JP5201166B2 - Secondary battery - Google Patents

Description

  The present invention relates to a secondary battery.

  Non-aqueous electrolyte lithium ion or lithium secondary batteries using carbon materials, oxides, lithium alloys or lithium metals for the negative electrode are attracting attention as power sources for mobile phones, laptop computers, etc. because they can achieve high energy density .

  In this secondary battery, it is known that a film called a surface film, a protective film, SEI, a film (hereinafter referred to as a surface film) is formed on the surface of the negative electrode. Since this surface film has a great influence on charge / discharge efficiency, cycle life and safety, it is known that control of the surface film is indispensable for improving the performance of the negative electrode.

  For carbon materials and oxide materials, it is necessary to reduce the irreversible capacity, and for lithium metal and alloy negative electrodes, it is necessary to solve the problem of safety due to the decrease in charge / discharge efficiency and the generation of dendrites (dendrites).

  Various techniques have been proposed as a technique for solving these problems. For example, it has been proposed to suppress the formation of dendrite by providing a film layer made of lithium fluoride or the like using a chemical reaction on the surface of lithium metal or lithium alloy.

  Patent Document 1 discloses a technique in which a lithium negative electrode is exposed to an electrolytic solution containing hydrofluoric acid, and the negative electrode is reacted with hydrofluoric acid to cover the surface with a lithium fluoride film.

Hydrofluoric acid is produced by the reaction of LiPF ₆ and a small amount of water. On the other hand, a surface film of lithium hydroxide or lithium oxide is formed on the surface of the lithium negative electrode by natural oxidation in air. When these react, a surface film of lithium fluoride is formed on the negative electrode surface.

  However, this lithium fluoride film is formed by utilizing the reaction between the electrode interface and the liquid, and side reaction components are easily mixed into the surface film, making it difficult to obtain a uniform film. Also, there may be cases where the surface film of lithium hydroxide or lithium oxide is not uniformly formed or there is a part where lithium is exposed. In these cases, a uniform thin film cannot be formed. In addition, there is a safety problem due to the reaction of lithium with water or hydrogen fluoride. Moreover, when reaction is inadequate, unnecessary compound components other than a fluoride remain, and bad influences, such as causing the fall of ion conductivity, are considered.

  Furthermore, in the method of forming a fluoride layer using such a chemical reaction at the interface, the selection range of the available fluoride and electrolyte is limited, and it is difficult to form a stable surface film with a high yield. there were.

  In Patent Document 2, a mixed gas of argon and hydrogen fluoride is reacted with an aluminum-lithium alloy to obtain a lithium fluoride surface film on the negative electrode surface.

  However, when a surface film is present on the lithium metal surface in advance, particularly when a plurality of types of compounds are present, the reaction tends to be non-uniform, and it is difficult to form a lithium fluoride film uniformly. For this reason, it becomes difficult to obtain a lithium secondary battery having sufficient cycle characteristics.

  Patent Document 3 discloses a technique for forming a surface film structure mainly composed of a substance having a rock salt type crystal structure on the surface of a lithium sheet having a uniform crystal structure, that is, a (100) crystal plane preferentially oriented. It is disclosed. By carrying out like this, it is said that uniform precipitation dissolution reaction, ie, charge / discharge of a battery, can be performed, dendrite precipitation of lithium metal can be suppressed, and the cycle life of the battery can be improved.

  It is stated that the substance used for the surface film preferably has a halide of lithium, and it is preferable to use a solid solution of LiF with at least one selected from LiCl, LiBr, and LiI.

  Specifically, in order to form a solid solution film of at least one of LiCl, LiBr, and LiI and LiF, a lithium sheet with a (100) crystal plane preferentially oriented formed by pressing (rolling) is used. A negative electrode for a non-aqueous electrolyte battery is prepared by immersing in an electrolyte solution containing at least one of chlorine molecules or chlorine ions, bromine molecules or bromine ions, iodine molecules or iodine ions, and fluorine molecules or fluorine ions. ing.

  In the case of this technology, a rolled lithium metal sheet is used, and since the lithium sheet is easily exposed to the atmosphere, a film derived from moisture and the like is easily formed on the surface, and the presence of active sites becomes uneven, which is the purpose. It became difficult to produce a stable surface film, and the effect of suppressing dentlite was not always sufficiently obtained.

  In addition, when a carbon material such as graphite or amorphous carbon capable of occluding and releasing lithium ions is used as a negative electrode, a technique for improving capacity and charge / discharge efficiency has been reported.

  In patent document 4, the negative electrode which coat | covered the carbon material with aluminum is proposed. Thereby, reductive decomposition on the carbon surface of solvent molecules solvated with lithium ions is suppressed, and deterioration of cycle life is suppressed. However, since aluminum reacts with a small amount of water, there is a problem that the capacity rapidly decreases when charging and discharging are repeated.

  Patent Document 5 proposes a negative electrode in which the surface of a carbon material is covered with a thin film of a lithium ion conductive solid electrolyte. Thereby, it is said that the decomposition | disassembly of the solvent which arises when using a carbon material can be suppressed, and especially the lithium ion secondary battery which can use a propylene carbonate can be provided.

  However, cracks generated in the solid electrolyte due to changes in stress during insertion and desorption of lithium ions lead to deterioration of characteristics. In addition, due to non-uniformity such as crystal defects in the solid electrolyte, a uniform reaction cannot be obtained on the negative electrode surface, leading to deterioration of cycle life.

  Further, in Patent Document 6, the negative electrode is made of a material containing graphite, and cyclic carbonate and chain carbonate are the main components as the electrolytic solution, and 0.1 to 4 wt% of 1,3-propane is contained in the electrolytic solution. Secondary batteries containing sultone and / or 1,4-butane sultone are disclosed.

  Here, 1,3-propane sultone or 1,4-butane sultone contributes to the formation of a passive film on the surface of the carbon material, and the active and highly crystallized carbon material such as natural graphite or artificial graphite is a passive film. It is considered that the coating has an effect of suppressing the decomposition of the electrolyte without impairing the normal reaction of the battery.

  Naoi et al. Reported on the effect of a complex of a lanthanoid-based transition metal such as europium and an imide anion on a lithium metal negative electrode at the conference presentations of Non-Patent Document 1 and Non-Patent Document 2.

Here, Eu (CF ₃ SO ₃ ) ₃ is further added to an electrolyte obtained by dissolving LiN (C ₂ F ₅ SO ₂ ) ₂ as a lithium salt in a mixed solvent of propylene carbonate or ethylene carbonate and 1,2-dimethoxyethane. A surface film made of Eu [N (C ₂ F ₅ SO ₂ ) ₂ ] ₃ complex is formed on Li metal added as an additive and immersed in the electrolytic solution.

Japanese Patent Application Laid-Open No. 07-302617 Japanese Patent Laid-Open No. 08-250108 Japanese Patent Laid-Open No. 11-288706 JP 05-234583 A JP 05-275077 A JP 2000-003724 A

Naoi et al., 2000 Electrochemical Fall Meeting (September 2000, Chiba Institute of Technology, lecture number: 2A24) Naoi et al., 41st Battery Discussion (November 2000, Nagoya International Conference Hall, Lecture Number: 1E03)

  However, the above-described prior art has the following common problems.

  The surface film formed on the surface of the negative electrode is deeply related to charge / discharge efficiency, cycle life, and safety depending on its properties, but there is still no method for controlling the film for a long time.

  For example, when a surface film made of lithium halide or glassy oxide is formed on a layer made of lithium or an alloy thereof, although a certain degree of dentite suppression effect can be obtained during initial use, The surface film is deteriorated and the function as a protective film is lowered.

  This is because a layer made of lithium or an alloy thereof changes in volume by occlusion / release of lithium, while a coating made of lithium halide or the like located on the upper layer hardly changes in volume. This is thought to be due to the generation of internal stress at the interface.

  Due to the occurrence of such internal stress, it is considered that a part of the surface film made of lithium halide or the like is particularly damaged, and the function of suppressing the formation of dendrite is lowered.

  For carbon materials such as graphite, charge due to decomposition of solvent molecules and anions appears as an irreversible capacity component, leading to a decrease in initial charge / discharge efficiency. Further, the composition, crystal state, stability, etc. of the film produced at this time have a great influence on the subsequent efficiency and cycle life.

  In addition, the method of forming an organic surface film on the lithium metal surface studied by Naoi et al. Has achieved a certain degree of effect in improving the cycle life as compared with the above-described conventional technique, but is still not sufficient.

  In this way, research has been progressing to improve the charge / discharge efficiency and cycle life by forming a film on the negative electrode for secondary batteries.However, sufficient characteristics have not been obtained yet, and how stable it is. The biggest challenge is to form a film that leads to sufficient charge and discharge efficiency.

As a result of extensive research, the present inventors have used a non-proton material in which an alloy layer made of Si and Li is formed on graphite (graphite / Si: Li) as a negative electrode active material constituting the negative electrode. In the case where a secondary battery is prepared using an electrolytic solution containing at least an imide anion, a transition metal ion, and a sulfone compound in the protic solvent, or in an electrolytic solution obtained by dissolving a lithium salt as an electrolyte salt in an aprotic solvent. When a secondary battery was prepared using an electrolyte solution containing a transition metal complex consisting of an imide anion and a transition metal ion and a sulfone compound, it was found that the charge / discharge efficiency was excellent and the cycle characteristics were good, leading to the present invention. It was.

That is, the present invention is a secondary battery having at least a positive electrode and a negative electrode, and the negative electrode active material constituting the negative electrode is formed by forming a graphite / Si: Li (alloy layer of Si and Li on graphite). a thing), and electrolyte, an aprotic solvent, at least imide anion, includes a transition metal ion and a sulfonic compound, said imide anion ^{_{is, - n (C n F 2n}} + 1 SO 2) (C _m F _{2m + 1} SO ₂ ) (n and m are natural numbers) and contained in the electrolyte as an imide anion or a metal complex thereof in an amount of 0.005 to 10 wt%, and the transition metal is europium, neodymium, erbium, The compound selected from the group consisting of holmium and having the sulfonyl group is selected from the group consisting of 1,3-propane sultone, 1,4-butane sultone, sulfolane, alkanesulfonic acid anhydride, γ-sulphone. At least one selected from the group consisting of tons compounds and sulfolene compound, a secondary battery, characterized in that contained 0.01-10 wt% in the electrolyte.

  According to the present invention, at least an imide anion in an electrolyte solution for a secondary battery containing a compound having an imide anion, a transition metal ion and a sulfonyl group in an aprotic solvent, or a solution in which a lithium salt is dissolved in an aprotic solvent. Provided is a lithium secondary battery having excellent characteristics such as energy density and electromotive force, and having excellent cycle life and safety, using an electrolytic solution containing a metal complex composed of a transition metal ion and a sulfone compound.

It is a schematic block diagram of the secondary battery which concerns on this invention.

  In the case of a system in which a transition metal ion and an imide anion are present, a metal complex of the imide anion and the transition metal ion is formed on the negative electrode surface by charge and discharge (Non-Patent Documents 1 and 2).

  Moreover, when the metal complex of a transition metal ion and an imide anion exists, the said metal complex is adsorb | sucked by the negative electrode surface irrespective of charging / discharging.

  The presence of the two compounds of the metal complex of the imide anion and the transition metal ion and the compound having a sulfonyl group on the surface of the negative electrode brings about the following effects.

  On the negative electrode surface, there are dangling bonds that cause a reaction with solvent molecules and non-reactive sites. The metal complex formed by the imide salt to be added or the metal complex formed by the imide salt and the transition metal ion forms a stabilized film by adsorbing to the non-reactive site, and conducts lithium ions. Moreover, the compound which has a sulfonyl group contributes to the passive film formation on the negative electrode surface, and suppresses decomposition | disassembly of a solvent molecule as a result.

Specific examples of the imide ^{_{anion, - N (C n F 2n}} + 1 SO 2) (C m F 2m + 1 SO 2) (n, m is a natural number) and the like.

  In the present invention, the transition metal is preferably a lanthanoid metal, particularly europium (Eu), neodymium (Nd), erbium (Er), and holmium (Ho).

  The imide anion or its metal complex is preferably contained in the electrolytic solution in an amount of 0.01 to 10 wt%. If it is less than 0.01 wt%, a sufficient effect may not be obtained for forming a film on the negative electrode surface, and if it exceeds 10 wt%, not only does not dissolve, but the viscosity of the electrolyte may increase, which is not preferable. In this invention, More preferably, it is the range of 0.05-5 wt%.

  Specific examples of the compound having a sulfonyl group include sulfolane (Japanese Patent Laid-Open No. 60-154478), 1,3-propane sultone and 1,4-butane sultone (Japanese Patent Laid-Open No. 62-1000094). JP-A-63-102173, JP-A-11-339850, JP-A-2000-3724), alkanesulfonic anhydride (JP-A-10-189041), 1,3,2-dioxaphospholane 2-oxide derivatives (Japanese Patent Laid-Open No. 10-50342), γ-sultone compounds (Japanese Patent Laid-Open No. 2000-235866), sulfolene derivatives (Patent Document 6), and the like, but are not limited thereto. .

  The compound having a sulfonyl group is preferably contained in the electrolytic solution in an amount of 0.01 to 10 wt%. If it is less than 0.01 wt%, there are many cases where the film formation on the negative electrode surface is not sufficiently effective, and if it exceeds 10 wt%, not only does not dissolve, but the viscosity of the electrolyte may increase, which is not preferable. In this invention, More preferably, it is the range of 0.05-5 wt%.

  Furthermore, according to the present invention, the cycle characteristics can be further improved by adding or mixing vinylene carbonate or a derivative thereof in the electrolytic solution. As vinylene carbonate or derivatives thereof, JP-A-4-16975, JP-A-7-122296, JP-A-8-45545, JP-A-5-82138, JP-A-5-74486, JP-A-6 -52887, JP-A No. 11-260401, JP-A No. 2000-208169, JP-A No. 2001-35530, JP-A No. 2000-138071 and the like may be appropriately selected and used. it can.

  When vinylene carbonate or a derivative thereof is used as an additive, the effect can be obtained by including 0.01 to 10 wt% in the electrolytic solution. Moreover, when using as a solvent, an effect is acquired by including 1-50 wt%.

  The aprotic organic solvent used in the present invention is an organic solvent of cyclic carbonates, chain carbonates, aliphatic carboxylic acid esters, γ-lactones, cyclic ethers, chain ethers and fluorinated derivatives thereof. From these, one kind or a mixture of two or more kinds is appropriately used.

In the present invention, LiPF ₆ , LiBF ₄ , LiAsF ₆ , LiSbF ₆ , LiClO ₄ , LiAlCl ₄ , LiN (C _n F _{2n + 1} SO ₂ ) (C _m F _{2m + 1} SO ₂ ) (n , M are natural numbers), and LiPF ₆ and LiBF ₄ are particularly preferable.

  Moreover, according to this invention, the secondary battery using the said electrolyte solution for secondary batteries provided with the positive electrode and negative electrode which use lithium as an active material is provided.

  As the negative electrode, a negative electrode active material made of a material capable of inserting and extracting lithium, lithium metal, a metal material capable of forming an alloy with lithium, an oxide material, or the like is used. Here, a material containing carbon is preferable as a material capable of inserting and extracting lithium, and graphite is particularly preferable.

  From this point of view, the present invention uses a negative electrode active material in which an alloy layer made of Si and Li is formed on graphite (referred to as “graphite / Si: Li” in this specification).

  The electrolytic solution of the present invention is obtained by adding in advance a transition metal complex of imide anion and transition metal ion or imide anion and transition metal ion that gives a stable film, and further adding a compound having a sulfonyl group.

  Here, the transition metal complex is a stable complex in which an imide anion is coordinated to a transition metal ion. By adsorbing this complex to the negative electrode surface, the negative electrode surface is stabilized.

  Moreover, the compound which has a sulfonyl group reacts with a dangling bond in a negative electrode interface, and forms a stable membrane | film | coat.

  By these two actions (adsorption and reaction), the decomposition of the solvent molecules can be suppressed, and the cycle characteristics are improved.

  In particular, since the negative electrode active material is graphite / Si: Li, the lithium fluoride which is a reaction product with lithium and a part of the transition metal alloy with lithium so that the current density distribution is uniform. And suppress the generation of dendrites and the like.

  In addition, a thin and stable lithium fluoride film is formed by the reaction between lithium on the negative electrode surface and imide anions adsorbed on the negative electrode surface. Furthermore, when the coating is mechanically broken, lithium on the negative electrode surface reacts with imide anions adsorbed on the negative electrode surface to repair the coating. For this reason, a long cycle life is realized by including the imide anion.

  In the present invention, a negative electrode using lithium as an active material and a positive electrode are combined with a separator interposed therebetween, inserted into the battery outer package, and then impregnated with an electrolytic solution containing a metal complex, and the battery outer package is sealed or sealed. By charging the battery after stopping, the above-described film is formed on the negative electrode.

  FIG. 1 shows a schematic structure of an example of a battery according to the present invention.

  The battery of the present invention includes a positive electrode current collector 11, a layer 12 containing a positive electrode active material made of any one or a mixture of oxides or sulfur compounds capable of occluding and releasing lithium ions, conductive polymers and stabilized radical compounds. , A carbon material or oxide that occludes / releases lithium ions, a metal that forms an alloy with lithium, a layer 13 containing a negative electrode active material made of lithium metal itself, or a mixture thereof, a negative electrode current collector 14, electrolysis It is comprised from the liquid 15 and the porous separator 16 containing this. The present invention is characterized in that the layer containing the negative electrode active material is composed of graphite / Si: Li.

  Here, the imide anion or the metal complex composed of a transition metal ion and an imide anion and the compound having a sulfonyl group are contained in the electrolytic solution 15 containing an imide anion or a lithium salt as an electrolyte.

Examples of the electrolytic solution in the present invention include propylene carbonate (PC), ethylene carbonate (EC), butylene carbonate (BC), cyclic carbonates such as vinylene carbonate (VC), dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl Chain carbonates such as methyl carbonate (EMC) and dipropyl carbonate (DPC), aliphatic carboxylic acid esters such as methyl formate, methyl acetate and ethyl propionate, γ-lactones such as γ-butyrolactone, 1, 2 -Chain ethers such as ethoxyethane (DEE) and ethoxymethoxyethane (EME), cyclic ethers such as tetrahydrofuran and 2-methyltetrahydrofuran, dimethyl sulfoxide, 1,3-dioxolane, formamide, acetamide, Dimethylformamide, acetonitrile, propylnitrile, nitromethane, ethyl monoglyme, phosphoric acid triester, trimethoxymethane, dioxolane derivative, sulfolane, methylsulfolane, 1,3-dimethyl-2-imidazolidinone, 3-methyl-2-oxazolidinone An aprotic organic solvent such as propylene carbonate derivative, tetrahydrofuran derivative, ethyl ether, 1,3-propane sultone, anisole, N-methylpyrrolidone, fluorinated carboxylic acid ester, or a mixture of two or more thereof, Lithium salts that dissolve in these organic solvents are dissolved. The lithium salt, lithium imide _{salt, LiPF 6, LiAsF 6, LiAlCl} 4, LiClO 4, LiBF 4, LiSbF 6 , and the like.

  The electrolytic solution in the present invention is a compound in which an imide compound and a transition metal salt are dissolved, and a compound having a sulfonyl group is further dissolved, and a metal complex composed of a transition metal ion and an imide anion is dissolved in advance, and further a compound having a sulfonyl group It is prepared by two methods for dissolving the lysate.

  In the former, an imide compound and a transition metal salt form a metal complex on the negative electrode through a charge / discharge process.

  In the latter, a metal complex is synthesized in advance and dissolved in an electrolytic solution to be adsorbed on the negative electrode.

  The metal complex containing the imide anion adsorbs on the surface of the negative electrode in the electrolytic solution, thereby preparing a uniform electric field during charging and providing a smooth and smooth lithium occlusion or precipitation process. In particular, when lithium metal is used, the film formed on the negative electrode is chemically and physically strong and has low resistance.

  A component of the surface film is a transition metal partially deposited and lithium fluoride generated by a reaction between lithium and fluorine contained in the imide anion. The deposited transition metal is stabilized by forming an alloy with lithium, and lithium fluoride is a chemically and physically stable compound.

  When the imide compound and the transition metal salt are dissolved, and the compound having a sulfonyl group is further dissolved, the imide compound and the transition metal salt contained in the electrolytic solution are not particularly limited, but preferably 0.005 with respect to the entire electrolysis solution. -10 wt%. If it is less than 0.005 wt%, the effect of the additive does not spread over the entire electrode surface, and if it exceeds 10 Wt%, the viscosity of the electrolyte increases and the liquid resistance increases.

  At this time, 0.01-10 wt% of the compound which has a sulfonyl group contained in the whole electrolyte solution is preferable. If it is less than 0.01 wt%, the effect of the additive does not spread over the entire electrode surface, and if it exceeds 10 Wt%, the viscosity of the electrolytic solution increases and the liquid resistance increases.

  In the case where a metal complex composed of a transition metal ion and an imide anion is dissolved in advance and a compound having a sulfonyl group is further dissolved, the metal complex contained in the electrolytic solution is not particularly limited, but is preferably 0.005 with respect to the entire electrolysis solution. -10 wt% is preferable. If it is less than 0.005 wt%, the effect of the additive does not spread over the entire electrode surface, and if it exceeds 10 Wt%, the viscosity of the electrolyte increases and the liquid resistance increases. At this time, the sulfone compound contained in the entire electrolyte is preferably 0.01 to 10 wt%. If the amount is less than 0.01 wt%, the effect of the additive does not spread over the entire electrode surface. If the amount exceeds 10 wt%, the viscosity of the electrolyte increases and the liquid resistance increases.

  As the transition metal, a lanthanoid transition metal is preferable, and any of europium (Eu), neodymium (Nd), erbium (Er), and holmium (Ho) or a mixture thereof is preferable. This is because the redox potential of Eu, Nd, Er, and Ho is the same as or close to that of graphite, alloy, and lithium metal, and can be reduced at a potential 0 to 0.8 V higher than lithium.

  Thus, by selecting a metal close to the redox potential of the negative electrode active material and selecting an anion that forms a stable complex with them, these metals are not easily reduced. Therefore, the complex composed of the lanthanoid metal ion and the imide anion shown in the present invention can exist stably at the interface between the negative electrode and the electrolytic solution.

The imide ^{_{anion, - N (C n F 2n}} + 1 SO 2) (C m F 2m + 1 SO 2) (n, m is a natural number) are preferable, particularly, perfluoro ethyl imide terms of aluminum corrosion inhibition anion ^{_{[- N (C 2 F 5}} SO 2) 2] is preferred.

  Furthermore, when the film is mechanically broken, lithium fluoride, which is a reaction product of lithium on the negative electrode surface and the imide anion adsorbed on the negative electrode surface, has a function of repairing the film. And has the effect of leading to the formation of a stable surface compound even after the coating is destroyed.

  As described above, the negative electrode according to the present invention is made of a lithium metal, a lithium alloy, or a material that can occlude and release lithium, such as a carbon material or an oxide.

  As this carbon material, graphite which occludes lithium, amorphous carbon, diamond-like carbon, carbon nanotube, or a composite thereof can be used. In the present invention, graphite is used.

  Further, as the oxide, any of silicon oxide, tin oxide, indium oxide, zinc oxide, lithium oxide, phosphoric acid, boric acid, or a composite thereof may be used, and it is particularly preferable to include silicon oxide. . The structure is preferably in an amorphous state. 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 forming 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 metal such as Al, Si, Pb, Sn, In, Bi, Ag, Ba, Ca, Hg, Pd, Pt, Te, Zn, La and lithium. . The lithium metal or lithium alloy is particularly preferably amorphous. This is because the amorphous structure hardly causes deterioration due to non-uniformity such as crystal grain boundaries and defects. From this viewpoint, an alloy of Si and Li is preferably used as the lithium alloy.

  Lithium metal or lithium alloy can be 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. it can.

  The negative electrode according to the present invention has a complex consisting of a transition metal ion and an imide anion at the interface with the electrolyte solution, thereby allowing flexibility in changing the volume of the metal and alloy phases, uniformity of ion distribution, physical and chemical properties. It is excellent in stability. As a result, dendrite formation and lithium atomization can be effectively prevented, and cycle efficiency and life are improved.

  In addition, dangling bonds existing on the surfaces of carbon materials and oxide materials have high chemical activity, and the solvent is easily decomposed. By adsorbing a complex composed of a transition metal ion and an imide anion on this surface, the decomposition of the solvent is suppressed and the irreversible capacity is greatly reduced, so the charge / discharge efficiency does not decrease.

In the present invention, examples of the positive electrode active material include lithium-containing composite oxides such as LiCoO ₂ , LiNiO ₂ , and LiMn ₂ O _4, and the transition metal portion of these lithium-containing composite oxides is substituted with other elements. It may be a thing.

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 can be, for example, a compound represented by the following general formula (I).
Li _a (M _x Mn _2-x ) O ₄ (I)
(In the formula, 0 <x <2, 0 <a <1.2. M is at least one selected from the group consisting of Ni, Co, Fe, Cr, and Cu.)

  In the positive electrode according to the present invention, these active materials are dispersed and kneaded 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). It can be obtained by applying it on a substrate such as an aluminum foil.

  The lithium secondary battery according to the present invention comprises a negative electrode and a positive electrode laminated in a dry air or inert gas atmosphere via a separator, or wound in a battery can after being laminated, or a synthetic resin A battery can be manufactured by sealing with a flexible film made of a laminate of metal foil and metal foil.

  In addition, as a separator, porous films, such as polyolefin, such as a polypropylene and polyethylene, a fluororesin, are used.

  The shape of the secondary battery according to the present invention is not particularly limited, and examples thereof include a cylindrical shape, a square shape, and a coin shape.

  Hereinafter, the present invention will be described by way of examples.

Example 1
(Production of battery)
As the positive electrode, an aluminum foil having a thickness of 20 μm was used as the positive electrode current collector, and LiMn ₂ O ₄ was used as the positive electrode active material. An alloy layer (thickness: 2 μm) made of Si and Li on graphite as a negative electrode active material on a 10 μm thick copper foil as a negative electrode current collector as a negative electrode (Si / Li ratio 1/4. 4. Hereinafter, graphite / Si: Li) was used. Further, the electrolyte solution uses a mixed solvent of EC and DEC (volume ratio: 30/70) as a solvent, and dissolves ¹ molL ⁻¹ of LiN (C ₂ F ₅ SO ₂ ) ₂ (hereinafter, LiBETI) as an electrolyte salt, Next, as an additive, a salt of Eu ³⁺ having CF ₃ SO ₃ ⁻ so as to be contained at 0.3 wt% in the electrolytic solution is melted, and 1,3-propane sultone (hereinafter referred to as 1,3-PS) is further melted. And 1 wt% in the electrolytic solution. And the negative electrode and the positive electrode were laminated | stacked through the separator which consists of polyethylene, and the secondary battery of a present Example was produced.

(Charge / discharge cycle test)
At a temperature of 20 ° C., the charge rate was 0.05 C, the discharge rate was 0.1 C, the charge end voltage was 4.2 V, the discharge end voltage was 3.0 V, and the utilization factor (discharge depth) of the lithium metal negative electrode was 33%. The capacity retention rate (%) is a value obtained by dividing the discharge capacity (mAh) after 300 cycles by the discharge capacity (mAh) at the 10th cycle. The results obtained in the cycle test are shown in Table 1 below.

(Comparative Example 1)
A secondary battery was produced in the same manner as in Example 1 without using a Eu ³⁺ salt having CF ₃ SO ₃ ^−, and the performance of the battery was evaluated in the same manner as in Example 1. The results are shown in Table 1.

(Comparative Example 2)
A secondary battery was produced in the same manner as in Example 1 without using 1,3-PS, and the performance of the battery was evaluated in the same manner as in Example 1. The results are shown in Table 1.

  Compared with Comparative Examples 1 and 2, the battery shown in Example 1 has an improved capacity retention rate after the cycle test, that is, improved cycle characteristics.

(Example 2)
In Example 2, the imide anion and the metal ion were added in Example 1, and a metal complex film was formed on the negative electrode by charging and discharging, whereas the transition metal complex was added as an additive in advance. The complex is adsorbed on the negative electrode surface.

The _secondary solution was the same as in Example 1 except that LiPF ₆ was used as the electrolyte salt and 0.1 wt% of the metal complex Eu [N (C ₂ F ₅ SO ₂ ) ₂ ] ₃ was used as the additive with respect to the total electrolyte. A battery was prepared and the performance of the battery was evaluated in the same manner as in Example 1. The results are shown in Table 1.

(Comparative Example 3)
A secondary battery was produced in the same manner as in Example 2 without using the metal complex Eu [N (C ₂ F ₅ SO ₂ ) ₂ ] _3, and the performance of the battery was evaluated in the same manner as in Example 2. The results are shown in Table 1.

(Comparative Example 4)
A secondary battery was produced in the same manner as in Example 2 without using 1,3-PS, and the performance of the battery was evaluated in the same manner as in Example 2. The results are shown in Table 1.

  The battery shown in Example 2 was confirmed to have an improved capacity retention rate after the cycle test, that is, improved cycle characteristics, as compared with Comparative Examples 3 and 4.

(Example 3)
In Example 3, the electrolytic solution further containing vinylene carbonate (VC) as an additive in Example 2 is used.

  A secondary battery was produced in the same manner as in Example 2 except that 1 wt% of VC was further added to the electrolyte as an additive, and the performance of the battery was evaluated in the same manner as in Example 2. The results are shown in Table 1.

  In the battery shown in Example 3, the capacity retention rate after the cycle test is further improved as compared with Example 2, that is, VC is further added to the electrolytic solution containing the metal complex and the sulfone compound. Thus, it was confirmed that the cycle characteristics were further improved.

11 Positive Electrode Current Collector 12 Layer Containing Positive Electrode Active Material 13 Layer Containing Negative Electrode Active Material 14 Negative Electrode Current Collector 15 Nonaqueous Electrolyte Solution 16 Porous Separator

Claims (6)

A secondary battery comprising at least a positive electrode and a negative electrode,
The negative electrode active material constituting the negative electrode is graphite / Si: Li (a film in which an alloy layer made of Si and Li is formed on graphite) , and
The electrolytic solution contains a compound having at least an imide anion, a transition metal ion, and a sulfonyl group in an aprotic solvent ,
The imide ^{_{anion, - N (C n F 2n}} + 1 SO 2) (C m F 2m + 1 SO 2) (n, m are natural numbers), and the electrolytic solution 0.005 imide anion or metal complex thereof -10 wt% included,
The transition metal is selected from the group consisting of europium, neodymium, erbium, holmium, and
The compound having a sulfonyl group is at least one selected from the group consisting of 1,3-propane sultone, 1,4-butane sultone, sulfolane, alkane sulfonic acid anhydride, γ-sultone compound, and sulfolene compound. A secondary battery comprising 0.01 to 10 wt% in the liquid .   The secondary battery according to claim 1, wherein the imide anion and the transition metal ion are a metal complex, and the electrolytic solution further contains a lithium salt as an electrolyte salt. The lithium salt is LiPF ₆ , LiBF ₄ , LiAsF ₆ , LiSbF ₆ , LiClO ₄ , LiAlCl ₄ , LiN (C _n F _{2n + 1} SO ₂ ) (C _m F _{2m + 1} SO ₂ ) (n and m are natural numbers) The secondary battery according to claim 2, which is at least one selected from the group consisting of: The secondary battery according to claim 1 , wherein the electrolytic solution further contains vinylene carbonate or a derivative thereof. The aprotic organic solvent is at least one selected from cyclic carbonates, chain carbonates, aliphatic carboxylic acid esters, γ-lactones, cyclic ethers, chain ethers, and fluorinated derivatives thereof. The secondary battery according to any one of claims 1 to 4 . The secondary battery according to claim 1 , wherein the positive electrode is made of a lithium-containing composite oxide capable of inserting and extracting lithium.

Images