JP2010102895A - Lithium secondary battery - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a lithium secondary battery having a satisfactory rate characteristic and capacity retention rate by using an active material coated with a solid electrolyte having ion conductivity, as a positive electrode. <P>SOLUTION: In the lithium secondary battery including a positive electrode, a negative electrode, a nonaqueous electrolyte and a separator, a positive electrode active material coated with a solid electrolyte composed mainly of: a copolymer 6 having a structure in which an organic polymer block 5 is bonded to a metal oxide polymer block 4 through oxygen; and a lithium salt, is used as the positive electrode. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a lithium secondary battery having a positive electrode, a negative electrode, a non-aqueous electrolyte, and a separator.

In recent years, developments on mobile electronic devices that are smaller, thinner, and lighter have been very active. In the wave of such downsizing, thinning, and weight reduction of electronic devices, high performance is required for secondary batteries that support these electric powers. Under such demand, development of a lithium secondary battery as a high energy density battery has been rapidly advanced. A lithium secondary battery is composed of a negative electrode, a positive electrode, a separator, an electrolytic solution, and the like, and the voltage of the battery is determined depending on the type of active material used in the positive electrode and the negative electrode. Currently, the positive electrode active material, with respect to the anode active material have been various materials studied, the positive electrode active material, lithium cobalt oxide, lithium nickel oxide or the like, a composite oxide having a layered structure represented by LiMO _2, Alternatively, a composite oxide having a spinel structure represented by LiM ₂ O ₄ , lithium iron phosphate having an olivine structure, and the like have been proposed. However, the present situation is that the problem of cycle characteristics has not been completely solved because the positive electrode is used under the severe condition of an oxidation state regardless of which active material is used. In particular, when spinel type lithium manganese oxide LiMn ₂ O ₄ is used as the positive electrode active material, it is said that one of the causes of deterioration is that Mn is eluted in the electrolyte during the charge / discharge cycle. An object of the present invention is to provide a non-aqueous electrolyte secondary battery having excellent cycle characteristics by providing a positive electrode that has a high capacity and does not decrease the battery capacity even after a charge / discharge cycle.

When the surface of the positive electrode is in an oxidized state, it is considered that one of the causes of deterioration of the cycle characteristics is that the electrolytic solution cannot withstand a high voltage state and decomposes and deteriorates. In particular, when spinel-type lithium manganese oxide LiMn ₂ O ₄ is used as the positive electrode active material, it is considered that elution of manganese is one of the causes of cycle characteristics deterioration. In order to solve this problem, there are several prior examples in which an ion conductive film is formed on the positive electrode active material to try to improve the electrode characteristics. For example, in Patent Documents 1, 3, and 4, an ion conductive film is coated on the surface of the positive electrode by spraying polyethylene oxide on the surface of the positive electrode. However, the bonding force that acts between the ion-conducting film produced here and the surface of the positive electrode active material is only intermolecular force and very weak, so the expansion / contraction of the film that occurs with the charge / discharge cycle is large. It is predicted that peeling will occur from the surface of the active material. Patent Documents 2 and 5 attempt to improve electrode characteristics by preparing an inorganic ion conductive film on the positive electrode surface. However, since a film made of only inorganic material is poor in flexibility, it cannot follow the magnitude of expansion / contraction of the film accompanying charge / discharge, and there is a concern that the film may be destroyed due to charge / discharge. The above causes contact between the positive electrode active material and the electrolytic solution, causes decomposition of the electrolytic solution, and deteriorates the performance of the electrode.
Japanese Patent Laid-Open No. 8-148183 Japanese Laid-Open Patent Publication No. 9-71813 Japanese Patent Laid-Open No. 11-97027 JP 2002-373643 A Japanese Patent Laid-Open No. 2003-173770

This invention is made | formed in view of such a situation, Comprising: The active material used as a positive electrode is coat | covered with the flexible solid electrolyte membrane which has ion conductivity, Electrolyte solution on the surface of a positive electrode An object of the present invention is to provide a lithium secondary battery that prevents decomposition of the lithium secondary battery and has good rate characteristics. In particular, when spinel-type lithium manganese oxide LiMn ₂ O ₄ is included as the positive electrode active material, deterioration of cycle characteristics is also suppressed by preventing elution of Mn.

  The lithium secondary battery according to the present invention is a lithium secondary battery having a positive electrode, a negative electrode, a non-aqueous electrolyte, and a separator. The positive electrode has a structure in which an organic polymer block is bonded to a metal oxide polymer block through oxygen. It is an active material material coated with a solid electrolyte mainly composed of a copolymer having a lithium salt and lithium salt. In addition, the metal in this specification is a broad concept including a semimetal such as Si in addition to a general metal.

  With this configuration, the positive electrode active material is covered with a solid electrolyte film containing a copolymer having a structure in which an organic polymer block is bonded to a metal oxide polymer block, and the positive electrode active material and the electrolyte solution are brought into a non-contact state. can do. It is considered that the coating layer on the positive electrode surface contributes to minimizing degradation and degradation of the electrolytic solution, and suppresses degradation of cycle characteristics.

  In addition, since the solid electrolyte including a copolymer having a structure in which an organic polymer block is bonded to a metal oxide polymer block through oxygen has ionic conductivity, favorable rate characteristics can be obtained. In addition, a solid electrolyte containing a copolymer having a structure in which an organic polymer block is bonded to a metal oxide polymer block becomes a flexible film on the surface of the positive electrode active material. Therefore, the film is not peeled off from the positive electrode active material along with the charge / discharge cycle, and a good capacity retention rate can be obtained.

  In the lithium secondary battery according to the present invention, it is preferable that 5 to 90% of metal atoms contained in the copolymer are bonded to a monovalent organic group. .

  According to this configuration, since the positive electrode active material can be coated with a dense film made of a solid electrolyte, the positive electrode active material and the electrolytic solution can be reliably brought into a non-contact state and decomposition of the electrolytic solution can be prevented.

  In the lithium secondary battery according to the present invention, the organic group may be an alkyl group or an alkenyl group having 1 to 5 carbon atoms.

  In the lithium secondary battery according to the present invention, it is preferable that the copolymer contains at least Si.

  According to this configuration, the positive electrode active material can be covered with the solid electrolyte film having good stability against moisture in the atmosphere.

  In the lithium secondary battery according to the present invention, the copolymer may contain at least one metal selected from the group consisting of Al, Ti, and Zr.

In the lithium secondary battery according to the present invention, the organic polymer block has the following general formula (1):
− ((CH ₂ ) _m —O) _n − (1)
(Wherein m represents an integer of 2 to 5 and n represents an integer of 1 or more).

  According to this configuration, the positive electrode active material can be reliably coated with the solid electrolyte film having good ion conductivity, and a lithium secondary battery with good rate characteristics can be provided.

  In the lithium secondary battery according to the present invention, the organic polymer block preferably has an average molecular weight of 100 to 2000.

  According to this configuration, the positive electrode active material can be more reliably coated with the solid electrolyte film having good ion conductivity.

  Moreover, in the lithium secondary battery according to the present invention, the precursor for forming the organic polymer block is preferably one or more selected from polyethylene glycol and polypropylene glycol.

In the lithium secondary battery according to the present invention, the copolymer has the following general formula (2):
R ¹ _b M (OR ² ) _c (OH) _abc (2)
(In the formula, M represents a metal, R ¹ represents a monovalent organic group, R ² represents a lower alkyl group having 1 to 8 carbon atoms, a represents the valence of metal M, and b represents 0 to 0. 2 represents an integer of 2 and c represents an integer of 0 or more, provided that 0 ≦ c ≦ a−b), and a product formed by polycondensation of one or more metal oxides represented by It may be obtained by reacting a polymer compound.

In the lithium secondary battery according to the present invention, as the lithium salt, the solid electrolyte includes CH ₃ COOLi (lithium acetate), LiClO ₄ (lithium perchlorate), LiCF ₃ SO ₃ (trifluoromethanesulfone). Acid lithium), LiN (CF ₃ SO ₂ ) ₂ (bis (trifluoromethanesulfonyl) aminolithium), LiN (C ₂ F ₅ SO ₂ ) ₂ (bis (pentafluoroethylsulfonyl) aminolithium) In addition, at least one kind may be included.

  Moreover, the lithium secondary battery which concerns on this invention WHEREIN: It is preferable that the film thickness of the said solid electrolyte is 50 nm-5 micrometers.

  According to this structure, decomposition | disassembly of electrolyte solution can be suppressed reliably, without inhibiting insertion and detachment | desorption of lithium ion in a positive electrode.

  In the lithium secondary battery according to the present invention, the weight ratio of the metal oxide polymer block to the organic polymer block constituting the copolymer is preferably 90:10 to 20:80.

  According to this configuration, the positive electrode active material can be covered with a uniform solid electrolyte film.

In the lithium secondary battery according to the present invention, it is preferable that the ionic conductivity of the solid electrolyte is 1.0 × 10 ⁻⁶ S / cm or more.

  According to this configuration, it is possible to provide a lithium secondary battery with good rate characteristics.

In the lithium secondary battery according to the present invention, the BET specific surface area of the solid electrolyte is preferably 10 m ² / g or less.

  According to this configuration, contact between the positive electrode active material and the electrolytic solution can be reliably prevented, and decomposition of the electrolytic solution can be reliably prevented.

Further, when spinel type lithium manganese oxide LiMn ₂ O ₄ is included as the positive electrode active material, elution of Mn can be prevented.

  According to the lithium secondary battery of the present invention, a positive electrode coated with a solid electrolyte mainly comprising a copolymer having a structure in which an organic polymer block is bonded to a metal oxide polymer block via oxygen and a lithium salt. Since the active material is used as the positive electrode, it is possible to provide a lithium secondary battery with good rate characteristics and capacity retention.

  Hereinafter, the present invention will be described in detail.

  The lithium secondary battery according to the present invention is configured to have a positive electrode, a negative electrode, a non-aqueous electrolyte, and a separator.

<Negative electrode>
In the present invention, various carbon materials excluding the diamond-type crystal structure can be used as the material constituting the negative electrode. Specific examples include artificial graphite, natural graphite, mesophase spherical carbon, pitch-based and polyacrylonitrile-based materials. Carbons obtained by calcining materials, vapor-grown carbon, glassy carbon, coke, calcined polymer materials, carbon black, acetylene black, etc., and their crystal structures are graphite, amorphous carbon, amorphous carbon and their intermediates. Either can be used.

<Positive electrode>
In the present invention, the material constituting the positive electrode is not particularly limited. For example, as the positive electrode active material, LiCoO ₂ (lithium cobaltate), LiFePO ₄ (lithium iron phosphate), LiNiO ₂ (lithium nickelate), Transition metal oxides such as LiMn ₂ O ₄ (lithium manganate), V ₂ O ₅ (vanadium pentoxide), MnO ₂ (manganese dioxide), TiS ₂ (titanium disulfide), MoS ₂ (molybdenum disulfide), Further, chalcogen compounds and the like can be used. Among these, when the spinel type lithium manganese oxide LiMn ₂ O ₄ is contained, an elution effect of Mn is also observed.

  The surface of the positive electrode active material described above is covered with a solid electrolyte film mainly composed of a copolymer having a structure in which an organic polymer block is bonded to a metal oxide polymer block through oxygen and a lithium salt. ing. Here, the metal oxide polymer block specifically refers to a block having a repeating unit (-MO-) formed by bonding a metal atom (hereinafter referred to as M) and an oxygen atom. . The metal may be any material and is not particularly limited, but Si, Al, Ti, and Zr are preferable.

  A solid electrolyte mainly composed of a copolymer having a structure in which an organic polymer block responsible for ionic conductivity is bonded to oxygen through a metal oxide polymer block that forms a strong skeleton is formed on the surface of the positive electrode active material. It is a strong and flexible film. In addition, since this copolymer has a hydroxyl group, it can be polycondensed with a functional group such as a hydroxyl group present on the surface of the positive electrode active material, and can be chemically bonded to the surface of the positive electrode material. Therefore, the film has good adhesion to the positive electrode active material.

  Moreover, it is preferable that 5 to 90%, more preferably 10 to 80% of the metal atoms contained in the copolymer are bonded to a monovalent organic group. Such organic groups bonded to metal atoms enter the pores in the solid electrolyte film covering the surface of the positive electrode active material, imparting flexibility to the solid electrolyte film, and the denseness of the solid electrolyte film. Play a role to improve. The monovalent organic group may be any one as long as it can improve the density of the solid electrolyte membrane, and is not particularly limited. 5 alkyl or alkenyl groups are preferred.

Further, the organic polymer block constituting the copolymer may have any structure as long as it has ionic conductivity, and may have a linear structure or a branched structure. However, the following general formula (1)
− ((CH ₂ ) _m —O) _n − (1)
(In the formula, m represents an integer of 1 to 3, and n represents an integer of 1 or more). Since the organic polymer block having such a structural unit has an oxygen atom in the molecule, it forms a complex with an alkali metal salt such as lithium and has high ionic conductivity.

  The average molecular weight of the organic polymer block is good as long as it exhibits good ionic conductivity and can form a good film on the surface of the positive electrode active material in a state of being bonded to the metal oxide polymer block. Although not particularly limited, 100 to 2000 is preferable, and 100 to 1000 is particularly preferable. When the average molecular weight is larger than 2000, there is a possibility that appropriate ion conductivity cannot be obtained. When the average molecular weight is smaller than 100, a skeleton for producing a coating on the surface of the positive electrode material is sufficiently developed. There is a risk of not.

  Specifically, for example, polyalkylene glycol and polyether are macroscopically solid in a rubber region having a glass transition temperature (Tg) or higher, but are microscopic due to a chemical or physical cross-linked structure. Specifically, the polymer chain is in a liquid state and exhibits ionic conductivity. Such polyalkylene glycols and polyethers are known to have a tendency that the glass transition temperature increases with an increase in molecular weight and the ionic conductivity decreases accordingly. In view of the above, it can be said that the molecular weight of the organic polymer block is preferably set low in order to provide the copolymer with high ionic conductivity. However, when the molecular weight of the organic polymer block is too low, the skeleton for producing the film may not be sufficiently developed, which may make it difficult to produce the film. Therefore, in the present invention, the average molecular weight of the organic polymer block is preferably 100 to 2000, and particularly preferably 100 to 1000, as described above.

  The precursor for forming the organic polymer block is not particularly limited, but an organic polymer compound such as polyalkylene glycol or polyether is preferable. Since organic polymer compounds such as polyalkylene glycol and polyether have hydroxyl groups at both ends, they can be polycondensed with the hydroxyl group of the metal oxide, and the organic polymer block is oxygenated in the metal oxide polymer block. It is possible to produce a copolymer having a structure bonded via the.

  Specific examples of polyalkylene glycol and polyether include polyethylene glycol, polypropylene glycol, glycerin polyether, silicone polyether, acrylic polyether, phosphazene polyether, and the like. Among these, polyethylene glycol and polypropylene glycol are relatively easy to obtain and are preferable from the viewpoint of cost.

  Further, the weight ratio of the metal oxide polymer block and the organic polymer block constituting the copolymer is particularly limited as long as it is a ratio capable of producing a uniform solid electrolyte film on the surface of the positive electrode active material. However, as a specific example, 90:10 to 20:80 is preferable. When the weight of the organic polymer block relative to the metal oxide polymer block is less than 10/90, the structure can be changed on the surface of the positive electrode active material following the expansion / contraction change of the positive electrode active material. There is a possibility that a solid electrolyte membrane, that is, a solid electrolyte membrane excellent in flexibility cannot be produced. In addition, a solid electrolyte membrane having appropriate ionic conductivity cannot be produced on the surface of the positive electrode active material, which may result in a lithium secondary battery having inferior rate characteristics. Further, when the weight of the organic polymer block relative to the metal oxide polymer block is larger than 80/20, there is a possibility that a solid electrolyte film having excellent adhesion cannot be produced on the surface of the positive electrode active material. .

For example, the copolymer as described above is represented by the following general formula (2).
R ¹ _b M (OR ² ) _c (OH) _abc (2)
(In the formula, M represents a metal, R ¹ represents a monovalent organic group, R ² represents a lower alkyl group having 1 to 8 carbon atoms, a represents the valence of metal M, and b represents 0 to 0. 2 represents an integer of 2 and c represents an integer of 0 or more, provided that 0 ≦ c ≦ a−b), and a product formed by polycondensation of one or more metal oxides represented by It can be obtained by reacting a polymer compound.

  Specifically, the metal represented by M can be selected from any metal elements, and preferred specific examples include Si, Al, Ti, and Zr.

Any organic group represented by R ¹ can be used as long as it does not easily become a steric hindrance during polycondensation and can sufficiently develop a skeleton necessary for film formation on the surface of the positive electrode active material. It may be an organic group. For example, examples of the organic group represented by R ¹ include an unsubstituted monovalent hydrocarbon group such as an alkyl group having 1 to 10 carbon atoms, a cycloalkyl group, an alkenyl group, an aryl group, and an aralkyl group, and hydrogen of these groups. Some or all of the atoms may be halogen atoms (chlorine, fluorine, bromine atoms, etc.), cyanoalkylene, oxyalkylene groups such as oxyethylene groups, polyoxyalkylene groups such as polyoxyethylene groups, (meth) acryl groups, (meth ) In substituted monovalent hydrocarbon groups substituted with functional groups such as acryloxy group, acryloyl group, methacryloyl group, mercapto group, amino group, amide group, ureido group, and epoxy group, these unsubstituted or substituted monovalent hydrocarbon groups, -O -, - NH -, - N (CH 3) -, - N (C 6 H 5) -, cited _{C 6 H 5 NH-, H 2} NCH 2 CH 2 NH- or the like is interposed group It is possible.

More specific examples of the organic group represented by R ¹ include alkyl groups such as CH ₃ —, CH ₃ CH ₂ —, CH ₃ CH ₂ CH ₂ —, CH ₂ ═CH—, CH ₂ ═CHCH ₂ —. , An alkenyl group such as CH ₂ ═C (CH ₃ ) —, an aryl group such as C ₆ H ₅ —, ClCH ₂ —, ClCH ₂ CH ₂ CH ₂ —, CF ₃ CH ₂ CH ₂ —, CNCH ₂ CH ₂ — CH ₃ — (CH ₂ CH ₂ O) m—CH ₂ CH ₂ CH ₂ — (where m is an integer of 1 or more), CH ₂ (O) CHCH ₂ OCH ₂ CH ₂ CH ₂ — (provided that , CH ₂ (O) CHCH ₂ represents a glycidyl _{group), CH 2 = CHCOOCH 2 -} , CH 2 = CHCOOCH 2 CH 2 CH 2 -, CH 2 = CCH 3 COOCH 2 CH 2 CH 2, HSCH 2 CH 2 CH _2- , NH ₂ CH ₂ CH ₂ CH _2- , NH ₂ CH ₂ CH ₂ N _{HCH 2 CH 2 CH 2 -,} NH 2 CONHCH 2 CH 2 CH 2 - and the like.

Among the organic groups described above, in particular, the alkyl group and alkenyl group having 1 to 5 carbon atoms are less likely to become a steric hindrance in the polycondensation reaction compared to other organic groups, and the surface of the positive electrode active material material can be reduced. This is preferable because a skeleton necessary for film formation can be sufficiently developed. When b is 2 in the general formula (2), the two organic groups represented by R ¹ may be the same organic group or different organic groups.

In the general formula (2), the lower alkyl group having 1 to 8 carbon atoms represented by R ² may be linear or branched, and specific examples include: , —CH ₃ , —CH ₂ CH ₃ , —CH (CH ₃ ), —CH ₂ CH ₂ CH _{3 and the} like. In the metal alkoxide represented by the general formula (2), when c is 2 or more, all c R ^{2 s} may be the same group or different groups.

Further, the metal oxide represented by the general formula (2) is not particularly limited, but specific examples thereof include the following general formula (3).
R ¹ _b M (OR ² ) _ab (3)
(In the formula, M represents a metal, R ¹ represents a monovalent organic group, R ² represents a lower alkyl group having 1 to 8 carbon atoms, a represents the valence of metal M, and b represents 0 to 0. 2 represents an integer of 2.) and can be generated by hydrolyzing a metal alkoxide represented by Incidentally, in the general formula (3), R ^1, M, and R ^2, respectively, it is similar to the R ^1, M, and R ² in the general formula (2).

  That is, in the present invention, the copolymer is one or more kinds of metal oxides represented by the above general formula (2) generated by hydrolyzing the alkoxy group of the metal alkoxide represented by the above general formula (3). A product obtained by proceeding a polycondensation reaction by dehydration reaction and dealcoholization reaction between substances may be further subjected to a polycondensation reaction with an organic polymer compound.

Specific examples of the metal alkoxide represented by the general formula (3) that does not have the organic group represented by R ¹ (b is 0) include tetramethoxysilane, tetraethoxysilane, and tetra-n-. Butoxy titanium (IV), tri-sec-butoxy aluminum, tetra-n-propoxy zirconium, tetramethoxy titanium, tetraethoxy titanium, tetraisopropoxy titanium, triethoxy aluminum, triisoporopoxy aluminum, tri-n-butoxy aluminum, Examples thereof include tri-tert-butoxyaluminum, tetraethoxyzirconium, tetra-n-butoxyzirconium and the like.

Specific examples of the metal alkoxide represented by the general formula (3) having an organic group represented by R ¹ (b is 1 or 2) include methyltriethoxysilane and vinyltriethoxysilane. Ethyltrimethoxysilane, ethyltriethoxysilane, n-propyltrimethoxysilane, phenyltrimethoxysilane, phenyltriethoxysilane, 3-aminopropyltriethoxysilane, N- (2-aminoethyl) -3-aminopropyltri Examples include methoxysilane, 2-chloroethyltriethoxysilane, diphenyldimethoxysilane, 3-iodopropyltrimethoxysilane, 3-mercaptopropyltrimethoxysilane, and n-octyltriethoxysilane.

  Among the metal alkoxides represented by the general formula (3), metal alkoxides in which the metal represented by M is Si, Al, Ti, or Zr are relatively easily available. Among these, Si alkoxides are excellent in terms of stability to moisture in the atmosphere, cost, and ease of handling.

  Further, these metal alkoxides represented by the general formula (3) may be used alone or in combination.

In addition, in order to produce | generate the copolymer containing the metal atom which the organic group couple | bonded using the metal alkoxide shown by above-mentioned General formula (3), it does not have the organic group shown by R < ¹ > (b. 0) hydrolyzing a mixture of a metal alkoxide represented by the general formula (3) and a metal alkoxide represented by the general formula (3) having an organic group represented by R ¹ (b is 1 or 2) A condensation reaction is carried out. Here, the metal alkoxide represented by the general formula (3) not having the organic group represented by R ¹ (b is 0) and the general formula (b being 1 or 2) having the organic group represented by R ¹ The metal alkoxide represented by (3) is preferably mixed at a molar ratio of 95: 5 to 10:90, more preferably 90:10 to 20:80. The metal alkoxide having no organic group represented by R ^1, if having an organic group represented by R ¹ (b is 1 or 2) metal alkoxide is too high, the organic group during hydrolysis and polycondensation reactions Becomes a steric hindrance and may not be able to produce a copolymer that can form a skeleton necessary for film formation on the surface of the positive electrode active material. There is a possibility that a copolymer capable of forming a dense film cannot be formed.

  Further, in order to obtain a copolymer having a weight ratio of the metal oxide polymer block to the organic polymer block of 90:10 to 20:80, one or more metal oxides represented by the general formula (2) and the organic The organic polymer compound is reacted with the product produced by polycondensation of the metal oxide so that the weight ratio with the polymer compound is 90:10 to 20:80.

As the lithium salt contained in the solid _{electrolyte, CH 3 COOLi, LiClO 4,} LiCF 3 SO 3, LiN (CF 3 SO 2) 2, LiN (C 2 F 5 SO 2) 2 and the like. The lithium salts described above can be used alone or in combination of two or more.

The ionic conductivity of the solid electrolyte is preferably 1.0 × 10 ⁻⁶ S / cm or more. When the density is less than 1.0 × 10 ⁻⁶ S / cm, there is substantially no ion permeability, and the current density as the battery is reduced, resulting in a battery with poor rate characteristics. More preferably, it is 1.0 × 10 ⁻⁵ S / cm or more.

  Note that the lithium ion permeability of the solid electrolyte corresponds to the lithium ion conductivity, and the lithium ion conductivity can be obtained by AC impedance measurement which is a normal evaluation method. Specifically, the impedance of the coated electrode immersed in the electrolytic solution is measured, the resistance value is obtained in the Cole-Cole plot, and the lithium ion conductivity can be obtained from the increased resistance of the resistance value obtained with the uncoated electrode.

Further, in the present invention, the solid electrolyte membrane plays a role of preventing the positive electrode active material and the electrolytic solution from contacting each other and preventing the electrolytic solution from being decomposed. Therefore, the solid electrolyte membrane should have few pores in the membrane. good. When there are many pores present in the membrane, that is, in the case of a coating having a large BET specific surface area, the electrolytic solution enters the coating, and the electrolytic solution is decomposed by reaching the carbon surface. Therefore, the BET specific surface area of the solid electrolyte membrane needs to have a small value to some extent. Specifically, the BET specific surface area of the solid electrolyte membrane is preferably 10 m ² / g or less. The BET specific surface area can be calculated from the adsorption isotherm using the BET isotherm adsorption formula as the BET specific surface area.

  Moreover, the film thickness of the solid electrolyte covering the surface of the positive electrode active material can sufficiently suppress the decomposition of the electrolytic solution, and can sufficiently insert and desorb lithium ions into the positive electrode active material. Although it will not specifically limit if it is thickness which can be done, As a specific example, it is preferable that it is 50 nm-5 micrometers, and it is especially preferable that it is 100 nm-3 micrometers. When the film thickness of the solid electrolyte is less than 50 nm, there is a possibility that the surface of the positive electrode active material can only be partially covered, and there is a possibility that decomposition of the electrolytic solution cannot be sufficiently suppressed. Moreover, when the film thickness of the solid electrolyte is thicker than 5 μm, the membrane resistance against lithium ion conduction increases, and there is a possibility that the insertion / extraction of lithium ions to / from the positive electrode active material cannot be performed sufficiently.

<Non-aqueous electrolyte>
In the present invention, the non-aqueous electrolyte is not particularly limited, but as a solvent, ethylene carbonate (hereinafter abbreviated as EC), propylene carbonate, butylene carbonate, diethyl carbonate (hereinafter abbreviated as DEC), dimethyl carbonate, methyl ethyl carbonate, Esters such as γ-butyrolactone, ethers such as tetrahydrofuran, 2-methyltetrahydrofuran, dioxane, dioxolane, diethyl ether, dimethoxyethane, diethoxyethane, methoxyethoxyethane, dimethyl sulfoxide, sulfolane, methylsulfolane, acetonitrile, methyl formate A polar solvent such as methyl acetate can be used. These solvents may be used alone, or two or more kinds may be mixed and used as a mixed solvent.

The non-aqueous electrolyte may contain an electrolyte salt. Examples of the electrolyte salt include LiClO ₄ , LiBF ₄ (lithium borofluoride), LiPF ₆ (lithium hexafluorophosphate), LiCF ₃ SO ₃ (lithium trifluoromethanesulfonate), LiF (lithium fluoride), LiCl (lithium chloride). ), LiBr (lithium bromide), LiI (lithium iodide), AlCl ₄ Li (lithium tetrachloroaluminate) and the like. These may be used alone or in combination of two or more.

  The concentration of the electrolyte salt is not particularly limited, but is preferably 0.5 mol / L to 2.5 mol / L, more preferably 1.0 mol / L to 2.2 mol / L. When the concentration of the electrolyte salt is less than 0.5 mol / L, the carrier concentration for carrying charges in the non-aqueous electrolyte is lowered, and the resistance of the non-aqueous electrolyte may be increased. Moreover, when the concentration of the electrolyte salt is higher than 2.5 mol / L, the degree of dissociation of the salt itself is lowered, and the carrier concentration in the nonaqueous electrolytic solution may not be increased.

<Separator>
The separator is not particularly limited, but a material that does not dissolve or swell in the organic solvent contained in the electrolyte is suitable. Specifically, a separator made of a polyolefin polymer such as nylon, cellulose acetate, nitrocellulose, polysulfone, polyacrylonitrile, polyvinylidene fluoride, polypropylene, polyethylene, or polybutene can be used. The separator is preferably made of polyolefin from the viewpoint of chemical and electrochemical stability, and is preferably made of polyethylene from the viewpoint of the self-closing temperature, which is one of the purposes of the battery separator.

  When a separator consists of polyethylene, it is preferable that it is ultra high molecular weight polyethylene from the point of high temperature shape maintenance property. The lower limit of the molecular weight of this polyethylene is preferably 500,000, more preferably 1,000,000, and most preferably 1,500,000. On the other hand, the upper limit of the molecular weight is preferably 5 million, more preferably 4 million, and most preferably 3 million. If the molecular weight is too large, the pores of the separator may not close when heated due to low fluidity. In addition, molecular weight here means the number average molecular weight measured by the chromatography method.

<Exterior material>
Although the exterior material of the lithium secondary battery according to the present invention is not particularly limited, a metal can such as a can made of iron, stainless steel, aluminum, or the like is preferable. Moreover, you may use the film which laminated aluminum with resin. The shape may be any of a cylindrical shape, a square shape, a thin shape, and the like.

<Application>
The use of the lithium secondary battery of the present invention is not particularly limited. For example, when mounted on an electronic device, a notebook computer, a sub-notebook computer, a pen input computer, a pocket (palmtop) computer, an electronic book player, a mobile phone, Cordless phone, handy terminal, portable fax, portable copy, portable printer, headphone stereo, video movie, LCD TV, handy cleaner, portable music player, electric shaver, electronic translator, transceiver, power tool, electronic notebook, calculator, IC recorders, radios, backup power supplies, etc. Others for consumer use include automobiles, electric vehicles, motors, lighting equipment, toys, game equipment, road conditioners, irons, watches, strobes, cameras, medical equipment (pacemakers, hearing aids, shoulder massagers, etc.). Furthermore, it can be used for various military use and space use. Moreover, it can also combine with another secondary battery and a solar cell.

  Hereinafter, the present invention will be specifically described with reference to examples and comparative examples, but the present invention is not limited to the following examples.

[Example 1]
<Production of negative electrode>
-Formation of negative electrode plate-
In producing the negative electrode, 100 g of Chinese scale natural powder graphite (average particle size 10 μm) is used as the negative electrode active material, 2.5 g of acetylene black is used as the conductive additive, and 12 g of polyvinylidene fluoride (hereinafter abbreviated as PVDF) is used as the binder. N-methyl-2-pyrrolidone (hereinafter abbreviated as NMP) was added as a solvent, and the mixture was kneaded and dispersed by a planetary mixer to prepare a negative electrode paste. The prepared paste was applied uniformly by setting an uncoated part on one side of a 10 μm thick copper foil as a negative electrode current collector using a coating apparatus. The coated electrode was pressed using a hydraulic press machine, and the coated part was cut out to a size of 30 mm × 30 mm to form a negative electrode plate.

<Preparation of positive electrode>
-Formation of positive electrode plate-
In the production of the positive electrode, 100 g of LiMn ₂ O ₄ as the positive electrode active material, 5 g of acetylene black as the conductive auxiliary material, 5 g of PVDF as the binder, and NMP as the solvent are added and kneaded and dispersed by a planetary mixer. A paste was prepared. The prepared paste was applied uniformly by setting an uncoated part on one side of a 20 μm thick aluminum foil as a positive electrode current collector using a coating apparatus. The coated electrode was further pressed using a hydraulic press, and the coated portion was cut out to a size of 28 mm × 28 mm to form a positive electrode plate. The positive electrode plate produced as described above was heat-treated at 150 ° C. under reduced pressure for 8 hours and dried.

-Preparation of coating solution (solid electrolyte)-
First, tetramethoxysilane and methyltriethoxysilane are mixed so that the molar ratio is 20:80, and further, the molar ratio is 20 times that of the mixed liquid of tetramethoxysilane and methyltriethoxysilane. , Ethanol was added. The solution was stirred for 30 minutes, and an aqueous 0.01 mol / L HCl solution was added so that the molar ratio was 4 times with respect to tetramethoxysilane and 3 times with respect to methyltriethoxysilane, and further 2 hours. Stir. Further, to this mixed solution, polyethylene glycol (average molecular weight 200), which is half the weight of the metal oxide when assuming that all of tetramethoxysilane and methyltriethoxysilane became metal oxide, was added and stirred for 1 hour. Further, CH ₃ COOLi was added to this mixed solution and stirred for 3 hours to obtain a coating solution.

-Production of coating (solid electrolyte membrane)-
FIG. 1 is an explanatory diagram for explaining a method of producing a coating film made of a solid electrolyte on the surface of a positive electrode in producing a lithium secondary battery according to Example 1 of the present invention.

  The positive electrode plate 2 previously formed is immersed in the coating solution 1 obtained as described above for 10 seconds, and then the positive electrode plate 2 is pulled up by the pulling motor 3 at a speed of 2.6 mm / sec. It was. A coating made of a solid electrolyte was formed on the surface of the active material constituting the positive electrode plate 2 by repeating immersion and pulling operations of the positive electrode plate 2 five times. The electrode on which the film was formed was heat-treated in air at 60 ° C. for 3 hours, and then heat-treated at 100 ° C. under reduced pressure for 8 hours. When the produced film was confirmed with an electron microscope, it was found to have a thickness of about 1 μm.

  FIG. 2 is an explanatory diagram for explaining the chemical structure of a coating film made of a solid electrolyte produced on the surface of the positive electrode in the lithium secondary battery according to Example 1 of the present invention.

The solid electrolyte constituting the coating was formed of polyethylene glycol (organic polymer compound) on the metal oxide polymer block 4 formed by hydrolysis / polycondensation reaction of tetramethoxysilane and methyltriethoxysilane (metal alkoxide). The organic polymer block 5 includes a copolymer 6 having a structure bonded through oxygen. Further, lithium ions (Li ⁺ ) resulting from CH ₃ COOLi are incorporated.

<Battery assembly>
As described above, a positive electrode plate coated with a solid electrolyte, a negative electrode plate, a 5 mm wide and 50 mm long aluminum tab as a battery current introduction terminal, and a 5 mm wide and 50 mm long nickel plate for the negative electrode plate. A tab made was welded to produce a positive electrode and a negative electrode.

  A porous polyethylene separator is sandwiched between the prepared positive electrode and negative electrode, and three sides are sealed with two rectangular aluminum laminate resins to form a bag-shaped exterior material (battery container) Inserted. The remaining one side that was not sealed with the aluminum laminate resin was used as an opening for injecting the electrolyte.

Then, 1 mol / L LiPF ₆ / EC + DEC (volume ratio 1: 2) non-aqueous electrolyte was impregnated in the exterior material. Thereafter, the opening of the exterior material was sealed to complete the production of the lithium secondary battery.

[Example 2]
After producing a positive electrode in the same manner as in Example 1, tetramethoxysilane and vinyltriethoxysilane were used as metal alkoxides by the method shown below. Further, in the same manner as in Example 1, polyethylene glycol (average molecular weight 200) was used. A coating solution was prepared using the organic polymer compound.

That is, tetramethoxysilane and vinyltriethoxysilane are mixed so that the molar ratio is 20:80, and further, the molar ratio is 20 times that of the mixed liquid of tetramethoxysilane and vinyltriethoxysilane. , Ethanol was added. The solution was stirred for 30 minutes, and a 0.01 mol / L aqueous HCl solution was added at a molar ratio of 4 times with respect to tetramethoxysilane and 3 times with respect to vinyltriethoxysilane, and further added for 2 hours. Stir. Furthermore, polyethylene glycol (average molecular weight 200) was added to this mixed solution and stirred for 1 hour so as to be half the weight when all of tetramethoxysilane and vinyltriethoxysilane were assumed to be metal oxides. Further, CH ₃ COOLi was added to this mixed solution and stirred for 3 hours to obtain a coating solution.

  Using the coating solution thus obtained, a coating (solid electrolyte membrane) was prepared in the same manner as in Example 1. Further, in the same manner as in Example 1, the production of the negative electrode and the battery Assembling was performed to obtain a lithium secondary battery according to Example 2.

[Example 3]
After producing a positive electrode in the same manner as in Example 1, tetra-n-butoxytitanium (IV) and methyltriethoxysilane were used as metal alkoxides by the method shown below. Further, in the same manner as in Example 1, polyethylene glycol A coating solution was prepared using (average molecular weight 200) as the organic polymer compound.

That is, tetra-n-butoxytitanium (IV) and methyltriethoxysilane are mixed so that the molar ratio is 20:80, and further, this tetra-n-butoxytitanium (IV) and methyltriethoxysilane are mixed. Ethanol was added so that the molar ratio was 20 times that of the liquid. This solution is stirred for 30 minutes so that 0.01 mol / L HCl aqueous solution is 4 times in molar ratio to tetra-n-butoxytitanium (IV) and 3 times in molar ratio to methyltriethoxysilane. And stirred for another 2 hours. Furthermore, polyethylene glycol (average molecular weight 200) was added to this mixed solution so that it would be half the weight when all of tetra-n-butoxytitanium (IV) and methyltriethoxysilane were assumed to be metal oxides. Stir for 1 hour. Further, CH ₃ COOLi was added to this mixed solution and stirred for 3 hours to obtain a coating solution.

  Using the coating solution thus obtained, a coating (solid electrolyte membrane) was prepared in the same manner as in Example 1. Further, in the same manner as in Example 1, the production of the negative electrode and the battery The lithium secondary battery which concerns on Example 3 was obtained by assembling.

[Example 4]
After producing a positive electrode in the same manner as in Example 1, tri-sec-butoxyaluminum and methyltriethoxysilane were used as metal alkoxides by the method shown below. Further, in the same manner as in Example 1, polyethylene glycol (average molecular weight) 200) as an organic polymer compound to prepare a coating solution.

That is, tri-sec-butoxyaluminum and methyltriethoxysilane were mixed at a molar ratio of 20:80, and the molar ratio with respect to the mixed liquid of tri-sec-butoxyaluminum and methyltriethoxysilane was further increased. Ethanol was added so as to be 20 times. The solution was stirred for 30 minutes, and a 0.01 mol / L aqueous HCl solution was added in a molar ratio of 3 times to tri-sec-butoxyaluminum and 3 times in molar ratio to methyltriethoxysilane. Stir for another 2 hours. In addition, polyethylene glycol (average molecular weight 200) was added to this mixed solution so that the weight of the metal oxide was half that assumed that all of tri-sec-butoxyaluminum and methyltriethoxysilane were metal oxides. The mixture was further stirred for 1 hour. Further, CH ₃ COOLi was added to this mixed solution and stirred for 3 hours to obtain a coating solution.

  Using the coating solution thus obtained, a coating (solid electrolyte membrane) was prepared in the same manner as in Example 1. Further, in the same manner as in Example 1, the production of the negative electrode and the battery Assembling was performed to obtain a lithium secondary battery according to Example 4.

[Example 5]
After producing a positive electrode in the same manner as in Example 1, tetra-n-propoxyzirconium (IV) and methyltriethoxysilane were used as metal alkoxides by the method shown below. Further, in the same manner as in Example 1, polyethylene glycol A coating solution was prepared using (average molecular weight 200) as the organic polymer compound.

That is, tetra-n-propoxyzirconium (IV) and methyltriethoxysilane are mixed so that the molar ratio is 20:80, and further, this tetra-n-propoxyzirconium (IV) and methyltriethoxysilane are mixed. Ethanol was added so that the molar ratio was 20 times that of the liquid. The solution is stirred for 30 minutes so that the 0.01 mol / L HCl aqueous solution is 4 times in molar ratio to tetra-n-propoxyzirconium (IV) and 3 times in molar ratio to methyltriethoxysilane. And stirred for another 2 hours. Furthermore, the polyethylene glycol (average molecular weight) was added to this mixed solution so that the total weight of tetra-n-propoxyzirconium (IV) and methyltriethoxysilane would be half of the weight of the metal oxide. 200) was added and stirred for 1 hour. Further, CH ₃ COOLi was added to this mixed solution and stirred for 3 hours to obtain a coating solution.

  Using the coating solution thus obtained, a coating (solid electrolyte membrane) was prepared in the same manner as in Example 1. Further, in the same manner as in Example 1, the production of the negative electrode and the battery Assembling was performed to obtain a lithium secondary battery according to Example 5.

[Example 6]
In the preparation of the coating solution shown in Example 1, polypropylene glycol (average molecular weight 400) was used instead of polyethylene glycol (average molecular weight 200) as the organic polymer compound, and the same procedure as in Example 1 was followed. 6 was obtained.

[Example 7]
After producing the positive electrode in the same manner as in Example 1, a coating solution was prepared by using the tetraethoxysilane alone as the metal alkoxide and further using polyethylene glycol (average molecular weight 200) as the organic polymer compound by the following method. did.

That is, ethanol was added so that the molar ratio with respect to tetraethoxysilane was 20 times. This solution was stirred for 30 minutes, 0.01 mol / L HCl aqueous solution was added 4 times in molar ratio to tetraethoxysilane, and the mixture was further stirred for 2 hours. Furthermore, polyethylene glycol (average molecular weight 200) was added to this mixed solution so as to be half the weight when all of the tetraethoxysilane was assumed to be a metal oxide polymer, and the mixture was stirred for 1 hour. Further, CH ₃ COOLi was added to this mixed solution and stirred for 3 hours to obtain a coating solution.

  Using the coating solution thus obtained, a coating (solid electrolyte membrane) was prepared in the same manner as in Example 1. Further, in the same manner as in Example 1, the production of the negative electrode and the battery Assembling was performed to obtain a lithium secondary battery according to Example 7.

[Example 8]
After producing a positive electrode in the same manner as in Example 1, tetraethoxysilane and methyltriethoxysilane were used as metal alkoxides and polyethylene glycol (average molecular weight 200) was used as an organic polymer compound by the following method. A coating solution was prepared.

First, tetraethoxysilane and methyltriethoxysilane are mixed so that the molar ratio is 95: 5, and further, the molar ratio is 20 times that of the mixed liquid of tetraethoxysilane and methyltriethoxysilane. , Ethanol was added. This solution was stirred for 30 minutes, and a 0.01 mol / L aqueous HCl solution was added at a molar ratio of 4 times with respect to tetraethoxysilane and 3 times with respect to methyltriethoxysilane, and further added for 2 hours. Stir. Furthermore, polyethylene glycol (average molecular weight of 200) was added to this mixed solution so that the weight of the metal oxide was half that when assuming that all of tetraethoxysilane and methyltriethoxysilane were converted to metal oxides, and 1 hour. Stir. Further, CH ₃ COOLi was added to this mixed solution and stirred for 3 hours to obtain a coating solution.

  Using the coating solution thus obtained, a coating (solid electrolyte membrane) was prepared in the same manner as in Example 1. Further, in the same manner as in Example 1, the production of the negative electrode and the battery Assembling was performed to obtain a lithium secondary battery according to Example 8.

[Example 9]
After producing the positive electrode in the same manner as in Example 1, as in Example 9, tetraethoxysilane and methyltriethoxysilane were used as metal alkoxides, and polyethylene glycol (average molecular weight 200) was used as the organic polymer compound. A coating solution was prepared. However, in this example, tetraethoxysilane and methyltriethoxysilane were mixed so that the molar ratio was 90:10. Using the coating solution thus obtained, a coating (solid electrolyte membrane) was prepared by the same method as in Example 1, and further, a negative electrode and a battery were assembled by the same method as in Example 1. And a lithium secondary battery according to Example 9 was obtained.

[Example 10]
After producing the positive electrode in the same manner as in Example 1, as in Example 9, tetraethoxysilane and methyltriethoxysilane were used as metal alkoxides, and polyethylene glycol (average molecular weight 200) was used as the organic polymer compound. A coating solution was prepared. However, in this example, tetraethoxysilane and methyltriethoxysilane were mixed so that the molar ratio was 50:50. Thus, using the obtained coating solution, a coating (solid electrolyte membrane) was prepared in the same manner as in Example 1. Further, in the same manner as in Example 1, preparation of the negative electrode and assembly of the battery were performed. The lithium secondary battery according to Example 10 was obtained.

[Example 11]
After producing the positive electrode in the same manner as in Example 1, as in Example 9, tetraethoxysilane and methyltriethoxysilane were used as metal alkoxides, and polyethylene glycol (average molecular weight 200) was used as the organic polymer compound. A coating solution was prepared. However, in this example, tetraethoxysilane and methyltriethoxysilane were mixed so that the molar ratio was 10:90. Thus, using the obtained coating solution, a coating (solid electrolyte membrane) was prepared in the same manner as in Example 1. Further, in the same manner as in Example 1, preparation of the negative electrode and assembly of the battery were performed. And a lithium secondary battery according to Example 11 was obtained.

[Example 12]
After producing the positive electrode in the same manner as in Example 1, as in Example 9, tetraethoxysilane and methyltriethoxysilane were used as metal alkoxides, and polyethylene glycol (average molecular weight 200) was used as the organic polymer compound. A coating solution was prepared. However, in this example, tetraethoxysilane and methyltriethoxysilane were mixed so that the molar ratio was 5:95. Using the coating solution thus obtained, a coating (solid electrolyte membrane) was prepared by the same method as in Example 1, and further, a negative electrode and a battery were assembled by the same method as in Example 1. The lithium secondary battery according to Example 12 was obtained.

[Example 13]
In the preparation of the coating solution shown in Example 1, polyethylene glycol (average molecular weight 100) was used as the organic polymer compound instead of polyethylene glycol (average molecular weight 200), and the same procedure as in Example 1 was followed. A lithium secondary battery according to No. 13 was obtained.

[Example 14]
In the preparation of the coating solution shown in Example 1, polyethylene glycol (average molecular weight 1000) was used as the organic polymer compound instead of polyethylene glycol (average molecular weight 200). 14 was obtained.

[Example 15]
In the preparation of the coating solution shown in Example 1, polypropylene glycol (average molecular weight 2000) was used instead of polyethylene glycol (average molecular weight 200) as the organic polymer compound, and the same procedure as in Example 1 was followed. 15 was obtained.

[Example 16]
In the preparation of the coating solution shown in Example 1, polypropylene glycol (average molecular weight 4000) was used instead of polyethylene glycol (average molecular weight 200) as the organic polymer compound, and the same procedure as in Example 1 was followed. 16 was obtained.

[Example 17]
After producing a positive electrode and a coating solution by the same method as in Example 1, a film (solid electrolyte membrane) was produced by the following method.

  That is, after the positive electrode plate 2 previously formed was immersed for 10 seconds in the coating solution 1 diluted 3-fold with ethanol in the same manner as in Example 1 (see FIG. 2), The positive electrode plate 2 was pulled up at a speed of 6 mm / sec. A coating made of a solid electrolyte was produced on the positive electrode active material constituting the positive electrode plate 2 by repeating the immersion and pulling operations of the positive electrode plate 2 twice. The electrode on which the film was formed was heat-treated in air at 60 ° C. for 3 hours, and then heat-treated at 100 ° C. under reduced pressure for 8 hours. When the produced film was confirmed with an electron microscope, it was found to have a thickness of about 50 nm.

  Further, a negative electrode was prepared and the battery was assembled in the same manner as in Example 1, and the lithium secondary battery according to Example 17 was obtained.

[Example 18]
After producing a positive electrode and a coating solution by the same method as in Example 1, a film (solid electrolyte membrane) was produced by the following method.

  That is, after the positive electrode plate 2 previously formed was immersed for 10 seconds in the coating solution 1 diluted 3-fold with ethanol in the same manner as in Example 1 (see FIG. 2), The positive electrode plate 2 was pulled up at a speed of 6 mm / sec. A coating made of a solid electrolyte was produced on the positive electrode active material constituting the positive electrode plate 2 by repeating the immersion and pulling operations of the positive electrode plate 2 three times. The electrode on which the film was formed was heat-treated in air at 60 ° C. for 3 hours, and then heat-treated at 100 ° C. under reduced pressure for 8 hours. When the produced film was confirmed with an electron microscope, it was found to have a thickness of about 100 nm.

  Further, a negative electrode was produced and the battery was assembled in the same manner as in Example 1, and the lithium secondary battery according to Example 18 was obtained.

[Example 19]
After producing a positive electrode and a coating solution by the same method as in Example 1, a film (solid electrolyte membrane) was produced by the following method.

  That is, after the positive electrode plate 2 previously formed was immersed in the coating solution 1 for 10 seconds in the same manner as in Example 1 (see FIG. 2), the speed was increased to 1.0 mm / sec by the lifting motor 3. The positive electrode plate 2 was pulled up. A coating made of a solid electrolyte was formed on the positive electrode active material constituting the positive electrode plate 2 by repeating the immersion and pulling operations of the positive electrode plate 2 once. The electrode on which the film was formed was heat-treated in air at 60 ° C. for 3 hours, and then heat-treated at 100 ° C. under reduced pressure for 8 hours. When the produced film was confirmed with an electron microscope, it was found to have a thickness of about 3 μm.

  Furthermore, a lithium secondary battery according to Example 19 was obtained by producing a negative electrode and assembling the battery by the same method as in Example 1.

[Example 20]
After producing a positive electrode and a coating solution by the same method as in Example 1, a film (solid electrolyte membrane) was produced by the following method.

  That is, after the positive electrode plate 2 previously formed was immersed in the coating solution 1 for 10 seconds in the same manner as in Example 1 (see FIG. 2), the speed was increased to 2.6 mm / sec by the pulling motor 3. The positive electrode plate 2 was pulled up. A coating made of a solid electrolyte was formed on the positive electrode active material constituting the positive electrode plate 2 by repeating the immersion and pulling operations of the positive electrode plate 2 eight times. The electrode on which the film was formed was heat-treated in air at 60 ° C. for 3 hours, and then heat-treated at 100 ° C. under reduced pressure for 8 hours. When the produced film was confirmed with an electron microscope, it was found to have a thickness of about 5 μm.

  Furthermore, a lithium secondary battery according to Example 20 was obtained by producing a negative electrode and assembling the battery by the same method as in Example 1.

[Example 21]
After producing a positive electrode in the same manner as in Example 1, as in Example 1, tetramethoxysilane and methyltriethoxysilane were used as metal alkoxides, and polyethylene glycol (average molecular weight 200) was used as the organic polymer compound. A coating solution was prepared. However, in this example, the polyethylene was adjusted so that the weight ratio of the metal oxide to the organic polymer compound was 90:10 when it was assumed that all of tetramethoxysilane and methyltriethoxysilane became metal oxides. Glycol (average molecular weight 200) was added to prepare a coating solution. Thus, using the obtained coating solution, a coating (solid electrolyte membrane) was prepared in the same manner as in Example 1. Further, in the same manner as in Example 1, preparation of the negative electrode and assembly of the battery were performed. And a lithium secondary battery according to Example 21 was obtained.

[Example 22]
After producing a positive electrode in the same manner as in Example 1, as in Example 1, tetramethoxysilane and methyltriethoxysilane were used as metal alkoxides, and polyethylene glycol (average molecular weight 200) was used as the organic polymer compound. A coating solution was prepared. However, in this example, the weight ratio of the metal oxide to the organic polymer compound when assuming that all of tetramethoxysilane and methyltriethoxysilane are metal oxides is 20:80, Polyethylene glycol (average molecular weight 200) was added to prepare a coating solution. Thus, using the obtained coating solution, a coating (solid electrolyte membrane) was prepared in the same manner as in Example 1. Further, in the same manner as in Example 1, preparation of the negative electrode and assembly of the battery were performed. And a lithium secondary battery according to Example 22 was obtained.

[Example 23]
Lithium cobaltate LiCoO ₂ was used as the positive electrode active material. About the other, the lithium secondary battery was produced by the method similar to Example 1. FIG. This is Example 23.

[Example 24]
Lithium iron phosphate LiFePO ₄ was used as the positive electrode active material. About the other, the lithium secondary battery was produced by the method similar to Example 1. FIG. This is referred to as Example 24.

[Comparative Example 1]
A lithium secondary battery according to Comparative Example 1 was manufactured using a LiMn ₂ O ₄ positive electrode on which no film was formed. That is, the lithium secondary battery according to Comparative Example 1 was manufactured by omitting the steps of preparing the coating solution and the coating (solid electrolyte membrane) in the manufacture of the lithium secondary battery according to Example 1. is there.

[Comparative Example 2]
A lithium secondary battery according to Comparative Example 2 was prepared using a lithium cobaltate LiCoO ₂ positive electrode on which no film was formed. That is, the lithium secondary battery according to Comparative Example 2 was prepared using the lithium cobalt oxide LiCoO ₂ instead of LiMn ₂ O ₄ as the positive electrode active material in the production of the lithium secondary battery according to Example 1, The film (solid electrolyte membrane) was produced by omitting the production process.

[Comparative Example 3]
A lithium secondary battery according to Comparative Example 3 was prepared using a lithium iron phosphate LiFePO ₄ positive electrode on which no film was formed. That is, in the production of the lithium secondary battery according to Example 1, the lithium secondary battery according to Comparative Example 3 uses lithium iron phosphate LiFePO ₄ instead of LiMnO ₄ as the positive electrode active material. The manufacturing process of the solid electrolyte membrane) is omitted.

<Battery performance test>
About the lithium secondary battery which concerns on above Examples 1-24 and Comparative Examples 1-3, the performance test was implemented with the method shown below.

  That is, about the lithium secondary battery which concerns on Examples 1-23 and Comparative Examples 1 and 2, after charging and discharging temperature to 25 degreeC and making it to upper limit voltage 4.2V by constant current 0.1C, Further, charging was performed at a constant voltage of 4.2 V until the current value reached 0.01C. Thereafter, discharging was performed at a constant current of 0.1 C until the battery voltage reached 3.0V. The discharge capacity at this time (first cycle) was measured. Next, after charging, discharging, and charging again under the same conditions, discharging was performed at a current value of 1C. The rate characteristics were calculated by 1C discharge capacity / 0.1C discharge capacity. The 0.1 C discharge capacity used in this calculation is a value obtained in the second discharge.

  Furthermore, charging and discharging were repeated under the same conditions (1C) to measure the discharge capacity at the 100th cycle, and the discharge capacity at the 100th cycle relative to the discharge capacity at the 1st cycle was obtained as the capacity retention rate at the 100th cycle (discharge) .

  The lithium secondary batteries according to Example 24 and Comparative Example 3 were in accordance with the above method, but after charging until the upper limit voltage was 3.6 V at a constant current of 0.1 C, the lithium secondary battery was further charged at a constant voltage of 3.6 V. Charging was performed until the current value reached 0.01C. Thereafter, discharging was performed at a constant current of 0.1 C until the battery voltage reached 2.0V. The discharge capacity at this time (first cycle) was measured. Next, after charging, discharging, and charging again under the same conditions, discharging was performed at a current value of 1C. The rate characteristics were calculated by 1C discharge capacity / 0.1C discharge capacity. The 0.1 C discharge capacity used in this calculation is a value obtained in the second discharge.

  Furthermore, charging and discharging were repeated under the same conditions to measure the discharge capacity at the 100th cycle, and the discharge capacity at the 100th cycle relative to the discharge capacity at the first cycle was determined as the capacity retention rate at the 100th cycle (discharge).

  In Table 1, the result of the performance test of the lithium secondary battery which concerns on Examples 1-6 and the comparative example 1 is shown with the ionic conductivity and BET specific surface area of the solid electrolyte membrane which coat | covers the active material which comprises a positive electrode. .

  From the results shown in Table 1, the lithium secondary batteries according to Examples 1 to 6 were compared with the lithium secondary battery according to Comparative Example 1 using an active material material not coated with a solid electrolyte as a positive electrode. Also, it was confirmed that the capacity retention was excellent.

  As for the discharge capacity, since an error of about ± 2 mAh / g is generally shown in the test under the same conditions and the same sample, the lithium secondary batteries according to Examples 1 to 7 and Comparative Example 1 are substantially the same. It can be said that the discharge capacity is shown.

In each of the lithium secondary batteries according to Examples 1 to 6, the solid electrolyte covering the active material constituting the positive electrode has an ionic conductivity of 1.0 × 10 ⁻³ S / cm or more. It showed a good rate characteristic of 0.87 or more.

  Table 2 shows the results of the performance tests of the lithium secondary batteries according to Examples 1, 7 to 12 and Comparative Example 1, and the ionic conductivity and BET specific surface area of the solid electrolyte membrane covering the active material constituting the positive electrode. By showing together, the result of a battery performance with respect to the mixing ratio of the metal alkoxide (tetramethoxysilane or tetraethoxysilane) which does not have an organic group, and the metal alkoxide (methyltriethoxysilane) which has an organic group is shown.

From the results shown in Table 2, it was confirmed that the lithium secondary batteries according to Examples 7 to 12 were all excellent in capacity retention as compared with the lithium secondary battery according to Comparative Example 1. In the lithium secondary batteries according to Examples 7 to 12, the solid electrolyte covering the positive electrode active material constituting the positive electrode has an ionic conductivity of 1.0 × 10 ⁻⁴ S / cm or more. It showed a good rate characteristic of 0.87 or more.

  Further, in the preparation of the coating solution, the lithium secondary batteries according to Example 1 and Examples 7 to 11 in which the metal alkoxide having an organic group (methyltriethoxysilane) was used, and the metal alkoxide having an organic group was used. The BET specific surface area of the solid electrolyte membrane was extremely small compared with Example 7 that was not performed, and it was confirmed that a dense solid electrolyte membrane was formed on the surface of the active material constituting the positive electrode.

  For this reason, the mixing ratio of the metal alkoxide having no organic group (tetramethoxysilane or tetraethoxysilane) and the metal alkoxide having an organic group (methyltriethoxysilane) used for the production of the copolymer is a molar ratio. The ratio is preferably 95: 5 to 10:90, and more preferably 90:10 to 20:80.

  The results of Table 2 show that the solid electrolyte membranes of the examples share the properties of organic and inorganic ion conductive membranes, and this membrane is a layer of an organic ion conductive membrane as in Patent Documents 1, 3, and 4. In the case of forming a film on the surface of the positive electrode, there is a defect of insufficient bonding force between the surface of the positive electrode active material and the surface of the film such as when the inorganic ion conductive film is coated on the surface of the positive electrode as in Patent Documents 2 and 5. This indirectly compensates for the fact that a strong and flexible film can be formed on the positive electrode active material by complementarily compensating for the lack of flexibility.

  Table 3 shows the results of the performance tests of the lithium secondary batteries according to Examples 1, 6, 13 to 16 and Comparative Example 1, and the ionic conductivity and BET of the solid electrolyte membrane covering the active material constituting the positive electrode. By showing together with the specific surface area, the result of the battery performance with respect to the average molecular weight of the organic polymer compound is shown.

  From the results shown in Table 3, the lithium secondary batteries according to Examples 1, 6, and 13 to 16 are all superior in charge / discharge efficiency and capacity retention rate as compared with the lithium secondary battery according to Comparative Example 1. It was recognized that

In each of the lithium secondary batteries according to Examples 1, 6, and 13 to 16, the solid electrolyte that covers the active material constituting the positive electrode has an ionic conductivity of 1.0 × 10 ⁻⁵ S / cm or more. It showed a good rate characteristic of 0.86 or more. In addition, Examples 1, 6, 13, and 14 using 100 to 1000 organic polymer compounds showed higher ionic conductivity as the average molecular weight of the organic polymer compound used to produce the copolymer was smaller. An extremely high ionic conductivity of 0 × 10 ⁻³ S / cm or more was exhibited.

  For this reason, the average molecular weight of the organic polymer compound used for the production of the copolymer, that is, the average molecular weight of the organic polymer block constituting the copolymer is preferably 100 to 2000, and particularly preferably 100 to 1000. It can be said.

  Table 4 shows the results of the performance tests of the lithium secondary batteries according to Examples 1, 17 to 20 and Comparative Example 1, and the ionic conductivity and BET specific surface area of the solid electrolyte membrane covering the active material constituting the positive electrode. By showing together, the result of the battery performance with respect to the film thickness of a solid electrolyte is shown.

  From the results shown in Table 4, it is recognized that the lithium secondary batteries according to Examples 1 and 17 to 20 are all superior in capacity retention compared to the lithium secondary battery according to Comparative Example 1. It was.

  Regarding the lithium secondary batteries according to Examples 17 and 20, the increase in the capacity retention rate with respect to the lithium secondary battery according to Comparative Example 1 was as small as about 2%.

In the lithium secondary batteries according to Examples 1 and 17 to 20, each of the solid electrolytes covering the active material constituting the positive electrode has an ionic conductivity of 1.0 × 10 ⁻³ S / cm or more. It had a good rate characteristic of 0.86 or more.

  For this reason, the thickness of the solid electrolyte is preferably 50 nm to 5000 nm, particularly preferably 100 nm to 3000 nm.

  Table 5 shows the results of the performance tests of the lithium secondary batteries according to Examples 1, 2, 22, and Comparative Example 1, and the ionic conductivity and BET specific surface area of the solid electrolyte membrane covering the active material constituting the positive electrode. By showing together, the result of the battery characteristic with respect to the weight ratio of the metal oxide at the time of producing | generating the copolymer contained in a solid electrolyte and an organic polymer compound is shown.

From the results shown in Table 5, it was confirmed that the lithium secondary batteries according to Examples 1, 2, and 22 were all superior in capacity retention compared to the lithium secondary battery according to Comparative Example 1. In the lithium secondary batteries according to Examples 1, 2, and 22, the solid electrolyte covering the positive electrode active material constituting the positive electrode has an ionic conductivity of 1.0 × 10 ⁻⁴ S / cm or more. It showed a good rate characteristic of 0.87 or more.

  Table 6 shows the results of the performance test of the lithium secondary batteries according to Examples 23 and 24 and Comparative Examples 2 and 3.

  From the results shown in Table 6, it was confirmed that the lithium secondary batteries according to Examples 23 and 24 were all superior in capacity retention compared to the lithium secondary batteries according to Comparative Examples 2 and 3.

<Mn dissolution test>
The battery produced in Example 1 and Comparative Example 1 was subjected to a charge / discharge test up to 100 cycles, then decomposed, the anode and the porous polyethylene separator were heated in a mixed acid of nitric acid and sulfuric acid, and the insoluble portion was perchlorated. Heat in a mixed acid of acid and sulfuric acid to dissolve completely. The amount of Mn in this solution was measured by inductively coupled plasma atomic emission spectrometry (ICP-AES), and the amount of Mn eluted per gram of the positive electrode active material was calculated.

  Table 7 shows the elution amount of Mn detected from the negative electrode and the separator, which was measured by disassembling the batteries prepared in Example 1 and Comparative Example 1 after being subjected to a charge / discharge test up to 100 cycles.

  From the results shown in Table 7, it was confirmed that the elution amount of Mn from the positive electrode produced in Example 1 was suppressed as compared with the positive electrode produced in Comparative Example 1.

It is explanatory drawing for demonstrating the method to produce the film by a solid electrolyte in the positive electrode surface in preparation of the lithium secondary battery which concerns on Example 1 of this invention. FIG. 2 is an explanatory diagram for explaining the chemical structure of a coating film made of a solid electrolyte produced on the surface of the positive electrode in the lithium secondary battery according to Example 1 of the present invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Coating solution 2 Positive electrode plate 3 Lifting motor 4 Metal oxide polymer block 5 Organic polymer block 6 Copolymer

Claims (15)

In a lithium secondary battery having a positive electrode, a negative electrode, a non-aqueous electrolyte, and a separator,
The positive electrode is a positive electrode active material coated with a solid electrolyte mainly comprising a copolymer having a structure in which an organic polymer block is bonded to a metal oxide polymer block through oxygen and a lithium salt. Lithium secondary battery.   2. The lithium secondary battery according to claim 1, wherein among the metal atoms contained in the metal oxide polymer block, 5 to 90% of metal atoms are bonded to a monovalent organic group.   The lithium secondary battery according to claim 1, wherein the organic group is an alkyl group or an alkenyl group having 1 to 5 carbon atoms.   The lithium secondary battery according to claim 1, wherein the metal oxide polymer block contains at least Si.   5. The lithium secondary battery according to claim 1, wherein the metal oxide polymer block contains at least one metal selected from the group consisting of Al, Ti, and Zr. The organic polymer block has the following general formula (1)
− ((CH ₂ ) _m —O) _n − (1)
(Wherein, m represents an integer of 2 to 5, and n represents an integer of 1 or more), the lithium secondary according to any one of claims 1 to 5, battery.   The lithium secondary battery according to claim 6, wherein the organic polymer block has an average molecular weight of 100 to 2,000.   The lithium secondary battery according to any one of claims 1 to 7, wherein the precursor for forming the organic polymer block is at least one selected from polyethylene glycol and polypropylene glycol. The copolymer has the following general formula (2)
R ¹ _b M (OR ² ) _c (OH) _abc (2)
(In the formula, M represents a metal, R ¹ represents a monovalent organic group, R ² represents a lower alkyl group having 1 to 8 carbon atoms, a represents the valence of metal M, and b represents 0 to 0. 2 represents an integer of 2 and c represents an integer of 0 or more, provided that 0 ≦ c ≦ a−b), and a product formed by polycondensation of one or more metal oxides represented by The lithium secondary battery according to any one of claims 1 to 8, wherein the lithium secondary battery is obtained by reacting a polymer compound. In the solid electrolyte, the lithium salt was selected from the group consisting of CH ₃ COOLi, LiClO ₄ , LiCF ₃ SO ₃ , LiN (CF ₃ SO ₂ ) ₂ , LiN (C ₂ F ₅ SO ₂ ) ₂ . The lithium secondary battery according to claim 1, comprising at least one kind.   The lithium secondary battery according to claim 1, wherein the solid electrolyte has a thickness of 50 nm to 5 μm.   The lithium secondary battery according to any one of claims 1 to 11, wherein a weight ratio of the metal oxide polymer block and the organic polymer block constituting the copolymer is 90:10 to 20:80. . The lithium secondary battery according to claim 1, wherein the solid electrolyte has an ionic conductivity of 1.0 × 10 ⁻⁶ S / cm or more. The lithium secondary battery according to claim 1, wherein the solid electrolyte has a BET specific surface area of 10 m ² / g or less. 15. The lithium secondary battery according to claim 1, comprising spinel type lithium manganese oxide LiMn ₂ O ₄ as the positive electrode active material.

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