JP2013175410A - Lithium secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a lithium secondary battery, whose positive electrode has an upper limit charging potential of 4.2 V or more but less than 4.35 V, exhibiting excellent effects of reducing internal resistance and suppressing battery expansion.SOLUTION: A lithium secondary battery includes: a positive electrode containing a cathode active material capable of inserting and extracting lithium ions; a negative electrode containing an anode active material capable of inserting and extracting lithium ions; a separator; and a nonaqueous electrolyte. The upper limit charging potential of the positive electrode is 4.2 V or more but less than 4.35 V. The nonaqueous electrolyte contains trialkoxy vinyl silane.

Description

  The present invention relates to a lithium secondary battery.

  In recent years, non-aqueous electrolyte secondary batteries typified by lithium secondary batteries with high energy density, low self-discharge and good cycle performance have attracted attention as power sources for portable devices such as mobile phones and laptop computers, and electric vehicles. ing.

  The current mainstream of lithium secondary batteries is a small lithium secondary battery mainly for mobile phones having a positive electrode potential of up to about 4.2 V. For example, automobile fields such as electric vehicles, hybrid vehicles, plug-in hybrid vehicles, etc. In addition, the application of medium- or large-sized lithium secondary batteries has been studied, and some of them have been put into practical use. In particular, in an electric vehicle, all devices are driven by electric power supplied from a lithium secondary battery installed. For this reason, in order to improve the cruising distance and comfort of an electric vehicle, it is strongly desired to increase the energy density of the lithium secondary battery.

  As a means for increasing the energy density of the lithium secondary battery, there is a method of setting the battery charging voltage high. By setting the charging voltage high, a high discharge voltage and a large discharge capacity can be obtained, so that the energy density of the lithium secondary battery can be increased. However, considering such a high voltage type lithium secondary battery, the current specification of a small lithium secondary battery is not necessarily sufficient from the viewpoint of suppressing battery swelling and reducing internal resistance.

  Here, Patent Document 1 (Japanese Patent Laid-Open No. 2002-134169) discloses a technique for reducing the internal resistance of a lithium secondary battery. That is, Patent Document 1 is excellent in cycle characteristics and low temperature characteristics for maintaining high electric capacity because the rate of change in electric capacity and internal resistance is small when charging and discharging are repeated and the increase in internal resistance at low temperatures is small. For the purpose of providing a non-aqueous electrolyte and a non-aqueous electrolyte secondary battery using the electrolyte, a technique in which a silicon compound having an unsaturated bond is contained in an electrolyte obtained by dissolving an electrolyte salt in an organic solvent. It has been proposed (patent document 1, abstract, etc.).

  More specifically, in Patent Document 1, the silicon compound is a compound that easily undergoes self-polymerization, and at the initial stage of the cycle, a stable film is formed by a polymerization reaction at the interface between the electrode and the electrolytic solution. In order to obtain the effect, it is disclosed that 0.05 to 0.5% by volume of the above silicon compound is added to the electrolytic solution ( Patent Document 1, paragraph number [0040] etc.). In addition, trimethoxyvinylsilane is exemplified as the silicon compound (paragraph number [0028] and the like).

  Further, as a technique for adding a similar silicon compound to an electrolytic solution, for example, Patent Document 2 (Japanese Patent Laid-Open No. 2002-042864) discloses a non-aqueous electrolyte secondary that has improved high-temperature storage characteristics and charge / discharge cycle characteristics after charging. For the purpose of a battery, a nonaqueous electrolyte secondary battery including a positive electrode and a negative electrode that are reversible with respect to charging and discharging, and a nonaqueous electrolyte containing an electrolyte and a silane coupling agent has been proposed (Patent Document 2, (Summary, claims, etc.) Only silicon compounds having amino groups are disclosed as silane coupling agents.

JP 2002-134169 A JP 2002-042864 A

  However, in the above Patent Documents 1 and 2, the safety from the viewpoint of suppressing the battery swelling in addition to the reduction of the internal resistance is not mentioned, and particularly the positive electrode potential is 4.2 V or more and less than 4.35 V. These studies have not been made on the lithium secondary battery. SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a lithium secondary battery that is excellent in reducing internal resistance and suppressing battery swelling in a lithium secondary battery having a positive charge upper limit potential of 4.2 V or more and less than 4.35 V. It is in.

  As a result of intensive studies by the present inventors to solve the above problems, the lithium secondary battery having a positive charge upper limit potential of 4.2 V or more and less than 4.35 V has an effect of reducing internal resistance and suppressing battery swelling. To achieve this, a positive electrode including a positive electrode active material capable of inserting / extracting lithium ions, a negative electrode including a negative electrode active material capable of inserting / extracting lithium ions, a separator, and a non-aqueous electrolyte are provided. In secondary batteries, if trialkoxyvinylsilane (especially triethoxyvinylsilane) is added to the non-aqueous electrolyte, the internal resistance is reduced and battery swelling is suppressed when the upper limit charge potential of the positive electrode is 4.2 V or more and less than 4.35 V. As a result, the present invention has been completed.

That is, the present invention
A positive electrode including a positive electrode active material capable of inserting / extracting lithium ions; a negative electrode including a negative electrode active material capable of inserting / extracting lithium ions; a separator; and a non-aqueous electrolyte.
The charge upper limit potential of the positive electrode is 4.2 V or more (vs. Li ^/ Li ⁺ ) less than 4.35 V (vs. Li ^/ Li ⁺ ),
The non-aqueous electrolyte contains trialkoxyvinylsilane;
A lithium secondary battery is provided.

  Here, the “charge upper limit potential of the positive electrode” in the lithium secondary battery refers to the highest potential that the lithium secondary battery reaches by charging in a charge / discharge cycle during normal use. In other words, “the positive charge upper limit potential of the positive electrode is 4.2 V or more and less than 4.35 V” means that when the lithium secondary battery is charged to the charging voltage determined by the rating, the positive electrode potential is 4.2 V or more and 4. It means having a history of charging until it is below 35V. In addition, the upper limit potential of the positive electrode is 4.35 V or more temporarily (for example, within 100 hours) within a range where the effects of the present invention are not lost due to initial activation treatment (chemical conversion), rapid charging, and / or unintended events. Even when the battery is charged, the effect of the present invention is not changed and is included in the scope of the present invention.

  In the lithium secondary battery of the present invention, it is preferable that the non-aqueous electrolyte contains 10% by mass or less of trialkoxyvinylsilane. If the trialkoxyvinylsilane content is less than or equal to this upper limit, the increase in the irreversible capacity of the lithium secondary battery due to the decomposition reaction of the trialkoxyvinylsilane is suppressed, and the internal resistance is increased without impairing the capacity of the lithium secondary battery. Can be suppressed.

  In the lithium secondary battery of the present invention, it is preferable that the nonaqueous electrolytic solution contains 0.2% by mass or more of trialkoxyvinylsilane. If the content of trialkoxyvinylsilane is equal to or higher than this lower limit, the effects of the present invention of reducing internal resistance and suppressing battery swelling can be obtained more reliably.

  In the lithium secondary battery of the present invention, the trialkoxyvinylsilane is preferably triethoxyvinylsilane. If triethoxyvinylsilane is used as the trialkoxyvinylsilane, the effects of the present invention such as reduction of internal resistance and suppression of battery swelling can be obtained more reliably.

  In addition, even if the lithium secondary battery of the present invention has a single cell structure, the lithium secondary battery has a structure in which a plurality of the single cell structures are connected in series and / or in parallel (assembled battery). Or a module battery).

The present invention also provides:
A positive electrode including a positive electrode active material capable of inserting / extracting lithium ions; a negative electrode including a negative electrode active material capable of inserting / extracting lithium ions; a separator; and a non-aqueous electrolyte.
The non-aqueous electrolyte contains trialkoxyvinylsilane;
Wherein the above 4.2V charging upper limit potential of the positive electrode (vs.Li/Li ⁺⁾ less than 4.35V (vs.Li/Li ⁺⁾ to also relates to the use of a lithium secondary battery.

  ADVANTAGE OF THE INVENTION According to this invention, the lithium secondary battery which is excellent in the effect of reduction of internal resistance and suppression of a battery swelling can be provided in the lithium secondary battery whose charge upper limit electric potential of a positive electrode is 4.2V or more and less than 4.35V. .

It is a schematic longitudinal cross-sectional view of one Embodiment (lithium secondary battery produced in the Example of this invention) of the lithium secondary battery of this invention.

  Hereinafter, preferred embodiments of the lithium secondary battery of the present invention will be described in detail with reference to the drawings, but the present invention is not limited thereto. In the following description, the same or corresponding parts are denoted by the same reference numerals, and duplicate descriptions may be omitted. The drawings are for conceptual description of the present invention. The dimensions of each component and their ratio may differ from the actual ones.

  FIG. 1 is a schematic longitudinal sectional view of a prismatic lithium secondary battery 1 which is an embodiment of the lithium secondary battery of the present invention. A lithium secondary battery 1 shown in FIG. 1 includes a flat wound electrode group 2. The flat wound electrode group 2 includes a positive electrode current collector and a positive electrode mixture layer provided on the positive electrode current collector. A plate-like positive electrode 3 containing a negative electrode current collector and a plate-like negative electrode 4 containing a negative electrode mixture layer provided on the negative electrode current collector are wound (interposed) via a separator 5. It is formed by.

  The flat wound electrode group 2 is housed in a battery case 6, and the end of the positive electrode current collector and / or the negative electrode current collector disposed on the outermost periphery of the flat wound electrode group 2 has an inner periphery. Both the outer side and the outer side may be exposed without carrying the positive electrode mixture layer and / or the negative electrode mixture layer, and the inner circumference side carries the positive electrode mixture layer and / or the negative electrode mixture layer. Only the outer peripheral side may be exposed. The exposed portions of the positive electrode current collector and / or the negative electrode current collector are desirably disposed on all side surfaces of the flat wound electrode group 2. In addition, the positive electrode current collector and / or the negative electrode current collector disposed on the inner periphery rather than the outermost periphery may be further exposed.

  The separator 5 holds an electrolytic solution (not shown), and the gap in the battery case 6 is also filled with the nonaqueous electrolytic solution. A battery lid 7 provided with a conventionally known safety valve 8 is attached to the battery case 6 by laser welding, the negative electrode 4 is connected to the negative electrode terminal 9 by a negative electrode lead 11, and the positive electrode 3 is connected to the negative electrode terminal 10 by a battery lead 7. Connected with.

  Here, in the lithium secondary battery 1 of the present embodiment, the non-aqueous electrolyte contained in the separator 5 and the battery case 6 includes a non-aqueous solvent and an electrolyte salt dissolved in the non-aqueous solvent. It is characterized by containing alkoxyvinylsilane. The trialkoxyvinylsilane that can be used in the present embodiment is a compound represented by the following formula (1).

However, in Formula (1), R < ₁ >, R < ₂ > and R < ₃ > show an alkyl group each independently, and carbon number of an alkyl group is 1-6.

  Specific examples of trialkoxyvinylsilane represented by the formula (1) include, for example, triethoxyvinylsilane, trimethoxyvinylsilane, tripropoxyvinylsilane, diethoxymethoxyvinylsilane, ethoxydimethoxyvinylsilane, and the like. In particular, the present inventors have confirmed that the effects of the present invention can be obtained more reliably when trimethoxyvinylsilane or triethoxyvinylsilane is used (see Examples described later).

  Although the lithium secondary battery 1 contains the trialkoxyvinylsilane of the formula (1) in the electrolytic solution, it has an excellent effect of suppressing battery swelling at a positive electrode potential of 4.2 V or more and less than 4.35 V as described above. The inventors consider the effects as follows.

That is, the trialkoxyvinylsilane represented by the formula (1) is (—Si—O—) and (—R ₁ ) in a solution such as a non-aqueous electrolyte regardless of the carbon number of R ₁ , R ₂ and R _3. , (—R ₂ ) or (—R ₃ ), and the surface of the positive electrode active material contained in the positive electrode mixture of the positive electrode is covered with OH groups (—OH). ) And (—OH) form a hydrogen bond, and trialkoxyvinylsilane molecules are immobilized on the surface of the positive electrode active material. Thereby, the addition polymerization reaction in the vinyl group portion of trialkoxyvinylsilane is promoted, adjacent trialkoxyvinylsilanes are bonded to each other, and a protective layer is formed on the surface of the positive electrode active material. By such a protective function by trialkoxyvinylsilane, the amount of oxidative decomposition of the non-aqueous solvent in the non-aqueous electrolyte solution is remarkably reduced, and the amount of gas generated as a reactive organism is also remarkably reduced, thereby suppressing battery swelling. It is thought that.

  Further, the reduction in internal resistance is considered as follows. The internal resistance (AC resistance, 1 kHz) of the lithium secondary battery is considered to correlate with the effective reaction area of the positive electrode active material particles at the interface between the positive electrode active material and the non-aqueous electrolyte. When the lithium secondary battery is charged to a high voltage range of 4.2 V or more and less than 4.35 V, the nonaqueous solvent in the nonaqueous electrolyte solution is oxidized and decomposed at the interface between the positive electrode and the nonaqueous electrolyte solution. In addition, the effective reaction area is reduced because the surface of the positive electrode is deteriorated due to the reaction with the positive electrode active material in the positive electrode. In contrast, when trialkoxyvinylsilane exhibits a protective function as described above, the oxidative decomposition of the non-aqueous solvent on the surface of the positive electrode at high potential is mainly suppressed, so that the reduction in the effective reaction area is suppressed. be able to. That is, it is considered that the protective function by trialkoxyvinylsilane sufficiently secures an effective reaction area of the positive electrode active material at the interface between the positive electrode active material and the non-aqueous electrolyte and suppresses an increase in internal resistance.

Moreover, in Formula (1), in Formula (1), R < ₁ >, R < ₂ > and R < ₃ > show an alkyl group each independently, and carbon number of an alkyl group is 1-6. The upper limit of the number of carbon atoms is 6 because the hydrophobicity increases as the number of carbon atoms increases, which may cause phase separation without dissolving in the electrolyte. Further, it is considered that since R ₁ , R ₂ and R ₃ are alkyl groups, the polymerization reaction easily proceeds on the positive electrode by having an alkyl group having an electron donating property.

As the electrolyte salt contained in the non-aqueous electrolyte solution of the lithium secondary battery 1, those conventionally known in the technical field of the present invention can be used. For example, LiClO ₄ , LiPF ₆ , LiBF ₄ , LiAsF ₆ , LiCF ₃ CO ₂ , LiC (CF ₃ ) ₃ , LiC (C ₂ F ₅ ) ₃ , LiCF ₃ SO ₃ , LiCF ₃ CF ₂ SO ₃ , LiCF ₃ CF ₂ CF ₂ SO ₃ , LiN (SO ₂ CF ₃ ) ₂ , LiN (SO ₂ CF ₂ CF ₃ ) ₂ , LiN (COCF ₃ ) ₂ , LiN (COCF ₂ CF ₃ ) ₂ , LiPF ₃ (CF ₂ CF ₃ ) ₃ , LiB (C ₂ O ₄ ) ₂ , LiBF ₂ (C _{2 O 4), LiPF 2 (C} 2 O 4) 2 and LiPF ₄ (C ₂ O _4), and the like. these may be used alone or in combination. From the viewpoint of conductivity, LiPF ₆ is suitable as the electrolyte salt, and other compounds such as LiBF ₄ can be mixed and used with LiPF ₆ as the main component.

  Further, as the non-aqueous solvent contained in the non-aqueous electrolyte, those conventionally known in the technical field of the present invention can be used, and examples thereof include cyclic carbonates, chain carbonates, and cyclic sulfones. For example, ethylene carbonate (EC), propylene carbonate (PC), cyclic carbonates such as butylene carbonate (BC), dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC). ), Chain carbonates such as dipropyl carbonate (DPC), aliphatic carboxylic acid esters such as methyl formate, methyl acetate, methyl propionate and ethyl propionate, lactones such as γ-butyrolactone and γ-valerolactone, 1,2-dimethoxyethane (DME), 1,2-diethoxyethane (DEE), chain ethers such as ethoxymethoxyethane (EME), cyclic ethers such as tetrahydrofuran and 2-methyltetrahydrofuran, dimethyl sulfoxide, 1,3-dioxolane, formamide, acetamide, dimethylformamide, dioxolane, acetonitrile, pro Pionitrile, nitromethane, ethyl monoglyme, phosphoric acid triester, trimethoxymethane, dioxolane derivative, sulfolane, methylsulfolane, 1,3-dimethyl-2-imidazolidinone, 3-methyl-2-oxazolidinone, propylene carbonate derivative, Examples include tetrahydrofuran derivatives, ethyl ether, 1,3-propane sultone, anisole, dimethyl sulfoxide, and N-methyl-2-pyrrolidone. These may be used alone, but may be used in combination of two or more from the viewpoint of adjusting the conductivity and viscosity of the non-aqueous electrolyte. Among these, a mixed solvent of a cyclic carbonate and a chain carbonate or a mixed solvent of a cyclic carbonate, a chain carbonate, and an aliphatic carboxylic acid ester is preferable. For example, a 3: 7 mixed nonaqueous solvent of ethylene carbonate (EC) and ethyl methyl carbonate (EMC) is preferably used.

  The mixing ratio of the electrolyte salt with respect to the nonaqueous solvent in the nonaqueous electrolytic solution may be appropriately selected within a range in which the effect of the nonaqueous electrolytic solution is obtained based on a conventionally known technique. For example, the amount of electrolyte salt dissolved in the non-aqueous solvent is not particularly limited, but is preferably 0.2 to 5 mol / liter, and more preferably 0.5 to 2.5 mol / liter, for example.

  Various additives can be added to the non-aqueous electrolyte for the purpose of improving the charge / discharge characteristics of the lithium secondary battery 1. Examples of the additive include vinylene carbonate (VC) and vinyl ethylene carbonate (VEC). These additives form a good film on the positive electrode 3 and / or the negative electrode 4 and contribute to extending the life of the battery. In addition, cyclohexylbenzene (CHB), fluorobenzene, and the like can be added to improve the stability during overcharge.

  The trialkoxyvinylsilane content in the nonaqueous electrolytic solution may be appropriately selected within a range not impairing the effects of the present invention, but the nonaqueous electrolytic solution preferably contains 10% by mass or less of trialkoxyvinylsilane. If the trialkoxyvinylsilane content is less than or equal to this upper limit, the increase in the irreversible capacity of the lithium secondary battery due to the decomposition reaction of the trialkoxyvinylsilane is suppressed, and the internal resistance is increased without impairing the capacity of the lithium secondary battery. Can be suppressed.

  Moreover, it is preferable that the non-aqueous electrolyte of the lithium secondary battery 1 contains 0.2% by mass or more of trialkoxyvinylsilane. If the content of trialkoxyvinylsilane is at least the lower limit value, the effect of the present invention of suppressing the increase in internal resistance can be obtained more reliably.

  Next, components other than the non-aqueous electrolyte in the lithium secondary battery 1 will be described.

  As the positive electrode current collector constituting the positive electrode 3, those conventionally known in the technical field of the present invention can be used, and examples thereof include an aluminum foil and an aluminum alloy foil.

The positive electrode mixture layer formed by being applied to both surfaces of the positive electrode current collector contains a positive electrode active material. As a positive electrode active material, a conventionally well-known thing can be used in the field | area of this invention, For example, lithium containing transition metal oxides, such as lithium cobaltate, lithium nickelate, and lithium manganate, are mentioned. A part of the transition metal of the lithium-containing transition metal oxide may be substituted with another element. More specifically, for example, layered rock salt type oxides such as LiNi _1/3 Mn _1/3 Co _1/3 O ₂ and LiMPO ₄ (M = Mn, Fe, Co and / or Ni) and the like can be mentioned. Moreover, the surface of the lithium-containing transition metal oxide particles may be coated with another element. One type of positive electrode active material may be used alone, or two or more types of positive electrode active materials may be used in combination.

  The positive electrode mixture layer is formed by applying and supporting a positive electrode mixture containing a positive electrode active material and a small amount of a binder (for example, polyethylene terephthalate (PTFE), polyvinylidene fluoride (PVDF), etc.) on a positive electrode current collector. can do. A small amount of a conductive material (for example, acetylene black, ketjen black, graphite) or a dispersion medium (for example, N-methyl-2-pyrrolidone (NMP)) may be added to the positive electrode mixture.

  On the other hand, as the negative electrode current collector constituting the negative electrode 4, those conventionally known in the technical field of the present invention can be used, and examples thereof include copper foil.

The negative electrode mixture layer formed by being applied to both surfaces of the negative electrode current collector contains a negative electrode active material. As the negative electrode active material, those conventionally known in the field of the present invention can be used. For example, carbon materials (for example, graphite (graphite), natural graphite, artificial graphite, hard carbon), elements that can be alloyed with lithium (for example, Al, Si, Zn, Ge, Cd, Sn, Pb), silicon compound (eg, SiO _x (0 <x <2)), tin compound (eg, SnO), lithium metal, alloy (eg, Ni—Si alloy, Ti—) Si alloy), conversion materials such as Co ₃ O ₄ , oxide materials such as Li ₄ Ti ₅ O ₁₂ and Li _1.1 V _0.9 O ₂ can be used. One type of negative electrode active material may be used alone, or two or more types of negative electrode active materials may be used in combination.

  The negative electrode active material may be directly deposited on the negative electrode current collector, but a small amount of a binder (for example, PVDF, styrene butadiene rubber (SBR), carboxymethyl cellulose (CMC), polyacrylic acid) may be used alone or in combination. The negative electrode mixture can also be formed by being applied to and supported on the negative electrode current collector. Further, like the positive electrode mixture of the positive electrode 3, a conductive material may be added to the negative electrode mixture. A small amount of a dispersion medium (for example, water) may be added.

  As the separator 5, those conventionally known in the field of the present invention can be used, and examples thereof include a microporous film made of a polyolefin resin such as polyethylene and / or polypropylene. Among these, a single layer film composed of polyethylene, a multilayer film composed of a polyethylene layer and a polypropylene layer, and the like can also be used. Moreover, you may use what coated the inorganic substance etc. on the surface of the separator.

  As the battery case 6 and the battery lid 7, those conventionally known in the field of the present invention can be used, and for example, those made of iron or aluminum can be used. Since iron cans are harder than aluminum cans, the deformation when subjected to an impact tends to be small, and the flat wound electrode group 2 in the battery case 6 is not easily damaged. In the case of using an aluminum can, the battery case 6 and the positive electrode 3 may be electrically connected. In that case, an exposed portion of the positive electrode current collector may be disposed on the outermost periphery of the flat wound electrode group 2. it can.

  In addition, the lithium secondary battery of the present embodiment is used together with a control circuit that controls charging. However, the control circuit may be attached to each lithium secondary battery, and a plurality of lithium secondary batteries may be installed. On the other hand, one control circuit may be mounted.

  As mentioned above, although one embodiment of the lithium secondary battery of the present invention has been described, the lithium secondary battery of the present invention is not limited to the square shape shown in FIG. 1, and may take various shapes. From the standpoint that the effect of suppressing the battery swelling is more prominent, the battery case preferably has a shape having a flat portion in its outer shape (for example, a rectangular shape or a long cylindrical shape).

  Next, the present invention will be specifically described based on examples, but the present invention is not limited to the following examples.

<< Example 1: Use of triethoxyvinylsilane >>
(1) Production of positive electrode LiNi _1/3 Mn _1/3 Co _1/3 O ₂ which is a positive electrode active material, acetylene black which is a conductive material, polyvinylidene fluoride (PVdF) which is a binder, 93: The mixture was mixed at a mass ratio of 3: 4, and N-methyl-2-pyrrolidone (NMP) as a dispersion medium was mixed therewith to prepare a paste-like positive electrode mixture.

The obtained paste-like positive electrode mixture was applied to both surfaces of a 15 μm thick aluminum foil to form a positive electrode mixture layer, and dried at 130 ° C. to remove NMP from the applied positive electrode mixture layer. The coating mass of the single-sided positive electrode mixture at this point was 18 mg / cm ² , respectively. Next, the positive electrode mixture layer after NMP removal was pressure-molded with a roller press heated to 110 ° C., and then dried under reduced pressure at 130 ° C. for 14 hours to completely remove moisture, and the positive electrode mixture layer was formed on both surfaces of the aluminum foil. A plate-like positive electrode having an agent layer was obtained.

(2) Production of Negative Electrode Graphite, which is a negative electrode active material, and SBR and CMC, which are binders, are mixed at a mass ratio of graphite: SBR: CMC = 97: 2: 1, and this is water as a dispersion medium. Were mixed to prepare a paste-like negative electrode mixture.

The obtained paste-like negative electrode mixture was applied to both surfaces of a 10 μm thick copper foil to form a negative electrode mixture layer, and dried at 80 ° C. to remove moisture. The coating mass of the single-sided negative electrode mixture at this time was 11 mg / cm ² , respectively. Next, the negative electrode mixture layer after moisture removal was pressure-molded with a roller press at room temperature, and then dried under reduced pressure at room temperature for 24 hours to completely remove moisture in the negative electrode mixture layer, and both sides of the copper foil A plate-like negative electrode having a negative electrode mixture layer was obtained.

(3) Preparation of non-aqueous electrolyte Ethylene carbonate and ethyl methyl carbonate were mixed at a volume ratio of 3: 7 to obtain a mixed non-aqueous solvent. In this mixed non-aqueous solvent, LiPF ₆ as an electrolyte salt was dissolved at a concentration of 1.0 mol / liter to obtain a solution. Further, triethoxyvinylsilane manufactured by Tokyo Chemical Industry Co., Ltd. as an additive was dissolved in this solution to a concentration of 0.5% by mass to prepare a nonaqueous electrolytic solution. The water content of this non-aqueous electrolyte was less than 50 ppm.

(4) Production of Lithium Secondary Battery In this example, a square lithium secondary battery having the structure shown in FIG. 1 was produced. A separator made of a polyethylene microporous film having a thickness of 27 μm is laminated so as to be positioned between the positive electrode and the negative electrode produced as described above, and the laminated body is wound to form flat portions opposed to both sides. Thus, a flat wound electrode group was prepared.

  Next, this flat wound electrode group is housed in a rectangular aluminum battery case (height 49 mm, width 34 mm, thickness 5.17 mm), and the non-aqueous solution prepared as described above is placed inside the battery case. 2.6 milliliters of electrolyte {limit injection volume (that is, 90% of the volume obtained by subtracting the volume of the element (electrode group) from the space volume of the battery case and adding the space volume in the element (electrode group))} The lithium secondary battery having a design capacity of 0.7 Ah was manufactured by pouring and sealing.

(5) Initial activation treatment This lithium secondary battery was subjected to an initial activation treatment. That is, under a temperature atmosphere of 25 ° C., a current of 0.2 CA (about 5 hours rate), a voltage of 4.2 V and a constant current and constant voltage of 8 hours are performed, and then a current of 0.2 CA (about 5 hours rate) and A constant current discharge with a final voltage of 2.75 V was performed (however, 1 hour rate (1 CA) = 0.7 A). A 10 minute rest period was provided between charging and discharging. As a result, the lithium secondary battery 1 of the present invention having a positive charge upper limit potential of 4.2 V or more and less than 4.35 V was obtained.

<< Example 2: Use of trimethoxyvinylsilane >>
A lithium secondary battery 2 was produced in the same manner as in Example 1 except that trimethoxyvinylsilane (manufactured by Tokyo Chemical Industry Co., Ltd.) was used instead of triethoxyvinylsilane added to the nonaqueous electrolytic solution.

<< Comparative Example 1: Trialkoxyvinylsilane not used >>
A comparative lithium secondary battery 1 was produced in the same manner as in Example 1 except that triethoxyvinylsilane was not added to the nonaqueous electrolytic solution.

<< Comparative Example 2: Use of 3- (2-aminoethylamino) propyltrimethoxysilane >>
A comparison was made in the same manner as in Example 1 except that 3- (2-aminoethylamino) propyltrimethoxysilane (manufactured by Tokyo Chemical Industry Co., Ltd.) was used instead of triethoxyvinylsilane added to the nonaqueous electrolytic solution. A lithium secondary battery 2 was produced.

<< Comparative Example 3: Use of aminopropyltrimethoxysilane >>
A comparative lithium secondary battery 3 was produced in the same manner as in Example 1 except that aminopropyltrimethoxysilane (manufactured by Tokyo Chemical Industry Co., Ltd.) was used instead of triethoxyvinylsilane added to the nonaqueous electrolytic solution. did.

<< Comparative Example 4: Use of trimethoxy (3,3,3-trifluoropropyl) silane >>
A comparison was made in the same manner as in Example 1 except that trimethoxy (3,3,3-trifluoropropyl) silane (manufactured by Tokyo Chemical Industry Co., Ltd.) was used instead of triethoxyvinylsilane added to the non-aqueous electrolyte. A lithium secondary battery 4 was produced.

[Evaluation and measurement]
(1) Internal resistance measurement For the lithium secondary batteries 1 and 2 and the comparative lithium secondary batteries 1 to 4 obtained as described above, the internal resistance R1 (mΩ, 1 kHz) 24 hours after the completion of the initial activation process. Was measured using Hioki Electric Co., Ltd. HIOKI3560 AC HITESTER. Table 1 shows the internal resistance difference ΔR1 between the internal resistance R1 and Examples 1, 2 and Comparative Examples 2, 3 and Comparative Example 1.

(2) Battery thickness measurement For the lithium secondary batteries 1 and 2 and the comparative lithium secondary batteries 1 to 4 obtained as described above, the center of the long side immediately after production and after 24 hours from the end of the initial activation process. The part was sandwiched with calipers from a direction substantially perpendicular to the long side surface (in a direction substantially horizontal to the surface direction of the short side surface), and the battery thickness was measured. The measured value T2 after 24 hours from the completion of the initial activation process is shown in Table 1 as “battery thickness (mm)”. The measured value T1 immediately after the production was 5.14 mm.

From the results shown in Table 1, it can be seen that the lithium secondary battery of the present invention in which the upper limit charging potential of the positive electrode is 4.2 V or more and less than 4.35 V is excellent in the effects of reducing internal resistance and suppressing battery swelling. In addition, about all the lithium secondary batteries of an Example and a comparative example, it confirmed that the positive electrode electric potential at the time of 4.2V charge was 4.29V (vs.Li/Li ^<+> ).

1 ... lithium secondary battery,
2 ... flat wound electrode group,
3 ... positive electrode,
4 ... negative electrode,
5 ... Separator,
6 ... Battery case,
7 ... Battery cover,
8 ... Safety valve,
9: negative terminal,
10: Positive electrode lead,
11: Negative electrode lead.

Claims (5)

A positive electrode including a positive electrode active material capable of inserting / extracting lithium ions; a negative electrode including a negative electrode active material capable of inserting / extracting lithium ions; a separator; and a non-aqueous electrolyte.
The charge upper limit potential of the positive electrode is 4.2 V or more (vs. Li ^/ Li ⁺ ) less than 4.35 V (vs. Li ^/ Li ⁺ ),
The non-aqueous electrolyte contains trialkoxyvinylsilane;
Rechargeable lithium battery. The non-aqueous electrolyte contains 10% by mass or less of trialkoxyvinylsilane;
The lithium secondary battery according to claim 1. The non-aqueous electrolyte contains 0.2% by mass or more of trialkoxyvinylsilane,
The lithium secondary battery according to claim 1 or 2. The trialkoxyvinylsilane is triethoxyvinylsilane;
The lithium secondary battery according to any one of claims 1 to 3. A positive electrode including a positive electrode active material capable of inserting / extracting lithium ions; a negative electrode including a negative electrode active material capable of inserting / extracting lithium ions; a separator; and a non-aqueous electrolyte.
The non-aqueous electrolyte contains trialkoxyvinylsilane;
The positive electrode charging upper limit voltage or 4.2V of (vs.Li/Li ⁺⁾ less than 4.35V (vs.Li/Li ⁺⁾ and Using lithium secondary battery.

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