JP2009199960A - Lithium-ion battery - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a lithium-ion battery made of an electrolyte or a gel electrolyte including at least ion liquid and lithium salt, a positive electrode active material, and a negative electrode active material, which can improve cycle characteristics and can maintain safety for a long period. <P>SOLUTION: In the lithium-ion battery having the electrolyte or the gel electrolyte including at least the ion liquid and the lithium salt, a positive electrode active material layer, and a negative electrode active material layer, an insulating layer 111 for intercepting ion conductivity is formed on an opposite section between an exposed section 104 of a positive electrode collector where the positive electrode active material layer is not formed and the negative electrode active material layer 101. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a lithium ion battery for realizing a battery having high safety.

  Lithium ion batteries are attracting attention as power sources for mobile phones, notebook computers, large power storages, and automobiles because of their high energy density.

  However, since it has a high energy density, higher safety is required when it is enlarged. For example, in large power storage power supplies and automotive power supplies, as safety measures, structural design of cells and packages, improvement of protection circuit, selection of safe electrode materials, addition of additives with overcharge prevention function, Measures such as strengthening the shutdown function of the separator are taken. Further, as one of means for further improving safety, there is a method of making the electrolyte solution flame-retardant.

  Lithium ion batteries or lithium secondary batteries use aprotic solvents such as cyclic carbonates and chain carbonates as electrolyte solvents, and these carbonates have a high dielectric constant and high ionic conductivity of lithium ions, It has a low flash point and flammability. In general, cyclic carbonates have a high dielectric constant but a high viscosity. On the other hand, chain carbonates have a low dielectric constant but a low viscosity. Therefore, the lithium ion battery mixes and uses these solvents according to a use as an electrolyte solution solvent.

  On the other hand, a technique has been proposed in which an ionic liquid (also referred to as a room temperature molten salt) that exhibits liquid at room temperature and has ionic conductivity is used as an electrolytic solution. Ionic liquids are not volatile and have a high decomposition temperature.

In Patent Documents 1 and 2, an ionic liquid having 1-methyl-3-ethylimidazolium cation is used as an electrolyte solution solvent. Even under a high temperature environment of 120 ° C., the electrolyte solvent does not volatilize and shows good performance and safety. However, the ionic liquid has low reduction stability and is reductively decomposed at a potential of 1 V or less with respect to Li / Li ⁺ . Therefore, when the negative electrode operates at 1 V or less with respect to Li / Li ⁺ , the cycle characteristics of the battery are remarkably deteriorated. Therefore, it is necessary to use a negative electrode active material in which the negative electrode operating potential is 1 V or more with respect to Li / Li ⁺ . I can't get it.

In Patent Document 3, N-methyl-N-ethylpyrrolidinium, N-methyl-N-propylpyridinium, N-methyl-N-ethylpiperidinium, and N-methyl- with improved reduction stability are disclosed. An ionic liquid containing at least one cation selected from the group consisting of N-propylpiperidinium is used. Excellent reduction stability is exhibited even when the operating potential of the negative electrode made of Li or Sn is 1 V or less with respect to Li / Li ⁺ . In particular, the battery characteristics when Li metal is used as the negative electrode and LiCoO ₂ is used as the positive electrode indicate that the battery has high energy density, excellent storage characteristics, and flame retardancy.

  Therefore, in order to reduce the viscosity of the ionic liquid while maintaining the flame retardancy of the electrolytic solution to some extent, a method of mixing carbonates with the ionic liquid has been studied.

  In Patent Document 4, a technique in which cyclic carbonate and / or chain carbonate is added to an ionic liquid in an amount of 0.1 to 30% by volume, in Patent Document 5, the amount as an additive, and in Patent Document 6, 50% by volume or more is mixed. Has been proposed. In these techniques, it has been shown that mixing a cyclic carbonate and / or a chain carbonate having a viscosity lower than that of the ionic liquid reduces the viscosity of the electrolyte solvent, thereby improving the charge / discharge characteristics.

Incidentally, a carbon electrode is generally used as a negative electrode material for a lithium ion battery. However, it is known that on the carbon surface, carbonates undergo reductive decomposition near 1 V with respect to Li / Li ⁺ , so that irreversible capacity increases and charge / discharge efficiency and cycle characteristics decrease.

  In addition, at the time of initial charge, the electrolyte solvent may be reduced and decomposed to form a protective film having high lithium ion permeability, SEI (solid electrolyte interface) at a higher potential than the carbonates used as the electrolyte solvent. Are known. This protective film enables lithium intercalation into the carbon electrode. Further, the protective film has an effect of suppressing reductive decomposition of the electrolyte solvent or ionic liquid. Therefore, the control of the protective film formation is greatly related to the performance of the negative electrode such as charge / discharge efficiency, cycle characteristics, and safety.

  Further, in a lithium battery using a lithium metal or alloy negative electrode, it is necessary to solve the problem of safety due to a decrease in charge / discharge efficiency and generation of dendrite (dendritic crystals).

  In Patent Documents 7 to 9, by separately adding a compound for forming a protective film, the viscosity of the ionic liquid is lowered while maintaining the flame retardancy of the electrolytic solution, the irreversible capacity is reduced, and the cycle characteristics can be improved. It has been shown to be.

  As described above, it can be seen that the electrolytic solution containing the ionic liquid can greatly contribute to the improvement of the safety of the lithium ion battery. However, there was no description regarding the area of the electrode and the area where the active material was applied.

Japanese Patent No. 3075766 Japanese Patent No. 3426869 JP 2003-331918 A Japanese Patent No. 3774315 JP 2001-319688 A JP 2003-288939 A JP 2002-367675 A JP 2002-373704 A JP 2005-026091 A

  Normally, in the manufacture of lithium ion batteries, in consideration of safety, the negative electrode capacity is larger than the positive electrode capacity (A / C balance is larger than 1), and when the electrodes are stacked, the stacking is shifted or the electrodes are wound. In consideration of the winding deviation, the negative electrode active material application area is designed to be larger than the positive electrode active material application area.

  That is, when the A / C balance is less than 1, the Li ion released from the positive electrode active material cannot be received by the negative electrode active material, and metal Li is deposited on the negative electrode. Further, when the positive electrode active material does not face the negative electrode active material but faces the negative electrode current collector, metal Li is deposited on the negative electrode current collector. Further, when the positive electrode active material is not opposed to the negative electrode active material, the capacity of the portion cannot be used, and the volume efficiency is lowered.

  As a result of the study, the inventors have charged / discharged the lithium ion battery using the above-described conventional technology for improving the safety of the battery when the battery is designed in consideration of safety from the viewpoint of A / C balance. It was found that the electrical characteristics were deteriorated due to.

  A lithium ion battery using an electrolytic solution containing an ionic liquid and a lithium salt is repeatedly charged and discharged to expand the volume of the negative electrode active material facing the exposed portion of the positive electrode current collector where the positive electrode active material is not formed. It was confirmed that peeling from the negative electrode current collector occurred and that the positive electrode current collector was deteriorated.

  This is a phenomenon that does not occur in a lithium ion battery using an ordinary aprotic organic solvent as an electrolyte, and is a phenomenon that is unique when an ionic liquid is contained. It was assumed that the cation of the ionic liquid intercalated into the negative electrode to make up for the lack of Li ions because it was not supplied, and at the same time, some reaction occurred in the positive electrode current collector to correct the charge.

  Therefore, as a result of intensive studies, the inventors have found that the negative electrode in which the negative electrode active material layer is formed on the negative electrode current collector does not have a portion facing the exposed portion of the positive electrode current collector in which the positive electrode active material layer is not formed. And having a portion that does not face the exposed portion of the positive electrode current collector, or suppressing ion conductivity at the facing portion between the negative electrode on which the negative electrode active material layer is formed and the exposed portion of the positive electrode current collector, That is, it has been found that the above problem can be solved by blocking the ion conductivity in the exposed portion of the positive electrode current collector in which the positive electrode active material layer is not formed.

  The lithium ion battery of the present invention includes an electrolytic solution containing at least an ionic liquid and a lithium salt, a positive electrode in which a positive electrode active material layer is formed on a positive electrode current collector, and a negative electrode active material layer on a negative electrode current collector. In a lithium ion battery having a laminate in which a formed negative electrode is laminated with a separator interposed therebetween, ionic conductivity is provided between an exposed portion of a positive electrode current collector where a positive electrode active material layer is not formed and a portion facing the negative electrode active material layer. An insulating layer is provided to block the above.

  In the lithium ion battery of the present invention, an insulating layer that blocks the ionic conductivity may be formed on the exposed portion of the positive electrode current collector.

  In the lithium ion battery of the present invention, an insulating layer that blocks the ionic conductivity may be formed on the negative electrode active material.

  In the lithium ion battery of the present invention, an insulating layer that blocks the ionic conductivity may be formed on the separator.

  In the lithium ion battery of the present invention, the insulating layer that blocks ionic conductivity may contain an inorganic compound.

  In the lithium ion battery of the present invention, the electrolytic solution may contain a polymer gel electrolyte.

  According to the present invention, since there is no ion-conductive negative electrode active material layer facing the exposed portion of the positive electrode current collector on which the positive electrode active material layer is not formed, intercalation of the ionic liquid into the negative electrode active material is suppressed. At the same time, by suppressing any reaction of the positive electrode current collector, the initial charge / discharge efficiency and the charge / discharge efficiency in the cycle test are improved.

  In addition, since the intercalation of the ionic liquid into the negative electrode active material is suppressed, the expansion of the negative electrode can be suppressed and the volume change can be suppressed, so that the distortion of the electrode accompanying the charge / discharge cycle can be reduced and the cycle characteristics improved. And resistance rise and cell swelling can be suppressed.

  In addition, since any reaction at the positive electrode current collector is suppressed, reaction product can be suppressed, and cycle characteristics can be improved and resistance increase and cell swelling can be suppressed.

  Moreover, although the ionic liquid is used for safety improvement, it can be used for a longer period than before because side reactions on the positive electrode current collector are suppressed.

  The configuration of the present invention will be described below.

  In the present invention, an electrolyte containing at least an ionic liquid and a lithium salt, a positive electrode using a lithium-containing composite oxide or the like as a positive electrode active material, and a negative electrode using a carbon material or the like as a negative electrode active material are stacked via a separator. In a lithium ion battery having a laminated body, ion conduction and electric conduction are suppressed at the facing portion of the negative electrode active material layer and the exposed portion of the positive electrode current collector, that is, ionic conduction and electricity at the exposed portion of the positive electrode current collector. It has been found that cycle characteristics can be improved by blocking conduction by some method.

  In the present invention, any method for blocking ionic conduction and electrical conduction may be used as long as it does not have ionic conduction and forms an insulating layer. Examples thereof include an insulating tape, an insulating resin layer, and an inorganic compound.

  Examples of the insulating tape and resin include polyethylene, polypropylene, polystyrene, nylon, silicone resin, Teflon (registered trademark), Daiflon (registered trademark), polyvinylidene fluoride, acrylic resin, ABS resin, polycarbonate, polyimide, and polyamideimide. , Polyphenylene sulfide, epoxy resin, rubber resin and the like, but are not limited thereto.

  Examples of inorganic compounds include, but are not limited to, glass fiber and alumina. Further, these inorganic compounds and the above resin may be combined.

  As a method of applying an insulator, for example, a method of applying a tape made of a material such as the resin on an electrode, a current collector, or a separator before applying an electrode active material, or applying an electrode active material After that, there is a method of attaching the tape.

  In addition, a method of applying the resin or the inorganic compound on the current collector before applying the electrode active material, or a method of applying the resin or the inorganic compound on the current collector after applying the electrode active material may be mentioned. It is done.

  Further, by providing the insulating layer and then pressing it, it is possible to improve the adhesion to the current collector, the electrode active material, the separator or the like, or to control the thickness of the insulating layer.

  The ionic liquid used in the present invention is preferably composed of at least a quaternary ammonium cation and an anion.

  Examples of the quaternary ammonium cation species of the ionic liquid used in the present invention include N-methyl-N-propylpyrrolidinium, N-methyl-N-butylpyrrolidinium, N-methyl-N-propylpiperidinium, N -Methyl-N-butylpiperidium, tetraethylammonium, triethylmethylammonium, N, N, N-trimethyl-N-propylammonium, 1-butyl-3-methylimidazolium, 1-ethyl-3-methylimidazolium, 1-hexyl-3-methylimidazolium, 1-octyl-3-methylimidazolium, 1-ethyl-2,3-dimethylimidazolium, 1-butyl-2,3-dimethylimidazolium, 1-hexyl-2, 3-dimethylimidazolium, 1-ethylpyridinium, 1-butylpyridinium, 1 Hexyl pyridinium, and the like, but not limited thereto.

Examples of the quaternary ammonium anion species used in the present invention include PF ₆ ⁻ , PF ₃ (C ₂ F ₅ ) ₃ ⁻ , PF ₃ (CF ₃ ) ₃ ⁻ , BF ₄ ⁻ , and BF ₂ (CF ₃ ) ₂ ⁻ , BF ₃ (CF ₃ ) ⁻ , AlCl ₄ ⁻ , N (CF ₃ SO ₂ ) ₂ ⁻ , N (C ₂ F ₅ SO ₂ ) ₂ ⁻ , CF ₃ SO ₃ ⁻ anion, etc. However, it is not limited to these.

  Examples of the polymer component contained in the gel electrolyte in the present invention include a monomer having two or more polymerizable groups capable of thermal polymerization per molecule, an oligomer, and a copolymer oligomer. As this gelling component, ethylene glycol diacrylate, diethylene glycol diacrylate, triethylene glycol diacrylate, tetraethylene glycol diacrylate, propylene glycol diacrylate, dipropylene glycol diacrylate, tripropylene glycol forming an acrylic polymer Bifunctional acrylates such as diacrylate, 1,3-butanediol diacrylate, 1,4-butanediol diacrylate, 1,6-hexanediol diacrylate, and 3 such as trimethylolpropane triacrylate and pentaerythritol triacrylate Functional acrylates and tetrafunctional acrylics such as ditrimethylolpropane tetraacrylate and pentaerythritol tetraacrylate Rate, and, like the methacrylate monomers. In addition to these, monomers such as urethane acrylate and urethane methacrylate, copolymer oligomers thereof, and copolymer oligomers with acrylonitrile are exemplified, but not limited thereto.

  In addition, polymers that can be dissolved in a plasticizer and gelled, such as polyvinylidene fluoride, polyethylene oxide, and polyacrylonitrile can also be used.

  The polymer component is not limited to the above-described monomer, oligomer, or polymer, and any polymer component that can be gelled can be used. Further, the gelation is not limited to one type of monomer, oligomer or polymer, and can be used by mixing two or more types of gelling components as required.

  In addition, benzoins, peroxides and the like can be used as thermal polymerization initiators as necessary, but are not limited thereto.

  In the present invention, an aprotic solvent can be contained as required. For example, cyclic carbonates such as propylene carbonate (PC), ethylene carbonate (EC), butylene carbonate (BC), vinylene carbonate (VC), dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), Chain carbonates such as dipropyl carbonate (DPC), aliphatic carboxylic acid esters such as methyl formate, methyl acetate and ethyl propionate, γ-lactones such as γ-butyrolactone, 1,2-ethoxyethane (DEE) , Chain ethers such as ethoxymethoxyethane (EME), cyclic ethers such as tetrahydrofuran and 2-methyltetrahydrofuran, dimethyl sulfoxide, 1,3-dioxolane, formamide, acetamide, dimethylformamide, Dioxolane, acetonitrile, propylnitrile, nitromethane, ethyl monoglyme, phosphoric acid triester, trimethoxymethane, dioxolane derivative, sulfolane, methylsulfolane, 1,3-dimethyl-2-imidazolidinone, 3-methyl-2-oxazolidinone, There are propylene carbonate derivatives, tetrahydrofuran derivatives, ethyl ether, anisole, N-methylpyrrolidone, fluorinated carboxylic acid esters, etc., and these aprotic organic solvents can be used alone or in combination of two or more, but limited to these Is not to be done.

  Moreover, the compound which has protective film formation ability can also be contained in the electrode active material surface as needed. For example, 1,3-propane sultone and vinylene carbonate can be used, but are not limited thereto.

Electrolyte contained in the non-aqueous electrolyte or a gel electrolyte in the present _{invention, LiPF 6, LiBF 4, LiAsF} 6, LiSbF 6, LiClO 4, LiAlCl 4, and _{LiN (C n F 2n + 1} SO 2) (C m F _{2m + 1} SO ₂ ) (n and m are natural numbers), LiCF ₃ SO _{3 and} other electrolytes generally used for lithium ion batteries can be used.

  In the present invention, as the negative electrode active material, for example, one or two or more substances selected from the group consisting of a lithium alloy and a material capable of inserting and extracting lithium can be used. As a material for inserting and extracting lithium ions, a carbon material or an oxide can be used.

  Examples of the carbon material include graphite that occludes lithium, amorphous carbon, diamond-like carbon, and carbon nanotube. Of these, graphite material or amorphous carbon is particularly preferable. In particular, the graphite material has high electron conductivity, excellent adhesion to a current collector made of a metal such as copper, and voltage flatness, and is formed at a high processing temperature, so it contains few impurities and has negative electrode performance. It is advantageous for improvement and is preferable.

  Further, as the oxide, silicon oxide, tin oxide, indium oxide, zinc oxide, lithium oxide, phosphoric acid, boric acid, or a composite thereof may be used, and particularly includes silicon oxide. preferable. The structure is preferably amorphous. This is because silicon oxide is stable and does not cause a reaction with other compounds, and the amorphous structure does not lead to deterioration due to nonuniformity such as crystal grain boundaries and defects. As a film formation method, a vapor deposition method, a CVD method, a sputtering method, or the like can be used.

  The lithium alloy is composed of lithium and a metal capable of forming an alloy with lithium. For example, it is composed of a binary or ternary alloy of a metal such as Al, Si, Pb, Sn, In, Bi, Ag, Ba, Ca, Hg, Pd, Pt, Te, Zn, La, and lithium. . As the lithium metal or lithium alloy, an amorphous one is particularly preferable. This is because the amorphous structure hardly causes deterioration due to non-uniformity such as crystal grain boundaries and defects.

  The lithium alloy is formed by an appropriate method such as a melt cooling method, a liquid quenching method, an atomizing method, a vacuum deposition method, a sputtering method, a plasma CVD method, a photo CVD method, a thermal CVD method, a sol-gel method, or the like. Can do.

In the battery of the present invention, a lithium-containing composite oxide can be used as the positive electrode active material. Examples of the lithium-containing composite oxide include lithium-containing composite oxides such as LiCoO ₂ , LiNiO ₂ , LiMn ₂ O ₄ , and LiFePO ₄ . In addition, the transition metal portion of these lithium-containing composite oxides may be replaced with another element.

Alternatively, a lithium-containing composite oxide having a plateau at 4.5 V or more at the metal lithium counter electrode potential can be used. Examples of the lithium-containing composite oxide include spinel-type lithium manganese composite oxide, olivine-type lithium-containing composite oxide, and reverse spinel-type lithium-containing composite oxide. The lithium-containing composite oxide is, for example, Li _a (M _x Mn _2−x ) O ₄ (where 0 <x <2 and 0 <a <1.2. M is Ni, And at least one selected from the group consisting of Co, Fe, Cr, and Cu.

  The positive electrode is prepared by dispersing and kneading the positive electrode active material in a solvent such as N-methyl-2-pyrrolidone (NMP) together with a conductive material such as carbon black and a binder such as polyvinylidene fluoride (PVDF). Can be obtained by coating on a positive electrode current collector such as an aluminum foil.

  The lithium ion battery of the present invention is a flexible film comprising a battery can or a laminate of a synthetic resin and a metal foil after a negative electrode and a positive electrode are laminated via a porous separator, or a laminate is wound. Etc., and impregnated with an electrolytic solution containing an ionic liquid. And it is obtained by charging a battery after sealing or sealing an exterior body. In addition, as a porous separator, polyolefin, such as a polypropylene and polyethylene, porous films, such as a fluororesin, are used.

  Further, in the secondary battery using the gel electrolyte of the present invention, 3.8% by mass and 1.0% by mass, for example, of triethylene glycol diacrylate and trimethylolpropane triacrylate, respectively, are added to the electrolytic solution containing an ionic liquid or the like. In addition, after mixing well, as a polymerization initiator, impregnated with 0.5% by mass of t-butyl peroxypivalate and impregnating and sealing the exterior body or heating at 80 ° C. for 2 hours It can produce by doing.

  The shape of the lithium ion battery or lithium polymer battery according to the present embodiment is not particularly limited, and examples thereof include a cylindrical shape, a square shape, a laminate outer shape, and a coin shape. In the examples described later, an example of a stacked lithium ion battery is shown, but examples of a positive electrode and a negative electrode used in a wound lithium ion battery are shown in FIGS. 5 and 6 are schematic views showing the embodiment of the lithium ion battery of the present invention, and show the positional relationship when the positive electrode and the negative electrode are laminated. FIG. 5 shows a structure in which an insulating layer 111 is formed on a portion of the exposed portion of the positive electrode current collector facing the negative electrode active material layer 101, and FIG. 6 shows how the negative electrode active material layer 101 is exposed to the exposed portion 104 of the positive electrode current collector. The insulating layer 112 is formed in the facing portion. The positive electrode and the negative electrode are laminated so that the insulating layers 111 and 112 are disposed in a portion facing the exposed portion 104 of the positive electrode current collector and the negative electrode active material layer 101 via a separator, and are wound and wound type lithium ion battery Is obtained.

  The invention will now be described by way of example with reference to the drawings. 1A and 1B are diagrams for explaining the configuration of a lithium ion battery according to the present invention. FIG. 1A is a plan view and FIG. 1B is an exploded side view. 1 shows the repeating unit structure of the laminate, and in FIG. 1A, the positional relationship between the positive electrode and the negative electrode is shown and the separator is omitted.

Example 1
Example 1 will be described with reference to FIG.

  First, preparation of the negative electrode will be described. 90% by mass of graphite and 10% by mass of polyvinylidene fluoride as a binder were mixed, and N-methylpyrrolidone was added and further mixed to prepare a negative electrode slurry. This was applied to both sides of a 10 μm-thick Cu foil serving as a negative electrode current collector so that the thickness after the roll press treatment was 120 μm and the electrode density was 1.50 g / cc to form a negative electrode active material layer 101. In addition, the exposed part 102 of the negative electrode collector in which the negative electrode active material was not apply | coated was provided.

Next, preparation of the positive electrode will be described. A mixture of 85% by mass of LiMn ₂ O ₄ , 7% by mass of acetylene black as a conductive auxiliary and 8% by mass of polyvinylidene fluoride as a binder is added to N-methylpyrrolidone and further mixed to prepare a positive electrode slurry. did. This was applied to both surfaces of a 20 μm-thick Al foil serving as a positive electrode current collector by a doctor blade method so that the thickness after roll press treatment was 160 μm to form a positive electrode active material layer 103. In addition, the exposed part 104 of the positive electrode collector which the positive electrode active material layer was not apply | coated was provided. A polyimide tape having a thickness of 10 μm was wound around the exposed portion 104 of the positive electrode current collector facing the negative electrode active material layer 101 to form an insulating layer 111.

  The production of the battery element will be described. The positive electrode and separator 105 made of a polyethylene microporous film having a film thickness of 25 μm and a porosity of 55% and the negative electrode are alternately arranged with four positive electrodes, five negative electrodes, and eight separators so that the outermost layer is a negative electrode. The aluminum tab was laminated on the positive electrode and the nickel tab was fused on the negative electrode by ultrasonic welding.

  This laminate was accommodated in an embossed laminate outer package, the positive electrode conductive tab and the negative electrode conductive tab were pulled out, and the laminate outer package was heat-sealed leaving the liquid injection part.

The electrolyte is 15% by mass of ethylene carbonate (EC) and 29% by mass of diethyl carbonate (DEC), and 1-methyl-1-propylpiperidinium bis (trifluoromethanesulfonyl) imide (MPPp-TFSI) is used as the ionic liquid. It was prepared by mixing 3% by mass of 1,3-propane sultone with respect to an electrolytic solution comprising 44% by mass and 12% by mass of LiPF ₆ as a lithium salt.

  Next, the electrolyte solution was injected from the laminated liquid injection portion that was sealed leaving the liquid injection portion, vacuum impregnation was performed, and the liquid injection portion was thermally fused to obtain a lithium ion battery.

  The obtained battery was charged to a battery voltage of 4.2 V (upper limit voltage of 4.2 V, current of 0.1 C, time of 11.5 hours, temperature of 20 ° C.), and then discharged to battery voltage of 3.0 V at 0.2 C. Table 1 shows the ratio of the obtained initial capacity to the design capacity.

  The cycle test of the obtained battery was performed by charging: upper limit voltage 4.2V, current 0.2C, time 6.5 hours, discharge: lower limit voltage 3.0V, current 0.2C, all at 45 ° C. Table 1 shows the ratio of the discharge capacity at the 500th cycle to the discharge capacity at the first cycle.

  When the cycle test of the obtained battery was performed, the ratio of the increase in the thickness of the battery after the cycle relative to the thickness of the battery before the cycle was shown in Table 1 as the cell swelling.

  In the combustion test, the battery after the cycle test was placed 10 cm above the tip of the flame of the gas burner, and the state was judged as follows from the state in which the electrolyte solvent volatilized and burned. The electrolyte was not ignited: ◎, extinguished after 2 to 3 seconds after ignition: ○, extinguished within 10 seconds after ignition: Δ, continued to burn without extinguishing: x.

(Example 2)
2A and 2B are diagrams for explaining the configuration of a lithium ion battery according to a second embodiment of the present invention. FIG. 2A is a plan view and FIG. 2B is a side exploded view. 2 shows the repeating unit structure of the laminate, and in FIG. 2A, the positional relationship between the positive electrode and the negative electrode is shown, and the separator is omitted. In Example 2, the polyimide tape provided in the exposed part of the positive electrode current collector in Example 1 was bonded to the negative electrode active material layer 101 facing the exposed part 104 of the positive electrode current collector to form an insulating layer 112. A lithium ion battery was produced in the same manner as in Example 1, and a cycle test and a combustion test were conducted.

(Example 3)
3A and 3B are diagrams for explaining the configuration of a lithium ion battery according to a third embodiment of the present invention. FIG. 3A is a plan view and FIG. 3B is a side exploded view. FIG. 3 shows the repeating unit structure of the laminate. In Example 3, the polyimide tape provided in the exposed part of the positive electrode current collector in Example 1 was applied to the separator 105 facing the exposed part 104 of the positive electrode current collector, and the insulating layer 113 was used. A lithium ion battery was prepared in the same manner as in Example 1, and a cycle test and a combustion test were performed.

Example 4
The fourth embodiment will be described with reference to FIG. As shown in FIG. 1, an epoxy resin is applied to a thickness of about 10 μm on a portion of the positive electrode current collector on which the positive electrode active material has been applied, which will be the exposed portion 104 of the positive electrode current collector, and dried at 120 ° C. A lithium ion battery was prepared in the same manner as in Example 1 except that the insulating layer 111 was used and no polyimide tape was used, and a cycle test and a combustion test were performed.

(Example 5)
Example 5 is the same as Example 4 except that the epoxy resin of Example 4 mixed with 5% by mass of alumina particles having a particle size of 5 μm was applied to a thickness of about 10 μm and pressed by a roll press. A lithium ion battery was prepared in the same manner as described above, and a cycle test and a combustion test were performed.

(Example 6)
In Example 6, the electrolyte solution was 1-methyl-1-propylpiperidinium-bis (trifluoromethanesulfonyl) imide (MPPp-TFSI) 80% by mass and the lithium salt was LiTFSI 20% by mass. On the other hand, a lithium ion battery was produced in the same manner as in Example 1 except that a material produced by mixing 3% by mass of 1,3-propane sultone was used, and a cycle test and a combustion test were performed.

(Comparative Example 1)
4A and 4B are diagrams for explaining the configuration of a conventional lithium ion battery. FIG. 4A is a plan view and FIG. 4B is a side exploded view. In Comparative Example 1, a lithium ion battery was produced in the same manner as in Example 1 except that no polyimide tape was applied as shown in FIG. 4, and a cycle test and a combustion test were performed.

(Comparative Example 2)
In Comparative Example 2, a lithium ion battery was produced in the same manner as in Example 6 except that no polyimide tape was applied, and a cycle test and a combustion test were performed. The results of Examples 1 to 6 and Comparative Examples 1 and 2 are shown in Table 1.

  As shown in Table 1, in Examples 1 to 5 to which the insulating layer was applied, the capacity retention rate and the cell swelling rate were improved with respect to Comparative Example 1. Moreover, what applied directly to the positive electrode electrical power collector had the improvement effect more. Even if an insulating layer is applied to the active material surfaces and separators of Examples 2 and 3, the electrolyte solution penetrates through the pores of the negative electrode active material, so that the ionic liquid is completely intercalated and the surface of the positive electrode current collector is exposed. Therefore, it is considered that a side reaction has occurred slightly. Further, in Example 4, the surface of the positive electrode current collector could be covered almost completely, and in Example 5, further improvement was achieved by suppressing the peeling of the epoxy layer due to the anchor effect of alumina. In addition, Examples 4 and 5 that were able to suppress side reactions with respect to combustibility were able to maintain high flame retardancy even after cycling.

  In Example 6, the capacity retention rate and the cell swelling rate were improved as compared with Comparative Example 2, and this was the effect that side reactions could be suppressed.

(Example 7)
Example 7 is a lithium ion battery (also referred to as a lithium polymer battery) using a gel electrolyte, and the pregel solution is 15% by mass of ethylene carbonate (EC) and 29% by mass of diethyl carbonate (DEC). Methyl-1-propylpiperidinium bis (trifluoromethanesulfonyl) imide (MPP _p -TFSI) is 44% by mass and 1,3-propane sultone is added to an electrolyte solution comprising 12% by mass of LiPF ₆ as a lithium salt. After adding 3% by mass and further adding 3.8% by mass and 1.0% by mass of triethylene glycol diacrylate and trimethylolpropane triacrylate as gelling agents, and mixing well, It was prepared by mixing 0.5% by mass of t-butyl peroxypivalate. .

  Next, a lithium ion battery was prepared in the same manner as in Example 1 except that the pregel solution was injected from the injection part, vacuum impregnation was performed, and a lithium ion battery was obtained by polymerization at 80 ° C. for 2 hours. A test and a combustion test were conducted.

(Comparative Example 3)
In Comparative Example 3, a lithium ion battery was produced in the same manner as in Example 7 except that no polyimide tape was applied, and a cycle test and a combustion test were performed. The results of Example 7 and Comparative Example 3 are shown in Table 2.

  As shown in Table 2, also in the case of Example 7 in which the electrolyte was a gel electrolyte, both the capacity retention ratio and the cell swelling were improved with respect to Comparative Example 3. In addition, the cell expansion rate was improved as compared with Example 1, because the cell expansion was suppressed due to the high binding properties of the electrode active material and the separator due to the polymer of the gel electrolyte. Moreover, since the side reaction could be suppressed, high flame retardancy could be maintained even after the cycle.

  As described above, in a lithium ion battery including an electrolytic solution or gel electrolyte containing at least an ionic liquid and a lithium salt, and a positive electrode active material and a negative electrode active material, a negative electrode including the negative electrode active material and a positive electrode current collector in which the positive electrode active material is not formed In the lithium ion battery in which a layer that is insulative and does not have ion permeability is formed on the opposite part of the body, the cycle capacity maintenance rate is good and the flame retardancy can be maintained even in the battery after the cycle test, more A lithium ion battery having high safety was obtained.

It is a figure explaining the structure of the lithium ion battery of this invention, Fig.1 (a) is a top view, FIG.1 (b) is a side exploded view. It is a figure explaining the structure of Example 2 of the lithium ion battery of this invention, Fig.2 (a) is a top view, FIG.2 (b) is a side exploded view. It is a figure explaining the structure of Example 3 of the lithium ion battery of this invention, Fig.3 (a) is a top view, FIG.3 (b) is a side exploded view. It is a figure explaining the structure of the conventional lithium ion battery, Fig.4 (a) is a top view, FIG.4 (b) is a side exploded view. The schematic diagram which shows embodiment of the lithium ion battery of this invention. The schematic diagram which shows embodiment of the lithium ion battery of this invention.

Explanation of symbols

101 Negative electrode active material layer 102 Exposed portion (of negative electrode current collector) 103 Positive electrode active material layer 104 Exposed portion of (positive electrode current collector) 105 Separator 106 Positive electrode tab 107 Negative electrode tab 111 Insulating layer 112 Insulating layer 113 Insulating layer

Claims (6)

  The separator includes an electrolytic solution containing at least an ionic liquid and a lithium salt, a positive electrode having a positive electrode active material layer formed on a positive electrode current collector, and a negative electrode having a negative electrode active material layer formed on a negative electrode current collector. In the lithium ion battery having a stacked body, an insulating layer that blocks ionic conductivity is provided at the facing portion between the exposed portion of the positive electrode current collector where the positive electrode active material layer is not formed and the negative electrode active material layer. The lithium ion battery characterized by the above-mentioned.   The lithium ion battery according to claim 1, wherein an insulating layer that blocks the ion conductivity is formed on an exposed portion of the positive electrode current collector.   The lithium ion battery according to claim 1, wherein an insulating layer that blocks the ion conductivity is formed on the negative electrode active material.   The lithium ion battery according to claim 1, wherein an insulating layer that blocks the ion conductivity is formed on the separator.   The lithium ion battery according to any one of claims 1 to 4, wherein the insulating layer that blocks ionic conductivity contains an inorganic compound.   The lithium ion battery according to claim 1, wherein the electrolytic solution contains a polymer gel electrolyte.

Images