JP4541432B2 - Lithium secondary battery - Google Patents

Description

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

  A carbon material as a negative electrode material for a lithium secondary battery has many advantages such as being inexpensive, excellent in safety, and having a relatively high density. For this reason, carbon materials such as graphite are used in most of the negative electrodes for lithium secondary batteries currently on the market.

However, when a lithium secondary battery is configured using a carbon material as the negative electrode and a lithium-containing compound as the positive electrode, a potential in the vicinity of 0.7 V with respect to the lithium potential observed at the beginning of the first cycle charge. It is known that an irreversible reaction showing a plateau is observed. One of the causes is a battery reaction such as Li ₂ CO ₃ (lithium carbonate) or LiF (lithium fluoride) on the negative electrode surface due to the reaction between the negative electrode that occludes lithium by charging and the organic solvent that constitutes the electrolyte. And an irreversible reaction that produces a lithium copolymer that does not contribute to the reaction. Such an irreversible reaction consumes lithium, leading to a decrease in discharge capacity and charge / discharge efficiency, as well as a cause of gas generation, leading to an increase in the internal pressure of the battery. That is, it causes a decrease in the energy density of the battery and adversely affects the charge / discharge cycle life.

  Therefore, conventionally, in a lithium secondary battery, in order to suppress an irreversible reaction at the time of initial charge, that is, to suppress decomposition of an electrolytic solution due to a reaction with a negative electrode, contact between a carbon material used as a negative electrode material and the electrolytic solution Attempts have been made to prevent this (see Patent Documents 1 to 8).

  For example, Patent Documents 1 to 3 disclose that a polymer solid is dissolved on a carbon surface by immersing a carbon material in a polymer solid electrolyte solution such as polyethylene oxide or polypropylene oxide dissolved in a solvent and further removing the solvent component. It is disclosed that an electrolyte membrane is produced to prevent contact between the carbon surface and the electrolytic solution.

  In Patent Document 4, a carbon material is immersed in a solution in which an ion exchange membrane is dissolved in a solvent, and boiled with a lithium hydroxide solution to produce a solid electrolyte membrane on the carbon surface. It is disclosed to prevent contact with the electrolyte.

Patent Documents 5 to 7 disclose that the carbon surface is covered with a silicon compound to prevent contact between the carbon surface and the electrolytic solution. Patent Document 8 discloses that the carbon surface is covered with a coating layer derived from an organic material and a metal oxide such as SnO (tin oxide (II)) to prevent contact between the carbon surface and the electrolytic solution. ing.
Japanese Patent Laid-Open No. 7-134989 JP-A-8-21001 Japanese Patent Laid-Open No. 2002-175806 JP-A-7-235328 JP-A-9-82313 JP 11-329435 A JP 2002-8657 A JP-A-11-279785

  However, since the solid electrolyte membrane and the carbon surface produced by the methods described in Patent Documents 1 to 4 are bonded only by intermolecular force, the bonding force is very weak. Therefore, along with the charge / discharge cycle of the battery, the solid electrolyte membrane peels off from the carbon surface, making it impossible to prevent contact between the carbon surface and the electrolytic solution, and a decrease in discharge capacity retention (hereinafter abbreviated as capacity retention). There is a risk of

  Moreover, in patent documents 5-7, since the silicon compound which covers a carbon material surface has little ion conductivity, the film by the silicon compound formed on carbon will increase the internal resistance of a battery, and is favorable. The rate characteristic cannot be obtained.

  Moreover, in patent document 8, since the organic material which comprises the film layer which covers the carbon surface is heat-processed at 200-400 degreeC, an organic part will carbonize. For this reason, the coating layer cannot be given flexibility. Since a non-flexible film cannot follow the structural change of carbon expansion and contraction that occurs during the charge / discharge cycle, the film peels off from the carbon along with the charge / discharge cycle, preventing contact between the carbon surface and the electrolyte. May not be possible, leading to a decrease in capacity retention.

  The present invention has been made in view of such a situation. A carbon material coated with a solid electrolyte having ion conductivity is used as a negative electrode, and lithium secondary battery having good rate characteristics and capacity retention is used. An object is to provide a secondary battery.

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 negative electrode includes the following repeating unit (A) formed by bonding metal atoms and oxygen atoms (A )
-MO -... (A)
(Wherein M represents a metal selected from Si, Al, Ti, and Zr). A metal oxide polymer block having the following general formula (1)
-((CH ₂ ) _m -O) _n- (1)
(Wherein m represents an integer of 1 to 3 and n represents an integer of 1 or more) a copolymer having a structure in which an organic polymer block having a structural unit represented by the above is bonded via oxygen and a lithium salt It is characterized by being a carbon material coated with a solid electrolyte containing as a main component. 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 carbon 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 carbon material and the electrolytic solution are brought into a non-contact state for electrolysis. The decomposition of the liquid can be prevented. 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. Further, 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 carbon material. Therefore, the film is not peeled off from the carbon along with the charge / discharge cycle, and a good capacity retention 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 carbon material can be covered with a dense film made of a solid electrolyte, the carbon material and the electrolytic solution can be reliably brought into a non-contact state, and decomposition of the electrolytic solution can be reliably prevented.

Alternatively, 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, wherein the negative electrode is a repeating unit formed by combining a metal atom and an oxygen atom. (B)
-R ¹ _b M-O- (B)
(However, M represents a metal selected from Si, Al, Ti, and Zr, R ¹ represents an alkyl group or an alkenyl group having 1 to 5 carbon atoms, and b represents an integer of 0 to 2. A metal oxide polymer block having the following general formula (1):
-((CH ₂ ) _m -O) _n- (1)
(Wherein m represents an integer of 1 to 3 and n represents an integer of 1 or more) a copolymer having a structure in which an organic polymer block having a structural unit represented by the above is bonded via oxygen and a lithium salt It is a carbon material coat | covered with the solid electrolyte which has as a main component, You may be characterized by the above-mentioned.

Moreover, in the lithium secondary battery according to the present invention, 5 to 90% of the metal atoms contained in the copolymer are bonded to an alkyl group or alkenyl group having 1 to 5 carbon atoms. Is preferred.

In the lithium secondary battery according to the invention, the copolymer contains at least Si.
It is preferable to do.

According to this configuration, the carbon 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 organic polymer block preferably has an average molecular weight of 100 to 2000 .

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

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) _a-b-c ... (2)
(Wherein M represents a metal selected from Si, Al, Ti, and Zr, R ¹ Represents an alkyl or alkenyl group having 1 to 5 carbon atoms, and R ² Represents a lower alkyl group having 1 to 8 carbon atoms. a represents the valence of the metal M. b represents an integer of 0 to 2, and c represents an integer of 0 or more. However, 0 ≦ c ≦ ab. And a product produced by polycondensation of one or more metal oxides represented by the following formula) may be obtained by reacting a polyalkylene glycol.

In the lithium secondary battery according to the present invention, the metal oxide polymer has the following general formula (3):
R ¹ _b M (OR ² ) _ab (3)
(In the formula, M represents a metal selected from Si, Al, Ti, and Zr, R ¹ represents an alkyl group or alkenyl group having 1 to 5 carbon atoms, and R ² represents a lower group having 1 to 8 carbon atoms. Represents an alkyl group, a represents the valence of metal M, b represents an integer of 0 to 2, and one or more metal oxides produced by hydrolyzing one or more metal alkoxides represented by It may be formed by the polycondensation reaction .

In the lithium secondary battery according to the present invention, the polyalkylene glycol may be one or more selected from polyethylene glycol and polypropylene glycol.

In the lithium secondary battery according to the present invention, the solid electrolyte may contain at least CH ₃ COOLi (lithium acetate) as the lithium salt.

In the lithium secondary battery according to the present invention, as the lithium salt, the solid electrolyte includes LiClO ₄ (lithium perchlorate), LiCF ₃ SO ₃ (lithium trifluoromethanesulfonate), LiN (CF ₃ SO ₂ ) ₂ (bis (trifluoromethanesulfonyl) aminolithium), LiN (C ₂ F ₅ SO ₂ ) ₂ (bis (pentafluoroethylsulfonyl) aminolithium) at least one selected from the group May be.

  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 configuration, the decomposition of the electrolytic solution can be reliably suppressed without inhibiting the insertion and desorption of lithium ions at the negative 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 carbon 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 carbon material and the electrolytic solution can be reliably prevented, and decomposition of the electrolytic solution can be reliably prevented.

  According to the lithium secondary battery of the present invention, carbon coated with a solid electrolyte mainly composed of 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 material is used as a negative 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.

<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.

<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.

  Further, the surface of the carbon material 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. Yes. 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 composed mainly of a copolymer having a structure in which an organic polymer block responsible for ionic conductivity is bonded via oxygen to a metal oxide polymer block that forms a strong skeleton, is solid on the surface of a carbon material. However, it becomes a film having both flexibility. In addition, since this copolymer has a hydroxyl group, it can be polycondensed with a functional group such as a hydroxyl group or a carboxyl group present on the surface of the carbon material and chemically bonded to the surface of the carbon material. Therefore, it becomes a film with good adhesion to carbon.

  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 membrane covering the surface of the carbon material, impart flexibility to the solid electrolyte membrane, and increase the density of the solid electrolyte membrane. 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.

  In addition, the average molecular weight of the organic polymer block shows good ionic conductivity and can form a good film on the surface of the carbon material in a state 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 ionic conductivity may not be obtained. When the average molecular weight is smaller than 100, a skeleton for producing a film on the surface of the carbon 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.

  Further, the weight ratio of the metal oxide polymer block and the organic polymer block constituting the copolymer is particularly limited as long as a uniform solid electrolyte film can be produced on the surface of the carbon material. However, a specific example is preferably 90:10 to 20:80. When the weight of the organic polymer block with respect to the metal oxide polymer block is less than 10/90, a solid electrolyte membrane capable of changing the structure following the expansion / contraction change of the carbon material on the surface of the carbon material That is, there is a possibility that a solid electrolyte membrane excellent in flexibility cannot be produced. In addition, a solid electrolyte membrane having appropriate ion conductivity cannot be produced on the surface of the carbon material, which may result in a lithium secondary battery inferior in 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 carbon 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.

In addition, the organic group represented by R ¹ is not limited to steric hindrance during polycondensation, and any organic group can be used as long as it can sufficiently develop a skeleton necessary for film formation on the surface of the carbon material. It may be a 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 _{CH 2 CH 2 CH 2 -,} NH 2 CONHCH 2 CH 2 CH 2 - and the like.

Among the organic groups described above, in particular, an alkyl group and an 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 a film is formed on the surface of the carbon material. It is preferable because the skeleton necessary for the above 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), a lower alkyl group having a carbon number of 1-8 represented by R ² may be of straight chain, be one having a branched chain, as a specific example Can include alkyl groups such as —CH ₃ , —CH ₂ CH ₃ , —CH (CH ₃ ) ₂ , —CH ₂ CH ₂ CH ₃ . Incidentally, in the metal oxide represented by the above general formula (2), when c is 2 or more, all c number of R ² may be the same group or may I Ah in 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 Is a steric hindrance, and it may not be possible to produce a copolymer that can form a skeleton necessary for film formation on the surface of the carbon material. There is a possibility that a copolymer capable of forming a thick film cannot be formed.

  Further, the organic polymer compound to be reacted with the product formed by polycondensation of the metal oxide represented by the general formula (2) is not particularly limited, but is organic such as polyalkylene glycol or polyether. High molecular compounds are preferred. Since organic polymer compounds such as polyalkylene glycol and polyether have hydroxyl groups at both ends, polycondensation with the hydroxyl group of the metal oxide represented by the general formula (2) is possible. It is possible to produce a copolymer having a structure in which an organic polymer block is bonded to a physical polymer block via oxygen.

  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. In order to provide the copolymer with an organic polymer block having an average molecular weight of 100 to 2000, an organic polymer compound having an average molecular weight of 100 to 2000 may be used.

  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. In particular, when CH ₃ COOLi is contained in the solid electrolyte, lithium ions are taken into the film structure, lithium ions are easily diffused into the film, and the rate characteristics are improved. 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 contact between the carbon surface and the electrolytic solution and preventing the decomposition of the electrolytic solution. Therefore, the solid electrolyte membrane should have few pores in the membrane. . 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.

Further, the thickness of the solid electrolyte covering the surface of the carbon material is such that the decomposition of the electrolytic solution can be sufficiently suppressed, and lithium ions can be sufficiently inserted into and desorbed from the carbon material. If it is, it will not specifically limit, 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 thinner than 50 nm, there is a possibility that the surface of the carbon material can only be partially covered, and there is a possibility that the decomposition of the electrolytic solution cannot be sufficiently suppressed. Moreover, when the film thickness of the solid electrolyte is thicker than 5 μm , the film resistance against lithium ion conduction increases, and there is a possibility that the insertion / extraction of lithium ions to / from the carbon 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),
Examples thereof include lithium salts such as AlCl ₄ Li (lithium tetrachloride aluminate). 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 CD, minidisc, electric shaver, electronic translator, transceiver, electric tool, electronic notebook, Calculators, 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, a solar cell, or a primary battery.

  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]
A lithium secondary battery according to Example 1 of the present invention was produced according to the following procedure.

<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 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 for producing a coating film made of a solid electrolyte on the negative electrode surface in the production of a lithium secondary battery according to Example 1 of the present invention.

  The negative electrode plate 2 previously formed is immersed in the coating solution 1 obtained as described above for 10 seconds, and then the negative electrode plate 2 is pulled up at a speed of 2.6 mm / sec by the pulling motor 3. It was. By immersing and pulling up the negative electrode plate 2 five times, a coating made of a solid electrolyte was produced on the carbon surface constituting the negative electrode plate 2. 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 a chemical structure of a film made of a solid electrolyte produced on the surface of the negative 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.

<Preparation of positive electrode>
In the preparation of the positive electrode, 100 g of LiFePO ₄ as a positive electrode active material, 5 g of acetylene black as a conductive additive, 5 g of PVDF as a binder, and NMP as a solvent are added and kneaded and dispersed by a planetary mixer to obtain a positive electrode paste. Produced. 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.

<Battery assembly>
The positive electrode plate produced as described above, and the negative electrode plate coated with the solid electrolyte, a positive electrode plate having a width of 5 mm and a length of 50 mm as a battery current introduction terminal, a negative electrode plate having a width of 5 mm and a long length. A 50 mm nickel tab 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 negative 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 positive electrode and the battery Assembling was performed to obtain a lithium secondary battery according to Example 2.

[Example 3]
After producing a negative 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 positive electrode and the battery The lithium secondary battery which concerns on Example 3 was obtained by assembling.

[Example 4]
After producing a negative 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 positive electrode and the battery Assembling was performed to obtain a lithium secondary battery according to Example 4.

[Example 5]
After producing a negative 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 positive 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]
In the preparation of the coating solution shown in Example 1, LiClO ₄ was used as the lithium salt instead of CH ₃ COOLi, and a lithium secondary battery according to Example 7 was obtained in the same manner as in Example 1.

[Example 8]
After producing a negative electrode in the same manner as in Example 1, a coating solution was prepared by the following method using only tetraethoxysilane as a metal alkoxide and further using polyethylene glycol (average molecular weight 200) as an organic polymer compound. 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 positive electrode and the battery Assembling was performed to obtain a lithium secondary battery according to Example 8.

[Example 9]
After producing a negative 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 positive electrode and the battery Assembling was performed to obtain a lithium secondary battery according to Example 9.

[Example 10]
After producing the negative 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. Further, by the same method as in Example 1, a positive electrode and a battery were assembled. The lithium secondary battery according to Example 10 was obtained.

[Example 11]
After producing the negative 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, the positive electrode was produced and the battery was assembled. And a lithium secondary battery according to Example 11 was obtained.

[Example 12]
After producing the negative 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, the positive electrode was produced and the battery was assembled. The lithium secondary battery according to Example 12 was obtained.

[Example 13]
After producing the negative 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. Further, by the same method as in Example 1, a positive electrode and a battery were assembled. And a lithium secondary battery according to Example 13 was obtained.

[Example 14]
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. 14 was obtained.

[Example 15]
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). 15 was obtained.

[Example 16]
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. 16 was obtained.

[Example 17]
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. A lithium secondary battery according to No. 17 was obtained.

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

That is, in the coating solution 1 diluted three times with ethanol, the negative electrode plate 2 previously formed was immersed for 10 seconds in the same manner as in Example 1 (see FIG. 1 ). The negative electrode plate 2 was pulled up at a speed of 6 mm / sec. A coating made of a solid electrolyte was formed on the carbon surface constituting the negative electrode plate 2 by repeating the immersion and pulling operations of the negative 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.

  In addition, a lithium secondary battery according to Example 18 was obtained by manufacturing a positive electrode and assembling the battery by the same method as in Example 1.

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

That is, in the coating solution 1 diluted three times with ethanol, the negative electrode plate 2 previously formed was immersed for 10 seconds in the same manner as in Example 1 (see FIG. 1 ). The negative electrode plate 2 was pulled up at a speed of 6 mm / sec. A coating made of a solid electrolyte was produced on the carbon surface constituting the negative electrode plate 2 by repeating the immersion and pulling operations of the negative 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.

  In addition, a lithium secondary battery according to Example 19 was obtained by manufacturing a positive electrode and assembling the battery by the same method as in Example 1.

[Example 20]
After producing a negative electrode and preparing 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 negative 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. 1 ), the speed was 1.0 mm / sec by the pulling motor 3. The negative electrode plate 2 was pulled up. A film made of a solid electrolyte was produced on the carbon surface constituting the negative electrode plate 2 by repeating the dipping and pulling operations of the negative 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.

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

[Example 21]
After producing a negative electrode and preparing 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 negative 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. 1 ), the speed was 2.6 mm / sec by the pulling motor 3. The negative electrode plate 2 was pulled up. By immersing and pulling up the negative electrode plate 2 eight times, a coating made of a solid electrolyte was produced on the carbon surface constituting the negative electrode plate 2. 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.

  Further, a lithium secondary battery according to Example 21 was obtained by producing a positive electrode and assembling a battery by the same method as in Example 1.

[Example 22]
After producing a negative electrode in the same manner as in Example 1, tetramethoxysilane and methyltriethoxysilane were used as metal alkoxides as in Example 1, 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 produced in the same manner as in Example 1, and further, production of a positive electrode and assembly of a battery were conducted in the same manner as in Example 1. And a lithium secondary battery according to Example 22 was obtained.

[Example 23]
After preparing the negative electrode in the same manner as in Example 1, tetramethoxysilane and methyltriethoxysilane were used as metal alkoxides as in Example 1, 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 20:80 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, the positive electrode was produced and the battery was assembled. The lithium secondary battery according to Example 23 was obtained.

[Comparative Example 1]
A lithium secondary battery according to Comparative Example 1 was prepared using a carbon negative 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 film (solid electrolyte film) in the manufacture of the lithium secondary battery according to Example 1. is there.

<Battery performance test>
About the lithium secondary battery which concerns on Examples 1-23 mentioned above and the comparative example 1, the performance test was implemented with the method shown below.

  That is, the charging / discharging temperature is 25 ° C., charging is performed until the upper limit voltage is 3.6 V at a constant current of 0.1 C, and further charging is performed until the current value reaches 0.01 C at a constant voltage of 3.6 V. It was. Thereafter, discharging was performed at a constant current of 0.1 C until the battery voltage reached 2.0V. The discharge capacity and charge / discharge efficiency at this time (first cycle) were 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 1-7 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 carbon material which comprises a negative electrode.

表１に示される結果より、実施例１〜実施例７に係るリチウム二次電池は、固体電解質により被覆されていない炭素材料を負極として使用した比較例１に係るリチウム二次電池に比べて、いずれも、充放電効率、及び容量保持率に優れていることが認められた。

From the results shown in Table 1, the lithium secondary batteries according to Examples 1 to 7 are compared with the lithium secondary battery according to Comparative Example 1 using a carbon material not coated with a solid electrolyte as a negative electrode. Both were found to be excellent in charge / discharge efficiency and capacity retention.

  Further, it was confirmed that the lithium secondary battery according to Example 1 had a larger discharge capacity than the lithium secondary battery according to Comparative Example 1. As for the discharge capacity, an error of about ± 2 mAh / g is generally shown in the test under the same conditions and the same sample, so that the lithium secondary batteries according to Examples 2 to 7 and Comparative Example 1 are almost the same. It can be said that the discharge capacity is comparable.

In the lithium secondary batteries according to Examples 1 to 7, all of the solid electrolytes covering the carbon material constituting the negative electrode have an ionic conductivity of 1.0 × 10 ⁻⁶ S / cm or more. It showed a good rate characteristic of 0.85 or more.

  In Table 2, the result of the performance test of the lithium secondary battery according to Example 1 and Examples 8 to 13 is shown together with the ionic conductivity and the BET specific surface area of the solid electrolyte membrane covering the carbon material constituting the negative electrode. Shows the result of the battery performance with respect to the mixing ratio of the metal alkoxide having no organic group (tetramethoxysilane or tetraethoxysilane) and the metal alkoxide having an organic group (methyltriethoxysilane).

表２に示される結果より、実施例８〜１３に係るリチウム二次電池は、いずれも、比較例１に係るリチウム二次電池と比べて、充放電効率及び容量保持率に優れていることが認められた。また、実施例８〜実施例１３に係るリチウム二次電池において、負極を構成する炭素材料を被覆する固体電解質は、いずれも、１.０×１０^-6Ｓ／ｃｍ以上のイオン伝導度を有しており、０．８５以上の良好なレート特性を示した。

From the results shown in Table 2, the lithium secondary batteries according to Examples 8 to 13 are all superior in charge / discharge efficiency and capacity retention compared to the lithium secondary battery according to Comparative Example 1. Admitted. In the lithium secondary batteries according to Examples 8 to 13, all of the solid electrolytes covering the carbon material constituting the negative electrode have an ionic conductivity of 1.0 × 10 ⁻⁶ S / cm or more. It showed a good rate characteristic of 0.85 or more.

  Further, in the preparation of the coating solution, the lithium secondary batteries according to Example 1 and Examples 9 to 13 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 as compared with Example 8 that was not performed, and it was confirmed that a dense solid electrolyte membrane was produced on the surface of the carbon material constituting the negative electrode.

  Furthermore, when the mixing ratio of the metal alkoxide having no organic group and the metal alkoxide having an organic group is within the range of 95: 5 to 20:80, the BET specific surface area increases as the number of metal alkoxides having an organic group increases. It was confirmed that the charge / discharge efficiency of the first cycle was improved. On the other hand, when the amount of the metal alkoxide having an organic group exceeds the above-mentioned molar ratio of 20:80, the charge / discharge efficiency of the first cycle decreases with an increase in the amount of the metal alkoxide having an organic group. The amount of increase in charge / discharge efficiency with respect to Comparative Example 1 in Example 13 in which the mixing ratio of the metal alkoxide having no organic group and the metal alkoxide having an organic group is 5:95 in molar ratio is considerably low as 1%. It was.

  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 forming the copolymer is a molar ratio. The ratio is preferably 95: 5 to 10:90, and more preferably 90:10 to 20:80.

  Table 3 shows the results of the performance tests of the lithium secondary batteries according to Example 1, Example 6, and Examples 14 to 17, and the ionic conductivity and BET ratio of the solid electrolyte membrane covering the carbon material constituting the negative electrode. By showing together with the surface area, the results of the battery performance with respect to the average molecular weight of the organic polymer compound are shown.

表３に示す結果より、実施例１４〜１７に係るリチウム二次電池は、いずれも、比較例１に係るリチウム二次電池に比べて、充放電効率及び容量保持率に優れていることが認められた。ただし、平均分子量が４０００である実施例１７の比較例１に対する充放電効率の増加量は、１％と少なかった。

From the results shown in Table 3, it is recognized that the lithium secondary batteries according to Examples 14 to 17 are superior in charge / discharge efficiency and capacity retention rate as compared with the lithium secondary battery according to Comparative Example 1. It was. However, the amount of increase in charge / discharge efficiency relative to Comparative Example 1 of Example 17 having an average molecular weight of 4000 was as small as 1%.

In the lithium secondary batteries according to Examples 14 to 17, all of the solid electrolytes covering the carbon material constituting the negative electrode have an ionic conductivity of 1.0 × 10 ⁻⁶ S / cm or more. It showed a good rate characteristic of 0.85 or more. Moreover, the smaller the average molecular weight of the organic polymer compound used for the production of the copolymer, the higher the ionic conductivity, and Examples 1, 6 and 14 to 100 using 1000 to 1000 organic polymer compounds. Example 15 showed an extremely high ionic conductivity of 1.0 × 10 ⁻³ S / cm or more.

  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 Example 1 and Examples 18 to 21 together with the ionic conductivity and the BET specific surface area of the solid electrolyte membrane covering the carbon material constituting the negative electrode. Shows the result of the battery performance with respect to the thickness of the solid electrolyte.

表４に示される結果より、実施例１８〜２１に係るリチウム二次電池は、いずれも、比較例１に係るリチウム二次電池に比べて、充放電効率及び容量保持率に優れていることが認められた。

From the results shown in Table 4, the lithium secondary batteries according to Examples 18 to 21 are all superior in charge / discharge efficiency and capacity retention compared to the lithium secondary battery according to Comparative Example 1. Admitted.

  In addition, the charge / discharge efficiency and capacity retention rate tend to increase as the film thickness increases within a range of 1000 nm or less, and tend to decrease as the film thickness increases beyond 1000 nm. It was recognized that there was. For this reason, about the lithium secondary battery which concerns on Example 18 and Example 21, the increase amount of charging / discharging efficiency and capacity retention with respect to the lithium secondary battery which concerns on the comparative example 1 was few with 1-2%.

In the lithium secondary batteries according to Examples 18 to 21, all of the solid electrolytes covering the carbon material constituting the negative electrode have an ionic conductivity of 1.0 × 10 ⁻⁶ S / cm or more. It showed a good rate characteristic of 0.85 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.

  By showing the result of the performance test of the lithium secondary battery which concerns on Example 1 and Examples 22-23 in Table 5 with the ionic conductivity and BET specific surface area of the solid electrolyte membrane which coat | covers the carbon material which comprises a negative electrode. 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.

表５に示す結果より、実施例２２〜２３に係るリチウム二次電池は、いずれも、比較例１に係るリチウム二次電池に比べて、充放電効率及び容量保持率に優れることが認められた。また、実施例２２〜実施例２３に係るリチウム二次電池において、負極を構成する炭素材料を被覆する固体電解質は、いずれも、１.０×１０^-6Ｓ／ｃｍ以上のイオン伝導度を有しており、０．８５以上の良好なレート特性を示した。

From the results shown in Table 5, it was confirmed that the lithium secondary batteries according to Examples 22 to 23 were excellent in charge / discharge efficiency and capacity retention rate as compared with the lithium secondary battery according to Comparative Example 1. . In the lithium secondary batteries according to Examples 22 to 23, the solid electrolyte covering the carbon material constituting the negative electrode has an ionic conductivity of 1.0 × 10 ⁻⁶ S / cm or more. It showed a good rate characteristic of 0.85 or more.

It is explanatory drawing for demonstrating the method to produce the film by a solid electrolyte in the negative 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 a chemical structure of a film made of a solid electrolyte produced on the surface of the negative electrode in the lithium secondary battery according to Example 1 of the present invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Coating solution 2 Negative 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 negative electrode includes the following repeating unit (A) formed by bonding a metal atom and an oxygen atom.
-MO -... (A)
(Wherein M represents a metal selected from Si, Al, Ti, and Zr). A metal oxide polymer block having the following general formula (1)
-((CH ₂ ) _m -O) _n- (1)
(Wherein m represents an integer of 1 to 3 and n represents an integer of 1 or more) a copolymer having a structure in which an organic polymer block having a structural unit represented by the above is bonded via oxygen and a lithium salt A lithium secondary battery characterized by being a carbon material coated with a solid electrolyte mainly composed of The lithium secondary battery according to claim 1,
A lithium secondary battery, wherein 5 to 90% of metal atoms contained in the copolymer are bonded to a monovalent organic group. In a lithium secondary battery having a positive electrode, a negative electrode, a non-aqueous electrolyte, and a separator,
  The negative electrode includes the following repeating unit (B) formed by bonding a metal atom and an oxygen atom.
  -R ¹ _b M-O -... (B)
(Where M represents a metal selected from Si, Al, Ti, and Zr, and R ¹ Represents an alkyl group or an alkenyl group having 1 to 5 carbon atoms. Moreover, b represents the integer of 0-2. The metal oxide polymer block having the following general formula (1)
  -((CH ₂ ) _m -O) _n -... (1)
(Wherein m represents an integer of 1 to 3 and n represents an integer of 1 or more) a copolymer having a structure in which an organic polymer block having a structural unit represented by the above is bonded via oxygen and a lithium salt A lithium secondary battery characterized by being a carbon material coated with a solid electrolyte mainly composed of The lithium secondary battery according to claim 1 or 3,
  A lithium secondary battery, wherein 5 to 90% of metal atoms contained in the copolymer are bonded to an alkyl group or alkenyl group having 1 to 5 carbon atoms. The lithium secondary battery according to any one of claims 1 to 4 ,
The lithium secondary battery, wherein the copolymer contains at least Si. A lithium secondary battery according to any one of claims 1 to 5 ,
Lithium secondary batteries having an average molecular weight of the organic polymer block, characterized in that 100 to 2000. The lithium secondary battery according to any one of claims 1 to 6 ,
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 selected from Si, Al, Ti, and Zr , R ¹ represents an alkyl group or alkenyl group having 1 to 5 carbon atoms , and R ² represents a lower group having 1 to 8 carbon atoms. Represents an alkyl group, a represents the valence of metal M, b represents an integer of 0 to 2, and c represents an integer of 0 or more, provided that 0 ≦ c ≦ ab. A lithium secondary battery obtained by reacting a product produced by polycondensation of one or more metal oxides with a polyalkylene glycol . The lithium secondary battery according to any one of claims 1 to 6,
The metal oxide polymer has the following general formula (3)
R ¹ _b M (OR ² ) _ab (3)
(In the formula, M represents a metal selected from Si, Al, Ti, and Zr, R ¹ represents an alkyl group or alkenyl group having 1 to 5 carbon atoms, and R ² represents a lower group having 1 to 8 carbon atoms. Represents an alkyl group, a represents the valence of metal M, b represents an integer of 0 to 2, and one or more metal oxides produced by hydrolyzing one or more metal alkoxides represented by A lithium secondary battery, which is formed by a polycondensation reaction . The lithium secondary battery according to claim 7 ,
The lithium secondary battery is characterized in that the polyalkylene glycol is at least one selected from polyethylene glycol and polypropylene glycol. The lithium secondary battery according to any one of claims 1 to 9,
The lithium secondary battery, wherein the solid electrolyte contains at least CH ₃ COOLi as the lithium salt. The lithium secondary battery according to any one of claims 1 to 10,
In the solid electrolyte, as the lithium salt, LiClO ₄ , LiCF ₃ SO ₃ , Li
A lithium secondary battery comprising at least one selected from the group consisting of N (CF ₃ SO ₂ ) ₂ and LiN (C ₂ F ₅ SO ₂ ) ₂ . The lithium secondary battery according to any one of claims 1 to 11,
A lithium secondary battery, wherein the solid electrolyte has a thickness of 50 nm to 5 μm. A lithium secondary battery according to any one of claims 1 to 12,
The lithium secondary battery, 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 any one of claims 1 to 13,
The lithium secondary battery, wherein the solid electrolyte has an ionic conductivity of 1.0 × 10 ⁻⁶ S / cm or more. The lithium secondary battery according to any one of claims 1 to 14,
A lithium secondary battery, wherein the solid electrolyte has a BET specific surface area of 10 m ² / g or less.

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