JP2019040722A - Lithium ion secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a lithium ion secondary battery in which Li deposition is suppressed, which can improve overcharge resistance while maintaining a more preferable battery capacity. The present invention relates to a lithium ion secondary battery including a wound electrode body and a non-aqueous electrolytic solution containing lithium fluorosulfonate and LiBOB. The positive electrode sheet includes a strip-shaped positive electrode current collector, an exposed portion set along an edge portion on one side in the width direction of the positive electrode current collector, and lithium phosphate held on the surface of the positive electrode current collector. And a positive electrode active material layer containing the same. The negative electrode sheet is a strip-shaped negative electrode current collector, an exposed portion set along an edge on one side in the width direction of the negative electrode current collector, and a negative electrode active material layer held on the surface of the negative electrode current collector. Equipped with. The total of the average lengths in the width direction of the current collector exposed portions on the positive electrode side and the negative electrode side is 21.5 mm or more and 28.5 mm or less. [Selection diagram] Fig. 4

Description

  The present invention relates to a lithium ion secondary battery. Specifically, the present invention relates to a lithium ion secondary battery including a wound electrode body and a non-aqueous electrolyte.

  Lithium-ion secondary batteries are lighter and have higher energy density than existing batteries, so in recent years, they have been used as so-called portable power sources such as personal computers and mobile terminals, and power sources for driving vehicles, such as electric vehicles (EV), It is expected to become increasingly popular as a high-output power source for driving vehicles such as hybrid vehicles (HV) and plug-in hybrid vehicles (PHV). Patent document 1 is mentioned as a prior art document regarding this kind of battery.

JP 2006-143454 A

  In the lithium ion secondary battery disclosed in Patent Document 1, a nonaqueous electrolytic solution containing lithium bis (oxalate) borate (LiBOB) and lithium fluorosulfonate is used. That is, by adding LiBOB to the non-aqueous electrolyte, an increase in internal resistance associated with the charge / discharge cycle can be suppressed. Furthermore, by including lithium fluorosulfonate in the non-aqueous electrolyte, it is possible to suppress the deposition of lithium (Li) metal in the negative electrode even when LiBOB is added to the non-aqueous electrolyte.

By the way, generally, as one means for improving the battery capacity per unit volume inside the battery case, the current collector exposed portions of the positive and negative electrodes constituting the electrode body accommodated in the battery case (that is, the active material in the positive and negative electrodes) For example, the portion where the current collector is exposed without the layer being formed is made as small (narrow) as possible.
However, if the current collector exposed portion is made too small, the heat capacity of the electrode becomes small and heat is easily generated. That is, there is a possibility that the resistance at the time of overcharging accompanied by heat generation is lowered.

  Accordingly, the present invention provides a non-aqueous electrolyte containing lithium bis (oxalate) borate (LiBOB) and lithium fluorosulfonate, and is a more preferable battery in a lithium ion secondary battery in which precipitation of lithium (Li) metal is suppressed. It aims at providing the lithium ion secondary battery which can improve overcharge tolerance, maintaining a capacity | capacitance.

  According to the present invention, a wound electrode body formed by laminating and winding a long positive electrode sheet and a negative electrode sheet with a separator interposed therebetween, and lithium fluorosulfonate and lithium bis (oxalate) borate are included. A lithium ion secondary battery comprising a non-aqueous electrolyte is provided.

  The positive electrode sheet is set on the positive electrode current collector along a positive electrode current collector formed of a long strip-shaped aluminum foil and an edge on one side in the width direction perpendicular to the longitudinal direction of the positive electrode current collector. And a positive electrode active material layer containing lithium phosphate held on the surface of the positive electrode current collector. The negative electrode sheet includes a negative electrode current collector formed of a long strip-shaped copper foil, and the negative electrode current collector along an edge on one side in a width direction perpendicular to the longitudinal direction of the negative electrode current collector. And an anode active material layer held on the surface of the anode current collector. Here, the sum of the average length in the width direction of the positive electrode current collector exposed portion and the average length in the width direction of the negative electrode current collector exposed portion is 21.5 mm or more and 28.5 mm or less.

  According to this configuration, a lithium ion secondary battery including a positive electrode active material layer suitable for improving overcharge resistance can be realized while using a non-aqueous electrolyte effective for suppressing lithium deposition. Furthermore, since the sum of the average length in the width direction of the positive electrode current collector exposed portion and the average length in the width direction of the negative electrode current collector exposed portion is controlled to an appropriate range, lithium metal deposition is further suppressed, In addition, a lithium ion secondary battery having improved overcharge resistance while maintaining a preferable battery capacity can be realized.

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 sum total (mm) of the width direction of the collector exposed part of positive and negative electrodes. It is a graph which shows the relationship between the temperature increase rate (%) after shutdown, and the sum total (mm) of the average length of the width direction of the collector exposed part of positive and negative electrodes.

  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 provided 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, 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 strip-shaped positive electrode (positive electrode sheet) 50, a long strip-shaped negative electrode (negative electrode sheet) 60 similar to the positive electrode sheet 50, and a total of two sheets Long strip separators 72 and 74 are provided. The positive electrode sheet 50 and the negative electrode sheet 60 are stacked with separators 72 and 74 interposed therebetween, and are 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 one edge portion in the width direction orthogonal to the longitudinal direction of the positive electrode current collector 52. Has been. 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.

  The average length a1 (hereinafter also referred to as “width a1”) of the positive electrode active material layer 53 in FIG. 2 and the average length a2 of the positive electrode current collector exposed portion 51 in the width direction (hereinafter referred to as “width a2”). Is also not particularly limited, but in a preferred embodiment, the positive electrode active material layer 53 has a width a1 of 80 mm to 130 mm (for example, 95 mm to 115 mm), and a width a2 of 13 mm to 16 mm. If the width a2 is too large, the amount of components (for example, aluminum ions) eluted from the positive electrode current collector 52 to the non-aqueous electrolyte solution 80 increases, and the elution components are deposited on the negative electrode sheet 60 to cause lithium precipitation. It tends to be easier. On the other hand, if the width a2 is too small, the heat capacity of the electrode becomes small and heat is likely to be generated, so that the overcharge resistance of the battery tends to deteriorate.

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 53 can be, for example, about 0.5 mass% to 10 mass%, and usually about 1 mass% to 5 mass%. 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.

In a preferred embodiment, the positive electrode active material layer 53 includes lithium phosphate (trilithium phosphate: Li ₃ PO ₄ ). According to the lithium ion secondary battery 100 including the positive electrode active material layer 53, heat generation of the electrode when overcharged can be suppressed. In particular, for the purpose of suppressing lithium deposition, the lithium ion secondary battery having a configuration in which the average length a2 in the width direction of the positive electrode current collector exposed portion 51 and / or the average length b2 in the width direction of the negative electrode current collector exposed portion 61 is reduced. Since the secondary battery 100 tends to have low overcharge resistance, it is meaningful to adopt a configuration including the positive electrode active material layer 53 containing lithium phosphate. The positive electrode active material layer 53 is formed by applying the mixture paste containing lithium phosphate to the positive electrode current collector 52 and drying it. The proportion of lithium phosphate in the entire positive electrode active material layer 53 is preferably 1% by mass or more and 5% by mass or less.

<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, a conductive copper foil can be suitably used. A negative electrode current collector exposed portion 61 in which the negative electrode active material layer 63 is not formed and the negative electrode current collector 62 is exposed is set along one edge in the width direction perpendicular to the longitudinal direction of the negative electrode current collector 62. Has been. The negative electrode active material layer 63 is held on both surfaces of the negative electrode current collector 62 except for the exposed portion 61 set on the negative electrode current collector 62. The negative electrode active material layer 63 contains a negative electrode active material.

  The average length b1 (hereinafter also referred to as “width b1”) of the negative electrode active material layer 63 in FIG. 2 and the average length b2 of the negative electrode current collector exposed portion 61 (hereinafter referred to as “width b2”). Is also not particularly limited, but in a preferred embodiment, the negative electrode active material layer 63 has a width b1 of 85 mm to 135 mm (for example, 100 mm to 120 mm) and a width b2 of 8.5 mm to 12.5 mm. It is as follows. When the width b1 is in the above-described range, a good effect can be obtained in the technology disclosed herein. On the other hand, if the width b <b> 2 is too large, the current flowing through the negative electrode current collector 62 is likely to be uneven, which may contribute to lithium deposition in the negative electrode sheet 60. On the other hand, if the width b2 is too small, the heat capacity of the electrode becomes small and heat is likely to be generated, so that the overcharge resistance tends to deteriorate.

  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, like the positive electrode 50, the negative electrode active material and other negative electrode active material layer components are dispersed in an appropriate solvent and kneaded to prepare a paste-like negative electrode active material layer forming compound (mixture paste). . An appropriate amount of this composite paste is applied onto the negative electrode current collector 62, dried and pressed, whereby the negative electrode 60 for a lithium ion secondary battery can be produced.

  Here, the sum of the average length a2 in the width direction of the positive electrode current collector exposed portion 51 and the average length b2 in the width direction of the negative electrode current collector exposed portion 61 (hereinafter also referred to as “width (a2 + b2)”). It is preferably 21.5 mm or more and 28.5 mm or less. If the width (a2 + b2) is too smaller than 21.5 mm, the heat capacity of the electrode becomes too small, and the lithium ion secondary battery 100 having such a configuration is likely to deteriorate overcharge resistance. Further, if the width (a2 + b2) is larger than 28.5 mm, current unevenness occurs or the amount of the current collector component eluted in the non-aqueous electrolyte solution 80 increases. This is not preferred because lithium deposition at 60 tends to be promoted.

<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.

  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 sheet 60 by the initial charge or discharge, and an increase in resistance value associated with the charge / discharge cycle can be suppressed.

  According to the technique disclosed herein, the nonaqueous electrolytic solution 80 preferably contains lithium fluorosulfonate. According to such a non-aqueous electrolyte solution 80, lithium can be suppressed from being deposited on the negative electrode sheet 60. In particular, in a battery in which a nonaqueous electrolyte solution 80 containing lithium fluorosulfonate together with LiBOB is used, the formation of a LiBOB-derived coating is inhibited in the central region of the negative electrode sheet 60 where the nonaqueous electrolyte solution 80 is relatively difficult to penetrate. Even in this case, lithium deposition can be suppressed by the presence of fluorosulfonic acid phosphoric acid in the central region.

  The amount of LiBOB added is preferably 0.01M to 0.1M, more preferably 0.015M to 0.07M, based on the total amount of the nonaqueous electrolyte solution 80. Moreover, it is preferable to set it as 0.1 mass%-4 mass% with respect to the total amount of the non-aqueous electrolyte 80, and, as for the addition amount of lithium fluorosulfonate, it is more preferable to set it as 0.5 mass%-2 mass%. 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 100 disclosed herein as a power source is provided. The lithium ion secondary battery 100 provided in the vehicle may 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>
For the positive electrodes according to Examples 1 to 5, Comparative Example 1 and Comparative Example 2, LiNi _1/3 Mn _1/3 Co _1/3 O ₂ (LNCM) as a positive electrode active material and trilithium phosphate (Li ₃ PO ₄ ), acetylene black (AB) as a conductive material, and polyvinylidene fluoride (PVdF) as a binder, the mass ratio of these materials is LNCM: Li ₃ PO ₄ : AB: PVdF = 90: 2: The mixture was put into a kneader so as to be 5: 3, and kneaded with N-methylpyrrolidone (NMP) to prepare a paste-like positive electrode active material layer forming mixture. The composite paste is applied to portions other than the exposed portion of the positive electrode current collector on both sides of a long aluminum foil (positive electrode current collector: width 120 mm), and after drying, is pressed with a roll press machine. The positive electrode sheet which has a positive electrode active material layer on both surfaces was produced. At this time, the width a2 of the exposed portion of the positive electrode current collector according to each example was set as shown in Table 1. The basis weight (based on solid content) of the positive electrode active material layer forming composite was adjusted to 10 mg / cm ² per side.

The positive electrodes according to Comparative Examples 3 to 6 were produced by the same production method as Example 1 except that the positive electrode active material forming composite material did not contain trilithium phosphate (Li ₃ PO ₄ ).

<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 is applied to portions of the long copper foil (negative electrode current collector: width 120 mm) other than the exposed portions on both sides, and is pressed after drying, whereby a negative electrode active material layer is formed on both sides of the negative electrode current collector. A negative electrode sheet was prepared. At this time, the width b2 of the exposed portion of the negative electrode current collector according to each example was set as shown in Table 1. 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>
As a non-aqueous electrolyte, a mixed solvent containing ethylene carbonate (EC), dimethyl carbonate (DMC), and ethyl methyl carbonate (EMC) in a volume ratio of EC: DMC: EMC = 30: 40: 30 is used as a supporting salt. LiPF ₆ was dissolved at a concentration of 1.1 mol / L, and 1% by mass of lithium fluorosulfonate and 0.05M of LiBOB were used.

  The positive electrode sheet and the negative electrode sheet produced 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 110 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. Thus, the lithium ion secondary battery which concerns on each example was constructed | assembled.

<Measurement of initial capacity>
The lithium ion secondary battery according to each example was charged and discharged in a voltage range of 3.0 V to 4.1 V according to the following procedures 1 to 3 in an environment of 25 ° C. 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 is subjected to pulse charging for 10 seconds at a constant current of 200 A in an environment of −10 ° C., pause for 5 seconds, pulse discharge for 20 seconds at 20 A, and pause for 5 seconds. A rectangular wave cycle test in which the charge / 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.

<Overcharge test>
Immediately after each of the lithium ion secondary batteries according to each example is forcibly charged until reaching 12 V at a constant current of 3 C in an environment of 25 ° C. Charging stopped. At that time, the battery temperature (T ₀ ) at the time of shutdown and the battery temperature (T ₁ ) after 1 second from the shutdown were measured. By dividing T ₁ by T ₀ , the rate of temperature increase (%) after shutdown was determined. The results are shown in the corresponding column of Table 1 and FIG.

  As is apparent from the results shown in Table 1 and FIG. 3, Examples 1 to 5 in which the sum of the average lengths (a2 + b2) in the width direction of the current collector exposed portions of the positive and negative electrodes is 28.5 mm or less and the comparison It was found that the lithium ion secondary battery of Example 1 was maintained with a high capacity retention rate after the low-temperature pulse cycle test. This is because lithium deposition in the negative electrode was appropriately suppressed.

  In addition, according to the results shown in Table 1 and FIG. 4, the lithium ion secondary batteries according to Examples 1 to 5 and Comparative Examples 1 and 2 in which the positive electrode active material layer includes trilithium phosphate are Compared with the lithium ion secondary batteries according to Comparative Examples 3 to 6 in which the positive electrode active material layer does not contain trilithium phosphate, the temperature rise after shutdown tends to be suppressed (that is, the overcharge resistance is improved). I found out. Further, Example 1 in which the positive electrode active material layer includes trilithium phosphate and the total length (a2 + b2) in the width direction of the current collector exposed portions of the positive and negative electrodes is 21.5 mm or more. It was found that in the lithium ion secondary batteries according to -5 and Comparative Example 2, the temperature increase after shutdown was further suppressed, and the overcharge resistance was further improved.

  The positive electrode active material layer contains trilithium phosphate, and the total length (a2 + b2) in the width direction of the current collector exposed portions of the positive and negative electrodes is 21.5 mm or more and 28.5 mm or less. As for the lithium ion secondary battery which concerns on 5, it became clear that lithium precipitation was suppressed, a high capacity | capacitance maintenance factor was maintained, and overcharge tolerance improved.

  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 wound electrode body formed by laminating and winding a long positive electrode sheet and a negative electrode sheet with a separator interposed therebetween;
A non-aqueous electrolyte containing lithium fluorosulfonate and lithium bis (oxalate) borate;
A lithium ion secondary battery comprising:
The positive electrode sheet is
A positive electrode current collector formed of a long strip-shaped aluminum foil;
The positive electrode current collector exposed portion set in the positive electrode current collector along the edge on one side in the width direction perpendicular to the longitudinal direction of the positive electrode current collector, and held on the surface of the positive electrode current collector, A positive electrode active material layer containing lithium phosphate,
The negative electrode sheet is
A negative electrode current collector formed of a long strip-shaped copper foil;
A negative electrode current collector exposed portion set on the negative electrode current collector along an edge on one side in the width direction perpendicular to the longitudinal direction of the negative electrode current collector, and a negative electrode held on the surface of the negative electrode current collector An active material layer,
The lithium ion secondary battery, wherein the total length of the positive electrode current collector exposed portion in the width direction and the average length of the negative electrode current collector exposed portion in the width direction is 21.5 mm or more and 28.5 mm or less. .

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