(19) 0
`
`) ee
`
`European PatentOffice
`Office européen des brevets
`
`IMMAA
`
`EP 0 746 050 B1
`
`(11)
`
`(12)
`
`EUROPEANPATENT SPECIFICATION
`
`(51) Intci.6: HO1M 10/40
`
`Sekundarbatterie mit nichtwassrigem Elektrolyten
`
`(45) Date of publication and mention
`of the grant of the patent:
`11.08.1999 Bulletin 1999/32
`
`(21) Application number: 96108102.3
`
`(22) Date offiling: 21.05.1996
`
`(54) Non-aqueous electrolyte secondary battery
`
`Batterie secondaire a électrolyte non-aqueux
`
`(84) Designated Contracting States:
`DE FR GB
`
`(80) Priority: 26.05.1995 JP 12780595
`31.10.1995 JP 28420095
`
`(48) Date of publication of application:
`04.12.1996 Bulletin 1996/49
`
`(73) Proprietor. SONY CORPORATION
`Tokyo (JP)
`
`(72) Inventor: Shimizu, Ryuichi, c/o Sony Corp.
`Tokyo (JP)
`
`
`
`(74) Representative: Miller, Frithjof E., Dipl.-Ing. et al
`Patentanwalte
`MULLER & HOFFMANN,
`Innere Wiener Strasse 17
`
`81667 Miinchen (DE)
`
`(56) Referencescited:
`EP-A- 0 319 182
`EP-A- 0 631 339
`
`US-A- 4 670 363
`
`EP-A- 0 390 145
`DE-A- 2 834 485
`
`¢ PATENT ABSTRACTSOF JAPANvol. 17, no. 178
`(E-1347) & JP-A-04 332479 (SONY CORP)
`¢ PATENT ABSTRACTSOF JAPANvol. 14, no. 502
`(E-0997) & JP-A-02 207464 (SHOWA DENKOKK)
`e PATENT ABSTRACTSOF JAPAN vol. 94, no. 012
`& JP-A-06 338347 (SONY CORP), 6 December
`1994,
`
`EP0746050B1
`
`Note: Within nine months from the publication of the mention of the grant of the European patent, any person may give
`notice to the European Patent Office of opposition to the European patent granted. Notice of opposition shall befiled in
`a written reasoned statement. It shall not be deemed to have been filed until the opposition fee has been paid. (Art.
`99(1) European Patent Convention).
`
`Printed by Jouve, 75001 PARIS (FR)
`
`1
`
`APPLE-1027
`
`1
`
`APPLE-1027
`
`

`

`EP 0 746 050 B1
`
`Description
`
`BACKGROUND OF THE INVENTION
`
`Field of the Invention
`
`10
`
`18
`
`20
`
`25
`
`30
`
`38
`
`40
`
`45
`
`50
`
`55
`
`[0001] The present invention relates to a non-aqueouselectrolyte secondary battery for obtaining electromotive force
`due to introduction and dischargeoflithium ions, and moreparticularly to a technique for preventing overcharge of the
`battery due to chemicalreactions of additives.
`
`Prior Art
`
`Security is the most important consideration for a lithium secondary battery (non-aqueous electrolyte second-
`[0002]
`ary battery). In particular, protection from overcharge is an important fact.
`[0003]
`For example, if the charge voltage for, for example, a nickel-cadmium battery, has been raised, consumption
`of charge energy taking place due to chemical reactions of water which causes an overcharge protective mechanism
`to act. However,for the lithium secondary battery, which is a non-aqueous type secondary battery, another mechanism
`must be found.
`
`[0004] Asanovercharge protective mechanism forthe lithium secondary battery, there have been suggested a meth-
`od using an electronic circuit, a method of mechanically interrupting an electric current by using gas generation when
`overcharge takes place, a shut down method using fusion of a separator and a method using chemical reactions of a
`reagent. However, each methodhas the following problem and, therefore, a satisfactory overcharge protective mech-
`anism has not been realized yet.
`[0005] The method using an electronic circuit or the method of mechanically interrupting an electric current causes
`the battery to have an additional structure. Therefore, the cost of the battery cannot be reduced and various limitations
`arise in designing a product of the battery.
`[0006] The shut down method using fusion of a separator is a method using rise in the temperature of the battery
`when overcharge has taken place to fuse the separator with heat to close (shut down) a multiplicity of small apertures
`formed in the separator so asto interrupt the overcharge electric current. In the foregoing case, the separator is made
`of material which can relatively easily be fused.
`[0007] Heat which raises the temperature of the battery is considered to be generated due to reactions of lithium of
`the negative pole deposited due to overcharge and metal oxides of the positive pole made unstable because lithium
`ions have been excessively drawn due to overcharge and the electrolyte. Since the foregoing heat generation takes
`place considerably rapidly, heat generation cannot be interrupted even after the separator has been shut down and,
`thus, the overcharge electric current has been interrupted. Therefore, the temperatureof the batteryis frequently raised
`excessively and thus a problem of thermal runaway arises. As a result, in practical batteries, the shut-downtype sep-
`arator has not been used to prevent overcharge but the same has been employed to prevent short circuit occurring
`with the outside of the battery.
`[0008] Accordingly, another method has been energetically researched and developed which uses chemical reac-
`tions to prevent overcharge. For example, a method has been attempted in which an appropriate oxidation-reduction
`reagent is added to the electrolyte. In a case wherethe reversibility of the oxidation-reduction reagent is excellent, a
`protective mechanism is realized in which the reagent reciprocates between the positive pole and the negative pole
`to consume the overcharge electric current.
`[0009] The foregoing oxidation-reduction reagent is called a "redox shuttle" or the like. Simplification of the safety
`apparatus of the lithium secondary battery by using the redox shuttle realizes advantages in that the cost can be
`reduced and lowering of the battery energy density occurring due to the safety apparatus can be prevented as compared
`with the electronic circuit method. As for possibility in applying the redox shuttle to the lithium secondary battery, a fact
`that application of ferrocene is advantageous in a case wherethe battery is a 3 V type battery has been suggestedin,
`for example, Japanese Patent Application Laid-Open publication No. 1-206571 (1989).
`it
`[0010] However, since the oxidation-reduction potential of the ferrocene with respectto lithium is 3.1 V to 3.5 V,
`cannot be adaptedto a battery having higher battery voltage. For example, a carbon-LiCoO2-typelithium ion battery,
`which is a 4-V class battery, must employ a compound having an oxidation-reduction potential of about 4.0 V to about
`4.5 V.
`
`Further improvements resulted in a disclosure in Japanese Patent Application Laid-Open publication No.
`[0011]
`6-338347 (1994) in which metal complexes, such as Fe (5-Cl-1, 10-phenanthroline)3X_ and Ru (phenanthroline)3Xp
`(where X is an anionic molecule), and cerium salts, such as Ce (HNy)o(NOq)s, have been suggested as oxidation-
`reduction reagents adaptable to the 4-V-classlithium ion secondary battery. Transition metals, such as Fe, Ru and Ce,
`which are the central metals of the oxidation-reduction reagents, have a plurality of stable oxidation-reduction states
`
`

`

`EP 0 746 050 B1
`
`due to statesof d-orbital or f-orbital. By coordinating appropriate ligands or by forming the same into solvated molecules,
`the oxidation-reduction potential can be controlled so that the foregoing transition metals are employed as preferred
`redox shuttles for the 4-V-class battery.
`[0012] However, since each of the foregoing metal complexes and cerium salts has a structure such that large group
`of atoms surroundsthe orbits of the central metals, they have large volume per molecular weight or per molecule.
`Therefore, the concentration and diffusion rate of the reagent molecules in the electrolyte are limited. Thus, there
`frequently arises a problem in that the effect of preventing overcharge cannot be obtained satisfactorily.
`[0013] As another redox shuttle adaptable to the 4-V class battery, a compound has been disclosed in Japanese
`Patent Application Laid-open publication No. 7-302614(1995) in which an electron donative substitutional group, such
`as an alkyl group or a methoxy group, is induced into a benzene ring. Since the foregoing compound has a small
`molecular weight and a small volume per molecule as compared with those of the metal complex and cerium salt,
`satisfactory solubility and operations to serve as a redox shuttle can be obtained.
`[0014] However, since the redox shuttle has a theoretical limiting current, a satisfactory effect of preventing over-
`charge cannot be obtained if the overcharge electric current is greater than a predetermined value. Specifically, the
`limiting current of each of the redox shuttles, which have been suggested, is not sufficiently large with respect to
`overcharge occurring in a case where charge has been performed at a rate (current capacity/charge period) of 1, that
`is, charge has been performed with a constant current of 1C (Ah/n) or greater.
`[0015]
`To prevent overcharge occurring with a great current, the foregoing method using an electronic circuit or the
`method of mechanically interrupting the electric current using generation of gas if overcharge takes placeis relatively
`effective. Therefore, in a case where the redox shuttle is employed in a battery system in which charge is performed
`with a great electric current, the foregoing method must also be employed.
`[0016] The addition of aromatic compounds, optionally having alkyl, alkoxy and/or halogen substituents, as corrosion-
`protective agents to the organic solventoflithium secondary batteries is disclosed in DE-A-28 34 485. Said corrosion-
`protective agents are selected such that they do not chemically react with the electrode and are not chemically modified
`during use of the battery.
`
`OBJECT AND SUMMARY OF THE INVENTION
`
`In view of the foregoing, an object of the present invention is to provide a non-aqueous electrolyte secondary
`[0017]
`battery having a reagent satisfactorily serving as a mechanism of preventing overcharge even adapted to a 4-V-class
`battery which is charged with a great electric current and exhibiting high energy density and satisfactory safety and
`low cost.
`
`To achieve the foregoing object, according to one aspect of the present invention, there is provided a non-
`[0018]
`aqueous electrolyte secondary battery according to claim 1. The battery comprises a negative pole made of metal
`material mainly composedoflithium or carbon material capable of doping and removing lithium; a positive pole made
`of a composite oxide oflithium and transition metal; and an electrolyte which is a non-aqueous electrolyte in which a
`support salt is dissolved in anon-aqueoussolvent, wherein the non-aqueous electrolyte contains a benzene compound
`having a small molecular weight, e.g., a molecular weight of 500 or less, more preferably 200 or less, and a reversible
`oxidation-reduction potential at a potential higher than the potential at the positive pole in a state where the non-aqueous
`electrolyte secondary battery is fully charged and having a p -electron orbital. The benzene compound is selected from
`the group consisting of compounds expressed by General Formulas[I] to [V]:
`
`R
`
`Al
`
`AS
`
`A2
`
`(I]
`
`A4
`
`A3
`
`10
`
`18
`
`20
`
`25
`
`30
`
`38
`
`40
`
`45
`
`50
`
`whereRis an alkyl group, A,, Ap, Ag, Ay and As are each H or halogen and at least any one of Aj, Ao, Ag, Ay and As
`is halogen;
`
`

`

`EP 0 746 050 B1
`
`R
`
`R
`
`Ag
`
`aA.
`
`([1T)
`
`A3
`
`A2
`
`where Ris an alkyl group, A;, Ao, Ag and Ay are each H or halogen and at least any one of Ay, Ao, Az and Ay is halogen;
`
`R
`
`R
`
`A4
`
`Al
`
`(IIT)
`
`A3
`
`A2
`
`whereR is an alkyl group, A;, Ao, Ag and Ay are each H or halogen and atleast any one of Ay, A>, Ag and Ay is halogen;
`
`R
`
`R
`
`A2
`
`Al
`
`10
`
`18
`
`20
`
`25
`
`30
`
`38
`
`whereRis an alkyl group, A,, A> and Ag are each H or halogen and at least any one of A,, Ao and Ag is halogen;
`
`40
`
`45
`
`50
`
`55
`
`R
`
`O-——R
`
`Aa
`
`Ai
`
`[V]
`
`A3
`
`A2
`
`WhereR is an alkyl group, A,, Az, Az and Ay are each halogen.
`[0019] According to another embodimentof the invention, there is provided a non-aqueous electrolyte secondary
`battery according to claim 3.
`In this embodiment, the support electrolyte is LiIBF, and the benzene compound is ex-
`pressed by Formula VI:
`
`

`

`EP 0 746 050 B1
`
`.
`
`CH3
`
`(vz]
`
`H3C
`
`CH3
`
`10
`
`18
`
`20
`
`25
`
`30
`
`38
`
`40
`
`45
`
`50
`
`55
`
`It is preferable that the non-aqueous electrolyte secondary battery containing the benzene compound in the
`[0020]
`non-aqueous electrolyte thereof employs a polyolefin porousfilm which is, as a separator, disposed between the pos-
`itive pole and the negative pole.
`[0021] Other objects, features and advantagesof the invention will be evident from the following detailed description
`of the preferred embodiments described in conjunction with the attached drawings.
`
`BRIEF DESCRIPTION OF THE DRAWINGS
`
`[0022]
`
`Fig. 1 is a vertical cross sectional view showing an example of the structure of a non-aqueous electrolyte secondary
`battery according to the present invention;
`Fig. 2 is a schematic view showing a measurementcircuit system for use in performing a constant electric current
`overcharge test of the non-aqueous electrolyte secondary battery; and
`Fig. 3 is a graph showing the terminal voltage whenthe battery has been overcharged and change in the temper-
`ature of the battery as the time passes of a battery in which 2-chloro-p-xylene is added to the electrolyte thereof
`and a battery to which no 2-chloro-p-xylene is addedto the electrolyte thereof.
`
`DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
`
`[0023] Each of the foregoing benzene compoundsacts as a mechanism for preventing overcharge. The mechanism
`for preventing overcharge is realized due to chemical reactions such that the benzene compound performsan oxidation-
`reduction reaction if the battery has been overcharged, and then the oxidized compoundscontinuously are dimerized
`to polymerized or adsorbedto the activated electrode or react with the same. The mechanism for preventing overcharge
`will now be described.
`
`[0024] The benzene compound hasaneffect to serve as the redox shuttle, that is, an effect of consuming the over-
`charge current by the oxidation-reduction reactions.
`[0025] The foregoing effect can be obtained because the benzene compound hasan appropriate oxidation-reduction
`potential as the redox shuttle for a 4-V-class battery and is able to chemically stabilize oxidation species and reduction
`species by selecting a substitutional group.
`[0026] That is, a covalent bond of two atoms of an organic compound, in principle, is such that two electrons forming
`a pair form one single bond. Therefore, when an organic compound is oxidized or reduced to remove or add one
`electron from an electron system of the bond of the organic compound, an unpaired electron is formedin the organic
`molecule compound. Although the unpaired electron can be stabilized when decomposition of the organic compound
`has been resulted in a novel bond with another molecule being formed, the state of the organic compound having the
`unpaired electron is instable in principle.
`[0027] However, in acase where unpaired electrons exist on a delocalized orbit and spread over two or more atoms
`ina molecule as can be observedin a p-orbital of an aromatic series, the organic compound is able to relatively stably
`exist even if the organic compound has unpaired electrons.
`If the reaction active point at which the density of the
`unpaired electrons is high is protected from attacks of other molecules due to a steric hindrance of the substitutional
`group, the organic compound even having unpaired electrons is made to be morestable.
`[0028]
`Since the oxidation-reduction potential is substantially determined depending upon the degree of spread of
`the unpaired electrons and the symmetryof the orbit, excess spread of the orbit causes an unsatisfactory state to be
`realized becausethe oxidation-reduction potential becomes inappropriate. Compoundsof the types expressed by the
`foregoing General Formulas[I] to [V] and formula [VI] having a basic skeleton composed of the benzene ring, which
`is an aromatic ring having a relatively small molecular weight, are preferred compoundsto serve as the redox shuttles
`in view of the oxicdation-reduction potential.
`[0029]
`Since the benzene ring, which is the basic skeleton of the foregoing compound, has a molecular weight of
`
`

`

`EP 0 746 050 B1
`
`78, the benzene ring has smaller molecular volume as compared with metal complex type molecule, such as metal-
`locene, polypyridine complex or cerium ions. The foregoing fact means that the volume sharing in the electrolyte is
`small and the dispersion rate is high. Thus, a satisfactory operation can be performed as the redox shuttle.
`[0030] The benzene compound hasaneffect of shutting down the separator, which is a porous polymer film.
`[0031] The reasonfor this is that the benzene compound generates Joule heat as the overcharge current is consumed
`and performs heat generative reactions such that oxidation is performed and then the benzene compound continuously
`are dimerized to polymerized or adsorbed to the activated electrode or react with the same. As a result of generation
`of heat due to the reactions, the separator is fused with heat. Moreover, the dimerized or polymerized polymers deposit
`in the form of solids on the separator to contribute to shutting down of the separator.
`[0032] Moreover, the benzene compounds adsorb to and react with the activated electrode so that overcharge re-
`action of the electrode is inhibited and a contribution to prevention of overcharge is made.
`[0033] Therefore, a battery containing the foregoing benzene compound in the non-aqueous electrolyte thereof can
`be charged with a great electric current. If the non-aqueous electrolyte secondary battery has been overcharged, the
`operation of the redox shuttle of the benzene compound causesthe overcharge current to be consumed sothatpro-
`ceeding of the overcharge reaction is inhibited. Moreover, generation of Joule heat as the overcharge current is con-
`sumed by the benzene compound, and heat generative reactions such as oxidation and then dimerization to polym-
`erization of the benzene compound or adsorption to the activated electrode or reaction with the same cause the sep-
`arator to be fused with heat or encounters solid deposition. Thus, the separator can be shut down. As a result, the
`overcharge current can be interrupted and also the overcharge reaction can be prevented.
`[0034] Note that shutting down of the separator due to the heat fusion is the most important factor for contributing
`to the prevention of the overcharge reaction in the case of the overcharge with a great electric current.
`[0035] The reasonfor this is that the heat generation due to the various reactions of the benzene compoundsis
`enhancedasthe electric current at the overcharge is made greater and the shutting down of the separator can easily
`take place. Thatis, shutting downof the separator due to the heat fusion has no upper limit electric current in a manner
`different from the effect of the redox shuttle. Thus, the shutting down can be performed considerably as the overcharging
`current is made larger.
`[0036]
`Since heat generation taking place due to ihe benzene compound is closely related to oxidation of the benzene
`compound, rise of the temperature is quickly interrupted after the overcharge current has been interrupted due to
`shutting down of the separator. Therefore, in a manner different from heat generation taking place in a case where no
`benzene compound is used, that is, heat generation due to reaction oflithium deposited on the negative pole or the
`metal oxide on the positive pole, which has been made instable, with the electrolyte, excess rise of the temperature
`of the battery causing thermal runaway to take place can be prevented. As a result, a significant advantage can be
`realized in improving security of the battery.
`[0037] Note that the benzene compoundfor use to realize the overcharge preventive mechanism has alkyl group R,
`alkoxy group OR or H or halogen groups A, to Ag induced thereto (two or more alky! group or alkoxy groups may be
`annularly bondedto each other),.
`[0038] The selection of the substitutional group to be introducedinto the benzene ring is mainly performedin con-
`sideration of the characteristic of the substitutional group for attracting electrons or electron donative characteristic on
`the basis of the oxidation-reduction potential and the operating voltage range due to the p-electron orbital energy of
`the molecule.
`
`[0039] That is, the oxidation-reduction potential of the organic compound is mainly determined depending upon the
`basic skeleton of the molecule thereof. The oxidation-reduction potential is varied by hundreds of mV depending upon
`the type of the electrolyte for dissolving the organic compound. Therefore, selection of the substitutional group must
`be selected appropriately to precisely adjust the potential.
`[0040] A fact about the benzene compound has been knownthat a substitutional group of a type attracting electrons,
`in many cases, raises the oxidation-reduction potential and a substitutional group of an electron donative,
`in many
`cases lowers the oxidation-reduction potential. Moreover, effects of plural substitutional groups frequently exhibits
`reversible characteristic.
`
`[0041] Among the substitutional groups to be induced into the benzene compound, the alkyl group and alkoxy group
`are electron donative substitutional group and mainly have aneffect of adjusting the oxidation-reduction reaction po-
`tential. On the other hand, the halogen group, whichis an electron attractive substitutional group, does not considerably
`affect the oxidation-reduction potential but has a function of improving the stability of the performance of the battery
`at high temperatures.
`[0042]
`Thatis, the electron donative group of the benzene compound lowers the oxidation-reduction potential as
`described above and activates the electrophilic substitution reactions of the oxidizer in the system. On the other hand,
`the electron abstractive group deactivates the electrophilic substitution reactions.
`[0043]
`Since LiPF¢ or the like, which is generally employed as a supportsalt in the electrolyte, is a strong Lewis salt,
`it sometimes becomesan oxidizer having a strength capable of attacking the benzene compound if the temperature
`
`10
`
`18
`
`20
`
`25
`
`30
`
`38
`
`40
`
`45
`
`50
`
`55
`
`

`

`EP 0 746 050 B1
`
`10
`
`18
`
`20
`
`25
`
`is relatively high.
`[0044]
`Inabattery system having strong Lewis acid, such as LiPFg, as a support salt thereof, the effect of the halogen
`group deactivates the electrophilic substitution reactions due to LiPFg, at high temperatures. As a result, the stability
`of the benzene compoundat high temperatures can be improved and deterioration in the performance of the battery
`taking place due to oxidation of the benzene compound can be prevented.
`[0045] The reason why the halogen group is selected as an electron attractive group for deactivating the electrophilic
`substitution reactions of the oxidizer is that the halogen group hasasignificant effect of deactivating the electrophilic
`substitutional reactions but a restrained effect of raising the oxidation-reduction potential. The reason for this is that
`the halogen group hasa great resonanteffect in the substitutional group. The resonanteffect in the substitutional group
`lowers the oxidation-reduction potential because of non-localization of the molecule orbit.
`[0046]
`In acase whererelatively weak Lewis salt, such as LIBF,, is employed as the support salt of the electrolyte,
`a benzene compound having no halogen group, as shownin Formula [VI], may be addedto the electrolyte.
`[0047] As described above, the molecular design of the benzene compoundis performed in view of the oxidation-
`reduction potential and the stability at high temperatures. Moreover, a state having the unpaired electrons, thatis,
`stability of the oxidation species, must be considered.
`[0048]
`To cause the benzene compound, having the foregoing three functions as described above, to serve as the
`redox shuttle, the reduction species and oxidation species of the benzene compound must chemically be stable.
`[0049] However, to cause the separator to be shut down or to inhibit the overcharge reactions of the electrode, the
`benzene compound mustbe dimerized, polymerized continuously to the oxidation, or absorbed to or allowed to react
`with the activated electrode. Therefore,
`in the case where the foregoing effect is expected, it is preferable that the
`oxidation species of the benzene compound berelatively instable.
`[0050]
`The stability of the oxidation species of the benzene compound is controlled by the steric hindrance of the
`substitutional group.
`If the reaction active point, at which the density of unpaired electrons is high, is protected from
`attacks of other molecules due to the steric hindrance, the oxidation speciesarerelatively stable. If the reaction active
`pointis allowed to expose outside and, therefore, they can easily be attached by other molecules, the oxidation species
`are relatively instable.
`[0051] Thatis, by controlling the steric hindrance due to the substitutional group, the stability of the oxidation species
`can be controlled. In a case wherethe effect of the redox shuttle is considered important, a substitutional group having
`a great steric hindrance must be employed to stabilize the oxidation species.
`In a case where shutting downof the
`separatoris intended or the effect of inhibiting the overcharge reactions of the electrode is considered important, a
`substitutional group must be selected whichhasa relatively small steric hindrance to makethe stability of the oxidation
`speciesto berelatively instable. The reactions of the dimerization and polymerization continued from the oxidation can
`easily be controlled by designing the substitutional group. Therefore, an overcharge preventive mechanism adaptable
`to the degree of the overcharge current can be established.
`[0052]
`In view of the foregoing, it is preferable that the benzene compound among those shownin Table 1 be em-
`ployed for a battery system having a negative pole made of carbon and a positive pole made of LiCoO,. Note that
`Table 1 shows the composition formulas and molecular weights as well as constitutional formulas.
`
`30
`
`38
`
`40
`
`45
`
`50
`
`55
`
`

`

`EP 0 746 050 B1
`
`Table 1
`
`
`
`CONSTITUTIONAL COMPOSITION|MOLECULAR
`
`
`vo]SNCS|
`
` comroun|SHERRSEA™|“sa
`
`4-chloro
`anisole
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`anisole
`
`C7H7C10
`
`142.6
`
`3
`
`5
`
`:
`
`F
`
`.
`
`¥
`
`OCH]
`
`OCH
`
`OCH}
`
`Br
`
`2,4-
`dGiflucoro
`anisole
`
`C7H6EF20
`
`144.1
`
`3,5-
`difluoro
`anisole
`
`.
`
`C7HsF20
`
`144.1
`
`4~flucra
`anisole
`
`C7H7FO
`
`126.1
`
`4-bromo
`anisole
`
`C7H7Bro
`
`187.0
`
`2-chloro
`anisole
`
`C7HIC1LO
`
`142.6
`
`
`
`3-chloro
`
`
`
`C7H7C1O
`
`142.6
`
`20
`
`25
`
`30
`
`38
`
`40
`
`45
`
`50
`
`55
`
`

`

`EP 0 746 050 B1
`
`CONSTITUTIONAL
`FORMULA
`oC:
`HY
`
`F
`
`COMPOUND
`
`COMPOSITION| MOLECULAR
`FORMULA
`WEIGHT
`
`C7H7FO
`
`126.1
`
`
`2,3,5,6-
`tetratluoro
`
`methylanisole
`
`CaH6F40
`
`194.1
`
` 4-fluoro
`
`anisole
`
`
`
`
`
`
`CHa
`
`
`
`
`2-fluoro
`mesitylene
`
`(2-fluoro-l1,
`
`3,5-trimethyl
`
`benzene
`
`
`
`
`14214
`tetrafluoro
`
`-3,6-
`
`dimethoxy
`
`benzene
`
`
`
`
`_
`
`_
`
`_
`
`CeHe
`F402
`
`210.1
`
`CoH12
`
`.
`120.2
`
`
`
`
`
`mesitylene
`(1,3,5-
`trimethyl
`benzene)
`
`
`
`
`[0053] The non-aqueous electrolyte secondary battery according to the present invention contains the foregoing
`benzene compound in the non-aqueous electrolyte thereof. As the separator to be disposed between the positive pole
`and the negative pole, the following material is employed.
`[0054] As the active material of the negative pole, a carbonaceous material of a type capable of doping and removing
`lithium metal, lithium alloy and lithium is employed. The carbonaceous material is exemplified by pyrolytic carbon, coke
`(pitch coke, needle coke, or petroleum coke), graphite, glass-type carbon, material prepared by baking organic polymer
`compound (carbonated by baking furan resin or the like at appropriate temperatures), carbon fiber and activated carbon.
`[0055] As the active material for the positive pole, a composite oxidized material oflithium transition metal, such as
`LiCoO,, expressed by Li,MO, (where M is one or more typesof transition metals, preferably at least any one of Mn,
`Co and Ni, and x satisfies 0.05 < x < 1.10).
`[0056] As the separator to be disposed between the positive pole and the negative pole, the shutting down effect of
`the benzene compound must be obtained if the battery has been overcharged by selecting a porous film of material
`of a type that can easily be fused with heat generated due to various reactions of the benzene compound.
`[0057] The material of the separator is exemplified by polyolefin, preferably polyethylene is a preferred material.
`
`10
`
`18
`
`20
`
`25
`
`30
`
`38
`
`40
`
`45
`
`50
`
`55
`
`

`

`EP 0 746 050 B1
`
`Polyethylene has a relatively low melting temperature of about 110°C. In a battery comprising the separator made of
`polyethylene, the separator is shut down whenthe temperature has been raised to about 110°C in the case where the
`overcharge state has been realized. Thus, the overcharge current can be interrupted so that the temperature of the
`benzene ring does not exceed 110°C. Although the separator may be composed of only the polyolefin porousfilm, a
`hybrid separator may be employed which is formed by stacking a polyolefin porous film and another porous film made
`of another polymer.
`[0058] As the electrolyte, non-aqueous electrolyte in which a support salt is dissolved in a non-aqueous solventis
`employed.
`[0059] As the non-aqueoussolvent, ethylene carbonate, propylene carbonate, dimethyl carbonate, methylethyl car-
`bonate, y-butyrolactone, methyl propionate or ethyl propionate or their combination may be employed.
`[0060] The supportsalt is exernplified by LiPF,, LiCIO,, LIBF4, LICF35O3, LiAsFg, LIN (CF3505). and LiC (CF2SO5)3.
`
`Examples
`
`[0061] The present invention will now be described in detail on the basis of results of experiments.
`
`Structure of Manufactured Battery
`
`[0062] Anon-aqueous electrolyte secondary battery manufactured in each example, to be describedlater, is shown
`in Fig. 1.
`[0063] The non-aqueous electrolyte secondary battery has a structure such that a negative pole 1, comprising a
`negative pole collector 10 to which a negative pole active material is applied, and a positive pole 2 having a positive
`pole collector 11, to which a positive pole active material is applied, are wound through a separator 3, and a battery
`can 5 is accommodatedin a state where insulators 4 are disposed on the two vertical ends of the member formed by
`winding.
`[0064] A battery covers 7 is attached to the battery can 5 by caulking through a gasket 6. The battery cover 7 is,
`through a negative pole lead 12 and a positive pole lead 13, electrically connected to the negative pole 1 or the positive
`pole 2 so as to be serve as a negative pole or a positive pole of the battery.
`[0065] Note that the battery according to this embodiment has a structure such that the positive pole lead 13 is
`welded to a pressure release valve 8 provided with a cut portion having a predetermined length. Thus, the electrical
`connection with the battery cover 7 is established through the pressurerelease valve 8.
`[0066]
`If the pressurein the battery having the foregoing structure has been raised, the foregoing cut portion of the
`pressurerelease valve 8 is widened. Thus, the internal pressure is released through the widenedcut portion.
`
`Example 1
`
`In this example, the foregoing non-aqueous electrolyte secondary battery was manufactured asfollows.
`[0067]
`Initially, the negative pole 1 was manufactured asfollows.
`[0068]
`Pitch coke was pulverized so that carbon powder (negative pole material) having a meanparticle size of 30
`[0069]
`lum was obtained. 90 parts by weight of the thus-obtained carbon powder was mixed with 10 parts by weight of poly-
`vinylidene fluoride (PVDF) serving as a binding agent. The negative pole mixture was formed into a negative pole
`mixture slurry by dispersing N-methyl-2-pyrrolidone, which was a solvent, so that a negative pole mixture slurry was
`obtained.
`
`[0070] The negative pole mixture slurry was uniformly applied to the two sides of a belt-like copper foil having a
`thickness of 10 um and serving as the negative pole collector 10, followed by being dried and followed by being com-
`pressed and moldedby a roll pressing machine so that the negative pole 1 was manufactured.
`[0071]
`Then, the positive pole 2 was manufactured asfollows.
`[0072]
`Lithium carbonate and cobalt carbonate were mixedat a Li/Co (molar ratio) of 1, followed by being baked in
`air at 900°C for 5 hours so that LiCoO, (positive pole active material) was prepared. 91 parts by weight of a mixture,
`obtained by mixing 99.5 parts by weight of thus-prepared LiCoQ, and 0.5 parts by weightoflithium carbonate, 6 parts
`by weight of graphite serving as a conductive material and 3 parts by weight of polyvinylidene fluoride (PVDF) were
`mixed. The thus-obtained positive pole mixture was dispersed in N-methyl-2-pyrrolidone, wh