TW201511390A - Lithium secondary cell and electrolyte for lithium secondary cell - Google Patents

Abstract

The present invention provides a lithium secondary cell having excellent cycle characteristics in which degradation of the anode active material accompanying charging and discharging is suppressed, and long life, particularly when used in high temperature environments, and also provides an electrolyte for use in such a lithium secondary cell. The lithium secondary cell of the invention has an electrolyte into which the cathode and anode which store and release lithium during charging and discharging are immersed, wherein the anode contains a silicon based anode active material, and the electrolyte contains an unsaturated phosphate ester represented by formula (1) shown below. [Chemical Formula 1] (1) (In the formula, each of R1to R3 independently represents a direct bond or an alkylene group with a carbon number of 1 to 5.).

Description

Lithium secondary battery and electrolyte for lithium secondary battery

The present invention relates to a lithium secondary battery which is high in capacity, and which is excellent in cycle characteristics particularly in a high-temperature environment and has a long service life, and relates to an electrolyte for a lithium secondary battery for a lithium secondary battery.

Lithium secondary batteries are widely used in mobile electronic devices and personal computers, and are required to be miniaturized and lightweight. On the other hand, they are required to be used for high-energy density and accompanying charging and discharging of high-performance electronic devices and electric vehicles. The deterioration is suppressed, the cycle characteristics are excellent, and the service life is long. The lithium battery has a structure in which a positive electrode active material layer containing a positive electrode active material formed on a current collector and a negative electrode active material layer containing a negative electrode active material are disposed opposite to each other via a separator, and the layered body The mixture is immersed in an electrolytic solution and stored in an exterior body; and the lithium ion is reversibly absorbed by the electrode active material to perform a charge and discharge cycle.

As such a negative electrode active material, a metal or a metal oxide such as lanthanum and cerium oxide or a tin alloyed with lithium can be used instead of the carbon-based material from the viewpoint of high energy density, low cost, and safety. However, the negative electrode active material containing ruthenium expands and contracts greatly with charge and discharge, and forms fine dust with repeated charge and discharge, and falls off from the negative electrode active material layer, and the battery capacity is lowered. In particular, when it is used in a high-temperature environment of 45 ° C or higher, it tends to be significantly deteriorated due to a decrease in battery capacity.

In order to suppress the deterioration of the ruthenium-based negative electrode active material having a large volume expansion and contraction rate due to the absorption and release of lithium, the following technique is employed: a film is formed on the negative electrode active material layer to suppress the negative electrode active material. The negative electrode active material layer is peeled off. However, it is not easy to form a film having a uniform thickness which can sufficiently suppress the deterioration of the cycle characteristics and the use of the ruthenium-based negative electrode active material.

On the other hand, in order to achieve an improvement in the charge and discharge cycle characteristics of the lithium secondary battery, the following technology is currently being carried out in an attempt to improve the cycle characteristics by adding a specific substance to the used electrolyte. Specifically, an electrolyte solution using a non-aqueous electrolyte solution using a highly crystalline crystalline carbon material such as graphite as an active material and a polymer carboxylate as an adhesive is proposed. In the secondary battery, an electrolyte containing an organic solvent, an electrolyte salt, or a specific unsaturated phosphate is used (Patent Documents 1 and 2); an alkoxy group substituted with a halogen atom, and an alkoxy group having an unsaturated bond; A halogen-containing phosphate compound and a non-aqueous electrolyte such as a lithium ion battery (Patent Document 3) can be used to suppress gas generation when a secondary battery in a charged state is stored at a high temperature. Further, in a lithium secondary battery having a negative electrode formed by depositing a thin film of an active material on a current collector, a non-electrolyte having at least one of a phosphate compound, a phosphite, and a boric acid ester is proposed as a non-electrolyte. A method of applying the ruthenium-based negative electrode active material having a large volume expansion and contraction ratio accompanying the absorption and release of lithium as described above (Patent Document 4).

However, in order to realize a battery having a high energy density, it is necessary to increase the thickness of the electrode in such a manner that the amount of the negative electrode active material per unit area is sufficient, and in the case of using a lanthanum-based negative electrode having a high energy density, it is also required to have a correspondence. With the flexibility of volume change of charge and discharge, formation of a uniform and stable film suppresses deterioration of charge and discharge of the negative electrode active material, and in particular, for use in a high-temperature environment, lithium having a long cycle life and long life can be achieved. Secondary battery. [Prior Technical Literature] [Patent Literature]

[Patent Document 1] JP-A-2011-124039 [Patent Document 2] JP-A-2011-77029 [Patent Document 3] JP-A-2011-96462 [Patent Document 4] JP-A-2002-319431

[Problems to be solved by the invention]

An object of the present invention is to provide a lithium secondary battery having a flexibility in which a volume of a ruthenium-based negative electrode active material having a large volume expansion and contraction ratio with respect to lithium absorption and release is accompanied by a change in volume of charge and discharge, and a stable film having a uniform thickness can be formed and suppressed. The negative electrode active material is accompanied by deterioration of charge and discharge, and in particular, it is improved in cycle characteristics in use in a high-temperature environment, and can be extended in life; and an electrolyte solution for a lithium secondary battery is provided. [Means for solving the problem]

The inventors of the present invention have found that, in the lanthanoid negative electrode active material, an unsaturated phosphate having an unsaturated triple bond at the three alkoxy terminals of the phosphate ester can be formed as a soft and stable material capable of forming a volume change accompanying charge and discharge. The film material was added to the electrolyte to increase the capacity retention rate in the charge and discharge cycle, and the present invention was completed based on this finding.

That is, the present invention relates to a lithium secondary battery comprising an electrolytic solution which immerses a positive electrode and a negative electrode which emit lithium in association with charge and discharge, and a negative electrode containing a lanthanoid negative electrode active material, wherein the electrolytic solution contains (1) an unsaturated phosphate ester as shown;

(1)

(wherein R ₁ to R ₃ independently represent a direct bond or a C 1 to 5 alkyl group).

Moreover, the present invention relates to an electrolyte solution for a lithium secondary battery which is obtained by immersing a positive electrode and a negative electrode which absorb and release lithium by charge and discharge, and is characterized by comprising: an unsaturated phosphate ester represented by the formula (1);

(1)

(wherein R ₁ to R ₃ independently represent a direct bond or a C 1 to 5 alkyl group). [Effects of the Invention]

In the lithium secondary battery and the electrolyte solution for a lithium secondary battery of the present invention, it is possible to suppress deterioration of the ruthenium-based negative electrode active material having a large volume expansion and contraction rate due to absorption and release of lithium due to charge and discharge, and particularly to a high temperature environment. The use of the cycle to achieve an improvement in the cycle characteristics, and can reach a longer life.

The lithium secondary battery of the present invention has a positive electrode and a negative electrode, and an electrolytic solution impregnated with the elements.

[negative electrode]

The negative electrode includes a ruthenium-based negative electrode active material capable of reversibly absorbing and releasing lithium ions by charge and discharge, and has a structure in which a negative electrode active material layer in which a negative electrode active material is integrated by a negative electrode adhesive is laminated on a current collector.

The negative electrode active material may be any one of the ruthenium-based negative electrode active materials, and examples thereof include ruthenium and iridium oxide (SiOx: 0 < x ≦ 2). Any one of these substances may be included, but it is preferred to include both of them. This is because, when these materials are used as the negative electrode active material, the potentials of charge and discharge of lithium ions are different. Specifically, the charge phase of lithium ions is lower than that of ruthenium oxide, and the charge and discharge of lithium ions are low. In the negative electrode active material layer, lithium ions can be gradually released in response to a voltage change at the time of discharge, and it is possible to suppress sudden discharge of lithium ion ions at a specific potential and cause a sudden shrinkage of the volume of the negative electrode active material layer. Cerium oxide is not easily reacted with the electrolyte and is stable. Specifically, SiO, SiO _2, etc. are mentioned.

In the negative electrode active material, the content of cerium may be 100% by mass, and when cerium oxide is contained in the negative electrode active material, it may be 0% by mass, preferably 5% by mass or more and 95% by mass or less, preferably 10% by mass or more and 90% by mass or less, more preferably 20% by mass or more and 50% by mass or less. In addition, the content of the cerium oxide in the negative electrode active material may be 100% by mass, and may be 0% by mass or less, preferably 5% by mass or more and 90% by mass or less, in the case where ruthenium is contained in the negative electrode active material. 40% by mass or more and 80% by mass or less, more preferably 50% by mass or more and 70% by mass or less.

Further, a metal other than cerium and a metal oxide may be contained as the negative electrode active material. The metal other than ruthenium is a metal which can form an alloy with lithium, and for example, a metal which releases lithium ions from a lithium alloy at the time of discharge and forms a lithium alloy at the time of charging. Specific examples thereof include aluminum, lead, tin, indium, antimony, silver, antimony, calcium, mercury, palladium, platinum, rhodium, zinc, and antimony. These elements may be selected from one type or two or more types. Among these elements, tin is preferred.

Specific examples of the metal oxide of the negative electrode active material include aluminum oxide, tin oxide, indium oxide, zinc oxide, and lithium oxide. These metal oxides may be used alone or in combination of two or more. These metal oxides are preferably used together with the above-mentioned metals. In particular, the same metal as that of the metal oxide is used, and lithium ions can be absorbed and released at different potentials during charge and discharge, and the negative electrode can be suppressed. It is preferred that the volume of the active material layer changes rapidly; tin oxide is preferably used together with the above tin.

Preferably, at least a portion of the cerium oxide and the metal oxide are amorphous. By making the cerium oxide and the metal oxide amorphous, it is possible to suppress the reaction with the electrolytic solution while suppressing the micronization of the negative electrode active material layer. In the negative electrode active material layer having amorphous cerium oxide and metal oxide, it is considered that factors such as defects included in the crystal structure and unevenness such as grain boundaries can be reduced, and uneven volume change can be suppressed.

The X-ray diffraction measurement can be used to confirm that the cerium oxide and the metal oxide are amorphous when the intrinsic peak of the crystal structure observed in the case of having a crystal structure is broadened.

Moreover, it is preferable to contain a carbon material as a negative electrode active material. Examples of the carbon material include black lead, amorphous carbon, diamond-like carbon, and carbon nanotubes. Black lead having high crystallinity has high conductivity, and can improve the current collecting property of the negative electrode active material layer, and amorphous carbon having low crystallinity can suppress deterioration of the negative electrode active material layer accompanying charge and discharge. The content of the carbon material in the negative electrode active material is preferably 2% by mass or more and 50% by mass or less, and more preferably 2% by mass or more and 30% by mass or less.

When the ruthenium and the ruthenium oxide, the metal, the metal oxide, and the carbon material are in the form of particles, it is preferable to suppress deterioration of the negative electrode active material due to charge and discharge. In the case of the particulate negative electrode active material, the volume is largely changed by charge and discharge, and it is preferable to reduce the volume of the negative electrode active material layer due to the change in volume of the particles. Specifically, the average particle diameter of cerium oxide is smaller than the average particle diameter of the carbon material. For example, the average particle diameter of cerium oxide is preferably 1/2 or less of the average particle diameter of the carbon material. The average particle diameter of cerium is smaller than the average particle diameter of cerium oxide. For example, the average particle diameter of cerium is preferably 1/2 or less of the average particle diameter of cerium oxide. When the average particle diameter is controlled within this range, the particles having a large volume change due to charge and discharge have a small diameter, and it is possible to obtain a secondary effect in which the volume change of the negative electrode active material layer is large, and the balance between energy density, cycle life, and efficiency is excellent. battery. Specifically, the average particle diameter of ruthenium is, for example, 20 μm or less, and it is preferable to ensure contact with the current collector, and it is preferably 15 μm or less.

In addition, from the viewpoint of suppressing deterioration of conductivity and suppressing deterioration of the negative electrode active material due to charge and discharge cycles, it is also possible to form amorphous cerium oxide around the cluster of cerium and to cover the surface of the particle with carbon. . When the thickness of the carbon coating film on the surface of the particle of the coating of the lanthanoid material is 0.1 to 5 μm, it is preferable because the negative electrode active material can be prevented from being deteriorated by charge and discharge and conductivity is improved at the same time. The thickness of the carbon film was measured by a transmission electron microscope (TEM), and the average value of the measured values of 100 particles was used.

As a method of producing a negative electrode active material having a carbon film in which cerium and a metal are dispersed in the above-mentioned amorphous cerium oxide, for example, a method described in JP-A-2004-47404 can be mentioned. Specifically, cerium oxide and a metal oxide can be subjected to CVD treatment in an organic gas atmosphere such as methane gas, whereby amorphous cerium oxide and metal oxide are formed around the nano cluster of cerium and metal. A carbon film can be formed around it. Further, for example, a method of mixing cerium oxide or metal oxide, cerium or metal, or a carbon material by mechanical polishing may be mentioned. The average particle diameter of the negative electrode active material having such a carbon film is, for example, about 1 to 20 μm.

As the negative electrode binder that agglomerates the above negative electrode active material, for example, polyvinylidene fluoride (PVdF), vinylidene fluoride-hexafluoropropylene copolymer, vinylidene fluoride-tetrafluoroethylene copolymer, styrene- can be used. Butadiene copolymerized rubber, polytetrafluoroethylene, polypropylene, polyethylene, polyimine, polyamidimide, and the like. These compounds may be used alone or in combination of two or more. Among these compounds, from the viewpoint of cohesive force, it is preferred to contain polyimine and polyamidimide. The amount of the adhesive for the negative electrode to be used is preferably from 5 to 25 parts by mass based on 100 parts by mass of the negative electrode active material from the viewpoint of "sufficient cohesive force" and "high energy" of the trade off relationship. .

The current collector that supports the negative electrode active material layer in which the negative electrode active material is integrated by the negative electrode adhesive agent may have conductivity capable of being electrically connected to an external terminal, and is preferably aluminum or nickel from the viewpoint of electrochemical stability. , copper, silver or an alloy of these metals. Examples of the shape thereof include a foil, a flat plate, and a mesh. The thickness of the current collector is, for example, about 5 to 30 μm.

The material for the negative electrode active material layer containing the negative electrode active material and the negative electrode binder can be used for the current collector to produce the above negative electrode. Examples of the method for producing the negative electrode active material layer include a coating method such as a doctor blade method or a die coating method; a CVD method, a sputtering method, and the like. After the negative electrode active material layer is formed in advance, aluminum, nickel, or an alloy thin film of these metals may be formed by a method such as vapor deposition or sputtering to serve as a negative electrode current collector. The thickness of the negative electrode active material layer is, for example, about 10 to 200 μm.

[Positive Electrode] The positive electrode includes a positive electrode active material that reversibly absorbs and releases lithium ions in association with charge and discharge, and has a structure in which a positive electrode active material layer in which a positive electrode active material is integrated by a positive electrode binder is laminated on a current collector.

The positive electrode active material releases lithium ions into the electrolytic solution during charging, and absorbs lithium from the electrolytic solution during discharge, and has, for example, a layer having LiMnO ₂ or Li _x Mn ₂ O ₄ (0<x<2). Lithium manganate, or lithium manganate having a spinel structure; replacing LiCoO ₂ , LiNiO ₂ or one of the transition metals with other metals; LiNi _1/3 Co _1/3 Mn ₁ The specific transition metal of _/3 O ₂ does not exceed half of the lithium transition metal oxide; in these lithium transition metal oxides, Li is excessive compared to the stoichiometric composition. Particularly suitable is Li _α Ni _β Co _γ Al _δ O ₂ (1≦α≦1.2, β+γ+δ=1, β≧0.7, γ≦0.2) or Li _α Ni _β Co _γ Mn _δ O ₂ (1≦α≦1.2 , β + γ + δ = 1, β ≧ 0.6, γ ≦ 0.2). The positive electrode active material may be used singly or in combination of two or more.

As the positive electrode binder in which the positive electrode active material is aggregated and integrated, specifically, the same as the above-described negative electrode adhesive can be used. As the positive electrode binder, from the viewpoint of versatility and low cost, it is preferably polyvinylidene fluoride. The amount of the positive electrode binder to be used is preferably 2 to 10 parts by mass based on 100 parts by mass of the positive electrode active material. When the content of the positive electrode binder is 2 parts by mass or more, the adhesion between the active materials can be improved, or the adhesion between the active material and the current collector can be improved, so that the cycle characteristics become good as long as the mass is 10 Below the balance, the active material ratio can be increased and the positive electrode capacity can be increased.

For the purpose of reducing the impedance of the positive electrode active material, a conductive auxiliary material may be added to the positive electrode active material layer. As the conductive auxiliary material, carbonaceous fine particles such as graphite, carbon black, or acetylene black can be used.

The current collector that supports the positive electrode active material layer in which the positive electrode active material is integrated with the positive electrode binder may have conductivity that can be electrically connected to an external terminal. Specifically, a set used in the above negative electrode can be used. The same electrical body.

A material for a positive electrode active material layer containing a positive electrode active material and a positive electrode binder may be used for the current collector to prepare the above positive electrode. As a method of producing the positive electrode active material layer, the same method as the method of producing the negative electrode active material layer can be used.

[Electrolytic Solution] In order to absorb and discharge lithium in the positive electrode negative electrode during charge and discharge, the electrolyte solution is impregnated with a positive electrode and a negative electrode to dissolve lithium ions, and the electrolyte is dissolved in a non-aqueous organic solvent.

The solvent of the above electrolyte solution is preferably stable under the action potential of the battery, and is preferably low in viscosity in the environment in which the battery is used to be able to impregnate the electrode. Specifically, for example, propylene carbonate (PC; propylene carbonate), ethylene carbonate (EC), butyl carbonate (BC), and vinyl carbonate (VC); And other cyclic carbonates; dimethyl carbonate (DMC; dimethyl carbonate), diethyl carbonate (EMC), ethyl methyl carbonate (EMC; ethyl methyl carbonate), dipropyl carbonate (DPC; A chain carbonate such as dipropyl carbonate; a carbonic acid stretch propylene derivative; an aprotic organic solvent such as an aliphatic carbonate such as methyl formate, methyl acetate or ethyl propionate. These organic solvents may be used alone or in combination of two or more. Among these organic solvents, it is preferably ethyl carbonate (EC), propyl carbonate (PC), butyl carbonate (BC), vinyl carbonate (VC), dimethyl carbonate (DMC), carbonic acid. A cyclic or chain carbonate such as diethyl ester (DEC), ethyl methyl carbonate (MEC) or dipropyl carbonate (DPC).

The electrolyte contained in the electrolytic solution is preferably a lithium salt. Specific examples of the lithium salt include LiPF ₆ , LiAsF ₆ , LiAlCl ₄ , LiClO ₄ , LiBF ₄ , LiSbF ₆ , LiCF ₃ SO ₃ , LiC ₄ F ₉ SO ₃ , Li(CF ₃ SO ₂ ) ₃ , LiN(CF ₃ SO ₂ ) ₂ and the like.

The concentration of the electrolyte in the electrolytic solution is preferably 0.01 mol/L or more and 3 mol/L or less, preferably 0.5 mol/L or more and 1.5 mol/L or less. When the electrolyte concentration is within this range, safety can be improved, and a battery having high reliability and contributing to reduction in environmental load can be obtained.

The above electrolyte solution contains an unsaturated phosphate represented by the formula (1).

(1)

In the unsaturated phosphate ester represented by the formula (1), the unsaturated triple bond forms a radical on the surface of the negative electrode active material in association with charge and discharge of the battery, and the polymer produced by the polymerization reaction coats the negative electrode active material, and further A film having a uniform thickness composed of a polymer is formed. It is considered that the polymer film penetrates lithium ions, but hinders the penetration of the electrolyte solution, and as a result, the reaction between the negative electrode active material and the electrolytic solution can be suppressed, and the battery capacity reduction due to repeated charge and discharge can be suppressed.

In the formula (1), R ₁ to R ₃ independently represent a direct bond or an alkylene group having 1 to 5 carbon atoms. When the unsaturated phosphate represented by the formula (1) is a compound represented by the formula (2) wherein R ₁ to R ₃ represent a methylene group, a uniform film can be formed on the negative electrode active material. Preferably.

(2)

The content of the unsaturated phosphate ester represented by the formula (1) in the electrolytic solution should be appropriately selected to form a film having a suitable thickness on the negative electrode active material. The unsaturated phosphate ester represented by the formula (1) contained in the electrolytic solution is polymerized or decomposed in the initial stage and after the charge and discharge of the battery. Therefore, when the amount of the unsaturated phosphate represented by the formula (1) contained in the electrolytic solution is too large, the unsaturated phosphate ester represented by the formula (1) is decomposed in the early stage of the charge and discharge cycle, and the decomposition product is attached. The absorption or release of lithium ions in the charge/discharge cycle after the electrode or the like is hindered, and the discharge capacity of the battery is decreased or the rate characteristics are deteriorated. The concentration of the unsaturated phosphate ester represented by the formula (1) in the electrolytic solution may be, for example, about 0.005 to 10% by mass, preferably 0.01 to 5.0% by mass, and more preferably about 0.5 to 3.0% by mass.

Further, the upper limit of the content of the unsaturated phosphate represented by the formula (1) in the electrolytic solution may be defined by the impedance (charge moving resistance) between the electrodes at the end of charging. Specifically, the content of the unsaturated phosphate ester represented by the formula (1) in the electrolytic solution is such that the inter-electrode resistance at the end of the charging is added to the unsaturated phosphate ester represented by the formula (1). It is preferable that the amount is less than about 10 times that of the case where it is not added, and the rate characteristic or the charge and discharge characteristics are not lowered.

[Separator] The separator may be any material as long as it can suppress conduction between the positive electrode and the negative electrode and does not inhibit the penetration of electric charges. As a specific material, a polyolefin-based microporous film such as polypropylene or polyethylene, cellulose, polyethylene terephthalate, polyimide or polyvinylidene fluoride can be used. These materials can be used as porous films, woven fabrics, non-woven fabrics, and the like.

[Battery exterior body] The outer casing preferably has a strength that can stably maintain the positive electrode and the negative electrode, the separator, and the electrolytic solution, and is stable with respect to electrochemical properties of the materials, and is water-tight. Specifically, for example, stainless steel coated with a laminated film, iron coated with nickel, aluminum, cerium oxide, or aluminum oxide can be used; as the resin for the laminated film, polyethylene, polypropylene, or the like can be used. Polyethylene terephthalate or the like. These resins may be one layer or two or more layers.

[Secondary Battery] The shape of the secondary battery may be any of a cylindrical type, a flat wound square type, a laminated square type, a coin type, a flat wound laminated type, and a laminated laminated type.

As an example of the above secondary battery, a laminated laminate type secondary battery 11 as shown in Fig. 1 can be exemplified. In the laminated laminate type secondary battery, the negative electrode 3 having the negative electrode active material layer 1 (which is provided on the negative electrode current collector 2 made of a metal such as copper foil) and the positive electrode active material layer 4 (which is provided in The positive electrode 6 of the positive electrode current collector 5 made of a metal such as aluminum foil is disposed to face the separator 7 made of a polypropylene microporous film in contact with the elements, and the components are housed in the laminate. Inside the outer body 8. The electrolyte is filled in the laminated outer casing, and the negative electrode active material layer 1 and the positive electrode active material layer 4 are immersed in the electrolytic solution, and are electrically connected to the current collector portion where the active material layer is not formed, and the negative electrode terminal 9 and the positive electrode terminal 10 are electrically connected. The outer portion of the laminated outer casing is guided to be connected to an external power source or a device to be used during charging and discharging. [Examples]

The lithium secondary battery of the present invention will be described in detail below. [Example 1] [Production of Lithium Secondary Battery] A ruthenium-based negative electrode active material in which a carbon film was formed on the surface of lanthanoid particles dispersed in an amorphous yttrium oxide (SiOx, 0 < x ≦ 2) as a negative electrode Active substance. Among the ruthenium-based negative electrode active materials, the mass ratio of ruthenium, amorphous ruthenium oxide, and carbon was 29:61:10. The negative electrode active material is measured at a mass ratio of 90:10 with a precursor of polyimine which is an adhesive for a negative electrode, and the components are mixed with N-methylpyrrolidone to serve as a negative electrode. Slurry. The negative electrode slurry was applied onto a copper foil having a thickness of 10 μm, dried, and further subjected to heat treatment at 300 ° C in a nitrogen atmosphere to prepare a negative electrode.

Lithium nickelate (LiNi _0.80 Co _0.15 Al _0.05 O ₂ ) as a positive electrode active material, carbon black as a conductive auxiliary material, and polyvinylidene fluoride as an adhesive for a positive electrode were measured at a mass ratio of 90:5:5. These components were mixed with N-methylpyrrolidone to serve as a positive electrode slurry. The positive electrode slurry was applied to an aluminum foil having a thickness of 20 μm, dried, and further pressed to prepare a positive electrode.

The obtained three layers of the positive electrode and the four layers of the negative electrode were sandwiched by a polypropylene porous film as a separator and alternately overlapped. The end portions of the positive electrode current collector not covered with the positive electrode active material are welded to each other, and the positive electrode terminal made of aluminum is welded to the welded portion, and the end portion of the negative electrode current collector not covered with the negative electrode active material is provided on the other hand. The electrodes are welded to each other, and the negative electrode terminal made of nickel is welded to the welded portion to obtain an electrode member having a planar laminated structure.

99 parts by mass of a carbonate-based nonaqueous electrolytic solution composed of EC/DEC=30/70 (volume ratio) of LiPF ₆ dissolved at a concentration of 1 mol/L, and a compound (1) represented by the formula (2) 1 part by mass (content ratio in the electrolytic solution: 1% by mass) was mixed to obtain an electrolytic solution.

(2)

The obtained electrode element was wrapped with an aluminum laminate film as an exterior body, and after the electrolyte solution was injected thereinto, it was sealed under reduced pressure to 0.1 atm to prepare a secondary battery.

[Evaluation of Charging and Discharging Cycle Characteristics] The obtained lithium secondary battery was evaluated for cycle characteristics. The charge and discharge were repeated in a voltage range of 2.5 V to 4.2 V in a thermostat maintained at 60 °C. The discharge capacity (DC100) after 100 cycles of the charge and discharge cycle was measured, and the ratio of the discharge capacity after 100 times to the initial discharge capacity (DC1) (DC100/DC1) was calculated, and the capacity retention rate after 100 cycles was obtained. The discharge capacity (DC250) after 250 cycles of the charge and discharge cycle was measured in the same manner, and the ratio of the discharge capacity after 250 cycles to the initial discharge capacity (DC1) (DC250/DC1) was calculated, and the cycle retention rate after 250 cycles was obtained. . The results are shown in Table 1.

[Comparative Example 1] A lithium secondary battery was produced in the same manner as in Example 1 except that the compound (1) represented by the formula (2) was not used, and the charge/discharge cycle characteristics were evaluated. The results are shown in Table 1.

[Comparative Example 2] A lithium secondary battery was fabricated and subjected to charge and discharge cycle characteristics in the same manner as in Example 1 except that the compound represented by the formula (2) was used, except for the compound (2) represented by the formula (3). evaluation of. The results are shown in Table 1.

(3)

[Comparative Example 3] A lithium secondary battery was produced and charged in the same manner as in Example 1 except that the compound (1) represented by the formula (2) was used, except for the compound (3) represented by the formula (4). Evaluation of discharge cycle characteristics. The results are shown in Table 1.

(4)

From the results, in the lithium secondary battery of the example, the charge and discharge capacity retention rate at 60 ° C was higher than that of the lithium secondary battery of the comparative example, and it was found that electrolysis using the unsaturated compound represented by the formula (1) was used. The liquid lithium secondary battery of the present invention is excellent in charge and discharge cycle characteristics.

In this case, all the matters described in Japanese Patent Application No. 2013-159397, filed on July 31, 2013, are incorporated herein by reference. [Industrial availability]

The lithium secondary battery of the present invention can be used in all industrial fields requiring a power source, and in an industrial field related to power transmission, storage, and supply. Specifically, it can be used for a power source of a mobile device such as a mobile phone or a notebook computer, a motor drive power source for a vehicle, or the like.

1‧‧‧Negative active material layer
2‧‧‧Negative current collector
3‧‧‧negative
4‧‧‧positive active material layer
5‧‧‧ positive current collector
6‧‧‧ positive
7‧‧‧Parts
8‧‧‧Outer body
9‧‧‧Negative terminal
10‧‧‧ positive terminal
11‧‧‧Lithium secondary battery

Fig. 1 is a configuration diagram showing a configuration of an example of a lithium secondary battery of the present invention.

1‧‧‧Negative active material layer

2‧‧‧Negative current collector

3‧‧‧negative

4‧‧‧positive active material layer

5‧‧‧ positive current collector

6‧‧‧ positive

7‧‧‧Parts

8‧‧‧Outer body

9‧‧‧Negative terminal

10‧‧‧ positive terminal

11‧‧‧Lithium secondary battery

Claims (4)

A lithium secondary battery comprising an electrolytic solution for immersing a positive electrode and a negative electrode for discharging lithium with charge and discharge, and a negative electrode comprising a lanthanoid negative electrode active material, wherein the electrolytic solution contains an unsaturated phosphoric acid represented by the formula (1) ester; (1) (wherein R ₁ to R ₃ independently represent a direct bond or an alkylene group having 1 to 5 carbon atoms). The lithium secondary battery of claim 1, wherein the unsaturated phosphate represented by the formula (1) is represented by the formula (2); (2). An electrolyte solution for a lithium secondary battery, which is characterized by immersing a positive electrode and a negative electrode which absorb lithium by charge and discharge, and is characterized by comprising: an unsaturated phosphate ester represented by the formula (1); (1) (wherein R ₁ to R ₃ independently represent a direct bond or an alkylene group having 1 to 5 carbon atoms). The electrolyte for a lithium secondary battery according to the third aspect of the invention, wherein the unsaturated phosphate represented by the formula (1) is represented by the formula (2); (2).