JP2008300099A - Lithium secondary battery - Google Patents

Abstract

A main object of the present invention is to provide a lithium secondary battery with reduced internal resistance and higher output.
The present invention provides a positive electrode current collector, a positive electrode layer formed on the positive electrode current collector, containing a positive electrode active material, a negative electrode current collector, and the negative electrode current collector. A negative electrode layer containing a negative electrode active material; a separator disposed between the positive electrode layer and the negative electrode layer; and an electrolyte containing a lithium salt filled in the positive electrode layer, the negative electrode layer, and the separator. The above-described problems are solved by providing a lithium secondary battery having a mesoporous metal oxide having higher acidity than mesoporous silica in the separator.
[Selection] Figure 1

Description

  The present invention relates to a lithium secondary battery with reduced internal resistance and higher output.

  With the miniaturization of personal computers, video cameras, mobile phones, etc., in the fields of information-related equipment and communication equipment, lithium secondary batteries have been put into practical use because of their high energy density as the power source used for these equipment. It is becoming popular. On the other hand, in the field of automobiles, the development of electric vehicles has been urgently caused by environmental problems and resource problems, and lithium secondary batteries have been studied as power sources for electric vehicles. In particular, when a lithium secondary battery is used as a power source for an electric vehicle, the output of the current lithium secondary battery is low. Therefore, it is necessary to increase the output of the lithium secondary battery.

  For example, in Patent Document 1, by adding mesoporous silica having nano-sized pores to any part of the positive electrode, the negative electrode, and the separator, the freezing point of the electrolyte contained in the pores decreases, It is disclosed that the characteristics are improved. However, since acid-treated mesoporous silica is used, the acidity of mesoporous silica is small, and the phenomenon that the conductivity of lithium ions is improved by improving the acidity cannot be used. It was difficult to reduce.

  Patent Document 2 discloses a separator characterized in that the surface is charged either negatively or positively in an electrolytic solution. This increases the ionization of the electrolyte solution in the vicinity of the separator and improves the lithium ion conductivity by giving the separator surface a surface potential. Further, as a method for obtaining a separator having a high surface potential, specifically, a method for coating the separator with inorganic oxide fine particles is disclosed. However, even when such inorganic oxide fine particles are added, the lithium ion conductivity cannot be sufficiently improved, and it is difficult to reduce the internal resistance of the battery.

JP 2005-243342 A JP 11-339754 A JP 2001-250529 A Japanese Patent Laid-Open No. 2005-320184 JP 2006-98284 A

  The present invention has been made in view of the above problems, and a main object of the present invention is to provide a lithium secondary battery with reduced internal resistance and higher output.

In order to achieve the above object, in the present invention, a positive electrode current collector, a positive electrode layer formed on the positive electrode current collector and containing a positive electrode active material, a negative electrode current collector, and the negative electrode current collector A negative electrode layer formed thereon and containing a negative electrode active material, a separator disposed between the positive electrode layer and the negative electrode layer, and the positive electrode layer, the negative electrode layer, and a lithium salt filled in the separator A lithium secondary battery comprising:
Provided is a lithium secondary battery characterized in that the separator has a mesoporous metal oxide having higher acidity than mesoporous silica.

  According to the present invention, by using a mesoporous metal oxide having a surface acidity higher than that of mesoporous silica, the lithium ion conductivity can be further improved, and the internal resistance of the lithium secondary battery is sufficiently reduced. High output can be achieved. Further, by using the mesoporous metal oxide that has been made mesoporous, the contact area with the electrolyte is increased, so that the internal resistance of the lithium secondary battery can be more effectively reduced and the output can be increased.

  In the above invention, the mesoporous metal oxide is preferably tungsten oxide. This is because the surface acidity is high and the lithium ion conductivity is excellent.

  In the said invention, it is preferable to make the said mesoporous metal oxide carry | support the lithium ion conductive group with higher acidity than the said mesoporous metal oxide. This is because the surface acidity can be further improved, and the internal resistance of the lithium secondary battery can be reduced and the output can be increased more effectively.

In the above invention, the lithium ion-conducting group is preferably a sulfonic acid group (-SO 3 _H). This is because the surface acidity is high and the lithium ion conductivity is excellent.

  In the present invention, there is an effect that it is possible to obtain a lithium secondary battery with reduced internal resistance and higher output.

The lithium secondary battery of the present invention will be described in detail below.
The lithium secondary battery of the present invention is formed on the positive electrode current collector, the positive electrode current collector, the positive electrode layer containing the positive electrode active material, the negative electrode current collector, and the negative electrode current collector. A negative electrode layer containing a negative electrode active material, a separator disposed between the positive electrode layer and the negative electrode layer, an electrolyte containing a lithium salt filled in the positive electrode layer, the negative electrode layer, and the separator; A lithium secondary battery having a mesoporous metal oxide having a higher acidity than mesoporous silica (hereinafter sometimes simply referred to as a mesoporous metal oxide) in the separator. It is.

  According to the present invention, the separator has the mesoporous metal oxide having a higher acidity than the mesoporous silica, whereby the lithium ion conductivity can be further improved, and the internal resistance of the lithium secondary battery can be sufficiently increased. Reduced output can be increased. In addition, by using a mesoporous metal oxide that has been made mesoporous, it is possible to increase the contact area with the lithium ions present in the electrolyte, and to improve the lithium ion conductivity efficiently, thereby improving the internal resistance of the lithium secondary battery. Reduction and higher output can be achieved.

FIG. 1 is a schematic cross-sectional view showing an example of the lithium secondary battery of the present invention. A lithium secondary battery shown in FIG. 1 includes a positive electrode current collector 1, a positive electrode layer 3 containing a positive electrode active material 2, a negative electrode current collector 4, a negative electrode layer 6 containing a negative electrode active material 5, and a positive electrode A separator 7 disposed between the layer 3 and the negative electrode layer 6; and a positive electrode layer, a negative electrode layer, and an electrolyte (not shown) containing a lithium salt filled in the separator. It contains mesoporous metal oxide 8.
Hereinafter, the lithium secondary battery of this invention is demonstrated for every structure.

1. Mesoporous Metal Oxide First, the mesoporous metal oxide used in the present invention will be described. The mesoporous metal oxide used in the present invention is filled in a separator and has a higher acidity than mesoporous silica.

  The mesoporous metal oxide is filled in a separator and has higher acidity than mesoporous silica, whereby the lithium ion conductivity can be further improved. Furthermore, by using a mesoporous metal oxide that has been made mesoporous, the contact area with lithium ions present in the electrolyte can be increased, and lithium ion conductivity can be improved efficiently.

  The surface acidity of the mesoporous metal oxide is not particularly limited as long as the acidity is higher than that of mesoporous silica and a desired acidity can be obtained, but the PZC value is, for example, 2.2 or less. Of these, 2.0 or less, particularly 1.0 or less is preferable. The surface acidity is measured by determining the isoelectric point (PZC) by measuring the zeta potential.

In the present invention, by using a mesoporous metal oxide (mesoporous metal oxide), lithium ions can be effectively conducted on the porous surface. The diameter of the pores of the mesoporous metal oxide is not particularly limited, but is preferably in the range of 2 nm to 10 nm, for example.
The specific surface area of the mesoporous metal oxide is preferably, for example, 50 m ² / g or more. Such a specific surface area can be calculated as a BET specific surface area from an adsorption isotherm using a BET isotherm adsorption formula.

  The shape of the mesoporous metal oxide is not particularly limited, and examples thereof include a spherical shape and an elliptical sphere. The average particle size of the mesoporous metal oxide is preferably in the range of 0.01 μm to 20 μm, particularly preferably in the range of 0.01 μm to 3 μm. If the average particle size of the mesoporous metal oxide is smaller than the above range, the mesoporous metal oxide particles tend to be too fine and the handling property tends to be extremely reduced. This is because the battery performance tends to decrease due to the increase in length.

The mesoporous metal oxide is not particularly limited as long as it has higher acidity than mesoporous silica and improves lithium ion conductivity. Specifically, the transition metal oxide may be increased. it can. Examples of the transition metal oxide include tungsten oxides such as tungsten oxide (IV) (chemical formula: WO ₂ ), tungsten oxide (V) (chemical formula: W ₂ O ₅ ), and tungsten oxide (VI) (chemical formula: WO ₃ ). And zirconium oxide such as zirconium dioxide (chemical formula: ZrO ₂ ). Among these, in the present invention, the mesoporous metal oxide is preferably mesoporous tungsten oxide (WO ₃ ). This is because the surface acidity is high and the lithium ion conductivity is excellent. The mesoporous metal oxide may have a different valence and may be a mixture of a plurality of metal oxides having the same metal element or a mixture of different metal oxides. Further, the mesoporous metal oxide used in the present invention is usually in a powder form.

In the present invention, the mesoporous metal oxide is preferably supported with a lithium ion conductive group having higher acidity than the mesoporous metal oxide. FIG. 2 is an explanatory view showing an example of the mesoporous metal oxide used in the present invention having the lithium ion conductive group supported thereon. In FIG. 2, mesoporous tungsten oxide carries a sulfonic acid group (—SO ₃ H) which is a lithium ion conductive group having higher acidity than mesoporous tungsten oxide.
By supporting the lithium ion conductive group, the surface acidity can be further improved, and the internal resistance of the lithium secondary battery can be more effectively reduced and the output can be increased.

  The reason why the lithium ion conductive group improves the lithium ion conductivity has not been clearly clarified, but the presence of a large number of Bronsted acids having proton donating ability such as sulfonic acid groups, for example, in an aqueous solvent. It is presumed that the same phenomenon as proton hopping conduction by the Grottus mechanism via water molecules and sulfonic acid groups occurs in the vicinity of the non-aqueous solvent used for the electrolyte and the lithium ion conductive group.

In the present invention, the lithium ion conductive group has higher acidity than the mesoporous metal oxide. The acidity difference is not particularly limited, but the PZC value is, for example, preferably 0.1 or more, particularly 0.5 or more, particularly 1.0 or more. In the present invention, the acidity of the lithium ion conductive group and the mesoporous metal oxide is determined by determining the isoelectric point (PZC) by measuring the zeta potential, and the following document (1): And a method of determining by the method described in (2).
Reference (1): Kodansha, super strong acid / super strong base, p4-7
Reference (2): Industrial books, acid-base catalysts, p159-177

The lithium ion conductive group is not particularly limited as long as it has higher acidity than the above-described mesoporous metal oxide. Specifically, a sulfonic acid group (—SO ₃ H), Examples thereof include a carboxylic acid group (—COOH) and a hydroxyl group (—OH). Among them, a sulfonic acid group and a carboxylic acid group, particularly a sulfonic acid group are preferable. This is because the acidity is high and the lithium ion conductivity is excellent.

  The amount of the lithium ion conductive group supported on the mesoporous metal oxide is not particularly limited as long as lithium ion conductivity can be further improved. For example, when the sulfonic acid group is supported, sulfonic acid Specifically, the molar ratio S / M between the sulfur S mol of the group and the metal element M mol composing the mesoporous metal oxide as the carrier is 0.001 or more, particularly within the range of 0.005 to 0.3 In particular, it is preferably within the range of 0.01 to 0.1.

  The ion exchange capacity of the mesoporous metal oxide carrying the lithium ion conductive group is not particularly limited. Further, the mesoporous metal oxide carrying a lithium ion conductive group used in the present invention is usually in a powder form.

The method for producing the mesoporous metal oxide used in the present invention is not particularly limited as long as it is a method capable of obtaining the above-described mesoporous metal oxide. For example, when obtaining mesoporous tungsten oxide (WO ₃ ), H ₂ WO ₄ powder is put in ultrapure water, hydrogen peroxide is added, stirred at a predetermined temperature, and evaporated under reduced pressure to obtain powder. Later, this powder is dissolved in a mixed solution of ethanol and water, and then a surfactant is added to obtain a solution having an organic / organic mesostructure. Thereafter, a method obtained by heat treatment and the like can be mentioned. More specifically, the method described in JP 2006-98284 A can be used.
Further, the method for supporting the lithium ion conductive group on the mesoporous metal oxide is not particularly limited as long as it is a method capable of obtaining the above-described mesoporous metal oxide supporting the lithium ion conductive group. . For example, when obtaining mesoporous tungsten oxide (WO ₃ ) carrying sulfuric acid, powdered mesoporous tungsten oxide is added to an aqueous sulfuric acid solution, stirred to form a slurry, and then dried to obtain a powder. A method of further firing this powder can be exemplified.

2. Next, the separator used in the present invention will be described. The separator used for this invention is arrange | positioned between a positive electrode layer and a negative electrode layer, has a function which hold | maintains electrolyte, and is filled with the electrolyte mentioned later and the mesoporous metal oxide mentioned above.

  In the present invention, the method of filling the separator with the mesoporous metal oxide is not particularly limited. For example, a method of forming a separator using a mesoporous metal oxide and a binder resin, and a binder are used. And a method for fixing the mesoporous metal oxide on the porous surface of the separator substrate.

  In a method of forming a separator using a mesoporous metal oxide and a binder resin, the mesoporous metal oxide is usually filled by fixing the mesoporous metal oxide with a binder resin to form a separator. Thereby, the separator comprised from a mesoporous metal oxide and binder resin is obtained.

The mesoporous metal oxide is the same as that described in “1. Mesoporous metal oxide”, and is not described here.
The binder resin is not particularly limited as long as it can fix the mesoporous metal oxide. Specifically, as the binder resin and the binder, The resin etc. which are used can be mentioned.

  The resin used for forming the separator can be the same as that used for a general lithium secondary battery, and is not particularly limited. Examples thereof include resins such as polyethylene (PE), polypropylene (PP), polyester, cellulose, and polyamide. Especially in this invention, it is preferable that the said resin is olefin resin, such as polyethylene (PE) and a polypropylene (PP). When such a resin is used, for example, the above-described mesoporous metal oxide and binder resin can be kneaded, heated and melted, and then extruded to obtain a separator.

  In addition, when the resin used to form such a separator is used, the content of the mesoporous metal oxide contained in the obtained separator is improved in lithium ion conductivity and desired internal resistance. There is no particular limitation as long as a lithium secondary battery having a sufficiently high level of output and a high output can be obtained. For example, it is preferably in the range of 30% by mass to 90% by mass, particularly in the range of 40% by mass to 80% by mass, and particularly in the range of 50% by mass to 80% by mass. Within the above range, lithium ion conductivity can be improved, a desired high output lithium secondary battery can be obtained, and the flexibility of the separator such as bending can be maintained. Because. The obtained separator may be any of a non-stretched film, a uniaxially stretched film, and a biaxially stretched film.

  On the other hand, the resin used as the binder is not particularly limited as long as it is used for a general lithium secondary battery. Specifically, polyvinylidene fluoride (PVDF), poly Examples thereof include fluorine resins such as tetrafluoroethylene (PTFE) and ethylenetetrafluoroethylene (ETFE). Among them, in the present invention, polyvinylidene fluoride (PVDF) and polytetrafluoroethylene (PTFE) are preferable. When such a resin is used, for example, a separator containing a mesoporous metal oxide, a binder resin, and a solvent is prepared, and the solution is applied to the negative electrode layer or the positive electrode layer and dried. Can be obtained.

  Further, when the resin used as such a binder is used, the weight ratio of the binder to the mesoporous metal oxide is such that the lithium ion conductivity is improved and the desired internal resistance is reduced. There is no particular limitation as long as a lithium secondary battery that is sufficiently reduced and has a high output can be obtained. Specifically, the mesoporous metal oxide is, for example, in the range of 300 parts by weight to 3000 parts by weight, particularly in the range of 500 parts by weight to 2500 parts by weight, in particular, 1000 parts by weight to 2000 parts by weight with respect to 100 parts by weight of the binder. It is preferably within the range of parts by weight. If it is in the said range, the lithium secondary battery which improved the electroconductivity of lithium ion and made desired high output can be obtained.

  In the method of fixing the mesoporous metal oxide to the porous surface of the separator substrate using the binder, the solution containing the mesoporous metal oxide and the binder is usually applied to the separator substrate. And mesoporous metal oxide. Thereby, the separator which has a separator base material and the mesoporous metal oxide carry | supported on the porous surface of the said separator base material can be obtained. The mesoporous metal oxide is the same as that described in “1. Mesoporous metal oxide”, and is not described here. Moreover, about the said binder, the thing similar to the material of the binder mentioned above can be mentioned.

  As said separator base material, the thing similar to the separator base material used for the general lithium secondary battery can be used, It does not specifically limit, It is used in order to form the separator mentioned above. The same resin can be used. Of these, polyethylene and polypropylene are preferred. The separator substrate may have a single layer structure or a multilayer structure. Examples of the separator base material having a multilayer structure include a separator base material having a two-layer structure of PE / PP and a separator base material having a three-layer structure of PP / PE / PP. Furthermore, in the present invention, the separator substrate may be a nonwoven fabric such as a resin nonwoven fabric or a glass fiber nonwoven fabric.

  Examples of a method for applying a paste containing a mesoporous metal oxide to the separator substrate include a spray method, a dispense method, a dipping method, and a blade coating method.

  In the present invention, a desired amount of mesoporous silica may be mixed with the mesoporous metal oxide in the separator.

  In the present invention, as described above, usually, the mesoporous metal oxide is mixed with the resin or the like to give flexibility, but the mesoporous metal oxide is not used without using the resin or the like. A separator may be formed by using only. For example, a product obtained by press-molding the mesoporous metal oxide powder may be used.

3. Next, the positive electrode layer and the negative electrode layer used in the present invention will be described.
The positive electrode layer used in the present invention contains at least a positive electrode active material and an electrolyte described later.
The positive electrode active material is not particularly limited as long as it can occlude and release lithium ions. Examples thereof include LiCoO ₂ , LiCoO ₄ , LiMn ₂ O ₄ , LiNiO ₂ , and LiFePO _4. Among these, LiCoO ₂ is preferable.

  The positive electrode layer usually contains a conductive material and a binder. Examples of the conductive material include carbon black and acetylene black. Since the binder is the same as that described in “2. Separator”, description thereof is omitted here.

On the other hand, the negative electrode layer used in the present invention contains at least a negative electrode active material and an electrolyte described later.
The negative electrode active material is not particularly limited as long as it can occlude and release lithium ions. For example, metal lithium, lithium alloy, metal oxide, metal sulfide, metal nitride, and graphite And carbon-based materials such as Of these, graphite is preferable.

  The negative electrode layer may contain a conductive material and a binder as necessary. As the conductive material and the binder, the same materials as those for the positive electrode layer can be used.

4). Electrolyte Next, the electrolyte used in the present invention will be described.
In the present invention, the separator, the positive electrode layer, and the negative electrode layer described above usually have an electrolyte containing a lithium salt.
Specifically, the electrolyte may be liquid or gelled, but is preferably liquid. Among these, a nonaqueous electrolytic solution is preferable. This is because the lithium ion conductivity becomes better. The non-aqueous electrolyte usually has a lithium salt and a non-aqueous solvent. The lithium salt is not particularly limited as long as it is a lithium salt used in a general lithium secondary battery. For example, LiPF ₆ , LiBF ₄ , LiN (CF ₃ SO ₂ ) ₂ , LiCF ₃ SO ₃ , LiC ₄ F ₉ SO ₃ , LiC (CF ₃ SO ₂ ) ₃ and LiClO ₄ . On the other hand, the non-aqueous solvent is not particularly limited as long as it can dissolve the lithium salt. For example, propylene carbonate, ethylene carbonate, diethyl carbonate, dimethyl carbonate, ethyl methyl carbonate, 1,2-dimethoxy Ethane, 1,2-diethoxyethane, acetonitrile, propionitrile, tetrahydrofuran, 2-methyltetrahydrofuran, dioxane, 1,3-dioxolane, nitromethane, N, N-dimethylformamide, dimethyl sulfoxide, sulfolane, γ-butyrolactone, etc. Can be mentioned. In the present invention, these non-aqueous solvents may be used alone or in combination of two or more. Moreover, room temperature molten salt can also be used as said non-aqueous electrolyte.

5. Positive electrode current collector and negative electrode current collector
Next, the positive electrode current collector and the negative electrode current collector used in the present invention will be described.
In the present invention, as illustrated in FIG. 1, a positive electrode current collector and a negative electrode current collector are usually disposed outside the positive electrode layer and the negative electrode layer, respectively.
Such a positive electrode current collector collects current from the positive electrode layer. The material of the positive electrode current collector is not particularly limited as long as it has conductivity, and examples thereof include aluminum, SUS, nickel, iron and titanium. Among them, aluminum and SUS are preferable. . Furthermore, the positive electrode current collector may be a dense metal current collector or a porous metal current collector.
The negative electrode current collector is a current collector for the negative electrode layer. The material for the negative electrode current collector is not particularly limited as long as it has electrical conductivity, and examples thereof include copper, stainless steel, nickel, and the like, among which copper is preferable. Furthermore, the positive electrode current collector may be a dense metal current collector or a porous metal current collector.

6). Others The lithium secondary battery of the present invention is usually produced by inserting a lithium secondary battery as exemplified in FIG. 1 into a battery case and sealing the periphery thereof. As the battery case, generally, a metal case is used, for example, a stainless steel case. Further, the shape of the battery case used in the present invention is not particularly limited as long as it can accommodate the separator, the positive electrode layer, the negative electrode layer, and the like described above. , Coin type, laminate type and the like.

  The method for producing a lithium secondary battery of the present invention is not particularly limited as long as a desired secondary resistance can be reduced and a high-power lithium secondary battery can be obtained. For example, using a coin cell as a battery case, a negative electrode is placed on a negative electrode can, and the non-aqueous electrolyte is dropped onto the negative electrode. Next, a method of obtaining a lithium secondary battery by placing the separator, dropping the non-aqueous electrolyte, placing a positive electrode, and caulking a positive electrode can can be exemplified.

  The present invention is not limited to the above embodiment. The above-described embodiment is an exemplification, and the present invention has substantially the same configuration as the technical idea described in the claims of the present invention, and any device that exhibits the same function and effect is the present invention. It is included in the technical scope of the invention.

  Hereinafter, the present invention will be described in more detail with reference to examples.

[Experiment 1]
Powdered mesoporous silica (SiO ₂ ) (SILFAM-A type, manufactured by Nippon Chemical Industry Co., Ltd.) and polytetrafluoroethylene (PTFE) are weighed and mixed at a volume ratio of 50/1 (vol / vol). did. About 2 cm ^{3 of} this mixture was put into a mold and pelletized. At this time, the pressure was 1 t / cm ² and the pellet shape was a cylinder of φ13 mm. The pellet was dried at 120 ° C. for 12 hours.
Next, an electrolyte solution (ethylene carbonate (EC) and dimethyl carbonate (DMC) mixed sufficiently in a volume ratio of 3: 7) in the pellet pores was mixed with lithium hexafluorophosphate (LiPF ₆ ) as a supporting salt. Was dissolved at a concentration of 1 mol / L), sandwiched between SUS plates, and a conductivity cell filled with an electrolyte solution between the SUS plates was produced.

[Experiment 2]
A conductivity cell was prepared in the same manner as in Experimental Example 1, except that mesoporous tungsten oxide (WO ₃ ) (described in the adjustment of mesoporous tungsten oxide (WO ₃ ) in Examples described later) was used instead of mesoporous silica. Produced.

(Lithium ion conductivity measurement)
In Experimental Examples 1 and 2, the thickness and weight of the pellets after drying at 120 ° C. for 12 hours were measured, and the solid content volume ratio was calculated. From this, the volume of the pores in the pellet was derived.
Next, using the conductivity cells obtained in Experimental Example 1 and Experimental Example 2, the lithium ion (Li ⁺ ) conductivity of the pellet was derived by impedance measurement.
The lithium ion conductivity in the pellet pore was derived by calculation using the volume of the pore in the pellet and the lithium ion (Li ⁺ ) conductivity of the pellet. The result is shown in FIG. As shown in FIG. 3, the lithium ion conductivity in the pellet pores was measured using mesoporous tungsten oxide (WO ₃ ) compared to the conductivity cell of Experimental Example 1 using mesoporous silica (SiO ₂ ). In the case of the conductivity cell of Example 2, the lithium ion conductivity was improved.

[Example]
(Adjustment of mesoporous tungsten oxide) (see JP 2006-98284 A)
The H ₂ WO ₄ powder was put in ultrapure water, hydrogen peroxide was added, and the mixture was stirred at 40 ° C. to obtain a yellow solution in which the H ₂ WO ₄ powder was dissolved. Excess hydrogen peroxide and solvent in this solution were removed by evaporation under reduced pressure at 40 ° C. to obtain yellow polytungstic acid (PWA) powder. After dissolving this polytungstic acid in a mixed solution of ethanol and water to obtain a yellow solution of polytungstic acid, an ethylene oxide-propylene oxide-ethylene oxide block copolymer (P123 = [EO] ₂₀ [PO]) was used as a surfactant. ₇₀ [EO] ₂₀ ) An ethanol solution was added to obtain a solution having a stable organic / organic mesostructure containing P123 and polytungstic acid. Next, heat treatment was performed at 400 ° C. for 24 hours in an air atmosphere to obtain mesoporous tungsten oxide (WO ₃ ).

(Separator production)
A mixture of 50 parts by weight of white powder obtained by adjusting the above mesoporous tungsten oxide as a mesoporous material, 15 parts by weight of high-density polyethylene having a weight average molecular weight of 1.4 million, and 35 parts by weight of mineral oil is kneaded and heated to melt. The film was formed into a 0.1 mm film by a shaft extruder. Next, the inorganic film is stretched in the longitudinal direction and the transverse direction by a tenter type stretching machine heated to 140 ° C., and further subjected to heat treatment at 145 ° C. for 15 seconds in an air atmosphere. It was immersed to extract and remove the mineral oil in the film, and dried to prepare a separator having a film thickness of 25 μm, high-density polyethylene 20 wt%, and the above powder 80 wt%.

(Preparation of positive electrode)
In 125 mL of a solvent n-methylpyrrolidone solution in which 5 g of polyvinylidene fluoride (PVDF) as a binder is dissolved, 85 g of lithium cobaltate (LiCoO ₂ ) powder as a positive electrode active material and 10 g of carbon black as a conductive material. It was introduced and kneaded until uniformly mixed to prepare a positive electrode paste. This positive electrode paste was applied on one side onto a 15 μm thick Al current collector, and then dried to produce an electrode. The electrode basis weight was 6 mg / cm ² . This electrode was pressed to a paste thickness of 45 μm and a paste density of 1.6 g / cm ³ . This electrode was cut out to have a diameter of 16 mm to obtain a positive electrode.

(Anode production)
92.5 g of graphite powder as a negative electrode active material is introduced into 125 mL of a solvent n-methylpyrrolidone solution in which 7.5 g of polyvinylidene fluoride (PVDF) as a binder is dissolved, and kneaded until uniformly mixed. Thus, a negative electrode paste was prepared. This negative electrode paste was applied on one side onto a 15 μm thick Cu current collector, and then dried to produce an electrode. The electrode basis weight was 4 mg / cm ² . This electrode was pressed to a paste thickness of 20 μm and a paste density of 1.2 g / cm ³ . This electrode was cut out to a diameter of 19 mm to obtain a negative electrode.

(Coin cell production)
A CR2032-type coin cell was obtained using the obtained separator, positive electrode and negative electrode. In addition, as a supporting salt, lithium hexafluorophosphate (LiPF ₆ ) was dissolved at a concentration of 1 mol / L in a mixed solution in which ethylene carbonate (EC) and dimethyl carbonate (DMC) were mixed at a volume ratio of 3: 7. What was done was used.

[Comparative example]
A coin cell was obtained in the same manner as in the example except that mesoporous silica was used instead of mesoporous tungsten oxide as the mesoporous material to be filled in the separator.

[Evaluation]
(Battery resistance measurement)
Li (lithium) ion resistance was measured using the coin cell obtained in the Example and the comparative example. The Li ion resistance was conditioned at 3.0 V to 4.1 V, adjusted to 60% SOC (state of charge), and measured by an AC impedance method at 25 ° C. and a frequency of 10 mHz to 100 kHz. The obtained resistance values are shown in Table 1.

  As shown in Table 1, in the example, the resistance value was 5.2Ω. On the other hand, in the comparative example, the resistance value was 6.0Ω. Thus, the Li ion resistance of the example using mesoporous tungsten oxide as the mesoporous material was smaller than that of the comparative example using mesoporous silica as the mesoporous material.

  From the above results, the coin cell obtained in the example can further improve the conductivity of lithium ions by using a mesoporous metal oxide having a higher surface acidity than mesoporous silica in the separator, It became clear that the internal resistance of the lithium secondary battery can be sufficiently reduced to increase the output. As described above, in the example, it was possible to obtain a lithium secondary battery with higher internal resistance and higher output.

It is a schematic sectional drawing which shows an example of the lithium secondary battery of this invention. It is explanatory drawing explaining an example of the mesoporous metal oxide used for this invention. It is a graph which shows the lithium ion conductivity measurement result of the conductivity cell obtained in Experimental example 1 and Experimental example 2.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Positive electrode collector 2 ... Positive electrode active material 3 ... Positive electrode layer 4 ... Negative electrode collector 5 ... Negative electrode active material 6 ... Negative electrode layer 7 ... Separator 8 ... Mesoporous metal oxide

Claims (4)

A positive electrode current collector, a positive electrode layer formed on the positive electrode current collector and containing a positive electrode active material, a negative electrode current collector, and a negative electrode layer formed on the negative electrode current collector and containing a negative electrode active material A lithium secondary battery comprising: a separator disposed between the positive electrode layer and the negative electrode layer; and an electrolyte containing a lithium salt filled in the positive electrode layer, the negative electrode layer, and the separator. ,
The lithium secondary battery, wherein the separator has a mesoporous metal oxide having a higher acidity than mesoporous silica. The lithium secondary battery according to claim 1, wherein the mesoporous metal oxide is mesoporous tungsten oxide (WO ₃ ).   3. The lithium secondary battery according to claim 1, wherein a lithium ion conductive group having a higher acidity than that of the mesoporous metal oxide is supported on the mesoporous metal oxide. The lithium secondary battery according to claim 3, wherein the lithium ion conductive group is a sulfonic acid group (—SO ₃ H).

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