JP5472970B2 - Lithium ion secondary battery - Google Patents

Description

  The present invention relates to a lithium ion secondary battery.

  In recent years, with the rapid miniaturization and diversification of consumer mobile phones, portable electronic devices, personal digital assistants, etc., the batteries that are the power source are small, light, high energy density, and repeated for a long period of time. There is a strong demand for the development of secondary batteries that can be charged and discharged.

  Among them, compared to lead batteries and nickel cadmium batteries that use aqueous electrolytes, lithium ion secondary batteries have been put into practical use as secondary batteries that satisfy these requirements, and active research has been conducted.

Such a lithium ion secondary battery includes, for example, a positive electrode plate in which a positive electrode active material that stores and releases lithium ions is held in a current collector, and a negative electrode active material that stores and releases lithium ions in a current collector. And a separator that holds an electrolytic solution in which a lithium salt such as LiBF ₄ or LiPF ₆ is dissolved in an aprotic organic solvent and that is interposed between the positive electrode plate and the negative electrode plate to prevent a short circuit. It is configured.

The electrolyte of a lithium ion secondary battery is generally a mixed solvent of a high dielectric constant solvent such as ethylene carbonate or propylene carbonate and a low viscosity solvent such as dimethyl carbonate or diethyl carbonate, and LiBF ₄ or LiPF ₆ . A solution in which a supporting salt is dissolved is used.

Examples of the positive electrode active material of the lithium ion secondary battery include titanium disulfide, vanadium pentoxide, general formulas Li _x MO ₂ , Li _x M ₂ O ₄ , Li _x MPO ₄ , and Li _x MSiO ₄ (where M is at least one kind) Various compounds represented by the above-mentioned transition metals are being studied.

Among them, lithium cobalt composite oxide, lithium nickel composite oxide, lithium manganese composite oxide, and the like are used as positive electrode active materials because they are charged and discharged at an extremely noble potential of 4 V (vs. Li ^/ Li ⁺ ) or higher. Thus, a lithium ion secondary battery having a high discharge voltage can be realized.

  Materials that can occlude and release lithium ions, including lithium-containing alloys, have been studied as negative electrode active materials for lithium ion secondary batteries. Among these, lithium ion secondary batteries with a long cycle life are used when carbon materials are used. There is an advantage that a secondary battery can be obtained and safety is high, and it is now in practical use.

  Such a lithium ion secondary battery has recently been increasingly used not only in a room temperature environment but also in an electronic device used in a wide temperature range environment. For example, in notebook computers, as the central processing unit increases in speed, the temperature inside the computer increases, and the battery is used for a long time in a high temperature environment. Mobile phones and portable devices are also increasingly used in high temperature environments. Therefore, there is a strong demand for improving the cycle life of lithium ion secondary batteries that are repeatedly used in such a high temperature environment.

  In Patent Document 1, a non-aqueous electrolyte that can provide a battery in which generation of gas and storage capacity reduction during high-temperature storage is suppressed while maintaining high cycle characteristics, and a non-aqueous electrolyte prepared using the non-aqueous electrolyte Providing a battery is described.

JP 2007-005242 A

  With respect to Patent Document 1, a battery in which generation of gas and capacity reduction during high-temperature storage is suppressed is provided, but regarding cycle characteristics, further improvement is desired in order to improve reliability.

  In lithium ion secondary batteries, the electrical and chemical stability of the electrolyte is inadequate, so when charging and discharging are repeated for a long time in a high-temperature environment, the electrolyte decomposition reaction proceeds depending on the conditions. May be consumed and the capacity maintenance rate may decrease.

  That is, the technical problem of the present invention is to provide a lithium ion secondary battery with a good long-term capacity maintenance rate.

（式中、Ｒはアルキル基からなり炭素数は２〜６、またはアルキレン基とメチル基の組合せからなりアルキレン基とメチル基の合計炭素数は３〜６） The lithium ion secondary battery of the present invention is a lithium ion secondary battery having a positive electrode made of a substance that absorbs and releases lithium ions, a negative electrode, and an electrolyte, and the electrolyte contains a substance represented by the chemical formula 1. It is characterized by that.

(In the formula, R is an alkyl group and has 2 to 6 carbon atoms, or a combination of an alkylene group and a methyl group, and the alkylene group and the methyl group have a total carbon number of 3 to 6)

  The lithium ion secondary battery of the present invention is characterized in that the chemical formula 1 is 1,1-ethanediol diacetate or 1,2-propanediol diacetate.

  The lithium ion secondary battery of the present invention is characterized in that the substance represented by Chemical Formula 1 contains 0.0005 mass% or more and 4 mass% or less in the electrolyte.

  The lithium ion secondary battery of the present invention is characterized in that the substance represented by Chemical Formula 1 adheres to the negative electrode in an amount of 0.0008% by mass to 4.5% by mass.

  In the lithium ion secondary battery of the present invention, the substance represented by Chemical Formula 1 contained in the electrolyte has two electron-withdrawing acetyl groups and a methyl group, so that the electrolyte reduction reaction on the surface of the negative electrode active material In order to suppress this, it was confirmed that the consumption of the solvent of the electrolyte was prevented and the long-term cycle life was improved.

  According to the present invention, it is possible to provide a lithium ion secondary battery with a good long-term capacity maintenance rate.

The schematic diagram which shows the structure cross section of the lithium ion secondary battery of this invention.

  An embodiment of the present invention will be described.

  Since the substance represented by Chemical Formula 1 has two acetyl groups with high electron-withdrawing properties, the reduction reaction of the electrolyte on the negative electrode active material surface can be suppressed.

  In addition, the substance represented by Chemical Formula 1 has a methyl group having a high electron-withdrawing property like the acetyl group, and has two functional groups with different electron-withdrawing properties, so that each of them is more efficient than the case where each exists alone In particular, the reduction reaction of the electrolyte can be suppressed. This effect is more effectively manifested by the presence of a methyl group at the R position in Chemical Formula 1.

  Thus, since the decomposition of the electrolyte solvent is suppressed by the substance represented by Chemical Formula 1 acting on the negative electrode, the type of the solvent used for the electrolyte is not limited. R is composed of an alkyl group and has 2 to 6 carbon atoms, or a combination of an alkylene group and a methyl group, except that the total carbon number of the alkylene group and the methyl group is 3 to 6, There is no particular limitation.

When R is an alkyl group, R can be represented by Formula 2. Here, n = 0 to 4.

As an example of the case where R is a combination of an alkylene group and a methyl group, R can be represented by Formula 3. In addition, the total carbon number of R is 3-6, and there may be two or more methyl groups.

  According to the present invention, since the electrolyte contains the substance represented by Chemical Formula 1, the decomposition of the electrolyte on the negative electrode surface is suppressed, and the consumption of the solvent of the electrolyte is prevented. An ion secondary battery can be obtained.

  In the present invention, 1,1-ethanediol diacetate or 1,2-propanediol diacetate can be used as the substance represented by Chemical Formula 1. These compounds are readily available and very easy to handle.

  According to the present invention, since the electrolyte contains 1,1-ethanediol diacetate or 1,2-propanediol diacetate, the consumption of the solvent of the electrolyte is more effectively prevented, and the long-term cycle life is particularly good. A lithium ion secondary battery can be obtained.

  In the present invention, the ratio of the substance represented by Chemical Formula 1 contained in the electrolyte in the electrolyte is in the range of 0.0005% by mass to 4% by mass, preferably 0.004% by mass to 3.6%. It is in the range of not more than mass%, particularly preferably not less than 0.06 mass% and not more than 2.3 mass%, more preferably not less than 0.8 mass% and not more than 1.3 mass%.

  If the content of the substance represented by Chemical Formula 1 is less than 0.0005% by mass, the effect of suppressing the decomposition of the electrolyte solvent in the negative electrode is poor, and the content of the substance represented by Chemical Formula 1 is less than 4% by mass. This is because there is a risk that the discharge characteristics will deteriorate such as an increase in the internal resistance of the battery and a decrease in the capacity retention rate.

  Furthermore, in the present invention, the substance represented by Chemical Formula 1 is preferably attached to the negative electrode in an amount of 0.0008% by mass to 4.5% by mass.

  When the adhesion amount of the negative electrode of the substance represented by the chemical formula 1 is less than 0.0008% by mass, the effect of suppressing the decomposition of the electrolyte solvent in the negative electrode is poor, and the negative electrode adhesion amount of the substance represented by the chemical formula 1 is 4 This is because if it exceeds 0.5 mass%, the discharge characteristics such as an increase in the internal resistance of the battery and a decrease in the capacity retention rate may be deteriorated.

As the positive electrode active material of the lithium ion secondary battery of the present invention, Li _x MO ₂ , Li _y M ₂ O ₄ (where M includes at least one transition metal. 0 ≦ x ≦ 1, 0 ≦ y ≦ 2 ), A metal chalcogenide having a tunnel structure or a layered structure, a metal oxide and a metal sulfide can be used alone or in admixture of two or more. Specific examples thereof include LiCoO ₂ , LiCo _x Ni _1-x O ₂ , LiMnO ₂ , LiMn ₂ O ₄ , LiFePO ₄ , MnO ₂ , TiO ₂ , V ₂ O ₅ , FeS ₂ , TiS ₂ , Li _{1 + x} NiO _2. , LiNi _x Mn _2-x O _{4 and the} like. In particular, it is preferable to use Co, Ni, or Mn as the transition metal M because of the high discharge voltage.

Examples of the negative electrode active material of the lithium ion secondary battery of the present invention include cokes, glassy carbons, graphites, non-graphitizable carbons, pyrolytic carbons, carbon fibers, Al, Si, Pb, Sn, An active material mainly composed of Zn, Cd, Sb or the like, or an alloy of these and lithium, LiFe ₂ O ₃ , WO ₂ , MoO ₂ , SiO, SiO ₂ , CuO, SnO, SnO ₂ , Nb ₃ O ₅ , Li _x Ti _2-x O ₄ (0 ≦ x ≦ 1), metal oxides such as PbO ₂ and PbO ₅ , metal sulfides such as SnS and FeS ₂ , metal lithium, lithium alloys, polyacene, polythiophene, Li ₅ (Li _{3 N), Li 7 MnN 4} , Li 3 FeN 2, Li 2.5 Co 0.5 N, Li 3 lithium nitride such as CoN, or or a single complex thereof with carbon It can be used as a mixture of at least species.

  The electrolyte solvent includes ethylene carbonate, propylene carbonate, butylene carbonate, vinylene carbonate, trifluoropropylene carbonate, γ-butyrolactone, 2-methyl-γ-butyrolactone, acetyl-γ-butyrolactone, γ-valerolactone, sulfolane, 1, 2-dimethoxyethane, 1,2-diethoxyethane, tetrahydrofuran, 2-methyltetrahydrofuran, dimethyltetrahydrofuran, 3-methyl-1,3-dioxolane, methyl acetate, ethyl acetate, methyl propionate, ethyl propionate, dimethyl carbonate, Diethyl carbonate, ethyl methyl carbonate, dipropyl carbonate, methyl propyl carbonate, ethyl isopropyl carbonate, dibutyl carbonate, dimethyl Formamide, dimethyl acetamide, can be used singly or as a mixture of two or more of methyl acetate, acetonitrile. In particular, a mixed system of a cyclic carbonate and a chain carbonate is preferable from the viewpoint of stability to oxidation / reduction.

The electrolyte is used by dissolving the supporting salt in these nonaqueous solvents. LiClO ₄ , LiAsF ₆ , LiPF ₆ , LiBF ₄ , LiCF ₃ SO ₃ , LiCF ₃ CF ₂ SO ₃ , LiCF ₃ CF ₂ CF ₂ SO ₃ , LiN (CF ₃ SO ₂ ) ₂ , LiN (C ₂ F) ₅ SO ₂ ) ₂ , LiPF ₃ (CF ₃ ) ₃ , LiCF ₃ CO ₂ , LiCl, LiBr, LiSCN, or other lithium salts can be used alone or in admixture of two or more. Among them, LiPF ₆ is preferably used as the supporting salt.

  Further, instead of such a liquid electrolyte, an ion conductive polymer electrolyte and an organic electrolyte can be used in combination. Specific examples of the ion conductive polymer electrolyte include polyethers such as polyethylene oxide and polypropylene oxide, polyolefins such as polyethylene and polypropylene, polyvinylidene fluoride, polytetrafluoroethylene, polyvinyl fluoride, polyvinyl chloride, polyvinylidene chloride, Polymethyl methacrylate, polymethyl acrylate, polyvinyl alcohol, polymethacrylonitrile, polyvinyl acetate, polyvinyl pyrrolidone, polycarbonate, polyethylene terephthalate, polyhexamethylene aipamide, polycaprolactam, polyurethane, polyethyleneimine, polybutadiene, polystyrene, polyisoprene and these These derivatives can be used alone or in combination.

  Furthermore, you may use the polymer containing the various monomers which comprise the said polymer. In addition to the polymer electrolyte, an inorganic solid electrolyte, a mixed material of an organic polymer electrolyte and an inorganic solid electrolyte, an inorganic solid powder bound by an organic binder, or the like can be used.

  The lithium ion secondary battery of the present invention is composed of a combination of a positive electrode, a negative electrode, a separator, and an electrolyte. The separator includes a woven fabric, a non-woven fabric, a polyolefin such as polyethylene and polypropylene, a polyimide, and a porous polypropylene. A porous polymer film such as a vinylidene fluoride film or an ion conductive polymer electrolyte film can be used alone or in combination.

  Furthermore, the shape of the battery can be various shapes such as a cylindrical shape, a square shape, a coin shape, a button shape, and a laminate shape. As the material of the battery case, stainless steel, nickel-plated iron, aluminum, titanium, or an alloy thereof and a plated material can be used. As the material of the laminate resin film, aluminum, aluminum alloy, titanium foil, or the like can be used. The material of the heat-welded portion of the metal laminate resin film may be any material as long as it is a thermoplastic polymer material such as polyethylene, polypropylene, polyethylene terephthalate. Further, the metal laminate resin layer and the metal foil layer are not limited to one layer, and may be two or more layers.

  Examples of the present invention are described in detail below.

  An embodiment to which the present invention is applied will be described, but the present invention is not limited to this embodiment, and can be implemented with appropriate modifications within a range not exceeding the gist thereof. FIG. 1 is a schematic view showing a cross section of a lithium ion secondary battery of the present invention.

  As shown in FIG. 1, a layer 12 containing a positive electrode active material capable of occluding and releasing lithium ions on a positive electrode current collector 11 made of metal such as aluminum foil, and a negative electrode current collector made of metal such as copper foil A layer 14 containing a negative electrode active material that occludes and releases lithium ions on 13 is disposed so as to face each other with a separator 15 made of an electrolyte 16 and a nonwoven fabric, polyolefin microporous film, or the like containing the electrolyte 16. Yes.

(Examples 1-8, 17, 18, Reference Examples 1-10 )
A mixture of Li (Li _0.1 Mn _1.9 ) O ₄ and LiNi _0.8 Co _0.15 Al _0.05 O ₂ in a mass ratio of 80:20 is used as the positive electrode active material, and 5% by mass of polyvinylidene fluoride is mixed as the binder. Thus, a positive electrode mixture was prepared and dispersed in N-methyl-2-pyrrolidone to prepare a slurry. The slurry was uniformly applied to both sides of an aluminum current collector having a thickness of 20 μm so as to have a thickness of 95 μm, dried, and then compression molded by a roll press to produce a positive electrode.

  A negative electrode was prepared by mixing 90% by mass of graphite as a negative electrode active material and 10% by mass of polyvinylidene fluoride as a binder to form a negative electrode mixture and dispersing it in N-methyl-2-pyrrolidone. . This slurry was uniformly applied to both sides of a copper current collector having a thickness of 10 μm so as to have a thickness of 80 μm, dried, and then subjected to compression molding with a roll press to produce a negative electrode.

As the separator, a microporous polyethylene film having a thickness of 25 μm was used. As the electrolyte, an electrolytic solution in which ethylene carbonate (EC) and diethyl carbonate (DEC) were mixed at a volume ratio of 30:70 and LiPF ₆ was dissolved at 1.0 mol / l as a lithium salt was used.

1,1-ethanediol diacetate (EDD) or 1,2-propanediol diacetate (PDD) was added to the above electrolytes with varying contents to produce lithium ion secondary batteries. It was set as 1-8, 17, 18, and Reference Examples 1-10 .

  The battery was formed by laminating a positive electrode and a negative electrode via a separator to obtain a laminated exterior type lithium ion secondary battery. The discharge capacity of the produced battery was 98 mAh.

  Next, a charge / discharge cycle test of these batteries was performed. At a temperature of 60 ° C., the charging condition is a constant current constant voltage method, the charging end voltage is 4.2 V, the charging current is 98 mA, the total charging time is 2.5 hours, the discharging condition is constant current discharging, the discharge end voltage is 3.0 V, Charging / discharging was performed with a discharge current of 98 mA. The cycle test was performed 500 cycles.

  Furthermore, the negative electrode after the cycle test was analyzed using a gas chromatograph mass spectrometer (GC-MS) to determine the amount of 1,1-ethanediol diacetate or 1,2-propanediol diacetate adhering to the negative electrode. went.

(Comparative Examples 1-4)
Except that nothing was added to the above electrolyte solution, or 1,2-ethanediol acetate (12EDD) not corresponding to Chemical Formula 1 was added at different contents, Examples 1 to 8, 17, 18, Reference Examples 1 to 10 were prepared as Comparative Examples 1 to 4, respectively.

  The battery was formed by laminating a positive electrode and a negative electrode via a separator to obtain a laminated exterior type lithium ion secondary battery. The discharge capacity of the produced battery was 98 mAh.

  Next, a charge / discharge cycle test of these batteries was performed.

  Furthermore, the negative electrode after the cycle test was analyzed using a gas chromatograph mass spectrometer (GC-MS), and 1,1-ethanediol diacetate, 1,2-propanediol diacetate or 1,1 attached to the negative electrode Quantification of 2-ethanediol acetate was performed.

Table 1 shows the capacity retention after 500 cycles and the adhesion amount to the negative electrode with respect to the additives and contents in Examples 1 to 8, 17, 18, Reference Examples 1 to 10 and Comparative Examples 1 to 4.

  In the “Additives” column of Table 1, EDD represents 1,1-ethanediol diacetate, PDD represents 1,2-propanediol diacetate, and 12EDD represents 1,2-ethanediol diacetate. The “content” column is the mass ratio (%) of 1,1-ethanediol diacetate, 1,2-propanediol diacetate or 1,2-ethanediol diacetate to the total mass of the electrolyte. The “capacity maintenance rate after 500 cycles” column is the ratio of the discharge capacity (mAh) after 500 cycles to the discharge capacity (mAh) at the 10th cycle. “Adhesion amount to negative electrode” column is 1,1-ethanediol diacetate, 1,2-propanediol diacetate or 1,2-ethane relative to the mass of the electrode portion excluding the mass of the current collector of the negative electrode. It represents the mass ratio (%) of diol diacetate.

From Table 1, Examples 1-8, 17, 18, and Reference Examples 1-10 by which the electrolyte contains EDD or PDD represented by Chemical Formula 1 are batteries using non-aqueous electrolytes that do not contain them at all ( It was confirmed that the capacity retention ratio was improved as compared with the batteries (Comparative Examples 2 to 4) to which Comparative Example 1) and 1,2-ethanediol acetate (12EDD) not corresponding to Chemical Formula 1 were added.

Of these, the content of 1,1-ethanediol diacetate (EDD) or 1,2-propanediol diacetate (PDD) in the electrolytic solution is 0.0005% by mass or more with respect to the electrolyte mass other than EDD or PDD. In batteries ( Examples 1-8, Reference Examples 1-8 ) using a nonaqueous electrolyte solution of 4% by mass or less, a battery (Comparative Example 1) using a nonaqueous electrolyte solution that does not contain these at all When compared with a battery (Comparative Examples 2 to 4) to which 1,2-ethanediol acetate (12EDD) not corresponding to Chemical Formula 1 was added, it was confirmed that the capacity retention rate after the cycle test was particularly improved and preferable. .

Even when the content of EDD and PDD is as low as 0.0001% by mass (Example 17, Reference Example 9 ), the capacity retention after the cycle test is improved as compared with Comparative Examples 1 to 4. In addition, the effect of including EDD, PDD and the like in the electrolytic solution was observed.

Furthermore, even when the content of EDD and PDD is as high as 5% by mass (Example 18, Reference Example 10 ), the discharge characteristics are not deteriorated due to an increase in internal resistance, etc. Compared with Comparative Examples 1 to 4. Thus, the capacity retention after the cycle test was improved, and the effect of including EDD, PDD and the like in the electrolytic solution was observed.

When the negative electrode after the cycle test was analyzed using GC-MS, in Examples 1 to 8 and Reference Examples 1 to 8 in which the capacity retention ratio was particularly improved, EDD and PDD were 0.0008 mass% or more, 4 Less than 5% by mass was detected. It is considered that EDD and PDD present in these negative electrodes acted to suppress the decomposition of the electrolyte.

  When 1,2-ethanediol diacetate was contained in the electrolyte (Comparative Examples 2 to 4), the negative electrode after the cycle test was analyzed using GC-MS. In spite of the detection of 02% or more and 1.4% or less, the capacity retention rate after the cycle test was similar to that of Comparative Example 1. 1,2-ethanediol diacetate has the same structure as Chemical Formula 1, but does not have a methyl group at the R position, so it has little effect of inhibiting the decomposition of the electrolyte, and maintains its capacity like EDD and PDD. It is thought that the rate did not improve. From the above results, it can be considered that a particularly high capacity retention improvement effect was obtained by having a structure represented by Chemical Formula 1 and further having a methyl group at the R position.

(Examples 21-28, 37, 38, Reference Examples 11-20 , Comparative Example 5)
The same conditions as in Examples 1-8, 17, 18, Reference Examples 1-10 , and Comparative Example 1 except that the positive electrode active material LiNi _0.8 Co _0.15 Al _0.05 O ₂ was 100% and the negative electrode active material was surface-treated graphite. Thus, batteries were prepared as Examples 21 to 28, 37, and 38, Reference Examples 11 to 20, and Comparative Example 5, respectively. A charge / discharge cycle test was performed, and the negative electrode after the cycle test was quantified for EDD or PDD present in the negative electrode using GC-MS. Table 2 shows the results of the capacity retention rate after 500 cycles and the amount of adhesion to the negative electrode. The column “Amount of adhesion to negative electrode” represents the mass ratio (%) of EDD or PDD to the mass of the negative electrode.

From Table 2, even when the positive electrode active material LiNi _0.8 Co _0.15 Al _0.05 O ₂ is 100% and the negative electrode active material is surface-treated graphite, the electrolyte contains EDD or PDD represented by Chemical Formula 1. As a result, it was confirmed that the capacity retention rate was improved as compared with the battery using the non-aqueous electrolyte not containing these at all (Comparative Example 5), and the effect of the present invention did not depend on the positive electrode / negative electrode active material. It was confirmed.

Of these, a battery using a non-aqueous electrolyte in which the content of EDD or PDD in the electrolyte is 0.0005 mass% or more and 4 mass% or less with respect to the electrolyte mass other than EDD or PDD (Examples 21 to 21). 28, Reference Examples 11 to 18 ), it was confirmed that the capacity retention rate after the cycle test was particularly improved as compared with the battery (Comparative Example 5) using a non-aqueous electrolyte not containing any of them. It was done.

Even when the content of EDD or PDD is as low as 0.0001 mass% (Example 37, Reference Example 19 ), the capacity retention after the cycle test is improved as compared with Comparative Example 5. The effect of including EDD, PDD and the like in the electrolytic solution was observed.

Furthermore, even when the content of EDD and PDD is as large as 5% by mass (Example 38, Reference Example 20 ), the discharge characteristics are not deteriorated due to an increase in internal resistance, etc. Compared to Comparative Example 5, The capacity retention after the cycle test was improved, and the effect of including EDD, PDD and the like in the electrolyte was observed.

When the negative electrode after the cycle test was analyzed using GC-MS, in Examples 21 to 28 and Reference Examples 11 to 18 in which the capacity retention ratio was particularly improved, EDD and PDD were 0.0009 mass% or more, 4 .49% by mass or less was detected. It is considered that EDD and PDD present in these negative electrodes acted to suppress the decomposition of the electrolyte.

(Examples 41-48, 57, 58, Reference Examples 21-30 , Comparative Example 6)
Examples 1 to 8 except that propylene carbonate (PC) and methyl acetate (MA), which are electrolytes, were mixed at a volume ratio of 40:60, and an electrolytic solution in which LiPF ₆ was dissolved at 1.0 mol / l as a lithium salt was used . Batteries were produced under the same conditions as in Examples 17 and 18, Reference Examples 1 to 10 and Comparative Example 1, and Examples 41 to 48, 57 and 58, Reference Examples 21 to 30 and Comparative Example 6 were used, respectively. A charge / discharge cycle test was performed, and the negative electrode after the cycle test was quantified for EDD or PDD present in the negative electrode using GC-MS. Table 3 shows the results of the capacity retention rate after 500 cycles and the amount of adhesion to the negative electrode. The column “Amount of adhesion to negative electrode” represents the mass ratio (%) of EDD or PDD to the mass of the negative electrode.

From Table 3, even when an electrolyte solution in which propylene carbonate (PC) and methyl acetate (MA), which are electrolytes, were mixed at a volume ratio of 40:60 and LiPF ₆ was dissolved at 1.0 mol / l as a lithium salt was used, the electrolyte Is confirmed to contain an EDD or PDD represented by the chemical formula 1, and the capacity retention rate is improved as compared with a battery using a non-aqueous electrolyte containing no EDD or PDD (Comparative Example 6). It was confirmed that the effect of the invention does not depend on the type of electrolyte.

Of these, a battery using a non-aqueous electrolyte in which the content of EDD or PDD in the electrolyte is 0.0005 mass% or more and 4 mass% or less with respect to the electrolyte mass other than EDD or PDD (Examples 41 to 41). 48, Reference Examples 21 to 28 ), it was confirmed that the capacity retention rate after the cycle test was particularly improved as compared with the battery using the non-aqueous electrolyte not containing these (Comparative Example 6). It was done.

Even when the content of EDD or PDD is as small as 0.0001 mass% (Example 57, Reference Example 29 ), the capacity retention after the cycle test is improved as compared with Comparative Example 6. The effect of including EDD, PDD and the like in the electrolytic solution was observed.

Furthermore, even when the content of EDD and PDD is as large as 5% by mass (Example 58, Reference Example 30 ), the discharge characteristics are not deteriorated due to an increase in internal resistance, etc. Compared with Comparative Example 6, The capacity retention after the cycle test was improved, and the effect of including EDD, PDD and the like in the electrolyte was observed.

When the negative electrode after the cycle test was analyzed using GC-MS, in Examples 41 to 48 and Reference Examples 21 to 28 in which the capacity retention ratio was particularly improved, EDD and PDD were 0.001% by mass or more, 4 Less than 5% by mass was detected. It is considered that EDD and PDD present in these negative electrodes acted to suppress the decomposition of the electrolyte.

  From this, it was confirmed that the capacity retention rate was improved by including the substance represented by Chemical Formula 1 in the electrolyte of the lithium ion secondary battery.

  Further, it was confirmed that the capacity retention rate was particularly improved by containing 0.005 mass% or more and 4 mass% or less of the substance represented by Chemical Formula 1 in the electrolyte of the lithium ion secondary battery.

  Further, it was confirmed that the capacity retention rate was particularly improved by adhering the substance represented by Chemical Formula 1 to 0.0008 mass% or more and 4.5 mass% or less to the negative electrode of the lithium secondary battery.

  Considering the examples comprehensively, it was found that the present invention can provide a lithium ion secondary battery with a good long-term capacity retention rate.

The embodiments of the present invention have been described above using the embodiments. However, the present invention is not limited to these embodiments, and the present invention is not limited to the scope of the present invention. Included in the invention. That is, various changes and modifications that can be naturally made by those skilled in the art are also included in the present invention.

DESCRIPTION OF SYMBOLS 11 Positive electrode collector 12 Layer containing positive electrode active material 13 Negative electrode collector 14 Layer containing negative electrode active material 15 Separator 16 Electrolyte

Claims (3)

A lithium ion secondary battery having a positive electrode made of a substance that absorbs and releases lithium ions, a negative electrode, and an electrolyte,
A lithium ion secondary battery, wherein the electrolyte contains 1,1-ethanediol diacetate . The 1,1-ethanediol diacetate, the electrolyte 0.0005 mass% or more in 4 wt% or less, a lithium ion secondary battery according to claim 1, wherein the free Murrell. The 1,1-ethanediol diacetate, the negative electrode in 0.0008 mass% or more, 4.5 wt% or less, a lithium ion secondary battery according to claim 1 or 2, characterized in that attachment.

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