JP2009301989A - Nonaqueous electrolyte and lithium ion secondary battery equipped therewith - Google Patents

Abstract

To improve cycle characteristics in repeated charge / discharge in a lithium ion secondary battery.
A lithium ion secondary battery includes a positive electrode having a positive electrode active material, a negative electrode having a negative electrode active material, and a non-aqueous electrolyte solution that is interposed between the positive electrode and the negative electrode to conduct lithium ions. It is equipped with. This nonaqueous electrolytic solution 20 includes an electrolyte salt containing lithium, lithium bis (oxalato) borate, divinyltetraalkyldisiloxane (alkyl having 1 to 4 carbon atoms), and a carbon chain having an unsaturated bond. And carbonate (preferably a carbon chain having 1 to 4 carbon atoms, such as vinylene carbonate) as an additional component. The amount of lithium bis (oxalato) borate, divinyltetramethyldisiloxane, and carbonate having a carbon chain having an unsaturated bond is preferably 0.05% by weight or more and 10% by weight or less.
[Selection] Figure 1

Description

  The present invention relates to a non-aqueous electrolyte and a lithium ion secondary battery including the same.

Conventionally, as a non-aqueous electrolyte used in a lithium ion secondary battery, by adding a silicon compound having an unsaturated bond to the electrolyte, the rate of change in electric capacity and internal resistance is small during repeated charging and discharging, and The thing which was excellent in the cycle characteristic and low temperature characteristic that an internal resistance increase at the time of low temperature is small and maintains a high electrical capacitance is proposed (for example, refer patent document 1).
JP 2002-134169 A

  However, the non-aqueous electrolyte described in Patent Document 1 has excellent cycle characteristics by adding a silicon compound, but it is not yet sufficient, and one having higher cycle characteristics has been desired. .

  The present invention has been made in view of such problems, and mainly provides a non-aqueous electrolyte that can further improve cycle characteristics in repeated charge and discharge, and a lithium ion secondary battery including the same. Objective.

  As a result of diligent research to achieve the above-mentioned object, the present inventors have further added an additive component containing lithium bis (oxalato) borate and divinyltetraalkyldisiloxane (the alkyl has 1 to 4 carbon atoms). Assuming that a carbonate having a carbon chain having an unsaturated bond is added, it has been found that the cycle characteristics in repeated charge and discharge can be further improved, and the present invention has been completed.

That is, the non-aqueous electrolyte of the present invention is
A non-aqueous electrolyte containing an electrolyte salt containing lithium and used for a lithium ion secondary battery,
The additive component includes lithium bis (oxalato) borate, divinyltetraalkyldisiloxane (alkyl having 1 to 4 carbon atoms), and a carbonate having a carbon chain having an unsaturated bond.

The lithium ion secondary battery of the present invention is
A positive electrode having a positive electrode active material;
A negative electrode having a negative electrode active material;
The non-aqueous electrolyte described above that is interposed between the positive electrode and the negative electrode and conducts lithium ions;
It is equipped with.

  In this non-aqueous electrolyte and a lithium ion secondary battery including the non-aqueous electrolyte, cycle characteristics in repeated charge / discharge can be further improved. The reason why such an effect is obtained is not clear, but is presumed as follows. For example, lithium bis (oxalato) borate forms a film on the surface of the negative electrode active material during the initial charge, prevents the deactivation of lithium ion migration on the surface of the negative electrode active material during charge and discharge, and suppresses battery capacity reduction. It is thought that it can be done. In addition, divinyltetraalkyldisiloxane has a Si—O bond and has an affinity for the positive electrode active material, and since it has an unsaturated bond, it is a compound that is easily self-polymerized. Accordingly, it is considered that a stable coating is formed by polymerization reaction on the surface of the positive electrode, and an increase in resistance at the positive electrode / electrolyte interface accompanying the charge / discharge cycle can be suppressed. In addition, a carbonate having a carbon chain having an unsaturated bond has an affinity with a film formed of lithium bis (oxalato) borate at the time of initial charge, and is easily self-polymerized because it has an unsaturated bond. It is a compound, and it is considered that a stable film is formed by polymerization reaction on the negative electrode surface as charging and discharging are repeated, and the increase in resistance at the positive electrode / electrolyte interface accompanying charging / discharging cycles can be further suppressed. And it is guessed that the effect by each compound is exhibited synergistically and there exists the effect mentioned above. Here, the “additional component” refers to a component having a small proportion in the non-aqueous electrolyte, such as a proportion in the non-aqueous electrolyte of 30% by weight or less or 20% by weight or less. In addition, as “cycle characteristics”, for example, a charge / discharge capacity maintenance ratio indicating a degree of suppression of a decrease in battery capacity after repeated charge / discharge, a battery resistance increase rate indicating a degree of increase in battery resistance after repeated charge / discharge, and the like. Can be mentioned.

  A lithium ion secondary battery of the present invention includes a positive electrode having a positive electrode active material, a negative electrode having a negative electrode active material, and a non-aqueous electrolyte that is interposed between the positive electrode and the negative electrode and conducts lithium ions. . The non-aqueous electrolyte solution includes an electrolyte salt containing lithium, lithium bis (oxalato) borate, divinyltetraalkyldisiloxane (alkyl having 1 to 4 carbon atoms), and a carbon chain having an unsaturated bond. Carbonate (hereinafter also referred to as unsaturated carbon chain carbonate) is included as an additive component.

The positive electrode of the lithium ion secondary battery of the present invention is prepared by mixing a positive electrode active material, a conductive material, and a binder, and adding a suitable solvent to form a paste-like positive electrode material on the surface of the current collector. It may be formed by coating and drying, and compressing to increase the electrode density as necessary. As the positive electrode active material, a sulfide containing a transition metal element, an oxide containing lithium and a transition metal element, or the like can be used. Specifically, transition metal sulfides such as TiS ₂ , TiS ₃ , MoS ₃ , FeS ₂ , Li _x MnO ₂ (0.5 ≦ x ≦ 1.5, etc.), Li _x Mn ₂ O _4, etc. Lithium manganese composite oxide, lithium cobalt composite oxide such as Li _x CoO ₂ , lithium nickel composite oxide such as Li _x NiO ₂ , lithium vanadium composite oxide such as LiV ₂ O ₃ , transition such as V ₂ O ₅ A metal oxide or the like can be used. Of these, lithium transition metal composite oxides and lithium transition metal phosphates are preferred. The conductive material is for ensuring the electrical conductivity of the positive electrode. For example, one or two kinds of graphite such as natural graphite and artificial graphite, carbon black such as acetylene black, and amorphous carbon such as needle coke are used. What mixed the above can be used. The binder plays a role of connecting the active material particles and the conductive material particles. For example, the binder is a fluorine-containing resin such as polytetrafluoroethylene, polyvinylidene fluoride, or fluororubber, or a thermoplastic resin such as polypropylene or polyethylene. Etc. can be used. In addition, an aqueous dispersion of a cellulose-based or styrene-butadiene rubber that is an aqueous binder can also be used. Examples of the solvent for dispersing the positive electrode active material, the conductive material, and the binder include N-methylpyrrolidone, dimethylformamide, dimethylacetamide, methyl ethyl ketone, cyclohexanone, methyl acetate, methyl acrylate, diethyltriamine, and N, N-dimethylaminopropyl. Organic solvents such as amine, ethylene oxide, and tetrahydrofuran can be used. As the current collector, foil of aluminum, stainless steel, nickel plated steel, or the like can be used.

  The negative electrode of the lithium ion secondary battery of the present invention is prepared by mixing a negative electrode active material, a conductive material, and a binder, and adding a suitable solvent to form a paste-like negative electrode material on the surface of the current collector. It may be formed by coating and drying, and compressing to increase the electrode density as necessary. As the negative electrode active material, a carbonaceous material capable of inserting and extracting lithium ions can be used. The carbonaceous material is not particularly limited, but graphite, petroleum-based coke, coal-based coke, petroleum-based pitch carbide, coal-based pitch carbide, phenolic resin, crystalline cellulose cellulose resin, and the like. Examples include carbonized carbon, furnace black, acetylene black, pitch-based carbon fiber, and PAN-based carbon fiber. In addition, as the conductive material, binder, solvent, and the like used for the negative electrode, those exemplified for the positive electrode can be used. Further, a conductive material may not be used. For the current collector of the negative electrode, a foil such as copper, nickel, stainless steel, or nickel-plated steel can be used.

  The lithium ion secondary battery of the present invention may include a separator between the negative electrode and the positive electrode. The separator can be used without particular limitation as long as it is a material that can withstand the use range of the secondary battery, such as a microporous film of a polymer compound. For example, polyethylene, polypropylene, polyvinylidene fluoride, polyvinylidene chloride, polyacrylonitrile, polyacrylamide, polytetrafluoroethylene, polysulfone, polyethersulfone, polycarbonate, polyamide, polyimide, polyethylene oxide, polypropylene oxide and other polyethers, carboxymethylcellulose And celluloses such as hydroxypropyl cellulose, polymer compounds mainly composed of poly (meth) acrylic acid and various esters thereof, derivatives thereof, and films made of copolymers or mixtures thereof. These may be used alone or as a multilayer film in which a plurality of films are superposed. These films may contain, for example, an additive that enhances ion conductivity and various additives that enhance strength and corrosion resistance. Of these microporous films, polyethylene, polypropylene, polyvinylidene fluoride, polysulfone and the like are preferably used. This separator is preferably microporous so that the non-aqueous electrolyte can penetrate and ions can easily pass therethrough. This microporosification method includes the “phase separation method” in which a film of the above polymer compound and a solvent is formed while microphase separation is performed, and the solvent is extracted and removed to make it porous. There is a “stretching method” in which a film is formed by extrusion and then heat-treated to arrange crystals in one direction, and a gap is formed between the crystals by stretching to make it porous.

  The non-aqueous electrolyte of the lithium ion secondary battery of the present invention contains lithium bis (oxalato) borate as an additive component. The content of lithium bis (oxalato) borate is more preferably 0.05% by weight to 10% by weight, and still more preferably 0.2% by weight to 5% by weight. If this content is 0.05% by weight, the effect of suppressing a decrease in battery capacity upon repeated charge / discharge can be exhibited, and if it is 10% by weight or less, the content of lithium bis (oxalato) borate By suppressing the resistance, it is possible to suppress an increase in resistance due to the film formed on the electrode. When the content is 0.2 wt% or more and 5 wt% or less, the above effect can be obtained. Here, the content of lithium bis (oxalato) borate refers to a value of an addition ratio (wt%) with respect to 100 wt% of a mixed solution of an organic solvent and an electrolyte salt containing lithium. .

  In addition, this nonaqueous electrolytic solution contains divinyltetraalkyldisiloxane (alkyl having 1 to 4 carbon atoms) as an additive component. The content of the divinyltetraalkyldisiloxane is more preferably 0.05% by weight or more and 10% by weight or less, and further preferably 0.2% by weight or more and 5% by weight or less. If this content is 0.05 wt%, the effect of suppressing an increase in battery resistance when charging and discharging is repeated can be exhibited, and if it is 10 wt% or less, the content of divinyltetraalkyldisiloxane is reduced. By suppressing it more, an increase in resistance due to the film formed on the electrode can be suppressed. When the content is 0.2 wt% or more and 5 wt% or less, the above effect can be obtained. The divinyltetraalkyldisiloxane preferably has a smaller alkyl group carbon number, and divinyltetramethyldisiloxane can be suitably used. Here, the content of divinyltetraalkyldisiloxane is 100% by weight of a mixed solution of an organic solvent and an electrolyte salt containing lithium, and is a value of an addition ratio (% by weight) with respect to 100% by weight.

  Moreover, this non-aqueous electrolyte contains an unsaturated carbon chain carbonate as an additive component. The unsaturated carbon chain carbonate preferably has a smaller carbon chain, and more preferably has 1 to 4 carbon atoms. Examples of the unsaturated carbon chain carbonate include vinylene carbonate, vinyl ethylene carbonate, and vinyl propylene carbonate. Among these, vinylene carbonate is preferable. The content of the unsaturated carbon chain carbonate is more preferably 0.05% by weight or more and 10% by weight or less, and further preferably 0.2% by weight or more and 5% by weight or less. If this content is 0.05% by weight, the effect of suppressing a decrease in battery capacity and an increase in battery resistance upon repeated charge / discharge can be exhibited, and if it is 10% by weight or less, an unsaturated carbon chain. By suppressing the carbonate content more, it is possible to suppress an initial increase in battery resistance caused by the addition of the unsaturated carbon chain carbonate. When the content is 0.2 wt% or more and 5 wt% or less, the above effect can be obtained. Here, the content of the unsaturated carbon chain carbonate refers to a value of an addition ratio (% by weight) with respect to 100% by weight of a mixed solution of an organic solvent and an electrolyte salt containing lithium.

  The lithium bis (oxalato) borate, divinyltetraalkyldisiloxane, and unsaturated carbon chain carbonate can be used within the above ranges, respectively, but lithium bis (oxalato) borate, divinyltetraalkyldisiloxane, and unsaturated carbon chain. The total amount of carbonate is preferably 30% by weight or less, more preferably 20% by weight or less, further preferably 15% by weight or less, and further preferably 6% by weight or less. . From the viewpoint of the relationship between the content and the effect to be obtained and the cost, it is more preferable to add at 0.1 wt% to 2.0 wt%.

  In the non-aqueous electrolyte solution of the lithium ion secondary battery of the present invention, the above-described additive components are dissolved in an organic solvent. As the organic solvent, carbonates, lactones, ethers, sulfolanes, dioxolanes and the like can be used. Specifically, cyclic carbonates such as ethylene carbonate, propylene carbonate, and butylene carbonate as carbonates, dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, ethyl-n-butyl carbonate, methyl-t-butyl carbonate, di-i- Sulfolanes such as chain carbonates such as propyl carbonate and t-butyl-i-propyl carbonate, lactones such as γ-butyllactone and γ-valerolactone, ethers such as dimethoxyethane, ethoxymethoxyethane, and diethoxyethane As sulfolane, tetramethylsulfolane and the like, and as dioxolane, 1,3-dioxolane and the like can be mentioned. Among these, the combination of cyclic carbonates and chain carbonates is preferable. According to this combination, not only the cycle characteristics representing the battery characteristics in repeated charge and discharge are excellent, but also the viscosity of the electrolyte, the electric capacity of the obtained battery, the battery output, etc. should be balanced. it can. The cyclic carbonates are considered to have a relatively high relative dielectric constant and increase the dielectric constant of the electrolytic solution, and the chain carbonates are considered to suppress the viscosity of the electrolytic solution.

Examples of the electrolyte salt included in the lithium ion secondary battery of the present invention include LiPF ₆ , LiBF ₄ , LiAsF ₆ , LiCF ₃ SO ₃ , LiN (CF ₃ SO ₂ ) ₂ , and LiC (CF ₃ SO ₂ ) _{3. , LiSbF 6, LiSiF 6, LiAlF} 4, LiSCN, LiClO 4, LiCl, LiF, LiBr, LiI, and the like LiAlCl _4. Among these, from the group consisting of inorganic salts such as LiPF ₆ , LiBF ₄ , LiAsF ₆ , LiClO ₄ , and organic salts such as LiCF ₃ SO ₃ , LiN (CF ₃ SO ₂ ) ₂ , LiC (CF ₃ SO ₂ ) _3. It is preferable from the viewpoint of electrical characteristics to use a combination of one or two or more selected salts. This electrolyte salt preferably has a concentration in the non-aqueous electrolyte of 0.1 mol / L or more and 3.0 mol / L or less, and more preferably 0.5 mol / L or more and 2.0 mol / L or less. When the concentration of the electrolyte salt is 0.1 mol / L or more, a sufficient current density can be obtained, and when the concentration is 3.0 mol / L or less, the electrolytic solution can be made more stable. Moreover, you may add flame retardants, such as a phosphorus type and a halogen type, to this non-aqueous electrolyte. Specifically, this flame retardant is phosphorous, for example, phosphoric esters such as trimethyl phosphate and triethyl phosphate, melamine polyphosphate and ammonium polyphosphate, polyethylene phosphate ethylenediamine, polyphosphate hexamethylenediamine, Polyphosphoric acids such as polyphosphate piperazine salts can be used. The content of the flame retardant is preferably 5 parts by weight or more and 100 parts by weight or less, and more preferably 10 parts by weight or more and 50 parts by weight or less with respect to 100 parts by weight of the total organic solvent constituting the nonaqueous electrolytic solution. When the content of the flame retardant is 5 parts by weight or more, a sufficient flame retardant effect is obtained, and when the content is 100 parts by weight or less, an increase in resistance of the electrolytic solution can be further suppressed.

  The shape of the lithium ion secondary battery of the present invention is not particularly limited, and examples thereof include a coin type, a button type, a sheet type, a laminated type, a cylindrical type, a flat type, and a square type. Moreover, you may apply to the large sized thing etc. which are used for an electric vehicle etc. FIG. 1 is a schematic view showing an example of a lithium ion secondary battery 10 of the present invention. The lithium ion secondary battery 10 includes a positive electrode sheet 13 in which a positive electrode active material 12 is formed on a current collector 11, a negative electrode sheet 18 in which a negative electrode active material 17 is formed on the surface of the current collector 14, a positive electrode sheet 13 and a negative electrode A separator 19 provided between the sheet 18 and a nonaqueous electrolytic solution 20 that fills between the positive electrode sheet 13 and the negative electrode sheet 18 are provided. In this lithium ion secondary battery 10, a separator 19 is sandwiched between a positive electrode sheet 13 and a negative electrode sheet 18, and these are wound and inserted into a cylindrical case 22, and a positive electrode terminal 24 and a negative electrode sheet connected to the positive electrode sheet 13. And a negative electrode terminal 26 connected to each other. This nonaqueous electrolytic solution 20 is an electrolyte salt containing lithium, 0.05 wt% or more and 10 wt% or less of lithium bis (oxalato) borate, and 0.05 wt% or more and 10 wt% or less of an organic solvent. Divinyltetramethyldisiloxane and 0.05% by weight or more and 10% by weight or less of vinylene carbonate are contained as additive components.

  It should be noted that the present invention is not limited to the above-described embodiment, and it goes without saying that the present invention can be implemented in various modes as long as it belongs to the technical scope of the present invention.

  Below, the example which produced the lithium ion secondary battery concretely is demonstrated as an experiment example.

[Production of lithium ion secondary battery]
85% by weight of LiNiO ₂ as a positive electrode active material, 10% by weight of acetylene black as a conductive material, 5% by weight of polyvinylidene fluoride as a binder, and an appropriate amount of N-methyl-2-pyrrolidone as a dispersant is added, A slurry-like positive electrode material was obtained. This positive electrode material slurry was uniformly applied on both surfaces of a 20 μm thick aluminum foil current collector, and dried by heating to prepare a positive electrode coated sheet. Thereafter, the coated sheet was pressed, cut into a rectangular shape of a predetermined size, and the positive electrode material at a portion to be a lead tab weld for extracting current was peeled off to obtain a sheet-like positive electrode. A negative electrode active material was mixed with 95% by weight of carbon material powder and 5% by weight of polyvinylidene fluoride as a binder, and a negative electrode slurry was prepared in the same manner as the positive electrode. This was uniformly applied to both sides of a 10 μm thick copper foil current collector And dried by heating to prepare a negative electrode coated sheet. Thereafter, this coated sheet was pressed, cut into a rectangular shape of a predetermined size, and the negative electrode material in a portion to be a lead tab weld for extracting current was peeled off to obtain a sheet-like negative electrode. These positive electrode and negative electrode are wound around a separator made of a microporous polyethylene film having a thickness of 25 μm to form a roll-shaped electrode body, and this roll-shaped electrode body is inserted into a 18650-type cylindrical case. Kept inside. At this time, the current collecting leads connected to the lead tab welds of the positive electrode and the negative electrode were respectively joined to the positive electrode terminal and the negative electrode terminal provided in the case. Thereafter, a non-aqueous electrolyte described later was poured into the case and sealed to obtain a cylindrical lithium ion secondary battery (see FIG. 1). The lithium ion secondary batteries of Experimental Examples 1 to 13 were obtained by changing the content of the nonaqueous electrolyte.

[Experiment 1]
As a non-aqueous electrolyte, LiPF ₆ was mixed with 1 mol / L of a mixed solvent in which ethylene carbonate (EC), dimethyl carbonate (DMC), and ethyl methyl carbonate (EMC) were mixed at a volume ratio of 1: 1: 1. A lithium ion secondary battery manufactured by using one dissolved at a concentration was set as Experimental Example 1.

[Experimental Examples 2-9]
A lithium ion secondary battery produced using 1.0% by weight of vinylene carbonate added to the nonaqueous electrolytic solution used in Experimental Example 1 was designated as Experimental Example 2. Further, 0.05% by weight, 0.20% by weight, 1.0% by weight, and 2.0% by weight of lithium bis (oxalato) borate and divinyltetramethyldisiloxane were added to the non-aqueous electrolyte used in Experimental Example 2, respectively. Lithium ion secondary batteries produced using those added with 5.0%, 5.0% by weight, and 10.0% by weight were designated as Experimental Examples 3 to 8, respectively. In addition, a lithium ion secondary battery produced by using 1.0% by weight of lithium bis (oxalato) borate and divinyltetramethyldisiloxane added to the nonaqueous electrolytic solution used in Experimental Example 1 is shown in Experimental Example 9. It was.

[Experimental Examples 10 and 11]
A lithium ion secondary battery produced by using 1.0% by weight of vinyl ethylene carbonate added to the nonaqueous electrolytic solution used in Experimental Example 1 was designated as Experimental Example 10. In addition, a lithium ion secondary battery manufactured by adding 1.0% by weight of lithium bis (oxalato) borate and divinyltetramethyldisiloxane to the nonaqueous electrolytic solution used in Experimental Example 10 was used in Experimental Example 11. It was.

[Experimental Examples 12 and 13]
A lithium ion secondary battery produced using 1.0% by weight of vinyl propylene carbonate added to the nonaqueous electrolytic solution used in Experimental Example 1 was designated as Experimental Example 12. Further, a lithium ion secondary battery produced by using 1.0% by weight of lithium bis (oxalato) borate and divinyltetramethyldisiloxane added to the nonaqueous electrolytic solution used in Experimental Example 12 was tested in Experimental Example 13. It was.

[Initial discharge capacity]
The lithium ion secondary batteries of Examples 1 to 13 were prepared, after the constant-current charging at 0.2 mA / cm ² up to 4.1 V, was constant current discharge to 3.0V at 0.2 mA / cm ² . Then, after charging at 0.2 mA / cm ² up to 4.1 V, a constant current discharge to 3.0V at 0.1 mA / cm ^2, and the discharge capacity at this time as the initial discharge capacity V0. The measurement was performed in an atmosphere at 20 ° C.

[High-temperature cycle characteristics test, discharge capacity maintenance rate]
Put a lithium ion secondary battery of the Experimental Examples 1 to 13 in a thermostat at ambient temperature 60 ° C., and a constant current charging to 4.1V at a discharge current 2.0 mA / cm ^2, at a discharge current of 2.0 mA / cm ² A high temperature cycle characteristic test was performed in which charging / discharging for performing a constant current discharge up to 3.0 V was defined as one cycle, and this cycle was performed for a total of 500 cycles. Thereafter the high-temperature cycle characteristics test, the atmospheric temperature 20 ° C., after which a constant current charged at 0.2 mA / cm ² up to 4.1 V, was constant current discharge to 3.0V at 0.2 mA / cm ^2. Then, after charging at 0.2 mA / cm ² up to 4.1 V, a constant current discharge at 0.1 mA / cm ² up to 3.0 V, and the discharge capacity at this time as a cycle after the discharge capacity Vc. Using the discharge capacity Vc after the cycle and the initial discharge capacity V0, the discharge capacity retention ratio Vk (%) was obtained by the following equation (1).
Discharge capacity retention rate Vk (%) = Vc / V0 × 100 (1)

[Battery resistance increase rate]
Using the lithium ion secondary batteries of Experimental Examples 1 to 13, the battery resistance increase rate Rin when the charge / discharge cycle was repeated was determined. The battery resistance was 20 ° C., constant current and constant voltage charge to 3.7 V at a charge current of 0.2 mA / cm ² , then constant current discharge at a discharge current of 10 mA / cm ² , and the voltage after 10 seconds was measured. Obtained by voltage drop. The value measured before the high temperature cycle characteristic test was defined as the initial battery resistance R0, and the value measured after the high temperature cycle characteristic test was defined as the battery resistance Rc after cycling. Using the battery resistance Rc and the initial battery resistance R0 after this cycle, the battery resistance increase rate Rin was obtained by the following equation (2).
Battery resistance increase rate Rin (%) = (Rc−R0) / R0 × 100 (2)

[Measurement result]
The measurement results of Experimental Examples 1-9 are shown in Table 1, the measurement results of Experimental Examples 10-11 are shown in Table 2, the measurement results of Experimental Examples 12-13 are shown in Table 3, and the lithium bis in Experimental Examples 2-8 FIG. 2 shows the relationship between the discharge capacity retention rate and the battery resistance increase rate with respect to the addition amount of (oxalato) borate and divinyltetramethyldisiloxane. As a result, as shown in Table 1 and FIG. 2, the addition amount of lithium bis (oxalato) borate and divinyltetramethyldisiloxane when 1.0% by weight of vinylene carbonate was added was 0.05% by weight to 10% by weight. %, Higher cycle characteristics are exhibited, battery capacity is decreased and battery resistance is increased, compared to those in which none of the additive components are added (Experimental Example 1) or only vinylene carbonate is added (Experimental Example 2). It became clear that can be suppressed. Further, when 1.0% by weight of vinylene carbonate is added and when the addition amount of lithium bis (oxalato) borate and divinyltetramethyldisiloxane is 0.2% by weight to 5% by weight, no vinylene carbonate is added ( As compared with Experimental Example 9), it was revealed that higher cycle characteristics were exhibited, and a decrease in battery capacity and an increase in battery resistance could be suppressed. In addition to vinylene carbonate, when vinyl ethylene carbonate, vinyl propylene carbonate, etc. are added to the non-aqueous electrolyte together with lithium bis (oxalato) borate and divinyltetramethyldisiloxane, higher cycle characteristics are exhibited, battery capacity is reduced and It became clear that the increase in battery resistance can be suppressed.

It is a schematic diagram which shows an example of the lithium ion secondary battery 10 of this invention. It is a related figure of the discharge capacity maintenance factor with respect to the addition amount of lithium bis (oxalato) borate and divinyltetramethyldisiloxane when a vinylene carbonate is added 1.0weight%, and a battery resistance increase rate.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 10 Lithium ion secondary battery, 11 Current collector, 12 Positive electrode active material, 13 Positive electrode sheet, 14 Current collector, 17 Negative electrode active material, 18 Negative electrode sheet, 19 Separator, 20 Nonaqueous electrolyte, 22 Cylindrical case, 24 Positive electrode Terminal, 26 Negative terminal.

Claims (6)

A non-aqueous electrolyte containing an electrolyte salt containing lithium and used for a lithium ion secondary battery,
A nonaqueous electrolytic solution comprising lithium bis (oxalato) borate, divinyltetraalkyldisiloxane (alkyl having 1 to 4 carbon atoms), and a carbonate having a carbon chain having an unsaturated bond as additive components.   The non-aqueous electrolyte according to claim 1, wherein the carbonate having a carbon chain having an unsaturated bond includes the carbon chain having 1 to 4 carbon atoms.   The nonaqueous electrolytic solution according to claim 1, comprising a carbonate having a carbon chain having 0.05 to 10% by weight of the unsaturated bond.   The nonaqueous electrolytic solution according to any one of claims 1 to 3, comprising 0.05% by weight or more and 10% by weight or less of lithium bis (oxalato) borate.   The nonaqueous electrolytic solution according to any one of claims 1 to 4, comprising 0.05% by weight or more and 10% by weight or less of divinyltetraalkyldisiloxane. A positive electrode having a positive electrode active material;
A negative electrode having a negative electrode active material;
The nonaqueous electrolytic solution according to any one of claims 1 to 5, which is interposed between the positive electrode and the negative electrode and conducts lithium ions,
Lithium ion secondary battery equipped with.

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