrence of a large-scale short circuit between the positive and negative electrodes due to down) can be prevented, and the safety of the battery can be ensured. On the other hand, when fine particles that can be softened at a high temperature are used for the core portion, a shutdown function can be provided, thereby ensuring safety. In addition, even when the battery electrode (for example, the negative electrode) has a large expansion during charging and discharging, the shell portion takes in the electrolyte and becomes a gel to have elasticity. Stress can be relieved and collapse of the electrode (active material-containing layer) due to expansion and contraction can be prevented. Therefore, in the lithium secondary battery into which the core-shell type fine particles are introduced, it is possible to ensure stable charge / discharge characteristics (charge / discharge cycle characteristics) with higher capacity. And even if the electrode expands, there is no risk of short circuit due to the presence of the core portion that does not substantially deform.

  According to the present invention, a lithium secondary battery having excellent battery characteristics (particularly charge / discharge cycle characteristics) and safety and good productivity can be provided.

<Core shell type fine particles>
The core-shell type fine particles of the present invention include a shell portion containing a polymer compound that can be dissolved in an organic solvent or can be gelled in an organic solvent, and a core that is stable at room temperature with respect to the organic solvent. It consists of a part.

  The polymer compound according to the shell part can be dissolved in an organic solvent or can be gelled in the organic solvent. In addition, since the core-shell type fine particles of the present invention are assumed to be used in a lithium secondary battery (non-aqueous electrolyte battery) as described above, the organic compound that can dissolve or gel the polymer compound related to the shell portion. Examples of the solvent include those used in conventionally known non-aqueous electrolytes (electrolytic solutions) of non-aqueous electrolyte batteries (specific examples of these solvents are shown in the description of the lithium secondary battery of the present invention). ).

  As the polymer compound related to the shell portion, for example, a polymer compound used in a conventionally known gel electrolyte can be applied. That is, fluororesin such as polyvinylidene fluoride (PVDF), vinylidene fluoride-hexafluoropropylene copolymer; polyacrylonitrile; polyalkylene oxide such as polyethylene oxide, polypropylene oxide, ethylene oxide-propylene oxide copolymer; main chain or side Examples thereof include host polymers capable of forming a conventionally known gel electrolyte such as a crosslinked polymer containing an ethylene oxide chain in the chain. In the present invention, as described above, since the polymer chain of the polymer compound related to the shell portion and the core portion are chemically bonded, the affinity for the electrolyte solution is good. Resins that could not be used as a host polymer for gel electrolytes because of their solubility in water, such as (meth) acrylate resins such as polymethyl acrylate, polyethyl acrylate, polymethyl methacrylate, and polyethyl methacrylate (Acrylate resins and methacrylate resins) can also be used.

  Furthermore, as the polymer compound related to the shell portion, a resin having a structure represented by the following general formula (1) into which a crosslinkable side chain (a side chain having crosslinkability) is introduced can also be used.

Wherein R ¹ and R ³ are each a hydrogen atom or an alkyl group having 1 to 3 carbon atoms, R ² is an alkyl group having 1 to 3 carbon atoms, a hydroxyalkyl group, or an alkylene oxide group, and R ⁴ is at least 1 (Indicating an alkyl group having 1 to 6 carbon atoms in which two hydrogen atoms are substituted with an oxetane group or an alicyclic epoxy group, m and n each represents an integer of 100 to 1000.)

Since the resin represented by the general formula (1) has an oxetane group or an alicyclic epoxy group in a side chain, for example, when heated in a battery, a lithium salt (for example, LiPF ₆ or LiBF ₄ or the like in an electrolytic solution) ) As an initiator to form a crosslinked structure, and thus a good gel electrolyte can be formed.

  The resin represented by the general formula (1) is, for example, a copolymer having a unit represented by the following general formula (2) and / or the following general formula (3) and a unit represented by the following general formula (4). It is preferable that

(Here, R ⁵ , R ⁷ and R ⁸ represent a hydrogen atom or a methyl group, and R ⁶ and R ⁹ represent an alkyl group having 1 to 6 carbon atoms.)

  Further, a copolymer in which the resin represented by the general formula (1) has a unit represented by the general formula (2) and / or the general formula (3) and a unit represented by the general formula (4). In this case, the ratio of the unit represented by the general formula (4) in the entire copolymer unit is 50 mol% or more, more preferably 75 mol% or more, and 98 mol% or less, more preferably 90 mol%. It is desirable that it is not more than mol%. In other words, the total ratio of the unit represented by the general formula (2) and the unit represented by the general formula (3) is 2 mol% or more, more preferably 10 mol% or more in all units of the copolymer. It is recommended that it be 50 mol% or less, more preferably 25 mol% or less. When the ratio of the unit represented by the general formula (4) is too small, the crosslink density in the shell portion becomes too high, and the electrolyte solution holding capacity of the shell portion may be reduced in the battery. On the other hand, when the ratio of the unit represented by the general formula (4) is too large, the number of side chains having a crosslinking ability may be reduced, and the crosslinking ability of the shell part may be lowered.

  Note that either one of the unit represented by the general formula (2) and the unit represented by the general formula (3) may be used, or both may be used simultaneously. The ratio of the unit represented by the general formula (2) and the unit represented by the general formula (3) is not particularly limited, and the total ratio of these units in all units of the copolymer is It is sufficient to satisfy the preferable value of.

  The copolymer having the unit represented by the general formula (2) and / or the general formula (3) and the unit represented by the general formula (4) is represented by the following general formula (5) and / or It can be obtained by copolymerizing a monomer represented by the general formula (6) and a monomer represented by the following general formula (7). In addition, since each said monomer has comparatively close reactivity, the said copolymer is normally obtained as a random copolymer or a block copolymer.

[Wherein R ⁵ , R ⁶ , R ⁷ , R ⁸ and R ⁹ are the same as those in the general formulas (2), (3) and (4), respectively. ]

  In synthesizing the above copolymer, for example, each of the above monomers and a polymerization initiator (such as potassium persulfate) are added to a dispersion medium (such as water), and the conditions are 30 to 80 ° C. in a nitrogen atmosphere. A method of dispersion polymerization with stirring can be employed. Further, at the time of this dispersion polymerization, core-shell type fine particles can be produced simultaneously with the synthesis of the above copolymer by adding the fine particles described later constituting the core part to the dispersion medium together with the respective monomers.

  The monomer represented by the general formula (5) can be produced by reacting an acid chloride such as acrylic acid chloride or methacrylic acid chloride with 3-ethyl-3-hydroxymethyloxetane. Moreover, the monomer of the said General formula (6) and General formula (7) can be obtained as a commercial item.

  The core part of the core-shell type fine particle is not particularly limited as long as it is a fine particle that is stable at room temperature with respect to an organic solvent (for example, an electrolyte solvent for a lithium secondary battery).

For example, when it is not necessary to expect the shutdown function from being provided by the core part, fine particles having high heat resistance can be used. In a battery having core-shell type fine particles whose core part is a high heat-resistant fine particle, even if the core part becomes abnormally high temperature due to overcharge or the like, the core part is not substantially deformed, so high insulation is exhibited. Since the occurrence of a large-scale short circuit between the positive and negative electrodes due to melting (meltdown) of the ion-permeable insulating layer (separator) between the positive and negative electrodes can be prevented, the safety is excellent. Specific examples of the high heat-resistant fine particles include, for example, a crosslinked polymer [crosslinked polystyrene, crosslinked (meth) acrylate resin (crosslinked polymethyl acrylate, crosslinked polyethyl acrylate, crosslinked polymethyl methacrylate, crosslinked polyethyl methacrylate, etc.), poly Divinylbenzene, polyimide, epoxy resin, polyurethane, etc.] and heat-resistant resins (polytetrafluoroethylene and its derivatives, polysulfone, polyethersulfone, thermoplastic polyimide, polyamideimide, polyetherketone, etc.) Resin fine particles (high heat resistant organic resin fine particles); inorganic fine particles such as inorganic oxide fine particles such as SiO ₂ , TiO ₂ , Al ₂ O ₃ , talc, CaCO ₃ , and BaTiO ₃ ; High heat-resistant fine particles may be used alone or in combination of two or more. Further, it may be fine particles containing two or more materials constituting the above high heat-resistant fine particles.

  For example, when the shutdown function is ensured by the core portion, the melting point or softening point of the thermoplastic resin measured in a state containing an organic solvent (for example, an electrolyte solution solvent) is 80 ° C. or higher. It is preferable to use fine particles having a constituent component of preferably 100 ° C. or higher and 130 ° C. or lower, more preferably 125 ° C. or lower. In a battery having core-shell type fine particles having a core part of fine particles composed of a thermoplastic resin having such a melting point or softening point, the internal temperature of the battery is, for example, 80 to 130 ° C., and the above melting point or softening of the thermoplastic resin. When the temperature exceeds a point, the core part melts or softens, and the shut-down function of increasing the internal resistance by closing the pores of the ion-permeable insulating layer (separator) interposed between the positive and negative electrodes Because it is demonstrated, it is excellent in safety. In addition, the said melting | fusing point of a thermoplastic resin means the melting temperature measured using a differential scanning calorimeter (DSC) according to the prescription | regulation of JISK7121, The said softening point is prescribed | regulated to JISK2207. It means the softening point measured according to the measurement method.

  Specific examples of the thermoplastic resin having the above softening point include polyolefins such as polyethylene (PE), polypropylene (PP), chlorinated polypropylene, and polycycloolefin; ethylene-vinyl acetate copolymer (EVA), ethylene-ethyl Examples thereof include copolymer polyolefins such as acrylate copolymers and ethylene-methyl methacrylate copolymers. The copolymerized polyolefin is a so-called hot melt resin, and preferably has a unit ratio derived from ethylene of 65 mol% or more. In constituting the core part, only one kind of these thermoplastic resins may be used, or two or more kinds may be used in combination. Further, two or more kinds of fine particles composed of different types of thermoplastic resins may be used in combination to form core-shell fine particles. Further, two or more types of the above-mentioned thermoplastic resins can be used to form fine particles having a two-layer structure in which one is a core and the other is a shell, and this can be used as a core part to form a core-shell fine particle having a three-layer structure. Among the above thermoplastic resins, chlorinated polypropylene or EVA having a unit ratio derived from ethylene of 65 mol% or more is preferable.

  In the core-shell type fine particles, the polymer chain of the polymer compound related to the shell part and the core part are chemically bonded. The method for chemically bonding the polymer chain of the polymer compound and the core part is not particularly limited. For example, in the production of core-shell type fine particles, the shell part and the core part are combined with a binder (known silane). A coupling agent, etc.), a method in which a functional group capable of forming a chemical bond with each other is introduced into the shell component (polymer compound) or the core component, Examples thereof include a method in which a polymer compound constituting the shell part is synthesized in the presence of the polymer compound and the core part are bonded to each other.

  For example, when the above-mentioned inorganic fine particles are used for the core portion, the surface of the fine particles is treated in advance using a silane coupling agent, and the core portion is attached with the shell portion. By reacting the functional group derived from the silane coupling agent present in the part with the polymer compound related to the shell part, the polymer chain of the polymer compound and the core part can be chemically bonded.

  In addition, when using the above high heat-resistant organic resin fine particles or fine particles composed of the above thermoplastic resin for the core portion, for example, an acid group (carboxyl group, carboxylic anhydride group, etc.) is introduced in advance. When a shell part is formed with a polymer compound in which a hydroxyl group or an amino group has been introduced in advance into the core part containing the resin, the acid group and the hydroxyl group or amino group are reacted to form a bond. can do. The functional group introduced into the resin related to the core part may be a hydroxyl group or an amino group, and the functional group introduced into the polymer compound related to the shell part may be an acid group (carboxyl group, carboxylic anhydride group, etc.). .

  Furthermore, in the case of using the above high heat-resistant organic resin fine particles or fine particles composed of the above thermoplastic resin for the core portion, by synthesizing the polymer compound related to the shell portion in the presence of the core portion, A part of the monomer for forming the polymer compound can also be bonded to the resin related to the core part to form a chemical bond between the polymer chain of the polymer compound related to the shell part and the core part.

  The particle diameter of the core-shell type fine particles is 15 μm or less and preferably 10 μm or less in a dry state (specifically, after being vacuum-dried at 60 ° C. for 15 hours or more). As will be described later, the core-shell type fine particles are contained in an ion-permeable insulating layer interposed between positive and negative electrodes in a lithium secondary battery, or used as a separator combined with a porous substrate. Therefore, if the particle diameter of the core-shell type fine particles is too large, the ion-permeable insulating layer and the separator become thick, so that the internal resistance of the battery is increased and the energy density is reduced. If the particle size is too large, especially when the above-mentioned inorganic fine particles are used in the core, for example, it is combined with a composition for forming an ion-permeable insulating layer (slurry etc.) or a porous substrate. In such a composition (slurry or the like), sedimentation of core-shell type fine particles is likely to occur. In addition, if the particle diameter of the core-shell type fine particles is too small, the fine particles tend to be solidified and difficult to handle. Therefore, the particle size is preferably 0.1 μm or more. The particle diameter of the core-shell type fine particles referred to in the present invention is a number average particle diameter obtained by image analysis by observing with a scanning electron microscope in a dry state. It is the number average particle diameter measured with a laser scattering device in a state dispersed in a medium such as

  Further, the particle size of the core part of the core-shell type fine particles is preferably, for example, not less than 1/4 and not more than 2/3 of the particle size of the core-shell type fine particles. If the particle size of the core part is too large, the volume of the shell part becomes too small, and the electrolyte holding function and the elasticity when made into a gel form are poor, which may cause a decrease in battery performance. Also, if the particle size of the core part is too small, the volume of the core part becomes too small, for example, when the inside of the battery becomes abnormally hot or when the expansion of the electrode is large, the insulation between the positive and negative electrodes May decrease the ability to hold and reduce the short-circuit prevention effect. The thickness of the shell part may be adjusted so that the particle diameter of the core-shell type fine particles becomes the above-mentioned predetermined value after setting the particle diameter of the core part to the above-mentioned preferable value.

<Lithium secondary battery>
The lithium secondary battery of the present invention is characterized by having the above-described aspect (A) or (B). In the aspect (A) of the lithium secondary battery of the present invention, the ion-permeable insulating layer interposed between the positive and negative electrodes for insulating them contains the core-shell type fine particles of the present invention, and An insulating layer is formed on the negative electrode surface.

  The ion-permeable insulating layer may be formed, for example, in a state where the shell portion of the core-shell type fine particles contains an electrolytic solution (that is, a gel state), or in a state where the shell portion does not contain an electrolytic solution. It may be formed.

  The ion permeable insulating layer uses an ion permeable insulating layer forming composition (slurry or the like) containing the core-shell type fine particles, which is applied to the negative electrode surface (the active material containing layer surface of the negative electrode) and dried. Etc. can be formed. When the ion-permeable insulating layer is formed in a state where the shell part of the core-shell type fine particles does not contain an electrolyte solution, a composition (slurry or the like) in which the core-shell type fine particles are dispersed in water or a suitable dispersion medium is used. It is desirable to adopt a method of preparing and applying this to the negative electrode surface using a conventionally known coating apparatus such as a blade coater, roll coater, die coater, spray coater, and the like, and then drying.

  When the ion-permeable insulating layer is formed in a state where the shell portion contains the electrolytic solution, core-shell type fine particles are dispersed in the electrolytic solution to prepare an ion-permeable insulating layer forming composition, which is used as the negative electrode. An ion-permeable insulating layer is formed by coating on the surface, and this electrode is used as it is to make a battery. In this case, if the dispersion medium (electrolyte) contains moisture, it may cause performance deterioration in the case of a battery. For example, a low moisture content solvent (electrolyte) having a moisture content of 50 ppm or less is used. It is desirable to use and form an ion-permeable insulating layer in a dry atmosphere. Alternatively, a method may be used in which the composition is applied in a state where the shell portion of the core-shell type fine particles is in a gel state, and once dried, an electrolytic solution is added to return to the gel state again. However, it is desirable to form the ion-permeable insulating layer in a state that does not contain the electrolyte solution, because it becomes easier to handle the electrode in the subsequent battery assembly process.

  In particular, when the particle diameter of the core-shell type fine particles is small, the fine particles are likely to aggregate. For the purpose of preventing the aggregation, it is desirable to add a dispersant to the composition for forming an ion-permeable insulating layer. As the dispersant, conventionally known ones [for example, polyvinyl pyrrolidone (PVP), polyvinyl alcohol, carboxymethyl cellulose (CMC) and the like] can be used. When using a dispersing agent, it is preferable to set it as 0.1-10 mass parts with respect to 100 mass parts of core-shell type fine particles, for example.

  When the adhesion between the core-shell type fine particles is insufficient, a binder may be added as appropriate within a range that does not impair the battery characteristics, and the adhesion between the fine particles can be enhanced. Examples of binders that can be used include EVA, ethylene-ethyl acrylate copolymer, ethylene-methyl methacrylate copolymer, ethylene-vinyl alcohol copolymer, PVDF, vinylidene-hexafluoropropylene copolymer, nitrile- A resin generally used as a binder for each member of a non-aqueous battery, such as a butadiene copolymer and a styrene-butadiene-styrene block copolymer (SBR), is preferable. When the composition for forming an ion-permeable insulating layer is an organic solvent system, it is preferable to use the binder resin exemplified above in a state dissolved in the organic solvent. Further, when the ion-permeable insulating layer forming composition is aqueous, it is recommended to use the binder resin exemplified above in the form of an aqueous dispersion such as an emulsion or latex. When the binder is used, for example, the amount is preferably 1 to 10 parts by mass with respect to 100 parts by mass of the core-shell type fine particles.

  The thickness of the ion-permeable insulating layer is, for example, 1 μm or more, more preferably 5 μm or more, and is preferably 50 μm or less, more preferably 30 μm or less. If the ion-permeable insulating layer is too thin, it is likely to be affected by unevenness on the electrode surface, and a short circuit may occur. In addition, if the ion-permeable insulating layer is too thick, the ion conduction path becomes long and the internal resistance of the battery may increase, and the proportion of the ion-permeable insulating layer in the battery becomes too large. The energy density of the battery may decrease.

  In the aspect (B) of the lithium secondary battery of the present invention, the separator interposed between the positive and negative electrodes has a separator formed by combining the porous base material and the core-shell type fine particles of the present invention between the positive and negative electrodes. Yes.

  In order to produce a separator according to the present invention by combining a porous base material and core-shell type fine particles, the composition (dispersant or binder) for forming the ion-permeable insulating layer according to the embodiment (A) is used. Adopting a method of removing water or organic solvent related to the composition after applying or impregnating a porous substrate having ion permeability to the same composition (including slurry containing an agent) it can. When the composition is applied to the porous substrate, the same method as the composition applying method described in the ion-permeable insulating layer forming method can be employed. In addition, when an electrolytic solution is used for the above composition, the step of removing the electrolytic solution solvent is unnecessary.

  As the porous substrate, a nonwoven fabric is preferable, and a nonwoven fabric made of polyolefin (polyethylene, polypropylene, etc.) or polyester (polyethylene terephthalate, polybutylene terephthalate, etc.) is particularly preferable. The thickness of the nonwoven fabric is preferably 10 to 50 μm, for example, and the porosity is preferably 10 to 50%, for example.

  Further, it is recommended that the separator after fabrication has a structure in which core-shell type fine particles are present not only in both surfaces (upper and lower surfaces) of such a porous substrate, but also in the voids of the porous substrate. For example, by the method of impregnating with the above composition, a structure in which core-shell type fine particles are present in the voids of the porous substrate can be obtained.

  In the separator (solid content) thus obtained, the ratio of the core-shell type fine particles is preferably 30% to 70% in terms of volume fraction. When the ratio of the core-shell type fine particles is too small, the retention of the electrolytic solution is lowered, and the effect of improving battery characteristics may be reduced. Moreover, when there are too many ratios of a core-shell type fine particle, there exists a possibility of causing the intensity | strength shortage as a separator.

Examples of the positive electrode active material that can be used for the positive electrode according to the lithium secondary battery of the present invention include LiNi _x Co _(1-x) O _{2 in} which a part of Ni in LiCoO ₂ , LiNiO ₂ , and LiNiO ₂ is replaced with Co. Chalcogenite-based oxides, spinel oxides such as LiMn ₂ O _4, layered MnNi-based compounds such as LiNi _{(1-x) / 2} Mn _{(1-x) / 2} Co _x O ₂ , LiMPO ₄ (M: Co, Ni, Examples thereof include inorganic oxides capable of occluding and releasing lithium ions used in ordinary lithium ion secondary batteries, such as olivine-based oxides such as Mn and Fe).

  These active materials are mixed with a conductive auxiliary agent for imparting conductivity and a binder for imparting binding properties, if necessary, and a dispersion medium [N-methyl-2-pyrrolidone (NMP), water, toluene Etc.] to form a slurry-like positive electrode mixture-containing composition, and this composition is applied to the surface of the current collector, dried, and further pressed to form an active material-containing layer on the surface of the current collector. can do. As the conductive auxiliary agent, a carbon material such as acetylene black (AB), ketjen black (KB), graphite, amorphous carbon and the like, which are usually used, may be used alone, or 2 More than one species may be used in combination. In addition, binders that are usually used, for example, fluorine resin materials such as PVDF and polytetrafluoroethylene (PTFE); rubber-based materials such as SBR; May be used in combination. In the active material-containing layer of the positive electrode, for example, it is desirable that the amount of active material is 50 to 99% by mass, the amount of conductive additive is 0.5 to 40% by mass, and the amount of binder is 0.5 to 20% by mass. The thickness of the active material-containing layer of the positive electrode is preferably 10 to 100 μm, for example.

  The core-shell type fine particles of the present invention may be present in the positive electrode (active material-containing layer). When the positive electrode contains the core-shell type fine particles, the expansion and contraction of the active material can be more effectively absorbed. The content of the core-shell type fine particles in the active material-containing layer is not particularly limited as long as it does not impair the conductivity in the electrode. For example, it is preferably 2% by mass or more and 10% by mass or less.

  As the positive electrode current collector, for example, an aluminum foil, a punching metal, a net, an expanded metal, or the like can be used. However, an aluminum foil having a thickness of 10 μm to 30 μm is preferably used. If the thickness is too small, the strength of the foil is too low and handling becomes difficult. If the thickness is too large, the proportion of the foil in the battery becomes too large and the energy density decreases.

As the negative electrode active material according to the lithium secondary battery of the present invention, at least one material can be used among materials capable of occluding and releasing lithium ions, lithium metal or lithium alloy, or metal that can be alloyed with lithium. . Examples of the lithium alloy include a lithium-aluminum alloy. Examples of the metal that can be alloyed with lithium include Sn and Si. Other materials that can occlude and release lithium include carbon-based materials such as amorphous carbon, artificial graphite, natural graphite, fullerene, and carbon nanotubes; titanic acids such as Li ₄ Ti ₅ O ₁₂ and Li ₂ Ti ₃ O _7. Examples include lithium.

  For example, in the case of lithium metal, a lithium alloy, or a metal that can be alloyed with lithium, a thin film (foil, etc.) composed of the metal is pressure-bonded to the current collector as an active material-containing layer, or sputtering, vapor deposition, plating, etc. A negative electrode can be obtained by forming a layer (active material containing layer) containing them on the current collector surface by a method. In the case of other negative electrode active materials, for example, it is dispersed in a dispersion medium (NMP, water, toluene, etc.) together with a conductive additive or a binder as necessary to obtain a slurry-like negative electrode mixture-containing composition. Is applied to the surface of the current collector, dried, and further pressed to obtain a negative electrode having an active material-containing layer formed on the surface of the current collector. As a conductive support agent, AB, KB, amorphous carbon etc. are mentioned, for example, These may be used individually by 1 type and may use 2 or more types together. Moreover, as a binder, PVDF, PTFE, SBR, CMC, hydroxypropyl cellulose etc. can be illustrated, for example, These may be used individually by 1 type and may use 2 or more types together. In the case where the active material-containing layer of the negative electrode is configured using a conductive additive and a binder, for example, the active material-containing layer has an active material amount of 50 to 99% by mass, a conductive auxiliary agent amount of 0 to 40% by mass, The binder amount is desirably 0.5 to 20% by mass. The thickness of the active material-containing layer of the negative electrode is preferably 30 to 150 μm, for example.

  The core-shell type fine particles of the present invention may be present in the negative electrode (active material-containing layer). When the negative electrode contains the core-shell type fine particles, the expansion and contraction of the active material can be more effectively absorbed. The content of the core-shell type fine particles in the active material-containing layer is not particularly limited as long as it does not impair the conductivity in the electrode. For example, it is preferably 2% by mass or more and 10% by mass or less.

  As the current collector for the negative electrode, a foil made of copper or nickel, a punching metal, a net, an expanded metal, or the like can be used, but a copper foil is usually used. The thickness of the negative electrode current collector is desirably 6 to 30 μm. If the current collector is too thin, its strength becomes too weak and difficult to handle, and if it is too thick, the volume ratio occupied by the current collector in the battery increases, and the energy density of the battery decreases.

Among the above negative electrode active materials, metals that can be alloyed with lithium, such as Sn, in particular, have electronic conductivity, and therefore do not need to be provided with a conductive auxiliary agent. Electroless or electroplating, sputtering, etc. It is preferable because a thin film electrode can be produced by the above method. However, metals that can be alloyed with lithium (especially Sn) are likely to become fine particles due to charge and discharge, which may cause a problem. From the viewpoint of avoiding such a problem, a metal that can be alloyed with lithium is used as a negative electrode active material. Is preferably used as an intermetallic compound containing the metal element. Such an intermetallic compound is preferably composed of a metal element that can be alloyed with lithium (such as Sn described above) and a metal element that is not alloyed with lithium. Sn is preferable as a metal element that can be alloyed with lithium, and examples of metal elements that are not alloyed with lithium include Cu and Ni, and Cu is particularly preferable. Therefore, as the intermetallic compound, a compound of Sn and Cn (for example, Cu ₆ Sn ₅ ) is preferable.

  The negative electrode using the intermetallic compound as an active material as described above is, for example, on the surface of a current collector composed of a metal element that is not alloyed with lithium (for example, a current collector composed of Cu or a Cu alloy) A method of forming a thin layer of a metal element (such as Sn) that can be alloyed with lithium and then heat-treating it can be employed. During this heat treatment, an intermetallic compound is formed by the metal element that is not alloyed with lithium on the surface of the current collector and the metal element in the layer of the metal element that can be alloyed with lithium, and an intermetallic compound is formed on the current collector surface. A layer containing a compound (that is, an active material-containing layer) is formed.

  Further, as shown in FIG. 1A, a thin layer 2 containing a metal element that can be alloyed with lithium and a thin layer 3 containing a metal element that is not alloyed with lithium are formed on the surface of the current collector 1. It is more preferable to adopt a method in which the layers are alternately formed and heat-treated to form the intermetallic compound-containing layer 4 (active material-containing layer) [FIG. 1 (b)]. In such a case, at the time of heat treatment, first, a metal element that can be alloyed with lithium in the thin layer 2 and a metal element that is not alloyed with lithium in the thin layer 3 adjacent to the top and bottom of the thin layer 2 are interfaced. For example, even when Cu or the like is used for the current collector 1, Cu on the surface of the current collector 1 diffuses at the interface with the thin layer 2 formed on the surface. However, interdiffusion of metal elements at the interface between the thin layer 2 and the thin layer 3 occurs first, and an intermetallic compound is formed. Therefore, by adjusting the thicknesses of the thin layer 2 and the thin layer 3 in accordance with the composition of the target intermetallic compound, an active material-containing layer containing an intermetallic compound having a desired composition can be easily formed. can do.

  Furthermore, as shown in FIG. 2 (a), by providing a protective layer 5 on the surface of the current collector 1 containing a metal element that does not alloy with lithium such as Cu, heat treatment (intermetallic compound formation) is achieved. At this time, the intermetallic compound-containing layer 4 can be formed while suppressing the diffusion of the constituent metal elements of the current collector into the other layer [FIG. 2 (b)]. The material constituting the protective layer 5 is preferably a metal element having a melting point higher than that of a metal element (for example, Sn) that can be alloyed with lithium according to the thin layer 2 and that is not alloyed with lithium. Is Ni or the like. Further, a metal element that can be used in the protective layer 5 may be used for the current collector 1 itself.

  Further, for example, when Cu is used for the current collector, a metal element (Ni, Zr, Fe, etc.) that does not alloy with lithium other than Cu is further added for the purpose of suppressing the diffusion of Cu particles from the current collector. It is good also as Cu alloy contained.

In the case where the intermetallic compound-containing layer 4 is formed by the method shown in FIGS. 1 and 2, Sn is used as a metal element that can be alloyed with lithium, and Cu is used as a metal element that is not alloyed with lithium. The atomic ratio of total Cu and total Sn in the thin layer 2 and the thin layer 3 excluding the current collector is preferably about the same, and further, the ratio is the atomic ratio, Cu: Sn = 6: 5 Is more preferable, and Cu: Sn = 6: 5 is particularly preferable. As described above, Cu ₆ Sn ₅ is suitable as the intermetallic compound composed of Cu and Sn, but the atomic ratio of all Cu and all Sn in the thin layer 2 and the thin layer 3 is from the above preferred value. In the case where the Sn is excessive and Sn is excessive, the components diffused during the heat treatment for forming the intermetallic compound are relatively increased. As a result, Sn that cannot be converted into an intermetallic compound remains in the intermetallic compound-containing layer 4. For example, when Cu is used for the current collector 1, Cu on the surface of the current collector 1 is converted into an intermetallic compound, so that Cu of the current collector 1 is consumed. There are things to do. On the other hand, when the atomic ratio of all Cu and all Sn in the thin layer 2 and the thin layer 3 deviates from the above preferred value and Cu is excessive, Cu ₃ Sn that cannot repeatedly occlude and release lithium ions is obtained. Since it is easily formed, there may be a demerit in the effective capacity of the battery.

  In the case where the intermetallic compound-containing layer 4 is formed by the method shown in FIGS. 1 and 2, Sn is used as a metal element that can be alloyed with lithium, and Cu is used as a metal element that is not alloyed with lithium. The thicknesses of the Sn thin layer 2 and the Cu thin layer 3 formed on the surface of the electric body are each preferably 3 μm or less. If each thin layer is too thick, the time required for interdiffusion of Cu and Sn during heat treatment for forming an intermetallic compound may become extremely long. The lower limit of the thickness of each of the Sn thin layer 2 and the Cu thin layer 3 is preferably about 1 μm. If the thickness is further reduced, the number of thin layers stacked increases when a high-capacity negative electrode is manufactured. The manufacturing process becomes complicated.

  As a method for forming the above-described thin layer of metal element that can be alloyed with lithium (thin layer 2), thin layer of metal element that is not alloyed with lithium (thin layer 3), and protective layer, for example, physical vapor deposition A method (PVD), a chemical vapor deposition method (CVD), a liquid phase growth method, or the like can be preferably employed. Examples of the PVD method include a vacuum deposition method, a sputtering method, an ion plating method, a molecular beam epitaxy (MBE) method, and a laser ablation method. As the CVD method, thermal CVD method, MOCVD (metal organic chemical vapor deposition) method, RF (Radio Frequency) plasma CVD method, ECR (electron cyclotron resonance) plasma CVD method, photo CVD method, laser CVD method, atomic layer epitaxy ( ALE) method. Examples of the liquid phase growth method include a plating method (electrolytic plating and electroless plating), an anodic oxidation method, a coating method, and a sol-gel method.

  The heat treatment for forming an intermetallic compound when Sn is used as the metal element that can be alloyed with lithium and Cu is used as the metal element that is not alloyed with lithium is the melting point of Sn in a vacuum atmosphere or a reducing atmosphere. It is performed in a region not exceeding 231.9 ° C. This is because, when the melting point of Sn is exceeded, Sn in the thin layer elutes before forming an intermetallic compound with Cu, and the actual processing conditions are, for example, 150 ° C. or more and 200 ° C. or less. Is preferred. The heat treatment time needs to be set long enough for Sn and Cu in the laminated thin layer to interdiffuse. For example, the heat treatment time is 5 hours or longer, within 24 hours, more preferably within 10 hours. In the case of the negative electrode having the intermetallic compound-containing layer thus obtained, the thickness of the intermetallic compound-containing layer is preferably, for example, 1 to 30 μm.

  A negative electrode using a material containing a metal element that can be alloyed with lithium (such as the above-mentioned intermetallic compound) as an active material has a large expansion / contraction during charge / discharge, and the active material-containing layer is likely to collapse. Although having a drawback, in the lithium battery of the present invention, the shell portion of the core-shell type fine particles is in a gel form, and this elasticity relieves stress due to expansion of the active material-containing layer of the negative electrode during charging. be able to. Therefore, since the collapse of the active material-containing layer in the negative electrode can be suppressed, a lithium secondary battery having higher capacity and stable charge / discharge characteristics (charge / discharge cycle characteristics) can be configured.

  When assembling the lithium secondary battery of the present invention, the positive electrode and the negative electrode are laminated via an ion-permeable insulating layer formed on the negative electrode surface, or the positive electrode and the negative electrode are interposed via the separator. And laminated to form a laminated electrode body, or further wound to obtain a wound electrode body. Such an electrode body is inserted into a rectangular or cylindrical outer can made of iron, stainless steel, aluminum or the like, injected with an electrolytic solution, and sealed, thereby providing a lithium secondary battery. It can be. In addition, a laminated battery can be obtained by inserting the above electrode body into a soft package using a laminated film on which a metal is deposited as an exterior material, injecting an electrolytic solution, and then sealing.

As the electrolytic solution, a solution obtained by dissolving a lithium salt used in a conventionally known lithium secondary battery in an organic solvent is used. The lithium salt is not particularly limited as long as it dissociates in a solvent to form Li ⁺ ions and does not cause a side reaction such as decomposition in a voltage range used as a battery. For example, inorganic compounds such as LiPF ₆ , LiBF ₄ , LiAsF ₆ , LiClO ₄ ; LiN (SO ₂ CF ₃ ) ₂ , LiN (SO ₂ C ₂ F ₅ ) ₂ , LiN (SO ₂ CF ₃ ) (SO ₂ O ₄ ) _{F 9), LiC (SO 2} CF 2) 3, LiC (SO 2 C 2 F 5) 2, LiPF 6-n (C 2 F 5) n (n is an integer from 1 to _6), LiSO 3 _{CF 3,} Organic compounds such as LiSO ₃ C ₂ F ₅ and LiSO ₃ O ₄ F ₈ can be used.

  The organic solvent used in the electrolytic solution is not particularly limited as long as it dissolves the above lithium salt and does not cause side reactions such as decomposition in the voltage range used as a battery. For example, cyclic carbonates such as ethylene carbonate, propylene carbonate, butylene carbonate, vinylene carbonate; chain carbonates such as dimethyl carbonate, diethyl carbonate, and ethyl methyl carbonate; cyclic esters such as γ-butyrolactone; dimethoxyethane, diglyme, triglyme, tetraglyme, etc. A cyclic ether such as dioxane, tetrahydrofuran and 2-methyltetrahydrofuran; nitriles such as acetonitrile, propionitrile and methoxypropionitrile; and these may be used alone or in combination. You may use together a seed or more. In order to obtain a battery with better characteristics, it is desirable to use a combination that can obtain high conductivity, such as a mixed solvent of ethylene carbonate and chain carbonate. In addition, vinylene carbonates, 1,3-propane sultone, diphenyl disulfide, cyclohexane, biphenyl, fluorobenzene, t- for the purpose of improving safety, charge / discharge cycleability, and high-temperature storage properties of these electrolytes. Additives such as butylbenzene can also be added as appropriate. As described above, the polymer compound related to the shell portion of the core-shell type fine particles of the present invention can be dissolved in the organic solvent exemplified above or can be gelled in the organic solvent exemplified above.

  The lithium salt concentration in the electrolytic solution is preferably 0.8 to 1.5 mol / l, for example.

  When the lithium secondary battery of the present invention thus obtained uses the resin represented by the above general formula (1) as the core-shell type fine particles and the polymer represented by the general formula (1), By applying a heat treatment after forming a secondary battery, core-shell type fine particles having a cross-linked structure derived from oxetane groups and / or alicyclic epoxy groups present in the side chain of the resin can be obtained, and a better gel state An electrolyte can be generated. As heat treatment conditions for forming a crosslinked structure, for example, the temperature is preferably 50 to 80 ° C. and the time is preferably 30 minutes to 5 hours. Moreover, as a method of heat processing, the method of leaving still in a thermostat can be employ | adopted, for example.

  Since the lithium secondary battery of the present invention is excellent in battery characteristics (particularly charge / discharge cycle characteristics) and safety, for example, power supplies for various devices such as mobile terminal devices such as mobile phones, notebook personal computers, and PDAs. Can be suitably used.

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

Example 1
<Preparation of core-shell type fine particles>
Cross-linked polymethylmethacrylate (PMMA) [Nippon Shokubai Co., Ltd. “Eposter MA1002” (trade name)]: 100 g is dispersed in water: 1000 g, and PVP: 10 g as a stabilizer, surfactant. Sodium dodecylbenzenesulfonate (SDS): 2 g as an agent, n-butyl acrylate (nBMA): 100 g as a monomer for forming a shell part, potassium persulfate (KPK): 10 g as a polymerization initiator, and in a nitrogen atmosphere, While stirring at 65 ° C. at a speed of 300 rpm, dispersion polymerization was performed for 5 hours to obtain an aqueous dispersion of core-shell type fine particles. A part of the obtained core-shell type fine particles was vacuum-dried at 60 ° C. for 15 hours, and the average particle size measured was 5 μm.

<Production of lithium secondary battery>
Production of positive electrode:
LiCoO _{2 as a} positive electrode active material: 80 parts by mass, acetylene black as a conductive auxiliary agent: 10 parts by mass, and PVDF as a binder: 10 parts by mass are mixed so that NMP is a uniform dispersion medium. A positive electrode mixture-containing paste was prepared. This paste was intermittently applied to both sides of an aluminum foil having a thickness of 15 μm and a width of 800 mm as a current collector so that the coating length was 280 mm on the front surface and 210 mm on the back surface, dried, and then subjected to a calendar treatment to obtain a total thickness. The thickness of the positive electrode material mixture layer (active material-containing layer) was adjusted so as to be 150 μm, and slitted so that the width was 43 mm to obtain a positive electrode. The exposed portion of the positive electrode current collector was tabbed.

Production of negative electrode:
An electrolytic copper foil (made by Furukawa Circuit Foil) with a thickness of 10 μm was immersed for 4 minutes in 10% sulfuric acid heated to 40 ° C. to remove the oxide film, oils and dirt on the surface, and sodium hydroxide: 5 g / Liter, sodium orthosilicate: 20 g / liter, sodium carbonate (anhydrous): 10 g / liter, n-dodecyltrimethylammonium chloride: 1 g / liter in a degreasing solution heated to 60 ° C. in a bath of 5 to 10 A / dm Cathodic electrolytic degreasing was performed at a current density of ² and for 1 minute. This copper foil is washed with distilled water and then immersed again in 10% strength sulfuric acid to completely remove the alkali neutralization and surfactant on the surface of the copper foil to obtain a copper foil current collector for electrolytic plating. It was. After performing a masking process on both sides of the copper foil so that only the length part of the front surface of 290 mm and the back surface of 230 mm can be plated, stannous sulfate: 40 g / liter, sulfuric acid: 60 g / liter, cresolsulfonic acid: 40 g / Liter, gelatin: 2 g / liter, β-naphthol: 1 g / liter of Sn plating bath was subjected to electrolytic plating at a current density of 1 A / dm ² for 30 minutes to obtain a Sn plating thin layer having a thickness of 1 μm. . After washing this thin film, electrolytic plating was carried out for 5 minutes at a current density of 1 A / dm ^{2 in} a Cu plating bath having a composition of copper sulfate: 100 g / liter and sulfuric acid: 100 g / liter to obtain a Cu plating thin layer having a thickness of 1 μm. It was. After repeating this Sn plating step and Cu plating step four times, finally a 9 μm thick Sn / Cu (5/4) multilayer thin layer obtained by applying Sn plating with a thickness of 1 μm again was washed with water, and then vacuum electric After heat treatment at 200 ° C. for 5 hours in an oven to form an intermetallic compound, it was gradually cooled to room temperature, the masking layer was peeled off, and cut to a width of 45 mm to obtain a negative electrode. A tab was attached to the exposed portion of the copper foil of the negative electrode.

Preparation of ion-permeable insulating layer:
The slurry obtained by adding 5% by mass of CMC as a binder to the aqueous dispersion of the core-shell fine particles is applied to the surface of the intermetallic compound-containing layer of the negative electrode using a die coater and dried. An ion-permeable insulating layer integrated with the negative electrode was obtained.

Battery assembly:
The negative electrode integrated with the ion-permeable insulating layer and the positive electrode were overlapped and wound in a spiral shape to obtain a wound electrode body. This fatigued electrode body is crushed into a flat shape, inserted into a laminate film exterior material (manufactured by Showa Aluminum Co., Ltd.), and LiPF ₆ is added to a solvent in which an electrolytic solution (ethylene carbonate and ethylmethyl carbonate is mixed at a volume ratio of 1: 2). A solution dissolved at a concentration of 1.2 mol / l) was injected and vacuum sealed to produce a laminated battery (lithium secondary battery).

Example 2
The fine particles for constituting the core portion are replaced with crosslinked PMMA, and the surface of SiO ₂ particles (“FB-3SDC” manufactured by Denki Kagaku Kogyo Co., Ltd.) is used as the silane coupling agent (“SZ6300” manufactured by Dow Corning Toray Silicone Co., Ltd.). An aqueous dispersion of core-shell type fine particles was prepared in the same manner as in Example 1 except that the fine particles treated with the above were used. The average particle diameter of a part of the obtained core-shell type fine particles measured in the same manner as in Example 1 was 8 μm. Further, a laminate battery was produced in the same manner as in Example 1 by using the aqueous dispersion of core-shell fine particles. The surface treatment of the SiO ₂ particles, and SiO ₂ particles and a silane coupling agent, 1 weight ratio were mixed at a ratio of 1, was performed by stirring for 2 hours in a ball mill.

Example 3
Instead of the cross-linked PMMA, the surface of the Al ₂ O ₃ particles (“AO-902H” manufactured by Admatechs) is used as the silane coupling agent (“SZ6300” manufactured by Dow Corning Toray Silicone Co., Ltd.). An aqueous dispersion of core-shell type fine particles was prepared in the same manner as in Example 1 except that the fine particles treated in (1) were used. The average particle diameter measured in the same manner as in Example 1 for a part of the obtained core-shell type fine particles was 2 μm. Further, a laminate battery was produced in the same manner as in Example 1 by using the aqueous dispersion of core-shell fine particles. The surface treatment of the Al ₂ O ₃ particles and Al ₂ O ₃ particles and a silane coupling agent, 1 weight ratio were mixed at a ratio of 1, was performed by stirring for 2 hours in a ball mill.

Example 4
Cross-linked polymethylmethacrylate (PMMA) [Nippon Shokubai Co., Ltd. “Eposter MA1002” (trade name)]: 100 g is dispersed in water: 1000 g, and PVP: 10 g as a stabilizer, surfactant. SDS: 2 g as an agent, methyl methacrylate (MMA): 70 g as a monomer for forming a shell part, represented by the above general formula (5), R ⁵ is a methyl group, and R ⁶ is a monomer having 2 carbon atoms: 30 g, As a polymerization initiator, 10 g of KPK was added. In addition, the ratio of MMA in all monomers is 80 mol%. The dispersion was subjected to dispersion polymerization for 5 hours while stirring at 65 rpm at a speed of 300 rpm in a nitrogen atmosphere to obtain an aqueous dispersion of core-shell type fine particles. A part of the obtained core-shell type fine particles was vacuum-dried at 60 ° C. for 15 hours, and the average particle diameter measured was 15 μm. A laminated battery was prepared in the same manner as in Example 1 except that this core-shell type fine particle aqueous dispersion was used, and then the battery was heat-treated at 60 ° C. for 30 minutes to form a crosslinked structure in the shell part of the core-shell type fine particles. Formed.

Example 5
Cross-linked polymethylmethacrylate (PMMA) [Nippon Shokubai Co., Ltd. “Eposter MA1002” (trade name)]: 100 g is dispersed in water: 1000 g, and PVP: 10 g as a stabilizer, surfactant. SDS: 2 g as an agent, methyl methacrylate (MMA): 70 g as a monomer for forming a shell part, represented by the above general formula (6), R ⁷ is a hydrogen atom monomer: 30 g, and KPK: 10 g is added as a polymerization initiator It was. In addition, the ratio of MMA in all monomers is 80 mol%. The dispersion was subjected to dispersion polymerization for 5 hours while stirring at 65 rpm at a speed of 300 rpm in a nitrogen atmosphere to obtain an aqueous dispersion of core-shell type fine particles. A part of the obtained core-shell type fine particles was vacuum-dried at 60 ° C. for 15 hours, and the average particle size measured was 12 μm. A laminated battery was prepared in the same manner as in Example 1 except that this core-shell type fine particle aqueous dispersion was used, and then the battery was heat-treated at 60 ° C. for 30 minutes to form a crosslinked structure in the shell part of the core-shell type fine particles. Formed.

Example 6
The core shell is the same as in Example 1 except that instead of the cross-linked PMMA, EVA emulsion [Sumika Flex S850HQ (trade name)] manufactured by Sumika Chemtex Co., Ltd. is used as the fine particles for constituting the core portion. An aqueous dispersion of fine particles was prepared. The average particle size of a part of the obtained core-shell type fine particles measured in the same manner as in Example 1 was 5 μm. Further, a laminate battery was produced in the same manner as in Example 1 by using the aqueous dispersion of core-shell fine particles.

Example 7
A negative electrode active material-containing paste was prepared by mixing 90 parts by mass of graphite as a negative electrode active material and 10 parts by mass of PVDF as a binder so as to be uniform using NMP as a dispersion medium. This was intermittently applied to both sides of a copper foil having a thickness of 10 μm and a width of 800 mm as a current collector so that the coating length was 290 mm on the front surface and 230 mm on the back surface, dried, and then calendered to obtain a total thickness. The thickness of the negative electrode mixture layer (active material-containing layer) was adjusted so as to be 142 μm, and slitting was performed so that the width was 45 mm, thereby producing a negative electrode. A tab was attached to the exposed portion of the negative electrode current collector. A laminated battery was produced in the same manner as in Example 1 except that the negative electrode thus obtained was used.

Example 8
A non-woven fabric made of PP having a thickness of 30 μm (“PF0830” manufactured by Nippon Kogyo Paper Co., Ltd.) is immersed in a bath containing an aqueous dispersion of core-shell fine particles produced in the same manner as in Example 1, and the aqueous dispersion is obtained by pulling up and applying. Was applied to the nonwoven fabric, the water dispersion was impregnated in the voids of the nonwoven fabric, and dried to obtain a separator. A positive electrode and a negative electrode obtained in the same manner as in Example 1 were wound through this separator to obtain a wound electrode body. A laminated battery was produced in the same manner as in Example 1 except that this wound electrode body was used.

Example 9
Production of positive electrode:
LiCoO _{2 as a} positive electrode active material: 80 parts by mass, acetylene black as a conductive auxiliary agent: 10 parts by mass, core-shell type fine particles prepared in Example 1: 8 parts by mass, and PVDF as a binder: 2 parts by mass NMP was mixed as a dispersion medium so as to be uniform to prepare a positive electrode mixture-containing paste. This paste was intermittently applied to both sides of an aluminum foil having a thickness of 15 μm and a width of 800 mm as a current collector so that the coating length was 280 mm on the front surface and 210 mm on the back surface, dried, and then subjected to a calendar treatment to obtain a total thickness. The thickness of the positive electrode material mixture layer (active material-containing layer) was adjusted so as to be 150 μm, and slitted so that the width was 43 mm to obtain a positive electrode. The exposed portion of the positive electrode current collector was tabbed.

Production of negative electrode:
Graphite as negative electrode active material: 90 parts by mass, core-shell type fine particles prepared in Example 1: 8 parts by mass, and PVDF as a binder: 2 parts by mass are mixed using NMP as a dispersion medium. Thus, a negative electrode mixture-containing paste was prepared. This was intermittently applied to both sides of a copper foil having a thickness of 10 μm and a width of 800 mm as a current collector so that the coating length was 290 mm on the front surface and 230 mm on the back surface, dried, and then calendered to obtain a total thickness. The thickness of the negative electrode mixture layer (active material-containing layer) was adjusted so as to be 142 μm, and slitting was performed so that the width was 45 mm, thereby producing a negative electrode. A tab was attached to the exposed portion of the negative electrode current collector.

Preparation of ion-permeable insulating layer:
A slurry obtained by adding 5% by mass of CMC as a binder to the aqueous dispersion of core-shell fine particles produced in Example 1 was applied to the surface of the active material-containing layer of the negative electrode using a die coater. By drying, an ion-permeable insulating layer integrated with the negative electrode was obtained.

  A laminated battery was produced in the same manner as in Example 1 except that the above positive electrode and negative electrode were used.

Comparative Example 1
A laminate battery was fabricated in the same manner as in Example 8, except that a PE microporous membrane (“N9420” manufactured by Asahi Kasei Co., Ltd.) having a thickness of 20 μm was used as the separator without being combined with the core-shell type fine particles.

Comparative Example 2
An aqueous dispersion of nBMA fine particles was produced in the same manner as in the method for producing core-shell fine particles of Example 1, except that crosslinked PMMA was not used. A laminated battery was produced in the same manner as in Example 1 except that this water dispersion was used in place of the core-shell type fine particle water dispersion.

Comparative Example 3
Production of negative electrode:
A negative electrode active material-containing paste was prepared by mixing 90 parts by mass of graphite as a negative electrode active material and 10 parts by mass of PVDF as a binder so as to be uniform using NMP as a dispersion medium. This was intermittently applied to both sides of a copper foil having a thickness of 10 μm and a width of 800 mm as a current collector so that the coating length was 290 mm on the front surface and 230 mm on the back surface, dried, and then calendered to obtain a total thickness. The thickness of the negative electrode mixture layer (active material-containing layer) was adjusted so as to be 142 μm, and slitting was performed so that the width was 45 mm, thereby producing a negative electrode. A tab was attached to the exposed portion of the negative electrode current collector. A laminated battery was produced in the same manner as in Comparative Example 1 except that the negative electrode thus obtained was used.

  The batteries of Examples 1 to 9 and Comparative Examples 1 to 3 were subjected to the following electrochemical evaluation and safety evaluation. The results are shown in Table 1.

[Electrochemical evaluation]
Each battery was subsequently charged at a constant voltage of 4.2 V until it reached 4.2 V at a constant current of 0.2C. The total time from the start of constant current charging to the end of constant voltage charging was 7 hours. Each battery after charge was initialized by discharging at 0.2 C until the voltage changed from 4.2 V to 3.0 V.

  About each battery after the said initialization, it charged with the constant voltage of 4.2V until it became 4.2V with the constant current of 0.5C. The total time from the start of constant current charging to the end of constant voltage charging was 3 hours. And each battery after charge was discharged at 0.5 C from 4.2 V to 3.0 V. This charging / discharging operation was defined as one cycle, and 100 cycles of charging / discharging were performed. And the discharge capacity of the 1st cycle and the discharge capacity of the 100th cycle were measured, and the discharge capacity ratio (%) of the 100th cycle to the discharge capacity of the 1st cycle was evaluated as a capacity maintenance rate. That is, the higher the capacity retention rate, the better the charge / discharge cycle characteristics of the battery.

[Safety evaluation]
Each battery after initialization under the above conditions was continuously charged at a constant voltage of 4.2 V until it reached 4.2 V at a constant current of 0.5 C. The total time from the start of constant current charging to the end of constant voltage charging was 3 hours. Each battery in this charged state was subjected to a high temperature holding test for 30 minutes in an environment of 150 ° C., and safety was evaluated based on the presence or absence of a short circuit.

  As shown in Table 1, in the batteries of Examples 1 to 9, the capacity retention rate is high, no short circuit is observed even during the high temperature holding test, and the battery characteristics (charge / discharge cycle characteristics) and safety are excellent. Further, since the core-shell type fine particles can be easily introduced into the battery, the gel electrolyte can be easily formed and the productivity is good. In the battery of Example 9 in which core-shell type fine particles are also contained in the positive and negative electrodes, the charge / discharge cycle characteristics are particularly excellent. On the other hand, the battery of Comparative Example 1 has a low capacity retention rate and inferior charge / discharge cycle characteristics, and also has a short circuit during a high temperature holding test and is inferior in safety. In addition, the battery of Comparative Example 3 also has a short circuit during the high temperature holding test, and is inferior in safety. In the battery of Comparative Example 2, the safety was very low, and a short circuit occurred at the initial stage of the battery and charging could not be performed. Therefore, the subsequent experiment was stopped.

It is a conceptual diagram for demonstrating the production | generation process of an intermetallic compound in the negative electrode containing an intermetallic compound as an active material. It is a conceptual diagram for demonstrating the production | generation process of an intermetallic compound in the negative electrode containing an intermetallic compound as an active material.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Current collector 2 Thin layer containing metal element which can be alloyed with lithium 3 Thin layer containing metal element which cannot be alloyed with lithium 4 Intermetallic compound content layer 5 Protective layer

Claims (15)

It is composed of a shell part containing a polymer compound that can be dissolved in an organic solvent or can be gelled in an organic solvent, and a core part that is fine particles stable at room temperature with respect to the organic solvent,
The polymer chain of the polymer compound related to the shell part is chemically bonded to the core part,
Core-shell type fine particles having a dry particle size of 15 μm or less.   The core-shell type fine particles according to claim 1, wherein the organic solvent is a chain carbonate, a chain carbonate, a chain ether, a cyclic ether, a cyclic ester or a nitrile.   The core-shell type fine particle according to claim 1 or 2, wherein the core part is a crosslinked polymer fine particle or an inorganic oxide fine particle. The core part contains a thermoplastic resin as a constituent component,
The core-shell type fine particles according to claim 1 or 2, wherein the thermoplastic resin has a melting point or softening point measured in a state containing the organic solvent of 80 to 130 ° C.   The core-shell type fine particles according to claim 4, wherein the thermoplastic resin is a polyolefin or a copolymerized polyolefin.   The core-shell type fine particles according to any one of claims 1 to 5, wherein the polymer compound according to the shell part is a (meth) acrylate resin. The core-shell type fine particles according to any one of claims 1 to 5, wherein the polymer compound according to the shell part is represented by the following general formula (1).

Wherein R ¹ and R ³ are each a hydrogen atom or an alkyl group having 1 to 3 carbon atoms, R ² is an alkyl group having 1 to 3 carbon atoms, a hydroxyalkyl group, or an alkylene oxide group, and R ⁴ is at least 1 (Indicating an alkyl group having 1 to 6 carbon atoms in which two hydrogen atoms are substituted with an oxetane group or an alicyclic epoxy group, m and n each represents an integer of 100 to 1000.) A copolymer in which the polymer compound represented by the general formula (1) has a unit represented by the following general formula (2) and / or the following general formula (3) and a unit represented by the following general formula (4) The core-shell type fine particles according to claim 7, wherein the ratio of units represented by the following general formula (4) is 50 to 98 mol% in all units of the copolymer.

(Here, R ⁵ , R ⁷ and R ⁸ represent a hydrogen atom or a methyl group, and R ⁶ and R ⁹ represent an alkyl group having 1 to 6 carbon atoms.)   The ion permeable insulating layer containing the core-shell type fine particles according to claim 1 is formed on the surface of the negative electrode, and the ion permeable insulating layer is disposed between the positive electrode and the negative electrode. A lithium secondary battery characterized by comprising:   It has a separator by which a porous substrate and the core-shell type fine particles according to any one of claims 1 to 8 are combined, and the separator is disposed between a positive electrode and a negative electrode. Rechargeable lithium battery.   The lithium secondary battery according to claim 10, wherein the porous substrate is a nonwoven fabric made of polyolefin or polyester.   The lithium secondary battery according to any one of claims 9 to 11, wherein the core-shell type fine particles according to any one of claims 1 to 8 are also present in the positive electrode and / or the negative electrode.   The core-shell type fine particle has a cross-linked structure derived from an oxetane group and / or an alicyclic epoxy group in the shell part of the core-shell type fine particle according to claim 7 or 8. The lithium secondary battery as described in.   The negative electrode has a layer containing an intermetallic compound of a metal element not alloyed with lithium and a metal element capable of alloying with lithium on the surface of a current collector containing a metal element not alloyed with lithium. The lithium secondary battery according to any one of 9 to 13. The lithium secondary battery according to claim 14, wherein the metal element that is not alloyed with lithium is Cu, and the metal element that can be alloyed with lithium is Sn.

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