JP2019040721A - Lithium ion secondary battery - Google Patents

Abstract

To provide a lithium ion secondary battery improved in resistance against Li precipitation.SOLUTION: The present invention relates to a lithium ion secondary battery comprising a positive electrode, a negative electrode and a nonaqueous electrolyte solution. The positive electrode includes a positive electrode current collector formed by aluminum foil, and a positive electrode active material layer formed on the positive electrode current collector. The nonaqueous electrolyte solution contains lithium fluorosulfonate. The positive electrode current collector is 0.1 mg/mor more and 2 mg/mor less in residual oil quantity, provided that a portion of the aluminum foil forming a positive electrode current collector exposed portion which is a portion of the positive electrode current collector where the positive electrode active material layer is not formed is cut out, and a difference X-Y(mg/m) between a dry weight X(mg/m) of the cut aluminum foil portion under the condition of a room temperature in the atmosphere and a measurement weight Y (mg/m) of the portion after having been subjected to a high-temperature treatment at 200°C for 30 minutes in the atmosphere is the residual oil quantity (mg/m) of the positive electrode current collector.SELECTED DRAWING: Figure 3

Description

  The present invention relates to a lithium ion secondary battery. Specifically, the present invention relates to a lithium ion secondary battery including a positive electrode current collector made of an aluminum foil having an appropriate amount of residual oil.

  Lithium ion secondary batteries that are lightweight and obtain high energy density are preferably used as high-output power sources for driving vehicles such as electric vehicles (EV), plug-in hybrid vehicles (PHV), and hybrid vehicles (HV). The demand for higher performance for such lithium ion secondary batteries is increasing. For example, Patent Document 1 discloses a lithium ion secondary battery in which lithium fluorosulfonate is contained in a nonaqueous electrolytic solution for the purpose of suppressing precipitation of lithium metal in a negative electrode.

JP 2006-143454 A

  However, in the conventional lithium ion secondary battery, there is still room for improvement in the performance of suppressing lithium (Li) precipitation (resistance to Li precipitation).

  The inventor paid attention to the aluminum foil constituting the positive electrode current collector as an object for realizing the above improvement. As a result of various investigations, by prescribing the remaining amount of oil component (typically rolling oil at the time of manufacturing the aluminum foil) that coats the surface of the aluminum foil, the occurrence of Li precipitation is effectively prevented. The inventors have found that it can be suppressed, and have completed the present invention.

  That is, an object of the present invention is to provide a lithium ion secondary battery that realizes suppression of lithium precipitation in the negative electrode from the viewpoint of the amount of residual oil in the aluminum foil constituting the positive electrode current collector.

According to the present invention, a lithium ion secondary battery including a positive electrode, a negative electrode, and a non-aqueous electrolyte is provided. The positive electrode includes a positive electrode current collector formed of an aluminum foil and a positive electrode active material layer formed on the positive electrode current collector. The non-aqueous electrolyte contains lithium fluorosulfonate. Here, the residual oil amount (mg / m ² ) of the positive electrode current collector measured by the measurement method described below is 0.1 mg / m ² or more and 2 mg / m ² or less.

The aluminum foil which comprises the positive electrode collector exposure part which is the part in which the said positive electrode active material layer in the said positive electrode collector is not formed is cut out, and the room temperature condition (typically) of the cut-out aluminum foil part is typically Is the difference between the dry weight X (mg / m ² ) under 20-25 ° C.) and the measured weight Y (mg / m ² ) after high temperature treatment of the part at 200 ° C. for 30 minutes in the atmosphere. Let XY (mg / m ² ) be the residual oil amount (mg / m ² ) of the positive electrode current collector.

  According to the lithium ion secondary battery having such a configuration, a suitable amount of residual oil coats the surface of the positive electrode current collector made of aluminum foil, so that a non-aqueous electrolyte (for example, fluorination in the non-aqueous electrolyte) is used. Elution of aluminum by hydrogen (HF) is suppressed. The lithium fluorosulfonate contained in the non-aqueous electrolyte also contributes to suppression of aluminum elution from the positive electrode current collector. Aluminum ions generated by such aluminum elution can be deposited on the negative electrode and serve as a starting point for lithium deposition. Therefore, according to the structure disclosed here, a lithium ion secondary battery in which lithium deposition in the negative electrode is suppressed can be realized.

  Moreover, according to the lithium ion secondary battery of this structure, generation | occurrence | production of the gas resulting from the oil component adhering to the surface of aluminum foil is suppressed, and a battery capacity is maintained with high use even for a long time use. That is, the lifetime reduction of the battery can be suppressed.

It is a longitudinal cross-sectional view which shows typically the cross-section of the lithium ion secondary battery which concerns on one Embodiment. It is a schematic diagram which shows the structure of the wound electrode body which concerns on one Embodiment. It is a graph which shows the relationship between the capacity | capacitance maintenance factor (%) after a low-temperature pulse cycle test, and the residual oil amount (mg / m < ² >) of the aluminum foil which is a positive electrode electrical power collector. It is a graph which shows the relationship between the capacity | capacitance maintenance factor (%) after a lifetime durability test, and the residual oil amount (mg / m < ² >) of the aluminum foil which is a positive electrode electrical power collector.

  Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings. Note that matters other than matters specifically mentioned in the present specification and necessary for the implementation of the present invention can be grasped as design matters of those skilled in the art based on the prior art in this field. The present invention can be carried out based on the contents disclosed in this specification and common technical knowledge in the field. Moreover, in the following drawings, the same code | symbol is attached | subjected to the member and site | part which show | play the same effect | action, and the overlapping description may be abbreviate | omitted or simplified. The dimensional relationship (length, width, thickness, etc.) in each drawing does not necessarily reflect the actual dimensional relationship.

  One embodiment of the lithium ion secondary battery of the present invention will be described with reference to the schematic diagrams shown in FIGS. FIG. 1 is a cross-sectional view of a lithium ion secondary battery 100 according to an embodiment of the present invention. FIG. 2 is a diagram showing an electrode body 40 housed in the lithium ion secondary battery 100.

  A lithium ion secondary battery 100 according to an embodiment of the present invention is configured in a flat rectangular battery case (that is, an outer container) 20 as shown in FIG. As shown in FIGS. 1 and 2, the lithium ion secondary battery 100 is configured such that a flat wound electrode body 40 is accommodated in a battery case 20 together with a non-aqueous liquid electrolyte (non-aqueous electrolyte) 80. Has been.

  The battery case 20 has a box-shaped (that is, a bottomed rectangular parallelepiped) case body 21 having an opening at one end (corresponding to an upper end portion in a normal use state of the battery 100), and is attached to the opening. It is comprised from the cover body (sealing board) 22 which consists of a rectangular-shaped plate member which plugs up an opening part. The material of the battery case 20 may be the same as that used in the conventional lithium ion secondary battery 100 and is not particularly limited. A battery case 20 mainly composed of a lightweight and highly heat conductive metal material is preferable, and aluminum or the like is exemplified as such a metal material.

  As shown in FIG. 1, a positive electrode terminal 23 and a negative electrode terminal 24 for external connection are formed on the lid 22. A thin safety valve 30 configured to release the internal pressure when the internal pressure of the battery case 20 rises above a predetermined level and a liquid injection port 32 are formed between both terminals 23 and 24 of the lid 22. Has been. In FIG. 1, the liquid injection port 32 is sealed with a sealing material 33 after the liquid injection.

<Winded electrode body>
As shown in FIG. 2, the wound electrode body 40 includes a long sheet-like positive electrode (positive electrode sheet) 50, a long sheet-like negative electrode (negative electrode sheet) 60 similar to the positive electrode sheet 50, and a total of two sheets. Long sheet-like separators 72 and 74 are provided. The positive electrode sheet 50 and the negative electrode sheet 60 are laminated with the separators 72 and 74 interposed therebetween, and further wound to form the wound electrode body 40.

<Positive electrode sheet>
The positive electrode sheet 50 includes a strip-shaped positive electrode current collector 52 and a positive electrode active material layer 53. According to the technique disclosed herein, a conductive aluminum foil is used for the positive electrode current collector 52. A positive electrode current collector exposed portion 51 in which the positive electrode active material layer 53 is not formed and the positive electrode current collector 52 is exposed is set along the edge on one side in the width direction of the positive electrode current collector 52. The positive electrode active material layer 53 is held on both surfaces of the positive electrode current collector 52 except for the positive electrode current collector exposed portion 51 set in the positive electrode current collector 52. The positive electrode active material layer 53 includes positive electrode active material particles, a conductive material, and a binder.

As the positive electrode active material, one or more of various materials known to be usable as the positive electrode active material of the lithium ion secondary battery 100 can be used without any particular limitation. As a suitable example, lithium composite metal oxides such as layered and spinel (for example, LiNiO ₂ , LiCoO ₂ , LiFeO ₂ , LiMn ₂ O ₄ , LiNi _0.5 Mn _1.5 O ₄ , LiCrMnO ₄ , LiFePO ₄ ) Is mentioned. Examples of the conductive material include carbon black such as acetylene black and ketjen black, and other powdery carbon materials (graphite and the like). Examples of the binder include polyvinylidene fluoride (PVDF), styrene butadiene rubber (SBR), polytetrafluoroethylene (PTFE), and the like.

  The proportion of the positive electrode active material in the entire positive electrode active material layer 53 is suitably about 60% by mass or more (typically 60% by mass to 99% by mass), and usually about 70% by mass to 95% by mass. % Is preferred. In the case of using a conductive material, the ratio of the conductive material in the entire positive electrode active material layer 53 can be, for example, approximately 2% by mass to 20% by mass, and usually approximately 3% by mass to 10% by mass. preferable. When using a binder, the ratio of the binder to the whole positive electrode active material layer can be, for example, about 0.5% by mass to 10% by mass, and usually about 1% by mass to 5% by mass is preferable. .

The mass (weight per unit area) of the positive electrode active material layer 53 provided per unit area of the positive electrode current collector 52 is 2 mg / cm ² or more per side of the positive electrode current collector 52 from the viewpoint of securing a sufficient battery capacity (for example, 3 mg / cm ² or more, typically 4 mg / cm ² or more). Further, from the viewpoint of securing input / output characteristics, it can be set to 30 mg / cm ² or less (for example, 20 mg / cm ² or less, typically 10 mg / cm ² or less) per side of the positive electrode current collector 52.

  When the positive electrode active material layer 53 is formed, a positive electrode active material, a conductive material, and a binder are dispersed in an appropriate solvent and kneaded to form a paste (including a slurry or an ink; the same applies hereinafter). A composite material for forming a positive electrode active material layer (composite paste) is prepared. The positive electrode 50 for a lithium ion secondary battery can be produced by applying an appropriate amount of the composite paste on the positive electrode current collector 52, drying and pressing. As the solvent, any of an aqueous solvent and an organic solvent can be used. For example, N-methyl-2-pyrrolidone (NMP) can be used. The operation of applying the composite paste can be performed using an appropriate coating apparatus such as a gravure coater, a slit coater, a die coater, a comma coater, or a dip coater. The removal of the solvent can be performed by, for example, heat drying or vacuum drying.

  Generally, oil components such as rolling oil (typically mineral oil) applied in the manufacturing process remain on the surface of the aluminum foil used as the positive electrode current collector 52. Here, before and after the lithium ion secondary battery 100 including the positive electrode current collector 52 made of aluminum foil is manufactured (that is, before and after battery assembly), the amount of oil component adhering to the positive electrode current collector 52 ( (Residual oil amount) is not always the same. Typically, a part of the oil component adhering to the surface of the positive electrode current collector 52 tends to volatilize and decrease after battery assembly due to the influence of heating, pressurization, and the like in the battery manufacturing process. The “residual oil amount of the positive electrode current collector” in this specification refers to the residual oil amount of the positive electrode current collector 52 after the lithium ion secondary battery 100 is constructed. Specifically, the “residual oil amount of the positive electrode current collector” in the present specification is defined as a value measured by the following measurement method.

<Residual oil amount of positive electrode current collector>
In lithium ion secondary battery 100, an aluminum foil constituting positive electrode current collector exposed portion 51, which is a portion where positive electrode active material layer 53 in positive electrode current collector 52 is not formed, is cut out, and the cut out aluminum foil portion After dry weight X (mg / m ² ) per unit surface area under atmospheric room temperature conditions (typically 20-25 ° C.) and after high temperature treatment at 200 ° C. for 30 minutes in the air The weight Y per unit surface area (mg / m ² ) is measured. The weight difference XY (mg / m ² ) is defined as the residual oil amount (mg / m ² ) of the positive electrode current collector 52.

According to the technique disclosed herein, the amount of residual oil of the positive electrode current collector is 0.1 mg / m ² or more and 2 mg / m ² or less. If the amount of the residual oil is less than 0.1 mg / m ² , the surface protection of the aluminum foil by the oil component is not properly performed, which can contribute to elution of aluminum into the non-aqueous electrolyte and lithium deposition. If the amount of residual oil is more than 2 mg / m ² , gas derived from the oil component is likely to be generated when the battery is used, which may contribute to a decrease in the non-aqueous electrolyte and a reduction in battery life.

  The method for controlling the residual oil amount of the positive electrode current collector 52 is not particularly limited. For example, the residual oil amount can be controlled by controlling the drying conditions when the positive electrode active material layer 53 is formed on the positive electrode current collector 52. For example, in the case of performing heat drying, if the heating temperature and / or heating time is increased, the amount of residual oil in the positive electrode current collector 52 decreases, and if the heating temperature and / or heating time is decreased, the remaining amount of the positive electrode current collector 52 is decreased. The amount of oil tends to increase. Alternatively, when the vacuum drying is performed, the residual oil amount can be controlled by controlling the set pressure, the drying time, and the like.

<Negative electrode sheet>
As shown in FIG. 2, the negative electrode sheet 60 includes a strip-shaped negative electrode current collector 62 and a negative electrode active material layer 63. For the negative electrode current collector 62, for example, a metal foil suitable for the negative electrode can be suitably used. In this embodiment, a strip-shaped copper foil is used for the negative electrode current collector 62. A negative electrode current collector exposed portion 61 in which the negative electrode active material layer 63 is not formed along the edge and the negative electrode current collector 62 is exposed is set on one side in the width direction of the negative electrode current collector 62. The negative electrode active material layer 63 is held on both surfaces of the negative electrode current collector 62 except for the negative electrode current collector exposed portion 61 set in the negative electrode current collector 62. The negative electrode active material layer 63 contains a negative electrode active material.

  As the negative electrode active material, one or more of various materials known to be usable as the negative electrode active material of the lithium ion secondary battery 100 can be used without any particular limitation. Preferable examples include carbon materials such as graphite (graphite), non-graphitizable carbon (hard carbon), graphitizable carbon (soft carbon), and carbon nanotubes. Especially, since it is excellent in electroconductivity and a high energy density is obtained, graphite-type materials (especially natural graphite), such as natural graphite and artificial graphite, can be used preferably.

Although the property of a negative electrode active material is not specifically limited, For example, it may be a particle form or a powder form. The average particle diameter of the particulate negative electrode active material may be 20 μm or less (typically 1 μm to 20 μm, for example, 5 μm to 15 μm). The specific surface area is 1 m ² / g or more (typically 2.5 m ² / g or more, for example, 3.4 m ² / g or more), and 10 m ² / g or less (typically 6 m ² / g). Hereinafter, for example, it may be 4.8 m ² / g or less.

In the present specification, the “average particle size” means particles corresponding to 50% cumulative from the fine particle side in the volume-based particle size distribution measured by particle size distribution measurement based on a general laser diffraction / light scattering method. Diameter (D50 particle diameter, also referred to as median diameter). In this specification, “BET specific surface area (m ² / g)” means a gas adsorption amount measured by a gas adsorption method (fixed capacity adsorption method) using nitrogen (N ₂ ) gas as an adsorbate. The value calculated by analyzing by the BET method (for example, the BET 1-point method).

In a preferred embodiment, a film derived from the film forming material is formed on the surface of the negative electrode active material. Such a film may include, for example, lithium ions (Li ⁺ ) and at least one of boron (B) atoms, phosphorus (P) atoms, and sulfur (S) atoms. This coating stabilizes the interface between the negative electrode active material and the nonaqueous electrolytic solution 80. Therefore, the decomposition reaction of the nonaqueous electrolytic solution 80 in the subsequent charge / discharge can be suppressed. The qualitative and quantitative determination of the film formed on the surface of the negative electrode active material is performed, for example, by ion chromatography (IC: Ion Chromatography) or inductively coupled plasma emission spectroscopy (ICP-AES: Inductively Coupled Plasma-Atomic Emission Spectrometry). X-ray absorption fine structure analysis (XAFS: X-ray Absorption Fine Structure) can be used.

  In addition to the negative electrode active material, the negative electrode active material layer 63 may include one or more materials that can be used as a constituent component of the negative electrode active material layer 63 in the general lithium ion secondary battery 100 as necessary. May be contained. Examples of such materials include binders and various additives. As a binder, the thing similar to the positive electrode 50 mentioned above can be used. In addition, various additives such as a thickener, a dispersant, and a conductive material can be appropriately used. For example, carboxymethyl cellulose (CMC) or methyl cellulose (MC) can be suitably used as the thickener.

  The proportion of the negative electrode active material in the entire negative electrode active material layer 63 is suitably about 50% by mass or more, and usually 90% by mass to 99% by mass (eg, 95% by mass to 99% by mass). Is preferred. When using a binder, the ratio of the binder to the whole negative electrode active material layer 63 can be, for example, about 0.1% by mass to 5% by mass, and usually about 0.3% by mass to 3% by mass. It is preferable to do. When using a thickener, the ratio of the thickener to the whole negative electrode active material layer 63 can be made into about 0.1 mass%-5 mass%, for example, and usually about 0.3 mass%- It is preferable to set it as 3 mass%.

The mass (weight per unit area) of the negative electrode active material layer 63 provided per unit area of the negative electrode current collector 62 is 1 mg / cm ² or more per side of the negative electrode current collector 62 from the viewpoint of securing a sufficient battery capacity (typically Specifically, it can be set to 2 mg / cm ² or more, for example, 3 mg / cm ² or more. In addition, from the viewpoint of securing input / output characteristics, the negative electrode current collector 62 can have a concentration of 30 mg / cm ² or less (typically 20 mg / cm ² or less, for example, 10 mg / cm ² or less) per side.

  Then, similarly to the positive electrode 50, the negative electrode active material and other negative electrode active material layer constituents are dispersed in an appropriate solvent and kneaded to prepare a paste-like negative electrode active material layer forming mixture. The negative electrode 60 for lithium ion secondary batteries can be produced by applying an appropriate amount of this composite paste on the negative electrode current collector, drying and pressing.

<Separator>
As shown in FIG. 2, the separators 72 and 74 are members that separate the positive electrode sheet 50 and the negative electrode sheet 60. In this example, the separators 72 and 74 are made of a strip-shaped sheet material having a predetermined width and having a plurality of minute holes. As the separators 72 and 74, for example, a single layer structure separator or a multilayer structure separator made of a porous polyolefin resin can be used. Moreover, you may further form the layer of the particle | grains which have insulation on the surface of the sheet | seat material comprised with this resin. Here, as the particles having insulating properties, inorganic fillers having insulating properties (for example, fillers such as metal oxides and metal hydroxides) or resin particles having insulating properties (for example, particles such as polyethylene and polypropylene). ).

  As shown in FIG. 2, the wound electrode body 40 is flatly pushed and bent in one direction orthogonal to the winding axis WL. In this embodiment, as shown in FIG. 1, the middle portions of the current collector exposed portions 51 and 61 are gathered together and the current collecting tabs 25 of the electrode terminals (internal terminals) arranged inside the battery case 20, 26 is welded. Reference numerals 25a and 26a in FIG. 1 indicate the welding locations.

<Non-aqueous electrolyte>
As the electrolytic solution (nonaqueous electrolytic solution) 80, the same one as the nonaqueous electrolytic solution 80 conventionally used in the lithium ion secondary battery 100 can be used. Such a nonaqueous electrolytic solution 80 typically has a composition in which a supporting salt is contained in a suitable nonaqueous solvent. Examples of the non-aqueous solvent include ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, 1,2-dimethoxyethane, 1,2-diethoxyethane, tetrahydrofuran, 1,3-dioxolane, and the like. One kind or two or more kinds selected from the group can be used. Examples of the supporting salt include LiPF ₆ , LiBF ₄ , LiAsF ₆ , LiCF ₃ SO ₃ , LiC ₄ F ₉ SO ₃ , LiN (CF ₃ SO ₂ ) ₂ , LiC (CF ₃ SO ₂ ) _{3 and the} like. Lithium salts can be used. As an example, a non-solvent containing LiPF ₆ at a concentration of about 1 mol / L in a mixed solvent of ethylene carbonate (EC), dimethyl carbonate (DMC), and ethyl methyl carbonate (EMC) (eg, volume ratio 3: 4: 3). A water electrolyte solution 80 may be mentioned.

  According to the technology disclosed herein, the non-aqueous electrolyte 80 includes lithium fluorosulfonate. According to such a non-aqueous electrolyte solution 80, lithium can be suppressed from being deposited on the negative electrode 60. In particular, in a configuration in which an aluminum foil is used as the positive electrode current collector 52, when a nonaqueous electrolytic solution 80 containing lithium fluorosulfonate is used, aluminum elution can be suppressed and lithium deposition on the negative electrode 60 can be suppressed. ,preferable. The amount of lithium fluorosulfonate added is preferably 0.1% by mass to 4% by mass, and more preferably 0.5% by mass to 2% by mass with respect to the total amount of the nonaqueous electrolytic solution 80.

  In a preferred embodiment, the non-aqueous electrolyte 80 contains lithium bis (oxalate) borate (LiBOB) as a film forming material. According to such a non-aqueous electrolyte solution 80, a LiBOB-derived film is formed on the surface of the negative electrode 60 by the initial charge or discharge, and an increase in resistance value associated with the charge / discharge cycle can be suppressed. When the non-aqueous electrolyte 80 contains LiBOB, the amount of LiBOB added is preferably 0.01M to 0.1M, and preferably 0.015M to 0.07M with respect to the total amount of the non-aqueous electrolyte 80. Is more preferable.

  Although the lithium ion secondary battery 100 disclosed herein can be used for various applications, lithium deposition hardly occurs even when the battery is charged and discharged at a large current or a low temperature range, and the battery performance after cycling is improved. Can keep. Therefore, taking advantage of such properties, for example, it can be suitably used as a driving power source mounted on a vehicle. Although the kind of vehicle is not specifically limited, For example, a plug-in hybrid vehicle (PHV), a hybrid vehicle (HV), an electric vehicle (EV) etc. are mentioned. Thus, according to this configuration, a vehicle including any of the lithium ion secondary batteries disclosed herein as a power source is provided. The lithium ion secondary battery provided in the vehicle can be, for example, in the form of an assembled battery in which a plurality of single cells are connected.

  Several examples relating to the present invention will be described below, but the present invention is not intended to be limited to the specific examples.

<Preparation of positive electrode>
LiNi _1/3 Mn _1/3 Co _1/3 O ₂ (LNCM) as a positive electrode active material, acetylene black (AB) as a conductive material, and polyvinylidene fluoride (PVdF) as a binder of these materials The mixture was put into a kneader so that the mass ratio was LNCM: AB: PVdF = 91: 6: 3, and kneaded with N-methylpyrrolidone (NMP) to prepare a paste-form positive electrode active material layer forming mixture. This composite paste is applied to both sides of a long aluminum foil (positive electrode current collector) with a width of 105 mm, and dried so that the residual oil amount of the aluminum foil measured by the measurement method described later becomes the value shown in Table 1. The positive electrode sheet which has a positive electrode active material layer on both surfaces of a positive electrode electrical power collector was produced by drying while controlling conditions, and pressing with a roll-press machine after that, and let this be the positive electrode which concerns on Examples 1-12. The basis weight (based on solid content) of the positive electrode active material layer forming composite was adjusted to 5 mg / cm ² per side.

<Measurement of residual oil amount>
For the positive electrode on which the positive electrode active material layer was formed, a part of the positive electrode current collector was cut out from the exposed portion of the positive electrode current collector of the positive electrode, and used as a target piece for a residual oil amount measurement test. The dry weight X (mg / m ² ) of the target piece in the air at room temperature was measured. Thereafter, the target piece was heated in the atmosphere at 200 ° C. for 30 minutes, and the weight Y (mg / m ² ) after heating was measured. The weight difference XY (mg / m ² ) was calculated, and this was used as the residual oil amount of the positive electrode current collector.

<Production of negative electrode>
Natural graphite (C) as a negative electrode active material, styrene butadiene rubber (SBR) as a binder, and carboxymethyl cellulose (CMC) as a thickener, the mass ratio of these materials is C: SBR: CMC = 98: The mixture was put into a kneader so as to be 1: 1, and kneaded with ion-exchanged water to prepare a paste-like negative electrode active material layer forming mixture. The composite paste was applied to both sides of a long copper foil (negative electrode current collector) with a width of 110 mm, and pressed after drying to produce a negative electrode sheet having a negative electrode active material layer on both sides of the negative electrode current collector. . The basis weight (solid content basis) of the negative electrode active material layer forming composite was adjusted to 3.5 mg / cm ² per side.

<Preparation of non-aqueous electrolyte>
The non-aqueous electrolyte according to Examples 1 to 5 is a mixture containing ethylene carbonate (EC), dimethyl carbonate (DMC), and ethyl methyl carbonate (EMC) in a volume ratio of EC: DMC: EMC = 30: 40: 30. A solution prepared by mixing lithium fluorosulfonate (FSO ₃ Li) in a solvent to a concentration of 1% by weight and further dissolving LiPF ₆ as a supporting salt at a concentration of 1.1 mol / L is used. It was. Moreover, LiBOB was added so that it might become 0.05M. As the non-aqueous electrolytes according to Examples 6 to 12, non-aqueous electrolytes were prepared in the same manner as the non-aqueous electrolyte preparation methods of Examples 1 to 5 except that lithium fluorosulfonate was not included.

  The positive electrode sheet and the negative electrode sheet prepared above are composed of two separator sheets (here, a three-layer structure in which polypropylene (PP) is laminated on both sides of polyethylene (PE), with a thickness of 20 μm and a width of 114 mm. After laminating and winding together, a flat wound electrode body was produced by pressing and ablating from the side direction. Next, the positive electrode terminal and the negative electrode terminal were attached to the lid of the battery case, and these terminals were welded to the positive electrode current collector and the negative electrode current collector exposed at the ends of the wound electrode body, respectively. The wound electrode body thus connected to the lid body was housed in the rectangular battery case from the opening, and the opening and the lid were welded. Then, with the battery case maintained in an atmospheric pressure atmosphere, a non-aqueous electrolyte was injected from an electrolyte injection hole provided in the lid, and the wound electrode body was impregnated with the non-aqueous electrolyte. In this way, lithium ion secondary batteries according to Examples 1 to 12 were constructed.

<Measurement of initial capacity>
Under an environment of 25 ° C., charging and discharging were performed in a voltage range of 3.0 V to 4.1 V according to the following procedures 1 to 3. This confirmed the initial capacity.
[Procedure 1]: After constant current charging (CC charging) at 5 A until the voltage reaches 4.1 V, constant voltage charging (CV charging) is performed until the current reaches 0.01 A.
[Procedure 2]: Pause for 1 hour.
[Procedure 3]: A constant current discharge (CC discharge) is performed at 5 A until the voltage reaches 3.0 V, and then a constant voltage discharge (CV discharge) is performed until the current reaches 0.01 A.
And the discharge capacity of CCCV discharge was made into the initial capacity of the lithium ion secondary battery which concerns on each example.

<Low-temperature pulse cycle test>
A lithium ion secondary battery (after initial charge) according to each example was separately prepared, and a low-temperature pulse cycle test was performed. Specifically, first, in an environment of 25 ° C., the battery was adjusted to a charged state of SOC 80%. Then, this battery was subjected to pulse charging for 10 seconds at a constant current of 200 A in an environment of −10 ° C., rested for 5 seconds, discharged for 20 seconds at 20 A, and rested for 5 seconds. A rectangular wave cycle test in which the discharge pattern was repeated 500 cycles was performed.
Then, the discharge capacity (capacity after the low-temperature pulse cycle test) is measured under the same conditions as the initial capacity, and the ratio “(battery capacity after the low-temperature pulse cycle test / initial capacity) × 100” is calculated. Was the capacity retention rate (%) after the low-temperature pulse cycle test. The results are shown in the corresponding column of Table 1 and FIG.

<Life endurance test>
A lithium ion secondary battery (after initial charging) according to each example was separately prepared and allowed to stand for 150 days in an environment of 70 ° C. For this battery, the discharge capacity (capacity after the life endurance test) was measured under the same conditions as the initial capacity, and the ratio “(battery capacity after the endurance endurance test / initial capacity) × 100” was calculated. This was defined as the capacity retention rate (%) after the life durability test. The results are shown in the corresponding column of Table 1 and FIG.

As is clear from the results shown in Table 1 and FIG. 3, Examples 1 to Examples using a non-aqueous electrolyte to which lithium fluorosulfonate (FSO ₃ Li) was added were used for capacity retention after the low-temperature pulse cycle test. The lithium ion secondary battery of No. 5 showed an overall high capacity retention rate as compared with Examples 6 to 12 using the non-aqueous electrolyte not added. This is because lithium deposition on the negative electrode was suppressed by the addition of lithium fluorosulfonate. Referring to FIG. 3, it can be seen that when the amount of residual oil in the aluminum foil is too small, the capacity retention rate tends to decrease (that is, the lithium deposition resistance decreases). Regarding the constitution in which the nonaqueous electrolytic solution contains lithium fluorosulfonate, Examples 1 to 5 in which the amount of residual oil is at least 0.1 mg / m ² or more have excellent capacity retention ratios (that is, excellent lithium precipitation Resistance).

As is apparent from the results shown in Table 1 and FIG. 4, Examples 1 to 12 in which the amount of residual oil of the aluminum foil was 2 mg / m ² or less were excellent for the capacity retention rate after the life durability test. The capacity maintenance rate was shown. That is, it was found that when the residual oil amount of the aluminum foil was 2 mg / m ² or less, the life reduction of the lithium ion secondary battery provided with the aluminum foil was suppressed.

  As mentioned above, although this invention was demonstrated in detail, the said embodiment and Example are only illustrations and what changed and changed the above-mentioned specific example is contained in the invention disclosed here.

20 Battery case 21 Case body 22 Lid (sealing plate)
23 Positive electrode terminal 24 Negative electrode terminal 30 Safety valve 32 Injection port 33 Sealing material 40 Winding electrode body 50 Positive electrode sheet 51 Exposed part 52 Positive electrode current collector 53 Positive electrode active material layer 60 Negative electrode sheet 61 Exposed part 62 Negative electrode current collector 63 Negative electrode Active material layer 72 Separator 74 Separator 80 Liquid electrolyte (non-aqueous electrolyte)
100 Lithium ion secondary battery

Claims (1)

A lithium ion secondary battery comprising a positive electrode, a negative electrode, and a non-aqueous electrolyte,
The positive electrode comprises a positive electrode current collector formed of an aluminum foil, and a positive electrode active material layer formed on the positive electrode current collector,
The non-aqueous electrolyte contains lithium fluorosulfonate,
Here, the residual oil amount (mg / m ² ) of the positive electrode current collector measured by the following measurement method:
Cut out the aluminum foil constituting the exposed portion of the positive electrode current collector, which is the portion where the positive electrode active material layer is not formed in the positive electrode current collector, and the dry weight of the cut-out aluminum foil portion under room temperature conditions in the atmosphere and X (mg / ^{m 2),} the difference between the measured partial after subjected to high-temperature treatment for 30 minutes at 200 ° C. in air weight ^{Y (mg / m 2) X} -Y a (mg / ^{m 2)} the The amount of residual oil in the positive electrode current collector (mg / m ² );
Is 0.1 mg / m ² or more and 2 mg / m ² or less, a lithium ion secondary battery.

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